Transporting a film tube, blown film line and method for producing a film

Abstract

The invention relates to a system (10) for transporting a film tube (2) in a blown film line (1) along a transport direction, having a guiding unit (51) for guiding the film tube (2), a bottleneck (13.1) at which a width (2.3) of the film tube (2) can be reduced, a severing apparatus (20) having at least one severing element (21) for severing the film tube (2), wherein the guiding unit (51) is arranged downstream of the bottleneck (13.1) in the transport direction of the film tube (2). The invention furthermore relates to a blown film line (1) and to a method (100) for producing a film.

Claims

1. A system for transporting a film of a blown film line along a transport direction, comprising a processing unit with a guide unit for guiding a film tube and a constriction point at which a width of the film tube is reduced, and a cutting device with at least one cutting element, wherein said cutting device has an actuation means for moving the at least one cutting element in the direction of the film tube and wherein said cutting device has: at least several cutting elements arranged in series, or a transverse drive for moving the at least one cutting element transversely to the transport direction of the film tube, wherein the guide unit is arranged downstream of the constriction point in the transport direction of the film tube, wherein the cutting device is configured in such a way that only a first tube side of a tube section of the film tube is cut by the at least one cutting element, so that air accumulated at the processing unit is released through the tube section.

2. The system according to claim 1, wherein a flattening device is provided for flattening the film tube to form two film layers which at least partially lie one on top of the other, the constriction point being formed by the flattening device.

3. The system according to claim 1, wherein the at least one cutting element is set at an oblique angle with respect to the transport direction of the film tube.

4. The system according to claim 1, wherein the actuation means has a drive for moving the at least one cutting element in the direction of the film tube or wherein the cutting device has a tube guide, through which the film tube is moved in regions towards the at least one cutting element.

5. The system according to claim 1, wherein at least the cutting device has a housing, it being possible for the cutting device to be brought into an activation state, in which the at least one cutting element protrudes at least partially from the housing, and into a deactivation state, in which the at least one cutting element is arranged within the housing or wherein the housing has a displacement unit through which the housing is moved between a release position for producing the activation state and a closure position for producing the deactivation state.

6. The system according to claim 1, wherein the cutting device is arranged in the transport direction of the film tube upstream of the guide unit, so that the film tube is cut through by the at least one cutting element before the film tube passes the guide unit.

7. The system according to claim 6, wherein the cutting device is arranged in the transport direction of the film tube upstream of the constriction point, so that the film tube is cut through by the at least one cutting element before the film tube passes the constriction point.

8. The system according to claim 1, wherein at least the processing unit has a stretching unit or a stretching unit is provided between the constriction point and the guide unit, it being possible to influence a length extension of the film tube through the stretching unit.

9. The system according to claim 1, wherein the at least one cutting element is configured to create an opening in the tube section of the film tube between the constriction point and the guide unit.

10. The system according to claim 1, wherein the guide unit has air channels to provide an air supply between the film tube and the guide unit.

11. The system according to claim 1, wherein the cutting device has a detection unit for detecting the film tube.

12. The system according to claim 1, wherein a movable sensor unit is provided for detecting a film parameter of the film tube, and the cutting device is coupled to the sensor unit so that when the sensor unit approaches the film tube, the film tube is cut by the at least one cutting element.

13. A blown film line for the production of a film with a blow head from which a film tube is extruded, and a system, for transporting the film tube along a transport direction, comprising: a processing unit with a guide unit for guiding the film tube and a constriction point at which a width of the film tube is reduced, and a cutting device with at least one cutting element for cutting the film tube, wherein the guide unit is arranged downstream of the constriction point in the transport direction of the film tube, wherein the cutting device is configured in such a way that only a first tube side of a tube section of the film tube is cut by the at least one cutting element, so that air accumulated at the processing unit is released through the tube section of the film tube; wherein said cutting device has an actuation means for moving the at least one cutting element in the direction of the film tube; wherein said cutting device has at least several cutting elements arranged in series or a transverse drive for moving the at least one cutting element transversely to the transport direction of the film tube.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Further advantages, features and details of the invention will be apparent from the following description, in which embodiments of the invention are described in detail with reference to the drawings. In this connection, the features mentioned in the claims and in the description may each be essential to the invention individually or in any combination. It schematically shows:

(2) FIG. 1 a blown film line according to the invention with a system for transporting a film tube,

(3) FIG. 2 a deflection system of the system of the first embodiment,

(4) FIG. 3 a cutting device of the system of the first embodiment,

(5) FIG. 4 a method of producing a film according to the invention,

(6) FIG. 5 a cutting device according to a further embodiment,

(7) FIG. 6 a cutting device according to a further embodiment,

(8) FIGS. 7+8 a cutting device according to a further embodiment,

(9) FIG. 9 a system according to the invention for transporting a film tube in another embodiment,

(10) FIG. 10 a cutting element for a cutting device according to a further embodiment, and

(11) FIG. 11 a cutting device according to a further embodiment,

(12) FIG. 12 processing unit in the form of a stretching unit.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

(13) In the following description of some embodiments of the invention, the identical reference signs are used for the same technical features even in different embodiments.

(14) FIG. 1 shows a sketch of a blown film line 1, in which a film tube 2 is extruded by a blow head 4 and conveyed in the transport direction Z. The material of the film tube 2 is initially still present as a melt-like extrudate. Plastic is first plasticized in an extruder 14. The resulting mass is fed via a connecting line to the blow head 4, with which the film tube 2 is formed from the mass. Further extruders may be associated with the blow head 4, so that multilayer films can be produced. A method 100 according to the invention for producing a film by the blown film line 1 is shown in FIG. 4. In the following description of the blown film line 1, reference is also made to the method 100.

(15) When extruding 101 the film tube 2 from the blow head 4 is initially present as a film bubble when leaving the blow head 4, in which there is a slightly increased internal pressure compared to the ambient pressure. Due to the increased internal pressure, the not yet solidified material of the film tube 2 expands. Ultimately, the diameter of the finished film tube 2 and/or the thickness of the film material are influenced in this way.

(16) Subsequently, the not yet solidified film bubble or film tube 2 passes into the calibration device 15. Here, the diameter of the film tube 2 is limited. Within or below the calibration device 15, the film tube 2 cools down to a temperature at which subsequent deformation is hardly possible, in particular only with the use of greater forces. The position at which this phase transition takes place is often referred to as the frost line.

(17) After leaving the calibration device 15, the film tube 2 passes into a flattening device 5, in which the film tube 2 is almost completely formed into a flattened, double-layered film web. Thus, a flattening of the film tube 2 into a double-layered plastic film, which is connected in particular in edge regions, takes place by the flattening device 5. For this purpose, the flattening device 5 has guide elements 5.1 through which a gradual or continuous reduction of a width 2.3 of the film tube 2 is made possible.

(18) In the present embodiment, the blown film line 1, in particular the flattening device 5, has a constricting point 13 with constricting rollers, in particular so-called nip rollers, which prevent a larger amount of air from remaining within the film tube 2 during its further transport. Preferably, one of the nip rollers or both nip rollers drivable to assist the transport of the film tube 2. By the flattening device 5 and/or the constricting points 13, a constriction 102 of the film tube 2 takes place, in which a width 2.3 of the film tube 2 is reduced when the film tube 2 is passed through the flattening device 5 and/or the constricting points 13. As a result, at least one constriction point 13.1 is formed by the flattening device 5 and/or the constricting points 13 in a system 10 according to the invention for transporting the film tube 2.

(19) The film tube 2 is further conveyed over transport rollers, some of which are not explicitly shown, which can form further constriction points 13.1, in the direction of two winding points 7, 8. A drive unit 50 is provided for transporting the film tube 2, which in particular also applies a web tension to the film tube 2. The constricting points 13 and the constriction point 13.1 formed thereby, together with at least one guide unit 51 and/or a deflection system 60, form a processing unit 30, through which at least partial transport and/or further processing of the film tube 2 is made possible.

(20) However, during the transport of the film tube 2 through the constriction point 13.1, in particular a smaller amount of air may be carried along, which may accumulate in the film in an air bubble 16 during the course of production. The accumulated air can, for example, form the air bubble 16 upstream of a deflection system 60, in particular upstream of a guide unit 51 for guiding 103, in particular deflecting 103, the film tube 2. In this case, air particles from the interior of the film tube 2 can, for example, be entrained through the constriction point 13.1 before being laid flat. In the region of the air bubble 16, the film tube 2 thus expands locally, which can already lead to negative influences on the quality of the film product. Furthermore, the air bubble 16 can cause an increased pressure between the film tube 2 and the guide unit 51, so that, if necessary, impurities can be pressed into the film tube 2 and thus lead to further quality losses.

(21) In order to be able to release the air accumulated in the air bubble 16, a cutting device 20 is provided which has at least one cutting element 21 for cutting 104 the film tube 2. The cutting device 20 is configured in such a way that only a first tube side 2.1 of a tube section 3.1 of the film tube 2 can sever the cutting element 21, in particular the cutting element 21 can be introduced into the first tube side 2.1, so that accumulated air can be released through the tube section 3.1 at the processing unit 30, i.e. in particular here in front of the constriction point 13.1 and/or between the constriction point 13.1 and the guide unit 51. In the embodiment example shown here, the cutting device 20 is arranged in the area of the flattening device 5. However, alternative arrangements of the cutting device 20 are also conceivable, as shown for example in FIG. 9. The cutting of the film tube 2 thus produces a tube section 3.1 which is cut with a severing cut 3 and which moves with the transport of the film tube 2 in the transport direction of the film tube 2. When the cut tube section 3.1 passes the region between the constriction point 13.1 and the guide unit 51, the air trapped in the air bubble 16 can escape, in particular since the severing cut 3 allows access from an outer region to an inner region of the film tube 2. As a result, an excess pressure in the interior of the film tube 2 can be compensated.

(22) FIG. 2 shows in schematic representation a more detailed view of the constriction point 13.1 and of the deflection system 60 with several guide units 51. One of the guide units 51 comprises an air supply 53, through which it is possible to form 103.1 an air cushion between the film tube 2 and the guide unit 51, so that a contactless deflection of the film tube 2 or of the transport direction of the film tube 2 can take place at the guide unit 51. The guide unit 51 can be provided in particular as a rotatable or rigid roller. Due to the deflection, in particular due to a large angle in the deflection, an accumulation of air may be favored. Preferably, the guide unit 51 is further a cooling roller by which the film tube 2 can be cooled after extrusion 101 from the blow head 4. Furthermore, a stretching unit 52 can be provided between the guide unit 51 and the constriction point 13.1, through which a stretching 105 of the film tube 2 can be carried out. Through the stretching unit 52, the film properties of the film tube 2 can be influenced by introducing a stretch into the material. The stretching unit 52 may form a further guide unit 51 and/or a constriction point 13.1. Furthermore, the system 10 for transporting the film tube 2 may comprise further guide units 51 and/or further stretching units 52.

(23) When the film tube 2 is cut 104 by the cutting device 20, only a first tube side 2.1 of the tube section 3.1 of the film tube 2 is cut. This leaves a second tube side 2.2 opposite the first tube side 2.2 as a closed film section. On the one hand, this has the advantage that, when the film tube 2 is wound up at the winding points 7, 8, only the first tube side 2.1 is damaged by the severing cut 3 and the tube section 3.1 with the severing cut 3 is fed to only one of the winding points 7, 8. Furthermore, it may be provided that the air supply 53 of the guide unit 51 is arranged in such a way that the air cushion between the film tube 2 and the guide unit 51 can be formed at the second tube side 2.2 of the film tube 2. As a result, air is not reintroduced into the film tube 2 by the air supply 53. In particular, a plurality of guide units 51 with a plurality of air supplies 53 may be provided, wherein preferably all air supplies 53 are configured to form an air cushion between the respective guide unit 51 and the second tube side 2.2.

(24) FIG. 3 shows the cutting device 20 in the area of the flattening device 5 in a further schematic representation. In this case, a drive 22 is provided through which the cutting element 21 of the cutting device 20 can be moved relative to the film tube 2 and/or to the flat-laying device 5. In particular, the drive 22 may comprise a transverse drive 22.1 by which the cutting element 21 is movable transversely to the transport direction Z of the film tube 2, in particular perpendicularly to the transport direction Z of the film tube 2. Preferably, the cutting element 21 is repeatedly movable towards and returnable from the film tube 2 by the transverse drive 22.1. As a result, a perforation of the film tube 2 can be made over an area of the film tube 2, so that the release of air in the area of the air bubble 16 can be improved. In particular, this allows an oblique cut pattern to be applied as the film tube 2 moves relative to the cutting element 21 and the cutting element 21 is moved transversely. Preferably, the cutting device 20 comprises a detection unit 27 configured to detect 104.1 the film tube 2, in particular an edge region of the film tube 2. In this way, it can be prevented that the cutting element 21 sets the severing cut 3 in the edge region of the film tube 2.

(25) FIG. 5 also shows a side view of the cutting device 20. In order to be able to make a severing cut 3 in the first tube side 2.1 of the film tube 2, the cutting device 20 has a drive 22.2 for the cutting element 21. The drive 22.2 may for example be of manual, pneumatic, hydraulic and/or electric configuration. Preferably, the cutting element 21 and/or the drive 22.2 is coupled to a sensor unit 12 for detecting a film parameter of the film tube 2, so that the drive 22.2 can be used for both components. Therefore, if an approach 106 of the sensor unit 12 to the film tube 2 occurs, the severing cut 3 can be automatically introduced into the first tube side 2.1. As a result, the cutting element 21 can be moved towards the film tube 2 until the cutting element 21 is introduced into the film tube 2 at the first tube side 2.1. As a result of the movement of the film tube 2 during transport, the film tube 2 is then cut. The arrangement in the region of the flattening device 5 or at least in front of the constriction point 13.1 has the advantage that the severing cut 3 can be introduced in a simple manner only into the first tube side 2.1, in particular because here the film webs are still spaced apart from one another. In this case, the cutting element 21, in particular in the form of a knife, has a high tolerance range when it is inserted into the film tube 2, since the second tube side 2.2 is still spaced apart from the first tube side 2.1. As a result, during transport of the film tube 2, the cut tube section 3.1 first passes through the constriction point 13.1 and then through the entire area between the constriction point 13.1 and the guide unit 51, so that air can escape permanently during this process. Preferably, a detection 104.1 of the film tube 2 and/or of an edge region of the film tube 2 is carried out before the cutting element 21 is introduced into the film tube 2 by the drive 22.2. In particular, the detection 104.1 may be performed by the sensor unit 12. Additionally or alternatively, a sensor unit 12 may be arranged downstream of the deflection system 60 and/or upstream of a drive unit 50, in particular rigidly, in order to detect the tube section 3.1 and/or film properties of the film tube 2.

(26) FIG. 6 shows a cutting device 20 for cutting a film tube 2 at only a first tube side 2.1 by a rigid cutting element 21. If air accumulates in the film tube 2, an air bubble 16 can form, which consequently inflates the film tube 2 locally. In this case, the rigid cutting element 21 is provided at a nominal distance 21.1 from the film tube 2, which is configured in such a way that cutting only takes place once a certain amount of accumulated air has been reached. Thus, when the air bubble 16 reaches a certain size 16.1 which is larger than the nominal distance 21.1 of the cutting element 21 to the film tube 2, cutting of the first tube side 2.1 can be performed automatically during transport of the film tube 2.

(27) FIGS. 7 and 8 further show a schematic side view of a cutting device 20 in another embodiment. Here, the cutting device 20 comprises a cutting element 21 for cutting a film tube 2 at only a first tube side 2.1 of the film tube 2. The cutting element 21 is provided in a housing 25, so that the cutting element 21 is at least partially protected from environmental influences. It is further provided that the cutting device 20 can be brought into a deactivation state II, in which the cutting element 21 is arranged within the housing 25. The deactivation state II is shown in FIG. 7. FIG. 8 further shows an activation state I of the cutting device 20, in which the cutting element 21 protrudes at least partially from the housing 25. Thus, a cutting of the film tube 2 can be realized. Furthermore, the housing 25 comprises a displacement unit 26 through which the housing 25 is movable between a release position A for producing the activation state I and a closure position B for producing the deactivation state II. The displacement unit 26 can resiliently support the housing 25, such that the housing 25 is pretensioned towards the closure position B. Furthermore, a tube guide 24 in the form of a roller is provided, through which the film tube 2 can be moved towards the housing 25 and the cutting element 21. Thus, during the movement of the tube guide 24, the film tube 2 is pressed onto the housing 25, which is correspondingly moved into the release position A, so that the cutting element 21 protrudes through an opening, for example in the form of a slot, of the housing 25. This allows a first tube side 2.1 to be cut through by the cut-through element 21. Preferably, the cutting device 20 of the present embodiment may be provided immediately adjacent the guide unit 51, preferably between the guide unit 51 and a stretching unit 52. Here, bubble formation is likely, so that when the film tube 2 is pressed against the housing 25 or the cutting element 21, only a surface of an air bubble 16 of the film tube 2 and thus the first tube side 2.1 is cut in an advantageous manner. For this purpose, a nominal distance 21.1 of the cutting element 21 to the film tube 2 and/or to the tube guide 24 can be configured according to the nominal distance 21.1 as shown in FIG. 6.

(28) FIG. 9 shows a system 10 according to the invention in a further embodiment with a processing unit 30 as a subsection of a blown film line 1 according to the invention with different possible positions of a cutting device 20 for cutting 104 a film tube 2. In this case, the cutting device 20 can be arranged upstream of a constriction point 13.1 at which a width 2.3 of the film tube 2 is reduced. This has the advantage that the cutting of only a first tube side 2.1 of the film tube 2 is possible in a simple manner, since the first tube side 2.1 is still spaced apart from a second tube side 2.2. Furthermore, this allows air already accumulated before the constriction point 13.1 at the processing unit 30 to escape from the film tube 2. Furthermore, it is conceivable that the cutting device 20 is arranged between the constriction point 13.1 and a guide unit 51 for guiding, in particular deflecting, the film tube 2. Here, accumulated air is to be expected and can thus be released directly in the region in which it could possibly have a damaging effect. Furthermore, it may be provided that the cutting device 20 is provided between two guide units 51. For example, it may be provided that the first guide unit 51 has only a small angle to the deflection and consequently air still passes the first guide unit 51. Also, as a result of this, the cutting device 20 can be used at a point where accumulated air is expected to be present. In particular, the constriction point 13.1 can also be formed by a further guide unit 51 which is arranged in front of the guide unit 51, in particular in the transport direction of the film tube 2.

(29) FIG. 10 shows a cutting device 20 in a further embodiment. In this case, the cutting device 20 has a cutting element 21 which is configured as a needle roller. The individual needles can thereby be introduced into the film tube 2, i.e. cut through the film tube 2 in order to perforate the film tube 2. This can also create a sufficient exchange between an inner region of the film tube 2 and an outer region of the film tube 2, in order to be able to release accumulated air.

(30) FIG. 11 further shows a cutting device 20 in another embodiment. In this case, the cutting device 20 has several, in particular two, cutting elements 21. In this way, two parallel severing cuts 3 can be achieved, so that a wide area of the film tube 2 can be covered to release accumulated air, in particular without transverse movement of the cutting elements 21.

(31) FIG. 12 shows a processing unit 30 in the form of a stretching unit 52 for carrying out a stretching process. Thus, two guide units 51 in the form of pairs of rollers are arranged one behind the other. Through the first pair of rollers 51 the film tube 2 is introduced into the processing unit 30, while through the second pair of rollers 51 with a higher rotational speed than the first pair of rollers 51 a longitudinal stretching, in particular as a stretching in left/right direction, as shown by the dashed arrow, takes place. Depending on a geometry, in particular edge geometry, of the film tube 2, an improved adhesion of the edge sections to the pairs of rollers 51 can preferably take place, so that a constriction or a reduction of the width of the film tube 2 transversely to the longitudinal direction is reduced or avoided. After longitudinal stretching, the edge sections may be cut off. The cut edge sections can then be recycled, for example, to the extent that they are recirculated as raw material.

(32) The foregoing explanation of the embodiment describes the present invention by way of example only. Of course, individual features of the embodiments can be freely combined with each other, provided that this is technically reasonable, without leaving the scope of the present invention.

LIST OF REFERENCE SIGNS

(33) 1 Blown film line 2 Film tube 2.1 First tube side 2.2 Second tube side 2.3 Width of 2 3 Severing cut 3.1 Tube section 4 Blow head 5 Flatting device 5.1 Flatting guide 6 Film web 7 Winding point 8 Winding point 9 Tubular film level 10 System 11 Guide unit 11.1 Start module 11.2 Winder module 11.3 Record module 12 Sensor unit 13 Constriction points 14 Extruder 15 Calibration device 16 Air bubble 16.1 Size of 16 20 Cutting device 21 Cutting elements 21.1 Nominal distance 22 Drive 22.1 Traverse drive 22.2 Drive 23 Adhesion device 24 Tube guide 25 Housing 26 Displacement unit 27 Detection unit 30 Processing unit 50 Drive unit 51 Guide unit, in particular a roller 52 Stretching unit 53 Air supply 60 Deflection system 70 Auxiliary separation unit 71 Separation unit 100 Method 101 Extrude 102 Constriction 103 Guiding, especially deflecting 103.1 Forming of air cushions 104 Cut 104.1 Detection of 2 105 Stretching 106 Approach of 12 A Release Position B Closure position D Extensibility H Retaining force I Activation state II Deactivation state Z Transport direction