Laminated retardation optical element, process of producing the same, and liquid crystal display

Abstract

The present invention provides a laminated retardation optical element that never lowers contrast and thus never degrades display performance even when placed between a liquid crystal cell and a λ/4 retardation film. In a liquid crystal display 90 , a laminated retardation optical element 10 is placed between a polarizer 102 A on the incident side and a liquid crystal cell 104 , and a λ/4 retardation film 102 C is placed between a polarizer 102 B on the emergent side and the liquid crystal cell 104 . The laminated retardation optical element 10 comprises: a λ/4 retardation layer 14 having the function of bringing, to light that passes through this retardation layer, a phase difference corresponding to a quarter of the wavelength of the light; and a C plate-type retardation layer 16 that acts as a negative C plate. The λ/4 retardation layer 14 and the C plate-type retardation layer 16 are laminated to a transparent substrate 12 in the order mentioned, and are optically bonded to each other. The λ/4 retardation layer 14 comprises as its main component a horizontally-aligned, cross-linked nematic liquid crystal, while the C plate-type retardation layer 16 comprises as its main component a cross-linked chiral nematic liquid crystal (a cross-linked nematic liquid crystal and a cross-linked chiral agent) or cross-linked discotic liquid crystal.

1 . A laminated retardation optical element comprising:
 an A plate-type retardation layer that acts as an A plate; and   a C plate-type retardation layer that is optically bonded to a surface of the A plate-type retardation layer and acts as a negative C plate;   wherein:   the A plate-type retardation layer comprises a cross-linked nematic liquid crystal, and the C plate-type retardation layer comprises a cross-linked chiral nematic liquid crystal; and   a difference between a mean refractive index of the A plate-type retardation layer and a mean refractive index of the C plate-type retardation layer is 0.05 or less.   
   
   
       2 . The laminated retardation optical element according to  claim 1 , wherein the A plate-type retardation layer is a λ/4 retardation layer having a function of bringing, to light that passes through this retardation layer, a phase difference corresponding to a quarter of a wavelength of the light. 
   
   
       3 . The laminated retardation optical element according to  claim 2 , further comprising a λ/2 retardation layer having a function of bringing, to light that passes through this retardation layer, a phase difference corresponding to a half of a wavelength of the light, the λ/2 retardation layer being optically bonded to a surface of the λ/4 retardation layer serving as the A plate-type retardation layer, on a side opposite to the C plate-type retardation layer. 
   
   
       4 . The laminated retardation optical element according to  claim 3 , wherein the λ/2 retardation layer comprises a cross-linked nematic liquid crystal. 
   
   
       5 . The laminated retardation optical element according to  claim 3 , wherein an angle between an axis of phase advance of the λ/4 retardation layer serving as the A plate-type retardation layer and that of the λ/2 retardation layer is 60±10 degrees. 
   
   
       6 . The laminated retardation optical element according to  claim 1 , wherein the C plate-type retardation layer has a thickness of 5 μm or less. 
   
   
       7 . The laminated retardation optical element according to  claim 6 , further comprising an additional C plate-type retardation layer that is optically bonded to a surface of the C plate-type retardation layer on a side opposite to the A plate-type retardation layer and acts as a negative C plate,
 wherein the additional C plate-type retardation layer comprises a cross-linked chiral nematic or discotic liquid crystal, a total thickness of the C plate-type retardation layer and the additional C plate-type retardation layer is 6 μm or more, and a thickness of the C plate-type retardation layer is nearly equal to that of the additional C plate-type retardation layer.   
   
   
       8 . The laminated retardation optical element according to  claim 2 , further comprising a polarization layer having a function of controlling a state of polarization of light that passes through the λ/4 retardation layer serving as the A plate-type retardation layer. 
   
   
       9 . The laminated retardation optical element according to  claim 8 , wherein an angle between an axis of phase advance of the λ/4 retardation layer serving as the A plate-type retardation layer and an axis of transmission of the polarization layer is 45±2 degrees. 
   
   
       10 . The laminated retardation optical element according to  claim 3 , further comprising a polarization layer having a function of controlling a state of polarization of light that passes through the λ/2 retardation layer. 
   
   
       11 . The laminated retardation optical element according to  claim 10 , wherein an angle between an axis of phase advance of the λ/2 retardation layer and an axis of transmission of the polarization layer is 15±5 degrees. 
   
   
       12 . The laminated retardation optical element according to  claim 1 , wherein nematic liquid crystalline components contained in the retardation layers bonded adjacently to each other are substantially the same. 
   
   
       13 . The laminated retardation optical element according to  claim 1 , wherein the A plate-type retardation layer is subjected to patterning to make it into a predetermined pattern. 
   
   
       14 . The laminated retardation optical element according to  claim 1 , wherein the C plate-type retardation layer is subjected to patterning to make it into a predetermined pattern. 
   
   
       15 . A laminated retardation optical element comprising:
 an A plate-type retardation layer that acts as an A plate; and   a C plate-type retardation layer that is optically bonded to a surface of the A plate-type retardation layer and acts as a positive C plate,   wherein the A plate-type retardation layer comprises a horizontally-aligned, cross-linked nematic liquid crystal, and the C plate-type retardation layer comprises a vertically-aligned, cross-linked nematic liquid crystal.   
   
   
       16 . The laminated retardation optical element according to  claim 15 , wherein the C plate-type retardation layer has a thickness of 5 μm or less. 
   
   
       17 . The laminated retardation optical element according to  claim 16 , further comprising an additional C plate-type retardation layer that is optically bonded to a surface of the C plate-type retardation layer on a side opposite to the A plate-type retardation layer and acts as a positive C plate,
 wherein the additional C plate-type retardation layer comprises a cross-linked nematic liquid crystal, a total thickness of the C plate-type retardation layer and the additional C plate-type retardation layer is 6 μm or more, and a thickness of the C plate-type retardation layer is nearly equal to that of the additional C plate-type retardation layer.   
   
   
       18 . The laminated retardation optical element according to  claim 15 , further comprising a polarization layer having a function of controlling a state of polarization of light that passes through the A plate-type retardation layer. 
   
   
       19 . The laminated retardation optical element according to  claim 15 , wherein a difference between mean refractive indices of the retardation layers bonded adjacently to each other is 0.05 or less. 
   
   
       20 . The laminated retardation optical element according to  claim 19 , wherein nematic liquid crystalline components contained in the retardation layers bonded adjacently to each other are substantially the same. 
   
   
       21 . The laminated retardation optical element according to  claim 15 , wherein the A plate-type retardation layer is subjected to patterning to make it into a predetermined pattern. 
   
   
       22 . The laminated retardation optical element according to  claim 15 , wherein the C plate-type retardation layer is subjected to patterning to make it into a predetermined pattern. 
   
   
       23 . A process of producing a laminated retardation optical element, comprising the steps of:
 forming an A plate-type retardation layer that is in a form of a film and acts as an A plate by applying a nematic liquid crystal to an alignment layer and cross-linking the applied liquid crystal; and   forming a C plate-type retardation layer that is in a form of a film and acts as a negative C plate by applying a chiral nematic or discotic liquid crystal to the formed A plate-type retardation layer and cross-linking the applied liquid crystal.   
   
   
       24 . The process according to  claim 23 , wherein the A plate-type retardation layer is a λ/4 retardation layer having a function of bringing, to light that passes through this retardation layer, a phase difference corresponding to a quarter of a wavelength of the light. 
   
   
       25 . The process according to  claim 23 , further comprising the step of forming a λ/2 retardation layer that is in a form of a film and has a function of bringing, to light that passes through this retardation layer, a phase difference corresponding to a half of a wavelength of the light by applying a nematic liquid crystal to the alignment layer and cross-linking the applied liquid crystal,
 wherein, in the step of forming the A plate-type retardation layer, the A plate-type retardation layer is formed by applying the nematic liquid crystal not to the alignment layer but to the λ/2 retardation layer and cross-linking the applied liquid crystal.   
   
   
       26 . The process according to  claim 23 , further comprising the step of forming an additional C plate-type retardation layer that is in a form of a film and acts as a negative C plate by applying a chiral nematic or discotic liquid crystal to the formed C plate-type retardation layer and cross-linking the applied liquid crystal. 
   
   
       27 . The process according to  claim 23 , wherein, in the step of forming the C plate-type retardation layer on the A plate-type retardation layer, an alignment regulation power of a surface of the A type-plate retardation layer is used to align the C plate-type retardation layer. 
   
   
       28 . The process according to  claim 27 , wherein the alignment regulation power is imparted to the surface of the A plate-type retardation layer by subjecting this surface to rubbing treatment. 
   
   
       29 . The process according to  claim 23 , further comprising the step of forming an additional alignment layer on a surface of the A plate-type retardation layer,
 wherein, in the step of forming the C plate-type retardation layer, an alignment regulation power of a surface of the additional alignment layer is used to align the C plate-type retardation layer.   
   
   
       30 . The process according to  claim 29 , wherein an azimuth of the alignment regulation power of the surface of the additional alignment layer is produced by means of rubbing treatment to which the additional alignment layer is subjected or of optical alignment of the additional alignment layer. 
   
   
       31 . The process according to  claim 25 , wherein, in the step of forming the A plate-type retardation layer on the λ/2 retardation layer, an alignment regulation power of a surface of the λ/2 retardation layer is used to align the A plate-type retardation layer. 
   
   
       32 . The process according to  claim 31 , wherein the alignment regulation power is imparted to the surface of the λ/2 retardation layer by subjecting this surface to rubbing treatment. 
   
   
       33 . The process according to  claim 25 , further comprising the step of forming an additional alignment layer on a surface of the λ/2 retardation layer,
 wherein, in the step of forming the A plate-type retardation layer, an alignment regulation power of a surface of the additional alignment layer is used to align the A plate-type retardation layer.   
   
   
       34 . The process according to  claim 33 , wherein an azimuth of the alignment regulation power of the surface of the additional alignment layer is produced by means of rubbing treatment to which the additional alignment layer is subjected or of optical alignment of the additional alignment layer. 
   
   
       35 . A process for producing a laminated retardation optical element, comprising the steps of:
 forming a C plate-type retardation layer that is in a form of a film and acts as a negative C plate by applying a chiral nematic or discotic liquid crystal to an alignment layer, and cross-linking the applied liquid crystal; and   forming an A plate-type retardation layer that is in a form of a film and acts as an A plate by applying a nematic liquid crystal to the formed C plate-type retardation layer and cross-linking the applied liquid crystal.   
   
   
       36 . The process according to  claim 35 , wherein the A plate-type retardation layer is a λ/4 retardation layer having a function of bringing, to light that passes through this retardation layer, a phase difference corresponding to a quarter of a wavelength of the light. 
   
   
       37 . A liquid crystal display comprising:
 a liquid crystal cell of VA mode;   a pair of polarizers between which the liquid crystal cell is sandwiched; and   a laminated retardation optical element according to  claim 3 , placed between the liquid crystal cell and at least one of the polarizers,   wherein the laminated retardation optical element is arranged so that the C plate-type retardation layer is situated on a side close to the liquid crystal cell.   
   
   
       38 . The liquid crystal display according to  claim 37 , further comprising: an additional λ/4 retardation layer having a function of bringing, to light that passes through this retardation layer, a phase difference corresponding to a quarter of the wavelength of the light, placed on the liquid crystal cell on a side opposite to the laminated retardation optical element; and an additional λ/2 retardation layer having a function of bringing, to light that passes through this retardation layer, a phase difference corresponding to a half of a wavelength of the light, placed on the additional λ/4 retardation layer on a side opposite to the liquid crystal cell. 
   
   
       39 . The liquid crystal display according to  claim 38 , wherein an angle between an axis of phase advance of the additional λ/4 retardation layer and that of the additional λ/2 retardation layer is 60±10 degrees. 
   
   
       40 . The liquid crystal display according to  claim 38 , further comprising an additional polarization layer having a function of controlling a state of polarization of light that passes through the additional λ/2 retardation layer, placed on the additional λ/2 retardation layer on a side opposite to the liquid crystal cell. 
   
   
       41 . The liquid crystal display according to  claim 40 , wherein an angle between an axis of phase advance of the additional λ/2 retardation layer and an axis of transmission of the additional polarization layer is 15±5 degrees. 
   
   
       42 . The liquid crystal display according to  claim 38 , wherein an angle between an axis of phase advance of the additional λ/2 retardation layer and that of the λ/2 retardation layer contained in the laminated retardation optical element is substantially equal to 90 degrees. 
   
   
       43 . The liquid crystal display according to  claim 37 , wherein liquid crystalline molecules sealed in the liquid crystal cell are inclined in two or more different directions when an electric field is applied