Printing with Electrostatics
What are Electrostatics?
What is Xerography?
Xerography, also known as electrophotography is a printing and photocopying technique that works on the basis of electrostatic charges. It is the process of reproducing images and printing computer data, which is used in photocpiers, laser printers, and fax machines. Originally, the first xerography process only allowed for the reproduction of grayscale images. The first commercial use of the machines was of a flat photosensor (an electronic component which detects the presence of visible light) with a copy camera and a separate processing unit to produce offset lithographic plates. However, later the machines allowed for the production of printing colour. Eventually, Xerography may supplement for traditional printing for the production of books and magazines.
The Xerography Process
Stage 1: Charging
-An electrostatic charge of 600 volts is uniformly distributed over the surface of the drum by a corona discharge or with the use of a contact roller with a charge applied to it
-A corona discharge is generated by a narrow wire 1/4 to 1/2 inch apart from the photoconductor.
-A negative charge is placed on the wire, which will ionize the space between the wire and conductor, therefore making the electrons repel the wire and push onto the conductor
Stage 2: Exposure
-A bright lamp illuminates the original document, and the white areas of the original document reflect the light onto the surface of the photoconductive drum
-The areas of the drum that are exposed become conductive, and discharge to the ground
-The area of the drum not exposed to light remains negatively charged
-This results in an electrical image on the surface of the drum
Stage 3: Developing
-The toner is positively charged
-When it is applied to the drum to develop the image,it is attracted (unlike charges attract) and sticks to the areas of the drum that are negatively charged
Stage 4: Transfer
-The toner image on the surface of the drum is transferred onto a piece of paper with a higher negative charge than the drum