Apparatus and method for uniaxial length change of a film web

Abstract

The invention relates to an apparatus for uniaxial length change of a film web in the machine direction, the apparatus having at least one processing gap defined by two rollers, through which the film web is guided in the machine direction, wherein a first roller in the film transport direction has a first peripheral speed and a second roller in the film transport direction has a second peripheral speed, in order to produce a film web with less transverse shrinkage and less edge accumulation and to improve the flatness of the film web. The invention also relates to a method for uniaxial length change of a film web in the machine direction.

Description

Technical Field

[0001] The invention relates to a device and a method for uniaxial length change of a film web in the machine direction. The device comprises at least one working gap defined by two rollers, through which the film web is guided in the machine direction, wherein a first roller in the film transport direction has a first peripheral speed and a second roller in the film transport direction has a second peripheral speed. Background Art

[0002] When producing films, stretching devices are used in order to reduce the thickness of the film after it has been produced. Stretching of the film is used not only in the case of tubular films but also in the case of cast films. Stretching devices usually comprise heating rollers in order to prepare the film for stretching, followed by stretching rollers between which the film is stretched. Stretching can be followed by so-called annealing or tempering rollers, in which the film is subjected to a heat treatment in order to influence the film properties. Finally, the film is cooled by means of cooling rollers. By stretching the film web, the film can not only be changed in terms of its geometric dimensions, but also its properties, such as transparency or strength, can be influenced in a targeted manner.

[0003] The stretching device is operated offline or inline in the film blowing device. The stretching of the tubular film can also be carried out inline in the film blowing device directly after the traction roller pair or after the deflection rod system following the traction roller pair.

[0004] During uniaxial stretching of a film web in the machine direction (also referred to as longitudinal stretching), a transverse retraction (so-called necking-in) occurs, together with a thickening of the edges (so-called edge stacking). This effect is highly detrimental to the further processing of the film. Neck-in is disadvantageous because it impedes the film manufacturing process with respect to the flatness required for further processing of the film. The greater the neck-in, the more difficult it is to achieve the required film quality in the economical production of uniaxially stretched films. This leads to disadvantages such as hanging film edges and other flatness errors when unwinding the produced coil. This leads to poor coil quality and therefore to poor further processing properties of the film, for example when printing, gluing or laminating.

[0005] DE102009046585A1 discloses a stretching device for longitudinally stretching a film web and a method therefor. The stretching device essentially consists of a heating device, a stretching machine and a cooling device. In order to reduce necking and edge accumulation when stretching the film web longitudinally, a pressing device in the form of a pressing roller is used, which presses the film web against the stretching roller.

[0006] DE102009046593A1 also discloses a stretching device for longitudinally stretching a film web and a method for this purpose. In order to reduce necking and edge accumulation, a deflection roller is used in the stretching gap between the two stretching rollers of the stretching machine. The film shrinks less.

[0007] During stretching, the transverse shrinkage or retraction of the uniaxially stretched film can also be suppressed by adjusting the temperature of the stretching rollers, as disclosed in DE 10 2011 085 735 A1. In addition, retraction can be suppressed by adapting the stretching gap. The reduction of the roller gap reduces the necking of the film.

[0008] In order to improve the flatness of films produced in a film blowing system, which are subsequently stretched in a stretching system, a thickness control method known, for example, from DE 10 2009 033 171 A1 is used. Here, edge accumulation is reduced during uniaxial stretching in the machine direction. For this purpose, when producing tubular films, those areas which subsequently form the flat film edge areas are provided with thin regions, so that after stretching a finished product with a thickness that is as uniform as possible transversely to the film web is produced. This method also has a positive effect on reducing transverse shrinkage. Summary of the invention

[0009] The object of the invention is to provide a solution which enables the production of a film web with improved flatness in an apparatus for uniaxial length change of a film web in the machine direction by reducing transverse shrinkage and thus edge accumulation. This improves the quality of the produced film roll.

[0010] According to the present invention, in this type of device for uniaxially changing the length of a film web along the machine direction, the purpose is achieved by the following features: a device for uniaxially changing the length of a film web along the machine direction, the device comprising at least one processing gap defined by two rollers, the film web being guided through the processing gap along the machine direction, wherein the first roller along the film conveying direction has a first circumferential speed, and the second roller along the film conveying direction has a second circumferential speed, characterized in that at least one of the rollers is a roller through which air can flow from the outside to the inside, and at least one of the rollers through which air can flow can be combined with a temperature control roller.

[0011] According to the invention, the object is achieved by means of an arrangement in which, compared to the prior art, at least one of the rollers defining the processing gap in which the film web undergoes a change in length is replaced by a roller through which air can flow. The roller through which air can flow is designed to be flow-through from the outside to the inside.

[0012] When conveying a film web via rollers, an air boundary layer is introduced onto the film web between the film web and the rollers. This air cushion has a negative effect on the flatness of the film web when it is stretched in the film processing gap. By using rollers through which air can flow from the outside to the inside, the air introduced along with it can flow out continuously into the inside via the rollers through which air can flow, and the film lies directly on the rollers over its entire width. The flatness of the film web is improved. The air cushion occurs precisely at high machine speeds. Transverse shrinkage and simultaneous edge accumulation caused by the stretching of the film web are also suppressed and reduced by the film lying on the rollers. If this effect is not sufficient, a negative pressure source can be connected to the rollers through which air can flow from the outside to the inside, by which the film web is drawn onto the rollers and adheres more strongly to the rollers and reduces shrinkage and edge accumulation.

[0013] The extent of necking and edge accumulation is particularly related to the adhesion of the film to the rollers that define the processing gap. The film slides more significantly in the transverse direction (i.e. perpendicularly to the conveying direction of the film web on the roller surface) in the outer area, and the film tries to balance the transverse forces acting on it. This transverse retraction occurs essentially in the processing gap and on the rollers themselves. The goal is now to adjust the negative pressure applied to the rollers so that the adhesion of the film web to the rollers is improved by increasing the friction and avoiding relative speeds between the film and the rollers in the transverse and longitudinal directions. A uniform contact of the film on the rollers is achieved over the contact width. In this way, there is a defined detachment edge of the film web from the rollers in the film conveying direction at the exit of the rollers, and there is also a defined contact edge of the film web on the rollers in the film conveying direction at the entry onto the rollers.

[0014] The magnitude of the negative pressure also depends on the desired length change of the film web, the machine speed and the film properties.

[0015] The force with which the film is attracted to the roller is achieved via the magnitude of the negative pressure. The negative pressure is approximately 100 to 300 mbar, and in special cases it can also be selected to be greater or lesser. The negative pressure is adjusted accordingly depending on the properties of the film and the desired length change. According to the invention, at least one of the rollers defining the working gap of the device for length change is designed as a roller through which air can flow from the outside to the inside.

[0016] In a preferred embodiment, the second roller after the processing gap is designed as a roller through which air can flow. The air drawn in flows out through the roller and the film lies against the roller over its entire width. If this effect is not sufficient, in another embodiment of the invention, the roller through which air can flow is connected to a negative pressure source. The negative pressure present on the roller through which air can flow causes the film web to be attracted to the roller. This increases the friction of the film web relative to the roller of the device and thus reduces the transverse shrinkage after the processing gap. In this case, the film is attracted to the roller evenly over its entire width, including the film edges.

[0017] In another embodiment of the invention, the first roller of the device before the processing gap is designed as an air-circulating roller. The contact between the film web and the roller is increased and the formation of an air cushion between the film web and the roller is avoided. As a result, the film web lies evenly on the roller. The film web reaches the processing gap with a small transverse retraction. This has a positive influence on the flatness. In another embodiment, the roller can also be connected to a negative pressure source. The effect is enhanced by increasing the force.

[0018] In another embodiment, the roller before the processing gap and the roller after the processing gap are designed as rollers through which air can flow. This achieves improved adhesion of the film web without air being trapped between the film web and the rollers, and reduces necking and edge accumulation on the film. In a preferred embodiment, the second roller is additionally connected to a negative pressure source. This suppresses transverse shrinkage. In rare cases, both rollers can also be connected to a negative pressure source.

[0019] In the device according to the invention, the air-circulating roller can cooperate with or without a pressing roller. The pressing roller is used to additionally fix the film web to the air-circulating roller. The pressing roller increases the contact of the film relative to the roller, so that the film lies evenly on the roller.

[0020] Depending on the stretching task, it may also be necessary to draw the film onto the roller through which air can flow with different strengths over its width, for example at the edges with greater strength than in the middle of the film. The roller through which air can flow is then designed so that a vacuum of different strengths can be present over the axial length of the roller through which air can flow.

[0021] Depending on the application, a combination of a roller through which air can flow and a temperature-controlled roller can also be used. On the one hand, this combination controls the temperature of the film web in order to provide an adapted temperature for the length change, and on the other hand, the air trapped between the film web and the roller can escape to the interior via the roller through which air can flow. The direct contact of the film web on the roller also improves the heat transfer from the roller to the film web. If negative pressure is additionally applied to the roller in order to draw the film web more strongly to the roller, the friction between the film and the roller is further increased and the necking is further reduced.

[0022] Temperature control can be heating or cooling. On one side of the combined roller, a fluid for temperature control (such as gas, steam, water or oil) is supplied to the roller and discharged from the roller via a rotating channel. A negative pressure source is connected to the opposite side of the fluid inlet and fluid outlet via a rotating channel and air is sucked in. If no negative pressure is applied, the air escapes through these openings. In the case of a roller that can only be traversed by air, there is no fluid inlet and fluid outlet for temperature control.

[0023] Like the rollers according to the prior art, the combined temperature-controlled and air-permeable rollers also consist of a double-layer roller with fluid temperature control, but the double-layer roller with fluid temperature control is additionally equipped with channels for guiding air and can be connected to a negative pressure source. The channels can also be constructed as small boreholes. Ideally, an air-permeable layer is applied, similar to a sintered structure. It is also possible that the roller is constructed of an open-porous material in the micrometer range. The roller is constructed of materials such as steel, high-quality steel or plastic. In a preferred embodiment, the sintered layer is made of stainless steel, which can also be highly polished. In addition, the friction or adhesion between the film web and the roller can be influenced via the surface roughness or surface structure of the roller. If temperature control is not necessary, a roller of the same type without a double-layer sleeve is used.

[0024] By reducing the transverse shrinkage of the film web, new physical properties of the film are obtained, which improve further processing in printing and in the lamination process through the improved flatness. In addition, this makes the edge trimming less.

[0025] The device for length change comprises a process gap defined by two rollers, wherein the film web undergoes a length change in the process gap, wherein the first roller has a first peripheral speed in the film web transport direction and the second roller has a second peripheral speed in the film web transport direction.

[0026] In the case of a second roller of the device having a greater circumferential speed than the first roller, a positive change in length of the film is produced. Depending on the length change ratio, stretching, extension or annealing is discussed. The transition from annealing to extension and to the change in length of the film is smooth. Length change ratios of from about 1:1 to 1:10 can be achieved.

[0027] In the case of annealing, in addition to the elongation, shrinkage of the film web can also be permitted, the second roller then having a lower peripheral speed than the first roller and producing a negative length change. The shrinkage ratio is typically about 0.5:1 to 1:1.

[0028] The two rollers defining the process gap can also have the same peripheral speed.

[0029] In one embodiment, the device according to the invention for changing the length of a film web is a component of a stretching device.

[0030] In a stretching device which usually consists of a heating roller assembly, a stretching roller assembly, an annealing roller assembly and a cooling roller assembly, the stretching rollers after the stretching gap or treatment gap are replaced by rollers through which air can flow, because this results in the greatest improvement in the stretching process.

[0031] Such a stretching device can be used in-line or off-line in a film production plant. It is also possible to provide a plurality of devices according to the invention, which have at least one processing gap defined by two rollers, in one stretching device. However, it is also possible that in a stretching device having a device according to the invention, further stretching rollers or further rollers (such as annealing rollers and cooling rollers following the stretching rollers, and also, for example, upstream heating rollers) are additionally designed as rollers through which air can flow, in order to further improve the film quality.

[0032] The device according to the invention for length variation of a film web can be installed in-line in a film blowing plant when producing tubular films.

[0033] In the film conveying direction, the film blowing equipment includes a plastic metering device, an extruder, followed by a film blowing head, a cooling device, and a calibration basket. Then the flattening device, the traction device, and the steering device are connected. Finally, the tubular film is wound in the winding device.

[0034] When producing tubular films in a blown film plant, a device according to the invention for length change, which has at least one processing gap defined by two rollers, wherein at least one of the rollers is a roller through which air can flow, can be arranged in the film conveying direction directly above the traction roller pair of the traction device before or after the deflection rod. It is also possible to arrange a plurality of devices according to the invention in the blown film plant, which devices include at least one processing gap defined by two rollers. These devices can be combined with further rollers through which air can flow. In this case, the traction device can be constructed stationary, rotating or as a reverse deflection traction device. It is also possible to do this without a deflection rod.

[0035] The device for uniaxial length change according to the invention can be a component of a stretching device and can be arranged in a blown film device in the film conveying direction above the traction roller pair, before or after the deflection rod, above the tubular film bubble. Alternatively, the device can also be arranged in-line in the stretching device on the ground next to the blown film device or offline on the ground next to the blown film device. The blown film device can also be constructed accordingly with or without a reverse deflection traction device.

[0036] The device according to the invention for uniaxial length change can also be provided as a component of a stretching device of a so-called MDO system, twice in-line after the film blowing system. The tubular film is then cut on both sides at opposite positions into two film webs and each film web is further processed in a respective stretching device.

[0037] In order to further optimize the quality of the film web, the use of the device according to the invention can be combined with the use of a thickness control system. In the case of the combined use of a thickness control system in the production of tubular films (e.g. according to DE 10 2009 033 171 A1) and a roller through which air flows in the device for length change, a further positive effect occurs, because with reduced necking of the film web caused by stretching, less energy must be introduced into the control system in order to optimize the flatness, which allows finely metered control and thus simplifies the process.

[0038] The device for carrying out the length change can also be used in a stretching device or an annealing device for processing cast films.

[0039] In a method according to the invention for uniaxial length change of a film web, the film web is guided through at least one processing gap defined by two rollers. In this case, a first roller in the film conveying direction has a first peripheral speed and a second roller in the film conveying direction has a second peripheral speed. At least one of the rollers is an air-permeable roller, which is used to make the film web guided thereon lie against it in order to suppress transverse shrinkage and edge accumulation of the film web and to avoid the formation of air cushions between the roller and the film web. In the combination of an air-permeable roller and a temperature-controlled roller, the heat transfer between the film and the roller is additionally increased, because the insulating air layer between the film and the roller can flow out through the air-permeable roller. As a result, a more stable stretching process is achieved and a more homogeneous film is obtained without flatness errors, because the film lies uniformly on the roller over its contact width.

[0040] The effect is enhanced by applying negative pressure. On the one hand, the edge of the film that leaves the roller at the outlet of the roller in the film conveying direction and on the other hand, the edge of the film that contacts the roller at the inlet of the roller in the film conveying direction are better fixed by suction, so that a smaller relative speed difference is generated in the transverse direction and the longitudinal direction over the contact width between the film and the roller.

[0041] In order to further optimize the film web quality, the method is combined with a film thickness control device described in DE 10 2009 033 171 A1. During the production of the tubular film in the blown film device, the tubular film is subjected to film thickness control, wherein the thickness profile of the tubular film is adjusted so that the tubular film has thin areas at the following locations: the locations form the edge areas of the flattened tubular film in the downstream inline stretching device, so that the film produced after the film is stretched in the stretching device has the smallest possible deviation from the average film thickness over the film width. If the film web is now additionally guided in the device for length change via rollers through which air can flow during stretching in the stretching device, which have a negative pressure source, and which attracts the film and thus avoids transverse shrinkage and edge accumulation, a film with further improved quality is produced. The quality is further improved by applying a negative pressure source to the rollers through which air flows. The flattened tubular film can be a closed film, a one-sided or two-sided tubular film, a double flattened tubular film, or a single-layer film processed in two stretching devices.

[0042] The use of flow-through rollers as rollers, in particular stretching rollers, connected or not connected to a negative pressure source, increases the adhesion of the film web to the rollers and thus results in less transverse shrinkage of the film web and less edge accumulation and thus improved flatness of the film. Thus, previously necessary edge waste is avoided. Both increase the economy in the production of stretched films. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Further details, features and advantages of the subject matter of the invention emerge from the following description of the drawings, which show preferred exemplary embodiments of the invention by way of example.

[0044] In the figure:

[0045] Figure 1 A stretching apparatus is shown having a method according to the invention for stretching a thin film in the machine direction.

[0046] a device for uniaxial length change of the film web, and

[0047] Figure 2 An apparatus for uniaxial length change of a film web in the machine direction is shown. DETAILED DESCRIPTION

[0048] Figure 1 A device according to the invention for uniaxial length change of a film web in the machine direction in a stretching device (also called MDO device) is shown as an application possibility of the device according to the invention. A film web 1 is introduced into the stretching device from above. First, the film web is guided via a heating section 2 with a heating roller 3. The film web 1 is then fed to a device 4 according to the invention for length change (here a stretching device 4) and stretched, the device having rollers 5 (here stretching rollers) and a processing gap (here a stretching gap 6) between the rollers. The stretching roller 5 can have a smaller diameter than the heating roller. Subsequently, the film web 1 is fed to an annealing section 7, which has an annealing roller 8 for temperature control, followed by a cooling section 9 with a cooling roller 10. Finally, the film 1 leaves the MDO device and can be wound up in a winding device. The film web is held on different rollers by means of a contact roller 11.

[0049] Figure 2 The device 4 for length change of the stretching device is shown in detail. The film web 1 is guided via a first stretching roller 5a to a second stretching roller 5b. The stretching gap 6 is located between the stretching rollers 5a and 5b. In this stretching device, the second stretching roller 5b has a higher peripheral speed than the first stretching roller 5a, so that a positive length change of the film web is produced. The contact roller 11 is used to additionally position the film web 1 on the stretching rollers 5a and 5b. The film web 1 then leaves the device 4 according to the invention. According to the invention, the stretching roller 5b is designed as an air-circulating roller, which can be connected to a negative pressure source not shown here. The stretching roller 5a and the stretching roller 5b can also be additionally embodied as temperature-controlled rollers. The stretching roller 5b is then a combination of an air-circulating roller and a temperature-controlled roller. Depending on the stretching task, individual or all contact rollers 11 can be omitted. The stretching device can also have more than two stretching rollers 5 and therefore a plurality of devices 4. The stretching device can accordingly have 2, 3 or more heating rollers, stretching rollers, annealing rollers or cooling rollers.

[0050] Reference numerals list

[0051] 1 Film web

[0052] 2 Heating zones

[0053] 3 Heating roller

[0054] 4 Device for length change / stretching device

[0055] 5 Rollers / Stretching Rollers

[0056] 5a First roller / stretching roller

[0057] 5b Second stretching roller / rollers

[0058] 6 Processing gap / stretching gap

[0059] 7 Annealing section

[0060] 8 Annealing roller

[0061] 9 Cooling section

[0062] 10 Cooling roller

[0063] 11 Pressing roller

Claims

1. A device (4) for uniaxial length change of a film web (1) in the machine direction, the device comprising at least one processing gap (6) defined by two rollers (5a, 5b), through which the film web (1) is guided in the machine direction, wherein: A first roller (5a) along the film conveying direction has a first peripheral speed, and a second roller (5b) along the film conveying direction has a second peripheral speed, characterized in that at least one of the rollers (5a, 5b) is a roller (5a, 5b) through which air can flow from the outside to the inside, at least one of the rollers (5a, 5b) through which air can flow can be combined with a temperature-controlled roller and consists of a double-layer roller with fluid temperature control, the double-layer roller with fluid temperature control is equipped with a channel for guiding air and can be connected to a negative pressure source, and the rollers (5a, 5b) through which air can flow can be loaded with negative pressure, so that transverse shrinkage is reduced during uniaxial stretching in the machine direction and thus edge accumulation is reduced, The roller through which air can flow has a gas-permeable layer of a sintered structure, which is made of highly polished stainless steel; or the roller through which air can flow is constructed of an open-porous material in the micrometer range.

2. The device (4) according to claim 1, characterized in that A vacuum source can be connected to the rollers (5a, 5b) through which air can flow.

3. The device (4) according to claim 2, characterized in that The rollers (5a, 5b) through which air can flow can be subjected to vacuum of varying intensity over their length.

4. The device (4) according to any one of claims 1 to 3, characterized in that The first roller (5a) in the film transport direction has a smaller peripheral speed than the second roller (5b) in the film transport direction, and the length change of the film web (1) is a positive length change.

5. The device (4) according to any one of claims 1 to 3, characterized in that The first roller (5a) in the film transport direction has a greater peripheral speed than the second roller (5b) in the film transport direction of the film web (1), and the length change of the film web is a negative length change.

6. The device (4) according to any one of claims 1 to 3, characterized in that The first roller (5a) in the film conveying direction and the second roller (5b) in the film conveying direction of the film web (1) have the same peripheral speed.

7. The device (4) according to any one of claims 1 to 3, characterized in that The device (4) is a component of the stretching equipment.

8. The device (4) according to claim 7, characterized in that The further rollers of the stretching device are designed as rollers through which air can flow, with and / or without an applied vacuum source.

9. The device (4) according to claim 7, characterized in that The stretching device is arranged in-line in the film blowing device.

10. A film blowing device for producing a tubular film, characterized in that: The device (4) according to any one of claims 1 to 9 is arranged in-line in a film blowing plant.

11. The film blowing equipment according to claim 10, characterized in that: The device (4) according to any one of claims 1 to 9 is arranged after the pair of take-off rollers in the film conveying direction and before or after the deflection bar of the film blowing device.

12. The film blowing equipment according to claim 10 or 11, characterized in that: The film blowing system comprises a plurality of devices (4) according to any one of claims 1 to 9.

13. A method for uniaxially changing the length of a film web (1) in the machine direction, wherein: A film web (1) is guided through at least one processing gap (6) defined by two rollers (5a, 5b), wherein a first roller (5a) in the film transport direction has a first peripheral speed and a second roller (5b) in the film transport direction has a second peripheral speed, characterized in that: The film web (1) undergoes a length change in the processing gap (6), and at least one of the rollers (5a, 5b) is implemented as a roller (5a, 5b) through which air can flow from the outside to the inside, wherein the air accumulated between the rollers (5a, 5b) through which air can flow and the film web (1) flows out through the rollers (5a, 5b) through which air can flow, and the film web (1) lies against the rollers (5a, 5b) through which air can flow, at least one of the rollers (5a, 5b) through which air can flow can be combined with a temperature-controlled roller and consists of a double-layer roller with fluid temperature control, the double-layer roller with fluid temperature control is equipped with a channel for guiding air and can be connected to a negative pressure source, and the rollers (5a, 5b) through which air can flow can be loaded with negative pressure, so that transverse shrinkage and thus edge accumulation are reduced during uniaxial stretching in the machine direction, The roller through which air can flow has a gas-permeable layer of a sintered structure, which is made of highly polished stainless steel; or the roller through which air can flow is constructed of an open-porous material in the micrometer range.

14. The method according to claim 13, characterized in that During the production of a film in a blown film device, the film is subjected to film thickness adjustment, whereby the film thickness profile of the tubular film produced in the blown film device is adjusted so that a predetermined target thickness profile has a deviation from a consistent film thickness, wherein the deviation is used to compensate for the change in film thickness over the film width produced during subsequent uniaxial stretching along the machine direction, thereby producing a film web (1) having the following thickness cross-section by stretching: the thickness cross-section has the smallest possible deviation from the average film thickness over the entire film width.

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