Abstract: The present invention relates to a multilayer protective coating for a substrate and a process for protecting a substrate by the deposition of a continuous, transparent, amorphous, inorganic coating essentially comprising silicon, carbon, nitrogen, oxygen and hydrogen by means of a plasma. The invention also concerns the application of the coatings according to the invention in the protection of substrates and in particular against electrostatic charges.

Abstract: Process for protecting a transparent optical substrate which is polymeric and has a vitreous transformation temperature and is selected from the group consisting of polycarbonate, polymethylmethacrylate, polystyrene acrylonitrile, crystalline polystyrene, polyimide, polyester, polyamide, polyvinyl chloride and glass, by deposition of an inorganic continous and transparent film consisting essentially of silicon, carbon, nitrogen, oxygen and hydrogen of the formula Si C.sub.x N.sub.y O.sub.z H.sub.t, in whichx is between 0 and 5y is between 0.3 and 0.8z is between 1.3 and 2.5t is between 0.5 and 1.2.A surface of the substrate is exposed to a plasma at a temperature below the temperature of vitreous transition of the substrate in the presence of precursors of Si, C, N, O and H is gaseous form, the precursor gas of the silicon being selected from the group consisting of SiH.sub.4, Si.sub.2 H.sub.6 and Si.sub.3 H.sub.