In plastic paint construction process or after the film can produce a variety of defects because of various aspects reason, many defects are related to the phenomenon of surface tension, the causes of surface tension is: asymmetric molecular force distribution on the liquid surface, interface of the liquid and the liquid inside the forces, surface free energy of the molecules are highly, per unit area up to the energy for the surface molecules.
In solid there is also a similar surface orientation effect, it has a surface free energy, surface force is used to reduce the surface free energy of liquid and solid, the surface tension causes the liquid into a ball, because the ball surface area ratio is the smallest volume.
If two different surface tension of liquid contact each other, low surface tension flow to cover higher surface tension of liquid, because the total surface free energy is lower.
This flow is the difference in surface tension force, some people called flows driven by surface tension gradient.
Uniform coating can be stably coated on the surface of the plastic, the main conditions of the surface tension of the coating must be smaller than the surface tension of the coating material.