Patent ID: 7148344

Claim:
A method of producing a cellulose acetate film, which method comprises the steps of: (a) reacting cellulose, which may contain hemicellulose, with acetic anhydride in the presence of a sulfuric acid catalyst to produce a cellulose acetate; (b) hydrolyzing the cellulose acetate to adjust its degree of acetylation; and (c) adding an alkali metal and/or an alkaline earth metal to the hydrolyzed cellulose acetate to produce the cellulose acetate, wherein the total content of alkali metal and alkaline earth metal in 1 gram of the cellulose acetate is 5.5×10 −6 equivalent or less in terms of ion equivalent or the total content of alkali metal and alkaline earth metal in 1 gram of the cellulose acetate is more than 5.5×10 −6 in terms of ion equivalent; (d) dissolving said cellulose acetate in a solvent to prepare a dope; (e) mixing an acid having an acid dissociation exponent pKa at 1.93 to 4.50 in water, or a metal salt thereof, with the dope, wherein the total content of the acid, the alkali metal salt of the acid, and the alkaline earth metal salt of the acid is 1×10 −9 to 3×10 −5 mole relative to 1 gram of the cellulose acetate and wherein the cellulose acetate has an average degree of acetylation of from 58 to 62.5%; and (f) casting said dope on a support and releasing the film from the support.