Patent ID: 8846900

Claim:
A cellulose diacetate for a retardation film, the cellulose diacetate having a total degree of acetyl substitution of from 2.27 to 2.56, wherein the cellulose diacetate has a polydispersity Mw/Mn of 3<Mw/Mn≦7.5, a degree of substitution at the 6-position of from 0.65 to 0.85, a half height width of acetylation distribution of from 1.0 to 2.3, said half height width of acetylation distribution being a width of an intermolecular acetylation distribution curve at a height which is half the peak height in the intermolecular acetylation distribution curve plotted with the abscissa indicating a degree of acetylation of the cellulose diacetate and the ordinate indicating an amount of the cellulose diacetate at the degree of acetylation, and a viscosity-average degree of polymerization from 182 to 213.