FIELD OF THE INVENTION

[0001 ] This invention is generally directed to a security documents and tokens, and is in particular directed to a diffractive optical element security device for providing validation of a security document or token. The present invention is also directed to a method of manufacturing security documents and tokens having the above-noted security device.

BACKGROUND OF THE INVENTION

[0002] A variety of different security devices have been developed for use on security documents and tokens to facilitate verification of that security document or token. One such development is the use of diffractive optical elements (DOEs) as a security device. These DOEs can generate a projected image when substantially collimated light from, for example, a point light source or laser is incident on the DOE.

[0003] Smart mobile phones are now commonly provided with a camera for taking photographs, and are therefore capable of photographing an image projected from a DOE. These smart phones also have the capacity to run various software applications on the phone. It would therefore be advantageous to have a security device which provides for verification of a security document or token using such smart mobile phone technology or other related electronic technology such as tablet computers and so on which incorporate a camera.

SUMMARY OF THE INVENTION

[0004] According to one aspect ot the present invention, there is provided a security device for a security document comprising a substrate, the security device being provided on or within the substrate and being in the form of a numerical-type diffractive optical element (DOE) for producing at least one barcode image when substantially collimated radiation is incident upon or transmitted through the diffractive optical element, wherein the barcode is in the form of a two dimensional "QR" barcode.

[0005] The DOE may be located on an outer surface of the substrate. It is also envisaged that the DOE may be located on an inner layer of the substrate. The DOE may be located on or in a transparent window or half window provided within the substrate of the security document. The QR barcode can then be revealed through transmission of substantially collimated light through the window area and therefore through the DOE. It is also envisaged that the QR barcode can be revealed by the reflection of substantially collimated light from the DOE, in which case the DOE can be located on any part of the substrate.

[0006] The QR barcode may be scanned by a smart mobile phone or other imaging device, e.g. by taking a photograph of the QR barcode, and an appropriate software application may then be used to read or decode the barcode and authenticate or verify the security document or token.

[0007] The security document may be a banknote, with the DOE security device located on the substrate of the banknote.

[0008] At least part of the DOE may be designed to operate in the visible part of the electromagnetic spectrum. In this case at least one QR barcode image produced by the DOE is visible to the naked eye when a point light source or other collimated light source is used to reveal the QR barcode. Alternatively, or additionally, at least part of the DOE may operate in a non-visible part of the electromagnetic spectrum, for example the IR region. In this case at least one QR barcode image produced by the DOE is not visible to the naked eye and can only be detected by the technology recording the image of the QR barcode, and not by the naked eye.

[0009] In one preferred embodiment, the DOE may be designed to produce a plurality of barcodes. For example, the security device may be in the form of a frequency selective DOE which can produce different QR barcode images at different pre-determined frequencies. This may be advantageous when only one of the QR barcodes is for public use, the other QR barcode(s) being for nonpublic use. Furthermore, it is envisaged that only one of the QR barcode images may be visible to the naked eye, the other image being covert in the IR or other non-visible region of the electromagnetic spectrum.

[0010] According to another aspect of the invention, there is provided a method of producing a security device for a security document comprising a substrate, and including applying a security device on or within the substrate, wherein the security device is a numerical type diffractive optical element (DOE) for producing at least one barcode image when substantially collimated radiation is incident upon or transmitted through the DOE, wherein the barcode is in the form of a two dimensional QR barcode.

[0011] The DOE security feature may be applied to the substrate by initially embossing the required diffractive optical element onto a transfer foil of metallic material, and transferring the foil bearing the diffractive optical element onto the required area of the security document in a hot stamping operation. Alternatively, the optical diffractive element may be formed by irradiation of an area of the substrate by laser ablation. It is also envisaged that the DOE security device may be formed from an embossed radiation curable ink, for example by using a method as described in the applicant's international patent application no. WO 2008/031 170.

[0012] According to a further aspect of the invention, there is provided a method of authenticating a security document which includes a security device in accordance with claim 1 , the method comprising: directing a substantially collimated beam of radiation so that it is incident upon or transmitted through the diffractive optical element (DOE) of the security device, and scanning the two dimensional QR barcode produced by the DOE, and decoding the QR barcode to authenticate the secu ity document. Preferably, in this method, the scanning and decoding of the two dimensional QR barcode is performed by a smart mobile phone.

[0013] The security device according to the present invention provides an authentication method that can be used by members of the public having access to a smart mobile phone. The security device may also be made specific to the currency of different countries and denominations by using a different QR barcode in each case. This can therefore provide another method for the public of distinguishing between different currencies.

DEFINITIONS

SECURITY DOCUMENT OR TOKEN

[0014] As used herein the term security documents includes all types of documents and tokens of value and identification documents including, but not limited to the following: items of currency such as banknotes and coins, credit cards, cheques, passports, identity cards, securities and share certificates, driver's licenses, deeds of title, travel documents such as airline and train tickets, entrance cards and tickets, birth, death and marriage certificates, and academic transcripts.

[0015] The invention is particularly, but not exclusively, applicable to security documents or tokens such as banknotes or identification documents such as identity cards or passports formed from a substrate to which one or more layers of printing are applied. The diffraction gratings and optically variable devices described herein may also have application in other products, such as packaging.

SECURITY DEVICE OR FEATURE

[0016] As used herein the term security device or feature includes any one of a large number of security devices, elements or features intended to protect the security document or token from counterfeiting, copying, alteration or tampering. Security devices or features may be provided in or on the substrate of the security document or in or on one or more layers applied to the base substrate, and may take a wide variety of forms, such as security threads embedded in layers of the security document; security inks such as fluorescent, luminescent and phosphorescent inks, metallic inks, iridescent inks, photochromic, thermochromic, hydrochromic or piezochromic inks; printed and embossed features, including relief structures; interference layers; liquid crystal devices; lenses and lenticular structures; optically variable devices (OVDs) such as diffractive devices including diffraction gratings, holograms and diffractive optical elements (DOEs).

SUBSTRATE

[0017] As used herein, the term substrate refers to the base material from which the security document or token is formed. The base material may be paper or other fibrous material such as cellulose; a plastic or polymeric material including but not limited to polypropylene (PP), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), polyethylene terephthalate (PET); or a composite material of two or more materials, such as a laminate of paper and at least one plastic material, or of two or more polymeric materials.

TRANSPARENT WINDOWS AND HALF WINDOWS

[0018] As used herein the term window refers to a transparent or translucent area in the security document compared to the substantially opaque region to which printing is applied. The window may be fully transparent so that it allows the transmission of light substantially unaffected, or it may be partly transparent or translucent partially allowing the transmission of light but without allowing objects to be seen clearly through the window area.

[0019] A window area may be formed in a polymeric security document which has at least one layer of transparent polymeric material and one or more opacifying layers applied to at least one side of a transparent polyme ic substrate, by omitting least one opacifying layer in the region forming the window area. If opacifying layers are applied to both sides of a transparent substrate a fully transparent window may be formed by omitting the opacifying layers on both sides of the transparent substrate in the window area.

[0020] A partly transparent or translucent area, hereinafter referred to as a "half-window", may be formed in a polymeric security document which has opacifying layers on both sides by omitting the opacifying layers on one side only of the security document in the window area so that the "half-window" is not fully transparent, but allows some light to pass through without allowing objects to be viewed clearly through the half-window.

[0021] Alternatively, it is possible for the substrates to be formed from an substantially opaque material, such as paper or fibrous material, with an insert of transparent plastics material inserted into a cut-out, or recess in the paper or fibrous substrate to form a transparent window or a translucent half-window area.

OPACIFYING LAYERS

[0022] One or more opacifying layers may be applied to a transparent substrate to increase the opacity of the security document. An opacifying layer is such that L _T < Lo, where L ₀ is the amount of light incident on the document, and L _T is the amount of light transmitted through the document. An opacifying layer may comprise any one or more of a variety of opacifying coatings. For example, the opacifying coatings may comprise a pigment, such as titanium dioxide, dispersed within a binder or carrier of heat-activated cross-linkable polymeric material. Alternatively, a substrate of transparent plastic material could be sandwiched between opacifying layers of paper or other partially or substantially opaque material to which indicia may be subsequently printed or otherwise applied.

DIFFRACTIVE OPTICAL ELEMENTS (DOES)

[0023] As used herein, the term diffractive optical element refers to a numerical-type diffractive optical element (DOE). Numerical-type diffractive optical elements (DOEs) rely on the mapping of complex data that reconstruct in the far field (or reconstruction plane) a two-dimensional intensity pattern. Thus, when substantially collimated light, e.g. from a point light source or a laser, is incident upon the DOE, an interference pattern is generated that produces a projected image in the reconstruction plane that is visible when a suitable viewing surface is located in the reconstruction plane, or when the DOE is viewed in transmission at the reconstruction plane. The transformation between the two planes can be approximated by a fast Fourier transform (FFT). Thus, complex data including amplitude and phase information has to be physically encoded in the micro-structure of the DOE. This DOE data can be calculated by performing an inverse FFT transformation of the desired reconstruction (i.e. the desired intensity pattern in the far field).

[0024] DOEs are sometimes referred to as computer-generated holograms, but they differ from other types of holograms, such as rainbow holograms, Fresnel holograms and volume reflection holograms.

EMBOSSABLE RADIATION CURABLE INK

[0025] The term embossable radiation curable ink used herein refers to any ink, lacquer or other coating which may be applied to the substrate in a printing process, and which can be embossed while soft to form a relief structure and cured by radiation to fix the embossed relief structure. The curing process does not take place before the radiation curable ink is embossed, but it is possible for the curing process to take place either after embossing or at substantially the same time as the embossing step. The radiation curable ink is preferably curable by ultraviolet (UV) radiation. Alternatively, the radiation curable ink may be cured by other forms of radiation, such as electron beams or X-rays.

[0026] The radiation curable ink is preferably a transparent or translucent ink formed from a clear resin material. Such a transparent or translucent ink is particularly suitable for printing light-transmissive security elements such as sub- wavelength gratings, transmissive diffractive gratings and lens structures.

[0027] In one particularly preferred embodiment, the transparent or translucent ink preferably comprises an acrylic based UV curable clear embossable lacquer or coating.

[0028] Such UV curable lacquers can be obtained from various

manufacturers, including Kingfisher Ink Limited, product ultraviolet type UVF-203 or similar. Alternatively, the radiation curable embossable coatings may be based on other compounds, eg nitro-cellulose.

[0029] The radiation curable inks and lacquers used herein have been found to be particularly suitable for embossing microstructures, including diffractive structures such as diffraction gratings and holograms, and microlenses and lens arrays. However, they may also be embossed with larger relief structures, such as non-diffractive optically variable devices.

[0030] The ink is preferably embossed and cured by ultraviolet (UV) radiation at substantially the same time. In a particularly preferred embodiment, the radiation curable ink is applied and embossed at substantially the same time in a Gravure printing process.

[0031] Preferably, in order to be suitable for Gravure printing, the radiation curable ink has a viscosity falling substantially in the range from about 20 to about 75 centipoise, and more preferably from about 30 to about 150 centipoise. The viscosity may be determined by measuring the time to drain the lacquer from a Zahn Cup #2. A sample which drains in 20 seconds has a viscosity of 30 centipoise, and a sample which drains in 63 seconds has a viscosity of 150 centipoise.

[0032] With some polymeric substrates, it may be necessary to apply an intermediate layer to the substrate before the radiation curable ink is applied to improve the adhesion of the embossed structure formed by the ink to the substrate. The intermediate layer preferably comprises a primer layer, and more preferably the primer layer includes a polyethylene imine. The primer layer may also include a cross-linker, for example a multi-functional isocyanate. Examples of other primers suitable for use in the invention include: hydroxyl terminated polymers; hydroxyl terminated polyester based co-polymers; cross-linked or uncross-linked hydroxylated acrylates; polyurethanes; and UV curing anionic or cationic acrylates. Examples of suitable cross-linkers include: isocyanates; polyaziridines; zirconium complexes; aluminium acetylacetone; melamines; and carbodi-imides.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Some preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0034] Figure 1 is a schematic perspective view of a security document having a security device according to the present invention;

[0035] Figure 2 is a detailed schematic view of a first embodiment of the security device of Figure 1 ; and [0036] Figure 3 is a detailed schematic view of a second embodiment of the security device of Figure 1.

DETAILED DESCRIPTION OF THE INVENTION

[0037] Referring initially to Figure 1 , there is shown a security document having a substrate 3. Located on the substrate 3 are one or more security devices 5 for the security document 1. The security device 5 may be in the form of a diffractive optical element (DOE) embossed on an upper surface 7 of the substrate 3. It is also envisaged that the DOE 5 may be located on an inner layer within the substrate 3.

[0038] Referring now to Figure 2, the security device 5 may be located over a window or half window area of the substrate 3. This then allows substantially collimated light from a point light source such as an LED light or laser to be transmitted through the substrate 3 and through the DOE thereby revealing a QR barcode 9. A photograph of the revealed QR barcode may then be taken by a smart phone, and the barcode 9 being read by an application stored within that smart phone. It is also envisaged that the DOE 5 may be held in front of a camera, and be directed to a point light source to reveal the DOE 5.

[0039] Alternatively, as shown in Figure 3, the DOE 5 can be located on any part of the substrate 3 or on a part of the substrate having a light reflective area. The QR barcode 9 can be revealed by reflecting substantially collimated light 2 from the DOE 5.

[0040] The security device according to the present invention can therefore provide a convenient means for the public to verify a security document using widely available smart mobile phone technology or related electronic technology.

[0041 ] Modifications and variations as would be deemed obvious to the person skilled in the art are included within the ambit of the present invention as claimed in the appended claims.