When using a UV-LED printer, the ink is cured directly onto the surface of the metal. Depending upon the type and smoothness of the metal, it may or may not need an adhesion promoter to ensure that the cure or bond meets the client’s expectations. Keep in mind, there are different methods that can be used for printing on metal as well as various finishes that can be incorporated.
Printed white is often used as an undercoat to make the graphic more vibrant. In other cases, white ink isn’t used at all to allow the metal to illuminate through the CMYK ink. The specific techniques employed depend upon the look the customer desires.
-Jay Roberts, Roland DGA