Film production method

A film production method comprising the steps of:

• melting and extruding a polymer, or casting and drying a polymer solution;
• and
• conveying with use of a drive roller a polymer film formed by the extruding or the casting, said drive roller including a corrugation profile in which corrugation valleys and corrugation peaks each having a substantially semicircular cross section are alternately formed on a peripheral surface along a circumferential direction of said drive roller, each of a pitch between said corrugation valleys and a pitch between said corrugation peaks being in the range of 0.01 to 2 mm, and a height from a lowest point of said corrugation valley to a highest point of said corrugation peak being in the range of 0.01 to 1 mm;
• wherein a curvature radius of said corrugation valley and a curvature radius of said corrugation peak are in the range of 0.1 to 0.5 mm;
• wherein a flat surface parallel to an axial direction of said drive roller is formed at each of said highest points of said corrugation peaks;
• wherein said flat surface has a width in the range of 0.05 to 0.5 mm in said axial direction,
• wherein said polymer film having a temperature in the range of 100° C. to 200° C. is conveyed by said drive roller, and
• wherein a difference in tension between an upstream side and a downstream side with respect to said drive roller in a conveying direction of said polymer film is in the range of 5 to 200 N/m, the value of said difference in tension being obtained per meter in a width direction of said polymer film.