EP2798396B1 - Manufacturing method of a security device - Google Patents

Description

The present invention relates to a method of manufacturing a security device based on a display of multiple patterns through a lenticular network.

Such a security device is typically intended to be affixed to a support, such as an identity document, in order to authenticate it.

To this end, a difficult to reproduce security device is sought in order to make it difficult to manufacture or reproduce such a device. In addition, such a security device is advantageously customizable in order to make it unique.

A lenticular network, also called lenticular sheet, is composed of elementary lenses with the same optical characteristics, the lenticles, which have the particularity of having a focal length such that the rear face, the smooth face, of the lenticular network is confused with the plane. focal lens. Each lenticle magnifies, in an image located under the lenticular network, an elementary zone which is located in alignment with the eye and the optical center of the lenticle.

In order to produce such a multiple-pattern image, at least two embodiments are known.

A first embodiment, which is called "pre-printed" allows, by having a specially adapted image under a lenticular network, to view different patterns, each pattern being visible individually along a specific viewing axis. It is thus possible to produce a composite image, adapted to the lenticular network under which it is arranged, comprising n patterns. Each such pattern is visible along an axis of vision specific to the pattern. We pass from an axis of vision to another neighboring axis of vision by a rotation according to a "Angular pitch" characteristic of the lenticular network. Such a suitable image is typically produced separately, taking account of said “angular pitch” and then being assembled with the lenticular network.

According to a second embodiment, which is called “post-engraved”, it is still possible to produce a pattern, by etching in a layer. Said layer is predisposed under a lenticular network and can be modified remotely through the lenticular network. The etching is typically carried out by means of a beam, such as a laser beam, through said lenticular network. Said beam modifies said layer by supplying energy. Said beam is oriented, relative to the device, along a main axis which determines an axis of vision along which said pattern thus engraved is then visible. It is also possible by modifying the relative orientation between the device and the engraving tool, between two successive engravings, to produce multiple patterns. If such a change in relative orientation between two engravings respects the “angular pitch” of the lenticular network, the engraved patterns will be distinct and visible separately, each according to its own line of vision, without interference between the patterns. Due to the principle of modification, engraving only allows for monochrome patterns.

The two preceding embodiments “pre-printed” and “post-engraved” make it possible to produce fairly similar devices, in that they comprise n separate patterns, each visible along an axis of vision specific to the pattern. We pass from one axis of vision of a pattern to another by a rotation of the device respecting the "angular step" or at an angle multiple of the "angular step" characteristic of the lenticular network. Each embodiment used alone offers, by its intrinsic complexity of implementation, relative protection against unauthorized reproduction.

However, more effective protection is desired for such a safety device.

It seems a priori impossible to combine the two previous embodiments. Indeed, it is necessary to respect the constraint of “angular step” between two patterns, at the risk if not of producing overlapping patterns.

In the first “pre-printed” embodiment, the “angular step” is intrinsically respected during the production of the image, which incorporates this “angular step”.

In the second “post-etched” embodiment, the “angular step” is respected by a change of relative orientation of the etching axis, between two engravings of successive patterns, according to a rotation respecting the “angular step”. Respect for the “angular pitch” is here achieved in relation to the viewing / engraving axis of the first pattern.

However, according to the first “pre-printed” embodiment, when the image is assembled under the lenticular network, an axis of vision corresponding to a first pattern is obtained, having a random orientation angle. The orientation angle of this line of vision being unknown, it seems impossible to engrave a second pattern, according to the second "post-engraved" embodiment, which would be distant from an angle respecting the "angular pitch".

The document US4765656 discloses a method which combines the two methods without precise measurement of the position of the first image after stitching.

The present invention provides a manufacturing process which ingeniously and non-obviously combines the two previously described embodiments "pre-printed" and "post-engraved". This combination, by integrating in the etching of a second pattern own characteristics resulting from the production of a first printed pattern is moreover highly synergistic.

According to an unclaimed aspect, a security device comprising at least a first pattern visible through a lenticular network along a first associated axis of vision and at least a second pattern visible through said lenticular network along a second associated axis of vision, each second axis of vision being oriented relative to at least a first vision axis according to a “angular pitch” characteristic of the lenticular network, said at least one second pattern being a function of at least one angle of a first vision axis relative to a normal to the device.

According to another characteristic, the second pattern is a function of at least one position of the first pattern relative to the device.

According to another characteristic, the second pattern is deformed by application of a transformation which is a function of at least one angle of the first axis of vision.

According to another characteristic, said transformation is such that it corrects on said at least one second pattern the effect produced by a rotation orienting the second axis of vision according to the normal, so that said at least one second pattern does not appear deformed when viewed along the second line of vision.

According to another characteristic, the device is planar and said transformation is an application of a multiplying coefficient to the dimension of the second pattern perpendicular to an axis of a rotation orienting the second axis of vision according to the normal, said ratio being equal to the cosine the angle of the second axis of vision relative to normal.

According to another characteristic, a second pattern, as seen along a second associated vision axis, is complementary to a first pattern, as seen along a first associated vision axis.

According to another characteristic, the lenticular network is cylindrical along an axis of extension.

An identity document including such a security device is also proposed.

The invention relates here to a method of manufacturing a security device comprising the following steps: printing at least one first pattern capable of being seen through a lenticular network, assembling said printed pattern under said lenticular network, determining of a first axis of vision along which a first pattern is visible, rotation of the device according to an "angular pitch" characteristic of the lenticular network in order to present the device along a second axis of vision, production of a second pattern along the second axis vision through the lenticular network.

According to a characteristic of the invention, the method also comprises, prior to the production step, a step of construction of the second pattern so that its content is a function of the angle of the first line of vision relative to a normal to the device.

According to another characteristic of the invention, the method also comprises, prior to the production step, a step of construction of the second pattern so that its content is a function of the position of a first pattern relative to the device.

According to another characteristic of the invention, the construction step is such that the second pattern has complementarity with the first pattern.

According to another characteristic of the invention, the assembly step comprises adding a layer of modifiable material, and the step of producing the second pattern comprises etching in said layer of modifiable material by means of a beam , through the lenticular network.

• la figure 1 présente un schéma de principe d'un dispositif à motifs multiples basé sur un réseau lenticulaire,
• la figure 2 présente un diagramme d'un procédé selon l'invention,
• la figure 3 illustre un exemple de transformation T,
• les figures 4-6 présentent différents exemples de complémentarité entre motifs.

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:

• the figure 1 presents a block diagram of a network-based multi-pattern device lenticular,
• the figure 2 presents a diagram of a process according to the invention,
• the figure 3 illustrates an example of transformation T,
• the figures 4-6 present different examples of complementarity between patterns.

As illustrated in figure 1 , a lenticular network 2 comprises a periodic succession of lenticles 3, each having a substantially semicircular profile.

It is possible to produce lenticular networks 2 of different types. A first type is a cylindrical lenticular network 2. In a cylindrical lenticular network 2, each lenticle 3 has a substantially semi-cylindrical profile. The cylindrical lenticles 3 are parallel to each other. Each lenticle 3 magnifies an elementary zone in the form of a band of width corresponding to the width of a lenticle 3, of an image situated under the lenticular network 2.

Another type of lenticular network is obtained by crossing in the same plane two such cylindrical lenticular networks. In such an array the lenticles 3 are substantially cubic with four rounded upper edges. Such a lenticle 3 has a square shape in the plane of the lenticular network 2 and a semicircular shape in the two perpendicular planes passing respectively through the two axes of the cylinders. The lenticles 3 are organized according to a square matrix. Each lenticle 3 enlarges an elementary area or pixel in the form of a square with two sides / square cross with two branches, the two widths of the sides / branches of which correspond to the width of a lenticle 3, of an image situated under the lenticular network 2 .

By generalizing, another type of lenticular network 2 is obtained by crossing in the same plane of n such cylindrical lenticular networks 2. In such an array the lenticles 3 are substantially polygonal with 2n sides with 2n rounded upper edges. Such a lenticle 3 has a polygonal shape with 2n sides in the plane of the lenticular network 2 and a semicircular shape in the n perpendicular planes passing respectively through the n axes of the cylinders. The lenticles 3 are organized according to a matrix. Each lenticle 3 magnifies an elementary area or pixel in the form of a polygon with 2n sides / cross with 2n branches, the widths of the 2n sides / branches of which correspond to the width of a lenticle 3, of an image situated under the lenticular network 2.

By considering an infinite number n, a spherical lenticular network 2 is obtained. In such a spherical network the lenticles 3 are substantially hemispherical. Such a lenticle 3 has a circular shape in the plane of the lenticular network 2 and a semicircular shape in any plane perpendicular to the plane of the lenticular network 2. The lenticles 3 are typically organized according to a square (checkerboard) or hexagonal (honeycomb) matrix. 'bee). Each lenticle 3 magnifies an elementary area or pixel in the shape of a circle with a diameter corresponding to the width / diameter of a lenticle 3, of an image situated under the lenticular network 2.

The invention is applicable to any type of lenticular network 2.

The figure 1 , unidimensional, is thus applicable to all types of lenticular network 2. It shows a section along a plane normal to the surface of the lenticular network 2. In the case of a cylindrical lenticular network 2, the section is perpendicular to an axis Δ extension cylinders.

Under the lenticular network 2 is arranged at least one image layer 4, 5. This image layer 4, 5 is periodically divided into sections 10, each section 10 corresponding to a lenticle 3 and is substantially opposite a lenticle 3. Each section 10 includes segments 6-9 of patterns A, B.

The figure 1 illustrates an example with two patterns A, B, but it is possible to have more patterns.

Due to the shape of the lens 3, an observer sees the segments 6 or 8 of a first pattern A when looking along a first axis of vision Δα. From all the segments 6 or 8 of all the sections 10 of a device 1, the eye reconstructs the first pattern A. Similarly, an observer sees the segments 7 or 9 of a second pattern B when he looks along a second axis of vision Δβ. From all the segments 7 or 9 of all the sections 10 of a device 1, the eye reconstructs the second pattern B. So that a segment 6, 8 of the first pattern A and a segment 7, 9 of the second pattern B do not overlap, at the risk of disturbing the rendering of one of the patterns A, B, an angle p.γ multiple of an “angular step” γ between the orientation α of the first axis of vision Δα must be respected and the orientation β of the second axis of vision Δβ.

If the first axis of vision Δα, respectively the second axis of vision Δβ, presents with respect to a reference, such as the normal ΔN on the surface of the device 1, an angle α, respectively an angle β, the angle β-α between the first axis of vision Δα and the second axis of vision Δβ, is a multiple of the "angular step" γ, according to a relation p.γ = β-α, with whole p.

It is clear that respecting such an “angular pitch” γ amounts to respecting a precise spacing between the segments 6, 8 of a first pattern A on the one hand and the segments 7, 9 of a second pattern B on the other hand .

As seen above, there are at least two known embodiments of multiple patterns A, B, with a lenticular network 2.

A first “pre-printed” embodiment consists in placing a specially adapted image layer 5 under a lenticular array 2. Such an image layer 5 is broken down into segments 8 corresponding to a first pattern A and into segments 9 corresponding to a second reason B. The content of segments 8, 9 depends on the respective content of different patterns A, B. The location of the segments 8, 9 depends on the characteristics of the lenticular network 2. Thus the segments 8, 9 must be located in the sections 10. The periodicity of the segments 8, 9 must respect the periodicity of the lenticles 3 of the lenticular network 2.

In this “pre-printed” embodiment, compliance with the “angular pitch” γ characteristic of the lenticular network 2 is obtained by correct spacing of the segments 8 of a first pattern A relative to the segments 9 of a second pattern B.

In this embodiment, an image comprising the different patterns is typically produced by printing, for example offset. Such an embodiment thus advantageously makes it possible to produce one or more patterns A, B in color.

The precision of this printing intrinsically makes it possible to respect a periodicity and a relative positioning of the segments 8, 9 of different patterns A, B which guarantees compliance with an "angular pitch" γ.

The printing of this image can be carried out on an image layer 5, then assembled with / under the lenticular network 2. Alternatively, the printing of this image can be directly carried out on the reverse plane of the lenticular network 2, which makes then function of image layer 5.

However, it should be noted that in both cases it is impossible to obtain a repeatable positioning of the image relative to the lenticular network 2. A lenticular network 2 typically has a period / section width 10 of between 30 μm and 1 mm , preferably between 60 and 150 µm. It results from inaccuracies in positioning the image layer 5 relative to the lenticular network 2, during the step of assembling an image layer 5 printed under a lenticular network 2, or inaccuracies in setting the print relative to the network lenticular 2, during the direct printing step under the lenticular network 2, an inevitable uncertainty relative positioning between the image and the lenticular network 2.

It follows from this uncertainty that the angle α of a first viewing axis Δα of a first printed pattern A is indeterminate and cannot be known in advance. The angle α results from the manufacturing process and can only be known after assembly / printing of the image layer 5 and of the lenticular network 2. It is the same for the angle β of a second axis of vision Δβ d 'a second pattern B printed.

Despite this, compliance with the relative "angular pitch" γ between a first axis of vision Δα and a second axis of vision Δβ, due to the intrinsic precision of the printing process, is achieved, and guarantees the effect of multiple patterns A, B, each visible under a separate associated axis of vision Δα, Δβ.

A second “post-etched” embodiment uses a modifiable layer 4. Such a modifiable layer 4 is assembled under the lenticular network 2. An etching is then carried out, typically by means of a beam, such as a laser beam, through said lenticular network 2. This etching is thus advantageously carried out remotely and further a posteriori, after assembling the lenticular network 2 and the different layers 4, 5. This etching, by varying the position and intensity of the beam, comes by energy input, modify said modifiable layer 4 and produce by etching at at least one motif A, B by engraving the corresponding segments 6 and / or 7.

A lenticle 3 is here used optically according to an optical path opposite to that of vision. However, such a path is symmetrical and by orienting the beam, relative to the device 1, along a main axis during the etching of a pattern A, respectively B, this main etching axis determines an axis of vision Δα, respectively Δβ, along which said pattern A, respectively B, thus etched is then visible. So a pattern A, respectively a pattern B, visible from an axis of vision Δα, respectively Δβ, must be engraved by orienting the engraving beam along said axis of vision Δα, respectively Δβ. With reference to the figure 1 , a beam oriented along the first axis Δα, etched in a modifiable layer 4, a segment 6 of a first pattern A. This first pattern A will then be visible along this first axis Δα. Similarly, a beam oriented along the second axis Δβ, etched in a modifiable layer 4, a segment 7 of a second pattern B. This second pattern B will then be visible along this second axis Δβ.

It is thus possible, by modifying the orientation of the device 1 or of the etching beam by an angle p.γ multiple of the "angular step" between two etchings, to respect the "angular step" γ and to produce patterns A, B multiple and distinct visible separately each one according to its own line of vision, without interference between the patterns.

It should be noted that due to the principle of modification, etching only allows monochrome patterns to be produced. Typically, the etching beam burns a layer 4, for example of transparent polycarbonate, enriched in carbon. This burn reveals carbon black. Advantageously, a white substrate or lower layer 11 provides a contrasting screen. A modulation of the beam power makes it possible to achieve a wide variety of gray levels.

Respect for the relative "angular step" γ is obtained here by a change in orientation of an angle p.γ multiple of the "angular step" γ, between a first etching angle α of a first pattern A, known because chosen arbitrarily for engraving a first pattern A and a second engraving angle β, of a second pattern B.

A combination of the two previous embodiments by printing (pre-printed) and by engraving (post-engraved) simply seems impossible. Indeed such a combination comes up against the following problem. To assume that at least a first pattern A is produced by printing, the orientation α of its axis of vision Δα is not known, due to the uncertainty introduced by the assembly of the image layer 5 with the lenticular network 2. To then consider an engraving of a second pattern B, it is imperative to know said orientation α in order to be able to respect the “angular step” γ. The orientation of the etching beam can only be done relative to an angle α of an axis of vision Δα of a pattern A previously produced.

This difficulty is taken advantage of in that it makes series production of a safety device 1 complex. The circumvention of this difficulty implies, according to the invention, a step of individual recovery and precision metrology of each device 1, which makes it very complex to reproduce the manufacturing process and therefore the device 1.

According to the invention, a security device is manufactured according to a method illustrated in the figure 2 and comprising the following steps.

A first step consists in printing E1 at least a first pattern A on an image layer 5, so that it is visible through a lenticular network 2. Thus said at least one first pattern A is produced according to the first “pre-printed” embodiment previously described by prior printing followed by assembly under the lenticular network 2. The fact that said at least one pattern A is visible through a lenticular network 2 implies that its printing is segmented in segments 8, 9 respecting an “angular step” γ of said lenticular network 2. This “angular step” γ, at the level of printing E1, results in the respect of a spatial period in the image thus printed.

Thus for a cylindrical lenticular network 2, the image layer 5 is printed by respecting parallel strips of width equal to the period 10 of the lenticular network 2. Each such strip is divided into n sub disjoint parallel bands, where n is the total number, printed and / or engraved with desired patterns in the end. These patterns are distributed in patterns printed in an image layer 5 during step E1 and in patterns etched in an modifiable layer 4 during a step E6 described later.

Likewise for a generalized lenticular network 2, the image layer 5 is printed respecting a checkerboard / matrix corresponding to the checkerboard / matrix of arrangement of the lenticles 3.

After printing E1, said at least one first pattern A, is assembled E2 under said lenticular network 2. The two preceding stages of printing E1 and of assembly E2 are distinct when the printing E1 is carried out on an image layer 5, assembled then under the lenticular array 2. The two preceding steps of printing E1 and assembling E2 are, on the contrary, confused when the printing E1 is carried out directly on the back, on the smooth face, of the lenticular array 2.

In both cases, the assembly step E2 introduces uncertainty about the orientation of the axis (or of the axes if the patterns A printed are multiple) of vision Δα under which the pattern A is visible.

This uncertainty is such that safety devices 1 arranged on a manufacturing plate, for which the assembly E2 is also carried out with a single image layer 5 covering the entire plate, do not produce identical axes of vision Δα of a device 1 to the other belonging to the same plate.

In order to remove this uncertainty, and to be able to carry out step E6 of etching another pattern B, it is appropriate to determine E3 precisely the viewing axis Δα of at least one pattern A.

It should be noted here, that if several patterns A have been printed, they necessarily respect each other the "angular pitch" γ of the lenticular network 2. The determination step E3 can therefore only be carried out for one of these patterns A , the axis of vision Δα of any other reasons Printed deducting it by application of a rotation of angle p.γ multiple of the “angular step”, function of the characteristics of the lenticular network 2. Also the step of determination E3 is described here only for a first motif A.

The axis of vision Δα of the first pattern A is determined by a metrological system capable of varying the relative orientation between a safety device 1 and an optical detector. The optical detector is able to determine that it is aligned with the optical axis Δα when it perceives a pattern A with clear vision. When this clear vision is obtained, the system detects the exact relative orientation of the device 1. The optical detector can be a human eye. However, in order to automate the process, the optical detector is advantageously an image sensor such as a camera, advantageously coupled with image analysis software capable of detecting when a pattern A is visible and sharp.

The orientation of a viewing axis Δα thus obtained is recorded in the form of angles. These angles, typically two in a general case, can be expressed in any coordinate system. Advantageously, by simplifying the reference, it is possible to have only one angle α. Such a simplification is possible by considering only the angle α made by the axis of vision Δα with the normal ΔN to the device.

It is still possible to simplify the reference when the lenticular network 2 is cylindrical. In this case the problem is one-dimensional. The safety device 1 is only oriented along an axis parallel to the axis Δ of the cylinders. Around this axis Δ, or what is equivalent in a plane perpendicular to said axis Δ, the axis of vision Δα makes with the normal ΔN to the device an angle α.

Once the orientation of the viewing axis Δα of the first pattern A has been identified, the method has an absolute reference. It is then possible according to the "angular step" γ, known as a characteristic of the network lenticular 2, and characteristics of said angular network 2, to orient the safety device 1 along a second axis of vision Δβ. This is achieved during a step E4 which applies to the safety device 1 a rotation of an angle respecting the "angular pitch" γ.

In the case of a cylindrical network, said rotation is applied around the axis Δ of the cylinders and at an angle p.γ multiple of the "angular step" γ, with p integer.

The device 1 is then oriented along a second axis of vision Δβ. It is then possible to go to the next step of producing E6 of at least one second pattern B along said second axis of vision Δβ through the lenticular network 2. Such an embodiment E6 through the lenticular network 2 implies using the second embodiment, the “post-engraved” mode.

It is possible to repeat steps E4 and E6, and to engrave a pattern B along an axis of vision Δβ, and then to apply a new rotation according to another angle p.γ multiple of the "angular step" γ in order to engrave at again another reason.

The step of determining E3 of the orientation of a first axis of vision Δα can only be done after the step of assembling E2 of said at least one first pattern A, since it is during assembly E2 that the orientation α of the viewing axis Δα is configured randomly. The step of determining E3 of the orientation of the axis of vision Δα must be done before any step of making E6, so that the making E6 makes said at least one second engraved pattern B correctly arranged relative to said at least one first motif A printed and correctly placed relative to any possible second engraved motif B already produced.

This step E3 is important in that in its absence, an embodiment E6, for example in an arbitrary orientation, has every chance of producing a second engraved pattern interfering with one of said first printed patterns.

The safety device 1 resulting from such a process is difficult to reproduce, in that a second engraved pattern depends, for its realization E6 to be possible, from the orientation α of the axis of vision Δα of a first printed pattern.

In order to reinforce the security of the security device 1 obtained, by mixing even more intimately said first printed patterns and said second engraved patterns and the two steps E1 / E2 and E6 producing them respectively, it is advantageous to add, before the production step E6, a construction step E5 of said at least one second pattern. This construction step E5 creates a second pattern, if necessary by modifying a second preexisting pattern. Its purpose is to include said angle α of the first axis of vision Δα, characteristic of a first printed motif, no longer only in the step of producing the second engraved motif, but also in the content of the second motif itself. .

Thus, according to one embodiment, the second engraved pattern comprises a representation of the angle α or alternatively or complementarily of the angle β of orientation of the viewing axis Δβ of the second engraved pattern. This is equivalent. Indeed, as seen above, the angle α and the angle β are necessarily linked by a relationship with the "angular step" γ. Such a representation may be a numerical value of the angle α or β or else a graphic representation of said angle α or β or any other coded representation of the angle α or β. Such an arrangement advantageously makes it possible to verify the authenticity of the security device 1 by checking that the coding of the angle α, respectively β, contained and therefore visible in the second engraved pattern corresponds to the angle α, respectively β, of effective orientation of the viewing axis Δα, respectively Δβ, under which can be seen a first printed pattern, respectively a second engraved pattern, on the safety device 1 considered.

The construction step E5 of the second engraved pattern may also be such that the content of said second engraved pattern is a function of a position YA of a first printed pattern A relative to the device 1. In fact, like the angle α, this position YA varies randomly, from one device 1 to another, essentially for the same reasons of reproducibility of the relative positioning of a first pattern A printed relative to the lenticular network 2 during the printing steps E1 and d E2 assembly.

Similarly, the position YA of a first printed pattern A can be introduced into the content of a second engraved pattern B. According to another embodiment, the position YA of the printed pattern A can be used to position relatively all or part of a second engraved motif B.

In order to be able to produce at least one second engraved pattern B through the lenticular network 2, the assembly step E2 further comprises an addition, in addition to the image layer 5, of a layer 4 of modifiable material. This modifiable layer 4 is assembled with the image layer 5 under the lenticular network 2. It can be indifferently placed under a transparent image layer 5, or alternatively inserted between an image layer 5 and the lenticular network 2, as illustrated in the figure 1 . In this second case, the modifiable layer 4 is advantageously transparent. The transparency of the upper layer, among the image layer 5 or the modifiable layer 4, means at least the parts covering the useful segments of the layer located below. So in the configuration of the figure 1 , the image layer 5 is printed on a segment 8 of a first pattern A. The modifiable layer 4, located above, is advantageously transparent, at least in line with said segment 8, ie at the level of segment 6 of the modifiable layer 4. Said transparency "at right" is understood along an optical path, that is to say along an axis of vision Δα, Δβ.

It can be noted that on the figure 1 some segments, corresponding to the same pattern, overlap. Thus a segment 8 corresponds to a printed pattern A. A segment 6 would correspond to a pattern A if the latter was engraved. If pattern A is printed, segment 6 is left free / transparent, so that a printed segment 8 can be seen. If pattern B is engraved, segment 7 is used. A segment 9 corresponds to a printed pattern B. If pattern B is engraved, segment 9 is unused.

It is still possible to spatially mix the two embodiments "pre-printed" and "post-engraved" in order to produce the same pattern A or B with a first part of the surface of the printed pattern and a second part of the surface of the engraved pattern. It goes without saying that the first part and the second part are necessarily separate.

So, with reference to the figure 1 , if a pattern A is partially printed, the pixels / bands in a first part of the printed surface use the segment 8. On the contrary the pixels / bands in a second part of the engraved surface use the segment 6.

In this variegated embodiment, the direction β of the axis of vision of a second engraved part merges with the direction α of the axis of vision Δα of a first printed part. The “angular step” is still respected here, with a value β-α = p.γ = 0, that is to say p = 0.

Again, such a variegated embodiment requires knowing the angle α at which the first printed part of the pattern is visible. This is necessary to arrange the engraving tool at an angle β identical to said angle α in order to engrave the second part.

The modifiable layer 4 having been assembled with the lenticular network 2 in step E2, the step of producing E6 of at least one second engraved pattern can be carried out by etching in the material of the modifiable layer 4, by means of a thermal directive beam, such as a laser beam. This beam performs an etching, through the lenticular network 2, along the associated axis of vision Δβ audit second reason B.

Said at least a first pattern is printed on a surface finally disposed under the smooth underside of the lenticular network 2. This can be achieved, according to one embodiment, by printing on a separate image layer 5 during printing, and then assembled under the lenticular network 2. According to another embodiment, this can be obtained by direct printing on the smooth underside of the lenticular network 2.

The invention also relates to a security device 1. This security device 1 comprises at least a first pattern A visible through a lenticular network 2 along a first associated axis of vision Δα and at least a second pattern B visible through of said lenticular network 2 along a second associated axis of vision Δβ, each second axis of vision Δβ being oriented relative to at least one first axis of vision Δα while respecting an "angular pitch" γ characteristic of the lenticular network 2. Such a safety device 1 could be produced only according to a first “pre-printed” embodiment where all the patterns are printed on an image layer 5. Similarly, such a security device 1 could be produced only according to a second “post-engraved” embodiment »Where all the patterns are engraved in a modifiable layer 4 through the lenticular network 2.

However, according to an important additional characteristic of the invention, said at least one second pattern B is a function of at least one angle α of a first axis of vision Δα, identified for example relative to a normal ΔN to the device 1.

It is important to note that such a safety device 1, where a first pattern is produced by printing E1 / assembly E2 according to the first "pre-printed" embodiment and a second pattern is produced by etching E6 through the network lenticular 2 according to the second “post-engraved” embodiment is not comparable nor with a device where all the patterns are printed, nor with a device where all the patterns are engraved. A detailed analysis of a device 1 makes it possible to determine, on the final product, the embodiment of each pattern. A simple means is the analysis of the image layer 5 and / or of the modifiable layer 4, most often distinct. An engraved pattern exhibits detectable deformation / burns of an modifiable layer 4, while a printed pattern exhibits only ink deposits on an image layer 5.

The fact that said at least one second engraved pattern is a function of an angle α of at least one first axis of vision Δα necessarily implies that this angle α is known at the time of the production of a second engraved pattern. For this the only solution is to use a second engraved embodiment for a second engraved pattern.

As indicated previously, said angle α can be contained in the second engraved pattern, for example by its value. It can also be done by transforming the second engraved pattern as a function of the angle α or what is equivalent as a function of the angle β.

According to another characteristic, a second engraved pattern can also be a function of the position YA of at least one first printed pattern. This position YA is tainted with uncertainty and therefore randomly individualized, due to the assembly step. Also, it must necessarily be measured, by a metrology step carried out individually for each device 1, similar to that making it possible to determine the angle α, with similar means.

An advantageous means of producing a second engraved pattern as a function of the angle α of the viewing axis Δα of a first printed pattern is to apply a transformation T to the second engraved pattern before its engraving, said transformation T being a function of l 'angle α or angle β.

Such a transformation T, particularly advantageous in that it allows a simple visual control, is such that it corrects on the second engraved pattern the effect produced by a rotation Rβ orienting the second axis of vision Δβ according to the normal ΔN, so that said at least one second engraved pattern does not appear distorted when seen according to the second viewing axis Δβ.

So as shown in the figure 3 , a pattern B, if it is engraved without prior transformation, when it is seen under the axis of vision Δβ, is deformed. Indeed, the fact of orienting the safety device 1 along the axis of vision Δβ so that the pattern B is visible, requires a rotation Rβ of the device 1 by an angle β relative to the normal ΔN. Such a rotation Rβ causes a deformation of the pattern B which is not seen according to the normal ΔN to the device 1. The transformation T advantageously corrects this effect by an inverse deformation.

Thus in the case where the safety device 1 is planar, a rotation Rβ causes an optical deformation of the pattern B in a direction perpendicular to the axis Δ of the rotation Rβ.

Also, the application of a transformation T, compressing the dimension Y by multiplication by a coefficient K = cos β, applied before engraving on the pattern B corrects said deformation. Thus, the pattern B, as seen from the viewing axis Δβ, appears undeformed, with a normal 1: 1 ratio. The application of such a transformation T requires to know and with precision the angle β and therefore beforehand the angle α to which it is linked by the "angular step" γ. The final effect is simple to verify in order to prove the authenticity of the security device 1 thus produced. Pattern B should appear unmodified, when viewed along the line of sight Δβ.

For an angle β of 70 °, the dimension Y is multiplied by K = 0.34. For an angle β of 0 °, the dimension Y is unchanged, K = 1.

It has been seen that a second engraved pattern can also be produced by taking account of the effective position YA of a first printed pattern.

A particularly advantageous embodiment of this characteristic consists in producing a safety device 1 where a second engraved pattern, as seen along a second associated Δβ vision axis, is complementary to a first printed pattern, as seen through a first associated axis of vision Δα.

Such complementarity appears, and can thus simply be verified, by orienting the safety device 1 successively along the line of sight Δα and along the line of sight Δβ. Thus, a rotation Rγ, at an angle p.γ multiple of the "angular step" γ, orienting the second axis of vision Δβ along the first axis of vision Δα, superimposes the first printed pattern and the second engraved pattern and reveals their complementarity .

The complementarity of a first printed motif and a second engraved motif can take several forms. Complementarity can be geometric. Thus a second engraved pattern, respectively a first printed pattern, can be adjusted edge to edge with a first printed pattern, respectively a second engraved pattern.

As illustrated in figure 4 , a second engraved pattern B visible along an axis of vision Δβ, respectively a first printed pattern A visible along an axis of vision Δα, can frame a first printed pattern A, respectively a second pattern B engraved, by a complementary shape, creating thus a juxtaposition effect during a tilting from the axis of vision Δα towards the axis of vision Δβ and vice versa.

Complementarity can also be constituted by two complementary patterns, for example, to create an apparent movement effect. This is illustrated by the figure 5 where the printed motif A and the engraved motif B include, for example, overlapping arrows, which when rocked give the impression of movement to the right.

The complementarity can still be colored. So as illustrated in the figure 6 a printed motif A includes a photo in a first frame and an engraved motif B includes a second frame of another color but covering the first frame identically.

A second engraved pattern B is (necessarily) produced in gray, while a first printed motif A can be produced using a different color.

Due to the embodiment, a first printed pattern A can be polychrome, while a second engraved pattern B is necessarily monochrome. Such a combination is advantageous in terms of feasibility and attractiveness for the user.

In all of these nonlimiting examples of complementarity, a precise geometric "adjustment" is made, between a first pattern A printed and a second pattern B engraved.

Such an adjustment requires very precise knowledge of both the angle α and the position YA of the first pattern A printed, in order to place the second pattern B, by etching, accordingly. The final effect thus obtained is advantageously difficult to obtain, since it requires at least one delicate metrology step, and at the same time easy to visually check, including without requiring a tool.

The principle of the invention can be varied to many different embodiments. It is possible to produce one or more printed patterns, on all or part of the surface of the device 1, each visible along an associated axis of vision. By measuring the angle of such an associated viewing axis, it is then possible to produce one or more engraved patterns respecting the “angular pitch” of the lenticular network 2 between them and with the printed patterns.

An engraved pattern can even be engraved along an axis of vision associated with a printed pattern, provided that the surface of the device 1 is shared between a first part used by the printed pattern and a part used by the engraved pattern, the first and second parts being disjoint.

In the case where the lenticular network 2 is cylindrical, it has an extension axis Δ coincident with the axis Δ of the cylinders.

In this case the "angular pitch" γ, characteristic of the lenticular network 2 is measured around said axis Δ. The axis Δ is also confused with the axis of rotations Rα, Rβ, Rγ.

The safety device 1 described above can be placed on any support, of any shape, by any known assembly means.

The invention also relates to the application of a security device according to one of the embodiments described, for producing an identity document, such as an identity card, a passport, a registration certificate, a bank card, etc., thus rendered unforgeable.

Claims (4)

1. A method for manufacturing a security device (1) characterized in that it comprises the following steps:

   - printing (El) at least a first pattern (A) adapted to be seen through a lenticular network (2),

   - assembling (E2) said pattern (A) printed under said lenticular network (2),

   - determining (E3) a first line of vision (Δα), having an angle (α) with respect to a normal (ΔN) to a surface of the device (1), according to which the first pattern (A) is visible,

   - rotating (E4) the device (1) according to an "angular pitch" (γ) characteristic of the lenticular network (2) in order to present the device (1) according to a second line of vision (Δβ), having an angle (β) with respect to the normal (ΔN), the angle (β-α) between the first line of vision (Δα) and the second line of vision (Δβ) being multiple of the "angular step" γ according to a relation p.γ = β-α, with p an integer,

   - constructing (E5) a second pattern (B), the second pattern being distorted by application of a transformation as a function of the angle (α), said transformation being such as it corrects on the second pattern the effect produced by a rotation (Rβ) orienting the second line of vision (Δβ) according to the normal (ΔN),

   - making (E6) the second pattern (B) by engraving through laser beam along the second line of vision (Δβ) across the lenticular network (2).
2. The method according to claim 1, further comprising, the construction step (E5) of the second pattern (B) so that its content depends on the position (YA) of a first pattern (A) relative to the device (1).
3. The method according to claim 1 or 2, wherein the construction step (E5) is such that the second pattern (B) has a complementarity with the first pattern (A).
4. The method according to any one of claims 1 to 3, wherein the assembly step (E2) comprises an addition of a layer of modifiable material (4), and wherein the step of making (E6) the second pattern (B) comprises an engraving in said layer of modifiable material (4) by means of the laser beam, through the lenticular network (2).

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