Corona treatment

All materials have an inherent surface energy (dyne level). Surface treatment is a process that improves the bonding characteristics of most materials such as: paper, films, foils, and polymers by raising surface energy (dyne level).

Surface Treatment systems are available for virtually any surface format including dimensional objects, sheets and roll goods that are handled in a web format. Corona treatment (sometimes referred to as air plasma) is the standard surface treatment method in the plastic film, extrusion, and converting industries.

Most plastics, such as polyethylene and polypropylene, have chemically inert and nonporous surfaces with low surface tensions causing them to be non-receptive to bonding with printing inks, coatings, and adhesives. Although results are invisible to the naked eye surface treating modifies surfaces to improve adhesion. Users of surface treatment systems benefit from enhanced quality and productivity.

Polyethylene, polypropylene, nylon, vinyl, PVC, PET, metalized surfaces, foils, paper, and paperboard stocks are commonly treated by this method. It’s safe, economical, and delivers high line speed throughput. Corona treatment is also suitable for the treatment of injection and blow molded parts, and is capable of treating multiple surfaces and difficult parts with a single pass.

Corona discharge equipment consists of a high-frequency power generator, a high-voltage transformer, a stationary electrode, and a treater ground roll. Standard utility electrical power is converted into higher frequency power which is then supplied to the treater station. The treater station applies this power through ceramic or metal electrodes over an air gap onto the material’s surface.

All substrates, provide a better bonding surface when they are treated at the time they are produced. This is called “pre-treatment.” The effects of corona treatment diminish over time. Therefore many surfaces will require a second “bump” treatment at the time they are converted to ensure bonding with printing inks, coatings, and adhesives.

Other technologies used for surface treatment include in-line atmospheric (air) plasma, flame plasma, and chemical plasma systems.

Atmospheric plasma is very similar to corona, yet there are only a few differences between them. Both systems use one or more high voltage electrodes which positively charge the surrounding blown air ion particles. However in atmospheric plasma systems, the rate oxygen molecules bonding to a material’s molecule ends develops up to a 100x more. From this increase of oxygen, a higher ion bombardment occurs. This results in stronger material bonding traits and increased reception for inks and coatings. Atmospheric plasma treatment technology also eliminates a possibility of treatment on a materials non-treated side; also known as backside treatment.

Flame plasma treaters generate more heat than other treating processes, but materials treated through this method tend to have a longer shelf-life. These plasma systems are different than air plasma systems because flame plasma occurs when flammable gas and surrounding air are combusted together into an intense blue flame. Objects’ surfaces are polarized from the flame plasma affecting the distribution of the surface’s electrons in an oxidation form.

Chemical plasma is based on the combination of air plasma and flame plasma. Much like air plasma, chemical plasma fields are generated from electrically charged air. But, instead of air, chemical plasma relies on a mixture of other gases depositing various chemical groups onto the treated surface.

Vetaphone A/S

Related Information

• Surface finishing