Preparation of dielectric coatings of variable dielectric constant by plasma polymerization

A process for the production of a non-conductive substrate coated with a polymer coating that is deposited on said substrate from the monomeric state and is resistant to corona discharge, comprising

• disposing a non-conductive substrate in a closed reactor between two temperature-controlled electrodes which are connected to a power supply,
• maintaining a vacuum within the reactor,
• establishing an atmosphere of monomer gas or monomer gas and diluent gas about the substrate,
• generating a plasma between the electrodes, thereby polymerizing the monomer gas or the monomer gas and diluent and depositing the polymerized substance on the substrate, and
• during the deposition, varying in one direction continuously or in stages at least one parameter selected from the group consisting of the gas partial pressures, the electric field strength and frequency and the current density, thereby producing a coated substrate wherein the coating is characterized by having a dielectric constant gradient, the variation in parameter being such as to initially produce on the substrate a polymeric stratum that has a dielectric constant closely approximating that of the substrate and to produce finally a surface stratum remote from the substrate that has a dielectric constant closely approximating that of the use environment.