Patent ID: 7107902

Claim:
A printing machine comprising: a plurality of active printing units for applying a liquid medium to a side of printing material at the operating speed of the machine; said active printing units each having a first cylinder and an associated sheet carrying cylinder; said sheet carrying cylinder of each active printing unit having grippers for engaging and transferring printing material through a nip defined between the first cylinder and the associated sheet carrying cylinder whereby a liquid medium can be applied to the printing material; at least one inactive printing unit having a first cylinder and an associated sheet carrying cylinder; said sheet carrying cylinder of each said inactive printing unit having grippers for engaging and transferring a sheet though a nip defined between the first cylinder and the associated sheet carrying cylinder of the inactive printing unit; said first cylinder of each inactive printing unit being moveable relative to the associated sheet carrying cylinder to a print-off position such that the printing unit is inactive during a printing operation and not involved in applying a liquid medium to a side the printing material during operation of the printing machine; and said first cylinder of each said inactive printing unit having a liquid repellant surface and being rotatable at the operating speed of the printing machine with the associated sheet carrying cylinder conveying printing material through the nip between the sheet carrying cylinder and the first cylinder with a printed side of the printing material facing the liquid repellant surface of the first cylinder for enabling passage of the printing material through the nip without smearing of liquid medium previously applied to the printing material in said active printing units.