Surface treatment, like most technology in the label and package printing market, has evolved. The need for it in 2025 is no different to the 1950s, when Verner Eisby established Vetaphone.

The principle is simple: “If you need a liquid, which could be ink, lacquer, or adhesive to adhere to a non-porous substrate, like plastic film or foil, you must ensure that the surface energy of both is closely matched otherwise the liquid will not ‘wet out’,” explains Kevin McKell, CSO, Vetaphone. “Failure to do so will result in poor adhesion and a faulty end-product that will require a costly reprint. Whether a liquid ‘wets’ a material well or poorly depends on the chemical nature of the liquid and the substrate to which it is applied. And it is measured in dyne/cm. The higher the dyne level, the better the ink or lacquer will adhere to the substrate.”

The process of corona treatment modifies the molecular structure of the substrate by directing a high-frequency discharge at the surface from close-range. By disrupting the carbon molecule chains on the surface, oxygen is introduced with the result that the newly created carbonyl groups have higher surface energy. This improves the chemical connectivity (dyne/cm) between the liquid and the substrate and allows better adhesion. 

Market trends

“Different substrates have different native dyne levels, and different dyne levels are required for different applications,” remarks McKell. “For example, water-based ink requires a higher dyne level than solvent-based, while coating and laminating can require even higher dyne levels.

“If the principle remains the same as ever, the technology that we see in today’s market is far more sophisticated in its control and capability,” McKell continues. “This is in response to the general trend across printed packaging for added-value techniques that make for greater on-shelf visual impact.  These additional techniques have brought about the development of new substrates that have more complex chemistry, and therefore require more careful and sophisticated processing.”

With line speeds continuing to increase, securing adhesion of inks, lacquers, and adhesives to these new substrates requires a detailed understanding and fine control of the surface treatment process if converters are to get it right the first time, every time. To facilitate this, Vetaphone has developed the VE1A-M model, which combines the higher speed and higher power (corona dosage) requirements. 

“There is a misconception in the industry that higher dosage requirement equates simply to higher power,” says McKell. “What’s needed is carefully controlled application of the corona discharge so that the delicate substrate is not damaged.”

The key to this dates back to Verner Eisby’s original patent in the 1950s, which allows the generator to monitor the treatment process and optimize the correct frequency to ensure the most efficient discharge. This gives the best treatment to the substrate. The generator will automatically monitor the output and self-match to any material, altering the frequency to ensure an efficient discharge. One of the key benefits of optimizing this process is that it prevents excessive heat, which is vital when dealing with sensitive substrates.

What about plasma?

So much for corona – what about plasma?  This is a debate that is becoming more prominent in discussions with converters as packaging becomes increasingly sophisticated. “First, let me quickly explain the difference,” says McKell. “Where corona works in ambient conditions, plasma requires a controlled environment to allow dosage of inert gases that are fine-tuned to each substrate and its intended use. Plasma also produces higher dyne levels that are easier to maintain – this is particularly useful with a substrate like BOPP that is notoriously difficult to treat. For more than 95% of applications, corona treatment provides the perfect solution. But in special cases, where the substrate has a complex structure, and downstream processing has specific requirements, the answer will be plasma grafting. 

Which is better?

So, which is better, corona or plasma? “The answer is they are not directly comparable,” explains McKell.  “Effectively, the only similarity is that they are both surface treatment techniques, but each uses a different method. And while the corona process relies on the ‘free’ ambient air, plasma requires far more investment in the technology and consumables (gas) that are required to make it work. This is why most plasma installations are with major international groups that use it for developing new packaging. Its value is both as an R&D tool and also its specialist commercial applications.

“I mentioned dyne levels earlier and dyne drop-off is a function of the additives in each substrate that over time migrate back to the treated surface, resulting in the need for subsequent bump or boost treatment before further processing,” continues McKell. “Getting this right is critical and the reason we invested in and opened our Test Lab facility back in 2020. It offers a unique opportunity to converters to run tests under controlled laboratory conditions prior to committing to the expense of commercial production. The same facilities are available to ink, lacquer, and substrate manufacturers too, each of which is under close market scrutiny to ensure that their new products meet or exceed the current international standards.”

If the fundamental need for surface treatment is unchanged, the technology surrounding it has adapted to the changes in market demand over the years. As the inventors of what has become known as corona treatment, Vetaphone is best placed to respond to any specific requirement going forward, the company notes.