AU2012101723A4 - Security Device including Multimode Authentication - Google Patents

Abstract

A security document including: a security device; a first authentication device; and a second authentication device, wherein the security document is arrangeable 5 into a first authentication arrangement corresponding to the first and second authentication devices overlapping the security device, wherein the security device is configured to provide at least one visual effect when the security document is in the first authentication arrangement, wherein the, or each, visual effect is associated with a viewing direction.

Description

1 SECURITY DEVICE INCLUDING MULTIMODE AUTHENTICATION FIELD OF THE INVENTION The invention relates to security features of documents, for example security features for banknotes. 5 BACKGROUND OF THE INVENTION Banknotes (and other security documents) include visual security features that are difficult to reproduce (and therefore counterfeit) using conventional means (for example, photocopiers). It is common for such visual security features to include a visual effect which is always visible, or, alternatively, that may be 10 visible upon application of a separate verification device. A verification device can be either located on the banknote in a different region to the security feature or disseminated to the user as a separate device. An advantage of providing the verification device on the same banknote is increased ease of use as the verification device can be placed directly opposite the area (security feature) to be 15 authenticated. Furthermore, the user will not need to carry a separate device or risk obtaining a questionable device with lower effectiveness, or a counterfeited verification device. A problem with security features is that a counterfeited visual effect, although not perfectly reproduced, can be reproduced sufficiently to escape 20 identification as a counterfeit by general users. A further problem applicable to both common implementations is that, as the sophistication of counterfeiting operations increases, the ability to reproduce the visual effects increases. Also, a security device including a single verification device only includes one hidden visual effect, which can be easier to reproduce 25 than more complex arrangements. SUMMARY OF THE INVENTION According to a first aspect of the present invention, there is provided a security document including: a security device; a first authentication device; and a second authentication device, wherein the security document is arrangeable into 30 a first authentication arrangement corresponding to the first and second authentication devices overlapping the security device, wherein the security device is configured to provide at least one visual effect when the security 2 document is in the first authentication arrangement, wherein the, or each, visual effect is associated with a viewing direction. Preferably, the security device includes a first side associated with a first viewing direction and a second side associated with a second viewing direction, 5 such that a user viewing the security device from the first viewing direction views the first side, and such that a user viewing the security device from the second viewing direction views the second side. Preferably, the first authentication arrangement corresponds to the first authentication device overlapping the first side of the security device and the 10 second authentication device overlapping the second side of the security device. The security device, the first authentication device and the second authentication device may each be located within a window region of the security document. Preferably, the first authentication device includes a microlens array including a plurality of microlenses, and wherein the microlenses are configured 15 for viewing a surface of the security device including a microimage pattern, the microimage pattern configured for providing a visual effect when viewed through the microlens array. The microlens array may be configured to provide the visual effect when the first authentication device is in contact with the security device. The second authentication device may include a linear polariser. The linear 20 polariser may be a liquid crystal linear polariser. Alternatively, the linear polariser may be a structural polariser. The first surface of the security device may include the microimage pattern. Alternatively, the second surface of the security device may include the microimage pattern. The microimage pattern may be revealed due to the transmission of polarised light, due to the second authentication 25 device, through the security device. Preferably, the first authentication arrangement is configured to provide a visual effect when viewed from the first direction and another visual effect when viewed from the second direction. Alternatively, preferably the first authentication arrangement is configured to provide a visual effect when viewed from the first direction and no visual effect 30 when viewed from the second direction. Preferably, the security device includes a second authentication arrangement corresponding to the second authentication device overlapping the first side of the security device and the first authentication device overlapping the 3 second side of the security device, wherein the security device is configured to provide one or more visual effects when in the second authentication arrangement. The first authentication device may include a linear polariser and the second authentication device may include a linear polariser. Each linear 5 polariser may be a liquid crystal linear polariser. Alternatively, each linear polariser may be a structural linear polariser. Preferably, for each viewing direction and for each of the first and second authentication arrangements, the security device is configured to show no, or substantially no, birefringence. The linear polariser of the second authentication device may include a polarising 10 direction perpendicular to the polarising direction of the linear polariser of the first authentication device. Preferably, the first authentication arrangement corresponds to the first authentication device and the second authentication device overlapping the first side of the security device. The first authentication device may include a first 15 linear polariser, and the second authentication device may include a second linear polariser. Preferably, the security device includes a linear polariser. The polarising direction of the security device may be perpendicular to the polarising direction of the second linear polariser, and the polarising direction of the first linear polariser may be rotated by 45 degrees with respect to the polarising 20 direction of the second linear polariser. The security device may include a first microimage pattern located on the first side of the security document, and a second microimage pattern located on the second side of the security document, and wherein the first authentication device includes a microlens array. The second authentication device may include: 25 a linear polariser; a transparent filter; or any other suitable filter. Preferably, the microlens array is configured to focus, or substantially focus, on the second microimage pattern when the first authentication device is in contact with the first side of the security device, and the microlens array is configured to focus on, or substantially on, the first microimage pattern when the first authentication device 30 is in contact with the second authentication device, when the second authentication device is in contact with the first side of the security device. The second authentication device may include a linear polariser.

4 Preferably, the security document includes one or more auxiliary devices. Preferably, the security document includes a plastic material. The substrate may include a BOPP material. The security document may be a banknote. According to a second aspect of the present invention, there is provided a 5 method for producing a security document according to the first aspect, including the steps of: providing a substrate; printing first and second opacifying layers to opposite sides of the substrate; and embossing, printing, or other wise providing security features into different regions of the substrate, the security features corresponding to the security device, first authentication device, and second 10 authentication device. Security Document or Token As used herein the term security documents and tokens includes all types of documents and tokens of value and identification documents including, but not limited to the following: items of currency such as banknotes and coins, credit 15 cards, cheques, passports, identity cards, securities and share certificates, driver's licenses, deeds of title, travel documents such as airline and train tickets, entrance cards and tickets, birth, death and marriage certificates, and academic transcripts. The invention is particularly, but not exclusively, applicable to security 20 documents or tokens such as banknotes or identification documents such as identity cards or passports formed from a substrate to which one or more layers of printing are applied. Substrate As used herein, the term substrate refers to the base material from which 25 the security document or token is formed. The base material may be paper or other fibrous material such as cellulose; a plastic or polymeric material including but not limited to polypropylene (PP), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), polyethylene terephthalate (PET); or a composite material of two or more materials, such as a laminate of paper and at least one 30 plastic material, or of two or more polymeric materials.

5 Transparent Windows and Half Windows As used herein the term window refers to a transparent or translucent area in the security document compared to the substantially opaque region to which printing is applied. The window may be fully transparent so that it allows the 5 transmission of light substantially unaffected, or it may be partly transparent or translucent partially allowing the transmission of light but without allowing objects to be seen clearly through the window area. A window area may be formed in a polymeric security document which has at least one layer of transparent polymeric material and one or more opacifying 10 layers applied to at least one side of a transparent polymeric substrate, by omitting least one opacifying layer in the region forming the window area. If opacifying layers are applied to both sides of a transparent substrate a fully transparent window may be formed by omitting the opacifying layers on both sides of the transparent substrate in the window area. 15 A partly transparent or translucent area, hereinafter referred to as a "half window", may be formed in a polymeric security document which has opacifying layers on both sides by omitting the opacifying layers on one side only of the security document in the window area so that the "half-window" is not fully transparent, but allows some light to pass through without allowing objects to be 20 viewed clearly through the half-window. Alternatively, it is possible for the substrates to be formed from an substantially opaque material, such as paper or fibrous material, with an insert of transparent plastics material inserted into a cut-out, or recess in the paper or fibrous substrate to form a transparent window or a translucent half-window area. 25 Opacifying layers One or more opacifying layers may be applied to a transparent substrate to increase the opacity of the security document. An opacifying layer is such that LT < Lo , where Lo is the amount of light incident on the document, and LT is the amount of light transmitted through the document. An opacifying layer may 30 comprise any one or more of a variety of opacifying coatings. For example, the opacifying coatings may comprise a pigment, such as titanium dioxide, dispersed within a binder or carrier of heat-activated cross-linkable polymeric material.

6 Alternatively, a substrate of transparent plastic material could be sandwiched between opacifying layers of paper or other partially or substantially opaque material to which indicia may be subsequently printed or otherwise applied. Security Device or Feature 5 As used herein the term security device or feature includes any one of a large number of security devices, elements or features intended to protect the security document or token from counterfeiting, copying, alteration or tampering. Security devices or features may be provided in or on the substrate of the security document or in or on one or more layers applied to the base substrate, and may 10 take a wide variety of forms, such as security threads embedded in layers of the security document; security inks such as fluorescent, luminescent and phosphorescent inks, metallic inks, iridescent inks, photochromic, thermochromic, hydrochromic or piezochromic inks; printed and embossed features, including relief structures; interference layers; liquid crystal devices; lenses and lenticular 15 structures; optically variable devices (OVDs) such as diffractive devices including diffraction gratings, holograms and diffractive optical elements (DOEs). BRIEF DESCRIPTION OF THE DRAWINGS Embodiment(s) of the invention will now be described with reference to the accompanying drawings. It is to be appreciated that the embodiments are given 20 by way of illustration only and the invention is not limited by this illustration. In the drawings: Figure la shows a security document including a security device and two authentication devices; Figure 1 b shows a side-on view of a security device; 25 Figure 2a shows an s-type authentication arrangement; Figure 2b shows another s-type authentication arrangement; Figure 3a shows a pair-wise authentication arrangement; Figure 3b shows another pair-wise authentication arrangement; Figure 3c shows another pair-wise authentication arrangement; 30 Figure 3d shows another pair-wise authentication arrangement; Figure 4a shows a circular-fold authentication arrangement; Figure 4b shows another circular-fold authentication arrangement; 7 Figure 4c shows another circular-fold authentication arrangement; and Figure 4d shows another circular-fold authentication arrangement. DESCRIPTION OF PREFERRED EMBODIMENTS For the purposes of this disclosure, the linear polarising filters can be 5 selected from: structural polariser for example as described in AU 2011100315; a liquid crystal polariser for example as described in AU 2012100299; or any other suitable linear polariser. Referring to Figure 1a, there is provided a security document 100 including a substrate 112, a security device 102, and a first authentication device 104 and a 10 second authentication device 106. In general, there can be two or more authentication devices associated with a security device 102. The security device 102 is configured for visual inspection by a user and/or a machine. The security device 102 can have a first side 108 and a second side 110, where the first side 108 corresponds to a first viewing direction 114 and the second side 110 15 corresponds to a second viewing direction 116 (as shown in Figure 1b). The first side 108 can be configured for viewing from the second viewing direction 116 and the second side 110 can be configured for viewing from the first direction 114, for example such that each side 108, 110 can be viewable through the substrate 112. An authentication device 104, 106 can further act, in alternative 20 configurations, as a security device 102, and vice versa, depending on the design and configuration of the security document 100. The security device 102 is configured to provide one or more visual effects when viewed in conjunction with at least one authentication device 104, 106. Each visual effect can be observed (directly by a user or via a machine) by 25 viewing the security device 102 from one of the viewing directions 114, 116, when the security device 102 is overlaid with one or more authentication devices 104, 106, such that the security device 102 is seen through one or more authentication devices 104, 106 and/or one or more authentication devices 104, 106 are seen through the security device 102. A visual effect can change with viewing angle 30 when the security device 102 is viewed from the same viewing direction 114, 116. A particular arrangement of security device 102 and one or more authentication devices 104, 106, wherein the security device 102 is viewed through one or more authentication devices 104, 106 and/or one or more authentication devices 104, 8 106 are viewed through the security device 102, constitutes an authentication arrangement. An authentication arrangement 104, 106 is defined by the ordering of authentication devices 104, 106 relative to the security device 102 when viewed from the same direction, preferably from the first direction 114. For 5 example, an authentication arrangement could correspond to the arrangement shown in Figure 2a, and be defined by a first authentication device 104 overlaying the first side 108 of the security device 102 and a second authentication device 106 overlaying the second side 110 of the security device 102. In this manner, each visual effect is associated with an authentication arrangement and a viewing 10 direction 114, 116. In general, a visual effect is a modification to the appearance of the security device 102 which is unexpected. Exemplary visual effects described in examples herein include different changes in appearance of the security device when different authentication arrangements are employed and revealing of an 15 image. Visual effects do not include expected modifications in appearance, for example, a visual effect is not the effect seen when simply viewing a surface through a coloured filter, as this is not an unexpected modification in appearance. Where the security device 102 is configured to provide a visual effect for two viewing directions 114, 116 for the same authentication arrangement, each 20 visual effect can appear the same, the same but for a mirror symmetry, or different. In general, observing the one or more visual effects can allow for the security document 100 to be distinguished from unauthorised reproductions (e.g. forgeries), thus the one or more visual effects can be used to verify the security document 100. The authentication devices 104, 106 can be configured to provide 25 a visual effect only when in physical contact with the security device 102, or another authentication device 104, 106, though this may not be a requirement for some types of authentication devices 104, 106 (for example, linear polarisers). The security document 100 can be configured to provide at least two visual effects. Alternatively, the security document 100 is configured to provide one 30 visual effect, and the visual effect is associated with an authentication arrangement including at least two authentication devices 104, 106. Figures 2a and 2b show s-type authentication arrangements. Referring first to Figure 2a, a first s-type authentication arrangement is shown corresponding to 9 the first authentication device 104 positioned overlaying the first side (108 of Figure 1b) of the security device 102 and the second authentication device 106 over the second side (110 of Figure 1 b) of the security device 102. The security device 102 operates, at least in part, in a transmission mode, such that the 5 second authentication device 106 can be viewed through the security device 102 and first authentication device 104 when viewed from the first direction 114. A visual effect can be visible when viewed from either the first direction 114 only or the second direction only 116. Alternatively, the authentication arrangement can provide two visual effects (which can be the same, mirror images, or different), 10 one corresponding to viewing the security device 102 from the first direction 114 and the other corresponding to viewing the security device 102 from the second direction 116. The security device 102 and each authentication device 104, 106 are located in one or more window regions of the security document 100. Preferably, the security device 102 and each authentication device 104, 106 are 15 located within different window regions of the security device. Figure 2b shows a second s-type authentication arrangement, which is a complementary authentication arrangement to the first s-type authentication arrangement, and corresponds to the second authentication device 106 overlaying the first side 108 of the security device 102 and the first authentication 20 device overlaying the second side 110 of the security device 102. The complementary authentication arrangement can be configured, similar to the first authentication arrangement, to provide visual effect when viewed from the first direction 114 only, the second direction 116 only, or two visual effects, one corresponding to each direction 114, 116, which can be the same as, or different 25 than, that of the arrangement of Figure 2a. According to an example of security document 100 including an s-type authentication arrangement, the substrate 112 of the security document 100 is based on a suitable plastic material which does not exhibit birefringence, for example Biaxially-Oriented Polypropylene (BOPP) as used in banknotes, and the 30 first authentication device 104 and the second authentication device 106 both include linear polarising filters, where the polarising direction of the linear polarising filter of the second authentication device 106 is rotated by 90 degrees with respect to the polarising direction of the linear polarising filter of the first 10 authentication device 104. When the security document 100 is folded such that the first authentication device 104 overlays the first side 108 and the second authentication device 106 overlays the second side 110 (i.e. is arranged according to an s-type authentication arrangement), the security device 102 will 5 appear uniformly black or dark. Where the plastic material of the substrate 112 is not of a suitable material, then a birefringent effect will be seen, where the security device 102 will appear to have regions of varying intensity and/or colour. Therefore, the visual effect in this case corresponds to the lack of birefringence. An advantage of this example is that suitable materials, particularly 10 polymer materials, which show this effect, are uncommon and not readily available for use in forgeries. According to this example, the visual effect will be present whether viewed from the first viewing direction 114 or the second viewing direction 116, and whether the first authentication device 104 is applied to the first side 108 or the second side 110 (with the second authentication device 106 15 applied to the opposite side 108, 110 to the first authentication device). Alternatively, the second authentication device 106 can be a reflective linear polariser, in which case the visual effect is only visible from the viewing direction 114, 116 opposite the side of the security device 102 to which the second authentication device 106 is applied. Preferably, the second authentication device 20 106 is configured to only produce a polarising effect on one surface, in which case there is only one viewing direction 114, 116 and one s-type authentication arrangement which will produce the visual effect. This example can advantageously be combined with visual effects of other examples where cross polarised are employed. For example, the lack of birefringence may correspond 25 to a dark border for an authentic security document 100, and a coloured border for a non-authentic document. In another example of a security document 100 including an s-type authentication arrangement, the first authentication device 104 includes a microlens array, and the second authentication device 106 includes a linear 30 polarising filter. In this example, the security device 102 includes an invisible microimage pattern on a surface (preferably the microimage pattern is located on the first side 108, but can be located on the second side 110) which is rendered visible by the application of polarised light. This can be achieved by either the 11 microimage pattern elements or the area surrounding the microimage pattern elements (the background) only allowing transmission of linearly polarised light polarised at a polarising direction perpendicular to the polarising direction of the second authentication device 106. The opposite region (the background or the 5 microimage pattern elements) can transmit linearly polarised light parallel to the polarisation direction of the second authentication device 106, or alternatively unpolarised light. By overlaying the second authentication device 106 against the second side 110 of the security device 102, the perpendicular linearly polarised regions (either the micromotif pattern elements or the background) will darken 10 relative to the parallel linearly polarised regions, revealing the micromotif pattern. In this way, the microlens array of the first authentication device 104 is capable of revealing a Moir6 effect of the security device 102 only when polarised light is used to illuminate the security device 102. Preferably, the first authentication device 104 is configured to reveal the Moir6 effect when the first security device 15 104 is in contact with the security device 102, such that the microlenses of the microlens array are a known distance from the microimage pattern. The microlenses can be configured to view the microimage pattern through the substrate 112 of either or both of the security device 102 and the first authentication device 104. The security device 102 can include a liquid crystal 20 linear polariser, a structural linear polariser, or any other suitable linear polariser, where the polariser includes first regions polarised in a first direction and second regions polarised in a second direction perpendicular to the first direction. A suitable liquid crystal linear polariser can be created by applying a liquid crystal polymer material to the substrate 112 in the region of the security device 25 102, where the substrate includes a microgroove structure with microgrooves aligned in a first direction in regions of the security device 102 corresponding to microimages, and aligned in a second direction, perpendicular to the first region, in regions corresponding to the background. After curing, the liquid crystal molecules within the liquid crystal polymer material will be substantially aligned 30 with the grooves of corresponding region of the security device 102. In this way, microimage regions will allow transmission of light polarised in one direction, and the background regions will emit light polarised in a perpendicular direction. When 12 viewed under correctly polarised light, the microimages will be visible against the background. Figures 3a to 3d show pair-wise authentication arrangements. The first authentication device 104 and the second authentication device 106 are each 5 configured to provide visual effects when overlaying the security device 102 individually. The appearance of the visual effects associated with a particular authentication device 104 or 106 overlaying each side 108, 110 of the security device 102 can be the same, mirror-images, or different (for example, referring to Figures 3a and 3b, the appearance of the visual effects can be the same or 10 different in each configuration shown). Furthermore, though Figures 3a to 3d show four different pair-wise authentication arrangements, the number of pair wise authentication arrangements can be limited to a subset of these. For example, Figures 3b and 3d can show no visual effect due to the security device 102 being located within a half-window region of the security document 100. The 15 arrangements of Figures 3b and 3d can be complementary arrangements to Figures 3a and 3c, respectively. For each authentication arrangement, there can be visual effects associated with one or both viewing directions 114, 116. In an example of pair-wise authentication arrangements, the two authentication devices 104, 106 each include a linear polarising filter, wherein 20 each linear polarising filter has a different polarisation direction. For example, the polarisation direction of the second authentication device 106 is perpendicular to the polarisation direction of the first authentication device 104. The security device 102 includes a reflective surface (i.e. the security device 102 operates in a reflection mode on each surface of the device). Each side 108, 110 of the security 25 device 102 can be configured to produce a different image depending on the polarisation direction of the applied polarising filter, therefore enabling different visual effects for each configuration shown in Figures 3a to 3d. Instead of applying a reflective surface to each side 108, 110, a reflective surface can be applied to one side 108 and is visible from both sides 108, 110. Alternatively, the 30 security device 102 can be a transparent security device 102 configured to produce a different visual effect depending on the polarising direction of the applied polarising filter. In this case, the visual effects corresponding to the arrangements of Figures 3a and 3b will be the same, and the visual effects 13 corresponding to the arrangements of Figures 3c and 3d will be the same, and different to the visual effect corresponding to the arrangements of Figures 3a and 3b. One implementation includes associated visual effects, where the visual 5 effect present when, for a particular viewing direction 114, 116, the security device 102 is viewed through the first authentication device 104 is the negative of the visual effect present when the security device 102 is viewed through the second authentication device 106 at the same viewing direction 114, 116. This can be achieved, for example, using a liquid crystal linear polariser or a structural 10 linear polariser with regions polarised in a first direction, and other regions polarised in a second direction perpendicular to the first direction. Where a reflective surface is incorporated, each side of the security device 102 can be configured to provide a different visual effect by including different configurations of the regions polarised in a first direction and regions polarised in a second 15 perpendicular direction on each side 108, 110. Another implementation, in which different, unrelated, visual effects occur depending on which linear polarising filter, and therefore which authentication device 104, 106, is applied to the security device 102, incorporates a structural polariser, where the structural polariser includes first regions, second regions, 20 and background regions. The first regions include groove structures arranged in a first direction and the second regions include groove structures arranged in a second direction perpendicular to the first region. The first region corresponds to a first image, and the second regions correspond to a second image. The background regions do not include a groove structure, and are therefore non 25 polarising. Therefore, whether the security device 102 is viewed through the first authentication device 104 or the second authentication device 106, the background regions will be visible. In another example of pair-wise authentication arrangements, the first authentication device 104 includes a microlens array and the second 30 authentication device 106 includes a linear polarising filter. The first authentication device 104 can be configured to produce a visual effect when overlapping the first side 108 only. Depending on the configuration of the security device 102, the second authentication device 106 can produce a visual effect 14 when applied to either the first side 108 or the second side 110, or alternatively visual effects when applied to both sides 108, 110. For example, the first side 108 or the second side 110 can include a microimage pattern which is configured to produce a Moir6 effect when viewed through the microlens array of the first 5 security device 104. The security device 102 can be configured to appear different when viewed through the linear polariser of the second authentication device 106 due to being configured to emit polarised light, for example by a polarising layer being applied to the top surface of the first side 108, or to the second side 110 overlapping the microimage pattern, where the polarising layer 10 can be applied in the shape of an image (e.g. with first regions polarised in a first direction and second regions polarised in a second direction perpendicular to the first direction, wherein one of the polarisation directions is perpendicular to the polarisation direction of the linear polariser of the second authentication device 106). 15 In another example of pair-wise authentication arrangements, the first and second authentication devices 104, 106 include a microlens array. The first authentication device 104 is configured to produce a visual effect when overlapping the first side 108 only. Depending on the configuration of the security device 102, the second authentication device 106 can produce a visual effect 20 when applied to either one of the first side 108 or the second side 110. For example, the first side 108 can include a microimage pattern which is configured to produce a particular Moir6 effect when viewed through the first authentication device 104. Where the security device 102 is transparent, the microlenses of the second authentication device 106 are configured for viewing the microimage 25 pattern of the first side 108, through the second side 110 and the substrate 112. Alternatively, where the security device 102 is opaque, the second side 110 can include a microimage pattern, preferably different to the microimage pattern of the first side 108, and the microlenses of the second authentication device 106 are configured to view the microimage pattern of the second side 110. 30 In another example, the first side 108 of the security device 102 includes a microimage array, and the first authentication device 104 and the second authentication device 106 are each configured for overlapping the first side 108, and each authentication device 104, 106 includes a microlens array. The 15 microlens array of the first authentication device 104 includes a different arrangement to the microlens array of the second authentication device 106, such that the Moir6 effect observed through each authentication device 104, 106 is different. For example, the Moir6 effect of the first authentication device 104 can 5 give the impression of the Moir6 image being located beyond the plane of the security device 102, whereas the Moir6 effect of the second authentication device 106 can give the impression of the Moir6 image being located in front of the plane of the security device 102. Figures 4a to 4d show circular-fold authentication arrangements. The 10 security device 102 is configured to provide a visual effect when the security device 102 is viewed through overlapping authentication devices 104, 106 and/or when the overlapping authentication devices 104, 106 are viewed through the security device 102. According to this arrangement, each authentication device 104, 106 is transparent or at least partially transparent. 15 As shown in Figures 4a and 4b, the security device 102 can be configured to produce a visual effect when viewed through both the first authentication device 104 and the second authentication device 106 from the first viewing direction 114 such that the first side 108 of the security device 102 is viewed through the overlapping authentication devices 104, 106 (though the second side 20 110 of the security device 102 may be visible through the first side 108). According to Figure 4a, the first authentication device 104 is located between the security device 102 and the second authentication device 106, whereas according to Figure 4b, the second authentication device 106 is located between the security device 102 and the first authentication device 103. It can be that the 25 visual effect is the same or different depending on the order of the authentication devices 104, 106. As shown in Figures 4c and 4d, the security device 102 can be configured to produce a visual effect when the two authentication devices 104, 106 overlap the second side 110 of the security device 102, and the security device 102 is 30 viewed from the second viewing direction 116. According to Figure 4c, the first authentication device 104 is located between the security device 102 and the second authentication device 106, whereas according to Figure 4d, the second 16 authentication device 106 is located between the security device 102 and the first authentication device 103. Optionally, the security device 102 can be configured to produce a visual effect when the security device 102 is viewed from the opposite viewing direction 5 114, 116 to the side 108, 110 of the security device 102 to which the authentication devices 104, 106 are overlapped. In an example of a security document 100 including a circular-fold authentication arrangement, the security device 102, first authentication device 104, and the second authentication device 106 each include a linear polarising 10 filter. The polarisation direction of the security device 102 is perpendicular to the polarisation direction of the second authentication device 106. The polarisation direction of the first authentication device 104 is rotated by 45 degrees with respect to the polarisation directions of both the second authentication device 106 and the security device 102. The security device 102 can be transparent, or 15 opaque with a reflective surface located under the linear polarising filter. When the security device 102 is viewed through the first authentication device 104, which in turn is viewed through the second authentication device 106, the visual effect corresponds to the appearance of the security device 102 being a non black colour (which may be a shade, a particular colour, or range of colours), as 20 there is no single instance of cross-polarisers acting to block the incident light. However, when the security device 102 is viewed through the second authentication device 106, which is in turn viewed through the first authentication device 104, the visual effect corresponds to the security device 102 appearing black, or at least substantially or noticeably darker than the previously described 25 configuration. This is because the second authentication device 106 and the security device 102 combine to form a cross-polariser, and therefore act to block incident light from transmission. Optionally, according to this example, the security device 102 can be transparent, in which case the configuration of Figure 4c will produce the same visual effect as the configuration of Figure 4a, and the 30 configuration of Figure 4d will produce the same visual effect as the configuration of Figure 4b. Furthermore, the visual effects associated with each viewing direction 114, 116 of each authentication arrangement will be the same. Alternatively, the security device 102 can be opaque, and therefore the 17 configurations of Figures 4c and 4d produce visual effects independent of the visual effects of Figures 4a and 4b, or no visual effect. For example, the second side 110 of the security device 102 may be configured as per a different example of the arrangement. It is noted that in this instance it is the difference in visual 5 effect of the authentication arrangements that provides the security feature. In another example of circular-fold authentication arrangements, a similar visual effect as previously discussed can be provided wherein the first authentication device 104 includes a microlens array and the second authentication device 106 includes a linear polarising filter. The security device 10 102 in this instance can be a transmission mode or reflection mode device including a micromotif array, where each element is configured to emit linearly polarised light. This example can produce the same effect whether the first or second authentication device 104, 106 is located directly in line with the security device 102. 15 In another example of circular-fold authentication arrangements, the security device 102 is transparent and the first side 108 includes a first microimage pattern and the second side 110 includes a second microimage pattern, the first authentication device 104 includes a microlens array, and the second authentication device 106 includes a transparent filter (which can 20 optionally be polarised). The microlens array of the first authentication device 104 is configured to focus on, or at least substantially focus on, the second side 110 of the security device 102 when applied directly to the first side 108, such that when viewing the security device 102 through the first authentication device 104, a visual effect corresponding to a Moir6 effect is seen corresponding to the 25 second microimage pattern. When the first authentication device 104 is applied directly to the second authentication device 106, which in turn is applied directly to the first side 108 of the security device 102, the microlenses of the first authentication device 104 are configured to focus, or substantially focus, on the first microimage pattern, such that a visual effect corresponding to a Moir6 effect 30 is seen corresponding to the first microimage pattern. Preferably, the first and second microimage patterns are different. When the second authentication device 106 includes a linear polarising filter, the security device can be configured to reveal one or both of the microimage patterns when viewed through the linear 18 polarising filter (as previously described). Alternatively, the security device 102 includes one microimage pattern located on preferably the first side 108 but optionally the second side 110. The microlens array of the first authentication device 104 is configured to produce visual effect corresponding to a Moir6 effect 5 only when the first authentication device 104 is directly applied to the second authentication device 106, which in turn is directly applied to the security device 102. The second authentication device in this example is acting as a spacer. The use of more than one authentication device 104, 106 for a particular security device 102 can advantageously provide a stronger security effect will 10 minimally increasing the required area of a security document 100 required for such devices. Embodiments and arrangements wherein the security device 102 can provide more than one visual effect depending on the authentication devices used 104, 106 and the arrangement of authentication devices 104, 106 advantageously provides a surprising overall effect to a user. 15 For examples described above including cross-polarises, each polariser may include alignment markings, such that when the polarisers are positioned in a cross-polariser configuration, the alignment markings can be aligned allowing for accurate positioning of the polarises. In examples employing microlens arrays, it is noted that the microlenses 20 can be formed using known methods, for example embossing and curing of a radiation curable ink (e.g. a UV curable ink) which has been applied to a surface of the substrate. In examples employing a microlens array and a microimage pattern, reference has been made to Moir6 effects. It is, however, understood that Moir6 25 effects constitute a subset of possible microlens based effects, and other effects can employed as appropriate, for example image switching effects or three dimensional illusion effects. Further modifications and improvements may be made without departing from the scope of the present invention. For example, each arrangement 30 described can constitute one of several authentication arrangements available on the same security document, for example a security device may be configured to produce a visual effect when in an arrangement according to one or more of 19 Figures 3a to 3d, and another visual effect when in an arrangement according to one or more of Figures 2a to 2b and 4a to 4d. 5

Claims (5)

1. A security document including: a security device; a first authentication device; and a second authentication device, wherein the security document is arrangeable into a first authentication arrangement corresponding to the first and 5 second authentication devices overlapping the security device, wherein the security device is configured to provide at least one visual effect when the security document is in the first authentication arrangement, wherein the, or each, visual effect is associated with a viewing direction.

2. A security document as claimed in claim 1, wherein the security device 10 includes a first side associated with a first viewing direction and a second side associated with a second viewing direction, such that a user viewing the security device from the first viewing direction views the first side, and such that a user viewing the security device from the second viewing direction views the second side. 15

3. A security document as claimed in claim 2, wherein the first authentication arrangement corresponds to the first authentication device overlapping the first side of the security device and the second authentication device overlapping the second side of the security device.

4. A security document as claimed in claim 2, wherein the first authentication 20 arrangement corresponds to the first authentication device and the second authentication device overlapping the first side of the security device.

5. A method for producing a security document according to any one of the previous claims, including the steps of: a) providing a substrate; 25 b) printing first and second opacifying layers to opposite sides of the substrate; and 21 c) embossing, printing, or other wise providing security features into different regions of the substrate, the security features corresponding to the security device, first authentication device, and second authentication device. 5 SECURENCY INTERNATIONAL PTY LTD WATERMARK PATENT & TRADE MARK ATTORNEYS UIP1331AU00