Application of Electrostatics
What is a Photocopier?
What are the parts of a photocopier?
- Metal roller covered by a layer of photoconductive material
- Made out of a semiconductor such as selenium
- Generates the positive charges on the surface of the drum and the copy paper
Lamp and lenses:
- Photocopiers need a light source to copy the original document
- When the lamp in the copier is turned on, it moves across the inside of the copier, illuminating one strip of the paper at a time
- The lenses allows you to focus the copy in a specific place by changing the distance between the lens and the original copy
- Toner is a fine black, negatively charged, powder that consists of pigments that coat tiny plastic beads
- It is stuck on larger, positively charged beads and stored inside a toner cartridge.
- When you apply heat to the toner, the plastic particles melt and fuce the pigment to the paper
- It provides the finishing touches to make the toner image on the paper permanent
- The fuser has to do two things: melt and press the toner image into the paper and prevent the melted toner and the paper from sticking to the fuser (Meeker-O’Connell, Ann).
How does it work?
- The sheet of paper is placed face down on the glass surface of the copier. When the copy button is pressed, the selenium drum gets a positive charge.
- A bright light then moves across the paper. The mirrors and lenses project an image of the paper onto the drum.
- The light is reflected from the white parts of the paper being copied. Where the reflected light hits the drum, the selenium conducts a charge.
- Electrons from the aluminum base of the drum move to the light areas, neutralizing the charge that was there. Dark areas on the drum (which is the information being copied), keeps a positive charge. The surface of the drum now has an electrostatic image of the paper being copied.
- Toner is then spread over the surface of the drum. The toner is attracted to the positive parts of the drum.
- As the drum rotates, it pulls out a sheet of paper from the tray. The sheet of paper gets a larger positive charge than the drum. The toner is transferred to the paper as it presses against the drum.
- The paper then passes though heated Teflon rollers. The heat melts the plastic beads in the toner, and the rollers press the black powder into the paper. As the copy emerges from the machine, it is still warm (Ryerson, McGraw-Hill).
- And there you have your final copy!
The lithograph duplicator was another invention used in the 70s and 80s. This machine was operated by hand and was able to duplicate copies of papers in a feint purple colour, but this did not make an instant copy. It took many steps and time to make just one copy. So, luckily the photocopier was invented and used in the later 1900.
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