WO2007008132A1

WO2007008132A1 - Device for heating

Info

Publication number: WO2007008132A1
Application number: PCT/SE2006/000634
Authority: WO
Inventors: Robert Rosberg; Morgan Svensson
Original assignee: Tetra Laval Holdings & Finance S.A.
Priority date: 2005-07-11
Filing date: 2006-05-31
Publication date: 2007-01-18
Also published as: TW200711825A; AR053937A1; SE0501637L; SE528871C2

Abstract

A device (42) for heating of a layer of heat-sealable plastic in a first edge portion (52) of a sheet (44) of packaging material, the first edge portion being arranged to, after heating, form a sealed, overlapping joint with an opposite second edge portion (54) of the sheet for forming of a tube (46), is provided. The device comprises a heat rail (10) having a heat surface (12) along which the heat rail is arranged to heat the first edge portion. The device further comprises a counter rail (34) having a counter surface (36) which is arranged to face the first edge portion. The rails are arranged to be positioned opposite each other on an inner side (48) and an outer side (50), respectively, of the first edge portion during heating. The device is characterized in that it further comprises a projecting positioning flange (16) which is arranged along the heat rail and arranged to be inserted on the inner side of the first edge portion to facilitate subsequent positioning of the rails for heating. The positioning flange is inclined in relation to the heat surface of the heat rail so that a material contact surface (22) of the positioning flange leans away from the counter surface of the counter rail.

Description

DEVICE FOR HEATING

TECHNICAL FIELD

The present invention relates to a device for heating of a layer of heat- sealable plastic in a first edge portion of a sheet of packaging material, the first edge portion being arranged to, after heating, form a sealed, overlapping joint with an opposite second edge portion of the sheet for forming of a tube. The device comprises a heat rail having a heat surface along which the heat rail is arranged to heat the first edge portion, and a counter rail having a counter surface which is arranged to face the first edge portion. The rails are arranged to be positioned opposite each other on an inner side and an outer side, respectively, of the first edge portion during heating.

BACKGROUND ART

Packages have been used for a long time for packing and transporting be- verages such as milk and juice but also other pourable products. The packages are often produced in that a web of packaging material is formed into a tube which is closed by sealing of the longitudinal edges of the web in an overlapping condition. The longitudinally sealed tube is continuously filled with a product and then transversally sealed, whereby filled "cushions" are formed. The transverse sealing is made along narrow, transverse, mutually spaced apart, sealing zones. After transverse sealing, the "cushions" are separated from the rest of the tube by incisions in the sealing zones and finally formed into the desired shape. A great many of today's food packages are made of a laminated packaging material comprising a relatively robust core layer of e.g. paper or paper-board and an outer, liquid-tight coating of thermoplastic material on at least that side of the core layer that will form the inside of the packages. Sometimes the packaging material also comprises a gas barrier, for example in the form of an aluminium layer. However, also other types of packaging materials exist, e.g. fibre free packaging materials with multi-layer structure, such as laminates of transparent plastic layers. One example of such a materia! is described in the

Swedish patent application SE 0401215-9, which is incorporated herein in its entirety. Packaging materials of this and similar kinds, but also packaging materials containing relatively little fibres, may be less stable and elastic than the fibre rich equivalents, for example the above described laminated paper-board. The above mentioned forming of the material web into a tube is made by means of a number of tube forming means, usually rings, through which the material web passes. If the packaging material comprises a coating of thermo- plastic, the seal in the longitudinal direction can be achieved by heating of the plastic in at least one of the longitudinal edges of the material web before the edges are pressed together with an overlap. Such heating can be achieved by letting one of the edges of the packaging material pass between two separated parallelly arranged plates where one of the plates is arranged to blow hot air on the edge. During normal operation of a machine for producing packages as described above, a material web is fed through the tube forming means and between the plates whereby the heating of the longitudinal edge becomes essentially even along the tube. In connection with a short-stop of the machine, the feeding of the tube is discontinued, but for practical reasons said one of the plates continues to blow hot air. In order not to risk burning of a portion of the packaging material, the material web should not be arranged between the plates during the operational stop. For this reason, the machine is arranged to automatically push the plates to the side during such an operational stop and back in place when the operational stop is over.

As mentioned above, fibre free and fibre poor packaging materials can be relatively unstable and, thus, at the longitudinal edges of the material web, a so- called "curling phenomenon" may occur. This means that the material, partly because of built-in strains in the material and partly because of heat in the produc- tion environment, rolls itself up. This could result in a problem in connection with positioning of the material web between the plates and, thus, a problem in connection with start-up of the machine after every short-stop as described above. This is due to the fact that the distance between the plates is limited and adapted to receive an essentially plane longitudinal edge of the material web. If the packaging material has rolled itself up along the edge, a situation may arise where the plates during a certain period of time push the edge ahead of themselves instead of receiving it between themselves. In such a case, it will not be possible to obtain a good longitudinal seal of the tube and, therefore, in connection with subsequent filling of the tube, the fill product will leak out into the machine. Then, the machine must be cleaned before it can be put into operation again, a procedure that can be both cumbersome, time-consuming and therefore costly.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a device for heating of a layer of heat-sealable plastic in a first edge portion of a sheet of packaging material which, at least partly, eliminates any limitations that may exist in prior art. The basic concept of the present invention is to provide the plate that attends to the heating of the longitudinal edge of the material web with a projecting angled flange which is arranged to contact the edge and guide this in a suitable way before the arrangement of the material web between the plates.

The device for achieving the object above is defined in the appended claims and discussed below. A device for heating of a layer of heat-sealable plastic in a first edge portion of a sheet of packaging material, the first edge portion being arranged to, after heating, form a sealed, overlapping joint with an opposite second edge portion of the sheet for forming of a tube, according to the present invention, comprises a heat rail having a heat surface along which the heat rail is arranged to heat the first edge portion, and a counter rail having a counter surface which is arranged to face the first edge portion. The rails are arranged to be positioned opposite each other on an inner side and an outer side, respectively, of the first edge portion during heating. The device is characterized in that it further comprises a projecting positioning flange which is arranged along the heat rail and arranged to be inserted on the inner side of the first edge portion to facilitate subsequent positioning of the rails for heating. The positioning flange is inclined in relation to the heat surface of the heat rail so that a material contact surface of the positioning flange leans away from the counter surface of the counter rail.

The packaging material can be composed solely of said layer of heat- sealable plastic, or it can be a laminate where said layer is a coating on a core layer.

The heat-sealable plastic can be any suitable plastic, for example a thermoplastic in a case of a packaging material of multi-layer type.

The sheet can be comprised in a material web to form a part of the same, and the device can be arranged for heating of a first edge portion of this material web. Such an alternative would be particularly useful in connection with a manufacturing method like the initially described.

In manufacturing of packages of the above described type, the overlapping joint corresponds to the seal in the longitudinal direction of the tube, and the purpose of the rails corresponds to that of the plates.

The inclination of the positioning flange should be larger than 0 degrees and smaller than 90 degrees. A preferred interval of the inclination is between 20 and 30 degrees.

The positioning flange can be arranged along the heat rail in a large num- ber of different ways, such as fixedly arranged by welding, soldering, gluing, and so on, hingedly arranged or integrally formed with the heat rail.

An advantage with the present invention is that it can be used with many different types of packaging materials, both fibre free and fibre poor packaging materials where the flange serves an important purpose by guiding a rolled edge so that the sheet can be received between the rails, and fibre rich materials where the flange is not required and automatically can be passive because of its inclination in relation to the heat surface of the heat rail and a plane edge of the sheet. Thereby, the same device can be used in connection with manufacturing of different types of packages, which may involve an economical advantage.

Another advantage with the invention is that already existent devices can be modified to achieve the inventive device.

In accordance with one embodiment, the inventive device can be construc- ted in such a way that the heat rail is arranged to heat the first edge portion by spreading hot air over it. An advantage with this embodiment is that it enables for the heat rail contactless heating of the packaging material.

According to one embodiment, the device is constructed in such a way that an edge thickness of the positioning flange at a maximum distance from a transition between the heat surface of the heat rail and the material contact surface of the positioning flange is less than a thickness of the heat rail at the heat surface. Thus, in this embodiment, the "free" edge of the positioning flange, which is arranged to be inserted first on the inner side of the first edge portion, is pointed in relation to the heat rail at the heat surface. This is advantageous since it facilitates insertion of the flange if the space is limited. As an example, in the case of manufacturing of packages of a tube of packaging material, the inventive device can be arranged just after one or more tube forming means. Then, a pointed flange may be preferable if the distance between the first and the second edge portion is small. The device can be constructed in such a way that the heat surface of the heat rail and the counter surface of the counter rail are essentially parallelly positioned during heating. This is advantageous since a relatively simple construction of the device thereby is enabled. in accordance with one possible embodiment, the device is arranged to move along a curved path for insertion of the positioning flange on the inner side of the first edge portion and the positioning of the rails for heating. The advantage with this construction is that already existing machines can be modified to obtain the inventive device.

The positioning flange can be arranged to contact the packaging materia! only during the insertion of it on the inner side of the first edge portion. This is possible depending on the construction of the flange, e.g. the length and the inclination of the flange, and the construction of the tube. The advantage with this embodiment is that the stresses on the packaging material can be considerably reduced since the flange does not graze the inside of the packaging material unnecessarily when the tube is fed between the rails. Thereby, it will be easier to control the form of the tube, and scratch marks on the inside of the tube can further be prevented. Another advantage is that no attendant changes of a machine in which the device is positioned are required to compensate for such effect of the packaging material that could be caused by means of a flange constantly grazing the inside of the tube.

The inventive device can be constructed in such a way that the counter rail comprises at least one opening arranged to divert heat from a space between the heat rail and the counter rail before the positioning of the rails for heating. This embodiment involves big advantages in a case where the device is included in a machine for manufacturing of packages like the initially described one. As previously explained, the known machine continues to generate heat, by blowing hot air, during short-stops. Even if the device has been pushed to the side, the heat will affect the packaging material since the displacement distance, for practical reasons, is not that large. In fact, the known counter plate has a solid surface and the heat blown out may bounce against the solid surface before hitting the packaging material. This may involve a disadvantage since heat increases the "curling phenomenon" for fibre free and fibre poor packaging materials. By constructing the counter rail with at least one opening, like in the inventive device, the heat can, during a short-stop, be diverted through the counter rail instead of bouncing against the packaging material and affecting this negatively.

The opening in the counter rail can be arranged in a large number of different ways, e.g. as a through hole which opens into the counter surface. Such a construction is relatively uncomplicated.

Of course, the features discussed above can be combined in the same embodiment.

BRIEF DESCRiPTSON OF THE DRAWINGS The invention will be described in further detail with reference to the appended schematic drawings, which show an example of a presently preferred non-limiting embodiment of a device according to the present invention.

Fig. 1 a is a front perspective view showing a heat rail of the device.

Fig. 1 b is a back perspective view showing the heat rail of the device. Fig. 2a is a back perspective view showing a counter rail of the device.

Fig. 2b is a front perspective view showing the counter rail of the device.

Fig. 3 is a cross sectional view illustrating how the heat rail and the counter rail according to fig. 1a-b and fig. 2a-b, respectively, are arranged in relation to each other. Fig. 4 is a perspective view illustrating a web and a tube of packaging material.

Fig. 5a is a front perspective view showing the device according to the invention. Fig. 5b is a back perspective view showing the device according to the invention.

Fig. 6a is a side view showing the device and the tube of packaging material during normal operation.

Fig. 6b is a view from above showing the device and the tube of packaging material during normal operation.

Fig. 7a is a side view showing the device and the tube of packaging material during a short-stop.

Fig. 7b is a view from above showing the device and the tube of packaging material during the short-stop.

DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 a-b and fig. 3 show a heat rail 10 arranged to heat a packaging material, as will be described in further detail below. The heating is done along a heat surface 12 of the front side of the heat rail 10, which heat surface is provided with a number of evenly distributed openings 14. Hot air is blown through the openings 14 and hits a packaging material arranged along the heat surface. The hot air blowing is made in accordance with techniques well known within the art and will therefore not be further discussed.

A projecting positioning flange 16 is arranged along the heat rail 10. The front side of the heat rail 10 and the positioning flange are integrally formed of a metal sheet 18 which is bent along a transition line 20 in such a way that the heat surface 12 of the heat rail 10 evenly transits into a material contact surface 22 of the positioning flange 16. The back side of the heat rail is formed of another metal sheet 24 which is joined to the metal sheet 18 along a weld 26. The advantage of this construction is that the packaging materia! never needs to contact a disturbing weld during norma! operation, which could be the case with an alternative construction. The positioning flange is inclined α = 22-23 degrees in relation to the heat surface 12, and the inventive construction results in that a thickness 28 of the positioning flange at an edge 30 is less than a thickness 32 of the heat rail at the spreading surface 12.

Fig. 2a-b and fig. 3 show a counter rail 34 arranged to, along a counter surface 36 of the back side thereof, face the packaging material which is heated by means of the heat rail 10. The counter surface is provided with a number of evenly distributed through holes 38 which during a short-stop divert the hot air blown through the openings 14 in the heat surface 12, as will be further explained below.

The heat rail 10 and the counter rail 34 are arranged to be positioned op- posite each other so that the heat surface 12 is essentially parallel to the counter surface 36, and the openings 14 in the heat rail 10 are arranged just in front of the holes 38 in the counter rail 34, as illustrated in fig. 3. During normal operation, the gap 40 formed between the parallel surfaces is arranged to receive the packaging material for heating. The heat rail 10, the positioning flange 16 and the counter rail 34 are comprised in a device for heating of a web 44 of packaging material for longitudinal sealing and the forming of a tube 46, which web and tub are shown in fig. 4. The device, which is denoted 42 and shown fig. 5a and 5b, is in turn comprised in a roll-fed machine for manufacturing of packages, which machine is not shown herein. The packaging material is of the initially described type, i.e. a laminate of transparent plastic layers where the outermost layers on both an inner side 48 and an outer side 50 of the material web is of thermoplastic. More particularly, the device is intended for heating of the thermoplastic layer on the inner side 48 in a first edge portion 52 of the web. In fact, also the thermoplastic layer on the outer side 50 in a second edge portion 54 of the web is heated, but for reasons of clarity this is not described in further detail. Thus, after heating, the tube 46 can be completely formed by joining, in an overlapping way, the two edge portions 52 and 54.

During normal operation, the device is arranged at the point A in fig. 4 with the heat rail 10 on the inner side and the counter rail 34 on the outer side of the partially formed tube 46, as shown in fig. 6a and 6b. The material web is fed in a direction B through the device, whereby continuous heating of the edge portion 52 is done by the hot air blown from the heat rail 10. Most of the heating is done one the inner side of the packaging material since this side is facing the heat rail. However, some degree of heating is done on the outer side since the counter rail 34 directs the hot air around, and to the outer side of, the first edge portion. In accordance with well known principles, the material web contacts feeding rolls 56 and 58 at the edge portions 52 and 54. However, these rolls and a number of other components shown in the figures and also some constructions in detail of the device do not directly influence the invention and will therefore not be further described. As apparent from fig. 6b, the positioning flange 16 does not contact the material web, and, thus, has no influence on the same, during normal operation. Sometimes it may be desired to temporarily stop the operation of the machine for manufacturing of packages, e.g. to make adjustments in the machine or change a roll of packaging material that is about to run out. During such a so- called short-stop, the feeding of the material web stops and the device 42 must be pushed to the side not to burn the packaging material since the heat rail 10 continues to blow hot air. The sidewise displacement of the device is made by a turning motion around an axis schematically illustrated and denoted C in fig. 6b and 7b. By the turning motion, the device moves along a curved path and takes a position which is illustrated in fig. 7a and 7b. Since there is no longer any packa- ging material between the heat rail and the counter rail, the heat rail will blow the hot air directly towards the counter rail which diverts it through the holes 38. As apparent from figs. 1-3, the holes 38 are larger than the openings 14, and thereby it will be possible to blow the air directly through the counter rail which makes the heat diversion effective. In this way, the hot air does not bounce against the packaging material with is positive form a curling point of view. For the previously mentioned reasons, a certain degree of material curling will, after all, appear in the edge portions of the web, as shown in figure 7b.

When the machine is to be started after an operational stop, the device must again be positioned in relation to the material web, as shown in figs. 6a and 6b. The displacement of the device to this operational position is achieved by a turning motion which makes the device move back along the curved path. During this motion, the positioning flange 16, as the first component of the device 42, will, with its material contact surface 22, contact the material web at the first edge portion 52. Contact will also take place between a back side 60 of the positioning flange 16 and the packaging material at the second edge portion 54 since the positioning flange pushes the second edge portion away to make the first edge portion more available. When the motion continues, the positioning of the device in the operational position will be completed. Thus, the positioning flange will be inserted on the inner side of the first edge portion to thereby guide it and make sure that material curling does not prevent subsequent positioning of the heat rail and the counter rail on one side each of the material web. Thus, the positioning flange will contact the material web during the very insertion and positioning of the device in relation to the material web. Thereafter, it will however not contact the material because of its inclination and the shape of the tube. This is advan- tageous since the positioning flange thereby becomes completely imperceptible during normal operation but serves its important purpose during the positioning of the device. Above, the purpose of the inventive device in connection with a short-stop of the machine has been described. As the name implies, such a stop is meant to last only during a limited time, and a part of the longitudinally sealed tube will be filled with the intended product during the short-stop. However, during a normal- stop, the tube is emptied of the intended product since such a stop may last for a considerably longer time. When the machine, at a later point of time, again is put into operation, it will be driven until everything works before the tube filling is reinitiated. During a normal-stop, the blowing of hot air from the heat rail is stopped. However, just like in connection with a short-stop, the device is pushed to the side in connection with a normal-stop, which means that the device serves an important purpose also in connection with a normal-stop of the machine.

The above described embodiment should only be seen as an example. A man skilled in the art realizes that this embodiment can be modified in a large number of different ways without deviating from the spirit of the invention. As an example, it would be possible to design the device in such a way that the positioning flange contacts the packaging material to some extent also during normal operation.

As an example, the positioning flange described above has a certain length and a certain inclination. In fact, there is a connection between its length and inclination. If the flange is relatively long, the inclination should be relatively large for the invention to work optimally, and vice versa.

In the embodiment above, the positioning flange is integrally formed with the front side of the heat rail. However, the positioning flange could be separately formed and attached to the heat rail in a suitable way, for example by hinges, screws, rivets or weld joints.

The holes in the counter rail above are through but they could be formed in any other suitable way. As an example, they could extend to a cavity in the counter rail, which cavity opens to the outside of the plate.

Further, the heat rail and the counter rail do not have to be fixedly arranged in relation to each other, in an alternative embodiment, the rails could be arranged with a variable distance that differs between normal operation and operational stop.

Finally, it should be pointed out that the figures are not drawn according to scale.

Claims

1.) A device (42) for heating of a layer of heat-sealable plastic in a first edge portion (52) of a sheet (44) of packaging material, the first edge portion being arranged to, after heating, form a sealed, overlapping joint with an opposite second edge portion (54) of the sheet for forming of a tube (46), comprising a heat rail (10) having a heat surface (12) along which the heat rail is arranged to heat the first edge portion, and a counter rail (34) having a counter surface (36) which is arranged to face the first edge portion, the rails being arranged to be positioned opposite each other on an inner side (48) and an outer side (50), respectively, of the first edge portion during heating, characterized in that it further comprises a projecting positioning flange (16) which is arranged along the heat rail and arranged to be inserted on the inner side of the first edge portion to facilitate subsequent positioning of the rails for heating, the positioning flange being inclined in relation to the heat surface of the heat rail so that a material contact surface (22) of the positioning flange leans away from the counter surface of the counter rail.

2.) A device (42) according to claimi , wherein the heat rail (10) is arran- ged to heat the first edge portion (52) by spreading hot air over it.

3.) A device (42) according to any one of the preceding claims, wherein an edge thickness (28) of the positioning flange (16) at a maximum distance from a transition (20) between the heat surface (12) of the heat rail (10) and the materia! contact surface (22) of the positioning flange is less than a thickness (32) of the heat rail at the heat surface.

4.) A device (42) according to any one of the preceding claims, wherein the heat surface (12) of the heat rail (10) and the counter surface (36) of the counter rail (34) are arranged to be essentially parallelly positioned during heating.

5.) A device (42) according to any one of the preceding claims, arranged to move along a curved path for insertion of the positioning flange (16) on the inner side (48) of the first edge portion (52) and the positioning of the rails (10, 34) for heating.

6.) A device (42) according to any one of the preceding claims, wherein the positioning flange (16) is arranged to contact the packaging material only during insertion of it on the inner side (48) of the first edge portion (52).

7.) A device (42) according to any one of the preceding claims, wherein the counter rail (34) comprises at least one opening (38) arranged to divert heat from a space (40) between the heat rail (10) and the counter rail before the positioning of the rails for heating.

8.) A device (42) according to claim 7, wherein said at least one opening (38) is arranged in the counter surface (36).

9.) A device (42) according to any one of claim 7 or 8, wherein said at least one opening is a through hole in the counter rail.