During Corona discharge treatment, electrons are accelerated into the surface of the plastic causing the long chains to rupture, producing a multiplicity of open ends and free valences are formed. The free valences are then able to form carbonyl groups with the atoms from the ozone created by the electric discharge, which gives the improved adhesion.
The adhesion is further enhanced by the cleaning effect that the ozone causes, by oxidation on the surface of the material. Read more about the Corona treatment process here.
In general, the following rule is true: “A material will be wetted, if its surface energy (=dyne/cm) is higher than that of the liquid and if not there will be an adhesion problem.” Read more about the Corona treatment process here.
The surface tension is then determined visually by estimating how the liquid reacts within the first two seconds following application. The test liquid can shrink and/or form itself into globules (individual droplets) or it can remain unchanged.
When a test liquid shrinks or forms into droplets it indicates that the film has a lower surface energy than the liquid applied. The test should be repeated as many times as necessary with a liquid of a lower surface tension until it remains unchanged for a period of two seconds or more. Once that has been achieved, the film can be said to have that level or surface energy at least equal to that of the liquid applied. Further applications should be made until shrinkage or droplets occur within two seconds. This last measurement should be taken as failure, and the surface energy of the liquid used for the previous measurement should be taken to be the surface energy of the film. Read more about our dyne pens here and order your dyne pens for testing today.
The only way to messure the dyne level is by using a water drop measurement. Read more about the Corona treatment process here.
Normally Vetaphone offers pressurized units which also prevents solvents of reaching the Corona discharge.