Reflection liquid crystal display element

• US 6,480,251 B1
• Filed: 01/23/2001
• Issued: 11/12/2002
• Est. Priority Date: 05/28/1998
• Status: Expired due to Fees

• Current Assignee: Toshiba Matsushita Display Technology (Japan Display Incorporated)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Ogawa, Tetsu, Sekime, Tomoaki, Iwai, Yoshio, Yamaguchi, Hisanori
• Primary Examiner(s): Ton, Toan
• Assistant Examiner(s): NGUYEN, HOAN C
• Application Number:
  US09/701,099
• Time in Patent Office: 658 Days
• Field of Search: 349/113, 349/115, 349/117, 349/118, 349/119
• US Class Current: 349/119
• CPC Class Codes: G02F 1/133531 characterised by the arrangement of polariser or analyser axes
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• CPC Class Codes: G02F 1/1396 the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell G02F1/141 takes precedence
• CPC Class Codes: G02F 2203/02 reflective
• CPC Class Codes: G02F 2413/08 with a particular optical axis orientation
• CPC Class Codes: G02F 2413/12 Biaxial compensators
• CPC Class Codes: G02F 2413/13 Positive birefingence

Abstract

In a reflective liquid crystal display device with a single polarizing film and two retardation films located in between the polarizing film and liquid crystal cell, the angle of twist of nematic liquid crystal is 45°˜90°, the product of the birefringence of the liquid crystal and the thickness of the liquid crystal layer is 0.20 μm˜0.30 μm, the retardation value of the retardation film on the polarizing film side is 0.13 μm˜0.18 μm, the retardation value of the retardation film on the liquid crystal cell side is 0.13 μm˜0.18 μm, and the Z coefficient of each of two retardation films is 0.3˜1.0. This invention is featured by the following optical relations, that is, Ø_P 75°˜195°, Ø_P−Ø_F1, 105°˜115°, and Ø_P−Ø_F2, 165°˜175°, where Ø_P, Ø_F1 and Ø_F2 are angles formed by the reference line and respectively the direction of the absorption axis of the polarizing film, the direction of the slow axis of the retardation film on the polarizing film side, and the direction of the slow axis of the retardation film on the liquid crystal cell side. With the foregoing construction, a high contrast display of bright achromatic white and achromatic black is achieved.

Claims

1. A reflective liquid crystal display device comprising;

a) a liquid crystal cell formed by injecting a nematic liquid crystal in between a first and a second substrates;

b) a polarizing film disposed on the first substrate of said liquid crystal cell;

c) two retardation films disposed in between said polarizing film and said liquid crystal cell; and

d) a light reflecting means disposed on the second substrate,

wherein a twist angle of said nematic liquid crystal Ω

_LC is 45°

˜

90°

, a product Δ

_LC·

d_LC is 0.20 μ

m˜

0.30 μ

m where Δ

n_LC and d _LC are respectively birefiringence of said nematic liquid crystal and thickness of a liquid crystal layer, a retardation value of said retardation film on said polarizing film side R_F1 is 0.13 μ

m˜

0.18 μ

m, a retardation value of said retardation film on said liquid crystal cell side R_F2 is 0.13 μ

m˜

0.18 μ

m, and the Z coefficient, Q_Z of each of said two retardation films is 0.3˜

1.0,

wherein when a bisector of a larger angle between angles which are formed by orientation directions respectively of liquid crystal molecules closest to said first substrate and liquid crystal molecules closest to said second substrate is set as a reference line inside the substrates, and when a direction, in which said nematic liquid crystal is twisted viewed from the first substrate to the second substrate, is positive,

Ø

_P is 75°

˜

195°

, Ø

_P−

Ø

_F1, 105°

˜

115°

, and Ø

_P−

Ø

_F2, 165°

˜

175°

,

where Ø

_P is an angle formed by the reference line and a direction of an absorption axis of said polarizing film, Ø

_F1 is an angle formed by the reference line and a direction of a slow axis of said retardation film on said polarizing film side, and Ø

_F2 is an angle formed by the reference line and a direction of a slow axis of said retardation film on said liquid crystal cell side, and the aforementioned Q_Z is a coefficient defined as

2. The reflective liquid crystal display device of claim 1, wherein the angle Ø

_P, formed by the reference line and the absorption axis of said polarizing film, is one of 90°

˜

120° and

150°

˜

180°

.

5. The reflective liquid crystal display device of one of claims 1˜

4, wherein the twist angle Ω

_LC of said nematic liquid crystal is 60°

˜

65°

.

6. The reflective liquid crystal display device of one of claims 1˜

4, wherein the Z coefficient, Q_Z of said retardation film on said polarizing film side is 0.3˜

0.7.

7. The reflective liquid crystal display device of one of claims 1˜

4, wherein the Z coefficient, Q_Z of each of said two retardation films is 0.3˜

0.7.

8. The reflective liquid crystal display device of one of claims 1˜

4, further comprising a scattering film on said first substrate.

9. The reflective liquid crystal display device of claim 8, wherein said scattering film is disposed in between said retardation films and the substrate.

10. The reflective liquid crystal display device of claim 8, wherein said scattering film is a front scattering film.

11. The reflective liquid crystal display device of one of claims 1˜

4, wherein said light reflecting means is a metallic electrode including at least one of aluminum and silver as a component.

12. The reflective liquid crystal display device of claim 11, wherein said metallic electrode has a mirror-like surface.

13. The reflective liquid crystal display device of claim 11, wherein a scattering film is disposed on said metallic electrode.

14. The reflective liquid crystal display device of claim 11, wherein said metallic electrode has an uneven surface with angles of slopes being 3°

˜

12°

on average.

15. The reflective liquid crystal display device of one of claims 1˜

4, wherein said second substrate is a transparent substrate, and on outer surface of which said light reflecting means is disposed.

16. The reflective liquid crystal display device of one of claim 15, wherein a layer of air is provided between said transparent substrate and said light reflecting means.

17. The reflective liquid crystal display device of one of claims 1˜

4, wherein a color filter is disposed on one of the substrates.

18. The reflective liquid crystal display device of one of claims 1˜

4, wherein a nonlinear switching device is disposed on said second substrate.

19. The reflective liquid crystal display device of claim 18, wherein a insulative flattened film is formed on said nonlinear device, and through a contact hole formed on said flattened film, said nonlinear switching device and an electrode on said second substrate side are interconnected.

20. The reflective liquid crystal display device of one of claims 1˜

4, wherein said retardation films are made with polycarbonate.

3. A reflective liquid crystal display device comprising;

a) a liquid crystal cell formed by injecting a nematic liquid crystal in between a first and a second substrates;

b) a polarizing film disposed on said first substrate of said liquid crystal cell;

c) two retardation films disposed in between said polarizing film and said liquid crystal cell; and

d) a light reflecting means disposed on said second substrate,

wherein a twist angle of said nematic liquid crystal Ω

_LC is 45°

˜

90°

, a product Δ

n_LC·

d_LC is 0.20 μ

m˜

0.30 μ

m where Δ

n_LC and d _LC are respectively birefringence of said nematic liquid crystal and thickness of a liquid crystal layer, a retardation value of said retardation film on said polarizing film side R_F1 is 0.13μ

m˜

0.18 μ

m, a retardation value of said retardation film on said liquid crystal cell side R_F2 is 0.13 μ

m˜

0.18 μ

m, and the Z coefficient, Q_Z of each of said two retardation film is 0.3˜

1.0,

wherein when a bisector of a larger of the angle formed by an orientation direction of liquid crystal molecules closest to said first substrate and an orientation direction of liquid crystal molecules closest to said second substrate is set as a reference line, and when a direction, in which said nematic liquid crystal is twisted from said first substrate to said second substrate, viewed from the side of said first substrate, is defined positive, Ø

_P is −

15°

˜

105°

, Ø

_P−

Ø

_F1, −

105°

˜

−

115°

, and Ø

_P−

Ø

_F2, −

165°

˜

−

175°

,

where Ø

_P is an angle formed by the reference line and a direction of an absorption axis of said polarizing film, Ø

_F1 is an angle formed by the reference line and a direction of a slow axis of said retardation film on said polarizing film side, and Ø

_F2 is an angle formed by the reference line and a direction of a slow axis of said retardation film on said liquid crystal cell side, and the aforementioned Q_Z is a coefficient defined as

4. The reflective liquid crystal display device of claim 3, wherein the angle Ø

_P, formed by the reference line and the absorption axis of said polarizing film is one of 0°

˜

30° and

60°

˜

90°

.