A security feature for a protected document and a protected document containing such a security feature

Abstract

The invention relates to a security element (2) for a security document, the security element (2) being multilayer and comprising an upper face (12) and a lower face (13) between which faces there are superposed, in this order, from the upper face (12) to the lower face (13): - a translucent layer of coloured ink (15), - an at least partially, preferably totally, transparent or translucent backing layer (17), - a relief-structures layer (19) exhibiting variable reflection so as to define an optical effect that varies according to the angle at which it is viewed and / or illuminated from the upper face (12), and - a layer (21) comprising plasmonic particles, preferably a layer (21) of plasmonic ink. The invention also relates to a security document comprising at least one such security element (2).

Description

[0001] DESCRIPTION

[0002] TITLE: SECURITY ELEMENT FOR A SECURITY DOCUMENT AND SECURITY DOCUMENT COMPRISING SUCH A SECURITY ELEMENT

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a security element for a security document such as a security document. It also relates to a security document, which comprises at least one such security element.

[0005] STATE OF THE ART

[0006] So-called first-level security features, i.e. those that are visible without additional equipment, are effective bulwarks against counterfeiting of security documents or valuable documents such as banknotes.

[0007] Also, manufacturers of this type of document focus on making these securities, ensuring that they remain very intuitive in their operation but complex to produce without the know-how and the appropriate equipment and, of course, very difficult or even impossible to counterfeit.

[0008] This implies that the technologies used for their creation are difficult for the general public to access and that the implementation of these tools is restricted and / or dedicated to specific document security professions. Indeed, these are elements that are easily identifiable by everyone and which allow everyone to authenticate a security document such as a banknote.

[0009] For example, document FR 3 087 386 A1 discloses a technique for forming a security element comprising a multi-layer assembly so as to form, in reflected light, an optical effect which changes depending on the angle of observation and / or illumination of this security element.

[0010] Such an optical effect is obtained in particular by a reflective structure comprising a layer of embossed varnish, which thus comprises raised microstructures with variable reflection depending on the angle of observation and / or illumination.

[0011] This is particularly interesting when one wishes to use this structure on an inserted security element such as a security thread (narrow strip intended to be integrated into a security document), or an added element such as a security “foil” (strip which can be applied by lamination or by transfer), and not by printing the security document.

[0012] Indeed, in the case of security threads, when they are integrated into a "window" in paper, the visible portions of these security threads are surfaces of approximately 1 to 6 mm in width and 4 to 16 mm in height in general, even if the trend is towards an increase in these surfaces. This means that such a security thread, called a "window thread", is incorporated into the mass of the paper, sometimes covered with fibers and sometimes flush with the surface of one of the faces of the paper, which explains the use of the term "window". A variant also exists in the form of a "patch", film or stripe or "foil" which can cover a local opening made in the basic support of the security document, which is for example made of paper.

[0013] In order to personalize and enhance the optical effect obtained, it is known, for example, to make the embossed varnish layer in such a way that it is colored. However, this implies that all the raised microstructures have the same color. This therefore limits the design possibilities of the security element, its attractiveness and its ease of authentication.

[0014] However, adding pigments or colorants to the embossed varnish layer can lead to pigment or colorant dispersion problems, causing, for example, heterogeneity in the final color.

[0015] Thus, there is a need to improve the optical effect that can be achieved by such security elements. Since their manufacturing is already complex, it is also necessary that such an improvement does not further complicate manufacturing for authorized suppliers, such as security element manufacturers.

[0016] Document EP 4 091 830 A1 describes in particular a valuable document which may include a security element using a plasmonic structural color.

[0017] The principle of structural colors is to generate these colors by macroscopic structures decomposing light rays. Such a structure makes it possible to create light effects due to the dimensions and incident light rays. The color variation is due to the topography of the structure.

[0018] Thus, this document EP 4 091 830 A1 describes a color change effect in transmission, but this effect is achieved with a particular structure, more precisely a transmissive sub-wavelength grating, which comprises nano-lamellae that form part of the transmissive sub-wavelength grating. Thus, in this document, a plasmonic effect is achieved by this structure. This document also describes nanostructures, but in this case, it is not the structure itself that is nanometric, but its structural topographic details, namely the "bumps" and "dips" of the structure, which can form "nano-reliefs".

[0019] STATEMENT OF THE INVENTION

[0020] The present invention aims in particular to provide a security element making it possible to improve the expected optical effect without complicating its manufacture for authorized suppliers.

[0021] According to a first aspect, the invention proposes a security element for a security document, the security element being multi-layered and comprising an upper face and a lower face between which are superimposed in this order, from the upper face to the lower face:

[0022] - a translucent layer of colored ink,

[0023] - a support layer which is at least partially, preferably totally, transparent or translucent,

[0024] - a layer of raised microstructures with variable reflection so as to define a variable optical effect depending on the angle of observation and / or illumination from the upper face, and

[0025] - a layer comprising plasmonic particles, preferably a layer of plasmonic ink, more preferably a layer of plasmonic ink comprising plasmonic particles and a binder, the binder preferably being capable of being set or dried subsequently by oxidative means, by hot air assisted or not by infrared radiation, or by polymerization initiated by ultraviolet radiation or even by mixed drying, in particular with hot air and ultraviolet radiation, designated in English by the expression “Dual Cure”.

[0026] By "plasmonic particles" we mean in particular nanometric or nanostructured particles, metallic or coated with a metal, and which are the site of a surface plasmonic resonance when they are illuminated with incident white light, which results in particular in a color perceived in reflected light different from that perceived in transmitted light.

[0027] In other words, it is important to understand that a plasmonic particle is a metallic nanoparticle capable of exciting surface plasmons when it interacts with light. Surface plasmons are collective oscillations of free electrons on the surface of a metal, generated by the electromagnetic field of the incident light. The main characteristics of plasmonic particles are as follows. Regarding the material, plasmonic particles are generally made of noble metals such as gold, silver or sometimes copper, because these materials have a high density of free electrons. Regarding the size, plasmonic particles, typically, have a nanometric scale. This small size has the effect that plasmonic effects are dominant.In surface plasmon resonance (SPR), light of a certain wavelength interacts with a plasmonic particle, inducing a collective oscillation of free electrons on the particle's surface. This resonance locally amplifies the electromagnetic fields near the particle. Furthermore, the plasmonic properties of a plasmonic particle may depend on its size, shape, chemical composition, and the environment (e.g., the medium in which the particle is immersed).

[0028] By "nanometric" we mean objects whose dimensions are between 1 and 1000 nanometers, preferably between 1 and 100 nanometers.

[0029] By “nanostructured” we mean objects comprising a surface relief whose dimensions are between 1 and 1000 nanometers, preferably between 1 and 100 nanometers.

[0030] Thus, the use of several layers, in particular ink layers, makes it possible to improve and expand the range of colors available for the desired optical effect while not complicating manufacturing for authorized suppliers. This produces a color in reflected light, which results from the combination of the color of the translucent layer of colored ink and the color seen in reflected light of the plasmonic ink layer, as well as a color in transmitted light, which results from the combination of the color of the translucent layer of colored ink and the color seen in transmitted light of the layer comprising plasmonic particles, preferably the plasmonic ink layer. Furthermore, the use of a plasmonic ink also makes it possible to obtain a metallized optical effect, and this in a significantly simpler manner for the manufacturer compared to metallization by deposition of a metal layer under vacuum.

[0031] According to a second aspect, the invention also proposes a security document, preferably a value document, comprising at least one security element in accordance with the first aspect.

[0032] The invention is advantageously and optionally supplemented by the following characteristics, taken alone or in any of their technically possible combinations: - The translucent layer of colored ink has an optical density less than or equal to 0.6. By optical density, it should be understood in particular that it is the decimal logarithm of the ratio between the quantity of incident light and the quantity of light transmitted through the translucent layer of colored ink. The optical density is in particular measured by spectrophotometry, according to standard NF ISO 12647-1:2013, in particular with an X-Rite spectrophotometer (registered trademark), for example from the eXact (registered trademark) Xp range.

[0033] - The backing layer is a plastic film, preferably based on PET, also called polyethylene terephthalate.

[0034] - The layer comprising plasmonic particles, preferably the plasmonic ink layer, is configured to obtain a “one-way mirror” effect, i.e. it is reflective when viewed in reflected light and semi-transparent when viewed in transmitted light.

[0035] - The plasmonic ink layer comprises pigments, in the form of nanoparticles chosen from the group of transition or post-transition metals, preferably silver. Alternatively, the plasmonic ink layer comprises pigments larger than nanoparticles but having a nanostructured support and coated with a layer of metal or coated with nano-agglomerates of metal, and where the metal is chosen from the group of transition or post-transition metals, preferably aluminum.

[0036] - The nanoparticles have a maximum dimension between 15 nm and 1000 nm, preferably between 15 and 100 nm.

[0037] - The variable reflection relief microstructure layer is an embossed varnish layer.

[0038] - The layer of variable reflection relief microstructures is transparent or translucent, preferably transparent.

[0039] - The layer of variable reflection relief microstructures is preferably free of any metallic elements.

[0040] - The security element comprises a layer of opaque ink arranged below the layer comprising plasmonic particles, preferably the plasmonic ink layer. Thus, the opaque ink layer makes it possible to reinforce the first color in reflected light, in particular because it blocks the transmission of light and thus prevents the visualization of the color seen in transmitted light of the layer comprising plasmonic particles, preferably the plasmonic ink layer. For the same optical effect, the quantity of plasmonic particles, preferably the quantity of plasmonic ink, used to produce the layer comprising plasmonic particles, preferably the plasmonic ink layer, can thus be reduced.

[0041] - The opaque ink layer comprises a region at least partially devoid of opaque ink. Thus, the region at least partially devoid of opaque ink, also called "openwork", allows the visualization of a color in transmitted light resulting from the color seen in transmitted light of the layer comprising plasmonic particles, preferably of the plasmonic ink layer.

[0042] - The region at least partially devoid of opaque ink is completely devoid of opaque ink. Thus, the color difference is improved between the color in reflected light and the color in transmitted light / reflected light.

[0043] - The region at least partially devoid of opaque ink forms a recognizable pattern. Thus, thanks to the presence of this pattern, particularly visible in transmitted light, a user can easily determine that the security element is not counterfeit.

[0044] - The security element comprises a translucent or transparent, preferably transparent, protective layer, which may be an additional support layer or an ink or varnish. Thus sandwiched between the base support layer and the protective layer, the majority of the constituent layers of the security element are protected from external influences. Said protective layer is preferably transparent so as not to alter the optical effect.

[0045] - The security element comprises a complementary support layer, in particular translucent or opaque. When the complementary support layer is translucent, it is arranged below the layer comprising plasmonic particles which is preferably the plasmonic ink layer, and preferably below the still opaque layer. Thus, the complementary support layer allows the visualization, from the upper face, of a color in transmitted light, that is to say a color obtained by light transmitted from the lower face to the upper face, or vice versa, resulting from the combination of the color of the translucent layer of colored ink and the color seen in transmitted light of the layer comprising plasmonic particles, preferably of the plasmonic ink layer.When the complementary support layer is opaque, it notably comprises at least one transparent region, preferably partially superimposed on, notably marked with, preferably entirely superimposed on, an opening in the opaque ink layer.

[0046] - The additional support layer is a plastic film, preferably based on PET, short for polyethylene terephthalate.

[0047] - The complementary support layer is coated with an adhesive composition on one side facing the support layer. Thus, the security element is obtained in a simple manner, the bond between the complementary support layer and an upper layer, such as an opaque ink layer, being achieved in a simple manner by the adhesive composition.

[0048] - The additional support layer is colored, in particular in mass. When the color of the additional support layer is substantially identical, preferably identical, to the color of the security document, the additional support layer is advantageously difficult to distinguish from the material forming the basis of the security document comprising the security element. The additional support layer is preferably white.

[0049] - The translucent layer of colored ink comprises a region at least partially, preferably completely, devoid of colored ink. When the color of the plasmonic particles, preferably of the plasmonic ink, is different from that of the colored ink, a color difference is perceived in reflected light, and where appropriate in transmitted light, between the region provided with colored ink and the region which is respectively at least partially, preferably completely, devoid of it. The region at least partially devoid of colored ink is also called "openwork". When said region is completely devoid of colored ink, a better contrast is obtained and the optical effect is thus improved.

[0050] - The region at least partially devoid of colored ink forms a recognizable pattern. Thus, thanks to the presence of this pattern, a user can easily determine that the security element is not counterfeit.

[0051] - The region at least partially devoid of colored ink is at least partially superimposed on, in particular marked with, preferably entirely superimposed on, the region at least partially devoid of opaque ink. Thus, a more complex optical effect can be obtained. As is known in particular in the fiduciary field, marked or “registered” elements are aligned so as to provide a pattern easily recognizable to an observer, such as an aligned sequence of numbers and / or letters.

[0052] - The layer comprising plasmonic particles, preferably the plasmonic ink layer, comprises a region at least partially, preferably totally, devoid of plasmonic particles, preferably devoid of plasmonic ink. Thus, an optical effect with good light contrast can be obtained in the region devoid of plasmonic ink, and the expected optical effect is improved. The region at least partially devoid of plasmonic particles, preferably the region at least partially devoid of plasmonic ink, is also called "openwork". When said region is totally devoid of plasmonic particles, preferably totally devoid of plasmonic ink, a better contrast is obtained and the optical effect is thus improved.

[0053] - The region at least partially devoid of plasmonic particles, preferably the region at least partially devoid of plasmonic ink, forms a recognizable pattern. Thus, thanks to the presence of this pattern, a user can easily determine that the security element is not counterfeit since he directly observes in this pattern the opaque ink layer, the appearance of which in reflection is different from that of the layer comprising plasmonic particles, preferably the plasmonic ink layer.

[0054] - The region at least partially devoid of plasmonic particles, preferably the region at least partially devoid of plasmonic ink, is at least partially superimposed on, in particular marked with, preferably fully superimposed on, the region at least partially devoid of colored ink, and the region at least partially devoid of plasmonic particles, preferably the region at least partially devoid of plasmonic ink, is at least partially superimposed on, in particular marked with, preferably fully superimposed on, the region at least partially devoid of opaque ink. Thus, a more complex expected optical effect can be obtained.

[0055] - The region at least partially devoid of plasmonic particles, preferably the region at least partially devoid of plasmonic ink, is fully superimposed on a portion of the region at least partially devoid of colored ink and on a portion of the region at least partially devoid of opaque ink. Thus, a clear pattern is obtained, which does not include any color and is easily observable, in particular in transmitted light. For example, such a pattern is a negative pattern (also called "cleartext" in English) recognizable in transmitted light, for example completely transparent. - The translucent layer of colored ink comprises a plurality of colored regions, among which a first colored region is of a first color and a second colored region is of a second color, the second color being different from the first color.Thus, the use of different colors within the translucent layer of colored ink makes it possible to improve and expand the palette of colors available for the desired optical effect while not complicating the manufacture of the security element. At least two colors are thus obtained in reflected light, each resulting from the entire color of the translucent layer of colored ink in a colored region and the color seen in reflected light of the layer comprising plasmonic particles, preferably the plasmonic ink layer, as well as at least two colors in transmitted light, each resulting from the entire color of the translucent layer of colored ink in a colored region and the color seen in transmitted light of the layer comprising plasmonic particles, preferably the plasmonic ink layer.Said colored regions can be delimited by clear boundaries (two colors identified in contact) or separated partially or gradually, for example in a gradient, or in a more or less wide variegated fade between two colors known to those skilled in the art under the name of “iris” in French or “rainbow printing” in English.

[0056] - The layer comprising plasmonic particles, preferably the plasmonic ink layer, comprises a plurality of regions comprising plasmonic particles, preferably a plurality of plasmonic ink regions, among which a first region comprising plasmonic particles, preferably a first plasmonic ink region, is such that a first color seen in transmitted light is different from a first color seen in reflected light and a second region comprising plasmonic particles, preferably a second plasmonic ink region, is such that a second color seen in transmitted light is different from a second color seen in reflected light, the first color seen in reflected light being different from the second color seen in reflected light and / or the first color seen in transmitted light being different from the second color seen in transmitted light.Thus, the use of different colors within the layer comprising plasmonic particles, preferably the plasmonic ink layer, makes it possible to improve and expand the palette of colors available for the desired optical effect while not complicating the manufacturing process for authorized printers. At least two colors are thus obtained in reflected light, each resulting from the combination of the color of the translucent layer of colored ink and the color seen in reflected light from a region comprising plasmonic particles, preferably from a region of plasmonic ink, and / or at least two colors in transmitted light, each resulting from the combination of the color of the translucent layer of colored ink and the color seen in transmitted light from a region comprising plasmonic particles, preferably from a region of plasmonic ink.Said regions comprising plasmonic particles, preferably said regions of plasmonic ink, can be delimited by clear boundaries (two colors identified in contact) or partially or gradually separated, for example in a gradient, or in a more or less wide variegated fade between two colors known to those skilled in the art under the name of "iris" in French or "rainbow printing" in English.

[0057] - The layer comprising plasmonic particles, preferably the plasmonic ink layer, is preferably detectable, in particular “machine readable”, i.e. in a banknote sorting machine or in a cash acceptor / exchanger, and thus constitutes an additional security feature of the security element. This involves, for example, detection or reading under infrared radiation.

[0058] - The security element comprises one or more optional layers that are detectable, in particular "machine readable", i.e. in a banknote sorting machine or in a cash acceptor / exchanger. This involves, for example, magnetic detection or reading, under invisible illumination, in particular under ultraviolet or infrared radiation.

[0059] - The security element comprises at least one sealing layer, preferably transparent, for example a layer of thermoadhesive (or thermoactivatable adhesive), intended for the definitive securing of the security element in and / or on the security document. Said at least one sealing layer preferably constitutes an external surface of the security element. Preferably the security element comprises two sealing layers arranged on its upper and lower surfaces respectively.

[0060] - The security element comprises, successively superimposed, from the upper face to the lower face:

[0061] - optionally a sealing layer, preferably transparent,

[0062] - the translucent layer of colored ink,

[0063] - the support layer at least partially, preferably totally, transparent or translucent,

[0064] - the layer of raised microstructures with variable reflection so as to define a variable optical effect depending on the angle of observation and / or illumination from the upper face 12,

[0065] - the layer comprising plasmonic particles, preferably the plasmonic ink layer,

[0066] - an opaque ink layer, - a protective layer,

[0067] - a sealing layer.

[0068] Thus, such a security element makes it possible to choose and improve an expected optical effect, by expanding the palette of colors available for the expected optical effect while not complicating manufacturing for authorized printers.

[0069] - The security document is a valuable document, such as a banknote.

[0070] - The security element is at least partially integrated into the security document or is reported on the security document.

[0071] - The security document is made from fibrous material, including paper, plastic material or a combination of these materials.

[0072] DESCRIPTION OF FIGURES

[0073] Other characteristics, aims and advantages of the invention will emerge from the detailed description below, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings, given as non-limiting examples and in which:

[0074] - figure 1 is a schematic top view of an exemplary embodiment of a security document comprising at least one security element;

[0075] - Figure 2 is a schematic cross-sectional view of a first embodiment of the security element;

[0076] - Figure 3 is a schematic cross-sectional view of a second embodiment of the security element;

[0077] - Figure 4 is a schematic cross-sectional view of a third embodiment of the security element;

[0078] - Figure 5 is a schematic cross-sectional view of a fourth embodiment of the security element.

[0079] Throughout the figures, similar elements are designated by identical references.

[0080] DETAILED DESCRIPTION OF THE INVENTION

[0081] Figure 1 represents a security document 1, preferably a valuable document, in this case a banknote. Advantageously, the security document 1 is based on fibrous material, in particular paper, plastic material or a combination of these materials.

[0082] Preferably, a white material forms the basis of the security document 1, the white material being, for example, fibrous material, paper, plastic material or a combination of these materials.

[0083] Security document 1 is preferably made from cotton paper, with or without chemical pulp, cellulose-based paper or any other material containing fibers of different types and weights, including at least some synthetic fibers. A hybrid support combining polymer(s) and paper may also be used.

[0084] Security document 1 includes at least one security element 2.

[0085] Preferably, the security element 2 is a security thread, a patch, a film or a security strip.

[0086] Advantageously, the security element 2 is at least partially integrated into the security document 1 or is reported on the security document 1, the security pattern(s) that this security element 2 comprises however not having been shown here.

[0087] Preferably, the security element 2 is partially incorporated into the security document 1.

[0088] Advantageously, the security element 2 emerges at the level of the front face 10 of the security document 1, in the form of windows F. The areas of the security element 2 which are integrated into the security document 1 and are therefore not completely visible, unlike the windows F, have been identified by the letter P, as shown in FIG. 1.

[0089] Thus, an observer can observe the security element 2 from the front face 10 of the security document 1.

[0090] Figure 2 represents a first embodiment of a security element 2.

[0091] The security element 2 is multi-layered. The security element 2 thus comprises a translucent layer of colored ink 15. The security element 2 also comprises a support layer 17 that is at least partially, preferably completely, transparent or translucent. The security element 2 further comprises a layer of variable reflection relief microstructures 19. The security element further comprises a layer 21 comprising plasmonic particles, preferably a layer 21 of plasmonic ink. Advantageously, the layer 21 comprising plasmonic particles, preferably the layer 21 of plasmonic ink, comprises plasmonic particles and a binder. Advantageously, the binder is set or dried. In other words, for example after the plasmonic particles have been added and mixed with the binder, the binder is capable of being set or dried subsequently by oxidative means or by polymerization initiated by ultraviolet radiation.

[0092] Preferably, the layer 21 comprising plasmonic particles, preferably the layer 21 of plasmonic ink, is such that its color seen in transmitted light is different from its color seen in reflected light.

[0093] Advantageously, the layer 21 comprising plasmonic particles, preferably the layer 21 of plasmonic ink, is configured to obtain a “one-way mirror” effect, that is to say that it is reflective when seen in reflected light and semi-transparent when seen in transmitted light. More precisely, the security element 2 comprises an upper face 12 and a lower face 13 between which are superimposed in this order, from the upper face 12 to the lower face 13:

[0094] - a translucent layer of colored ink 15,

[0095] - a support layer 17 at least partially, preferably totally, transparent or translucent,

[0096] - a layer of raised microstructures with variable reflection 19 so as to define a variable optical effect depending on the angle of observation and / or illumination from the upper face 12,

[0097] - a layer 21 comprising plasmonic particles, preferably a layer 21 of plasmonic ink.

[0098] An observer can observe the security element 2 from the upper face 12 of the security element 2, with a variable observation angle, for example by tilting said security element.

[0099] Advantageously, the upper face 12 of the security element 2 and the front face 10 of the security document 1 are coplanar.

[0100] Preferably, the translucent layer of colored ink 15 has an optical density measured in reflection less than or equal to 0.6.

[0101] Advantageously, the support layer 17 is a plastic film, preferably based on PET, abbreviation for polyethylene terephthalate. Advantageously, the layer of variable reflection relief microstructures 19 is transparent or translucent, preferably transparent.

[0102] Preferably, the variable reflection relief microstructure layer 19 is an embossed varnish layer.

[0103] Preferably, the variable reflection relief microstructure layer 19 is free of any metallic element. In other words, the variable reflection relief microstructure layer 19 is not a metallic structure, it does not comprise any metal.

[0104] Advantageously, the plasmonic ink layer 21 comprises pigments formed from nanoparticles chosen from the group of transition or post-transition metals, preferably silver. Alternatively, the plasmonic ink layer 21 comprises pigments larger than nanoparticles but having a nanostructured support coated with a layer of metal or coated with nano-agglomerates of metal and where the metal is chosen from the group of transition or post-transition metals, preferably aluminum.

[0105] Preferably, the nanoparticles have a maximum dimension of between 15 nm and 1000 nm.

[0106] Advantageously, the security element 2 comprises at least one detectable layer, preferably “machine readable”. Thus, the security element 2 comprises one or more optional detectable layers, in particular “machine readable”.

[0107] Preferably, the layer 21 comprising plasmonic particles, preferably the layer 21 of plasmonic ink, is detectable, in particular “machine readable”.

[0108] Advantageously, the security element 2 also comprises a layer of opaque ink 23. Preferably, the layer of opaque ink 23 is arranged below the layer 21 comprising plasmonic particles, preferably the layer 21 of plasmonic ink.

[0109] Advantageously, the security element 2 also comprises an additional support layer 25. Preferably, the additional support layer 25 is translucent or opaque.

[0110] Preferably, the complementary support layer 25 is translucent. Preferably, the complementary support layer 25 is arranged below the layer 21 comprising plasmonic particles which is preferably the layer 21 of plasmonic ink, and is preferentially arranged below the opaque still layer 23, as shown in FIG. 2.

[0111] Alternatively, the complementary support layer 25 is opaque. When the complementary support layer 25 is opaque, it notably comprises at least one transparent region preferably partially superimposed on, notably marked with, preferably entirely superimposed on, an opening in the opaque ink layer 23.

[0112] Advantageously, the additional support layer 25 is a plastic film, preferably based on PET, abbreviation for polyethylene terephthalate.

[0113] Preferably, the complementary support layer 25 is coated with an adhesive composition 27 on one face facing the support layer 17. The assembly formed by the complementary support layer 25 and the adhesive composition 27 can be replaced by a layer of opaque ink, for example reflective, in particular metallic and preferably silver or white.

[0114] Preferably, the complementary support layer 25 is colored, in particular in mass.

[0115] Advantageously, the security element 2 comprises a translucent or transparent, preferably transparent, protective layer. Preferably, the protective layer is the complementary support layer 25 or an ink or varnish.

[0116] Preferably, the security element 2 comprises at least one sealing layer 29, preferably transparent.

[0117] Preferably, the sealing layer 29 is a layer of heat-activatable adhesive.

[0118] For example, said at least one sealing layer 29 is a layer of thermoadhesive (or thermoactivatable adhesive), intended for the definitive securing of the security element 2 in and / or on the security document 1.

[0119] Said at least one sealing layer 29 preferably constitutes an external surface of the security element 2. Preferably, the security element 2 comprises two sealing layers 29 arranged on its upper and lower surfaces respectively. Thus, advantageously, the security element 2 comprises at least one sealing layer 29 forming the upper face 12 and a second sealing layer 29 forming the lower face 13.

[0120] Advantageously, as shown in Figure 2, the security element 2 comprises, successively superimposed, from the upper face 12 to the lower face 13:

[0121] - a sealing layer 29, preferably transparent, forming the upper face 12,

[0122] - the translucent layer of colored ink 15,

[0123] - the support layer 17 at least partially, preferably totally, transparent or translucent,

[0124] - the layer of raised microstructures with variable reflection 19 so as to define a variable optical effect depending on the angle of observation and / or illumination from the upper face 12,

[0125] - layer 21 comprising plasmonic particles, preferably layer 21 of plasmonic ink,

[0126] - a layer of opaque ink 23,

[0127] - an additional support layer 25,

[0128] - a sealing layer 29, preferably transparent, forming the lower face 13.

[0129] Figure 3 represents a second embodiment of a security element 2. The security element 2 according to this second embodiment is distinguished from the security element 2 according to the first embodiment previously described mainly in that the opaque ink layer 23 comprises a region at least partially devoid of opaque ink 33.

[0130] Advantageously, the translucent layer of colored ink 15 comprises a region at least partially devoid of colored ink 35.

[0131] The region at least partially devoid of opaque ink 33, respectively the region at least partially devoid of colored ink 35, is also called “openwork”.

[0132] Advantageously, the region at least partially devoid of opaque ink 33 is completely devoid of opaque ink.

[0133] Preferably, the at least partially opaque ink-free region 33 forms a recognizable pattern.

[0134] Advantageously, the at least partially ink-free region 35 is completely ink-free. Preferably, the at least partially ink-free region 35 forms a recognizable pattern.

[0135] Advantageously, the region at least partially devoid of colored ink 35 is at least partially superimposed on, in particular marked with, preferably entirely superimposed on, the region at least partially devoid of opaque ink 33. Preferably the patterns formed respectively by the regions at least partially devoid of colored and opaque ink are identical in shape and size.

[0136] Figure 4 represents a third embodiment of a security element 2. The security element 2 according to this third embodiment is distinguished from the security element 2 according to the second embodiment previously described mainly in that the translucent layer of colored ink 15 comprises a plurality of colored regions.

[0137] Advantageously, a first colored region 15a is of a first color and a second colored region 15b is of a second color, the second color being different from the first color.

[0138] Advantageously, the region at least partially devoid of colored ink 35 is at least partially superimposed with the region at least partially devoid of opaque ink 33.

[0139] Preferably, the at least partially ink-free region 35 is superimposed with the at least partially ink-free region 33 such that viewed orthogonally from the upper face 12, the at least partially ink-free region 35 is contained within the at least partially ink-free region 33.

[0140] Figure 5 represents a fourth embodiment of a security element 2. The security element 2 according to this fourth embodiment is distinguished from the security element 2 according to the third embodiment previously described mainly in that the layer 21 comprising plasmonic particles, preferably the layer 21 of plasmonic ink, comprises a region at least partially devoid of plasmonic particles, preferably of plasmonic ink 37. The region at least partially devoid of plasmonic particles, preferably of plasmonic ink 37, is also called "openwork". Advantageously, the region 37 at least partially devoid of plasmonic particles, preferably of plasmonic ink, is completely devoid of plasmonic particles, preferably of plasmonic ink.

[0141] Preferably, the region 37 at least partially devoid of plasmonic particles, preferably plasmonic ink, forms a recognizable pattern.

[0142] Advantageously, the region 37 at least partially devoid of plasmonic particles, preferably of plasmonic ink, is at least partially superimposed on, in particular marked with, preferably entirely superimposed on, the region at least partially devoid of colored ink 35.

[0143] Preferably, the region 37 at least partially devoid of plasmonic particles, preferably of plasmonic ink, is at least partially superimposed on, in particular marked with, preferably entirely superimposed on, the region at least partially devoid of opaque ink 33.

[0144] Preferably, the region 37 at least partially devoid of plasmonic particles, preferably of plasmonic ink, is entirely superimposed on a part of the region at least partially devoid of colored ink 35 and on a part of the region at least partially devoid of opaque ink 33.

[0145] Thus, the region 37 at least partially devoid of plasmonic particles, preferably of plasmonic ink, is superimposed with the region at least partially devoid of opaque ink 33 and with the region at least partially devoid of colored ink 35 such that seen orthogonally from the upper face 12, the region 37 at least partially devoid of plasmonic particles, preferably of plasmonic ink, is contained in the region at least partially devoid of colored ink 35 and in the region at least partially devoid of opaque ink 33, and preferably, the region at least partially devoid of colored ink 35 is contained in the region at least partially devoid of opaque ink 33.

[0146] Advantageously, as shown in Figure 5, the layer 21 comprising plasmonic particles, preferably the layer 21 of plasmonic ink, comprises a plurality of regions comprising plasmonic particles, preferably a plurality of regions of plasmonic ink.

[0147] Preferably, a first region 21a comprising plasmonic particles, preferably a first region 21a of plasmonic ink, is such that a first color seen in transmitted light is different from a first color seen in reflected light and a second region 21b of plasmonic particles, preferably a second region 21b of plasmonic ink, is such that a second color seen in transmitted light is different from a second color seen in reflected light, the first color seen in reflected light being different from the second color seen in reflected light and the first color seen in transmitted light being different from the second color seen in transmitted light.

[0148] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art. In particular, it is possible to combine the embodiments with each other.

Claims

1. A security element (2) for a protected document (1), wherein said security element (2) is multi-layered and has an upper surface (12) and a lower surface (13), between which, in the specified order, from the upper surface (12) to the lower surface (13), the following layers are located: translucent layer (15) of colored paint, a substrate layer (17) that is at least partially, preferably completely, transparent or translucent, a layer (19) of relief microstructures with variable reflection, designed to create an optical effect that changes depending on the viewing angle and / or illumination from the upper surface (12), and a layer (21) containing plasmonic particles, preferably a layer (21) of plasmonic paint.

2. The security element (2) according to claim 1, which comprises a layer (23) of opaque paint located under a layer (21) containing plasmonic particles.

3. The security element (2) according to claim 2, in which the layer (23) of opaque paint comprises a region (33) which is at least partially free of opaque paint, wherein said region (33) is preferably completely free of opaque paint.

4. A security element (2) according to one of claims 1-3, wherein the translucent layer (15) of coloured paint comprises an area (35) which is at least partially free of coloured paint, wherein said area (35) is preferably completely free of coloured paint.

5. The security element (2) according to claim 3, in which the translucent layer (15) of coloured paint comprises a region (35) which is at least partially free of coloured paint, wherein said region (35) is preferably completely free of coloured paint, wherein the region (35) which is at least partially free of coloured paint is at least partially, preferably completely superimposed on the region (33) which is at least partially free of opaque paint, in particular, aligned with said region (33).

6. The security element (2) according to one of claims 1-5, wherein the layer (21) containing plasmonic particles comprises a region (37) at least partially free of plasmonic particles, wherein said region (37) is preferably completely free of plasmonic particles.

7. The security element (2) according to claim 5, wherein the layer (21) containing plasmonic particles comprises a region (37) at least partially free of plasmonic particles, wherein said region (37) is preferably completely free of plasmonic particles, wherein the region (37) at least partially free of plasmonic paint is at least partially, preferably completely, superimposed on a region (35) at least partially free of coloured paint, in particular, aligned with said region (35), and the region (37) at least partially free of plasmonic paint is at least partially, preferably completely, superimposed on a region (33) at least partially free of opaque paint, in particular, aligned with said region (33).

8. A security element (2) according to one of claims 1-7, wherein the translucent layer (15) of colored paint has colored areas, wherein the first colored area (15a) is an area colored in a first color, and the second colored area (15b) is an area colored in a second color, wherein the second color differs from the first color.

9. The security element (2) according to one of claims 1-8, wherein the layer (21) containing plasmonic particles contains regions containing plasmonic particles, among which there is a first region (21a) containing plasmonic particles, which is made in such a way that the first color visible in transmitted light differs from the first color visible in reflected light, and a second region (21b) containing plasmonic particles, which is made in such a way that the second color visible in transmitted light differs from the second color visible in reflected light, wherein the first color visible in reflected light differs from the second color visible in reflected light, and the first color visible in transmitted light differs from the second color visible in transmitted light.

10. A protective element (2) according to one of claims 1-9, which comprises at least one transparent protective layer (29), preferably a transparent protective layer (29) forming an upper surface (12), and a transparent protective layer (29) forming a lower surface (13).

11. The security element (2) according to one of paragraphs 1-10, in which the layer (21) containing plasmonic particles is designed with the possibility of recognition, in particular, machine-readable.

12. A protective element (2) according to one of paragraphs 1-11, which comprises the following layers superimposed on each other and extending sequentially from the upper surface (12) to the lower surface (13): a protective layer (29), preferably transparent, forming the upper surface (12), translucent layer (15) of colored paint, transparent or translucent layer (17) of the substrate, a layer (19) of relief microstructures with variable reflection, designed with the possibility of creating an optical effect that changes depending on the viewing angle and / or illumination from the upper surface (12), a layer (21) containing plasmonic particles, preferably a layer (21) of plasmonic paint, layer (23) of opaque paint, additional layer (25) of the substrate, a protective layer (29), preferably transparent, forming the lower surface (13).

13. A secure document (1), preferably a valuable document, characterized in that it contains at least one security element (2) according to one of paragraphs 1-12.

14. The secure document (1) according to claim 13, wherein the security element (2) is at least partially integrated into the secure document (1) or attached to the secure document (1).

15. A secure document (1) according to paragraph 13 or 14, which is made on the basis of a fibrous material, in particular paper, plastic or a combination of these materials.