CN117460625A

CN117460625A - Reflective visible optical security element, production of such an element and security document provided with such an element

Info

Publication number: CN117460625A
Application number: CN202280038284.6A
Authority: CN
Inventors: S·埃斯赛迪; V·佩蒂顿
Original assignee: Su Lisi
Current assignee: Su Lisi
Priority date: 2021-04-09
Filing date: 2022-04-08
Publication date: 2024-01-26
Also published as: FR3121629A1; FR3121629B1; WO2022214689A1; EP4319987A1

Abstract

The invention relates to an optical security element (40), which optical security element (40) is configured to be optically secured to a light source in a direction (delta _L ) Forming an observation angle (theta) _obs ) Is (delta) _O ) The above is observed in reflection. The component comprises a diffractive structure having a first pattern consisting of a set of parallel facets having a varying slope in a slope varying direction and arranged to vary over a given range of tilt angles (delta theta _tilt ) A dynamic visual effect is generated inside. In at least one region, the first pattern is modulated by a grating designed to produce 1 st and-1 st order reflection diffraction effectsAnd (5) fruits. The period of the grating, the maximum angle value of the slope and the viewing angle are designed to be within a first portion (Δθ _B ) And in a second part (delta theta) _R‑ ；Δθ _R+ ) The same animation of iridescence is produced, which rainbow animation joins the achromatic animation on both sides of the first part of the range of inclination angles.

Description

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

Technical Field

The present description relates to the field of security markings. More particularly, the present description 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 provided with such an element.

Background

Many techniques are known for authentication of documents or products, in particular for protection of documents, such as documents of value, such as banknotes, passports or other identification documents. The aim of these techniques is to produce an optical security element with an optical effect that presents a very characteristic and verifiable configuration, depending on the viewing parameters (orientation of the element with respect to the viewing axis, position and size of the light source, etc.). The general 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 (stands for "diffractive optically variable image device") is the naming of the optical component that produces the diffractive variable image, commonly referred to as a hologram.

For example, it is known to produce an effect consisting of dynamic variations of the optical effect, for example in the form of a movement of a bright and/or coloured area in a given direction (sometimes referred to as a "scrollbar"), which movement is caused by a rotation (tilting) of the component. Thus, the observer can see bright and/or colored areas moving along the image as the part is rotated, serving as an additional authentication check.

Such a dynamic optical effect exhibiting a "scroll bar" is described, for example, in published patent WO2015154943[ reference 1] in the name of the applicant. The optical security element described in the above-referenced application has the effect of being reflective and visible. The optical security element comprises a diffractive structure etched on a layer of dielectric material. The structure exhibits a first pattern comprising a bas-relief having a first set of facets shaped to simulate a series of reflective visible concave or convex cylindrical optical elements, the first pattern being modulated by a second pattern forming a sub-wavelength grating. Such an optical security element, when rotated by tilting about an axis parallel to one of the main directions of the cylindrical element, presents the dynamic visual effect of a movement of the bright bands of different colours in opposite directions.

More complex dynamic visual effects than those disclosed in [ reference 1], such as the movement of intersecting and/or tilting segments of two segments "moving" in the same direction at different speeds or in opposite directions, are described in published patent WO2018224512[ reference 2] in the applicant's name.

To achieve these dynamic visual effects, the optical security element described in [ reference 2] comprises a first layer of dielectric material and a diffractive structure etched on the first layer. The diffractive structure comprises a first pattern having a set of modules arranged side by side in a given arrangement direction, each module defined in the arrangement direction having a maximum width of less than 300 μm. Each module comprises a bas-relief with a first set of facets shaped to simulate a reflective visible optical element having at least one raised or depressed region, said optical element having a profile of slope that continuously varies in a single direction perpendicular to the direction of arrangement, referred to as the slope variation direction. Furthermore, for two modules arranged side by side, the slope along at least one line parallel to the direction of arrangement differs between the two modules. The minimum number of modules is determined by the maximum width of the modules so that the diffractive structure is visible to the naked eye. Such an optical security component presents a dynamic visual effect in reflection and under the effect of a tilting movement about an axis parallel to the direction of arrangement, which dynamic visual effect comprises the movement of one or more complex graphic elements depending on the arrangement of the modules, and which allows for safer authentication and stronger technical barriers than a simple horizontal scroll bar due to the design and manufacture of the modules necessary to obtain the above-mentioned visual effect.

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

The present application describes an optical security element having an original structure that can not only achieve a complex dynamic visual effect or "animation" as described in [ reference 2], but also allow continuous switching from a white achromatic animation to the same but iridescent animation simply by tilting the optical security element over a wider angular range, thereby ensuring more reliable authentication without requiring a specific device through a simple visual inspection.

Disclosure of Invention

In this specification, the term "comprising" has the same meaning as "comprising" or "contains", is inclusive or open-ended, and does not exclude additional elements not described or shown. Further, in this specification, the term "about" or "substantially" is the same as "having a margin of less than and/or greater than 10% (e.g., 5%) of the corresponding value".

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

-a first layer made of a dielectric material, the first layer being transparent in visible light;

-etching at least a first diffractive structure on the first layer; and

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

-the first diffractive structure comprises a first pattern consisting of a set of parallel facets having a slope varying in a slope varying direction, the slope comprising an angle value comprised between a minimum angle value and a maximum angle value in absolute terms, the facets having a given maximum height, the set of facets being arranged to produce a reflective observable dynamic visual effect under the effect of a tilting motion along an axis substantially perpendicular to the slope varying direction and within a given range of tilting angles when the component is illuminated with white light along the illumination axis;

-in at least a first region, the first pattern being modulated by a second pattern forming a periodic grating having a predetermined period size between 450nm and 650nm, the grating comprising a grating vector having a direction collinear with the direction of slope change, the grating being determined to produce a diffraction effect of order 1 and-1 in reflection after deposition of the second layer.

The period of the grating, the maximum angle value of the slope and the viewing angle are determined to produce an achromatic animation in a first portion of a range of tilt angles surrounding specular reflection and an identical animation of iridescence in a second portion of the range of tilt angles, the iridescent animation joining the achromatic animation on both sides of the first portion of the range of tilt angles.

In the present 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 400nm and about 800 nm). Such a transparent layer makes it possible to visually observe the layer located under the transparent layer.

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

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.

Rotation of the component along an axis contained in the plane of the component is commonly referred to as "tilting movement" of the component.

The applicant has shown 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 change of the slope, presents a dynamic visual effect or reflective, bright achromatic "animation" about specular reflection, then presents the same but iridescent animation that joins the achromatic animation on both sides of the first part of the range of tilting angles. This effect allows for safer authentication and stronger technical barriers due to the design and manufacture of the components necessary to obtain the visual effect described above.

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

For example, the viewing angle is defined with respect to a vertical illumination direction.

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 the normal viewing position of the viewer for vertical illumination.

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

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

Conventionally, in this specification, the positive direction of the angle value for measuring the slope of the facet is the clockwise (or reverse triangular) direction.

According to one or more examples, the dimension (or "width") of the facets 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 size may be selected as a function of the grating period. For example, the minimum dimension of the width of the facets is equal to about 2 μm.

According to one or more examples, the facets have a width of 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.

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.

According to one or more examples, the set of facets have substantially the same height. The height of the facets is for example less than 2 microns, advantageously less than 1 micron.

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

According to one or more embodiments, at least some of the facets of the set of facets are arranged with a varying slope, the variation of which is increasing or decreasing, respectively, in order to simulate a reflective element having a convex or concave region, respectively. In this specification, a dynamic effect of "half wave" refers to a visual effect caused by such arrangement of facets when the change in the angle value of the slope of the facets is increasing or decreasing but the sign is the same. The dynamic effect of the "wave" type refers to the visual effect caused by this arrangement of facets when the change in the angular value of the slope of the facets is an increase or decrease and there is at least one sign change. During tilting movements of the components, the dynamic effect of a "wave" or "half wave" appears to the observer as a continuous movement of white light.

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

According to one or more observation examples, the period of the diffraction grating, the maximum angle value (measured in absolute value) of the slope, and the observation angle are determined such that the first portion of the tilt angle range comprises an angular superposition (overlap) of the first portion of the angle range with the second portion of the tilt angle range on both sides of the first portion of the angle range, the angular superposition (overlap) being between about 1 ° and about 10 °, preferably between about 3 ° and about 8 °, for example equal to about 5 °. This design of the optical safety component according to the present description ensures that the iridescent animation engages the achromatic animation uninterrupted on both sides of said first portion of said range of inclination angles. However, in extreme cases, the angular superposition may be zero, as long as there is continuity between the achromatic animation and the iridescent animation.

According to one or more observation examples, a period of the diffraction grating, a maximum angle value (measured in absolute value) of the slope, and the observation angle are determined such that the tilt angle range is between about 45 ° and about 120 ° (measured in air).

According to one or more observation examples, the period of the diffraction grating, the maximum angle value of the slope (measured in absolute value) and the observation angle are determined such that the first portion 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).

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 viewing angle are determined such that the second portion of the range of tilt angles (measured in air) is between about 30 ° and about 70 °, advantageously between about 40 ° and about 60 °, on both sides of the first range of tilt angles.

According to one or more embodiments, the one-dimensional diffraction grating is a diffraction grating having a sinusoidal profile. An advantage of a grating with a sinusoidal profile is that it allows symmetry of the diffraction efficiencies of the +1 and-1 orders, and thus allows symmetry in the visual efficiency of the iridescent animation on both sides of the achromatic animation. However, other grating profiles are also possible, such as, as a non-limiting example, a diffraction grating with a pseudo-sinusoidal profile (defined as the sum of sinusoids with an amplitude and phase that are adjustable according to the intended profile), a diffraction grating with a rectangular profile, or advantageously any other grating with a symmetrical profile, in order to have similar visual efficiency for an iridescent animation on both sides of an achromatic animation.

According to one or more embodiments, the depth of the diffraction grating is determined so as to optimize the diffraction efficiency of the grating at 1 st and-1 st order at least one wavelength of the visible spectrum (e.g. at the center wavelength of the visible spectrum, e.g. around 550 nm).

According to one or more embodiments, the second layer comprises a metallic material.

The metallic material comprises one material or an alloy of materials selected from the group consisting of: 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 frequency range; for example, for aluminum, the thickness of the metal material layer is between about 20nm and about 60 nm.

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) and titanium dioxide (TiO ₂ ) Or silicon nitride (Si) ₃ N ₄ )。

In general, the material forming the second layer makes it possible to give the component a spectral band of reflection 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 ].

According to one or more embodiments, the smallest dimension of the first structure is greater than 300 μm, preferably greater than 1mm, preferably greater than 2mm, preferably greater than 5mm. Such minimum dimensions make it possible to make the structure visible to the naked eye.

According to one or more embodiments, the first structure has a contour that forms an identifiable graphical shape when viewed from a viewing surface.

According to one or more embodiments, the optical security component 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 a non-limiting example, the second structure is configured to form a diffusing structure, a holographic structure, a diffractive structure, such that what is known as applicants' development may occurIs effective in (1).

When the component includes at least a second structure, the structures may be juxtaposed, each structure having an identifiable shape.

According to one or more embodiments, the first pattern has a contour that forms an identifiable graphical shape when viewed from a viewing surface.

According to one or more embodiments, the first pattern is interrupted in areas forming identifiable graphical objects that are visible during the achromatic animation and during the iridescent animation when viewed from the viewing surface.

According to one or more embodiments, in at least a second region, the first pattern is not modulated or is modulated by a third pattern forming a periodic grating that is different from the second pattern, the second region forming an identifiable graphical object that is visible only during iridescent animation when viewed from a viewing surface.

Thus, a "visual scene" may be generated using graphical objects that appear during both animations (achromatic and iridescent) or only during iridescent animations.

According to one or more embodiments, the optical security component according to the first aspect comprises one or more additional layers, which additional layer or layers do not contribute to the desired visual effect, depending on the requirements of the use.

Thus, according to one or more embodiments, the optical security element is configured to protect an object (e.g. a document or product) and further comprises, on the side opposite to the viewing side, a layer (e.g. an adhesive layer or a reactive adhesive layer) adapted to transfer the element to the document or product.

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

According to one or more embodiments, the optical security component is configured for manufacturing a security track for protecting banknotes and comprises one or more protective layers on the side of the first viewing surface and/or on the surface opposite to the first viewing surface.

According to a second aspect, the present description relates to a security object (e.g. a security document) comprising a substrate and an optical security element according to the first aspect, the optical security element being deposited on the substrate or, in the case of a multilayer substrate, on one layer of the substrate.

As a non-limiting example, such a security object is: banknotes, or identity documents or travel documents on paper or polymeric substrates.

According to a third aspect, the present description relates to a method for manufacturing an optical security component according to the first aspect.

The present description thus relates to a method for manufacturing an optical security element intended to be observed in reflection with the naked eye along at least a first viewing surface, comprising:

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

-forming at least a first diffractive structure on the first layer such that:

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

-depositing a second layer at least partially covering said first diffractive structure and having a reflection spectral band in visible light, wherein

-the period of the grating, the maximum angle value of the slope and the viewing angle are determined such that after deposition of the second layer an achromatic animation is generated in reflection in a first part of a range of tilt angles around specular reflection and an identical animation of iridescence is generated in a second part of the range of tilt angles, the iridescent animation joining the achromatic animation on both sides of the first part of the range of tilt angles.

Drawings

Other features and advantages of the present invention will become apparent upon reading the following description, which is illustrated by the accompanying drawings in which:

fig. 1A schematically shows a (partial) cross-sectional view of an embodiment of a component according to the present description.

Fig. 1B schematically shows a (partial) cross-sectional view of another embodiment of a component according to the present description.

Fig. 2 consists of several diagrams showing parameters of the diffraction structure in the security element according to the present description.

Fig. 3 is a diagram showing the engagement of an iridescent animation and an achromatic animation of an optical safety device according to the present specification during tilting motion.

Fig. 4A is made up of several diagrams showing, according to one example, a first iridescent animation in an optical safety feature according to the present description as a function of the tilt angle of the feature in a first part of the tilt angle range.

Fig. 4B is made up of a plurality of graphs showing, in the same optical safety component as that of fig. 4A, an achromatic animation as a function of the tilt angle of the component in a second portion of the tilt angle range, where the achromatic animation interfaces with the first iridescent animation.

Fig. 4C is made up of a plurality of diagrams showing, in the same optical safety component as that of fig. 4A, a second iridescent animation as a function of the tilt angle of the component in a third portion of the tilt angle range, wherein the second iridescent animation interfaces with the achromatic animation and exhibits a reversal of color with respect to the first iridescent animation.

Fig. 5A consists of curves, which respectively show: in a facet arrangement configured to produce a "half-wave" dynamic effect, for a given height, an example of the spatial distribution of facet widths; in a facet arrangement configured to produce a "half-wave" dynamic effect, for two facet heights, the angular value of the slope of the facet (in degrees) is 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 (in degrees) of the slope of the facet is a function of the facet width.

Fig. 5B is a diagram showing an example of distribution of facets to form "pixels".

Fig. 5C is made up of a plurality of curves showing the effect of the slope of the facets for three tilt angles of the component located in the first portion of the tilt angle range.

Fig. 6 is a graph 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 both sides of the first part of the tilt angle range.

Fig. 7 consists of a plurality of curves showing the efficiency of a diffraction grating having a sinusoidal profile at either the +1 or-1 order as a function of grating depth for a wavelength of 550 nm.

Fig. 8 shows an example of an optical security element according to the present description, having a "patch" type format.

Fig. 9A is a diagram showing an example of a value document (e.g., a banknote) protected with an optical security component according to the present specification.

Fig. 9B is an enlarged view showing the security document shown in fig. 9A.

Fig. 10A is composed of a plurality of diagrams showing designs of the first pattern and the second pattern, respectively, in the example of the optical security component according to the present specification.

Fig. 10B is made up of a plurality of diagrams showing achromatic and iridescent visual animations according to a given visual scene based on the pattern as schematically shown in fig. 10A.

Detailed Description

In the drawings, elements are not shown to scale for better visibility. Fig. 1A and 1B show schematically and in (partial) cross-sectional views two examples of an optical security component according to the present description. The optical security element 101 shown in fig. 1A represents an optical security element intended to be transferred to a document or product for protection thereof, for example. According to this example, it comprises a support film 111, for example a film made of a polymeric material, such as a polyethylene terephthalate (PET) film of a few tens of micrometers, typically 15 to 100 μm, and a release layer 112, for example made of natural or synthetic wax. The release layer allows the polymer support film 111 to be removed after the optical component is transferred to the product or document to be protected. The optical security element 101 further comprises a first layer 113 made of a dielectric material, the first layer 113 having a first refractive index n ₁ And at least one first diffractive structure S comprising a first pattern M ₁ The first pattern M ₁ From a second pattern M forming a periodic grating ₂ Modulation, imprinted on the first layer 113 and described in more detail below.

In the example of fig. 1A, the optical security component 101 further comprises a second layer 114, which second layer 114 at least partly covers said 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 refractive index changing layer, which layer has a different refractive index than the first layer, the refractive index difference between the layers 113 and 114 having a value at least equal to 0.3, advantageously at least equal to 0.5. Layer 114 ensures reflection of incident light.

The optical security element further comprises one or more optional layers which are not optically functional but are adapted to the requirements of use.

For example, in the example of fig. 1A, the optical security component further includes an adhesive layer 117, such as a thermally reactive adhesive layer, for transferring the optical security component to a product or document.

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

The optical security component 102 shown in fig. 1B represents, for example, an optical security component intended to protect banknotes; this is for example part of a security thread (security thread) intended to be integrated into the paper during the manufacture of the banknote, or a lamination track covering a window in the paper, or a patch. In this example, as previously described, the component 102 includes: a support film 111 (12 μm to 25 μm), which support film 111 will also serve as a protective film for the security thread; a first layer 113 made of a dielectric material as shown in the example in fig. 1A, the first layer 113 having a first refractive index n ₁ At least one first diffractive structure S imprinted on said first layer 113; and a second layer 114, the second layer 114 at least partially covering the first structure S and having a reflection spectral band in visible light. In the example of fig. 1B, the optical security element 102 further comprises a set of optional layers 115, 116, 118. Layer 115 (optional) is formed, for example, fromA layer 115 of dielectric material, such as a transparent layer; layer 116 (optional) is, for example, a security layer 116, for example, a discontinuous layer with a specific pattern locally printed with UV ink to create additional indicia that can be inspected by the naked eye or by machine; layer 118 (optional) is, for example, a protective layer, such as a second polymer film or paint. In the case of laminated rails, layer 118 may be an adhesive layer. As in the previous example, the fabrication may be performed by stacking these layers on the support film 111. The dielectric layer 115 and the security layer 116 may form only one layer. The protective layer (or adhesive layer) 118 and the layer 115 may also form the same layer.

It will be apparent to those skilled in the art that in each of the examples shown in fig. 1A and 1B, other optically nonfunctional layers may be added depending on the requirements of use, and that alternative embodiments shown in fig. 1A and 1B may be combined.

Note that if the optically non-functional additional layer (e.g. layer 117) or layers 115, 116, 118 are transparent together with the target carrier, the optical security component is visible from both sides, wherein an inversion of the curvature of the optical element is generated.

Fig. 2 shows the parameters of the diffraction structure S (fig. 23) according to the present description in more detail. The structure S is formed by a first pattern M ₁ Forming a first pattern M ₁ Comprising a set of facets F _i (FIG. 22) the pattern is at least partially formed by a second pattern M ₂ Modulated, second pattern M ₂ Defined by the projection of a one-way diffraction grating (fig. 21) labeled G, and in a plane pi parallel to the component plane (and thus parallel to the viewing surface 100).

All facets F _i Are all parallel, that is, they exhibit a slope change in the same direction (labeled y in the example of fig. 2). Characterized by a height h defined by the distance between the lowest level and the highest level of the facets, measured along an axis perpendicular to the plane pi (which is parallel to the plane of the component), i.e. along the z-axis in the example of fig. 2. In the example of fig. 2, the facets all have the same height h, which is less than about 2 μm, advantageously less than about 1 μm, for example at about 0.Between 5 μm and about 1 μm.

The facets are further characterized by a width Λ defined by a dimension in the slope change direction y, 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 facets will be greater than about 4 times the grating period, advantageously greater than about 8 times the grating period.

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

Facet F _i Having a slope with an angle value alpha _i Included between a minimum angle value (e.g., 0 °) and a maximum angle value (e.g., between about 7 ° and about 15 °) in absolute terms. As shown in fig. 2, in the present specification, the positive direction of the angle value selected for measuring the slope is the clockwise or reverse triangular direction.

As shown in fig. 21, the diffraction grating G is a one-way diffraction grating characterized by a pitch or period d and a depth t. The raster vector is designated as k _g Which is collinear with the slope change direction y and has a modulus equal to 2 pi/d.

As can be seen from fig. 23 of fig. 2, the structure S resulting from the modulation of the first pattern comprising a set of facets by the diffraction grating G comprises a one-dimensional diffraction grating G each supported _i Is a group of facets F _i . In the component according to the present description, the facets Fi each have an angle α with respect to a plane parallel to the plane of the component _i . A diffraction grating G having a constant pitch d and having a grating vector in a direction collinear with the direction of slope change is present on each facet F _i The projection onto can result in a varying pitch (labeled d in fig. 23 _Mi ) Projection grating G of (2) _i . Since the slope of the facets has a low angular value, typically an absolute value of less than 15 °, becauseThis can be neglected in most practical examples for the effects of these variations in grating spacing on the different facets.

In the example of fig. 2 (fig. 21), the 1 st 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. This symmetrical profile has the advantage of exhibiting similar diffraction efficiencies at the +1 and-1 orders. Symmetrical grating profile means that the grating has a central symmetrical profile (about a point).

Once the structure S is determined due to the definition of the first pattern and the second pattern, a process of recording the structure may be performed to manufacture the optical security component, as will be described in more detail below.

In an optical security element according to the present description, the period d of the diffraction grating, the maximum angle value α of the slope (measured in absolute value) and the viewing angle are determined so as to view an achromatic animation in a first part of the range of angles of inclination around specular reflection and to view the same but iridescent animation in a second part of the range of angles of inclination, which iridescent animation joins the achromatic animation on both sides of said first part of the range of angles of inclination.

Fig. 3 shows a diagram describing the desired engagement of an iridescent animation and an achromatic animation of an optical safety component 40 during tilting motion according to the present description.

The illumination axis (e.g., vertical illumination corresponding to natural light) is designated as delta _L The viewing axis corresponding to the viewing direction of the observer (represented by the eye in fig. 3) is designated as delta _O Whereas the axis delta _L And delta _O The observation angle therebetween is designated as θ _obs . In the rest of the present specification, θ _obs Equal to the absolute value of the angle measurement of the viewing angle.

In practice, when checking the authenticity of a document protected by an optical security component according to the present description, the document is rotated (tilted) about a tilt axis Δ, which is contained in the component plane and is substantially perpendicular to the direction of change of the slope. Thus, the tilt axis is substantially parallel to the x-axis (fig. 2).

In practice, the direction of illumination and observation is fixed and the tilting movement of the component causes a variation in the angle of incidence θi of the light incident on the component, with respect to Δj perpendicular to the plane of the component _N The shaft is defined. Conventionally, in this specification, the positive direction of the incident angle is a triangular direction. As will be described in more detail below, the variation of the incident angle θi results from the inclusion of the second pattern M ₂ Modulated first pattern M ₁ Angle theta of light diffracted by structure S (see fig. 2) _o Variation of (c) such that θ _O ＝θ _i -θ _obs Wherein θ is _obs Taken as absolute value. Thus, the diffraction angle θ _o From the normal to the component and the viewing direction delta _O The angle between them is defined. Conventionally, in this specification, the positive direction of the diffraction angle is a triangular direction as well as the incident angle. In the diagram of fig. 3, the optical safety component 40 is shown in a central position for which a normal axis Δ perpendicular to the component plane _N Angle of observation θ _obs Divided into two angular sectors of equal measurement (specular reflection position for which θ _o ＝-θi)。

As shown in fig. 3, a range of tilt angles Δθ is sought _tilt Is a first part of delta theta _B Wherein achromatic animation is seen, a first part delta theta of the range of inclination angles _B At a location around specular reflection. It is also sought to see the same but iridescent animation in a second part of the range of tilt angles, which rainbow animation joins the achromatic animation on both sides of said first part of the range of tilt angles. Thus, as shown in FIG. 3, the second portion of the tilt angle range includes the angle range Δθ _R -and angular range Δθ _R+ From the viewpoint of the observer, the angular range Δθ _R- And an angular range delta theta _R+ Corresponding to the rearward or forward tilting of the optical safety element, respectively.

Iridescent animation is a "rainbow" animation in which an observer sees rainbow colors traveling. For simplicity, in the 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).

Fig. 4A to 4C show examples of dynamic visual effects obtained with an optical security component according to the invention in more detail.

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

Fig. 4B shows the graph labeled Δθ in fig. 3 _B Achromatic animation effects in a first range of tilt angles. More specifically, fig. 44 corresponds to the position of the optical safety member 40 labeled 4 in fig. 3, fig. 45 corresponds to the position of the optical safety member 40 labeled 5 in fig. 3 (corresponds to the center position of specular reflection), and fig. 46 corresponds to the position of the optical safety member 40 labeled 6 in fig. 3. In fig. 4B, the achromatic animation includes, for example, a circular white line moving on a black background.

Fig. 4A shows an iridescent animation effect in a second part of the range of tilt angles, labeled Δθ in fig. 3 _R+ And corresponds to a forward tilting movement of the component from the perspective of the viewer. More specifically, fig. 41 corresponds to the position of the optical safety member 40 labeled 1 in fig. 3, fig. 42 corresponds to the position of the optical safety member 40 labeled 2 in fig. 3, and fig. 43 corresponds to the position of the optical safety member 40 labeled 3 in fig. 3. In fig. 4A, each color is shown by a texture similar to that used in fig. 3.

FIG. 4C illustrates an iridescent animation effect in a second portion of the range of tilt angles, labeled Δθ in FIG. 3 _R- And corresponds to a backward tilting movement of the component from the perspective of the viewer. More specifically, fig. 47 corresponds to the position of the optical safety member 40 labeled 7 in fig. 3, fig. 48 corresponds to the position of the optical safety member 40 labeled 8 in fig. 3, and fig. 49 corresponds toThe position of the optical security element 49 is marked 3 in fig. 3. In fig. 4C, each color is shown by a texture similar to that used in fig. 3.

Thus, as shown in fig. 4A to 4C, an achromatic dynamic visual effect is observed around specular reflection, which is caused by the arrangement of the facets forming the first pattern, as explained in more detail below, and the same dynamic visual effect is observed on both sides, which is iridescent, wherein the rainbow colors are travelling.

Also as described in detail below, the iridescent effect is a diffraction of +1 and-1 orders (respectively for the tilt angle range Δθ _R+ And delta theta _R- ) Resulting in that.

The iridescent animation is connected on two sides of the achromatic animation. In the examples of fig. 4A to 4C, two specific angles of incidence, θ respectively, may thus be defined _T ⁺ (FIGS. 43 and 44) and θ _T ^- (fig. 46 and 47) corresponding to the incident angles of transitions between the achromatic animation and the iridescent animation of +1 order and between the achromatic animation and the iridescent animation of-1 order, respectively.

Note that, as shown in fig. 4A and 4C, in two tilt angle ranges Δθ _R+ And delta theta _R- There is a reversal of color between them. In other words, for example, in the angular range Δθ _R+ Facets that diffract red toward the viewer are at an angular range Δθ _R- The inner diffracts blue.

The steps in designing the structure, in particular the selection of parameters as shown in fig. 2, to obtain a dynamic visual effect according to the present description and as shown for example in fig. 3 and 4A to 4C will now be described.

To achieve the dynamic visual effect described above, the structure of the first pattern, that is, the position, size and slope of the facets, is first determined to be in a first portion of the range of inclination angles (Δθ in fig. 3 _B ) The desired achromatic animation is obtained.

Fig. 5A shows an example of a spatial distribution of facet widths (fig. 51) that can produce a dynamic effect, and a graph showing angular values of slopes of facets as a function of width, as a tool for designing a first pattern in an optical safety component according to the present description to construct a desired animation.

More specifically, fig. 51 shows a curve 510, which curve 510 depicts the spatial distribution of the width of a facet along the slope change axis y (see fig. 2) in a first arrangement of facets configured to produce a dynamic effect. As shown in fig. 51, the variation in width is reduced, and this is continuously increased at a constant height h of the facet as a variation in the angle value of the slope, for simulating a concave reflecting element.

For example, FIG. 51 shows a continuously decreasing variation, which follows what can be written asWherein a and b are the tuning parameters of the function. Note that other functions may also be used.

In practice, the variations in the width and angle of the facets comprise discrete values selected according to the size of the diffractive structure. Thus, for example, if it is desired to create a "wave" type effect in a region of a given size, a greater number of facets may be selected in a larger region, and the dynamic effect will be more fluid and continuous.

In practice, for a given facet height h, the facet width may be selected as a function of the desired facet angle.

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

In the same way, fig. 53 shows the arrangement for facets configured to form a "wave" type (bump) dynamic effect, the angular value of the slope of the facet (in degrees) as a function of the facet width for two facet heights, namely 1 μm (curve 531) and 0.5 μm (curve 532). As shown in fig. 53, the widths of the facets increase and then decrease, which results in a change in the angular value of the slope of the facets at a constant height that decreases and increases.

Facets of varying angle and width as depicted in FIG. 5A are used to design a first pattern of structures that will be at a first tilt angle range Δθ _B An achromatic animation is internally generated.

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 movement ("active" facets) are those whose response is such that they can be oriented in the direction Δ _O (in other words, toward the observer of the operating document) of the reflected energy. Thus, when the document is in the first portion of the tilt angle range Δθ _B When tilted, the "active" facets will appear white (lit) while the other facets will appear black (off).

To obtain the optical effect shown in fig. 3 or fig. 4A and 4B, first, an observation angle θ is defined _obs Make it equal to the illumination direction delta _L (e.g. vertical illumination direction) and viewing direction delta _O Absolute value of the angle between them. For example, in air, the observation angle θ _obs Between about 30 deg. and about 60 deg.. For example, in air, the viewing angle is equal to about 45 °.

The achromatic animation in the first part of the range of inclination angles is defined as the maximum slope (expressed in absolute value) α of the facet _max In other words Δθ _B，n1 ＝2|α _max I, wherein Δθ _B，n1 Is limited to a refractive index n ₁ Is shown in fig. 1A and 1B). In air, the angular range is greater, corresponding to Δθ _B ＝arcsin(n ₁ sin(2|α _max I) are provided. For example, for refractive index value n ₁ =1.5 sum α _max =7.1°, a first part Δθ of the angular range measured in air _B Equal to 21.5 °.

The facets that participate in the graphical dynamic visual effect are determined by observing the optical response of each facet for a given illumination defined by the tilt of the sample.

By calculating an angle theta _i The fourier transform FT of the phase shift ΔΦ undergone by the light incident on the optical security element, obtains the optical response of the facets of width Λ and depth h. The phase shift Δφ is represented as follows:

[ mathematics 1]

Where λ is the central operating wavelength of the visible light region, e.g. 550nm, n ₁ Is the refractive index of the first layer (113, fig. 1A and 1B) of dielectric material, h is the height of the facets. Thus, the optical response of the facets is expressed as follows:

[ math figure 2]

Where v is the spatial frequency, given by:

[ math 3]

In this form, the distribution and direction that maximizes the energy reflected at 0 th order for each facet for a given tilt angle can be predicted, so that the first pattern of structures can be designed to produce the desired animation.

In white light, the slope is alpha _i The optical response of the facets of (a) corresponds to a diffraction lobe (diffraction lobe) obtained by taking into account the envelope of the diffraction order range in the wavelength range of 400nm to 800 nm. Slope angle alpha _i With angular position theta of the diffraction lobes of the facets of (2) _o ＝-θ _i +2·α _i Is central.

An example of a diffraction lobe is shown in fig. 5B, where three scenarios are modeled. Each scene corresponds to a different tilt of the file. Therefore, the incident angle θ _i (in the direction perpendicular to the plane of the component. Delta. Of _N And the illumination direction delta of the light source _L An angle defined therebetween) is also different. The values of this angle were 7.68 ° (fig. 57), 15 ° (fig. 58) and 21.8 ° (fig. 59).

In each scenario, three faceted diffraction lobes are shown: two opposite 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 substantially zero angle central facet (curve 501), corresponding to a width of 80 μm and a depth of 1 μm.

Note that the smaller the facet width, the greater the angular extent of the diffraction lobes, which results in a widening of the reflected beam.

FIG. 58 shows a center position (specular position) for which the normal axis Δ perpendicular to the component plane _N Angle of observation delta theta _obs Divided into two angular sectors of equal measurement, in other words θ _i ＝-θ _o 。

In this case, it is the facet having a slope angle of substantially zero that enables light to be reflected toward the eye (specular reflection), and in fig. 58 (curve 501), the direction of observation by the observer of the operation document is symbolized by the eye. Thus, a facet with a slope angle of substantially zero will appear to be "active". The diffraction lobes 502 and 503 do not reflect energy along the viewing axis and the corresponding facets will appear to be closed.

By tilting the sample from side to side, the angle of incidence θ _i Is modified, the diffraction lobes are translated by delta theta _i Corresponding to the angle theta experienced after sample tilting _i Is a variation of (c).

Note that due to the air/n at the refractive index ₁ The angle of inclination and angle of incidence of the sample are different from the refraction of light experienced after the interface change.

FIG. 57 corresponds to illumination at an angle of incidence of 7.68, in which case the facets participating in the achromatic animation are diffraction lobes facing delta _O Facets that are directionally reflective. In particular, the facet involved in the visual effect in fig. 57 is a facet at an angle of-7.1 ° (curve 502). The direction of observation by the observer is represented by the eye.

When the sample is tilted to the other side of the center position, the facets with an angle of incidence of 21.8 ° and a relative slope angle of +7.1° are lit (fig. 59).

Thus, the first pattern may be designed by spatially arranging 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.

For illustration purposes, FIG. 5C shows facet F in the region of the structure used to form the number "2" (FIGS. 4A-4C) _i Is a diagram of the arrangement of (a).

"Pixel" P _i May be defined as a spatial region comprising one facet or several adjacent facets of the same width and the same slope angle. In practice, the pixels may have a rectangular shape, with at least one dimension smaller than 100 μm, advantageously smaller than about 60 μm, in order to make the eye invisible. Of course, other shapes of pixels are also contemplated. Each "pixel" forms a spot for a given tilt angle of the component. Thus, an achromatic animation as shown in fig. 4B can be created.

It will now be described how the parameters of the +1-order and-1-order diffraction gratings G are selected so as to obtain the first part Δθ of the achromatic and iridescent animation over the tilt angle range _B Is connected on both sides of (a).

The same facets modulated by the grating G generate an iridescent animation in a second part of the tilt angle range, in addition to the achromatic animation.

The parameters of the raster affect the engagement of the two animations (achromatic and iridescent). The period d of the diffraction grating can thus be selected as a function of the maximum angle value α of the slope (measured in absolute value) and the viewing angle so as to see an achromatic animation in a first part of the range of angles around the specular reflection and to see the same but iridescent animation in a second part of the range of angles, which iridescent animation joins the achromatic animation on both sides of the shown first part of the range of angles.

More specifically, it was determined that, in order to obtain a link between achromatic animation and iridescent animation, period d of raster G advantageously follows the following condition:

[ mathematics 4]

Wherein:

[ math 5]

Is at a refractive index of n ₁ Transition between achromatic and iridescent animation in medium (in other words, consider air/n ₁ A transition between positions 6 and 7 of the optical security element 40 as shown in fig. 3), and:

[ math figure 6]

Furthermore lambda _VIS Is the wavelength at which the iridescent animation starts, e.g. lambda _VIS Between about 400nm and about 450 nm.

This condition is directly derived from the grating formula according to which the direction of the +/-1 order diffraction will correspond to the viewing direction delta _O And wherein the angle of incidence on the grating corresponds to a transition angle between two ranges of tilt angles calculated with respect to the normal of the facet of the maximum slope angle.

For example, consider |α _max |＝7.1°，n ₁ ＝1.5，θ _obs =45° and λ _vis =450 nm, the following was calculated:and->

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

Note that by processing the period value and the maximum slope of the facets, a strictly positive overlap angle range can be defined between the first angle range (achromatic animation) and the second angle range (iridescent animation).

For example, in period d of selecting diffraction grating ₂ In the case of (a), the overlapping range delta theta is defined _rec 。

[ math 7]

Wherein if period d of grating G is selected ₂ Rather than the optimal period d where the overlap is zero, the angle of incidence θ ₂ Corresponding to the start of an iridescent animation:

[ math figure 8]

For example, consider period d using the parameters of the previous example ₂ =520 nm, in which case the angle θ ₂ Equal to 8.1 deg., in this case, the overlap range in air is therefore Δθ _rec ＝1.8°。

For example, FIG. 6 depicts when used in terms of illumination direction delta _N Different facets modulated by the grating G diffract (+1 and-1 orders), directed delta _O The wavelength of the reflection is a function of the angle of incidence. Curves 61, 62, 63, 64 and 65 correspond to facets at angles of-7.1 °, -3.55 °, 0 °, +3.55° and +7.1° respectively, overmodulated by a grating having a period of 520 nm.

Calculating a curve using the equation given above for d, where λ _vis Instead of the diffraction wavelength, d is instead the period selected for the diffraction grating G.

Dividing the total tilt angle range into 3 angle ranges: iridescent animation range delta theta corresponding to-1 order diffraction _R- Achromatic animation tilt range Δθ around specular reflection _B And a second iridescent animation range Δθ corresponding to +1st order diffraction _R+ 。

At a fixed incident angle theta _i Each facet modulated by the grating G diffracts a different wavelength in the viewing direction. The wavelength depends on the slope specific to 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.

Furthermore, as shown in fig. 6, a facet with a given slope, diffracting a given wavelength of +1 order, diffracts another wavelength of-1 order, which creates a reversal of color during the iridescent animation on both sides of the achromatic animation.

In addition to the selection period, the depth t (fig. 2) of the grating G may be selected so as to optimize the efficiency of the +/-1 order diffraction, as shown in fig. 7.

More specifically, in fig. 7, curves 70, 71, 72 and 73 show curves of the efficiency of the order 1 grating as a function of grating depth for four grating periods (i.e., 400nm, 460nm, 520nm and 580nm, respectively) for an incident light wavelength corresponding to 550 nm. This curve makes it possible to optimize the value of the depth of the diffraction grating G. For example, for a grating G with a period of 520nm, a depth t of 150nm may be chosen so as to have maximum 1 st and-1 st diffraction efficiencies.

Examples of optical security components for protecting value documents are shown using fig. 8 and 9A, 9B.

Fig. 8 shows an example of an optical security element (e.g., a label) according to the present description that is a "patch" or stamp, the patch being configured to be secured to, for example, a banknote or product.

In this example, the optical security element comprises a laminate, such as that shown in FIG. 1B, and the layer 118 may then be an adhesive layer.

The optical security element comprises a first diffractive structure etched in the first layer (113, fig. 1B) and delimited by a profile marked 81 in fig. 8, which according to the present description, generates achromatism in a first range of inclination anglesDynamic visual effects, and the same dynamic visual effects, which are iridescent, are generated in the tilt angle ranges on both sides of the first tilt angle range. The optical safety component also includes other structures defined by contours 82, 83 and 84. These may be, for example, allowing for the generation ofAn effective diffusing structure, holographic structure, or diffractive structure. In this example, a reflective layer (114, fig. 1B) (e.g., a metal or high refractive index layer) may be applied to the entire component, with regions 81, 82, 83, 84 being distinguished only by differences in the structure etched in the first layer.

Fig. 9A is a diagram showing an example of a value document 900 (e.g., a banknote) protected with the optical security component 91 according to the present specification, and fig. 9B is an enlarged diagram showing the security document shown in fig. 9A.

More specifically, in this example, the optical security element comprises a laminate, such as that shown in FIG. 1A, and the layer 117 may be, for example, a layer of thermally reactive adhesive for transferring the optical security element to a carrier of the banknote 900.

The optical security element 91 comprises a first diffractive structure etched in the first layer (113, fig. 1B) and defined by a profile in the form "2" marked 911 in fig. 9A, and a second diffractive structure etched in the first layer and defined by a profile in the form "5" marked 912. The two diffractive structures are diffractive structures according to the present description for generating an achromatic dynamic visual effect in a first range of inclination angles and for generating the same dynamic visual effect, but iridescent, in the range of inclination angles on both sides of the first range of inclination angles. As shown in fig. 9B, the animation caused by the two diffractive structures may exhibit different patterns.

Further, as can also be seen in fig. 9B, the second (reflective) layer is partially absent to expose an area 915, which area 915 exposes a carrier of the banknote on which the optical security component is secured. Thus, in this example, the reflective layer (114, fig. 1A) does not completely cover the diffractive structure.

Finally, as can also be seen in fig. 9B (diffraction structure with contours 911, 912), the first pattern forming the diffraction structure may present a region 918 in which region 918 there is no modulation with a 1 st order grating. These areas will be imperceptible when the optical safety member is subjected to tilting movement in a first angular range (achromatic animation), but will appear black to the observer when the optical safety member is subjected to tilting movement in a range of tilting angles on both sides of the first range of tilting angles. Thus, during iridescent animation, additional protection can be provided with messages that only appear at significant tilt angles.

In the same manner, the region 918 may be modulated by a second grating (e.g., a 1 st order second grating having a pitch and/or orientation different from the first grating) that is different from the first grating in order to reveal spectral shifts of iridescence or to allow azimuthal control if the orientation is different from the direction of the 1 st order grating modulating the rest of the first pattern.

The optical safety component shown in fig. 9A and 9B also includes another structure defined by a contour 913. For example, it may be a diffractive structure comprising a set of facets as described in the present specification but not modulated by a diffraction grating. Thus, region 913 will present an achromatic dynamic visual effect to the viewer. For example, the inclination angle range of the region 913 for seeing the achromatic animation in the entire inclination angle range in which the animations of the regions 911 and 912 are visible may be calculated. In this way both achromatic and iridescent animation can be seen in the part at the same time. More specifically, the concatenation of achromatic and iridescent animation in a region within a tilt range can be seen simultaneously, while adjacent regions experience only achromatic animation for that same tilt range. In addition, in the diffractive structure forming the region 913, the reflective layer can also be partially demetallized (or partially removed) to expose a region 915 in which the carrier of the security document can be seen.

Fig. 10A and 10B show examples of original "visual scenes" obtained by examples of optical security components according to the invention.

Thus, fig. 10A shows graphs 1001 and 1002 depicting the design of the first pattern and the second pattern, respectively.

As can be seen in the diagram 1001, the first pattern 1012 includes a set of facets arranged according to the present description to follow the illumination axis Δ with white light _L When the component is irradiated, a tilt angle range delta theta is generated under the action of the tilting motion _tilt In the reflection, a dynamic visual effect observable in the reflection. In this example, the first pattern is defined by a disk and is interrupted in an area 1011, the area 1011 forming a first identifiable graphical object (in this case, a contour of a bulb and a bulb base).

The diagram 1002 shows the second pattern 1022, that is, the 1 st order grating (grating G, fig. 2) of the modulated first pattern. This is present in the entire first pattern except for the region 1021, which region 1021 corresponds on the one hand to the region 1011 in which the first pattern is not present, but also to the additional region forming the second identifiable graphical object (in this example the bulb filament and light).

Fig. 10B depicts a diagram showing an achromatic and iridescent visual animation obtained by the pattern schematically shown in fig. 10A, according to a predefined visual scene.

During the achromatic animation shown in fig. 1201, in the first portion 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. Thus, the viewer sees the outline and base (first graphical object) of the bulb during the achromatic animation.

The animation continues in the second portion of the tilt angle range, except at the positions corresponding to regions 1011 (no first pattern) and 1021 (no first pattern or second pattern), but continues in an iridescent manner due to the presence of the first diffraction grating of 1 st order. Thus, in addition to the contours of the bulb and base, the viewer sees filaments and rays (second graphical object) that appear during the achromatic animation. Thus, the resulting structure produces a flickering scene during tilting between the first and second portions of the tilt angle range. In the example presented, during animation, the viewer perceives the bulb to "light up" during iridescent animation and to "go out" during achromatic animation, visible as a whole on a disc-shaped animated background.

An example of a method for manufacturing an optical security component according to the present description will now be described.

The first step comprises designing at least one first diffractive structure and possibly other structures according to the above embodiments.

The next step is to record the original replica, also called the master optical (master). The optical master is, for example, an optical carrier having structures formed thereon.

The optical master may be formed by electronic or optical lithography methods known in the art.

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

According to another embodiment, optical lithography (or photolithography) techniques may be used. In this example, the optical master is a plate of photosensitive resin, and the initiating step is performed by exposing the plate one or more times by mask projection of a phase shift mask type and/or an amplitude mask type and then developing in an appropriate chemical solution. For example, the first exposure is performed by an amplitude mask whose transmission coefficient is adapted such that, after development, a relief corresponding to the first pattern is formed in the region in which the first pattern is planned.

Next, a second blanket exposure is performed, and a diffraction grating (diffraction grating G, fig. 2) corresponding to the second pattern is recorded at least in the first area in which the second pattern is planned, according to an interference lithography method known to those skilled in the art. Similar steps may be provided to generate other relief, such as a second diffraction grating in other areas. The order of formation of the patterns is arbitrary and can be modified. Subsequently, a developing step is performed. In this way, an optical master is obtained after development, which comprises the structure resulting from the first pattern modulated by the second pattern.

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

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

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

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

Although described with a certain number of embodiments, the optical safety component and the method for manufacturing the component according to the invention comprise various variations, modifications and improvements which are obvious to a person skilled in the art, it being understood that these various variations, modifications and improvements fall within the scope of the invention as defined by the appended claims.

Reference to the literature

Reference 1: WO2015154943

Reference 2: WO2018224512

Reference 3: US4856857

Claims

1. An optical security component (101, 102) configured to detect a light in a direction (delta) corresponding to a given illumination direction (delta _L ) Forming a given viewing angle (theta _obs ) Is (delta) _O ) And from at least a first viewing surface (100), for viewing in reflection with the naked eye, the component comprising:

-a first layer (113) made of a dielectric material, the first layer being transparent in visible light;

-etching at least a first diffractive structure (S) on the first layer; and

-a second layer (114) at least partially covering said first diffractive structure and having a reflection spectral band in visible light; and wherein:

-said first diffractive structure comprises a first pattern (M ₁ ) The first pattern is formed by a set of parallel facets (F _i ) The facets have a slope that varies in the direction of slope variation (y) including, in absolute terms, the value of the angle (alpha _min ) And a maximum angle value (alpha) _max ) The angle value between the facets having a given maximum height (h _m ) The set of facets is arranged to, when illuminating the component with white light along the illumination axis, provide a light distribution along a tilt axis (delta) substantially perpendicular to the direction of change of the slope and within a given tilt angle range (delta theta _tilt ) Under the action of the inner tilting motion, a dynamic visual effect with observable reflection is generated;

-in at least a first area, the first pattern being formed by a second pattern (M ₂ ) Modulating, said second pattern forming a periodic grating of a predetermined period (d) size between 450nm and 650nm, said grating comprising a grating vector (k) having a direction collinear with said slope change direction (y) _g ) The grating is determined to produce a diffraction effect of 1 st order and-1 st order in reflection after deposition of the second layer,

-period (d) of the grating, maximum angle value (α _max ) And the observation angle (θ _obs ) Is determined to be in reflection at a first part (delta theta _B ) And in a second part (delta theta) _R- ；Δθ _R+ ) And an iridescent animation that engages the achromatic animation on both sides of the first portion of the range of tilt angles.

2. An optical security component according to claim 1, wherein the first portion of the tilt angle range (Δθ _B ) Included in the first portion (Δθ _B ) Is superimposed with an angle of between about 1 deg. and about 10 deg. of the second portion of the range of inclination angles.

3. An optical security element according to any of the preceding claims, wherein the given viewing angle (θ _obs ) Between about 30 deg. and about 60 deg..

4. An optical security component according to any of the preceding claims, wherein the minimum angular value of the slope is equal to 0 °.

5. An optical security component according to any one of the preceding claims, wherein the maximum angular value of the slope is between about 7 ° and about 15 °.

6. An optical security element according to any one of the preceding claims wherein the set of facets have substantially the same height.

7. An optical security component according to any one of the preceding claims, wherein the set of facets comprises one or more sub-sets of facets, each of the sub-sets of facets being configured to produce a "wave" type dynamic effect.

8. An optical security element according to any of the preceding claims, wherein the second layer comprises a metallic material.

9. The optical security component according to any one of claims 1 to 7, wherein the dielectric material of the first layer has a first refractive index (n ₁ ) And the second layer includes a light source having a second refractive index (n ₂ ) Such that the second refractive index (n ₂ ) Is equal to the first refractive index (n ₁ ) The difference therebetween is greater than or equal to about 0.3.

10. An optical security element according to any of the preceding claims, wherein the first pattern has contours (911, 912), the contours (911, 912) forming an identifiable graphical shape when viewed from the viewing surface.

11. An optical security element according to any of the preceding claims, wherein the first pattern is interrupted in a region (1011), the region (1011) forming a recognizable graphical object visible during the achromatic animation and during the iridescent animation when viewed from the viewing surface.

12. The optical security component of any of the preceding claims, wherein in at least a second region (918, 1021) the first pattern is not modulated or modulated by a third pattern forming a periodic grating that is different from the second pattern, the second region forming an identifiable graphical object that is visible only during the iridescent animation when viewed from the viewing surface.

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

14. A method for manufacturing an optical security element intended to be observed with the naked eye in reflection along an observation plane, comprising:

-forming at least a first diffractive structure (S) on the first layer such that:

-said first diffractive structure comprises a first pattern (M ₁ ) The first pattern is formed by a set of parallel facets (F _i ) The facets have a slope that varies in the direction of slope variation (y) including, in absolute terms, the value of the angle (alpha _min ) And a maximum angle value (alpha) _max ) The angle value between the facets having a given maximum height (h _m ) The set of facets is arranged to, when the component is illuminated with white light along an illumination axis, at an oblique axis (delta) along a direction substantially perpendicular to the direction of change of the slope and at a given oblique angle range (delta theta _tilt ) Under the action of the inner tilting motion, a dynamic visual effect with observable reflection is generated;

-period (d) of the grating, maximum angle value (α _max ) And the observation angle (θ) _obs ) Is determined to be, after deposition of the second layer, reflected at a first portion (Δθ _B ) And in a second part (delta theta) _R- ；Δθ _R+ ) And an iridescent animation that engages the achromatic animation on both sides of the first portion of the range of tilt angles.