We sell a lot of laser printer toner cartridges, and we get a fair number of questions on the subject. To understand them better, it helps to understand how laser printers (and their close relative, LED printers) work.

While toner serves a similar purpose to the ink in cartridges for inkjet printers (AKA “bubblejet”)- making marks on the paper- the way it does this is quite different. Read on to find out more- don’t worry, we’ll keep it short!

The slightly simplified explanation goes as follows.

1 – Laser “Draws” Image on Charged Drum

The laser printer is based around a rotating drum. Initially, this is given an electrically negative charge (around -600v) via a corona wire or similar mechanism. Meanwhile, as the drum rotates, a laser beam is directed so that it “draws” successive lines across the drum. The laser beam is turned on and off while this happens- if it’s turned on while it’s scanning across a particular piece of the drum, the electrical charge of that part of the drum is neutralised.

At this point the drum has an invisible “virtual” image of charged areas (corresponding to the bits that will be white on the paper) and uncharged areas (corresponding to black).

2 – Toner Attracted to Uncharged Areas on Drum

The toner itself consists of non-conductive plastic resin, which is mixed with some form of conductive material so that it is affected by magnetic and electrical fields. This electrically-conductive toner is then charged to the same potential (“voltage”) as the charge on the drum.

This means that as the drum passes by the toner, the toner is only attracted to the uncharged areas of the drum (which, as we mentioned above is where the laser shone, and correspond to black- it’s all coming together now!). It’s not attracted to the charged areas, because they have the same charge as the toner itself.

3 – Toner Image Pattern Transferred to Paper

Now the drum is covered with a “real” image made up of black toner. As the drum rotates, the paper passes by and the toner is transferred onto it. However, at this point the image is still powdery and can be easily brushed off the paper.

4 – Fuser Melts Toner Making It “Permanent”

The final stage is where the paper passes by the fuser, a heated roller that causes the powdery toner to melt and stick to the paper. This is why paper is usually slightly hot when it comes out of a laser printer.

At this stage, your printout is ready and comes rolling out of the printer. That’s it!

When Is a Laser Printer not a Laser Printer?

Answer: When it’s an LED printer.

LED printers use the same basic principles as laser printers. The difference is in the light source used to create the charge-image pattern on the drum. Whereas true laser printers use a scanning laser beam to knock the charge off, LED printers have a row of LEDs (light-emitting diodes) which are turned on and off in the appropriate pattern as the drum sweeps past them.

Stay tuned for the exciting Part 2- Coming Soon!