Corona treatment is a high frequency discharge that increases the adhesion of plastic surfaces. It increases the surface energy of plastic films, foils and papers to improve the wettability and adhesion of inks, coatings and adhesives. The treatment is best when the substrate is treated during extrusion and processed online prior to conversion. Corona treatment improves quality and productivity by improving print quality, increasing printing speed and reducing waste. Polymeric films have chemically inert and non-porous surfaces with low surface tension making them unacceptable for adhesion to substrates, printing inks, coatings and adhesives.
Pretreated films, ie films that have been surface treated at the time of production, exhibit higher surface energy, which is essential for the production of high quality printing, coating or laminate products. Untreated films are not well accepted for printing, coating or lamination at the time of production. The opposite is not always the case. Even if the film is processed during production, there is no guarantee that printing, coating or lamination can be easily done at any time in the future.
Each film type has an inherent surface energy, also known as a dyne level, which can be increased by corona treatment during production. This level of treatment will decrease over time. Thus, films that can be easily printed and coated immediately after production can lose sufficient surface energy in a few days or weeks to become unprintable and non-coatable.
Since it is almost impossible to guarantee that the movie you receive will be converted within the specified time limit, it usually needs to be returned online. It is worth noting that online processing is not a substitute for primary processing at the time of production. Many films, especially polyolefins (polyethylene and polypropylene), are almost unusable after production. To ensure consistent quality, use a film that has been processed at the time of production and return it online. In order to make the quality of the converter and the final customer’s product acceptable, two corona treatments are required, one at the time of production and the other before the conversion.
How corona treatment works:
The corona treatment system is designed to increase the surface energy of plastic films, foils and papers in order to improve the wettability and adhesion of inks, coatings and adhesives. As a result, the treated material will exhibit improved printing and coating quality, as well as greater laminate strength.
The corona treatment system consists of two main parts:
1. Power: Accepts a standard 50/60 Hz utility and converts it to a single-phase, higher-frequency (nominal 10 to 30 kHz) power supply to the processing station.
2. Processing station: This power is applied to the surface of the material by an air gap to a high potential electrode and is rolled at the ground potential of the support material. Only the side of the material facing the high potential electrode will show an increase in surface tension.
The simplest form of corona treatment system can be depicted as a capacitor. A voltage is applied to the top plate, which in the case of a corona treatment system will be an electrode. The dielectric portion of the capacitor will consist of some type of roll cover, air and substrate in the corona processor.
The final part or base plate is in the form of an electrical grounding roller. In a corona treatment system, an increase in voltage ionizes the air in the air gap, creating a corona which increases the surface tension of the substrate through the electrical ground roller.
