Cellulose acetate and producing method therefor

Abstract

The purpose of the present invention is to provide a cellulose acetate which can be used to obtain an optical film having a very small amount of bright spot foreign matters, with excellent production efficiency, even when cellulose containing a small amount of hemicellulose components and having a high degree of crystallinity is used as a raw material. A cellulose acetate in which a content ratio by mole of mannose units to a sum of xylose units, mannose units and glucose units, which are sugar chain components, is 0.04 mol % or less, and a filtration index K measured by the following measurement method is 30 mLor less. (Measurement method) The cellulose acetate is dissolved in a mixed solvent containing methylene chloride and methanol at a weight ratio of methylene chloride/methanol of 9/1 to obtain a solution with a solid concentration of 16% by weight. The temperature of the solution is adjusted to 25° C., and the solution is subjected to constant-pressure filtration under a pressure of 3 kg/cmusing a cloth obtained by stacking three sheets of calico (s 618) (diameter: 15 mm, filtration area: 1.77 cm). At this time, the filtration index k (mL) is calculated from the following expression, where Prepresents the amount of filtration (mL) up to 20 minutes after the start of filtration, and Prepresents the amount of filtration (mL) from 0 to 60 minutes.