WO2012046212A1 - Multi-layer structure - Google Patents

Abstract

The present invention relates to a multi-layer structure (10) comprising at least: a front layer (11) having at least one non-transparent region (11a); a back layer (12) having at least one non-transparent region (12a); preferably at least one inner layer (13; 16) located between the front and back layers; a first microperforation (20) through the non-transparent region of the front layer; a second microperforation (30) through the non-transparent region of the back layer, at least one of the microperforations extending at an angle, the layers and the microperforations being arranged such that the microperforations appear to have different respective colours on the front and back sides, at least for certain observation conditions.

Description

 Multilayer structure

 The present invention relates to the field of security documents.

 The invention relates to a multilayer structure comprising microperforations, a security article incorporating such a structure and a method for authenticating such a structure or such a security article.

 It is known, including Swiss banknotes, to make vertical perforations in a paper to secure it. The visual effect obtained is the only observation in light transmitted perforations.

 The patent application EP 1 525 100 describes a security document comprising a support through which a plurality of perforations of ellipsoidal section, orientated according to the normal to the support, extend.

 WO 00/43216 discloses a security element against forgery, having non-through perforations, resulting in different depths, and in particular may include oblique perforations. The perforations are visible in the form of a gray gradient when the structure is observed in transmission.

 The application WO 02/33652 describes a security element comprising conical perforations normally oriented to the element, passing through or not, to form a multi-tone image.

 There is a need to further enhance the security of security documents.

The invention thus has, according to one of its aspects, a multilayer structure comprising at least:

 a front layer having at least one non-transparent region, a back layer having at least one non-transparent region, preferably at least one inner layer between the front and back layers,

 a first microperforation through the non-transparent region of the front layer,

 a second microperforation through the non-transparent region of the back layer,

at least one of the first and second microperforations extending obliquely, or being non-traversing, that is to say not traversing the entire structure, said layers and said microperforations being arranged in such a way that the microperforations appear on the front side and the back side of respective colors different from each other, for certain observation conditions at least.

 We can play on the thickness of the layers, the dimensions of the microperforations and their inclination to obtain this result.

 Thanks to the invention, the user can observe at least one first color at the first microperforation by observing the front of the article or security document that incorporates the structure and at least a second color, different from the first one. , looking at the back of the article or document. The first color is different from the color of the outer face of the front layer, at least in the non-transparent region where the first microperforation is located, so that the first microperforation is detectable by the difference in color that appears between the microperforation and said region. The same is true for the second color, which is different from the color of the outer face of the backing layer, at least at the level of the region in which the second microperforation is located. The user can thus, by observing in turn the front and back of the article or document that incorporates the structure, deduce information on the authenticity of the document.

 The conditions of observation on the front and back side may be the same, that is to say at the same angle of observation relative to the normal to the structure, for example under normal incidence or oblique on both sides.

 The observation conditions on the front and back sides may also differ, the observation taking place for example according to the normal on one side and obliquely on the other.

By "color" is meant a color observed under an illuminant which may be visible light, especially daylight, or non-visible light, especially UV or IR light. The front and back layers can have different colors. Said at least one inner layer may have a color different from that of the front or back layers. At least one of the layer (s) encountered by the first microperforation preferably has a color different from at least one of the layer (s) encountered by the second microperforation. By "microperforation" is meant a hole optionally filled with a non-opaque material having a greater transverse dimension of millimetric or micrometric size, especially between 200 microns and 5 microns, better between 50 and 10 microns. The transverse dimension is measured perpendicularly to the axis of the microperforation. The cross section of the microperforation has an area less than or equal to 0.1 mm ² , more preferably 0.002 mm ² .

 A microperforation has the advantage of being detectable only under certain observation conditions, and is thus not visible to the naked eye if these observation conditions are not respected.

 A microperforation may especially be of constant cross section or not. It may be of circular or non-circular section, in particular polygonal, in particular polygonal regular or non-regular, oblong, in particular elliptical.

 By "oblique" microperforation means a microperforation extending in the structure along a direction forming a non-zero angle with the normal to the structure.

 By "front" and "back" layers are meant front and back side layers. A front-side layer is closer to the front-facing face of the user than a back-side layer, and vice versa. It is not excluded that these layers are covered with additional layers, for example a layer of transparent varnish from covering or obstruct the microperforations, especially when the structure is incorporated in an article or a security document.

 The first and second microperforations can communicate with each other or not.

 The first and / or second microperforations may extend along an oblique axis, making a non-zero angle with the normal to the structure, in particular an angle of between 10 and 80 °, preferably between 30 and 60 °. Alternatively, the first and / or second microperforations can be oriented along an axis normal to the structure.

The first and second microperforations may be of the same axis or not. According to a first embodiment, the structure has no inner layer, the front and back layers being adjacent to each other and each having a different color. The first microperforation can pass partially through the front layer, or even completely through the front layer and lead to the back layer without penetrating or penetrating or even through the entire structure.

 The second microperforation can partially cross the back layer, or even cross the entire back layer and lead to the front layer without penetrating or penetrating or even through the entire structure.

For a structure of total thickness e _r + e _v , the angles a and / or β can be chosen such that:

 and or

e _r + e _v ≥ d ₂ / sin (β) and β ≠ 0

e where _r denotes the thickness of the front layer, e _v denotes the thickness of the back layer, a denotes the angle which the axis of the first microperforation with the normal to the multilayer structure and di denotes the greater transverse dimension of the orifice through which said microperforation opens onto the outer face of the recto of the structure, measured perpendicularly to the axis of the microperforation, and

β denotes the angle made by the axis of the second microperforation with the normal to the multilayer structure and d ₂ denotes the largest transverse dimension of the orifice through which said microperforation opens onto the external back side of the structure, measured perpendicular to the axis of the microperforation.

 This can advantageously allow, especially if one of the first and second microperforations is oblique through or if they together define an oblique through microperforation, to avoid that we can see, during the observation in transvision of the structure, the through the structure via the oblique through microperforation.

 When the first and second perforations communicate with each other and have the same dimension D measured parallel to the plane of the structure,

, Σ) - g _r e _r tPC thicknesses e _v being fixed, as well as the angle a, one can have β> tg ^"(-) _v e to avoid see through the structure.

In the absence of an inner layer, the observer can see, in an exemplary implementation of the invention, on the front side the color of the back layer through the first microperforation and on the reverse side the color of the front layer through the second microperforation.

 According to a preferred embodiment, the structure comprises at least one inner layer, located between the front and back layers. The presence of at least one inner layer has the advantage, when the microperforation opens on or passes through this inner layer, to allow the observation of a color change at the microperforation when the direction of observation changes. The hue of the color is also modified because, thanks to the presence of at least one inner layer, the depth of the microperforation changes, and depending on the angle of observation, the color appears more or less dark. This also offers greater freedom of choice in the colors and materials that can be used.

 The first microperforation can partially cross the front layer or even completely cross the front layer and lead to the inner layer without penetrating or penetrating or even completely through the inner layer and lead to the back layer without entering or penetrating, or even completely through the structure.

 The second microperforation can partially cross the back layer or even cross the entire back layer and lead to the inner layer without penetrating or penetrating, or through the entire inner layer and lead to the front layer without entering or penetrating, or even completely through the structure.

For a structure of total thickness e _r + ei + e _v , the angles a and β can be chosen such that:

e _r + ei + e _v ≥di / sin (a) and a ≠ 0

 and or

e _r + ei + e _v ≥ d ₂ / sin (β) and β ≠ 0

e where _r denotes the thickness of the front layer, e _v denotes the thickness of the back layer, ei is the thickness of the inner layer, a denotes the angle which the axis of the first microperforation with the normal to the multilayer structure and di denotes the largest transverse dimension of the orifice through which said microperforation opens on the outer face of the recto of the structure measured perpendicularly to the axis of the microperforation, and β denotes the angle made by the axis of the second microperforation with the normal to the multilayer structure and < ₂ denotes the largest transverse dimension of the orifice through which said microperforation opens on the outer side of the back of the structure, measured perpendicular to the axis of the microperforation.

 This can advantageously allow, especially if one of the first and second microperforations is oblique through or if they together define an oblique through microperforation, to avoid that we can see, during the observation in transvision of the structure, the through the structure via the oblique through microperforation.

 According to a still more preferred embodiment, the structure comprises a plurality of inner layers located between the front and back layers, preferably being of different colors, including at least first and second inner layers. For example, the first inner layer is adjacent to the front layer, the second inner layer adjacent to the back layer, and the first and second inner layers adjacent to each other. During a recto observation, the observer can see the color of the first inner layer through the first microperforation and that of the second inner layer through the second microperforation on the back side.

 The first microperforation can pass partially through the front layer, or even completely through the front layer and lead to the first inner layer without penetrating or penetrating.

 The first microperforation can still completely cross the first inner layer and lead to the second inner layer without penetrating or penetrating, or even completely through the second inner layer and lead to the back layer without penetrating or penetrating or even cross entirely the structure.

 The second microperforation can partially cross the back layer, or even completely cross the back layer and lead to the second inner layer without penetrating or penetrating.

The second microperforation can still completely cross the second inner layer and lead to the first inner layer without penetrating or penetrating, or even completely through the first inner layer and lead to the front layer without entering or entering or even cross entirely the structure. For thicknesses e ₁ and e ₂ of the first and second given internal layers, the angles a and β can be chosen such that:

 and or

e ₂ ≥d ₂ / sin) οί β ≠ 0

where ei denotes the thickness of the first inner layer, a denotes the angle made by the axis of the first microperforation with the normal to the multilayer structure and di denotes the largest transverse dimension of the orifice through which said microperforation opens on the outer face of the recto of the structure, measured perpendicularly to the axis of the orifice, and

e ₂ denotes the thickness of the second inner layer, β denotes the angle that the axis of the second microperforation with the normal to the multilayer structure and d ₂ denotes the largest transverse dimension of the orifice through which said microperforation opens on the outer face of the recto of the structure, measured perpendicularly to the axis of the orifice.

 This may advantageously allow, especially if one of the first and second microperforations is oblique through or if they together define an oblique through microperforation, to avoid that we can see through the structure via said microperforation observed in transvision. In addition, this may prevent the color of the innermost layer from being seen at normal incidence.

 For a given total thickness multilayer structure, the angles a and β can thus be chosen such that:

e _r + ei + e ₂ + e _v ≥ di / sin (a) + d ₂ / sin (β)

where _r e is the thickness of the front and e _v layer refers to the thickness of the back layer.

 The structure may further comprise an intermediate inner layer, in particular a reflective layer, separating the first and second inner layers.

 According to any one of the preceding embodiments, the structure may comprise, in addition to the first and second microperforations, a third microperforation completely traversing the multilayer structure, the first and second microperforations being non-traversing.

The structure may further comprise at least two non-coaxial microperforations that meet at a common end and have opposite ends disjoint. One or both of these microperforations may be the first microperforation and / or the second microperforation. As a variant, these may be distinct microperforations of the first and second microperforations.

 Said at least two non-coaxial microperforations may extend in directions forming between them an angle γ of between 20 ° and 90 °.

 The structure may further comprise at least three non-coaxial microperforations joining at a common end and having opposite ends disjoint. One of these microperforations, or even two, may be the first microperforation and / or the second microperforation. As a variant, these may be distinct microperforations of the first and second microperforations.

 At least one of the non-coaxial microperforations may be normal to the security structure and the other two arranged symmetrically with respect to the axis of the first microperforation.

 The structure may be covered by at least one transparent protective layer, covering one end of the first or second microperforations.

 The inner layer (s) may comprise a waveguide material, receiving light from an input surface of the light, in particular defined by an aperture through the front layer and / or the layer. on the other hand, said entrance surface being distinct from the first and second microperforations.

 The back and front layers can be at least partially reflective, especially metallized.

 According to another of its aspects, the invention relates to a security article, in particular a wire, a foil or a patch, comprising a multilayer structure according to the invention.

 According to yet another of its aspects, the invention relates to a security document constituting or comprising a multilayer structure according to the invention.

In general, the security document can be a means of payment, such as a bank note, a check or a restaurant ticket, an identity document, such as an identity card, a visa, a passport or a driving license, a lottery ticket, a ticket or a ticket for cultural or sporting events. Finally, the invention relates to a method of authenticating an article or a security document incorporating a multilayer structure according to the invention, comprising the following steps:

 observe the front and back of the article or document,

 determining, on the basis of at least a comparison of the first and second colors observed through the microperforations, the authenticity of the article or the security document.

 The invention will be better understood on reading the detailed description which follows, examples of non-limiting implementation thereof, and on examining the appended drawing, in which:

 FIG. 1 represents, in section, an example of a multilayer structure according to the invention,

 Figures 2 to 15 and 24-25 are views similar to Figure 1 showing alternative embodiments of the multilayer structure,

 FIGS. 14a-14h illustrate the multilayer structure of FIG. 14, seen under different viewing directions, in front view and in section,

 FIGS. 16 to 18c show in section, schematically and partially, a microperforation,

 Figures 19 to 23 show examples of security documents according to the invention, Figure 22 being a sectional view of Figure 21.

 In the figures, the actual proportions of the various elements represented have not always been respected, for the sake of clarity of the drawing.

 For the same reason, the micro-perforations have been represented in one and the same plane of section, but they can extend in different planes, in particular parallel to one another.

 Identical or similar elements found in separate embodiments have been designated in the figures by the same reference numeral.

FIG. 1 shows a multilayer structure 10 according to the invention, comprising at least one recto layer 11, a backside layer 12, and at least a first inner layer 13 having a first color, located between layers 11 and 12. The structure 10 also comprises a first microperforation 20 made through a non-transparent region 11a of the recto layer 11 and a second microperforation 30 made through a non-transparent region 12a of the backing layer 12.

 Advantageously, for a proper orientation of the observation direction, coinciding with the axis of the microperforation 20, the first color of the first inner layer 13 is visible on the front side of the structure 10, through the orifice 21 through which the first microperforation 20 opens on the face 14 of the front layer 11, while a second color, different from the first, is visible on the back side of the structure, through the hole 31 through which the second microperforation 30 opens on the external face 15 of the back layer 12. The second color is that of a second inner layer 16, located between the front and back layers. The first and second inner layers 13 and 16 are for example, as illustrated, contiguous.

 Moreover, when the orientation of the observation direction is shifted with respect to the axis of the microperforation 20, preferably the viewing direction is at an angle to the axis of the microperforation 20 between 10 and 30 degrees, the first color of the first inner layer 13 is visible on the walls of the recto-side microperforation of the structure 10, through the orifice 21 through which the first microperforation 20 opens on the face 14 of the front layer 11. It is understood that the shift between the observation direction and the axis of the microperforation provides an observation surface of the inner layer 13 which is greater than that observable in the case where the observation direction is confused with the axis of microperforation. As a result, the first color of the inner layer 13 is more visible. In the same way, the second color, different from the first, can also be observed in an observation direction offset with respect to the axis of the microperforation 30 so as to obtain an observation surface of the inner layer 16 which is greater than that observable in the case where the direction of observation is coincident with the axis of the microperforation. As a result, the second color of the inner layer 16 is more visible.

In the example considered, the microperforations 20 and 30 are non-traversing and extend obliquely in different directions, making for example respective angles a and β between 30 ° and 80 ° with the normal to the structure. The first microperforation 20 completely crosses the front layer 11 and its bottom 22 is defined by the first inner layer 13. The second microperforation 30 completely crosses the back layer 12 and its bottom 32 is defined by the second inner layer 16.

 Layers 11 and 12 of front and back can consist of impressions or a coating reported or lying on the rest of the structure. The layers 11 or 12 may also be constituted by a metallization or a laminated film on the rest of the structure. They may have respective thicknesses e and ev of between 2 and 20 microns, for example being close to 10 microns.

 The first inner layer 13 may be made of fibrous material, for example paper, or synthetic material, for example polyester, having for example a yellow color in visible light. It may have a thickness ei of between 20 microns and 70 microns, being for example close to 50 microns.

The second inner layer 16 may be made of fibrous material, for example paper, or of synthetic material, for example polyester, having for example a cyan color. It may have a thickness e ₂ of between 20 microns and 70 microns, being for example close to 50 microns.

In general, the color difference ΔΕ under illuminant D ₆₅ between the colors of the inner layers 13 and 16 is, for example, greater than or equal to 2. The color of one of the layers 13 and 16 is, for example, achromatic, like white or black.

 In a variant, at least one of the layers 13 and 16 is luminescent, for example phosphorescent or fluorescent. In this case, the observation of the inner layers must be performed by means of a light source emitting radiation for example in a wavelength range corresponding to ultraviolet or infrared. According to this arrangement, it is also preferable that the recto / verso outer layers 11 and 12 are opaque to the light emitted by the layers 13 and 16. The layers 13 and 16 may have different colors of luminescence.

In general, the micro-perforations may be carried out using a laser or micro-needles, or by water jet. Preferably, the microperforations are made after all the layers are assembled together when they do not completely pass through one of the layers. On the other hand, when a microperforation is intended for completely through one of the layers, it is preferable to perform the perforation prior to assembling the layers.

The microperforations may have a larger cross section less than or equal to 0.1 mm ² , for example of the order of 0.002 mm ² . In the illustrated examples, the microperforations have a circular cross section, but the invention is not limited to a particular section. The section can be constant or variable.

 The structure of Figure 1 provides a first level of security to the user in that it allows the user to observe two different colors on the back and front, at the microperforations, for a proper orientation of the direction observation.

 In FIG. 1, the layers 11 and 12 appear homogeneous and completely cover the underlying layers, but in a variant the layers 11 and 12 may cover only a part of the underlying layers, being, for example, absent or transparent to the underlying layers. a certain distance from the microperforations, as shown in the following figure.

 The multilayer structure shown in FIG. 2 differs from that of FIG. 1 in that the first and second microperforations 20 and 30 respectively open, without penetrating, onto the first and second inner layers 13 and 16. This variant has the advantage next: if the outer surface of the layer 13 for example, which is in contact with the layer 11, is colored, fluorescent or metallic, the effect at the bottom 22 of the microperforation will be even more visible.

 The multilayer structure illustrated in FIG. 3 differs from that of FIG. 1 in particular in that the first microperforation 20 completely traverses the first inner layer 13 and opens, without penetrating, onto the second inner layer 16. The second microperforation 30 passes entirely through the second inner layer 16, and opens, without penetrating, on the first inner layer 13. If the faces of the inner layers 13 and / or 16, which are in contact, have a different appearance, for example have a colored surface, fluo or metallic, a difference is noted during the observation recto / verso.

In addition, FIG. 3 illustrates the possibility for the different layers to be seen from above, of different dimensions. For example, the inner layer 13 on the Figure 3 may belong to a fibrous substrate and the inner layer 16 to an insert on this fibrous substrate, such as a patch, foil or safety wire.

FIG. 16 shows a first microperforation 20, in the case where the latter is oblique of angle α relative to the normal to the structure and passes right through the first inner layer 13. This figure illustrates the limiting case where the thickness ei of the first layer is equal to a minimum thickness ei _m i _n which prevents to see through the first microperforation or see the color of an underlying inner layer, under normal observation. This minimum thickness ei _mm is calculated as a function of the largest transverse dimension di of one of the orifices of the first microperforation, measured perpendicular to the axis of the orifice, and of the angle a that this microperforation makes with the local normal, so that:

 ei min = di / sin (a) with a ≠ 0.

 The thickness e 1 of the first layer 13 is preferably greater than or equal to

Similarly, there is shown in Figure 17 a second microperforation 30, in the case where it is oblique angle β relative to the normal to the structure and passes right through the second layer. This figure illustrates the limiting case where the thickness e ₂ of the second layer is equal to a minimum thickness e _2m i _n which prevents to see through the second microperforation or to see the color of an overlying internal layer, in normal observation. This minimum thickness e _2m i _n is calculated as a function of the largest transverse dimension d ₂ of one of the orifices of the second microperforation, measured perpendicularly to the axis of the orifice, and of the angle β that this microperforation with the local normal, so that:

e _2m in = d ₂ / sin (β) with β ≠ 0.

The thickness e ₂ of the second layer 16 is preferably greater than or equal to 6 ₂ min.

According to the variant illustrated in Figure 4, the multilayer structure 10 differs from that of Figure 1 in that the first microperforation 20 completely through the first inner layer 13 and enters the second inner layer 16 without passing through it, opening therein . This may for example make it possible to observe, on the side of the front layer 11, through the orifice 21 of the first microperforation 20, an additional color, in this case that of the second inner layer 16, when one observed substantially in the axis of the microperforation. This figure illustrates the possibility for the second microperforation to be oriented normally to the structure. It has also been illustrated that at least one of the microperforations may be filled with a material or a fluid other than air, translucent or transparent, for example a transparent resin, a surface treatment as described in FIG. EPI 319104 or a varnish.

 According to the variant illustrated in FIG. 5, the multilayer structure 10 differs from that of FIG. 3 in that the first and second microperforations 20 and 30 communicate with each other, meeting at the interface between the first and second inner layers 13 and 16. Such an achievement is difficult to reproduce by a counterfeiter.

 According to the variant illustrated in Figure 6, the multilayer structure differs from that of Figure 5 in that the first and second microperforations 20 and 30 are of the same axis, for example of identical and constant cross sections. Thus, the first and second microperforations 20 and 30 together define a single through microperforation obliquely crossing the multilayer structure 10 from one end to the other. Such an embodiment adds a possibility of observing the microperforations in transmitted light.

The microperforation of FIG. 6 is partly shown in FIG. 18a on an enlarged scale. Within it, the first microperforation 20 forms an angle α with the normal to the structure and has an orifice of greater cross section di , measured perpendicular to the axis of the orifice. The second microperforation 30 makes an angle β with the normal to the structure and has an orifice of larger cross section d ₂ , measured perpendicularly to the axis of the orifice. The first and second microperforations are of the same axis, of identical and constant sections in the example considered, α = β and di = d ₂ , but it may be otherwise.

The structure has a total thickness E, the first inner layer 13 having a thickness e, the second inner layer 16 having a thickness e ₂ , the front layer 11 having a thickness e _r and the backing layer 12 having a thickness e _v . The total thickness of the inner layers 13 and 16 is denoted e. Preferably, we have _r + e + e _v ≥ di / sin (a) + d ₂ I sin (β), so as to prevent that we can see through the structure through the through microperforation in normal observation.

In the particular case illustrated in FIG. 18c where α ≠ β and where the first microperforation 20 extends over the thickness e _r + ei and the second over e _v + e ₂ , D being the dimension of the microperforations measured parallel to the plane of the micro structure, e _v , e _r and a being fixed, we can have β> tg ^"1 ) _{; to} avoid seeing through the

structure.

FIG. 18b illustrates the case where the structure comprises only one inner layer, in this case the layer 13 with a thickness ei. Preferably E> _r e + e + e ≥ _v di / sin (a) and / or E> _r e + e + e _v ≥ d ₂ / sin (β).

 The total thickness E of the structure may be between 20 microns and 500 microns, being for example close to 100 microns.

 In the variant illustrated in Figure 7, the multilayer structure comprises one or more intermediate layers 40, extending between the first and second inner layers 13 and 16, for example a single intermediate layer 40 adjacent thereto. The intermediate layer or layers 40 may be opaque or transparent, one of them being for example reflective. The reflective layer may advantageously make it possible to increase the quantity of light in the perforation and in particular during the observation of the walls of the perforation. The intermediate layer or layers 40 may be used to assemble the inner layers 13 and 16, comprising for example an adhesive.

 The first and second microperforations 20 and 30 open on the intermediate layer 40, without penetrating. The bottoms 22 and 32 of the first and second microperforations may for example, as illustrated, be placed facing each other on either side of the intermediate layer, the orifice 21 of the first microperforation 20 front side for example, being aligned with the orifice 31 of the second microperforation 30 on the back side, so as to give the illusion of a single perforation when we observe in turn the front and back of the structure.

The multilayer structure 10 can also comprise other microperforations, for example an oblique perforation 41 passing right through the structure, including the intermediate layer 40, opening on the outer face 14 of the layer of recto 1 1 through an orifice 42 and on the outer face 15 of the back layer 12 by an orifice 43.

The example of FIG. 8 shows the structure 10 of FIG. 7, the first and second inner layers 13 and 16 each comprising a waveguide type light collecting material, for example a polycarbonate-based luminescent film. marketed by Bayer under the name LISA ^® .

 The presence of the "waveguide" material is advantageous in that it makes it possible to better distinguish the colors returned by the first and second inner layers 13 and 16 through microperforations 20, 30 and 41. The waveguiding material layers 13 and 16 may comprise luminescent materials.

 The front and back layers 11 and 12 comprise respective openings 51 and 52, distinct from the orifices 21, 31, 42 and 43 of the microperforations, defining light entry surfaces. The layers 11 and 12 may be reflective, in order to accentuate the "waveguide" effect. In the example considered, the microperforations 20, 30 and 41 are oblique, but they could be normal to the structure, as illustrated in FIG. 9.

 The light that enters through the inlet surfaces 51 and 52 is propagated in the layers 13 and 16 and emerges through the microperforations. Thus, during the implementation of the authentication process, the user illuminates the openings 51 and / or 52 and observes the light emerging from the microperforations.

 According to the variant illustrated in FIG. 10, the first and second microperforations 20 and 30 are traversing and converging, joining at a common end, in this case a same orifice 60, and have opposite ends disjoint, in this case the orifices 21 and 31. Thus, the microperforations 20 and 30 open on the one hand outside the recto layer 11 through the orifice 60 and on the other hand outside the back layer 12 through the orifices. 21 and 31. The first and second microperforations 20 and 30 extend for example in directions forming between them an angle γ between 20 ° and 90 °.

According to the variant illustrated in FIG. 11, the multilayer structure 10 comprises, besides the first and second microperforations 20 and 30 of FIG. 1, two convergent microperforations 20 'and 30' similar to the microperforations 20 and 30 described with reference to FIG. 10 . According to the variant illustrated in Figure 12, there is shown a multilayer structure 10 in which the first and second microperforations 20 and 30 are through, convergent and communicate with a third microperforation 70, the three microperforations being non-coaxial, joining at one end common, in this case the same orifice 72, and having opposite ends disjoint, in this case the orifices 21, 31 and 71. The microperforations open on the one hand outside the front layer 11 by the orifice 72, and secondly outside the backing layer 12 through the orifices 21, 31 and 71. The maximum angular difference γ between the microperforations, in this case the first and second microperforations 20 and 30, is preferably between 20 ° and 90 °. In the example considered, the third microperforation 70 is normal to the safety structure 10 and the first and second microperforations 20 and 30 are arranged symmetrically with respect to the axis of the third microperforation 70, but it may be otherwise. For example, the three microperforations can be arranged according to three different angles, which are non-zero relative to the normal to the structure, so that the microperforations are not detectable under normal observation.

 In the exemplary implementation of the invention illustrated in FIG. 13, there is shown a structure 10 such as that described with reference to FIG. 12, in which the front 11 and back 12 layers are covered by transparent protective layers 80 and 90 closing the orifices 21, 31, 71, 72 of the microperforations. In the example considered, the layers 80 and 90 completely cover the two faces 14 and 15 of the structure 10. In a variant, the layers 80 and 90 may only partially cover the structure in the vicinity of the orifices of the microperforations, so as to to seal them. A transparent protective layer 80 or 90 is not specifically related to this embodiment and may cover the multilayer structure 10 according to any of the previously described embodiments, or illustrated thereafter.

FIG. 14 shows an example of a multilayer structure 10 according to the invention, comprising a plurality of sets G 1 ... G _n of oblique crossing microperforations pi ... p _n . Each set Gi, G ₂ ... G _n comprises microperforations p; extending parallel in the same direction Xi. The directions X ₁ , X ₂ , ... X _n of the n sets G 1,..., G _n with respect to the normal are preferably distinct from each other, as illustrated. For example, the first set Gi may comprise at least three microperforations pi extending in a direction forming an angle δι with the normal, the second set G ₂ may comprise at least three microperforations p ₂ extending in a direction forming an angle δ ₂ with the normal, and the nth set G _n can comprise at least three microperforations p _n extending in a direction making an angle δ _η with the normal.

The angles δι, δ ₂ ,. . . δ _η may advantageously be chosen respecting the relationship δι <δι <... <δ _η , with the different sets Gi, ... G _n succeeding in one direction, for example from left to right in the example of Figure 14. This scheduling can allow, during the observation of the structure in transvision and by continuously varying the angle of the direction d observation, to create an impression of movement because the maximum luminous intensity resulting from the microperforations passes successively by the different sets when the angle of observation changes.

 When the colors observed in the microperforations change from one set of microperforations to the other, the impression of movement can be combined with a color change effect.

FIGS. 14a to 14h show an example of a multilayer structure 10 having a microperforation arrangement similar to that of FIG. 14, observed along different directions of observation. The structure 10 here comprises three sets Gi, G ₂ and G ₃ of microperforations, these sets being arranged for example so as to form three adjacent patterns, in this case the letters AWS, visible in front view of the structure.

 The set Gi comprises microperforations pi extending parallel in the same direction Xi forming an angle δι with the normal, and opening through orifices Oi on the outer face 14 of the backing layer January 1, as shown in Figure 14b .

The assembly G ₂ comprises microperforations p ₂ extending parallel in the same direction X ₂ forming an angle δ ₂ with the normal, and opening through orifices o ₂ on the outer face 14, as shown in Figure 14f.

The assembly G ₃ comprises microperforations P3 extending parallel in the same direction X3 forming an angle 8 with the normal, and opening through orifices 03 on the outer face 14, as shown in Figure 14h.

The angles δι, δ ₂ , 03 are chosen such that δι <δ ₂ <δ3. The structure 10 shown in FIGS. 14a and 14b corresponds to an observation in transvision, according to a first direction of observation substantially coinciding with the direction Xi of the first set Gi of microperforations. The pattern A formed by the pi microperforations of the first set thus appears bright whereas the patterns W and S formed by the microperforations p ₂ , p ₃ of the second and third sets G ₂ and G ₃ appear relatively obscure, as illustrated in FIG. 14a.

The same structure 10, shown in FIGS. 14c and 14d, is observed in transvision along a second direction of observation, different from the directions X ₁ , X ₂ , X ₃ of the three sets, for example according to the normal to the structure 10, as illustrated in Figure 14d. The three AWS patterns then appear dark, as shown in Figure 14c.

When the structure 10 is observed in transvision along a third direction of observation corresponding substantially to the direction X ₂ of the second set G ₂ of microperforations, as illustrated in FIG. 14f, the patterns A and S formed by the microperforations pi, P3 of the first and third sets Gi, G ₃ appear obscure and that W formed by the microperforations p ₂ of the second set G ₂ appears bright, as shown in Figure 14e.

Finally, when the structure 10 is observed in transvision along a fourth direction of observation substantially corresponding to the direction X ₃ of the third set G ₃ of microperforations, as illustrated in FIG. 14h, the patterns A and W formed by the pi microperforations, p ₂ of the first and second sets Gi, G ₂ appear relatively obscure and the pattern S formed by the microperforations P3 of the third set G ₃ appears bright, as shown in Figure 14g.

Thus, when the observation direction is varied by continuously scanning the interval [δι _; δ ₂ ; 83] the letters AWS appear alternately luminous then obscure, giving the impression of being animated by a movement. Such a method can be useful for determining the authenticity of the structure, especially when it is incorporated in a security document.

FIG. 15 shows a variant of multilayer structure 10 according to the invention, in which the multilayer structure comprises, in addition to the aforementioned layers, a third inner layer 18 and a fourth inner layer 19 contiguous, for example having respectively a third and a fourth color, located between the first and second inner layers 13 and 16. The structure has a plurality of non-through microperforations, defining for example several sets of microperforations Ui, U ₂ , ...., U _n distinct, of which there are six in the illustrated example. . The microperforations of the same set Ui are oriented in the same direction. Within the same set Ui, at least two or even all the microperforations can lead into distinct layers, as is the case in particular microperforations 100 and 101 or in the same layer, as is particularly the case of microperforations 102 and 103, for example to create different color effects. The inclination specific to each set of microperforations can furthermore make it possible to obtain color effects that vary according to the angle of observation of the microperforations.

In an exemplary embodiment not illustrated, the structure 10 comprises several sets Gi, ... G _n microperforations, all microperforations p; of the same set Gi having the same inclination δ; and terminating in one and the same inner layer, all the microperforations of at least one other set G _j and preferably those of all the other sets resulting in respective different inner layers. Thus, when the inner layers are of different colors, a color change can be observed when the viewing angle changes.

 A multilayer structure 10 according to the invention may comprise only one inner layer 13, located between the recto 1 1 and back 12 layers, as illustrated in FIG. 24, for example if the opposite faces of the layer 13 present different phosphorescent or fluorescent materials. For example, the first microperforation 20 normally extends through the front layer and the second microperforation 30 extends obliquely through the back layer 12, the two microperforations 20, 30 opening on the inner layer 13 without enter. Thus, by observing the first microperforation 20 following the normal N to the structure, we see a first color, for example that of the inner layer 13. The inclination of the second microperforation is advantageously chosen to allow to see, at the level of the second microperforation 30, in normal observation to the structure, a second color, different from the first, being for example that of the inner wall 33 of the second microperforation 30.

A multilayer structure 10 according to the invention may not comprise an inner layer, as illustrated in FIG. microperforation 20 perpendicularly crosses the recto layer 1 1 and opens on the back layer without entering, and the second microperforation 30 crosses obliquely back layer 12 and opens on the front layer without penetrating. The front layer may have a first color and the back layer a second color, different from the first. Thus, by observing the front of the normal incidence structure N, we see at the first microperforation the second color, and observing at oblique incidence O the back of the structure along an axis substantially corresponding to that of the second microperforation, we see at this level the first color. FIGS. 19 to 23 show exemplary embodiments of security documents 105 according to the invention, comprising a security structure 10 according to the invention.

 In general, the security document can be a means of payment, such as a bank note, a check or a restaurant ticket, an identity document, such as an identity card, a visa, a passport or a driving license, a lottery ticket, a ticket or a ticket for cultural or sporting events.

 In FIG. 19, the security structure 10 according to the invention is directly integrated in the security document 105, for example a banknote. The microperforations p draw for example a pattern on it. The front and back layers can be prints and the inner layers of the paper jets of different colors. The arrangement of the microperforations is preferably similar to that of Figure 6 but may be other, in particular similar to that of the other previously described figures.

 In FIG. 20, the document 105 comprises a security thread or a foil 107 defining with the remainder of the document a security structure 10 according to the invention. The wire or foil 107 may appear wholly on the surface 109 of the document and extend over the entire width / document between two opposite edges 111 and 113.

 The width of the wire or foil 107 may be between 0.5 mm and 30 mm.

In the case of a structure at least partially deflected by a security thread, the recto layer 11 or back can be constituted for example by a metallization, a fluorescent printing or not, a laminated film; the inner layers may comprise films of colored thermoplastic material in the mass or incorporating luminescent compounds into the mass, or coatings of inks, varnishes or colored or luminescent adhesives.

 When the wire or foil 107 is not visible from one side of the document, for example due to a layer of paper or other opaque material covering the wire or foil, the structure 10 may be formed in part by a layer of such as a fibrous or thermoplastic substrate and the remainder of the structure 10 may be defined by the wire or foil.

 It is advantageous in this case that the micro-perforations are made, at least for those located on the opposite side to the wire or foil, after incorporation of the wire or foil to the document.

 In the variant of FIG. 23, the wire 107 integrated in windows, called "window thread", appears in one or more windows 115. It is advantageous to provide windows on the two opposite sides of the document, so as to allow observe microperforations on both sides of the document, on the wire.

 In FIG. 21, the document 105 comprises a window 117, in which is integrated a security structure 10 according to the invention. Shown in FIG. 22 is a sectional view of FIG. 21, illustrating the case where the window 117 is defined by an aperture, the security structure being sandwiched between two paper jets of the document.

 According to a variant not shown, the window can be defined by a transparent area of the document.

 In general, the structure according to the invention and / or the security document which incorporates such a structure may comprise additional security elements, as defined below.

 Among the additional security features, some are detectable to the eye, daylight or artificial light, without the use of a particular device. These security elements comprise for example colored fibers or boards, fully or partially printed or metallized wires. These security elements are called first level.

Other types of additional security elements are detectable only with a relatively simple apparatus, such as a lamp emitting in the ultraviolet (UV) or infrared (IR). These security elements comprise, for example, fibers, boards, strips, wires or particles. These security elements can be visible to the naked eye or not, being for example luminescent under a lighting a Wood lamp emitting in a wavelength of 365 nm. These security elements are said to be second level.

 Other types of additional security elements require for their detection a more sophisticated detection device. These security elements are for example capable of generating a specific signal when they are subjected, simultaneously or not, to one or more external excitation sources. The automatic detection of the signal makes it possible to authenticate, if necessary, the document. These security elements comprise, for example, tracers in the form of active materials, particles or fibers capable of generating a specific signal when these tracers are subjected to optronic, electrical, magnetic or electromagnetic excitation. These security elements are said to be third level.

 The additional security element or elements present in the security document, or the security structure that it comprises, may have first, second or third level security features.

 Of course, the invention is not limited to the embodiments described. In particular, the number of microperforations, their distribution, their shape and their size can be modified. It is the same for the number of layers, their nature, their respective thickness and their arrangement within the multilayer structure, depending on the desired optical effect.

 The characteristics of the different embodiments can be combined with each other, within non-illustrated variants.

 Expressing "with one" must be understood as being synonymous with "having at least one", unless otherwise specified.

Claims

 A multilayer structure (10) comprising at least:  a front layer (11) having at least one non-transparent region (Ha),  a backing layer (12) having at least one non-transparent region (12a)  preferably, at least one inner layer (13; 16) located between the front and back layers,  a first microperforation (20) through the non-transparent region of the front layer,  a second microperforation (30) through the non-transparent region of the back layer, at least one of the microperforations extending obliquely, the layers and the microperforations being arranged such that the microperforations appear on the front and back side of respective different colors, for certain observation conditions at least.  2. Structure according to claim 1, comprising one, and preferably several internal layers, preferably still of different colors, including at least first (13) and second (16) inner layers, said respective different colors being preferably the colors. said inner layers.  3. Multilayer structure according to claim 2, the first microperforation (20) opening on the inner layer (13) without penetrating.  4. Structure according to claim 2, the first microperforation (20) opening on the inner layer (13) penetrating therethrough.  5. Structure according to claim 4, the first microperforation (20) completely passing through the inner layer (13), or even completely through the structure. 6. Structure according to claim 4 and claim 2, comprising at least first (13) and second (16) inner layers, the first microperforation (20) completely passing through the first inner layer (13) and penetrating into the second inner layer (16) crossing it entirely, or even completely through the structure. 7. Structure according to any one of claims 1 to 6 with at least one attachment to claim 2, the second microperforation (30) opening on the inner layer (16) without penetrating.  8. Structure according to any one of claims 1 to 6 with at least one attachment to claim 2, the second microperforation (30) opening on the inner layer (16) penetrating, including passing through.  9. Structure according to any one of claims 1 to 6 with at least one attachment to claim 2, comprising at least first (13) and second (16) inner layers, the second microperforation (30) opening on the first layer internal (13), or even crossing it, or even completely through the structure.  10. Multilayer structure according to any one of the preceding claims, the first (20) and second (30) microperforations communicating with each other.  11. multilayer structure according to any one of the preceding claims, at least one of the first (20) and second (30) microperforations extending along an oblique axis, making a non-zero angle with the normal to the structure, in particular an angle between 30 ° and 60 °.  12. multilayer structure according to any one of the preceding claims, the first (20) and second (30) microperforations being of the same axis.  Multilayer structure according to any one of the preceding claims, wherein:

 and or e ₂ ≥d ₂ / sin $) οί β ≠ 0 where ei denotes the thickness of the inner layer (13), a designates the angle that the axis of the first microperforation (20) makes with the normal to the multilayer structure and di denotes the largest transverse dimension of the orifice. (21) whereby said microperforation opens on the outer face of the recto of the structure, measured perpendicularly to the axis of the orifice, and e ₂ denotes the thickness of another possible inner layer (16), β denotes the angle that the axis of the second microperforation (30) makes with the normal to the multilayer structure and d ₂ denotes the largest transverse dimension of the orifice (31) by which the microperforation opens on the outer face of the recto of the structure, measured perpendicularly to the axis of the orifice.  14. Multilayer structure according to the preceding claim, wherein: e _r + ei + e _v ≥ di / sin (a) and / or e _r + ei + e _v ≥ d2 / sin (β) and / or e _r + ei + e2 + e _v ≥ di / sin (a) + d2 / sin (β) where _r is the thickness of the front layer (11) and e _v is the thickness of the back layer (12).  15. multilayer structure according to any one of the preceding claims, comprising, besides the first (20) and second (30) microperforations, a third microperforation (41) completely through the multilayer structure, the first and second microperforations being non-traversing.  16. multilayer structure according to any one of the preceding claims, comprising at least two non-coaxial microperforations and joining at a common end and having opposite ends disjoint, these two non-coaxial microperforations comprising the first microperforation (20) and / or the second microperforation (30).  17. Multilayer structure according to any one of claims 1 to 15, comprising at least two non-coaxial microperforations (20 ') and (30') joining at a common end and having opposite ends disjoint, distinct from the first (20). and second (30) microperforations.  18. A multilayer structure according to one of the two immediately preceding claims, said at least two non-coaxial microperforations extending in directions forming between them an angle γ between 20 ° and 90 °.  19. Multilayer structure according to any one of claims 16 to 18, comprising at least three non-coaxial microperforations joining at a common end and having opposite ends disjoint. 20. multilayer structure according to the preceding claim, at least one of the non-coaxial microperforations being normal to the security structure and the other two being arranged symmetrically with respect to the axis of the first microperforation. 21. Multilayer structure according to any one of the preceding claims, being covered by at least one transparent protective layer (80; 90) covering one end of the first (20) or second (30) microperforations.  A multilayer structure according to any one of the preceding claims with at least one attachment to claim 2, the inner layer (13; 16) having a waveguide material receiving light from an entrance surface (51). 52) of the light, in particular defined by an aperture through the front layer and / or the back layer, said input surface being distinct from the first (20) and second (30) microperforations.  23. Multilayer structure according to claim 2, comprising first (13) and second (16) inner layers separated by an intermediate inner layer (40), in particular a reflective layer.  24. multilayer structure according to any one of the preceding claims, the backsheet layers (12) and front (11) being in particular at least partially reflective.  25. Multilayer structure (10) comprising at least:  a front layer (11) having at least one non-transparent region (11a), a backing layer (12) having at least one non-transparent region (12a), at least one inner layer (13; 16) located between the front and back layers, said inner layer comprising a waveguide material, a first microperforation (20) through the non-transparent region of the front layer,  a second microperforation (30) through the non-transparent region of the backing layer, at least one of the microperforations being non-traversing, the layers and the microperforations being arranged in such a way that the microperforations appear on the front and back side of respective different colors, for certain observation conditions at least.  26. A security article, in particular a wire, foil or patch, comprising a multilayer structure according to any one of claims 1 to 25. 27. Security document constituting or comprising a multilayer structure according to any one of claims 1 to 25. 28. A method of authenticating an article or a security document incorporating a multilayer structure as defined in any one of claims 1 to 25, comprising the following steps:  observe the front and back of the article or document, - determine, on the basis of at least a comparison of the first and second colors observed through the microperforations, the authenticity of the article or the security document.