EP3083258B1 - Security item - Google Patents

Description

The present invention relates to security articles, in particular security structures intended to be introduced into documents for securing them, as well as the secured documents themselves. "Secure document" means 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 passport. driver's license, a lottery ticket, a ticket or a ticket or an entry card to cultural or sporting events.

In order to guard against attempts to falsify or counterfeit a secure document, it may be useful that its authentication and / or identification can be done simply.

It is known to apply by coating or printing an iridescent pigment to provide first-level security. Such security may nevertheless be relatively easy to counterfeit.

WO2011 / 120917 discloses a banknote which comprises a support sheet of which at least one side comprises a transparent protective varnish of non-glossy appearance. This varnish is applied in the form of a continuous solid surface covering preferentially completely the surface of the note, and allows to observe a bottom filled with offset printing. It is partially coated with a second layer of protection of shiny appearance which contrasts with the layer of varnish. Patterns defined by the second layer are thus observable to the naked eye in reflected light. The document only provides observation in reflected light and does not exploit a difference in appearance between a transmitted light observation and a reflected light observation. This document also provides for the application of the different layers on both sides of the note, in order to benefit from the front and back sides effect.

EP 0 518 740 relates to a secure document containing an opaque security thread, visible in transmitted light, and having iridescent marks on at least one face.

The document WO 2004/030928 A1 relates to a security article having a plurality of layers such as a set of images generated in reflection and which are not visible in transmission. There is a need for further refinement of security items including security structures and secure documents with new effects easily recognizable by the man in the street, while being difficult to counterfeit.

• une première couche au moins partiellement visible en lumière réfléchie,
• une deuxième couche diffusante au moins partiellement visible en lumière réfléchie, au moins partiellement superposée à la première couche, modifiant la réflectance de la première couche, de façon à faire apparaître en observation en lumière réfléchie par contraste entre la première couche seule et la superposition des première et deuxième couches, au moins un motif observable à l'oeil nu, le motif apparaissant en lumière réfléchie n'étant pas visible à l'oeil nu en lumière transmise, en particulier lorsque la première couche est observée à travers la deuxième couche.

The aim of the invention is to meet this need and, according to one of its aspects, to provide a security article comprising:

• a first layer at least partially visible in reflected light,
• a second at least partially visible scattering layer in reflected light, at least partially superimposed on the first layer, modifying the reflectance of the first layer, so as to appear in observation in reflected light by contrast between the first layer alone and the superposition of the first and second layers, at least one pattern observable with the naked eye, the pattern appearing in reflected light not being visible to the naked eye in transmitted light, in particular when the first layer is observed through the second layer.

Preferably, the security article comprises a non-opaque substrate.

In a variant, the security article does not comprise a substrate that is distinct from the layers. The first layer may for example be a film comprising bulk iridescent pigments and act as a support for printing the second layer.

Similarly, the second layer may be a film comprising a mass of colloidal silica and act as a support for the coating of the first iridescent layer.

By diffusing layer, it is necessary to understand any layer diffusing the incident light.

The term "nanometric modification" and "nanometric particle" denotes respectively a modification whose range is between 1 and 1000 nm and a particle whose largest dimension is between 1 and 1000 nm.

By "transmitted light" it is necessary to understand a light that propagates through the possible substrate and the first and second layers.

Unless otherwise stated, "observable", "observation", "visible" means "observable", "observation", "visible" in reflected light.

For example, if the first and second layers are deposited on the recto side of a substrate, the latter is illuminated on the back side, and the observation is done on the front with the only light transmitted through the article, at incidence normal.

The lack of visibility of the pattern in transmitted light may be due to the nanometric size of the local modifications of the article, especially particles.

The invention makes it possible to benefit from the difference in appearance in reflected light and transmitted light of a first level security easily recognizable by the man in the street and which can be easily combined with other securities.

In addition, the first layer may be similar to security which the man in the street is already familiar, including being iridescent.

The security article may be a security structure intended to be integrated with or reported on a document to secure it, such as a security thread, a patch, a foil, a lamination film or a protective film of mentions variables.

The security article can still be a secure document, the various layers being for example carried by the substrate of the document itself and deposited by a coating technique, surfacing or printing.

Contrast between the first and second layers

According to the invention, a contrast is observable in reflected light between the first layer alone and the superposition of the first and second layers.

This contrast is related to different reflectances. Reflectance refers to the ratio of the reflected light flux to the incident light flux at given angles.

The superposition of the first and second layers preferably constitutes a set which is not totally transparent in at least one zone, thanks to the scattering of the light, at least in part of the visible spectrum, by the second layer, which thus modifies the Intensity of the reflectance of the first layer

Preferably, the superposition of the first and second layers has an appearance, in particular a hue and / or gloss, similar to that of the non-opaque substrate.

The pattern is for example an alphanumeric character, and the corresponding information can be found elsewhere on the document.

For example, in the case of a bank note, the reason may be the value of the note, the name of the currency, the bank or the country.

In the case of an identity document, the reason corresponds for example to the name or the photograph of the bearer of the document, or in the name of the issuing state of the document.

The reflectance of the superposition of the first and second layers must be less than 10%, preferably 20%, than the reflectance of the first layer alone. Reflectance is measured using a goniometer with an illumination / observation geometry of 45 ° / 45 ° and at the wavelength having the maximum reflectance for the first layer, preferably in the visible spectrum , ie a wavelength between 400 and 800 nm.

Any non-opaque substrate

The optional non-opaque substrate may be a transparent or translucent substrate. A translucent substrate is a substrate that diffuses light, that is to say that it allows a certain luminous intensity to pass without being transparent.

The substrate does not have to be entirely transparent or translucent. It is sufficient for it to be in an area overlapping at least partially with the first and second layers, and preferably in an area encompassing a region where only the first layer and a region are shown. both layers.

The substrate can be made transparent or translucent by incorporation or application of a suitable compound, in particular a transparentizing ink or by compression or embossing, in particular by localized application of pressure and / or heat.

This transparency can advantageously be made in the form of a pattern so as to obtain a pseudo-watermark.

In the case of a transparent substrate, it may be a film of a plastic material, especially thermoplastic, or a complex comprising several layers of plastic superimposed, including several layers of transparent thermoplastics superimposed.

In the case of a translucent substrate, it may be a fibrous substrate or a substrate having at least one layer of plastic material having light-scattering properties, for example due to its surface condition and / or the presence of diffusing charges or microcavities within it.

It may also be a hybrid substrate comprising at least one fibrous layer and at least one transparent or translucent plastic layer.

When the substrate is at least partially fibrous, the fibers are preferably natural fibers such as cellulosic fibers, but they may also be synthetic fibers, especially as described in the application FR1359135 .

The fibers may be selected from different types of cellulosic fibers, for example wood fibers or annuals such as cotton, hemp, abaca or flax fibers. When the substrate comprises at least one layer of a synthetic material, this material is for example chosen from polyolefins, and other thermoplastics, in particular PET (polyethylene terephthalate) and PC (polycarbonate).

In the case of an at least partially fibrous substrate, this may comprise a watermark or a pseudo watermark.

The thickness of the substrate is preferably between 5 and 1000 μm, better between 50 and 200 μm.

Preferably, the substrate does not have, in at least one area superimposed with the first and second layers, optical properties capable of preventing observation in reflected light of the pattern formed by contrast of appearance between the two layers.

The substrate may incorporate a first, second or third level security element. In particular, the substrate may advantageously be watermarked when it is a paper, and the first and second layers may optionally be superimposed on the watermark. The pattern visible in light reflected by contrast of appearance between the first layer alone and the superposition of the first and second layers may be superimposed on a non-opaque area of the substrate, for example said watermark in the case of a watermarked paper.

First layer

The first layer makes it possible to obtain a visual contrast in observation in reflected light with the superposition of the first and second layers.

The first layer may be entirely transparent but, preferably, it provides an optical effect that is not limited to a single contribution of brightness.

Thus, the first layer is preferably other than a simple transparent varnish, and preferably the superposition of the first layer and the second layer is a non-totally transparent assembly diffusing the light in at least a portion of the visible spectrum.

The first layer preferably comprises one or more particles conferring on it particular optical properties, in particular one or more particles reflective, chromatic, interferential, preferably goniochromatic, especially iridescent. These particles may be spherical or lamellar. These are in particular pigments or platelets.

The first layer is not completely opaque so as to allow observation therethrough in transmitted light, especially in an area where the first and second layers are superimposed and / or in the area of the pattern formed in observation in contrast reflected light of appearance between the first layer and the superposition of the first and second layers.

The first layer may never be opaque, or alternatively opaque in places, provided that there remains an area for observation in transmitted light through it and the second layer.

In the presence of openings in the first layer, the second layer may or may not extend into the openings of the first layer.

The first layer may be deposited on the possible substrate in multiple ways, for example in the fluid state, for example in the form of an impression, a surfacing or a coating coating.

The first layer may extend from one end of the substrate to the other without necessarily covering its entire surface. The first layer may especially take the form of a band.

The first layer may be perforated or not. The opening or openings, for example, define one or more negative writing patterns.

The first layer may also be deposited on the substrate in sheet form, for example comprising a film which is laminated or extruded onto the substrate or coextruded with the substrate.

The first layer may cover an area of the substrate that has homogeneous properties in transmitted light. Alternatively, this region of the substrate has inhomogeneous properties in transmitted light, so that a pattern related to these inhomogeneous properties can occur in transmitted light, where appropriate preferably in an area where the first and second layers are superimposed.

The first layer may be in direct contact with the substrate, being for example in contact with the fibers thereof when it is fibrous, or covering the substrate with interposition of one or more intermediate layers, when they have, for example, homogeneous optical properties in transmitted light.

The first layer can still be embedded in the substrate in places, which is for example the case when the article according to the invention is a security element which is in the form of a wire introduced into windows in a substrate in paper.

The first layer is preferably closer to the substrate than is the second layer.

The first layer may comprise a thermoplastic film comprising one or more pigments within it, for example incorporated during extrusion into the thickness of the film. It can be a raw thermoplastic film or a hybrid material with several layers coextruded. This is preferably a thermoplastic film with microcavities as described in the application WO 2010146065 .

The first layer may also be formed by printing, in particular being deposited by screen printing, intaglio, inkjet or gravure printing, preferably it is carried out by screen printing or gravure printing. The non-opaque substrate can be printed, including a partial print, the unprinted areas can then form a pattern that appears "negative" in reflected light, or even transmitted light.

The first layer may also result from a surface treatment such as surfacing or coating.

The layer, when deposited by printing, surfacing or coating, may comprise a binder and at least one pigment dispersed in the binder.

Preferably, the first particle (s) used in order to confer on the first layer its optical properties are chosen from among the interference pigments, preferably from goniochromatic and / or iridescent pigments, in particular nacres containing mica, titanium, silica, aluminum, tin oxide, zirconium oxide, alumina, iron oxide, or borosilicate.

The structure of these particles may be a non-opaque or opaque core, in particular a metal core, coated with one or more thin layers having different refractive indices, said thin layers possibly being made of metals and / or dielectric materials.

This or these particles may be chosen to give the first layer a shiny aspect in observation in reflected light and not shiny in transmission.

The binder of the first layer may be chosen from binders based on polyvinyl alcohol, polyacrylic acid, polyurethane, polyvinylacetate and the associated copolymers.

The first layer is preferably glossy. This brightness is in particular conferred by the particles and / or the binder.

The total mass quantity of particle (s), by dry weight, in the first layer may be between 10 and 60%, better still between 20 and 40%

The thickness of the first layer may be, on the article, between 3 and 30 microns.

• Liant polyvinyl alcohol (Mowiol 47-88 de la société Kuraray) + pigments (Mearlin Firemist Gold de la société BASF) à 20% en poids sec,
• Liant polyacrylique (Revacryl 5732 de la société Synthomer) + pigments (Pearl Sparkling Yellow de la société QolorTech) à 37% en poids sec, ou
• Liant polyurethane (Witcobond 391-64 de la société Baxenden) + pigments (Lustrepack Gold de la société Merck) à 50% en poids sec.

The amount of particle (s) in the first layer can be adapted according to the intrinsic opacity of the retained particle (s) so that the first layer retains a certain transparency.
The first layer can be one of the following examples:

• Binder polyvinyl alcohol (Mowiol 47-88 from Kuraray) + pigments (Mearlin Firemist Gold from BASF) at 20% by dry weight,
• Polyacrylic binder (Revacryl 5732 from Synthomer) + pigments (Pearl Sparkling Yellow from QolorTech) at 37% by dry weight, or
• Polyurethane binder (Witcobond 391-64 from Baxenden) + pigments (Lustrepack Gold from Merck) at 50% dry weight.

The first layer may carry at least one security element, in particular a metallization and / or demetallization.

The first layer preferably does not have a microstructured relief such as a diffraction grating or a lenticular network. In a variant, the first layer has a microstructured relief, such as for example a diffraction grating, in particular a hologram.

The first layer may contain, where appropriate, a security element being a phosphor in particular fluorescent and / or phosphorescent. Such a security element has the effect of allowing a disappearance under illumination, by for example a UV illumination, a pattern comprising nanoscale particles of the second layer. The second layer is detailed below.

Second layer

The second diffusing layer comprises a matrix having an index of refraction n _matrix and local nanometric modifications in the matrix, of refractive index n _{modifications} , which can differ from that of the matrix with a difference | n _matrix - n _{modifications} | greater than or equal to 0.01, more preferably 0.03. According to a preferred variant, this layer comprises a polymeric matrix having a refractive index n _matrix , and a dispersion of nanometric particles in the matrix, of refractive index n _particles different from that of the matrix, with a deviation | n _matrix - n _particles | greater than or equal to 0.01, more preferably 0.03.

The second layer is only partially superimposed on the first layer, which means that there is at least one visible area by the observer of the first layer which is not covered by the second layer, in order to reveal a pattern by contrast. In particular, the second layer may be perforated so as to reveal the first layer in places, the total area occupied by this or these openings then advantageously being less than half of the total area defined by the outer perimeter of the second layer.

The second layer can be superimposed entirely on the first except in the openings formed in the second layer, where the first layer is not covered by the second and remains apparent. This can make it possible to form one or more visible patterns in negative writing within the second layer.

The second layer may be partially but not totally superimposed on the first, particularly because of the presence of openings.

The second layer may have a diffusing character located so as to make said pattern appear. These may be nanoscale changes localized to the pattern regions only.

As a variant, the second layer is non-perforated and the pattern or patterns are formed in at least some positive writing on the first layer.

It may be interesting to combine one or more patterns that appear in positive writing and one or more patterns, including identical, which appear in negative writing on the first layer. In this case, care should be taken to observation in reflected light an aspect, in particular a hue and / or a brightness, similar between the superposition of the two layers and the possible substrate. Preferably the presence of the second layer is not easily perceptible by the observer in transmitted light, even is not perceptible, because of the nanoscale extent of the local modifications, and in particular of the size of the particles of the second layer.

The second layer may not contain any opacifying particulate filler, especially any intrinsically opaque pigment.

The second layer can be an impression. The second layer may be devoid of goniochromatic pigment and / or reflective metal pigment, especially pigment comprising a layer of a metal such as aluminum.

When the second layer is deposited by printing, this printing can be performed by screen printing, intaglio, inkjet or gravure, preferably it is performed by screen printing or gravure.

The local nanoscale modification or modifications, in particular the particles, present in the second layer are preferably chosen so as to confer on it different optical properties from those of the first layer.

Thus, preferably, the first and second layers contain different particles, in particular pigment particles of different colors.

Preferably, the particles are inorganic, preferably metal oxides or carbonates, more preferably based on silica, and more preferably based on fumed silica.

The local modifications contained in the second layer have a range of between 1 and 1000 nm and preferably between 1 and 200 nm. In particular, the particles contained in the second layer have a larger dimension of between 1 and 1000 nm and preferably between 1 and 200 nm.

The layer, in particular the polymeric matrix, comprises, for example, a material chosen from polyvinylalcohols, polyacrylics, polyurethanes, polyethylene threphthalates, polysiloxanes, polycarbonates and polyvinylacetates as well as copolymers.

The particles can constitute between 20 and 70% by dry weight, preferably between 30 and 50% by dry weight, of the total mass of the second layer.

The second layer may comprise at least one additional security element, in particular a security element as described below. This or these additional security elements may be superimposed where appropriate at least partially with a pattern created by contrast in reflected light between the first layer alone and the superposition of the first and second layers.

The thickness of the second layer on the article may be between 1 and 30 microns.

The second layer may contain, where appropriate, a security element being a phosphor, a photochromic substance, and / or a thermochromic substance.

In the case where these substances comprise particles, they are preferably of nanometric size, so as to preserve the invisibility to the naked eye in transmitted light of the second layer.

The pattern or patterns formed by contrast of appearance with the first layer can nevertheless be visible independently of the revelation of a luminescent, photochromic or thermochromic effect.

It may be particularly interesting that the second layer comprises a luminescent compound to reveal the pattern or patterns formed by the second layer, especially in light transmitted under UV or IR.

For example, the second layer comprises a pigment or fluorescent dye under UV. The first layer may be devoid or have a luminescent compound appearing of another color under UV or IR excitation.

The first layer may alternatively comprise a luminescent compound which allows a disappearance of a pattern of the second layer under UV excitation.

In particular, the binders of the first and second layers may be the same.

For example, the second layer may comprise, dispersed in an ALBERDINGK U5201 binder from the company Alberdingk Boley a load HDK XK20030 from the company Wacker in a proportion of 50% by dry weight

Additional security features

The article or the secured document may comprise one or more additional security elements as defined below, in particular within the first, the second layer or the substrate.

Among the additional security features, some are detectable to the naked 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 may be visible to the naked eye or not, being for example luminescent under a 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 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.

According to another of its aspects, the subject of the invention is also a method of authenticating a document according to the invention, in which a user observes the document successively in reflected light and then in transmitted light, deduces therefrom information concerning the authenticity of the document on the basis of a comparison of the aspects observed, notably the visibility of the pattern in reflected light and its non-visibility in transmitted light.

When the second layer comprises a luminescent compound, especially a fluorescent compound, the method may further comprise a UV or IR illumination step in transmitted light, in order to reveal the pattern formed by the second layer.

According to another of its aspects, the subject of the invention is also a method for manufacturing a document as defined above, in which a first layer is partially covered by a second layer modifying the reflectance of the first layer, so as to show in observation in reflected light by contrast between the first layer and the superposition of the first and second layers an observable pattern on said face, this pattern not being visible to the naked eye in transmitted light, because of low contrast in transmitted light, even non-existent contrast, given the low opacity of the second layer.

• la figure 1 représente en coupe partielle et schématique un article sécurisé selon l'invention,
• les figures 2A à 2C illustrent des variations d'aspect selon l'observation d'un exemple d'article selon l'invention, et
• les figures 3A et 3B représentent un autre exemple de variation d'aspect pouvant être obtenue dans un autre exemple de réalisation selon l'invention.

The invention will be better understood on reading the detailed description which follows, examples of non-limiting implementation thereof, as well as the examination of the attached drawing, in which:

• the figure 1 represents in partial and schematic section a secure article according to the invention,
• the FIGS. 2A to 2C illustrate variations in appearance according to the observation of an example of an article according to the invention, and
• the Figures 3A and 3B represent another example of variation in appearance that can be obtained in another embodiment of the invention.

In the appended drawing, the actual proportions of the various constituent elements or their spacings have not always been respected for the sake of clarity.

We have shown on the figure 1 an example of security article 1 according to the invention, in this case a secure document.

Article 1 comprises a substrate 11 covered with a first layer 12 in contact with it, itself covered with a second layer 13.

The first layer 12 may have a shiny appearance in reflected light, for example when observed along the OR path of the figure 1 .

The glossy appearance of the first layer 12 is for example obtained by producing this layer 12 by means of a thermoplastic film including at least a first particle P1, preferably interference, for example a particle comprising mica platelets coated with carbon dioxide. titanium TiO ₂ .

The second layer 13 covers only partially the first, which allows the observer to distinguish a pattern M ₂ delimited by the extent of the second layer 13.

The second layer 13 preferably has a matte appearance in reflected light when observed along the OR path. The second layer 13 includes for example a charge or particle P2, for example fumed silica, as detailed above.

Preferably, the second layer 13 is deposited by printing, which makes it possible to easily form a pattern with the desired contour, for example a positive or negative writing pattern, in particular an alphanumeric pattern or corresponding to information which is found elsewhere on the screen. Article.

The printing 13 is for example performed by screen printing. The formulation of the second layer 13 is such that in light transmitted following illumination of the back of the article, that is to say of an observation according to the path OT, the pattern M ₂ is not visible to the naked eye from the front of the article.

We have shown figure 2 an exemplary embodiment according to the invention, wherein the first layer 12 is perforated and defines a first negative pattern M ₁ , revealing the substrate 11.

The second layer 13 is deposited, for example printed by screen printing, so as to have a contour 131 which draws a second pattern M ₂ , for example of similar shape to the first pattern M ₁ and visible only in reflected light.

The second layer 13 has for example substantially the same color as the substrate 11.

The Figure 2A is a reflected light view of the article from the figure 2 and the Figure 2B is a transmitted light view. We see on the Figure 2B that the patterns M ₂ are no longer discernible in transmitted light.

The second layer 13 may have no luminescence property by not including for example any dye or fluorescent pigment, under UV or IR.

As a variant, the second layer 13 is made to have luminescence properties, and may comprise, for example, a UV fluorescent dye or pigment P2, so that the second or second patterns are visible in transmitted light in the presence of radiation. ultraviolet, as illustrated in Figure 2C but are invisible in transmitted light in the absence of ultraviolet radiation.

The Figures 3A and 3B illustrate another embodiment of the invention in which only the printing 13 has an outline defining a pattern M. figure 3A is a reflected light view of the substrate covered with the film 12 and the printing 13, and the figure 3B is a transmitted light view. We see on the figure 3B that the patterns M formed by the second layer 13 do not appear in transmitted light.

The figure 4 illustrates another embodiment of the article according to the invention. The article comprises a first plastic layer 12, for example PET in which particles P1 are dispersed, preferably goniochromatic particles, more preferably iridescent particles.

A second layer 13 is partially disposed on the first layer. This second layer comprises nanometric modifications, preferably it comprises nanometric particles P2.

The figure 5 illustrates another embodiment of the article according to the invention. The article comprises a plastic layer 13, for example made of PET, comprising nanometric modifications localized so as to form one or more patterns. On this layer 13 is disposed a layer 12 comprising particles P1, preferably goniochromatic particles, preferably iridescent particles. The plastic material in the layer 13 can completely cover the layer 12. In this embodiment, the observation is made from the layer 13.

The expression "having one" shall be understood as being synonymous with "having at least one", unless the opposite is specified.

Claims (15)

1. Security article comprising:

   - a first layer (12) at least partially visible in reflected light, the first layer (12):

   - comprising a thermoplastic film including one or more pigments therein, or

   - comprising a binder and at least one pigment dispersed in the binder when the first layer is deposited by printing, by surfacing or by coating,

   - a second diffusing layer (13) at least partially visible in reflected light, partially superimposed on the first layer (12) and modifying the reflectance of the first layer (12) such that at least one pattern that can be observed with the naked eye appears when observed in reflected light by contrast between the first layer (12) alone and the superimposition of the first (12) and second layers (13), the pattern appearing in reflected light not being visible to the naked eye in transmitted light, particularly when the first layer (12) is observed through the second layer (13).
2. Article according to claim 1, the superimposition of the first layer (12) and the second layer (13) forming a not totally transparent assembly diffusing light at least in part of the visible spectrum.
3. Article according to one of the preceding claims, the first layer (12) comprising one or more first particles (P1), the first particle or particles (P1) being selected from the group consisting of reflective, chromatic, interference, preferably goniochromatic, particularly iridescent particles.
4. Article according to any one of claims 1 to 3, the first layer (12) comprising a thermoplastic film.
5. Article according to any one of the preceding claims, the second diffusing layer comprising a matrix having a refractive index n_matrix and local nanoscale modifications within the matrix having a refractive index n_{modifications} different from that of the matrix having a difference |n_matrix - n_{modifications}| greater than or equal to 0.01, preferably 0.03.
6. Article according to any one of the preceding claims, the second layer (13) being devoid of a goniochromatic pigment.
7. Article according to any one of the preceding claims, the second layer comprising local nanoscale modifications the extent of which is between 1 and 1000 nm, preferably between 1 and 200 nm.
8. Article according to any one of the preceding claims, the second layer comprising particles of greater dimensions of between 1 and 1000 nm, preferably between 1 and 200 nm.
9. Article according to any one of the preceding claims, the second layer comprising mineral particles (P2) preferably of metal oxides or carbonates, more preferably based on silica and most preferably based on pyrogenic silica.
10. Article according to any one of the preceding claims, the second layer comprising particles forming between 20 and 70 % by dry weight, preferably between 30 and 50 % by dry weight of the total weight of the second layer.
11. Article according to any one of the preceding claims, the second layer being partially but not totally superimposed on the first layer.
12. Article according to any one of the preceding claims, the first layer comprising a luminescent, preferably fluorescent and/or phosphorescent substance.
13. Article according to any one of claims 1 to 12, the second layer having a localised diffusing character such that the said pattern appears.
14. Process for authenticating an article (10) according to any one of the preceding claims, in which a user observes the article successively in reflected light, then in transmitted light, compares the appearances observed and thereby obtains information about authenticity as a function of the result of the comparison.
15. Process for the manufacture of an article (10) according to any one of claims 1 to 13, in which a first layer is partially covered by a second layer modifying the reflectance of the first layer such that a pattern that can be observed on the said face appears when observed in reflected light by contrast between the first layer and the superimposition of the first and second layers, this pattern not being visible to the naked eye in transmitted light.

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