Liquid crystal polyimide alignment free of scattering domains

Abstract

A liquid crystal display element comprising a pair of substrates, a pair of electrodes provided on the respective substrates, at least one of which is transparent and a liquid crystal layer disposed between said substrates, the liquid crystal layer comprising a nematic liquid crystal, which exhibits a positive dielectric constant anisotropy and contains an optically active substance, the liquid crystal moleccule orientation direction in the liquid crystal layer is twisted in the range of 200 DEG to 250 DEG from the one substrate surface toward the other substrate surface so as to form a helical structure therein. A polyimide orientation film is provided between the electrodes and the liquid crystal layer. The polyimide orientation film is one made of a polyimide prepared by reacting a diamine compound having a long-chain hydrocarbon group or a diamine compound having a trifluoromethyl group with a tetracarboxylic dianhydride and causes a pretilt angle of at least 3 DEG relative to the nematic liquid crystal molecules. The liquid crystal display element of the present invention is free from a scattering domain.

What is claimed is: 
     
       1. A liquid crystal display element comprising a pair of substrates, a pair of electrodes provided on said respective substrates, at least one of which is transparent and a liquid crystal layer disposed between said substrates, said liquid crystal layer comprising a nematic liquid crystal, which exhibits a positive dielectric constant anisotropy and contains an optically active substance, the liquid crystal molecule orientation direction in said liquid crystal layer being twisted in the range of 200° to 250° from the surface of one of said substrates toward the surface of the other said substrate so as to form a helical structure, characterized in that a polyimide orientation film is provided between said electrode and said liquid crystal layer, said polyimide orientation film being one made of a polyimide prepared by reacting one of diamine compounds selected from the group consisting of a diamine compound having a long chain hydrochain group .[.and a diamine compound having a trifluoromethyl group.]. with a tetracarboxylic dianhydride and causing a pretilt angle of at least 3° relative to the nematic liquid crystal molecules. 
     
     
       2. A liquid crystal display element according to claim 1, wherein said diamine compound having a long-chain hydrocarbon group is selected from among compounds. represented by the general formula (I):   X--(CH.sub.2).sub.n --X                                    (I)     (wherein X is --NH 2  or --CONHNH 2  and n an integer of 8 to 13) .[.and said diamine compound having a trifluoromethyl group is selected from among compounds represented by the general formula (II):.]. ##STR35## .[.(wherein X is or.]. ##STR36##   
     
     
       3. A liquid crystal display element according to claim 1, wherein said diamine compound contains at least one compound selected from among diaminodiphenyl ethers represented by the general formula (III): ##STR37## (wherein n is an integer of 0 or 1), and diaminosiloxanes represented by the general formula .[.(IV:).]. (.Iadd.IV): .Iaddend. ##STR38## (wherein Ar 1  is an alkylene or phenylene group and Ar 2  and alkyl or aryl group). 
     
     
       4. A liquid crystal display element comprising a pair of substrates, a pair of electrodes provided on said respective substrates, at least one of which is transparent and a liquid crystal layer disposed between said substrates, said liquid crystal layer comprising a nematic liquid crystal, which exhibits a positive dielectric constant anisotropy and contains an optically active substance, the liquid crystal molecular orientation direction in said liquid crystal layer being twisted in the range of 200° to 250° from the surface of one of said substrates toward the surface of the other said substrate so as to form a helical structure, characterized in that a polyimide orientation film is provided between said electrode and said liquid crystal layer, said polyimide orientation film being made of a polyimide copolymer prepared by reacting a diamine compound having a longchain hydrocarbon group and a diamine compound having a trifluoromethyl group with a tetracarboxylic dianhydride and causing a pretilt angle of at least 3° relative to the nematic liquid crystal molecules. 
     
     
       5. A liquid crystal display element according to claim 4, wherein said diamine compound having a long-chain hydrocarbon group is selected from among compounds represented by the general formula (I): .[.X--(CH n ) 2  --S.]. .Iadd.X--(CH 2 ) n  --X .Iaddend.(I)   (wherein X is --NH 2  or --CONHNH 2  and n an integer of 8 to 13), and said diamine compound having a trifluoromethyl group is selected from among compounds represented by the general formula (II): ##STR39## wherein X is ##STR40##   
     
     
       6. A liquid crystal display element according to claim 4, wherein said diamine compound contains at least one compound selected from among diaminodiphenyl ethers represented by the general formula (III): ##STR41## (wherein n is an integer of 0 or 1), and diaminosiloxanes represented by the general formula (IV): ##STR42## (wherein Ar 1  is an alkylene or phenylene group and Ar 2  an alkyl or aryl group). .Iadd. 
     
     
       7.  A liquid crystal display element according to claim 1, wherein the diamine compound having a long-chain hydrocarbon group does not contain fluorine..Iaddend. .Iadd.8. A liquid crystal display element according to claim 7, wherein said diamine compound having a long-chain hydrocarbon group and not containing fluorine is selected from among compounds represented by the general formula (I):   X--(CH.sub.2).sub.n --X                                    (I)     (wherein X is --NH 2  or --CONHNH 2  and n an integer of 8 to 13)..Iaddend. .Iadd.9. A liquid crystal display element according to claim 7, wherein said diamine compound contains at least one compound selected from among diaminodiphenyl ethers represented by the general formula (III): ##STR43##.Iaddend. (wherein n is an integer of 0 to 1), and diaminosiloxanes represented by the general formula (IV): ##STR44##   
     
     
         10. A liquid crystal display element according to claim 4, wherein the diamine compound having a long-chain hydrocarbon group does not contain fluorine. .Iadd.11. A liquid crystal display element according to claim 10, wherein said diamine compound having a long-chain hydrocarbon group, and which does not contain fluorine, is selected from among compounds represented by the general formula (I):   X--(CH.sub.2).sub.x --X     wherein X is --NH 2  or --CONHNH 2  and n an integer of 8 to 13), and said diamine compound having a trifluoromethyl group is selected from among compounds represented by the general formula (II): ##STR45##   
     
     
       .Iaddend.  .Iadd.12.  A liquid crystal display element according to claim 10, wherein said diamine compound contains at least one compound selected from among diaminodiphenyl ethers represented by the general formula (III): ##STR46##.Iaddend.  (wherein n is an integer of 0 or 1), and diaminosiloxanes represented by the general formula (IV): ##STR47## (wherein Ar 1  is an alkylene or phenylene group and Ar 2  an alkyl or aryl group).