Reflection type liquid crystal display with selective reflecting means

• US 5,408,344 A
• Filed: 01/11/1994
• Issued: 04/18/1995
• Est. Priority Date: 01/11/1993
• Status: Expired due to Term

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Takahashi, Hiroyuki, Takiguchi, Yasuyuki, Kanemoto, Akihiko
• Primary Examiner(s): Gross, Anita Pellman
• Assistant Examiner(s): MILLER, CHARLES LELAND
• Application Number:
  US08/179,681
• Time in Patent Office: 462 Days
• Field of Search: 359/40, 359/41, 359/51, 359/66, 359/70, 359/71, 359/530, 359/542, 359/454, 359/455, 359/459, 359/605, 359/606, 359/607
• US Class Current: 349/57
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 1/133553 Reflecting elements associated to illuminating devices G02F1/133605

Abstract

A reflection type liquid crystal display (LCD) made up of polymer dispersion type display elements each having a liquid crystal dispersion film in which liquid crystals are dispersed in a tridimensional microstructure implemented by a polymer or similar resin. Selective light reflecting or diffusing means introduces forwardly scattered light components from scattering pixels again into a liquid crystal layer without effecting non-scattering pixels. Hence, high reflection intensity and, therefore, high contrast is achieved. A light source unit is positioned such that at least a part of illumination light is reflected in the reflection angle range of the selective reflecting means. Hence, forward scattering with high scattered light intensity can be used, insuring extremely light white display.

Claims

1. A reflection type liquid crystal display (LCD) having a cell made up of a pair of spaced light transmitting substrates each having transparent electrodes on an inner surface thereof, and a dispersion layer of liquid crystals held between said pair of substrates, and using a phenomenon that said dispersion layer turns to a transmitting state when applied with a voltage or to a scattering state when not applied with a voltage, said LCD comprising:

at least one of selective light reflecting means and selective light diffusing means having angle selectivity and provided on a rear of said dispersion layer with respect to a viewer for transmitting light incident thereto from a viewer'"'"'s side at angles lying in a particular range and reflecting and scattering, respectively, light incident at angles lying in the other range; and

light absorbing means provided on a rear of said at least one of said selective light reflecting means and said selective light diffusing means for absorbing incident light.

2. An LCD as claimed in claim 1, wherein said dispersion layer comprises a liquid crystal region and a support dividing said liquid crystal region minutely.

3. An LCD as claimed in claim 1, wherein said selective light diffusing means reflects, when said dispersion layer is in the transparent state, the light in an angular range which causes said light to leave said LCD in a direction not visible to the viewer.

4. An LCD as claimed in claim 1, wherein said selective reflecting means reflects, when said dispersion layer is in the transparent state, the light in an angular range which causes said light to leave said LCD in a direction not visible to the viewer.

5. An LCD as claimed in claim 1, wherein said selective reflecting means comprises a prism array sheet having a group of prisms formed on a surface of a flat transparent substrate.

6. An LCD as claimed in claim 5, wherein said group of prisms each has a substantially triangular cross-section and an apex angle of 30°

to 150°

.

7. An LCD as claimed in claim 5, wherein said group of prisms have a pitch which is less than twice a pixel pitch of said cell.

8. An LCD as claimed in claim 5, wherein a distance between said dispersion layer and said prism array sheet is less than five times a pixel pitch of said cell.

9. An LCD as claimed in claim 5, wherein said prism array sheet comprises a plurality of arrays of elongate prisms extending in one direction, said plurality of arrays extending in a direction substantially coincident with a lengthwise direction, said prism array sheet being oriented such that a lengthwise direction of said prisms substantially does not coincide with a right-and-left direction as seen from a viewer'"'"'s side.

10. An LCD as claimed in claim 9, wherein said prism array sheet is oriented such that the lengthwise direction of said prisms is substantially coincident with an up-and-down direction or a front-and-rear direction as viewed from the viewer'"'"'s side.

11. An LCD as claimed in claim 5, wherein said prism array sheet is rotatable such that a lengthwise direction of said prisms coincides with a direction matching a lighting environment.

12. An LCD as claimed in claim 5, wherein said prism array sheet has angle selectivity differing from one portion to another portion of said prism array sheet.

13. An LCD as claimed in claim 5, wherein said prism array sheet has angle selectivity implemented by a difference in prism structure.

14. An LCD as claimed in claim 13, wherein the difference in prism structure is provided by at least one of an inclination of a triangular prism structure and an inclination of a bottom of the prism.

15. An LCD as claimed in claim 1, wherein said selective light reflecting means comprises a lenticular lens array sheet having a group of lenses each having a substantially semicircular cross-section.

16. An LCD as claimed in claim 5, wherein said selective light reflecting means comprises prisms arranged bidimensionally.

17. An LCD as claimed in claim 5, wherein said selective light reflecting means has a refractive index of 1.4 to 2.0.

18. An LCD as claimed in claim 1, further comprising light source means for illuminating said selective light reflecting means.