To address issues with faint printing, increase the darkness setting on your printer. You can also reduce print speed to further resolve the problem.
There is likely not enough heat applied to the ribbon to efficiently transfer the ink to the label, especially if you are using a resin ribbon.
The settings can be easily adjusted if you use the BarTender label printing software. Press the Print button and select “Document Properties” underneath your printer’s name.
Verify that the current settings in the “Stock” tab are correct. Your print method should display “Thermal-Transfer” and the Media Type should reflect your label type.
Select the “Options” tab and uncheck “Use current printer settings” in the “Darkness” field. With “Relative” selected, move the bar to the right to about 20 and confirm by clicking OK. This should increase the darkness of your printout. Please increase the darkness further if the problem persists.
If the printout is still not as expected, even with the darkness set to maximum, uncheck “Use current printer settings” in the “Speed Settings” field. Then reduce the printing speed to 3.00 in/sec or 2.00 in/sec.
If you do not use BarTender, you will have to adjust the darkness settings in your printer settings directly. For your Citizen CL-S631 printer, please refer to pages 31 and 34 of your printer manual for changing the settings. For your Zebra GX430t printer, please refer to page 107 of your printer manual.