AU2014279723B2

AU2014279723B2 - Security structure having a diffractive optical element

Info

Publication number: AU2014279723B2
Application number: AU2014279723A
Authority: AU
Inventors: Pierre Sarrazin
Original assignee: Oberthur Fiduciaire SAS
Current assignee: Oberthur Fiduciaire SAS
Priority date: 2013-06-10
Filing date: 2014-06-10
Publication date: 2018-04-26
Anticipated expiration: 2034-06-10
Also published as: WO2014199296A1; FR3006795A1; EP3007903A1; EP3007903B1; AU2014279723A1; JP2016530118A; FR3006795B1

Abstract

The present invention relates to a security structure (1) comprising: at least one non-opaque microzone (30), having a section no larger than 1,000,000 µm²; at least one diffractive optical element (40) generating at least one interference pattern (66) in a view plane (62) separated from the diffractive optical element (40), at least partially vertically adjacent to the non-opaque microzone (30).

Description

The present invention relates to a security structure (1) comprising: at least one non-opaque microzone (30), having a section no larger than 1,000,000 pm²; at least one diffractive optical element (40) generating at least one interference pattern (66) in a view plane (62) separated from the diffractive optical element (40), at least partially vertically adjacent to the non-opaque micro zone (30).

(57) Abrege : La presente invention conceme une structure de securite(l) comportant: - au moins une microzone non opaque (30), de section inferieure ou egale a 1000000 pm², - au moins un element optique diffractif (40) generant au moins un motif d'interferences (66) dans un plan de visualisation (62) eloigne de l'element optique diffractif (40), superpose au moins partiellement a la mi crozone non opaque (30).

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Security structure having a diffractive optical element

The present invention relates to security structures and secure articles, notably documents, comprising such structures.

Background

The use of diffractive optical elements (DOEs) as security elements is known for producing an interference pattern starting from a light source. These elements may be formed with a view to being illuminated by a monochromatic or polychromatic light, in order to generate the interference pattern by diffraction and transmission through the element toward an image-forming plane. Depending on the case, this image-forming plane may be virtual and situated between the element and the light source or may be materialized by a real surface situated behind the element with respect to the source.

The international application WO 01/00418 describes a diffractive optical element formed directly on a document by laser ablation.

The Australian patent application AU 2013100172 describes a security document comprising a multitude of openings formed by laser ablation generating a diffractive optical element and a reflective layer having on its surface a series of grooves and a layer of liquid crystal.

The international application WO 99/37488 describes security documents using plastic material in which the diffractive optical element is positioned on or in a transparent or semi-transparent window, in such a manner as to be viewed using a collimated polychromatic light source thanks to the presence of another window situated, on the same document, at a distance from the element.

The international application WO 2007/079549 describes the use and the viewing of diffractive optical elements on security documents. The elements are formed in such a manner as to record individual data, notably data present elsewhere on the document, such as a portrait or a civil status in the case of an identity document.

The international application WO 2008/031170 describes the fabrication and the use of security documents comprising at least one diffractive optical element and an optical structure with lenses or another security element having a relief

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PCT/IB2014/062097 structure formed by embossing. This application also describes the use and the viewing of binary diffractive optical elements or elements with several phase levels.

The Australian patent application AU 2011101567 describes the use and the viewing of diffractive optical elements sensitive to at least three different wavelengths on security documents. The diffractive optical elements are recorded with three different lengths and the interference pattern is reproduced by illuminating at the appropriate wavelengths.

There exists a need to be able to use diffractive optical elements with various types of substrates without requiring, at the time of fabrication of the element, the presence of the entirety of the document.

There also exists a need for further enhancing security structures and the secure articles integrating such structures, notably in order to render counterfeiting more difficult.

The invention aims to meet all or part of these needs.

Summary

One subject of the invention, according to a first of its aspects, is a security structure comprising:

- at least one non-opaque micro-region with a cross section less than or equal to 1000000 pm²,

- at least one diffractive optical element generating at least one interference pattern in an image-forming plane at a distance from the diffractive optical element, superposed, at least partially, onto the non-opaque micro-region.

Non-opaque micro-region

The term “non-opaque micro-region” denotes a region that is sufficiently permeable to light in order to enable the viewing of the interference pattern by virtue of the light passing through this region, having a transverse cross section with a surface area less than or equal to 1000000 pm², or better less than or equal to 200000 pm², or even better in the range between 10 pm² and 200000 pm², or even better in the range between 5000pm² and 200000 pm². Preferably, the non-opaque microregion has a transverse cross section that is sufficient for observing the DOE in

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PCT/IB2014/062097 transmitted light and sufficiently small so as not to be substantially visible in reflection. A non-opaque micro-region is thus of limited extent, being bounded by an opaque periphery. The non-opaque micro-region may be translucent, notably scattering a part of the light passing through it, or transparent, not scattering the light passing through it. Preferably, the non-opaque micro-region is transparent.

The term “an opaque periphery” should be understood to mean a higher optical density of the periphery or equal to 1, or better 1.5.

A non-opaque micro-region offers the advantage of only being easily detectable under certain conditions of observation, and thus is not readily visible by the naked eye if these conditions of observation are not met. Thus, the use of a nonopaque micro-region allows the diffractive optical element to be more easily hidden and renders counterfeiting more difficult to achieve.

The non-opaque micro-region may be of circular or non-circular cross section, notably polygonal, in particular regular or irregular polygonal, or oblong, notably elliptical.

The non-opaque micro-region may be formed within a layer of a fibrous material or otherwise which runs all around the non-opaque micro-region.

The non-opaque micro-region may be a micro-perforation of a layer of a substantially opaque material filled at least partially, preferably entirely, by a transparent material notably comprising a protecting adhesive material. By penetrating into the micro-perforation, the transparent material allows the layer of substantially opaque material and the layer carrying the diffractive optical element to be rigidly joined together. The fact that the micro-perforation is at least partially filled allows it to be protected from the external environment, notably from dust and dirt.

For example, the or each non-opaque micro-region may be defined by an absence of material within a layer of a substantially opaque material, and notably may be defined by a micro-perforation through this opaque material when the latter is, for example, a fibrous substrate, or be defined by a de-metallization when the opaque material is a metal.

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In the presence of micro-perforations, the latter are preferably formed by means of a laser. As a variant, the micro-perforations are formed by means of microneedles or by water jet.

When the non-opaque micro-region consists of a micro-perforation, the axis of this micro-perforation is preferably oriented substantially normal to the surface of the layer through which the micro-perforation is formed. The axis may, as a variant, form an angle with the normal to the surface of the layer traversed by the micro-perforation.

The non-opaque micro-region may, when it is defined by a microperforation, have a constant transverse cross section or otherwise over the thickness of the layer traversed by the micro-perforation.

The non-opaque micro-region may further be bounded by printing with an opaque ink, notably printing of a transparent film of plastic material, for example the same film as that on which the diffractive optical element is formed.

The same layer of the structure according to the invention may have a plurality of non-opaque micro-regions each being superposed, at least partially, on the same diffractive optical element.

The non-opaque micro-region or regions may each form a pattern which is found within at least a part of the interference pattern generated by the diffractive optical element.

For example, the non-opaque micro-region has a contour which is located within the interference pattern, for example the same geometric shape.

Several non-opaque micro-regions may define together a pattern which is found within at least a part of the interference pattern, for example the image of the same famous person, place, monument or object, or the same text, for example the value of a banknote or the name of a bank. The pattern facilitates the authentication by the observer by comparing said pattern with the interference pattern. This arrangement enhances the security of the document owing to the fact that counterfeiting requires the reproduction of the pattern both in the micro-regions and within the interference pattern of the security structure.

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In the case of a non-opaque micro-region formed by a micro-perforation, the thickness of the layer traversed by the micro-perforation may be in the range between 10 and 1000000 pm.

The number of non-opaque micro-regions is, preferably, in the range between 1 and 1500 non-opaque micro-regions per cm², preferably between 10 and 500 per cm², even more preferably between 10 and 300 per cm².

Diffractive optical element

The diffractive optical element which generates the interference pattern in an image-forming plane at a distance from the diffractive optical element is preferably of the digital type. Its fabrication is then, as described in WO 2008/031170, based on a die patterning applied as a function of complex data that are reconstructed in the image-forming plane so as to form an interference pattern in two dimensions. Thus, when the diffractive optical element is illuminated by a collimated light source, it generates an interference pattern producing an image in this imageforming plane, which is visible on a surface positioned in this plane, or visible in transmission starting from this plane.

The mathematical transformation between the element and the imageforming plane can be related to a fast Fourier transform (FFT). Thus, the complex data, comprising phase and amplitude information, must be physically encoded within the microstructure of the element. The relief to be given to the microstructure may be calculated by performing the inverse FFT transform of the desired pattern in the image-forming plane.

The diffractive optical elements are sometimes classed as computergenerated holograms, and are different from the other types of holograms such as rainbow, Fresnel or 3D reflection holograms.

Preferably, the diffractive optical element is an embossed structure.

Preferably, the interference pattern generated by the diffractive optical element is found, at least in part, or better in its entirety, on the security structure, or on the article, notably the document incorporating it, notably in the form of a printed feature and/or of a security element, notably a watermark, and/or of a pattern

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PCT/IB2014/062097 generated by micro-perforations or a metallization or de-metallization. In the case of micro-perforations, one of the latter can define the non-opaque micro-region.

For example, the diffractive optical element generates the image of a famous person and a watermark reproducing the same famous person is present on a fibrous substrate on which a micro-perforation is formed defining the non-opaque micro-region.

The non-opaque micro-region may also belong to a security element that reproduces all or part of the interference pattern. For example, the non-opaque micro-region is formed by de-metallization of a metallized security thread and the image of a famous person produced by the interference pattern is found on the thread, being formed by de-metallization on the latter, with or without superposition with the diffractive optical element.

Preferably, the diffractive optical element is smaller, notably in all the directions of its plane, than the non-opaque micro-region. As a variant, the diffractive optical element may be larger in at least one direction of its plane than the nonopaque micro-region.

The diffractive optical element is preferably formed on a thermoplastic film, preferably transparent, having a thickness less than or equal to 50 pm, notably by embossing of the latter. This thermoplastic film may be laminated, at least partially, with the layer carrying the non-opaque micro-region or through which the non-opaque micro-region is formed. As a variant, the thermoplastic film comprising the diffractive optical element is fixed to the layer carrying the non-opaque microregion by an adhesive, preferably also protective, structure comprising an adhesive material. As previously described, the adhesive structure may be introduced in the liquid state between the thermoplastic film and the layer carrying the non-opaque micro-region via at least one micro-perforation notably forming at least one nonopaque micro-region.

The presence of the thermoplastic film allows the diffractive optical element to be formed independently from the rest of the secure article, hence its fabrication to be facilitated.

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The thermoplastic film may be laminated with or bonded to a security element, notably a security thread or foil, having at least one transparent region, notably the non-opaque micro-region, being at least partially superposed with the diffractive optical element. This security element may comprise a securitizing pattern, notably in the form of a printed feature, of micro-perforations or of a metallization or de-metallization. As indicated hereinabove, this pattern may correspond, at least partially, to the interference pattern produced by the diffractive optical element.

The diffractive optical element may be recorded on the thermoplastic film by a ‘roll-to-rolf process.

The diffractive optical element may be viewed under polychromatic or monochromatic light.

The diffractive optical element may be associated with an optical filter, of the interference, iridescent or absorbing type, placed in the path of the light arriving at or leaving the diffractive optical element. This filter may belong to the security structure or to the article and, as such, thus constitute an additional security element.

Security structure

The security structure may take the form of an element which is integrated into a fibrous substrate during the fabrication of the latter or which is transferred onto its surface.

The security structure may take the form of a patch, of a security thread, of a foil or a film.

The security structure may be exposed to the external environment on its two opposing faces or only exposed on one of them or may be coated on both its faces by one or more not completely opaque layers, for example a protective film or a varnish.

The security structure may consist of a single element at the time of its integration into or onto the rest of the article, notably of the document, or may be composed of several sub-elements which are assembled by means of the rest of the article, notably of the document, for example being transferred onto different faces of

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PCT/IB2014/062097 a substrate of the document. These sub-elements may come into contact or otherwise with one another. For example, a first sub-element may carry the diffractive optical element and a second sub-element may carry the associated non-opaque microregion, and the two may be separated by at least one substrate layer of the document or be assembled directly with one another.

Preferably, the security structure comprises a protective adhesive structure or an adhesive structure associated with a protective structure disposed between the first sub-element carrying the diffractive optical element, notably the diffractive optical element, and the second sub-element carrying the non-opaque micro-region.

The term “protective adhesive structure or protective structure” is understood to mean a layer, or a plurality of layers, designed to protect, mechanically and/or optically, the diffractive optical element, notably when the diffractive optical element is an embossed structure.

The protective adhesive structure preferably comprises a layer of a mixture of an HRI (high refractive index) material and of an adhesive material which is disposed on the diffractive optical element.

As a variant, the first sub-element comprises a layer of an HRI material, preferably deposited by vacuum evaporation onto the diffractive optical element, on which a layer of an adhesive material is preferably disposed, the layer of adhesive material being, preferably, disposed between the layer of an HRI material and the second sub-element carrying the non-opaque micro-region. The superposition of the layer of HRI material and of the layer of adhesive material forms the protective adhesive structure. The adhesive layer provides a mechanical protection for the diffractive optical element.

The HRI material allows the diffractive optical element to be protected from attenuation or cancelling of its optical effect which could result from the presence of the adhesive material.

As a further variant, the protective structure associated with the adhesive structure comprises a mixture of an HRI (high refractive index) material and of a binder, which is disposed on the diffractive optical element, the adhesive structure

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PCT/IB2014/062097 preferably being disposed on the protective structure, notably between the second sub-element carrying the non-opaque micro-region and the protective structure.

As yet another variant, the first sub-element comprises a layer of an HRI material disposed, notably deposited by vacuum evaporation, on the diffractive optical structure, on which a layer comprising a binder is disposed, the superposition of the layer of HRI material and of the layer comprising a binder forming the protective structure associated with the adhesive structure. The adhesive structure is, preferably, disposed on the protective structure, notably between the protective structure and the second sub-element carrying the non-opaque micro-region.

Preferably, the binder is made secure for example by the presence of a specific marker or of a luminescent compound. The layer of HRI material provides an optical protection for the diffractive optical element, and the layer of binder provides a mechanical protection for the diffractive optical element.

The HRI material allows the diffractive optical element to be protected from attenuation or cancelling of its optical effect which could result from the presence of the adhesive material and/or of the layer comprising a binder.

“An HRI material” is understood to mean a material having a high index of refraction, preferably greater than or equal to 1.7. The HRI material is preferably chosen from amongst zinc sulfide (ZnS), zinc oxide (ZnO), zirconium oxide (ZrO₂), titanium dioxide (TiO₂), carbon (C), indium oxide (In₂O₃), indium-tin oxide (ITO), tantalum pentoxide (Ta₂O₅), cerium oxide (CeO₂), yttrium oxide of (Y₂O₃), europium oxide (Eu₂O₃), iron oxides, hafnium nitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO₂), lanthanum oxide (La₂O₃), magnesium oxide (MgO), neodymium oxide (Nd₂O₃), praseodymium oxide (Pr₆On), samarium oxide (Sm₂O₃), antimony trioxide (Sb₂O₃), silicon carbide (SiC), silicon nitride (Si_zN_u), silicon monoxide (SiO), selenium trioxide (Se₂O₃), tin oxide (SnO₂), tungsten trioxide (WO₃), their combinations and other similar compounds.

The protective adhesive structure or the adhesive structure associated with a protective structure may be introduced via one or more micro-perforations of the second sub-element, notably at least one micro-perforation defining a non-opaque micro-region. The protective adhesive structure or the adhesive structure associated

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PCT/IB2014/062097 with a protective structure may partially, or preferably completely, fill the microperforation or micro-perforations.

As a variant, the diffractive optical element is disposed on a first side of the first sub-element, the second side of the sub-element not having any diffractive optical element and the adhesive structure being disposed between the second subelement and the second side of the first sub-element. The adhesive structure is not therefore in contact with the diffractive optical element.

The security structure may comprise a plurality of said diffractive optical elements, each generating an interference pattern in an image-forming plane at a distance from the diffractive optical element.

These diffractive optical elements may generate different or identical interference patterns, being complementary or otherwise.

Preferably, the protective adhesive structure or the protective structure is applied to all the diffractive optical elements.

The security structure may comprise a plurality of non-opaque microregions each being superposed, at least partially, onto at least one respective diffractive optical element.

Preferably, a plurality of non-opaque micro-regions is superposed onto the same diffractive optical element.

The non-opaque micro-region or regions may visually define a pattern which is found, at least partially, within the interference pattern generated by at least one diffractive optical element. For example, several non-opaque micro-regions are disposed according to an arrangement which reproduces one or more alphanumeric characters, and the interference pattern produces an image of these same alphanumeric characters in the image-forming plane. The pattern facilitates the authentication by comparing the pattern with the pattern of the interference. This arrangement further increases the difficulty for the potential counterfeiter who would have to reproduce the pattern both in the micro-regions and in the interference pattern of the security structure.

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The security structure may comprise at least one absorbing or interference filter, notably a colored filter, being superposed at least partially onto the non-opaque micro-region.

The security structure may comprise at least two non-opaque microregions each formed by a micro-perforation with an axis forming an angle with the normal to the surface of the security structure, the angles being different. At least two diffractive optical elements may each be superposed, at least partially, onto a respective non-opaque micro-region. This disposition allows, by orienting the beam of light differently, the ability to view one or the other of the interference patterns produced and the ability to create, for example, an animation by alternately observing the two interference patterns.

Secure article, notably document

Another subject of the invention is a secure article, notably a document, comprising a security structure according to the invention.

The secure document may comprise a substrate, notably fibrous, having at least one window, the window being at least partially superposed both on the diffractive optical element and on the non-opaque micro-region. The security structure may be transferred onto this substrate or integrated into the latter.

The secure article may have at least a second non-opaque micro-region, at least partially superposed both onto the diffractive optical element and onto the first non-opaque micro-region. The or each non-opaque micro-region may be defined by the absence of material, notably by a micro-perforation. The micro-perforations may each be formed in a fibrous layer. The observation is carried out through the two non-opaque micro-regions.

The secure article may comprise a substrate, notably fibrous, comprising a micro-perforation defining the non-opaque micro-region, and the diffractive optical element may be present on a security element transferred onto said substrate or integrated into the latter. In this case, the security structure consists of the security element and the substrate.

The secure article may comprise a security element having at least one non-opaque micro-region being superposed on the diffractive optical element. The

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PCT/IB2014/062097 latter may be formed on a thermoplastic film, which is assembled, for example, by lamination with the security element, whereas the latter is already in place or not on the document.

The secure article may be a passport, an identity card, an access card, a 5 driver’s license, an interactive playing card or collector’s card, a means of payment, notably a payment card, a banknote, a tax stamp, a vignette, a coupon, a travel card, loyalty card, service or membership card, a token or a casino chip.

The secure article preferably carries at least one security element or pattern at least partially identical or similar to the interference pattern.

“Similar” is understood to mean that the two patterns may become identical with the application of a transformation, notably a re-scaling, may be the same shape, may present the same information notably in alphanumeric characters, where the typography could be different. The two patterns comprise, for example, the same written information, notably on the civil status, the currency of a banknote, the name of a place, a date, or the same visual information, notably a photograph or a drawing.

Method of authentication

One further subject of the invention is a method of authentication of a security structure or of a secure article, notably document, according to the invention, comprising the steps consisting in:

- illuminating the diffractive optical element with a light source,

- verifying, notably through the non-opaque micro-region, the presence of an interference pattern in an image-forming plane at a distance from the diffractive optical element.

The light is preferably collimated.

Preferably, when the diffractive optical element is illuminated, the light traverses the non-opaque micro-region before encountering the diffractive optical element and generating an interference pattern.

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The light source may be polychromatic, the image-forming plane being virtual and positioned between the light source and the security structure. The polychromatic light may be a white light. The interference pattern is observed through the non-opaque micro-region which acts as a viewfinder.

The method may comprise the step consisting in disposing at least one filter, for example colored or interference, between the beam of light and the security structure, or between the image-forming plane and the observer.

The presence of the filter allows a single wavelength to be selected and an element that is hidden or difficult to see without the filter to be seen more easily, notably in the case of a complex multi-tone pattern consisting of a superposition of simple patterns with different colors.

As a variant, the light source may be monochromatic, being notably a coherent and/or collimated light, the image-forming plane being real and positioned after the security structure with respect to the light source.

The verification of the presence of an interference pattern may be carried out by means of a device equipped with a camera, notably a mobile telephone, with focusing located in the image-forming plane. The use of a device other than the eye allows any risk for the eye associated with a high intensity light, notably in the case of the use of a laser, to be avoided.

The method may comprise the step consisting in comparing an interference pattern generated by the diffractive optical element with a pattern present on the article, notably defined by a watermark, a printed feature, a metallization or a de-metallization or micro-perforations, or in a form not directly observable, for example recorded on an RFID chip or on a server to which access may be gained by virtue of a link present on the document.

The method may comprise the step consisting in verifying that the data from the interference pattern really does correspond to data carried elsewhere by the document.

In the case of the observation of the interference pattern generated by the diffractive optical element by an electronic device, the latter may be configured to automatically analyze the image observed and, for example, to compare it with

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PCT/IB2014/062097 reference information, or to decrypt it so as to extract from it information to be compared with reference information, in order to verify the authenticity of the article, notably of the document.

The electronic device may be configured for analyzing the interference 5 pattern observed and accessing a database allowing the authenticity of the article, notably of the document, to be verified.

The article, notably the document, may carry information that allows reference data to be accessed via a remote server, which data then allow it to be verified that the image observed originates from an authentic diffractive optical element.

This information may be stored in an RFID chip present on the document and read by the device used for observing the interference pattern, for example using NFC technology.

The invention will be able to be better understood from reading the 15 detailed description that follows of non-limiting exemplary embodiments of the latter, and upon examining the appended drawings, in which:

- figure 1 shows schematically one example of a secure document according to the invention,

- figure 2 is a cross section along II-II in figure 1,

- figures 3 to 6 are views, analogous to figure 2, of variant embodiments of the example in figure 1,

- figure 7 shows schematically another example of a secure document according to the invention,

- figure 8 is a cross section along VIII-VIII in figure 7,

- figure 9 shows schematically another example of a secure document according to the invention,

- figure 10 is a cross section along X-X in figure 8,

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- figure 11 shows schematically another example of a secure document according to the invention,

- figure 12 is a cross section along XII-XII in figure 10,

- figure 13 is a view analogous to that in figure 12,

- figures 14 to 20 show other examples of security structures according to the invention,

- figures 21 and 22 show, in cross section, variants of security structures according to the invention,

- figures 23 to 26 are views, analogous to figure 2, of variant embodiments of the example in figure 1,

- figure 27 shows another security element according to the invention,

- figures 28A and 28B show variants of the non-opaque micro-region, and

- figures 29 and 30 illustrate schematically the viewing of the interference pattern.

In the figures, which are schematic, the real relative proportions of the various constitutive elements have not necessarily been followed, for the sake of clarity of the drawing. Certain layers may have been represented as being monolithic for the sake of simplification, whereas, in reality, they may be composed of several sub-layers. In addition, certain layers may be assembled by the use of adhesive layers disposed between them, which are not always shown in the figures. Lastly, in the presence of juxtaposed opaque and non-opaque regions, this presence is only shown schematically with only two regions disposed side-by-side, it being understood that, in reality, there will most often be more than two of these various regions, where arrangements can be complex, in order to define a text or a raster image for example. The diffractive optical element has been shown in a very simple and schematic manner in the figures. Any potential surface relief which could be caused by

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PCT/IB2014/062097 embossing is notably not shown; this does not at all exclude the possibility of their presence.

The secure article 10 shown in figures 1 and 2, for example a document such as a banknote, comprises a security structure 2 according to the invention, comprising a diffractive optical element 40 being superposed, at least partially, onto a non-opaque micro-region 30.

The article 10 comprises a substrate 11, notably made of paper, having a window 15 which gives visual access to the diffractive optical element 40.

In the example being considered, the non-opaque micro-region 30 is formed by a micro-perforation with an axis X formed through a substrate 18, notably made of paper, of the document 10, assembled with the substrate 11.

The diffractive optical element is formed on a film 43 of transparent plastic material, which is assembled with a security element 20 having a non-opaque region 23 superposed, at least partially, on the diffractive optical element 40 and on the micro-perforation 30.

The thermoplastic film 43 may be made of polyethylene terephthalate (PET).

The diffractive optical element 40 generates an interference pattern in an image-forming plane at a distance.

The alignment, at least partial, of the various openings and transparent regions defines a non-opaque region A which goes from one side to the other of the secure document 1.

Examples of methods for viewing the security structure 2 according to the invention will be described with reference to figures 29 and 30.

The viewing of the interference pattern of the security structure 2 is achieved by illuminating the non-opaque micro-region 30 with a light source 60, in a plane 62 at a distance from the diffractive optical element 40.

The security structure 2 is, preferably, disposed in such a manner that its plane is oriented orthogonal to the incident light originating from the light source 60 and that the non-opaque micro-region 30 is preferably positioned on the side of the light source 60.

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The non-opaque micro-region 30 notably allows the diffractive optical element 40 to be targeted with the incident beam.

The light source 60 is, preferably, collimated.

As illustrated in figure 29, the light source 60 may be a monochromatic light source, notably a laser. The image-forming plane 62 is then real and is positioned downstream of the security structure 2 with respect to the light source 60. The viewing of the interference pattern 66 can be achieved with the aid of a portable device, notably of a mobile telephone set in photo or video mode and positioned in the image-forming plane 62. The interference pattern 66 is viewed through the nonopaque micro-region 30.

As illustrated in figure 30, the light source 60 may be a polychromatic source. The image-forming plane 62 is then virtual and positioned upstream of the security structure 2 with respect to the light source 60. The interference pattern 66 is viewed by observing the light source 60 through the non-opaque micro-region 30.

The authentication of the security structure 2 may require the use of a filter 68 positioned upstream or downstream of the security structure 2. This filter can enable the wavelengths visible to the eye to be filtered.

The security structure 2 can be authenticated by comparing the interference pattern 66 generated by the diffractive optical element 40 with one or more additional pieces of information present on the security structure 2 or the associated article 10, for example with a comparison pattern defined by a watermark, a printed feature, a metallization or a de-metallization or micro-perforations. The non-opaque micro-region 30, being notably a de-metallization or a micro-perforation, may constitute, at least partially, the comparison pattern.

The invention is not limited to a secure article in particular, and the latter may be other than a document of value, notably an identity document or a card. The substrates 11 and 18 of the example in figures 1 and 2 may thus be non-fibrous.

The diffractive optical element 40 may be formed on a thermoplastic film 43 according to one of the methods previously described. The thickness e of the diffractive optical element 40 is, preferably, less than or equal to 50 pm, or better less than or equal to 25 pm.

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The diffractive optical element 40 may have, as illustrated in figure 2, a cross section greater than that of the non-opaque micro-region 30.

The non-opaque micro-region 30 has, preferably, a cross section S less than 1000000 pm², or better less than or equal to 200000 pm², or even better in the range between 10 pm² and 200000 pm², or even better in the range between 5000 pm² and 200000 pm².

The non-opaque micro-region 30, when it takes the form of a microperforation, may be configured in various ways.

As illustrated in figure 14, the non-opaque micro-region 30 may have a variable cross section, notably becoming narrower in the direction of the diffractive optical element 40.

Figure 15 shows a non-opaque micro-region 30 formed by a microperforation whose axis X forms a non-zero angle a with the normal to the surface of the security structure 2. The angle a may be in the range between -45° and 45°.

As illustrated in figure 16, the security structure 2 may comprise at least two non-opaque micro-regions 30i and 30₂ opening out onto the same surface Si₂, where each non-opaque micro-region 30i and 30₂ may be superposed onto a respective diffractive optical element 4Ch or 40₂. By varying the viewing angle, this configuration allows the diffractive optical element that it is desired to observe to be chosen. An animation could, where desired, be observed by alternating the viewing of the two interference patterns.

The non-opaque micro-region 30 may be formed in a different manner than that of a micro-perforation through an opaque layer.

As illustrated in figure 17, the non-opaque micro-region 30 may be filled with a transparent non-opaque material, colorless or otherwise.

As illustrated in figure 18, the non-opaque micro-region 30 may be bounded by a printed feature 35. The layer 38 on which the printed feature is formed may be a transparent film which carries, on the opposite face to the print, the diffractive optical element 40.

As a variant, the non-opaque micro-region 30 may be formed by a demetallization of a metal layer 37, as illustrated in figure 19.

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The security structure 2 may comprise an optical filter placed in the path of the light arriving at or leaving the diffractive optical element.

Figure 20 shows a security structure 2 comprising an optical filter 80, absorbing or interference, notably colored, being superposed onto the non-opaque micro-region 30.

The filter 80 may be positioned upstream or downstream of the diffractive optical element 40. The filter 80 allows one or more wavelengths of light to be selected when the interference pattern is viewed. The filter enables the interference pattern to be personalized by allowing a choice of the display color.

As illustrated in figure 21, the security structure 2 may comprise a plurality of diffractive optical elements 40i, ..., 40i and of respective non-opaque micro-regions 30i,..., 30i with respective axes Xi,..., Xi, each non-opaque microregion 30i ; ... ; 30i being superposed onto a corresponding diffractive optical element 40i; ... ; 40i.

The security structure 2 may comprise a security element 20 comprising one or more non-opaque regions 23, each non-opaque region being superposed, at least partially, with at least one diffractive optical element 40_b ..., 40i. A non-opaque region 23 may be superposed with at least two diffractive optical elements 40_b ..., 40i.

In the variant shown in figure 23, the security structure 2 comprises a plurality of colored filters 60_b..., 60i, notably of different colors, each being superposed onto at least one respective diffractive optical element 40_b ..., 40i.

It can be seen in figure 2 notably that the security structure 2 may comprise a security element 20 which is superposed, at least partially, onto the diffractive optical element 40 and onto the non-opaque micro-region 30. More particularly, as illustrated, this security element 20 can be seen through the window 15 and interposed between the substrate 11 and the film 43 carrying the diffractive optical element 40.

The security element 20 is, preferably, at least partially opaque, being for example metallized.

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The non-opaque region 23 may be formed by de-metallization or perforation.

The element 20 can provide a security feature visible through the window 15, for example in the form of a pattern 50 situated outside of the non-opaque region 23, this pattern 50 being for example formed by printing or de-metallization, as illustrated in figure 1.

The pattern 50 is for example composed of alphanumeric characters, as illustrated in figure 1. This may be a text informing on the name of the bank, of the country and/or on the value of the banknote.

The pattern 50 may be formed according to the teaching of the application WO 2006/066927, in the form of raster points reproducing an image in transmitted light, where one of the de-metallizations or perforations of the pattern 50 can form the non-opaque micro-region 30.

The pattern 50 is preferably found, partially or completely, within the interference pattern 66 generated by the diffractive optical element 40. For example, in figure 1, the pattern 50 representing the value of the banknote is found within the interference pattern which also represents the value of the banknote, where the typography may be identical or different.

Generally speaking, in the case of a security element 20 comprising a metallized layer, as usable metals may be mentioned: aluminum, copper, gold, iron, silver, chrome, nickel, zinc, cadmium, bismuth and their alloys and oxides.

The security element 20 may take the form of a security patch, thread or foil.

In the case where the security element 20 is a security thread, its width may be relatively small, preferably less than or equal to 10 mm.

The window 15 may be formed by cut-out and may have a contour of any shape, for example circular, elliptical or polygonal, as illustrated in figure 1, notably in the shape of a polygon, regular or otherwise.

There may be a single window 15 on the document or the latter may comprise several of them. In this case, the windows 15 may be disposed on the same face of the document or on opposite faces.

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The window 15 may be formed by modifying, for example, the accumulation of the fibers on the forming web and the non-opaque micro-region 30 may be formed, notably, by means of micro-needles or by water jet, preferably by laser ablation. The layers 11, 18 are for example fibrous layers assembled in the wet phase.

The two layers 11, 18 each have a thickness I for example in the range between 10 and 1000 pm, or better between 50 and 700 pm.

The two layers 11,18 may comprise natural and/or synthetic fibers.

The substrates 11 and 18 may alternatively be non-fibrous.

More generally, the document 10 may have a multilayer structure comprising at least one fibrous layer and a layer of thermoplastic material.

Preferably, the diffractive optical element 40 is laminated with the security element 20 prior to being incorporated into the secure document 1.

As a variant, the diffractive optical element 40 is fixed to the security element 20 by adhesive bonding, hot or cold. The adhesive used is for example a transparent adhesive of the polymer adhesive type such as NOLAX.

The assembly composed of the security element 20 and of the diffractive optical element 40 may be incorporated between the two layers 11, 18, the security element 20 being positioned on the side of the window 15, as illustrated in figure 2.

Generally speaking, the article 10 may comprise various appended security elements, of first, second or third level. Amongst the additional security elements, some are detectable by eye, in daylight or under artificial light, without using a particular device. These security elements comprise for example fibers or colored planchettes, printed or totally or partially metalized threads. These security elements are said to be of the first level.

Other types of additional security elements are detectable only with the aid of a relatively simple device, such as a lamp emitting in the ultraviolet (UV) or the infrared (IR). These security elements comprise for example fibers, planchettes, strips, threads or particles. These security elements may be visible or not with the naked eye, being for example luminescent under illumination from a Wood lamp

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Other additional types of security elements require a more sophisticated detection device for their detection. These security elements are for example capable of generating a specific signal when they are subjected, simultaneously or otherwise, to one or more external sources of excitation. The automatic detection of the signal allows the document, where desired, to be authenticated. These security elements comprise for example tracers that take the form of active materials, of particles or of fibers, capable of generating a specific signal when these tracers are subjected to an optronic, electrical, magnetic or electromagnetic excitation. These security elements are said to be of the third level.

At least one of these security elements may define information to be found within the interference pattern generated by the diffractive optical element 40.

The diffractive optical element 40 and the layer 18 defining the nonopaque micro-region 30 may be in contact with one another, as is the case notably in the example in figure 2.

As a variant, the diffractive optical element 40 and the layer 18 defining the non-opaque micro-region 30 may be separated by one or more intermediate layers.

For example, as illustrated in figure 3, the film 43 carrying the diffractive optical element 40 may be positioned in a manner adjacent to the substrate 11 comprising the window 15, and the security element 20 may be interposed between the film 43 and the non-opaque micro-region 30.

Preferably, and as illustrated in figure 23, the diffractive optical element 40, notably on the side of the film 43 carrying the latter, and the layer 18 are separated by a protective adhesive structure 45 preferably comprising a layer of a mixture of an adhesive material and of an HRI material. The protective adhesive structure 45 allows the film 43 carrying the diffractive optical element 40 and the layer 18 to be firmly attached together. The presence of the HRI material avoids the attenuation or cancelling of the optical effects of the diffractive optical element

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The diffractive optical element 40 may, as a variant, carry a layer of an HRI material 47, notably deposited on the diffractive optical element 40 by vacuum evaporation, itself carrying a layer of an adhesive material. In this case, the layer 47 enables the diffractive optical element 40 to be protected against an attenuation or cancelling of its optical effect due to the presence of the adhesive structure. The mechanical protection of the latter is obtained by the layer of adhesive material 46.

As a variant, as illustrated in figure 24, the diffractive optical element 40, notably the side of the film 43 carrying the latter, and the layer 18 are separated by an adhesive structure 46 comprising an adhesive material and a protective structure 47 comprising an HRI material, the protective structure 47 being applied on the diffractive optical element 40, notably on the side of the film 43 carrying the diffractive optical element 40, and the adhesive structure 46 being disposed between the protective structure 47 and the layer 18.

The protective structure 47 may comprise a binder, preferably made secure.

In the variant illustrated in figure 25, the film 43 and the layer 18 are separated by an adhesive structure 46, the latter being situated on the side of the film 43 not having the diffractive optical element 40. A protective structure 47 comprising an HRI material may be present on the diffractive optical element 40, and notably may completely cover the latter. This protective structure 47 notably allows the diffractive optical element 40 to be mechanically protected during the assembly of the security structure 2 with the article 10 while at the same time conserving the optical properties.

In the variant illustrated in figure 26, the film 43 and the layer 18 are separated by a protective structure 47 comprising a layer of an HRI material 47a, a layer of a binder 47b and an adhesive structure 46 comprising an adhesive material. The layer of HRI material 47a preferably covers, at least partially, the diffractive optical element 40 and the layer of binder 47b preferably covers the layer of HRI material 47a.

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Preferably, the binder is made secure, notably by one or more substances being luminescent or absorbing under excitation by UV, visible and/or IR light. Preferably, the luminescent or absorbing substances are non-scattering and the layer of binder 47b is transparent. The luminescent or absorbing substances are, preferably, particles of nanometric size.

Preferably, the layers 47a, 47b and 46 are transparent so as not to interfere with the optical effect generated by the diffractive optical element.

The deposition of the protective structure 47 may be carried out by printing onto the diffractive optical element 40, as explained in the patent application FR 2961319, in other words the hollows of the diffractive optical element 40 are filled with the HRI material.

The protective structure 47 or the protective adhesive structure 45 may comprise nanoparticles of metal oxides, such as TiO2, notably having a diameter in the range between 1 and 100 nm, or better between 5 and 25 nm and/or a transparent varnish and/or a reticulatable organic binder and/or a pigment dispersing agent.

The thickness of the protective adhesive structure 45 is, preferably, in the range between 1 and 10 microns, or better between 2 and 5 microns.

Preferably, the adhesive structure 46 or the protective adhesive structure 45 is introduced via the micro-perforations between the diffractive optical element 40, and/or the film 43 carrying it, and the layer 18. Preferably, as illustrated in figures 23 and 24, the layers 46 or 45 are introduced so as to fill the microperforations in order to protect them against the external environment, notably dust and dirt, as explained in the application DE 10 2011 004935.

As illustrated in figure 4, the security element 20 may be positioned in the window 15, the film 43 still extending between the two layers 11 and 18.

The diffractive optical element 40 may be formed within a film 43 which extends continuously around the diffractive optical element 40. As a variant, the film 43 which has been used to form the diffractive optical element 40 does not extend beyond the latter, as illustrated in figure 5.

As illustrated in figure 6, the film 43 may be positioned within the window 15. The same may be true for the security element 20, where present.

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As illustrated in figures 7 and 8, the security structure 2 may comprise a diffractive optical element 40 and a security element 20 having a non-opaque microregion 30 being superposed, at least partially on the diffractive optical element 40.

The first ply 11 may have a window 15 and the second layer 18 may have a non-opaque region 32. The window 15 and the non-opaque region 32 may or may not have the same shape and size and be superposed, at least partially, with the diffractive optical element 40 and the non-opaque micro-region 30 in such a manner as to form a transparent region A on and through the secure document 1. The security structure 2 may have substantially the same shape as the window 15 and be positioned within the latter.

The secure document 1, shown in figure 9, comprises two substrates 11, 18 formed by first and second layers 11, 18 each having a micro-perforation 30, 16, preferably formed by laser ablation, and receive a diffractive optical element 40 between them. The diffractive optical element 40 and the two micro-perforations 30, 16 are superposed.

The secure document 1, shown in figure 11, comprises a first substrate 11 forming the first layer, having a window 15, and a second substrate 18 forming the second layer, having a non-opaque micro-region 30. The window 15 and the microperforation 30 are superposed so as to form, within the secure document, a transparent region A going from one side to the other of the secure document 1 in which the diffractive optical element 40 is positioned.

As illustrated in figure 12, in particular when the diffractive optical element 40 is carried by a thermoplastic film 43, the diffractive optical element 40 may be positioned between the two layers 11, 18, the film 43 being directly in contact with the latter.

As illustrated in figure 13, the optical security element 40 may be positioned between a substrate 18 and a security element 20, the substrate comprising the non-opaque micro-region 30.

As illustrated in figure 27, the security element 20 may comprise a pattern 50, here the letters AW, formed by a plurality of micro-perforations 19, where one of these micro-perforations can form the non-opaque micro-region 30, for

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PCT/IB2014/062097 example the point of the A. The pattern AW can be reproduced on the interference pattern generated by the diffractive optical element 40.

The non-opaque micro-region 40 may be of various shapes, notably circular, as illustrated in figure 1, or any other, for example triangular as illustrated in figure 28 A, or in the shape of a crescent, as illustrated in figure 28B.

The invention is not limited to the examples illustrated.

The features of the examples illustrated may be combined within variants not illustrated.

The expression “comprising a” is synonymous with “comprising at least one”, except where the contrary is specified.

2014279723 15 Mar 2018

Claims

1. A security structure (2) comprising:

- at least one non-opaque micro-region (30), with a cross section less 5 than or equal to 1000000 pm²,

- at least one diffractive optical element (40) of the digital type generating at least one interference pattern (66) in an image-forming plane (62) at a distance from the diffractive optical element (40), the at least one diffractive optical element (40) being superposed, at least partially, onto the non-opaque micro-region

10 (30).

2. The structure as claimed in claim 1, the non-opaque micro-region (30) being defined by the absence of material within a layer (18 ; 20) of a substantially opaque material.

3. The structure as claimed in either of claims 1 and 2, the non-opaque 15 micro-region (30) being defined by a micro-perforation.

4. The structure as claimed in either of claims 1 and 2, the non-opaque micro-region (30) being defined by a de-metallization.

5. The structure as claimed in any one of the preceding claims, the nonopaque micro-region (30) being bounded by printing with an opaque ink.

20 6. The structure as claimed in any one of the preceding claims, the nonopaque micro-region (30) having a cross section less than or equal to 200000 pm², or better in the range between 10 pm² and 200000 pm², or even better in the range between 5000pm² and 200000 pm².

7. The structure as claimed in any one of the preceding claims, the

25 interference pattern (66) generated by the diffractive optical element (40) being found, at least in part, or better in its entirety, on the security structure (2), or on the article (10) incorporating it, notably in the form of a printed feature, of a watermark, of a pattern generated by micro-perforations or a metallization or de-metallization.

8. The structure as claimed in any one of the preceding claims, the

30 interference pattern (66) being found, at least in part, or better in its entirety, on the security structure (2) or the article (10) incorporating it, in the form of a pattern

2014279723 17 Nov 2017 generated by micro-perforations (19) one of which defines said non-opaque microregion (30).

9. The structure as claimed in any one of the preceding claims, the nonopaque micro-region (30) forming a pattern being found on at least a part of the

5 interference pattern (66), preferably identical or similar to the latter.

10. The structure as claimed in any one of the preceding claims, comprising a protective adhesive structure (45), disposed between the diffractive optical element (40) and a sub-element carrying the non-opaque micro-region (30).

11. The structure as claimed in claim 10, the protective adhesive structure

10 (45) comprising a mixture of an adhesive material and of an HRI material.

12. The structure as claimed in claim 10, the protective adhesive structure (45) being formed of a layer of an HRI material, preferably deposited by vacuum evaporation on the diffractive optical element, and of a layer of an adhesive material.

13. The structure as claimed in any one of claims 10 to 12, the protective 15 adhesive structure (45) filling, at least partially, or better completely, at least one micro-perforation.

14. The structure as claimed in any one of claims 1 to 9, comprising an adhesive structure (46) associated with a protective structure (47), disposed between the diffractive optical element (40) and a sub-element carrying the non-opaque micro20 region (30).

15. The structure as claimed in claim 14, the protective structure (47) comprising a mixture of an HRI material and of a binder and being applied to the diffractive optical element (40).

16. The structure as claimed in claim 14, the adhesive structure (46) being 25 disposed between a sub-element carrying the non-opaque micro-region (30) and the protective structure (47).

17. The structure as claimed in any one of claims 14 to 16, the protective structure (47) being formed from the superposition of a layer of an HRI material (47a) and of a layer comprising a binder (47b), the layer comprising a binder (47b) being

30 disposed on the layer of HRI material (47a).

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18. The structure as claimed in any one of claims 14 to 17, the adhesive structure (46) being disposed between a second sub-element carrying the non-opaque micro-region (30) and the side with no diffractive optical element (40) of a first subelement carrying the diffractive optical element (40).

19. The structure as claimed in any one of claims 14 to 18, the adhesive structure filling, at least partially, or better completely, at least one micro-perforation.

20. The structure as claimed in any one of the preceding claims, the diffractive optical element (40) being formed on a thermoplastic film (43), preferably transparent, having a thickness less than or equal to 50 pm.

21. The structure as claimed in claim 20, the thermoplastic film (43) being laminated with a layer (20) at least partially opaque defining said non-opaque micro-region (30).

22. The structure as claimed in claim 21, the thermoplastic film (43) being laminated with a security element (20), notably a security thread or foil, having at least one transparent region (23) being superposed, at least partially, with the diffractive optical element (40) and a security element notably in the form of a printed feature, of a watermark, of a pattern generated by micro-perforations or a metallization or de-metallization.

23. The structure as claimed in any one of the preceding claims, comprising a plurality of said diffractive optical elements (40) and a plurality of nonopaque micro-regions (30), each notably being superposed, at least partially, onto at least one respective diffractive optical element (40).

24. The structure as claimed in any one of the preceding claims, comprising at least one optical filter (80), notably a colored filter, being superposed, at least partially, with the non-opaque micro-region (30).

25. The structure as claimed in any one of the preceding claims, forming a patch, a foil or a security thread.

26. The structure as claimed in any one of claims 1 to 25, comprising a fibrous layer (18), at least partially opaque, defining said non-opaque micro-region.

27. A secure article (10) comprising a security structure (2) as claimed in any one of claims 1 to 26.

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28. The secure article as claimed in claim 27, comprising a substrate (11), notably fibrous, having at least one window (15), this window (15) being, at least partially, superposed both onto the diffractive optical element (40) and onto the first non-opaque micro-region (30).

29. The secure article as claimed in claim 27, comprising a substrate (11) having at least a second non-opaque micro-region (16), the second non-opaque micro-region (16) being, at least partially, superposed both onto the diffractive optical element (40) and onto the non-opaque micro-region (30).

30. The secure article as claimed in any one of claims 27 to 29, the article being a passport, an identity card, a driver’s license, an interactive playing card or collector’s card, a means of payment, notably a payment card, a banknote, a coupon or a voucher, a secure tag, a travel card, a loyalty card, a service card or a membership card, or a specific means of payment such as a token or a chip notably used in casinos.

31. The secure article as claimed in any one of claims 27 to 30, having at least one security element or pattern identical or similar, at least partially, to the interference pattern (66).

32. A method of authentication of a security structure as claimed in any one of claims 1 to 26, comprising the steps consisting in:

- illuminating the diffractive optical element with a light source (60),

- verifying, notably through the non-opaque micro-region, the presence of an interference pattern (66) in an image-forming plane (62) at a distance from the diffractive optical element (40).

33. The method as claimed in claim 32, the verification of the presence of an interference pattern (66) being carried out by means of a device equipped with a camera, notably a mobile telephone.

34. The method as claimed in any one of claims 32 to 33, comprising the step consisting in comparing the interference pattern (66) generated by the diffractive optical element (40) and a pattern (50) present on the document, notably defined by a watermark, a printed feature, a metallization or de-metallization, or microperforations.

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Fig. 3

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43 11 16 Az-X pf40

50 \ 13

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