Stacked color photodisplay

• US 20080309598A1
• Filed: 07/01/2008
• Published: 12/18/2008
• Est. Priority Date: 01/28/2004
• Status: Active Grant

• Current Assignee: Kent Displays Incorporated
• Original Assignee: Kent Displays Incorporated
• Inventors: Venkataraman, Nithya, Doane, J. William, Khan, Asad A., Montbach, Erica
• Granted Patent: US 8,199,086 B2
• Time in Patent Office: Days
• US Class Current: 345/87
• CPC Class Codes: C09K 2323/00 Functional layers of liquid crystal optical display excluding electroactive liquid crystal layer characterised by chemical composition
• CPC Class Codes: C09K 2323/02 Alignment layer characterised by chemical composition
• CPC Class Codes: G02F 1/13475 in which at least one liquid crystal cell or layer is doped with a pleochroic dye, e.g. GH-LC cell G02F1/13476 takes precedence
• CPC Class Codes: G02F 1/13476 in which at least one liquid crystal cell or layer assumes a scattering state
• CPC Class Codes: G02F 1/13478 based on selective reflection

Abstract

The invention comprises a stacked color photodisplay apparatus using a photosensitive cholesteric liquid crystalline material on which an image can be optically addressed, retained without degradation for an indefinite period of time, electrically erased and a new image addressed. This is similar to a photographic film except that the photodisplay film can be used over and over again similar to digital display but without the cost of addressing electronics. Included is a device for enhancing the brightness of the image and electrooptical devices for optically writing digital images on the photodisplay. Each cell in the stack can be selectively addressed with a different optical image such as the red, green and blue components of a color digital image.

Claims

1. A stacked photodisplay comprising:

at least first and second layers of cholesteric liquid crystal material stacked in a fixed relation to each other including a first and a second photosensitive chiral additive, respectively;

electrically conductive layers flanking each of said first and second liquid crystal layers;

a light absorbing layer positioned to absorb light passing through said first and second layers;

wherein said first liquid crystal layer includes a first fixed image portion and said second liquid crystal layer includes a second fixed image portion that is different than said first fixed image portion, said first and second fixed image portions including a focal conic texture that is stable in an absence of an electric field and a planar texture, wherein said first and second fixed image portions combine to form an image on said photodisplay.

2. The photodisplay of claim 1 comprising:

a third layer of cholesteric liquid crystal material stacked in a fixed relation to said first and second liquid crystal layers, and including a third photosensitive chiral additive;

electrically conductive layers flanking said third liquid crystal layer;

said light absorbing layer absorbing light passing through said first, second and third liquid crystal layers;

wherein said third liquid crystal layer includes a third fixed image portion that is different than said first and second fixed image portions, wherein said first, second and third fixed image portions combine to form an image on said photodisplay.

3. The photodisplay of claim 1 wherein said first cholesteric liquid crystal material has a pitch length effective to reflect light of a first color in ambient light and said second cholesteric liquid crystal material has a pitch length effective to reflect light of a second color in ambient light that is different than said first color.

4. The photodisplay of claim 2 wherein said first cholesteric liquid crystal material has a pitch length effective to reflect light of a first color in ambient light, said second cholesteric liquid crystal material has a pitch length effective to reflect light of a second color in ambient light and said third cholesteric liquid crystal material has a pitch length effective to reflect light of a third color in ambient light, wherein said first, second and third colors are different from each other.

5. The photodisplay of claim 4 wherein said first, second and third colors are red, green and blue in any order.

6. The photodisplay of claim 1 comprising at least one substrate over which said first and second liquid crystal layers are disposed in the fixed relation.

7. The photodisplay of claim 2 comprising at least one substrate over which said first, second and third liquid crystal layers are disposed in the fixed relation.

8. The photodisplay of claim 6 wherein said substrate is flexible and comprises a transparent polymer or transparent flexible glass.

9. The photodisplay of claim 7 comprising a plurality of said substrates comprised of transparent polymer or transparent flexible glass, including said substrates forming outer surfaces of said photodisplay and one or two of said substrates disposed between adjacent said liquid crystal layers.

10. The photodisplay of claim 1 wherein each of said liquid crystal layers comprises a dispersion of the liquid crystal material in a polymer matrix.

11. An article comprising the photodisplay of claim 1, wherein said article is selected from the group consisting of:

point of sales signs, debit cards, stored value cards, smart cards, credit cards, name plates, name tags, security badges, identification badges, informational signs, electronic shelf labels and combinations thereof.

12. An apparatus for writing on a photodisplay, the photodisplay including two or three layers of cholesteric liquid crystal material stacked relative to each other each including a photosensitive chiral additive, electrically conductive layers flanking each of said liquid crystal layers and a light absorbing layer positioned to absorb light passing through said liquid crystal layers, said apparatus comprising:

a controller adapted to provide electronic image data signals corresponding to image data and to provide electronic light source signals;

an electronic display device including a plurality of pixels adapted to form images when said pixels are in ON or OFF states;

a display driver adapted to supply voltage pulses to said display device in response to said image data signals from said controller effective to independently place said pixels of said display device in said ON or OFF states;

a light source adapted to be energized or de-energized in response to said light source signals from said controller effective to project ultraviolet light through said display device onto said photodisplay;

wherein when said light source is energized to produce ultraviolet light and said display driver applies said voltage pulses forming the image on said display device the ultraviolet light passing through the image of said display device addresses said photodisplay with an image portion formed of optically addressed regions at a first twisting power and optically unaddressed regions at a second twisting power; and

a pulse driver adapted to apply fixing voltage pulses to said electrically conductive layers flanking a selected one of said liquid crystal layers effective to form a fixed image portion by placing one of said optically addressed or optically unaddressed regions of said selected layer in a focal conic texture that is stable in an absence of an electric field and the other of said optically addressed or optically unaddressed regions of said selected layer in a planar texture, said pulse driver being further adapted to apply erasing pulses that erase said fixed images from said photodisplay,

wherein said light source can be energized to apply visible light to said photodisplay effective to erase all images from said photodisplay except for said fixed image portions.

13. The apparatus of claim 12 wherein said display device is a backlit liquid crystal display.

14. The apparatus of claim 12 including a computer for processing said electronic image data used by said controller.

15. A method of optically writing on a stacked color photodisplay comprising

a) providing a photodisplay including two or three layers of cholesteric liquid crystal material stacked on each other, said liquid crystal layers each comprising nematic liquid crystal and a photosensitive chiral additive that is adapted to be reversibly changed between a first twisting power and a second twisting power, said liquid crystal material of said liquid crystal layers having a pitch length effective to reflect light of different predetermined colors in ambient light, electrically conductive layers flanking each of said liquid crystal layers, and a light absorbing layer that absorbs light passing through said liquid crystal layers;

b) projecting electromagnetic radiation to address said photodisplay with an image portion formed of optically addressed regions where said photosensitive additives are at said first twisting power and optically unaddressed regions where said photosensitive additives are at said second twisting power;

c) applying fixing voltage pulses to said electrically conductive layers flanking a selected one of said liquid crystal layers effective to form a fixed image portion by placing one of said optically addressed or optically unaddressed regions of said selected layer in a focal conic texture that is stable in an absence of an electric field and the other of said optically addressed or optically unaddressed regions of said selected layer in a planar texture;

d) erasing all images from said photodisplay except for said fixed image portions; and

e) repeating steps c) and d) until said photodisplay reflects a fixed image comprising an additive mixture of two or three different said fixed image portions each being at said predetermined colors.

16. The method of claim 15 comprising applying erasing voltage pulses to the conductive layers effective to place all of said liquid crystal layers in an all planar texture.

17. The method of claim 15 wherein said fixing voltage pulses places the optically addressed regions of said selected liquid crystal layer in said focal conic texture and said optically unaddressed regions of said selected liquid crystal layer in said planar texture producing a negative said fixed image portion.

18. The method of claim 15 wherein said fixing voltage pulses places the optically unaddressed regions of said selected liquid crystal layer in said focal conic texture and said optically addressed regions of said liquid crystal layer in said planar texture producing a positive said fixed image portion.

19. The method of claim 15 wherein step d) is carried out by applying visible light to said photodisplay without said image mask.

20. The method of claim 15 wherein step d) is carried out by applying heat to said photodisplay without said image mask.

21. The method of claim 19 wherein said application of said visible light further returns each said fixed image portion to said predetermined color.

22. The method of claim 19 wherein said application of said heat further returns each said fixed image portion to said predetermined color.

23. The method of claim 15 wherein said image mask is a digital image from a liquid crystal display.

24. The method of claim 15 carried out on said photodisplay as a component of an article selected from the group consisting of:

point of sales signs, debit cards, stored value cards, smart cards, credit cards, name plates, name tags, security badges, identification badges, informational signs, electronic shelf labels and combinations thereof.

25. The method of claim 15 comprising three of said liquid crystal layers, wherein said predetermined colors are blue, green and red in any order.

26. The method of claim 15 wherein photosensitive additives are reversed between said twisting powers using as said electromagnetic radiation visible or ultraviolet light.

27. The method of claim 15 wherein photosensitive additives are reversed between said twisting powers using as said electromagnetic radiation ultraviolet light or electromagnetic radiation without ultraviolet light.

28. The method of claim 15 wherein photosensitive additives are reversed between said twisting powers using as said electromagnetic radiation or heat.