The present invention discloses a thin aramid film which has an average thickness of from 1 to 9 µm and 20/1,000 m 2 and less of pinholes, detected by a current flow during the application of a voltage satisfying the formula mentioned below, and which is used as a base material of a magnetic tape: detection voltage (V) = 20 x (average thickness of the film represented by micrometers).
In the production of an aramid film by a film-forming method wherein a solution of an aramid resin is cast from a die in an atmosphere having a cleanness of up to JIS class 6, and the cast resin is subjected to wet treatment at a solvent removal rate of 3 x 10 -5 g/sec·µm·cm 2 and less to form a solidified film, the thin aramid film of the present invention is produced by continuously inspecting the film for pinholes in an area of at least 500 m 2 with an optical pinhole inspection apparatus and a current application type of pinhole detection apparatus.
The locations of pinholes in the longitudinal and transverse directions of the film can be calculated and outputted if necessary.