Optically visible safety components, manufacture of such components and safety documents equipped with such components

Description

Domaine technique de l'invention

[0001] This description relates to the field of security marking. More particularly, it relates to optical security components visible in reflection for verifying the authenticity of a document, to a method of manufacturing such a component and to a secure document equipped with such a component. État de la technique

[0002] There are many known technologies for the authentication of documents or products, and in particular for the security of documents such as valuable documents, documents such as banknotes, passports or other identification documents. These technologies aim at the production of security optical components whose optical effects, depending on the observation parameters (orientation of the component relative to the observation axis, position and dimensions of the light source, etc.), take on very characteristic and verifiable configurations. The general purpose of these optical components is to provide new and differentiated optical effects, from physical configurations that are difficult to reproduce. Among these components, DOVID stands for "Diffractive Optical Variable Image Device", the optical components producing diffractive and variable images that are commonly called holograms.

[0003] It is known, for example, to generate an effect consisting of a dynamic variation of an optical effect, for example in the form of movement in a given direction of a luminous and / or colored area, sometimes called a "rolling bar" or "rolling bar" according to the Anglo-Saxon expression, the movement resulting from a rotation (tilt) of the component. An observer can then observe a luminous and / or colored area which moves along an image when he rotates the component, which constitutes an additional authentication control.

[0004] Such dynamic optical effects featuring "rolling bars" are for example described in the published patent application WO2015154943 [Ref. 1] in the name of the applicant. A security optical component described in the aforementioned application has an effect visible in reflection. The security optical component comprises a diffractive structure etched on a layer of a dielectric material. The structure has a first pattern comprising a bas-relief with a first set of facets whose shapes are determined to simulate a series of concave or convex cylindrical optical elements, visible in reflection, this first pattern being modulated by a second pattern forming a subwavelength grating.Such an optical security component presents a dynamic visual effect of light strips of different colors scrolling in opposite directions when it undergoes tilt rotation around an axis parallel to one of the main directions of the cylindrical elements.

[0005] More complex dynamic visual effects than those shown in [Ref. 1], such as the crossing of two line segments “moving” in the same direction at different speeds or in opposite directions, and / or the movement of an oblique line segment, are described in published patent application WO2018224512 [Ref. 2] in the name of the applicant.

[0006] To achieve these dynamic visual effects, the optical security component described in [Ref. 2] comprises a first layer of dielectric material and a diffractive structure etched on the first layer. The diffractive structure comprises a first pattern with a set of modules arranged side by side, according to a given arrangement direction, a maximum width of each module, defined in the arrangement direction, being less than 300 µm. Each module comprises a bas-relief with a first set of facets whose shapes are determined to simulate an optical element visible in reflection, with at least one convex or concave region, said optical element having a profile with a continuously variable slope according to a single direction, called the slope variation direction, perpendicular to the arrangement direction.Furthermore, for two modules arranged side by side, the slope along at least one line parallel to the arrangement direction is different between said two modules. The minimum number of modules is determined by the maximum width of the modules, such that the diffractive structure is visible to the naked eye.

[0007] Such an optical security component presents, in reflection and under the effect of a tilt movement around an axis parallel to said arrangement direction, a dynamic visual effect comprising the movement of one or more complex graphic elements, depending on the arrangement of said modules, and allows, compared to simple horizontal scrolling bars, more secure authentication and a stronger technological barrier, due to the design and manufacture of the modules necessary to obtain the visual effect described above.

[0008] Furthermore, the first pattern can be modulated by a second pattern forming a periodic network of sub-wavelength period, determined to produce, after deposition of a second layer having a reflection spectral band in the visible, a resonant filter in a given spectral band, making it possible to combine the dynamic visual effect with a colored effect of order 0.

[0009] WO 03 / 084764 [Ref. 4] describes a security element with optically active structures. In at least one region with dimensions greater than 0.4 mm, the optically active structures comprise a diffraction structure formed by the additive or subtractive overlap of an overlap function (M) describing a macroscopic structure with a relief profile (R), for example a diffraction grating, the overlap function (M) being slowly variable relative to the relief profile (R). When the security element is tilted, in exemplary embodiments, continuously moving visible color bands are observed.

[0010] The present application describes an optical security component with an original structure allowing not only access to complex dynamic visual effects or "animations" as described in [Ref. 2] but also allowing continuous switching from an achromatic, white animation to the same iridescent animation, by a simple tilt movement of the optical security component over a wider angular range, ensuring even more robust authentication, by simple visual control and without specific equipment. Résumé de l'invention

[0011] In this description, the term "comprise" means the same as "include", "contain", and is inclusive or open and does not exclude other elements not described or shown. Furthermore, in this description, the term "approximately" or "substantially" means the same as "having a margin less than and / or more than 10%, for example 5%", of the respective value.

[0012] According to a first aspect, the invention relates to an optical security component according to claim 1.

[0013] In the present description, a layer transparent in the visible range is defined as a layer having a transmission of at least 70%, preferably at least 80% for a wavelength included in the visible range, i.e. a wavelength between approximately 400 nm and approximately 800 nm. A layer thus transparent makes it possible to observe with the naked eye the layers located under the transparent layer.

[0014] In this description, a set of "parallel" facets is a set of facets having a variation in slope in a single direction, called the "direction of variation of the slope". The slope of the facets can, however, vary in this direction, in opposite directions.

[0015] The "height" of a facet is a distance between a lowest level of the facet and a highest level, the distance being measured along an axis perpendicular to a plane of the component.

[0016] A rotation of the component along an axis contained in the plane of the component is generally called a "tilt movement" of the component.

[0017] The applicant has shown that such an optical security component exhibits, in reflection and under the effect of a simple tilt movement around an axis perpendicular to the direction of variation of the slope, a dynamic visual effect or achromatic, reflective and brilliant “animation” around the specular reflection, then the same iridescent animation which is linked with the achromatic animation on either side of the first part of the tilt angular range. Such an effect allows for more secure authentication and a stronger technological barrier, due to the design and manufacture of the component necessary to obtain the visual effect described above.

[0018] Specular reflection in this description corresponds to the position of the component which allows a reflection of the incident light with an angle of reflection of opposite measurement to that of the incident angle. In other words, the normal to the plane of the component separates the angle of observation into two angular sectors of the same measurement.

[0019] The observation angle is, for example, defined relative to a vertical lighting direction. According to one or more exemplary embodiments, the observation angle is between approximately 30° and approximately 60°. For example, the observation angle is equal to approximately 45°, which corresponds, for vertical lighting, to a conventional observation position for an observer.

[0020] According to one or more exemplary embodiments, said minimum angular value of the slopes (in absolute value) is equal to 0°.

[0021] According to one or more examples, said maximum angular value of the slopes (in absolute value) is between approximately 7° and approximately 15°.

[0022] By convention, in this description, the positive direction for measuring the angular values ​​of the slopes of the facets is the clockwise (or anti-trigonometric) direction.

[0023] According to one or more examples, the facets have a dimension in the direction of the slope (or “width”) greater than or equal to approximately 4 times, advantageously greater than or equal to approximately 8 times, said period of the grating. The minimum dimension may therefore be chosen according to the period of the grating. For example, a minimum dimension of the width of the facets is equal to approximately 2 µm.

[0024] According to one or more examples, the widths of the facets are between approximately 2 µm and approximately 100 µm, advantageously between approximately 2 µm and approximately 80 µm, advantageously approximately 4 µm and approximately 80 µm.

[0025] According to one or more examples, the facets have a substantially rectangular shape and have a "length" measured in a direction perpendicular to the direction of the slope. The length is for example less than about 100 µm.

[0026] According to one or more examples, all of the facets have a substantially identical height. The height of the facets is, for example, less than 2 microns, advantageously less than 1 micron.

[0027] According to one or more examples, the facets of the set of facets have different heights. In this case, however, the facets have a maximum height. Said maximum height is, for example, less than 2 microns, advantageously less than 1 micron.

[0028] According to one or more exemplary embodiments, at least a portion of the facets of the set of facets are arranged with variable slopes, the variation of which is increasing, respectively decreasing, in order to simulate a reflective element with a convex, respectively concave region. In the present description, the visual effect resulting from such an arrangement of facets will be referred to as a "half-wave" type dynamic effect when the slopes of the facets have angular values ​​whose variation is increasing or decreasing, but which are of the same sign. The visual effect resulting from such an arrangement of facets will be referred to as a "wave" type dynamic effect when the slopes of the facets have angular values ​​whose variation is increasing or decreasing, and for which at least one change of sign is observed.A dynamic effect of the "wave" or "half-wave" type appears to an observer, during a tilt movement of the component, as a continuous scrolling of a line of white light.

[0029] According to one or more exemplary embodiments, the set of facets comprises one or more subsets of facets each configured to produce a dynamic “wave” type effect.

[0030] According to one or more observation examples, said period of the diffraction grating, said maximum angular value of the slopes, measured in absolute value, and said observation angle are determined such that said first part of the tilt angular range comprises an angular superposition (overlap) with the second part of the tilt angular range of between approximately 1° and approximately 10°, preferably between approximately 3° and approximately 8°, for example equal to approximately 5°, on either side of the first part of the angular range. By thus designing the optical security component according to the present description, an uninterrupted sequence of the iridescent animation with the achromatic animation is ensured on either side of said first part of the tilt angular range. In a limiting case, however, the angular superposition may be zero as long as there is continuity between the achromatic animation and the iridescent animation.

[0031] According to one or more observation examples, said period of the diffraction grating, said maximum angular value of the slopes, measured in absolute value, and said observation angle are determined such that the tilt angular range is between approximately 45° and approximately 120° (measured in air).

[0032] According to one or more observation examples, said period of the diffraction grating, said maximum angular value of the slopes, measured in absolute value, and said observation angle are determined such that the first part of the tilt angular range is between approximately 15° and approximately 50° (measured in air), advantageously between approximately 20° and approximately 35° (measured in air).

[0033] According to one or more exemplary embodiments, said period of the diffraction grating, said maximum angular value of the slopes, measured in absolute value, and said observation angle are determined such that the second part of the tilt angular range (measured in air) is comprised, on either side of the first tilt angular range, between approximately 30° and approximately 70°, advantageously between approximately 40° and approximately 60°.

[0034] According to one or more exemplary embodiments, said one-dimensional diffraction grating is a sinusoidal profile diffraction grating. A sinusoidal profile grating is advantageous in that it allows symmetry of the diffraction efficiencies at orders +1 and -1 and therefore, symmetry in terms of visual efficiency for the iridescent animation on either side of the achromatic animation. However, other grating profiles are possible, such as, for example and in a non-limiting manner, a diffraction grating with a pseudo-sinusoidal profile, defined as a sum of sinusoids with amplitudes and phases adjustable according to the expected profile, a diffraction grating with a rectangular profile, or any other advantageously symmetrical profile grating to have similar visual efficiency for the iridescent animation on either side of the achromatic animation.

[0035] According to one or more exemplary embodiments, a depth of the diffraction grating is determined so as to optimize a diffraction efficiency of the grating at order 1 and at order -1 at at least one wavelength of the visible spectrum, for example at a central wavelength of the visible spectrum, for example around 550 nm.

[0036] According to one or more exemplary embodiments, the second layer comprises a metallic material. The metallic material comprises one of the materials or an alloy of materials chosen from: Aluminum (Al), Silver (Ag), Chromium (Cr), Gold (Au), Copper (Cu). For example, a thickness of the layer of metallic material is greater than approximately 2 to 3 times the skin thickness of the metal or alloy from which it is formed in the visible frequency range; for example, a thickness of the layer of metallic material is between approximately 20 nm and approximately 60 nm for aluminum.

[0037] According to one or more exemplary embodiments, the dielectric material of the first layer has a first refractive index and the second layer comprises a dielectric material having a second refractive index such that the difference between the second refractive index and the first refractive index is greater than or equal to approximately 0.3, advantageously greater than or equal to approximately 0.5. For example, said second layer comprises a material chosen from: zinc sulfide (ZnS), titanium dioxide (TiO 2 ) silicon nitride (Si 3 N 4 ).

[0038] Generally speaking, the material from which the second layer is formed makes it possible to give the component a spectral band of reflection in the visible and to make said first diffractive structure visible. Such materials suitable for said second layer are described for example in patent US4856857 [Ref. 3].

[0039] According to one or more exemplary embodiments, a minimum dimension of the first structure is greater than 300 µm, preferably greater than 1 mm, preferably greater than 2 mm, preferably greater than 5 mm. Such a minimum dimension makes it possible to make the structure visible to the naked eye.

[0040] According to one or more exemplary embodiments, said first structure has an outline forming, seen from the observation face, a recognizable graphic shape.

[0041] According to one or more exemplary embodiments, the optical security component according to the first aspect comprises at least a second structure etched on said first layer, said second layer at least partially covering said second structure. The second structure is configured to form, for example and in a non-limiting manner, a diffusing structure, a holographic structure, a diffracting structure making it possible to produce a so-called Alphagram ® effect developed by the applicant.

[0042] Where the component includes at least one second structure, the structures may be juxtaposed, each with recognizable shapes.

[0043] According to one or more exemplary embodiments, said first pattern has an outline forming, seen from the observation face, a recognizable graphic shape.

[0044] According to one or more exemplary embodiments, said first pattern is interrupted in regions forming, seen from the observation face, a recognizable graphic object visible during the achromatic animation and during the iridescent animation.

[0045] According to one or more exemplary embodiments, in at least a second region, said first pattern is not modulated or is modulated by a third pattern forming a periodic network different from said second pattern, said second region forming, seen from the observation face, a recognizable graphic object visible only during the iridescent animation.

[0046] It is thus possible to generate a “visual scenario” using graphic objects which appear either during the two animations (achromatic and iridescent) or only during the iridescent animation.

[0047] According to one or more exemplary embodiments, the optical security component according to the first aspect comprises one or more additional layers depending on the needs of the application, without this or these additional layers contributing to the desired visual effect.

[0048] Thus, according to one or more exemplary embodiments, the optical security component is configured for securing an object, for example a document or a product, and further comprises, on the face opposite the observation face, a layer suitable for transferring the component onto the document or the product, for example an adhesive layer or a reactivatable adhesive layer.

[0049] According to one or more exemplary embodiments, the optical security component further comprises, on the side of the first observation face, a support film intended to be detached after transfer of the component onto the document or product.

[0050] According to one or more exemplary embodiments, the optical security component is configured for the manufacture of a security track for securing banknotes, and comprises on the side of the first observation face and / or on the face opposite the first observation face, one or more protective layers.

[0051] According to a second aspect, the present description relates to a secure object, for example a secure valuable document, comprising a substrate and an optical security component according to the first aspect, deposited on said substrate or on one of the layers of said substrate in the case of a multilayer substrate.

[0052] Such a secure object is, for example, and without limitation: a banknote, an identity or travel document, on a paper or polymer substrate.

[0053] According to a third aspect, the present description relates to methods of manufacturing security optical components according to the first aspect.

[0054] Thus, the present description relates to a method of manufacturing an optical security component according to claim 14. Brève description des figures

[0055] Other characteristics and advantages of the invention will appear on reading the description which follows, illustrated by the following figures: There FIG. 1A , schematically illustrates a (partial) sectional view of an exemplary embodiment of a component according to the present description. FIG. 1B , schematically illustrates a (partial) sectional view of another exemplary embodiment of a component according to the present description. FIG. 2 , diagrams illustrating parameters of a diffractive structure in a security component according to the present description. FIG. 3 , a diagram illustrating the sequence of iridescent animations and achromatic animation, during a tilt movement of an optical security component according to the present description. FIG. 4A , diagrams illustrating according to an example, a first iridescent animation in a security optical component according to the present description, as a function of the tilt angle of the component, in a first part of the tilt angular range. FIG. 4B , diagrams illustrating, in an optical security component identical to that of the FIG. 4A , an achromatic animation depending on the tilt angle of the component, in a second part of the tilt angular range, the achromatic animation following the first iridescent animation. The FIG. 4C , diagrams illustrating, in an optical security component identical to that of the FIG. 4A , a second iridescent animation depending on the tilt angle of the component, in a third part of the tilt angular range, the second iridescent animation following the achromatic animation and presenting an inversion of the colors with respect to the first iridescent animation. FIG. 5A , curves illustrating respectively: an example of spatial distribution of the widths of the facets, for a given height, in an arrangement of facets configured to produce a dynamic effect of the “half-wave” type; angular values ​​of slopes (in degrees) of facets as a function of the widths of facets, for two heights of facets, in an arrangement of facets configured to produce a dynamic effect of the “half-wave” type; angular values ​​of slopes (in degrees) of facets as a function of the widths of facets, for two heights of facets, in an arrangement of facets configured to produce a dynamic effect of the “wave” type. FIG. 5B , a diagram illustrating an example of the distribution of facets to form “pixels”. The FIG. 5C , curves illustrating the effect of the facet slopes for three component tilt angles located in the first part of the tilt angular range. FIG. 6 , a curve illustrating the effect of the slopes of the facets and of the grating, as a function of the tilt angle of the component, in the second part of the tilt angular range, on either side of the first part of the tilt angular range. FIG. 7 , curves showing the efficiency at order +1 or -1 of a sinusoidal profile diffraction grating, as a function of the grating depth, for a wavelength of 550 nm. FIG. 8 , an example of an optical security component according to the present description, with a “patch” type format. The FIG. 9A , a diagram illustrating an example of a valuable document, for example a banknote, secured with an optical security component according to the present description. FIG. 9B , a diagram showing an enlargement of the secure document illustrated on the FIG. 9A . There FIG. 10A , diagrams respectively illustrating designs of a first pattern and a second pattern in an exemplary security optical component according to the present disclosure. FIG. 10B , diagrams illustrating according to a given visual scenario, achromatic and iridescent visual animations, based on the patterns as schematized on the FIG. 10A . Description détaillée

[0056] In the figures, the elements are not shown to scale for better visibility. FIG. 1A and the FIG. 1B schematically represent, in (partial) sectional views, two examples of optical security components according to the present description. The optical security component 101 shown in the FIG. 1A represents for example an optical security component intended to be transferred onto a document or a product for the purpose of securing it. According to this example, it comprises a support film 111, for example a film made of polymer material, for example a polyethylene terephthalate (PET) film of a few tens of micrometers, typically 15 to 100 µm, as well as a detachment layer 112, for example made of natural or synthetic wax. The detachment layer makes it possible to remove the polymer support film 111 after transfer of the optical component onto the product or document to be secured. The optical security component 101 further comprises a first layer 113 made of dielectric material, having a first refractive index n 1 and at least one first diffractive structure S, comprising a first pattern M 1 , modulated by a second pattern M 2 forming a periodic grating, stamped on said first layer 113 and which will be described in more detail later.

[0057] In the example of the FIG. 1A , the optical security component 101 also comprises a second layer 114 at least partially covering said first structure S, and having a spectral band of reflection in the visible. The second layer 114 is for example a metallic layer or a so-called index variation layer having a refractive index different from that of the first, the difference in index between the layers 113 and 114 having a value at least equal to 0.3, advantageously a value at least equal to 0.5. The layer 114 makes it possible to ensure the reflection of the incident light.

[0058] The optical security component also includes one or more optional layers, not optically functional but adapted to the application.

[0059] For example, in the example of the FIG. 1A , the optical security component further comprises an adhesive layer 117, for example a heat-reactivatable adhesive layer, for transferring the optical security component onto the product or document.

[0060] In practice, as will be detailed later, the optical security component can be manufactured by stacking the layers on the support film 111, then the component is transferred onto a document / product to be secured using the adhesive layer 117. Optionally, the support film 111 can then be detached, for example by means of the detachment layer 112. The main observation face 100 of the optical security component is thus located on the side of the first layer 113 opposite the etched face of the layer 113.

[0061] The optical safety component 102 shown in the FIG. 1B represents for example an optical security component intended for securing banknotes; it is for example a part of a security thread intended to be integrated into the paper during the manufacture of the note or a laminated track covering a window in the paper or a patch. In this example, the component 102 comprises as previously a support film 111 (12 to 25 µm) which will also serve as a protective film for the security thread, and, as in the example of the FIG. 1A , a first layer 113 of dielectric material having a first refractive index n 1 , at least one first diffractive structure S, stamped on said first layer 113, and a second layer 114 at least partly covering said first structure S, and having a spectral band of reflection in the visible. The optical security component 102 further comprises, in the example of the FIG. 1B , a set of optional layers 115, 116, 118. The layer 115 (optional) is for example a layer of dielectric material 115, for example a transparent layer; the layer 116 (optional) is for example a security layer 116, for example a discontinuous layer with a specific pattern printed locally with a UV ink to produce a complementary marking that can be checked by eye or by machine; and the layer 118 (optional) is for example a protective layer, for example a second polymer film or a varnish. In the case of a laminated track, the layer 118 may be an adhesive layer. As in the previous example, the manufacturing may be carried out by stacking the layers on the support film 111. The dielectric layer 115 and the security layer 116 may form only one layer. The protective layer (or adhesive layer) 118 and the layer 115 may also form a single layer.

[0062] It will be apparent to those skilled in the art that other optically non-functional layers may be added depending on the needs of the application in each of the examples shown in the FIGS. 1A et 1B and that the implementation variants presented on the FIGS. 1A et 1B can be combined.

[0063] Note that if the additional, optically non-functional layers, for example layer 117, or layers 115, 116, 118, are transparent, as well as the destination support, the optical security component may be visible from both sides, with an inversion of the curvatures of the optical elements generated.

[0064] There FIG. 2 illustrates in more detail the parameters of a diffractive structure S (diagram 23) according to the present description. The structure S is formed of a first pattern M 1 comprising a set of facets F i (diagram 22), said pattern being at least partially modulated by a second pattern M 2 defined by the projection of a diffraction grating to a direction referenced G (diagram 21) and defined in a plane π parallel to the plane of the component (and therefore parallel to the observation face 100).

[0065] All the facets Fi are parallel, that is to say they present a variation of the slope in a single and same direction, referenced y in the example of the FIG. 2 They are characterized by a height h, defined by the distance between a lowest level of the facet and a highest level, the distance being measured along an axis perpendicular to the plane π parallel to the plane of the component, namely along the z axis in the example of the FIG. 2 . In the example of the FIG.2 , the facets all have the same height h, said height being less than approximately 2 µm, advantageously less than approximately 1 µm, for example between approximately 0.5 µm and approximately 1 µm.

[0066] The facets are also characterized by a width A, defined by the dimension along the direction y of variation of the slope, the width generally being comprised for example between approximately 2 µm and approximately 100 µm, for example between approximately 2 µm and approximately 80 µm, for example approximately 4 µm and approximately 80 µm. Advantageously, a minimum width of the facets will be greater than approximately 4 times, advantageously greater than approximately 8 times, the period of the grating.

[0067] The facets generally have a roughly rectangular shape. The dimension of the facets along the x axis included in a plane xy (π plane) parallel to the plane of the component and perpendicular to the y axis, called "length" in this description, defines the width of a pixel, that is to say an elementary region of the structure which reflects the light in the same direction. In general, we will seek to ensure that the length is less than approximately 100 µm, advantageously less than 60 µm, so as not to be visible to the eye.

[0068] The facets F i include slopes whose angular values ​​α i are included, in absolute value, between a minimum angular value, for example 0° and a maximum angular value, for example between approximately 7° and approximately 15°. As illustrated in the

[0069] FIG. 2 , in the present description, the positive direction chosen for the measurement of the angular values ​​of the slopes is the clockwise or anti-trigonometric direction.

[0070] As illustrated in Figure 21, the diffraction grating G is a one-directional diffraction grating, characterized by a pitch or period d and a depth t. We note k g the network vector which is collinear to the direction y of variation of the slope and whose modulus is equal to 2π / d .

[0071] As can be seen in diagram 23 of the FIG. 2 , the structure S resulting from the modulation of the first pattern comprising all the facets by the diffraction grating G, comprises a set of facets F i each supporting a one-dimensional diffraction grating G i .

[0072] In the component according to the present description, the facets F i each have an angle α relative to the plane π parallel to the plane of the component. i . The projection on each facet F i of a diffraction grating G of constant pitch dand whose network vector has a direction collinear with the direction y of variation of the slope can result in a projected network G i of variable pitch, referenced d Mi in diagram 23. The slopes of the facets having low angular values, typically less than 15° in absolute value, we can neglect in most of the examples of realization, the effect of these variations of the network pitch on the different facets.

[0073] In the example of the FIG. 2 , diagram 21, the diffraction grating G at order 1 has a sinusoidal profile. Other profiles are possible, such as a quasi-sinusoidal profile, defined as a sum of sinusoids with amplitudes and phases adjustable according to the expected profile, or a rectangular profile. Such symmetrical profiles have the advantage of having a diffraction efficiency similar to order + 1 and order -1. By symmetrical grating profile, we mean a grating whose profile has a central symmetry (with respect to a point).

[0074] Once the structure S has been determined by defining the first and second patterns, the structure recording process can be carried out for the purpose of manufacturing the optical security components, as will be described in more detail later.

[0075] In an optical security component according to the present description, the period d of the diffraction grating, the angular valueα maximum of the slopes, measured in absolute value, and the observation angle are determined to observe an achromatic animation in a first part of the angular tilt range around the specular reflection, and to observe the same animation, iridescent, in a second part of the angular tilt range, the iridescent animation being linked with the achromatic animation on either side of said first part of the angular tilt range.

[0076] There FIG. 3 shows a diagram illustrating the desired sequence of iridescent animations and achromatic animation, during a tilt movement of an optical security component 40 according to the present description.

[0077] We note Δ L the lighting axis, for example vertical lighting corresponding to natural light, we note Δ O the observation axis corresponding to the direction of observation by an observer (symbolized by an eye on the FIG. 3 ) and θ obs the observation angle between the axes Δ L and Δ O . In the rest of the description, we assimilate θ obs to the absolute value of the angular measurement of the observation angle.

[0078] In operation, when checking the authenticity of a secure document using an optical security component conforming to the present description, the latter undergoes a rotation (tilt) around a tilt axis Δ contained in the plane of the component and substantially perpendicular to the direction of variation of the slope. The tilt axis is therefore substantially parallel to the x axis ( FIG. 2 ).

[0079] In operation, the lighting and observation directions are fixed and the tilt movement of the component results in a variation of the angle of incidence θi of the light incident on the component, defined with respect to an axis Δ N normal to the plane of the component. By convention, in the present description, the positive direction of the angle of incidence is the trigonometric direction. As will be described in more detail later, the variation of the angle of incidence θi results in a variation of the angle θ o of the light diffracted by the structure S comprising the first pattern M 1 modulated by the second pattern M 2 (see FIG. 2 ) such as θ o = θ i - θ obs Or θ obs is taken as an absolute value. The diffraction angle θ o is thus defined by the angle between the normal to the component and the direction of observation Δ O . By convention, in the present description, the positive direction of the diffraction angle is, as for the angle of incidence, the trigonometric direction. On the diagram of the FIG. 3 , the optical security component 40 is represented in a central position for which the normal axis Δ N perpendicular to the plane of the component cuts the observation angle θ obs into two angular sectors of the same measurement (specular reflection position for which θ o = - θi).

[0080] As illustrated on the FIG. 3 , we seek to observe an achromatic animation in a first part Δθ B of an angular tilt range Δθ tilt , the first part Δθ B of the angular tilt range being located around the specular reflection. We also seek to observe the same animation, iridescent, in a second part of the angular tilt range, the iridescent animation being linked with the achromatic animation on either side of said first part of the angular tilt range. Thus, as illustrated in the FIG. 3 , the second part of the tilt angular range comprises an angular range Δθ R- and an angular range Δθ R+ corresponding respectively, from the point of view of an observer, to a tilt of the optical safety component backwards or forwards.

[0081] Iridescent animation is a "rainbow" animation in which an observer sees the colors of the rainbow scroll by. For the sake of simplification, in the figures, only 4 colors of the rainbow are represented, symbolized by textures, namely red (texture 311), yellow (texture 312), green (texture 313), blue (texture 314).

[0082] THE FIGS 4A - 4C illustrate in more detail an example of a visual dynamic effect obtained with an optical security component according to the present description.

[0083] The optical security component comprises in this example two diffractive structures according to the present description, a structure 401 forming a number “2” and a structure 402 forming a number “5”. The diffractive structures have contours delimited for example by demetallization, or more generally by localized removal of the reflective layer or in other embodiments, due to a delimitation of the structure itself.

[0084] There FIG. 4B illustrates the achromatic animation effect in the first tilt angular range referenced Δθ B on the FIG. 3 . More precisely, diagram 44 corresponds to the position of the optical safety component 40 referenced 4 on the FIG. 3 , diagram 45 corresponds to the position of the optical safety component 40 referenced 5 on the FIG. 3 (central position corresponding to specular reflection), diagram 46 corresponds to the position of the optical safety component 40 referenced 6 on the FIG. 3 . On the FIG. 4B , achromatic animation includes for example a movement of circular white lines on a black background.

[0085] There FIG. 4A illustrates the iridescent animation effect in the second part of the tilt angular range referenced Δθ R+ on the FIG. 3 and which corresponds, from the observer's point of view, to a tilt movement of the component towards the front. More precisely, diagram 41 corresponds to the position of the optical safety component 40 referenced 1 on the FIG. 3 , diagram 42 corresponds to the position of the optical safety component 40 referenced 2 on the FIG. 3 , diagram 43 corresponds to the position of the optical safety component 40 referenced 3 on the FIG. 3 . On the FIG. 4A , each color is illustrated by a texture similar to that used on the FIG. 3 .

[0086] There FIG. 4C illustrates the iridescent animation effect in the second part of the tilt angular range referenced Δθ R- on the FIG. 3 and which corresponds, from the observer's point of view, to a tilt movement of the component towards the rear. More precisely, diagram 47 corresponds to the position of the optical safety component 40 referenced 7 on the FIG. 3 , diagram 48 corresponds to the position of the optical safety component 40 referenced 8 on the FIG. 3 , diagram 49 corresponds to the position of the optical safety component 40 referenced 9 on the FIG. 3 . On the FIG. 4C , each color is illustrated by a texture similar to that used on the FIG. 3 .

[0087] So, as illustrated on the FIGS 4A - 4C , we observe a dynamic achromatic visual effect around the specular reflection which, as explained in more detail below, results from the arrangement of the facets forming the first pattern and we observe on both sides the same dynamic but iridescent visual effect, with a parade of rainbow-type colors.

[0088] As also detailed below, the iridescent effect results from diffraction at orders +1 and -1 of the grating (respectively for the tilt angular ranges Δθ R+ and Δθ R- ) which modulates the facets.

[0089] The iridescent animation is chained on either side of the chromatic animation. In the example of FIGS 4A - 4C , we can thus define two particular angles of incidence, respectively θ T +< (diagrams 43 and 44) ​​and θ T -< (diagrams 46 and 47) which correspond to the transition angles of incidence between respectively the achromatic animation and the iridescent animation at order +1 and the achromatic animation and the iridescent animation at order -1.

[0090] Note that as is visible on the FIGS 4A And 4C , we observe an inversion of the colors between the two angular tilt ranges Δθ R+ and Δθ R- . In other words, the facets which diffract, for example, from red towards the observer in the angular range Δθ R+ diffract from blue in the angular range Δθ R- .

[0091] We now describe the design steps of the structure, and in particular the choice of parameters as illustrated in the FIG. 2 , to obtain a dynamic visual effect according to the present description and illustrated for example on the FIG. 3 and the FIGS 4A - 4C .

[0092] To access the dynamic visual effects described above, we start by determining the structure of the first pattern, i.e. the positions of the facets, their dimensions and the slopes of the facets to obtain the desired achromatic animation in the first part of the tilt angular range (Δθ B on the FIG. 3 ).

[0093] There FIG. 5A shows an example of spatial distribution of facet widths to produce a dynamic effect (diagram 51) as well as diagrams illustrating the angular values ​​of the facet slopes as a function of width, as a tool for designing the first pattern in a security optical component according to the present description to construct the desired animation.

[0094] More specifically, diagram 51 represents a curve 510 illustrating, in a first arrangement of facets configured to produce a dynamic effect, the spatial distribution of the widths of the facets along the axisy of variation of the slope (see FIG. 2 ). As illustrated in diagram 51, the variation of the widths is decreasing, which translates at constant height h of the facets by a continuous and increasing variation of the angular values ​​of the slopes, with the aim of simulating a concave reflective element.

[0095] For example, Figure 51 illustrates a decreasing continuous variation that follows a mathematical curve that can be written as a y + b , where a and b are the fitting parameters of the function. Note that other functions can be used.

[0096] In practice, the variation of the widths and angles of the facets includes discrete values ​​chosen according to the size of the diffractive structure. Thus, for example, if we seek to produce a "wave" type effect in a region of given dimension, we can choose a larger number of facets in a larger region and the dynamic effect will be more fluid and continuous.

[0097] In practice, we can choose, for a height h given facets, facet widths as a function of the desired facet angles.

[0098] Diagram 52 thus represents angular values ​​of slopes (in degrees) of the facets as a function of the facet widths, for two facet heights, namely 1 µm (curve 521) and 0.5 µm (curve 522), for a facet arrangement configured to form a dynamic effect equivalent to that of a concave optical element. As shown in diagram 52, the width of the facets is decreasing, which results, at constant height, in an increasing variation in the angular value of the slope of the facets.

[0099] Similarly, diagram 53 shows angular values ​​of slopes (in degrees) of the facets as a function of the facet widths, for two facet heights, namely 1 µm (curve 531) and 0.5 µm (curve 532), for a facet arrangement configured to form a dynamic “wave” (convex) type effect. As shown in diagram 53, the width of the facets is increasing then decreasing, which results, at constant height, in a decreasing variation of the angular value of the slope of the facets, then increasing.

[0100] The facets of variable angle and width as described on the FIG. 5A are used to design the first pattern of the structure which will generate the achromatic animation in the first angular range of tilt Δθ B .

[0101] Each of the facets considered allows light to be returned towards a given direction depending on the slope of the facet and according to a precise angular distribution. At a fixed angle of incidence, the facets participating in the movement ("active" facets) are those whose response allows energy to be returned in the Δ direction O (i.e. towards the observer handling the document). Thus, when the document is tilted in the first part of the tilt angular range Δ θ B , the “active” facets will appear white (on) while the other facets will appear black (off).

[0102] To obtain the optical effect shown in FIG. 3 Or 4A - 4B , we first define the observation angle θ obs equal to the absolute value of the angle between the lighting direction Δ L , for example a vertical lighting direction, and the observation direction Δ O . For example, the observation angle θ obs is between about 30° and about 60° in air. For example, the observation angle is equal to about 45° in air.

[0103] The achromatic animation in the first part of the tilt angular range is defined based on the maximum slope (in absolute value) of the facets α max , namely Δ θ B,n 1 = 2 | α max | where Δ θ B,n 1 is defined in the first layer (113, FIGS 1A, 1B ) of refractive index n 1 . In air, this angular range is larger and corresponds to Δθ B = arcsin ( n 1 sin (2| α max |)). For example, for a refractive index value n 1 =1.5 and a value α max = 7.1°, the first part of the angular range measured in air Δ θ B is worth 21.5°.

[0104] To determine the facets participating in the dynamic graphic visual effect, the optical response of each of the facets is studied for a given illumination defined by the tilt of the sample. The optical response of a facet of width A and depth h is obtained by calculating the Fourier transform TF of the phase shift Δϕ undergone by a light ray incident on the optical security component with an angle θ i The phase shift Δϕ is expressed by: Δϕ = exp 4 πn 1 j λ h . y Λ ; y ∈ 0 Λ

[0105] Or λ is a central working length of the visible range, for example 550 nm, n 1 is the index of the first layer of dielectric material (113, FIG. 1A et FIG. 1B ), h is the height of the facets. The optical response of the facet is expressed as: TF ν = ∫ 0 Λ Δϕ e − i 2 πνy dy

[0106] Or vis the spatial frequency given by: ν = 2 πn 1 λ sin θ i .

[0107] Using this formalism, we can predict the distribution and direction maximizing the energy returned to order 0 by each of the facets for a given tilt angle, which allows us to design the first pattern of the structure to produce the desired animation. In white light, the optical response of the slope facets α i corresponds to a diffractive lobe obtained by considering the envelope of the amplitude of the diffracted orders for wavelengths ranging from 400 nm to 800 nm. The diffractive lobe of a facet with a slope angle α i is centered on the angular position θ o = -θ i + 2. α i .

[0108] Examples of diffractive lobes are shown on the FIG. 5B where three scenarios were modeled. Each case corresponds to a different tilt of the document. The angle of incidence θ i (angle defined between the direction Δ N normal to the plane of the component and the lighting direction of the light source Δ L ) is therefore also distinct. This angle takes the value 7.68° (diagram 57), 15° (diagram 58), and 21.8° (diagram 59).

[0109] In each of these cases, the diffractive lobes of three facets are represented: Two opposite facets with angles -7.1° and 7.1° corresponding to a width of 8 µm and a depth of 1 µm (respectively curves 502 and 503) and a central facet with a substantially zero angle (curve 501) corresponding to a width of 80µm and a depth of 1µm.

[0110] Note that the smaller the width of the facets, the more the diffractive lobe is angularly extended, which results in a broadening of the reflected beam.

[0111] Diagram 58 represents the central position for which the normal axis Δ N perpendicular to the plane of the component intersects the observation angle Δ θ obs in two angular sectors of the same measurement (specular reflection position), namely θ i = - θ o .

[0112] In this case, it is the facets with a substantially zero slope angle that allow light to be returned to the eye (specular reflection), the direction of observation by an observer handling the document being symbolized by an eye in diagram 58 (curve 501). Thus, the facets with a substantially zero slope angle will appear "active". The diffractive lobes 502 and 503 return energy outside the observation axis, the corresponding facets will appear extinguished.

[0113] By tilting the sample from side to side, the angle of incidence θ i is modified and the diffractive lobes are translated by a value of Δ θ i corresponding to the variation of the angle θ i suffered following a tilt of the sample.

[0114] Note that the sample tilt angles and the incidence angle are distinct due to the refraction of light undergone following the change in the air / n 1 index interface.

[0115] Diagram 57 corresponds to lighting with an angle of incidence of 7.68°, in this case the facet which participates in the achromatic animation is the one whose diffractive lobe is returned towards the direction Δ O . In particular, the facet participating in the visual effect in diagram 57 is the facet with angle -7.1° (curve 502). The direction of observation by an observer is symbolized by an eye.

[0116] When the sample is tilted to the other side of the central position, with an angle of incidence of 21.8°, it is the opposite angle facet with a slope of +7.1° that lights up (diagram 59).

[0117] The first pattern can therefore be conceived by a spatial arrangement of facets of variable slopes, the facets being determined to return the light energy in the direction of the observer, for a given angle of incidence which corresponds to a given tilt angle.

[0118] As an illustration, the FIG. 5C represents a diagram of an arrangement of facets F i in a region of the structure used to form the digit "2" ( FIG. 4A - 4C ).

[0119] We can define "pixels" Pi as spatial regions containing one or more adjacent facets of the same width and the same slope angle. In practice, a pixel can have a rectangular shape with at least one dimension less than 100 µm, advantageously less than about 60 µm so as not to be visible to the eye. Of course, other pixel shapes can be considered. Each "pixel" forms a luminous point for a given tilt angle of the component. We can thus create the achromatic animation as illustrated in the FIG. 4B .

[0120] We now describe how to choose the parameters of the diffractive diffraction grating G at order +1 and -1 to obtain a sequence of the achromatic animation with iridescent animations on either side of the first part Δθ B of the tilt angular range.

[0121] In addition to the achromatic animation, the same facets modulated by the G-grating generate an iridescent animation in a second part of the tilt angular range.

[0122] The grating parameters have an impact on the sequence of both achromatic and iridescent animations. Thus, we can choose the period d of the diffraction grating according to the angular value α maximum of the slopes, measured in absolute value, and of the observation angle to observe an achromatic animation in a first part of the angular tilt range around the specular reflection, and to observe the same animation, iridescent, in a second part of the angular tilt range, the iridescent animation being linked with the achromatic animation on either side of said first part of the angular tilt range.

[0123] More precisely, we determine that to obtain a sequence between the achromatic and iridescent animations, the period d of the network G advantageously respects the following condition: d = λ VIS n 1 sin θ obs , n 1 − sin θ T , n 1 − − 2 α max Or : θ T , n 1 − = θ obs , n 1 2 − α max is the angle of incidence of transition between the achromatic and iridescent animations in the medium of index n 1 , namely the transition between positions 6 and 7 of the optical security component 40 as referenced on the FIG. 3 taking into account the air / n 1 refraction, and: θ obs , n 1 = arcsin sin θ obs / n 1

[0124] Moreover, λ VIS is the wavelength with which we want to start the iridescent animation, for example λ VIS is between about 400 nm and about 450 nm.

[0125] This condition follows directly from the grating formula according to which the direction of the diffracted order + / -1 would correspond to the direction of observation Δ O and where the angle of incidence on the network corresponds to the transition angle between the two angular ranges of tilt calculated with respect to the normal of the facet of maximum slope angle.

[0126] For example, considering | α max | = 7.1°, n 1 = 1.5, θ obs = 45° and λ vis =450 nm, we calculate θ obs , n 1 = 28.1 ° et θ T , n 1 − = 6.9 ° .

[0127] In this case, to ensure the sequence as described previously, d is chosen equal to 502 nm by applying the equation defined above.

[0128] Note that it is possible, by playing on the value of the period and the maximum slope of the facets, to define a strictly positive angular range of overlap between the first angular range (achromatic animation) and the second angular range (iridescent animation).

[0129] For example, we define an overlap range Δθ rec in the case of choosing a period d 2 of the diffraction grating. Δ θ Rec = arcsin n 1 sin θ 2 − θ T , n 1 − where the angle of incidence θ 2 corresponds to the start of the iridescent animation if a period d 2 of the network G was chosen instead of the optimal period for which the overlap is zero: θ 2 = arcsin sin θ obs , n 1 − λ vis n 1 d 2 + 2 α max

[0130] For example, using the parameters of the previous example, considering a period d 2 =520nm, the angle θ 2 in this case is 8.1° and therefore the coverage range in the air in this case is Δ θ rec = 1.8°.

[0131] As an illustration, the FIG.6 describes the diffracted wavelengths (orders +1 and -1) by different facets modulated by the G grating, returned towards the Δ direction O as a function of the angle of incidence, when the component is illuminated with white light according to the lighting direction Δ N . Curves 61, 62, 63, 64 and 65 correspond respectively to facets of angles -7.1°, -3.55°, 0°, +3.55° and +7.1°, overmodulated by a grating of period 520 nm. The curves are calculated by exploiting the equation giving d above, where λ vis is replaced by the diffracted wavelength and d by the period chosen for the diffractive grating G.

[0132] The total tilt angular range is divided into 3 angular ranges, an iridescent animation range Δ θ R- corresponding to diffraction of order -1, an achromatic animation range of tilt Δ θ B around the specular reflection and a second iridescent animation range Δ θ R + corresponding to diffraction of order +1.

[0133] At a fixed angle of incidence θ i , each of the facets modulated by the G grating diffracts a different wavelength in the direction of observation. This wavelength depends on the slope specific to each facet. The chromatic dispersion generated by the different facets modulated by the G grating follows the same graphic pattern previously defined on the first tilt range.

[0134] Moreover, as can be seen on the FIG. 6 , facets with a given slope diffracting a given wavelength to order +1 diffract another wavelength to order -1, which produces an inversion of the colors during the iridescent animation on either side of the achromatic animation.

[0135] In addition to the choice of the period, we can choose the depth t of the network G ( FIG. 2 ) so as to optimize the diffraction efficiency of + / -1 orders, as illustrated in the FIG. 7 . More precisely, on the FIG. 7 , curves 70, 71, 72 and 73 illustrate the efficiency curve of the grating at order -1 as a function of the grating depth for four grating periods, namely 400 nm, 460 nm, 520 nm, 580 nm respectively for an incident light wavelength corresponding to 550 nm. This curve makes it possible to optimize the value of the depth of the diffraction grating G. For example, for a grating G with a period of 520 nm, a depth t of 150 nm can be chosen to have a maximum diffraction efficiency at order 1 and -1.

[0136] Examples of optical security components for securing valuable documents are illustrated by means of the FIG. 8 And 9A, 9B .

[0137] There FIG. 8 represents an example of an optical security component of the “patch” or stamp type according to the present description, for example a label, the patch being configured to be fixed for example on a banknote or a product.

[0138] In this example, the optical security component comprises a stack of layers, for example a stack of layers as illustrated in the FIG. 1B , layer 118 then being able to be an adhesive layer.

[0139] The security optical component comprises a first diffractive structure etched in the first layer (113, FIG. 1B ) and delimited by the contour referenced 81 on the FIG. 8 , this first diffractive structure being in accordance with the present description for generating an achromatic dynamic visual effect in a first tilt angular range and the same dynamic visual effect, but iridescent, in tilt angular ranges on either side of the first tilt angular range. The optical security component further comprises other structures delimited by the contours 82, 83 and 84. These may be, for example, diffusing structures, holographic structures or diffracting structures making it possible to produce so-called Alphagram ® effects. In this example, a reflective layer (114, FIG. 1B ), for example a metallic or high index layer, may be applied over the entire component, with regions 81, 82, 83, 84 being distinguished only by differences in the structure etched in the first layer.

[0140] There FIG. 9A represents a diagram illustrating an example of a valuable document 900, for example a banknote, secured with an optical security component 91 according to the present description and the FIG. 9B represents a diagram showing an enlargement of the secure document illustrated in the FIG. 9A .

[0141] More specifically in this example, the optical security component comprises a stack of layers, for example a stack of layers as illustrated in the FIG. 1A , the layer 117 being able to be for example a layer of heat-reactivatable adhesive, for the transfer of the optical security component onto the support of the banknote 900.

[0142] The security optical component 91 comprises a first diffractive structure etched in the first layer (113, FIG. 1B ) and delimited by the outline in the shape of a “2” referenced 911 on the FIG. 9A as well as a second diffractive structure etched in the first layer and delimited by the “5” shaped contour referenced 912. These two diffractive structures are diffractive structures in accordance with the present description for generating an achromatic dynamic visual effect in a first tilt angular range and the same dynamic visual effect, but iridescent, in tilt angular ranges on either side of the first tilt angular range. As illustrated in the FIG. 9B , the animations resulting from the two diffractive structures can present different patterns.

[0143] Furthermore, as also appears on the FIG. 9B , the second (reflective) layer is locally non-existent to allow regions 915 to appear in which the support of the banknote on which the optical security component is fixed appears. Thus in this example, the reflective layer (114, FIG. 1A ) does not completely cover the diffractive structure.

[0144] Finally, as is also visible on the FIG. 9B (diffractive structures with contours 911, 912), the first pattern forming said diffractive structure may have regions 918 in which there is no modulation with the first-order grating. These regions will not be perceptible when the optical security component undergoes a tilt movement in the first angular range (achromatic animation) but will appear black to an observer when the optical security component undergoes a tilt movement in the angular tilt ranges on either side of the first angular tilt range. It is thus possible to offer additional protection with a message that only appears in large tilt angles, during the iridescent animation.

[0145] Similarly, the 918 regions could be modulated by a second grating different from the first grating, for example a second grating of order 1 with pitch and / or orientation different from those of the first grating so as either to cause a spectral shift of the iridescence to appear, or to allow azimuthal control in the case where the orientation is different from the direction of the first grating of order 1 which modulates the rest of the first pattern.

[0146] The optical safety component illustrated on the FIGS 9A, 9B further comprises another structure delimited by the contour 913. This may be, for example, a diffractive structure comprising a set of facets as described in the present description but not modulated by a diffraction grating. Thus, the region 913 will present to an observer a dynamic achromatic visual effect. It is for example possible to calculate the angular tilt range of the region 913 to observe an achromatic animation over the entire angular tilt range over which the animations of the regions 911 and 912 are visible. In this way, it will be possible to simultaneously observe achromatic and iridescent animations in the component. More precisely, it will be possible to simultaneously observe the sequence of achromatic and iridescent animations on a region in a tilt range while the neighboring region undergoes only an achromatic animation for this same tilt range.Furthermore, in the diffractive structure forming region 913, partial demetallization (or local removal of the reflective layer) is also possible to reveal regions 915 in which the support of the security document can be seen.

[0147] THE FIGS. 10A et 10B illustrate an example of an original “visual scenario”, obtained by means of an example of an optical security component according to the present description.

[0148] There FIG. 10A thus illustrates diagrams 1001 and 1002 respectively illustrating designs of a first pattern and a second pattern.

[0149] As illustrated in diagram 1001, the first pattern 1012 comprises a set of facets arranged according to the present description to produce, when the component is illuminated with white light along the lighting axis Δ L , a dynamic visual effect observable in reflection under the effect of a tilt movement and in the given tilt angular range Δθ tilt . The first pattern is delimited in this example by a disc and interrupted in regions 1011, the regions 1011 forming a first recognizable graphic object, here the outline of a bulb and a base of the bulb.

[0150] Diagram 1002 symbolizes the second pattern 1022, i.e. a network of order 1 (network G, FIG. 2 ) which modulates the first pattern. It is present throughout the first pattern except in regions 1021 which correspond on the one hand to regions 1011 in which there is no first pattern but also to additional regions which form a second recognizable graphic object, in this example a bulb filament and light rays.

[0151] There FIG. 10B shows diagrams illustrating, according to the predefined visual scenario, the achromatic and iridescent visual animations obtained thanks to the patterns as schematized on the FIG. 10A .

[0152] In the achromatic animation illustrated in diagram 1201, in the first part of the tilt angular range, an achromatic animation 1003 is observed over the entire component except at locations 1011 in which there is no first pattern. An observer therefore sees the outline of a bulb and the base during the achromatic animation (first graphic object).

[0153] The animation continues in the second part of the tilt angle range but in an iridescent way thanks to the presence of the first diffractive grating of order 1, except at the locations corresponding to regions 1011 (no first pattern) and 1021 (no first pattern or second pattern). An observer thus sees the filament and the rays (second graphic object) appear during the iridescent animation, in addition to the outline of the bulb and the base.

[0154] The resulting structure thus produces a blinking scenario during tilt between the first and second parts of the tilt angular range. In the proposed example, during the animation, the observer perceives a light bulb that "turns on" during the iridescent animation and "turns off" during the achromatic animation, the whole being visible on an animated disc-shaped background.

[0155] Examples of methods for manufacturing optical security components according to the present description are now described.

[0156] A first step comprises the design of said at least one first diffractive structure according to the methods described above, and any other structures.

[0157] Next comes the step of recording an original copy, also called an optical master. The optical master is, for example, an optical medium on which the structure(s) are formed.

[0158] The optical master can be formed by state-of-the-art electronic or optical lithography methods.

[0159] For example, according to a first embodiment, the optical master is produced by etching a resist sensitive to electromagnetic radiation using an electron beam. In this exemplary embodiment, the structure having the first pattern modulated by the second pattern can be etched in a single step.

[0160] According to another embodiment, an optical lithography (or photolithography) technique can be used. The optical master is in this example a photosensitive resin plate and the origination step is carried out by one or more exposures of the plate by projections of masks, of the phase mask type and / or of the amplitude mask type, followed by development in an appropriate chemical solution. For example, a first exposure is carried out by projection of amplitude masks whose transmission coefficients are adapted so that, after development, a relief corresponding to the first pattern is formed, in the regions in which the first pattern is provided. Then, a second global exposure is carried out, according to interference photolithography methods known to those skilled in the art, a diffraction grating

[0161] (diffraction grating G, FIG. 2 ) corresponding to the second pattern is recorded at least in first regions in which the second pattern is provided. Similar steps can be provided to generate other reliefs, such as for example a second diffraction grating in other regions. The order of formation of the patterns is arbitrary and can be modified. Subsequently, the development step is carried out. In this way, an optical master comprising a structure which results from the first pattern modulated by the second pattern is obtained after development.

[0162] The step of metallic copying of the optical master can then be carried out, for example by electroplating, as mentioned above, in order to obtain the metallic matrix or "master". According to a variant, a step of matrix duplication of the metallic master can be carried out to obtain a large-scale production tool suitable for replicating the structure in industrial quantities.

[0163] The manufacture of the optical security component then includes a replication step. For example, the replication can be carried out by stamping (by hot embossing of the dielectric material) of the first layer 113 ( FIGS. 1A, 1B ) made of dielectric material with a refractive index of n 1 , for example a low index layer, typically a stamping varnish a few microns thick. The layer 113 is advantageously carried by the support film 111, for example a film of 12 µm to 100 µm made of polymer material, for example PET (polyethylene terephthalate). The replication can also be done by molding the stamping varnish layer before drying then UV crosslinking ("UV casting"). Replication by UV crosslinking makes it possible in particular to reproduce structures having a large depth range and makes it possible to obtain better fidelity in the replication. Generally speaking, any other high-resolution replication method known from the prior art can be used in the replication step.

[0164] Next comes the deposition on the layer thus embossed of all the other layers, for example the reflective layer 114, the layer of dielectric material 115 (optional), the security layer 116 (optional) which can be deposited uniformly or selectively to represent a new pattern and the glue or varnish type layer (117, 118) by a coating process.

[0165] Optional steps known to those skilled in the art are possible, such as partial demetallization of the reflective layer 114.

[0166] Although described through a certain number of exemplary embodiments, the optical security component according to the invention and the method of manufacturing said component comprise different variants, modifications and improvements which will be obvious to those skilled in the art, it being understood that these different variants, modifications and improvements are part of the scope of the invention as defined by the following claims. Références

[0167] Ref. 1: WO2015154943 Ref. 2: WO2018224512 Ref. 3: US4856857 Ref. 4: WO 03 / 084764

Claims

1. An optical security component (101, 102) configured to be viewed in reflection, with the naked eye, from at least a first viewing face (100), in a direction of viewing (ΔO) forming a given viewing angle (θobs) with a given lighting direction (ΔL), the component comprising: - a first layer (113) made of dielectric material, transparent in the visible; - at least a first diffractive structure (S) etched on said first layer; and - a second layer (114), covering said first diffractive structure at least partially, and having a spectral band of reflection in the visible; and wherein: - said first diffractive structure comprises a first pattern (M1) consisting of a set of parallel facets (Fi), said facets having slopes that are variable in a slope variation direction (y), said slopes comprising angular values included, in absolute value, between a minimum angular value (αmin) and a maximum angular value (αmax), said facets having a given maximum height (hm), said set of facets being arranged to produce, when the component is illuminated with white light along said lighting axis, a dynamic visual effect observable in reflection under the effect of a tilting movement along a tilt axis (Δ) substantially perpendicular to the slope variation direction, and within a given angular range of tilting (Δθtilt); - in at least a first region, said first pattern is modulated by a second pattern (M2) forming a periodic grating with a predetermined period (d) dimension of between 450 nm and 650 nm, said grating comprising a grating vector (kg) with a direction collinear with said slope variation direction (y), said grating being determined to produce, after deposition of the second layer, a diffractive effect in reflection at order 1 and at order -1, - said period (d) of the grating, said maximum angular value (αmax) of the slopes and said viewing angle (θobs) being determined to produce, in reflection, an achromatic animation in a first part (ΔθB) of the angular range of tilting around specular reflection, and to produce the same animation, iridescent, in a second part (ΔθR-; ΔθR+) of the angular range of tilting, the iridescent animation being sequenced with the achromatic animation on either side of said first part of the angular range of tilting.

2. The optical security component as claimed in claim 1, wherein said first part (ΔθB) of the angular range of tilting comprises an angular superposition with the second part of the angular range of tilting of between approximately 1° and approximately 10° on either side of the first part (ΔθB) of the angular range.

3. The optical security component as claimed in any one of the preceding claims, wherein said given viewing angle (θobs) is between approximately 30° and approximately 60°.

4. The optical security component as claimed in any one of the preceding claims, wherein said minimum angular value of the slopes is equal to 0°.

5. The optical security component as claimed in any one of the preceding claims, wherein said maximum angular value of the slopes is between approximately 7° and approximately 15°.

6. The optical security component as claimed in any one of the preceding claims, wherein the set of facets have a substantially identical height.

7. The optical security component as claimed in any one of the preceding claims, wherein the set of facets comprises one or more subsets of facets each configured to produce a dynamic effect of "wave" type.

8. The optical security component as claimed in any one of the preceding claims, wherein the second layer comprises a metal material.

9. The optical security component as claimed in any one of claims 1 to 7, wherein the dielectric material of the first layer has a first refractive index (n1) and the second layer comprises a dielectric material having a second refractive index (n2) such that the difference between the second refractive index (n2) and the first refractive index (n1) is greater than or equal to approximately 0.3.

10. The optical security component as claimed in any one of the preceding claims, wherein said first pattern has a contour (911, 912) forming, when seen from the viewing face, a recognizable graphical shape.

11. The optical security component as claimed in any one of the preceding claims, wherein said first pattern is interrupted in regions (1011) forming, when seen from the viewing face, a recognizable graphical object visible during the achromatic animation and during the iridescent animation.

12. The optical security component as claimed in any one of the preceding claims, wherein in at least a second region (918, 1021), said first pattern is not modulated or is modulated by a third pattern forming a periodic grating different from said second pattern, said second region forming, when seen from the viewing face, a recognizable graphical object visible only during the iridescent animation.

13. A secure object, for example a secure valuable document, comprising a substrate and an optical security component as claimed in any one of the preceding claims, deposited on said substrate.

14. A method for manufacturing an optical security component intended to be viewed in reflection, with the naked eye, along a viewing face, the method comprising: - depositing, on a support film, a first layer made of dielectric material, transparent in the visible; - forming, on said first layer, at least a first diffractive structure (S), such that: - said first diffractive structure comprises a first pattern (M1) consisting of a set of parallel facets (Fi), said facets having slopes that are variable in a slope variation direction (y), said slopes comprising angular values included, in absolute value, between a minimum angular value (αmin) and a maximum angular value (αmax), said facets having a given maximum height (hm), said set of facets being arranged to produce, when the component is illuminated with white light along said lighting axis, a dynamic visual effect observable in reflection under the effect of a tilting movement along a tilt axis (Δ) substantially perpendicular to the slope variation direction, and within a given angular range of tilting (Δθtilt); - in at least a first region, said first pattern is modulated by a second pattern (M2) forming a periodic grating with a predetermined period (d) dimension of between 450 nm and 650 nm, said grating comprising a grating vector (kg) with a direction collinear with said slope variation direction (y), said grating being determined to produce, after deposition of the second layer, a diffractive effect in reflection at order 1 and at order -1, - depositing a second layer, covering said first diffractive structure at least partially, and having a spectral band of reflection in the visible, wherein - said period (d) of the grating, said maximum angular value (αmax) of the slopes and said viewing angle (θobs) are determined to produce in reflection, after deposition of said second layer, an achromatic animation in a first part (ΔθB) of the angular range of tilting around specular reflection, and to produce the same animation, iridescent, in a second part (ΔθR-; ΔθR+) of the angular range of tilting, the iridescent animation being sequenced with the achromatic animation on either side of said first part of the angular range of tilting.