WO2016131881A1

WO2016131881A1 - Process for modifying the appearance of a structure exhibiting an interferential colour effect

Info

Publication number: WO2016131881A1
Application number: PCT/EP2016/053382
Authority: WO
Inventors: Henri Rosset
Original assignee: Arjowiggins Security
Priority date: 2015-02-20
Filing date: 2016-02-17
Publication date: 2016-08-25
Also published as: FR3032910B1; EP3259142A1; FR3032910A1

Abstract

Process for modifying the appearance of a structure (21) exhibiting an interferential colour effect and taking the form of a diffractive structure, including applying a matt scattering layer (30) containing scattering particles to the structure exhibiting an interferential colour effect.

Description

Method for modifying the appearance of a structure with a colored interference effect

The present invention relates to the field of secure documents. A 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 permit. driving, a lottery ticket, a ticket, a tax stamp or stamp, a security label, a patch, a closure seal, a secure sleeve for covering the opening of a container or a ticket for entry to cultural or sporting events.

It is known to secure the substrates used for the production of secure documents with diffractive security elements, and in particular holographic ones.

These security elements conventionally comprise a reflective layer and a microrelief that produces colored interference effects.

The patent application EP2660067 discloses the application to the substrate of a document of a protective layer comprising a silica gel. It is stated that the matting effect provided by this protective layer poses a problem at the level of security elements such as holograms, whose effect it modifies the optical effect, and thus discourages the affixing thereof. The solution recommended in this application then consists in using a masking layer protecting the optically variable security elements during the application of the protective layer.

There is a need to further improve the manufacturing of security elements and secure documents and to develop the processes of personalization and authentication of these documents.

The object of the invention is to respond to this need and thus, according to a first aspect, to a method for modifying the appearance of a structure having a colored interference effect, comprising the application to the structure with a colored interference effect. a diffusing matte layer comprising diffusing particles.

The interfering color structure can be a diffractive structure. When the structure with a colored interferential effect is a diffractive structure, the application on said structure of the diffusing matt layer locally renders, where the diffusing layer covers the diffractive structure, the latter substantially achromatic. By "substantially achromatic", or "achromatize", it should be understood that the observer does not perceive, or very difficult, the colored interference effect of the diffractive structure, which would otherwise be easily perceptible in the absence of diffusing layer.

The diffusing particles may be micro-particles.

The diffusing particles can protrude on the surface of the diffusing layer, so that the diffusing layer provides a surface diffusion.

For surface diffusion, the scattering particles may have substantially the same refractive index as a binder of the scattering layer in which they are dispersed.

The diffusing layer can bring volume diffusion. The refractive index of the scattering particles is then preferably different from that of a binder in which they are dispersed.

In the case of volume diffusion, the diffusing particles may not protrude on the surface of the scattering layer.

The diffusing particles may, in particular and very advantageously, be silica particles. Preferably, the silica particles are then amorphous silica particles.

The invention makes it possible to modify in a simple manner the aesthetics of various structures having a colored interference effect, in particular those for which the colored interference effect is due to a microrelief, such as, for example, micro-embossed holographic structures.

For example, a holographic foil having an optically variable pattern thus treated becomes matt and achromatic, while retaining an optically variable effect with the viewing angle, with for example the light gray to dark gray moving pattern when the direction of observation varies. The effect can be obtained for example by rotating the security document around a vertical axis perpendicular to the document surface.

The invention makes it possible to modify the optical effects of existing diffractive structures, whether these structures are already integrated into a substrate of the document or that these structures belong to security elements to be integrated into a substrate.

The term "security element" denotes, in particular, a security thread, a foil or a patch, a data protection film or any other element introduced into or on a substrate of the document.

Among the many advantages of the invention is the possibility of not having to create specific optical structure to obtain the aforementioned achromatic effect. The application of the diffusing layer may be carried out so as to cover only partially the interfering colored structure, especially diffractive. This can make it possible to define, by contrast between the covered area and the uncoated area, at least one positive or negative pattern, especially visible to the naked eye in reflected light. Security is enhanced by allowing the observer to display to authenticate the document a contrast between an area where the structure produces the colored interference effect, and another area, preferably adjacent, where the structure has been made substantially achromatic.

Colored and achromatic interferential effects can for example appear / disappear alternately by rotation of the observation direction around an axis perpendicular to the structure with colored interference effect.

The scattering layer may be applied to show a pattern in a patterned manner with respect to a pattern of the interfering colored structure. Alternatively, the application is carried out without registration.

When the application is carried out in a marked manner, it is possible to create, for example, with at least one pattern of the diffusing layer and at least one pattern of the colored interferential structure, an overall pattern in which the pattern of the diffusing layer and that of the structure with interferential color effect complement each other. The pattern of the diffusing layer can still be superimposed exactly on that of the interfering colored structure.

The diffusing layer can be easily applied by printing, especially by conventional printing methods such as offset, soft-sizing, screen printing, gravure printing, flexography or inkjet printing.

The diffusing layer may be printed in such a way as to personalize a document comprising the structure with a colored interferential effect, in particular by printing a variable mention, a portrait of a document holder, or the value of the cut in the case of a bank note. The printed motif may also appear on the document, identically or on a different scale, or even with an appearance transformation retaining on the ground its meaning for the observer.

The diffusing layer can still be applied in a uniform manner, so as to completely cover the colored interference-effect structure, or even a whole face of the document integrating the diffractive structure.

The diffusing layer may be applied in the liquid state to the colored interference structure, and when this is a diffractive structure with microreliefs, come to contact microreliefs thereof, for example. The diffusing layer can then marry the shape of the microreliefs.

The diffusing particles, and in particular silica particles, may be mixed with a binder which may crosslink on drying or under the action of an energy provided by UV or thermal radiation or EB ("electron beam" or "electron beam").

In a variant, the diffusing layer is applied in the liquid state to a transparent layer covering the colored interference-effect structure, such as a protective varnish for example.

As a further variant, the diffusing layer is carried by a film which at least partially covers the colored interference-effect structure, this film being for example glued or hot-rolled thereon, or applied to a transparent layer covering it. .

By "covering" of the diffusing layer and the interferential structure colored, it comprises a superposition during a front view of the document of the structure with interference color effect and the diffusing layer.

The diffusing layer can be applied to the colored interference structure and beyond, on a substrate of the document for example. This further enhances security, and creates more complex patterns on the secure document.

The diffusing layer may at least partially cover only one optically variable structure constituted by the interfering colored structure.

In a variant, the diffusing layer at least partially covers not only the colored interferential structure, in particular diffractive, but also another optically variable structure, in particular interferential multilayer structure. This can make it possible to highlight the specific behavior of the diffusing layer vis-à-vis certain structures producing a color by a phenomenon of optical interference. The other structure is for example a layer of multilayer interference pigments such as nacres, for example with a mica or glass substrate, coated with at least one metal oxide, or a layer of liquid crystals producing an interference color.

The diffusing layer can be applied with a substantially uniform thickness, or alternatively with a variable thickness.

The presence of a variable thickness may make it possible to modify the optical behavior of the diffusing layer, for example by influencing the level of achromatization as a function of the thickness, or even in case of transparency by a revealing layer applied thereto, as described herein. -after. The method according to the invention may comprise the application on the diffusing layer of a revealing layer which at least partially restores the colored interference effect. In order for the revelation (or the return to a colored interference effect) to be optimal, it is preferable for the revealing layer to level the surface state of the diffusing layer by blurring the micro-protuberances formed by the diffusing particles, in particular of silica, by relief, that is to say that one returns to a substantially "flat" surface close to the level of brilliance of the revealing layer if it had been deposited on a support without diffusing layer. The level of brightness of the revealing layer may be the level of brightness of the substrate carrying the diffusing layer or better still substantially greater, thus creating an overall visual effect of variable brightness, that is to say with zones juxtaposed on the substrate of which the brightness levels are different, creating a brightness contrast that can be seen by the naked eye.

According to a particular example of application of this method, said diffusing layer is applied at least on a part of the colored interferential effect structure so as to create, at said at least part of the colored interferential effect structure, a achromatic zone, in particular of uniform silver appearance. Said developer layer is then applied or printed on top of said diffusing layer, preferably in a pattern. A pattern with a colored interferential effect, in particular holographic type "rainbow" is thus obtained.

Such a method has the advantage of allowing, if necessary, securing of the secure document comprising the colored interferential effect structure, which takes place at an advanced stage of the manufacturing process. Thus, the interferential colored structure before application or printing of the revealing layer, preferably the revealing layer pattern, can not be used for the production of counterfeits.

Moreover, such a method implementing a holographic structure as a colored interferential structure can be considered as a holographic printing process since the colored hologram is formed only when the application or the printing of the revealing layer.

The invention also relates to a security element obtained by the implementation of the method described above. This security element is for example a security thread, a patch, a foil or a data protection film.

The invention also relates to a secure document, comprising a security element according to the invention. The interfering colored structure, especially diffractive, may be affixed superficially on the substrate of the document to be secured, or be part of the internal structure of a multilayer structure with laminated or laminated layers. This last configuration has a great advantage of protecting the diffractive structure, which becomes more easily resistant to mechanical attack, including abrasion and chemical attacks, or even attempts to counterfeit by removal.

The diffusing layer, in addition to its properties of brightness modification and achromatization of structures with colored interference effect, especially diffractive, also has a transparency or translucency less than that would have this same layer if it was free of scattering particles.

Another aspect of the invention exploits the fact of being able to cancel the combined effects of achromatization and matting and, in addition, to recover the level of transparency or translucency of the diffusing layer as if it were free of scattering particles, by the application of a revealing layer.

According to this aspect of the invention, a diffusing matte layer according to the invention is applied to a non-opaque, preferably transparent, substrate, preferably with diffusing particles which are silica particles, in an area which does or does not cover a interferential effect structure, especially diffractive, for example on the entire substrate. Then, in this zone, a developer layer is applied so as to transparent the diffusing layer locally. This makes it possible to create, for example, with the aid of the diffusing layer, an ink-receiving surface, thanks to the absorbing properties of the diffusing particles, in particular when these particles are silica particles.

The revealing layer makes it possible to locally diffuse the diffusing layer and to create a visual window therethrough that makes it possible to observe, through the substrate, or within or on the surface thereof, a hidden security element or possibly blurred by the diffusing layer.

This aspect of the invention is more particularly advantageous for treating a substrate comprising a multilayer structure, preferably carrying a transparent window, with an outer layer of transparent thermoplastic material, carrying the diffusing layer.

The color interferential structure may be a diffractive structure with a colored interference effect, in the form of a frame or pattern corresponding to a coded image resulting from combined images, the pattern and the frame being on areas that can move relatively to the other or overlapping areas, one of the pattern and the weft being formed by the diffractive structure and the other by a diffusing layer, the pattern being able to interact visually with the weft when superimposed thereon to reveal an image among the combined images, the displacement or the change of the observation angle making it possible to successively reveal several images, with alternating colored and achromatic visual effects.

Also disclosed is a method in which the diffractive color interference structure is observed during the relative displacement of the frame and the coded image or during the change of the viewing angle, and it is determined whether this relative displacement or this change produces an alternation of colored and achromatic visual effects.

The invention also relates to a security element obtained by implementing the method described above.

The invention also relates to a secure document comprising a security element as defined above.

The invention also relates to a method for verifying a secure document as defined above, in which a revealing layer is applied to the diffusing layer and it is determined whether the application of this revealing layer restores the effect. interference of the structure with a colored interference effect.

In the process according to the invention, the achromatization provided by the diffusing layer may be reversible and canceled by the revealing layer; achromatization can also be permanent.

Colorful interferential structure

The structure having a colored interferential effect according to the invention is preferably a diffractive structure.

The diffractive structure generates by a phenomenon of light interferences colored effects, by decomposition of the white light which illuminates it.

The diffractive structure may be opaque or not.

The diffractive structure is preferably reflective, and the interferences are produced by the reflection of light on microreliefs of the structure.

The diffractive structure may thus comprise a reflective metal layer, especially formed of a metal selected from Al, Ag, Cu, Au, Ti, Sn, Pt, Cr, Ni, Fe and their alloys.

The thickness of metal may be such that the reflective layer is opaque; alternatively, the metal thickness is sufficiently small that the reflective layer is semi-reflective. The reflective layer may be openwork or not perforated. When it is perforated, it preferably defines at least one pattern using at least one ajour. This is for example an alphanumeric pattern or a halftone image, producing a relief impression thanks to a shading effect. The presence of an ajour can be used to observe the diffractive structure in transmission, and then check for example the presence of a pattern appearing in transmitted light.

In order to manufacture the diffractive structure, a surface with a microrelief is produced, for example, which is metallized, for example under vacuum or electrochemically. One can still achieve a microrelief on a layer of metal already formed.

The microrelief can form a diffraction grating that separates the chromatic components of the light, producing a color effect when the diffractive structure is illuminated with white light, with preferably a variation of the color observed as the viewing angle changes.

Among the diffractive structures producing a colored interference effect, and suitable for the invention, we can distinguish those for which the desired effect is obtained for the zero-order device ("Zero-Order Device" or "ZOD") and those for which the desired effect is of order one ("First-Order Structure").

Examples of "ZOD" are surface diffraction gratings and buried gratings.

Examples of order one structures are the transmission holograms, in particular of the DOE type, the Fourier transformation holograms and the "Kinoforms", the 3D rainbow holograms, in particular the 2D / 3D multi-hologram holograms, static rainbow 3D holograms, real-color holograms, and so-called "Fiat 2D artwork" holograms.

We can refer to the book "Optical Document Security" Third Edition

VAN RENESSE ISBN: 58053-258-6, pp 171-221, for the detailed description of examples of such structures.

The diffractive structure may belong to a security element that extends from one edge of the document to the opposite edge, such as a security thread, a foil, or a variable data protection film. The diffractive structure may still belong to a security element such as a patch, which is affixed to the surface of the document or extends into a window.

The structure with a colored interferential effect may be formed of diffractive pigments whose particles have a diffraction grating on their surface. The structure having a colored interferential effect may also be a liquid crystal structure or a multilayer iridescent interferential structure, in particular with iridescent pigments, such as an iridescent pigment coating. The application of the diffusing layer according to the invention to colored effect structures such as goniochromatic multilayer structures or such as structures carrying a liquid crystal, tends to alter the visibility of the color change by altering the gloss level. However, this application does not lead to achromatization in the case of such structures. The application of the revealing layer restores a level of gloss to recover at least a portion of the initial color change.

Diffused matte layer

The diffusing matte layer makes it possible to achromatize at least locally the colored interference-effect structure, when this structure is diffractive.

The diffusing matte layer can still, or alternatively, serve to protect underlying security elements or the document substrate, and / or serve as a print receiving layer.

The diffusing matte layer preferably comprises silica particles of micrometric size. In the case of a reversible achromatization, the particles act in particular by their ability to create surface dullness and the diffusion of the associated light, by favoring a partial overshoot of the plane formed by the surface of the layer of the binder carrier. The particle is preferably non-opaque.

By "micro-metric size" it is necessary to understand in the range of magnitude of the thickness of the diffusing matte layer.

Preferably, the thickness of the binder layer of the diffusing matte layer is between 0.5 times and 3 times the size of the particles, preferably between 1 and 2 times the size of the particles, so as to create a diffusion surface, particles found on the surface.

The silica particles according to the invention can have a mean size in number D50 of between 0.5 and 15 μιη, better still between 1 and 12 μιη, and even more preferably between 3 and 7 μιη.

The silicas can be chosen in particular from those proposed by GRACE DAVISON and EVONIK.

The diffusing layer may have, after drying, a thickness ranging from 0.5 to

15μιη. The amount of silica particles in the diffusing layer is preferably between 2 and 10% by dry weight.

The amorphous silica may be precipitated silica, fumed silica, silica gel, colloidal silica or arc-milled and milled silica. Preferably, it is precipitated or fumed silica. Because of the particle sizes, the colloidal silicas are nanometric and are not suitable for reversible achromatization related to surface diffusion, but are suitable for the case of a permanent achromatization related to a diffusion of volume.

The silica particles may be applied in the form of a meltable fluid composition, by being mixed with a binder and / or dispersed in a solvent, to form, for example, an ink or a varnish. This fluid matifying composition can be applied by coating or printing.

This composition may comprise at least one luminescent agent, for example a phosphorescent or fluorescent compound and / or other markers, for example chemical or biochemical. The fluorescence can in particular be visible emission during a UV excitation, emission in the visible during an IR excitation, or emission in the IR during excitation in the IR.

More generally, those skilled in the art will preferably choose luminescent agents or markers that do not interfere with the observation of the interfering colored structure, in particular luminescent agents or transparent markers.

The use of organic luminescent agents, especially in solubilized form, is thus preferable so as not to unduly affect the transparency of the mattifying composition. Alternatively, those skilled in the art will adapt the concentration of luminescent agents or markers of the diffusing matte layer so as not to interfere with the observation of the colored interferential effect structure.

Where appropriate, the scattering layer is applied in the form of a frame that can be combined with an encoded image formed of a plurality of interleaved elementary images, each elementary image having colored interferential effects through the use of a diffractive structure.

For example, it is applied to a holographic foil carried by a document, by overprinting with a diffusing matte ink as described above a frame consisting of parallel lines of defined thickness and spacing.

Alternatively, the document carries a transparent window on which is printed using a diffusion-based ink-based printing as described above, a pattern corresponding to a coded image resulting from combined images, this coded image interacting with a frame carried by the document elsewhere and superimposable with the coded image. By overlapping and translation of the window on the printed frame, we reveal an animation alternating colored and achromatic diffractive visual effects. Alternatively, the frame may be on the window and the image coded on the document.

The coded image and the frame can be produced according to the teaching of the publications WO2011 / 007344 A1, WO2011 / 007343 A1 or WO2011 / 007342 A1.

To obtain the reversibility of the achromatization effect, the thickness of the deposit of the revealing layer must cancel the relief effects of the scattering particles and the refractive index must not be too far from that of a resin of protecting the diffractive element to limit volume diffusion due to the difference in refractive index between the layer binder, the surface particles and the developer layer. This condition on the refractive index is true for all layers likely to cover the diffractive element in order to maintain, as far as possible, its initial effect after revelation.

If necessary, an impression of the diffusing layer can be made to have both areas where the effect is reversible and others where it is not, because of the thickness applied.

The diffusing layer may be an integral part of the security element as a layer applied for example over a layer of protective varnish of the diffractive structure.

The diffusing layer may be in contact with a support film used for the transfer of the security element, in particular in the case of a foil.

The diffusing matte layer can be uniformly applied, and in this case all of the diffractive structure is matte and achromatic once the diffusing layer has been transferred.

In a variant, the diffusing matte layer is applied in a localized manner, in the form of patterns, and in this case, a colored and achromatic double-effect structure is created from the diffractive starting structure with a colored interferential effect, and this without it is necessary to create a specific micro-embossing.

As mentioned above, the diffractive structure coated with diffusing matte layer can be revealed by a post-application treatment of the security element on the substrate of the document, namely by application of a revealing layer. Revealing layer

Advantageously, as mentioned above, the achromatization effect induced by the diffusing matte layer may be attenuated, or even eliminated, by application to the diffusing layer of a revealing layer.

We can distinguish two cases:

1 / Reversible achromatization: the diffusing particles, in particular silica particles, are on the surface of the diffusing matte layer: In this case, the diffusing layer is diffused and matified, and the revealing layer makes it possible to find a colored and shiny appearance. The diffusing particles and the binder may have close refractive indices.

Permanent achromatization: the diffusing particles, in particular of silica, are en masse in the diffusing layer: In this case, the diffusing layer makes it possible to diffuse but does not matify, and the revelation layer does not make it possible to find the colored aspect. The diffusing particles and the binder must have different refractive indices. Indeed, the diffusion power of the layer is a function of the difference in refractive index between the scattering particles and the medium in which they are and the particle size. The higher the difference in refractive index, the higher the diffusion power. The size of the particles impacts this diffusion power with respect to the wavelength. Particles of very small size in front of the wavelength (in this case those of visible light) will diffuse the light with a dependence on the wavelength (Rayleigh scattering); the layer then has a colored appearance. For particles of dimension near the wavelength or much higher, we have an identical diffusion for all wavelengths (diffusion of Mie), and the layer has a white appearance.

When the diffusing layer is in the first case, the revealing layer can "re-chromatize" the diffractive structure.

By "re-chromatizing" it should be understood that the interferential effect of the diffractive structure becomes more noticeable due to the presence of the revealing layer.

The revealing layer may optionally have at least one function in addition to the optical effect it provides, in particular to protect one or more security elements of the document and / or to protect the document substrate.

The revealing layer may make it possible to locally transparent the document or the security element, when the diffusing matte layer according to the invention is made transparent by the application of the revealing layer. The diffusing matte layer is transparent by applying it to the revealing layer, that is to say that the diffusing matte effect is canceled. However, for the cancellation of the effect to be visible, it is better to have a diffractive structure under the diffusing matte layer. The revealing layer preferably comes into contact with the diffusing layer.

Preferably, the developer layer has a refractive index close to that of the "binder" of the diffusing layer, preferably with a difference in refractive index of less than 0.5.

Also preferably, the revealing layer is bright, that is to say that it itself generates a negligible diffusion of light. Its brightness, when measured with the BYK GARDNER MICRO GLOSS 75 ° device and according to the ISO 8254-1 standard, is preferably greater than or equal to 20, more preferably greater than or equal to 30.

Advantageously, the brightness is at a minimum such that the contrast between the brightness of the diffusing matte layer and the revealing layer is sufficiently high to be perceptible to the eye. In addition, it is preferable that the level of brightness of the revealing layer is close to that of the diffractive structure. Advantageously, the brightness contrast between the two layers is strong, which in addition allows the achromatization effects described, to create an additional optical effect. The revealing layer is preferably free of particulate fillers, especially mineral.

The revealing layer is preferably film-forming when the effect is to be durable, which is particularly the case when it is applied by printing or coating.

Alternatively, when the developer composition is used temporarily to authenticate a secure document; in this case, the developer composition is preferably non-polymeric, being for example a liquid such as water applied for authentication.

The revealing composition may be based on polyurethane or comprise a polymer crosslinkable under UV radiation, and more generally be any binder or transparent liquid.

The revealing layer is preferably transparent. It can be colorless or colored. Preferably, the revealing layer is colorless. The revealing layer may comprise a luminescent agent and / or a dye.

More generally, those skilled in the art will preferably choose luminescent agents or markers that do not interfere with the observation of the effect structure. interferential colored, in particular luminescent agents or transparent markers. The use of organic luminescent agents, especially in solubilized form, is thus preferable so as not to unduly affect the transparency of the mattifying composition.

Alternatively, one skilled in the art will adapt the concentration of luminescent agents or markers of the developing layer so as not to hinder the observation of the desired effect.

The developer layer may be applied to the diffractive structure and beyond it on a substrate of the document, for example. This adds optical effects and increases security.

The developing layer may form a pattern that encompasses the diffractive structure, or that completes a pattern thereof.

The developing layer may be applied by printing, preferably by inkjet printing for variable indications. Alternatively, the developer layer is applied by coating, for example to the size-press.

The revealing layer can be applied uniformly. However, it is preferable that the revealing layer be applied, in particular by printing, so as to customize the security element and / or the document containing the diffractive structure, in particular by printing a variable mention, a portrait of a carrier of the document, or the value of a cut (in this case, preferably by inkjet printing). The printed pattern can be found elsewhere on the document or security element.

The revealing layer can still be applied using a pen, especially when it comes to verifying the reversibility of achromatization. In this case, the application of a liquid, for example water or a drop of water, can temporarily recapitalize, until evaporation or wiping of the deposited water, the diffractive structure .

The revealing layer may be aqueous, and / or comprise a volatile organic solvent.

The revealing layer may be constituted by a revealing, transparent and glossy ink. This ink may be in the aqueous phase, in a solvent medium or be a UV-crosslinking ink. Alternatively, it may be transparent but slightly colored, and may contain additional security agents invisible or partially visible to the naked eye, for example luminescent, especially fluorescent.

It can be a fatty ink with oxidative drying, for example a soft ink, or an ink applied in serigraphy or flexography or by any other process printing. The amount of developer ink deposited may be large enough to create tactile relief effects, if any.

The developer layer may be applied within an area of the security element having the diffractive structure or may protrude from the element and form an integral part of a printing pattern of the substrate of the printed secure document.

In particular, an interesting effect is obtained by performing the printing of a continuous pattern with a transparent and brilliant disclosure ink passing through the security element and partially covering it and the document substrate. The printing of the revealing layer is brilliant, and contrasts both with the mattness of the printed-matter substrate and with that of the diffractive diffuse layer-coated structure. Moreover, the overprinted portion of the security element provides additional contrast by the localized revelation of the colored interference effect.

In the context of a bank note application, it is advantageous to use the same security element of the holographic patch or foil type, coated with a diffusing matte layer, and to differentiate the cuts by superimposing a layer. revealing in the form of revealing ink in a specific pattern for each cut, or a kind of personalization reduced to the differentiation of cuts by a printing process.

Another aspect of the invention is a method of personalizing a security element or a secure document.

This method comprises the step of applying to a diffractive structure of the security element or the secure document a diffusing layer according to the invention, according to at least one predefined pattern. This is for example to reproduce a variable mention related to the identity of the bearer of the document or a reason specific to the document, for example the value of a cut in the case of a bank note.

According to another of its aspects, another subject of the invention is a method for personalizing a security element or a secure document, comprising the step of applying to a diffusing matte layer covering a diffractive structure of the security element or document, a revealing layer, the latter attenuating or even eliminating the achromatization effect provided by the diffusing layer, the revealing layer being applied in at least one predefined pattern. It is for example, as above, to reproduce a variable mention or to make a specific pattern to the document.

In an exemplary implementation, a security element, for example a holographic foil achromatized by application of the diffusing matte layer, is present on the security document and offers achromatic security, with patterns whose appearance varies depending on the viewing angle. It is applied, in particular by inkjet printing, a revealing layer in the form of a high gloss transparent ink, to form a variable customization, for example a portrait. The bright transparent print locally reveals the colorful holographic effect. Thus, the superimposed portrait appears as the only holographic pattern with a colored effect on an achromatic holographic background. The observed visual effect is enhanced by the double contrast color / achromatic and matte / glossy. The customization is highlighted. Counterfeiting is made extremely difficult.

The invention also relates to a method for verifying a secure document according to the invention.

It is a question of revealing a diffractive structure, in particular holographic, with interferential colored effect, which is masked by a scattering layer according to the invention.

According to this method, a diffusing layer is applied to the diffusing layer according to the invention covering the diffractive structure and it is determined whether the application of this revealing layer restores the colored interferential effect of the diffractive structure.

The application can be done using a pen for example.

Preferably, the developer layer is in this case water-based, and preferably it is non-polymeric.

It may consist of water with possibly a preservative and / or at least one other reagent intended to highlight the presence of a particular chemical compound on the document, for example in combination with a chemical authenticity. In an exemplary implementation, the diffusive layer diffractive structure is present on the secure document in the form of a foil, a patch, or a label, or a seal / sleeve of a bottle or bottle containing a luxury product, perfume or spirits and offers for example the appearance of an achromatic hologram. By applying a transparent ink film or even a drop of water with a pen, the holographic color effect is locally revealed.

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

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

FIG. 2 is a section along II-II of FIG. 1, FIG. 3 is a section along III-III of FIG. 1,

FIG. 4 is a section along IV-IV,

FIG. 5 is a front view of a variant embodiment, and

- Figure 6 is a view similar to Figure 2, an alternative embodiment.

In the drawing, the actual relative proportions have not always been respected, for the sake of clarity. Likewise, certain elements have been represented in contact whereas in reality they may be separated by a layer of adhesive for example.

There is shown in Figure 1 a secure document 10 according to the invention, for example a bank note.

This document 10 comprises a substrate 11 and one or more security elements, including at least one security element comprising a diffractive structure.

The substrate 11 is for example paper; the substrate 11 can still be made of plastic or be hybrid paper and plastic.

In the example considered, the document 10 has a security element 20 in foil form, that is to say a band applied by transfer to the surface of the substrate 11.

The security element 20 has a diffractive structure 21 having a colored interference effect, such as a hologram formed by microreliefs on a reflecting surface.

According to the invention, the diffractive structure 21 is at least partially covered by a diffusing matte layer 30.

In the example of FIG. 2, the diffusing layer 30 is applied only over a fraction of the width of the diffractive structure 21.

Thus, the observer can perceive a contrast between the colored interferential effect due to the diffractive structure 21 and the achromatic effect related to the presence of the diffusing layer 30.

The diffractive structure 21 may be covered, in sections, over its entire width by the diffusing layer 30, as illustrated in FIG.

In the examples of FIGS. 2 and 3, the diffusing layer 30 does not extend on the substrate 11, being confined to the security element 20.

FIG. 5 illustrates a variant embodiment in which the diffusing layer 30 has a portion 30a that covers the diffractive structure 21 and at least one other portion 30b that protrudes over the substrate 11 of the document. Portions 30a and 30b are for example simultaneously applied by printing. The diffusing layer 30 locally makes the diffractive structure 21 substantially achromatic, and can also modify the appearance of the substrate 11 of the document covered with the portion 30b.

A developer layer 40 may cover the diffusing layer 30 to rechract the underlying diffractive structure 21 as illustrated in FIG. 4.

The achromatization and re-chromatization effect of the diffractive structure can be obtained even if the diffractive structure 21 is covered with one or more polymer layers, or even sandwiched between plastic films, and the diffusing matte layer. 30 is not applied directly to the diffractive structure 21.

FIG. 6 illustrates such an alternative embodiment. It can be seen in this figure that the diffractive structure 21 is separated from the diffusing layer 30 by at least one transparent intermediate layer 23, for example constituted by a plastic film.

The interval e which separates the diffractive structure 21 from the diffusing layer 30 is, for example, between 5 and the thickness of a card of approximately 800 μιη.

Special case of security thread

According to a particular case of implementation of the invention, the diffractive structure is carried by a security thread, preferably wide. The diffractive structure with a colored interference effect is then preferably a holographic structure.

A diffusing matte layer may be applied by incorporating silica particles into a lacquer present on one of the layers above the holographic structure, for example a heat sealer which serves to enhance the adhesion of the wire to the substrate of the document. In a variant, the diffractive structure is already covered with a heat-sealing varnish and, locally or totally, a varnish comprising silica particles is overprinted to form a diffusing matte layer according to the invention, thus creating a totally matt achromatic yarn. As a variant, discontinuous patterns are overprinted with the varnish, and a security thread is obtained with both brilliant and dull effects, achromatic and with a colored interference effect.

The security thread can still have a biplex structure, with a base film that carries the holographic structure with a colored interference effect, and a second film, which brings the achromatization, for example a thin film of polyester coated on the surface of a layer with matte and diffusing effect.

In the field of the bank note, the trend is to broad security son and large windows, with for example tickets carrying at least one window or only two large windows across the width of the ticket. The diffusing matte layer, and possibly in addition the revealing layer, can be arranged in one of the windows of a secure document, the other window having a diffractive structure. In the case where the ticket has a transparent window, whether it is obtained by papermaking or by forming a punch hole and covering with a polymer film, the achromatic effects can in a preferred case of the invention. invention to appear by superposition of two different windows of two secured documents, or by folding of a same secure document on itself to superimpose the diffractive structure and the diffusing layer, and possibly the revealing layer.

It is possible to apply a matte diffusing layer over the entire surface of the substrate and that of the optically variable security elements, so as to protect the entire document, including the security elements. Then, the developer layer can be applied, for example in the form of a layer of a transparent and glossy binder, by printing, only on the security elements for which it is desired to find the colored interference effect and the brightness.

The secure document may have a multilayer structure, for example printable external plastic film / heart / printable external film. The outer films, for example PET, may be coated with a diffusing matte layer according to the invention, which also serves as a printability layer. The core is for example a multilayer complex, especially based on Polyart ® or a security paper or a "hybrid" paper consisting of at least one layer of paper and at least one layer of polymer (s). The diffractive structure is for example a holographic foil, internal to the heart or present between the heart and one of the outer films. Each outer film makes the interferential effect, including holographic, achromatic. At the level of the diffractive structure, a new effect appears at the level of the motives of this one; depending on the inclination, the pattern is for example either dark gray on a white background, or white on a dark gray background. The document is then coated, at the level of the diffractive structure, to recover the holographic effect, for example with a revealing layer constituted by a polyurethane-based resin.

As a variant, whatever the configuration of the colored diffractive element, wire, patch, film or other, it is possible, in the case of colored holographic structures having judiciously defined and contiguous zones, which are better alternating, to obtain, after total recovery of the surface by the diffusing layer, by zones, shades of gray more or less dark according to the angle of observation, or the rotation of the document around an axis perpendicular to the plane formed by the document, or by south / north or north / south or east / west or west / east deflection of the document, creating the illusion of an effect of displacement or motion depending on the angle of view or inclination of the document. The Grayscale more or less dark depending on the angle of observation are obtained using the diffractive grating. Advantageously one can have two holographic zones rendered achromatic, distinct parallel or interlaced, having a diffractive structure ranging from light gray or dark gray on one side and dark gray to light gray on the other. This doubles the illusion of moving speed by varying the angle of view, the direction of rotation or the deflection of the document according to a visualization mode as described above. The achromatization process thus makes it possible to transform more or less standard holographic structures into a dynamic achromatic security element. As a variant, the application of a superimpression ink overprinting net, for example in interlaced fashion, may make it possible to further improve the aesthetics and the level of security by discretely revealing a complementary colored holographic touch. This gives less expensive equivalents for "Motion Rapid" effects.

testing

a) The complexing of a diffractive structure with a PET film without diffusing layer does not modify the colored effects of the diffractive structure. Neither the laminating glue nor the lamination process alter these effects.

b) The complexing with a PET film made printable by means of a diffusing layer according to the invention eliminates the gloss and the colored interferential effects of the diffractive structure when it is a hologram, without however eliminating the optically variable nature of certain patterns of the hologram that change from light gray to dark gray and vice versa depending on the viewing angle. The diffusing layer transforms the colored holographic effects into achromatic holographic effects.

The application of a revealing layer such as a varnish or a binder, in particular a polyurethane-based coating, makes it possible to recover the brightness and color of the hologram.

Furthermore, the application of the revealing layer, on either side of the finished complex, on a window area, allows to find brightness and transparency at the window, regardless of the presence or absence of the diffractive structure.

Thus, it can be seen that the reversibility provided by the revealing layer makes it possible to avoid making reserve zones by coating the printable layers, as is envisaged on certain solutions relating to hybrid tickets.

c) The application of a water-based diffusing layer according to the invention to a matured iridescent coating and significantly disturbs the iridescent effect. However, overprinting with a polyurethane-based developer layer only restores shine. d) Different loads were evaluated, to highlight the influence of the mineral nature and the size of the particles.

This evaluation was carried out by applying the coatings directly to a diffractive structure, constituted by two-metal holographic foil comprising two different metals, for example in accordance with the publication EP 1 809 486, and on the outer face of a PET film of a PET / Polyart biplexe integrating a diffractive structure.

Results

All the amorphous and precipitated silicas evaluated make it possible, at equivalent incorporation rate, to bring mattness, to remove the colored holographic effect, while ensuring the maintenance of an optically variable achromatic effect, and this in a reversible manner, with a return to a colorful and brilliant holographic effect after being covered by a revealing layer constituted by a solvent-based printable varnish, free of matifying agent.

The phenomenon observed is robust since one can go up to a size of silica particles of more than ΙΟμιη retaining all the effects. Beyond, and in particular from 14 μιη, the coating becomes granular and achromatization imperfect.

e) The application of a revealing layer such as a varnish or a binder, such as a polyurethane coating, on a hybrid paper comprising a liquid crystal wire covered by a diffusing layer according to the invention makes it possible to recover the brightness of origin of the security thread before its complexing.

In another exemplary embodiment, the matte layer is deposited on a monochrome colored interference-effect structure, and is authenticated by the application of a layer of revelation. For example, a monochromatic colored interfering effect structure may be a monochromatic diffractive structure obtained from a diffractive structure to which a subterranean filter is applied which filters only one color but retains the diffractive appearance. It is possible to have a specific colored interfering effect color specific for a type of product, for example a secure sleeve for a bottle or container. Thus for the same achromatic rendering, once the diffusing matte layer has been applied, the revelation by the application of the revealing layer can generate specific monochrome color effects.

The invention is not limited to the examples described. The expression "comprising a" should be understood as being synonymous with "comprising at least one".

Claims

A method for modifying the appearance of a colored interferential structure (21) being a diffractive structure, comprising applying to the interfering colored structure a diffusing matte layer (30) having scattering particles.

2. Method according to claim 1, the diffusing particles being micrometric particles.

3. Method according to one of claims 1 and 2, the diffusing particles being silica particles, in particular the silica being an amorphous silica.

4. Method according to any one of claims 1 to 3, the diffusing layer providing a surface diffusion.

5. Method according to claim 4, the diffusing particles having substantially the same refractive index as a binder of the scattering layer in which they are dispersed.

6. Method according to claim 4 or 5, the diffusing particles protruding from the surface of the diffusing layer.

7. Method according to any one of claims 1 to 3, the diffusing layer providing a volume diffusion.

8. The method of claim 7, the refractive index of the scattering particles being different from that of a binder in which they are dispersed.

9. The method of claim 7 or 8, the diffusing particles not protruding from the surface of the diffusing layer.

10. Method according to any one of claims 1 to 9, the application of the diffusing matte layer being carried out so as to cover the entire structure of interferential color effect (21) or to only partially cover it .

11. A method according to any one of the preceding claims, the diffusing matte layer (30) being applied by printing, preferably by offset printing, intaglio printing, screen printing, gravure printing, flexography or inkjet, by coating or coating.

12. Method according to the preceding claim, the diffusing matte layer being printed in such a way as to personalize a document comprising the colored interferential effect structure, in particular by printing a pattern, a variable mention, a portrait of a wearer. of the document, or the value of a cut.

13. A method according to any one of claims 1 to 11, the diffusing matte layer (30) being applied uniformly.

14. A method according to any one of the preceding claims, comprising the application on the diffusing matte layer (30) of a revealing layer (40), preferably transparent and shiny, applied in the liquid state.

The method of claim 14, wherein the developer layer (40) is applied to overlap the color interference structure (21) and beyond.

16. The method of claim 14 or 15, the developing layer (40) being applied by printing, preferably by offset printing, intaglio, screen printing, gravure printing, flexography or inkjet, coating, coating, or the revealing layer being applied using a pen.

17. The method of claim 16, the developing layer being printed so as to customize a document comprising the structure with interferential color effect (21), in particular by printing a pattern, a variable mention, a portrait of a bearer of the document, or the value of a cut.

18. A method according to any one of claims 14 to 17, the developer layer being aqueous and / or comprising a volatile organic solvent and / or comprising a photo-crosslinking polymer under UV.

19. A method according to any one of claims 14 to 18, the developing layer having a refractive index, preferably close to that of a binder of the diffusing layer, with a difference in index less than 0.5.

20. Process according to any one of claims 14 to 19, the developer layer and / or the diffusing matte layer comprising a luminescent agent and / or a dye.

21. A method according to any one of the preceding claims, the diffusing matte layer (30) being applied directly in contact with a microrelief of the colored interferential structure (21).

22. A method according to any one of claims 1 to 20, the diffusing matte layer being applied without direct contact with a microrelief of the interfering color structure.

23. A method according to any one of claims 1 to 22, the diffusing layer (30) being applied to the colored interference effect structure (21) and beyond.

24. Method according to any one of the preceding claims, the structure with a colored interference effect being a diffractive structure (21) holographic, including micro-embossed.

25. Method according to any one of the preceding claims, the diffusing particles having a mean size in number D50 of between 0.5 and 15 μιη, more preferably between 1 and 12 μιη, more preferably between 3 and 7 μιη.

A method according to any one of the preceding claims, wherein the color interference structure is a diffractive structure having a color interference effect, in the form of a frame or pattern corresponding to a coded image resulting from combined images, the pattern and the weft. being on areas that can move relative to one another or superimposed areas, one of the pattern and the frame being formed by the diffractive structure and the other by a diffusing layer, the pattern being able to interact visually with the frame when superimposed thereon to reveal an image among the combined images, moving or changing the viewing angle to successively reveal multiple images, with alternating color and achromatic visual effects.

27. Security element obtained by the implementation of the method according to any one of the preceding claims.

28. Secure document comprising a security element as defined in the preceding claim.

29. A method of verifying a document according to claim 28, without appending to claims 14 to 20, wherein is applied to the diffusing layer (30) a revealing layer (40) and determining whether the application of this revealing layer restores the interferential effect of the interfering color structure.

30. The method of claim 29, the achromatization provided by the diffusing layer being reversible and canceled by the developer layer.

31. The method of claim 29, the achromatization provided by the diffusing layer being permanent.

32. A method of verifying a document according to any one of claims 29 to 31, wherein one observes the diffractive structure with colored interference effect during the relative displacement of the frame and the coded image or during the change of the image. angle of observation, and it is determined whether this relative displacement or this change produces an alternation of colored and achromatic visual effects.