Patent ID: 8257614

Claim:
A method of selecting a threshold agent for inducing or enhancing the threshold voltage of an electrophoretic dispersion, comprising the steps of: (a) forming an electrophoretic dispersion comprising electrophoretic pigment particles dispersed in a dielectric solvent or solvent mixture; (b) adding an agent to said electrophoretic dispersion; and (c) testing the agent to determine if it meets the following criteria: (i) it carries or induces on the electrophoretic pigment particles, a charge opposite the charge of the electrophoretic pigment particles, and (ii) the charge characteristics provided by the threshold agent is insensitive to the change of an applied voltage, if the charge characteristics of the electrophoretic pigment particles is sensitive to the change of the applied voltage, or vice versa and (d) selecting the agent as a threshold agent if it meets the criteria.