PLASMA TREATMENT OF SUBSTRATES

A process for plasma treating a substrate comprises applying a radio frequency high voltage to at least one electrode positioned within a dielectric housing having an inlet and an outlet while causing a process gas, usually comprising helium, to flow from the inlet past the electrode to the outlet, thereby generating a non-equilibrium atmospheric pressure plasma. An atomised or gaseous surface treatment agent is incorporated in the non-equilibrium atmospheric pressure plasma. The substrate is positioned adjacent to the plasma outlet so that the surface is in contact with the plasma and is moved relative to the plasma outlet. The velocity of the process gas flowing past the electrode is less than 100 m/s. Process gas is also injected into the dielectric housing at a velocity greater than 100 m/s. The volume ratio of process gas injected at a velocity greater than 100 m/s to process gas flowing past the electrode at less than 100 m/s is from 1:20 to 5:1.