FR3004839A1 - DEVICE FOR SAFETY WITH DIFFRACTIVE OPTICAL ELEMENT FOR ENSURING THE VALIDATION OF A SECURITY DOCUMENT - Google Patents

Abstract

The invention relates to a security device (5) for a security document (1) comprising a substrate (3), the security device being provided on or in the substrate and in the form of an optical element. diffractive optical element (DOE) designed for the production of at least two-dimensional QR-bar code when a substantially collimated radiation is incident on or transmitted through the DOE. The QR barcode can be photographed and read by a smart phone or other imaging device to authenticate the security document.

Description

FIELD OF THE INVENTION The invention relates generally to documents and tokens of security, and more particularly to a security device with a diffractive optical element. to validate a document or security token. The present invention also relates to a method of manufacturing documents and security tokens comprising the aforementioned security device.

BACKGROUND OF THE INVENTION Various types of security devices have been developed for use on security documents and tokens for the purpose of facilitating the verification of this type of document or security token. One of these developments concerns the use of diffractive optical elements (DOEs) as safety devices. These DOEs can generate a projected image when a substantially collimated light from, for example, a point light source or a laser, is incident on the DOE. Smart mobile phones are now generally equipped with a camera to take photographs, and are therefore able to photograph a projected image of a DOE. These smart mobile phones also have the ability to run various software applications on the phone. It would therefore be advantageous to have a security device that verifies a document or security 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 According to one aspect of the present invention, there is provided a security device for a security document comprising a substrate, the security device being provided on or in the substrate and in the form of a security document. diffractive optical element (DOE) of digital type for producing at least one barcode image when a substantially collimated radiation is incident on or transmitted through the diffractive optical element, the barcode being in the form of a "QR" barcode (two-dimensional Quick Response abbreviation). The DOE may be located on an external surface of the substrate. It is also contemplated 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 within the security document substrate. The QR barcode can then be revealed by the transmission of substantially collimated light through the window area and therefore through the DOE. It is also contemplated that the QR bar code may be revealed by the reflection of a substantially collimated light from the DOE, in which case the DOE may be located on any portion of the substrate. The QR barcode can be scanned by a smart mobile phone or other imaging device, for example by taking a photograph of the QR barcode and an appropriate software application can then be used to read or decode the code. -barres and to authenticate or verify the document or the security token. The security document may be a bank note with the DOE security feature located on the banknote substrate.

At least a portion of the DOE may be designed to operate in the visible portion 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 in addition, at least a portion of the DOE may operate in a non-visible portion of the electromagnetic spectrum, for example in the infrared 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. In a 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 predetermined frequencies.

This may be advantageous when only one of the QR barcodes is for public use, the other (other) QR barcode (s) being intended for non-public use. In addition, it is contemplated that only one of the QR barcode images could be visible to the naked eye, the other image being converted into an infrared zone or other non-visible area of the electromagnetic spectrum.

According to another aspect of the invention, there is provided a method for producing a security device for a security document comprising a substrate, and comprising applying a security device on or in the substrate, in a wherein the security device is a digital type diffractive optical element (DOE) for producing at least one barcode image when a substantially collimated radiation is incident on or transmitted through the DOE, which barcode is in the form of a two-dimensional QR barcode. The security feature of the DOE may be applied to the substrate by initially embossing the required diffractive optical element on a metal material transfer film and transferring the film carrying the diffractive optical element to the required area of the security document in part of a hot stamping procedure. Alternatively, the diffractive optical element can be formed by irradiating an area of the substrate by laser ablation. It is also contemplated that the DOE security device may be formed from a relief-embossed radiation-curable ink, using, for example, a method described in International Patent Application no. WO 2008/031170 of the applicant. According to another aspect of the invention there is provided a method of authenticating a security document which comprises a security device according to claim 1, the method comprising the steps of: directing a substantially collimated radiation beam so that it is incident on or transmitted through the diffractive optical element (DOE) of the security device and scan the bidimensional QR bar code produced by the DOE, and decode the QR barcode to authenticate the document of security. Preferably, in this method, the scanning and decoding of the QR two-dimensional bar code is performed by a smart mobile phone. 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 can also be made specific to the currency of different countries and different denominations by using a different QR barcode in each case. This can therefore provide the public with another method of distinguishing between different currencies. DEFINITIONS SECURITY DOCUMENT OR TOTE As used in this document, the term security documents refers to all types of documents and tokens and identification documents including, but not limited to, monetary items such as banknotes and coins, credit cards, checks, passports, identity cards, securities and stock certificates, driver's licenses, title deeds, travel documents such as airline and train tickets, cards and admission tickets and birth, death and marriage certificates and official documents. 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 is / are applied one or more printing layers. The diffraction gratings and devices with variable optical properties described herein may also have application in other products such as packaging.

SECURITY DEVICE OR CHARACTERISTIC As used herein, the term device or security feature refers to any device of a large number of intended security features, elements, or security features. for the protection of documents or security tokens against counterfeiting, copying, modification or falsification. The devices or security features may be provided in or on the security document substrate or in or on one or more layers applied to the base substrate and may take a variety of forms, such as security 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 elements, including relief structures; interference layers; liquid crystal devices; lentils and lenticular structures; devices with variable optical properties (OVDs) such as diffractive devices, such as diffraction gratings, holograms and diffractive optical elements (DOEs). SUBSTRATE As used herein, the term substrate refers to a base material from which the document or security 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 paper laminate and at least one plastic or two or more polymeric materials. TRANSPARENT WINDOWS AND HALF WINDOWS As used herein, the term window refers to a transparent or translucent area in the security document compared to the substantially opaque area on which printing is applied. The window may be completely transparent so as to allow the transmission of substantially unaffected light, or it may be partially transparent or partially translucent allowing light transmission but without allowing objects to be clearly visualized through the window. A window area may be formed in a polymeric security document that has at least one layer of transparent polymeric material and one or more opacifying layers applied to at least one side of a transparent polymeric substrate, by omission of at least one layer opacifying in the region forming the window area. If the opacifying layers are applied to both sides of a transparent substrate, it is possible to form a completely transparent window by omitting the opacifying layers on both sides of the transparent substrate in the window area. It is possible to form a partially transparent or translucent zone, hereinafter referred to as "half-window", in a polymeric security document that has opacifying layers on both sides, by omitting the opacifying layers on only one side of the document in the window area so that the "half-window" is not completely transparent, but allows some light to pass through without allowing objects to be clearly viewed through half window. Alternatively, it is possible to form the substrate from a substantially opaque material, such as paper or fibrous material, with a transparent plastic insert introduced into a slot or recess of the fibrous paper or substrate to forming a transparent window or a translucent half-window area. OPACIFYING LAYERS One or more opacifying layers can be applied to a transparent substrate to increase the opacity of the security document. An opacifying layer is such that LT <L0, where Lo is the amount of light incident on the document, and LT is the amount of light transmitted through the document. An opacifying layer may include one or more opacifying layer varieties. For example, the opacifying coatings may consist of a pigment such as titanium dioxide, dispersed in a binder or a crosslinkable polymeric material activated by heat. On the other hand, a transparent plastic substrate could be sandwiched between opacifying layers of paper or other partially or substantially opaque material on which indicia can be subsequently printed or otherwise applied. DIFFRACTIVE OPTICAL ELEMENTS (DOE) As used herein, the term diffractive optical element refers to a digital type diffractive optical element (DOE). Digital-type diffractive optical elements (DOEs) rely on complex data mapping that reconstructs a two-dimensional form of intensity in the far field (or in the reconstruction plane). Therefore, when a substantially collimated light, from, for example, a point light source or a laser, is incident on the DOE, an interference pattern is generated that produces a projected image in the reconstruction that is visible when a suitable viewing surface is located in the reconstruction plane, or when the DOE is viewed during transmission at the reconstruction plane. The transformation between the two planes can be determined approximately by a fast Fourier transform (FFT for fast Fourier transform). As a result, complex data, including amplitude and phase information, must be physically encoded into the DOE microstructure. These DOE data can be calculated by performing an inverse FFT transformation of the desired reconstruction (i.e. the desired intensity form in the far field). DOEs are sometimes called computer-generated holograms, but they differ from other types of holograms, such as rainbow holograms, Fresnel holograms, and reflective volume holograms.

RADIATION-CURABLE INK-CURABLE INK The term embossable radiation-curable ink used herein refers to any ink, varnish, or other coating that may be applied to the substrate as part of a process. and which may be embossed while soft / soft to form a relief structure and which is radiation-cured to fix the embossed structure. The curing process does not take place until the radiation-curable ink is etched, but it is possible that the curing process takes place after the embossing or at substantially the same time as the etching step. in relief. The radiation curable ink is preferably curable by ultraviolet radiation (RU). Alternatively, the radiation curable ink may be cured by other forms of radiation such as electron beams or X-rays. The radiation-curable ink is preferably a clear or translucent ink formed from a transparent resinous material. Such transparent or translucent ink is particularly suitable for printing reflective security elements such as wavelength gratings ("sub-wavelength gratings" in English terminology), transmissive diffractive gratings (" In a particularly preferred embodiment, the transparent or translucent ink comprises a lacquer or an acrylic-based, ultraviolet-curable and etchable transparent coating. Such UV-curable lacquers can be obtained from various manufacturers, including Kingfisher Ink Limited, for example UV-curable UVF-203 or the like, or radiation-curable coatings capable of being embossed. may be based on other compounds, for example nitro-cellulose.

The radiation curable inks and varnishes used in this document have been found to be particularly suitable for relief etching microstructures, including diffractive structures such as diffraction gratings and diffraction holograms, as well as microlenses and gratings. of lentils. However, they can be embossed with larger relief structures, such as devices with variable non-diffractive optical properties. The ink is preferably embossed and cured by ultraviolet (UV) radiation essentially at the same time. In a preferred embodiment, the radiation curable ink is applied and embossed substantially at the same time as part of a gravure printing process. Preferably, so as to be usable in a gravure printing process, the radiation curable ink should have a viscosity substantially in the range of about 20 to about 175 centipoise, and preferably about 30 to about 150 centipoise. The viscosity can be determined by measuring the emptying time of the varnish from a Zahn # 2 cut. A sample that flushes in 20 seconds at a viscosity of 30 centipoise and a sample that empties in 63 seconds has a viscosity of 150 centipoise.

With some polymeric substrates, it may be necessary to apply an interlayer to the substrate prior to application of the radiation curable ink to improve 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 contains a polyethylene imine. The primer layer may also contain a crosslinking agent, such as, for example, a multifunctional isocyanate. Examples of other primer layers that may be used in the invention include: hydroxyl terminated polymers; hydroxyl-terminated polyester copolymers; crosslinked or uncrosslinked hydroxylated acrylates; polyurethanes; and anionic or cationic ultraviolet curing acrylates. Examples of crosslinking agents that may be used include: isocyanates; polyaziridines; zirconium complexes; aluminum acetylacetone; melamines; and carbodiimides.

BRIEF DESCRIPTION OF THE DRAWINGS Some preferred embodiments of the present invention will now be described, by way of illustration only, with reference to the accompanying drawings in which: FIG. 1 is a schematic perspective representation of a security document according to the present invention; Fig. 2 is a detailed schematic representation of a first embodiment of the security device of FIG. 1; and FIG. 3 is a detailed schematic representation of a second embodiment of the security device of FIG.

DETAILED DESCRIPTION OF THE INVENTION Referring initially to FIG. 1, there can be seen a security document 1 having a substrate 3. On the substrate 3 are located one or more security devices 5 for the security document 1. The security device 5 can be in the form of an element diffractive optics (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 in the substrate 3. Referring now to FIG. 2, the security device 5 can be located over a window or half-window area of the substrate 3. This then allows a substantially collimated light from a point light source such as an LED or laser light to be transmitted through the substrate 3 and through the DOE thus revealing a QR barcode 9. A photograph of the QR barcode revealed can then be taken by a smart mobile phone and the barcode 9 can be read by an application stored in this smart mobile phone. It is also contemplated that the DOE can be held in front of a camera and pointed at a point light source to reveal the DOE 5. Alternatively, as shown in FIG. 3, the DOE 5 may be located on any part of the substrate 3 or on a portion of the substrate having a light reflecting area. The QR bar code 9 can be revealed by reflecting a substantially collimated light 2 from the DOE 5. The security device according to the present invention can therefore provide a convenient means for the public to verify a security document using a technology. intelligent mobile phone or related electronic technology widely available. Modifications and variations judged obvious to those skilled in the art are included within the scope of the present invention as set forth in the appended claims.

Claims (4)

1. A security device (5) for a security document (1) characterized in that the security document comprises a substrate (3), and in that the security device is provided on or in the substrate and is in the form of a digital type diffractive optical element (DOE) designed to produce at least one barcode image when a substantially collimated radiation (2) is incident on or transmitted through the diffractive optical element, said barcode being in the form of a two-dimensional QR code bar. 2. Safety device according to claim 1, characterized in that at least a portion of the DOE is designed to operate in the visible part of the electromagnetic spectrum so that at least one barcode image produced by the DOE is visible at the naked eye, and / or at least a portion of the DOE is designed to operate in the non-visible portion of the electromagnetic spectrum so that at least one bar code image produced by the DOE is not visible to the eye bare. 3. Safety device according to claim 1 or claim 2, characterized in that the safety device is in the form of a frequency selective SEEs capable of producing different bar codes at different predetermined frequencies. 4. Security document (1), preferably a banknote, characterized in that the security document comprises a security device (5) according to any one of the preceding claims. . Security document according to claim 4, characterized in that the DOE is located in a transparent window or half-window of the security document. A method of producing a security device (5) for a security document (1) comprising a substrate (3), characterized in that the method comprises applying a security device to or on the substrate, the device security device being a digital type diffractive optical element (DOE) for the production of at least one barcode image when a substantially collimated radiation is incident on or transmitted through the DOE, said bar code being under the shape of a two-dimensional QR barcode. 7. A method of producing a security device according to claim 6 characterized in that the method comprises an application of the DOE over a window or a half-transparent window included in the substrate. The method of producing a security device according to claim 6 or claim 7, characterized in that the method comprises forming the DOE on the substrate using a relief-etched radiation-curable ink. A method of authenticating a security document (1) which comprises a security device (5) according to claim 1, characterized in that the method comprises the steps of: directing a substantially collimated radiation beam (2 ) so that it is incident on or transmitted through the diffractive optical element (DOE) of the security device, and scan the bidimensional QR bar code produced by the DOE and decode the QR barcode to authenticate the document of sécurité.10. Method according to claim 9, characterized in that the scanning and decoding of the QR two-dimensional bar code is performed by a smart mobile phone.