COLOR DISPLAY DEVICE

• US 20140340735A1
• Filed: 05/15/2014
• Published: 11/20/2014
• Est. Priority Date: 05/17/2013
• Status: Active Grant

• Current Assignee: E Ink Holdings Incorporated
• Original Assignee: SiPix Imaging, Inc. (E Ink Holdings Incorporated)
• Inventors: LIN, Craig, Du, Hui, Wang, Ming
• Granted Patent: US 9,170,468 B2
• Time in Patent Office: Days
• US Class Current: 359/296
• CPC Class Codes: G02F 1/167 by electrophoresis
• CPC Class Codes: G02F 1/1681 having two or more microcells partitioned by walls, e.g. of microcup type
• CPC Class Codes: G02F 1/1685 Operation of cells; Circuit arrangements affecting the entire cell
• CPC Class Codes: G02F 2001/1678 characterised by the composition or particle type
• CPC Class Codes: G02F 2203/34 Colour display without the use of colour mosaic filters

Abstract

The present invention provides a color display device in which each pixel can display four high quality color states. More specifically, an electrophoretic fluid is provided which comprises four types of particles, dispersed in a solvent or solvent mixture. The fluid may further comprise substantially uncharged neutral buoyancy particles.

Claims

1. An electrophoretic fluid comprising four types of charged pigment particles dispersed in a solvent or solvent mixture, wherein the four types of charged pigment particles are high positive charged pigment particles, high negative charged pigment particles, low positive charged pigment particles and low negative charged particles and the low charged particles have a charge intensity which is less than 75% of the charge intensity of the high charged particles.

2. The fluid of claim 1, wherein the low positive charged particles have a charge intensity which is less than 50% of the charge intensity of the high positive charged particles and the low negative charged particles have a charge intensity which is less than 75% of the charge intensity of the high negative charged particles.

3. The fluid of claim 2, wherein the high positive charged particles are black particles, the high negative charged particles are yellow particles, the low positive charged particles are red particles and the low negative charged particles are white particles.

4. The fluid of claim 2, further comprising substantially uncharged neutral buoyancy particles.

5. The fluid of claim 4, wherein the substantially uncharged neutral buoyancy particles are non-charged.

6. A display layer comprising an electrophoretic medium and having first and second surfaces on opposed sides thereof, the electrophoretic medium comprising a first type of positive particles, a first type of negative particles, a second type of positive particles, and a second type of negative particles, all dispersed in a solvent or solvent mixture, the four type of particles having respectively optical characteristics differing from one another, such that:

(a) application to a pixel an electric field having the same polarity as the first type of positive particles will cause the optical characteristics of the first type of positive particles to be displayed at the first surface;

or

(b) application to a pixel an electric field which has the same polarity as the first type of negative particles will cause the optical characteristic of the first type of negative particles to be displayed at the first surface;

or

(c) once the optical characteristic of the first type of positive particles is displayed at the first surface, application to a pixel an electric field having the same polarity as the second type of negative particles, but not strong enough to overcome the attraction force between the first type of positive particles and the first type of negative particles, but sufficient to overcome the attraction forces between other oppositely charged particles will cause the optical characteristic of the second type of negative particles to be displayed at the first surface;

or

(d) once the optical characteristic of the first type of negative particles is displayed at the first surface, application to a pixel an electric field having the same polarity as the second type of positive particles, but not strong enough to overcome the attraction force between the first type of positive particles and the first type of negative particles, but sufficient to overcome the attraction forces between other oppositely charged particles will cause the optical characteristic of the second type of positive particles to be displayed at the first surface.

7. The layer of claim 6, wherein the first type of positive particles is black particles, the first type of negative particles is yellow particles, the second type of positive particles is the red particles and the second type of negative particles is the white particles.

8. The layer of claim 6, wherein the charges of the first type of positive particles and the first type of negative particles are higher than the second type of positive particles and the second type of negative particles.

9. The layer of claim 8, wherein the charges of the lower charged particles are less than 50% of the charges of the higher charged particles.

10. The layer of claim 8, wherein the charges of the lower charged particles are 5% to 30% of the charges of the higher charged particles.

11. The layer of claim 8, wherein the charges of the lower charged particles are less than 75% of the charges of the higher charged particles.

12. The layer of claim 8, wherein the charges of the lower charged particles are 15% to 55% of the charges of the higher charged particles.

13. The layer of claim 6, wherein the electrophoretic medium further comprising substantially uncharged neutral buoyancy particles.

14. The layer of claim 13, wherein the neutral buoyancy particles are non-charged.

15. A driving method for an electrophoretic fluid comprising four types of charged pigment particles dispersed in a solvent or solvent mixture, wherein the four types of charged pigment particles are high positive charged pigment particles, high negative charged pigment particles, low positive charged pigment particles and low negative charged particles;

the method comprises;

(a) driving a pixel to the color state of one of the low charged particles, followed by

(b) driving the pixel to the color state of high charged particles;

wherein the low charged particles of (a) and the high charged particles of (b) carry opposite charge polarities.

16. The driving method of claim 15, further comprising a shaking waveform.

17. The driving method of claim 15, wherein the high positive charged particles are black.

18. The driving method of claim 15, wherein the high negative charged particles are yellow.

19. The driving method of claim 15, wherein the low positive charged particles are red.

20. The driving method of claim 15, wherein the low negative charged particles are white.

21. The driving method of claim 15, wherein the high positive charged particles are black, the high negative charged particles are yellow, the low positive charged particles are red, and the low negative charged particles are white.

22. A driving method for an electrophoretic fluid comprising four types of charged pigment particles dispersed in a solvent or solvent mixture, wherein the four types of charged pigment particles are high positive charged pigment particles, high negative charged pigment particles, low positive charged pigment particles and low negative charged particles;

the method comprises;

(a) applying a shaking waveform,

(b) applying a high driving voltage having the same polarity as one type of high charged pigment particles to drive to a color state of the high charged pigment particle,

(c) applying a low driving voltage having the same polarity as one type of low charged pigment particles to drive to a color state of low charged pigment particles; and

(d) applying a high driving voltage having the same polarity as the high charged pigment particles to drive to a color state of the high charged pigment particles;

wherein the high charged pigment particles of (d) and the low charged pigment particles of (c) are oppositely charged and the driving method is DC balanced.