Electrophoretic dispersions

1. A method for inducing or enhancing the threshold voltage of an electrophoretic displays comprising the steps of:

(i) forming an electrophoretic dispersion comprising electrophoretic pigment particles dispersed in a fluorinated dielectric solvent or solvent mixture selected from the group consisting of perfluoroalkanes, perfluorocycloalkanes, perfluoroarylalkanes, perfluoro-tert-amines, perfluoropolyethers, hydrofluoropolyethers, poly(chlorotrifluoroethylene), and trifluoro(trifluoromethyl)-oxirane homopolymers, wherein said fluorinated dielectric solvent or solvent mixture comprises a dye or pigment in addition to the electrophoretic pigments particles;

(ii) adding a fluorinated threshold agent of fluorinated dyes or fluorinated pigments selected from the group consisting of phthalocyanine, naphthalocyanine, anthraquinone, perylene, quinacridone, diketopyrrolopyrrole, naphthalimide, diazine, polyaniline and porphyrin to the electrophoretic dispersion,

wherein the fluorinated threshold agent carries a charge opposite the charge of the electrophoretic pigment particles in the electrophoretic dispersion, or the fluorinated threshold agent induces on the electrophoretic pigment particles a charge opposite the charge of the electrophoretic pigment particles in the electrophoretic dispersion; and

(iii) filling the resulting electrophoretic dispersion of (ii) into display cells of the electrophoretic display.

2. The method of claim 1 wherein the charge of said electrophoretic pigment particles is positive and the charge provided by the fluorinated threshold agent is negative.

3. The method of claim 1 wherein the charge of said electrophoretic pigment particles is negative and the charge provided by the fluorinated threshold agent is positive.

4. The method of claim 1 wherein said fluorinated threshold agent is soluble in the fluorinated dielectric solvent or solvent mixture.

5. The method of claim 1 wherein said fluorinated threshold agent is dispersible in the fluorinated dielectric solvent or solvent mixture.

6. The method of claim 5 wherein the fluorinated threshold agent has a particle size at least about 4 times smaller than the electrophoretic pigment particles.

7. The method of claim 1 wherein said fluorinated threshold agent is absorbed onto the surface of the electrophoretic pigment particles.

8. The method of claim 1 wherein the electrophoretic pigment particles carry a charge of the same polarity, before and after addition of the fluorinated threshold agent and at a voltage beyond a threshold voltage.

9. The method of claim 1 wherein the electrophoretic pigment particles carry a charge of the same polarity as the charge provided by the fluorinated threshold agent, after addition of the fluorinated threshold agent and at a voltage beyond a threshold voltage.

10. The method of claim 1 wherein said electrophoretic pigment particles are charged primary pigment particles, pigment-containing particles, core-shell particles or hollow particles.

11. The method of claim 1 wherein said fluorinated dielectric solvent is a perfluoropolyether.

12. The method of claim 1 wherein the fluorinated dye or fluorinated pigment is present in about 0.01 to about 20% by weight based on the total dry weight of the electrophoretic pigment particles.

13. The method of claim 1 wherein when present in said electrophoretic dispersion, the charge of the fluorinated threshold agent is insensitive to the change of an applied voltage when the charge of the electrophoretic pigment particles in the electrophoretic dispersion is sensitive to the change of the applied voltage, or the charge of the fluorinated threshold agent is sensitive to the change of an applied voltage when the charge of the electrophoretic pigment particles in the electrophoretic dispersion is insensitive to the change of the applied voltage.

14. The method of claim 13 wherein the electrophoretic pigment particles show more than about (120/V op )% of change in charge density or electrophoretic mobility when there is a change of one volt of an applied voltage beyond a threshold voltage.

15. The method of claim 14 wherein the charge carried or induced by the fluorinated threshold agent shows less than about (30/V op )% of change in charge density of electrophoretic mobility when there is a change of one volt of the applied voltage beyond the threshold voltage.

16. The method of claim 14 wherein the charge carried or induced by the fluorinated threshold agent shows less than about (15/V op )% of change in charge density of electrophoretic mobility when there is a change of one volt of the applied voltage beyond the threshold voltage.

17. The method of claim 13 wherein the electrophoretic pigment particles show more than about (150/V op )% of change in charge density or electrophoretic mobility when there is a change of one volt of an applied voltage beyond a threshold voltage.

18. The method of claim 17 wherein the charge carried or induced by the fluorinated threshold agent shows less than about (30/V op )% of change in charge density of electrophoretic mobility when there is a change of one volt of the applied voltage beyond the threshold voltage.

19. The method of claim 17 wherein the charge carried or induced by the fluorinated threshold agent shows less than about (15/V op )% of change in charge density of electrophoretic mobility when there is a change of one volt of the applied voltage beyond the threshold voltage.

20. The method of claim 13 wherein the charge carried or induced by the fluorinated threshold agent shows more than about (120/V op )% of change in charge density or electrophoretic mobility when there is a change of one volt of an applied voltage beyond a threshold voltage.

21. The method of claim 20 wherein the electrophoretic pigment particles show less than about (30/V op )% of change in charge density of electrophoretic mobility when there is a change of one volt of the applied voltage beyond the threshold voltage.

22. The method of claim 20 wherein the electrophoretic pigment particles show less than about (15/V op )% of change in charge density of electrophoretic mobility when there is a change of one volt of the applied voltage beyond the threshold voltage.

23. The method of claim 13 wherein the charge carried or induced by the fluorinated threshold agent shows more than about (150/V op )% of change in charge density or electrophoretic mobility when there is a change of one volt of an applied voltage beyond a threshold voltage.

24. The method of claim 23 wherein the electrophoretic pigment particles show less than about (30/V op )% of change in charge density of electrophoretic mobility when there is a change of one volt of the applied voltage beyond the threshold voltage.

25. The method of claim 23 wherein the electrophoretic pigment particles show less than about (15/V op )% of change in charge density of electrophoretic mobility when there is a change of one volt of the applied voltage beyond the threshold voltage.