BLOW-FOIL PLANT AND METHOD FOR PRODUCEING A FOIL TRACK

Description

[0001] The invention relates to a blown film plant, the use of a twin-screw extruder for feeding a ring die of a blown film plant and a method for producing a film web.

[0002] More specifically, the invention relates to a blown film machine for producing a film web from a recycled material, the use of a twin-screw extruder for feeding a ring die of a blown film machine and a method for producing a film web from a recycled material.

[0003] Blown film lines in various configurations are already known from the prior art. Prior art blown film lines are also capable of producing a film web from recycled material. A blown film line typically includes an extruder, which serves to melt and homogenize the material to be extruded. Furthermore, it is known that an annular die is provided for extruding a film tube, and that the blown film line includes an annular die melt pump in a melt stream between the extruder and the annular die to convey the melt to the annular die. The blown film line can also include a tube formation zone for longitudinal and transverse drawing or stretching of the film tube.Additionally, prior art blown film lines may also include a coolant for the film tube moving in the machine direction, and the blown film line may have a flattening section beyond the tube formation zone for flattening the film tube into a double-layer film web. Furthermore, prior art blown film lines may include a take-off roller pair beyond the coolant for removing the film tube.

[0004] EP 2 631 060 A1 describes a blown film system with an extruder, a ring nozzle melt pump and a filter in the melt stream.

[0005] WO 2016 / 059572 A2 discloses blown film plants for the production of film webs from recycled material, in which filtration equipment is used and different process flows are described.

[0006] US 5,122,315 A describes an extrusion system with an extruder, gravimetric material feed, a geared pump module, and a controller that records input and output values ​​and regulates the speed of the pump.

[0007] US 2013 / 0229888 A1 discloses kneading and extrusion systems with several gear pumps connected in series and a control system with feedback and feedforward regulation to avoid pressure fluctuations upstream of the pumps.

[0008] A particular disadvantage of the known solutions is that the material – especially films from production and / or use intended for recycling – must first be shredded, melted, and pelletized before it can be extruded in the next step. This can lead to additional process steps, lower material quality, and higher energy consumption. Task and solution

[0009] It is therefore an object of the present invention to at least partially overcome the disadvantages described above. In particular, it is an object of the present invention to provide rapid material changes and changeover times, improved melt quality with a high recycled content, improved layer distribution, films with low and / or high stress and shrinkage, a high degree of automation, and / or good operability.

[0010] The foregoing problem is solved by a blown film line having the features of claim 1 and by a method having the features of claim 8. Further features and details of the invention will become apparent from the respective dependent claims, the description, and the drawings. Features and details described in connection with the blown film line according to the invention naturally also apply in connection with the method according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always makes, or can make, reciprocal references.

[0011] According to the invention, a blown film line for producing a film web from recycled material is proposed, which, in accordance with a blown film line of the generic type, can have an extruder for melting and homogenizing the recycled material into a melt and an annular die for extruding a film tube. Furthermore, the blown film line particularly includes an annular die melt pump in a guide for a melt flow between the extruder and the annular die for conveying the melt to the annular die. In the present context, the melt flow is also to be understood as a guide for such a melt flow, so that the features do not necessarily refer to a blown film line with a melt, but also to a blown film line with a guide for a melt flow.

[0012] Furthermore, the blown film line may be equipped with a tube-forming zone for longitudinal and transverse drawing of the film tube, as well as a coolant for the film tube moving in the machine direction. Additionally, beyond the tube-forming zone, the blown film line may include a flattening unit for flattening the film tube into a double-layer film web and a pair of take-off rollers beyond the coolant for removing the film tube.

[0013] It is further proposed to design the extruder of the blown film line as a twin-screw extruder. The twin-screw extruder is a multi-screw extruder. In plastics engineering, it is used for processing and shaping polymer melts. In this case, the recycled material or a material mixture containing recycled material is conveyed through a heated cylinder by means of two rotating, intermeshing screw shafts and melted in the process. Twin-screw extruders are typically distinguished by the center-to-center distance between the two screw shafts and their direction of rotation into tangential or closely meshing co-helical twin-screw extruders or tangential or closely meshing counter-helical twin-screw extruders.

[0014] The counter-rotating twin-screw extruder introduces less shear into the material being extruded and therefore places less stress on it. The counter-rotating twin-screw extruder is thus preferably used for processing temperature-sensitive materials. However, in this case, the co-rotating twin-screw extruder, and in particular the closely meshing co-rotating twin-screw extruder, is especially preferred.

[0015] In other words, twin-screw extruders can be divided into counter-rotating and co-rotating designs. Within these designs, a distinction is made between intermeshing and non-intermeshing screws. In intermeshing screws, the webs of one screw typically engage with the channels of the other screw, while in non-intermeshing screws, the screw profiles do not overlap axially. Another distinguishing feature is the relative position of the screws. A common distinction is between parallel screws and conically arranged screws.

[0016] Counter-rotating twin-screw extruders typically form C-shaped, closed conveying chambers that transport the extrusion mass through the extruder regardless of its tribological properties. This type of material transport is known as forced conveying. The screws rotate apart at the top—similar to a gear pump—to facilitate material feeding. Due to the closed conveying chambers, the mass throughput is essentially independent of back pressure. A calender flow develops in the meshing area of ​​the screws, resulting in high shear forces in the gaps. These forces can be used for the dispersion of additives. Counter-rotating twin-screw extruders are primarily used for processing PVC. Difficulties in processing PVC arise from the material's tendency to wall slip and its thermal sensitivity.The use of counter-rotating twin-screw extruders forces the material through the extrusion process, achieving a narrow residence time range. This counteracts wall slippage and prevents excessive material degradation due to prolonged thermal stress.

[0017] In conical twin-screw extruders, the screw axes are no longer parallel but arranged at an angle, thus reducing the center-to-center distance of the screws towards the discharge zone. The conical design offers advantages including a shorter overall length with comparable throughput, reduced shear stress in the discharge area due to the decreasing screw peripheral speed, and easier torque application thanks to the larger center-to-center distances. Three main distinctions can be made: a constant, decreasing, or increasing flute depth allows the required volume to be adapted to the specific application.

[0018] Twin-screw extruders with co-rotating, intermeshing screws generally do not form closed conveying chambers, but rather represent an axially open system. Consequently, forced conveying does not occur; instead, conveying is largely based on so-called drag flow. The screws preferably rotate at the same angular velocity and in the same direction. The extruded material is conveyed in channels that encircle both screws in a figure-eight pattern, with the cross-section narrowing in the engagement zone due to the geometry. A portion of the melt is forced conveyed regardless of adhesion conditions; this occurs due to the geometric conditions in the engagement zone. At all points in the engagement zone, both screws slide past each other at the same relative velocity, thus stripping off the adhering extruded material if the clearance between the screws is sufficiently small.Co-rotating twin-screw extruders are also important processing machines due to this self-cleaning effect.

[0019] Co-rotating twin-screw extruders are used in many industries today. The plastics industry is by far the most prevalent application area (based on the number of installed machines). Here, co-rotating twin screws are primarily used in plastics processing, but also increasingly in direct processing during extrusion and injection molding. The advantages here include eliminating the need for a second melting step (energy savings, prevention of polymer damage from double melting) and the flexibility in adjusting material properties resulting from the freedom from fixed formulations. Other significant application areas for these machines are the rubber and food industries.

[0020] To adapt to a wide range of processing and product requirements, twin-screw extruders can generally be designed modularly. This applies to both the barrel and the screws. The extruder screws preferably consist of elements that are slid onto and secured to a central shaft. The advantages of this design include: easy modification of the screw geometry for test setups during plant start-up or when process conditions change, standardization of the screw elements, and the creation of different and optimized processing zones.

[0021] Typical process zones of a twin-screw extruder are: the intake zone, the melting zone, the distributive mixing zone, the dispersive mixing zone, the degassing zone and the discharge zone.

[0022] In the feed zone, the solid plastic is typically fed into the extruder. The solid is then conveyed towards the discharge zone and compressed. Another function of the feed zone is preferably to remove any air that may have been drawn in. The conveying capacity of the solid material conveying zone depends on the free screw volume, the rotational speed, and the bulk density of the solid.

[0023] The plastic can be fed to the twin-screw extruder via a hopper and / or a side feeder. In any case, when dosing in general and designing hoppers and / or side feeders in particular, it must be taken into account that plastic waste (granules and / or fluff) is difficult to flow due to its low bulk density.

[0024] This is primarily due to the unfavorable shape and the associated low bulk density: In the case of fluff, it is inherent to the material itself ("chips"), while in the case of recycled granules, it is due to their unfavorable particle shape and uneven particle size distribution. Without specific measures, bridging or channeling often occurs in the hopper. While bridging completely interrupts the flow of material, channeling leads to segregation and the formation of dead zones, for example, in the hopper. Both effects often result in production interruptions or significant fluctuations in throughput. In simple cases, this problem can be addressed by appropriately sloping the hopper walls. The next step is then preferably the installation of so-called feeder inserts in the hopper. If this also proves unsuccessful, an agitator or compression screw can be used in the hopper.In addition to polymers in granular or fluff form, powdered or liquid additives such as fillers (CaCO3, TiO2) or processing aids can also be fed into a twin-screw extruder in the downstream area.

[0025] One advantage of the twin-screw extruder is that the starting material does not necessarily have to be in granular form, as with a single-screw extruder, but can also be fed in the form of chips / shreds, so-called "fluff." To produce "fluff," the starting material must be broken down from its original form, e.g., web material (e.g., as a roll), edge strips, offcuts, or PCR material after sorting (film or laminate in sizes DIN A6 to DIN A0, or larger), melt lumps, or film / laminate scraps, which were previously shredded in a first step after sorting and cleaning.

[0026] Comminution is a fundamental operation and a prerequisite for virtually all subsequent processing and recycling methods. The selected particle sizes must be adapted to the downstream processes. At the same time, the particle sizes should not be smaller than necessary, as comminution is associated with high costs. Furthermore, in addition to a suitable particle size, a uniform particle size distribution and shape are required; otherwise, differing geometric dimensions will have a significant negative impact on subsequent sorting.

[0027] For comminution performance and success, the material properties, especially toughness, elasticity, and heat resistance of the feed material, are crucial. Energy input is possible in various ways. However, with thermoplastics, stresses from pressure, shear, and impact often lead to insufficient results. Under normal conditions, pressure and impact are absorbed by the tough elasticity of plastic granules, while shear leads to the melting of the plastic particles. Therefore, in large-scale comminution, primarily cutting and impact stresses are used.

[0028] During cutting, the grain is separated along the cutting edge due to shear stress in the shear gap. The difference between shear and cutting is that, in cutting, the shear has a very localized effect on the shear gap, whereas shear stress affects the entire grain. Therefore, shearing only leads to insufficient comminution of solids.

[0029] The comminution of the grain by impact is achieved through inertial forces, whereby the existing kinetic energy from the collision with one or more grains or from impact against a solid at high relative velocities is converted into deformation work. The difference between the stresses of pressure, impact, and collision lies in the relative velocity of the particles to each other or between the particles and the solid. While relative velocities of < 5 m / s are achieved under pressure, these are greater than 5 m / s under impact. In contrast, comminution by collision involves relative velocities between 20 m / s and several hundred m / s. Particularly high relative velocities are applied in fine comminution. For the production of fluff to feed a twin-screw extruder from the aforementioned waste materials, comminution by cutting is a suitable method.

[0030] For shredding by cutting, mainly cutting roller shredders (also called rotor shears, twin shaft cutters or shredders) or, less frequently, guillotine shears (also called splitters) are used.

[0031] In a roller shredder, the material being fed in is gripped by ripping teeth arranged on parallel, counter-rotating shafts and drawn between the shafts. The waste is shredded partly by cutting and partly by tearing until it can exit downwards through the interlocking rollers.

[0032] In addition to roller shredders, cutting mills are frequently used. These mills are ideally suited for shredding tough, elastic materials and can therefore be used for almost all plastics. Cutting mills are available in various designs, but all operate on the same principle. The material to be shredded enters the intake area of ​​the open rotor by gravity via the feed chute. The rotor circulates the material and continuously shreds it between rotor and stator blades. If the particle size of individual grains is smaller than the mesh size of the screen, they leave the grinding chamber by gravity and, to some extent, by centrifugal force.

[0033] Cutting roller shredders are particularly good at handling the wide variety of film and laminate waste and shredding it into fluff, and are therefore especially suitable for fluff production in a plant with a counter-rotating twin-screw extruder in direct processing in film extrusion.

[0034] The melting or plasticizing zone serves to convert the solid into a melt; furthermore, fillers are pre-dispersed. Depending on the subsequent process zones, it is not always necessary to achieve a melting degree of 100% at the end of the plasticizing zone.

[0035] Unmelted solid particles can be melted in subsequent zones, such as the dispersive mixing zone. The functions of the dispersive mixing zone are to distribute solids and fluids within the melt and to homogenize the melt temperature. Mixing is achieved by dividing and redirecting the melt flow. Mixing elements are generally designed to minimize shear-intensive dispersion, resulting in reduced self-cleaning. In the dispersive mixing zone, solid or polymer agglomerates, as well as liquid droplets, are to be cleaved by high shear forces. In addition to the shear stress, the duration of the stress is also crucial for the cleavage effect.

[0036] The degassing zone serves to remove water, residual monomers, and dissolved gases. To prevent the melt from escaping through the degassing port, the melt pressure must first be adjusted to the ambient pressure. The channels upstream of the degassing zone must be completely filled to prevent the extraction of unincorporated components or the intake of air via the feed hopper. This is achieved using suitable baffles.

[0037] Degassing offers the possibility of removing low-molecular-weight components, gases, or air from the melt during the extrusion process. However, the substances to be degassed vary due to the specific composition of the recycled materials.

[0038] Degassing tasks that frequently occur during the recycling of plastics include: Drying: Removal of residual moisture, which may eliminate the need for complex and expensive pre-drying of the material; blistering and molecular weight reduction through hydrolysis can be prevented. Shifting the equilibrium: If low-molecular-weight components, especially from polycondensates, are removed, the equilibrium shifts towards high-molecular-weight chains, resulting in an increase in molecular weight. Removal of external contaminants: Volatile, mostly organic compounds that adhere to the plastics as contaminants are removed from the melt, e.g., fats, oils, and some printing inks or varnishes. Removal of internal contaminants: Substances that have diffused into the material during use and cannot be removed by a washing process are removed by degassing, e.g., gasoline, diesel, antifreeze.Removal of low-molecular-weight degradation products: Degradation products released during processing or use, which exist in the form of chain fragments, monomers, or oligomers and which permanently impair the performance and processing properties of the plastic, are removed. Degassing of solvents: Solvents that have entered the material due to partially used cleaning and separation stages in the processing are removed.

[0039] However, degassing also removes some substances that should remain in the material. These can include short-chain polymer components as well as added additives, especially stabilizers, antioxidants, light protectants, plasticizers, etc.

[0040] The following relationships apply to degassing performance: With increasing temperature, influencing factors such as viscosity, vapor pressure, volatility and diffusion equilibrium are positively affected and result in increased degassing performance.

[0041] As the pressure in the degassing zone decreases, the degassing performance increases.

[0042] A large interface area combined with a thin layer promotes degassing. Interface areas and layer thicknesses are determined by the dimensions of the degassing apparatus. Since the layer thickness cannot be arbitrarily thin, attempts are made to increase degassing performance through continuous surface renewal, i.e., high rotational speeds. A long residence time in the degassing zone also leads to better degassing performance. This relationship conflicts with the pursuit of efficiency and thus short residence times.

[0043] A twin-screw extruder with co-rotating, intermeshing screws, as used in direct processing, advantageously has, in addition to a so-called atmospheric degassing zone, at least one, but preferably two, degassing zones where a vacuum is applied. The pressure in such a process zone is in any case below 1 bar down to 1 mbar. Typical pressures are between 800 and 10 mbar, preferably between 500 and 50 mbar.

[0044] The discharge zone serves to build up the necessary pressure for the subsequent processes.

[0045] In melt filtration of plastics, the melted material is passed through a filter element to remove impurities and other solids. The plastic is subjected to pressure and high temperatures as it passes through a filter element that removes the solids. Melt filtration is a crucial step in plastics recycling, as it helps improve the quality of the recycled material and remove as many contaminants as possible. It is often used in combination with other techniques, such as degassing, to make the recycled material as pure as possible.

[0046] Filtration, also known as filtering, generally refers to the separation of solid or liquid particles from fluids using a filter medium. In extrusion, the purpose of filtration is therefore to separate all types of foreign particles, according to a selected filter fineness, and thus to provide the purest possible melt.

[0047] This problem arises to an even greater extent in the processing of plastic waste, which, despite elaborate cleaning stages during processing, still contains a greater amount of contaminants than is the case with virgin plastic.

[0048] For process optimization and economic reasons, the following requirements must be met by melt filtration: Filtration at nearly constant pressure and temperature; filter changes without interruption or impact on production; minimal additional residence time of the melt; minimal pressure drop in the filter media; maximum possible filter service life

[0049] Due to the sometimes very high levels of contamination in plastic waste, conventional filtration systems for virgin materials quickly reach their limits with regard to these requirements. Even a foreign matter content of 0.3% by volume is considered a very high level of contamination for filtration, and even for a screen wheel filter, which is one of the continuously operating filter systems, an upper limit of 0.5% by volume of contamination applies for economical operation.

[0050] Typical filter finenesses depend on the application and thus on the melt filter used. Large-area filters are used when the production process runs continuously, few recipe and batch changes are required, and the end product demands high purity, for example, for products that must be crystal clear and free of visible particles. This often requires filter finenesses below 50 pm, and in special cases, below 5 pm. Screen changers, on the other hand, are designed for processes with frequent recipe and / or color changes and / or high levels of contamination (e.g., recycling). Filter finenesses > 50 pm are used in these applications. Typical filter finenesses when using co-rotating twin-screw extruders in direct processing in a film extrusion line range from 50 pm to 500 pm, preferably between 80 and 200 pm. Suitable filter areas (per screen opening) range from 10 cm² to 1.5 m², preferably between 50 and 500 cm².

[0051] The complete process unit of a twin-screw conveyor (cylinder and screws) is typically modular in design, making it highly adaptable to a wide variety of process applications. This unit is usually heated electrically or with saturated steam (in very large units) and can be cooled with water (evaporation) or air.

[0052] For torque transmission, the worm gears often feature modified toothing, splined or polygonal geometries. Due to the necessary safety margins for transmitting very high torques, keyed connections are practically no longer used.

[0053] Screw and barrel lengths are specified relative to the screw's outside diameter (L / D). The demand for long screw lengths (L / D) has increased in recent years due to the requirements of polymer blend processing, such as intensive mixing and kneading, multi-stage additive feeding, multi-stage degassing, etc. Screw lengths (L / D) influence the duration of mixing and kneading processes (dispersive and distributive mixing), chemical reactions during compounding, etc. In short, a longer L / D results in a longer residence time. Today, twin-screw extruders are generally used with screw lengths (L / D) of 12 mm and more for laboratory extruders and up to L / D = 420 mm for extruders in the chemical industry.Typical ratios for the use of co-rotating twin-screw extruders in direct processing in a film extrusion plant are between L / D = 30-60, preferably between L / D = 40-50.

[0054] Typical casings are 3 or 4 D long; in some cases, for economic reasons, up to 8 D are used. Casings are designed for a wide variety of process tasks. These tasks correspond to typical process zones and include, among others, intake, melting, feeding with back venting, mixing, degassing, and discharge / pressure build-up.

[0055] Typical rotational speeds of a co-rotating twin-screw extruder in the mid-20th century, following its market launch, initially ranged from 100 to 200 rpm. Today, maximum speeds have reached a range of 600 to 1500 rpm, with a yearly trend toward increasing speeds. High screw speeds improve throughput and mixing under high shear forces. A particularly high screw speed of up to 2500 rpm is sometimes used to control the morphology of polymer alloys. Typical rotational speeds for co-rotating twin-screw extruders in direct processing within a film extrusion line range from 100 to 600 rpm, with 200 to 500 rpm being more common.

[0056] For the process engineering design of co-rotating twin-screw extruders, several geometric and drive-related parameters are crucial: The so-called screw profile results from the ratio of the outer diameter Da to the inner diameter Di: Da / Di. The center distance a of the two screws is then calculated as: (Da + Di) / 2. In practice, a slightly larger center distance is used due to the necessary clearances. The projected cross-sectional area of ​​the screw, or more precisely, of the two screw elements at any point in the extruder, is always smaller than the cross-sectional area of ​​the figure-eight-shaped cylinder. The resulting free cross-sectional area, in addition to the outer and inner diameters, is another geometric parameter of a co-rotating, intermeshing twin-screw extruder. The free cross-sectional area Afree increases with an increasing diameter ratio Da / Di.This provides more free volume in the process section for intake, conveying, and degassing. The so-called channel depth h is calculated as (Da - Di) / 2.

[0057] Typical outer diameters of co-rotating twin-screw extruders today range from approximately 12 mm for laboratory extruders to approximately 260 mm for large production plants. Typical outer diameters of co-rotating twin-screw extruders used in direct processing in a film extrusion line range from 30 to 180 mm, preferably from 50 to 120 mm, and most preferably from 55 to 95 mm.

[0058] The following are also important for the possible throughputs: the specific torque, the quotient of the installed torque per worm shaft Md and the center distance a in the third power: Md / a 3< and the worm speed n.

[0059] To achieve higher throughput and better mixing performance of the twin-screw extruder, the Da / Di ratio and the specific torque have steadily increased since the market launch of the co-rotating twin-screw extruder in the middle of the last century: Initially, the diameter ratio Da / Di was only 1.22, but over the years it rose to over 1.44, then to 1.55, then 1.66 and finally even 1.8.

[0060] The specific torque of the first generation of co-rotating twin-screw extruders in the mid-20th century was only 3 to 5 Nm / cm³; typical values ​​today are 15 to 20 Nm / cm³. A higher specific torque allows for better mixing at higher throughput. Furthermore, it means that a polymer can be processed at lower temperatures (i.e., higher melt viscosity and less thermal degradation).

[0061] The recycled material is preferably a plastic or a mixture of plastics, particularly preferably a plastic or a mixture of plastics from the group consisting of polymers, polycondensates such as polyethylenes (LDPE, LLDPE, mLLDPE, HDPE, MDPE, VLDPE, etc.), polypropylenes (homo- and copolymers, compounds), plastomers, ionomers, ethylene copolymers (EVA, EVOH, EPM / EPDM, EMMA, EAA, EEA, CPE, etc.), cycloolefin copolymers, polyamides (PA 6, PA 66, PA 6 / 66, PA 11, etc.), thermoplastic elastomers (TPE-E, TPE-O, TPU), terephthalates (polyethylene terephthalate (PET), polybutylene terephthalate (PBT)), polyisobutylene (PIB), polystyrene PS), bio-based plastics and biodegradable plastics (PLA, PHA, etc.). TPS, PCL, PBAT, PBS).

[0062] The recycled material may also contain additives (antioxidants, antistatic agents, colorants, fillers such as calcium carbide, titanium dioxide, lubricants, antiblocking agents, adhesion promoters, etc.). The recycled material may also be printed or labeled, etc. The twin-screw extruder exhibits particularly good mixing action, which allows the plastic to be processed. Recycling and / or the incorporation of additives using a twin-screw extruder is especially advantageous.

[0063] According to the invention, the blown film line has a filter with at least one filter element for filtering the melt from an unfiltered side to a filtered side. The filter serves as a dirt trap screen. The filter is preferably a filter from the group consisting of melt filters, extruder screens, filter discs, and strainer screens. The filter element can be single-layered, multi-layered, or pleated. The filter element can comprise a metal wire mesh, metal fiber fleece, and / or sintered fabric laminate.

[0064] The filter is preferably arranged in the melt stream between the extruder and the annular die. The filter can also be part of the extruder. Preferably, the filter is arranged between the extruder and the annular die melt pump.

[0065] According to the invention, the filter has a cleaning device that continuously and / or discontinuously renews the filter element. In this context, the term "renews" is understood to mean both cleaning a filter element and inserting a new filter element that has not previously been used as a filter element or has been cleaned before reuse. Insertion can be performed manually or, preferably, automatically.

[0066] According to one embodiment, the cleaning device is designed to renew the filter element during operation of the system, i.e., during the production of a film web. With this embodiment, the blown film line does not need to be stopped to renew the filter element.

[0067] In one embodiment, the cleaning device has a rotatable filter element or a rotatable cleaning element for renewing the filter element. The rotatable filter element can rotate on a scraper element such that filtered-out dirt is removed from the filter element. Alternatively, a scraper element can rotate on the filter element to remove filtered-out dirt from the filter element. In another embodiment, the cleaning device has a filter element or a cleaning element that is movable relative to the melt flow in which it engages, for renewing the filter element.

[0068] According to one embodiment, the cleaning device has a diverting mechanism for cleaning the filter element by temporarily directing the melt from the filtered side to the unfiltered side, i.e., against the usual melt flow. This diversion of the melt flow removes the filtered-out dirt from the filter element. Preferably, the cleaning device has a cleaning outlet through which the melt, which has been directed from the filtered side to the unfiltered side, is discharged. It is particularly preferred that the discharged melt contains the filtered-out dirt.

[0069] According to one embodiment, the cleaning device has a screen changer designed to divide the molten stream and thus direct it through several filter elements. Preferably, the screen changer is designed to direct the molten stream through only one of the filter elements instead of through a first and a second filter element, so that the first filter element can be replaced while the second filter element is in the molten stream.

[0070] According to one embodiment, the cleaning device or the screen changer is designed to selectively direct the melt flow through individual and / or all available filter elements.

[0071] According to the invention, the blown film line has a filter melt pump located between the extruder and the annular die melt pump, which pumps the melt to the filter. The extruder is designed such that pressure is built up in the melt flow to overcome the flow resistance of the extruder. In a configuration with the filter, the pressure of the extruder is often insufficient to overcome the flow resistance at the filter. In this case, the filter melt pump, which overcomes the flow resistance of the filter, is preferred.

[0072] The filter melt pump is preferred to ensure a particularly constant material feed per unit of time and thus constant material processing.

[0073] According to the invention, the twin-screw extruder has at least one degassing unit, which enables the extraction of impurities and contaminants. The degassing unit can be designed as a degassing zone within the extruder. Volatile components can be extracted from the melt using the degassing unit. To improve degassing, it is preferred that the fill level in the twin-screw extruder is below 100%, and in particular, it is preferred that the fill level is below 80%. Such a fill level is preferred because otherwise the melt would be forced into degassing ports and escape from the degassing unit. According to one embodiment, the twin-screw extruder has at least one degassing unit designed as an atmospheric degassing unit. In this design, the volatile components can be released from the degassing unit without applying a vacuum.

[0074] According to one embodiment, the twin-screw extruder has at least one degassing unit designed as a vacuum degassing unit. In this embodiment, a vacuum is applied to the degassing unit. This vacuum can be generated by a vacuum pump. This design enables particularly thorough degassing of volatile components. It is preferred that the degassing unit, especially the vacuum degassing unit, includes a means for collecting the volatile components, preferably in the form of condensate.

[0075] According to one embodiment, the extruder has a recycling material feed with a plugging screw. The plugging screw allows the recycling material to be fed to the extruder particularly uniformly. The recycling material feed preferably has a hopper in which the plugging screw is arranged. The plugging screw is preferably driven by a drive independent of the extruder. According to the invention, the blown film line preferably has at least two pressure sensors for detecting pressures within the melt flow guide, one in the melt flow guide at the extruder and one upstream of the annular die. The pressure sensors are designed to detect the melt pressure in the melt flow during operation of the blown film line.

[0076] According to the invention, the first pressure sensor is arranged directly on the extruder. The second pressure sensor is arranged upstream of the annular die melt pump. The extruder and / or the annular die melt pump and / or the recycled material feed can be regulated depending on the melt pressure in the melt stream, which is detected by the first and / or second pressure sensor on the extruder and / or upstream of the annular die.

[0077] According to one embodiment, the blown film line has two additional pressure sensors for measuring the melt pressure in the melt stream before and after the filter. These additional pressure sensors are therefore present in addition to the pressure sensors mentioned above. These additional pressure sensors can be installed directly before and after the filter. However, it is preferred that the additional pressure sensors are positioned immediately before the filter and immediately before the annular die. In this embodiment, the second pressure sensor is preferably positioned immediately after the filter.

[0078] Preferably, the extruder and / or the annular nozzle melt pump and / or the recycled material feed and / or the filter deflection device and / or the filter element changing device are adjustable depending on the melt pressure before and / or after the filter.

[0079] Particularly preferred is the extruder and / or the annular die melt pump and / or the recycled material feed and / or the deflection device of the filter, which are regulated depending on the pressure sensors for detecting the melt pressure in the melt stream at the extruder and in front of the annular die and the additional pressure sensors for detecting the melt pressure in the melt stream in front of and after the filter.

[0080] According to an embodiment which is not covered by the invention, the blown film plant has a storage silo for holding the recycled material.

[0081] According to an embodiment not covered by the invention, the blown film plant has a screw conveyor that conveys the recycled material from the storage silo to the recycled material feed. The screw conveyor is preferably arranged horizontally or substantially horizontally.

[0082] According to an embodiment not covered by the invention, the storage silo has a means for mixing the recycled material within the silo. This is preferred because it allows potential blockages of recycled material within the silo to be resolved. The mixing means is preferably a comb system within the storage silo, but it could also be, for example, a shaker that shakes the silo.

[0083] According to an embodiment not covered by the invention, the storage silo has a means for determining its fill level with the recycled material. The means for determining the fill level can be a weighing device of the storage silo. It is preferred that the means for determining the fill level be an optical and / or capacitive sensor.

[0084] According to an embodiment not covered by the invention, the storage silo has a means for determining its recycling material consumption. The means for determining the recycling material consumption is preferably a weighing device in the storage silo. The recycling material consumption can thus be recorded by measuring the weight loss over time.

[0085] According to one embodiment, which is not part of the invention, the blown film plant has a pre-silo for filling the storage silo with recycled material.

[0086] According to an embodiment not covered by the invention, the blown film line has a shredder for shredding a feed material. The feed material can be a plastic or a mixture of plastics from the aforementioned group. The feed material can be in the form of web material, shredded web material, shredded film, etc. The shredded web material can be in sizes ranging from a few millimeters up to DIN AO and larger web pieces. The shredder is preferably designed to reduce the feed material to the recycled material. The recycled material is preferably in the form of fluff. The recycled material can be in the form of flakes. Preferably, the flake size of the recycled material is between 1 mm and 40 mm; particularly preferably, the flake size of the recycled material is between 5 mm and 12 mm.

[0087] According to an embodiment not covered by the invention, the blown film line has a transport device for conveying the recycled material from the shredder to the storage silo and / or the pre-silo. In a configuration with a pre-silo, it is preferred that the transport device conveys exclusively into the pre-silo. The transport device is preferably designed as a conveyor belt and / or a screw conveyor or as a pressure conveying system. A configuration with a conveyor belt and screw conveyor is particularly preferred, as this allows for a particularly continuous conveying of material.

[0088] According to one embodiment, the blown film plant has a mixing silo for mixing the recycled material with other materials. The blown film plant can also include several mixing silos. The mixing silo(s) can also serve as intermediate storage for various recycled materials. Other extrudable materials can also be stored in the mixing silos alongside recycled materials. The mixing silo preferably has a mixing device inside it.

[0089] The mixing silo is preferably connected to the storage silo and / or the pre-silo via a blower and / or a conveyor belt and / or a screw conveyor for introducing the recycled material and / or mixtures thereof.

[0090] According to one embodiment, the recycling material feed is designed to receive, in addition to or as a substitute for, the recycled material, a pelletized and / or granulated material in order to convey it to the extruder. Besides the recycled material, the additional material can also be other extrudable materials.

[0091] The blown film line preferably includes a pellet metering device for holding and metering the pelletized material. The pelletized material is preferably virgin material and / or higher-grade recyclates compared to recycled material.

[0092] According to one embodiment, the blown film line is configured to produce the film web with a layer of recycled material and at least one additional layer. Preferably, the blown film line is configured to produce a film web with 1 to 11 or 13 layers; particularly preferably, the blown film line is configured to produce a film web with 1 to 5 layers.

[0093] According to one embodiment, the blown film line has at least one additional extruder which melts and homogenizes the material of at least one additional layer. Preferably, the additional layers are made of a plastic or a mixture of plastics from the group mentioned above.

[0094] The additional extruder could be an additional twin-screw extruder.

[0095] According to one embodiment, the blown film plant is designed to produce a film web in which the recycled material is arranged between at least two further layers in the film web.

[0096] According to one embodiment, two or more layers are formed by a single extruder. In this embodiment, it is not essential that these layers lie directly on top of each other. According to one embodiment, the blown film line has a machine direction that is essentially vertical, from bottom to top.

[0097] The invention also includes the use of a twin-screw extruder for feeding a ring die of a blown film line. The blown film line is preferably configured according to one of the embodiments described above.

[0098] The invention further relates to a method for producing a film web from a recycled material, preferably on a blown film line. It is provided that a twin-screw extruder melts and homogenizes the recycled material. The melt is then conveyed via a melt stream by an annular die melt pump to an annular die. The melt is extruded through the annular die into a film tube, and the film tube is subsequently drawn longitudinally and transversely at a tube-forming zone. Following the tube-forming zone, the film tube is flattened, which folds the film tube into a double-layer film web beyond the tube-forming zone. A pair of take-off rollers is located beyond the flattening zone for removing the film tube.

[0099] According to the invention, the melt stream is additionally filtered by means of a filter with at least one filter element within the melt stream, by passing the melt stream from an unfiltered side to a filtered side. According to the invention, the filter is arranged in the melt stream between the extruder and the annular die, preferably between the extruder and the annular die melt pump.

[0100] The filter system is designed according to the invention in accordance with the filter system of the blown film plant described above. According to the invention, a filter melt pump is provided, which is arranged between the extruder and the annular die melt pump, which pumps the melt to the filter or increases the pressure within the melt flow to the filter system.

[0101] According to the invention, the twin-screw extruder additionally has at least one degassing unit as described above, which degasses the melt, thereby extracting impurities and contaminants.

[0102] According to one embodiment, the extruder is filled with the recycled material via a recycling material feed using a screw conveyor described above.

[0103] According to the invention, a pressure sensor detects the melt pressure in the melt stream at the extruder, and another pressure sensor detects the melt pressure in the melt stream upstream of the annular die. A control unit regulates the extruder and / or the annular die melt pump and / or the recycled material feed depending on the melt pressure in the melt stream at the extruder and / or upstream of the annular die. This enables constant extrusion of recycled material.

[0104] According to one embodiment, an additional pressure sensor detects the melt pressure in the melt stream upstream of the filter, and an additional pressure sensor detects the melt pressure in the melt stream downstream of the filter. The first pressure sensor detects the melt pressure directly at the extruder. According to the invention, the second pressure sensor is arranged upstream of the annular die melt pump and detects the melt pressure there.

[0105] Preferably, a pressure sensor located directly at the annular die monitors the melt pressure. This cut-off pressure indicates whether a maximum pressure in the melt flow is reached. This maximum pressure can occur, for example, if the temperature at the annular die is too low and the required quantity of recycled material can no longer be conveyed through the die. The pressure sensor located directly at the annular die can be used to control the speed of the annular die melt pump. A further pressure sensor for monitoring another cut-off pressure can be located directly upstream of the filter. This pressure sensor can also activate or deactivate the cleaning system. The pressure sensor located directly downstream of the extruder is preferably used to control the extruder speed.The pressure sensor, which is located immediately after the filter, is preferably used to control the speed of the filter melt pump and / or the speed of the ring nozzle melt pump.

[0106] According to one embodiment, a control and regulating device controls the extruder and / or the ring nozzle melt pump and / or the recycled material feed and / or the filter deflection device and / or the filter element changing device depending on the melt pressure in the melt stream before and / or after the filter.

[0107] The control and regulating device controls the extruder and / or the annular nozzle melt pump and / or the recycled material feed and / or the filter deflection device depending on the pressure sensors for detecting the melt pressure in the melt stream at the extruder and in front of the annular nozzle and the additional pressure sensors for detecting the melt pressure in the melt stream before and after the filter.

[0108] In the simplest case, the pressure sensors detect the pressure drop across the filter, i.e., the resistance the filter offers within the filter flow. If a threshold value is exceeded, the filter's cleaning mechanism described above can be activated to renew the filter element.

[0109] According to an embodiment which is not part of the invention, the blown film plant has a screw conveyor which conveys the recycled material from a storage silo described above to the recycled material feed.

[0110] According to an embodiment which is not covered by the invention, the screw conveyor conveys the recycled material from the storage silo depending on the fill level of the storage silo and / or depending on the recycled material consumption and / or depending on the melt pressure in the melt stream at at least one of the pressure sensors described above to the recycled material feed of the extruder.

[0111] According to an embodiment not covered by the invention, the storage silo is filled with recycled material from the pre-silo depending on its fill level. Preferably, the storage silo is filled with recycled material from the pre-silo depending on its recycled material consumption. The storage silo is preferably filled in such a way that a minimum quantity of recycled material in the storage silo is not undercut. This is intended to ensure a constant and uniform supply of the recycled material, more precisely the fluff, to the twin-screw extruder.

[0112] According to an embodiment not covered by the invention, the recycled material is mixed with other materials in a mixing silo. The mixing silo is preferably connected to the storage silo and / or the pre-silo via a blower and / or a conveyor belt and / or a screw conveyor for introducing the recycled material and / or mixtures thereof into the storage silo. This design enables a particularly consistent material feed to the extruder and consistent material processing.

[0113] According to an embodiment not covered by the invention, a starting material is shredded into recycled material by a shredder. The shredder is preferably designed according to an embodiment described above.

[0114] According to an embodiment not covered by the invention, a transport device moves the recycled material from the shredder to the storage silo and / or the pre-silo via a conveyor belt or a pressure conveying system. If the blown film plant has a mixing silo, this is preferably also filled with shredded material from the shredder.

[0115] According to one embodiment, which is not part of the invention, a pelletized material, preferably a pelletized recycled material, is added to the extruder in addition to or as a substitute for the recycled material. According to one embodiment, the pelletized material is added to the extruder or the recycled material feed via a pellet metering device.

[0116] According to an embodiment which is not covered by the invention, depending on the fill level of the storage silo and / or the consumption of recycled material and / or depending on the melt pressure in the melt stream at one of the pressure sensors described above, the pelletized material is added to the extruder in addition to the recycled material or as a substitute.

[0117] According to an embodiment which is not part of the invention, the film web containing the recycled material is extruded next to a layer of the recycled material with at least one further layer of another plastic.

[0118] According to an embodiment which is not covered by the invention, the recycled material is extruded on each flat side with at least one further layer of another plastic.

[0119] Further advantages and aspects of the invention will become apparent from the claims and from the following description of a preferred embodiment of the invention, which is explained below with reference to a figure.

[0120] Figure 1 shows a partial schematic embodiment of a blown film production system according to the invention. Detailed description of the exemplary embodiment

[0121] Figure 1 Figure 1 shows a blown film line 10 according to the invention, which is designed for producing a film web from a recycled material 4. The blown film line 10 has an extruder 20 for melting and homogenizing the recycled material 4 into a melt. In this embodiment, the extruder 20 is arranged horizontally at the bottom.

[0122] The extruder 20 is designed as a twin-screw extruder. In this embodiment, it is a closely meshing co-helical twin-screw extruder.

[0123] The recycled material 4 in this case is a plastic from the group consisting of polymers, polycondensates, polyethylenes, polypropylenes, plastomers, ionomers, ethylene copolymers, cycloolefin copolymers, polyamides, thermoplastic elastomers, polyethylene terephthalates, polyisobutylene, bio-based and biodegradable plastics.

[0124] The extruder 20 is driven by an electric motor. In this embodiment, the extruder 20 has both atmospheric degassing and a vacuum degassing unit 24. The vacuum degassing unit 24 is operatively connected to a vacuum pump 26. The vacuum degassing unit 24 has a means for collecting condensate. The extruder 20 has a guide for a melt stream 40 to an annular die 30 for extruding a film tube 6. An annular die melt pump 42 is arranged between the extruder 20 and the annular die 30, which conveys the melt to the annular die 30. Due to this design, pressure in the melt stream does not have to be generated exclusively by the extruder 20, but can be generated and / or increased by the annular die melt pump 42. The ring nozzle 30 is followed by a tubing formation zone 32 for pulling the foil tubing 6 lengthwise and crosswise.The blown film line 10 has a coolant 34 for the film tube 6, which moves in the direction of the machine. The coolant 34 is air, which is blown into the blown film tube 6. Beyond the tube formation zone 32, the blown film line 10 has a flattening unit 36 ​​for flattening the film tube 6 into a double-layer film web 8. Beyond this flattening unit 36, a pair of take-off rollers 38 is arranged, which are located beyond the coolant 34 and are used to remove the film tube 6.

[0125] In this embodiment, the blown film line 10 has a filter 50, which is arranged between the annular die melt pump 42 and the extruder 20. A filter melt pump 60 is also arranged between the filter 50 and the extruder 20. The extruder 20 also has a recycled material feed 44 with a screw conveyor 46. The screw conveyor 46 is driven by an electric motor. In this embodiment, the blown film line 10 has a shredder 80 into which a feed material 2 can be fed, which is then shredded into recycled material 4. The feed material 2 can be a plastic from the group mentioned above. The feed material 2 can be in the form of web material, shredded web material, shredded film, etc. The shredder 80 shreds the feed material 2 into flakes between 5 mm and 12 mm in size.The shredder 80 has a transport device 82 which conveys the shredded recycling material 4 to a pre-silo 100. The pre-silo 100 is located above the storage silo 90 and has a metering device 102, through which the recycling material 4 can be dispensed into the storage silo 90 as needed. In this embodiment, the metering device 102 is designed as a slide gate. The storage silo 90 has a means for mixing the recycling material 92, which in this embodiment is designed as an agitator. From the storage silo 90, the recycling material 4 is conveyed via a screw conveyor 94 into the recycling material feed 44 at the extruder 20.

[0126] Storage silo 90 is equipped with means for determining the consumption of recycled material. In this embodiment, the means for determining the consumption of recycled material is designed as a weighing device of storage silo 96. This allows the consumption of recycled material 4 to be determined in units of weight per unit of time. In this embodiment, the means for determining the fill level of storage silo 90 is implemented by the weighing device of storage silo 96. As soon as the fill level, and thus the weight, of storage silo 90 falls below a predetermined value, storage silo 90 is filled with recycled material 4 from the pre-silo 100.

[0127] The recycling material feed 44 is designed to receive, in addition to or as a replacement for, the recycled material 4, a pelletized recycled material 4 in order to convey it to the extruder 20. For this purpose, the blown film line 10 has a pellet metering device 110 for storing and metering the pelletized material. The pelletized material is preferably virgin material and / or higher-quality recyclates compared to the recycled material.

[0128] A pressure sensor 70 detects the melt pressure in the melt stream at the extruder 20, and another pressure sensor 76 detects the melt pressure in the melt stream upstream of the annular die 30. A control device (not shown) regulates the extruder 20, the annular die melt pump 42, and the recycled material feed 44 depending on the melt pressure in the melt stream at the extruder 20 and upstream of the annular die 30. This enables constant extrusion of recycled material 4.

[0129] An additional pressure sensor 72 detects the melt pressure in the melt stream upstream of the filter 50, and another additional pressure sensor 74 detects the melt pressure in the melt stream downstream of the filter 50. The first pressure sensor 70 detects the melt pressure beyond the extruder 20. The second pressure sensor 76 detects the melt pressure directly at the annular die 30.

[0130] A pressure sensor 76, which detects the melt pressure directly at the annular nozzle 30, monitors a cut-off pressure. The cut-off pressure indicates whether a maximum pressure in the melt flow has been reached. This maximum pressure in the melt flow can be reached, for example, if the temperature at the annular nozzle 30 is too low and the recycled material 4 can no longer be conveyed through the annular nozzle 30 in the required quantity. The pressure sensor 76, which is located directly at the annular nozzle 30, is used to control the speed of the annular nozzle melt pump 42. Another pressure sensor 72 for monitoring a further cut-off pressure is located directly upstream of the filter 50. The pressure sensor 72 located directly upstream of the filter 50 is also used to control the cleaning device. The pressure sensor 70, which is located directly downstream of the extruder 20, is used to control the extruder speed.The pressure sensor 74, which is located immediately after the filter 50, is used to control the speed of the filter melt pump 60 and the speed of the ring nozzle melt pump 42. Reference symbol list

[0131] 2 Starting material 4 Recycled material 6 Film tube 8 Double-layer film web 10 Blown film line 20 Extruder 22 Atmospheric degassing unit 24 Vacuum degassing unit 26 Vacuum pump 28 Condensate collector 30 Ring die 32 Tubing zone 34 Coolant 36 Flattening 38 Take-off roller pair 40 Guide for a melt stream 42 Ring die melt pump 44 Recycled material feed 46 Plugging screw 50 Filter 52 Filter element 60 Filter melt pump 70 Pressure sensor 72 Pressure sensor 74 Pressure sensor 76 Pressure sensor 80 Shredder 82 Conveyor 90 Storage silo 92 Mixing agent for the recycled material 94 Screw conveyor 96 Weighing device of the storage silo 100 Pre-silo 110 Metering device 110 Pellet metering device

Claims

1. Blown film plant (10) for producing a film web from a recycled material (4) with the following features: a. the blown film plant (10) comprises an extruder (20) for melting and homogenizing the recycled material (4) into a melt, b. the blown film plant (10) comprises an annular die (30) for extruding a film tube (6), c. the blown film plant (10) comprises a conduit for a melt stream (40) between the extruder (20) and the annular die (30) via an annular die melt pump (42), for conveying the melt to the annular die (30), d. the blown film plant (10) comprises a tube formation zone (32) for longitudinally and transversely drawing the film tube (6), e. the blown film plant (10) comprises a cooling medium (34) for the film tube (6) moving in the machine direction, f. the blown film plant (10) comprises, downstream of the tube formation zone (32), a collapsing unit (36) for collapsing the film tube (6) into a double-layer film web (8), g. the blown film plant (10) comprises a haul-off roller pair (38) downstream of the cooling medium (34) for hauling off the film tube (6), h. the extruder (20) is configured as a twin-screw extruder, i. the blown film plant (10) comprises a filter (50) with at least one filter element (52) for filtering the melt from an unfiltered side to a filtered side, j. the blown film plant (10) comprises at least two pressure sensors (70, 72, 74) for detecting pressures within the conduit for the melt stream (40), in each case one pressure sensor (70) in the melt stream (40) immediately downstream of the extruder (20) and one pressure sensor (72, 74) upstream of the annular die melt pump (42), and k. the filter (50) is arranged in the conduit for the melt stream (40) between the extruder (20) and the annular die (30), preferably the filter is arranged between the extruder (20) and the annular die melt pump (42), l. the twin-screw extruder comprises at least one degassing unit (22) which enables extraction of impurities and contaminations, characterized by the further features: m. the blown film plant (10) comprises, between the extruder (20) and the annular die melt pump (42), a filter melt pump (60) which pumps the melt to the filter (50), and n. the extruder (20) and the recycled-material feed (44) are adjustable depending on the melt pressure in the melt stream (40) at the extruder (20), and the annular die melt pump (42) is adjustable depending on the melt pressure in the melt stream (40) at the annular die melt pump (42), and o. a control and regulating unit configured to regulate the extruder (20) and the recycled-material feed (44) depending on the melt pressure in the melt stream (40) at the extruder (20) and to regulate the annular die melt pump (42) depending on the melt pressure in the melt stream (40) at the annular die melt pump (42), and p. the filter (50) comprises a cleaning device which renews the filter element (52) continuously and / or discontinuously.

2. Blown film plant (10) according to claim 1 with at least one of the following further features: a. the cleaning device is configured to renew the filter element (52) during operation of the plant, i.e. during production of a film web, b. the cleaning device comprises a rotatable filter element (52) or a rotatable cleaning element for renewing the filter element (52), c. the cleaning device comprises a filter element (52) movable relative to the melt stream or a cleaning element movable relative to the melt stream for renewing the filter element (52), d. the cleaning device comprises a diversion device for cleaning the filter element (52) by temporarily guiding the melt from the filtered side to the unfiltered side, i.e. counter to the usual direction of the melt stream, e. the cleaning device comprises a cleaning outlet through which the melt that was guided from the filtered side to the unfiltered side is to be discharged, f. the cleaning device comprises a screen changer configured to guide the melt stream through a plurality of filter elements (52), g. the cleaning device is configured to guide the melt stream selectively through individual and / or through all available filter elements (52).

3. Blown film plant (10) according to one of the preceding claims with at least one of the following further features: a. the at least one degassing unit (22) is configured as an atmospheric degassing unit (22), b. the at least one degassing unit (22) is configured as a vacuum degassing unit (24), wherein the vacuum degassing unit (24) comprises means for collecting condensate that occurs during vacuum degassing.

4. Blown film plant (10) according to one of the preceding claims with the following further feature: a. the extruder (20) comprises a recycled-material feed (44) with a stuffing screw (46).

5. Blown film plant (10) according to one of the preceding claims with the following further features: a. the blown film plant (10) comprises two additional pressure sensors (70, 72, 74, 76) for detecting the melt pressure in the melt stream upstream and downstream of the filter (50), b. the extruder (20) and / or the annular die melt pump (42) and / or the recycled-material feed (44) and / or the diversion device of the filter (50) and / or the filter element changing device are adjustable depending on the melt pressure upstream and / or downstream of the filter (50), preferably with the additional feature: c. the extruder (20) and / or the annular die melt pump (42) and / or the recycled-material feed (44) and / or the diversion device of the filter (50) are adjustable depending on the pressure sensors (70, 72, 74, 76) for detecting the melt pressure in the melt stream at the extruder (20) and upstream of the annular die (30) and the additional pressure sensors (70, 72, 74, 76) for detecting the melt pressure in the melt stream upstream and downstream of the filter (50).

6. Blown film plant (10) according to one of the preceding claims with the following further features: a. the blown film plant (10) comprises at least one mixing silo for mixing the recycled material (4) with further materials, preferably with the additional feature: b. the mixing silo is connected to the storage silo (90) and / or the presilo (100) via a blower and / or a conveyor belt and / or a conveyor screw for introducing the recycled material (4) and / or mixtures thereof, wherein c. the recycled-material feed (44) is configured to receive, in addition to or alternatively to the recycled material (4), a pelletized recycled material (4) in order to convey it to the extruder (20), preferably with at least one of the additional features: d. the blown film plant (10) comprises a pellet metering device (110) for holding and metering the pelletized material, e. the pelletized material is virgin material and / or higher-grade recyclates compared to the recycled material, wherein f. the pellet metering device (110) comprises a conveyor screw which conveys the recycled material (4) to the extruder (20).

7. Blown film plant (10) according to one of the preceding claims with the following further features: a. the blown film plant (10) is configured to produce the film web, in addition to a layer of the recycled material (4), with at least one further layer, b. the blown film plant (10) comprises at least one additional extruder (20) which melts and homogenizes the material of at least one additional layer into a melt, preferably with the additional feature: c. the additional extruder is configured as a twin-screw extruder, wherein, d. the blown film plant (10) is configured to produce a film web in which the recycled material (4) is arranged between at least two further layers in the film web, wherein e. the blown film plant (10) comprises a machine direction oriented substantially vertically from bottom to top.

8. Method for producing a film web from a recycled material (4), using a blown film plant according to one of claims 1 to 7, with the following features: a. the twin-screw extruder melts and homogenizes the recycled material (4) into a melt, b. the melt is conveyed to the annular die (30) via the melt stream with the annular die melt pump (42), c. the melt is extruded via the annular die (30) into a film tube (6), d. at a tube formation zone (32) the film tube (6) is longitudinally and transversely drawn, e. the collapsing unit (36) for the film tube (6) collapses the film tube (6) downstream of the tube formation zone (32) into a double-layer film web (8), f. the haul-off roller pair (38) downstream of the collapsing unit (36) hauls off the film tube (6), g. the melt stream is filtered, by means of the filter (50), with the at least one filter element (52) within the melt stream, by guiding the melt stream from an unfiltered side to a filtered side, h. the filter (50) is arranged in the melt stream between the extruder (20) and the annular die (30), preferably the filter (50) is arranged between the extruder (20) and the annular die melt pump (42), and i. the filter melt pump (60), which is arranged between the extruder (20) and the annular die melt pump (42), pumps the melt to the filter (50), and j. the melt is degassed in the twin-screw extruder via the at least one degassing unit (22), whereby extraction of impurities and contaminations takes place.

9. Method according to preceding claim 8 with the following further feature: a. the extruder (20) is fed with the recycled material (4) via a recycled-material feed (44) with a stuffing screw (46).