Even a high-puridity clean surface may provide only poor adhesion. In particular in case of polymer materials (plastics) a low surface energy of the substrate material itself restricts wetting, in case of metalls it may be an oxidized surface.
Plasma activation provides perfect surface adhesion
Plasma Activation of plastics
Most plastics have a very low surface energy. That means that surface molecules of the plastic only cause low attracting forces for molecules of extrinsic sucstances. The most essential reason is, that most plastic polymers are non polar. That means that no electric dipol momentum occurs at their surface. However oxygene plasma can provide polar groups on these surfaces
A plastic surface will automatically be activated if a plasma treatment by oxygene plasma will continue after the cleaning process is completed.
After plasma activation almost all substrates can be perfectly wetted and consequently also coated by glueing, printing or painting.
However there is a rest of substrates which are impossible candidates for glueing. Even for those plasma technology provides solutions as will be explained in clause "Etching"