Safety device and method of manufacturing the same

Abstract

A security device is disclosed, comprising: a substrate having opposite first and second surfaces; a surface relief structure on the first surface of the substrate, the surface relief structure being formed from one or more cured, at least semi-transparent materials; a printed layer on the second surface of the substrate. In at least a first region of the security device, the substrate is transparent or translucent in at least part of the at least first region, the surface relief structure and the printed layer are each defined according to a common image and are aligned with one another, the surface relief structure presents a first set of features of the common image, and the printed layer presents a second set of features of the common image. The common image is presented by the surface relief structure and the printed layer in combination with one another, and the surface relief structure provides a tactile sensation for the common image.

Description

[0001] Cross Reference to Related Applications

[0002] The entire contents of each of the following six international patent applications, filed on 10 September 2021 in the name of De La Rue International Limited and claiming priority from the following UK patent applications (all filed on 11 September 2020), are incorporated herein by reference: GB2014325.1, GB2014326.9, GB2014327.7, GB2014328.5, GB2014329.3, GB2014330.1 and GB2014331.9. TECHNICAL FIELD

[0003] The present invention relates to security devices, such as can be used as indicia of authenticity associated with valuable articles, such as security documents including banknotes, passports, certificates, licences and the like. Methods for manufacturing the security devices are also disclosed. BACKGROUND

[0004] Typically, valuable articles, especially valuable documents, such as banknotes, cheques, passports, identity documents, certificates and licences are provided with a number of visible security devices for checking the authenticity of the article. Examples include features based on one or more patterns, such as microtext, fine line patterns, latent images, louver 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 shift or luminescent / fluorescent inks. What all such devices have in common is that the visual effect presented by the device is extremely difficult or impossible to reproduce using available reproduction techniques, such as photocopying. Security devices which present invisible effects, such as magnetic materials, can also be employed.

[0005] One class of security devices which is widely used in banknotes and other documents is intaglio printing. For example, many of the banknotes in circulation carry images, such as portraits or architectural scenes, applied by intaglio printing. Typically, the whole or part of the image is formed from an array of image elements, such as fine lines or dots, which can be individually discerned under close inspection and / or magnification. The intaglio printing technique not only ensures high resolution and accurate reproduction of the image, which prevents the production of circulatable counterfeit notes by readily available commercial printing techniques, but can also be used to impart a tactile quality to the image. This significantly increases the level of security, since a potential counterfeiter can use a highly accurate printing system which can reproduce the visual appearance of the intaglio printing, but not its three-dimensional quality, and hence not its tactile (haptic) feel. On the other hand, due to the nature of intaglio printing, it is difficult to produce images in more than one colour, at least in a fully controllable manner.

[0006] In addition, in other classes of security devices, it is known that casting of curable materials, such as UV resins, can produce a high haptic effect. However, due to the nature of casting a single resin, the final feature will be colourless or monochromatic. To increase security, it is better to have a multi-coloured haptic feel. SUMMARY

[0007] The present invention provides a security device, the security device comprising:

[0008] a substrate having opposite first and second surfaces;

[0009] a surface relief structure on the first surface of the substrate, the surface relief structure being formed from one or more cured, at least translucent materials; and

[0010] a printed layer on the second surface of the substrate;

[0011] wherein, in at least a first region of the security device, the substrate in at least part of the at least first region is transparent or translucent, the surface relief structure and the printed layer are each defined according to a common image and are aligned with each other, the surface relief structure presents a first set of features of the common image, and the printed layer presents a second set of features of the common image, whereby the common image is presented by the surface relief structure and the printed layer in combination with each other, and the surface relief structure provides a haptic feel to the common image.

[0012] The present invention also provides a method of manufacturing a security device, the method comprising the following steps performed in any order or simultaneously:

[0013] forming a surface relief structure on the first surface of the substrate from one or more at least translucent curable materials, and

[0014] printing a printed layer onto the second surface of the substrate,

[0015] wherein, in at least a first region of the security device, the substrate in at least part of the at least first region is transparent or translucent, the surface relief structure and the printed layer are each defined according to a common image and are aligned with each other, the surface relief structure presents a first set of features of the common image, and the printed layer presents a second set of features of the common image, whereby the common image is presented by the surface relief structure and the printed layer in combination with each other, and the surface relief structure provides a haptic feel to the common image.

[0016] Accordingly, embodiments of the present application envisage tactile embossing of a curable material (e.g. a UV cast resin) on one side of a substrate, which tactile embossing is combined with register offset printing on the opposite face. (If desired, the offset printing can be RGB for full colour images). The term "offset" printing is used herein to refer to lithographic printing in which one or more colours to be printed are applied to a patterned printing plate. The ink is then transferred to a blanket roller from which the print is applied to the substrate. However, although lithographic printing is preferred, other printing techniques can also be used to form the printed layer of the present application, as discussed below.

[0017] The present inventors have recognised that the high resolution and complex colour artefacts achievable in images printed by photolithography or other comparable printing techniques cannot be reproduced in relief alone, and vice versa, the tactile sensation of a relief cannot be reproduced by photolithography alone. By combining a cured surface relief structure with a printed layer to display an image in the manner defined above, the resulting security device has a tactile sensation and at the same time can present any desired arrangement of one or more colours in a controllable and reproducible manner. Since the surface relief structure and the printed layer are on opposite surfaces of the substrate, they can be applied with very high register between them, meaning that their relative positions are identical on every copy of the security device produced. For example, the translational register between the surface relief structure and the printed layer in the machine direction and / or the cross direction is preferably such that any misregister is too small to be visible to the naked eye, for example no more than + / - 75 pm. The skew register between the surface relief structure and the printed layer is preferably 1 degree or less, more preferably 0.1 degrees or less, still more preferably 0.05 degrees or less, most preferably 0.02 degrees or less.

[0018] The steps of forming the surface relief structure and the printed layer can be performed one after the other (in either order, with or without intervening steps) or simultaneously at any one lateral location on the substrate, as discussed further below. The printed layer can be applied by a planar printing technique (i.e. one which does not cause a significant tactile sensation), such as offset printing, and so this technique can be selected to achieve the desired visual effect (such as multiple colours) without the limitations of a relief process, whilst the cured surface relief structure provides the desired tactile sensation. This not only allows greater design freedom, but also enables more complex security devices to be formed with a corresponding higher level of security.

[0019] It will be understood that the common image presented by the security device is formed by the combined viewing of the surface relief structure and the printed layer (i.e. simultaneously - either the surface relief structure is between the printed layer and the viewer, or the printed layer is between the surface relief structure and the viewer). That is, the common image is a composite static macroscopic image resulting from the spatial arrangement of the surface relief and the printed layer - no composite magnification or other optically variable effect is generated. In at least a portion of the first region (where the common image is presented), the substrate will be transparent or translucent so as to enable viewing of the combination in this way. Depending on the optical density of the substrate or other superposed layers present (if any), the common image can be visible under reflected light or only under transmitted light. By "transmissive" is meant that the substrate is substantially optically clear, i.e. results in low or zero optical scattering, although it can carry a visible tint. By "translucent" is meant that some light can pass through the substrate but will be scattered. If the relevant portion of the substrate is translucent, its optical density must be low enough so that the surface relief structure and the printed layer can be viewed simultaneously by the naked eye under transmitted light. Standard paper banknote substrates and standard polymeric banknote substrates (with an opaque layer) meet this requirement. At least a portion of the first region can correspond to a window or semi-window region of the substrate (i.e. a region having a lower optical density relative to the remainder of the substrate), but this is not essential as discussed further below. In some embodiments, the substrate is transparent or translucent over the first region of the security device. If desired, the entire substrate can also be transparent or translucent.

[0020] It should be noted that, due to the presence of the base layer, the cast for the haptics will be different from a simple printed haptic - this will have an impact on the colour of the device (whether bright, dyed or pigmented). In other words, the cast-cured surface relief structure will comprise a continuous body of cured material (one or more types) having a different profile of heights - for example, if it comprises raised protrusions, these will be connected to each other by the base layer of lower height. This will not be the case in products having haptic protrusions formed by local printing of the material. The continuous nature of the cast relief structure needs to be taken into account in the design of the security device to achieve the desired optical effects as described below.

[0021] The surface relief structure and the printed layer each present a set of features of the common image (in other words, at least a portion of the common image). A "feature" of the common image is a content defining an information content of the common image, which can include any of the following: a line or edge dividing an object in the image; the object itself; an area of a contour or shading; a shape or portion thereof; an alphanumeric character or symbol, or a portion thereof, etc. The nature of the feature will depend on the image content. Examples will be given below.

[0022] Depending on the implementation, the surface relief structure and the printed layer can contribute to the common image to varying degrees. In some preferred implementations, it can be desirable for each of the two components of the security device to display the entire common image - that is, the surface relief structure and the printed layer each define the same image as one another. In this case, the first and second sets of features are the same as one another, the surface relief structure and the printed layer each present all of the features of the common image. It will be understood that the surface relief structure and the printed layer will be superposed in register, such that corresponding features have the same lateral position in both components of the security device.

[0023] In other preferred implementations, the first and second sets of features are different from one another, the first set of features and / or the second set of features being a subset of the features of the common image. In other words, the surface relief structure can present a first portion of the common image, while the printed layer presents a second portion, these portions being different from one another and can be separate, overlapping or interleaved. Thus, in one example, the printed layer can present the complete common image, while the surface relief structure presents only a portion thereof, and vice versa. Alternatively, each component can present only a portion of the common image, with the complete image only being apparent when the two are combined. Preferably, one or more of the features of the common image are included in both the first and second sets of features, and are presented by both the surface relief structure and the printed layer. Again, it will be understood that the surface relief structure and the printed layer will be superposed in register, such that corresponding features have the same lateral position in both components of the security device.

[0024] The selection of features contributed by the surface relief structure and the selection of features contributed by the printed layer can be decided in a number of ways. In some cases, the division can be arbitrary. However, in preferred examples, the first set of features comprises features of the common image that are located in a first portion of the common image, and the second set of features of the common image comprises features of the common image that are located in a second portion of the common image, the first and second portions being different from one another, preferably laterally offset from one another. The first and second portions are preferably each a single contiguous region of the image. For example, the first portion can correspond to the entire lateral extent of the common image, while the second portion is only a sub-region thereof (or vice versa). By "laterally offset" is included (only) partially overlapping one another or not overlapping one another at all (e.g. the first and second portions can be spaced apart from one another or abut one another). For example, the surface relief structure can contribute half of the common image, while the printed layer can contribute the other half of the common image.

[0025] These principles can be used to design security devices with visual and tactile effects that interact with each other in unexpected ways. For example, a user might expect the tactile areas of a device to match the visible features of the device. However, the device can be designed so that this is not the case, and there is a deliberate mismatch between the two components - for example, a selected visible sub-portion of the device can be configured to be touchless, or a tactile sub-portion can be located where the printed layer makes no visible contribution. These memorable and distinctive features can be overlooked by a potential counterfeiter.

[0026] In yet further implementations, the first set of features preferably corresponds to a first colour component of the common image, and the second set of features preferably corresponds to at least a second colour component of the common image. In this case, the overall range of the two compositions can overlap to a large extent, but at a microscopic scale, the configuration of each composition will differ in order to provide the desired colour for each point of the common image.

[0027] Preferably any of:

[0028] The first set of features of the common image, presented by the surface relief structure, preferably by the entire surface relief structure, is laterally entirely within the bounds of the second set of features of the common image, presented by the printed layer; and / or

[0029] The second set of features of the common image, presented by the printed layer, preferably by the entire printed layer, is laterally entirely within the bounds of the second set of features of the common image, presented by the surface relief structure.

[0030] These options all encompass the case where the surface relief structure and the printed layer share the same bounds. It should be noted that the surface relief structure and / or the printed layer can continue beyond the common image (this applies to all implementations), but in this case will be configured differently beyond the common image so that the common image remains distinct. Examples will be provided below. In other implementations, it can be preferable for the surface relief structure and / or the printed layer to be absent beyond the common image for maximum visual distinction.

[0031] In some implementations, the cast surface relief structure (or a portion thereof) can be one or more single volumes of material that are raised above the base layer, for example each defining a surface whose height varies, optionally in a continuous, gradual or stepwise manner. However, in other cases, the surface relief structure can comprise a plurality of discrete raised portions. In preferred implementations, the common image is defined at least in part by an array of image elements that are spaced apart from each other, and:

[0032] The surface relief structure comprises a plurality of raised elements that are spaced apart from each other, the plurality of raised elements forming image elements that define the first set of features of the common image; and / or

[0033] The print layer comprises a plurality of print elements spaced apart from one another, the plurality of print elements forming image elements defining a second set of features of a common image.

[0034] Formation of the common image from an array of image elements enables the security device to more closely mimic conventional intaglio printing, as intaglio images typically comprise line work or other screened artefacts. The image elements are visually distinguishable from one another, although this can require close inspection and / or low level magnification to discern. The image elements can be expressed by one or both of the surface relief structure and the print layer. If both, then the corresponding image elements defined in each component will be in overlapping alignment.

[0035] Preferably, the common image is a screened image, the image elements varying in size, shape, colour, optical density and / or pitch across the array to express the common image, the array of image elements preferably being arranged on a regular grid. The image elements can advantageously be linear or curvilinear line elements, dot elements or elements having a marked shape, the marked shape preferably being an alphanumeric or printed symbol (e.g. a currency symbol such as “￡”, “$”, etc.). For example, the image elements can define line work (e.g. akin to a conventional line intaglio image) or a dot screen of image elements, such as a halftone screen. The image can comprise a moire pattern. Desirably, the image is a portrait or architectural drawing. Preferably, the image is a 3D object or scene. In embodiments where the image is a screened image, the elements of the image are preferably arranged on a regular grid, although typically the elements can or can not be arranged on a regular grid.

[0036] As noted above, the cast-cured surface relief structure will comprise a continuous body of cured material having a varying height profile. The particular profile will depend on the desired image and / or haptic pattern. In preferred implementations, the surface relief structure comprises a plurality of spaced-apart protrusions connected to one another by a base layer of lesser height. The protrusions may, for example, correspond to the image elements of the common image just described. Advantageously, the base layer can extend over a peripheral region (away from the common image) surrounding the plurality of spaced-apart protrusions. Typically, any such peripheral region will be narrow, extending for between 0.01 mm and 5 mm, for example, from the edge of the common image. In preferred examples, the ratio of the height of at least one protrusion to the height of the base layer connecting the raised element to an adjacent protrusion is at least 10, preferably at least 20, and furthermore preferably no greater than 400, preferably no greater than 200. In some embodiments, the ratio of the height of each protrusion to the height of the base layer is at least 10, preferably at least 20, and furthermore preferably no greater than 400, preferably no greater than 200. This is particularly the case where the protrusions are configured to form image elements, in particular image elements of a multi-tone image.

[0037] The tactile effect of the security device can also be configured to interact with other tactile elements on the security document. For example, the disclosed security device can be provided on a document substrate that also bears a traditional intaglio feature, on the same surface of the substrate as the surface relief structure formed by the cured material (e.g., both can be adjacent to one another). The overall appearance formed by the combination of the disclosed security device and intaglio printing can be a complex tactile image, with lower complexity images, haptics, and colors provided by the intaglio feature, and higher complexity images, haptics, and colors provided by the disclosed security device. For example, the disclosed device can present a common image in the form of a photographic portrait, while the intaglio printing can provide a patterned (relatively low complexity) background around the portrait, for example in the form of a coarse intaglio line structure.

[0038] As noted at the outset, some advantages of the present invention are to provide greater design freedom in the colors and better color arrangements presented by the device. That is, rather than applying large blocks of each color (as in traditional intaglio printing), individual lines or dots of an image can each have a different color, if desired. Possible implementations in preferred embodiments include:

[0039] • Color combinations using dyed or colored UV cast resin

[0040] • Dyed resin can be combined with offset printing colors to produce 4th, 5th, or 6th colors

[0041] • Dyed resin can be embossed at different heights to increase / decrease color intensity for better definition / color combinations

[0042] The common image can be of any type, including block colors / shapes, alphanumeric text, or “macro” images without fine detail. Preferably, however, the common image is a multi-tone and / or multi-colored image, most preferably a grayscale image or a full-color image. Such images can mimic or even improve the appearance of traditional intaglio printing.

[0043] In many preferred implementations, at least one of the curable materials is colorless (to the naked eye, under standard white illumination), and the printed layer presents one or more visible colors. Most preferably, the printed layer is an RGB (red, green, blue) or CMYK (cyan, magenta, yellow, black) printed layer. However, other color combinations can also be used, such as orange, green, and violet. It will be understood that the printed layer can be laid down in one or more printed articles (this applies to all embodiments).

[0044] In other preferred implementations, the at least one curable material carries a tint of a first colour and the printed layer presents at least the first colour and / or a (different) second colour, preferably configured such that, when viewed in combination, a multi-coloured version of the common image is visible. It should be noted that, if desired, the surface relief structure can be formed from a plurality of curable materials, each forming a different lateral portion of the structure, which materials can carry different tinted colours to introduce a further level of complexity. The printed layer can also present more than two different colours.

[0045] In one particularly preferred implementation, the first colour is one of red, green and blue and the printed layer presents the other two of red, green and blue such that, when viewed in combination, a full-colour version of the common image is visible. In another particularly preferred implementation, the first colour is one of cyan, magenta, yellow and black and the printed layer presents the other three of cyan, magenta, yellow and black such that, when viewed in combination, a full-colour version of the common image is visible.

[0046] Advantageously, the printed layer presents two regions of different respective colours and presents an intermediate region in which the colour gradually transitions between the different respective colours, preferably in a manner that is continuous even under magnification. This achieves a visual effect similar to the "rainbowing" in traditional lithographic security printing, but with the added benefit of a tactile sensation. "Rainbowing" is not possible via traditional intaglio printing because the viscous nature of intaglio inks prevents their mixing as they are laid down within the recesses of the intaglio printing plate. It has therefore not previously been possible to produce a tactile "rainbow" coloured image, and so this implementation provides a new security effect that is not achievable by traditional means.

[0047] The surface relief structure and the printed layer can be configured such that they combine visually to present the same appearance no matter which direction around the device it is viewed from (i.e. from the surface relief structure side or from the printed layer side). However, in other preferred implementations, it can be desirable to produce different appearances, one viewable from each side. In this case, the common image will be presented at least on one side of the device. For example, in a preferred example, the at least one curable material carries a tint of at least one colour and the printed layer has a visual opacity such that the colour appearance of the common image is different when the security device is viewed from the side of the surface relief structure than when the security device is viewed from the side of the printed layer. That is, the printed layer is sufficiently opaque such that it blocks the visibility of the surface relief structure through it, resulting in a different appearance.

[0048] The print layer can be applied using standard, visible, pigmented inks. To further increase the level of security, in other embodiments the print layer can comprise one or more substances that are responsive to non-visible wavelengths (preferably UV or IR), the print layer optionally being invisible under white light illumination. For example, the print layer can comprise a pair of inks that appear to match one another under one illumination condition (e.g. white light) and to differ from one another under another illumination condition (e.g. UV light). Examples of suitable materials that can form the print layer are disclosed in WO-A-2004 / 050376 and WO-A-2018 / 206936. In other examples, the print layer can contain substances that emit red, green and blue light under illumination corresponding to the excitation wavelength band, thereby presenting a full-colour version of the common image. Examples of suitable substances are disclosed in WO-A-2020 / 030893.

[0049] The variation in height (and / or other dimensions / shape) of the cured material over the surface relief structure can be arbitrary or otherwise independent of the common image (the first set of features being expressed primarily by the lateral configuration of the surface relief rather than its height). For example, the features of the common image presented by the surface relief structure can all be expressed by protrusions having the same height from one another, spaced apart by the base layer. However, in preferred embodiments the height, width, length and / or geometry of the surface relief structure varies according to the common image. This can be used, for example, to link the tactile feel of the surface relief structure to certain parts of the common image, or to emphasise the three-dimensional quality of the image. In examples, the common image can depict a three-dimensional object, such as a portrait of a person, the features corresponding to parts of the object closer to the viewer corresponding to parts of the surface relief structure having higher height, and vice versa. The surface relief can comprise a single raised element having different heights, or multiple discrete elements having different heights from one another and / or having a height that varies within one element.

[0050] As mentioned above, one or both components of the security device can be used to provide additional visual effects (preferably further security effects) beyond those provided by the common image - for example, one or both components can continue beyond the common image if desired. Thus, in some preferred embodiments the security device further comprises a second region in which one or both of the surface relief structure and the print layer are present, the second region being laterally offset from and not overlapping with the first region, or interleaved with the first region. In the second region, the surface relief structure and / or the print layer have a respective configuration that is different from their arrangement in the first region, such that the common image remains visibly distinct from the second region. For example, the surface relief structure and the print layer preferably do not display aligned, matching features in the second region. Neither component in the second region presents a static common image (as in the first region).

[0051] It should be noted that the surface relief structures and / or the print layer can or can not be continuous between the first and second regions of the security device. For example, there can be a gap between the surface relief structures in the first region and the surface relief structures in the second region. However, all of the surface relief structures (in both regions) will be produced in the same pass and from the same casting tool, preferably from the same curable material. The first and second regions can be finally disposed in one and the same window (or half-window) region on the security document, or can each be disposed in a different respective window (or half-window) region. In the latter case, the respective window (or half-window) regions will be separated from each other by a region of lower transparency of the security document.

[0052] In preferred embodiments, in the second region, the surface relief structures are present and form any one of the following: one or more optical elements, such as focusing elements, facets, prisms, pyramids or caustic elements, preferably an array of such optical elements; haptic structures or matte structures. Advantageously, in the second region, the print layer is present and forms any one of the following: background printing, a visually uniform region, a colour shift layer, a printed colour filter and an image array, such as a microimage array or an interlaced image. It is particularly advantageous to provide the print layer in the form of a colour shift layer, wherein the surface relief structures comprise an array of prisms and the colour shift layer is configured to interact with the array of prisms. Examples of suitable colour shift layers that can be printed include layers comprising liquid crystals (e.g. liquid crystal pigments), interference pigments (including magnetically oriented interference pigments), pearlescent pigments or photonic pigments.

[0053] It is particularly advantageous if, in the second region, the surface relief structures form an array of focusing elements and the print layer forms an image array located substantially in the focal plane of the focusing elements, and the array of focusing elements and the image array are configured to cooperate with each other to produce an optically variable effect. In this way, an additional optically variable security device can be provided on the substrate in the same manufacturing step as that which provides the security device already described. By optically variable, it is meant that the appearance of the device is different from different viewing angles, and thus cannot be mimicked by standard copying (e.g. photocopying or scanning).

[0054] The present application also provides a plurality of substantially identical security devices, each security device being as described above, in each of which the respective surface relief structure and printed layer have the same position relative to each other. This is due to the two components being accurately registered to each other during manufacture. By "same position" is meant that the relative position of the respective surface relief structure and printed layer varies by an amount that is not detectable by the naked eye between the security devices, if at all. For example, the translational registration in the machine or cross directions can be + / - 75 pm or less. The skew registration is preferably 1 degree or less, more preferably 0.1 degrees or less, still more preferably 0.05 degrees or less, most preferably 0.02 degrees or less. The plurality of security devices will typically be produced on the same production line and according to the same design sequence - for example, the plurality can comprise a whole batch of security devices, or an entire print run. The plurality can comprise at least 10 security devices, more preferably at least 100 security devices. Each of the plurality of security devices can end up on a different security document.

[0055] In a preferred method of manufacturing a security device according to the present application, the forming of the surface relief structure and the printing of the printed layer are performed in registration with each other. Again, preferably, any misregistration is less than can be seen by the naked eye. For example, the translational registration in the machine or cross directions can be + / - 75 pm or less. The skew registration is preferably 1 degree or less, more preferably 0.1 degrees or less, still more preferably 0.05 degrees or less, most preferably 0.02 degrees or less. This is preferably achieved by performing the two steps in one online process on the same equipment. When performing the two steps, the substrate can be processed in web form, but more preferably in the form of individual sheets. Most preferably, the forming of the surface relief structure and the printing of the printed layer are simultaneous, occurring at the same position in the machine direction. This achieves the highest level of registration between the two components of the security device, as there is no slippage or distortion of the substrate occurring after one step is performed and before the other step is performed (as there is no interval between them). Suitable equipment for simultaneous cast-cure and printing on opposite sides of a substrate is disclosed in WO-A-2018 / 153840 and WO-A-2017 / 009616. The level of registration that can be provided using the equipment disclosed therein by simultaneous casting and printing cannot be achieved on a rotary printing press or in two separate processes.

[0056] The print layer can be applied by any selected printing technique that can achieve the desired resolution and number of colours. A flat printing technique will generally be selected, i.e. one that does not result in embossing of the substrate. In preferred embodiments, the print layer is printed by lithographic printing, but other printing methods such as flexographic printing, screen printing, gravure printing or microgravure printing can alternatively be used (none of which involve embossing of the substrate). It will be appreciated that the print layer can comprise a plurality of printed articles laid down in succession or (preferably) simultaneously, e.g. from a collection roller or blanket, each printed article possibly formed from a different material (e.g. a different ink colour).

[0057] Preferably, the surface relief structure is formed by cast-curing one or more at least semi-transparent curable materials on the first surface of the substrate. In preferred embodiments, the surface relief structure is cast-cured by:

[0058] providing a casting tool having a mould relief defined therein corresponding to the surface relief structure;

[0059] applying one or more at least semi-transparent curable materials to the casting tool or the substrate;

[0060] contacting the casting tool and the substrate with the one or more at least semi-transparent curable materials therebetween, thereby forming (i.e. shaping) the one or more at least semi-transparent curable materials into the surface relief structure; and

[0061] causing the one or more at least semi-transparent curable materials to cure to leave the surface relief structure during and / or after the contacting.

[0062] The mode of curing will depend on the type of curable material used. In a preferred example, the material is radiation-curable (e.g. UV-curable) and the curing step will involve irradiating the material with radiation of an appropriate wavelength to cause cross-linking of the material.

[0063] In many preferred implementations, the at least semi-transparent curable material is applied to the mould relief of the casting tool so as to substantially completely fill the recesses of the mould relief and form a layer of the at least semi-transparent curable material on the raised portions of the relief structure. Substantially the entire body of curable material (including the portions inside the recesses and the layer over the raised portions) will be cured and transferred to the substrate. In such implementations, there is no wiping or scraping step to remove curable material from the raised portions.

[0064] However, in alternative examples, the curable material can be applied only to the recesses of the relief structure of the casting tool, preferably by using a removal device such as a doctor blade, and the method further comprises, after applying the one or more curable materials to the relief structure and before bringing the substrate and the casting tool together, applying a further layer of the curable material or another curable material to substantially the entire surface of the casting tool to improve the retention of the cured material on the substrate. In such examples, the further layer serves to improve the adhesion of the curable material (which is only located within the recesses of the relief structure of the casting tool) to the substrate. When the further layer is applied substantially to the entire surface of the casting tool (i.e. on the filled recesses of the relief structure and the landings between them in the surface of the tool), the resulting surface relief structure comprises an integral base layer as described above. The curable material of the further layer can be the same one or more curable materials as used to form the elements of the surface relief structure, or can be a different curable material.

[0065] The method of manufacture can be configured to provide a security device having any of the preferred features described above.

[0066] The present application also provides a security document comprising a document substrate and a security device on the security substrate, the security device being a security device according to the present application, wherein the document substrate can or can not act as a substrate for the security device, the document substrate preferably comprising paper, polymer, cellulose or a mixture thereof. Suitable substrate materials formed from regenerated cellulose are disclosed, for example, in WO-A-2020156655. It will be understood that the security document can thus comprise a single substrate which acts as both the document substrate (i.e. a self-supporting sheet which forms the body of the document) and the security device substrate (i.e. a security device substrate which carries a surface relief structure on one surface and a printed layer on the other surface). In this case, the document substrate will need to be transparent or translucent, at least at the location of the security device. To this end, the entire document substrate can be sufficiently translucent, or it can comprise a window / half-window region for this purpose. Alternatively, the security document can comprise two substrates - a document substrate and a security device substrate which carries the security device and which is attached to or incorporated into the document substrate. In this case, the document substrate can be transparent, translucent or opaque.

[0067] The common image can be located anywhere on the security document - entirely inside or outside the window / half window area (if one is provided), or partially inside and partially outside the window / half window area (if one is provided). In preferred embodiments, the first region of the security device is at least partially located in a window or half window area of the document substrate, which has a lower optical density than the surrounding area of the window or half window area. In other preferred embodiments, the document substrate is translucent and the first region of the security device is at least partially located in a non-window area of the document substrate. In the case where the security device is not formed directly on the document substrate, the substrate of the security device is preferably attached to or incorporated into the document substrate, preferably on a transparent or translucent area of the document substrate which is optionally formed as an aperture.

[0068] The appearance of the common image can differ in reflected light versus transmitted light and / or from either side of the security document, and in preferred embodiments this can be influenced by the opacity of the security document at the location of the security device. For example, parts of the same security device can provide different sets of appearances depending on whether they are located in a (transparent) window area, a (highly) translucent half window area, or a (less translucent or opaque) non-window area. By providing multiple different arrangements on one security document, this can be used to create more complex combinations of appearances. Thus, preferably the first region comprises parts located in at least two of: a window area of the document substrate, a half window area of the document substrate, and a non-window area of the document substrate, respectively.

[0069] Similarly, it can be desirable to provide more than one security device as disclosed above on a security document to achieve more complex combined effects. Thus, preferably the security document comprises at least two security devices, each as described above, wherein the at least two security devices are at least partially located in at least two of: a window area of the document substrate, a half window area of the document substrate, and a non-window area of the document substrate, respectively.

[0070] The document substrate can be of any type, including a fibrous substrate such as paper or cellulose (as disclosed in WO-A-2020156655) or a non-fibrous substrate such as a polymer (or a mixture of both). In preferred examples, the document substrate comprises a core polymer substrate having at least one opaque layer disposed on one or both surfaces of the core polymer substrate, optional gaps in one or more of the opaque layers forming a window or half window area of the document substrate. For example, the security document can be a polymer banknote. The opaque layer is preferably a non-fibrous material such as a coating comprising a binder containing light-scattering pigments, preferably in white, off-white or grey colour (such as Ti02).

[0071] In some embodiments, the document substrate can also comprise an integral printed indicium, which is preferably located between the at least one opaque layer and the core polymeric substrate. A "printed indicium" (as opposed to the printed layer described above) is incorporated into the substrate during its production, rather than during its later processing into a security document. For example, the printed indicium can be applied in the same process as the application of the opaque layer, e.g. intaglio printing. The printed indicium is integral with the document substrate. The integral printed indicium can be independent of the security device presently disclosed. However, preferably the integral printed indicium is defined in terms of the common image and the integral printed indicium is aligned with the surface relief structure and the printed layer, the integral printed indicium presenting a third set of features of the common image, whereby the common image is presented by the surface relief structure, the printed layer and the integral printed indicium in combination with each other. In another embodiment, the printed indicium can present another copy of the common image (or a version thereof, e.g. the same image but in different colours) but not aligned with the security device - for example it can be located in another part of the security document. This allows easy checking between the printed indicium and the security device.

[0072] Preferably, the security document is any of the following: a banknote, a passport, an identity document, an identity card, a bank card, a driving licence, a visa, a stamp, a cheque or a certificate.

[0073] The present application also provides a method of manufacturing a security document, the method comprising: providing a document substrate; forming a security device on the document substrate or on a security device substrate; and then applying the security device substrate to the document substrate or incorporating the security device substrate into the document substrate, in each case using the method described above to manufacture the security device. The method can be configured to provide a security document having any of the preferred features described above. BRIEF DESCRIPTION OF DRAWINGS

[0074] Examples of security devices and security documents according to the present application, and methods of their manufacture, will now be described with reference to the accompanying drawings, in which:

[0075] Figures 1 (a) and 1 (b) show comparative examples of security documents in plan and cross-section respectively, Figure 1 (c) showing an enlarged detail of the cross-section of Figure 1 (b);

[0076] Figures 2(a) and 2(b) show a first embodiment of a security document having a security device according to the present application in plan and cross-section respectively;

[0077] Figures 3(a), 3(b), 4(a) and 4(b) each show a further embodiment of a security device according to the present application in cross-section and plan respectively;

[0078] Figure 5(a) to Figure 5(c)three variants of a further embodiment of a security device according to the present application are illustrated in cross-section and plan view;

[0079] Figure 6(a) illustrates a further embodiment of a security device in cross-section, wherein Figures 6(b), 6(c) and 6(d) depict three different variants of a printed layer in plan view;

[0080] Figure 7 a further embodiment of a security device according to the present application is illustrated in cross-section and plan view;

[0081] Figure 8 a further example of a security device according to the present application is schematically depicted in exploded view;

[0082] Figure 9(a) illustrates a further embodiment of a security device according to the present application in cross-section and plan view, Figure 9(b) shows an exploded view of the security device;

[0083] Figure 10(a) illustrates a further embodiment of a security device according to the present application in cross-section and plan view, Figure 10(b) shows an exploded view of the security device;

[0084] Figure 11 a further embodiment of a security device according to the present application is illustrated in cross-section and plan view;

[0085] Figures 12 to 14 a further embodiment of a security device according to the present application is illustrated in cross-section and plan view;

[0086] Figure 15(a) illustrates a further embodiment of a security device according to the present application in cross-section and plan view, Figures 15(b) and 15(c) show plan views of a surface relief structure and a printed layer, respectively;

[0087] Figures 16(a), 16(b) and 16(c) each illustrate a further embodiment of a security device according to the present application in (i) plan view and (ii) cross-section;

[0088] Figure 17(a) to Figure 17(d) a further embodiment of a security device according to the present application is shown, Figure 17(a) in plan view, Figure 17(b) in cross-section, Figures 17(c) and 17(d) show enlarged details;

[0089] Figure 18(a) to Figure 18(e) and Figures 19 to 24 a further embodiment of a security device according to the present application is illustrated in cross-section and plan view;

[0090] Figure 25 a further example of a security device according to the present application is schematically depicted in exploded view;

[0091] Figure 26(a) shows in cross-section and plan view a further embodiment of a security device according to the application, Figure 26(b) shows an exploded view of the security device;

[0092] Figure 27(a) shows in cross-section and plan view an intermediate product that exists during the process of making an embodiment of a security device, and Figure 27(b) shows in cross-section and plan view a completed security device;

[0093] Figures 28(a), (b), (c) and (d) show in cross-section four further embodiments of a security device according to the application;

[0094] Figures 29(a), (b) and (c) each show in cross-section and plan view three further embodiments of a security device according to the application;

[0095] Figures 30(a), (b) and (c) show in cross-section three further embodiments of a security device according to the application;

[0096] Figure 31 A further example of a security device according to the application is depicted schematically in exploded view;

[0097] Figure 32(a) to Figure 32(g) A further embodiment of a security device according to the application is shown;

[0098] Figure 33 A further embodiment of a security device according to the application is shown in cross-section;

[0099] Figures 34(a), (b) and (c) show in cross-section three embodiments of a security document having a security device according to the application;

[0100] Figure 35(a) shows in cross-section an embodiment of a security device according to the application, and Figure 35(b) shows (i) the appearance of the security device as viewed in reflected light from the position of an observer Ol, and (ii) the appearance of the security device as viewed in transmitted light;

[0101] Figure 36(a) shows in cross-section an embodiment of a security device according to the application, and Figure 36(b) shows (i) the appearance of the security device as viewed in reflected light from the position of an observer Ol, and (ii) the appearance of the security device as viewed in transmitted light;

[0102] Figure 37(a) shows in cross-section an embodiment of a security document having three security devices each according to the present application, Figure 37(b) shows (i) the appearance of the security devices as viewed in reflected light from the position of an observer Ol, and (ii) the appearance of the security devices as viewed in transmitted light from the position of an observer Ol, and Figure 37(c) shows (i) the appearance of the security devices as viewed in reflected light from the position of an observer 02, and (ii) the appearance of the security devices as viewed in transmitted light from the position of an observer 02;

[0103] Figures 38(a), 38(b) and 38(c) show in cross-section three variants of a further embodiment of a security device according to the present application, and Figure 38(d) shows (i) the appearance of the security device in reflected light from the position of an observer Ol, and (ii) the appearance of the security device in transmitted light;

[0104] Figure 39(a) schematically depicts in an exploded view a further example of a security device according to the present application, and Figure 39(b) shows (i) the appearance of the security device in reflected light from the position of an observer Ol, and (ii) the appearance of the security device in transmitted light;

[0105] Figure 40(a) shows in cross-section an embodiment of a security device according to the present application, Figure 40(b) shows (i) the appearance of the security device as viewed in reflected light from the position of an observer Ol, (ii) the appearance of the security device as viewed in transmitted light from the position of an observer Ol; and (iii) the appearance of the security device as viewed in reflected light from the position of an observer 02;

[0106] Figure 41(a) schematically depicts in cross-section a further example of a security device according to the present application, and Figure 41(b) shows (i) the appearance of the security device in reflected light from the position of an observer Ol, and (ii) the appearance of the security device in transmitted light;

[0107] Figure 42 Further embodiments of security devices according to the present application are each shown in cross-section and plan view;

[0108] Figures 43(a), 43(b), 43(c) and 43(d) each show in cross-section and plan view four further embodiments of security devices according to the present application;

[0109] Figure 44(a) schematically depicts in an exploded view a further example of a security device according to the present application, and Figure 44(b) shows (i) the appearance of the security device in a first illumination condition, and (ii) the appearance of the security device in a second illumination condition;

[0110] Figures 45(a), 45(b) and 45(c) each illustrate in cross-section and plan view three further embodiments of security devices according to the application;

[0111] Figure 46(a) schematically depicts an exemplary apparatus suitable for casting-curing a surface relief structure in embodiments of the application, and Figure 46(b) illustrates in perspective view the formation of a surface relief structure;

[0112] Figure 47 and Figure 48 two exemplary apparatuses for simultaneous formation of a surface relief structure and a printed layer used in embodiments of the application are schematically depicted; and

[0113] Figure 49 a further example of an apparatus used in embodiments of the application is schematically depicted. DETAILED DESCRIPTION

[0114] The following description will focus on security devices formed directly on a document substrate, which are ultimately used as the basis of a security document such as a banknote, passport, certificate, licence, identity card or the like. In many cases, the security devices are depicted as being arranged in a window region of the document substrate. However, as will be explained with reference to Figure 32(a) to Figure 32(g) this is not essential and the devices can alternatively or additionally be located in a semi- window or non-window region (or any mix of such regions). Likewise, as will be explained with reference to Figure 34(a) to Figure 34(c) all embodiments of the security devices can alternatively be formed on a separate substrate which is applied to (or incorporated into) the security document. The security devices can be formed on a separate substrate before and / or after it is joined with the security document substrate.

[0115] For comparison, Figures 1(a) to 1(c) show an example of a conventional security device in the form of a intaglio print 110 on a security document 100. Figure 1(a) illustrates the security document 100 in plan view, and Figure 1(b) shows a schematic cross-section along the line Q-Q'. It should be noted that, for simplicity, Figure 1(b) does not show the embossed nature of the substrate caused by intaglio printing and which will be present in practice. This is shown in the enlarged detail of Figure 1(c). In this example, the intaglio print is shown as being formed on a document substrate 2 formed from an inner core substrate 2a, which can be a polymeric material such as BOPP, and an outer opaque layer 2b such as a white ink. This is a typical construction for a polymeric banknote substrate. However, the intaglio print 110 can be formed on any document substrate, including a paper substrate.

[0116] As shown in Figure 1(a), the intaglio print 110 here comprises a line drawing of a kingfisher and a line of text “De La Rue” with a logo above it. The image of the kingfisher is multi-tonal, consisting of an array 112 of image elements in the form of spaced ink lines of different sizes and shapes, configured as necessary to express the features of the image. The image is formed in two colours CI (e.g. dark green) and C2 (e.g. orange). The intaglio process involves providing a printing plate in which all the lines defining the desired image elements are etched. A first ink 114a of colour CI and a second ink 114b of colour C2 are applied to respective areas of the printing plate corresponding to the areas requiring both colours. The inks are pressed into the etched lines and the intervening surface of the plate is cleared using a wiping blade or similar tool. The printing plate is then applied to a substrate 2 under high pressure against a platen roller, forcing the substrate 2 into the etched lines, resulting in embossing of the substrate. On separation, the inks 114a, 114b are transferred from the printing plate onto the top of the raised elements of the now embossed substrate 2. The raised elements and the inks carried thereon form the image elements 112 of the intaglio print 110. The embossed nature of the print 110 results in a tactile quality.

[0117] While it is possible to form intaglio prints with more than one colour, as shown in Figures 1(a) to 1(c), the design options are limited. Due to the composition of intaglio inks (which are very thick and paste-like) and the method of applying the inks to the intaglio printing plate, it is very difficult to place separate inks on the intaglio printing plate. The high pressure required to push the thick ink paste into the intaglio printing plate recesses makes the process difficult to control and limits the placement of separate inks to blocks (groups) of recesses rather than individual recesses. When the inks are pushed into the recesses and merge with adjacent inks, the inks will always spread out. The wiping effect that cleans the non-recessed areas of the plate as part of the intaglio process also contributes to the merging. For these reasons, each colour area needs to be large enough that the merged area is a small fraction of the printed area (presented to the observer in a single colour) or sufficiently separated from other colours to minimise merging. It is therefore not possible to place different colours closely together or in a high resolution arrangement such as would be required to present a full colour image (e.g. an image with photographic quality). The number of colours that can be presented in an image is also limited, as it is not possible to spatially combine the inks in a controlled manner, which is necessary to provide a full spectrum via additive or subtractive mixing.

[0118] Figures 2(a) and 2(b) illustrate a first embodiment of a security document 100 having a security device 10 according to the application. Again, in this example, the document substrate 2 is shown as a multi-layer substrate having a transparent polymeric core substrate 2a (e.g. BOPP) and opaque layers 2b on either side, the security device 10 being placed in a window region 51 thereof in which there are no opaque layers 2b on either side. However, this is not essential and the security device 10 can be formed on any type of substrate and (for example) in a window region 51 or a non-window region 50, provided there is sufficient transparency / translucency, as explained below. Other arrangements will also be exemplified below.

[0119] The security device 10 comprises a surface relief structure 20 and a printed layer 30 superposed and in register with each other. The surface relief structure 20 is formed from a body of cured material 20a having a profile of varying height (parallel to the z-axis) and is disposed on a first surface 3a of the substrate 2. The surface relief structure can comprise a single raised element or a plurality of discrete raised elements. In this example, the cured material 20a forming the surface relief structure 20 is transparent and colourless. The printed layer 30 is a flat print disposed on an opposite second surface 3b of the substrate 2. The printed layer 30 can be mono- or multi-coloured. In this example, it is formed from two materials 30a, 30b (e.g. inks) having different respective colours CI and C2. In a first region Rl of the substrate, the surface relief structure 20 and the printed layer 30 are each configured such that they combine to present a common image - i.e. a composite macro-image - here the same line image of a kingfisher discussed in relation to Figures 1(a) to 1(c), consisting of an array of spaced apart image elements 11 which vary in size, shape and / or pitch on the array to express the features of a multi-tone image (e.g. the head, beak, eyes, body, numeral "50" etc. of the kingfisher). The image elements 11 preferably have a size such that they are individually distinguishable under close inspection or low magnification (e.g. at least 50 pm in width, more preferably at least 150 pm).

[0120] In this example, the surface relief structure 20 and the printed layer 30 are each configured to present all the features of a common image. Thus, they are each configured to present the entire desired array of image elements 11 and each define according to one and the same image. In the surface relief structure 20, the image elements 11 are defined by corresponding raised elements (protrusions) 21 and in the printed layer 30, the image elements 11 are defined by corresponding printed elements 31. The two components (i.e. the surface relief structure 10 and the printed layer 30) are relatively positioned so that each raised element 21 is aligned over one of the printed elements 31. When viewed in combination, the printed layer 30 thus imparts colour to the common image, while the surface relief structure 20 provides a tactile sensation and contributes to its appearance (even if formed from a colourless transparent material, the reflective surface of the surface relief structure 20 will be apparent).

[0121] As will be seen from Figure 2(b), the raised elements 21 of the surface relief structure 20 are joined to one another by a base layer 29 of the same cured material 20a, which extends between each raised element 21 and around the surface relief structure 20 (typically only a small distance, for example 0.01 mm to 5 mm). The base layer 29 is a product of the cast-cure process by which the surface relief structure 20 is formed. If desired, the height of the base layer 29 can vary across the security device 10.

[0122] The embodiment of Figures 2(a) and 2(b) results in a security device 10 which mimics the appearance and tactile sensation of the intaglio print 110 described with reference to Figures 1(a) to 1(c), albeit formed via a different method and having a different structure. However, since the printed layer 20 can now be applied by a flat printing process (such as offset printing), it can be formed at a higher resolution and in any number of colours, with colour arrangements achievable which are far superior to those possible in intaglio printing. This means that the degree of design freedom is greatly increased, allowing for a greater variety of visual effects and more complex designs (and hence higher security levels), as will be described below.

[0123] While in many implementations a complex common image can be chosen (such as the kingfisher shown in Figs. 1 (a) to (c), Figs. 2 (a) and (b), or a portrait, a photograph, etc.), the presently disclosed technology is equally suitable for displaying simpler images, such as geometric shapes, logos, alphanumeric text, printed symbols, etc. The common image C.I. can or can not comprise an array of spaced-apart image elements as in the previous example. Thus, Fig. 3 (a) shows an embodiment of the security device 10 wherein the common image C.I. features the numeral "5", expressed in a single continuous block of the desired shape. The image is of a size suitable for easy reading by the naked eye, e.g. a few mm wide. As before, the security device 10 comprises a surface relief structure 20 formed of transparent curable material 20a on one surface 3a of the substrate 2, and a printed layer 30 formed of ink 30a (e.g. red ink) on the opposite surface 3b. Both the surface relief structure 20 and the printed layer 30 are configured to present the same feature in register with each other, namely the numeral "5". The surface relief structure 20 comprises a raised protrusion 28 having a lateral extent corresponding to the shape of the numeral "5" and surrounded by a base layer 29 extending around its periphery. The printed layer 30 likewise comprises a continuous ink region 30a having the same lateral extent as the raised protrusion 28 in the shape of the numeral "5".

[0124] Thus, the surface relief structure 20 and the printed layer 30 in combination display the common image C.I. in the form of a uniformly coloured numeral "5" (labelled with reference numeral 18 in Fig. 3 (a)), surrounded by a colourless peripheral region 19 corresponding to the base layer 29. Since there are inherent limitations to the lateral size of individual intaglio elements (which the present invention does not encounter), the resulting security device can be configured to have a tactile feel different from that achieved via intaglio, e.g. a broad, smooth raised region.

[0125] Alternatively, the security device can be designed to more closely mimic intaglio printing to express the features of the image by using an array of spaced-apart image elements 11. An example is shown in Figure 3(b), which is substantially the same as already described with reference to Figure 3(a). However, in this case the common image C.I. is the numeral "10" and each feature of the image (i.e. "1" and "0") is formed by a series of spaced-apart line elements 11, 11'. In this example, the line elements 11 forming the "1" are narrower than the line elements forming the "0", so the two features will appear at different colour intensities ("1" will appear lighter than "0"). There are two surface relief structures 20, each formed of the same colourless solidified material 20a, one corresponding to the numeral "1" and the other corresponding to the numeral "0". Each surface relief structure comprises an array of raised elements 21 corresponding to the line elements 11, 11' and a base layer 29. On the opposite surface there is provided two print layers 30 formed of ink 30a and arranged as print elements 31, 31' in register with the corresponding raised elements 21, 21'. The resulting common image will appear as the numeral "10" with the colour determined by the colour of the ink 30a, with the "1" appearing lighter than the "0". On close inspection, the presence of the line elements will be discernible. Each numeral "1" and "0" has a peripheral border 19 corresponding to the base layer 29.

[0126] Figures 4(a) and 4(b) show embodiments corresponding to Figures 3(a) and 3(b) respectively, except that the print layer 30 is formed of two colours. Thus, in the embodiment of Figure 4(a), the print layer 30 comprises two inks 38a, 38b in different respective colours C1, C2. The first ink 38a is arranged to cover the area corresponding to the left half 18a of the numeral "5" in the common image C.I., while the second ink 38b is arranged to cover the area corresponding to the right half 18b of the numeral "5". Thus, the print layer 30 as a whole presents all the features of the common image as before (i.e. the complete numeral "5"), but in two colours. Similarly, in the example of Figure 4(b), the print elements 31a forming the numeral "1" are provided in a first ink 38a of a first colour C1, while the print elements 31b forming the numeral "0" are provided in a second ink 38b of a second colour C2. Thus, the common image C.I. presented by the security device in Figures 4(a) and 4(b) is a multi-coloured image. It will be appreciated that three or more different colours can be readily presented by providing inks in the print layer 30 as appropriate.

[0127] In the preceding example, the surface relief structure 20 and the printed layer 30 match each other in the sense that the printing is arranged so that ink is present at locations corresponding to the raised projections of the surface relief structure 20 and nowhere else. However, this is not essential, and different visual effects can be achieved by varying the relative lateral extent of the two components. The features of the respective representations of the common image must of course still be aligned. Figure 5(a) to Figure 5(c) Some examples are shown. Figure 5(a) again shows the embodiment of Figure 3(b) in order to facilitate comparison with Figures 5(b) and 5(c). (It will be noted here that the details of the substrate 2 are not shown - it can take any form so long as it is not opaque). Figure 5(b) shows a variant in which the printed layer 30 is no longer provided in the form of an array of printed elements 31, 31', but as two contiguous ink regions 38, the first in the shape of the numeral "1" and the second in the shape of the numeral "0". The result will be to show a common image C.I. of the numeral "10" with a solid colour fill, although the image elements 11 will still be visible (at least at certain viewing angles) due to the surface relief structure 20. As before, the numeral will have a colourless peripheral border region 19. Figure 5(c) shows another variant in which the two ink regions 38 extend laterally so that their outer boundaries match the outer boundaries of the two regions of solidified material, including the peripheral region formed by the base layer 29. The common image C.I. presented by the security device will now also present a coloured peripheral border 19.

[0128] It should be noted that, while the printed layer 30 can be configured to precisely match (or "mirror") the cast structure, as in some of the embodiments above, this is not essential. Figure 6(a) to Figure 6(d) Some options are shown. Figure 6(a) shows in cross-section an example of a security device, which can be part of any of the devices described above (e.g. part of the multi-tone image shown in Figures 2(a) and 2(b)). As shown in the plan view of Figure 6(b), in a first variant the raised projections 21 of the solidified surface relief structure 20 and the printed image elements 31 can be configured to match and align with each other. Alternatively, as shown in Figure 6(c), the printed image elements can comprise an array 31a of dots or other elements arranged in a spaced apart fashion along the path of the raised projections 21. Still alternatively, the printed elements 31 need not have the same orientation as the raised projections 21, but can have some other arrangement, such as the orthogonal line pattern shown in Figure 6(d).

[0129] While in the embodiments described above the security device is depicted as being located in a window region on the substrate 2 and visible from both sides, this is not essential. In Figure 7 In another embodiment shown, a subsequent print or other layer 70 can be applied over the printed layer 30. Figure 7 The embodiment of Figure 3(b) is otherwise identical to the embodiment of Figure 3(a). The layer 70 can be, for example, an ink or other coating (e.g. a screen-printed white ink) or applied feature such as a foil. This subsequent process can make the substrate in the region of the security device semi- transparent or opaque. Such an additional layer 70 on the printed layer 30 can be provided in any of the embodiments disclosed herein.

[0130] Figure 8 A further embodiment of a security device is shown in exploded form so that the two-dimensional configuration of each component can be shown. In this embodiment, the RGB (red green blue) image 30 is printed on one side of a transparent substrate 2, for example by flexographic printing. This can be, for example, a window region of a polymeric security document. On the other side of the transparent substrate, the same image is provided in the form of an achromatic relief structure 20 formed by cast curing. The relief structure is defined according to the same image, for example by sharing the same periphery of the image and / or by replicating features within the image, for example via different heights of the cast. The cast can be a single unit of cured material (with height optionally varying) or can comprise a plurality of spaced apart elements, for example dots or lines, to produce a more tactile feel (although a base layer will typically still exist between them). When viewed through the cast, the user sees a full colour image C.I. and through the cast provides a tactile feel for the image. The two components 20, 30 are in precise register with each other. Figure 8

[0131] Figures 9(a) and 9(b) depict in more detail embodiments based on the use of a cast 20 and a printed image 30, respectively. Figure 8 ​Fig. 9(a) shows a further embodiment of the concept of the same concept as the embodiment of Fig. 8. As shown in Fig. 9(a), a surface relief structure 20 formed from solidified material 20a is provided on the first surface 3a of the substrate 2, in the transparent portion thereof. A print layer 30 is provided on the opposite surface 3b and here is an RGB (red green blue) print formed from three corresponding inks 30a, 30b, 30c. It should be noted that, although in the figure, the inks appear to be stacked on top of each other, giving the impression of height, this is purely for the sake of clarity of illustration, in practice the print layer 30 will typically be substantially flat (with the exception that the print layer 30 is formed from microintaglio). More generally, the print layer 30 can comprise any of the following: abutting colour blocks, superimposed colour blocks, spaced apart elements (as shown) or standard halftone image elements. The surface relief structure 20 and the print layer 30 are superimposed in register and are manufactured in register with each other. The surface relief structure 20 and the print layer 30 are both configured to render features of the same common image C.I., which here is a full colour photograph portrait (of, for example, the owner of the security document). Thus, the print layer 30 will typically comprise the red, green and blue components of the image (shown separately in Fig. 9(b)), which can be applied in successive print runs or simultaneously (first being collected on a blanket or flexographic printing roller).

[0132] The surface relief structure 20 expresses features of the common image by providing one or more raised protrusions 22, which can or can not match the arrangement of inks in the print layer (but the image features expressed by each component will be in register). For example, the surface relief structure 20 can comprise raised protrusions across the area bounded by the outline of the head of the person, so that the tactile area matches the portrait. Alternatively, the nature of the surface relief can vary so that different features of the portrait correspond to areas of different tactile feel. For example, the surface relief structure can be configured so that the area corresponding to the person’s hair feels rougher than the area corresponding to their face (feeling relatively smooth). In another example, the height of the surface relief structure can be configured to vary according to the common image. For example, those features of the portrait that are closer to the observer in real life (such as the person’s nose) can correspond to raised elements of higher height, or the surface relief structure can comprise a single raised element having the 3D profile of the person’s face, with varying height. The surface relief structure 20 can additionally or alternatively be formed as a screened version of the common image, i.e. with an array of spaced apart raised elements that vary in size, shape or pitch across the array in order to produce a multi-tone version of the image that will be visible due to the reflective properties of the solidified material 20a. A base layer 29, which is smaller than the protrusions 22, will be present as before and will form uncoloured border regions that are not shown.

[0133] The embodiments of Figures 10(a) and 10(b) are substantially identical to those of Figures 9(a) and 9(b), except that the printed layer 30 is a CMYK (Cyan, Magenta, Yellow, Black) print formed from four corresponding inks 30a, 30b, 30c, 30d. Once again, a tactile, full-color photographic portrait is formed as the common image C.I. Of course, a monochrome (e.g., grayscale) image can also be formed, as shown in the embodiments of Figure 11 Figures 11(a) and 11(b). This is identical to the embodiments of Figures 9(a) and 9(b) and Figures 10(a) and 10(b), except that here the printed layer 30 is a monochrome (e.g., grayscale) version of the photographic portrait formed from a single ink 30a (e.g., black).

[0134] In the embodiments presented so far, the surface relief structure 20 and the printed layer 30 each present the entire common image C.I. - i.e., have the same set of features as each other. However, this is not necessary, and in other embodiments each component can contribute a different set of features of the common image to the final appearance of the device. The set of features can or can not include one or more features in common. Figures 12 to 15(c) Some examples are provided in which the two sets of features are different.

[0135] Figure 12 The embodiment of Figures 12(a) and 12(b) is a variation of the embodiment already described with reference to Figures 3(a) and 4(a), the only difference being the configuration of the printed layer 30. In the embodiment of Figures 12(a) and 12(b), the printed layer 30 is configured to present only the features that define the right half of the number "5" in the common image C.I. The printed layer 30 is otherwise absent. In the resulting security device 10, the common image C.I. thus includes a tactile number "5", the left half 18a of which is colorless while the right half exhibits the color of the ink 30a. The entire number "5" is clear due to the reflective properties of the surface of the solidified material 20a. Figure 12 Similarly, the embodiment of Figures 13(a) and 13(b) is a variation of the embodiment already described with reference to Figures 3(b) and 5(b), the only difference being the configuration of the printed layer 30. In the embodiment of Figures 13(a) and 13(b), the printed layer 30 is configured to present only the printed elements 31, 31' that correspond to the right half of each of the numbers "1" and "0", and is otherwise absent. In the resulting security device 10, the common image C.I. thus includes tactile numbers "1" and "0", each of which has a colorless left half and a right half colored by the ink 30a. The entirety of each number is clear due to the reflective properties of the surface of the solidified material 20a.

[0136] Figure 13 Figure 13

[0137] ​​​In both of the above examples, the set of features of the common image presented by the surface relief structure 20 is the entire set of features required to define the common image C.I., while what is presented by the printed layer 20 is a subset of those features. One of the components can also present features of the common image while the other does not. For example, in the embodiment of Figure 12 the surface relief structure can be modified so that it exists only to define the left half 18a of the numeral "5" and not on the right half 18b. In the embodiment of Figure 13 the raised protrusions 21, 21' can likewise exist only where the printed elements 31, 31' do not.

[0138] Figure 14 The embodiment of Figure 14 provides a further example. Here, the common image C.I. is a set of geometric shapes: a circle 15 within a solid-filled square 16 within the outline of a larger square 17. The surface relief structure 20 includes raised protrusions corresponding to the solid square feature 16 and the center portion 17a of each side of the square outline feature 17. The printed layer 30 includes an outer square 37a of ink and a central circular inking region 37b. In combination, a complex design is formed as shown in plan view, with the circle 15 having the color of the ink 30a, the solid square 16 being colorless but tactile, and the square outline 17 being colored around but tactile only in the portions 17a and not at the corners 17b (it should be noted that the portions 17a are not shown colored so that the presence of the solidified material 20a can be inferred from the figure, but in fact will be colored). Thus, the common image C.I. is composed of features contributed by each of the components 20, 30. The image is preferably designed to demonstrate accurate registration between the surface relief structure and the printed layer. In the embodiment of Figure 14 this is particularly well achieved by providing the tactile portions 17a on the square outline 17, the misregistration of which is easily noticed.

[0139] A further example of this principle is shown in Figures 15(a), 15(b) and 15(c). Plan views of the cast structure 20 and the printed layer 30 are shown in Figures 15(b) and 15(c) respectively. In this case, the final common image C.I. is a circular design comprising a complex "stained glass" like arrangement with 12 petal-shaped regions arranged radially around a central cross of four inwardly pointing arrows and 12 radial lines aligned with the centers of the petal shapes. The surface relief structure 20 is configured with a series of raised regions 23 with the depressions between them providing the petal-shaped features and the central circular region of the common image. The printed layer 30 is composed of a set of printed regions 34 configured to present the radial lines and the central cross features. The registration between the two components is demonstrated by the complex nature of the common image C.I. and the need to center the two parts precisely to achieve the intended alignment.

[0140] While in many embodiments it will be desirable for the haptic effect of the cast structure to match the visual configuration of the printed layer, in other cases, a unique security effect can be achieved by purposefully including partial mismatches. This is a subtle but surprising and therefore memorable feature that a potential counterfeiter can nonetheless miss. Clever placement of the cast haptic / printed elements can facilitate further inspection of the device. For example, in the embodiment of Figures 2(a) and 2(b), on the image of the kingfisher, the beak and back feathers can be haptic (i.e. there are raised elements 21) by the cast, while the eyes and breast feathers have no cast (i.e. there are no raised elements 21) and so are not haptic. Here the appearance of the printed layer 30 (which is continuous in both areas) suggests that they will feel the same, but a careful inspection reveals that they do not.

[0141] Figures 16(a), 16(b) and 16(c) present another example. Each figure shows the device in (i) plan view and (ii) cross-section. The device of Figure 16(a) has matching cast structures 20 and printed elements 30 each expressing a repeating array of the number “5”. In this case, each number “5” will be coloured (by the printed layer 30) and haptic (due to the cast structure 20) as expected. In the embodiment of Figure 16(b), the same repeating array of the number “5” is again printed 30, and all but one of the images has a corresponding cast structure 20. Thus, the one number “5” that is not haptic is prominent on inspection. The reverse is also possible, as shown in Figure 16(c). Here the device includes a complete set of cast images (again, here in the form of the number “5”), but now one of the numbers is not printed and so is less visually prominent, but can be detected by feel.

[0142] The cast structures 20 can also be configured to provide more complex haptic (i.e. tactile) effects. Figure 17(a) to Figure 17(d)An example is shown. Here, the security device is shown in plan in Figure 17(a) and in cross-section in Figure 17(b). Here, two common images, CI1 and CI2, are formed, each appearing as a "£" symbol. Corresponding print layers 301, 302 provide colour for each image and aligned cast structures 201, 202 provide a tactile sensation. However, the two cast structures 201 and 202 are different from each other, such that the tactile sensation presented by the common image CI1 is different from the common image CI2. This difference can take any form (e.g. roughness level, directionality, etc.). In this example, the two cast structures are shown in enlarged detail in Figures 17(c) and 17(d) respectively. Both cast structures 201 and 202 comprise an array of raised protrusions 21 having a tactile structure formed by facets 241, 242 at the top of the protrusions 21. The facets 241, 242 are asymmetric and are arranged in opposite directions in the two structures. Thus, a user will find that image CI1 feels relatively smooth and CI2 relatively rough when they swipe their finger from left to right across the device (as shown). However, when they move their finger in the opposite direction across the device, the relative sensations will be reversed. Other tactile elements that can be used include symmetric facets, prisms (symmetric or asymmetric), pyramids, cubic structures, cones, curves and irregular structures.

[0143] Figures 18(a), 18(b), 18(c) and 18(d) illustrate four further examples in which the common image comprises a full-colour photographic image (here a portrait). Both implementations are variants of the implementations described above with reference to Figures 9(a) and 9(b), and so the printed layer 30 is an RGB image. However, the printed layer 30 could alternatively be a CMYK image as described with reference to Figures 10(a) and 10(b), or potentially could comprise some other colour set such as orange, green and violet. In the implementation of Figure 18(a), the security device 10 is the same as that shown in Figures 9(a) and 9(b), except for the configuration of the surface relief structure 20, which in Figure 18(a) only presents the features of the right half of the common image. As a result, although the entire portrait 18 is visible in full colour in the completed security device 10, only the right half 18b thereof is tactile. There is no surface relief structure 20 in the left half 18a. In the implementation of Figure 18(b), the situation is exactly the reverse. Here, the security device 10 is the same as that shown in Figures 9(a) and 9(b), except for the configuration of the printed layer 30, which in Figure 18(b) only presents the features of the right half of the common image. As a result, although the entire portrait 18 is tactile in the completed security device 10, only the right half 18b thereof is visible in full colour. The left half 18a is still visible to some extent due to the reflective properties of the solidified material 20a. In the implementation of Figure 18(c), the solidified surface relief structure 20 and the printed layer 30 overlap each other only in the central region of the device. Thus, the portrait 18 comprises three distinct regions: a first portion 18a in which only the printed layer 30 is present; a second portion 18b in which both the printed layer 30 and the solidified surface relief structure 20 are present; and a third portion 18c in which only the solidified surface relief structure 20 is present. Thus, the first portion 18a will appear in full colour but not tactilely; the second portion 18b will be full colour and tactile; and the third portion 18c will be tactile but not full colour (the third portion 18c can still be visible in grey-scale / monochrome form due to the reflective nature of the cast 20 and / or any coloured undercoat it can carry).

[0144] A further variant is shown in Figure 18(d). Here, instead of being formed from a plurality of discrete raised elements, the solidified surface relief structure 20 comprises a continuous surface having different geometrical shapes (e.g. heights, lengths, widths, etc.) For example, the structure can provide a three-dimensional profile corresponding to the face of the person shown in the image CI. In this case, the printed layer 30 provides the fine details of the image, while the cast 20 is used primarily to provide the tactile sensation.

[0145] In Fig. 18(e), the surface relief structure 20 is configured to present all the details of the photographic portrait 18 forming a major part of the common image C.I., in this case via a set of spaced-apart raised elements of different heights. In addition, the surface relief structure includes a protrusion 22a forming a laterally rectangular border 17 framing the portrait. The print layer 30 presents only a subset of the features of the common image C.I., namely a uniform area 38a of a first ink 30a corresponding to the face area 18' of the portrait 18, and a laterally rectangular line 38b in a second ink 30b corresponding to the border 17. The resulting common image includes a haptic representation of the portrait 18', which is partially haptically colored within the haptically colored border 17, and partially uncolored.

[0146] The ability to control color placement very precisely not only allows to display full color images, such as those exemplified above, but also to display other color effects. In traditional lithographic printing, it is known to produce multi-colored effects by a process called "rainbowing", in which two differently colored inks are applied to the surface of the printing plate adjacent to each other. When at the border, the inks mix with each other to produce an intermediate color which is spatially continuously varying. The present invention can be used to form devices with "rainbow" colors, which are also haptic, which was not possible before.

[0147] Figure 19 and Figure 20 Two examples are shown, which correspond to the examples of Fig. 3(a) and Fig. 3(b), respectively, except that here the print layer 30 is formed by a plurality of inks each. In Figure 19 embodiments of the present invention, the print area 38 in the form of the number "5" is formed by at least two inks, such that its left part has a first color CI (e.g. red), its right part has a second color C2 (e.g. blue), and the intermediate part located between them has one or more intermediate colors C3 (e.g. purple). This is achieved by "rainbow" lithographic printing using two inks of colors CI and C2, thereby creating the appropriate spatial mixing in the intermediate area. In this way, the transition from the first color CI to the second color C2 via the intermediate color C3 is truly continuous, as no discrete change from one color to the other is displayed, even under magnification. The same principle applies to Figure 20 embodiments of the present invention, the only difference being that here the image is expressed via an array of image elements 11, 11'. The corresponding print elements 31, 31' are formed by lithographic printing in the appropriate colors to achieve the rainbow effect as described before. It is also possible to provide more than two such rainbow effects in the same print layer 30. For example in Figure 20 embodiments of the present invention, the number "1" can be arranged to show a transition from red to blue, while the number "0" can be arranged to show a transition from green to yellow.

[0148] In the examples so far, the solidified material 20a forming the surface relief structure has been transparent and colourless, so it does not contribute to the colour appearance of the common image C.I. However, in more complex implementations, the solidified material 20a can carry a colour tint. This can be used as an additional variable to create new visual effects, especially since the colour density of the surface relief structure 20 can now vary according to its height (the raised protrusions will typically have a greater colour intensity than the lower parts such as the base layer 29, due to the greater amount of coloured material 20a through which the light passes). Reference will be made to Figures 21 to 26(b) Some examples will be explained, but it will be understood that the same principles can be applied to any other implementation disclosed herein.

[0149] Figure 21 and Figure 22 Two implementations are shown, which correspond respectively to the implementations of Figures 3(a) and 3(b), except that here the surface relief structure 20 is formed from a solidified material 20a which is transparent (i.e. clear) but carries a colour tint (e.g. blue). As before, the printed layer 30 is formed in a single coloured ink 30a (e.g. red). In Figure 21 In the implementation of Figure 3(a), the result is to depict the number “5” as a common image C.I. of contiguous areas 18, whose colour results from the mixing of the colour of the material 20a and the colour of the ink 30a. For example, in the example, the areas 18 can appear purple, at least when viewed from the side of the security device carrying the surface relief structure 20. The areas 18 are surrounded by border areas 19 which have only the colour of the material 20a (e.g. blue). Thus, a two-colour common image C.I. is obtained. Similarly, in the implementation of Figure 3(b), the image elements 11 and 11’ defining the numbers “1” and “0” now appear in a mixed colour (e.g. purple), while the border 19 surrounding them appears in the colour of the material 20a (e.g. blue). Figure 22 In the implementation of Figure 3(a), the result is to depict the number “5” as a common image C.I. of contiguous areas 18, whose colour results from the mixing of the colour of the material 20a and the colour of the ink 30a. For example, in the example, the areas 18 can appear purple, at least when viewed from the side of the security device carrying the surface relief structure 20. The areas 18 are surrounded by border areas 19 which have only the colour of the material 20a (e.g. blue). Thus, a two-colour common image C.I. is obtained. Similarly, in the implementation of Figure 3(b), the image elements 11 and 11’ defining the numbers “1” and “0” now appear in a mixed colour (e.g. purple), while the border 19 surrounding them appears in the colour of the material 20a (e.g. blue).

[0150] If the ink 30a forming the printed layer 30 is sufficiently transparent, then Figure 21 and Figure 22 The appearance of the device in Figure 3(a) and 3(b) will be very similar from either side of the substrate, under reflected light and transmitted light. However, more complex effects can be introduced by increasing the opacity of the ink 30a. If the ink 30a is sufficiently opaque, then when the device is viewed from the side carrying the printed layer 30, it will obscure the parts of the surface relief structure lying behind it, resulting in a different colour appearance. This variant can be applied to all the implementations disclosed herein. Thus, in Figure 21In an embodiment where the ink 30a is red and opaque, the appearance of the common image when viewed in reflection from the side of the surface relief structure will be as previously described (purple "5" with a blue border around it). However, when viewed from the other side in reflection, the common image will show a red "5" with a blue border around it. In transmission, the "5" can appear dark (e.g. backlit) with a blue border around it.

[0151] While it will be desirable in many cases for the color of the cured material 20a to be different from the color of the ink 30a, this is not necessary, and different effects can be achieved if the colors are the same or similar. For example, Figure 23 An embodiment is shown that is identical to the embodiment described above with reference to Figure 21 In an embodiment where the ink 30a is red and opaque, the appearance of the common image when viewed in reflection from the side of the surface relief structure will be as previously described (purple "5" with a blue border around it). However, when viewed from the other side in reflection, the common image will show a red "5" with a blue border around it. In transmission, the "5" can appear dark (e.g. backlit) with a blue border around it.

[0152] More complex effects can be achieved if the printed layer 30 itself is formed in multiple colors. For example, Figure 24 An embodiment is shown where the security device 10 is identical to the one described above with reference to Figure 21 In an embodiment where the ink 30a is red and opaque, the appearance of the common image when viewed in reflection from the side of the surface relief structure will be as previously described (purple "5" with a blue border around it). However, when viewed from the other side in reflection, the common image will show a red "5" with a blue border around it. In transmission, the "5" can appear dark (e.g. backlit) with a blue border around it.

[0153] The same principles can be applied to security devices that present full color images. Figure 25 An example is shown that is identical to the one described above with reference to Figure 8The embodiment of Figures 10(a) and 10(b) is identical to the embodiment of Figures 9(a) and 9(b), but wherein the haptic cast 20 has a color tint - in this case blue. The print 30 of the image on the opposite side is printed in red and green only. When the combination is viewed through the blue haptic cast, the full color RGB version of the image will be seen. The necessary variation in the blue level in the cast can be achieved by varying the height of the cast (the higher parts of the cast will have a greater color density than the lower parts due to the increased amount of material present) and / or by providing elements (e.g. dots) of the haptic cast only where a blue contribution is needed. Such raised elements will have a higher optical density than the base layer between them.

[0154] Another embodiment employing this principle is shown in Figures 26(a) and 26(b). This embodiment is a variant of the embodiment of Figures 10(a) and 10(b), with a common image C.I. in the form of a haptic full-color photograph portrait composed of CMYK channels. However, in this implementation, the print layer 30 is formed from three inks 30b (yellow), 30c (magenta) and 30d (black), resulting in a "MYK" printed image lacking a cyan channel. The cyan contribution is made by a surface relief structure 30 formed from a solidified material 20a having a cyan tint. As in the previous embodiment, the intensity of the cyan presented will vary across the surface relief structure 20 according to its height distribution - the protrusions 22 each exhibit a relatively strong color, while the lower areas including the base layer 29 exhibit a more pale or even no color.

[0155] It is also possible to form the surface relief structure 20 from two or more solidified materials which can have different optical properties from each other (e.g. different visible colors). The two or more solidified materials will typically be laterally offset from each other (preferably not superposed). If they abut each other to produce a continuous body of solidified material, these will be considered to form one and the same surface relief structure, while if they are spaced apart from each other, these will be separate surface relief structures. Either approach can be employed in embodiments of the invention. Figures 27(a) and 27(b) show an example of the latter case - Figure 27(a) shows an intermediate step in the manufacture of the final security device 10 shown in Figure 27(b). The security device 10 is similar to the security device described above with reference to Figure 5(b), wherein the common image C.I. presents the digits "1" and "0" each defined by an array of image elements 1 la, 1 lb.

[0156] The surface relief structures 20 are each formed from different materials having different respective colours. Figure 27(a) shows two materials 20’a and 20’b applied to the first surface 3a of the substrate 2 in their uncured state. As will be described below with reference to Figures 46(a) and 46(b), this can be achieved by printing the curable materials onto the substrate, preferably in overprint (e.g. using a non-impact printing method such as inkjet), or by applying the two or more curable materials to a casting tool. The first curable material 20’a has a shade of a first colour, for example yellow, while the second curable material 20’b has a shade of a second colour, for example blue. The curable materials 20’a, 20’b each form a desired surface relief structure to define raised elements 21, 21’ corresponding to image elements 1 la, 1 lb of a common image C.I. On the second surface 3b of the substrate 2, there is provided a printed layer 30 comprising two areas 38 of ink 30a (e.g. red) shaped to correspond to the numerals “1” and “0” respectively. The resulting common image will comprise a numeral “1” defined by image element 1 la having a colour formed by a mixture of the colours of the material 20a and the ink 30a (e.g. orange), surrounded by a border 19a having a colour corresponding to that of the material 20a (e.g. yellow), and a numeral “0” defined by image element 1 lb having a colour formed by a mixture of the colours of the material 20b and the ink 30a (e.g. purple), surrounded by a border 19b having a colour corresponding to that of the material 20b (e.g. blue).

[0157] As shown in each of the above embodiments, the surface relief structures 20 and the printed layer 30 are configured such that their combination presents a common image C.I. on the first region R1 of the substrate. Optionally, the security device can comprise a second region R2 which can be adjacent to the first region in which the image is located. The cast structure and / or the printed layer can extend (continuously or discontinuously from the first region) into the second region, but here the two components (if they are both present) need not be aligned with each other or defined based on a common image (as is the case with the first region). For example, in the second region, the printed layer can take the form of a microimage or another array of images, and the cast structure can take the form of an array of focusing elements, to combine to form an optically variable device. Where the security device is ultimately arranged in a window (or half-window) region of a security document, the first and second regions of the security device can both be in the same window (or half-window) region, or in different such regions.

[0158] Thus, one or both of the surface relief structure 20 and the print layer 30 can be present elsewhere on the substrate 2, such as in a second region R2 laterally offset from the first region R1 and not overlapping the first region. In this second region R2, the configuration of the surface relief structure 20 and / or the print layer 30 is different from that in the first region R1, such that the common image C.I. does not continue into the second region, and the two regions appear visibly different from one another. Figure 28(a) to Figure 28(d) Some options are schematically illustrated - in each case, the form of the surface relief structure 20 and the form of the print layer 30 are not accurately depicted and should only be considered as representing the lateral extent of each component. Figure 28(a) illustrates the same arrangement as in each of the previous embodiments - the surface relief structure 20 and the print layer 30 are present only in the first region R1 and only present the common image. In Figure 28(b), the surface relief structure is again present only in the first region R1, but now the print layer 30 extends into the adjacent second region R2. In the second region R2, the print layer 30 will have a different appearance to that in the first region R1, such that the common image is clearly kept distinct. For example, in the second region R2, the print layer 30 can provide a background for the common image, for example in a contrasting colour and / or as a uniform region. In the embodiment of Figure 28(c), the print layer 30 is present only in the first region R1, while the surface relief structure 20 extends into the second region R2. Again, the surface relief structure 20 will have a different configuration in each region, such that the common image can be detected as different from the second region R2 by feel due to its different tactile sensation. Finally, in the embodiment of Figure 28(d), both the surface relief structure 20 and the print layer 30 are present in the second region R2. Here they will both be configured differently from their respective arrangements in the first region R1, such that the common image is kept distinct.

[0159] Figures 29(a), 29(b) and 29(c) illustrate some specific examples. In each case, the arrangement of surface relief structures 20 and printed layer 30 in the first region R1 is the same as described with reference to Figures 9(a) and 9(b), resulting in a common image C.I. in the form of a tactile full-colour RGB photographic image. In the embodiment of Figure 29(a), surface relief structures 20 are present only in the first region R1 and not in the second region R2. Printed layer 30 extends across the second region R2 and is here configured to present a relatively uniform background pattern 35. The resulting security device 10 will therefore have background printing in the non-tactile second region R2 surrounding the tactile full-colour portrait. In the embodiment of Figure 29(b), printed layer 30 is confined to the first region R1 and is not present in the second region R2. Surface relief structures 20 continue into the second region R2 and are here provided with a different tactile structure compared to those present in the first region R1, for example a set of parallel raised ridges 25. The resulting security device 10 displays the common image C.I. under a solid-coloured background (in this case, colourless / transparent, but more generally having the local appearance of the substrate 2) with a different tactile feel. In the embodiment of Figure 29(c), both surface relief structures 20 and printed layer 30 are present in the second region R2 and have the features just described, with the result that the portrait C.I. is surrounded in region R2 by a differently coloured tactile background region.

[0160] It is also possible to exploit surface relief structures 20 and / or printed layer 30 to provide one or more additional security features in the second region R2. For example, the two components can be configured to combine in the second region to form an optically variable security device 40, such as a Moire magnifier, lenticular device, integral imaging device or a focal point scatter device. Figures 30(a), 30(b) and 30(c) illustrate two such examples. In Figure 30(a), the first and second regions R1 and R2 are discrete and laterally offset from one another as before (in this case, abutting one another - although they could be spaced apart or even placed in separate windows on the security document). In the first region R1, surface relief structures 20 and printed layer 30 are configured to present a tactile common image, in accordance with any of the embodiments described above. In the second region R2, the surface relief structures are configured to define an array of focusing elements 41, such as lenses. The array of focusing elements can have one-dimensional periodicity (e.g. cylindrical elements) or two-dimensional periodicity (e.g. spherical or aspherical elements). Printed layer 30 is configured to provide an array of images 42, and is substantially located in the focal plane of the array of focusing elements.

[0161] In a moiré magnifier, image array 42 will typically comprise an array of microimages, and the pitch and / or orientation of image array 42 will not match the pitch and / or orientation of focusing element array 41, so as to produce a synthetically magnified image of the microimages due to the moiré effect. In a lens arrangement, image array 42 will typically comprise sets of image elements, each set being a segment of an image to be displayed on second region R2. The segments of multiple images will be interleaved. In this case, the pitch and orientation of image array 42 will typically match the pitch and orientation of focusing element array 41. At any viewing angle, the focusing element array directs light from image elements originating from the same image to the viewer, so that a complete image is displayed. As the viewing angle changes, a different one of the interleaved images is displayed. Thus, the security device 10 as a whole will display a static, tactile, common image CI in its first region R1 (as before), alongside the optically variable device 40 in the second region R2. In a variation of this embodiment, as shown in FIG. 30( b ), the first and second regions R1, R2 themselves can be interleaved with each other across the entire security device. This will produce a visual impression of a static, tactile common image superimposed on the optically variable background. It should be noted that Figure 30(b) is highly schematic and that in practice the relative sizes of the lenses and surface relief structural elements will typically be such that there will be many lenses in each interleaved portion of the optically variable device, between each portion of the common image.

[0162] FIG30( c ) illustrates another embodiment in which the second region R2 includes a caustic device 45. A caustic device is a surface relief that projects a caustic image CA when illuminated by light L. WO-A-2019 / 063778, WO-A-2019 / 063779, and WO-A-2020 / 070304 disclose various methods for designing relief structures that project specific caustic images. In each of these documents, the caustic image is a "real" image that is visualized by projecting onto a suitable surface, such as a wall or screen. Similarly, WO-A-2020 / 070299 discloses techniques for forming a relief structure that generates a "virtual" caustic image that does not require projection onto a surface but can be directly observed with the naked eye. In the example shown, the first region R1 and the second region R2 do not overlap, but are positioned adjacent to each other. As in the other embodiments, the first region R1 displays a common image formed by the surface relief structure 20 and the printed layer 30. The caustics 45 in the second region R2 are formed as an extension of the same surface relief structure 20 by appropriate configuration of the casting tool.

[0163] In most of the examples described above, the first region R1 displaying the common image has been located in the transparent window region 51 of the substrate 2. However, while it can be desirable in many cases to arrange the features in the window region as described above so that the image is clearly visible from both sides of the substrate, in other cases it can be preferable to form the security device on a substrate which is not transparent, but only translucent. For example, the features can be formed on a paper substrate. Alternatively, it can be located on a non-window region of a polymeric banknote, where at least one opaque layer 2b is present on the substrate. Figure 31 An example of this is shown. In other aspects, the security device corresponds to the security device already described above with reference to Figure 8 The security device described. In this case, the offset image will generally be invisible (or almost invisible) under reflected light from the side of the cast. The tactile hint image, and when held up to the light, will display the offset image C.I. Of course, Figure 25 The configuration of FIG. 1 1 can equally be applied in this way to a non-window region. It can also be that part of the image is in the window region and part in the non-window region.

[0164] Figure 32(a) to Figure 32(g) Examples of some possible configurations are provided. In each case, the substrate 2 is depicted as a multi-layer substrate comprising a transparent core substrate 2a of polymer such as BOPP, with an opaque layer 2b arranged on each side. However, other forms of substrate 2 can alternatively be used. The region of the substrate 2 having its standard, base level of opacity is referred to as the non-window region 50. In the examples shown, this corresponds to the region where both opaque layers 2b are present uniformly on both sides 3a, 3b of the substrate. Here the substrate 2 has its highest level of opacity. In the examples shown, the security device 10 has been arranged in the window region 51, i.e. where both opaque layers 2b are not present, so the substrate 2 is locally transparent (unless additional layers are applied, such as in the examples of FIGS. 1 1 and 1 1 1). Figure 2(a) to Figure 30(c) Figure 7 ​The security device is positioned such that at least a portion of the first region R1 is located in the half-window region 52, i.e. one of the opaque layers 2b is absent and the other is present. Thus, the half-window region 52 is translucent rather than transparent and has a lower opacity than the non-window region 50. In this example, the half-window region 52 is formed by locally omitting the opaque layer 2b on the first surface 3a of the substrate, such that the surface relief structure is formed directly on the surface of the transparent core substrate 2a (optionally via a primer layer or other surface treatment). The printed layer 30 is disposed such that the remaining opaque layer 2b on the second surface 3b is located between the printed layer 30 and the core substrate 2a. As shown in Figure 32(b), the opposite arrangement is also possible, in which the half-window 52 is formed by leaving the opaque layer on the first surface 3a and omitting the opaque layer on the second surface 3b. The appearance of the security device shown in Figures 32(a) and 32(b) will be similar or identical.

[0165] In the embodiments of Figures 32(a) and 32(b) and Figure 2(a) to Figure 30(c) If desired, the non-window region 50 of the substrate 2 can be opaque. All that is required is that at least a portion of the first region R1 (preferably all) is located on a transparent region of the substrate 2 or a translucent region such as the half-window 52 (or indeed the window region 51 of the previous embodiments). In other cases, as shown in Figure 32(c), the security device 10 is located in a non-window region 50, the standard base level opacity of the substrate 2 must be low enough so that the common image can be observed when the security device 10 is viewed under transmitted light. Standard polymer banknote substrates and conventional paper banknote substrates typically meet this requirement.

[0166] In yet further examples, the security device 10 can be arranged partly in a window or half-window region and partly in a non-window region. An example of this is shown in Figure 32(d). In this case, the non-window region 50 can be opaque or translucent. If desired, the window or half-window region can be designed to cooperate with the common image, for example by interlocking with the common image, repeating elements of the common image or having a shape that matches a feature of the common image.

[0167] Similarly, the security device can be configured to interact with any watermark or pseudo watermark features provided in the base material 2. Although in the Figures, for clarity, the opaque layers 2b of the polymeric type document base material 2 are shown as a single layer on each side of the core 2a, in practice they can each be made up of multiple layers. For example, it is common for multiple opaque layers to be provided on each side of the core 2a - for example, in many cases there will be three layers per side, namely a first white opaque layer, a second conductive opaque layer (which can be off-white), and then a third white opaque layer. The individual layers can each be laid down in different degrees, for example in the form of portions of an image, to produce a watermark-like effect that can be seen under transmitted light (sometimes under reflection). Examples of such features can be found in WO-A-2017 / 055823. The presently disclosed security device can be designed to display a combined effect with the watermark or pseudo watermark.

[0168] Figure 32(e) shows a simple example. As shown in the cross-section of Figure 32(e)(i), here the pseudo watermark presents two shades - namely, the shade of the bulk base material 2 where all the opaque layers are present (region 55) and a more translucent shade where one or more (but not all) of the opaque layers are not present on each side of the core (region 54). The surface relief structure 20 and the printed layer 30 are each configured as in the embodiment of Figure 21 That is, both define an image of the number “5”, with the surface relief structure 20 being formed from cured material having a coloured shade (e.g. blue) and the printed layer having one or more colours (e.g. red). As shown in Figure 32(e)(ii), when the device 10 is viewed under reflected light from the surface relief structure 20 side (observer Ol), the image appears as the number “5” in the colour of the curable material (e.g. blue), with a lighter border region formed by the base layer 29. Any contribution from the printed layer 30 is substantially hidden by the base material 2. When viewed under reflected light from the opposite side (observer 02), now only the printed layer 30 is visible, so the device appears as the number “5” in the colour of the printed layer (e.g. red), as shown in Figure 32(e)(iii). As seen in Figure 32(e)(iv), when the device is viewed under transmitted light from either side, the two components combine so that in the region 54 where the watermark feature provides translucency to the base material, the image appears in the combined colour (e.g. purple). However, since the device 10 is placed on top of the watermark, only the left-hand portion of the image is visible. The right-hand portion of the image is hidden by the relatively opaque region 55 of the base material. It will be appreciated that whilst this embodiment has been illustrated using a pseudo watermark formed from the presence / absence of opaque layers in a polymeric document base material, the same effect can be achieved using a traditional watermark formed in a fibrous base material (e.g. a paper base material) where different levels of opacity are provided by varying the fibre density or thickness of the base material.

[0169] It will also be appreciated that different regions of the security device can be located in respective different window (or half-window) regions of the security document and / or that each such window (or half-window) region can carry a respective security device. For example, Figure 32(f) shows an embodiment of a security document 100 having three security devices 10 (each according to any one of the present embodiments) disposed in separate corresponding window regions 51. The window regions 51 are spaced apart from one another by non-window regions 50 in which there is an opaque layer 2b. The surface relief structures 20 in each window 51 are preferably formed simultaneously in a common cast-cure process. That is, a single casting tool carries surface reliefs defining each surface relief structure 20 and its position relative to the others, which shapes are transferred into the curable material in one processing step. The curable material itself can or can not extend between the window regions. Figure 32(g) shows another example in which the document 100 has two window regions 51 again separated by non-window regions. In this case, there is a single device 10 with a first region R1 displaying the common image located in one window region 51 and a second region R2, for example in the form of an optically variable security device, located in the other window region 51. Again, the curable material forming the surface relief 20 can or can not extend between the window regions, as can the printed layer 30, which can or can not be continuous between the window regions.

[0170] As noted above, while at least a portion of the first region R1 (on which the common image is displayed) needs to be located in a region of the substrate between the surface relief structure and the printed layer which is transparent or translucent, not all of the first region R1 has to be so located (although this can be preferred). It can be that the combination of the surface relief structure 20 and the printed layer 30 is required to complete only a portion of the common image C.I. Figure 33 Embodiments are shown in which the first region R1 in which the surface relief structure 20 and the printed layer 30 are configured to present the common image includes both non-window regions 50 and window regions 51 of the substrate 2. The non-window regions 50 can be translucent or opaque.

[0171] In all of the embodiments described so far, as mentioned in the outset, it has been assumed that the security device is formed on a substrate 2 which also acts as the document substrate of the final security document 100. Suitable document substrates include polymeric document substrates of the type already mentioned above and illustrated again in Figure 34(a), in which the substrate 2 comprises a core substrate of transparent polymeric material, such as polypropylene (PP) (most preferably biaxially oriented PP (BOPP)), polyethylene terephthalate (PET), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), nylon, acrylic, a cyclic olefin polymer (COP) or a cyclic olefin copolymer (COC), or any combination thereof. The polymeric substrate 2a can be monolithic, for example formed from a single one of the above-mentioned materials, or multilayered, for example having multiple layers of the same type of polymer (optionally with different orientations) or layers of different polymer types. As previously mentioned, “transparent” means that the polymeric substrate 2a is substantially clear to the eye, although it can carry a tint of colour and / or another optically detectable substance, such as a fluorescent material.

[0172] One or both surfaces of the polymeric substrate 2a can be treated to improve the adhesion / retention of subsequently applied materials. For example, a primer layer can be applied to all or part of either surface of the polymeric substrate 2a, for example by printing or coating. The primer layer is preferably also transparent and can again be tinted or carry another optically detectable material. Suitable primer layers include compositions comprising polyethyleneimine, hydroxyl-terminated polymers, hydroxyl-terminated polyester-based copolymers, cross-linked or uncross-linked hydroxylated acrylates, polyurethanes and UV-cured anionic or cationic acrylates.

[0173] Alternatively or in addition to applying a primer layer, the surface of the polymeric substrate 2a can be prepared for subsequent treatment by controlling its surface energy. Suitable techniques for this purpose include plasma or corona treatment.

[0174] The opaque layers 2b each comprise an opaque material, the primary purpose of which is generally to provide a suitable background for the printing of graphics thereon at a later stage. Thus, preferably, the opaque layers comprise a polymeric non-fibrous material which comprises at least a light-scattering substance, such as a pigment. The opaque layers 2b are preferably lightly coloured, most preferably white or another light colour such as off-white or grey, so that the graphic layers applied later will form a strong contrast therewith. In a preferred example, each of the opaque layers has a lightness L* in the CIE L*a*b* colour space of at least 70, preferably at least 80, more preferably at least 90. For example, each of the opaque layers can comprise a resin, such as a polyurethane-based resin, a polyester-based resin or an epoxy-based resin, and an opaque pigment, such as titanium dioxide (Ti02), silica, zinc oxide, tin oxide, clay or calcium carbonate.

[0175] Two or more opaque layers can be applied to each surface of the polymeric substrate 2a to achieve the necessary opacity. The optical density of each layer in itself can typically be in the order of 0.2 to 0.5. Preferably, 3 or more layers are applied to each surface, one on top of the other.

[0176] In preferred embodiments, at least one of the opaque layers, preferably one on each surface of the polymeric substrate 2a, is made electrically conductive, for example by the addition of conductive pigments thereto. This reduces the effects of static electrical charge that can otherwise build up on the security document during handling.

[0177] The opaque layer 2b is preferably applied to the polymeric substrate 2a using a printing process such as gravure printing or the like prior to manufacture of the security device 10 of the present disclosure, although in other cases the opaque layer can be coated onto the substrate, or applied by flexographic printing, flexographic printing, lithographic printing or any other convenient method. Depending on the design of the security document, the opaque layer can be omitted across the gap on one or both surfaces of the polymeric substrate to form a window region (which can be a full window or a half window, or a mixture of the two), as described above. This can be achieved by appropriate patterning of the opaque layer during the application process. In alternative constructions, the opaque layer 2b can comprise a self-supporting preformed layer (optionally including apertures to form a window later), which is then laminated to the polymeric substrate 2a. In this case, the opaque layer can be polymeric or can be a fibrous construction, such as paper, thereby making the security document a “hybrid” paper / polymeric construction.

[0178] In other embodiments, such as shown in Figure 34(b), the security device 10 can be formed on a conventional document substrate 2. Such substrates are typically fibrous in nature, including for example paper or regenerated cellulose (for example as disclosed in WO-A-2020156655). As before, the surface relief structure 20 is provided on the first surface 3a of the substrate 2 and the printed layer 30 is applied to the opposite surface 3b.

[0179] The security device 10 can also be formed on a substrate different from the document substrate 2. For example, the security device 10 can be formed on its own substrate, resulting in a security article 1 such as a security thread, stripe, foil or patch. Prior to or after this, the security article substrate can be attached or incorporated into the security document 100. An example of this is shown in Figure 34(c) where the security device 10 is formed on a substrate 2' such as a transparent polymer film (e.g. PET) prior to or after it is joined to the security document 100. This security device substrate 2' will typically be thinner than the document substrate 2 (e.g. of the order of 30 to 50 microns in thickness rather than 100 microns or more). The surface relief structure 20 is formed on a first surface 3'a of the substrate 2' and the print layer 30 is formed on a second surface 3'b of the substrate 2'. In this example, the security article 1 is shown attached to the first surface 3a of the document substrate 2 with the security device 10 (or at least a portion thereof) over the window region 51 of the document formed by a hole through the document substrate 2, as is typically the case where the document substrate 2 can be paper or similar. Such a security article 1 with the security device 10 can also be positioned in the non-window region 50 of the document substrate 2 as the combination of the surface relief structure 20 and print layer 30 can still be seen due to the transparent or semi-transparent nature of the device substrate 2'. The security article 1 can alternatively be applied to a polymer type document substrate in its window region, semi-window region and / or non-window region.

[0180] In the case where the substrate 2 on which the security device 10 is formed is translucent rather than transparent, the appearance of the common image CI will generally differ when viewed in reflected light versus transmitted light, and may also differ when viewed from different sides in reflected light. Figures 35(a) and 35(b) illustrate this with reference to a simple embodiment in which the common image comprises a set of parallel straight lines within a rectangular area. As shown in Figure 35(a), a surface relief structure 20 is formed from a colorless solidified material 20a and is disposed on a first surface of the translucent substrate 2 (e.g., in a non-window or semi-window area of ​​a paper or polymer substrate). The surface relief structure 20 comprises a set of raised line elements corresponding to the parallel lines of the image. On the opposite surface of the substrate 2, a print layer 30 is disposed and comprises a set of line elements, again corresponding to the parallel lines of the image, aligned with the raised elements of the surface relief structure 20. The ink 30a forming the printed lines may, for example, be yellow. As shown in Figure 35(b)(i), when the security device is viewed in reflected light from the side of the observer O1, only the surface relief structure is visible, while the contribution of the printed layer 30 is substantially obscured by the substrate 2. Consequently, the common image CI appears as a set of colorless parallel lines made visible by the reflective properties of the cured material 20a. When the same device 10 is viewed in transmitted light (from either side), the printed layer 30 is visible, and the common image thus now appears as a set of parallel yellow lines against a colorless background (or, more precisely, the background will be the same color as the substrate 2). Due to the surface relief structure, the common image will be tactile.

[0181] Figures 36(a) and 36(b) illustrate another embodiment identical to the embodiment of Figures 35(a) and 35(b), except that here the cured material 20a forming the surface relief structure is colored with a tint, such as blue. Thus, as shown in Figure 36(b)(i), when the security device 10 is viewed in reflected light from the side of the observer O1, only the surface relief structure will be visible, while the contribution of the printed layer 30 will be substantially obscured by the substrate 2. Thus, as shown, the common image CI can be represented as a blue rectangle with a superimposed set of parallel lines made visible by the reflective properties of the cured material 20a. Alternatively, depending on the intensity of the blue tint in the cured material 20a and the relative heights of the raised elements and the base layer, the background area may appear lighter in color (or even colorless) than the raised elements, resulting in the appearance of a set of blue parallel lines. When the same device 10 is viewed in transmitted light (from either side), the printed layer 30 is visible, so the common image now appears as a set of parallel green lines against a blue rectangular background. Alternatively, if the blue tint in the base layer of the surface relief structure is very light, the background may appear essentially colorless. The color of the line is produced by the mixture of the color of the cured material 20a and the color of the ink 30a. Due to the surface relief structure, the common image will have a tactile feel.

[0182] The opacity level of the substrate 2 can also be used to produce different visual effects from one security device configuration and the same security device configuration. This is illustrated by reference to the embodiment of Figure 37(a) to Figure 37(c) where three copies of a security device having the same construction are provided on one security document 100. The security devices 10a, 10b and 10c each comprise a surface relief structure 20 formed from a cured material 20a having a coloured tint (e.g. blue) on the first surface of the substrate 2 and an aligned printed layer 30 formed from an ink 30a (e.g. red) on the opposite surface. The only difference between the three security devices 10a, 10b and 10c is their peripheral shape, which here is different in order to quickly identify the three devices. The security device 10a is circular, the security device 10b is square and the security device 10c is triangular. As best shown in the cross-section of Figure 37(a), the circular security device 10a is located in a half-window region 52 of the security document 100 in which one of the opaque layers 2b is present but the other is not, so that this region is translucent. The square security device 10b is located in a (full) window region 51 in which both of the opaque layers 2b are not present, so that this region is transparent. The triangular security device 10c is located in a non-window region 50 of the security document 100 which is translucent (but smaller than the half-window region 52).

[0183] Figure 37(b) shows the appearance of the security document from the perspective of the observer Ol under reflected light. The circular security device 10a in the half-window region 52 appears as a set of spaced apart parallel blue lines against a background of the same colour as the substrate 2 (here it is assumed that the colour level and relative height of the raised elements and base layer are such that the base layer appears substantially colourless), since the contribution of the printed layer 30 is obscured by the substrate 2. The square security device 10b appears in the transparent window as a set of purple line elements, resulting from the mixing of the blue raised elements in the surface relief 20 and the red printed elements 30. The triangular security device 10c appears against a background having the same appearance as the substrate 2 as a set of blue line elements and so is similar in appearance to the security device 10a. When the security document 100 is viewed under transmitted light from the position of the observer Ol (Figure 37(b)(ii)), all three security devices 10a, 10b, 10c appear to present a set of line elements in purple resulting from the mixed colours. Thus, the appearance of the group of security devices changes between the reflected viewing mode and the transmitted viewing mode.

[0184] Similarly, when the security document is viewed from the opposite side (observer 02), as shown in Figure 37(c)(i), the triangular security device 10c and the circular security device 10a each present a set of reference lines (corresponding to the colour of the printed layer 30) as the contribution of the surface relief structure is now hidden by the semi- transparent nature of the substrate 2 in these areas. The square security device 10b still appears as a set of purple lines in the transparent window. Under transmitted light, as shown in Figure 37(c)(ii), the three security devices each present a set of purple lines, as before. In this way, a complex effect can be achieved in which the security document presents at least three different colour appearances depending on the side of the document being viewed and the mode of observation. It will be appreciated that while three separate security devices 10 have been employed in this example to illustrate the principle, the same can equally be applied to different laterally offset portions of a single security device 10. That is, each portion of the security device can be located on any of the following: a window region, a half-window region and a non-window region, and preferably a mix of these regions is provided.

[0185] In a refinement of the application, further complexity can be achieved by additionally providing an integral printed mark 60 in the substrate 2. The printed mark is formed during the manufacture of the document substrate, rather than being applied to the substrate during its subsequent processing. Typically, the printed mark can be integrated into the multi-layer polymeric document substrate during the same process as the application of the opaque layer 2b to the core substrate 2a, for example via intaglio printing. Thus, the integral printed mark 60 will register precisely with the opaque layer 2b, in particular any window regions or half-window regions they define. Such printed marks can be incorporated into the kind of security device disclosed herein (in addition to the printed layer 30) by arranging the first region R1 to partially or completely overlie or otherwise interact with (e.g. appear to abut, surround or interlock with) the printed mark 60. It will be appreciated that the degree of registration between the printed mark 60 and the remainder of the security device 10 can not be as accurate as that between the surface relief structure 20 and the printed layer 30, as it is formed in a separate, earlier process (not coincident with the application of the surface relief structure 20 and the printed layer 30). Reference will now be made to Figures 38(a) to 42 Some examples of security devices 10 incorporating printed marks 60 are described.

[0186] Figures 38(a), 38(b) and 38(c) are cross-sections through a simple implementation of a security device 10 formed on a substrate 2 having printed indicia 60, showing three different possible arrangements of the printed indicia 60. In each example, the security device 10 comprises a surface relief structure 20 formed from a colourless cured material and a printed layer 30 formed from a coloured ink (e.g. yellow). The common image is a set of parallel lines in a rectangular region. In the implementation of Figure 38(a), printed indicia 60 in the form of a blue rectangle (formed from a semi-transparent blue dyed ink) are located on the surface of the transparent core substrate 60 adjacent to the printed layer 30, with an opaque layer 2b located between them. Alternatively, as shown in Figure 38(b), the same printed indicia 60 can be located on the opposite surface of the transparent core substrate 2a. Yet alternatively, the printed indicia 60 can be distributed between the two surfaces of the core substrate 2a - for example, as shown in Figure 38(c), a first half 60a of the printed indicia can be located on one side of the core substrate 2a, while a second half 60b is located on the other side. If the opaque layer 2b has sufficient optical density, then the security devices 10 shown in Figures 38(a), 38(b) and 38(c) will all appear identical to each other, as shown in Figure 38(d). From the perspective of the observer Ol in reflected light, the common image will appear as a colourless rectangle (of the same colour as the opaque layer 2b) with a set of lines visible (Figure 38(d)(i)) through the reflective properties of the cured material. From either side in transmitted light, the contribution made by the printed layer 30 and the printed indicia 60 will now be visible as shown in Figure 38(d)(ii), resulting in the common image showing a blue rectangle with green lines superimposed on it. If the opaque layer is more semi-transparent, then the device shown in Figure 38(a) will behave as before as shown in Figure 38(d), but the devices of Figures 38(b) and 38(c) will exhibit a blue colour shade in reflection in the regions where the printed indicia are located on the observer side of the substrate.

[0187] While in the above example the overall printed indicia 60 has been positioned such that it is covered by at least one opaque layer 2b, this is not essential and the printed indicia 60 can be located on the outer surface of the substrate 2. The printed indicia is still considered to be integral with the substrate 2 because it is formed during manufacture of the substrate 2, rather than during a subsequent process of working the substrate into a security document. As before, the printed indicia 60 can be applied in register with the opaque layer 2b, for example via intaglio printing. Figures 39(a) and 39(b) illustrate an embodiment utilising this approach. Here, the security device is located in a half window region or a non-window region of a polymeric substrate, with at least one opaque layer 2b present on the transparent core substrate 2a. The common image C.I. to be viewed under transmitted light is a full colour photographic portrait (Figure 39(b)(i)). The image is formed in CMYK colour channels (although RGB could alternatively be used). An overall printed indicia 60 is incorporated on the outer surface of the substrate 2 during manufacture of the substrate 2, and is configured to provide one of the colour components of the portrait, for example the cyan colour. To form the security device, a surface relief structure defining the same portrait is applied to the same surface of the substrate 2, over and in register with the printed indicia 60. The surface relief structure is formed from an achromatic cured material and as before provides a tactile sensation to the common image. On the opposite surface of the substrate, a printed layer 30 is applied which includes the magenta, black and yellow components of the portrait. When the security device is viewed under reflected light from the position of the observer Ol, the contribution of the printed layer 30 is obscured by the opaque layer 2b, so the common image appears as a monochrome, multi-tonal version of the cyan portrait. When the security device is viewed under transmitted light from either side, the full colour version of the image can be seen.

[0188] Another example is shown in Figures 40(a) and 40(b). Here, the security device 10 has a simpler design in which the common image comprises a set of parallel spaced lines in a rectangular area. The security device is formed on a non-window region of the substrate 2, which comprises a printed mark 60 on the outside of its second surface 3b. The printed mark 60 is here a blue rectangle. A printed layer 30 is applied over the printed mark 60 and comprises a set of line elements printed in ink (such as yellow) corresponding to the set of line elements of the common image. A surface relief structure 20 formed in a colourless solidified material is applied to the opposite surface of the substrate 2 and defines a set of parallel raised line elements. When the security device 10 is viewed in reflected light from the position of the observer Ol, the common image appears as a colourless area (matching the appearance of the substrate 2) with the set of lines superimposed over it, which become visible by the reflective properties of the solidified material. This is shown in Figure 40(b)(i). In transmitted light (Figure 40(b)(ii)), the contribution of the printed layer 30 and the printed mark 60 results in the common image appearing as a set of green lines on a blue rectangle area, the green resulting from the mixing of the colour of the printed mark and the colour of the ink forming the printed layer 30. When viewed in reflected light from the position of the observer 02, the image appears as a set of yellow lines on a blue background (Figure 40(b)(iii)).

[0189] In a variation of this embodiment shown in Figures 41(a) and 41(b), the same security device is now located in a transparent window region 51 of the substrate 2. The printed mark 60 is also located in the transparent window. Now, the appearance of the security device 10 will be the same in reflected and transmitted light and from either side of the device, including a set of green lines on a blue background.

[0190] Figure 42 A further embodiment similar to Figures 39(a) and 39(b) is shown. In this case, what is provided by the printed mark 60 is the black component of a full-colour portrait, although any one or more components could be formed in this way. In this embodiment, the surface relief structure 20 is configured to encapsulate the printed mark 60 - i.e. to completely cover the printed mark 60 and seal it from contact with the atmosphere or anything external. In this way, the printed mark 60 is protected from external influences and the lifetime of the security device is improved.

[0191] In another example, a register "border" effect (registered to the original mark as the standard) using this method can be applied around a hidden intaglio printed mark. For example, the cast haptic structure can define only the outer shape of the image, while the printed mark defines the complete image.

[0192] Optionally, the substrate itself can carry a colour tint, for example in one or more opaque layers. This colour will contribute to the overall appearance of the image in transmitted light and so can act as a colour channel in a "full-colour" image.

[0193] In each of the above examples, the cast haptic structure can take a variety of different forms depending on the nature of the desired tactile sensation and / or the manner in which the structure contributes to the visible image. In some examples, the cast structure can comprise an array of screen elements constituting a screened version of the image. In other cases, the cast UV resin can cover the entire image (sharing its periphery or matching certain features thereof to show register) and can be provided with a textured upper surface. In still further cases, the cast structure can follow the contours of a 3D version of the image.

[0194] In all of the above implementations, the printed layer 30 has been formed from one or more visible pigmented materials (e.g., inks) such that the collective image is visible to the naked eye under standard illumination conditions (e.g., white light). However, in all of the implementations, one or more substances can be used to form the printed layer 30 that are reactive to a stimulus (such as an invisible illumination wavelength) and / or exhibit different behavior outside of the visible spectrum (which can be detected by a suitable camera device). For example, one or more materials (e.g., inks) forming the printed layer 30 can be luminescent (e.g., fluorescent or phosphorescent) and / or can absorb certain invisible wavelengths (such as IR). The printed layer 30 can also be formed from materials having other security effects such as optically variable inks, pearlescent inks, iridescent inks, metallic inks, conductive inks, thermochromic inks, magnetic inks, etc.

[0195] Figures 43(a) to 43(d) Some examples of security devices using one or more inks that luminesce in response to UV wavelengths are shown. All of these implementations are haptic due to the presence of a surface relief structure 20 as before, here formed from a colorless cured material 20a. In the implementation of Figure 43(a), the entire printed layer 30 is formed from a material 30a that exhibits a first color under standard visible illumination (e.g., white light) and luminesces in the same color under suitable UV illumination. The collective image is the numeral "5". For example, under standard visible illumination, the collective image C.I. v may appear as a yellow image of the numeral "5", while under non-visible (UV) illumination, the collective image C.I. n will again be a yellow-luminescing numeral "5". In the implementation of Figure 43(b), the printed layer 30 is formed from a material 30a that is colorless (non-visible) under standard illumination, so that under these conditions, the collective image C.I. v is a colorless numeral "5" made visible by the reflective properties of the cured material 20a. Under suitable non-visible illumination (e.g., UV), the material 30a luminesces in a selected color (e.g., yellow) such that the device now appears to present a colored numeral "5".

[0196] In the embodiment of Figure 43(c), the printed layer 30 is formed from a material 30a which has one visible colour (e.g. green) under standard illumination and which emits light of a different colour (e.g. yellow) under non-visible (e.g. UV) illumination. Thus, under visible light, the collective image C.I. v is a green digital ‘5’, whereas under UV light, the appearance of the device changes and the collective image C.I. n now appears as a yellow digital ‘5’. In more complex examples, two or more materials can be used to form the printed layer 30, with some materials being responsive to non-visible wavelengths and some not, or presenting a plurality of responsive materials which change colour differently to each other. For example, in the embodiment of Figure 43(d), the printed layer 30 is divided into two halves by the line Z-Z’. The left half of the printed layer is formed from a first material 30a which has no response to UV and which exhibits a first colour (e.g. green) under visible light. The right half of the printed layer 30 is formed from a second material 30b which exhibits substantially the same first colour (e.g. green) under visible light and which emits light of a different second colour (e.g. yellow) when illuminated by appropriate non-visible light (e.g. UV). Thus, under standard visible illumination, the collective image C.I. v appears as a complete representation of a green digital ‘5’ (the two halves of colour matching each other). However, under appropriate non-visible illumination (e.g. UV), only the right half of the digital is visible and presents a colour change, exhibiting yellow, revealing the pattern hidden within the printed layer 30. Likewise, an opposite arrangement can be provided in which the right and left hands of the ‘5’ can appear different to each other (e.g. one is red and the other is blue) under visible light, whereas under UV illumination, both regions can emit the same colour (e.g. yellow). Two or more UV responsive materials which match under visible illumination and each present a different emission colour under UV illumination can also be used. Examples of suitable inks are disclosed in WO-A-2004 / 050376 and WO-A-2018 / 206936.

[0197] Figures 44(a) and 44(b) illustrate a further embodiment in which the printed layer 30 comprises substances 30a, 30b, 30c which emit red, green and blue light respectively. This embodiment is otherwise identical to the embodiment of Figures 9(a) and 9(b) described above. Under illumination of a corresponding excitation wavelength (e.g. UV), the device presents a full colour version of the collective image. Examples of suitable substances are disclosed in WO-A-2020 / 030893. These substances can be invisible under standard visible illumination. In this case, as shown in Figure 44(b)(i), under visible light, the collective image C.I. vThe printed layer 30 will be excited and show a full colour RGB image under UV illumination. In a variation of this example, the printed layer 30 can comprise three colour components which combine to present a full colour image under standard visible light (as shown in Figures 44(a) and 44(b)), but only one of the materials emits light under UV illumination. For example, the three components can appear red, green and blue under white light, and only the green material can be fluorescent, for example emitting yellow light under UV. Thus, when the device is observed under white light and the illumination conditions are then changed to UV, the image appears to change from full colour to single colour.

[0198] Figures 45(b) and 45(c) show two embodiments using an infrared (IR) absorbing material in the printed layer 30. For comparison, Figure 45(a) shows an embodiment in which the printed layer 30 is a standard pigmented ink 30a which does not absorb the IR spectrum. When viewed with the naked eye under standard illumination, the common image C.I. v appears as the number “5” in the colour of the material 30a (for example, yellow). This image is not visible in the IR spectrum. In the embodiment of Figure 45(b), the printed layer 30 is formed from a material 30a which has a visible colour such as yellow and is IR absorbing. When viewed with the naked eye under standard illumination, the common image C.I. v appears again as the number “5” in the colour displayed by the materials 30a and 30b (for example, yellow). When viewed via a suitable camera device in the IR spectrum, the left half 18a of the number “5” is no longer visible, while the right half 18b appears as an absorbing region.

[0199] In all of the above examples, the arrangement of the printed layer on one side of the substrate and the arrangement of the relief structure on the other side means that both can be applied simultaneously. This enables extremely high register between the printed layer and the relief structure, as there is no movement of the substrate between the application of the two components: they are both applied to opposite surfaces of the substrate at the same location along the substrate (in the machine direction - the direction in which the substrate moves through the manufacturing equipment) at the same time. The substrate can be in the form of a sheet or web.

[0200] WO-A-2018 / 153840 and WO-A-2017 / 009616. In particular, the relief structure can be formed using the in-line casting apparatus described in detail in WO-A-2018 / 153840 (e.g., the 80 designated in Figures 4(a) and 4(b) thereof) using an embossing tool 85 with a suitably designed micro-optical structure that can cast the desired relief structure shape. Similarly, the cast-cure apparatus and method disclosed in Section 2.1 of WO-A-2017 / 009616 (e.g., the 220 designated in Figures 2(a) and 2(b) thereof) can also be used to form the presently disclosed relief structure by replacing the relief 225 carried on the casting tool 220 with a suitable relief that can cast the desired shape. In particular, it will be noted that while WO-A-2017 / 009616 describes using the apparatus to form focusing elements, the same apparatus can be used to form any desired relief structure by suitably reconfiguring the relief 225, including as contemplated herein. Figures 4(a) to 8

[0201] Regardless of which casting apparatus is used, the curable material used to cast the relief structure can be applied 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 can 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 pressing the tool into the deposited curable material). Both options are described in the aforementioned documents. Preferably, the latter option is employed and the curable material is applied to the substrate by screen printing as described in detail in WO-A-2018 / 153840 and then the desired relief structure is formed. If the former option is employed, it should be noted that the casting tool surface relief is preferably not wiped between the application of the curable material to the casting tool surface relief and the bringing of the casting tool surface relief into contact with the substrate, such that a base layer of the curable material remains joining the projections of the relief structure together on the substrate (the height of the base layer will be much less than that of the projections).

[0202] A suitable curable material is disclosed in WO-A-2017 / 009616, Section 2.1. A UV-curable material is most preferred. Curing of the material preferably occurs simultaneously with the contact of the casting tool with the curable material, against the substrate.

[0203] In all of the above embodiments, the transparent curable material forming the surface relief structure 20 can have a variety of different compositions. The curable material is preferably radiation-curable and can comprise a resin that can generally be one of two types, namely:

[0204] ​a) Free radical curing resins, which are typically unsaturated resins or monomers, prepolymers, oligomers etc., containing for example vinyl or acrylate unsaturation, and which are crosslinked by using photoinitiators activated by the radiation source used (eg UV).

[0205] b) Cationic curing resins, where the ring opening is effected (eg epoxy type) using photoinitiators or catalysts that generate ionic entities under the radiation source used (eg UV). The ring opening is followed by intermolecular crosslinking.

[0206] The radiation used to effect curing is typically UV, but may also include electron beam, visible or even infrared or higher wavelength radiation, depending on the material, its absorbance and the process used. Examples of suitable curable materials include UV curable acrylic based transparent embossing lacquers, or those based on other compounds such as nitrocellulose. Suitable UV curable lacquers are the product UVF-203 from Kingfisher Ink Limited or the photopolymer NOA61 available from Norland Products, Inc, New Jersey.

[0207] Due to the nature of the cast-and-cure process, the resulting relief structure will typically include a base layer of material on top of the substrate, which base layer connects the protrusions of the relief at their base. In many cases, this base layer is integral with the relief structure and is formed from the same curable material, resulting from the shape of the cast relief and / or the way the curable material is pressed between the substrate and the casting tool during processing. Figure 8 Examples of such base layers and their formation are disclosed in WO-A-2017 / 09620. It is also possible to provide (alternatively or additionally) a base layer in the form of a base layer applied in a previous step. Figures 8 to 12 An apparatus and method for providing such a base layer are disclosed in .

[0208] An example of a suitable cast-and-cure process for forming a surface relief structure 20 suitable for use in the security devices disclosed herein will be described with reference to Figures 46(a) and 46(b), which illustrate the structure 20 only schematically. The process is shown as being applied to a support layer 201 comprising a transparent or translucent film, which may be the document substrate 2 described above or another substrate 2' that may be later applied to the document substrate 2. Figure 46(a) depicts the apparatus from a side view, while Figure 46(b) shows the support layer in perspective, with the manufacturing apparatus itself removed for clarity.

[0209] The transparent curable material 205 is first applied to the support layer 201 using an application module 210, which here comprises a patterned printing cylinder 211 which is supplied with curable material from a doctor chamber 213 via an intermediate roller 212. For example, the components shown can form part of a flexographic printing system. Other printing techniques such as lithographic, screen or gravure printing can also be used. Printing processes such as these are preferred because the curable material 205 can then be laid down on the support 201 only in its selected regions 202, the size, shape and location of which can be selected by control of the printing process, for example by appropriate configuration of the pattern on the cylinder 211. However, in other cases a blanket coating method can be used, for example if a surface relief structure is to be formed across the whole of the support 201. The curable material 205 is applied to the support 201 in an uncured (or at least not fully cured) state, and so can be a fluid or a formable solid.

[0210] The support 201 is then conveyed to a casting module 220, which here comprises a casting tool 221 in the form of a cylinder, with a surface relief 225 defining the shape of the surface relief structure to be cast into the curable material 205. As each region 202 of the curable material 205 comes into contact with the cylinder 221, the curable material 205 fills the corresponding region of the relief structure, thereby forming the surface of the curable material into the shape defined by the relief. The cylinder 221 can be configured so that the relief structure 225 is provided only at regions corresponding to the shape and location of the first regions 202 of the curable material 205.

[0211] Having formed the correct surface relief structure, the curable material 205 is cured by exposing it to appropriate curing energy, such as radiation R from a source 222. This preferably occurs while the curable material is in contact with the surface relief 225, although it can be performed after separation if the material is sufficiently viscous. In the example shown, the material is irradiated through the support layer 201, although the source 222 can instead be positioned above the support layer 201, for example within the cylinder 221 if it is formed of a suitable transparent material such as quartz. In alternative embodiments, the curable material 205 can be applied directly to the casting tool 221 rather than to the substrate 201. This can be done in a blanket or patterned fashion.

[0212] Generally, in embodiments where the curable material is applied directly to the casting tool 221, the curable material is applied to substantially fill the trenches 121, and to form a thin layer of curable material in the first region over substantially the entire surface of the casting tool 221 - i.e. over the raised portions of the relief on the casting tool, as well as over the raised portions. There is no wiping / doctoring step. After the casting process, this thin layer of curable material forms the integral base layer of the surface relief structure. In alternative methods, the curable material 205 can be applied to the casting tool to be present only within the trenches 121, e.g. by removing material from the top of the raised portions using a doctor blade or other removal device. In such examples, a tie-coat layer is then applied to substantially the entire surface of the die form 221 - i.e. coating the filled recessed areas of the trenches and the raised areas between these recessed areas. The curable material of the tie-coat layer can or can not have the same composition as the curable material 205 in the trenches. In particularly preferred embodiments, the tie-coat layer composition can be selected to improve adhesion between the curable material 205 and the support layer. The tie-coat layer is applied by a tie-coat layer application module. It is desirable to apply the tie-coat layer in a continuous, homogenous manner at the micron scale, so it is preferably applied in a metered manner via a slot die and transfer roller combination. The tie-coat layer can be partially cured before the casting tool and substrate are brought into contact.

[0213] In all embodiments of the application, the printed layer 30 can be applied to the substrate using any convenient printing technique, but a technique is preferably chosen which does not cause any embossing of the substrate. Gravure printing, lithographic printing, flexographic printing, wet or dry offset printing, inkjet or microgravure printing are particularly preferred techniques. If the printed layer 30 is to comprise multiple printed articles, they are preferably collected on a transfer roller or blanket before being applied together to the substrate. Preferably, where multiple inks are used, these are accurately registered to one another to the extent that any misregistration between them is too small to be perceived by the naked eye. For example, the translational colour-to-colour registration (i.e. in the machine direction x or cross direction y) can be within + / - 5 - 10 pm. The skew registration (i.e. rotational alignment) can be within 0.02 degrees. The pitch registration (i.e. the extent to which the coverage of one colour is stretched relative to another) can be within 0.01%. Gravure printing cannot achieve such levels of registration, so the colour reproduction of the application is significantly better.

[0214] WO-A-2018 / 153840 and WO-A-2017 / 009616 also disclose printing stations which can be provided downstream of the above-described casting apparatus (but alternatively can be located upstream, or at the same point in the machine direction, as described below). Printing stations such as these are suitable for applying any print layer 30 to the side of the substrate opposite to the side bearing the cast relief structure. The apparatus disclosed in WO-A-2018 / 153840 can achieve particularly high register between such cast relief structures and printing elements.

[0215] For example, in the preferred method, the relief structure and print layer are preferably registered with each other sufficiently accurately that any misregistration is too small to be perceived by the naked eye. Preferably, the translational register (i.e. in the machine direction x or cross direction y) is within 150 pm (+ / - 75 pm). Desirably, the skew register (i.e. rotational alignment) is within 1 degree (preferably less than 0.1, more preferably less than 0.05, most preferably less than 0.02 degrees). Advantageously, the pitch register (i.e. the extent to which one component is stretched relative to the other) is within 0.01%. The precision of register achieved will depend on the consumables used in the machine (substrate, inks, resin, printing plates) and the actual machine configuration.

[0216] It is highly desirable to apply the surface relief structure 20 and print layer 30 to opposite surfaces of the substrate 2 simultaneously. That is, at the same location along the conveyance path in the machine direction. This makes it possible to achieve the highest register between the two components. The apparatus of WO-A-2018 / 153840 is suitable for this purpose. Figure 7 A suitable apparatus to achieve this is shown.

[0217] Figure 47 A schematic example is shown in the case where the surface relief structure 20 and print layer 30 are applied to first and second surfaces of a document substrate 2 (which can be a web or sheet). However, the same principles can be applied to the construction of articles such as security threads, in which case the substrate 2 would be replaced by some other, typically thinner, transparent or semi-transparent film. The surface relief structure 20 and print layer 30 can be formed using any of the processes described above. For clarity, Figure 47Only selected components of the apparatus for forming the surface relief structure 20 and the print layer 30 are depicted, namely the casting tool 221 (e.g. as shown in Figs. 46(a) and 46(b)) and the common print roller 302 which is supplied with the three inks 30a, 30b and 30c via corresponding inking rollers 303a, 303b, 303c. Other components of the production line are not shown. The curable material can be applied to the substrate 2 upstream of the casting tool 221 or directly to the casting tool 221. The casting tool 221 and the print roller 302 are arranged on opposite sides of a transport path along which the substrate 2 is transported to form a (low pressure) nip through which the substrate 2 passes. At each location along the polymer substrate 2, thus, the first surface 3a of the substrate 2 is in contact with the casting tool 221 while the second surface 3b of the substrate 2 is in contact with the print roller 302. As a result, the surface relief structure 20 and the print layer 30 are formed simultaneously at each point of the substrate.

[0218] This has the significant advantage that any deformation of the substrate 2 due to variations in processing temperature etc. will be exactly the same as when the surface relief structure 20 is applied to the polymer substrate 2, i.e. when the print layer 30 is applied. The substrate has no time to expand or contract between the instant the surface relief structure 20 is applied and the print layer 30 is applied, as they occur simultaneously. Thus, a very high degree of register between the two components is automatically achieved.

[0219] Figure 47 A disadvantage of the arrangement shown in Fig. 46 is that because the nip between the casting tool 221 and the print roller 302 constitutes the first point of contact between the substrate and the casting tool 221, the transparent curable material 205 forming the surface relief structure 20 will be substantially uncured as it enters the nip. Therefore, the pressure applied between the casting tool 221 and the print roller 302 should be low to avoid damaging the cast surface relief structure 20.

[0220] Figure 48 An improved arrangement is shown in which the formation of the surface relief structure 20 and the application of the print layer 30 can still be considered to occur simultaneously, as the curable material 205 is still in contact with the surface relief on the casting tool 221 at the nip position between the casting tool 221 and the print roller 302. The curable material can be applied to the substrate 2 upstream of the casting tool 221 or directly to the casting tool 221. The substrate is wound from a first point on the roll 61 over a portion of the casting tool 221 at which point the casting of the surface relief structure 20 starts until the nip with the print roller 302 at which point the surface relief structure 20 will be relatively well cured, preferably fully cured. Therefore, the pressure between the two components 221, 302 can be relatively high with respect to the pressure in the nip between the casting tool 221 and the print roller 302. Figure 47The pressure increase in embodiments where the material 205 is relatively hard and not easily damaged. This improves the quality achieved during the formation of the print layer 30. A further benefit of the arrangement shown is that the length of the substrate 2 wound around the print roll 302 is increased, thereby also allowing for extended curing here. The substrate 2 is in contact with the print roll 302 from the nip position until the take-up roll 62.

[0221] The simultaneous application of the surface relief structure and the print layer is preferred but not essential. Figure 49 An exemplary arrangement for sequentially (rather than simultaneously) applying two components 20, 30 on opposite sides of a substrate 2 (which here is in the form of a sheet) is shown. This can be described as forming two components in-line in the same pass. The arrangement generally comprises a print and cast module 410 for forming the surface relief and a print station 420. The substrate enters the apparatus at arrow A and exits at arrow B. The curable material 205 is first applied to the first side of the sheet substrate 2 as it passes through a nip formed by a screen print cylinder 411a and an intermediate roll 412a. However, as mentioned previously, other print technologies can be used, such as lithographic, flexographic, offset or inkjet printing. The sheet 2 is then conveyed to a cast tool 421a in the form of a cylinder which defines the shape of the surface relief structure to be cast into the curable material 205. Having been formed (shaped) into the desired surface relief structure, the curable material 205 is cured by exposing it to the appropriate curing energy, such as UV radiation from the source 222. This preferably occurs while the curable material is in contact with the surface relief 225, although this can be performed after separation if the material is already sufficiently viscous.

[0222] The sheet substrate 2, now with the cured surface relief structure 20, is conveyed to the print station 420. In this example, the print station 420 is a lithographic printing apparatus comprising a patterned print cylinder 302 which is selectively supplied with one or more inks 30a, 30b, 30c via inking rollers 303a, 303b, 303c. The image is transferred from the print cylinder 302 to a blanket cylinder 306 and then to the substrate 2 at the nip between the blanket cylinder 306 and a impression cylinder 305. The substrate 2, now with the surface relief 20 and the print layer 30 on the opposite side, is then conveyed away from the print module 420 by arrow B.

[0223] Suitable substrates on which the disclosed devices can be formed are disclosed in Section 1 of WO-A-2017 / 009616, and the equipment / methods for applying the opaque layer thereto, including the formation of window regions, are disclosed in Section 4. Preferably, the opaque layer is applied on the substrate prior to the formation of the presently disclosed security device thereon. For example, the sheet material supplied to the equipment of WO-A-2018 / 153840 can comprise a polymer substrate of the kind disclosed in WO-A-2017 / 009616 which has already been provided with one or more opaque layers. The security devices disclosed herein can be provided in a window region defined by the opaque layer, or in a non-window region.

[0224] Some preferred aspects of the present application are set out in the following clauses:

[0225] Clause 1. A security device comprising:

[0226] a substrate having opposite first and second surfaces;

[0227] a surface relief structure on the first surface of the substrate, the surface relief structure being formed from a cured, at least semi-transparent material; and

[0228] a printed layer on the second surface of the substrate;

[0229] wherein, in at least a first region of the security device, the surface relief structure and the printed layer are each defined according to the same image and are aligned with one another, whereby the surface relief structure provides a tactile sensation for the image.

[0230] Clause 2. The security device of clause 1, wherein the curable material is colourless and the printed layer defines a multi-coloured image, preferably a full-colour image, most preferably an RGB or CMYK image.

[0231] Clause 3. The security device of clause 1, wherein the curable material is tinted with a first colour and the printed layer defines an image in at least a second colour, such that a multi-coloured version of the image is visible when viewed in combination.

[0232] Clause 4. The security device of clause 3, wherein the first colour is one of red, green and blue and the printed layer defines an image in the other two of red, green and blue, such that a full-colour RGB version of the image is observed when viewed in combination.

[0233] Clause 5. The security device of any one of the preceding clauses, wherein the height of the surface relief structure varies according to the image.

[0234] Clause 6. The security device according to any of the preceding clauses, wherein the security device further comprises a second area in which one or both of the surface relief structure and the printed layer are present.

[0235] Clause 7. The security device according to any of the preceding clauses, wherein the substrate is transparent in at least part, preferably all, of the first area of the security device.

[0236] Clause 8. A method of manufacturing a security device, the method comprising forming a surface relief structure on a first surface of a transparent substrate by cast-curing at least a translucent curable material on the first surface of the transparent substrate, and printing a printed layer on a second surface of the transparent substrate, wherein the surface relief structure and the printed layer are each defined according to the same image and are aligned with each other, whereby the surface relief structure provides a tactile sensation for the image.

[0237] Clause 9. The method according to clause 8, wherein the forming of the surface relief structure and the printing of the printed layer are simultaneous, occurring simultaneously at the same location along the machine direction.

[0238] Clause 10. The method according to clause 8 or 9, the method being configured to provide any of the features of clauses 1 to 7 for the security device.

Claims

1. A safety device, comprising: a substrate having first and second opposing surfaces; a surface relief structure on the first surface of the substrate, the surface relief structure being formed from one or more cured, at least translucent materials; as well as a printing layer, the printing layer being on the second surface of the substrate; wherein, in at least a first area of ​​the security device, the substrate in at least a portion of the at least first area is transparent or translucent, the surface relief structure and the printed layer are each defined according to a common image and aligned with each other, the surface relief structure presents a first set of features of the common image, and the printed layer presents a second set of features of the common image, whereby the common image is a static macroscopic image and is presented by the surface relief structure and the printed layer in combination with each other, and the surface relief structure provides a tactile feel to the common image, and wherein the surface relief structure comprises a plurality of spaced-apart protrusions connected to each other by a base layer having a height lower than the height of the plurality of spaced-apart protrusions.

2. The safety device according to claim 1, wherein: The first feature set and the second feature set are identical to each other, and the surface relief structure and the printed layer each exhibit all features of the common image.

3. The safety device according to claim 1, wherein: The first feature set and the second feature set are different from each other, and the first feature set and / or the second feature set are a subset of features of the common image.

4. The safety device according to claim 3, wherein: One or more of the features of the common image are included in the first set of features and the second set of features, and the one or more features are represented by both the surface relief structure and the printed layer.

5. The safety device according to claim 3 or 4, wherein: The first feature set includes features of the common image located in a first portion of the common image, and the second feature set of the common image includes features of the common image located in a second portion of the common image, the first portion and the second portion being different from each other.

6. The safety device according to claim 5, wherein: The first portion and the second portion are laterally offset from each other.

7. The safety device according to any one of claims 1 to 4, wherein: The first set of features corresponds to a first color component of the common image, and the second set of features corresponds to at least a second color component of the common image.

8. The safety device according to any one of claims 1 to 4, wherein: the first set of features of the common image exhibited by the surface relief structure being laterally entirely within the boundaries of the second set of features of the common image exhibited by the printed layer; and / or The second set of features of the common image exhibited by the printed layer is located completely laterally within the boundaries of the second set of features of the common image exhibited by the surface relief structure.

9. The safety device according to claim 8, wherein: the entire surface relief structure is completely laterally located within the boundaries of the second set of features of the common image exhibited by the printed layer; and / or The entire printed layer is laterally completely within the boundaries of the second set of features of the common image exhibited by the surface relief structure.

10. The safety device according to any one of claims 1 to 4, wherein: The common image is at least partially defined by an array of image elements that are spaced apart from one another, and: the surface relief structure comprising a plurality of raised elements spaced apart from one another, the plurality of raised elements forming image elements defining the first set of features of the common image; and / or The print layer includes a plurality of print elements spaced apart from one another, the plurality of print elements forming image elements defining the second set of features of the common image.

11. The safety device according to claim 10, wherein: The common image is a screened image, and the image elements on the array vary in size, shape, color, optical density and / or spacing of the image elements to express the common image.

12. The safety device according to claim 11, wherein: The array of picture elements is arranged on a regular grid.

13. The safety device according to claim 10, wherein: The image element is a straight or curved line element, a point element, or an element having a marked shape.

14. The safety device according to claim 13, wherein: The elements having the shape of a mark are alphanumeric characters or printed symbols.

15. The safety device according to any one of claims 1 to 4, wherein: The base layer extends over a peripheral region surrounding the plurality of spaced apart protrusions.

16. The safety device according to any one of claims 1 to 4, wherein: The common image is a multi-tonal and / or multi-colored image.

17. The safety device according to claim 16, wherein: The common image is a grayscale image or a full-color image.

18. The safety device according to any one of claims 1 to 4, wherein: At least one of the cured, at least translucent materials is colorless and the printed layer exhibits one or more visible colors.

19. The safety device according to claim 18, wherein: The printing layer is an RGB printing layer, a CMYK printing layer or an orange-green-purple printing layer.

20. The safety device according to any one of claims 1 to 4, wherein: At least one of the cured, at least translucent materials has a tint of a first color, and the printed layer exhibits at least the first color and / or a second color.

21. The safety device according to claim 20, wherein: The first color and / or the second color are configured such that when viewed in combination, a multi-colored version of the common image is visible.

22. The safety device of claim 20, wherein: The first color is one of red, green, and blue, and the printed layers exhibit the other two of red, green, and blue such that when viewed in combination, a full color version of the common image is visible.

23. The safety device of claim 20, wherein: The first color is one of cyan, magenta, yellow, and black, and the printed layers present the other three of cyan, magenta, yellow, and black such that when viewed in combination, a full color version of the common image is visible.

24. A safety device according to any one of claims 1 to 4, wherein: The printed layer presents two areas with different corresponding colors and an intermediate area in which the colors gradually transition between the different corresponding colors.

25. A safety device according to any one of claims 1 to 4, wherein: At least one of the cured, at least translucent materials has a tint of at least one color and the printed layer has a visual opacity such that the color appearance of the common image is different when the security device is viewed from the side of the surface relief structure than when the security device is viewed from the side of the printed layer.

26. A safety device according to any one of claims 1 to 4, wherein: The printed layer includes one or more substances responsive to invisible wavelengths.

27. The safety device of claim 26, wherein: The one or more substances are UV or IR responsive, and the printed layer is invisible under white light.

28. The safety device of claim 26, wherein: The printed layer includes substances that emit red, green, and blue light when illuminated with corresponding excitation wavelength bands, thereby presenting a full-color version of the common image.

29. A safety device according to any one of claims 1 to 4, wherein: The height, width, length and / or geometry of the surface relief structures vary according to the common image.

30. A safety device according to any one of claims 1 to 4, wherein: The security device further comprises a second region in which one or both of the surface relief structure and the printed layer are present, the second region being laterally offset from the first region and not overlapping the first region, or being interleaved with the first region.

31. The safety device of claim 30, wherein: In the second area, the surface relief structure is present and forms any of the following: one or more optical elements; a tactile structure or a matte structure.

32. The safety device of claim 31, wherein: The one or more optical elements are focusing elements, facets, prisms, pyramids or caustic elements.

33. The safety device of claim 30, wherein: In the second region, the printed layer is present and forms any of the following: background printing, a visually uniform area, a color shifting layer, a printed color filter, and an image array.

34. A safety device according to claim 33, wherein: The image array is a micro-image array or an interlaced image.

35. The safety device of claim 31 , wherein: In the second region, the surface relief structure forms an array of focusing elements and the printed layer forms an image array substantially in a focal plane of the focusing elements, and the array of focusing elements and the image array are configured to cooperate with each other to generate an optically variable effect.

36. A safety device according to any one of claims 1 to 4, wherein: The substrate is transparent or translucent in the first region of the security device.

37. A group of substantially identical safety devices, wherein: The security device is a security device according to any one of claims 1 to 36, wherein in each security device of the plurality of security devices the respective surface relief structure and printed layer have the same position relative to each other.

38. A security document comprising a document substrate and a security device on the document substrate, wherein the security device is a security device according to any one of claims 1 to 36, wherein: The document substrate may or may not serve as the substrate for the security device.

39. A security document according to claim 38, wherein The document substrate includes paper, polymer, cellulose or a mixture thereof.

40. A security document according to claim 38 or 39, wherein: The first area of ​​the security device is at least partially located in a window or semi-window area of ​​the document substrate, the window or semi-window area having a lower optical density than the surrounding area of ​​the window or semi-window area.

41. A security document according to claim 38 or 39, wherein: The document substrate is translucent and the first area of ​​the security device is at least partially located in a non-window area of ​​the document substrate.

42. A security document according to claim 38 or 39, wherein: The first area includes portions located in at least two of the following: a window area of ​​the document substrate, a semi-window area of ​​the document substrate, and a non-window area of ​​the document substrate.

43. A security document according to claim 38 or 39, wherein: The security document comprises at least two security devices, each of which is a security device according to any one of claims 1 to 36, wherein the at least two security devices are respectively at least partially located in at least two of the following: the window area of ​​the document substrate, the semi-window area of ​​the document substrate, and the non-window area of ​​the document substrate.

44. A security document according to claim 38 or 39, wherein: The document substrate comprises a core polymer substrate having at least one opaque layer disposed on one or both surfaces of the core polymer substrate, wherein gaps in one or more of the opaque layers form a window or semi-window area of ​​the document substrate.

45. A security document according to claim 44, wherein: The document substrate further includes integrally printed indicia positioned between at least one of the opaque layers and the core polymer substrate.

46. ​​A security document according to claim 45, wherein: The integral printed mark is defined according to the common image and is registered with the surface relief structure and the print layer, the integral printed mark exhibiting a third set of features of the common image, whereby the common image is exhibited by the surface relief structure, the print layer, and the integral printed mark in combination with each other.

47. A security document according to claim 38 or 39, wherein: The substrate of the security device is attached to or incorporated into the document substrate.

48. A security document according to claim 47, wherein The substrate of the security device is attached to or bonded to a transparent or translucent area of ​​the document substrate.

49. A security document according to claim 48, wherein The transparent or translucent areas of the document substrate are formed as holes.

50. A security document according to claim 38 or 39 wherein: The security document is any one of the following: a banknote, a passport, an identification document, an identity card, a bank card, a driving license, a visa, a stamp, a check or a certificate.

51. A method of manufacturing a security device, the method comprising the following steps performed in any order or simultaneously: forming a surface relief structure on the first surface of the substrate from one or more at least translucent curable materials; and printing a printing layer onto the second surface of the substrate, in, In at least a first area of ​​the security device, the substrate in at least a portion of the at least first area is transparent or translucent, the surface relief structure and the printed layer are each defined according to a common image and aligned with each other, the surface relief structure presents a first set of features of the common image, and the printed layer presents a second set of features of the common image, whereby the common image is a static macroscopic image and is presented by the surface relief structure and the printed layer in combination with each other, and the surface relief structure provides a tactile feel to the common image, and wherein the surface relief structure includes a plurality of spaced-apart protrusions connected to each other by a base layer having a height lower than the height of the plurality of spaced-apart protrusions.

52. A method of manufacturing a security device according to claim 51, wherein: The forming of the surface relief structure and the printing of the print layer are performed in register with each other.

53. A method of manufacturing a security device according to claim 52, wherein: The skew registration between the surface relief structure and the printed layer is 1 degree or less.

54. A method of manufacturing a security device according to claim 52, wherein: The skew registration between the surface relief structure and the printed layer is 0.1 degrees or less.

55. A method of manufacturing a security device according to claim 52, wherein: The skew registration between the surface relief structure and the printed layer is 0.05 degrees or less.

56. A method of manufacturing a security device according to claim 52, wherein: The skew registration between the surface relief structure and the printed layer is 0.02 degrees or less.

57. A method of manufacturing a security device according to claim 52, wherein: The formation of the surface relief structure and the printing of the printing layer are simultaneous and occur at the same location in the machine direction.

58. A method of manufacturing a security device according to any one of claims 51 to 57, wherein: The printing layer is printed by gravure printing, offset printing, flexographic printing, wet or dry offset printing, inkjet printing or micro-gravure printing.

59. A method of manufacturing a security device according to any one of claims 51 to 57, wherein: Forming the surface relief structure includes cast-curing one or more at least translucent curable materials on the first surface of the substrate by: providing a casting tool having a mold relief defined therein corresponding to the surface relief structure; applying one or more of the at least translucent curable materials to the casting tool or the substrate; contacting the casting tool and the substrate with the one or more at least translucent curable materials between the casting tool and the substrate, thereby forming the one or more at least translucent curable materials into the surface relief structure; as well as During and / or after said contacting, said one or more at least translucent curable materials are cured to leave said surface relief structure.

60. A method of manufacturing a security device according to claim 59, wherein: The at least translucent curable material is applied to the mold relief of the casting tool to substantially completely fill the recessed portions of the mold relief and to form a layer of the at least translucent curable material on the elevated portions of the relief structure.

61. A method of manufacturing a security device according to any one of claims 51 to 57, wherein: The method is configured to provide a safety device according to any one of claims 1 to 36.

62. A method of manufacturing a security document, wherein: The method comprises: providing a document substrate; forming a security device on a document substrate according to the method of any one of claims 51 to 61, or forming a security device on a security device substrate according to the method of any one of claims 51 to 61; and then applying the security device substrate to the document substrate or incorporating the security device substrate into the document substrate.

63. A method of manufacturing a security document according to claim 62, wherein: The method is configured to provide a security document according to any one of claims 38 to 50.

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