Methods for driving four particle electrophoretic display
View Patent ↗The present invention provides driving methods for 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.
1. A driving method for driving a pixel of an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side, and an electrophoretic fluid disposed between a first light-transmissive electrode and a second electrode, the electrophoretic fluid comprising a first type of particles, a second type of particles, a third type of particles, and a fourth type of particles, all of which are dispersed in a solvent, wherein
(a) the four types of pigment particles have different optical characteristics;
(b) the first type of particles and the third type of particles are positively charged, wherein the first type of particles have a greater magnitude of positive charge than the third particles; and
(c) the second type of particles and the fourth type of particles are negatively charged, wherein the second type of particles have a greater magnitude of negative charge than the fourth particles,
the method comprises the steps of:
(i) applying a first driving voltage to the pixel of the electrophoretic display for a first period of time at a first amplitude to drive the pixel to a color state of the first or the second type of particles at the viewing side; and
(ii) applying a second driving voltage to the pixel of the electrophoretic display for a second period of time, wherein the second driving voltage has a polarity opposite to that of the first driving voltage and a second amplitude smaller than that of the first amplitude, to drive the pixel from the color state of the first type of particles towards the color state of the fourth type of particles, or from the color state of the second type of particle towards the color state of the third type of particles, at the viewing side.
2. The driving method of claim 1 , wherein the second period of time in step (ii) is longer than the first period of time in step (i).
3. The driving method of claim 1 , further comprising repeating steps (i) and (ii).
4. The driving method of claim 3 , wherein steps (i) and (ii) are repeated at least 8 times.
5. The driving method of claim 1 , further comprising the step of: (iii) applying no driving voltage to the pixel for a third period of time.
6. The driving method of claim 5 , further comprising repeating steps (i)-(iii).
7. The driving method of claim 1 , wherein the amplitude of the second driving voltage is less than 50% of the amplitude of the first driving voltage.
8. The driving method of claim 1 , wherein the magnitude of the positive charge of the third particle is less than 50% of the magnitude of the positive charge of the first particle.
9. The driving method of claim 1 , wherein the magnitude of the negative charge of the fourth particle is less than 75% of the magnitude of the negative charge of the second particle.
10. The driving method of claim 1 , further comprising applying a voltage with a shaking waveform to the pixel before step (i).
11. A driving method for driving a pixel of an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side, and an electrophoretic fluid disposed between a first light-transmissive electrode and a second electrode, the electrophoretic fluid comprising a first type of particles, a second type of particles, a third type of particles, and a fourth type of particles, all of which are dispersed in a solvent, wherein
(a) the four types of pigment particles have different optical characteristics;
(b) the first type of particles and the third type of particles are positively charged, wherein the first type of particles have a greater magnitude of positive charge than the third particles; and
(c) the second type of particles and the fourth type of particles are negatively charged, wherein the second type of particles have a greater magnitude of negative charge than the fourth particles,
the method comprises the steps of:
(i) applying a first driving voltage to the pixel of the electrophoretic display for a first period of time at a first amplitude to drive the pixel to a color state of the first or the second type of particles at the viewing side;
(ii) applying no driving voltage to the pixel for a second period of time;
(iii) applying a second driving voltage to the pixel of the electrophoretic display for a third period of time, wherein the second driving voltage has a polarity opposite to that of the first driving voltage and a second amplitude smaller than that of the first amplitude, to drive the pixel from the color state of the first type of particles towards the color state of the fourth type of particles, or from the color state of the second type of particle towards the color state of the third type of particles, at the viewing side; and
(iv) applying no driving voltage to the pixel for a fourth period of time.
12. The driving method of claim 11 , wherein the third period of time in step (iii) is longer than the first period of time in step (i).
13. The driving method of claim 11 , further comprising repeating steps (i)-(iv).
14. The driving method of claim 11 , wherein the amplitude of the second driving voltage is less than 50% of the amplitude of the first driving voltage.
15. The driving method of claim 11 , wherein the magnitude of the positive charge of the third particle is less than 50% of the magnitude of the positive charge of the first particle.
16. The driving method of claim 11 , wherein the magnitude of the negative charge of the fourth particle is less than 75% of the magnitude of the negative charge of the second particle.
17. The driving method of claim 11 , further comprising applying a voltage with a shaking waveform to the pixel before step (i).
18. The driving method of claim 11 , further comprising the following steps:
(v) applying a third driving voltage to the pixel for a fifth period of time, wherein the third driving voltage has polarity same as that of the first driving voltage;
(vi) applying a fourth driving voltage to the pixel for a sixth period of time, wherein the fifth period of time is shorter than the sixth period of time and the fourth driving voltage has a polarity opposite to that of the first driving voltage to drive the pixel from the color state of the first type of particles towards the color state of the fourth type of particles or from the color state of the second type of particles towards the color state of the third type of particles, at the viewing side; and
(vii) applying no driving voltage for a seventh period of time.
19. The driving method of claim 18 , wherein the amplitudes of both the third driving voltage and the fourth driving voltage are less than 50% of the amplitude of the first driving voltage.
20. A driving method for driving a pixel of an electrophoretic display comprising a first surface on a viewing side, a second surface on a non-viewing side, and an electrophoretic fluid disposed between a first light-transmissive electrode and a second electrode, the electrophoretic fluid comprising a first type of particles, a second type of particles, a third type of particles, and a fourth type of particles, all of which are dispersed in a solvent, wherein
(a) the four types of pigment particles have different optical characteristics;
(b) the first type of particles and the third type of particles are positively charged, wherein the first type of particles have a greater magnitude of positive charge than the third particles; and
(c) the second type of particles and the fourth type of particles are negatively charged, wherein the second type of particles have a greater magnitude of negative charge than the fourth particles,
the method comprises the steps of:
(i) applying a first driving voltage to the pixel of the electrophoretic display for a first period of time at a first amplitude to drive the pixel to a color state of the first or the second type of particles at the viewing side;
(ii) applying a second driving voltage to the pixel of the electrophoretic display for a second period of time, wherein the second driving voltage has a polarity opposite to that of the first driving voltage and a second amplitude smaller than that of the first amplitude, wherein the second period is not sufficiently long to drive the pixel to a color state of the second type of particles at the viewing side, or when the first driving voltage drives the pixel to a color state of the second type of particles, the second period is not sufficiently long to drive the pixel to a color state of the first type of particles at the viewing side; and
(iii) applying a shaking waveform.