It's a good idea to clean the print head on your thermal label printer each time you load a new roll of labels in the printer.
To clean the print head:
Open the printer case by pulling the cover release tabs forward (these tabs are located on both sides near the top of the printer).
Rub the cleaning pen (supplied with the printer) across the dark area of the print head.
Wait one minute, and then close the printer case.
For further cleaning assistance, refer to your printer documentation.