Liquid crystal display device

Abstract

A liquid crystal display device includes an OCB mode liquid crystal display panel, and an optical compensation element which is disposed outside of the liquid crystal display layer. The optical compensation element includes a polarizer plate, a first retardation plate which is disposed between the polarizer plate and the liquid crystal layer, and a second retardation plate which is disposed between the polarizer plate and the first retardation plate and has a biaxial refractive index anisotropy. The optical compensation element compensates a difference of a polarization state that differs between azimuth directions of light passing through the liquid crystal layer and compensates a shift of the polarization state of light, which passes through the retardation plate, from an azimuth direction of an absorption axis of the polarizer plate.

1 . A liquid crystal display device comprising:
 an OCB mode liquid crystal display panel which is configured such that a liquid crystal layer is held between a first substrate and a second substrate; and   an optical compensation element which is disposed outside of the liquid crystal layer and optically compensates a retardation of the liquid crystal layer in a predetermined display state in which a voltage is applied to the liquid crystal layer,   wherein the optical compensation element includes:   a polarizer plate;   a first retardation plate which is disposed between the polarizer plate and the liquid crystal layer and imparts a phase difference of a ¼ wavelength; and   a second retardation plate which is disposed between the polarizer plate and the first retardation plate and has a biaxial refractive index anisotropy, and   the second retardation plate has a refractive index anisotropy which is set in such a manner as to compensate (a) a difference of a polarization state due to an influence of optical rotatory power that differs between azimuth directions of light passing through the liquid crystal layer and to compensate (b) a shift of the polarization state of light, which passes through the first retardation plate, from an azimuth direction of an absorption axis of the polarizer plate.   
   
   
       2 . The liquid crystal display device according to  claim 1 , wherein the liquid crystal display panel includes a reflective electrode on the first substrate, and
 the optical compensation element is disposed on an outer surface of the second substrate.   
   
   
       3 . The liquid crystal display device according to  claim 2 , wherein an Nz coefficient in the second retardation plate is set in a range of between 0.15 and 0.3, the Nz coefficient being given by
     Nz =( nx−nz )/( nx−ny ),   
     where nx and ny are refractive indices in mutually perpendicular directions in a plane of the second retardation plate, and nz is a refractive index in a normal direction to the second retardation plate. 
   
   
       4 . The liquid crystal display device according to  claim 3 , wherein the absorption axis of the polarizer plate is substantially perpendicular to an optical axis of the second retardation plate. 
   
   
       5 . The liquid crystal display device according to  claim 2 , wherein an Nz coefficient in the second retardation plate is set in a range of between 0.7 and 0.9, the Nz coefficient being given by
     Nz =( nx−nz )/( nx−ny ),   
     where nx and ny are refractive indices in mutually perpendicular directions in a plane of the second retardation plate, and nz is a refractive index in a normal direction to the second retardation plate. 
   
   
       6 . The liquid crystal display device according to  claim 5 , wherein the absorption axis of the polarizer plate substantially agrees with an optical axis of the second retardation plate. 
   
   
       7 . The liquid crystal display device according to  claim 1 , wherein the liquid crystal display panel includes a transmissive electrode on the first substrate, and
 the optical compensation element is disposed on one of an outer surface of the first substrate and an outer surface of the second substrate.   
   
   
       8 . The liquid crystal display device according to  claim 7 , wherein an Nz coefficient in the second retardation plate is set in a range of between 0.4 and 0.6, the Nz coefficient being given by
     Nz =( nx−nz )/( nx−ny ),   
     where nx and ny are refractive indices in mutually perpendicular directions in a plane of the second retardation plate, and nz is a refractive index in a normal direction to the second retardation plate. 
   
   
       9 . The liquid crystal display device according to  claim 8 , wherein the absorption axis of the polarizer plate substantially agrees with, or is substantially perpendicular to, an optical axis of the second retardation plate. 
   
   
       10 . The liquid crystal display device according to  claim 1 , further comprising a retardation plate RA with a refractive index anisotropy corresponding to an A-plate and a retardation plate RC with a refractive index anisotropy corresponding to a C-plate, which are disposed between the liquid crystal display panel and the first retardation plate. 
   
   
       11 . The liquid crystal display device according to  claim 1 , further comprising a retardation plate RB with a biaxial refractive index anisotropy corresponding to an A-plate and a C-plate, which is disposed between the liquid crystal display panel and the first retardation plate. 
   
   
       12 . The liquid crystal display device according to  claim 1 , further comprising a retardation plate Rwv with such a refractive index anisotropy that a major axis thereof is inclined to a normal direction, which is disposed between the liquid crystal display panel and the first retardation plate. 
   
   
       13 . The liquid crystal display device according to  claim 1 , further comprising a retardation plate RA with a refractive index anisotropy corresponding to an A-plate, which is disposed between the liquid crystal display panel and the first retardation plate,
 wherein the first retardation plate imparts a phase difference of a ¼ wavelength between light components of a predetermined wavelength, which pass through a fast axis and a slow axis thereof, and has a biaxial refractive index anisotropy corresponding to a C-plate.   
   
   
       14 . A liquid crystal display device comprising:
 an OCB mode liquid crystal display panel which is configured such that a liquid crystal layer is held between a first substrate and a second substrate; and   a first optical compensation element and a second optical compensation element which are disposed, respectively, outside of the liquid crystal layer, and optically compensate a retardation of the liquid crystal layer in a predetermined display state in which a voltage is applied to the liquid crystal layer,   wherein the first optical compensation element includes:   a first polarizer plate;   a first retardation plate which is disposed between the first polarizer plate and the liquid crystal layer and imparts a phase difference of a ¼ wavelength; and   a second retardation plate which is disposed between the first polarizer plate and the first retardation plate and has a biaxial refractive index anisotropy,   the second optical compensation element includes:   a second polarizer plate;   a third retardation plate which is disposed between the second polarizer plate and the liquid crystal layer and imparts a phase difference of a ¼ wavelength; and   a fourth retardation plate which is disposed between the second polarizer plate and the third retardation plate and has a biaxial refractive index anisotropy, and   the second retardation plate and the fourth retardation plate have a refractive index anisotropy which is set in such a manner as to compensate (a) a difference of a polarization state due to an influence of optical rotatory power that differs between azimuth directions of light passing through the liquid crystal layer and to compensate (b) a shift of the polarization state of light, which passes through the first retardation plate, from an azimuth direction of an absorption axis of the polarizer plate.   
   
   
       15 . The liquid crystal display device according to  claim 14 , wherein the absorption axis of the first polarizer plate substantially agrees with an optical axis of the second retardation plate, and the absorption axis of the second polarizer plate is substantially perpendicular to an optical axis of the fourth retardation plate,
 an Nz coefficient in the second retardation plate is set in a range of between 0.7 and 0.9, the Nz coefficient being given by
     Nz =( nx−nz )/( nx−ny ), 
   
     where nx and ny are refractive indices in mutually perpendicular directions in a plane of the retardation plate, and nz is a refractive index in a normal direction to the retardation plate, and
 the Nz coefficient in the fourth retardation plate is set in a range of between 0.15 and 0.3. 
 
   
   
       16 . The liquid crystal display device according to  claim 14 , wherein the absorption axis of the first polarizer plate is substantially perpendicular to an optical axis of the second retardation plate, and the absorption axis of the second polarizer plate substantially agrees with an optical axis of the fourth retardation plate,
 an Nz coefficient in the second retardation plate is set in a range of between 0.15 and 0.3, the Nz coefficient being given by
     Nz =( nx−nz )/( nx−ny ), 
   
     where nx and ny are refractive indices in mutually perpendicular directions in a plane of the retardation plate, and nz is a refractive index in a normal direction to the retardation plate, and
 the Nz coefficient in the fourth retardation plate is set in a range of between 0.7 and 0.9. 
 
   
   
       17 . The liquid crystal display device according to  claim 14 , wherein the absorption axis of the first polarizer plate is substantially perpendicular to an optical axis of the second retardation plate, and the absorption axis of the second polarizer plate is substantially perpendicular to an optical axis of the fourth retardation plate, and
 an Nz coefficient in each of the second retardation plate and the fourth retardation plate is set in a range of between 0.15 and 0.3, the Nz coefficient being given by
     Nz =( nx−nz )/( nx−ny ), 
   
     where nx and ny are refractive indices in mutually perpendicular directions in a plane of each of the second retardation plate and the fourth retardation plate, and nz is a refractive index in a normal direction to each of the second retardation plate and the fourth retardation plate. 
   
   
       18 . The liquid crystal display device according to  claim 14 , wherein the absorption axis of the first polarizer plate substantially agrees with an optical axis of the second retardation plate, and the absorption axis of the second polarizer plate substantially agrees with an optical axis of the fourth retardation plate, and
 an Nz coefficient in each of the second retardation plate and the fourth retardation plate is set in a range of between 0.7 and 0.9, the Nz coefficient being given by
     Nz =( nx−nz )/( nx−ny ), 
   
     where nx and ny are refractive indices in mutually perpendicular directions in a plane of each of the second retardation plate and the fourth retardation plate, and nz is a refractive index in a normal direction to each of the second retardation plate and the fourth retardation plate. 
   
   
       19 . The liquid crystal display device according to  claim 14 , further comprising a retardation plate RA with a refractive index anisotropy corresponding to an A-plate and a retardation plate RC with a refractive index anisotropy corresponding to a C-plate, which are disposed between the liquid crystal display panel and the first retardation plate and between the liquid crystal display panel and the third retardation plate. 
   
   
       20 . The liquid crystal display device according to  claim 14 , further comprising a retardation plate RB with a biaxial refractive index anisotropy corresponding to an A-plate and a C-plate, which is disposed between the liquid crystal display panel and the first retardation plate and between the liquid crystal display panel and the third retardation plate. 
   
   
       21 . The liquid crystal display device according to  claim 14 , further comprising a retardation plate Rwv with such a refractive index anisotropy that a major axis thereof is inclined to a normal direction, which is disposed between the liquid crystal display panel and the first retardation plate and between the liquid crystal display panel and the third retardation plate. 
   
   
       22 . The liquid crystal display device according to  claim 14 , further comprising a retardation plate RA with a refractive index anisotropy corresponding to an A-plate, which is disposed between the liquid crystal display panel and the first retardation plate and between the liquid crystal display panel and the third retardation plate,
 wherein each of the first retardation plate and the third retardation plate imparts a phase difference of a ¼ wavelength between light components of a predetermined wavelength, which pass through a fast axis and a slow axis thereof, and has a biaxial refractive index anisotropy corresponding to a C-plate.