Optical film, optical compensation film, polarzing plate and liquid crystal display

Abstract

An optical film is provided and has retardations satisfying relations (1) to (3): 0≦ Re (550)≦10;  (1) −25≦ Rth (550)≦25; and  (2) | I|+|II|+|III|+|IV|>0.5 (nm),   (3) with definitions: I=Re(450)−Re(550); II=Re(650)−Re(550); III=Rth(450)−Rth(550); and IV=Rth(650)−Rth(550), wherein Re(450), Re(550) and Re(650) are in-plane retardations measured with lights of wavelength of 450, 550 and 650 nm, respectively; and Rth(450), Rth(550) and Rth(650) are retardations in a thickness direction of the optical film, which are measured with lights of wavelength of 450, 550 and 650 nm, respectively.

What is claimed is: 
     
         1 . An optical film having retardations satisfying relations (1) to (3):
   0≦ Re (550)≦5;  (1)
     −15 ≦Rth (550)≦15, and  (2)
     | I|+|II|+|III|+|IV|> 0.5 (nm),  (3)
   
       with definitions:
 I=Re(450)−Re(550); 
 II=Re(650)−Re(550); 
 III=Rth(450)−Rth(550); and 
 IV=Rth(650)−Rth(550), 
 
       wherein Re(450), Re(550) and Re(650) are in-plane retardations measured with lights of wavelength of 450, 550 and 650 nm, respectively; and Rth(450), Rth(550) and Rth(650) are retardations in a thickness direction of the optical film, which are measured with lights of wavelength of 450, 550 and 650 nm, respectively, and 
       wherein I, II, III and IV satisfy relations (4-B) to (7-B):
   −50 ≦I< 0;  (4-B)
 
   0 <II≦ 50;  (5-B)
 
   0 ≦III≦ 50; and  (6-B)
 
   −50 ≦IV≦ 0,  (7-B)
 
 
       wherein the optical film has a spectral transmittance, at a wavelength of 380 nm, of 45 to 95%. 
     
     
         2 . The optical film according to  claim 1 , wherein −15≦Rth(550)≦−0.5. 
     
     
         3 . The optical film according to  claim 1 , wherein the optical film is stretched. 
     
     
         4 . The optical film according to  claim 1 , wherein the optical film has a thickness of from 20 to 200 μm. 
     
     
         5 . The optical film according to  claim 1 , wherein the optical film has a spectral transmittance, at a wavelength of 350 nm, of 10% or less. 
     
     
         6 . The optical film according to  claim 1 , wherein a material for forming the optical film comprises at least one resin selected from the group consisting of an acrylic polymer, a styrenic polymer and cellulose acylate. 
     
     
         7 . The optical film according to  claim 6 , wherein the material for forming the optical film is cellulose acylate. 
     
     
         8 . The optical film according to  claim 7 , wherein the cellulose acylate has an acyl substituent, the acyl substituent is substantially only an acetyl group, and a total substitution degree of the acyl substituent is from 2.56 to 3.00. 
     
     
         9 . A polarizing plate comprising: a polarizer; and the optical film according to  claim 1 . 
     
     
         10 . A liquid crystal display comprising: a substrate; the optical film according to  claim 1 ; and a liquid crystal cell containing liquid crystal molecules aligned to be substantially parallel to the substrate in a black display state of the liquid crystal display.