Watch with an analog display device the dial of which is formed by a liquid crystal display cell

• US 4,488,818 A
• Filed: 09/29/1982
• Issued: 12/18/1984
• Est. Priority Date: 10/28/1981
• Status: Expired due to Term

• Current Assignee: Asulab SA (The Swatch Group AG)
• Original Assignee: Asulab SA (The Swatch Group AG)
• Inventors: Saurer, Eric, Ruedin, Yves, Gharadjedaghi, Fereydoun
• Primary Examiner(s): Roskoski, Bernard
• Application Number:
  US06/426,384
• Time in Patent Office: 811 Days
• Field of Search: 368/71, 368/82, 368/84, 368/239, 368/242, 340/754, 350/334, 350/336-338
• US Class Current: 368/71
• CPC Class Codes: G04G 9/0094 using light valves, e.g. liquid crystals

Abstract

A watch display comprises time display hands (3, 4) and a reflecting digital display (5) which acts as dial for the hands, the display being transparent under the effect of an electric field and opaque in the absence of the field.

Claims

1. In a watch comprising time display hands adapted to be mechanically driven;

and a digital display cell positioned behind said hands to form a dial for said hands, said digital display cell including a composite layer comprising at least one layer of liquid crystal and having display zones which respond to an electrical field provided in response to an external action by a modification of their opacity;

a fluid-tight enclosure comprising a front plate, a rear plate and spacing and closing means which define a closed space containing the layer of liquid crystal; and

light-reflecting and diffusing means disposed behind said composite layer;

the improvement wherein said cell is of the type in which said composite layer is transparent under the effect of said field and opaque in the absence of the field, with the result that said layer has a uniformly opaque appearance in the absence of said field and thus forms itself the dial for said hands.

2. The watch of claim 1, wherein the composite layer comprises a first polarizer located in front of the layer of liquid crystal and a second polarizer located between the layer of liquid crystal and said light-reflecting and -diffusing means;

the layer of liquid crystal has a helical structure the axis of which is substantially at a right angle to the plane of said layer, the angle of twist of the helix being 90°

; and

the axes of said polarizer are parallel to each other.

3. The watch of claim 1, wherein the composite layer further comprises a polarizer and the layer of liquid crystal comprises a nematic compound and a pleochroic dye.

4. The watch of claim 3, wherein said polarizer is adjacent to the light-reflecting means.

5. The watch of claim 1, wherein the layer of liquid crystal comprises a nematic compound, a pleochroic dye and a chiralic compound which induces a helical structure in said layer.

6. The watch of claims 3, 4 or 5, wherein the pleochroic dye has a relatively high coefficient of absorption for substantially all of the wave-lengths of visible light.

7. The watch of claim 3, 4 or 5 wherein said spacing and closing means comprises a bonding material and a pigmentation agent having substantially the same colour as the pleochroic dye.

8. The Watch of claims 1, 2, 3, 4 or 5 wherein the front plate carries a partly reflective layer on one of its surfaces.

9. The watch of claim 6 wherein said spacing and closing means comprises a bonding material and a pigmentation agent having substantially the same colour as the pleochroic dye.

10. The watch of claim 6 wherein the front plate carries a partly reflective layer on one of its surfaces.

11. The watch of claim 7 wherein the front plate carries a partly reflective layer on one of its surfaces.