In order to weld two or more plastic films, we must heat the welding joint up to the melting temperature while pressing. It is necessary to keep the pressure until the joint is cold enough.

A polar plastic (PU, PVC, PET, EVA, ...) is heated when is subjected to the action of a high frequency electric field.

When we are welding by high frequency, the plastic portion between the electrode and the table undergoes an uniform heating due to the dielectric losses developed on it by the high frequency current. The electrode and the table are at ambient temperature and therefore the plastic surfaces in contact with them become cooled. In such conditions, the hottest area is in the middle of the joint, exactly where it's needed.

The plastics are melt inside but are kept cool outside, allowing to put very high power densities and then very short welding times, between 1 and 5 seconds.

This is the principle of high frequency welding and there is no other system able to give such a high quality of welded joints.