Transflector for illuminated electrooptic displays

• US 4,196,973 A
• Filed: 08/21/1978
• Issued: 04/08/1980
• Est. Priority Date: 08/21/1978
• Status: Expired due to Term

• Current Assignee: Timex Corporation (Tanager Group BV)
• Original Assignee: Timex Corporation (Tanager Group BV)
• Inventors: Hochstrate, Paul E.
• Primary Examiner(s): Bauer, Edward S.
• Application Number:
  US05/935,187
• Time in Patent Office: 596 Days
• Field of Search: 350/338, 350/345
• US Class Current: 349/68
• CPC Class Codes: G02F 1/133555 Transflectors
• CPC Class Codes: G02F 2203/09 transflective

Abstract

Disclosed is an improved transflector especially useful in illuminated liquid crystal display devices operative in the reflective and transmissive modes for significantly enhancing the optical viewability thereof, especially in the daytime reflective mode. Typically, the improved transflector is a transluscent plate-like member including as an essential feature a layer portion of white transluscent material having a certain minimum effective thickness in the primary direction of light propagation in the device such that ambient light incident upon the white layer during daylight viewing is subjected to enhanced diffusion, fringing and brightening to provide a brighter appearing background and darker-appearing display characters to the daytime viewer for improved contrast and also to provide an apparent increase in the "brush-stroke" width of the display characters to the same viewer.

Claims

1. In an electrooptic device including an electrooptic display cell operative either in a reflective or a transmissive mode and having a plurality of selectively actuatable electrode segments to form display characters, a light source for night illumination and a transflector member made of transluscent material and disposed behind the display cell to diffuse and reflect incident ambient light for daytime viewing and to diffuse, reflect and transmit light received from the light source for night viewing, the improvement which comprises:

a transflector member which includes a sandwich construction of at least two translucent layers, at least one of which layers is made of white transluscent material having at least a minimum effective thickness in the principal direction of light propagation in the device such that ambient light incident upon said white transflector layer is subjected to sufficiently enhanced diffusion, fringing and brightening to provide a brighter-appearing background and darker-appearing display characters to the daytime viewer and also to provide an apparent increase in the "brush-stroke" width of the display characters to the same viewer, thereby improving daytime contrast and overall viewability, said improved transflector member also enhancing the readability of the display characters during night viewing as a result of enhanced diffusion, fringing and brightening of light received from said light source.

2. The electrooptic device of claim 1 wherein:

the electrooptic cell is a liquid crystal cell and first and second polarizers are disposed on the top and bottom sides of the cell, the improved transflector member being disposed behind said second polarizer.

3. The electrooptic device of claim 1 wherein:

the white transluscent layer is a sheet of white styrofoam of effective thickness.

4. The electrooptic device of claim 3 wherein:

the other transparent layer is selected from the group consisting of polystyrene, polypropylene and styrofoam.

5. The electrooptic device of claim 1 wherein:

said layer portion of white transluscent material is at least 0.040 inch in thickness.

10. The liquid crystal display device of claim 5 wherein:

the actuatable electrode segments are configured to form horological display characters.

6. In a liquid crystal display device including a liquid crystal cell operative either in a reflective or a transmissive mode and having a plurality of selectively actuatable electrode segments to form display characters, first and second polarizers on the top and bottom sides of the cell, respectively, a light source for night illumination and a transflector member made of transluscent material and disposed behind the second polarizer to diffuse and reflect incident ambient light for daytime viewing and to diffuse, reflect and transmit light received from the light source for night viewing, the improvement which comprises:

a transflector member in the form of a plate-like member which includes a sandwich construction of at least two transluscent layers, at least one of which layers is a layer of white transluscent material having at least a minimum effective thickness in the principal direction of light propagation in the device such that ambient light incident upon said white transflector layer is subjected to sufficiently enhanced diffusion, fringing and brightening to provide a brighter-appearing background and darker-appearing display characters to the daytime viewer and also to provide an apparent increase in the "brush-stroke" width of the display characters to the same viewer, thereby improving daytime contrast and overall viewability, said improved transflector member also enhancing the readability of the display characters during night viewing as a result of enhanced diffusion, fringing and brightening of light received from said light source.

7. The liquid crystal display device of claim 6 wherein:

the transflector sandwich and bottom polarizer are joined together to form a one-piece component.

8. The liquid crystal display device of claim 6 wherein:

the white transluscent layer is a sheet of white styrofoam of required thickness bonded to another sheet of a material selected from the group consisting of polystyrene, polypropylene and styrofoam.

9. The liquid crystal display device of claim 8 wherein:

the styrofoam sheet is on the bottom of the sandwich.