Electrostatic Application

Laser PrintersLaser printers use electrostatic force between charged particles to print a document in a very similar manner as a photocopier. The static electricity is the main means of getting the toner onto the paper. The process takes place in several steps

A laser (semiconductor laser) forms the image or document to be printed on a rotating drums coated with selenium. This drum has a positive charge.

Where the laser falls onto the drum, the electric charge would leak away. In other words, these areas become discharged.

The drum is coated with a positively charged toner (a fine black powder.) The positively charged toner then clings to the discharged areas formed by the laser. Since like charges repel, the toner will only accumulate in areas which are discharged.

With the toner in position, the drum then rolls onto a sheet of paper which moves along a belt. Before the paper makes contact with the drum, it is given a negative charge by a corona wire (a wire with an electrical current running through it).

The negatively charged paper pulls the positively charged powder towards it. The drum and the paper will be moving at the same speed and because of this, the paper would gain the exact image formed on the drum.

The paper is quickly discharged afterwards to prevent it from sticking to the drum due to the opposing charges.

Simple Diagram of a Laser Printer’s Components