| 摘要 |
PROBLEM TO BE SOLVED: To provide a polyimide film whose thickness nonuniformity in the longitudinal direction is reduced, which is applicable especially to the support of an electric wiring plate on which metal foil or metal thin film represented by copper foil is laminated and to a cover-lay film for protecting a flexible printed circuit. SOLUTION: In a polyimide film produced by a process in which a polyamide acid solution is cast continuously as a film onto a rotating support by extrusion or application, the five-pont average of local thickness nonuniformity in the longitudinal direction is 0.9 μm or below, and the maximum value of the local thickness nonuniformity is 1.0 μm. In a method for producing a polyimide film, in a casting process in which the polyamide acid solution is cast continuously as a film onto the rotating support 4 by extrusion or application, a gas pressurizing apparatus 1a is arranged on the cast rotation direction side, or a pressure reducing apparatus is arranged on the cast reverse rotation direction side so that a web pressure on the cast rotation direction side is made higher by 10-750 Pa than that on the opposite side. |
