Nonwoven fabric, felt and production processes therefor

Abstract

A nonwoven fabric which contains pitch-based carbon fibers having a high elongation and a high elastic modulus which are not attained in the prior art and is obtained by improving the tensile elongation of carbon fibers derived from mesophase pitch, a felt obtained from the nonwoven fabric, and production processes therefore. The nonwoven fabric contains pitch-based carbon fibers, wherein the pitch-based carbon fibers have (i) an average fiber diameter (D 1 ) measured by an optical microscope of more than 2 μm and 20 μm or less, (ii) a percentage of the degree of fiber diameter distribution (S1) to average fiber diameter (D 1 ) measured by an optical microscope of 3 to 20%, (iii) a tensile elastic modulus of 80 to 300 GPa and (iv) a tensile elongation of 1.4 to 2.5%.

1 . A nonwoven fabric containing pitch-based carbon fibers, wherein the pitch-based carbon fibers have (i) an average fiber diameter (D 1 ) measured by an optical microscope of more than 10 μm and 20 μm or less, (ii) a percentage of the degree of fiber diameter distribution (S 1 ) to average fiber diameter (D 1 ) measured by an optical microscope of 3 to 20%, (iii) a tensile elastic modulus of 80 to 300 GPa and (iv) a tensile elongation of 1.4 to 2.5%. 
     
     
         2 . The nonwoven fabric according to  claim 1 , wherein the pitch-based carbon fibers have a tensile elastic modulus of 100 to 300 GPa and a tensile elongation of 1.5 to 2.4%. 
     
     
         3 . The nonwoven fabric according to  claim 1 , wherein the average fiber diameter (D 1 ) measured by an optical microscope of the pitch-based carbon fibers is more than 10 μm and 15 μm or less. 
     
     
         4 . The nonwoven fabric according to  claim 1  which has a tensile strength of 10 N/5 cm piece or more. 
     
     
         5 . A process for producing a nonwoven fabric, comprising the steps of:
 (1) spinning mesophase pitch to produce a precursor web containing carbon fiber precursors;   (2) stabilizing the precursor web in an oxidative gas atmosphere to produce a stabilized web including carbon fibers containing 8 to 15 wt % of oxygen; and   (3) baking the stabilized web at 800 to 1,800° C.   
     
     
         6 . The production process according to  claim 5 , wherein spinning is carried out by a melt blowing method. 
     
     
         7 . The production process according to  claim 5 , wherein the average fiber length of the carbon fiber precursors of the precursor web is 4 to 25 cm. 
     
     
         8 . The production process according to  claim 5 , wherein the amount of oxygen added to the carbon fibers of the stabilized web is 9 to 12 wt %. 
     
     
         9 . The production process according to  claim 5 , wherein the fiber length retention (%) defined by the following equation (I) before and after baking is 90% or more.
   Fiber length retention=100× L   1   /L   0    (I)
   L 0 : fiber length before baking   L 1 : fiber length after baking   
     
     
         10 . A felt obtained by needle punching the nonwoven fabric of  claim 1 . 
     
     
         11 . The felt according to  claim 10  which has a delamination strength in the thickness direction of 0.25 N/5 cm piece or more. 
     
     
         12 . The felt according to  claim 10 , wherein the carbon fibers have an average fiber diameter of more than 10 μm and 20 μm or less and a weight of 250 to 1,000 g/m 2 . 
     
     
         13 . A graphitized felt obtained by further heating the felt of  claims 10  at 2,000 to 3,500° C. 
     
     
         14 . A process for producing a felt, comprising the steps of:
 (1) spinning mesophase pitch to produce a precursor web containing carbon fiber precursors;   (2) stabilizing the precursor web in an oxidative gas atmosphere to produce a stabilized web including carbon fibers containing 8 to 15 wt % of oxygen;   (3) baking the stabilized web at 800 to 1,800° C. to produce a nonwoven fabric; and   (4) needle punching the nonwoven fabric.   
     
     
         15 . The production process according to  claim 14 , wherein the nonwoven fabric is punched 15 to 100 punches/cm 2  with a needle having a barb depth of 0.15 mm or more. 
     
     
         16 . A composite obtained by impregnating the felt of  claim 10  with a resin. 
     
     
         17 . A composite obtained by impregnating the graphitized felt of  claim 13  with a resin. 
     
     
         18 . A heat insulating material obtained by heating the composite of  claim 16  at 500 to 2,200° C. 
     
     
         19 . A process for producing a heat insulating material, comprising the steps of:
 (1) impregnating the felt of  claim 10  with a resin to produce a composite; and   (2) heating the composite at 500 to 2,200° C.   
     
     
         20 . A nonwoven fabric containing pitch-based carbon fibers, which has a weight reduction rate of less than 3% when it is heated up to 500° C. at a rate of 10° C./min in the air and then maintained at 500° C. for 8 hours. 
     
     
         21 . The nonwoven fabric according to  claim 20  which has a weight reduction rate of less than 2% when it is heated at 3,000° C. in an inert gas atmosphere for 1 hour. 
     
     
         22 . The nonwoven fabric according to  claim 20 , wherein the pitch-based carbon fibers have a true density of 1.9 g/cm 3  or more. 
     
     
         23 . The nonwoven fabric according to  claim 20  which has a volume reduction rate of less than 2% when it is heated at 3,000° C. for 1 hour. 
     
     
         24 . The nonwoven fabric according to  claim 23  which has a volume reduction rate of less than 1% when it is heated at 3,000° C. for 1 hour. 
     
     
         25 . The nonwoven fabric according to  claim 23  which has a volume reduction rate of less than 0.5% when it is heated at 3,000° C. for 1 hour.