Printing on engineered films is more challenging than printing on paper. Getting ink to wet out on polymer and metalized films may require specialized formulations, coatings and printing processes. In many industries, such as flexographic printing, corona treatment has long been used as a tool to increase surface energy in-line and promote adhesion. The technology is adaptable to other printing technologies as well. It can be both an insurance policy to ensure adhesion as well as a must have requirement.
When most films are extruded from resin their surfaces are non-porous and chemically inert with very low surface energy. Film extruders will corona treat their freshly extruded films to increase their surface energy. In fact, films that are not corona treated at the time of extrusion may never be receptive to future corona treatment. However, there is often a significant time lapse between the time the film is created and the time it is printed on. The effects of time, storage conditions, additives rising to the surface, and contamination combine to lower the surface energy of a substrate. This is why corona treating is often employed to "bump treat" materials to improve wettability and promote adhesion.