Mitsui Toatsu Chemicals, Incorporated

Yasuko Honji

Masumi Saruwatari

Yasuhiro Fujii

Yasuhiko Ohta

Shoichi Tsuji

Shinobu Moriya

A polyimide film essentially consisting of polyimide having recurring units of the formula (I): ##STR1## which has a density of 1.335 to 1.390 g/cm.sup.3 at 23.degree. C. and/or a refractive index of 1.605 to 1.680 at 23.degree. C. in the direction of thickness and is transparent; and a preparation process of the polyimide film by extruding the polyimide having recurring units of the above formula (I) through a common melt-extrusion process, casting in a chill-roller to obtain an unstretched film, uniaxially or biaxially stretching the unstretched film to cause molecular orientation, and successively setting the stretched film through heat-treatment.

Polyimide film and preparation process of the film

A process for the preparation of a polyimide molded form comprising the steps of swelling a primary-molded form consisting essentially of polyimide having recurring units of the formula (I) ##STR1## by using an aprotic polar solvent and subsequently stretching the swelled form.

Process for preparing a polyimide molded form

In the preparation of a film by melt-extrusion process of thermoplastic polyimide, static charge is applied to a molten film, primary cooling is carried out by adhering the film to a cooling roller having a surface temperature in the range of from the glass transition temperature of said polyimide -50.degree. C. to the glass transition temperature -15.degree. C., the film is successively cooled to 60.degree. C. and less without bringing the film into contact with rollers, and is taken up under tension to give a polyimide film.

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Ichinomiya, Japan

Yasuko Honji