Security element for a security document and security document provided therewith

Abstract

The invention relates to a security element (1) which comprises a grid (R) of at least two raised lines (2, 2') in directions of axes X and Y, with one raised pattern oriented in a direction of axis Z, at least one of these lines (2, 2') being delimited by two consecutive grooves (S) or ridges (C), from which two opposite flanks originate, characterised in that: - at least one flank has, in the plane (Y, Z), an average slope varying between two values SlopeMin and SlopeMax, such that SlopeMin < SlopeMax, at least a first portion (P1) of the line (2, 2') being such that the transition from SlopeMin to SlopeMax takes place over a distance that is visible to the naked eye; and - there is a second portion (P2), contained in the first portion, in which there is a position Yp, wherein the cross-section in the plane (X, Z) of at least one of the flanks describes a non-constant continuous function, comprised between two extreme values.

Description

[0001] DESCRIPTION

[0002] TITLE: Security element for a secure document and secure document provided with it

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a security element for a secure document and to a secure document provided with it. Preferably, the latter is a valuable document, in particular a banknote.

[0005] STATE OF THE ART

[0006] In document W02020 / 083938 a security element based on light reflection is described, which comprises a network of at least two contiguous or adjacent lines, at least one of these lines being in relief and having two opposite sides, at least one of which is partly inclined, sides which each originate along one of said longitudinal and opposite edges of said line.

[0007] Figure 1 shows, as a reminder, a security element that complies with the instructions in this document.

[0008] This element is only very partially represented in order to make consultation of the figure easier.

[0009] In the example shown here, element 1 comprises a network R formed of three contiguous lines 2, 2' and 2" which extend alongside each other along the Y axis of the three-dimensional reference system (X,Y,Z).

[0010] Of course, it is possible to provide an element with a much larger number of lines. The length K of the lines (along the X axis) is, in this particular case, identical and can be of the order of a few millimeters to a few centimeters. Only a portion is shown here. Similarly, the width k of each of the lines is identical in this specific case.

[0011] The height of each line, along the Z axis, is referenced h.

[0012] Of course, in an embodiment not shown, lines of different widths k can be provided.

[0013] In the example shown, lines 2 to 2" are straight.

[0014] However, in a variant not illustrated here, the network R may comprise curved, circular lines and more generally any shape, or even a single line, for example in the form of a spiral, so that the network R is formed by the plurality of turns of the spiral. In the example shown and in accordance with this prior document, each of the raised lines 2 to 2" has two opposite inclined flanks 20 and 21 which each originate along one of the longitudinal and opposite edges 200 and 210 of the line. Here, the flanks are inclined upwards, which means that they extend towards each other towards an altitude, along the Z axis, higher than that of the longitudinal edges 200 and 210.

[0015] By the expression "inclined flanks" is meant that at least a portion of at least one of these two flanks is inclined. In other words, this does not exclude the flanks being locally vertical or horizontal. These two flanks 20 and 21 join in a single, uninterrupted junction zone 22 of sinuous shape which extends in the longitudinal direction of the line, these flanks 20 and 21 having no discontinuity or interruption, at least in the longitudinal direction. In other words, the crests of this three-dimensional network which individually constitute the aforementioned junction zone, have a sinusoidal modulation (i.e. variation) in the (X,Y) plane.

[0016] Figure 2 shows in an even more simplified manner a network R conforming to a variant of this previous document.

[0017] Here, only two lines 2 and 2' are represented and we have refrained from showing the flanks which connect the ridges and the furrows of the R network. We note that the ridge lines C do not undergo any modulation, that is to say no variation, so that they are always located at the same altitude, along the Z axis. On the other hand, the furrow lines S present a large sinusoidal modulation in the vertical plane, that is to say along the (X,Z) plane.

[0018] Figure 3 shows schematically, seen from above, a network R, formed of a plurality of parallel lines conforming to the embodiment of Figure 2. The network R is represented here in gray level, the black shade corresponding to the highest points of the structure, while the white shade corresponds to the lowest points of the structure. Of course, the different gray shades correspond to intermediate altitudes between these highest and lowest points. It should be noted that the dimensions have been deliberately exaggerated for better visualization.

[0019] Furthermore, we note the presence of a ring-shaped area A in the network R, an area in which the identical slopes of the network take the form of a ring. This makes it possible to generate a ring-shaped pattern that is very easily visually recognizable.

[0020] Of course, other variations in the amplitude of the ridge and / or furrow lines, i.e. along a plane other than the (X,Z) plane, are possible but have not been shown here. Such a safety element generally gives satisfaction. However, it can be improved in terms of visual rendering.

[0021] Indeed, we note that with a reflective structure in relief such as that of figure 3, and when the lighting is very directional, the resulting visual effect is sometimes very, or even too, bright, sometimes almost imperceptible, depending on the position of the light source and / or that of the observer.

[0022] This is easily explained by the fact that the reflective structure is unidirectional, since the modulation of the groove lines allows the generation of movement effects according to the tilt only from top to bottom and vice versa (i.e. around the X axis). A continuous variation of the slopes of the sides therefore takes place along horizontal and parallel "lines". This variation in slope is due to a variation in depth.

[0023] This phenomenon of "great brilliance" and "quasi-imperceptibility" is encountered regardless of the plane in which the modulation of the ridge lines and / or furrow lines is included.

[0024] More precisely, if a directional light is in the plane orthogonal to the lines (and assuming that the observer is also looking perpendicular to the lines), the effect is perceived as very bright, whereas if the light is not perpendicular to the lines, one may not see anything at all.

[0025] It is possible to illustrate this situation using simulations. For example, we propose to reveal a "Pop-up" effect (which materializes as light spots that gradually become black depending on the angle of inclination) of dimension 1x2 millimeters, with a structure formed by "lines" of width 15 pm, with a maximum depth of 4 pm and under point lighting.

[0026] This is illustrated very schematically in the attached figures 4 and 5. In these figures, the safety element is referenced D, the lighting E, the observer O, and the double arrow f corresponds to the direction of the lines of the structure.

[0027] In Figure 4, it is assumed that the observer O looks at the element D perpendicular to the direction f of the lines. In the case of directional lighting oriented perpendicular to the lines of the element D, the visual effect is well contrasted when the lighting E is in a plane orthogonal to the lines of the structure.

[0028] On the other hand, and as shown in Figure 5, when the illumination E is inclined at an angle a of 10° relative to the plane orthogonal to the direction of the lines, the contrast decreases sharply, until the generated pattern disappears when this inclination angle a is 20°. This is again illustrated in Figures 6 to 8.

[0029] From these simulations, it is also possible to measure the contrast, that is to say the ratio between the maximum intensity observed and the maximum possible intensity, starting from lighting in a plane orthogonal to the lines of the structure and gradually tilting this lighting.

[0030] This is illustrated in Figures 9 and 10, in which two particular cases have been considered, namely a first case in which the lighting is initially normal to the structure (Figure 9) and a second case (Figure 10) in which the lighting initially makes an angle of 20° with respect to the normal to the structure (but always in a plane orthogonal to the lines).

[0031] A careful observation of the graphs gives a contrast which decreases very quickly until it is zero beyond 25° of inclination with respect to the plane orthogonal to the lines.

[0032] The present invention aims to improve the security element of the aforementioned prior document so as to render, for the observer, a less brilliant visual effect in normal lighting (in other words when observing in the direction of specular reflection), while being clearly perceptible for lighting angles far from normal (in other words when observing outside the direction of specular reflection).

[0033] Document WO2018 / 045938 is an illustration of a technological background in this field.

[0034] SUMMARY OF THE INVENTION

[0035] Thus, the present invention relates to a security element for a secure document which comprises a network of at least two contiguous or adjacent lines in relief, these lines being generally oriented in longitudinal and transverse directions of respective axes X and Y, while said relief is generally oriented in a direction of axis Z perpendicular to said axes X and Y, at least one of these lines in relief being delimited by two consecutive grooves or two consecutive ridges, from which two opposite flanks originate joining in a single and uninterrupted junction zone forming a ridge, respectively a groove, characterized by the fact that:

[0036] - on the one hand, at least one of said two opposite flanks has in the plane (Y, Z) orthogonal to said longitudinal direction X an average slope varying continuously along said longitudinal direction X between two extreme values ​​PenteMin and PenteMax such that PenteMin is strictly less than PenteMax, at least a first portion of said raised line being such that the transition from PenteMin to PenteMax occurs over a distance, along said longitudinal direction (X), visible to the naked eye, and - on the other hand, there is at least a second portion of said raised line, which is contained in said first portion, which does not produce diffraction and which is invisible to the naked eye, and within which there is a position Yp, along the Y axis, for which the section in the plane (X, Z) of said at least one of said two opposite flanks describes a continuous function,non-constant and between two extreme values ​​Min and Max such that Min is strictly less than Max, and successively taking the values ​​Min, Max and Min, or Max, Min and Max.,

[0037] Thanks to the characteristics of the invention and more particularly due to the presence of the second modulation, the slopes of the sides of the structure are slightly and locally varied, which makes it more diffusive. In this way, there will always be a main and privileged direction of specular reflection, but with locally secondary directions, which opens the angle of perception of the optical effect.

[0038] According to other advantageous and non-limiting characteristics of the invention, taken in isolation or according to a technically compatible combination of at least two of them:

[0039] - PenteMin and PenteMax are such that PenteMin is equal to - PenteMax;

[0040] - the said distance visible to the naked eye is strictly greater than one millimeter;

[0041] - said second portion extends over a distance along said longitudinal direction X strictly greater than 1 pm;

[0042] - said second portion extends over a distance along said longitudinal direction X strictly less than 150 pm.

[0043] The invention also relates to a secure document characterized by the fact that it comprises at least one security element according to one of the preceding characteristics.

[0044] Advantageously, said security element defined above is integrated or added thereto.

[0045] According to a possible embodiment, this document may be a banknote and is characterized in that it is made of paper, fibrous material, plastic, or a combination of at least two of these materials.

[0046] BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Other features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention. This description is made with reference to the appended drawings in which:

[0048] Figure 1 is a schematic, three-dimensional and partial view of a network of lines of a security element according to the prior art; Figure 2 is an even more simplified view of an alternative embodiment of the security element of Figure 1;

[0049] Figure 3 is a schematic representation, seen from above, of a network formed of a plurality of parallel lines in accordance with the embodiment of Figure 2;

[0050] Figure 4 is a first diagram intended to illustrate what is visible, by an observer, on a security element, according to a first lighting direction;

[0051] Figure 5 is a second diagram intended to illustrate what is visible, by an observer, on a security element, according to a second lighting direction;

[0052] Figure 6 is a first diagram intended to illustrate a variation in contrast, on a security element, depending on the inclination of the lighting;

[0053] Figure 7 is a second diagram intended to illustrate a variation in contrast, on a security element, depending on the inclination of the lighting;

[0054] Figure 8 is a third diagram intended to illustrate a variation in contrast, on a security element, depending on the inclination of the lighting;

[0055] Figure 9 is a first graph giving a measurement of the contrast resulting from the observation of the security element of the previous figures, with lighting initially normal to the structure;

[0056] Figure 10 is a second graph giving a measure of the contrast resulting from the observation of the security element of the previous figures, with lighting forming an angle of 20° relative to the normal to the structure;

[0057] Figure 11 is a simplified perspective view of a section of line of a safety element according to the invention;

[0058] Figure 12 is a simplified perspective view of two sections of contiguous lines of a security element according to the invention, according to an alternative embodiment;

[0059] Figure 13 is a top view of a security element according to the embodiment of Figure 12;

[0060] Figure 14 is a simplified perspective view of two sections of contiguous lines of a security element according to the invention, according to an alternative embodiment;

[0061] Figure 15 is a top view of a security element according to the embodiment of Figure 14;

[0062] Figure 16 is a simplified perspective view of two sections of contiguous lines of a security element according to the invention, according to an alternative embodiment;

[0063] Figure 17 is a top view of a security element according to the embodiment of Figure 16; Figure 18 is a simplified perspective view of two sections of contiguous lines of a security element according to the invention, according to an alternative embodiment;

[0064] Figure 19 is a top view of a security element according to the embodiment of Figure 17;

[0065] Figure 20 is a simplified perspective view of two sections of contiguous lines of a security element according to the invention, according to an alternative embodiment;

[0066] Figure 21 is a top view of a security element according to the embodiment of Figure 20;

[0067] Figure 22 is a simplified perspective view of two sections of contiguous lines of a security element according to the invention, according to an alternative embodiment;

[0068] Figure 23 is a top view of a security element according to the embodiment of Figure 22;

[0069] Figure 24 is a simplified perspective view of two sections of contiguous lines of a security element according to the invention, according to an alternative embodiment;

[0070] Figure 25 is a top view of a security element according to the embodiment of Figure 24;

[0071] Figure 26 is a first diagram intended to illustrate what is visible, by an observer, on a security element according to the invention, according to a first lighting direction;

[0072] Figure 27 is a second diagram intended to illustrate what is visible, by an observer, on a security element, according to a second lighting direction;

[0073] Figure 28 is a partial top view of a safety element according to the invention, intended to illustrate the optical phenomena implemented;

[0074] Figure 29 is a top view of a first series of simulations of security elements in accordance with the invention;

[0075] Figure 30 is a top view of a second series of simulations of security elements in accordance with the invention;

[0076] Figure 31 is a top view of a third series of simulations of security elements in accordance with the invention;

[0077] Figure 32 is a first graph giving a measurement of the contrast resulting from the observation of the security element of the invention, compared to a security element according to Figure 9, with lighting initially normal to the structure; Figure 33 is a second graph giving a measurement of the contrast resulting from the observation of the security element of the invention compared to a security element according to Figure 10, with lighting forming an angle of 20° relative to the normal to the structure.

[0078] DETAILED DESCRIPTION OF THE INVENTION

[0079] DEFINITIONS AND VOCABULARY

[0080] As indicated above, the security element according to the invention is characterized firstly by the fact that at least one of said two opposite flanks has in the plane (Y, Z) orthogonal to said longitudinal direction (X) an average slope varying continuously along said longitudinal direction (X) between two extreme values ​​PenteMin and PenteMax such that PenteMin is strictly less than PenteMax, at least a first portion of said raised line being such that the transition from PenteMin to PenteMax takes place over a distance, along said longitudinal direction (X), visible to the naked eye.

[0081] In the remainder of the description and to make it easier to read, this characteristic will be referred to interchangeably as “large modulation” or “first modulation”.

[0082] The element is characterized secondly by the fact that there is at least a second portion of said raised line, which is contained in said first portion, which does not produce diffraction and which is invisible to the naked eye, and within which there is a position Yp, along the Y axis, for which the section in the plane (X,Z) of said at least one of said two opposite flanks, describes a continuous, non-constant function between two extreme values ​​Min and Max such that Min is strictly less than Max, and successively taking the values ​​Min, Max and Min, or Max, Min and Max.

[0083] In the remainder of the description and also to make it easier to read, this characteristic will be referred to indifferently as “small modulation” or “second modulation”.

[0084] The expression "average slope" means the slope measured between the furrow and the crest which delimit the flank in question, which does not prevent this flank from having a concave, convex or any other non-rectilinear profile.

[0085] By the expression, "there is at least a second portion of said raised line, which is contained in said first portion", is meant portions, that is to say line segments, such that the first portion is delimited by coordinates X1 and X2 along the X direction, and the second portion is delimited by coordinates X3 and X4 along the X direction, said coordinates being such that X1 <X3<X4<X2. De préférence, selon un premier cas, les deux portions se superposent (c'est-à-dire quand elles se situent toutes les deux au niveau d’une même crête, respectivement au niveau d’un même sillon) ou, selon un deuxième cas, les deux portions sont en regard l’une de l’autre (l’une étant située au niveau d’une crête et l’autre au niveau d’un sillon, ou inversement).

[0086] In any event, the second portion has a length at most equal to the first portion.

[0087] METHODS OF IMPLEMENTATION

[0088] Preamble :

[0089] For the sake of simplification, in all the following embodiments, except in the embodiment illustrated in Figure 11, the large GM modulation is the result of a variation in the longitudinal direction (X) of the position of the groove (S) in the plane (Y, Z).

[0090] However, the invention is not limited to a large modulation resulting from a variation in the longitudinal direction (X) of the position of the groove (S) in the plane (Y, Z). Indeed, according to the invention the large modulation GM is the result of a variation in the longitudinal direction (X) of the position in the plane (Y, Z) of said at least one of said two opposite flanks at the level of the groove (S), the crest (C) or any other point located between the groove (S) and the crest (C). a / General information which applies to all embodiments.

[0091] In the attached figures 12, 14, 16, 18, 20, 22 and 24 are shown in a very partial manner different embodiments of a security element 1 according to the invention, so as to make consultation of these figures easier.

[0092] This element 1 is for example formed on a plastic material such as polyethylene terephthalate (PET) or biaxially oriented polypropylene (BOPP), without this being limiting.

[0093] The network R of raised lines shown in these figures only has two lines 2 and 2', also for reasons of clarity. However, such a network can have a significantly larger number of such lines.

[0094] A person skilled in the art is able to determine the dimensions of the network R of raised lines, and in particular the number of lines, for example as a function of the width of the lines, so that the effect is visible to the naked eye, preferably at a normal viewing distance from the security element, in particular at an viewing distance of between 20 and 40 cm.

[0095] These lines are shown contiguous, but they can be adjacent.

[0096] The length K of the lines is, in this particular case, identical (they can however be of different lengths) and can be of the order of a few millimeters to a few centimeters. Only a portion is shown here. Similarly, the width k of each of the lines is identical in this specific case and is between a lower limit which will diffract the incident light (in the vicinity of 1 pm, which we wish to avoid) and 100 pm, preferably the upper limit is less than 50 pm and even more preferably less than 40 pm.

[0097] The height H is, for example, between 1 and 50 pm and preferably of the order of 10 pm or less.

[0098] Of course, in an embodiment not shown, lines of different widths k could be provided.

[0099] In the example shown, lines 2 and 2' are rectilinear, in direction X. However, in a variant not illustrated in the figures, the network R may comprise curved, circular lines and more generally any shape, or even a single line, for example in the shape of a spiral, so that the network R is formed by the plurality of turns of the spiral.

[0100] As can be clearly seen in the figure, each of the lines of the network R is in relief. However, when the number of lines of the network R is greater than two, it is possible to envisage that some of them are in relief while the remaining lines are strictly flat. Thus, for example, one could envisage an alternation of lines in relief and flat lines. The presence of flat lines could be used to make visually discernible information elements appear between the lines in relief.

[0101] In the above figures, the flanks which connect the ridges C and the furrows S have not been shown for the sake of simplicity.

[0102] In Figures 13, 15, 17, 19, 21, 23 and 25 are shown schematically and purely for illustrative purposes, seen from above, networks R, formed from a plurality of parallel lines conforming respectively to Figures 12, 14, 16, 18, 20, 22 and 24.

[0103] The R network is represented here in grayscale, the black shade corresponding to the highest points of the structure, while the white shade corresponds to the lowest points of the structure. Of course, the different gray shades correspond to intermediate altitudes between these highest and lowest points. The same grayscale therefore corresponds to points of equal altitude forming an isoline acting on the direction of light reflection according to its local curvature, the incident angle of illumination and the position of the observer.

[0104] It should be noted that the dimensions have been deliberately exaggerated for better visualization.

[0105] It is also specified that in figures 13, 15, 17, 19, 21, 23 and 25, it would be sufficient to reverse the convention between black and white shades to "return" the structures and make the furrows become ridges and vice versa.

[0106] Furthermore, still in figures 13, 15, 17, 19, 21, 23 and 25, we note the presence of a ring-shaped zone A in the network R, a zone in which the identical slopes of the network take the form of a ring. This makes it possible to generate a ring-shaped pattern that is very easily visually recognizable.

[0107] What is described in this section applies to all embodiments of the invention, unless otherwise stated. b / Large and small modulations of the same shape, arranged on a furrow or on a ridge and progressing in different planes.

[0108] In the embodiment of Figure 12, the peaks C of lines 2 and 2' are strictly rectilinear and extend at a constant height.

[0109] On the other hand, at least one of the two opposite flanks which extend on either side of a groove S, has in the plane (Y, Z) orthogonal to the longitudinal direction (X) an average slope varying continuously along said longitudinal direction (X) between two extreme values ​​PenteMin and PenteMax such that PenteMin is strictly less than PenteMax.

[0110] In the case presented here, the average slope variation is the result of both a linear variation of the Z height of the groove corresponding to the “large modulation” GM and also a sinusoidal variation of the groove in the (X,Y) plane corresponding to the “small modulation” PM.

[0111] In Figure 13, this results in straight black isolines and a small sinusoidal PM modulation whose altitude varies according to the annular macroscopic pattern.

[0112] Here, the PM sinusoids of the two lines have an unchanged period over their entire length. In addition, these adjacent lines are in phase opposition, but it could of course be otherwise. Thus, they could be in phase (parallel evolution of the sinusoids) or even out of phase.

[0113] In embodiments not shown, this small PM modulation may be sinuous but not sinusoidal, or sawtooth-shaped, each tooth having a profile that fits within a non-right triangle. This may be an isosceles or equilateral triangle.

[0114] In accordance with a characteristic of the invention, this “large modulation” GM extends over at least a first portion P1 of the relief lines 2 and 2' so that the transition from PenteMin to PenteMax occurs over a distance, along said longitudinal direction (X), which is visible to the naked eye.

[0115] Advantageously, this distance is strictly greater than one millimeter.

[0116] Still according to a characteristic of the invention, there is at least a second portion P2 of the lines 2 and 2' in relief, which is contained in said first portion P1, which does not produce diffraction and which is invisible to the naked eye, and within which there is a position Yp, along the Y axis, for which the section in the plane (X,Z) of the two opposite flanks, describes a continuous, non-constant function and comprised between two extreme values ​​Min and Max such that Min is less than Max, and successively taking the values ​​Min, Max and Min, or Max, Min and Max.

[0117] Of course, in the case described above, both modulations extend to the level of the S grooves, but they could of course extend to the level of the peaks.

[0118] Advantageously and so that it does not produce diffraction of the light, the second portion P2 extends over a distance along said longitudinal direction (X) strictly greater than 1 pm.

[0119] Advantageously and so that it is not visible to the naked eye, the second portion P2 extends over a distance along said longitudinal direction (X) strictly less than 150 pm. c / Large and small modulations of the same general shape, arranged one on a furrow, the other on a ridge, and progressing along different planes.

[0120] In the embodiment of Figure 14, at least one of the two opposite flanks which extend on either side of a ridge, has in the plane (Y, Z) an average slope varying continuously along said longitudinal direction (X) between two extreme values ​​PenteMin and PenteMax such that PenteMin is strictly less than PenteMax.

[0121] In the case presented here, the average slope variation results both from a sinusoidal-type undulating variation of the grooves in the (X,Z) plane and corresponding to the "large modulation" and from a sinusoidal-type undulating variation of the peaks in the (X,Y) plane corresponding to the "small modulation" Here, the sinusoids of the two lines have an unchanged period over their entire extent. In addition, these adjacent lines are in phase (parallel evolution of the sinusoids), but it could of course be otherwise.

[0122] In embodiments not shown, this variation may be sinuous but not sinusoidal, or sawtooth-shaped, each tooth having a profile that preferably fits within a non-right triangle. It may be an isosceles or equilateral triangle.

[0123] In accordance with a characteristic of the invention, this “large modulation” GM extends over at least a first portion P1 of the relief lines 2 and 2' so that the transition from PenteMin to PenteMax occurs over a distance, along said longitudinal direction (X), which is visible to the naked eye.

[0124] Advantageously, this distance is strictly greater than one millimeter.

[0125] Still according to a characteristic of the invention, there is at least a second portion P2 of the lines 2 and 2' in relief, which is contained in said first portion P1 which does not produce diffraction and which is invisible to the naked eye, and within which there is a position Yp, along the Y axis, for which the section in the plane (X,Z) of the two opposite sides, describes a continuous, non-constant function and comprised between two extreme values ​​Min and Max such that Min is less than Max, and successively taking the values ​​Min, Max and Min, or Max, Min and Max.

[0126] This second PM modulation is located at the level of the C peaks of lines 2 and 2' and has been represented very schematically in figure 14 for illustrative purposes only.

[0127] Thus, the small PM modulation is in the (X,Y) plane at the level of peak C (the height Z of this peak is constant, which corresponds to the black isolines in figure 15).

[0128] Of course, in the case described above, the first and second modulations extend respectively one to the level of the S grooves, and the other to the level of the C peaks, but it is quite possible that it is the other way around.

[0129] Advantageously and so that it does not produce diffraction of the light, the second portion P2 extends over a distance along said longitudinal direction (X) strictly greater than 1 pm.

[0130] Advantageously and so that it is not visible to the naked eye, the second portion P2 extends over a distance along said longitudinal direction (X) strictly less than 150 pm. d / Large and small modulations of the same general shape arranged one on a furrow, the other on a ridge, and progressing along parallel planes. This embodiment, which is illustrated in Figure 16, differs only from that of Figure 14 by the fact that the two modulations extend in the plane (X,Z).

[0131] Under these conditions and with this exception, everything expressed above in relation to Figure 14 is valid here.

[0132] Figure 17 reflects the structure of Figure 16. Apart from the influence of the annular pattern which progressively modifies the altitude of the large GM modulation, it is possible to find the isolines linked to the small PM modulation at a given intermediate gray level. e / Large and small modulations of the same general form, arranged on a furrow or on a ridge and progressing in the same plane.

[0133] This embodiment, which is illustrated in Figure 18, differs only from that of Figure 12 by the fact that the two modulations extend in the (X,Z) plane.

[0134] The large GM modulation corresponds to a progressive variation in the height of the S groove. And the small PM modulation is a sinusoidal variation in the (X,Z) plane of the S groove.

[0135] Under these conditions and with this exception, everything expressed above in relation to Figure 12 is valid here.

[0136] Figure 19 reflects the structure of Figure 18. Apart from the influence of the annular pattern which progressively modifies the altitude of the large GM modulation, it is possible to find the isolines linked to the small PM modulation at a given intermediate gray level.

[0137] From the four preceding examples and as indicated in each of them, four other embodiments can be obtained by simply reversing the ridges and furrows.

[0138] Preferably, the case where the large modulation is located in the (X,Z) plane will be favored, while the small modulation can evolve in the (X,Y) plane and / or in the (X,Z) plane. Under these conditions, it is possible to have a small modulation which ultimately evolves in the (X,Y,Z) space.

[0139] According to another embodiment, a detail of which is shown in Figure 11, the small and large modulation are arranged on the crest of the lines.

[0140] In addition, this figure 11 shows:

[0141] - the first portion P1 between X1 and X2, - the second portion P2 between X3 and X4,

[0142] - the slopes ZMin and ZMax characteristic of the large GM modulation on the portion P1, and

[0143] - the points Min, Max and Min corresponding to the successive values ​​Min, Max and Min characteristic of the small modulation PM on the portion P2, for the position Yp along the axis (Z) in the plane (X,Z).

[0144] Under these conditions and with these exceptions, everything that has been expressed above in relation to figure 12 is valid here. f / Large and small modulations of different general form, arranged one on a furrow, the other on a crest, and progressing along parallel planes.

[0145] This embodiment, which is illustrated in Figure 20, differs only from that of Figure 16 in that the large GM modulation is undulating of the sinusoidal type, while the small PM modulation has a sawtooth profile according to the definition given above.

[0146] Under these conditions and with this exception, everything that has been expressed above in relation to figure 16 is valid here. And the same is true for figures 17 and 21. g / Large and small modulations of different shape, one arranged on a furrow, the other on a crest and progressing in different planes.

[0147] This embodiment, which is illustrated in Figure 22, differs only from that of Figure 20 by the fact that the large GM modulation evolves in the (X,Z) plane, while the small PM modulation has a sawtooth profile (according to the definition given above) and evolves in the (X,YZ) plane.

[0148] Under these conditions and with this exception, everything that has been expressed above in relation to figure 20 is valid here. And the same is true for figures 14 and 23. h / Large and small modulations of different or different form, the small modulation being present both on the grooves and on the peaks, the large modulation being present on the grooves

[0149] In this embodiment, shown in Figure 24, the small modulations are located in the (X,Z) plane on both the peaks and the grooves, and the S grooves are provided with an additional large GM modulation (not shown here) which also evolves in the (X,Z) plane, for example over a larger portion such as a variation in the Z height of the groove.

[0150] The S grooves and C ridges each have a small PM modulation with a triangular profile.

[0151] Additionally, the S grooves are provided with a large additional GM modulation (not shown here) which also evolves in the (X,Z) plane.

[0152] Once again, Figure 25 translates into gray level the projection of the structure of Figure 24 in the (X,Y) plane.

[0153] The set of figures 12 to 25 is not intended to be exhaustive but rather to describe a series of illustrative cases of the present invention. In particular, the form of the large modulation is not confined to rectilinear, sinusoidal, etc. mathematical functions, but may be any form provided that the corresponding characteristics of the attached independent claim are verified.

[0154] TECHNICAL EFFECT AND TESTS

[0155] Thanks to the invention, a security element is obtained which is bright in normal lighting (in other words when observed in the direction of specular reflection), while being perceptible for lighting angles far from normal (in other words when observed outside the direction of specular reflection).

[0156] This is illustrated in Figures 26 and 27 in which the alphabetical references have the same meanings as those in Figures 4 and 5.

[0157] This result is achieved by opening the angle of the reflective effect by introducing an additional modulation of the position of the groove S and / or the ridge C within each line. We will therefore combine a slow variation in the depth of the grooves or ridges (which generates the movement) and a rapid variation in the position or depth of these grooves or ridges (which opens the viewing angle). This second modulation slightly and locally varies the slopes of the structure, which makes it more diffusive.

[0158] We will always have a main direction of specular reflection (see arrow g in figure 28) but with locally secondary directions (see arrows h in figure 28), which opens the angle of perception of the visual effect.

[0159] Of course, if the small modulation is too large, then the structure becomes too diffusive. Thus, tests were carried out on security elements whose large modulation is sinuous in the (X,Z) plane and the small modulation is sinusoidal in the (X,Y) plane.

[0160] Figures 29 to 31 show the results of these tests.

[0161] These figures are all presented in the same way. Thus, on the left column, we observe views of the microstructures projected onto the (X,Y) plane and, on the right column, the macroscopic view of the result where we can notably distinguish a design in the form of a horizontal wave (one period of a macroscopic sinusoid to be exact).

[0162] Thus, in Figure 29, the period P of the small modulation is equal to L, L being the width of the lines of the structure. In Figure 30, P=2L and in Figure 31, P=4L. In addition, for each period P, five different amplitudes of sinusoid for the small PM modulation were tested (A=L, A=L / 2, A=L / 3, A=L / 4 and A=L / 5).

[0163] For the position of the light source, a fairly large angle a was chosen, i.e. 20° relative to the normal since, in the classic case of the prior art, the simulation gives almost zero contrast from 20°. Ideally, the best compromise is the one whose simulation gives the best contrast.

[0164] According to the observations, it is therefore a small modulation for which the period is equal to the width L of the lines of the structure and the amplitude is equal to 1 / 3 of the width L of the lines.

[0165] From this ideal compromise, we can measure the contrast based on simulations, in order to confirm the benefit of adding the small modulation.

[0166] Figures 32 and 33 show this comparison. In these figures, the element according to the present invention is referenced “sinus15”, while that according to the prior art is called “normal”.

[0167] Thus, by observing figure 32, we see that the contrast measurement gives an identical result when the sample is "flat" ("tilt" equal to 0°), which is easily explained since the perceived light is here reflected by the "lines" of the structure for which the depth is zero (therefore the modulation is also zero).

[0168] On the other hand, by consulting figure 33, we note that the impact of the small sinusoidal modulation is very effective when the sample is inclined (tilt at 20°).

[0169] Indeed, it is noted not only that the contrast decreases sharply for a lighting angle a of 0°, which confirms the fact that the structure will be less bright, but also that from a lighting angle a of 15° the contrast is greater than for the element of the prior art. Even with lighting of 40°, the contrast is not zero. Overall, the contrast of the element according to the invention is much more constant as a function of the lighting angle than that of the element according to the prior art.

[0170] SECURE DOCUMENT INCLUDING A SECURITY ELEMENT

[0171] The security element according to the invention can be applied or integrated within a secure document such as a banknote or a passport.

[0172] It can take various forms such as a "patch", a stripe or a security thread, in particular intended to be integrated into windows. Finally, it can also be directly constructed on a support indifferently based on natural materials (such as cellulose) or artificial, either fossil (BOPP, PET etc.), recycled or bio-sourced, from a resin deposited on said support and which would receive an imprint according to the invention by embossing (for example by "UV casting" or by another process).

Claims

CLAIMS 1. Security element (1) for a secure document which comprises a network (R) of at least two contiguous or adjacent raised lines (2, 2'), these lines (2, 2') being generally oriented in longitudinal and transverse directions of respective axes X and Y, while said relief is generally oriented in a direction of axis Z perpendicular to said axes X and Y, at least one of these raised lines (2, 2') being delimited by two consecutive grooves (S) or two consecutive ridges (C), from which two opposite flanks originate joining in a single and uninterrupted junction zone forming a ridge (C), respectively a groove (S), characterized in that: - on the one hand, at least one of said two opposite flanks has in the plane Y, Z orthogonal to said longitudinal direction X an average slope varying continuously along said longitudinal direction X between two extreme values ​​PenteMin and PenteMax such that PenteMin is strictly less than PenteMax, at least a first portion (P1) of said line (2, 2') in relief being such that the transition from PenteMin to PenteMax takes place over a distance, along said longitudinal direction X, visible to the naked eye, and - on the other hand, there is at least a second portion (P2) of said raised line (2, 2'), which is contained in said first portion (P1), which does not produce diffraction and which is invisible to the naked eye, and within which there is a position Yp, along the Y axis, for which the section in the X,Z plane of said at least one of said two opposite flanks, describes a continuous, non-constant function between two extreme values ​​Min and Max such that Min is strictly less than Max, and successively taking the values ​​Min, Max and Min, or Max, Min and Max.

2. Security element (1) according to claim 1, characterized in that PenteMin and PenteMax are such that PenteMin is equal to - PenteMax.

3. Security element (1) according to claim 1 or 2, characterized in that said distance visible to the naked eye is strictly greater than one millimeter.

4. Security element (1) according to at least one of claims 1 to 3, characterized in that said second portion (P2) extends over a distance in said longitudinal direction X strictly greater than 1 pm.

5. Security element (1) according to at least one of claims 1 to 4, characterized in that said second portion (P2) extends over a distance along said longitudinal direction X strictly less than 150 pm.

6. Secure document, characterized in that it comprises at least one security element (1) according to one of the preceding claims.

7. Secure document according to claim 6, characterized in that said security element is integrated therein or is attached thereto.

8. Secure document, in particular banknote, according to claim 6 or claim 7, characterized in that it is made of paper, fibrous material, plastic, or a combination of at least two of these materials.

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