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Deflecting Electrostatic Printing Problems.

Photocopying, laser printing, and industrial digital printing all have roots in electrophotographic technology, and companies like AGFA-Gevaert, Xerox, Sharp, Hewlett-Packard, and others have incorporated various forms of this technology in their printers.

A toner source delivers charged toner particles through a printhead structure (a polymeric substrate with apertures and at least one set of control electrodes) to the image receiver (a sheet of paper, for example) in front of a back electrode. Negatively charged toner particles are attracted to the receiver upon the back electrode, creating an image on the paper. Earlier systems had several drawbacks, including fluctuations in the distances between critical component surfaces, resulting in poor imaging.

AGFA researchers have designed a printhead that uses enhanced shield and control electrodes separated by an insulating plastic sheet. The shield and control electrodes are placed around the toner apertures so that the electrostatic fields can be concentrated and individually controlled to produce high contrast, less clogging, and better imaging. Plasma-etching technology has created precise and accurate nozzle geometries that enable high-quality dot printing over the complete printing width.

The distance or "nip" between the toner source and the printhead structure is critical and variation leads to variation in toner flux and printing quality.

AGFA solved the nip issue by devising an intermediate image receiving member--a belt positioned between the printhead and the material being printed. The particular electrostatic properties introduced enable the electrostatic field between the printhead and receiver to remain as constant as possible, achieving optimal image quality.

Finally, to address toner quality, AGFA's researchers have developed an optimal rounded particle shape with a mean diameter of 6 to 10 microns.

The rounded particles offer uniform particle size distribution and electrical charge, better toner flow, and less stickiness to prevent clogging.

The result: a simpler, more accurate system with less components, greater accuracy, and improved imaging.

Desie is the chief engineer/DEP Technologies at AGFA-Gevaert, Mortsel, Belgium. This article appears as a Technology of the Week selection on the Web site. is an intellectual property marketplace based in Cambridge, Mass.

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Author:Desie, Guido
Publication:R & D
Article Type:Brief Article
Geographic Code:1USA
Date:Apr 1, 2001
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