What is corona treatment? Why is corona treatment needed for the packaging roll film during coding?

What is coronavirus?

Corona refers to the phenomenon where partial discharge occurs on the surface of a charged body in a gas or liquid medium, often occurring around high-voltage conductors and near high-quality charged materials, producing substances such as ozone and nitrogen oxides. In substations and lines above 110kV, a light layer similar to a solar halo often appears, producing "sizzling" and "sizzling" sounds. Corona can consume electrical energy and interfere with radio waves. A corona is a stable discharge in the form of electron burst—flow injection—unique to highly uneven electric fields.

Corona treatment

Most plastic films (such as polyhydrocarbon films) are non-polar polymers with relatively low surface tension, generally 29-30 mN/m. Theoretically, if an object's surface tension is below 33 mN/m, known inks and adhesives cannot adhere firmly to it, so the surface must be treated by corona electrolysis. The treatment principle is to apply high-frequency and high-voltage electricity to the processing equipment, causing high-frequency and high-voltage discharges that produce fine, dense purple-blue sparks. Various ions produced after air ionization accelerate and impact the plastic film inside the treatment device under the strong electric field. This breaks and degrades the chemical bonds of plastic molecules, increasing surface roughness and surface area. Discharge also generates a large amount of ozone. Ozone is a strong oxidizing agent that oxidizes plastic molecules, producing strongly polar groups such as carbonyl and peroxide, thereby increasing their surface energy.

The role of coronavirus

Since various types of polyethylene (PE) and polypropylene (OPP) are non-polar molecules, it is difficult for polar ink molecules to adhere to the surface of PE film. Therefore, before printing PE film, electro-discharge treatment (also called corona treatment) is performed to form a polar surface layer to improve adhesion to polar inks.

Various packaging roll films are corona-treated for better coloring and less likely to fall off.