The role of corona treatment: discharge between the electrode and the corona treatment rod through the electrode to ionize the air and form ozone and nitrogen oxide. At the same time, high-energy electrons and ions attack the surface of the film, causing its chain molecules to break, producing free radicals, and oxidizing cross-linking reactions with the corona products of the air to form polar groups such as hydroxyl and carbonyl groups, improving the surface tension and polarity of the film.

The addition of additives may also have certain effects on the polarity and surface tension of the film surface. The commonly used additive in BOPET films is an anti-adhesion agent, usually silica. The silicon-oxygen bond in silicon dioxide has strong polarity, and the surface of silicon dioxide particles is often adsorbed with a certain amount of combined water and hydroxyl, so the silicon dioxide particles exposed on the surface of the film help to increase the polarity and surface tension of the film surface, which is conducive to aluminum plating. Sometimes, in order to improve the compatibility of silica particles with PET and promote their dispersion in the PET polymerization process, surface treatment agents (dispersants, coupling agents, etc.) are used to surface treat them to reduce their surface tension and polarity. In this case, the distribution of silica particles on the surface of the film will affect the polarity and surface tension of the film surface, and excessive surface treatment agent may migrate to the surface of the film, resulting in poor aluminum plating performance.