This term is relevant for screen printers that are printing on “dark” color garments.
An underbase is a layer of ink (generally white or other light color) that is printed as a "base" on a dark shirt for other colors to sit on. This gives the top colors more brilliance. Since the underbase is generally a high opacity ink, it is flash-cured before the top colors are printed over it. Not only does underbasing slow production, but it is often an extra color (which costs more money). Underbases are also called an underlay (very common) or a mask (not as common).
Tips of screen printing on dark colored fabrics:
1. light color inks on dark goods generally require a base white screen and a flash.
2. Designs that have white in the image will only need a flash.
3. Any fluorescent inks need a white underbase+flash
Here are the reasons:
Shirts are fabric, and when ink is layered on it soaks into the fabric resulting in a muted look. Flash curing dries the ink enough to lay a second coat on top of the first coat (instead
of the fabric) resulting in a brighter color. Note that the ink also will feel thicker, because it is. Another reason for flashing is dye migration. This is most often seen on red shirts as the dyed
color of the shirt (especially with white ink) tends to “migrate” through the ink and turn it pink. Flashing reduces this dramatically.
There is no underbasing without a flash-cure unit (or some other method to flash dry the fabric). If you plan to do a lot of flashing make sure the unit is large enough to meet your production capacity.
You should position the flash unit so that you can get a cure in a matter of seconds. Plastisol will cure to the touch at around 120 degrees C (consult with your flash unit manufacturer for proper temperature suggestions based on their machine). If you fully cure the fabric, the top colors may not adhere properly and can flake off when washing the shirt. The length of time for the curing process is critical.
You may also want to learn about direct to garment printing machinery and processes.
It is important to know proper Underbase & Flash technique
for printing textile with dark colors.
technique for printing textile with dark colors.