Optical element and method for manufacturing the same

Abstract

The present invention provides an optical element capable of improving the adhesion between the alignment property providing layer, for providing the alignment property to the refractive index anisotropic layer, and the refractive index anisotropic layer, as well as improving durability of each layer. An optical element 10 comprises an alignment property providing layer 12 laminated on the transparent base material 11 , and a refractive index anisotropic layer 13 laminated on the alignment property providing layer 12 . The alignment property providing layer 12 is an alignment film which provides the alignment property to the refractive index anisotropic layer 13 . And the alignment property providing layer 12 is made from an alignment film composition capable of exhibiting the alignment limiting force by the photo-alignment method. The refractive index anisotropic layer 13 comprises a liquid crystal layer formed by curing (polymerizing) a liquid crystalline composition including a polymerizable liquid crystal material. In the refractive index anisotropic layer 13 , the curing degree of the refractive index anisotropic layer 13 changes monotonously with a predetermined gradient in its thickness direction such that, within the refractive index anisotropic layer 13 , the curing degree of the portion closer to the alignment property providing layer 12 is larger, compared with the curing degree of the portion farther from the alignment property providing layer 12 . It is preferable that the average curing degree of the refractive index anisotropic layer 13 is 90% or more.

1 . A method for manufacturing an optical element comprising: a step of preparing a transparent base material with an alignment film, made from a alignment film composition capable of exhibiting an alignment limiting force by a photo-alignment method, laminated thereon as an alignment property providing layer;
 a step of coating a liquid crystalline composition including a polymerizable liquid crystal material onto the alignment property providing layer of the transparent base material; and   a step of forming a refractive index anisotropic layer, comprising a liquid crystal layer, whose curing degree changes monotonously with a predetermined gradient in its thickness direction, on the alignment property providing layer of the transparent base material by curing the liquid crystalline composition while delaying a curing rate of the liquid crystalline composition near a surface on the side not adjacent to the alignment property providing layer, compared with the curing rate near a surface on the side adjacent to the alignment property providing layer.   
     
     
         2 . The method for manufacturing an optical element according to  claim 1 , wherein, in the step of forming the refractive index anisotropic layer, a radioactive ray is irradiated to the liquid crystalline composition in a state that, among the liquid crystalline composition, only the side not adjacent to the alignment property providing layer is exposed to an air atmosphere. 
     
     
         3 . The method for manufacturing an optical element according to  claim 2 , wherein the radioactive ray is an ultraviolet ray, and the liquid crystalline composition includes a polymerization initiator together with the polymerizable liquid crystal material.