Patent Grant
11946165
The present invention relates to the forming and treatment of extruded and subsequently solidified synthetic fibers.
Cellulose may be dissolved in aqueous solutions of amine oxides, in particular in solutions of N-methylmorpholine-N-oxide (NMMO), in order to produce spun products, such as filaments, staple fibers, foils and the like, from the resulting spinning solution. This is achieved by means of precipitating the extrudates in water or diluted amine oxide solutions after transferring the extrudates from the extruder into the precipitation bath via a gas gap. Usually, cellulose solutions within a range of 4% to 23% are used for the production of extrusion products. In the further course, the precipitated extrudates in the form of foil or filament strands are forwarded, wherein suitable drawing roller mills provide the required stretching forces (in the gas gap). This method is also referred to as lyocell method, and the cellulose filaments thus obtained are correspondingly referred to as lyocell filaments.
Document U.S. Pat. No. 4,416,698 relates to an extrusion and spinning method for cellulose solutions in order to form cellulose filaments. In this method, a fluid spinning material—a solution of cellulose and NMMO (N-methylmorpholine-N-oxide) or other tertiary amines—is formed by extrusion and transferred to a precipitation bath for solidification and expansion.
Documents U.S. Pat. No. 4,246,221 and DE 2913589 describe methods for producing cellulose filaments or foils, wherein the cellulose is stretched in a fluid form.
Document WO 94/28218 A1 describes a method for producing cellulose filaments, wherein a cellulose solution is formed into a plurality of strands using a nozzle. Through a gas circulation gap, said strands are then transferred to a precipitation bath where they are continuously leached.
Document CA 2057133 A1 describes a method for producing cellulose fibers, wherein a spinning mass is extruded and introduced via an air gap into a cooled NMMO-containing water bath.
Document WO 03/014432 A1 describes a precipitation bath with a central fiber discharge device arranged underneath a cover sheet.
Document EP 1 900 860 A1 describes a two-step coagulation bath of a spinning device, wherein the baths may have different H2SO4 compositions.
Document WO 97/33020 A1 relates to a method for producing cellulosic fibers, in which a solution of cellulose in a tertiary amine oxide is extruded through spinning holes of a spinning nozzle, the extruded filaments are guided through an air gap, a precipitation bath and across a drawing gear by means of which the filaments are stretched, and the stretched filaments are processed to form cellulosic fibers, wherein during processing the stretched filaments are subjected to a tensile load of not more than 5.5 cN/tex in a longitudinal direction.
Document DE 10200405 A1 describes a lyocell device having a blowing device arranged in the gas gap. Mentioned therein is a precipitation bath device, in which a filament curtain is immersed in the precipitation bath, is deflected in the precipitation bath and leaves the precipitation bath in a slanting upward direction to be transferred to a bundling device. As single-strand bundling is applied here, a strong bundling is to be expected in the deflection process.
Document WO 02/12600 describes a spinning method in which the maximum economic spinning speed may be calculated using a formula based on fiber titer, spinning hole row number and a variable operating parameter.
Document WO 02/12599 describes a spinning method in which a filament curtain is deflected in a coagulation bath and is subsequently merged in a point-shaped manner.
Document WO 96/20300 describes deflection angles of filaments in the lyocell method calculated according to a formula.
The problem of causing damage to the filaments in the drawing process is addressed in WO 2008/019411 A1 and is solved with the aid of a mechanical drawing gear which is arranged in the spinning bath, wherein said drawing gear is also supposed to provide part of the drawing forces acting during operation. Besides the sheer complexity of the construction, it is a further notable disadvantage that individual, very fine filaments may become entangled in the mechanical construction and may thus functionally impair both the spinning process and the mechanical device itself.
Document WO 2014/057022 describes serial spinning baths comprising different media.
In the currently applied lyocell methods, all single filaments (single extrudates) which directly abut the deflection device (such as a rod) are pressed against the deflection device by the normal forces resulting from the tensile force of the whole bundle. Due to the frictional resistances, this may lead to tear-offs and filament rupture. In particular in case of strong bundling, the high normal force resulting from the total drawing force is exerted on only a few single filaments which are in direct contact with the deflection device. These few single filaments may be seriously damaged by the high frictional load, in particular at high drawing speeds. This is aggravated by the fact that the filaments in the coagulation bath are swollen and potentially still at a high temperature, which reduces their mechanical strength.
It is thus an object of the present invention to minimize the frictional load that is exerted on each single filament at deflection points and thus to facilitate higher productivity and higher spinning speeds. Such frictional forces occur in spinning baths in which the medium employed requires the use of rigid deflection devices or of deflection devices with driven or freely rotating rollers, such as e. g. in a filament drawing gear.
The present invention allows for computationally evaluating a system with respect to the frictional load exerted on the filaments as well as for determining suitable measures for adjusting the system in such a manner that the frictional load exerted on all filaments that are in direct contact with the deflection device can be maintained at a minimum level.
It is a further object of the present invention to ensure manual manageability of the filament curtain and accessibility of the deflection point in the treatment zone between spinning nozzle and drawing gear without the necessity of using highly complex and delicate splicing aids or drawing gears.
The present invention provides a method for producing solid cellulose filaments from a cellulosic fluid, the method comprising the steps of extruding said fluid through a plurality of extrusion openings, whereby fluid filaments are formed, preferably passing said fluid filaments through a gas gap, and solidifying said filaments in a coagulation bath, wherein the filaments are bundled and deflected as a bundle in the coagulation bath in order to be drawn from the coagulation bath above the coagulation bath level, wherein the bundle of filaments occupies a deflection width L on a deflection device, the deflection width L being controlled according to Formula 1:
L>(2×LZ×cos(B/2)×v2,5)/(10×ccell0,5×Q) Formula 1,
wherein L is the deflection width of the bundle in mm, LZ is the number of extrusion openings, B is the deflection angle (calculated as 180° minus the wrap angle of the filaments around the deflection device in angular degrees), v is the drawing speed of the filaments in meters per second, ccell is the cellulose concentration of the extruded fluid in % by mass, and Q is a dimensionless load number, with Q being 15 or lower. In Formula 1, “>” has the meaning of “greater than”, “x” is a multiplication sign and “cos” refers to the cosine.
The present invention further relates to a device that is suitable for conducting said method, the device comprising an extrusion plate having a plurality of extrusion openings, a collection container for taking up a coagulation bath, preferably a gas gap arranged between the extrusion openings and the collection container, a deflection device arranged in the collection container for deflecting a filament bundle from the collection container, and a bundling device which determines a deflection width L occupied by the filament bundle on the deflection device, wherein the filament bundle occupies a deflection width L corresponding to the above-mentioned Formula 1 on the deflection device, wherein L, LZ, B, v, ccell and Q are as defined in the above, Q is 15 or lower and v is at least 35 m/min, according to which the device is thus adapted.
According to the present invention, there are usually large deflection widths L; the present invention thus also relates to a method for producing solid cellulose filaments from a cellulosic fluid, the method comprising the steps of extruding said fluid through a plurality of extrusion openings, whereby fluid filaments are formed, preferably passing said fluid filaments through a gas gap, and solidifying said filaments in a coagulation bath, wherein the filaments are bundled and deflected as a bundle in the coagulation bath in order to be drawn from the coagulation bath above the coagulation bath level, wherein the extrusion openings are arranged within a length LL and the bundle of filaments occupies a deflection width L on a deflection device which is at least 70% of the length LL. Analogously, the present invention also relates to a device that is suitable for conducting said method, the device comprising an extrusion plate having a plurality of extrusion openings, a collection container for taking up a coagulation bath, preferably a gas gap arranged between the extrusion openings and the collection container, a deflection device arranged in the collection container for deflecting a filament bundle from the collection container, and a bundling device which determines a deflection width L occupied by the filament bundle on the deflection device, wherein the extrusion openings are arranged within a length LL and the bundle of filaments occupies a deflection width L on the deflection device which is at least 70% of the length LL.
The following detailed description relates to devices and methods in equal measure, i. e. preferred method features also correspond to properties or the suitability of the device and/or the respective components thereof, and preferred device features also correspond to means that are employed in the method according to the present invention method. All preferred features may be combined, unless explicitly stated otherwise. All method features, including the above-mentioned, may be combined. All device features, including the above-mentioned, may be combined.
The present invention relates to the deflection of filament curtains or at least unilaterally bundled filament bundles. The deflection is performed in the coagulation bath in order to convey the filaments out of the bath. In the deflection process, the filaments are merged perpendicularly to the deflection axis, such that the filaments in the first layer rest on a deflection device and the filaments in the other layers rest one layer upon one another. As already mentioned, this exerts a certain stress on the material, in particular at high speeds. According to the present invention, the deflection width was enlarged in order to enable the drawing of filaments at arbitrary, i. e. also high, speeds of, e. g., 35 m/min or higher.
In the deflection process according to the present invention, the filaments are guided in the form of a broad band. The term “filament bundle” thus includes bands of jointly guided filaments having a cross-sectional width and height, wherein the width is greater than the height.
The above Formula 1, with Q=15 or lower, in particular relates to a deflection process performed in the coagulation bath, in which the filaments are particularly susceptible to the frictional forces as mentioned in the summary due to temperature and swelling conditions. The coagulation bath represents part of the treatment zone for the extruded filaments. According to the lyocell method, the filaments have not yet obtained their final structure and stability at this point. Initially, structure and stability vary due to stretching (especially in the gas gap) and a solvent exchange (especially in the coagulation bath). Material changes may still occur after withdrawal from the coagulation bath, so that the path covered by the filaments/extrudates between the exit from the spinning nozzles and the step of washing the solvent out of the filaments/extrudates, including a drawing gear, is referred to as treatment zone. As the extruded filaments have not yet obtained their final form, they are referred to as “extrudates” while still in the treatment zone. A drawing gear is a device which provides the deformation forces that are required for filament formation as well as the frictional forces acting on the filaments/extrudates during the transport from the spinning nozzles to the drawing gear. Due to the hydrodynamic conditions prevailing in the coagulation bath, there is a very high risk of entanglements with the use of driven or freely rotating deflection devices, so that the use of fixed deflection devices is preferred within the coagulation bath. Outside the coagulation bath, however, fixed deflection devices should possibly provide only a slight deflection or freely rotating and/or driven deflection devices should be used. With the use of freely rotating and/or driven deflection devices, the filaments/extrudates will be less susceptible to frictional effects, so that also smaller deflection widths L, as calculated according to Formula 1, may be employed. However, a certain width will still be maintained, in particular for the deflection process at the drawing gear, as frictional effects also occur here. Depending on the throughput (per extrusion opening), the drawing gear ensures provision of the required drawing speed. A drawing gear transfers the drawing speed to the filaments/extrudates by means of driven deflection devices or a plurality of deflection devices, such as reels or rollers. In this instance, the deflection force of the reel is initially transferred to the inner filaments/extrudates (in direct contact with the reel/roller), which in turn transfer said force to the outer filaments/extrudates (not in direct contact with the reel/roller). Thus, there is a greater strain on the inner filaments/extrudates than on the outer filaments/extrudates. This imbalance is minimized according to the present invention by maintaining a deflection width to such an extent that the inner filaments/extrudates will only be covered by a limited number of outer filaments/extrudates, thus maintaining swift and efficient operation. The extrusion openings may be bores or holes, as well as capillaries, provided in an extrusion plate. For all these instances, the number of extrusion openings will be referred to as hole number. The drawing process may be performed in a gas compartment, into which the filaments are introduced upon exiting the coagulation bath.
According to the present invention, a deflection device is a machine part which enables a change in direction of individual extrudates, of extrudate curtains or of extrudate bundles, wherein the deflection width L of the deflected curtain itself is preferably not influenced by the deflection device.
In principle, such deflection devices may also be implemented as rigid deflection devices or rotating deflection devices. Rotating deflection devices may or may not be driven. Rotating deflection devices offer the advantage of a reduction in frictional forces between extrudate and deflection device and the deflection may thus be performed in a very gentle manner—except in case of a deflection in a drawing gear, when forces are transferred from the deflection device to the filaments/extrudates. It is, however, a disadvantage of rotating deflection devices that individual extrudates may adhere to the rotating deflection device due to their stickiness, thus potentially causing entanglements, tear-offs and other malfunctions. The use of rotating deflection devices is also problematic in liquids (in the coagulation bath), as hydrodynamic vortices in the surface area of the deflection device pose a high risk of dragging individual extrudates along the circumference of the deflection device, again potentially causing entanglements, tear-offs and other malfunctions.
With spinning bath liquids, but also with sticky, wet or otherwise adhering extrudate curtains or bundles, the use of rigid deflection devices is preferred, e. g. in the form of rods, spools, cage-shaped deflection devices or any other suitable form.
Any materials having lowest possible slide friction values may be considered as materials for rigid deflection devices. Besides metals (either coated or uncoated), textile ceramics or synthetic materials may also be considered.
A deflection device is preferably employed in the coagulation bath. Also possible is the provision of two or more deflection devices in the coagulation bath, thereby increasing the number of options for (greater) deflection angles B per deflection device. According to the present invention, the requirements according to Formula 1 are met by the first, preferably also the second or also every deflection device in the coagulation bath. In this context, “first”, “second” etc. refers to the respective procedural proximity to the extrusion process and to the order in which the filaments/extrudates pass the deflection devices.
Also subsequently to the coagulation bath in the treatment zone, the filaments/extrudates are kept in the form of a band having a certain deflection width, as also at this point, in particular in a drawing gear, frictional forces are exerted which could cause damage in the deflection process. Subsequently to the coagulation bath, however, the deflection width may be kept narrower than in the coagulation bath itself, as the negative effects on filament stability due to temperature and swelling may be less pronounced here. According to the present invention, the deflection process outside the coagulation bath is preferably conducted with at least a deflection width Loutside, which corresponds to L according to Formula 1 (with Q 15) divided by 30, preferably divided by 20, preferably divided by 10 and particularly preferably divided by 5, and/or the filament bundle is preferably kept at said width Loutside (also between deflection processes)—at least up to the point of entering a drawing gear and/or a washing device. Alternatively, Loutside may be calculated according to Formula 1, wherein Q can have a higher value, e. g. with Q=up to 300 or up to 250, such as 10 to 300 or 40 to 250. In a washing device, the filament bundle is usually fanned out even more broadly in order to facilitate the washing process. Loutside can also be at least L according to Formula 1 (with Q up to 15), e. g. in the washing process.
Loutside (deflection or band width outside the coagulation bath) may also be defined independently of L according to Formula 1. Loutside will preferably be selected such that a filament density per mm deflection width of not more than 7,000 dtex/mm, preferably of not more than 6,000 dtex/mm, not more than 5,000 dtex/mm and particularly preferably of not more than 4,000 dtex/mm, is achieved at a given drawing speed.
Said deflection or band width outside the coagulation bath, Loutside, is preferably maintained in the immediately subsequent deflection process conducted after the filaments/extrudates have been withdrawn from the coagulation bath, when the filaments/extrudates are still very delicate, and/or maintained in the drawing gear, when the filaments/extrudates are particularly stressed by the transmission of forces. Upon exiting the coagulation bath and during their passage through the entire treatment zone or during the entire processing of the filaments/extrudates, the filament bundles are preferably always kept at a minimal width Loutside until the final products will be cut and/or reeled. Processing usually includes the following steps: spinning in a coagulation bath (as described above), withdrawal from the coagulation bath, drawing by means of a drawing gear, washing, drying, reeling and/or cutting the filaments as final products.
A spinning method, including processing, may alternatively or additionally comprise the following steps: extruding the filaments/extrudates through a spinning nozzle, guiding the filaments/extrudates through a gas gap (into which preferably a gas stream is injected, see supra) into a coagulation bath (precipitation bath), deflecting the filaments/extrudates in the precipitation bath, preferably by means of a deflection device arranged opposite the spinning nozzle, withdrawal of the coagulated filaments/extrudates from the coagulation bath, deflecting the filaments/extrudates outside the coagulation bath and without any further bundling with other coagulated filaments/extrudates, feeding the filaments/extrudates onto a drawing gear (also referred to as drawing apparatus or drawing device) and/or stretching device and subsequently conveying the filaments/extrudates to a filament reception unit and/or stretching gear, washing, drying and optionally other steps, as desired. The device according to the present invention is provided with the corresponding equipment. In another embodiment, the method can include the following steps: extruding the filaments/extrudates through a spinning nozzle, guiding the filaments/extrudates through a gas gap (into which preferably a gas stream is injected, see supra) into a coagulation bath, deflecting the filaments/extrudates outside the coagulation bath and subsequently bundling or merging them with other filaments/extrudates, feeding the filaments/extrudates onto one or more drawing gears, washing, drying and optionally other steps and/or devices, as desired.
Some of the steps can be combined; for instance, a washing step may be performed in the drawing gear. The embodiments, as described in detail or preferred herein, can be employed in each of the steps. It is also possible to combine driven and non-driven rollers or reels in one drawing gear, as has been described, e. g., in document CN 105887226 (A). A heat treatment, such as drying, as has been described, e. g., in CN 205133803 U, may also be conducted in the drawing gear. In the start-up phase of the method, a splicing aid, as described, e. g., in CN 205258674 U, may be employed; however, this is only an auxiliary step and is not essentially required.
Other steps or devices suitable for the purposes according to the present invention may be provided. For instance, a drying step may be performed subsequently to the washing step, or a drying device may be provided downstream of the washing device, wherein prior to the drying process or upstream of the drying device one or more other treatment steps, such as finishing the filaments/extrudates, may be conducted or a corresponding finishing device may be provided. Furthermore, other process steps, such as dyeing, cross-linking, sonication, may be conducted prior to the drying step, i. e. correspondingly suitable devices may be provided.
At any point in the process up to the drying step, a cutting device (for cutting) or a reeling device (for reeling) may preferably be interposed in order to produce staple fibers or continuous yarns from the continuous fibers.
Preferably, a tensile force of less than or equal to 3 cN/dtex, preferably of less than or equal to 2 cN/dtex or of less than or equal to 1.5 cN/dtex is exerted on the filaments/extrudates in the drawing gear.
The filament bundles of a plurality of spinning points may be combined to form a combined bundle. Usually, such a combination is performed (immediately) upon exiting the coagulation bath, such that the downstream plant components, like drawing or washing devices, are able to process the combined bundle. The width L or Loutside is herein mostly given with reference to one spinning point and increases correspondingly upon combination. For instance, Loutside can be at least 8 mm, e. g. 8 mm to 100 mm and preferably 12 mm to 70 mm, per spinning point.
The bundling device represents a machine part which narrows the deflection width of the extrudate curtain depending on the geometric shape of the bundling device, thereby forming an extrudate bundle from a plane or tubular or also round or otherwise shaped extrudate curtain. Optionally, the bundling device also enforces a change in direction of the formed extrudate bundle. The bundling device may thus also represent a deflection device which is subject to the rules and preferred embodiments according to the present invention. Analogously to the description of the deflection device, bundling devices may be implemented as rigid or rotating devices. Identical materials may be used. For the use in spinning bath liquids, but also in the presence of sticky, wet or otherwise adhesive extrudate curtains or bundles, rigid bundling devices in the form of rods, spools, cage-shaped deflection devices, hooks, loops, U-shaped guides or devices of any other suitable design will preferably be employed.
The load factor Q is an empirical measure of the filaments layered on top of one another at the deflection device. The lower Q, the gentler the method and the larger L has to be selected. In the coagulation bath, Q should be 15 or lower, preferably Q is 12 or lower, preferably 8 or lower or 5 or lower. In connection herewith, Q is 2 or higher, preferably 3 or higher or 4 or 5 or higher, wherein particularly preferably Q is from 2 to 15 or more preferably from 4 to 12. Possible values for Q are 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or any other value in between. As already mentioned above, Q may be higher outside the bath. In this instance, L is exchanged for Loutside, with Q being up to 300. Unless explicitly stated otherwise, Q refers to a deflection process conducted in the coagulation bath.
The number of extrusion openings (also referred to as hole number and abbreviated as “LZ”) determines the number of filaments which have to be deflected. The method according to the present invention is, in particular, dimensioned for the large, industrial scale. The number of extrusion openings LZ preferably is 2,000 or more, preferably 5,000 or more or 10,000 or more. Either independently or in combination, LZ may be 500,000 or less, preferably 200,000 or less, 100,000 or less or 50,000 or less. If a simultaneous production of larger product amounts and thus of a higher number of filaments is required, a plurality of extrusion devices according to the present invention may be employed in order to produce a plurality of parallel filament bundles or curtains, optionally in a jointly used coagulation bath or even with the joint use of one deflection device. The above-mentioned hole numbers refer to a bundle or a group of filaments being jointly deflected and bundled.
The deflection angle B is determined by the angle enclosed by filaments which are transferred to the deflection device and the deflected filaments (see the Figures). A sharper angle will result in stronger shearing and frictional forces acting on the filaments. The sharper the angle, the more L has to be increased (while the other parameters of Formula 1 remain constant). Preferably, the deflection angle B is an angle of 10° to 90°, preferably of 20° to 60° or of 25° to 45°. Unless explicitly stated otherwise, the angle B refers to a deflection process conducted in the coagulation bath. Outside the coagulation bath, e. g. in a drawing gear and/or washing device, the deflection angle can be 0° to 150°, in particular any angle within said range, as has already been indicated, e. g., for the angles in the coagulation bath.
According to the present invention, the large deflection widths L allow for high drawing speeds. The filaments are drawn through the coagulation bath, generally with the aid of a drawing gear. The drawing gear itself is generally arranged outside the coagulation bath, downstream of the deflection device and optionally also of the bundling device. A corresponding deflection width L is selected depending on the drawing speed. Preferably, the drawing speed (at the deflection device) is at least 35 m/min. The drawing speed v may be 36 m/min or higher, preferably 40 m/min or higher or 45 m/min or 50 m/min or higher. Independently or in combination, the drawing speed v may be 200 m/min or lower or 150 m/min or lower.
In the method according to the present invention, an extrusion medium is used as a fluid. Said fluid preferably is a solution or a mixture of cellulose and other medium components, such as solvents. The cellulose concentration is selected as is conventional for lyocell methods. Thus, the cellulose concentration of the extruded fluid ccell may be 4% to 23%, preferably 6% to 20% and in particular 8% to 18% or 10% to 16% (all percentages refer to % by mass). The extrusion medium employed in the lyocell method usually is a cellulose solution or melt with NMMO (N-methylmorpholine-N-oxide) and water, as mentioned in the introduction. Other solutions of cellulose, in particular ionic solvents of cellulose, may also be employed. Ionic solvents are, for example, described in document WO 2006/000197 A1 and preferably contain organic cations, such as ammonium, pyrimidium or imidazolium cations, preferably 1,3-dialkylimidazolium halogenides. Also in this instance, the use of water as a solvent additive is preferred. Particularly preferred is a solution of cellulose and butyl-3-methylimidazolium (BMIM), e. g. with chloride as a counter ion (BMIMCl), or 1-ethyl-3-methylimidazolium (also preferably as a chloride) and water.
The step of passing the fluid filaments through a gas gap in the method according to the present invention or the provision of the gas gap according to the present invention device is optional, i. e. a gas gap may or may not be provided. This step/measure distinguishes between a wet spinning and a dry-wet spinning process. In case of wet spinning, the filaments are directly introduced into the coagulation bath. In case of dry-wet spinning, the gas gap is provided and the filaments pass through it prior to being introduced into the coagulation bath.
Optionally, a gas stream may (and preferably will, in particular in large, industrial-scale plants) be injected into the gas gap, to which end a blower is provided in the device. The injected gas stream preferably has a temperature of 5° C. to 65° C., preferably of 10° C. to 40° C. The fluid material may be extruded at a temperature of 75° C. to 160° C. Preferably, the gas gap is kept at a lower temperature than the extruded fluid material. In particular, a gas stream in the gas gap will be kept at a lower temperature than the extruded fluid material.
The gas gap itself, i. e. the distance between the extrusion openings and the coagulation bath, and/or containers suitable for this purpose, such as a tank, may preferably have a length of between 10 mm and 200 mm, in particular between 15 mm and 100 mm, or between 20 mm and 80 mm. Preferably, said length is at least 15 mm. The gas present in the gas gap is preferably air. The gas stream preferably is an air stream, while the use of other inert gases is also possible. The term “inert gas” refers to a gas that does not undergo a chemical reaction with the fluid filaments in the gas gap, and preferably neither with the coagulation medium, such as water or a diluted, aqueous NMMO solution or other solvent components, depending on the extrusion medium employed.
In a wet spinning method, the treatment zone will substantially consist of liquid containers, liquid funnels or liquid channels. The extrudates discharged from the spinning nozzle are directly introduced into the spinning bath liquid for precipitating and/or cooling. The wet (precipitated and/or cooled) extrudates are then transferred to washing baths and/or—through a gas or air compartment—to the drawing gear.
In a dry-wet spinning method, the treatment zone will substantially consist of a gas or air gap and downstream liquid containers, liquid funnels or liquid channels. The extrudates discharged from the extrusion openings pass a gas gap and, in the further course, a coagulation bath, which is also referred to as spinning bath. The wet (precipitated and/or cooled) extrudates are transferred to the drawing gear through one or more washing baths and/or through a gas or air compartment.
The wet or dry-wet spinning method is characterized by the occurrence of turbulences and vortices owing to displacement and dragging interactions between the coagulation bath liquid and the extrudates occurring at higher speeds. With the use of deflection points with rigid deflection devices, there is also an additional run-dry risk at the points of contact between extrudate and deflection device. Said run-dry risk will increase proportionally to the drawing speed and to the amount of pressure exerted on the extrudate curtains or bundles thereof, which is pressing the latter against the deflection device.
The extrusion openings are preferably arranged in a longitudinal shape in order to form the extruded filaments in a geometry that is favorable for deflection and bundling in the deflection process. Thus, the longitudinal arrangement of the extrusion openings preferably also corresponds to a longitudinal direction of the deflection device. Said longitudinal direction of the deflection device thus preferably corresponds to a deflection axis (or, with the use of curved deflection devices, follows a plurality of deflection axes). The extrusion openings may be arranged in a rectangular, curved, annular or ring segment-shaped manner. The longitudinal form may have a ratio of length to width from 100:1 to 2:1, preferably from 60:1 to 5:1 or from 40:1 to 10:1.
The extrusion openings preferably have a diameter of 30 μm to 200 μm, preferably of 50 μm to 150 μm or of 60 μm to 100 μm, thus facilitating the production of filaments suitable for (woven and non-woven) textile products.
The extrusion throughput will preferably be adjusted to yield a linear density of the resulting single fibers of 1.3 dtex±50%, preferably ±25% or ±10%, at a given drawing speed. The extrusion throughput can be adjusted by regulating the pressure of the extruded mass, i. e. the cellulose solution. Examples for possible pressures are 5 to 100 bar or preferably 8 to 40 bar.
An overall large deflection width L is particularly preferred, also in the sense of a discrete main feature of the present invention and independently of Formula 1. Either depending on Formula 1 or independently thereof, the extrusion openings may be arranged along a length LL, wherein according to this feature of the present invention the deflection width L is at least 70%, preferably at least 80% or also at least 90% of the length LL. The deflection width may also be equivalent to the length LL or even larger, such as 110% of the length LL or more. Loutside is preferably at least 1%, at least 3%, preferably at least 5% or also at least 10% of the length LL. For the purpose of bundling, Loutside will preferably be a maximum of 50% of the length LL. All method parameters and pertaining device settings according to the present invention may be combined. For instance, a particularly preferred combination would be a drawing speed v of 40 m/min to 150 m/min and a load factor Q of 4 to 13 or of 5 to 12. All values described herein, either within or outside these ranges, are of course also possible.
The liquid treatment zone in a dry-wet spinning method may be implemented in a number of variants, some of which are described in
A deflection angle (B) is derived from the normal distance (H) between nozzle discharge (5) and bundling device (2) as well as the given geometric ratios of the nozzle (5). The deflection width (L) represents the portion of the deflection device with which the extrudates are actually in contact and at which they are deflected and/or bundled. With the use of a torus-shaped bundling device (2), the deflection width (L) is derived from the product of bundling diameter (D) and the number Pi (3,1415 . . . ). The deflection angle (B) is derived from the respectively selected geometric ratios. The minimum required deflection width (L) is calculated according to Formula 1.
The normal distance (H) between nozzle discharge (5) and bundling device (2) is adjusted such that the nozzle draft angle will have a value of less than 45°, less than 30°, less than 15° or preferably less than 10°. This measure ensures that the extrudates can be drawn from the nozzle channel gently and with a minimum deflection. Depending on the normal distance (H) and the nozzle draft angle, the deflection angle (B) will emerge at given geometric ratios. The deflection width (L) represents the longitudinal portion of the deflection device with which the extrudates are in direct contact and by which they are deflected and/or bundled; in case of a curved (concave) deflection device, the deflection width (L) represents the stretched length of the contact line occupied by the extrudates. The deflection angle (B) is derived from the respectively selected geometric ratios. The minimum deflection width (L) is calculated according to Formula 1.
Upon exiting the coagulation bath, the bundles are transferred to a jointly conducted drawing and washing process via a drawing gear and a washing station, which may also be combined. The first drawing gear after the bath confers the drawing speed of the filaments in the spinning process.
Alternatively and in parallel to the lyocell method with NMMO/water as a solvent, an ionic solution was prepared for producing the cellulose solution. The cellulose employed (type: Eucalyptus pulp) was suspended in desalinated water. Once the cellulose fibers were completely suspended in the water, the excess water was separated by filtration and the resulted pulp cake was compressed until a solids concentration of about 50% cellulose was obtained. Subsequently to the dehydration process, the pulp cake was guided across a needle roller and shredder for fraying. The resulting finely frayed wet cellulose was introduced in a continuous process into the aqueous ionic liquid 1-N-butyl-3-methylimidazolium chloride (BMIMCl) to obtain the pre-mix. Suitable devices for this purpose are ring layer mixers and/or turbulent mixers.
In the further course of the process, the resulting mixture of water, cellulose and BMIMCl was introduced into a continuously operating vertical kneading device (type: Reactotherm by Buss-SMS-Canzler GmbH) in order to prepare the cellulose solution. In the different reactor zones and method steps, similar kneading and reactor devices as well as any types of extruders, high-viscosity thin-film processors, stirred-tank reactors and/or disk reactors may be used for preparing the cellulose solutions, either individually or in combination. Owing to its intense mixing and kneading action, the present, vertically implemented Reactotherm kneading device allowed for the lump-free and continuous production of the cellulose solution. Treatment periods of 20 to 80 in the individual reactor zones minutes resulted in a complete dissolution of the cellulose.
To ensure secure process management, further stabilizers for stabilizing the solvents and preventing cellulose degradation were added to the aqueous mixture of ionic liquid and cellulose prior to the conversion from pre-mix into cellulose solution. Under application of temperature, negative pressure (vacuum) and shearing, the continuously produced pre-mix was converted into a highly viscoelastic solution. The temperatures applied in the individual method steps varied between 85° C. and 150° C., wherein the removal of excess water was conducted under reduced pressure of between 10 and 150 mbar. The shearing rates applied for homogenizing the pre-mix were within a range of of 20 to 200 rpm, while maintaining the settings for shearing power and torque, thus ensuring the dissolution of cellulose in the ionic fluid. The highly viscous cellulose solution obtained in this manner was subjected to additional process steps, such as degassing and filtration, prior to the spinning process. In order to adjust the corresponding cellulose spinning mass quality, the solution was additionally fed to one or more high-viscosity heat exchangers (type: Sulzer SMR/SMXL), which had been adapted to the respective method steps. In addition to temperature regulation, these devices particularly also serve to adjust the desired spinning viscosity as well as the degree of polymerization of the cellulose. These heat exchangers thus provided efficient temperature regulation, such as cooling or heating, of the highly viscous cellulose solution as they facilitated an effective mixing process and a controlled transfer of heat.
The spinning process for forming filaments from the cellulose solution as well as other processing steps were carried out according to the present invention, wherein the spinning solution was fed via a spinning pump to a heated spinning block, consisting of spinning nozzle filter, distributor plates and the spinning nozzle. The spinning temperatures were within a range of of 85° C. to 150° C., preferably within a range of 95° C. to 115° C. After the step of preparing the solution, short residence times under elevated temperatures were maintained in the process system in order to adapt the cellulose solution with respect to the processing speed and undesired cellulose degradation.
The spinning method employed has been described according to the present invention and is usually referred to as dry-wet spinning method, wherein the variable, height-adjustable air gap is arranged between the spinning nozzle and the aqueous coagulation bath containing the ionic liquid. The gas stream fed into the air gap and thus passing through the filaments is injected in a conditioned manner and may consist of conditioned air or any other inert spinning gas. According to the present invention, the filaments are guided through the coagulation bath, withdrawn from the bath and subsequently transferred to further treatment steps, as described above. The parameters and product characteristics of the experiments conducted with BMIMCl and NMMO as solvents are summarized in Table 2.
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|---|---|---|---|
| PCT/EP2019/073163 | 8/30/2019 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2020/043860 | 3/5/2020 | WO | A |
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| 20210189599 A1 | Jun 2021 | US |
