Corona Treating Basics
Corona treating increases the surface energy of plastic films, foils, paper and polymer objects to improve wettability and adhesion of inks, coatings and adhesives.
Treating works best when a substrate is treated at the time of extrusion and in-line prior to converting.
Corona treating increases quality and productivity through improved print quality, faster press speeds and less scrap.
Why do I need it?
Polymer films and objects have chemically inert and non-porous surfaces with low surface tensions causing them to be non-receptive to bonding with substrates, printing inks, coatings, and adhesives.
Pretreated films, that is films that have been surface treated at the time they were produced, exhibit a higher surface energy that is crucial to producing quality printed, coated or laminated products.
Film that is not treated at the time of production will not accept printing, coating or lamination well. The opposite is not always true. Even if film is treated at the time of production, it will not always guarantee that printing, coating or laminating will be easily accomplished at any future time.
Each film type has an inherent surface energy (dyne level) that can be increased through corona treatment at the time of production. This level of treatment diminishes over time. So, film that can be easily printed and coated immediately after production can, within a few days or weeks, lose sufficient surface energy to become unprintable and uncoatable.
Since it’s nearly impossible to guarantee that the film you receive will be converted within the required time limit, retreating in-line is often a necessity. It’s important to note that treating in-line cannot replace primary treatment at the time of production. In fact many films, especially polyolefins (Polyethylene and Polypropylene) are almost untreatable when they set after production.To ensure consistent quality, use films that have been treated at the time of production and retreat in-line. In order to make a product that is of acceptable quality to the converter and to the end customer, the substrate must be corona treated twice:
- At the time of production.
- Prior to converting.
How does surface treating work?
A corona treating system is designed to increase the surface energy of plastic films, foils and paper in order to allow improved wettability and adhesion of inks, coatings and adhesives. As a result, the materials treated will demonstrate improved printing and coating quality, and stronger lamination strength.
A corona treating system consists of two major components: the power supply and the treater station.
The power supply accepts standard 50/60 Hz utility electrical power and converts it into single phase, higher frequency (nominally 10 to 30 kHz) power that is supplied to the treater station.
The treater station applies this power to the surface of the material, through an air gap, via a pair of electrodes at high potential and roll at ground potential which supports the material. Only the side of the material facing the high potential electrode should show an increase in surface tension. (If treatment is applied to the other side of the material it is referred to as backside treatment.)
A corona treating system in its simplest form can be portrayed as a capacitor. Voltage is applied to the top plate which, in the case of a corona treating system, would be the electrode. The dielectric portion of the capacitor would be made up of some type of roll covering, air, and substrate in the corona treater.
The final component, or bottom plate, takes the form of an electrically grounded roll. In the corona treating system, the voltage buildup ionizes the air in the air gap, creating a corona, which will increase the surface tension of the substrate passing over the electrically grounded roll.
