Patent ID: 9598546
Date: 2017-03-21
CPC Classifications: C08G,C08J,C09K,G02B,G02F

Claim:
1. A method of producing an optical film comprising the steps of, (i) melt extruding a copolymer to form an extruded film, and (ii) stretching the extruded film 1.05 to 5 times in both longitudinal and transverse directions to obtain the optical film, wherein R (i) a thickness (d) is 20 to 80 μm; (ii) the following formulas (1) and (2) are satisfied: wherein R(450), R(550) and R(650) are retardations within a plane of the film at wavelengths of 450 nm, 550 nm and 650 nm, respectively; (iii) R(550) is 125 to 160 nm R(550) is a retardation within the plane of the film at a wavelength of 550 nm; (iv) the birefringence (Δn) represented by the following formula (3) is not less than 1.5×10 wherein d is the thickness (μm) of the film; and (v) the Nz coefficient represented by the following formula (4) is 1.20 to 2.40: wherein n