Liquid crystal display device and manufacturing method thereof

Abstract

The present invention provides a liquid crystal display device in which even in the case of using a photo-alignment technique, excellent afterimage characteristics can be stably obtained. Provided is a liquid crystal display device including a TFT substrate having an alignment film, an opposed substrate which is arranged to face the TFT substrate and on which an alignment film is formed, and a liquid crystal layer sandwiched between the alignment films, wherein the alignment films are materials that can provide a liquid crystal alignment restraining force by irradiating polarized light, and the ratio of oxygen atoms on the surface of the alignment film is higher than that in the alignment film.

What is claimed is: 
     
         1 . A liquid crystal display device comprising:
 a thin-film transistor (TFT) substrate which includes a base substrate, pixel electrodes and TFTs and on which an alignment film is formed on a pixel; and   an opposed substrate which is arranged to face the TFT substrate,   wherein liquid crystal molecules are sandwiched between the alignment film of the TFT substrate and that of the opposed substrate, the alignment film is a polyimide material that can provide a liquid crystal alignment restraining force by irradiating polarized light,   the polyimide material is made from a polyamide acid precursor or a polyamide acid ester precursor,   the liquid crystal molecules are aligned in parallel with the base substrate,   the ratio of oxygen atoms at a position with the highest oxygen concentration is 25% or higher than at a position with the lowest oxygen concentration in the alignment film,   the ratio of oxygen atoms of the alignment film is gradually decreased from the surface contacting with the liquid crystal molecules towards the inside of the alignment in an alignment film thickness direction, and   the alignment film is a photo degradation-type photo-alignment.   
     
     
         2 . The liquid crystal display device according to  claim 1 ,
 wherein the alignment film includes a first layer having the surface and a second layer, and   wherein the ratio of oxygen atoms at a position with the highest oxygen concentration in the first layer is 25% or higher than at a position with the lowest oxygen concentration in the first layer of the alignment film.   
     
     
         3 . The liquid crystal display device according to  claim 1 ,
 wherein the alignment film includes a first layer having the surface and a second layer, and   wherein the thickness of the first layer is smaller than the entire thickness of the alignment film by 50% or less.   
     
     
         4 . The liquid crystal display device according to  claim 1 ,
 wherein the surface includes polyimide of (Chemical formula 1), and   
       
         
           
           
               
               
           
         
         in which the inside of the parentheses [ ] represents a chemical structure of a repeating unit, the index n represents a number of a repeating unit, N represents nitrogen atoms, O represents oxygen atoms, A represents a quadrivalent organic group including a cyclobutane ring, D represents a divalent organic group, and n is integer and one or greater than one. 
       
     
     
         5 . The liquid crystal display device according to  claim 1 ,
 wherein a root-mean-square of a size of irregularities on the surface of the alignment film is 1 nm or less.   
     
     
         6 . The liquid crystal display device according to  claim 1 ,
 wherein the alignment film includes a first layer having the surface and a second layer, and   wherein the first layer is a photo-alignment upper layer capable of photo-alignment and the second layer is smaller in resistivity than the photo-alignment upper layer.   
     
     
         7 . The liquid crystal display device according to  claim 1 ,
 wherein the liquid crystal display device is an In-plane switching (IPS) liquid crystal display device.   
     
     
         8 . The liquid crystal display device according to  claim 1 ,
 wherein a contact angle of water on the surface of the alignment film is 38 degrees or more.   
     
     
         9 . The liquid crystal display device according to  claim 4 ,
 wherein the A of the (Chemical formula 1) represents formula 2 and the D of the (Chemical formula 1) represents formula 4 or 5,   
       
         
           
           
               
               
           
         
       
     
     
         10 . The liquid crystal display device according to  claim 4 , wherein the A of the (Chemical formula 1) represents formula 2 and the D of the (Chemical formula 1) represents formula 4, 
       
         
           
           
               
               
           
         
       
     
     
         11 . The liquid crystal display device according to  claim 4 ,
 wherein the second layer includes polyimide of (Chemical formula 6), and   
       
         
           
           
               
               
           
         
         in which the inside of the parentheses [ ] represents a chemical structure of a repeating unit, the index n represents a number of a repeating unit, N represents nitrogen atoms, O represents oxygen atoms, A represents formula 7, D represents a divalent organic group, and n is integer and one or greater than one,