Reflective colour display device

• US 20060232731A1
• Filed: 03/23/2006
• Published: 10/19/2006
• Est. Priority Date: 03/29/2005
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Sikharulidze, David
• Granted Patent: US 7,633,581 B2
• Time in Patent Office: Days
• US Class Current: 349/113
• 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
• CPC Class Codes: G02F 1/167 by electrophoresis

Abstract

A reflective colour display device comprising a display element including two opposed cell walls enclosing a layer of an electro-optic material, each cell wall being provided with at least one electrode on an inner surface thereof for applying an electric field across at least some of the electro-optic material, and a selective reflector on one of said cell walls, wherein the electro-optic material is electrically-switchable between a first state in which the display element will diffusely reflect substantially all wavelengths of visible light transmitted by the selective reflector, and a second state in which the display element will reflect light transmitted by the selective reflector at a substantially lower intensity than it does when the electro-optic material is in the first state.

Claims

1. A reflective colour display device comprising:

a) a display element including two opposed cell walls enclosing a layer of an electro-optic material, each cell wall being provided with at least one electrode on an inner surface thereof for applying an electric field across at least some of the electro-optic material, and

b) a selective reflector on one of said cell walls, said selective reflector being distinct from said electro-optic material;

wherein the electro-optic material is electrically-switchable between a first state in which the display element will diffusely reflect substantially all wavelengths of visible light transmitted by the selective reflector, and a second state in which the display element will absorb substantially all visible light transmitted by the selective reflector.

2. A device according to claim 1, wherein the selective reflector is a film or layer of a cholesteric polymer material.

3. A device according to claim 1, wherein the selective reflector comprises a plurality of different films or layers side by side, each different film or layer capable of selectively reflecting a different wavelength band.

4. A device according to claim 1, wherein the electro-optic material is a composition comprising a mixture of a dark-dyed fluid and light-coloured pigment particles.

5. A device according to claim 4, wherein said fluid is a liquid crystal material.

6. A device according to claim 5, wherein the dye is a non-pleochroic dye and wherein the device further comprises at least one surface alignment on an inner surface of a cell wall for inducing a local homeotropic alignment of said liquid crystal material.

7. A device according to claim 4, wherein said pigment is TiO₂.

8. A device according to claims 4, wherein said pigment has a particle size in the range 100-500 μ

m.

9. A device according to claim 4, wherein said pigment comprises 5-50% w/w of said composition.

10. A device according to claims 1, wherein the electro-optic material is a liquid crystal material.

11. A device according to claim 10, wherein the display element has a dark backplane and the liquid crystal material is switchable between a first diffuse reflective state in which it will reflect substantially all wavelengths of visible light transmitted by the selective reflector, and a second transmissive state in which substantially all light transmitted by the selective reflector is absorbed by the dark backplane.

12. A device according to claim 11, wherein the liquid crystal material is dispersed as small droplets in a polymer matrix.

13. A device according to claim 11, wherein the liquid crystal material is a cholesteric material which scatters light in the absence of an applied electric field.

14. A device according to claim 11, wherein the liquid crystal material is a nematic liquid crystal which substantially transmits light in the absence of an applied field but which scatters light when a suitable electric field is applied so that the display element is capable of operating in a dynamic scattering mode.

15. A device according to claim 10, wherein the display element has a white backplane and the liquid crystal material has a pleochroic dye dissolved therein;

the liquid crystal material being switchable between a homeotropic state in which molecules of the liquid crystal material align substantially normally to the plane of the cell walls and in which most light transmitted by the selective reflector is transmitted to the white backplane, and a state in which molecules of the pleochroic dye absorb substantially all of the light transmitted by the selective reflector.

16. A device according to claim 15, wherein the liquid crystal material is a polymer-dispersed liquid crystal material (PDLC).

17. A device according to claim 15, wherein the liquid crystal material is a cholesteric material.

19. A reflective colour display device comprising a selective reflector mounted on a display element that is electrically-switchable between a first diffuse reflective state in which it will reflect substantially all wavelengths of visible light transmitted by the selective reflector, and a second state in which the display element will reflect substantially less light than it does in the first state.