The object of surface treating is to improve the wettability of the surface, thereby improving the ability to bond to solvents, adhesives, and coatings. In order for a surface to be properly wet by a liquid, the surface energy of the plastic must be higher than the surface tension of the liquid. Surface energy is measured in dynes per centimeter. Ideally, the surface energy of the plastic should be 7 to 10 dynes/cm higher than the surface tension of the solventor liquid. For example, a printing ink having a surface tension of 30 dynes/cm would not adequately wet or bond to a material having a surface energy less than 37 to 40 dynes/cm (use drop let comparison image).
Non-porous substrates, such as polyethylene, polypropylene and foils have inherently low surface energy causing them to be non-receptive to bonding with substrates, printing inks, coatings, and adhesives.
There are a number of tests that can be used to measure surface energy. The most common are Dyne Pens, Cotton Swab Applicator Method, and Draw-Down Test Methods. Enercon’s EnerDyne™ pens provide a quick, safe and simple means of testing surface energy.
Follow these links to read about the pros and cons of each surface energy measurement method and specific instructions for performing tests with each of these techniques Dyne Pens, Cotton Swab Applicator Method, and Draw-Down Test Methods.