Cold
Gas Plasma Treatment For
Re-engineering Films - Page 3
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Activation and
Reactions
The effect of a plasma on a given material is
determined by the chemistry of the reactions between the surface and the reactive species
present in the plasma. At the low-exposure energies typically present in glow-discharge
plasma systems, the interactions occur only in the top few molecular layers. The majority
of activation processes are related to preparing the surface for subsequent operations
(such as printing or altering the surface wetting characteristics).
Gases, or mixtures of gases, used for cold
plasma treatment of polymers include air, nitrogen, argon, oxygen, nitrous oxide, helium,
tetrafluoromethane, water vapor, carbon dioxide, methane. and ammonia. Each gas produces a
unique plasma composition and results in different polymer surface properties.
For example, the surface energy that is
analogous to wettability and chemical reactivity can be increased very quickly and
effectively by plasma induced oxidation, nitration, hydrolyzation, or amination.
Conversely, plasma induced fluorination depresses surface energy, producing an inert and
nonwettable surface.
The Gas Plasma
Reactor
The physical process of cold gas plasma
surface treatment is as straightforward and easy to describe as the equipment is to
operate. The reactor is a combination of a vacuum chamber with vacuum pump and purge
plumbing, a source of electromagnetic energy (rf generator), process gas sources and
regulators, and a system controller to orchestrate the process.
In the pilot line operated at this company,
the roll product to be treated (up to 60 in. width and 19 in. package diameter) is loaded
in the payoff chamber and threaded through the chamber to the take-up reel. The plasma
treatment operation is then initiated and entirely controlled by the push of a single
button.
The process steps are: 1) pump down to
predetermined vacuum pressure (base pressure); 2) introduce a process gas and
stabilization at a desired process pressure; 3) initiate the plasma by providing rf
energy; 4) transport product through the system; 5) after treating the desired length,
shut rf power and process gas delivery; 6) pump down to base pressure to eliminate
residual process gas(es); 7) vent to atmosphere; 8) remove treated product. (See Figure
2.)
Figure 2
[Technical Publications][Back]
Paper Film Foil Converter, June 1997,
Volume 71, No. 6, Stephen L. Kaplan |
