Printing unit with an electrostatic printing aid comprising electrodes contained in a lid structure

A printing unit comprising an electrostatic printing aid for assisting the transfer of ink from an impression cylinder onto a dielectric substrate web, and further comprising an inductor device concealed against outside access on at least one end face of an outer-shell layer of a back-up cylinder, said inductor being connected in operation with a high voltage source for the electrostatic charging of the outer shell layer, wherein the inductor device has at least one inductor electrode which is connected to a high-voltage supply and is aligned by means of an electrode tip with the edge of said end-face for the purpose of applying the electrostatic charge to said outer-shell layer in a contactless manner, wherein the inductor device (7) has an electrode carrier (12) in the form of a lid with inner face (13) which covers concentrically and conforms in shape to the outer end face (35) of the back-up cylinder (4) and end face edge (10) of its outer shell layer (5) over its entire periphery, in such a way that an annular air gap (15) is formed between the electrode carrier (12) and the outer end faces (35) of the back-up cylinder, and wherein in this annular air gap and located opposite the end-face edge of the outer-shell layer there is an annular groove (16) in which are embedded several inductor electrodes (9), the electrode tips (11) of which, aligned with the end-face edge, project into the annular groove.