Inclusions for use in security papers, method of manufacturing them and authenticatig method

Abstract

An inclusion (2) for incorporation into a security paper substrate (92) is disclosed. The inclusion (2) comprises a substrate (4); a first luminescent region (6) on a first and / or second side of the substrate (4), the first luminescent region (6) emitting visible light of (i) a first colour when viewed under ultraviolet light of a first wavelength and (ii) a second, different, colour when viewed under ultraviolet light of a second, different, wavelength. The substrate (4) also comprises a second luminescent region (8) on the first and / or second side of the substrate, the second luminescent region (8) emitting visible light of a different colour to the first luminescent region (6) when viewed under ultraviolet light of the first wavelength and / or emitting visible light of a different colour to the first luminescent region (6) when viewed under ultraviolet light of the second wavelength. A security paper (90) and a security document comprising such an inclusion (2), and a method (150) of manufacturing such an inclusion (2) are also disclosed.

Description

Field of the Disclosure

[0001] The present disclosure concerns inclusions (e.g. fibres and / or planchettes) that can be incorporated into pulp used to produce a security paper. More particularly, but not exclusively, this disclosure concerns inclusion for incorporation into a security paper substrate. The disclosure also concerns a method of authenticating a security document comprising such inclusions and a method of manufacturing such an inclusion.Background of the Disclosure

[0002] Security documents, for example banknotes, passports, lottery tickets, tax stamps, some certificates and other items of potentially high value, are targets for counterfeiters, who seek to produce counterfeit copies of the security documents and thus illegally benefit from the high value of the genuine items. Security documents typically include various security devices that are difficult for a counterfeiter to simulate.

[0003] A security device may take the form of an inclusion (or particulate), for example a fibre or planchette, that is mixed into the pulp used to produce a security paper. An example of such an inclusion is a security fibre (hereafter a fibre). EP 125 546 458 (D W Spinks (Embossing) Ltd) discusses examples of such fibres having coloured fluorescent stripes or regions.

[0004] In order to be effective, a security device must exhibit characteristics that are easily identified by a user seeking to verify the authenticity of the security document concerned whilst increasing the burden for a potential counterfeiter. To that end, security documents may include luminescent (fluorescent or phosphorescent) security features. Typically, the luminescent materials used in security documents emit visible light when illuminated with ultraviolet light. However, the colour of light emitted may depend on the wavelength of ultraviolet used. This can make the verification of such documents problematic, as only small changes in the wavelength of the ultraviolet light can lead to very different coloured light being emitted by the luminescent materials. As a consequence, producers of security devices will typically use luminescent materials that emit light of the same colour over a substantial region of the ultraviolet spectrum, for example over the whole of the near ultraviolet region. In contrast, the present disclosure seeks to exploit this behaviour to provide an improved security device.

[0005] The burden on counterfeiters is also increased when legitimate producers of security documents have a variety of security devices and effects from which to choose. Consequently, it is advantageous to provide new security devices and methods of verification per se.

[0006] Alternatively or additionally, the present disclosure seeks to provide an improved security devices for security documents and / or methods of verification of security documents.Summary of the Disclosure

[0007] The present disclosure provides according to a first aspect an inclusion for incorporation into a security paper substrate, the inclusion comprising: a substrate; a first luminescent region on a first and / or second side of the substrate, the first luminescent region emitting visible light of (i) a first colour when viewed under ultraviolet light of a first wavelength and (ii) a second, different, colour when viewed under ultraviolet light of a second, different, wavelength; and a second luminescent region on the first and / or second side of the substrate, the second luminescent region emitting visible light of a different colour to the first luminescent region when viewed under ultraviolet light of the first wavelength and / or emitting visible light of a different colour to the first luminescent region when viewed under ultraviolet light of the second wavelength.

[0008] In a further aspect, there is provided a security paper comprising a security paper substrate having a plurality of inclusions according to the first or any other aspect.

[0009] In a further aspect, there is provided a method of authenticating a security document, the security document comprising a security paper substrate and a plurality of inclusions incorporated into the security paper substrate, each inclusion comprising: a substrate; and a first luminescent region on a first and / or second side of the substrate; the method comprising: illuminating the document with ultraviolet light of a first wavelength thereby causing the first luminescent region to emit light of a first colour; illuminating the document with ultraviolet light of a second wavelength thereby causing the first luminescent region to emit light of a second, different, colour; and authenticating the security document in dependence on the change in the appearance of the inclusions under ultraviolet light of the first and second wavelengths.

[0010] In a further aspect, there is provided a method of manufacturing an inclusion for use in a security paper, the method comprising: applying a first luminescent ink to a sheet of paper to provide a plurality of first luminescent regions, wherein the first luminescent ink emits visible light of (i) a first colour when viewed under ultraviolet light of a first wavelength and (ii) a second, different, colour when viewed under ultraviolet light of a second, different, wavelength; and applying a second luminescent ink to the sheet of paper to provide a plurality of second luminescent regions, wherein the second luminescent ink emits visible light of a different colour to the first luminescent ink when viewed under ultraviolet light of the first wavelength and / or emits visible light of a different colour to the first luminescent ink when viewed under ultraviolet light of the second wavelength; and then cutting the substrate sheet to produce a plurality of inclusions, each inclusion comprising at least one first luminescent region and at least one second luminescent region.

[0011] It will of course be appreciated that features described in relation to one aspect of the present disclosure may be incorporated into other aspects of the present disclosure. For example, the method of the disclosure may incorporate any of the features described with reference to the apparatus of the disclosure and vice versa.Description of the Drawings

[0012] Embodiments of the present disclosure will now be described by way of example only with reference to the accompanying schematic drawings of which: Fig. 1 (a) and (b) show a plan view of a fibre according to a first example embodiment under (a) ultraviolet light of a first wavelength and (b) ultraviolet light of a second, different, wavelength; Fig. 2 (a) and (b) show a plan view of a fibre according to a second example embodiment under (a) ultraviolet light of a first wavelength and (b) ultraviolet light of a second, different, wavelength; Fig. 3 (a) and (b) show a plan view of a fibre according to a third example embodiment under (a) ultraviolet light of a first wavelength and (b) ultraviolet light of a second, different, wavelength; Fig. 4 shows a plan view of a planchette according to a fourth example embodiment; Fig. 5 shows a plan view of a sheet of security paper according to a fifth example embodiment; Fig. 6 shows a flow chart of an example method of authenticating a security document, in accordance with the present disclosure; and Fig. 7 shows a flow chart of an example method of manufacturing a security document comprising a plurality of inclusions, in accordance with the present disclosure. Detailed Description

[0013] In a first aspect of the disclosure there is provided an inclusion for incorporation into a security paper substrate, the inclusion comprising: a substrate; a first luminescent region on a first and / or second side of the substrate, and / or a second luminescent region on the first and / or second side of the substrate. It may be that the first luminescent region emits visible light of a first colour when the first luminescent region is viewed under ultraviolet light of a first wavelength. It may be that the first luminescent region emits visible light of a second, different, colour when the first luminescent region is viewed under ultraviolet light of a second, different, wavelength. It may be that the second luminescent region emits visible light of a different colour to the first luminescent region when the second luminescent region is viewed under ultraviolet light of the first wavelength. It may be that the second luminescent region emits visible light of a different colour to the first luminescent region when the second luminescent region is viewed under ultraviolet light of the second wavelength.

[0014] Thus, inclusions in accordance with the first aspect may provide a striking visual effect when illuminated using ultraviolet light of different wavelengths.

[0015] For brevity, the phrase 'under the nth wavelength' is used herein as shorthand for 'when viewed under ultraviolet light of the nth wavelength', where nth wavelength may refer to the first, second, or any further wavelength.

[0016] It may be that the second luminescent region emits light of the first colour when viewed under ultraviolet light of the first wavelength. Thus, it may be that the first and second luminescent regions emit light of the same colour under the first wavelength. This may allow for an inclusion having a region that appears as a single colour under one ultraviolet wavelength, but is multicoloured under another ultraviolet wavelength. This may provide a striking visual effect. Additionally, or alternatively, this may avoid the need for a user to detect a specific colour in order to authenticate a document, instead a user can look for a single-colour region becoming a patterned region with a change of wavelength. Thus, inclusions in accordance with the present disclosure may allow a more robust and / or easier authentication.

[0017] It may be that all the luminescent regions of an inclusion emit visible light of the first colour under the first wavelength.

[0018] It may be that the second luminescent region emits light of the first colour when viewed under ultraviolet light of the second wavelength. For example, it may be that the second luminescent regions emit light of the same colour under the first wavelength and the second wavelength. This may increase the burden on counterfeiters by providing a difficult to reproduce effect.

[0019] It may be that the second luminescent region emits light of the second colour when viewed under ultraviolet light of the first wavelength. For example, it may be that second luminescent region emits light of the second colour under the first wavelength and emits light of the first colour under the second wavelength. This may provide a striking visual effect in which the stripes of the inclusion appear to switch places with a change in wavelength.

[0020] It may be that the second luminescent region emits light of a third, different, colour when viewed under ultraviolet light of the second wavelength. For example, it may be that the second luminescent region emits light of the first colour under the first wavelength and the third colour under the second wavelength. This may provide for a striking visual effect in which a single-colour region changes to a patterned region of different colours with a change in wavelength.

[0021] It may be that the second luminescent region emits light of a fourth, different, colour, when viewed under ultraviolet light of the first wavelength. For example, it may be that the second luminescent region emits light of the third colour under the second wavelength and the fourth colour under the first wavelength.

[0022] As used herein, ultraviolet light is defined as light having wavelengths of from 10 nm to 400 nm inclusive. It may be that the ultraviolet light is near ultraviolet light. As used herein, near ultraviolet light is defined as light having wavelengths of from 300 nm to 400 nm inclusive. Thus, it may be that the first and second wavelengths are both in the range of from 300 nm to 400 nm inclusive. Thus, the effects described herein may be produced with relatively small changes in wavelength within the ultraviolet spectrum, thereby increasing the burden on counterfeiters. It may be that the difference in wavelengths as between the first and second wavelengths is 50 nm or less. For example, it may be that the difference in wavelengths as between the first and second wavelengths is from 10 nm to 50 nm inclusive. It will be appreciated that the first and second wavelengths are not the same wavelength.

[0023] It may be that the first wavelength is in the range of from 350 nm to 380 nm inclusive, for example from 360 nm to 375 nm inclusive. It may be that the second wavelength is in the range of from 390 nm to 400 nm inclusive, for example from 395 nm to 400 nm inclusive.

[0024] It may be that the inclusion comprises a third luminescent region, a fourth luminescent region and / or one or more further luminescent regions. It may be that each luminescent region emits light of one colour under the first wavelength and light of another colour under the second wavelength. It may be that the third, fourth and / or any further luminescent region emits light of the first colour under the first wavelength. It may be that each luminescent region emits light of a different colour to any other luminescent region under the second wavelength.

[0025] It may be that the inclusion comprises a plurality of first luminescent regions. It may be that the inclusion comprises a plurality of second luminescent regions. It may be that the inclusion comprises a plurality of each of any other type of luminescent regions (e.g. third, fourth, further) if present.

[0026] It may be that the all the luminescent regions of the inclusion are either first luminescent regions or second luminescent regions.

[0027] It may be that the inclusion comprises a repeating pattern of luminescent regions. For example, it may be that the inclusion comprises a repeating pattern of first and second luminescent regions. It may be that each second luminescent region is adjacent, for example immediately adjacent, a first luminescent region. It may be that the first luminescent region and the second luminescent region (and optionally any other luminescent regions, if present) form a continuous luminescent region. It may be that the first, second and any other (if present) luminescent region(s) extend across the majority of, for example the whole of, the surface area of the first and / or second side of the substrate.

[0028] It may be that each luminescent region is a region of the substrate comprising a luminescent ink. The luminescent ink for each region emits visible light in the manner described above for each region. For example, the first luminescent region comprises a first luminescent ink which emits visible light of (i) a first colour when viewed under ultraviolet light of a first wavelength and (ii) a second, different, colour when viewed under ultraviolet light of a second, different, wavelength. Similarly, the second luminescent region comprises a second luminescent ink which emits visible light of a different colour to the first luminescent region when viewed under ultraviolet light of the first wavelength and / or emits visible light of a different colour to the first luminescent region when viewed under ultraviolet light of the second wavelength. The luminescent ink may be applied to the substrate, for example printed on the first and / or second side (or surface) of the substrate. The luminescent ink may bleed through the substrate from one side of the substrate to the other.

[0029] It may be that the substrate of the inclusion (hereafter the substrate) is made of a cellulose material. For example, the substrate may be made from plant based cellulosic material, for example wood pulp or other plant based cellulosic material. The substrate may be transparent. The substrate may be paper. The substrate may be tissue paper. The substrate may be without optical brighteners. The substrate may be paper of a high porosity, high wet strength tissue paper. The tissue paper may have a nominal basis weight of between 12g / m 2< and 45g / m 2< inclusive, for example between 23 g / m 2< and 28 g / m 2< , for example 25 g / m 2< . The tissue paper may have a wet tensile strength of from 4 N / 15mm to 6 N / 15mm inclusive, for example from 4.5 to 5.9 N / 15mm.

[0030] It may be that each inclusion is at least 1 mm in length and / or diameter. It may be that each inclusion is not more than 10 mm in length and / or diameter. In the case that the security device is a fibre, the length of the fibre may be from 4.5 mm to 5.5 mm (inclusive) in length. The fibre may be from 0.25 mm to 0.35 mm (inclusive) in width.

[0031] It may be that the substrate has a first or front face (on the first side). It may be that the substrate has a second or back face, being the opposite face of the substrate to the front face. It may be that the substrate and / or the inclusion is substantially planar. It may be that the substrate has a thickness of 10 to 50 microns, for example 20 to 40 microns.

[0032] It may be that the luminescent region is a fluorescent region. It may be that the luminescent ink is a fluorescent ink.

[0033] It may be that each luminescent region is a stripe, for example extending across the (width of) the substrate. It may be that the luminescent regions form a repeating pattern along the length or diameter of the substrate.

[0034] It may be that each inclusion is a fibre or a planchette. In the case that the inclusion is a fibre, it may be that the substrate is rectangular when viewed in plan. In the case that the inclusion is a planchette, it may be that the substrate is square, circular, triangular, star shaped, or irregularly shaped when viewed in plan.

[0035] It may be that each luminescent region is substantially invisible in visible light. This may increase the burden on counterfeiters and / or provide a striking visual effect. It may be that a luminescent region is substantially invisible in visible light because the colour of the luminescent region in visible light matches the colour of the substrate of the inclusion. It may be that a luminescent region is substantially invisible in visible light because it is substantially colourless and transparent in visible light.

[0036] References to colour and / or visibility above may apply equally to colour and / or visibility in transmission and / or reflection.

[0037] In another aspect of the disclosure, there is provided a security paper comprising a plurality of inclusions as described above.

[0038] Security papers in accordance with the present disclosure are made by mixing slurry paper pulp with the inclusions (e.g. fibre, planchettes) of the present disclosure. The inclusions become an integral part of the web or sheet of paper forming the security paper. For example, it may be that the inclusions of the present disclosure form a hydrogen bond with the cellulose fibres in the paper pulp. Thus, the security paper may comprise a security paper substrate having a plurality of inclusions integrated therein.

[0039] It may be that the substrate of each inclusion has substantially the same visible appearance, for example the same colour under visible light, as the security paper substrate (the rest of the substrate of the security paper of which the inclusions become an integral part). It may be that the security paper substrate has any of the material properties described above in connection with the substrate of the inclusion. For example, the security paper substrate may be made of a cellulose material and / or may be a tissue paper substrate etc. It may be that the security paper substrate and the substrate of each inclusion are the same material.

[0040] It another aspect of the disclosure, there is provided a security document, for example a banknote, passport or other identity document, lottery ticket, tax stamp, or certificate, comprising a security paper as described above. In another aspect of the disclosure, there is provided a method of authenticating a security document, the security document comprising a security paper substrate and a plurality of inclusions incorporated into the security paper substrate. It may be that each inclusion comprises a substrate; and a first luminescent region on a first and / or second side of the substrate. It may be that the method comprises: illuminating the document with ultraviolet light of a first wavelength thereby causing the first luminescent region to emit light of a first colour; illuminating the document with ultraviolet light of a second wavelength thereby causing the first luminescent region to emit light of a second, different, colour; and then authenticating the security document in dependence on the change in the appearance of the inclusions under the ultraviolet light of the first and second wavelengths. It will be appreciated that the method and inclusion of the present aspect may have any of the features described above with reference to the other aspects, and vice versa.

[0041] It may be that each inclusion comprises a second luminescent region on the first and / or second side of the substrate. It may be that illuminating the document with ultraviolet light of the first wavelength causes the second luminescent region to emit light of a different colour to the first luminescent region. It may be that illuminating the document with ultraviolet light of the second wavelength causes the second luminescent region to emit light of a different colour to the first luminescent region.

[0042] It may be that said step of illuminating the document with ultraviolet light of the first wavelength also causes the second luminescent region to emit light of the first colour.

[0043] It may be that said step of illuminating the document with ultraviolet light of the second wavelength also causes the second luminescent region to emit light of the first colour.

[0044] It may be that said step of illuminating the document with ultraviolet light of the second wavelength also causes the second luminescent region to emit light of a third, different, colour.

[0045] It may be that said step of illuminating the document with ultraviolet light of the second wavelength causes the second luminescent region to emit light of the third colour; and said step of illuminating the document with ultraviolet light of the first wavelength causes the second luminescent region to emit light of a fourth, different, colour.

[0046] The method may comprise using a lighting apparatus (a light), for example a lamp or a flashlight, to illuminate the document with ultraviolet light. It may be that the lighting apparatus comprises a first light source that emits light of the first wavelength and a second light source that emits light of the second wavelength. Thus, a single lighting apparatus may be used to authenticate the document. It may be that said steps of illuminating the document with ultraviolet light of the first wavelength and illuminating the document with ultraviolet light of the second wavelength are carried out using a flashlight or a lamp, said flashlight / lamp comprising a first light source that emits light of the first wavelength and a second light source that emits light of the second wavelength. Each light source may be a bulb or a light emitting diode (LED) or some other light source. It may be that the method comprises switching the single lighting apparatus between a first mode in which the first light source emits light but the second light source does not, and a second mode in which the second light source emits light but first light source does not.

[0047] It a further aspect of the disclosure, there is provided a method of manufacturing an inclusion for use in a security paper, the method comprising: applying a first luminescent ink to a sheet of paper to provide a plurality of first luminescent regions, wherein the first luminescent ink emits visible light of (i) a first colour when viewed under ultraviolet light of a first wavelength and (ii) a second, different, colour when viewed under ultraviolet light of a second, different, wavelength; and applying a second luminescent ink to the sheet of paper to provide a plurality of second luminescent regions, wherein the second luminescent ink emits visible light of a different colour to the first luminescent ink when viewed under ultraviolet light of the first wavelength and / or emits visible light of a different colour to the first luminescent ink when viewed under ultraviolet light of the second wavelength; and then cutting the substrate sheet to produce a plurality of inclusions, each inclusion comprising at least one first luminescent region and at least one second luminescent region.

[0048] The method may comprise printing the first luminescent ink on the first and / or second side of the sheet of paper to provide the first luminescent regions. The method may comprise printing the second luminescent ink on the first and / or second side of the sheet of paper to provide the second luminescent regions.

[0049] The method may comprise cutting the substrate sheet to produce an inclusion. It may be that the step of cutting the substrate sheet produces a plurality of inclusions simultaneously, for example with a single cutting motion. Thus, the present methods may be suitable for use in the bulk manufacture of inclusions. Each cutting motion may produce at least 10 inclusions, for example at least 50, for example at least 100 inclusions simultaneously.

[0050] The method may comprise cutting the substrate in a cutting pattern. The cutting pattern may comprise a plurality of instances of a shape, for example a geometric shape, for example squares, rectangles, triangles and / or other shapes arranged side by side and / or end to end. The cutting pattern may be a tessellating pattern (i.e. a pattern with no overlaps and / or gaps) of a shape corresponding to the shape of the inclusions, for example a tessellating pattern of squares, rectangles, triangles and / or other shapes. In the case that the cutting pattern comprises a plurality of rectangles, for example arranged side by side and / or end to end, the step of cutting the substrate may provide a plurality of security fibres. In the case that the cutting pattern comprises a plurality of squares, stars and / or circles, for example arranged side by side and / or end to end, the step of cutting the substrate may provide a plurality of planchettes having a corresponding shape.

[0051] FIG. 1 (a) shows a plan view of a security fibre 2 according to a first example embodiment viewed under ultraviolet light having a first wavelength. The security fibre 2 comprises a substrate 4 having first luminescent regions 6 and second luminescent regions 8 printed thereon. In Fig. 1 the first and second luminescent regions 6,8 are shown as alternating stripes, but it will be appreciated that arrangements of the regions may be used. In some embodiments, the first and second luminescent regions 6, 8, are printed on the same side (or surface) of the substrate. In other embodiments, they are printed on opposite sides, with the ink bleeding through from one side of the substrate to the other. In FIG. 1(a), under light of the first wavelength, the first and second luminescent regions emit light of the same colour (e.g. yellow), as indicated schematically by the use of dots in Fig. 1.

[0052] FIG. 1 (b) shows a plan view of the security fibre 2 viewed under ultraviolet light having a second, different, wavelength. The second luminescent regions 8 emit light of (appear) the same colour in FIG. 1(b) as in FIG. 1 (a), but the appearance of the first luminescent regions has changed, and these now emit light of a second, different colour (e.g. red), as indicated schematically by the hatching in FIG. 1(b). In some embodiments, the ultraviolet light in near ultraviolet light. In the same or yet further embodiments, the first wavelength is in the range of from 365 nm to 370 nm inclusive, and the second wavelength is in the range of from 395 nm to 400 nm inclusive.

[0053] Security fibres in accordance with the present embodiment provide a striking visual effect, whereby under the first ultraviolet wavelength the first and second regions emit light of the same colour and the fibre appears to have a single colour but under the second wavelength, the fibre appears striped. Authentication of the document in which the inclusions are used may also be more reliable, as a decision as to the genuineness of the document can be reached based on observing a change from a single colour fibre to a striped fibre, rather than detecting a specific colour.

[0054] FIG. 2 (a) and (b) show a plan view of a security fibre 2 in accordance with a second example embodiment under ultraviolet light of a first wavelength and a second wavelength, respectively. Only those aspects of the second embodiment which differ with respect to the first are discussed here, and like reference numerals indicate like elements as between the two embodiments. In the FIG. 2 embodiment, the appearance of the second luminescent regions 8 changes as between FIG. 2(a) and FIG. 2(b). Under light of the first wavelength, the second luminescent regions 8 appear the same colour (e.g. yellow) as the first luminescent regions 6. However, the second luminescent regions 8 are a different colour (e.g. green, indicated schematically using diamonds in Fig. 2) under the second wavelength (FIG. 2(b)). The colour of the second luminescent regions 8 under the second wavelength is also different from the colour of the first luminescent regions under the second wavelength.

[0055] Again, security fibres in accordance with the present embodiment provide a striking visual effect, whereby under the first ultraviolet wavelength the first and second regions emit light of the same colour and the fibre appears to have a single colour but under the second wavelength, the fibre appears striped. Verification may also be more reliable as it can depend upon seeing a change from a single colour fibre to a striped fibre, rather than detecting a particular colour. The presence of an additional colour under the second wavelength may increase the burden on counterfeiters.

[0056] FIG. 3 (a) and (b) show a plan view of a security fibre 2 in accordance with a third example embodiment under ultraviolet light of a first wavelength and a second wavelength, respectively. Only those aspects of the third embodiment which differ with respect to the first are discussed here, and like reference numerals indicate like elements as between the two embodiments. In the FIG. 3 embodiment, the first and second luminescent regions 6, 8 emit different coloured light under the first wavelength (e.g. red and purple) - see FIG. 3(a). Under light of the second wavelength, the colour of the first and second luminescent regions 6, 8 changes from their colour under the first wavelength (e.g. to green and yellow) - see FIG. 3(b).

[0057] Security fibres in accordance with the present embodiment provide a striking visual effect, whereby the colour of the stipes changes under different wavelengths of ultraviolet light.

[0058] FIG. 4 shows a plan view of a planchette 2 in accordance with a fourth example embodiment. Like reference numerals denote like elements as between FIG. 1 and FIG. 4. While the fibre of FIG. 1 is rectangular when viewed in plan, the planchette of FIG. 4 is circular. It will be apparent that the first and second luminescent regions 6, 8 of the planchette 2 can be used to provide the visual effects described above in connection with the first to third embodiments.

[0059] FIG. 5 shows a sheet of security paper 90 comprising a security paper substrate 92 having a plurality of inclusions 2 (e.g. security fibres or planchettes as described above) incorporated therein (the inclusions being shown as dots in FIG. 5).

[0060] FIG. 6 shows a flow chart of an example method 100 of authenticating a security document having a plurality of inclusions (for example the fibres of FIG. 1 to 3, or the planchette of FIG. 4) incorporated into the security paper from which the document is made. The method comprises illuminating 102 the document with ultraviolet light of a first wavelength, causing first luminescent regions on the inclusion to emit 104 light of a first colour. Optionally, illuminating 102 the document with ultraviolet light of the first wavelength also causes second luminescent regions on the inclusion to emit 106 light. The method comprises illuminating 108 the document with ultraviolet light of a second wavelength, causing first luminescent regions on the inclusion to emit 110 light of a second, different, colour. Optionally, illuminating 108 the document with ultraviolet light of the second wavelength also causes second luminescent regions on the inclusion to emit 112 light. Where second luminescent regions are present, for at least one of steps 106 and 112, the light emitted by the second luminescent regions is of a different colour to the light emitted by the first luminescent regions at that wavelength. The method comprises authenticating 114 the document in dependence on the change in appearance of the inclusions when exposed to the different wavelengths of light (i.e. when illuminated 102, 108 with ultraviolet light of the first and second wavelengths). It will be appreciated that steps 102 and 108 can be carried out in either order. In some embodiments, step 114 may comprise authenticating the document in dependence on whether the inclusions appear as a single colour under one of the first and second wavelengths, and multicoloured under the other of the first and second wavelengths. Optionally, steps 102 and 108 are carried out using a torch that comprises a first light source (e.g. a bulb or light emitting diode (LED)) that emits light of the first wavelength and a second light source that emits light of the second wavelength.

[0061] FIG. 7 shows a flow chart of an example method 150 of manufacturing a security document having a plurality of inclusions (for example the fibres of FIG. 1 to 3, or the planchette of FIG. 4) incorporated therein. The method comprises applying 152 (e.g. printing on) a plurality of first luminescent regions and second luminescent regions (as described above) to a sheet of paper. The method then comprises cutting 154 the sheet of paper into a plurality of inclusions simultaneously. The method then comprises mixing 156 the inclusion with a wet paper pulp and then forming 158 the resulting mixture into a sheet of security paper. The method comprises using 160 the sheet of security paper as the paper substrate of a security document.

[0062] Whilst the present disclosure has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the disclosure lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0063] In the examples above, first and second luminescent regions are shown forming a striped, repeating, pattern. It will be appreciated that further luminescent regions, which emit light in further, different, colours under the first and / or second wavelengths may be present. It will also be appreciated that the luminescent regions need not form stripes but could create other regular patterns or have a random distribution across the substrate.

[0064] In the above embodiments the colours yellow, red, green and purple are referred to, but it will be appreciated that different colours could be used.

[0065] The present disclosure includes the following aspects / embodiments / features in any order and in any combination: 1. An inclusion for incorporation into a security paper substrate, the inclusion comprising: a substrate; a first luminescent region on a first and / or second side of the substrate, the first luminescent region emitting visible light of (i) a first colour when viewed under ultraviolet light of a first wavelength and (ii) a second, different, colour when viewed under ultraviolet light of a second, different, wavelength; and a second luminescent region on the first and / or second side of the substrate, the second luminescent region emitting visible light of a different colour to the first luminescent region when viewed under ultraviolet light of the first wavelength and / or emitting visible light of a different colour to the first luminescent region when viewed under ultraviolet light of the second wavelength. 2. An inclusion according to clause 1, wherein the second luminescent region emits light of the first colour when viewed under ultraviolet light of the first wavelength. 3. An inclusion according to clause 1 or clause 2, wherein the second luminescent region emits light of the first colour when viewed under ultraviolet light of the second wavelength. 4. An inclusion according to clause 1, wherein the second luminescent region emits light of a third, different, colour when viewed under ultraviolet light of the second wavelength. 5. An inclusion according to clause 1 or clause 4, wherein the second luminescent region emits light of a fourth, different, colour, when viewed under ultraviolet light of the first wavelength. 6. An inclusion according to any previous clause, wherein the ultraviolet light is near ultraviolet light, both of the first and second wavelengths being in the range of from 300 nm to 400 nm inclusive. 7. An inclusion according to any previous clause, wherein the difference between the first and second wavelengths is 50 nm or less. 8. An inclusion according to any previous clause, wherein the first wavelength is in the range of from 360 nm to 375 nm inclusive, and the second wavelength is in the range of from 395 nm to 400 nm inclusive. 9. An inclusion according to any previous clause, wherein the inclusion comprises a repeating pattern of first and second luminescent regions, and optionally further luminescent regions. 10. An inclusion according to any previous clause, wherein each luminescent region is a stripe extending across the majority of the width or diameter of the substrate. 11. An inclusion according to any previous clause, wherein each luminescent region is a fluorescent region. 12. An inclusion according to any previous clause, wherein each luminescent region is substantially invisible in visible light. 13. An inclusion according to any previous clause, wherein the substrate is made of a cellulose material, for example wherein the substrate is paper. 14. An inclusion according to any previous clause, wherein each inclusion is a fibre or a planchette. 15. A security paper comprising a security paper substrate having a plurality of inclusions according to any previous clause incorporated therein. 16. A security document comprising a security paper in accordance with clause 15. 17. A method of authenticating a security document, the security document comprising a security paper substrate and a plurality of inclusions incorporated into the security paper substrate, each inclusion comprising: a substrate; and a first luminescent region on a first and / or second side of the substrate; the method comprising: illuminating the document with ultraviolet light of a first wavelength thereby causing the first luminescent region to emit light of a first colour; illuminating the document with ultraviolet light of a second wavelength thereby causing the first luminescent region to emit light of a second, different, colour; and authenticating the security document in dependence on the change in the appearance of the inclusions under ultraviolet light of the first and second wavelengths. 18. A method according to clause 17, wherein each inclusion comprises a second luminescent region on the first and / or second side of the substrate, and wherein said step of illuminating the document with ultraviolet light of the first wavelength also causes the second luminescent region to emit light of a different colour to the first luminescent region; and / or said step of illuminating the document with ultraviolet light of the second wavelength also causes the second luminescent region to emit light of a different colour to the first luminescent region. 19. A method according to clause 18, wherein said step of illuminating the document with ultraviolet light of the first wavelength causes the second luminescent region to emit light of the first colour. 20. A method according to clause 18 or clause 19, wherein said step of illuminating the document with ultraviolet light of the second wavelength causes the second luminescent region to emit light of the first colour. 21. A method according to clause 18 or clause 19, wherein said step of illuminating the document with ultraviolet light of the second wavelength causes the second luminescent region to emit light of a third, different, colour. 22. A method according to clause 18, wherein said step of illuminating the document with ultraviolet light of the second wavelength causes the second luminescent region to emit light of the third colour; and said step of illuminating the document with ultraviolet light of the first wavelength causes the second luminescent region to emit light of a fourth, different, colour. 23. A method according to any of clause 17 to 22, wherein the ultraviolet light is near ultraviolet light, the first wavelength is in the range of from 360 nm to 375 nm inclusive, and the second wavelength is in the range of from 395 nm to 400 nm inclusive. 24. A method according to any of clause 17 to 23, wherein said steps of illuminating the document with ultraviolet light of the first wavelength and illuminating the document with ultraviolet light of the second wavelength are carried out using a flashlight comprising a first light source that emits light of the first wavelength and a second light source that emits light of the second wavelength. 25. A method of manufacturing an inclusion for use in a security paper, the method comprising: applying a first luminescent ink to a sheet of paper to provide a plurality of first luminescent regions, wherein the first luminescent ink emits visible light of (i) a first colour when viewed under ultraviolet light of a first wavelength and (ii) a second, different, colour when viewed under ultraviolet light of a second, different, wavelength; and applying a second luminescent ink to the sheet of paper to provide a plurality of second luminescent regions, wherein the second luminescent ink emits visible light of a different colour to the first luminescent ink when viewed under ultraviolet light of the first wavelength and / or emits visible light of a different colour to the first luminescent ink when viewed under ultraviolet light of the second wavelength; and then cutting the substrate sheet to produce a plurality of inclusions, each inclusion comprising at least one first luminescent region and at least one second luminescent region.

[0066] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present disclosure, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the disclosure that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the disclosure, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. An inclusion for incorporation into a security paper substrate, the inclusion comprising: a substrate; a first luminescent region on a first and / or second side of the substrate, the first luminescent region emitting visible light of (i) a first colour when viewed under ultraviolet light of a first wavelength and (ii) a second, different, colour when viewed under ultraviolet light of a second, different, wavelength; and a second luminescent region on the first and / or second side of the substrate, the second luminescent region emitting visible light of a different colour to the first luminescent region when viewed under ultraviolet light of the first wavelength and / or emitting visible light of a different colour to the first luminescent region when viewed under ultraviolet light of the second wavelength.

2. An inclusion according to claim 1, wherein the second luminescent region emits light of the first colour when viewed under ultraviolet light of the first wavelength, and / or, wherein the second luminescent region emits light of the first colour when viewed under ultraviolet light of the second wavelength.

3. An inclusion according to claim 1, wherein the second luminescent region emits light of a third, different, colour when viewed under ultraviolet light of the second wavelength, and / or wherein the second luminescent region emits light of a fourth, different, colour, when viewed under ultraviolet light of the first wavelength.

4. An inclusion according to any previous claim, wherein the ultraviolet light is near ultraviolet light, both of the first and second wavelengths being in the range of from 300 nm to 400 nm inclusive, for example, wherein the first wavelength is in the range of from 360 nm to 375 nm inclusive and the second wavelength is in the range of from 395 nm to 400 nm inclusive.

5. An inclusion according to any previous claim, wherein the inclusion comprises a repeating pattern of first and second luminescent regions, for example, wherein each luminescent region is a stripe extending across the majority of the width or diameter of the substrate.

6. An inclusion according to any previous claim, wherein each luminescent region is a fluorescent region, and optionally, wherein each luminescent region is substantially invisible in visible light.

7. An inclusion according to any previous claim, wherein the substrate is made of a cellulose material, for example wherein the substrate is paper.

8. An inclusion according to any previous claim, wherein each inclusion is a fibre or a planchette9. A security paper comprising a security paper substrate having a plurality of inclusions according to any previous claim incorporated therein.

10. A security document comprising a security paper in accordance with claim 9.

11. A method of authenticating a security document, the security document comprising a security paper substrate and a plurality of inclusions incorporated into the security paper substrate, each inclusion comprising: a substrate; and a first luminescent region on a first and / or second side of the substrate; the method comprising: illuminating the document with ultraviolet light of a first wavelength thereby causing the first luminescent region to emit light of a first colour; illuminating the document with ultraviolet light of a second wavelength thereby causing the first luminescent region to emit light of a second, different, colour; and authenticating the security document in dependence on the change in the appearance of the inclusions under ultraviolet light of the first and second wavelengths.

12. A method according to claim 11, wherein each inclusion comprises a second luminescent region on the first and / or second side of the substrate, and wherein said step of illuminating the document with ultraviolet light of the first wavelength also causes the second luminescent region to emit light of a different colour to the first luminescent region; and / or said step of illuminating the document with ultraviolet light of the second wavelength also causes the second luminescent region to emit light of a different colour to the first luminescent region, and optionally wherein said step of illuminating the document with ultraviolet light of the first wavelength causes the second luminescent region to emit light of the first colour.

13. A method according to claim 12 or claim 13, wherein said step of illuminating the document with ultraviolet light of the second wavelength causes: the second luminescent region to emit light of the first colour; or the second luminescent region to emit light of a third, different, colour, and optionally, said step of illuminating the document with ultraviolet light of the first wavelength causes the second luminescent region to emit light of a fourth, different, colour.

14. A method according to any of claims 11 to 13, wherein said steps of illuminating the document with ultraviolet light of the first wavelength and illuminating the document with ultraviolet light of the second wavelength are carried out using a flashlight comprising a first light source that emits light of the first wavelength and a second light source that emits light of the second wavelength.

15. A method of manufacturing an inclusion for use in a security paper, the method comprising: applying a first luminescent ink to a sheet of paper to provide a plurality of first luminescent regions, wherein the first luminescent ink emits visible light of (i) a first colour when viewed under ultraviolet light of a first wavelength and (ii) a second, different, colour when viewed under ultraviolet light of a second, different, wavelength; and applying a second luminescent ink to the sheet of paper to provide a plurality of second luminescent regions, wherein the second luminescent ink emits visible light of a different colour to the first luminescent ink when viewed under ultraviolet light of the first wavelength and / or emits visible light of a different colour to the first luminescent ink when viewed under ultraviolet light of the second wavelength; and then cutting the substrate sheet to produce a plurality of inclusions, each inclusion comprising at least one first luminescent region and at least one second luminescent region.

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