METHOD FOR WINDING A MATERIAL SHEET AND WINDING DEVICE

Abstract

A method for winding a material sheet, in particular a plastic film, by a winding device, wherein the material sheet is guided from at least one first roller to at least one second roller in a conveying direction. At least one cutting device is arranged between the first roller and the second roller to cut the material sheet into at least two partial sheets. The partial sheets are each wound up into a bobbin in the conveying direction behind the second roller. The at least one first roller and the at least one second roller are each driven by a drive so that the tensile stress in the material sheet or in the partial sheets changes periodically over time in the conveying direction of the material sheet.

Claims

1. A method for winding a material sheet, in particular a plastic film, by means of a winding device, wherein the material sheet is guided from at least one first roller to at least one second roller in a conveying direction, wherein at least one cutting device is arranged between the first roller and the second roller, which cutting device cuts the material sheet into at least two partial sheets, wherein the partial sheets are each wound up into a bobbin in the conveying direction behind the second roller, wherein the at least one first roller and the at least one second roller are each driven by a drive in such a way that the tensile stress in the material sheet or in the partial sheets changes periodically over time in the conveying direction of the material sheet.

2. The method according to claim 1, wherein the at least one first roller and the at least one second roller are each driven by their drive in such a way that the tensile stress in the material sheet or in the partial sheets changes essentially sinusoidally around an average value.

3. The method according to claim 1, wherein the maximum tensile stress applied to the material sheet or to the partial sheets varies such that the maximum value of the tensile stress is higher than the minimum value of the tensile stress by at least 0.1%, preferably by at least 1.5% and particularly preferably by at least 5.0%.

4. The method according to claim 1, wherein the at least one first roller cooperates with a further roller in order to be able to build up a tensile stress in the material sheet or in the partial sheets.

5. The method according to claim 1, wherein the at least one second roller cooperates with a further roller in order to be able to build up a tensile stress in the material sheet or in the partial sheets.

6. The method according to claim 1, wherein the at least one first roller is driven at a constant rotational speed and the at least one second roller is driven at a time-varying rotational speed.

7. The method according to claim 6, wherein the time-varying rotational speed is changed in such a way that the maximum value of the rotational speed is higher than the minimum value of the rotational speed by at least 0.1%, preferably by at least 1.5% and particularly preferably by at least 5.0%.

8. The method according to claim 1, wherein the change in the tensile stress in the material sheet or in the part sheets is effected in such a way that the width of the material sheet or of the part sheets changes by a value of +/?0.1 mm to +/?5 mm about the average value of the width.

9. A winding device for winding a material sheet, in particular a plastic film, which comprises: at least one first roller and at least one second roller with which the material sheet can be guided in a conveying direction, wherein the first roller and the second roller are each connected to a drive with which the rollers can be rotated, at least one cutting device arranged between the first roller and the second roller in order to be able to cut the material sheet into at least two partial sheets, at least one winder for winding up the partial sheets, wherein the winder is arranged downstream of the second roller in the conveying direction, wherein the drives of the first roller and the second roller are connected to a control device, wherein the control device is designed to drive one of the rollers at a periodically variable rotational speed.

10. The winding device according to claim 9, wherein the control device is designed to drive one of the rollers in such a way that the rotational speed of the roller varies substantially sinusoidally around an average value.

11. The winding device according to claim 9, wherein the at least one first roller cooperates with a further roller and/or that the at least one second roller cooperates with a further roller, preferably at least one of the rollers being provided with a profiling on the roller surface.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0027] In the drawing:

[0028] FIG. 1 shows a schematic side view of a winding device for winding a film sheet cut into partial sheets according to a first embodiment of the invention,

[0029] FIG. 2 shows an alternative design of the winding device to FIG. 1,

[0030] FIG. 3 schematically shows three partial sheets cut out of the film sheet, illustrating the change in width due to the application of different tensile stresses, and

[0031] FIG. 4 shows the partial sheets wound up into a bobbin after the winding process has been completed.

DETAILED DESCRIPTION OF THE INVENTION

[0032] FIGS. 1 and 2 show two very similar embodiments of a winding device 2, with which a sheet of material 1 in the form of a plastic film is cut into partial sheets 1a, 1b, 1c and the latter are then wound up into finished wound film bobbins 15.

[0033] Essential elements of the winding device 2 are a first roller 3, which is preferably designed as a driven fixed-point roller, and a second roller 4, which is preferably designed as a lower cutting roller. In the conveying direction R of the material sheet 1 between the two rollers 3 and 4 there is a cutting device 5 with which the material sheet 1 is cut into the partial sheets 1a, 1b, 1c.

[0034] Not shown are drives with which on the one hand the first roller 3 and on the other hand the second roller 4 are driven in rotation. Likewise not shown is a control device with which the drives of the rollers are controlled.

[0035] The central aspect of the proposed concept is that the tensile stress in the material sheet 1 or in the partial sheets 1a, 1b, 1c (after the cut) is variable over time. Although the first roller 3 is driven with a constant rotational speed determined for the production process, the second roller 4 is driven with a non-constant rotational speed. Preferably, a sinusoidal curve is superimposed on a basic rotational speed of the second roller 4, so that the rotational speed of the second roller 4 changes accordingly.

[0036] As a result, the material sheet 1 or the partial sheets 1a, 1b, 1c between the two rollers 3 and 4 are subjected to a variable tensile stress, which is illustrated in FIG. 3. At the points marked with arrows in FIG. 3, those sections are marked where the material web was subjected to increased tensile stress. Accordingly, the material sheet 1 or the partial sheets 1a, 1b, 1c cut out from it have constricted as shown in FIG. 3.

[0037] If the partial sheets cut in this way are wound, the result is film bobbins 15 as depicted in FIG. 4. The cutting edges 9 do not all lie on top of each other, but run variably, which facilitates the unwinding of the film from the film bobbin 15.

[0038] FIGS. 1 and 2 also show a number of elements, some of which are advantageous for the present invention, but some of which are also sufficiently known in the prior art.

[0039] Mention should be made of the further roller 6, which interacts with the first roller 3 and which is designed as a driven fixed-point roller.

[0040] FIG. 1 does not show that the second roller 4 interacts with another roller. However, this is illustrated in FIG. 2, where reference is made to the other roller 7, which acts as a pressure roller.

[0041] Downstream of the second roller 4 in conveying direction R is a winder 8 with several winding stations on which the finished film bobbins 15 are wound.

[0042] FIGS. 1 and 2 also show an upper cutting roller 10, a strip discharge roller (conveying roller for strip) 11, a roller for tension measurement 12, a satellite roller 13 and a contact roller 14, which are useful for the proper production process.

[0043] The tension in the material sheet 1 or the partial sheets 1a, 1b, 1c can be measured in the longitudinal direction via the roller for tension measurement 12. This makes it possible, for example, to specify a sinusoidal course for the tension in the material and to regulate it accordingly.

[0044] The material sheet, i.e. the film, is thus stretched in the conveying direction (longitudinal direction) by the proposed change in tensile stress in the material, which changes the width of the film (see FIG. 3).

[0045] This means that the cutting edge does not always meet at the same point when the partial sheet is wound up, as shown in FIG. 4.

[0046] The first and second rollers 3 and 4 and, if applicable, the further rollers 6 and 7 cooperating with these rollers can have a profiled, in particular spiralised and/or roughened surface so that the corresponding tension can be reliably built up in the material web between the rollers.

[0047] Generally, the rollers between which the tensile stress is built up (as a result of targeted acceleration or braking of the rollers) are one or more rollers before the cut and one or more rollers after the cut, wherein the first roller 3 and the second roller 4 can be: the upper cutting roller and the lower cutting roller; the fixed-point roller and the roller for tension measurement or the satellite roller; the fixed-point roller and the contact roller.

[0048] If the adhesion on the surface of the roller is not sufficient to build up the required tension in the material web between the first and the second roller 3, 4, a pressure roller (as shown in FIG. 2) can be provided, which in this embodiment is placed at the lower cutting roller and interacts with it.

[0049] Preferably, the roller or rollers before the cut (in the embodiment the first roller 3 together with the further roller 6) is used as a fixed point, i.e. these rollers move with a constant rotational speed. The roller or rollers after the cut (in the embodiment the second roller 4 together with the further roller 7) are driven with a non-uniform rotational speed, so that the material web between the first and second roller is periodically accelerated or decelerated by changing the rotational speed of these rollers.

[0050] As shown in FIG. 3, this changes the width of the film; the cut edges 9 are not wound in the same place during winding.

[0051] According to a preferred embodiment of the invention, the rotational speed of one roller (e.g. roller 4) is periodically changed in such a way that, starting from a nominal value of 100%, the roller is accelerated for a period of e.g. 1 s, whereby an increased value of the rotational speed of 101.5% is achieved by the acceleration. The roller is then braked for approximately the same period of time (e.g. 1.1 s) until the nominal value of the rotational speed of 100% is reached again. This process is repeated periodically to achieve the described effect of changing the width of the web.

[0052] While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.