Corona treaters and plasma cleaners generate and expose organic or polymer substrates to ionized gas in order to improve the wettability of adhesives, paints, inks or other coatings. To create multiple bonding sites, corona treaters and plasma cleaners raise the surface energy (surface tension) of plastics such as ethylene propylene diene monomer (EPDM), polyolefin, polyethylene (PE), and polypropylene (PP). Plasma cleaners are also used to remove organic contaminants from metal, plastic, and rubber substrates. Although corona treaters are seldom used in industrial cleaning and surface preparation applications, they are often used to improve the adhesion properties of inks and coatings applied to three-dimensional (3D) parts. Typically, corona treaters and plasma cleaners are used with molded or extruded objects.
Selecting corona treaters and plasma cleaners requires an analysis of vacuum and atmospheric technologies. Vacuum plasma cleaners use electrode elements inside a vacuum chamber to produce a high-frequency electrical discharge under low pressure. In some applications, treatment gases such as argon or oxygen are required. Treatment cycle times range from 2 to 120 seconds, and are a function of the surface’s shape and material. Typically, vacuum plasma treating equipment is used to treat plastic profiles, containers, molds, and extrusions. Unlike vacuum equipment, atmospheric plasma cleaners do not use a vacuum chamber and electrodes. Instead, a generator and transformer produce plasma and use air pressure to move the plasma through a nozzle. Often, these types of corona treaters and plasma cleaners are used for component preparation in bonding, painting, soldering, and varnishing applications.
Corona treaters and plasma cleaners use several corona technologies. The most common technique discharges high voltage into the air. Typically, 3D parts are passed through a discharge region between two electrodes with a sustained, high-potential difference. Corona discharge at frequencies of 15 to 25 KHZ is most effective because of how the electrons oscillate in the gap between the electrodes. Such electrical surface treatment (EST) systems include a high-frequency generator, high-voltage transformer, and treatment electrodes. The frequency of the generator’s output signal is adjusted automatically, and the range depends on the load impedance. The transformer then steps-up the generator’s output signal to the level needed to generate the discharge. Such corona treaters and plasma cleaners also feature two electrodes: a treating electrode and a counter electrode.