Field of the Invention

The present invention relates to security document substrate separation apparatus, together with a method of separating security document substrates.

Background to the Invention

Security documents have been used for many years throughout the world. Examples of security documents include bank notes, identification documents, security certificates and passports. Such documents may include single sheet forms such as bank notes or multi-page forms such as passports. Since security documents are usually required to be produced in significant numbers, they are typically printed and otherwise processed as larger sheets for example having approximate dimensions of 1 metre by 1 metre. In this way the security documents are batch processed in two ways, firstly since multiple security documents are formed within a single sheet and secondly since these sheets are usually processed in large stacks of such sheets. The processing of the security documents includes the addition of various security features and other methods which are provided so as to deliver overt or covert security features within the security documents. Examples of such features include intaglio printing and the application of optically variable elements. Only once all of the required security features and processing has been applied to the security documents are they then finally subdivided by a cutting process into the individual security documents for use.

Security documents are therefore formed by the application of various processes to sheets of security document substrate material. An example of such a substrate material is the specialised paper used in the production of bank notes in many countries around the world. It is noted here that, whilst many security features are added to the substrate material during its processing to form a security document, in some applications the substrate itself is formed so as to have inherent security features, an example of which is a watermark in a bank note substrate. Continuing the example of the printing of bank notes, it is usually the case that the sheets of bank note substrate material are provided in a stack which is handled manually, sometimes with the aid of mechanical assistance, at various stages of entry and exit of the various printing processes involved in bank note production. For example, a stack of around 200 sheets of approximate dimension of 1 metre by 1 metre and a sheet thickness of around 100 micrometres may be primarily handled manually as part of a bank note production process.

One of the more recent developments in the production of security document substrates is a transition to using "polymer" rather than "paper" substrates. Typically a polymer substrate for a bank note may take the form of biaxially oriented polypropylene. Unlike paper however, this material is inherently transparent or translucent and therefore the substrate has to be formed with at least one opacifying layer so as to enable any later printing upon the substrate to be readily visible. Sheets of polymer substrates can be handled in a very similar manner to paper substrate. However, one of the problems encountered when using polymer substrates for security documents is that there is an increased tendency for the substrate sheets to adhere together. This behaviour causes problems within processes which require the rapid and reliable separation, and individual processing, of sheets of such substrates. This problem of sheet adhesion is not exclusive to polymer substrates and indeed it can be found within certain security document substrates formed of paper under certain conditions. Thus, a problem exists in how to process security document substrate material which encounters this "blocking" behaviour. The blocking effect is most pronounced in polymer substrates although the cause of this is not fully understood. For example, the problem seems to worsen when a stack of polymer substrates is left undisturbed for a period of days. The problem is also seen to occur increasingly as the number of processes applied to the polymer substrate (such as bank note printing) are performed. Whilst a manual user can attempt to overcome this problem by agitating the stack of sheets, this solution is unsatisfactory and incurs a significant manual handling risk. For example, in comparison with a paper substrate, there is a 50% increase in unblocking labour required and also a 75% increase in unblocking time. There is therefore a need to provide a solution to address this problem and in particular to reduce the manual handling risk to the workforce in a security document manufacturing plant.

Summary of the Invention

In accordance with a first aspect of the invention we provide a security document substrate separation apparatus comprising: a separation member having a curved surface against which a stack of security document substrates sheets are urged when in use; and a retaining device adapted to cause the sheets in a first location of the stack to remain in a fixed geometry with respect to one another whilst the stack of sheets is urged against the curved surface, whereby at least parts of the surfaces of the sheets which are distal from the first location and are in contact with other sheets in the stack, are caused to undergo relative movement with respect to the other sheets as a result of being urged against the curved surface.

We have therefore devised a security document substrate separation apparatus which can be used quickly and efficiently by for example an operator of a security document printing press. The apparatus utilises a combination of a retaining device and a separation member to cause localised shearing between the surfaces of the sheets in a stack of such sheets to be processed. The shearing action is caused by the sheets conforming to the curved surface, since the radius of curvature of each sheet will be slightly different. The sheets are thereby "unblocked" by breaking the surface bonding by this shearing action.

As will be understood, in principle the radius of curvature of the curved surface, at least within a substantial part of it, is necessarily finite rather than infinite. The curved surface may be a convex surface or a concave surface or a combination thereof such as a serpentine or other regular or irregular curve. The separation member may have a circular cross section wherein the curve surface is a circumferential surface member. The cross section of the separation member may of course be non-circular such as taking an elliptical or other form. The separation member could be hollow such that it may receive the substrate stack through an aperture within the member and in which case the curved surface may be an internal circumferential surface. However, it may be more convenient to use the external or outer surface of the separation member. The separation member may be static so as to provide a static surface. However, it is preferred that the separation member is rotatable and, as such, may take the form of a roller. The roller may be rotatable along its major axis. In order to improve the shearing effect, preferably the circumference of the curved surface exceeds the length of the sheets in a separation direction. The separation direction can be defined as that along which the relative moment occurs. This provides particular advantage because the shearing effect is distributed homogeneously along the entire length of the sheets. It is noted above that security document substrates are particularly susceptible to sheet adhesion problems. The lengthwise distribution of the shearing effect increases the reliability of sheet separation where strong adhesion occurs. In particular, this avoids localised "sticking" which can lead to rucking of the sheets which may, in turn, inhibit the successful application of downstream printing and other processes. In order to achieve this even distribution of shearing whilst ensuring a relatively high radius of curvature, typically the circumference of the curved surface is between 1 and 2 times the length of the sheet, preferably between 1 and 1 .5 times the length of the sheet. Similarly, the lateral width of the curved surface, that is, in a direction orthogonal to the separation direction, preferably exceeds the dimension of the sheet.

The retaining device may take a number of different forms although preferably it comprises an elongate clamp and a clamping mechanism for urging the clamp towards the separation member so as to hold the sheets in the stack between the clamp and the separation member. When engaged, the stack of sheets may therefore be firmly held between the clamp and the curved surface of the separation member. The elongated clamp may therefore take the form of a bar, cylinder or other prismatic shape so as to provide the clamping effect across the full dimension of the stack of sheets. The clamping mechanism may comprise clamping actuators at each end of the clamp, for example adjacent the edges of the stack. Although the clamping actuators are arranged to drive their respective end of the clamp towards or away from the separation member, typically of course they are arranged to act in unison such that the gap between the clamp and the curved surface of the separation member is, at all times, equal along the length of the clamp. It is also desirable to have actuators situated along the length of the clamp. This would offer less stress/equal loading for the actuators, in comparison with them being situated only at the extremities of the clamp.

Whilst the retaining device may be used to grip the stack firmly in the first location, further advantage is provided by the use of at least one support member which is adapted in use to urge the distal parts of the sheets (with respect to the retaining device) against the separation member. The location of the region of contact between the support member and the adjacent sheet of the stack may be arranged at a number of different positions, particularly adjacent a rearmost edge of the stack. It is preferred that the separation member and the support member undergo mutual relative movement and therefore the contact location of the support member with the stack may move during the use of the apparatus to separate the sheets. For example, the support member may initially contact the stack at a location relatively proximal to the leading edge of the stack of sheets in the vicinity of the retaining device. Thereafter, due to relative movement between the separation member and the support member, the position of contact between the support member and the sheet of the stack may move rearwards towards the rear of the stack as the separation member moves (such as by a rotational movement in the case of a roller for example). For this reason, the support member may comprise a support roller. Such a roller may be driven or indeed free. The support member may be movable between an urging position in which the stack is forced against the separation member, and a rest position in which the stack is not forced against the separation member. A number of such support members may be provided, for example distributed across or around the surface of the separation member.

In order to assist with the feeding of the stack, the apparatus may further comprise a loading table having a surface upon which the stack of documents may be positioned, the loading table being positioned adjacent the separation member so as to allow the stack to be moved across the table and into a loading position where the stack may be engaged by the retaining device. It is envisaged that the sliding of the stack across the table may be performed by a manual operator although of course it may be performed by a mechanical process such as using belts or rollers, this allowing an extra degree of automation of the apparatus. Indeed, with use of an appropriate control system using feedback from the appropriately positioned sensors, it is conceivable that the apparatus as a whole may be fully automated so as to enable a stack to be loaded from an input position, fed into the apparatus, separated by automatic application of the retaining device and any support member, and fed to an output position for further onward processing, such as entry into a printing press. In order to further assist with the loading of the stack of sheets into the retaining device, the security document substrate separation apparatus may further comprise a retractable guide, moveable between a loading position in which the sheets are guided into the retaining device, and a retracted position. Such a guide may have a curved or angled surface so as to direct the leading edge of the sheets in the desired direction when in use.

As has been mentioned, the number of sheets in the stack, is preferably within a range so as to allow manual handling. In the present case, such a range is between 100 and 300 sheets. With a more automated system, which avoids the need for manual handling directly and for example uses only mechanical assistance for a manual operator, or indeed is full automated, then the number of sheets in the stack may be considerably higher. Typically, the thickness of each sheet within the stack is within the range 85 to 1 10 micrometres, this thickness being preferred to provide an advantageous combination of strength of the sheets and flexibility.

Whilst the sheets may be formed of a paper-based material, the invention finds particular advantage where each sheet of the substrate is formed from a polymeric material, in particular one having at least one opacifying layer there upon. This is due to the increased unblocking behaviour exhibited by the polymeric substrate material. We note here that the term "polymer" in the context of security document substrates has a special meaning within the security document industry. For example the "paper" used in the production of bank notes is not in fact produced from wood pulp but rather a combination of cotton and linen fibres. Each of these materials is inherently polymeric at a molecular level. However in the security document industry the term "polymer" relates principally to non-fibrous polymeric films such as polypropylene (PP) (most preferably bi-axially oriented PP (BOPP)), polyethylene terephthalate (PET), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), nylon, acrylic, Cyclic Olefin Polymer (COP) or Cyclic Olefin Copolymer (COC).

The separation apparatus is particularly advantageous where the security document comprises a substrate for a bank note, identification document, passport, licence, cheque, visa, stamp or certificate.

In accordance with a second aspect of the invention, we provide a method of separating sheets of security document substrates comprising: obtaining a stack of sheets of security document substrate; operating a retaining device to cause the sheets in a first location of the stack to remain in a fixed geometry with respect to one another; and, whilst the sheets in the first location are in said fixed geometry, urging the stack of sheets against a curved surface of a separation member; whereby at least parts of the surfaces of the sheets which are distal from the first location and which are in contact with other sheets in the stack, are caused to undergo relative movement with respect to the other sheets as a result of being urged against the curved surface.

As will be understood, the method of the second aspect of the invention may be put into effect by using the apparatus described in association with the first aspect of the invention. As will be further understood, the surfaces of the sheets are generally planar surfaces. The first location comprises a region at or adjacent a leading edge of the stack of sheets with respect to the feed direction of the retaining device. It is advantageous for the first location to be adjacent the leading edge since this provides a convenient arrangement for the retaining device with respect to the separation member. Other arrangements are of course contemplated.

When the stack of sheets is engaged with the curved surface, it is the relative minor differences between the radius of curvature of each of the sheets in the stack which causes the shearing effect thereby breaking the adhesive bond between the respective sheets. In principle therefore, the urging of the stack of sheets against the surface may be performed by numerous different means. In its simplest form, the urging of the stack of sheets may be achieved at least in part by using gravitational force. This is advantageous in that it applies an even distribution of the urging effect. However, alternatively, or in addition, a support member may be used to provide this function by force being applied to the stack. Whilst such a force may be most conveniently applied mechanically, in principle it may also be applied using a centripetal force or a pressurised fluid such as a gas. The urging step itself may be provided by the support member at either a location at the trailing edge of the stack or at a location that moves towards the trailing edge of the stack as the method progresses (this particularly being the case with relative movement of the support member and separation member). The method may be partially or fully automated, in each case under the control of a control system. Preferably in addition to the automated loading of the sheets, the method further comprises the automated removal of the sheets from the retaining device and the provision of the sheets to an output location for downstream processing.

In a preferred arrangement having a retaining device in the form of an elongate clamp and the separation member in the form of an elongate roller, the method preferably further comprises: a) locating the stack of sheets with respect to a retaining device in the form of an elongate clamp; b) operating the elongate clamp so as to hold a leading edge of the stack against the outer circumferential surface of a separation member in the form of an elongate roller; c) rotating the elongate roller about its axis so as to draw the stack of sheets around the roller surface; and d) releasing the retaining device. As will be understood, it is preferred therefore that the retaining device adopts an orbital path about the circumferential surface of the separation member. Prior to step a), the loading of the stack may be achieved into the retaining device by sliding the leading edge of the stack across a loading table surface and across a sheet guide located adjacent the retaining device. The sheet guide is to ensure that the leading edge of the stack is accurately positioned in the retaining device. It is noted here also that, advantageously, a support roller may be used to urge a part of the stack, distal from the leading edge, against the separation roller. Unlike the retaining device, it is preferred that the support roller does not orbit the separation member when in use and therefore the contact location between the support roller and the stack moves during step c).

Following effecting the release of the stack by the retaining device in step d), the method may proceed by further comprising removing the separator stack from the separator and thereafter replacing it in a stack jogger so as to align the sheet within the stack. Such a stack jogger may be thought of as a vibrating container with orthogonal walls for engagement with the sheets of the stack, together with an inclined base such that, by virtue of the vibrating action, the sheets realign within the stack. This is beneficial for providing a stack of sheets having straight sides for further processing downstream. The stack jogger is a supplementary piece of equipment and not essential since the sheets can be realigned by hand. However its use does help significantly.

As will be understood by those of ordinary skill in the art, the production of a security document from an initial security document substrate typically involves a number of separate processes such as applying different printing processes and other security features. The apparatus and method according to the invention may be used at one or more points during such an end to end process. Typically therefore the method further comprises performing one or more further procedures, each of which comprises: performing a further process on each of the sheets in the stack; and thereafter; performing the method according to the second aspect; wherein any said further process is the same as or different from any other said further process, and wherein each further process is selected from the group of: lithographic printing, intaglio printing, application of transfer stripes or patches, letterpress printing, screen printing varnishing and cutting. Furthermore, a stack jogger may be used after each application of the separating process, or where deemed necessary.

Brief Description of the Drawings Figure 1 shows a side view, partly in section, of a first example apparatus in a loading phase;

Figure 2 shows the first example apparatus at a ¾ stage in the cycle;

Figure 3 shows an end view, partly in section, of the first example apparatus; Figure 4 shows a schematic side view of an automated second example apparatus;

Figure 5 is a flow diagram of the operation of a cylinder based separation apparatus such as is illustrated in Figures 1 to 3;

Figure 6 is a flow diagram showing the repeated use of the method in

association with other security document processes.

Description of Examples

We now describe two examples of an apparatus and method in which a stack of substrate sheets are separated for the purpose of downstream processing. The examples are described in the context of bank note substrate processing although the examples are equally applicable to other types of security document substrate.

Referring now to Figure 1 , a first example substrate separation apparatus for separating security document substrates is illustrated generally at 100. The apparatus 100 has a separation member in the form of a main cylinder 101 which is a right circular cylinder mounted on a main cylinder axis 102. The main cylinder may be formed from any suitable material, such as steel. In the present case it has an outer surface 103 which is provided with an elastomeric material which is suitable for gripping substrate sheets. In the present example the axial length of the cylinder is about 900mm and the external diameter is about 320mm. The length of the cylinder is chosen to be in excess of the width dimension of the substrate sheets to be processed. The diameter is likewise chosen such that the circumference of the cylinder exceeds the length dimension of the substrate sheets. The length and width dimensions of the substrate sheets are each approximately 1000mm in this example.

A retaining device 104 includes an elongate sheet clamp 105 which is positioned adjacent the outer surface 103 and extends parallel with the cylinder axis 102, this again having a length in excess of that of the width dimension of the substrate sheets to be processed. Clamp actuators in the form of pneumatic clamp cylinders 106 are provided at each end of the elongate sheet clamp 105. The elongate sheet clamp 105 can be thought of as a bar which extends lengthways above the surface of the main cylinder 101 . It is a 40x10x1000mm rectangular bar with an additional curved section of 5mm thickness welded to the leading edge all along its length. The curvature matches that of the main cylinder and causes the leading edge of the sheets to form to the main cylinder profile. The idea of this is to prevent the front edge of the sheets protruding from the cylinder at a tangent which can potentially cause jams as the main cylinder rotates.

The function of the elongate sheet clamp is to grip the stack of sheets against the outer surface 103 of the main cylinder 101 . Accordingly the surface of the elongate sheet clamp 105 which contacts the sheets may be provided with a suitable surface coating such as an elastomeric material. Nevertheless in the absence of a surface coating a steel surface has been demonstrated to be effective. The gripping action is achieved by the clamp cylinders 106 which enable the elongate sheet clamp to be moved radially towards and away from the main cylinder axis 102, and therefore towards and away from the outer surface 103.

The main cylinder 101 is configured to be rotatable about the cylinder axis 102. This is driven by a cylinder motor 107 (shown in Figure 3), this in turn being controlled by a control system 108. Notably the clamping device 104 (including the elongate sheet clamp 105 and clamp cylinders 106) is rotatable about the main cylinder axis 102 so that the elongate sheet clamp 105 is able to trace a circumferential path having a given radius. In practice this means that the elongate sheet clamp 105 is arranged to remain positioned above a particular part of the cylinder outer surface 103. Mechanically this may be most simply achieved by the mounting of the clamping device 104 to the main cylinder itself.

Returning to Figure 1 , the apparatus 100 is shown in a loading configuration. In this case the clamping device is located at the lowermost part of the main cylinder 101 . A loading table 1 10 is positioned, laterally and orthogonally offset with respect to main cylinder axis 102. The loading table has an upper surface 1 1 1 positioned at a height such that, when a stack of substrate sheets is located on the table, the uppermost sheet is lower than the lowest point of the outer surface 103 of the main cylinder 101 .

The lateral offset between the lowermost point of the main cylinder 101 and the edge of the loading table 1 10 provides a gap to accommodate the orbital movement of the clamping device 104 about the main cylinder axis 102. It also provides space for the positioning of two further devices to be now described.

The first is a retractable guide 1 15 which is elongate (again, at least across the width of the substrate sheets). The retractable guide is positioned beneath the main cylinder 101 and adjacent the clamping device 104 (when this is in the loading configuration). The retractable guide has a surface for receiving the stack of sheets. The retractable guide 1 15 is moveable between a loading position and a retracted positioned. In the loading position, the surface which receives the stack of sheets is positioned so as to guide the sheets into the gap between the elongate sheet clamp 105 and the outer surface 103 of the main cylinder 101 . In the retracted position the retractable guide 1 15 is at a position sufficiently far from the main cylinder to avoid engagement with the stack of sheets when loaded into the clamping device 104.

The retractable guide 1 15 is positioned adjacent the retaining device 104 when the retaining device is in its loading configuration. A support member 120 is positioned adjacent the retractable guide 1 15, between this and the loading table 1 10. The support member is formed from a small support roller 120 arranged so as to have an axis which is parallel with that of the main cylinder axis 102 and a length in excess of that of the width dimension of the sheets. In a similar manner to the retractable guide 1 15 the support roller 120 is moveable, using three support cylinders 121 positioned at opposing ends of the support roller 120 and at the centre, between an engagement position and a rest position. In the engagement position the support roller is extended towards the outer surface 103 of the main cylinder 101 so as to urge the stack of sheets against the curved outer surface. Whilst the support roller 120 could be driven, in this example it is freely mounted. In the rest position the support roller 120 is withdrawn so as to be positioned below the plane defined by the upper surface 1 1 1 of the loading table 1 10.

A stack of about 130 sheets (typically between 100 and 250 sheets) represented by sheet stack 125 in Figure 1 is illustrated positioned upon the upper surface 1 1 1 of the loading table 1 10 and fed into the retaining device 104. In this case each sheet is of approximately square geometry having length and width dimensions of approximately 1000 mm. Each sheet is formed from a biaxially oriented polypropylene material of thickness around 75 micrometres and having an opacifying layer, upon each major external surface of about 10 micrometres in thickness. Figure 3 shows the apparatus 100 of Figure 1 viewed schematically from the end. This illustrates mountings 130 which support the main cylinder 101 , together with the cylinder motor 107 and drive train 131 for providing rotational drive force from the cylinder motor 107. The sheet stack 125 is illustrated in the loading configuration with the clamp cylinders 106 fully extended and the lowermost sheet of the sheet stack 125 resting upon the upper surface of the elongate sheet clamp 105. It will be noted that the elongate sheet clamp 105 lies beneath the main cylinder 101 in this configuration.

An example method of operating the substrate separation apparatus 100 is now described with reference to Figure 5.

Initially at step 500 a sheet stack 125 of about 130 sheet is separated from a batch stack of polymer substrate sheets (biaxially oriented polypropylene). These sheets within the sheet stack 125 typically are "blocked" in that they exhibit considerable surface adhesion which prevents their individual separation. The sheet stack is typically manually lifted onto the loading table 1 10 by a human operator. The operator of the apparatus ensures that the apparatus is in the loading configuration as illustrated in Figure 1 . In particular this includes ensuring that the retaining device 104 is located at its lowermost position beneath the main cylinder 101 , the retractable guide is in the loading position (extended towards the main cylinder 101 ) and the support roller 120 is in its rest position. At step 501 an operator of the apparatus 100 ensures general alignment of the leading edge of the sheet stack 125 with the axis of the elongate sheet clamp 105. Thereafter the operator manually pushes the sheet stack 125 across the surface 1 1 1 into the clamping device 104. In so doing the leading edge of the sheet stack 125 projects from the edge of the table, passes clear of and above the support roller 121 , and across an upper surface of the retractable guide 1 15. In the present example the retractable guide 1 15 has a curved upper surface which angles the leading edge of the sheet stack 125 in an upward direction as it progresses in a feeding direction so as to direct the leading edge into the gap presented between the elongate sheet clamp 105 (beneath the stack edge) and the lower part of the outer surface 103 of the main cylinder 101 . The operator continues to push the sheet stack 125 in the feed direction until the leading edge passes a few centimetres beyond the distal edge of the elongate sheet clamp 105 (this distance depends on sheet size and orientation). This arrangement is illustrated in Figure 1 .

At step 502 the operator actuates two switches, these being positioned laterally spaced such that the operator must use two hands, one for each switch. This acts as a safety mechanism to ensure that the operator's hands are clear of the retaining device 104. The operation of the switches is detected by the control system 108 which causes the clamp cylinders 106 to draw the elongate sheet clamp 105 towards the outer surface 103. This causes a region adjacent the front edge (in the feed direction) of the sheet stack 125 to be clamped between the upper surface of the elongate sheet claim 105 and the outer surface 103. Once the sheet stack 125 is securely clamped, at step 503 the control system of the apparatus 100 operates the retractable guide to move away from the lower surface of the sheet stack 125 into the retracted position. The support cylinders 121 are also operated so as to move the support roller 120 upwards from the rest position so as to contact the lowermost surface of the sheet and to continue into the engagement position in which the sheet stack 125 is lifted against the outer surface 103 of the main cylinder 101 . The part of the sheet stack 125 between the retaining device 104 and the support roller 120 is therefore urged against and conforms with the lower part of the outer surface 103.

At step 504 the control system operates the motor 107 and drive train 131 so as to rotate the main cylinder 101 . With reference to Figure 1 this rotation is in a clockwise direction. The retaining device 104, which is mounted to the main cylinder 101 , therefore moves in an orbital path about the main cylinder axis 102 and away from the support roller 120. As will be recalled, the support roller 120 is mounted freely on its axis. The rotation of the main cylinder 101 draws the sheet stack progressively through the nip between the support roller 120 and the opposing part of the outer surface 103. The rotation of the main cylinder 101 continues and eventually the trailing edge of the sheet stack 125 passes through the support roller nip. In this configuration the entire surface of what was previously the uppermost sheet of the stack is now in contact with the outer surface 103 and forms approximately 270 degrees of arc about the main cylinder 101 . With in excess of 100 sheets in the sheet stack 125, each of thickness around 100 micrometres, the thickness of the stack is of the order of 13 mm. Since the sheets are firmly clamped at the leading edge, the difference in the radius of curvature between the innermost and outermost sheets cause by the stack thickness means that the outermost sheet is displaced about 60 mm circumferentially around the cylinder in comparison with the innermost sheet. This means that each of the interfaces between the sheets is subjected to a shear displacement as a result of this difference in the radius of curvature, the shear displacement being sufficient to enable the sheets to be readily separated. The rotation of the main cylinder 101 then reaches a position of about ¾ of a full rotation of the main cylinder 101 about its axis as the trailing edge clears the roller 120. In this position most of the sheet stack 125 is pressed against the outer surface by the action of gravity.

Once the support roller 120 is no longer in contact with the sheet stack 125, the control system operates the support cylinders 121 which withdraw the support roller 120 away from the main cylinder 101 and into the rest position. It should be noted that the distance of this withdrawal is sufficient to enable the retaining device 104 to pass between the support roller 120 and the outer surface 103. At step 506 the rotation of the main cylinder is continued with the retaining device holding the leading edge of the sheet stack 125 and passing the retracted roller 120 so as to return to the initial loading position. Thus a full rotation of the main cylinder 101 about its axis 102 is completed, this rotation taking 5 to 8 seconds. During this final rotation (which is a continuous process from its initiation at step 504) the free end of the sheet stack falls on to the upper surface 1 1 1 of the loading table 1 10. Finally, at step 507 the clamp cylinders 106 are operated to extend the elongate sheet clamp 105 and release ("unclamp") the sheet stack. Likewise the retractable guide 1 15 is extended to its loading position. The operator then manually removes the stack of separated sheets. In this first example the method in Figure 5 ends at step 507. The additional steps in Figure 5 are described in association with the second example.

Figure 6 shows how the use of substrate separation apparatus, of any example described herein, may be used in a security document production process. Step 600, in which the stack of substrate sheets is initially received, for example from a security substrate production facility, is equivalent to step 500 of Figure 5. Thereafter steps 501 to 507 (or 509 in the second example to be described) which detail the unblocking operation are represented by step 601 in Figure 6. Having removed the unblocked sheet stack 125 from the loading table 1 10, the stack is then placed, at step 602, in a jogger apparatus. As mentioned previously this apparatus vibrates the stack so as to cause relative movement between the sheets. The combination of vibration and the force of gravity due to an angled base of the jogger causes the sheets to align with two orthogonal side walls of the jogger. The realignment takes about 15 to 30 seconds. The realigned unblocked stack is then ready for processing by other apparatus in the security document printing process, such as lithographic printing, intaglio printing, application of optical elements, and varnishing, also flexographic printing, letterpress, screen printing and cutting. Note that the jogger may be used to retain a number of stacks of sheets until around 500 sheets are ready to be processed.

As the further steps of Figure 6 indicate, the sheet handing during the application of the security document processes actually causes an increase in blocking behaviour of the stack. This is particularly problematical for "polymer" substrates.

At step 603 the sheet stack 125 is then loaded into an apparatus for applying a first security document production process, such as a printing process. In this example this first process is a lithographic printing process. For example with reference to United Kingdom currency, the majority or background printing on currency notes is produced using an lithographic printing process. Having processed each of the sheets in the stack the outputted stack is then found to exhibit increased blocking behaviour. The unblocking process described in Figure 5 is then applied to the lithographically printed sheet stack at step 604. Thereafter the jogger process is used to realign the sheets at step 605.

These three processes in steps 603, 604 and 605 are then repeated a number of times (represented by integer "n") for selected, or indeed, all other sheet handling processes in the security document production process. This "loop" within the process is shown at step 606. For example in the second instance of step 603, an intaglio printing process may be used. On United Kingdom currency this includes printing the hair of Her Majesty the Queen's head, together with the wording "Bank of England". A further iteration of the loop may include the application of an "optic" by a hot transfer process for step 603.

Having performed each of the processes for which the unblocking loop of steps 603, 604 and 605 are deemed required, the process then proceeds to step 607 where further downstream processes of the security document are performed. These including finishing, the cutting of the sheets into individual bank notes and packaging processes.

A second example apparatus for the separation of security document substrates is now described with reference to Figure 4. In Figure 4 components which are analogous to those in Figure 1 are given similar second and third digits within their reference numeral. This second example is an automated apparatus 300 so as to provide automated unblocking. It functions according to a similar principle as the first example, here using a main cylinder 301 . The principal differences between the apparatus of the first and second example are the provision of five retractable support rollers, an output table and a control system which obtains data from a number of distributed sensors.

Referring to Figure 4, a loading table 310 and first support roller 321 a are provided in an analogous manner to Figure 1 (components 1 10, 121 respectively). Likewise a retaining device 304 is provided to force the sheet stack 325 against the main cylinder 301 . In this second example the retractable guide is not provided and instead the profile of the elongate sheet clamp 305 is curved at its receiving edge (first contacted by the sheet stack 325) so as to assist with the guiding of the sheet stack 325 into the gap between the elongate sheet clamp 305 and the main cylinder 301 . Of course a retractable guide could be provided in this example also, as an alternative. A second support roller 321 e is located symmetrically (about a mirror plane containing the vertical and main cylinder axes) with respect to the support roller 321 a such that the retaining device 304 (when in its loading position) is positioned centrally between the support rollers 321 a,321 e. Further support rollers 321 b, 321 c, 321 d are located evenly distributed (120 degree spacing) about the main cylinder 301 . Unlike the freely mounted roller 121 of Figure 1 , in this automated example the support rollers 321 a to 321 e are each driven and are configured to rotate at a speed which it matched to that of the outer surface due to the rotation of the main cylinder 301 .

Although not shown in Figure 4 a number of optical sensors are distributed about the apparatus so as to accurately monitor the positions of the front and rear edges of the sheet stack 325. For example one such sensor may be mounted to the elongate sheet clamp 305 so as to monitor for the presence of the leading edge of the sheet stack as it passes into the clamping device 304. Other sensors may be placed upon the retractable support members 321 a-e since each of these is arranged so as to be retracted when not in contact with the sheet stack so as to allow passage of the retaining device 304 as it orbits the main cylinder 301 . The optical sensors provide feedback to an automated control system 340 which operates the cylinder motor and drive train for the main cylinder 301 . An output table 335 is positioned symmetrically (about the same mirror plane as mentioned above) with respect to the loading table 310 and the main cylinder axis 302, therefore on an "output side" of the apparatus. Each of the loading table 310 and output table 335 is provided with a belt conveyor 336 on its upper surface and upon which the sheet stack is positioned when in use. These belt conveyors, under the control of automated control system 340 allow the automated drive of the sheet stack 325 across the surfaces of the tables 310,335. Suitable driven rollers may be used in a similar manner to provide this function. When in use the sheet stack is positioned and correctly aligned upon the loading table 310 by either a manual operator or an automated stack delivery system. The automated control system 340 is alerted to the presence of the sheet stack, either by the manual operator pressing a button, or an automated control signal. The automated control system then operates an analogous method to that shown in Figure 5 as now described.

At step 501 the automated control system 340 operates the belt conveyor 336 of the apparatus 300 so as to move the sheet stack towards the retaining device 304. In this case the support roller 321 a may be positioned so that its upper surface acts to guide the leading edge of the sheet stack to the profiled edge of the elongate sheet clamp. The sheet stack 325 is driven into the retaining device 304 and its correct loading is detected by an optical sensor which causes the automated control system 340 to halt the belt conveyor 336 of the loading table 310.

The retaining device 304 is then operated by the automated control system 340 at step 502 to clamp the sheet stack 325 to the outer surface 303 of the main cylinder 301 . The support roller 321 a is then driven towards the main cylinder 301 so as to urge the sheet stack against the outer surface 303 at step 503. At step 504 the automated control system 340 operates the main cylinder 301 which causes clockwise (in the Figure 4 view) rotation of the main cylinder 301 . Notably the automated control system ensures that the support roller 321 e is in a retracted position during the start of the rotation of the main cylinder 301 so as to allow passage of the retaining device 304. Once the retaining device 304 has passed, the automated control system 340 operates the support roller 321 e to engage with the surface of the sheet stack 325 and press it against the outer surface 303 of the main cylinder 301 . The rotation may be halted during this engagement operation, although with careful control this can be achieved during the continued rotation of the main cylinder 301 . As the rotation of the main cylinder 301 continues, the retaining device 304 approaches the position of the next support roller 321 b. Again, the automated control system 340 ensures that this is retracted as the retaining device 304 approaches and passes the support roller 321 b. It should be noted that the rotational position of the main cylinder 301 and therefore the retaining device 304 is monitored not only by the optical sensors but also by the use of an encoder fitted to the main cylinder.

Once the retaining device 304 has safely passed the location of the support roller 321 b, the automated control system 340 operates so as to move the support roller to engage with the sheet stack 325 in a similar manner to support roller 321 e. Similar functionality is provided for the two further support rollers 321 c and 321 d. This means that, as the sheet stack 325 is entrained about the outer surface 303 of the main cylinder 301 , either one, two or three support rollers are at any time engaged with the surface of the sheet stack 325 so as to press it against the curved surface 303. Note that rollers 321 a-e would need to be monitored/interconnected on their drive as any difference in speed could result in stretching/rucking of the substrate sheet.

The rotation of the main cylinder 301 continues so as to reach step 505 of the method of Figure 5. Here the retaining device 304 begins to approach the support roller 321 a. With a suitably designed radius of the main cylinder 301 in comparison with the length of the sheets, the rear edge of the sheet stack 325 passes through the nip between the support roller 321 a and the outer surface 303 prior to the approach of the retaining device 304. Thus, at step 505 the automated control system 340 retracts the support roller 321 a to a position where it may allow passage of the retaining device 304. The retaining device 304 is continued to be driven to its lowest position (the initial loading position) at step 506. Once in the loading position once more, at step 507 the main cylinder 301 rotation is ceased and the retaining device 504 is operated to release the sheet stack 335.

At step 508 in Figure 5 which, together with step 509, is an additional step in comparison with the first example, thereafter each of the support rollers 321 a,e is moved to a position where their upper surfaces are slightly above the plane defined by the surfaces of the belt conveyors 336. Once in this position the roller 321 a is in contact with the lower surface of the sheet stack 335. The automated control system 340 then retracts rollers 321 b, 321 c and 321 d to allow the rearward part of the sheet stack 325 to move freely with respect to the outer surface 303. The automated control system 340 then operates the drive of each of the support rollers 321 a and 321 e. The operation of roller 321 a drives sheet stack 335 forwards, through the gap between the elongate sheet clamp 305 and the main cylinder 301 . The front edge of the sheet stack 325 passes into engagement with the driven support roller 321 e and the stack is driven forward onto the belt conveyor 336 of the output table 335. It should be noted here that the action of gravity assists in driving the sheet stack 325 into engagement with the support rollers 321 a, 321 e. If required due to the particular application, substrate type, sheet size or stack size in question, additional rollers and guides may be provided in a circumferential arrangement, at least upon the "loading" half of the main cylinder 302, so as to assist the driving of the sheet stack 325 out of the apparatus in step 508.

At step 509, once the leading edge of the sheet stack 325 is resting on the belt conveyor 336 of the output table, the sheet stack is driven to an output position on the output table from which it may then be removed as part of a further manual or mechanical automated process. Such processes may be similar to those discussed in association with Figure 6. A further approach would be to use the apparatus of the first example and modify the infeed/outfeed tables to incorporate lateral pushers to load and remove the sheets.