Patent Grant
12187064
The entire content of each of the six international patent applications filed on 10 Sep. 2021 in the name of De La Rue International Limited and claiming priority from the following British patent applications (each filed on 11 Sep. 2020) is hereby incorporated by reference: GB2014325.1, GB2014326.9, GB2014327.7, GB2014328.5, GB2014329.3, GB2014330.1 and GB2014331.9.
This invention relates to security devices such as may be used as a mark of authenticity associated with an object of value, such as a security document including banknotes, passports, certificates, licences and the like. Methods for manufacturing security devices are also disclosed.
Objects of value, and particularly documents of value such as banknotes, cheques, passports, identification documents, certificates and licences, are frequently the target of counterfeiters and persons wishing to make fraudulent copies thereof and/or changes to any data contained therein. Typically such objects are provided with a number of visible security devices for checking the authenticity of the object. Examples include features based on one or more patterns such as microtext, fine line patterns, latent images, venetian blind devices, lenticular devices, moiré interference devices and moiré magnification devices, each of which generates a secure visual effect. Other known security devices include holograms, watermarks, embossings, perforations and the use of colour-shifting or luminescent/fluorescent inks. Common to all such devices is that the visual effect exhibited by the device is extremely difficult, or impossible, to copy using available reproduction techniques such as photocopying. Security devices exhibiting non-visible effects such as magnetic materials may also be employed.
One class of security device which is widely used on banknotes and other documents is the intaglio print. For instance, many banknotes in circulation carry an image, such as a portrait or an architectural drawing, applied by intaglio printing. Typically all or part of the image is formed of 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 passable counterfeit by readily available commercial printing techniques), but can also be used to impart tactility to the image. This significantly increases the security level, since would-be counterfeiters may have access to highly accurate printing systems which can reproduce the visual appearance of an intaglio print, but not its three-dimensional quality and hence its haptics (feel). On the other hand, due to the nature of intaglio printing, it is difficult to produce images of more than one colour, at least in a fully controllable manner.
Separately, in other classes of security device, it is known that casting of curable materials (e.g. UV resins) can produce highly tactile effects. However, due to the nature of casting a single resin, the resulting feature will be is either colourless or of a single colour. For increased security it would be better to have multicolour tactility.
The present invention provides a security device, comprising:
The present invention also provides a method of manufacturing a security device, comprising, in any order or simultaneously:
Embodiments of the present invention therefore envisage the tactile emboss of a curable material (e.g. a UV casting resin) on one side of a substrate, combined with registered offset printing on the reverse. (Offset can be RGB for full colour images if required). The term “offset” printing is used herein to refer to lithographic printing, in which the one or more colours to be printed are applied to a patterned printing plate. The ink(s) are then transferred to a blanket roller from which the print is applied to the substrate. However, while lithographic printing is preferred, other printing techniques can also be used to form the print layer of the present invention, as discussed below.
The present inventors have recognised that the high resolution and complex colour workings achievable in an image printed by lithography or another comparable print technique cannot be reproduced in intaglio alone and vice-versa that the tactility of intaglio cannot be reproduced by lithography alone. By combining a cured surface relief structure with a print layer to display an image in the manner defined above, the resulting security device possesses tactility and at the same time can exhibit any desired arrangement of one or more colours in a controllable and reproducible manner. Since the surface relief structure and print layer are located on opposite surfaces of the substrate, they can be applied with extremely high register between them meaning that their relative positions are the same on every copy of the security device produced. For instance, the translational register between the surface relief structure and the print layer in the machine direction and/or the cross direction is preferably such that any mis-register is too small to be seen by the naked eye, e.g. no more than +/−75 μm. The skew register between the surface relief structure and the print layer is preferably 1 degree or less, more preferably 0.1 degree or less, still preferably 0.05 degrees or less, most preferably 0.02 degrees or less.
At any one lateral location on the substrate, the steps of forming the surface relief structure and printing the print layer can be performed either one after the other (in either order, with or without intervening steps) or simultaneously as discussed further below. The print layer can be applied by a flat printing technique (i.e. one which does not induce noticeable tactility), such as offset printing, which can therefore be selected to achieve the desired visual result (such as multiple colours) without the limitations imposed by the intaglio process, while the cured surface relief structure provides the desired tactility. This allows not only a greater degree of design freedom but also enables the formation of more complex security devices with a correspondingly higher security level.
It will be appreciated that the common image exhibited by the security device is that formed by the surface relief structure and the print layer viewed in combination (i.e. simultaneously—the surface relief structure being located between the print layer and the viewer, or the print layer being located between the surface relief structure and the viewer). That is, the common image is a composite, static macro-image arising due to the spatial arrangement of the surface relief and of the print layer—there is no synthetic magnification or other optically variable effect being generated. In at least part of the first region (where the common image is exhibited) the substrate will be transparent or translucent in order to enable the combination to be viewed in this way. Depending on the optical density of the substrate or other overlapping layers present (if any) the common image may be viewable in reflected light or only in transmitted light. “Transparent” means that the substrate is substantially optically clear, i.e. causing low or zero optical scattering, although it may carry a visibly coloured tint. “Translucent” means that some light is able to pass through the substrate but it will be scattered. If the relevant part of the substrate is translucent, its optical density must be sufficiently low that both the surface relief structure and the print layer can be observed by the naked eye simultaneously in transmitted light. Standard paper banknote substrates and standard polymer banknote substrates (with opacifying layers) meet this requirement. The at least part of the first region could correspond to a window or half-window region of the substrate (i.e. an area of lower optical density to the remainder of the substrate), but this is not essential as discussed further below. In some embodiments the substrate is transparent or translucent across the first region of the security device. The whole substrate may also be transparent or translucent if desired.
It should be noted that casting for tactility will be different to simply printing tactility, due to the presence of a base layer—that will have an effect on the colour in the device (whether it is clear, tinted or pigmented). In other words, the cast-cured surface relief structure will comprise a continuous body of cured material (of one or multiple types) with a varying height profile—if for instance it includes raised protrusions, these will be connected to one another by a base layer of lesser height. This would not be the case in a product having tactile protrusions formed by local printing of 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 effect as described below.
The surface relief structure and the print layer each exhibit a set of features of the common image (in other words, at least part of the common image). “Features” of the common image are what define the information content of the common image, and could include any of: lines or edges demarcating objects in the image; objects themselves; regions of contouring or shading; shapes or parts thereof; alphanumeric characters or symbols, or parts thereof, etc. The nature of the features will depend on the image content. Examples will be given below.
The surface relief structure and the print layer can contribute to the common image to various different relative extents, depending on the embodiment. In some preferred implementations, it may be desirable for each of the two constituents of the security device to display the whole common image—that is, both the surface relief structure and the print layer each define the same image as one another. In this case, the first and second sets of feature(s) are the same as one another, the surface relief structure and the print layer each exhibiting all the features of the common image. It will be appreciated that the surface relief structure and the print layer will be in overlapping alignment so that the corresponding features have the same lateral position within the security device in both constituents.
In other preferred embodiments, the first and second sets of feature(s) are different from one another, the first set of feature(s) and/or the second set of feature(s) being a subset of the features of the common image. In other words, the surface relief structure may exhibit a first part of the common image and the print layer a second part, which parts are different from one another and may be separate, overlapping or interleaved. Hence, in one example the print layer may exhibit the complete common image and the surface relief structure only part of it—or vice versa. Alternatively, each constituent may exhibit only a part 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 feature(s) and are exhibited by both the surface relief structure and the print layer. Again, it will be appreciated that the surface relief structure and the print layer will be in overlapping alignment so that the corresponding features have the same lateral position within the security device in both constituents.
The selection of features to be contributed by the surface relief structure and those to be contributed by the print layer could be decided in a variety of ways. In some cases, the division could be arbitrary. However in preferred examples, the first set of feature(s) consists of the features of the common image located in a first portion thereof and the second set of feature(s) of the common image consists of the features of the common image located in a second portion thereof, 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 area of the image. For example, the first portion could correspond to the whole lateral extent of the common image while the second portion is only a sub-area thereof (or vice versa). “Laterally offset” includes the portions (only) partially overlapping one another, or not overlapping one another (for example the first and second portions may be spaced from one another or abutting one another). For instance the surface relief structure could contribute one half of the common image, and the print layer the other half of the common image.
These principles can be used to design security devices with visual and tactile effects which interact with one another in unexpected ways. For instance, a user might expect the tactile region(s) of the device to match the visible features of the device. However, the device could be designed so that this is not the case, and there is an intentional mis-match between the two components—e.g. a selected visible sub-portion of the device may be configured without tactility, or a tactile sub-portion may be located in a position without a visible contribution from the print layer. These are memorable and distinctive features which are likely to be missed by would-be counterfeiters.
In still further embodiments, the first set of feature(s) preferably corresponds to a first colour component of the common image, and the second set of feature(s) preferably corresponds to at least a second colour component of the common image. In this case the overall extent of the two constituents may largely overlap, but on a micro-scale the configuration of each will vary so as to contribute the desired colour(s) to each point of the common image.
Preferably either:
Both of these options encompass the scenario in which the surface relief structure and the print layer share the same boundary. It should be noted that the surface relief structure and/or print layer could continue outside the common image (this applies to all embodiments) but in such cases will be configured differently outside the common image so that the common image remains distinct. Examples will be provided below. In other implementations it may be preferred that the surface relief structure and/or print layer does not exist outside the common image, for greatest visual distinction.
In some implementations, the cast surface relief structure (or part of it) could be one or more single volume(s) of material raised above the base layer, e.g. each defining a surface which varies in height optionally in a continuous, gradual or stepwise manner. However, in other cases the surface relief structure may comprise multiple discrete raised portions. In preferred embodiments, the common image is defined at least in part by an array of image elements spaced from one another, and either:
Forming the common image from an array of image elements enables the security device to more closely mimic a conventional intaglio print, since intaglio images usually comprise linework drawings or other screened workings. The image elements are visually distinguishable from one another, although this may require close inspection and/or low level magnification to discern. The image elements may be conveyed by either or both of the surface relief structure and the print layer. If both, the corresponding image elements defined within each constituent will be in overlapping alignment.
Preferably, the common image is a screened image, the image elements varying across the array in terms of their size, shape, colour, optical density and/or spacing in order to convey the common image, the array of image elements preferably being arranged on a regular grid. The image elements may advantageously be rectilinear or curvilinear line elements, dot elements or elements having the shape of indicia, preferably alphanumeric or typographic symbols (e.g. currency signs such as “£”, “$” etc). For instance, the image elements could define a line-work (e.g. similar to a conventional line intaglio image) or a dot screen of image elements, such as a half tone screen. The image may comprise a Guilloche pattern. Desirably the image is a portrait or architectural drawing. Preferably, the image is of a 3D object or scene. In embodiments in which the image is a screened image, the elements of the image are preferably arranged on a regular grid, although in general the elements may or may not be arranged on a regular grid.
As mentioned above, the cast-cured surface relief structure will comprise a continuous body of cured material with a varying height profile. The particular profile will depend on the desired image and/or tactility pattern. In preferred implementations, the surface relief structure includes a plurality of spaced protrusions, joined to one another by a base layer of lesser height. The protrusions may for example correspond to image elements of the common image as just described. Advantageously, the base layer may extend (away from the common image) over a peripheral region surrounding the plurality of spaced protrusions. Typically any such peripheral region will be narrow, e.g. extending between 0.01 mm and 5 mm away from the edge of the common image. In preferred examples, a ratio of the height of at least one protrusion to the height of the base layer joining the raised element to an adjacent protrusion is at least 10, preferably at least 20, and furthermore is preferably no greater than 400, preferably no greater than 200. In some embodiments, a ratio of the height of each protrusion to the height of the base layer is at least 10, preferably at least 20, and furthermore is preferably no greater than 400, preferably no greater than 200. This is especially the case where the protrusions are configured to form image elements, particularly of multi-tonal images.
The haptic effects of the security device may also be configured to interact with other tactile elements on the security document. For instance, the disclosed security device could be provided on a document substrate which also carries a conventional intaglio feature, disposed on the same surface of the substrate as the surface relief structure formed of cured material (e.g. the two might be adjacent one another). The overall appearance formed by the disclosed security device and the intaglio print in combination may be a complex haptic image, with the lower complexity imagery, tactility and colour being provided by the intaglio feature while the higher complexity imagery, tactility and colour is provided by the disclosed security device. For example, the disclosed device may present a common image in the form of a photographic portrait, while the intaglio print may provide a patterned (relatively low complexity) background surrounding the portrait, e.g. in the form of a coarse intaglio line structure.
As noted at the outset, some of the advantages of the invention are to provide greater design freedom in terms of the colour(s) exhibited by the device, and better colour placement. That is, instead of applying large blocks of each colour (as in conventional intaglio printing), individual lines or dots of an image could each have a different colour if desired. Possible implementations in preferred embodiments include:
The common image could be of any type, including block colours/shapes, alphanumeric text or “macro” images with no fine detail. However, preferably the common image is a multi-tonal and/or multi-coloured image, most preferably a grayscale image or a full colour image. Such images can mimic or even improve on the appearance of conventional intaglio prints.
In many preferred implementations, the at least one curable material is colourless (under standard white lighting, to the naked eye), and the print layer exhibits one or multiple visible colour(s). Most preferably the print layer is a RGB (red, green, blue) or CMYK (cyan, magenta, yellow, black) print layer. However, other combinations of colours can also be used such as orange, green and violet. It will be understood that the print layer may be laid down in one or multiple print workings (this applies to all embodiments).
In other preferred implementations, the at least one curable material carries a tint of a first colour and the print layer exhibits 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 the surface relief structure could, if desired, be formed of multiple curable materials, each forming a different lateral part of the structure, which materials could carry different coloured tints to introduce a further level of complexity. It is also possible for the print layer to exhibit more than two different colours.
In one particularly preferred embodiment, the first colour is one of red, green and blue, and the print layer exhibits 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 embodiment the first colour is one of cyan, magenta, yellow and black, and the print layer exhibits 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.
Advantageously, the print layer exhibits two areas of different respective colours and an intervening area in which the colour transitions gradually between the different respective colours, preferably in a manner which is continuous even under magnification. This achieves a visual effect akin to “rainbowing” in conventional lithographic security print, but with the additional benefit of tactility. “Rainbowing” is not possible via conventional intaglio printing, because the viscous nature of intaglio inks prevents them intermingling, as does their placement inside recesses of the intaglio printing plate. As such, it has not previously been possible to produce a tactile “rainbow”-coloured image and hence this embodiment provides a new security effect unachievable by conventional means.
The surface relief structure and the print layer could be configured that they combine visually to exhibit the same appearance whichever way round the device is viewed (i.e. from the side of the surface relief structure or from the side of the print layer). However, in other preferred embodiments, it may be desirable to give rise to different appearances, one being viewable from each side. In this case the common image will be exhibited at least on one side of the device. For instance, in a preferred example, the at least one curable material carries a tint of at least one colour and the print 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 as compared with when viewed from the side of the print layer. That is, the print layer is sufficiently opaque that it blocks the visibility of the surface relief structure through it, leading to the different appearance.
The print layer could be applied using standard, visibly coloured ink(s). To further increase the security level, in other embodiments, the print layer may comprise one or more substances which are responsive to non-visible wavelength(s), preferably UV or IR, the print layer optionally being invisible under white light illumination. For instance, the print layer could comprise a pair of inks which appear matched to one another under one illumination condition (e.g. white light) and different from one another under another illumination condition (e.g. UV light). Examples of suitable materials from which the print layer may be formed are disclosed in WO-A-2004/050376 and WO-A-2018/206936. In other examples, the print layer may comprises substances which emit red, green and blue light under illumination by a corresponding excitation waveband whereby a full colour version of the common image is exhibited. Examples of suitable substances are disclosed in WO-A-2020/030893.
The variation in height (and/or other dimensions/shape) of the cured material across the surface relief structure could be arbitrary or otherwise unrelated to the common image (the first set of features being conveyed primarily by the lateral configuration of the surface relief rather than its height). For instance, the features of the common image exhibited by the surface relief structure could all be conveyed by raised protrusions having the same height as one another, spaced by a base layer. However in preferred embodiments, the height, width, length and/or geometry of the surface relief structure varies in accordance with the common image. For instance, this can be used to link the tactile feel of the surface relief structure to certain part(s) of the common image or to emphasise a three-dimensional quality of the image. In an example, the common image could depict a three-dimensional object such as a portrait of a person, with features corresponding to parts of the object closer to the viewer corresponding to portions of the surface relief structure with greater height, and vice versa. The surface relief could comprise a single raised element of varying height, or multiple discrete elements which have different heights from one another and/or have a height which varies within one element.
As mentioned above, one or both constituents of the security device can be used to provide additional visual effects (preferably further security effects) beyond that provided by the common image along—for instance one or both constituents may continue outside the common image if desired. Hence 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 either laterally offset from and not overlapping the first region, or interlaced with the first region. In the second region, the surface relief structure and/or the print layer have different respective configurations from their arrangements in the first region so that the common image remains visibly distinct from the second region. For instance, the surface relief structure and the print layer preferably do not display aligned, matching features in the second region. There is no static common image exhibited by the two constituents in the second region (unlike in the first region).
It should be noted that the surface relief structure and/or the print layer may or may not be continuous between the first and second regions of the security device. For instance, there may be a gap between the surface relief structure in the first region and that in the second region. However, all of the surface relief structure (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 may ultimately be disposed in one and the same window (or half-window) region on a security document, or could each be disposed in a different respective window (or half-window) region. In the latter cases, the respective window (or half-window) regions will be separated from one another by a less translucent area of the security document.
In preferred embodiments, in the second region the surface relief structure is present and forms any of: one or more optical elements such as focusing elements, facets, prisms, pyramids or caustic elements (preferably an array of such optical elements); a tactile structure or a matte structure. Advantageously, in the second region the print layer is present and forms any of: a background print, a visually uniform area, a colour-shifting layer, a printed colour filter, and an image array such as an array of microimages or an interlaced image. Providing the print layer in the form of a colour-shifting layer is particularly advantageous where the surface relief structure comprises an array of prism and the colour shifting layer is configured to interact with the array of prisms. Examples of suitable colour shifting layers which can be printed include layers incorporating liquid crystals (e.g. a liquid crystal pigment), interference pigments (including magnetically orientated interference pigments), pearlescent pigments, or photonic pigments.
It is especially advantageous if in the second region the surface relief structure forms an array of focusing elements and the print layer forms an image array located approximately in the focal plane of the focusing elements, and the array of focusing elements and the image array are configured so as to co-operate with one another to generate an optically variable effect. In this way an additional, optically variable, security device may be provided on the substrate in the same manufacturing steps as those in which the security device already described is provided. Optically variable means that the appearance of the device is different from different viewing angles, making it impossible to imitate by standard copying (e.g. photocopying or scanning).
The invention also provides a plurality of substantially identical security devices, each as described above, in each of which the respective surface relief structures and print layers have the same position relative to one another. This arises from the two constituents being accurately registered to one another during manufacture. By “same position” it is meant that the relative position of the respective surface relief structures and print layers varies by an amount less than can be detected by the naked eye between the security devices, if at all. For example, the translational variation in the machine or cross-direction may be +/−75 μm or less. The skew variation is preferably 1 degree or less, more preferably 0.1 degree or less, still preferably 0.05 degrees or less, most preferably 0.02 degrees or less. The plurality of security devices will typically be produced sequentially on the same manufacturing line and according to the same design—for instance the plurality may include a whole batch of security devices, or the whole of a print run. The plurality may include at least 10 security devices, more preferably at least 100 security devices. Each security device of the plurality may ultimately be located on a different security document. In preferred methods of manufacturing security devices in accordance with the invention, the formation of the surface relief structure and the printing of the print layer are performed in register with one another. Again, preferably any mis-register is less than can be seen with the naked eye. For example, the translational register in the machine or cross-direction may be +/−75 μm or less. The skew register is preferably 1 degree or less, more preferably 0.1 degree or less, still preferably 0.05 degrees or less, most preferably 0.02 degrees or less. This is preferably achieved by performing both steps in one in-line process on the same apparatus. The substrate could be processed in the form of a web but is more preferably in the form of separate sheets when the two steps are performed. Most preferably, the formation of the surface relief structure and the printing of the print layer are simultaneous, taking place at the same position along the machine direction, at the same time. This achieves the highest level of registration between the two constituent parts of the security device, since there can be no slippage or distortion of the substrate occurring after one step is performed and before the other (since there is no interval between them). Suitable apparatus for performing simultaneous cast-curing 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 by simultaneous casting and printing using the apparatus disclosed therein cannot be achieved on a web press or in two separate processes.
The print layer can be applied by any selected printing technique which can achieve the desired resolution and number of colours. Typically a flat printing technique will be selected, i.e. one which does not cause embossing of the substrate. In preferred embodiments, the print layer is printed by lithographic printing, but alternatively other print methods such as flexographic, screen, gravure or micro-intaglio printing could be used (none of which involve embossing the substrate). It will be understood that the print layer could comprise multiple print workings, laid down sequentially or (preferably) simultaneously, e.g. from a collection roller or blanket, each print working potentially being formed of a different material (e.g. a different ink colour).
Preferably, the surface relief structure is formed by cast-curing one or more at least semi-transparent curable material(s) on the first surface of the substrate. In preferred embodiments, the surface relief structure is cast-cured by:
The mode of curing will depend on the type of curable material used. In preferred examples the material is radiation-curable (e.g. UV-curable) and the curing step(s) will involve irradiating the material with appropriate wavelength radiation so as to cause cross-linking of the material.
In many preferred implementations, the at least semi-transparent curable material(s) are applied to the mould relief of the casting tool so as to substantially completely fill recesses of the mould relief and form a layer of the at least semi-transparent curable material(s) over elevations of the relief structure. Substantially the whole body of curable material (including the parts inside the recesses and the layer over the elevations) will be cured and transferred onto the substrate. In such implementations there is no wiping or doctoring step which would otherwise remove the curable material(s) from the elevations.
However, in alternative examples, the curable material(s) may be applied only to recesses of the relief structure of the casting tool, preferably through the use of a removal means such as a doctor blade, and the method further comprises, subsequent to applying the one or more cured materials to the relief structure and before bringing the substrate and casting tool together, applying a further layer of the or another curable material(s) to substantially the whole surface of the casting tool so as to improve the retention of the cured material(s) on the substrate. In such examples, the further layer acts to improve the adhesion of the curable material(s) —which are located only within the recesses of the casting tool relief structure—to the substrate. As the further layer is applied to substantially the whole surface of the casting tool (i.e. over the filled recesses of the relief structure in the surface of the tool and the elevations between them), the resulting surface relief structure comprises an integral base layer as described above. The curable material of the further layer may be the same curable material or materials used to form the elements of the surface relief structure, or may be a different curable material.
The manufacturing method can be configured to provide the security device with any of the preferred features described above.
The present invention further provides a security document comprising a document substrate and a security device thereon, the security device being in accordance with any of the preceding claims, wherein the document substrate may or may not act as the substrate of the security device, the document substrate preferably comprising paper, polymer, cellulose or a hybrid thereof. For instance, a suitable substrate material formed of regenerated cellulose is disclosed in WO-A-2020156655. It will be understood that the security document could therefore include a single substrate, which acts as both the document substrate (i.e. the self-supporting sheet forming the body of the document) and as the security device substrate (i.e. that carrying the surface relief structure on one surface and the print layer on the other). In this case the document substrate will need to be transparent or translucent, at least at the location of the security device. The whole document substrate may be sufficiently translucent for this purpose, or it may include a window/half-window region for this reason. Alternatively, the security document could comprise two substrates—a document substrate and a security device substrate which carries the security device and which is affixed to or incorporated into the document substrate. In this case, the document substrate could be transparent, translucent or opaque.
The common image could be located anywhere on the security document—entirely inside or entirely outside a window/half-window region (if one is provided), or partially inside and partially outside a window/half-window region (if one is provided). In preferred embodiments, the first region of the security device is located at least in part in a window or half-window region of the document substrate, which has lower optical density than the surroundings thereof. In other preferred embodiments, the document substrate is translucent and the first region of the security device is located at least in part in a non-window region of the document substrate. In cases where the security device is not formed directly on the document substrate, the substrate of the security device is preferably affixed to or incorporated into the document substrate, preferably over a transparent or translucent region of the document substrate optionally formed as an aperture.
The appearance of the common image may be different in reflected vs. transmitted light, and/or from either side of the security document and in preferred implementations this may be influenced by the opacity of the security document at the location of the security device. For instance, parts of the same security device may provide different sets of appearances depending on whether they are located in a (transparent) window region, a (highly) translucent half window region or a (less translucent or opaque) non-window region. This can be made use of to create a more complex combination of appearances by providing several of these different arrangements on one security document. Hence, preferably, the first region includes parts located respectively in at least two of: a window region of the document substrate, a half-window region of the document substrate and a non-window region of the document substrate.
Similarly, it may be desirable to provide more than one security device of the sort disclosed above on a security document, to achieve a more complex combined effect. Preferably therefore the security document comprises at least two security devices, each as disclosed above, wherein the at least two security devices are respectively located at least in part in at least two of: a window region of the document substrate, a half-window region of the document substrate and a non-window region of the document substrate.
The document substrate could be of any type, including fibrous substrates such as paper or cellulose (e.g. as disclosed in WO-A-2020156655) or non-fibrous substrates such as polymer (or a hybrid of both). In preferred examples, the document substrate comprises a core polymer substrate with at least one opacifying layer disposed on one or both surfaces of the core polymer substrate, optional gaps in one or more of the opacifiying layers forming window or half-window regions of the document substrate. For example the security document could be a polymer banknote. The opacifying layers are preferably of non-fibrous materials such as a coating of binder containing light-scatting pigments, preferably white, off-white or grey in colour (such as TiO2).
In some embodiments, the document substrate may further comprise an integral print mark, preferably located between at least one of the opacifying layers and the core polymer substrate. “Print marks” (unlike the print layer described above) are incorporated into the substrate during its production rather than during its later processing into security documents. For instance, the print mark may be applied during the same process as that by which the opacifying layers are applied, e.g. gravure printing. The print mark is integral to the document substrate. The integral print mark could be unrelated to the presently disclosed security device. However, preferably, the integral print mark is defined in accordance with the common image and is in alignment with the surface relief structure and the print layer, the integral print mark exhibiting a third set of feature(s) of the common image, whereby the common image is exhibited by the surface relief structure, the print layer and the integral print mark in combination with one another. In another embodiment, the print mark may exhibit another copy of the common image (or a version thereof, e.g. the same image but in a different colour) but is not aligned with the security device—for instance it could be located in another part of the security document. This allows easy checking between the print mark and the security device.
Preferably, the security document is any of: a banknote, passport, identification document, identification card, bank card, driving licence, visa, stamp, cheque or certificate.
The invention further provides a method of manufacturing a security document, comprising providing a document substrate and either forming a security device on the document substrate or forming a security device on a security device substrate, and then applying the security device substrate to 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 may be configured to provide the security document with any of the preferred features described above.
Examples of security devices and security documents in accordance with the present invention, as well as methods for their manufacture, will now be described with reference to the accompanying drawings, in which:
The following description will focus on security devices formed directly on document substrates ultimately used as the basis for security documents such as banknotes, passports, certificates, licences, ID cards and the like. In many cases the security device is depicted as being arranged in a window region of the document substrate. However, as will be explained with reference to
For comparison,
As shown in
Whilst it is possible to form an intaglio print having more than one colour, as illustrated in
The security device 10 comprises a surface relief structure 20 and a print layer 30 which overlap and are registered to one another. The surface relief structure 20 is formed of 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 could comprise a single raised element or multiple discrete raised elements. In this example the cured material 20a forming the surface relief structure 20 is transparent and colourless. The print layer 30 is a flat print disposed on the opposite second surface 3b of the substrate 2. The print layer 30 could be single-coloured or multi-coloured. In this example, it is formed of two materials 30a, 30b (e.g. inks) having different respective colours C1 and C2. In a first region R1 of the substrate, the surface relief structure 20 and the print layer 30 are each configured so that in combination they exhibit a common image—i.e. a composite macro-image—which here is the same linework image of a kingfisher discussed in relation to
In this example, both the surface relief structure 20 and the print layer 30 are each configured to exhibit all the features of the common image. As such, they are each configured to exhibit the whole desired array of image elements 11 and are each defined in accordance with one and the same image. In surface relief structure 20, the image elements 11 are defined by corresponding raised elements (protrusions) 21 and in print layer 30 the image elements 11 are defined by corresponding print elements 31. The two constituents (i.e. surface relief structure 10 and print layer 30) are relatively positioned so that each raised element 21 is aligned over one of the print elements 31. When viewed in combination, the print layer 30 therefore gives colour to the common image while the surface relief structure 20 provides tactility and contributes to its appearance (even where formed by a colourless clear material, the reflective surface of the surface relief structure 20 will be apparent).
It will be seen from
The
While in many implementations a complex common image may be selected (such as the kingfisher shown in
In combination, the surface relief structure 20 and print layer 30 therefore display a common image C.I. in the form of a uniformly coloured digit “5” (labelled with reference numeral 18 in
Alternatively, the security device can be designed to more closely mimic an intaglio print by using an array of spaced image elements 11 to convey features of the image. An example is shown in
In the previous examples, the surface relief structure 20 and the print layer 30 have matched one another in the sense that the print layer is arranged such that ink is present in locations corresponding to raised protrusions of the surface relief structure 20, and not elsewhere. However this is not essential and different visual effects can be achieved by varying the relative lateral extents of the two constituent parts. The features of the common image which each conveys must of course still be aligned.
It should be noted that while the print layer 30 can be configured to exactly match (or “mirror”) the cast structure, as in some of the embodiments above, this is not essential.
Whilst in the above embodiments the security device is depicted as located in a window region on the substrate 2, and visible from both sides, this is not essential. In another embodiment, shown in
The surface relief structure 20 conveys features of the common image through the provision of one or more raised protrusions 22, which may or may not match the arrangement of inks in the print layer (but the features of the image conveyed by each constituent will be aligned). For example, the surface relief structure 20 could include raised protrusions across an area bounded by the outline of the person's head, so that the area of tactility matches the portrait. Alternatively, the nature of the surface relief could vary such that different features of the portrait correspond to areas of different tactility. For instance, the surface relief structure could be configured such that an area corresponding to the person's hair feels rough as compared with the area corresponding to their face, which feels relatively smooth. In another example, the height of the surface relief structure could be configured to vary in accordance with the common image. For example, those features of the portrait which would be closer to the viewer in real life (such as the person's nose) could correspond to raised elements of greater height, or the surface relief structure could comprise a single raised element having a surface of varying height which is a 3D contour of the person's face. The surface relief structure 20 could additionally or alternatively be formed as a screened version of the common image, i.e. having an array of spaced raised elements which varying in size, shape or spacing across the array so as to give rise to a multitonal version of the image, which will be visible due to the reflective nature of the cured material 20a. A base layer 29 of lesser height than the protrusion(s) 22 will be present as before and will form a colourless border region, not shown.
The
In the embodiments presented so far, the surface relief structure 20 and the print layer 30 each exhibit the whole common image C.I. —i.e. the same set of features as one another. However, this is not essential and in other embodiments each of the constituents may contribute a different set of features of the common image to the final appearance of the device. The sets of features may or may not include one or more features which are common to both.
The
Similarly, the
In both of the above examples, the set of features of the common image exhibited by surface relief structure 20 is the whole set of features needed to define the common image C.I., while that exhibited by print layer 20 is a subset of those features. It is also possible for one of the constituents to exhibit feature(s) of the common image which the other does not. For example, in the
The
Another example of this principle is shown in
Whilst in many embodiments it will be desirable for the tactile effect of the cast structure to match up with the visual configuration of the print layer, in other cases distinctive security effects could be achieved by purposefully including a partial mis-match. This is a subtle yet surprising and therefore memorable feature, which may nonetheless be missed by would-be counterfeiters. Clever placement of the casted tactile/print elements can promote further inspection of the device. For example in the
The cast structure 20 can also be configured to provide more complex haptic (i.e. tactile) effects. An example is shown in
Another variation is shown in
In
The ability to control colour placement very precisely not only allows for the display of full colour images, such as those exemplified above, but also other colour effects. In conventional lithographic printing, it is known to produce multi-coloured effects by a process known as “rainbowing”, in which two different coloured inks are applied to the print plate surface adjacent one another. When at the boundary, the inks mix with one another to produce intermediate colours which vary continuously in a spatial sense. The present invention can be used to form device with “rainbow” colour which are also tactile, which was not previously possible.
In the examples so far, the cured material 20a from which the surface relief structure is formed has been transparent and colourless, such that it does not contribute to the colour appearance of the common image C.I. However, in more complex embodiments, the cured material 20a may carry a coloured tint. This can be used as a further variable to create new visual effects, especially since the colour density of the surface relief structure 20 may now vary in dependence on its height (raised protrusions will typically have greater colour intensity than lower portions such as the base layer 29, due to the greater amount of tinted material 20a through which light passes). Some examples will be explained with reference to
If the ink 30a forming the print layer 30 is sufficiently transparent, the appearance of the devices in
While in many cases it will be desirable for the colour of the cured material 20a to be different from that of the ink 30a, this is not essential and different effects can be achieved if the colours are the same or similar. For instance,
Still more complex effects can be achieved if the print layer 30 is itself formed in multiple colours. For example,
The same principles can be applied to security devices exhibiting full colour images.
Another embodiment employing this principle is shown in
It is also possible to form the surface relief structure 20 of two or more cured materials, which may have different optical characteristics from one another (e.g. different visible colours). The two or more cured materials will typically be laterally offset from one another (preferably non-overlapping). If they abut one another so as to produce a continuous body of cured material these will be consider to form one and the same surface relief structure whereas if they are spaced from one another these will be separate surface relief structures. Either approach can be employed in embodiments of the invention.
The surface relief structures 20 are each formed of a different material with different respective colours.
As illustrated in each of the above embodiments, the surface relief structure 20 and print layer 30 are configured such that in combination they exhibit the common image C.I. across a first region R1 of the substrate. Optionally, the security device may include a second region R2 which may be adjacent the first region in which the image is located. The cast structure and/or the print layer may extend into (continuously or discontinuously from the first region) the second region but here the two components (if they are both present) need not be aligned with one another or be defined based on a common image (as is the case in the first region). For instance, in the second region the print layer could take the form of microimages or another image array and the cast structure could be in the form of an array of focusing elements, to form in combination an optically variable device. In the case 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 could both be in the same window (or half-window) region, or in different such regions.
Hence it is possible for one or both of the surface relief structure 20 and the print layer 30 to be present elsewhere on the substrate 2, such as in a second region R2 which is laterally offset from and does not overlap the first region R1. In this second region R2 the configuration of the surface relief structure 20 and/or print layer 30 is different from that in the first region R1, so that the common image C.I. does not continue into the second region, and the two regions appear visibly distinct from one another.
It is also possible to utilise the surface relief structure 20 and/or print layer 30 to provide one or more additional security features in the second region R2. For example, the two constituents can be configured to form in combination an optically variable security device 40 in the second region, such as a moiré magnifier, a lenticular device, an integral imaging device or a caustic device.
In a moiré magnifier, the image array 42 will typically comprise an array of microimages and the pitch and/or orientation of the image array 42 will be mismatched with those of the focusing element array 41 so as to give rise to synthetically magnified images of the microimages due to the moiré effect. In a lenticular device, the image array 42 will typically comprise a set of image elements, each being a section of an image to be displayed across the second region R2. Sections of multiple images will be interleaved. In this case the pitch and orientation of the image array 42 will typically match that of the focusing element array 41. At any one viewing angle, the focusing element array directs light from image elements all derived from the same image to the viewer so that the complete image is displayed. Upon changing the viewing angle, a different one of the interleaved images is displayed. Thus, the security device 10 as a whole will display a static, tactile common image C.I. in a first region R1 thereof (as before), alongside an optically variable device 40 in a second region R2. In a variant of this embodiment, shown in
In most of the above examples, the first region R1 where the common image is displayed has been located in a transparent window region 51 of the substrate 2. However, whilst arranging the feature in a window region as described above may be desirable in many cases, so that the image is overtly visible from both sides of the substrate, in other cases it may be preferable to form the security device on a substrate which is not transparent but only translucent. For instance, the feature could be formed on a paper substrate. Alternatively it could be located on a non-window area of a polymer banknote in which at least one opacifying layer 2b is present on the substrate. An example of this is shown in
In the embodiments of
In still further examples, the security device 10 could be arranged partially in a window or half-window region and partially in a non-window region. An example of this is shown in
Similarly, the security device can be configured to interact with any watermark or pseudo-watermark features provided in the substrate 2. Whilst in the Figures, the opacifying layers 2b of a polymer-type document substrate 2 are shown for clarity as a single layer on each side of the core 2a, in practice they may each be made up of multiple layers. For instance, it is typical for multiple opacifying layers to be disposed on each side of the core 2a—for instance in many cases there will be three layers on each side namely a first white opacifying layer, a second conductive opacifying layer (which may be off-white) and then a third white opacifying layer. The individual layers can each be laid down with differing extents, e.g. in the form of parts of an image, resulting in a watermark-like effect which can be seen in transmitted light (and sometimes in 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.
It will also be appreciated that different regions of the security device could be located in respective different window (or half-window) regions of a security document and/or each such window (or half-window) region could carry a respective security device. For instance,
As noted above, while at least part of the first region R1 (across which the common image is displayed) needs to be located in a region where the substrate between the surface relief structure and print layer is transparent or translucent, it is not essential for all of the first region R1 to be so located (although this may be preferred). The combination of the surface relief structure 20 and the print layer 30 may be needed to complete only part of the common image C.I.
In all of the embodiments described so far, as noted at the outset, it has been assumed that the security device is formed on a substrate 2 which also acts as the document substrate for the eventual security document 100. Suitable document substrates include polymer document substrates of the type already referred to above and shown again in
One or both surfaces of the polymer substrate 2a may be treated to improve adhesion/retention of subsequently applied materials. For example, a primer layer may be applied to all or part of either surface of the polymer substrate 2a, e.g. by printing or coating. The primer layer is preferably also transparent and again could be tinted or carry another optically detectable material. Suitable primer layers include compositions comprising polyethylene imine, hydroxyl terminated polymers, hydroxyl terminated polyester based co-polymers, cross-linked or uncross-lined hydroxylated acrylates, polyurethanes and UV curing anionic or cationic acrylates.
Alternatively or in addition to the application of a primer layer, the surface of the polymer substrate 2a may be prepared for onward processing by controlling its surface energy. Suitable techniques for this purpose include plasma or corona treatment.
The opacifying layer(s) 2b each comprise a non-transparent material, the primary purpose of which is usually to provide a suitable background for later printing of graphics thereon. Thus, preferably, the opacifying layers comprise polymeric, non-fibrous material containing at least a light scattering substance such as a pigment. The opacifying layers 2b are preferably light in colour, most preferably white or another light colour such as off-white or grey so that a later-applied graphics layer will contrast well against it. In preferred examples, the opacifying layers each have a brightness L* in CIE L*a*b* colour space of at least 70, preferably at least 80 and more preferably at least 90. For example, each opacifying layer may comprise a resin such as a polyurethane based resin, polyester based resin or an epoxy based resin and an opacifying pigment such as titanium dioxide (TiO2), silica, zinc oxide, tin oxide, clays or calcium carbonate.
Two or more opacifying layers may be applied to each surface of the polymer substrate 2a, in order to achieve the necessary opacity. The optical density of each layer by itself may typically be around 0.2 to 0.5. Preferably, 3 or more layers are applied to each surface, overlapping one another.
In a preferred embodiment, at least one of the opacifying layers (preferably one on each surface of the polymer substrate 2a) is made electrically conductive, e.g. by the addition of a conductive pigment thereto. This reduces the effect of static charges which may otherwise build up on the security document during handling.
The opacifying layers 2b are preferably applied to the polymer substrate 2a before the manufacture of the presently disclosed security device 10, using a printing process such as gravure printing, although in other cases the opacifying layers could be coated onto the substrate, or applied by offset, flexographic, lithographic or any other convenient method. Depending on the design of the security document, the opacifying layers may be omitted across gaps on one or both surfaces of the polymer substrate to form window regions (which may be full windows or half windows, or a mixture of both) as described above. This can be achieved through appropriate patterning of the opacifying layers during the application process. In alternative constructions, the opacifying layers 2b could comprise self-supporting pre-formed layers (optionally including apertures to later form windows) which are then laminated to the polymer substrate 2a. In this case, the opacifying layers could be polymeric or could be of fibrous construction, such as paper, thus rendering the security document a “hybrid” paper/polymer construction.
In other embodiments, such as is shown in
It is also possible to form the security device 10 on a substrate other than the document substrate 2. For instance, the security device 10 can be formed on its own substrate, resulting in a security article 1 such as a security thread, strip, foil or patch. Before or after this takes place, the security article substrate can be affixed to or incorporated into a security document 100. An example of this is shown in
Where the substrate 2 on which the security device 10 is formed is translucent rather than transparent, the appearance of the common image C.I. will typically be different when viewed in reflected light versus transmitted light, and may also be different when viewed in reflected light from different sides.
The opacity level of the substrate 2 can also be utilised to create different visual effects from one and the same security device configuration. This is illustrated by reference to the embodiment of
Similarly, when the security document is viewed from the opposite side (observer O2), as shown in
In a development of the invention, further complexity can be achieved by additionally providing an integral print mark 60 in the substrate 2. Print marks are formed during manufacture of a document substrate, rather than being applied to the substrate during later processing thereof. Typically, a print mark may be integrated into a multilayer polymer document substrate during the same process as that which applies the opacifying layer 2b to the core substrate 2a, e.g. via gravure printing. Thus, the integral print mark 60 will be in precise register with the opacifying layers 2b and particularly any window regions or half-window regions they define. Such print marks can be incorporated into security devices of the sort herein disclosed (in addition to the print layer 30), by arranging the first region R1 to partially or fully overlap the print mark 60 or otherwise interact with it (e.g. appearing to abut, surround or interlock with the print mark). It will be appreciated that the degree of register between the print mark 60 and the rest of the security device 10 may not be as accurate as the register between the surface relief structure 20 and the print layer 30, since it is formed in a separate, earlier process (not in-line with the application of the surface relief structure 20 and the print layer 30). Some examples of security devices 10 incorporating print marks 60 will now be described with reference to
While in the above examples the integral print mark 60 has been located such that it is covered by at least one of the opacifying layer 2b, this is not essential and the print mark 60 could be located on an external surface of the substrate 2. The print mark is still considered integral with substrate 2 since it is formed during manufacture of the substrate 2 rather than during later processing of the substrate into security documents. As before the print mark 60 may be applied in line with the opacifying layers 2b, e.g. via gravure printing.
Another example is shown in
In a variant of this embodiment, shown in
In another example, a registered ‘border’ effect using this method could be applied around a hidden gravure print mark (the registration to the original mark as standard). For instance, the cast tactile structure could define only an outline of the image while the print mark defines the full image.
Optionally, the substrate itself could carry a coloured tint, e.g. in one or more of the opacifying layers. This colour will contribute to the overall appearance of the image in transmitted light and can therefore act as a colour channel in a ‘full colour’ image.
In each of the above examples, the cast tactile structure could take various different forms depending on the nature of the tactility desired and/or on the manner in which the structure contributes to the visible image. In some examples, the cast structure could comprise an array of screen elements, making up a screened version of the image. In other cases the cast UV resin may cover the whole of the image (sharing its periphery or matching certain features thereof to reveal the register) and may carry a textured upper surface. In still further cases the cast structure could follow the contours of a 3D version of the image.
In all of the above embodiments, the print layer 30 has been formed of one or more visibly coloured materials (e.g. inks) such that the common image is visible to the naked eye under standard lighting conditions, e.g. white light. However, in all of the embodiments it is possible to form the print layer 30 using one or more substances which are responsive to stimuli such as non-visible illumination wavelengths and/or which exhibit different behaviours outside the visible spectrum (which may be detected by suitable camera apparatus). For instance, one or more of the materials (e.g. inks) forming the print layer 30 could be luminescent (e.g. fluorescent or phosphorescence) and/or could absorb certain non-visible wavelengths (such as IR). It is also possible to form the print layer 30 from materials with other secure effects such as optically variable inks, pearlescent inks, iridescent inks, metallic inks, electrically conductive inks, thermochromic inks, magnetic inks etc.
In the
In all of the above examples, the arrangement of the print layer on one side of the substrate and the relief structure on the other means that it is possible to apply both simultaneously. This achieves extremely high registration between the print layer and the relief structure since 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 position along the substrate (in the direction along which the substrate moves through the manufacturing apparatus—the machine direction), at the same time. The substrate could be in the form of a sheet or a web.
Suitable apparatus, materials and methods for forming the relief structures disclosed herein are described in WO-A-2018/153840 and WO-A-2017/009616. In particular, the relief structures can be formed by the in-line casting devices detailed in WO-A-2018/153840 (e.g. that designated 80 in FIG. 4 thereof), using an embossing tool 85 carrying an appropriately designed micro-optical structure from which can be cast the desired relief structure shape. Similarly, the cast-curing apparatuses and methods disclosed in section 2.1 of WO-A-2017/009616 (e.g. in FIGS. 4 to 8 thereof) can also be used to form the presently disclosed relief structures, by replacing the relief 225 carried on casting tool 220 with an appropriate relief from which can be cast the desired shapes. In particular it will be noted that whilst WO-A-2017/009616 describes the use of the apparatus to form focusing elements, the same apparatus can be used to form any desired relief structure by appropriate reconfiguration the relief 225, including that envisaged herein.
Whichever casting apparatus is used, the curable material(s) from which the relief structure is cast may be applied either directly to the tool carrying the desired relief shape (e.g. to the embossing tool 85 of WO-A-2018/153840 or to the casting tool 220 of WO-A-2017/009616), or the curable material(s) may be applied directly to the substrate on which the relief structure is to be formed, and then brought into contact with the tool (e.g. by impressing the tool onto the deposited curable material). Both options are described in the aforementioned documents. Preferably, the latter option is employed and the curable material(s) are applied to the substrate by screen printing as detailed in WO-A-2018/153840, before being formed into the desired relief structure. If the former option is employed, it should be noted that there is preferably no wiping of the casting tool surface relief between applying the curable material to it, and bringing it into contact with the substrate, so that a base layer of curable material remains connecting the protrusions of the relief structure together on the substrate (the base layer will be of much lesser height than the protrusions).
Suitable curable materials are disclosed in WO-A-2017/009616, section 2.1. UV-curable materials are most preferred. Curing of the material(s) preferably takes place while the casting tool is in contact with the curable material, against the substrate.
In all of the above embodiments, the transparent curable material in which the surface relief structure 20 is formed can be of various different compositions. The curable material is preferably radiation-curable and may comprise a resin which may typically be of one of two types, namely:
The radiation used to effect curing will typically be UV radiation but could comprise electron beam, visible, or even infra-red or higher wavelength radiation, depending upon the material, its absorbance and the process used. Examples of suitable curable materials include UV curable acrylic based clear embossing lacquers, or those based on other compounds such as nitro-cellulose. A suitable UV curable lacquer is the product UVF-203 from Kingfisher Ink Limited or photopolymer NOA61 available from Norland Products. Inc, New Jersey.
Due to the nature of the cast-cure process, the resulting relief structure will typically include a base layer of material on top of the substrate, connecting the protrusions of the relief at their base. In many cases this base layer is integral with the relief structure and formed of the same curable material(s), resulting from either the shape of the casting relief and/or the manner in which the curable material is pressed between the substrate and the casting tool during processing. An example of such a base layer and its formation is disclosed in WO-A-2017/009619, FIG. 8. It is also possible to provide (alternatively or in addition) a base layer in the form of a pedestal layer, applied in a preceding step. Apparatus and methods for providing such a pedestal layer are disclosed in WO-A-2017/09620, FIGS. 8 to 12.
An example of a suitable cast-cure process for forming surface relief structures 20 suitable for use in the security devices disclosed herein will be described with reference to
A transparent curable material 205 is first applied to the support layer 201 using an application module 210 which here comprises a patterned print cylinder 211 which is supplied with the curable material from a doctor chamber 213 via an intermediate roller 212. For example, the components shown could form part of a flexographic printing system. Other printing techniques such as lithographic, screen, or gravure printing could also be used. Print processes such as these are preferred since the curable material 205 can then be laid down on the support 201 only in selected regions 202 thereof, the size, shape and location of which can be selected by control of the print process, e.g. through appropriate configuration of the pattern on cylinder 211. However, in other cases, an all over coating method could be used, e.g. if the surface relief structure is to be formed all over the support 201. The curable material 205 is applied to the support 201 in an uncured (or at least not fully cured) state and therefore may be fluid or a formable solid.
The support 201 is then conveyed to a casting module 220 which here comprises a casting tool 221 in the form of a cylinder carrying a surface relief 225 defining the shape of the surface relief structure which is to be cast into the curable material 205. As each region 202 of curable material 205 comes into contact with the cylinder 221, the curable material 205 fills a corresponding region of the relief structure, forming the surface of the curable material into the shape defined by the relief. The cylinder 221 may be configured such that the relief structure 225 is only provided at regions corresponding to shape and position of the first regions 202 of curable material 205.
Having been formed into 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 takes place while the curable material is in contact with the surface relief 225 although if the material is already sufficiently viscous this could be performed after separation. In the example shown, the material is irradiated through the support layer 201 although the source 222 could alternatively be positioned above the support layer 201, e.g. inside cylinder 221 if the cylinder is formed from a suitable transparent material such as quartz. In an alternative embodiment, the curable material 205 could be applied directly onto casting tool 221 rather than on to the substrate 201. This could be done in an all-over or patternwise manner.
Typically, in embodiments in which the curable material is applied directly onto casting tool 221, the curable material is applied so as to substantially fill the trenches 121, as well as form a thin layer of curable material over substantially the whole of the surface of the casting tool 221 in the first region—i.e. over elevations of the relief on the casting tool, as well as the elevations. There is no wiping/doctoring step. Following 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 may be applied to the casting tool so as to be present only within the trenches 121, for example by using a doctor blade or other removal means to remove material from the tops of the elevations. In such examples, a tie-coat layer is then applied over substantially the whole surface of the die form 221, i.e. coating both the filled recessed areas of the trenches and the raised areas between them. The curable material of the tie coat may or may not be of the same composition as the curable material 205 in the trenches. In particularly preferred embodiments, the tie coat composition may be selected so as to improve the adhesion between the curable material 205 and the support layer. The tie coat is applied by a tie coat application module. It is desirable for the tie coat to be applied in a continuous, homogenous manner at the micron level hence it is preferably applied in a metered way via a slot die and transfer roller combination. The tie coat may be partially cured before the casting tool and the substrate are brought into contact.
In all embodiments of the invention, the print layer 30 can be applied to the substrate using any convenient printing technique, but preferably one which does not cause any embossing of the substrate is selected. Gravure, lithographic, flexographic, wet or dry offset, inkjet or micro-intaglio printing are particularly preferred techniques. If the print layer 30 is to comprise multiple print workings, preferably these are collected on a transfer roller or blanket before being applied to the substrate together. Preferably, where multiple inks are used, these are accurately registered to one another to such a degree that any mis-register between them is too small to be perceivable to the naked eye. For instance, the translational colour to colour registration (i.e. in the machine direction x or cross direction y) may be within +/−5-10 μm. The skew register (i.e. rotational alignment) may be to within 0.02 degrees. The pitch register (i.e. the degree to which the coverage of one colour is stretched relative to the other) may be to within 0.01%. Such registration levels are not achievable with Intaglio printing, so colour reproduction is significantly better with the present invention.
WO-A-2018/153840 and WO-A-2017/009616 also disclose print stations, which may be disposed downstream of the above-described casting apparatus (but alternatively could be located upstream, or at the same point along the machine direction as explained below). Print stations such as these are suitable for applying any the print layer 30, to the opposite side of the substrate from that carrying the cast relief structure. The apparatus disclosed in WO-A-2018/153840 can achieve particularly high registration between such cast relief structures and the printed elements.
For example, in preferred methods, the relief structure and print layer are preferably registered to one another sufficiently accurately that any mis-register 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 to within 150 μm (+/−75 μm). Desirably, the skew register (i.e. rotational alignment) is to within 1 degrees (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 degree to which one component is stretched relative to the other) is to within 0.01%. The precise registration achieved will depend on the consumables that are used in the machine (substrate, inks, resin, print plates) as well as the actual machine configuration.
It is highly desirable for the surface relief structure 20 and the print layer 30 to be applied to the opposite surfaces of the substrate 2 simultaneously. That is, at the same position along the transport path in the machine direction. This makes it possible to achieve the highest registration between the two components. FIG. 7 of WO-A-2018/153840 shows suitable apparatus for achieving this.
This has the significant advantage that any deformation experienced by the substrate 2, as a result of changes in processing temperature or the like, will be exactly the same when the surface relief structure 20 is applied to the polymer substrate 2 as it is when the print layer 30 is applied. The substrate has no time to expand or contract between the instant at which the surface relief structure 20 is applied and when the print layer 30 is applied, since they occur at the same time. As such, a very high degree of register between the two components is automatically achieved.
The arrangement shown in
Simultaneous application of the surface relief structure and print layer is preferred but not essential.
The sheet substrate 2, now carrying the cured surface relief structure 20, is the conveyed to the print station 420. In this example, the print station 420 is a lithographic print 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 print cylinder 302 to a blanket roller 306 and then onto the substrate 2 at a nip between blanket roller 306 and an impression roller 305. The substrate 2, now carrying both the surface reliefs 20 and the print layer 30 on opposite sides is then conveyed away from the print module 420 via at arrow B.
Suitable substrates on which the disclosed devices can be formed are disclosed in WO-A-2017/009616, section 1, and apparatus/methods for applying opacifying layers thereto in section 4, including the formation of window regions. Preferably, the opacifying layers are applied before formation of the presently disclosed security devices on the substrate. For instance, the sheet material supplied to the apparatus of WO-A-2018/153840 may comprise a polymer substrate of the sort disclosed in WO-A-2017/009616, already provided with one or more opacifying layers. The security devices disclosed herein may be disposed in a window region defined by the opacifying layers, or in a non-window region.
Some preferred aspects of the invention are set out in the following clauses:
Clause 1. A security device, comprising:
Clause 2. A security device according to Clause 1, wherein the curable material is colourless and the print layer defines a multi-colour image, preferably full-colour image, most preferably a RGB or CMYK image.
Clause 3. A security device according to Clause 1, wherein the curable material carries a tint of a first colour and the print layer defines an image in at least a second colour such that, when viewed in combination a multi-coloured version of the image is visible.
Clause 4. A security device according to Clause 3, wherein the first colour is one of red, green and blue, and the print layer defines the image in the other two of red, green and blue, such that when viewed in combination a full colour RGB version of the image is viewed.
Clause 5. A security device according to any of the preceding Clauses, wherein the height of the surface relief structure varies in accordance with the image.
Clause 6. A security device according to any of the preceding Clauses, wherein the security device further comprises a second region in which one or both of the surface relief structure and the print layer are present.
Clause 7. A security device according to any of the preceding Clauses, wherein the substrate is transparent in at least part, preferably all, of the first region of the security device.
Clause 8. A method of manufacturing a security device, comprising forming a surface relief structure on a first surface of a transparent substrate by cast-curing an at least semi-transparent curable material thereon, and printing a print layer on the second surface of the transparent substrate, wherein the surface relief structure and the print layer are each defined in accordance with the same image and are in alignment with one another, whereby the surface relief structure provides tactility to the image.
Clause 9. A method according to Clause 8, wherein the formation of the surface relief structure and the printing of the print layer are simultaneous, taking place at the same position along the machine direction, at the same time.
Clause 10. A method according to Clause 8 or 9, configured to provide the security device with any of the features of Clauses 1 to 7.
| Number | Date | Country | Kind |
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| 2014330 | Sep 2020 | GB | national |
| 2014331 | Sep 2020 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2021/052361 | 9/10/2021 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2022/053826 | 3/17/2022 | WO | A |
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