Dimensionally stable poly-m-phenylene isophthalamide film

Abstract

A process for producing an aromatic polyamide film, which comprises drawing an undrawn aromatic polyamide film biaxially at a draw ratio of at least 1.5 in a solvent mixture consisting of (a) 5% to 75% by weight of a good solvent of the aromatic polyamide and (b) 25% to 95% by weight of a non-solvent of the aromatic polyamide, and heat treating the drawn film, which contains at least 1% by weight, based on the weight of the film, of a good solvent of said aromatic polyamide, at a temperature of not lower than 150.degree. C. An m-phenyleneisophthalamide polymer film having extremely excellent dimensional stability under moist conditions, which film has a density d of from 1.35 to 1.41 g/cm.sup.3 and principal refractive indices n.sub..alpha., n.sub..beta. and n.sub..gamma. (n.sub..alpha. >n.sub..beta. >n.sub..gamma.) for D-line of a wavelength of 589 nm satisfying the following formula: ##EQU1##

Dependencies are inferred from the claim text.