Ube Industries, Inc.

Yasuji Narahara

Hiroshi Inoue

Tadao Muramatsu

Tetsuji Hirano

Kanzo Tabata

A process for the preparation of an aromatic polyimide film having a surface provided with extremely small sized protrusions having an average diameter of 40 to 2,000 angstroms, the number of protrusions being in the range of 1.times.10.sup.4 to 1.times.10.sup.9 /mm.sup.2 is disclosed. The process comprises the steps of coating a coating composition (aromatic polyamic acid solution containing inorganic particles having an average diameter of not larger than 1,000 angstroms) on at least one surface of an aromatic polyimide gel film containing a volatile material in an amount of 10 to 90 wt. % (aromatic polyimide gel film has been obtained by ring closure and imidation of an aromatic polyamic acid in an organic polar oslvent containing a dehydrating agent and a catalyst at a temperature of not higher than 200.degree. C.); drying the obtained film composite at a temperature of 50.degree. to 200.degree. C.; and subjecting the film composite to a heat treatment including heating at a temperature of not lower than 300.degree. C.

Process for the preparation of aromatic polyimide film

A shaped and drawn aromatic imide polymer article, for example, a film or filament, is produced by shaping an aromatic polyamic acid solution containing an imidizing agent in a polar organic solvent while simultaneously imidizing a portion of the aromatic polyamic acid to an extent such that the resultant self-supporting precursory article contains 20% to 87% by weight of a volatile substance and has a tensile strength of at least 1.5 kg/mm.sup.2 and an ultimate elongation of at least 30%, by drawing the precursory article at a draw ratio of 1.3 or more and by heat-treating the drawn article at a temperature of 150.degree. C. or more.

Process for producing a shaped and drawn aromatic imide polymer article

An aromatic polyimide film containing very fine particles of an inert inorganic material having an average particle diameter of 40 to 1,000 angstroms in an amount of 0.02 to 6.0 wt. %, wherein a surface of the film is provided with extremely small sized protrusions having a maximum height of 50 to 500 angstroms and an average diameter of 50 to 2,000 angstroms, the number of protrusions is in the range of 2.times.10.sup.5 to 1.times.10.sup.8 /mm.sup.2, and the number of protrusions having a diameter of not less than 1.5 times as much as the average diameter is not more than 5% of the total number of the protrusions. This polyimide film is suitably employable as a support of a magnetic recording medium.

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Hirakata, Japan

Yasuji Narahara