Patent Publication Number: US-11383507-B2

Title: Printing press with in-line casting device for the replication and formation of a micro-optical structure

Description:
This application is the U.S. national phase of International Application No. PCT/EP2018/054104 filed 20 Feb. 2018, which designated the U.S. and claims priority to EP Patent Application No. 17157503.8 filed 22 Feb. 2017, and EP Patent Application No. 17167792.5 filed 24 Apr. 2017, the entire contents of each of which are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention generally relates to a printing press—especially an offset printing press—adapted to carry out printing on a sheet-like or web-like substrate, in particular for the production of security documents such as banknotes, comprising a printing unit designed to print a first side and/or a second side of the substrate. 
     BACKGROUND OF THE INVENTION 
     Offset printing presses for the production of security documents such as banknotes are known as such in the art, in particular from European Patent Publication No. EP 0 949 069 A1 and International PCT Publications Nos. WO 2007/042919 A2, WO 2007/105059 A1, WO 2007/105061 A1, WO 2008/099330 A2 and WO 2016/071870 A1, which publications are all incorporated herein by reference in their entirety. 
     International PCT Publication No. WO 2007/042919 A2 in particular discloses a recto-verso offset printing press adapted for simultaneous recto-verso printing of sheets that further comprises an additional printing group placed upstream of a main printing group of the printing press. 
       FIGS. 1 and 2  illustrate such a recto-verso printing press that is adapted to carry out simultaneous recto-verso printing of sheets, as typically used for the production of banknotes and like security documents, which printing press is designated globally by reference numeral  100 . Such printing press is in particular marketed by the present Applicant under the product designation Super Simultan® IV. The basic configuration of the printing press  100  shown in  FIGS. 1 and 2  is similar to that shown and discussed with reference to  FIG. 1  of International PCT Publication No. WO 2007/042919 A2. 
     This printing press  100  comprises a printing unit  2 , which is specifically adapted to perform simultaneous recto-verso printing of the sheets (according to the so-called Simultan-offset printing principle) and comprises, as is typical in the art, two blanket cylinders (or printing cylinders)  5 ,  6  rotating in the direction indicated by the arrows and between which the sheets are fed to receive multicolour impressions. In this example, blanket cylinders  5 ,  6  are three-segment cylinders which are supported between a pair of side frames designated by reference numeral  20 . The blanket cylinders  5 ,  6  receive and collect different ink patterns in their respective colours from plate cylinders  15  and  16  (four on each side) which are distributed around a portion of the circumference of the blanket cylinders  5 ,  6 . These plate cylinders  15  and  16 , which each carry a corresponding printing plate, are themselves inked by corresponding inking apparatuses  25  and  26 , respectively. The plate cylinder  15 ,  16  together with the associated inking apparatus  25 ,  26  hereby form a kind of colour separation delivery branch, delivering the respective separation for collecting on the respective blanket cylinder  5 ,  6 . The two groups of inking apparatuses  25 ,  26  are advantageously supported in two inking carriages  21 ,  22  that can be moved toward or away from the centrally-located plate cylinders  15 ,  16  and blanket cylinders  5 ,  6 . 
     As is known in the art, each printing plate is wrapped around the corresponding plate cylinder  15 ,  16  and clamped at its leading end and trailing end by a suitable plate clamping system, which plate clamping system is located in a corresponding cylinder pit of the plate cylinder (see e.g. International (PCT) Publications Nos. WO 2013/001518 A1, WO 2013/001009 A1 and WO 2013/001010 A2, which are also incorporated herein by reference in their entirety). 
     Sheets are fed from a substrate feeding device, e.g. sheet feeder  1  onto a feeder table  1 * located next to the printing unit  2  (on the right-hand side in  FIGS. 1 and 2 ) to a succession of transfer cylinders  9 ,  8 ′, 10  (three cylinders in this example) placed upstream of the blanket cylinders  5 ,  6 . While being transported by the transfer cylinder  8 ′, the sheets receive a first impression on one side of the sheets using an additional printing group, the transfer cylinder  8 ′ fulfilling the additional function of impression cylinder. This additional printing group consists of, in addition to the transfer cylinder  8 ′, a blanket cylinder  8  (a two-segment cylinder in this example) that collects inks from two plate cylinders  18  that are inked by corresponding inking apparatuses  28 . The inking apparatuses  28  are advantageously supported in an inking carriage  24  that can be moved toward or away from the plate cylinders  18  and blanket cylinder  8 . The sheets that are printed by means of the additional printing group are first dried/cured by a drying/curing unit (designated by reference numeral  50  in  FIG. 2 ) while being transported by the sheet transfer cylinder  8 ′ before being transferred to the downstream-located main printing group. 
     In the example of  FIGS. 1 and 2 , the sheets are transferred onto the surface of blanket cylinder  5  where a leading edge of each sheet is held by appropriate gripper means located in cylinder pits between each segment of the blanket cylinder  5 . Each sheet is thus transported by the blanket cylinder  5  to the printing nip between the blanket cylinders  5  and  6  where simultaneous recto-verso printing occurs. Once printed on both sides, the printed sheets are then transferred, as known in the art, to a sheet conveying system  3  (such as a chain gripper system with spaced-apart gripper bars) for delivery in a substrate delivery unit  4 , e. g. sheet delivery unit  4 , comprising multiple (e.g. three) delivery pile units. Reference numeral  31  in  FIG. 2  designates a pair of chain wheels located at the upstream end of the sheet conveying system  3 . 
     In the example of  FIGS. 1 and 2 , first and second transfer cylinders or drums  11 ,  12 , such as suction drums or cylinders, are interposed between the sheet conveying system  3  and the blanket cylinder  5 . These first and second transfer cylinders  11 ,  12  are optional (and could therefore be omitted) and are designed to carry out inspection of the sheets on the recto and verso sides as described for instance in International application No. WO 2007/105059 A1. Reference numerals  61 ,  62  in  FIG. 2  designate corresponding inspection cameras (such as line-scan cameras) that cooperate with cylinder or drums  11 ,  12 . 
     The printing press of  FIGS. 1 and 2  is especially used for the purpose of printing multicolour patterns with a very high colour-to-colour register. Such multicolour patterns can in particular be combined with a micro-optical structure (such as a micro-lens structure) to create optically-variable effects as for instance disclosed in International Publications Nos. WO 2007/020048 A2, WO 2014/039476 A1 and WO 2014/085290 A1, which publications are incorporated herein by reference. 
     The relevant micro-optical structures are typically applied in a separate and dedicated process, in particular in combination with transparent windows that are formed in the substrate material, whether prior to or during the formation of the relevant micro-optical structures. Known processes for creating such micro-optical structures are disclosed for instance in European Patent Publication No. EP 1 878 584 A2 and International Publications Nos. WO 94/27254 A1, WO 2007/020048 A2, WO 2014/125454 A1, WO 2015/022612 A1 and WO 2015/107488 A1, which publications are likewise incorporated herein by reference. 
     The WO 2015/022612 A1 more precisely discloses a substrate with a window region filled with transparent polymer material and with a micro-optical structure covering the filling on one side of the window region. Furthermore there are disclosed two alternative methods and a device to create such an substrate. Such provided substrate as part of the production of security can be printed on the side opposing the micro-optical structure. 
     Application of a separate and dedicated process to create the necessary micro-optical structures is however cumbersome and adds up to the complexity and cost of the production of the relevant security features and documents incorporating the same. There is therefore a need for an improved solution, especially such a solution that streamlines and simplifies the production of documents that are to be provided with security elements incorporating micro-optical structures. 
     SUMMARY OF THE INVENTION 
     A general aim of the invention is to improve the known printing presses of the aforementioned type. 
     More precisely, an aim of the present invention is to provide such a printing press that allows to achieve high register between micro-optical structures to be provided on the substrate material and the printed patterns to be printed in combination with such micro-optical structures. 
     Another aim of the present invention is to provide such a printing press where machine operability and accessibility are not compromised. 
     These aims are achieved thanks to the printing press defined in the claims. In particular there is provided a printing press adapted to carry out printing on a sheet-like or web-like substrate, in particular for the production of security documents such as banknotes, comprising a printing unit with at least a first printing group and a casting device comprising an embossing tool, preferably an embossing cylinder, which embossing tool is acting as counter-pressure means, especially as counter-pressure cylinder, for a printing cylinder of the at least one printing group and/or which in-line casting device and the at least first printing group being arranged at the substrate transport path such way, that in-line casting of the micro-optical structure, on one side of the sheets S, and printing of the associated pattern, on the other side of the sheets S, are performed in a same step, without this involving any sheet transfer operation. 
     Although the expressions “embossing cylinder” and “counter-pressure cylinder” are used below and being a preferred embodiment, the invention shall be understood to be able to be generalized to the above and more general embossing tool and counter-pressure means unless otherwise explicitly stressed or conflicting. 
     The printing press advantageously comprising a printing unit with at least one first printing group designed to print at least one side of the substrate, preferably designed to enable the patterns of at least two plate cylinders to be printed onto the at least one side of the substrate while the embossing cylinder acting as counter-pressure cylinder. 
     This in a first embodiment can be realized by way of printing cylinders of at least two first printing groups co-operating with the counter-pressure cylinder successively around its circumference. 
     Preferably, the printing press comprising a printing unit designed to print a first side and/or a second side of the substrate, preferably comprising a printing unit with the at least first printing group and/or one or more further printing groups designed to print a first side and/or a second side of the substrate by collecting different ink patterns in their respective colours and/or several impressions from several plate cylinders on a cylinder, e. g. collecting cylinder, in advance before being printed as a whole onto the substrate. Such printing group further shortly is named as impressions collecting group or, as further cited, collect printing group. The term “first” side and “second” side for the sides of the substrates are in principle arbitrarily chosen and can be inverted. 
     Instead or preferably in addition to the above, in a preferred embodiment the respective printing group is designed as printing group for indirect printing, such as indirect lithographic printing, i.e. offset printing, or an indirect relief printing, e. g. letterset printing, or a combination with both of them. 
     The printing unit or especially a respective printing group preferably can be configured with at least one or more inking apparatuses and associated plate cylinders designed to enable and/or carry out offset printing, comprising for example a dampening system and/or at least the possibility to place lithographic printing plates onto the respective plate cylinder. Although these inking apparatuses possibly can also be run for letterset printing without or with inactive dampening system and with a letterpress printing plate, the printing group or printing unit nevertheless is designed—at least partly—as an offset printing group respectively printing unit. In addition to plate cylinders and inking apparatuses designed to enable and/or carry out offset printing a collect printing group or unit can comprise additional plate cylinders with associated inking apparatuses designed to especially carry out only other kinds of printing, for example letterset printing. In this sense, the above collect printing unit or group shall be understood as an offset printing unit or group, provided at least one, more or all of its plate cylinders and corresponding inking apparatuses is or are designed to enable and/or carry out offset printing. 
     In an alternative embodiment, the printing unit or especially the collect printing group can be configured only with one or more plate cylinders and associated inking apparatuses designed to enable and/or carry out indirect relief printing, e.g. such as letterset printing. 
     According to the invention, the printing press further comprises an in-line casting device adapted to apply a layer of material acting as an optical medium on a portion of the first or second side of the substrate and to replicate and form a micro-optical structure in the layer of material acting as optical medium. Furthermore, the printing unit is adapted to print at least one printed pattern on the first or second side of the substrate in register with the micro-optical structure. 
     In accordance with a preferred embodiment of the invention, the in-line casting device comprises at least one application unit, e. g. a screen-printing unit acting as application unit, for applying at least a part of the layer of material acting as optical medium. In the context of the present invention, more than one application unit, e. g. screen-printing unit, could be provided, especially if the quantity of material acting as the optical medium is to be increased. Other processes than screen printing could furthermore be contemplated to apply the relevant material acting as optical medium, it being however to be appreciated that screen printing remains a preferred process in the context of the invention. An alternative may for instance consist in using a flexographic-printing unit as the respective application unit. According to another preferred embodiment of the invention, the in-line casting device may advantageously comprise at least one embossing tool with an embossing form, e. g. an embossing cylinder, acting as carrier supporting a replicating medium designed to replicate and form the micro-optical structure in the layer of material acting as optical medium. In this context, it is particularly advantageous to additionally provide at least one pressure cylinder or roller cooperating with the embossing cylinder to press the substrate against the replicating medium, which ensures optimal replication and formation of the relevant micro-optical structures. The aforementioned embossing cylinder could in particular be located immediately after the aforementioned application unit. 
     In a preferred embodiment, the material acting as optical medium preferably can be applied directly onto the substrate before being brought into contact with the embossing tool, i.e. the embossing cylinder. The application in this case is being placed at the substrate path upstream the embossing tool. 
     In an alternative embodiment, the material acting as optical medium can be applied directly onto the embossing form, e. g. onto the surface of the embossing cylinder before the substrate being arranged on it. The application unit in this case is being placed at the embossing tool, preferably at the circumference of the embossing cylinder, especially in a peripheral section between delivery and take over of the substrate. 
     Although the casting device can be designed that the embossing cylinder to act onto the substrate only in a nip with a transport or conveying cylinder carrying the substrate, in a preferred embodiment, the embossing cylinder acts as a transport or conveying cylinder carrying and/or supporting the substrate over a—especially significant—angle range, e. g. for at least 90° of revolution. 
     By way of preference, the printing press could further comprise a washing device that can selectively be brought in contact with the embossing cylinder during maintenance operations to clean the surface of the embossing cylinder. This would be particularly advantageous in facilitating removal of residues of the material used to form the micro-optical structure. 
     In accordance with a particularly preferred embodiment of the invention, as mentioned before the embossing cylinder acting as counter-pressure cylinder and cooperating with the cylinder of the at least one printing unit acting as a printing cylinder, e. g. a transfer cylinder of indirect printing, especially a blanket cylinder, and cooperating with one or advantagely more associated plate cylinders to apply the at least one printed pattern on a side of the substrate which is opposite to the side of the substrate where the micro-optical structure is replicated. This solution ensures highly optimal register accuracy between the print and the associated micro-optical structure. Especially in case of the embossing cylinder acting as a counter-pressure cylinder of a collect printing group, the registration between the micro-optical structure as well as the registration between the different ink pattern/impressions collected in advance can be optimized. 
     Furthermore, the printing press could advantageously be designed as a sheet-fed printing press adapted to carry out printing on individual sheets, wherein transfer of the sheets between the in-line casting device and the printing unit is carried out exclusively from cylinder to cylinder via cooperating cylinder grippers, which solution ensure optimal register accuracy between the print and the associated micro-optical structure. 
     According to a further embodiment of the invention, the in-line casting device could further be provided with at least one drying/curing unit (preferably a UV-curing unit, advantageously such as a UV-LED curing unit) to dry or cure the layer of material acting as optical medium during and/or following replication of the micro-optical structure in the layer of material acting as optical medium. 
     This could advantageously be performed by means of a drying/curing unit located to dry or cure the layer of material acting as optical medium from the side of the substrate which is opposite to the side of the substrate where the micro-optical structure is replicated, especially while the substrate is still being processed on the aforementioned embossing cylinder (in which case the drying/curing unit is to be located about a portion of the circumference of the embossing cylinder. 
     Alternatively, or in addition to the above measures, a drying/curing unit could be located to dry or cure the layer of material acting as optical medium from the side of the substrate where the micro-optical structure is replicated, especially while the substrate is being transported by a transfer cylinder located immediately after the aforementioned embossing cylinder (in which case the drying/curing unit is to be located about a portion of the circumference of this transfer cylinder). 
     The printing press of the invention can in particular be of a type where the printing unit is designed to operate as an indirect printing unit, e.g. such as an offset or indirect relief printing unit in the above sense, especially a Simultan-type printing unit, especially Simultan-type offset printing unit—preferably in the above sense—for the simultaneous recto-verso printing of the substrate. 
     By way of preference, the micro-optical structure is replicated by the in-line casting device upstream of a location where the printed pattern is printed by the printing unit. Within the scope of the present invention, the in-line casting device could however be provided at any appropriate location in the printing press, be it after the relevant printing unit or between two printing units, or even form an integral part of a printing unit. 
     Further advantageous embodiments of the invention form the subject-matter of the dependent claims and are discussed below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is schematic illustration of recto-verso printing press exhibiting a configuration similar to that disclosed in International PCT Publication No. WO 2007/042919 A2; 
         FIG. 2  is a schematic partial side view of the printing unit of the printing press of  FIG. 1 ; 
         FIGS. 3A and 3B  are schematic illustrations of a substrate that is provided with a micro-optical structure on top of a window-forming portion created in the substrate; 
         FIG. 4  is a schematic partial side view of the printing unit of a printing press in accordance with a first embodiment of the invention; 
         FIG. 5  is a schematic partial side view of the printing unit of a printing press in accordance with a second embodiment of the invention; 
         FIG. 6  is a schematic partial side view of the printing unit of a printing press in accordance with a variant to the second embodiment of the invention; 
         FIG. 7  is a schematic partial side view of the printing unit of a printing press in accordance with a third embodiment of the invention; 
         FIG. 8  is a schematic partial side view of the printing unit of a printing press in accordance with a fourth embodiment of the invention; and 
         FIG. 9  is a schematic partial side view of the printing unit of a printing press in accordance with a variant to the third and fourth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Although the present invention in principle is not limited to such an embodiment of the printing press respectively printing unit, it will be described in the particular context of preferred embodiments of a printing press, preferably sheet fed printing press, comprising a printing unit with at least a printing group ( 91 ;  92 ;  93 ;  94 ) designed as an collect printing group ( 91 ;  92 ;  93 ;  94 ) as mentioned above and/or a, preferably sheet-fed, recto-verso printing press, especially based on indirect printing, exhibiting a (m)-over-(m) configuration (see embodiment of  FIG. 4  where m equals 4), a (m+n)-over-(m+n) configuration (see embodiment of  FIG. 5  where m, n respectively equal 4 and 2), or a (m)-over-(m+n) configuration (see embodiments of  FIGS. 6 and 7  where m, n respectively equal 4 and 3). The expression “(m)-over-(m) configuration” is to be understood a simultaneous recto-verso printing with m colour separations or frames printed on each side and/or a configuration of a recto-verso printing press, printing unit or group comprising a first set of m plate cylinders cooperating with a first printing cylinder and a second set of m plate cylinders cooperating with a second printing cylinder, which first and second printing cylinders cooperate to build a common printing nip. It shall be appreciated however that the invention is not limited to these particular printing press configurations, the number of plate cylinders being purely illustrative. This being said, the printing press configurations as shown in  FIGS. 4 to 7  are of particular advantage as they allow very high colour-to-colour register accuracy. 
     An collect printing group ( 91 ;  92 ;  93 ;  94 ) is designed to print at least one side of the substrate by firstly collecting several impressions or patterns from several plate cylinders on a cylinder, e. g. a so called collecting cylinder, before being printed as a collected image as a whole onto the substrate. 
     In the context of the present invention, the expression “printing cylinder(s)” will be used to designate the relevant cylinders of a printing group ( 91 ;  92 ;  93 ;  94 ), e.g. of a main printing group ( 91 ,  92 ) and of any additional printing group ( 93 ,  94 ), that directly cooperate with the first and second sides of the substrates (e.g. sheets) to transfer printing patterns thereon. This expression preferably is interchangeable with the expression “transfer cylinder” or “blanket cylinder”, it being to be understood that the relevant printing cylinders for example each carry an number, e. g. one or several, printing blankets. 
     The expression “printing group” ( 91 ;  92 ;  93 ,  94 ) will be used for the equipment, e.g. the cylinders, rollers and the means of the inking unit(s), belonging to a printing nip for at least printing on one side of the substrate. A double sided printing group ( 91 ,  92 ;  93 ,  94 ) therefor is a special printing group ( 91 ,  92 ;  93 ,  94 ) with two printing groups ( 91 ;  92 ;  93 ;  94 ), one on or for each side of the substrate path, sharing a same printing nip for printing simultaneously both sides of a passing substrate and mutually acting with its printing cylinders as counter-pressure cylinders for the other printing group ( 92 ;  91 ;  94 ;  93 ). 
     It is to be understood, that several printing groups  91 ;  92 ;  93 ;  94  can be arranged in a same printing unit  2 ;  2 *;  2 **;  2 ***;  2 ****, with these printing groups  91 ;  92 ;  93 ;  94  for example being arranged in single- or multi-part frame walls. 
     The expression “first side” (designated by reference I) and “second side” (designated by reference II) are used in the following description to designate the two opposite sides of the sheets being printed. More precisely, in the illustrations of  FIGS. 4 to 9 , the “first side” I designates the side of the sheets that is designated by the white triangles, while the “second side” II designates the side of the sheets that is designated by the black triangles. These expressions are however interchangeable. 
       FIGS. 3A-B  schematically illustrate an example of a substrate S that is provided with an opening (or through-hole) H extending through the substrate S. This opening H is preferably filled by a suitable filling material, which material is preferably substantially transparent, so as to form a transparent or substantially transparent window W visible from both sides I, II of the substrate S. The particular shape and geometry of the opening H and resulting window W may be varied depending on the design requirements. The cross-sectional shape of the opening H could also be different from the depicted example. 
     In accordance with the invention, one wishes to replicate a micro-optical structure L on one or the other side of the substrate S. More precisely, according to the illustrated example, one wishes to replicate a micro-optical structure L, such as a field of micro-lenses, on top of the window W, on the second side II of the substrate S. To this end, side II of the substrate S is first provided in the relevant portion of the substrate S with a layer of material acting as an optical medium (for instance by means of a suitable screen-printing unit as discussed hereafter) before being brought into contact with and pressed against the surface of a replicating medium RM that is provided with a corresponding replicating structure (formed as a recessed structure in the surface of the replicating medium RM). Any desired shape and geometry could be imparted to the replicating structure in order to form the desired micro-optical structure L. 
     As schematically illustrated in  FIG. 3B , the replicating medium RM is conveniently carried by a suitable carrier CR, especially a cylinder acting as embossing cylinder as described hereinafter. 
     Subsequent to, or preferably during the replication process, the relevant material acting as optical medium is subjected to a drying or curing process (especially a UV-curing process). This is preferably carried out, as schematically illustrated in  FIG. 3B , while the substrate S is still in contact with the replicating medium RM, advantageously by subjecting the substrate S and the relevant material acting as optical medium to UV radiation from the first side I of the substrate, through the window portion W. 
     It should be appreciated that the invention is equally applicable to other types of substrates than the one illustrated in  FIGS. 3A-B , especially polymer or hybrid substrates as for instance described in International Publication No. WO 2014/125454 A1. The illustrations of  FIGS. 3A-B  are therefore by no way limiting the application scope of the present invention and the substrate material can be any suitable substrate material that can be used as printable material, such as paper, polymer, or combinations thereof. 
       FIG. 4  schematically shows a partial side view of a printing unit, designated by reference numeral  2 *, of a printing press  100 * in accordance with a first embodiment of the invention. 
     The printing press  100 * in this embodiment comprises a printing group  91 ,  92 , especially as a main printing group  91 ,  92 , which comprises two printing groups  90 ;  91 , one for each side of the substrate path, forming a so-called double sided printing group  91 ,  92  for simultaneous printing on both sides. This double sided printing group  91 ,  92  consists of elements  5 ,  6 ,  15 ,  16 ,  25 ,  26 , including first and second printing cylinders  5 ,  6  cooperating with one another to form a first printing nip between the first and second printing cylinders  5 ,  6 , especially transfercylinder, where the first and second sides I, II of the sheets S are simultaneously printed, the first printing cylinder  5  acting as a sheet conveying cylinder of the main respectively double sided printing group. The configuration of the main printing group for example is as such identical to that of the main printing group illustrated in  FIGS. 1 and 2 . In this embodiment, printing cylinders  5 ,  6  are likewise three-segment cylinders which are supported between a pair of side frames  20 . The printing cylinders  5 ,  6  serve as ink collecting cylinders  5 ,  6  and receive and collect different ink patterns in their respective colours from first and second sets of four (m=4) plate cylinders  15 , respectively  16 , which are distributed around a portion of the circumference of the printing cylinders  5 ,  6 . These plate cylinders  15  and  16 , which each carry a corresponding printing plate, are again inked by corresponding sets of four inking apparatuses  25  and  26 , respectively. The two sets of inking apparatuses  25 ,  26  are preferably supported in two retractable inking carriages  21 ,  22  that can be moved toward or away from the centrally-located plate cylinders  15 ,  16  and printing cylinders  5 ,  6 . 
     In contrast to the configuration illustrated in  FIGS. 1 and 2 , no additional printing group is provided upstream of the main printing group. Instead, an in-line casting device  80  is interposed between the transfer cylinder  9  located at the infeed and the transfer cylinder  10  that transfers the sheets to the main printing group, which in-line casting device  80  will now be described. 
     In a variant of the first embodiment depicted in  FIG. 4 , the printing unit  2  can be designed as a on side printing group  91 , i.e. can comprise a printing group  91  only on one side of the substrate path. 
     In this and in the following embodiments, the press  100 * or printing unit  2  or main printing group  91 ;  92  comprises at least one printing group  91 ;  93  on that side of the substrate path for printing onto the substrate side I; II which opposes the side II, I having already been or still have to be provided with the micro-optical structure upstream. Preferably, this at least one printing group  91 ;  93  is designed as above mentioned collect printing group  91 ;  93 . 
     By way of preference—at least for embodiments with application of the material directly onto the substrate—the in-line casting device  80  depicted in  FIG. 4  (and in  FIG. 5 —see also  FIG. 7  where the in-line casting device is designated by reference numeral  80 *) is of the type comprising a screen-printing unit  82 ,  82   a ,  84 , namely a printing unit comprising a rotary screen cylinder  82  inside which is provided a squeegee device  82   a , which rotary screen cylinder  82  cooperates with an impression cylinder  84 , serving as a counter-pressure cylinder, onto which the sheets S are fed in succession from the transfer cylinder  9  at the infeed. More precisely, in according with this first embodiment, the sheets S are transferred in succession to the impression cylinder  84  which supports the first side I of the sheets S and the rotary screen cylinder  82  is brought in contact with the second side II of the sheets S. In this particular context, the screen-printing unit  82 ,  82   a ,  84  is adapted to apply a layer of material acting as an optical medium on a portion of the second side II of the sheets S (for instance on a window-forming region W formed in the substrate S as depicted in  FIGS. 3A-3B ). The relevant material could be any suitable material, especially a transparent polymer material that is preferably curable by UV radiation. 
     As this will be appreciated from looking at the embodiment depicted in  FIG. 7 , the screen-printing unit  82 ,  82   a ,  84  could alternatively be designed to apply a layer of material acting as the optical medium on a portion of the first side I of the sheets S (for instance on a window-forming region W formed in the substrate S as depicted in  FIGS. 3A-3B , however on side I rather than on side II). The substrate then preferably will be printed downstream at least onto its other side, here side II. 
     The aforementioned screen-printing unit  82 ,  82   a ,  84  is designed to act a first application unit for applying the required layer of material where the micro-optical structure is to be replicated. The configuration and operation of the screen-printing unit  82 ,  82   a ,  84  is known as such in the art and does not need to be described in detail. Reference can in particular be made to European Patent Publication No. EP 0 723 864 A1 in the name of the present Applicant, which is incorporated herein by reference in its entirety. 
     In the illustration of  FIG. 4  (and  FIGS. 5 and 7 ), only one screen-printing unit is depicted. It should however be appreciated that multiple screen-printing units could be provided, which screen-printing units could cooperate with one and a same impression cylinder. Furthermore, while screen printing is a preferred process for applying the required material, other application processes could be contemplated. For instance, flexographic printing could be contemplated (see for instance the embodiment depicted in  FIG. 7 ). 
     Downstream of the impression cylinder  84 , there is preferably provided at least one embossing cylinder  85 , serving as embossing tool  85 , which cooperates with the second side II of the sheets S, i.e. the side where the layer of material acting as optical medium was applied by the application unit  82 ,  82   a ,  84 , especially screen-printing unit  82 ,  82   a ,  84 . This embossing cylinder  85  preferably carries on its circumference a replicating medium RM (as schematically illustrated in  FIG. 3B ) designed to replicate a micro-optical structure L, such as but not limited to a field of micro-lenses, into the layer of material applied on the sheets S. In that respect, the screen-printing unit  82 ,  82   a ,  84  should be adapted to supply a sufficient amount of material to fill the recessed portion of the replicating medium RM. 
     A pressure roller or cylinder  86  is furthermore advantageously provided about the circumference of the embossing cylinder  85  in order to cooperate with the first side I of the sheets S and press the sheets S against the circumference of the embossing cylinder  85  (and the surface of the replicating medium RM located thereon), thereby ensuring proper replication of the micro-optical structure L into the layer of material acting as optical medium. 
     The in-line casting device  80  further comprises a first drying/curing unit  51  located about a portion of the circumference of the embossing cylinder  85 , downstream of the possibly pressure roller or cylinder  86 , to dry or cure the layer of material acting as optical medium while the sheets S are still being processed and pressed against the circumference of the embossing cylinder  85  and the surface of the replicating medium RM located thereon, thereby ensuring optimal replication and formation of the desired micro-optical structure L. In this context, it shall be understood that the drying/curing operation is carried out from the side opposite to the side being provided with the layer to be cured, here for example the first side I of the substrate, e.g. sheets S, which is especially adequate in the event that the micro-optical structure L is replicated on top of a window-forming portion W as schematically illustrated in  FIG. 3B . 
     Alternatively, or in addition to the aforementioned drying/curing unit  51 , the in-line casting device  80  could be provided with a (second) drying/curing unit  52  located about a portion of the circumference of a transfer cylinder  87  that is located immediately after the embossing cylinder  85  as depicted in  FIG. 4 . In this case, it shall be understood that the drying/curing operation is carried out from the second side II of the sheets S, where the micro-optical structure L has been replicated. 
     The aforementioned drying/curing units  51 ,  52  could advantageously be UV-curing units, especially UV-LED curing units, in which case the relevant layer of material acting as optical medium evidently has to be a UV-curable material. 
     Subsequent to the replication of the micro-optical structure L, the sheets S are transferred to the downstream-located printing unit  2 *, namely to the sheet transfer cylinder  10 . 
     In accordance with this first embodiment, the sheets S are accordingly fed in succession from the sheet feeder (not shown in  FIG. 4 ) onto the feeder table  1 * where they are conventionally aligned before being fed to the sheet transfer cylinder  9  at the infeed. As illustrated, the sheets are fed in succession by the sheet transfer cylinder  9  to and through the in-line casting device  80  (via cylinders  84 ,  85  and  87 ) to the transfer cylinder  10  and then to the first printing cylinder  5  of the main printing group  91 ,  92 . 
     It will therefore be appreciated in this embodiment that the sheets S are initially provided with micro-optical structures L on side II and then receive at least first impressions on the opposite side I, preferably first and second impressions on both sides I, II, which impressions are performed simultaneously at the printing nip between the first and second printing cylinders  5 ,  6  of the main printing group  91 ,  92 . It will also be appreciated that transfer of the sheets S from the in-line casting device  80  to the printing unit  2 * is carried out exclusively from cylinder to cylinder via cooperating cylinder grippers. Optimal register accuracy between the micro-optical structures L that are replicated by means of the embossing cylinder  85  and the impressions performed by the printing unit  2 * is thereby guaranteed. 
       FIG. 5  schematically shows a partial side view of a printing unit, designated by reference numeral  2 **, of a printing press  100 ** in accordance with a second embodiment of the invention. 
     This printing press  100 ** shares a number of common features with the first embodiment of  FIG. 4 , in particular the same basic components  5 ,  6 ,  15 ,  16 ,  25 ,  26  constitutive of the main printing group  91 ,  92  and the same basic components  82 ,  82   a ,  84 ,  85 ,  86 ,  87 ,  51 ,  52  constitutive of the in-line casting device  80 . The difference between this second embodiment and the first embodiment resides in that an additional printing group  93 ,  94  is interposed between the in-line casting device  80  and the main printing group. More precisely, the printing press  100 ** of  FIG. 5  comprises third and fourth printing cylinders  7 ,  8  cooperating with one another to form a second printing nip between the third and fourth printing cylinders  7 ,  8  where the first and second sides I, II of the sheets S are simultaneously printed, the third printing cylinder  7  acting as a sheet conveying cylinder of the additional printing group  93 ,  94 . Each printing cylinder  7 ,  8  collects inks from corresponding sets of two (n=2) plate cylinders  17 , respectively  18 , that are inked by corresponding inking apparatuses  27 ,  28 . These two sets of inking apparatuses  27 ,  28  are likewise preferably supported in two retractable inking carriages  23 ,  24  that can be moved toward or away from the centrally-located plate cylinders  17 ,  18  and printing cylinders  7 ,  8 . 
     Alternatively, the sets of inking apparatus  25 ,  27  on the right side of the printing unit  2  and/or the sets of inking apparatus  26 ,  28  on the left side of the printing unit  2  could be supported in one and a same inking carriage (one on each side). 
     In the illustrated example, the additional printing group  93 ,  94  with the basic components  7 ,  8 ,  17 ,  18 ,  27 ,  28  is placed upstream of and above the main printing group  91 ,  92 , the first and second printing cylinders  5 ,  6 , on the one hand, and the third and fourth printing cylinders  7 ,  8 , on the other hand, being advantageously aligned along two horizontal planes. 
     The main printing group  91 ,  92 , comprising the basic components  5 ,  6 ,  15 ,  16 ,  25 ,  26 , and the additional printing group  93 ,  94 , comprising the basic components  7 ,  8 ,  17 ,  18 ,  27 ,  28 , are coupled to one another by means of an intermediate sheet conveying system comprising, in the illustrated embodiment, first to third sheet-transfer cylinders  10 ′, 10 ″, 10 ′″ interposed between the first and third printing cylinders  5 ,  7 . More precisely, the sheets printed in the additional printing group  93 ,  94  are transferred from the third printing cylinder  7  in succession to the first sheet-transfer cylinders  10 ′, to the second sheet-transfer cylinders  10 ″, to the third sheet-transfer cylinder  10 ′″, and then to the first printing cylinder  5  of the main printing group  91 ,  92 . 
     On their way to the main printing group  91 ,  92 , the sheets are preferably dried/cured by third and fourth drying/curing units  55 ,  56 . As illustrated, the third drying/curing unit  55  advantageously cooperates with the first sheet-transfer cylinder  10 ′, i.e. the sheet-transfer cylinder located immediately downstream of the third printing cylinder  7 , and the fourth drying/curing unit  56  cooperates with the second sheet-transfer cylinder  10 ″. The drying/curing units  55 ,  56  are advantageously UV curing units, preferably UV-LED curing units. 
     Drying/curing of the second side II of the sheets could alternatively be performed directly onto the third printing cylinder  7 , provided suitable measures are taken to ensure that the drying/curing unit does not degrade the performance or usability of the printing blankets on the third printing cylinder  7 . 
     In accordance with this other embodiment, the sheets S are accordingly fed in succession from the sheet feeder (not shown in  FIG. 5 ) onto the feeder table  1 * where they are once again conventionally aligned before being fed to the sheet transfer cylinder  9  at the infeed. As illustrated, the sheets are then fed in succession by the sheet transfer cylinder  9  to and through the in-line casting device  80  (via cylinders  84 ,  85  and  87 ) to the transfer cylinder  10 , to the third printing cylinder  7  of the additional printing group  93 ,  94  and then to the first printing cylinder  5  of the main printing group  91 ,  92  via the three intermediate sheet transfer cylinders  10 ′ to  10 ′″. 
     It will therefore be appreciated that the sheets S are initially provided with micro-optical structures L on side II and then receive first and second impressions on both sides I, II, which impressions are performed simultaneously at the printing nip between the third and fourth printing cylinders  7 ,  8  of the additional printing group and at the printing nip between the first and second printing cylinders  5 ,  6  of the main printing group. It will likewise also be appreciated that transfer of the sheets S from the in-line casting device  80  to the printing unit  2 ** is carried out exclusively from cylinder to cylinder via cooperating cylinder grippers. Optimal register accuracy between the micro-optical structures L that are replicated by means of the embossing cylinder  85  and the impressions performed by the printing unit  2 ** is once again guaranteed. 
       FIG. 6  shows an alternative embodiment for applying the material acting as optical medium. In this embodiment, the material acting as optical medium is applied directly onto the embossing form, e.g. onto the surface of the embossing cylinder  85  before the substrate, i.e. the sheet S, being arranged on it. In this case the application unit is being placed at the embossing tool  85 , preferably at the circumference of the embossing cylinder  85 , especially in a peripheral section between take over and delivery of the substrate, respectively sheet S. The application unit can be designed as a screen printing unit or flexographic-printing unit as above, but preferably it is designed like an inking apparatus with at least a fountain roller receiving the material from a reservoir and directly or through other rollers transfer the material onto the surface of the embossing cylinder  85 . 
     The embodiment with direct application onto the embossing cylinder  85  described in the context of the first embodiment is to be transferred to the second embodiment. 
       FIG. 7  schematically shows a partial side view of a printing unit, designated by reference numeral  2 ***, of a printing press  100 *** in accordance with a third embodiment of the invention. 
     This printing press  100 *** shares a number of common features with the second embodiment of  FIG. 5 , in particular the same basic components  5 ,  6 ,  15 ,  16 ,  25 ,  26  constitutive of the main printing group  91 ,  92  and the same basic components  8 ,  18 ,  28  constitutive of the additional printing group  93 , including the three transfer cylinders  10 ′, 10 ″ and  10 ′″ ensuring transfer of the sheets S from the additional printing group  93  to the main printing group  91 ,  92 . The main differences between this third embodiment and the second embodiment reside in that (i) the additional printing group is designed in this case to print only the second side II of the sheets S (and comprises three plate cylinders  18  and associated inking apparatuses  28  instead of two) and in that (ii) the in-line casting device, designated by reference numeral  80 * in  FIG. 7 , is adapted to apply a layer of material acting as the optical medium on a portion of the first side I of the sheets S (rather than on the second side II as in the embodiments of  FIGS. 4 and 5 ). 
     Furthermore, in accordance with this third embodiment, the embossing cylinder  85  is arranged so as to act as counter-pressure cylinder for the (third) printing cylinder  8  of the additional printing group  93 . In other words, and in contrast to the first and second embodiments, in-line casting of the micro-optical structure L is performed from and on the first side I of the sheets S and a printed pattern is printed on the second side II of the sheets S, while the sheets S are still being supported on the embossing cylinder  85 , i.e. without this involving any sheet transfer between the in-line casting of the micro-optical structure L and the printing of the printed pattern. This is even more favourable in terms of achieving a high register between the micro-optical structure L and the associated printed pattern as in-line casting of the micro-optical structure, on one side of the sheets S, and printing of the associated pattern, on the other side of the sheets S, are performed in a same step, without this involving any sheet transfer operation. 
     In an non-depicted alternative to the depicted embodiment of  FIG. 7 , the printing group  93  being designed as collect printing group in the embodiment of  FIG. 7  can be replaced by two or more printing groups designed as printing groups comprising only one plate cylinder each. In this embodiment printing cylinders of at least two such printing groups co-operating with the counter-pressure cylinder successively around its circumference. The printing groups accordingly being arranged around the counter-pressure cylinder. 
     In a variant of the third embodiment depicted in  FIG. 7  or its cited alternative, the printing press  100 *** do not comprise the double sided printing group  91 ,  92 , but only the printing group  93  co-operating with the casting unit  80 *;  80 **;  80 ***. In just another variant the press comprises an further printing group downstream the printing group  93  co-operating with the casting unit, but of any other type. 
     Thus, also in this and in the following embodiments, the press  100 * or printing unit  2  or main printing group comprises a printing group  91 ;  93  at least on that side of the substrate path for printing onto the substrate side I; II which opposes the side II; I having been provided with the micro-optical structure upstream and/or downstream the casting device  80 ;  80 *;  80 **;  80 ***. Instead or in addition, the embossing cylinder  85  acts as counter-pressure cylinder and cooperates with a cylinder  8  of the at least one printing group  93 . Preferably, this at least one printing group  93  preferably is designed as above mentioned collect printing group  93 , i.e. the cylinder  8  acting as collecting or transfer cylinder, especially as collecting blanket cylinder, and cooperating with several associated plate cylinders  18  to apply the at least one, preferably several collected, printed pattern on a side II; I of the substrate S which is opposite to the side I; II of the substrate S where the micro-optical structure L is replicated. 
     Operation of the in-line casting device  80 * (and of the components thereof  82 ,  82   a ,  84 ,  85 ,  86 ) is basically identical to that of the in-line casting device  80  depicted in  FIGS. 4 and 5 , except that the micro-optical structure L is ultimately formed on the first side I of the sheets S. It will be appreciated that an additional transfer cylinder  9 ′ is provided downstream of the transfer cylinder  9  at the infeed and that transfer cylinder  87  has been omitted as the sheets S can be transferred directly from the embossing cylinder  85  to the transfer cylinder  10 ′. Transfer cylinder  10 ″ is furthermore a double-sized cylinder in this third embodiment to increase space between the additional printing group and the main printing group, thereby allowing the integration of a third plate cylinder  18  and associated inking apparatus  28  in the additional printing group. 
     As transfer cylinder  87  has been omitted, so has the associated drying/curing unit  52 , as well as the downstream-located sheet transfer cylinder  10 . This being said, an additional drying/curing unit could be provided about the circumference of the embossing cylinder  85 , downstream of the printing cylinder  8  and upstream of the sheet transfer cylinder  10 ′. 
     In accordance with this third embodiment, the sheets S are accordingly fed in succession from the sheet feeder (not shown in  FIG. 7 ) onto the feeder table  1 * where they are once again conventionally aligned before being fed to the sheet transfer cylinder  9  at the infeed. As illustrated, the sheets are then fed in succession by the sheet transfer cylinder  9  to the additional sheet transfer cylinder  9 ′, through the in-line casting device  80 * (via cylinders  84  and  85 ), and then to the first printing cylinder  5  of the main printing group via the three intermediate sheet transfer cylinders  10 ′ to  10 ′″. 
     It will therefore be appreciated that the sheets S are initially provided with micro-optical structures L on side I and immediately receive a first impression on side II thanks to the additional printing unit. Further impressions are then formed on both sides I, II of the sheets S by means of the main printing group, which impressions are performed simultaneously at the printing nip between the first and second printing cylinders  5 ,  6  of the main printing group. As already mentioned, and in contrast to the first and second embodiments, it will be appreciated that the in-line casting device  80 * is designed in this case to be an integral part of the printing unit  2 *** (the same applies in respect of the in-line casting device  80 ** depicted in  FIG. 8  which likewise forms an integral part of the printing unit  2 ****). Highly optimal register accuracy between the micro-optical structures L that are replicated by means of the embossing cylinder  85  and the impressions performed by the printing unit  2 *** is therefore guaranteed. 
       FIG. 8  schematically shows a partial side view of a printing unit, designated by reference numeral  2 ****, of a printing press  100 **** in accordance with a fourth embodiment of the invention. 
     This printing press  100 **** shares a number of common features with the third embodiment of  FIG. 7 . The sole difference between this fourth embodiment and the third embodiment resides in that the in-line casting device, designated by reference numeral  80 **, is making use of a flexographic-printing unit  83 ,  83   a ,  84 * to applying at least a part of the layer of material acting as the optical medium, instead of the screen-printing unit  82 ,  82   a ,  84  depicted in  FIG. 7 . This flexographic-printing unit  83 ,  83   a ,  84 * includes a plate-cylinder  83 , which cooperates with an impression cylinder  84 *. The plate cylinder  83  carries a suitable flexographic printing plate (with relief portions corresponding in shape and position to the area on the sheets S where the layer of material is to be applied) which cooperates with an anilox roller  83   a  equipped with an associated supply chamber where the material to be applied is supplied. Flexographic-printing units are known as such in the art, especially for varnishing applications (see e.g. International PCT Publication No. WO 2011/145028 A1). 
     Processing of the sheets S on printing press  100 **** of  FIG. 8  is carried out in the same way as on printing press  100 *** of  FIG. 7 , with the only difference that the layer of material designed to act as optical medium is applied by flexographic-printing rather than by screen-printing. It shall be understood that a similar flexographic-printing unit  83 ,  83   a ,  84 * could also be used as application unit in the context of the first and second embodiments in lieu of (or even as a complement to) the screen-printing unit  82 ,  82   a ,  84 . 
       FIG. 9  shows an alternative embodiment for applying the material acting as optical medium. In this embodiment, the material acting as optical medium is applied directly onto the embossing form, e. g. onto the surface of the embossing cylinder  85  before the substrate, i.e the sheet S, being arranged on it. In this case the application unit  80 *** is being placed at the embossing tool  85 , preferably at the circumference of the embossing cylinder  85 , especially in a peripheral section between take over and delivery of the substrate, respectively sheet S. The application unit  80 *** can be designed as a screen printing unit or flexographic-printing unit as above, but preferably, it is designed similar to an inking apparatus with at least a fountain roller receiving the material acting as the optical medium from a reservoir and directly or through on or more further rollers transfer the material onto the surface of the embossing cylinder  85 . 
     Variants of the aforementioned embodiments could be contemplated without departing from the scope of the invention as defined by the annexed claims. For instance, the main printing group  5 ,  6 ,  15 ,  16 ,  25 ,  26  in the embodiments of  FIGS. 5 and 7 to 9  could be omitted altogether and the additional printing group  7 ,  8 ,  17 ,  18 ,  27 ,  28 , respectively  8 ,  18 ,  28  used exclusively for the purpose of printing the desired pattern in register with the micro-optical structure L. The integrated solution depicted in  FIGS. 7 to 9  could in particular be conceived as a combined printing and in-line casting platform or module that could serve as a stand-alone printing press or as modular printing unit that could be combined with additional printing units if necessary. 
     It should be appreciated that the actual numbers m and n of plate cylinders  15 ,  16 ,  17 ,  18  illustrated in  FIGS. 4 to 7  are not limitative and that other combinations are possible. This being said, the illustrated examples are particularly advantageous in that machine footprint is limited and machine operability and accessibility are not compromised. 
     As a possible refinement of the invention, as illustrated in  FIGS. 4 to 7 , it may be convenient to additionally provide the printing press with a recto-verso inspection system  11 ,  12 ,  61 ,  62  adapted to inspect the first and second sides I, II of the sheets printed by the additional printing group and the main printing group, including the micro-optical structures formed by means on the in-line casting device  80 ,  80 * or  80 **. 
     Furthermore, the printing presses  100 * of  FIGS. 4 and 6 and 100 ** of  FIG. 5  can also conveniently equipped, as illustrated, with automatic blanket washing devices  71 ,  72 ,  73 ,  74  adapted to clean the surface of the first, second, third and fourth printing cylinders  5 ,  6 ,  7 ,  8 , respectively, during maintenance operations. The printing presses  100 *** of  FIGS. 7 and 100 **** of  FIGS. 8 and 100 ***** of  FIG. 9  can likewise be equipped, as illustrated, with automatic blanket washing devices  71 ,  72 ,  74  adapted to clean the surface of the first, second and third printing cylinders  5 ,  6 ,  8 , respectively, during maintenance operations. By the same token, as illustrated for instance in  FIGS. 7 and 8 , a suitable automatic washing device  88  could be provided to clean the surface of the embossing cylinder  85  during maintenance operations (which automatic washing device  88  could also be contemplated in the context of the embodiments of  FIGS. 4, 5 and 6 ). 
     Various modifications and/or improvements may be made to the above-described embodiments without departing from the scope of the invention as defined by the annexed claims. In particular, while the embodiments of the invention where described with reference to sheet-fed printing press configurations, the invention could equally be applied to print on web-like substrates, i.e. successive portions of a continuous web of printable material. 
     Furthermore, the in-line casting device could be adapted to apply a layer of material acting as an optical medium on a portion of either the first or second side of the substrate and to replicate and form the micro-optical structure accordingly. In that respect, the configurations of the in-line casting devices  80 ,  80 *,  80 ** shown in  FIGS. 4 to 7  are only illustrative of possible machine configurations. 
     LIST OF REFERENCE NUMERALS USED THEREIN 
       100  printing press (prior art of  FIGS. 1 and 2 ) 
       100 * printing press (first embodiment of  FIGS. 4 and 6 ) 
       100 ** printing press (second embodiment of  FIG. 5 ) 
       100 *** printing press (third embodiment of  FIG. 7 ) 
       100 **** printing press (fourth embodiment of  FIG. 8 ) 
       100 ***** printing press (fourth embodiment of  FIG. 9 ) 
       1  sheet feeder 
       1 * feeder table 
     S substrate material (e.g. individual sheets) 
     I first side (“side I” or “recto side”) of the substrate material S 
     II second side (“side II” or “verso side”) of the substrate material S 
     H through opening in substrate S 
     W window-forming portion of substrate S 
     L micro-optical structure (e.g. lens structure) replicated/formed into a layer of material acting as optical medium applied on e.g. side II of the substrate material S 
     RM replicating medium used to replicate and form the micro-optical structure L 
     CR carrier supporting the replicating medium RM (e.g. embossing cylinder  85 —embodiments of  FIGS. 4 to 7 ) 
       2  printing unit (prior art of  FIGS. 1 and 2 ) 
       2 * printing unit (first embodiment of  FIGS. 4 and 6 ) 
       2 ** printing unit (second embodiment of  FIG. 5 ) 
       2 *** printing unit (third embodiment of  FIG. 7 ) 
       2 **** printing unit (fourth embodiment of  FIG. 8 ) 
       2 ***** printing unit (fourth embodiment of  FIG. 9 ) 
       3  sheet conveying system (chain gripper system with spaced-apart gripper bars) 
       4  substrate delivery unit, sheet delivery unit 
       5  sheet conveying cylinder/(first) printing cylinder (main printing group)/three-segment blanket cylinder 
       6  (second) printing cylinder (main printing group)/three-segment blanket cylinder 
       7  sheet conveying cylinder/(third) printing cylinder (additional printing group)/two-segment blanket cylinder (embodiment of  FIG. 5  only) 
       8  (third, resp. fourth) printing cylinder (additional printing group)/two-segment blanket cylinder (prior art of  FIGS. 1, 2 /second to fourth embodiments of  FIGS. 5 to 7 ) 
       8 ′ sheet conveying cylinder/two-segment cylinder (prior art of  FIGS. 1 and 2  only) 
       9  sheet transfer cylinder (infeed) 
       9 ′ sheet transfer cylinder (third and fourth embodiments of  FIGS. 6 and 7 ) sheet transfer cylinder (prior art of  FIGS. 1, 2 /first and second embodiments of  FIGS. 4 and 5 ) 
       10 ′, 10 ″, 10 ′″ sheet transfer cylinders (intermediate sheet conveying system interposed between additional printing group and main printing group—embodiments of  FIGS. 5 to 7  only) 
       11  inspection cylinder or drum (part of inspection system) 
       12  inspection cylinder or drum (part of inspection system) 
       15  (m=4) plate cylinders cooperating with printing cylinder  5   
       16  (m=4) plate cylinders cooperating with printing cylinder  6   
       17  (n=2) plate cylinders cooperating with printing cylinder  7  (embodiment of  FIG. 5 ) 
       18  (n=2, resp.  3 ) plate cylinders cooperating with printing cylinder  8  (prior art of  FIGS. 1, 2 /second to fourth embodiments of  FIGS. 5 to 7 ) 
       20  printing press main frame 
       21  retractable inking carriage supporting inking apparatuses  25   
       22  retractable inking carriage supporting inking apparatuses  26   
       23  retractable inking carriage supporting inking apparatuses  27  (embodiment of  FIG. 5 ) 
       24  retractable inking carriage supporting inking apparatuses  28  (prior art of  FIGS. 1, 2 /second to fourth embodiments of  FIGS. 5 to 7 ) 
       25  (m=4) inking apparatuses each cooperating with a corresponding one of the plate cylinders  15   
       26  (m=4) inking apparatuses each cooperating with a corresponding one of the plate cylinders  16   
       27  (n=2) inking apparatuses each cooperating with a corresponding one of the plate cylinders  17  (embodiment of  FIG. 5 ) 
       28  (n=2, resp.  3 ) inking apparatuses each cooperating with a corresponding one of the plate cylinders  18  (prior art of  FIGS. 1, 2 /second to fourth embodiments of  FIGS. 5 to 7 ) 
       31  pair of chain wheels of sheet conveying system  3  (upstream end) 
       50  drying/curing unit (prior art of  FIGS. 1, 2 ) 
       51  (first) drying/curing unit acting on side I of the sheets S, e.g. UV-LED curing unit (located about a portion of the circumference of embossing cylinder  85 ) 
       52  (second) drying/curing unit acting on side II of the sheets S, e.g. UV-LED curing unit (located about a portion of the circumference of transfer cylinder  87 /first and second embodiments of  FIGS. 4 and 5 ) 
       55  (third, resp. second) drying/curing unit acting on side I of the sheets S, e.g. UV-LED curing unit (located about a portion of the circumference of transfer cylinder  10 ′/embodiments of  FIGS. 5 to 7 ) 
       56  (fourth, resp. third) drying/curing unit acting on side II of the sheets S, e.g. 
     UV-LED curing unit (located about a portion of the circumference of transfer cylinder  10 ″/embodiments of  FIGS. 5 to 7 ) 
       61  inspection camera (side I of the sheets S) cooperating with inspection cylinder or drum  11 , e.g. line-scan camera 
       62  inspection camera (side II of the sheets S) cooperating with inspection cylinder or drum  12 , e.g. line-scan camera 
       71  automatic blanket washing device cooperating with printing cylinder  5   
       72  automatic blanket washing device cooperating with printing cylinder  6   
       73  automatic blanket washing device cooperating with printing cylinder  7  (embodiment of  FIG. 5 ) 
       74  automatic blanket washing device cooperating with printing cylinder  8  (embodiments of  FIGS. 5 to 7 ) 
       80  in-line casting device for the application of a layer of material acting as optical medium and for the replication and formation of the micro-optical structure L in the said layer of material acting as optical medium (first and second embodiments of  FIGS. 4 and 5 ) 
       80 * in-line casting device for the application of a layer of material acting as optical medium and for the replication and formation of the micro-optical structure L in the said layer of material acting as optical medium (third embodiment of  FIG. 6 ) 
       80 ** in-line casting device for the application of a layer of material acting as optical medium and for the replication and formation of the micro-optical structure L in the said layer of material acting as optical medium (fourth embodiment of  FIG. 7 ) 
       82  screen-printing cylinder (part of the screen-printing unit acting as application unit for the layer of material acting as optical medium/first to third embodiments of  FIGS. 4 to 6 ) 
       82   a  squeegee device of screen-printing cylinder  82   
       83  plate-cylinder (part of the flexographic-printing unit acting as application unit for the layer of material acting as optical medium/fourth embodiment of  FIG. 7 ) 
       83   a  anilox roller and associated supply chamber for plate-cylinder  83   
       84  impression cylinder (remaining part of the screen-printing unit acting as application unit for the layer of material acting as optical medium) 
       84 * impression cylinder (remaining part of the flexographic-printing unit acting as application unit for the layer of material acting as optical medium) 
       85  embossing cylinder carrying replicating medium RM for the replication and formation of the micro-optical structure L 
       86  pressure cylinder or roller cooperating with embossing cylinder  85   
       87  transfer cylinder cooperating with embossing cylinder  85  for transfer of the sheets S to the downstream-located printing unit  2 *,  2 ** (first and second embodiments of  FIGS. 4 and 5 ) 
       88  automatic washing device cooperating with embossing cylinder  85  (embodiments of  FIGS. 6 and 7 ) 
       91  printing group, preferably collect printing group 
       92  printing group, preferably collect printing group 
       93  printing group, preferably collect printing group 
       94  printing group, preferably collect printing group