Combined printing press

There is described a combined printing press (10) for the production of security documents, in particular banknotes, comprising a screen printing group (3) and a numbering group (4) adapted to process printed substrates in the form of individual sheets or successive portions of a continuous web. The screen printing group (3) is located upstream of the numbering group (4) and comprises at least one screen printing unit (32-33) designed to print a pattern of optically-variable ink, which optically-variable ink contains flakes that can be oriented by means of a magnetic field. The screen printing group further comprises a magnetic unit (36) located downstream of the screen printing unit (32-33), which magnetic unit (36) is designed to magnetically induce an optically-variable effect in the pattern of optically-variable ink applied by the screen printing unit (32-33) prior to drying/curing of the optically-variable ink. The screen printing group (3) further comprises at least one drying/curing unit (37) designed to dry/cure the pattern of optically-variable ink in which the optically-variable effect has been induced by the magnetic unit (36), prior to transfer of the printed substrates to the numbering group (4).

This application is the U.S. national phase of International Application No. PCT/IB2015/056967 filed 11 Sep. 2015, which designated the U.S. and claims priority to EP Patent Application No. 14184681.6 filed 12 Sep. 2014, the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention generally relates to a combined printing press of the type comprising a screen printing group and a numbering group. The present invention is in particular applicable for the production of security documents, such as banknotes.

SUMMARY OF THE INVENTION

There is described a combined printing press for the production of security documents, in particular banknotes, comprising a screen printing group and a numbering group adapted to process printed substrates (i.e. printed material) in the form of individual sheets or successive portions of a continuous web. The screen printing group is located upstream of the numbering group and comprises at least one screen printing unit designed to print a pattern of optically-variable ink, which optically-variable ink contains flakes that can be oriented by means of a magnetic field. The screen printing group further comprises a magnetic unit located downstream of the screen printing unit, which magnetic unit is designed to magnetically induce an optically-variable effect in the pattern of optically-variable ink applied by the screen printing unit prior to drying/curing of the optically-variable ink. The screen printing group further comprises at least one drying/curing unit designed to dry/cure the pattern of optically-variable ink in which the optically-variable effect has been induced by the magnetic unit, prior to transfer of the printed substrates, to the numbering group.

Preferably, the magnetic unit includes a rotating magnetic cylinder assembly carrying magnetic-field generating devices on its circumference. In this particular context, it is advantageous to provide the at least one drying/curing unit so as to cooperate directly with the magnetic cylinder assembly, which at least one drying/curing unit is located on a downstream portion of the circumference of the magnetic cylinder assembly, i.e. a portion of the circumference of the magnetic cylinder assembly that is located before and close to the location where the printed substrates are taken away from the magnetic cylinder assembly. The purpose of this drying/curing unit is to initiate drying/curing of the ink pattern before the printed substrates are taken away from the magnetic cylinder assembly.

The drying/curing unit may advantageously be a UV curing unit, in particular a UV-LED curing unit.

Advantageously, a recto-verso varnishing group may further be provided downstream of the numbering group.

Further advantageous embodiments of the combined printing press are discussed below.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention will be described in the particular context of a sheet-fed printing press for the production of security documents, such as banknotes.

FIG. 1is a schematic side view of a combined printing press in accordance with one illustrative embodiment of the invention, which printing press is generally designated by reference numeral10and is configured to process individual sheets which are fed in succession through the printing press10from a sheet feeder1located upstream of the relevant printing groups to a delivery8located downstream of the relevant printing groups.

More precisely, individual sheets are fed in succession from the feeder1onto an infeed table2as is typical in the art and then via a suitable sheet transfer mechanism to a first printing group, namely a screen printing group3, and then to a second printing group, namely a numbering group4. In the illustrated example, the infeed table2forms part of an infeed module20which comprises a sheet transfer cylinder21feeding the sheets in succession to the screen printing group3(see alsoFIG. 2).

In the illustrated example, the sheets are further transported from the numbering group4via a suitable sheet transport system5, such as chain gripper system, to a varnishing group6which is designed to varnish both sides of the sheets, in a manner similar to the solution described in International (PCT) Publication No. WO 2011/145028 A1, which is incorporated herein by reference in its entirety.

As schematically illustrated inFIG. 1, the varnishing group6is constructed as a varnishing module60supporting first and second cylinders61,64where the recto side and the verso side of the sheets are varnished in succession. These cylinders61,64are advantageously two-segment cylinders. More precisely, in the illustrated example, two varnishing units62are disposed about a part of the circumference of the first cylinder61in order to varnish the recto side of the sheets, and one varnishing unit65is disposed about a part of the circumference of the second cylinder64is order to varnish the verso side of the sheets. The varnishing units62,65are advantageously designed as flexographic units.

A suitable drying unit, in particular a UV-curing unit,63is provided downstream of the two varnishing units62in order to dry/cure the recto side of the sheets before transfer thereof from the first cylinder61to the second cylinder64. Likewise, a suitable drying unit, in particular a UV-curing unit,66is provided downstream of the varnishing unit65in order to dry/cure the verso side of the sheets before these are taken away from the second cylinder64to be transported by a sheet transport system7to the delivery8.

The numbering group4consists in this example of a numbering module40supporting a sheet transfer cylinder or drum41and a two-segment impression cylinder42that transports the individual sheets coming from the screen printing group3in succession past three letterpress forme cylinders43,44,45that are distributed about a part of the circumference of the impression cylinder42. In the present example, the first letterpress forme cylinder43can carry a letterpress printing plate used e.g. for printing a date and/or signature, while the two remaining letterpress forme cylinders44,45are preferably designed as first and second numbering cylinders carrying a plurality of numbering boxes.

The letterpress forme cylinders43,44,45are inked by corresponding inking devices (not shown inFIG. 2) that are advantageously supported in a mobile inking carriage46that can be retracted away from the letterpress forme cylinders43,44,45during maintenance operations.

A numbering group4of the type shown inFIGS. 1 and 2is known as such in the art, for instance from International (PCT) Publications Nos. WO 2006/129245 A2, WO 2007/060624 A1 and WO 2011/145028 A1, which publications are incorporated herein by reference in their entirety.

Once printed in the numbering group4, the sheets are taken away from the impression cylinder42by the intermediate sheet transport system5for further transport to the previously-described varnishing group6. In the illustrated example, the intermediate sheet transport system5is designed as a chain gripper system comprising a pair of endless chains carrying spaced-apart gripper bars for holding the leading edge of the sheets, which endless chain are driven between two pairs of chain wheels51,52, so that sheets are taken away from the impression cylinder42of the numbering group4and transported to the varnishing group6where the sheets are transferred to the first cylinder61. As further illustrated inFIG. 1, a drying unit55(such as a UV-curing unit) is preferably provided along the path of the intermediate sheet transport to dry/cure the sheets (namely the recto side thereof) before transfer to the varnishing group6.

Prior to being processed by the numbering group4, the sheets are first processed by the screen printing group3that will now be described in greater detail.

In the example ofFIGS. 1 and 2, the screen printing group3is advantageously designed to print the same side (i.e. the recto side) of the sheets as the subsequent numbering group4. The screen printing group3is preferably constructed as a screen printing module30that is interposed between the infeed module20and the numbering module40. More precisely, the screen printing module30is designed in such a way that it can be decoupled from the infeed module20and the numbering module40and that the infeed module20can be coupled directly to the feeding section of the numbering module40.

The screen printing module30includes a one-segment sheet transfer cylinder31receiving sheets fed from the infeed table2and transferred by the sheet transfer cylinder21, which sheet transfer cylinder31transfers the sheet to a one-segment impression cylinder32that cooperates with a one-segment screen (or stencil) cylinder33. Ink is fed from the interior of the screen cylinder33and applied through the screen under the action of a squeegee in a manner known as such in the art (see e.g. EP 0 723 864 A1).

In accordance with the invention, the screen printing unit formed by the association of the impression cylinder32and the screen cylinder33is advantageously designed to apply a pattern of optically-variable ink, which optically-variable ink contains flakes that can be oriented by means of a magnetic field. Such ink may be a so-called Optically Variable Magnetic Ink (or OVMI®) as available from SICPA SA.

Once printed by the screen printing unit32-33, the sheets are fed to another sheet transfer cylinder or drum34before reaching a magnetic unit36designed to magnetically induce an optically-variable effect in the pattern of optically-variable ink applied by the screen printing unit32-33prior to drying/curing of the optically-variable ink. This technology is known as the Spark® technology (OVMI® and Spark® being registered trademarks of SICPA HOLDING SA).

The purpose of the magnetic unit36is to induce a desired optically-variable effect in the pattern of optically-variable ink by subjecting the relevant portion of the pattern to a magnetic field exhibiting a suitable distribution of the magnetic field lines as generally described in e.g. International (PCT) Publications Nos. WO 2004/007095 A2, WO 2005/000585 A1 and WO 2005/002866 A1.

The magnetic unit36preferably includes a rotating magnetic cylinder assembly36carrying magnetic-field generating devices on its circumference (as for instance taught by International (PCT) Publications Nos. WO 2005/000585 A1, WO 2008/102303 A2, WO 2012/038531 A1, WO 2014/037221 A1 and European Patent Publication No. EP 2 433 798 A1). Preferably a drying/curing unit37(advantageously a UV curing unit) is located on a downstream portion of the circumference of the magnetic cylinder assembly36, i.e. a portion of the circumference of the magnetic cylinder assembly36that is located before and close to the location where the sheet is taken away from the magnetic cylinder assembly36. The purpose of this drying/curing unit37is to initiate drying/curing of the ink pattern before the sheet is taken away from the magnetic cylinder assembly36.

It will be understood that the magnetic cylinder assembly36is brought in contact with the lower (i.e. verso) side of the sheets in the example ofFIGS. 1 and 2, i.e. the side that is opposite to the side where the pattern of ink has been printed by the screen printing unit32-33. On the other hand, the drying/curing unit37is located above the path of the sheets so as to dry/cure the ink printed on the upper (i.e. recto) side of the sheets.

In the illustrated example, the sheets are transferred away from the magnetic cylinder assembly36to the sheet transfer cylinder or drum41and then to the impression cylinder42of the numbering group4.

In the example ofFIGS. 1 and 2, the sheet transfer cylinder or drum34can advantageously be constructed as a sheet transfer drum designed to prevent or minimize contact with the printed side of the sheets. In addition, a suitable sheet guiding device35may be provided about the circumference of the sheet transfer cylinder or drum34in order to assist transport of the sheets from the impression cylinder32to the magnetic cylinder assembly36.

The drying/curing unit37may advantageously be a LED unit, in particular a UV-LED curing unit.

Various modifications and/or improvements may be made to the above-described embodiments. In particular, while the embodiments discussed above relate to sheet-fed printing presses, the invention is also applicable to web-fed printing presses. In addition, the screen printing group3may comprise more than one screen printing unit and magnetic unit.

LIST OF REFERENCE NUMERALS USED THEREIN

10combined printing press1feeder2infeed table3screen printing group4numbering group5intermediate sheet transport system (chain gripper system)/transport of printed sheets from numbering group4to varnishing group66(recto-verso) varnishing group7sheet delivery system (chain gripper system)/transport of printed sheets to delivery88delivery20infeed module21sheet transfer cylinder receiving sheets fed from infeed table230screen printing module31sheet transfer cylinder receiving sheets fed from infeed table2and transferred by sheet transfer cylinder21(one-segment cylinder)32impression cylinder (one-segment cylinder)33screen (stencil) cylinder cooperating with impression cylinder32(one-segment cylinder)34sheet transfer cylinder or drum (one-segment cylinder or drum)35sheet guiding device associated to sheet transfer cylinder or drum36rotating magnetic cylinder assembly (magnetic unit)37drying/curing unit (e.g. UV curing unit, preferably UV-LED curing unit) cooperating with magnetic cylinder assembly3640numbering module41sheet transfer cylinder or drum (one-segment cylinder)42impression cylinder (two-segment cylinder)43letterpress forme cylinder (one-segment cylinder)44letterpress forme cylinder/first numbering cylinder (one-segment cylinder)45letterpress forme cylinder/second numbering cylinder (one-segment cylinder)46retractable/mobile inking carriage of numbering module4051chain wheels of intermediate sheet transport system5where sheets are taken away from impression cylinder4252chain wheels of intermediate sheet transport system5where sheets are transferred to first cylinder61of varnishing group660varnishing module61first cylinder of varnishing group (recto side/two-segment cylinder)62varnishing units (e.g. flexographic units) cooperating with first cylinder6163first drying unit (UV curing unit) cooperating with first cylinder6164second cylinder of varnishing group (verso side/two-segment cylinder)65varnishing unit (e.g. flexographic unit) cooperating with second cylinder6466second drying unit (UV curing unit) cooperating with second cylinder64