CHIRAL NEMATIC PHOTO DISPLAYS

• US 20070237906A1
• Filed: 06/13/2007
• Published: 10/11/2007
• Est. Priority Date: 01/28/2004
• Status: Active Grant

• Current Assignee: Kent Displays Incorporated, Kent State University
• Original Assignee: Kent Displays Incorporated, Kent State University
• Inventors: Li, Quan, Venkataraman, Nithya, Shiyanovskaya, Irina, Khan, Asad, Doane, J., Green, Lisa
• Granted Patent: US 8,329,058 B2
• Time in Patent Office: Days
• US Class Current: 428/1.200
• 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: C09K 2323/03 Viewing layer characterised by chemical composition
• CPC Class Codes: G02F 1/133305 Flexible substrates, e.g. plastics, organic film
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals

Abstract

A photodisplay device in which an optically addressed image can be viewed indefinitely, erased and readdressed with a new image is disclosed. Optically responsive reversible photochiral materials are incorporated into a bistable cholesteric liquid crystal in an electrooptic display cell. A high resolution image exposed on the cell is fixed by a low voltage pulse to unpatterned electrodes and can be, at a later time, erased with a high voltage pulse.

Claims

1. A chiral nematic liquid crystal photodisplay comprising:

a liquid crystal layer including cholesteric liquid crystal material, said liquid crystal material comprising nematic liquid crystal and at least one photosensitive chiral additive, wherein said photosensitive chiral additive is adapted to change a reflective wavelength of said liquid crystal layer at exposed regions at which addressing electromagnetic radiation is incident on said liquid crystal layer thereby producing a planar image in a planar texture of said liquid crystal layer;

electrically conductive layers flanking said liquid crystal layer; and

electrical addressing means for applying an electric field to said liquid crystal layer between said conductive layers, wherein said electrical addressing means applies the electric field at a magnitude that switches the exposed regions to a focal conic texture producing a fixed negative image.

3. The photodisplay of claim 1 wherein said electrical addressing means applies a voltage pulse to said conductive layers of a magnitude that switches said exposed regions to the focal conic texture producing said fixed negative image.

5. The photodisplay of claim 1 wherein said planar image is erased from the planar texture by thermal relaxation of the exposed photosensitive chiral additive.

7. The photodisplay of claim 1 wherein said electrical addressing means applies a voltage pulse to said conductive layers that returns said fixed negative image to said planar image.

9. The photodisplay of claim 7 wherein said voltage pulse is of sufficient magnitude to drive all of the chiral nematic material of said display to a homeotropic state during application of the pulse and into the planar texture following the pulse.

11. The photodisplay of claim 1 wherein the planar image is erased from the planar texture by exposure of visible light to the photosensitive chiral additive.

13. The photodisplay of claim 1 wherein said addressing radiation is ultraviolet light.

15. The photodisplay of claim 1 wherein said electric field is applied in the form of a voltage pulse of a magnitude that places all of said liquid crystal material of said display in one of the focal conic texture or a homeotropic state resulting in said planar image not being displayed, and said electric field is applied in the form of a voltage pulse of a magnitude that places all of said liquid crystal material of said display in the planar texture resulting in said planar image being displayed.

17. The photodisplay of claim 1 comprising a substrate, one of said conductive layers being disposed between said substrate and said liquid crystal layer.

18. The photodisplay of claim 17 wherein said substrate is flexible and selected from the group consisting of a polymer, fabric, electrotextile, a metal foil, a flexible printed circuit board, a flexible graphite foil sheet, a flexible composite or nanocomposite film, a flexible opto-electronic device, a flexible glass sheet, a nanofiber fabric and combinations thereof.

19. The photodisplay of claim 18 comprising a second substrate that is flexible, another of said conductive layers being disposed between said second substrate and said liquid crystal layer.

23. The photodisplay of claim 1 wherein said photosensitive chiral additive comprises the following structure:

wherein R₁ and R₂ may independently be a straight chain or branched chain alkyl group which each contains at least one substituent selected from the group consisting of;

any chiral center, halogen, NO₂, CN, O, S, C═

C, C≡

C, an aromatic group, a polyaromatic group, a heterocyclic group, a cycloalkyl group, and combinations thereof.

24. The photodisplay of claim 1 wherein said photosensitive chiral additive comprises the following structure:

wherein R₁ and R₂ may independently be a straight chain or branched chain alkyl group which each contains at least one substituent selected from the group consisting of;

any chiral center, halogen, NO₂, CN, O, S, C═

C, C≡

C, an aromatic group, a polyaromatic group, a heterocyclic group, a cycloalkyl group, and combinations thereof.

27. A device comprising the photodisplay of claim 1 wherein said device is selected from the group consisting of:

point of sales signs, debit cards, credit cards, name plates, name tags, informational signs, and electronic shelf labels.

29. The photodisplay of claim 1 wherein said liquid crystal layer comprises a dispersion of the liquid crystal material in a polymer matrix.

31. The photodisplay of claim 1 wherein said conductive layers are unpatterned.

2. A chiral nematic liquid crystal photodisplay comprising:

a liquid crystal layer including cholesteric liquid crystal material, said liquid crystal material comprising nematic liquid crystal and at least one photosensitive chiral additive, wherein said photosensitive chiral additive is adapted to change a reflective wavelength of said liquid crystal layer at exposed regions at which addressing electromagnetic radiation is incident on said liquid crystal layer thereby producing a planar image in a planar texture of said liquid crystal layer;

electrically conductive layers flanking said liquid crystal layer; and

electrical addressing means for applying an electric field to said liquid crystal layer between said conductive layers, wherein said electrical addressing means applies the electric field at a magnitude that switches unexposed regions, which are not exposed to said addressing radiation, to a focal conic texture producing a fixed positive image.

4. The photodisplay of claim 2 wherein said electrical addressing means applies a voltage pulse to said conductive layers of a magnitude that switches said unexposed regions to the focal conic texture producing said fixed positive image.

6. The photodisplay of claim 2 wherein said planar image is erased from the planar texture by thermal relaxation of the exposed photosensitive chiral additive.

8. The photodisplay of claim 2 wherein said electrical addressing means applies a voltage pulse to said conductive layers that returns said fixed positive image to said planar image.

10. The photodisplay of claim 8 wherein said voltage pulse is of sufficient magnitude to drive all of the chiral nematic material of said display to a homeotropic state during application of the pulse and into the planar texture following the pulse.

12. The photodisplay of claim 2 wherein the planar image is erased from the planar texture by exposure of visible light to the photosensitive chiral additive.

14. The photodisplay of claim 2 wherein said addressing radiation is ultraviolet light.

16. The photodisplay of claim 2 wherein said electric field is applied in the form of a voltage pulse of a magnitude that places all of said liquid crystal material of said display in one of the focal conic texture or a homeotropic state resulting in said planar image not being displayed, and said electric field is applied in the form of a voltage pulse of a magnitude that places all of said liquid crystal material of said display in the planar texture resulting in said planar image being displayed.

20. The photodisplay of claim 2 comprising a substrate, one of said conductive layers being disposed between said substrate and said liquid crystal layer.

21. The photodisplay of claim 20 wherein said substrate is flexible and selected from the group consisting of a polymer, fabric, electrotextile, a metal foil, a flexible printed circuit board, a flexible graphite foil sheet, a flexible composite or nanocomposite film, a flexible opto-electronic device, a flexible glass sheet, a nanofiber fabric and combinations thereof.

22. The photodisplay of claim 21 comprising a second substrate that is flexible, another of said conductive layers being disposed between said second substrate and said liquid crystal layer.

25. The photodisplay of claim 2 wherein said photosensitive chiral additive comprises the following structure:

wherein R₁ and R₂ may independently be a straight chain or branched chain alkyl group which each contains at least one substituent selected from the group consisting of;

any chiral center, halogen, NO₂, CN, O, S, C═

C, C≡

C, an aromatic group, a polyaromatic group, a heterocyclic group, a cycloalkyl group, and combinations thereof.

26. The photodisplay of claim 2 wherein said photosensitive chiral additive comprises the following structure:

wherein R₁ and R₂ may independently be a straight chain or branched chain alkyl group which each contains at least one substituent selected from the group consisting of;

any chiral center, halogen, NO₂, CN, O, S, C═

C, C≡

C, an aromatic group, a polyaromatic group, a heterocyclic group, a cycloalkyl group, and combinations thereof.

28. A device comprising the photodisplay of claim 2 wherein said device is selected from the group consisting of:

point of sales signs, debit cards, credit cards, name plates, name tags, informational signs, and electronic shelf labels.

30. The photodisplay of claim 2 wherein said liquid crystal layer comprises a dispersion of the liquid crystal material in a polymer matrix.

32. The photodisplay of claim 2 wherein said conductive layers are unpatterned.

33. A chiral nematic liquid crystal photodisplay comprising:

a liquid crystal layer including cholesteric liquid crystal material, said liquid crystal material comprising nematic liquid crystal and at least one photosensitive chiral additive;

electrically conductive layers flanking said liquid crystal layer;

electrical addressing means for applying an electric field to said liquid crystal layer between said conductive layers;

a first light filter disposed near a viewing side of said display upstream of said liquid crystal layer relative to a direction of incident light used to view the display, said first light filter being able to absorb incident visible and ultraviolet light, said first light filter being movable between a closed position that covers said liquid crystal layer and an open position in which said liquid crystal layer is uncovered and in which regions of said liquid crystal layer are exposed to addressing electromagnetic radiation, wherein said photosensitive chiral additive is adapted to change a reflective wavelength of said liquid crystal layer at said exposed regions thereby producing a planar image in the planar texture of said liquid crystal layer; and

a second light filter disposed on a side opposite the viewing side of the display downstream of said liquid crystal layer that absorbs visible light that passes through said liquid crystal layer.

34. The photodisplay of claim 33 wherein said addressing radiation travels in the direction of incident light to the viewing side of the display and said first light filter possesses an absorption spectrum sufficient to prevent degradation of said planar image by the incident light.

35. The photodisplay of claim 33 wherein said second light filter absorbs all visible light that passes said first filter and said liquid crystal layer such that said second filter appears black.

36. The photodisplay of claim 33 wherein said addressing radiation travels opposite to the direction of incident light to the side opposite the viewing side of the display and said second filter permits transmission of said addressing radiation to said liquid crystal layer.

37. The photodisplay of claim 33 wherein said second filter absorbs light of a particular color.

38. The photodisplay of claim 33 wherein said electrical addressing means applies a voltage pulse to said conductive layers of a magnitude that switches unexposed regions, which are not exposed to said addressing radiation, to a focal conic texture producing a fixed positive image.

39. The photo display of claim 33 wherein said electrical addressing means applies a voltage pulse to said conductive layers of a magnitude that switches said exposed regions to a focal conic texture producing a fixed negative image.

40. The photodisplay of claim 39 wherein said electrical addressing means applies a voltage pulse to said conductive layers that returns said fixed negative image to said planar image.

41. The photodisplay of claim 38 wherein said electrical addressing means applies a voltage pulse to said conductive layers that returns said fixed positive image to said planar image.

42. The photodisplay of claim 33 wherein said addressing radiation is ultraviolet light.

43. The photodisplay of claim 33 wherein said electric field is applied in the form of a voltage pulse of a magnitude that places all of said liquid crystal material of said display in one of a focal conic texture or a homeotropic state resulting in said planar image not being displayed, and said electric field is applied in the form of a voltage pulse of a magnitude that places all of said liquid crystal material of said display in the planar texture resulting in said planar image being displayed.

44. A device comprising the photodisplay of claim 33 wherein said device is selected from the group consisting of:

point of sales signs, debit cards, credit cards, name plates, name tags, informational signs, and electronic shelf labels.

45. The photodisplay of claim 33 wherein said liquid crystal layer comprises a dispersion of the liquid crystal material in a polymer matrix.

46. A chiral nematic liquid crystal photodisplay apparatus comprising:

said photodisplay of claim 33;

and

optical addressing means for addressing said exposed regions of said liquid crystal layer with said addressing electromagnetic radiation of a particular wavelength.

47. The photodisplay apparatus of claim 46 wherein said optical addressing means is a device including a component selected from the group consisting of:

a light emitting diode, an organic light emitting diode, a fluorescent display and a backlit liquid crystal display.

48. The photodisplay apparatus of claim 46 comprising a mask including an image, said mask being interposed between said optical addressing means and said photodisplay for producing said planar image on said display.