Random Mat and Fiber-Reinforced Composite Material

Abstract

There is provided a random mat including carbon fibers and a matrix resin, wherein the carbon fibers in the random mat have an average fiber length in a range of 3 mm to 100 mm, a fiber areal weight of the carbon fibers is 25 to 10,000 g/m 2 , the carbon fibers include a specific carbon fiber bundles having a specific opening degree in a specific amount per the total carbon fibers, and the specific carbon fiber bundles with a thickness of 100 μm or more are included in a ratio of less than 3% of the number of the total specific carbon fiber bundles.

1 . A random mat comprising carbon fibers and a matrix resin,
 wherein the carbon fibers in the random mat have an average fiber length in a range of 3 mm to 100 mm,   a fiber areal weight of the carbon fibers is 25 to 10,000 g/m 2 ,   at least one of fiber bundles including the carbon fibers of less than a critical number of single fiber being defined by the following formula (1) and a single fiber, and carbon fiber bundles (A) constituted by the carbon fibers of the critical number of single fiber or more are present in the random mat,   a ratio of the carbon fiber bundles (A) to a total amount of the carbon fibers in the random mat is a range of 20 Vol % to 99 Vol %,   an average number (N) of fibers in the carbon fiber bundles (A) satisfies the following formula (2), and   a ratio of carbon fiber bundles having a thickness of 100 μm or more of the carbon fiber bundles (A) is less than 3% of the number of whole carbon fiber bundles (A):
   Critical number of single fiber=600/ D   (1)
 
   0.6×10 4   /D   2   <N< 1×10 5   /D   2   (2)
 
   wherein D is an average fiber diameter (μm) of single carbon fibers.   
     
     
         2 . The random mat according to  claim 1 ,
 wherein the carbon fiber bundles (A) have an average fiber thickness of 20 μm or more to less than 100 μm.   
     
     
         3 . The random mat according to  claim 1  or  2 ,
 wherein adhesion strength between the carbon fibers and the matrix resin evaluated by a strand tensile shear test is 20 MPa or more. 
 
     
     
         4 . The random mat according to any one of  claims 1  to  3 ,
 wherein the matrix resin is a thermoplastic resin. 
 
     
     
         5 . The random mat according to any one of  claims 1  to  4 ,
 wherein an amount of the matrix resin in the random mat is 10 to 800 parts by weight per 100 parts by weight of the carbon fibers. 
 
     
     
         6 . The random mat according to any one of  claims 1  to  5 , further comprising a sizing agent,
 wherein the sizing agent contains a resin having the same main chain structure as a main chain of the matrix resin as a main component. 
 
     
     
         7 . A fiber-reinforced composite material obtained by molding the random mat according to any one of  claims 1  to  6 . 
     
     
         8 . The fiber-reinforced composite material according to  claim 7 , having tensile strength of 400 MPa or more. 
     
     
         9 . The fiber-reinforced composite material according to  claim 7  or  8 ,
 wherein a volume fraction of the carbon fibers is from 30 to 65%. 
 
     
     
         10 . The fiber-reinforced composite material according to any one of  claims 7  to  9 ,
 wherein unevenness in thickness of a carbon fiber mat in the fiber-reinforced composite material is 20% or less in terms of a coefficient of variation CV defined by the following formula (7):
   Coefficient of variation CV(%)=standard deviation/average value×100  (7).