Intaglio printing press systems for recto-verso intaglio-printing of sheets for the production of banknotes and like securities

Abstract

Intaglio printing press systems for recto-verso intaglio printing of sheets, in particular for the production of banknotes and the like securities, wherein first and second intaglio printing presses are operatively-coupled to one another by a sheet processing and transporting system comprising an automated guided vehicle system for automatically transporting sheets from a sheet delivery station of the first intaglio printing press where recto printing is performed to a sheet feeding station of the second intaglio printing press where verso printing is performed.

Claims

1. An intaglio printing press system for recto-verso printing of sheets for the production of banknotes and securities, wherein the intaglio printing press system comprises first and second intaglio printing units each comprising an impression cylinder cooperating with a plate cylinder carrying at least one intaglio printing plate which is inked by an inking system and wiped by a wiping system, said first and second intaglio printing units being operatively-coupled to one another directly by a sheet transporting system comprising a chain conveyor system with spaced-apart gripper bars for transporting the sheets from the first intaglio printing unit where recto printing is performed to the second intaglio printing unit where verso printing is performed, said first and second intaglio printing units being disposed in a tandem configuration such that said impression cylinder and said plate cylinder of the first intaglio printing unit rotate in the same directions as said impression cylinder and said plate cylinder of the second intaglio printing unit, said sheet transporting system further comprising a sheet transfer arrangement for performing reversal of the sheet transport direction of the sheets before transfer thereof directly to impression cylinder of the second intaglio printing unit; wherein the sheets are taken away from the impression cylinder of the first intaglio printing unit by said chain conveyor system with a leading edge of the sheets held by the chain conveyor system and wherein said sheet transfer arrangement comprises a first transfer drum or cylinder placed at a downstream end of the chain conveyor system for getting hold of a trailing edge of the sheets transported by the chain conveyor system; wherein said sheet transfer arrangement further comprises a second transfer drum or cylinder placed between the impression cylinder of the second intaglio printing unit and said first transfer drum or cylinder for transferring the sheets from the first transfer drum or cylinder directly to the impression cylinder of the second intaglio printing unit.

2. The intaglio printing press system according to claim 1, further comprising at least one drying unit for drying a recto or verso side of the sheets.

3. The intaglio printing press system according to claim 1, further comprising at least one inspection unit for controlling the printing quality of a recto or verso side of the sheets.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the present invention will appear more clearly from reading the following detailed description of embodiments of the invention which are presented solely by way of non-restrictive examples and illustrated by the attached drawings in which:

(2) FIGS. 1a to 1c are schematic views of a first embodiment of an intaglio printing press system for recto-verso printing of sheets according to the invention;

(3) FIGS. 2a to 2c are schematic views of a second embodiment of an intaglio printing press system for recto-verso printing of sheets according to the invention;

(4) FIGS. 3a to 3c are schematic views of a third embodiment of an intaglio printing press system for recto-verso printing of sheets according to the invention;

(5) FIGS. 4a and 4b are schematic views of a fourth embodiment of an intaglio printing press system for recto-verso printing of sheets according to the invention; and

(6) FIGS. 5a and 5b are schematic views of a fifth embodiment of an intaglio printing press system for recto-verso printing of sheets according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(7) The intaglio printing press systems which will be described in the following for the sake of illustration all basically share a more or less identical or similar configuration as far as the printing units for recto printing and the printing units for verso printing are concerned. As this will be apparent from the following description, each printing unit, whether for recto printing or verso printing of the sheets, exhibits a configuration similar to that disclosed in European patent application EP 0 406 157 A1 in the name of the present Applicant, which application is incorporated herein by reference in its entirety.

(8) More precisely, each printing unit at least comprises (i) an impression cylinder, (ii) a plate cylinder carrying intaglio printing plates and contacting the impression cylinder to form a printing nip therebetween where the sheets are actually printed, (iii) an inking system for inking the intaglio printing plates carried by the plate cylinder, and (iv) a wiping system for wiping the surface of the inked intaglio printing plates prior to printing.

(9) In the below-discussed embodiments, the inking system is preferably an indirect inking system, i.e. an inking system wherein a multi-colour ink pattern formed by means of a plurality of inking devices is first collected on an ink-collecting cylinder (or Orlof cylinder) contacting the surface of the plate cylinder. Alternatively, so-called direct inking systems wherein one or more inking devices directly ink the surface of the plate cylinder are also possible. Indirect inking systems are however preferred in that they permit substantial ink savings. A combination of indirect and direct inking systems is also possible (see for instance European patent application EP 0 091 709 A1 in that respect). Within the scope of the present invention, the actual configuration of the inking system is not as such critical and is not to be regarded as being a factor limiting the scope of the invention as claimed.

(10) According to the exemplary embodiments given below, the impression cylinder, the plate cylinder and the ink-collecting cylinder all advantageously have the same diameter, in this case a triple-sized diameter, that is, a diameter such that each cylinder comprises three segments (i.e. three blankets in the case of the impression cylinder and ink-collecting cylinder, and three intaglio printing plates as regards the plate cylinder). The diameter or size ratio of the impression cylinder, plate cylinder and ink-collecting cylinder can thus be expressed as 3:3:3. Any other diameter or size ratio among the impression cylinder, plate cylinder and ink-collecting cylinder is however possible, such as for example 3:3:2 (as in the case of the printing presses described in European patent applications EP 0 091 709 A1 and EP 0 873 866 A1, which are both incorporated herein by reference in their entirety), 2:3:2 or 2:3:3 (as illustrated in FIGS. 2 and 3 of European patent application EP 1 602 482 A1 which is also incorporated herein by reference in its entirety), 2:2:2 (as disclosed in European patent application EP 0 563 007 A1), 3:3:4, 3:4:4, 4:4:4, etc. All possible permutations will not be listed herein for the sake of conciseness. In general, the diameter or size ratio among the impression cylinder, plate cylinder and ink-collecting cylinder can be X:Y:Z, where X, Y, Z respectively designate the number of segments (or size) of the impression cylinder, the plate cylinder and the ink-collecting cylinder, values X, Y, Z being integer numbers preferably equal to 1, 2, 3, 4 or 5. While greater numbers of segments (or sizes) are possible (i.e. X, Y, Z>5), this implies relatively large machine configurations for a given size of sheets to be processed. Values X, Y, Z are therefore preferably kept in practice at low values ranging from 1 to 5, preferably from 1 to 4, even more preferably from 1 to 3.

(11) Triple-sized cylinders, as disclosed in EP 0 406 157 A1, for instance allow the use of up to five distinct inking devices placed around the periphery of the ink-collecting cylinder (as illustrated in the Figures). A greater number of inking devices might necessitate increasing the size of the ink-collecting cylinder to a greater size in order to provide more space for additional inking devices.

(12) Preferably, the impression cylinder, the plate cylinder and the ink-collecting cylinders are disposed in such a way that contact and passage of the respective segments and cylinder pits typically present between the segments of the three cylinders are synchronized as described in European patent application EP 1 602 482 A1, which is incorporated herein more particularly in that respect. This also preferably applies to the arrangement of the wiping system with respect to the plate cylinder, which wiping system typically includes a wiping roller rotating in the same direction as the plate cylinder.

(13) The following reference numerals are used in the Figures and in the following description: 1a, 1b: intaglio printing press (first, respectively second) 1.1, 1.2: sheet feeding location/station 2.1, 2.2: intaglio printing unit 2a.1, 2a.2: impression cylinder 2b.1, 2b.2: plate cylinder (with intaglio printing plates) 3.1, 3.2: inking system (indirect) 3a.1, 3a.2: ink-collecting cylinder (Orlof cylinder) 4.1, 4.2: wiping unit/system 5.1, 5.2: endless chain conveyor system (with spaced-apart gripper bars for holding the leading edge of the sheets) 6.1, 6.2: drying unit/system (e.g. infrared or UV) 7.1, 7.2: inspection system for quality control (recto-side, respectively verso-side) 8.1, 8.2: sheet delivery location/station 9: sheet processing and transporting system (with automated guided vehicle system or AGV) 10.1: transfer cylinder/drum 11: sheet feeding location/station 12.1, 12.2: intaglio printing unit (first, respectively second) 12a.1, 12a.2: impression cylinder 12b. 1, 12b.2: plate cylinder (with intaglio printing plates) 13.1, 13.2: inking system (indirect) 13a. 1, 13a.2: ink-collecting cylinder (Orlof cylinder) 14.1, 14.2: wiping unit/system 15.1, 15.2: endless chain conveyor system (with spaced-apart gripper bars for holding the leading edge of the sheets) 16.1: drying unit/system (e.g. infrared or UV) 17.1, 17.2: inspection system for quality control (recto-side, respectively verso-side) 18: sheet delivery location/station 20.1: transfer cylinder/drum 21: sheet feeding location/station 22.1, 22.2: intaglio printing unit (first, respectively second) 22a.1, 22a.2: impression cylinder 22b. 1, 22b.2: plate cylinder (with intaglio printing plates) 23.1, 23.2: inking system (indirect) 23a. 1, 23a.2: ink-collecting cylinder (Orlof cylinder) 24.1, 24.2: wiping unit/system 25.1, 25.2: endless chain conveyor system (with spaced-apart gripper bars for holding the leading edge of the sheets) 26.1: drying unit/system (e.g. infrared or UV) 27.1, 27.2: inspection system for quality control (recto-side, respectively verso-side) 28: sheet delivery location/station 30.1, 30.2: transfer cylinder/drum 31: sheet feeding location/station 32.1, 32.2: intaglio printing unit (first, respectively second) 32a.1, 32a.2: impression cylinder 32b. 1, 32b.2: plate cylinder (with intaglio printing plates) 33.1, 33.2: inking system (indirect) 33a. 1, 33a.2: ink-collecting cylinder (Orlof cylinder) 33b.2: ink-transfer cylinder 34.1, 34.2: wiping unit/system 35: endless chain conveyor system (with spaced-apart gripper bars for holding the leading edge of the sheets) 36.1, 36.2: drying unit/system (e.g. infrared or UV) 37: inspection system for quality control (verso side) 38: sheet delivery location/station 40: sheet transfer arrangement (leading edge-trailing edge sheet transfer/substitution) 40.1: transfer cylinder/drum (for reversal of sheet transporting direction) 40.2: transfer cylinder/drum 41: sheet feeding location/station 42.1, 42.2: intaglio printing unit (first, respectively second) 42a.1, 42a.2: impression cylinder 42b. 1, 42b.2: plate cylinder (with intaglio printing plates) 43.1, 43.2: inking system (indirect) 43a.1, 43a.2: ink-collecting cylinder (Orlof cylinder) 44.1, 44.2: wiping unit/system 45.1, 45.2: endless chain conveyor system (with spaced-apart gripper bars for holding the leading edge of the sheets) 45a. 1: chain wheels (at sheet transfer location of conveyor system 45.1) 46.1, 46.2: drying unit/system (e.g. infrared or UV) 47.1, 47.2: inspection system for quality control (recto-side, respectively verso-side) 48: sheet delivery location/station

(14) The endless chain conveyor systems 5.1, 5.2, 15.1, 15.2, 25.1, 25.2, 35, 45.1, 45.2 are as such known in the art and do not need to be described in detail here. Such conveyor systems typically comprise a pair of endless chains driven into rotation by chain wheels, gripper bars being attached to the endless chains at selected intervals in order to hold sheets to be transported by their leading edges.

(15) The inspection systems 7.1, 7.2, 17.1, 17.2, 27.1, 27.2, 37, 47.1, 47.2 are also known as such in the art. A suitable inspection system for this application is for instance disclosed in International application No. WO 03/070465 A1 which is assigned to the present Applicant.

(16) The drying units 6.1, 6.2, 16.1, 26.1 36.1, 36.2, 46.1, 46.2 may be any suitable drying device, especially an infrared drying device or heating-generating device, or a UV (ultraviolet) drying device, depending on the type of intaglio printing ink used.

(17) A first embodiment of the invention will now be described in reference to FIGS. 1a to 1c. According to this first embodiment, the intaglio printing press system comprises first and second intaglio printing presses 1a, 1b respectively for recto and verso printing, which intaglio printing presses 1a, 1b are operatively-coupled to one another by a sheet processing and transporting system 9 (see FIG. 1c) comprising an automated guided vehicle (referred to by acronym AGV) system which automatically transports loads of sheets processed by the first intaglio printing press 1a from the sheet delivery station 8.1 thereof to the sheet feeding station 1.2 of the second intaglio printing press 1b in order to be further processed. According to this first embodiment, the first and second intaglio printing presses 1a, 1b exhibit identical configurations (different configurations could alternatively be used depending on the actual job to carry out).

(18) As illustrated in FIG. 1c, the two intaglio printing presses 1a, 1 b are disposed with the same orientation, i.e. with the sheet feeding stations 1.1, 1.2 thereof oriented on the right-hand side in FIG. 1c and the sheet delivery stations 8.1, 8.2 oriented on the left-hand side. According to a variant, the two intaglio printing presses 1a, 1 b could be oriented in a head-to-tail configuration, i.e. with opposite directions.

(19) Automated guided vehicle systems are known as such in the art and do not need to be described in detail in the present description. These AGV systems are used for a wide variety of logistical applications where loads of material or processed items have to be transported from one processing location to another. Within the scope of the present invention, care should be taken that the AGV system is adapted to be coupled to the output (sheet delivery station of the first intaglio printing press 1a and to the input (sheet feeding station of the second intaglio printing press 1b.

(20) Preferably, the sheet processing and transporting system 9 may additionally comprise one or more buffers (not illustrated) for temporarily storing the sheets produced by the first intaglio printing press 1a. The advantage of such buffers is to enable temporary storage of the sheets already printed by the first intaglio printing press 1a in case of machine halts or maintenance operations on the second intaglio printing press 1b.

(21) In the context of this first embodiment, the sheet processing and transporting system 9 preferably further comprises an automated unloading apparatus for unloading the loads of sheets from the sheet delivery station 8.1 of the first intaglio printing press 1a. Such an unloading apparatus is for instance taught in European patent application EP 0 870 712 A1 in the name of the present Applicant, which is incorporated herein by reference. A similar system might be used to automatically load the partially-printed sheets at the sheet feeding station 1.2 of the second intaglio printing press 1b. Such automated unloading or loading apparatus might also be provided with pile-robot systems for manipulating the sheets by processing sets of sheets placed on vertically superposed stacking boards of a paternoster system, either in an individual manner (i.e. one stacking board at a time) or in a simultaneous manner (i.e. several stacking boards at a time).

(22) Advantageously, an automated stacking board inserting apparatus might also be provided at the sheet delivery station 8.1, 8.2 of the first and/or second intaglio printing presses 1a, 1b in order to automatically insert a new stacking board on top of a previous stacking board onto which a complete set of sheets has been delivered. Such an automated stacking board inserting apparatus (and stacking boards for use therewith) is disclosed in European patent application EP 0 725 027 A2 which is incorporated herein by reference in its entirety.

(23) According to the first embodiment, one will appreciate and understand that the side of the sheets which is freshly printed (i.e. the recto side on the first intaglio printing press 1a and the verso side on the second intaglio printing press 1b) is oriented towards the exterior of the corresponding impression cylinder 2a.1, 2a.2. In the chain conveyor system 5.1, 5.2 which delivers the sheets from the printing unit 2.1, 2.2 to the sheet delivery unit 8.1, 8.2 (which chain conveyor system 5.1, 5.2 runs in a counter-clockwise direction in the illustration of FIG. 1a), the freshly printed sheets are oriented with their freshly-printed side oriented downwards, past the drying unit 6.1, 6.2 and the inspection unit 7.1, 7.2. Before being delivered in the sheet delivery unit 8.1, 8.2, the sheets are subjected to a 180 rotation and thus delivered with their freshly-printed side oriented upwards. In other words, once printed on the first intaglio printing press 1a, the sheets are oriented with their recto-side oriented upwards. The sheets are directly transferred with this same orientation to the sheet feeding station 1.2 of the second intaglio printing press 1b. The recto-side of the sheets which was printed on the first intaglio printing press is thus oriented towards the interior of the impression cylinder 2a.2 of the second intaglio printing press 1b where the verso-side is printed. The sheet delivered at the output 8.2 of the second intaglio printing press 1b, which are printed on the recto and verso sides, are oriented with their verso-side oriented upwards.

(24) For the sake of explanation and illustration, white and black triangles indicating the orientation of the printed sheets will be used in the illustrations of FIGS. 2a-2c, 3a-3c, 4a, 4b, 5a and 5b to respectively designate the printed recto-side and the printed verso-side of the sheets.

(25) A second embodiment of the invention will now be described in reference to FIGS. 2a to 2c. It will be appreciated that FIGS. 2a to 2c are partially-overlapping side-view illustrations of one and the same intaglio printing press system, taken from left to right. According to this second embodiment the intaglio printing press system comprises first and second intaglio printing units 12.1, 12.2 respectively for recto and verso printing, which intaglio printing units 12.1, 12.2 are operatively-coupled to one another directly by a sheet transporting system comprising a chain conveyor system 15.1 with spaced-apart gripper bars for transporting the sheets from the first to the second intaglio printing units 12.1, 12.2. According to this second embodiment, the two intaglio printing units 12.1, 12.2 are disposed in a mirrored configuration (i.e. with the cylinders rotating in opposite directions) with the sheet feeding station 11 of the intaglio printing press system being located between the two intaglio printing units 12.1, 12.2 (see FIGS. 2b and 2c) and the sheet delivery station 18 of the intaglio printing press system being located at an outermost end of the intaglio printing press system, i.e. on the outermost left-hand side in the illustrated example (see FIG. 2a).

(26) Besides, the chain conveyor system 15.1 which couples the two intaglio printing units 12.1, 12.2 runs in this example in a clockwise direction (i.e. in the same direction as the impression cylinder 12a.2 of the second intaglio printing unit 12.2), the sheets being accordingly transferred to the downstream-located second intaglio printing unit 12.2 on a lower part of the path of the chain conveyor system 15.1 (where the drying unit 16.1 and the inspection unit 17.1 are located).

(27) More precisely, according to this second embodiment, the sheet transfer location between the impression cylinder 12a.1 of the first intaglio printing unit 12.1 to the chain conveyor system 15.1 is disposed at a side of the impression cylinder which is located, with respect to a vertical plane intersecting the rotation axis of the impression cylinder 12a.1 of the first intaglio printing unit 12.1, opposite to the second intaglio printing unit 12.2 (i.e. on the right-hand side of the impression cylinder 12a.1see FIG. 2c).

(28) At the sheet transfer location between the chain conveyor system 15.1 and the impression cylinder 12a.2 of the second intaglio printing unit 12.2 there is provided a transfer cylinder (or drum) 10.1, which transfer cylinder rotates in a counter-clockwise direction in the illustration, for transferring the sheets from the chain conveyor system 15.1 to the impression cylinder 12a.2 of the second intaglio printing unit 12.2.

(29) In this way, the sheets are appropriately oriented for recto printing in the first intaglio printing unit 12.1 and verso printing in the second intaglio printing unit 12.2.

(30) A second drying unit for drying the verso side of the sheets is not illustrated in FIGS. 2a, 2b along the path of the chain conveyor system 15.2 leading to the delivery station 18. It will however be appreciated that a similar drying unit as drying unit 16.1 might be provided (in a manner similar to what is illustrated in FIG. 5a).

(31) A third embodiment of the invention will now be described in reference to FIGS. 3a to 3c. It will be appreciated that FIGS. 3a to 3c are partially-overlapping side-view illustrations of one and the same intaglio printing press system, taken from left to right. This third embodiment is highly similar to the second embodiment of FIGS. 2a to 2c. The only difference resides in the actual configuration of the chain conveyor system 25.1 which operatively-couples the two intaglio printing units 25.1, 25.2 to one another. More precisely, according to this third embodiment, the sheet transfer location between the impression cylinder 22a.1 of the first intaglio printing unit 22.1 to the chain conveyor system 25.1 is disposed at a side of the impression cylinder 22a.1 which is located, with respect to a vertical plane intersecting the rotation axis of the impression cylinder 22a.1 of the first intaglio printing unit 22.1, on the same side as the second intaglio printing unit 22.2 (i.e. on the left-hand side of the impression cylinder 22a.1see FIG. 3c). All other elements are identical to the second embodiment and do not accordingly need to be discussed again.

(32) A fourth embodiment of the invention will now be described in reference to FIGS. 4a and 4b. It will be appreciated that FIGS. 4a and 4b are partially-overlapping side-view illustrations of one and the same intaglio printing press system, taken from left to right. According to this fourth embodiment the intaglio printing press system comprises first and second intaglio printing units 32.1, 32.2 respectively for recto and verso printing, which are disposed vertically, one on top of the other. The two intaglio printing units 32.1, 32.2 are operatively-coupled to one another directly by a sheet transporting system comprising a pair of transfer cylinders 30.1, 30.2. In contrast to the second and third embodiments, no chain conveyor system is used and a more compact printing press configuration is obtained as a result. While the height of the printing press system is increased as compared to the other embodiments, the foot-print of the system is similar to that of a conventional single-side intaglio printing press.

(33) The two transfer cylinders 30.1, 30.2 are advantageously provided with an ink-repellent coating aimed at reducing smearing problems.

(34) The first intaglio printing unit 32.1 is preferably located at the bottom of the system with the sheet feeding unit 31 (and preferably the sheet delivery station 38 as well) resting on the floor so as to facilitate loading of sheets to be printed onto the intaglio printing press system. The second intaglio printing unit 32.2 is accordingly located on top of the first intaglio printing unit 32.1.

(35) According to this fourth embodiment, the impression cylinder 32a.1 and the plate cylinder 32b.1 of the first intaglio printing unit 32.1 and the impression cylinder 32a.2 and the plate cylinder 32b.2 of the second intaglio printing unit 32.2 are disposed in a mirrored configuration (a tandem configuration might alternatively be possible), i.e. the impression cylinder 32a.1 and the plate cylinder 32b.1 of the first intaglio printing unit 32.1 (which rotate respectively in a clockwise and counter-clockwise directionsee FIG. 4b) rotate in opposite direction as compared to the impression cylinder 32a.2 and the plate cylinder 32b.2 of the second intaglio printing unit 32.2 (which rotate respectively in a counter-clockwise and clockwise directionsee FIG. 4b).

(36) In addition, according to the fourth embodiment, the inking systems 33.1, 33.2 of both intaglio printing units 32.1, 32.2 are disposed on the same side, with both ink-collecting cylinders 33a.1, 33a.2 rotating in the same direction (i.e. clockwise in the illustration of FIGS. 4a and 4b), thereby providing suitable access to the wiping systems 34.1, 34.2 of both intaglio printing units 32.1, 32.2. This implies that an intermediate ink-transfer cylinder 33b.2 is interposed between the ink-collecting cylinder 33a.2 and the plate cylinder 32b.2 of the second intaglio printing unit 32.2, as illustrated in FIG. 4b. This additional ink-transfer cylinder 33b.2 is preferably a cylinder having a same diameter as the ink-collecting cylinder 33a.2 (and the plate cylinder 32b.2 in this example).

(37) According to this fourth embodiment, and in contrast to the previously-described embodiments, it will be appreciated that the chain conveyor system 35 which transports the sheets from the second intaglio printing unit 32.2 to the sheet delivery unit 38 runs in a clockwise direction, i.e. the freshly-printed sheets are transported to the sheet delivery unit 38 on a lower path of the chain conveyor system 35 (where the drying unit 36.2 and the inspection unit 37 are located). A drying unit 36.1 cooperates with the second transfer cylinder 30.2 in order to appropriately dry the recto-side of the sheets just printed in the first intaglio printing unit 32.1 prior to transfer thereof onto the surface of the impression cylinder 32a.2 of the second intaglio printing unit 32.2.

(38) According to the fourth embodiment, an inspection of the recto-side of the printed sheets might also be carried out along the sheet delivery path of the printed sheets, or at any other suitable location.

(39) A variant of the fourth embodiment of the invention may consist in adapting the configuration of the second intaglio printing unit 32.2 such that the inking system 33.2 would be located on the opposite side of the plate cylinder 32b.2 as compared to the fourth embodiment. According to this variant, an ink-transfer cylinder 33b.2 as in the fourth embodiment would not anymore be required.

(40) A fifth embodiment of the invention will now be described in reference to FIGS. 5a and 5b. It will be appreciated that FIGS. 6a and 6b are partially-overlapping side-view illustrations of one and the same intaglio printing press system, taken from left to right. This fifth embodiment is somewhat similar to the second and third embodiments in that the first and second intaglio printing units 42.1, 42.2 are operatively-coupled to one another directly by a sheet transporting system comprising a chain conveyor system 45.1 with spaced-apart gripper bars for transporting the sheets from the first 42.1 to the second intaglio printing unit 42.2. In contrast to the second and third embodiments, the two intaglio printing units 42.1, 42.2 are however disposed in a tandem configuration (i.e. with the cylinders 42a. 1, 42b.1, 43a. 1, 42a.2, 42b.2, 43a.2 rotating in the same direction). This implies that a sheet transfer arrangement must be provided along the path of the chain conveyor system 45.1 between the first and second intaglio printing units 42.1, 42.2 in order to transfer the sheet to the second intaglio printing unit 42.2 in the appropriate way for the verso side to be printed.

(41) As the two intaglio printing units 42.1, 42.2 are disposed in a tandem configuration with the same sheet transporting and printing orientations, a similar sheet transfer configuration as in the case of the second and third embodiments is not possible. The sheet transfer arrangement necessary in the context of the fifth embodiment must be designed in such a way that the sheets coming from the first intaglio printing unit 42.1, which sheets are held at their leading edge by the gripper bars of the chain conveyor system 45.1 are transferred via their trailing edge to the downstream-located second intaglio printing unit 42.2. In other words, upon transfer of the sheets from the chain conveyor system 45.1 towards the second intaglio printing unit 42.2, the trailing edge of the sheets becomes the leading edge of the sheets, thereby enabling printing of the verso side of the sheets.

(42) To this effect, the fifth embodiment is preferably provided with a sheet transfer arrangement 40 comprising first and second sheet transfer cylinders (or drums) 40.1, 40.2 interposed between the sheet transfer location of the chain conveyor system 45.1 and the impression cylinder 42a.2 of the second intaglio printing unit 42.2. The first transfer cylinder 40.1 (which performs reversal of the sheet transport direction) is synchronized with the passage of the sheets transported by the chain conveyor system 45.1 is such a way that the gripper means (not illustrated) of the first transfer cylinder 40.1 are brought in synchronism with the trailing edge of the sheet being transferred. This means that the chain conveyor system 45.1 holds the sheet to be transferred by its leading edge past the output chain wheels 45a.1 of the chain conveyor system 45.1 (over a distance substantially equal to the length of the sheet) until the trailing edge of the sheet is brought in the vicinity of the gripper means of the first transfer cylinder 40.1. Once the gripper means of the first transfer cylinder 40.1 have got hold of the trailing edge of the sheet, the gripper bar of the chain conveyor system 45.1 still holding the leading of the sheet is released so as to free the sheet and enable it to be transported further by the first transfer cylinder 40.1 in the opposite direction. The sheet is then transferred from the first transfer cylinder 40.1 to the second transfer cylinder 40.2 and then to the impression cylinder 42a.2 of the second intaglio printing unit 42.2. One will thus appreciate that while the sheet is still held by the chain conveyor system 45.1, the leading edge of the sheet is moved past the chain wheels 45a.1 (from left to right in FIGS. 5a, 5b) and, upon transfer to the first sheet transfer cylinder 40.1, is moved in the opposite direction (from right to left in FIGS. 5a, 5b). In all of the previously-described embodiments, the sheets are always transferred by way of their leading edge.

(43) An alternate way of performing this leading edge-trailing edge transfer (or reversal) could consist is designing the chain conveyor system 45.1 is such a way that it gets hold of the sheets from the impression cylinder 42a.1 of the first intaglio printing unit 42.1, not by their leading edge, but by their trailing edge, in a manner similar to what has been described hereinabove.

(44) It will be understood that various modifications and/or improvements obvious to the person skilled in the art can be made to the embodiments described hereinabove without departing from the scope of the invention defined by the annexed claims.