What does laser have to do with printing?

The arrival of the laser printers made many people wonder how exactly laser can be used inside a printer. Here you will get to know briefly this fairly recent printing method.

How is it possible for a laser to produce character or graphics on paper? The essence of the answer is hidden within one basic scientific principle: static electricity. We are all familiar with the situation of removing a pullover and having our hairs up in the air after that. This happens because electrical charge is built up on your hair and on the clothes you are wearing – one is positive and the other negative. This causes them to attract.

How is the principle of static electricity used inside a printer?

The drum – one of the major components in laser printers – receives a positive charge by a special wire (corona wire), which has an electrical current running through it. When the paper is fed into the printer, the drum starts rotating. Then laser plays its role – it "draws" on the drum all characters, which need to be printed. All the points at which the precise laser beam is directed become negatively charged. The rest of the drum remains positively charged.

Once the laser has done its job, the printer brings into use the positively charged toner. This is very fine black powder. The toner immediately sticks to the negatively charged areas of the drum. During this time the paper is rolling on a belt under the drum. The drum is ready to paste the fixed toner pattern on the paper, but before it does that the paper receives a negative charge by the same wire, which charged the drum positive. The negative charge of the paper is stronger than the negative charge that is holding the positively charged toner on the drum. Therefore the paper attracts the toner. Right after this the paper is discharged by another wire, called detac corona wire so that it does not get attracted to the positive drum. At the same time the drum goes through another procedure: a discharge lamp goes through its entire surface and erases the electrical image. Then the drum’s surface again receives a positive charge from the corona wire, making it ready for the next page waiting to be printed.

The drum and the paper move at the same speed so the image that was on the drum is pasted in exactly the same way on the paper. One more operation is needed before you can take your ready printout – the toner needs to become tightly fixed to the paper fibers. For this purpose the paper is rolled quickly between two heated rollers, called fusers. They melt the toner and thus it fuses with the paper. Then the paper arrives hot at the output tray, from where you can take it.

Did you like this article? Continue to the further reading:

Curious fact: The laser does not move on its own. In fact, it is always directed in the same way, but it has a moveable mirror in front, which bounces the beam. Then the beam goes through a series of lenses and gets projected on the drum’s surface.

Curious fact: The laser accounts for the high speed and the high precision of laser printers. The reason lies in the fact that a laser beam can move much faster than any inkjet cartridge. The high precision comes from the fact that the laser always has the same shape and diameter, which cannot be controlled to such a high extent in an ink droplet.