Patent ID: 7572394

Claim:
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.