Retardation films for the elimination of leakage of light through cross polarizers in LCD

1. A compensator for two polarizers in dark-state comprising layers of birefringent materials, wherein one of said layers operates as a positive A-plate, another of said layers operates as a negative A-plate, and a C-plate is placed between said A-plates.

2. The compensator according to claim 1 , wherein said C-Plate is a negative C-plate.

3. The compensator according to claim 1 , wherein said negative A-plate comprises at least one layer of a birefringent material wherein the birefringent material has a crystal structure formed by at least one polycyclic organic compound with conjugated π-system, and an intermolecular spacing of 3.4±0.3 Å is in the direction of at least one of optical axes.

4. The compensator according to claim 2 , wherein said negative C-plate comprises at least one layer of a birefringent material wherein the birefringent material has a crystal structure formed by at least one polycyclic organic compound with conjugated π-system, and an intermolecular spacing of 3.4±0.3 Å is in the direction of at least one of optical axes.

5. The compensator according to claim 1 , wherein said C-Plate is a positive C-plate.

6. The compensator according to claim 1 , further comprising at least two polarizers, wherein axes of transmission of said polarizers are mutually perpendicular.

7. The compensator according to claim 1 further comprising at least two polarizers, wherein at least one layer of birefringent material having optical thickness so as a direction of light polarization incident upon second polarizer is perpendicular to axis of transmission of this polarizer.

8. The compensator according to any of claims 3 or 4 , wherein the organic compound comprises modifying ionogenic functional groups selected from the group consisting of —COOH, —SO 3 H, PO 3 H, and NH 2 .

9. The compensator according to claim 8 , wherein the organic compound is an acenaphtho[1 ,2-b]quinoxaline sulfoderivative of the general structural formula:

Where n is an integer in the range of 1 to 4;

m is an integer in the range of 0 to 4;

z is an integer in the range of 0 to 6, and m+z+n≦b 10 ;

X and Y are individually selected from the group consisting of CH 3 , C 2 H 5 , OCH 3 , OC 2 H 5, Cl, Br, OH, and NH 2 ;

M is a counterion; and

J is the number of counterions in the molecule.

10. The compensator according to claim 9 , wherein the structural formula of acenaphtho[1,2-b]quinoxaline sulfoderivative is chosen from the group consisting of structures I-VIII:

where m is an integer in the range of 0 to 3, and z is an integer in the range of 0 to 6;

where m is an integer in the range of 0 to 4, and z is an integer in the range of 0 to 5;

where m is an integer in the range of 0 to 2, and z is an integer in the range of 0 to 6;

where m is an integer in the range of 0 to 4, and z is an integer in the range of 0 to 4;

where m is an integer in the range of 0 to 3, and z is an integer in the range of 0 to 5;

where m is an integer in the range of 0 to 3, and z is an integer in the range of 0 to 4;

where m is an integer in the range of 0 to 2, and z is an integer in the range of 0 to 5;

where m is an integer in the range of 0 to 2, and z is an integer in the range of 0 to 4;

and where X, Y are individually selected from the group consisting of CH 3 , C 2 H 5 , OCH 3 , OC 2 H 5 , Cl, Br, OH, and NH 2 , M is a counterion, and j is the number of counterions in the molecule.

11. The compensator according to claim 1 , wherein retardance of said each A-plate is λ/6.

12. The compensator according to claim 1 , wherein retardance of said C-plate is √{square root over (3)}λ/6.

13. A liquid crystal display, comprising:

a liquid crystal cell, and a compensator according to claim 1 .