How does a laser printer work?

Here’s how a laser printer works. Inside the printer is a large metal roller (the “photoreceptive drum”).

As the drum rotates past an electrified wire (“the corona”), the surface gets a positive electrical charge in preparation for the laser beam.

The beam is guided by the computer, of course, invisibly scanning the text and images onto the photoreceptive drum.

The metal parts the laser hits build up a temporary negative electrical charge and immediately get brushed with toner powder, a mix of positively charged plastic and pigment dust.

Because opposites attract, the positive toner sticks to the parts that had been zapped negatively by the laser, but is repelled by the rest of the drum, which is still positively charged.

At this instant, that part of the drum looks like a mirror image of the page being printed. But not for long, because it immediately makes contact with the paper.

An electric wire under the paper (the “transfer release corona”) zaps the paper with negative electricity, which pulls the powder off the roller and onto the page in the pattern drawn by the laser.

Its ink held on only by gravity at this point, the paper then passes between the “fusers,” a pair of hot metal rollers. The heat melts the powder to the fibers of the paper and spits it out of the printer.

This is why paper coming out of a laser printer is always so toasty warm.