Personalised image formed from a metal layer and a lenticular array

Abstract

The invention relates, in particular, to a security document (10) comprising: a metal layer (14) comprising an arrangement of diffractive nanostructures arranged periodically in the metal layer so as to form a diffractive holographic structure forming an arrangement of pixels each comprising a plurality of sub-pixels of distinct colours; a lenticular array (12) comprising convergent lenses (13) positioned facing the metal layer; and a support layer (16) on which the metal layer is disposed so that the metal layer (14) is sandwiched between the lenticular array (12) and the support layer (16). The metal layer comprises perforations (20) formed by focusing laser radiation (RY) through the lenticular array on the metal layer (14), the perforations comprising at least one group of perforations (RY) produced by focusing the laser radiation (RY) at a respective angle of incidence (Θ) so as to reveal a corresponding personalised image (IG) when the security document is observed at this angle of incidence.

Description

Domaine Technique

[0001] The invention relates to a technique for forming images in greyscale or colour, and more particularly to a document comprising a lenticular network and a laser-perforated metallic layer, an image being formed from the combination of the metallic layer and the laser perforations. Technique antérieure

[0002] The identity market today demands increasingly secure identity documents. These documents must be easily authenticated and difficult to counterfeit (ideally, impossible to forge). This market encompasses a wide variety of documents, such as identity cards, passports, access badges, driver's licenses, etc., which can come in different formats (cards, booklets, etc.).

[0003] Various types of secure documents containing images have been developed over time, particularly for the secure identification of individuals. Passports, identity cards, and various other official documents now generally include security features that allow for document authentication and limit the risks of fraud, falsification, or counterfeiting. Electronic identity documents with a smart card, such as electronic passports, have thus seen significant growth in recent years.

[0004] Various printing techniques have been developed over time to produce color prints. The production of identity documents, such as those mentioned above, requires secure image creation to minimize the risk of falsification by malicious individuals. The manufacturing of such documents, particularly the bearer's identity image, must be sufficiently complex to make reproduction or falsification by an unauthorized person difficult.

[0005] One known solution involves printing a pixel matrix composed of colored sub-pixels onto a substrate and then creating grayscale levels by laser carbonization in a laser-etched layer adjacent to the pixel matrix. This reveals a customized color image that is difficult to falsify or reproduce. Examples of this technique are described, for instance, in documents EP 2 580 065 B1 (dated August 6, 2014) and EP 2 681 053 B1 (dated April 8, 2015).

[0006] Although this well-established technique offers good results, improvements are still possible, particularly in terms of the visual quality of the resulting image. Achieving high levels of color saturation with this image formation technique is indeed difficult. In other words, the color gamut (the ability to reproduce a range of colors) of this technique can be limited, which can be problematic in certain use cases. This stems primarily from the fact that the color subpixels are formed using a conventional printing method, such as offset printing, which does not allow for the creation of sufficiently straight and continuous lines of subpixels. This leads to inconsistencies in the printing of the subpixels (breaks in the pixel lines, irregular edges, etc.) and a degraded color rendering.

[0007] Document WO 2020 / 174153 A1 describes a secure document comprising a holographic structure, which is an arrangement of pixels and subpixels. This document discloses that regions of the holographic structure can be locally destroyed by laser ablation, these regions then forming means for color modulation. Furthermore, this document discloses, in one embodiment, the presence of a lenticular grating which, during the observation phase, amplifies the brightness of certain subpixels.

[0008] Current printing techniques also offer limited positioning accuracy due to the imprecision of printing machines, which also reduces the quality of the final image due to poor positioning of pixels and sub-pixels relative to each other (sub-pixel overlap problems, misalignments...) or due to the presence of a tolerance interval without printing between sub-pixels.

[0009] Today, there is a need for secure, high-quality custom image creation (in color or grayscale), particularly for documents such as identity cards, official documents, and others. Specifically, there is a need for flexible and secure customization of color or grayscale images, ensuring that the resulting image is high-quality, difficult to falsify or reproduce, and easily authenticated.

[0010] There is also a need for a solution to produce secure images with good brightness and a wide color gamut, particularly to obtain the color nuances needed to form certain high-quality color images, for example when image areas need to have a highly saturated level in a given color. Exposé de l'invention

[0011] In view of the problems and shortcomings mentioned above, one technique consists of forming a personalized image by arranging a holographic structure, forming an arrangement of colored pixels, alongside an opaque layer.

[0012] Thus the figure 1 represents a manufacturing technique for forming a secure image 100 (in color or grayscale) with good image quality that is difficult to falsify or reproduce. To achieve this, a holographic layer 114 is positioned opposite a second layer 116 that is opaque to at least the visible wavelength spectrum. The holographic layer 114 comprises a metallic holographic structure 146 forming an arrangement 130 of pixels 132 visible to an observer OB. Each of these pixels 132 contains a plurality of sub-pixels 134 of distinct colors.

[0013] As illustrated in figure 1 ,The holographic layer 114 includes perforations 120 formed by laser radiation LS1. These through-perforations locally reveal through the holographic structure 146 dark areas 142 in the sub-pixels 134, these dark areas 142 being formed by underlying regions 141 of the opaque layer 116 located opposite the perforations 120, so as to form a personalized IG image from the arrangement 130 of pixels combined with the dark areas 142.

[0014] This technique makes it possible in particular to form a personalized image which is secure and of good quality, without the use of powerful laser radiation which could generate air bubbles by heating in the holographic structure 146 which would lead to irreversible destruction of the holographic structure.

[0015] However, this technique requires creating a significant number of perforations in the holographic layer 114, particularly when high contrast is desired in the final IG image. It has been observed that large quantities or concentrations of perforations can undesirably degrade the physical integrity of the holographic layer 114 in certain areas, potentially leading to loss of adhesion of the holographic layer to its substrate. The applicant has thus observed the formation of delaminations when the holographic layer no longer adheres sufficiently to its substrate due to the excessive density of perforations passing through it.

[0016] One need, therefore, is to address the additional problems and deficiencies mentioned above. The present invention aims in particular to enable the formation of personalized images that are both secure and of good quality, while avoiding the adhesion loss problem described above.

[0017] To this end, the present invention relates to a secure document comprising: a metallic layer comprising a diffractive arrangement of nanostructures; a lenticular array comprising converging lenses positioned opposite the metallic layer; and a support layer on which the metallic layer is disposed so that said metallic layer is intercalated between the lenticular array and the support layer; in which the metallic layer includes perforations formed by focusing laser radiation through the lenticular array onto the metallic layer, the perforations comprising at least one group of perforations made by focusing the laser radiation at a respective angle of incidence so as to reveal a corresponding personalized image when the secure document is viewed at said angle of incidence.

[0018] The invention enables the creation of color or grayscale nuances within a metallic layer incorporating a diffractive nanostructure arrangement, thereby revealing at least one secure image. The lenticular array of the invention focuses the laser beam onto small portions of the metallic layer during the image personalization phase, ensuring good adhesion of the metallic layer to the substrate and thus preventing delamination. Furthermore, the invention allows for storing a greater amount of information in a single image than with conventional image formation techniques.

[0019] According to a particular embodiment, the lenticular network comprises a plurality of converging cylindrical lenses extending parallel along a first direction.

[0020] According to a particular embodiment, the nanostructures in the metallic layer are arranged periodically so as to form a diffractive holographic structure.

[0021] According to a particular embodiment, the nanostructures in the metallic layer (14) are arranged aperiodically so as to control (or modify) the colorimetry of the reflected light as a function of the angle of incidence on the metallic layer.

[0022] According to a particular embodiment, the metallic layer comprises a holographic structure forming an arrangement of pixels, each comprising a plurality of sub-pixels of distinct colors, the perforations locally revealing through the holographic structure shades of color or gray level caused by underlying regions of the support layer located opposite the perforations, the underlying regions modifying the colorimetric contribution of the sub-pixels.

[0023] According to a particular embodiment, each pixel of said pixel arrangement is configured such that each sub-pixel exhibits a unique color in said pixel.

[0024] According to a particular embodiment, the support layer is opaque to at least the visible wavelength spectrum, wherein the perforations locally reveal through the holographic structure dark areas in the sub-pixels caused by underlying regions of the support layer located opposite the perforations, so as to form a personalized image from the arrangement of pixels combined with the dark areas.

[0025] According to a particular embodiment, the support layer includes an ultraviolet (UV) sensitive ink, so that the image is visible when the secure document is exposed to ultraviolet (UV) light.

[0026] According to a particular embodiment, the support layer is transparent to at least the visible wavelength spectrum, wherein the perforations locally reveal clear areas in the sub-pixels through the holographic structure when incident light in the visible spectrum is projected through the perforations so as to form a customized image from the arrangement of pixels combined with the clear areas.

[0027] According to a particular embodiment, the lenticular array comprising a plurality of converging cylindrical lenses extending parallel along a first direction, wherein the pixel arrangement comprises lines of sub-pixels of the same color extending perpendicularly to the first direction of the converging cylindrical lenses.

[0028] In a particular embodiment, the lenticular array comprises a plurality of converging semi-spherical or aspherical lenses. The use of aspherical lenses, for example, makes it possible to compensate for optical aberrations.

[0029] According to a particular embodiment, in which the perforations comprise a plurality of perforation groups, each perforation group being made by focusing the laser beam along a distinct angle of incidence so as to reveal interlaced custom images which are observable from the different angles of incidence.

[0030] According to a particular embodiment, the metallic layer is positioned approximately in the focal plane of the lenticular array.

[0031] The invention also relates to a corresponding manufacturing method. Thus, the present invention also relates to a manufacturing method for producing a document as defined herein. In particular, the invention provides a method for manufacturing a secure document, comprising: formation of a metallic layer on a support layer; positioning of a lenticular layer, comprising converging lenses, opposite the metallic layer, the metallic layer being intercalated between the lenticular array and the support layer; and formation of perforations by focusing laser radiation through the lenticular array onto the metallic layer, the perforations comprising at least one group of perforations made by focusing the laser radiation at a respective angle of incidence so as to reveal a corresponding personalized image when the secure document is viewed at said angle of incidence.

[0032] Note that the various embodiments mentioned above (as well as those described below) in relation to the secure document of the invention and the associated advantages apply in a similar way to the manufacturing process of the invention. Brève description des dessins

[0033] Other features and advantages of the present invention will become apparent from the description below, with reference to the accompanying drawings which illustrate non-limiting examples of embodiments. In the figures: [ Fig. 1 ] There figure 1 is a cross-sectional view of a multilayer structure according to a particular implementation; [ Fig. 2 ] There figure 2 schematically represents a secure document according to a particular embodiment of the invention; [ Fig. 3-4 ] THE figures 3 et 4 are cross-sectional views schematically representing a multilayer structure according to a particular embodiment of the invention; [ Fig. 5 ] There figure 5 is a perspective view schematically representing a multilayer structure according to a particular embodiment of the invention; [ Fig. 6 ] There figure 6 is a perspective view schematically representing a multilayer structure according to a particular embodiment of the invention; [ Fig. 7 ] There figure 7 is a cross-sectional view schematically representing a multilayer structure according to a particular embodiment of the invention; [ Fig. 8 ] There figure 8 is a top view schematically representing a multilayer structure according to a particular embodiment of the invention; [ Fig. 9 ] There figure 9 schematically represents perforations formed in sub-pixels, according to a particular embodiment of the invention; [ Fig. 10A ] There figure 10A is a top view of a multilayer structure according to a particular embodiment of the invention; [ Fig. 10B ] There figure 10B is a top view of a multilayer structure lacking a lenticular lattice and in which perforations have been made to form an image; [ Fig. 11 ] There figure 11 schematically represents a multi-layered structure before and after personalization, according to a particular embodiment of the invention; [ Fig. 12 ] There figure 12 schematically represents the reliefs of a holographic structure, according to a particular embodiment of the invention; [ Fig. 13-14 ] THE figures 13 et 14 schematically represent an arrangement of pixels and sub-pixels, according to a particular embodiment of the invention; [ Fig. 15-16-17 ] THE figures 15 , 16 et 17 schematically represent arrangements of pixels and sub-pixels, according to particular embodiments of the invention; and [ Fig. 18 ] There figure 18 schematically represents a manufacturing process according to a particular embodiment of the invention. Description des modes de réalisation

[0034] As previously stated, the invention relates generally to the formation of an image (in color or in greyscale) and relates in particular to a secure document containing such an image.

[0035] In this description, the term "grayscale" refers to shades of gray that are generated to customize a grayscale image. The grayscale level of an area of ​​an image defines a value between white and black. Generally, the invention can be applied to both grayscale and color images. In this description, the terms "grayscale" and "color" are interchangeable, depending on whether the desired image is grayscale or color. The concept of the invention can thus be applied to create both color and grayscale images.

[0036] The invention aims to securely form a personalized image from a metallic layer and a lenticular grating positioned opposite the metallic layer. The metallic layer comprises an arrangement of diffractive nanostructures capable of diffracting light (at least) in the visible spectrum. The metallic layer further includes perforations (or holes) formed by focusing laser beams through the lenticular grating onto the metallic layer. To achieve this, the lenticular grating comprises converging lenses designed to focus the aforementioned laser beams onto the metallic layer.

[0037] These perforations allow for the revelation of one or more custom images—in color or grayscale—when the document is viewed from one or more appropriate viewing angles. Thus, by observing the document at an angle of incidence of the radiation layer used to create perforations in the metallic layer, one can visualize an image revealed by these perforations in the metallic layer.

[0038] As explained below, it is therefore possible to create at least one personalized image, in color or in greyscale, which is of good quality (especially with good contrast), easy to authenticate, robust against the risks of fraud, falsification or counterfeiting, while avoiding the formation of delaminations between the metallic layer and its support due to the phenomenon of loss of adhesion already described above.

[0039] The invention also relates to a method for forming such a personalized image.

[0040] Other aspects and advantages of the present invention will emerge from the exemplary embodiments described below with reference to the drawings mentioned above.

[0041] In the following sections, examples of implementations of the invention are described for documents containing at least one personalized image based on the principle of the invention. This document can be any type of document, referred to as a secure document, such as a booklet, card, or other. The invention finds particular applications in the creation of identity images in identity documents such as identity cards, credit cards, passports, driver's licenses, secure access badges, etc. The invention also applies to security documents (banknotes, notarized documents, official certificates, etc.) containing at least one personalized image. Other implementations are also possible.

[0042] Similarly, the implementation examples described below aim to create an identity image. It is understood, however, that the personalized image created according to the concept of the invention can be of any kind (shape, nature, colors, etc.). It could, for example, be an image representing the portrait of the holder of the document in question, although other implementations are possible.

[0043] Unless otherwise indicated, elements common or similar to several figures bear the same reference signs and have identical or similar characteristics, so that these common elements are generally not described again for the sake of simplicity.

[0044] As already mentioned, the document within the meaning of the invention can be any document. figure 2 represents, according to a particular embodiment, a secure document 2 comprising a document body 4 in or on which is formed at least one secure image IG according to the concept of the invention.

[0045] In the following implementation examples, we assume that the secure document 20 is an identity document, such as a card like an identity card, identification badge, or similar. In these examples, the IG image(s) are grayscale or color images whose design corresponds to the portrait of the document holder. As already mentioned, other examples are possible. If one or more IG images are created, they can be viewed by varying the viewing angle relative to the secure document 2.

[0046] There figure 3 represents a multilayer structure 10 in an initial (blank) state, from which at least one custom IG color image can be formed as shown in figure 2 . As explained later with reference to the figure 4 , This structure 10 can be customized to form at least one custom IG image. This structure 10 constitutes, for example, document 2 as shown in figure 2 or can be included in document 2 in order to form the IG image(s).

[0047] As illustrated in figure 3 , The multilayer structure 10 includes a lenticular network 12 positioned opposite (above) a metallic layer 14. The metallic layer 14 is itself disposed on a support layer (or substrate) 16 so that this metallic layer 14 is intercalated between the lenticular network 12 and the support layer 16.

[0048] The metallic layer 14 comprises an arrangement of diffractive nanostructures (also more simply called "nanostructures"). Various types (shapes, sizes, etc.) of diffractive nanostructures can be considered within the scope of the invention (for example, an arrangement of nanowires). Generally, the diffractive nanostructures present in the metallic layer 14 are configured to diffract light in the visible wavelength spectrum. The size of the diffractive nanostructures is therefore chosen accordingly: the size of the diffractive nanostructures is typically on the order of, or smaller than, the wavelength spectrum in the visible range. These diffractive nanostructures can be arranged periodically to form a diffractive holographic structure (as described below). In this case, the period is, for example, on the order of the wavelength of visible light (for example, 300 nm).Alternatively, the arrangement of the diffractive nanostructures can be aperiodic (non-periodic or arbitrary), which notably allows control (or modification) of the colorimetry of the reflected light as a function of the angle of incidence of the light on the metallic layer 14. The colorimetry of the reflected light is then a function of the combination of light-matter interaction phenomena (diffraction, diffusion, absorption...) occurring at the level of the arrangement of the diffractive nanostructures.

[0049] The lenticular array 12 comprises converging lenses (or microlenses) 13 positioned opposite (above) the metallic layer 14. Various arrangements and configurations of lenses 13 can be considered, as described below. These lenses allow, in particular, the focusing of laser radiation onto the metallic layer 14 in order to form one or more IG images according to the principle of the invention.

[0050] As described below, the support layer 16 can be opaque (non-reflective) or transparent depending on the embodiment considered.

[0051] As already mentioned, the metallic layer 14 shown in figure 3 is blank in the sense that it does not contain the information defining the pattern of the final IG image(s) that we wish to form. In its initial state, the multilayer structure 10 does not form any custom IG image. To form a custom IG image, perforations are created by laser radiation in the metallic layer 14 as described below.

[0052] More specifically, as represented in figure 4 ,The metallic layer 14 of the multilayer structure 10 includes perforations (or holes) 20 formed by laser radiation RY (by laser etching). These perforations 20 penetrate the thickness of the metallic layer 14 so as to reveal (or uncover) in a custom IG image, through the metallic layer 14, areas Z2 formed (or caused) by underlying regions Z1 of the support layer 16 located opposite the perforations 20. These Z2 areas are colorimetric shade areas revealed in the IG image. These Z2 areas can, for example, be dark if the underlying regions Z1 of the support layer 16 are opaque (with respect to at least the visible wavelength spectrum) or can be light if the underlying regions Z1 of the support layer 16 are transparent (with respect to at least the visible wavelength spectrum).By exposing these Z1 regions through the perforations 20, color nuances or shades of gray can be created to personalize a final IG image. In other words, the underlying Z1 regions modify the colorimetric contribution of corresponding areas of the metallic layer 14 to form the final IG image. This IG image can be viewed by an observer OB by observing the multilayer structure 10 either in reflection (in the case of the opaque support layer 16) or in transmitted light from the back face of the structure 10 (in the case of the transparent support layer 16).

[0053] As depicted in figure 4 ,It is possible to adjust the angle of incidence θ at which the RY laser beam is projected through the converging lenses 13 in order to adapt the position at which the RY beam is focused on the metallic layer 14. This allows precise control of the position at which the perforations 20 are made in the metallic layer 14. In general, the metallic layer 14 includes at least one group of perforations 20 made by focusing the RY laser beam at a respective angle of incidence θ so as to reveal a corresponding personalized image IG when the structure 10 (or the secure document 2) is observed at said angle of incidence θ.

[0054] Alternatively, the metallic layer 14 can comprise a plurality of perforation groups 20. For each of these groups, the perforations 20 are then created by means of a laser beam RY projected at the same respective angle of incidence θ. Laser beams are thus projected at distinct angles of incidence onto the multilayer structure 10 in order to form a plurality of images IG which can be viewed by an observer OB through the lenses 13 by adjusting the viewing angle.

[0055] There figure 4 This represents a particular example in which a first laser beam RY1 is focused at normal incidence on the multilayer structure 10 (angle of incidence θ1 = 0°) to form a first group of perforations 201 in the metallic layer 14 and in which a second laser beam RY2 is focused at oblique incidence on the multilayer structure 10 (angle of incidence 0° < θ2 < 90°) to form a second group of perforations 202 in the metallic layer 14. The first group of perforations 201 and the second group of perforations 202 thus form two distinct personalized IG images which are visualizable by an observer OB by observing the multilayer structure 10 at an angle of observation equal to θ1 and θ2, respectively.

[0056] The multilayer structure 10 is subsequently considered to include, for example, two distinct custom IG images viewable from two different viewing angles. The number and configuration of the IG images formed within the multilayer structure 10 can, however, be adapted to suit the use case. Alternatively, the multilayer structure 10 can be customized to include only a single IG image.

[0057] Furthermore, the RY laser radiation used to form the perforations (or holes) 20 in the metallic layer 14 ( figure 4 )is preferably to a wavelength spectrum different from the visible spectrum. For this purpose, one can, for example, use a YAG laser (e.g., at a wavelength of 1064 nm), a blue laser, a UV laser, etc. One can also apply, for example, a pulse frequency between 1 kHz and 500 kHz, although other configurations are possible. It is up to a person skilled in the art to choose the appropriate laser beam configuration for the specific application.

[0058] The metallic layer 14 is designed to absorb at least some of the energy delivered by the RY laser radiation to create the perforations 20 described above. In other words, the RY laser radiation is characterized by a spectrum of wavelengths that are absorbed at least partially by the metallic layer 14. The materials of the metallic layer 14 are therefore chosen accordingly.

[0059] In one particular example, the materials forming the metallic layer 14 are selected so that they do not absorb visible light. In this way, it is possible to create perforations 20 using laser radiation emitted outside the visible spectrum and to generate one or more custom IG images that are visible to the human eye through a diffractive effect.

[0060] As illustrated in figure 4 ,The metallic layer 14 can be positioned at a distance d1 from the lenticular grating 12. According to a particular example, this distance d1 is chosen so that the metallic layer 14 is positioned in (or approximately in) the focal plane of the lenticular grating 12. This configuration allows the laser RY radiation to be focused to the maximum during the personalization phase and thus to limit as much as possible the proportion of the metallic layer 14 that is perforated, so as to ensure the best possible adhesion of said metallic layer 14 to the underlying support layer 16.

[0061] According to a particular embodiment, the support layer 16 is reactive to at least the ultraviolet (UV) wavelength spectrum, for example by means of printing on the support layer 16 with a UV-reactive fluorescent ink. In this case, the perforations 20 locally reveal, through the arrangement of diffractive nanostructures, fluorescent Z2 areas caused by underlying Z1 regions of the support layer 16 located opposite the perforations 20, so as to form a personalized IG image from the fluorescent Z2 areas when the multilayer structure 10 (and more particularly the support layer 16) is exposed to UV radiation.

[0062] Furthermore, as represented in figure 5 ,In the remainder of this presentation, we will consider the specific case where the converging lenses 13 are cylindrical lenses extending parallel to each other along a first direction DR1. It should be noted, however, that other implementations are possible. The figure 6 represents for example a variant in which the converging lenses 13 are semi-spherical, or even aspherical (which makes it possible to compensate for optical aberrations).

[0063] In reference to the figures 7-9 And 10A-10B, is described a particular embodiment of the multilayer structure 10 represented in figures 3-6 .

[0064] More specifically, as represented in figure 7 ,The metallic layer 14 is considered to be a holographic layer comprising a holographic structure 46 that forms an arrangement 30 of pixels 32. Each of these pixels 32 has a plurality of sub-pixels 34 of distinct colors. Therefore, the personalized IG images are considered here to be in color, although the concept of the invention can be applied analogously to form personalized IG images in grayscale.

[0065] The arrangement of pixels 30 can have various configurations depending on the use case, as described in more detail later. The pixels 32 can, for example, be arranged in a matrix forming rows and columns of sub-pixels 34 (according to an orthogonal matrix, for example).

[0066] In the example implementation considered here, each pixel 32 of the arrangement 30 is configured so that each sub-pixel 34 has a unique color in said pixel, although other implementation examples are possible.

[0067] In general, the holographic structure 46 intrinsically forms a pixel arrangement 30 that is blank, in the sense that the pixels 32 do not contain the information defining the pattern of the color image(s) IG that one wishes to form. As described below, it is by combining this pixel arrangement 30 with dark or light areas Z2 ( figure 7 ) that a pattern of one or more custom IG color images is revealed.

[0068] The holographic structure 46 is now described in detail below according to a particular embodiment.

[0069] The holographic structure 46 produces the arrangement 30 of pixels 32 in the form of a hologram by diffraction (and possibly also by refraction and / or reflection) of incident light. Although the principle of the hologram is well known to those skilled in the art, certain elements are recalled below for reference. Examples of the realization of holographic structures are described, for example, in document EP 2 567 270 B1.

[0070] As depicted in figure 7 , In this example, the holographic layer 14 comprises a layer (or sub-layer) 40 and reliefs (or relief structures) 42, containing three-dimensional information, which are formed from the layer 40 serving as a support. These reliefs 42 form protruding portions (also called "mountains") separated by recesses (also called "valleys").

[0071] The holographic layer 14 further comprises a layer (or sub-layer) 44, referred to as the "high refractive index layer," which has a refractive index n2 greater than the refractive index n1 of the reliefs 42 (it is assumed here that the reliefs 42 are an integral part of the layer 40 serving as a support, so that the reliefs 42 and the layer 40 have the same refractive index n1). The high refractive index layer 44 is considered here to be a metallic layer covering the reliefs 42 of the holographic layer 14. As a person skilled in the art understands, the reliefs 42, in combination with the layer 44, form a holographic structure 46 that produces a hologram (a holographic effect).

[0072] The raised features 42 of the holographic structure 46 can be formed, for example, by embossing a layer of stamping varnish (included in layer 40 in this example) in a manner known for producing diffring structures. The embossed surface of the raised features 42 thus exhibits a periodic lattice shape. For example, the depth of this lattice can be on the order of tens of nanometers and the lattice period on the order of hundreds of nanometers. This embossed surface is coated with the metallic layer 44, for example by vacuum deposition of a metallic material. The holographic effect results from the combination of the raised features 42 and the layer 44, forming the holographic structure 46.

[0073] The holographic layer 14 may optionally include other sub-layers (not shown) necessary to maintain the optical characteristics of the hologram and / or to ensure mechanical and chemical resistance of the assembly.

[0074] The high refractive index metallic layer 44 ( figure 7 ) may include at least one of the following materials: aluminium, silver, copper, zinc sulfide, titanium oxide...

[0075] In the embodiment examples described in this document, the holographic layer 14 is transparent, so that the holographic effect producing the arrangement 30 of pixels 32 is visible by diffraction, reflection and refraction.

[0076] The holographic structure 14 is produced by any suitable process known to a person skilled in the art.

[0077] The reliefs 42 have a refractive index noted n1, of the order for example of 1.56 at a wavelength λ = 656 nm.

[0078] In the example considered here ( figure 7 ), Layer 40 is a transparent varnish layer. The holographic structure 46 can be coated with a thin film 44, for example made of aluminum or zinc sulfide, having a high refractive index n2 (compared to n1). The thin film 44 has, for example, a thickness between 30 and 200 nm.

[0079] Layer 40 can be a thermoformable layer, allowing the reliefs 42 of the holographic structure 46 to be formed by embossing onto the layer 40, which serves as a substrate. Alternatively, the reliefs 42 of the holographic structure 46 can be produced using an ultraviolet (UV) curing technique. Since these manufacturing techniques are known to those skilled in the art, they are not described in further detail for the sake of simplicity.

[0080] Furthermore, as represented in figure 7 ,The perforations 20 locally reveal, in one or more IG custom images, through the holographic structure 46 (and the holographic layer 14), Z2 areas of color or grayscale shade caused by the underlying Z1 regions of the support layer 16 located opposite the perforations 20. These Z2 areas of color or grayscale shade constitute areas visible to an observer OB in the final IG image(s) when observing the multilayer structure 10 through the lenticular array 12. These Z2 areas, dark or light (e.g. fluorescent) depending on the nature of the support layer 16 used, form in combination with the arrangement 30 of pixels 32 at least one IG custom image. In other words, the formation of perforations 20 makes it possible to make visible through the holographic layer 14 the underlying regions Z1 of the support layer 16, which induces corresponding Z2 areas in the sub-pixels 34.Thus, the underlying Z1 regions modify the colorimetric contribution of the 34 subpixels so as to form the IG custom image(s).

[0081] More specifically, as represented in figure 7 The perforations 20 constitute regions in which the holographic layer 14 is destroyed or removed by the perforation effect of the laser. The perforations 20 are through perforations that extend through the thickness of the holographic structure 46 (and more generally through the thickness of the holographic layer 14) so ​​as to reveal, at the level of the pixel arrangement 30 32, areas Z2 (more or less dark or light) corresponding to the underlying regions Z1 of the support layer 16.

[0082] Thus, the perforations 20 occupy all or part of a plurality of sub-pixels 34 of the holographic structure 46. The more or less opaque or transparent nature of the support layer 16 then determines the appearance that the Z1 areas take in the perforated parts of the sub-pixels 34.

[0083] To achieve this, the 20 perforations can have various shapes and dimensions which may vary depending on the case.

[0084] In the example considered here, support layer 16 is opaque (non-reflective) to at least the visible wavelength spectrum. In other words, support layer 16 absorbs at least the wavelengths in the visible spectrum. For example, it is a dark layer (black in color, for instance). In this disclosure, the visible wavelength spectrum is assumed to be approximately between 400 and 800 nanometers (nm), or more precisely between 380 and 780 nm in a vacuum.

[0085] It should be noted that this support layer 16 can, however, be transparent to other wavelengths, particularly infrared. In particular, the spectrum of the RY laser radiation is preferably chosen so that it is not absorbed by the support layer 16 during the formation of the perforations 20.

[0086] As depicted in figure 7 , The underlying Z1 regions revealed by the perforations 20 thus allow, in this particular case, the creation of dark areas Z2 within the subpixels 34 of the holographic layer 14, thereby customizing an IG image formed by the combination of the pixel arrangement 30 and the dark areas Z2. An observer OB can therefore view a customized IG image by observing (normal or oblique) the reflection. In this particular example, the observer OB can further view the two distinct IG images by adjusting the viewing angle relative to the multilayer structure 10.

[0087] According to a particular example, the support layer 16 is such that the black density of said at least one custom IG image formed in the secure document 2 ( figure 2 ) starting in particular from said support layer 16 is greater than the intrinsic black density of the holographic layer 14 without (independently of) the support layer 16. As is well known to those skilled in the art, black density is measurable by means of an appropriate measuring device (for example, a colorimeter or a spectrometer).

[0088] In a specific example, the opaque support layer 16 comprises an opaque black surface opposite the holographic layer 14 and / or includes black or opaque (or dark) pigments throughout its mass. The opaque support layer 16 may include, in particular, black ink, or a material dyed throughout by black or opaque (or dark) pigments.

[0089] In one particular embodiment, the support layer 16 is reactive (or sensitive) to at least the UV wavelength spectrum, for example by means of printing a UV-reactive fluorescent ink onto the support layer 16. Thus, in one particular example, the support layer 16 contains an ultraviolet-sensitive ink, so that the image is visible when the multilayer structure 10 (and more generally the secure document) is exposed to UV light.More specifically, under UV exposure, the perforations 20 locally reveal, through the holographic structure 14, fluorescent Z2 areas in the sub-pixels 34, these fluorescent Z2 areas being caused by underlying Z1 regions of the support layer 16 located opposite the perforations 20, so as to form a custom IG (fluorescent) image from the arrangement 30 of pixels 32 combined with the fluorescent Z2 areas when the multi-layer structure 10 (and more specifically the support layer 16) is exposed to UV radiation.

[0090] According to one variant, the support layer 16 is transparent to at least the visible wavelength spectrum. In this case, an observer OB can view a customized IG image by observing (normal or oblique) light transmitted from the back face of the structure 10. The underlying regions Z1 revealed by the perforations 20 thus allow, in this particular case, the creation of clear (or brightened) areas Z2 in the subpixels 34 of the holographic layer 14, so as to customize one or more IG images formed by the combination of the arrangement 30 of pixels 32 and the clear areas Z2. The clear areas Z2 are brighter areas that allow the corresponding pixels 32 (or subpixels 34) in which the clear areas are located to be brightened.

[0091] As already indicated, the observer OB can in this particular case also visualize at least two distinct IG images by playing on the observation angle of the structure 10, although it is also possible to form only one personalized IG image by means of the technique of the invention.

[0092] More generally, regardless of the nature of the support layer 16 (opaque, transparent, or fluorescent), the perforations 20 are arranged to select the color (or grayscale level) of the pixels 32 by modifying the colorimetric contribution of the sub-pixels 34 relative to each other in at least a portion of the pixels 32 formed by the holographic layer 14, so as to reveal the personalized IG image(s) from the arrangement 30 of pixels combined with the Z2 areas (more or less dark or light). In other words, the IG image(s) thus created are color or grayscale images resulting from a selective modulation of the colorimetric contributions of the sub-pixels 34.

[0093] In particular, laser perforation in the holographic layer 14 results in the local removal (or deformation) of the geometry of the holographic structure 46, and more specifically of the reliefs 42 and / or the layer 44 covering said reliefs. These local destructions lead to a modification of the behavior of light (i.e., the reflection, diffraction, transmission, and / or refraction of light) in the corresponding pixels and sub-pixels. By locally destroying, through perforation, all or part of the sub-pixels 34 and revealing, in their place, underlying dark or light regions Z1 of the support layer 16, grayscale levels or shades of color are thus generated in the pixels 32 by modifying the colorimetric contribution of certain sub-pixels 34, relative to each other, in the visual rendering of the final IG image(s).The creation of the Z2 zones (dark or light) allows in particular to modulate the passage of light so that, for at least part of the pixels 32, a sub-pixel 34 or more has an increased or decreased colorimetric contribution (or weight) compared to that of at least one other sub-pixel 34 near the pixel 32 concerned.

[0094] In particular, the selective destruction, partial or total, of one or more subpixels 34 in at least some of the pixels 32 results in a modification of the holographic effect in the affected regions. The holographic effect is eliminated, or reduced, in the perforated regions of the holographic structure 46, which diminishes (or even completely eliminates) the relative color contribution of the subpixels 34 that are at least partially perforated compared to at least one other neighboring subpixel 34 of the pixels 32 concerned. Furthermore, as already indicated, this selective destruction reveals underlying regions Z2 that modify the colorimetric contribution of the subpixels in the personalized IG image(s).

[0095] According to a particular example represented in figures 5 And 8 ,The lenticular array 10 comprises a plurality of converging cylindrical lenses 13 extending parallel to each other along a first direction DR1. The arrangement 30 of pixels 32 may, in particular, include lines LN of sub-pixels 34 of the same color extending perpendicularly to the first direction DR1 of the converging cylindrical lenses 13. Thus, in the example shown in figure 8 , The 30-pixel arrangement comprises a series of 3 LN sub-pixel lines in 3 distinct respective colors, this series repeating periodically.

[0096] In the particular embodiment of the figure 8 ,Regardless of the angle of incidence θ at which a laser beam RY passes through a cylindrical lens 13 at a given point, this beam is systematically focused onto the same line LN of subpixels. This line LN is defined by the position of the point of incidence on the cylindrical lens 13 relative to the underlying pixel arrangement 32. Thus, it is possible to precisely focus the laser beam RY onto an LN of a desired color during the personalization phase, thereby reducing registration problems between the lenses 13 and the pixel arrangement 30, and consequently improving the quality of the final IG image(s).

[0097] According to another particular example, the LN lines of subpixels 34 of the same color extend parallel to the first direction DR1 of the converging cylindrical lenses 13 so as to obtain monochrome images with black or grey areas.

[0098] Various visual effects can be obtained in the custom IG image(s) when the LN lines of subpixels 34 are parallel to the cylindrical lenses 13 of the lenticular array. Thus, according to a first variant, the period of the lenses 13 corresponds to (or is equal to) the period of the LN lines of subpixels, which makes it possible to obtain a monochrome rendering of an image corresponding to the color of a subpixel over a given angle range, and possibly to obtain a sequence of different monochrome images over the aperture angle range of the lenses 14.

[0099] According to a second variant in which the LN lines of subpixels 34 are parallel to the cylindrical lenses 13, a Moiré effect can be obtained in the IG custom image(s) by fixing the pitch of the lenses 13 so that it is close to (but different from) that of the pixels 32.

[0100] According to a third variant in which the LN lines of subpixels 34 are parallel to the cylindrical lenses 13, one or more custom IG images in greyscale can be obtained by fixing the pitch of the lenses 13 so that it is very large compared to the pitch of the pixels 32.

[0101] There figure 9 This schematically represents an example in which two groups of perforations 20 are formed in the holographic layer 14 by focusing RY laser beams at two distinct angles θ1 and θ2 through the lenticular grating 12, in order to form two corresponding IG custom images. By adjusting the power delivered by the RY laser, areas Z2 of varying shades of color or shades of gray (opaque areas in this case) of the desired size can be formed at specific positions in the pixel arrangement 30 to create two IG custom images. In the example considered here, the larger the opaque areas Z2, the darker the color of the corresponding subpixel 34.

[0102] As illustrated in figure 9 ,The larger a perforation 20 is (the more surface area it occupies), the larger the opaque area Z2 revealed by that perforation. Furthermore, the larger the opaque area Z2 present in a subpixel 34, the more it will influence (modify) the colorimetric contribution of that subpixel 34 in the final image IG to which that subpixel 34 belongs. Thus, in this particular example, the larger an opaque area Z2, the less space there is for the color of the corresponding subpixel 34 to be expressed, so that the overall color of the subpixel 34 in question (and the corresponding pixel 32) becomes darker. Therefore, if a given subpixel 34 has no area Z2 of color shade (or shade of gray) at a particular viewing angle θ through the lenticular grating 12, then an observer will see the original color of the subpixel 34 at that position, according to the viewing angle θ.On the other hand, if a given sub-pixel 34 is occupied mainly by a zone Z2 according to a particular viewing angle θ through the lenticular grating 12, then an observer will see at this position according to the viewing angle θ essentially the color of the zone Z2 considered (namely, a dark area in the example of the . figure 9 ). It is thus possible to modulate the color of each sub-pixel 34, and of the corresponding pixels 32, according to the nature of the support layer 16 and the configuration (position, number, size) of the perforations 20 in this support layer 16.

[0103] In the particular example shown in figure 9 ,In particular, perforations 20 of different sizes can be made in the same line LN of sub-pixels, by focusing a laser RAY via the same point of a cylindrical lens 13, by changing the angle of incidence with which the laser RAY is projected onto the lens in question.

[0104] As illustrated in figure 9 , Thus, a group of N parallel lines LP of perforations 20 can be formed in the holographic layer 14 through each cylindrical lens 13, by focusing a laser beam RY at N distinct angles of incidence θ (N being an integer at least equal to 2). N distinct personalized images IG can thus be formed, which are interlaced with each other such that each image IG is viewable by an observer OB by observing the multilayer structure 10 through the lenticular grating 12 at a respective viewing angle θ. figure 9 represents the special case where N = 2, two lines LP1 and LP2 of perforations 20 being formed by projecting a laser RY beam through the cylindrical lenses 13 at angles of incidence θ1 and θ2 respectively, so as to form two interlaced IG images.

[0105] There figure 10A This represents another embodiment in which four parallel lines LP (labeled LP1 to LP4) of perforations 20 are formed in the holographic layer 14 through each cylindrical lens 13 so as to form four interlaced (N=4) personalized images IG in the structure 10. As illustrated in the figure, the use of the lenses 13 allows the perforations 20 to be concentrated in smaller regions of the holographic layer 14 (according to groups of LP lines, in this example). The perforations 20 are smaller and concentrated in smaller regions than if the lenticular array 12 were not present to focus the RY laser beam during the customization phase of the pixel arrangement 30. Thus, a significant portion of the holographic layer 14 can be retained without perforations 20, which ensures good adhesion of the holographic layer 14 to the support layer 16.

[0106] For comparison, the figure 10B This represents a holographic layer in which perforations have been created using laser radiation, but without using a lenticular grating during the personalization phase as in the invention. As shown in the figure, a large number of perforations are arranged on the surface of the holographic layer. In the absence of areas without perforations, this holographic layer is at risk of experiencing adhesion losses leading to delamination, according to the phenomenon described above.

[0107] There figure 11 represents, according to an example of an embodiment of the invention, the arrangement 30 of pixels 32 in the blank state (before personalization) and then the visual rendering of a personalized image IG formed by the combination of the arrangement 30 of pixels 32 and perforations 20 made by focusing a laser beam RY through the lenticular network 12, as already described above.

[0108] In general, the invention advantageously allows for the creation of color or grayscale nuances in a metallic layer comprising an arrangement of diffractive nanostructures, to reveal at least one secure image. As described above, perforations are made in the metallic layer by focusing laser beams through a converging lens array. These perforations create areas of varying shades of color, from dark to light, thus revealing the pattern of the desired image(s). The invention therefore makes it possible to form, within the metallic layer, a single personalized image or, alternatively, a plurality of interlaced images by projecting laser beams onto the lenticular array at different angles of incidence.

[0109] For example, by using an opaque support layer, dark areas can be advantageously created within the metallic layer, revealing at least one secure, high-quality (particularly high-contrast) custom image. Similarly, at least one high-quality secure image can be created using a transparent support layer, which allows light areas to appear within the metallic layer when the final image is viewed in light transmitted through the structure. In this specific case, it is possible to create a negative image, inverting the colors or grayscale levels of the original image.

[0110] The lenticular array of the invention allows the laser beam to be focused onto small portions of the metallic layer during the image personalization phase. Thanks to the invention, it is possible to maintain a significant portion of the metallic layer free of perforations, thus ensuring good adhesion of the metallic layer to the underlying substrate and preventing the delamination problems described above. The converging lenses, in particular, allow for limiting the size of the perforations in the metallic layer and also for concentrating the perforations in specific regions of the metallic layer. As described above, the perforations can, for example, be created in the form of parallel lines.

[0111] Perforating a metallic film beneath a lens array, according to the principle of the invention, significantly increases the number of images per angle (and therefore the amount of information) compared, for example, to a device with a laser-etched layer that is carbonized by a laser. In particular, the invention allows adjustment of at least one of the following parameters to increase the amount of information encoded in the image: the etching thickness (or depth) and the perforation diameter. Thus, the etching thickness in the present invention can be much smaller (for example, a few tens of nanometers, compared to typically a few tens of micrometers in the case of a laser-etched layer carbonization technique), which makes it possible, in particular, to customize the image in an area close to the focal plane of the lenticular array and therefore obtain better angular resolution.The perforation diameter can also be adjusted in the invention to be on the order of a nanometer (as opposed to tens of micrometers in the case of a carbonization technique of a laserizable layer).

[0112] Thanks to the present invention, it is possible to create a very high-density 2D barcode. The resulting image can, in particular, comprise multiple interleaved barcodes. The density of coded information is thus increased compared to a conventional barcode.

[0113] In particular, the size of the perforations can be finely adjusted in order to create one or more high-quality personalized images.

[0114] As mentioned above, the metallic layer of the invention can be a holographic layer, although other embodiments are possible. Using a holographic layer allows for increased image quality, namely improved overall brightness of the final image (greater brilliance, more vivid colors) and better color saturation. This makes it possible to produce a high-quality color image with an enhanced color gamut compared to, for example, a printed image.

[0115] Using a holographic structure to form the pixel arrangement is advantageous because this technique offers high precision in positioning the pixels and sub-pixels thus formed. This technique notably avoids any potential overlaps or misalignments between sub-pixels, thereby improving the overall visual rendering of the image.

[0116] The invention enables the production of personalized images that are easily authenticated and resistant to falsification and fraudulent reproduction. The level of complexity and image security achieved through the invention does not compromise the quality of the image's visual rendering.

[0117] The invention also eliminates the need for one or more laserizable layers, which would require the projection of powerful laser radiation to create color or grayscale nuances in the final image through carbonization. Projecting such powerful laser radiation could indeed lead to structural defects (blistering problems) due to overheating within the structure during the image customization process.

[0118] There figure 12 represents examples of reliefs 42 of a holographic structure 46 as represented in the particular example in figures 7-8 And 11.As illustrated, this holographic structure 46 has protruding portions and recesses. Various shapes and dimensions of the holographic structure are possible within the scope of the present invention.

[0119] Furthermore, as already mentioned, the holographic layer 46 represented in figures 7-8 And 11 forms an arrangement of 30 pixels. Each pixel comprises a plurality of 34 sub-pixels of color (or exhibiting a level of grey).

[0120] THE figures 13 et 14 represent a particular example in which each pixel 32 comprises 3 sub-pixels 34. The number, shape and more generally the configuration of pixels and sub-pixels may however vary depending on the case.

[0121] An external observer OB can thus visualize, according to a particular observation direction, the arrangement 30 of pixels from light refracted, reflected and / or diffracted from the holographic structure 46 of the holographic layer 14 ( figures 7-8 ).

[0122] More precisely, each pixel 32 is formed by a region of the holographic structure 46 present in the holographic layer 14. Here, the reliefs 42 of the holographic structure 46 are considered to form parallel lines LN of sub-pixels (as represented in figure 8 ), although other implementations are possible. For each pixel 32, its constituent sub-pixels 34 are thus formed by a portion of a respective LN line, this portion constituting a respective holographic grating (or portion of a holographic grating) configured to generate by diffraction and / or reflection a corresponding color of said sub-pixel.

[0123] In the example considered here, the pixels 32 thus comprise 3 sub-pixels 34 of distinct colors, although other examples are possible. We assume that each sub-pixel 34 is monochromatic. Each holographic grating is configured to generate a color in each sub-pixel 34 corresponding to a predetermined viewing angle, this color being modified at a different viewing angle. For example, we assume that the sub-pixels 34 of each pixel 32 exhibit a distinct primary color (e.g., green / red / blue or cyan / yellow / magenta) at a predetermined viewing angle.

[0124] As represented in figures 13 et 14 ,The holographic gratings corresponding to the three lines LN, which form the sub-pixels 34 of the same pixel 32, have particular geometric specifications in order to generate a distinct desired color. In particular, the holographic gratings forming the 3 sub-pixels 34 in this example have a width denoted I and a pitch between each holographic grating denoted p.

[0125] Thus, according to another specific example where each pixel 32 is composed of 4 sub-pixels 34, the maximum theoretical saturation capacity S in one of the colors of the sub-pixels in the same pixel can be stated as follows: S = 25 100 × l l + p

[0126] As an example, we can consider that I = 60 µm and p = 10 µm which leads to a maximum theoretical saturation capacitance S = 0.21.

[0127] It is possible to form the holographic networks forming the sub-pixels 34 so that the step p tends towards zero, which makes it possible to increase the maximum theoretical saturation capacity in a color of a sub-pixel (S then tending towards 0.25).

[0128] In one particular example, the step size is set to p = 0, which allows for a maximum theoretical saturation capacity S of 0.25. In this case, the LN lines of subpixels are as represented in figures 13 et 14 are contiguous (no space or white area is present between the sub-pixel lines).

[0129] The invention, according to a particular embodiment, thus makes it possible to form lines of sub-pixels that are contiguous, that is, adjacent to one another, without the need for separating white areas between each line, or possibly by maintaining separating white areas of limited size between the lines of sub-pixels (with a small pitch p). This particular configuration of holographic gratings makes it possible to significantly improve the quality of the final IG image (better color saturation) compared to conventional image formation techniques that do not use a holographic structure. This is possible in particular because the formation of holographic structures allows for greater sub-pixel positioning accuracy and homogeneity than conventional sub-pixel printing (by offset or other methods).

[0130] As already indicated, the arrangement 30 of pixels 32 formed by the holographic layer 14 in the structure 10 represented in figures 7-8 And 11 It can take various forms. Examples of implementation are described below.

[0131] In general, the arrangement 30 of pixels can be configured so that the sub-pixels 34 are uniformly distributed in the holographic layer 14. The sub-pixels 34 can, for example, form parallel lines LN of sub-pixels or a hexagonal (Bayer type) array, other examples being possible.

[0132] The 34 sub-pixels can, for example, form an orthogonal matrix.

[0133] The pixels 32 can be evenly distributed in the arrangement 30 so that the same pattern of sub-pixels 34 is repeated periodically in the holographic layer 14.

[0134] Furthermore, each pixel 32 in the arrangement 30 can be configured so that each subpixel 34 has a unique color within that pixel. In a particular example, each pixel 32 in the arrangement 30 of pixels forms an identical pattern of colored subpixels.

[0135] Specific examples of pixel arrangements (or tiling) 30 that can be implemented in the secure document 2 ( figure 2 ) are now described with reference to figures 15 , 16 et 17 . It should be noted that these implementations are presented here only as non-limiting examples, many variations being possible in terms of arrangement and shape of pixels and sub-pixels, as well as the colors assigned to these sub-pixels.

[0136] According to a first example represented in figure 15 ,The 32 pixels of the 30 pixel arrangement are rectangular (or square) in shape and comprise 3 sub-pixels 34a, 34b, and 34c (collectively denoted as 34) of distinct colors. As already described with reference to figures 13-14 , The 34 subpixels can each be formed by a portion of an LN line of subpixels. In this example, the tiling 30 thus forms a matrix of rows and columns of pixels 32, orthogonal to each other.

[0137] There figure 16 is a top view representing another example of a regular tiling in which each pixel 32 is composed of 3 sub-pixels 34, labeled 34a to 34c, each of a distinct color. The sub-pixels 34 are hexagonal in shape here.

[0138] There figure 17 is a top view representing another example of a regular tiling in which each pixel 32 is composed of 4 sub-pixels 34, labeled 34a to 34d, each of a distinct color. The sub-pixels 34 are triangular in shape here.

[0139] For each of the pixel arrangements considered, it is possible to adapt the shape and dimensions of each pixel 32 and also the dimensions of the white separating areas present, if any, between the sub-pixels, so as to achieve the desired maximum color saturation level and the desired brightness level.

[0140] Furthermore, the present invention also relates to a manufacturing method for producing at least one personalized IG image according to any of the previously described embodiments. Also, the various variants and technical advantages described above with reference to the multilayer structures 10, and more generally to a secure document 2 conforming to the concept of the invention, apply analogously to the manufacturing method of the invention for obtaining such a structure or such a document.

[0141] A method for manufacturing a color IG image as described previously is now described with reference to the figure 18 , according to a particular embodiment. For example, we assume that at least one color image IG is formed in a document 2 as illustrated in figure 2 .

[0142] During a formation step S2, a metallic layer 14 is formed on a support layer 16. The metallic layer 14 and the support layer 16 are as described in the preceding embodiments. In particular, the metallic layer 14 comprises an arrangement of diffractive nanostructures. As already mentioned, this diffractive arrangement is configured to diffract light at least in the visible wavelength spectrum. These diffractive nanostructures can be arranged periodically (to form, for example, a diffractive holographic structure) or aperiodically (non-periodically) so as to control (or modify) the colorimetry of the reflected light as a function of the angle of incidence of the light on the metallic layer 14, as described previously.In addition, the support layer 16 can be opaque to at least the visible wavelength spectrum or transparent to at least the visible wavelength spectrum, depending on the visual effect that one wishes to create in one or more custom IG images.

[0143] An adhesive layer and / or glue (not shown) can be used to ensure adhesion of the metallic layer 14 to the support layer 16.

[0144] During a positioning step S4, a lenticular network 12 as already described in the above embodiments is positioned (or formed) opposite the metal layer 14. In this example, the lenticular network 12 is formed directly on the metal layer 14 although other implementations are possible or at least an intermediate layer is present between the lenticular network 12 and the metal layer 14.

[0145] As already described, the lenticular network 12 includes converging lenses 13 positioned opposite (above) the metallic layer 12, the latter being thus intercalated between the lenticular network 12 and the support layer 16.

[0146] During a formation step S6, perforations (or holes) 20 as already described in the embodiments above are formed in the holographic layer 22 by focusing a laser beam RY through the lenticular grating 12 onto the metallic layer 14. These perforations 20 thus comprise at least one group of perforations 20 made by focusing a laser beam RY at a respective angle of incidence θ so as to reveal a corresponding personalized image IG when the secure document 2 (or the structure 10) is observed at said angle of incidence θ.

[0147] Groups of perforations 20 can thus be created by focusing a laser beam RY through the lenticular grating 12 at distinct angles of incidence θ. In this case, each group of perforations 20 represents a personalized image IG viewable by an observer at a corresponding viewing angle θ. The different images IG are thus formed by perforation in an interlaced manner within the metallic layer 12.

[0148] As described earlier in the implementation example of the figures 7-8 ,The perforations 20 are made so as to occupy all or part of a plurality of sub-pixels 34 of the holographic layer 14. These perforations 20 locally reveal, through the holographic structure 46, dark or light areas Z2 in the sub-pixels 34, these areas Z2 being caused (or produced) by underlying regions Z1 of the support layer 16 located opposite the perforations 20. To achieve this, the perforations 20 are here through-hole perforations that extend through the thickness of the holographic structure 46 (and more generally through the thickness of the holographic layer 14) so ​​as to reveal underlying regions Z2 of the support layer 16 at the level of the arrangement 30 of pixels 32. In other words, the underlying regions 34 modify the contribution of the sub-pixels 34 so as to form the final image IG.We can thus form one or more custom IG images from the arrangement of 30 pixels combined with the said dark or light Z2 areas.

[0149] Once step S6 is completed, we thus obtain a multilayer structure 10 as previously described in different embodiments.

[0150] In the specific case where the metallic layer 12 is a holographic layer as already described with reference in particular to figures 7-8 , The S2 formation of the metallic layer 14 may include the application of a varnish undercoat 40 forming the raised areas 42 of a holographic lattice; and the formation of a metallic undercoat 44 on the raised areas 42 of the varnish undercoat 40, the metallic undercoat 44 having a higher refractive index than the varnish undercoat. The holographic layer 14 is then positioned on the support layer 16.

[0151] Layer 40 ( figure 7) The holographic layer 14 can, for example, be a thermoformable layer, allowing the reliefs 42 of the holographic structure 46 to be formed by embossing onto the layer 40, which serves as a support. Alternatively, the reliefs 42 of the holographic structure 46 can be produced using a UV curing technique. Since these manufacturing techniques are known to those skilled in the art, they are not described in further detail for the sake of simplicity.

[0152] A person skilled in the art will understand that the embodiments and variations described above are merely non-limiting examples of how the invention can be implemented. In particular, a person skilled in the art may consider any adaptation or combination of the embodiments and variations described above to meet a specific need in accordance with the claims set forth below.

Claims

1. Secure document (10) comprising: - a metal layer (14) including an arrangement of diffractive nanostructures, the diffractive nanostructures being disposed periodically in the metal layer (14) so as to form a diffractive holographic structure; - a lenticular array (12) comprising convergent lenses (13) positioned facing the metal layer; and - a support layer (16) on which the metal layer is disposed so that said metal layer is interposed between the lenticular array and the support layer; wherein the metal layer comprises perforations (20) formed by focusing a laser radiation through the lenticular array (12) onto the metal layer (14), the perforations comprising at least one group of perforations (201; 202) produced by focusing the laser radiation at a respective angle of incidence (θ) so as to reveal a corresponding personalized image (IG) when the secure document is observed at said angle of incidence, wherein the holographic structure, formed by the diffractive nanostructures of the metal layer (14), forms an arrangement of pixels (32) each including a plurality of subpixels (34) of distinct colors, the perforations (20) revealing, under observation, locally through the holographic structure, color or gray-level shades caused by underlying regions (Z1) of the support layer located facing the perforations, the underlying regions modifying the colorimetric contribution of the subpixels.

2. Document according to claim 1, the lenticular array (12) including a plurality of cylindrical convergent lenses extending parallel in a first direction (DR1).

3. Document according to claim 1 or 2, wherein each pixel (32) of said arrangement of pixels is configured so that each subpixel (34) has a unique color in said pixel.

4. Document according to any one of claims 1 to 3, the support layer (16) being opaque with respect to at least the visible wavelength spectrum, wherein the perforations (20) locally reveal, through the holographic structure, dark zones (Z2) in the subpixels (34) caused by underlying regions (Z1) of the support layer (16) located facing the perforations, so as to form a personalized image (IG) from the arrangement of pixels combined with the dark zones.

5. Document according to any one of claims 1 to 3, wherein the support layer (16) includes an ink sensitive to ultraviolet, so that the image is visible when the secure document is exposed to ultraviolet.

6. Document according to any one of claims 1 to 3, the support layer (16) being transparent with respect to at least the visible wavelength spectrum, wherein the perforations (20) locally reveal, through the holographic structure, light zones (Z2) in the subpixels when an incident light in the visible spectrum is projected to the perforations so as to form a personalized image (IG) from the arrangement of pixels combined with the light zones.

7. Document according to any one of claims 1 to 6, the lenticular array (12) comprising a plurality of cylindrical convergent lenses extending parallel in a first direction (DR1), wherein the arrangement (30) of pixels includes lines (LN) of subpixels (34) of the same color extending perpendicular to the first direction of the convergent cylindrical lenses.

8. Document according to any one of claims 1 to 7, wherein the lenticular array includes a plurality of semispherical or aspherical convergent lenses.

9. Document according to any one of claims 1 to 8, wherein the perforations (20) comprise a plurality of groups of perforations, each group of perforations being produced by focusing the laser radiation (RY) at a distinct angle of incidence (θ)so as to reveal interlaced personalized images that can be observed at the various angles of incidence.

10. Document according to any one of claims 1 to 9, wherein the metal layer is positioned approximately in the focal plane of the lenticular array.

11. Method for manufacturing a secure document (10), comprising: - forming (S2), on a support layer (16), a metal layer (14) including an arrangement of diffractive nanostructures, the diffractive nanostructures being disposed periodically in the metal layer (14) so as to form a diffractive holographic structure; - positioning (S4) a lenticular layer (12), comprising convergent lenses, facing the metal layer, the metal layer being interposed between the lenticular array and the support layer; and - forming (S6) perforations (20) by focusing a laser radiation (RY) through the lenticular array onto the metal layer, the perforations comprising at least one group of perforations produced by focusing the laser radiation at a respective angle of incidence so as to reveal a corresponding personalized image (IG) when the secure document is observed at said angle of incidence, wherein the holographic structure, formed by the diffractive nanostructures of the metal layer (14), forms an arrangement of pixels (32) each including a plurality of subpixels (34) of distinct colors, the perforations (20) revealing, under observation, locally through the holographic structure, color or gray-level shades caused by underlying regions (Z1) of the support layer located facing the perforations, the underlying regions modifying the colorimetric contribution of the subpixels.

Images