Nonwoven fabric containing nanoporous fibers

Abstract

The present invention relates to a method for producing a nonwoven fabric containing nanoporous fibers. The method includes the steps of: preparing a spinning stock (10) comprising at least fiber raw materials, particularly a polymer, and a solvent; producing untreated fibers (20) from the spinning stock, particularly by extruding the spinning stock through capillaries (12); accelerating the produced untreated fibers (20) using an accelerating fluid flow (14); depositing the accelerated untreated fibers (20) as a wet nonwoven fabric precursor (26) containing fluid (16); and drying the nonwoven fabric precursor (26) while avoiding capillary action of the liquid in the wet nonwoven fabric precursor (26) in order to produce a nonwoven fabric containing nanoporous fibers (18). Furthermore, the present invention relates to a nonwoven fabric and manufacturing equipment.

Description

Technical Field

[0001] The present invention relates to a method for producing a nonwoven fabric comprising nanoporous fibers, particularly aerogel fibers. Furthermore, the present invention relates to a nonwoven fabric comprising nanoporous fibers, and to a production facility for producing a nonwoven fabric comprising nanoporous fibers. Background Art

[0002] Aerogel is a highly porous solid, wherein for example more than 99% of its volume consists of pores. The pore diameter is, for example, in the nanometer range. Aerogels can be formed, for example, on a silicate basis. Aerogels are extremely lightweight and have excellent thermal insulation properties and filter properties. However, the production of aerogels on an industrial scale is extremely expensive, and the use of aerogels as monolithic solids is extremely cumbersome, difficult, or even impossible for certain applications.

[0003] Patent Document 1 describes an aerogel fiber material, a method for producing the same, and uses thereof. According to this, aerogels can be processed into nonwoven fabrics, for example. However, the production of aerogel fibers is still very cumbersome. In particular, drying of the fibers during production is cumbersome, and only large-diameter fibers can be produced. Furthermore, when large-diameter fibers are further processed into a fleece, numerous fiber breakages may occur. The flexibility of the fleece may be significantly reduced.

[0004] Non-Patent Document 1 describes the production of cellulose-based aerogel nonwoven fabrics. Here again, only large-diameter fibers can be produced, and drying of the fleece remains cumbersome.

[0005] Patent Document 2 describes a method and an apparatus for forming a directly formed cellulose web. Prior Art Documents Patent Documents

[0006] [Patent Document 1] German Patent Application Publication No. 102006049179 [Patent Document 2] European Patent Application Publication No. 3529405 [Non-patent literature]

[0007] [Non-Patent Document 1] Dissertation “Herstellung von Aerogelvlies”, Jens Mroszczok, 2019 [Overview of the project]

[0008] A first aspect of the present invention relates to a method for producing a nonwoven fabric containing nanoporous fibers. The nonwoven fabric may be a fleece-like fabric (Vliesstoff). The nonwoven fabric may be a structure consisting of a fiber layer or fibers bonded to a nonwoven fabric layer. The fibers may be arranged in the nonwoven fabric with non-uniform and / or random partial orientations. The fibers may have orientations that are randomly dispersed within a range of a certain preferred orientation direction. The nanoporous fibers may be composed of, for example, aerogel fibers. The nanoporous fibers may be elastically deformable. The fibers may be composed of, for example, finite-length fibers or continuous fibers. Each pore of the fiber may be open or closed. The pores may be filled with a gas such as air or carbon dioxide (CO2).

[0009] This method includes the step of preparing a spinning solution. The spinning solution contains fiber raw materials. The fiber raw materials may be, for example, polymers. The spinning solution contains a solvent. The fiber raw materials may be dissolved in the solvent. In the production of fibers, the fibers may be formed purely from the fiber raw materials, and the solvent may be removed afterward. The solvent may be a process aid. For example, the fiber raw materials may exist in a solid state and be dissolved in the solvent and liquefied to prepare the spinning solution. The spinning solution may consist of fiber raw materials and a solvent. However, the spinning solution may contain additives. Furthermore, the spinning solution may contain water in addition to the solvent, as long as water does not form a solvent. Also, the spinning solution may contain multiple fiber raw materials and a solvent. The spinning solution may be a highly viscous fluid.

[0010] This method includes the step of producing untreated fibers from a spinning solution. Untreated fibers can be formed, for example, by extruding the spinning solution through capillaries. In this case, the extrusion process can also be used for mixing and / or general preparation of the spinning solution. For example, the fiber material can be supplied to the extruder as a solid, with the solvent supplied separately, and these can be mixed only during the extrusion process to form the spinning solution. Untreated fibers may be formed from, for example, partially crosslinked fiber material. Untreated fibers may still contain the solvent. Untreated fibers may have, for example, a gel-like consistency. Untreated fibers may be moldable and correspond to a state in which the individual fiber components have not yet completely solidified into fibers. It is also possible to produce multiple untreated fibers in parallel. For example, a spinnblock may have 10,000, 20,000, 50,000 or more capillaries, and one untreated fiber may be formed at the outlet simultaneously through them during extrusion. The untreated fibers may be composed of, for example, continuous fibers. The untreated fibers may already have a nanoporous structure that is largely retained in later process steps. Alternatively, the nanoporous structure may be generated for the first time at a later point in time.

[0011] This method includes the step of accelerating the generated untreated fibers using an accelerating fluid flow. The accelerating fluid flow may include, for example, water and / or air. The accelerating fluid may be the same as or different from the solvent. For example, a non-solvent can be selected as the accelerating fluid flow. The accelerating fluid flow can be oriented substantially parallel to the extrusion direction of the untreated fibers. By accelerating the untreated fibers, their diameter can be reduced and / or their length can be stretched. The untreated fibers are stretched by the acceleration. By making the cross-section finer, the nonwoven fabric thus produced can have significantly improved flexibility. Furthermore, drying can be performed particularly quickly and / or with low energy intensity. This acceleration does not reduce nanoporosity with little or no effect, in contrast to other methods that reduce the cross-section, for example. Also, the risk of the untreated fibers breaking is low when accelerating with an accelerating fluid flow. Furthermore, acceleration with an accelerating fluid flow can contribute to the formation of the nonwoven fabric by turbulence of the untreated fibers. The untreated fibers may be accelerated non-uniformly. For example, an accelerating fluid flow can act on untreated fibers from both sides of a spinning block. In this case, the untreated fibers on the outside facing the fluid flow are accelerated more strongly than, for example, the untreated fibers on the inside. This makes it possible to increase the bonding between fibers in the nonwoven and / or improve the fiber density of the nonwoven. The accelerating fluid flow can also solidify the untreated fibers in the initial stages and / or act as an antisolvent. The accelerating fluid flow can also act on the untreated fibers in the gaps between individual capillary openings. The production of untreated fibers with acceleration as described here is also called the Solution Blown Process. The accelerating fluid can be recovered and reused. The accelerating fluid can flow, for example, at nearly the speed of sound. For example, the accelerating fluid can be directed to the untreated fibers at about Mach 0.8.

[0012] This method includes the step of depositing accelerated untreated fibers as a moist nonwoven precursor containing a fluid. This fluid may exist in a liquid aggregated state at the time of deposit. In the nonwoven precursor, the untreated fibers may, for example, already be arranged in a nonwoven manner. This nonwoven arrangement may be a random wirrage. The fibers in the nonwoven precursor may, for example, be partially attached to each other, intertwined with each other, or form a partially integrated structure. The nonwoven precursor may still contain a considerable proportion of solvent and / or accelerating fluid, particularly incorporated into the pores of the fibers. Further fluids may also be added for storage purposes or protection from environmental influences. For example, all fibers in the nonwoven precursor may be wetted with a liquid and / or completely or nearly completely covered before the subsequent drying step. The fluid wetting the nonwoven precursor may, alternatively or additionally, be retained within the fiber structure. Thus, the untreated fibers are not dry at any point in the process until, for example, an explicit drying step is performed. For example, liquid may remain in the pores of individual fibers until drying is performed. However, this liquid can also be replaced with another liquid before drying. Deposition can be performed, for example, by collection, particularly on a conveyor belt. The fibers in the nonwoven precursor may be arbitrarily oriented or may have a preferred orientation. If there is a preferred orientation, the nonwoven can withstand high loads in a certain direction and / or bend more easily in a certain direction.

[0013] This method includes a step of drying the nonwoven fabric precursor. In this drying, the state in which the fluid in the wet nonwoven fabric precursor exhibits capillary action is avoided. For example, a state without capillary action is created by combining temperature and pressure increases before the fluid is substantially removed from the fibers. This produces a nonwoven fabric containing nanoporous fibers. When capillary action is present, the fluid in the wet nonwoven fabric precursor may have a deformable interface with respect to the surrounding atmosphere. For example, this capillary action may correspond to the surface tension of the fluid. For example, frozen or supercritical water or alcohol does not exhibit capillary action. From this state, it is possible to transition directly to the gas phase by avoiding the liquid phase, for example, by sublimation or superheating. The fluid that was previously held as a liquid within the fibers can escape from the fibers in the gas phase. The fibers may be completely solidified during drying, or they may already be completely solidified beforehand.

[0014] In drying, for example, the material can transition from the liquid phase to a frozen or supercritical phase with little to no drying initially, i.e., with fluid removal from the nonwoven precursor being negligible. Once this phase is reached, it becomes possible to directly sublimate or superheat, i.e., transition from a frozen or supercritical condensed state to a gaseous condensed state. This prevents residual fluid from contracting and collapsing the individual pores of the fibers due to capillary action. As a result, nanoporosity can be maintained on a large scale or completely during drying. Because the diameter of individual fibers is reduced by acceleration, this drying process is very efficient and can be rationally operated on an industrial scale. Drying is carried out in a sealed space, such as an autoclave.

[0015] Nonwoven fabrics containing nanoporous fibers can be manufactured inexpensively and are easy to process and use, for example, due to their draping properties. For instance, nonwoven fabrics can be used as fillers in thermal clothing, particularly as a substitute for down. They can also be used as insulation materials in aircraft manufacturing, vehicle manufacturing, and buildings. Nonwoven fabrics can also be made biodegradable. Therefore, they can be used not only as functional materials in the textile field but also in sanitary products. They can also be used as bandage materials or wound dressings. Furthermore, nonwoven fabrics can be used, for example, as filters in catalysts or water filters.

[0016] In one embodiment of this method, drying includes supercritical drying. For example, drying can be carried out exclusively by supercritical drying. In supercritical drying, the atmosphere surrounding the nonwoven fabric precursor can be brought into a supercritical condensation state. To this end, the pressure and / or temperature can be increased. For example, CO2, i.e., carbon dioxide, can be supplied to lower the required pressure and / or temperature. In supercritical drying, the fluid within the nonwoven fabric precursor can be replaced by CO2 or other gases from within the pores of the fibers. By using supercritical drying, the nanoporosity of the fibers of the nonwoven fabric can be made particularly high.

[0017] In one embodiment of this method, drying includes freeze-drying. For example, drying can be carried out exclusively by freeze-drying. Freeze-drying involves condensing the atmosphere surrounding the nonwoven fabric precursor and / or the liquid of the moist nonwoven fabric precursor into a solid aggregated state. To achieve this, the pressure is increased and / or the temperature is decreased. Then, drying by sublimation can be carried out, for example, by decreasing the pressure while maintaining the reduced temperature. Freeze-drying can be carried out at a particularly low cost on an industrial scale.

[0018] In one embodiment of this method, CO2 is supplied for drying. By supplying carbon dioxide, drying can be performed with less energy consumption. Furthermore, this results in the storage of mainly CO2 within the pores of the fibers, which can provide advantageous properties for the nonwoven fabric. For example, the air in the autoclave can be substantially replaced with CO2 for drying. After drying, the CO2 can be recovered and reused.

[0019] In one embodiment of this method, the solvent is washed off after the untreated fibers are generated. For example, the solvent can be washed off with a non-solvent or, inexpensively, with water. This makes it possible to stabilize the untreated fibers. An accelerated fluid flow can also be used to contribute to this washing. Alternatively or additionally, washing can be performed separately, for example, during or after deposition, before drying. This prevents the fibers from being damaged by the solvent during drying. The washed-off solvent can be recovered and reused.

[0020] In one embodiment of this method, the fluid in the wet nonwoven fabric precursor is replaced before drying. This makes it possible to select a particularly energy-efficient fluid for drying. For example, water can be replaced with isopropanol and / or ethanol. The replacement liquid may be a mixture of liquids. By performing replacement, it becomes possible to perform supercritical drying at lower temperatures and / or pressures, for example. For example, the replacement liquid allows drying at a temperature that is harmless to the fibers or fibrous material. Otherwise, if the pressure or temperature is too high, materials such as cellulose may decompose. For example, water may require supercritical drying at a temperature at which cellulose decomposes. In this case, the nonwoven fabric precursor can also be washed at the same time by replacement. In this case, alcohol can form a phase with CO2, which also improves drying. The replacement liquid may be a non-solvent for the fibrous raw material. During replacement, solvents, accelerating fluids, and / or washing liquids can be replaced. Replacement can be performed, for example, by simply rinsing the nonwoven fabric precursor with the replacement liquid.

[0021] In one embodiment of this method, the fiber material is cellulose. Cellulose is inexpensive, biodegradable, highly compatible with the human body, and, when the fiber diameter is small, has high fracture resistance and is very flexible. This makes it possible to produce, for example, an insulating material that can be easily handled without protective equipment. The cellulose fibers can also be treated with additives such as flame retardants after drying. Additives may also be added in other steps.

[0022] In one embodiment of this method, the solvent is NMMO. N-methylmorpholine-N-oxide (NMMO) is an easy-to-handle solvent for cellulose. Furthermore, NMMO is easily recovered for reuse, thereby keeping costs low.

[0023] Further combinations of fiber raw materials and solvents suitable for nonwoven fabric production from spinning solutions include, for example, PAN (polyacrylonitrile) and DMSO (dimethyl sulfoxide), and TEOS (tetraethyl orthosilicate) and ethanol. These combinations made it possible to produce nonwoven fabrics containing highly porous fibers with minimal effort. Examples of other organic or inorganic polymers suitable as fiber raw materials include PUR (polyurethane), PET (polyethylene terephthalate), lignin, PHA (polyhydroxyalkanoate), para and meta-aramids, glucans, and protein fibers. Suitable solvents include, for example, alcohols and organic solvents. Appropriate solvents depending on the selected fiber raw material include acetone, water, and NaSCN (sodium thiocyanate). Examples of organic solvents include DMSO (dimethyl sulfoxide), DMF (dimethylformamide), and DMAc (dimethylacetamide).

[0024] In one embodiment of the method, the accelerating fluid comprises water, a non-solvent for the fiber raw material, and / or air. This allows the accelerating fluid to be used very inexpensively and easily. Furthermore, the accelerating fluid can already replace sorbitol and / or wash protofibrils. The accelerating fluid may consist of water, a non-solvent for the fiber starting material and / or air.

[0025] In one embodiment of the method, the accelerating fluid stream is configured as an aerosol. For example, the accelerating fluid can be configured as a flowing water mist or a solvent mist. This allows untreated fibers to be wetted particularly well and prevents drying. At the same time, the amount of liquid required for supplying the fluid stream can be kept low.

[0026] The second aspect of the present invention relates to a nonwoven fabric comprising nanoporous fibers, particularly aerogel fibers, wherein the nonwoven fabric is manufactured by the method according to the first aspect. This is identifiable, for example, based on the varying diameters of fibers within the nonwoven, the highly nanoporous structure of the fibers, and / or their extremely small diameters. Features and advantages corresponding to the first aspect can also be features and advantages of the second aspect, and vice versa. The nonwoven fabric may consist exclusively of nanoporous fibers. The nonwoven fabric may comprise other fibers and layers. For example, more than 30%, particularly more than 50%, 75% or 95% of the nonwoven fabric may be configured as nanoporous fibers.

[0027] In one embodiment of the method, more than 30%, particularly more than 50%, more than 60%, more than 70%, more than 90%, more than 95% of the cross-section of the nanoporous fiber is formed by nanopores. The cross-section may be a cut plane perpendicular to the elongation in the length direction. The nanopores are, for example, openings or voids within the fiber, the diameter of which is less than 1500 nm, particularly less than 1000 nm, 750 nm or 500 nm. Due to the high proportion of nanopores in the cross-section, the nonwoven fabric can have particularly strong thermal insulation properties. Increasing this proportion can be achieved, for example, by the production method described above.

[0028] In one embodiment of this method, the diameter of the nanoporous fibers is less than 100 μm, particularly less than 75 μm, less than 50 μm, less than 25 μm, less than 20 μm, less than 15 μm, or less than 10 μm. The small diameter makes it possible to achieve this by accelerating the untreated fibers during manufacturing. The small diameter allows for efficient and rapid drying, which can contribute to the high flexibility of the nonwoven fabric. The diameter can be the minimum, maximum, or average diameter of the fibers. Some fibers may be incidentally thicker or thinner. For example, the average diameter of the nanoporous fibers may be less than 100 μm, particularly less than 75 μm, 50 μm, 25 μm, 20 μm, less than 15 μm, or less than 10 μm. However, only 90% of the total fibers of the nonwoven fabric, and in particular at least 95%, 97%, or 99%, may have a diameter of less than 100 μm, in particular less than 75 μm, 50 μm, 25 μm, 20 μm, 15 μm, or 10 μm. Other fibers in the nonwoven fabric may be thicker. Some fibers may even be significantly thinner. For example, at least 0.1% of the total fibers, and in particular at least 0.5%, 1%, 5%, or 10%, may have a diameter of less than 5 μm, in particular less than 2 μm, 1 μm, or 0.8 μm. For example, the diameter of individual fibers in the nonwoven fabric may be significantly smaller than the diameter of the capillary tube of the spinning head. The diameters of most fibers are in the range from low micrometers (e.g., less than 10 μm) to high nanometers (e.g., greater than 800 nm). Fibers may have a minimum thickness in the range of, for example, two orders of magnitude nanometers, for example greater than 10 nm, 50 nm, or 75 nm.

[0029] In one embodiment of this method, the thickness of the nonwoven fabric layer is less than 5 mm, particularly less than 4 mm, less than 3 mm, less than 2 mm, less than 1.5 mm, or less than 1 mm. Reducing the layer thickness is possible, for example, by the diameter of individual, finer fibers. The layer thickness may be the thickness of a single nonwoven fabric. The thickness may also be the thickness in the direction perpendicular to the planar spread. Because a thin thickness can be easily provided, this thin layer thickness facilitates post-processing. If a greater thickness is desired, multiple nonwoven fabric layers can be used.

[0030] In one embodiment of this method, the bending radius of the nonwoven fabric is less than 5 mm, particularly less than 4 mm, less than 3 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, less than 0.5 mm, or less than 0.1 mm. For example, the nonwoven fabric can be folded like a pocket tissue or a thin paper napkin. In this case, no substantial fiber breakage occurs. For example, even when bent or folded without the use of auxiliary means, no dust generation or broken edges are observed in the nonwoven fabric. Therefore, this nonwoven fabric can be easily processed.

[0031] In one embodiment of this method, the basis weight (Flaechengewicht) of the nonwoven fabric is less than 100 gsm, particularly less than 75 gsm, less than 50 gsm, or less than 30 gsm, at a layer thickness of 1 mm. Depending on the layer thickness, the basis weight can be proportionally smaller or larger. Basis weight can be the weight in grams per square meter. As a result, the nonwoven fabric is very lightweight despite having excellent thermal insulation properties. Lightweight is particularly desirable in aircraft manufacturing or functional textiles.

[0032] A third aspect of the present invention relates to a manufacturing apparatus for producing a nonwoven fabric containing nanoporous fibers. The manufacturing apparatus can be configured to carry out the production of the nonwoven fabric according to the second aspect and / or the method according to the first aspect. The corresponding features and advantages of the first or second aspect may also be the features and advantages of the third aspect, and vice versa.

[0033] The manufacturing equipment may include a production apparatus configured to produce untreated fibers from a spinning solution containing fiber raw materials and a solvent. For example, the manufacturing equipment may include an extruder and a spinning head including capillaries. The manufacturing equipment may also include a mixing apparatus for preparing the spinning solution. In this case, the mixing apparatus may be part of the production apparatus. For example, the extruder may form the mixing apparatus.

[0034] The manufacturing equipment may include an accelerator configured to accelerate untreated fibers using an accelerating fluid flow. For example, the accelerator may include a fluid reservoir, a pump, and at least one nozzle. The nozzle is positioned adjacent to the spinning head, and its opening may generally be oriented in the same direction as the capillary tube. Alternatively, the nozzle may be integrated into the spinning head.

[0035] The manufacturing equipment may include a deposition apparatus configured to deposit the accelerated untreated fibers as a liquid-containing, moist nonwoven fabric precursor. The deposition apparatus may include, for example, a conveyor belt onto which the moist nonwoven fabric precursor is deposited. The deposition apparatus can be configured to avoid drying of the nonwoven fabric precursor.

[0036] The manufacturing equipment may include a washing device. The washing device may be configured to wash away any residual solvent from the wet nonwoven precursor. The manufacturing equipment may also include a fluid replacement device. The fluid replacement device may be configured to replace the solvent in the wet nonwoven precursor (particularly in the pores of the fibers of the nonwoven precursor) and, optionally, other fluids. This replacement can be carried out with alcohol and / or without drying the wet nonwoven precursor. The washing device and the fluid replacement device may be formed by a common apparatus.

[0037] The manufacturing equipment may include a drying apparatus configured to dry the wet nonwoven fabric precursor while avoiding the phase in which the liquid in the wet nonwoven fabric precursor exhibits capillary action. The drying apparatus may include an autoclave. The drying apparatus may include a freezing apparatus. The drying apparatus may include a device for adding CO2 to a sealed atmosphere surrounding the wet nonwoven fabric precursor. This drying makes it possible to produce the finished nonwoven fabric.

[0038] The manufacturing facility may include a recycling device. For example, the recycling device can recover the solvent after the production of untreated fibers, the accelerating fluid after the deposition of the nonwoven fabric precursor, the replaced and / or washed liquid, the supplied CO2, and / or the liquid that escapes from the wet nonwoven fabric precursor during drying, and provide it for reuse and / or regeneration. This makes it possible to keep material costs in manufacturing particularly low. [Brief explanation of the drawing]

[0039] [Figure 1] This document illustrates a method for manufacturing nonwoven fabrics containing nanoporous fibers. [Figure 2] Figure 1 shows a schematic example of the manufacturing equipment required to implement the method described. [Figure 3] This example shows a cross-section of a fiber with high macroporosity and low nanoporosity. [Figure 4] This shows an example of a cross-section of a fiber with high nanoporosity. [Modes for carrying out the invention]

[0040] Figure 1 illustrates a method for manufacturing a nonwoven fabric containing nanoporous fibers. This method can be carried out using the manufacturing equipment shown in Figure 2.

[0041] In step 10, a spinning solution containing fiber raw material (cellulose in this case) and solvent (NMMO in this case) is prepared. In step 12, a large number of untreated fibers 20 are produced from the spinning solution. For this purpose, the manufacturing equipment is equipped with an extruder 22. Inside the extruder, the cellulose and NMMO are mixed to form a highly viscous solution, which is extruded from the capillaries of the spinning head 24. At this time, the untreated fibers 20 are discharged vertically downward from the spinning head 24 and remain moist because the solvent is trapped within the pores of the fibers 20.

[0042] The generated untreated fibers are accelerated by a flow of accelerating fluid in step 14, either as they exit the spinning head 24 or thereafter. The accelerating fluid can be water, air, or an aerosol mixture of water and air. This acceleration stretches the untreated fibers so that their diameter is significantly smaller than the diameter of the capillary or the diameter at the capillary outlet of the spinning head 24. Accordingly, the manufacturing equipment includes an accelerator configured to accelerate the untreated fibers using a flow of accelerating fluid. In the illustrated example, the accelerator has nozzles, which are incorporated into or located on both sides of the spinning head 24. Details of the accelerator are not shown in Figure 2.

[0043] The accelerated or stretched untreated fibers 20 are deposited in step 16 as a wet nonwoven fabric precursor 26. For this purpose, the manufacturing facility is equipped with a depositing device, which is configured as a belt conveyor 28 with a recovery tank 30. On the belt conveyor 28, the wet nonwoven fabric precursor solidifies by coagulation, but the nonwoven fabric precursor and its fibers do not dry out during this process. The separated solvent or excess mixture of NMMO and accelerating fluid is recovered in the recovery tank 30 and can be reused.

[0044] Next, the wet nonwoven fabric precursor 26 is optionally wound up in the winding device 32 of the manufacturing equipment. Before winding, the nonwoven fabric precursor 26 can optionally be washed, for example, to reduce the amount of solvent in the nonwoven fabric precursor. For washing, for example, water or other non-solvents for cellulose can be used. The wound wet nonwoven fabric precursor 26 has solidified, but it remains wet because each pore of the fibers of the nonwoven fabric precursor 26 still contains water and possibly residual NMMO.

[0045] Next, an optional step is performed in which the fluid replacement device 34 replaces the liquid trapped in the pores of the nonwoven fabric precursor 26 fibers. The replacement liquid is selected here as a non-solvent that enables supercritical drying of the wet fibers of the nonwoven fabric precursor 26 without decomposition due to excessively high temperatures, for example. In the example above, isopropanol and / or ethanol are used to displace water and NMMO from the pores. In another embodiment, washing and / or acceleration using a fluid suitable for supercritical drying can eliminate the need for liquid replacement within the pores.

[0046] Finally, in step 18, the moist nonwoven fabric precursor 26 is dried. This removes the liquid from within the fiber pores. This drying is performed as supercritical drying, but freeze-drying is also possible. In supercritical drying, the liquid within the fiber pores is transformed into a supercritical aggregated state where capillary action does not occur. In supercritical drying, the fluid within the fiber pores has no surface tension. Therefore, even if the amount of fluid within the pores is reduced, the pore walls do not shrink, and the nanopores within the fibers can be completely or largely preserved. In both supercritical drying and the alternative freeze-drying, the state in which the moist nonwoven fabric precursor 26 or the liquid within the fiber pores exhibits capillary action is avoided. After drying, the production of a nonwoven fabric containing nanoporous fibers is completed.

[0047] For drying, the manufacturing equipment is equipped with a drying apparatus 36. This drying apparatus is equipped with an autoclave. CO2 is supplied into the autoclave to reduce the pressure and temperature to reach a supercritical state. This makes it possible to supercritically dry the ethanol or isopropanol in the pores at a temperature of approximately 50°C and a pressure of approximately 92 bar. At that time, if there is any water or NMMO residue, they are also dried simultaneously.

[0048] Figure 3 shows fibers with a low proportion of nanopores. These fibers were manufactured without stretching and by atmospheric pressure drying, and contain PAN as the fiber material. The non-solvent in the wet fiber was water, but similar results may be obtained using other non-solvents if supercritical drying is not performed. Nanopores are almost without exception found only in the outer peripheral region 40 of the fiber. On the other hand, in the central region 42, the fiber has many substantially larger macropores. Nonwoven fabrics containing such fibers have low thermal insulation properties. In the central region 42, nanopores collapse due to capillary action during drying. Drying here was performed only by conventional methods such as heating or leaving at room temperature. The cross-section of the fiber in Figure 3 is shown as circular here, but it may be flattened due to the collapse of nanopores in the central region 42.

[0049] Figure 4 shows the fibers of the nonwoven fabric produced by the method described above, which have been supercritically dried with a non-solvent (in this case, a combination of ethanol and isopropanol). These fibers have nanopores uniformly and finely dispersed throughout their entire cross-section. More than 80% of the cross-section of these nanoporous fibers is formed by nanopores. Where the nanopores have collapsed, only small defects in the form of shrinkage cavities 44 exist. [Explanation of symbols]

[0050] 10. Steps to prepare the spinning solution 12 Steps to generate untreated fibers 14. Step to accelerate the generated untreated fibers. 16. Step of depositing accelerated untreated fibers. 18. Step of drying the nonwoven fabric precursor. 20 Untreated fibers (Rohfasern) 22 Extruder 24 spinning heads 26 Nonwoven fabric precursors (Vliespraekursors) 28 Belt conveyor 30 times collection tank 32 Winding device 34 Fluid displacement device 36 Drying equipment 40 Peripheral area (Randbereich) 42 Central area 44 Lunker

Claims

1. A method for producing a nonwoven fabric containing nanoporous fibers, particularly aerogel fibers, The aforementioned method, at least • Fiber raw materials, especially polymers, Includes a solvent Step (10) of preparing the spinning solution, - Untreated fibers (20) are obtained from the spinning solution. In particular, step (12) of generating by extruding the spinning solution through a capillary tube, - A step (14) of accelerating the generated untreated fibers (20) using an accelerating fluid flow, - A step (16) of depositing the accelerated untreated fibers (20) as a fluid-containing moist nonwoven fabric precursor (26), - In order to produce a nonwoven fabric containing nanoporous fibers, the process includes the step (18) of drying the nonwoven fabric precursor (26) while avoiding a state in which the liquid in the moist nonwoven fabric precursor (26) exhibits capillary action, Methods that include...

2. The drying (18) includes supercritical drying. and / or The drying includes freeze-drying. The method according to claim 1.

3. CO2 is supplied for the drying (18) The method according to claim 1 or 2.

4. After the untreated fibers (20) are produced (12), the solvent is washed. The method according to any one of claims 1 to 3.

5. Prior to the drying (18), the fluid in the moist nonwoven fabric precursor (26) is replaced. In particular, the substitution liquid is a non-solvent for the fiber raw material. and / or In particular, the solvent, the accelerating fluid, and / or the cleaning solution are replaced. The method according to any one of claims 1 to 4.

6. The aforementioned fiber raw material is cellulose, and / or The solvent is NMMO. The method according to any one of claims 1 to 5.

7. The accelerating fluid includes water, a non-solvent for the fiber raw material, and / or air. and / or The aforementioned accelerating fluid flow is configured as an aerosol. The method according to any one of claims 1 to 6.

8. A nonwoven fabric containing nanoporous fibers, particularly aerogel fibers, A nonwoven fabric manufactured by the method described in any one of claims 1 to 7.

9. More than 30% of the cross-section of the aforementioned nanoporous fiber, particularly more than 50%, 60%, 70%, 90%, and 95%, is formed by nanopores. and / or The diameter of the nanoporous fiber is less than 100 μm, particularly less than 75 μm, less than 50 μm, less than 25 μm, less than 20 μm, less than 15 μm, or less than 10 μm. The nonwoven fabric according to claim 8.

10. The thickness of the nonwoven fabric is less than 5 mm, especially less than 4 mm, less than 3 mm, less than 2 mm, less than 1.5 mm, or less than 1 mm. and / or The bending radius of the nonwoven fabric is less than 5 mm, especially less than 4 mm, less than 3 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, less than 0.5 mm, or less than 0.1 mm. and / or The basis weight of the nonwoven fabric is less than 100 gsm per 1 mm layer thickness, particularly less than 75 gsm, less than 50 gsm, or less than 30 gsm. The nonwoven fabric according to claim 8 or 9.

11. A manufacturing apparatus for producing a nonwoven fabric containing nanoporous fibers, which is configured to produce a nonwoven fabric according to any one of claims 8 to 10, and / or to carry out the method according to any one of claims 1 to 7. The aforementioned manufacturing equipment is A generating apparatus (22) configured to produce untreated fibers (20) from a spinning solution containing fiber raw materials and a solvent (12), An accelerator configured to accelerate the untreated fibers using an accelerating fluid flow (14), A deposition apparatus (28, 30) configured to deposit the accelerated untreated fibers (20) as a liquid-containing moist nonwoven fabric precursor (26) (16), A drying apparatus (36) configured to dry the moist nonwoven fabric precursor (26) (18) while avoiding the phase in which the liquid in the moist nonwoven fabric precursor (26) exhibits capillary action, Manufacturing equipment equipped with these features.

Images