Nonwoven having nanoporous fibers

Abstract

The present invention relates to a method for manufacturing a nonwoven having nanoporous fibers. The method comprises at least the following steps: - providing (10) a spinning solution having a fiber starting material, in particular a polymer, and having a solvent, - producing (12) raw fibers (20) from the spinning solution, in particular by extruding the spinning solution through capillaries; - accelerating (14) the produced raw fibers (20) by means of an acceleration fluid flow; - depositing (16) the accelerated raw fibers (20) as a moist nonwoven precursor (26) with a fluid; - drying (18) the nonwoven precursor (26) while avoiding a state of the liquid of the moist nonwoven precursor (26) in which the liquid has a capillarity, in order to produce the nonwoven having nanoporous fibers. The invention also relates to a nonwoven and to a manufacturing system

Description

[0001] Nonwoven with nanoporous fibers

[0002] Technical area

[0003] The present invention relates to a method for producing a nonwoven fabric with nanoporous fibers, in particular aerogel fibers. Furthermore, the invention relates to a nonwoven fabric with nanoporous fibers and a production system for producing a nonwoven fabric with nanoporous fibers.

[0004] State of the art

[0005] Aerogels are highly porous solids in which, for example, more than 99% of their volume consists of pores. The pore size is in the nanometer range. The aerogel can be formed from silicates, for example. Aerogels are exceptionally lightweight and exhibit excellent thermal insulation and filtration properties. However, the production of aerogels on an industrial scale is extremely expensive, and their use as a monolithic solid is very complex, difficult, or even impossible for certain applications.

[0006] DE 10 2006 049 179 describes aerogel fiber materials, a process for their production, and their use. The aerogels can be processed into nonwovens, for example. However, the production of aerogel fibers remains very complex. In particular, drying the fibers during production is laborious, and only very thick fibers can be produced. Furthermore, the further processing of the thick fibers into nonwovens can lead to numerous fiber breaks. The flexibility of the nonwovens can be very low.

[0007] Jens Mroszczok's 2019 dissertation "Production of Aerogel Nonwovens" describes the production of cellulose-based aerogel nonwovens. Even in this case, only very thick fibers can be produced, and drying the nonwovens is still complex. EP 3 529 405 A1 describes a method and apparatus for forming directly molded cellulose webs.

[0008] Description of the invention

[0009] A first aspect of the invention relates to a method for producing a nonwoven fabric with nanoporous fibers. The nonwoven fabric can be a nonwoven fabric. The nonwoven fabric can be a structure made of fibers that have been combined to form a fiber layer or nonwoven ply. The fibers can be arranged unevenly and / or partially randomly aligned in the nonwoven fabric. For example, the fibers can have a randomly scattered orientation within a preferred orientation. The nanoporous fibers can be formed, for example, as aerogel fibers. The nanoporous fibers can be elastically deformable. The fibers can be formed, for example, as fibers of limited length or continuous fibers. The respective pores of the fibers can be open or closed. The pores can be filled with a gas, such as air or CO2.

[0010] The method comprises providing a spinning solution. The spinning solution comprises a fiber starting material. The fiber starting material can be a polymer, for example. The spinning solution comprises a solvent. The fiber starting material can be dissolved in the solvent. During fiber production, a fiber can be formed purely from the fiber starting material, and the solvent can be removed later. The solvent can be a processing aid. For example, the fiber starting material can be in solid form and, to provide the spinning solution, can be dissolved with the solvent and thus liquefied. The spinning solution can consist of the fiber starting material and the solvent. The spinning solution can also comprise additives. Furthermore, the spinning solution can comprise water in addition to the solvent, provided that water does not form the solvent. The spinning solution can also contain multiple fiber starting materials and solvents.The spinning solution can be a highly viscous fluid.

[0011] The method comprises a step of producing crude fibers from the spinning solution. The crude fibers can be formed, for example, by extruding the spinning solution through capillaries. The extrusion process can also be used for mixing and / or generally preparing the spinning solution. For example, the fiber starting material as a solid and the solvent can be fed separately to the extruder and only mixed during the extrusion process to form the spinning solution. The crude fibers can, for example, be formed from partially cross-linked fiber starting materials. The crude fibers can still contain solvent. The crude fibers can, for example, have a gel-like consistency. The crude fibers can be moldable and correspond to a state in which individual fiber components have not yet completely solidified into the fiber. Multiple crude fibers can be produced in parallel.For example, a spinning block can have 10,000, 20,000, 50,000, or more capillaries, each of which simultaneously forms a raw fiber upon exiting during extrusion. The raw fibers can, for example, be formed as continuous fibers. The raw fibers can already have a nanoporous structure, which is largely retained in subsequent process steps. The nanoporous structure can also be created at a later time.

[0012] The method comprises a step of accelerating the produced raw fibers using an accelerating fluid stream. The accelerating fluid stream can comprise, for example, water and / or air. The accelerating fluid can be identical to or different from the solvent. For example, a non-solvent can be selected as the accelerating fluid stream. The accelerating fluid stream can be aligned substantially parallel to an extrusion direction of the raw fibers. By accelerating the raw fibers, their diameter can decrease and / or the raw fibers can stretch in length. The raw fibers can be stretched by the acceleration. Due to the thinner cross-section, the nonwoven fabric produced in this way can exhibit significantly improved flexibility. Furthermore, drying can be particularly fast and / or low-energy intensive.In contrast to other cross-section-reducing measures, for example, acceleration can only reduce nanoporosity slightly or not at all. The risk of crude fiber breakage is also low when accelerating using the accelerating fluid flow. Furthermore, acceleration using the accelerating fluid flow can contribute to web formation by swirling the crude fibers. The crude fibers can be accelerated unevenly. For example, an accelerating fluid flow can act on the crude fibers from both sides of the spinning block. For example, crude fibers on the outside, facing the fluid flow, are accelerated more strongly than crude fibers on the inside. This can lead to a strong bond between the fibers in the web and / or an increased fiber density of the web. The accelerating fluid flow can initially strengthen the crude fibers and / or act as an antisolvent.The accelerating fluid flow can also act on the raw fibers in the space between the respective capillary openings. Crude fiber production with acceleration as described here can also be referred to as a solution-blown process. The accelerating fluid can be collected and reused. For example, the accelerating fluid can flow at nearly the speed of sound. For example, the accelerating fluid can be directed to the raw fibers at approximately 0.8 Mach.

[0013] The method comprises a step of depositing the accelerated raw fibers as a moist nonwoven precursor with a fluid. The fluid can be in its liquid state during deposition. In the nonwoven precursor, the raw fibers can, for example, already be arranged in a nonwoven manner. A nonwoven arrangement can be a random layer. The fibers in the nonwoven precursor can, for example, partially adhere to one another, be entangled with one another, or even partially form a uniform structure. The nonwoven precursor can also contain a significant proportion of solvent and / or acceleration fluid, in particular embedded in pores of the fibers. Additional fluid can also be added for storage purposes and / or for protection against environmental influences. For example, all fibers in the nonwoven precursor can be wetted and / or completely or almost completely covered with liquid before the subsequent drying step.The fluid that makes the nonwoven precursor moist can alternatively or additionally be stored in the fiber structure. Thus, for example, the raw fibers are never dry at any point in the process before an explicit drying step. For example, liquid can remain in the pores of the respective fibers until drying occurs. However, the liquid can also be replaced by other liquids before drying. The deposition can occur, for example, by collecting them, in particular on a conveyor belt. The fibers in the nonwoven precursor can be randomly aligned or have a preferred orientation. With a preferred orientation, the nonwoven can withstand higher loads in one direction and / or be more easily flexible in one direction. The method comprises a step of drying the nonwoven precursor. During drying, a fluid state of the moist nonwoven precursor in which the liquid exhibits capillarity is bypassed.For example, before a significant amount of liquid is removed from the fibers, a state without capillarity is achieved, for example by increasing the temperature together with an increase in pressure. This is how the nonwoven fabric with nanoporous fibers is created. With capillarity, the fluid in the moist nonwoven precursor can have a deformable interface with the surrounding atmosphere. For example, the capillarity can correspond to a surface tension of the fluid. For example, water or alcohol in a frozen or supercritical state has no capillarity. From this state, a direct transition to a vapor phase can then be achieved, bypassing a liquid phase, for example by sublimation or superheating. In the vapor phase, the fluid, which was previously stored in the fibers as a liquid, can escape from the fibers. The fibers can completely solidify during drying or can already be completely solidified beforehand.

[0014] During drying, for example, the material can initially transition from the liquid phase to the frozen or supercritical phase with little or no drying, i.e., with at most an insignificant removal of fluid from the nonwoven precursor. Once this phase is reached, direct sublimation or superheating can occur, i.e., a transition from the frozen or supercritical state to the vapor state can occur. This means that any residual fluid, due to its capillarity, cannot contract and collapse the pores of the fibers. Nanoporosity can thus be retained to a large extent or even completely during drying. Due to the small diameters of the fibers resulting from the acceleration, this drying process is very efficient and can also be used effectively on an industrial scale. Drying takes place, for example, in a closed space, such as an autoclave.

[0015] The fleece with the nanoporous fibers is cost-effective to produce and easy to process and use, for example, due to its drapability. For example, the fleece can be used as filling material in insulating clothing, particularly as a down substitute. The fleece can be used as insulation material in aircraft construction, vehicle construction, and buildings. The fleece can also be biodegradable. This makes it usable not only as a functional material in the textile sector, but also as a hygiene product. It can also be used as a bandage or wound dressing. The fleece can also be used as a filter, for example, in catalysts or water filters.

[0016] In one embodiment of the method, it is provided that the drying comprises supercritical drying. For example, the drying can be carried out exclusively supercritically. During supercritical drying, the atmosphere around the nonwoven precursor can be brought into its supercritical state. For this purpose, a pressure and / or a temperature can be increased. For example, CO2, i.e. carbon dioxide, can be added to reduce the necessary pressure and / or temperature. During supercritical drying, the fluid in the nonwoven precursor from the pores of the fibers can be replaced by CO2 or other gases. During supercritical drying, the nanoporosity of the fibers of the nonwoven can be particularly high.

[0017] In one embodiment of the method, the drying step includes freeze-drying. For example, the drying step can be performed exclusively by freeze-drying. During freeze-drying, the atmosphere surrounding the nonwoven precursor and / or the liquid of the moist nonwoven precursor can be converted to its solid state. For this purpose, the pressure can be increased and / or the temperature can be reduced. The pressure can then be reduced to dry by sublimation, for example, while maintaining the reduced temperature. Freeze-drying can be performed particularly cost-effectively on an industrial scale.

[0018] In one embodiment of the method, it is provided that CO2 is added for drying. By adding carbon dioxide, drying can be less energy-intensive. In addition, CO2 can be stored primarily in the pores of the fibers, which can result in advantageous nonwoven properties. For example, air in an autoclave can be essentially replaced by CO2 for drying. After drying, the CO2 can be collected and reused. In one embodiment of the method, it is provided that after the raw fibers have been produced, the solvent is washed out. For example, the solvent can be washed out using a non-solvent or, cost-effectively, using water. This can stabilize the raw fibers. The accelerating fluid flow can contribute to the washing process. Alternatively or additionally, the washing can take place separately, for example during or after deposition and before drying.This prevents damage to the fibers during drying by the solvent. The washed-out solvent can be collected and reused.

[0019] In one embodiment of the method, fluid in the moist nonwoven precursor is replaced before drying. This allows a fluid to be selected that is particularly energy-efficient for drying. For example, water can be replaced with isopropanol and / or ethanol. The replacement fluid can also be a liquid mixture. By replacing it, supercritical drying can be carried out at lower temperatures and / or pressures, for example. For example, the replacement fluid can enable drying at temperatures that are harmless to the fibers or fiber material. At excessively high pressures and temperatures, the material, such as cellulose, can otherwise decompose. For example, water can require supercritical drying at temperatures at which cellulose decomposes. The replacement can simultaneously wash the nonwoven precursor.Alcohol can form a phase with CO2, which also improves drying. A replacement fluid can be a non-solvent for the fiber starting material. The replacement fluid can replace the solvent, the accelerator fluid, and / or a washing fluid. For example, the replacement can be achieved by simply rinsing the nonwoven precursor with the replacement fluid.

[0020] In one embodiment of the process, the fiber starting material is cellulose. Cellulose is inexpensive, biodegradable, human-compatible, and, at low fiber thicknesses, highly flexible with only a low tendency to break. This allows, for example, an insulating material to be produced that is simple and safe to handle without the need for protective equipment. The cellulose fibers can be treated with an additive, such as a flame retardant, after drying. Additives can also be added during other steps.

[0021] In one embodiment of the process, the solvent is NMMO. N-Methylmorpholyne N-oxide is an easily handled solvent for cellulose. Furthermore, NMMO can be easily recycled for reuse, which can keep costs low.

[0022] Other suitable combinations of fiber starting materials and solvents for nonwoven production from spinning solution include PAN (polyacrylonitrile) and DMSO (dimethyl sulfoxide), as well as TEOS (tetraethyl orthosilicate) and ethanol. These combinations allow nonwovens with highly porous fibers to be produced with minimal effort. Other examples of suitable organic or inorganic polymers as fiber starting materials include PUR (polyurethane), PET (polyethylene terephalate), lignin, PHA (polyhydroxyalkonoate), para and meta aramids, glucan, and protein fibers. Suitable solvents can include alcohols and organic solvents. Depending on the fiber starting material selected, suitable solvents can be acetone, water, and NaSCn (sodium thiocyanate). Examples of organic solvents are DMSO (dimethyl sulfoxide), DMF (dimethylformamide), and DMAC (dimethylacetamide).

[0023] In one embodiment of the method, the accelerating fluid comprises water, a non-solvent for the fiber starting material, and / or air. This makes the accelerating fluid very cost-effective and easy to reuse. Furthermore, the accelerating fluid can thus replace the solvent and / or wash the raw fibers. The accelerating fluid can also consist of water, a non-solvent for the fiber starting material, and / or air.

[0024] In one embodiment of the method, the accelerating fluid stream is embodied as an aerosol. For example, the accelerating fluid can be embodied as a flowing water mist or solvent mist. This allows the raw fibers to be utilized particularly effectively and prevents drying out. At the same time, the amount of liquid required to provide the fluid stream can be low. A second aspect of the invention relates to a nonwoven fabric with nanoporous fibers, in particular with aerogel fibers. The nonwoven fabric was produced using the method according to the first aspect. This can be recognized, for example, by the different diameters of the fibers in the nonwoven fabric, the highly nanoporous structure of the fibers, and / or their very small diameters. Corresponding features and advantages of the first aspect can also form features and advantages of the second aspect, and vice versa. The nonwoven fabric can consist of the nanoporous fibers.The nonwoven fabric may also comprise additional fibers and layers. For example, more than 30%, in particular more than 50%, 75%, or 95% of the nonwoven fabric may be formed as nanoporous fibers.

[0025] In one embodiment of the method, it is provided that a cross-section of the nanoporous fibers is formed by more than 30% nanopores, in particular more than 50%, 60%, 70%, 90%, or 95% nanopores. The cross-section can be a section orthogonal to a longitudinal extent. Nanopores can, for example, be openings or cavities in the fiber that have a diameter of less than 1500 nm, in particular less than 1000 nm, 750 nm, or 500 nm. Due to the high proportion of nanopores in the cross-section, the nonwoven can be particularly highly thermally insulating. This high proportion can be achieved, for example, by the manufacturing process described above.

[0026] In one embodiment of the method, it is provided that the diameter of the nanoporous fibers is less than 100 μm, in particular less than 75 μm, 50 μm, 25 μm, 20 μm, 15 μm, or less than 10 μm. The small diameter can be achieved by accelerating the raw fibers during production. The small diameter enables efficient and rapid drying and can contribute to the nonwoven's great flexibility. The diameter can be a smallest, largest, or average diameter of a fiber. Some fibers may randomly be thicker or thinner. For example, the diameter of the nanoporous fibers on average across all fibers can be less than 100 μm, in particular less than 75 μm, 50 μm, 25 μm, 20 μm, 15 μm, or less than 10 μm.However, the diameter of only at least 90%, in particular at least 95%, 97% or 99% of all fibers of the nonwoven fabric can be less than 100 pm, in particular less than 75 pm, 50 pm, 25 pm, 20 pm, 15 pm or less than 10 pm. Other fibers of the nonwoven fabric can be thicker. Some of the fibers can even be considerably thinner. For example, at least 0.1%, in particular at least 0.5%, 1%, 5% or 10% of all fibers can have a diameter of less than 5 pm, in particular even less than 2 pm, 1 pm or 0.8 pm. For example, respective fiber diameters in the nonwoven fabric can be considerably smaller than the diameter of the capillaries of the spinning head. Most fiber diameters are in the low micrometer range, for example less than 10 pm, and in the upper nanometer range, for example more than 800 nm. The fibers can, for example, have a minimum thickness in the double-digit nanometer range, for example at least more than 10nm, 50nm or 75nm.

[0027] In one embodiment of the method, the nonwoven fabric has a layer thickness of less than 5 mm, in particular less than 4 mm, 3 mm, 2 mm, 1.5 mm, or 1 mm. The low layer thickness can be made possible, for example, by the respective small fiber diameters. A layer thickness can be the thickness of a single nonwoven fabric. The thickness can be orthogonal to a planar extension. The low layer thickness enables simple further processing, since even small thicknesses are easily provided. If a greater thickness is desired, multiple nonwoven layers can be used.

[0028] In one embodiment of the method, the nonwoven fabric has a bending radius of less than 5 mm, in particular less than 4 mm, 3 mm, 2 mm, 1.5 mm, 1 mm, 0.5 mm, or 0.1 mm. For example, the nonwoven fabric can be foldable like a handkerchief or a thin paper napkin. This avoids significant fiber breakage. For example, when bending or folding without aids, no dust formation or broken edges can be discernible in the nonwoven fabric. The nonwoven fabric can thus be easily processed.

[0029] In one embodiment of the method, the nonwoven fabric has a basis weight of less than 100gsm, in particular less than 75gsm, 50gsm, or 30gsm, with a layer thickness of 1 mm. Depending on the layer thickness, the basis weight can be proportionally smaller or larger. The basis weight can be a weight in grams per square meter. The nonwoven fabric is thus very lightweight, despite its excellent insulating properties. Low weight is particularly desirable in aircraft construction or for functional textiles.

[0030] A third aspect of the invention relates to a manufacturing system for producing a nonwoven fabric with nanoporous fibers. The manufacturing system can be configured to produce a nonwoven fabric according to the second aspect and / or to perform a method according to the first aspect. Corresponding features and advantages of the first or second aspect can also form features and advantages of the third aspect, and vice versa.

[0031] The production plant may comprise a production device designed to produce raw fibers from a spinning solution containing a fiber starting material and a solvent. For example, the production plant may comprise an extruder and a spinning head with capillaries. The production plant may comprise a mixing device for providing the spinning solution. The mixing device may be part of the production device. For example, the extruder may also form the mixing device.

[0032] The production plant may comprise an acceleration device configured to accelerate the raw fibers using an acceleration fluid flow. For example, the acceleration device may comprise a fluid reservoir, a pump, and at least one nozzle. The nozzle may be arranged adjacent to the spinneret, with its opening generally oriented in the same direction as the capillaries. The nozzle may also be integrated into the spinneret.

[0033] The production plant can comprise a depositing device designed to deposit the accelerated raw fibers as a moist nonwoven precursor containing a liquid. The depositing device can comprise, for example, a conveyor belt on which the moist nonwoven precursor is deposited. The depositing device can be designed to prevent the nonwoven precursor from drying out.

[0034] The production system can comprise a washing device. The washing device can be configured to wash any remaining solvent from the moist nonwoven precursor. The production system can comprise a fluid exchange device. The fluid exchange device can be configured to replace the solvent and optionally other fluids in the moist nonwoven precursor, in particular in the pores of the fibers of the nonwoven precursor. The replacement can be performed with an alcohol and / or without drying the moist nonwoven precursor. The washing device and fluid exchange device can be formed by a common device.

[0035] The manufacturing plant may comprise a drying device configured to dry the moist nonwoven precursor while bypassing a liquid phase of the moist nonwoven precursor in which the liquid exhibits capillarity. The drying device may comprise an autoclave. The drying device may comprise a freezing device. The drying device may comprise a device for adding CO2 to a closed atmosphere around the moist nonwoven precursor. The finished nonwoven can be produced by drying.

[0036] The manufacturing plant may include a recycling device. For example, the recycling device can collect solvents after raw fiber production, accelerating fluid after nonwoven precursor deposition, exchanged and / or washed-out liquids, added CO2, and / or liquids released from the moist nonwoven precursor during drying, and make them available for reuse and / or processing. This can significantly reduce material consumption during production.

[0037] Short description of the characters

[0038] Fig. 1 illustrates a process for producing a nonwoven fabric with nanoporous fibers.

[0039] Fig. 2 schematically illustrates a manufacturing plant for carrying out the process according to Fig. 1.

[0040] Fig. 3 illustrates a cross-section of a fiber with high macroporosity and low nanoporosity.

[0041] Fig. 4 illustrates a cross-section of a fiber with high nanoporosity. Detailed description of embodiments

[0042] Fig. 1 illustrates a process for producing a nonwoven fabric with nanoporous fibers. This process can be carried out by a production line shown in Fig. 2.

[0043] In a step 10, a spinning solution containing a fiber starting material, here cellulose, and a solvent, here NMMO, is provided. In a step 12, a plurality of raw fibers 20 are produced from the spinning solution. For this purpose, the production plant has an extruder 22. In the extruder, the cellulose and NMMO are mixed to form a viscous solution, which is extruded through capillaries of a spinning head 24. The raw fibers 20 exit the spinning head 24 in a vertical downward direction and are moist, in this case because the solvent is trapped in the pores of the raw fibers 20.

[0044] The produced raw fibers are accelerated in a step 14 upon or after leaving the spinning head 24 by means of a stream of accelerating fluid. Water, air, or a water-air aerosol mixture is used as the accelerating fluid. The acceleration stretches the raw fibers so that their diameter is significantly smaller than a capillary diameter or a diameter upon exiting the capillaries of the spinning head 24. The production system accordingly comprises an acceleration device designed to accelerate the raw fibers by means of the accelerating fluid stream. In the example shown, the acceleration device comprises nozzles that are integrated into or arranged on two sides of the spinning head 24. The details of the acceleration device are not shown in Fig. 2.

[0045] The accelerated or stretched raw fibers 20 are deposited as a moist nonwoven precursor 26 in a step 16. For this purpose, the production plant has a depositing device, which here is designed as a conveyor belt 28 with a collecting basin 30. On the conveyor belt 28, the moist nonwoven precursor solidifies through coagulation, but without the nonwoven precursor and its fibers drying. A separated excess mixture of solvent or NMMO and acceleration fluid is collected in the collecting basin 30 and can thus be reused.

[0046] Subsequently, the moist nonwoven precursor 26 is optionally wound up in a winding device 32 of the production system. Before winding up, the nonwoven precursor 26 can optionally be washed, for example, to reduce the amount of solvent in the nonwoven precursor. Water or another non-solvent for the cellulose can be used for washing, for example. The wound moist nonwoven precursor 26 is solidified but still moist, since the respective pores of the fibers of the nonwoven precursor 26 still contain water and any residues of NMMO.

[0047] Subsequently, this liquid trapped in the pores of the fibers of the nonwoven precursor 26 is optionally exchanged by a fluid exchange device 34. A non-solvent is selected as the replacement liquid, which allows supercritical drying of the moist fibers of the nonwoven precursor 26 without decomposition, for example, due to excessively high temperatures. In the example described, isopropanol and / or ethanol are used, which displaces water and NMMO from the pores. In another embodiment, washing and / or acceleration are performed with a fluid suitable for supercritical drying, so that the liquid exchange in the pores may be unnecessary.

[0048] Finally, in step 18, the moist nonwoven precursor 26 is dried. This removes the liquid in the pores of the fibers. The drying process here is carried out as supercritical drying, although freeze-drying is also possible. During supercritical drying, the liquid in the pores of the fibers is brought into a supercritical state of aggregation in which the liquid has no capillarity. In the supercritical state, the fluid in the pores of the fibers has no surface tension. If the amount of fluid in the pores is reduced, the pore walls are not contracted and the nanopores in the fibers can be fully or largely preserved. During supercritical drying and also the alternatively possible freeze-drying, a state of the liquid in the moist nonwoven precursor 26 or the pores of the fibers in which the liquid has capillarity is avoided.After drying, the fleece with the nanoporous fibers is finished.

[0049] For drying, the production plant has a drying device 36. The drying device includes an autoclave. CO2 is fed into the autoclave to reduce the pressure and temperature necessary to achieve the supercritical state. This enables supercritical drying of the ethanol or isopropanol in the pores at temperatures of approximately 50°C and a pressure of approximately 92 bar. Any remaining water and NMMO are also dried in the process.

[0050] Fig. 3 shows a fiber with a low proportion of nanopores. The fiber was produced without stretching during ambient drying and contains PAN as its fiber material. The non-solvent in the moist fibers was water, although other non-solvents can also lead to this result without supercritical drying. The nanopores are found almost exclusively in an edge region 40 of the fiber. In a central region 42, however, the fiber essentially has much larger macropores. The insulating properties of a nonwoven with such fibers are low. In the central region 42, the nanopores have collapsed because capillarity acted during drying. Drying, for example, is conventionally only achieved by heating or storage at room temperature. The cross-section of the fiber according to Fig. 3 is shown as round here, but can also be flattened due to the collapse of nanopores in the central region 42.

[0051] Fig. 4 shows a fiber of a nonwoven fabric produced using the previously described process and a corresponding non-solvent, here a combination of ethanol and isopropanol, supercritically dried. The fiber exhibits finely distributed nanopores regularly throughout its entire cross-section. More than 80% of the cross-section of the nanoporous fibers is formed by nanopores. There are only small defects in the form of cavities 44, in which the nanopores have collapsed. Reference symbol

[0052] 10 Step of preparing a spinning solution

[0053] 12 steps of producing raw fibers

[0054] 14 Step of accelerating the produced raw fibers

[0055] 16 Step of depositing the accelerated crude fibers

[0056] 18 Step of drying the nonwoven precursor

[0057] 20 crude fibers

[0058] 22 extruders

[0059] 24 spinning head

[0060] 26 fleece precursor

[0061] 28 assembly line

[0062] 30 retention basins

[0063] 32 winding device

[0064] 34 Fluid exchange device

[0065] 36 Drying device

[0066] 40 Marginal area

[0067] 42 midrange

[0068] 44 blowholes

Claims

Patent claims 1 . A process for producing a nonwoven fabric with nanoporous fibers, in particular aerogel fibers, the process comprising at least the following steps: - Providing (10) a spinning solution with a fiber starting material, in particular a polymer, and a solvent, - producing (12) raw fibers (20) from the spinning solution, in particular by extruding the spinning solution through capillaries; - accelerating (14) the produced raw fibers (20) by means of an accelerating fluid stream; - depositing (16) the accelerated raw fibers (20) as a moist nonwoven precursor (26) with a fluid; - drying (18) the nonwoven precursor (26) while avoiding a state of the liquid of the moist nonwoven precursor (26) in which the liquid has capillarity in order to produce the nonwoven with nanoporous fibers.

2. The method according to claim 1, wherein the drying (18) comprises supercritical drying. And / or wherein the drying comprises freeze-drying.

3. Method according to one of the preceding claims, wherein CO2 is supplied for the drying (18).

4. Method according to one of the preceding claims, after the production (12) of raw fibers (20) the solvent is washed out.

5. Method according to one of the preceding claims, wherein prior to drying (18) a replacement of fluid in the moist nonwoven precursor (26) takes place, in particular wherein a replacement liquid is a non-solvent for the fiber starting material and / or in particular wherein the solvent, the acceleration fluid and / or a washing liquid is replaced.

6. A process according to any one of the preceding claims, wherein the fiber starting material is cellulose and / or the solvent is NMMO.

7. Method according to one of the preceding claims, wherein the accelerating fluid comprises water, a non-solvent for the fiber starting material and / or air and / or wherein the accelerating fluid stream is in the form of an aerosol.

8. Nonwoven fabric with nanoporous fibers, in particular with aerogel fibers, wherein the nonwoven fabric was produced by a process according to one of claims 1 to 7.

9. Nonwoven fabric according to claim 8, wherein a cross section of the nanoporous fibers is formed by more than 30% nanopores, in particular more than 50%, 60%, 70%, 90%, 95% nanopores and / or wherein a diameter of the nanoporous fibers is less than 100 pm, in particular less than 75 pm, 50 pm, 25 pm, 20 pm, 15 pm or less than 10 pm.

10. Fleece according to claim 8 or 9, wherein the fleece has a layer thickness of less than 5 mm, in particular less than 4 mm, 3 mm, 2 mm, 1.5 mm or 1 mm and / or wherein the nonwoven has a bending radius of less than 5 mm, in particular less than 4 mm, 3 mm, 2 mm, 1.5 mm, 1 mm, 0.5 mm or 0.1 mm and / or wherein the nonwoven has a basis weight of less than 100 gsm, in particular less than 75 gsm, 50 gsm or 30 gsm with a layer thickness of 1 mm.

11. A manufacturing plant for producing a nonwoven fabric with nanoporous fibers, in particular designed to produce the nonwoven fabric according to one of claims 8 to 10 and / or designed to carry out a method according to one of claims 1 to 7, wherein the manufacturing plant comprises a production device (22) designed to produce (12) raw fibers (20) from a spinning solution with a fiber starting material and a solvent, an acceleration device designed to accelerate (14) the raw fibers by means of an acceleration fluid flow, a depositing device (28, 30) designed to deposit (16) the accelerated raw fibers (20) as a moist nonwoven fabric precursor (26) with a liquid, and a drying device (36) designed to dry (18) the moist nonwoven fabric precursor (26) bypassing a phase of the liquid of the moist nonwoven fabric precursor (26) in which the liquid has, is formed, has capillarity.

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