Reflective visible optical security element, production of such an element and security document equipped with such an element

Abstract

The present invention relates to an optical safety component (40), which is configured to be arranged in a direction opposite to an illumination direction (Δ L ) forms an observation angle (θ obs ) in the viewing direction (Δ O ) is observed in reflection on a surface. The component comprises a diffractive structure having a first pattern, the first pattern consisting of a set of parallel facets having a varying slope in a slope varying direction and arranged to be within a given tilt angle range (Δθ tilt ). In at least one region, the first pattern is modulated by a grating designed to produce 1st and ‑1st order reflective diffraction effects. The period of the grating, the maximum angle value of the slope, and the observation angle are designed to be within a first part of the tilt angle range (Δθ B ) produces an achromatic animation and in the second part of the tilt angle range (Δθ R‑ ; Δθ R+ ) produces the same rainbow-colored animation, which is connected to the achromatic animation on both sides of the first part of the tilt angle range.

Description

Technical Field

[0001] The present invention relates to the field of security markings. More specifically, the present invention relates to a reflective visible optical security element for verifying the authenticity of a document, to a method for manufacturing such an element, and to a security document equipped with such an element. Background Art

[0002] Many technologies are known for the authentication of documents or products, in particular for the protection of documents (e.g. documents of value, such as banknotes, passports or other identification documents). The aim of these technologies is to produce optical security components with an optical effect that, depending on the observation parameters (orientation of the component with respect to the observation axis, position and size of the light source, etc.), presents a very characteristic and verifiable configuration. The overall goal of these optical components is to provide new and distinctive optical effects based on a physical configuration that is difficult to replicate. Among these components, DOVID (standing for "Diffractive Optically Variable Image Device") is the name given to optical components that produce diffractive variable images, generally known as holograms.

[0003] For example, it is known to produce an effect consisting of a dynamic variation of the optical effect, for example in the form of a bright and / or colored area moving in a given direction (sometimes referred to as a "rolling bar"), the movement being caused by the rotation (tilting) of the component. Thus, an observer can see the bright and / or colored area moving along the image when the component is rotated, serving as an additional authentication check.

[0004] This dynamic optical effect of presenting a "rolling bar" is described, for example, in the patent publication WO2015154943 [reference 1] applied for in the name of the present applicant. The optical security component described in the above-referenced application has a reflective visible effect. The optical security component includes a diffractive structure etched on a dielectric material layer. The structure presents a first pattern, which includes a bas-relief having a first set of facets, the shape of which is determined to simulate a series of reflectively visible concave or convex cylindrical optical elements, and the first pattern is modulated by a second pattern forming a sub-wavelength grating. This optical security component presents a dynamic visual effect of bright bands of different colors moving in opposite directions when it rotates by tilting around an axis parallel to one of the main directions of the cylindrical element.

[0005] The published patent WO2018224512 [Reference 2] applied for in the name of the present applicant describes more complex dynamic visual effects than those disclosed in [Reference 1], such as the intersection of two line segments "moving" in the same direction at different speeds or in opposite directions and / or the movement of inclined line segments.

[0006] In order to achieve these dynamic visual effects, the optical security component described in [Reference 2] includes a first layer of dielectric material and a diffractive structure etched on the first layer. The diffractive structure includes a first pattern having a group of modules arranged side by side in a given arrangement direction, and the maximum width of each module defined in the arrangement direction is less than 300 μm. Each module includes a bas-relief having a first group of facets, the shape of which is determined to simulate a reflective visible optical element having at least one raised or concave area, the optical element having a profile with a slope that continuously changes in a single direction perpendicular to the arrangement direction, the single direction being referred to as the slope change direction. In addition, for two modules arranged side by side, the slope along at least one line parallel to the arrangement direction is different between the two modules. The minimum number of modules is determined by the maximum width of the module so that the diffractive structure is visible to the naked eye. This optical security component presents a dynamic visual effect in reflection and under the effect of tilting movement around an axis parallel to the arrangement direction, which dynamic visual effect includes the movement of one or more complex graphic elements depending on the arrangement of the modules, and due to the design and manufacture of the modules necessary to obtain the above-mentioned visual effects, this optical security component allows more secure authentication and stronger technical barriers compared to a simple horizontal scroll bar.

[0007] Furthermore, the first pattern can be modulated by a second pattern forming a periodic grating with a sub-wavelength period, which second pattern is determined to produce a filter resonating in a given spectral band after deposition of a second layer (having a reflective spectral band in visible light), so that dynamic visual effects can be combined with 0th order color effects.

[0008] The present application describes an optical security component with an original structure that not only enables complex dynamic visual effects or "animations" as described in [Reference 2], but also allows continuous switching from a white achromatic animation to the same but iridescent animation simply by tilting the optical security component over a wider range of angles, thereby ensuring more reliable authentication through simple visual inspection without the need for special equipment. Summary of the invention

[0009] In this specification, the term "include" has the same meaning as "include" or "contains", is inclusive or open, and does not exclude other elements that are not described or shown. In addition, in this specification, the term "about" or "substantially" has the same meaning as "having a margin of less than and / or greater than 10% (e.g., 5%) of the corresponding value".

[0010] According to a first aspect, the invention relates to an optical security component configured to be observed with the naked eye in reflection in a viewing direction forming a given viewing angle with a given illumination direction and along at least a first viewing face, the component comprising:

[0011] - a first layer made of a dielectric material, which first layer is transparent in visible light;

[0012] - at least a first diffractive structure etched on said first layer; and

[0013] - a second layer at least partially covering the first structure and having a reflection spectral band in the visible light; and wherein:

[0014] - said first diffractive structure comprises a first pattern consisting of a set of parallel facets, said facets having a slope varying in a slope variation direction, said slope comprising an angular value in absolute value comprised between a minimum angular value and a maximum angular value, said facets having a given maximum height, said set of facets being arranged so as to generate a dynamic visual effect observable in reflection under the effect of a tilting movement along an axis substantially perpendicular to said slope variation direction and within a given tilting angle range, when said component is illuminated with white light along said illumination axis;

[0015] - in at least a first area, the first pattern is modulated by a second pattern, the second pattern forming a periodic grating with a predetermined period size between 450nm and 650nm, the grating comprising grating vectors having a direction colinear with the slope variation direction, the grating being determined to produce 1st and -1st order diffraction effects in reflection after deposition of the second layer.

[0016] The period of the grating, the maximum angular value of the slope and the observation angle are determined to produce an achromatic animation in a first part of the tilt angle range around specular reflection, and to produce the same animation in rainbow colors in a second part of the tilt angle range, wherein the rainbow color animation connects the achromatic animation on both sides of the first part of the tilt angle range.

[0017] In this specification, a layer transparent in visible light is defined as a layer having a transmittance of at least 70%, preferably at least 80%, for wavelengths included in visible light (i.e., wavelengths between about 400 nm and about 800 nm). Such a transparent layer allows the layer located below the transparent layer to be observed with the naked eye.

[0018] In this specification, a set of "parallel" facets is a set of facets having a slope change in the same direction, which is referred to as the "slope change direction." However, the slope of the facets may change in this direction, in the opposite direction.

[0019] The "height" of a facet is the distance between the lowest level and the highest level of the facet, measured along an axis perpendicular to the plane of the component.

[0020] Rotation of the component about an axis contained in the plane of the component is often referred to as "tilt motion" of the component.

[0021] The Applicant has demonstrated that such an optical security element, in reflection and under the effect of a simple tilting movement about an axis perpendicular to the direction of variation of the slope, presents a dynamic visual effect or a reflective, bright, achromatic "animation" around a specular reflection, followed by the same but iridescent animation that joins the achromatic animation on both sides of a first portion of the tilt angle range. This effect allows a more secure authentication and a stronger technical barrier, thanks to the design and manufacture of the components necessary to obtain the above-mentioned visual effect.

[0022] In this specification, specular reflection corresponds to a component position that allows incident light to be reflected at a reflection angle having a measurement opposite to the angle of incidence. In other words, the normal to the component plane divides the viewing angle into two angular sectors of equal measurement.

[0023] For example, the viewing angle is defined relative to a vertical lighting direction.

[0024] According to one or more embodiments, the viewing angle is between about 30° and about 60°. For example, the viewing angle is equal to about 45°, which corresponds to a normal viewing position of an observer for vertical illumination.

[0025] According to one or more embodiments, the minimum angle value (absolute value) of the slope is equal to 0°.

[0026] According to one or more examples, the maximum angle value (absolute value) of the slope is between about 7° and about 15°.

[0027] By convention, in this specification, the positive direction of the angle value used to measure the slope of the facet is the clockwise (or anti-trigonometric) direction.

[0028] According to one or more examples, the dimension (or "width") of the facet in the direction of the slope is greater than or equal to about 4 times the grating period, advantageously greater than or equal to about 8 times the grating period. Thus, the minimum dimension can be selected as a function of the grating period. For example, the minimum dimension of the width of the facet is equal to about 2 μm.

[0029] According to one or more examples, the width of the facet is between about 2 μm and about 100 μm, advantageously between about 2 μm and about 80 μm, advantageously between about 4 μm and about 80 μm.

[0030] According to one or more examples, the facet has a substantially rectangular shape and has a “length” measured in a direction perpendicular to the direction of the slope. The length is, for example, less than about 100 μm.

[0031] According to one or more examples, the set of facets has substantially the same height. The height of the facets is, for example, less than 2 micrometers, advantageously less than 1 micrometer.

[0032] According to one or more examples, the facets in the set of facets have different heights. However, in this case, the facets have a maximum height. The maximum height is, for example, less than 2 micrometers, advantageously less than 1 micrometer.

[0033] According to one or more embodiments, at least some of the facets of the group of facets are arranged with a varying slope, the variation of the varying slope being respectively increasing or decreasing, so as to simulate a reflective element having respectively raised or concave areas. In the present specification, a "half-wave" type of dynamic effect refers to the visual effect caused by such an arrangement of facets when the variation of the angular value of the slope of the facet is increasing or decreasing but the sign is the same. A "wave" type of dynamic effect refers to the visual effect caused by such an arrangement of facets when the variation of the angular value of the slope of the facet is increasing or decreasing and there is at least one change of sign. During the tilting movement of the component, the "wave" or "half-wave" type of dynamic effect appears to the observer as a continuous movement of white light.

[0034] According to one or more embodiments, the set of facets includes one or more sub-sets of facets, each sub-set of facets being configured to produce a "wave" type dynamic effect.

[0035] According to one or more observation examples, the period of the diffraction grating, the maximum angular value of the slope (measured in absolute value) and the observation angle are determined so that the first part of the tilt angle range comprises an angular superposition (overlap) with the second part of the tilt angle range on both sides of the first part of the angular range, which angular superposition (overlap) is between about 1° and about 10°, preferably between about 3° and about 8°, for example equal to about 5°. This design of the optical security element according to the present description ensures that the iridescent animation continues the achromatic animation without interruption on both sides of the first part of the tilt angle range. However, in an extreme case, the angular superposition can be zero, as long as there is continuity between the achromatic animation and the iridescent animation.

[0036] Based on one or more observation examples, the period of the diffraction grating, the maximum angular value of the slope (measured in absolute value), and the observation angle are determined so that the tilt angle range is between about 45° and about 120° (measured in air).

[0037] Based on one or more observation examples, the period of the diffraction grating, the maximum angular value of the slope (measured in absolute value) and the observation angle are determined so that the first part of the tilt angle range is between about 15° and about 50° (measured in air), advantageously between about 20° and about 35° (measured in air).

[0038] According to one or more embodiments, the period of the diffraction grating, the maximum angular value of the slope (measured in absolute value), and the observation angle are determined so that the second part of the tilt angle range (measured in air) is between about 30° and about 70°, advantageously between about 40° and about 60°, on both sides of the first tilt angle range.

[0039] According to one or more embodiments, the one-dimensional diffraction grating is a diffraction grating with a sinusoidal profile. The advantage of a grating with a sinusoidal profile is that it allows symmetry of the diffraction efficiency of the +1st and -1st orders, and therefore, symmetry in terms of the visual efficiency of the rainbow color animation on both sides of the achromatic animation. However, other grating profiles are also possible, such as, as non-limiting examples, a diffraction grating with a pseudo-sinusoidal profile (defined as a sum of sinusoids with amplitude and phase adjustable according to the desired profile), a diffraction grating with a rectangular profile, or any other grating that advantageously has a symmetrical profile in order to have similar visual efficiency for the rainbow color animation on both sides of the achromatic animation.

[0040] According to one or more embodiments, the depth of the diffraction grating is determined to optimize the diffraction efficiency of the grating at the 1st and -1st orders at at least one wavelength of the visible spectrum, such as at the central wavelength of the visible spectrum, such as around 550 nm.

[0041] In accordance with one or more embodiments, the second layer includes a metallic material.

[0042] The metal material includes a material or an alloy of materials selected from the following: aluminum (Al), silver (Ag), chromium (Cr), gold (Au), copper (Cu). For example, the thickness of the metal material layer is greater than about 2 to 3 times the skin depth of the metal or alloy forming the metal material layer in the visible light frequency range; for example, for aluminum, the thickness of the metal material layer is between about 20nm and about 60nm.

[0043] According to one or more 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 about 0.3, advantageously greater than or equal to about 0.5. For example, the second layer comprises a material selected from the group consisting of zinc sulfide (ZnS), titanium dioxide (TiO 2 ) or silicon nitride (Si 3 N 4 ).

[0044] Generally speaking, the material forming the second layer makes it possible to give the component a reflection spectral band in visible light and to make the first diffractive structure visible. Such a material suitable for the second layer is described, for example, in patent US4856857 [reference 3].

[0045] According to one or more embodiments, the minimum dimension of the first structure is larger than 300 μm, preferably larger than 1 mm, preferably larger than 2 mm, preferably larger than 5 mm. Such a minimum dimension makes it possible to make the structure visible to the naked eye.

[0046] According to one or more embodiments, the first structure has an outline that forms a recognizable graphical shape when viewed from a viewing surface.

[0047] According to one or more embodiments, the optical security element according to the first aspect comprises at least a second structure etched on the first layer, the second layer at least partially covering the second structure. As non-limiting examples, the second structure is configured to form a diffuse structure, a holographic structure, a diffractive structure, so that the so-called effect.

[0048] When the component comprises at least a second structure, the structures may be juxtaposed, each structure having a recognisable shape.

[0049] According to one or more embodiments, the first pattern has an outline that forms a recognizable graphical shape when viewed from a viewing surface.

[0050] According to one or more embodiments, the first pattern is interrupted in an area forming a recognizable graphical object visible during an achromatic animation and during an iridescent animation when viewed from a viewing surface.

[0051] According to one or more embodiments, in at least a second area, the first pattern is not modulated or is modulated by a third pattern forming a periodic grating different from the second pattern, and when viewed from a viewing surface, the second area forms a recognizable graphical object visible only during the rainbow color animation.

[0052] Thus, a "visual scene" can be generated using graphical objects that appear during both animations (achromatic and iridescent) or that appear only during the iridescent animation.

[0053] According to one or more embodiments, depending on the use requirements, the optical security element according to the first aspect comprises one or more additional layers, without this additional layer or layers contributing to the desired visual effect.

[0054] Thus, according to one or more embodiments, the optical security component is configured to protect an object (e.g. a document or a product) and further comprises, on the side opposite to the viewing side, a layer (e.g. an adhesive layer or a reactive adhesive layer) suitable for transferring the component to the document or product.

[0055] According to one or more embodiments, the optical security element further comprises a support film on the side of the first viewing face, which support film is intended to be peeled off after transferring the element to the document or product.

[0056] According to one or more embodiments, the optical security component is configured for producing a security track for protecting a banknote and comprises one or more protective layers on the side of the first viewing face and / or on the face opposite to the first viewing face.

[0057] According to a second aspect, the present description relates to a security object, such as a security document of value, comprising a substrate and an optical security element according to the first aspect, deposited on the substrate or, in the case of a multilayer substrate, on one layer of the substrate.

[0058] As non-limiting examples, such security objects are: banknotes, or identity or travel documents on a paper or polymer substrate.

[0059] According to a third aspect, the present description relates to a method for producing an optical security element according to the first aspect.

[0060] The present description therefore relates to a method for producing an optical security element intended to be viewed with the naked eye in reflection along at least a first viewing surface, the method comprising:

[0061] - depositing on the support film a first layer made of a dielectric material, the first layer being transparent in visible light;

[0062] - forming at least a first diffractive structure on said first layer, such that:

[0063] - said first diffractive structure comprises a first pattern consisting of a set of parallel facets, said facets having a slope varying in a slope variation direction, said slope comprising an angular value in absolute value comprised between a minimum angular value and a maximum angular value, said facets having a given maximum height, said set of facets being arranged to generate a dynamic visual effect observable in reflection under the effect of a tilting movement along a tilting axis substantially perpendicular to said slope variation direction and within a given tilting angle range, when said component is illuminated with white light along said illumination axis;

[0064] - in at least a first area, the first pattern is modulated by a second pattern, the second pattern forming a periodic grating with a predetermined period size between 450nm and 650nm, the grating comprising grating vectors having a direction colinear with the slope variation direction, the grating being determined to produce 1st and -1st order diffraction effects in reflection after deposition of the second layer.

[0065] - depositing a second layer which at least partially covers the first diffractive structure and has a reflection spectral band in the visible, wherein

[0066] - The period of the grating, the maximum angular value of the slope and the observation angle are determined so that, after deposition of the second layer, an achromatic animation is generated in reflection in a first part of the tilt angle range around specular reflection, and an identical animation is generated in rainbow colors in a second part of the tilt angle range, the rainbow color animation adjoining the achromatic animation on both sides of the first part of the tilt angle range. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Other features and advantages of the present invention will emerge from reading the following description, which is illustrated by the following drawings:

[0068] Figure 1A Schematically shown are (partial) cross-sectional views of embodiments of components according to the present description.

[0069] Figure 1B A (partial) cross-sectional view of another embodiment of a component according to the present description is schematically shown.

[0070] Figure 2 It consists of a number of figures showing parameters of a diffractive structure in a security component according to the present description.

[0071] Figure 3 is a diagram showing the convergence of iridescent and achromatic animations of an optical security element according to the present specification during a tilting motion.

[0072] Figure 4AConsists of a number of graphs which show, according to one example, a first rainbow colour animation in an optical security element according to the present description as a function of the tilt angle of the element in a first part of the tilt angle range.

[0073] Figure 4B It consists of a number of graphs showing Figure 4A The optical security element of the same optical security element, in a second part of the tilt angle range, the achromatic animation as a function of the tilt angle of the element, wherein the achromatic animation merges with the first iridescent animation.

[0074] Figure 4C It consists of several figures showing the Figure 4A The same optical security component of the optical security component has, in a third part of the tilt angle range, a second rainbow color animation as a function of the tilt angle of the component, wherein the second rainbow color animation merges with the achromatic animation and exhibits a color inversion relative to the first rainbow color animation.

[0075] Figure 5A It is composed of curves, which respectively show: in a facet arrangement configured to produce a "half-wave" type dynamic effect, for a given height, an example of the spatial distribution of the facet width; in a facet arrangement configured to produce a "half-wave" type dynamic effect, for two facet heights, the angular value of the facet slope (in degrees) as a function of the facet width; in a facet arrangement configured to produce a "wave" type dynamic effect, for two facet heights, the angular value of the facet slope (in degrees) as a function of the facet width.

[0076] Figure 5B is a diagram showing an example of the distribution of facets to form a "pixel".

[0077] Figure 5C It consists of a number of curves showing the effect of the slope of the facet for three tilt angles of the component lying in a first part of the tilt angle range.

[0078] Figure 6 are graphs showing the slope of the facets and the effect of the grating as a function of the tilt angle of the component in a second part of the tilt angle range, on either side of a first part of the tilt angle range.

[0079] Figure 7 Consists of a number of curves showing the efficiency of a diffraction grating with a sinusoidal profile in the +1st or -1st order as a function of the grating depth for a wavelength of 550 nm.

[0080] Figure 8 One example of an optical security element according to the present description is shown, which has a "patch" type format.

[0081] Fig. 9A is a diagram showing an example of a valuable document (eg, banknote) protected by an optical security element according to the present specification.

[0082] Fig. 9B It is shown Fig. 9A A magnified view of the security document shown in .

[0083] Fig. 10A The figure consists of a plurality of figures which respectively show the designs of the first pattern and the second pattern in an example of the optical security element according to the present specification.

[0084] Fig. 10B It consists of multiple graphs, which are based on the given visual scene, such as Fig. 10A The patterns shown schematically are used to illustrate the visual animation of achromatic and iridescent colors. DETAILED DESCRIPTION

[0085] In the drawings, elements are not shown to scale for the sake of better visibility. Figure 1A and Figure 1B Two examples of optical security components according to the present description are shown schematically and in (partial) cross-section. Figure 1A The optical security element 101 shown in represents an optical security element intended, for example, to be transferred to a document or a product in order to protect it. According to this example, it comprises a support film 111, for example a film made of a polymer material, such as a polyethylene terephthalate (PET) film of a few tens of micrometers, typically 15 μm to 100 μm, and a peeling layer 112, for example made of a natural or synthetic wax. The peeling layer makes it possible to remove the polymer support film 111 after the optical element has been transferred to the product or document to be protected. The optical security element 101 also comprises a first layer 113 made of a dielectric material, which first layer 113 has a first refractive index n 1 and at least one first diffractive structure S, the first diffractive structure S comprising a first pattern M 1 , the first pattern M 1 The second pattern M forming a periodic grating 2 The modulation is imprinted on said first layer 113 and is described in more detail below.

[0086] exist Figure 1AIn the example of , the optical security element 101 further comprises a second layer 114, which at least partially covers the first structure S and has a reflection spectral band in visible light. The second layer 114 is, for example, a metal layer or a layer called a refractive index variation layer, which has a refractive index different from that of the first layer, the refractive index difference between the layers 113 and 114 having a value at least equal to 0.3, advantageously having a value at least equal to 0.5. The layer 114 ensures the reflection of the incident light.

[0087] The optical security element may also comprise one or more optional layers which are not optically functional but are suitable for the requirements of use.

[0088] For example, in Figure 1A In the example of FIG. 4 , the optical security element further comprises an adhesive layer 117 , such as a thermo-reactive adhesive layer, for transferring the optical security element to a product or document.

[0089] In practice, as will be described in detail below, the optical security element can be manufactured by stacking the layers on a support film 111 and then transferring the element to the document / product to be protected using an adhesive layer 117. Optionally, the support film 111 can then be peeled off, for example by peeling off the layer 112. Thus, the main viewing face 100 of the optical security element is located on the side of the first layer 113 opposite to the etched face of the layer 113.

[0090] Figure 1B The optical security component 102 shown in the figure represents an optical security component intended, for example, to protect a banknote; this is, for example, part of a security thread intended to be integrated into the paper during the manufacture of the banknote, or a laminated track covering a window in the paper, or a patch. In this example, as previously described, the component 102 comprises: a support film 111 (12 μm to 25 μm), which will also serve as a protective film for the security thread; Figure 1A The first layer 113 made of a dielectric material shown in the example in FIG. 1 has a first refractive index n 1 , at least one first diffraction structure S, which is embossed on the first layer 113; and a second layer 114, which at least partially covers the first structure S and has a reflection spectrum band in visible light. Figure 1BIn the example of , the optical security component 102 also includes a set of optional layers 115, 116, 118. Layer 115 (optional) is, for example, a layer 115 made of a dielectric material, such as a transparent layer; layer 116 (optional) is, for example, a security layer 116, such as a discontinuous layer with a specific pattern partially printed with UV ink to produce an additional mark that can be inspected by the naked eye or by a machine; layer 118 (optional) is, for example, a protective layer, such as a second polymer film or paint. In the case of a laminated track, layer 118 can be an adhesive layer. As in the previous example, the manufacturing can be performed by stacking these layers on the support film 111. The dielectric layer 115 and the security layer 116 can form only one layer. The protective layer (or adhesive layer) 118 and the layer 115 can also form the same layer.

[0091] It is obvious to those skilled in the art that Figure 1A and Figure 1B In each of the examples shown, other optical non-functional layers may be added depending on the use requirements, and may be combined Figure 1A and Figure 1B An alternative embodiment is shown in .

[0092] Note that if the optically non-functional additional layer, such as layer 117, or the layers 115, 116, 118 together with the target carrier are transparent, the optical security component may be visible from both sides, wherein a reversal of the curvature of the optical element is generated.

[0093] Figure 2 The parameters of the diffractive structure S (FIG. 23) according to the present specification are shown in more detail. The structure S consists of a first pattern M 1 Forming the first pattern M 1 Includes a set of small faces F i (FIG. 22), the pattern is at least partially composed of a second pattern M 2 Modulation, second pattern M 2 It is defined by the projection of a single-direction diffraction grating labeled G ( FIG. 21 ) and is confined in a plane π parallel to the plane of the component (and therefore parallel to the viewing plane 100 ).

[0094] All small faces F i are parallel, that is, they are in the same direction (in Figure 2 It is characterized by a height h defined by the distance between the lowest level and the highest level of the facet, measured along an axis perpendicular to the plane π (which is parallel to the plane of the component), i.e., Figure 2 In the example, the z axis is measured. Figure 2In the example of , the facets all have the same height h, which is less than about 2 μm, advantageously less than about 1 μm, for example between about 0.5 μm and about 1 μm.

[0095] The facet is also characterized by a width Λ, which is defined by the dimension in the slope variation direction y, and which is generally, for example, between about 2 μm and about 100 μm, for example, between about 2 μm and about 80 μm, for example, between about 4 μm and about 80 μm. Advantageously, the minimum width of the facet will be greater than about 4 times the grating period, advantageously greater than about 8 times the grating period.

[0096] In general, the facets have a substantially rectangular shape. The dimension of the facets along the x-axis (referred to in this description as "length"), included in the plane xy (plane π, which is parallel to the plane of the component) and perpendicular to the y-axis, defines the width of the pixel (that is to say, the elementary area of ​​the structure reflecting light in the same direction). In general, a length of less than about 100 μm, advantageously less than 60 μm, will be sought, so as to be invisible to the naked eye.

[0097] Small noodles F i has a slope whose angle value is α i In absolute value, it is comprised between a minimum angle value (e.g., 0°) and a maximum angle value (e.g., between about 7° and about 15°). Figure 2 As shown, in this specification, the positive direction of the angle value selected for measuring the slope is the clockwise or anti-trigonometric direction.

[0098] As shown in Figure 21, the diffraction grating G is a unidirectional diffraction grating characterized by a pitch or period d and a depth t. The grating vector is designated as k g , which is collinear with the direction of slope change y and has a modulus equal to 2π / d.

[0099] from Figure 2 As can be seen from FIG. 23 , the structure S resulting from the modulation of the diffraction grating G on the first pattern comprising a set of facets comprises a plurality of diffraction gratings G each supporting a one-dimensional diffraction grating. i A group of small faces F i In the component according to the present description, the facet F i Each has an angle α relative to a plane parallel to the plane of the component i A diffraction grating G with a constant spacing d and with a grating vector having a direction collinear with the direction of slope variation is formed on each facet F. i The projection on the Mi ) of the projection grating G iSince the slopes of the facets have low angular values, typically less than 15° in absolute value, the effect of these variations in the grating pitch on the different facets can be neglected in most implemented examples.

[0100] exist Figure 2 In the example of (Fig. 21), the 1st order diffraction grating G has a sinusoidal profile. Other profiles are also possible, such as a quasi-sinusoidal profile (which is defined as the sum of sinusoids with amplitude and phase adjustable according to the desired profile) or a rectangular profile. Such a symmetrical profile has the advantage of presenting similar diffraction efficiencies in the +1st and -1st orders. A symmetrical grating profile means that the grating has a profile that is centrally symmetrical (about a point).

[0101] Once the structure S is determined due to the definition of the first and second patterns, a process of recording this structure can be carried out to manufacture the optical security element, as will be described in more detail below.

[0102] In an optical security component according to the present specification, the period d of the diffraction grating, the maximum angular value α of the slope (measured in absolute value) and the observation angle are determined so that an achromatic animation is viewed in a first part of the tilt angle range around mirror reflection, and the same but iridescent animation is viewed in a second part of the tilt angle range, the iridescent animation adjoining the achromatic animation on both sides of the first part of the tilt angle range.

[0103] Figure 3 A diagram depicting the desired convergence of iridescent and achromatic animations of an optical security element 40 according to the present specification during a tilting motion is shown.

[0104] The illumination axis (e.g. vertical illumination corresponding to natural light) is designated as Δ L , corresponding to the observer (in Figure 3 The viewing axis of the viewing direction (represented by the eye in FIG. 1 ) is designated as Δ O , and the axis Δ L and Δ O The observation angle between obs In the rest of this specification, θ obs The absolute value of the angle measurement equal to the observation angle.

[0105] In practice, when checking the authenticity of a document protected by an optical security element according to the present description, the document is rotated (tilted) about a tilt axis Δ which is contained in the plane of the element and is substantially perpendicular to the direction of slope variation. The tilt axis is thus substantially parallel to the x-axis ( Figure 2 ).

[0106] In practice, the directions of illumination and observation are fixed, and tilting motion of the component causes a change in the angle of incidence θi of the light incident on the component relative to a direction Δ N By convention, in this specification, the positive direction of the incident angle is the trigonometric direction. As will be described in more detail below, the change in the incident angle θi results in the second pattern M 2 The first modulated pattern M 1 The structure S (see Figure 2 )The angle of diffracted light is θ o The change of θ O =θ i -θ obs , where θ obs is taken as an absolute value. Therefore, the diffraction angle θ o The normal of the component and the viewing direction Δ O By convention, in this specification, the positive direction of the diffraction angle is the same as the incident angle. Figure 3 In the figure, the optical security component 40 is shown in a central position, for which the normal axis Δ perpendicular to the component plane N The observation angle θ obs is divided into two angular sectors of equal measurement value (specular reflection position, for which θ o =-θi).

[0107] like Figure 3 As shown, the tilt angle range Δθ is sought tilt The first part Δθ B See the achromatic animation for the first part of the tilt angle range Δθ B It is also sought to see the same but iridescent animation in the second portion of the tilt angle range, which is joined by the achromatic animation on both sides of the first portion of the tilt angle range. Figure 3 As shown, the second part of the tilt angle range includes the angle range Δθ R- and angle range Δθ R+ , from the observer's perspective, the angle range Δθ R- and angle range Δθ R+ Corresponding to the optical safety component tilting backwards or forwards respectively.

[0108] The rainbow color animation is a "rainbow" animation in which the observer sees the colors of the rainbow marching. For simplicity, in the attached figure, only four colors of the rainbow are shown, which are represented by textures, namely red (texture 311), yellow (texture 312), green (texture 313), blue (texture 314).

[0109] FIG. 4A to FIG. 4C An example of a dynamic visual effect obtained with an optical security element according to the invention is shown in more detail.

[0110] In this example, the optical security element comprises according to the present description two diffractive structures, a structure 401 forming the number "2" and a structure 402 forming the number "5". The diffractive structures have contours defined, for example, by demetallization or, more generally, by local removal of a reflective layer or, in other embodiments, by the boundaries of the structure itself.

[0111] Figure 4B Shown in Figure 3 is marked as Δθ B More specifically, FIG. 44 corresponds to Figure 3 The position of the optical safety component 40 marked as 4 in FIG. 45 corresponds to Figure 3 The position of the optical safety component 40 marked as 5 in FIG. 46 corresponds to the center position of the mirror reflection. Figure 3 The position of the optical safety element 40 is marked as 6 in FIG. Figure 4B In , achromatic animations include, for example, the movement of a circular white line on a black background.

[0112] Figure 4A The rainbow color animation effect is shown in the second part of the tilt angle range, which is in the Figure 3 is marked as Δθ R+ , and corresponds to a forward tilting movement of the component from the perspective of the observer. More specifically, FIG. 41 corresponds to Figure 3 The position of the optical safety component 40 marked as 1 in FIG. 42 corresponds to Figure 3 The position of the optical safety component 40 marked as 2 in FIG. 43 corresponds to Figure 3 The position of the optical safety element 40 is marked as 3 in FIG. Figure 4A In the example, each color is represented by a Figure 3 The textures used in are shown.

[0113] Figure 4C The rainbow color animation effect is shown in the second part of the tilt angle range, which is in the Figure 3 is marked as Δθ R- , and corresponds to a backward tilting movement of the component from the perspective of the observer. More specifically, FIG. 47 corresponds to Figure 3 The position of the optical safety component 40 marked as 7 in FIG. 48 corresponds to Figure 3 The position of the optical safety component 40 marked as 8 in FIG. 49 corresponds to Figure 3 The position of the optical safety element 49 is marked as 3. Figure 4C In the example, each color is represented by a Figure 3 The textures used in are shown.

[0114] Therefore, if FIG. 4A to FIG. 4C As shown, an achromatic dynamic visual effect is observed around the specular reflection, which is caused by the arrangement of the small faces forming the first pattern as explained in more detail below, and the same but iridescent dynamic visual effect is observed on both sides, where the colors of the rainbow are traveling.

[0115] As also described in detail below, the rainbow effect is caused by the +1st and -1st order diffraction (for the tilt angle range Δθ, respectively) of the grating modulating the facets. R+ and Δθ R- ) caused by.

[0116] The rainbow animation is connected to the achromatic animation on both sides. FIG. 4A to FIG. 4C In the example, two specific incident angles can be defined, namely θ T + (Figures 43 and 44) ​​and θ T - (Figures 46 and 47), which correspond to the incident angles for the transition between the achromatic animation and the +1st order iridescence animation and between the achromatic animation and the -1st order iridescence animation, respectively.

[0117] Please note that if Figure 4A and Figure 4C As shown, in the two tilt angle ranges Δθ R+ and Δθ R- In other words, for example, within the angle range Δθ R+ The inward-facing observer diffracts the red facet over the angle range Δθ R- Internal diffraction blue.

[0118] The steps in designing the structure will now be described, in particular, Figure 2 The parameters shown are chosen to obtain the following according to the present specification and for example in Figure 3 and FIG. 4A to FIG. 4C Dynamic visual effects shown in .

[0119] In order to achieve the above dynamic visual effect, the structure of the first pattern is first determined, that is, the position, size and slope of the facets are determined so as to Figure 3 Δθ in B ) to obtain the desired achromatic animation.

[0120] Figure 5AAn example of a spatial distribution of facet widths that can produce a dynamic effect is shown ( FIG. 51 ), as well as a graph showing the angular value of the slope of the facet as a function of the width, as a tool for designing a first pattern in an optical security component according to the present specification in order to construct a desired animation.

[0121] More specifically, FIG. 51 shows a curve 510 that depicts the width of the facet along the slope variation axis y (see FIG. 51 ) in a first arrangement of facets configured to produce a dynamic effect. Figure 2 As shown in FIG51 , the width varies as a function of decreasing, and this is reflected as a continuous increase in the value of the angle of the slope at a constant height h of the facet for simulating a concave reflective element.

[0122] For example, FIG. 51 shows a continuously decreasing variation, which follows can be written as where a and b are the tuning parameters of the function. Note that other functions can also be used.

[0123] In practice, the variation of the width and angle of the facets comprises discrete values ​​selected according to the size of the diffractive structure. Thus, for example, if a "wave" type effect is desired in an area of ​​a given size, a greater number of facets can be selected over a larger area, and the dynamic effect will be more fluid and continuous.

[0124] In practice, for a given facet height h, the facet width can be selected as a function of the desired facet angle.

[0125] Thus, Figure 52 shows the angle value (in degrees) of the slope of the facet as a function of the facet width for two facet heights, 1 μm (curve 521) and 0.5 μm (curve 522), for an arrangement of facets configured to create a dynamic effect equivalent to a concave optical element. As shown in Figure 52, the width of the facet decreases, which results in a change in the angle value of the slope of the facet to increase at a constant height.

[0126] In the same way, FIG53 shows the angle value (in degrees) of the slope of the facet as a function of the facet width for two facet heights, 1 μm (curve 531) and v.5 μm (curve 532) for the arrangement of the facets configured to form a "wave" type (convex) dynamic effect. As shown in FIG53, the width of the facet increases first and then decreases, which results in a change in the angle value of the slope of the facet at a constant height that first decreases and then increases.

[0127] like Figure 5A The facets with varying angles and widths described in the embodiment are used to design a first pattern of structures, which will be in a first tilt angle range Δθ B Generate achromatic animations internally.

[0128] Each facet in question makes it possible to reflect light in a given direction according to the slope of the facet and according to a precise angular distribution. At a fixed angle of incidence, the facets involved in the motion (the "active" facets) are those whose response makes it possible to reflect light in a direction Δ O (in other words, facing the observer handling the document). Thus, when the document is tilted in the first part of the angle range Δθ B At medium tilt, the "active" facets will appear white (lit up) and the other facets will appear black (off).

[0129] To obtain Figure 3 or Figure 4A and Figure 4B The optical effect shown, first, limits the observation angle θ obs , making it equal to the lighting direction Δ L (e.g. vertical lighting direction) and viewing direction Δ O For example, in air, the observation angle θ obs Between about 30° and about 60°. For example, in air, the viewing angle is equal to about 45°.

[0130] The achromatic animation in the first part of the tilt angle range is defined as the maximum slope of the facet (expressed in absolute value) α max function, in other words, Δθ B,n1 =2|α max |, where Δθ B,n1 is limited to the refractive index n 1 The first layer (113, Figure 1A and Figure 1B ). In air, this angle range is larger, corresponding to Δθ B =arcsin(n 1 sin(2|α max |)). For example, for a refractive index value n 1 =1.5 and value α max = 7.1°, the first part of the angular range Δθ measured in air B Equal to 21.5°.

[0131] The facets participating in the dynamic visual effect of the pattern are determined by observing the optical response of each facet to a given illumination defined by the tilt of the sample.

[0132] By calculating the angle θ i The Fourier transform FT of the phase shift Δφ experienced by light incident on the optical security element yields the optical response of the facet of width Λ and depth h. The phase shift Δφ is expressed as follows:

[0133] [Mathematical formula 1]

[0134]

[0135] Where λ is the central operating wavelength in the visible light domain, such as 550nm, n 1 is the first layer of dielectric material (113, Figure 1A and Figure 1B ) is the refractive index of the facet, and h is the height of the facet. Therefore, the optical response of the facet is expressed as follows:

[0136] [Mathematical formula 2]

[0137]

[0138] where ν is the spatial frequency and is given by:

[0139] [Mathematical formula 3]

[0140]

[0141] In this manner, the distribution can be predicted as well as the direction that maximizes the energy reflected at the 0th order by each facet for a given tilt angle, so that a first pattern of structures can be designed to produce the desired animation.

[0142] In white light, the slope is α i The optical response of the facet corresponds to the diffraction lobe obtained by considering the envelope of the range of diffraction orders in the wavelength range from 400 nm to 800 nm. i The diffraction lobes of the facets are at angular position θ o =-θ i +2·α i As the center.

[0143] Figure 5B An example of diffraction lobes is shown in , where three scenarios are modeled. Each scenario corresponds to a different tilt of the document. Thus, the incident angle θ i (in the direction perpendicular to the plane of the component Δ N and the illumination direction of the light source Δ L The angle defined between the two angles is also different. The values ​​of this angle are 7.68° (Figure 57), 15° (Figure 58) and 21.8° (Figure 59).

[0144] In each scenario, the diffraction lobes of three facets are shown: two opposing facets (curves 502 and 503, respectively) with angles of -7.1° and 7.1°, corresponding to a width of 8 μm and a depth of 1 μm; and a central facet with essentially zero angle (curve 501), corresponding to a width of 80 μm and a depth of 1 μm.

[0145] Note that the smaller the width of the facet, the larger the angular range of the diffraction lobes, which results in a broadening of the reflected beam.

[0146] FIG. 58 shows the center position (specular reflection position) for which the normal axis Δ N The observation angle Δθ obs is divided into two angular sectors of equal measure, in other words, θ i =-θ o .

[0147] In this case, it is the facets with a slope angle of substantially zero that enable light to be reflected towards the eye (specular reflection), the direction of observation of the observer operating the document being symbolized by the eye in FIG. 58 (curve 501). Thus, the facets with a slope angle of substantially zero will appear "active". Diffraction lobes 502 and 503 do not reflect energy along the viewing axis, and the corresponding facets will appear closed.

[0148] By tilting the sample from one side to the other, the incident angle θ i is modified, and the diffraction lobe is shifted by Δθ i The value of θ corresponds to the angle θ experienced by the sample after tilting i changes.

[0149] Note that due to the refractive index of air / n 1 The refraction of light experienced after the interface changes, the tilt angle of the sample and the incident angle are different.

[0150] Figure 57 corresponds to an illumination with an incident angle of 7.68°. In this case, the facets participating in the achromatic animation are diffracted lobes towards Δ O Directionally reflective facets. In particular, the facets that participate in the visual effect in Figure 57 are the facets with an angle of -7.1° (curve 502). The direction of observation by the observer is represented by the eye.

[0151] When the sample was tilted to the other side of the center position, the incident angle was 21.8° and the facet with an opposite slope angle of +7.1° lit up (Figure 59).

[0152] Thus, the first pattern may be designed by a spatial arrangement of facets of varying slope, the facets being determined to reflect light energy in the direction of the observer for a given angle of incidence corresponding to a given angle of inclination.

[0153] For illustration purposes, Figure 5C shows the number "2" ( FIG. 4A to FIG. 4C ) is a diagram of the arrangement of small faces Fi in the area of ​​the structure.

[0154] "Pixel" P iIt can be defined as a spatial region containing a facet or several 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 to be invisible to the eye. Of course, other shapes of pixels can also be considered. Each "pixel" forms a light spot for a given tilt angle of the component. Thus, it is possible to create a pixel such as Figure 4B Achromatic animation shown.

[0155] We will now describe how to select the parameters of the +1st and -1st order diffraction gratings G in order to obtain the achromatic and iridescent animations in the first part of the tilt angle range Δθ B The connection on both sides.

[0156] In addition to the achromatic animation, the same facets modulated by the grating G generate an iridescent animation in the second part of the tilt angle range.

[0157] The parameters of the grating influence the junction of the two animations (achromatic and iridescent). Thus, the period d of the diffraction grating can be chosen as a function of the maximum angular value α of the slope (measured in absolute value) and the observation angle so that the achromatic animation is seen in a first part of the tilt angle range around the specular reflection, and the same but iridescent animation is seen in a second part of the tilt angle range, which joins the achromatic animation on both sides of the shown first part of the tilt angle range.

[0158] More specifically, it has been determined that, in order to obtain a transition between an achromatic animation and an iridescent animation, the period d of the grating G advantageously complies with the following conditions:

[0159] [Formula 4]

[0160]

[0161] in:

[0162] [Formula 5]

[0163]

[0164] is the refractive index n 1 The transition between achromatic animation and iridescent animation in a medium (in other words, consider air / n 1 refraction, such as Figure 3 The angle of incidence of the transition between positions 6 and 7 of the optical security element 40 shown, and:

[0165] [Mathematical formula 6]

[0166]

[0167] In addition, λm is the wavelength at which the rainbow color animation begins, e.g., λ VIS Between about 400 nm and about 450 nm.

[0168] This condition follows directly from the grating formula, according to which the direction of the + / -1st order diffraction will correspond to the viewing direction Δ O , and wherein the angle of incidence on the grating corresponds to the transition angle between the two tilt angle ranges calculated relative to the normal of the facet with the maximum slope angle.

[0169] For example, consider |α max |=7.1°,n 1 =1.5,θ obs =45° and λ vis =450nm, calculate the following terms: and

[0170] In this case, in order to ensure the connection as described above, d is chosen equal to 502 nm by applying the equation defined above.

[0171] Note that by manipulating the period value and the maximum slope of the facets, a strictly positive overlapping angle range can be defined between the first angle range (achromatic animation) and the second angle range (rainbow-colored animation).

[0172] For example, when choosing the period d of the diffraction grating 2 In the case of rec .

[0173] [Formula 7]

[0174]

[0175] If the period d of the grating G is chosen 2 Instead of the optimal period d where the overlap is zero, the incident angle θ 2 Corresponds to the start of the rainbow color animation:

[0176] [Mathematical formula 8]

[0177]

[0178] For example, using the parameters from the previous example, consider the period d 2 =520nm, in this case the angle θ 2 is equal to 8.1°, so in this case the overlap in air is Δθ rec =1.8°.

[0179] For example, Figure 6 Describes the use of the illumination direction ΔN When the component is illuminated by white light, the different facets modulated by the grating G diffract (+1 order and -1 order) and emit light in the direction Δ O Reflected wavelength as a function of angle of incidence. Curves 61, 62, 63, 64 and 65 correspond to facets overmodulated by a grating with a period of 520 nm at angles of -7.1°, -3.55°, 0°, +3.55° and +7.1° respectively.

[0180] Calculate the curve using the equation given above for d, where λ vis is replaced by the diffraction wavelength and d is replaced by the period selected for the diffraction grating G.

[0181] The total tilt angle range is divided into three angle ranges: the rainbow color animation range Δθ corresponding to the -1st order diffraction R- , the achromatic animation tilt range Δθ around the specular reflection B , and the second rainbow color animation range Δθ corresponding to the +1 order diffraction R+ .

[0182] At a fixed incident angle θ i In this case, each facet modulated by the grating G diffracts a different wavelength in the viewing direction. This wavelength depends on the specific slope of each facet. The dispersion generated by the different facets modulated by the grating G follows the same graphical pattern previously defined in the first tilt range.

[0183] In addition, if Figure 6 As shown, a facet with a given slope that diffracts a given wavelength at +1 order will diffract another wavelength at -1 order, which produces a reversal of color during the rainbow color animation on both sides of the achromatic animation.

[0184] In addition to selecting the period, the depth t of the grating G can be selected ( Figure 2 ) in order to optimize the efficiency of the + / -1st order diffraction, e.g. Figure 7 shown.

[0185] More specifically, in Figure 7 In FIG. 1 , curves 70, 71, 72 and 73 show the efficiency of the -1 order grating as a function of the grating depth for four grating periods (i.e., 400 nm, 460 nm, 520 nm and 580 nm, respectively) for an incident light wavelength corresponding to 550 nm. The curves make 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 selected in order to have the maximum 1st and -1st order diffraction efficiencies.

[0186] use Figure 8 and Fig. 9A , Fig. 9B An example of an optical security element for protecting a value document is shown.

[0187] Figure 8 An example of an optical security element of the "patch" or stamp type according to the present description (eg a label) is shown, which is configured to be fixed on, for example, a banknote or a product.

[0188] In this example, the optical security component comprises a stack of layers, such as Figure 1B In the illustrated laminate, layer 118 may be an adhesive layer.

[0189] The optical security element comprises a first diffractive structure etched in a first layer (113, Figure 1B ) and by Figure 8 The first diffractive structure is defined by the contours marked 81 in the figure, and according to the present specification, generates an achromatic dynamic visual effect in a first tilt angle range and generates the same but iridescent dynamic visual effect in the tilt angle ranges on both sides of the first tilt angle range. The optical security component also includes other structures defined by contours 82, 83 and 84. For example, these can be structures that allow the generation of In this example, the reflective layer (114, Figure 1B ) (eg a metal or high refractive index layer) may be applied to the entire component, with regions 81, 82, 83, 84 distinguished only by differences in the structures etched into the first layer.

[0190] Fig. 9A is a diagram showing an example of a valuable document 900 (eg a banknote) protected by an optical security element 91 according to the present specification, Fig. 9B It is shown Fig. 9A A magnified view of the security document shown in .

[0191] More specifically, in this example, the optical security component comprises a stack of layers, e.g. Figure 1A In the illustrated stack, layer 117 may be, for example, a layer of a heat-reactive adhesive for transferring the optical security element to a carrier of the banknote 900 .

[0192] The optical security component 91 comprises a first diffraction structure and a second diffraction structure, wherein the first diffraction structure is etched in the first layer (113, Figure 1B ) and by Fig. 9A The first layer is defined by an outline in the form of "2" marked as 911, and the second diffractive structure is etched in the first layer and defined by an outline in the form of "5" marked as 912. These two diffractive structures are diffractive structures according to the present specification for generating an achromatic dynamic visual effect within a first tilt angle range, and generating the same but iridescent dynamic visual effect within the tilt angle ranges on both sides of the first tilt angle range. Fig. 9BAs shown, the animations caused by the two diffractive structures can present different patterns.

[0193] In addition, from Fig. 9B It can also be seen in FIG. 1 that the second (reflective) layer is partially absent to reveal an area 915 which exposes the carrier of the banknote to which the optical security element is fixed. Thus, in this example, the reflective layer (114, Figure 1A ) does not completely cover the diffraction structure.

[0194] Finally, as in Fig. 9B As can also be seen in (diffractive structure with profiles 911, 912), the first pattern forming said diffractive structure may present areas 918 in which there is no modulation with the 1st order grating. These areas will be imperceptible when the optical security element is subjected to a tilting movement within the first angle range (achromatic animation), but will appear black to the observer when the optical security element is subjected to a tilting movement within the tilting angle ranges on either side of the first tilting angle range. Thus, during the rainbow color animation, additional protection may be provided with a message that only appears at significant tilting angles.

[0195] In the same manner, region 918 can be modulated by a second grating different from the first grating (e.g., a 1st-order second grating having a spacing and / or orientation different from the first grating) to reveal a spectral shift of rainbow colors or to allow azimuthal control when the orientation is different from that of the 1st-order grating that modulates the rest of the first pattern.

[0196] Fig. 9A and Fig. 9B The optical security component shown in also includes another structure defined by contour 913. For example, it can be a diffractive structure, which includes a set of facets as described in this specification but not modulated by a diffraction grating. Therefore, area 913 will present an achromatic dynamic visual effect to the observer. For example, the tilt angle range of area 913 for seeing the achromatic animation in the entire tilt angle range in which the animation of areas 911 and 912 is visible can be calculated. In this way, achromatic animation and iridescent animation can be seen in the component at the same time. More specifically, the connection of achromatic animation and iridescent animation in areas within the tilt range can be seen simultaneously, while adjacent areas only experience achromatic animation for the same tilt range. In addition, in the diffractive structure forming area 913, it is also possible to partially demetallize (or locally remove the reflective layer) to expose area 915, in which the carrier of the security document can be seen.

[0197] Fig. 10A and Fig. 10B An example of an original "visual scene" obtained by means of an example of an optical security element according to the invention is shown.

[0198] therefore, Fig. 10A Diagrams 1001 and 1002 are shown depicting designs of a first pattern and a second pattern, respectively.

[0199] As can be seen in Figure 1001, the first pattern 1012 includes a set of facets arranged in accordance with the present specification to illuminate the image along the illumination axis Δ L When irradiating a component, a tilting motion is generated within a given tilt angle range Δθ. tilt In this example, the first pattern is bounded by a circular disk and interrupted in region 1011, which forms the first recognizable graphical object (in this case the outline of the bulb and the bulb base).

[0200] Figure 1002 shows a second pattern 1022, that is, a 1st order grating (grating G, Figure 2 ). This exists throughout the first pattern except for the area 1021, which corresponds on the one hand to the area 1011 in which the first pattern is not present, but also to an additional area forming a second recognizable graphical object (in this example, the light bulb filament and light).

[0201] Fig. 10B Depicts a predefined visual scene showing Fig. 10A The patterns schematically shown in the figure show the obtained achromatic and iridescent visual animations.

[0202] During the achromatic animation shown in FIG. 1201, in the first part of the tilt angle range, the achromatic animation 1003 can be seen on the entire part except for the position 1011 where the first pattern does not exist. Therefore, the observer sees the outline and the base of the light bulb (the first graphical object) during the achromatic animation.

[0203] Except at positions corresponding to areas 1011 (absence of the first pattern) and 1021 (absence of either the first or the second pattern), the animation continues in the second part of the tilt angle range, but in an iridescent manner due to the presence of the 1st order first diffraction grating. Thus, in addition to the outlines of the bulb and the base, the observer also sees the filament and the light (the second graphical object) appearing during the iridescent animation. The resulting structure thus produces a flickering scene during the tilt between the first and second parts of the tilt angle range. In the presented example, during the animation, the observer perceives the bulb to be "lit" during the iridescent animation and "extinguished" during the achromatic animation, the whole being visible on a disc-shaped animated background.

[0204] An example of a method for producing an optical security element according to the present specification will now be described.

[0205] A first step comprises designing at least one first diffractive structure according to the above-described embodiments and possibly other structures.

[0206] Next comes the step of recording a replica of the original, also called an optical master. An optical master is, for example, an optical carrier on which the structure is formed.

[0207] The optical master can be formed by electronic or optical lithography methods known in the art.

[0208] For example, according to a first embodiment, an optical master is produced by etching a resin sensitive to electromagnetic radiation using an electron beam. In this embodiment, a structure exhibiting a first pattern modulated by a second pattern can be etched in a single step.

[0209] According to another embodiment, optical lithography (or photolithography) techniques may be used. In this example, the optical master is a plate of photosensitive resin, the initial step being performed by exposing the plate one or more times by mask projection of phase shift mask type and / or amplitude mask type and subsequently developing in a suitable chemical solution. For example, the first exposure is performed by an amplitude mask whose transmission coefficient is adapted so that after development, a relief corresponding to the first pattern is formed in the area where the first pattern is planned.

[0210] Next, a second full exposure is performed, and a diffraction grating (diffraction grating G, D) corresponding to the second pattern is recorded at least in the first region in which the second pattern is planned according to interference lithography known to those skilled in the art. Figure 2 ). Similar steps can be provided to generate other reliefs, such as second diffraction gratings in other areas. The order of formation of the patterns is arbitrary and can be modified. Subsequently, a development step is performed. In this way, an optical master is obtained after development, which includes a structure resulting from the first pattern modulated by the second pattern.

[0211] Then, as previously described, a step of producing a metal replica of the optical master can be performed, for example by electroplating, to obtain a metal matrix or "master". According to a variant, a matrix replication step of the metal master can be performed to obtain a large production tool suitable for replicating structures in industrial quantities.

[0212] The manufacture of the optical security element then comprises a replication step. For example, replication can be carried out by embossing (by hot embossing of a dielectric material) from a dielectric material having a refractive index n 1 The first layer 113 ( Figure 1A , Figure 1B), the first layer 113 being, for example, a low-refractive-index layer, typically a few micrometers thick embossing lacquer. Advantageously, layer 113 is carried by a support film 111, for example a film of 12 μm to 100 μm made of a polymer material, such as PET (polyethylene terephthalate). Replication can also be carried out by molding the embossing lacquer layer before drying and then UV crosslinking ("UV casting"). Replication by UV crosslinking makes it possible in particular to replicate structures with a wide depth range and to obtain more reliable replication. In general, any other high-resolution replication method known in the prior art can be used in the replication step.

[0213] Next, all other layers, such as a reflective layer 114, a dielectric material layer 115 (optional), a security layer 116 (optional) (which can be deposited uniformly or selectively to form a new pattern) and adhesive or lacquer layers (117, 118) are deposited on the layer thus embossed by a coating process.

[0214] Optional steps known to those skilled in the art, such as partial demetallization of the reflective layer 114, may be performed.

[0215] Although described by a certain number of embodiments, the optical security component according to the present invention and the method for manufacturing the component include various variations, modifications and improvements, which are obvious to those skilled in the art and should be understood to fall within the scope of the present invention as defined by the appended claims.

[0216] References

[0217] Reference 1: WO2015154943

[0218] Reference 2: WO2018224512

[0219] Reference 3: US4856857

Claims

1. An optical safety component (101, 102) configured to be arranged with respect to a given illumination axis (Δ L ) forms a given observation angle (θ obs ) in the viewing direction (Δ O ) and observed by naked eye in reflection from at least a first viewing surface (100), the component comprising: - a first layer (113) made of a dielectric material, which is transparent in visible light; - at least a first diffractive structure (S) etched on said first layer; and - a second layer (114) at least partially covering the first diffractive structure and having a reflection spectral band in the visible light; and wherein: - the first diffractive structure comprises a first pattern (M1) consisting of a set of parallel facets (F i ), these facets have a slope that varies in the slope variation direction (y), the slope including in absolute value the minimum angle value (α min ) and the maximum angle value (α max ), the facet has a given maximum height (h m ), the set of facets being arranged so that when the component is illuminated with white light along the illumination axis, the facets are inclined along an axis (Δ) substantially perpendicular to the direction of slope change. And within a given tilt angle range (Δθ tilt ) produces a dynamic visual effect that can be observed by reflection under the action of the tilting movement within; - in at least a first region, the first pattern is modulated by a second pattern (M2), the second pattern forming a one-dimensional periodic grating having a predetermined period (d) between 450 nm and 650 nm, the grating comprising a grating vector (k) having a direction collinear with the slope variation direction (y) g ), the grating being determined to produce 1st and -1st order diffraction effects in reflection after deposition of the second layer, - the period (d) of the grating, the maximum angle value (α) of the slope max ) and the observation angle (θ obs ) is determined as the first part of the tilt angle range (Δθ B ) produces an achromatic animation, and in the second part of the tilt angle range (Δθ R -; Δθ R+ ), the rainbow color animation adjoining the achromatic animation on both sides of the first portion of the tilt angle range, wherein the first portion of the tilt angle range (Δθ B ) is between 20° and 35°, the second portion (Δθ R -; Δθ R+ ) is between 40° and 60°, and the first portion of the tilt angle range (Δθ B ) is included in the first part (Δθ B ) on both sides thereof and superimposed with an angle between 1° and 10° of the second part of the inclination angle range.

2. The optical security component according to claim 1, wherein: The given observation angle (θ obs ) is between 30° and 60°.

3. The optical security component according to claim 1, wherein: The minimum angle value of the slope is equal to 0°.

4. The optical security component according to claim 1, wherein: The maximum angle value of the slope is between 7° and 15°.

5. The optical security component according to claim 1, wherein: The set of facets have substantially the same height.

6. The optical security component according to claim 1, wherein: The group of facets includes one or more subgroups of facets, each of which is configured to produce a "wave" type dynamic effect.

7. The optical security component according to any one of claims 1 to 6, wherein: The second layer includes a metallic material.

8. The optical security component according to any one of claims 1 to 6, wherein: The dielectric material of the first layer has a first refractive index (n1), and the second layer includes 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 0.

3.

9. The optical security component according to claim 1, wherein: The first pattern has an outline (911, 912), and when viewed from the viewing surface, the outline (911, 912) forms a recognizable graphical shape.

10. The optical security component according to claim 1, wherein: The first pattern is interrupted in a region (1011) which, when viewed from the viewing surface, forms a recognizable graphical object visible during the achromatic animation and during the iridescent animation.

11. The optical security component according to claim 1, wherein: In at least a second region (918, 1021), the first pattern is unmodulated or modulated by a third pattern forming a periodic grating different from the second pattern, the second region forming a recognizable graphical object visible only during the rainbow color animation when viewed from the viewing surface.

12. A security object, such as a security document of value, comprising a substrate and an optical security element according to any one of claims 1 to 11 deposited on the substrate.

13. A method for producing an optical security element intended to be viewed with the naked eye in reflection along a viewing surface, the method comprising: - depositing on the support film a first layer made of a dielectric material, the first layer being transparent in visible light; - forming at least a first diffractive structure (S) on said first layer such that: - the first diffractive structure comprises a first pattern (M1) consisting of a set of parallel facets (F i ), these facets have a slope that varies in the slope variation direction (y), the slope including in absolute value the minimum angle value (α min ) and the maximum angle value (α max ), the facet has a given maximum height (h m ), the set of facets being arranged so that when the component is illuminated with white light along the illumination axis, the facets are tilted along an inclined axis (Δ) substantially perpendicular to the slope variation direction and within a given tilt angle range (Δθ tilt ) produces a dynamic visual effect that can be observed by reflection under the action of the tilting movement within; - in at least a first region, the first pattern is modulated by a second pattern (M2), the second pattern forming a one-dimensional periodic grating having a predetermined period (d) between 450 nm and 650 nm, the grating comprising a grating vector (k) having a direction collinear with the slope variation direction (y) g ), the grating being determined to produce a 1st and -1st order diffraction effect in reflection after deposition of a second layer having a reflection spectral band in the visible, - depositing said second layer, which at least partially covers said first diffractive structure, wherein - the period (d) of the grating, the maximum angle value (α) of the slope max ) and observation angle (θ obs ) is determined as, after deposition of the second layer, the first part of the tilt angle range (Δθ B ) produces an achromatic animation, and in the second part of the tilt angle range (Δθ R -;Δθ R+ ), the rainbow color animation adjoining the achromatic animation on both sides of the first portion of the tilt angle range, wherein the first portion of the tilt angle range (Δθ B ) is between 20° and 35°, the second portion (Δθ R -;Δθ R+ ) is between 40° and 60°, and the first portion of the tilt angle range (Δθ B ) is included in the first part (Δθ B ) on both sides thereof and superimposed with an angle between 1° and 10° of the second part of the inclination angle range.

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