Why do I have to pre-treat a digitally-printed shirt if I am printing white ink?
Pre-treatment is the cornerstone of direct-to-garment printing; proper application yields a better result. It is a liquid solution that allows the printing and washability of white ink and is used for full color images on a variety of colored shirts, most commonly, black shirts.
The pre-treatment acts just like primer does for paint. It allows white ink to adhere to and sit on top of the shirt. If white ink soaks into the shirt, it doesn’t come out looking white and does not provide a smooth surface for the CMYK inks to print on.
Pre-treatment also reacts with white ink. This reaction is similar to when a screen printer uses a “flash” unit to semi-cure plastisol ink so the next colors printed on top don’t smear or mix together (a result of printing wet-on-wet). The pre-treatment “flashes” the white ink so that it becomes more or less a semi-solid surface. When CMYK inks are printed on top of the white ink, it doesn’t mix and look muddy.