1. Print head is not clean.
Power off the printer,wait till the print head cools down.Clean the print head with alcohol using a soft towel or cotton swab.Do not use water or other liquids.
2. Paper of low quality.Solution:
Use Nelko labels for best results.
3. Density setting.
For Windows, go to "Settings"-"Devices"-"Printers & Scanners"-"PL70e-BT", click on "Manage", click on "Printing preference", click on "Parameters" to adjust print speed and density.
For Mac, Open any PDF file, click on printi icon, slide down, click on "Printer Features", then set print speed and darkness(concetration) and print.