A sheet is bent at the entrance to the fusing unit and comes into contact with the edge of the paper delivery tank, where static electricity builds up on the sheet through friction. This causes scattering of unfixed toner on the paper surface.
This may occur if:
Printing is done at low temperature or humidity
The thickness of the paper is equivalent to Paper Weight 2 or lower
Halftone images are printed in black and white
To adjust the following settings, pre-register the type of paper in use as a custom paper. For details about registering custom papers, see "Registering a Custom Paper", Paper Settings.