Corona treatment is a process where the surface of an item is changed through exposure to plasma. A coronal plasma discharge array, made of hundreds or thousands or small points of plasma, exposes the surface of a material to a special low-temperature plasma. This exposure alters the properties of the material, usually imparting properties that weren’t present before. Corona treatment is a safe and low-cost method of treating material surfaces and is used in hundreds of ways. One of the most common uses of coronal treatment is in preparing non-porous surfaces for printing or adhesion.
Plasma is a state of matter that occurs when a gas is exposed to an electrical current. The structure of the gas begins to break down into its constituent particles. This breakdown causes the gases to exhibit properties that they didn’t possess before and will often result in excess energy being bled off into the plasma’s surroundings. This energy bleed is usually heat or light and accounts for the glow from fluorescent lights and neon signs.
Corona plasma is created when an electrode is exposed to a non-enclosed system, such as open air. This electrode will charge the gas around it and create a small ball of plasma. This plasma will naturally move away from the electrode until it is far enough away that it recollects into normal gas. As the plasma moves, it creates convection, which pulls unaltered air closer to the electrode. This converts the new gas to plasma, making the corona area constant.
In order to harness this plasma for corona treatment, manufacturers use coronal discharge array. This is an area covered in electrodes, so when it is turned on, the coronas overlap and create a solid area of plasma. This is often set up so items can move through a corona plasma curtain on a conveyor belt.
Since corona treatment uses forms of plasma that exist at just higher than room temperature, it can be used on many different materials. Everything from paper to plastic to metal can undergo a coronal treatment. When an item is first manufactured, it is often exposed to coronal plasma, but the structure will often slowly move back to its original composition, so further exposure is occasionally needed.
The most common mass use of coronal treatment is with sheet plastic. Since plastics, such as polypropylene, are both chemically inert and non-porous, printing inks, adhesives and other common agents have no way to stick to them. The substances will simply slide off over time. Using corona treatment, the surfaces of these plastic are altered to accept certain types of common chemical bonds.