Method and apparatus for adjusting the thickness of tubular membranes manufactured by membrane blow molding.

Abstract

A method for adjusting the film thickness of a stretched tubular membrane, wherein the tubular membrane is manufactured by membrane blow molding, flattened and transferred in a flip-pull section, uniaxially stretched in a stretching device, and wound in a winding machine, and the film thickness profile of the tubular membrane manufactured in the membrane blow molding device is adjusted by a film thickness profile adjustment system, the profile adjustment system including segmented adjustment areas and measuring devices, such that a preset nominal film thickness profile has a deviation from a uniform film thickness in the form of a thin position, which is used to compensate for film thickness variations in the film width, the film thickness variations being generated during uniaxial stretching in the stretching device, so that a film with a film thickness profile in the film width is manufactured by stretching, and the film thickness profile has the smallest possible deviation from the nominal film thickness in the film width, and the thin position with a defined geometry is imprinted on the tubular membrane by individual control and / or adjustment of each adjustment link in the segmented adjustment area, taking into account the influence of the running direction of the flip-pull section on the geometry of the thin position.

Description

Technical Field

[0001] This invention relates to a method for adjusting the film thickness of a tubular membrane manufactured by a membrane blow molding process and an apparatus for using the method. The invention relates to a method for adjusting the film thickness of a stretched tubular membrane manufactured by a membrane blow molding process, flattened and transferred in a flip-pull section, stretched uniaxially in the machine direction in a stretching device, and wound in a winding machine. The film thickness profile of the tubular membrane manufactured in the membrane blow molding device is adjusted using an adjustment system consisting of segmented adjustment areas and at least two measuring devices for film thickness, such that a preset nominal film thickness profile has a deviation from a uniform film thickness in the form of one or two opposing thin positions. This deviation is used to compensate for film thickness variations across the film width, which occur during uniaxial stretching along the machine direction, thereby producing a membrane having a film thickness profile across the film width with the smallest possible deviation from the nominal film thickness across the entire film width.

[0002] Furthermore, the present invention relates to an apparatus for performing the method. Background Technology

[0003] Film blow molding is suitable for manufacturing stretchable plastic films. Here, plastic granules are fed to an extruder via a metering device, melted, and then fed to a film blow molding head. The film blow molding head has an annular nozzle from which the extruded plastic clump is discharged and formed into a tubular film, which is then blown in with cooling air. Simultaneously, the tubular film is cooled from the outside by cooling air from a cooling ring. The tubular film passes through a calibration basket. After the plastic solidifies, the tubular film is flattened in a flattening unit and guided by a flip-pull section. The flattened film is then fed to a winding machine and wound into a film roll. The flattened tubular film can be stretched uniaxially in the machine direction in a stretching device arranged between the flip-pull section and the winding machine; alternatively, the flattened tubular film can be stretched in a stretching device within the flip-pull section, between a pair of pull rollers and a flip bar, thereby obtaining a film with a reduced film thickness. Stretching improves film properties such as tensile strength, stiffness, transparency, barrier properties, and / or machine mobility. These films are used, for example, in flexible packaging.

[0004] A membrane thickness profile adjustment system with segmented adjustment zones is used in the manufacturing of tubular membranes. These systems allow for adjustment of the membrane thickness profile to minimize the average membrane thickness deviation across the entire tubular circumference.

[0005] DE 10 2009 033 171 B4 discloses a method for adjusting the film thickness of a tubular membrane manufactured by a film blow molding process and subsequently stretched uniaxially in the machine direction in a stretching device while in a flattened state. Furthermore, DE 10 2009 033 171 B4 discloses an apparatus for performing this method. To achieve a film with the most uniform average film thickness possible, one or two opposing thin positions are imprinted on the tubular membrane. To adjust the film thickness profile, the actual film thickness profile on the circumference of the tubular membrane is detected between a segmented adjustment unit and a flipping traction unit, and the actual film thickness profile across the width of the flattened and stretched film is detected between the stretching device and a winding machine. The actual film thickness profile measured by the measuring device is supplied to the equipment control unit, and the film thickness is adjusted through the segmented adjustment region by means of cascaded adjustment.

[0006] DE 10 2019 215 492 A1 discloses a blown film apparatus having at least two thickness measuring devices for measuring the film thickness profile after the stretching device, wherein at least one thickness measurement is performed at a single layer of the film.

[0007] DE 10 2016 012 424 A1 discloses a method for operating a blown film equipment, in which a tube film having two thin positions is output from a film blown head, the thin positions forming edge regions in the flattened state of the tube film and being truncated in a separation device.

[0008] In longitudinal stretching within a stretching device, the film is stretched in the machine direction according to the degree of stretching, thereby reducing the film thickness. When the tubular film is flattened and in the case of a film web, the film simultaneously shrinks in the transverse direction, thereby reducing the width of the film. This shrinkage causes the stretched film to gradually thicken from the center towards the edge, even though the film has been pre-adjusted to a thickness as constant as possible in the film blow molding process. This increase in thickness in the edge region is particularly noticeable. This causes an edge structure on the film roll immediately following film winding. The film web stretches increasingly at the edges with increasing roll diameter, which is highly detrimental to further processing, such as printing or lamination.

[0009] Shrinkage and thus edge formation on the film roll can be reduced through measures such as minimizing stretch gaps, appropriate roller coatings, mechanical or electrostatic fixing of film edges, optimized temperature control, or suitable selection of plastic materials. Additionally, thin sections are imprinted onto the tubular film during manufacturing to resist edge formation. However, this is insufficient for many subsequent processing steps. Only by trimming the film edges can the remaining film web have a sufficiently small deviation from the film thickness profile and nominal thickness, which is necessary for subsequent winding and further processing of the film web. However, trimming results in a loss of film width. Summary of the Invention

[0010] Therefore, the object of the present invention is to provide a solution in which a tubular film is uniaxially stretched along the machine direction in a stretching device, having a flattening section and a reversing section in the flipping and stretching section, such that the final film has a film thickness profile with the smallest possible thickness increase from the film center to the film edge, and improves the flatness of the film. At the same time, the loss of film width caused by the separation of the edge strips should be kept as small as possible.

[0011] In the method for adjusting the thickness of the film of the type described at the beginning, this task is accomplished according to the invention by means of the method and by means of the apparatus according to the invention.

[0012] In the method for adjusting film thickness according to the invention, this task is achieved by adjusting the film thickness profile of the tubular film manufactured in the film blow molding equipment such that the film produced by the stretching process has a film thickness profile having the smallest possible deviation from the nominal film thickness over the entire film width. Here, the actual film thickness profile measured on the tubular film before stretching and on at least one monolayer film after stretching serves as the basis for adjusting the film thickness. To further optimize the adjustment result, the adjustment links in the segmented adjustment region imprint thin positions with defined geometries on the tubular film to compensate for the thin position geometry affected by the running direction of the reverse flipping traction section.

[0013] In manufacturing tubular membranes according to existing technology, a membrane thickness profile adjustment system with segmented adjustment regions is typically used. The aim is to obtain a tubular membrane with a membrane thickness profile whose thickness deviation around the circumference of the membrane is as small as possible.

[0014] To this end, a measuring device is arranged after the membrane blow molding head and before the flattening section. This measuring device detects the actual membrane thickness profile on the circumference of the tubular membrane. The actual profile is compared with the rated profile, and if there is a deviation, a specific adjustment intervention is performed during the membrane blow molding process.

[0015] If a stretching device is integrated into the membrane blow molding equipment, a second measurement of the actual membrane thickness profile is performed in addition to the measurements described above. This second measurement measures the flattened tubular membrane after stretching across the membrane width. Both profiles are supplied to cascaded adjustments for targeted adjustment interventions during the membrane blow molding process.

[0016] After cooling, the film is flattened in the flattening section and guided by the reverse flipping and pulling section. The reverse flipping and pulling section has the task of improving the roll quality of the wound film by transferring the thickness profile fixed relative to the position of the film blow molding head across the width of the flattened film. By transferring the thick and thin positions across the roll width, a defect-free roll, also known as a piston ring, is produced.

[0017] The flattened membrane is supplied to a stretching device, also known as MDO, and stretched uniaxially in the machine direction. The stretching device is arranged after the reverse flipping stretching section.

[0018] Alternatively, the stretching device can be placed in the pulling section after the flattening section. Following stretching is the reversal of the membrane.

[0019] Here, stretching equipment should be understood as any device that achieves a change in the length of the membrane web. This is understood not only as stretching that results in irreversible stretching of the membrane, but also as stretching that results in reversible stretching of the membrane.

[0020] The stretched film is wound into a roll in a winding machine.

[0021] If stretching is performed after the flipping and pulling section, the flattened membrane is separated in the separation device on one or both sides of the edge between the flipping and pulling sections and before the stretching device.

[0022] The flattened membrane strip, separated on both sides, is then separated and supplied individually to the two stretching devices. Alternatively, the membrane strip, cut on both sides, can also be supplied to the stretching devices as a double-layer membrane, i.e., stacked on top of each other. If the flattened membrane strip is separated on only one side, it is unfolded and supplied to the stretching devices as a single-layer membrane.

[0023] However, the tubular membrane can also be supplied directly to the stretching equipment as a flattened tubular membrane and then split on one or both sides of the edge.

[0024] If the stretching equipment is located in the traction section, the separation is carried out on one or both sides downstream of the flipping traction section. Alternatively, the membrane is separated before the traction rollers in the flattening section.

[0025] If the edge area is not thin enough, edge strips of a defined width are cut on each side of the double-layer or single-layer film web, so that only the middle area of ​​the film web with a uniform thickness is wound into a roll in the winding machine.

[0026] Membrane edge trimming is performed after membrane web stretching and before winding. The device for edge trimming can be a separate unit between the stretching and winding machines, or it can be integrated into either the stretching or winding machine.

[0027] The single-layer film web can finally be supplied to the winding machine. The single-layer film web is either supplied to the winding machine individually or supplied as a double-layer film web with the single layers overlapping each other and then wound into a roll.

[0028] The influence of film thickness profile is achieved by segmented adjustment regions, such as by air temperature or air volume adjustment, or alternatively by a heat source, such as an infrared source.

[0029] These segmented adjustment zones can be integrated into the film blow molding head, in a fixed or rotating cooling ring, in a thickness adjustment unit between the film blow molding head and the flattening section, or in a subsequently arranged thickness adjustment unit that moves synchronously with the reverse flipping and pulling section. Multiple segmented adjustment zones can also be combined.

[0030] To obtain a stretched tubular membrane with a uniform membrane thickness, a membrane thickness profile adjustment system with segmented adjustment regions is used.

[0031] The measuring device for detecting the actual film thickness profile during film blow molding is preferably positioned between the film blow molding head and the drawing section before stretching. Alternatively, the measuring device can also be positioned between the drawing section and the stretching equipment. In the first case, the film thickness is measured on the circumference of the tubular film and thus on a single layer of the film. In the second case, the film thickness is measured across the width of the flattened tubular film of the double-layer film web. The measured actual film thickness profile is compared with the nominal profile so that intervention can be made in the segmented adjustment area to determine the film blow molding process in case of deviation.

[0032] To counteract the effects of the stretching process, which is performed as a thickening in the edge region of the membrane web, a second measurement of the actual membrane thickness profile is taken after stretching and before winding the membrane. It is known in the prior art that the membrane thickness on a bilayer membrane web is measured in width.

[0033] According to the present invention, the actual profile of the second film thickness is measured on both sides of the edge over the width of the two separated and isolated single-layer film webs.

[0034] In other embodiments of the invention, the actual membrane thickness profile is measured once across the width of the bilayer membrane web and once across the width of one of the two single-layer membrane webs. In this case, the membrane thickness profile of the second single-layer membrane web is calculated from the difference between the profiles of the bilayer membrane web and the measured profiles of the single-layer membrane web.

[0035] In another embodiment of the invention, the actual profile of the membrane thickness is measured on the width of the single-layer membrane strip that is separated and unfolded on one side of the edge of the flattened tubular membrane.

[0036] Membranes can be measured more accurately and completely by taking measurements on at least one single-layer membrane web. This greater accuracy enables more precise correction of membrane thickness, particularly in segmented adjustment areas at the edges.

[0037] If the actual membrane thickness profile, as known in the prior art, is measured on a double-layer membrane web after stretching, the sum of the thicknesses of the two overlapping membrane webs is obtained. What may occur here is that one membrane half is thinner at the edge than the other. This can be avoided by measuring the actual membrane thickness profile across the width of a single-layer membrane web.

[0038] In another embodiment of the invention, the actual film thickness profile is not measured over the entire width of the film web after stretching and before winding, but only over the width of the edge region, where the strongest deviation in film thickness occurs due to stretching and the imprinting of thin positions.

[0039] In another embodiment of the invention, the actual contour measurement of the film thickness is performed using a single sensor or multiple separate sensors on the separated edge strips and the remaining main film. This provides the advantage of allowing for accurate and complete measurements of all partial areas.

[0040] In other embodiments of the invention, the actual profile of the second membrane thickness can be measured only on the remaining main membrane web after edge trimming. The disadvantage here is that it less significantly affects the membrane profile at the edges and therefore results in a greater loss of membrane width.

[0041] The actual profiles of the thickness of the first and second films can also be measured multiple times in succession.

[0042] In a preferred embodiment of the invention, edge trimming is performed on the film width after the second measurement and before winding the film web.

[0043] Then, from the actual contour of the second measured film thickness, the width of the thick or thin position still retained in the edge region can be derived, and the width of the edge strip to be separated can be determined. The position of the cutter in the device used to separate the edge strip can then be set manually or automatically.

[0044] The width of the edge strip is readjusted after each roll change in the winding machine.

[0045] In another embodiment of the invention, edge trimming is performed before stretching. This allows for the removal of trapped air between the membrane layers. Furthermore, excessively thick edges or edge wrinkles can thus be removed.

[0046] Because the flattened tubular film web shrinks during stretching and thickens at the film edge regions, the preset film thickness rating of the circumferential profile is not constant during film blow molding. Instead, it is set such that after uniaxial stretching along the machine direction, the resulting film has a thickness profile with the smallest possible deviation across the entire film width due to thickness variations during stretching. For example, a tubular film with two opposing thin positions is manufactured during film blow molding. The tubular film is then flattened such that the thin positions form the film edge regions, and the stretched film thus has a thickness profile with the smallest possible deviation from the film's rated thickness. The same applies to tubular films that are cut on both sides. In the case of a tubular film cut on one side, a tubular film with only one thin position is manufactured during film blow molding. At the center of this position, the tubular film is split so that the thin position is divided into film edge regions on the left and right sides after splitting, thereby forming a film with a thickness profile with only a small deviation after stretching.

[0047] In order to apply the thin position to the tubular membrane, the adjustment links of the segmented adjustment area have so far been manipulated symmetrically around the thin position to be applied, for example in the form of a Gaussian distribution, thereby producing different imprinted thin position geometries on the side of the thin position through the influence of the reverse flipping traction section.

[0048] To further optimize the adjustment results, the thin positions with a defined geometry are imprinted on the tubular membrane by individual manipulation and / or adjustment of each adjustment link in the segmented adjustment area, in order to compensate for the influence of the running direction of the thin position geometry by the reverse flipping traction section.

[0049] In the reverse direction of the running section, thin sections with different shaped sides appear. When moving in the reverse direction, the movement enters the cold film, so the film's response to adjustment intervention is less noticeable. However, when moving in the hot film in the reverse direction, the film's response to adjustment intervention is more intense. Therefore, thin sections with different shaped sides are formed.

[0050] By measuring the thickness of the edge region on a single-layer membrane web, the actual profile of the membrane thickness on each side of the membrane web can be accurately detected during measurement. This allows for individual manipulation of the adjustment links of the segmented adjustment regions, thereby imprinting the desired asymmetrical thin position profile onto the membrane, resulting in a membrane with thin positions having approximately symmetrical sides.

[0051] In other embodiments of the invention, the imprinting of the thin position of the adjustment section is superimposed and implemented by means of different functions for the right and left sides of the thin position. These functions take into account the different characteristics of the membrane caused by the running direction of the reverse section when the thin position is applied. The left and right sides of the thin position are respectively understood as the sides of the thin position viewed from the edge of the flattened membrane.

[0052] After cooling, the film is flattened and fed into a reverse-rotating traction section, where it is transferred by a rotating rod and steering rollers such that the film always encounters a fixed horizontal steering roller after the traction section, where it is turned vertically downwards towards the stretching equipment and / or winding machine. Through this reverse movement, the current film thickness profile is continuously displaced, meaning that the predetermined thin position in the film produced in the stationary extrusion zone of the equipment must follow the reverse movement of the reverse traction section, thereby supplying a film with the desired nominal film thickness profile, i.e., with thinner film edges, to the stretching equipment. This is achieved by superimposing an offset onto the segmented adjustment area of ​​the film profile adjustment section, which takes into account the angular deviation caused by the rotating traction section and follows the rotation of the rotating rod. Therefore, one or more circumferential points of the flattened tubular film in the traction section are assigned to one or more segmented adjustment areas. An adjustment algorithm is used to make the thin position in the nominal profile parallel to the reverse movement of the reverse traction section.

[0053] The preset film thickness nominal profile used in the film blow molding process is calculated by an algorithm and continuously corrected by the actual film thickness profile measured on the width of the film web after stretching. As a result, the deviations generated by the stretching process are also corrected in the thickness profile of the produced film, thereby improving the roll quality and producing film rolls with uniform roll diameters.

[0054] This also significantly reduces the width of the membrane strips that are cut off on both sides during membrane trimming.

[0055] In another embodiment of the invention, the roll profile is measured.

[0056] Therefore, the actual film thickness profile over the roll width can be detected summatically in the second measuring device. This results in the possibility that the nominal film thickness profile is superimposed with the actual roll profile to eliminate even minimal thickness deviations that always appear in the same area of ​​the manufactured film, since these thickness deviations can only be determined after a longer time interval when they are manifested in general by changes in the roll diameter.

[0057] In another embodiment of the invention, a camera is used to detect the roll profile on the formed roll. A line camera or a surface camera is used. The roll profile can then be used to detect whether edge trimming was successful across its width, or whether the roll profile needs adjustment.

[0058] The adjustment of each segmented adjustment zone is calculated by an algorithm based on the superposition of the film thickness profiles described below. These segmented adjustment zones can be integrated into the film blown head, in a fixed or rotating cooling ring, in a thickness adjustment unit between the film blown head and the flattening section, or in a subsequently arranged thickness adjustment unit that moves synchronously with the reverse flipping and pulling section. Multiple segmented adjustment zones can also be combined.

[0059] The thickness profile is as follows:

[0060] - Basic profile, which is the actual profile of the film thickness detected between the film blow molding head and the stretching device on the circumference of the tubular film or on the width of the flattened film between the stretching section and the stretching device.

[0061] - Stretch profile, which is detected across the entire film width after stretching equipment, takes into account the angular deviation caused by the reverse flipping traction section and the thickness of the film edge area during stretching.

[0062] - Roll profile, which is the sum of the measured stretched profile and the corresponding evaluation, or detected by a camera on the formed roll.

[0063] Additionally, the geometry of the thin position caused by the running direction of the reverse flipping pull section is considered, as well as the superposition of offsets, which take into account the angular deviation caused by the rotating pull section, and the offsets track the rotation of the flipping rod and are continuously readjusted.

[0064] This indicates a cascaded control unit, because the following control loops are superimposed:

[0065] - Adjust the membrane thickness around the circumference of the membrane tube during the membrane blow molding process;

[0066] - Adjust the film thickness across the entire width of the stretched film;

[0067] - Adjust the reel diameter based on the reel width.

[0068] In this process, at least one of the basic contour and the stretched contour is superimposed.

[0069] The rated profile of the film thickness can also be manually input into the adjustment system, where the rotation of the flip lever must be continuously tracked.

[0070] The method used to adjust membrane thickness can also be used in equipment without a flipping and pulling section. This eliminates the need for tracking.

[0071] Further details, features, and advantages of the subject matter of the invention will become apparent from the following description of the accompanying drawings, in which preferred embodiments of the invention are illustrated, for example. Attached Figure Description

[0072] As shown in the attached figure:

[0073] Figure 1 A film blow molding apparatus having a downstream stretching device in which the method for adjusting film thickness according to the invention is applied.

[0074] Figure 2 : The nominal profile of membrane thickness of a tubular membrane having two thin sites with an asymmetric thin site geometry. Detailed Implementation

[0075] Figure 1 A film blow molding apparatus 1 is shown, comprising a downstream stretching device 2 and two winding machines 3. Plastic granules to be processed are supplied to an extruder 5 via a metering device 4, where they are melted, homogenized, and supplied to a film blow molding head 6. In the manufacture of multilayer films, multiple extruders are used depending on the number of layers. The film blow molding head 6 has an annular nozzle from which the extruded plastic clumps are discharged. Cooling air is supplied via the film blow molding head 6 for blow molding a tubular film 7. The tubular film 7 is cooled from the outside by a cooling ring 15 and guided by a calibration basket 8. After the plastic solidifies, the tubular film 7 is flattened in a flattening section 9 and continuously drawn out and transferred by a reverse flipping stretching section 10. The film is then uniaxially stretched in the machine direction in the stretching device 2.

[0076] The tubular membrane 7 is cut on both sides in the pre-stretching section 11 before the stretching device 2 and supplied to the stretching device 2 as a double-layer membrane web.

[0077] Alternatively, an annealing device or a temperature control device may be combined with the pre-stretching section 11, which is not shown here. After stretching, the two overlapping single film webs are separated and supplied separately to the winding station 3. The film edges are trimmed in the winding machine 3, and then the trimmed film is wound into a film roll.

[0078] The membrane blow molding equipment 1 has a membrane thickness profile adjustment system. The membrane thickness profile adjustment system includes a segmented adjustment area and at least two measurement positions 12 and 13 for detecting the actual profile of the membrane thickness.

[0079] To adjust the film thickness profile, the actual film thickness profile needs to be detected at at least two locations. The actual film thickness profile around the circumference of the tubular membrane 7 is detected between the segmented adjustment unit in the film blow molding head 6 or cooling ring 15 and the flattening portion 9 or flipping tension portion 10 on the measuring device 12. The measuring device 12 for measuring the actual film thickness profile of the blown tubular membrane 7 is preferably arranged at a constant height, rotating around the tubular membrane 7 above the film blow molding head 6.

[0080] The actual profile of the film thickness of each of the two stretched monolayer film webs across its width is detected after the webs are separated on the measuring device 13 between the stretching device 2 and the winding machine 3.

[0081] The entire membrane blow molding process is regulated by the equipment control unit, especially the driver, cooling air, segmented adjustment areas in the cooling ring 15, the membrane blow molding head 6 or the additional thickness adjustment unit, and the stretching speed of the tubular membrane 7.

[0082] The actual membrane thickness profile measured by measuring devices 12 and 13 is supplied to the equipment control unit and a signal is transmitted to the segmented adjustment area via a rated / actual comparison.

[0083] Alternatively, the stretching device 2 can be integrated into the flipping and pulling section after the flattening section 9 and before the flipping rod 16, which is not shown in the accompanying drawings.

[0084] The double-layer membrane web is cut before or after stretching. After the flip-pull section 10, the tubular membrane 7 is divided into two single-layer membrane webs, and each single-layer membrane web is supplied to a winding station 3. The first measuring position 12 is also located before the flattening section 9 and measures the actual membrane thickness profile on the circumference of the tubular membrane 7. The second measuring position 13 is located after the flattened and stretched tubular membrane 7 is divided into single layers, after the flip-pull section 10 and before the winding machine 3, and measures the actual membrane thickness profile across the width of each single-layer membrane web. Alternatively, the measurement of the actual membrane thickness profile can also be performed after stretching at one of the measuring positions 13 on the single-layer membrane web and at the measuring position 14 on the double-layer membrane web.

[0085] Before the film web is wound in the winding machine 3, the edges are trimmed.

[0086] Figure 2 The diagram shows the actual profile of a defective film thickness with two thin positions 18, which should be corrected according to the method according to the invention. The adjustment links of the adjustment region are asymmetrically operated, imprinting opposing thin positions 18 onto the tubular membrane 7. Here, consider the running direction of the reverse flipping pull portion 10, wherein a flat side 19 is imprinted in the running direction of the reverse portion of the flipping pull portion of the thin position 18 due to movement into the cold film, and wherein a steep side 20 is imprinted in the opposite running direction to the reverse portion of the flipping pull portion of the thin position 18 due to movement into the hot film.

[0087] The membrane is separated at two positions 17 and then two flat membrane webs are supplied to stretching device 2 or separately to individual stretching devices. The membrane is then measured, the edges are trimmed, and it is wound in membrane winding machine 3.

[0088] List of reference numerals

[0089] 1. Film blow molding equipment

[0090] 2. Stretching equipment

[0091] 3 winding machine

[0092] 4 Metering devices

[0093] 5 Extruder

[0094] 6-film blow molding head

[0095] 7-tube membrane

[0096] 8 calibration baskets

[0097] 9-section flat section

[0098] 10. Flipping and pulling section

[0099] 11 Pre-tensioning section

[0100] 12 Thickness measuring devices

[0101] 13 Thickness measuring device

[0102] 14 Thickness measuring device

[0103] 15 Cooling rings

[0104] 16-Flip Bar

[0105] 17-interface

[0106] 18 thin positions

[0107] 19. Flat side of thin position

[0108] 20. Steep side of thin position.

Claims

1. Method for adjusting the film thickness of a stretched tubular film (7) manufactured in a film blowing process, flattened and transferred in a turning pull-off (10), uniaxially stretched in the machine direction in a stretching device (2) and wound up in a winder (3), the film thickness profile of the tubular film (7) manufactured in a film blowing device (1) is adjusted with a film thickness profile adjustment system, which comprises segmented adjustment regions and at least two measuring devices (12, 13) for the film thickness: such that the preset film thickness target profile has a deviation from the uniform film thickness in the form of one thin location or two opposing thin locations (18), which is used to compensate for film thickness variations over the film width, which arise upon uniaxial stretching in the machine direction, so that a film is manufactured by stretching with a film thickness profile over the film width, which has as little deviation as possible from the film target thickness over the film width, characterized in that, a thin location (18) with a defined geometry is imprinted on the tubular film (7) by individual actuation and / or adjustment of the individual adjustment segments of the segmented adjustment regions, wherein the influence of the running direction of the turning pull-off (10) on the thin location geometry is taken into account, wherein different functions are stored for the left and right side (19, 20) of the thin location (18) in the adjustment algorithm of the adjustment. wherein The left and right side (19, 20) of the thin location (18) is imprinted differently in terms of geometry depending on the running direction of the turning pull-off (10). At least a first film thickness actual profile of the tubular film (7) is measured before stretching, and at least a second film thickness actual profile of the flattened and stretched tubular film (7) is measured after the stretching and before winding up the film web. At least a first film thickness actual profile of the tubular film (7) is measured before stretching over the circumference of the blown tubular film (7) between the film blowing head (6) and the flattening (9), and at least a second film thickness actual profile of the flattened and stretched tubular film (7) is measured after the stretching and before winding up the film web. The second film thickness actual profile is measured over the film width on at least one single-layer film web after the stretching and before winding up the film web. The second film thickness actual profile is measured over the film width on two single-layer film webs of a separate flattened tubular film web after the stretching and before winding up the film web.

2. The method of claim 1, wherein, The second film thickness actual profile is measured on a single-layer film web over the width of an edge strip after the stretching and before the winding up.

3. The method of claim 1, wherein, The extruded tubular film (7) is adjusted to a preset film thickness target profile over the circumference by means of a film thickness profile adjustment system.

4. The method of claim 1, wherein, 9. The method according to any of claims 1 to 4, characterized in that, the adjustment algorithm for actuating the individual segmented adjustment regions comprises a superposition of: - a basic profile resulting from the film thickness profile adjustment of the film blowing device (1); - a profile resulting from the film thickness profile adjustment of the stretching device (2); - a profile resulting from the film thickness profile adjustment of the winder (3).

5. The method according to claim 3 or 4, characterized in that, The adjustment algorithm for actuating the individual segmented adjustment regions comprises a superposition of: - a basic profile resulting from the film blowing device (1); - a profile resulting from the film thickness profile adjustment of the stretching device (2); - a profile resulting from the film thickness profile adjustment of the winder (3).

6. The method of claim 5, wherein, ​ 7. The method according to claim 3 or 4, characterized in that, ​ 8. The method according to any one of claims 1 to 4, characterized in that, ​ ​ ​ ​ - a stretching profile resulting from the influence of the transfer and stretching process of the tube film (7) by the reversing pull-off (10); - and in consideration of the geometry of the thin location (18) caused by the direction of travel of the reversing pull-off (10), an offset is superimposed which takes into account the angular deviation caused by the rotating pull-off and which tracks the rotation of the reversing lever and is continuously readjusted.

10. The method of claim 9, wherein, The control algorithm for controlling the individual segment control regions also comprises the superimposition of a winding profile resulting from the evaluation of the film reel.

11. The method of claim 10, wherein, At least a first film thickness actual profile of the tube film (7) is measured before the stretching, and at least a second film thickness actual profile of the flattened and stretched tube film (7) is measured after the stretching and before the winding of the film web, wherein the winding profile is detected from the measurement of the second film thickness actual profile summatively over the film reel width.

12. The method of claim 10, wherein, The winding profile on the formed film reel is detected with a camera.

13. The method of claim 12, wherein, The camera is a line camera or a face camera.

14. The method of claim 7, wherein, The edge strip width to be cut at the subsequent edge strip trimming is derived from the measurement of the second film thickness actual profile on the single-layer film web and is set manually or automatically at the edge strip trimming.

15. An apparatus for performing the method according to any one of claims 1 to 14, characterized in that The device comprises a film blowing plant (1) with a reversing pull-off (10) and at least one stretching device (2) and at least one winder (3) and at least one film thickness profile control system, wherein, by individual control and / or regulation of the individual control steps of the segment control regions, a thin location (18) with a defined geometry is imprinted on the tube film (7), wherein the influence of the direction of travel of the reversing pull-off (10) on the thin location geometry is taken into account; wherein different functions are stored for the left and right side (19, 20) of the thin location (18) in the control algorithm of the control.

16. The apparatus of claim 15, wherein, The film thickness profile control system comprises segment control regions, at least two measuring devices (12, 13) for the film thickness, at least one measuring device for measuring the film thickness actual profile of the tube film (7) after the film blowing head (6) and before the stretching device (2), and at least one measuring device for measuring the film thickness actual profile of the stretched film after the stretching device (2).

17. The apparatus of claim 16, wherein, The film thickness profile control system comprises segment control regions, at least two measuring devices (12, 13) for the film thickness, at least one measuring device for measuring the film thickness actual profile of the tube film (7) after the film blowing head (6) and before the stretching device (2) on the circumference of the blown tube film (7), and at least one measuring device for measuring the film thickness actual profile of the stretched film after the stretching device (2).

18. The apparatus of claim 16 or 17, wherein, The measuring device (13) for measuring the film thickness actual profile of the stretched tube film (7) after the stretching device (2) and before the winder (3) is arranged at least on one of the separate and individual single-layer film webs.

19. The apparatus of any one of claims 15-17, wherein, Behind the stretching device (2) and behind the measuring device (13) a device for performing edge trimming is arranged, wherein the positioning of the cutting device of the device for performing edge trimming can be set manually or automatically.

20. The apparatus of claim 16 or 17, wherein, The segmented conditioning zone is integrated in the film blowing head (6), in a fixed or rotating cooling ring (15), in a thickness conditioning device between the film blowing head (6) and the front of the flattening (9), in a subsequently arranged thickness conditioning unit moving in synchronism with the turn-over pulling (10), or in a combination thereof.

Images