DE2349500A1 - METHOD FOR TREATMENT OF THE PLASTIC FILM OF A SO-CALLED SHRINK-ON FILM SHELL TO ACHIEVE AN EASILY Tearable PLASTIC FILM - Google Patents

Description

Dr E. Bo.-mvM
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D <! M -i: i ι; he Ii 3 0
Lucüe-Grahii-br 3a, 'XeL 47 51 55 <τιρ

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TETRA PAK INTERNATIONAL AB, Fack, S-221 01 Lund 1 (Sweden)

Process for treating the plastic film to achieve a so-called shrunk-on film envelope an easily tearable plastic film

The invention relates to a method for treating the plastic film of a so-called shrunk-on film envelope with the aim of obtaining an easily tearable plastic film, in which the object to be wrapped in known Way, a plastic film removed from supply rolls is fed, which is placed around the object and along it at least one sealing seam sealed and separated from the rest of the plastic film on the supply rolls is, and the object so wrapped is passed through a heating zone to shrink the plastic film.

In packaging technology, more are needed to hold them together For more grouped or closely stacked objects in the stacked state, films are increasingly shrunk on used because it has proven to be practical and cheaper in many cases instead of the conventional items Procedure in different types of collection containers

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to accommodate, to use a shrunk film cover. However, the shrunk-on film envelope will also XB club with support plates, basin-shaped containers o, the like, used, so that a support for the housed objects is created and the shrink wrap is reinforced.

It has been found, however, that there is a need to produce a shrunk-on film that can be easily torn open, since shrink film is relatively tough and strong and therefore does not tear easily without the aid of a sharp tool such as a pair of scissors or a knife can, when used for packaging articles. In addition, for the same reason, the shrink film is difficult to tear and it is difficult to achieve a reasonably controlled tear; (to adhere to the desired course of the tear line).

It has already been suggested, to facilitate the Tearing open a shrink wrap on the inside the shrink film, i.e. between the shrink film cover umd. the objects held together by these, one To insert tear strips in such a way that one end of it is accessible from the outside of the shrink film sleeve. By. Grasping this accessible part of the tear strip, from a flexible, non-shrinking and only in If there is a low degree of elastic material, the shrink film can then be torn open, the shrink film is split along an extension which corresponds essentially to the course of the tear strip.

However, it has worked despite the use of a tear strip proved difficult to tear open a shrink film and the reason for this is of course the toughness of the plastic film. In addition, the tear strip causes an increase

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the cost of the otherwise so practical shrink film cover. By, the method according to the invention can do this Difficulties, however, will be overcome, and this will be done appropriately the invention achieved in that the plastic film after unrolling from the supply rolls, but before them Introduction into the heating zone by means of a knife or punch device to form at least two lines of weakness is perforated, which preferably extend parallel to one another over the width of the plastic film and between which the plastic film material later on when opening the plastic film by tearing it along the line of weakness should be eliminated.

The method according to the invention is explained in more detail below with reference to the drawing, the examples of the device to carry out the procedure as well as after the procedure shows the manufactured shrink film.

1 illustrates the principle of a shrunk-on film sleeve;

Fig. 2 is a side view of the sealing means of a shrink film packaging apparatus which is provided with a Embodiment of a device for implementation of the method according to the invention is equipped;

Fig. 3 is a side view of another embodiment an apparatus for performing the method according to the invention; and

Figure k is a perspective view of a number of articles packaged in a shrink film treated by the method according to the invention.

Fig. 1 illustrates the basic and usual process

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wise when wrapping items in shrink film; the objects 1 are on a roller conveyor 2 or a similar conveyor to a collecting table 3 supplied. From a roll 4, which is above the supplied objects is arranged, a plastic film 5 is peeled off, which is welded to a second plastic film 7 is, the ΐίοη one below the conveyor for the objects arranged roller 6 is withdrawn. This welding together of the foils. 5 and 7 will be respectively performed ^ after a number of items den Plastic foils fed and wrapped with these. The plastic foils are joined together along a Seam welded so that the objects are enveloped. The welding is carried out by means of a welding jaw 8 and one Counter-pressure welding jaw 9 performed, which serves as a support tool (holding-up tool). The welding jaw can be made consist of a permanently heated welding tool, and the welding jaws and / or the counter pressure jaws are against each other and movable apart. A further roller conveyor 11 is used for discharging the objects 10 wrapped in this way provided, which feeds the wrapped objects to a conveyor belt 12. This conveyor belt, which usually consists of a There is an endless belt, the objects now wrapped in the film lead into and through a shrink tunnel 13 with a conveying speed appropriate for the shrinking process. Under the conveyor belt is behind the shrink tunnel 13 a cooling fan 15 is provided for accelerated cooling of the plastic film envelope.

Fig. 2 shows a welding jaw 8 and on a larger scale a counterpressure jaw 9 in the moved apart position after a weld. The welding jaws are provided with welding strips 16 made of electrical resistance material, Surfaces or the like. for performing the weld when sealing provided with a plastic film cover. Sealing can be done by the fact that along a zone

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adjacent plastic foils 5 »7 heat and higher Pressure can be brought into effect. In addition, the welding jaws are provided with a recess 17 between the welding surfaces 16 provided in which a knife 18, for example in the form of a heated wire for separating the two plastic foils 5 »7 which are welded together the welding is housed. Cooling channels 19 are also provided in the welding jaws.

In an embodiment of the device for carrying out the method according to the invention, the welding jaw according to FIG. 2 has a yoke 20 which is spring-loaded by means of a spring element 21 and on which toothed knives 22 are arranged, adjustable by means of screws or a similar connection 23. The knives 22 are intended to perforate the plastic films 5, 7 to produce lines of weakness and have serrated edges which are designed in such a way that a perforation or weakening suitable for tearing the plastic material can be achieved. A knife with less than 90 serrated edges has proven to be a suitable sharpening of the knives. The counterpressure jaw 9 has counterpressure surfaces 2h made of a material suitable for this purpose and a recess 25 between these surfaces. In order to separate the plastic foils, the cutting element 18 must be able to be lowered into the recess. The plastic films are separated when a plastic film sleeve is to be separated from the plastic films 5 and 7 pulled off the supply rolls h _{t 6.}

In a second embodiment, the perforation of the plastic films 5-7 is carried out during their movement from the supply rolls k _f 6 to the objects to be packaged. 3 shows a knife element 27 with two cutting edges which is designed in such a way that it perforates the plastic film from one side thereof. On the other side of the

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Plastic film, an iderlagerwerkzeug 28 is provided. The knife element is adjustable and set up in such a way that -that the weakening lines are in a suitable position on the Plastic film envelope with respect to the shape of the grouped Objects can be created. Such lines of weakness can, of course, be attached to several places on the cover and a further two-edged knife 29 can therefore be provided (FIG. 3).

4 shows the arrangement of the individual wavy lines, the individual exemplary embodiments between the wavy lines. 33 and 3k , a mat required 35 and 36, respectively, is retained, which forms the actual tear strip.

The invention is of course not limited to the exemplary embodiments described above, but can be modified in many ways within the scope of the inventive concept. For example, it is customary for the objects 1 to be delivered to the foils 5, 7 to be welded by means of a conveyor device. As a result, one side, as well as the top and bottom of the grouped objects, are removed from the. Plastic films 5, 7 covered. The plastic films can of course not only be made of polyethylene, polypropylene or laminates containing such plastic film materials, but also of oriented plastic film material.

It is of course possible, without deviating from the inventive concept, to modify the described method for the treatment of plastic films of a so-called shrink film cover. Thus, the measuring element 22, 27, 29 can be arranged in such a way that the perforation of the plastic films, unlike in the figures , is carried out from the opposite side of the film. The alignment of the plastic films between the supply rolls h or 6 and the location

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the attachment of the foil to the article to be packaged can be different from the _s also given for the Äusführungsbeispie-Ie representation and it is also common in this context, to give the film by use of guide rollers or rails, a suitable direction. In the embodiment according to FIG. 2, a single knife 22 can also suffice for perforating the plastic films 5, 7 when they are welded together. There is also the possibility of designing one of the jaws, preferably the counter-pressure jaws 9, to be stationary and only the other jaws S to be movable. The objects to be wrapped in the plastic foils are usually fed to the interconnected plastic foils 5, 7 by means of a conveying device, with the result that one side as well as the top and bottom of the grouped objects themselves with the plastic when the objects are brought up. Sheets 5-7 are covered while the remaining side to be covered is simulated by the movement of the jaw or jaws. Moreover Τγ "τππ the blade be arranged such that the plastic film either perforated along parallel-extending or different diverging lines. Finally, the plastic films can consist of polyethylene, polypropylene or laminates containing such plastic film materials as well as oriented plastic film material of this type. The method according to the invention is therefore not restricted to the cases discussed, for example.

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Claims (5)

Claims 1.} Method of treating the plastic film of a so-called sohrump film cover with the aim of creating a easy-to-tear plastic film, in which the object (or objects) to be wrapped in a known manner a heat-shrinkable plastic film material removed from supply rolls is fed, which is placed around the object and at least along a weld seam and from the Remnant of the plastic film material to the supply— rolls is separated, and the object so wrapped for shrinking the plastic film through a heating zone is performed, characterized in that the plastic film by means of at least one knife element to form two lines of weakness extending across the width of the plastic film after it has been peeled off the plastic film from the supply rolls, but before the object to be wrapped is wrapped in it is perforated and that the mutual position between the object and plastic film is set in such a way that the plastic film material between the weakening lines, which is necessary for the opening of the plastic film eliminated by tearing open the lines of weakness is to be, according to the shape of the encased object in terms of its accessibility for tearing open the plastic film is given a suitable position. 2. The method according to claim 1, characterized in that the plastic film to form the weakening lines by means of a double-edged knife element or by means of two spaced apart Knife elements is perforated _a -9- + welded 4Q9816 / 0374 23495 3. The method according to claim 1 or 2, characterized in that that the weakling lines generated thereby that the plastic foils lie one on top of the other by means of a foil penetrating the thickness of both Knife element are perforated. 4. The method according to any one of claims 1 to 3 _9, characterized in that the plastic film is perforated by means of the knife element along mutually parallel weakening lines. 5. The method according to any one of claims 1 to 3 »thereby characterized in that the plastic film diverges along one another by means of the knife element Lines of weakness is perforated. 409816/0314 L e rs e i t e