Have you ever wondered why it is difficult to write or print on plastic – why the ink is smearing when you rub it? The reason is the relative energy between the two surfaces, and the only way to solve the problem is to modify the surface of the plastic and increase its adhesive capability. The process capable of this is called Corona treatment.

Corona Treatment

Being a man-made synthetic material, plastic consists of chains of molecules joined end to end to form even longer chains. These linked chains present few opportunities for bonding at the surface and need to be opened to increase wettability.

Directing a high frequency discharge at the plastic surface from close-range simply disrupts the molecules by oxidising it. The discharge splits the carbon molecules and breaks the oxygen into ions, some of which enter the surface layer of the plastic and improve the bonding, while others form into ozone that needs to be extracted.

The new carbonyl groups created have a higher surface energy, and this improves the chemical connectivity (dyne/cm) between the liquid and the plastic.

Corona treatment affects only the surface layer of the plastic, to a depth of 0.01 micron, and does not change its appearance or strength.


The effectiveness of Corona treatment depends on the specific material being used, as different materials have different characteristics and different amounts of slip and additives – and will therefore behave in different ways. Even two rolls of supposedly the same material can behave differently; it all depends on their precise chemical composition.

There are no limits to the substrates that can be Corona treated, but the intensity of the treatment required will vary significantly according to their chemical make-up. The best way to determine the exact value is by testing a sample of the actual film that is being used for a specific application.

Plasma Treatment

Vetaphone has developed a method of surface treatment that offers the fine-tuning required by the chemical make-up of these materials. It is cost effective and environmentally-friendly, and offers a real alternative to using the harmful components that are otherwise needed to do the job.

It is called Plasma, and where Corona treatment is a Dielectric Barrier Discharge (DBD) carried out in ambient air (blue groups in the illustration below), Plasma needs a controlled atmosphere because it uses small quantities of dopant gas for grafting (red groups in the illustration below). This allows Plasma to offer a different functionality to Corona and provide a range of surface capabilities.

What makes Plasma unique is the control level that it offers, which is missing on older Plasma systems. Whether you are considering full-scale production or a lab-sized testing system, Plasma offers complete control of the process and the ability to create a variety of different surface conditions.


Plasma has been successfully tested on a variety of substrates including: PET, PP, BOPP, PA, PE, PVC, PVDC, Printed Polymers and Fluorinated Polymers (PVF, PVDF, ECTFE, ETFE, FEP,and PTFE). If the substrate you are looking to treat is not on this list it is still very likely that Plasma will be successful, so please contact us to arrange a test in our lab facility.

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