Twisted nematic type liquid crystal display device having a color polarizer to provide an achromatic or colorless background

• US 4,759,612 A
• Filed: 07/23/1986
• Issued: 07/26/1988
• Est. Priority Date: 08/02/1985
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Nakatsuka, Hideaki, Tojo, Toshihiko, Hasegawa, Shinji, Kando, Yasuhiko, Kanazaki, Mikio
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Mai, Huy V.
• Application Number:
  US06/888,429
• Time in Patent Office: 734 Days
• Field of Search: 350/337, 350/350 F
• US Class Current: 349/97
• CPC Class Codes: G02F 1/133533 Colour selective polarisers G02F1/1347 takes precedence
• CPC Class Codes: G02F 1/1397 the twist being substantially higher than 90°, e.g. STN-, SBE-, OMI-LC cells

Abstract

A liquid crystal display device comprises a liquid crystal layer sandwiched between upper and lower electrode substrates subjected to aligning treatment. The liquid crystal layer includes a nematic liquid crystal added with a chiral material and has a 160°-360° twisted helical structure. A pair of polarizers are disposed adjacent to the electrode substrates with their polarization or absorption axes inclined by respective predetermined angles with respect to the aligning directions of the electrode substrates. At least one of the polarizers is formed by a color polarizer for compensating a wavelength dependence of transmittance (or the coloring due to birefringence) resulting from the anti-coincidence between the polarization or absorption axis of the polarizer and the aligning direction of the electrode substrate, i.e. an optical axis of liquid crystal molecules adjacent to the substrate, so that light emerging from the device becomes approximately achromatic or colorless.

Claims

1. A liquid crystal display device comprising:

a pair of electrode substrates disposed opposite to each other and a liquid crystal layer sandwiched therebetween, said liquid crystal layer including a nematic liquid crystal which has a positive dielectric anisotropy and is added with a chiral material, each of said electrode substrates having a surface structure which aligns molecules of the liquid crystal adjacent to that electrode substrate in a predetermined direction, said liquid crystal layer having a helical structure twisted within a range between 160° and

360°

along a direction of thickness thereof; and

a pair of polarizers disposed adjacent to said electrode substrates at both sides of said liquid crystal layer, each of said polarizers having its polarization axis inclined by a predetermined angle with respect to the liquid crystal molecule aligning direction of the electrode substrate adjacent to that polarizer, at least one of said polarizers being formed by a color polarizer having a spectral characteristic which compensates coloring due to an effect of birefringence resulting from anticoincidence between the polarization axis of the polarizer and the liquid crystal molecule aligning direction of the electrode substrate, whereby light emerging from the device becomes approximately achromatic.

2. A liquid crystal display device according to claim 1, wherein said predetermined angle of inclination of the polarization axis of the polarizer with respect to the liquid crystal molecule aligning direction of the electrode substrate is in a range from 20°

to 70°

.

3. A liquid crystal display device according to claim 2, wherein a product Δ

n·

d of the thickness d (μ

m) of said liquid crystal layer and an optical anisotropy Δ

n of said nematic liquid crystal is in a range from 0.7 μ

m to 1.2 μ

m.

4. A liquid crystal display device according to claim 3, wherein the spectral characteristic of said color polarizer is selected to fall within an area enclosed between curves A and B of FIG. 9.

5. A liquid crystal display device according to claim 2, further comprising a reflector plate disposed adjacent to one of said polarizers, the one polarizer being formed by said color polarizer and the other of said polarizers being formed by a neutral polarizer.

6. A liquid crystal display device according to claim 3, wherein said color polarizer is a magenta polarizer.