Chelating negative charge director for liquid electrographic toner

Abstract

The invention is a negative charge director for liquid electrographic toners. The charge director comprises a very weakly associating, charged functional group covalently bonded in the resin coating of the toner particle, and a very strongly chelating, preferably neutrally charged, molecule dispersed in the liquid phase to achieve charge separation. The weak association site on the resin is prepared, via well-known ion-exchange chemistry, in the metal form desired. Preferred metals are those with no regulatory, health or environmental issues, such as K+, Na+, Ca.sup.2+, Al.sup.3+, Zn.sup.2+, Zr.sup.4+, Mg.sup.2+, ammonium (NH.sub.4 +), and organic cations. The cation-associated resin is brought into dispersion with the solution phase chelating molecule. When this is done, the equilibria that compete for the cation are such that it is released from the resin and bound in the chelate. The toner particle is left with a net negative charge which is permanent, but which is balanced by an equal, opposite charge on the chelated cationic species in the continuous phase. Preferably, there are no other sources of charge in the dispersion, and there is no excess of charge carriers in the continuous phase which would interfere with development.