Surface Tension Testing or
Metal Cleanliness Testing

The surface energy is one decisive criterion for the adhesion of printing ink, glue, varnish, etc. on many plastic and metal surfaces.

It is given in mN/m (milliNewton per meter, currently valid unit) or in dyne/cm (dyne per centimeter, old unit, same numerical value).

Apart from some exceptions the general rule is: The higher the surface energy of a material, the better is the adhesion of anything meant to be fixed to its surface.

Reasons for a low surface energy on the one hand might be material specific. For example, many plastics show a very low surface energy and therefore need a chemical or physical treatment to achieve a good adhesion on them.

On the other hand, contaminations of the surface (grease, oil, or finger prints) might be a reason for a low surface energy.