WO2014097093A1

WO2014097093A1 - Security structure

Info

Publication number: WO2014097093A1
Application number: PCT/IB2013/060926
Authority: WO
Inventors: Michel Camus; Stéphane Mallol
Original assignee: Arjowiggins Security
Priority date: 2012-12-20
Filing date: 2013-12-13
Publication date: 2014-06-26
Also published as: EP2935696A1; EP2935696B1; FR3000112A1; FR3000112B1

Abstract

The present invention relates to a security structure (1) observable from at least one face (15), the structure (1) comprising: - a network of elementary patterns (5) made from a polymeric material (9), the elementary patterns having a unitary dimension (D) of at least 75 micrometers, that network defining a non-planar surface, - in a first area (20) of said network, a reflective layer (19) that is at least partially visible from the observation face (15), that reflective layer defining a reflective surface following the relief of said network, - in a second area (21) of said network, different from the first, at least one recess (24) formed in the reflective layer (19) and/or one element observable from the observation face (15), said observable element having a surface situated on the side of the observation face (15), which follows the relief of said network, that surface having a different appearance from that of the reflective surface.

Description

Security structure

The present invention relates to security structures, especially those intended to be introduced in secure documents.

"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 to cultural or sporting events.

In order to guard against attempts to falsify or counterfeit such a document, it is useful that the authentication and / or identification of the security structure or structures that the document comprises can be done simply.

It is known to make security structures with lenticular arrays associated with specific impressions, in order to produce movement, depth and / or stereoscopic effects. The company CRANE markets under the brand MOTION ^® .

Such security structures exploit an optical structure whose face is exposed to the air, so that the difference between the refractive indices of the air and the material of the structure produces the desired refraction of the light rays.

Publications FR 2 952 194, WO 2007/133613, US 2008/0182084, US 2005/0180020 and US 2008/0160226 are still known from various examples of safety structures comprising optical structures.

FR 2 952 194 discloses a reflective surface formed of mirrors made by metallization of an embossed surface. The metal layer defining the reflective surface may have been demetallized. The mirrors may be concave mirrors towards the observer, of diameter for example between 50 and 70 microns. The mirrors serve, for example, to give the observer an enlarged or reduced image of a pattern. A Fresnel lens can be made to enlarge the image given by a mirror.

WO 2007/133613 discloses a substrate having a lenticular array with lenses having at their base a diameter of less than 50 microns and a pattern spatially coordinated with images produced by the lenticular array. US 2008/0182084 teaches canceling the effect of lenses by applying an adhesive to their surface. In one example, the structure comprises a substrate carrying on one side a lenticular array with areas coated with varnish and on the other a diffraction structure and micro-images. The lenses have a diameter of between 10 and 150 microns.

US 2005/0180020 discloses a multilayer structure having a lenticular array capable of receiving printing. The lenses have a diameter less than 50 microns.

US 2008/0160226 discloses a microlens array of about 20 microns in diameter, associated with micro-images to create a moire effect.

There is a need to benefit from security structures capable of producing new optical effects that can contribute to the authentication and / or identification of an object, particularly in a simplified manner.

The invention thus has, according to one of its aspects, an observable safety structure of at least one face, the structure comprising:

a network of elementary patterns formed in a polymeric material, the elementary units having a unit dimension of at least 75 microns, better still at least 100 microns, this network defining a non-planar surface,

in a first zone of said grating, a reflective layer at least partially visible from the observation face, this reflective layer defining a reflective surface along the relief of said grating,

in a second zone of said network, different from the first, at least one recess formed in the reflective layer and / or an observable element from the observation face, this observable element having a surface located on the side of the observation face; which follows the relief of said network, this surface having a different appearance from that of the reflective surface.

According to the invention, the elementary patterns are visible to the naked eye by their relatively large unit size and create a reflective structured background, aesthetically attractive and easy to recognize by the observer. This structured background is relatively easy to manufacture, given the size of the patterns, and may help to attract the attention of the man on the street safety elements annexes that comprises the structure, these ancillary elements being for example arranged in the first and / or second zone.

It is possible to play on the shape of the patterns of the network to vary the optical effects.

The second zone is preferably completely surrounded by the first. The first or second field can define alphanumeric characters that can be found elsewhere on the document, for example the name of a bank, a country and / or the value of a cut. The structure can be made to allow observation through it in at least a region of the second zone.

The recess in the reflective layer and / or the observable element from the observation face preferably form a geometric pattern, a portrait, an animal, a landscape, a symbol, in particular an alphanumeric symbol, a line, a guilloche. This geometric pattern may comprise a set of points appearing more or less distant, when observed in transmitted light. Advantageously, this geometric pattern can be found elsewhere on the security document bearing the security structure. For example, the security document has a watermark, a wire, a foil, a patch, or a print representing the same geometric pattern.

The reflective layer is preferably a layer of a metal, the reflection of the light being effected on the surface of this layer facing the observation face. Alternatively, the reflective layer is formed of a material whose refractive index is sufficiently different from that of an adjacent material, so that at the interface between the two occurs a reflection of the light from the low angles impact. Thus, the reflective layer may have a succession of sub-layers formed of different refractive index materials deposited for example by a vacuum deposition technique. If necessary, the reflective layer produced by an interference phenomenon a color varying with the angle of observation. The reflective layer may also have only a metallic, non-goniochromatic appearance. The reflective layer may be formed of a HRI (High Refractive Index) material.

The reflective layer may be opaque or semi-reflective, depending for example on the thickness of metal deposited when the reflective layer is metallic. The reflective layer, especially when metallic, may have a thickness of between 0.1 and 0.3 μπι. The reflective layer may be formed of a single material. A semi-reflective layer is also called semi-transparent layer. The reflective layer can be holographic.

The reflective layer, especially when metallic, can be applied to the polymeric material by vaporization, so that the reflective layer conforms to the shape of the relief of the patterns.

The reflective layer, in the first zone, can be continuous, that is to say without microscopic opening. As a variant, it has openings that are small enough to give the naked eye, in reflection, an appearance similar to that of a layer devoid of these microscopic openings.

The reliefs of the network can be made by embossing, in particular by thermo-embossing or by embossing followed by ultraviolet crosslinking. In particular, the array of patterns can be formed by embossing hollow or embossed with a varnish, which can be a resin. The polymeric material may include an epoxy or acrylic resin. The polymeric material may comprise a thermoplastic material such as polyethylene (PE), PET or polyester, among others.

Preferably, the array of patterns is formed by embossing a varnish. The latter can be applied in the fluid state on a support before embossing. The varnish may be colorless or colored, and optionally incorporate a luminescent agent, in particular a fluorescent agent.

The network of patterns can thus be embossed in relief in a varnish and covered with a reflective layer metallized on the face of the patterns facing the observation face. The reflective layer can thus be located between the observation face and the polymeric material. Alternatively, the pattern pattern can be embossed hollow in a varnish and the reflective layer can be applied in the hollow patterns on the side of the concave face. In this case, the polymeric material may be between the observation face and the reflective layer.

The network of patterns can still be embossed hollow for some reasons and embossed for other reasons.

In a preferred embodiment, the structure comprises one or more recesses in the second zone, which makes it possible, for example, to see through the structure in this or these recesses, and to approach, for example, a security of the "CLEAR TEXT" type. . The patterns of the grating may define convex or concave mirrors or a combination of concave-convex mirrors towards the observation face with the metallized layer, each mirror being for example of revolution about an axis perpendicular to the plane of the structure, cylindrical around an axis parallel to the plane of the structure or of another shape, for example of pyramidal shape, representing a geometric pattern, a portrait, an animal, a landscape, a symbol ...

The patterns of the network may be of various shapes depending on the effect to be reproduced. A preferred embodiment implements patterns each in the form of a Fresnel lens type structure, the base of which is not necessarily circular, which may have the advantage of allowing the production of a relatively large reflecting mirror. high with a relatively small thickness of the layer of polymeric material. In particular, to produce the patterns in Fresnel structure, it is possible from a volume representing the pattern, to subdivide the pattern into equally spaced slices in the plane of the pattern, to remove the portions of slices that have a constant thickness for obtain a thin plate in the manner of a Fresnel lens.

The structure may comprise a support carrying the polymeric material. The support may be at least partially transparent or translucent. The support may for example be or comprise a film of a transparent or translucent thermoplastic material, for example polyethylene (PE), polyester or PET.

The support may constitute, where appropriate, the polymeric material in which the reliefs are formed. When the polymeric material is attached to the support, it can be directly in contact or not.

The thickness of the support is for example between 5 and 100 μιτι, preferably 20 and 30 μιη. The support may have a constant thickness.

The pattern network can completely cover one side of the support, or alternatively cover only partially. The pattern network may or may not extend from one edge to another of the support, depending on the length and / or the width of the support. The support may have one or more areas devoid of the pattern network and one or more areas covered by the pattern network.

The reflecting layer may be covered with a smoothing varnish, in particular intended to allow the application, preferably printing, of one or more ancillary elements. In addition, the smoothing varnish can help protect the network from patterns coated with the reflective layer. This smoothing varnish may be colorless or colored.

The reflective layer may be associated with one or more other layers having a safety function, especially magnetic, fluorescent and / or phosphorescent.

The network of patterns may have, when viewed from the front, an elongated shape along a longitudinal axis which is for example a longitudinal axis for the security structure.

The array of patterns may have any contour of any geometric shape, for example polygonal or not, for example square, rectangle, rhombus, triangle, trapezoid, parallelogram, circular, elliptical, among others. It is the same for the outline of each pattern.

The patterns of the pattern network may or may not all have the same geometric shape. These patterns can be arranged on the security structure at regular intervals or not. The thickness of the pattern network is for example between 2 and 30μιη, better 2 and 15 μιη.

The patterns can be randomly distributed.

The structure may comprise one or more ancillary elements, in particular visible on the side of the observation face, through the polymeric material.

The structure may comprise one or more ancillary elements, in particular visible on the side of the face to be observed, superimposed at least partially on the reflecting surface, at a distance from the latter.

The aforementioned ancillary elements can be formed by printing, for example a macro-printing or a holographic printing, by metallization or demetallization. The ancillary elements may be metallic. A metal pattern disposed in front of a metal reflective layer is particularly attractive, especially when it is made of a different metal, and therefore constitutes an immediately recognizable security. An additional element may correspond for example to an alphanumeric character, sign, logo, symbol, character or object. An ancillary element may be carried on the support for example by a printing process such as offset, intaglio, laser, inkjet, micro-lithography, gravure printing or screen printing. An additional element can be printed with colored or non-colored inks, visible to the naked eye, under ultraviolet (UV) and / or infrared (IR), opaque, fluorescent, phosphorescent, thermochromic, photochromic, translucent and / or transparent, among others.

The structure according to the invention may comprise an auxiliary element which covers both partially the first zone and partially the second zone, or covers only the first zone or the second zone. The ancillary element may be arranged in a way that is marked or not with respect to the patterns of the network. If necessary, the ancillary element is centered on the optical axis of the mirror associated with a pattern or the lens associated with a pattern.

In a preferred embodiment, the structure comprises recesses in the second zone and disposed in or behind these recesses optically variable or luminescent ancillary elements, which will be visible through the recesses, especially when we observe from the observation face. The structure may comprise an optically variable ancillary element, in particular goniochromatic, which appears in the second zone.

Where appropriate, an ancillary element may be disposed behind a pattern of the grating without a reflective layer so that this pattern produces a visible image when the ancillary element is observed through the pattern. The first or second zone may be made in such a way as to reveal points or raster lines formed with the reflective layer, in positive or in negative, the set of points or raster lines making it possible to generate when the structure is observed. with the naked eye at a sufficient distance, for example of the order of twenty centimeters, an image, for example representing an object in perspective. The number of points or raster lines per cm is, for example, from 1 to 500, or even greater than 500. The first and second zones can be arranged according to the teaching of the application EP 1 674 286 B 1. When the first zone is arranged according to a reflective image, the appearance of this zone is not homogeneous, some regions may appear more reflective than others.

The second zone can form a text whose characters are themselves formed of microtext in negative.

The first zone may define a shape that is reproduced by the second zone, the same or a scale factor and / or a rotation close to, where or so reversed. The first zone or the second zone may define a pattern that appears elsewhere on the document, for example in the form of an impression or a watermark.

The security structure may be coated on its outer faces with a heat-sealable varnish, in particular to facilitate the adhesion of the structure to a substrate of a security document incorporating it, including a security paper. The heat-sealable varnish can furthermore make it possible to standardize the surface of the external faces of the security structure. The heat-sealable varnish can be a protective layer. The heat-sealable varnish may partially or completely cover the surface of the outer faces of the security structure. The heat-sealable varnish may possibly come into contact with the reflective layer or pattern network. The security structure according to the invention may thus comprise one or more adhesive layers on the surface, facilitating its incorporation into a document, in particular its adhesion to a fibrous paper mass.

The security structure may constitute a security thread, a security film (foil) or a patch. Preferably, the security structure is a security thread. The security structure may have a width greater than or equal to 4 mm, better 5 mm, better still 6 mm, for example between 6 and 8 mm, better still between 6 and 10 mm.

The invention also relates to a secure document comprising a security structure according to the invention.

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

The security structure may or may not be incorporated into window (s) in the document.

The security structure incorporated in the document can be visible totally or partially, according to only one of its faces or on its two faces.

The document, or the security structure according to the invention that it comprises, may comprise 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 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.

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

The security structure according to the invention may in particular be made by depositing a metal layer over the entire surface of said elementary pattern network, depositing a transparent layer resistant to soda to form the first zone and performing a step of soda attack to remove the metallization outside the first zone so as to form the second zone. Alternatively, the security structure can be achieved by depositing a soluble ink on the surface of the elementary pattern network defining the second zone, depositing a metal layer on the entire surface of said network and applying a solvent agent to dissolve the ink and thus remove the metal layer at the location of the soluble ink so as to form the second zone, and therefore the first.

Another subject of the invention is a method of authenticating a secure document according to the invention, comprising the observation of the security structure according to the invention, in particular in reflection from one face or the other, and the determination to leave at less of this observation of the authenticity or otherwise of the document. The method may also include the observation in transmitted light of the document, in particular to observe through the second area of the security structure when it corresponds to the demetallization of a reflective metallized layer.

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 represents, in section, an example of a security structure according to the invention,

FIGS. 2A to 2C show in section other examples of patterns of the network,

- Figures 3 and 4 show, in section, schematically and partially, other examples of safety structures according to the invention, and

FIG. 5 represents an exemplary document incorporating a security structure in accordance with the invention.

In the drawing, the various constituent elements have not always been represented with a respect of the real proportions, for the sake of clarity.

FIG. 1 shows a security structure 1 according to an exemplary embodiment of the invention, having an outer face 15 facing the observer and called the "observation face".

The security structure 1 is for example in the form of a security thread, for example for incorporation into windows in a document 10, as shown in FIG.

The security structure 1 comprises a support 4, preferably transparent, for example polyethylene terephthalate (PET). The support 4 carries on one side 4a a layer 9 of a polymeric material such as a varnish, an embossed surface of which defines an array of patterns 5.

The patterns 5 are partially covered by a reflective layer 19 formed in the example in question by a layer of a metal, for example aluminum, or alternatively copper, gold, silver, or a magnetic oxide. The reflective layer 19 extends in a first zone 20 and recesses 24 are formed in the reflective layer 19 in a second zone 21. The latter may be completely surrounded by the first zone 20 and defining a text or other symbols in negative writing, as illustrated in FIG. 5.

The reflecting layer 19 defines a reflecting surface 19a visible in reflection from the face 15.

According to a preferred characteristic, the patterns 5 each consist of a Fresnel lens. Thus, after metallization, these patterns 5 are each substantially equivalent from the optical point of view to a convex mirror of relatively large diameter, of focal length for example between 1 and 30 mm.

The reflecting layer 19 may or may not completely cover at least one pattern 5. Preferably, the reflective layer 19 completely covers a plurality of patterns 5.

The unit dimension D of a pattern 5 is greater than 75 microns, better is greater than 100 microns, more preferably 150 or 200 microns, or even 500 microns or 1000 microns, or even 2 mm, which gives them good visibility to the naked eye. The dimension D of a pattern is measured parallel to the observation face 15. In the case where the pattern 5 has the profile of a Fresnel lens, the dimension D of the pattern 5 is measured between the outer sides of the extreme ridges. of the lens, as shown in Figure 1. The dimension D of a pattern 5 is for example of the order of 1 or 2 mm, preferably less than or equal to 3 mm. For example, a pattern 5 may consist of either a complete Fresnel lens, i.e. with a circular base, or a Fresnel lens portion, i.e. with a base truncated circular, so that the pattern network 5 appears as an entanglement of lenses.

When the patterns 5 are made in the form of Fresnel lenses, the patterns may comprise streaks S which constrict each other away from the center of the lens. The height of the streaks S is for example between 1 and 10 microns, the lens advantageously having a constant thickness.

A convex mirror obtained by means of a reflective Fresnel lens makes it possible to produce a thin and thin security structure 1 that is perfectly adapted to secure documents such as bank notes whose thickness is about 100 μπι.

FIGS. 2A to 2C show schematically other examples of patterns 5, in section. A pattern 5 may have a convex surface towards the observation face 15, in particular rounded, for example spherical, as illustrated in FIG. 2A, pyramidal as shown in Figure 2B, or concave as shown in Figure 2C. A pattern 5 may still have a parabolic or elliptical profile surface.

In top view, a pattern 5 may be circular, polygonal, for example hexagonal or square, or other contour.

Two adjacent patterns 5 may be contiguous or not, being for example separated by an intermediate region 16, plane and parallel to the observation face 15.

The patterns can be repeated, preferably identically, in at least one direction, better in at least two directions. The spacing between two adjacent patterns is preferably constant, but may alternatively be variable. Where appropriate, two adjacent patterns 5 are not identical in shape. For example, there is a succession of patterns whose shape varies from one pattern to another, periodically, so that all the n patterns have the same succession of pattern shapes. This can make it more difficult for the counterfeiter to reproduce the patterns.

In the example of FIG. 1, the patterns 5 define convex mirrors with the reflective layer 19 towards the observation face 15, the focus of which is located behind the reflective layer.

The reflective layer 19 is preferably a layer of a metal deposited by a known metallization technique, for example by vacuum deposition. The recesses 24 formed in the reflective layer 19 may be formed by a chemical etching of the metal reflective layer, after application of a protective varnish, which may be left in place or removed after the etching step.

The polymeric material 9 is for example a varnish and the network of patterns 5 a network of Fresnel lenses for example formed by embossing in relief (in the sense of observation) of this varnish. The latter is for example an epoxy or acrylic resin.

The Fresnel lens array, especially when it is embossed in the varnish 9, may have a thickness of between 1 and 15 μπι, or even 1 and 10 μπι.

The reflective layer 19 is located in the example of FIG. 1 between the patterns 5 and the observation face 15.

The reflective layer 19 may be opaque or semi-reflective. In the example shown, the reflective layer 19 is continuous in the first zone 20 but in a variant the reflective layer 19 is made in the first zone in the form of a weft whose points or lines are sufficiently close together to give printing to the user of a continuous reflective surface. However, the presence of openings between the dots or lines makes the reflective layer 19 semi-transparent.

The metal thickness of the reflective layer 19 may be between 0.1 and 0.3 μιη.

The reflective layer 19 is in the example of Figure 1 covered with a smoothing varnish 7 which also covers the recesses 24 so as to create a flat surface 7a located on the side of the observation face 15. This flat surface 7a can receive various safety ancillary elements 2, such as for example impressions, metallizations or demetallizations.

The ancillary elements 2 may be arranged with or without reference to the patterns 5 or the recesses 24 or the possible plane regions 16 situated between the patterns 5.

An embodiment at the reference of the ancillary elements 2 may make it possible to create additional optical effects, for example by making it possible to observe an image of these ancillary elements by reflection on the reflective layer 19 or to observe the ancillary elements 2 in transmitted light thanks to the recesses 24, with in this case a possible transformation of their appearance due to the crossing of the patterns 5.

The smoothing varnish 7 may be replaced by an adhesive layer. A heat-sealable varnish 6 advantageously covers, as illustrated, the two outer faces of the security structure 1, to improve the holding of the security structure 1 in the security document 10.

The patterns can be made otherwise. The pattern network 5 can be embossed directly into the support 4.

The pattern network 5 may be embossed hollow (in the opposite direction to the observation) in the varnish 9 and a reflective layer 19 may be applied in the hollow of the patterns 5 on the side of their concave face, as illustrated in FIG. .

In a general manner, the array of patterns can be embossed in relief or recessed, the patterns be of concave or convex shape to the outside.

The security structure may comprise both projecting embossed reliefs and others recessed, and / or both relief concave outwards and other convex outward. The reflecting layer 19 may comprise an ink based on fine particles, for example nanoparticles, in particular metal nanoparticles, which make it possible to give a reflective effect during the observation. This layer 19 may be applied in a localized manner so as to define the first 20 and second 21 zones. Alternatively, the entire surface of the patterns 5 is first metallized and then a demetallization is performed in the second zone 21.

A smoothing varnish, not shown in FIG. 3, is optionally applied on the side of the concave surface of the patterns 5 so as to cover the reflecting layer 19 in order to protect it and to benefit from a planar outer face, opposite to the observation face. .

The security structure 1 may comprise, as illustrated in FIG. 4, additional elements 30, such as impressions, metallizations or others, arranged in the second zone 21, on the opposite side to the observation face 15.

At least one additional element 30 can be visible through a recess 24 of the reflective layer 19.

The structure 1 may comprise, instead of a recess 24, an observable element 26 whose surface 26a situated on the side of the face 15 follows the relief of the pattern 5.

This observable element 26 may occupy the entire second zone 21 or it may comprise both a recess and the observable element. The observable element 26 is, for example, an impression or a metallization made of a metal different from that of the reflective layer 19.

The observable element 26 may still be a particular diffractive or optical structure.

The observable element 26 may be based on an ink having particular optical or magnetic properties.

If necessary, the observable element 26 covers the reflective layer 19 to modify its appearance seen from the face 15. For example, the observable element is a second metallization limited to the second zone 21, formed by locally covering the layer reflective 19. Figure 5 shows the security structure 1 introduced in window (s) in the security document 10. Alternatively, the security structure 1 can be incorporated en masse in the security document 10, totally or partially, or in the form of a foil. The security document 10 may comprise other security elements, for example of first, second or third level.

The second zone 21 may define information, for example in the form of alphanumeric characters, which is also found on the document, for example in the form of an impression 11, as illustrated in FIG.

When the observer observes the face 15, he sees a reflecting surface having for example the appearance of a hammered metal, with recesses for example in the form of text.

In general, the first zone 20 or the second zone 21 may define alphanumeric characters in positive or in negative.

It is the same for the ancillary elements.

The reflective layer 19 may be a semi-transparent layer.

The reflective layer 19 may have its reflective character because of the use, in place of a metal, a high refractive index material, said HRI (High Refractive Index).

The reflective layer 19 may be holographic, if appropriate.

The patterns of the pattern network 5 can be distributed regularly or not, for example random.

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

The ranges of values extend by default inclusive limits.

Claims

1. Safety structure (1) observable from at least one face (15), the structure (1) comprising:

a network of elementary patterns (5) formed in a polymeric material

(9), the unitary patterns having a unit dimension (D) of at least 75 micrometers, which network defines a non-planar surface,

in a first zone (20) of said network, a reflective layer (19) at least partially visible from the observation face (15), this reflective layer defining a reflecting surface along the relief of said network,

in a second zone (21) of said network, different from the first, at least one recess (24) formed in the reflective layer (19) and / or an observable element (26) from the observation face (15), this an observable element (26) having a surface (26a) located on the side of the viewing face (15), which follows the relief of said grating, this surface (26a) having a different appearance from that of the reflective surface.

2. Structure according to claim 1, the pattern network (5) being formed by embossing a varnish (9).

3. Structure according to one of claims 1 and 2, the network comprising Fresnel structures, preferably of the Fresnel lens type (5).

4. Structure according to any one of the preceding claims, the patterns

(5) defining with the reflective layer (19) convex or concave mirrors or a combination of concave-convex mirrors towards the observation face (15).

5. Structure according to any one of the preceding claims, comprising one or more ancillary elements (30), visible from the side of the observation face (15) through the polymeric material (9).

6. Structure according to any one of the preceding claims, comprising one or more ancillary elements (2) visible on the side of the face to be observed (15), in particular at least partially superimposed on the reflective layer (19), at a distance of it.

7. Structure according to any one of the preceding claims, the second zone (21) being completely surrounded by the first (20), when the structure (1) is observed at normal incidence from the observation face (15).

8. Structure according to any one of the preceding claims, the first or the second zone (20) defining alphanumeric characters.

9. Structure according to any one of the preceding claims, for observing through it in at least one region of the second zone (20).

10. Structure according to any one of the preceding claims, comprising a transparent support (4), in particular PET, carrying the polymeric material (9).

11. Structure according to any one of the preceding claims, forming a security thread, a patch or a foil.

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

13. A method of authenticating a document (10) according to claim 12, comprising the observation of the security structure (1) in reflection and the determination from at least this observation of the authenticity or non-authenticity of the document ( 10).