Liquid crystal display device with biaxial birefringent plates and light shielding film

• US 5,369,513 A
• Filed: 12/07/1992
• Issued: 11/29/1994
• Est. Priority Date: 03/28/1989
• Status: Expired due to Term

• Current Assignee: Optrex Corporation (Kyocera Corporation)
• Original Assignee: Asahi Glass Company, Limited (AGC, Inc.)
• Inventors: Sawada, Kazutoshi, Sohda, Yuji, Akatsuka, Minoru
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Duong, Tai V.
• Application Number:
  US07/987,455
• Time in Patent Office: 722 Days
• Field of Search: 359/63, 359/73, 359/67, 359/68, 359/102, 359/93, 359/500
• US Class Current: 349/118
• 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 1/1397 the twist being substantially higher than 90°, e.g. STN-, SBE-, OMI-LC cells

Abstract

The liquid crystal display device of the present invention comprises a liquid crystal layer of a nematic liquid crystal having positive dielectric anisotropy and including a chiral material, the liquid crystal layer being interposed between a pair of substrates with transparent electrodes each having an aligning layer which are arranged substantially in parallel to provide a twist angle of 160°-300°, a driving means to apply a voltage across the electrodes attached to the substrates which interpose the liquid crystal layer, a pair of polarizing plates arranged outside the liquid crystal layer, and at least one birefringent plate provided between the liquid crystal layer and the polarizing plate at at least one side of the liquid crystal layer, wherein the product Δn₁ ·d, of the anisotropy of refractive index Δn, of liquid crystal molecules in the liquid crystal layer and the thickness d, of the liquid crystal layer is in a range of 0.4-1.5 μm, and three main refractive indices n_x, n_y and n_z of the birefringent plate are in a relation of n_x ≧n_z >n_y where n_x and n_y respectively represent the refractive indices in the direction of film plane of the birefringent plate (provided n_x >n_y) and n_z represents the refractive index in the direction of film thickness of the birefringent plate.

Claims

1. A liquid crystal display device comprising a background portion and a picture element portion which comprises:

a) a liquid crystal layer of a nematic liquid crystal having positive dielectric anisotropy and including a chiral material, wherein the product Δ

n₁ ·

d₁ of the anisotropy of refractive index Δ

n₁ of liquid crystal molecules in the liquid crystal layer and the thickness d₁ of the liquid crystal layer is in a range of 0.4-1.5 μ

m,

b) said liquid crystal layer being interposed between a pair of substrates with transparent electrodes each having an aligning layer which are arranged substantially in parallel to provide a twist angle of 160°

-300°

,

c) a driving means to apply a voltage across the electrodes attached to said substrates, and

d) a pair of polarizing plates arranged outside the liquid crystal layer, wherein

at least one birefringent plate is provided between the liquid crystal layer and the polarizing plate at at least one side of said liquid crystal layer, and three main refractive indices n_x, n_y and n_z of the birefringent plate are in relation of n_x >

n_z >

n_y wherein n_x, n_y respectively represent the refractive indices in the direction of film plane of the birefringent plate (provided n_x >

n_y) and n_z represents the refractive index in the direction of film thickness of the birefringent plate, and wherein

a light shielding film is provided to cover the background so that a background portion except for pixel portions is in a light shielding state.

2. The liquid crystal device according to claim 1, wherein said birefringent plate is arranged between the liquid crystal layer and the polarizing plate at one side of the liquid crystal layer.

3. The liquid crystal display device according to claim 1, wherein said birefringent plate is arranged between the liquid crystal layer and the polarizing plate at each side of the liquid crystal layer.

4. The liquid crystal display device according to claim 1, wherein the refractive index of the birefringent plate is (n_z -n_y)/(n_x -n_y)>

0.1.