Patent ID: 7863439

Claim:
A cellulose ester fulfilling the following formula: 0.5<( B )/( A )<1.2 wherein (A) is the total molar amount of residual sulfuric acid in 1 gram of said cellulose ester, (B) is the total molar amount of calcium contained in 1 gram of said cellulose ester, the total amount (A) of residual sulfuric acid in 1 gram of said cellulose ester is from 1Ã—10 âˆ’7 to 500Ã—10 âˆ’7 mol, and wherein the cellulose ester is a cellulose acetate having an average degree of acetylation from 58 to 62.5%; and wherein a heat stability of the cellulose ester under wet conditions, or heat resistance under wet conditions, is not more than 0.08% based on the following formula: % heat stability or resistance under wet conditions=(Câˆ’D)Ã—FÃ—0.06/sample weight in grams wherein â€œCâ€: a titer in terms of ml of 0.01N-NaOH aqueous solution, Dâ€: a titer in terms of ml of 0.01N-NaOH aqueous solution in the blank test, and â€œFâ€: a factor of 0.01N-NaOH aqueous solution wherein said cellulose ester is prepared by acetylating a cellulose in the presence of a sulfuric acid catalyst; hydrolyzing the acetylated cellulose to obtain the cellulose acetate; neutralizing said sulfuric acid at least in part with a neutralizing agent before or after the hydrolyzing step, wherein the neutralizing agent is a magnesium containing component; and adding a calcium component after the neutralizing step to thereby obtain the cellulose ester.