One very common question about electrical surface treatment is, “What is the difference between corona and plasma treatment?” With a follow up question, “What best fits my application?” Both corona and plasma treatment increase the surface energy of numerous materials improving the adhesion of inks, adhesives, coatings and other agents. But, they both have unique properties that require consideration in terms of applications.
Sorting Out the Science
The word corona is used in a number of circumstances. For clarification, in this article, we will concentrate on corona that is created by an electromagnetic field. When atmospheric air is exposed to different voltage potentials, electrical discharge can develop. When this occurs, an avalanche effect is created caused by the voltage (consisting of electrically loaded molecules) colliding with neutral molecules and changing them to be electrically loaded. The result is a heavily loaded zone of lightning as we know it today, which is in fact atmospheric plasma.
When this phenomenon is contained inside an electrically grounded chamber, an air stream can be introduced to this chamber to force the plasma outwards in a controlled fashion and onto materials in a process called plasma treatment or atmospheric plasma treatment. However, when an insulator is placed between the two electrodes, the avalanche effect is avoided and the result is a cloud of ionized air. This ionized air – Corona Discharge – can now be used for the surface treatment of a wide number of materials which show poor or no adhesion properties to media such as printing inks, adhesives, etc.
Plasma discharge has a relatively narrow treating width but is capable of imparting enormous surface energies onto substrates. The plasma treating heads can also be quickly mounted onto existing lines with little setup. The plasma discharge is virtually potential free so it can be used to treat conductive materials. Plasma also produces no ozone gas which is a natural byproduct of the corona process. Alternatively, corona discharge typically imparts less surface energy but can treat very large areas. Corona treatment also has the advantage of being able to treat inside parts or in the recesses of 3-dimensional parts.
Let’s take a look at three of our most popular corona and plasma systems designed and manufactured here at 3DT and how these technologies are employed:
3DT’s MultiDyne™ System uses a low frequency air blown corona treatment that can treat a 2” wide band of material for virtually an unlimited length. The corona discharge is created by applying a high voltage between two electrodes. An air stream is passed through the electric arc created by the high voltage and results in a discharge blown out of the treating head that consists of corona and atmospheric plasma. As the voltage difference is contained inside the treating head no external ground reference is needed and the system can be simply “dropped in” onto virtually any non-conductive substrate.
3DT’s PolyDyne™ system utilizes high frequency corona discharge to treat virtually any surface. The material is placed between two electrodes subjected to high intensity corona discharge for a powerful, uniform treatment. Polymer films and foam several feet wide, the inside of syringes, or complex 3-dimensional parts- this versatile system can treat virtually any size and shape.
3DT’s PlasmaDyne™ systems come in either stationary or rotating head versions. The stationary head treats a 10-12 mm width while the rotating head treats up to 40 mm. The stationary head is ideal for small treating widths which requires higher intensity treatments and/or faster line speeds. The rotating heads give a wider treatment band and slightly lower treating intensities. Several of either heads can be integrated as one system to cover complex treating geometries. Plasma treatment can be used for micro-cleaning (the removal of residue and organic compounds) as well as surface modification to improve adhesion and thereby productivity.