WO2016059001A1

WO2016059001A1 - Security element and security document

Info

Publication number: WO2016059001A1
Application number: PCT/EP2015/073581
Authority: WO
Inventors: Jacques MACHIZAUD; Michel Camus
Original assignee: Arjowiggins Security
Priority date: 2014-10-13
Filing date: 2015-10-12
Publication date: 2016-04-21
Also published as: EP3206884B1; FR3026987B1; EP3206884A1; FR3026987A1

Abstract

The invention relates to a security element (10) for a security document, comprising: an at least partially transparent support (11); a first layer (12) borne by the support and formed by metal deposition or printing, the first layer only partially covering the support such as to define at least a first region (12a) that appears solid but not completely opaque and a first cutout (12b) that at least partially delimits at least a first pattern (M1); and a second layer (13) borne by the support, at least partially overlapping the first layer and only partially covering the support such as to define at least a second region (13a) that appears solid but not completely opaque and at least a second cutout (13b) that at least partially delimits at least a second pattern (M2). The first pattern (M1) is visible under light transmitted from both faces of the security element and under light reflected only from the front of the security element, and the second pattern (M2) is visible under light transmitted from both faces of the security element and under light reflected only from the back of the security element.

Description

SECURITY ELEMENT, AND SECURE DOCUMENT

The present invention relates to security elements for secure documents.

The invention relates more particularly to security elements comprising an at least partially transparent support and layers carried by this support for revealing patterns when the element is observed in transmitted light or in reflection.

It is widely known to use as security element security threads consisting of a strip of a transparent thermoplastic coated on one side of at least one metal deposit with openings formed by demetallization, showing patterns when the element is observed transmitted light, such security is still called CLEARTEXT.

The application WO 2009/053673 discloses such a security element. This document describes a security thread comprising a support provided with a perforated opaque metal layer defining a pattern, this layer being coated with a scattering layer deposited in the form of a pattern. In transmitted light, the appearance of the wire is substantially the same as in the absence of diffusing layer. However, when the observation is carried out in reflected light, the pattern of the scattering layer may appear.

The invention aims to further improve the security elements, to propose new effects, particularly visible to the naked eye, white light, infrared or ultraviolet, without complicating their manufacture.

The invention thus has, according to a first aspect, a security element for secure document, comprising:

an at least partially transparent support,

a first layer carried by the support, formed by an impression or a deposit of metal, the first layer covering only partially the support so as to define at least a first region appearing full but not completely opaque and a first opening delimiting at least partially at least one first visible pattern,

a second layer carried by the support, superimposed at least partially on the first, covering only partially the support so as to define at least one second region appearing full but not completely opaque and at least one second aperture delimiting at least partially at least one second pattern.

Preferably ¹ pattern is visible in transmitted light from both sides of the security element and reflected light from only the front side of the security element, and the ^2nd pattern is visible in transmitted light from both sides of the security element and in reflected light only from the back of the security element.

The invention makes it possible to have at least one visible information on one side of the element, in reflected light, in particular on the back side and on the front face, without having to provide relatively expensive and complex optical structures to manufacture. , such as interferential structures, in particular multilayer interference structures of the PVD type, respectively on the front and on the back.

Compared to the structure described in the publication WO 2009/053673, the structure according to the invention makes it possible to obtain additional effects. The resistance to counterfeiting is in particular improved because it is more difficult to counterfeit a semi-transparent layer than an opaque layer. The invention also makes it possible to combine, by observation in transmitted light, the visible information in reflection respectively on the front and on the back. This provides a more attractive effect for the general public.

The invention makes it possible to achieve, if desired, a level 1 security revealing to the naked eye and daylight different patterns according to the observed faces and / or the observation conditions, in transmitted light or in reflected light.

In particular, one of these patterns may conventionally appear in transmitted light in the manner of a CLEARTEXT.

The second pattern may have a position marked with respect to the first pattern. In particular, the second aperture may overlap at least partially with the first region appearing full of the first layer. This can make it possible to use the first layer to define the appearance of the second pattern in reflected light.

The first aperture may overlap at least partially with the second region appearing full of the second layer.

The first layer may be scattering or not.

The first pattern can be exclusively superimposed on the second region appearing full. The second pattern can be superimposed exclusively on the first region appearing full. The openings of the first layer can be superimposed

exclusively to regions appearing full of the second layer.

The first layer may be formed by printing. Alternatively, the first layer is formed by a metal deposit. The metal deposit can be

thin enough so that the first region appearing full is non-opaque.

The first region appearing full can also have its non-opaque character due to the presence of a frame.

The second layer can be formed by printing. This is particularly a non-reflective printing, preferably non-metallic.

The second layer may advantageously comprise a diffusing ink. The second layer may alternatively be formed by a metal deposit. The latter may be thin enough so that the second region appearing full is non-opaque. The second region appearing full may have a non-opaque character due to the presence of a frame.

The first pattern can be completely surrounded by the first region appearing full, in front view.

The second pattern can be completely surrounded by the second region appearing full, in front view.

The first and second layers are preferably located respectively on the front and back of the support.

The different appearance of the front and back faces, especially when the first layer is metallic and the back side white, can facilitate the manufacture of documents incorporating the element, constituting a visual cue very easy to discern when inserting of the element and its control.

By "at least partially transparent support" it should be understood that there is at least one region of the support that is sufficiently transparent or translucent that the first transmitted light pattern can be observed through the security element.

By "appearing full region", one must understand that the aspect of this region is that of a full region. The region can be effectively full on a microscopic scale. It may also not be, but keep the appearance of a full region, this which is the case for example during the realization in said region of a thin frame whose lines are sufficiently close to not be distinguishable by the naked eye because of the resolving power thereof. In particular a frame whose resolution is greater than 300 dots per inch ("dot per inch" or "dpi" in English) is invisible to the eye, especially for an individual with a medium vision, at a distance of 25 cm ( which corresponds to a mean observation distance). Thus, two points spaced about 70 μιη or less are not distinguishable at this distance.

By "marked position", it should be understood that the first pattern is arranged with a predefined and non-random positioning with respect to the second pattern due to the knowledge, during manufacture, of the position of the first pattern when the second is created.

By "non-completely opaque layer" it is to be understood that the layer passes white light under at least some observation conditions, with a transmission factor (or transmittance) preferably of at least 10%, preferably from minus 20% measured according to ISO 15368. Also known as semi-transparency.

The semi-transparent nature of the layer may be independent of the angle of observation, which is for example the case for a metal deposit of homogeneous thickness but very thin. The semi-transparent nature can also depend on the angle of observation, which is the case when using opaque plates oriented in the same direction, not parallel to the plane of the substrate. In this case, when the layer is observed in said direction, it allows the light to pass between the wafers and when it is observed in a direction substantially perpendicular to the orientation direction of the wafers, the latter obstruct the light.

The security element is in particular a security thread, a film, for example a foil or a lamination film, or a patch. It is preferably a security thread.

The invention also relates to a secure document incorporating a security element according to the invention.

Said secure document is for example a means of payment, such as a bank note, a payment card, a check or a restaurant ticket, an identity document, such as an identity card, a visa, passport or a driving license, a card, including access, a lottery ticket, a ticket or a ticket to cultural or sports events, a loyalty card, a card of service, a membership card, a playing or collectible card, a voucher or a voucher. It is preferably a document comprising a fibrous layer, especially when the security element is a security thread. In this case, the security element is introduced into the secure document in mass or in window (s), and preferably in window (s).

When the security element is a film, for example a foil or a lamination film, or a patch, it is applied to the surface of the secure document.

Since the element is integrated into the document substrate, the presence of the second layer, visible on the back, preferably of white or metallic color, can reduce the visibility of the element out of the possible windows of the document when the latter is observed on the back side. .

Surprisingly, the appearance of the security element on the side of the first layer may appear substantially uniform in reflection, especially when the second layer is diffusing and has substantially the same color as the substrate in which the element is inserted or on which it is fixed. In this way, during the observation in reflected light from the front side, the zones facing the openings of the second layer have the same color as the zones with respect to the second layer.

The security element may or may not extend from one edge to the other of the document.

The element and / or document may include one or more 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 additional security elements comprise, for example, colored fibers or boards, fully or partially printed or metallized wires. These additional security features are said to be 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 additional security elements include, for example, fibers, boards, strips, wires or particles. These security elements may be visible to the naked eye or not, being for example luminescent under the lighting of a Wood lamp emitting at 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 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 additional 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 additional security features are said to be third-level.

The additional security element or elements present within the security element according to the invention and / or the document may have first, second or third level security features.

The invention further relates, in another aspect, to a method of authenticating a secure document comprising a security element as defined above. Observation can be done through a window of the document.

The invention further relates, in another of its aspects, to a method of manufacturing a document as defined above, in which is incorporated in window (s) or on the surface of the security element according to the invention.

The invention may be better understood on reading the following detailed description, nonlimiting examples of implementation thereof, and on examining the appended drawing, in which:

FIG. 1 schematically represents an example of a secure document according to the invention,

- Figure 2 shows in cross section along II-II the secure document and the security element,

FIGS. 3A to 3C respectively represent the security element observed in reflection on the front, in reflection on the back, and in transmission, and

Figures 4 to 6 show variants of safety elements in cross section.

In the figures, the respective actual proportions of the various constituent elements have not always been respected, for the sake of clarity of the drawing. Moreover, some layers may appear monolithic in the figures whereas they are actually made of several sub-layers. Adhesive layers may not have been shown between different constituent layers.

FIGS. 1 and 2 show an example of a secure document 1 in accordance with an exemplary implementation of the invention, for example a banknote.

The document 1 comprises a substrate 2, preferably made of paper, formed of one or more fibrous jets, which integrates a security element 10 according to the invention, in the form of a thread ("thread" in English) in the example under consideration. .

The security element 10 comprises a support 11 made of thermoplastic material, which ensures the mechanical strength of the wire. This support 11 is for example transparent thermoplastic material such as PET or polyester. The thickness e of the support 11 is, for example, from 2 to 30 μιη and the width w of the element 10 from 1 to 30 mm and preferably from 4 to 10 mm. The support 11 may also be an adhesive layer, particularly in the case of a foil.

The security element 10 comprises a first layer 12, for example formed by metallization and demetallization. The layer 12 thus comprises, for example, one or more regions appearing full 12a and one or more openings 12b. The one or more openings 12b are visible in transmitted light through a window 3 of the document 1 and define one or more first patterns M1 as illustrated in FIG. 3C for example. The Ml patterns are for example alphanumeric patterns, or representations of various subjects such as characters, animals, plants, landscapes, monuments. The M1 patterns can be found elsewhere on the document 1, being for example printed on the substrate or being for example a watermark.

The pattern (s) M1 can still be raster images, giving a relief impression thanks to a shading effect. In this case, the openings 12b have sizes and a distribution adapted to create such images.

The first layer 12 can thus form a recognizable image, whose subject is for example present elsewhere on the document.

Although the first layer 12 preferably comprises a metallization, it may also comprise printed patterns, in positive or negative writing, for example with a metallic, magnetic or electrically conductive ink. The first layer may comprise a diffusing ink. The region or regions appearing full 12a may be without microscopic opening, that is to say truly full. In this case, the semi-transparency is obtained by sufficiently reducing the thickness of deposited metal.

The metal is, for example, aluminum, copper, tin, gold, nickel, chromium, silver, and one of their alloys.

As a variant, the region or regions 12a appear solid and are non-opaque due to the presence of microscopic openings such as closely spaced frames, so as to give them semi-transparency. In this case, the deposited metal thickness may be greater, because the semi-transparency is no longer necessarily obtained by the small thickness deposited.

The first layer 12 can pass at least 10% of the white light in the regions appearing full. The transmittance or transmission factor is measured according to ISO 15368.

The first layer 12 may be colored, in particular by a dye and not by a pigment, for example an azo compound.

The security element 10 comprises a second layer 13, situated for example as illustrated in FIG. 2, opposite the first layer 12 with respect to the support 11.

The second layer 13 may not cover the entire face 11a of the support 11 and have one or more regions appearing full 13a and one or more openings 13b. These define patterns M2 visible in reflection on the side of the back side 6 of the element 10, as shown in Figure 3B.

The second layer 13 may be non-opaque, the region or regions appearing full 13a being semi-transparent.

This semi-transparency may be due to the non-opaque nature of the material of the second layer 13. As a variant, the regions 13a are rasterized, being formed of thin closely spaced frames which let the light pass in transmission, but appear solid in reflection.

Preferably, the second layer 13 is of a color similar to that of the substrate 2 of the document 1, and will thus be most often white.

The composition of the second layer can thus be adjusted according to the color (L *, a *, b *) of the substrate 2 of the document 1. The second layer 13 is preferably diffusing and based on pigment (s) dispersed in a binder.

When a diffusing effect is desired, the second layer 13 may comprise a mixture of at least two charges, in particular nanometric charges, of different refractive indices.

Without being bound by a theory, the Applicant estimates that the mixture of the said at least two nanometric charges of different refractive indices makes it possible to amplify the diffusion phenomenon because the nanometric charge of a lower refractive index refracts little the incident light which runs through then a larger optical path and penetrates further into the layer, while the nanoscale load of higher refractive index increases the number of diffusions within the layer. This provides a significant penetration and diffusion of light within the layer, allowing the layer to hide the underlying structure in reflection without the layer is opaque, which would adversely affect the visibility of the security element in transmitted light.

The second layer 13 may be in the form of a single masking layer, comprising said aforementioned mixture of at least two nanometric charges.

More preferably, at least one of the nanometric fillers comprises colloidal silica (silicon dioxide), in particular pyrogenic silica, and is better composed of fumed colloidal silica. A nanometric charge comprising silica is advantageous because it has the advantage of not absorbing the UV radiation useful for luminescence, which makes it possible to produce the security element with one or more luminescent layers, in particular fluorescent under UV.

One of the nanometric charges of the mixture, and preferably the colloidal silica, may be present in a mass quantity of between 20 and 80%, better still between 30 and 70%, and still more preferably between 40 and 60% relative to the mass of the mixture. the second layer 13.

The colloidal silica preferably has a D50 dimension of between 30 and 1000 nm, more preferably between 30 and 500 nm, more preferably between 50 and 300 nm.

The security element may comprise as nanometric charge titanium dioxide in the second layer 13. Preferably, the amount of titanium dioxide is sufficiently weak not to excessively absorb the UV radiation and to allow the use within the security element of at least one luminescent compound, especially fluorescent under UV (365 nm), for example applied by printing on the second layer 13 or mixed with the second coat or varnish or adhesive of the security element.

Titanium dioxide is preferably of anatase nature, because it then has the advantage of having a lower UV absorption compared to titanium dioxide of rutile nature. The anatase titanium dioxide is in particular at least partially transparent to UV, and in particular transparent over at least one wavelength range of the UV range.

The other of the nanometric charges of the mixture, and preferably titanium dioxide, may be present in a mass quantity of between 1 and 40%, better still between 2 and 30%, and even more preferably between 3 and 15% relative to the mass. of the second layer.

In the case of a colloidal silica-titanium dioxide mixture, the mass ratio of colloidal silica to titanium dioxide is preferably between 0.5 / 1 and 4/1, more preferably between 2/1 and 3/1.

The titanium dioxide preferably has a D50 dimension of between 30 and 1000 nm, more preferably between 30 and 500 nm, more preferably between 50 and 300 nm.

According to a preferred variant, said at least two nanometric fillers are respectively colloidal silica, preferably fumed, and titanium dioxide, preferably anatase.

According to this variant, the colloidal silica induces a greater scattering of the light in the short wavelengths (blue) and one thus obtains a predominantly red-orange color in transmission (thus in specular reflection if the particles are placed on an at least partially reflective layer). Titanium dioxide makes it possible to modify the path of light by increasing the diffusion within the second layer 13, which brings greater opacity and thus reduces the red-orange reflective appearance produced by the colloidal silica.

According to a preferred variant, the second layer 13 further comprises a multilayer interference pigment.

The multilayer interference pigment has the particularity of preferentially selecting certain wavelengths in reflection and in transmission. By for example, a blue iridescent pigment reflects in the specular direction (angle of reflection equal to the angle of incidence) more blue wavelengths than the others. In transmission, the color obtained is then complementary to the color in reflection, that is to say red-orange. The multilayer interference pigments may be relatively transparent, because they are not very absorbent, and consequently a layer of multilayer interference pigment will have, in diffuse reflection (in all other directions other than the specular direction), the same color as in transmission (complementary to the color in specular reflection). Using the example above, the layer of blue iridescent pigment spread on a white paper will give a red-orange color.

The term "multilayer interference pigment" is intended to mean a pigment producing a color by an interference phenomenon by virtue of a succession in the path of light of at least two different refractive index materials. A multilayer interference pigment is still sometimes referred to as "nacre" in the case of layers deposited on a platelet-based base. A multilayer interference pigment is different from a liquid crystal, which can also generate a color by an interference phenomenon due to its intrinsic structure.

By combining the color associated with the light scattering by the nanometric charges and that related to the diffuse reflection by the multilayer interference pigment, it is possible to obtain, by additive synthesis, colors, a color substantially similar to that of the substrate of the document 1 for example white, by suitably selecting the color of the pigment and that of the filler; preferably, a blue, green or blue-green multi-layer interference pigment, or a mixture of green and blue pigments, is combined with the nanometric fillers.

The combination of the pigment and nanometric charges enhances the diffusion of incident light within the second layer. This combination also makes it possible to limit the proportion of the nanometric filler having the highest refractive index, in particular titanium dioxide, and thus to limit the opacification in transmitted light and, if appropriate, the absorption of UV.

Preferably, the multilayer interference pigment according to the invention comprises a transparent base, preferably mineral, coated with at least one layer of a refractive index material different from that of the base. The pigment may comprise a platelet base, preferably of mica or glass. For example, the pigment comprises mica or silica (silicon dioxide) coated with titanium dioxide.

The pigment preferably has a transparent substrate, for example made of mica, and in particular optical characteristics that are complementary to those of colloidal fumed silica. When the substrate is white, the pigment is preferably blue or green or blue-green. The color of the pigment is that obtained in specular reflection of non-normal incidence.

Preferably, as explained above, the interference pigment has a blue, green or blue-green color.

The average size D50 of the pigment is preferably between 2 and 150 microns, more preferably between 5 and 40 microns, more preferably between 5 and 25 microns.

The multilayer interference pigment may be non-goniochromatic, and may comprise for example only one layer coating a base.

The mass quantity of multilayer interference pigment relative to the mass of the second layer 13 is preferably between 1 and 40%, better still between 2 and 30%, and more preferably between 5 and 15%.

Alternatively, the second layer 13 is formed by a metal deposit.

The element 10 may comprise a layer of heat-sealable adhesive on each of its outer faces, not shown.

When the element 10 is observed in reflection on the side of the front face 5, one can observe the M1 units by contrast between the color of the region or regions appearing full 12a of the first layer 12 and that of the opening or openings 12b formed in this, as illustrated in Figure 3A. M2 patterns do not appear or appear little, especially when the second layer 13 is diffusing and its color is close to that of the substrate 2.

When the element 10 is observed in transmission on the side of the front face 5, being illuminated from the back side 6, not only the patterns M1 are visible but also the patterns M2, thanks to the semi-transparency of the regions 12a of the first layer 12, as shown in FIG. 3C.

When the element 10 is observed in reflection on the side of the back side 6, only the patterns M2 are visible, as shown in Figure 3B. They are all the more visible as the color of the first layer 12 contrasts with that of the second layer 13. The invention is not limited to the examples which have just been described.

The security element 10 according to the invention may be in a form other than a security thread, and for example in the form of a patch or a structure applied on the surface by transfer, also called "foil" .

In a variant not shown, the first and second layers are on the same side of the support January 1.

The first layer 12 may, in a variant, comprise magnetically steerable wafers. Such platelets constitute an opaque screen for a certain angle of observation, generally perpendicular to their direction of orientation. When the oriented plates are observed in a direction substantially parallel to their direction of orientation, it is possible to see them and the layer becomes semi-transparent. A first layer comprising magnetically steerable wafers, which may be suitable for producing the first layer, is described in the publications WO 2012/176169 A1 or WO 2013/190522 A2.

The security element 10 according to the invention can receive any additional security-enhancing structure, such as, for example, a layer of liquid crystals or goniochromatic pigments, a diffraction grating, a hologram, or an optical structure such as a lens. Fresnel, among other examples.

In the variant illustrated in FIG. 4, the security element 10 comprises, on the front face of the support 1 1, an intermediate layer of variable opacity 20 comprising magnetically oriented plates, as described in the publications WO 2012/176169 A1 or WO 2013/190522 A2 mentioned above. This intermediate layer 20 has an opacity that varies with the direction of observation. Thus, under normal incidence for example, the first layer 12 which covers the intermediate layer 20 is opaque and at an incidence which corresponds substantially to the direction of orientation of the wafers, the intermediate layer 20 is non-opaque.

The intermediate layer 20 extends for example continuously over the entire surface of the support January 1.

In the variant of Figure 5, the first layer 12 is a metal layer covered by an embossed layer 12c, so as to create at each first region 12a a visible diffraction grating in reflection. The first layer 12 can follow under the relief of the embossed layer

12c.

Alternatively, the first layer 12 covers the embossed layer 12c.

In the variant of FIG. 6, the first layer 12 is formed by an impression of an absorbent ink, and it is covered by a layer 12c of cholesteric liquid crystals, which covers, for example, the solid regions 12a and the openings 12b.

The liquid crystals are non-opaque and their goniochromatic effect is visible only where they overlap with the solid regions 12a.

The expression "comprising a" should be understood as being synonymous with "comprising at least one".

Claims

Security element (10) for secure document (1), comprising:

a support (11) at least partially transparent, a first layer carried by the support, formed by a deposit of metal or an impression, the first layer covering only partially the support so as to define at least a first region appearing solid (12a) but not completely opaque and a first aperture (12b) delimiting at least partially at least one first pattern (Ml), - a second layer (13) carried by the support, overlapping at least partially with the first , only partially covering the support so as to define at least a second region (13a) appearing solid but not completely opaque and at least a second aperture (13b) defining at least partially at least a second pattern (M2), the first pattern (Ml) being visible in light transmitted from both sides of the security element and in reflected light only from the front of the security element, and the second word if (M2) being visible in light transmitted from both sides of the security element and in reflected light only from the back of the security element.

2. Element according to claim 1, the second pattern (M2) having a position marked with respect to the first pattern (Ml).

3. Element according to claim 1 or 2, the second aperture (13b) superimposed at least partially on the first region appearing full (12a) of the first layer (12).

4. Element according to any one of claims 1 to 3, the first ajour

(12b) overlapping at least partially with the second appearing solid region (13a) of the second layer (13).

5. Element according to any one of claims 1 to 4, the first layer (12) being formed by printing.

6. Element according to any one of claims 1 to 4, the first layer (12) being formed by a metal deposition.

7. Element according to any one of claims 1 to 5, the first layer (12) being diffusing.

The element of claim 6, wherein the metal deposit is sufficiently thin so that the first full appearing region (12a) is non-opaque.

9. Element according to one of claims 1 to 7, the first region appearing full (12a) having its non-opaque character due to the presence of a frame.

10. Element according to any one of claims 1 to 9, the second layer (13) being formed by an impression, in particular non-metallic.

11. Element according to any one of claims 1 to 10, the second layer (13) comprising a diffusing ink.

12. Element according to any one of claims 1 to 11, the second layer (13) being formed by a metal deposition.

The element of claim 12, wherein the metal deposit is sufficiently thin so that the second full appearing region (13a) is non-opaque.

14. Element according to claim 12, the second region appearing full (13a) having its non-opaque character due to the presence of a frame.

15. Element according to any one of the preceding claims, the first pattern (Ml) being completely surrounded by the first region appearing full (12a), in front view.

16. Element according to any one of the preceding claims, the second pattern being completely surrounded by the second region appearing full (13a), in front view.

17. Element according to any one of the preceding claims, the first and second layers (12,13) being located respectively on the front and back of the support (11).

18. Element according to any one of the preceding claims, the second pattern (M2) superimposed exclusively on the first region appearing full (12a).

19. Element according to any one of claims 1 to 18, the first pattern (Ml) being exclusively superimposed on the second region appearing full (13a).

20. Secure document (1) comprising a security element (10) as defined in any one of the preceding claims.

21. Document according to claim 20, the second layer (13) having a color close to that of a substrate of the document in which the element is integrated or on which the element is fixed.

22. Document according to claim 21, the substrate and the second layer being white.

23. A method of authenticating a document as defined in one of claims 20 to 22, comprising the steps of:

- observe the security element (10) in transmission,

- observe the security element (10) in reflection, on the front and back,

- generate information regarding the authenticity of the document at least on the basis of said observations.