WO2022161584A1

WO2022161584A1 - Blown-film system and method for operating a blown-film system

Info

Publication number: WO2022161584A1
Application number: PCT/DE2022/200010
Authority: WO
Inventors: Christoph Lettowsky; Holger Schumacher; Uwe Süßmann; Andreas Neuss
Original assignee: Reifenhäuser GmbH & Co. KG Maschinenfabrik
Priority date: 2021-01-28
Filing date: 2022-01-27
Publication date: 2022-08-04
Also published as: DE202022002884U1; DE112022000841A5

Abstract

The invention relates to a plastics-shaping system, especially a blown-film system or a flat-film system or some other system designed to manufacture a film web, comprising a treatment roller line with process rollers, the treatment roller line comprising a retaining roller and a drawing roller and optionally additional rollers, which are set at different circumferential speeds from each other, specifically the drawing roller having a higher circumferential speed than the retaining roller, wherein the retaining roller and/or the drawing roller and/or an additional process roller sucks the film web onto its relevant rotating surface by means of a negative pressure so that the film web lies against the roller as uniformly as possible and/or so that a static-friction zone which is as extensive as possible is made possible. The invention also relates to a method for operating a system, wherein the negative pressure is brought to the external region of the roller through a permeable surface on the roller in order to suck the film web onto the roller.

Description

Blown film plant and method for operating a blown film plant

FIELD OF APPLICATION AND PRIOR ART

The invention relates to a blown film system for producing at least one film web from a thermoplastic material, the blown film system partially having a vertical process path, and the blown film system having a processing station for the film web along the process path.

Blown film systems are known from the prior art. Such blown film plants are usually supplied with plastics in granulated form, which are then plasticized in extruders under high pressure to form a viscous mass. This viscous mass is ring-shaped in a blow head and escapes from the blow head through an annular nozzle. As soon as it leaves the ring nozzle, the viscous mass already forms a film tube. The film tube is drawn off upwards along a tube formation zone, with pressurized air being introduced into the interior of the film tube. This leads to a transverse stretching of the film tube. An active coolant for the ascending film tube cools down the viscous mass or melt at a tolerable distance from the annular nozzle. On its way up, the tubular film passes through a calibration basket and then a film processing station which can stretch the film to a desired transverse diameter and/or to a desired thickness. A flattening or flattening unit, by means of which the film tube is laid flat to form a double-layer film web, can then be present. The flattening unit feeds this double-layer film web to a pre-squeeze. This is followed by folding, in which an almost atmospherically evacuated double-layer film web is finally formed from the film tube. From there at the latest, or rather even from the time of merging, there is a double-layer film web (simplified here also called "film web" or just "film"), which is ultimately wound up into a roll for further transport.

A blown film line has a processing line which has one or more line sections running vertically. Individual processing stations are arranged in or on the blown film line, ie along the processing line. In this processing line, the double-layer film web is "stretched" in the machine direction. Within the scope of the present patent application, "stretching/stretching" is understood as a generic term for "stretching" and for "stretching".

A "stretching" system stretches the film by more than 5%, at least in the longitudinal direction, preferably 50% and more, often up to 1,000%. Such systems are often referred to as "MDO", which stands for "machine direction orientation", i.e for orienting the plastic molecules in the machine direction, i.e. the direction in which the material is transported through the system.

As an alternative to an MDO, a so-called flatness pack can be provided as a stretching device. This "stretches" the film irreversibly, usually between 0.5% and 5% in the machine direction, which only serves to compensate for run length differences across the width of the double-layer film web and when the film web is running straight, so that the film can be wound up and processed more easily. directions, i.e. an MDO and a lay-flat package, are technically comparable insofar as they stretch the film lengthways For example, after further, passive rollers, a faster-driven roller ("fast-running stretching roller"). The difference in speed between the two rollers, which can also be designed as pairs of squeezing rollers, which transport the film with static friction, results in a change in length of the film.

The publication DE102012015462 describes such a stretching device. In addition to the previously described stretching section (distance between the two areas in which the film is transported at the peripheral speed of the respective roller), the following areas are characteristic of such a device: at least one heating device in which the film web can be heated, at least one cooling device, in which the film web can be re-cooled, and mostly annealing or annealing rolls positioned between the stretch gate and the chill rolls.

These areas are usually designed as rollers ("process rollers"), which are usually driven individually and temperature controlled. In an approximately central section of the wrapping of the film web around such a process roller, the film web is transported with static friction, i.e. with the peripheral speed of the roller. The static friction ends even before the film web leaves the roll surface at a lifting/unwinding point.This is particularly important if the following roll runs at a higher peripheral speed (i.e. in particular for the two rolls that make up the stretch section of the processing line), which The film web therefore already on the roll surface first changes from static friction to faster sliding friction and only then lifts off the roll surface but first beyond the point of impact. "Points" are used here for simplicity. A film web lifts off a roller at a lifting line and runs onto a roller surface with a contact line. However, when viewed from the side, the two-dimensional film web is reduced by one dimension to a line, and reduced accordingly the lift-off line and the line-up line each move to points by one dimension.When a (blown) film is stretched monoaxially, the film constricts in the area of the stretching section, the so-called neck-in.This results in a reduction in the initial width of the film and on the other hand, this results in a greater film thickness in the edge areas of the plastic film web produced. These edge areas with a greater thickness must be cut away during later processing. The real net output of the system is thus reduced. In addition, the introduction of force into the film and with it also in the machine direction due to the resulting Di Differences in the thickness and the clamping situation of the plastic film between the rollers of the stretching section are unfavorable, so that so-called flatness errors occur in the plastic film web produced. These have an effect on the "evenness" of the film and are unfavorable in further processing (printing, laminating, etc.). In order to avoid such unevenness, the two rollers in the stretching section, but also the other rollers (heating, Cooling and annealing or tempering) of the stretching device Pressing devices prior art. With such a pressing device, the film web is pressed against the first roller along a line which is in the region of the detachment edge of the film web from the first roller and/or with a pressing device which the foil pressed against the second roller along a line which lies in the region of the feed line of the film web to the second roller.

The pressing device today is usually a rubberized roller ("feed roller"), which is applied to the process roller with pneumatic cylinders at or near the run-up and/or run-off point of the film. The diameter of this feed roller is in the Usually smaller than the diameter of the process roller.

By using the rubberized feed rollers with a diameter D, it is not possible to adjust the stretching gap to a minimum size (< D/2). However, this condition is desirable for the least possible constriction of the plastic film.

The clamping of the plastic film and the resulting forces acting in the longitudinal direction are not uniform, especially for wide systems, due to the deflection of the rollers across the film width, so that flatness errors occur in the stretched plastic film due to the different application of forces. Due to the geometric design as a slim, long hollow cylinder, the rubber-coated feed rollers in particular are affected by increased deflection. In principle, it is possible to compensate for the resulting deflection by bulging the rubber coating, but this is difficult due to the complexity of the load conditions, especially for wide systems. On the other hand, in the case of large widths, the ratio of the constriction of the plastic film to the usable film width is particularly favorable, since the constriction is primarily dependent on the geometric conditions in the stretching gap.

Various solutions are conceivable. All solutions are aimed at fixing the film in the entire area of wrap around the process roller from its run-up point to its run-off point, ie in the entire area of wrap-around over the entire lying width of the film to achieve frictional contact, i.e. static friction. The force acting on the film should be even across the lying width of the film and at the same time as low as necessary for "static friction".

If "plastic film" or a "film web" is mentioned below, the proposed solutions apply to a single film web, a previously blocked film tube and also to a tube that has been folded into a double flat film web ("double-layer film web"). This Film web can be slit on one or two sides The solutions described apply - even if described differently to clarify the principle - both for the run-up point and for the run-off point of the film on any process roller of the stretching device.

TASK AND SOLUTION

The object of the invention is to further develop a blown film system of the type described above in such a way that a plastic film web (film web) is fixed as precisely as possible on a process roller. In particular with a force that is as small and uniform as possible over a lying width on the film web.

The blown film system according to the invention enables static friction to be built up between the process roller and the film web at an already described run-on point and/or up to the already described run-off point of the process roller and thus ensures a defined “stretching” process. Furthermore, the distance between the process rollers is minimal in a design according to the invention and the resulting transverse projection, so-called neck-in, is as small as possible. This improves the uniformity of the product properties, such as flatness.

According to the invention, the film web is fixed on a slow-running stretching roller that maintains the fixing force, on a faster-running stretching roller or on process rollers that follow in the machine direction in the process via a vacuum roller.

This vacuum roller is understood to mean a roller to which a negative pressure is applied, for example but not exclusively via a radial compressor. The lateral surface (hereinafter also surface) of the roller is provided with holes and/or a porous surface, so that the film web is sucked onto the roller by the vacuum applied. The negative pressure is below ambient pressure, typically in the range from 0 to 950 mbar, preferably in the range from 0 to 600 mbar, particularly preferably in the range from 0 to 100 mbar.

Another embodiment of the vacuum roller is designed in such a way that the negative pressure acts via a suction chamber only in segments across the bed width, with the effective area preferably being in the edge area of the plastic film web or preferably in the central area of the plastic film web.

Another embodiment of the vacuum roller is designed in such a way that the negative pressure via a suction chamber inside the roller is only effective at a certain angle. This turns out to be advantageous in order not to shift the natural run-on point of the plastic film onto the process roller or to shift it in a defined manner. The working area of the surface of the vacuum roller on which an effective vacuum is applied is at an angle of <210°, preferably at an angle of <90°, more preferably at an angle between 5° and 45°.

Another embodiment of the vacuum roller is designed in such a way that the negative pressure acts via a suction chamber inside the roller at least over the entire lying width of the film web and at least over the entire angle of wrap of the film. This increases the friction between the foil and the process roller. This increases the transmittable power. Therefore, in addition to the contact roller, a so-called pressure roller can also be dispensed with.

In addition, the temperature of the vacuum roller can be controlled in a targeted manner so that the film adheres to the vacuum roller, i.e. it clings better, thereby increasing friction. This leads to better, and above all more even, power transmission and thus local slipping is prevented. The tempering is preferably a heating process.

A vacuum blade is also included in the invention.

A further embodiment provides for the vacuum not to be realized via the process roller itself, but rather via a specially provided bar (vacuum sword) near the point at which the plastic film hits the process roller. As described above, a vacuum is applied to this bar in order to fix the film web on the bar. The bar has a non-stick coating that allows the film to slide and reduces surface defects caused by friction. With the help of this beam, it is possible to fix the stretching point in a defined manner between the two stretching rollers. In a further embodiment, the point of the minimum foil width for the first time is determined as a result of the transverse indentation. The determination can be made with an optical system, for example. Another execution makes it possible to control or even regulate the stretching point based on the position of the initial minimum film width via a relative movement of the vacuum sword in the horizontal between the process rollers. The negative pressure is below ambient pressure, typically in the range from 0 to 950 mbar, preferably in the range from 0 to 600 mbar, particularly preferably in the range from 0 to 100 mbar.

In one embodiment, the system has an air sword.

The plastic film running onto a process roller is fixed to the process roller with an air knife. A preferably tangential force is applied to the running film web via an air stream, which fixes the plastic film on the process roller and increases the transmittable frictional force. The angle can deviate from the tangential position by a few degrees in order not to influence or specifically influence the run-on point of the plastic film onto the process roller. The use of preheated air is advantageous in order not to cool down the plastic film, which is usually heated to near the melting point in this area, by the impingement of air.

A variant of this design provides for the construction of the air sword in the form of a rod, which is used in the position of the previous rubber-coated contact roller. The rod has openings on its surface that are distributed over the width and circumference, via which an air cushion is generated with the help of overpressure, which exerts a force on the film web. Furthermore, it is conceivable to design the surface with a porous structure that forms this air cushion. Due to the prevailing temperature conditions with a film temperature close to the melting point of the plastic film, it has proven to be advantageous to use preheated air for the impingement.

A variant of this design provides for the position of the rod to be changed in such a way that the resulting wrap angle of the process roller is increased.

A further embodiment provides for the rod to be provided with a defined bend in order to apply a force transverse to the machine direction, which leads to a force counteracting the transverse indentation.

In one embodiment, the system has a vacuum chamber.

The running of the film onto a process roller can be supported by a vacuum that is applied near the point at which the film runs onto the process roller. The plastic film is fixed securely and more firmly on the process roller by means of a vacuum in the area of its run-on point, thus increasing the transferable frictional force. The applied vacuum can vary over the lay width of the web.

A variant of this design envisages changing the position of the vacuum chamber in such a way that the resulting wrap angle of the process roller is increased. The negative pressure is below ambient pressure, typically in the range from 0 to 950 mbar, preferably in the range from 0 to 600 mbar, particularly preferably in the range from 0 to 100 mbar.

In one embodiment, the system has an immersed roller.

The plastic film running between two process rollers is deflected with the help of a dipping deflection roller, so that the resulting increase in film tension between the two process rollers leads to a defined run off or run onto the process rollers. Due to the decoupling of the resulting two film areas with intermediate adhesion on the deflection roller, it is possible to minimize the resulting neck-in. Furthermore, it can be advantageous to design the immersing deflection roller as a vacuum roller according to the model described above, in order to guarantee adhesion of the plastic film to the deflection roller in this area with minimal wrapping.

A variant of the immersing roller consists of the above-mentioned air sword in the form of a rod, in which case no adhesion of the plastic film to the rod is sought in this embodiment. Rather, the increased film tension results from the now longer path of the plastic film between the natural run-up and run-off points on the process rollers.

In all cases, the dipping roller can optionally be steplessly dipped into the film web in order to regulate the angle of wrap of the roller. This stepless adjustment makes it possible to regulate the state of stretching with the help of a suitable characteristic value.

In one embodiment, the system has an electrostatic treatment of the plastic film.

It is known from the literature that a plastic film can be activated via an electrostatic treatment in such a way that it can be fixed to a surface via electrostatic compensating movements. This method is already being used successfully, for example, when changing the rolls of a produced web (keyword: adhesive-free winding) or for fixing the plastic film on a roller in front of a measuring device aligned with this roller (keyword: Fraunhofer flatness measurement). In the case of the present invention, the electrostatic treatment of the plastic film takes place shortly before it runs onto the following process roller in the machine direction, on which the plastic film is to be fixed. This is preferably the second, faster-running stretching roller. It can also be used for all other process rollers.

Prevention of transverse shrinkage via mechanical stress The transverse shrinkage of the plastic film during monoaxial stretching, the so-called neck-in, is a direct function of the distance between the slow-running stretching roller and the fast-running stretching roller that follows it in the machine direction. If the applied forces prevent the plastic film from slipping on the process rollers and the plastic film is already adhering to the process roller at the point at which the plastic film hits the surface, the point at which the minimum width is reached for the first time is between the process rollers in an area in which the plastic film is not fixed parallel to the running direction.

In order to minimize or completely eliminate this area, the plastic film is mechanically clamped in the running direction. The clamping can take place on or shortly after the slow-running stretching roller and be maintained until shortly before, on or after the fast-running stretching roller that follows in the machine direction. Since the acceleration of the film web in the stretching gap has to be compensated for in the case of complete clamping, the segmented clamping elements can be driven individually and perform an acceleration movement in the machine direction that is adapted to the stretching roller speeds. A simpler embodiment of the above invention relates to mechanical tensioning between the two drafting rollers running at different speeds, with the tensioning unit in the machine direction either operating at the slower speed, at the faster roller speed or at an intermediate speed. low machine direction speed. The tensioning unit is designed in such a way that the free distance between the tensioning unit and the process roller, which is unguided for the plastic film, is as small as possible, so that the transverse shrinkage that occurs is minimized.

Various versions of the clamping unit are possible. Exemplary designs are: rubber bands running over one another, ropes pressed against each other, conveyor belts with high frictional force on the plastic film, mechanical bracing elements (clips), offset positioned pairs of wheels, etc.

In one embodiment, the system has a segmented feed roller.

In order to minimize the deflection of the feed roller, it is segmented so that it only acts on individual areas of the film web. These areas are preferably located at the edges of the film web or in the middle of the film web. Due to the segmentation of the roller, the effective length for the individual segments is significantly lower, so that the resulting deflection can be neglected.

The segments preferably have a size of % of the plastic film web, more preferably 1/6 of the plastic film web and more preferably 1/10 of the plastic film web. The optimal design does not exceed the width of the edge strip that will be separated later or the area in which the thickness of the plastic film deviates by more than 10% from the rest of the film.

In one embodiment, the system has electromagnetic feed rollers.

The deflection of the contact roller is caused by the introduction of force via, for example, pneumatically operated cylinders in the outer area of the journal. Since the diameter of the contact roller should be as small as possible in order to keep the distance between the process rollers as small as possible, the result is a slim, long roller body. This is prone to deflection, especially when the load is applied at a point.

The aim of the invention is not to introduce the force at specific points via cylinders, but rather to generate a surface force between the contact roller and the process roller with the aid of an electromagnetic field. The more favorable application of force minimizes the deflection of the contact roller and ensures even pressure. Due to the minimal deflection, the diameter of the adjacent roll can be made much smaller, so that the process rolls can be positioned geometrically closer together.

In one embodiment, the system has vacuum feed rollers.

The aim of the invention is not to introduce the force at specific points via cylinders, but with the help of a vacuum in the system roller, so that a surface force is generated between the contact roller and the process roller. The contact roller can be particularly advantageously coated with, for example, open-pored foam rubber. The more favorable application of force minimizes the deflection of the contact roller and ensures even pressure. Due to the minimal deflection, the diameter of the adjacent roll can be made much smaller, so that the process rolls can be positioned geometrically closer together. The negative pressure is below ambient pressure, typically in the range from 0 to 950 mbar, preferably in the range from 0 to 600 mbar, particularly preferably in the range from 0 to 100 mbar.

In one embodiment, the system has a roll mill/back-up roll

In order to prevent the rubberized feed roller from deflecting, it is possible to use one or more support rollers, which compensate for the deflection of the feed roller. Such designs are known, for example, from roller calenders. The advantage of this solution is that there is no need to introduce a camber of the rubberized contact roller. With the help of the solution, a uniform pressure across the lying width can be achieved, which has a positive effect on the force transmitted to the film and minimizes flatness errors.

The present invention can be combined particularly advantageously with a blown film line. Such a blown film plant is preferably fed with plastics in granulated form, which are then plasticized in extruders under high pressure to form a viscous mass. This mass is formed into a ring in a blow head and escapes from the blow head through an annular nozzle. As soon as it leaves the ring die, the mass already forms a film tube. The film tube is drawn upwards along a tube formation zone in which compressed air is introduced into the interior of the film tube. This leads to transverse stretching of the film tube. Cooling of the melt is achieved at a tolerable distance from the annular die by means of an active coolant for the ascending film tube. On its way up, the film tube, mostly in a semi-crystalline state, passes through a calibration basket and then a flattening process, which flattens the tube. The flattening unit feeds the double-layer film web to a pre-squeeze. The pre-squeezing usually consists of a pair of rollers, through whose roller gap - often called "nip" - the foil runs even after the pre-squeezing, there is a double-layer film web. The distance from the pre-squeezing to the squeezing is dimensioned in such a way that the film can give off heat originating from the extrusion process during transport between the two pairs of rollers. In this way, the film tube is additionally cooled, so that it can then be further processed.

Many systems work without a preliminary squeezing, but feed the film directly from the flattening to the squeezing. Even with such a system design, the rising film at the pair of squeezing rollers has already cooled down so much that a powerful attack on the surface of the film causes little or no damage. This is because the squeezing normally pulls the film upwards at a significantly higher speed than is extruded at the annular die. An example speed ratio is 10:1 to 20:1. Compressed air is applied to the blown film from the inside above the annular die as soon as the tubular shape is formed, and it is thus pulled in the transverse direction. At the same time, the pair of squeezing rollers pulls the film upwards at high speed so that longitudinal stretching occurs below the frost line.

Overall, therefore, the tubular film is stretched biaxially below the frost line. Depending on the planned application of the film end product, the proportion of longitudinal or transverse stretching can predominate. However, a blown film line always has to contend with the technical disadvantage that the optical film quality cannot keep up with the film quality of cast films. This is because the ascending tubular film cools relatively slowly. The longer the cooling process of the plastic melt lasts, the cloudier and less glossy the film surface becomes.

However, in order to be able to exert sufficient force on the rising film with the pair of squeeze rollers, the film must have cooled down relatively quickly. In view of the slow cooling rate of the extruded film, this leads to a high installation height in blown film lines. The double-layer film web is therefore deflected horizontally as quickly as possible above the pinch point, guided next to the system and from there downwards for the further treatment steps. There is usually a winder next to the system on the floor of the installation site, which winds the double-layer film web onto a roll for further transport.

Stretching devices are sometimes provided upstream of the winder, with “stretching/stretching” being understood as a generic term for “stretching” and “stretching” within the scope of the present patent application.

A "stretching" system stretches the film by more than 5%, at least in the longitudinal direction, preferably 50% and more, often up to 1,000%. Such systems are often referred to as "MDO", which stands for "machine direction orientation", i.e. for orienting the plastic molecules in the machine direction, i.e. the direction of transport of the material through the system.

As an alternative to an MDO, a so-called flatness package can be provided as a stretching device before the winder. This "stretches" the film irreversibly, usually between 0.5% and 5% in the machine direction, which only serves to compensate for differences in run length across the width of the double-layer film web and when the film web is running straight, so that the film can be wound up and processed more easily.

Both stretching devices, i.e. an MDO and a lay-flat pack, are technically very comparable in that they stretch the film lengthways. For this purpose, a faster-driven roller runs immediately after a first, slower roller or, for example, after further, passive rollers. The difference in speed between the two rollers, which can also be designed as pairs of squeezing rollers, which each transport the film with static friction, results in a change in the length of the film.

The distance between the two areas in which the film is transported at the peripheral speed of the respective roll is referred to as the "draw section", or in the projection on the machine direction as the "draw length".

In an approximately central section of the wrapping of the film web around a roller, the film web is transported with static friction, thus with the peripheral speed of the roller. The static friction ends even before the film web leaves the roller surface at a lifting point. This is particularly important when the following roller is running at a higher peripheral speed, i.e. the film web changes from static friction to faster sliding friction on the roller surface and only then lifts off the roller surface.

The same principle can also be observed when running onto a roller: The film web is already in contact with the surrounding surface of the roller from one point of contact, but the static friction only begins beyond the point of contact. "Points" are used here for simplicity. A film web lifts off a roller at a lifting line and runs onto a roller surface with a contact line. However, when viewed from the side, the two-dimensional film web is reduced by one dimension to a line, and reduced accordingly the lift-off line and the berth line each move by one dimension.

It should be pointed out that instead of a roller, a pair of squeezing rollers can generally just as well be used for transporting the film. For the sake of simplicity, the present application usually only speaks of one roller, but also means a pair of squeeze rollers as a means of exchange that is notorious in the art.

A pair of nip rollers can tend to provide a more secure gripping of the film because the film surfaces are gripped from both sides. However, a roller acting from one side can also exert a sufficient longitudinal force on the film, which depends, for example, on the surface design of the roller in conjunction with the film to be processed and, for example, on the angle of wrap of the roller. In any case, a pressure roller is usually provided with a simple driven roller in order to ensure more reliably that the film can actually be gripped by the driven roller securely, with the exclusion of slippage.

The film blowing process is suitable for the production of stretchable plastic films. These films are stretched monoaxially in the machine direction in stretching systems, resulting in films with a reduced film thickness. By stretching z. B. improved the following film properties: tensile strength, rigidity, transparency, barrier properties and / or machinability. These slides can be found e.g. B. Use in flexible packaging.

Film thickness profile control systems with segmented control zones are used in the production of tubular films. With these systems, the film thickness profile can be regulated in such a way that the thickness deviations over the entire circumference of the tube are as small as possible.

During longitudinal stretching in a stretching system, the film is stretched in the machine direction according to the degree of stretching, thereby reducing the film thickness. At the same time, the film constricts in the transverse direction, which reduces the width of the film. The consequence of this constriction is that the stretched film becomes increasingly slightly thicker from the center of the film towards the edges of the film, although it was previously regulated to a thickness which is as constant as possible in the blow molding process. This increase in thickness is particularly pronounced in the edge areas of the film. This causes edge build-up on the film roll when the film is subsequently wound up. The film web is stretched more and more at the edges with increasing winding diameter, which is important for further processing, e.g. B. printing or laminating is very disadvantageous.

Measures such as the smallest possible stretching gap, suitable roller coating, mechanical or electrostatic holding of the film edges, optimized temperature control or suitable selection of plastic materials can reduce constriction and thus edge build-up on the film roll. However, this is not sufficient for many subsequent processing steps. Only by trimming the film edges does the remaining film web have a sufficiently small deviation in the thickness profile, which is required for the subsequent winding of the film web and further processing. However, a large part of the film width is lost when trimming. Regardless of the foil width, approx. 200 mm are omitted on each foil side. In the context of the present patent application, a reversing device should not be understood as a “treatment roller section”.

A treatment roller section also preferably comprises only rollers, turning bars or other means for guiding or deflecting film are also conceivable.

In addition, reversing does not include active heating for the double-layer film web.

Such a blown film line preferably has an annular die for extruding a film tube, with a tube formation zone for transversely drawing the film tube, with a cooling agent for the ascending film tube, with a flattening for the film tube to form a double-layer film web and with a pair of take-off rollers above the cooling agent for longitudinally drawing the film tube, The blown film system is characterized in that a treatment roller section with a heating means for the double-layer film web is provided above the pair of take-off rollers.

The following is explained conceptually:

The "pair of take-off rollers" can - as already explained above - preferably be a simple pair of take-off rollers. However, it also falls under the aspect of the present invention if the pair of take-off rollers is preceded by a pair of pre-take-off rollers, with the deduction often also being referred to as a squeezing or squeezing unit.

In the case of such an arrangement with two pairs of rollers, the pair of take-off rollers that ultimately squeezes is usually above the pair of pre-take-off rollers.

A pair of take-off rollers differs in principle from the rollers or pairs of rollers underneath in that it guides the tube either completely flattened or almost completely flattened, i.e. as a double-layer film web. The pair of pull-off rollers grips the surface of the flattened film on both sides, also in order to reduce the possibility of compressed air being pushed through upwards from the interior of the film tube.

The diameter of a take-off roller is often around 300 mm, often with diameters between 200 mm and 400 mm or more. If pre-draw rollers are additionally provided, these are often of the same order of magnitude as the draw-off rollers. The "treatment roller line" is a designated transport path for the double-layer film web, within which the double-layer film web is to be subjected to mechanical treatment. In particular, irreversible stretching is intended, especially in the machine direction, i.e. viewed at the local level in the film longitudinal direction of transport.

At least two, three, four, five, six or more rollers (or pairs of squeezing rollers) are generally provided for a treatment roller train, these usually fulfilling at least two, three, four, five, six or more different functions within the treatment roller train. In particular, the following functions are considered: holding, heating, stretching, tempering, cooling, spreading, embossing or laminating.

A roller can perform several functions at the same time, such as holding and heating.

Normally, the goal is to keep the number of rollers as small as possible.

The "heating means" should be an active heating means, i.e. in particular provided with a heating coil through which current can flow, an infrared radiator, a laser emitter, a hot water flow line, an oil heater, generally a fuel-operated NEN heating with a circuit and / or a comparable active heating medium. A lot of heat is generated during extrusion. This is going up anyway. This and the fact that the film tube carries heat and transports it into the suit means that the system parts above the pair of take-off rollers are quite warm when the system is running. However, the heating means does not mean these passively heating components. Rather, an active heating means should actually be provided.

In most cases, such a heating means will be recognizable by the fact that it has a temperature sensor in addition to the actual heating, or that the heating means has a controller, in particular with a quasi-permanent or intermittent controller having a temperature hysteresis.

In this context, it should be pointed out that whenever a “regulation” is mentioned in the context of the present patent application, a technical “regulation” is meant, ie with a sensor for comparing the current values.

Alternatively or in addition to a temperature sensor on the heating means, a heating means can also be easily distinguished from an apparatus that has become hot during operation because the heating means can be used quickly to heat up the heating means relevant here even when the system is cold. The heating means can therefore be used for heating, which takes place faster than the heating of the plant components in the upper area of the plant would take place during operation of the plant.

Positioning “above” the pair of take-off rollers means, in a particularly preferred embodiment, such a design in which the treatment roller section is at least partly vertically directly above the pair of take-off rollers, with a projection onto a horizontal plane which runs through the pair of take-off rollers, i.e. at an overlap would lead to the projection of the pair of take-off rollers.

It can already be sufficient if a surrounding line around the treatment roller section can be projected in this way. It is therefore not necessary for one of the rollers of the processing roller line to be projected onto the horizontal with an overlap, with the latter representing a preferred embodiment.

It is considered to be particularly advantageous if at least one, two, three, four, five, six or more rollers of the processing roller line are located parallel to the axis in space to the take-off rollers.

As already mentioned, each individual roller can be replaced by a pair of squeeze rollers

Alternatively and cumulatively, the rollers of the treatment roller line can be of the same order of magnitude as the pair of take-off rollers, for example with diameters between 200 mm and 400 mm or more, preferably between 250 mm and 300 mm, and also much smaller than the pair of take-off rollers, for example with diameters between 100 mm and 200 mm or less.

A particularly compact arrangement results when at least one roller of the treatment roller line, preferably two, three, four, five, six or more rollers of the treatment roller line, can be projected in the horizontal plane overlapping at least half onto one or both of the take-off rollers or to let. In such an embodiment, the rollers of the treatment roller line are quite compact above the take-off rollers. Alternatively and cumulatively, it is advantageous if the rollers of the treatment roller section also overlap one another at least half when projected onto the horizontal.

It goes without saying that a greater than half overlap can be even more advantageous with a suitable design.

Not quite as compact in construction, but still within the expanded scope of the invention, would be a somewhat different geometric relationship in which the aforementioned projections do not directly lead to an overlap with the draw-off rollers. Rather, a circular environment is intended around the pair of take-off rollers. The surrounding forms a horizontal, circular surface. If the vertical projection of one, several or even all rollers of the treatment roller line falls into this area, in part or even completely, a very compact plant shape is still achieved. In simple terms, the rollers of the treatment roller section are not necessarily exactly vertically above the pair of take-off rollers, but in the immediate vicinity.

In a broader sense, the "above" can also be realized if the treatment roller section is provided laterally next to the pair of take-off rollers or the upper area of the blown film line, but is arranged geodetically with at least one roller of the treatment roller line higher than the pair of take-off rollers, preferably with several or even all rolls of the processing roll section.

The blown film line to be combined preferably has an arrangement of the treatment roller section above the pair of take-off rollers with a heating means for the double-layer film web which can be used to heat the film above a temperature that the film has after passing through the take-off rollers. It has already been explained that the film must have cooled down in order to safely run through the pair of take-off rollers because forces are exerted on the film there. It must therefore have been cooled below a temperature at which there is dimensional stability in order not to damage the film.

However, for further mechanical processing of the film, in particular in the form of stretching by means of tensile force, it can be advantageous if the film is heated. For example, an MDO heats the film using a powerful heating roller before it is mechanically longitudinally stretched.

In a blown film line of the type described, the film loses temperature on the way from the upper area of the blown film line to the winder. As a result, the warm-up for the mechanical intervention must then be quite strong.

In a blown film system of the type described, the first heat is present, i.e. the film has cooled just enough for it to be gripped by the pair of take-off rollers - the other way around, it is still relatively warm, so it does not have to be heated up so much. She suggests providing the heating means above the pair of take-off rollers, because there the heating means does not have to reheat as much as would be necessary at other positions in the system. For any type of mechanical processing that requires heat, this arrangement leads to a significant energy saving.

The present invention can be combined particularly advantageously with a blown film system which has a ring die for extruding a film tube, with a tube formation zone for transversely drawing the film tube, with a coolant tel for the ascending film tube, with a flattening for the film tube to form a double-layer film web and with a pair of take-off rollers above the coolant for longitudinally drawing the film tube, the blown film system being characterized in that above the pair of take-off rollers a transversely aligned treatment roller section is provided below a reversing device for the double-layer film web .

It should be explained conceptually that a "transverse" orientation should exist when the double-layer film web runs more horizontally than vertically. In particular, a double-layer film web that runs horizontally at least in the west is thought of. In view of the course of the film web around rollers or turning bars, the course can be defined by the actual running of the film and/or by the position of the axes of rotation of two rollers or turning bars in relation to one another.

In particular, it should be borne in mind that the connecting paths between two, three, four, five, six or more reels, either without exception or with exceptions lying between them, are horizontal rather than vertical.

Particularly preferably, two, three, four, five, very or more rollers should be arranged horizontally to one another.

It is indeed already known from US Pat. No. 6,413,346 B1 to provide a treatment roller section with a plurality of pairs of rollers and intermediate stretching sections running transversely to the vertical direction of extrusion. However, the pairs of rollers there lie exactly horizontally to the side of the pair of take-off rollers and then lead further down to a winder. A turning bar unit is not disclosed in the publication. It therefore makes sense to guide the film web across to the side there, because it ultimately has to be guided down afterwards.

If the document contained a reversing device above the pair of take-off rollers, then the film would have to arrive again above the take-off after the treatment roller section. So far, this thought has prevented the system designers from guiding the film web transversely on the - in any case very short - piece between the take-off and reversing, let alone guiding it horizontally. This is because every section by which the film web is guided laterally there, it must then be guided back again, which necessitates a number of rollers.

The blown film line to be combined can have a larger number of rollers and/or turner bars in a treatment roller section. However, a blown film line with a reversing unit is significantly lower if the several rollers of the processing roller line between the draw-off and the reversing unit are arranged as horizontally as possible. With the lower overall height, a lower hall height is also necessary, so that considerable costs can be saved.

The blown film line to be combined is preferably designed in such a way that the film produced in the blown film line can be stretched monoaxially in the machine direction after flattening in a stretching line, so that the final film has a thickness profile with the smallest possible increase in thickness from the center of the film to the edges of the film - namely with first heat stretching of the film.

In a method for controlling the film thickness of the type described above, this is achieved in that the film thickness profile of the tubular film produced in the blown film plant is controlled in such a way that the stretching produces a film with a transverse thickness profile with the smallest possible deviations from the average film thickness over the entire film width will be produced. Film thickness profile control systems with segmented control zones are usually used in the production of these tubular films. For this purpose, a measuring device is arranged after the film blowing head, which records the actual thickness profile over the circumference of the tubular film. The actual profile is then compared with the target profile, and in the event of deviations, defined control interventions are made in the film blowing process. The thickness profile is influenced via the segmented control zones, e.g. B. by air temperature control or air volume control.

After cooling, the tubular film is laid flat in a take-off device and guided over a turning take-off. The turning take-off has the task of improving the roll quality of the wound-up foils by shifting the thickness profile, which is stationary relative to the foil blowing head, across the width of the flattened foil. By shifting the thick and thin points across the width of the roll, windings are created without defects, the so-called piston rings.

The flattened tube is now fed to the stretching system and monoaxially stretched in the machine direction and then wound up into a coil.

The measuring device for recording the actual thickness profile in the film blowing process can, as already described, be arranged between the film blowing head and the take-off, or also between the take-off and the stretching system.

The blown film line to be combined can preferably include regulation of the film thickness, so that the tubular films can be stretched not only in the blocked or flattened state, but also as flat films. To do this, they are either cut open on one side or in the middle and unfolded. It is also possible to cut open the tubular film on both sides in order to stretch two webs of the same width in a stretching system and then wind them up.

Since the film constricts during stretching and thick spots appear at the edge areas of the film, the specified target value of the peripheral profile in the film blowing process is not constant, but is set in such a way that after monoaxial stretching in the machine direction, a film with a thickness profile with as few deviations as possible is produced due to thickness deviations during stretching across the entire width of the film. For example, in the film blowing process, a tubular film is produced that has two opposing thin areas. The tubular film is then laid flat in such a way that the thin areas form the film edge regions and the stretched film then has a thickness profile with the smallest possible deviations from the average film thickness. The same applies to tubular films that are cut open on both sides. In the case of a tubular film that is cut open on one side, a tubular film with only one thin area is produced in the film blowing process. The tubular film is cut open in the middle of this point in order to divide the thin area into the film edge areas on the left and right after cutting open, so that a film with a thickness profile with only minor deviations is produced after stretching.

After the extrusion and cooling unit, the film is fed into the reversing flattening unit, where it is laid over the turning bars and deflection rollers of the turning take-off in such a way that it always hits the stationary horizontal deflection roller after the take-off, where it is deflected vertically downwards to the stretching system . This reversing movement continuously shifts the current thickness profile, which means that the specified thin areas in the film that is produced in the stationary extrusion area of the system must follow the reversing movement of the turning take-off so that the film has the required target thickness profile, i.e. with the thinner foil edges, the Stretching system is supplied. This is done by superimposing an offset on the segmented control zones of the film profile control, which takes into account the angular offset caused by the rotating take-off and follows the rotation of the turner bar.

One or more peripheral points of the tubular film laid flat in the hood are therefore assigned to one or more segmented control zones. The control algorithm ensures that only the thin areas in the target profile reverse parallel to the turning deduction.

For the control system, a measuring device for measuring the actual thickness profile across the width of the flat, stretched film is arranged downstream of the stretching system, i.e. beyond the stretching gap in the machine direction. This is preferably still installed in the area of the stretching system, above all still within the treatment roller section. The specified target thickness profile for the film blowing process is calculated using an algorithm from the transverse thickness profile measured after the stretching system and is continuously corrected uniform winding diameters are to be produced. At the same time, this means that the width of the film strips, which are cut away on both sides when the film is trimmed, is significantly reduced.

In addition, the film thickness over the winding width can be summed up in the measuring device - the so-called roll profile - which results in the possibility of overlaying the target thickness profile with values of the actual roll profile in order to detect even the smallest thickness deviations, which are always in the same area of the finished Foil occur to be eliminated, since they can only be determined after a longer period of time when they show up as a result of changes in the roll diameter.

The regulation for controlling the individual control zones can be calculated from a superimposition of the thickness profiles mentioned below using an algorithm. These segmented control zones can be integrated in the blow head, in a stationary or rotating cooling ring or in a downstream thickness control unit that moves synchronously with the turning haul-off.

The thickness profiles are:

- the basic profile, which captures the actual thickness profile on the circumference of the tubular film between the blow head and the stretching system;

- the stretching profile, which covers the entire film width after the stretching system, it takes into account the angular offset due to the reversing turning take-off and the compensation of the thickness of the film edge area during stretching;

- the roll profile, which represents a sum of the measured stretching profiles with a corresponding evaluation (summary thickness profile, which takes the roll quality into account).

- This represents a cascaded control since the following control circuits are superimposed:

- Regulation of the film thickness via the tubular film circumference during the film blowing process;

- regulation of the film thickness over the film width of the stretched film-; Regulation of the winding diameter via the winding width.

The target thickness profile can also be entered manually into the control system, but it then has to be continuously adjusted to the rotation of the turner bars.

The process for controlling the film thickness can also be used in systems where no reversing device is installed. The treatment roller section can have a temperature control which allows the heating means to heat the double-layer film web at the entrance to the treatment roller section by less than 80 K, preferably by less than 30 K.

It is irrelevant whether the controller picks up the current temperature on the double-layer film web, for example, or on the roller surface if a heated roller is used. In practice, a variant is preferred in which the temperature of a fluid return from the roll is measured.

Theoretically, the control can even do without a temperature sensor, because with a given temperature profile of the melt at the blow head and rising to the take-off, the temperature at which the double-layer film web enters the treatment roller section is known relatively precisely.

The highlight of the heating means in the treatment roller section is that it provides heating that is only slightly above the incoming temperature of the double-layer film web.

In general, it should be pointed out that the temperature data given in the context of the present patent application are to be understood as technical mean temperatures. In practice, the temperatures fluctuate over the length of a roller, i.e. over the width of the film web, usually by 1 to 4 K.

This allows the energy balance of the blown film system to be optimised: The cooling of the film tube that is pulled upwards is adjusted so that it is just sufficiently cool when it reaches the calibration basket and at the draw-off rollers; It then passes through the mechanically critical point on the draw-off roller and only needs to be heated to a very small extent afterwards in order to be easily stretchable.

For example, polypropylene can be used for the films. In the endothermic process, i.e. during melting and blowing out, melting occurs at around 160 °C to 168 °C. On the other hand, while the film is rising, i.e. while it is cooling down, crystallization occurs at around 115 °C to 135 °C. Below these temperatures, the double-layer film web can be reliably squeezed off the pair of take-off rollers and thus pulled. After the pair of take-off rollers, a heating of, for example, 10 K to 50 K is sufficient in order not to bring the film back to the melting point, but still to stretch the film web reliably.

For example, it is also assumed that the room air temperature TU at the installation site of a blown film line is around 30 °C. In conventional systems, the film web then reaches the stretching device at around 30 °C, usually at a slightly higher temperature. Because of the strong air movement on the surface of the film web - as a result of the fast forward movement of the film web - a rapid drop in temperature of the film web can generally be observed as soon as the film web is continued laterally after it has passed through the hood. This is because the double-layer film web usually has a temperature of between around 60 °C and around 80 °C at the trigger.

Temperatures of around 80 °C are usually sufficient for the planned stretching process with a flat package. Temperatures of around 85 °C are usually sufficient for a pre-stretch process of an MDO. And for stretching as part of an MDO, temperatures of 100 °C to 105 °C for polyethylene, 130 °C to 140 °C for polypropylene and around 70 °C for polyamide should prevail in the film web. Depending on the application, heating by just a few K is sufficient immediately after the extraction, or even simply maintaining the temperature, which is also made possible by a heating means. In a particularly preferred embodiment, the treatment roller line has a heating roller for heating the double-layer film web for easier treatment within the treatment roller line.

A heating roller is a roller which is in mechanical contact with the double-layer film web as soon as the blown film line is in operation. The double-layer film web is in contact with the heating roller along a predetermined section of the roller surface, given by the angle of wrap. During this contact phase in particular, there is a good flow of heat from the heating roller to the film.

The heating roller itself is preferably designed as an active heating means in its interior, for example as close as possible to the surface.

A heating station for the double-layer film web can also be designed with something other than a heating roller, for example with a heating section with radiant heaters.

An analogous idea can also be applied to all of the following types of "rollers", which are each only to be understood as - albeit preferred - examples for "stations".

The heating station, that is to say primarily the heating roller, preferably has a temperature meter so that it can be adjusted within a fixed, definable temperature interval. This temperature interval should be adjustable in such a way that the resulting temperature of the running double-layer film web is less than 80 K, preferably less than 30 K or 20 K, above that of the incoming double-layer film web.

The blown film line that can be combined particularly advantageously is illustrated below using three examples:

In the case of a flat package in the treatment film section, the inlet temperature of the double-layer film web can be 60° C., ie a normal temperature at the pair of take-off rollers. If a temperature of 80 °C is desired for stretching within the flatness package, then the heating station should only heat the double-layer film web by around 20 K. Compared to a conventional system, in which the double-layer film web is first stretched, for example on the hall floor, i.e. with an inlet temperature to the flattened pack of around 30 °C, which requires post-heating of around 50 K, the amount of energy for post-heating of 30 K is now saved.

It is suggested that the temperature of the double-layer film web has increased by between plus 5 K and plus 80 K as it exits the heating roller; Preferred values are between plus 5 K and plus 20 K for a flat pack, especially with a discharge temperature of around 80 °C; plus 5 K to plus 25 K for pre-stretching, especially with around 85 °C in the outflow.

It is proposed that the treatment roller section has a stretching section for stretching the double-layer film web longitudinally.

It has already been explained above that a stretching section is structurally implemented by initially providing a holding roller or other holding means in the machine direction, whereupon the stretching section has a stretching roller on its side downstream from the machine direction, or, as explained above, a pair of stretching rollers, for faster transport of the Double-layer film web than at the nip roll.

For example, if the diameters of a holding roller and a stretching roller are of the same size, a higher rotational speed can be set on the stretching roller and a lower rotational speed can be set on the holding roller. In both cases, it is about the amount of peripheral speed. Depending on how the film is handled a stretching section can be achieved with rollers running in the same direction as well as with rollers running in opposite directions. If the film crosses the direct connection of the two roller axes within the stretching section, then the rollers should run in opposite directions, otherwise in the same sense of rotation.

A "stretch" ratio within the stretch section is preferably 1:2 to 1:4, more preferably 1:2 for pre-stretch film for agricultural use. Generally, a stretch ratio in the stretch section is from 1:2 to 1:10 than advantageous to look at, but in particular the first-mentioned framework from 1:2 to 1:4.

A "stretch" ratio within the stretch section is greater than 1:1, but preferably only to about 1:1.05.

The holding roller can preferably assume two functions, that is, for example, be embodied by a heating roller or embody a heating station in some other way.

In general, it should be pointed out that in the context of the present patent application, the indefinite numerals "a", "two" etc. should not be understood as "exactly", "exactly two" etc., but normally as indefinite articles. A statement of the type "one ...", "two ..." etc. is therefore to be understood as "at least one ...", "at least two ..." etc., unless it is clear from the respective context that that only "exactly one", "exactly two" etc. are meant.

In a particularly far-reaching idea, even the take-off roller or the pair of take-off rollers, ideally in the form of a pair of squeezing rollers, can represent the heating means and possibly even serve as a holding roller at the same time. As a rule, however, this will lead to a deteriorated embodiment, because a heated take-off roller always harbors the risk of heating the film too much during the mechanical action of the take-off and thereby damaging it in an uncontrolled manner. Ultimately, of course, the pair of take-off rollers also acts indirectly as a holding mechanism for the treatment roller section, because it specifies a specific, very narrow speed range. Nevertheless, for the reasons described above, it is preferred if at least one roller, which transports slowly compared to the stretching roller, is provided as a holding roller between the pair of take-off rollers and the stretching roller, which transports much faster.

The stretched section or the stretched length as such can ideally have a length of at most 120 cm, in particular a length of at most 50 cm or 15 cm, in particular at most 10 cm or 5 cm.

Tests by the inventors have shown that the shortest possible stretching section is advantageous in order to keep transverse constriction of the double-layer film web as small as possible. On the other hand, threading the double-layer film web when starting up the plant is made considerably easier if there is a clearance of at least 5 cm, preferably at least 10 cm, between the rollers of the processing roller section. The beginning of the film can then be threaded more easily between the rollers.

It is considered preferable if at least one of the rollers forming the treatment roller line can be moved or pivoted out of position to facilitate threading. This principle can be adopted from US Pat. No. 4,086,045 without any inventive step.

It is proposed that the treatment roller section after the stretching section has an annealing roller or a pair of annealing rollers or a differently designed annealing station for relaxing the double-layer film web after stretching. It has been shown that a memory effect of the film stretched in the machine direction in the stretching section can be significantly reduced if the stretching section is followed by a second active heating device, in particular in the form of a tempering station with a tempering roller.

The first annealing roll can also be represented by the stretching roll and/or one or more separate annealing rolls can be provided.

In the annealing section, the double-layer film web should assume a temperature of between minus 5 K and up to plus 30 K, preferably between plus/minus 0 K and plus 20 K, in each case compared to the temperature of the double-layer film web in the region of stretching. The stretching roller is particularly preferably designed as a first tempering roller, which can be followed by a first or even a second further tempering roller. A number of tempering rollers preferably have the same temperature regulation, ie they are regulated in such a way that they give the double-layer film web the same temperature as it runs off. In practice, this is easily set, for example—while accepting deviations—by means of a return flow of heating fluid that is set to the same temperature.

There is no deviation from the idea of "the same temperature regulation" if successive rollers give the double-layer film web slightly different temperatures, in particular within a range of plus/minus 5 K or plus/minus 10 K.

It may be desirable to purposefully generate an ascending or descending temperature cascade in the double-layer film web by means of the heating and/or tempering rollers.

In general, each station, that is to say in particular the heating station, tempering station and cooling station, can have a plurality of rollers through which the double-layer film web can pass in succession. This makes it easier to adjust the film temperature to the desired values.

Finally, it is proposed that the treatment roller section has a cooling station for the double-layer film web, in particular a cooling roller, primarily with an active coolant.

In the temperature cascade mentioned above, it is proposed that the cooling station imposes a temperature jump on the double-layer film web between minus 5 K and minus 80 K, in particular between minus 10 K and minus 20 K, in particular to about 60 °C and/or about to room temperature and/or up to about 40°C to 60°C. Any existing reversal runs reliably even at film temperatures of around 60 °C.

A chill roll can already be regarded as a chill roll if it has no active heating means. However, it preferably has an active coolant.

In particular, a chill roll can have an explicit heat dissipation means, for example a water circuit or another fluid circuit for a coolant, which is fed into the chill roll and out of the chill roll again by means of a line.

In a preferred embodiment, a heat exchanger, an electrically driven fluid pump and/or a cold pump are integrated into the circuit and connected to the cooling roll.

The treatment roller section can advantageously have a control for improving flatness, with the double-layer film web being stretched longitudinally by 0.5% to 5%. Alternatively, the treatment roller section can have a regulation for a stretching, namely with a longitudinal stretching of the double-layer film web by more than 5%, preferably by more than 100%, or by more than 500%. Data on a possible configuration for stretching, i.e. as MDO, has already been given above, with a stretching ratio within the stretching section of ideally from 1:2 to 1:10, and/or with a stretching ratio from the nip roll to the chill roll of ideally 1 :2 to 1:4.

Possible jumps in temperature between the discharge temperatures of the double-layer film web from the rollers or other stations within the processing roller section have already been explained above.

Irrespective of the additional boundary conditions mentioned above, it is proposed that the treatment roller section has a heating roller for the double-layer film web with a temperature level of plus/minus 0 K or from plus 1 K to plus 80 K or more in the case of high-speed double-layer film webs, in particular polypropylene, in particular compared with the previous station in the machine direction and/or the roll temperature of the take-off roll.

Alternatively and cumulatively, it is proposed that the treatment roller line has a stretching roller for the double-layer film web with a temperature level of minus 10 K, preferably plus 5 K, to plus 30 K, or of plus 50 K or more in the case of high-speed double-layer film webs, compared to the in machine direction previous station.

Alternatively and cumulatively, it is proposed that the treatment roller line has a tempering roller for the double-layer film web with a temperature level of minus 10 K, preferably plus 5 K, to plus 30 K, or of plus 50 K or more in the case of high-speed double-layer film webs, compared to the in machine direction previous station.

Alternatively or cumulatively, it is proposed that the treatment roller line has a cooling roller for the double-layer film web with a temperature level of minus 10 K to minus 80 K, or minus 100 K in the case of high-speed double-layer film webs, compared to the previous station in the machine direction.

In order to have the entire system built as flat as possible, especially if a reversing unit is arranged above, it is proposed that the treatment roller line has two transversely aligned sections in the course of the double-layer film web, preferably three transversely aligned sections, in particular each spanning a vertical direction of rise above the pair of take-off rollers.

With regard to a "transverse" orientation, it has already been explained above that this should already be present when, when viewed from the side of the rollers, i.e. parallel to the axis of rotation of the rollers, the direct connection between two consecutive rollers is more horizontal than vertical , ie a maximum of 45° to the horizontal, preferably a maximum of 30°, particularly preferably a maximum of 15°, 10° or 5°.

Decisive for the overall height is not so much the running of the film as the arrangement of the individual rollers. Depending on the given arrangement of the rollers, the foil can be designed to run around on one side or the other, but due to its practically negligible thickness it does not take up any real height. It can even be advantageous if the film in the transversely arranged sections is less horizontal than the connection between the two axis rollers. The feature described above, that a section spans a vertical direction of rise above the pair of take-off rollers, is to be understood in such a way that the film travel path provided between the two successive rollers crosses that virtual, vertically arranged plane which is located above the nip of the pair of take-off rollers.

With such a design, rollers are arranged on both sides of the plane that rises vertically above the pair of take-off rollers, with the film running across the sides, preferably running back and forth, so that a very long film running distance is achieved for the treatment roller section, but at the same time the overall height is kept low becomes.

A preferred embodiment of the invention provides that the treatment roller section has three equally transversely aligned partial sections, in particular spanning a vertical direction of rise above the pair of take-off rollers only once.

In such an embodiment, for example, four rollers are arranged at least essentially in one line, namely in a line lying transversely to the direction of ascent, preferably almost or exactly horizontally.

For threading, the treatment roller section can have a threading aid with a displaceable or pivotable roller. This has already been explained.

The blown film line that is preferably to be combined also preferably has a method for producing a blown film web in a blown film line, especially in a blown film line as described above, with the steps

- Extruding a film tube;

- inflating the film tube on a tube formation zone for transverse drawing of the film tube;

- Cooling the ascending film tube with a coolant;

- Flattening the film tube to form a double-layer film web with a flattening;

- Taking off the double-layer film web with a pair of take-off rollers while pulling the film tube lengthwise; the method being characterized by the further steps

- Leading the double-layer film web above the pair of take-off rollers further upwards and through a treatment roller section with a heating means in order to heat the double-layer film web; and

- Treating the double-layer film web in the treatment roller line, in particular stretching the double-layer film web in a stretching section of the treatment roller line.

It has already been explained above that these treatment steps are of great advantage. The fact that the film in the form of the double-layer film web is guided further upwards above the take-off rollers eliminates the need for a long web guide, which avoids energy-consuming further cooling of the film after the pair of take-off rollers.

The film can thus be brought to a temperature level that is easier to process from the first heat with only a little additional energy and then, for example, stretched, in particular stretched or stretched, or treated in some other way, for example the surface can be treated and/or the film can be embossed, and/or components can be attached or inserted, such as active or passive resonant circuits, often referred to as RFID chips, and/or the foil can be irradiated and/or the foil can be laminated and/or corona treatment of the surface can be done be carried out and / or the film can be embossed and / or an adhesive can be applied and / or a lubricant can be applied and / or an anti-fog coating can be applied and / or it can be a targeted annealing of the Double-layer film web to support the migration of aggregates are carried out when aggregates are to migrate to the film surface to act there, so that a downstream tempering or storage can be omitted, with the migration essentially being a function of the temperature.

And/or the shrinkage values of the film can be specifically influenced. By annealing for a sufficiently long time, the shrinkage after stretching can be reduced, up to the point of producing a so-called "dead film" without shrinkage. Alternatively, an increase in shrinkage values, in particular the shrinkage values in the machine direction, can be achieved by targeted "freezing" of stresses.

And/or there is a targeted adjustment of the tendency to curl up to the point of avoiding the tendency to curl in the case of asymmetrical film structures.

The method described here and the blown film system described here can advantageously be used in a targeted manner for the above applications.

To thread the double-layer film web when starting up the blown film line, one or more rollers of the processing roller line can be moved or swiveled from their working position and the double-layer film web can be tensioned after threading by means of a backwards movement or backwards swivelling.

Both the system and the process have a noticeable and comprehensible effect on the finished film: because it leads to a particularly homogeneous biaxially stretched film if the molecules from the first heat are immediately reheated and then stretched instead of first allowing them to cool.

Once the film has cooled down, it naturally has to be heated very quickly to the desired high temperature range in order to be able to operate the blown film line economically, which will lead to the film properties described, which cannot be predicted uniformly.

The quality of the film product produced with the proposed method is therefore also demonstrably advantageous in the film, provided the parameters in the blown film production are suitably set according to the present invention.

The invention is explained in more detail below using six exemplary embodiments with reference to the drawing. show there

1 shows a first variant of a treatment roller section with five rollers and a reversing device arranged above it, schematically in a vertical sectional plane perpendicular to a pair of take-off rollers,

FIG. 2 shows a second variant of a treatment roller section with five rollers and a reversing unit arranged above it in a view otherwise unchanged from FIG.

3 shows a third variant of a treatment roller section with five rollers and a reversing unit arranged above, in a view otherwise unchanged from FIG. FIG. 4 shows a diagram of a fourth variant of a treatment roller section with five rollers and a reversing device arranged above it in a vertical sectional plane through a pair of take-off rollers, with a lower overall height, in particular as an embodiment for an MDO unit,

Figure 5 shows a schematic diagram of a fifth variant of a treatment roller train with four rollers and a reversing unit arranged above it in a vertical sectional plane through a pair of take-off rollers, in particular as an embodiment for a flat pack, and Figure 6 shows a highly schematic representation of a possible sixth variant for a treatment roller train with the lowest possible overall height,

FIG. 7 shows a diagram of the development of the longitudinal tensile stress o over a longitudinal expansion E of a plastic film,

FIG. 8 shows a schematic diagram of a sixth variant of a treatment roller section with five rollers and a reversing unit arranged above it in a vertical sectional plane through a pair of take-off rollers,

FIG. 9 shows a seventh variant of a treatment roller line with six rollers for four treatment stations and with a reversing unit arranged above, schematically in a vertical sectional plane through a pair of take-off rollers,

10 is a highly schematic representation of a blown film line from the prior art, like FIGS. 11 to 13 from EP 2 277 681 A1, with a downstream stretching line in which the method there for controlling the film thickness is used; FIG. 11 is a plan view of the blown film line from figure 10,

FIG. 12 shows an example of the actual thickness profile of a film tube with two thin areas and

FIG. 13 shows an example of the actual thickness profile of a film tube with a thin area.

The blown film line 1 (shown only in the upper area) in Figure 1 consists essentially of an extruder, a blow head with an annular slot die, a riser section arranged above it for an extruded film tube, a calibration basket, a flattening and a pair of take-off rollers 2 above the flattening, with one the position of the first take-off roller 3 can be finely adjusted by a first holder 4 , while a second take-off roller 5 is mounted on a plain bearing holder 7 so that it can be displaced horizontally by an adjusting cylinder 6 . The adjustment cylinder 6 can thus move the second take-off roller 5 horizontally towards the first take-off roller 3 and away from it.

A treatment roller section 8 is provided above the pair of take-off rollers 2 . There are a total of five rollers, namely a first roller 9, a second roller 10, a third roller 11, a fourth roller 12 and a fifth roller 13.

The five rollers of the treatment roller line 8 are arranged alternately on different sides of a virtual plane 14 which is parallel to the central axes 15 (marked as an example) of the two take-off rollers and runs vertically through the nip between the two take-off rollers. The virtual plane contains the area that the flattened film would pass through if the flattened film, coming out of the nip of the take-off rollers, simply rose vertically upwards. In the vertical section perpendicular to the central axes 15, the virtual plane 14 is therefore represented as a vertically running line, namely following the vertical direction of rise of the film and beginning at the nip of the pair of take-off rollers. The first roller 9, the third roller 11 and the fifth roller 13 lie on a first side 16 of the virtual plane 14; the second roller 10 and the fourth roller 12, on the other hand, lie on an opposite second side 17 of the virtual plane 14.

At the same time, all five rollers of the treatment roller section 8 are placed so close together vertically that when the rollers are projected horizontally onto the virtual plane 14, the first roller 9 overlaps with the second roller 10, and the second roller 10 overlaps with the third roller 11, the third roll 11 with the fourth roll 12 and the fourth roll 12 with the fifth roll 13, each at about one third of the total diameter size of the five rolls.

The first four rollers 9, 10, 11, 12 of the treatment roller section 8 are made the same size, while the two take-off rollers 3, 5 of the take-off roller pair 2 and the fifth roller 13 are made larger.

Distances 18 (marked as an example) between the five rollers of the treatment roller section 8 are at least 50 mm.

The first roller 9 is provided with a speed control, so that its surface speed can be adjusted quite precisely to a predetermined level during rotation.

The second roller 10 is provided with a drive and a controller, which can adjust the second roller 10 to a significantly higher peripheral speed than the first roller 9.

The third and fourth rollers 11, 12 can be driven, for example at the same speed as the second roller 10 or preferably slower than the second roller 10.

The fifth roller 13 can also be driven, for example at least essentially at the same speed as the fourth roller 12 or preferably slower than the fourth roller 12.

It should be noted that it can be advantageous to slow down after a stretch in order to relieve stress in the film.

The first roller 9 is also equipped with an active heating means and a temperature sensor (both not shown), namely a pipe guide for a heating fluid with a thermally conductive connection to the surface of the first roller 9, while the temperature sensor either via a non-contact measurement of the surface temperature of the first roller 9 and/or the running double-layer film web.

The temperature sensor is preferably arranged in a return flow of the heating fluid, so that it can be assumed, at the expense of a certain inaccuracy, that the film will run off somewhat cooler than the return flow temperature of the heating fluid.

Ideally, the run-off temperature of a double-layer film web is exactly the same as the temperature of the roll surface. In practice, on the other hand, the film running off will usually be a little warmer or cooler, depending on whether it was cooled or heated by the roller.

In a particularly precise embodiment, the person skilled in the art can measure the run-off temperatures of the film from the individual rollers, for example without contact using an infrared sensor, and adjust the roller temperatures based on the actual film temperatures.

The second roller 10, the third roller 11 and the fourth roller 12 can also each be equipped independently of one another with such an active heating means. In any case, one roller, here the fifth roller 13, is equipped with a temperature measurement and an active coolant.

Two non-driven deflection rollers 19 (marked as an example) are arranged above the treatment roller section 8 on the way to a reversing unit 20 arranged above the take-off roller pair 2 and the treatment roller section 8, with the deflection rollers 19 and the reversing unit 20 being sufficiently known from the prior art and therefore not to be explained further here.

Both the two take-off rollers 3, 5 of the pair of take-off rollers 2 and the five treatment rollers of the treatment roller line 8 and finally also the deflection rollers 19 are mounted on a machine frame 21 at their end faces.

Two temperature control devices 22 (marked as examples) are provided on the side of the machine frame 21 . The temperature-controlled rollers of the treatment roller section 8 are connected to the temperature control devices 22 via coolant lines or heating medium lines, preferably also via temperature sensor data lines (not shown). Electronic microcontrollers (not shown) are provided in the temperature control devices 22 or at least with access to the temperature control devices 22 and can carry out the set regulation of the temperature of the temperature-controlled rollers using the fluid return.

During operation of the blown film system 1, a film tube (not shown) is extruded from the extruder (not shown) through the annular slit die (not shown). The film tube is pulled up along the blown film line 1, through the calibration basket (not shown) and the flattening (not shown). At the end of the flattening process, the tubular film is largely flattened and enters the pair of take-off rollers 2 in this form. From there, a double-layer film web 23 is mentioned.

The double-layer film web 23 can optionally be guided in a straight ascent direction above the pair of take-off rollers 2, congruent with the virtual plane 14, between the rollers 9, 10, 11, 12, 13 of the treatment roller section 8 and immediately onto the deflection rollers 19 and from there to the Reversing unit 20 are performed.

In this case, the blown film line 1 corresponds to a conventional blown film line. The reversing unit rotates during operation of the blown film system 1 and thus produces a film roll to be wound up as evenly as possible on a roll (not shown) on the floor of the installation area (not shown).

In an alternative - and here preferred - film guide path, however, the double-layer film web 23 runs around the five rollers 9, 10, 11, 12, 13 of the treatment roller section 8, whereby due to the geometry of the rollers to each other at least on the second roller 10, the third Roller 11 and the fourth roller 12 results in a wrap angle of more than 180 °. The angle of wrap of the first roller 9 depends in particular on the positioning height of the first roller 9 in relation to the pair of take-off rollers 2, as well as on the diameters of the three rollers and also on the distance between the first roller 9 and the virtual plane 14. In the arrangement selected here, the angle of wrap is at the first roll 9 approximately 170°.

The same applies to the fifth roller 13, with the positioning in relation to the virtual plane 14, to the first deflection roller 19 and the diameter between the fifth roller 13 and the first deflection roller 19 being particularly relevant here. In the configuration described, the double-layer film web 23 then runs in the extrusion direction, i.e. in the machine direction, upwards through the pair of take-off rollers 2 and from there is initially clockwise (all information on the clockwise or counterclockwise direction refers to the sectional plane view of the figures) around the first roller 9 led around. The first roller 9 serves as a holding roller. At the same time, a first of a total of three heating or coolant circuits within the treatment roller section 8 flows through the first roller 9, namely a heating circuit.

In a configuration of the first variant of the blown film system 1 in FIG. 1, the double-layer film web 23 can come from the pair of take-off rollers 2 with a film inlet temperature of approximately 60° C. to approximately 80° C., for example.

The first roller 9 is adjusted in such a way that its circumferential speed is the same as that of the double-layer film web 23 in the pair of take-off rollers 2 . In the distance between the pair of take-off rollers 2 and the first roller 9, the double-layer film web 23 is therefore not subjected to any mechanical influence.

Due to the high angle of wrap of the double-layer film web 23 around the first roller 9, the double-layer film web 23 runs on the first roller 9 with static friction, i.e. at exactly the same speed as the roller surface specifies, even if the static friction is not present over the entire angle of wrap.

The first temperature circuit, i.e. the heating circuit, which runs through the first roller 9 in its function as a holding roller, is set, for example, to a temperature difference in the film of between plus 5 K and plus 10 K, based on the film temperature when it exits the previous one first take-off roller 3. The double-layer film web 23 is thus when rotating the first roller 9 by about 5 K to

10 K heated. Even this small temperature difference is sufficient to significantly increase the processability of the double-layer film web 23, because the blown film system 1 is set (below the area shown in Figure 1) in such a way that the film only cools as it rises and thus when it passes through the two take-off rollers 3, 5 still has a temperature that is quite high anyway, between 60 °C and 80 °C in the tested example.

With only very little energy that has to be made available by the temperature control device 22, the film can thus be quickly brought back to a temperature level that can be processed very well from the first heat, in order to facilitate longitudinal stretching.

In the exemplary embodiment shown, the second roller 10 is designed as a stretching roller. In the positive tests, it was driven at three to four times the peripheral speed in relation to the first roller 9 . With stretch ratios approaching 1:3, the quality of the film was more suitable for silage pre-stretch; On the other hand, with a higher stretching ratio, i.e. more in the direction of 1:4 or more, the processability was broader, especially with regard to the optical film qualities.

In the positive tests, the second roller 10, ie the stretching roller, was provided as the first of a total of three rollers in a second temperature cycle, namely an annealing cycle. The annealing circuit flows through the second roller 10, the third roller

11 and the fourth roll 12. The temperature in the return of the annealing circuit was adjusted to plus 5 K to plus 20 K compared to the return of the preceding first roll 9, ie the holding roll. The second roller 10 thus has two functions: on the one hand, it is a stretching roller and, on the other hand, it is a tempering station in the form of a tempering roller.

The third roller 11 and the fourth roller 12 are designed as tempering rollers, i.e. they essentially maintain the very high temperature level of the stretching roller and thus lead to a relaxation of the stretched double-layer film web 23, which helps to minimize a memory effect of the shrinkback that would otherwise occur.

The fifth roller 13, designed as a cooling roller, is connected to the third of the three temperature circuits, namely a cooling circuit. The temperature level in the return of the cooling circuit was ideally between minus 10 K and minus 20 K compared to the return of the preceding roll, i.e. the last tempering roll.

On all five rollers of the treatment roller line 8, the double-layer film web 23 runs predominantly with static friction. Ideally, therefore, the surface of the five rollers should be coated, in particular a spiral groove or a silicone coating should be considered.

It goes without saying that at least one feed roller or pressure roller can be provided for each roller. In the prototype tests, however, driving without contact rollers has already proven to be quite sufficient.

Water has proven itself as a heating and cooling medium for the temperature control devices 22 and the three temperature control circuits.

In the outlet, the blown film line 1 was run at a film speed of between 94 m/min and 340 m/min and with a stretching ratio between the first roll 9 and the fifth roll 13 of between 1:2 and 1:3, with the lower stretching ratio again i.e. going more towards 1:2, seemed more suitable for silage prestretch products.

In implementing the various aspects of the invention, the blown film line 1 provides a treatment roller section 8 above the pair of take-off rollers 2 with heating means for the double-layer film web 23, namely with the heated fluid circuit in the first roller 9 and additionally with the tempering circuit in the second roller 10, in the third roller 11 and in the fourth reel 12.

In this case, several active heating means are provided for the double-layer film web 23, specifically in four different rollers.

The provision of a heating means in several rolls, at least in two rolls, especially with two different fluid circuits, is also an advantage in itself.

In the implementation of the second aspect of the invention, a transversely aligned treatment roller section is provided above the pair of take-off rollers 2 as a section, because from roller to roller within the treatment roller section 8, the rollers are at an angle of approximately 35° to 40° to the horizontal, i.e. they are more horizontal as vertically aligned to each other. This means that the rolls can be arranged so low because of their sufficient lateral offset that they result in a projection of the virtual plane 14 overlaps, so overall build less high than the sum of the diameters of the five rolls would amount to.

In the second variant of a blown film line 1' in FIG.

Five rollers are again arranged above the pair of take-off rollers 2 and below the reversing unit 20, namely a first one

Roller 9', a second roller 10', a third roller 11', a fourth Roller 12' and a fifth roller 13' before a deflection roller 19 is then provided at the top.

The five rollers perform the same function as described in the first variant from FIG. 1, and the same three temperature control circuits are also present.

In the second variant, however, the second roller 10' and the fourth roller 12' are arranged on the same side of the virtual plane 14 as the first roller 9', the third roller 11' and the fifth roller 13'. All the rollers are therefore arranged on the same side of the virtual plane 14 .

A direct connection between the nip of the pair of take-off rollers 2 and the deflection roller 19 is free, so that the double-layer film web 23 can optionally be guided vertically upwards without rotating the rollers in the treatment roller section 8 .

However, this variant is also preferably set up as an MDO system, ie for longitudinal stretching of the film beyond the plastic flow of the double-layer film web 23 .

The five rollers of the treatment roller line 8 have a very small clearance, which is in any case less than 5 cm. When starting up the blown film line 1', it is therefore very difficult to thread the film between the rollers of the treatment roller section 8 in the operating position shown, even if the rollers are driven in the opposite direction of rotation to their predecessor.

To thread in a start (not shown) of the double-layer film web 23, two rollers, namely the second roller 10' and the fourth roller 12', can therefore be moved to the left, i.e. on the opposite side of the virtual plane 14. The double-layer film web 23 can then simply be moved vertically be threaded through the five rollers, then the second roller 10' and the fourth roller 12' are moved back onto the same side 17 of the virtual plane 14 as the other three rollers are positioned, and the extrusion process can be run as a steady-state process will.

Preferably, the second roller 10' can optionally be adjusted up to the imaginary plane of the axes of the rollers 9', 11', 13' or even beyond, resulting in a continuously adjustable stretching section. In preliminary tests, the ability to set the stretched length has proven to be advantageous in terms of process technology, for example because there was a higher error tolerance for defects when passing through the imaginary plane.

In the threading position of the second roller 10' and the fourth roller 12', the blown film line 1' can be operated like a conventional blown film line.

In the third variant of a blown film line 1" in Figure 3, essentially the same structure is selected as in the second variant of the blown film line 1' in Figure 2, however the five rollers of the treatment roller line 8'' are all located on the first side 16 of the virtual plane 14. Since an entry side into the reversing unit 20 is also on the first side 16 of the virtual plane 14, it can be guided directly from the fifth roller 13'' to the reversing unit 20. A deflection roller 19 is not necessary.

The fifth roller 13'' is also arranged opposite the four preceding rollers in such a way that its edge directed towards the virtual plane 14 protrudes beyond the preceding four rollers, so that the double-layer film web 23 does not thread and without passing through the treatment roller section 8 around the four preceding rollers can be guided around. The angle of wrap of the double-layer film web 23 µm the fifth roller 13" around is almost 90° even without threading, and even almost 180° when threaded, so that sufficient guidance is guaranteed.

Also in the third variant of the blown film line 1" in Figure 3 - as in the second variant of the blown film line 1' from Figure 2 - the second and fourth rollers are combed, so that the start of the film is threaded in with a simple straight passage when the line is started up can be.

The fourth embodiment of the blown film line 1'" in

Up to a pair of take-off rollers 2″″, FIG. 4 is identical to the variants described above.

In the fourth variant of the blown film line 1"" that first take-off roller 3'' which is on the same side 16 as the entry into the reversing unit 20 is designed to be displaceable for threading and for closing the pair of take-off rollers 2''. On the other hand, a second take-off roller 5′”, which lies on an opposite side 17 of the virtual plane 14, is in principle designed to be fixed.

Above the pair of take-off rollers 2′″ are four rollers of a treatment roller line 8′″ arranged horizontally next to one another, and a fifth roller 13′″ offset laterally and vertically thereto.

With regard to the virtual plane 14 above the pair of take-off rollers 2"', there are three rollers of the treatment roller line 8"' on the second, here right, side 17, whereas two rollers of the treatment roller line 8"' are on the first, here left, side of the virtual level 14, i.e. on the same side as the entry into the reversing unit 20.

For this purpose, a machine frame 21″ for the rollers of the treatment roller section 8″ has a collar 24 which protrudes laterally relative to a main body of the machine frame 21″. The first roller 9 ′″ is mounted on the collar 24 .

Due to the horizontal arrangement of several rollers of the treatment roller line 8"" next to each other, i.e. here a total of four rollers of the treatment roller line 8"", the blown film line 1"" is built very low overall, although above the pair of take-off rollers 2"" and the treatment roller line 8"" the Reversing unit 20 is arranged.

Two of the rollers within the treatment roller section 8′″, here the second roller 10″ and the fourth roller 12′″, are designed to be displaceable again in a meshing manner, so that threading into the system when starting up is facilitated. Pivoting can also be provided, especially when space is limited, for example the second roller 10″ can be designed to be pivotable around the first roller 9″, while the fourth roller 12″ can be pivoted around the fifth roller 13″ or around the third roller 11'” can be pivoted around.

In a straight extension above the

Pull-off roller pair 2'", i.e. in the virtual plane 14, a straight path 25 for the double-layer film web 23 is left open, so that the double-layer film web 23 can also be produced without passing through the MDO treatment roller section 8'". It then runs straight up to a Straight path deflection roller 26 and from there further into an inlet 27 of the reversing unit 20.

Alternatively, the double-layer film web 23 can be guided along an IVI DO running path 28 which pivots directly into the opposite side 17 of the virtual plane 14 in relation to the inlet 27 and runs around the first roller 9′″ on the outside. there the passage through the other four rollers, already described above, follows, which also have the same functions as already described above.

From the fifth roller 13"", the double-layer film web 23 finally runs either over a further deflection roller 29 or directly, if the wrap around the fifth roller 13"" is already sufficient, to the inlet 27 of the reversing unit 20.

The fifth roller 13 ′″ serving as a cooling roller and/or a further deflection roller 29 that may be provided, as well as further cooling units, can be adjusted with one another or against one another, individually or jointly, so that the cooling path is easily adjustable. For example, the fifth roller 13'' and the further deflection roller 29 can be mounted together on the machine frame, which rotates about an axis that is parallel to the axis of the rollers shown; or, for example, the further deflection roller 29 can be moved or pivoted vertically downwards, so that the angle of wrap of the double-layer film web 23 on the MDO path 28 around the fifth roller 13″ can be set with very simple movements and dosed practically steplessly. Even with a predetermined cooling temperature, it is then possible to set the cooling effect before the double-layer film web 23 enters the reversing unit 20 .

A similar idea can be implemented, for example, with the first roller 9'', which ideally serves as a holding roller and at the same time as a heating roller. This can also be adjusted in height or laterally, for example, so that the changed geometry of the MDO path of the double-layer film web 23 results in a changed angle of wrap around the first roller 9″ and a changed stretch length.

A similar effect can also be achieved with a further pressure roller provided there.

In the fifth variant of the blown film line 1””, there is a flatness section 30 above a pair of take-off rollers 2 and a reversing unit 20 with an inlet 27 arranged above it.

Within the flattening section 30, a first roller 31, a second roller 31, a third roller 33 and a fourth roller 34 are provided. From there, a designated film run is provided over a number of passive deflection rollers 35 (the first one marked as an example) to the inlet 27 into the reversing unit 20 .

The four rollers of the flatness section 30 are in turn provided at a lateral distance from the virtual plane 14, so that there is a straight path 25 for the double-layer film web 23 from the pair of take-off rollers 2 directly to the first passive deflection roller 35 and from there on to the reversing unit 20 when the double-layer film web 23 should not run through the flatness system.

As an alternative, the double-layer film web 23 - here, for example, around a first deflection 36 - can be guided to the first roller 31, from there around roller 32, from there around the third roller 33 and finally around the fourth roller 34, until the double-layer film web 23 also cuts back into the straight path 25 on this flat path 37 .

Two of the total of four rolls of the flatness section 30 are essentially at the same height, they each form a pair with a low overall height. A projection onto the virtual plane 14 results in an overlapping area between the first roller 31 and the second roller 32 and even congruence between the third roller 33 and the fourth roller 34. However, even a slight overlap is sufficient to achieve a lower overall height compared to a structure as shown in FIGS.

All four rollers of the flatness section 30 ideally have a pressure roller 38 (marked as an example), which is pressed into the respective roller in an articulated manner with a pressure arm 39 (marked as an example).

In the present exemplary embodiment, pressure rollers are only provided on two of the rollers, namely on the first roller 31, which serves as a holding roller and heating roller, and on the second roller 32, which serves as a stretching roller and tempering roller.

There is thus a stretching section 40 between the first roller 31 and the second roller 32, and high tangential forces arise at the circumferences of the first roller 31 and the second roller 32.

In contrast, the surface speeds of the third roll 33 and the fourth roll 34, designed as cooling rolls, are set in coordination with the surface speed of the second roll 32 in such a way that there are no longer any elongations, or even slower, so that relaxation can occur.

The embodiment described is intended as a lay-flat package, ie usually with a maximum stretching of 1:1.05. The stretch length is quite long compared to the MDO variants.

The resulting longer residence time in the stretching section is advantageous for a wide process window.

Because only slight stretching is carried out, small drive powers are sufficient. Individual drives are also unnecessary, since the foil worked only minimally. It is therefore entirely sufficient if the holding roller and the second roller 32 are each driven and their speed can be regulated.

Since only a low temperature and thus energy level has to be reached, a water heater is completely sufficient according to the prototype tests by the inventors.

In the lay-flat package design, the second roll preferably has the same temperature as the first roll. The first roller serves as a heating and holding roller. The second roll serves as a stretching and tempering roll. The stretch between the second and the subsequent third roll is then an annealing section.

In contrast, a stretch of 1:10 or even more is readily possible in an MDO embodiment.

The length of the stretch should be as short as possible in order to reduce lateral contraction, the so-called neck-in.

The process control is significantly more critical because only a very short dwell time can be recorded in the very short stretching gap.

Since more rolls have to be tempered, there is a higher energy consumption, and a quite long tempering section is necessary overall.

The drives have to be kept quite strong to overcome the yield point of the plastic and easily exceed the yield range.

Individual drives are proposed in order to enable individual process control.

For a simple flatness improvement, an MDO design is actually too large and therefore usually uneconomical.

Since MDO requires high temperatures, it is usually suggested to use oil heating. In the fifth embodiment variant in FIG. 6, a transverse processing section is also provided above the pair of take-off rollers, specifically a horizontal one for four rollers, with a cooling roller being arranged further up and above the pair of take-off rollers would enable the double-layer film web to pass straight through. Two rollers are movable within the horizontal roller section, namely a second roller that can be pivoted around the first roller, and a fourth roller that is displaceable or pivotable and arranged on the other side of the virtual plane 14 .

Otherwise, the fifth variant in FIG. 6 can be used in a blown film system just like the variants described above.

A graphic explanation of the basic behavior of the films to be processed can be found in the diagram in Figure 7.

The longitudinal expansion s of the film is plotted there on an abscissa 41, while the longitudinal stress within the film is plotted on an ordinate 42, ie a variable proportional to the longitudinal tensile force within the film. The longitudinal voltage is denoted by the letter o.

Starting from a zero point 43, the film usually behaves in a linear stress increase field 44 with increasing longitudinal elongation s. Above a certain longitudinal elongation s* or the associated stress o*, the film leaves the area of the linear stress increase and the stress curve flattens out i.e. a lower gradient compared to the abscissa 41.

From the longitudinal strain s* introduced longitudinal strains are irreversible.

The voltage o then assumes a first maximum 45 . At this point, the so-called plastic flow of the film begins. The associated longitudinal strain sStretch is referred to as the yield point. A flow area 46 extends from the first maximum 45 of the longitudinal stress o, referred to as o ^stretch , to that area of the branch 47, which then rises again, where the longitudinal stress o again reaches the stress o ^stretch . From there, the longitudinal stress o increases steadily with increasing longitudinal expansion s until a sudden failure occurs in the form of a foil tear 48 .

An ^MDO working range 49 extends from when the tension is reached again until the foil breaks.

In contrast, a flatness pact working range is in the range beyond the linear stress increase field 44, but below the yield point s ^stretch . The film behaves elastically in the linear stress increase field 44, ie up to the longitudinal expansion s*. In simple terms, the stretching of a flatness package takes place between s* and the local maximum. On the other hand, the stretching of an MDO takes place once <j ^stretch is reached again.

The treatment roller section 50 in Figure 8 corresponds in principle to the second variant from Figure 2 and the third variant from Figure 3 with regard to its structure with five rollers, but with its first roller 51, its third roller 52 and its fifth roller 53 it contains three intermeshing rollers, while its second roller 54 and its fourth roller 55 are designed to rotate stationary.

To thread the double-layer film web at the beginning of a blowing process, the three intermeshing rollers, i.e. the first roller 52, the third roller 52 and the fifth roller 53, are moved out of their intermeshing position, i.e. to the left of the virtual plane 14 in Figure 8, so that the Double-layer film web from a nip 56 of the pair of take-off rollers 57 are simply guided vertically upwards to a deflection roller 58 can. The deflection roller 58 is the first roller which lies beyond the processing roller line 50 . From the deflection roller 58, the double-layer film web is guided transversely towards an inlet 59 in a reversing unit 60.

When combing, the first roller 51 can not only be moved into the plane of the stationary rollers, ie the second roller 54 and the fourth roller 55 (represented in FIG. 8 by a first contour 61 of the first roller 51 that has been combed in); Rather, the first roller 51 can even be moved combing through this plane, so that the central axis of the first roller 51 moves beyond the plane formed by the central axes of the second roller 54 and the fourth roller 55 . The first roller 51 can thus assume a combed-through position for the blowing operation (represented in FIG. 8 by a second contour 62 of the first roller 51).

In prototype tests, it has been found that a preferably stepless adjustability of the combing depth, in particular with a combing depth through the plane of the stationary rollers, can be advantageous for process reliability and the resulting film quality.

The treatment roller section 63 according to the seventh variant in Figure 9 shows a slightly different structure:

Above the pair of squeezing rollers 64 is the treatment roller section 63 in a vertical orientation.

A first roller 65 is constructed as a heating roller and a nip roller at the same time. It can be moved combing through the virtual plane 14 . The combing has already been described several times above. Its advantages and also the possibility of combing through the plane of the static rollers are now assumed to be known.

A second roller 66 is provided with a significantly smaller diameter than the first roller 65.

A third roller 67 is also provided with a smaller diameter than the first roller 65, preferably with the same diameter as the second roller 66 as constructed here.

The second roller 66 and the third roller 67 form a stretching station, in which the third roller 67 is designed to mesh. Due to the stepless adjustability of at least one of the two rollers 66, 67 of the stretching station, the stretching length can be steplessly adjusted, which has proven to be very advantageous in prototype tests.

The second roller 66, which at the same time represents a first roller of the stretching station, is preferably driven at the same peripheral speed as the first roller 65, ie like the large holding roller. With regard to the function of the holding station, the second roller 66 would actually be assigned to the holding station rather than to the stretching station, together with the first roller 65. Only with regard to their diameter is it also possible to assign the second roller 66 together with the third roller 67 to the stretching station .

The two small rollers, ie the second roller 66 and the third roller 67, are not heated but are driven. This makes it possible to construct the second roller 66 and the third roller 67 with a very small diameter.

However, the third roller 67 is driven at a higher circumferential speed than the second roller 66. A stretching section for the double-layer film web is therefore formed between the second roller 66 and the third roller 67. If one assumes that, given the given geometric conditions, there is static friction of about 70° around the circumference of the faster-driven third roller 67, then the stretching length of the stretching section is between approximately 250 mm and 290 mm for large roller diameters and between 100 mm and 140 for small roller diameters mm about 15 cm to 19 cm, specifically in a prototype test about 17 cm.

A first annealing roller 68 and a second annealing roller 69 are provided in the treatment roller section 63 following the faster driven third roller 67, the latter also being able to be brought into its working position so as to mesh.

The two tempering rollers 68, 69 are followed by a cooling roller 70 - in the present example with a slightly larger diameter. The cooling roller 70 has a feed roller 71. The cooling roller 70 together with its feed roller 71 forms the last station of the treatment roller section 63. From there, the double-layer film web is guided to the infeed into the reversal.

The rollers of the treatment roller section 63 are arranged very close to one another, with a clearance in the vertical arrangement of only about 10 mm to 30 mm, in order to achieve the lowest possible overall height.

Several or even all of the roller surfaces of the treatment roller section 63 preferably have a rough, non-slip surface, ideally with embedded silicone.

DE 10 2009 033 171 A1 describes the control process as follows, with the following statements being part of the overall disclosure of the present patent application:

10 shows a blown film system 72 with a downstream stretching system 73 and winder 74. The plastic granules to be processed are fed to an extruder 75 via a dosing device, melted in this, homogenized and fed to the film blowing head 76. In the production of multi-layer films, several extruders are used depending on the number of layers. The film blowing head 76 has an annular nozzle from which the extruded plastic mass emerges. Cooling air for inflating the tubular film 77 is supplied through the film blowing head 76. After the plastic has solidified, the tubular film 77 is laid flat in the flattening unit 79 and continuously pulled off and laid with the turning trigger 80. The blocked film is then monoaxially stretched in the machine direction in the stretching unit 73 . The foil is fed to the winder 74 and rolled up into foil rolls.

To control the film thickness profile, the actual film profile must be recorded, preferably at two points. The actual thickness profile on the circumference of the tubular film 77 is recorded between the segmented control unit 78 and turning take-off 80 on the measuring device 81, and the actual thickness profile of the stretched film across its width is recorded between the stretching system 73 and the winder 74 on the measuring device 82. The measuring device 81 for measuring the actual thickness profile of the tubular film 77 is preferably arranged at a constant height above the blow head 76 rotating around the tubular film.

The entire film blowing process is regulated via the system control 83, in particular the drives, cooling air, the segmented control zone 78, which is located in the cooling ring, in the film blowing head 76 or downstream, and the take-off speed of the tubular film.

The film actual profiles measured by the measuring devices 81 and 82 are fed to the system control 83 and signals are passed on to the segmented control zone 78 by means of a target/actual comparison. In Fig. 11 the system is shown in plan view. It is made clear that the turning trigger 80 performs a reversing movement between 0° and 180° in each direction (see double arrow) and as a result the tubular film 77 is not always folded together at the same edges. If this offset were not taken into account in the regulation, then the thin points that were impressed on the thickness profile of the tubular film 77 in the blowing process ran back and forth over an area of the width of the flattened film and did not represent the film edges.

FIG. 12 shows the actual thickness profile of a film tube with two thin areas 85. Such a thickness profile is z. B. detected by the film thickness measuring device 81 between the segmented control zone 78 and flattening device 79 in the corrected state. The two dashed lines 86 indicate the folded edges which form the two side edges of the flat sheet. The two thin areas 85 form the two edge areas when the film is fed to the stretching system 73 as a blocked tube.

In a further, previously described embodiment of this invention, the blown and flattened film tube is cut open at these two positions 86 and then the two flat film webs are each fed to a separate stretching system 73 . Here too, the two thinner areas, ie one half of the thin areas 85 shown in FIG.

FIG. 13 shows the actual thickness profile of a film tube with only one thin area 85, as is used in a third embodiment of the invention. The tubular film is cut open at only one point 86 in the area of the thin point 85 . The tube that has been cut open is then unfolded as a flat web and fed to the stretching system 73 . Here, too, half of the thin area 85 is found as the edge area of the film fed to the stretching system.

Claims

37

PATENT CLAIMS Plastic molding plant, especially blown film plant or flat film plant or other plant designed for the production of a film web, with a treatment roller section with process rollers, which has a holding roller and a stretching roller and, if necessary, further rollers, which are set to different peripheral speeds, namely the stretching roller with a higher peripheral speed than the holding roller, with the holding roller and/or the stretching roller and/or another process roller sucking the film web onto its respective circumferential surface with a vacuum in order to ensure that the film web rests as uniformly as possible on the roller and/or as far-reaching as possible To allow zone with static friction, where optionally the following can be provided (in each case to be understood as and/or link): a. A device for influencing the exit surface of the negative pressure b. A vacuum level control c. A regulation for the strength of the negative pressure d. A display on the system e. Optical monitoring on the system i. In particular, both at the holding and at the draw roll ii. ii. The precision of the plant component alignment to each other f. A transmitter and a receiver for wireless transmission of data at the plant g. A transmitter and a receiver for wired data transmission at the plant h. A data acquisition box according to the earlier patent application WO 2018/072775 A of the present applicant i. Any feature laid out as a heading in this patent application j. A device for the targeted differentiation of the negative pressure over the circumference of the roller and/or over its length k. An electrostatic charger

I. Touchpad on the system 38 m. A human-machine interface with i. a real-time display of the degree of stretching and/or ii. peripheral speeds of the nip and draw rolls and/or iii. other process or non-process rolls. IV. ii. A real-time display of the system's connectivity to a data server v. iii. An alarm in the event of a sudden rupture, or vi. The negative pressure drops, in particular with a transmitter to a server Method for operating a system according to Claim 1, the negative pressure being brought to the outside of the roller through a permeable surface in order to suck the film web onto the roller.