ELECTROPHORETIC MEDIUM WITH GASEOUS SUSPENDING FLUID

• US 20040112750A1
• Filed: 09/03/2003
• Published: 06/17/2004
• Est. Priority Date: 09/03/2002
• Status: Active Grant

• Current Assignee: E Ink Holdings Incorporated
• Original Assignee: E Ink Holdings Incorporated
• Inventors: Jacobson, Joseph M., Zehner, Robert W., Whitesides, Thomas H.
• Granted Patent: US 8,129,655 B2
• Time in Patent Office: Days
• US Class Current: 204/601
• CPC Class Codes: G02F 1/1671 involving dry toners
• CPC Class Codes: G02F 1/16757 Microcapsules
• CPC Class Codes: G09F 9/372 the positions of the elements being controlled by the application of an electric field

Abstract

An electrophoretic medium (102) comprises a plurality of capsules (104), each capsule comprising an internal phase comprising a plurality of electrophoretically mobile particles (106, 108) in a gaseous suspending medium, and a capsule wall surrounding the internal phase. Various processes for producing such an electrophoretic medium are also described.

Claims

1. An electrophoretic medium comprising a plurality of capsules, each capsule comprising an internal phase comprising a plurality of electrophoretically mobile particles in a gaseous suspending medium, and a capsule wall surrounding the internal phase.

2. An electrophoretic medium according to claim 1 wherein each capsule comprises a single type of electrophoretically mobile particle, each capsule having a pair of opposed surfaces differing in size.

3. An electrophoretic medium according to claim 1 comprising two types of particles having differing optical characteristics and differing electrophoretic mobilities.

4. An electrophoretic medium according to claim 3 wherein one type of particle has substantially zero electrophoretic mobility.

5. An electrophoretic medium according to claim 3 wherein the two types of particles bear charges of the same polarity but differ in electrophoretic mobility.

6. An electrophoretic medium according to claim 1 wherein the capsule walls of a plurality of capsules are merged with one another, so that the medium comprises a plurality of bubbles, each containing the electrophoretically mobile particles and the gaseous suspending medium, the bubbles being dispersed in a continuous solid phase.

7. An electrophoretic medium according to claim 1 wherein the gaseous suspending medium comprises carbon dioxide.

8. An electrophoretic display comprising an electrophoretic medium according to claim 1 and at least one electrode disposed adjacent the electrophoretic medium and arranged to apply an electric field to the medium.

9. A process for producing an electrophoretic medium according to claim 1, the process comprising:

forming a medium comprising a plurality of capsules, each capsule comprising an internal phase comprising a plurality of particles in a liquid suspending medium, and a capsule wall surrounding the internal phase; and

replacing the liquid suspending medium with a gaseous suspending medium.

10. A process according to claim 9 wherein the replacement of the liquid suspending medium is effected by evaporating the liquid suspending medium while diffusing a gas suspending medium into the capsules.

11. A process according to claim 9 wherein the formation of the medium comprising the liquid suspending medium is effected by forming a plurality of droplets, each comprising the liquid suspending medium and the particles, in a continuous phase comprising a curable binder, and thereafter at least partially curing the curable binder.

12. A process for producing an electrophoretic medium according to claim 1, the process comprising:

admixing particles with a material capable of generating gas;

dispersing the mixture of particles and gas-generating material in a curable binder;

at least partially curing the binder; and

exposing the gas-generating material to conditions effective to cause generation of gas therefrom, thereby causing the formation within the binder of capsules containing the particles.

13. A process according to claim 12 wherein the gas-generating material comprises a volatile liquid, and the gas is formed by evaporation of the liquid.

14. A process according to claim 12 wherein the gas is generated by reaction of the gas-generating material with a material present in the binder.

15. A process for producing an electrophoretic medium according to claim 1, the process comprising:

admixing a material capable of generating gas with a wall-forming material;

exposing the gas-generating material to conditions effective to cause generation of gas therefrom, thereby causing the formation of gas-filled cavities within the wall-forming material; and

introducing solid particles into the cavities.

16. A process for producing an electrophoretic medium according to claim 1, the process comprising:

admixing particles with a supercritical fluid;

surrounding the mixture of particles and supercritical fluid with a capsule wall, thereby forming a capsule; and

reducing the pressure on the capsule below the critical pressure of the supercritical fluid, thereby causing the supercritical fluid to form a gaseous suspending medium within the capsule.

17. A process according to claim 16 wherein the surrounding of the mixture of particles and supercritical fluid with a capsule wall is effected by forming a droplet of the mixture in a curable binder, and at least partially curing the binder before reducing the pressure below the critical pressure.

18. A process according to claim 16 wherein the surrounding of the mixture of particles and supercritical fluid with a capsule wall is effected by forming a droplet of the mixture in a liquid phase immiscible with the supercritical fluid, and forming the capsule at the interface between the supercritical fluid and the liquid phase.

19. A process according to claim 16 wherein the supercritical fluid is carbon dioxide.

20. A process according to claim 16 further comprising replacing the gaseous suspending fluid formed from the supercritical fluid with a different gaseous suspending medium.