Induction heating sealing device

Abstract

An apparatus (50, 50') for induction sealing a packaging material (20) for producing a sealed package (30) of a pourable food product in a package making machine (10) is provided. The packaging material (20) has at least one metallized film (20d). The induction sealing apparatus (50, 50') comprises an AC power source (54) and an inductor coil (52) connected to the AC power source (54) and configured to induce eddy currents in the metallized film (20d) for heating the packaging material (20). The AC power source (54) is configured to generate a variable voltage / current signal (S) at a frequency greater than 1 MHz.

Description

Technical Field

[0001] The present invention relates to an induction heating sealing device for induction heating welding of packaging materials in a package manufacturing machine. The present invention also relates to a method for manufacturing a packaging container.

Background Art

[0002] In the packaging industry, welding of laminated packaging materials by induction heating is commonly used. One example of such a laminated material is a paper carrier layer, an aluminum foil barrier layer, and thermoplastic coatings along the inner and outer surfaces of the laminate. The induction welding technique is based on Faraday's law, and an alternating magnetic field generated around a conductor can induce an electric current in another conductor (workpiece) arranged in proximity. Then, heat is generated in the workpiece by the Joule effect. In this way, in induction welding, an inductor is arranged near the laminate containing the aluminum foil, and the materials to be joined, usually two layers of packaging material, are pressed together. The aluminum foil is heated by induction to a temperature high enough to melt the adjacent thermoplastic resin layers, fusing the bonded thermoplastic resin layers to form a firm and durable seal.

[0003] The welding process depends on several parameters, such as the characteristics of the inductor and the workpiece. Currently, for commercially available packaging materials, the workpiece is an aluminum foil with a thickness of about 6 microns. To achieve an efficient and robust seal, the inductor is driven by an AC power source that generates a variable voltage / current with a frequency of about 535 kHz. Although this method shows very good results in terms of seal quality, it is sensitive to the relative position between the inductor and the workpiece, that is, the packaging material.

[0004] Induction heating can be used to provide longitudinal and transverse seals. Longitudinal welding is typically performed continuously to seal the longitudinal direction of a web of packaging material as it travels through a packaging machine. The web of packaging material, initially flat, folds into a tubular shape with overlapping longitudinal edges. These overlapping edges travel along longitudinally oriented inductors, providing induction heating to the packaging material and forming a longitudinal seal on the tube of packaging material.

[0005] Because the web of the packaging material is flexible, it is difficult to ensure the precise positioning of the sealing area (i.e., overlapping longitudinal edges) relative to a normally stationary inductor. During the operation of the packaging machine, the packaging material tube may move in directions other than the machine direction, which can cause the sealing area to shift relative to the inductor.

[0006] Electromagnetic simulations were used to analyze the sensitivity of the induction heating process to mispositioning of overlapping edges of packaging material at the inductor's location. In particular, induction heating efficiency and the uniformity of power density in the sealing region were evaluated for deviations of the gap, tilt angle, and offset of the sealing region relative to the inductor, compared to a reference position. To further explain, the inductor can be observed as a rectangular parallelepiped facing a flat sealing region. The gap is the desired distance in the normal direction between the inductor and the sealing region (reference: Gap=0). The tilt angle is the angle of the plane of the inductor with respect to the plane of the sealing region (reference: angle=0), and the offset is the positional displacement in the direction parallel to the planes of the inductor and the sealing region (reference: offset=0).

[0007] Using a 6.35-micron thick aluminum 6063 workpiece and operating it with an AC power supply at a frequency of 535 kHz, the following observations were made, considering a typical inductor used in longitudinal sealing applications.

[0008] [Table 1]

[0009] Percentage variations must be interpreted based on the nominal uniformity and efficiency corresponding to the reference position.

[0010] The table above shows that precise control of the inductor placement and sealing area is crucial for managing the quality of longitudinal seals. This requires manual checking and operation, and ideally, only skilled, professionally trained engineers should be permitted to perform this work.

[0011] In view of the above, it is desirable to provide an improved induction heating sealing device and an improved induction heating sealing system that are more robust and less affected by the positioning of the packaging material relative to the inductor. [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] Given the aforementioned shortcomings of prior art solutions, there is a need for induction heating sealing devices and systems that provide reliable results without relying on the precise positioning of components used in the induction heating of packaging materials.

[0013] Surprisingly, the inventors discovered that reducing eddy currents on the workpiece could be achieved by significantly reducing the thickness of the workpiece, noting that this reduces the reverse magnetic field (Lenz's Law) provided by the workpiece in response to the primary magnetic field generated by the inductor. In parallel with the reduction in workpiece thickness, the magnetic field frequency needs to be increased to increase the electromotive force induced in the workpiece (Faraday's Law) in order to maintain a relatively high induced power for melting the polymer in the package. By increasing the frequency, sufficient power can be supplied to the workpiece without having to increase the inductor current to values ​​that would compromise the reliability of the system, thus avoiding the risk of overheating or discharge.

[0014] According to a first embodiment, an induction heating sealing device for induction welding of packaging material is provided. The packaging material is configured to be transformed into a sealed package for liquid food in a packaging machine, and the packaging material has at least one layer of metallized film. The induction heating sealing device comprises an AC power supply and an inductor coil connected to the AC power supply and configured to induce eddy currents in the metallized film to induction heat the packaging material. The AC power supply is configured to generate a variable voltage / current signal with a frequency greater than 1 MHz. The metallized film may be a metallized coating. In this case, the packaging material has at least one layer of metallized coating on a substrate which is a polymer film or paper, or on another cellulose-based substrate / sheet.

[0015] In one embodiment, the AC power supply is configured to generate a variable voltage / current signal with a frequency in the range of 1 MHz to 30 MHz, preferably 6.78 MHz or 13.56 MHz, which are available for industrial applications. A frequency of 27.12 MHz is also possible. In addition, using a frequency of approximately 2 MHz can provide the magnetic field required by a standard AC power supply. All of these frequencies have been proven to provide the high efficiency necessary to keep the power induced in the package material constant without increasing the inductor current to a level that could compromise the reliability of the entire induction heating system, and are further suitable for industrial use.

[0016] The inductor coil may be configured to provide a longitudinal seal to the tubular web of the packaging material, or to provide a transverse seal to the tubular web of the packaging material. Therefore, the inductor can be used in the most common sealing operations in modern packaging machines, thereby providing an efficient and robust seal for packaging containers, particularly for liquid food products. Food safety is a critical issue in the manufacture of liquid food packaging containers, and the quality of the seal is a critical factor in determining the shelf life of the contents.

[0017] According to a second embodiment, an induction heating seal system is provided. The induction heating seal system comprises a packaging material having at least one layer of metallized film, and an induction heating seal device comprising an AC power supply and an inductor coil connected to the AC power supply. The inductor coil is configured to induce eddy currents in the metallized film for induction heating of the packaging material, and the AC power supply is configured to generate a variable voltage / current signal with a frequency higher than 1 MHz, preferably less than 30 MHz.

[0018] Typically, replacing aluminum foil, which is about 6 microns thick, with a metallized film significantly reduces the metal content of packaging materials. Furthermore, reducing the thickness of the aluminum has been proven to match the frequency of AC power very well, improving the efficiency of the sealing system and reducing its sensitivity.

[0019] The metallized film may contain a metal layer, such as aluminum, having a thickness of less than 0.5 μm, preferably 20 to 70 nm thick, and more preferably 25 to 50 nm thick. The metal layer may be provided using existing metal deposition techniques.

[0020] The metal layer may have a sheet resistance between 0.5 and 10 Ω / sq. The inventors have recognized that the efficiency of the sealing system depends on the sheet resistance, and that a sufficient level of efficiency can be obtained for a specific range of sheet resistances.

[0021] The AC power supply may be configured to generate a variable voltage / current signal with a frequency in the range of 1 MHz to 30 MHz, preferably with frequencies of approximately 2 MHz, 6.78 MHz, 13.56 MHz, or 27.12 MHz.

[0022] The packaging material may include an innermost heat-sealable thermoplastic resin layer having a melting temperature lower than that of the metallized film. This prevents the metallized film, particularly the metal layer, from being damaged before the innermost heat-sealable thermoplastic resin layer reaches a sufficient sealing temperature.

[0023] According to a third aspect, a package manufacturing machine is provided. The package manufacturing machine comprises at least one induction heat sealing system according to the second aspect.

[0024] According to a fourth aspect, a method for manufacturing a packaging container is provided. This method comprises: i) providing a packaging material having at least one layer of metallized film, ii) disposing at least two layers of the packaging material on the induction coil of an induction heat sealing apparatus, iii) controlling an AC power supply to generate a variable voltage / current signal with a frequency higher than 1 MHz to supply power to the inductor coil, and iv) inducing eddy currents in the metallized film for induction heating of the packaging material, to heat seal the at least two layers of the packaging material.

[0025] The power supply to the inductor coil can be performed by controlling the AC power supply to generate a variable voltage / current signal with a frequency in the range from 1 MHz to 30 MHz, and preferably, the frequency is about 2 MHz, 6.78 MHz, 13.56 MHz, or 27.2 MHz.

[0026] The inductor coil may be oriented in the longitudinal direction to provide a longitudinal seal of the packaging material, or the inductor coil may be oriented in the transverse direction to provide a transverse seal of the packaging material. [Means for Solving the Problems]

[0027] Hereinafter, embodiments of the present invention will be described by way of example with reference to the accompanying drawings. [Brief Description of the Drawings]

[0028] [Figure 1] It is a schematic diagram of a package manufacturing machine. [Figure 2] It is a perspective view of an induction heat sealing system according to one embodiment. [Figure 3] It is a side view of an induction heat sealing system according to another embodiment. [Figure 4] This is a schematic diagram of an induction heating sealing device according to one embodiment. [Figure 5] This is a cross-sectional view of a packaging material that forms part of an induction heating seal system according to one embodiment. [Figure 6] This figure shows the efficiency of a typical induction heating seal system as a function of the workpiece thickness with varying magnetic field frequencies. [Figure 7] This figure shows the efficiency of another typical induction heating seal system as a function of sheet resistance with varying magnetic field frequency. [Figure 8] This is a schematic diagram of a method according to one embodiment. [Modes for carrying out the invention]

[0029] Figure 1 illustrates the basic principle of a roll-feed carton-based packaging machine 10. The packaging machine 10 is configured, for example, for continuous packaging of liquid foods and forms a general technical concept used in various different packaging systems, such as the commercially successful TetraBrick® packaging system. The packaging machine 10 receives the packaging material 20, preferably in the form of a continuous web (as shown in Figure 1).

[0030] After unwinding the packaging material 20, its longitudinal edges 21a and 21b are joined together to form a longitudinal seal LS, thereby forming a tube 22 of the packaging material 20. More specifically, the longitudinal edges 21a and 21b are attached to each other in an overlapping manner, in some cases by adding a strip to one of the edges 21a and 21b. The tube 22 is filled from the filling pipe 12 with the desired product, preferably a liquid food.

[0031] A series of packages 30 are formed from the tube 22 by creating a lateral seal TS at the end of the tube 22 and cutting the sealed portion, with each sealed portion forming an individual package 30. Different forming tools can be used during the lateral sealing operation to form the packages 30, or another forming process can be performed after the lateral sealing is completed.

[0032] Alternatively, a blank-feed packaging machine is used. The blank is supplied to the filling machine in the form of pre-cut pieces of packaging material, with both ends heat-sealed together to form a folded tubular sleeve. The blank is assembled as an open sleeve and then folded and sealed to form a closed top or bottom. The product is then filled, sealed, and folded to obtain a filled packaging container.

[0033] In relation to Figure 1 and the example shown in Figure 1, the term "longitudinal direction" refers to the supply direction of the tube 22, i.e., the mechanical supply direction. The term "lateral direction" refers to the direction perpendicular to the longitudinal direction.

[0034] The longitudinal seal LS and / or transverse seal TS can be provided by induction heating sealing devices according to various embodiments described below.

[0035] Figure 2 shows an example of an induction heating seal system 40. The induction heating seal system 40 is configured to provide a longitudinal seal LS to the tube 22 of the packaging material 20.

[0036] Before reaching the induction heating seal system 40, the web 20 of the packaging material gradually interacts with the forming assembly 13 and folds so that the longitudinal edges of the packaging material 20 overlap to form the shape of the tube 22.

[0037] The induction heating sealing system 40 comprises an induction heating sealing device 50 and packaging material 20. The induction heating sealing device 50 comprises an induction coil 52 and an AC power supply 54 coupled to the induction coil 52.

[0038] By activating the induction heating sealing device 50 (preferably always in operation to provide a continuous longitudinal seal LS), the overlapping longitudinal edges of the packaging material 20 are heated, and the innermost heat-sealable thermoplastic resin layer of the packaging material 20 melts.

[0039] Heating occurs in the metallized film of the packaging material due to the alternating current from the inductor coil 52, which generates eddy currents.

[0040] Next, the tube 22 is supplied through a circular passage defined by the arrangement of molding rollers and pressure rollers 14. This compresses the longitudinal edges of the packaging material 20, blending the heat-sealable thermoplastic resin layer of the longitudinal edges of the packaging material 20, thereby forming a longitudinal seal LS.

[0041] Figure 3 shows another example of the induction heating sealing system 40'. The induction heating sealing system 40' is configured to provide a transverse seal TS to a tube 22 of packaging material 20, which already has a longitudinal seal LS.

[0042] In the illustrated example, the induction heating sealing system 40' includes a packaging material 20 and two induction heating sealing devices 50'. One induction heating sealing device 50' is located downstream of the other induction heating sealing device 50'.

[0043] Similar to the induction heating sealing device 50 described with reference to Figure 2, the induction heating sealing device 50' in Figure 3 includes an induction coil 52 and an AC power supply 54, respectively. The induction heating sealing devices 50' share a common AC power supply 54.

[0044] The operation of the induction heating seal system 40' causes the inductor coil 52 and counter element 53, positioned on the movable seal jaw, to move and press together the filled packaging material tube 22. Electromagnetic losses, such as eddy currents, are generated in the metallized film of the packaging material 20, so the packaging material 20 is heated by induction heating to form lateral seals TS at predetermined intervals.

[0045] The movement of the seal jaw also provides forward movement of the tube 22, thereby positioning the lateral seals TS at predetermined intervals.

[0046] Schematic diagrams of the induction heating sealing devices 50 and 50' are shown in Figure 4. The inductor coil 52 has an elongated shape, and the welding surface 52a is adapted to face the area of ​​the packaging material 20 to be sealed. It should be noted that the exact configuration and design of the induction coil 52 may be substantially modified from that shown in Figure 4, as long as it is possible to provide induction heating of the packaging material 20 in the packaging manufacturing machine 10.

[0047] The inductor coil 52 is connected to an AC power supply 54, which also forms part of the induction heating sealing device 50, 50'. The AC power supply 54 is configured to generate an alternating magnetic field that yields a current / voltage signal S with a frequency of 1 MHz or higher. Preferably, the frequency is in the range of 1 to 30 MHz, particularly about 2 MHz, 6.78 MHz, 13.56 MHz, or 27.12 MHz. The peak voltage is about several hundred (e.g., 500) volts, the power signal S is continuous or pulsed, and the maximum power is in the range of, for example, 2500 watts.

[0048] The inductor coil 52 receives an AC power signal S and generates a pulsating magnetic field, which is defined by a winding that generates eddy currents within the packaging material 20. Therefore, the packaging material 20, which constitutes part of the induction heating sealing system 40 described above, includes a workpiece in the form of a metal layer of a metallized film.

[0049] When the workpiece is subjected to a high-frequency magnetic field from the inductor coil 52, eddy currents are generated in the workpiece. This workpiece was conventionally provided in the form of an aluminum layer with a thickness of about 6 microns, but instead, it is provided as a metallized film contained in the packaging material 20.

[0050] An example of the packaging material 20 is shown in cross-section in Figure 5. Note that the different thicknesses of the various layers 20a to h shown in Figure 5, including the metal layer 20g of the metallized film 20d, are not to scale.

[0051] The 20g metal layer, i.e., the workpiece, can be placed at any interface between different packaging material layers.

[0052] From the outside of the packaging material 20, i.e., the side intended to form the outside of the final package 30, the packaging material 20 is formed by a decorative layer 20a placed on top of a core bulk layer 20b. The core bulk layer 20b may be a fibrous material such as a cellulose-based material. The core bulk layer 20b may also be a cellulose-based material such as paper, carton, or cardboard. The packaging material 20 also has a thin layer 20c of LDPE covering the opposite side of the core bulk layer 20b. A metallized film 20d is laminated on the LDPE layer 20c. The metallized film 20d may include, for example, a thin paper layer 20e, an intermediate layer 20f of PVOH optionally compounded with starch, and a metal layer 20g that forms the workpiece of the induction heating seal system 40, 40'. The metal layer 20g may be, for example, an aluminum layer having a thickness of 20 to 70 nm, such as about 50 nm. Inside the metallized film 20d, the innermost heat-sealable thermoplastic resin layer 20h is positioned.

[0053] The metallized film 20d can, for example, be embedded in the packaging material 20 or placed on the outer surface of the packaging material 20.

[0054] Although not described above, in some embodiments, the metallized film 20d can be distributed over the entire width and length of the packaging material 20 so that it forms a continuous layer.

[0055] However, in order to enable induction sealing, the metallized film 20d must be provided only locally in one or more regions, thereby forming local workpieces of the associated sealing systems 40, 40'.

[0056] Next, with reference to Figure 6, a figure illustrating some of the characteristics of the induction heating seal systems 40, 40' described above will be presented. This figure shows the efficiency of the induction heating seal system as a function of the workpiece thickness (t), i.e., the thickness of the metal layer 20g in the embodiments described herein. The plotted efficiency (η) is the induction efficiency, i.e., the total power of the metal layer workpiece 20g divided by the total power supplied to both the workpiece and the inductor. Three different curves are plotted. The solid line represents a power signal at 535 kHz, the dashed line represents a power signal at 6.78 MHz, and the dotted line represents a power signal at 13.56 MHz.

[0057] Two circles are marked on the curve starting at 535 kHz. One represents a thickness of 50 nm. Here, the efficiency is slightly above 0.5. The other circle represents a thickness of approximately 6 microns, indicating the setting of the prior art. Here, the efficiency is approximately 0.9.

[0058] At higher frequencies, namely 6.78 MHz and 13.56 MHz respectively, the efficiency is significantly higher with a thin metal layer of 20 g. This is indicated by the circles on the curves corresponding to the above frequencies, showing a thickness of 50 nm. In all curves, the workpiece material is aluminum 6063 with resistivity (ρ) 2.65 * 10⁻¹⁵. -8 It is Ωm.

[0059] As is evident from the curve in Figure 6, using higher frequencies can result in significantly higher efficiency than using conventional frequencies, especially when the workpiece is a thin metal film.

[0060] Figure 7 shows another diagram illustrating the same concept as above, with respect to the sheet resistance defined as SR = ρ / t, and plotting the efficiency of a different inductive sealing system as a function of sheet resistance for several different frequencies of the magnetic field. As can be seen from the figure, the efficiency is maintained at the maximum level as the spacing of the sheet resistance increases, and at the low frequency of 535 kHz, high efficiency is obtained when the sheet resistance is less than 0.1 Ω / sq, i.e., for relatively thick workpieces, while at the frequency of 13.56 MHz, the maximum efficiency is obtained when the sheet resistance is between 0.1 and 10 Ω / sq.

[0061] Referring to Figure 8, a method 100 for manufacturing a packaging container is schematically shown. The method 100 comprises the steps of: providing a packaging material having at least one layer of metallized film; arranging at least two layers of the packaging material on an inductor coil of an induction heating sealing device; supplying power to the inductor coil by controlling an AC power supply to generate a variable voltage / current signal with a frequency higher than 1 MHz; and heat sealing at least two layers of the packaging material by inducing eddy currents in the metallized film for induction heating of the packaging material.

[0062] Step 106, which supplies power to the inductor coil, is preferably performed by controlling an AC power supply to generate a variable voltage / current signal with a frequency in the range of 1 MHz to 30 MHz, preferably with frequencies of approximately 2 MHz, 6.78 MHz, 13.56 MHz, or 27.12 MHz.

Claims

1. An induction heat sealing system (40, 40') comprising a packaging material (20) having at least one metallized film (20d), The induction heating sealing device (50, 50') comprises an AC power supply (54) and an inductor coil (52) connected to the AC power supply (54) and configured to induce eddy currents in the metallized film (20d) for heating the packaging material (20), wherein the AC power supply (54) is configured to generate a variable voltage / current signal (S) from 1 MHz to 30 MHz. The metallized film (20d) includes a metal layer (20g) having a thickness of less than 0.5 μm. Induction heating sealing system (40, 40').

2. The thickness of the aforementioned metal layer (20 g) is 20 to 70 nm. The induction heating seal system (40, 40') according to claim 1.

3. The thickness of the aforementioned metal layer (20 g) is 25 to 50 nm. The induction heating seal system (40, 40') according to claim 1.

4. The aforementioned metal layer (20 g) has a sheet resistance of 0.5 to 10 Ω / sq. The induction heating seal system (40, 40') according to claim 1.

5. The aforementioned metal layer (20g) is aluminum. The induction heating seal system (40, 40') according to claim 1.

6. The AC power supply (54) is configured to generate a 2 MHz variable voltage / current signal (S). The induction heating seal system (40, 40') according to claim 1.

7. The AC power supply (54) is configured to generate a variable voltage / current signal (S) of 6.78 MHz, 13.56 MHz, or 27.12 MHz. The induction heating seal system (40, 40') according to claim 1.

8. The packaging material (20) includes an innermost layer (20h) of a heat-sealable thermoplastic resin layer (20h) having a melting temperature lower than that of the metallized film (20d). The induction heating seal system (40, 40') according to claim 1.

9. The inductor coil (52) is configured to provide a longitudinal seal (LS) to the tubular web of the packaging material (20). The induction heating seal system (40, 40') according to claim 1.

10. The inductor coil (52) is configured to provide a lateral seal (TS) to the tubular web of the packaging material (20). The induction heating seal system (40, 40') according to claim 1.

11. A package manufacturing machine (10) comprising at least one induction heating seal system (40, 40') according to any one of claims 1 to 10.

12. A method for manufacturing packaging containers, A packaging material having at least one layer of metallized film is provided. At least two layers of the packaging material are placed in the inductor coil of the induction heating sealing device. AC power is supplied to the inductor coil to generate a variable voltage / current signal from 1 MHz to 30 MHz. By inducing eddy currents in the metallized film and inductively heating the packaging material, at least two layers of the packaging material are heat-sealed. The metallized film (20d) includes a metal layer (20g) having a thickness of less than 0.5 μm. method.

13. The AC power supply is configured to generate a variable voltage / current signal (S) of 2 MHz, 6.78 MHz, 13.56 MHz, or 27.12 MHz. The method according to claim 12.

14. In order to provide a longitudinal seal of the packaging material, the inductor coil is oriented in the longitudinal direction. The method according to claim 12 or 13.

15. To provide a lateral seal of the packaging material, the inductor coil is oriented laterally. The method according to claim 12 or 13.

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