Plasma breaks the organic bonds of heavy organic molecules to produce lighter and more volatile ones, which evaporate from the surface leaving it in an ultra-clean state. The reactive chemical species oxidise organic contaminants to form carbon oxides and water vapour. These processes also sterilise the surface, destroying microbial contamination.
When in direct contact with the substrate, electric discharges will erode it on the micrometre scale, creating microstructures that improve the mechanical binding of an adhesive. Plasma can also deposit polar hydroxyl and nitric oxide groups on the cleaned surface, to increase its energy and wettability. The result is that an adhesive will wet more efficiently and can fill microstructures due to capillary action.
The benefits of cold plasma
The cold plasma method avoids wet chemistry and requires no expensive vacuum chambers, improving the cost, safety and environmental impact of the process. It also offers fast processing speeds, which can be beneficial in some applications. In addition to the energetic ions and electrons, the surface is irradiated by very short wave ultraviolet light, enhancing the cleaning effect.
Cold atmospheric pressure plasma is very effective, does not overheat the surface and does not visually affect the surface. It requires no toxic chemicals and the reactive chemical species decay rapidly after treatment, making it safe and environmentally friendly. Compared with low-pressure plasmas, atmospheric plasma equipment is usually less expensive.
Our customers have had success using plasma cleaning for one- and two-dimensional products, cylindrical products, complex structures and granulates and powders. This has occurred in a range of sectors, including medical, electronics, automotive, consumer, food, cosmetics and professional model making.
Atmospheric plasma cleaning technology is available in compact and easy-to-integrate forms. For example, the Plasmabrush PB3, a compact plasma generator that can be easily integrated into automated treatment systems. For smaller objects or laboratory work, the low-power, handheld Piezobrush PZ2 may be suitable.
About the author:
Peter Swanson is Managing Director of adhesives specialist, Intertronics - www.intertronics.co.uk