AU2015100575A4 - Security Device with Non-diffractive Switching Image - Google Patents

Security Device with Non-diffractive Switching Image Download PDF

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AU2015100575A4
AU2015100575A4 AU2015100575A AU2015100575A AU2015100575A4 AU 2015100575 A4 AU2015100575 A4 AU 2015100575A4 AU 2015100575 A AU2015100575 A AU 2015100575A AU 2015100575 A AU2015100575 A AU 2015100575A AU 2015100575 A4 AU2015100575 A4 AU 2015100575A4
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security
substrate
relief
coating
image
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AU2015100575B4 (en
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Phei Lok
Gary Fairless Power
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CCL Security Pty Ltd
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Innovia Secutiry Pty Ltd
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Abstract

The invention relates to a security device 10 and a method of making the security device 10. The security device 10 has a substantially transparent substrate 11, an embossed relief structure 14 provided on a surface 12 on a first side of the substrate. The relief structure 14 defines a non-diffractive switching image. When the security device 10 is viewed from a first viewing angle, a first image is visible. A second image is visible when the security device 10 is viewed from the second viewing angle, which is different from the first viewing angle. At least one coating is applied to a non-structured surface 13 on a second, opposite side of the substrate 11. Fig 1 Figure 1 11 3 m"""J L~j15 13 16 16 16 Figure 2

Description

1 SECURITY DEVICE WITH NON-DIFFRACTIVE SWITCHING IMAGE FIELD OF THE INVENTION [0001] The invention relates to security devices and security documents or tokens, such as banknotes or the like, and is particularly concerned with providing with an overt optically variable security device that is readily discernible but difficult to copy or counterfeit. BACKGROUND OF THE INVENTION [0002] The use of security elements is well established in the field of security documents. One such type of security element is an optically variable device (OVD) which is a security feature or device that changes in appearance. OVDs provide an optically variable effect when the banknote is tilted and/or when the viewing angle of the observer relative to the OVD changes. One type of OVD is a diffractive optically variable device (DOVD) which may be provided by a diffractive device, such as a diffraction grating or a volume hologram. [0003] US 6,296,281 relates to another type of OVD, a non-diffractive OVD, which is a latent image structure having a relief structure formed of relief structures comprising an array of relief elements which define first and second latent images. When viewed from a normal viewing angle, the latent images are difficult to discern. However, when viewed from a first viewing angle offset to the normal, the first latent image can be seen, and when viewed from a second viewing angle offset to the normal and rotated laterally relative to the first viewing angle, the second latent image can be seen. Thus, as the latent image structure is rotated relative to the viewer, the image seen by the viewer 'switches' between the first and second images. [0004] WO 2006/095161 discloses another type of non-diffractive security device having at least two regions, each region comprising a prismatic surface 2 structure defining an array of substantially planar facets. Each region forms a reflector due to total internal reflection when viewed at a first viewing angle, and is transparent when viewed at a second viewing angle. The first viewing angle for one region is different from the first viewing angle of the other region. This structure produces an image with transparent and reflective regions when viewed from a normal viewing direction, and an inverse image with the transparent and reflective regions reversed when the document is tilted to change the viewing angle from the normal. [0005] Attempts have been made to improve the counterfeit resistant properties of non-diffractive security devices having prismatic structure. For example, it has been proposed to provide one or more colour shifting materials in combination with a prismatic structure. US 8,105,678 discloses an optically variable device having a substrate with an array of pyramidal structures. The pyramidal structures are formed either by printing pyramids with an optically variable colour shifting ink, or by embossing a layer of ink with pyramids. WO 2009/066048 discloses a security device comprising first and second layers of colour shifting materials with a light control layer at least partially applied over an exposed surface of one of the colour shifting layers. However, these security devices are quite complex to manufacture and not usually amenable to high speed application methods, such as printing. [0006] Such non-diffractive prismatic and pyramidal structures can provide interesting visual effects, but can be susceptible to counterfeit attack. One way to add complexity to deter counterfeiting is to coat the prismatic structures with various coatings. However, many coatings will match the refractive index of the structures and render the structures substantially invisible. Also, relatively deep structures are challenging to coat with metallized layers and high refractive index coatings without impacting on the visual effect. Often these coatings are unable to be applied in sufficient thickness to protect the structures fully from mechanical copying.
3 [0007] It is therefore desirable to provide an optically variable security device which alleviates at least some of the disadvantages of the prior art and/or which provides a useful alternative. It is also desirable to provide an optically variable security device which has an attractive visual appearance, and which is difficult to counterfeit. It is further desirable to provide a security document incorporating such an optically variable security device, and a method of manufacturing such a security document or device which can be performed at a relatively low cost. SUMMARY OF THE INVENTION [0008] According to a first aspect, the present invention provides a security device including a substantially transparent substrate, an embossed relief structure provided on a surface on a first side of the substrate, wherein the relief structure defines a non-diffractive switching image in which a first image is visible when the security device is viewed from a first viewing angle, and in which a second image is visible when the security device is viewed from a second viewing angle different from the first viewing angle, and wherein at least one coating is applied to a non-structured surface on a second, opposite side of the substrate. [0009] In this aspect, and the other aspects detailed below, the relief structures are preferably microstructures, and more preferably have a height (h) (from the layer on which the relief structure if formed) of between 4pm and 25pm, further more preferably between 6pm to 16pm. [0010] The period of the relief structures are, preferably, such that an unaided human eye finds it difficult, or cannot, discriminate individual relief elements. Further preferably, the period is less than 50pm. Further preferably, the minimum period is around 2 times the height of the relief structure. Further preferably, the period is 2.2 times the height plus 2 pm (2.2h + 2pm). For example, if h = 6pm, the minimum is period approximately 15.2pm.
4 [0011] In one embodiment, the at least one coating applied to the second, opposite side of the substrate is an opacifying coating. The opacifying coating is preferably a white opacifying coating, preferably a white opacifying ink. Alternatively, the opacifying coating may be a coloured opacifying coating or a black coating. [0012] In another embodiment, the at least one coating applied to the second, opposite, side of the substrate may be an optically variable coating, preferably a colour shifting coating. A colour shifting coating has a first colour at some viewing angles and a second colour at other viewing angles. The colour shifting coating is preferably a colour shifting ink, but may also be provided by a thin film interference coating or by at least one liquid crystal layer. [0013] The at least one coating applied to the second, opposite side of the substrate is preferably an ink coating. [0014] An optically variable coating applied to the non-structured surface on the second side of the security device or document may take a wide variety of forms, including colour shifting inks; other security inks such as fluorescent, luminescent and phosphorescent inks, metallic inks, iridescent inks, photochromic, thermochromic, hydrochromic or piezochromic ink; thin film interference layers; liquid crystal layers; photonic crystal layers; and polarizing layers. [0015] One colour shifting ink composition suitable for use in the invention includes a major proportion of an optically variable pearlescent interference pigment, such as KW Pearl Pigments produced by Kunwei Pearl Pigment Co. Ltd, and a minor proportion of a colour pigment, which may be organic or inorganic. The interference pigment and particles of the colour pigment may be mixed with a transparent binder or resin to form a colour shifting ink composition which is suitable for application to a substrate in a printing process.
5 [0016] The colour shifting ink is preferably formed from a formulation including from about 10% to about 30% of a pearl lustre interference pigment (for example, interference pigments produced by the Kunwei Pearl Pigment Co. Ltd). The colour shifting ink preferably includes from about 0.5% to about 10% of an organic or inorganic colour pigment, eg phtalocynanine blue. The colour shifting ink may also include from about 60% to 90% of transparent binder or resin. Preferably, the pearl lustre interference pigments have a particle size from about 1 pm (micron) to about 200pm (microns) and, more preferably, from about 5pm to about 60pm. This forms a colour shifting ink composition which has a transparent or translucent colour at some viewing angles generally taken from the colour pigment and an interference colour at other viewing angles which is a derived from the colour pigment and the interference pigment. [0017] When "colour pigment" is used herein, this is a reference to an organic or inorganic colour pigment and when "interference pigment" is used herein, this is a reference to interference pigments in general, one example of which is a pearl lustre interference pigment. [0018] The at least one coating applied to the second, opposite side of the substrate may be applied over the whole extent of the security device. [0019] Alternatively, at least one coating applied to the second, opposite side of the substrate may be applied in a partial region or a plurality of partial regions of the security device. [0020] In some embodiments, a combination of two or more coatings may be applied to the second, opposite side of the substrate. For example, an opacifying coating may be applied in a first partial region or regions, and one or more colour shifting coatings may be applied in a second partial region or regions. In another embodiment, a first colour shifting coating may be applied in a first partial region or regions, and a second colour shifting coating may be applied in a second partial region or regions.
6 [0021] The relief structure preferably includes a plurality of facets facing in different directions. The relief structure may be formed from a transparent or translucent material. In a preferred embodiment of the invention, however, the facets of the relief structure, even though they are made from a transparent material, cause light to be reflected (that is the facets reflect impinging light). In an alternative embodiment, the relief structure is designed such that the facets act as microprisms and reflect light due to total internal reflection. [0022] In one preferred embodiment, the relief structure includes least four facets facing in different directions. The relief structure may include a plurality of pyramidal or truncated pyramid structures, such as tetrahedra, pyramids and truncated pyramids having a square or other polygonal base structures. In one preferred embodiment, at least some of the relief structures have cross-sectional shapes in the form of lozenges. Alternatively, the relief structure may include a plurality of lines having a triangular cross-section. [0023] The relief structure preferably includes at least two sets of relief structures, with each set of relief structures being rotated relative to the other set or sets of relief structures about an axis substantially normal to the substrate. At least one of the sets of relief structures may define a first transitory image and at least one other set of relief structures defines a second transitory image. Alternatively, or additionally, at least one set of relief structures may define an image background. [0024] In a preferred embodiment, at least four sets of relief structures are provided. [0025] According to a second aspect, the invention provides a security document incorporating a security device according to the first aspect of the invention.
7 [0026] According to a third aspect of the invention, there is provided a method of manufacturing a security device or document comprising the steps of: (a) providing a substrate of substantially transparent polymeric material; (b) forming a relief structure on a surface on a first side of the substrate, wherein the relief structure defines a non-diffractive switching image in which a first image is visible when the security device is viewed from a first viewing angle, and a second image is visible when the security device is viewed from a second viewing angle different from the first viewing angle; (c) applying at least one coating to a non-structured surface on a second, opposite side of the substrate. [0027] In one embodiment, the at least one coating applied to the second, opposite side of the substrate is an opacifying coating, preferably a white opacifying coating. [0028] In another embodiment, the at least one coating applied to the second, opposite side of the substrate is an optically variable coating, preferably a colour shifting coating. [0029] The at least one coating applied to the second, opposite side of the substrate is preferably an ink coating which is applied by printing. [0030] Providing the at least one coating on the non-structured surface on the second, opposite side of the substrate from the relief structure has various advantages. The at least one coating adds complexity to the security device without significantly affecting the intricate visual effect of the relief structure which could otherwise occur by providing a coating on the relief structure, for example 8 by ink flowing into and settling on the uneven surface to form an uneven coating. This could also result in 'picking', ie tiny holes being formed, where the ink has not fully coated the structure, adversely affecting the intended effect. Thus, the present invention results in less spoilage during manufacture in large volumes. Applying the at least one coating on the smooth, non-structured side also allows more intricate designs, such as fine line patterns, to be printed, providing more detail and permitting different combinations of colours to provide further deterrence to counterfeiters. [0031] The smooth, non-structured surface on the second, opposite side of the substrate may be surface treated to provide a better ink adhesion before the at least one coating is applied. The adhesion promoting surface treatment may be selected from: flame treatment; corona discharge treatment; and plasma treatment, to provide a good surface energy and surface tension for good ink adhesion. [0032] The relief structure preferably includes a plurality of facets facing in different directions. In one preferred embodiment, the relief structure includes at least four facets facing in different directions. The relief structure may include a plurality of pyramidal or truncated pyramid structures, such as tetrahedra, pyramids and truncated pyramids having a square or other polygonal base structures. In one preferred embodiment, at least some of the relief structures have cross-sectional shapes in the form of lozenges. Alternatively, the relief structure may include a plurality of lines having a triangular cross-section. [0033] The relief structure preferably includes at least two sets of relief structures, with each set of relief structures being rotated relative to the other set or sets of relief structures about an axis substantially normal to the substrate. At least one of the sets of relief structures may define a first transitory image and at least one other set of relief structures defines a second transitory image. Alternatively, or additionally, at least one set of relief structures may define an image background.
9 [0034] In a preferred embodiment, at least four sets of relief structures are provided. [0035] The relief structure is preferably formed by embossing. In one embodiment, a surface on the first side of the substrate may be directly embossed with the relief structure. Alternatively, in a preferred embodiment, an embossable, curable coating is applied to a surface on the first side of the substrate, embossed with the relief structure and cured to fix the relief structure of the security device. [0036] The embossable, curable coating is preferably soft-embossed by performing the embossing step and the curing step substantially simultaneously. [0037] The curable coating is preferably applied by a printing process, such as flexographic printing; gravure printing; or silkscreen printing. [0038] Preferably the curable coating is a radiation curable coating, and more preferably a UV-curable coating, such as a UV-curable, epoxy based coating. [0039] Alternatively, other forms of embossable curable coatings and curing systems may be used, such as electron-beam (EB) curable coatings, or cationic curing coatings. [0040] The first surface of the document substrate may be subjected to an adhesion promoting process prior to application of the radiation sensitive coating. Optionally, the adhesion promoting process is selected from: flame treatment; corona discharge treatment; and plasma treatment. [0041] The method may further include applying an adhesion promoting layer or a primer layer to the first surface of the document substrate prior to applying the radiation sensitive coating. Preferably the adhesion promoting layer raises the surface energy of the first surface by at least five times more than the surface 10 energy of the adhesion promoting layer. In a further preferred form, the surface energy of the first surface is raised at least ten times more than that of the adhesion promoting layer. The adhesion promoting layer may comprise one or more of: a UV-curing layer; a solvent based layer; and a water based layer. Preferably, the adhesion promoting layer is dried before the radiation sensitive coating is applied. [0042] A protective coating may be applied to the relief structure. The protective coating is preferably substantially transparent and has a refractive index selected relative to the refractive index of the relief structure such that the protective coating does not substantially detract from the optical properties of the security device. [0043] According to a further aspect of the invention, there is provided a security document comprising: a substrate formed from a substantially transparent material, at least one opacifying layer applied to a first surface on a first side of the substrate, at least one opacifying layer applied to a second surface on a second, opposite side of the substrate, the at least one opacifying layer being omitted on one or both of the first and second surfaces to form a half window or window area, and a security device in accordance with the first aspect of the invention provided in the half window or window area. [0044] The security device may be a separate element which is affixed to the security document in the window or half window area. More preferably, however, the security device is formed as an integral part of the security document with the substrate of the security document forming the substrate of the security device, the relief structure is formed on the first surface of the security document substrate in the half window or window area, and the at least one coating of the security device is applied to a non-structured surface in the half window or window area on the second, opposite side of the security document substrate on the opposite side of the security document.
11 [0045] The substantially transparent substrate is preferably formed from a polymeric material, such as biaxially oriented polypropylene. [0046] The opacifying layers are preferably opacifying coatings of ink which may be applied in a printing process. Alternatively, the opacifying layer or layers may be layers of a substantially opaque material, such as paper or opaque plastics material that is laminated or otherwise secured to the substrate. [0047] When the security device is provided in a half window area, the at least one opacifying layer applied to the second surface of the security document in the half-window area may be an opacifying coating that forms the coating of the security device applied to the non-structured surface of the security device. [0048] When the security device is provided in a full window with the at least one opacifying layer being omitted on both of the first and second surfaces to form the full window area, the coating of the security device may be applied to the non-structured surface of the security document substrate. [0049] The coating applied to the non-structured surface on the second side of the security device or document may take a wide variety of forms, including colour shifting inks; other security inks such as fluorescent, luminescent and phosphorescent inks, metallic inks, iridescent inks, photochromic, thermochromic, hydrochromic or piezochromic ink; thin film interference layers; liquid crystal layers; and polarizing layers. [0050] When the security device is provided in a full window with the at least one opacifying layer being omitted on both of the first and second surfaces to form the full window area, the coating of the security device applied to the non structured surface of the security device is preferably a colour shifting coating.
12 [0051] The colour shifting coating is preferably a colour shifting ink, though other colour shifting coatings such as thin film interference coatings and liquid crystal coatings may also be used to provide a colour shifting appearance. [0052] In one embodiment, the security element area is in the form of a stripe across the security document. Optionally, the security element area is a discrete region of the security document. Optionally, the discrete region is in the form of a graphical design. [0053] Preferably, the security document is a banknote. Security Document or Token [0054] 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 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. [0055] The invention is particularly, but not exclusively, applicable to security 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 [0056] As used herein, the term "substrate" refers to the base material from which the security device or document 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), biaxially- 13 oriented polypropylene (BOPP); or a composite material of two or more materials, such as a laminate of paper and at least one plastic material, or of two or more polymeric materials. Transparent Windows and Half Windows [0057] 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 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. [0058] 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 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. [0059] A half-window area may be formed in a polymeric security document which has opacifying layers on both sides by omitting the opacifying layers on a first side only of the security document in the half window area. Such a half window may be opaque in reflected and transmitted light, or if the at least one opacifying layer on the second side of the substrate in the half window area is sufficiently thin, the half window will appear opaque in reflected light and translucent in transmitted light allowing some light to pass through without allowing objects to be viewed clearly through the half-window. [0060] Alternatively, it is possible for the substrate to be formed from a substantially opaque material, such as paper or fibrous material, with an insert of 14 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. Embossable Curable Ink [0061] The term "embossable curable ink" used herein refers to any ink, lacquer or other coating which may be applied to the substrate in a printing process, and which can be embossed while soft to form a relief structure and cured to fix the embossed relief structure. The curing process does not take place before the curable ink is embossed, but it is possible for the curing process to take place either after embossing or at substantially the same time as the embossing step. The curable ink is preferably a radiation curable ink curable by radiation, such as ultraviolet (UV) radiation. Alternatively, the radiation curable ink may be cured by other forms of radiation, such as electron beams or X-rays. [0062] The radiation curable ink is preferably a transparent or translucent ink formed from a clear resin material. Such a transparent or translucent ink is particularly suitable for printing light-transmissive security elements such as sub wavelength gratings, transmissive diffractive gratings and lens structures. [0063] In one particularly preferred embodiment, the transparent or translucent ink preferably comprises an acrylic based UV curable clear embossable lacquer or coating. [0064] Such UV curable lacquers can be obtained from various manufacturers, including Kingfisher Ink Limited, product ultraviolet type UVF-203 or similar. Alternatively, curable embossable coatings may be based on other curing systems, such as EB curing systems or cationic curing systems. [0065] The radiation curable inks and lacquers used herein have been found to be particularly suitable for embossing microstructures, including diffractive structures such as diffraction gratings and holograms, and microlenses and lens 15 arrays. However, they may also be embossed with larger relief structures, such as non-diffractive optically variable devices. [0066] The ink is preferably embossed and cured by ultraviolet (UV) radiation at substantially the same time. In a particularly preferred embodiment, the radiation curable ink is applied and embossed at substantially the same time in a Gravure printing process. [0067] Preferably, in order to be suitable for Gravure printing, the radiation sensitive coating has a viscosity falling substantially in the range from about 20 to about 175 centipoise, and more preferably from about 30 to about 150 centipoise. The viscosity may be determined by measuring the time to drain the lacquer from a Zahn Cup #2. A sample which drains in 20 seconds has a viscosity of 30 centipoise, and a sample which drains in 63 seconds has a viscosity of 150 centipoise. [0068] With some polymeric substrates, it may be necessary to apply an intermediate layer to the substrate before the radiation sensitive coating is applied to improve the adhesion of the embossed structure formed by the ink to the substrate. The intermediate layer preferably comprises a primer layer, and more preferably the primer layer includes a polyethylene imine. The primer layer may also include a cross-linker, for example a multi-functional isocyanate. Examples of other primers suitable for use in the invention include: hydroxyl terminated polymers; hydroxyl terminated polyester based co-polymers; cross-linked or uncross-linked hydroxylated acrylates; polyurethanes; and UV curing anionic or cationic acrylates. Examples of suitable cross-linkers include: isocyanates; polyaziridines; zirconium complexes; aluminium acetylacetone; melamines; and carbodi-imides. BRIEF DESCRIPTION OF THE DRAWINGS 16 [0069] The invention will now be described by way of example only with reference to the accompanying drawings, in which: [0070] Figure 1 is a schematic cross section through a first embodiment of a security device in accordance with the invention; [0071] Figure 2 is a schematic cross-section through a second embodiment of a security device in accordance with the invention; [0072] Figure 3 is a schematic cross section through a security document incorporating a security device in accordance with the invention; [0073] Figure 4 is a schematic cross-section through a security document incorporating another embodiment of a security device in accordance with the invention; [0074] Figure 5 is a view of the security document of Figure 3 from one viewing angle; [0075] Figure 6 is a view of the security document of Figure 3 from another viewing angle; [0076] Figure 7 is an enlarged plan view of a first transitory image formed from an embossed relief pattern in the form of first and second sets of lines; [0077] Figure 8 is an enlarged plan view of a second transitory image formed from an embossed relief pattern in the form of third and fourth sets of lines; [0078] Figure 9 is an enlarged plan view of an embossed relief structure formed by combining the embossed relief patterns of Figures 5 and 6; 17 [0079] Figure 10 is an enlarged plan view of a section of an alternative embossed microprismatic relief structure to that of Figure 9; [0080] Figure 11 is a view of the security document of Figure 4 from one viewing angle; and [0081] Figure 12 is a view of the security document of Figure 4 from another viewing angle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0082] Figures 1 and 2 show a security device 10 which comprises a transparent or translucent substrate 11, having a first surface 12 on a first side of the substrate 11 and a second surface 13 on the second, opposite side of the substrate 11. The substrate 11 is preferably formed from a transparent or translucent polymeric material, preferably biaxially oriented polypropylene (BOPP). A relief structure 14 is applied to the first surface 12 of the substrate 11. Applied to the second, opposite surface 13 of the substrate 11 is a coating layer 15. The coating layer 15 is preferably a layer of ink. As shown in Figure 1, the coating layer 15 may be applied to the second, opposite side of the substrate over the whole extent of the relief structure. Alternatively, as shown in Figure 2, the coating layer 15 may be applied over a partial region or a plurality of partial regions 16 of the security device 10. [0083] The relief structure 14, which in this example is a series, or set, of triangular cross-section lines, which define a non-diffractive switching image in which a first image is visible when the security device is viewed from a first viewing angle 17, and a second image is visible when the security device is viewed from a second viewing angle 18, which is different to the first viewing angle 17. As can be seen from Figures 1 and 2, rotating the device 10 about an axis parallel to the first surface 12 and the apexes of the triangular cross-section lines (that is, the axis is normal to the side view of Figures 1 and 2, projecting out 18 of the plane of the document), will allow a viewer at the first viewing angle 17 to see one side of the relief structure 14, first, and, at the second viewing angle 18, the other side of the relief structure 14. This is explained in greater detail with reference to Figures 5 to 12. [0084] The relief structure 14 is preferably formed by applying an embossable, curable coating to the surface 12 on the first side of the substrate 11, embossing the relief structure 14 into the embossable, curable coating and curing the embossed coating to fix the relief structure 14 of the security device. The embossable, curable coating is preferably a radiation curable ink which may be applied by printing and cured by radiation, such as UV. [0085] In one form of the invention, the at least one coating layer 15 applied to the second, opposite side of the substrate 11 is an opacifying coating. The opacifying coating is preferably a white opacifying coating, preferably a white opacifying ink. Alternatively, the opacifying coating may be a coloured opacifying coating or a black coating. In this embodiment, when the opacifying coating is applied to the second, opposite side of the substrate 11 over the whole extent of the relief structure 14 as shown in Figure 1, the non-diffractive switching image is viewable in reflection only from the first side of the security device. When an opacifying coating 15 is applied to the second, opposite side of the substrate 11 over a partial region or regions 16 of the relief structure 14 as shown in Figure 2, part of the non-diffractive switching image may be viewable in transmission. [0086] In another form of the invention, the at least one coating layer applied to the second, opposite side of the substrate is a colour shifting layer. The colour shifting layer is preferably a coating of colour shifting ink. However, other forms of colour shifting coating layers, such as thin film multilayer interference coatings and liquid crystal coatings may be provided. The at least one coating layer may be an opaque colour shifting coating layer, so that the non-diffractive switching image is viewable in reflection only from the first side of the security device. In another embodiment, the at least one coating layer is a transparent or translucent 19 colour shifting coating so that the non-diffractive switching image may be viewable in reflection and in transmission from both sides of the security device. [0087] The security device of Figure 1 or 2 may be incorporated into a security document by applying the device to the window of the security document, for example, as a laminate applied to the surface of the surface of the security document, or as an insert within an aperture in the security document. However, in preferred embodiments, a security device in accordance with the invention may be integrally formed within a window or half window of a security document as described with reference to Figures 3 and 4 below. [0088] Figures 3 to 6, 11 and 12 show different embodiments of security documents incorporating security devices 20 in accordance with the invention. [0089] Referring to Figures 3, 5 and 6, a security document 30 comprises a transparent substrate 21 of polymeric material, preferably biaxially oriented polypropylene (BOPP), having a first surface 22 on a first side of the substrate and a second surface 23 on the second, opposite side of the substrate. At least one opacifying layer 24 is applied to the first surface 22, and at least one opacifying layer 25 is applied to the second surface 23. The at least one opacifying layer 24 is omitted in an area 26 where a security device 20 is applied to the first surface 22. The at least one opacifying layer 25 completely covers the second, opposite side 23 of the substrate in at least the security element area 26. Preferably, the at least one opacifying layer 25 extends outside the security element area 26 and covers at least a substantial portion of the second, opposite side 23 of the substrate. The arrangement of opacifying layers shown in Figure 3 thus forms a half window area 26 in which the security device 20 is provided. [0090] The opacifying layers 24 and 25 are preferably print receptive layers, and may be overprinted with a wide variety of indicia 29 and images.
20 [0091] The security device 20 comprises an embossed relief structure comprising triangular cross-section lines 27 provided on the first surface 22 on the first side of the substrate 21. The triangular cross-section lines 27 may be embossed directly on the first surface 22 of the substrate, but in a preferred embodiment, the triangular cross-section lines 27 are embossed into a layer of radiation curable ink 28 applied to the first surface 22 of the substrate 21 in the half window area 26. [0092] As shown in Figures 5 and 6, the triangular cross-section lines 27 of the security device 20 define a non-diffractive switching image in which a first transitory image 31,depicted by a circle in Figure 5, is visible when the security device 20 is viewed from a first viewing angle 33, and a second transitory image 32,depicted by a triangle in Figure 6, is visible when the security device 20 is viewed from a second viewing angle 34 rotated about an axis normal to the surface of the security document relative to the first viewing angle 33. [0093] The switching image effect may also be achieved by rotating the security document 30 relative to the viewer about an axis normal to the plane of the substrate to change the viewing angle. As the document is rotated beyond viewing angle 34, the first image 31 will appear at a third viewing angle, and then the second image will appear at a fourth viewing angle. Thus the image seen by the viewer continually switches between the first and second images as the document is rotated through a full revolution. [0094] Embodiments of relief structures and the manner in which the relief structures forms a non-diffractive switching image is described with reference to Figures 7 to 10. [0095] Figure 7 shows a first transitory image structure 70 comprising a first set of lines 71 extending horizontally defining a background and a second set of lines 72 extending vertically defining a first image 75 in the form of a circle. Figure 8 shows a second transitory image structure 80 comprising a first set of lines 81 21 extending diagonally from bottom left to top right and defining a background, and a second set of lines 82 extending perpendicularly to the first set of lines 81 and defining a second image 85 in the form of a triangle. [0096] Figure 9 shows a relief structure 90, which corresponds to a superposition of the two transitory image structures of Figures 7 and 8. The relief structure 90 is formed by an array of four sets of relief structures 91, 92, 93 and 94, each of which is provided at the intersection between superimposed lines of the two transitory image structures 70 and 80 of Figures 7 and 8. Most of the relief structures 91, 92, 93 and 94 are in the shape of a lozenge having four facets. Accordingly, the lozenge is pyramidal in form, having four sloped facets facing in different directions. The lozenges of each set of relief structures have a different orientation from the lozenges of the other sets of relief structures. The first set of relief structures 91 corresponds to the intersections between the first sets of lines 71 and 81 which define the background of the transitory images 70 and 80 of Figures 7 and 8. The second set of relief structures 92 corresponds to the intersections between the second sets of lines 72 and 82 which define the image portions of the transitory images 70 and 80 of Figures 7 and 8. The third set of relief structures 93 corresponds to the intersections between the first set of lines 71 which define background portions of the transitory image 70 of Figure 7 and the second set of lines 82 which define the image portions of the transitory image 80 of Figure 8. The fourth set of relief structures 94 corresponds to the intersections between the second set of lines 72 which define image portions of the transitory image 70 of Figure 7 and the first set of lines 81 which define the background portions of the transitory image 80 of Figure 8. [0097] The effect of the relief structure 90 of Figure 9 is that when the structure is viewed normally, that is, perpendicular to the surface of the substrate on which the structure is formed, the transitory images are barely discernible. However, when the relief structure 90 is viewed from a first viewing angle 33 offset to the normal, the first transitory image 31 is visible. This is represented by the circle in Figure 5. When the relief structure 90 is viewed from a second 22 viewing angle 34 offset to the normal and rotated laterally relative to the first, the second transitory image 32 is visible. This is represented by the triangle in Figure 6. [0098] Figure 10 shows a modified relief structure 100, which in this case is an enlargement of the area 95 highlighted in Figure 9, which produces substantially the same visual effect as the structure of Figure 9. Instead of the relief structures in the shape of lozenges of Figure 9, the relief structure 100 comprises sets of lines, which have a triangular cross-section 101 and1 02. The apex of each of the lines being parallel with the edges of the lines. [0099] As shown in the plan view of Figure 10, each of the lines 101 and 102 has planar surfaces facing in four different directions, being two different directions for each of the original images that have been superposed (as the cross-section of the structure is triangular). Each planar surface therefore forms a facet corresponding to a respective one of the facets of the relief structures of Figure 9, which in turn corresponds to the two transitory image structures of Figures 7 and 8. The first set of lines 101 corresponds to the first sets of lines 71 and 81, which define the background of the transitory images 70 and 80 of Figures 7 and 8. The second set of lines 102 corresponds to the sets of lines 72 and 81 which define the image portion of the first transitory image 70 and the background portions of the second transitory image 80 of Figures 7 and 8. Corresponding lines are created for each combination of lines in Figures 7 and 8. [00100] The effect of the alternative relief structure 100 of Figure 10 described above is very similar to that of Figure 9. Thus, when the alternative structure is viewed normally, the transitory images are barely discernible. However, when the alterative relief structure 100 is viewed from a first viewing angle offset to the normal, the first transitory image 31 is visible. This is represented by the circle in Figure 5. When the relief structure 90 is viewed from a second viewing angle offset to the normal and rotated laterally relative to the first, the second transitory image 32 is visible. This is represented by the triangle in Figure 6.
23 [0100] Figures 4, 11 and 12 show a security document 40 incorporating another embodiment of a security device 50 in accordance with the invention. The security document 40 comprises a transparent substrate 41 of polymeric material, preferably biaxially oriented polypropylene (BOPP), having a first surface 42 on a first side of the substrate and a second surface 43 on the second, opposite side of the substrate. At least one opacifying layer 44 is applied to the first surface 42, and at least one opacifying layer 45 is applied to the second surface 43. The opacifying layers 44 and 45 on opposite sides of the substrate 41 are omitted in a window area 46 where the security device 50 is applied to the first surface 42. The arrangement of opacifying layers 44 and 45 shown in Figure 4 thus forms a full window area 46 in which the security device 50 is provided. [0101] The opacifying layers 44 and 45 are preferably print receptive layers, and may be overprinted with a wide variety of indicia 49 and images. [0102] The security device 50 comprises an embossed relief structure comprising triangular cross-section structures 47 provided on the first surface 42 on the first side of the substrate 41. The triangular cross-section structures 47 may be embossed directly on the first surface 22 of the substrate, but in a preferred embodiment, the triangular cross-section structures 47 are embossed into a layer of radiation curable ink 48 applied to the first surface 42 of the substrate 41 in the full window area 46. [0103] On the second surface 43, on the opposite side of the substrate 41, a colour shifting layer 55 is applied in the window area 46. The colour shifting layer is preferably a coating of colour shifting ink. However, other forms of colour shifting coating layers, such as thin film multilayer interference coatings and liquid crystal coatings may be provided. [0104] As shown in Figures 11 and 12, the triangular cross-section structures 47 of the security device 50 define a coloured non-diffractive switching image in which a first transitory image 51 (depicted by the circle in Figure 11) is 24 visible in a first colour when the security device 50 is viewed from a first viewing angle 33, and a second transitory image 52 (depicted by the triangle in Figure 12) is visible in a second colour when the security device 50 is viewed from a second viewing angle 34 rotated about an axis normal to the surface of the security document relative to the first viewing angle. [0105] The switching image effect and colour switching effect may also be achieved by rotating the security document 40 relative to the viewer about an axis normal to the document to change the viewing angle. As the document is rotated beyond viewing angle 33, the first image will appear in the first colour at a third viewing angle, and then the second image will appear in the second colour at a fourth viewing angle. Thus, the image seen by the viewer continually switches between the first and second images as the document is rotated through a full revolution. [0106] It will be appreciated from the foregoing that the present invention provides a security device which has an added complexity and an improved resistance to counterfeiting. Security devices and documents in accordance with the invention cannot be reproduced by photocopying, and are difficult to replicate because of the combination of the relief structure on one side of a transparent substrate and the at least one coating on the opposite side of the substrate. These require expensive embossing and printing equipment for forming the relief structure on one side and applying the at least one coating in register on the opposite side of the substrate, and also require appropriate materials to be sourced for forming the relief structure and printing the coating or coatings. On the other hand, a security printer with the suitable embossing and printing equipment and the appropriate materials is able to manufacture security documents, such as banknotes, incorporating the security device, in a high volume at relatively low cost per document.
25 [0107] A skilled addressee will readily recognise many variations and modifications to the described embodiments, which do not depart from the spirit and scope of the broad inventive concept.

Claims (5)

1. A security device including a substantially transparent substrate, an embossed relief structure provided on a surface on a first side of the substrate, wherein the relief structure defines a non-diffractive switching image in which a first image is visible when the security device is viewed from a first viewing angle, and in which a second image is visible when the security device is viewed from a second viewing angle different from the first viewing angle, and wherein at least one coating is applied to a non-structured surface on a second, opposite side of the substrate.
2. A security device according to any one of the preceding claims wherein the relief structure includes a plurality of facets, preferably at least four facets, facing in different directions.
3. A method of manufacturing a security device with a structured security element, the method comprising: (a) providing a substrate of substantially transparent polymeric material; (b) forming a relief structure on a surface on a first side of the substrate, wherein the relief structure defines a non-diffractive switching image in which a first image is visible when the security device is viewed from a first viewing angle, and in which a second image is visible when the security device is viewed from a second viewing angle different from the first viewing angle; (c) applying at least one coating to a non-structured surface on a second, opposite side of the substrate.
4. A security document incorporating the security device of any one of claims 1 to 11. 27
5. A method of manufacturing a security document with a security device, wherein the method comprises: (a) providing a substrate of substantially transparent polymeric material; (b) applying at least one opacifying layer to a first surface on a first side of the substrate, and applying at least one opacifying layer to a second surface on a second, opposite side of the substrate, the at least one opacifying layer being omitted on at least the first surface to form a half window or window area; (c) forming a relief structure on the first surface on a first side of the substrate in the half window or window area, wherein the relief structure defines a non-diffractive switching image in which a first image is visible when the security device is viewed from a first viewing angle, and a second image is visible when the security device is viewed from a second viewing angle different from the first viewing angle; and (d) applying at least one coating to a non-structured surface on the second, opposite side of the substrate in the half window or window area. INNOVIA SECURITY PTY LTD WATERMARK PATENT AND TRADE MARK ATTORNEYS UIP1469AUOO
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102015010811A1 (en) * 2015-08-21 2017-02-23 Veridos Gmbh Multi-layered data carrier with a flat see-through window
GB2563187A (en) * 2017-02-03 2018-12-12 De La Rue Int Ltd Method of forming a security sheet substrate
US10752040B2 (en) 2017-02-03 2020-08-25 De La Rue International Limited Method of forming a security device

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100279937B1 (en) * 1993-06-08 2001-04-02 엠 커티스 Embossing as a security measure such as banknote
NZ539221A (en) * 2002-10-07 2007-06-29 Note Printing Au Ltd Embossed optically variable devices

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102015010811A1 (en) * 2015-08-21 2017-02-23 Veridos Gmbh Multi-layered data carrier with a flat see-through window
US10513141B2 (en) 2015-08-21 2019-12-24 Veridos Gmbh Multilayer data storage device having a flat see-through window
GB2563187A (en) * 2017-02-03 2018-12-12 De La Rue Int Ltd Method of forming a security sheet substrate
GB2563187B (en) * 2017-02-03 2020-07-22 De La Rue Int Ltd Method of forming a security sheet substrate
US10752040B2 (en) 2017-02-03 2020-08-25 De La Rue International Limited Method of forming a security device
US10759214B2 (en) 2017-02-03 2020-09-01 De La Rue International Limited Method of forming a security sheet substrate

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