Translations:AY Honors/Printing/Answer Key/42/en

Xerographic Photocopy Process

How a photocopier works (using xerography):

First, the surface of a cylindrical drum is given an electro-static charge by a high-voltage wire called a corona wire. The drum is coated with a photoconductive semiconductor material, such as selenium or germanium.
Then the light reflected from the scanned original document is beamed in a narrow band onto the surface of the drum. Only the white areas of the original document reflect light. The reflected light then hits the drum, which is specially conditioned to make it photoconductive. This means that wherever light hits it, the positive charges are conducted away to a ground.
As a result, the white areas of the picture are now neutral, and the black areas remain positively charged, yielding a latent electrical image on the surface of the drum.
The toner is negatively charged. Therefore, when it is applied to the drum to develop the image, it is attracted and sticks to the areas that are positively charged, just as paper sticks to a toy balloon with a static charge.
The toner image is then transferred from the drum onto a positively charged piece of paper.
The drum is then wiped clean and completely discharged by light, before beginning the process again.
The toner is a dry powder. If copies were to exit the photocopier covered in dry toner it would easily brush off. Toner usually contains a styrene or polyester resin, and with the application of high heat and pressure it melts and binds (or fuses) to the paper.