| 摘要 |
PROBLEM TO BE SOLVED: To obtain an optical compensation film having an intra-surface difference of a specific value and excellent smoothness by heat treating a thermoplastic resin film under specific conditions. SOLUTION: The thermoplastic film is transversely uniaxially stretched in a temp. atmosphere above the glass transition point thereof. Specified tension is applied continuously between rolls arranged with driers in the flow direction of the film and the film is heat treated. In such a case, the film is heat treated under the conditions under which an inter-roll gap LMD and a film width LTD attains LMD/LTD>1.0 and at the temp. at which the coefft. of linear expansion thereof increases or above and below the glass transition point, by which the major axis direction of the refractive index ellipsoid within the plane is changed 90. As a result, the phase difference within the film plane attains 5nm<=|nx -ny|xd<80nm when the main refractive indices within the film plane are defined as nx , ny and the thickness is defined as d. The deviation width thereof attains <=10%.
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