Liquid crystal orientating agent and liquid crystal display element using it

Abstract

To provide a liquid crystal aligning agent useful to obtain a liquid crystal alignment film excellent in liquid crystal alignment properties, alignment controlling power and rubbing resistance, having high voltage retention characteristics and having reduced charge accumulation, and a liquid crystal display device which is less susceptible to display failure, to lowering of contrast or to image persistence. A liquid crystal aligning agent comprising a low resistance polyimide precursor having a volume resistivity of from 1×10 10 to 1×10 14 Ωcm when formed into a film, and a high alignment polyimide precursor or polyimide having a specific structure, and a liquid crystal display device employing this liquid crystal aligning agent.

1 . A liquid crystal aligning agent comprising a polyimide precursor having a structural unit represented by the formula (1) and having a volume resistivity of from 1×10 1  to 1×10 14  Ωcm when formed into a film, and a polyimide precursor having a structural unit represented by the formula (2-1) or a polyimide having a structural unit represented by the formula (2-2):  
     
       
         
         
             
             
         
       
     
     in the formula (1), R represents a hydrogen atom or an alkyl group, X represents a tetravalent organic group, and A represents a bivalent organic group,  
     
       
         
         
             
             
         
       
     
     in the formulae (2-1) and (2-2), R represents a hydrogen atom or an alkyl group, Y represents a tetravalent organic group, B represents a bivalent organic group, and from 10 to 100 mol % of B is a bivalent organic group having any one of the following structures (3) to (5) in its structure, or a paraphenylene group:  
     
       
         
         
             
             
         
       
     
     in the formula (3), ml is an integer of from 2 to 18,  
     
       
         
         
             
             
         
       
     
     in the formula (4), one or a plurality of optional hydrogen atoms on the benzene rings may be substituted by a monovalent organic group other than a primary amino group, and m 2  is an integer of from 1 to 8,  
     
       
         
         
             
             
         
       
     
     in the formula (5), one or a plurality of optional hydrogen atoms on the benzene rings may be substituted by a monovalent organic group other than a primary amino group, and m 3  is an integer of from 1 to 4.  
   
   
       2 . The liquid crystal aligning agent according to  claim 1 , wherein from 10 to 100 mol % of A in the formula (1) is a bivalent organic group having a nitrogen atom.  
   
   
       3 . The liquid crystal aligning agent according to  claim 1 , wherein from 10 to 100 mol % of A in the formula (1) is a bivalent organic group having the following structure (6) or (7):  
     
       
         
         
             
             
         
       
     
     in the formula (6), p is an integer of from 1 to 5,  
     
       
         
         
             
             
         
       
     
   
   
       4 . The liquid crystal aligning agent according to any one of  claims 1  to  3 , wherein from 20 to 100 mol % of X in the formula (1) is a tetravalent organic group having an alicyclic structure or a tetravalent organic group having an aliphatic structure.  
   
   
       5 . The liquid crystal aligning agent according to any one of  claims 1  to  4 , wherein from 20 to 100 mol % of Y in the formula (2-1) or (2-2) is a tetravalent organic group having an aromatic structure.  
   
   
       6 . The liquid crystal aligning agent according to any one of  claims 1  to  5 , wherein the polyimide precursor having a structural unit represented by the formula (1) is contained in an amount of from 10 to 95 wt % based on the total amount of said polyamide precursor and the polyimide precursor having a structural unit represented by the formula (2-1) or the polyimide having a structural unit represented by the formula (2-2).  
   
   
       7 . A liquid crystal display device obtained by using the liquid crystal aligning agent as defined in any one of  claims 1  to  6 .