To obtain a maleimide based resin excellent in flexibility, flame resistance or the like suitable for film or the like of a flexible printed circuit board including layered clay mineral and having a specific repeating unit.
This resin includes the layered clay mineral (e.g. saponite, montmorillonite, synthetic mica or the like) and having repeating unit expressed by formula I [R1 and R2 are each H, an alkyl or (substituted)phenyl; R3 is a divalent organic group selected from an aliphatic group of C≥2, a cycloaliphatic group, a monocyclic aromatic group, a polycyclic aromatic group]. The maleimide resins are obtained by mixing the composition comprising powder of analogues of maleic acid of formula II (e.g. maleic acid, citraconic acid or the like) and powder of diamine (e.g. 4,4'-diaminodiphenyl-methane or the like) in molar ratio of 1:1, and layered clay mineral, in solid state and heating the mixture at 80-200°C in the solid state.
YAMAMORI YOSHIYUKI