SURFACE TENSION -

Surface Tension is the interfacial tension at the surface of a liquid/air interface. This surface tension allows a liquid film to form on the surface of a liquid and is equal to the surface energy of the liquid per unit length of the film at the equilibrium.

The surface tension of a liquid can be visualized as the ease with which it wets a solid surface. Liquids with low surface tension wet any surface more easily than those with higher surface tension. In the same way, a solid surface can be characterized in terms of its surface energy.

For reasons of paintability, recoatability, good adhesion and prevention of surface defects, it is important for paint and substrate surface tensions to have similar values, with the paint having a lower surface tension than the substrate to ensure wetting. Prevention of surface tension related problems depends on at the work site or on the paint line, good surface preparation, viscosity control, as well as on paint properties. Often, low surface tension solvents and/or surfactants must be added in order to prevent defects. Unfortunately, there is not yet a practical method for measuring surface tension during drying and baking, which is when defects occur.