Packaging of objects using top covering plastic film

Abstract

A method for automatically packaging objects using heat-shrinkable plastic film in a packaging plant comprises the sequential automatic steps of placing a sheet of heat-shrinkable plastic film on top of the object, with the edges of the sheet falling onto the sides of the object, carrying out horizontal perimetral strapping of said sheet along its edges on the sides of the object, providing vertical strapping on the object, transverse to the horizontal strapping, applying shrinking heat to the sheet of heat-shrinkable plastic film which is firmly held on the object by means of the horizontal and vertical strapping. A plant comprising stations (13, 14, 15, 16) and a system (11) for sequentially transporting between them objects (12) for packaging thereof in accordance with the aforementioned method are also described.

Description

[0001] The present invention relates to an innovative automatic plant and to an innovative method for packaging objects, in particular but not exclusively, crates which have a large perimeter and small height, by covering them at the top with a sheet of plastic film, in particular heat-shrinkable film. During recent years, in certain industrial sectors, there has been an increasing need to protect with plastic films at least the top part of relatively large-size objects, in particular storage crates. With the known methods, however, the results appear to be unsatisfactory.

[0002] The known automatic packaging technologies are usually based on pack wrapping or pack hooding.

[0003] Wrapping involves the use of an automatic packaging station in which a head for dispensing a strip of film laterally wraps the pack, while moving vertically upwards so as to deposit around the pack a certain number of turns of the film from the bottom of the pack up to its top end. The film is usually of the stretch type and is subject to a pulling force during winding around the pack so as to grip the pack in a suitably tight manner. If the top surface of the pack also needs to be covered, a plastic sheet of suitable size is positioned on the top surface of the object before the strip of film is wound around, so that said sheet is firmly held by the last upper turns of the laterally wound film. In this way, the top of the pack is protected and closed, but this system is unable to provide a top surface of the sheet which is sufficiently taut and flat, with the result that undesirable depressions often form thereon.

[0004] Hooding instead involves the use of a packaging station which fits a tube of plastic film over the pack, starting from the top end thereof. The tube of plastic film may be automatically unwound from a reel, cut to size for the height of the pack to be packaged and welded at the top so as to form a hood.

[0005] The tube of film usually has a square cross-section, folded in pleats so that it can be flattened and wound to form the reel which the hooding machine unwinds over a suitable length and welds transversely to form the hood to be fitted vertically over the product.

[0006] If the film is of the stretch (or extendable) type, the tube of film must have a circumferential size smaller than the perimeter of the object onto which it is to be fitted and the hood is pulled transversely by special grippers of the station so as to widen it and allow it to be fitted over the object. In this way the hood will thus tighten around the sides of the pack once it is fitted and then released. This system, however, is also such that the top surface of the hood on the pack is not taut and has undesirable wrinkles and depressions.

[0007] If the film is of the heat-shrinkable type, the tubular film has instead a circumference greater than the perimeter of the object onto which it must be fitted and the hood is heat-shrunk by means of application of a suitable stream of hot air after the hooding machine has fitted it over the object, so as to cause it to shrink and tighten around the object.

[0008] The use of hooding, in particular when used with heat-shrinkable film, ensures a greater stability of the packaged product. Where packs with relatively large dimensions must be packaged, it is therefore preferred to use the hooding technique, and in particular that which uses heat-shrinkable film.

[0009] In the case of packs with relatively small dimensions, for example 800 x 1200 mm, they may be easily packaged with the films which can be normally found on market using any of the aforementioned techniques.

[0010] Where there is an increase in the dimensions of the objects to be packaged, however, various technical limitations of the technology used to cover objects with plastic film have emerged.

[0011] In fact, the hooding technique encounters in particular the problem of the limited size of the films which can be found on the market because the film manufacturers are unable to produce tubes of film with perimeters greater than 10 metres owing to technical issues which are difficult to resolve. Moreover, even the construction of a hooding station able to handle tubes of film with large perimeters is very complicated and costly.

[0012] In view of the current technical problems, therefore, it is possible to package properly only relatively small-size packs. For example, considering also tubular films with 10 metres circumference, if the film is of the stretch type, products with a maximum perimeter of 11-12 metres may be hooded owing to the fact that the film is stretched before application, while if the film is of the heat-shrinkable type, products with a maximum perimeter of 9 metres can be hooded since there must be sufficient play to fit the hood over the pack before heat-shrinking it.

[0013] It is thus impossible or in any case very costly to use the hooding technique when the packs exceed a certain perimeter, even only horizontally.

[0014] For example, in order to be able to hood a crate with dimensions of 2000 x 3800 mm it would be necessary to use a tubular film with a circumference of much more than 10 m. In fact, the perimeter of this crate is: 2000 x 2 + 3800 x 2 = 11600 mm. In order to manage to fit a tubular heat-shrinkable film onto a crate with such a perimeter a tubular film with a circumference equal to at least 12 - 12.4 metres and therefore much greater than the aforementioned limit would be necessary.

[0015] Even leaving aside the dimensional limitations of the film, when using any of the conventional techniques mentioned above, the quality of the packaging is limited in the top part of the pack owing to the depressions which form in the film on the top surface of the pack.

[0016] These depressions are all the greater and deeper the greater the area of the top surface of the pack.

[0017] This negative effect is accentuated even further when crates which are open at the top are packaged, since usually in this case the product contained inside the crates does not fill them as far as the edge, but is normally lower, and the film placed in the top part does not remain taut, but forms a depression which may also be relatively deep.

[0018] In any case, the upper depressions in the film create the so-called "swimming pool" effect when the packaged crates or packs are placed or stored outside and are subject to humidity or to rain or to the direct action of the sunlight.

[0019] In fact, the top film (even in the case of heat-shrunk hoods) tends to accumulate water in the depressions, resulting in problems for subsequent handling of the packs. The weight of the water also tends to cause the depressions to sink even further, with more water accumulating.

[0020] The problems associated with the current packaging methods increase even further when a relatively high perimeter of the object is associated with a relatively small height. In fact, the large area of the top surface of the pack makes it difficult to keep the film tensioned on top of the pack, while the limited height of the object does not allow the film to be adequately secured laterally such that it tends to sink down even more or even slip off the edges of the pack. This happens when using both the method of lateral wrapping of a film strip and the hooding method. The hooding method, as mentioned above might be preferable, but it suffers from an increased difficulty in fitting the hood properly owing to the low height of the pack (and therefore the corresponding limited length of the hood) compared to the horizontal dimensions of the pack and therefore the perimeter required for the hood.

[0021] All these difficulties in achieving a satisfactory result for covering with plastic film are particularly evident in the case of objects to be covered with protective plastic film, having horizontal dimensions for example four or five times greater than their height. A typical example consists of objects with a generally parallelepiped shape having horizontal dimensions of at least 2 metres and height of not more than 0.5 metres. In particular, objects of this type which cannot be satisfactorily packaged on their upper surface using the known methods are horizontally extending crates with a low height, especially if open at the top.

[0022] The general object of the present invention is to overcome the drawbacks of the prior art, by providing a packaging method and plant which are able to cover at the top in a rapid and efficient manner using plastic film also packs with large horizontal dimensions (for example with a perimeter of more than 10 m) and also, but not exclusively, with a relatively low height compared to their horizontal dimensions.

[0023] In view of this object the idea which has occurred is to provide, according to the invention, a method for automatically packaging objects using sheets of heat-shrinkable plastic film in a packaging plant, comprising the sequential automatic steps of placing a sheet of heat-shrinkable plastic film on top of the object, with the edges of the sheet falling onto the sides of the object, carrying out horizontal perimetral strapping of said sheet along its edges on the sides of the object, providing vertical strapping on the object, transverse to the horizontal strapping, applying shrinking heat to the sheet of heat-shrinkable plastic film which is firmly held on the object by means of the horizontal and vertical strapping.

[0024] Still according to the invention, the idea which has occurred is to provide a plant for the automatic packaging of objects using sheets of heat-shrinkable plastic film, comprising in sequence a first station for depositing a sheet of heat-shrinkable plastic film, suitable for placing the sheet of heat-shrinkable plastic film on top of an object passing through it, with the edges of the sheet falling onto the sides of the object, a second horizontal strapping station suitable for placing a horizontal strap around the sides of the object, a third vertical strapping station suitable for placing on the object vertical straps arranged transverse to the horizontal strap, and a fourth heat-shrinking station designed to apply shrinking heat to the sheet of heat-shrinkable plastic film firmly held on the object by means of the horizontal straps and vertical straps, the plant also comprising a system for sequential transport of objects to be packaged through the first, second, third and fourth stations.

[0025] In order to illustrate more clearly the innovative principles of the present invention and its advantages compared to the prior art, an example of embodiment applying these principles will be described below with the aid of the accompanying drawings. In the drawings: Figures 1 and 2 show schematic top plan and side elevation views, respectively, of a plant designed according to the invention; Figure 3 shows a schematic elevation view of a first station of the plant, along the line III-III of Figure 1; Figure 4 shows a schematic elevation view of a second station of the plant, along the line IV-IV of Figure 1; Figure 5 shows a schematic elevation view of a third station of the plant, along the line V-V of Figure 1; Figure 6 shows a schematic elevation view of a fourth station of the plant, along the line VI-VI of Figure 1; Figures 7-11 show schematic perspective views of packaging steps performed according to the present invention.

[0026] With reference to the figures, Figures 1 and 2 show an overall view of an example of a packaging plant - generically indicated by 10 - which is designed in accordance with the principles of the present invention and is able to implement the packaging method according to the invention.

[0027] The plant 10 comprises a sequential transport line 11 which transports the objects 12 to be packaged (for example crates with a relatively small height compared to the horizontal dimensions) so that they pass in sequence through a series of stations 13, 14, 15, 16 of the plant between an inlet 17 and an outlet 18 of the plant. The plant 10 may comprise a perimetral safety enclosure 19 which encloses the stations.

[0028] The transport line 11 may be of any known type considered to be suitable and will therefore not be described or shown in detail. In general it may comprise a support surface on which the products are placed so as to be transported through the plant between the inlet and the outlet of the plant. The line 11 may be advantageously formed for example by means of a belt or chain conveyor with rollers for supporting and moving the objects 12.

[0029] As may be easily imagined by the person skilled in the art, the various stations may also comprise their own support surfaces for transfer through the station so as to form together the transport system 11 or part thereof. This is visible for example in Figures 1 and 2 with rectangular surfaces situated close to each station.

[0030] Below terms such as "longitudinal", "transverse", "length", "width", "front" and "rear" will preferably be in relation to the direction of movement of the objects in the plant. The objects 12 may for example be rectangular crates with a relatively small height compared to the longitudinal and transverse dimensions, which are much bigger than the height as can be seen for example in Figure 7.

[0031] The first station 13 of the plant forms a station for depositing a sheet 20 of heat-shrinkable plastic film on the object 12 passing through the station. As can be seen in Figure 8, the sheet 20 is advantageously wider than the top surface of the object 12 so as to hang with its edges along the side faces of the object.

[0032] Various alternatives methods may be chosen to obtain the made-to-measure sheet and deposit it on top of the object so that it hangs from the sides.

[0033] For example, the sheet 20 may be advantageously unrolled and cut from a roll of film inside the station 13. The station 13 may for this purpose for example comprise an unwinder device 21 for unwinding a roll of heat-shrinkable plastic film strip which hangs with a free edge downwards across the path of the objects on the transport system 11, as is clearly visible in Figure 3. The strip of film is chosen to be suitably wider than the transverse dimension of the object 12 to be packaged and the sheet is separated from the strip so as to be also longer than the object such that, when deposited on the object, it is able to hang from the four sides of the object.

[0034] As is clearly visible again in Figure 3, the station 13 may be such as to cause the free flap of the strip of film to hang from above such that said free edge may be engaged by the front edge of the moving object 12, with the strip which is supplied at a speed synchronized with the speed of displacement of the object through the station. In this way, the film may be easily deposited on the entire top side of the object as it passes through the station. Once the strip of film has been dispensed with a length suitable for covering the object over its entire length (plus the part of the film which is to hang from the front and rear edges of the object), a transverse guillotine 22 of the station 13 transversely cuts the strip of film so as to form the separate sheet 20 on the top side of the object, as shown in Figure 8.

[0035] The sheet deposition station may alternatively be differently designed, as may now be easily imagined by the person skilled in the art.

[0036] For example, the sheet 20 may also be applied when the pack is at a standstill, with the station which moves the film, releasing it on top of the product, or the station may first dispense the film required, cut it and then deposit it in the manner of a tablecloth on top of the product by means of special grippers.

[0037] Since in the plant products of varying width may also pass through, the sheet deposition station may also be provided with several reels, each having a film width suitable for a width or width range of products.

[0038] In any case the object 12 covered at the top with the sheet of suitable size continues along its travel path until it reaches the next station 14 in the plant.

[0039] The second station 14 of the plant forms a horizontal strapping station which binds a strap 23 around the perimeter of the object 12 by means of a horizontal strapping head 24. As shown in broken lines in Figure 4, the head 24 (known per se) is advantageously movable vertically so as to be arranged at the correct height and place the strap 23 around the object 12, firmly holding the hanging edges of the sheet 20 against the sidewalls of the object 12 at least at the four corners of the object, as schematically shown in Figure 9. Advantageously, the strap 23 is made of suitable plastic material (for example polyester or polypropylene) and the strapping head 24 cuts it from a continuous strip unwound from a roll and welds it at its ends so as to close it around the object 12, using dispensing, cutting and welding means of the type known per se and therefore not described or not described in detail here, since they may be easily imagined by the person skilled in the art.

[0040] The object 12 covered at the top by the sheet 20 fixed peripherally by the strap 23 continues along its travel path until it reaches the next station 15 of the plant.

[0041] The third station 15 (a front view of which is shown in Figure 5) forms a vertical strapping station with a vertical strapping head 25 which binds further straps 26 at intervals along the longitudinal extension of the object 12 in the station 5, as is clearly visible in Figure 10. The straps 26 thus form rings in vertical planes which are parallel to each other and which intersect the horizontal plane defined by the horizontal peripheral strap 23. The head 25 may advantageously be of the displaceable type so as to move on rails along an object 12 inside the station between a position (shown in solid lines in Figures 1 and 2) at one end of the object into a position (shown in broken lines in Figures 1 and 2) at the other end of the object. Owing to this movement, the strapping head 25 may arrange vertical straps 26 at intervals along the length of the object. Advantageously, the movement of the head is in the direction of movement of the transport system 11 through the station.

[0042] The movement of the head on the product may in any case be a relative movement and, as an alternative to the movement of the head 25 on the product, the transport system 11 may be designed so as to move the object stepwise through station 15. The strapping head 25 may also perform a vertical movement in order to move closer to the top of the product during the step of recovery, welding and cutting of the strap on the product.

[0043] The vertical strapping station may also be a multiple-head station, namely a station which is designed to place simultaneously several vertical straps spaced along the length of the product. The straps placed simultaneously may be all those which are required on the product or a submultiple thereof. In the first case, the product may remain stationary with respect to the multiple head during application of the straps. In the second case there will be a movement so as to place along the length of the product all the straps to be provided. For example, if there is a head which simultaneously places two vertical spaced straps and the product for example requires four vertical spaced straps, then, after the multiple head has placed the first two straps, the product is displaced by two positions with a relative movement with respect to the head, so that the other two straps are simultaneously placed parallel to the first two straps. "Relative movement" is also understood here as meaning that the displacement may occur with a movement of the head relative to the product and / or of the product relative to the head. Advantageously, the straps 26 are made of suitable plastic material (for example polyester or polypropylene) and the strapping head 25 cuts them from a continuous strip and welds them at the ends so as to close them around the object 12, using dispensing, cutting and welding means of the type known per se and therefore not described or not described in detail here, since they may be easily imagined by the person skilled in the art.

[0044] The number of straps 26 applied to the object will depend for example on the length of the object 12. The number of straps will be chosen depending on the desired degree of fixing required for the sheet 20: the longer the object the greater the number of straps 26 which may be applied. For example, the straps 26 may be arranged at a distance of between 20 and 40 cm from each other.

[0045] The object 12 covered at the top by the sheet 20 fixed peripherally by the strap 23 and transversely by the straps 26 continues along its travel path until it reaches the next station 16 of the plant.

[0046] The fourth station 16 of the plant forms a heat-shrinking station with a heat-shrinking head 27 which emits one or more streams of hot air heated to a temperature suitable for causing heat-shrinking of the sheet of plastic film 20. Said temperature will depend on the characteristics of the heat-shrinkable sheet 20, as is well-known to the person skilled in the art. For example, it may be around 100-150°C.

[0047] The heat-shrinking head may for example of the gantry type known per se, i.e. in the form of a transverse bridge or gantry, as can be seen for example in Figure 6, which emits hot air towards the object 12 which crosses it at a suitable speed. The heat-shrinking station 16 is in any case of the known type and therefore is not further shown or described in detail since it may be easily imagined by the person skilled in the art.

[0048] The heat-shrinking head may also be a multiple head, namely a head formed by several heat-shrinking heads so as to direct the hot air flows in several directions and suitably heat-shrink the various sides of the sheet 20. In particular, the station 16 may have, for example, one or more hot air sources with different inclinations of the hot air flow or one or more upper hot air source which are movable so as to obtain or suitably direct the hot air flow during the heat-shrinking operation and make it more uniform.

[0049] The hot air source may be only at the top or also on the sides, depending on the need.

[0050] Moreover, hot air sources of any known type, such as electric heaters, gas burners, etc., may be used.

[0051] After the pack has passed into the fourth station, the packaging of the object 12 is thus completed and pack may leave the plant through the outlet 18.

[0052] Obviously, during operation of the plant, the objects 12 may be introduced into the plant through the inlet 17 at small distances so that there is always an object 12 in each station of the plant and a packaged object 12 is leaving through the outlet 18 while an object 12 to be packed is entering into the inlet 17.

[0053] At this point it is clear how the objects of the invention have been achieved.

[0054] Owing to the method described which involves the deposition of a top sheet, perimetral horizontal strapping of said sheet, application of vertical strapping and, finally, heat-shrinking, perfect packaging of the top part of the pack with a taut film devoid of depressions is obtained. In addition to the improved packaging quality without the need to use over-sized tubular hoods, the risk of water accumulating on the top surface of the packs is thus also avoided, even in the case of packs with large upper surface areas.

[0055] In fact, owing to the heat-shrinking operation with the sheet of film 20 fixed peripherally on the upper corner edges of the object 12 by means of the straps 23 and 26 which prevent lateral slipping of the sheet, the sheet is tensioned such that it forms a substantially rigid surface without depressions. In addition, owing to the heat-shrinking temperature, the sheet 20 may be glued to the straps which are in contact therewith, so as to further help the heat-shrinkable film to remain flat on the broad upper surface.

[0056] For this purpose, if required, the sheet 20 may be heated during heat-shrinking so as to cause it to adhere at least partially to the vertical straps in contact therewith. The heat-shrinking temperature may be advantageously chosen sufficiently high to assist gluing of the sheet to the straps. The exact temperature will depend on the material chosen for the sheet and the straps.

[0057] Owing to the method described, there is no limit to the horizontal dimensions of the object to be packaged, this depending only the dimensions chosen for the stations in the plant in order to allow the objects to be packaged to pass through. The design of the sheet deposition station may be simple also in the case of large-size sheets and the strapping stations may be easily realized also for long strap lengths, as may be easily imagined by the person skilled in the art. The stations in the plant make use of technologies which are known per se and well-known and may therefore have a relatively low cost and be easily designed.

[0058] An automated control system or control systems for each station supervised by a central control system (known per se and for example realized with a suitably programmed microprocessor) may control the operation of the various stations and the transport system so as to perform in sequence the various operations which are required of the plant 10.

[0059] Obviously the description given above of a plant applying the innovative principles of the present invention is provided by way of example of these innovative principles and must therefore not be regarded as limiting the scope of the rights claimed herein. For example, the stations in the plant, while they must have the functions described, may have a different form depending on the specific requirements and the particular forms and dimensions of the objects to the packaged. In particular, the width for the passage of the objects through the stations will depend on the maximum transverse dimension of the objects to be packaged and the size and structure of the station for applying the horizontal strap will depend on the perimeter of the objects to be packaged, as may now be easily imagined by the person skilled on the art.

[0060] For example, the first sheet deposition station may also have arms for gripping the sheet and depositing it on the object while keeping the sheet in a horizontal plane. Moreover, although a substantially straight transport line 11 is preferable, other configurations may be used, also so as to adapt to spaces with a particular shape and reduce the overall dimensions of the plant in certain directions.

[0061] All the stations may also have vertically directed movements of the operating heads, in the case where it is considered necessary or preferable to adapt to incoming objects which have different heights.

Claims

1. A method for automatically packaging objects using sheets of heat-shrinkable plastic film in a packaging plant, comprising the sequential automatic steps of placing a sheet of heat-shrinkable plastic film on top of the object, with the edges of the sheet falling onto the sides of the object, carrying out horizontal perimetral strapping of this sheet along its edges on the sides of the object, providing vertical strapping on the object, transverse to the horizontal strapping, applying shrinking heat to the sheet of heat-shrinkable plastic film which is firmly held on the object by means of horizontal and vertical strappings.

2. Method according to claim 1, characterized in that the vertical strappings consist of a plurality applied parallel to each other along a greater horizontal extension of the object.

3. Method according to claim 1, characterized in that the sheet (20) is heated during heat-shrinking so as to cause at least partial adhesion thereof to the vertical strapping in contact therewith.

4. Plant (10) for the automatic packaging of objects (12) using sheets of heat-shrinkable plastic film (20) and applying the method of one or more of the preceding claims, comprising in sequence a first station (13) for deposition of a sheet of heat-shrinkable plastic film, suitable for placing the sheet of heat-shrinkable plastic film (20) on top of an object (12) passing through it, with the edges of the sheet falling on the sides of the object (12), a second horizontal strapping station (14) suitable for placing a horizontal strap (13) around the sides of the object (12), a third vertical strapping station (15) suitable for placing on the object vertical straps (26) arranged transverse to the horizontal strap (13), and a fourth heat-shrinking station (16) designed to apply shrinking heat to the sheet of heat-shrinkable plastic film (20) firmly held on the object (12) by means of the horizontal straps (23) and vertical straps (26), the plant (10) further comprising a system (11) for sequential transport of objects (12) to be packaged through the first, second, third and fourth stations.

5. Plant according to claim 4, characterized in that the first station (13) comprises an unwinder device (21) for unwinding a roll of heat-shrinkable plastic film strip which hangs with a free edge across the path of the objects on the transport system (11), the first station further comprising means for unrolling the film strip when an object to be covered passes through it, said object being transported through the first station by the transport system, and means (22) for transversally cutting the film strip so as to separate the sheet (20) of heat-shrinkable plastic film from the strip.

6. Plant according to one or more of the preceding claims, characterized in that the second station (14) comprises a head (24) for dispensing a horizontal strap (23), which is vertically movable so as to perform the peripheral wrapping, with the horizontal strap (23), of an object transported through the second station (14) by the transport system (11).

7. Plant according to one or more of the preceding claims, characterized in that the third station (15) comprises a head (25) which is displaced with a relative motion along the product and dispenses vertical straps, so as to perform winding of the vertical straps (26) around an object transported through the third station (15) by the transport system (11).

8. Plant according to one or more of the preceding claims, characterized in that the fourth station (16) comprises one or more heads (27) for emitting hot air towards an object transported through the third station (16) by the transport system (11).

9. Plant according to one or more of the preceding claims, characterized in that the first, second, third and fourth stations are suitable for sequentially receiving objects (12) to be packaged having horizontal dimensions at least four times greater than the height of the objects.

10. Plant according to one or more of the preceding claims, characterized in that the first, second, third and fourth stations are suitable for sequentially receiving objects (12) to be packaged having horizontal dimensions greater than two metres.

11. Plant according to one or more of the preceding claims, characterized in that the first, second, third and fourth stations are suitable for sequentially receiving objects to be packaged (12) in the form of crates open at the top.

Images