Laser printers, Toner, and Color
Printers come in two varieties: inkjet and laser. Inkjet printers are pretty self explanatory–they basically spray ink all over the paper to form word or picture documents. But what about laser printers? Besides having a cool name (c’mon, anything to do with lasers is cool) and a larger price tag, most people don’t know what differentiates the two. Hopefully, this will help clarify the complex (and fascinating) process involved with laser printing.
Surprisingly, laser printers rely heavily on static electricity, the mundane phenomenon that can make clothes out of the dryer stick together. Basically, static electricity happens when an electrical charge builds up on an insulated object. These electrical charges become attracted opposite charge, which explains the fabric sticking together.
Laser printers use static electricity by the way of a positively-charged, rotating drum (or cylinder). The material of the drum is made of photoconductive material that becomes discharged by the light photons of a laser (hence the name).
As the drum revolves, information is given to the laser to “draw” the images or letters on it, thereby removing the positive charge from those areas of the drum. These images are what ends up being printed onto the paper. The result is the positively-charged spinning drum with newly-created negatively charged letters/images.
Once the pattern is set, a positively charged toner covers the drum.
Side note: toner is a fine powder what actually creates the images in laser printing. Many people think ink is used in this process, but ink is only used in inkjet printers.
Anyway, when the drum is covered with toner, the positively-charged powder sticks to the negatively-charged areas made possible by the laser, but not anywhere else on the drum. The process is similar to using glitter in elementary school: pour glitter all over a piece of paper and then turn it upside down. The only parts that stick are the glued areas.
With the toner set in the desired pattern, the drum rolls over the paper moving under it. Since the paper is negatively-charged in the process, it pulls the positively-charged toner off the drum and onto the paper. A detac corona wire discharges the paper immediately after picking up the toner, so it will not stick to the drum
The paper then moves through two heated rollers which melt the toner (set in the desired pattern) to the paper. Up until now, the toner has been in the form of a loose powder, but these heated rollers bond the images to the paper. Have you ever noticed that sheets coming from a laser printer are hot, or “fresh out of the printer”? This is because they’ve just been fused with the words or images.
The process is amazingly fast; and after one sheet is done the whole cycle starts all over again. Lasers are fast by nature–which makes this incredible process possible.
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