Patent ID: 8062562
Filing Date: 2011-11-22
Classification: C08J,C08L,C09K,G02B,G02F,Y10T

Abstract:
1. A method for producing a cellulose ester film, comprising steps of: casting a dope containing at least a plasticizer and cellulose ester to form a web; stretching the web while the web still contains a solvent; drying the web until an amount of residual solvent decreases to 0.3% to obtain a cellulose ester film; and treating the film at 105-170° C. under a rate of atmosphere replacement of 12 times per hour or more while the web is transported, wherein a free volume radius of the cellulose ester film determined by positron annihilation lifetime spectroscopy is in the range of 0.25 to 0.31 nm and a half-width of the cellulose ester film determined by positron annihilation lifetime spectroscopy is in the range of 0.04 to 0.1 nm; wherein Ro of the cellulose ester film is in the range of 0 to 10 nm and Rt of the cellulose ester film is in the range of −30 to +20 nm, wherein Ro and Rt are defined by the following equations: wherein Ro represents an in-plane retardation value, Rt represents a retardation value in a thickness direction of the film, nx represents an in-plane refractive index in a slow axis direction, ny represents an in-plane refractive index in a fast axis direction, nz represents a refractive index in the thickness direction of the film (each refractive index is determined at a wavelength of 590 nm), and d represents a thickness of the film (nm); and wherein the dope in the casting step further comprises an additive selected from the group consisting of a polymer having an average molecular weight of 500 to 30,000, the polymer being prepared from a monomer having an ethylenically unsaturated bond; and an additive selected from the group consisting of compounds represented by Formulas (1), (2), (3), (5), (6), (7), (8), (9), (10), (11), (12) and (14):