Polyimide precursor fibrid, polyimide paper, polyimide composite paper and polyimide composite board obtained therefrom, and process for producing the fibrid and the paper products

A process for producing a polyimide composite paper product, which comprises:

• paper-making a poly(amic acid) composite paper from a poly(amic acid) fibrid and a staple fiber, and imidizing the resulting poly(amic acid) composite paper,
• said polyimide having a repeating unit represented by the following formula (1):
• wherein R is a tetravalent aromatic group having at least one six-membered carbon ring, wherein two pairs of the tetravalent elements each bond to adjacent carbon atoms on a six-membered carbon ring, and R′ represents a divalent aromatic group having 1 to 4 six-membered carbon rings, and
• said poly(amic acid) having a repeating unit represented by the following formula (2):
• wherein R is a tetravalent aromatic group having at least one six-membered carbon ring, wherein two pairs of the tetravalent elements each bond to adjacent carbon atoms on a six-membered carbon ring, and R′ represent a divalent aromatic group having 1 to 4 six-membered carbon ring, and
• the weight ratio of the imidized polyimide fibrid to the staple fiber being from 5:99 to 99.5:0.5.