Vertical film fixing

Abstract

The invention relates to a blown film plant (BA) for continuously producing an extruded and simultaneously biaxially stretched, single- or multi-layered film (PF) made of plastic in the form of a tubular film (PFS), wherein the blown film plant (BA) has a vertical flat fixing unit (VFFU) having a heating means (VFFUHU), to a process for continuously producing the tubular film (PFS), and to corresponding uses. A vertical flat fixing unit (VFFU) for an extruded and simultaneously biaxially stretched, single- or multi-layered film (PF) made of plastic in the form of a laid-flat tubular film (PFS), wherein the machine direction (MD) of the vertical flat fixing unit (VFFU) deviates from the vertical (V) by at most 15°, preferably at most 10°, more preferably at most 5°, and is especially parallel to the vertical (V); wherein the vertical flat fixing unit (VFFU) has a holder means (HE); wherein the holder means (HE) is suitable or configured for holding the laid-flat tubular film (PFS), preferably at its lateral edges; wherein the holder means (HE) is suitable or configured for guiding or moving or transporting the laid-flat tubular film (PFS) in the machine direction (MD) of the vertical flat fixing unit (VFFU); wherein the holder means (HE) is not suitable or configured for stretching the laid-flat tubular film (PFS) in the machine direction (MD) or in the transverse direction (TD) of the vertical flat fixing unit (VFFU) when said laid-flat tubular film (PFS) is guided in the vertical flat fixing unit (VFFU); and wherein the holder means (HE) is preferably configured such that it allows relaxing of the laid-flat tubular film (PFS) of at most 15%, preferably at most 10%, especially at most 5%, in the machine direction (MD), in the transverse direction (TD) or in each of the machine direction (MD) and the transverse direction (TD) of the vertical flat fixing unit (VFFU) when the laid-flat tubular film (PFS) is guided or moved or transported; wherein the vertical flat fixing unit (VFFU) has a heating means (VFFUHU) for heating the laid-flat tubular film (PFS), wherein the heating means (VFFUHU) of the vertical flat fixing unit (VFFU) can be used to supply the laid-flat tubular film (PFS) with heated air, infrared radiation, ultrasonic radiation, steam or any combination thereof, preferably heated air, infrared radiation or steam, as heating medium.

Description

[0001] Description

[0002] Vertical film fixation

[0003] Definitions

[0004] Within the scope of the present invention, the term "extrusion" also includes "co-extrusion" when referring to a film with multiple layers, wherein "co-extrusion" means the simultaneous extrusion of at least two layers to form a film without subsequent extrusion coating or lamination of separately extruded layers or layer packages. Similarly, the term "extruded" also includes "co-extruded" (in the case of multiple layers).

[0005] According to the invention, the term "single-layer film" or "single-layer foil" means a polymer film that consists of a single layer.

[0006] According to the invention, the term "multilayer film" or "multilayer foil" means a polymer film consisting of two or more layers.

[0007] According to the invention, the term "vertical" means a straight line that is arranged or aligned parallel to the plumb line at the location.

[0008] Within the scope of the present invention, the terms “in the region of the lower end” of a unit and “in the region of the upper end” of the unit each mean an end region or end section of that unit, wherein the lower end of the unit is located closer to the center of the earth than the upper end of the unit.

[0009] According to the invention, the term "upwards" means a direction along the vertical away from the Earth's center, and the term "downwards" means a direction along the vertical towards the Earth's center. If, within the scope of the present invention, the term "upwards" refers to the machine direction of the vertical flat fixing unit, then the term "upwards" means a direction along or parallel to the machine direction, specifically away from or moving away from the Earth's center. If, within the scope of the present invention, the term "downwards" refers to the machine direction of the vertical flat fixing unit, then the term "downwards" means a direction along or parallel to the machine direction, specifically towards or approaching the Earth's center.

[0010] Within the scope of the present invention, the term "downstream" means that an element or component X of the blown film system according to the invention is arranged downstream of another element or component A of the blown film system in the manufacturing process, i.e., that the film first passes through element A and then element X during the manufacturing process (in the manufacturing process: X). Consequently, element X is "downstream" of element A within the meaning of the present invention, while element A is "upstream" of element X within the meaning of the present invention. "Downstream" can, but does not necessarily, mean "immediately downstream" or "directly downstream," but does not preclude the possibility that further elements are interposed between elements A and X, for example: A - B - C - ... -> X. In this case as well, element X is downstream of element A within the meaning of the present invention, namely indirectly downstream. "Immediately downstream" or "directly downstream" means that no further element is interposed between the elements in question, for example: A - X or C D) The same applies to the terms “upstream” and “immediately upstream”.

[0011] According to the invention, the term "mean residence time of the film tube in the vertical flat fixing unit" means the arithmetic mean of the time between the entry of a specific section of the film tube into the vertical flat fixing unit and the exit of the same section of the film tube from the vertical flat fixing unit. The same applies to parts or sections of the vertical flat fixing unit. According to the invention, the "shrinkage" (used synonymously with "residual shrinkage" or "heat shrinkage") is measured in water at 90 °C, preferably within 1 second after immersion, but at least within 10 seconds after immersion. According to the invention, to determine the shrinkage, the sample is immersed in water at 90 °C for a predetermined period, in particular the aforementioned period, and immediately cooled to room temperature with water after removal.The length of a pre-marked section after this treatment is measured and divided by the measured length of the same section of the sample before treatment. The resulting length ratio ("shrunk" to "unshrunk"), expressed as a percentage, defines the shrinkage. Depending on the direction of the length measurement, the shrinkage is calculated in the machine direction (MD, longitudinal direction) and in the transverse direction (TD, transverse direction). The total shrinkage is calculated by adding the shrinkage in the machine direction and in the transverse direction. Multiple measurements, such as three or five measurements, and the calculation of the corresponding arithmetic means advantageously increase the accuracy of the determination. The shrinkage and total shrinkage are determined according to ASTM D2732-14, 2020 edition, April 14, 2020.

[0012] According to the definition, "roll tendency" of a film is understood to be the property that the film curls or rolls up to a certain extent at a cut edge in the machine direction and / or in the transverse direction of the film. To determine the roll tendency in the machine direction of the film, a test piece of the film measuring 150 mm x 50 mm is cut, with the long side aligned parallel to the machine direction of the film. To determine the roll tendency in the transverse direction of the film, a test piece of the film measuring 150 mm x 50 mm is cut, with the long side aligned parallel to the transverse direction of the film. The roll tendency of the test pieces on the short side is measured with regard to the contour or...The roll angle is determined by measuring the cross-sectional view perpendicular to the cut edge under specified conditions (1013.25 hPa, 293.15 K (20 °C), 60% relative humidity, measurement 24 hours after cutting) according to the scheme shown in Fig. 1 (this applies to determining the roll tendency in both the machine direction and the transverse direction). In Fig. 1: 1 = complete roll-up; 2 = strong roll-up; 3 = medium roll-up; 4 = slight roll-up; 5 = no roll-up. Complete roll-up (= 1) means that the film rolls up > 360° (roll angle) to multiple rolls in the cross-sectional view. Strong roll-up (= 2) means that the film rolls up at an angle of > 270° to 360° (roll angle) in the cross-sectional view. A medium roll inclination (= 3) means that the film rolls up at an angle of > 90° to 270° (roll angle) in the cross-sectional view.A low roll tendency (= 4) means that the film rolls up at an angle of > 0° to 90° (roll angle) in the cross-sectional view. No roll tendency (= 5) means that the film rolls up at an angle of 0° (roll angle) in the cross-sectional view, i.e., no rolling.

[0013] The roll angle (a) is defined in the cross-sectional view of the film at the cut edge of the short side of the test piece as shown in Fig. 2.

[0014] Preferably, the roll angle is determined as above, at least by three measurements, and the arithmetic mean is calculated from the individual measurements, and this mean is then used as the roll angle. This applies to the roll angle in both the machine direction of the film and the transverse direction of the film.

[0015] According to the invention, the “temperature of the film” (e.g. during stretching, heat fixing, relaxing or treatment in the vertical flat fixing unit) is the temperature of the film surface, preferably measured without contact using an IR temperature sensor.

[0016] Within the scope of the present invention, the term "ambient pressure" means the atmospheric pressure outside the film tube (PFS), but in its immediate vicinity (maximum distance to the film tube: 10 m). Within the scope of the present invention, the term "doubled" or "doubled" with reference to a film tube means that the film tube is not inflated, but laid flat (= simply flattened), i.e., double-layered with sealed edges or side edges. This condition excludes both a single-layer flat film, such as a cut-open, unfolded film tube, and a doubly "doubled" film tube, i.e., a flattened film tube with a total of four layers on top of each other.Accordingly, the term "flattened" in relation to the foil tube excludes the possibility that, at least in the section where the foil tube is flattened, there is a gas bubble in the foil tube that would lead to a convex bulge or sausage-shaped formation of this section (with two constricted ends).

[0017] Within the scope of the present invention, the calibration device can be any suitable calibration device known to the person skilled in the art, for example, those commercially distributed by the applicant.

[0018] Within the scope of the present invention, "biaxial stretching" of a film means that the film is stretched both in the machine direction and in the transverse direction. The stretching in both directions can occur simultaneously or sequentially. Accordingly, a "biaxially stretched film" has been produced by biaxial stretching.

[0019] Within the scope of the present invention, "simultaneous biaxial stretching" of a film means that the film is stretched simultaneously in both the machine direction and the transverse direction. Accordingly, a "simultaneously biaxially stretched film" has been produced by simultaneous biaxial stretching.

[0020] Within the scope of the present invention, the term "plastic" means a polymer, copolymer, or a mixture of several polymers and / or copolymers suitable for producing a film or a component thereof (e.g., a film layer). Problem statement of the invention

[0021] The present invention addresses the problem that conventional blown film lines, particularly those employing double-bubble or triple-bubble technology, are not suitable for producing single- or multi-layer films with very low shrinkage of < 3%, preferably < 2%, more preferably < 1%, and particularly 0%, in both the machine direction (MD) and the transverse direction (TD). A film with very low shrinkage is typically characterized by high crystallinity. Experts have found that, particularly with double-bubble or triple-bubble technology, the shrinkage of the produced film in the third bubble or in an attached fixing unit, such as a tenter frame unit, can only be reduced slowly and by applying high temperatures.In most cases, given the existing conditions (properties of the film being produced and the equipment available), the residual shrinkage remaining in the finished film cannot be completely removed using currently available methods. For example, the temperature during heat setting cannot be set as high as required for complete shrinkage removal because the film cannot withstand such a high temperature and would be damaged during production. Alternatively, the required exposure time would be so long that the equipment would have to be extremely large, making it impossible to implement technically, or there simply isn't enough space at the installation site.

[0022] Those skilled in the art are familiar with conventional blown film plants and extruded, single- or multi-layer polymer films, for example, from the publications US 3 814 785 A, DE 10 2020 111 879 Al, US 4 061 707 A, US 9 522 983 B2 and DE 69 024 417 T2.

[0023] Object of the invention

[0024] It is therefore an object of the present invention to provide a blown film line for producing an extruded, simultaneously biaxially stretched, single- or multi-layer film with very low shrinkage of < 3%, preferably < 2%, more preferably < 1%, and particularly 0%, in both the machine direction (MD) and the transverse direction (TD). The blown film line should have the smallest possible footprint. Furthermore, it is an object of the present invention to provide a suitable fixing unit for such a blown film line.

[0025] Furthermore, it is an object of the present invention to provide a corresponding manufacturing process for such a film, a film produced therewith, and corresponding uses. It is also an object of the present invention to provide a method for the continuous treatment of an extruded and simultaneously biaxially stretched, preferably thermally fixed, flattened, single- or multi-layer plastic film in the form of a film tube.

[0026] An important aspect of the present invention is to eliminate as completely as possible the shrinkage remaining in the film due to biaxial stretching. The film produced by the blown film system or the inventive method is intended to be preferably suitable for the production of banknotes or battery foil. A prerequisite for such use is that the film is mechanically stable up to a temperature of 150 °C, i.e., does not become too soft or thermally damaged, and that the film exhibits very low shrinkage of < 3% or better, or no shrinkage at all.

[0027] Summary of the invention

[0028] The problem addressed by the invention is solved by the subject matter of the independent claims. Advantageous embodiments of the invention are the subject matter of the dependent claims. The present invention is based on the inventor's finding that, due to the limited thermal resistance of the film to be produced, the elimination of shrinkage can be controlled, in particular, by the exposure time of the applied temperature.However, specifying a certain exposure time at a specific temperature during the post-treatment of shrinkage reduction in production means that, given a predetermined film transport speed through the unit where shrinkage reduction takes place, this post-treatment must be carried out over a sufficiently long distance. This would result in the post-treatment unit extending over several tens or even hundreds of meters in a single plane, for example, 50 to 150 meters, as is often the case with conventional tenter-frame systems. These dimensions would significantly increase the already large footprint of conventional systems.

[0029] Therefore, the inventor of the present application has developed a novel blown film line by combining a conventional blown film line with a post-treatment unit for the flattened film or film tube to eliminate shrinkage, wherein the post-treatment unit deviates from the previous horizontal orientation and instead provides the vertical or substantially the vertical as the machine direction of the post-treatment unit. Therefore, in the post-treatment unit according to the invention, the machine direction deviates from the vertical (V) by at most 15°, preferably at most 10°, more preferably at most 5°, or the machine direction of the post-treatment unit even runs parallel to the vertical. For this reason, the post-treatment unit is also referred to in this application as a vertical flattening unit.

[0030] Within the framework of the blown film line according to the invention, a conventional double-bubble line, which has a stretching unit for the continuous, simultaneous biaxial stretching of the film tube produced during extrusion or co-extrusion in its inflated state, can be combined with the vertical flattening unit according to the invention. Single- or multi-layer films produced with a conventional double-bubble line typically exhibit a shrinkage of 10 to 50% in both the machine direction and the transverse direction after simultaneous biaxial stretching, depending on the raw material used. By downstream of the stretching unit, the vertical flattening unit according to the invention and post-treating the stretched film within it, the shrinkage can be reduced to approximately 2 to 5% in both the machine direction and the transverse direction, or even less.

[0031] In a particularly advantageous embodiment of the blown film line according to the invention, a conventional triple-bubble line is combined with the vertical flat fixing unit according to the invention. The heat-setting of the film in the third bubble typically reduces shrinkage to 10 to 20% in both the machine direction and the transverse direction. Further treatment of the film in the vertical flat fixing unit according to the invention reduces shrinkage to 1 to 3% in both the machine direction and the transverse direction, or even lower.

[0032] At the same time, when using the vertical flat fixing unit according to the invention in a known blown film line, the film surprisingly does not become softer, as is the case with conventional relaxation treatments. Rather, despite the low shrinkage of 0 to 3% or 0 to 2% or even only 0 to 1% in both the machine direction and the transverse direction, the film produced with the blown film line according to the invention exhibits sufficient strength that exceeds that of conventionally produced, highly relaxed film.

[0033] The blown film line according to the invention is therefore able to produce a sufficiently strong film with a very low residual shrinkage of at most 3%, without significantly increasing the footprint of a conventional blown film line. This is achieved by providing a post-treatment unit designed according to the invention as a vertical flat fixing unit, in which the stretched film is post-treated to minimize shrinkage. A key difference between the blown film line according to the invention and a conventional line with, for example, a downstream tenter-frame unit, is that the conventional tenter-frame unit provides biaxial stretching and relaxation in the same unit.Therefore, a conventional tenter-frame unit is designed to pick up the unstretched film, which essentially still retains its original thickness from extrusion / co-extrusion, from the holding device of the tenter-frame unit after the film tube has been cut. As it passes horizontally through the tenter-frame unit, the film is first stretched and then thermally relaxed. The machine direction of the tenter-frame unit is always horizontal, as these systems must accommodate a long treatment path within this unit.

[0034] In contrast, in the blown film line according to the invention, the film is already in the form of a stretched film, specifically a flattened film tube, when it is introduced into the vertical flattening unit. Therefore, further stretching of the flattened film tube in the vertical flattening unit of the blown film line according to the invention is neither provided for nor possible by the device, as the vertical flattening unit is neither suitable nor designed for this purpose. As a positive side effect, the comparatively uneven stretching of the film, as typically occurs in tenter-frame units, and the associated occurrence of waves in the film and areas of varying film thickness are avoided. This also eliminates the need to cut off unusable edge strips, which reduces the yield of conventional lines.The vertical flat fixing unit according to the invention does not replace conventional tenter-frame units, or vice versa, since the holding device for the film tube of the vertical flat fixing unit according to the invention is designed to hold and guide the stretched and flattened film, whereas a conventional tenter-frame unit is designed to hold, stretch, and guide a single-layer flat film (cut and unfolded film tube; single or multi-layered). Furthermore, in the conventional tenter-frame unit, the holding device for the film is designed for a film thickness as it exists before the film is stretched.The inventor has further determined that the vertical or substantially vertical guidance of the film in the post-treatment unit according to the invention (vertical flat fixing unit) is advantageous compared to the previous horizontal guidance, as used, for example, in post-treatment in conventional tenter-frame units. Thus, during post-treatment in the vertical flat fixing unit of the blown film line according to the invention, the flattened film tube exhibits a more uniform temperature distribution within the film compared to horizontal guidance. This means that the same temperature prevails within the vertical flat fixing unit at the same (vertical) height when measured in the transverse direction of the vertical flat fixing unit, i.e., perpendicular to the machine direction.This ensures that the film, during its transport through the vertical flat fixing unit along the machine direction, exhibits essentially the same temperature across its entire width. However, if the film is guided horizontally, the inventor has determined that there is always a temperature difference between the top and bottom surfaces of the film (measured by measuring the temperature of the film surface), and possibly also across the entire width of the film.

[0035] A further advantage of the vertical flat fixing unit according to the invention arises from the fact that the film is doubled during processing in the vertical flat fixing unit (flattened film tube). Due to the double thickness of the stretched film, the film is mechanically easier to guide and can withstand higher mechanical and thermal loads. To achieve optimal guiding properties of the flattened film, the invention provides that the flattened film is doubled (= simply flattened) and thus double-layered, which is why it has twice the thickness of the single-layer film when stretched. However, it is excluded according to the invention to flatten the film tube twice, so that the film would have to be guided and processed through the vertical flat fixing unit at four times the thickness (four-layered).

[0036] In principle, when carrying out the inventive process, and in particular when using the inventive blown film line, a number of process techniques known to those skilled in the art can be considered and applied – individually or in combination. These include, in particular, the aforementioned triple-bubble and double-bubble processes with downstream heat setting. In heat setting, the films are passed through an oven and treated with heat, in most cases, as with the tenter-frame process, using hot air. Alternatively, in the triple-bubble process, heat setting of the film with infrared or steam is also used to reduce the shrinkage generated during drawing. Alternatively, in the double-bubble process, downstream heat setting can be carried out using tempering rollers or a hot-air oven.Accordingly, the film according to the invention can be produced using these process techniques or other suitable process techniques known to those skilled in the art. Such process techniques are known to those skilled in the art from the relevant literature, for example from the standard work Savic, Z., Savic, I.: “Sausage Casings”, published by VICTUS Lebensmittelindustriebedarf Vertriebsgesellschaft mbH, Vienna, 1st edition, June 2002, Chapter 7, in particular Subchapter 4.2, pages 244 to 301, or from their practical experience.

[0037] Specifically, for the blown film plant, the claimed method and the film according to the invention, the plant components and methods of the known double-bubble and in particular the triple-bubble process can be used and provided, for which the applicant provides suitable plants.The film can, for example, be co-extruded from the respective resin melts using a nozzle blowing head of the applicant designed for the production of single-layer or composite films with two, three, or more layers, preferably with thermal separation of the individual layers. It is then cooled with water cooling, reheated using a preheating device (e.g., using infrared radiation, steam, warm water, or warm air), simultaneously biaxially stretched (at the same time in the machine direction and in the transverse direction) using an enclosed gas bubble, in particular a compressed air bubble, and finally, in a further step, thermoset and optionally relaxed within a defined temperature regime. The relaxation can occur in both directions, i.e., both in the machine direction and in the transverse direction.

[0038] The blown film production line according to the invention can advantageously be designed based on a device or system of the applicant for the production of tubular food films for food packaging using the nozzle blowing process, to which the vertical flat fixing unit according to the invention is connected. In addition, the device disclosed in patent DE 199 16 428 B4 of the same applicant for the rapid cooling of thin thermoplastic tubes after their extrusion can be used. A corresponding further development according to patent DE 100 48 178 B4 can also be taken into account for this purpose.

[0039] In this process, the tubular film (film tube) produced from the molten plastic in the die-cutting head is subjected to intensive cooling, during which the amorphous structure of the thermoplastics from the molten plastic is preserved. The tubular film, vertically extruded from the molten plastic in the die-cutting head, initially moves into the cooling device for cooling without contacting the wall, as described in detail in German patent applications DE 199 16 428 B4 and DE 100 48 178 B4. For details regarding the procedures, construction, and operation of this cooling device, also referred to as a calibration device, reference is made to the contents of German patent applications DE 199 16 428 B4 and DE 100 48 178 B4 to avoid repetition.

[0040] The tubular film then passes through supports in the cooling unit. Due to a pressure differential between the interior of the tubular film and the coolant, the film is pressed against these supports, maintaining a liquid film between the film and the supports, thus preventing the tubular film from sticking. The diameter of the supports influences the diameter of the tubular film, which is why this cooling unit of the same applicant is also referred to as a calibration unit. In the stretching unit of the blown film system according to the invention, a gas bubble is generated and maintained by at least two squeezing devices, between which the gas bubble of the film tube is enclosed.The squeezing device can, for example, be a pair of metal rollers that compress the film tube from the outside in such a way that a bubble of pressurized gas, in particular air, enclosed in the film tube between two squeezing devices is sealed gas-tight or substantially gas-tight. However, the squeezing device is not limited to a pair of rollers, but can also be another device suitable for the aforementioned purpose, which is known to those skilled in the art. If a bubble fixing device is provided in the blown film system according to the invention, the squeezing device there can be the same squeezing device as that of the stretching device. However, the squeezing device of the bubble fixing device can also be another suitable squeezing device that is suitable for the aforementioned purpose of securing the gas bubble.

[0041] In the blown film system according to the invention, the take-up mechanism for continuously flattening the film tube can, for example, be designed as a pair of rollers, a roller or another suitable device for flattening the film in the form of a film tube or in tubular form.

[0042] The heating device of the vertical flat fixing unit according to the invention is a device that supplies heated air, infrared radiation, ultrasonic radiation, water vapor, or any combination thereof to the flattened film tube, thereby heating it to a predetermined temperature. It can, for example, have one or more emitters (e.g., surface or point emitters) for emitting infrared or ultrasonic radiation and / or outlets, in particular nozzles, for water vapor or heated air, which are designed and arranged in or on the vertical flat fixing unit of the blown film system according to the invention in such a way as to bring the respective heating medium into contact with the flattened film tube held and guided in the vertical flat fixing unit and thereby heat it. The heating device of the vertical flat fixing unit according to the invention, or its components, is arranged as follows:configured to allow for uniform heating of the flattened foil tube, especially at the same vertical height (e.g., by evenly distributed arrangement of steam outlets or infrared emitters at the same vertical height around the foil tube).

[0043] The optionally provided bubble fixing device (e.g., the third bubble of a triple-bubble system) of the blown film system according to the invention is typically arranged between the stretching unit and the vertical flat fixing unit of the blown film system according to the invention. The bubble fixing device is designed to enclose a gas bubble, preferably an air bubble, within the film tube and to achieve fixation by setting a predetermined gas pressure within the gas bubble or a predetermined differential pressure between the gas bubble and the environment and a predetermined temperature of the film tube. The machine direction of the bubble fixing device can be any direction in space, but is preferably vertical or horizontal.If it is intended that the film tube be fixed in the bubble fixing unit at a predetermined temperature of the film tube, which is usually the case, the bubble fixing unit of the blown film system according to the invention can comprise a further heating device for the film tube, not shown in detail, which is arranged in or upstream of the bubble fixing unit. The heating media (infrared radiation, ultrasonic radiation, steam, heated air) and components (outlets, nozzles, emitters) mentioned above in connection with the heating device of the vertical flat fixing unit can also be used analogously in this heating device.

[0044] The holding device provided in an advantageous embodiment of the vertical flat fixing unit according to the invention is suitable for holding the flattened film tube, preferably at its side edges or in the region of its side edges. Since the holding device is also movable, at least in the machine direction of the vertical flat fixing unit, it is also suitable for guiding, moving, or transporting the flattened film tube within the vertical flat fixing unit in its machine direction. However, the holding device of the vertical flat fixing unit according to the invention prevents the holding device from stretching or extending the flattened film tube in the machine direction or in the transverse direction of the vertical flat fixing unit when holding or guiding it within the unit.

[0045] The holding device can be designed as a plurality of clamps that point-by-point contact and hold the flattened film tube at its left and right edges (viewed in the machine direction of the vertical flattening unit) at a predetermined distance from each other. The clamps always approach the flattened film tube from the side, moving towards the center of the flattened film tube, i.e., in the transverse direction of the vertical flattening unit. During continuous operation of the blown film line, this transverse approach is superimposed on a simultaneous movement of the film tube and the clamps in the machine direction of the vertical flattening unit.

[0046] When the holding device is designed, for example, in the form of a group of left clamps and a group of right clamps that can grip and hold the left or right side edge of the flattened film tube, it is impossible for the clamps to stretch or extend the flattened film tube in the machine direction or in the transverse direction of the vertical flat fixing unit.This can be ensured, for example, by configuring the left and right clamps such that the respective distance, measured in the transverse direction (i.e., perpendicular to the machine direction) of the vertical flat fixing unit, between opposing pairs of left and right clamps remains constant or decreases by a maximum of 15%, preferably a maximum of 10%, and particularly a maximum of 5%, but does not increase, when both groups of clamps move at the same speed in the machine direction of the vertical flat fixing unit. This configuration allows relaxation of the film tube in the transverse direction but avoids any stretching or elongation in the transverse direction.Furthermore, the left clamps are configured such that the respective distance, measured in the machine direction of the vertical flat fixing unit, between two adjacent clamps of the group of left clamps remains constant or decreases by a maximum of 15%, preferably a maximum of 10%, and in particular a maximum of 5%, when the left clamps move in the machine direction of the vertical flat fixing unit (VU), but does not increase. Furthermore, the right clamps are configured such that the respective distance, measured in the machine direction of the vertical flat fixing unit, between two adjacent clamps of the group of right clamps remains constant or decreases by a maximum of 15%, preferably a maximum of 10%, and in particular a maximum of 5%, when the right clamps move in the machine direction of the vertical flat fixing unit, but does not increase.The configuration described above effectively prevents stretching or distortion of the flattened film tube in the machine direction.

[0047] The holding device according to the invention is characterized in that it enables and is limited to the uniform movement or transport of the flattened film tube in the machine direction of the vertical flat fixing unit. This means that, if the holding device is designed as a plurality of clamps, the left clamps and the right clamps move or are moved at the same speed in the machine direction when guiding the flattened film tube in the vertical flat fixing unit.

[0048] If the vertical flattening unit of the blown film line according to the invention has a feed for the flattened film tube at its lower end and also a discharge for the flattened film tube at its upper end, this has the advantage, firstly, that approximately the entire vertical extent of the vertical flattening unit can be used as a path for guiding the flattened film tube within the vertical flattening unit and thus for its processing. Secondly, this has the advantage that the flattened film tube can be guided from bottom to top in the vertical flattening unit or upwards in the machine direction of the vertical flattening unit.Since heat naturally accumulates in the upper part of the vertical fixing unit, and the lower part is the coolest, the flattened film tube is fed into the unit from the bottom for heating. This ensures that, due to the higher temperature in the vertical fixing unit compared to the surrounding environment, the "temperature shock" to the film is minimized upon entering the lower section, thus treating the film more gently. This is also advantageous because the film is less crystalline and therefore more temperature-sensitive when fed into the vertical fixing unit, i.e., before the heat treatment, than when it reaches the warmer upper section.

[0049] As the film is guided upwards within the vertical unit, the heating of the film tube is not only achieved by the heating element of the vertical flat fixing unit, but is also supported by the naturally increasing temperature inside the vertical flat fixing unit as the film tube is transported upwards. This achieves maximum efficiency of the heat or primary energy used, while also ensuring that the film tube is heated gently within the vertical flat fixing unit thanks to the lower temperature gradient.Due to the increasing crystallinity of the film during the temperature treatment in the vertical flat fixing unit, the film has already achieved a higher stability when the highest temperature is reached in the upper area of ​​the vertical flat fixing unit, so that the film is not too soft for guiding within the vertical flat fixing unit and transfer to further processing or winding despite the increased temperature prevailing in the upper area of ​​the vertical flat fixing unit.

[0050] Alternatively, the vertical flat fixing unit of the blown film line according to the invention can have a feed for the flattened film tube at its upper end or at its upper end, and also a discharge for the flattened film tube at its lower end. This has the advantage that approximately the entire vertical extent of the vertical flat fixing unit can be used as a path for guiding the flattened film tube within the unit and thus for its processing. Furthermore, in systems where the stretched or heat-set film tube is pulled off the top from the upstream units, this has the advantage that the flattened film tube can also be inserted into the vertical flat fixing unit at the top, i.e., at its upper end, over the shortest possible distance.In this case, the flattened film tube is guided downwards within the vertical device or at least within a first section thereof. A second section of the vertical flattening unit may also be provided in this case, in which the machine direction or transport direction is upwards.

[0051] A further advantage of the invented blown film line arises from the fact that the already stretched and, if necessary, relaxed film is fed to the vertical flattening unit in the form of a flattened film tube and is heated during transport within the vertical flattening unit, for example, upwards in the machine direction, to eliminate shrinkage. This allows the full height of the vertical flattening unit, and thus a maximum length within it, to be used for film treatment, since the film no longer needs to be guided or held by a holding device during cooling. In contrast, after treatment in the conventional tenter-frame line, the film must be held in place even while cooling to a predetermined temperature (e.g., room temperature).Consequently, in the blown film system according to the invention, it may be provided that the vertical flat fixing unit does not have such a device for cooling the flattened film tube or that no such device is connected downstream of the vertical flat fixing unit.

[0052] A further advantage of the blown film system according to the invention is that, unlike the conventional tenter-frame system, it is not limited to hot air as the sole heating medium. The use of steam for horizontal film guidance in the tenter-frame system is problematic because the condensation behavior of steam on the top of the film differs from that on the underside, resulting in an inhomogeneous heating effect. Furthermore, in the conventional tenter-frame system, downward sagging of the film due to gravity, especially when the film is heated, cannot be avoided with horizontal film guidance. This downward sagging of the film due to gravity can be avoided in the vertical or substantially vertical film guidance of the vertical flat fixing unit according to the invention.

[0053] Furthermore, the blown film line according to the invention, and in particular the vertical flat fixing unit according to the invention, allows the film to be heated not only with hot air, but also with steam and, in particular, with infrared or ultrasonic radiation. The technology according to the invention allows for a virtually unlimited use of heating media, since the homogeneity of the temperature distribution within the film is significantly improved compared to conventional methods due to the vertical or substantially vertical transport direction of the film. In addition, a number of practical advantages arise. For example, with the film guidance system according to the invention, no steam condensate can remain on the film within the vertical flat fixing unit, which would cause a temperature difference between the top and bottom of the film.Furthermore, for example, in film heating with IR emitters, if the film tears, it does not fall onto the laterally arranged emitters in the vertical flat fixing unit according to the invention, but rather collapses downwards in on itself. In contrast, if heat sources were arranged below the horizontally guided film for heating (conceivable, for example, in a tenter-frame system), the film would fall directly onto the heat sources in the event of a tear during the manufacturing process, and these sources would be contaminated, melted, or burned due to the high temperature of the heat sources. Therefore, tenter-frame systems involuntarily forgo the arrangement of heat sources below the horizontally guided film, and the film is heated, for example, only from above. This, in turn, inevitably leads to an inhomogeneity in the temperature distribution within the film and the associated consequences.

[0054] If, in an advantageous embodiment of the blown film system according to the invention, the vertical flat fixing unit has a first section in which the flattened film tube can be moved upwards in the machine direction of the vertical flat fixing unit and thereby heated, and a second section in which the flattened film tube can be moved downwards in the machine direction of the vertical flat fixing unit and thereby cooled, then the distance over which the flattened film tube is transported in the vertical flat fixing unit can be considerably increased.Ideally, both the first and second sections extend vertically over the entire height of the vertical flat fixing unit, so that the distance traveled by the flattened film tube through the unit is approximately twice the (clear) height of the unit, measured along the vertical axis. The same advantage is achieved if the flattened film tube moves downwards in the first section of the unit and upwards in the second section.

[0055] If the first section of the vertical flat fixing unit is heated to warm the film tube during its transport within the vertical flat fixing unit in the upward direction, the advantages mentioned above in connection with the lower feed of the film tube and its upward movement within the vertical device under heating are achieved.Furthermore, this embodiment of the vertical flat fixing unit according to the invention has the advantage that the flattened film tube can be cooled gently and energy-efficiently during its downward movement (downward in the machine direction) within the second section of the vertical flat fixing unit, since the film tube is naturally exposed to increasingly lower internal temperatures of the vertical flat fixing unit on its downward path until it reaches the discharge point at the lower end or at the lower end of the vertical flat fixing unit. With this embodiment of the vertical flat fixing unit of the blown film line according to the invention, a longer path length is therefore achieved.The treatment section (approximately twice the clear height of the vertical flat fixing unit) for the film tube is combined with an advantageous temperature regime (easier heating on the upward movement and easier cooling on the downward movement). Alternatively, the film tube can be heated during its upward movement in the vertical flat fixing unit, and the maximum temperature reached can be maintained during its downward movement, thus extending the exposure time to the maximum temperature compared to the procedure described above.

[0056] In another variation of the blown film line according to the invention, the film tube can be heated during its downward movement in the first section of the vertical flattening unit. Due to the higher internal temperature in the upper part of the first section, where the film tube enters, the film tube is heated more quickly. Furthermore, the film tube is cooled during its upward movement in the second section of the vertical flattening unit. Because of the lower internal temperature at the bottom of the second section, where the film tube enters, compared to the reverse direction, the film tube is also cooled more quickly during its upward movement.In both sections, the temperature difference between the foil tube and the interior is therefore greater at the entrance to the respective section than when guiding in the opposite direction, which is why the heating and cooling of the foil tube occurs faster in each case.

[0057] In a preferred embodiment of the blown film line according to the invention, the height of the vertical flattening unit, measured parallel to the vertical, can be limited to 50 m or less, preferably to 40 m or less. This ensures that the overall height, i.e., the vertical extent, of the blown film line according to the invention is not increased, or not significantly increased, by the presence of the vertical flattening unit, compared to, for example, conventional double-bubble or triple-bubble lines. Preferably, the blown film line according to the invention is characterized in that the height of the vertical flattening unit does not exceed the height of the stretching unit of the blown film line, in each case measured parallel to the vertical.This limitation ensures that the vertical extent of the overall system is not increased by the inventive provision of the vertical flat fixing unit and that comparatively compact dimensions of the entire blown film system can be achieved.

[0058] In the inventive process, the individual process steps are carried out using the following elements of the inventive blown film plant:

[0059] Step (a) is carried out for a single-layer film using the extruder and the blowing head as defined in claim 1, or for a multi-layer film using a plurality of extruders and the blowing head to which all extruders are connected. A key feature of the blown film system according to the invention and the process operated therewith is that, in the case of the production of a multi-layer film, all layers are co-extruded in one step. This eliminates the separate extrusion of different layers or layer packages and subsequent joining of the individual parts to form the composite film, a process also known in the trade as lamination or "extrusion coating". Following (co-)extrusion, the single-layer, single-layer, or multi-layer continuous film tube exiting the annular die of the blowing head is formed and cooled by means of a calibration device.

[0060] Step (b) is carried out using the stretching device after the film tube has been heated to a predetermined temperature by the preheating device. The temperature of the film tube is adjusted to a suitable temperature for the plastic and layer structure used for stretching, as in conventional processes (e.g., double- or triple-double processes). During stretching, a gas bubble, preferably an air bubble, is enclosed in a section of the film tube according to conventional process technology. Preferably, an upper and a lower pair of rollers (as viewed in the machine direction) are used to enclose the gas bubble; however, other technical solutions for generating and maintaining the gas bubble, which are known and suitable to those skilled in the art, are also conceivable.With the aid of this enclosed gas bubble, stretching occurs simultaneously in both the machine direction and the transverse direction (simultaneous biaxial stretching). Stretching in the transverse direction is achieved primarily by the gas pressure of the gas bubble in the transverse direction, while stretching in the machine direction can be accomplished both by the gas pressure of the bubble, which also acts in the machine direction, and by setting different transport or rotational speeds of the two pairs of rollers enclosing the gas bubble. The transport speed of the roller pair downstream in the machine direction (e.g., the lower roller pair) is typically higher than that of the upstream roller pair (e.g., the upper roller pair), thus causing stretching in the machine direction.After simultaneous biaxial stretching and before further treatment, the film exhibits a shrinkage of > 10% or > 20% or > 30% in the machine direction (MD) and in the transverse direction (TD).

[0061] The optional thermal fixing of the stretched film tube (step (c)) can preferably be carried out using the optional bubble fixing device located downstream of the stretching unit in the blown film line according to the invention. The continuous thermal fixing of the heated film tube can be carried out according to a conventional method, in particular by means of a gas bubble enclosed in the film tube between two pairs of rollers. If the transport speed of the roller pair downstream (in the machine direction) is lower than that of the roller pair upstream, this allows the film tube to relax, i.e., shrink, in the machine direction as it passes through the bubble fixing device.The internal pressure of the gas bubble enclosed in the film tube during film stretching in step (b) is at least 20 kPa (0.2 bar), preferably at least 50 kPa (0.5 bar), preferably 20 to 50 kPa, higher than the ambient pressure outside the film tube. The internal pressure of the gas bubble enclosed in the film tube during thermal fixing in step (c) is at least 10 kPa (0.1 bar), preferably at least 30 kPa (0.3 bar), preferably 10 to 30 kPa, higher than the ambient pressure outside the film tube. Since the internal pressure of the gas bubble enclosed in the film tube during thermal fixing in step (c) is always lower than that set during film stretching in step (b), this allows the film tube to relax in the transverse direction. The temperature of the film tube is thus controlled as in conventional methods (e.g.,The triple-double process) is set to a temperature suitable for relaxation of the plastic used. After thermal fixing and before further treatment, the film exhibits a shrinkage of > 5%, > 10%, or > 20% in both the machine direction (MD) and the transverse direction (TD).

[0062] The flattening of the stretched and optionally fixed film tube according to step (d) is preferably carried out by means of the take-up device, which consists, for example, of a pair of rollers or a roll.

[0063] The guiding of the flattened film tube according to step (e) is carried out by means of or within the vertical flattening unit, in which the flattened film tube is guided in the machine direction and, using the holding device and preferably the heating device of the vertical flattening unit, is either not relaxed, only relaxed in the machine direction, only relaxed in the transverse direction, or relaxed in both the machine direction and the transverse direction. After completion of step (e), the flattened film tube is discharged from the vertical device and preferably wound onto a roll.

[0064] Furthermore, the flattened film tube can be cooled to a temperature of < 40 °C, measured at the film surface, either in the vertical flat fixing unit or after leaving the vertical flat fixing unit and before winding, by means of a known cooling device, which is not described in detail here. The blown film line according to the invention may, but need not, include this cooling device. The vertical flat fixing unit mentioned in connection with the claimed uses is the same vertical flat fixing unit as defined and described in the claims relating to the blown film line according to the invention or above. The vertical flat fixing unit may be limited by any of the features mentioned therein relating to the vertical flat fixing unit.The blown film system mentioned in connection with a claimed use can in particular be a blown film system comprising at least the following components: at least one extruder, each with at least one metering device for continuously metering a polymer granulate, and at least one blowing head with an annular die for continuously extruding the film in the form of a film tube; a calibration device for cooling the continuous film tube exiting the annular die; a preheating device for continuously heating the film tube; a take-up device for continuously flattening the film tube; and a stretching device for continuously, simultaneously biaxially stretching the film tube in the inflated state, wherein the stretching of the film in the stretching device is carried out by means of a gas bubble enclosed in the film tube between two squeezing devices.feasible; wherein the spreading device is connected downstream of the preheating device and upstream of the extraction (AZ).

[0065] The features and modifications and combinations thereof mentioned in this application in connection with the blown film plant according to the invention and its components may also apply analogously to the blown film plant of the claimed use and are also deemed disclosed for this use.

[0066] While the flattened film tube is guided within the vertical flat fixing unit in the machine direction of the vertical flat fixing unit (step (e)), the film tube preferably has a temperature of 60 to 280 °C, more preferably 80 to 260 °C, measured at the surface of the film tube (PFS). The film tube is preferably moved at a speed of 30 to < 300 m / min, more preferably 50 to 100 m / min, in the machine direction of the vertical flat fixing unit. The average dwell time of the film tube in the vertical flat fixing unit can be 3 to 100 seconds, preferably 20 to 40 seconds.

[0067] In contrast to conventional tenter-frame systems, the flattened film tube can be guided or transported through the vertical flattening unit at a significantly lower speed, as reflected in the aforementioned speeds. To achieve a sufficient dwell time of the film tube in the vertical flattening unit, the distance traveled within the vertical flattening unit according to the invention does not need to be as great as in conventional tenter-frame systems. Consequently, the vertical flattening unit does not need to be as tall (clear height measured vertically) as the length of a corresponding tenter-frame system (length measured horizontally). This, among other things, contributes to the high compactness of the blown film system according to the invention with regard to its spatial dimensions and, in particular, its footprint.

[0068] The temperature or maximum temperature selected for treatment in the vertical flat fixing unit is essentially determined by the polymer material of the film. It is typically 20 to 40 °C higher than the treatment temperature in the horizontal tenter-frame system. According to the invention, the following temperatures are typically selected for the film (maximum temperature during treatment, measured at the surface of the film), depending on the polymer material:

[0069] • 80 to 90 °C for polyethylene (PE);

[0070] • 100 to 120 °C for polypropylene (PP);

[0071] • 180 to 200 °C for polyamides (PA); and

[0072] • 220 to 260 °C for polyethylene terephthalates (PET). In a particularly preferred embodiment of the inventive method, the film tube is not stretched during step (e) in either the machine direction of the vertical flat fixing unit or in the transverse direction of the vertical flat fixing unit (VU). Alternatively or additionally, during step (e), the film tube can be relaxed by at most 15%, preferably at most 10%, and particularly at most 5%, in either the machine direction or the transverse direction of the vertical flat fixing unit. Technically, the relaxation of the film in the transverse direction and, in particular, in the machine direction can be achieved, for example, by linear drives in conjunction with a plurality of clamps as a holding device.According to the invention, the film should be relaxed as little as possible in the vertical flat fixing unit or in step (e), as this ensures that the film remains or becomes as crystalline as possible. On the other hand, if relaxation of the film is completely omitted and the film is held or guided by the holding device without slight flexion in the transverse direction, the inventor has observed that – depending on the film materials used, the number of layers, the layer thicknesses, and the preceding stretching treatment – ​​adversely high tensile stress forces can occur within the film, and the film can tear out of the holding device or even tear itself.

[0073] In a further preferred embodiment of the inventive method, the film tube can, during step (e), first be moved upwards in the machine direction of the vertical flat fixing unit and heated during the upward movement to a temperature between 60 and 280 °C, preferably between 80 and 260 °C, measured at the surface of the film tube. Subsequently, the film tube can be moved downwards in the machine direction of the vertical flat fixing unit and cooled during the downward movement to a temperature between 0 and 60 °C, preferably between 20 and 60 °C, measured at the surface of the film tube. Furthermore, the present invention comprises an extruded and simultaneously biaxially stretched, single-layer plastic film or a coextruded and simultaneously biaxially stretched, multi-layer plastic film, preferably in the form of a film tube.in tubular form, wherein the film exhibits a shrinkage of < 3%, preferably < 2%, more preferably < 1%, and particularly 0%, in both the machine direction and the transverse direction. The film according to the invention is preferably mechanically stable up to a temperature of 150 °C, i.e., it does not become too soft or thermally damaged up to this temperature during production, further processing, or end application. Surprisingly, compared to conventionally produced films, the film according to the invention exhibits a significantly reduced tendency to curl, with a curl angle of 0 to 90°, preferably 0°, in both the machine direction and the transverse direction of the film. The film according to the invention can be produced using the blown film machine according to the invention. Furthermore, the film according to the invention can be produced using, or has been produced using, the method according to the invention.If the film according to the invention has two or more layers, all layers have been co-extruded simultaneously. Production of the film according to the invention by lamination or "extrusion coating" is not possible, so the film according to the invention is not laminated.

[0074] The present invention also claims the use of the vertical flat fixing unit according to the invention, as described above, for reducing or removing the shrinkage of a single- or multi-layer plastic film, preferably a flattened, single- or multi-layer plastic film in the form of a film tube or in tubular form, in particular the film according to the invention.

[0075] Furthermore, the present invention also claims the use of the vertical flat fixing unit according to the invention in a blown film line for the continuous production of extruded or co-extruded and simultaneously biaxially stretched, single- or multi-layer plastic film in the form of a film tube or in tubular form. According to the invention, the vertical flat fixing unit according to the invention is used to reduce or completely eliminate the shrinkage of the flattened, single- or multi-layer film treated therein.

[0076] Plastic is used in the form of a foil tube or in tubular form.

[0077] The features, combinations of features, modifications and advantages discussed above in connection with the blown film system or the method according to the invention apply analogously to the uses according to the invention.

[0078] In addition to the blown film line according to the invention, a vertical flat fixing unit, as described in the claims and suitable for use in the blown film line according to the invention, is also claimed. The features, combinations of features, modifications, and advantages disclosed in the claims and discussed above in connection with the vertical flat fixing unit of the blown film line according to the invention or with the method according to the invention can apply analogously to the separately claimed vertical flat fixing unit according to the invention.

[0079] Furthermore, a system comprising a single- or multi-layer plastic film in the form of a film tube and a blown film production line according to the invention, or comprising a single- or multi-layer plastic film in the form of a film tube, preferably a single- or multi-layer extruded and simultaneously biaxially stretched plastic film in the form of a flattened film tube, and a vertical flat fixing unit according to the invention. The features, combinations of features, modifications, and advantages disclosed in the claims and discussed above in connection with the vertical flat fixing unit, the blown film production line, or the method according to the invention apply analogously to the system according to the invention.

[0080] Furthermore, a method for the continuous treatment of an extruded and simultaneously biaxially stretched, preferably thermally fixed, flattened, single- or multi-layer plastic film (PF) in the form of a film tube (PFS), which is preferably producible or has been producible using steps (a) to (d) of the inventive method according to one of claims 12 to 17, is disclosed; wherein the film (PF) preferably exhibits a shrinkage of

[0081] < 3%, preferably < 2%, more preferably < 1%, in particular 0%, in each case in the machine direction (MD) and in the transverse direction (TD); wherein the treatment is carried out by means of the vertical flat fixing unit (VFFU) according to the invention according to one of claims 21 to 28; wherein the method comprises at least the following step (x):

[0082] (x) Guiding the flattened film tube (PFS) within the vertical unit (VU) in the machine direction (MD) of the vertical flat fixing unit (VFFU); wherein the machine direction (MD) of the vertical flat fixing unit (VFFU) deviates from the vertical (V) by at most 15°, preferably at most 10°, more preferably at most 5°, and is in particular parallel to the vertical (V).

[0083] In a preferred embodiment of the continuous treatment method, the film tube (PFS) has a temperature of 60 to 280 °C, preferably 80 to 260 °C, measured at the surface of the film tube (PFS) during step (x); and / or wherein, during step (x), the film tube (PFS) is moved at a speed of > 30 to < 600 m / min, preferably > 40 to

[0084] < 400 m / min, in particular > 50 to < 200 m / min, guided or moved in the machine direction (MD) of the vertical flat fixing unit (VFFU); and / or wherein the mean dwell time of the film tube (PFS) in the vertical flat fixing unit (VFFU) is 3 to 100 seconds, preferably 20 to 40 seconds.

[0085] In a preferred embodiment of the continuous treatment method, the film tube (PFS) is not stretched in either the machine direction (MD) or the transverse direction (TD) of the vertical flat fixing unit (VFFU) during step (x). In a preferred embodiment of the continuous treatment method, the film tube (PFS) is relaxed by at most 15%, preferably at most 10%, and particularly at most 5%, in both the machine direction (MD) and the transverse direction (TD) of the vertical flat fixing unit (VFFU) during step (x).or wherein, during the execution of step (x), the film tube (PFS) is allowed to relax by at most 15%, preferably at most 10%, in particular at most 5%, in the machine direction (MD) of the vertical flat fixing unit (VFFU), and is not allowed to relax in the transverse direction (TD) of the vertical flat fixing unit (VFFU); or wherein, during the execution of step (x), the film tube (PFS) is allowed to relax by at most 15%, preferably at most 10%, in particular at most 5%, in the machine direction (MD) of the vertical flat fixing unit (VFFU), and is not allowed to relax in the machine direction (MD) of the vertical flat fixing unit (VFFU); or wherein, during the execution of step (x), the film tube (PFS) is not allowed to relax in either the machine direction (MD) or the transverse direction (TD) of the vertical flat fixing unit (VFFU).

[0086] In a preferred embodiment of the continuous treatment method, during step (x) the film tube (PFS) is first moved upwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) and heated during the upward movement to a temperature between 60 and 280 °C, preferably between 80 and 260 °C, measured at the surface of the film tube (PFS); and the film tube (PFS) is then moved downwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) and cooled during the downward movement to a temperature between 0 and 60 °C, preferably between 20 and 40 °C, measured at the surface of the film tube (PFS).

[0087] In a preferred embodiment of the continuous treatment method, which can be implemented as an alternative to the embodiment described immediately above, during step (x) the film tube (PFS) is first moved downwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) and heated during the downward movement to a temperature between 60 and 280 °C, preferably between 80 and 260 °C, measured at the surface of the film tube (PFS); and the film tube (PFS) is then moved upwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) and cooled during the upward movement to a temperature between 0 and 60 °C, preferably between 20 and 40 °C, measured at the surface of the film tube (PFS).

[0088] The features, modifications, and advantages disclosed in the claims and discussed above in connection with the vertical flat fixing unit according to the invention, the blown film system according to the invention, or the method according to the invention apply analogously to the continuous treatment method according to the invention as described above and to its embodiments. The preferred embodiments of the continuous treatment method according to the invention described above can be combined as desired. This means that any two, three, four, or more of the preferred embodiments of the continuous treatment method described above can be combined as desired according to the invention, provided that such a combination is technically feasible and not excluded above.

Claims

Claims 1. A vertical flat fixing unit (VFFU) for an extruded and simultaneously biaxially stretched, single- or multi-layer plastic film (PF) in the form of a flattened film tube (PFS); wherein the machine direction (MD) of the vertical flat fixing unit (VFFU) deviates from the vertical (V) by at most 15°, preferably at most 10°, more preferably at most 5°, and is in particular parallel to the vertical (V); wherein the vertical flat fixing unit (VFFU) has a holding device (HE); wherein the holding device (HE) is suitable or configured for holding the flattened film tube (PFS), preferably at its side edges; wherein the holding device (HE) is suitable or configured for guiding, moving, or transporting the flattened film tube (PFS) in the machine direction (MD) of the vertical flat fixing unit (VFFU).is configured; wherein the holding device (HE) is not suitable or configured to stretch the flattened film tube (PFS) when guiding it in the vertical flat fixing unit (VFFU) in the machine direction (MD) or in the transverse direction (TD) of the vertical flat fixing unit (VFFU); and wherein the holding device (HE) is preferably configured such that it does not stretch the film tube (PFS) when guiding or moving ...) in the vertical flat fixing unit (VFFU) in the vertical flat fixing unit (VFFU) in the vertical flat fixing unit (VFFU) in the vertical flat fixing unit (VFFU) in the vertical flat fixing unitTransporting the flattened film tube (PFS) allows a relaxation of the flattened film tube (PFS) of at most 15%, preferably at most 10%, and in particular at most 5%, in the machine direction (MD), in the transverse direction (TD), or each in the machine direction (MD) and in the transverse direction (TD) of the vertical flat fixing unit (VFFU); wherein the vertical flat fixing unit (VFFU) has a heating device (VFFUHU) for heating the flattened film tube (PFS); wherein the heating device (VFFUHU) of the vertical flat fixing unit (VFFU) supplies the flattened film tube (PFS) with heated air, infrared radiation, ultrasonic radiation, or water vapor as a heating medium. or any combination thereof, preferably heated air, infrared radiation or water vapor, can be supplied.

2. Vertical flat fixing unit (VFFU) according to claim 1, wherein the holding device (HE) comprises or consists of a plurality of clamps; wherein a group of left clamps (CL) is configured and arranged in the vertical flat fixing unit (VFFU) such that the group of left clamps (CL) can sectionally receive and hold a left side edge of the flattened film tube (PFS) as seen in the machine direction (MD) of the vertical flat fixing unit (VFFU); wherein a group of right clamps (CR) is configured and arranged in the vertical flat fixing unit (VFFU) such that the group of right clamps (CR) can sectionally receive and hold a right side edge of the flattened film tube (PFS) opposite the left side edge of the flattened film tube (PFS) as seen in the machine direction (MD) of the vertical flat fixing unit (VFFU);wherein the left clamps (CL) and the right clamps (CR) are each movably arranged in the machine direction (MD) of the vertical flat fixing unit (VFFU); wherein the left clamps (CL) and the right clamps (CR) are configured such that the respective distance measured in the transverse direction (TD) of the vertical unit (VU) between opposing pairs of left clamps (CL) and right clamps (CR) remains constant or decreases by a maximum of 15%, preferably a maximum of 10%, and in particular a maximum of 5%, but does not increase, when the two groups of clamps (CL, CR) move at the same speed in the machine direction (MD) of the vertical flat fixing unit (VFFU);wherein the left clamps (CL) are configured such that the respective distance between two adjacent clamps of the group of left clamps (CL), measured in the machine direction (MD) of the vertical flat fixing unit (VFFU), remains constant when the left clamps (CL) are moved in the machine direction (MD) of the vertical flat fixing unit (VFFU); or decreases by at most 15%, preferably at most 10%, in particular at most 5%, but does not increase; and wherein the right clamps (CR) are configured such that the respective distance between two adjacent clamps of the group of right clamps (CR), measured in the machine direction (MD) of the vertical flat fixing unit (VFFU), remains constant or decreases by at most 15%, preferably at most 10%, in particular at most 5%, but does not increase, when the right clamps (CR) are moved in the machine direction (MD) of the vertical flat fixing unit (VFFU).

3. Vertical flat fixing unit (VFFU) according to claim 1 or 2, wherein the vertical flat fixing unit (VFFU) has a feed (ZU) for the flattened film tube (PFS) in the region of its lower end (VFFULE); and wherein the vertical flat fixing unit (VFFU) preferably has a discharge (AB) for the flattened film tube (PFS) in the region of its upper end (VFFUUE); or wherein the vertical flat fixing unit (VFFU) has a feed (ZU) for the flattened film tube (PFS) in the region of its upper end (VFFUUE); and wherein the vertical flat fixing unit (VFFU) preferably has a discharge (AB) for the flattened film tube (PFS) in the region of its lower end (VFFULE).

4. Vertical flat fixing unit (VFFU) according to any one of claims 1 to 3, wherein the vertical flat fixing unit (VFFU) has a first section (VFFU 1) and a second section (VFFU2); wherein the vertical flat fixing unit (VFFU) is configured to move the flattened film tube (PFS) upwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) in the first section (VFFU 1) and to heat the flattened film tube (PFS) in the process; wherein the vertical flat fixing unit (VFFU) is configured to move the flattened film tube (PFS) downwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) in the second section (VFFU2) and to cool the flattened film tube (PFS) in the process; and wherein the second section (VFFU2) of the vertical flat fixing unit (VFFU) is downstream of the first section (VFFU1) of the vertical flat fixing unit (VFFU).

5. Vertical flat fixing unit (VFFU) according to any one of claims 1 to 4, wherein the first section (VFFU 1) of the vertical flat fixing unit (VFFU) has a feed (ZU) for the flattened film tube (PFS) in the region of its lower end; and wherein the second section (VFFU2) of the vertical flat fixing unit (VFFU) has a discharge (AB) for the flattened film tube (PFS) in the region of its lower end.

6. Vertical flat fixing unit (VFFU) according to any one of claims 1 to 5, wherein the vertical flat fixing unit (VFFU) comprises a first section (VFFU 1) and a second section (VFFU2), wherein the vertical flat fixing unit (VFFU) is configured to move the flattened film tube (PFS) downwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) in the first section (VFFU 1) and to heat the flattened film tube (PFS) thereby; wherein the vertical flat fixing unit (VFFU) is configured to move the flattened film tube (PFS) upwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) in the second section (VFFU2) and to cool the flattened film tube (PFS) thereby; wherein the second section (VFFU2) of the vertical flat fixing unit (VFFU) is connected downstream of the first section (VFFU 1) of the vertical flat fixing unit (VFFU).

7. Vertical flat fixing unit (VFFU) according to claim 6, wherein the first section (VFFU1) of the vertical flat fixing unit (VFFU) has a feed (ZU) for the flattened film tube (PFS) in the region of its upper end; and wherein the second section (VFFU2) of the vertical flat fixing unit (VFFU) has a discharge (AB) for the flattened film tube (PFS) in the region of its upper end.

8. Vertical flat fixing unit (VFFU) according to any one of claims 1 to 7, wherein the height of the vertical flat fixing unit (VFFU), measured parallel to the vertical (V), does not exceed 50 m, preferably 40 m.

9. Blown film line (BA) for the continuous production of an extruded and simultaneously biaxially stretched, single- or multi-layer film (PF) made of plastic in the form of a film tube (PFS), wherein the film (PF) has a shrinkage of < 3%, preferably < 2%, more preferably < 1%, and in particular 0%, in each case in the machine direction (MD) and in the transverse direction (TD); wherein the blown film line (BA) comprises at least: at least one extruder (EX), each with at least one metering device (DE) for the continuous metering of a polymer granulate (PG), and at least one blow head (BK) with an annular die (RD) for the continuous extrusion of the film (PF) in the form of the film tube (PFS); a calibration device (KE) for cooling the continuous film tube (PFS) exiting the annular die (RD); a preheating device (PHU) for the continuous heating of the film tube (PFS);a dispensing unit (Z) for continuously flattening the film tube (PFS); and a stretching device (VE) for continuously, simultaneously biaxially stretching the film tube (PFS) in the inflated state, wherein the stretching of the film (PF) in the stretching device (VE) is carried out by means of an intermediate; two squeezing devices (SD) in the film tube (PFS) the gas bubble enclosed is or can be carried out; wherein the stretching device (VE) is connected downstream of the preheating device (PHU) and upstream of the vent (AZ); characterized in that the blown film system (BA) further comprises: a vertical flat fixing unit (VFFU) for holding the flattened film tube (PFS) and for guiding or moving it.Transporting the flattened film tube (PFS) in the machine direction (MD) of the vertical flat fixing unit (VFFU); wherein the machine direction (MD) of the vertical flat fixing unit (VFFU) deviates from the vertical (V) by at most 15°, preferably at most 10°, more preferably at most 5°; wherein the vertical flat fixing unit (VFFU) has a heating device (VFFUHU) for heating the flattened film tube (PFS); wherein heated air, infrared radiation, ultrasonic radiation, water vapor or any combination thereof, preferably heated air, infrared radiation or water vapor, can be supplied to the flattened film tube (PFS) as a heating medium by means of the heating device (VFFUHU) of the vertical flat fixing unit (VFFU); and wherein the vertical flat fixing unit (VFFU) is connected downstream of the stretching device (VE).

10. Blown film line according to claim 9, wherein the blown film line (BA) further comprises: a bubble fixing device (BFU) for continuously, thermally fixing the film tube (PFS) in the inflated state after stretching, wherein the fixing of the film (PF) in the bubble fixing device (BFU) is carried out or can be carried out by means of a gas bubble enclosed in the film tube (PFS) between two squeezing devices (SD); wherein the bubble fixing device (BFU) is connected downstream of the stretching device (VE); and the vertical flat fixation unit (VFFU) is downstream of the bladder fixation unit (BFU).

11. Blown film line according to claim 9 or 10, wherein the vertical flat fixing unit (VFFU) comprises a holding device (HE); wherein the holding device (HE) is suitable or configured for holding the flattened film tube (PFS), preferably at its side edges; wherein the holding device (HE) is suitable or configured for guiding, moving, or transporting the flattened film tube (PFS) in the machine direction (MD) of the vertical flat fixing unit (VFFU); wherein the holding device (HE) is not suitable or configured to stretch the flattened film tube (PFS) when guiding it in the vertical flat fixing unit (VFFU) in the machine direction (MD) or in the transverse direction (TD) of the vertical flat fixing unit (VFFU); and wherein the holding device (HE) is preferably configured such that, when guiding, moving, or transporting the flattened film tube (PFS), it does not stretch the film tube (PFS) in the machine direction (MD) or in the transverse direction (TD) of the vertical flat fixing unit (VFFU).Transporting the flattened film tube (PFS) allows a relaxation of the flattened film tube (PFS) of at most 15%, preferably at most 10%, in particular at most 5%, in the machine direction (MD), in the transverse direction (TD) or each in the machine direction (MD) and in the transverse direction (TD) of the vertical flat fixing unit (VFFU).

12. Blown film line according to claim 11, wherein the holding device (HE) comprises or consists of a plurality of clamps; wherein a group of left clamps (CL) is configured and arranged in the vertical flat fixing unit (VFFU) such that the group of left clamps (CL) can sectionally receive and hold a left side edge of the flattened film tube (PFS) as seen in the machine direction (MD) of the vertical flat fixing unit (VFFU); wherein a group of right clamps (CR) is configured and arranged in the vertical flat fixing unit (VFFU) such that the group of right clamps (CR) can sectionally receive and hold a left side edge of the flattened film tube corresponding to the left side edge of the flattened film tube. (PFS) opposite the right side edge of the flattened film tube (PFS) as seen in the machine direction (MD) of the vertical flat fixing unit (VFFU) in sections; wherein the left clamps (CL) and the right clamps (CR) are each movably arranged in the machine direction (MD) of the vertical flat fixing unit (VFFU); wherein the left clamps (CL) and the right clamps (CR) are configured such that the respective distance, measured in the transverse direction (TD) of the vertical unit (VU), between opposing pairs of left clamps (CL) and right clamps (CR) remains constant or decreases by a maximum of 15%, preferably a maximum of 10%, and in particular a maximum of 5%, but does not increase, when the two groups of clamps (CL, CR) move at the same speed in the machine direction (MD) of the vertical flat fixing unit (VFFU);wherein the left clamps (CL) are configured such that the respective distance between two adjacent clamps of the group of left clamps (CL), measured in the machine direction (MD) of the vertical flat fixing unit (VFFU), remains constant or decreases by a maximum of 15%, preferably a maximum of 10%, and in particular a maximum of 5%, but does not increase when the left clamps (CL) are moved in the machine direction (MD) of the vertical flat fixing unit (VFFU);and wherein the right clamps (CR) are configured such that the respective distance between two adjacent clamps of the group of right clamps (CR), measured in the machine direction (MD) of the vertical flat fixing unit (VFFU), remains constant or decreases by at most 15%, preferably at most 10%, and in particular at most 5%, when the right clamps (CR) are moved in the machine direction (MD) of the vertical flat fixing unit (VFFU), but does not increase.

13. Blown film production line according to any one of claims 9 to 12, wherein the vertical flat fixing unit (VFFU) has a feed (ZU) for the flattened film tube (PFS) in the region of its lower end (VFFULE); and wherein the vertical flat fixing unit (VFFU) preferably has a discharge (AB) for the flattened film tube (PFS) in the region of its upper end (VFFUUE); or wherein the vertical flat fixing unit (VFFU) preferably has a feed (ZU) for the flattened film tube (PFS) in the region of its upper end (VFFUUE); and wherein the vertical flat fixing unit (VFFU) preferably has a discharge (AB) for the flattened film tube (PFS) in the region of its lower end (VFFULE).

14. Blown film line according to any one of claims 9 to 13, wherein the vertical flattening unit (VFFU) has a first section (VFFU 1) and a second section (VFFU2); wherein the vertical flattening unit (VFFU) is configured to move the flattened film tube (PFS) upwards in the first section (VFFU 1) in the machine direction (MD) of the vertical flattening unit (VFFU) and to heat the flattened film tube (PFS) thereby; wherein the vertical flattening unit (VFFU) is configured to move the flattened film tube (PFS) downwards in the machine direction (MD) of the vertical flattening unit (VFFU) in the second section (VFFU2) and to cool the flattened film tube (PFS) thereby; and wherein the second section (VFFU2) of the vertical flat fixing unit (VFFU) is downstream of the first section (VFFU 1) of the vertical flat fixing unit (VFFU).

15. Blown film machine according to claim 14, wherein the first section (VFFU 1) of the vertical flat fixing unit (VFFU) has a feed (ZU) for the flattened film tube (PFS) in the region of its lower end; and wherein the second section (VFFU2) of the vertical flat fixing unit (VFFU) has a discharge (AB) for the flattened film tube (PFS) in the region of its lower end.

16. Blown film line according to any one of claims 9 to 12, wherein the vertical flattening unit (VFFU) has a first section (VFFU1) and a second section (VFFU2), wherein the vertical flattening unit (VFFU) is configured to flatten the film tube (PFS) in the first section (VFFU1) in the to move the flattened film tube (PFS) downwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) and to heat the flattened film tube (PFS) in the process; wherein the vertical flat fixing unit (VFFU) is configured to move the flattened film tube (PFS) upwards in the second section (VFFU2) in the machine direction (MD) of the vertical flat fixing unit (VFFU) and to cool the flattened film tube (PFS) in the process; wherein the second section (VFFU2) of the vertical flat fixing unit (VFFU) is downstream of the first section (VFFU1) of the vertical flat fixing unit (VFFU).

17. Blown film machine according to claim 16, wherein the first section (VFFU 1) of the vertical flat fixing unit (VFFU) has a feed (ZU) for the flattened film tube (PFS) in the region of its upper end; and wherein the second section (VFFU2) of the vertical flat fixing unit (VFFU) has a discharge (AB) for the flattened film tube (PFS) in the region of its upper end.

18. Blown film production line according to any one of claims 9 to 17, wherein the height of the vertical flat fixing unit (VFFU) does not exceed the height of the stretching unit (VE), in each case measured parallel to the vertical (V); and / or wherein the height of the vertical flat fixing unit (VFFU), measured parallel to the vertical (V), does not exceed 50 m, preferably 40 m.

19. System (S) comprising a single- or multi-layer film (PF) made of plastic in the form of a film tube (PFS) and a blown film system (BA) according to a of claims 9 to 18, or a vertical flat fixing unit (VFFU) according to any one of claims 1 to 8.

20. A method for the continuous production of an extruded and simultaneously biaxially stretched, single- or multi-layer plastic film (PF) in the form of a film tube (PFS), wherein the film (PF) has a shrinkage of < 3%, preferably < 2%, more preferably < 1%, and in particular 0%, in both the machine direction (MD) and the transverse direction (TD); wherein the production is carried out using the blown film line (BA) according to any one of claims 9 to 18 or using the vertical flat fixing unit (VFFU) according to any one of claims 1 to 8; wherein the method comprises at least the following steps: (a) Extruding the single or multi-layer plastic film (PF) into a tube form, resulting in a film tube (PFS); (b) Simultaneous biaxial stretching of the extruded film tube (PFS) by means of a gas bubble (GBV), in particular an air bubble, enclosed in the film tube (PFS) for stretching, wherein the internal pressure (piV) of the gas bubble (GBV) enclosed for stretching inside the film tube is at least 20 kPa (0.2 bar), preferably at least 50 kPa (0.5 bar), higher than the ambient pressure (pa) outside the film tube (PFS); wherein the film (PF) exhibits a shrinkage of > 10% or > 20% or > 30% immediately after the simultaneous biaxial stretching in both the machine direction (MD) and the transverse direction (TD); (c) preferably thermal fixing of the stretched film tube (PFS) by means of a gas bubble (GBF) enclosed in the film tube (PFS) for fixing, in particular an air bubble, wherein the internal pressure (piF) of the gas bubble (GBF) enclosed for fixing inside the film tube is at least 10 kPa (0.1 bar), preferably at least 30 kPa (0.3 bar), higher than the ambient pressure (pa) outside the film tube (PFS); wherein the internal pressure (piF) of the gas bubble (GBF) enclosed for fixing is less than the internal pressure (piV) of the gas bubble (GBV) enclosed for stretching; wherein the film (PF) exhibits a shrinkage of > 5% or > 10% or > 20% immediately after thermal fixing, in both the machine direction (MD) and the transverse direction (TD); (d) Flattening the film tube (PFS) resulting from step (b) or (c) and feeding the flattened film tube (PFS) into the vertical flattening unit (VFFU) of the blown film line (BA); and (e) Guiding the flattened film tube (PFS) within the vertical unit (VU) in the machine direction (MD) of the vertical flat fixing unit (VFFU); wherein the machine direction (MD) of the vertical flat fixing unit (VFFU) deviates from the vertical (V) by at most 15°, preferably at most 10°, more preferably at most 5°, and is in particular parallel to the vertical (V).

21. The method of claim 20, wherein during the execution of step (e) the film tube (PFS) has a temperature of 60 to 280 °C, preferably 80 to 260 °C, measured at the surface of the film tube (PFS); and / or wherein during the execution of step (e) the film tube (PFS) is guided or moved in the machine direction (MD) of the vertical flat fixing unit (VFFU) at a speed of > 30 to < 600 m / min, preferably > 40 to < 400 m / min, in particular > 50 to < 200 m / min; and / or wherein the mean residence time of the film tube (PFS) in the vertical flat fixing unit (VFFU) is 3 to 100 seconds, preferably 20 to 40 seconds.

22. Method according to claim 20 or 21, wherein during the execution of step (e) the film tube (PFS) is not stretched in the machine direction (MD) of the vertical flat fixing unit (VFFU) nor in the transverse direction (TD) of the vertical flat fixing unit (VFFU).

23. A method according to any one of claims 20 to 22, wherein during the execution of step (e) the film tube (PFS) is relaxed by at most 15%, preferably at most 10%, and in particular at most 5%, both in the machine direction (MD) of the vertical flat fixing unit (VFFU) and in the transverse direction (TD) of the vertical flat fixing unit (VFFU); or wherein during the execution of step (e) the film tube (PFS) is relaxed by at most 15%, preferably at most 10%, and in particular at most 5%, in the machine direction (MD) of the vertical flat fixing unit (VFFU), and is not relaxed in the transverse direction (TD) of the vertical flat fixing unit (VFFU);or wherein, during the execution of step (e), the film tube (PFS) is relaxed by no more than 15%, preferably no more than 10%, and in particular no more than 5%, in the transverse direction (TD) of the vertical flat fixing unit (VFFU) and is not relaxed in the machine direction (MD) of the vertical flat fixing unit (VFFU); or wherein, during the execution of step (e), the film tube (PFS) is not relaxed either in the machine direction (MD) of the vertical flat fixing unit (VFFU) or in the transverse direction (TD) of the vertical flat fixing unit (VFFU).

24. Method according to any one of claims 20 to 23, wherein during the execution of step (e) the film tube (PFS) is first moved upwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) and is heated during the upward movement to a temperature between 60 and 280 °C, preferably between 80 and 260 °C, measured at the surface of the film tube (PFS); and the film tube (PFS) is then moved downwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) and is cooled during the downward movement to a temperature between 0 and 60 °C, preferably between 20 and 40 °C, measured at the surface of the film tube (PFS).

25. Method according to any one of claims 20 to 23, wherein during the execution of step (e) the film tube (PFS) is first moved downwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) and is heated during the downward movement to a temperature between 60 and 280 °C, preferably between 80 and 260 °C, measured at the surface of the film tube (PFS); and the film tube (PFS) is then moved upwards in the machine direction (MD) of the vertical flat fixing unit (VFFU) and is cooled during the upward movement to a temperature between 0 and 60 °C, preferably between 20 and 40 °C, measured at the surface of the film tube (PFS).

26. Extruded and simultaneously biaxially stretched, single-layer film (PF) made of plastic or co-extruded and simultaneously biaxially stretched, multi-layer film (PF) made of plastic, preferably in the form of a film tube (PFS); wherein the film (PF) has a shrinkage of < 3%, preferably < 2%, more preferably < 1%, and in particular 0%, in each case in the machine direction (MD) and in the transverse direction (TD); wherein the film (PF) has a roll tendency with a roll angle of 0 to 90° in each case in the machine direction and in the transverse direction of the film; wherein the film (PF) can be produced using the blown film line (BA) according to any one of claims 9 to 18 or using the vertical flat fixing unit (VFFU) according to any one of claims 1 to 8 and / or was produced or can be produced using the method according to any one of claims 20 to 25.

27. Use of a vertical flat fixing unit (VFFU), preferably the vertical flat fixing unit (VFFU) according to any one of claims 1 to 8, for reducing or removing the shrinkage of a single or multilayer film (PF) made of plastic, preferably a flattened, single or multilayer film (PF) made of plastic in the form of a film tube (PFS); wherein the vertical flat fixing unit (VFFU) is configured to hold the flattened film tube (PFS) and to guide, move, or transport the flattened film tube (PFS) in the machine direction (MD) of the vertical flat fixing unit (VFFU); wherein the machine direction (MD) of the vertical flat fixing unit (VFFU) deviates from the vertical (V) by at most 15°, preferably at most 10°, more preferably at most 5°, and is particularly parallel to the vertical (V); wherein the vertical flat fixing unit (VFFU) has a heating device (VFFUHU) for heating the flattened film tube (PFS); wherein heated air, infrared radiation, ultrasonic radiation, water vapor, or any combination thereof, preferably heated air, infrared radiation, or water vapor, can be supplied to the flattened film tube (PFS) as a heating medium by means of the heating device (VFFUHU) of the vertical flat fixing unit (VFFU).

28. Use of a vertical flat fixing unit (VFFU), preferably the vertical flat fixing unit (VFFU) according to any one of claims 1 to 8, in a blown film line (BA) for the continuous production of an extruded and simultaneously biaxially stretched, single- or multi-layer film (PF) made of plastic in the form of a film tube (PFS), preferably use according to claim 27; wherein the vertical flat fixing unit (VFFU) is suitable for holding the flattened film tube (PFS) and for guiding, moving, or transporting the flattened film tube (PFS) in the machine direction (MD) of the vertical flat fixing unit (VFFU).is configured; wherein the machine direction (MD) of the vertical flat fixing unit (VFFU) deviates from the vertical (V) by at most 15°, preferably at most 10°, more preferably at most 5°, and is in particular parallel to the vertical (V); wherein the vertical flat fixing unit (VFFU) has a heating device (VFFUHU) for heating the flattened film tube (PFS); wherein the heating device (VFFUHU) of the vertical flat fixing unit (VFFU) is used to heat the flattened film tube (PFS). The heating medium can be heated air, infrared radiation, ultrasonic radiation, water vapor or any combination thereof, preferably heated air, infrared radiation or water vapor; and wherein the vertical flat fixing unit (VFFU) is preferably connected downstream of a stretching device (VE) of the blown film system (BA) for continuous, simultaneous biaxial stretching of the film tube (PFS) in the inflated state.

Images