Printing machine with laser perforating

1. A laser perforating system for applying at least one perforation pattern onto printed sheets, in particular sheets for the production of securities, banknotes, passports, ID cards and other valuable documents, comprising

a sheet transport system for transporting the printed sheets along a transporting path,

a laser perforating unit with at least one laser head disposed along the transporting path of the sheet transport system for perforating said printed sheets, and

a first aspiration unit to maintain the printed sheets against an aspiration surface of the first aspiration unit during perforation by said laser perforating unit, said aspiration surface being part of the first aspiration unit and non-movable in the direction of sheet transportation;

said first aspiration unit being disposed between said laser perforation unit and said transporting path of the sheet transport system and comprising at least one opening in said aspiration surface through which is directed said at least one laser head,

wherein the first aspiration unit is distinct from and not a part of the sheet transport system,

wherein the sheet transport system is able to transport the sheets in front of the sheet perforation system and relative to the aspiration surface of the first aspiration unit while the sheets are being perforated and

wherein the sheet transport system is configured to take separate, successive sheets from a first pile;

wherein said sheet transport system is a chain gripper system comprising a plurality of gripper bars each carrying a plurality of grippers for holding a leading edge of the sheets, the plurality of grippers of the sheet transport system passing in front of the aspiration surface.

2. A laser perforating system as claimed in claim 1 , wherein said opening exhibits a V-shape with a narrower part of the opening oriented towards the sheets to perforate.

3. A laser perforating system as claimed in claim 1 , wherein said at least one laser head comprises a suction part located at an extremity of said laser head and disposed in said opening, said suction part comprising aspiration means for drawing the sheets to perforate against said suction part.

4. A laser perforating system as claimed in claim 3 , wherein said aspiration means comprise a suction plate with a planar suction surface which is flush with the aspiration surface of the first aspiration unit.

5. A laser perforating system as claimed in claim 3 , wherein said suction part is further provided with evacuation means for evacuating the fumes and burnt material resulting from perforation of the sheets.

6. A laser perforating system as claimed in claim 1 , wherein said laser unit comprises a plurality of laser heads distributed transversely to a direction of displacement of the sheets along the transporting path of said sheet transport system in order to perform a plurality of perforation patterns at sheet locations which are distributed transversely to the direction of displacement of the sheets.

7. A laser perforating system as claimed in claim 1 , wherein each laser head is activated several times during processing of a sheet in order to perform a plurality of successive perforation patterns distributed longitudinally onto said sheets.

8. A laser perforating system as claimed in claim 6 , wherein a position of each laser head, transversely to the direction of displacement of the sheets, is adjustable.

9. A laser perforating system as claimed in claim 1 , wherein said laser unit further comprises a second aspiration unit to evacuate the fumes and burnt material resulting from perforation of the sheets on a side of the sheets opposite the laser perforating unit.

10. A laser perforating system as claimed in claim 1 , wherein the laser unit is pivotable laterally by a swing arm.

11. A laser perforating system as claimed in claim 10 , further comprising an actuating mechanism with a drive unit for performing swinging of the laser unit.

12. A laser perforating system as claimed in claim 1 , wherein each gripper bar of the chain gripper system further comprises brushes for pushing the sheet held by said grippers against the aspiration surface.

13. A production process for applying at least one perforation pattern onto printed sheets, in particular sheets for the production of securities, banknotes, passports, ID cards and other valuable documents, comprising the following steps:

a) transporting separate, successive sheets along a transporting path of a sheet transportation system in front of a laser perforating unit;

b) aspirating the sheets against an aspiration surface of an aspiration unit in front of the laser perforating unit, wherein the aspiration unit is distinct from and not a part of the sheet transportation system, said aspiration unit being disposed between said laser perforation unit and said transporting path of the sheet transportation system and comprising at least one opening in said aspiration surface through which is directed said at least one laser head, said aspiration surface being part of the aspiration unit and non-movable in the direction of sheet transportation;

c) while the sheets are being aspirated against said aspiration surface, and transported past the laser perforating unit and relative to the aspiration surface, perforating the sheets by means of the laser perforating unit;

wherein said sheet transportation system is a chain gripper system comprising a plurality of gripper bars each carrying a plurality of grippers for holding a leading edge of the sheets, the plurality of grippers of the sheet transportation system passing in front of the aspiration surface.

14. A production process as claimed in claim 13 , wherein said aspiration surface is additionally formed by an aspiration surface provided on said laser perforating unit.

15. A production process as claimed in claim 13 , applied in a printing machine comprising a printing unit for performing a printing operation on at least one side of the sheets, wherein the perforation process is performed downstream of the printing unit.

16. A production process as claimed in claim 15 , wherein transporting of the sheets through the printing unit is independent of the transporting of the sheets in front of the laser perforating unit.

17. A production process as claimed in claim 15 , comprising the step of inspecting the quality of the printed sheets before the perforation process.

18. A production process as claimed in claim 15 , comprising the step of drying the printed sheets before the perforation process.