Optical film, optical compensation film, polarizing 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.

1 . An optical film having 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.  
     
     
         2 . The optical film according to  claim 1 , wherein I, II, III and IV satisfy relations (4-A) to (7-A):  
         −50 ≦I≦ 0;   (4-A)  0≦II≦50;   (5-A)  −50 ≦III< 0; and   (6-A)  0<IV≦50.   (7-A)  
     
     
         3 . The optical film according to  claim 1 , 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)  
     
     
         4 . The optical film according to  claim 1 , wherein I, II, III and IV satisfy relations (4-C) to (7-C):  
         0≦I≦50;   (4-C)  −50 ≦II≦ 0;   (5-C)  0<III≦50; and   (6-C)  −50 ≦IV< 0.   (7-C)  
     
     
         5 . The optical film according to  claim 1 , wherein I, II, III and IV satisfy relations (4-D) to (7-D):  
         0<I≦50;   (4-D)  −50 ≦II< 0;   (5-D)  −50 ≦III≦ 0; and   (6-D)  0≦IV≦50.   (7-D)  
     
     
         6 . The optical film according to  claim 1 , which is formed from a cellulose acylate a raw material polymer of the optical film.  
     
     
         7 . The optical film according to  claim 6 , 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.  
     
     
         8 . The optical film according to  claim 6 , wherein the cellulose acylate has an acyl substituent, the acyl substituent is substantially at least two of acetyl group, propionyl group and butanoyl group, and a total substitution degree of the acyl substituent is from 2.50 to 3.00.  
     
     
         9 . The optical film according to  claim 1 , which comprises a compound capable of reducing Rth(550) within a range satisfying relations (8) and (9):  
         ( Rth ( A )− Rth (0))/ A≦− 1.0; and   (8)  0.01≦A≦30,   (9)  
       wherein: 
 Rth(A) means Rth(nm) at 550 nm of the optical film containing the compound capable of reducing Rth(550) by A %;  
 Rth(0) means Rth(nm) at 550 nm of the optical film not containing the compound capable of reducing Rth(550); and  
 A means a weight % of the compound capable of reducing Rth(550) with respect to a weight of a raw material polymer of the optical film, which is taken as 100.  
 
     
     
         10 . The optical film according to  claim 1 , which comprises a compound capable of increasing ΔRth, which is represented by a relation (10), within a range satisfying relations (11) and (12):  
         Δ Rth=Rth (450)− Rth (650);   (10)  (Δ Rth ( B )−Δ Rth (0))/ B≧ 1.0; and   (11)  0.01≦B≦30,   (12)  
       wherein: 
 ΔRth(B) means ΔRth(nm) of the optical film containing the compound capable of increasing ΔRth by B %;  
 ΔRth(0) means ΔRth(nm) of thje optical film not containing the compound capable of increasing ΔRth; and  
 B means a weight (%) of the compound capable of increasing ΔRth with respect to a weight of a raw material polymer of the optical film, which is taken as 100.  
 
     
     
         11 . The optical film according to  claim 1 , which has a thickness of 20 to 200 μm.  
     
     
         12 . An optical compensation film comprising: an optical film according to  claim 1;  and an optically anisotropic layer satisfying relations (13) and (14):  
         0≦Re≦400;and   (13)  −400 ≦Rth≦ 400,   (14)  
       wherein Re and Rth are an in-plane retardation and a retardation in a thickness direction of the optically anisotropic layer, respectively, which are measured with a light having a wavelength within a visible region.  
     
     
         13 . A polarizing plate comprising: a polarizer; and an optical film according to  claim 1 .  
     
     
         14 . A liquid crystal display comprising an optical film according to  claim 1 .  
     
     
         15 . A liquid crystal display comprising: an optical film according to  claim 1;  and an optically anisotropic layer satisfying relations (15) and (16):  
         0≦Re≦400; and   (15)  −400 ≦Rth≦ 400,   (16)  
       wherein Re and Rth are an in-plane retardation and a retardation in a thickness direction of the optically anisotropic layer, respectively, which are measured with a light having a wavelength within a visible region.  
     
     
         16 . The liquid crystal display according to  claim 14 , which further comprises a liquid crystal cell containing liquid crystal molecules aligned in one of a vertical alignment, a parallel alignment and a bent alignment in a black display state of the liquid crystal display.  
     
     
         17 . The liquid crystal display according to  claim 16 , wherein the liquid crystal molecules are aligned in the vertical alignment in the black display state, and the liquid crystal display comprises an optically anisotropic layer, the optically anisotropic layer including a layer satisfying relations (17) and (18):  
         10≦Re≦150; and   (17)  50≦Rth≦400,   (18)  
       wherein Re and Rth are an in-plane retardation and a retardation in a thickness direction of the optically anisotropic layer, respectively, which are measured with a light having a wavelength within a visible region.  
     
     
         18 . The liquid crystal display according to  claim 16 , wherein the liquid crystal molecules are aligned in the parallel alignment in the black display state, and the liquid crystal display comprises an optically anisotropic layer, the optically anisotropic layer including a layer satisfying any one of relations from (19) to (22):  
         100 ≦Re≦ 400, and −50 ≦Rth≦ 50;   (19)  0 ≦Re≦ 20, and −400 ≦Rth≦− 50;   (20)  60≦Re≦200, and 20≦Rth≦120; and   (21)  30≦Re≦150, and 100≦Rth≦400,   (22)  
       wherein Re and Rth are an in-plane retardation and a retardation in a thickness direction of the optically anisotropic layer, respectively, which are measured with a light having a wavelength within a visible region.  
     
     
         19 . The liquid crystal display according to  claim 16 , wherein the liquid crystal molecules are aligned in the bent alignment in the black display state, and the liquid crystal display comprises an optically anisotropic layer, the optically anisotropic layer including a layer containing a discotic liquid crystal compound.