Driving methods to produce a mixed color state for an electrophoretic display
The present invention is directed to driving methods for a color display device which can display high quality color states. The display device utilizes an electrophoretic fluid which comprises three types of pigment particles having different optical characteristics, and provides for displaying at a viewing surface not only the colors of the three types of particles but also the colors of binary mixtures thereof.
1. A driving method for an electrophoretic display comprising a first surface on the viewing side, a second surface on the non-viewing side and an electrophoretic fluid which comprises a first type of particles, a second type of particles and a third type of particles, all of which are dispersed in a liquid, wherein
a) the three types of pigment particles have optical characteristics differing from one another;
b) the first type of pigment particles and the second type of pigment particles carry opposite charge polarities; and
c) the third type of pigment particles has the same charge polarity as the second type of pigment particles but a lower zeta potential,
the method comprising the following steps:
(i) applying a first driving voltage to a pixel in the electrophoretic display for a first period of time, the first driving voltage having a polarity driving the first type of pigment particles towards the first surface, thereby causing the pixel to display the optical characteristic of the first type of pigment particles at the first surface;
(ii) applying a second driving voltage to the pixel for a second period of time, the second driving voltage having a polarity driving the third type of pigment particles towards the first surface, thereby driving the pixel towards the optical characteristic of the third type of pigment particles at the first surface; and
(iii) applying a third driving voltage for a third period of time, the third driving voltage having the same polarity and the same magnitude as the first driving voltage, and the duration of the third period of time being from about 10 to about 60 percent of the duration of the first period of time, thereby producing a mixture of the optical characteristics of the first and third types of particles at the viewing surface.
2. The method of claim 1 , wherein the duration of the third period of time is from about 20 to about 40 percent of the duration of the first period of time.
3. The method of claim 1 , further comprising applying a shaking waveform prior to step (i).
4. The method of claim 3 , further comprising applying, prior to the shaking waveform, a driving voltage driving the first type of pigment particles towards the first surface.