Achieving reliable adhesion can be challenging across a wide range of materials. Whether you’re printing, coating or laminating, the surface properties of the material play a critical role in how well inks, coatings and adhesives will bond.
In this article, we look at why adhesion issues occur, how corona treatment helps overcome them, and the key factors that influence consistent surface treatment in production.
Why do adhesion issues occur?
Writing, printing, coating or laminating on plastic films presents well-known challenges. Untreated plastic films have a surface structure that prevents inks, coatings and adhesives from bonding correctly. A simple example is when you try to write on a plastic bag with a pen – the ink doesn’t stick because the surface energy of the plastic is too low.
For industrial processes, this same issue leads to poor adhesion, print defects, coating failures, and delamination if surface treatment is not correctly applied.
As you can see from the above, without surface treatment most plastic films fall well below what is required for reliable production.
What causes adhesion problems?
Whether a liquid wets a material effectively depends primarily on the chemical process of both the liquid and the substrate. Wetting is defined as the ratio between the surface energies of the liquid and substrate. In general, a material will be wetted, if its surface energy (dyne/cm) is higher than that of the liquid. If not there will be adhesion problems.
How to avoid adhesion issues?
To obtain sufficient wetting and adhesion on plastic films or metallic foils during production, inline pre-treatment before printing, laminating or coating is necessary. Corona treatment has proven to be a highly effective and cost efficient solution. It can be integrated directly into the production line and delivers consistent surface activation.
Why corona treatment?
Corona is a high frequency electric discharge directed towards the materials surface. The result is an improvement of the chemical bonding capability (dyne/cm) of the material surface, allowing inks, coatings, and adhesives to anchor properly. Surface treatment does not alter the strength, thickness or appearance of the treated material.
Determining the correct treatment level
The effectiveness of corona treatment depends on several factors:
• Material type
• Required dyne level
• Line speed
• Web width
• Number of sides to be treated
• Material age and prior treatment history
There are no limitations on the types of materials that can be corona treated, but the required treatment intensity (Watt/min/m²) varies significantly by application.
The treatment level can be calculated using the following formula: Power (Watt) = T × S × W × M
P = Total power (Watt) required
T = Number of sides to treat
S = Line speed (m/min)
W = Web width (m)
M = Material factor (Watt/m²/min)
The exact value is best determined by testing a sample of the actual material used for a specific application.
Why Automatic Power Regulation?
Vetaphone treaters are equipped with automatic power regulation. When the needed treatment level (watt/min/ m2) has been determined, the treater automatically adjusts power output to ensure the material is exposed to the same energy level, regardless of line speed variations. This ensures stable and repeatable surface treatment throughout production.
What is the durability of corona treatment?
Over time, treated surfaces will experience a reduction in dyne level. This occurs more rapidly when materials contain slip additives, which migrate to the surface. Older or thicker films can also be more difficult to treat for the same reason. For optimal results, it may be necessary to re-treat materials shortly before use. Materials pre-treated during extrusion often benefit from a final corona boost/refresh prior to printing, coating, or laminating.
Is maintenance important on corona systems?
To maintain consistent dyne levels, it’s essential that electrodes and insulators remain clean. Vetaphone’s quick change system has electrodes mounted in pull-out/push-in cartridges, enabling fast and safe maintenance without removing the treated material from the line. Additionally, the treater stations are designed to operate reliably in environments with high humidity.
Vetaphone’s generator technology
Vetaphone generators offer outputs from 1-80 kW with unlimited power capacity on request, and feature a unique resonance system. This ensures highly efficient power transfer, making them among the most energy efficient corona generators available on the market.
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