Device for joining strips of plastic foil material.

DESCRIPTION

The invention relates to a device for joining strips of plastic foil material so as to obtain at least one foil seam, comprising supply means for supplying the two overlapping strips of foil material to a joining position, as well as joining means made up of at least one assembly consisting of at least one stamp element and at least one anvil element, which at least one stamp element and at least one anvil element are each disposed on either side of the joining position and which can be brought into abutment with each other for the purpose of forming said at least one foil seam.

Such a device is generally known, it is used in the packaging industry, where products are to be packaged or enveloped in foil material. With such an application, one or two strips of foil material are wound around the product in an automated process, after which the two overlapping strips of foil material are joined together at the location of a joining position in the device by joining means which are known per se, for example by means of a heating filament.

A drawback of the devices that are currently known is that in order to form a foil seam between the two strips of foil material, the stamp element that forms part of the joining means and the anvil element that cooperates therewith have a constructional length dimension such that the quality of foil seam to be formed, and in particular the bond along the entire length of the foil seam between the two strips of foil material, is adversely affected thereby. This is especially the case with foil seams of considerable length, when the stamp element and the anvil element to be brought into abutment with each other deform under the influence of gravity and thus do not abut each other properly along the entire length of the foil seam to be formed.

The incomplete abutment of the anvil element and the stamp element caused by deformation or sagging results in a foil seam that locally exhibits a weak bond or, in the worst case, no bond at all between the strips of foil material. The foil seam thus realised is of a lesser quality and may come loose locally as a result of the poor bond between the two strips of foil material. Moreover, a locally incorrect abutment or poor bond of the two strips of foil material will lead to a "leaky" foil seam, which is undesirable in those cases in which the product in question must

be hermetically sealed in the foil material.

The object of the invention is to obviate the above drawbacks and to provide a device according to the introductory paragraph by means of which improved foil seams can be formed between the foil material, which strips of foil material are joined along the entire length of the foil seam, so that the foil seam that is obtained in this manner will not only be stronger, and will thus come loose less easily, but which above all will be hermetically sealed without any "leaking", incorrectly abutting strips of foil material.

According to the invention, the device is characterised in that abutment means are provided, which, in order to form said at least one foil seam, aid in achieving a full abutment of said at least one stamp element and said at least one anvil element against each other along the entire length of the foil seam to be formed. In this way any deformation of the joining means along the length of the foil seam to be formed is compensated (or prevented), and as a result of the full abutment of the joining means against each other a completely sealed foil seam between the two strips of foil material will be realised, which foil seam will not only be stronger but will also come loose less easily.

More specifically, the abutment means form part of said at least one stamp element and/or said at least one anvil element, and in a special embodiment the abutment means comprise several magnets disposed along the entire length dimension of said at least one stamp element and/or said at least one anvil element.

As a result, a proper abutment along the entire length, and thus a correct clamping together of the strips of foil material can be realised, which leads to an improved quality and strength of the foil seam to be formed. As a result of the use of magnets, the clamping together of the two strips of foil material is reproducible and takes place in a constant and uniform manner along the entire seam length, which makes it possible to form successive foil seams of the same quality.

Furthermore, this achieves that the strips of foil material are clamped together with a constant, uniform clamping force along the entire seam length, as a result of which the foil seam to be formed will not exhibit any weak points anywhere along its length.

In one embodiment, said at least one stamp element and said at least one anvil element in particular have a length dimension which is at least equal to the length dimension of the foil seam to be formed.

The quality of the foil seam to be formed, at least along the entire

length thereof, is further ensured in that said at least one stamp element can be moved into abutment with said at least one anvil element against a return force. In this way the two strips of foil material are clamped together with a constant force along the length of the foil seam, which leads to a foil seam that will not exhibit any weak points.

In a specific embodiment, said at least one stamp element is mounted on a support that can be moved along a guide.

A spring element which bears on the support may be arranged around the guide in that case. According to a special embodiment of the device according to the invention, said at least one stamp element and said at least one anvil element are arranged for forming two foil seams extending parallel to each other. Said at least one stamp element may that case be made up of two stamp element members extending parallel to each other. More specifically, a cutting element may be disposed between the two stamp element members. In this way two parallel foil seams can be formed in one operation, which foil seams can moreover be separated from each other in the same operation.

To that end said at least one anvil element is made up of two parallel anvil element members that co-operate with corresponding stamp element members, whilst a stop element that co-operates with the cutting element may be disposed between the two anvil element members.

To improve the quality of the foil seam to be formed, each anvil element member comprises a clamping element for clamping the two strips of foil material together and a seam forming element for forming the foil seam.

The seam forming elements may be provided with a heating filament in that case.

The invention will now be explained in more detail with reference to a drawing, in which: Figure 1 is a view of an embodiment of a device according to the invention;

Figure 2 is a larger-scale view of the joining means according to the invention;

Figure 3 is another larger-scale view of the joining means according

to the invention.

Figure 4 is a view of another embodiment of a device according to the invention.

For a better understanding of the invention, like parts of the device according to the invention will be indicated by the same numerals in the description below.

Figure 1 shows an embodiment of a device 10 according to the invention for joining two strips of foil material 8a-8b (see figure 3) so as to obtain a foil seam. Such a device is used in particular for enveloping various products

5-5'-5", which may be supplied to a joining position 6 in the device 10 by specific supplying means 20, in strips of foil material.

In this embodiment the products 5-5'-5", for example boxes, may have considerable dimensions. Said products 5-5'-5" are supplied to the joining position 6 via a working surface 11 by means 20 consisting of an endless carrier 21 that is passed over rollers 22a-22b, of which the roller 22a can be driven by means of a drive unit 23 that is known per se, for example an electric motor. The product 5-

5'-5" to be enveloped in foil material is introduced into the device by means of a pusher element 24 provided with a pushing surface 25, which can be moved to the joining position 6 by means of the endless carrier 21 , in which device foil material is arranged around the product.

To join the foil material that has been wound around the product 5- 5'-5" together, joining means 30 are provided at the location of the joining position 6. The joining means 30 are made up of at least one assembly, which consists of at least one stamp element 31 and one anvil element 32, which are disposed on either side of the joining position 6 and which can be moved towards and away from each other by suitable moving means.

In this embodiment, the stamp element 31 is movably mounted in the device 10. Guides 33 are to that end disposed in the device, between which guides the stamp element 31 is movably provided. The stamp element 31 can be moved towards and away from the anvil element by suitable moving means, for example an endless carrier 34 that is passed over two or more rollers 35a-35b, of which the roller 35a can be driven by a drive unit 36 that is known per se (for example an electric motor).

Upon movement of the stamp element 31 in the direction of the anvil element 32, the strips of foil material 8a-8b present therebetween are pressed together and, using heat, for example, fused together so as to obtain a foil seam.

As figure 2 discloses, the joining means 30 and in particular the stamp element 31 and the anvil element 32 may have a considerable constructional length dimension. A drawback of this known construction is the fact that the stamp element 31 and/or the anvil element 32 may sag, and consequently deform, under the influence of their weight and gravity. As a result, the stamp element 31 and the anvil element 32 will not abut each other properly along their entire length, which corresponds to the length of the foil seam to be formed), so that the two strips of foil material 8a-8b will not be pressed together properly, either, resulting in a reduced quality of the foil seam thus realised, which may easily come loose. With the existing constructions there is above all a risk that the two strips of foil material will not fully abut each other when the foil seam is being formed, resulting in a "leaky" foil seam. In the embodiment as shown in figure 2, the stamp element 31 can be moved towards and away from the stationary anvil element 32. To that end (see also figure 3) the stamp element 31 comprises a girder 310, which can be moved along the guide 33 of the device 10 with its ends 310a-310b (see also figure 1 ). The movement of the girder 310 is effected by the moving means 34-35a-35b-36 as shown in figure 1.

As shown, the joining means 30 are built up of two assemblies, each consisting of a stamp element 311a and 311 b and an anvil element 321 a and 321 b, respectively. Using this construction, two separate foil seams can be formed simultaneously in separate strips of foil material. It will be apparent, however, then it is also possible to use an embodiment of the device according to the invention in which the joining means 30 comprise only one stamp element 311 a and one anvil element 321a.

According to the invention, the device is provided with abutment means 50, which ensure that the stamp element 31 and the anvil element 32 abut each other along the entire length of the foil seam to be formed between the strips of foil material. The abutment means 50 consist of magnets, which are provided along the entire length (longitudinal direction) of the anvil element 32. The magnets 50 may also be provided on the stamp element 31 in a similar manner.

As is shown in the detail view of figure 3, the abutment means,

which ensure that the stamp element 31 and the anvil element 32 will fully abut each other (along the entire length of the foil seam to be formed), comprise magnets 50, which form part of the anvil element 32 in this embodiment. In another embodiment, however, the abutment means 50 may also form part of the stamp element 31. Preferably, and as shown in figure 2, the stamp element 31 is built up of a thin, flexible strip 315, which is slightly deformable and which consequently conforms to the contour of the possibly deformed anvil element 32 when the stamp element 31 is brought into abutment with the anvil element 32 at the location of the joining position 6. As a result of the use of the flexible, deformable strips 315 and the magnets 50 (which are provided either in the anvil element 32 or in the stamp element 31 , or in both elements) a full abutment of the strip 315 against the anvil element 32 along the entire length of the foil seam to be formed is realised, leading to an improved quality of the foil seam that is to be formed in this manner. Since the magnets exert a constant magnetic force between the stamp element 31 and the anvil element 32, the strips of foil material 8a-8b being clamped between the two elements are pressed together along the entire length of the foil seam to be formed. In this way a foil seam that is sealed along its entire length and which does not exhibit any weak or "leaky" spots is realised. Depending on the material properties of the foil material that is used

(such as the thickness, the strength or the plasticizing temperature thereof), it is also possible, however, not to configure the abutment magnets 50 as permanent (natural) magnets, but as electromagnets. In this latter - controllable - version it is possible to adjust the magnetic force by which the stamp element is "pressed" (or "drawn") against the anvil element and thus influence the quality (or strength) of the foil seam to be formed. Thus it is possible to set the magnitude of the magnetic force (using a constant force, or a variable force along the length of the foil seam) along the entire length of the foil seam to be formed.

As is shown in figure 3 (and partially in figure 2), the anvil element 32 is mounted on a girder 320, by which a stationary orientation of the anvil element 32 in the device 10 is realised. The anvil element 32 that is mounted on the girder 320 and the stamp element 31 that is mounted on the movable girder 310 are arranged for jointly forming two parallel foil seams in the strips of foil material 8a and 8b, respectively. The stamp element 31 is to that end built up of two parallel stamp

element members 311 a and 31 1 b. A cutting element 316 is disposed between the two stamp element members 311 a-311 b.

As already indicated in the foregoing, the elongated strip element 315a-31 b has a length at least equal to that of the foil seam to be formed between the two strips of foil material 8a-8b. Accordingly, each stamp element member 31 1 a- 311 b comprises one or more supports 313, on which the elongated strip element 315a-315b is mounted. The various supports 313 are movable along a guide 314. This enables the elongated strip 315a-315b to conform to the contour of the (deformed) anvil element 32. Thus an adequate abutment of the strips 315a-315b against the anvil element 32 can be realised along the entire length of the foil seam to be formed between the strips of foil material 8a-8b. As a result, the strips of foil material 8a-8b are pressed together along the entire length of the foil seam to be formed, thus providing a fully sealed foil seam of uniform strength, which foil seam will not easily come loose and which does not have any weak or "leaky" spots.

Analogously to the construction of the stamp element 31 , which is made up of stamp element members 31 1 a-31 b, the anvil element 32 is according to the invention similarly built up of two parallel anvil element members 321 a-321 b. More specifically, each anvil element member 321 a-321 b is made up of a clamping element 322a-322b, respectively, for clamping the strips of foil material 8a-8b against the strip 315a-315b that forms part of each stamp element member 31 l a- Si b.

In addition to that, each anvil element member 321 a-321 b is provided with a seam forming element 323a-323b, respectively, which cooperates with the clamping element 322a-32b, which seam forming element likewise clamps the two strips of foil material 8a-8b between the strips 315a-315b and forms the foil seam by means of heat, for example by using a heating filament 324a-324b extending in the longitudinal direction. Also other methods of forming the foil seam by means of heat are possible, however, for example by using ultrasound. The function of the two clamping elements 322a-32b is to orient or fix the two strips of foil material 8a-8b in place relative to each other and relative to the seam forming elements 323a-323b so as to prevent the strips of foil material from shifting or coming loose, which might lead to an incorrectly formed foil seam.

In figure 3 the heating filament by means of which the foil seam is

formed between the strips of foil material 8a-8b is indicated by numerals 324a-324b, whilst the clamping surface of the respective clamping elements 322a and 322b is indicated by the numerals 325a-32b.

As already explained in the foregoing, each stamp element 31 is mounted on a support 313 which is movable along a guide 314. Said movement of the stamp element 31 takes place against a return force, which may for example be provided by a spring element 317, which is arranged around the guide 314 and which is confined between the support 313 and the girder 310 that more or less forms part of the fixed structure (but which is movable within the device). To form the foil seam between the strips of foil material 8a-8b, the moving means 34-35a-35b-36 move the girder 310 along the guides 36 in the device 10 towards the anvil element 32, which is fixedly disposed in the device 10. The two strips of foil material 8a-8b are clamped between the strips 315a-31 b and the corresponding clamping elements 322a-32b and the seam forming elements 323a- 32b. After two parallel foil seams have been formed (viz. the foil seam for enveloping a product 5 in foil material and the first part of a seam for the next product 5'), a further movement in the direction of the anvil element 32 is imparted to the girder 310.

The two stamp element members 311a-311 b will at the same time move along the guide 314 against the spring force of the spring element 317. The cutting element 316 will move in the direction of the strips of foil material 8a-8b, cutting the strips through at the location indicated C between the foil seams A-B that have been formed. A stop element 326 is to that end provided between the two anvil element members 321a-321 b. Then the girder 310 is moved upwards in the device 10, thereby moving the stamp element away from the anvil element 32. In this way space is created for discharging the product 5, which is now enveloped in foil material that has been joined at the location of the foil seam B.

The joined strips of foil material 8a-8b at the location of the foil seam A can now be arranged around the next product 5'. In a next operation, the girder 310 is moved downwards together with the stamp element 31 in the direction of the anvil element 32 for forming the end part a seam B (for product 5') and the first part of a seam A (for the next product 5") in one operating step. In this case, too, the two foil seams A and B are separated from each other by means of the cutting element 316.

When the girder 310 carrying the stamp element 31 is moved upwards again, the two stamp element members 311a-311 b will move back along the guide 314 under the influence of the compressed spring element 311 , so that the cutting element 316 "retracts" between the two stamp element members 311a-311 b and the respective stamp strips 315a-31 b.

It will be understood that it is possible to obtain foil seams of a homogeneous, stable quality, without any weak or "leaky" spots, by means of this device, in which magnets 50 cause each stamp element 31 to abut against the anvil element 32 along the entire length of the foil seam to be formed. Figure 4 shows another embodiment of a device according to the invention, in which, in contrast to the embodiment as shown in figure 3, both the stamp element and the anvil element are single elements. The stamp element is provided with one single flexible strip 315, which can be placed on the (likewise single) anvil 320. In this embodiment, too, the flexible strip will be deformed under the influence of the abutment means or the magnets 50 upon forming the foil seam so as to effect a full abutment against the anvil 320 in this manner.

In contrast to the embodiment of figure 3, the foil seam that is formed is not cut through in this embodiment, therefore.