Corona treatment is the most widely used surface activation process for plastic films, paper and aluminum foil before printing, lamination and coating. This guide walks you through the technology from principle to practice.
1. How Corona Treatment Works
A corona treater uses a high-frequency, high-voltage transformer to generate a strong electric field between the electrode and the grounded roll. Air near the electrode is ionized into low-temperature plasma. These energetic particles bombard the material surface, triggering oxidation that introduces polar groups such as hydroxyl and carboxyl — significantly raising the surface energy (dyne level).
In short: corona treatment turns a plastic surface from “non-stick” into “printable.”
2. Why Corona Treatment Is Necessary
Most plastic films (BOPP, PE, PET, etc.) have naturally low surface energy, typically 29–31 mN/m. For inks and adhesives to bond firmly, the substrate usually needs a surface tension of 38–40 mN/m or higher. Printing on untreated film leads to poor ink adhesion, pinholes and delamination.
3. Dyne Level — The Key Indicator
The dyne level measures whether treatment is sufficient, using dyne pens or test fluids. Different processes require different levels:
- Solvent-based ink printing: ≥ 38 mN/m
- Water-based ink printing: ≥ 40 mN/m
- Lamination / coating: ≥ 40 mN/m
4. Treatment Decay & Timing
Treatment effect decays over time, especially on PE. Ideally, printing should be completed within 24–72 hours after treatment. For long-stored materials, re-treatment or an in-line system with time compensation is recommended.
5. Common Problems
- Under-treatment: dyne level too low → increase power or reduce line speed
- Over-treatment: brittle surface, film blocking → reduce power
- Uneven treatment: worn electrode or uneven gap → inspect electrode and roll
Corona treatment remains one of the most mature and cost-effective surface treatment solutions. To learn more about selection, feel free to browse our products or contact us.