Vertically aligned liquid crystal display having negative compensation film

• US 20060244884A1
• Filed: 01/27/2004
• Published: 11/02/2006
• Est. Priority Date: 01/28/2003
• Status: Active Grant

• Current Assignee: LG Chem Limited (LG Corporation)
• Original Assignee: LG Chem Limited (LG Corporation)
• Inventors: Belyaev, Sergey, Yu, Jeong-su, Jeon, Byoung-kun
• Granted Patent: US 7,330,232 B2
• Time in Patent Office: Days
• US Class Current: 349/119
• 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 1/1393 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) comprising a negative compensation film including one or more of a first retardation film (+A-plate) satisfying the condition of n_x>n_y=n_z and a first retardation film (−A-plate) satisfying the condition of n_x<n_y=n_z, and one or more of a second retardation film (−C-plate) satisfying the condition of n_x=n_y>n_z, wherein the first retardation film is arranged such that its optical axis is perpendicular to an optical absorption axis of a neighboring polarizing plate, and a total thickness retardation (R_−C+R_VA) including the thickness retardation of the second retardation film and the thickness retardation of a VA-panel has a negative value. The VA-LCD in accordance with 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 vertically aligned LCD (VA-LCD) in a multi-domain mode or using a chiral additive, provided with a negative compensation film, in which a vertically aligned panel (VA-panel) is obtained 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, 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, and a cell gap in the range of 3 μ

M to 81m is maintained, comprising;

the negative compensation film including one or more of a first retardation film (+A-plate) satisfying the condition of n_x>

n_y=n_z, and a first retardation film (−

A-plate) satisfying the condition of n_x<

n_y=n_z, and one or more of a second retardation film (−

C-plate) satisfying the condition of n_x=n_y>

n_z, for forming a liquid crystal cell, wherein said n_x and n_y represent in-plane refractive indexes between the VA-panel and the upper and lower polarizing plates, and said n_z represents a thickness refractive index,

wherein said first retardation film is arranged such that an optical axis of said first retardation film is perpendicular to an optical absorption axis of the neighboring polarizing plate, and a total thickness retardation (R<sub>−

C</sub>+R_VA) including the thickness retardation of said second retardation film and the thickness retardation of the VA-panel has a negative value.

2. The VA-LCD according to claim 1, wherein

said negative compensation film includes one of said first retardation film (+A-plate and −

A-plate) and one of said second retardation film (−

C-plate) in which

one of said first retardation film and said second retardation film is selectively arranged between the VA-panel and the upper polarizing plate, and the other one of said second retardation film is arranged between the VA-panel and the lower polarizing plate, or

said first retardation film and said second retardation film are arranged at one area between the VA-panel and the upper polarizing plate, or between the VA-panel and the lower polarizing plate.

3. The VA-LCD according to claim 1, wherein

said negative compensation film includes two of said first retardation film (+A-plates or −

A-plates) and one of said second retardation film (−

C-plate) in which

one of said first retardation film, and one of said second retardation film are arranged at one area between the VA-panel and the upper polarizing plate, or between the VA-panel and the lower polarizing plate, and the other one of said first retardation films is arranged at the other area between the VA-panel and the upper polarizing plate, or between the VA-panel and the lower polarizing plate.

4. The VA-LCD according to claim 1, wherein

said negative compensation film includes two of said first retardation film (+A-plates or −

A-plates) and two of said second retardation film (−

C-plate) in which

one of said first retardation film and one of said second retardation film are arranged between the VA-panel and the upper polarizing plate, and the other one of said first retardation film and the other one of said second retardation film are arranged between the VA-panel and the lower polarizing plate.

5. The VA-LCD according to claim 1, wherein

said first retardation film (+A-plate and −

A-plate) 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

the total thickness retardation (R<sub>−

C</sub>+R_VA) including the thickness retardation of said second retardation film and the thickness retardation of the VA-panel is in the range of −

10 nm to −

180 nm, being proportional to a wavelength in the range of visible rays.

6. The VA-LCD according to 5, wherein

said first retardation film (+A-plate) has an in-plane retardation (R_A(550)) at a wavelength of 550 nm, which is in the range of 250 nm to 500 nm, and said first retardation film (−

A-plate) has an in-plane retardation (R_A(550)) at a wavelength of 550 nm, which is more than −

250 nm; and

said second retardation film (−

C-plate) has a thickness retardation (R<sub>−

C</sub>(550)) at a wavelength of 550 nm, which is in the range of −

500 nm to −

180 nm, and the absolute value (|R<sub>−

C</sub>(550)|) thereof, which is larger than the absolute value (|R_VA(550)|) of the thickness retardation of the VA-panel.

7. The VA-LCD according to 5, wherein

the ratio (R₄₅₀/R₅₅₀) of the thickness retardations of said second retardation film (−

C-plate) is smaller than that of the VA-panel; and

the ratio (R₅₅₀/R₅₅₀) of the thickness retardations of said second retardation film (−

C-plate) is larger than that of the VA-panel, wherein said R₄₅₀, R₅₅₀ and R₆₅₀ represent thickness retardations of said second retardation film (−

C-plate) at wavelengths of 450 nm, 550 nm and 650 nm, respectively.

8. The VA-LCD according to 5, wherein directors of liquid crystalline polymers of the VA-panel, under the condition that no voltage is applied to the VA-panel, have a pretilt angle in the range of 75°

to 90°

between the upper and lower glass substrates.

9. The VA-LCD according to claim 8, wherein said pretilt angle is in the range of 87°

to 90°

.

10. The VA-LCD according to claim 8, wherein said pretilt angle is in the range of 89°

to 90°

.

11. The VA-LCD according to claim 5, wherein a liquid crystalline layer formed on said VA-panel has a retardation in the range of 80 nm to 400 nm at a wavelength of 550 nm.

12. The VA-LCD according to claim 11, wherein a liquid crystalline layer formed on said VA-panel has a retardation in the range of 80 nm to 300 nm at a wavelength of 550 nm.

13. The VA-LCD according to claim 5, wherein a rubbed direction of the liquid crystals injected into said VA-panel has an angle of 45°

with the optical absorption axes of said polarizing plates.

14. The VA-LCD as set forth in claim 5, wherein

the ratio (R_A,450/R_A,550) of the in-plane retardations of said first retardation film (A-plate) is in the range of 0.6 to 0.9;

and

the ratio (R_A,550/R_A,650) of the in-plane retardations of said first retardation film (A-plate) is in the range of 1.1 to 1.5, wherein said R_A,450, R_A,550 and R_A,650 represent in-plane retardations at wavelengths of 450 nm, 550 nm and 650 nm, respectively.

15. The VA-LCD as set forth in claim 5, wherein:

the ratio (R<sub>−

C,450</sub>/R<sub>−

C,550</sub>) of the thickness retardations of said second retardation film (−

C-plate) is in the range of 0.9 to 1.2; and

the ratio (R<sub>−

C,550</sub>/R<sub>−

C,650</sub>) of the thickness retardations of said second retardation film (−

C-plate) is in the range of 0.9 to 1.2, wherein said R<sub>−

C,450</sub>, R<sub>−

C,550</sub> and R<sub>−

C,650</sub> represent thickness retardations at wavelengths of 450 nm, 550 nm and 650 nm, respectively.