Optical structure with relief effect - Patents.com

Abstract

The present invention relates to an optical structure (5) with a relief effect, comprising a support (7) suitable for aligning liquid crystals, a deposit (9) of substance in the form of at least one pattern (11) in contact with the support and partially covering the support, wherein the substance is an ink or varnish, and a layer (13) of liquid crystals at least partially covering the support and the pattern and in contact with the support.

Description

[Technical field]

[0001] The present invention relates to an optical structure with a relief effect, in particular for secure documents and / or security elements, and to a method for manufacturing same.

[0002] More particularly, the present invention relates to optical structures carrying liquid crystals. [Background technology]

[0003] Liquid crystals are widely used in optical structures, especially in security elements, due to their goniochromatic properties.

[0004] Typically, the liquid crystals are deposited in direct contact with a polymer film, commonly made of PET, that has been previously stretched in at least one direction, and even in two perpendicular directions, the stretching of the film encouraging the alignment of the liquid crystals, thereby giving the optical structure the effect of a change in color when there is a change in the viewing direction and / or the illumination direction.

[0005] To enhance the visibility of the goniochromatic effect, a dark background, typically black, is disposed on the side of the support opposite to that on which the liquid crystal is applied.

[0006] To the applicant's knowledge, such applied liquid crystals are not currently used to obtain relief effects, but only goniochromatic effects.

[0007] Optical structures with a relief effect are known, for example, from US 2013 / 0288024 A1, which comprise a substrate coated with a first layer that can be embossed and covered with a second layer, the first layer and / or the second layer comprising pigments with an optical effect. The embossing is stated to induce an optically detectable change in the alignment of the pigments, thereby enhancing the 3D effect of the pattern defined by the embossed zones.

[0008] EP 2 886 343 A1 describes an optical structure comprising a substrate, a primer formed on the substrate, and a UV-crosslinkable layer disposed on the primer. The UV-crosslinkable layer may contain liquid crystals and is embossed, thereby obtaining a three-dimensional visual effect. The assembly formed by the crosslinkable layer and the primer is surrounded by an anti-dust coating.

[0009] The relief effect is obtained either by the production of dark images formed by printing or metallization or demetallization processes, or by holographic structures.

[0010] The impression of relief given by a dark image is not dynamic unless its appearance changes very slightly with the angle of observation. Holographic structures are more eye-catching but are relatively expensive to produce. Summary of the Invention [Problem to be solved by the invention]

[0011] As a result, there is a need to benefit from new optical structures that are capable of producing dynamic relief effects while being relatively simple and economical to produce. [Means for solving the problem]

[0012] The present invention aims to address this need and achieves this by means of an optical structure with a relief effect, said optical structure comprising: A support suitable for aligning liquid crystals, a deposit of material in the form of at least one pattern in contact with and partially covering the support; and a layer of liquid crystal at least partially covering the support and the pattern and in contact with the support.

[0013] Surprisingly, the deposit located between the support and the layer of liquid crystal can provide a visual effect of relief. This deposit creates at least one transition zone, delimited by the contour of the pattern and extending at least partially around the pattern, which appears darker or lighter in at least one observation direction and / or one illumination direction than a first zone in which the liquid crystal is superimposed on the deposit, in particular in contact with the deposit, and than a second zone, separate from the first zone, in which the liquid crystal is in contact with the support. The variation in contrast between the first and second zones on the one hand and the transition zone on the other hand results in a visual effect of relief for the observer of the optical structure.

[0014] A portion of the transition zone may appear dark, particularly with a matte appearance, and another portion of the transition zone may appear light, particularly with a mirror-like glossy appearance.

[0015] In particular, when the optical structure is illuminated by optical radiation directed from a first end of the stack towards an opposite second end of the stack, the incident direction of which includes a component parallel to the support, the portion of the transition zone in contact with the second end can have a specular glossy appearance, for example when viewed from a direction perpendicular to the support, and vice versa, the portion of the transition zone in contact with the first end can appear dark.

[0016] The relief effect obtained is dynamic since the appearance, especially the impression of the relief, changes when the viewing direction and / or the illumination direction changes, in particular certain areas of the transition zone can change from a matte and / or dark appearance to a light and / or shiny appearance when the viewing direction and / or the illumination direction changes.

[0017] The transition zone may have a width of less than 1 mm, in particular between 100 μm and 500 μm. It extends from the inner edge defined by the contour of the pattern to the second zone, where the relief effect is not observed. The width of the transition zone corresponds to the maximum value measured in a direction perpendicular to the inner edge between the inner edge and the part of the second zone closest to the inner edge.

[0018] The first zone and the second zone may each appear darker according to a first viewing direction and / or according to a first illumination direction than according to a second viewing direction and / or according to a second illumination direction, respectively.

[0019] According to one viewing direction, the first zone and the second zone may appear dark and the transmission zone may appear matte, and according to another viewing direction, the first zone and the second zone may appear light and the transition zone may have a mirror-like glossy appearance.

[0020] Furthermore, the optical structure can have goniochromatic properties. In particular, the first zone and the second zone can appear one color according to a first viewing direction and / or according to a first illumination direction, respectively, and another color according to a second viewing direction and / or according to a second illumination direction. Furthermore, the transition zone can appear dark according to the first viewing direction and / or according to the first illumination direction, respectively, and can have a specular glossy appearance according to the second viewing direction and / or according to the second illumination direction, respectively.

[0021] When observed according to the first viewing direction and / or according to the first illumination direction, the first zone and the second zone may have different colors, and when observed according to the second viewing direction and / or according to the second illumination direction, the first zone and the second zone may have different colors.

[0022] Alternatively, the first zone and the second zone may have the same color when observed according to the first observation direction and / or according to the first illumination direction, and the first zone and the second zone may have different colors when observed according to the second observation direction and / or according to the second illumination direction.

[0023] Alternatively, when observed according to the first observation direction and / or according to the first illumination direction, the first and second zones and the transition zone may have the same color, and when observed according to the second observation direction and / or according to the second illumination direction, the first and second zones and the transition zone may have the same color.

[0024] Furthermore, when observed according to the first observation direction and / or according to the first lighting direction, the color of the transition zone can be different from the color of the first zone and / or the color of the second zone, and when observed according to the second observation direction and / or according to the second lighting direction, the color of the transition zone can be different from the color of the first zone and / or the color of the second zone.

[0025] sediment The relief effect is obtained according to the invention despite the small thickness of the deposit.

[0026] Preferably, said deposit is a print, especially of an ink or varnish.

[0027] Preferably, so that the visual effect of the relief is relatively noticeable, the dry weight of the substance expressed on the area of ​​the face of the support covered by the deposit is less than 1.5 g / m 2 Less than 1 g / m 2 Below 0.1 g / m 2 ~0.5g / m 2 , is.

[0028] The material may contain less than 40% liquid crystals, as a weight percentage expressed based on the dry weight of the material. The material may be free of liquid crystals.

[0029] The material may contain, as a weight percentage expressed based on its weight, less than 40% liquid crystal.

[0030] The substance can be an ink or a varnish.

[0031] The varnish or the ink can be transparent or colorless in the visible range, so that the deposit does not produce any opacity detectable by the naked eye in transmitted light.

[0032] The varnish or the ink may comprise a solvent. The solvent may be non-aqueous and may comprise an alcohol and / or a polyol. Alternatively, the solvent may be water-soluble.

[0033] The varnish or the ink may be curable under irradiation by radiation, especially by UV radiation.

[0034] The varnish or the ink can be applied by inkjet, flexographic, screen printing, or gravure printing.

[0035] The deposit, especially when in the form of a varnish or ink, may comprise components which are absorptive or excitable under illumination with ultraviolet or infrared radiation, in particular near infrared radiation.

[0036] In particular, the varnish or the ink may be colorless and transparent in the visible range and may contain luminescent components, especially fluorescent components, which may be visible only under UV or IR illumination, preferably UV, and the support may be transparent or translucent. Thus, when observed in transmitted light, the optical structure appears for example transparent or translucent to the observer under illumination with an illuminant in the visible range, the pattern is indistinguishable from the support, and the pattern is revealed under illumination with an illuminant causing luminescence, especially an illuminant emitting in the UV.

[0037] Preferably, the substance is an ink, thereby facilitating its deposition by ink printing techniques.

[0038] The ink may comprise nematic liquid crystals and the layer of liquid crystals at least partially covering the support may comprise cholesteric liquid crystals with a goniochromatic effect. Advantageously, the pattern is linearly polarized and the layer of liquid crystal is circularly polarized, so that in addition to the relief effect another optical effect is obtained.

[0039] When the structure is observed in polarized light according to a first observation configuration, the zones where the pattern and the layer of cholesteric liquid crystal are superimposed have a first appearance and the zones where the layer of cholesteric liquid crystal is in contact with the support have a second appearance different from the first appearance.

[0040] Preferably, the appearance is color.

[0041] Furthermore, preferably, the zone in which the pattern and the cholesteric liquid crystal layer are superimposed and the zone in which the cholesteric liquid crystal layer is in contact with the support each change appearance according to a second observation configuration and have different aspects from each other, the transition between the first and second observation configurations being preferably performed by rotation of the optical structure around an axis perpendicular to the support, preferably over an angle of 90°.

[0042] Preferably, the appearance of the zone in which the pattern and the cholesteric liquid crystal layer are superimposed in the first observation configuration is identical to the appearance of the zone in which the cholesteric liquid crystal layer is in contact with the support in the second observation configuration, and vice versa.

[0043] The material can be colored. It can have the same color as the color of the substrate or a different color.

[0044] The ink can be black, preferably pigmented, with a pigment concentration of less than 10%. The ink preferably comprises a non-aqueous solvent and is intended to be deposited on the substrate by inkjet printing. Alternatively, it can also be deposited by flexographic printing.

[0045] The ink can be pigmented. It can be light-colored. It can have a saturation difference ΔC with the support that is greater than 10, preferably greater than 15, and even better greater than 20. Such a saturation difference focuses the observer's gaze towards the transition zone. The saturation difference is measured in the colorimetric space LCH defined according to the ISO 5631-1 standard.

[0046] Preferably, the ink contains less than 10% of pigments, especially colored, as a percentage by weight expressed based on the dry weight of the ink. Preferably, the ink is not pigmented. Non-pigmented inks result in particularly striking relief effects. Preferably, the ink contains less than 10% of pigments, especially colored, as a percentage by weight expressed based on its weight.

[0047] Preferably, the ink comprises a solvent and a colorant dissolved in the solvent.

[0048] The ink can be for printing with an inkjet printer. It can be, inter alia, yellow or cyan in colour for an inkjet printer.

[0049] The ink may include a water-soluble base, which may represent 60% to 90%, or even 65% to 85% of the volume of the ink. It may further include a polar solvent, such as pyrrolidone-2. The polar solvent may represent less than 7.5% of the volume of the ink. It may include a plasticizer, such as pental-1,5-diol, which may represent less than 10% of the volume of the ink. It may also include anhydrous magnesium nitrate, which may represent less than 5% of the volume of the ink.

[0050] Alternatively, the ink may comprise at least one polyol and / or one alcohol, which may represent more than 75% of the volume of the ink.

[0051] The polyol comprises, for example, 2 to 32 carbon atoms, in particular 2 to 16 carbon atoms, more particularly 3 to 8 carbon atoms. By "polyol" is to be understood any organic molecule comprising at least two free hydroxyl groups. In particular, the polyol may be selected from ethylene glycol, pentaerythritol, trimethylolpropane, propylene glycol, 1,3-propanediol, butylene glycol, isoprene glycol, pentylene glycol, hexylene glycol, glycerin, diglycerol, and mixtures thereof. Preferably, the polyol is glycerin.

[0052] The alcohol may be selected from among lower C1-C6 alkanols, in particular from among ethanol, propanol and isopropanol. Preferably, the alcohol is ethanol.

[0053] The ink may contain a surfactant. The surfactant may be selected from amphoteric, anionic, cationic or non-ionic surfactants, used alone or in mixtures. It may be used, optionally, in conjunction with a co-surfactant. If the ink is an emulsion, the surfactant is appropriately selected according to the emulsion to be obtained (water-in-oil or oil-in-water). Preferably, the surfactant is a non-ionic surfactant. Examples of non-ionic surfactants that may be cited in particular include oxyethylene derivatives of tetramethyl-2,4,7,9-decyne-5-diol-4,7 and preferably tetramethyl-2,4,7,9-decyne-5-diol-4,7 oxyethylene with 3.5 molecules of ethylene oxide, sold under the name Surfynol 440.

[0054] It may contain fatty substances to modify the alignment of the liquid crystals in the transition zone. "Fats" is understood to mean organic compounds that are insoluble in water at ambient temperature (25°C) and atmospheric pressure (760mmHg), i.e. have a solubility of less than 5%, preferably less than 1%, or even more preferably less than 0.1%. The fats are lower C6-C 16 They may be chosen from among alkanes, non-silicone oils of animal, vegetable or synthetic origin, hydrocarbons of mineral or synthetic origin, fatty alcohols, fatty acids, esters of fatty acids and / or fatty alcohols, non-silicone waxes and silicones.

[0055] Additionally, the ink may exhibit a surface tension, measured according to the ISO 304 standard, of 28 mN / m to 32 mN / m.

[0056] For example, the substance is selected from the following: a black ink sold by Toyo Ink America under the reference LIOJET AP KB027-K for inkjet printing with piezoelectric technology; Yellow ink sold by HP under the part number HP343 for printing on the HP Deskjet 6540 printer sold by HP, HP70 Gloss Enhancer Varnish sold by HP Corporation; Yellow ink sold by HP under the part number HP304 for printing on the Envy 5030 printer sold by HP, Yellow ink sold by HP under the part number HP72 for printing on the T610 DesignJet printer sold by HP, Yellow ink sold by HP under the part number GT52 for printing on the GT5810 Deskjet printer sold by HP, A nematic liquid crystal ink sold by BASF under the part number Lumogen Hide N700.

[0057] The deposit may be non-opaque, in particular transparent or translucent.

[0058] The deposit can be in the form of a solid color, thus simplifying the method for manufacturing the optical structure. A solid color can be easily produced on the support, for example by printing, in particular by inkjet printing, flexographic printing, screen printing or gravure printing. The deposit can thus be other than in the form of a halftone raster image.

[0059] The deposit can preferably be produced by inkjet printing. This method makes it possible, inter alia, to Deposition of small amounts of material per unit of surface area, and / or Customization of the pattern without the need for any printing forms.

[0060] The pattern can be continuous or discontinuous. It can be formed by portions of the pattern spaced apart from one another. Adjacent portions of the pattern can be spaced apart by a material-free zone, preferably by a distance of more than 100 μm. Thus, at least one transition zone can be formed in the zone to separate the spaced apart portions of the pattern.

[0061] The pattern, or at least a part of the pattern, may surround a zone free of material. Preferably, the largest dimension of said surrounded zone is greater than 100 μm.

[0062] The pattern may take the form of at least one alphanumeric symbol, or may represent a logo, a person, an animal, a landscape, a plant, a monument, a texture, or an object. It may represent one or more geometric figures, for example polygons of various sizes, ellipses, or disks. It may constitute a sequential number. The same pattern, at the same scale or at a different scale, may be located elsewhere on the document, for example present on another security element or in the form of a print on the substrate of the document to be secured.

[0063] The pattern may have a maximum dimension of 0.5 to 30 mm.

[0064] The pattern can be repeated at regular intervals along the substrate.

[0065] support The support is suitable for the alignment of the liquid crystals. In particular, it may have a surface texture suitable for the alignment of the liquid crystals.

[0066] Preferably the support comprises an axially, preferably biaxially, stretched film.

[0067] The film is made of a plastic material chosen from among polyesters, especially polyethylene terephthalate, also called PET, polypropylene, polyethylene, and mixtures thereof. The film preferably consists of PET.

[0068] The stretching induces alignment of the liquid crystals.

[0069] The film can have a thickness of 6 μm to 500 μm, for example, it has a thickness of 12 μm to 50 μm, for example approximately 19 μm.

[0070] The support may also be provided with a layer of a primer, especially an adhesion primer, covering, preferably completely, one side of the film and in contact with the film and the layer of liquid crystal, which improves the adhesion of the liquid crystal to the support without preventing the film from contributing by its intrinsic structure to the alignment of the liquid crystal.

[0071] The thickness of the adhesion primer is preferably less than 1000 nm, preferably less than 100 nm, so that the structure of the underlying film remains effective and promotes alignment of the liquid crystals during the fabrication of the optical structure.

[0072] The adhesion primer is preferably transparent.

[0073] The adhesion primer may comprise a polyolefin, preferably chosen from among polyethylene, polyurethane, polyester, polycarbonate, and polyacrylic acid, one of their copolymers. Preferably, it comprises polyacrylic acid.

[0074] The supports are, for example, selected from among the Sarafil™ S56C and Sarafil™ SF150 polyester supports sold by TPL, the transparent polyester supports sold by Technifilm, the transparent polyester supports selected from the Lumirror™ series sold by Toray, and the transparent polyester supports sold by Mitsubishi.

[0075] Preferably, the support can be selected such that the layer formed by the liquid crystal in contact with the support has a reflection haze, measured according to the ASTM D4039-09 standard, of greater than 50, in particular between 50 and 100, preferably greater than 60, in particular between 60 and 90.

[0076] The "reflective haze", measured according to the ASTM D4039-09 and ISO13803 standards, characterizes the reflective scattering haze effect of the liquid crystal layer. The reflective scattering haze produces a milky appearance associated with low intensity light scattering, with the main reflection corresponding to the reflection in the specular direction. The measurement can be performed according to the ASTM D4039-09 (reapproved in 2015) or ISO13803:2014 standards. This allows the visibility of the goniochromatic effect over a more extended angular range, and therefore allows the masking of the background over a more extended angular range. Thus, the optical structure can be arranged in a through window formed in the substrate. Thus, the goniochromatic effect and / or the relief effect of the liquid crystal layer can be observed, especially without the optical structure being arranged between the observer and a dark background.

[0077] Preferably, the support comprises a film and an adhesive primer as described above, the adhesive primer being selected such that the reflective haze, measured according to the ASTM D4039-09 standard, of the layer formed by the liquid crystal in contact with the support is greater than the reflective haze of a layer of liquid crystal not covered with the adhesive primer and arranged in contact only with the film.

[0078] Furthermore, the support can be transparent or translucent. The relief effect can be observed from the front and back of the support.

[0079] Preferably, zones of the optical structure that appear visually protruding when the front side of the optical structure is viewed in reflected light appear as recesses when the back side of the optical structure is viewed in reflected light.

[0080] Furthermore, in order to enhance the durability of the optical structures, an additional support, preferably made of PET, can be fixed to the film with the optical structures by any suitable means, in particular by lamination with an adhesive, preferably to the side of the film that is coated with the adhesive primer.

[0081] The film may be made of polypropylene, especially biaxially oriented, also called BOPP film. Such polypropylene films are sold, for example, by CCL Secure under the name Guardian or by De La Rue under the trade name Safeguard. The adhesion primer is sold, for example, by Mica Corporation under the item number Mica-A-131-X.

[0082] liquid crystal A layer of the liquid crystal may be in contact with the stack.

[0083] The liquid crystal has at least one goniochromatic property. It can be nematic or, preferably, cholesteric. The layer of liquid crystal can include nematic and cholesteric liquid crystals.

[0084] The liquid crystals are preferably non-thrombocytic.

[0085] The layer of liquid crystal is preferably crosslinked, which can be obtained by printing with a crosslinkable ink containing liquid crystals, followed by drying and then crosslinking the ink, in particular under UV, to fix the alignment of the liquid crystals.

[0086] Preferably, the reflection haze of at least a portion of the layer of the liquid crystal superimposed on the stack and of at least a portion of the layer of the liquid crystal in contact with the support, measured according to the ASTM D4039-09 standard, is greater than the reflection haze of the transition zone.

[0087] The layer of liquid crystal may at least partially, or even completely, cover the face of the support on which it is disposed.

[0088] The thickness of the liquid crystal layer may be less than 100 μm, in particular between 2 μm and 30 μm.

[0089] Furthermore, the optical structure may have microcavities formed between the layer of liquid crystal and the support layer, in particular between the layer of liquid crystal and the deposit of said substance.

[0090] The maximum dimension of each microcavity, measured in the plane of the support, is in particular less than 100 μm.

[0091] Preferably, the thickness of the optical structure is constant, for example between 14 μm and 55 μm. The thickness of the liquid crystal layer in at least one zone in which it is in contact with the support is preferably equal to the sum of the thickness of the stack, the thickness of microcavities, if present, and the thickness of the liquid crystal layer in the zone in which it is superimposed on the stack.

[0092] The liquid crystals preferably have a lower alignment quality in the zone directly covering the support than in the transition zone. Because the liquid crystals are better aligned in the transition zone, light reflection is only observed for certain viewing and / or illumination directions, for which it is stronger there than in the first and second zones.

[0093] The alignment quality of the liquid crystal in a zone of the optical structure can be measured by acquiring an image of the surface of a given area by optical microscopy with polarized or unpolarized light. Individual zones, called "domains", in which the liquid crystal has substantially the same alignment are observed on the image. The smaller the domain size, i.e. the more domains there are in a zone of a given area, the lower the alignment quality of the liquid crystal in said zone. For example, it is possible to evaluate the alignment quality of the liquid crystal in a zone by acquiring the light spectrum transmitted over the zone by spectroscopy. The profile of the light spectrum transmitted over the zone depends on the alignment quality of the liquid crystal in said zone.

[0094] The alignment quality of the liquid crystal in the transition zone can be uniform.

[0095] The width of the transition zone can be measured by using images of the optical structure obtained by optical microscopy, with polarized light, or alternatively with unpolarized light, to determine the extent over which the alignment quality of the liquid crystal is uniform and better than adjacent zones.

[0096] The optical structure may include at least one other layer of liquid crystal containing a different liquid crystal than the layer of liquid crystal covering the deposit, in particular the layer of liquid crystal and the other layer of liquid crystal may have different goniochromatic properties.

[0097] The layer of liquid crystal and the other layer of liquid crystal can be partially superimposed on each other to define zones, in particular three zones, with different goniochromatic properties.

[0098] In one embodiment, the optical structure may comprise: A translucent, or preferably transparent, support; a first deposit of a first material in contact with a first surface of the substrate in the form of a first pattern; a second deposit of a second material in contact with a second side of the support in the form of a second pattern, wherein the first side and the second side of the support are opposite one another; First and second liquid crystal layers at least partially covering the first and second faces of the support, respectively, and superimposed on, and in particular in contact with, the first and second patterns, respectively.

[0099] When the optical structure is viewed in transmitted light, the first and second patterns may complement each other by association, thereby defining a third pattern, which may be at the same scale or at a different scale, located elsewhere on the document or on another security element.

[0100] Furthermore, when observed with reflected light on either one of the first and second surfaces, the visual effects of the relief produced by the first and second sets formed by the support, the first and second deposits, and the first and second liquid crystal layers, respectively, can be combined with each other.

[0101] The optical structure may comprise a dark background which may be provided below the layer of liquid crystal, in particular on the side of the support opposite to the side covered by the layer of liquid crystal, which dark background enhances the relief effect and, if necessary, the goniochromatic effect of the liquid crystal.

[0102] Alternatively, the layer of liquid crystal can be sandwiched between the support and the dark background, so that the deposit and the layer of liquid crystal can be protected by the support and the dark background.

[0103] The dark background can be obtained by printing a colorant, such as Indanthren PA-FS from Dystar Colours Distribution, or a dye, especially a metal oxide. The dye can be, for example, absorbing or interfering.

[0104] Alternatively, the dark background can be obtained by metallization, especially in vacuum or by electrochemical means, or by any other technique for depositing metals, metal oxides or metal oxide salts. The dark background can also be carried by an additional support, which is preferably fixed to the support on the side opposite to that covered by the layer of liquid crystal.

[0105] A metallization layer provided with openings through its thickness, for example obtained by demetalization, can be deposited on the face of the support opposite to that on which the layer of liquid crystal is deposited. As a variant, said metallization layer can also be carried by the additional support, which is preferably fixed to the support on the side opposite to that covered by the layer of liquid crystal.

[0106] The dark background may be covered with magnetic particles arranged such that the remanence of the optical support varies along the dark background, thereby defining a third level of security, e.g., a magnetic code.

[0107] Preferably, the dark background is at least partially superimposed over the layer of liquid crystal.

[0108] The dark background is preferably arranged in register with respect to the layer of liquid crystal, in particular so that the dark background can be precisely superimposed on the liquid crystal.

[0109] The dark background may have a transmittance of less than 80% and is preferably opaque.

[0110] In a variant, the optical structure does not have a dark background, as specifically described above.

[0111] The optical structure may be present on a security element, for example chosen from among a security wire, a security foil, a security film or a security patch.

[0112] The invention also relates to a security element comprising an optical structure according to the invention.

[0113] The security element may comprise at least one additional security structure, in particular chosen from among the first, second or third level security structures. It may involve: A pattern that appears in transmitted light and is formed by metallization and / or demetallization; colorants, luminescent dyes, interference dyes in printed form or mixed with at least one constituent layer of the security element, compounds, colorants and / or photochromic or thermochromic dyes, especially in printed form or mixed with at least one constituent layer of the security element, ultraviolet (UV) light absorbers, especially in coated form or mixed with at least one constituent layer of the security element, Interferometric multilayer structure, a refractive, birefringent or polarizing layer; Diffractive structure, means for generating a "moiré effect" or parallax effect, for example an effect which makes it possible to reveal a pattern generated by the superposition of two security measures, for example by the focusing, in particular by folding, of the lines of the two security measures, Colored filters, An automatically readable security measure having specific measurable properties, especially luminescence (e.g., fluorescence, phosphorescence), light absorption (e.g., ultraviolet, visible, or infrared), Raman activity, magnetism, microwave interaction, interaction with X-rays, or electrical conductivity. Security Elements

[0114] The security element can be chosen among a security wire, a security foil, a security film or a security patch. It can even be a card or a protective or tamper-evident film.

[0115] The security element may comprise several optical structures according to the invention.

[0116] The security element may be a security wire, the pattern being repeated regularly, preferably at regular intervals along the length of the wire.

[0117] In the variant in which the security element is a security wire, the security wire can be incorporated into a window in a secure document, such as a banknote, and the security element can extend from one end of the document to the other.

[0118] The security wire may have a width of 1 mm to 10 mm and / or a thickness of 10 μm to 100 μm.

[0119] In the variant in which the security element is a foil, the security element is applied by transfer, for example to the surface of paper, film or card.

[0120] By "patch" is meant a film that does not cover the entire surface of the underlying substrate.

[0121] The invention also relates to a security document comprising an optical structure according to the invention and / or a security element according to the invention.

[0122] Preferably, the optical structures are visible on the front and back of the document, in particular zones of the optical structures that appear to be protruding when the front of the document is viewed can be seen as indentations when the back of the document is viewed.

[0123] The secure document may comprise a fibrous substrate, the security element being disposed within a window in the fibrous substrate.

[0124] The secure document may be selected from among a payment instrument, such as a banknote, a cheque, or a lunch voucher, an identity document, such as an identity card, a visa, a passport, or a driver's license, a lottery ticket, a transport document, and a ticket for a cultural or sporting event.

[0125] The security element may extend from one end of the secure document to the other end.

[0126] The pattern of optical structures can be located at another location on the secure document, thus establishing an association between the secure document and the security element. Preferably, in the variant in which the secure document is a banknote, the pattern represents for example the currency, the name of a bank, or a face value.

[0127] Manufacturing method The present invention also relates to a method for manufacturing an optical structure according to the present invention, in which the substance is deposited on a support so as to form at least one pattern partially covering the support, and at least one layer of liquid crystal is deposited on the support and on the appropriately formed pattern.

[0128] Prior to deposition of the material on the support, the method may include stretching the element in at least one direction.

[0129] The method may include depositing a primer, especially an adhesion primer, onto the film, as explained above, to form the support, prior to deposition of the material.

[0130] The deposition of the material can be carried out by printing onto the substrate, inter alia by inkjet printing, gravure printing, screen printing, letterpress printing, or flexographic printing.

[0131] Preferably, the substance is an ink. The deposition can be carried out using a cartridge containing the ink or an inkjet printer equipped with a continuous ink supply. The inkjet printer can be a piezoelectric inkjet printer or a thermal inkjet printer.

[0132] Preferably, the ink supply rate of the substrate is higher than 20%. The ink supply rate of the substrate corresponds to the ratio between the volume of ink deposited by the printer in a zone of the substrate and the maximum volume of ink that can be printed in said zone of the substrate.

[0133] After printing, the coated substrate may be dried for a period of up to 5 minutes, such as 1 minute, and / or at a temperature of from 50°C to 100°C, such as around 60°C.

[0134] The support can be fixed to a substrate, in particular paper, during printing of the pattern, for example, the substrate comprises a recess and the pattern is printed on the part of the support superimposed on the recess.

[0135] The layer of liquid crystal can be printed onto the substrate and the pattern by flexography, screen printing, gravure printing or letterpress printing, in particular with an ink comprising a solvent and the liquid crystal dispersed in the solvent. It can be printed by inkjet. The ink can be deposited in the form of a solid color or a pattern, which at least covers the pattern and in those parts of the substrate not covered by the pattern.

[0136] The liquid crystals are aligned during evaporation of the solvent, for example by "air" drying, preferably in a horizontal direction to promote alignment of the liquid crystals. Preferably, the ink is crosslinkable under UV, allowing the crosslinking following the deposition to permanently fix the alignment of the liquid crystals.

[0137] The evaporation may be carried out in an oven for a period of 1 minute to 5 minutes, for example 3 minutes, and / or at a temperature of 50°C to 100°C, for example around 95°C.

[0138] Finally, the invention relates to a method for authenticating a security element according to the invention or a secure document according to the invention, in which the optical structure is observed according to at least one observation direction and a determination is made from this observation whether the pattern appears giving the impression of a relief image.

[0139] In particular, the optical structure can be observed in at least two different observation directions from the same side of the support, and when the angle of observation is changed, a change in appearance of or around the pattern can be detected, in particular a change in appearance consistent with the observed relief effect.

[0140] The optical structure can be observed, in particular by illuminating it according to two different illumination directions on the same side of the support, according to the same observation direction, and when the illumination angle is changed, a change in the appearance of the pattern or of the surroundings of the pattern can be detected, in particular a change in appearance consistent with the observed relief effect.

[0141] The pattern can be viewed in front of a dark background to enhance the visual effect of the relief.

[0142] Furthermore, it is contemplated that observations can be made on the front and back and that an inversion of the relief between the two observations is detected, where inversion of the relief is understood to mean that zones which appear protruding when one side of the optical structure is observed appear recessed when the opposite side is observed and vice versa.

[0143] Furthermore, authenticating the security element may include observing the optical structure to determine whether a goniochromatic effect is observed, and generating information regarding authenticity based on at least this observation.

[0144] The authentication method may include the steps of observing the security element through a polarizing filter to reveal an orientation of the support and generating information regarding authenticity based on at least this observation, which observation through a polarizing filter may reveal differences in alignment quality of the liquid crystal between the transition zone and the first and second zones.

[0145] For example, according to the variant in which the support comprises a biaxially stretched film, the biaxial orientation of the film can be confirmed by analyzing the birefringence of the film in a conventional manner. A linear polarizer, for example a filter, placed over the security element can be used, which is rotated by 90° to determine whether there is a change from a dark to a light appearance in response thereto.

[0146] In the described variant, in which the ink comprises nematic liquid crystals and the layer of liquid crystals at least partially covering the support comprises cholesteric liquid crystals having a goniochromatic effect, the method can further comprise observing the optical structure in polarized light to detect a difference in appearance between the zone where the pattern and the layer of cholesteric liquid crystals are superimposed and the zone where the layer of cholesteric liquid crystals is in contact with the support.

[0147] Preferably, the optical structure is moved and / or rotated, in particular around an axis perpendicular to the support, preferably through an angle of 90°, in order to detect a change in appearance of the zone in which the pattern and the cholesteric liquid crystal layer are superimposed and of the zone in which the cholesteric liquid crystal layer is in contact with the support, the change in appearance being such that the appearance of the zone in which the pattern and the cholesteric liquid crystal layer are superimposed and the appearance of the zone in which the cholesteric liquid crystal layer is in contact with the support are also different from each other.

[0148] According to a preferred variant of the authentication method described above, the polarized light is emitted, for example, by an LCD screen of a phone or computer, so that authentication of the security element or the secure document is easily performed, for example by placing the security element or the secure document between the LCD screen and the observer.

[0149] The invention can be better understood on reading the following description of non-limiting examples of its implementation and on examining the accompanying drawings, in which: [Brief description of the drawings]

[0150] [Figure 1] FIG. 1 shows a schematic top view of an example of an optical structure according to the invention. [Diagram 2] FIG. 2 shows a cross section taken along line II in FIG. [Figure 3a] FIG. 3a shows the visual effect of the different reliefs observed for different illumination directions. [Figure 3b]FIG. 3b shows the visual effect of the different reliefs observed for different illumination directions. [Figure 3c] FIG. 3c shows the visual effect of different reliefs observed for different illumination directions. [Figure 3d] Figure 3d shows the visual effect of different reliefs observed for different illumination directions. [Figure 4] FIG. 4 is a cross-sectional view of an element of the modified embodiment. [Diagram 5] FIG. 5 is a cross-sectional view of another alternative embodiment. [Figure 6] FIG. 6 is a cross-sectional view of another alternative embodiment. [Figure 7] FIG. 7 shows a front view of a secure document according to the present invention. [Figure 8] FIG. 8 is a cross-sectional view of another example of a secure document. [Figure 9] FIG. 9 is a photograph of an example of PET coated with ink deposits. [Figure 10] FIG. 10 is a photograph of an example optical structure made from the coated film of FIG. [Figure 11] FIG. 11 is a photomontage of half of the photographs in FIGS. 10 and 11 at the same scale. [Figure 12] FIG. 12 is a photograph, obtained by optical microscopy in polarized light, of a portion of the optical structure of FIG. [Figure 13] FIG. 13 is a photograph of another example of a coated film carrying optical structures. [Figure 14] FIG. 14 is a photographic montage of a photograph of the optical structure made from the coated film of FIG. 13 and the corresponding portion of the photograph of FIG. [Figure 15a] FIG. 15a is a photograph of the front side of an example optical structure. [Figure 15b] FIG. 15b is a photograph of the back side of the optical structure of FIG. 15a. [Figure 16a] FIG. 16a is a photograph of an exemplary optical configuration illuminated according to a certain illumination direction. [Figure 16b]FIG. 16b is a photograph of the optical structure of FIG. 16a illuminated according to another illumination direction. [Figure 16c] FIG. 16c is a photographic montage including the left and right portions of FIGS. 16a and 16c, respectively, and a central portion corresponding to the central portions of FIGS. 16a and 16c that are not covered by a layer of liquid crystal. [Figure 17a] FIG. 17a is a photograph of an example optical structure viewed with unpolarized light. [Figure 17b] FIG. 17b is a photograph of the optical structure of FIG. 17a viewed in polarized light. [Figure 17c] FIG. 17c is a photograph of the optical structure of FIG. 17a viewed in polarized light after being rotated 90° about an axis perpendicular to the substrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0151] In the figures, components of the structure are not necessarily drawn to scale for the sake of clarity.

[0152] 1 and 2 show an example of an optical structure 5 according to the invention, which comprises a support 7, a deposit 9 of material on the support to form a pattern 11, and a layer 13 of liquid crystal.

[0153] The substance is, for example, an ink printed onto the substrate using a thermal or piezoelectric inkjet printer. It partially covers the face 15 of the substrate on which it is deposited. In the examples of figures 1 and 2, the pattern has a circular form, but any other form can be envisaged, for example a series of alphanumeric symbols, currency, landscapes, figures or monuments, among others.

[0154] The deposit 9 is in contact with the support 7 and with the layer of liquid crystal.

[0155] When observed according to at least one observation direction D1, the optical structure has in particular the visual effect of a relief in a transition zone 17, which is delimited by and extends around the pattern 11. In the transition zone 17, the layer of liquid crystal can be in contact with the support 7. The transition zone 17 extends between a first zone 19, in which the liquid crystal is superimposed on, in particular in contact with, the material of the deposit 9, and a second zone 21, in which the liquid crystal is in contact with the support 7. Thus, the alignment quality of the liquid crystal in the transition zone 17 can be different from the alignment quality of the liquid crystal in the first zone 19 and in the second zone 21.

[0156] The optical structure emits light E having a component parallel to the support and directed from the left end 23 of the stack 9 towards the opposite right end 25. 1g 3a, a portion 27 of the transition zone in contact with the right edge, delimited by a dashed line in Fig. 3a, may appear bright and have a particularly specular glossy appearance, and a portion 29 of the transition zone in contact with the left edge, delimited generally by a short dashed line in Fig. 3a, may appear dark and have a particularly matte appearance.

[0157] The optical structure emits light E 1g 2 from the left end 23 towards the right end 25 of the stack 9, and the light radiation E 1g and light radiation E, with different angles of incidence. 2g 3b, the portion 27 of the transition zone appears brighter and its appearance may differ from that observed in FIG. 3a, and the appearance of the portion 29 of the transition zone may differ from that observed in FIG. 3a when illuminated by illumination E. 1g In particular, the portion 29 is changed with respect to what is observed using the direction E 1g In particular, it can have a specular, glossy appearance.

[0158] Furthermore, the first zone 19 and the second zone 21 are 1g and E 2g When illuminated by a 3D reflector, the 3D reflector can have a goniochromatic effect that can be substantially identical.

[0159] The optical structure is 1g and E 2g , i.e. from the right end 25 towards the left end 23 of the pile. 1d and E 2d When illuminated in the direction E, the observed effect is reversed, as shown diagrammatically in Figures 3c and 3d. 1d When illuminated according to the direction E, the portion 27 of the transition zone appears dark and the portion 29 appears light, 2d When illuminated according to

[0160] The optical structure may comprise a dark background 31, as shown in Fig. 4. The dark background may take the form of an opaque layer 33 covering the face 35 of the support opposite to the face 15 on which the deposit and the layer of liquid crystal are arranged in contact. The opaque layer is, for example, a print of black ink or a metal coating. It is at least partially overlapped with the deposit and the layer of liquid crystal. Thus, when observed from the side of the support on which the liquid crystal is arranged, as indicated by the arrow D2, the visibility of the liquid crystal is improved and the relief effect is enhanced.

[0161] As a variant, as shown in Fig. 5, the dark background 31 is arranged on the opposite side of the support, which is semi-transparent or preferably transparent. It is in contact with the layer of liquid crystal 13. The dark background 31 and the support 7 sandwich the layer of liquid crystal and the deposit. Thus, the relief effect is enhanced when the optical structure is observed from the side of the support opposite to the side covered by the deposit, as indicated by the arrow D3.

[0162] The example shown in Fig. 6 differs from the example shown in Fig. 4 in that the optical structure comprises another transparent film 37, for example made of PET, fixed, for example glued, to a semi-opaque dark background. The optical structure also comprises a metallization layer 39, with at least one recess 41, for example made by selective demetalization and opening through to the other film 37. The optical structure thus provides a visual effect of relief when observed from the side of the support covered with the layer of liquid crystal and the deposit. It obtains another visual effect when observed on the other side of the support, the metallization layer having a glossy appearance according to at least one direction and the dark background being recognizable through one or more of the recesses.

[0163] 7 represents a secure document 45 in the form of a banknote, comprising a fibrous substrate 47, for example made of paper, and a security element 49 in the form of a security wire extending in one or more windows between two ends 53, 55 of the substrate 47. The security wire comprises a part inserted in the bulk of the substrate, represented by a dashed line, and another part arranged in a window 57 emerging on the surface of the fibrous substrate 47. The security wire contains the optical structure, the deposit 9 being arranged in the window 57. The pattern 11 can be located elsewhere on the document, for example in the same form 58.

[0164] 8 represents another example of a secure document 45 in the form of a banknote, comprising a fibrous substrate 47, for example made of paper, and a security element 49 in the form of a security film, which at least partially covers an opening 60 extending between two ends 53, 55 of the substrate 47 and passing completely through the thickness of the substrate 47. The security film contains the optical structure, and the deposit 9 is at least partially, for example completely, superimposed on the opening 60. The pattern 11 can be located elsewhere on the document, for example in the same form 58.

[0165] The optical structure may comprise a background as shown in Figures 4 and 5. As a variant, as represented in Figure 8, the optical structure may be according to the example shown in Figure 1, and the secure document may be arranged facing a separate dark background 31 in order to increase the visual effect of the relief.

[0166] Working Example

[0167] Example 1 A polyester PET film was selected with the part number Sarafil S56C sold by Polyplex, Inc. It has a surface texture suitable for alignment of the liquid crystals. The Sarafil S56C film is a double oriented film coated with a copolyester based adhesion primer.

[0168] Several optical structures were created by inkjet printing deposits of yellow or cyan ink onto the surface of the film.

[0169] The yellow ink has part number C8766[Y] and is printed using an inkjet printer with part number HP 6540. The cyan ink has part number C8766[C] and is printed using an inkjet printer with part number HP 6540.

[0170] Prints are made at different inking rates and for each deposit the dry weight of the ink deposit is measured by basis weight. Table 1 below summarizes the results of these measurements and of the color of the film alone and each deposit according to the ISO5631-1 standard. It also mentions the saturation difference ΔC and the transparency difference ΔL between the support film and the deposit. Value C * and L * corresponds to a measure of the saturation and transparency of the deposit and the uncoated film.

[0171] [Table 1]

[0172] The various coated samples were then dried at a temperature of 60° C. for 5 minutes.

[0173] Furthermore, samples of the films coated with the different deposits are printed with an ink containing liquid crystals with a yellow / green goniochromatic effect at 576 nm, sold by the company BASF under the designation Lumogen S ink 6525T.

[0174] The liquid crystal ink was deposited on a coating bar to a thickness of 2-3 microns, the liquid crystals were then aligned while the ink dried under blown hot air, and then cured by UV crosslinking.

[0175] The most accentuated visual relief effect was observed for deposits having an ink delivery rate of at least 60%.

[0176] 9 to 16 are photographs showing the relief effect obtained for different optical structures with a deposit of yellow ink with an ink feed rate of 60%.

[0177] Figure 9 is a photograph of a zone of a film of Sarafil S56C covered with a deposit of yellow ink forming a rose-shaped pattern on the film, and Figure 10 is a photograph of the same zone covered with a layer of liquid crystal. The zone has a height of 10 mm and a width of 13 mm. As can be seen, the contour 59 of the pattern appears in relief. Transition zones are defined around each part of the pattern. Parts 171 of the transition zone 17 appear dark and matte, while others 172 appear bright and glossy, giving a visual indication of printing depth.

[0178] FIG. 12 is a photograph of a portion of the optical structure obtained by optical microscopy in unpolarized light, in which a transition zone 17 with a width of approximately 300 μm extends between a first zone 19, where the ink is in contact with the support, and a second zone 21, where the liquid crystal is in contact with the support. Analysis by optical microscopy in unpolarized light gives information about the alignment of the liquid crystal. Thus, the density of domains gives information about the alignment of one or more of the liquid crystals photographed. As can be seen in FIG. 12, domains 18a-c are observed, in which the alignment of the liquid crystals hardly differs. The size of the domains is different in the transition zone and in the first and second zones. In other words, the number of domains per unit of surface area is different in the transition zone and in the first and second zones. In particular, the domains appear to be larger in size in the zone 17, which indicates that the alignment quality of the crystals is better in the zone 17 than in the first and second zones.

[0179] The deposit, shown photographically in Figure 13, is discontinuous and defines a pattern of animal forms. A visual effect of relief is observed as can be seen in Figure 14, which superimposes a photograph of the optical structure with a photograph of the support covered only with the deposit, making it possible in particular to see precisely the position of the transition zone relative to the contours of the pattern.

[0180] Figure 15a is a photograph of another example of an optical structure viewed from the front side of the support, and Figure 15b is a photograph of the optical structure viewed from the opposite back side of the support, where the transition zone that appears in relief on the back side appears recessed on the front side and vice versa.

[0181] A dynamic effect is achieved and is illustrated by the photographs presented in Figures 16a-c.

[0182] An example of an optical structure illuminated according to a first direction is shown as a photograph in Fig. 16a. The components of the illumination direction in the plane of the support are oriented from bottom to top in the plane of the paper of Fig. 16. A portion 171 of the transition zone extending around an edge of a printed pattern oriented downwards appears dark, whereas a portion 172 around an edge of the same pattern oriented upwards appears light. Furthermore, the first zone 19 and the second zone 21 have different, in particular slightly different, colors.

[0183] When illuminated according to a second direction different from the first direction, the visual appearance of the optical structure changes. The parts of the transition zone that appear dark and light, respectively, in Fig. 16a appear light and lighter, respectively, in Fig. 16b. Furthermore, a color change effect is observed in the first and second zones. They have two hues that gradually change from yellow-green to yellow-green according to the angle of observation and / or the angle of illumination.

[0184] Example 2 A polyester PET film was selected with the part number Sarafil S56C sold by Polyplex, which has a surface texture suitable for alignment of the liquid crystals. The Sarafil S56C film is a double oriented film coated with a copolyester based adhesion primer.

[0185] Optical structures were created by inkjet printing deposits of black ink onto the surface of the film.

[0186] The black ink has part number Liojet AP-KB027-K and is printed using a Kyocera KJ4B-1200 part number piezoelectric printhead.

[0187] The properly coated film was then dried at a temperature of 60° C. for 5 minutes.

[0188] The coated film was then printed with an ink containing liquid crystals with a 576 nm yellow / green goniochromatic effect, sold by BASF under the designation LumogenS ink 6525T.

[0189] The liquid crystal ink was deposited on the coating bar to a thickness of 2-3 microns, the liquid crystals were then aligned while the ink dried under blown hot air, and then cured by UV crosslinking.

[0190] Black ink was deposited on the backside of the coated film to act as a dark background to enhance the visibility of the liquid crystal.

[0191] Examination of the surface on which the liquid crystal was printed revealed a strong relief effect.

[0192] Example 3 A polyester PET film was selected with the part number Sarafil S56C sold by Polyplex, which has a surface texture suitable for alignment of the liquid crystals. The Sarafil S56C film is a double oriented film coated with a copolyester based adhesion primer.

[0193] Optical structures were created by flexographically applying black ink deposits onto the surface of the film.

[0194] The black ink has the part number Liojet AP-KB027-K. Its viscosity was modified by adding 0.35% of a cellulose derivative sold by Shin Etsu under the part number Tylose HS100000YP2. Application was performed using a Flexiproof 100 flexo applicator from Rk Print.

[0195] The properly coated film was then dried at a temperature of 60° C. for 5 minutes.

[0196] The coated film was then printed with an ink containing liquid crystals with a 576 nm yellow / green goniochromatic effect, sold by BASF under the designation LumogenS ink 6525T.

[0197] The liquid crystal ink was deposited on the coating bar to a thickness of 2-3 microns, the liquid crystals were then aligned while the ink dried under blown hot air, and then cured by UV crosslinking.

[0198] Black ink was deposited on the backside of the coated film to act as a dark background to enhance the visibility of the liquid crystal.

[0199] Examination of the surface on which the liquid crystal was printed revealed a strong relief effect.

[0200] Example 4 A polyester PET film was selected with the part number Sarafil S56C sold by Polyplex, which has a surface texture suitable for alignment of the liquid crystals. The Sarafil S56C film is a double oriented film coated with a copolyester based adhesion primer.

[0201] Optical structures were fabricated on the surface of the film by inkjet printing deposits of ink containing nematic liquid crystals.

[0202] The ink has the part number Lumogen Hide N700 and is printed by gravure printing.

[0203] The properly coated film was then dried at a temperature of 105° C. for 5 minutes to align the liquid crystals, which was then cured by UV crosslinking.

[0204] The coated film was then printed with an ink containing liquid crystals with a 576 nm yellow / green goniochromatic effect, sold by BASF under the designation LumogenS ink 6525T.

[0205] The liquid crystal ink was deposited on the coating bar to a thickness of 2-3 microns, the liquid crystals were then aligned while the ink dried under blown hot air, and then cured by UV crosslinking.

[0206] As can be seen in FIG. 17a, a strong relief effect was obtained by examining the surface on which the liquid crystal was printed.

[0207] Furthermore, to detect other optical effects in polarized light, the optical structure was placed between the LCD screen and the observer. Alternatively, a non-polarized light source and a polarizing filter can be used. The optical structure can be placed between the non-polarized light source and the polarizing filter, and the observer can view the optical structure through the polarizing filter.

[0208] As can be seen in FIG. 17b, in a first observation configuration of the optical structure, zone 19 where a pattern comprising a layer of nematic crystals and cholesteric liquid crystal is superimposed has a blue color, and zone 21 where the cholesteric liquid crystal is in contact with the support has a pink color.

[0209] When the optical structure is rotated 90° relative to the support, a change in the appearance of each of the zones 19 and 21 is observed in the form of a color inversion: the zone 19 has a pink color and the zone 21 has a blue color.

[0210] The invention is not limited to the examples described.

[0211] In particular, the present invention is also suitable for producing coatings or decorations.

[0212] When the invention is applied to the production of security documents, the optical structure according to the invention can be present on security elements other than the security wire.

[0213] It is very particularly advantageous for the pattern of the optical structure to be located elsewhere on the document, either in the same form or at a different scale, or in any other recognizable form, where the observer can recognize a link that exists between the pattern of the structure and a pattern appearing elsewhere.

Claims

1. An optical structure (5) having a relief effect, A support (7) suitable for aligning liquid crystals; a deposit (9) of a substance in the form of at least one pattern (11) in contact with said support and partially covering said support, said substance being an ink or a varnish, and a layer (13) of liquid crystal at least partially covering said support and said pattern and in contact with said support; wherein the liquid crystal has a lower alignment quality in a zone directly covering the support than in a transition zone delimited by a contour of the pattern and extending at least partially around the pattern, The optical structure (5), wherein the material does not comprise liquid crystals.

2. 10. The structure of claim 1, wherein the varnish is transparent and colorless in the visible region.

3. 3. The structure of claim 1 or 2, wherein the substance is an ink.

4. A structure according to any one of claims 1 to 3, wherein said pattern is deposited in the form of a solid colour.

5. The dry weight of the material is 1.5 g / m ２ 5. The structure of any one of claims 1 to 4, wherein:

6. The structure of any one of claims 1 to 5, wherein the support is transparent or translucent.

7. A structure according to any one of claims 1 to 6, wherein the support comprises a film of axially stretched plastic material.

8. 8. The structure of claim 7, wherein said support comprises a layer of an adhesive primer covering at least one surface of said film and in contact with said film and said layer of liquid crystal.

9. A structure according to any one of claims 1 to 8, wherein the layer of liquid crystal is in contact with the deposit.

10. A security element (49) comprising at least one optical structure according to any one of the preceding claims.

11. A secure document (45), comprising an optical structure according to any one of claims 1 to 9.

12. The document of claim 11 , wherein the optical structures are visible on the front and back of the document.

13. 13. The document according to claim 11 or 12, wherein the document comprises a fibrous substrate (47) having a window, and the optical structure is constituted by a security element arranged in the window.

14. A method for manufacturing an optical structure according to any one of claims 1 to 9, wherein the substance is deposited on a support so as to form at least one pattern partially covering the support, and at least one layer of liquid crystal is deposited on the support and on the appropriately formed pattern.

15. 15. The method of claim 14, wherein the deposition of the substance is performed by printing onto the support and / or the layer of liquid crystal is deposited onto the support and the pattern by inkjet, flexographic, screen printing, gravure printing or letterpress printing.

16. 11. Method for authenticating a security element according to claim 10, wherein the optical structure is observed in at least one observation direction and a determination is made from this observation whether the pattern appears giving the impression of a relief image.

17. 17. The method of claim 16, wherein the optical structure is observed in at least two different observation directions from the same side of the support, and a change in the appearance of the pattern is detected when the angle of observation is changed.

18. 18. The method according to claim 16 or 17, wherein the optical structure is observed in at least two different views, one of the at least two different views being from a front side of the support and another of the at least two different views being from a back side of the support opposite to the front side, and an inversion of the relief between the at least two different views is detected, such that a zone which appears protruding in one of the at least two different views appears recessed in the other of the at least two different views, and vice versa.

Images