Technical Field

The present invention relates to an inductor coil for induction welding of a packaging material having at least one layer of metal foil . The present invention also relates to an induction sealing device comprising such inductor coil, a sealing machine comprising the induction sealing device, and a related method of manufacturing an inductor coil for induction welding of a packaging material having at least one layer of metal foil .

Background

The welding of laminated packing material by means of induction heat is used in the packaging industry. One example of such a laminated material is a carrier layer of paper, aluminium foil and thermoplastic coatings along the inner and outer surfaces of the laminate. The technique of induction welding is based on the fact that the magnetic field around a conductor, generated by an alternating current is capable of inducing a current in an adjoining electrically conducting material, which depending on the resistance of the material, warms up the material . Thus, in induction welding an inductor loop or coil provided against the laminate containing the aluminium foil, and the laminate is pressed together with the material to which it is to be joined. The aluminium foil is heated by means of appropriately chosen current and processing period. The material is heated to a temperature which is high enough to seal adjoining layers of thermoplastic, causing the combined thermoplastic layers to fuse together, thus producing a tight and durable seal.

Typically, the induction sealing device, and accordingly the inductor coil, provided in such sealing process often works in an aggressive environment. The inductor coil may be exposed to high temperatures, high pressures, and chemicals in the sealing machine. This combination creates an aggressive environment which in certain applications causes rapid corrosion and wear of the inductor coil. Consequently, the sealing devices have to be replaced regularly, each replacement causing a stop in the production of packages. Significant resources have to be spent on such maintenance and monitoring of the condition of the induction sealing device. Corrosion and wear may also have impact at an early stage on the sealing process which often is highly optimized, for example by exact impedance matching in the induction heating circuit of the system, in order to accommodate the demands in high-speed sealing

production lines. The wear of the inductor may thus counteract such

optimization efforts, and further have negative impact on the quality of the sealing in such high-speed systems.

It is desired to improve previous solutions for preventing corrosion and wear, for example by further minimizing the risk of mechanical failure such as cracking of the welding surface of the inductor coil in demanding environments.

Hence, an improved inductor coil would be advantageous and in particular allowing for avoiding more of the above mentioned problems and compromises, including improving the robustness and resistance in aggressive environments such as high-temperature and/or corrosive environments, to increase the lifetime of the inductor coil and facilitate the inductive sealing process

optimization in high speed sealing systems. A related induction sealing device and sealing machine comprising such inductor coil would also be advantageous as well as a method of manufacturing such inductor coil for induction welding of a packaging material.

Summary

Accordingly, examples of the present invention preferably seek to mitigate, alleviate or eliminate one or more deficiencies, disadvantages or issues in the art, such as the above-identified, singly or in any combination by providing a device according to the appended patent claims.

According to a first aspect an inductor coil for induction welding of a packaging material having at least one layer of metal foil is provided. The inductor coil being configured to induce an alternating current in the metal foil for inductive heating of the packaging material. The inductor coil comprises a base layer material, a top layer material bonded to the base layer material to form an irreversible bonding interface comprising a mixture of the base layer material and the top layer material.

According to a second aspect an induction sealing device is provided comprising at least one inductor coil according to the first aspect and a supporting body encapsulating said at least one inductor coil apart from an outer surface of the at least one inductor coil, wherein at least the outer surface comprises a top layer material bonded to a base layer material to form an irreversible bonding interface comprising a mixture of the base layer material and the top layer material.

According to a third aspect a sealing machine for sealing of packaging material is provided. The sealing machine comprises at least one inductor coil according to the first aspect or an induction sealing device according to the second aspect.

According to a fourth aspect a method of manufacturing an inductor coil for induction welding of a packaging material having at least one layer of metal foil is provided. The method comprises bonding a top layer material to a base layer material to form an irreversible bonding interface comprising a mixture of the base layer material and the top layer material, and providing an outer surface of the inductor coil with the top layer material.

Further examples of the invention are defined in the dependent claims, wherein features for the second, third, and fourth aspects of the disclosure are as for the first aspect mutatis mutandis.

Some examples of the disclosure provide for an inductor coil for induction welding of a packaging material that is more robust and resistant in aggressive environments such as high-temperature and/or corrosive environments.

Some examples of the disclosure provide for an inductor coil for induction welding of a packaging material that has an increased lifetime in sealing applications.

Some examples of the disclosure provide for an inductor coil for induction welding of a packaging material that requires less maintenance in sealing applications.

Some examples of the disclosure provide for an inductor coil for induction welding of a packaging material that has a welding surface which is less susceptible to mechanical failure such as cracking in aggressive environments in filling machines.

Some examples of the disclosure provide for an inductor coil for induction welding of a packaging material that has a welding surface which is more easily provided in varying geometries for optimizing the sealing process, while maintaining mechanical stability.

Some examples of the disclosure provide for an inductor coil for induction welding of a packaging material that allows for increased stability in the electrical parameters of the inductive heating circuit applied for the welding. Some examples of the disclosure provide for an inductor coil for induction welding of a packaging material that allows for improved control of the sealing process.

Some examples of the disclosure provide for more reliable sealing of packaging material containers.

Some examples of the disclosure provide for an increased throughput in an inductive sealing production line.

It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Brief Description of the Drawings

These and other aspects, features and advantages of which examples of the invention are capable of, will be apparent and elucidated from the following description of examples of the present invention, reference being made to the accompanying drawings, in which;

Fig. 1 is a schematic illustration, in a perspective view, of an inductor coil according to an example of the disclosure;

Fig. 2 is a schematic illustration of a detailed section (A) of Fig. 1 , in a perspective view, of an inductor coil according to an example of the disclosure;

Fig. 3 is a schematic illustration, in a cross-sectional side view, of an inductor coil according to an example of the disclosure;

Fig. 4 is a schematic illustration, in a cross-sectional side view, of an induction sealing device, comprising an inductor coil, according to an example of the disclosure;

Fig. 5 is a schematic illustration, in a cross-sectional side view, of an inductor coil according to an example of the disclosure; and

Figs. 6a-b are flowcharts of a method of manufacturing an inductor coil for induction welding of a packaging material according to examples of the disclosure. Detailed Description

Specific examples of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the examples set forth herein; rather, these examples are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the examples illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements.

Fig. 1 is a schematic illustration, in a perspective view, of an inductor coil 100 for induction welding of a packaging material (not shown). The packaging material has at least one layer of metal foil in which an alternating current can be induced. The inductor coil 100 is configured to induce an alternating current in the metal foil for inductive heating of the packaging material. Fig. 2 is a magnified view of a section (A) of the inductor coil 100 in Fig. 1 . The inductor coil 100 comprises a base layer material 103 and a top layer material 104. The top layer material 104 is bonded to the base layer material 103 to form an irreversible bonding interface 109 comprising a mixture of the base layer material 103 and the top layer material 104. Such bonded interface 109 between the base layer material 103 and the top layer material 104 provides for a more robust inductor coil with improved integrity of the top layer material 104 in aggressive environments, such as corrosive high-temperature environments, also in combination with mechanical abrasion against the top layer material 104. Having two layers of material 103, 104, provides for optimization to

accommodate both the electrical characteristic requirements, by choosing an appropriate base layer material 103, while the top layer 104 material can be optimized to protect the base layer material 103 from the surrounding

environment. Having the top layer material 104 bonded so that the interface 109 comprises a mixture of both materials 103, 104, thus provides for the mentioned improvements in the integrity of the layers 103, 104, due to a stronger bonding interface, and improved corrosion protection of the base layer 103. This is particularly advantageous compared to previous techniques where instead a coating is applied on top of the base layer material. Such coating is not bonded to the base layer material as described above, but is rather applied as a superficial layer producing an interface between the materials in which the materials are distinctly separated. This is due to the coating being deposited on top of the base layer without chemical and/or mechanical bonding

therebetween, but instead only by means of producing an adhesive effect between the materials. The adhesive effect can typically be achieved for example by having the coating applied by spraying, or otherwise deposited on the base layer material, and subsequently dried or otherwise hardened on top of the base layer material. Thus, by having the material layers 103, 104, bonded the mechanical integrity thereof can be improved, and the risk of failure such as cracking of the top layer 104 can be minimized. The interface 109 comprising a mixture of the materials 103, 104, as a result of the bonding should be construed as the bas- and top layer materials 103, 104, being mixed to overlap at the interface 109 along the vertical direction in e.g. Fig. 3 (i.e. in a direction perpendicular to a plane in which the welding surface 102 of the inductor coil 100 extends). Such bonding of the inductor coil 100 can be achieved by subjecting the materials 103, 104, thereof to a defined pressure and/or temperature so that the materials 103, 104, propagate into each other in the mentioned direction.

The inductor coil 100 accordingly allows for facilitated maintenance in sealing applications and related sealing machines. Furthermore, since the integrity of the top layer material 104 is improved as elucidated above, it is easier to customize the surface of the inductor coil 100 arranged towards the packaging material, i.e. the welding surface, such as for example by shaping the welding surface 102 in different geometries, as seen in e.g. Fig. 5, with a minimized risk of the surface cracking in aggressive environments. E.g.

protrusions and/or recesses of the surface may otherwise be more sensitive to failures of the mechanical integrity thereof. The improved abilities to adapt the welding surface, i.e. outer surface 101 , thus allows for optimizing the inductor coil 100 to different sealing applications.

The top layer material 104 may be joined to the base layer material 103 by diffusion bonding. Such bonding provides for a strong bonding force between the base- and top layer materials 103, 104, at the bonding interface 109, which will provide for improved mechanical integrity of the base- and top layer materials 103, 104, and a more robust inductor coil 100 in aggressive

environments.

The base layer material 103 may have a lower resistivity (p) than the top layer material 104. The base layer material 103 may thus be adapted to provide for the electrical characteristics needed for an optimized induction welding process, while the top layer material 104 is configured for the wear- and corrosion resistance without affecting the desired electrical properties. The inductor coil 100 can thus fulfil the tolerances required, e.g. with respect to impedance characteristics in an inductive heating circuit in a sealing machine and being resistant the aggressive environment therein.

The inductor coil 100 comprises an outer surface 101 . At least part of the outer surface 101 may comprise the top layer material 104. The top layer material 104 is thus arranged as a barrier between the surrounding corrosive environment and the base layer material 103. Substantially the entire surface of the inductor coil 100 facing the surrounding medium may comprise the top layer material 104 to further optimize the corrosion resistance, or resistance to outer wear.

In particular, the inductor coil 100 may comprise a welding surface 102 configured to be arranged opposite the packaging material for inductive heating thereof. The welding surface 102 may comprise the top layer material 104. The welding surface 102 is exposed to the surrounding environment in order to interact with the packaging material, and it is thus particularly advantageous to have the welding surface 102 comprising the top layer material 104. Some parts of the outer surface 101 of the inductor coil 100 may not be directly arranged opposite the packaging material, but it may be advantageous for such parts of the outer surface 101 to also comprise the top layer material 104 if being exposed to the surrounding environment. The welding surface 102 may be particularly exposed to mechanical wear such as abrasion etc. The top layer material 104 may improve the resistance to such wear due to the increased mechanical integrity thereof as discussed above.

The top layer 104 may cover the base layer material 103 with a predefined thickness 105. Fig. 3 illustrates an example, in a cross-sectional side view of the inductor coil 100, where the thickness 105 of the top layer material 104 is shown. The thickness 105 may be in the range of 50 - 150 micrometers. Having a thickness 105 in this range allows for a particularly strong and robust top layer 104 while maintaining the desired functionality of the base layer material 103 in terms of inducing the alternating current in the packaging material. The inductor coil 100 may be elongated and extend with a length in a longitudinal direction 107 as schematically illustrated in the example of Fig. 1 . The thickness 105 of the top layer material 104 may be substantially uniform along the length of the inductor coil 100. It is however conceivable that the thickness 105 may be varied along the length. For example, some parts of the inductor coil 100 may be particularly exposed to mechanical wear and a locally increased thickness 105 may improve resistance to e.g. abrasion along such particularly exposed parts.

The top layer material 104 and the base layer material 103 may form a substantially rectangular or square cross-section of the inductor coil 100 along the length 107. Fig. 2 illustrates a magnified view of section (A) in Fig. 1 . Having a uniform rectangular or square cross-section of the bonded-together cross- section, as illustrated in Fig. 2, provides for minimizing localized weaknesses along the length of the inductor coil 100, which otherwise may cause cracks in the materials 103, 104.

The inductor coil 100 may comprise a protruding ridge 1 10 formed from the top layer material 104, as illustrated in the example of Fig. 5. Having the top layer material 104 bonded to the base layer material 103 as described above provides for a more robust surface that can be adapted into varying geometries with a minimized risk cracks in the top layer material 104. Surface structures, such as the protruding ridge 1 10, may thus be formed with a smaller radius of curvature, i.e. sharper bends in the outline of the surface structure, while not risking cracking of the material in the aggressive environment. Customization to various sealing applications and packaging materials requiring different welding surfaces 102 can thus be facilitated.

The top layer material 104 may comprise a silver-palladium (AgPd) alloy.

The AgPd alloy is particularly effective in providing corrosion and wear resistance to the base layer material 103. Substantially the entire outer surface 101 , or the welding surface 102, may comprise the AgPd alloy, for an optimized corrosion resistance. It is conceivable however that sufficient corrosion resistance may be achieved if parts or at least the majority of the surface area of the outer surface 101 or the welding surface 102 comprise the AgPd alloy. It is further conceivable that the top layer material 104 may comprise other materials or alloys that provides for an improved corrosion and wear resistance of the base layer material 103. The top layer material 104 may for example comprise any materials, or combination of materials, or various alloys thereof, of the following; Ni, Cr, Ag, Ta, Au, Cu, stainless steel. Other materials or alloys providing for corrosion and/or wear resistance may also be bonded together with the base layer material 103 to provide for the advantageous effects as described above. The materials or combinations of materials, may be provided in different layers of top layer materials 104 being bonded together to form a multi-layered top layer 104. AgPd may in such case be provided at the outermost layer due to its particularly advantageous chemical and mechanical properties. Having the AgPd bonded together with the base layer material, by e.g. diffusion bonding, provides for a synergistical effect in that the

advantageous properties of the AgPd alloy are combined with the strength and robustness of the top layer 104 by the bonding to the base layer material 103 to form the mixture of the mentioned materials at the interface 109. The base layer material 103 may comprise Cu, Al, Ag, Au, or any alloy comprising any of the these or other materials providing for the desired electrical properties of the induction coil 100.

An induction sealing device 200 is provided comprising at least one inductor coil 100 as described above in relation to Figs. 1 - 3 and 5. The induction sealing device 200 comprises a supporting body 201 encapsulating at least one inductor coil 100 apart from an outer surface 101 of the at least one inductor coil 100. Fig. 4 is a schematic illustration of an example of an induction sealing device 200, where a supporting body is arranged around the inductor coil 100, apart from an outer surface 101 , effectively being the welding surface 102 of the inductor coil 100. At least the outer surface 101 comprises the top layer material 104 being bonded to the base layer material 103 to form an irreversible bonding interface 109 comprising a mixture of the base layer material 103 and the top layer material 104, as described above. The induction sealing device 200 thus provides for the advantageous effects described above in relation to the inductor coil 100 and Figs. 1 - 3 and 5.

The base layer 103 may comprise protrusions or recesses 108, 108', configured to interlock with the supporting body 201 . This is illustrated in the detailed side-view of Fig. 3. The positioning of the inductor coil 100 in the supporting body 201 is thus facilitated since the protrusions or recesses 108,

108', may readily interlock with corresponding mating surfaces of the supporting body 201 as seen in Fig. 4. Such locking surfaces may also enhance the stability of the fixation of the inductor coil 100 to the base layer and contribute to the overall robustness of the induction sealing device 200.

A sealing machine (not shown) for sealing of packaging material is provided. The sealing machine comprises at least one inductor coil 100 as described above in relation to Figs. 1 - 3 and 5. Accordingly, the sealing machine may also comprise an induction sealing device 200 as described above in relation to Fig. 4. The sealing procedure of packaging material in the sealing machine can thus be improved due to the advantageous effects described above, and in particular allowing for an improved control of the sealing process, a more reliable sealing and ultimately increased throughput in an inductive sealing production line.

Fig. 6a illustrates a flow chart of a method 300 of manufacturing an inductor coil 100 for induction welding of a packaging material having at least one layer of metal foil. The order in which the steps of the method 300 are described and illustrated should not be construed as limiting and it is

conceivable that the steps can be performed in varying order. A method 300 is thus provided, comprising bonding 301 a top layer material 104 to a base layer material 103 to form an irreversible bonding interface 109 comprising a mixture of the base layer material 103 and the top layer material 104. The method 300 further comprises providing 302 an outer surface 101 of the inductor coil 100 with the top layer material 104. The method 300 thus provides for the

advantageous benefits as described above in relation to the inductor coil 100 and the induction sealing device 200 in conjunction with Figs. 1 - 5.

Fig. 6b illustrates a further flow chart of a method 300 of manufacturing an inductor coil 100 for induction welding of a packaging material having at least one layer of metal foil. The order in which the steps of the method 300 are described and illustrated should not be construed as limiting and it is

conceivable that the steps can be performed in varying order. The top layer material 104 may be bonded to the base layer material by diffusion bonding 303 as discussed above.

The method 300 may comprise providing 304 a welding surface 102 of the inductor coil with the top layer material 104. The welding surface 102 is configured to be arranged opposite the packaging material for inductive heating thereof. The method 300 may comprise providing 305 the top layer material 104 to extend along the base layer material 103 in a longitudinal direction 107 of the inductor coil 100 with a predefined thickness 105 in the range of 50 - 150 micrometers.

The method 300 may comprise joining 301 ' a first portion of material comprising the top layer material 104 to a second portion of material comprising the base layer material 103. The method 300 may comprise applying 301 " pressure and/or temperature to the first and second portions of material for the bonding thereof, and forming 302' the inductor coil 100 from the bonded first and second portions of material so that the outer surface 101 of the inductor coil is provided with the top layer material 104. The top layer material 104 may comprise a silver-palladium (AgPd) alloy with the particularly advantageous properties as elucidated above. The present invention has been described above with reference to specific examples. However, other examples than the above described are equally possible within the scope of the invention. The different features and steps of the invention may be combined in other combinations than those described. The scope of the invention is only limited by the appended patent claims.

More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used.