DE7023915U - Device for producing shrink films - Google Patents

Description

G 7ο 23 915.5 14 854 G / we

S. August 1974

Windmöller δ Hölscher, 454o Lengerich i. W.

Device for producing shrink films

The innovation relates to a device for implementation a method for producing shrink films from thermoplastics, in which in the tubular bladder a film tube formed by a film die, an internal air pressure is generated, dec a for Achievement of the shrinkback capacity sufficient transverse leakage ratio of the plastic film tube, the film tube after exiting the nozzle gap over at least half the distance between the nozzle gap and the film solidification line from the outside in such a way ctb-

it is supported that it has essentially the same diameter until the viscoelastic state is reached how the nozzle gap maintains, and that an internal air pressure is chosen which is at least twice as great as that with freiebiasenef tubular film to achieve the desired The required pressure in relation to the lateral stretching ratio.

As is well known, shrink films are blown film made of thermoplastic material which, due to special inflation conditions and possibly also a shrink-back capacity due to a special cooling of about 5o% in the longitudinal and transverse directions when briefly heated over in a shrink oven exposed to the softening point. It tightly encloses the enclosed packaged goods, so that, for example Highly packed pallets are given a firm bond, which means that the pallet can be transported without slipping the load and a very good weather protection is achieved in the case of outdoor storage.

It is known to use such shrink films on conventional blown film systems without any special additional device to produce that compared to an inflation or transverse stretching ratio of about 1: 2 for normal films without shrinkage properties one of about 1: 4 to 1: 7 is selected, whereby the shrinkback capacity is achieved. With such Systems, however, it is difficult to increase the output, since then the control of the film bubble and cooling is also very difficult. Change due to the increasing melt temperatures at higher output rates the cooling conditions and thus also the shrinkback capacity.

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It is also already known to produce thin, stretched tubular films in such a way that one is produced without stretching Hose cools below the solidification temperature, then through suitable heat sources up to the viscous-aesthetic area if it heats up and then iait expands to a large stretching ratio. This gives a film with high strength, which is suitable for certain packaging purposes or other technical use cases with Advantage can be used.

In this process, too, high shrinkback values are achieved because the stretching occurs at a level just above the Solidification temperature lying film temperature takes place. However, the first complete drawback is a considerable disadvantage Cooling down and the subsequent heating of the hose, since these processes are operationally safe only when comparatively low output can be mastered. In this process, the required blowing pressures are also which cause the greater ability to shrink back, many times higher than with a blown tubular film.

According to a method proposed by the applicant To produce shrink films from thermoplastics, one of a Blown film head formed film tube an internal air pressure is generated, which is necessary to achieve the shrinkback ability causes sufficient transverse stretching ratio of the plastic film tube, the film tube after exiting the nozzle gap over at least half the distance between the nozzle gap and the film solidification line is supported from the outside in such a way that he

until the viscoelastic state is essentially reached maintains the same diameter as the nozzle gap, and an internal air pressure is selected which is at least twice as great as that in the case of the free-blown Tubular film to achieve the desired transverse stretching ratio required pressure. When this method is used, the film tube is only removed from the support rings then released when its temperature is just above that Solidification temperature is, and is then through the high Internal pressure stretched to the desired hose diameter. Due to the compared to the conventional method The reduced stretching temperatures and the increased internal pressure result in a significantly increased shrinkback capacity .

The innovation is based on the task of a device to implement the method described above.

This object is achieved according to the invention in that several tightly to support the tubular film in a holding frame Support rings arranged one above the other are provided with an easily rotatable covering.

Advantageous refinements of the innovation are described in more detail in claims 2 and 3.

The innovation is explained in more detail in the following description with reference to the drawing, in which an exemplary embodiment is illustrated. Show in the drawing

1 shows the blow head and the stretching zone of the film tube in one blow molding system according to the invention,

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Fig. 2 shows an embodiment for

the structure of the film support device and d

Fig. .3 two examples of the slightly rotatable ^Un cash Eelacr the Stützrinae.

The extruder 1 shown in Fig. 1 promotes the melt through the pipe socket 2, in which the melt channel 3 is located, up to your annular space 4 in the blow head housing 5 <

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The film tube 6 is formed through the nozzle ring gap 7 which is formed between the outer ring 8 and the inner ring 9. Hit 10 is the outer air cooling ring, which the outer cooling air through the singing nozzle Π directly above the nozzle gap 7 on the still soft plastic film hose? 5 blows. The cooling air is supplied through the pipe i2 and partially reaches the external cooling air ring 10 through the pipe i3. The internal cooling air flows through the annular channel to the internal cooling air ring i7, which is formed between the centrally arranged air outlet pipe 14 and the inner wall 19 of the blow head housing 5, where it is passed through the annular gap 18, which is opposite the external cooling air annular nozzle, onto the film tube, then the The internal cooling air ring 17 flows around it and exits through the channel 14. The AuFolas ratio can be set by means of the throttle valve 15 in the inner cooling air supply duct 22. The air discharge pipe 14 is held in the plastic head housing by means of the webs 20. At 21 is a heat insulating lining is of shown the air to the inside of the film tube feeding annular channel, which is intended to prevent excessive heating of the cooling air, heated by the hot walls of the Bla "head housing and through which the tube ie 14 durchströine" in the tube interior air . The shown inner film cooling device 14 to 22 is the subject of an older German patent application from the applicant.

According to the invention is now that of the nozzle split rings 8, 9 with the gap 7 formed film tube 6 from the support rings 23 cit supported on the rotatable lining 24 and essentially »on the same diameter as the nozzle gap 7 ge

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keep. Shortly before reaching the first opening of the valve, the film tube 6 is released from the support device 23 _T 24, so that it is stretched over the stretching area 6 * to the finished tube 6 ¹ * aiHjere.

The support rings 23 are favorable in terms of flow Holder 25 attached to the base frame 26, which is with ä ^ i Brackets 27 supported on the KSn j ring 10, so r-o is ksi-i disturbing influence on the cooling air flow of the outer cooling ridge 10, 11 results. In the simplest case, the support rings 23 and the holders 25 are each made of a U-shaped bent wire formed on which either rolls 24, for example made of polytetrafluoroethylene or a flexible hose 24 '' ' made of silicone rubber with support rollers 24 '' made of polyamide or polytetrafluoroethylene run easily rotatable, so that the supported Hose 6 cannot be braked inadmissibly and stretched lengthways. Clamping rings 29 prevent it from running off of the rotatable covering from the support ring wires.

In the withdrawal direction behind the film solidification line 28, the film tube can be ^{guided and supported by similarly structured support rings 23S 24%} with holders 25 ', 26. These support rings must be arranged behind or above the solidification line 28 so as not to influence the streaking of the hose.

As in Fig. 2 schematically in a perspective illustration shown, each support ring of two opposing U-shaped wires 23, 25 of a rotatable covering

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formed, "with a distance between the two supporting wires It is useful, which corresponds approximately to the diameter of the rollers 24 * The distance between the individual, so constructed Seat rings from each other should be a few inches, so that on the one hand, the soft plastic film 6 is not stretched transversely due to the increased blowing pressure in the interior of the tube can be -and on the other hand the cooling air of the external cooling- ring has unhindered access to the film surface.

As already mentioned at the beginning »it is advantageous» if. the support rings can either be telescopically adjusted in height by appropriately designing the frames 26 or, if the support rings can easily be exchanged, so that individual rings can be removed or added.

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Claims (3)

G 70 23 915.5 August 2, 1974 Eye protection claims 1. Device for carrying out a process for producing shrink films from thermoplastics, at wedle? » in the tube bubble of a formed from a film die film tube, an inner air pressure is generated, the sufficient for achieving the Rüekschruiapfvermögens Qusrreekungsverhält-nis causes the plastic film tube _t where the film tube after leaving the die gap of at least half the distance between the nozzle gap and the film solidification line τοη outside is supported in such a way that it retains essentially the same diameter as the nozzle gap until the viscoelastic state is reached, and that an internal air pressure is selected which is at least twice as high as the pressure required for the desired transverse stretching ratio when the tubular film is blown free characterized in that, to support the tubular film (6) in a holder frame (26), a plurality of support rings (23) arranged closely one above the other with an easily rotatable covering (24, 24 ^ri and 24 '") are provided. 2. Apparatus according to claim 1, characterized in that the support rings (23) are adjustable in height. 3. Device according to claim 1, characterized in that at ^least: supporting rings (23) are attached to the end of the support track in the holder frame (26). 7021116-7.11.7 *