EP4259450A1 - Dispositif de sécurité et son procédé de fabrication - Google Patents

Dispositif de sécurité et son procédé de fabrication

Info

Publication number
EP4259450A1
EP4259450A1 EP21827634.3A EP21827634A EP4259450A1 EP 4259450 A1 EP4259450 A1 EP 4259450A1 EP 21827634 A EP21827634 A EP 21827634A EP 4259450 A1 EP4259450 A1 EP 4259450A1
Authority
EP
European Patent Office
Prior art keywords
image
colour filter
caustic
relief structure
colour
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP21827634.3A
Other languages
German (de)
English (en)
Inventor
Lawrence Commander
John Godfrey
Robert Whiteman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
De la Rue International Ltd
Original Assignee
De la Rue International Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by De la Rue International Ltd filed Critical De la Rue International Ltd
Publication of EP4259450A1 publication Critical patent/EP4259450A1/fr
Pending legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/324—Reliefs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/20—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof characterised by a particular use or purpose
    • B42D25/29—Securities; Bank notes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/333—Watermarks
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/351—Translucent or partly translucent parts, e.g. windows
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
    • B42D25/364—Liquid crystals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
    • B42D25/373—Metallic materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
    • B42D25/378—Special inks
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/40—Manufacture
    • B42D25/405—Marking
    • B42D25/425—Marking by deformation, e.g. embossing
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/20—Filters
    • G02B5/22—Absorbing filters
    • G02B5/223—Absorbing filters containing organic substances, e.g. dyes, inks or pigments
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/20—Filters
    • G02B5/28—Interference filters
    • G02B5/285—Interference filters comprising deposited thin solid films
    • G02B5/286—Interference filters comprising deposited thin solid films having four or fewer layers, e.g. for achieving a colour effect
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • G02B1/002—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of materials engineered to provide properties not available in nature, e.g. metamaterials
    • G02B1/005—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of materials engineered to provide properties not available in nature, e.g. metamaterials made of photonic crystals or photonic band gap materials

Definitions

  • This invention relates to security devices such as may be used as a mark of authenticity associated with an object of value, such as a security document including banknotes, passports, certificates, licences and the like. Methods for manufacturing security devices are also disclosed.
  • Objects of value, and particularly documents of value are frequently the target of counterfeiters and persons wishing to make fraudulent copies thereof and/or changes to any data contained therein.
  • security devices for checking the authenticity of the object. Examples include features based on one or more patterns such as microtext, fine line patterns, latent images, Venetian blind devices, lenticular devices, moire interference devices and moire magnification devices, each of which generates a secure visual effect.
  • Other known security devices include holograms, watermarks, embossings, perforations and the use of colour-shifting or luminescent I fluorescent inks. Common to all such devices is that the visual effect exhibited by the device is extremely difficult, or impossible, to copy using available reproduction techniques such as photocopying. Security devices exhibiting non-visible effects such as magnetic materials may also be employed.
  • a “caustic” is the envelope of light rays reflected or refracted by a curved surface or object, and the visualisation of that envelope of light rays is referred to herein as a “caustic image”, projected by the relief structure (which defines the curved surface(s)) when illuminated by a light source.
  • the image is formed as a result of the relief structure redirecting the incident light to form bright spots (where redirected light rays converge) and dark spots (where the redirected light rays are largely absent), the relative arrangement of the bright and dark spots combining to convey an image.
  • WO-A- 2019/063778 discloses techniques for forming a relief structure which generates a “virtual” caustic image, which does not require projection onto a surface but can be viewed directly by the naked eye.
  • a security device comprising: a substrate; a relief structure on a first side of the substrate, the relief structure being a reflective or refractive light-redirecting relief structure configured to redirect light from a light source to thereby project a caustic image; and a colour filter, the colour filter being configured to overlap in use at least part of the relief structure, the colour filter comprising one or more at least semi- transparent materials, at least one of the materials transmitting only a subset of visible lightwavelengths corresponding to a respective non-white colour, whereby the caustic image projected by the security device exhibits one or more colour(s) when the security device is illuminated with white light.
  • a caustic image is the visualisation of the envelope of light rays reflected or refracted by a curved surface or object, here provided by the relief structure. That is, the relief structure includes one or more curved surfaces, configured as necessary to give rise to the desired caustic image.
  • the caustic image may be a real image or a virtual image.
  • the caustic image can take any desired form, such as defining alpha-numeric text, one or more symbols, a logo, a portrait or another graphic.
  • a “colour filter” is something which selectively transmits only certain wavelengths of light, so that when the incident light is white, the light transmitted by the colour filter is non-white.
  • the material could include a substance which absorbs certain wavelengths and transmits others.
  • the wavelength-selective nature of the material(s) may be due to the or each material’s structure and/or interactions between components of the or each material - for example, the material could be structured to generate plasmonic colour (e.g. providing an array of nanoholes or nanopillars) or could comprise multiple internal layers giving rise to colour by way of interference effects.
  • the security level of the device is thereby increased. This is because, as a minimum, when viewed in reflected light, the device will exhibit at least one non-white colour due to the colour filter, which is hard to imitate since a would-be counterfeiter will need to have access to one or more suitable at least semi-transparent materials of the right colour(s), which do not impede the generation of the caustic image, and to provide the at-least semi-transparent material(s) in the right position(s).
  • the colour filter can also help to camouflage the presence of the caustic device.
  • the colour(s) exhibited by the caustic image may also include one or more non-white colours (as is preferred), which presents a further challenge to the counterfeiter seeking to imitate the device.
  • the caustic relief structure may result in mixing of two or more of those colours such that the caustic image exhibits a different, combined colour.
  • the colour filter could comprise red, green and blue regions, which colours could be mixed by the caustic relief resulting in a white (or near-white) caustic image.
  • the caustic relief structure may result in display of multiple tones of that non-white colour in the caustic image.
  • colour used herein includes any visible colour, including white, hence the use of the term “non-white colour” where white is to be excluded.
  • the relief structure being “on” the substrate, it is meant that the relief structure is carried by the substrate (and may or may not be integral therewith). “On” does not require direct contact between the two items in question (although the contact may indeed be direct) - for example an intermediate layer such as a primer layer may exist between the relief structure and the substrate. Nor does the term “on” impose any limitation in terms of orientation, since for example an item may be “on” the underside, or “on” the lateral side, of another item to the same extent that it may be “on” top of that item. The term “on” should be interpreted in this manner wherever it appears herein unless otherwise stated.
  • the colour filter will be fixed in overlapping relation with the relief structure and can be embodied in various different ways as will be explained below.
  • the first aspect of the invention provides a security device, comprising: a substrate; a relief structure on a first side of the substrate, the relief structure being a reflective or refractive light-redirecting relief structure configured to redirect light from a light source to thereby project a caustic image; and a colour filter overlapping at least part of the relief structure, the colour filter comprising one or more at least semi-transparent materials, at least one of the materials transmitting only a subset of visible light wavelengths corresponding to a respective non-white colour, whereby the caustic image projected by the security device exhibits one or more colour(s) when the security device is illuminated with white light.
  • the colour filter separate from the relief structure in such a way that the overlapping can be achieved by a user during examination of the security device in an authentication test. Examples will be provided below.
  • the colour filter may be arranged to overlap only part of the relief structure, e.g. if only part of the caustic image is to appear non-white in colour or if a masking component is also provided elsewhere (see below). However, preferably, in use the colour filter overlaps substantially all of the relief structure.
  • the colour filter may also extend laterally beyond the relief structure in one or more directions.
  • the colour and/or tone of the light transmitted by the filter could be uniform over its full lateral extent. For instance, this will be the case if the whole filter is made of the same material (or overlapping set of materials) with constant thickness. However, in preferred embodiments, the light transmitted by the colour filter varies in colour and/or tone between laterally offset regions of the colour filter. This increases the complexity and hence security level of the device.
  • the colour filter could consist of a single material, which material transmits a desired non-white colour, in which case at least part of the caustic image will typically exhibit the same non-white colour (although different tones of that nonwhite colour may be exhibited across the at least part of the caustic image).
  • the colour filter comprises a plurality of different at least semi-transparent materials arranged in respective laterally offset regions, each region of the colour filter being formed of (only) one of the at least semitransparent materials, or an overlapping combination of two or more of the at least semi-transparent materials, whereby the colour of light transmitted by the colour filter varies across the colour filter in accordance with the regions.
  • the colour transmitted by the colour filter is uniform across any one region, but differs from region to region of the colour filter.
  • Each region could be formed of a single material or, in some embodiments, multiple overlapping materials depending on how the colour filter is constructed.
  • the colour filter may comprise a semi-transparent material which varies in thickness between regions of the colour filter, the tone of the transmitted light depending on the thickness of the semi-transparent material.
  • the wavelength-selectivity is caused by a bulk property of the material, such as its absorption characteristics (rather than a surface structure for instance).
  • the colour (hue) of the transmitted light will be determined by the intrinsic characteristics of the material itself, the tone of the transmitted light will depend on the absolute volume of material through which the light passes. Hence, the greater the thickness of a semi-transparent material in a certain region, the darker the tone of the light transmitted by that region of the colour filter.
  • the thickness of the at least one semi-transparent material in each respective region could be varied between a minimum (but non-zero) thickness corresponding to a minimum transmitted tone (regions of zero thickness, which are possible if the colour filter is implemented as a layer separate from that carrying the caustic relief, correspond to regions in which the colour filter is omitted) and a maximum thickness corresponding to a maximum transmitted tone (at which some light will still be transmitted by the filter).
  • a minimum (but non-zero) thickness corresponding to a minimum transmitted tone regions of zero thickness, which are possible if the colour filter is implemented as a layer separate from that carrying the caustic relief, correspond to regions in which the colour filter is omitted
  • a maximum thickness corresponding to a maximum transmitted tone at which some light will still be transmitted by the filter.
  • the same at least one semi-transparent material could be provided at a still greater thickness, which does not transmit light, to form a masking component (discussed below).
  • the provision of regions with different transmitted colours and/or tones does not necessarily mean that the caustic image will appear multicoloured or multi-tonal (although as noted below this is preferred) since the various transmitted colours and/or tones could become mixed by the caustic relief as mentioned above.
  • This not only allows the appearance of the projected image to be made more complex, but also enables the colour filter itself to exhibit a nonprojected image, arising from the arrangement of regions, which may or may not be the same as the caustic image as will be discussed further below.
  • the nonprojected image is that seen when the colour filter itself is viewed, either in reflected light or in transmitted light (as opposed to the projected caustic image, which will be generated elsewhere, e.g.
  • the non-projected image may appear in different colours depending on whether it is viewed in reflected or transmitted light, although its information content will be the same in both modes of viewing.
  • the non-projected image could be multi-tonal and/or multi-coloured. If the colour filter is formed of a single material varying only in thickness from region to region, then the non-projected image will be multi-tonal but not multi-coloured (i.e. it will appear in multiple shades of one and the same colour).
  • the colour filter comprises a colourless transparent material forming one or more of the regions and a semi-transparent material transmitting only a subset of visible light wavelengths corresponding to a non-white colour forming another one or more of the regions.
  • a colourless transparent material alongside a semi-transparent material with a nonwhite colour enables the display of either a single colour caustic image (in which all the bright spots of the image have substantially the same hue and intensity), or a two-colour caustic image (containing parts with a non-white colour and other parts which appear white), or a multi-tonal caustic image (in which different parts of the image have the same hue but different intensities).
  • the colour filter comprises at least two different semi-transparent materials each transmitting only a subset of visible light wavelengths corresponding to a different respective non-white colour, each forming one or more different respective (laterally offset) regions of the colour filter.
  • the use of at least two different materials alongside one another, each transmitting a different subset of visible light wavelengths and hence a different non-white colour enables the display of images exhibiting more than one non-white colour although as noted above there is not necessarily a direct correspondence between the colours of the materials and the colours of the caustic image.
  • a colourless material may also be included in the colour filter (in one or more dedicated regions thereof), which allows for straightforward creation of white portions of the caustic image and/or multiple tones of individual hues.
  • the security device is configured such that the caustic image projected by the security device when illuminated with white light exhibits a multi- tonal and/or multi-coloured appearance.
  • “Multi-tonal” means that at least two different intensity levels of the same colour are exhibited simultaneously (e.g. light blue and dark blue), whereas multi-coloured means that at least two different non- white hues are exhibited simultaneously (e.g. red and yellow). In some cases this is achieved through configuration of the regions of the colour filter, e.g. differently coloured regions as described above.
  • the caustic relief structure can be configured to redirect light in such a way that different parts of the image receive different amounts of same-coloured light resulting in different intensities and hence different apparent tones in the projected image.
  • the various regions and colours (or tones) of the colour filter could be arranged without any relation to the caustic relief structure, in which case the colouration/tonality of the caustic image may bear no relation to the image content.
  • the caustic relief structure is configured to project an image of the number “20”
  • the caustic image will exhibit a red “2” alongside a blue “0”. It will be appreciated that the correlation between the arrangement of regions and the relief structure need not be exact, since even if a small proportion of light contributing to the “2” is coloured blue, it will be overwhelmed by the largely red light forming that element.
  • a first group of one or more of the regions of the colour filter which overlap one or more first areas of the relief structure configured to generate a first portion of the caustic image, are formed of a first set of one or more at least semi-transparent materials, such that the first portion of the caustic image exhibits a first colour which is determined by the colour(s) transmitted by the first set of materials, the first portion of the caustic image preferably being a first distinct element of the caustic image.
  • a “distinct element” of an image may be, for example, the whole of a contiguous bright part of the image, e.g. one letter or number in an image comprising alphanumeric text. Alternatively the elements may be distinguishable by context, e.g.
  • the first set of materials will comprise a single material which transmits the first colour (preferably non-white).
  • each of the regions in the first group will be formed of one and the same material, which by itself determines the colour of the first portion of the caustic image.
  • the first colour could be a mixed colour resulting from the use of a first set of more than one materials, each with a different colour.
  • Each region will still be formed of a single material, but since the group of regions which contribute to the first portion of the caustic image now includes regions of different colour, the result is that the first portion exhibits a colour which is a mixture of the colours transmitted by those materials.
  • the relief structure could mix the colours to result in green and purple parts of the image.
  • all of the colours visible on the colour filter in reflected light may be combined such that the caustic image appears monochromatic, typically in a non-white colour - although if the colour filter contains red, green and blue regions it is also possible to arrange for the caustic image to appear white, or close to white, which is a surprising visual effect and one which is hard for a counterfeiter to emulate.
  • segments of the relief structure which contribute to a first portion of the caustic image are arranged to alternate periodically with segments of the relief structure which contribute to a second portion of the caustic image, and the cells of the colour filter exhibit a corresponding periodic pattern.
  • This can be extended to include any number of image portions: segments contributing to each image portion will be interleaved with those contributing to other image portions in a periodic manner.
  • the periodicity can be one-dimensional or two-dimensional. This results in the direct appearance of the device (i.e. the non-projection image) being patterned or uniform (if the cells are too small to be individually resolved), which is markedly different from the caustic image.
  • the relief structure and the colour filter are spaced from one another in the direction normal to the plane of the security device, the colour filter preferably being provided on the second side of the substrate and the substrate being transparent, such that upon tilting of the security device relative to the light source, the colour(s) exhibited by the caustic image change and/or a different portion of the caustic image displays a non-white colour.
  • the segments and cells are arranged periodically as discussed immediately above.
  • the ratio of the spacing between the relief structure and the colour filter to the lateral width of the cells in the colour filter is such that, on tilting, the first and second portions of the caustic image appear to switch colours.
  • the spacing between the relief structure and the colour filter is greater than or equal to the lateral width of the cells.
  • the cells (and hence the segments) have a lateral width of 200 microns or less, preferably 100 microns or less, more preferably 50 microns or less. This enables the optical spacing and hence the thickness of the security device to be kept suitably small as is advantageous for use of the security device in documents and the like.
  • the segments of the relief structure (whether redistributed or not) will abut one another directly. However, in other embodiments some or all of them may be spaced apart. In a particularly preferred case, at least some of the segments are laterally spaced from one another in the relief structure by scattering areas of the relief structure which substantially do not contribute to the caustic image. This can be useful to help ensure that each cell of the colour filter only overlaps its allocated segment and does not extend over any other segment, e.g. due to poor registration.
  • the material(s) forming the colour filter will each reflect the same colour as they transmit. This will be the case, for instance, for typical dyes and pigments which operate on a wavelength absorption mechanism. In such cases, any non-projection image exhibited by the colour filter will have the same appearance whether it is viewed in reflected light or in transmitted light.
  • at least one (preferably all) of the materials forming the colour filter transmits only a first subset of visible light wavelengths corresponding to a first non-white colour and reflects only a second subset of visible wavelengths corresponding to a second non-white colour, such that the colour exhibited by the material is different when viewed under reflected light and in transmitted light.
  • this can be achieved through the use of materials comprising plasmonic pigments, plasmonic structures, interference pigments, interference structures or liquid crystals.
  • materials comprising plasmonic pigments, plasmonic structures, interference pigments, interference structures or liquid crystals.
  • the colour filter comprises a plurality of different at least semi-transparent materials arranged in respective laterally offset regions, each region of the colour filter being formed of one of the at least semi-transparent materials, and the colour filter exhibits a non-projected image arising due to the arrangement of regions. If at least one of the materials has different reflected and transmitted colours, then one or more colours in the non-projected image will be different when viewed under reflected light and in transmitted light. In particularly preferred embodiments, all of the colours in the non-projected image may be different under the two viewing conditions.
  • additional effects can be achieved by forming the colour filter out of a first material which has the same first colour in reflection and transmission, and a second material which has different colours in reflection and transmission.
  • the materials will be arranged in respective laterally offset regions. In this case, one of the regions will appear to change colour when the colour filter is viewed directly in reflected versus transmitted light, whereas the other region will not. If the second material is selected such that either its reflected colour or its transmitted colour is the same as the first colour exhibited by the first material, the two regions will match under one viewing condition and not match under the other viewing condition. By designing the regions appropriately, this can be used to make an image appear/disappear or change between reflection and transmission modes of direct viewing.
  • the colour filter can be implemented in various different ways. However, in all implementations it is advantageous if the colour filter is located on the same side of the relief structure as that on which the light source is positioned to project the caustic image. For instance, where the caustic relief structure is transparent and operates on refraction, such that the projected caustic image will be viewed on the opposite side of the device from that on which the light source is located, the colour filter is preferably located between the light source and the relief structure in use. This achieves better results than locating the colour filter on the opposite side of the device from the light source, since having passed through the relief structure, the light rays will not be parallel and hence there may be some unintended mixing of colours.
  • the colour filter is fixed in overlapping relation to the surface relief. This is optimal since then the alignment of the colour filter and the relief structure can be accurately controlled. This can be achieved in various ways.
  • the colour filter is integral with the substrate, the substrate being formed of the one or more at least semi-transparent materials. This may be appropriate for instance where the colour filter consists of a single material overlapping the whole device, in which case the colour filter could be implemented as a tint throughout the substrate material. More complex multicoloured configurations could be implemented by forming the substrate of a multilayered laminate, with different coloured inserts at the appropriate locations.
  • the relief structure may be formed in the surface of an embossing layer applied to the substrate, the colour filter being integral with the embossing layer, the embossing layer being formed of the one or more at least semi-transparent materials.
  • the embossing layer could comprise one or more polymeric materials which are deformable under heat and/or pressure to receive the relief structure in a surface thereof.
  • the embossing layer could be formed by cast-curing, in which case the embossing layer typically comprises one or more curable resins which have been cast into the desired relief structure shape and cured (e.g. by exposure to UV light). This will be described further below.
  • the colour filter is a colour filter layer formed of the one or more at least semi-transparent materials, the colour filter layer being disposed on the first or second surface of the substrate, or on the surface relief. That is, the colour filter is provided by a separate layer rather than being integral with one of the components already described.
  • a colour filter layer could be disposed on either side of the substrate, for instance on the first side of the substrate between the relief structure and the substrate, or on the relief structure surface itself (in which case the colour filter layer either conforms to the relief structure and/or has a different refractive index from the material in which the relief structure is formed in order to maintain the necessary optical interfaces).
  • the colour filter layer could be located on the second side of the substrate.
  • any combination of the above and/or distribute the colour filter such that different lateral parts of it are provided by different components.
  • more than one colour filter layer could be provided at different positions within the device structure (e.g. one on either side of the substrate) which may or may not partially or fully overlap one another.
  • a tinted substrate could be used in combination with one or more colour filter layers and/or an embossing layer formed of colour filter materials.
  • the security device could comprise a first caustic relief area of its relief structure in a first window of a security document and a second caustic relief area of its relief structure in a second window of a security document.
  • the first and second windows will be spaced from one another by a non-transparent region of the document, e.g. carrying one or more opacifying layers.
  • the first and second windows should of course be located sufficiently close to one another that they can be illuminated simultaneously by the same light source at substantially the same illumination angle.
  • Embodiments such as those mentioned above in which the colour filter and relief structure are fixed overlapping one another have the advantage that the relative positions of the colour filter and the relief structure can be carefully controlled during manufacture.
  • the colour filter may be provided on the substrate at a first location and the surface relief is provided on the substrate at a second location (laterally offset from the first), the substrate being transparent and foldable such that the colour filter can be positioned so as to overlap the surface relief in use.
  • each component may be arranged such that when the substrate is folded with its comers matching up, the colour filter and relief structure come into the desired alignment with one another.
  • the present invention also provides a security device assembly, comprising a substrate; a relief structure on a first side of the substrate, the relief structure being a reflective or refractive light-redirecting relief structure configured to redirect light from a light source to thereby project a caustic image; and a colour filter laterally offset from the relief structure, the colour filter comprising one or more at least semi-transparent materials, at least one of the materials transmitting only a subset of visible lightwavelengths corresponding to a respective non-white colour, whereby when the colour filter is arranged to overlap the relief structure, a security device of the sort disclosed above is formed and the caustic image projected by the security device when the security device is illuminated with white light exhibits one or more colour(s).
  • the colour filter is a printed colour filter, preferably formed by offset printing, gravure printing, lithographic printing, flexographic printing or screen printing. This is relevant not only to implementations in which the colour filter is a colour filter layer, but also those in which the colour filter is integral with an embossing layer carrying the relief structure in its surface, since the material(s) forming the embossing layer may also be applied by printing.
  • the or each material transmitting only a subset of visible light wavelengths corresponding to a respective non-white colour comprises any of: an absorptive dye, an absorptive pigment, a plasmonic material (such as a plasmonic structure or a plasmonic pigment), an interference layer structure, an interference layer pigment or a liquid crystal material.
  • the material(s) forming the colour filter must give rise to minimal (preferably zero) optical scattering, in order to avoid disrupting the light rays and hence inhibiting the caustic image. Hence if the material(s) derive their colour(s) from additives, dyes or very finely ground pigments or other particles are preferred.
  • the particle size is below 500 nm, more preferably equal to or less than 100nm.
  • the additives may be carried in a suitable binder.
  • the materials may comprise inks.
  • the material(s) could comprise vapour-deposited layers, such as dielectric stacks, which derive their colour from interference between the layers, or structures such as nanopillars or nanoholes which provide plasmonic colour.
  • the security device may further comprise a masking component configured to overlap in use a sub-part of the relief structure, the masking component comprising one or more materials which are substantially opaque to visible light. Since the masking component is substantially opaque, parts of the relief structure which it overlaps will not contribute to the caustic image. However, the masking component will be visible when the security device is viewed directly (in reflected or transmitted light) and so may supplement any non-projected image exhibited by the colour filter. Indeed, the masking component could be formed integrally with the colour filter or as a separate layer.
  • the masking component is integral with the colour filter, it could be formed by the same process and take the form of one or more regions of substantially opaque material(s) which are either laterally offset from the colour filter or partially overlap it.
  • the masking component could be formed by the thickest area(s) of that material. The presence of the masking component will need to be taken into account in the design of the caustic relief.
  • the relief structure may be configured to project a real caustic image which can be viewed on a projection screen, or to project a virtual caustic image which can be viewed directly by the naked eye.
  • Examples of relief structures (and methods for designing them) which project real caustic images can be found in WO-A-2019/063778, WO-A-2019/063779 and WO-A- 2020/070304, while WO-A-2020/070299 discloses techniques for forming a relief structure which generates a “virtual” caustic image.
  • the relief structure is a refractive lightredirecting relief structure, the relief structure and the substrate being transparent.
  • the caustic relief will be illuminated by a controlled light source and the transmitted or reflected light will fall onto an electronic sensor.
  • the illumination will be distorted by the caustic element either to form an image that would be the same as seen by the public or to form a distorted image (if there is not sufficient distance between the caustic and the sensor) which in either case will be characteristic of the caustic device and therefore useable for document validation.
  • the sensor will be a linescan camera and the image will be built up from sequential scans as the document is moved in front of the linescan camera.
  • the sensor can work in the visible spectrum but could equally work with infra-red light so long as the caustic element refracts or reflects light in infrared as well as the visible spectrum.
  • the invention also provides a security article comprising a security device as defined above, the security article preferably being a security thread, strip, patch, label, foil or insert.
  • a security document comprising a security device or a security article, each as defined above, the security document preferably being a banknote, a passport, an identity document, a driver’s licence, a certificate, a visa or a stamp.
  • Such a security document may alternatively comprise a security device assembly as mentioned above.
  • the security device is located in one or more first transparent window region(s) of the security document.
  • a window region can be formed, for example, in a security document based on a transparent document substrate with one or more opacifying layers thereon which are omitted in the window region, or in a security document based on any type of substrate with an aperture provided therethrough corresponding to the window region.
  • parts of the security device it is also possible for parts of the security device to be distributed between multiple transparent window regions.
  • This embodiment provides the advantage that both the visual effects generated by the security device on one hand and by the supplementary security feature on the other can be observed in the same viewing mode, preferably simultaneously, by the observer.
  • authenticity of the security document can be checked by comparing the two images against one another.
  • the images will be complementary if one provides a missing element of the other (e.g. “£” and “10”), or if both provide related information content (e.g. “QEH” and a portrait of the Queen).
  • the use of corresponding colours provides a particularly strong visual effect.
  • the first aspect of the invention further provides a method of manufacturing a security device, comprising: providing a substrate; forming a relief structure on a first side of the substrate, the relief structure being a reflective or refractive light-redirecting relief structure configured to redirect light from a light source to thereby project a caustic image; and providing a colour filter, the colour filter being configured to overlap in use at least part of the relief structure, the colour filter comprising one or more at least semi-transparent materials, at least one of the materials transmitting only a subset of visible light wavelengths corresponding to a respective non-white colour, whereby at least part of the caustic image projected by the security device exhibits one or more colour(s) when the security device is illuminated with white light.
  • the relief structure could be formed using any available technique, including direct embossing into the substrate, or embossing into a suitable layer applied thereto, using heat and/or pressure to deform the surface into the desired relief structure.
  • the relief structure is formed by cast-curing.
  • the relief structure is formed by applying an embossing layer comprising one or more curable materials to the first side of the substrate or to a casting relief on the surface of a casting tool, the casting relief defining the relief structure therein, bringing the casting tool into contact with the substrate with the embossing layer therebetween to thereby form the relief structure into the surface of the embossing layer, and curing the embossing layer to retain the relief structure.
  • the colour filter may be integral with the embossing layer, in which case the curable material(s) of the embossing layer comprises the one or more at least semi-transparent materials.
  • the application of the various curable materials will be in accordance with the desired arrangement of regions of the colour layer (if any).
  • This method of manufacture is particularly preferred since the colour filter and the relief structure will both be formed during one and the same cast-cure process and hence the register between them can be particularly accurately controlled.
  • the colour filter may be provided by applying a colour filter layer formed of the one or more at least semi-transparent materials, the colour filter layer being applied to the first or second surface of the substrate, or onto the surface relief.
  • the colour filter layer may be applied by printing, preferably offset printing, gravure printing, lithographic printing, flexographic printing or screen printing.
  • the colour filter layer and the relief structure are applied to the substrate on the same processing line, while the substrate is being conveyed along the processing line in the machine direction. This could be a sheet-fed or a web-fed process.
  • the colour filter layer is applied to the second surface of the substrate, the colour filter layer and the relief structure being applied simultaneously to opposite surfaces of the substrate at the same position along the machine direction. This assists in ensuring exact register between the colour filter and relief structure, since they are applied to the same part of the substrate at the same instant, so no deformation or slippage of the substrate can have taken place between the application of one component and the application of the other.
  • the colour filter can alternatively by provided integrally with the substrate, as mentioned previously.
  • Suitable apparatus, materials and methods for forming the relief structures disclosed herein, and (if desired) applying a separate colour filter layer are described in WO-A-2018/153840 and WO-A- 2017/009616.
  • the colour filter comprises a plurality of different at least semi-transparent materials arranged in respective laterally offset regions, each region of the colour filter being formed of (only) one of the at least semitransparent materials, whereby the colour of light transmitted by the colour filter varies across the colour filter in accordance with the regions. Additionally or alternatively the thickness of the at least one semi-transparent material may be different from one region to another to achieve different tones of the transmitted light.
  • the security device is configured such that the caustic image projected by the security device when illuminated with white light exhibits a multi- tonal and/or multi-coloured appearance.
  • a first group of one or more of the regions of the colour filter which overlap one or more first areas of the relief structure configured to generate a first portion of the caustic image, are formed of a first set of one or more at least semitransparent materials, such that the first portion of the caustic image exhibits a first colour which is determined by the colour(s) transmitted by the first set of materials, the first portion of the caustic image preferably being a first distinct element of the caustic image.
  • the colour filter is created by: selecting a first portion of the caustic image and a first colour for the selected first portion; identifying the one or more first areas of the relief structure which generate the selected first portion, preferably by ray tracing; designating the one or more regions of the colour filter which overlap the identified first area(s) as the first group, and assigning the first set of one or more at least semi-transparent materials to the designated region(s), wherein the first set of one or more at least semi-transparent materials transmit in combination the first colour.
  • the relief structure comprises a first sector configured to project the first caustic image under illumination from a first range of illumination angles which includes the first illumination angle, and a second sector configured to project the second caustic image under illumination from a second range of illumination angles which includes the second illumination angle, the first and second sectors being laterally offset from one another.
  • the designer would normally aim to maximise useability by minimising the sensitivity to the incoming illumination angle.
  • the caustic structure may be designed to operate over a wide range of projection angles, e.g. from -45 degrees to +45 degrees either side of the substrate normal.
  • the relief structure is configured to project a real caustic image which can be viewed on a projection screen, or to project a virtual caustic image which can be viewed directly by the naked eye.
  • the relief structure is a refractive light-redirecting relief structure, the relief structure and the substrate being transparent.
  • the fourth aspect of the invention further provides a security article comprising a security device according to the fourth aspect, the security article preferably being a security thread, strip, patch, label, foil or insert.
  • the security device is preferably arranged in one or more windows of the security document, which may be defined by gaps in an opacifying layer.
  • the first and second sectors of the relief structure are located in a window region of the security document. By placing the two sectors in one and the same window, this further hides the fact that two caustic structures are present.
  • the first sector may be located in a first window region of a security document and the second sector may be located in a second window region of the security document, the first and second window regions being spaced from one another by a non-transparent region of the security document.
  • the fourth aspect of the invention further provides a method of manufacturing a security device, comprising: providing a substrate; forming a relief structure on the substrate, the relief structure being a reflective or refractive light-redirecting relief structure configured to redirect light from a first light source at a first illumination angle to thereby project a first caustic image and to redirect light from a second light source at a second, different, illumination angle to thereby project a second caustic image, the first caustic image being different from the second caustic image.
  • the relief structure is formed by applying an embossing layer comprising one or more curable materials to the substrate or to a casting relief on the surface of a casting tool, the casting relief defining the relief structure therein, bringing the casting tool into contact with the substrate with the embossing layer therebetween to thereby form the relief structure into the surface of the embossing layer, and curing the embossing layer to retain the relief structure.
  • an embossing layer comprising one or more curable materials to the substrate or to a casting relief on the surface of a casting tool, the casting relief defining the relief structure therein, bringing the casting tool into contact with the substrate with the embossing layer therebetween to thereby form the relief structure into the surface of the embossing layer, and curing the embossing layer to retain the relief structure.
  • the method can be adapted to provide the security device with any of the preferred features described above.
  • Figure 3(a) schematically depicts a second embodiment of a security device in cross-sectional view
  • Figures 3(b), (c) and (d) respectively showing schematic plan views of the colour filter, surface relief and caustic image projected by the security device when illuminated by a light source
  • Figure 4(a) schematically depicts a third embodiment of a security device in cross-sectional view
  • Figures 4(b), (c) and (d) respectively showing schematic plan views of the colour filter, surface relief and caustic image projected by the security device when illuminated by a light source
  • Figure 5(a) schematically depicts a fourth embodiment of a security device in cross-sectional view
  • Figures 5(b), (c) and (d) respectively showing schematic plan views of the colour filter, surface relief and caustic image projected by the security device when illuminated by a light source
  • Figure 6(a) schematically depicts a fifth embodiment of a security device in cross-sectional view
  • Figures 4(b), (c) and (d) respectively showing schematic plan views of the colour filter, surface relief and caustic image projected by the security device when illuminated by a light source
  • Figure 8(a) schematically depicts a seventh embodiment of a security device in cross-sectional view, Figures 8(b), (c) and (d) respectively showing schematic plan views of the colour filter, surface relief and caustic image projected by the security device when illuminated by a light source;
  • Figure 9(a) schematically depicts a eighth embodiment of a security device in cross-sectional view under illumination by a first light source, Figures 9(b), (c) and (d) respectively showing schematic plan views of the colour filter, surface relief and caustic image projected by the security device;
  • Figure 11 (a) schematically depicts a ninth embodiment of a security device in cross-sectional view, Figures 11 (b), (c) and (d) respectively showing schematic plan views of the colour filter, surface relief and caustic image projected by the security device when illuminated by a light source;
  • Figure 12(a) schematically depicts a tenth embodiment of a security device in cross-sectional view
  • Figures 12(b), (c) and (d) respectively showing schematic plan views of the colour filter, surface relief and caustic image projected by the security device when illuminated by a light source;
  • Figure 13 shows an embodiment of a security document provided with an exemplary security device in accordance with the invention, illuminated by an exemplary light source, and the corresponding projected caustic image;
  • Figures 14 to 19 show six further embodiments of security devices in accordance with the invention, (a) in cross-section, (b) under reflected light, (c) in transmitted light and (d) projecting the caustic image;
  • Figures 20 to 28 show nine further embodiments of security devices in accordance with the invention (a) in cross-section, (b) under reflected light and (c) the caustic image projected by the security device;
  • Figure 29(a) schematically depicts in cross-section a first example of apparatus which may be used to manufacture security devices in accordance with embodiments of the invention, Figure 29(b) showing a perspective view of the corresponding security devices at various stages of manufacture;
  • Figure 30 schematically depicts in cross-section a second example of apparatus which may be used to manufacture security devices in accordance with embodiments of the invention
  • Figure 31 schematically depicts an embodiment of a security document in accordance with the present invention (a) in plan view, and (b) in cross section along the line X-X’;
  • Figure 33 shows a comparative example of a security device when illuminated by a first light source (a) in cross-section, (b) under reflected light and (c) the caustic image projected by the security device;
  • Figure 36 shows the comparative example of Figure 35 when illuminated by a second light source (a) in cross-section, (b) under reflected light and (c) the caustic image projected by the security device;
  • Figures 37 and 38 shows two further comparative examples of security device when illuminated by a first light source and a second light source respectively, (a) in cross-section, (b) under reflected light and (c) the caustic image projected by the security device;
  • Figure 39 shows a further embodiment of a security device in accordance with the invention when illuminated by first and second light sources (a) in crosssection, (b) under reflected light and (c) the caustic image projected by the security device;
  • Figures 40(a) to (d) schematically show four alternative arrangements of the relief structure in the Figure 39 embodiment, in plan view;
  • Figure 41 schematically shows another embodiment of a security device in accordance with the invention in cross section (a) when illuminated by a first light source and (b) when illuminated by a second light source;
  • Figures 42, 43 and 44 show three exemplary security documents carrying security devices in accordance with embodiments of the present invention (a) in plan view, and (b) in cross-section; and
  • Figure 45 illustrates a further embodiment of an security document carrying a security device in accordance with the present invention, (a) in front view, (b) in back view and (c) in cross-section.
  • the caustic relief is transparent and the caustic image is generated by the mechanism of refraction.
  • all described embodiments can be converted into reflective devices by applying a reflection enhancing material to the caustic relief, such as a vapour-deposited metal layer or a metallic ink, in which case the caustic image will be formed as a result of reflection.
  • the caustic image is a real image, which can be observed by projecting the image onto a surface, such as a wall, screen or worksurface.
  • all described embodiments can be converted to instead generate virtual caustic images which can be observed directly by the naked eye.
  • WO-A-2019/063778 Details of the mechanisms involved in forming caustic images by refraction and by reflection are set out in WO-A-2019/063778, WO-A-2019/063779 and WO-A- 2020/070304.
  • WO-A-2020/070299 explains how to convert a relief which generates a real caustic image into one which generates a virtual caustic image.
  • These documents also disclose methods for designing a surface relief configured to project a certain caustic image upon illumination, which can be used to create the relief structures used in embodiments of the present invention.
  • the security device 10 comprises a substrate 12, a relief structure 20 which is configured to project a caustic image Cl when illuminated by a light source L, and a colour filter 30 overlapping at least part (preferably all) of the relief structure 20.
  • the relief structure 20 forms the caustic image Cl by redirecting the incident light rays as a result of either refraction or reflection, so as to form bright and dark spots which together define the desired image.
  • the relief structure 20 is carried in the surface of an embossing layer 14 which is disposed on first surface 12a of the substrate 12, and the colour filter 30 is embodied as a colour filter layer 18 disposed on the second surface 12b of the substrate 12.
  • the overall thickness of the security device 10 (comprising the substrate 12, caustic relief structure 20 and colour filter 30) in the direction normal to its plane is preferably 1 mm or less, more preferably 500 microns or less, still preferably 150 microns or less, most preferably 100 microns or less.
  • the colour filter 30 comprises at least one material 32a which is semi-transparent and transmits only a subset of the visible spectrum corresponding to a non-white colour Ci.
  • the colour filter consists of a single such material 32a, covering the whole of the colourfilterwhich here is rectangular, as shown in Figure 1 (b) which is a plan view of the colour filter 30.
  • Figure 1 (b) which is a plan view of the colour filter 30.
  • the relief structure 20 is configured to generate a caustic image Cl of the currency symbol “$”. To achieve this, the relief structure will comprise some area(s) 21a which redirect light towards, and hence contribute to the bright portion Pi of the caustic image, forming the symbol “$”.
  • the relief structure may also comprise some area(s) 21b with a non-caustic surface which do not contribute to the bright portion Pi of the caustic image - for instance these areas 21b may redirect light away from the image and/or scatter light so as to ensure the background to bright portion Pi appears dark.
  • the area(s) 21b will be flat relative to the area(s) 21 a.
  • Figure 1 (c) which is a plan view of the relief structure, shows the area 21a as having a lateral shape approximately corresponding to that of the caustic image, this is schematic and will not necessarily be the case, although it may be preferred.
  • the lateral shape of area 21a may be selected to corresponding to an image (referred to as a “periphery image”) which is different from the caustic image.
  • a peripheral image an image which is different from the caustic image.
  • the outline of area 21 a could correspond to the shape of a country while the caustic image Cl could display the currency symbol of that country.
  • the colour Ci exhibited by the bright portion Pi will depend on the colour transmitted by the material 32a forming the colour filter 31. For example, if material 32a transmits red light, then when the security device 10 is illuminated by a white light source L, the bright portion Pi of caustic image Cl will appear largely red. In this particular example, since the colour filter does not cover all of the area 21a, some of the redirected light will remain white and so the edges of the bright portion Pi may appear pink (as a result of the mixing of red and white light), resulting in a multi-tonal caustic image.
  • any number of different tones can be provided in the image by arranging for different proportions of red and white light to be mixed in different parts of the image by the caustic relief 20. If a mono-chromatic image is preferred, the colour filter 30 can be extended to cover the whole of area 21 a.
  • the security device 10 is illuminated from “infinity”, the relief structure 20 and projected image are each 15mm wide, and the projected image Cl is 70mm from the device 10, then the largest deflection required (from one extremity of the surface relief to the opposite extremity of the caustic image) is 12 degrees. In turn, this requires an angle of the surface relief (e.g. a microprism) out of the surface plane of 23 degrees. If the surface relief 20 incorporated such a microprism 70 microns long with an angle of 23 degrees, it would protrude from the document (in the y-axis) by about 30 microns. Hence the surface relief 20 typically has a depth profile (i.e.
  • the security device 10 is of course suitable for inspection by the naked eye, with a user being able to determine the authenticity of the device by illuminating it with a suitable light source (such as a torch on a smart phone, or a desk lamp) and observing the projected caustic image Cl. This can if necessary be compared against a reference image, potentially provided on the same security document or separately.
  • a suitable light source such as a torch on a smart phone, or a desk lamp
  • the security device 10 can equally be inspected by machine. Security documents are often inspected by machines as part of an automated process (e.g. banknote and cheque acceptors, passport e-gate inspection).
  • a colour filter layer 18 (of the sort provided in the Figure 1 embodiment) are also possible.
  • the colour filter layer 18 could be located on the same side of the substrate 12 as the relief structure 20, either between the relief structure 20 and the substrate 12 ( Figure 2(d)) or on the relief structure 20 itself ( Figures 2(e) and 2(f)). In the latter case it is important to maintain the contours of the relief structure 20 either at the interface between the embossing layer 14 and colour filter layer 18 and/or at the opposite surface of the colour filter layer 18.
  • the latter option can be achieved by arranging the colour filter layer 18 to follow the contours of the surface relief structure on both of its sides, as shown in Figure 2(e).
  • colour filter layers 18a and 18c overlap, resulting in a mixed colour (e.g. purple) being transmitted.
  • a mixed colour e.g. purple
  • colour filter layers 18a and 18b are present so its colour determines the colour of transmitted light (e.g. red).
  • colour filter layers 18a and 18b are present resulting in a different mixed colour (e.g. orange) being transmitted.
  • region R 4 only colour filter layer 18b is present so it determines the transmitted colour (e.g. yellow).
  • one of more of the colour filter layers 18a, 18b, 18c could have a more complex design and be formed of more than one material.
  • the colour filter 30 it is preferable for the colour filter 30 to be on the light source side of the caustic relief 20, so that the light passes through the colour filter, and takes on the colour thereof, before it is redirected by the relief structure 20. This is particularly important where the colour filter 30 comprises multiple regions of different colour as discussed below, since otherwise, if the colour filter is located such that the redirected light rays pass through it, unintended mixing of the various colours may occur.
  • the security device is transparent and that the caustic relief 20 operates on refraction.
  • a reflective-mode device could be performed by applying a reflection enhancing layer to the relief structure 20 (not shown in Figure 2).
  • the light source and the caustic image will be on the same side of the device as one another.
  • the colour filter 30 it is desirable for the colour filter 30 to be in close contact with the relief structure 20 so that light rays only pass through it when they are in the immediate vicinity of the relief structure 20 and inadvertent colour mixing is minimised.
  • the arrangements of Figures 2(c) or 2(e) are preferred.
  • the substrate 12 will be at least semi-transparent (i.e. optically clear, with low optical scattering, but may carry a coloured tint as noted above).
  • the substrate 12 may comprise one or more plastics materials such as BOPP, polyethylene, polycarbonate, PET or the like.
  • the security device is a reflective device
  • a nontransparent substrate 12 such as paper, in which case the configuration of Figure 2(e) would be utilised, with the reflective layer (not shown) inserted at the interface between embossing layer 14 and colour filter layer 18 (both the light source and the caustic image being located to the first side 12a of the substrate 12).
  • the first region 31a comprising first material 32a which transmits first colour Ci
  • second region 31 b comprising second material 32 which transmits second colour C2
  • first region 31a has the form of a rectangle and makes up the left half of colour filter 30, while second region 31 b, comprising second material 32 which transmits second colour C2, forms another rectangle making up the right half of the filter.
  • the security device will display a two-coloured rectangle as shown in Figure 3(b).
  • the areas 21a, 21 b of the relief structure which contribute to each respective portion Pi, P 2 of the caustic image can be identified, for instance, for a given relief structure 20 by ray tracing techniques. These could be performed using a computer model of the relief structure 20 and appropriate ray tracing software. Alternatively, the areas 21 could be identified manually by applying colour(s) to various parts of the relief structure 20 and observing where those colours appear in the caustic image. Alternatively still, the correlation between the areas 21 and the portions of the caustic image could be known from the process according to which the relief structure 20 was generated.
  • the first portion Pi of the caustic image Cl will exhibit the first colour Ci.
  • the second region 31 b of the colour filter 30 overlaps second area 21 b of the relief structure, the second portion P 2 of the caustic image Cl will exhibit the second colour C 2 .
  • any number of image portions could be coloured in this way by providing appropriate coloured materials in corresponding regions of the colour filter.
  • the two regions 31 a, 32b transmit the same colour of light but different tones (shades), Ti , T 2 .
  • the different tones are also visible in the non-projected image R displayed directly by the colour filter 30.
  • the projected caustic image Cl now appears wholly in the first colour Ci , but the first portion Pi of the image exhibits a first tone T 1 which is darker than a second tone T 2 exhibited by the second portion P 2 of the image.
  • Figure 5 shows a further embodiment based on that of Figure 4, like reference numerals denoting like features.
  • the colour filter 30 comprises three regions 31a, 31 b and 31c each having a different thickness of the first material 32a’, 32a” and 32a’”.
  • the thickness of the first material 32a’” is such that, locally, it is substantially opaque to the incident light L.
  • light striking the third region 31c does not contribute to the caustic image Cl and the third region 31a can be considered to constitute a masking component.
  • the masking component will be visible in the non-projected image R (in this case, taking the form of an annular shape as shown in Figure 5(b), but will not be visible in the projected caustic image Cl.
  • the caustic relief structure 20 will need to be designed taking into account the presence and extent of the masking component, so that the desired caustic image Cl is still achieved.
  • the particular shape of the relief structure 20 in the Figure 5 embodiment will be different (if only in minor respects) from that of the Figure 4 embodiment, in order to achieve identical caustic images Cl.
  • Figure 7 shows a further embodiment which is a variant of that described with respect to Figure 6.
  • the Figure 7 embodiment is identical to that of Figure 6 except for the addition of a masking component 40.
  • the masking component 40 has the same effect as that disclosed in relation to Figure 5 above.
  • the masking component 40 is formed as a separate layer.
  • the masking component 40 could be provided by a separate print of a suitable substantially opaque ink, or as a patterned layer of metal or another substantially opaque material.
  • the masking component could lie over the colour filter 30 as shown or could take any other position within the layer structure of the device 10, e.g. between the colour filter layer 18 and the substrate 12, or between substrate 12 and embossing layer 14.
  • the masking layer overlaps a sub-part of the relief structure 20, which will no longer contribute to the caustic image Cl since light is no longer transmitted through the device at that position.
  • the masking component 40 is preferably provided in the form of a pattern or image, e.g. alphanumeric text. In this example, the masking component forms the word “TEN”.
  • the masking component 40 will be visible when the security device is viewed directly (in reflection or transmission) and therefore contributes to any nonprojected image displayed by the colour filter. As such, the design of the masking component 40 may be chosen to complement or enhance the non-projected image.
  • the pattern formed by masking component 40 will not be visible in the projected caustic image Cl, the relief structure 20 having been designed so as to account for the presence of the masking component 40.
  • the correlation between the regions 31 of the colour filter 30 and the areas 21 of the relief structure 20 is coarse, with the result that the reflective appearance of the colour filter is typically of a set of coloured stripes or blocks.
  • the caustic relief structure 20 is a continuous relief structure, such as may be formed by the methods disclosed in any of WO-A-2019/063779, WO-A-2020/070304 and WO- A-2020/070299
  • the relative positions of the areas 21 in the relief structure will typically correspond, at least approximately, to the relative positions of the portions P of the caustic image which those areas contribute to.
  • the necessary arrangement of the regions 31 in the colour filter will also broadly correspond to what is seen in the caustic image.
  • the relief structure 20 is configured to generate a caustic image Cl which here depicts a flower as shown in Figure 8(d).
  • a first portion Pi of the image corresponding to the petals of the flower, is generated by a first area 21a of the relief structure 20, shown in Figure 8(c), which occupies an approximately square area at the centre top of the structure (corresponding to the position of the first portion Pi in the image Cl).
  • a second portion P 2 of the image, corresponding to the stem and leaf of the flower, is generated by a second area 21b of the relief structure 20, occupying a chevron-shaped part of the relief structure 20 below the first area 21a.
  • first and second regions 31a, 31 b are designated corresponding to and overlapping the first and second areas 21 a, 21 b of the relief structure 20, each being formed by a material transmitting the desired colour for that portion of the image.
  • the first material 32a forming first region 31a may be purple while the second material 32b forming second region 31 b may be green, with the result that the caustic image will exhibit a corresponding image in which the petals of the flower (first portion Pi) are purple, while the stem and leaves are green.
  • the non-projected image here termed reflected image Rl
  • the non-projected image Cl is a version of the caustic image Cl, in that the colours have the same general relative arrangement.
  • the materials forming the colour filter are each assumed to have the same reflected and transmitted colour, with the result that any non-projected image will have the same appearance in reflected and transmitted light.
  • the non-projected image is described in terms of its reflected appearance only (and hence may be referred to as the reflection or reflected image Rl) but this will be the same as its transmitted appearance. All of these embodiments can instead be implemented using colour filter materials which have different reflection and transmission colours. Further embodiments which make particular use of such materials will be given below.
  • the security level can be significantly enhanced by decoupling the non-projected appearance of the colour filter 30 from that of the caustic image Cl. That is, the arrangement of material(s) in the colour filter is independent of the eventual projected caustic image. This enables the non-projected image (if any) to be different from the caustic image.
  • This can be achieved by use of a segmented relief structure 20, the segments 25 of which are laterally distributed relative to one another such that the areas 21 which contribute to respective portions P of the caustic image do not have the same relative positions in the relief structure 20 as to the portions P in the caustic image Cl.
  • the corresponding regions 31 of the colour filter, the arrangement of which is determined by that of areas 21 of the relief structure will therefore also have different relative positions compared to the portions P in the caustic image Cl, with the result that the dependence of one on the other is removed.
  • Figure 9 shows an embodiment which makes use of this principle.
  • the construction of the security device 10 is the same as described with reference to Figure 1 aside from the modifications explained here.
  • the relief structure 20 comprises an array of segments 25i, 25 2 ,... 25 n -i , 25 n .
  • Figure 9(a) illustrates the segments as being demarcated from each other through the thickness of embossing layer 14, in practice the segment boundaries may exist only in the design of the surface relief 20 itself.
  • Each segment 25 contributes light to (only) one portion P of the caustic image Cl, but each portion P of the caustic image Cl may be generated by one or many segments 25.
  • the colour filter 30 is arranged according to a corresponding array of cells 35i , 35 2 ,...
  • Each cell 35 overlaps a single one of the segments 25 and has substantially the same size and shape thereof. It should be noted that whilst all the segments 25 (and hence all the cells 35) in this example have the same size and shape as one another, this is not essential.
  • a segmented relief structure 20 can be derived in a number of ways.
  • the process may begin with a computer model of a nonsegmented (continuous) relief structure which has been designed to project a certain caustic image, such as those described with reference to Figures 1 and 3 to 8.
  • the non-segmented relief structure can then be divided into segments. In one example, this could be performed by dividing the relief structure into an arbitrary array of segments, e.g. with the same size and shape as one another, without reference to the contours of the relief structure.
  • the segments used for redistribution of the caustic element are preferably arranged as a regular grid, e.g.
  • each segment 25i primarily redirects light, in which case that segment 25i is designated as part of the corresponding area 21 i.
  • This can be achieved using ray tracing software or any of the other techniques for identifying areas of the relief structure already mentioned above.
  • the various areas 21 of the relief structure 20 could be identified before division into segments takes place and then the segments can be defined with reference to the areas, e.g. by drawing segment boundaries around each part of the relief structure which redirects light primarily to a single portion P of the image.
  • a segmented relief structure 20 can be derived directly without being based on a non-segmented relief structure.
  • the generation process can begin with a desired grid defining the segment boundaries. Each position in the grid can then be allocated a certain relief, forming a segment of the eventual relief structure, configured to redirect incident light to a certain portion P of the image.
  • the segments which contribute to first portion Pi of the caustic image are interspersed in a periodic manner with those which contribute to the second portion P 2 of the caustic image Cl.
  • the first segment 25i provides part of first area 21a of the relief structure
  • the second segment 25 2 provides part of second area 21 b of the relief structure, and so on.
  • the periodicity is in two dimensions (i.e. along both the x and z-axes) although in other examples it could be one dimensional (i.e. along either the x-axis or the z-axis).
  • the cells 35 of the colour filter 30 are arranged accordingly in a periodic pattern, with all of the cells (such as cell 35i) which overlap segments providing first area 21a being formed of a first material 32a, and collectively forming a first (discontinuous) region of the colour filter. Likewise, all of the cells (such as cell 35 2 ) which overlap segments providing second area 21b are formed of a second material 32b and collectively forming a second (discontinuous) region of the colour filter 30.
  • the colour filter 30 appears either as a periodic pattern of different materials or, if the cells are sufficiently small such that they cannot be individually resolved by the naked eye, as a uniform area of mixed colour.
  • each segment 25i of the relief structure When illuminated by light source L, each segment 25i of the relief structure redirects light of the colour transmitted by corresponding cell 35j towards a respective portion P of the caustic image to thereby recreate the image. It will be appreciated that the distribution of the segments 25 does not significantly change the caustic image, since the generation of the bright and dark spots is more heavily dependent on the angles to which the various light rays are directed, rather than the specific position within the relief structure from which each light ray emanates.
  • the first portion Pi of the caustic image will exhibit the transmitted colour of material 32a - for instance, in this case the petals of the flower in caustic image Cl may appear purple.
  • the second portion P 2 of the caustic image will exhibit the transmitted colour of material 32b - for instance, in this case the stem and leaf of the flower in caustic image Cl may appear green.
  • each portion P of the caustic image will depend on the colour(s) transmitted by a set of material(s) provided in the cells 35 of the colour filter 30 corresponding to the relevant segments 25 of the relief structure 20.
  • each set comprises a single material.
  • one or other of the sets could comprise multiple materials. For instance, instead of forming all of the cells (such as cell 35 2 ) which overlap segments forming part of second area 21 b of a green second material 32b, half of those cells could be formed of a yellow material and the other half of a blue material. The yellow and blue transmitted colours will be mixed by the caustic relief with the result that the second portion P 2 of the caustic image once again appears green.
  • the colour filter could be formed as a pixel array where a pixel is the smallest unit and each pixel can only comprise a single material.
  • Each cell may comprise one pixel, or may comprise multiple pixels (e.g. a 4x4 group of pixels). All of the pixels formed of the same material make up one region of the colour filter, which may be continuous or non-continuous depending on the arrangement of pixels.
  • the arrangement of the segments 25 (and hence of the cells 35) is periodic. This has particular advantages as will be explained below. However, it will be apparent that the segments 25 could be arranged laterally in any desired order, including at random (or pseudo-random) positions across the relief structure 20. In this case, the arrangement of cells 35 in the colour filter 30 will also be random (or pseudo-random), which if the cells are sufficiently small can lead to the reflective appearance of the colour filter being substantially uniform (e.g. a mixed colour) with no discernible image information. This helps to conceal the presence of the security feature, and the projection of a well-defined image Cl with distinct colours in different portions thereof is particularly unexpected.
  • the colour filter 30 could, for instance, take the form of a regular grid of lines or pixels in a selection of colours such as RGB or CMYK. Since RGB and CMYK palettes can be used to achieve any colour, such implementations have the advantage that the same design of colour filter could be used for any device, with the caustic relief determining which colour(s) are displayed and where in the caustic image.
  • Periodic arrangements of the segments and cells can also be used to achieve particularly good optically variable effects in which the colour(s) of the caustic image change or switch upon tilting of the device relative to the light source.
  • this spacing is provided by the substrate 12 and the body of embossing layer 14, and has a combined thickness t.
  • suitable spacings can also be achieved using the alternative device constructions shown in Figures 2(b) and 2(d), for example.
  • the light ray incident on a particular location of the relief structure 20 will pass through a different position on the colour filter 30 depending on the tilt angle of the device relative to the incident light. If the colour transmitted by the colour filter 30 varies between those different positions, the colour contributed to the caustic image by that location of the relief structure will also change.
  • Figure 10 illustrates this effect using the same exemplary security device 10 as already discussed with respect to Figure 9.
  • the light source designated L’
  • the security device which is equivalent to tilting the security device about the z-axis
  • the resulting light rays are shown in solid lines.
  • the light rays from the original position of the light source (designated (L)) are shown in dashed lines for comparison (and are identical to what is shown in Figure 9(a)). It will be seen that each segment 25i no longer receives light having passed through the overlapping cell 35i, but rather light which has passed through the adjacent cell 35M .
  • the first segment 25i of the relief structure will receive light having passed through cell 35 0 , which contains second material 32b, while the second segment 25 2 of the relief structure will receive light having passed through cell 35i , which contains first material 32a (as also shown in Figure 9(b)).
  • the colour of light redirected by all of the interleaved segments 25 which form part of first area 21a and thus contribute to the first portion Pi of the caustic image is now determined by the second material 32b.
  • the colour of light redirected by all of the interleaved segments 25 which form part of second area 21 b and thus contribute to the second portion P 2 of the caustic image (the stem and leaf, in this example) is now determined by the first material 32a. Therefore, if the first material 32a transmits purple light while the second material 32b transmits green light, in the caustic image Cl’, the flower petals will now appear green while the stem and leaf of the flower appear purple. When the security device 10 is tilted relative to the light source between the position shown in Figure 9(a) and that shown in Figure 10(a), the caustic image will therefore appear to switch colours.
  • the cells 35 (and hence the segments 25) have a lateral width w of 200 microns or less, preferably 100 microns or less, more preferably 50 microns or less. While in the embodiment shown in Figures 9 and 10, there are only two portions Pi , P 2 of the caustic image, and hence two interleaved areas 21a and 21b in the relief structure 20, it will be appreciated that any number of image portions and corresponding areas of the relief structure could be provided and interleaved in a periodic manner.
  • All of the segments 25 which contribute to the second portion P 2 of the caustic image are placed in a rectangular area surrounding the square, collectively forming second area 21 b.
  • the corresponding cells 35 of the colour filter 30 are allocated the necessary materials, resulting in the above-described reflection image Rl shown in Figure 11 (b).
  • the reflection image Rl will be visible (e.g. a red square surrounded by a blue rectangle), whereas when the security device 10 is illuminated by white light (typically in transmitted mode), the caustic image Cl will be projected (e.g. the letters “AB” where the “A” is red and the “B” is blue).
  • the reflected colour of the or each material forming the colour filter 30 will most often be the same as its transmitted colour, this is not always the case - for instance if the colour filter comprises an interference layer material, the reflected and transmitted colours thereof will typically be different.
  • the set of materials provided in cells overlapping the first area 21a of the relief structure 20 is a set of one material (first material 32a) and so the colour of the first portion Pi of the caustic image corresponds to that transmitted by the first material 32a.
  • the second portion P 2 of the caustic image has the colour transmitted by second material 32b.
  • each portion P of the caustic image may have its colour determined by a set of one or more materials forming the colour filter which overlap the areas of the relief structure which contribute to that portion P. If the set comprises multiple materials with different transmitted colours, the portion P will exhibit a mixed colour.
  • An example is shown in Figure 12.
  • the construction of the security device is much the same as that of Figure 11 .
  • the colour filter 30 (and hence the reflection image Rl) is modified, with the previously blue rectangular background being replaced by two regions 31 b, 31c each having the shape of a square bracket.
  • Region 31b is formed of material 32b which transmits colour C 2 (e.g. blue)
  • region 31c is formed of material 32c which transmits colour C 3 (e.g. yellow).
  • the caustic image Cl displays its first portion Pi (e.g. letter “A”) in colour Ci corresponding to the transmitted colour of material 32a (e.g. red), but now the second portion P 2 (e.g. letter “B”) appears in a different colour C4 which is a mixture of the colours transmitted by materials 32b and 32c (e.g. green).
  • the segments 25 of the relief structure may abut one another, as shown in the preceding embodiments, or may be spaced from one another (not shown). In the latter case, it may be advantageous to space the segments 25 from one another with light-scattering relief structures disposed between them, which redirect incoming light such that it does not significantly contribute to the caustic image. This acts as a “buffer zone” around the segment so that if the alignment of the cells 35 with the segments 25 is not exact, light passing through an adjacent cell may be intercepted by the light-scattering zone and removed from the system such that the colour of the caustic image is as intended. This makes the security device 10 more tolerant of misregistration between the colour filter 30 and the relief structure 20.
  • scattering zones need not be provided between every segment 25.
  • scattering zones provided only at interfaces between different areas 21a, 21 b of the relief will typically be sufficient.
  • devices of this sort can, in one embodiment, be designed by: providing (e.g. drawing or selecting) a non-projection image to be exhibited by the colour filter, comprising a plurality of laterally-offset regions which vary in colour and/or tone from one region to another; for each region of the non-projection image, providing a relief structure segment based on the colour and/or tone of the region; and arranging the relief structure segments according to the arrangement of regions of the non-projection image.
  • the non-projected image is selected first and the relief structure is then designed to account for the desired nonprojected image and place the projected light rays in the correct positions to achieve the required arrangement of colours in the caustic image.
  • “Providing” the relief structure segments could involve reallocating segments of a pre-designed caustic relief configured to display a certain projected image and/or creating a relief for each segment, which is designed to redirect the light transmitted through that region to the desired position on a screen to thereby build up a caustic image.
  • the resulting structure can then be physically made, e.g. by etching the design into a suitable surface from which the relief structure can be cast.
  • FIG. 13 An example of a security device 10 configured to display more complex images is depicted in Figure 13.
  • the security device is shown illuminated by a preferred light source L, namely the torch of a smart phone or other mobile device 90.
  • the security device 10 is carried on a security article 5 in the form of a strip applied to a security document 100 such as a banknote.
  • the strip 5 is positioned over a transparent window region of the security document 100 (not visible in Figure 13).
  • the security device 10 could occupy the whole strip 5, or just a portion thereof as shown here (in which case the portion will be aligned with the transparent window region).
  • the strip 5 displays a reflection image Rl, corresponding to the colour filter 30, which in this example exhibits an array of the number “20” with both digits in red.
  • Each number “20” has a thick white outline region.
  • the remainder of the colour filter is blue and provides a background to the array. This image can be continued across the whole of strip 5 (as shown), even if only a portion of it overlaps the relief structure 20 (not visible in Figure 13) to thereby form security device 10.
  • the relief structure is configured to project a caustic image Cl which here comprises a flag, such as the Union Jack.
  • the areas of the relief structure which generate the red “cross” elements of the flag (first portion Pi) are aligned with the red “20s” of the colour filter image Rl, so that these elements of the caustic image appear red.
  • non-projection image Rl of colour filter 30 - in the Figure 13 embodiment this corresponds to defining the shape of the “20”s and their contoured outlines, as well as their placement on the background. More generally, the non-projection image Rl can be complex, e.g. a rectangular array of dots that when viewed appear as an image, or simplistic, e.g. a macro shape on a square background.
  • projected caustic image Cl - in the Figure 13 embodiment this corresponds to defining the shape of the Union Jack flag. Again, this image could take any form. It will be appreciated that steps 1 and 2 could take place in either order.
  • the caustic structure can be physically formed, e.g. by cast-cure, in accordance with the designed surface structure.
  • the material(s) forming the colour filter 30 have the same colour(s) in reflection and in transmission.
  • one or more of the materials forming the colour filter could be of a type which exhibits different colours in reflection and in transmission, such as a plasmonic material (e.g. plasmonic particles or a plasmonic structure), or an interference material (e.g. interference pigments, a thin film structure or liquid crystal).
  • the reflection images Rl in each of the above embodiments i.e. the appearance of the non-projected image exhibited by the colour filter 30 in reflected light
  • the appearance of one or more different colours in the reflected image as compared with those seen when the non-projected image is viewed in transmitted light and with those seen in the caustic image provides a strong security effect.
  • the colour filter 30 is formed of a single semi-transparent material 32a which exhibits different colours in reflected and transmitted light, such as a plasmonic material or an interference material.
  • the material 32a may appear gold in reflected white light and blue in transmitted white light.
  • the non-projected image NPI R therefore appears as uniform area with no information content, which is gold in colour.
  • the caustic image Cl is projected, e.g. onto screen S as shown in Figure 14(d), it appears in the transmitted colour of the material 32a, e.g. blue.
  • the caustic image Cl is of the number “20”.
  • Figure 15 shows a more complex embodiment in which the colour filter 30 is formed of two materials 32a, 32b in respective regions.
  • Each of the materials 32a, 32b exhibits a different colour in reflection and in transmission, and in this case the two materials also contrast with one another under both viewing conditions.
  • material 32a may appear gold in reflected white light and blue in transmitted white light
  • material 32b may appear green in reflected white light and red in transmitted white light.
  • the regions may be aligned with the caustic relief structure such that certain portions of the caustic images appear in certain colours, as explained above with reference to Figure 3 for example.
  • the embodiment of Figure 16 expands on the same principle by adding a third material 32c to the colour filter 30, which again exhibits different colours in reflection and transmission.
  • the third material 32c appears orange in reflected white light and green in transmitted white light.
  • This transmitted colour is the same as the reflective colour of second material 32b.
  • the non-projected image NPIR is a circle with a gold left half and two quadrants in the right half which appear green (top) and orange (bottom).
  • the non-projected image NPI T has the same image content but the colours are different.
  • the left half is blue while the quadrants appear red (top) and green (bottom).
  • the left portion (“2”) appears blue as in the previous embodiment while the top of the right portion (“0”) is red and the bottom is green.
  • the colourfilter is formed of at least three materials 32a, 32b, 32c arranged to convey when viewed directly a graphic such as a portrait or (as shown here) a landscape.
  • each of the three materials exhibits different colours in reflection and transmission (e.g. gold/blue; orange/green; and green/red) although standard materials could also be provided.
  • the non-projected image when viewed under reflected white light, the non-projected image exhibits a complex graphic of a sunset scene, in which the sky is yellow, the sun green and the cactus orange.
  • the relief structure 20 and the colour filter 30 may or may not have the same lateral extent as one another.
  • Figures 20 and 21 show two embodiments in which the colour filter extends beyond the bounds of the relief structure 30.
  • the security device 10 is formed in a window region 101 of a security document bounded by opacifying layer 15 arranged on transparent substrate 12.
  • the caustic relief structure 20a is formed in an embossing layer 14 disposed on a first surface of the substrate and the colour filter 30 is formed in a colour filter layer 18 disposed on the second surface.
  • the colour filter 30 could be implemented in any of the alternative ways described above in relation to Figure 2.
  • the colour intensity of the halo H will typically be less than that of the caustic image Cl since it is formed by unfocussed light.
  • the Figure 21 embodiment is the same as that shown in Figure 20 except here the colour filter 30 is formed of a first material 32a in a circular area corresponding to that of the caustic relief area 20a, and a second material 32b in an annular area surrounding material 32a and corresponding to (at least part of) the non-caustic area 20c.
  • the first and second materials transmit different colours Ci, C2.
  • the caustic image Cl appears in a first colour (e.g. green) while the surround halo H appears in a second colour (e.g. red).
  • the Figure 23 embodiment is substantially the same as the Figure 22 embodiment, except that here the colour filter 30 is not provided across the whole window region 101 but rather only in alignment with the two caustic relief areas 20a, 20b.
  • the non-projected image appears to have the same shape as the caustic relief areas 20a and 20b, appearing as two coloured areas within the window 101 separated by a colourless area corresponding to the non-caustic region 20c.
  • the security device projects a coloured caustic image Cl as before. However in this case there may be no halo effect since the light passed by the non-caustic region 20c is not coloured.
  • the multiple caustic relief areas 20a, 20b can be provided within one and the same window region 101 as just shown.
  • the security device 10 comprises a first caustic relief structure area 20a located in a first window region 101a and a second caustic relief structure area 20b located in a second window region 101b.
  • a colour filter 30 is provided in both window regions 101a, 101b and in this case it has a uniform colour in both regions.
  • the two window regions 101a, 101 b are separated from one another by a non-transparent part of the substrate in which the opacifying layers 15 are present.
  • the first and second caustic relief structure areas 20a, 20b in this case are each configured to form a respective portion Pi , P 2 of the caustic image projected onto screen S when the device 10 is illuminated.
  • the caustic image Cl is the number “10”, formed of a first portion Pi which is the digit “1”, and a section portion P 2 which is the digit “0”.
  • the colour filter 30 is of the same transmissive colour in both windows 101a, 101b, both portions Pi, P 2 appear in the same colour Ci (e.g. red).
  • Figure 25 shows a variant in which the colour filter 30 is formed of a first material 32a in window 101a and a second material 32b in window 101 b, the first and second materials having different transmissive colours Ci, C 2 .
  • the security device 10 is otherwise the same as in Figure 24.
  • the caustic image now appears in two colours, with the first portion Pi appearing in a first colour Ci (e.g. red) and the second portion P 2 in a second colour C 2 (e.g. blue).
  • the security level can be enhanced by arranging for the periphery of the caustic relief 20 to itself convey image information, which is preferably different from that of the caustic image. It should be noted that this concept could be deployed with or without a colour filter forming part of the device 10. Figures 27 and 28 provide examples of this.
  • the relief structure preferably comprises at least one area of caustic relief 20a and at least one area 20c of noncaustic surface, which may be relatively flat or could carry a matte or scattering structure, for example.
  • the embossing layer 14 (if one is used) may or may not be present in the non-caustic surface 20c.
  • the periphery image can be of any form, comprising for example any of: alphanumeric text (as in the above examples), a typographic symbol, a currency symbol, a geometric shape, a logo, a flag, a map, a country outline, a portrait, a drawing, or a scene such as of a landscape, an architectural structure (e.g. a building or bridge), a person, animal or plant.
  • alphanumeric text as in the above examples
  • a typographic symbol e.g., a currency symbol, a geometric shape, a logo, a flag, a map, a country outline, a portrait, a drawing, or a scene such as of a landscape, an architectural structure (e.g. a building or bridge), a person, animal or plant.
  • a typographic symbol e.g., a currency symbol, a geometric shape, a logo, a flag, a map, a country outline, a portrait, a drawing, or a scene such as of
  • the curable material(s) from which the caustic relief structure 20 is cast may be applied either directly to the tool carrying the desired relief shape (e.g. to the embossing tool 85 of WO-A-2018/153840 or to the casting tool 220 of WO-A-2017/009616), or the curable material(s) may be applied directly to the substrate on which the relief structure is to be formed, and then brought into contact with the tool (e.g. by impressing the tool onto the deposited curable material). Both options are described in the aforementioned documents. Preferably, the latter option is employed and the curable material(s) are applied to the substrate by printing (e.g.
  • Suitable curable materials are disclosed in WO-A-2017/009616, section 2.1 . UV- curable materials are most preferred. Curing of the material(s) preferably takes place while the casting tool is in contact with the curable material, against the substrate.
  • the resulting relief structure will typically include a base layer of material on top of the substrate, connecting the protrusions of the relief at their base.
  • this base layer is integral with the relief structure and formed of the same curable material(s), resulting from either the shape of the casting relief and/or the manner in which the curable material is pressed between the substrate and the casting tool during processing.
  • An example of such a base layer and its formation is disclosed in WO-A- 2017/009619, Figure 8. It is also possible to provide (alternatively or in addition) a base layer in the form of a pedestal layer, applied in a preceding step. Apparatus and methods for providing such a pedestal layer are disclosed in WO-A- 2017/09620, Figures 8 to 12.
  • the colour filter 30 of the presently disclosed security device could be provided integrally with such a pedestal layer.
  • WO-A-2018/153840 and WO-A-2017/009616 also disclose print stations, which are disposed in line with the above-described casting apparatus. Print stations such as these are suitable for applying a colour filter layer 18, if used, to the same side of the substrate as the cast relief structure, or to the opposite side.
  • the apparatus disclosed in WO-A-2018/153840 can achieve particularly high registration between such cast relief structures and the printed colour filter layer.
  • Suitable substrates 12 on which the disclosed security devices can be formed are disclosed in WO-A-2017/009616, section 1 , and apparatus/methods for applying opacifying layers thereto in section 4, including the formation of window regions.
  • the opacifying layers are applied before formation of the presently disclosed security devices on the substrate.
  • the sheet material supplied to the apparatus of WO-A-2018/153840 may comprise a polymer substrate of the sort disclosed in WO-A-2017/009616, already provided with one or more opacifying layers.
  • the colour filter 30 may be formed of various different types of material(s) 32.
  • the colour filter 30 is integral with a cast-cured embossing layer 14 it will need to be formed of one or more curable materials, whereas if the colour filter 30 is applied as a separate colour filter layer it could be formed of material(s) such as inks, or deposited layers/structures such as an thin film interference layer structure, or plasmonic pillars or holes.
  • the material(s) forming the colour filter 30 need to be at least semitransparent (i.e. optically clear, with low or zero optical scattering), in order to avoid redirection of the light rays and preserve the caustic image Cl.
  • this is most preferably an absorbent dye and/or very finely ground pigment, of which examples will be given below.
  • Preferred particle sizes are less than 500 nm, more preferably equal to or less than 100 nm.
  • the dye and/or pigment may be disposed in a suitable binder, such as an ink binder or a curable resin, as appropriate for the form in which the colour filter 30 is to be provided.
  • a suitable binder such as an ink binder or a curable resin
  • FIG. 29 shows the apparatus in schematic cross-section
  • Figure 29(b) shows the result of each manufacturing step on the substrate 12 in perspective view.
  • the relief structure 20 is formed by cast-cure
  • the embossing layer 14 is formed of two different curable at least semi-transparent materials 32a, 32b, each of which transmits a different colour of light therethrough.
  • a first material 32a is applied to the substrate 12 using a first application module 51a which here comprises a patterned print cylinder 54a which is supplied with the curable material 32a from a doctor chamber 52a via an intermediate roller 53a.
  • a first application module 51a which here comprises a patterned print cylinder 54a which is supplied with the curable material 32a from a doctor chamber 52a via an intermediate roller 53a.
  • the components shown could form part of a gravure printing system. Other printing techniques such as lithographic, flexographic, screen printing or offset printing could also be used. Print processes such as these are preferred since the curable material 32a can then be laid down on the substrate only in first regions 31a thereof, the size, shape and location of which can be selected by control of the print process, e.g.
  • a casting module 55 which here comprises a casting tool 56 in the form of a cylinder carrying a surface relief 57 defining the shape of the caustic relief structure 20 which is to be cast into the curable materials 32a, 32b (collectively forming the embossing layer 14 in this example).
  • a casting tool 56 in the form of a cylinder carrying a surface relief 57 defining the shape of the caustic relief structure 20 which is to be cast into the curable materials 32a, 32b (collectively forming the embossing layer 14 in this example).
  • the curable materials 32a, 32b fill corresponding parts of the surface relief 57, forming the surface of the curable materials into the shape defined by the relief.
  • the cylinder 56 will typically be configured such that the surface relief 57 is only provided at regions corresponding to the shapes and positions of the applied patches of curable material forming colour filters 30.
  • the curable materials 32a, 32b are cured by exposure to appropriate curing energy E such as UV radiation from a source 58.
  • curing energy E such as UV radiation from a source 58.
  • the source 58 is positioned above the substrate 12, e.g. inside cylinder 56 if the cylinder is formed from a suitable transparent material such as quartz, although curing could instead be performed through the substrate 12.
  • the result of the Figure 29 process is a security device 10 with a colour filter 30 integral with the embossing layer 14 in which the relief structure 20 is formed, and comprising multiple different materials such that the transmitted colour varies across the device.
  • This can be adapted to implement any of the embodiments described above (although the device will not be optically variable) through appropriate configuration of the application modules 51a, 51 b such that the materials 32a, 32b are applied according to the desired layout of the colour filter 30, and of the casting module 55 so as to impart the appropriate relief structure 20 into the materials.
  • Highly accurate registration between the materials 32 and the relief structure 20 e.g. to ⁇ 75pm
  • third and optionally additional materials can also be incorporated by providing corresponding application modules as necessary.
  • the areas of curable material 69 affix to the substrate 12 and curing preferably takes place at this stage to ensure strong bonding.
  • the colour filter 30 is not integral with the relief structure 20 in this embodiment, it can be applied by a printing process which preferably takes place simultaneously as the relief structure 20 is cast onto substrate 12, at the same position along the machine direction MD.
  • Figure 30 shows a print module 70 arranged so as to achieve this, comprising a print cylinder 71 configured to transfer material(s) 32a, 32b, arranged on its surface 72 in accordance with the desired colour filter 30, onto the second surface 12b of substrate 12.
  • the inking system by which the materials 32a, 32b are transferred to print cylinder 71 are standard and hence not shown here.
  • the security device 10 in the Figure 31 embodiment is a security device including a colour filter 30, such as any of those described with reference to the preceding embodiments.
  • a colour filter 30 such as any of those described with reference to the preceding embodiments.
  • the image displayed by the supplemental security feature 150 when viewed in transmitted light exhibits the same one or more colours as those exhibited by the caustic image projected by security device 10.
  • the supplementary security feature 150 could be a traditional watermark, caused by varying the density of paper fibres across the area.
  • the two window regions 101 , 102 are formed by omission of opacifying layers 115 in the relevant areas of transparent document substrate 112, in the same manner as previously described.
  • the relief structure 20 can be formed in any of ways previously mentioned but here is exemplified as carried in a cast-cured embossing layer on a first side of the substrate 112.
  • the colour filter 30 can be embodied integrally with the substrate 112 (not shown) or as a colour filter layer (as shown), in which case it can be located on either surface of the substrate.
  • the security device 10 comprises a relief structure 20 arranged on a substrate, preferably in a window region of a security document.
  • a caustic image Cl When the device is illuminated by a first light source Li , at an illumination angle which falls within the device’s operational range 0, a caustic image Cl will be projected and can be displayed on a suitably positioned screen S.
  • the light source Li is positioned such that the illumination angle falls with range 0, the caustic image Cl will be projected although its position on the screen S may vary in the x and/or z axes.
  • the operational illumination range 0 is designed to be wide (e.g. -45 to +45 around normal incidence so a range 0 of 90 degrees) so that the device generates the expected caustic image Cl over a wide range of illumination angles.
  • This principle is made use of in embodiments of the present invention by configuring the relief structure to project a first caustic image when illuminated from a first illumination angle, and a second (different) caustic image when illuminated from a second (different) illumination angle.
  • This is achieved by combining two caustic reliefs into the relief structure, each configured to operate over a different operational illumination angle range 0.
  • Figure 37 and 38 show two different security devices (which each are comparative examples) to help illustrate this.
  • the security device 10’ comprises a first caustic relief structure 20’ which is configured to project a first caustic image Ch when illuminated from a first illumination angle Li which falls within a first illumination angle range 01.
  • the first caustic image C is of the numeral “10”.
  • the first illumination angle range 01 is preferably offset from the substrate, e.g. in the -x direction.
  • the security device 10 comprises a second caustic relief structure 20” which is configured to project a second caustic image Ch when illuminated from a second illumination angle L 2 which falls within a second illumination angle range 0 2 .
  • the second caustic image CI2 is of the currency symbol “£”.
  • the second illumination angle range 0 2 is preferably offset from the substrate, e.g. in the +x direction.
  • Each of the security devices shown in Figures 37 and 38 will project a single caustic image.
  • the Figure 37 device will display its image Ch under illumination from a light source Li within the first angle range 01 (and not elsewhere), while the Figure 38 device will display its image CI2 under illumination from a light source L 2 within the second angle range 0 2 (and not elsewhere).
  • FIG 39 shows a security device 10 in accordance with an embodiment of the present invention, which comprises the security devices 10’ and 10” of Figures 37 and 38 respectively in combination.
  • the security device 10 shown in Figure 39 comprises a relief structure 20 which comprises both caustic structures 20’ and 20”.
  • the first caustic image Ch will be projected (here the number “10”)
  • the second caustic image Cl 2 will be projected (here the symbol).
  • Figures 41 (a) and (b) show another embodiment of a security device 10 in accordance with the present invention, in which the first and second sectors 20’, 20” of the relief structure are provided in separate window regions 101a, 101 b of the security document, separated from one another by a nontransparent region formed by the presence of opacifying layers 15.
  • Figure 41(a) shows the security device 10 illuminated by a first light source Li at a first illumination angle. It will be seen that the caustic relief in the first sector 20’ redirects the incident light to project first caustic image Ch onto screen S. Meanwhile the light incident on the second sector 20” of the relief structure is scattered. As such only the first caustic image C is exhibited.
  • the illumination angle is changed to L 2 , as shown in Figure 41(b), now the first sector 20’ of the relief structure scatters the incident light while the second sector 20” projects the second caustic image Cl 2 .
  • the illumination angle between Li and L 2 the caustic image displayed by the device can therefore be switched.
  • FIGs 41 (a) and (b) also illustrate an optional colour filter 30 which may be provided.
  • the colour filter 30 could take any of the forms described in the preceding embodiments.
  • the colour filter 30 could be of uniform colour and tone across the whole device.
  • the colour filter defines laterally offset regions 31a, 31 b thereof which correspond to the different sectors 20’, 20” of the relief structure.
  • the regions 31a, 31 b may be configured to transmit light of different colours and/or tones. This leads to the first and second caustic images Ch, Cl 2 appearing in different colours/tones from one another thereby further enhancing the security level.
  • the security device has been configured to project first and second caustic images which are different from one another.
  • the same principle can be extended to provide for three or more caustic images to be projected at different illumination angles. This can be arranged to provide for more complex visual effects such as morphing, zooming or animation.
  • Each caustic image could take any form, e.g. alphanumeric text, a typographic symbol, a currency symbol, a geometric shape, a logo, a flag, a map, a country outline, a portrait, a drawing, a photographic image, or a scene such as of a landscape, an architectural structure (e.g. a building or bridge), a person, animal or plant.
  • Such security articles can be arranged either wholly on the surface of the base substrate of the security document, as in the case of a stripe or patch, or can be visible only partly on the surface of the document substrate, e.g. in the form of a windowed security thread.
  • Security threads are now present in many of the world's currencies as well as vouchers, passports, travellers' cheques and other documents. In many cases the thread is provided in a partially embedded or windowed fashion where the thread appears to weave in and out of the paper and is visible in windows in one or both surfaces of the base substrate.
  • windowed threads can be found in EP-A- 0059056.
  • Base substrates suitable for making security substrates for security documents may be formed from any conventional materials, including paper and polymer. Techniques are known in the art for forming substantially transparent regions in each of these types of substrate.
  • WO-A-8300659 describes a polymer banknote formed from a transparent substrate comprising an opacifying coating on both sides of the substrate. The opacifying coating is omitted in localised regions on both sides of the substrate to form a transparent region.
  • the transparent substrate can be an integral part of the security device or a separate security device can be applied to the transparent substrate of the document.
  • WO-A-0039391 describes a method of making a transparent region in a paper substrate. Other methods for forming transparent regions in paper substrates are described in EP-A-723501 , EP-A-724519, WO-A-03054297 and EP-A-1398174.
  • the security article may also be applied to one side of a paper substrate, optionally so that portions are located in an aperture formed in the paper substrate.
  • An example of a method of producing such an aperture can be found in WO-A- 03054297.
  • An alternative method of incorporating a security element which is visible in apertures in one side of a paper substrate and wholly exposed on the other side of the paper substrate can be found in WO-A-2000/39391 .
  • Figure 42 depicts an exemplary document of value 100, here in the form of a banknote.
  • Figure 42a shows the banknote in plan view whilst Figure 42b shows a cross-section of the same banknote along the lines X-X'.
  • the banknote is a polymer (or hybrid polymer/paper) banknote, having a transparent substrate 112.
  • Two opacifying layers 115 are applied to either side of the transparent substrate 112, which may take the form of opacifying coatings such as white ink, or could be paper layers laminated to the substrate 112.
  • the banknote 100 is a conventional paper-based banknote provided with a security article 120 in the form of a security thread, which is inserted during paper-making such that it is partially embedded into the paper so that portions of the paper 110 lie on either side of the thread.
  • a security thread 120 is inserted during paper-making such that it is partially embedded into the paper so that portions of the paper 110 lie on either side of the thread.
  • the window regions 101 may for example be formed by abrading the surfaces of the paper in these regions after insertion of the thread.
  • the security device 10 is formed on the thread 120, which comprises a transparent substrate with a relief structure 20 provided on one side and colour filter 30 provided on the other (again, the alternative constructions of Figure 2 are available). Windows 101 reveal parts of the device, which may be formed continuously along the thread. Alternatively several security devices could be spaced from each other along the thread, with different or identical images displayed by each.
  • the banknote 100 is again a conventional paper-based banknote, provided with a strip element or insert 125.
  • the strip 125 is based on a transparent substrate and is inserted between two plies of paper 110a, 110b.
  • the security device 10 is formed by a relief structure 20 on one side of the strip substrate, and colour filter 30 on the other (again, the alternative constructions of Figure 2 are available).
  • the paper plies 110a, 110b are apertured across region 101 to reveal the security device 10, which in this case may be present across the whole of the strip 125 or could be localised within the aperture region 101.
  • Security article 130 is a strip or band comprising a security device 10 according to any of the embodiments described above.
  • the security article 130 is formed into a security document 100 comprising a fibrous substrate 110, using a method described in EP-A-1 141480.
  • the strip is incorporated into the security document such that it is fully exposed on one side of the document ( Figure 45(a)) and exposed in one or more windows 101 on the opposite side of the document ( Figure 45(b)).
  • the security device is formed on the strip 125, which comprises a transparent substrate with a relief structure 20 formed on one surface and a colour filter 30 as previously described on the other (again, the alternative constructions of Figure 2 are available).
  • a similar construction can be achieved by providing paper 110 with an aperture 101 and adhering the strip element 125 onto one side of the paper 110 across the aperture 101.
  • the aperture may be formed during papermaking or after papermaking for example by die-cutting or laser cutting.
  • the arrangement shown in Figure 45 is particularly suitable for implementing the Figure 13 embodiment, for example.
  • the complete security device could be formed entirely on one surface of a security document which could be transparent, translucent or opaque, e.g. a paper banknote irrespective of any window region.
  • the adhesive could be applied to the relief structure as a pattern that leaves an intended windowed zone of the relief structure uncoated, with the strip or patch then being applied in register (in the machine direction of the substrate) so the uncoated lens region registers with the substrate hole or window.
  • the security device of the current invention can be made machine readable by the introduction of detectable materials in any of the layers or by the introduction of separate machine-readable layers.
  • Detectable materials that react to an external stimulus include but are not limited to fluorescent, phosphorescent, infrared absorbing, thermochromic, photochromic, magnetic, electrochromic, conductive and piezochromic materials.
  • taggants in the layer forming the caustic relief structure 20 (e.g. embossing layer 14 or substrate 12).
  • suitable taggants include any luminescent, fluorescent or phosphorescent, or a material which exhibits Raman scattering, for example.
  • Exemplary phosphors can be any compound that is capable of emitting IR- radiation upon excitation with light.
  • Suitable examples of phosphors include, but are not limited to, phosphors that comprises one or more ions capable of emitting IR radiation at one or more wavelengths, such as transition metal-ions including Ti-, Fe-, Ni-, Co-and Cr-ions and lanthanide-ions including Dy-, Nd-, Er-, Pr-, Tm- , Ho-, Yb- and Sm-ions.
  • the exciting light can be directly absorbed by an IR- emitting ion.
  • Acceptable phosphors also include those that use energy transfer to transfer absorbed energy of the exciting light to the one or more IR-emitting ions such as phosphors comprising sensitizers for absorption (e.g.
  • Acceptable infrared emitting phosphors include Er-doped yttrium aluminium garnet, Nd-doped yttrium aluminium garnet, or Cr-doped yttrium aluminium garnet.
  • a direct bandgap semiconductor for example a group ll-VI (e.g. ZnO, ZnS, ZnSe, CdS, CdTe, CdSe etc ) or a group I l-V (eg GaN, GaAs, AIN, InN etc) semiconductor can show strong luminescence.
  • a group ll-VI e.g. ZnO, ZnS, ZnSe, CdS, CdTe, CdSe etc
  • a group I l-V eg GaN, GaAs, AIN, InN etc
  • nanostructured materials e.g. such as metallic, semiconductor and dielectric materials and combinations thereof, which can show many different types of luminescence such as fluorescence, phosphorescence, elastic and inelastic scattering.
  • the predetermined output radiation to be detected when authenticating a security device incorporating this substance can be regarded as that falling within the output waveband which has a width of about 40 nm.
  • the wavebands of the input and output radiation of Er-Yb-KGP are thus relatively narrow. This is advantageous.
  • the machine readable substance may take the form of particles, pigments or a dye which can be incorporated into a material such as curable material forming embossing layer 14.
  • the size of the particles or pigments should preferably be sufficiently small and/or their concentration should be sufficiently low to avoid introducing optical scatter.
  • Additional optically variable devices or materials can be included in the security device such as thin film interference elements, liquid crystal material and photonic crystal materials. Such materials may be in the form of filmic layers or as pigmented materials suitable for application by printing. If these materials are transparent they may be included in the same region of the device as the security feature of the current invention or alternatively and if they are opaque may be positioned in a separate laterally spaced region of the device.

Landscapes

  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Finance (AREA)
  • Accounting & Taxation (AREA)
  • Business, Economics & Management (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Printing Methods (AREA)
  • Optical Elements Other Than Lenses (AREA)
  • Control Of Vending Devices And Auxiliary Devices For Vending Devices (AREA)
  • Burglar Alarm Systems (AREA)
  • Credit Cards Or The Like (AREA)

Abstract

Un dispositif de sécurité est divulgué, comprenant : un substrat (12) ; une structure en relief (20) sur un premier côté du substrat, la structure en relief étant une structure en relief de redirection de lumière réfléchissante ou réfractrice conçue pour rediriger une lumière provenant d'une source de lumière, ce qui permet de projeter une image caustique ; et un filtre coloré (30). Le filtre coloré est conçu pour chevaucher, lors de l'utilisation, au moins une partie de la structure en relief, et comprend un ou plusieurs matériaux au moins semi-transparents, au moins l'un des matériaux transmettant uniquement un sous-ensemble de longueurs d'onde de lumière visible correspondant à une couleur non blanche respective. L'image caustique projetée par le dispositif de sécurité présente une ou plusieurs couleurs lorsque le dispositif de sécurité est éclairé à l'aide d'une lumière blanche.
EP21827634.3A 2020-12-09 2021-12-08 Dispositif de sécurité et son procédé de fabrication Pending EP4259450A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB2019383.5A GB202019383D0 (en) 2020-12-09 2020-12-09 Security device and method of manfacture thereof
PCT/GB2021/053209 WO2022123241A1 (fr) 2020-12-09 2021-12-08 Dispositif de sécurité et son procédé de fabrication

Publications (1)

Publication Number Publication Date
EP4259450A1 true EP4259450A1 (fr) 2023-10-18

Family

ID=74166039

Family Applications (1)

Application Number Title Priority Date Filing Date
EP21827634.3A Pending EP4259450A1 (fr) 2020-12-09 2021-12-08 Dispositif de sécurité et son procédé de fabrication

Country Status (4)

Country Link
EP (1) EP4259450A1 (fr)
AU (1) AU2021397868A1 (fr)
GB (2) GB202019383D0 (fr)
WO (1) WO2022123241A1 (fr)

Family Cites Families (29)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4434010A (en) 1979-12-28 1984-02-28 Optical Coating Laboratory, Inc. Article and method for forming thin film flakes and coatings
IN157644B (fr) 1981-02-19 1986-05-10 Portals Ltd
NL193903C (nl) 1981-08-24 2001-02-05 Commw Scient Ind Res Org Verbeterde bankbiljetten en dergelijke.
DE4314380B4 (de) 1993-05-01 2009-08-06 Giesecke & Devrient Gmbh Sicherheitspapier und Verfahren zu seiner Herstellung
AT401365B (de) 1993-10-11 1996-08-26 Oesterr Nationalbank Wertpapier
DE4334847A1 (de) 1993-10-13 1995-04-20 Kurz Leonhard Fa Wertdokument mit Fenster
EP0657297B2 (fr) 1993-12-10 2003-04-23 Agfa-Gevaert Document de sécurité ayant un support transparent ou translucide et contenant des pigments d'interference
GB9828770D0 (en) 1998-12-29 1999-02-17 Rue De Int Ltd Security paper
DE10163381A1 (de) 2001-12-21 2003-07-03 Giesecke & Devrient Gmbh Sicherheitspapier sowie Verfahren und Vorrichtung zu seiner Herstellung
GB2388377B (en) 2002-05-09 2004-07-28 Rue De Int Ltd A paper sheet incorporating a security element and a method of making the same
EP1398174A1 (fr) 2002-09-10 2004-03-17 Kba-Giori S.A. Substrat renforcé pour papiers de valeur
EP1422283B1 (fr) 2002-11-02 2014-03-05 Merck Patent GmbH Matériau à cristaux liquides imprimable
AU2014256335B2 (en) 2009-11-27 2015-08-06 Basf Se Coating compositions for security elements and holograms
JP6271855B2 (ja) * 2013-04-16 2018-01-31 興和紡株式会社 印刷物
EP2963463A1 (fr) * 2014-07-02 2016-01-06 Ecole Polytechnique Fédérale de Lausanne (EPFL) Conception de surface de réfraction
DE102014011692A1 (de) * 2014-08-07 2016-02-11 Giesecke & Devrient Gmbh Sicherheitselement mit photochromem Farbstoff
MA42899A (fr) 2015-07-10 2018-05-16 De La Rue Int Ltd Procédés de fabrication de documents de sécurité et de dispositifs de sécurité
GB2542783B (en) 2015-09-29 2018-02-07 De La Rue Int Ltd Security print media and method of manufacture thereof
GB2547717B (en) 2016-02-29 2020-09-16 De La Rue Int Ltd Security elements and security documents
GB2557167B (en) * 2016-09-30 2020-03-04 De La Rue Int Ltd Security devices
EP3366474B1 (fr) 2017-02-22 2020-06-24 KBA-NotaSys SA Presse à imprimer avec dispositif de coulée en ligne pour la réplication et la formation d'une structure micro-optique
GB2564122B (en) * 2017-07-04 2021-01-13 De La Rue Int Ltd Optical devices and methods for their manufacture
PT3687825T (pt) * 2017-09-29 2022-01-10 Sicpa Holding Sa Elemento de segurança óptico
MA52447B1 (fr) * 2017-09-29 2021-11-30 Sicpa Holding Sa Élément mince de sécurité optique et son procédé de conception
GB2572746B (en) 2018-03-22 2021-10-27 De La Rue Int Ltd Security elements and method of manufacture thereof
DE102018005447A1 (de) * 2018-07-09 2020-01-09 Giesecke+Devrient Currency Technology Gmbh Optisch variables Sicherheitselement mit reflektivem Flächenbereich
EP3860861B1 (fr) * 2018-10-05 2023-06-07 Sicpa Holding Sa Éléments de sécurité optique, objet marque, procédé d'authentification d'un objet et utilisation d'éléments de sécurité optique pour authentifier ou protéger contre la contrefaçon
CN112805156B (zh) * 2018-10-05 2022-07-26 锡克拜控股有限公司 设计焦散层的光重定向表面的方法、包括所设计的焦散层的光重定向表面的光学安全元件、被标记的物品、认证该物品的用途及方法
WO2020083794A1 (fr) 2018-10-25 2020-04-30 Basf Se Compositions comprenant des nanoplaquettes d'argent

Also Published As

Publication number Publication date
GB2604011A (en) 2022-08-24
AU2021397868A1 (en) 2023-06-22
GB202117708D0 (en) 2022-01-19
WO2022123241A1 (fr) 2022-06-16
GB202019383D0 (en) 2021-01-20
AU2021397868A9 (en) 2024-08-08
GB2604011B (en) 2023-05-03

Similar Documents

Publication Publication Date Title
CN108538187B (zh) 一种组合荧光图案及其应用
DK2643162T3 (en) Value document and / or security document as well as method for making the same
EP3648982B1 (fr) Dispositifs optiques et leurs procédés de fabrication
US20230347679A1 (en) Security devices and method of manufacture thereof
EA014543B1 (ru) Защитное устройство
US20210260909A1 (en) Security devices and methods of authentication thereof
EP3774374B1 (fr) Dispositif optique et son procédé de fabrication
US10780728B2 (en) Secure article comprising a combined image and/or a revelation screen
US20220144006A1 (en) Security device and method of manufacture thereof
AU2021397868A9 (en) Security device and method of manufacture thereof
US20240025194A1 (en) Security device and method of manufacture thereof

Legal Events

Date Code Title Description
STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: UNKNOWN

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE INTERNATIONAL PUBLICATION HAS BEEN MADE

TPAC Observations filed by third parties

Free format text: ORIGINAL CODE: EPIDOSNTIPA

PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: REQUEST FOR EXAMINATION WAS MADE

17P Request for examination filed

Effective date: 20230628

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

DAX Request for extension of the european patent (deleted)
RAV Requested validation state of the european patent: fee paid

Extension state: MA

Effective date: 20230628

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: EXAMINATION IS IN PROGRESS

17Q First examination report despatched

Effective date: 20240718