Plasma cleaning of large areas in low vacuum

We have pioneered the use of plasma etching to remove oil lubricant films from sheet metal coils in a roll-to-roll process. Preliminary investigations of oil removal from aluminum and steel strips employed a scaleable linear multi-orifice hollow cathode (LMHC) as an oxygen plasma source (Figure 1). LMHC operates in the pressure range of about 50-130 Pa in oxygen, air, and other gases. During operation of the LMHC, a remote oxygen plasma jet impinges on the substrate located about 2-3 cm from the cathode. The substrate is subjected to both, electron bombardment and chemical etching with atomic oxygen. LMHC can be powered by DC, RF, or best by pulsed DC.
            Using a LMHC, a lubricant oil coating on Al foil coupons, cut off from Alcoa Al rolls,  has been removed at speeds of up to 5 m/min. Potential industrial application of a LMHC has been demonstrated by cleaning one-meter-wide Al rolls (Figure 1).

Figure 2. One-meter-wide LMHC device is tested in a roll-to-roll system

Cleaning efficiency depends strongly on the surface temperature. The surface temperature during the cleaning process is determined by the equilibrium of the heat delivered to the surface, mainly be electrons, and heat dissipation through the foil. Substantial part of the lubricant oil is removed by evaporation. Therefore, surface recontamination with oil is a serious issue in cleaning large-area surfaces. A LMH is an intensive plasma source that could be used for various treatments of extremely large surface areas. It can be used in both direct plasma contact and remote modes. The last one is especially important for setting up plasma treatment of polymers.


1. A. Belkind, S. Krommenhoek, H. Li, Z. Orban, and F. Jansen, Removal of oil from metals by plasma techniques, Surf.Coat.Technol., 68/69 (1994) 804-808.
2. A. Belkind, H. Li, and H. Clow, Cleaning oil from metal in a coil-to-coil process, in: Proceedings of Nigth International Conference on Vacuum Web Coating, Ed. R. Bakish (Bakish Materials Corp., Englewood, NJ, 1995), p. 239.
3. A. Belkind, H. Li, H. Clow, and F. Jansen, Oil removal from metals by linear multi-orifice hollow cathode, Surf.Coat.Technol, 76-77 (1995) 738.
4. A. Belkind, F. Engle, and S. Zarrabian, Plasma cleaning of metals: lubricant oil removal, Metal Finishing, 94 (1996) 19.
5. A. Belkind, F. Jansen, H. Li, and Z. Orban, An in situ XPS study of hollow cathode plasma cleaning and recontamination of an aluminum surface, Surf.Coat.Technol., 92 (1997) 171.