FISH-EYES CONTAMINATION, COATING SYSTEMS
Causes:
Fish-eyes can be caused when a coating is applied to a substrate that is contaminated with low surface energy particles such as oil, wax, grease or silicone, fish-eyes may develop in the coating as it is applied. Similar situation when adding cooking oil in a nonstick pan.
These fish-eyes are produced because the coating is unable to wet out the contaminated area.
Potential causes of fish-eyes include:
▪ Improper or insufficient surface cleaning or preparation
▪ Effects of old finish or previous repair
▪ Contamination of air supply, if spray applied
Surface Energy of Different Materials
Surface energy is a term used to describe the surface of a given substrate; surface energies range from high to low. The molecular force of attraction between unlike materials determines their adhesion. The strength of attraction is depending on the surface energy of the substrate. High surface energy means a strong molecular attraction, while low surface energy means weaker attractive forces.
High Surface Energy
Molecules on the surface are so strongly attracted to each other that they will very happily be
attracted to liquid molecules as well. As a result, these materials are relatively easy to wet out and, in turn, to bond. High surface energy materials have surface energies on the order of 100s or 1000s of dynes/cm and include many metals and glass.
Solid surface has high surface energy; Liquid will spread or “wet out” the surface.