I nk adhesion is a complex issue involving the chemical and physical attachment between an ink and substrate. The attachment is primarily influenced by the chemistry of the ink, the method used to dry or cure the ink on the substrate, the type of substrate used, and the substrate's precise surface characteristics, which is the most variable aspect of the adhesion equation. This means that the ink forms a bond that is made permanent in the drying or curing process.
Wetting is very critical on smooth, non-absorbent surfaces, such as plastics.
In a previous column, we discussed such substrates and pointed out that plastics such as polyethylene and polypropylene will not accept ink in their natural states. On two recent occasions, we have seen clients suffering through adhesion problems on corrugated polypropylene board. The ink would dry but refused to maintain adhesion, even though the polypropylene had, at one time, been treated to provide a higher surface energy. The problem in this case was that time and storage conditions degraded the surface pretreatments to the point where surface energy dropped too low. The result was a very weak adhesive bond from the ink.