Color electrophotography for high quality half-tone images

Claim 1

A process for development of electrophotographic images exposed by laser scan techniques by applying liquid toner, comprising a) charge sensitizing a photoconductive layer surface to give a first electric field above said surface, b) exposing a half-tone image onto said surface by laser scan thereby forming an imagewise distribution of electrostatic charges, c) applying said toner between a developer electrode and a said surface at a rate in excess of that required by said development in the presence of a second electric field of at least 5000 volts/cm, said second field being normal to the surface and opposed to said first field, said toner comprising toner particles dispersed in a non-polar insulating liquid, whereby said toner particles are deposited imagewise on said surface, said toner being characterized as having the following properties i) an initial equivalent solids conductivity of less than 10 -10 mho/cm, ii) a ratio of background conductivity to initial conductivity of less than 0.3, iii) the toner particles having a zeta potential in the range of 60 mV to 200 mV, and iv) a concentration of said toner particles in the liquid toner being in the range 0.1 to 1.0 weight %.