What is corona discharge
Corona refers to the phenomenon of partial discharge on the surface of a charged body in a gas or liquid medium, which often occurs around high-voltage wires and near the tip of the charged body, and can produce substances such as ozone and nitrogen oxides. On substations and power lines above 110kV, there is often a layer of light similar to the solar halo, emitting sounds of "hiss" and "pi li". Corona energy consumes electrical energy and interferes with radio waves. Corona is a stable discharge in the form of electron avalanche and streamer, which is unique to extremely non-uniform electric fields.

Corona treatment
Most plastic films, such as polyolefin films, are non-polar polymers with low surface tension, generally ranging from 29-30mN/m. In theory, if the surface tension of an object is lower than 33mN/m, known inks and adhesives cannot adhere firmly to it, so the surface needs to be treated with corona discharge. The processing principle is to apply high-frequency and high-voltage electricity to the processing equipment, causing it to generate high-frequency and high-voltage discharge, producing small and dense purple blue sparks. The various ions generated after air ionization accelerate and impact the plastic film inside the processing device under the action of a strong electric field. Causing the chemical bonds of plastic molecules to break and degrade, increasing surface roughness and surface area. During discharge, a large amount of ozone is also generated. Ozone is a strong oxidant that can oxidize plastic molecules, producing polar groups such as carbonyls and peroxides, thereby increasing their surface energy.

The effect of corona discharge
Due to the non-polar nature of various polyethylene (PE) and polypropylene (OPP) molecules, it is difficult for polar ink molecules to adhere to the surface of PE films. So before printing PE film, electrical discharge treatment (or corona treatment) is carried out to form a polar surface layer to improve the adhesion with polar ink.