The basic requirement for sufficient adhesive performance of a surface is to be wetted by the substance which should adhere to the surface. Wetting can only take place if the surface energy of the substrate is higher than the surface tension of the substance.
Most plastic materials have very low surface energy and consequently are have low adhesion to glues, varnish or printings. It is a large field of applications for plasma treatment to provide surfaces of plastics which can be glued, printed and coated.
Wetting of a surface can be controlled by test inks. Diener electronic provides a standard set of 7 test inks which is applicable for most applications. These liquids can control surface energies in between 28 mN/m and 105 mN/m. A test ink spreading on a surface has lower surface energy than the surface.
Test inks and procedures are spcified by standards DIN 53364 and ISO 8296.