Reason 1:  The source file may not have been created with the ideal quality. 

Solution: Print the sample label to test if your printer is working well. 

               If the sample label is good, check the file quality.

Reason 2:  High print speed or density. 

Solution: Try reducing your print speed (try 3 in/sec) and density (try 3 as well) to see if you get a better result.

For Mac

①Select "Printer Features" in "Preview"


②Set the print density in "Darkness" 


③Set the print speed in "Print Speed" 


For Windows

①Open "Devices and Printers" -> right click on "Label Printer" -> choose "Printer Preferences” 


②Set the print speed in "Print Speed"


③Set the print density in "Print Density"