| 摘要 |
PURPOSE:To obtain the title sheet improved in low permittivity properties, processability and dimensional stability by impregnating a porous substrate with a fluoropolyimide having specified repeating units. CONSTITUTION:A polyamide acid of an intrinsic viscosity of 0.2-0.7 (in N- methyl-2-pyrrolidone in a 0.5dl/g concentration at 30 deg.C) obtained by reacting a fluorinated tetracarboxylic acid (derivative) [e.g. bis(3,4-dicarboxyphenyl) difluoromethane] with a fluorinated diamine [e.g. 2,2,-bis(4-amino-2-alkylphneyl) hexafluoropropane] at 0-90 deg.C for 1-24hr in an organic polar solvent (e.g. N- methyl-2-pyrrolidone) is imidated to obtain a fluoropolyimide having repeating units of the formula (wherein Ar1 is a tetravalent aliphatic or aromatic group; Ar2 is a bivalent aromatic group, and at least one of Ar1 and Ar2 contains a perfluoroalkylene group). A porous fluororesin substrate of a pore diameter of 0.1-5mum, a void volume of 50-85% and a thickness of 5-500mum is impregnated with this polyimide to obtain a low-permittivity sheet of a permittivity <=3 at 1MHz. |
