Stretching device and method for uniaxially stretching a film web in the transport direction thereof

Abstract

The invention relates to a stretching device for uniaxially stretching a film web in the transport direction thereof, the stretching device comprising: a first roll (holding roll), via which the film web can be run and which rotates at a first circumferential speed; a second roll (stretching roll), which is arranged downstream of the first roll and via which the film web can be run and which rotates at a second circumferential speed; wherein the second circumferential speed is greater than the first circumferential speed; wherein at least one clamping roll is provided, by means of which the film web can be pressed against one of the rolls. At least one holding arrangement is provided relative to which the clamping roll can be rotated about its rotational axis. The clamping roll is supported on the holding assembly by a support point extending over part of, in particular over more than a quarter of, the axial length of the clamping roll, or by a plurality of support points distributed over the axial length of the clamping roll and / or the circumference of the clamping roll. A first movement device is provided by means of which the one or more support points can be or are moved relative to the clamping roll in a direction parallel to the rotational axis of the clamping roll.

Description

[0001] Stretching device and method for monoaxially stretching a film web in its transport direction

[0002] The invention relates to a stretching device for monoaxially stretching a film web in its transport direction according to claim 1 and to a method according to claim 9.

[0003] A generic stretching device, which is often arranged inline, particularly in or downstream of a blown film line or a flat film line, comprises at least a first roller, which can also be referred to as a holding roller, over which the film web can be guided and which rotates at a first peripheral speed. Downstream of the first roller is a second roller, which can also be referred to as a stretching roller and over which the film web can be guided after it has left the first roller. The second roller rotates at a second peripheral speed, this second peripheral speed being greater than the first peripheral speed. In the section in which the film web has already left the first roller and has not yet reached the second roller, the film is stretched, i.e. extended, in its transport direction. This section of the section is often referred to as the stretching nip.In addition, the first and second rollers usually rotate in opposite directions so that the film web is guided over each of the two rollers with the largest possible wrap angle. Overall, the stretching process described specifically changes important properties of the film web. However, this stretching process also gives rise to the undesirable phenomenon of neck-in, where the film web becomes narrower than its original width. In addition, the edges of the film web thicken, resulting in an uneven thickness profile in the transverse direction. The edges therefore have to be cut off, which reduces the usable width of the film web. The cut-off edges are unusable and therefore incur unwanted costs. Many improvements have been proposed in the past to reduce these effects. One measure is the provision of at least one pressure roller with which the film web can be pressed against one of the rollers.Reducing the stretching gap has also led to improvements in the past.

[0004] However, if a pressure roller is used, the stretching gap cannot be reduced to the desired extent with conventional stretching devices. The as yet unpublished patent application PCT / EP2022 / 081608 shows a pressure roller with a reduced diameter that is supported by support points to reduce deflection. This measure made it possible to reduce the stretching gap, resulting in a larger usable portion of the film web. However, since the support points have interruptions, there is a risk that these interruptions will appear as defects in the transverse direction at the same locations on the film web, which can lead to poor film quality.

[0005] The task is therefore to propose a stretching device and a method with which the above-mentioned disadvantages can be reduced.

[0006] The above object is achieved by a stretching device having the features of claim 1 and a method having the features of claim 9. Further features and details of the invention emerge from the subclaims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the stretching device according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0007] The stretching device according to the invention is characterized in that

[0008] • that at least one holding arrangement is provided, relative to which the pressure roller is rotatable about its axis of rotation,

[0009] • that the pressure roller is supported on the holding arrangement via a support point extending over a part, in particular over more than a quarter, of the axial length of the pressure roller or several support points distributed over the axial length of the pressure roller and / or the circumference of the pressure roller and

[0010] • that a first movement device is provided with which the support point or the support points can be moved relative to the pressure roller in a direction parallel to the axis of rotation of the pressure roller.

[0011] The invention is based in particular on the finding that the support points, in particular the support rollers, although reducing the deflection of the pressure roller, always rest on the same points on the pressure roller. Since a pressure roller generally has an elastic circumferential surface, the areas where the support points rest are pressed in more deeply than other points. By the time the pressed-in areas reach the film web, they often have not returned to their original position, which leads to uneven pressure of the pressure roller on the film web. The pressed-in areas can also be pressed in more and more deeply, which increases the described effect. Furthermore, different levels of contamination can occur depending on whether surface areas of the pressure roller are contacted by the support points or not.

[0012] By moving the support points relative to the pressure roller, the contact points between the pressure roller and the support point can be changed. This can be done periodically. The advantage of this is that the aforementioned effects no longer occur at the same locations and are not transferred to the same parts of the film web. Since increasingly large indentations of the pressure roller are also avoided, the overall quality of the film web is improved.

[0013] Furthermore, according to the invention, a holding arrangement is provided relative to which the pressure roller is rotatable, wherein the pressure roller is supported on the holding arrangement via a support point extending over a part, in particular over more than a quarter, of the axial length of the pressure roller or via a plurality of support points distributed over the axial length of the pressure roller and / or the circumference of the pressure roller.

[0014] These measures make it possible to absorb the forces acting on the pressure roller by means of a holding arrangement that is located further away from the first and / or second roller in the radial direction. The space available here can then be used to design the holding arrangement with high flexural rigidity. This leads to a more uniform thickness of the film web and thus to improved quality.

[0015] Conversely, or in addition, it is possible to reduce the diameter of the pressure roller compared to the prior art. A reduced diameter of the pressure roller results in the stretching gap being or can be reduced while still positioning the pressure roller at the detachment line or the impact line. A reduced stretching gap is advantageous because it further reduces the neck-in effect. It can be advantageous if at least one of the rollers is assigned multiple pressure rollers.

[0016] Furthermore, the invention makes it possible for the film web to run over the pressure roller at a wrap angle. The force exerted by the film web on the pressure roller in this case can be easily compensated for by the inventive design, while simultaneously preventing any streaking on the film web. It is advantageous if the film web wraps around the pressure roller at a wrap angle between 0° and 90°. In particular, the wrap angle is between 0.1° and 90°, preferably between 0.5° and 90°. With the aforementioned measure, the stretching gap can be further reduced to reduce neck-in.

[0017] In an advantageous embodiment of the invention, it is provided that the holding arrangement comprises at least one carrier which extends parallel to the axis of rotation and is arranged immovably relative to the first and / or second roller. This carrier extends in particular the entire length of the pressure roller and thus provides the required counterforce to compensate for the deflection of the pressure roller. This carrier therefore provides the required supporting force for the support points and thus for the pressure roller. The carrier can be formed in one piece, but can also be composed of individual carrier pieces. This enables a modular design of the carrier, in which the carrier can be composed of a different number of carrier pieces depending on the working width of the stretching device, which in particular reduces the manufacturing costs of the stretching device.Regardless of the design of the support, it must be designed so that the force acting on the pressure roller does not cause the support to deflect. The support and the roller to which it is assigned are preferably arranged immovably relative to each other. This means that an adjustment movement to adjust the roller also adjusts the associated support, preventing any shift in the forces acting on the pressure roller.

[0018] In order to ensure easy displacement of the support points relative to the pressure roller, it is advantageously provided that the first movement device comprises a frame on which each support point is supported, wherein the frame is movable relative to the pressure roller and in particular relative to the carrier. This makes it possible to provide a simple displacement drive that acts on the frame. In particular, this creates a stable device that allows displacement but has only a minor impact on the forces acting on the pressure roller. In a further embodiment, it is provided that the frame is supported on the carrier and is displaceable relative to it, in particular via sliding or rolling devices. A sliding device can be a rail-slide combination, which results in a cost-effective design.A rolling device can, for example, be a roller conveyor, with a plurality of rollers arranged on the support or frame. A roller conveyor can minimize friction between the support and the frame.

[0019] It is advantageous if the first movement device comprises at least one drive device with which each support point and / or in particular the frame can be moved alternately in a first direction and in a second direction opposite to the first direction. This drive device can be a linear motor or a servomotor, for example. A drive designed as a double-acting piston-cylinder unit is also conceivable. Alternatively, a rotating drive can be provided, the rotational movement of which can be converted into a linear movement via gear elements. A drive device can be provided to set the support elements in particular in a periodic movement. It is particularly advantageous if the amplitude of the movement is adjustable. In particular, it is advantageous if the movement in the first and second directions is each greater than 0 mm and less than 300 mm, in particular less than 200 mm.

[0020] It is particularly advantageous if a first row and at least one second row of support points are provided, wherein the rows extend in the longitudinal direction of the pressure roller, wherein in particular the first and second rows are displaceable relative to one another. This makes it possible to carry out the movements of the individual rows independently of one another. In this case, it can be provided to provide a separate drive for each row or, if a single drive is provided, to enable relative displaceability of the two rows via a coupling. In particular, it can be provided that the displacement movement of the two rows relative to one another is adjustable and in particular independently of one another. This makes it possible to provide the best possible adjustability of the operating parameters even with different film webs in order to achieve the best possible quality of the film web.It is also advantageous if the support points of each row are arranged in a separate frame, again to facilitate simple assembly. Each frame can be displaced relative to the support, as described above in connection with a single frame.

[0021] In this context, it is advantageous to provide at least two rows of support points, or at least two support points, each arranged at different angular positions in the circumferential direction of the pressure roller. In this way, the pressure roller runs in a groove-like recess, which can also be referred to as a roller bed. This supports the pressure roller at various points, so that the contact pressure provided by the holding arrangement is better distributed over the outer circumference of the pressure roller. Furthermore, this measure makes it easier to hold the pressure roller in its position.

[0022] In order to further mitigate the disadvantages described above, a second movement device is provided with which the pressure roller can be moved in its axial direction. This allows the pressure roller to be moved relative to the first or second roller in order to further even out the force acting on the film web, which in turn can lead to improved quality of the film web. The second movement device can comprise a second drive which is arranged on the holding arrangement. A double-acting, compressed-air-operated piston-cylinder unit can be used as the second drive for the second movement device. A permanently rotating motor is also conceivable, the rotational movement of which is converted into a linear movement, for example via a wheel and a coupling rod. Finally, a servo motor or a linear motor are also conceivable.In order to enable such a displacement of the pressure roller, it is provided that the pressure roller is connected to the holding arrangement via at least one holder or via at least one extension piece, wherein in particular the pressure roller is movable with the second movement device relative to the holder or extension piece or the holder or extension piece together with the pressure roller relative to the holding arrangement. It can therefore be provided to move the holder or extension piece relative to the holding arrangement, in particular relative to its carrier, wherein the pressure roller is thus also displaceable. Instead or additionally, the pressure roller can also be mounted displaceably relative to the holder or extension piece, for example in plain bearings.

[0023] It is advantageously provided that each pressure roller is rotatably mounted at its ends in holders or extension pieces of the holding arrangement, wherein in particular a relative displaceability of the pressure rollers to the holders or extension pieces in the radial direction of the pressure roller is also provided.

[0024] Preferably, each pressure roller is assigned a holding arrangement.

[0025] The holding arrangement is preferably supported on the machine frame in which the first and / or second roller is also supported.

[0026] In an advantageous embodiment of the invention, the at least one support point comprises at least one roller (also called a support roller), on whose circumferential surface the pressure roller rolls. In particular, each support point comprises several rollers. The roller, in turn, is supported on the holding arrangement. Such a roller reduces the friction of the pressure roller, so that its surface remains as undamaged as possible.

[0027] In a further development, it is provided that the at least one support point comprises at least one support roller, which is mounted on an axle via at least one bearing, wherein the axle is fastened to the holding arrangement, in particular to a displaceable frame of the holding arrangement, by means of an axle carrier or holder. In particular, it is provided that the roller is rotatably supported on the axle via ball, roller, or needle bearings. Such bearings can withstand large forces, which are necessary for supporting a pressure roller in a stretching device. Each axle is fastened to the holding arrangement, in particular at both ends, by means of an axle carrier. An axle carrier can be a common axle carrier for two adjacent axles. Furthermore, axle carriers can be distributed over the axial length of an axle. A separate axle can be provided for each roller, but it is advantageous to provide at least two rollers on each axle.Instead of a plurality of rollers, elongated rollers whose axial length is greater than their outer diameter can also be provided.

[0028] Alternatively or additionally, it is advantageous if the at least one support point comprises at least one roller, each roller being attached to a shaft, the shaft being rotatably mounted on a shaft bearing, which in turn is attached to a frame of the support assembly. The above-described configurations with respect to the axes can also be applied analogously to the shaft assembly.

[0029] The rollers disclosed in the aforementioned embodiments can be provided in various designs. For example, to reduce friction between a roller and a pressure roller, the roller can be provided with a smooth peripheral surface, i.e., the surface on which the pressure roller rolls. This can be achieved, for example, by chrome-plating the roller surface. In this context, to avoid damage, it can be advantageous if the peripheral surface is hard or rigid, which can be achieved in particular by a peripheral surface comprising a metal. A hard or rigid peripheral surface and / or a smooth peripheral surface are particularly advantageous if the pressure roller comprises a soft peripheral surface. This can ensure that the pressure roller does not suffer excessive wear or even damage, even during relative movement between the pressure roller and the support elements.It can further be provided that the circumferential surface of at least one roller comprises a structure. A structure means that there are depressions on the circumferential surface. Such a structure can be regular, for example comprising grooves and / or bores. Such a regular structure is therefore created in particular by tool-based machining or production of the circumferential surface, in particular by contact machining. Additionally or alternatively, an irregular structuring of the circumferential surface of the at least one roller can be provided. Such irregular structuring can be achieved in particular by projectile bombardment of the circumferential surface, as occurs, for example, in sandblasting or glass bead blasting. A structure with depressions serves primarily to absorb the air entrained by the pressure roller into the roller-Z-roller gap and thus prevent contact between the roller and the pressure roller from breaking off.

[0030] In general, the circumferential surface properties can be determined depending on the roller, i.e., the holding roller and / or the stretching roller. If the roller comprises a flexible circumferential surface, in particular by means of an at least partially elastomeric coating, an associated pressure roller can comprise a very hard circumferential surface, for example, if it comprises polished steel. In this case, it is preferred that the support roller at least partially comprises a flexible circumferential surface.

[0031] The at least one roller can be concavely shaped on its peripheral surface, i.e., it has a larger diameter at its edges in the direction of its axis of rotation than in the center. Alternatively, the peripheral surface can be convexly shaped. A concave or convex peripheral surface can reduce the contact area between the pressure roller and the roller and thus surface wear. However, a convex shape is particularly advantageous, so that the displaceability of the roller relative to the pressure roller is improved. Within the scope of the present invention, a roller is also understood to mean a sleeve in which, in particular, the axial length is greater than the diameter.

[0032] In a further advantageous embodiment of the invention, the support point comprises at least one concavely shaped channel element in which the pressure roller lies, wherein the inner surface of the channel element is provided with openings through which a pressurized fluid can be conducted into the area between the channel element and the pressure roller. This fluid is preferably a gas, in particular air. With this measure, the pressure roller can thus be held by the support point without physical contact and guided during rotation. This results in a "floating bearing" of the pressure roller. The channel element can be an elongated shell made of a plastic, a fiber-reinforced plastic, or a metal.The openings on the inner surface, whose radius is preferably only slightly larger than the outer radius of the pressure roller, can be fluidically connected to supply lines, such as through-holes, so that the fluid under overpressure (higher than ambient pressure) can be easily supplied from the outside. To achieve better distribution of the fluid between the inner and outer surfaces of the pressure roller, the inner surface of the channel element can be covered or coated with a fine-pored material, such as sintered plastic and / or sintered metal. It is also possible to construct the channel element exclusively from a sintered material.

[0033] In order to apply a force to the pressure roller against the at least one support point, at least one pulling device is provided, with which a force can be provided which can act on the pressure roller and which acts in the direction of the holding arrangement and in particular in the radial direction of the pressure roller. Even if end holders are provided for the pressure roller, as described above, such a pulling device is advantageous in order to hold the pressure roller over its entire length at or in the at least one support point. This is particularly important when the not yet rotating pressure roller is brought into contact with the first and / or second roller, which is already rotating, or with the film web. The pulling device prevents the pressure roller from jumping out of the support point or from jamming with the support point.

[0034] It is particularly advantageous if at least one pulling device is provided with which the pressure roller can be acted upon with a force directed in the direction of the holding arrangement, wherein the pulling device comprises at least one magnet and at least one magnetizable element. The magnet is arranged in or on the holding arrangement and the magnetizable element is arranged in or on the pressure roller and / or in or on the holding arrangement. In other words, to generate an attractive, magnetic force, one element must be partially magnetizable and the second element must carry at least one magnet. The magnet is preferably a permanent magnet, but can also be a switchable electromagnet.

[0035] Alternatively or additionally, it is advantageous if at least one pulling device is provided with which the pressure roller can be acted upon with a force directed in the direction of the holding arrangement, wherein the pulling device comprises at least one suction device arranged on the holding arrangement, with which the pressure roller can be subjected to a suction force acting in the direction of the holding arrangement. A suction device can, for example, be a bore, a hose, a pipe or the like, one end of which is located in the immediate vicinity of the pressure roller and the other end of which is connected to a vacuum generator, such as a blower or a vacuum pump. The advantage of using such a suction device to generate the pulling force is that the magnitude of the pulling force can be varied.

[0036] Furthermore, it is advantageous if at least one cleaning element is arranged on the holding arrangement, in particular on the carrier of the holding arrangement, with which the outer surface of the pressure roller can be cleaned. Such a cleaning element can, for example, be a cloth, piece of felt or the like extending at least partially over the length of the pressure roller, which in particular is in permanent contact with the pressure roller. However, the cleaning element can also be a cleaning element attached to a carriage. This carriage is movable in the axial direction of the pressure roller along a guide, which is preferably attached to the carrier. The surface of the pressure roller can thus be cleaned by continuous movement of the carriage or by movement carried out as needed. The carriage can also be movable beyond at least one end of the pressure roller in order to be able to change or clean the cleaning element itself.Cleaning the pressure roller has the advantage that no deposits or dirt build up that could lead to damage to the film web.

[0037] Furthermore, it is preferred if the pressure roller is provided with a coating, in particular a rubber coating, on its outer surface. The coating is advantageously made of a compressible material so that the film web experiences sufficient static friction.

[0038] It is also advantageous if the pressure roller can be driven in rotation by a drive. In other words, a drive is provided with which the pressure roller can be set in rotation or held in place. This drive can be a conventional electric motor or an air motor. The advantage is that the pressure roller can be set in rotation before it is placed on an already moving film web. This reduces wear on the pressure roller, while also preventing damage to the film web when the pressure roller is placed on the film web.

[0039] It is also advantageous if the pressure roller can be pressed against the roller within an angular range of at most + / - 30 degrees around the line on the roller defined by the common tangential plane of both rollers. For this purpose, the holding arrangement is provided for moving relative to the roller, wherein the holding arrangement is movable at least in the circumferential direction of the at least one roller. In particular, it is advantageous if the pressure roller can be moved beyond the said line as seen in the transport direction of the film web. In this case, the film web does not leave or touch the roller at the detachment line or the impact lines, but rather before or after. In concrete terms, this means that in the case of the holding roller, the film web initially runs on the pressure roller, and in the case of the stretching roller, it first runs on the pressure roller before hitting the stretching roller.In this case, the stretch gap can be shortened again, so that the neck-in is further reduced.

[0040] In a further embodiment of the invention, at least two holding assemblies are provided for the holding roller and / or for the stretching roller, with both holding assemblies being connected to one another via connecting elements. In total, two holding assemblies can therefore be provided per roller, with the two holding assemblies being fastened to a connecting element. The dimensions of the connecting element are designed such that the pressure roller of the first holding assembly presses the film web against the roller in the region of its impact line, and that the pressure roller of the second holding assembly presses the film web against the roller in the region of the detachment line. The connecting element can be movable relative to the respective roller in the circumferential direction and / or in the radial direction by means of at least one adjusting mechanism, such that the pressure rollers can also be moved with the movement of the connecting element.To move the connecting element, the adjusting element preferably comprises at least one air-operated piston-cylinder unit. It is preferred that the connecting element is supported on the machine frame on which the respective roller is also supported. If two holding assemblies, which are connected to one another via a connecting element, can be adjusted on different lines of the respective roller, this achieves an increased adjusting force, since the connecting element, which is in particular rigid, also contributes to a normal force in the radial direction of the roller. Overall, for a given adjusting force, the film web is pressed even more strongly against the roller, so that the neck-in can be further reduced. It is particularly preferred if both the holding roller and the stretching roller are each assigned two holding assemblies and one connecting element.The stretching device described above and the advantageous embodiments can be provided within any film production or film processing system. In particular, the stretching device according to the invention can be provided inline within a blown film line or a flat film line. In a blown film line, the stretching device can be provided, for example, in the transport direction of the film web between a flattening device and a reversing device, or downstream of the reversing device but upstream of a winding device. In a blown film line, the film web can also be a two-layer film web that was combined from a film bubble. The two layers of the film web can then be connected to one another at both lateral edges or only at one lateral edge, or separated from one another by prior cutting on both sides.

[0041] The above-mentioned object is additionally achieved by a method for monoaxially stretching a film web in its transport direction,

[0042] • wherein the film web is guided over a first roller (holding roller) which rotates at a first peripheral speed,

[0043] • wherein the film web is guided over a second roller (stretching roller) arranged downstream of the first roller, which rotates at a second peripheral speed,

[0044] • wherein the second peripheral speed is greater than the first peripheral speed,

[0045] • wherein the film web is pressed against one of the rollers by at least one pressure roller.

[0046] The method according to the invention is characterized in that at least one holding arrangement is provided, relative to which the pressure roller rotates, wherein the pressure roller is supported on the holding arrangement via a support point extending over more than a quarter of the axial length or via a plurality of support points distributed over the axial length of the pressure roller and / or the circumference of the pressure roller, wherein the support point or the support points are moved relative to the pressure roller in a direction parallel to the axis of rotation of the pressure roller by means of a first movement device.

[0047] This makes it possible to achieve the same advantages as those already described above in connection with the stretching device according to the invention.

[0048] In one embodiment of the method according to the invention, it is provided that the pressure roller is also moved in the direction of its rotational axis. The movements of the support point and / or the pressure roller can occur periodically. In particular, it is provided that the directions of movement of the pressure roller and the support points are opposite. In this case, it can be provided that the speed profiles of the movements of the pressure roller and the support points are identical. However, different speed profiles can also be provided, in particular in connection with different distances traveled by the pressure roller and the support points. The aforementioned measures make it possible to adapt the movements to the properties of the film web.The movements can also be adapted to the process and operating parameters of a production device for the film web, in particular if the stretching device according to the invention is arranged inline.

[0049] Further advantages, features and details of the invention will become apparent from the following description, in which various embodiments are explained in detail with reference to the figures. The features mentioned in the claims and in the description can each be essential to the invention individually or as any combination of mentioned features. Within the scope of the entire disclosure, features and details described in connection with the method according to the invention naturally also apply in connection with the stretching device according to the invention and vice versa, so that with regard to the disclosure, reference is or can always be made to the individual aspects of the invention. The individual figures show: Fig. 1 Schematic representation of an inventive

[0050] Stretching device

[0051] Fig. 2 Representation of further details of the inventive

[0052] Stretching device

[0053] Fig. 3 View III-III from Figure 4

[0054] Fig. 4 View IV-IV from Figure 2

[0055] Fig. 5 Representation of a further development of an inventive

[0056] Stretching device.

[0057] Figure 1 shows a schematic representation of a stretching device according to the invention. The film web 101 enters the stretching device 100 in the transport direction T. The film web initially runs onto one or successively onto several preheating rollers, of which only one preheating roller 102 is shown. The task of a preheating roller is to bring the film to a predefined temperature. For this purpose, a preheating roller is usually temperature-controlled, with a temperature-controlled fluid often being introduced into the preheating roller.

[0058] After leaving the preheating roller(s) 102, the film web 101 reaches a first roller 110, which can also generally be referred to as a holding roller 110. This holding roller can be connected to a drive (not shown), for example, a dedicated electric motor that rotates the roller 110 at a first peripheral speed. Additionally or alternatively, a braking device can be provided.

[0059] The first roller 110 is preferably assigned a first pressure roller 111, which together with the first roller 110 provides an inlet gap for the film. Preferably, the inlet gap or the travel path of the film web 101 is configured such that the film web 101 runs tangentially to the rollers 110, 111 in the inlet gap. The roller gap already serves to minimize the air between the holding roller 110 and the film. A second pressure roller 112 is assigned above the first roller 110 and forms an outlet gap with the roller 110. The second pressure roller 112 can be adjustable in the circumferential direction and / or in the radial direction of the first roller 110. The second pressure roller 112 ensures that the film leaves the first roller 110 along a line that runs parallel to the axial direction of the first roller 110.

[0060] Viewed downstream in the transport direction T of the film 101, a second roller 120 is arranged, which can be referred to as a stretching roller 120. The stretching roller 120 is connected to a further drive (not shown), for example a separate electric motor, which drives the roller 120 to rotate at a second peripheral speed. The rotation directions R1 of the roller 110 and R2 of the roller 120 are opposite. This ensures that the film web has the largest possible wrap angle around each roller 110, 120. The second peripheral speed is greater than the first peripheral speed, so that the stretching roller 120 has a greater peripheral speed than the holding roller 110. This results in the film 101 being stretched between the outlet gap of the first roller 110 and the inlet edge of the second roller 120 in the ratio of the peripheral speeds in its transport direction.The distance between the outlet gap and the inlet edge is often referred to as the stretching gap.

[0061] It is possible for the first roller 110 and the second roller 120 to be movable relative to each other. This allows the stretching gap to be influenced. Changing the stretching gap can influence the properties of the film. The smallest possible stretching gap is preferred, i.e., the shortest possible distance between the rollers 110 and 120, in which the film web is guided freely.

[0062] The second roller 120 is preferably associated with a third pressure roller 121, which, together with the second roller 120, provides a second inlet gap for the film. Preferably, the inlet gap or the path of the film 101 is configured such that the film 101 runs tangentially to the rollers 120, 121 in the inlet gap. The roller gap serves to minimize the air between the stretching roller 120 and the film, thus minimizing the friction between the film web and the roller 120.

[0063] In the event that the stretching gap is to be set very small, the third application roller 121 would collide with the roller 110, so that in this case the third application roller would have to be swiveled away.

[0064] The second roller 120 is optionally assigned a fourth pressure roller 122, which forms an outlet gap with the roller 120. The fourth pressure roller 122 can also be adjustable in the circumferential direction of the second roller 120. The fourth pressure roller 122 serves to ensure that the film leaves the second roller 120 along a line that runs parallel to the axial direction of the roller 120.

[0065] In principle, one or more contact rollers can be dispensed with in a stretching device according to the invention. Nevertheless, the term "inlet gap" or "outlet gap" can be used. This refers to the line along which the film contacts the holding or stretching roller, or along which the film separates from the holding or stretching roller.

[0066] Further rollers, in particular each with one or two pressure rollers, can be provided, wherein two rollers arranged directly one after the other are driven in such a way that the roller arranged downstream has a higher peripheral speed than the preceding roller.

[0067] Downstream of the rollers 110, 120, at least one cooling roller 130 is arranged, with which the film web 101 can be cooled again, so that the new molecular orientation resulting from the stretching solidifies within the film web. Figure 2 shows further details of the stretching device 100 according to the invention. In addition to the holding roller 110 and the stretching roller 120, the second pressure roller 112 and the third pressure roller 121 are shown. One embodiment of the invention is explained in connection with the pressure roller 112, although further or all pressure rollers, in particular the pressure roller 121, can be related to an embodiment of the invention.

[0068] The second pressure roller 112 and / or the third pressure roller 121 are preferably supported on a support 140, in particular a cross member, which runs transversely to the transport direction of the film web. The support 140, in turn, is supported directly or indirectly on the machine frame, on which the roller(s) are also supported. The support 140 itself can consist of several interconnected individual pieces. Since the roller 110 or the rollers 110, 120 can be movable relative to the machine frame, adjustment devices such as pivot bearings or carriage-rail combinations can be provided between the machine frame and the rollers 110, 120. The supports 140 can also be supported on these adjustment devices, wherein the supports 140 and thus the pressure rollers can be moved separately relative to the adjustment devices in order to be able to move the pressure rollers relative to the first and / or the second roller 110, 120.The manner in which the pressure rollers are supported on the supports is described below using an exemplary embodiment, although the invention is not limited to this exemplary embodiment.

[0069] The further preferred embodiment of a holding arrangement 113 for a pressure roller will now be described as an example for the pressure roller 112, but is of course valid for all other pressure rollers. Figures 3 and 4 show further views of the holding arrangement, to which reference is also made in the following description.

[0070] A frame 146 is connected to a plurality of holders 141, which are distributed along the longitudinal direction of the frame and thus along the axial direction of the pressure roller 112. The axial direction is represented by the rotational axis 142 of the pressure roller. Each holder 141 carries an axle 143, whereby a separate axle 143 can be provided between each two holders 141, or an axle 143 can extend through several holders 141. Alternatively, shafts can be provided instead of axles, which are then rotatably mounted in the holders, so that the following description with regard to the axles 143 also applies to shafts. The axle 143 between two holders 141 is also referred to below as the axle section.

[0071] The frame 146 is in turn supported on the carrier 140, with rails 147 preferably being fastened to the carrier 140, on which the frame can be displaceably mounted, in particular via sliding elements or carriages. The displaceability parallel to the axis 142 of the pressure roller 112 is represented by the double arrow 149. To enable a back-and-forth movement along the double arrow, a displacement drive 148 is provided, which is fastened, for example, directly or indirectly, to the carrier 140. The displacement drive 148 is connected to the frame, for example, via a push rod 151. The components described in this paragraph, in particular the rails 147, the frame 146, the displacement drive 146 and / or the push rod 151, can be components of a movement device within the meaning of claim 1. Of these components, only the frame 146 can be seen in Figure 4.

[0072] A first and at least one second axle 143 or a first and at least one second row of axles 143 are provided, which extend parallel to one another and parallel to the axial direction of the pressure roller 112. Each axle 143 carries one or more rollers 144 that are rotatably mounted on the axle. In the case of shafts, these rollers 144 can be fixedly connected to the shaft. Thus, along with the axles 143, the rollers 144 are also distributed over the axial direction of the pressure roller. During operation, the pressure roller 112 rolls on these rollers 144, so that these are components of the support device via which the pressure roller 112 is supported on the holding arrangement 113. One group of rollers 144 can be provided per axle 143 or axle section.It is advantageous if axle sections of the first axle or row of axles are arranged offset in the axial direction to at least one axle section of the second axle or row of axles in order to avoid localized contamination or wear, which would otherwise occur due to uneven rolling of the rollers on the pressure roller.

[0073] The two parallel axes or rows of axes, with their rollers 144, together form a groove-like depression in which the pressure roller 112 lies, thus preventing any movement other than the intended rotational and / or displacement movement. The pressure roller 112 itself can be rotatably mounted in the end-face holders 141 or in extension pieces 150 of these holders via a pivot bearing. The pivot bearing can be displaceably arranged in the holder or its extension piece in order to reduce any radial forces acting on the pivot bearing in the event of varying contact forces. This displaceability can be realized, for example, by means of elongated holes in the extension pieces 150, in which the pivot bearings are displaceably arranged. In addition, a displacement drive 152 for the pressure roller 112 can be arranged on the extension piece 150 so that it can be moved back and forth along its axis 142, i.e. in the direction of the double arrow 153.

[0074] In order to keep the pressure roller in constant contact with the rollers 144, several magnets 145 can be arranged directly or indirectly on the support in the axial direction along the length of the pressure roller 112. In this exemplary embodiment, the pressure roller comprises at least one magnetizable element in its body, preferably an iron core extending in the axial direction, which is attracted by the magnets, which are preferably permanent magnets, via a magnetic force. The magnetizable element within the pressure roller is not shown.

[0075] Overall, the arrangement described in connection with Figures 2 to 4 reduces the deflection of the pressure roller. This makes it possible, on the one hand, to increase the contact force of the pressure roller against the roller 110 and / or 120 and / or to shorten the stretching gap. Both options lead to a reduction in the neck-in effect and thus to the more cost-effective production of a marketable film web. Furthermore, the rollers 144 and / or the pressure roller can be moved to ultimately avoid markings on the film web 101.

[0076] Figure 5 now represents an advantageous development of the stretching device according to the invention. Shown are two holding assemblies for two pressure rollers, preferably according to Figures 2 to 4, wherein one pressure roller is assigned to the line of impact of the film web on the roller and the second pressure roller is assigned to the detachment line. Both holding assemblies are connected to one another via a connecting element 160. The connecting element offers the advantage that, with a common adjusting device 161, both holding assemblies, together with the pressure rollers, can be moved relative to the roller 112. The adjusting device can, for example, comprise a compressed air-operated piston-cylinder unit, with which the connecting element can be adjusted in the radial direction of the roller 112 (represented by the double arrow 162). For adjustment in the circumferential direction of the roller 112, the connecting element 160 can be slidably arranged on the adjusting device 161.It is also conceivable that the adjustment device is pivotably mounted on the machine frame or on a console supporting the roller 112.

[0077]

Claims

Patent claims 1. Stretching device for monoaxially stretching a film web in its transport direction with • a first roller (holding roller) over which the film web can be guided and which rotates at a first circumferential speed, • a second roller (stretching roller) arranged downstream of the first roller, over which the film web can be guided and which rotates at a second peripheral speed, • wherein the second peripheral speed is greater than the first peripheral speed, • wherein at least one pressure roller is provided with which the film web can be pressed against one of the rollers, characterized in that at least one holding arrangement is provided, relative to which the pressure roller can be rotated about its axis of rotation, that the pressure roller is supported on the holding arrangement via a support point extending over a part, in particular over more than a quarter, of the axial length of the pressure roller or several support points distributed over the axial length of the pressure roller and / or the circumference of the pressure roller and that a first movement device is provided with which the support point or the support points can be moved relative to the pressure roller in a direction parallel to the axis of rotation of the pressure roller.

2. Stretching device according to the preceding claim, characterized in that the holding arrangement comprises at least one carrier which extends parallel to the axis of rotation and is arranged immovably relative to the first and / or second roller.

3. Stretching device according to one of the preceding claims, characterized in that the first movement device comprises at least one frame on which each support point is supported, wherein the frame is movable relative to the pressure roller and in particular relative to the carrier.

4. Stretching device according to the preceding claim, characterized in that the frame is supported on the carrier and is displaceable relative to the latter, in particular via sliding or rolling devices.

5. Stretching device according to one of the preceding claims, characterized in that the first movement device comprises at least one drive device with which each support point and in particular the frame can be moved alternately in a first direction and in a second direction opposite to the first direction.

6. Stretching device according to one of the preceding claims, characterized in that a second movement device is provided with which the pressure roller can be moved in its axial direction.

7. Stretching device according to one of the preceding claims, characterized in that the pressure roller is connected to the holding arrangement via a holder, where- in particular the pressure roller is movable with the second movement device relative to the holder or the holder together with the pressure roller is movable relative to the holding arrangement.

8. Stretching device according to one of the preceding claims, characterized in that a first row and at least one second row of support points are provided, wherein the rows extend in the longitudinal direction of the pressure roller, wherein in particular the first and the second row are displaceable relative to one another.

9. Method for monoaxially stretching a film web in its transport direction, • wherein the film web is guided over a first roller (holding roller) which rotates at a first peripheral speed, • wherein the film web is guided over a second roller (stretching roller) arranged downstream of the first roller, which rotates at a second peripheral speed, • wherein the second peripheral speed is greater than the first peripheral speed, • wherein the film web is pressed against one of the rollers by at least one pressure roller, characterized in that at least one holding arrangement is provided, relative to which the pressure roller rotates, that the pressure roller is supported on the holding arrangement via a support point extending over a part, in particular over more than a quarter, of the axial length of the pressure roller or via a plurality of support points distributed over the axial length of the pressure roller and / or the circumference of the pressure roller, and that the support point or the support points are moved relative to the pressure roller in a direction parallel to the axis of rotation of the pressure roller by a first movement device.

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