Optical film, process of producing the same, and polarizing plate and image displaying device employing the same

Abstract

An optical film comprising a first domain of a polymer composition and a second domain disposed inside the first domain, wherein the second domain is a bubble having a morphology anisotropy, and the mean alignment direction of the main chain of the polymer molecule in the first domain differs from the mean direction of the major axis of the second domain, is capable of contributing toward display performance unification and body thickness reduction of an image display device.

1 . An optical film comprising a first domain of a polymer composition and a second domain disposed inside the first domain, wherein the second domain is a bubble having a morphology anisotropy, and the mean alignment direction of the main chain of the polymer molecule in the first domain differs from the mean direction of the major axis of the second domain. 
     
     
         2 . The optical film according to  claim 1 , wherein the ratio of the major axis mean length of the second domain to the minor axis mean length in the film in-plane direction of the second domain is from 1.1 to 30. 
     
     
         3 . The optical film according to  claim 1 , wherein the ratio of the major axis mean length of the second domain to the minor axis mean length in the film thickness direction of the second domain is from 30 to 300. 
     
     
         4 . The optical film according to  claim 1 , wherein the refractive index of the first domain is larger by from 0.01 to 1.00 than the refractive index of the second domain. 
     
     
         5 . The optical film according to  claim 1 , wherein the sphere-corresponding diameter of the second domain is at least 0.02 μm. 
     
     
         6 . The optical film according to  claim 1 , wherein the volume fraction of the second domain is from 20 to 70%. 
     
     
         7 . The optical film according to  claim 1 , wherein the second domain has a density distribution in the film thickness direction. 
     
     
         8 . The optical film according to  claim 1 , which has a haze of at least 15%. 
     
     
         9 . The optical film according to  claim 1 , wherein the polymer composition contains a cellulose acylate polymer as the main ingredient thereof. 
     
     
         10 . A method for producing an optical film comprising a first domain of a polymer composition and a second domain disposed inside the first domain, wherein the second domain is a bubble having a morphology anisotropy, and the mean alignment direction of the main chain of the polymer molecule in the first domain differs from the mean direction of the major axis of the second domain, which comprises:
 stretching a film comprising a polymer composition and having a haze of at most 1% at a stretching temperature of from (Tg-20)° C. to Tc° C. and at a draw ratio of from 1 to 300% wherein Tg means the glass transition temperature (unit, ° C.) of the film and Tc means the crystallization temperature (unit, ° C.) of the film).   
     
     
         11 . The method for producing an optical film according to  claim 10 , wherein the stretching maximum stress to the film in the stretching direction during the stretching is controlled to be from 10 MPa to 60 MPa. 
     
     
         12 . The method for producing an optical film according to  claim 10 , wherein the temperature difference between the surface temperature and the back temperature of the film during the stretching is controlled to be at least 0.1 degrees. 
     
     
         13 . A polarizer having at least one optical film of  claim 1 .