Gas plasma process
Following treatments are possible in one and the same
equipment:
- Surface activation
- Surface cleaning
- Micro etching
- Plasma polymerisation
The formed reactive particles react in a direct way with the
surface without damaging the bulk properties of the treated part. In fact the
surface modification is limited to the outermost 10 to 1000A of the
substrate. Following process mechanisms are possible on polymer, fluoropolymer
and other plastic surfaces:
Surface activation
Is the replacement of weak bondings by high reactive
carbonyl, carboxyl and hydroxyl groups. The surface is super active after
treatment which is not the case for an untreated polymer surface. Activation
can also be performed with amino groups or other functional groups.
Cleaning
Is the removal of the organic contaminants at the surface.
Non visible oil films, rest contamination layers, Sicontamination and even
partially absorbed contaminations can be removed by plasma cleaning. Particles
or anorganic contamination are not removed by plasma, because there is no
mechanical interaction. Also visible oil films will not be removed economically
by this technique. Therefore it is called super-fine cleaning.
Micro-Etching
Is the process to break down the weak covalent bondings at
the surface. The outer most molecular layers are affected by this as is also present contaminant layers which are of the same type of weak C-H bondings. In this way the
surface is cleaned, oil films and possible plastic injection moulding additives
or weak bondings at the surface are removed to result in a uniform active
polymer surface.
Deposition
Is the process where out of gases a thin polymer coating is
formed at the surface. By choosing the gas and process parameters these thin
coatings can be deposited with various properties or acting as barrier layer.
Cross linking
Is the result of an inert gas action to cross link the
polymer surface. A stronger and harder micro surface is formed. In some
occasions it leads to more wear or chemical resistance of the polymer.
Through gas selection and parameter setting it can be
determined which of these physical processes will be the main one.
For metals and ceramics plasma treatment is mainly a matter
of cleaning and deposition as can be understand from the physics described
above.
