Patent ID: 8034177

Claim:
An inner electrode for barrier film formation that is inserted inside a plastic container being formed with an opening, supplies a medium gas to the inside of the plastic container, and supplies high frequency power to an outer electrode arranged outside the plastic container to generate discharge plasma on an inner surface of the plastic container for forming a barrier film on the inner surface of the plastic container, the inner electrode for barrier film formation comprising: a gas supply pipe being formed with a gas flow path therein to supply the medium gas, wherein a distal end thereof being provided with a convex portion and the convex portion has a diameter smaller than that of the gas supply pipe; a cap member screwed onto the convex portion such that an outer side surface of the gas supply pipe and an outer side surface thereof are flush with each other, having equal maximum outer diameters, wherein the cap member is formed with an opening in a center portion of an end face thereof and the inside thereof is hollow; an insulating member being screwed onto an inner surface of the cap member until it engages a step portion provided to the opening of the cap member, wherein the insulating member is formed in a center portion through a longitudinal central axis thereof with a gas outlet communicated with the gas flow path, wherein the gas supply pipe and the cap member integrally form a substantially cylindrical body which extends along the longitudinal length of the plastic container, the convex portion and the cap member compose a falling-off preventing structure in order for the insulating member to prevent from being fallen-off, and an end portion of the cap member on the side of the gas blow-off for the medium gas has a rounded shape on its corner so as to prevent local plasma concentration.