Chemicals, Printing Tools & Printing Product

Electrostatic printing is a technique in which electrostatic forces are used to produce copies of documents; it is currently the most popular type of copying machine, having essentially superseded earlier types. Several reproducing processes are based on the principles of ELECTROSTATICS. The two main one are Xerography and Electrofax.

In each method of photoconductive surface is given an electrostatic charge. A discharge occurs when the charge surface is illuminated. Thus, after the surface is illuminated by an image upon it, the amount of charge remaining will depend on the darkness of the original, since while background dissipates the charge.

In xerography the photoconductive surface is a drum coated with the chemical selenium. At the beginning of the copying process the drum is positively charged. Flash lamp illuminate the document to be copied, which has been placed face down on a glass plate. Areas on the drum that correspond to printed area on the document will not receive light reflected from the document: but where the document is white or unprinted, the corresponding area on the drum will be illuminated and will lose their charge. A negatively charged dark powder called areas will hold the toner. Positively charged copy paper is brought against the drum surface, and the toner is transferred to the paper, which is heated to fuse the toner particles into the paper fiber.

Xerography (meaning “dry printing”) was invented by Chester F. Carlson in 1938 and developed by Xerox corporation. The Electrofax process is similar to xerography, except that the paper itself, rather than the drum, is coated. Other newer electrostatic printing methods use laser, ink jets, or heat-sensitive ribbons to print.