Physical theory of charged pigment electrophotography

A formal approach to the theory of electrophotography is introduced in which imaging systems are defined and classified according to the dominant physical interactions responsible for the imaging process. The usefulness of the approach lies in the fact that it provides a powerful means of comparative analysis as well as ideal standards against which the performance of real systems can be compared. Application of the theory to charged pigment electro-photography, defined as that branch of electrophotography which exploits the electric field-monopole interaction to drive development, naturally leads to two broad subclasses: charged pigment xerography (CPX), in which development is achieved through the interaction of uniformly charged pigment with a varying electric field; and photoactive pigment electrophotography (PAPE), in which development is achieved through the interaction of a uniform electric field with a varying charge on the pigment. A comparative study of the two systems reveals that the inherent noisiness of adhesion severely limits their sensitivity when it must be coped with directly. Under these circumstances, it is further seen that fluctuations in charge on the pigment leads (via the electrostatic image force) to a limitation of the force available for driving development in CPX only. Since the same limitation does not arise in PAPE, any system of the latter type may have a sensitivity two orders of magnitude higher than its corresponding CPX system, providing the two are equivalent in every other respect (equal resolving power and latent image forming efficiency).