Surface tension is crucial as it is the determining factor for ink adhesion and, therefore, the film's printability. It is a parameter for judging how well certain liquids can wet a given surface, and is determined by the film’s physical (surface structure) and chemical (formulation) characteristics. High peak count and Rz value increase surface tension, while surface-active lubricants (silicone) reduce it. The industry commonly tests surface tension using specified dyne inks.
Polymer resins vary significantly in surface tension, as do film formulations and surface structures. PVC has natural values around 32 to 34. Polyolefins (PP, PE) are much lower, and consequently they can only be printed after corona treatment. Corona treatment should be avoided when possible because the treatment itself has a limited shelf life and is difficult to monitor.
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