Patent ID: 7771792

Claim:
A method for alkaline saponification of a polymer film, comprising: an alkaline-solution coating step of coating a polymer film with an alkaline solution; a temperature keeping step of keeping the polymer film coated with the alkaline solution at temperature equal to or higher than room temperature; a reaction terminating step of terminating the reaction by applying a diluting solvent or an acid solution to the polymer film kept at the temperature; and a washing step of washing away the alkaline solution from the polymer film on which the reaction has been terminated, wherein the reaction terminating step uses a bar coater having a bar with a flat surface and without a groove to apply the diluting solvent or acid solution to the polymer film and remove the alkaline solution from the polymer film, and wherein the flat bar has a maximum surface roughness Rmax of 1 μm or smaller and a straightness of 500 μm or lower.