Cellulose ester film, method of manufacturing the same, polarizing plate and liquid crystal display

Abstract

An object of this invention is to provide a cellulose ester film which satisfies the requirement 0.95<plasticizer content of A surface/plasticizer content of B surface<1.05, provided that A surface represents one surface of the cellulose ester film and B surface represents the other surface, has a high sound velocity of the film and is excellent in light leakage and color unevenness, and a film-forming method of this cellulose ester film. The cellulose ester film of the present invention, which contains a cellulose ester, is characterized by satisfying the requirement 0.95<plasticizer content of A surface/plasticizer content of B surface<1.05, provided that A surface represents one surface of the cellulose ester film and B surface represents the other surface, and having a sound velocity along at least one of a film transport direction and the lateral direction at 23.° C. 55% RH of 2.0-2.7 km/s.

1 . A cellulose ester film comprising a cellulose ester, wherein
 the cellulose ester film satisfies a condition:   0.95<(a content of a plasticizer on A surface)/(a content of a plasticizer on B surface)<1.05, provided that A surface represents one surface of the cellulose ester film and B surface represents the other surface of the cellulose ester film; and   a sound velocity along at least one of a film transport direction and the lateral direction of the cellulose ester film is 2.0-2.7 km/s at 23° C. under 55% RH.   
     
     
         2 . The cellulose ester film of  claim 1  comprising a phosphorus-containing compound having a phosphonite structure or a phosphite structure. 
     
     
         3 . The cellulose ester film of  claim 1 ,
 wherein
 a total acyl substitution degree of the cellulose ester film is 2.5-2.9; and 
 a propionyl substitution degree of the cellulose ester film is 1.0-1.5. 
   
     
     
         4 . A film producing method of the cellulose ester film of  claim 1  comprising the steps of:
 heating to melt a composition comprising the cellulose ester and an additive to a temperature at which the composition exhibits fluidity, whereby a melt of the composition is obtained;   casting the melt followed by cooling to obtain the cellulose ester film; and   stretching the cellulose ester film at a stretching rate of 1000%/min -30000%/min, the stretching rate being represented by following Equation (1):
   stretching rate (%/min)=((a dimension after stretching)/(a dimension before stretching)−1)×100(%)/a time needed for stretching (Min).  Equation (1) 
   
     
     
         5 . The film producing method of  claim 4 , wherein the cellulose ester film is stretched in the lateral direction of the cellulose ester film at a stretching rate represented by above Equation (1) of 400%/min-1500%/min. 
     
     
         6 . The film producing method of  claim 4 , wherein the cellulose ester film is stretched at a stretching ratio of 50%-200% in at least one of the film transport direction and the lateral direction of the cellulose ester film. 
     
     
         7 . A polarizing plate comprising the cellulose ester film of  claim 1 . 
     
     
         8 . A liquid crystal display comprising the polarizing plate of  claim 7 . 
     
     
         9 . A polarizing plate comprising a cellulose ester film produced by the film producing method of  claim 4 . 
     
     
         10 . A liquid crystal display comprising the polarizing plate of  claim 9 .