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Atmospheric pressure plasma activation of free-form surfaces

: Gredner, A.; Janker, C.; Gerhard, C.; Wieneke, S.

Parker, Margaret (Ed.):
Atmospheric pressure plasmas : Processes, technology and applications
New York: Nova Science Publishers, 2016
ISBN: 978-1-63485-180-0 (Print)
ISBN: 1-63485-214-1
ISBN: 978-1-63485-214-2
Aufsatz in Buch
Fraunhofer IST ()

Atmospheric pressure plasmas are powerful tools for the activation of various material surfaces and thus allow significant increase in adhesion of glues or lacquers. Such increase is mainly due to a plasma-induced formation of polar groups at the surface. However, the activation of complexly-shaped free-form surfaces, which is quite easily to be realized in low-pressure plasma chambers, can become a challenging task when working at atmospheric pressure. In this chapter, we present several approaches for such free-form plasma activation of different plastics and polymers based on direct and indirect dielectric barrier discharge (DBD) plasmas. Here, the use of DBDs allows the treatment of temperature-sensitive materials due to the marginal gas temperatures of this type of plasma discharge. First, a basic comparison of the efficiency of direct and indirect plasma treatment of polymers is given where the particularly obtained changes in surface energy, polarity and adhesion pull strength of applied lacquers are presented and discussed in more detail. Second, selected geometries of plasma devices for the activation of quasi free-form surfaces and the respective characteristics and perfomances of these devices are demonstrated: For the activation of 3D-shaped objects, a hand-held plasma device with a specifically designed roll-shaped discharge geometry is introduced. Here, the curved electrode surface conforms to Paschen’s law for plasma ignition at least one location at all times. So an easy use and the applicability on free form surfaces are enabled. Further, a foldable multiple pin plasma source which can be adapted to cylindrical work pieces with a minimum radius of 15 mm is presented. This source allows a large-scale treatment. Moreover, the guiding of indirect plasmas (jets) within flexible tubes is discussed. It is shown that such guiding can be performed for tube lengths of several tens of centimeters without any loss in efficiency of the plasma. Indirect plasmas can thus easily be brought to regions of interest of complexely-shaped free-form work piece surfaces where the plasma source itself cannot be used, for example due to restrictions of the accessible space in the case of bore holes or undercuts. In addition to the characterization of these plasma sources, the particular treatment efficiencies are presented by means of contact angle and surface energy measurements.