Bi-axial retardation compensation film and vertically aligned liquid crystal display using the same

• US 20060132686A1
• Filed: 01/27/2004
• Published: 06/22/2006
• Est. Priority Date: 01/28/2003
• Status: Active Grant

• Current Assignee: LG Chem Limited (LG Corporation)
• Original Assignee: LG Chem Limited (LG Corporation)
• Inventors: Jeon, Byoung-Kun, Yu, Jeong-Su, Belyaev, Sergey
• Granted Patent: US 7,782,428 B2
• Time in Patent Office: Days
• US Class Current: 349/117
• CPC Class Codes: G02F 1/133634 the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis
• CPC Class Codes: G02F 1/133637 characterised by the wavelength dispersion
• CPC Class Codes: G02F 1/1393 the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells G02F1/1396, G02F1/141 take precedence

Abstract

The present invention relates to a vertically aligned LCD (VA-LCD) employing a bi-axial retardation compensation film, in which an in-plain refractive index (n_x, n_y) and a thickness refractive index (n_x) of the film is n_x>n_y>n_z. The film has a reversed wavelength dispersion in which retardation is increased in proportion to the increase of a wavelength in the range of visible rays and has a normal wavelength dispersion in which an absolute value of the thickness retardation is decreased in proportion to the increase of a wavelength in the range of visible rays. The VA-LCD cell having a retardation compensation characteristic is comprised by arranging a bi-axial retardation compensation film between the vertically aligned panel and a upper and lower polarizing plate. The VA-LCD of the present invention improves contrast characteristics on a front surface and at a tilt angle and minimizes coloring in a black state according to the tilt angle.

Claims

1. A bi-axial retardation compensation film having n_x>

n_y>

n_z, R_in=(n_x−

n_y)×

d>

0 and R_th=(n_z−

n_y)×

d<

0, wherein n_x and n_y are in-plain refractive indexes, n_z is a thickness refractive index, R_in is a in-plain retardation, R_th is a thickness retardation and d is a thickness.

2. The bi-axial retardation compensation film according to claim 1, wherein a wavelength dispersion (R_in,400/R_in,550) is in the range of 0.4˜

0.9 at wavelengths of 400 nm and 550 nm, and a wavelength dispersion (R_in,700/R_in,550) is in the range of 1.1˜

1.8 at wavelengths of 700 nm and 550 nm, wherein R_in,400, R_in,550 and R_in,700 are in-plain retardations at wavelengths of 400 nm, 550 nm and 700 nm.

3. The bi-axial retardation compensation film according to claim 1, wherein a in-plain retardation (R_in) is in the range of 30˜

150 nm at a wavelength of 550 nm.

4. The bi-axial retardation compensation film according to claim 1, wherein a wavelength dispersion (R_th,400/R_th,550) is in the range of 1.05˜

1.4 at wavelengths of 400 nm and 550 nm, and a wavelength dispersion (R_th,700/R_th,550) is in the range of 0.5˜

0.95 at wavelengths of 700 nm and 550 nm, wherein R_th,400, R_th,550 and R_th,700 are thickness retardations at wavelengths of 400 nm, 550 nm and 700 nm.

5. The bi-axial retardation compensation film according to claim 1, wherein a thickness retardation (R_th) is in the range of −

50˜

500 nm at 550 nm.

6. The bi-axial retardation compensation film according to claim 1, wherein said bi-axial retardation compensation film is manufactured by elongating a polymer prepared with co-polymerization of a first monomer and a second monomer, wherein the first monomer has a characteristic positive of a double refraction and the second monomer has a characteristic negative of a double refraction.

7. The bi-axial retardation compensation film according to claim 1, wherein said bi-axial retardation compensation film is manufactured by elongating a polymer prepared by mixing a first monomer and a second monomer, wherein the first monomer has a characteristic positive of a double refraction and the second monomer has a characteristic negative of a double refraction.

8. The bi-axial retardation compensation film according to claim 1, wherein said bi-axial retardation compensation film is prepared by laminating more than two sheets having different dependability of a in-plane retardation (R_in) and a thickness retardation (R_th).

10. The vertically aligned LCD according to claim 2, wherein a liquid crystal cell is prepared by arranging the bi-axial retardation compensation film at one place of between the vertically aligned panel and upper polarizing plate, or between the vertically aligned panel and lower polarizing plate.

9. In a vertically aligned LCD (VA-LCD) using a multi-domain mode or a chiral additive, provided with a bi-axial retardation compensation film, in which a vertically aligned panel is formed by injecting liquid crystal having a negative dielectric anisotropy (Δ

ε

<

0) or a positive dielectric anisotropy (Δ

ε

>

0) into a gap between upper and lower glass substrates, and upper and lower polarizing plates are arranged above the upper and lower surfaces of the VA-panel so that optical absorption axes of the polarizing plates are perpendicular to each other with the VA-panel as the central figure, and a cell gap in the range of 3 μ

m to 8 μ

m is maintained,

a liquid crystal cell is prepared by arranging a bi-axial retardation compensation film between the vertically aligned panel and a upper and lower polarizing plate in which a in-plain refraction index (n_x, n_y) and a thickness refraction index (n_z) of the bi-axial retardation compensation film is n_x>

n_y>

n_z; and

an optical axis of the bi-axial retardation compensation film is arranged to be perpendicular to an absorption axis of an adjacent polarizing plate, and the bi-axial retardation compensation film has a reversed wavelength dispersion in which a in-plain retardation is increased in proportion to the increase of a wavelength in the range of visible rays, and has a normal wavelength dispersion in which an absolute value of the thickness retardation is decreased in proportion to the increase of a wavelength in the range of visible rays.

11. The vertically aligned LCD according to claim 9, wherein a liquid crystal cell is prepared by arranging one of the individual bi-axial retardation compensation films between the vertically aligned panel and upper polarizing plate, and between the vertically aligned panel and lower polarizing plate.

12. The vertically aligned LCD according to claim 9, wherein the total of a thickness retardation including the vertically aligned panel and the bi-axial retardation compensation film being applied in the vertically aligned LCD is in the range of 30˜

150 nm in proportion of a wavelength in the range of visible rays.

13. The vertically aligned LCD according to claim 12, wherein directors of liquid crystalline polymers of the VA-panel, under the condition that no voltage is applied to the VA-panel, may have a pretilt angle in the range of 75°

to 90°

between the upper and lower glass substrates.

14. The vertically aligned LCD according to claim 13, wherein the pretilt angle is in the range of 87°

to 90°

.

15. The vertically aligned LCD according to claim 13, wherein the pretilt angle is in the range of 89°

to 90°

.

16. The vertically aligned LCD according to claim 12, wherein a liquid crystalline layer of the VA-panel has a retardation in the range of 80 nm to 400 nm at a wavelength of 550 nm.

17. The vertically aligned LCD according to claim 16, wherein a liquid crystalline layer of the VA-panel has a retardation in the range of 80M to 300 nm at a wavelength of 550 nm.

18. The vertically aligned LCD according to claim 12, wherein a rubbed director of the liquid crystals of the VA-panel, under the condition that voltage is applied to the VA-panel, has an angle of 45°

with the optical absorption axes of the polarizing plate.