Process for producing carbon fiber reinforced carbon composite material, carbon fiber reinforced carbon composite material and sliding material

A carbon fiber reinforced carbon composite material formed by laminating and molding sheets in which a short fibrous bundle of carbon fibers are in a two-dimensional random orientation, wherein a dispersion index of a bundle of carbon fibers is different by not less than 0.05 between an inner layer portion thereof and a surface layer portion thereof, the dispersion index being evaluated based on the formula (2) or (3):

• Dispersion index (X)=t/W (2)
• wherein t represents an entire sheet thickness (mm) and W represents an entire sheet weight (g),
• Dispersion index (Y)=100-T (3)
• wherein T represents light transmittance (%).

A method for controlling production conditions in a process for producing a carbon fiber reinforced carbon composition material which includes the steps of:

• dispersing a short fibrous bundle of carbon fibers composed of a plurality of single fibers, preparing a sheet in which fibers are in the two-dimensional random orientation, impregnating the sheet with a resin or pitch, laminating and molding the sheet, and then baking and densifying the sheet to form the carbon fiber reinforced carbon composition,
• said method comprising (a) determining a dispersion index required for obtaining a coefficient of friction, based on formula (1);
• Dispersion index=A-B.times.coefficient of friction (1)
• wherein A and B are constants determined by the steps of:
• (i) preparing a plurality of carbon fiber reinforced carbon composites by changing the dispersion conditions while maintaining factors other than the dispersion conditions constant,
• (ii) measuring the dispersion index and coefficient of friction of each of the carbon fiber reinforced carbon composites prepared in (i), the dispersion index being defined by formula (2) or (3):
• Dispersion index=t/W (2)
• wherein t is entire thickness of the impregnated sheets and W is the weight of the impregnated sheets when the impregnated sheets of an area and a number are placed under a load,
• Dispersion index=100-T (3)
• wherein T is the transmittance of the impregnated sheets of a weight and an, and thereafter
• (iii) determining constants A and B from the measured dispersion indexes and coefficients of friction based on the formula (1), and (b) selecting conditions of dispersing the short carbon fibrous bundle and preparing a sheet having the dispersion index calculated in step (a).