EP4088946A1 - Production of an image from a holographic structure - Google Patents

Abstract

The invention relates to a method comprising: providing a metallic holographic layer (6) comprising an underlayer (10) of metal and forming an arrangement (26) of pixels (27), each pixel comprising a plurality of sub-pixels (28) of distinct colors; partial destruction, by a first laser radiation (LS1), of the holographic layer so as to selectively remove portions of the metal underlayer to form demetallized areas (30); and laminating the holographic layer with top (4) and bottom (12) polymer layers; and personalization of the arrangement (26) of pixels by forming, by means of a second laser radiation (LS2), in the holographic layer, perforations (40) locally revealing zones (44) of shade of color in the undersides -pixels (28) caused by underlying regions (42) of the lower layer located opposite said perforations, so as to form a personalized image (IG).

Description

Technical area

The invention relates to a technique for forming color images and relates more particularly to a document comprising a holographic structure forming an arrangement of pixels from which an image is formed.

Prior technique

The identity market today requires increasingly secure identity documents (also known as identity documents). These documents must be easily authenticated and difficult to counterfeit (if possible tamper-proof). This market concerns a wide variety of documents, such as identity cards, passports, access badges, driving licenses, etc., which can be in different formats (cards, booklets, etc.).

Various types of secure documents comprising images have thus been developed over time, in particular for securely identifying people. The majority of passports, identity cards, driving licenses, etc. as well as many other official documents today include security elements which make it possible to authenticate the document and to limit the risks of fraud, falsification or counterfeiting.

Various printing techniques have been developed over time to make color prints. The production in particular of identity documents such as those mentioned above requires the production of color images in a secure manner in order to limit the risks of falsification by malicious individuals. The production of such documents, in particular at the level of the bearer's identity image, needs to be sufficiently complex to make reproduction or falsification by an unauthorized individual difficult.

Thus, a known solution consists in printing on a support a matrix of pixels composed of color sub-pixels and in forming gray levels by laser carbonization in a laserable layer located opposite the matrix of pixels, so as to reveal a custom color image that is difficult to forge or reproduce. Examples of embodiments of this technique are described for example in the documents EP 2 580 065 B1 (dated August 6, 2014 ) and EP 2 681 053 B1 (dated April 8, 2015 ).

However, it is indeed difficult to achieve high levels of color saturation when the color sub-pixels are formed by a conventional printing method, from type “offset” for example. The color gamut (ability to reproduce a range of colors) of this known technique may prove to be limited, due in particular to the fact that this known technique does not make it possible to form sufficiently rectilinear and continuous lines of sub-pixels, which generates homogeneity defects when printing sub-pixels (breaks in pixel lines, irregular outlines, etc.) and degraded colorimetric rendering.

Current printing techniques also offer limited positioning accuracy due to the inaccuracy of printing machines, which also reduces the quality of the final image due to poor positioning of the pixels and sub-pixels. to each other (problems with overlapping sub-pixels, misalignments...) or due to the presence of a non-printing tolerance gap between sub-pixels.

Another technique described in the document FR 3 093 302 aims to make color images from a hologram. This technique makes it possible to form good quality color images while being secure and therefore resistant to falsifications and fraudulent reproductions. Although this technique offers numerous advantages, improvements are still desirable in terms in particular of the quality of the image obtained.

Today there is a need to form images (in color or in grayscale) which are secure and of good quality, in particular in documents such as identity documents, official documents or others. A need exists in particular to allow flexible and secure personalization of images (in color or in grayscale), so that the image thus produced is difficult to falsify or reproduce and can be easily authenticated. It is also desirable that the images produced have a good level of image brightness as well as a sufficient color gamut, in particular to obtain the shades of color necessary for the formation of certain high quality color images, for example when image areas should exhibit a highly saturated level in a given color.

Disclosure of Invention

• fourniture d'une première couche comprenant une structure holographique métallique formant un arrangement de pixels, ladite structure holographique comprenant une sous-couche de métal, chaque pixel comportant une pluralité de sous-pixels de couleurs distinctes ;
• destruction partielle, par un premier rayonnement laser, de la première couche de sorte à retirer sélectivement au moins des portions de la sous-couche de métal pour former des zones démétallisées dans l'arrangement de pixels ; et
• lamination de la première couche avec une couche supérieure en polymère et une couche inférieure en polymère de sorte que la première couche soit intercalée entre les couches supérieure et inférieure ; et
• personnalisation de l'arrangement de pixels par formation au moyen d'un deuxième rayonnement laser, dans la première couche, de perforations révélant localement au travers de la structure holographique des zones de nuance de couleur dans les sous-pixels causées par des régions sous-jacentes de la couche inférieure situées en regard desdites perforations, de sorte à former une image personnalisée à partir de l'arrangement de pixels combiné aux zones de nuances de couleur.

To this end, the present invention relates to a method for manufacturing a secure document, said method successively comprising:

• providing a first layer comprising a metallic holographic structure forming an array of pixels, said holographic structure comprising a metal sub-layer, each pixel comprising a plurality of sub-pixels of distinct colors;
• partial destruction, by a first laser radiation, of the first layer so as to selectively remove at least portions of the metal sub-layer to form demetallized zones in the arrangement of pixels; and
• laminating the first layer with a top polymer layer and a bottom polymer layer such that the first layer is sandwiched between the top and bottom layers; and
• personalization of the arrangement of pixels by forming, by means of a second laser radiation, in the first layer, perforations revealing locally through the holographic structure areas of color nuance in the sub-pixels caused by sub-regions adjacent of the lower layer located opposite said perforations, so as to form a personalized image from the arrangement of pixels combined with the areas of shades of color.

The invention makes it possible to form images (in color or in levels of gray) which are secure and of good quality, in particular in documents such as identity documents, official documents or others. The invention allows flexible and secure customization of images (in color or in grayscale), so that the image thus produced is difficult to falsify or reproduce and can be easily authenticated. The images produced have a good level of image brightness as well as a high color gamut, which makes it possible, for example, to obtain the shades of color necessary for the formation of certain high-quality color images, for example when Image areas should exhibit a highly saturated level in a given color.

According to a particular embodiment, in which the demetallized zones form, during said lamination, polymer-to-polymer adhesion zones between the upper layer and the lower layer.

According to a particular embodiment, the first layer comprises an underlayer of varnish forming the reliefs of a holographic network,
the metal underlayer being deposited on the reliefs of the varnish underlayer to form the holographic structure, said metal underlayer having a refractive index greater than that of the varnish underlayer.

According to a particular embodiment, each pixel of said arrangement of pixels forms an identical pattern of color sub-pixels.

According to a particular embodiment, during the partial destruction, the demetallized zones are formed so that the cumulative surface of the demetallized zones is less than or equal to 30% of the total surface of the arrangement of pixels.

According to a particular embodiment, the demetallized zones are lines or islands distributed periodically in the first layer.

According to a particular embodiment, the demetallized zones form demetallization lines with a maximum width of 50 μm.

According to a particular embodiment, the demetallized zones form at least one group of demetallization lines parallel to each other, the distance between two consecutive demetallization lines of said at least one group being at most 60 μm.

According to a particular embodiment, the demetallized lines comprise a first group of demetallized lines arranged periodically so as to extend parallel along a first direction and comprise a second group of demetallized lines arranged periodically so as to extend parallel along a second direction, the lines of the first and second groups intersecting with each other.

According to a particular embodiment, the arrangement of pixels forms parallel lines of sub-pixels of the same color extending along a third direction, the first and second directions being different from the third direction.

According to a particular embodiment, during the partial destruction, the spot size of the first laser radiation in the first layer is less than or equal to 3 μm.

According to a particular embodiment, the first laser radiation used during the partial destruction is a UV (ultraviolet) laser.

According to a particular embodiment, the lower layer is an adhesive polymer layer, the method comprising, before lamination, an assembly by hot stamping of a polymer support layer on the lower layer so that the lower layer is at the interface between the first layer and the support layer.

According to a particular embodiment, the zones of shades of color are dark zones caused by said underlying regions of the lower layer of black color.

• détection des repères visuels ;
• détermination, à partir des repères visuels, de positions dans l'arrangement de pixels correspondant à des sous-pixels à personnaliser ; et
• projection du deuxième rayonnement laser pour former lesdites perforations dans la première couche au niveau des positions à personnaliser,

dans lequel, lors de la destruction partielle, les zones démétallisées sont formées dans des zones, de la première couche, distinctes des repères visuels.According to a particular embodiment, the holographic structure also forms visual cues in the arrangement of pixels, in which the personalization is implemented by a personalization device, said personalization comprising:

• detection of visual cues;
• determination, from the visual cues, of positions in the arrangement of pixels corresponding to sub-pixels to be personalized; and
• projection of the second laser radiation to form said perforations in the first layer at the positions to be personalized,

in which, during the partial destruction, the demetallized zones are formed in zones, of the first layer, distinct from the visual cues.

• une première couche comprenant une structure holographique métallique formant un arrangement de pixels, ladite structure holographique comprenant une sous-couche de métal, chaque pixel comportant une pluralité de sous-pixels de couleurs distinctes ;
• des zones démétallisées dans l'arrangement de pixels formées par une destruction partielle par un premier rayonnement laser de la première couche de sorte à retirer sélectivement au moins des portions de la sous-couche de métal ; et
• une couche supérieure en polymère et une couche inférieure en polymère qui sont laminées avec la première couche, ladite première couche étant intercalée entre les couches supérieure et inférieure, les zones démétallisées formant des zones d'adhésion de polymère à polymère par lamination de la couche supérieure avec la couche inférieure laminées ensemble ; et
• des perforations dans la première couche formée au moyen d'un deuxième rayonnement laser pour personnaliser l'arrangement de pixels, lesdites perforations révélant localement au travers de la structure holographique des zones de nuance de couleur dans les sous-pixels causées par des régions sous-jacentes de la couche inférieure situées en regard desdites perforations, de sorte à former une image personnalisée à partir de l'arrangement de pixels combiné aux zones de nuances de couleur.

The present invention also relates to a corresponding secure document (or multilayer structure) having structural characteristics corresponding to the result of the manufacturing method of the invention. In particular, the invention provides a secure document comprising:

• a first layer comprising a metallic holographic structure forming an arrangement of pixels, said holographic structure comprising a metal sub-layer, each pixel comprising a plurality of sub-pixels of distinct colors;
• demetallized areas in the pixel array formed by partial destruction by a first laser radiation of the first layer so as to selectively remove at least portions of the metal underlayer; and
• an upper polymer layer and a lower polymer layer which are laminated with the first layer, said first layer being interposed between the upper and lower layers, the demetallized zones forming polymer-to-polymer adhesion zones by lamination of the upper layer with the bottom layer laminated together; and
• perforations in the first layer formed by means of a second laser radiation to customize the arrangement of pixels, said perforations locally revealing through the holographic structure areas of color nuance in the sub-pixels caused by sub-pixel regions adjacent of the lower layer located opposite said perforations, so as to form a personalized image from the arrangement of pixels combined with the areas of shades of color.

It should be noted that the various embodiments mentioned above (as well as those described below) in relation to the manufacturing method of the invention as well as the associated advantages apply analogously to the secure document of the invention. .

According to a particular embodiment, the demetallized zones are formed so that the cumulative surface of the demetallized zones is less than or equal to 30%, even 20%, even 5%, even 3% of the total surface of the arrangement of pixels.

According to a particular embodiment, the demetallized zones are distributed periodically in the first layer.

According to a particular embodiment, the demetallized zones form demetallization lines with a maximum width of 50 μm.

According to a particular embodiment, the demetallized zones form at least one group of demetallization lines parallel to each other, the distance between two consecutive demetallization lines of said at least one group being at most 60 μm.

Brief description of the drawings

• [Fig. 1] La figure 1 représente une structure multicouche avant personnalisation, selon un exemple particulier ;
• [Fig. 2] La figure 2 représente la structure multicouche de la figure 1 après personnalisation, selon un mode de réalisation particulier de l'invention ;
• [Fig. 3A-3D] Les figures 3A, 3B, 3C et 3D représentent une structure multicouche ainsi que les étapes d'un procédé de fabrication d'une telle structure multicouche, selon un mode de réalisation particulier de l'invention ;
• [Fig. 4A-4B] Les figures 4A et 4B représentent des vues de dessus d'un arrangement de pixels avant démétallisation et après démétallisation, selon un mode de réalisation particulier de l'invention ;
• [Fig. 5] La figure 5 représente sous forme d'un diagramme les étapes d'un procédé de fabrication, selon un mode de réalisation particulier de l'invention ;
• [Fig. 6] La figure 6 représente schématiquement le rendu visuel d'une structure multicouche avant et après personnalisation, selon un mode de réalisation particulier de l'invention ;
• [Fig. 7] La figure 7 représente sous forme d'un diagramme les étapes d'un procédé de fabrication, selon un mode de réalisation particulier de l'invention ;
• [Fig. 8A-8C] Les figures 8A, 8B et 8C représentent des vues de dessus d'un arrangement de pixels avant démétallisation et après démétallisation, selon un mode de réalisation particulier de l'invention ; et
• [Fig. 9] La figure 9 représente schématiquement un système de fabrication, selon un mode de réalisation particulier de l'invention.

Other characteristics and advantages of the present invention will become apparent from the description given below, with reference to the appended drawings which illustrate examples of embodiments which are devoid of any limiting character. In the figures:

• [ Fig. 1 ] The figure 1 represents a multilayer structure before customization, according to a particular example;
• [ Fig. 2 ] The figure 2 represents the multilayer structure of the figure 1 after customization, according to a particular embodiment of the invention;
• [ Fig. 3A-3D ] The Figures 3A, 3B , 3C and 3D represent a multilayer structure as well as the steps of a method of manufacturing such a multilayer structure, according to a particular embodiment of the invention;
• [ Fig. 4A-4B ] The figures 4A and 4B represent top views of an arrangement of pixels before demetallization and after demetallization, according to a particular embodiment of the invention;
• [ Fig. 5 ] The figure 5 represents in the form of a diagram the steps of a manufacturing method, according to a particular embodiment of the invention;
• [ Fig. 6 ] The figure 6 schematically represents the visual rendering of a multilayer structure before and after personalization, according to a particular embodiment of the invention;
• [ Fig. 7 ] The figure 7 represents in the form of a diagram the steps of a manufacturing method, according to a particular embodiment of the invention;
• [ Fig. 8A-8C ] The figures 8A, 8B and 8C represent top views of an arrangement of pixels before demetallization and after demetallization, according to a particular embodiment of the invention; and
• [ Fig. 9 ] The figure 9 schematically represents a manufacturing system, according to a particular embodiment of the invention.

Description of embodiments

The invention proposes to form an image in color or in levels of gray in a secure manner from a metallic holographic layer forming an arrangement of pixels. The figures 1 and 2 represent an embodiment which does not implement the principle of the invention. More specifically, the figure 1 represents a multilayer structure 2, in an initial (virgin) state, from which a personalized color image can be formed. The multilayer structure 2 comprises a stack of layers laminated together, namely an upper layer 4 in polymer, a holographic layer 6 comprising a metallic holographic structure, an adhesive lower layer 12 in polymer and a support layer 14. The holographic layer 6 is positioned on the lower layer 12 and the lamination is carried out so that the assembly formed by the holographic layer 6 and the lower layer 12 is interposed between the upper layer 4 on the one hand and the support layer 14 on the other hand.

The metallic holographic structure in the holographic layer 6 intrinsically forms an arrangement of pixels (not represented) which is blank, in the sense that the pixels do not include the information defining the pattern of the final color image. Each pixel includes a plurality of color sub-pixels.

The holographic layer 6 comprises a metallic film (made of aluminum for example) covering reliefs containing three-dimensional information, these reliefs comprising protruding portions (also called “mountains”) separated by recesses (also called “valleys”). By effect of diffraction, refraction and/or reflection of an incident light, the holographic structure produces a hologram which represents the arrangement of pixels which it is advisable to personalize in order to form the desired final image.

According to a particular example, the holographic layer 6 is transparent, so that the holographic effect producing the arrangement 29 of pixels is visible by diffraction, reflection and refraction.

So, as shown in picture 2 , a personalization of the pixel arrangement can be achieved by the formation of perforations 16 in the holographic layer 6 by projecting a laser 18 (laser engraving). The holographic layer 6 is thus destroyed locally by the effect of the perforation of the laser 18.

The perforations 16 reveal locally through the holographic layer 6 areas of shade of color (opaque, clear, or other) in the arrangement of pixels, these areas of shade of color being caused by underlying regions, of the lower layer 12, located opposite (under) the perforations 16, so as to form a personalized color image from the arrangement of pixels combined with the color shade zones. By adapting the position and size of the color shade areas, it is thus possible to modulate the colorimetric contribution of the different color sub-pixels present in each pixel, and thus to reveal the personalized image from the arrangement of pixels.

If this technique makes it possible to form safe color images of relatively good quality compared to conventional techniques, improvements are however desirable.

Indeed, it has been observed that the quality of the adhesion between metal and polymer is often limited. However, the projection of the laser radiation 18 ( figure 2 ) on the metal film of the holographic layer 6 generates significant mechanical stresses in the multilayer structure during the personalization of the arrangement of pixels. The exposure of the metallic film to the laser 18 leads in particular to the sublimation of the metal present in the metallic film, which significantly degrades the adhesion between the layers. The layers of the multilayer structure 2 are then no longer in contact in these sublimation zones. The adhesion of the holographic structure is therefore thus reduced, which can lead to a loss of cohesion of the multilayer structure during personalization, possibly going as far as the generation of delaminations in the multilayer structure (so-called “blistering” effect). This phenomenon of sublimation of the metal and delamination significantly degrades the quality of the final color image obtained at the end of the personalization.

The invention proposes in particular to solve this problem of delamination which occurs in such multilayer structures during laser personalization of the arrangement of pixels.

As described below in particular embodiments, the invention provides in particular a method of manufacturing (or method of forming) an image from a multilayer structure comprising a holographic layer, the latter comprising a sub- metallic layer (or metallic film) and forming an arrangement of pixels by holographic effect. The method comprises in particular a step of partial destruction (also called step of “demetallization”) of the holographic layer by a first laser radiation, so as to remove (or delete, or demetallize) selectively at least portions of the metallic sub-layer to form demetallized (metal-free) areas in the pixel array. This partial destruction step is carried out before a delamination step during which the holographic layer, at least one lower polymer layer and at least one upper polymer layer are delaminated together.

After the lamination step, the arrangement of pixels can be personalized by forming, by means of a second laser radiation, in the holographic layer, perforations revealing locally through the holographic structure areas of shade of color in the sub-pixels caused by underlying regions of the lower layer located opposite said perforations, so as to form a personalized image from the arrangement of pixels combined with the areas of color shades.

As described later, the absence of metal in the demetallized areas of the holographic layer has the consequence that there is no sublimation caused in these areas during the subsequent personalization of the pixel arrangement with the laser. The demetallized zones form zones of reinforced adhesion which make it possible to avoid delaminations or loss of adhesion during personalization. During lamination, the polymer of the upper and lower layers migrates into the demetallized zones so as to establish a polymer adhesion bridge (from polymer to polymer) between these two layers.

The invention also relates to a corresponding document (also called secure document or multilayer structure). In particular, the invention relates to a document comprising structural characteristics identical to those obtained by the manufacturing method of the invention.

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

In the remainder of this document, examples of implementations of the invention are described in the case of a document comprising a color image according to the principle of the invention. This document can be any document, called a secure document, of the booklet, card or other type. The invention finds particular applications in the formation of identity images in identity documents such as: identity cards, credit cards, passports, driving licenses, secure entry badges, etc. The invention also applies to security documents (banknotes, notarized documents, official certificates, etc.) comprising at least one color image.

Generally, the image according to the invention can be formed on any suitable support.

Similarly, the exemplary embodiments described below aim to form an identity image. It is however understood that the image considered can be arbitrary. It may for example be an image representing the portrait of the holder of the document concerned, other implementations being however possible.

It should be noted that the invention makes it possible to form both color images and grayscale images. Also, in this document, unless otherwise indicated, the notion of color also covers black, gray and white. The invention makes it possible to form images of various colors, including grayscale images. In general, reference is therefore made to color images in this document.

Unless otherwise indicated, the elements common or similar to several figures bear the same reference signs and have identical or similar characteristics, so that these common elements

A secure document 25 and a method of manufacturing such a document are now described with reference to the figures 3A-3D , 4A-4B , 5 and 6 according to a particular embodiment of the invention. The figure 5 represents in particular in the form of a diagram the steps S2 to S8 of the manufacturing process according to a particular embodiment.

During a step S2 of providing ( Figure 3A ), a holographic layer 6 (also called “first layer”) is provided (or formed) comprising a metallic holographic structure. This holographic structure is formed by reliefs (or structures in relief) 8 and by a metal sub-layer 10 (or metal sub-layer, or metal film) covering the reliefs 8 of the holographic layer 6. The reliefs 8 form salient portions (also called "mountains") separated by recesses (also called "valleys"). These protruding portions and recesses define three-dimensional information.

The metal sub-layer 10 is a layer with a high refractive index which has a refractive index n2 greater than the refractive index n1 of the reliefs 8. As understood by those skilled in the art, the reliefs 8 form in combination with the metal underlayer 10 a holographic structure which produces a hologram (a holographic effect).

In this example, the holographic layer 6 is provided (or included) within a multilayer structure 25 ( Figure 3A ) which comprises a stack of layers, namely an upper layer 4 in polymer, the holographic layer 6, a lower layer 12 in polymer and a support layer 14. The holographic layer 6 is positioned on the lower layer 12 and the lamination is carried out so that the assembly formed by the holographic layer 6 and the lower layer 12 is interposed between the upper layer 4 on the one hand and the support layer 14 on the other hand. Thus, the holographic layer is located at the interface between the upper layer 4 and the lower layer 12.

The upper layer 4 and the support layer 14 are for example made of polycarbonate, or of another polymer.

In this example, the bottom layer 12 is an adhesive polymer layer (or polymer glue layer). In addition, the assembly of the layers 4, 6, 12 and 14 is for example carried out by hot stamping (known as “hot stamping”). Note however that during step S2 of the manufacturing process, it is possible to envisage providing the holographic layer 6 without the other layers 4, 6 and 14 (or at least one of them), and to assemble subsequently these layers by hot stamping (for example after step S4 of partial destruction described below).

According to a variant, layers 12 and 14 form one and the same polymer adhesive layer.

The multilayer structure 25 is at this stage (S2) in an initial state (or virgin state), from which can be formed a personalized color image IG (also called final image) as represented by way of example in figure 6 . As explained below, the multilayer structure 25 can be customized by laser so as to form this personalized image IG.

More precisely, the holographic structure of the holographic layer 6 intrinsically forms an arrangement 26 of pixels 27. Each pixel 27 comprises a plurality of sub-pixels 28 of distinct colors. Each sub-pixel has for example an elementary color of a color base (for example a color in the red-green-blue base).

In this example, it is assumed that each pixel 27 comprises 3 sub-pixels 28 of distinct colors, although other examples are possible. The number and arrangement of sub-pixels 28 in each pixel 27 can be adapted as appropriate (with 4 sub-pixels per pixel for example).

According to a particular example, each pixel 27 of the arrangement 26 of pixels forms an identical pattern of sub-pixels 28 of color.

Further, consider here that each pixel 27 of the pixel array 26 is configured such that each sub-pixel 28 has a unique (distinct) color in said pixel.

Each sub-pixel 28 in the array 26 of pixels may be formed by a respective holographic grating configured to generate by diffraction a corresponding color of said sub-pixel.

Additionally, the manner in which the pixels 27 are arranged in the array 26 may vary depending on the case. According to a particular example, the holographic structure is configured so that the sub-pixels 28 are uniformly distributed in the arrangement 26 of pixels. The arrangement 26 can take the form of a matrix of sub-pixels, forming rows of sub-pixels.

As depicted in figure 4A , the arrangement 26 of pixels forms for example lines 29 of sub-pixels of the same color. These lines 29 can be rectilinear and parallel to each other as shown in the figure. These lines 29 can also be contiguous. Other exemplary embodiments are however possible. In particular, the pixels 27 can be arranged to form various tessellations, such as hexagonal pixel tessellations or triangular pixel tessellations.

At the stage of supply step S2 represented in Figure 3A , the arrangement 26 of pixels is blank, in the sense that the pixels 27 do not include the information defining the pattern of the final image IG that it is desired to form. As described later, it is in combining this 26 pixel arrangement with areas of color shading one reveals the pattern of the final IG image.

The holographic structure produces the arrangement 26 of pixels 27 in the form of a hologram by diffraction, refraction and/or reflection of incident light. In other words, the holographic layer 6 forms the arrangement 26 of pixels by holographic effect. The principle of the hologram is well known to those skilled in the art so that only certain elements are recalled below for reference. Examples of embodiments of holographic structures are described for example in the document EP 2 567 270 B1 .

The holographic structure is produced by any suitable method known to those skilled in the art. The reliefs 8 of the holographic layer 6 can be formed, for example, by embossing a layer of stamping varnish (not shown) which is included in the holographic layer 6, in a known manner for producing diffractive structures. This layer of varnish is, for example, thermo-formable to allow the formation of the reliefs 8 by embossing. The stamped surface of the reliefs 8 thus has the form of a periodic network whose depth and period can be respectively of the order of a hundred to a few hundred nanometers for example. This stamped surface is coated with the metallic underlayer 10, for example by means of vacuum deposition of a metallic material. The holographic effect results from the combination of the reliefs 8 and the metal underlayer 10 forming the holographic structure.

According to a particular example, the holographic layer 6 comprises a varnish underlayer forming the reliefs 8 of a holographic network, the metallic underlayer 10 being deposited on the reliefs of the varnish underlayer to form the holographic structure, said metal sub-layer 10 having a refractive index n2 greater than the refractive index n1 of the varnish sub-layer.

As a variant, the reliefs 8 of the holographic layer 6 can be made using an ultraviolet (UV) crosslinking technique. This manufacturing technique being known to those skilled in the art, it is not described in detail for the sake of simplicity.

The holographic layer 6 may possibly comprise other sub-layers (not shown) necessary for maintaining the optical characteristics of the hologram and/or making it possible to ensure mechanical and chemical resistance of the assembly.

The metallic underlayer 10 with a high refractive index ( Figure 3A ) can comprise at least one of the following materials: aluminum, silver, copper, zinc sulphide, titanium oxide, etc. It is assumed here, for example, that the metal underlayer is made of aluminum, in an aluminum alloy or zinc sulfide.

According to a particular example, the reliefs 8 have a refractive index denoted ni, of the order of 1.56 at a wavelength λ1=656 nm. The reliefs 8 are formed from a transparent varnish undercoat. The metal sub-layer 10 has for example a high refractive index n2=2.346 at a wavelength λ2=660 nm for zinc sulphide. The metal sub-layer 12 has for example a thickness of between 30 and 200 nm.

As already indicated, the holographic layer 6 intrinsically forms an arrangement 26 of pixels which is blank before personalization, in the sense that the pixels 27 do not include the information defining the pattern of the final image IG that one wishes to form. . In the initial state (before customization) represented for example in figure 6 , the structure 22 therefore forms no personalized image IG.

During a step S4 of partial destruction ( figure 3B and 5 ), the holographic layer 6 is partially destroyed by means of a first laser radiation LS1, so as to selectively remove (or delete, or demetallize) at least portions of the metallic sub-layer 10 to form demetallized zones 30 in the 26 pixel arrangement.

This step S4 of partial destruction is for example implemented by means of a device DV1 ( figure 5 ) capable of projecting the laser radiation LS1 at particular positions where it is desired to form demetallized areas 30 in the arrangement 26 of pixels.

As illustrated in FIG. 3B, this demetallization step amounts here to forming perforations or holes 30 in the holographic structure of the first layer 6. At this stage, these destroyed zones are through perforations which extend through the thickness of the holographic layer 6, at the interface between the upper layer 4 and the lower layer 12. As will appear below, this partial destruction step S4 aims more particularly to remove the metal in certain areas 30 of the holographic layer 6 in order to prevent sublimation of the metal from occurring in these zones during the subsequent personalization step S8.

At the end of this step S4 of partial destruction, the final image IG is still not visible insofar as the arrangement 26 of pixels has not yet been personalized according to the pattern of the desired image.

The arrangement, position, shape and dimensions of the demetallized zones 30 formed during step S4 of partial destruction can be adapted as appropriate. However, these demetallized zones 30 preferably have limited dimensions and preferably occupy a limited cumulative space with respect to the total surface of the arrangement 26 of pixels, in order in particular to prevent an observer OB from being able to distinguish these demetallized zones 30 with the naked eye, so as not to degrade the quality of the final IG image that will be formed after the upcoming S8 customization.

Thus, according to a particular example, the demetallized zones 30 are formed in S4 ( Figure 3B ) so that the cumulative surface of the demetallized zones is less than or equal to 30%, or even 20%, or even 5%, or even 3% of the total surface of the arrangement 26 of pixels.

The demetallized areas 30 can be formed in various demetallization patterns. The demetallized zones 30 can thus form (or constitute) demetallized lines, for example rectilinear lines. As a variant, the demetallized zones 30 can constitute islands (of any shape, rectangular or square for example) which are for example distributed periodically in the holographic layer 6.

As depicted in figure 4B , according to a particular example, the demetallized zones 30 form demetallization lines with a maximum width of 50 μm, or even 40 μm, or even 5 μm, or even 2 μm.

According to a particular example, the demetallized zones 30 form islands or lines whose smallest size dimension in the plane of the arrangement 26 of pixels (island size or line width) is less than or equal to 50 μm, or even less or even 40 μm, or even 5 μm, or even 2 μm. Thus, if the demetallized zones 30 are rectangular, then their smallest dimension (width) in the plane of the arrangement 26 of pixels is less than or equal to one of the aforementioned threshold values. If the demetallized areas 30 are circular islands, then their radius in the plane of the arrangement 26 of pixels is less than or equal to one of the aforementioned threshold values.

Although a certain latitude exists in the configuration of the demetallized zones 30, it is advisable to avoid if possible the formation of demetallized patterns likely to produce a Moiret effect (image which moves) well known to those skilled in the art, which which would degrade the quality of the final IG image.

According to a particular example, the demetallized zones 30 form at least one group of demetallization lines 29 parallel to each other, the distance (or space) between two consecutive demetallization lines 30 of said at least one group being at most 60 μm, or even 50 µm. Beyond this maximum space, there is a risk that an OB observer could distinguish the lines of demetallization with the naked eye in the final personalized IG image. An interline distance of 60 µm corresponds to 1 minute of angle for an observer's eye located at a distance of 30 cm from the personalized image.

According to a particular example, the demetallization lines 29 of said at least one group are arranged periodically in the holographic layer 6 (in the plane of the arrangement 26 of pixels).

According to a particular example represented in figure 4B , the demetallized lines 29 comprise a first group of demetallized lines LN1 arranged periodically so as to extend parallel in a first direction DR1 and comprising a second group of demetallized lines LN2 arranged periodically so as to extend parallel in a second direction DR2 (different from DR1), the lines LN1, LN2 of the first and second groups intersecting with each other.

The figure 4B thus represents a particular example according to which the demetallized zones 30 are made in the form of a grid extending continuously over the surface of the arrangement 26 of pixels. Crossing the demetallization lines to form a grid significantly reduces the risk of delamination during future S8 customization. In particular, it has been found that if only one group of demetallized lines is formed in any direction, the risks of delamination are reduced but, despite everything, delaminations or cohesion defects in bands may still occur, c that is to say along the strips of the arrangement 26 located between (and delimited by) these lines of demetallization.

According to a particular example represented figure 4B , the arrangement 26 of pixels forms parallel rows 29 of sub-pixels of the same color extending along a third direction DR3, the first and second directions DR1, DR2 being different from the third direction DR3. In other words, the demetallization lines LN1, LN2 are not parallel to the lines of sub-pixels 29 to avoid the Moiret effect which would otherwise be likely to occur and which would degrade the quality of the personalized image IG.

Moreover, during step S4 of partial destruction, the spot size (that is to say the impact surface) of the first laser radiation LS1 in the holographic layer 6 is less than or equal to 3 μm. The spot size is preferably less than 2 μm, in particular in the case where demetallized lines are produced with a maximum width of 2 μm, in order to limit the size of the demetallized zones 30 and thus prevent these zones from being visible to naked eye, which ensures good quality of the IG custom image as already explained.

The first laser radiation LS1 used during the partial destruction at S4 is for example a UV (ultraviolet) laser, which makes it possible to carry out high-precision local demetallization in the metallic film 10. Alternatively, the laser LS1 is located in the spectrum of the green color or possibly near IR (infrared), but the precision during the demetallization is lower than for a UV laser and therefore does not make it possible to form such fine demetallized zones 30 .

After formation (S4) of the demetallized zones 30, a step S6 ( figure 3C and 5 ) of lamination during which the holographic layer 6, the upper layer 4 and the lower layer 12 are laminated together so that the holographic layer 6 is sandwiched between the upper and lower layers 4, 12.

As already indicated, in this particular example, the holographic layer 6 is provided in a multilayer structure 25 so as to be already interposed between the upper and lower layers 4, 12, these layers being arranged together on the support layer 14. Thus, the The lamination step S4 consists in this particular example of laminating together the holographic layer 6, the upper layer 4, the lower layer 12 and the support layer 14. Other examples are however possible in which the lower layer 12 and the support layer 14 form the same bottom layer, preferably adhesive.

A lamination is a mechanical process well known to those skilled in the art during which mechanical pressure is applied for an appropriate duration, with or without the supply of heat, so as to form a substantially coherent laminated assembly.

As depicted in Fig. 3C , due to the absence of metal in the demetallized zones 30, the polymer of the upper layer 4 and the polymer of the lower layer 12 migrate into the demetallized zones 30, through the holographic layer 6, so as to establish polymer adhesion bridges between the two layers 4, 12. This migration is represented by the reference 34 in Fig. 3C . These polymer bridges (or junctions) formed through the demetallized zones 30 constitute zones of reinforced adhesion, from polymer to polymer, of the upper and lower layers 4, 12 on either side of the holographic layer 6, which makes it possible to increase the mechanical resistance of the structure, in particular in the face of the stresses generated during the step S8 of customization to come.

Thus, during lamination S6, the upper and lower layers 4, 12 are pressed at pressure and temperature such that the polymer materials which constitute them reach their Vicat softening point and interpenetrate locally, through the holographic layer. 6 at the demetallized zones 30, to form a laminated structure having better consistency and increased resistance to mechanical stress.

After the lamination step S6, a step S8 is carried out ( 3d figures and 5 ) personalization of the arrangement 26 of pixels by formation by means of a second laser radiation LS2, in the holographic layer 6, of perforations (or holes) 40 revealing locally through the holographic structure (that is to say say through the holographic layer 6) areas 44 of shades of color in the sub-pixels 28, so as to form a personalized image IG from the arrangement 26 of pixels combined with the areas 44 of shades of color. These zones 44 of shade of color (or zones of colorimetric shade) are caused by underlying regions 42 of the lower layer 12 located opposite the perforations 40 (these underlying regions 42 therefore being visible by an observer OB through perforations 40). Once this personalization step S8 has been carried out, the multilayer structure 25 thus constitutes a secure document comprising a personalized color image IG.

This personalization step S8 is for example implemented by means of a personalization device DV2 ( figure 5 ) which projects the second laser radiation LS2 at particular positions of the arrangement 26 of pixels, to modulate (modify) the colorimetric contribution of certain sub-pixels 28 so as to reveal the desired personalized image IG.

The perforations 40 constitute regions in which the holographic layer 24 is destroyed or eliminated by the perforation effect of the laser. The areas 44 of shade of color thus produced (S8) in the arrangement 26 of pixels have a color which is a function of the nature of the underlying lower layer 12. In the case for example of a bottom layer 12 that is opaque or black, the areas 44 of shade of color are dark or black. If, on the contrary, the lower layer 12 is clear, the areas 44 of shade of color revealed through the perforations 40 are also clear. By adapting the position and the size of the zones 44 of shade of color, it is thus possible to modulate the colorimetric contribution of the various sub-pixels 28 of color present in each pixel 27, and thus to reveal the personalized image IG in the pixel arrangement. In other words, by making these perforations 40 with the laser LS2 through the thickness of the holographic layer 6, it is possible to discover underlying regions 42 of the lower layer 12 so as to produce zones 44 of colorimetric nuance, for example dark or light, in all or parts of sub-pixels 28. To do this, the perforations 40 may have various shapes and dimensions which may vary depending on the case.

More particularly, the perforations 40 are arranged so as to select the color of the pixels 27 by modifying the colorimetric contribution of the sub-pixels 28 relative to each other in at least part of the pixels 27 formed by the holographic layer 6, so revealing the personalized IG image from the arrangement 29 of pixels combined with the areas 44 of color swatch. The laser perforation in the holographic layer 24 leads to a local elimination (or deformation) of the geometry of the holographic structure, and more particularly of the reliefs 8 and/or of the metal underlayer 10 covering these reliefs. These local destructions lead to a modification of the behavior of light (ie reflection, diffraction, transmission and/or refraction of light) in the corresponding pixels and sub-pixels. By locally destroying all or part of the sub-pixels 28 by perforation and by revealing, instead, dark, light or other areas in the lower layer 12, levels of gray (or shades of colors) are thus generated in the pixels 27 by modifying the colorimetric contribution of certain sub-pixels, relative to each other, in the visual rendering of the final IG image. The creation of zones 44 of shade of color makes it possible in particular to modulate the passage of the incident light which is reflected on the arrangement 26 of pixels towards an observer OB, so that, for at least part of the pixels 27, a sub -pixel 28 or plus has an increased or decreased colorimetric contribution (or weight) relative to that of at least one other sub-pixel close to the pixel concerned. In particular, the holographic effect is eliminated, or reduced, in the perforated regions of the holographic structure, which decreases (or even completely eliminates) the relative color contribution of the at least partially perforated sub-pixels 28 with respect to at least another neighboring sub-pixel 28 of the pixels 27 concerned.

FIG. 6C illustrates the visual rendering of a personalized image IG at the end of the personalization step S8. It is assumed here that the image IG thus created is a color image resulting from a selective modulation of the colorimetric contributions of sub-pixels 28 of color. As already indicated, it is however possible to produce a personalized image IG in shades of gray in the same way, for example by adapting the colors of the sub-pixels 28 accordingly.

According to a particular example, the lower layer 12 positioned facing the holographic layer 6 is opaque (non-reflecting) with respect to at least the spectrum of visible wavelengths. In other words, the lower layer 12 absorbs at least the wavelengths in the visible spectrum. It is for example a dark layer (of black color for example). It is considered in this document that the visible wavelength spectrum is approximately between 400 and 800 nanometers (nm), or more precisely between 380 and 780 nm in a vacuum. It should be noted that this lower layer 12 may on the other hand be transparent to other wavelengths, in particular to infrared.

According to a particular example, the lower layer 12 is such that the black density of the personalized image IG is greater than the intrinsic black density of the holographic layer 6 without (independently of) the lower layer 12. skilled in the art, the black density can be measured by means of a suitable measuring device (for example, a colorimeter or a spectrometer).

According to a particular example, the lower layer 12 comprises an opaque black surface facing the holographic layer 6 and/or comprises black or black opacifying (or dark) pigments in its mass. The lower layer 12 may include in particular a black ink, or even a material tinted in its mass by black or opacifying (or dark) pigments.

The lower layer 12 can be of a color other than black or can be transparent.

The second laser radiation LS2 used in S8 to form the perforations 40 in the holographic layer 6 is preferably at a spectrum of wavelengths SP2 different from the spectrum of wavelengths of the visible. To do this, it is possible for example to use a YAG laser (for example at a wavelength of 1064 nm), a blue laser, a UV laser, etc. It is also possible to apply, for example, a pulse frequency of between 1 kHz and 100 kHz, although other configurations are possible. It is up to the person skilled in the art to choose the configuration of the laser radiation LS2 according to the specific case.

According to a particular example, the second laser radiation LS2 is identical to the first laser radiation LS1 used during demetallization S4 ( figure 5 ).

In addition, it is necessary for the holographic layer 6 (and more particularly its holographic structure) to at least partially absorb the energy delivered by the laser radiation LS2 to create the perforations 40 previously described. In other words, the laser radiation LS2 is characterized by a spectrum of wavelengths SP2 which is absorbed at least partially by the holographic structure. It is therefore possible to choose the materials of the holographic layer 6 accordingly.

According to a particular example, the materials forming the holographic structure are selected so that they do not absorb light in the visible. In this way, it is possible to create perforations 40 by means of laser radiation LS2 emitting outside the visible spectrum and to generate a personalized image IG which is visible to the human eye by holographic effect. Examples of materials are described later (transparent polycarbonate, PVC, transparent glue, etc.).

On the other hand, the spectrum SP2 is preferably chosen so that the laser radiation LS2 is not absorbed by the lower layer 12.

Additional layers (not shown), made of polymer such as polycarbonate or any other suitable material can also be applied on either side of the multilayer structure 25, in particular to protect the assembly.

As already indicated, the absence of metal in the demetallized zones 30 makes it possible to avoid the phenomenon of sublimation which would otherwise be caused in these zones during the personalization S8 by laser. The demetallized zones 30 thus form zones of increased adhesion which make it possible to avoid delaminations during customization S8. The adhesion bridges between the polymer material of the upper and lower layers 4, 12 make it possible to ensure better cohesion to the multilayer structure. The invention thus makes it possible to increase the mechanical resistance of the multilayer structure, in particular in the face of the stresses generated during step S8 of personalization by the second laser radiation LS2, and therefore to avoid or significantly reduce the phenomenon of delamination described above. Thanks to the invention, it is possible to produce high-quality secure images in color or in levels of gray.

The use of a holographic layer makes it possible to obtain an increased image quality, namely a better overall luminosity of the final image (more brilliance, more vivid colors) and a better capacity for color saturation. We can thus form a high quality color image with an improved color gamut compared to a printed image for example.

The use of a holographic structure to form the arrangement of pixels is advantageous in that this technique offers high positioning precision for the pixels and sub-pixels thus formed. This technique makes it possible in particular to avoid overlaps or misalignments between sub-pixels, which improves the overall visual rendering.

The invention makes it possible to produce personalized images that are easily authenticated and resistant to falsifications and fraudulent reproductions. It is in particular possible to produce the demetallized zones 30 according to complex patterns which are recognizable and authenticated using appropriate display means. The level of complexity and security of the image which is achieved thanks to the invention is not at the expense of the quality of the visual rendering of the image.

According to a particular example, it is also possible to dedicate (metallized) zones of the holographic layer which are intended to be subsequently demetallized by laser LS1 during the partial destruction S4. Thus, during the manufacture of the holographic layer, it is possible to configure certain metallized zones of the holographic structure (more precisely of the metal sub-layer) so that they are subsequently demetallized. For example a white line can be formed between each line of sub-pixels in the array of pixels, these white lines being for example of smaller width than the lines of sub-pixels. It is also possible to form within the arrangement of pixels a group of lines of sub-pixels (for example the lines of sub-pixels of the same color) so that the lines of this group have a greater width than the width of the other sub-pixel lines (for example the sub-pixel lines in the other colors). The larger width sub-pixel lines can thus be partially amputated (demetallized) during the demetallization, for example so that the lines of the group in question present after demetallization a width equal (or substantially equal) to that of the other rows of sub-pixels. Thus, a precise demetallization (with vision) is necessary to allow the demetallization in registration of the metallized portions designed for this purpose in the holographic layer, which makes it possible to add an additional level of security.

Furthermore, as shown in figures 4A and 4B , it is possible to use visual markers (or visual marks) 46 formed by the holographic layer 6 in the arrangement 26 of pixels in order to precisely position the laser shots LS2 produced by the device DV2 during the personalization S8. The use of these visual markers 46 makes it possible to form perforations 40 in registration with the sub-pixels 28. Good registration (that is to say a good relative positioning of the laser shots with respect to the sub-pixels) is necessary to allow precise customization of the arrangement 26 of pixels and thus the formation of a quality image.

To do this, the device DV2 can comprise display means for displaying during customization S8 the visual markers 46 present in the arrangement 26 of pixels, as well as laser projection means for projecting the laser radiation LS2 at determined positions. from the visual cues 46. The visualization function is represented by the reference VS in figure 7 . The device DV2 is in particular capable of moving relative to the arrangement 26 of pixels so as to detect the visual markers 46 and to position the laser projection means so as to form, by perforation with the laser LS2, the perforations 40 through the holographic layer 6.

The arrangement, position, shape and dimensions of the visual cues 46 can be adapted as appropriate. According to a particular example, the visual cues 46 (rectangular, square or other in shape) are distributed uniformly or periodically in the arrangement 26 of pixels (cf. by way of example the figure 4A ).

According to a particular example represented in figure 7 , during the manufacturing process previously described, the personalization device DV2 detects (S20) visual markers 46 present in the arrangement 26 of pixels, then determines (S22) from the visual markers 46, positions in the arrangement 26 pixels corresponding to 28 sub-pixels to customize. The device DV2 then projects the second laser radiation LS2 to form the perforations 40 in the holographic layer 6 at the positions thus determined.

However, it has been observed that the formation of the demetallized zones 30 during the partial destruction step S4 can make the personalization step S8 which follows more difficult. Indeed, the presence of the demetallized zones 30 can lead, during the personalization S8, to a degradation of the visibility of the visual markers 46 and/or to an alteration of the shape of the visual markers 46. This thus makes it more difficult to detect the visual cues during S8 customization, which can lead to punch 40 positioning errors and thus degraded IG custom image quality.

The figure 8A represents for example visual cues 46 as displayed by the display means of the device DV2 during the personalization step S8 (more particularly during the detection step S20, figure 7 ), in the particular example where the demetallized zones are configured as shown in figure 4B . As illustrated in figure 8A , the visual cues 46 appear for the personalization device DV2 with limited contrast and are difficult to detect for the DV2 device.

Also, according to a particular example, during step S4 ( figure 3B and 5 ) partial destruction laser LS1, the demetallized areas 30 are formed in areas (or regions) of the holographic layer 6 without altering the visual cues 46 formed intrinsically by the holographic layer 6 in the arrangement 26 of pixels. In other words, the areas demetallized 30 are formed in S4 so as not to alter or cover (or overlap with) visual markers 46 formed intrinsically by the holographic layer 46.

As shown for example in figure 8B , during step S4 partial destruction ( figure 3B and 5 ), the demetallized zones 30 are formed so as to define at least one window 50 devoid of demetallized zone 30, the visual markers 46 each being positioned in one of these windows 50. Thus, the demetallized zones 30 do not affect the visual rendering of the visual markers 46 so that the personalization device DV2 can detect them more easily during step S20 of detection ( figure 7 ).

The Fig. 8C represents for example the visual markers 46 as displayed by the display means of the device DV2 during the personalization step S8 in the particular case where the demetallized zones 30 are configured as represented in figure 8B . As illustrated in Fig. 8C , the visual cues 46 appear with better contrast and are easier to detect for the personalization device DV2.

Thanks to the invention, once the demetallization has been carried out in registration with respect to the visual cues 46 used for personalization, it is possible to know precisely the position of the demetallized zones 30 thus obtained. However, it has been observed in practice that laser parameters during S8 personalization with the LS2 laser can be adapted to optimize the quality of the personalized IG image (using a more energetic laser beam), but this more energetic optimization is likely to pose a problem because it can lead to delaminations in the demetallized zones 30. Since the position of the demetallized zones with respect to the visual markers is known with precision, it is thus possible to create a knockout in the image to be personalized so as not to affect the zones demetallized, which makes it possible to use a more energetic beam without risk of delamination.

The figure 9 represents, according to a particular example, a manufacturing system SY1 comprising the device DV1 configured to form the demetallized zones 30 during the step S4 of partial destruction. System SY1 further comprises a system of rollers (including rollers 52 and 54) for moving holographic layer 6 relative to device DV1.

The device DV1 comprises display means (for example a camera) for displaying the arrangement 26 of pixels formed by the holographic layer 6. The display function of the display means is represented by the reference VS in figure 9 . The visualization function VS in particular allows the device DV1 to examine the surface of the holographic layer and to detect visual cues, namely the visual cues 46 or other visual cues present for this purpose in the arrangement 26 of pixels to allow demetallization in S4 in registration with pixels 27.

The device DV1 further comprises laser projection means configured to project the first laser radiation LS1 onto the holographic layer 6 so as to form the demetallized areas 30. To do this, the device DV1 can locate visual cues as indicated above , determining positions in the arrangement 26 of pixels from these visual markers, and projecting the laser LS1 at the positions determined in the holographic layer 6 so as to form the desired demetallized areas 30 .

• une couche holographique 6 comprenant une structure holographique métallique formant l'arrangement 26 de pixels, cette structure holographique comprenant une sous-couche métallique 10, chaque pixel 28 comportant une pluralité de sous-pixels 28 de couleurs distinctes ;
• des zones démétallisées 30 dans l'arrangement 26 de pixels formées par une destruction partielle par un premier rayonnement laser LS1 de la couche holographique 6 de sorte à retirer sélectivement au moins des portions de la sous-couche métallique 10 ; et
• une couche supérieure 4 en polymère et une couche inférieure 12 en polymère qui sont laminées avec la couche holographique 6, cette couche holographique 6 étant intercalée entre les couches supérieure et inférieure 4,12, les zones démétallisées 30 formant des zones d'adhésion de polymère à polymère par lamination de la couche supérieure 4 avec la couche inférieure 12 laminées ensemble ; et
• des perforations 40 dans la couche holographique 6 formée au moyen d'un deuxième rayonnement laser LS2 pour personnaliser l'arrangement 26 de pixels, ces perforations révélant localement au travers de la structure holographique des zones 44 de nuance de couleur, dans les sous-pixels 28, causées par des régions sous-jacentes 42 de la couche inférieure 12 situées en regard des perforations 40, de sorte à former une image personnalisée IG à partir de l'arrangement 26 de pixels combiné aux zones 44 de nuances de couleur.

As already indicated, the invention relates to the method of manufacture as well as a secure document comprising a personalized image comprising the corresponding structural characteristics. In particular, the invention relates to a multilayer structure 25 (or secure document) as previously described with particular reference to the 3d figure and 6 , this multilayer structure comprising:

• a holographic layer 6 comprising a metallic holographic structure forming the arrangement 26 of pixels, this holographic structure comprising a metallic sub-layer 10, each pixel 28 comprising a plurality of sub-pixels 28 of distinct colors;
• demetallized areas 30 in the arrangement 26 of pixels formed by partial destruction by a first laser radiation LS1 of the holographic layer 6 so as to selectively remove at least portions of the metallic sub-layer 10; and
• an upper polymer layer 4 and a lower polymer layer 12 which are laminated with the holographic layer 6, this holographic layer 6 being interposed between the upper and lower layers 4,12, the demetallized zones 30 forming polymer adhesion zones to polymer by laminating top layer 4 with bottom layer 12 laminated together; and
• perforations 40 in the holographic layer 6 formed by means of a second laser radiation LS2 to personalize the arrangement 26 of pixels, these perforations revealing locally through the holographic structure areas 44 of shade of color, in the sub-pixels 28, caused by underlying regions 42 of the lower layer 12 located opposite the perforations 40, so as to form a personalized image IG from the arrangement 26 of pixels combined with the zones 44 of shades of color.

The various embodiments and variants described above with reference to the manufacturing method apply analogously to the multilayer structure (or secure document) of the invention. In particular, the demetallized zones 30 can be formed so that the cumulative surface of the demetallized zones 30 is less than or equal to 30%, even 20%, even 5%, even 3% of the total surface of the arrangement of pixels. .

The demetallized areas 30 can be distributed periodically in the holographic layer 6.

The demetallized zones 30 can form demetallization lines with a maximum width of 50 μm, or even 40 μm, or even 5 μm, or even 2 μm.

The demetallized zones 30 can form at least one group of demetallization lines parallel to one another, the distance between two consecutive demetallization lines of said at least one group being at most 60 μm, or even 50 μm.

A person skilled in the art will understand that the embodiments and variants described above only constitute non-limiting examples of implementation of the invention. In particular, those skilled in the art may consider any adaptation or combination of the embodiments and variants described above, in order to meet a very specific need in accordance with the claims presented below.

Claims (13)

Method for manufacturing a secure document (25), said method successively comprising: - supply (S2) of a first layer (6) comprising a metallic holographic structure forming an arrangement (26) of pixels (27), said holographic structure comprising an underlayer (10) of metal, each pixel comprising a plurality of sub-pixels (28) of distinct colors; - partial destruction (S4), by a first laser radiation (LS1), of the first layer so as to selectively remove at least portions of the metal sub-layer to form demetallized zones (30) in the arrangement of pixels ; and - lamination (S6) of the first layer with an upper layer (4) of polymer and a lower layer (12) of polymer so that the first layer is interposed between the upper and lower layers; and - customization (S8) of the arrangement (26) of pixels by forming, by means of a second laser radiation (LS2), in the first layer, perforations (40) locally revealing through the holographic structure areas (44 ) color shading in the sub-pixels (28) caused by underlying regions (42) of the lower layer located opposite said perforations, so as to form a personalized image (GI) from the arrangement of pixels combined with areas of color swatches. Process according to Claim 1, the demetallized zones (30) forming, during the said lamination, polymer-to-polymer adhesion zones between the upper layer and the lower layer. Process according to Claim 1 or 2, in which during the partial destruction (S4), the demetallized zones are formed so that: - the cumulative surface of the demetallized zones (30) is less than or equal to 30% of the total surface of the arrangement of pixels. Process according to any one of Claims 1 to 3, in which the demetallized zones (30) are lines or islands distributed periodically in the first layer. Method according to any one of Claims 1 to 4, in which the demetallized zones (30) form lines (LN1, LN2) of demetallization with a maximum width of 50 µm. Method according to claim 5, in which the demetallized zones (30) form at least one group of demetallization lines parallel to each other, the distance between two consecutive demetallization lines of said at least one group being at most 60 µm. Method according to claim 6, the demetallized lines comprising a first group of demetallized lines (LN1) arranged periodically so as to extend parallel in a first direction (DR1) and comprising a second group of demetallized lines (LN2) arranged periodically so to extend parallel in a second direction (DR2), the lines of the first and second groups intersecting with each other. A method according to claim 7, wherein the arrangement (26) of pixels forms parallel rows of same color sub-pixels extending along a third direction (DR3), the first and second directions being different from the third direction. A method according to any of claims 1 to 8, wherein upon partial destruction the spot size of the first laser radiation in the first layer is less than or equal to 3 µm. Method according to one of Claims 1 to 9, in which the first laser radiation (LS1) used during the partial destruction is a UV laser. Method according to any one of Claims 1 to 10, the lower layer (12) being an adhesive layer of polymer, the method comprising, before the lamination (S6), an assembly by hot stamping of a support layer (14) of polymer on the lower layer so that the lower layer (12) is at the interface between the first layer (6) and the support layer (14). A method according to any one of claims 1 to 11, wherein the areas (44) of color shading are dark areas caused by said underlying regions of the lower layer (12) of black color. A method according to any of claims 1 to 12, wherein the holographic structure further forms visual cues (46) in the pixel array (26), wherein the personalization is implemented by a personalization device (DV1), said personalization comprising: - detection (S20) of the visual cues; - determination (S22), from the visual cues, of positions in the arrangement of pixels corresponding to sub-pixels to be personalized; and - projection (S24) of the second laser radiation to form said perforations in the first layer at the positions to be personalized, wherein, upon partial destruction, the demetallized areas (30) are formed in areas of the first layer separate from the visual cues.

Images