SECURITY DOCUMENT AND CORRESPONDING MANUFACTURING PROCESS WITH A PERFORATED LIGHT-PROOF LAYER OVER A MATRIX OF COLORED SUBPIXELS.

Description

Technical Field

[0001] The invention relates to the field of security documents, and in particular to security documents on or within which images can be observed, and to the method of their manufacture. The invention applies, but not exclusively, to physical identity documents, such as a passport, an identity card, a driver's license, a residence permit, etc. Previous technique

[0002] The identity market today demands increasingly secure physical identity documents (also called identity documents or security documents). 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.). Security documents must be easily and quickly authenticated. Furthermore, they must be difficult to counterfeit (ideally unforgeable), especially given the latest counterfeiting techniques.

[0003] Security documents typically feature coloured images, for example photographs of the faces of a security document holder.

[0004] Color image formation techniques for secure identity documents use matrices of colored sub-pixels (e.g., with Red-Green-Blue sub-pixels or Cyan-Magenta-Yellow sub-pixels) and techniques to blacken a layer that will mask portions of sub-pixels to obtain pixels of a desired color.

[0005] For example, it is known to use laserizable layers, as described in earlier document FR 2 972 553 in which a laserizable layer is placed on top of a matrix of colored sub-pixels.

[0006] Other examples of conventional safety documents and corresponding manufacturing processes are described in the following documents: WO2016 / 030315-A1, FR3055112-A1, US2005 / 001419-A1, EP3828000-A1, WO2019 / 034398-A1 and JP2005219296-A.

[0007] Laserizable means that applying a laser beam to the layer (generally called laserizing) generates visible shades of gray through carbonization within that layer. For example, a laserizable layer can be a transparent polycarbonate layer and may contain additives that are sensitive to the passage of a laser beam, as this beam carbonizes them. Such a laserizable layer will be blackened or at least partially grayed throughout its thickness, depending on the laser's power, since the laser-sensitive additives are distributed uniformly throughout the layer's thickness.

[0008] Current color image formation techniques, such as those using laser-etched layers, particularly in secure identity documents, do not always produce satisfactory visual quality. Problems arise especially when the image formation techniques used are limited in their ability to produce certain colors. In other words, the color gamut (the range of achievable colors) of known color image formation techniques is sometimes limited.

[0009] A solution to this problem was described in document FR 3 079 052, which proposes implementing lenses opposite colored pixels to focus light onto white sub-pixels and improve the color gamut. This solution has the drawback of heating the documents, which can produce distortions. Furthermore, the lens magnification is insufficient to achieve a wide enough gamut.

[0010] There is a need for security documents with colour images that present a less limited colour gamut. Description of the invention

[0011] To this end, the present invention proposes a security document comprising a stack of layers having a matrix of colored sub-pixels, an opaque layer appearing white above the matrix of colored sub-pixels, in which the opaque layer appearing white has perforations opposite (e.g. above) sub-pixels of the matrix of colored sub-pixels such that when the device is viewed from above, a colored image appears, the document further comprising a laserizable layer arranged above the opaque layer appearing white and configured to be laserized by application of a laser beam at at least one laserization wavelength, and the document further comprising a filter limiting the passage of at least the laserization wavelength, the filter being arranged between the laserizable layer and the opaque layer appearing white.

[0012] Thus, the invention proposes using an opaque, white-appearing layer that can be perforated to reveal colored sub-pixels that were previously hidden by this opaque, white-appearing layer. This allows for the creation of image pixels with colored sub-pixels and a white contribution from the opaque white layer, as well as entirely white pixels, resulting in a wider color gamut and, in particular, brighter colors.

[0013] The invention also makes it possible to do without the use of lenses, the manufacture of which can heat up the documents.

[0014] It should be noted that a skilled professional will know how to select the opaque, white-appearing layer so that perforations can be made in it. Furthermore, this layer is opaque, so that the matrix of colored sub-pixels is not visible to the naked eye through it, except by using, for example, a lamp on the back of the document. Thus, "opaque" refers to a good level of opacity, for example, a level that hides the matrix of colored sub-pixels without using a lighting device underneath the document. Therefore, "opaque" can also be defined as meaning that the opaque, white-appearing layer masks the matrix of colored sub-pixels from a user observing it, without using a lighting device underneath the document (for example, lighting above the document is possible).

[0015] In the resulting colored image, pixels are defined as regions comprising colored sub-pixels visible through one or more perforations, possibly a portion of the opaque layer that appears white, or even just a portion of the opaque layer that appears white (which may correspond to a white sub-pixel). Dividing the image into pixels of equal dimensions is possible. It follows that one can thus obtain a colored image with pixels that are entirely white, partially white, or even with no portion of the opaque layer that appears white.

[0016] As explained above, a laser-etched coating is one in which applying a laser beam generates visible shades of gray through carbonization. For example, a laser-etched coating can be a transparent polycarbonate layer and may contain additives that are sensitive to the passage of a laser beam, as this beam carbonizes them. Such a laser-etched coating will be blackened or at least partially grayed throughout its thickness, depending on the laser's power, since the laser-sensitive additives are distributed uniformly throughout the coating's thickness.

[0017] The use of the laserizable layer will allow the color gamut to be extended towards dark colors, since completely black pixels can be obtained by laserization.

[0018] The laserizable layer can be transparent, and therefore the opaque layer, which appears white, is more opaque than this layer.

[0019] Finally, the use of a filter is well suited for fragile opaque layers with a white appearance, for example thin layers of metal oxides, which could be affected, for example perforated by the laser beam at the laserization wavelength.

[0020] The filter can either be a laminated filter layer or, alternatively, the laserizable layer itself. For example, a laserizable layer that filters ultraviolet (UV) radiation and is sensitive to UV radiation can be used for laserizing.

[0021] According to a particular embodiment, the laserizable layer includes portions blackened by laserization.

[0022] For example, these darkened areas are positioned above colored sub-pixels to affect the perceived hue. Similarly, these darkened areas can be positioned above portions of the opaque layer that appear white, or above perforations in that layer. Therefore, it's easy to see how the color gamut is enhanced (a black channel is added).

[0023] The blackened areas improve the contrast of the resulting coloured images.

[0024] According to a particular embodiment, the opaque layer with a white appearance is chosen to be perforated by a laser beam of a perforation wavelength.

[0025] This particular method of implementation allows for simple customization of the colored image.

[0026] According to a particular embodiment, the perforation wavelength differs from the laserization wavelength.

[0027] For example, this allows the opaque, white-looking layer to be perforated without the laserizable layer being laserized.

[0028] A laser beam can be used for laserization with a higher energy than the laser beam used for perforation.

[0029] For example, for a laserization wavelength in the UV range, a perforation wavelength in the infrared range can be used (the filter can be configured to allow this wavelength to pass through).

[0030] According to a particular embodiment, a pixel of the coloured image comprises a coloured sub-pixel visible through a perforation and a white-appearing portion of the white-appearing opaque layer forming a white sub-pixel of the pixel.

[0031] According to a particular embodiment, the opaque, white-appearing layer comprises a metallic oxide.

[0032] The invention also proposes a method for manufacturing a security document in which a matrix of colored sub-pixels is assembled with, above the matrix of colored sub-pixels, an opaque layer appearing white, the method further comprising forming perforations through the opaque layer appearing white and opposite sub-pixels of the matrix of colored sub-pixels such that when the device is viewed from above, a colored image appears, in which a laserizable layer is further assembled above the opaque layer appearing white and configured to be laserized by application of a laser beam at at least one laser wavelength, and in which a filter is further assembled limiting the passage of at least the laser wavelength between the laserizable layer and the opaque layer appearing white, orThe laserizable layer is configured to form a filter limiting the passage of at least the laser wavelength.

[0033] This process can be adapted for the manufacture of all embodiments of the safety document as described above.

[0034] The filter prevents degradation of the opaque, white-appearing layer, which can be very fragile as it can be perforated, for example, by the application of a laser beam.

[0035] The filter can be one that filters at least the laser wavelength but allows other wavelengths to pass through.

[0036] According to a particular implementation method, the laserizable layer is laser-etched to obtain blackened portions.

[0037] According to a particular implementation method, the opaque white-appearing layer is perforated by a laser beam of a perforation wavelength to obtain the perforations.

[0038] According to a particular implementation method, the perforation wavelength differs from the laserization wavelength (the perforation wavelength is preferably unfiltered by the filter).

[0039] This particular embodiment proposes to use two different laser wavelengths, which is advantageous since the energy required for carbonization can be several times that required for perforation.

[0040] In fact, if a laser beam of a given wavelength is used for carbonization and is subsequently stopped by the filter, it is no longer possible to transmit sufficient energy to penetrate the opaque, white-appearing layer beneath the filter without further carbonizing the laser-sensitive layer. However, it is desirable to be able to make a colored subpixel visible beneath the opaque, white-appearing layer without carbonizing that subpixel. Therefore, using a different wavelength, not stopped by the filter or at least less stopped by the filter, can penetrate the opaque, white-appearing layer without contributing to carbonization. This allows for the independent generation of colors and a black channel that provides contrast.

[0041] According to a particular implementation method, the process includes a registration phase in which the position of a group of colored sub-pixels is observed prior to the formation of the perforations that form the colored image.

[0042] The registration phase is a phase during which the position of the colored sub-pixels of the colored sub-pixel matrix is ​​determined, so that the formation of the perforations takes these positions into account.

[0043] Since the colored subpixels are arranged in a matrix, they are aligned along two orthogonal directions. For example, the matrix of colored subpixels can include subpixels with a number N of colors (for example, N=3), arranged in a pattern in which at least N subpixels, all of different colors, are repeated along the two orthogonal directions to form the matrix of colored subpixels.

[0044] The position of a sub-pixel of a given color at a given position allows the position of the other sub-pixels to be deduced during the registration process.

[0045] The position of several colored sub-pixels allows for interpolation between these sub-pixels to more accurately deduce the position of the other sub-pixels during registration. This allows for the consideration of distortions in the colored sub-pixel matrix.

[0046] The registration step facilitates the subsequent implementation of perforation formation in the opaque, white-appearing layer, since it allows us to know the color of the sub-pixels that will be revealed by the perforations.

[0047] According to a particular implementation method, the colored sub-pixels of the colored sub-pixel group are observable through one or more perforations in the opaque layer that appears white.

[0048] The perforations used in this step may not be the perforations that will be used to make the colored image appear, but perforations formed before those that will be used to make the colored image appear (although they may be visible within the colored image).

[0049] According to a particular method of implementation, a series of trenches are formed in a grid pattern through the opaque, white-looking layer.

[0050] For example, these trenches are created by a demetallization process during the application of the opaque, white-appearing layer. Alternatively, the opaque, white-appearing layer can be applied to the entire surface and then partially removed, for example in a grid pattern, before this layer is laminated into the document.

[0051] This series of trenches helps to improve the adhesion of the opaque, white-looking layer to the other layers of the security document.

[0052] According to a particular method of implementation, the position of the group of colored sub-pixels is observed through these trenches.

[0053] This method of implementation is particularly advantageous since it uses trenches which improve the adhesion of the opaque white-appearing layer to the other layers of the security document to observe the sub-pixels and implement a registration.

[0054] It can be noted that the trenches can be made during a step other than that of perforation formation; in particular, the trenches are made here before the perforations. Brief description of the drawings

[0055] 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 security document before perforation, according to an example, [ Fig. 2 ] There figure 2 is a cross-sectional view of the document of the figure 1 after perforation, [ Fig. 3 ] There figure 3 is a cross-sectional view of the document of the figure 2 after laser treatment, [ Fig. 4 ] There figure 4 is a top view of the matrix of colored sub-pixels, [ Fig. 5 ] There figure 5 is an illustration of interpolations determined during a registration, [ Fig. 6 ] There figure 6 is a cross-sectional view of a document with trenches before perforation, [ Fig. 7 ] There figure 7 is a top view of the document of the figure 6 , And [ Fig. 8 ] There figure 8 is a cross-sectional view of a document with a filtering laserizable layer. Description of the implementation methods

[0056] We will now describe security documents comprising both matrices of colored sub-pixels and opaque layers of white appearance, with an improved color gamut at least in terms of brightness.

[0057] The images formed by these sub-pixels are customizable images, which can be different for each document, and which can be unique to each document user.

[0058] The documents described here can be physical identity documents such as a passport, identity card, driver's license, residence permit, etc. In fact, the documents described here can be associated with a user, and the colored images that will be obtained can be images of the users' faces.

[0059] On the figure 1 We have schematically represented a document 100 obtained by the assembly of different layers, which may have been implemented by means of a lamination.

[0060] Document 100 specifically includes a colored subpixel matrix 101, for example, a transparent or opaque layer on which colored elements have been printed, each forming a colored subpixel. Here, the colored subpixel matrix comprises subpixels with three possible colors: cyan subpixels (SB), magenta subpixels (SM), and yellow subpixels (SJ). These are the three colors of the color model well known to those skilled in the art by the acronym CMY ("Cyan Magenta Yellow"). The invention is not limited to this color model and can also use a model such as RGB ("Red Green Blue"). Of course, other color triplets that differ from CMY and RGB can be used.

[0061] The sub-pixels are arranged according to a matrix which will be described in more detail with reference to the figure 4 However, it can be noted that a PM pattern of three sub-pixels SB, SM, and SJ is repeated several times in the section visible on the figure 1 .

[0062] Above the array of colored sub-pixels, an opaque layer with a white appearance (102) has been assembled, for example, a thin layer of metal oxide. This layer can be chosen so that perforations can be easily formed in it, for example, by applying a laser beam with a given wavelength called the perforation wavelength.

[0063] Above the opaque, white-appearing layer 102, a laserizable layer 103 has been arranged. This laserizable layer is initially transparent and contains particles that can be carbonized by the application of a laser beam, specifically a laser beam at a given wavelength called the laserization wavelength. Applying the laser beam creates grayscale areas, or even black areas, within the laserizable layer. For reference, the laserizable layer comprises polycarbonate and the particles that react to the laser beams.

[0064] To prevent damage to the white-appearing opaque layer 102 during the laser engraving of document 100, a filter 104 is arranged between the laserizable layer 103 and the white-appearing opaque layer 102. This filter is configured to limit the passage of a laser beam at the laser engraving wavelength, so that this wavelength does not reach the white-appearing opaque layer. Conversely, this filter preferably allows passage at the perforation wavelength mentioned above, which differs from the laser engraving wavelength.

[0065] For example, the filter may consist of a polymer layer (possibly the same type of polymer as other layers in the document) but loaded with a substance that absorbs a given spectrum including the laser wavelength. The filter's transmittance is therefore low at the laser wavelength and higher at other wavelengths (particularly the perforation wavelength).

[0066] It should be noted that the substance used may differ depending on whether the goal is to block / filter infrared or ultraviolet radiation. It is also possible to use a layer of laser-etched polycarbonate, which also filters UV rays and is laser-etched using UV radiation.

[0067] For example, and as will be described with reference to the figure 8 , one can use a layer of polycarbonate which is carbonized on the surface with a laser having UV radiation, and implement the perforation of the opaque white-looking layer with low-power infrared radiation (so that it does not carbonize the laserizable layer).

[0068] Optionally, an intermediate transparent layer 105, for example made of polycarbonate, is arranged between the opaque white-looking layer 102 and the filter 104.

[0069] Also, optionally, under the colored sub-pixel matrix 101, a protective layer 107 has been arranged which can be opaque or transparent, for example made of polycarbonate.

[0070] There figure 2 Figure 100 shows after a step in which PF perforations are formed in the opaque, white-appearing layer has been implemented. This step may involve applying a laser beam at the perforation wavelength.

[0071] At this stage, we note that each pattern of colored PM sub-pixels is associated with different perforations. From left to right in the figure: The first pattern is associated with a single perforation above its cyan sub-pixel; when viewed from above the document, it will have a very bright cyan appearance (it is associated with two white-appearing portions); the second pattern is associated with two perforations above its cyan sub-pixel and above its yellow sub-pixel; it will have a very bright green appearance (it is associated with a white-appearing portion); the third pattern has no perforations; it will appear white when viewed from above; and the fourth pattern has perforations above all its sub-pixels; it will have a grey appearance due to the combination of the three components: cyan, yellow, and magenta.

[0072] A colorful image appears when viewing document 100, with colors brighter than those produced using prior art techniques. It can be noted that the combination of patterns and perforations forms image pixels, but, as will be described below, those obtained after the optional laserization step are called pixels.

[0073] On the figure 3 Document 100 was represented after a laserization step was implemented. In this step, a laser beam was applied to the top of document 100 to form blackened (or at least grey) areas within the thickness of the laserizable layer 103.

[0074] More specifically, a blackened area PN1 was formed above the yellow subpixel of the leftmost subpixel pattern in the figure, and a blackened area PN2 was formed above the magenta and yellow subpixels of the third subpixel pattern from the left in the figure. Thus, a colored image is obtained when viewing document 100 from above, comprising (considering the pixels from left to right in the figure): a PX1 pixel with a cyan appearance, less bright than the one obtained for the figure 2 in the same location; a green-appearing PX2 pixel, identical to that of the figure 2 at the same location; a gray-appearing pixel PX3, resulting from the presence of the blackened portion PN2 on two-thirds of the surface of pixel PX3; and a gray-appearing pixel PX4, identical to that of the figure 2 in the same location.

[0075] It is understood that the combination of the opaque, white-looking layer 102, which is perforated, with the laser-etched layer 103, makes it possible to obtain a very wide color gamut, especially for the brightest colors.

[0076] On the figure 4 A top view of the 101 colored sub-pixel matrix is ​​shown. For reference, the area occupied by pixel PX1 is described in reference to the figure 3 is represented by a rectangle with a dashed line.

[0077] Here, colored lines are aligned in groups of three colors, i.e., three lines.

[0078] It's worth noting that in solutions based on prior art, a fourth white line can be added to obtain brighter colors. However, adding this fourth line increases the pixel size and decreases image resolution, while also being less satisfactory in terms of color gamut because the maximum possible color saturation will be lower. Indeed, when only three colors are present without white, each covers 1 / 3 of the surface, whereas if white lines are present, each color covers only 1 / 4 of the surface, leading to lower saturation.

[0079] Other arrangements are possible, including with other colours and other matrix formats.

[0080] On the figure 5 The result of a calibration phase was represented.

[0081] This registration phase is implemented prior to the formation of the perforations and aims to determine the position of the colored sub-pixels of the colored sub-pixel matrix, particularly in the event of deformations of this matrix within a document.

[0082] The registration process can be implemented automatically, for example by means of a computer system equipped with a camera to view the documents.

[0083] In this phase, we can observe the position of a group of colored sub-pixels, labeled PO, on the figure 5 For example, these subpixels can be observed through initial perforations used solely for registration. Alternatively, the colored subpixels can be observed by transparency through the document, for example, by using a powerful lighting device beneath the document.

[0084] From the observed positions of the colored sub-pixels PO (which have expected colors in expected locations), we can, for example, deduce polynomial regression equations that pass through these points and obtain a transformation to apply to the matrix to estimate the position of each colored sub-pixel. This transformation effectively distorts an initially orthonormal grid.

[0085] This step is advantageous for sub-pixels with dimensions on the order of 60 to 70 micrometers, to ensure that a laser beam is applied over the correct sub-pixels to produce a colored image with the correct hues on each document.

[0086] On the figure 6 A document 100' was shown in a variant in which a TR trench was formed in an opaque, white-appearing layer 102'. The elements bearing the same references in this figure and on the figures 1 à 5 are identical.

[0087] This TR trench improves adhesion between the opaque, white-looking layer 102', which may contain a metallic oxide, and the other layers of the document, which are, for example, made of polymer.

[0088] Furthermore, through this trench, which is formed before the perforations, colored sub-pixels can be observed. This allows for registration, as the pixels of the pixel group are visible through the trench (or trenches if there are several, as in the image). figure 7 ).

[0089] An advantageous arrangement for TR trenches is shown on the figure 7 , on which, in top view, we see that a grid pattern is formed by the TR trenches.

[0090] On the figure 8 A 100" document was represented according to another variant. The elements that bear the same references in this figure and in the figures 1 à 5are identical. Here, the laserizable layer 103' reacts, for laserization, to radiation with a laserization wavelength in the ultraviolet (UV) range. This layer is further configured to act as a UV filter (carbonization can occur on the upper surface shown in the figure). As a result, UV radiation does not affect the opaque, white-appearing layer 102 and does not degrade it during laserization.

[0091] The opaque, white-appearing layer can nevertheless be perforated with a laser beam of a wavelength in the infrared range, for example, a low-intensity beam. The laserizable layer 103' can be configured to allow this infrared laser beam to pass through. This embodiment is advantageous because it requires fewer layers to form a document.

[0092] It's worth noting that the perforations described here can be the size of a subpixel or even smaller than a subpixel. The blackened areas can also be the size of a subpixel or even smaller than a subpixel. This allows for fine-tuning the colors of each pixel.

Claims

1. Security document comprising a stack of layers comprising a matrix (101) of colored sub-pixels (SB, SM, SJ), an opaque layer with a white appearance (102) above the matrix of colored sub-pixels, wherein the opaque layer with a white appearance comprises perforations (PF) facing sub-pixels of the matrix of colored sub-pixels such that, when the device is observed from above, a colored image appears, the document furthermore comprising a laserable layer (103) arranged above the opaque layer with a white appearance and configured to be laserized by applying a laser beam at at least one laserization wavelength, and the document furthermore comprising a filter (104) limiting the passage of at least the laserization wavelength, the filter being arranged between the laserable layer and the opaque layer with a white appearance.

2. Document according to Claim 1, wherein the laserable layer comprises portions (PN1, PN2) that are blackened by laserization.

3. Document according to any one of Claims 1 or 2, wherein the opaque layer with a white appearance is chosen so as to be perforated by a laser beam with a perforation wavelength.

4. Document according to Claims 1 to 3, wherein the perforation wavelength is different from the laserization wavelength.

5. Document according to any one of Claims 1 to 4, wherein a pixel (PX1) of the colored image comprises a colored sub-pixel visible through a perforation and a portion with a white appearance of the opaque layer with a white appearance forming a white sub-pixel of the pixel.

6. Document according to any one of Claims 1 to 5, wherein the opaque layer with a white appearance comprises a metal oxide.

7. Method for manufacturing a security document, comprising assembling a matrix (101) of colored sub-pixels (SB, SM, SJ) with, above the matrix of colored sub-pixels, an opaque layer with a white appearance (102), the method furthermore comprising forming perforations (PF) through the opaque layer with a white appearance and facing sub-pixels of the matrix of colored sub-pixels such that, when the device is observed from above, a colored image appears, wherein a laserable layer (103) is furthermore assembled above the opaque layer with a white appearance and configured to be laserized by applying a laser beam at at least one laserization wavelength, and wherein a filter (104) limiting the passage of at least the laserization wavelength is furthermore assembled between the laserable layer and the opaque layer with a white appearance.

8. Method according to Claim 7, wherein the laserable layer is laserized so as to obtain blackened portions.

9. Method according to any one of Claims 7 or 8, wherein the opaque layer with a white appearance is perforated by a laser beam with a perforation wavelength so as to obtain the perforations.

10. Method according to Claim 9, wherein the perforation wavelength is different from the laserization wavelength.

11. Method according to any one of Claims 7 to 10, comprising a registration phase comprising observing the position of a group of colored sub-pixels prior to the formation of the perforations that form the colored image.

12. Method according to Claim 11, wherein the colored sub-pixels of the group of colored sub-pixels may be observed through one or more perforations in the opaque layer with a white appearance.

13. Method according to any one of Claims 7 to 12, wherein a set of trenches (TR) is formed in a grid-shaped pattern through the opaque layer with a white appearance.

14. Method according to Claims 12 and 13, wherein the position of the group of colored sub-pixels is observed through the trenches.|