FR3054478A1 - METHOD FOR MANUFACTURING A SECURITY DEVICE COMPRISING A COLOR IMAGE - Google Patents

Abstract

A method of manufacturing a security device (1) comprising a final color image (5), comprising the steps of: - printing a background (3) differing from the final color image (5) on a substrate (2) ), the bottom (3) comprising at least two colored elements (7), each having a different and alternating color, - determining a complement, such as the printing of the complement on the bottom (3) modifies the visual representation at least one colored element (7), so as to visually represent the final color image (5), - printing of the complement on the bottom (3). Safety device (1) produced by such a method.

Description

054 478

57422 ® FRENCH REPUBLIC

NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY © Publication number:

(only to be used for reproduction orders) © National registration number

COURBEVOIE © Int Cl ⁸ : B 42 D 25/405 (2017.01)

PATENT INVENTION APPLICATION

A1

©) Date of filing: 07.29.16. © Applicant (s): OBERTHUR TECHNOLOGIES (© Priority: Public limited company - FR. @ Inventor (s): REMY ALBAN and LEGUY CLEMENT. (© Date of public availability of the request: 02.02.18 Bulletin 18/05. ©) List of documents cited in the report preliminary research: Refer to end of present booklet (© References to other national documents ® Holder (s): OBERTHUR TECHNOLOGIES Company related: anonymous. ©) Extension request (s): © Agent (s): CABINET BEAU DE LOMENIE.

THE METHOD FOR MANUFACTURING A SECURITY DEVICE INCLUDING A COLOR IMAGE.

FR 3 054 478 - A1

Method for manufacturing a security device (1) comprising a final color image (5), comprising the following steps:

- printing a background (3) which differs from the final color image (5) on a substrate (2), the background (3) comprising at least two colored elements (7), each having a color, different and alternating,

- determination of a complement, such as printing the complement on the background (3) modifies the visual representation of at least one colored element (7), so as to visually represent the final color image (5),

- printing of the complement on the bottom (3).

Safety device (1) produced by such a process.

i

The present invention relates to a security device comprising a color image and its production method. A security device is a difficult means to achieve, in order to avoid counterfeiting, making apparent an attempt to modify in order to discourage such an attempt, and moreover, ideally, authenticated in order to confirm with the greatest certainty, its origin origin from an authorized source.

In the field of security devices, it is known to secure a color image by producing it by fiduciary printing, and / or to print it on secure paper. Fiduciary printing covers several printing techniques including very precise positioning between colors, very fine resolution, specific technologies such as the use of color lines rather than dots, etc. in order to constitute an identifiable and reserved image quality, in that it is substantially impossible to obtain with consumer printing tools. A security paper is a paper on which printing is very difficult to modify a posteriori and is characterized in that it contains security elements, such as: watermark, visible or invisible UV fibers, security thread, lack of reactivity to UV. It is also known to add to the color image an additional element, such as a laminate deposited above the image so as to prevent direct access to the image, or even a secondary image, providing redundancy. allowing to make visible a modification of the image alone.

As illustrated in FIGS. 1 and 2, it is also known to produce a color image by etching, by means of a laser 8, of a gray level mask superimposed with an image layer 3 comprising several primary colors. Such an image layer 3 can be produced in a transparent layer arranged above a substrate 2 or alternatively can be produced directly in or on such a substrate 2. In the example illustrated, the image layer 3 comprises elements 7C, 7M , 7Y and 7W, of different colors, for example respectively Cyan, Magenta, Yellow (Yellow), in order to constitute a base of primary colors, as well as White (White). Here these elements are identical, linear and periodic. The etching, typically carried out in a suitable layer 10, allows, by carbonization, to produce blackout elements 11, which carry out a selection of the colors contained in the elements 7C, 7M, 7Y, 7W of the image layer 3, in an opposite measure at the height / thickness of the element 11. The mask must be determined according to the colors present in the image layer 3 and their respective positions, and must be positioned relative to the image layer 3 with great precision. The assembly is most often protected by an upper protective layer 9. This technology is described by W02013 / 093230.

This technology is advantageous in that it makes it possible to separate in two steps, on the one hand, a step of printing the generic image layer 3, identical for all the devices 1, carried out initially, typically in batches, of a step engraving, which effectively produces the final color image, individualized, subsequently, typically device by device, and individualizes or personalizes the device 1.

Thus, if the final color image is for example an identity photo of a passport, advantageously secure, the blank passports, and an impression of the image layer 3, can be produced, by batch, in the factory, and then be personalized, one by one, by personalization adding the identity photo of the bearer, one passport at a time, by the agency responsible for issuing the passport.

Such an embodiment produces a security device 1 comprising a definitive color image of a completely satisfactory security level.

However, due to the laser engraving step, such an embodiment excludes the use of certain substrates because of their material which is liable to burn, such as for example paper. In addition, such an embodiment reproduces a color space (or gamut) limited by the basic colors present in the image layer 3 and the combinations of these colors.

The present invention overcomes these various drawbacks and proposes a modified manufacturing process in order to be able to be used on any substrate, and allowing an increase in the color space (gamut), while retaining its numerous safety characteristics and if necessary in adding.

The subject of the invention is a method of manufacturing a security device 1 comprising a final color image 5, comprising the following steps: printing a background 3 different from the final color image 5 on a substrate 2, the background 3 comprising at least two colored elements 7, each comprising a color, alternating, determining a complement the impression of the complement 4 on different backgrounds and 4, such that 3 modifies the visual representation of at least one colored element 7, in such a way as to visually represent the final color image 5, printing of the complement 4 on the background 3.

According to another characteristic, the complement 4 represents an image identical to the final color image 5 but of different color (s).

According to another feature, The impression of complement 4 uses an ink that at least penetrates partially in the bottom 3. According to another feature, The impression of complement 4 uses a partially transparent ink, and an image color final color 5 results of mix of the color of complement 4 and the color of background 3. According to another feature, The impression of complement 4 uses a covering ink, and a color of

the final color image 5 is the color of the complement 4 if it is present, and the background color 3 if not.

According to another characteristic, the complement 4 is polychrome.

According to another characteristic, the printing of the bottom 3 and the printing of the complement 4 are carried out with separate techniques

According to another characteristic, the substrate 2 is made of absorbent material, preferably made of paper, still preferably made of security paper.

According to another characteristic, the colors of the background 3 are in substantially equal proportions, interlaced, preferably regularly, again preferably periodically, and still preferably arranged over substantially the entire surface of the device 1.

According to another characteristic, the colors of the background 3 are arranged in identical elements 7, preferably linear.

According to another characteristic, the background 3 comprises at least three primary colors, and preferably white and / or black.

According to another characteristic, the bottom 3 has a fineness of less than 80 μm.

According to another characteristic, the fineness of the complement 4 is sub-multiple of the fineness of the background 3.

According to another characteristic, the method also includes a step of measuring the precise position of the bottom 3, before printing the complement 4.

According to another characteristic, the method also includes a step of analyzing the background 3, before determining the complement 4.

According to another characteristic, at least one printing step is carried out in fiduciary printing.

According to another characteristic, the complement 4 comprises black, preferably covering.

According to another characteristic, the complement 4 comprises white, preferably covering.

According to another characteristic, the complement 4 comprises three primary colors, preferably miscible with the colors of the background 3.

The invention also relates to a security device 1 produced by such a method.

Other characteristics, details and advantages of the invention will emerge more clearly from the detailed description given below by way of indication in relation to the drawings in which:

FIG. 1, already described, illustrates, in front view, a device according to the prior art,

FIG. 2, already described, illustrates in cut view along A-A, the device of FIG. 1,

FIG. 3 illustrates a front view of a device according to the invention,

- Figure 4 illustrates in cut-away view along B-B, the device of Figure 3.

As illustrated in FIGS. 3 and 4, the security device 1 according to the invention comprises a substrate 2.

Starting from a definitive color image 5 which we want to reproduce in the security device 1, the manufacturing process comprises the following steps.

During a first step, a background 3 is printed on the substrate 2. Said background 3 is not united and therefore comprises at least two different colors. This step can be carried out by any type of printing. The bottom 3 is advantageously common to several, see all the devices 1 of the same batch. The first printing step can therefore advantageously be carried out by implementing techniques suitable for manufacturing in (large) series on a large number of devices 1. Production by offset printing is preferred.

Background 3 is different from a solid background, conventionally white, usually used to print a color image. The bottom 3 is formed by at least two colored elements 7. Each colored element 7 has one color and only one. The colored elements 7 forming the bottom 3 are different and alternate. The colored elements 7 of the background 3 form a distinct pattern unrelated to the final color image 5.

Also the printed color image must be modified to take account of the content of the background 3. This is achieved by a second step of calculation, aimed at determining a complement 4, in the form of an image, such as the printing of the complement 4 on the background 3 reproduces the desired final color image 5. The principle of this determination is to perform a colorimetric "subtraction" removing the background 3 from the color image 5 to obtain the complement 4. Thus the printing of the complement 4 on the background 3 performing an "addition", reproduces the image final color 5.

In practice, this "subtraction" is complicated by numerous parameters, such as the absorption of the substrate 2, the diffusion / dispersion of the inks in the substrate 2, or even the miscibility of the inks.

Once this complement 4 has been correctly determined, typically by means of specific software, during a third step, the complement 4 is printed, on the substrate 2, above the background 3, in order to reproduce the color image. final 5. The second impression, printing the complement 4 is advantageously carried out by means of a technique making it possible to individualize an impression, such as an inkjet impression, advantageously according to a technology deposited on demand (from English “Drop on Demand ”or DoD).

According to an optional feature, the complement forms an image similar to the final color image 5, but has different colors.

The properties of the inks used, both for printing the background 3 and for printing the complement 4 may vary. These variations can provide a different visual appearance and / or even improve the security of the security device 1. These properties of the inks can be identical or different between the base 3 and the complement 4. They can still vary, from one color to the other. or from one part of the image to another.

Thus a first property is the penetration of the ink. Thus an ink used for the base 3 can penetrate the support or, on the contrary, remain on its surface. Similarly, an ink used for complement 4 can penetrate the support or, on the contrary, remain on its surface. Similarly, an ink used for the complement 4 can penetrate an ink already deposited for the base 3 or, on the contrary, be deposited above an ink pre-deposited for the base 3.

Another variable property is the transparency of the ink, particularly for printing the complement 4. Such an ink may be partially transparent. Thus this ink being deposited over an ink of the bottom 3, leaves partially visible by transparency the ink of the underlying background. Thus it follows that the color of a point of the final color image 5 results from the mixture, here colorimetric, of the combination of the colors, the ink of the background 3 and the ink of the complement 4, if it is present, as it becomes transparent.

This transparency can be zero. In this case the ink is covering and masks an ink on which it is deposited. Thus it follows that the color of a point in the final color image 5 results from the mixture, here spatial, of the two impressions, and is: - the color of the complement 4 if it is present at this point and hides the color underlying the background 3, and - the color of the background 3 if the complement 4 is absent (does not contain any printing / ink) at this same point.

Like laser engraving, the complement can be monochrome, preferably in gray level. Thus the complement 4 allows, for each point, a color selection, among the basic colors present in the background 3.

Advantageously also, the complement can be polychrome. It can reuse the same colors as the background 3 or introduce new basic colors. This characteristic of the complement thus advantageously makes it possible to increase the initial gamut provided by the background 3 with the new colors or not provided by the complement 4.

According to a reassuring characteristic, the printing of the bottom 3 and the printing of the complement 4 are carried out with separate techniques. Thus advantageously, it is possible, with the naked eye, or more probably using a magnifying glass or a wire account, to distinguish the impression of the background 3 from the impression of the complement 4, by observing details of their respective achievements. This characteristic makes it possible to authenticate the security device 1. Thus with the example of a printing of the background 3 by offset, and a printing of the complement by ink jet, it is possible with a magnifying means, to distinguish the bottom 3 showing a screening or nets, the complement showing droplets, if necessary of different sizes.

The substrate 2 on which the device 1 is produced can be of any material, capable of receiving the two impressions. If the material is non-absorbent, the inks from the printing steps are deposited on the surface of the substrate 2. According to a preferred embodiment, the material of the substrate 2 is absorbent. Thus, the inks are absorbed and are found intimately linked to the material in its thickness, making any attempt at tampering more difficult, in order to increase security.

An absorbent material with many applications is paper, widely used for many documents requiring a security device.

According to a particular preferred case, this paper is a security paper, of the type used to produce fiduciary documents. A security paper is a paper on which printing is very difficult to modify a posteriori and is characterized in that it contains security elements, such as: watermark, visible or invisible UV fibers, security thread, lack of reactivity to UV.

The background 3 can be arbitrary, as soon as it includes at least two colors and makes it necessary to determine a complement 4, different from the color image 5. However, embodiments of the background 3 can be advantageous in that they induce advantageous characteristics of the first impression and / or of the supplement 4 and / or of the security device 1.

According to one embodiment, the background 3 comprises several colors, present in substantially equal proportions, and interlaced. The arrangement of colors and interlacing are preferably regular. An advantageous regularity is a periodicity. As regards the spatial extent of the colors on the surface of the security device 1 dedicated to accommodating the color image 5, it may be partial and occupy only a part of said surface, but is preferably extended to the whole. from the surface.

It has been seen that the colors of the background 3, in that they differ from a usual plain background, require a modification of the complement 4, which must take account, at each point, of the color present and of its exact position. The regularity or the periodicity in that it improves the knowledge of the positions and the colors advantageously makes it possible to simplify the step of determining the complement 4. It further makes it possible to simplify the step of printing the background 3.

According to one embodiment, the colors of the background 3 are arranged in identical elements 7, preferably linear. This is in accordance with the example illustrated in Figures 3 and 4.

All these characteristics of the bottom 3, and more particularly insofar as they remain visible after the printing of the supplement 4, contribute to offering intrinsic characteristics of the safety device 1, which remain visible on the final product and then allow easy verification. security device 1 and its authenticity.

The first printing step, printing an advantageously generic background 3, is advantageously compatible with mass production. The printing of the background is preferably carried out according to a dry offset process.

According to a particularly interesting embodiment, the background 3 comprises at least three primary colors. Primary colors form a colorimetric base, containing compatible colors, making it possible to create complex hues in an additive manner, and more or less evenly distributed throughout the palette of colors. A classic plο primary color triplet is, for example: Cyan, Magenta, Yellow (Yellow), or: Red, Green (Green), Blue.

The presence of these primary colors, in substantially equal proportions, distributed in a regular or periodic arrangement, and possibly interlaced, makes it possible to compose an image reproducing the color image 5. The principle is then to selectively mask the primary colors from background 3 to means of complement 4, in order to let the unmasked colors express.

Since such masking has the drawback of darkening the image produced, the background 3 can advantageously include, in addition to the primary colors, white. FIG. 3 illustrates a background 3 comprising colored, identical, linear elements, of three primary colors 7C, 7M, 7Y, supplemented by white elements 7W, on which is printed a complement 4 partially shown schematically.

Alternatively or additionally, the background 3 may also include black. The selective masking of white, respectively black, makes it possible to darken, respectively to lighten, locally the image produced.

It follows from the above that a pixel of the color image 5 is reproduced by a homologous pixel of the background 3 comprising at least one sub-pixel of each of the colors. The hue of a pixel of the color image 5 is then reproduced, possibly approximately, by composition of the colors of the sub-pixels. For a pixel of image 5, its hue is colorimetrically broken down into as many components as there are primary colors. Each sub-pixel of the homologous pixel in the background 3 is then masked as an opposite function of the component corresponding to its color.

Also, it appears that the resolution of the reproduced image is all the better as the pixels / sub-pixels of the background 3 are small. By definition, the fineness of an impression is the smallest size of an element 7 printed, either here the small dimension of an element 7 of color, or even the width (or height) of a line of color, in the case of a linear element or the diameter in the case of a point element. Technologically, this fineness corresponds to the resolution of the print and can be compared to the minimum achievable size of a drop of ink. The smaller this fineness, the higher the resolution of the image produced. Also this fineness is advantageously the smallest possible. A fineness, for the background 3, of less than 80 μm, thus allows appreciable resolution. This fineness may be smaller depending on the printing technology. For example, an ink droplet of 3.5 to 8 picoliter obtained by advanced inkjet technologies has a diameter between 15 and 60pm, preferably 25pm.

When the base is deposited on an absorbent substrate, the diffusion of the ink in the substrate will be taken into account to determine the setting of the printing machine to obtain the quantity of ink allowing to obtain the desired fineness, after penetration. ink in the substrate.

Such a resolution thus advantageously makes it possible to carry out all the checks usually carried out on the basis of an identity photo.

Another advantage of a low finesse of this order of magnitude is the need for high performance printing materials, currently reserved for official bodies and not easily accessible to individuals. This limits, legally or economically, the possibility of access for counterfeiters. In addition, this incorporates a specific characteristic in the final product which advantageously makes it authentic.

It has been seen that the second impression, printing the complement 4, is carried out according to the content and the position of the elements of the bottom 3, in that the complement 4 completes and / or modifies the bottom 3. Also, it is necessary that the fineness of the complement 4, as determined, and therefore that the resolution of the printing means of the complement 4 is in agreement with those of the background 3. The complement can be produced by any type of printing, preferably by inkjet technologies of very high precision allowing to obtain a fineness up to 15pm as mentioned further on in the description.

A sub-pixel of the background 3 must be able to be modified by at least one drop of ink. It follows that the fineness (that is to say the dimension in a chosen direction) of the complement 4 must be at most equal to the fineness (the dimension in the same direction) of the bottom 3.

In order to be able to achieve partial or proportional masking effects of a sub-pixel of the background 3, it is advantageous that a drop of ink of the complement 4 spatially covers only a portion of a sub-pixel. So for a pixel, broken down into sub-pixels, with a finesse, here the diameter of an ink drop, half, four drops are necessary to completely hide a sub-pixel of the background 3, and 4 + 1 progressive levels of masking: 0/4, 1/4, 2/4, 3/4 and 4/4 are possible.

Similarly, for linear colored elements 7, a pixel has at least a rectangular shape comprising a sub-pixel, for example rectangular, of each color. With a drop having a diameter half the width of a line, at least two drops are necessary to completely hide a subpixel of the background 3, and 2 + 1 progressive levels of masking: 0/2, 1/2, 2/2 by base color are possible.

By generalizing, the fineness of the complement 4 should be an integer sub-multiple of the fineness of the background 3. The degree of sub-multiplicity indicates, for example, the number of possible gray levels.

The following drop parameters can be adjusted to achieve the desired results:

- shade and opacity of the ink of the drop,

- density or number of drops per sub-pixel,

- diameter of the drop deposited (this parameter is itself a function of the volume of the drop, the viscosity of the ink and the porosity of the paper),

- overlap / distance between the drops (this parameter is itself a function of the number of drops per sub-pixel and diameter of the drops).

The inkjet heads and the colored elements 7 of the background 3 should have the same resolution or that the resolution of the heads is a multiple of the resolution of the colored elements 7.

It has been seen that the complement 4 is printed on the background 3 so as to modify and / or hide a pixel / sub-pixel of the background 3. In order to correctly hide / mix the inks resulting from the printing of the background 3 and the inks from the printing of the complement 4, it is necessary to know with precision the position of the elements / colors of the background 3, in order to relatively position the printing of the complement 4. For this, and taking into account the relatively low finesse envisaged, a method consists in carrying out a step of measuring the precise position of the background 3, prior to the step of printing the complement 4. üsuch a step of "registration" is advantageously carried out by a measurement by means of a video sensor.

Such an essential step, conventional in the field of security devices, can advantageously be carried out in an integrated manner with a printer used to produce security devices, such as passports and capable of performing the second step of printing the supplement 4. A such equipment is difficult to access by the general public, which further strengthens the security of the safety device 1.

Similarly, and particularly, if the bottom 3 is not regular or even if several different types of funds 3 are envisaged, the method can advantageously include a step of analyzing the bottom 3. Such a step can advantageously be carried out prior to the stage of

determination of complement 4. The purpose of a such step East to identify the background type 3: its colors, his dimensions, his periodicity, in order to characterize it entirely and to be able to effectively determine the complement 4 in result. A such analysis step East

advantageously carried out by a measurement using a video sensor.

In order to further stand out from the technologies accessible to the general public, and to increase the security of the security device 1, at least one, and preferably both, the printing steps are / are carried out in fiduciary printing. Fiduciary printing implements materials and techniques reserved exclusively for security devices. It includes, for example, a lower fineness of printing, the use of continuous nets rather than raster, direct colors rather than compound.

In order to be able to “complete” the background 3 so as to form a reproduction of the color image 5, the complement 4 comprises at least one color. According to a first advantageous embodiment, this color can be black. Such a black is preferably covering. Thus, the color image 5 is reproduced by composing the colors present in the sub pixels of the background 3 with the complement 4, by masking. The black ink is then used to selectively mask the colors of the background 3, in order to obtain the desired hues, expressed by composition of the unmasked colors. In this mode, the background 3 provides a palette of colors and the complement 4 defines the contours and shades of the image 5 by selective masking. It is thus only possible to express the shades from the colors present in the background 3. A background 3 comprising at least three primary colors, regularly distributed, then makes it possible to reproduce any shade resulting from a composition of these primary colors, at any point on the surface of the device 1. A triplet of primary colors, forming a colorimetric base, makes it possible to reproduce an approximation of any image 5.

Black alone for the complement 4 allows, with a suitable background 3, a good quality of expression. The use of black to mask can however lead to undesirable darkening of the image produced.

According to an alternative or complementary embodiment, the complement 4 comprises white. Such a white is preferably covering. Thus, the color image is reproduced by composing the colors present in the pixels / sub pixels of the background 3 with the complement 4, by masking. The white ink is then used to selectively mask the colors of the background 3, in order to obtain the desired hues, expressed by composition of the unmasked colors.

The use of white color is still advantageous in that white ink is rarer and for reserved use. In addition, white requires a specific adjustment specific to the printer used. This characteristic thus makes it possible to secure the security device 1.

Like black used alone, white alone for complement 4 thus allows, with a suitable background 3, a good quality of expression. Unlike black, the use of white to mask can however lead to an undesirable lightening of the image produced. Also, a combined use of black and white to alternate the masking performed, advantageously makes it possible to reduce these two opposite disadvantages, by masking with lighter areas of white, and by masking with darker darker areas of image 5. The calculation carried out during the step of determining the complement 4 then takes these particularities into account and integrates them as variables.

Figure 4 illustrates points 4a-e of the complement 4, printed above the bottom 3 and its colored elements 7C, 7M, 7Y, 7W. Points 4d, 4e are illustrative of a masking point.

While the points 4d, 4e have a size / fineness substantially equal to the size fineness of the colored elements 7C, 7M, 7Y, 7W, the point 4b has a reduced fineness allowing partial masking.

According to another characteristic, the complement 4 may also include other colors. According to one embodiment, it can include three primary colors. In this case, these colors are used to combine with the background colors 3, rather than to hide them. These colors are therefore preferably miscible with the background colors 3. The use of such colors advantageously makes it possible to widen the color space and therefore to increase the resolution of the image produced.

Indeed, to produce, for example a green dot / pixel, a complement 4 performing only a masking must mask the sub-pixel Magenta, so that a combination of cyan and yellow is expressed, forming by composition of green. The achievable resolution is thus of the order of a pixel. On the contrary, a complement 4 comprising primary colors, to obtain the same result, can combine cyan provided by the complement 4, with the yellow sub-pixel of the background 3, or combine yellow provided by the complement 4, with the sub -pixel Cyan background 3, or both. This therefore makes it possible to substantially double the spatial and / or colorimetric resolution.

Figure 4 illustrates points 4a-e of the complement 4, printed above the bottom 3 and its colored elements 7C, 7M, 7Y, 7W. Points 4a, 4c are illustrative of combining points. The point 4a is illustrative of a point having a size / fineness substantially equal to the size fineness of the colored elements 7C, 7M, 7Y, 7W, of the background 3, the point 4c has a reduced fineness allowing a proportional combination.

The color combination requires that the inks be miscible, in order to be able to mix with each other. This can be carried out on the surface, both for the bottom 3 and for the complement 4, in the case of a substrate 2 of non-absorbent material, such as a plastic material, or can be carried out in the depth of a substrate 2 of material absorbent. This second embodiment is preferred in that the two prints are intimately linked in the thickness of the substrate 2, which makes any operation aimed at removing or modifying one of the prints more difficult.

The invention also relates to a security device 1 produced by such a method. Advantageously, such a safety device 1 is identifiable as a product necessarily resulting from such a process. Its own characteristics, such as typically the visible presence of the particular organization of the colors in the background 3, still make it possible to authenticate the safety device 1 and its origin.

The invention is also safer than the photos currently printed by conventional technologies on the paper pages of passports. The invention is safe in that the base 3 or the complement 4 is irreversibly deposited on the substrate 2. An attempt to remove or erase the ink would cause a modification / degradation of the colored elements 7 of the base 3 and / or the substrate which would reveal an attempt at fraud.

In addition, the invention is safe in that it has a specific geometric signature for each image formed by said at least two colored elements 7, each having a color, different and alternating, and the printing of the complement 4 constituting the final color image 5 and proof of its authenticity.

Claims (20)

1. Method for manufacturing a security device (1) comprising a final color image (5), characterized in that it comprises the following steps: printing of a background (3) different from the final color image (5) on a substrate (2), the background (3) comprising at least two colored elements (7), each having a different and alternate color, - determination of a complement (4), such as printing the complement (4) on the background (3) modifies the visual representation of at least one colored element (7), so as to visually represent the image final color (5), - printing of the complement (4) on the bottom (3). 2. Method according to claim 1, wherein the complement (4) represents an image identical to the final color image (5) but of different color (s). 3. Method according to any one of claims 1 or 2, wherein the printing of the complement (4) uses an ink which penetrates at least partially into the bottom (3). 4. Method according to any one of claims 1 to 3, wherein the printing of the complement (4) uses a partially transparent ink, and where a color of the final color image (5) results from the mixing of the color of the complement (4) and the background color {3}. 5. Method according to any one of claims 1 to 4, where the printing of the complement (4) uses a covering ink, and where a color of the final color image (5) is the color of the complement (4) s 'it is present, and the background color (3) otherwise. 6. Method according to any one of claims 1 to 5, wherein the complement (4) is polychrome. 7. Method according to any one of claims 1 to 6, wherein the printing of the background (3) and the printing of the supplement ¢ 4) are carried out with separate techniques. 8. Method according to any one of claims 1 to 7, wherein the substrate (2) is made of absorbent material, preferably paper, still preferably security paper. 9. A method according to any one of claims 1 to 8, wherein the background colors (3} are in substantially equal proportions, preferably arranged regularly, still preferably periodically, optionally interleaved, and still preferably arranged over substantially all the surface of the device (D · 10. The method of claim 9, wherein the colored elements (7) of the bottom (3) are of identical shape, preferably linear. 11. The method of claim 10, wherein the background (3) comprises at least three primary colors, and preferably white and / or black. 12. Method according to any one of claims 1 to 11, wherein the bottom (3) has a fineness of less than 80 µm. 13. The method of claim 12, wherein the fineness of the complement (4) is submultiple of the fineness of the bottom (3). 14. Method according to any one of claims 1 to 13, further comprising a step of measuring the precise position of the bottom (3), prior to the printing of the complement (4). 15. Method according to any one of claims 1 to 14, comprising, prior to the determination of the complement (4), a step of analyzing the bottom (3) to identify the type of said bottom among different types of possible bottom. 16. Method according to any one of claims 1 to 15, where at least one printing step is carried out according to a fiduciary printing technique specific to the production of security devices. 17. Method according to any one of claims 1 to 16, where the complement (4) comprises black, preferably covering. 18. Method according to any one of claims 1 to 17, where the complement (4) comprises white, preferably covering. 19. Method according to any one of claims 1 to 18, where the complement (4) comprises three primary colors, preferably miscible with the background colors (3). 20. Security device (1) produced by the method according to any one of the preceding claims. 1/2