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Title:
MANUFACTURE OF A SECURITY DEVICE
Document Type and Number:
WIPO Patent Application WO/2021/048539
Kind Code:
A1
Abstract:
A method of producing security devices (30), for example fibres, planchettes or starlights is disclosed. The method comprises printing on a substrate (2) having a first surface (4) and a second surface. A pattern (6) of printed regions is provided on a surface of the substrate (2), by printing inks that fluoresce under ultra violet light emitting coloured light and/or coloured inks that are visible under visible light. The method comprises cutting the substrate (2) according to a cutting pattern (32) to produce a plurality of security devices (30). The period B of the pattern (6) of printed regions differs from the period B' of the cutting pattern (32) and/or the direction A in which the printed regions repeats is at an angle with respect to the direction A' in which the cutting pattern repeats. A set of security devices produced using the method and a security document including such a set of security devices is also disclosed as is a method of authenticating a security document including such security devices.

Inventors:
SPINKS GARY DONALD (GB)
Application Number:
PCT/GB2020/052161
Publication Date:
March 18, 2021
Filing Date:
September 09, 2020
Export Citation:
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Assignee:
SECURITY FIBRES UK LTD (GB)
International Classes:
B42D25/355; B41M3/14; B42D25/29; B42D25/387; B42D25/40; D21H21/48; G07D7/12; G07D7/20
Domestic Patent References:
WO2015173753A12015-11-19
WO2010040991A12010-04-15
WO2004025028A12004-03-25
Foreign References:
US20090074231A12009-03-19
EP2372019A12011-10-05
US8287993B22012-10-16
Attorney, Agent or Firm:
Abel & Imray (GB)
Download PDF:
Claims:
Claims

1. A method of producing a plurality of security devices for inclusion in a security document, each security device being a particulate for incorporation into a pulp for use in production of a security-document substrate, the method comprising providing a substrate having a first surface and a second surface; providing a pattern of printed regions on at least the first surface and/or second surface of the substrate, the pattern of printed regions repeating in a direction with a period; cutting the substrate according to a cutting pattern to produce a plurality of security devices, the cutting pattern repeating in a direction with a period; and wherein

(i) the period of the pattern of printed regions differs from the period of the cutting pattern and/or

(ii) the direction in which the pattern of printed regions repeats is at an angle with respect to the direction in which the cutting pattern repeats.

2. A method according to claim 1, wherein the pattern of printed regions is provided by printing inks that fluoresce under ultra violet light emitting coloured light.

3. A method according to claim 1 or claim 2, wherein the pattern of printed regions is provided by printing inks that reflect coloured light when viewed under visible light.

4. A method according to any previous claim, wherein the security device is a planchette, a fibre or a starlight.

5. A method according to any previous claim, wherein the step of cutting the substrate produces a plurality of security devices simultaneously, for example with a single cutting motion.

6. A method according to any previous claim wherein the direction in which the printed regions repeat is at an angle of between 10 degrees and 80 degrees, for example between 20 degrees and 70 degrees, for example between 30 degrees and 60 degrees, for example around 45 degrees, with respect to the direction in which the cutting pattern repeats.

7. A method according to any previous claim wherein the period of the pattern of printed regions is at least 10 percent, for example at least 20%, for example at least 50% longer and/or shorter than the period of the cutting pattern.

8. A method according to any previous claim wherein the pattern of printed regions comprises a plurality of first printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a first colour; a plurality of second printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a second colour; the plurality of first printed regions and second printed regions being arranged in a repeating pattern on the at least first or second surface such that the coloured light emitted by first and second fluorescing printed regions mixes to produce light of further, different, colours, the colours so produced varying over a portion of at least one of the first or second surfaces.

9. A method according to claim 8, wherein the pattern of printed regions further comprising a plurality of third printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a third colour; and the plurality of third printed regions are arranged in a repeating pattern on the at least first or second surface such that coloured light emitted by first, second and third fluorescing printed regions mixes to produce light of further, different, colours, the colours so produced varying over a portion of at least one of the first or second surfaces.

10. A method according to claim 8 or claim 9, wherein the printed regions are arranged such that the colour so produced varies in a continuous spectrum over a portion of at least one of the first or second surfaces.

11. A method according to any previous claim wherein the printed regions are arranged such that the coloured light emitted by the fluorescing printed regions mixes to produce white light at one or more points in the repeating pattern.

12. A method of producing a security document, the method comprising the steps of producing a plurality of security devices using the method of any previous claim and then mixing the plurality of security devices with a pulp.

13. A method according to claim 12, comprising forming the pulp and security device mix into a continuous web to produce a security-document substrate.

14. A method according to claim 13, comprising using the security-document substrate in the production of a security device that is affixed to a security document and/or as the substrate of a security document.

15. A set of security devices for inclusion in a security document, each security device being a particulate for incorporation into a pulp for use in producing a security- document substrate, each security device having a first surface and a second surface; and a plurality of printed regions being provided on at least one of the first and/or second surface,; wherein the arrangement of the plurality of printed regions of each device is different to the arrangement of the plurality of printed regions of any other device in the set; and wherein when the security devices of the set are arranged side by side the plurality of printed regions thereon together form a repeating pattern.

16. A set of security devices according to claim 15, wherein said printed regions fluoresce under ultraviolet light emitting coloured light.

17. A set of security devices according to claim 15 or 16, wherein said printed regions appear coloured when viewed under visible light.

18. A set of security devices according to any of claims 15 to 17, wherein the plurality of printed regions comprises a plurality of first printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a first colour; a plurality of second printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a second colour; the plurality of first printed regions and second printed regions being arranged in a repeating pattern on the at least first or second surface such that the coloured light emitted by first and second fluorescing printed regions mixes to produce light of further, different, colours, the colours so produced varying over a portion of at least one of the first or second surfaces.

19. A set of security devices according to claim 18, the plurality of printed regions further comprising a plurality of third printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a third colour; and the plurality of third printed regions are arranged in a repeating pattern on the at least first or second surface such that coloured light emitted by first, second and third fluorescing printed regions mixes to produce light of further, different, colours, the colours so produced varying over a portion of at least one of the first or second surfaces.

20. A security document including a set of security devices according to any of claims 15 to 19 or a plurality of security devices produced using the method of any of claims 1 to 11, or being produced using the method of claims 12 to 14 .

21. A security document according to claim 20, wherein the security document is a bank note, a cheque, a passport or other identity papers, tax stamp or fiduciary papers.

22. A method of authenticating a security document comprising a security- document substrate having incorporated therein a plurality of security devices produced using the method of any of claim 1 to 11 and/or in accordance with any of claims 15 to 19 or being produced using the method of claims 12 to 14, the method comprising authenticating the security document in dependence on whether the appearance of the security devices in the security-document substrate matches that of a previously captured image of the security document.

23. A method of authenticating a security document according to claim 22, wherein the method comprises capturing an image of the security document to be authenticated using a portable electronic device and the step of authenticating the security document comprises the portable electronic device comparing the captured image of the security document and the previously-captured image of the security document and providing an indication to the user as to the authenticity of the document in dependence on the similarity between the appearance of the security devices in the captured image and the previously-captured image.

24. A method of authenticating a security document according to claim 23, wherein the method comprises the portable electronic device obtaining the previous- captured image from a database, for example a database on a remote server.

25. A portable electronic device having a camera and one or more processors adapted to execute one or more of the following steps in accordance with the method of claims 22 to 24:

- capturing an image of the security document using the camera;

- accessing a database to obtain a previously-captured image of the security document;

- comparing the captured image of the security document and the previously-captured image of the security document;

- providing an indication to the user as to the authenticity of the document in dependence on the similarity between the appearance of the security devices in the captured image and the previously-captured image.

26. A computer program product comprising instructions to cause the portable electronic device of claim 25 to execute the following steps in accordance with the method of any of claims 22 to 24:

- capturing an image of the security document with the camera; - accessing a database to obtain a previously-captured image of the security document;

- comparing the captured image of the security document and the previously-captured image of the security document;

- providing an indication to the user as to the authenticity of the document in dependence on the similarity between the appearance of the security devices in the captured image and the previously-captured image.

Description:
Manufacture of a Security Device

Field of the Invention

The present invention concerns improvements in and relating to security documents. More particularly, but not exclusively, this invention concerns a method of manufacturing a security device, particularly a fibre, for inclusion in a security document. The invention also concerns a set of security devices produced using such a method, a security document including such a set of security devices and a method of authenticating a security document including security devices produced using such a method.

Background of the Invention

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. 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.

A security device may take the form of an inclusion (or particulate), for example a fibre, planchette or starlight that is included into the pulp from which the paper of a security document (or part thereof) is produced.

WO 2004/025028 (D W Spinks (Embossing) Ltd) discloses a fibre for inclusion into a security document having a plurality of differently coloured regions printed on front and rear sides, wherein the colours are visible only under ultra-violet light. The regions may be in the form of stripes or a pseudo-random pattern. Such security fibres take the form of small strips of paper, for example approximately 4mm x 0.3mm, that can be added to the paper pulp during manufacture. A fibre may be cut from a larger fibre having a repeating pattern of printed stripes or regions in a random or pseudo-random fashion so that the pattern of printed stripes or regions in each fibre starts and finishes in a different place. The effect of cutting the fibres in this manner is to provide a number of different fibres that can be used to create an unpredictable pattern when incorporated into a paper product. The provision of a plurality of fibres in a paper product, each fibre having a series of stripes or regions staring in a different position can result in an overall pattern that is unpredictable and difficult to replicate, yet relatively straightforward to describe.

It would be advantageous to provide a more efficient method for producing fibres (or other inclusions) having different patterns of printed stripes or regions.

Alternatively or additionally, it would be advantageous to provide fibres (or other inclusions) that produce effects that are yet more difficult for counterfeiters to reproduce.

Alternatively or additionally, the present invention seeks to provide an improved security feature for inclusion in a security document.

Summary of the Invention

The present invention provides a method of producing a plurality of security devices for inclusion in a security document. It may be that each security device is a particulate, for example a particulate for incorporation into a pulp for use in production of a security-document substrate. The method may comprise one or more of providing a substrate having a first surface and a second surface; providing a pattern of printed regions on at least the first surface and/or second surface of the substrate, for example by printing inks that fluoresce under ultra violet light emitting coloured light and/or by printing coloured inks that are visible under visible light , optionally the pattern of printed regions repeating in a direction with a period; cutting the substrate according to a cutting pattern to produce a plurality of security devices, optionally the cutting pattern repeating in a direction with a period. It may be that (i) the period of the pattern of printed regions differs from the period of the cutting pattern and/or (ii) the direction in which the printed regions repeat is at an angle with respect to the direction in which the cutting pattern repeats. It may be that, after cutting, each security device comprises a portion of the pattern of printed regions on at least the first surface and/or second surface of the device. It may be that, after cutting, each security device comprises a portion of the pattern that differs (for example in respect of the pattern of shapes and colours that are visible when viewed under ultraviolet light) with respect to the portion of pattern of other security devices, for example any other security device.

Providing a pattern of printed regions and a cutting pattern that have different periods and/or wherein the direction in which the patterns repeat are inclined with one another may provide a simple and effective method of manufacturing a plurality of security devices having a difficult to predict selection of different patterns thereon. Additionally and/or alternatively, the method of the present invention may allow such a plurality of security devices to be produced in an efficient manner, for example by efficiently partitioning the substrate while still producing a difficult to predict selection of different patterns on the security devices.

Additionally and/or alternatively, the method of the present invention may facilitate authentication of an individual security document, which may be of particular use for very high value security documents. The method of the present invention may produce a set of security devices having a difficult to predict selection of different patterns thereon. When such security devices are then incorporated into the pulp used to produce a security-document substrate, the distribution of security devices within the security-document substrate is also very difficult to predict. Taken together the combination of the selection of different patterns on the security device and their distribution in the security document substrate produces a security-document substrate having an appearance that is effectively unique and/or difficult to reproduce. The distribution of the security device in the security-document substrate may therefore be used to authenticate a particular security document because it is highly unlikely that any other security document would have exactly the same distribution of security devices. A security-document substrate may refer to a substrate used in the production of a security document (the term being used herein to distinguish from the substrate used in the production of the security devices). The security-document substrate may be the substrate of the security document and/or the substrate of a security device affixed to a security document.

The pattern of printed regions may be provided by printing inks that fluoresce under ultra violet light emitting coloured light. Additionally or alternatively, the pattern of printed regions may be provided by printing inks that reflect coloured light under visible light (i.e. coloured inks that are visible under visible light). That is to say, the printed regions may be fluorescent printed regions and/or visible coloured printed regions. The period of a pattern may be defined as the interval, for example the distance, over which the pattern repeats in a given direction. A pattern may repeat in more than one direction, for example two directions, and therefore may have more than one period.

The term ‘at an angle’ as used herein denotes that the direction in which the printed regions repeat is inclined with respect to the direction in which the cutting pattern repeats. Thus, it may be that the direction in which the printed regions repeat is neither perpendicular nor parallel with respect to the direction in which the cutting pattern repeats.

The security device may be a particulate, for example a planchette, a fibre or a starlight. A particulate may be a device that is incorporated into the pulp used to produce the security-document substrate, for example the paper, from which a security document is produced. Each security device may be at least 1 mm in length and/or diameter. The security device may be not more than 10 mm in length and/or diameter. In the case that the security device is a fibre the fibre may be approximately 4mm in length by 0.3mm in width.

It may be that the step of cutting the substrate produces a plurality of security devices simultaneously, for example with a single cutting motion. Thus, the present methods may be suitable for use in the bulk manufacture of security devices. Each cutting motion may produce at least 10 security devices, for example at least 50, for at least 100 security devices simultaneously.

The direction in which the printed regions repeat may be at an angle of between 10 degrees and 80 degrees, for example between 20 degrees and 70 degrees, for example between 30 degrees and 60 degrees, for example around 45 degrees, with respect to the direction in which the cutting pattern repeats.

The period of the pattern of printed regions may be at least 10 percent, for example at least 20%, for example at least 50% longer and/or shorter than the period of the 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 security devices, 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. It may be that the cutting pattern is configured so that there is no gap between security devices cut from adjacent portions of the substrate. It may be that the cutting pattern cuts the substrate such that the portion of the repeating pattern of printed regions on one of said plurality of security devices is continuous with the portion of the repeating pattern of printed regions on another of said plurality of security devices (e.g. the security device cut from the portion of substrate adjacent said one of said plurality of security devices). It may be that each security device is cut from a portion of substrate immediately adjacent, for example that touches, a portion of substrate from which another security device is cut. Thus, it may be that the portion of the pattern of printed regions continues to at least one edge, for example all the edges of each security device. It may be that there is no margin around the portion of the pattern of printed regions on each security device.

The first and second surfaces of the substrate may be opposing surfaces.

The step of providing printed regions on both the first and second surface of the substrate may comprise printing on one of the front or the rear sides of the substrate and allowing the ink to soak through to the other side of the substrate. The step of providing printed regions on both the first and second surface of the substrate may comprise individually printing on the first surface of the substrate and printing on the second surface of the substrate.

The pattern of printed regions may comprise a plurality of first printed regions being printed in an ink which fluoresces under ultra violet light to emit light in a first colour and/or being printed in an ink which appears a first colour when viewed under visible light. The pattern of printed regions may comprise a plurality of second printed regions being printed in an ink which fluoresces under ultra violet light to emit light in a second colour and/or being printed in an ink which appears a second colour when viewed under visible light. The pattern of printed regions may comprise a plurality of third printed regions being printed in an ink which fluoresces under ultra violet light to emit light in a third colour and/or being printed in an ink which appears a third colour when viewed under visible light. It may be that the plurality of first, second and third (if present) printed regions are arranged to produce a repeating pattern. Thus, methods in accordance with the present invention may use different colours in printed regions to produce a striking visible effect that is difficult to counterfeit.

It may be that the pattern of the printed regions appears substantially similar under both ultra violet and visible light. For example the pattern of printed regions may comprise a plurality of first, second (if present) and third (if present) regions and each of the first regions appears the same, first, colour when viewed under ultraviolet and visible light, each of the second regions (if present) appears the same, second, colour when viewed under ultraviolet and visible light and (if present) each of the third regions appears the same, third, colour when viewed under ultraviolet and visible light. Thus it may be that each region is printed with both fluorescent and visible coloured inks, the fluorescent and visible inks appearing the same colours when viewed under ultraviolet and visible light respectively. Thus, methods in accordance with the present invention may use both fluorescent and visible coloured printed regions to produce a striking visible effect that is difficult to counterfeit.

The pattern of printed regions may comprise a plurality of first printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a first colour. The pattern of printed regions may comprise a plurality of second printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a second colour. It may be that the plurality of first printed regions and second printed regions are arranged in a repeating pattern on the at least first or second surface such that the coloured light emitted by first and second fluorescing printed regions mixes to produce light of further, different, colours, the colours so produced varying over a portion of at least one of the first or second surfaces.

Thus, methods in accordance with the present invention may use tonal variation in printed regions to produce a striking visible effect that is difficult to counterfeit. Moreover, use of tonal variation may allow a wide variety of differently coloured light to be produced using only two colours. Additionally or alternatively, security devices in accordance with the present invention may facilitate an efficient manufacturing process as a wide variety of colours can be produced with only two print stations (one print station for each colour). The varying tone density may be provided by halftone printing. Thus, the method may comprise using halftone printing to provide a tone density that varies across a printed region. Halftone printing is a known reprographic technique whereby dots of different size, pattern and/or spacing are used to give an appearance of different tones. The tone density of each printed region may vary in a smooth (i.e. non-discontinuous) manner across the region. Thus the resulting colour pattern may have diffuse boundaries between different colours. The tone density of each region may vary between 0% and 100%. The tone density may vary in one or more gradations or discrete steps, for example in ten degree gradations (e.g. having densities of 10%, 20%, 30% etc). Thus the resulting colour pattern may have discrete boundaries between different colours. There may be two or more gradations in each printed region, for example three or more gradations, for example five or more gradations. The tone density may increase with distance across a region, decrease with distance across a region or vary (both increasing and decreasing at different points) across a region.

It may be that only a single colour is applied in each printed region. This may allow for improved repeatability of the visual effect as a different print station (e.g. roller) may be used to apply each colour. This is in contrast with ‘split duct’ printing where inking rollers are charged along their length with different colours so that inks merge with their neighbour to produce a graphic ‘spectrum’ effect. The tendency for the inks to merge may cause a loss in purity of the individual colours which is particularly detrimental for fluorescent effects.

The pattern of printed regions may further comprise a plurality of third printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a third colour. It may be that the plurality of third printed regions are arranged in a repeating pattern on the at least first or second surface such that coloured light emitted by first, second and third fluorescing printed regions mixes to produce light of further, different, colours, the colours so produced varying over a portion of at least one of the first or second surfaces.

Using a third colour having varying tone density may facilitate the production of a wider range of visual effects, thereby increasing the difficulty of counterfeiting. Additionally or alternatively, security devices in accordance with the present invention may facilitate an efficient manufacturing process as all colours (e.g. a full colour spectrum) can be produced with only three print stations (one print station for each colour).

The first, second and third (if present) printed regions having varying tone density may be arranged such that the colour so produced varies in a continuous spectrum over a portion of at least one of the first or second surfaces. It may be that a graduated spectrum or ‘rainbow’ effect pattern is produced. The differently coloured light (which may give the appearance of differently coloured regions when the device is viewed under ultra violet light) may appear in the same order in a repeating pattern.

Alternatively, it may be that the pattern of printed regions comprises a plurality of first printed regions having constant tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a first colour; a plurality of second printed regions having constant tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a second colour; and the plurality of first printed regions and second printed regions being arranged in a repeating pattern on the at least first or second surface such that the coloured light emitted by first and second fluorescing printed regions mixes to produce light of further, different, colours. Optionally, the pattern of printed regions may comprise a plurality of third printed regions having constant tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a third colour; and the plurality of third printed regions are arranged in a repeating pattern on the at least first or second surface such that coloured light emitted by first, second and third fluorescing printed regions mixes to produce light of further, different, colours. Thus, the method may comprise printing to provide a constant tone density across a printed region.

The printed regions may be provided using an ink that fluoresces under ultra violet light to produce one of red, blue or green light or a mixture thereof. Each of the first, second and third (if present) printed regions may be produced using an ink that fluoresces to produce a different one of red, blue or green light or a different mixture thereof. Each of the first, second and third (if present) printed regions may be produced using an ink comprising a mixture of two or more differently coloured pigments (for example red, green and blue pigments) that fluoresce to produce light having a colour resulting from the mixture of said different colours. Each of the first, second and third (if present) printed regions may be provided using an ink of a single colour. As an alternative to red, blue and green inks, cyan, magenta and yellow inks may be used. Where red, green and blue inks are used, additive mixing of the light from each printed region may allow white light to be produced. Where cyan, magenta and yellow inks are used subtractive mixing of the light from each printed region may allow black light to be produced.

The printed regions may be arranged such that the coloured light emitted by the fluorescing printed regions mixes to produce white light at one or more points in the repeating pattern.

The first, second and/or third (if present) printed regions (whether fluorescent and/or visible coloured) may be provided on the first and/or second surface of the substrate such that there are regions where inks from two or three printed regions at least partially overlap, for example completely overlap. The first, second and/or third (if present) printed regions may be provided on the first and/or second surface of the substrate such that there are regions where inks from two different regions do not overlap. The first, second and/or third (if present) printed regions may be provided on the first and/or second surface of the substrate such that there are regions where only two of the inks overlap.

The first, second and/or third (if present) printed regions (whether fluorescent and/or visible coloured) may be provided on the first and/or second surface of the substrate such that for every one region that two regions overlap, there are two printed regions in which the inks do not overlap. The first, second and/or third (if present) printed regions may be provided on the first and/or second surface of the substrate such that for every one region that three regions overlap, there are three printed regions in which the inks do not overlap. The first, second and/or third (if present) printed regions may be provided on the first and/or second surface of the substrate such that there are regions where each one of the inks overlaps with one of each of the other inks.

The method may further comprise the step of applying a layer of varnish on at least the (fluorescent and/or visible coloured) printed regions. The security device may further comprise a layer of varnish on at least the printed regions.

The method may further comprise the step of mixing the plurality of security devices with a pulp, for example with a slurry paper pulp such that the fibres form a hydrogen bond with the cellulose fibre in the paper pulp. The method may comprise forming the pulp and security device mix into a continuous web, for example forming the paper pulp and security device mix into a continuous web of paper. The method may comprise using the continuous web, for example the continuous web of paper, in the production of a security document, for example in the production of a security device that is affixed to a security document and/or in the production of a security- document substrate for use in a security document.

Depending on the arrangement of the printed regions, for example whether the different gradation of tonal density are discrete or continuously varying and/or whether the tonal density of a region is constant, the boundaries between the different colours visible under ultraviolet and/or visible light may be discrete (discontinuous) or diffuse (continuous). The repeating pattern may be a geometric pattern, for example a repeating pattern of triangles, squares, rectangles, circles and/or combinations thereof. The repeating pattern may comprise a plurality of discrete (discontinuous) blocks of colour. It may be that each block of colour has a shape, for example the same shape, for example a triangular, square, rectangular or other shape. Each block of colour may appear as a single colour when viewed under ultraviolet light. Thus, the printed regions may be arranged to produce a repeating geometric pattern when viewed under ultraviolet light. The repeating pattern may comprise a gradually varying colour spectrum.

The (fluorescent and/or visible-coloured) printed regions may be arranged on the first and/or second surface of the substrate such that they at least partially overlap. The printed regions may be arranged on the first and/or second surface of the substrate such that they completely overlap. The first, second and/or third (if present) printed regions may be provided on the same one of the first or second surface. The first, second and/or third (if present) printed regions may be provided on only one of the first or second surface. The first, second and/or third (if present) printed regions may be provided on both the first surface and second surface of the substrate.

The fluorescent printed regions may be provided using inks that have an excitation wavelength of 365 nm (long wave) and/or 254 nm (short wave). The printed regions maybe provided using inks that comprise microencapsulated fluorescent organic or organometallic dyes. The microencapsulated inks may each comprise a fluorescent dye of more than one colour. The printed regions may be provided using inks that have a lightfastness of at least 3 on the blue wool scale, for example 8 on the blue wool scale. In some circumstances, the inks may have a lightfastness of less than 3 on the blue wool scale, for example 1 or less. It will be appreciated that such inks will be less resistant to fading but there may be circumstances where this is acceptable.

The visible coloured printed regions that are visible under visible light may be provided using conventional coloured inks, for example having a lightfastness of at least 3 on the blue wool scale, for example 8 on the blue wool scale. In some circumstances, the inks may have a lightfastness of less than 3 on the blue wool scale, for example 1 or less. It will be appreciated that such inks will be less resistant to fading but there may be circumstances where this is acceptable.

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 with a nominal basis weight of between 12g/m2 and 45g/m2, for example between 23 g/m2 and 28 g/m2.

The substrate may be paper of a high porosity, high wet strength tissue paper with a nominal basis weight of 25 g/m2.

The repeating pattern of (fluorescent and/or visible coloured) printed regions may be continuous across at least part of the first and/or second surface of the substrate, for example at least 20 percent, for example at least 50 percent of the area of the first or second surface of the substrate.

In a second aspect of the invention there is provided a set of security devices for inclusion in a security document. Each security device may have a first surface and a second surface; and a plurality of printed regions being provided on at least one of the first and/or second surface, for example wherein said printed regions fluoresce under ultraviolet light emitting coloured light and/or said printed regions reflect coloured light under visible light. It may be that the arrangement of the plurality of printed regions of each device is different to the arrangement of the plurality of printed regions of any other device in the set. It may be that when the security devices of the set are arranged side by side the plurality of printed regions thereon together form a repeating pattern. Thus, it may be that there is a plurality of security devices in the set, each with a different pattern but when assembled together the repeating pattern of printed regions of the substrate from which they were formed is visible. The set of security devices may be produced using the method described above. Accordingly, the set of security devices may have any of the features described with reference to the plurality of security devices above (and vice versa).

Each security device may comprise a portion of the substrate described above. It may be that, when the plurality of security devices are viewed together from the same direction (e.g. the same surface of each device being visible) the printed regions thereon together from a repeating pattern. It will be appreciated that the printed regions will from the repeating pattern when the security devices are laid out according to the cutting pattern - for example side by side and/or end to end and/or with security devices produced from adjacent regions of a substrate being adjacent each other.

It may be that the arrangement of the plurality of printed regions on each security device of the set appear random when viewed individually. For example the combination of colours and the shapes of the coloured regions when viewed under ultraviolet light and/or visible light may differ significantly and/or unpredictably as between different security devices of the set.

It may be that the plurality of printed regions, for example when the printed regions of the plurality of security devices in the set are taken together, comprises a plurality of first printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a first colour; a plurality of second printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a second colour; the plurality of first printed regions and second printed regions being arranged in a repeating pattern on the at least first or second surface such that the coloured light emitted by first and second fluorescing printed regions mixes to produce light of further, different, colours, the colours so produced varying over a portion of at least one of the first or second surfaces.

It may be that the plurality of printed regions further comprises a plurality of third printed regions having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a third colour; and the plurality of third printed regions are arranged in a repeating pattern on the at least first or second surface such that coloured light emitted by first, second and third fluorescing printed regions mixes to produce light of further, different, colours, the colours so produced varying over a portion of at least one of the first or second surfaces. The security device may be a particulate, for example a planchette, a fibre or a starlight. Thus a set of fibres, planchettes or starlights may be provided.

According to a third aspect of the invention there is provided a security document including a set of security devices according to any other aspect of the invention, for example produced using the method of any other aspect. The security document is a bank note, a cheque, a passport or other identity papers, tax stamp or fiduciary papers.

According to a fourth aspect of the invention there is provided a method of authenticating a security document comprising a security-document substrate having a plurality of security devices produced using the method of any other aspect of the invention and/or security devices in accordance with any other aspect of the invention incorporated therein, for example wherein each security device is a particulate incorporated into the pulp of a security document substrate used in the production of the security document (for example as the substrate of the security document and/or as the substrate of a (macro) security device affixed to a security document). It may be that each security device has a first surface and a second surface; and a plurality of printed regions being provided on at least one of the first and/or second surface, for example wherein said printed regions fluoresce under ultraviolet light emitting coloured light and/or said printed regions reflect coloured light under visible light. It may be that the arrangement of the plurality of printed regions of each device is different to the arrangement of the plurality of printed regions of any other device in the set. It may be that when the security devices of the set are arranged side by side the plurality of printed regions thereon together form a repeating pattern. Thus, it may be that there is a plurality of security devices in the set, each with a different pattern but when assembled together the repeating pattern of printed regions of the substrate from which they were formed is visible.

The method may comprise authenticating the security document in dependence on whether the appearance of the security devices in the security- document substrate matches the appearance of the security devices in a previously captured image of the security document. Thus, methods in accordance with the present invention may use a previously captured image of the security document to subsequently authenticate the security document based on the random distribution of the security devices of the invention in a security-document substrate used in the production of the security document. That is to say, the random distribution and appearance of the security devices in the security-document substrate may be used as a unique identifier (or code) for that document thereby increasing the burden on any counterfeiter.

The term “a previously captured image of the security document” may refer to an image of the security document that is to be validated (e.g. the security document itself and not, for example, another security document which can serve as a reference/example as in the case of security features that are reproduced across many documents). The previously captured image may have been captured days, weeks months, or years previously, for example by the issuing authority. The step of authenticating the security document may be carried out by the issuing authority and/or an end user. The previously captured image may be captured at or before the time the security document is issued by the issuing authority.

Authenticating the security document in dependence on whether the appearance of the security devices in the security-document substrate matches a previously captured image of the security document may comprise analysing the pattern on and/or location of individual security devices incorporated into the security- substrate and, optionally comparing the pattern on and/or location of said individual security devices with the pattern on and/or location of individual security devices in the previously-captured image.

The previously captured image may be stored in a database, for example by the issuing authority. The method may comprise accessing the database, for example on a remote server, to obtain a copy of the previously captured image.

The method of authenticating the security document may comprise capturing an image of the security document to be authenticated, for example using a digital camera, for example a camera of a portable electronic device, and authenticating the security document in dependence on whether the appearance of the security devices in the image matches the appearance of the security devices in the previously captured image. The method may comprise using image recognition software to compare the appearance of the security devices in the captured image and the previously captured image.

The portable electronic device may be a smart phone or other similar device.

The step of accessing the database may be carried out by the smart phone in response to a user command and/or as part of an automated process to provide an indication as to the authenticity of the security document to a user. The portable electronic device may compare the captured image of the security document and the previously-captured image of the security document and provide an indication to a user as to the authenticity of the document in dependence on the similarity between the appearance of the security devices in the captured image and the previously-captured image. Such a comparison may be carried out using conventional image recognition software.

There may be a number of security devices in the security-document substrate (for example the security-document substrate may comprise more than ten security devices, for example more than twenty security devices, for example more than fifty security devices) such that it would be difficult and/or time consuming for a user to accurately compare the appearance of the security devices with a previously captured image using the naked eye. Thus, use of a portable electronic device may increase the usability of the method of authenticating the document.

The portable electronic device may carry out one or more of the steps of the method of authenticating the security document (for example capturing an image, obtaining the previously-captured image, comparing the captured image and the previously captured image, and/or providing an indication of the authenticity of the document), for example in response to a user input, for example a user input to start the authentication process. It may be that following the user input the steps of capturing an image, obtaining the previously-captured image, comparing the captured image and the previously captured image and/or providing an indication of the authenticity of the document are carried out automatically (e.g. without further user input).

In further aspects of the invention there is provided a portable electronic device adapted to execute one or more steps of the method of authenticating a security document and a computer program product comprising instructions to cause a portable electronic device to execute one or more steps of the method of authenticating a security document.

The security document may comprise a machine-readable image, for example a QR code. The machine readable image may be configured to provide a prompt to a user to download the computer program product and/or provide a link to a remote server where the computer program product is available. Additionally and/or alternatively, the machine-readable image may provide a link to a remote server where the previously captured image is available and/or a link to the previously captured image on the remote server. The security document may comprise a reference code, for example an alphanumeric reference code visible under visible light, that allows the user to locate the previously captured image in a database of such images.

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

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 (a) shows an intermediate stage in the production of a security fibre according to a first example method in accordance with the invention;

Figure 1 (b) shows a set of security fibres according to an example embodiment of the invention produced using the first example method;

Figure 2 shows a schematic example of additive printing of the type used in the first example method;

Figure 3 shows a flow chart summarising the steps of the first example method;

Figure 4 (a) shows an intermediate stage in the production of a security fibre according to a second example method in accordance with the invention;

Figure 4(b) shows a set of security fibres according to an example embodiment of the invention produced using the second example method;

Figure 5 shows a schematic example of additive printing of the type used in the second example method;

Figure 6 shows a flow chart summarising the steps of the second example method;

Figure 7 shows an intermediate stage in the production of a planchette according to a third example method in accordance with the invention;

Figure 8 shows a flow chart summarising the steps of the third example method; Figure 9 shows a security document including a set of security devices produced in accordance with methods of the invention; and Figure 10 shows a flow chart of an example method of authenticating a security document .

Detailed Description

Figure 1 (a) shows an intermediate stage in a first example method in accordance with the invention. In the first example method a substrate 2 having a first surface 4 and a second surface (not shown) is printed with a repeating geometric pattern 6 as shown in Fig. 1(a). A unit of the repeating geometric pattern 6 is indicated with dashed line 8 in Fig. 1(a). The geometric pattern 6 repeats in a first direction, labelled A in Fig. 1(a), and the length of a unit of the geometric pattern 6 (i.e. the period of the pattern) is labelled B in Fig. 1(a).

The repeating geometric pattern 6 is visible only under ultra violet light and is printed using three inks which fluoresce to produce red, green and blue light respectively. In some embodiments, the colours are visible under ultraviolet light having a wavelength between 245 nm and 365 nm. The pattern is produced by printing regions of the first surface 4 and/or second surface (not shown) with one or more of the three inks. In one embodiment, the inks are provided on the first surface 4 of the substrate to produce geometric pattern 6. In an alternative embodiment, the inks are provided on the first surface 4 and the second opposing surface to produce geometric pattern 6. Figure 2 shows a schematic example of additive printing of the type used in the method of the first embodiment. A pattern 6’ comprises three printed “layers” 10’, 12’, 14’. Each printed layer comprises a single ink that is provided on a substrate 2’. The first printed layer 10’ fluoresces under ultra-violet light to produce red light. The second printed layer 12’ fluoresces under ultra-violet light to produce green light. The third printed layer 14’ fluoresces under ultra-violet light to produce blue light. Pattern 6’ comprises printed regions 16’, 18’, 20’ where two printed layers of any of 10’ and 12’, 12’ and 14’, or 14’ and 10’ overlap. When those regions are viewed under ultra violet light the red and blue, blue and green, green and red colours produced additively mix to produce magenta 16’, cyan 18’, or yellow 20’ coloured light respectively. The pattern 6’ also comprises regions 22’, 24’, 26’ where printed layers 10’, 12’ and 14’ do not overlap at all. When those regions are viewed under ultra violet light, the region 22’ where layer 10’ does not overlap produces red light, the region 24’ where layer 12’ does not overlap produces green light, and the region 26’ where layer 14’ does not overlap produces blue light. The pattern 6’ also comprises a region 28’ where all three printed layers 10’, 12’, 14’ overlap. When that region 28’ is viewed under ultra violet light it produces white light. In Fig. 1 this method has been used to provide geometric pattern 6 comprising triangular regions 16, 18, 20, 22, 24, 26, 28 that when viewed under ultraviolet light produce magenta (16), cyan (18), yellow (20), red (22), green (24), blue (26) and white (28) light respectively. In other embodiments it may that one or more of those colours are not present in the pattern.

The substrate of Fig. 1 is cut according to a cutting pattern 32 to produce a plurality of fibres 30 (see Fig. 1(b)) each fibre 30 comprising a rectangular strip of substrate 2. The cutting pattern 32 is indicated by lines superimposed on pattern 6 in Fig. 1 and comprises a repeating pattern of rectangles covering a portion of the substrate 2 with no gaps and no overlaps. In other embodiments the cutting pattern may comprise repeating patterns of other geometric shapes, for example triangles, circles, squares. The cutting pattern 32 repeats in a second direction labelled A’ in Fig. 1(a), and the length of a unit of the cutting pattern 32 (i.e. the period of the cutting pattern) is labelled B’ in Fig. 1(a). Period B’ is shorter than the period B of the pattern 6, and direction A’ is at an angle relative to direction A. In other embodiments, period B’ may be longer than the period B of pattern 6.

Fig. 1(b) shows a set of fibres 30 produced by cutting substrate 2. Each fibre 30 comprises a portion of the geometric pattern 6 on its first 34 and/or second (not shown) surface. As a consequence of the difference in the first and second directions A, A’ and the lengths B, B’ of the geometric pattern 6 and the cutting pattern 32 the portion of the pattern 6 present on each fibre 30 is different thereby producing a plurality of different fibres 30.

The geometric pattern 6 is straightforward to print, and the cutting pattern 32 is relatively geometrically simple and produces the fibres 30 with little waste of the substrate 2. Accordingly, methods in accordance with the present invention may provide a simpler and/or more efficient way of producing a large number of fibres with differing (and difficult to predict) patterns thereon. Further, in embodiments where fluorescent inks are used the use of additive mixing allows for the production of a fibre with up to seven colours thereon using only three print stations (a red, a blue and a green print station in this embodiment). Additionally, the use of additive mixing allows the production of a fibre that produces white light when viewed under ultraviolet light - such regions being challenging for counterfeiters to reproduce. Methods in accordance with the present embodiment may therefore provide a security device that provides a striking and difficult to reproduce visual effect which can be manufactured without undue burden.

Figure 3 shows a flow chart summarising the steps of the first example method. The geometric pattern 6 is printed 80 on substrate 2. The step of printing 80 comprises printing one or more regions with an ink that appears red when viewed under ultraviolet light (step 80a), printing one or more regions with an ink that appears green when viewed under ultraviolet light (step 80b) and printing one or more regions with an ink that appears blue when viewed under ultraviolet light (step 80c). The substrate 2 is then cut 82 into a plurality of fibres 30 according to cutting pattern 32. In the present embodiment all of the cuts in the cutting pattern 32 are executed simultaneously - that is to say the fibres are all cut from the substrate in one go. In other embodiments, the cuts that make up the cutting pattern may be carried out in series. The resulting fibres 30 are then mixed 84 with a slurry paper pulp, where they form a hydrogen bond with the cellulose fibre in the paper pulp. The paper pulp and fibre mix is then formed 86 into a continuous web of paper which can be used in a security document.

In the embodiment and methods described above the repeating printed pattern is produced using fluorescent inks. In other embodiments coloured inks that are visible under visible light may be used as well as or instead or fluorescent inks to produce the repeating printed pattern. The pattern may then comprise different regions that are different colours when viewed under visible light. In some embodiments, both fluorescent inks and coloured inks are used. The combination of fluorescent inks and coloured inks may be used to produce patterns appear the same under ultra violet and visible light or different under ultra violet and visible light. It will be appreciated that the steps of cutting the substrate and using the resulting fibres (or other particulates such as planchettes) in the production of a security document when visible inks are used are substantially as described above for fluorescent inks. Similarly the methods of authentication as described below will apply equally well for security devices including coloured inks, with the exception that where only coloured inks are used a UV lamp is not required to observe the security devices. Figure 4(a) shows an intermediate stage in a second example method in accordance with the invention. Elements that are similar as between Figs. 1 and 4 have been indicated in Fig. 4 using their reference numeral from Fig. 1 incremented by 100 (i.e. pattern 6 in Fig. 1 is referred to as pattern 106 in Fig. 4). In the second example method, a substrate 102 having a first surface 104 and a second surface (not shown) is printed with a repeating graduated pattern 106. A unit of the repeating graduated pattern 106 is indicated with dashed line 108 in Fig. 4 (a). The graduated pattern 106 repeats in a first direction, labelled A in Fig. 4(a), and the length of a unit of the geometric pattern 106 (i.e. the period of the pattern) is labelled B in Fig. 4(a).

In contrast to the first example method, in the second example method varying tonal densities are used to produce a graduated repeating pattern 106 of printed regions on the substrate 102. As for the first embodiment, the repeating graduated pattern 106 is visible only under ultra violet light and is printed using three inks which fluoresce to produce red, green and blue light respectively. In some embodiments, the colours are visible under ultraviolet light having a wavelength between 245 nm and 365 nm.

The pattern is produced by printing regions of the first surface 104 and/or second surface (not shown) with one or more of the three inks. In one embodiment, the inks are provided on the first surface 104 of the substrate to produce geometric pattern 106. In an alternative embodiment, the inks are provided on the first surface 104 and the second opposing surface to produce geometric pattern 106. Figure 5 shows a schematic example of additive printing of the type used in the second example method.

A pattern 106’ comprises three halftone printed “layers” 110’, 112’, 114’ (halftone printing represented as blocks in Fig. 5). The halftone printed layers comprise a strip of ink that is provided on the substrate at graded tonal densities either increasing or decreasing along the strip as required to achieve the various colours of the graduated rainbow pattern. The first halftone printed layer 110’ fluoresces under ultra violet light to produce red light. A second halftone printed layer 112’ fluoresces under ultra violet light to produce blue light. And a third halftone printed layer 114’ fluoresces under ultra violet light to produce green light. Pattern 106’ comprises printed regions where two halftone printed layers of any of 110’ and 112’, 112’ and 114’, or 114’ and 110’ overlap. When those regions are viewed under ultra violet light the red and blue, blue and green, green and red colours produced additively mix to produce magenta 116’, cyan 118’, or yellow 120’ coloured light respectively (Figure 3). Pattern 106’ also comprises regions where printed layers 110’, 112’ and 114’ do not overlap at all. When those regions are viewed under ultra violet light, the region 124’ where layer 110’ does not overlap produces red light, the region 126’ where layer 112’ does not overlap produces blue light and the region 128’ where layer 114’ does not overlap produces green light. As a result of the tonal variation and overlap of these colours, pattern 106’ produces a continuous spectrum of colours when viewed under ultra violet light. Depending on whether the different gradations of tonal density are discrete or continuously varying, the boundaries between the different colours may be discrete (discontinuous) or diffuse (continuous).

In an alternative embodiment, pattern 106 comprises a further region where all three of the fluorescent inks overlap and each carry equal tonal weights; such that when this region is viewed under ultra violet light, the colours additively mix to produce white light (not shown).

In an alternative embodiment (not shown), a first halftone printed region fluoresces under ultra violet light to produce magenta light, a second halftone printed region fluoresces under ultra violet light to produce cyan light and a third halftone printed region fluoresces under ultra violet light to produce yellow light. When two of those regions overlap and are viewed under ultra violet light the magenta and cyan, cyan and yellow, yellow and magenta colours produced subtractively mix to produce blue, green, or red coloured light respectively. As a result of the tonal variation and overlap of these colours, a continuous spectrum of colours is produced when viewed under ultra violet light. In an alternative embodiment, a further region where all three of the fluorescent inks overlap and each carry equal tonal weights is provided; such that when this region is viewed under ultra violet light, the colours subtractively mix to produce black light (not shown). In Fig. 4 this method has been used to provide graduated pattern 106 comprising striped regions that when viewed under ultraviolet light produce magenta, cyan, yellow, red, green, blue, and white light respectively.

In other embodiments it may that one or more of those colours are not present in the pattern.

The substrate of Fig. 4(a) is cut according to a cutting pattern 132 to produce a set of fibres 130 (shown laid out side by side and end to end such that pattern 106 is visible in Fig. 4(a)) each fibre 130 comprising a rectangular strip of substrate 102.

The cutting pattern 132 is indicated by lines superimposed on pattern 106 in Fig. 4(a) and comprises a repeating pattern of rectangles covering a portion of the substrate 102 with no gaps and no overlaps. In other embodiments the cutting pattern may comprise repeating patterns of other geometric shapes, for example triangles, circles, squares. The cutting pattern 132 repeats in a second direction labelled A’ in Fig. 4 (a), and the length of a unit of the cutting pattern 132 (i.e. the period of the cutting pattern) is labelled B’ in Fig. 4(a). Period B’ is shorter than the period B of the pattern 106, and direction A’ is at an angle relative to direction A. In other embodiments, period B’ may be longer than the period B of pattern 106.

Each of the plurality of fibres produced by cutting substrate 102 comprises a portion of the graduated pattern 106 on its first 104 and/or second (not shown) surface. As a consequence of the difference in the first and second directions A, A’ and the lengths B, B’ of the graduated pattern 106 and the cutting pattern 132 the portion of the pattern 106 present on each fibre is different thereby producing a plurality of different fibres.

The advantages of the second example method are similar as for the first example method. Additionally, the use of additive (or subtractive) mixing with varying tone density facilitates the production of a fibre having a graduated pattern of colours with diffuse boarders, which is yet more difficult to reproduce.

Figure 6 shows a flow chart summarising the steps of the second example method. The graduated pattern 106 is printed 180 on substrate 2. The step of printing 180 comprises printing one or more regions with an ink that appears red when viewed under ultraviolet light in a varying tone density (step 180a), printing one or more regions with an ink that appears green when viewed under ultraviolet light in a varying tone density (step 180b) and printing one or more regions with an ink that appears blue when viewed under ultraviolet light in a varying tone density (step 180c). The substrate 102 is then cut 182 into a plurality of fibres according to cutting pattern 132. In the present embodiment all of the cuts in the cutting pattern 132 are executed simultaneously - that is to say the fibres are all cut from the substrate in one go. In other embodiments, the cuts that make up the cutting pattern may be carried out in series. The resulting fibres are then mixed 184 with a slurry paper pulp, where they form a hydrogen bond with the cellulose fibre in the paper pulp. The paper pulp and fibre mix is then formed 186 into a continuous web of paper which can be used in a security document.

Figure 7 shows an intermediate stage in a third example method for producing a planchette in accordance with the invention. Elements that are similar as between Figs. 1 and 7 have been indicated in Fig. 7 using their reference numeral from Fig. 1 incremented by 200 (i.e. pattern 6 in Fig. 1 is referred to as pattern 206 in Fig. 7). In the third example method, a substrate 202 having a first surface 204 and a second surface (not shown) is printed with the same repeating geometric pattern 206 as shown in Fig. 1. In other embodiments a different geometric pattern may be used. A unit of the repeating graduated pattern 206 is indicated with dashed line 208 in Fig. 4. The graduated pattern 206 repeats in a first direction, labelled A in Fig. 7, and the length of a unit of the geometric pattern 206 (i.e. the period of the pattern) is labelled B in Fig. 7.

The cutting pattern 232 is indicated by lines superimposed on pattern 206 in Fig. 7. In contrast to the first example method, in the third example the cutting pattern comprises a repeating pattern of triangles covering a portion of the substrate 202 with no gaps and no overlaps. The cutting pattern 232 repeats in a second direction labelled A’ in Fig. 4, and the length of a unit of the cutting pattern 232 (i.e. the period of the cutting pattern) is labelled B’ in Fig. 7. Period B’ is shorter than the period B of the pattern 206, and direction A’ is at an angle relative to direction A. In other embodiments, period B’ may be longer than the period B of pattern 206.

Each of the plurality of planchettes produced by cutting substrate 202 comprises a portion of the geometric pattern 206 on its first 204 and/or second (not shown) surface. As a consequence of the difference in the first and second directions A, A’ and the lengths B, B’ of the geometric pattern 206 and the cutting pattern 132 the portion of the pattern 106 present on each triangular planchette is different thereby producing a plurality of different planchettes. Each planchette is small, typically having a maximum dimension of between 2mm and 5mm.

Figure 8 shows a flow chart summarising the steps of the second example method. The geometric pattern 206 is printed 180 on substrate 2. The substrate 202 is then cut 282 into a plurality of planchettes according to cutting pattern 232. In the present embodiment all of the cuts in the cutting pattern 232 are executed simultaneously - that is to say the planchettes are all cut from the substrate in one go. In other embodiments, the cuts that make up the cutting pattern may be carried out in series. The resulting planchettes are then mixed 184 with a slurry paper pulp, where they form a hydrogen bond with the cellulose fibre in the paper pulp. The paper pulp and planchette mix is then formed 186 into a continuous web of paper which can be used in a security document. In some embodiments of the invention the printed regions of the security device are coated with a varnish. In some embodiments the varnish is a 4% solution of Solvitose NX in acrylic water based binder.

In some embodiments of the invention the substrate (2, 102, 202) is a thin and porous paper and printing on a single side of the substrate with an appropriate amount of ink means that the ink soaks through the substrate and so both sides of the substrate have been printed on. In other embodiments each side of the substrate is printed individually.

In one embodiment the security devices 92, for example the fibres or planchettes described above, are incorporated into paper pulp used to manufacture a banknote 90 as shown in Figure 9. The bank note 90 also comprises an alphanumeric code 94 and a QR code 96 that are visible under visible light. In other embodiments a different machine-readable image may be used. Under visible light (Fig. 9(a)), the security devices 92 which comprise printed regions produced using fluorescent inks are unremarkable, blending in with other cellulose fibres that make up the paper of the banknote 90. However, under ultraviolet light, the devices 92 fluoresce, forming an unpredictable pattern of colours in the banknote 90 (shown schematically for ease of illustration by the dotted pattern in Fig. 9(b)). Thus a UV light is used for a check of the validity of the security paper, e.g. in a shop, or by a bank teller. In other embodiments the security devices, alphanumeric code and QR code may be incorporated into different security papers, for example passports, lottery tickets, tax stamps, certificates and other items of potentially high value. In embodiments where the security devices, for example fibres or planchettes, have coloured printed regions that are visible under visible light the security devices may be visible under visible light. In that case, security papers may be authenticated without a UV light.

Fig. 10 shows a flow chart for an example method of authenticating a security document, for the bank note of Fig. 9. It will be appreciated that this method can also be used with other security documents including the security devices described above and, optionally, an alphanumeric code and/or QR code or other machine readable image. The method comprises capturing 1002 a first image of the security document to be authenticated. In some embodiments capturing 1002 is done using the camera of a smart phone or other portable electronic device. The method comprises retrieving 1004 a reference image of the security document to be authenticated (this step may be carried out before or after step 1002), for example from a remote database. In some embodiments the retrieving 1004 is done using a smart phone or other portable electronic device. Optionally, the step of retrieving 1004 comprises using 1005a an alphanumeric code to locate the reference image in a database and/or following 1005b a link, for example provided by a machine readable image, e.g. a QR code, to the reference image in a database. The method comprises authenticating 1006 the document. The step of authenticating 1006 comprises comparing 1008 the first image of the security document with the reference image. In some embodiments the step of comparing 1008 may be carried out (at least in part) by a computer processor, for example a processor of a smart phone or other portable electronic device. Such a comparison can be carried out using conventional image-processing software. In some embodiments, the smart phone or other portable electronic device provides 1009 an indication to the user as to the authenticity of the document following the comparison 1008. In other embodiments, a user may carry out the comparing step 1008 themselves, by comparing the first image to the reference image by eye. Optionally, prior to the capturing 1002 of the first image, the method may comprise an issuing authority capturing 1010 a reference image of the security document and, optionally, storing 1012 said reference image in a database. Optionally, the method may comprise a step of a smart phone or other portable electronic device downloading 1014 software to enable the processor of the portable electronic device to carry out one or more of steps 1004, 1005a, 1005b, 1006, 1008, 1009. In some embodiments the step of downloading comprises following 1015 a link to a downloadable version of the software on a remove server, for example an app store, for example a link contained in a machine readable image e.g. a QR code.

Thus methods in accordance with the present example may use the unique distribution of security devices in the substrate of a security document as a code to verify the authenticity of the security document. Additionally or alternatively, methods in accordance with the present invention may allow some or more of the steps in that verification process to be automated using a smart phone or other portable electronic device, thereby rendering the methods more user-friendly and/or practicable.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. 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 invention, 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 invention 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 invention, may not be desirable, and may therefore be absent, in other embodiments.