SECURITY DOCUMENT COMPRISING A PERFORATED OPAQUE LAYER WITH A WHITE APPEARANCE ABOVE A MATRIX OF COLOURED SUB-PIXELS

Abstract

A security document having a stack of layers including a matrix of coloured sub-pixels, an opaque layer with a white appearance above the matrix of coloured sub-pixels, the opaque layer with a white appearance having perforations facing sub-pixels of the matrix of coloured sub-pixels such that, when the device is observed from above, a coloured image appears.

Claims

1. A security document comprising: a stack of layers having a matrix of coloured sub-pixels; and an opaque layer with a white appearance above the matrix of coloured sub-pixels, wherein the opaque layer with a white appearance includes perforations facing sub-pixels of the matrix of coloured sub-pixels such that, when the security document is observed from above, a coloured image appears.

2. The security document according to claim 1, further comprising: a laserable layer 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.

3. The security document according to claim 2, wherein the laserable layer comprises portions that are blackened by laserization.

4. The security document according to claim 2, further comprising a filter limiting passage of at least the laserization wavelength, the filter being arranged between the laserable layer and the opaque layer with a white appearance, or wherein the laserable layer is configured to form the filter limiting the passage of at least the laserization wavelength.

5. The security document according to claim 1, wherein the opaque layer with a white appearance is chosen to be perforated by a laser beam with a perforation wavelength.

6. The security document according to claim 2, wherein a perforation wavelength is different from the laserization wavelength.

7. The security document according to claim 1, wherein a pixel of the coloured image includes a coloured 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.

8. The security document according to claim 1, wherein the opaque layer with a white appearance includes a metal oxide.

9. A method for manufacturing a security document, comprising: assembling a matrix of coloured sub-pixels with, above the matrix of coloured sub-pixels, an opaque layer with a white appearance, and forming perforations through the opaque layer with a white appearance and facing sub-pixels of the matrix of coloured sub-pixels such that, when the security document is observed from above, a coloured image appears.

10. The method according to claim 9, wherein a laserable layer is furthermore assembled above the opaque layer with a w % bite appearance and configured to be laserized by applying a laser beam at at least one laserization wavelength.

11. The method according to claim 10, wherein the laserable layer is laserized to obtain blackened portions.

12. The method according to claim 10, wherein a filter limiting passage of at least the laserization wavelength is furthermore assembled between the laserable layer and the opaque layer with a white appearance, or wherein the laserable layer is configured to form the filter limiting the passage of at least the laserization wavelength.

13. The method according to claim 9, wherein the opaque layer with a white appearance is perforated by a laser beam with a perforation wavelength sees to obtain the perforations.

14. The method according to claim 10, wherein a perforation wavelength is different from the laserization wavelength.

15. The method according to claim 9, further comprising, in a registration phase, observing a position of a group of coloured sub-pixels prior to formation of the perforations that form the coloured image.

16. The method according to claim 15, wherein the coloured sub-pixels of the group of coloured sub-pixels are observable through one or more perforations in the opaque layer with a white appearance.

17. The method according to claim 9, wherein a set of trenches is formed in a grid-shaped pattern through the opaque layer with a white appearance.

18. The method according to claim 15, wherein the position of the group of coloured sub-pixels is observed through trenches.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Other features and advantages of the present invention will become apparent from the description given below, with reference to the appended drawings, which illustrate exemplary embodiments thereof that are completely non-limiting in nature. In the figures:

[0061] FIG. 1 is a sectional view of a security document before perforation, according to one example,

[0062] FIG. 2 is a sectional view of the document of FIG. 1 after perforation,

[0063] FIG. 3 is a sectional view of the document of FIG. 2 after laserization,

[0064] FIG. 4 is a plan view of the matrix of coloured sub-pixels,

[0065] FIG. 5 is an illustration of interpolations determined during a registration,

[0066] FIG. 6 is a sectional view of a document with trenches before perforation,

[0067] FIG. 7 is a plan view of the document of FIG. 6, and

[0068] FIG. 8 is a sectional view of a document with a filtering laserable layer.

DESCRIPTION OF EMBODIMENTS

[0069] A description will now be given of security documents comprising both matrices of coloured sub-pixels and opaque layers with a white appearance, with a colour gamut that is improved at least in terms of brightness.

[0070] The images formed by these sub-pixels are customizable images, which may be different for each document, and which may be specific to each document user.

[0071] The documents described here may be physical identity documents such as a passport, an identity card, a driving licence, a residence permit, etc. In fact, the documents described here may be associated with a user, and the coloured images that will be obtained may be images of the faces of the users.

[0072] FIG. 1 schematically shows a document 100 obtained by assembling various layers, which may have been implemented by way of lamination.

[0073] Very particularly, the document 100 comprises a matrix of coloured sub-pixels 101, for example a transparent or opaque layer on which there have been printed coloured elements that each form coloured sub-pixels. Here, the matrix of coloured sub-pixels comprises sub-pixels having three possible colours, cyan sub-pixels SB, magenta sub-pixels SM, and yellow sub-pixels SJ. The three colours of the colour model well known to a person skilled in the art by the acronym CMY (cyan magenta yellow) are found here. The invention is not limited to this colour model and may also use a model such as the RGB (red green blue) model. Of course, it is possible to use other colour triplets different from CMY and RGB.

[0074] The sub-pixels are arranged in a matrix, which will be described in more detail with reference to FIG. 4. It may nevertheless be noted that a pattern PM of three sub-pixels SB, SM and SJ is repeated multiple times in the section visible in FIG. 1.

[0075] An opaque layer with a white appearance 102, for example a thin metal oxide layer, has been assembled above the matrix of coloured sub-pixels. This layer may be chosen such that perforations are able to be formed easily in this layer, for example by applying a laser beam with a given wavelength, called perforation wavelength.

[0076] A laserable layer 103 has been arranged above the opaque layer with a white appearance 102. This laserable layer is an initially transparent layer that contains particles that are able to be carbonized by applying a laser beam, and very particularly a laser beam at a given wavelength, called laserization wavelength. The application of the laser beam will create greyscale portions or even black portions in the laserable layer. By way of indication, the laserable layer comprises polycarbonate and the particles that react to the laser beams.

[0077] In order not to damage the opaque layer with a white appearance 102 during the laserization of the document 100, a filter 104 is arranged between the laserable layer 103 and the opaque layer with a white appearance 102. This filter is configured to limit the passage of a laser beam at the laserization wavelength, such that this wavelength does not reach the opaque layer with a white appearance. By contrast, preferably, this filter lets through the abovementioned perforation wavelength, which differs from the laserization wavelength.

[0078] For example, the filter may comprise a polymer layer (possibly of the same type of polymer as other layers of the document), but one that is charged with a substance that absorbs a given spectrum comprising the laserization wavelength. The transmittance of the filter is therefore low over the laserization wavelength and greater over other wavelengths (in particular the perforation wavelength).

[0079] It may be noted that the substance that is used may be different depending on whether it is desired to stop/filter infrared or ultraviolet radiation. It is also possible to use a laserable polycarbonate layer that also filters UV and that is laserized by UV radiation.

[0080] For example, and as will be described with reference to FIG. 8, it is possible to use a polycarbonate layer that carbonizes on its surface with a laser having UV radiation, and to implement the perforation of the opaque layer with a white appearance with low-power infrared radiation (such that it does not carbonize the laserable layer).

[0081] Optionally, a transparent intermediate layer 105, for example made of polycarbonate, is arranged between the opaque layer with a white appearance 102 and the filter 104.

[0082] Therefore, optionally, a protective layer 107, which may be opaque or transparent, for example made of polycarbonate, has been arranged underneath the matrix of coloured sub-pixels 101.

[0083] FIG. 2 shows the document 100 after a step of forming perforations PF in the opaque layer with a white appearance has been implemented. This step may comprise applying a laser beam at the perforation wavelength.

[0084] At this stage, it should be noted that each pattern of coloured sub-pixels PM is associated with various perforations. From left to right in the figure: [0085] the first pattern is associated with a single perforation above its cyan sub-pixel; when it is observed from above the document, it will have a very bright cyan appearance (it is associated with two portions with a white appearance); [0086] the second pattern is associated with two perforations above its cyan sub-pixel and above its yellow sub-pixel; it will have a fairly bright green appearance (it is associated with one portion with a white appearance); [0087] the third pattern does not have any perforation; it will appear white when observed from above; and [0088] the fourth pattern comprises perforations above all of its sub-pixels; it will have a grey appearance due to the combination of the three cyan, yellow and magenta components.

[0089] A coloured image appears facing the document 100, with colours that are brighter than in the techniques according to the prior art. It may be noted that the combination of the patterns and perforations forms image pixels but, as will be described below, those obtained after the optional laserization step are called pixels.

[0090] FIG. 3 shows the document 100 after a laserization step has been implemented. In this step, a laser beam has been applied to the top of the document 100 so as to form blackened (or at least greyed) portions in the thickness of the laserable layer 103.

[0091] More specifically, a blackened portion PN1 has been formed above the yellow sub-pixel of the sub-pixel pattern furthest to the left in the figure, and a blackened portion PN2 has been formed above the magenta and yellow sub-pixels of the third sub-pixel pattern from the left in the figure. This thus gives a coloured image when observing the document 100 from above, comprising (considering the pixels from left to right in the figure): [0092] a pixel PX1 with a cyan appearance, not as bright as the one obtained in FIG. 2 at the same location; [0093] a pixel PX2 with a green appearance, identical to the one of FIG. 2 at the same location; [0094] a pixel PX3 with a grey appearance, which results from the presence of the blackened portion PN2 over two thirds of the surface area of the pixel PX3; and [0095] a pixel PX4 with a grey appearance, identical to the one of FIG. 2 at the same location.

[0096] It will be understood that the combination of the perforated opaque layer with a white appearance 102 with the laserized layer 103 makes it possible to obtain a very broad colour gamut, in particular for the brightest colours.

[0097] FIG. 4 shows a plan view of the matrix of coloured sub-pixels 101. By way of indication, the surface area occupied by the pixel PX1 described with reference to FIG. 3 is represented by a dashed rectangle.

[0098] Here, coloured rows are aligned in groups of three colours, that is to say three rows.

[0099] It may be noted that, in solutions according to the prior art, a fourth white row may be added to obtain brighter colours. That being the case, the addition of this fourth row will increase the size of the pixels and reduce the resolution of the images, while at the same time being less satisfactory in terms of colour gamut, since the maximum possible saturation of the colours will be lower. Indeed, when only 3 colours are present without white, each one of them covers ? of the surface area, while if the white rows are present, each colour covers only ? of the surface area, leading to lower saturation.

[0100] Other arrangements are possible, and in particular with other colours and other matrix formats.

[0101] FIG. 5 shows the result of a registration phase.

[0102] This registration phase is implemented prior to the formation of the perforations and aims to ascertain the position of the coloured sub-pixels of the matrix of coloured sub-pixels, in particular in the event of deformations of this matrix within a document.

[0103] The registration may be implemented automatically, for example by way of a computer system equipped with a camera for observing documents.

[0104] In this phase, it is possible to observe the position of a group of coloured sub-pixels denoted PO in FIG. 5. For example, these sub-pixels may be observed through initial perforations used only for the registration. Alternatively, it is possible to observe the coloured sub-pixels transparently through the document, for example using a powerful lighting device underneath the document.

[0105] Given the observed position of the coloured sub-pixels PO (which have expected colours at expected locations), it is possible to deduce for example regression polynomial equations that pass through these points and obtain a transformation to be applied to the matrix to estimate the position of each coloured sub-pixel. In fact, this transformation deforms an initially orthonormal grid pattern.

[0106] This step is advantageous for sub-pixels having dimensions of the order of 60 to 70 micrometres, to ensure that a laser beam is applied above the correct sub-pixels to make a coloured image with the correct hues appear on each document.

[0107] FIG. 6 shows a document 100 according to one variant in which a trench TR has been formed in an opaque layer with a white appearance 102. Elements bearing the same references in this figure and in FIGS. 1 to 5 are identical.

[0108] This trench TR makes it possible to improve adhesion between the opaque layer with a white appearance 102, which may comprise a metal oxide, and the other layers of the document, which are for example made of polymer.

[0109] Furthermore, it is possible to observe coloured sub-pixels through this trench that is formed before the perforations. This makes it possible to implement the registration, the pixels of the pixel group being visible through the trench (or the trenches if there are several of them, as in FIG. 7).

[0110] One advantageous arrangement for trenches TR is shown in FIG. 7, in which it is seen, from above, that a grid pattern is formed by the trenches TR.

[0111] FIG. 8 shows a document 100 according to another variant. Elements bearing the same references in this figure and in FIGS. 1 to 5 are identical. Here, the laserable layer 103 reacts, for the laserization, to radiation with a laserization wavelength in the ultraviolet (UV) range. This layer is furthermore configured to act as a filter for the UV (the carbonization may take place on the upper surface in the figure). Therefore, the UV radiation does not affect the opaque layer with a white appearance 102 and does not damage it during the laserization.

[0112] The opaque layer with a white appearance may nevertheless be perforated with a laser beam with a wavelength in the infrared range, for example one with low intensity. The laserable layer 103 may be configured to let this infrared laser beam through.

[0113] This embodiment is advantageous in that it requires fewer layers to form a document.

[0114] It may be noted that the perforations described here may have dimensions of the order of those of a sub-pixel or even dimensions smaller than those of a sub-pixel. The blackened portions may also have dimensions of the order of those of a sub-pixel or even dimensions smaller than those of a sub-pixel. It will be understood that this makes it possible to have fine adjustment of the colours of each pixel.

[0115] A person skilled in the art will understand that the embodiments and variants described above are merely non-limiting exemplary implementations of the invention. In particular, a person skilled in the art will be able to envisage any adaptation or combination of the embodiments and variants described above, in order to meet a particular need according to the claims presented below.