Xerography - What is xerography?
A method of printing; this process creates an image by using static electricity to attract toner to an imaging drum before it is transferred and bonded onto a substrate. Xerography is used to create copies of images or documents and is the printing process used in photocopiers.
The xerographic process is a combination of the electrostatic printing process and photography; like electrostatic printing, a latent image is created first using a photoconductive surface and static electricity, but in xerography the latent image is a negative of the original document or image (similar to the transparent negatives that are created in photography when a photosensitive film is exposed to light) and is created on a photoconductive drum (the image carrier or imaging device), rather than on the substrate itself.
Xerography has six basic steps; charging, exposure, development, transfer, fusing, and cleaning. First, the photoconductive drum (image drum) is given a negative (or positive) charge by the primary charge corona roller or wire. Exposure involves the creation of a latent image (an “invisible” image that is created by exposing a photosensitive material to light); in xerography, the original document or image is scanned with a moving light, which will either pass through or be reflected onto the image drum. The “content” of the document will block or absorb light while the “non-content” (blank white areas) will allow light to pass through or reflect light onto the drum. Where light falls onto the drum, the negative (or positive) charge is discharged, creating a negative latent image of the original document that is made up of negatively (or positively) charged areas on the drum.
The latent image is then developed as the drum rotates past a toner cartridge; the toner particles have a positive (or negative) charge, meaning that they will be attracted to the charged areas of the drum. At this point, the substrate is passed between the image drum and the transfer corona; the transfer corona gives the substrate a negative (or positive) charge that is stronger than that of the image drum. The toner is attracted to the paper and, because the paper has a stronger charge than the drum, transfers onto the substrate. The substrate then passes through a fuser unit, which uses heat and pressure to bond the toner in place.
In the final stage, light discharges the remaining charge on the drum, and any excess toner is brushed away in order to clean the drum before the next sheet is printed.
While xerography usually uses one black toner to create black and white copies, it is possible to use a different colour to produce monochromatic images, and some xerographic printers and photocopiers use four toners to create full colour images (there is one toner for each of the four process colours, which are applied in sequence, with each colour requiring the process of charging and discharging specific areas of the image to be repeated before it is applied).Go Back to Glossary