EP0718198A1 - Method and device for wrapping articles in shrinkable film - Google Patents

Abstract

The procedure involves wrapping different objects(18,19) with shrinkable foil on a conveyor belt within a tunnel (15) and then passing them onwards, it is required that only some objects are wrapped yet others are not. Both sets of objects pass through the tunnel and when the objects pass which are not to be wrapped, the duration of heat application to the foil is reduced so as to be insufficient to seal it around these objects. The choice of which objects not to seal may depend on type, format, thickness, composition or weight. The sequence of both sorts of objects is random. Alternatively, the non-application of foil may be done by temporarily doubling the speed of transit of objects on the belt.

Description

Field of application and state of the art

The invention relates to a method and a device for packaging different objects, in which the objects are covered with shrinkable film and transported on a packaging line that contains a shrink tunnel. A part of the shrink film wrapping of the objects is shrunk and the shrink film wrapping of another part of the objects remains unshrunk.

When packaging objects, in particular sheets of paper, such as, for example, publishing products or computer printouts, which are then to be dispatched, it often happens that thinner and thicker stacks have to be packed in a disordered sequence. The thicker stacks should be wrapped very tightly so that they have the necessary stability for transport. They are therefore packed in shrink film and shrunk by subsequent heating, so that it lies close to the object. However, if you very thin stacks would also shrink, the sheet layers contained therein would contract, bend or wrinkle.

It has therefore already become known to sort the objects covered with shrink film according to their thickness and to guide all objects of a certain thickness around the shrink tunnel or to let them pass under it in order to subsequently re-insert them into the product line in the original order. This is complex in terms of device and leads to malfunctions.

Task and solution

The object of the invention is to provide a method and a device which make it possible to package both thin and thick layers, which are covered with shrink film, with less expenditure on equipment and improved reliability.

This object is achieved by a method in which both parts of the objects are passed through the shrink tunnel and when the part which is not to be shrunk is passed through, the heat effect on the shrink film is briefly reduced to an extent which is insufficient to initiate shrinkage.

The shrinkage or non-shrinkage of the covered objects is preferably determined on the basis of the type, format, thickness, nature and / or weight. Depending on the material properties of the object and the film, the limit is set up to which shrinkage is still reasonable. Below this limit, the only encased object is then passed through the shrink tunnel without shrinking. Both parts (shrunk and unshrunk) can be fed to the shrink tunnel in an unordered order, ie chaotic.

Various measures can be used to reduce the heat impact on the shrink film. One of the most effective is to increase the rate at which the articles pass through the shrink tunnel over the speed intended for shrinkage. This increase will normally be more than twice, preferably three to five times the shrinking speed or more. This shortens the dwell time in the shrink tunnel. When the term "shrink tunnel" is used here, it means the area in which the film can be shrunk under the influence of heat.

Another measure, preferably carried out at the same time as the speed increase, to avoid shrinking is to reduce the heat transfer conditions in the shrink tunnel, in particular by reducing the hot air speed or swirl. In shrink tunnels, the heat transfer is usually carried out by hot air circulation. If, for example, the fans are stopped or their speed is greatly reduced, the heat transfer through the air which is then almost at a standstill is orders of magnitude lower than with full recirculation mode, so that the unshrunk passage can also be made possible or facilitated thereby.

Even in the case of objects that have not been shrink-wrapped, the packaging should fit so tightly that the objects, especially sheet layers, cannot slip in the packaging and thus also ensure data security is. On the other hand, a certain shrink film reserve should be present in the case of shrunk articles, in order to prevent the shrink film, which is stretched too tightly, from tearing at the edges of the article. This is also important for any subsequent barcode or plain text reading. This problem can be solved in that the objects to be packaged are provided with a covering which is sealed on all sides by welding before they pass through a shrink tunnel and the relative excess that the covering has compared to the outer dimensions of the object, depending on the dimensions, in particular of the thickness of the items to be packaged. This means that a relatively thin sheet layer, which will not be shrunk later, can be packed very tightly, while the later shrunk sheet layer receives a corresponding addition when wrapped with the shrink film. This can be solved by a device in which the wrapping line contains a wrapping station for wrapping the objects with shrink film and a subsequent longitudinal welding station, the welding jaws of the longitudinal welding station being dependent on signals from a sensor, for example for thickness measurement, for the objects at a distance are controllable from the longitudinal edges of the objects.

A packaging device for articles can preferably contain control means for reducing the heat effect on the shrink film to a level that does not cause shrinkage, which can be actuated selectively and at short notice when passing through part of the articles.

These control means can include speed control for the conveyor which conveys the articles through the shrink tunnel. At the same time or instead, a control for a circulating air heating device can also be used Control means can be provided, in particular by speed control or shutdown of one or more blower motors. Since it is electrically switchable, this embodiment is particularly simple to set up in terms of apparatus, while possible mechanical deflections or shutdowns of the air flow are also mechanically more complex because of the necessary controllable flaps.

When controlling the circulating air heating, a heating control should also be provided in order to avoid overheating of the heating. To automatically and depending on the type, thickness, nature, weight or format of the objects to decide the shrunk or unshrunk passage, sensors can be provided, for example height sensors in the manner of light barriers, load cells or the like. These can be arranged in front of the shrink tunnel. However, they can preferably be provided in front of an upstream coating station or longitudinal welding station. In this case, depending on the dimensions, in particular the thickness, of the objects, the longitudinal welding station could be controlled so that it envelops the objects with different densities by controlling the distance of the longitudinal welding jaws from the longitudinal edges of the objects and thus from one another.

In order to prevent the shrink tunnel from switching from shrinking operation to non-shrinking operation while an object is in it, which would then lead to incomplete shrinkage, it should be ensured that the shrinking tunnel is free of objects before the switchover. This can be detected by appropriate sensors (light barriers or the like), for example at the shrink tunnel entrance and / or exit, which control a buffer station which is connected upstream of the shrink tunnel and which, in the case of a switchover, ie in the sequence of objects to be shrunk and not to be shrunk, creates the corresponding gap in the flow of the objects.

These and further features emerge from the claims and also from the description and the drawings, the individual features being realized individually or in groups in the form of sub-combinations in one embodiment of the invention and in other fields and being advantageous and capable of being protected by themselves Can represent versions for which protection is claimed here.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1

eine schematische Seitenansicht einer Verpackungslinie mit Schrumpftunnel,

Fig. 2

eine Draufsicht auf die Verpackungslinie und

Fig. 3

eine schematische teilgeschnittene Seitenansicht des den Schrumpftunnel enthaltenen Details der Verpackungslinie.

An embodiment of the invention is shown in the drawings and is explained in more detail below. The drawings show:

Fig. 1

a schematic side view of a packaging line with shrink tunnel,

Fig. 2

a top view of the packaging line and

Fig. 3

is a schematic partially sectioned side view of the shrink tunnel contained details of the packaging line.

DESCRIPTION OF THE EMBODIMENT

A packaging line 11 subsequently contains the following stations: a banding station 12, a longitudinal welding station 13, a buffer station 14, a shrink tunnel 15 and an outlet and cooling station 16.

A multiply subdivided belt conveyor 17 runs through all stations and conveys objects 18, 19 one after the other in the conveying direction 20 through the stations.

At the entrance to the packaging line there is a system table 21 on which the objects, for example printed products or printouts from an individual printer, for example computer lists, are placed manually or automatically. The system table has a transport system with grippers 22 which reach through the free-running conveyor belt and push the objects into the banding station 12 in precise alignment.

In the banding station 12, a film curtain is formed from two shrink film webs 23, 24, which are unwound from supply rolls 25, 26 above and below the conveyor level 17, into which the article 19 is inserted by the gripper 22 in the exemplary embodiment. The film, which may possibly be conveyed in synchronism with the movement, therefore lies closely around the front edge and over the top and bottom of the object and beyond the rear edge. There it is separated by a cross welding station 27, consisting of an upper and lower welding jaw, and at the same time the two separate foils are welded together again at the wrapping and foil process. The object is thus surrounded by a closed band, which has a weld seam on the front and rear edge and is temporarily open on both sides, the film projecting over the side edges there. The control of the cross welding station can already take place depending on the thickness of the object, so that the weld seam runs as far as possible in the middle of the height of the front or rear edge.

It can be seen that two types of objects, namely a relatively tall object 18, for example a stack of more than 100 sheets of normal paper (10 mm and more), and a very thin object 19, for example a stack of paper of less than 100 sheets , are shown. Both are treated differently below.

In the longitudinal welding station 13, in which the objects are introduced on the belt conveyor 17 with additional guidance of an upper belt 28, there are longitudinal welding jaws 58 which can be adjusted and controlled both in their height and in their mutual distance. This can be done via hydraulic, pneumatic or electromotive drives, not shown, as well as the closing movement of the longitudinal welding jaws.

The subsequent buffer station 14 contains a belt conveyor 29 which is independently driven by the other belt conveyors 17 by an individually controllable drive 30 and which can convey an object 18 or 19 lying thereon (see FIG. 3) into the shrink tunnel 15 by moving the object to the Shrink tunnel conveyor 31 passes. This is also driven by an independent drive 32, which can be speed-controlled or controlled within wide limits, and consists of a heat-insensitive conveyor belt which runs along the underside of the actual shrink tunnel area 33 and then runs back, via tensioning and drive rollers, on the underside of the shrink tunnel unit.

The shrink tunnel 15 shown in more detail in FIG. 3 contains a basic housing 33 in which the conveyor 31 is guided and supported. The strand 34 of the belt conveyor which acts as a conveyor and which forms the conveying plane for the objects 18, 19 runs at the upper edge of this basic housing and Above a heating trough 35, in which a fan 37 driven by an electric motor 36 and a heater 38 consisting of electric heating elements are arranged. The heating is regulated by a temperature control to avoid overheating with low heat consumption.

Air guide channels 39 extend laterally upward from the heating trough and form the side walls of a shrink hood 40 which surrounds the tunnel region 41. The objects run into and out of the tunnel region through their inlet and outlet openings 42, 43, which are equipped with corresponding curtains or locks.

The side air channels have outlet slots 44 with control slides or flaps, not shown, in order to be able to direct the circulating hot air as uniformly as possible onto the objects. Near the inlet opening 42, there is a lateral suction channel 45 which, via a suction opening 46, directs the air out of the tunnel back into the blower 37, from which, as symbolized by the arrows 47, it exits into the tub 35 again. A heating air circulation system is thus created which, in operation, enables rapid heat transfer to the shrink film covering 48 of the objects, thanks to high turbulence and air speed.

Sensors, for example light barriers 49, for the detection of the objects can be arranged in the area of the inlet and outlet openings 42, 43.

The outlet and cooling station adjoining the shrink tunnel 15 also contains a belt conveyor and ensures rapid cooling of the shrink film. From there, the items are forwarded or palletized.

FUNCTION

The incoming objects can already be measured on the system table 21 or at any point with regard to their type and dimensions, the measuring point e.g. depending on the cycle sequence. For example, a light barrier measuring device 49 can be provided there, which differentiates objects above or below a certain thickness or also measures the thickness in certain steps or continuously. This is of interest for the different work stages. Already during the banding in the banding station 12, the welding jaw movement can be controlled depending on the thickness of the objects, in order, as already stated, to adjust the height of the weld seam approximately to the middle of the rear edge.

This is even more important in the subsequent longitudinal welding station. On the one hand, the height of the upper straps 28 can be adjusted according to the thickness of the object and, on the other hand, not only the height at which the longitudinal welding takes place is set there by correspondingly raising the lower welding jaw according to the thickness of the object, but also the distance between the Welding jaws from the longitudinal edges 50 of the objects. Format information (measured or set) is also taken into account. For example, in the case of a very thin object, this distance is chosen to be as small as possible, especially if this object is to be passed through the shrink tunnel without being shrunk in a manner to be explained later. Then the longitudinal welding results in a packaging which is closed on all sides and is relatively close-fitting and which, owing to the relatively low weight of the entire object, is also good and without slipping of individual parts of the object, for example the individual sheets of one Stack of paper that is transportable. This is particularly important because, in the case of packaged documents, such as computer lists, it should be impossible to be able to see between the individual sheets of the stack without opening the cover.

In contrast, depending on the result of the thickness measurement and controlled by a control and operating device 51 for a thicker object 18, the distance of the longitudinal welding jaws from the side edges 50 of the object is increased in order to create some shrinkage reserve and to avoid that a shrink film stretched too tightly , especially at the edges and corners, tears when shrinking.

An object thus encased on all sides is conveyed to the buffer station 14, from where it is passed on to the shrink tunnel. If it is a thick object 18, which is therefore above a limit thickness set on the operating device, then the shrink tunnel is operated in normal operation, ie the speed of the shrink tunnel conveyor 31 is such that the residence time of the object in the shrink tunnel together with that by the fan 37 generated and heated by the heater 38 air flow is sufficient to heat the envelope 48 above the shrinkage limit of the film and shrink the film tightly around the object. For this purpose, the air is strongly circulated at a temperature of approximately 180 ° C. and the conveyor 31 is operated at a speed of between approximately 2.5 and 5 m per minute. These values depend on the length of the shrink tunnel, its dimensions, the size of the air movement, the type of objects, the shrink film, etc.

After leaving the shrink tunnel, the object passes through the outlet station and is further processed after cooling.

If an object 19 with a thickness entered below the limit value arrives in the buffer zone 29, the controller 51 first checks whether there is no object 18 with the covering 48 to be shrunk in the shrink tunnel. This can be determined via the sensors 49 either directly by means of the thickness values measured by them or by an electronic control which passes on the values measured at the measuring station 49, so to speak. If this is not the case, the shrink tunnel is prepared for ineffective passage through the fact that the conveyor 31 is brought to a substantially higher speed, for example a speed of 15 to 30 m per minute. At the same time, the fan 37 can be practically switched off by switching off or down-regulating the motor 36, for example by frequency control of the motor, so that the air only moves slightly within the shrink tunnel. As a result, the heat transfer values from the air to the film decrease so much that the article 19, especially due to the shorter dwell time due to the higher speed, can pass through the shrink tunnel without the film wrapping 48 being subjected to shrinkage. It is thereby avoided that the shrinkage associated with considerable forces curls up or wrinkles the relatively thin and flexible object. Through the passage of the non-shrunk items through the shrink tunnel, there is the advantage that the items are at the end of the packaging line in the same order as they were entered, which is important for later processing, such as shipping can be, although they are "chaotic" in succession in terms of their shrinkage or non-shrinkage.

The shrinkage limit can also be chosen depending on other conditions, such as the resistance of a paper in a stack, the weight or other conditions.

If several of the same, i.e. either objects 18, 19 to be shrunk or not to be shrunk follow one another, the buffer station can be overrun without having to intervene. If a series of objects that are not to be shrunk is followed by an object 18 that is to be shrunk, then it is held in the buffer station until the last object 19 that is not to be shrunk has left the shrink tunnel. The speed of the conveyor belt is then reduced to the "shrinking speed" and the fan is turned up again. Depending on the circumstances, it could also be sufficient to only reduce the dwell time and let the blower continue to run if objects that are not to be shrunk are passed through. The buffer station 14 also serves to accelerate the objects in such a way that they can be brought to the different speeds with as little interference as possible. It only takes a short time to start up and shut down the shrink tunnel so that the maximum performance of the shrink tunnel is not reduced. The method and the device for the passage of the objects with or without shrinkage are also for only banded, i.e. Objects not provided with a cover that is closed on all sides.

Claims (12)

Method for packaging different objects, in which the objects (18, 19) are covered with shrinkable film (23, 24) and transported on a packaging line (11) which contains a shrink tunnel (15), with some of the objects (18) the shrink wrap (48) is shrunk and the shrink wrap (48) remains unshrunk for another part of the objects (19), characterized in that both parts of the objects (18, 19) are passed through the shrink tunnel (15) and when the part (19) which is not to be shrunk is passed through, the heat effect on the shrink film covering (48) is briefly reduced to an extent which is not sufficient to initiate shrinkage. Method according to claim 1, characterized in that the shrinking or non-shrinking of the covering (48) of the objects (18, 19) is initiated depending on the type, format, thickness, nature and / or weight of the objects. Method according to claim 1 or 2, characterized in that both parts of the encased objects (18, 19) are fed to the shrink tunnel (15) in an unordered order (chaotic). Method according to one of the preceding claims, characterized in that, for non-shrinking, the speed of the passage of the objects (19) through the shrinking tunnel (15) is increased compared to the speed intended for shrinking, in particular by at least twice, preferably by that 3 to 5 times or more. Method according to one of the preceding claims, characterized in that the heat transfer conditions in the shrink tunnel (15) are reduced for non-shrinkage, in particular by reducing the warm air speed or swirl. Method in particular according to one of the preceding claims, characterized in that objects (18, 19) to be packaged are provided with an envelope (48) which is closed on all sides by welding before passing through a shrink tunnel (15), the relative excess that the envelope (48) compared to the outer dimensions of the object (18, 19), depending on the dimensions, in particular the thickness, of the objects (18, 19) to be packaged is changed. Packaging device for objects (18, 19) in shrink film (23, 24) with a packaging line (11) containing a shrink tunnel (15) by control means (51) for reducing the heat effect on the shrink film covering (48) to a level which does not cause shrinkage, which can be actuated selectively and at short notice when passing through part of the objects (19). Packaging device according to claim 7, characterized in that the control means (51) contain a speed control for a conveyor (31) which conveys the articles (18, 19) through the shrink tunnel (15). Packaging device according to claim 7 or 8, characterized in that the control means (51) comprises a control for a circulating air heating device (37, 38) of the shrink tunnel (15), in particular by speed control or shutdown of a blower motor (36), optionally connected with a heating control for the circulating air. Packaging device according to one of claims 7 to 9, characterized in that the control means (51) contain sensors for the objects (18, 19), in particular their type, format, thickness, nature and / or weight, depending on their signals the control means initiate shrinking or non-shrinking of the shrink wrap (48) of the articles (18, 19). Packaging device according to one of claims 7 to 10, characterized in that a buffer station (14) is provided in the packaging line (11) in front of the shrinking tunnel (15), which, when the type of packaging is changed (shrunk or unshrunk), of objects (18 , 19) packed differently Retains objects until the previous object has essentially left the shrink area in the shrink tunnel (15) and this is possibly signaled by a sensor (49) placed at the end of the shrink area (41). Packaging device for carrying out the method according to claim 6, characterized in that the packaging line (11) contains a wrapping station (12) for wrapping the objects with shrink film (23, 24) and a subsequent longitudinal welding station (13), welding jaws (58) of the longitudinal welding station (13) as a function of signals from a sensor (49) for the type or dimensions of the objects (18, 19) for the objects (18, 19) in their distance from the longitudinal edges (50) of the objects (18, 19) can be controlled .

Images