Optical safety components, manufacturing of such components and safety-critical objects equipped with such components

Abstract

The invention relates to a safety optical component comprising: a first layer (313) of dielectric material, a second reflective layer (314) forming a reflective interface with said first layer in at least a first region. The reflective interface comprises a first optical structure (S) resulting from the sum of a first microstructure (321) and a second microstructure (322).The first microstructure consists of first elementary surfaces (I1) and second elementary surfaces (I2), at least the first elementary surfaces (I1) following the profile of a first matrix (ML1) of cylindrical microlenses arranged along a first arrangement direction (ΔL), the first microstructure being configured to exhibit, upon reflection and under the effect of a tilt movement around an axis perpendicular to said first arrangement direction, a micro-image displacement effect by Moiré effect; the second microstructure is configured to reflect incident light at normal incidence anisotropically, mainly in a plane orthogonal to a principal axis (Δ) substantially parallel to said first arrangement direction. Fig. 3A.

Description

Title of the invention: Optical security components, manufacture of such components and secure objects equipped with such components. Technical field of the invention

[0001] This description relates to the field of security marking. More particularly, it relates to optical security components for verifying the authenticity of an object, for example, a product or a valuable document, such as an identity document or a banknote. This description also relates to a method for manufacturing such a component and to a security object equipped with such a component. In particular, this description relates to optical security components for verifying the authenticity of an object by observation in reflection, with the naked eye. State of the art

[0002] Numerous technologies are known for authenticating documents or products, and in particular for securing documents such as valuables, banknotes, passports, or other identification documents. These technologies aim to produce security optical components whose optical effects, depending on the observation parameters (orientation of the component relative to the positions of the source and the observer, tilt and / or azimuth orientation of the component, etc.), take on highly characteristic and verifiable configurations. The general purpose of these optical components is to provide novel and differentiated optical effects from physical configurations that are difficult to reproduce. Among these components, DOVID stands for "Diffractive Optical Variable Image Device," referring to optical components that produce diffractive and variable images commonly known as holograms.

[0003] Among these components, optical components for the authentication of documents or products are known, including microlens arrays for the magnification of micro-images by Moiré effect.

[0004] A safety optical component comprising such microlens arrays is described, for example, in US7738175 [Ref. 1]. The safety optical component comprises a periodic arrangement of microlenses in two directions with a first step, the microlenses defining a focal plane. The optical component further comprises a corresponding periodic arrangement of microimages, also arranged in two directions with a second step, the microimages being located in a plane close to the focal plane of the microlenses, and separated from the plane of the microlenses by a substrate forming an optical separator. As explained For example, in the article by MC Hutley et al. [Ref. 2], a magnification effect of the microimages is visible to an observer when the step ratio differs from 1, even very slightly, or when the microlens and microimage arrangements are rotated relative to each other. This magnification is known as Moiré magnification. Furthermore, when the component is tilted around an axis parallel to one of the directions of the focusing element arrangement, an observer perceives different portions of the microimages, resulting in visual image shift effects.

[0005] Such a 3-layer arrangement (upper microlens layer, optical separator, lower layer supporting the microimages) nevertheless presents several drawbacks.On the one hand, the manufacturing process for such a component requires very precise relative positioning of the microlenses and micro-images, which can lead to reproducibility problems. On the other hand, the minimum thickness of the resulting optical security component is on the order of a few tens of microns, which is in itself a limitation in the field of security components: indeed, a thick component is more easily manipulated and therefore reusable for counterfeiting; moreover, such thicknesses are not compatible with DOVID-type components, in which the structured layer is much thinner.

[0006] Published patent application US20140367957 [Ref. 3] describes an optical security component with a Moiré magnification effect, in which the traditional 3-layer arrangement is replaced by a structured layer compatible with the manufacturing processes of DOVID-type components.

[0007] Figure 1B reproduces such an optical component. The optical component 10 shown in Figure 1B is designed from a 3-layer arrangement as illustrated in Figure 1A. The 3-layer arrangement illustrated in Figure 1A comprises, as in Ref. 1, a periodic arrangement of microlenses 11, a periodic arrangement of micro-images 12, located in a plane close to the focal plane 14 of the microlenses by means of an optical separator 13. By drawing imaginary cutting lines 15 extending from the ends of the micro-images towards the microlenses (Figure 1A), and by removing from the microlenses 11 "slices" corresponding to the imprints of the micro-images 12, relief features 18 (Figure 1B) characteristic of the micro-images are obtained. The raised elements 18 include microstructures 17 formed from "sections" of microlenses and which therefore have curved external surfaces which follow the profile of the microlenses.As illustrated in [Fig. 1B], the curved external surfaces of the microstructures 17 reflect incident light according to the laws of reflection, in all directions (rays Ri), while the flat surfaces 16 between the microstructures 17 reflect incident light only by specular reflection. From the point of view of an observer, each raised element 18. The resulting structure of a microlens, based on the imprint of a corresponding micro-image, will present a visible point of light illustrated by ray R2 (the dotted ray reflected towards the observer) and corresponding to a portion of the micro-image magnified by the Moiré effect. By tilting the optical component 10, the points of light visible to the observer will originate from other regions of the microstructures 17, leading to the formation of new images for the observer. Thus, the images obtained by the Moiré effect can exhibit, in addition to a magnification effect, dynamic visual effects of movement and other effects resulting from the specific characteristics of the microlenses, such as depth effects.

[0008] The optical component described in [Fig.1B] exhibits effects comparable to those of the components described in [Ref. 1], including a magnification effect by Moiré effect of micro-images and dynamic visual effects when the component undergoes a tilt rotation, but has the advantage in particular of better reproducibility during manufacturing, the micro-image matrix being automatically positioned relative to that of the microlenses and has the advantage of being compatible with the manufacturing processes of DOVID type components.

[0009] More recently, other optical safety components have been described which, like the component illustrated in [Fig. 1B], exhibit visual effects of moiré magnification of micro-images and are compatible with the manufacturing processes of DOVID-type components. Such components are described in EP3694725 [Ref. 4] and EP3470235 [Ref. 5] on behalf of the applicant. Compared to the optical safety component as described in [Ref. 3], an optical safety component as described in [Ref. 4] or [Ref. 5] offers an additional advantage: it allows an observer, when the component undergoes a tilt movement, to observe uninterrupted movement without any contrast disturbance at specular reflection, and therefore, greater ease of control and even more robust authentication.

[0010] Fig. 2A schematically represents, in a top view, a reflective interface of a safety optical component as described in Ref. 4 or Ref. 5. Plane P schematically represents a section plane for the cross-sectional representation of the interfaces as illustrated in Fig. 2B (from Ref. 4) and Fig. 2C (from Ref. 5).

[0011] As illustrated in [Fig. 2A], [Fig. 2B], [Fig. 2C], a safety optical component as described in [Ref. 4] or [Ref. 5] comprises a reflective interface with a first optical structure having first elementary surfaces L and second elementary surfaces I2, the first and second elementary surfaces being complementary in top view. The first surfaces elementary surfaces Ii are curved and follow the profile of a first matrix MLi in one dimension of first identical cylindrical microlenses Li. These curved surfaces are arranged periodically along a first direction AL ([Fig. 2A]), with a first pitch pb. As a reflective interface, such microlenses behave like cylindrical micromirrors. The first elementary surfaces Ii or the second elementary surfaces I2 form, in top view, recognizable and identical micro-images MI, arranged periodically along a second direction and with a second pitch p2. Thus, in the example of [Fig. 2A], the micro-images, here "6", are arranged along a direction A1 collinear with the direction AL of the microlenses Li and with a first pitch p2 different from the pitch pi of the microlens matrix MLh. As illustrated in [Fig.[2A], the first elementary surfaces L and the second elementary surfaces I2 are complementary: if the first elementary surfaces Ii form, in top view, micro-images, for example the "6" shown in [Fig.2A], then the second elementary surfaces I2 form the background, and conversely, if the second elementary surfaces I2 form, in top view, micro-images, for example the "6" shown in [Fig.2A], then the first elementary surfaces Ii form the background.

[0012] In the example of [Fig.2B] ([Ref. 4]), the second elementary surfaces I2 follow the profile of a second matrix ML2 with one dimension of second identical cylindrical microlenses L2, superimposed on the first matrix MLi, the curvature of said second cylindrical microlenses L2 being less than that of said first cylindrical microlenses Lp. Such a safety optical component exhibits, in reflection and under the effect of a tilt movement around an axis perpendicular to the first direction AL, a magnification of the micro-images by Moiré effect and an effect of movement of the enlarged images uninterrupted, that is to say without "accident" of contrast at specular reflection, this effect resulting from the non-zero and different curvatures of the first elementary surfaces and the second elementary surfaces.

[0013] In the example of [Fig. 2C] ([Ref. 5]), the second elementary surfaces I2 follow the same profile as the first one-dimensional MLi matrix of first cylindrical microlenses Lp. The first elementary surfaces Ii are nanostructured so as to form at least one first diffusing structure or at least one first one- or two-dimensional array, while the second elementary surfaces I2 are not nanostructured in the example of [Fig. 2C]. Here again, such a safety optical component exhibits, under the effect of a tilt movement around an axis perpendicular to the first AL direction, a magnification micro-images by Moiré effect and an effect of uninterrupted movement of the enlarged images due to the non-zero curvatures of the first elementary surfaces and the second elementary surfaces which are distinguished by the different nanostructuring.

[0014] The optical components as described in [Ref. 4] and [Ref. 5] have thus shown great ease of control and very robust authentication when observed in reflection, with the naked eye.

[0015] The optical component which is the subject of this description is intended to further facilitate control during authentication. Summary

[0016] According to a first aspect, the invention relates to a safety optical component intended to be observed in reflection, with the naked eye, from at least one observation face, the safety optical component comprising: - a first layer of dielectric material, at least partially transparent in the visible spectrum, exhibiting a first refractive index, - a second reflective layer forming a reflective interface with said first layer in at least a first region, in which: - said reflective interface comprises at least a first optical structure resulting from the sum of a first microstructure and a second microstructure; - the first microstructure consists of first elementary surfaces and second elementary surfaces, in which: - The first elementary surfaces and the second elementary surfaces are complementary in top view, - at least the first elementary surfaces follow the profile of a first one-dimensional matrix of first identical cylindrical microlenses, arranged periodically according to a first arrangement direction, with a first step, a maximum width of said first cylindrical microlenses measured according to said first arrangement direction being less than about 300 sqm; - said first elementary surfaces or said second elementary surfaces form, in top view, recognizable and identical micro-images, arranged periodically along a second direction and with a second step, the first micro-structure being configured to present in reflection and under the effect of a tilt movement around an axis perpendicular to said first direction of arrangement, a displacement effect of said first micro-images by Moiré effect; - the second microstructure is configured to reflect incident light at normal incidence anisotropically, mainly in a plane orthogonal to a principal axis substantially parallel to said first arrangement direction.

[0017] A layer that is "at least partially transparent in the visible" is defined, for the purposes of this description, as a layer having a transmission of at least 70%, preferably at least 80%, for a wavelength within at least one spectral subband of the visible spectrum, i.e., between approximately 400 nm and approximately 700 nm. A layer that is at least partially transparent in this way makes it possible to observe with the naked eye the layers located beneath the at least partially transparent layer.

[0018] In an optical component according to the first aspect, the first elementary surfaces of the first microstructure follow the profile of a first one-dimensional matrix of first cylindrical microlenses. Cylindrical microlenses are defined in this description as segments of cylinders in the broad sense, that is, shapes obtained by translating a curve along a generatrix. The generatrix of the cylinders is perpendicular to said first direction of arrangement of the cylindrical microlenses. The curve can be a portion of a circle, a parabola, or any other shape. A plane of the first microstructure can be defined as a plane parallel to a plane comprising the generatrices of the first cylindrical microlenses.

[0019] According to the present description, the first microstructure consists of first elementary surfaces and second elementary surfaces, in which the first and second elementary surfaces are complementary in top view. For example, the first elementary surfaces form the micro-images in top view, and the second elementary surfaces constitute the background, or vice versa. In all cases, the first microstructure consists of the union of the first and second elementary surfaces.

[0020] According to the present description, the second microstructure is configured to reflect incident light at normal incidence anisotropically; more precisely, the second microstructure is configured to reflect incident light at normal incidence primarily in a plane orthogonal to a principal axis substantially parallel to said first arrangement direction. In this description, "primarily" means that a light beam incident on the second microstructure at normal incidence is reflected into a pyramidal cone whose angular dimension in a direction parallel to the principal axis is very small, i.e., less than about 5°, advantageously less than about 3°.

[0021] A safety optical component according to the first aspect presents, in reflection and under the effect of a tilt movement around an axis perpendicular to said first arrangement direction (or parallel to the generatrix of the cylinders forming said first cylindrical microlenses), a displacement of micro-images by Moiré effect, this as in the state of the art [Ref. 4] and [Ref. 5] in particular.

[0022] Unlike the prior art, however, due to the second microstructure, the observed effect is always visible when the security optical component is tilted around an axis parallel to the first arrangement direction. In other words, if the security optical component undergoes a given rotation around said axis parallel to the first arrangement direction, within a defined angular range on either side of a nominal position, a moiré effect of micro-image displacement will always be observed under the effect of a tilt movement around the axis perpendicular to said first arrangement direction. This property facilitates the control of the effect for an observer and thus makes authentication more robust, particularly with regard to changing lighting conditions.

[0023] Tilt movement about an axis perpendicular to said first arrangement direction means a rotation of the component about said axis. The tilt angle is, for example, + / - 45°, preferably + / - 30°, about a nominal viewing position. The nominal viewing position is defined for observation along a given viewing direction and with a given illumination direction, the illumination direction and the viewing direction being contained in a plane perpendicular to a plane of the component. The component is arranged so as to present a given angle between the normal to the component and the illumination direction, for example, an angle between 30 degrees and 45 degrees broadly.For example, the nominal observation position can be defined for observation under vertical illumination, with the component tilted so as to present a given angle between the normal to the component and the vertical, for example an angle between 30 degrees and 45 degrees broadly.

[0024] According to one or more embodiments, the second reflective layer comprises a metallic layer, for example a layer of Aluminium, Copper, Chrome, Silver or an alloy of these metals.

[0025] According to one or more embodiments, the second reflective layer comprises a layer having a refractive index different from that of the neighboring layers, preferably such that the difference in refractive index values ​​is at least equal to 0.3, advantageously at least equal to 0.5. Such a layer is called a "variation index layer" in the present description.

[0026] In exemplary embodiments, the second reflective layer may include a metallic layer and a refractive index variation layer.

[0027] According to one or more embodiments, the component further has a third encapsulation layer of dielectric material, said second reflective layer being encapsulated between said first layer and said third layer.

[0028] According to one or more embodiments, the second microstructure has a depth between about 50 nm and about 10 pm, advantageously between about 100 nm and about 10 pm.

[0029] According to one or more embodiments, the second microstructure comprises a periodic arrangement of microlenses and / or a set of substantially straight and parallel undulations, and / or a set of facets configured to generate a plurality of cylindrical optical elements.

[0030] According to one or more embodiments, the second microstructure comprises a one-dimensional array of identical cylindrical microlenses arranged periodically at a given pitch, each microlens being formed by a segment of a cylinder, that is, a shape obtained by translating a curve along a generatrix parallel to the principal axis of the second microstructure. For example, the curve is a portion of a circle, a parabola, or any other shape. The microlenses of the second microstructure are arranged in a direction perpendicular to the principal axis. According to one or more embodiments, the pitch is between approximately 10 pm and approximately 300 pm, advantageously between approximately 30 pm and approximately 80 pm.According to one or more embodiments, the depth, defined as the maximum height of the second microstructure along an axis perpendicular to a plane of the second microstructure, is advantageously between approximately 500 nm and approximately 10 pm, or advantageously between approximately 1 pm and approximately 5 pm. A plane of the second microstructure can be defined as a plane parallel to a plane containing the generatrices of the microlenses. Such a microstructure reflects incident light at normal incidence anisotropically. More precisely, such a microstructure reflects a light beam incident at normal incidence into a pyramidal cone whose angular dimension in a direction parallel to the principal axis is close to zero, and whose angular dimension in a direction perpendicular to the principal axis depends on the ratio between the depth and the pitch.For example, the ratio between depth and pitch is between approximately 0.01 and approximately 0.2, advantageously between approximately 0.05 and approximately 0.15. In embodiment examples, the angular dimension in a direction perpendicular to the principal axis is between approximately 5° and approximately 80°; however, in preferred embodiment examples, the angular dimension in a direction perpendicular to the principal axis is between approximately 15° and approximately 60°, this angular range being a good compromise between seeking an effect visible over a wide angular range and seeking a sufficiently bright effect.

[0031] According to one or more embodiments, the second microstructure comprises a set of substantially straight undulations parallel to the same axis, identical to each other, arranged periodically with a given pitch, the axis of the The undulations form the principal axis of the second microstructure. By undulation, we mean a shape that exhibits a continuously varying profile in a plane perpendicular to the axis of the undulations. According to one or more embodiments, the profile of the undulations is sinusoidal or quasi-sinusoidal (also called "pseudosinusoidal"), that is, a profile deformed with respect to a sinusoid, with a duty cycle other than 0.5, advantageously between 0.4 and 0.6. According to one or more embodiments, the pitch is between approximately 10 pm and approximately 300 pm, advantageously between approximately 30 pm and approximately 80 pm. According to one or more embodiments, the depth, defined as the maximum height of the second microstructure along an axis perpendicular to a plane of the second microstructure, is advantageously between approximately 1 pm and approximately 20 pm, advantageously between approximately 4 pm and approximately 10 pm.A plane of the second microstructure can be defined as a plane parallel to a plane comprising the lines formed by the vertices of each undulation (ridge lines). Such a microstructure reflects incident light at normal incidence anisotropically. More precisely, such a microstructure reflects a beam of light incident at normal incidence into a pyramidal cone whose angular dimension in a direction parallel to the principal axis is close to zero, and whose angular dimension in a direction perpendicular to the principal axis depends on the ratio between the depth and the pitch. For example, the ratio between the depth and the pitch is between approximately 0.02 and approximately 0.4, advantageously between approximately 0.1 and approximately 0.3. The angular dimension in a direction perpendicular to the principal axis is, according to embodiment examples, between approximately 5° and approximately 80°, and advantageously between approximately 15° and approximately 60°.

[0032] According to one or more exemplary embodiments, the second microstructure comprises an array of microfacets whose shapes are determined to generate a plurality of concave or convex optical elements, for example, cylindrical elements each formed from a segment of a cylinder whose generatrix is ​​parallel to the principal axis of the second microstructure. The microfacets are determined in a known manner, for example, by a method for forming Fresnel lenses, as described in EP3129238 B1 [Ref. 6]. The microfacets may be formed by plane sections inclined with respect to a reference plane. The microfacets may, for example, have rectangular shapes, with at least one dimension (width) for example less than about 80 pm, for example between about 1 pm and about 80 pm.The height of a micro-facet, defined along an axis perpendicular to the reference plane, is for example between approximately 300 nm and approximately 5 pm, advantageously between approximately 0.5 pm and approximately 3 pm. The depth of the second microstructure can be defined by a height. maximum of microfacets. Such a microstructure reflects incident light at normal incidence anisotropically. More precisely, such a microstructure reflects a normal incident light beam into a pyramidal cone whose angular dimension in a direction parallel to the principal axis is close to zero, and whose angular dimension in a direction perpendicular to the principal axis depends on the ratio of the depth to the width of the facet with the smallest width. For example, the ratio of the depth to the width of the facet with the smallest width is between approximately 0.06 and approximately 1, advantageously between approximately 0.1 and approximately 0.7. The angular dimension in a direction perpendicular to the principal axis is, according to embodiment examples, between approximately 5° and approximately 80°, and advantageously between approximately 15° and approximately 60°.

[0033] According to one or more embodiments, the second microstructure is an anisotropic diffusing microstructure and comprises a microrelief formed of randomly positioned peaks and / or valleys, wherein the height of the peaks and the height of the valleys, measured with respect to a reference plane, is each less than approximately 2 pm. According to one or more embodiments, the height of the peaks and the height of the valleys are each between approximately 50 nm and approximately 1 pm, preferably between approximately 100 nm and approximately 1 pm, preferably between approximately 200 nm and approximately 800 nm. The effectiveness of the dispersive character of the diffusing nanostructure depends on the density and size of the peaks and valleys, which can be fixed by those skilled in the art according to the desired product.Thus, in the second microstructure according to the present description, the peaks and valleys are arranged along a preferred direction, the main axis of the second microstructure, so as to reflect an incident light beam at normal incidence into a light intensity scattering lobe which has a very small angular dimension at half maximum in a direction parallel to the main axis, for example less than 5°, and which has a much larger angular dimension at half maximum in a direction perpendicular to the main axis, for example greater than 15°.

[0034] According to one or more embodiments, the micro-images formed by the first or second elementary surfaces of the first microstructure include alphanumeric characters, simple or complex geometric elements, and graphic elements, without this list being exhaustive. In practice, due to selective magnification along a single axis, they can be designed to be distorted at the level of the first microstructure, so as to appear undistorted to an observer after magnification by the Moiré effect.

[0035] According to one or more embodiments, the first arrangement direction of the cylindrical microlenses and the second arrangement direction of the microimages are collinear; in this case, the first step and the second step are different to ensure the Moiré effect.

[0036] According to one or more embodiments, the first step of arrangement of the cylindrical microlenses in the first microstructure is between 10 qm and 300 qm, advantageously between 20 qm and 150 qm, and the second step of arrangement of the micro-images is equal to the first step plus or minus a percentage of said first step, the percentage being between about 0.1% and about 10%, advantageously between about 0.1% and about 5%.

[0037] According to one or more embodiments, the first arrangement direction of the cylindrical microlenses and the second arrangement direction of the microimages form a non-zero angle, for example an angle between approximately 0.1 degrees and approximately 5 degrees, advantageously between 0.1 degrees and 3 degrees. In this case, the first and second steps may be identical, for example between 10 µm and 300 µm, or different.

[0038] According to the present description, a maximum width of the first cylindrical microlenses, measured along said first direction of arrangement, is less than about 300 sqm; this allows the microlenses not to be individually visible to the naked eye.

[0039] According to one or more embodiments, the minimum number of first cylindrical microlenses is determined based on the maximum width of the cylindrical microlenses, such that visual effects are visible to the naked eye. Thus, according to one or more embodiments, a minimum dimension of the first microstructure along said first direction of microlens arrangement may be greater than approximately 1 mm, preferably greater than approximately 2 mm, and preferably greater than approximately 4 mm.

[0040] According to one or more embodiments, a minimum length of said first cylindrical microlenses is determined such that visual effects are visible to the naked eye, along the direction perpendicular to said first direction of microlens arrangement (direction parallel to the generatrix). Thus, according to one or more embodiments, a minimum length of said first cylindrical microlenses along the direction perpendicular to said first direction of microlens arrangement is greater than 1 mm, preferably greater than 2 mm, preferably greater than approximately 4 mm.

[0041] The dimensions of the second microstructure can be substantially equal to the dimensions of the first microstructure.

[0042] Thus, according to one or more embodiments, a dimension of said first optical structure, measured along said first arrangement direction, is greater than about 1 mm, preferably greater than about 2 mm, preferably greater than about 4 mm and can be equal to a few tens of millimeters, depending on the application.

[0043] According to one or more embodiments, a minimum dimension of said first optical structure, measured along the direction perpendicular to said first arrangement direction, is greater than 1 mm, preferably greater than 2 mm, preferably greater than about 4 mm and may be equal to a few tens of millimeters, depending on the application.

[0044] According to one or more embodiments, a height of said first optical structure, measured in a direction perpendicular to the plane of the component, is between approximately 2 pm and approximately 20 pm.

[0045] According to one or more embodiments, the second elementary surfaces of the first microstructure follow the profile of a second one-dimensional matrix of identical cylindrical microlenses superimposed on said first matrix, the curvature of said second cylindrical microlenses being less than that of said first cylindrical microlenses. When the first elementary surfaces and the second elementary surfaces follow matrices of cylindrical microlenses, this results in an uninterrupted movement effect of the magnified microimages, i.e., without any "accident" of contrast at specular reflection; this effect results from the non-zero and different curvatures of the first elementary surfaces and the second elementary surfaces as described in [Ref. 4].

[0046] For the purposes of this description, "a curvature of the second cylindrical microlenses less than the curvature of the first cylindrical microlenses" means that at any point of said second matrix of second cylindrical microlenses, or almost at any point, the radius of curvature is strictly greater than that of said first matrix of first cylindrical microlenses at the level of that point.

[0047] For the purposes of this description, the first matrix of first cylindrical microlenses and the second matrix of second cylindrical microlenses are superimposed when they are arranged one above the other in a direction normal to the plane of the first microstructure, such that a first cylindrical lens coincides with a second cylindrical lens; the second cylindrical microlenses are thus arranged in the same first direction, and with the same first pitch as the first cylindrical microlenses.

[0048] The first cylindrical microlenses and the second cylindrical microlenses are either all concave, seen from said first observation face, or all convex, seen from said first observation face.

[0049] According to one or more embodiments, the maximum height difference between said first matrix of first cylindrical microlenses and said second matrix of second cylindrical microlenses, defined in a direction perpendicular to the plane of the first microstructure, is between about 400 nm and about 10 pm, preferably between about 600 nm and about 3 pm.

[0050] According to one or more embodiments, the height of said first microstructure, defined in a direction perpendicular to the plane of the first microstructure, is between about 2 pm and about 20 pm, preferably between about 3 pm and about 10 pm.

[0051] According to one or more embodiments, at least one of said first elementary surfaces or of said second elementary surfaces are nanostructured so as to form a one- or two-dimensional sub-wavelength network or a diffusing nanostructure.

[0052] According to one or more embodiments, the second elementary surfaces follow, like the first elementary surfaces, the profile of the first one-dimensional matrix of first cylindrical microlenses, as in [ref. 5]. The first elementary surfaces are nanostructured so as to form at least one first diffusing nanostructure or at least one first one- or two-dimensional sub-wavelength lattice, while the second elementary surfaces are not nanostructured or are nanostructured with a nanostructure having different parameters.Here again, such a safety optical component exhibits a magnification of micro-images by Moiré effect and, under the effect of a tilt movement around an axis perpendicular to the first arrangement direction, an effect of uninterrupted movement of the enlarged images due to the non-zero curvatures of the first elementary surfaces and the second elementary surfaces which are distinguished by the different nanostructuring.

[0053] According to one or more embodiments, said one- or two-dimensional sub-wavelength network has a pitch between 100 nm and 700 nm, advantageously between 200 nm and 500 nm, determined to produce, after deposition of the second reflective layer, a resonant filter in a first spectral band.

[0054] According to one or more embodiment examples, the modulation depth of the one- or two-dimensional sub-wavelength network, defined in a direction perpendicular to the plane of the component, is between 50 nm and 500 nm, preferably between 50 nm and 300 nm.

[0055] According to one or more embodiments, said second reflective layer comprises a metallic layer and said subwavelength grating is configured to produce plasmonic resonances in said first spectral band. Colored visual effects related to the plasmonic resonances can be observed in reflection in the case of a sufficiently thick metallic layer, and in transmission in the case of a sufficiently thin metallic layer and with encapsulation of the metallic layer between two layers of dielectric material.

[0056] According to one or more embodiments, the component further comprises a third encapsulation layer, and said second reflective layer includes a layer of dielectric material having a refractive index different from that of said first and third dielectric layers. Said first sub-wavelength array is then configured to produce waveguide-type resonances in said first spectral band. According to one or more embodiments, the difference in refractive index values ​​is at least 0.3, advantageously at least 0.5.

[0057] According to one or more embodiments, said reflective interface of the safety optical component according to the first aspect comprises at least a second optical structure. The second optical structure is, for example and without limitation: an optical structure resulting, like the first optical structure, from the sum of a first microstructure and a second microstructure defined similarly to the first and second microstructures of the first optical structure, but with different parameters; a diffusing structure; a holographic structure; a diffractive structure enabling, for example, the realization of an effect known as Alphagram® developed by the applicant.

[0058] The optical safety component according to the first aspect may include one or more additional layer(s) depending on the needs of the application, without this or these additional layer(s) contributing to the desired visual effect.

[0059] Thus, according to one or more embodiments, the optical security component is adapted to secure a document or product, and further includes, on the face opposite the observation face, a layer adapted for transferring the component onto the document or product, for example a layer of permanent adhesive or a layer of reactivatable adhesive.

[0060] According to one or more embodiments, the optical security component further includes, on the side of the first viewing face, a support film intended to be detached after transfer of the component onto the document or product.

[0061] According to one or more embodiments, the optical safety component includes on the side of the first observation face and / or on the face opposite to the first observation face, one or more protective layers.

[0062] According to one or more embodiments, the said several protective layers are at least partially transparent in the visible, further allowing observation of the optical safety component according to a second observation face, opposite to said first observation face.

[0063] Such a security optical component is suitable for example for the manufacture of a security thread for securing banknotes, payment cards and other security documents.

[0064] According to a second aspect, the present description relates to a secure object, for example a secure valuable document, comprising a substrate and a security optical component according to the first aspect, deposited on said substrate.

[0065] According to a third aspect, the present description relates to methods for manufacturing safety optical components according to the first aspect.

[0066] According to one or more embodiments, the manufacturing process comprises: - the deposition on a support film of said first layer of dielectric material. - the formation by replication on said first layer of said at least first structure; - the deposition on said first layer of structured dielectric material of a reflective layer to form said reflective interface. Brief description of the figures

[0067] Other features and advantages of the invention will become apparent from the following description, illustrated by the following figures:

[0068] [Fig. 1 A], already described, a figure illustrating the design principle of a component security optics with micro-image magnification by Moiré effect, as described in [Ref.3];

[0069] [Fig.1B], already described, a figure schematically representing a safety optical component with micro-image magnification by Moiré effect, as described in [Ref.3];

[0070] [Fig. 2A], already described, a figure schematically representing a component safety optics with micro-image magnification by Moiré effect, as described in [Ref.4] or [Ref.5];

[0071] [Fig.2B], already described, a figure schematically representing, according to a view in cross-section, a safety optical component with micro-image magnification by Moiré effect, as described in [Ref.4];

[0072] [Fig.2C], already described, a figure schematically representing, according to a view in cross-section, a safety optical component with micro-image magnification by Moiré effect, as described in [Ref.5];

[0073] [Fig. 3A], a figure schematically representing an example of a component optical according to the present description, according to a cross-sectional view in a first plane of section;

[0074] [Fig. 3B], a figure schematically representing an example of a component optical according to the present description, according to a cross-sectional view in a second cross-sectional plane;

[0075] [Fig.3C], a diagram illustrating a first optical structure (partial view) resulting from the sum of a first microstructure (partial view) and a second microstructure, according to an example, in an optical component according to the present description;

[0076] [Fig.4], a diagram illustrating, by way of example, a pyramidal reflection cone of a light beam incident on a second microstructure at normal incidence;

[0077] [Fig. 5A], a first example of a second microstructure comprising a cylindrical microlens matrix;

[0078] [Fig. 5B], a second example of a second microstructure comprising a a set of undulations;

[0079] [Fig. 5C], a third example of a second microstructure comprising a set of facets configured to generate cylindrical optical elements;

[0080] [Fig. 5D], a fourth example of a second microstructure comprising a anisotropic diffusing micro structure;

[0081] [Fig. 6A], a diagram illustrating, by way of example, a visual effect obtained with a example of a safety optical component according to this description, in a tilt movement along an axis parallel to the first arrangement direction of the cylindrical microlenses of the first microstructure;

[0082] [Fig. 6B], a diagram illustrating, for comparative purposes, the visual effect obtained with a state-of-the-art safety optical component, in a tilt movement similar to that illustrated in [Fig.6A];

[0083] [Fig.7], a diagram illustrating, by way of example, a visual effect obtained with a example of a safety optical component according to this description, in a tilt movement along an axis parallel to the first arrangement direction of the cylindrical microlenses of the first microstructure and along an axis perpendicular to the first arrangement direction of the cylindrical microlenses of the first microstructure;

[0084] [Fig.8A], a diagram illustrating, by way of example, a light reflection cone with an example of a safety optical component according to the present description;

[0085] [Fig.8B], a diagram illustrating, for comparative purposes, a light reflection cone with an example of a state-of-the-art safety optical component. Detailed description

[0086] In the figures, the elements are not shown to scale for better visibility.

[0087] Fig. 3A and Fig. 3B represent, according to (partial) sectional views, an example of a safety optical component according to the present description, respectively along a first section plane Pi and a second section plane P2.

[0088] The security optical component 301 shown in [Fig. 3A] and [Fig. 3B] represents, for example, a security optical component intended, for instance, to be transferred onto a document or product for the purpose of securing it. In this example, it comprises a support film 311, 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 sq m, and a release layer 312, for example, made of natural or synthetic wax. The release layer allows the polymer support film 311 to be removed after the optical component has been transferred onto the product or document to be secured. The security optical component 301 also comprises a first layer 313 made of dielectric material, having a first refractive index ni, and a second reflective layer 314 which, together with the first layer 313 made of dielectric material, forms a reflective interface.The said reflective interface forms, in at least a first region, a first structure S, whose height along a direction perpendicular to the plane of the component is referenced hs, and which will be described in more detail later.

[0089] The second layer 314 is for example made of a metallic layer, for example a layer of Aluminium, Copper, Chrome, Silver or an alloy of these metals, and its thickness is for example between 20 nm and 80 nm.

[0090] The second layer 314 can also be made of a so-called index variation layer, having a refractive index different from that of the neighboring layers, the index difference between layers 313 and 314 having a value of at least about 0.3, preferably at least about 0.5. Materials for index variation layers are described for example in US patent 4856857 [Ref. 7] for example, the second layer 314 is a layer of TiO2 or ZnS, with a thickness of between 40 and 150 nm.

[0091] In exemplary embodiments, the second layer 314 may comprise a metallic layer and a refractive index variation layer.

[0092] The second layer 314 ensures the reflection of incident light.

[0093] The optical safety component further comprises one or more optically non-functional layers adapted to the application, for example, in this example, an encapsulation layer made of dielectric material 317. The component The security optics may also include an adhesive layer, for example a heat-activated adhesive layer, for transferring the security optics component onto the product or document. In some embodiments, the encapsulation layer may be the adhesive layer.

[0094] In practice, as will be detailed later, the optical safety component can be manufactured by stacking layers 312 and 313 on the support film 311, then layer 313 is structured to form said first structure S and covered by the reflective layer 314 to form the reflective interface. The optically non-functional layer(s) can then be deposited, such as the adhesive layer 317. The component can then be transferred onto a document / product to be secured using layer 317. Optionally, the backing film 311 can be detached, for example by means of the detachment layer 312. The main viewing face 300A of the optical security component is thus located on the side of the first layer 313 opposite the interface with the reflective layer 314. The structure is thus encapsulated, and therefore protected against natural degradation (such as dirt) or against attacks by a counterfeiter.

[0095] In other embodiments (not shown), the optical security component may be intended, for example, for securing banknotes, payment cards, or other security documents; it may, for example, be part of a security thread intended to be embedded in the paper during banknote manufacturing. In this example, the component comprises, as before, a support film (10 to 40 µm) which may also serve as a protective film for the security thread, a first layer of dielectric material having a first refractive index ni, and a second reflective layer forming a reflective interface with the first layer of dielectric material, thus forming the first structure S.The optical security component may also include a set of additional layers, for example, an encapsulation layer, a colored contrast layer (optional), which may be opaque and / or discontinuous, and a protective layer, for example, a second polymer film or a varnish to give the security wire the necessary physicochemical resistance. The encapsulation and colored contrast layers are optional and may be combined into a single layer. The protective and encapsulation layers may also be combined into a single layer performing both functions.

[0096] It will be apparent to a person skilled in the art that other optically non-functional layers can be added according to the needs of the application in each of the examples described above and that the embodiment variants can be combined.

[0097] It should be noted that if the additional, optically non-functional layers are at least partially transparent in the visible spectrum, as is the receiving substrate, the optical security component can be observed not only from the first viewing face 300A (front) but also from a second viewing face 300b, opposite said first viewing face (back). Depending on whether the observation is from the front or back, a reversal of the curvatures of the elementary surfaces forming the reflective interface will allow for differentiated observation, characterized in particular by a reversal of motion effects. Such an optical security component is, for example, suitable for securing a security document such as a banknote or card, which includes a transparency window for front / back observation.

[0098] Furthermore, in a safety optical component as described herein, the reflective interface may have at least one second optical structure (not shown), allowing for the juxtaposition or interlocking of different effects resulting from structures such as those described in this application or other visual effects. The second optical structure is configured to form, for example, but not limited to, another structure as described herein, a diffusing structure, a holographic structure, a diffractive structure, for example, a structure enabling the creation of an effect known as Alphagram® developed by the applicant.

[0099] In a safety optical component according to this description, the second reflective layer 314 can also be interrupted, for example by means of partial demetallization, thus forming different regions, each region being able to comprise one or more structures. The different regions can form juxtaposed or interlocking patterns.

[0100] According to the present description, the first optical structure S results from the sum of a first microstructure and a second microstructure.

[0101] Fig. 3C schematically illustrates a partial view of an example of such a first optical structure S resulting from the sum of a first microstructure 321 (partial view) and a second microstructure 322.

[0102] The first microstructure 321 consists of first elementary surfaces I1 and second elementary surfaces I2, see [Fig. 3A] and [Fig. 3B], in which the first elementary surfaces and the second elementary surfaces are complementary in top view. Moreover, at least the first elementary surfaces L follow the profile of a first one-dimensional matrix MLi of identical cylindrical first microlenses LH arranged periodically along a first arrangement direction AL, with a first step size p,.

[0103] The first elementary surfaces L or said second elementary surfaces I2 form, in top view, recognizable and identical micro-images, The first microstructure is periodically arranged along a second direction and with a second pitch p2. The first microstructure is configured to exhibit, upon reflection and under the effect of a tilt movement around an axis perpendicular to said first arrangement direction, a displacement of said first microimages due to the Moiré effect. The first microstructure is thus similar, for example, to the microstructure illustrated in [Fig. 2A], [Fig. 2B], or [Fig. 2C], with reference to a state-of-the-art optical component. In [Fig. 3C], however, to avoid cluttering the figure, only the one-dimensional array of identical cylindrical microlenses Li, periodically arranged along the first arrangement direction AL, with a first pitch pb, is shown. In other words, the microimages MI visible in [Fig. 2A] are not shown.

[0104] The second microstructure 322 ([Fig.3C]) is configured to reflect normal incident light anisotropically, mainly in a plane orthogonal to a principal axis A substantially parallel to said first arrangement direction.

[0105] The sum of the two motifs results in a first optical structure S illustrated in [Fig.3C].

[0106] Fig. 3A and Fig. 3B correspond respectively to cross-sectional views along planes Pi and P2 shown in Fig. 3C, planes Pi and P2 being chosen perpendicular to a plane of the component and parallel to the first arrangement direction AL. The plane of the component is a plane parallel to the plane of the first microstructure.

[0107] Because the first optical structure S results from the sum of the first microstructure and the second microstructure, between the cross-sectional views illustrated in [Fig.3A] and [Fig.3B] along two different planes, there is a difference in height between the first structure S and a plane of the safety optical component, for example in the example illustrated in [Fig.3A] and [Fig.3B], a difference in height between the first structure S and a plane corresponding to the face 300B of the component.

[0108] According to one or more embodiment examples, the height hs of said first structure, defined in a direction perpendicular to the plane of the component, is between about 2 pm and about 20 pm, preferably between about 3 pm and about 10 pm.

[0109] Cylindrical microlenses Li are defined by segments of cylinders in the broad sense, that is, shapes obtained by translating a curve along a generatrix. The generatrix of the cylinders is perpendicular to said first direction AL arrangement of cylindrical microlenses. The curve can be a portion of a circle, a parabola, or any other shape.

[0110] A dimension L of the cylindrical microlenses ([Fig.3C]), measured in a direction parallel to the generatrix of the cylinders, is for example greater than 1 mm, advantageously greater than 2 mm, advantageously greater than 4 mm, to form visual effects visible to the naked eye.

[0111] A width X of the cylindrical microlenses, measured in a direction perpendicular to the generatrix of the cylinders (and therefore deformed by tilting movement of the safety optical component), is less than 300 sq m, so as not to be visible to the naked eye. A sufficient number of cylindrical microlenses can be provided so that the total dimension of the first structure, measured in a direction parallel to the first AL direction of arrangement of the cylindrical microlenses, is greater than 1 mm, advantageously greater than 2 mm, advantageously greater than 4 mm, to form visual effects visible to the naked eye.

[0112] In the example of [Fig. 3A] and [Fig. 3B], the second elementary surfaces I2 of the first motif follow the profile of a second one-dimensional matrix ML2 of identical cylindrical microlenses, superimposed on the first matrix M1, the curvature of the second cylindrical microlenses being less than that of the first cylindrical microlenses. When the first and second elementary surfaces follow matrices of cylindrical microlenses, as described in [Ref. 4], this results in an uninterrupted motion effect of the magnified microimages, i.e., without any "accident" of contrast at specular reflection; this effect results from the non-zero and different curvatures of the first and second elementary surfaces.

[0113] Of course, the present description is not limited to this example. For example, at least one of said first elementary surfaces b or of said second elementary surfaces L may be nanostructured so as to form a one- or two-dimensional sub-wavelength network, or a diffusing nanostructure, so as to increase the contrast. Moreover, in exemplary embodiments, both the first elementary surfaces and the second elementary surfaces may be nanostructured, the characteristics of the nanostructures being different.

[0114] In exemplary embodiments, the second elementary surfaces I2 may follow the same profile as the first one-dimensional MLi matrix of first cylindrical microlenses Li as in [Ref. 5]. For example, the first elementary surfaces Ii are nanostructured so as to form at least a first diffusing structure or at least a first one- or two-dimensional lattice while the second elementary surfaces I2 are not nanostructured or are nanostructured in a different way.

[0115] In exemplary embodiments, the second reflective layer 314 is metallic, adapted to form plasmonic resonances at the interface between said first layer of dielectric material and said second metallic layer. The metallic layer is sufficiently thick, and colored visual effects are visible in reflection. Such plasmonic resonances are described, for example, in patent application FR 2982038 [Ref. 8] filed by the applicant.

[0116] In exemplary embodiments, the safety optical component further comprises a third encapsulating layer 317 of dielectric material, and the second reflective layer 314 is a layer of dielectric material, arranged between said first and third dielectric material layers, having a refractive index different from that of said first and third dielectric material layers, adapted to form waveguide-type resonances in said first spectral band. The differences between the refractive index values ​​of said second dielectric material layer and said adjacent first and third layers are at least 0.3, advantageously at least 0.5. Such waveguide-type resonances are described, for example, in US patent application 4484797 [Ref. 9].

[0117] Figure 4 shows a diagram illustrating, by way of example, the reflection of a light beam incident on a second microstructure 322 at normal incidence. The beam originates from an extended source 410. As illustrated in Figure 4, according to the present description, the light is reflected into a pyramidal cone of angular dimensions e and [3], where e is the angular dimension in a direction parallel to the principal axis A and [3] is the angular dimension in a direction orthogonal to the principal axis A. The second microstructure is such that the reflected light lies mainly in a plane perpendicular to the principal axis; in other words, the angle e is very small, typically less than about 5°, advantageously less than about 3°.

[0118] Figs. 5A, 5B, 5C, and 5D illustrate examples of a second microstructure conforming to the present description.

[0119] Figure 5A illustrates a second microstructure 501 comprising a one-dimensional array of identical cylindrical microlenses 511 arranged periodically with a given pitch p3, each microlens being formed by a segment of a cylinder, i.e., a shape obtained by translating a curve along a generatrix parallel to the principal axis of the second microstructure. For example, the curve is a portion of a circle, a parabola, or any other shape. The microlenses of the second microstructure are arranged in a direction perpendicular to the principal axis A. According to one or more embodiments, the pitch p3 is between approximately 10 pm and approximately 300 pm, advantageously between approximately 30 pm and approximately 80 pm. A plane of the second microstructure can be defined as a plane parallel to a plane comprising the generatrices of the microlenses. According to one or more embodiments, the depth h3, defined by the maximum height of the second microstructure along an axis perpendicular to the plane of the second microstructure, is advantageously between approximately 500 nm and approximately 10 pm, advantageously between approximately 1 pm and approximately 5 pm. Such a microstructure reflects incident light at normal incidence anisotropically. More precisely, such a microstructure reflects a light beam incident at normal incidence in a pyramidal cone (see [Fig.4]) with a value of the angular range e close to zero and a value of the angular range [3] which depends on the ratio between the depth and the pitch. For example, the ratio between the depth and the pitch is between about 0.01 and about 0.2, advantageously between about 0.05 and about 0.15. The angular range [3] in the direction perpendicular to the principal axis is between about 5° and about 80°, and advantageously between about 15° and about 60°, the inventors having shown that a good compromise is obtained between a wide angular range and a sufficiently intense luminous effect.

[0120] Figure 5B illustrates a second microstructure 502 comprising a set of substantially straight undulations 512 parallel to a common axis, identical to each other, arranged periodically with a given pitch p3, the axis of the undulations being parallel to the principal axis A of the second microstructure. By undulation is meant a shape that has a continuously varying profile in a plane perpendicular to the axis of the undulations. According to one or more embodiments, the pitch p3 is between approximately 10 pm and approximately 300 pm, advantageously between approximately 30 pm and approximately 80 pm. According to one or more embodiments, the depth h3, defined as the maximum height of the second microstructure along an axis perpendicular to a plane of the second microstructure, is advantageously between approximately 500 nm and approximately 10 pm, advantageously between approximately 1 pm and approximately 5 pm.We can define a plane of the second microstructure as a plane parallel to a plane comprising the lines formed by the vertices of each undulation (ridge lines). Such a microstructure reflects incident light at normal incidence anisotropically. More precisely, such a microstructure reflects a light beam incident at normal incidence into a pyramidal cone (see [Fig. 4]) with an angular range e close to zero and an angular range [3] that depends on the ratio between the depth and the pitch. For example, the ratio between the depth and the pitch is between approximately . 0.01 and about 0.2, advantageously between about 0.05 and about 0.15. Again, in embodiment examples, the angular range [3 in the direction perpendicular to the main axis is between about 5° and about 80°, and advantageously between about 15° and about 60°, the inventors having shown that a good compromise is obtained between a wide angular range and a sufficiently intense luminous effect.

[0121] As illustrated in [Fig. 5B], the wave profile can be sinusoidal. In exemplary embodiments, the profile can be quasi-sinusoidal (also called "pseudo-sinusoidal"), i.e., a profile distorted relative to a sinusoid, with a duty cycle other than 0.5. Such a quasi-sinusoidal profile is shown in diagram 552 of [Fig. 5B]. The duty cycle of the pseudo-sinusoid is defined as the ratio, measured over a period p3, between the smaller of the lengths px1 and px2 and the total length of the period p3, with px1 being the length for which the value of the pseudo-sinusoid is greater than the median value of the pseudo-sinusoid and px2 the length for which the value of the pseudo-sinusoid is less than the median value of the pseudo-sinusoid. For example, the duty cycle can be between approximately 0.4 and approximately 0.6.

[0122] Figure 5C illustrates a second microstructure 503 comprising an array of microfacets 513 configured to generate a plurality of concave or convex cylindrical optical elements, each formed from a segment of a cylinder whose generatrix is ​​parallel to the principal axis of the second microstructure. The microfacets are determined in a known manner, for example by a method for forming Fresnel lenses, as described in Ref. 6. The microfacets may be formed by plane sections inclined with respect to a reference plane. The microfacets may, for example, have rectangular shapes, with at least one dimension (width) ranging from approximately 1 pm to approximately 100 pm, for example, from approximately 3 pm to approximately 80 pm. The height h3 of a micro-facet, defined along an axis perpendicular to the reference plane, is for example between about 300 nm and about 5 pm, advantageously between about 0.5 pm and approximately 3 pm. The depth of the second microstructure can be defined by a maximum height of the microfacets. Such a microstructure reflects incident light at normal incidence anisotropically. More precisely, such a microstructure reflects a light beam incident at normal incidence into a pyramidal cone whose angular dimension in a direction parallel to the principal axis is close to zero, and whose angular dimension in a direction perpendicular to the principal axis depends on the ratio of the depth to the width of the facet with the smallest width (the "blaze angle"). For example, the ratio of the depth to the width of the facet with the smallest width is between . between about 0.06 and about 1, advantageously between about 0.1 and about 0.7. The angular dimension in a direction perpendicular to the principal axis is, according to embodiment examples, between about 5° and about 80°, and advantageously between about 15° and about 60°.

[0123] In the example illustrated in [Fig. 5C], only the microfacets configured to generate a single cylindrical element (convex in this example) are shown. Of course, other microfacets are present (not shown) to generate the plurality of cylindrical elements, arranged parallel to each other in a direction perpendicular to the generatrix of the cylinders, which is the principal axis A of the microstructure. The microfacets can be, as illustrated in [Fig. 5C], inclined plane sections with, for example, a continuously varying angle of inclination that decreases (in absolute value) from the facet located at one end of the reflective element towards the central facet. However, other arrangements of the microfacets known to those skilled in the art can be implemented to obtain the same optical effect of generating a plurality of concave or convex cylindrical optical elements.

[0124] Fig. 5D illustrates a second microstructure 504, in this example an anisotropic diffusing microstructure.

[0125] Such a microstructure comprises a microrelief formed of randomly positioned peaks and / or valleys, wherein the height of the peaks and the height of the valleys, measured with respect to a reference plane, is each substantially less than about 2 pm. According to one or more embodiments, the height of the peaks and the height of the valleys are each between about 100 nm and about 1 pm, preferably between about 200 nm and about 800 nm. The effectiveness of the dispersive character of the diffusing nanostructure depends on the density and size of the peaks and valleys, which can be fixed by those skilled in the art according to the desired product.Thus, in the second microstructure according to the present description, the peaks and valleys are arranged along a preferred direction, the main axis of the second microstructure, so as to reflect an incident light beam at normal incidence into a light intensity scattering lobe which has a very small angular dimension at half maximum in a direction parallel to the main axis, for example less than about 5°, and which has a much larger angular dimension at half maximum in a direction perpendicular to the main axis, for example greater than about 15°.

[0126] Fig. 6A is a diagram illustrating, by way of example, a visual effect obtained with an example of a safety optical component 601 according to this description, in a tilt movement about an axis parallel to the first arrangement direction AL.

[0127] Fig. 6B illustrates, by way of comparison, the visual effect obtained with a safety optical component 602 according to the state of the art, in a tilt movement similar to that illustrated in Fig. 6A.

[0128] In an up / down tilt movement (around an axis perpendicular to said first arrangement direction), a displacement of the micro-images (a set of graphic elements "G") by Moiré effect is visible with the safety optical component 601 or 602 (but the effect is not shown on [Fig.6A] and [Fig.6B]).

[0129] As shown in [Fig.6B], unlike the state of the art ([Fig.6A]), due to the second microstructure, the observed effect is always visible when a right / left tilt is applied to the safety optical component, i.e. around an axis parallel to the first arrangement direction, in an angular range [3. In other words, if the safety optical component undergoes a given rotation around said axis parallel to the first arrangement direction, in an angular range [3 / 2 (for example 30°) defined on either side of a nominal position 61 (positions 62, 63) the Moiré effect of displacement can always be observed under the effect of a tilt movement around the axis perpendicular to said first arrangement direction. However, as illustrated in [Fig.6B], the Moiré effect is no longer visible with a state-of-the-art safety optical component after a right / left tilt movement has been applied.

[0130] In this example, the nominal observation position is defined, for example, for observation under vertical illumination, by a component inclined so as to present a given angle between the normal to the component and the vertical direction, for example an angle between 30 degrees and 45 degrees in the broad sense.

[0131] Fig. 7 illustrates, by way of example, a visual effect obtained with an example of a safety optical component 701 according to this description, in an up / down tilt movement, i.e. along an axis perpendicular to the first arrangement direction of the microlenses of the first microstructure, and in a right / left tilt movement, i.e. along an axis parallel to the first arrangement direction.

[0132] Position 710 corresponds to a nominal position, for example, an observation under illumination along a given axis, with the component arranged so as to present a given angle between the normal to the component and the vertical direction, for example, an angle between 30 degrees and 45 degrees broadly. During an up / down tilt, within an angular range a, for example + / - 40 degrees, a displacement effect of micro-images (here, an alphanumeric character "5") is observed due to the Moiré effect. The alphanumeric character "5" appears to move away (positions 711, 713 in an up tilt, 712, 714 in a down tilt) when deviating from the nominal position 710.

[0133] The optical safety component 701 now undergoes a right / left tilt movement (positions 720, 740 for a left tilt and positions 730, 750 for a right tilt) within an angular range [3, for example + / - 30 degrees. For each position 720, 740, 730, 750, an observer will be able to see the same effect of displacement of the alphanumeric character “5” during an up / down tilt movement within the angular range a. Thus, the alphanumeric character "5" appears to move away (positions 721, 723 in an upward tilt, 722, 724 in a downward tilt) when moving away from position 720. The alphanumeric character "5" appears to move away in the same way (positions 741, 743 in an upward tilt, 742, 744 in a downward tilt) when moving away from position 740 as long as one remains within the angular range [3.Similarly, the alphanumeric character "5" appears to move away (positions 731, 733 in an upward tilt, 732, 734 in a downward tilt) when moving away from position 730. The alphanumeric character "5" appears to move away in the same way (positions 751, 753 in an upward tilt, 752, 754 in a downward tilt) when moving away from position 750 as long as one remains within the angular range [3. .

[0134] Thus, as illustrated by means of [Fig. A], [Fig. B], [Fig. 7], the optical security component which is the subject of this description facilitates the control of the Moiré effect for an observer and thus makes authentication more robust depending on lighting conditions.

[0135] The [Fig.8A] is a diagram illustrating, by way of example, a pyramidal cone 821 inside which an observation of the Moiré effect is visible to an observer.

[0136] In order not to overload the figure, the first elementary surfaces and the second elementary surfaces of the first microstructure are not shown in [Fig.8A].

[0137] As illustrated in [Fig.8A], the pyramidal cone 821 comprises a first angular dimension a measured in a direction parallel to the first arrangement direction AL (also parallel to the principal axis A of the second microstructure) and a second angular dimension [3 measured in a direction perpendicular to the first arrangement direction AL of the microlenses of the first microstructure.

[0138] During an up / down tilt movement (around an axis perpendicular to the first arrangement direction AL), a displacement of the micro-images due to the Moiré effect is visible in the angular range α, on either side of a nominal position. The nominal observation position is defined, for example, for observation under a given illumination, by a component arranged so as to present a given angle between the normal to the component and the illumination direction, for example, an angle between 30 degrees and 45 degrees broadly.

[0139] The angle a is for example between about 10° and about 160°.

[0140] As explained previously, due to the second microstructure, the observed effect is always visible in the same angular range a when a tilt is applied to the left / right safety optical component, i.e. around an axis parallel to the first arrangement direction, in the angular range [3. In other words, if the safety optical component undergoes a given rotation around said axis parallel to the first arrangement direction, in an angular range [3 / 2 (for example 30°) defined on either side of the nominal position, the Moiré effect of displacement can always be observed under the effect of a tilt movement around the axis perpendicular to said first arrangement direction, in the same angular range a.

[0141] The angle [3 is for example between about 5° and about 80°, and in preferred embodiment examples, between about 15° and about 60°.

[0142] Fig. 8B is a diagram illustrating, for comparison, a cone 822 inside which an observation of the Moiré effect is visible to an observer with an example of a safety optical component 802 according to the state of the art.

[0143] In this example, the reflective interface comprises an arrangement of spherical lenses 812, as described for example in [Ref. 3]. Again, in order not to clutter the figure, the structuring of the reflective interface to obtain the Moiré effect is not illustrated.

[0144] As illustrated in [Fig. 8B], during an up / down tilt movement, a displacement of the micro-images due to the moiré effect is visible within an angular range of 0, on either side of a nominal position. The nominal observation position is defined, for example, for observation under a given illumination, with the component arranged so as to present a given angle between the normal to the component and the direction of illumination, for example, an angle between 30 degrees and 45 degrees broadly.

[0145] On the other hand, since the cone 822 is a cone of revolution due to the rotational symmetry of the microlenses 812, when a right / left tilt movement is applied to the optical safety component, the observation of the Moiré effect will be visible, when moving away from the center of the cone, in an angular range that reduces until it disappears.

[0146] The process for manufacturing optical safety components according to this description advantageously comprises the following steps.

[0147] The first optical structure for forming the structured interface of the safety optical component according to this description can be recorded by electron beam lithography (or "e-beam" lithography) or by direct laser writing. An electroplating step allows the optical structure to be transferred into a resistant material, for example, a nickel-based material, to create a metallic matrix or "master" containing the optical structure. The fabrication of the The safety optical component then includes a replication step. For example, replication can be performed by hot embossing (or "hot pressing" of the dielectric material) of the first layer 313 ([Fig. 3A], [Fig. 3B]) made of a dielectric material with a refractive index of nh, for example, a low-index layer, typically a hot embossing varnish a few microns thick. The layer 313 is advantageously supported by the substrate film 311, for example, a 10 µm to 100 µm film made of a polymer material, for example, PET (polyethylene terephthalate). Replication (the preferred method) can also be performed by casting the hot embossing varnish layer before drying and then UV curing ("UV casting"). Casting replication makes it possible, in particular, to reproduce structures with a large depth range and provides better fidelity in the replication.In general, any other high-resolution replication method known from prior art can be used in the replication step. Next comes the deposition onto the embossed layer of all the other layers, including the reflective layer 314, the encapsulation layer (optional), the opaque coloured contrast layer (optional) which can be deposited uniformly or printed to represent a new pattern, and the glue or varnish type layer by a coating process or a UV-curable varnish, for example.

[0148] Although described through a number of embodiment examples, the optical safety component according to the invention and the method of manufacturing said component include various variants, modifications and improvements which will be obvious to a person skilled in the art, it being understood that these various variants, modifications and improvements form part of the scope of the invention as defined by the following claims. References

[0149] Ref. 1: US7738175

[0150] Ref. 2: MC Hutley et al., “The Moiré magnifier”, Pure Appl. Opt. 3 (1994) 133-142)

[0151] Ref. 3: US20140367957

[0152] Ref. 4: EP3694725

[0153] Ref. 5: EP3470235

[0154] Ref. 6: EP3129238

[0155] Ref. 7: US 4856857

[0156] Ref. 8: FR 2982038

[0157] Ref. 9: US 4484797

Claims

Demands

1. Optical safety component (301) intended to be observed in reflection, with the naked eye, according to at least one first observation face (300a), comprising: - a first layer (313) of dielectric material, at least partially transparent in the visible, having a first refractive index (n J, - a second reflective layer (314) forming a reflective interface with said first layer in at least one first region, in which: - said reflective interface comprises at least one first optical structure (S) resulting from the sum of a first microstructure (321) and a second microstructure (322);- the first microstructure consists of first elementary surfaces (IJ) and second elementary surfaces (I2), in which: - the first elementary surfaces and the second elementary surfaces are complementary in top view, - at least the first elementary surfaces (IJ) follow the profile of a first matrix (MLJ) with one dimension of first identical cylindrical microlenses (LJ), arranged periodically along a first arrangement direction (AL), with a first pitch (pJ), a maximum width of said first cylindrical microlenses measured along said first arrangement direction being less than about 300 sqm;- said first elementary surfaces (IJ) or said second elementary surfaces (I2) form, in top view, recognizable and identical microimages, arranged periodically along a second direction and with a second pitch (p2), the first microstructure being configured to exhibit, in reflection and under the effect of a tilt movement around an axis perpendicular to said first direction of arrangement, a displacement effect of said first micro-images by Moiré effect; - the second microstructure is configured to reflect incident light at normal incidence anisotropically, mainly in a plane orthogonal to a principal axis (A) substantially parallel to said first direction of arrangement.

2. Optical component according to claim 1, wherein the second microstructure comprises a periodic arrangement of microlenses and / or an array of substantially straight and parallel undulations, and / or an array of facets configured to generate a plurality of cylindrical optical elements.

3. Optical safety component according to claim 2, wherein said first elementary surfaces (IJ) or said second elementary surfaces (I2) are nanostructured to form a diffusing nanostructure or a one- or two-dimensional network.

4. Optical component according to claim 1, wherein the second microstructure comprises an anisotropic diffusing structure.

5. Optical component according to any one of the preceding claims, wherein the second microstructure has a depth of between about 50 nm and about 10 sqm.

6. Optical component according to any one of the preceding claims, wherein the second elementary surfaces (I2) follow the profile of a second matrix (ML2) with a dimension of second identical cylindrical microlenses (L2), superimposed on said first matrix (MLJ, the curvature of said second cylindrical microlenses being less than that of said first cylindrical microlenses.

7. Optical component according to any one of the preceding claims, wherein a minimum length of said first cylindrical microlenses, measured in a direction perpendicular to said first direction of arrangement, is greater than about 1 mm.

8. Optical component according to any one of the preceding claims, wherein a dimension of said first optical structure, measured along said first arrangement direction, is greater than about 1 mm, preferably greater than about 2 mm, preferably greater than about 4 mm and / or a minimum dimension of said first optical structure, measured along the direction perpendicular to said first arrangement direction, is greater than 1 mm, preferably greater than 2 mm, preferably greater than 4 mm.

9. Optical component according to any one of the preceding claims, wherein a height of said first structure optical, measured in a direction perpendicular to a plane of the component, is between approximately 2 pm and approximately 20 pm.

10. Optical component according to any one of the preceding claims, wherein said second reflective layer (314) comprises a metallic layer.

11. Optical component according to any one of the preceding claims, wherein said second reflective layer (314) comprises a layer of dielectric material, having a refractive index different from that of the adjacent layers.

12. Optical safety component according to any one of the preceding claims, further having a third encapsulation layer of dielectric material (317), said second reflective layer (314) being encapsulated between the first layer and the third layer.

13. Optical safety component according to any one of the preceding claims, observable along a second observation face, opposite said first observation face (300A).

14. Secure object, for example secure valuable document, comprising a substrate and a security optical component according to any one of the preceding claims, deposited on said substrate.

15. A method for manufacturing a safety optical component according to any one of claims 1 to 12, the method comprising: - deposition on a support film (311) of said first layer of dielectric material (313); - formation by replication on said first layer of said at least first structure; - deposition on said first layer of structured dielectric material (313) of a reflective layer (314) to form said reflective interface.

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