Conductive nonwoven

Abstract

The invention relates to a conductive nonwoven fabric that is carbonized and/or graphitized and possesses a bending rigidity <8 taber, a density of 0.1 g/m 3 to 0.5 g/m 3 , a thickness of 80 μm to 500 μm, and an electrical conductivity of 10 to 300 S/cm in the nonwoven fabric strip and 30 to 220 S/cm 2 perpendicular to the nonwoven fabric strip.

What is claimed is:  
     
         1 . A conductive nonwoven fabric, wherein it is carbonized and/or graphitized and possesses a bending rigidity <8 taber, a density of 0.1 g/m 3  to 0.5 g/m 3 , a thickness of 80 μm to 500 μm, and an electrical conductivity of 10 to 300 S/cm 2  in the nonwoven fabric strip and 30 to 220 S/cm 2  perpendicular to the nonwoven fabric strip.  
     
     
         2 . The conductive nonwoven fabric according to  claim 1 , obtained from preoxidized fibers for carbon fibers that are mixed, if necessary, with up to 30 wt.-% of a percursor fiber that serves as a binding fiber, as well as up to 30 wt.-% of a water-soluble fiber having fiber titers of 0.5 to 6.7 dtex, by being laid up to form a fiber sheet having a mass per unit area of 30 to 300 g/m 2 , bonding of the fiber sheet using high-pressure fluid jets at pressures of 100 to 300 bar, compression of the bonded fiber fabric by 50 to 90% of its starting thickness by calandering, and carbonization and/or graphitization under an inert gas atmosphere, at 800° C. to 2500° C.  
     
     
         3 . The conductive nonwoven fabric according to  claim 1  or  2 , wherein 80 to 90 wt.-% of a mixture of precursor fibers and preoxidized fibers in a weight ratio of 0:1 to 1:3 and 10 to 20 wt.-% of a water-soluble fiber having fiber titers of 0.8 to 3.3 dtex are used.  
     
     
         4 . The conductive nonwoven fabric according to one of  claims 1  to  3 , wherein two different water-soluble fibers were used, one of which is water-soluble at temperatures of 10 to 40° C. and the other of which is water-soluble at temperatures of 80 to 120° C.  
     
     
         5 . The conductive nonwoven fabric according to  claim 4 , wherein the ratio of the water-soluble fibers relative to one another is 3:1 to 1:3.  
     
     
         6 . The conductive nonwoven fabric according to one of  claims 1  to  5 , wherein it is made up of several fiber layers having different pore sizes, the fibers of the individual layers possessing different titers.  
     
     
         7 . The conductive nonwoven fabric according to one of  claims 1  to  6 , wherein at least two nonwoven fabric layers that have been bonded by high-pressure fluid jets are combined by calandering.  
     
     
         8 . The conductive nonwoven fabric according to one of  claims 1  to  7 , wherein partially crosslinked phenolic resin fibers, polyester and/or polypropylene fibers are used as the precursor fibers, homopolymers, copolymers, and/or terpolymers of PAN (polyacrylic nitrile) fibers, cellulose fibers and/or phenoloresin fibers are used as the preoxidized fibers, and PVA (polyvinyl alcohol) fibers are used as the water-soluble fibers.  
     
     
         9 . The conductive nonwoven fabric according to one of  claims 1  to  8 , wherein it is hydrophobized by application of a hydrophobization agent such as PTFE (polytetrafluoroethylene).  
     
     
         10 . A method for the production of the conductive nonwoven fabric according to one of  claims 1  to  9 , wherein 
 a) preoxidized fibers, if necessary in a mixture with up to 30 wt.-% carbonizable precursor fibers that serve as binding fibers, and up to 30 wt.-% water-soluble fibers, are mixed,  
 b) laid up to form a fiber sheet having a mass per unit area of 30 to 300 g/m 2 , using the dry method, and using stripper and/or carding machines,  
 c) bonded with high-pressure fluid jets, at pressures of 100 to 300 bar,  
 d) predried to a residual moisture of 10 to 50%,  
 e) calandered at contact pressures of 20 to 1000 N/cm 2  and temperatures of 100 to 400° C., and  
 f) carbonized as well as graphitized at temperatures between 800 and 2500° C.  
 
     
     
         11 . The method according to  claim 10 , wherein in step 
 a) fibers having a fiber titer of 0.8 to 3.3. dtex and a fiber length of 30 to 70 mm are used,    b) fiber sheets having a mass per unit area of 30 to 180 g/m 2  are laid,    e) calandering takes place at a contact pressure of 40 to 700 N/cm 2  and a temperature of 180 to 300° C., and    f) carbonization as well as graphitization takes place at a temperature between 1000 and 1800° C.    
     
     
         12 . The method according to  claim 10  or  11 , wherein in step e) at least two nonwoven fabric layers are calandered together.  
     
     
         13 . The conductive nonwoven fabric according to one of  claims 1  to  12 , wherein they are used as the base material for electrodes and gas diffusion layers, at a density of 0.1 g/cm 3  to 0.25 g/cm 3 .  
     
     
         14 . The conductive nonwoven fabric according to one of  claims 1  to  12 , wherein they are used as gas diffusion layers in polymer electrolyte fuel cells, at a density of 0.25 g/cm 3  to 0.40 g/cm 3 .  
     
     
         15 . The conductive nonwoven fabric according to one of  claims 1  to  12 , wherein they are used as electrodes in supercapacitors, at a density of 0.40 g/cm 3  to 0.50 g/cm 3 .