What is corona

Corona refers to the phenomenon of partial discharge on the surface of charged body in gas or liquid medium, which often occurs around high-voltage conductors and near the tip of charged body, and can produce ozone, nitrogen oxide and other substances. On the substations and lines above 110kV, light layers similar to the solar halo often appear, giving out "sniff" and "sire" sounds. Corona consumes electrical energy and interferes with radio waves. Corona is a kind of stable discharge in the form of electron avalanche streamer, which is unique to the extremely uneven electric field.

Corona treatment

Most plastic films (such as polyolefin films) are non-polar polymers with low surface tension, generally 29-30mN/m. Theoretically, if the surface tension of an object is lower than 33mN/m, the known ink and adhesive cannot be firmly attached to it. Therefore, corona treatment is required for its surface. The treatment principle is to apply high frequency and high voltage electricity to the treatment equipment to generate high frequency and high voltage discharge and produce small and dense purple blue sparks. Various ions generated after air ionization accelerate and impact the plastic film in the treatment device under the action of strong electric field. The chemical bond of the plastic molecule breaks and degrades, increasing the surface roughness and surface area. When discharging, a large amount of ozone will also be produced. Ozone is a strong oxidant, which can oxidize plastic molecules and produce strong polar groups such as carbonyl and peroxide, thus improving its surface energy.

Effect of corona

Since various polyethylene (PE) and polypropylene (opp) are non-polar molecules, it is difficult to attach polar ink molecules to the surface of PE film. Therefore, before PE film printing, electric spark treatment (or corona treatment) is carried out to form a polar surface layer to improve the combination fastness with polar ink.

Zhengfei Packaging（ http://zfpack.com/ ）After corona treatment, all kinds of packaging roll films are dyed more firmly and are not easy to fall off.