METHOD FOR PRODUCING THIN CARBON FIBER NONWOVEN FABRICS USING A HORIZONTAL SPLITTING PROCESS

Description

[0001] The invention relates to a method for producing a layer of carbon fiber nonwoven by horizontally splitting rolls of carbon fiber nonwoven in the sample thickness and to uses of the material produced.

[0002] Horizontal means horizontal. Splitting is a manufacturing process for cutting a workpiece using a wedge-shaped tool.

[0003] Roll form, or "roll goods," means that a textile fabric is rolled up or is in a rolled form. This can be felt with a length of 20 to 70 m and a width of 1.2 to 1.5 m, which is rolled up onto a cardboard tube approximately 10 cm wide.

[0004] Carbon fiber fleeces are available in thicknesses ranging from approximately 2 mm to 20 mm, suitable for furnace insulation or as porous electrodes in special battery systems. These applications can be manufactured using multi-stage temperature processes at 600 to 3000°C. This high temperature is required to achieve certain properties such as high purity or low electrical resistance. The high-temperature treatment carried out at the end of the manufacturing process can be performed discontinuously in batch furnaces, although this should be avoided whenever possible for cost reasons. The final temperature treatment step is therefore usually carried out continuously, with the material being drawn through the system.

[0005] High-temperature treatment in the sense of the invention means treatment of material in the temperature range from 1800 to 3000°C.

[0006] Due to the tensile forces that occur, the more technically relevant continuous process is limited to a minimum material thickness, which makes the production of very thin materials, for example less than 2 mm in thickness, very difficult in this process.

[0007] The finished carbon fiber nonwoven rolls are only processed in a flat manner. The strength of the materials is determined solely by the thickness of the raw material; subsequent processing to reduce the thickness is not possible.

[0008] A major disadvantage of this state-of-the-art technology is the limitation regarding the material thicknesses that can be continuously processed. The production of very thin felts is currently only possible in batch processes. This results in limited flexibility, since the geometry of the raw material determines the final geometry in terms of thickness. In industrial production, when using roll material as a semi-finished product, finishing is only possible over a large area.

[0009] DE 2547958 discloses a process for producing thin fiber nonwovens from natural and chemical fibers.

[0010] GB 1,116,320 discloses a method for producing nonwovens using a splitting process.

[0011] The object of the present invention is therefore to provide a simple and cost-effective process for the continuous production of thin carbon fiber nonwovens on an industrial scale.

[0012] This problem is solved by a method for producing a layer of carbon fiber fleece. A carbon fiber fleece as the starting material is subjected to a horizontal splitting process in the sample thickness. The carbon fiber fleece is moved relative to a knife structure to split one or more layers from the carbon fiber fleece. The one or more layers are continuously removed after splitting from the carbon fiber fleece. This makes it possible to produce thin carbon fiber fleece cost-effectively in industrial production.

[0013] Horizontal splitting is used in plastics processing (soft foams, see DE 10 2010 004 205 A1 or rubber), in leather production (split leather, see DE 44 12 432 A1 or DE 195 06 370 C2), as well as in the production and processing of nonwovens and wool felt (see DE 3835007 A1). For carbon fiber nonwovens, also known as soft felts, and similar materials, no splitting process is used in the current state of the art.

[0014] The specific properties of the original carbon fiber fleece (mechanical, thermal and electrical) remain largely unaffected.

[0015] Sample thickness is the thickness of a sample. A synonym for sample is "specimen." Thickness is the standardized term (DIN 6730) for the measurement between opposing surfaces. A carbon fiber fleece represents a flat structure. The sample thickness is thus the measurement between the two surfaces (when positioned horizontally: top and bottom) of the flat structure subjected to the process according to the invention. Horizontal splitting therefore refers to the splitting of a flat structure across its entire surface between its surfaces, resulting in two flat structures, each of which has the same area as the original flat structure.

[0016] With the method according to the invention, several thin, flexible soft felts made of carbon fibers can surprisingly be cut out, even from a single thick textile semi-finished product, which both massively increases the process efficiency and makes the continuous production of thin, high-temperature treated nonwovens possible in the first place.

[0017] The carbon fiber nonwovens used are preferably produced by needling or hydroentanglement. In needling, carded fiber webs are mechanically bonded together, with barbed metal needles pulling fibers through the material. Hydroentanglement uses a powerful water jet instead of needles.

[0018] It is preferred that the thickness of the carbon fiber nonwoven is 3-50 mm, and the thickness of a cleaved layer is at least 0.2 mm. It is particularly advantageous that thin carbon fiber nonwovens can be produced continuously, and thick carbon fiber nonwovens can be used as semi-finished products. A thin carbon fiber nonwoven within the meaning of this invention is, for example, a cleaved layer with a thickness of 0.2 mm to 2 mm.

[0019] It is preferred that the carbon fiber nonwoven be based on viscose, polyacrylonitrile (PAN), pitch, or lignin. Other nonwoven materials are also possible, including materials made from all currently available carbon fibers from various carbon sources. This allows for a high degree of flexibility with regard to the fiber raw material.

[0020] The blade design preferably comprises a milling cutter-like cutting tool, a band blade, a double band blade with two adjacent, single-sided, single-blade blades, or a rigid, ruler-like splitting blade with an oscillating drive. The blades of the blade design according to the invention can be ground, particularly preferably continuously or at intervals, and automatically adjusted to maintain a constant horizontal position. The grinding dust is extracted during this process. An additional extraction system beneath the rollers ensures that the lower layer, including the resulting material, is cleanly removed.

[0021] Preferably, the separation and removal of one or more layers is carried out evenly and with a constant pulling force. This allows even thin layers of significantly less than 5 mm to be removed in a controlled and safe manner.

[0022] Tensile force is a force that pulls a mechanical body, i.e., acts on the body toward the force generator. In a system according to the invention, a mechanical winder can set a speed on the system, whereby felt is drawn off the system. In this case, the tensile force can be less than one kilonewton. The two split felts ( Fig. 1 ) are preferably peeled off with controlled identical force, which leads to a stable stress state and consistent thicknesses.

[0023] A further aspect of the present invention is the layer of carbon fiber nonwoven produced according to the method according to the invention. As described above, thin carbon fiber nonwovens are originally produced using known methods, i.e., the corresponding nonwoven forming machine immediately delivers the nonwoven in the desired thickness. Due to the textile manufacturing process, the surface of these originally produced layers is not completely uniform and exhibits unevenness. However, the surface of the layer of carbon fiber nonwoven produced according to the invention is significantly more uniform and level due to the precise splitting with a sharp band knife. A further distinguishing feature is that the cutting process creates an accumulation of terminal carbon fibers on the surface of the nonwoven layer. Thin carbon fiber nonwovens split according to the invention and those produced originally can therefore be distinguished from one another visually, i.e., by observation.

[0024] According to the claim, the invention also relates to a layer of carbon fiber fleece which is suitable as electrode material for battery applications, high-temperature batteries, redox flow batteries, as high-temperature insulation material or for gas diffusion layers in fuel cells, wherein this layer can be produced by a method in which a carbon fiber fleece as starting material is subjected to a horizontal splitting process in the sample thickness, wherein the carbon fiber fleece is moved relative to a knife construction in order to split off one layer or several layers in succession from the carbon fiber fleece, and in which the one layer or the several layers are continuously removed from the carbon fiber fleece after the splitting.

[0025] The use of one or more layers of carbon fiber fleece produced by the process according to the invention is preferably as electrode material for battery applications, high-temperature batteries, redox flow batteries, or high-temperature insulation material. This ensures versatility. Since energy storage technologies in particular are under considerable price pressure, the cost-effective process according to the invention is of great advantage for renewable energies.

[0026] More preferably, the one or more layers of carbon fiber nonwoven fabric produced according to the inventive method are used for gas diffusion layers (GDL) in fuel cells. Examples of GDL materials used are a 3D nonwoven fabric or a 2D paper. Since the inventive method is also applicable to these very thin materials, an even broader technology spectrum is possible.

[0027] In Figure 1It shows how a carbon fiber nonwoven body (1) according to the invention is split into two halves using a rotating band knife (4) and processed into rolls via transport rollers (3). Of course, in addition to this symmetrical splitting process, an asymmetrical splitting process is also technically feasible. Since continuous grinding is possible, continuous processing can be carried out, resulting in a consistently good cutting pattern.

[0028] The invention is explained in more detail with the help of the following exemplary embodiment: A 6 mm thick viscose-based carbon fiber felt is split into two 3 mm thick halves. The thickness of the split rolls is determined by the vertical positions of the feed rollers that convey the material through the machine. For a symmetrical splitting result, identical settings must be made for the upper and lower rollers.

[0029] Since the material must be slightly compressed to ensure transport, the gap should be set slightly smaller than half the initial density. For the carbon fiber felt, a compression of 10% is used, as this value does not cause material damage. This results in the upper and lower offset of the transport rollers being 2.7 mm.

[0030] The system's feed rate is 8 m / min, and the band knife's rotation speed is 5 m / s. The band knife is continuously sharpened to ensure a clean cut.

[0031] The result is two rolls of split felt. The split surface is surprisingly good (visually smooth and uniform). A specific electrical resistance is measurable along the thickness.

[0032] An extraction system across the entire width of the felt ensures that the split product is largely free of dust and particles.

[0033] Measured property values (testing of carbon materials) of the split carbon fiber felts based on PAN or viscose: Determination of the ash value (solids) Ash value according to DIN 51903 (at 580°C):

[0034] <0.05% (PAN-based); <0.1% (viscose-based) Determination of specific electrical resistance using the current-voltage method (solids) ER (x / y) based on DIN 51911 (perpendicular to the felt plane):

[0035] < 5 Ωmm (PAN-based); < 12 Ωmm (viscose-based) Determination of specific electrical resistance using the current-voltage method (solids) ER (z) based on DIN 51911 (in felt plane):

[0036] < 2 Ωmm (PAN-based); < 4 Ωmm (viscose-based) Thermal conductivity at room temperature according to the comparative method (solids) WLF according to DIN 51908 (perpendicular to the felt plane):

[0037] 0.1 - 0.4 W / mK (PAN-based); 0.02-0.1 W / mK (viscose-based). Legend for Figure 1

[0038] 1. Carbon fiber nonwoven body 2. Split layer 3. Deflection roller 4. Transport roller

Claims

1. Layer of carbon fibre non-woven (1) which is suitable as electrode material for battery applications, high-temperature batteries, redox flow batteries, as high-temperature insulation material or for gas diffusion layers in fuel cells, characterised by an accumulation of terminal carbon fibres on the split surface of the layer.

2. Layer of carbon fibre non-woven according to claim 1, wherein the thickness of the layer is 0.2 to 2 mm.

3. High-temperature battery comprising a layer of carbon fibre non-woven according to one of claims 1 or 2 as electrode material.

4. Redox flow battery comprising a layer of carbon fibre non-woven according to one of claims 1 or 2 as electrode material.

5. Fuel cell comprising a layer of carbon fibre non-woven according to one of claims 1 or 2 as a gas diffusion layer.

6. Furnace insulation comprising a layer of carbon fibre non-woven according to one of claims 1 or 2 as high-temperature insulation material.

7. Use of the layer of carbon fibre non-woven according to one of claims 1 or 3 as electrode material for battery applications, high-temperature batteries, redox flow batteries or high-temperature insulation material.

8. Use of the layer of carbon fibre non-woven according to one of claims 1 or 3 for gas diffusion layers in fuel cells.

9. Method for producing a layer of carbon fibre non-woven (1), wherein a carbon fibre non-woven as a starting material is subjected to a horizontal splitting process in the sample thickness, wherein the carbon fibre non-woven is moved relative to a blade construction (4) in order to split off one layer or a plurality of layers in succession from the carbon fibre non-woven, and in which the one layer (2) or the plurality of layers is / are continuously removed from the carbon fibre non-woven (1) after the splitting.

10. Method according to claim 9, wherein the thickness of the carbon fibre non-woven to be split is 3-50 mm.

11. Method according to claim 9, wherein the carbon fibre non-woven which acts as a starting material of the horizontal splitting process is produced in a multi-stage temperature process at 1800 to 3000°C.

12. Method according to claim 9, wherein the carbon fibre non-woven is based on viscose, PAN, pitch or lignin.

13. Method according to claim 9, wherein the blade construction relates to milling cutter-like cutting tools, band knives, double band knives having two adjacent single band knives each sharpened on one side, or rigid, ruler-like splitting knives having an oscillating drive.

14. Method according to claim 9, wherein the splitting and removal of one or more layers is carried out uniformly and with constant tensile force.