Patent ID: 10927189

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 mL−1 or 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/cm2 using a cloth obtained by stacking three sheets of calico (s 618) (diameter: 15 mm, filtration area: 1.77 cm2). At this time, the filtration index k (mL−1) is calculated from the following expression, where P1 represents the amount of filtration (mL) up to 20 minutes after the start of filtration, and P2 represents the amount of filtration (mL) from 0 to 60 minutes.