Flat foil printing press having foil web and sheet guidance

The flat foil printing press comprises an evacuable back-pressure plate (9), with suction regions (15k) which run in the sheet running direction (X) and which are next to embossing regions (16k), in which foil webs (6k) run. The suction regions are subdivided into several suction segments (10i) which are successive in the sheet running direction, and are each connected to a vacuum source (14) by way of a vacuum feed line (12i) via a vacuum switching element (13i). With the running-out of an embossed sheet (5), firstly all suction segments (10i) covered by the sheet are evacuated, and subsequently the suction segments which are no longer covered by the sheet are successively disconnected from the vacuum source. This results in an error-free separation of foil webs and sheets, for a greater picture quality and machine output.

The invention relates to a flat foil printing press with a foil web guidance for several foil webs and with a sheet guidance, according to the preamble of claim1. Particularly high printing outputs of the best quality and also for demanding printing tasks can be carried out with such flat foil printing presses. These flat foil printing presses on the one hand place particularly high demands upon the guidance and the precise feeding of thin, narrow and very sensitive embossing printing foil webs and on the other hand upon the precise guidance and positioning of the sheets. Thereby, several foil webs need to be guided and conveyed simultaneously in a perfectly flat manner and the foil guidance needs to be effected in a perfectly plane, flat and correctly positioned manner, without deformation, arching, creases and dislocations. The guidance of the sheets must likewise be effected in this manner, in order to be able to achieve high outputs and picture qualities. Such flat foil printing presses are known e.g. from EP 1 593 503 and WO 2009/143644.

Not only must an optimal, error-free positioning of foil webs and sheets be achieved, but above all also after the embossing, a gentle and perfect separation of the foil webs from the sheet with the continued transport, for demanding picture embossing tasks, in particular for hologram embossing with picture security features, e.g. for tickets, identity documents or banknotes, in the case of several picture foil webs over the whole printing table.

Here however, large problems still result with the increasing demands on the output and picture quality.

According to EP 0 739 722 for example, a blower producing a laminar airflow counter to the sheet running direction and between sheet and the foil webs is applied at the outlet of the flat press, for keeping the sheet flat and level in the printing station. This however is no longer sufficient for more demanding tasks, specifically for narrow foil webs (e.g. only 10 mm wide) and for thin paper sheets. Given a poor detachment of the foil webs which remain stuck to the sheet, on the one hand the foils webs become deformed, overstretched and damaged and on the other hand the sheet also becomes deformed, uneven and warped and creases can form, to the extent that faulty and completely unusable individual pictures subsequently arise on cutting the sheets to size into individual pictures—just as in the case of deformed foil webs.

It is therefore the object of the present invention to provide a better and more precise foil web guidance and sheet guidance for flat foil printing presses, with a significantly improved separation of foils webs and sheets after the embossing, and thus to provide an error-free, level guidance of foil webs and sheets after the embossing, so that the sheets remained unchanged in their level and flat state and the foils webs are not overstretched and damaged.

According to the invention, this object is achieved by a flat foil printing press with a foil web guidance and with a sheet guidance, by way of an evacuated or evacuable back-pressure plate, according to claim1, by a back-pressure plate with integrated suction regions which run in the sheet running direction and which are next to and between the embossing regions, in which the foil webs run, wherein the suction regions are each subdivided into several suction segments which are successive in the sheet running direction and wherein the suction segments each comprise a switchable vacuum feed line from a vacuum source, so that after the embossing, all suction segments covered by the sheet are evacuated, and subsequently, with the running-out of the embossed sheet, the suction segments which are no longer covered by the sheet are successively disconnectable from the vacuum source.

FIG. 1shows a flat foil printing press1according to the invention, with a foil web guidance2for several foil webs6kand with a sheet guidance3which by way of gripper bars30moves sheets5from a feeder31onto the embossing location on a back-pressure plate9of a flat bed press4with a printing and tool plate7and moves them further onto a delivery means32after the embossing procedure.

The back-pressure plate9is evacuable and comprises suction regions15kwhich run in the sheet running direction X and which have suction openings22. These suction regions are arranged next to and between embossing regions16k, in which the foil webs6krun (→FIG. 2). The suction regions15kare subdivided into several suction segments10iwhich are successive to one another in the sheet running direction X, wherein the suction segments are each connected to a vacuum source14via a vacuum switching element13iby way of a vacuum feed line12iand controlled, in a manner such that given a standstill of the embossed sheet5, firstly all suction segments10icovered by the sheet are evacuated (by which means the sheet is pressed onto the back-pressure plate9) and subsequently, with the running-out of the embossed sheet5, the suction segments10iwhich are no longer covered by the sheet are successively disconnectable from the vacuum source14(and these suction segments are thus no longer evacuated). With the running-out of the sheet, above all it is also its rear end which is held back by the vacuum in the suction segments, and the sheet is stretched by way of this, so that even thin paper sheets can be kept flat and no creases can form.

The example ofFIG. 1comprises four suction segments10.1-10.4and accordingly also four vacuum feed lines12.i=12.1-12.4and four vacuum switching elements13.i=13.1-13.4. At least two suction segments10iare provided, preferably also more, e.g. three to five suction segments, depending on the application.

The vacuum source14and its power can also be set or switched on and off by way of a machine control19.

A mechanical vacuum pump with a switching valve can be applied as a vacuum source14or preferably also a rapidly switchable injector pump. The vacuum in the suction regions15kcan be switched on with this, preferably given a standstill of the sheet5, and can be switched off after the last suction segment10iis no longer covered by the running-out sheet.

The example ofFIG. 1shows a flat foil printing press with a sheet running direction X and a foil web running direction F which are the same. The lowering of the back-pressure plate begins after the embossing and, in a settable manner, shortly thereafter the initial drawing of the foil webs6kand of the sheet5. The inventive, evacuable back-pressure plate9can likewise also be applied in flat foil printing presses with sheet running directions and foil web running directions which are counter to one another.

FIG. 2schematically shows a back-pressure plate9with five embossing regions16k=16.1-16.5, in which the foil webs6.1-6.5run, and with six suction regions15k=15.1-15.6next to and between the embossing regions. AsFIG. 1shows, this example shows four suction segments10i=10.1-10.4which, departing from the sheet end, extend past the middle of the back-pressure plate9.

Here, a longer, larger sheet5.1covers all suction segments10.1-10.4, whereas a shorter, smaller sheet5.2e.g. now merely covers the suction segments10.3and10.4. The suction segments10.1and10.2can then be disconnected or covered. For embossing a narrower sheet—e.g. with suction regions15.1and15.6which are not covered—these can be covered or disconnected.

The suction segments10iare connected to the vacuum source14via the feed lines12iand the vacuum switching elements13i.

Vacuum suction valves can preferably be applied as vacuum switching elements13iin the vacuum feed lines12i.

However, vacuum switching valves can also be applied.

Vacuum suction valves are self-controlling. When the suction openings22of a suction segment10iare covered (closed) by a sheet5, then the vacuum suction valve opens and a vacuum arises in the corresponding suction segment. The vacuum suction valve closes again when the suction segment is no longer covered by a sheet. The vacuum is therefore retained in the suction segments which are still covered.

Controlled vacuum switching valves can hence be opened and closed by way of the machine control19according to adjustable/settable machine rotation angles W, so that the suction segments10iare evacuated at the desired times.

As a further example,FIG. 3shows a part of a back-pressure plate9which is at the run-in side, wherein in each suction segment10i, the back-pressure plate comprises a vacuum chamber11iwith suction openings22and with a connection opening23to the respective vacuum feed line12i.

The back-pressure plate9here is divided into an upper plate9aand a lower plate9b. In each suction segment10i, the upper plate9acomprises vacuum chambers11iwith suction openings22, and the separate lower plate9bcomprises vacuum feed lines12iwith a connection opening23to each vacuum chamber11i. This division into an upper and a lower plate permits a simple manufacture of the evacuable back-pressure plate9according to the invention, said plate lying on the printing table8.

FIG. 4a, 4bshow a further advantageous embodiment variant of the back-pressure plate9. According toFIG. 4a, in the suction regions15k, here an upper plate9acomprises suction strips20kwhich comprise vacuum chambers11iand suction openings22, as well as a support mask24which surrounds the suction strips20in the embossing regions16k.

Adjustable suction strips20kwhich can be screwed on and which can be displaced according to a changed arrangement (layout) of foil webs6kor of embossing regions16kare also particularly advantageous. The support mask24here is also accordingly adapted or exchanged.

FIG. 4bshows the lower plate9bseen from below, with the vacuum feed lines12i=12.1-12.3, here visible as open channels which lie on the surfaces of the printing table8(shown inFIG. 5aandFIG. 6) and are coved by this surface and which are connected to the vacuum chambers11iby way of connection openings23.FIG. 4a, 4brepresents an example with seven suction regions15k=15.1-15.7and with three suction segments10i=10.1-10.3and with just as many vacuum feed lines12iand vacuum switching elements13i.

FIGS. 5a, 5bin a cross section through a suction region15kshow a further example with suction strips20k, with suction chambers11iand with a surrounding support mask24as an upper plate9a, here with five suction segments10i=10.1-10.5, and with vacuum feed lines12ias well as connection openings23in the lower plate9b.

The surface of the suction regions15kor of the suction strips20kcan advantageously have an increased adhesion to the sheets5. For this, their surface can be designed more roughly than in the embossing regions16k, or the surface can comprise a rubber coating.

FIG. 6illustrates the construction of the example ofFIG. 5. The lower plate9bwith the five vacuum feed lines12.1-12.5which are connected to the five vacuum switching elements13iand to the vacuum source14lies on the printing table8. The upper plate9awith the five suction segments10.1-10.5each in the seven suction strips20k=20.1-20.7which form the suction regions15kand with the support mask24lies on this lower plate

FIGS. 7 and 8show views of a back-pressure plate9with six embossing regions16k=16.1-16.6and seven suction regions15k=15.1-15.7and with suction strips20kwhich comprise three suction segments10i=10.1-10.3, and with a corresponding support mask24. Here, make ups42are evident on the support mask24, in the embossing regions16k.

FIG. 8a, bshow a sheet5which is embossed by way of six foil webs6k, with foil pictures40as picture strips, said sheet having been applied onto the back-pressure plate9in accordance with the course of the foil webs. As to how the finished, printed and embossed sheet is cut to size into individual pictures41is also indicated on this sheet. An identical picture from the picture strip40must then be present on each individual picture41at the same location (specifically in quality and security printing—e.g. for tickets and banknotes).

This illustrates that an error-free, secure detachment of the foil webs from the sheet after the embossing, without any warping, squashing and dislocation on the part of the foil webs and the sheet is an absolute precondition for challenging embossing tasks and error-free, registered pictures of the highest quality.

On detachment, the foil web tension and the suction force of the vacuum in the suction segments upon the sheet can also be matched to one another for this.

FIG. 9a, bshow a further example of an evacuable back-pressure plate9with additional separation air nozzles34beneath the foil webs6kand with an additional suction region36running in the transverse direction Y. The separation air nozzles34with compressed air feed lines35, at the inlet side, are attached to the back-pressure plate directly behind the sheet5and below the foil webs6k, and the suction region36with a vacuum feed line37is arranged below the rear edge of the sheet5. After the embossing, the rear sheet end is pressed onto the back-pressure plate9by way of evacuation, and compressed air is blown between the foil webs6kand the sheet5with the subsequent lowering of the back-pressure plate, so that the separation of foil webs and sheet is significantly improved here.

The suction region36can also comprise a suction strip, analogously to the suction regions15kin the longitudinal direction.

FIG. 9aperspectively shows the back-pressure plate andFIG. 9bschematically shows a cross section through a separation air nozzle34and the suction region36with the lying-on edge of the sheet5beneath a foil web6k. An arrangement of separation air nozzles34is also illustrated inFIG. 2.

The vacuum feed lines11with the vacuum switching elements12iand the vacuum source14as well as their control in the machine control19also belong the evacuable back-pressure plate9according to the invention.

The back-pressure plate9with the vacuum switching elements12ican preferably be designed in an exchangeable manner.

The following reference numerals are used in the scope of this description:1flat foil printing press2foil web guidance3sheet guidance4flat bed press5sheet6foil webs7printing plate with tool plate8printing table with supporting face for99back-pressure plate (evacuable)9aupper plate of9with11iand229blower plate with12iand2310isuction segments (in Y-direction)11,11ivacuum chambers12,12ivacuum feed lines13,13ivacuum switching elements14vacuum source15,15ksuction regions (in X-direction)16,16kembossing regions19machine control20,20ksuction strips with11iand2222suction openings23connection openings (11i-12i)24support mask30gripper bar31feeder32delivery means34separation air nozzle, blower on935compressed air fed line36suction region in Y-direction37vacuum feed line40embossed foil pictures as picture strips on541cut-to-size singe picture42make upF foil web running directionW machine rotation angleX sheet running directionY transverse directionZ vertical direction