When a laserprinter prints, the toner (providing ink) will put ink on the drum, and the fuser will then transfer the ink from the drum to the paper.
If for some reason, there was no paper when the fuser attempted to tranfer the ink from the drum to the paper, it will stick to the drum (as it is very hot). As a result, whenever you print, a little bit of ink will be transferred to your paper with each print. Cleaning the drum sometimes helps, but more often than not will the drum requires to be replaced.
Typical reasons for this to happen:
- The user attempted to print outside of the paper margins
- There was a paperjam but the printer kept printing because the sensor still detected paper to be present (can happen if the paper gets sideways before it jams) This is usually the result of improper placement of the paper in the tray.
Alternatively, it is possible your drum just needs to be replaced. Each drum can print a certain amount of prints before the drum wears out and no longer can correctly release the ink from the drum.