Nematic liquid crystal displays for low voltage direct current operation

• US 4,005,928 A
• Filed: 08/01/1973
• Issued: 02/01/1977
• Est. Priority Date: 06/01/1971
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Kmetz, Allan Robert, Creagh, Linda Truitt
• Primary Examiner(s): Bauer, Edward S.
• Application Number:
  US05/384,651
• Time in Patent Office: 1,280 Days
• Field of Search: 350/160 LC, 252/299, 252/408
• US Class Current: 349/195
• CPC Class Codes: B60R 1/088 using a cell of electrically changeable optical characteristic, e.g. liquid-crystal or electrochromic mirrors
• CPC Class Codes: C09K 19/582 Electrically active dopants, e.g. charge transfer agents
• CPC Class Codes: G02F 1/133 Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements arrangements or circuits for control of liquid crystal elements in a matrix, not structurally associated with these elements G09G3/36
• CPC Class Codes: G02F 1/1375 using dynamic scattering

Abstract

A low current d.c. operated liquid crystal display comprises a liquid crystal material composition having impurities therein to effect a current density at 25° C in the range of 0.5 to 3.0 μa/cm². In one aspect of the invention, the liquid crystal composition is provided by purifying the material to 99.95 percent or greater and then adding controlled amounts of preselected impurities so that the total amount of impurities in the liquid crystalline composition comprises 1/2 to 2 percent by weight. In another aspect of the invention, the liquid crystalline material is initially prepared so that it has a purity in the range of 98.0 to 99.5 percent by weight. An adsorbed layer may be formed on the electrodes to enhance electrical charge injection. In one specific embodiment, the liquid crystalline composition is utilized to form a display panel that is directly compatible with 12 volts d.c., which is typically available in automotive vehicles. In a different embodiment, the liquid crystal cell is utilized to form an electronically dimable mirror.

Claims

1. An electro-optic display device comprising in combination:

a first optically transmissive substrate having an optically transmissive and electrically conductive region on one surface thereof,

a second substrate having an electrically conductive region on one surface thereof,

said first and second substrates spaced apart in a substantially parallel relationship such that said conductive regions face one another,

a body of a mesomorphic liquid crystal composition substantially filling the space between said first and second substrates, said mesomorphic liquid crystal composition comprising liquid crystalline material in an amount from 98.0 to 99.5% by weight and electrical conductivity modifiers dispersed in said liquid crystalline material in an amount from 0.5 to 2.0% by weight of said mesomorphic liquid crystal composition, said mesomorphic liquid crystal composition being effective to scatter incident light in response to an electric field applied thereacross, and said conductivity modifiers dispersed in said liquid crystalline material cooperating therewith to effect a current density in said mesomorphic liquid crystal composition in the range of from 0.5 to 3.0 μ

a/cm² at 15 volts d.c., and

an adsorbed layer of ion donor material formed on said conductive regions for enhancing electrical charge injection in sadi mesomorphic liquid crystal composition.