The present invention relates to the inductive sealing of containers. In particular, this invention relates to induction sealing of a top of a gable-top container made from a thermoplastics-coated paperboard material.

As is known, containers such as gable-top containers can be produced on so-called blank-fed packaging machines. In such machines, container blanks, made from a laminate material comprised of a paperboard substrate and having one or both of its surfaces of thermoplastics laminate, in the form of tubular sleeves, are formed into packages, sealed at one end, sterilized, filled with the product and finally sealed at the other end by means of a jaw-type sealing device. By providing heat up to a specific temperature melting of the thermoplastics layers occurs and the top fin of the gable-top carton is gripped between two pressure-applying members of the jaw-type sealing device.

In known induction sealing methods, the laminate packaging material comprises a layer of an electrically conductive material, typically aluminium, and involves the induction of electric currents in the aluminium layer. In this way heat is produced which melts and seals together thermoplastics layers in a face-to-face relationship at a sealing zone.

If a container, such as a gable-top container, includes a multiplicity of layers of material face-to-face in a sealing fin region, then the final seal made across all of those layers is often non-optimal owing to the thickness of the material at that region.

According to the present invention, there is provided apparatus comprising a first sealing member and a second sealing member movable relative to said first member, the sealing members serving to seal a container sealing fin therebetween, the first sealing member including a loop-form inductor device, said loop-form inductor device being embedded in a magnetic field concentrator.

Owing to this aspect, a seal of a multi-layered packaging material is obtainable by one heating and pressing cycle. Advantageously, the inductor device is of a loop-form.

The first and second sealing members are preferably a pair of sealing jaws. Specifically, one of the pair is a fixed sealing jaw and the other is a movable sealing jaw movable relative to the fixed one. Advantageously, both sealing members include an inductor device.

Preferably, the or each sealing member further comprises a cover member serving to cover the inductor. The cover member is, advantageously, made from a nonmagnetic, electrically non-conductive material and provides a required press pattern for sealing of the fin. The required press pattern is necessary where there are different multiples of layers in different regions of the container fin. For example, it is common for there to be, owing to the construction of a thermoplastics coated laminate paperboard container blank from which the container is made, more layers of the laminate paperboard material when the blank is folded, in the lower region of the sealing fin compared to the upper region.

The cover member may comprise a socket for connecting the loop-form inductor with a power supply by way of, for example, one or more flexible coaxial cables. In this way, the movable sealing jaw is thereby free to move during the press operation.

It is also preferable that the loop-form inductor is supported by a support member in the form of a press beam member.

According to a second aspect of the present invention, there is provided a method comprising providing a laminate comprised of a paperboard layer, an electrically conductive layer and a thermoplastics layer, shaping said laminate into a partially formed gable-top container having a top sealing fin region so as to bring a multiplicity of layers of said thermoplastics layer into a face-to-face relationship with each other in said region, and sealing said multiplicity of layers face-to-face with each other using first and second sealing members, wherein the sealing of the multiplicity of layers is performed in a single induction sealing operation. Owing to this aspect, a sufficient seal of a multi-layered packaging material is obtainable by one heating and pressing cycle.

The multiplicity of layers of material to be sealed together is at least three.

Advantageously, the induction sealing operation is by way of an inductor located in at least one of the sealing members and embedded in a magnetic field concentrator.

Preferably, the sealing operation comprises a heating phase and a cooling phase.

In order that the present invention can be clearly and completely disclosed, reference will now be made, by way of example, to the accompanying drawings, in which:-

Figure 1 is a schematic perspective view of a sealing jaw,

Figure 2 is an exploded view of the components of the sealing jaw of Figure 1 , and Figures 3A to 3C show the configuration of a pair of sealing jaws during a sealing operation.

Referring to the Figures, a sealing jaw 2 comprises a press beam member 4, a loop- form inductor device or member 6 and a cover member 10. The inductor 6, which is preferably of a hollow tube-like form and constructed from an electrically conductive material, sits in a recess 8 of the press beam 4 and the cover 10 also fits into the recess over the inductor 6 with its external surfaces substantially flush with the immediately surrounding external surfaces of the press beam 4. The inductor 6 is also capable of being cooled by a cooling fluid, such as a cooling liquid, introduced into the sealing jaw 2. The cover 10 comprises holes 12 which allow a passage to corresponding sockets 14 in the inductor 6. Coaxial cables (not shown) pass through the holes 12 and plug elements on the end of the cables connect with the sockets 14 to deliver electrical power to the inductor. The inductor member 6 also includes a magnetic field concentrator. The magnetic concentrator may preferably be made of soft magnetic composites. The sealing devices of Figures 1 to 3 is suitable for use on aseptic-type packaging machines where the laminate material used comprises at least one layer of an electrically conductive material, typically aluminium. The top sealing operation of gable-top cartons 16 is performed after a product filling stage, and is provided by the induction of electrical currents in the aluminium layer.

Induction heating is the non-contact electromagnetic process where a conductive material, such as an aluminium layer in the thermoplastics coated paperboard laminate, passes through a magnetic field that emanates from the inductor member 6. An electrical current is fed through the inductor member 6 supplied through the coaxial cables at a specific frequency and power level to bring about the heating of the fin of the container. The magnetic field is applied for a relatively short time whilst the container has stopped at the sealing station of the packaging machine. Since only the magnetic field that intersects the fin actually does any useful work, the magnetic field concentrator is used to conduct the magnetic field asymmetrically so that the energy generated by the magnetic field is concentrated towards the area where the magnetic field intersects the fin. Thus, the concentrator conducts the magnetic field more efficiently than air thereby effectively aiming and intensifying the asymmetric magnetic field at the area of the fin to be heated.

Referring to Figure 3A, a pair of sealer jaws 2 are shown in a sealing position, sealing the top fins of two gable top cartons 16. The sealer jaw 2 on the right-hand side of the top fins is a fixed jaw whilst that jaw 2 on the left-hand side of the fins is movable relative to the fixed jaw 2. Figure 3B shows the position of the two cartons 16 with the movable jaw 2 removed. The cover member 10, on its face 18 which contacts the top fin 20 of each of the cartons 16 has a first thickness in an upper section 18' and a second thickness 18" in a lower section. The first thickness is different from the second thickness in order to accommodate the amount of different layers of laminate material in the fins 20 of the cartons 16. At a lower gable seal region 20' of the fin 20 there are more layers arranged in a face-to-face relationship than in an upper gable seal region 20" of the fin 20 and so the thickness of the section 18" is less than the upper section 18' in order to accommodate that extra material thickness at the gable seal region 20'. Figure 3C shows, schematically the position of the inductor member 6 in the fixed jaw 2. The inductor member 6 is advantageously of a loop-form and, for sealing, arranged so that the loop is substantially vertical to be in close proximity and substantially parallel to the substantially vertical top fins 20 of the cartons 16.

The press beam member 4 comprises a recess 22 at the rear underside in order to accommodate a pour spout fitment 24 attached to a top roof sub-panel 26 of the cartons 16.

Such an arrangement allows a sealing configuration with up to five layers of the laminate packaging material arranged face-to-face in the lower gable seal region 20' and up to three layers in the upper gable seal region 20".

The inducing of the asymmetric electromagnetic field simultaneously produces a flow of heat-producing eddy currents within all electrically conductive aluminium layers of the cartons 16. The pair of jaws 2 are able to perform a top sealing operation within a single heating and pressing cycle, perform the sealing operation with one or, if using a double-indexing packaging form-fill-seal machine, two cartons 16 in parallel (as shown in Figures 3A to 3C), apply sealing energy symmetrically from two electrically active sealing jaws 2, apply the asymmetric electromagnetic field at relatively lower frequencies up to 200 kHz, and apply an electrical current in the inductor members 6 flowing in an opposite direction.

The fluid cooled inductor member 6 present in each of the pair of jaws 2 may have a variable cross-section in the top and bottom gable seal areas. Since the degree of heating energy generated by the magnetic field is proportional to the cross-sectional area of the inductor member 6, this variable cross-section allows the ability to adjust the energy output according to the number of layers of material in the lower and upper gable seal regions 20' and 20" respectively.

The whole sealing cycle is approximately 1800 milliseconds in length of time and comprises a relatively short heating phase when the asymmetric magnetic field is generated of around 400 to 500 milliseconds. This heating phase is then followed by a cooling phase when a cooling fluid is introduced into the sealing jaws. The cooling phase is not only important for cooling the inductor member but also provided a useful cooling effect on the sealing fin of the container in order to achieve a sufficient seal over substantially the whole region of the fin 20. This cooling phase of the sealing cycle is preferably carried out at the same location as the heating phase, but could alternatively be carried out at a separate cooling station located at a subsequent indexing position of the containers in the packaging machine.

The cover member 10 is preferably non-magnetic, electrically non-conductive and advantageously made of thermoplastics or ceramic material providing the required press pattern, as discussed above.

The holes 12 for connecting the inductor 6 with a power supply through the flexible coaxial cables (not shown), enable the movable jaw 2 to move relatively freely during the sealing operation.

The present invention thus enables the reduction in the time needed for performing the sealing operation of a top sealing fin of gable-to containers, the minimizing of space requirements as well as providing the efficient heating of the multi-layered packaging material.