Method for producing a security device with at least a first image visible at a first angle and a second image visible at a second angle, security device obtained by the method and identity document containing the security device

Abstract

The invention relates to a method for manufacturing an identity document (10) from a laser device emitting laser radiation and comprising a processing system, comprising the steps of: - supplying the identity document comprising at least one window (16), a metallic patch (18) and an ink layer (22) reacting to a second radiation (30), - receiving, by the laser processing system, data relating to a first pattern (24), intended to be observable on the metallic patch (18) under visible radiation (19), - decomposing the first pattern (24) into gray-level pixels, each gray level of the pixel corresponding to a dimension of at least one perforation (20) of the patch, - determining a minimum perforation dimension (32) (20) transmitting the second radiation (30), - assigning the minimum perforation dimension (32) to a gray level of the pixel among the ten percent darkest gray levels,- and application of laser radiation to the patch so as to create perforations (20) forming the first pattern (24) observable under visible radiation (19) and forming a second pattern (28) observable under the effect of the second radiation (30.,

Description

[0001] The invention relates to identity documents and their security features.

[0002] More specifically, it relates to an identity document comprising a security element positioned in a transparent window and comprising a metal patch forming a pattern by perforating said patch.

[0003] Identity documents comprising such patches are known from the prior art. This is described in patent application EP0956975 which discloses a protective element in an identity card containing a non-transparent metal layer reflecting incidentally directed light, and comprising characters or patterns obtained with laser radiation by local removal of the metal layer.

[0004] The present invention proposes to improve the security of such documents by adding a layer of ink observable under radiation outside the visible spectrum. The layer of ink associated with the metal patch adds an additional level of security to the identity document.

[0005] To this end, the invention relates to a method for manufacturing an identity document from a laser device emitting laser radiation and comprising a processing system, comprising the following steps: Contribution to the laser device of the identity document comprising at least one window comprising two transparent plastic layers, a metal patch and an ink layer reacting to a second radiation of wavelength shorter than that of the visible radiation and positioned partially opposite the metal patch, the metal patch and the ink layer being arranged substantially opposite one another so as to obtain a superposition of the ink layer and the metal patch in observation perpendicular to the plane of the document, the metal patch being adapted to be perforated under the action of the laser radiation, Reception, by the laser processing system, of data relating to a first pattern, intended to be observable on the metal patch under visible radiation, Decomposition, by the laser processing system, of the first pattern into gray level pixels,each gray level of the pixel corresponding to a dimension of at least one perforation of the metal patch in a perforation zone, Determination of a minimum perforation dimension transmitting the second radiation reflected through the ink layer under determined conditions, Allocation, by the laser processing system, of the minimum perforation dimension to a gray level of the pixel among the ten percent of the darkest gray levels, Application of the laser radiation to the patch so as to produce perforations forming the first pattern observable under visible radiation and forming a second pattern observable under the effect of the second radiation, under the determined conditions.

[0006] Thanks to these provisions, the identity document presents two patterns with distinct contours when viewed respectively under visible radiation and under a second radiation, the two patterns being produced in a single metal patch. Part of the elements dedicated to the definition of the first pattern are used, in association with the UV ink, to define the second pattern.

[0007] It is thus possible to produce, in a single manufacturing step, the elements defining the first pattern and those dedicated solely to the second pattern.

[0008] This allows for a rapid manufacturing process to produce an identity document secured by two personalized and difficult-to-reproduce designs.

[0009] Other advantageous and non-limiting characteristics of the method according to this first embodiment, taken individually or in all technically possible combinations, are the following:the minimum dimension is assigned to the darkest gray level of a pixel, the method further comprises a step by the processing system of replacing a perforation dimension of a gray level among the 90% least dark by a minimum dimension, the method further comprises a step of receiving by the laser processing system data relating to the second pattern intended to be formed by perforation of the metal patch and intended to be observable under the second radiation, and prior to the assignment step, the method comprises a step of determining the position of the perforations of dimensions equal to or greater than the minimum dimension assigned to the second pattern, and the step of assigning the minimum perforation dimension to a gray level of the pixel being carried out so as to visualize the second pattern under the second radiation and the first pattern under visible radiation,in which the ink layer reacts under ultraviolet radiation, the perforation has substantially the shape of a disc and the minimum dimension is a diameter of the disc and has a length of 19nm. The invention also relates to an identity document obtained by the manufacturing method described above, the document comprising a plastic body provided with a transparent window comprising transparent plastic layers between which are positioned a metal patch and an ink layer sensitive to a second radiation of wavelength shorter than that of visible radiation, the metal patch and the ink layer being arranged substantially opposite one another so as to obtain a superposition of the ink layer and the metal patch in observation perpendicular to the plane of the document, and in which the metal patch comprises perforations forming a first pattern decomposable into grayscale pixels and observable under visible radiation and forming a second pattern observable under the effect of a second radiation, under determined conditions, perforations having at least one minimum perforation dimension, the minimum perforation dimension being assigned to a gray level of the pixel among the ten percent of the darkest gray levels.

[0010] According to other characteristics of the document, the metal patch is a thin metal sheet or a layer of metal oxide with a thickness of less than 35nm, the ink layer reacts to ultraviolet radiation, the metal patch and the ink layer are positioned at the interface of two transparent plastic layers, the document has a second metal patch positioned on one of the transparent plastic layers, on the side opposite the interface.

[0011] The invention also relates to a method for authenticating an identity document obtained by the manufacturing method described above, comprising the following steps: Positioning the document window on an opaque background blocking visible light, acquiring data from the identity document under visible radiation, projecting ultraviolet radiation onto the face of the identity document so that the UV ink is positioned under the metal patch, acquiring the second pattern observable under UV radiation, verifying the second pattern with a reference element, authenticating the document if the verification is approved.

[0012] Other embodiments and advantages of the invention are described below with reference to the figures, in which: There figure 1a represents a front view of an identity document according to the invention, represented in the form of a card, under ambient light, in transmission, that is to say positioned at a distance from an opaque background so that the light passes through the card and is not reflected, The figure 1b represents the same view as the figure 1a , in reflection mode, that is to say positioned near or on an opaque background, the figure 1c is a detailed view of the map of figures 1a et 1b , there figure 2a is a front view of a card according to the invention under a second radiation, in transmission, The figure 2b represents the same view as the figure 2a , in reflection mode, that is to say positioned near or on an opaque background, The figures 3a And 3b represent the path of one or more light rays of the second radiation through the card according to the invention, The figures 4 et 5 represent two different card structures that can be applied to the present invention, the figure 6 represents a detailed view of the perforation areas.

[0013] In the representation of the drawings, scale and proportions are not respected in order to increase clarity. In addition, in the listed figures, similar features may have the same reference.

[0014] The identity document 10 according to the invention may be an identity card, a driving license, a bank card, a credit card, an official document in the form of a booklet, such as a passport. These identity documents are used to verify the identity of their holder.

[0015] The identity document 10 according to the invention comprises at least one assembly 12 of plastic layers, such as polycarbonate traditionally used for this type of document. When the identity document 10 is in the form of a card, it consists of an assembly 12 of at least two plastic layers in ID-1 bank card format as specified in the ISO 7810 standard. When the identity document is in the form of a passport, it consists of a paper booklet to which is assembled a data page in ID-3 format, as specified in the ISO 7810 standard, the data page being made up of an assembly of several plastic layers. Generally the assembly 12 of the plastic layers comprises printing over the entire surface of the plastic layers, making the assembly non-transparent under ambient light.

[0016] The invention relates to the integration of a security element 14. To this end, so that the security element 14 can be seen in transmission or reflection, it is integrated into a transparent window 16 of the identity document 10. It is known from the prior art to produce a transparent window 16 in an assembly of partially or totally opaque printed layers. For example, patent FR3045432 describes the production of such windows 16.

[0017] On the figures 3 à 6 , the window is made of two transparent plastic layers 16a, 16b. For reasons of simplification, the figures 3 à 6 of the present application represent a sectional view of a part of the document comprising only two plastic layers. But a more complex assembly requiring a higher number of plastic layers is conceivable in the present invention to produce the assembly 12 of the document and the window.

[0018] The security element 14 can be visible in transmission, that is to say when incident radiation passes through the transparent plastic layers 16a, 16b, or in reflection, that is to say when incident radiation passes through the transparent plastic layers 16a, 16b and is then reflected by an opaque background 17 in front of which the identity document 10 is positioned.

[0019] The present invention relates particularly to the security element 14 integrated into the identity document 10. This security element 14 is formed of a metal patch 18 consisting of a thin metal layer diffracting the incident light deposited on a support and forming a hologram or element producing a variable colored effect depending on the lighting and observation directions. For example, patent WO 01 / 07268 describes such a patch with a holographic effect. The metal patch 18 is produced by techniques known to those skilled in the art working in the field of holography. The metal patch 18 is sandwiched between two transparent plastic layers forming the window 16 of the document as described further on.

[0020] The metal patch 18 is made up of a thin metal sheet 10 to 20 nanometers thick or a metal oxide coating with a thickness of between 5 and 35nm, less than 35nm. The metal patch 18 comprises an arrangement of diffractive nanostructures making it possible to diffract light at least in the visible range. The metal patch 18 may comprise at least one of the following materials: aluminum, silver, copper, zinc sulfide, titanium oxide.

[0021] The metal patch 18 further comprises perforations 20 passing through the thickness of the patch and of different dimensions to reveal a first personalized pattern 24. Indeed, the pattern to be produced is broken down into a set of perforation zones 26, perforated or not, each forming a pixel. Each perforation zone 26, of which only one zone is illustrated schematically on the figure 1c for reasons of illustration simplification, or pixel, can be perforated one or more times, or even be made without perforations, the number and size of the perforations 20 defining the gray level of the pixel of the pattern. By gray level of the pixel, we mean a value on a gray scale defining all the gray tones used in an image. The number of gray gradient levels makes it possible to define the size of the scale, for example, a scale of 256 gray levels is known, ranging from the darkest gray level, seen as black by an observer, and the lightest gray level seen as white by an observer. This scale of 256 values ​​is given only as an example and the terms "darkest" or "lightest" will be used to express the extreme values ​​of the scale.

[0022] The gray level of the pixel also depends on the observation mode of the metal patch 18. In transmission, the lightest pixel is associated with the perforation 20 of maximum dimension and the maximum number of perforations 20 per perforation zone, and the darkest pixel is associated with a non-perforated perforation zone. Conversely, in reflection, the darkest pixel is associated with the perforation of maximum dimension and the maximum number of perforations 20 per perforation zone, and the lightest pixel is associated with a non-perforated perforation zone. For information purposes, four examples of perforations 20 of different dimensions and each made in a perforation zone 26 are illustrated in the figure 6 .

[0023] In order to simplify the description of the application, the formation of the first pattern 24 will be carried out using a method forming a single perforation 20 per perforation zone 26. The figure 1c schematically illustrates areas 26 perforated with perforations 20 of respective diameters d1, d2 and d3, such that d1 <d2<d3. Ainsi, en transmission, la partie du patch perforée avec des perforations 20 de diamètre d3 apparaît plus clair que celles perforées avec des perforations 20 de diamètre d1 ou d2. Inversement, en réflexion, la partie du patch perforée avec des perforations de diamètre d3 apparaît plus foncée que celles perforées avec des perforations 20 de diamètre d1 ou d2.

[0024] These perforations 20 are produced by focusing laser radiation emitted for example by a YAG type laser device emitting laser radiation of wavelength 1063nm, focal length 98.3, on the metal layer, through the thickness of the transparent plastic layer, to carry out local ablation of the metal patch 18 by sublimation of the material. The transparent plastic layer is made of a material that is not sensitive to the laser, so as not to be marked by the passage of the radiation through its thickness. The laser radiation is adapted to produce perforations 20 of different dimensions, namely of different diameters for perforations 20 of substantially circular shape.

[0025] In transmission, that is to say when the incident light of a visible radiation 19 passes through the identity document 10, the first pattern 24 obtained has pixels with light gray levels in the areas 26 comprising perforations 20 of rather large dimensions and darker pixels with darker gray levels in the areas 26 not perforated or comprising perforations of rather small dimensions. This is illustrated schematically by the figure 1a in which the hair 24a has a light gray level, the eyes 24b and lips have a dark gray level, and the cheeks 24c and forehead have a gray level even darker than that of the eyes 24b and lips.

[0026] In reflection, that is to say when the window 16 of the identity document 10 is positioned on an opaque background 17 which does not allow the incident light of the visible radiation 19 to pass through and partially reflects it, the incident light of the visible radiation 19 passes through the document, but the opaque background 17 is visible through perforations 20. This is illustrated by the figure 1b wherein the hair 24a has a dark gray level, the eyes 24b and lips have a lighter gray level than the hair 24a, and the cheeks 24c and forehead have an even lighter gray level than the eyes 24b and lips.

[0027] The pattern seen in reflection is therefore similar to that seen in transmission, but with black and white color effects, or inverted gray levels. Thus a pixel classified as "light" in transmission will be seen as "dark" in reflection, the intensity of the "light" color being defined by the intensity of the incident light ray, and the intensity of the "dark" level depending on the color of the opaque background 17 on which the window 16 is positioned. The aim here is to determine a color intensity scale ranging from a lightest level to a darkest gray level, under a given lighting and opaque background 17.

[0028] The present invention proposes to produce a second security pattern 28 in the same metal patch 18 without interfering with the observation of the first pattern 24 under visible radiation 19. It is thus possible to integrate a second pattern 28 in the metal patch 18 while keeping intact the effect of the first pattern 24 under observation under ambient light.

[0029] To this end, the present invention proposes adding a layer of ink 22 reacting to a second radiation 30 of shorter wavelength than that of the visible radiation 19, such as Ultra-Violet radiation 30, as illustrated in the figure 2a The layer is for example an ink transparent under visible radiation 19 and sensitive to Ultra-violet radiation 30 by changing color under the action of UV radiation 30. The ink layer 22 is positioned partially opposite the metal patch 18 as visible on the figures 2a , 2b And 3 à 6 , under the metal patch 18 relative to the observer's positioning.

[0030] Thus when the document is observed, in transmission in a direction perpendicular to the plane of the document under the effect of the second radiation 30, the ink changes color and the perforated zones 26 transmit the color emitted by the ink under the second radiation. This effect is schematically illustrated by the figure 3a , in which all the perforations 20 allow the ultraviolet radiation 30 to pass through in transmission, and the first pattern 24 colored by the ink excited under the ultraviolet radiation 30 is then observed under ultraviolet radiation 30. This is illustrated in figure 2a in which the hair 24a', the eyes 24b', the lips, the cheeks 24c' and the forehead have a color specific to the ink when it is excited under the second radiation 30.

[0031] When the document is observed under determined conditions, that is to say observed in reflection, in a determined direction, for example perpendicular, relative to the plane of the document, under the effect of the second radiation 30, the ink 22, excited by the second radiation 30, transmits the latter in another color and only a part of the perforations 20 transmit the colored light emitted by the ink under the effect of the second incident radiation 30. It will be considered in the present invention that the light re-emitted by the ink layer 22 is of the same wavelength as that of the second radiation 30 which excites it. This effect is schematically illustrated by the figure 3b , in which only the perforations 20 whose dimensions are equal to or greater than the minimum dimension 32 allow the reflected ultraviolet radiation 30 to pass through, then transmitted by the ink. The second pattern 28 observable under ultraviolet radiation 30 has a different outline from that of the first pattern 24. The minimum dimension 32 is determined by the second incident radiation 30, the observation mode, i.e. in reflection, and the observation direction.

[0032] For Ultra-violet radiation 30, the minimum dimension 32 has approximately the shape of a disc with a diameter of 19nm. figure 6 schematically illustrates a perforation 20 of minimum dimension 32 defined in the perforation zone 26.

[0033] The second pattern 28, observable under ultraviolet radiation 30, in reflection, is schematically illustrated by the figure 2b The reflected ultraviolet radiation 30 is transmitted only by the perforations 20 having a dimension greater than or equal to the minimum dimension 32. These perforations 20 are shown on the figure 2b at the level of the hair 28a, the eyes 28b and the lips 28b. On the other hand, the perforations 20 of the cheeks and the forehead have a dimension smaller than that of the minimum dimension 32 and therefore do not allow the second reflected radiation 30 to pass.

[0034] A document is thus obtained from which it is possible to observe a first pattern 24 under visible radiation 19, the visible radiation 19 passing through all the perforations 20 and to observe a second pattern 28 from the perforations 20 of the first pattern 24 whose dimensions are greater than or equal to the minimum dimension 32.

[0035] To obtain a document according to the invention, the following manufacturing method will be implemented by the laser device emitting laser radiation and comprising a processing system. The method comprises a prior step of providing, on the laser device, an identity document comprising at least one window 16 comprising at least two transparent plastic layers 16a, 16b, a metal patch 18 and an ink layer 22 being sandwiched between the plastic layers 16a, 16b.

[0036] As indicated previously, the ink layer 22 is printed partially or totally opposite the metal patch 18, that is to say below the metal patch 18 when the document is observed in a direction perpendicular to its plane, and the ink layer 22 reacts, that is to say is excited, under the incidence of a second radiation 30 of wavelength shorter than that of the visible radiation 19.

[0037] To implement the manufacturing method, the laser device is adapted to perforate the metal patch 18. For this purpose, the processing system of the laser device is adapted to process data which will be used to control the positioning of the laser beam perforating the metal patch 18. For this, the manufacturing method comprises a step of reception by the laser processing system of data relating to the first pattern 24. Then the processing system carries out a step of decomposition of the first pattern 24 into gray level pixels, each gray level of the pixel corresponding to a dimension of at least one perforation in a perforation zone.

[0038] Then the manufacturing method comprises a step of determining the minimum dimension 32 of perforation allowing the second radiation 30 to pass through. The value of the minimum dimension 32 can vary according to the observation conditions and the second radiation 30 chosen. It will be determined beforehand and transmitted to the processing system, or directly determined by the processing system, according to the observation conditions of the second pattern 28. In the present invention, the second pattern 28 is considered to be observed in a direction perpendicular to the plane of the document, in reflection, under incidence of the second radiation 30. When the second radiation 30 is an ultraviolet radiation, it has been found that the minimum dimension 32 of perforation allowing the ultraviolet radiation 30 to pass through is in the form of a disc with a diameter of 19nm.

[0039] The manufacturing method then comprises a step of assigning the minimum perforation dimension 32 to a pixel gray level of the first pattern 24. Thus, all the pixels having this assigned gray level will be formed from the creation of a perforation of dimension at least equal to the minimum dimension 32. To create the second pattern 28, the assigned gray level is chosen from the darkest 10% of gray levels. Preferably, the minimum perforation dimension 32 is assigned to the darkest gray level in the pixel gray scale.

[0040] It is then possible to carry out the perforation step by local ablation of the metal patch 18 so as to produce all of the perforations 20 forming both the first pattern 24 observable under visible radiation 19 and forming the second pattern 28 observable under the determined conditions, namely under ultraviolet radiation 30 and in reflection.

[0041] According to a variant, it is also possible to carry out, by the processing system, the replacement of a perforation dimension of a gray level among the 90% least dark by a minimum dimension 32, so as to form the second pattern 28 without however modifying the first pattern 24 observable under visible radiation 19. It is preferable in this case that the replaced perforations 20 are isolated, that is to say not neighboring, from the other perforations 20 of dimensions equal to or greater than the minimum dimensions so as not to modify the perception of the first observed pattern 24.

[0042] The perforations 20 of dimensions equal to or greater than the minimum dimensions are thus dedicated to the formation of the second pattern 28 observable under determined conditions.

[0043] According to an alternative embodiment, the processing system receives data relating to the second pattern 28 intended to be formed by perforation of the metal patch 18 and intended to be observable under the second radiation 30. The processing system then defines the position of the perforations 20 dedicated to the second pattern 28, these perforations 20 each having dimensions greater than or equal to the minimum dimensions. Then the processing system assigns the minimum perforation dimension 32 32 to a gray level of the pixel so as to visualize the second pattern 28 under the second radiation 30, in reflection and the first pattern 24 under visible radiation 19.

[0044] The manufacturing method makes it possible to obtain an identity document 10 with two security patterns. The identity document 10 comprises a plastic body provided with a transparent window 16 formed from transparent plastic layers 16a, 16b between which the metal patch 18 and the ink sensitive to the second radiation 30 are positioned. The ink and the patch are arranged substantially opposite each other so as to obtain a superposition of the ink and the patch when observed perpendicular to the plane of the identity document 10.

[0045] As indicated previously, the metal patch 18 of the document is a thin metal sheet reflecting the incident light and the ink is excited under the second incident radiation 30, for example ultraviolet radiation. The patch and the ink have negligible thicknesses compared to the thicknesses of the plastic layers 16a, 16b constituting the window 16. The metal patch 18 and the ink layer 22 are positioned at the interface of two transparent layers, without deforming and creating excess thickness in the plastic layer.

[0046] Several embodiments are illustrated on the figures 4 à 6 . There figure 4 illustrates an embodiment in which the metal patch 18 is positioned at the interface of the two transparent plastic layers 16a, 16b of the window 16, and the ink layer 22 is positioned below the interface layer of the patch 18. The ink 22 and the patch 18 are not in direct contact, but produce the technical effects described further in the description.

[0047] There figure 5 illustrates a more complex embodiment involving two metal patches 18a, 18b. It is thus possible to engrave the two patches 18a, 18b in order to secure the front face and the rear face of the window 16 by hiding information.

[0048] The document described in the present invention is used in the context of a method for authenticating an identity document 10. This method is implemented by a step of positioning the window 16 of the document on an opaque background 17 blocking visible light, then reading / acquiring data from the identity document 10 under visible radiation 19. Then the document is illuminated under a second radiation 30, namely Ultra-violet radiation on the face of the identity document so that the UV ink is positioned under the metal patch 18. It is then possible to acquire the second pattern 28 visible under UV radiation and to verify this second pattern 28 with a reference element, for example the first pattern 24. If the two patterns correspond, the verification is approved and the authentication of the document is validated.

Claims

1. Method for manufacturing an identity document (10) from a laser device emitting laser radiation and comprising a processing system, comprising the following steps: Providing the identity document on the laser device comprising at least one window (16) comprising two transparent plastic layers (16a, 16b), a metal patch (18) and an ink layer (22) reacting to a second radiation (30) of wavelength shorter than that of the visible radiation (19) and positioned partially opposite the metal patch (18), the metal patch (18) and the ink layer (22) being arranged substantially opposite one another so as to obtain a superposition of the ink layer (22) and the metal patch (18) in observation perpendicular to the plane of the document, the metal patch (18) being adapted to be perforated under the action of the laser radiation; Receiving, by the laser processing system, data relating to a first pattern (24),intended to be observable on the metal patch (18) under visible radiation (19), Decomposition, by the laser processing system, of the first pattern (24) into gray level pixels, each gray level of the pixel corresponding to a dimension of at least one perforation (20) of the metal patch (18) in a perforation zone (26), Determination of a minimum dimension (32) of perforation (20) transmitting the second radiation (30) reflected through the ink layer (22) under determined conditions, Allocation, by the laser processing system, of the minimum dimension (32) of perforation to a gray level of the pixel among the ten percent of the darkest gray levels, Application of the laser radiation to the patch so as to produce perforations (20) forming the first pattern (24) observable under visible radiation (19) and forming a second pattern (28) observable under the effect of the second radiation (30), under the determined conditions., 2. A manufacturing method according to claim 1, wherein the minimum dimension (32) is assigned to the darkest gray level of a pixel.

3. Manufacturing method according to one of the preceding claims, further comprising a step, by the processing system, of replacing a perforation dimension corresponding to a gray level among the least dark 90%, by a minimum dimension (32).

4. Manufacturing method according to one of the preceding claims, further comprising a step of receiving by the laser processing system data relating to the second pattern (28) intended to be formed by perforation of the metal patch (18) and intended to be observable under the second radiation (30), and prior to the allocation step, a step of determining the position of the perforations (20) of dimensions equal to or greater than the minimum dimension (32) allocated to the second pattern (28), and the step of allocating the minimum dimension (32) of perforation to a gray level of the pixel being carried out so as to visualize the second pattern (28) under the second radiation (30) and the first pattern under visible radiation (19).

5. Manufacturing method according to one of the preceding claims, in which the ink layer (22) reacts under ultraviolet radiation.

6. Manufacturing method according to one of the preceding claims, in which the perforation (20) has substantially the shape of a disc and the minimum dimension (32) is a diameter of the disc and has a length of 19nm.

7. Identity document (10) obtained by the manufacturing method according to one of the preceding claims, the document (10) comprising a plastic body provided with a transparent window (16) comprising transparent plastic layers (16a, 16b) between which are positioned a metal patch (18) and an ink layer (22) sensitive to a second radiation (30) of wavelength shorter than that of the visible radiation (19), the metal patch (18) and the ink layer (22) being arranged substantially opposite one another so as to obtain a superposition of the ink layer (22) and the metal patch (18) in observation perpendicular to the plane of the document, and in which the metal patch (18) comprises perforations (20) forming a first pattern (24) decomposable into grayscale pixels and observable under visible radiation (19) and forming a second pattern (28) observable under the effect of a second radiation (30),under determined conditions, the perforations (20) having at least a minimum perforation dimension (32) (20), the minimum perforation dimension (32) being assigned to a gray level of the pixel among the ten percent of the darkest gray levels., 8. Identity document (10) according to the preceding claim, in which the metal patch (18) is a thin metal sheet or a layer of metal oxide with a thickness of less than 35nm.

9. Identity document (10) according to one of claims 7 to 8, in which the ink layer (22) reacts to ultraviolet radiation (30).

10. Identity document according to one of claims 7 to 9, in which the metal patch (18) and the ink layer (22) are positioned at the interface of two transparent plastic layers (16a, 16b).

11. Identity document (10) according to the preceding claim, in which the document comprises a second metal patch (18b) positioned on one of the transparent plastic layers (16a, 16b), on the side opposite the interface.

12. Method for authenticating an identity document (10) obtained by the manufacturing method according to claim 1, comprising the following steps - Positioning the window (16) of the document on an opaque background (17) blocking visible light - acquiring data from the identity document (10) under visible radiation (19), - projecting Ultra-violet radiation (30) onto the face of the identity document (10) so that the UV ink is positioned under the metal patch (18), - Acquiring the second pattern (28) observable under UV radiation (30), - Verifying the second pattern (28) with a reference element - Authenticating the document if the verification is approved.

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