Ion modulator having independently controllable bias electrode

Claim 2

A process for producing copies of a graphic original comprising the steps of: 1. applying an electrostatic charge to an ion modulator in blanket light while applying a bias potential of the same polarity as said electrostatic charge, 2. projecting upon said ion modulator a pattern of light and shadow corresponding to said graphic original while applying an AC corona and a bias potential of a polarity opposite to that of said electrostatic charge, 3. flooding said ion modulator with blanket light, 4. projecting ions of the opposite polarity to that of said electrostatic charge in blanket light with zero bias potential applied, whereby ions are transmitted through said modulator in a pattern corresponding to said original, 5. creating a latent electrostatic image corresponding to said pattern upon a dielectric surface in the path of said transmitted ions, and 6. developing said latent electrostatic image, said ion modulator comprising a conductive screen, a thin metal film, an electrically insulating layer interposed between said screen and said film, a photoconductive layer overcoating one of said screen and said film and an electrically insulating non-photoconductive layer overcoating said photoconductive layer.

Claim 3

A process according to claim 1 wherein said electrostatic charge is of negative polarity, said ions are of positive polarity and the process operates in the positive mode.

Claim 4

A process according to claim 1 wherein said electically insulating layer is photoconductive.

Claim 5

A process according to claim 1 wherein said ion modulator is a member selected from the group consisting of a. a conductive screen having a photoconductor coated on one side thereof, an electrically insulating layer coated on the other side thereof, a thin metal film applied to said electrically insulating layer and an electrically insulating non-photoconductive layer applied to said photoconductor; b. a conductive screen overcoated with a photoconductive layer, said photoconductive layer being coated on one side thereof with a thin metal film and on the other side thereof with an electrically insulating non-photoconductive layer; c. a conductive screen having an electrically insulating layer partially coated thereon, a thin metal film coated only on said electrically insulating layer, a photoconductive layer coated only on said metal film and an electrically insulating non-photoconductive layer coated only on said photoconductive layer and d. a conductive screen having a photoconductive layer partially coated thereon, an electrically insulating non-photoconductive layer coated over said photoconductive layer and the portion of said screen not coated with said photoconductive layer and a thin metal film coated only upon the portion of said electrically insulating non-photoconductive layer overlying that portion of said screen not coated with said photoconductive layer.