EP3901333A1 - Production of filaments with controlled gas flow - Google Patents

Abstract

The present invention relates to a device suitable for producing material filaments by extruding a material fluid and solidifying the material fluid, with an extrusion head (1) with a plurality of extrusion openings, a collecting bath (2) for receiving extruded fluid filaments (5) from the extrusion openings, a gas gap (A) between the extrusion openings and the collecting bath, whereby a gas treatment area (4 ') for extruded material fluid is formed, a gas flow device (3,6) for generating a gas flow in the gas gap, characterized in that laterally of the gas treatment area and in the direction of the At least one gas flow restriction (4) is provided for the gas flow; and a method for producing solid filaments of material from a fluid of material by extruding the fluid of material.

Description

The present invention relates to the shaping and treating of extruded synthetic fibers before and during their solidification.

Background of the invention

Cellulose can be dissolved in aqueous solutions of amine oxides, in particular solutions of N-methyl-morpholine-N-oxide (NMMO), in order to produce spinning products such as filaments, staple fibers, foils, etc. from the spinning solution obtained. This is done by precipitating the extrudates in water or dilute amine oxide solutions after the extrudates are fed from the extruder through a gas gap into the precipitation bath. Cellulose solutions in the range from 4% to 23% are usually used for processing into extrusion products. This process is also called the lyocell process or the cellulose filaments obtained are called lyocell filaments.

The spinning process can, depending on the required end product, be carried out via an extrusion channel or several extrusion channels installed in an extruder. A single-channel extrusion process depending on the diameter of the extrusion opening is described in the article " Spinning of Fibers through the N-Methyl-Morpholin-N-Oxide Process "(SA Mortimer and A. Peguy; in Zellulose and Zellulose Derivatives: Physico - Chemical Aspects and Industrial Applications; Woodhead Publishing Ltd., 1995 ). In it, the authors describe the effects of the spinneret diameter and the spinning draft ratio, as well as the effect on the fibrillation of the fibers in the NMMO process, whereby this process was carried out as a monofilament spinning process in the air gap.

An industrial NMMO multifilament line is installed in U.S. 4,246,221 and consists of an extruder with an extrusion plate with several extrusion openings, a gas gap and a collecting container with a reimbursement medium.

EP 0 430 926 B1 describes extrusion openings with capillaries, which allow a higher hole density of the extrusion openings.

WO 93/19230 A , WO 94/28218 A and EP 0 700 463 B1 describe a cooling of the extruded filaments after extrusion by blowing with a gas stream. According to the WO 94/282218 In addition to blowing, air is also sucked out.

In WO 94/28210 and WO 98/18983 describes spinnerets for the production of Lyocell fiber, the extrusion openings being provided in several plates welded into a frame structure. The entirety of the plates results in a cluster-like arrangement of the extrusion nozzles corresponding to the respective plates.

DE 10 200 405 A1 describes a lyocell process in which a filament curtain is cooled with a wide nozzle in an air gap with a widely fanned gas stream.

WO 2013/030399 A1 describes a Lyocell process in which the gas flow is divided into a heating sub-flow and a cooling sub-flow.

WO 02/12600 describes a lyocell process which was adjusted with regard to the withdrawal speed of the lyocell filaments.

In the area of melt spinning which is remote from the lyocell process, in which the filaments are solidified in the gas region immediately after a melt has been extruded, according to FIG U.S. 4,283,364 an extrusion plate for small systems with channels known. In this system, the channels are intended to improve the yarn count with fewer bumps. However, the processes in the gas area after extrusion are not comparable between melt spinning and lyocell spinning: while melt spinning takes place in the process of solidification, in the lyocell process this only takes place in the solidification medium, e.g. in a precipitation bath, while the fluid filaments are pretreated in the gas gap, e.g. in order to stretch them to a specific level Adjust the humidity ( U.S. 4,246,221 ), to pre-cool them or to remove harmful particles ( WO 2013/030399 A1 ).

JP 05044104 A2 describes a dry-jet wet spinning process for the production of filaments in which a gas is caused to flow through the air gap under the spinneret in a direction perpendicular to the direction of travel of the filament in order to remove remaining solvent vapor from the extruded filaments. As a result, filament breakage, adhering filaments, unusually thick parts, and unevenness in size are prevented from occurring, which noticeably improves the quality and productivity of the fibers. In addition, the gas is captured by a suction device after passing through the air gap, the gas is deflected by 90 ° so that the exhaust air flow is discharged approximately parallel and opposite to the direction of travel of the filaments.

WO 03/014436 A1 describes a process for the production of cellulosic moldings in which a solution of cellulose in a tertiary amine-N-oxide and optionally water is molded in a hot state and the molded solution is cooled by a gaseous medium in a gas gap before being introduced into a coagulation bath , wherein the gaseous medium flows through the formed solution from a gas inlet side to a gas outlet side. The method is characterized in that the gaseous medium is sucked off on the gas outlet side in a direction essentially parallel or essentially opposite to the direction of movement of the molding solution

Summary of the invention

The present invention relates to a filament spinning process or a wet spinning process in which filaments extruded in a solidification medium are solidified after they have been pretreated in a gas gap. It is an aim of the invention to achieve the highest possible material throughput with optimal treatment in the gas gap and good quality of the filaments obtained. The qualities of a monofilament process are aimed for for multifilament processes.

Another goal is to keep productivity as high as possible. In addition, it is an aim of the invention to achieve the highest possible spinning speeds with appropriate spinning reliability and product quality (no sticking, uniform fiber fineness).

The present invention relates to a device suitable for producing material filaments by extrusion of a material fluid and solidification of the material fluid. The device has an extrusion head 1 with a plurality of extrusion openings, a collecting bath 2 for receiving extruded fluid filaments 5 from the extrusion openings, a gas gap A between the extrusion openings and the collecting bath, whereby a gas treatment area 4 'for extruded material fluid is formed, a gas flow device 3 6 for generating a gas flow in the gas gap, with at least one gas flow restriction 4 being provided to the side of the gas treatment area and in the direction of the gas flow.

The invention further relates to a method for producing solid filaments of material from a material fluid Extrusion of the material fluid through several extrusion openings, whereby fluid filaments 5 arise, passage of the fluid filaments through a gas gap A, and solidification of the filaments in a coagulation liquid in a collecting bath 2, a gas stream 6, 7 flowing through in the gas gap A, the gas stream with at least one gas flow restriction 4 is passed, the gas flow restriction laterally delimiting a gas treatment area 4 'in which the filaments are treated with the gas flow. Because of the design of the spinning system, which is partially open to the environment, so-called "false air streams" 8 are introduced into the spinning system.

All details and embodiments described herein relate to all aspects of the invention, the device and the method equally. The device or parts thereof can be used in the process. Details of the method can preferably be the suitability of the device for carrying out these methods.

Figure description

• In Fig. 1 an extrusion device for producing material filaments by extrusion of a material fluid and solidification of the material fluid with a gas flow restriction 4, 4 ', 4 "is shown in a side view.
• In Fig. 2 an arrangement of the extrusion device is made Fig. 1 in the front view (view on Fig. 1 from left). The filament curtain 5 is formed by individual filaments. The gas flow restriction 4 is located on the side.
• Fig. 3 shows an embodiment of a gas flow restriction 4 according to the invention in detail. The gas flow restriction 4 has a perforation, here slots, in a partial area.
• Fig. 4 shows an alternative embodiment of a gas flow restriction 4. The gas flow restriction 4 is basically the same as the embodiment in FIG Fig. 3 . Instead of the slots, the perforation is made with a mesh or grid.
• Fig. 5 represents a further alternative embodiment of a gas flow restriction 4. The gas flow restriction 4 is basically the same as the embodiment in FIG Fig. 3 . Instead of the slots, the perforation is made with regularly arranged recesses. The recesses can be round, square, rectangular, rhombic, triangular or designed in any shape.
• Fig. 6 represents a further alternative. In this case, the gas flow restriction 4 is not continuously designed as a flat surface, but has a three-dimensionally structured surface, in particular a grooved riblet surface, at least in a partial area (in Fig. 6 shown in dashed lines).
• Fig. 7 shows a sectional view from above (top view) of the edge area. The filament curtain 5 is flowed through by the gas stream 6. In the edge zone, “secondary gas” 8 'is additionally sucked in by the primary gas flow 6, which gas is swirled due to the three-dimensionally structured surface of the gas flow restriction 4.
• Fig. 8 describes a system similar to Fig. 7 . The difference too Fig. 7 is that the three-dimensionally structured surface of the gas flow restriction 4 is partially perforated, so that by the suction effect of the secondary gas 8 'sucked in in the edge area, even more "secondary gas" 8 "' is introduced into the system.
• Fig. 9 is identical to Fig. 8 however, the gas flow restriction 4 is designed as a flow chamber, whereby the "secondary gas" 8 "'is introduced in a dosed quantity as a forced flow.
• Fig. 10 represents a special form of execution compared to Fig. 6 The gas flow restriction 4 is in this case a restriction which has indentations at regular intervals which contain openings in the air flow direction which allow an air flow from the outside to the inside into the gas treatment area.
• Fig. 11 FIG. 13 shows a sectional view from above (top view) of the edge region of FIG Fig. 10 The filament curtain 5 is flowed through by the gas stream 6. In the edge zone, “secondary gas” 8 'is additionally sucked in by the gas flow 6, which gas is swirled due to the three-dimensionally structured surface of the gas flow restriction 4. As a result of the suction effect of the secondary gas 8 'sucked in in the edge area, "secondary gas" 8 "' is additionally introduced into the system from the outside through the gas flow restriction 4.

Detailed description of the invention

The invention relates to a device with an extrusion head 1 with a plurality of extrusion openings, a collecting bath 2 for receiving extruded fluid filaments 5 from the extrusion openings, a gas gap A between the extrusion openings and the collecting bath, whereby a gas treatment area 4 'is formed for extruded material fluid, a gas flow device 3, 6 for generating a gas flow in the gas gap, with at least one gas flow restriction 4 being provided to the side of the gas treatment area and in the direction of the gas flow. The device can be used for producing material filaments by extrusion of a material fluid and solidification of the material fluid. For solidification, a coagulation liquid is usually provided in the collecting bath (the container for it). In terms of its composition, this coagulation liquid is not a solvent for the material fluid, which means that it coagulates and forms coagulated filaments which are essentially solid.

The gas gap is an essential treatment zone for the extruded filaments, in which the filaments, which are still fluid, are e.g. stretched or surface-treated (volatilization of solvent components). The treatment zone in the gas gap is determined by the distance between the extrusion openings and the surface of the coagulation bath. In the device according to the invention, this surface level can be marked in the collecting bath, which is essentially a tub, in particular this surface level is determined by an overflow, above which the level of the coagulation liquid cannot rise during operation. In preferred embodiments, the collecting bath therefore has a liquid level provided for a coagulation liquid that can be taken up in the collecting bath.

The invention also relates to a method for producing solid material filaments from a material fluid by extruding the material fluid through several extrusion openings, whereby fluid filaments 5 are formed, the fluid filaments pass through a gas gap A, and the filaments solidify in a coagulation liquid in a collecting bath 2, whereby A gas stream 6, 7 flows through in the gas gap A, the gas stream being guided with at least one gas flow limiter 4, the gas flow limiter having a gas treatment area (4 '), in which the filaments are treated with the gas stream, laterally limited.

The invention relates to the production of material filaments, e.g. as continuous molded bodies, from a molding compound such as a spinning solution. The process is preferably a lyocell process, that is to say a spinning process for a cellulose solution, such as a spinning solution containing cellulose, water and tertiary amine oxide. Lyocell is a generic generic name given by BISFA (The International Bureau for the Standardization of Man-Made Fibers) for cellulose fibers that are made from cellulose without the formation of a derivative. It is extruded from a large number of extrusion openings through which the molding compound (material fluid) is extruded to form the fluid filaments. The fluid filaments are solidified in the coagulation liquid, which is also referred to as the solidification medium or precipitation bath. A gas treatment area for the filaments is located in the gas gap between the extrusion openings and the coagulation liquid.

The gas treatment area is spatially defined by the height of the gas gap (distance between extrusion openings and coagulation liquid, in particular the intended liquid level in the collecting bath) and laterally by the dimensions of the extrusion openings arranged. The extruded filaments flow from these extrusion openings into the coagulation liquid (the collecting bath) during operation. The area delimited by the (outer) extruded filaments is called the gas treatment area, as the filaments in it are treated by the gas flow. It is therefore the space that is formed by the area of the arrangement of the extrusion openings (limited by the extrusion openings at the edge of the arrangement) times the height of the gas gap at the location of the extrusion openings. The multitude of filaments in the gas gap is also known as an extrudate curtain. This determines the gas treatment area.

A gas stream is moved through the gas gap, usually in a linear manner, at least in plan view. The gas flow enters the gas treatment area on one inlet side and exits again on an opposite outlet side. In the gas treatment area itself, the gas flow flows around the filaments.

According to the invention, at least one gas flow restriction is provided to the side of the gas treatment area. "Lateral" usually means essentially normal to the extrusion direction or essentially parallel to the surface of the coagulation bath and also laterally on the gas treatment area with regard to the continuous gas flow, i.e. running essentially parallel to this, but offset to the edge of the gas treatment area. The gas flow restriction is a physical barrier that is an area between the extrusion orifices and the coagulation bath and along the boundary of the gas treatment area in the direction of the gas flow. The gas flow restriction is, for example, a wall that rests on the side of the gas treatment area. It is usually only a short distance away. Of course, the gas flow restriction must not touch the extruded filaments in order not to impede their flow from the extrusion openings into the collecting bath. The gas flow limitation merely changes the gas flow, in particular in the edge areas of the gas treatment area. These changes relate to turbulence that would otherwise occur and / or any lateral inflow or outflow to / from the gas flow.

In particular, conditions are created for guiding the gas through the filaments in the gas gap through the use of the gas flow restriction according to the invention, which represent a considerable further development compared to previous spinning systems in terms of quality of the filaments, productivity and maintenance of trouble-free operation.

The gas flow restriction according to the invention influences the gas flow in the edge zones of the gas treatment area. The gas flow limitation according to the invention influences the streamlines of the gas flow; depending on the configuration of the limitation, they can be deflected, compressed, swirled and / or mixed with secondary gas. Gas that flows in a direct line from the inlet side to the outlet side to and through the gas treatment area is referred to as primary gas. It is usually blown into the gas treatment area by a blower. Secondary gas is indirectly introduced gas, which is, for example, entrained by the primary gas. According to the invention, it was found that this secondary gas at the edge areas of the gas treatment area to disturbances of the Spinning process can lead, such as sticking or tearing of the filaments. Recirculation gas is also disruptive. This is gas that has already passed through the filament curtain. As a result, it has already absorbed solvent through the first contact with the filaments or the coagulation bath and / or has been heated (the extrusion is usually carried out under heat, for example 80 ° C. or more), which makes it less suitable for further treatment of the filaments and has a destabilizing effect on the spinning process. The proportion of secondary air and the supply of recirculation gas are minimized by restricting the gas flow. The purpose of limiting the gas flow is that, on the one hand, the gas flow can be passed through the filaments over the entire length and width of the gas treatment area under the same conditions as possible. In addition, the gas flow restriction also has the effect of calming the solidification bath surface.

In the case of closed round nozzles / ring nozzles that are not sectioned over the circumference, i.e. extrusion openings arranged in a ring, their inherent "infinity" achieves the same gas flow conditions over the entire circumference. A specific feature of ring nozzles, however, is that in the solidification bath inside the closed filament curtain, bath eddies or bath backflows occur, which cause considerable turbulence on the solidification bath surface. In the case of ring nozzles, the maximum take-off speed must therefore be kept low, since higher take-off speeds (as is common with "open" filament curtains) lead to massive spinning disturbances due to the bath turbulence.

Rectangular nozzles (extrusion openings arranged in a rectangle) or sectional nozzles, split ring nozzles or other extrusion devices that form "open" (not closed) filament curtains are therefore preferred. These arrangements allow faster operation and here the gas flow restrictions according to the invention can contribute to considerable advantages, since they minimize or prevent the "marginal accessibility" of the gas flow and turbulence on the solidification bath surface. The extrusion openings are preferably arranged in a rectangular shape, the narrow side of the rectangular shape facing the gas flow restriction. The gas flow flows against the long side or faces a fan. Possible Shapes of the arrangement of the extrusion openings are rectangular, curved, ring or ring segment shape. The elongated shape can have a length to width ratio of 100: 1 to 2: 1, preferably from 60: 1 to 5: 1 or from 40: 1 to 10: 1. A gas flow restriction as described herein is preferably used on both sides of the gas treatment area (left and right, viewed from the gas flow).

In the case of a rectangular shape, the lateral gas flow limitation can be connected to the side of the gas flow feed (usually the longitudinal side - as described above, side of the fan or side against the gas flow direction). With gas flow restrictions attached on both sides of the gas treatment area, a U-shaped restriction is thus created, also referred to together as a blown air box. The connecting part (on the side of the gas flow device) can be designed in the same way as the lateral gas flow restrictions and, for example, protrude into the coagulation liquid in the collecting bath (or into the level provided for this in the device according to the invention) to avoid secondary air being drawn in. One end of the connecting part (such as the lateral gas flow restriction) without protruding into the coagulation liquid in the collecting bath (or into the level provided for this in the device according to the invention), i.e. one end above this level, is also possible.

The gas flow restriction (and / or the connecting part) can be arranged perpendicular to the collecting bath (coagulation liquid level) or at an angle deviating from the perpendicular, e.g. 0 ° to 30 °. The slope is preferably widening downwards (in the direction of the collecting bath) (ie away from the extruded material fluid) or narrowing (towards the extruded material fluid). The distances specified here between the gas flow restriction and the extruded material fluid / gas treatment area relate to the distance at the narrowest point.

Advantages of the invention in the gas treatment area are uniform gas flow temperature and gas flow moisture; uniform gas flow rate; uniform gas flow velocity gradient along the filaments in the extrusion direction (from the extrusion openings to the collecting bath); uniform loading of the filaments by the flowing gas stream; Reduction or avoidance of turbulence on the solidification bath surface.

The gas flow limitation at least partially limits the gas flow laterally over the gas gap height. The gas flow limitation can be guided from the extrusion head in the direction of the surface of the coagulation liquid over the entire height of the gas gap or only partially extend over the gas gap height so that part of the gas gap height is not limited. The area not limited by the height of the gas gap can lie directly above the surface of the coagulation liquid, in the area directly below the extrusion openings or else between the coagulation liquid surface and the extrusion openings. According to the invention, the gas flow restriction can also immerse into the coagulation liquid and, according to an immersion depth, end below the surface of the coagulation liquid.

The gas flow limiter can be mounted directly on the extrusion head, on the collecting bath or on the gas flow device (suction, blower). A combination of several gas flow restrictions is also possible; these can be connected separately, possibly with a gap (a full-area barrier is not necessary and is not made in preferred embodiments, especially in the examples) or connected to one another.

The gas flow restriction preferably extends over the entire length B of the gas treatment area, i.e. in the length there are all extrusion openings arranged in the longitudinal direction (gas flow direction to which the gas flow restriction runs or is essentially parallel). The extension over the entire length B of the gas treatment area means that the area of the gas flow limitation covers this area, in particular the edges of the gas flow limitation reach at least these dimensions. You can also go beyond that. Furthermore, as mentioned, the gas flow restriction can be perforated, i.e. covering and extension does not necessarily mean a complete closure of this area. It can partially block the area.

The gas flow limitation preferably extends over an area L, 4 "in the gas flow direction after the gas treatment area. The gas flow limitation can therefore extend beyond the gas treatment area, according to this feature in the direction of the gas flow or in the direction of the suction device, if present if the length L this subsequent area in the gas flow direction is at least half the length B of the gas treatment area of all extrusion openings arranged in the longitudinal direction. The length L is preferably greater than or equal to the length B.

Furthermore, it is preferred that the gas flow restriction extends over an area K against the gas flow direction in front of the gas treatment area, that is, in the direction of a fan, if present. The length K of this previous region against the direction of gas flow is preferably at least half of the length B of the gas treatment region of all extrusion openings arranged in the longitudinal direction.

The gas flow in the gas gap can be brought about or forced by a gas flow device. For this purpose, the gas flow device can comprise, for example, a fan or a suction device or both. Both are preferably provided. Different flows can be set in both devices. Usually, a higher flow is set in the suction device than in the blower, since secondary air is sucked in in addition to the primary air. According to the invention, this inequality can be reduced due to the secondary air reduction.

In preferred embodiments of the device according to the invention or in the method according to the invention, a fan and / or a suction device 3 is provided as the gas flow device or for the gas flow. The suction device can have an extraction channel which is preferably oriented at an angle X of 0 ° to 45 ° to the horizontal (collecting bath / coagulation bath surface). Likewise, the suction device is preferably arranged above the gas gap, so that the gas treatment area is accessible on a horizontal plane. Through this accessibility, the filament curtain can be seen or a user of the device can take corrective action. The angle X is preferably 10 ° to 40 °, for example 20 ° to 35 °. 0 ° corresponds to the horizontal or the coagulation bath surface. Thus, it is preferred that the suction device allows an undisturbed direct view of the filaments in the gas gap, the exhaust gas is deflected as little as possible during removal from the gas gap, whereby a particularly efficient suction is achieved; the amount of ambient air (secondary air) that is excessively extracted can be kept as low as possible. Furthermore In this way, in combination with the gas flow restriction, the solidification bath can be kept as turbulence-free as possible. Because of the relatively small distance from the suction opening of the suction device, there is namely the risk that the exhaust gas flow also entrains the solidification bath and can thus contribute to turbulence in the solidification bath. This is reduced with the invention.

In the method, the gas flow can therefore be achieved by blowing in 6 and sucking in 7, with a sucked gas stream preferably being greater than a blown gas stream. The ratio of the sucked gas stream to the injected gas stream is preferably greater than 1.2: 1, e.g. greater than 1.4: 1 or greater than 1.6: 1. This inequality can also be limited by the invention; thus the ratio is preferably less than 2: 1, preferably less than 1.8: 1, less than 1.6: 1: or less than 1.5: 1 or also less than 1.4: 1.

In the gas gap, a gas stream can optionally (and preferably, especially in the case of large, industrially relevant systems) be blown in and / or sucked out. The gas stream entering the treatment zone (immediately before the treatment zone, for example with the fan) preferably has a temperature of 5 ° C to 65 ° C, preferably 10 ° C to 40 ° C, in particular room temperature, e.g. 20 ° C to 25 ° C . The material fluid can be extruded at a temperature of 75 ° C to 160 ° C. The gas gap preferably has a lower temperature than that of the extruded material fluid. In particular, a gas flow is guided in the gas gap at a lower temperature than the extruded material fluid.

Possible lengths of the gas gap, that is to say the distance between the extrusion openings and the surface of the coagulation bath, are preferably between 10 mm and 200 mm, in particular between 15 mm and 100 mm, or between 20 mm and 80 mm. Preferably it is at least 15 mm. The gas in the gas gap is preferably air. The gas flow is preferably an air flow. Other inert gases are also possible. Inert gas is a gas that does not react chemically with the fluid filaments in the gas gap and preferably also not with the solidification medium such as water or a dilute NMMO in water solution or other solvent components - depending on the extrusion medium used.

The flow into the gas treatment area (injection, blower) is preferably adjusted so that a desired cooling of the gas in the gas gap in the gas treatment area (especially at the gas outlet end). Preferably, especially in a Lyocell process, the inflow is adjusted so that the temperature in the gas treatment area is cooled to 40 ° C to 80 ° C, preferably 50 ° C to 70 ° C or 55 ° C to 65 ° C.

By choosing the gas flow and the gas flow limitation, turbulence in the gas flow at the lateral edge of the gas treatment area can also be avoided.

In order to achieve the advantages of the invention, in particular to influence the gas flow behavior, the gas flow restriction does not have to cover the entire lateral surface. The gas flow restriction preferably has a height in the gas treatment area in the extrusion direction of at least 70% of the height of the gas gap. The height of the gas flow restriction corresponds to its dimension in the direction of the extrusion direction, that is to say essentially vertical or normal to the surface of the coagulation liquid; in particular in the gas treatment area, that is between the extrusion openings and the coagulation bath, in preferred embodiments it should extend over at least 70%, particularly preferably at least 80% or at least 90%, of this height.

The gas flow restriction can be completely closed, slotted or perforated, i.e. it can have openings that allow a gas flow through it. The perforation can be carried out over the entire surface or only on partial surfaces. The perforation can be realized with sieves, slots or holes or other openings in the surface. The gas flow restriction preferably has perforations in the area of the gas treatment area. In this area with perforations, preferably at least 25% of the area of the gas flow limitation in the area of the gas treatment area is closed, i.e. not permeable to gas flow. So 75% or less of the area can be open. Particularly preferably at least 35% are closed in this area, preferably at least 45%, or at least 55%, at least 65% or at least 75% or at least 85% of the area in the area with the perforations can be closed.

The gas flow restriction can be flat, curved, single or multiple corrugated or beveled. The bending, corrugated or The direction of the edge can be aligned horizontally, vertically or even at an angle between a horizontal and a vertical orientation.

The perforations are preferably holes or strips, preferably strips in the extrusion direction. Particularly preferably, at least one strip is provided every 4 cm, preferably every 2 cm or every 3 cm, length of the gas flow limitation in the area of the gas treatment area in the gas flow direction.

In further preferred embodiments, the gas flow restriction has a corrugated, grooved or ribbed surface in the area of the gas treatment area. Such a surface is, for example, a riblet or waveguide surface. The corrugated, grooved, ribbed or riblet surface is preferably combined with the above-mentioned perforations. The corrugated, grooved or ribbed or riblet surface can furthermore have the perforations mentioned. A riblet surface is a surface geometry with ribs that cause a stall. The ribs are preferably designed in such a way that, in the direction of flow, the ribs protrude more and more into the gas treatment area in order to then break off and return to the wall level of the. They are essentially jagged or serrated indentations. The perforations can be in the continuous area or in the break-off area of the prongs. The gas flow restriction can be designed as a plate which has openings embossed at regular intervals which, after flowing through the plate, cause the gas flow to be deflected. Depending on the design of the embossing, the gas flow can be deflected by 15 ° to 90 ° compared to the vertical flow through "open" holes. The corrugations, grooves, ribs, riblets, spikes and the like are preferably caused to cause turbulence on the surface of these grooves, ribs, riblets, spikes and the like. In particular, these surfaces are used to generate low air resistance. Alternatively, the gas flow restriction can also be smooth.

The gas flow restriction 4 can be designed as a flow chamber. This essentially means that the gas flow restriction is double-walled, as a result of which the chamber is formed. Here, the wall facing the gas treatment area has perforations, due to the double-walled design a gas flow (secondary gas) through the chamber and thus through the perforations can be limited, controlled or controlled.

The gas flow restriction is preferably tempered. This can occur on the one hand with a gas flowing through the gas flow restriction and / or with cooling or heating means different from the gas, e.g. an electrical heater or a heat transfer fluid that can temper the gas flow restriction.

The gas flow restriction rests on the side of the gas treatment area and is at a distance from it (distance from the filaments). This distance is e.g. 2-20 times the distance between the filaments (or the extrusion openings). Thus, the gas flow restriction to the gas treatment area is preferably present at a distance J of at least twice the distance C between the extrusion openings in the direction transverse to the gas flow direction. The gas flow restriction to the gas treatment area is preferably at a distance J of at most 30 times the distance C of the extrusion openings from one another in the direction transverse to the gas flow direction.

Suitable and optimal distances and sizes of the gas flow restriction from the gas treatment area (extruded material) can be determined in tests by recording the spinning instabilities in the edge zones. Typically, recording can be done by visual or video recording and flow simulation when examining the flow with or without the presence of certain gas flow restrictions (such as riblet surfaces and the like, and / or perforations) at a selected gas flow rate. The visualization of gas flows can be done with artificially generated smoke mist so that the flow can be understood and reproduced and the spinning system can be constructed as a whole.

The gas flow restriction can be selected from various materials, such as metal or plastic, e.g. thermoformed plastic.

An extrusion medium is used as the fluid in the method according to the invention. This is preferably a solution or mixture of cellulose and other medium components such as solvents. The cellulose concentration is selected in the sizes customary for lyocell processes. Thus, the cellulose concentration of the extruded fluid can be 4% to 23%, preferably 6% to 20%, in particular 8% to 18% or 10% to 16% (all% figures in% by mass). In the Lyocell process, the extrusion medium is usually a cellulose solution or melt with NMMO (N-methylmorpholine-N-oxide) and water, as described in the introduction. Other solutions of cellulose, particularly ionic solvents of cellulose, can also be used. Alternatively or additionally, it can be an ionic solvent. Such ionic solvents are for example in WO 03/029329 ; WO 2006/000197 A1 ; Parviainen et al., RSC Adv., 2015, 5, 69728-69737 ; Liu et al., Green Chem. 2017, DOI: 10.1039 / c7gc02880f ; Hauru et al., Cellulose (2014) 21: 4471-4481 ; Fernández et al. J Membra Sci Technol 2011, S: 4 ; etc. and preferably contain organic cations, such as ammonium, pyrimidium or imidazolium cations, preferably 1,3-dialkyl-imidazolium salts, such as halides. Again, water is preferably used as a nonsolvent for cellulose. A solution of cellulose and butyl-3-methyl-imidazolium (BMIM), e.g. with chloride as the counterion (BMIMC1), or 1-ethyl-3-methyl-imidazolium (also preferably as chloride, acetate or diethyl phosphate) or 1 is particularly preferred -hexyl-3-methylimidazolium or 1-hexyl-1-methylpyrrolidinium (preferably with a bis (trifluoromethylsulfonyl) amide anion), and water. Other ionic solvents are 1,5-diazabicyclo [4.3.0] non-5-enium, preferably as acetate; 1-ethyl-3-methylimidazolium acetate, 1,3-dimethylimidazolium acetate, 1-ethyl-3-methylimidazolium chloride, 1-butyl3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium diethyl phosphate, 1-methyl-3- methylimidazolium dimethyl phosphate, 1-ethyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazolium octanoate, 1,3-diethylimidazolium acetate and 1-ethyl-3-methylimidazolium propionate. The material fluid preferably contains cellulose, preferably a solution or melt of cellulose, a solvent of cellulose, preferably an amine oxide, and water.

In dry-wet spinning, the treatment zone essentially consists of a gas or air gap and downstream liquid containers, liquid funnels or liquid channels. The extrudates emerging from the extrusion openings pass through a gas gap and subsequently a coagulation bath, also known as a spinning bath. The moist (felled and / or cooled) extrudates are fed to the extraction unit through one or more washing baths and / or through a gas or air space.

In the wet or dry-wet spinning process, turbulence and eddies occur at higher speeds due to displacement and drag processes between the coagulation bath liquid and the extrudate. In addition, in the case of deflection points with rigid deflections, there is also the risk of running dry at the contact points between the extrudate and the deflector. The higher the take-off speed and the more the extrudate curtains or bundles thereof are pressed against the deflection device, the greater the risk of running dry. The filaments are preferably deflected in the collecting bath. A deflection device can be provided for this purpose.

The gas flow restriction preferably dips into the coagulation bath or extends below the surface level of the coagulation bath (or the level provided for this in the collecting bath). This immersion can reduce turbulence in the bathroom. This immersion depth is preferably 1 mm to 50 mm.

The extrusion openings preferably have a diameter of 30 μm to 200 μm, more preferably 50 μm to 150 μm or 60 μm to 100 μm. This enables filaments suitable for textiles (woven and non-wovens) to be produced.

The extrusion throughput is preferably set in such a way that, at the given take-off speed, the individual fibers have a fineness of 1.3 dtex +/- 50%, preferably +/- 25% or +/- 10%. The extrusion throughput can be adjusted by the pressure of the extruded mass, i.e. the cellulose solution. Possible pressures are, for example, 5 to 100 bar, preferably 8 to 40 bar.

The present invention is further described by the following figures and examples, without being restricted to these embodiments of the invention.

In Fig. 1 a typical arrangement of a spinning device is shown in side view. The filament curtain 5 emerging from the extrusion head 1 or the extrusion openings passes through the gas gap A in order to subsequently dip into the coagulation bath 2. A gas flow feed 6 supplies the gas gap A with a gas flow which passes through the filament curtain 5 and is then deflected by the deflection angle X through the suction device 3 to leave the spinning area as a discharged gas stream 7.

In addition to the supplied gas 6, secondary gas 8 'is supplied to the gas gap A. The secondary gas 8 ′ enters the gas gap A both from the direction of the supplied gas 6 and from the lateral direction via the perforated gas flow restriction 4. An essential feature of the invention is to use the inventive design of the gas flow restriction 4 and the design of the perforation of the gas flow restriction 4 to create conditions such that trouble-free spinning operation and high take-off speeds of the filaments can be achieved. A preferred embodiment was determined by a series of tests, the spinning stability and the degree of turbulence of the coagulation bath surface 2 being evaluated.

The gas flow 7 drawn off by the suction device 3 is the sum of the supplied gas flow 6, secondary gas 8 'and ambient gas 8 ″ which are sucked in from the environment due to the open construction.

The gas flow restriction 4 is designed as a flat, at least partially planar structure with a height M. The gas flow restriction 4 covers the gas gap A at least partially laterally in the vertical direction. The gas flow limitation shown in the figure is also immersed in the coagulation bath 2 by the amount of the immersion depth O. The vertical distance N is also shown, which represents the vertical distance between the exit plane of the filament curtain and the upper edge of the gas flow restriction 4. This distance is preferably 0 mm to 20 mm.

The gas flow limiter 4 preferably extends in the horizontal direction over the width of the filament curtain B (dimension in the gas flow direction, e.g. 5 mm to 100 mm) and additionally over an overhang to the gas treatment area on the gas inlet side K and additionally over an overhang to the gas treatment area on the gas outlet side L. The protrusion of the gas flow restriction on the gas inlet side K is, for example, 0 mm to 200 mm. The protrusion of the gas flow restriction on the gas outlet side L is preferably 0 mm to 400 mm.

The gas flow restriction 4 is in Figure 1 shown in one piece. Possible embodiments of the gas flow limiter 4 are also designed in several parts, for example the gas flow limiter be executed divided in the horizontal, vertical but also in every other direction.

In Fig. 2 a typical arrangement of a spinning device is shown in front view. The filament curtain 5 is formed by individual filaments which extend over the filament curtain length T (dimension transverse to the gas flow direction). The filaments are spaced apart from one another over the length T of the filament curtain 5 at a distance C. This distance between the filaments is, for example, 0.4 mm to 10 mm. The gas flow restriction 4 is spaced from the filament curtain as an extension of the filament curtain length T by the amount of the lateral distance of the gas flow restriction J. This distance is, for example, 1 mm to 20 mm.

Fig. 3 shows an embodiment of a gas flow restriction 4 according to the invention in detail. The gas flow restriction 4 has a perforation in a partial area. The position of the perforation is determined in the horizontal direction via the horizontal distance from the end of the gas flow restriction on the gas flow restriction to the perforation P and the horizontal length of the perforation Q. For example, P is 1 mm to 50 mm. The perforation is shown here for a gas treatment area and an overhang in the direction of the gas flow inlet. It can also only be present in part of the gas treatment area. Q can be a fraction of the width of the gas treatment area. The length L of an area with perforation can be selected depending on the intended gas flow, filament withdrawal speed and number of filaments; for example, Q can be between 20 mm and 200 mm.

The perforation is preferably not immersed in the coagulation liquid. The position of the perforation is determined in a vertical orientation via the vertical distance from the end of the gas flow restriction on the spinning nozzle side to the perforation R and the height of the area with the perforation S. The vertical position of the area with perforation is designed in such a way that the perforation is present at least in a partial area of the gas gap A. In a vertical orientation, the perforation can also extend over the entire gas gap A and also into the coagulation bath 2.

In Fig. 3 the perforation is designed with vertical slots as an example. Slots in horizontal or oblique Alignment is also possible, but slots in a curved or other non-straight shape are also possible. R is, for example, 1 mm to 15 mm; S is preferably 10 mm to 40 mm.

Fig. 4 shows an alternative embodiment of a gas flow restriction 4. The gas flow restriction 4 is basically the same as the embodiment in FIG Fig. 3 . Instead of the slots, the perforation is made with a mesh or grid.

Fig. 5 represents a further alternative embodiment of a gas flow restriction 4. The gas flow restriction 4 is basically the same as the embodiment in FIG Fig. 3 . Instead of the slots, the perforation is designed with a large number of openings. In addition to round holes, square holes, rectangular holes, rhombic holes but also all other possible geometric shapes can be used to design the perforation.

Fig. 6 shows as a modification of Fig. 3 a gas flow restriction, which is structured 3-dimensionally. The area shown in dashed lines is provided with a vertically oriented 3-dimensional structure (grooves, ribs, riblets, prongs) which is repeated in the direction of gas flow.

Fig. 7 Fig. 13 is an enlarged sectional view (plan view) of the 3-dimensional structure. The gas flow 6 passes through the treatment area 5. The intermediate space between the edge zone of the gas treatment area 5 and the gas flow restriction 4 is flowed through by secondary gas 8 'entrained from the surroundings. The 3-dimensional structure of the gas flow restriction 4, which is arranged in the form of scales, ensures that the secondary gas flow 8 is swirled. The structure shown here is an example. As shown, it can be vertically continuous, but it can also be vertically subdivided or staggered.

Fig. 8 shows an identical version Fig. 7 however, openings are also incorporated into the 3-dimensional structure. The additional perforation has the effect that, in addition to the secondary gas flow 8 ', secondary gas 8''' is also sucked in from the outside. Depending on the design of the 3-dimensional structure and the selected gas flow rates 6, either secondary gas 8 '''can be sucked in or secondary gas 8' be pressed outwards. It can also be in partial areas sucked in the gas guide device 4 and pressed in other subregions of the gas flow restriction 4.

Fig. 9 shows an identical version Fig. 8 however, in this case the gas stream 8 "'is fed in as a forced gas stream. In an alternative mode of operation, the gas stream 8"' can also be sucked off. Executions according to Fig. 9 are not limited to three-dimensional structures alone, but can also be used in the case of "flat" gas guide devices according to FIG Figures 2 to 5 be used.

Fig. 10 represents an alternative embodiment to the aforementioned 3-dimensional structures. The gas flow restriction 4 is in this case a flat structure which has indentations (dents) at regular intervals. The indentations can, as shown here, have a triangular shape, but can also be designed in any size and shape. The embossing of the surface obtained by the indentations leads to a thorough mixing or turbulence of the secondary air. Alternatively, the indentations can additionally have an opening in order to enable a secondary gas flow exchange.

Fig. 11 FIG. 13 shows a sectional view from above (top view) of the edge region of FIG Fig. 10 In this case, the indentations have an opening which enables a secondary gas flow exchange. The filament curtain 5 is flowed through by the gas stream 6. In the edge zone, “secondary gas” 8 'is additionally sucked in by the gas flow 6, which gas is swirled due to the three-dimensionally structured surface of the gas flow restriction 4. As a result of the suction effect of the secondary gas 8 'sucked in in the edge area, "secondary gas" 8 "' is additionally introduced into the system from the outside through the gas flow restriction 4.

Examples: Example 1 (comparative example): Simple device

An NMMO spinning mass consisting of 12.8% cellulose type MoDo Crown Dissolving-DP 510-550, 76% NMMO and 11% water was stabilized at a temperature of 91 ° C with propyl gallate of a rectangular spinneret with a drilled length L of approx. 250 mm fed. The extrusion orifices of the spinneret were oriented in staggered positions along the long side of the nozzle Arranged in rows (zigzag arrangement). The spinneret had a total of 10,384 extrusion orifices.

The spinneret was inserted into a housing which was heated to a temperature of approx. 95 ° C. during the experiment. The space between the surface of the solidification bath and the spinneret outlet surface was formed by a gas gap of approx. 25 mm in height. The filament curtain formed passed through the gas gap with a gas flow feed essentially along the drilled width of the spinneret. The gas flow was generated by means of several multi-channel compressed air nozzles arranged in a row next to one another. The diameter of each compressed air nozzle was approx. 0.8 mm. The amount of air was regulated in such a way that an exhaust gas temperature between 50 and 60 ° C. is established after flowing through the rows of filaments. A gas suction device was not used in this test arrangement. A side gas flow restriction was also not installed.

The coagulation of the individual filaments to form cellulosic molded bodies took place in a coagulation bath in which a collecting bath was arranged below the extrusion openings, spaced by the gas gap.

The assessment of the spinning stability gave a value of “2 to 3”, with the value 1 meaning very good and 5 bad, that is to say not operable.

In the gas gap, especially in the edge zones of the filament curtain, there were recurring faults which could be eliminated by manual intervention, but which reappeared after a short time. The disturbances manifested themselves in the occurrence of multiple sticking of the filaments in the gas gap, which also caused a disturbance of the gas flow, which in turn caused a further deterioration in the spinning stability. The malfunctions that occurred in this way could only be eliminated by manual intervention, and the same malfunction reappeared after a short time.

Observations on the surface of the coagulation bath also showed that there were significant bath turbulences that caused uncontrolled movement of the filament curtain. The coagulation bath was stirred up by the gas flow, especially in the edge zones. The described turbulence in the coagulation bath was at least partially responsible for the sticking in the gas gap.

Example 2 (comparative example): device with gas suction

The arrangement in this experiment was basically the same as in Example 1, however, a gas suction device was also provided, which acts as a suction strip on the gas downstream side of the gas gap, as in FIG Fig. 1 was represented, designed. The suction gas flow was generated by means of a speed-controlled suction fan. The gas flow was regulated in such a way that no increased gas flow temperature was measured on the side of the gas suction device facing away from the filament curtain. This measure made it possible to ensure that the entire gas flow supply was recorded by the gas suction device.

The assessment of the spinning stability gave a value of “2 to 3”, the frequency of the spinning defects occurring slightly decreasing in comparison with Example 1, but trouble-free operation could not be achieved. The use of gas suction created additional turbulence in the solidification bath.

Example 3: Device with gas flow restriction in the gas treatment area

The arrangement in this experiment was basically the same as in Example 2, but a gas flow restriction was additionally provided which, according to the invention, was attached to the side edges of the filament curtain in the gas gap. The "short" gas flow restriction essentially only extended below the extrusion nozzles; it was not perforated. The gas flow restriction extended vertically over the entire gas gap and was also immersed in the coagulation bath. The gas evacuation was set as described in Example 2.

The assessment of the spinning stability gave an improved value of "2". The frequency of spinning defects that occurred decreased noticeably. In the coagulation bath, turbulence was still evident, which was caused on the one hand by the gas flow supply at the edges of the filament curtain and on the other hand by the gas flow discharge in the area of the gas suction.

Example 3 ': extended gas flow restriction

The arrangement in this experiment was basically the same as in Example 3, in addition the lateral gas flow restriction was modified in this experiment so that the gas flow restriction extended not only below the extrusion openings but also laterally below the suction device. The imperforate gas flow restriction extended vertically over the entire gas gap and was also immersed in the coagulation bath. The gas evacuation was set as described in Example 2.

The assessment of the spinning stability gave a further improved value of “1 to 2”. The frequency of the spinning defects that occurred decreased again, with slight disturbances still occurring. The turbulence in the coagulation bath was reduced compared to the previous tests, but not eliminated.

Example 4: gas flow restriction with perforation

In comparison to example 3 ', in this example vertical slits were additionally made in the lateral gas flow restriction. The slots were made in the area below the extrusion openings. No slots were provided in the area below the suction device. The degree of perforation (ratio of open area to total area) was 30% in this arrangement.

This measure made it possible to raise the spinning behavior to a stable level, since no significant turbulence was discernible either in the gas gap or on the surface of the coagulation bath. The filament curtain was essentially calm, stable, and without sticking.

Example 4 ': gas flow restriction with round holes

Compared to Example 4, in this example, instead of the vertical slots, bores, as in FIG Fig. 5 shown, introduced into the lateral gas flow restriction. The holes were made in the area below the extrusion openings. No holes were provided in the area below the suction device. The degree of perforation (ratio of open area to total area) was 7% in this arrangement.

Compared to Example 4, this arrangement resulted in a reduction in the spinning stability which was rated “1 to 2”. Table 1: Summary of Examples 1-4 example 1 2 3 3 ' 4th 4 ' Rectangular nozzle Rectangular nozzle Rectangular nozzle Rectangular nozzle Rectangular nozzle Rectangular nozzle Gas flow restriction without gas flow restriction without gas flow restriction with "short" gas flow restriction with "long" gas flow restriction with "long" gas flow restriction with "long" gas flow restriction Gas flow restriction - horizontal position no no 4 'below extrusion device 4 '+ 4 "below extrusion and suction device 4 '+ 4 "below extrusion and suction device 4 '+ 4 "below extrusion and suction device Gas flow restriction - vertical position no no immersed in a coagulation bath immersed in a coagulation bath immersed in a coagulation bath immersed in a coagulation bath perforation - - no no Vertical slots Vertical holes Degree of perforation - - - - 30% 7% without suction with suction with suction with suction with suction with suction Fiber titer [dtex] 1.33 1.36 1.38 1.32 1.35 1.31 Spinning solution throughput per capillary [g / min] 0.038 0.039 0.040 0.043 0.049 0.047 Gas gap (4) [mm] 25th 25th 25th 25th 25th 25th Overall spinning stability (1 ... good, 5 ... bad) 2 to 3 2 to 3 2 to 3 2 1 to 2 2 Fault in the gas gap 0 ... none 1 ... very rarely 2 ... recurring 3 ... irreparable 2 1 to 2 1 to 2 2 0 to 1 2 Coagulation bath turbulence (visual assessment) 0 ... none 1 ... light - not disturbing 2 ... medium - cause filament movement 3 ... heavy - cause filaments to stick in the gas gap 2 to 3 2 to 3 2 to 3 2 1 2

Claims (15)

Device suitable for producing material filaments by extruding a material fluid and solidifying the material fluid, with an extrusion head (1) with a large number of extrusion openings, a collecting bath (2) for receiving extruded fluid filaments (5) from the extrusion openings, a gas gap (A) between the extrusion openings and the collecting bath, whereby a gas treatment area (4 ') is formed for extruded material fluid, a gas flow device (3,6) for generating a gas flow in the gas gap, characterized in that at least one gas flow limitation ( 4) is provided. Device according to Claim 1, characterized in that the gas flow restriction extends over the entire length (B) of the gas treatment area of all extrusion openings arranged in the longitudinal direction. Device according to claim 1 or 2, characterized in that the gas flow restriction extends over an area (L, 4 ") in the gas flow direction after the gas treatment area, the length of this subsequent area in the gas flow direction being at least half the length (B) of the gas treatment area all in Is arranged longitudinally extrusion openings. Device according to one of Claims 1 to 3, characterized in that the gas flow restriction extends over an area (K) against the gas flow direction in front of the gas treatment area, the length of this previous area against the gas flow direction at least half the length (B) of the gas treatment area is arranged in the longitudinal direction extrusion openings. Device according to one of claims 1 to 4, characterized in that the gas flow device contains a fan and / or a suction device (3), preferably wherein the suction device has an exhaust duct which is in a Angle (X) is oriented from 0 ° to 45 ° to the horizontal, and / or preferably wherein the suction device is arranged above the gas gap, so that the gas treatment area is accessible in a horizontal direction. Device according to one of Claims 1 to 5, characterized in that the gas flow restriction has a height in the gas treatment area in the extrusion direction of at least 70% of the height of the gas gap. Device according to one of Claims 1 to 6, characterized in that gas flow restrictions are connected on both sides of the gas treatment area on the part of the gas flow device, in particular are connected in a U-shape. Device according to one of claims 1 to 7, characterized in that the gas flow limitation in the area of the gas treatment area has a grooved, corrugated or ribbed surface, preferably a riblet surface, and / or perforations, preferably at least 25% of the area of the gas flow limitation in the area the gas treatment area is closed; and / or wherein the perforations are preferably holes or strips, particularly preferably strips in the extrusion direction, particularly preferably wherein at least one strip is provided for every 4 cm length of the gas flow restriction in the area of the gas treatment area in the gas flow direction. Device according to one of claims 1 to 8, characterized in that the gas flow limitation to the gas treatment area is at a distance (J) of at least twice the distance (C) of the extrusion openings from one another in the direction transverse to the gas flow direction and / or that the gas flow limitation to the gas treatment area in a distance (J) of a maximum of 20 times the distance (C) of the extrusion openings to one another in the direction transverse to the gas flow direction is present. Device according to one of Claims 1 to 9, characterized in that the extrusion openings are in a rectangular shape are arranged, the narrow side of the rectangular shape facing the gas flow restriction. Process for the production of solid material filaments from a material fluid by extruding the material fluid through several extrusion openings, whereby fluid filaments (5) arise, passing the fluid filaments through a gas gap (A), and solidifying the filaments in a coagulation liquid in a collecting bath (2), wherein a gas stream (6, 7) flows through in the gas gap (8 '), characterized in that the gas stream is passed with at least one gas flow limiter (4), the gas flow limiter having a gas treatment area (4) in which the filaments are treated with the gas flow are limited laterally. Method according to claim 11 with a device according to one of claims 1 to 10. Method according to claim 11 or 12, characterized in that the material fluid contains cellulose, preferably a solution or melt of cellulose, a solvent of cellulose, preferably an amine oxide, and water. A method according to any one of claims 11 to 13, characterized in that the gas flow is achieved by blowing in (6) and sucking in (7), wherein preferably a sucked gas flow is greater than a blown gas flow, particularly preferably wherein the ratio of sucked gas flow to blown in Gas flow is greater than 1.2: 1. Method according to one of Claims 11 to 14, characterized in that turbulence in the gas flow at the lateral edge of the gas treatment area is avoided by the choice of the gas flow and the gas flow limitation.

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