Sheet-fed printing press for simultaneous recto-verso printing of sheets, in particular for the production of security documents

A sheet-fed printing press adapted to carry out recto-verso printing of individual sheets, comprising one or more printing units each adapted to carry out simultaneous recto-verso printing of the sheets, each printing unit including two printing cylinders cooperating with one another and forming a printing nip where both sides of the sheets are simultaneously printed, a first printing cylinder of the two printing cylinders collecting ink patterns from at least two plate cylinders associated with the first printing cylinder and a second printing cylinder of the two printing cylinders collecting ink patterns from at least two plate cylinders associated with the second printing cylinder and wherein the two printing cylinders are located one above the other such that the sheets travel laterally through each printing unit from a first lateral side located upstream of the printing nip to a second lateral side opposite to the first lateral side and located downstream of the printing nip, characterized in that the sheet-fed printing press is comprising at least two of said printing units that are located one after the other, wherein a number of at least two sheet transfer elements is provided downstream of the printing nip of a first one of the at least two printing units and upstream of the printing nip of a second one of the at least two printing units to transfer the sheets from the first printing unit to the second printing unit and in that the plate cylinders are each inked by an associated inking apparatus, and in that for each ink fountain, there is defined at least one reference plane, that intersects with that respective ink fountain and that contains the rotational axis of the plate cylinder associated with that respective ink fountain each inking apparatus being characterized in that the at least one respective reference plane contains at least one straight reference line, and in that this at least one straight reference line is oriented perpendicularly to the rotational axis of the plate cylinder associated with that respective ink fountain and in that this at least one straight reference line together with a vertical straight line confines an angle that is smaller than 35°.