The present invention is directed towards a security sheet comprising a plastic substrate and a reinforcement layer embedded within it. The present invention is further directed to a security document made from such a security sheet and a method of manufacturing such a security sheet.

Security documents commonly comprise one or more security sheets on which information is provided. Exemplary security documents include cards, such as identity cards and driving licences, and booklets, such as passports, passbooks, identification documents, certificates, licences, cheque books and the like. The security sheet may be formed from a sheet comprising a plastic, which is typically polycarbonate. Plastic sheets are more durable than fibrous substrate security sheets and are resistant to delamination by a counterfeiter. During manufacture a number of thin plastic layers are laid over one another and fused together, thereby forming a thicker plastic sheet.

The security sheet usually contains personal data, which may in the form of laser markings or the like and located within the thickness of the security sheet. A plastic security sheet may also comprise various security features, such as UV responsive arrangements, optically variable features, windowed or transparent features, laser-perforations, laser markings and tactile features.

Counterfeiters are known to counterfeit such security sheets by changing the personal data whilst maintaining the other security features. As the personal data is usually located beneath the surfaces of the security sheet, the counterfeiter will often try to abrade the material from one of the surfaces to reach the personal data. Counterfeiters typically abrade the surface underneath the personal data as any adaption of the top surface would be more visible to a document inspector. After changing the personal data the counterfeiter may add further plastic over the abraded area in an attempt to hide the counterfeit.

An object of the present invention is to provide a security sheet that is adapted to resist counterfeiting in this manner. A further object is to provide an improved method of manufacture such a security document.

The present invention therefore provides a security sheet for displaying personal data comprising a plastic substrate and a reinforcement layer embedded within the plastic substrate, the reinforcement layer being formed from a material which is different from and harder than that from which the plastic substrate is formed, wherein the reinforcement layer is permeable such that plastic substrate is fused through the reinforcement layer.

The reinforcement layer may significantly increase the difficulty of abrading the plastic substrate and thereby deter counterfeiters. Furthermore, an attempted counterfeit may become more visible as a counterfeiter may have to attempt to replace the

reinforcement layer when covering the abraded area in order to hide the counterfeit.

The term "harder than" refers to the hardness of the reinforcement layer and plastic substrate. Hardness is the measure of a materials resistance to deformation by surface indentation or by abrasion. Hardness can be measured using any of the well-known tests, such as on the Rockwell scale (e.g. ASTM Standard E 18, ISO 6508-1 or ISO 2039-2), the Brinell scale (e.g. ASTM Standard E 10 or ISO 6506-1), the Knoop scale and/or the Vickers scale (e.g. ASTM Standard E92 and E 384 or ISO 6507-1). Therefore, the term the material of the reinforcement layer may be harder than the material of the plastic substrate by virtue of being harder when measured on the Rockwell, Brinell, Knoop and/or Vickers scale(s).

The security sheet may comprise a plurality of reinforcement layers. The

reinforcement layer preferably has a higher softening point than the plastic substrate. In a preferred embodiment the reinforcement layer comprises a mesh. The mesh may comprise a plurality of apertures.

The present invention further provides a plurality of security documents, each security document comprising the aforementioned security sheet, each security document comprising different personal data.

The present invention further provides a method of manufacturing a security sheet comprising the steps of: feeding, into a laminator, a plurality of plastic layers and a reinforcement layer located between two of the plurality of plastic layers; and applying heat and pressure to the plurality of plastic layers in the laminator to form a plastic substrate, wherein the reinforcement layer is formed from a material which is different from and harder than that from which the plastic substrate is formed; and wherein the reinforcement layer is permeable such that, during the applying step, the plastic of the plurality of plastic layers flows through the reinforcement layer such that the plastic substrate is fused through the reinforcement layer. By way of example only, embodiments of a security document, a security sheet and methods of manufacture in accordance with the present invention are now described with reference to, and as shown in, the accompanying drawings, in which:

Figure 1 is a plan view of a passport, in an open configuration, comprising a security sheet according to the present invention;

Figure 2 is a cross-sectional side elevation of the security sheet of Figure 1 through section A-A;

Figure 3 is a cross-sectional side elevation of the security sheet of Figure 1 through section B-B;

Figure 4 is a perspective view of a partially cutaway portion of the security sheet of

Figure 1 illustrating a reinforcement layer embedded within it;

Figure 5 is a cross-sectional side elevation of an apparatus for use in a method of manufacturing the security sheet of the passport of Figure 1 ; and

Figure 6 is a cross-sectional side elevation of a plurality of plastic layers prior to being laminated into a plastic substrate by the apparatus of Figure 5.

Figures 1 to 4 illustrate a security document 10 comprising a security sheet 11 , in this case a data page, attached along a fold line 12 by a hinge or stitch arrangement to a plurality of visa pages 13 and a cover (not shown). The plurality of visa pages 13 are typically made from a fibrous substrate 14, such as paper, and may include a number of security features, such as security fibres and watermarks.

The security sheet 11 comprises a plastic substrate 15 formed from a plurality of layers which are fused together into a substantially non-laminar or unitary structure. The plastic from which the plastic substrate 15 is formed may be a thermoplastic polymer such as polycarbonate, polyester, polyethylene, polypropylene or polyvinyl chloride.

Polycarbonate is particularly suitable due to its high durability, its ease of manufacture and the ease with which security features can be incorporated within it. The plastic substrate 15 has a first outer surface 16 and a second outer surface 17. Each of the first and second outer surfaces 16, 17 is preferably substantially flat and planar.

The security sheet 11 may be substantially rigid or at least semi-rigid, this preferably being a result of the thickness of the plastic substrate 15. The thickness of the plastic substrate 15, which is the distance between the first and second outer surfaces 16, 17, is preferably at least approximately 150 μηι and more preferably at least approximately 300 μηι. In particular, the plastic substrate 15 may be between approximately 300 μηι and 1000 μηι thick and, for example, may be approximately 300 μηι thick or approximately 800 μηι thick.

The plastic substrate 15 preferably comprises a substantially opaque region 18 within its thickness and separated from the first and second outer surfaces 16, 17 by first and second substantially transparent regions 19, 20. As illustrated in Figure 3, the opaque region 18 may at least partially border at least one third substantially transparent region 21. The first, second and third transparent regions 19, 20, 21 form at least one window 22 through the plastic substrate 15. In the illustrated embodiment a single, square window 22 extends through the thickness of the plastic substrate 15. The window 22 may,

alternatively, be of another shape, such as a pattern, indicia, symbol, logo or the like. The window 22 is substantially transparent such that light can pass through it and objects can be seen through it. The window 22 may be clear or coloured. The security sheet 11 further comprises at least one security element 23 located in and/or on the plastic substrate 15. The at least one security element 23 may, for example, comprise laser markings, printed ink, holograms, UV responsive features, optically variable features, windowed or transparent features, antenna, electronic chips, laser-perforations and the like. The at least one security element 23 may be visible when viewed in reflected light by virtue of being located in the first, second and/or third transparent region 19, 20, 21. Alternatively the at least one security element 23 may be covert and located in the opaque region 18 such that it is not visible when viewed in reflected light.

A plurality of security elements 23 may form personal data 24 identifying the holder of the security document 10. As illustrated in Figure 2, the personal data 24 is preferably located within the plastic substrate 15 and is separated from the first and/or second outer surface 16, 17. The personal data 24 is preferably located in the first transparent region 19 between the opaque region 18 and the first outer surface 16 and preferably comprises laser marking or printed ink.

Such personal data 24 is known as "variable data" or "biographical data" and, typically, no two identity documents 10 issued by an issuing authority contain the same personal data 24. The Seventh Edition (2015) of Document 9303 ("Machine Readable Travel Documents") issued by the International Civil Aviation Organization (ICAO) describes such biographical data and its contents are incorporated herein by reference. The personal data 24 of the illustrated embodiment includes an image 25, text 26, comprising a plurality of indicia, providing the holder's name, nationality and date of birth and a machine readable zone 27 containing machine readable data.

The security sheet 11 further comprises a reinforcement layer 28, such as a sheet, embedded within the plastic substrate 15. The reinforcement layer 28 is located within the opaque region 18 such that it is not visible when viewed in reflected light incident upon the first or second outer surfaces 16, 17. As a result, the reinforcement layer 28 is separated from the first outer surface 16 and the plurality of security elements 23 forming the personal data 24 is located between the reinforcement layer 28 and first outer surface 16.

The reinforcement layer 28 is selected and positioned to increase the difficulty for a counterfeiter to reach the personal data 24 by abrading through the plastic substrate 15 from the second outer surface 17. In particular, the material of the reinforcement layer 28 is such that it is substantially harder, and thereby more resistant to abrasion, than the plastic substrate 15.

The reinforcement layer 28 also provides a distinct boundary from the plastic substrate 15 to improve the resistance to abrasion. Therefore, the reinforcement layer 28 comprises a different material to the plastic substrate 15 and is preferably not plastic. The reinforcement layer 28 preferably comprises a hard and abrasion resistant material, such as a metal. Suitable materials include at least one of bronze, phosphor bronze, aluminium bronze, aluminium copper, copper alloys, steel, stainless steel, PVC coated steel and tin. Alternatively, the reinforcement layer 28 may comprise fibre reinforced polymers, which may be reinforced with fibres including, for example, at least one of glass, carbon, aramid and basalt.

The reinforcement layer 28 may be substantially permeable or porous such that, during manufacture, plastic substrate 15 can flow and be fused together through the reinforcement layer 28. As a result, the reinforcement layer 28 is fully embedded and integrated within the plastic substrate 15 such that it does not form a fully laminar structure. The plastic substrate 15 is thereby more resistant to delamination. In particular, the reinforcement layer 28 may comprise a plurality of apertures extending through it.

As illustrated in Figure 4, the reinforcement layer 28 therefore preferably comprises a mesh 29. The mesh 29 comprises a plurality of apertures, each aperture having an area of from approximately 0.1 mm ² to approximately 10 mm ² and more preferably to approximately 5 mm ² . The mesh 29 may have a thickness in the range of from

approximately 30 μηι to approximately 300 μηι. The mesh 29 may be a wire mesh and woven or non-woven, depending upon the materials used. The mesh 29 may comprise a perforated sheet or woven wired mesh, formed of metal or plastic, having apertures of any suitable shape, such as round, square, rectangular, slotted, hexagonal or the like. The mesh 29 may alternatively comprise expanded metal, which may be flattened or the like. The mesh 29 may alternatively comprise extruded plastic or moulded plastic.

In the illustrated embodiment the reinforcement layer 28 does not extend into the window 22 such that its presence is not immediately visible to a counterfeiter. For example, the mesh 29 may comprise an aperture within it which is aligned with the rest of the window 22 during manufacture. However, in other embodiments no window 22 may be present, the reinforcement layer 28 may not extend to the window 22 or the reinforcement layer 28 may be visible in the window 22.

The reinforcement layer 28 also extends to all edges 30 of the security sheet 1 1 , but in other embodiments it may be separated from at least one of or all of the edges 30. For example, the reinforcement layer 28 may extend only underneath some or all of the personal data 24. Alternatively, the security sheet 1 1 may comprise a plurality of reinforcement layer 28, each located under one or more items of personal data 24. The plurality of reinforcement layers 28 may thereby provide localised reinforcement and abrasion resistance.

In order to counterfeit such a security document 10 a counterfeiter would attempt to abrade the plastic substrate 15 between the second outer surface 17 and the personal data 14. However, in doing so they would need to abrade through the reinforcement layer 28 and, given its hardness, this would take a considerable amount of time. Furthermore, abrading the reinforcement layer 28 may require complex and/or heavy duty tools that make it more likely for a mistake by the counterfeiter to irreparably damage the rest of the plastic substrate 15 such that it must be discarded. If the counterfeiter does reach the personal data 14 and counterfeit it, the counterfeiter may also need to replace the reinforcement layer 28, which may be difficult to achieve (particularly if it is a mesh 29).

The security sheet 11 and visa pages 13 are usually formed separately before being attached along the fold line 12. The security sheet 11 is generally manufactured by forming an insert 42, forming a plurality of plastic layers 32 (shown in Figure 5) including the insert 42 and reinforcement layer 28 therein and laminating the plurality of plastic layers 32 together in a laminator 33 (shown in Figure 6) to form the plastic substrate 20.

Figure 5 illustrates a suitable structure for the plurality of plastic layers 32 prior to entering the laminator 33 and after being positioned to overlie one another. The plurality of plastic layers 32 comprises first and second opaque layers 34, 35, which are typically white and/or opaque, and an inlay 36 therebetween. Substantially transparent first and second overlays 37, 38 are located at the outer most sides of the plurality of plastic layers 32 and form the first and second outer surfaces 16, 17 of the plastic substrate 15. First and second intermediate layers 39, 40 for holding at least one security element 23 may be located between the first opaque layer 34 and the first overlay 37. In particular, the first

intermediate layer 39 may be substantially opaque and located adjacent to the first opaque layer 34. The second intermediate layer 40 is located between the first overlay 37 and the first intermediate layer 39 and is substantially transparent. In other embodiments any suitable number of intermediate layers 39, 40, on either side of the first and second opaque layers 34, 35, may be used in order to provide different security features.

The at least one security element 23 may be applied to a surface of one of the plurality of plastic layers 32 (preferably the first opaque layer 34 or one of the first and second intermediate layers 39, 40) prior to entering the laminator 33 and before being positioned to overlie one another. In particular, if the at least one security element 23 comprises printed ink, it may be applied by inkjet printing, dye sublimation, dye diffusion thermal transfer (D2T2) processes and the like. As a result, the printed ink forming the at least one security element 23 is embedded in the final plastic substrate 15.

A strip of substantially transparent plastic may initially be cut by a punching tool to form a plurality of inserts 42 before or during the arrangement of the plurality of plastic layers 32. The shape of the perimeter of each insert 42 forms the shape of the perimeter of each window 22. Each insert 42 is located in an aperture 43 through the first and second opaque layers 34, 35, the inlay 36 and the first intermediate layer 39. The opposing outer surfaces of each insert 42 are overlaid by the second overlay 38 and second intermediate layer 40. Alternatively, each aperture 43 may be formed in, and each insert 42 located in, only one or two of the first opaque layer 34, the second opaque layer 35, the inlay 36 and/or the first intermediate layer 39. Preferably the aperture 43 and insert 42 are formed and brought together in line, as is disclosed in WO-A-2015/10401 1. In particular, a single punch tool may be operated to form an aperture 43, cut or punch an insert 42 from the strip and place the insert 42 into the correspondingly shaped aperture 43.

Each of the plurality of plastic layers 32 may be between approximately 0.05 mm thick and approximately 3 mm thick and is comprised of the plastic forming the plastic substrate 15, such as polycarbonate, although they may be formed of different plastics provided that they are able to fuse together. Each insert 42 may have a thickness of between approximately 0.1 mm and approximately 0.4 mm and may be the same plastic from which the plurality of plastic layers 32 are formed, such as polycarbonate or the like.

As illustrated in Figure 5 the reinforcement layer 28 may be located between the inlay 36 and first opaque layer 34 and may define an aperture through which the insert 42 can be located. Alternatively, reinforcement layer 28 may be located between any of the plurality of plastic layers 32 and may at least partially overlie the insert 42.

Figure 6 illustrates an embodiment of a laminator 33 suitable for manufacturing the security sheet 1 1 from the plurality of plastic layers 32. The laminator 33 is similar to the devices disclosed in US-B-6669813 and US-A-2011/0226408, the contents of which are incorporated herein by reference. A plurality of feeders 31 for feeding the plurality of plastic layers 32 laid over one another into the laminator 33. The laminator 33 fuses the plurality of plastic layers 32 together by the application of heat and pressure to form the plastic substrate 1 1.

The laminator 33 comprises first and second continuous belts 45, 46 which rotate in opposite directions and comprise first and second support surfaces 47, 50 respectively. At least one of the first and second continuous belts 45, 46 is intermittently driven to draw the plurality of plastic layers 32 in a machine direction into a laminating region 53 of the laminator 33 through a nip 58 between first and second inlet drums 48, 51. Initially a region of the plurality of plastic layers 32 is moved into between opposing heating devices 54, 55. The heating devices 54, 55 move towards the first and second support surfaces 47, 50 to heat and apply pressure to the region of plurality of plastic layers 32 to form the plastic substrate 15. After a set period of time, typically less than a minute, the heating devices 54, 55 move away from the first and second support surfaces 47, 50 and the first and/or second continuous belt 45, 46 is driven to move the region to between opposing cooling devices 56, 57. The cooling devices 56, 57 move towards the first and second support surfaces 47, 50 and cool and apply pressure to the plastic substrate 15 in order to maintain its structure. This heating, cooling and pressure application process is repeated along the plurality of alternating heating and cooling devices 54, 55, 56, 57 until the fully formed plastic substrate 15 exits the laminator 33. The reinforcement layer 28 may be incorporated into the plurality of plastic layers 32 either before or during entry into the laminator 33. For example, the reinforcement layer 28 may be positioned and/or adhered on one of the plurality of plastic layers 32. The reinforcement layer 28 may be fed in the machine direction into the plurality of plastic layers 32 at the nip 58 as illustrated in Figure 6. However, the reinforcement layer 28 may also be located in the plurality of plastic layers 32 by being fed across the plane of the plurality of plastic layers 32 in a direction that is perpendicular to the machine direction. This feed direction is particularly suitable where the reinforcement layer 28 is only being provided in localised areas. During the heating process each of the plurality of plastic layers 32 and insert 42 become at least softened or semi-molten (i.e. a liquid of relatively high viscosity) so that the plastic flows and mixes together across the interfaces between them. The first overlay 37 and second intermediate layer 40 form the first transparent region 19. The first and second opaque layers 34, 35, the inlay 36 and the first intermediate layer 39 form the opaque region 18. The second overlay 38 forms the second transparent region 20. The insert 42 forms the third transparent regions 21 and window 22.

In order to achieve such fusing the heating devices 54, 55 may be suitably controlled to raise the temperature and pressure applied to the plurality of plastic layers 32 to reach the softening point of the plastic. A temperature at which deformation and therefore fusion is possible at a certain pressure can be ascertained using the Vicat softening point test using the ASTM D 1525 and ISO 306 standards. The Vicat softening point may be the temperature at which a specimen is penetrated to a depth of 1 mm by a flat-ended needle with a 1 mm ² circular or square cross-section. In a particular example, the Vicat softening point for polycarbonate can be determined using a heating rate of

50°C/hr and a load of 50N. In a further example for polycarbonate, the heating devices 54, 55 may apply a temperature of approximately 180 °C at approximately 8 MPa to the plurality of plastic layers 32 and the cooling devices 56, 57 may apply a temperature of approximately 20 °C to 30 °C and a pressure of 10 MPa to the plurality of plastic layers 32. In yet a further example for polycarbonate, the heating devices 54, 55 may apply a temperature of approximately 180 °C at approximately 1.6 N/mm ² to the plurality of plastic layers 32 and the cooling devices 56, 57 may apply a temperature of approximately 20 °C to 30 °C at a pressure of 3.2 N/mm ² to the plurality of plastic layers 32. This latter example is particularly appropriate where the region of the plurality of plastic layers 32 between the heating or cooling devices 54, 55, 56, 57 has a surface area of 130 mm by 190 mm.

During lamination, the plurality of plastic layers 32 and reinforcement layer 28 preferably remain unfused from one another with discrete interfaces between them. This may be achieved by virtue of the material choices of the plurality of plastic layers 32 and reinforcement layer 28 and by the control of heating in the laminator 33. For example, the reinforcement layer 28 may have a higher softening point than that of the plurality of plastic layers 32 and resulting plastic substrate 15. Therefore, the laminator 33 is controlled such that during lamination the softening point of the reinforcement layer 28 is not reached and it remains a solid whilst the plastic of the plurality of plastic layers 32 flows. The plastic of the plurality of plastic layers 32 may flow through the reinforcement layer 28 by virtue of its porosity and thereby solidify and fuse within the reinforcement layer 28. This is particularly the case where the reinforcement layer 28 comprises a mesh 28 as the plastic forms in the apertures of the mesh 29. The reinforcement layer 28 therefore forms an integral part of the security sheet 1 1 , as it cannot be delaminated from the plastic substrate 15, but forms a distinct reinforcing structure.

After the plastic substrate 20 has exited the laminator 33 it may be subjected to further processing, such as by being cut into a plurality of security sheets 1 1. Each of the plurality of security sheets 11 is bound along the fold line 12, for example by stitching, with the visa pages 13 and cover to form the passport or other security document 10.

The at least one security element 23 may subsequently be applied to the security sheet 1 1. In particular, the personal data 24 relating to the holder of the security document 10 may be applied by laser marking within the plastic substrate 15. The at least one security element 23 may also or alternatively be applied to the first and/or second outer surface 16, 17.

Various alternatives to those described above also fall within the scope of the present invention. The security document 10 may be of any suitable type having the security sheet 1 1 , including cards, such as identity cards, driving licences and the like, and booklets, such as passports, passbooks, identification documents, certificates, licences, cheque books and the like.

Graphical information, colours and/or patterns may be printed on the outer surfaces of the any of the plurality of plastic layers 32 prior to lamination and particularly on the first and second opaque layers 34, 35. Electronic chips and antenna or the like may also be located within plurality of plastic layers 32, particularly the inlay 36 or first and second opaque layers 34, 35. In the embodiment of Figures 1 to 4 the at least one security element 23, in the form of the personal data 24, is applied at a predetermined depth within the plastic substrate 15. The predetermined depth may not correspond to the thicknesses of each of the plurality of plastic layers 32, such that the at least one security element 23 is located at a depth that corresponds to a position within the thickness of one of the plurality of plastic layers 32. However, at least one security element 23 may also be added during manufacture to the surfaces of the plurality of plastic layers 32, for example by printing or the like. For example, fixed data (e.g. "Name", "Nationality" and "Date of Birth" in Figure 1) may be applied in this manner. The variable data (e.g. "A B C Smith, "British" and "10/02/1980) may be applied by an issuing authority after the formation of the security sheet 1 1 via laser marking or the like.