Polymer stabilized black-white cholesteric reflective display

• US 5,847,798 A
• Filed: 05/06/1997
• Issued: 12/08/1998
• Est. Priority Date: 05/02/1991
• Status: Expired due to Term

• Current Assignee: Kent State University
• Original Assignee: Kent State University
• Inventors: Ma, Ruiqing, Yang, Deng-Ke
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Parker, Kenneth
• Application Number:
  US08/851,673
• Time in Patent Office: 581 Days
• Field of Search: 349/169, 349/115, 349/88, 349/168
• US Class Current: 349/169
• CPC Class Codes: C09K 19/02 characterised by optical, electrical or physical properties of the components, in general
• CPC Class Codes: C09K 19/586 Optically active dopants; chiral dopants
• CPC Class Codes: G02F 1/0131 based on photo-elastic effects, e.g. mechanically induced birefringence
• CPC Class Codes: G02F 1/13718 based on a change of the texture state of a cholesteric liquid crystal
• CPC Class Codes: G02F 1/13775 Polymer-stabilized liquid crystal layers

Abstract

A new liquid crystalline light modulating cell and material are characterized by liquid crystalline light modulating material of liquid crystal and polymer, the liquid crystal being a chiral nematic liquid crystal having positive dielectric anisotropy and including chiral material in an amount effective to form focal conic and twisted planar textures, the polymer being distributed in phase separated domains in the liquid crystal cell in an amount that stabilizes the focal conic and twisted planar textures in the absence of a field and permits the liquid crystal to change textures upon the application of a field. In one embodiment, the material is light scattering in a field-OFF condition and optically clear in a field-ON condition, while in another embodiment, the material is optically clear in a field-OFF condition and light scattering in a field-ON condition. In still another embodiment, the material exhibits stability at zero field in a colored, light reflecting state, a light scattering state and multiple stable reflecting state therebetween, as well as being optically clear in the presence of a field. This embodiment allows for a display with a substantially white background with substantially black characters much like a printed page. In yet another embodiment, the application of mechanical force to the cell changes the material from an optically clear state to a light reflecting state.

Claims

1. A light modulating reflective cell comprising cell wall structure and a polymer containing chiral nematic liquid crystal light modulating material having positive dielectric anisotropy and a pitch length effective to reflect light in the visible spectrum, said cell wall structure and liquid crystal cooperating to form focal conic and twisted planar textures that are stable in the absence of a field, and means for addressing said liquid crystal material, said means adapted to selectively establish a first voltage pulse of a magnitude effective to transform at least a portion of said liquid crystal from a focal conic texture to a light reflecting twisted planar texture, and a second voltage pulse of a magnitude effective to transform at least a portion of said liquid crystal from a light reflecting twisted planar texture to a focal conic texture, wherein the light reflecting twisted planar texture appears substantially white.

2. The cell according to claim 1, wherein the light reflecting twisted planar texture appears substantially white and wherein the focal conic texture is weakly scattering and appears as the same color as a bottom plate coupled to the cell.

3. The cell according to claim 1, wherein an absorption layer is coupled to the cell and the light reflecting twisted planar texture appears substantially white and the focal conic texture appears substantially black.

4. The cell according to claim 1, wherein the polymer is present in an amount of about 3% based on the total weight of the polymer and liquid crystal in the cell.

5. The cell according to claim 4, wherein the polymer is polymerized while the liquid crystal material is in a homeotropic texture.

6. The cell according to claim 4, wherein the liquid crystal material has an intrinsic pitch of about 600 nm.