Additive particles for improving optical performance of an electrophoretic display
The present invention is directed to an electrophoretic fluid which comprises additive particles. The concentration of the additive particles in the electrophoretic fluid does not exceed 25% by weight and the additive particles are not seen at the viewing side during operation of the display. The resulting fluid can improve optical performance of a display device, such as image stability and contrast ratio. The present invention is also directed to an electrophoretic display comprising the electrophoretic fluid.
1. A display comprising:
two electrodes; and
an electrophoretic fluid disposed between the electrodes, the electrophoretic fluid comprising:
two types of charged pigment particles that have opposite charges, and
neutral buoyancy particles, wherein the neutral buoyancy particles are uncharged or have a charge which is less than 50% of the average charge carried by the charged pigment particles,
wherein all types of particles are dispersed in a solvent or solvent mixture, and
the concentration of the neutral buoyancy particles in the electrophoretic fluid does not exceed 25% by weight,
wherein the two types of charged pigment particles move to opposed electrodes when a voltage difference is applied between the two electrodes,
wherein only a color of the charged pigment particles is visible at a viewing side of the display for all voltage differences applied between the two electrodes.
2. The display of claim 1 , wherein the neutral buoyancy particles have the same color as one type of charged pigment particles.
3. The display of claim 1 , wherein the neutral buoyancy particles have a color different from that of the charged pigment particles.
4. The display of claim 1 , wherein the neutral buoyancy particles are formed from a material selected from the group consisting of polyacrylate, polymethacrylate, polystyrene, polyaniline, polypyrrole, polyphenol and polysiloxane.
5. The display of claim 1 , wherein the neutral buoyancy particles are formed from a material selected from the group consisting of poly(pentabromophenyl methacrylate), poly(2-vinylnapthalene), poly(naphthyl methacrylate), poly(alpha-methystyrene), poly(N-benzyl methacrylamide) and poly(benzyl methacrylate).
6. The display of claim 1 , wherein the neutral buoyancy particles are formed from a material having a refractive index different from that of the solvent or solvent mixture.
7. The display of claim 1 , wherein the concentration of the neutral buoyancy particles in the electrophoretic fluid does not exceed 15% by weight.
8. The display of claim 1 wherein the concentration of the neutral buoyancy particles in the electrophoretic fluid does not exceed 10% by weight.
9. The display of claim 1 wherein the refractive index of the neutral buoyancy particles is the same as that of the solvent or solvent mixture.
10. The display of claim 1 wherein the refractive index of the neutral buoyancy particles is different than that of the solvent or solvent mixture.
11. The display of claim 1 , wherein the neutral buoyancy particles take up less than 20% by volume of the fluid.
12. The display of claim 1 , wherein the neutral buoyancy particles take up less than 10% by volume of the fluid.
13. The display of claim 1 , wherein the neutral buoyancy particles are uncharged or have a charge which is less than 25% of the average charge carried by the charged pigment particles.
14. The display of claim 1 , wherein the neutral buoyancy particles are uncharged or have a charge which is less than 10% of the average charge carried by the charged pigment particles.
15. The display of claim 1 , wherein the size of the neutral buoyancy particles is in the range of 100 nanometers to 5 microns.
16. The electrophoretic display of claim 1 further comprising a plurality of microcells containing the electrophoretic fluid.
17. The electrophoretic display of claim 1 further comprising a plurality of microcapsules containing the electrophoretic fluid.