Induction sealing device and method of sealing a packaging material using said induction sealing device

Abstract

The present invention relates to an induction sealing device for heat sealing of packaging material. The sealing device comprises a conductor partly encapsulated in a supporting body for cooperation with the packaging material during sealing. The coil conductor has a reduced cross sectional area at at least one position along the coil conductor so as to concentrate the magnetic flux induced by the coil conductor at the at least one position. The invention also relates to a method of heat sealing a packaging material using the induction sealing device.

Claims

1. A method of heat sealing a packaging material, the method comprising the steps of: sealing together a first, inner edge and a second, outer edge of a packaging material blank in an overlapping area in which the two edges overlap using an induction sealing device, the induction sealing device comprising: a first conductive strip having a first cross-sectional area and a second cross-sectional area that is smaller than the first cross-sectional area; and a second conductive strip having a third cross-sectional area that is larger than the first and second cross-sectional areas; wherein, when the first, inner edge and the second, outer edge of the packaging material blank overlap, the packaging material blank has a first end and a second end, a length of the packaging material blank extending between the first and second ends; positioning the induction sealing device on an outer side of the overlapping area such that the second conductive strip is proximate to the second, outer edge of the packaging material blank; and positioning the induction sealing device over the overlapping area such that the first conductive strip is aligned with the first, inner edge of the packaging material blank and the second cross-sectional area is positioned over the first end of the packaging material blank.

2. The method according to claim 1, wherein a height of the first cross-sectional area is larger than a height of the second cross-sectional area.

3. The method according to claim 1, wherein a width of the first cross-sectional area is larger than a width of the second cross-sectional area.

4. The method according to claim 1, wherein a height of the first cross-sectional area is larger than a height of the second cross-sectional area and wherein a width of the first cross-sectional area is larger than a width of the second cross-sectional area.

5. The method according to claim 1, wherein the second cross-sectional area is 30-70% the first cross-sectional area.

6. The method according to claim 5, wherein a height of the first conductive strip is constant, and wherein a width of the second cross-sectional area is 30-70% of a width of the first cross-sectional area.

7. The method according to claim 1, wherein said induction sealing device comprises first and second connectors configured to connect to a power supply, wherein said first connector is connected to a first end of the first conductive strip, and wherein said second connector is connected to a first end of the second conductive strip, and wherein the induction sealing device further comprises a conductive bridge electrically interconnecting second ends of the first and second conductive strips in order to allow electrical current to flow therethrough.

8. The method according to claim 7, wherein the first and second conductive strips are parallel and rectilinear.

9. The method according to claim 7, wherein the first and second conductive strips are exposed to the environment at a working surface of the induction sealing device, said working surface configured to contact the packaging material blank during sealing, each of the first and second conductive strips comprising a protrusion extending outwardly beyond the working surface.

10. The method according to claim 7, wherein a height of the third cross-sectional area of the second conductive strip is larger than the a height of the second cross-sectional area of the first conductive strip.

11. The method according to claim 1, wherein a height of the first and second conductive strips is constant, and a width of the third cross-sectional area of said second conductive strip is about 15-35% larger than a width of the first cross-sectional area of said first conductive strip.

12. The method according to claim 1, wherein the induction sealing device further comprises an elongated supporting body that at least partially encapsulates the first and second conductive strips, wherein the first and second conductive strips comprise a metallic material and the elongated supporting body comprises a polymeric material and a core of a metallic material.

13. The method according to claim 12, wherein the induction sealing device further comprises a flux-concentrating insert, and wherein the elongated supporting body comprises heat-conducting material and houses said flux-concentrating insert.

14. The method according to claim 1, wherein said first and second conductive strips together comprise a single loop coil.

15. The method according to claim 1, wherein said second cross-sectional area spans a portion of a length of the first conductive strip, and wherein the second cross-sectional area is placed over the first end of the packaging material blank at a center of the portion.

16. The method according to claim 1, further comprising placing a heat sealable material around a portion of the inner edge of the packaging material blank.

17. The induction sealing device according to claim 13, wherein said flux concentrating insert comprises a magnetic compound of a polymer and soft magnetic particles.

18. The method according to claim 1, wherein the induction sealing device further comprises an elongated supporting body having cavities, each cavity at least partially encapsulating one of the first and second conductive strips, the elongated supporting body further comprising a cutting groove positioned in between the cavities.

19. The method according to claim 18, further comprising cutting a portion of the packaging material blank simultaneously when sealing together the first, inner edge and the second, outer edge of the packaging material blank in the overlapping area.

20. The method according to claim 1, further comprising wrapping the packaging material around a mandrel of a filling machine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and favorable characterizing features will be apparent from the following detailed description. Equal or corresponding elements are denominated by the same reference numbers in all figures. The features described in connection with the different embodiments can be combined as far as technically possible. The embodiments will be described with reference to the appended figures, in which:

(2) FIG. 1 is a perspective view of an inductor sealing device according to a first embodiment,

(3) FIG. 2 is a side view of the inductor sealing device,

(4) FIG. 3 is a bottom view of the inductor sealing device,

(5) FIG. 4 is a perspective view of a packaging material sleeve, for which the inductor sealing device can be applied,

(6) FIG. 5 is a partial view of the inductor sealing device, indicating the location of the packaging material sleeve, in use,

(7) FIG. 6 is a partial, sectional view of the inductor sealing device, the section being taken along line VI-VI in FIG. 3,

(8) FIG. 7 is a partial, sectional view of the inductor sealing device, the section being taken along line VII-VII in FIG. 3,

(9) FIG. 8 is a partial, sectional view of the inductor sealing device and the packaging material sleeve,

(10) FIG. 9 is cross sectional view of a transversal sealing device along the line C in FIG. 11,

(11) FIG. 10 is cross sectional view of a transversal sealing device along the line D in FIG. 11,

(12) FIG. 11 is a view of the coil conductor showing the locally reduced cross section of the coil conductor,

(13) FIG. 12 is a perspective view of the coil conductor of the sealing device according to the present invention showing the locally reduced cross section of the coil conductor,

(14) FIG. 13 is cross sectional view of the magnetic field of a transversal sealing device along the line C in FIG. 11, and

(15) FIG. 14 is cross sectional view of the magnetic field of a transversal sealing device along the line D in FIG. 11.

DETAILED DESCRIPTION OF EMBODIMENTS

(16) A first embodiment will be described in relation to FIGS. 1-8. This is an induction sealing device for use in longitudinal sealing, i.e. sealing the longitudinal ends of a sleeve of packaging material, as described in the background in relation to the carton bottle.

(17) With reference to FIG. 1-3, an exemplary induction sealing device 1 for longitudinal sealing comprises an elongate supporting body 2 having a working surface 7 for cooperation with the packaging material during the sealing process. Partly encapsulated in the supporting body 2 is a conductor 10, often referred to as an inductor coil. A first connector 3 and a second connector 4 are protruded from the supporting body 2 and are arranged to be connected to a power supply (not shown), and are also connected to opposite ends of the conductor 10 for allowing electrical current to flow through the conductor 10. The conductor 10 extends rectilinearly from a first end 1a of the sealing device 10 to an opposite end 1b. It has a longitudinal extension between the first and the second ends 1a, 1b.

(18) The supporting body 2 is typically made of a polymeric material, preferably glass-fiber reinforced polymeric material, and comprises a core of a metallic material, e.g. aluminium or steel. The conductor is made of a metallic material, preferably of one of the following materials: copper (Cu), aluminium (Al), silver (Ag), gold (Au), stainless steel, or of an alloy comprising one or several of said materials.

(19) As seen in FIG. 1 the conductor 10 is partly encapsulated in the supporting body 2, but exposed on the working surface 7 for cooperation with the packaging material. The conductor 10 has a sealing surface substantially in level with the working surface. However, the conductor 10 is provided with a first protrusion 5 and a second protrusion 6, both protruding slightly from the working surface 7 of the induction sealing device 1, see FIG. 2. Further, the conductor 10 comprises a first conductive strip 11, a conductive bridge 13 and a second conductive strip 12. These are best seen in FIG. 3. The first and second conductive strips 11, 12 are arranged in the longitudinal direction of the induction sealing device 1, and are parallel. The conductive bridge 13 is arranged transversally to the longitudinal extension of the induction sealing device 1. The strips together form the sealing surface.

(20) The first and second protrusions 5, 6 do not have a functional effect on the sealing quality. Instead, they are provided for enabling accurate measurements of the location of the seal on the finished package. It is also possible to modify the shape of the protrusions 5, 6 in order to identify which induction sealing device that made which sealing, in case several induction sealing devices are mounted in a filling machine.

(21) A cross-sectional area A.sub.3 of the second conductive strip 12 is larger than a cross-sectional area A.sub.2 of the first conductive strip 11. One way to accomplish different cross-sectional areas is to change the size of the widths of the first and second conductive strips.

(22) The first conductive strip 11 has a width W.sub.2, in the working surface, in a direction transversal to the longitudinal extension of the induction sealing device 1. The second conductive strip 12 has a width W.sub.1, in the working surface, in a direction transversal to the longitudinal extension of the induction sealing device 1, which is illustrated in FIG. 5. In one embodiment the width W.sub.1 of the second conductive strip 12 is slightly wider than the width W.sub.2 of the first conductive strip 11, and is typically about 15-35% wider, preferably around 25% wider. The second conductive strip 12 is between 2.0 and 3.0 mm wide, or between 2.25 and 2.75 mm wide, or 2.5 mm wide. The first conductive strip 11 is between 1.5 and 2.5 mm, or between 1.75 and 2.25 mm, or 2.0 mm wide. The height H, shown in FIG. 6, of the first and second conductive strips is equal. In an alternative embodiment, not shown, the widths W.sub.1 and W.sub.2 are equal but the height H is not equal for the first and second conductive strips. In a further alternative embodiment the cross-sectional areas A.sub.3 and A.sub.2 are equal in size.

(23) The first conductive strip 11 has a portion 11b, at a position 9, with a cross-sectional area A.sub.1 being smaller than the cross-sectional area A.sub.2 of portions 11a and 11c of the rest of the first conductive strip 11. The cross-sectional area A1 of the portion 11b is 30-70% of the cross sectional area A.sub.2 of the portions 11a and 11c of the rest of the first conductive strip 11. The cross-sectional area A.sub.1 of the portion 11b is 40-60% of the cross sectional area A.sub.2 of the portions 11a and 11c of the rest of the first conductive strip 11. The cross-sectional area A.sub.1 of the portion 11b is 50% of the cross sectional area A.sub.2 of the portions 11a and 11c of the rest of the first conductive strip 11. The difference in cross-sectional area is illustrated in FIGS. 6 and 7 showing two sections, one taken along line VI-VI (FIG. 6) and the other taken along line VII-VII (FIG. 7) of FIG. 3.

(24) One way to accomplish a portion 11b with a smaller cross-sectional area A.sub.1 is to give the portion 11b a width W.sub.3 which is narrower than the width W.sub.2 of the rest of the first conductive strip. Preferably, the width W.sub.3 is half as wide as W.sub.2. This is best shown in FIG. 5. With regard to the embodiment shown the width W.sub.3 should be about 50% of the width W.sub.2, or between 0.75 and 1.25 mm or between 0.875 and 1.125 mm or about 1.0 mm wide. A length L, along the longitudinal extension of the induction sealing device, of the portion 11b is between 5 and 15 mm, or between 7 and 11 mm, or about 9 mm. The centre of the portion 11b, in the longitudinal direction, is located about 1,5 times the length L from the first end of the first conductive strip 11. The centre of the portion 11b, in the longitudinal direction, will be centred over a free edge of the packaging material during sealing. This will be described later.

(25) In use, the induction sealing device 1 of the invention is mounted in a holder which is provided with some means for bringing the induction sealing device 1 into contact with the packaging material to be sealed.

(26) In one particular application, the induction sealing device 1 is used for making a longitudinal seal on a sleeve 50, see FIG. 4, to be used for manufacturing a carton bottle package of the type mentioned in the introduction. The sleeve 50 is made by wrapping a packaging material blank around a mandrel of the filling machine, and by sealing together edges 51, 52 thereof in an overlapping area A. The width W.sub.4 of the overlap determines the size of the induction sealing device 1. In a typical application, the edges 51, 52 overlap each other by 8 mm. The total width W.sub.t between outer edges of the first and second conductive strips 11, 12 is almost as wide, or between 7 and 8 mm, or between 7 and 7.5 mm, or about 7.2 mm. The sealing of the inner edge 51 is the most important, and this is handled by the first conductive strip 11, whose outer edge is aligned with the inner edge 51 of the packaging material sleeve. The outer edge of the second conductive strip 12 is either aligned with the outer edge 52 of the packaging material sleeve 50, or is arranged slightly inside said edge, see FIG. 5. FIG. 5 is a partial view of the induction sealing device, which partial view corresponds to the dashed circle IV of FIG. 3.

(27) A top edge 53 of the sleeve, as seen in the longitudinal direction of the sleeve, is to be located, during sealing, in the centre of the portion 11b having the smaller width W.sub.3, i.e. the top edge 53 is arranged at half the length L of the portion 11b, see dashed line E indicating said top edge 53 of the sleeve 50. I.e. the centre of the portion 11b is centred over the top edge 53. The magnetic field from the conductor 10 extends outside the top edge 53 of the sleeve 50, but the induced current will follow the aluminium foil. The current will hence bend off before the edge 53 in a way that may not be optimal. In order to shape the bending of the induced current, and decrease the bending off at the top edge 53, the portion 11b with a smaller cross-sectional area A.sub.1 is arranged over the edge 53 to increase the current density at that point. Since the electromagnetic field depends on the current density, according to Ampre's law, it is thus possible to shape the electromagnetic field in this way. This similarly shapes the induced current in the aluminium foil, such that sufficient heating is achieved where needed, in this case at the intersection of the inner edge 51 and the top edge 53.

(28) FIG. 8 shows a section through the inductor sealing device along line VI-VI (FIG. 3) together with a portion of the sleeve of FIG. 4. As can be seen in the figure a strip 14 of heat sealable polymeric material is surrounding the edge 51 of the sleeve. This is to prevent the liquid food inside the package to be sucked into the raw paper edge. The strip 14 adds extra material to the area to be sealed, and therefore requires more heat to be created. This is the reason the cross-sectional area of the first conductive strip 11 is smaller than the cross-sectional area of the second conductive strip 12. The induced current will be more concentrated in the aluminium foil where the cross-sectional area is smaller, and will therefore locally create more heat.

(29) A second embodiment of the invention will be described in relation to FIGS. 9-14. This is an induction sealing device for use in transversal sealing, i.e. transversally seal a tube of packaging material, as described in the background in relation to the parallelepiped-shaped package.

(30) FIG. 9 is a cross-sectional view of a transversal induction sealing device 1 seen along the cross section at line C in FIG. 11. A supporting body 2 has a cavity 22, in which cavity 22 inductor device 20 is positioned. The inductor device 20 comprises a coil conductor 10 and has active surfaces 25, 26 adapted to be pressed against a packing material surface (not shown) to induce current and thereby heat in a metal layer of the packing material during a sealing process. In the cavity 22 a flux-concentrating insert 30 is moulded around the inductions means 20, without covering the active surfaces 25, 26 of the inductor device. The flux-concentrating insert has an interacting surface 31 that is in level with the active surface 25 of the inductor device 20. The inductor device 20 has a circumferential recess 27 along the outside wall of the coil conductor 10 of the inductor device for locking the inductor device in the cavity. The flux-concentrating insert 30 is moulded by a magnetic compound of a polymer and soft magnetic particles (not shown), the polymer being made by polyamide or polyphenylene sulphide and the magnetic particles being ferrite, NiZn ferrite, FeSiAl, FeSiB or FeNi-alloys. Ni Zn ferrite is preferred. The moulded material may also be reinforced by e.g. glass fiber (not shown). A cutting groove 40 is formed in the supporting body 2 to allow a packing material to be cut simultaneously with the sealing of a packing material on either side of the cutting groove 40. The opening cross section surface of each cavity 22 is smaller than the cross section surface further down in each cavity, locking the moulded flux-concentrating inserts 30 in the cavities 22. The height of the coil conductor 10, in this cross-sectional view, is denoted H.sub.t.

(31) FIG. 10 is a cross-sectional view of a transversal induction sealing device 1 seen along the cross section at line D in FIG. 11. As can be seen the height of the coil conductor 10 is reduced at that position to concentrate the magnetic field, thus increasing the field strength near the active surface 25, 26. The reduced height is denoted H.sub.r in the figure.

(32) FIG. 11 is a planar view of a coil conductor 10 of the inductor device 20. The groove 27 is also visible except at the position 9 where the cross section of the coil conductor is reduced.

(33) FIG. 13 is a perspective view of two coil conductors 10. The groove 27 is also visible except at the position 9 where the cross section of the coil conductor is reduced. In this embodiment only the height of the coil conductor is reduced to locally reduce the cross-sectional area of the coil conductor.

(34) FIG. 13 is a cross sectional view of the magnetic field of a transversal sealing device along the line C in FIG. 11, i.e. the same cross section as in FIG. 9. The magnetic field around the coil conductor at a position without a cross-sectional reduction is shown. In FIG. 14 a cross sectional view of the magnetic field of a transversal sealing device is shown along the line D in FIG. 11, where the cross-sectional area is reduced by reducing the height of the coil conductor. As seen in FIG. 14, the magnetic field is concentrated and locally increased around the active surfaces 25, 26 adding extra power to the heat sealing of the packaging material 50.

(35) As can be seen in the figures the width of the coil conductor is constant in this second embodiment. The width is denoted W.sub.5 and shown in FIG. 3.

(36) It is understood that other variations in the present invention are contemplated and in some instances, some features of the invention may be employed without a corresponding use of other features. It is e.g. understood that the coil conductor may have multiple sections where the cross-sectional area is reduced. Accordingly, it is appropriate that the appended claims be construed broadly in a manner consistent with the scope of the invention.