Scavengeless development apparatus for use in highlight color imaging

Apparatus for forming latent electrostatic images on a charge retentive surface and rendering them visible with black and at least one highlight color toner in a single pass of the imaging surface through the processing areas of a printing system, said apparatus comprising:

• first and second developer apparatuses for applying toner particles to said latent electrostatic images, said apparatuses being arranged so said images are moved past said first apparatus prior to moving past said second apparatus;
• said second developer apparatus including:
• a supply of toner;
• a donor structure spaced from said charge retentive surface for conveying toner from said supply of toner to an area opposite said charge retentive surface;
• an electrode structure;
• means for establishing an alternating electrostatic field between said donor structure and said electrode structure;
• said electrode structure being positioned in a space between said charge retentive surface and said donor structure and sufficiently close to said donor structure to permit detaching of toner from the surface of said donor structure with the use of a relatively high alternating electrostatic field without risk of air breakdown to thereby produce toner clouding about said electrode structure;
• and
• means for creating an electrostatic field between said charge retentive surface and said electrode structure for effecting movement of detached toner to said latent electrostatic images.

The method of forming highlight color images on a charge retentive surface containing at least two image areas, said method including the steps of:

• providing first and second developer apparatuses;
• positioning a donor structure of said second developer apparatus adjacent said charge retentive surface;
• positioning an electrode structure between said charge retentive surface and said donor structure and spacing it a relatively short distance from the latter;
• depositing a monolayer of well charged toner on said donor structure;
• applying a relatively low alternating electrical bias to one of said structures to establish a relatively high alternating electrostatic field between said donor structure and said electrode structure to effect detachment of said toner from said donor structure to thereby form a cloud of toner around said electrode structure;
• establishing an electrostatic field between said charge retentive surface and said donor structure for effecting movement of toner to said charge retentive surface to thereby render some of said latent electrostatic images visible;
• and moving said charge retentive surface past said first and second developer apparatuses in that order.