AU2012101505B4 - Security element including a reflective surface - Google Patents

Abstract

A security element including a reflective layer, wherein the reflective layer includes a reflective surface, wherein the reflective surface includes image 5 element regions configured to produce an image upon reflection of incident light, and wherein the image element regions are substantially undetectable to a user upon direct inspection.

Description

1 SECURITY ELEMENT INCLUDING A REFLECTIVE SURFACE FIELD OF THE INVENTION The invention generally relates to security elements including a reflective surface. 5 BACKGROUND It is well known that many of the world's banknotes, as well as other security documents, carry optical security elements which produce images that vary with angle of view of the element or angle of illumination by an external light source, provide an illusion of depth, and/or another optical effect, such that it 10 cannot be copied by conventional photographic, computer scanning or other reprographic printing technologies. The incorporation of such optical security elements into security documents therefore acts as a deterrent against counterfeiting of the document. Nevertheless, over recent years as counterfeiting groups have become 15 better organised and more technically competent, and the high returns from counterfeiting, in spite of the risks, have become more readily appreciated by unscrupulous groups, the attempts at simulation of genuine elements have become more and more successful. This problem is exacerbated by the fact that the authentication process for the banknote by members of the public has long 20 been recognised as the weakest point in the security system. Members of the public often spend very little, if any, time authenticating their banknotes, which makes it easier for simulations to pass through. Furthermore, a common feature of optical security elements is that the images created are viewable by directly viewing the optical security element. Therefore, though it is difficult to reproduce 25 the optical effect of the optical security element, it is possible to create a passable forgery that may appear similar to the optical effect. It would therefore be desirable to create an optical effect suitable for use as optical security element, where the optical effect is not viewable by directly viewing the optical security element. 30 SUMMARY OF THE INVENTION According to a first aspect of the present invention, there is provided a security element including a reflective layer, wherein the reflective layer includes a reflective surface, wherein the reflective surface includes image element 2 regions configured to produce an image upon reflection of incident light, and wherein the image element regions are substantially undetectable to a user upon direct inspection. The reflective surface may be outwardly curved. Alternatively, reflective 5 surface may be flat. Preferably, the security element includes a substrate. The image element regions may correspond to perturbations of the reflective surface. The perturbations may correspond to protrusions of the reflective surface. Alternatively, the perturbations may correspond to depressions 10 of the reflective surface. In another alternative, the perturbations include an image element region corresponding to a protrusion of the reflective surface and an image element region corresponding to a depression of the reflective surface. Preferably, the security element includes a shaping layer, wherein the shaping layer includes a shaping surface in contact with the reflective layer, and including 15 perturbations corresponding to the image element regions such that the reflective surface profile corresponds to the shaping surface profile. The shaping layer may be located on the same side of the reflective layer as the reflective surface. Alternatively, the shaping layer may be located on the opposite side of the reflective layer to the reflective surface. 20 Alternatively, the image element regions may correspond to changes in reflectivity of the reflective surface. The security device may include a partially reflective surface located on the reflective surface. The reflective surface may be located on the same side of the reflective layer as the substrate. Alternatively, the reflective surface may be located on the opposite side of the reflective layer to the 25 substrate. Preferably, the image is viewable on a viewing screen. According to another aspect of the previous invention, there is provided a security document including a security element according to the previous aspect. Preferably, the security document includes a secondary security device. The security document may be a banknote. The security document may instead be a 30 credit card or other inflexible security document. According to another aspect of the present invention, there is provided a method of manufacturing a security device including the steps of: providing a substrate including a first surface and a second surface; and applying to the first 3 surface a reflective layer, wherein the reflective layer includes a substantially mirror-like reflective surface, and wherein the reflective surface includes one or more image element regions configured to alter the reflective properties of the reflective layer. 5 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 cards, cheques, passports, identity cards, securities and share certificates, 10 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 documents or tokens such as banknotes or identification documents such as 15 identity cards or passports formed from a substrate to which one or more layers of printing are applied. The diffraction gratings and optically variable elements described herein may also have application in other products, such as packaging. Substrate As used herein, the term substrate refers to the base material from which 20 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 25 plastic material, or of two or more polymeric materials. DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described with reference to the accompanying drawings. It is to be appreciated that the embodiments are given by way of illustration only and the invention is not limited by this illustration. In the 30 drawings: Figure 1 shows a security element according to an embodiment; 4 Figure 2 shows a security element including a convex surface according to an example of a first embodiment; Figure 3 shows a security element including a flat surface according to an example of a first embodiment; 5 Figure 4 shows a security element including a flat surface and a curved substrate according to an example of a first embodiment; Figure 5 shows a security element including a convex surface according to an example of a second embodiment; Figure 6 shows a security element including a flat surface according to an 10 example of a second embodiment; Figure 7 shows a security element including a flat surface and a curved substrate according to an example of a second embodiment; Figure 8 shows a security element including a convex surface according to an example of a third embodiment; 15 Figure 9 shows a security element including a flat surface according to an example of a third embodiment; Figure 10 shows a security element including a flat surface and a curved substrate according to an example of a third embodiment; Figure 11 shows an image element region according to an embodiment; 20 Figure 12 shows an intensity profile of a reflected light; Figure 13 shows a projection from a surface; Figure 14a shows a security element including a flat surface according to an example of a fourth embodiment; Figure 14b shows a security element including a flat surface according to 25 an example of a fourth embodiment; and Figure 15 shows a security document including a security element. Archaeological (and current) examples of Makyoh (from the Japanese for magic mirror') mirrors have been found in a range of sizes and a first approximation they are all similar in being circular metal disks. One side (the 30 reverse) is patterned in relief with a decorative image. The front side is apparently smooth, polished, reflective and slightly convex. The reason these mirrors are referred to as 'magic' is because when sunlight (or nearly parallel light from another source) shines on the polished 5 convex surface of the mirror, a pattern, often corresponding to the pattern on the back of the mirror, can be projected on a screen in front of the mirror. This occurs even though no trace of a corresponding pattern can be discerned by the observer on the reflecting face. The pattern on the screen is not the result of the 5 focusing responsible for conventional image formation, because its sharpness is independent of distance, and also because the magic mirrors are usually slightly convex. The established theory of operation is that weak undulations on the reflecting surface cause the deviation of incoming light rays. The surface 10 undulations can be reproduced from the much stronger relief embossed on the back. There have been a number of attempts to explain the method of production of the mirror whose upper surface is supposed to consist of sub-micron features. These are mostly concerned with methods of how the embossed image on the 15 reverse of the mirror may be transferred to the front. One theory holds that the relief is generated following the casting process while the mirror is cooling through unequal contraction of the thick and thin parts of the pattern. Other theories suggest that cooling generates stresses, and that during vigorous grinding and polishing one part yields more than another, with some areas of the 20 design being worn down faster than others. What is unclear is whether the thinner parts or the thicker parts of the structures are eroded the quickest. Berry, M V Oriental Magic Mirrors and the Laplacian Image (2006) has published a mathematical model of the effect, based upon mirrors with surface features of -400nm height and -0.5mm width. 25 Some workers have stated that it is possible to construct different types of magic mirror. Superficially, the images generated by the images look the same but careful inspection reveals differences. According to Mak, Se-yuen & Yip, Din yan Secrets of the Chinese Magic Mirror Replica (2001) there are three types: Type 1: An image that consists of dark lines on a brighter background field. 30 The image can be captured on a screen at any distance from the mirror. Type 2: Bright lines against a darker background. This image-type needs to be focussed onto a screen (presumably since it relies upon a convergence of beams that are divergent at other distances).

6 Type 3: Dark lines several centimetres long, with 'full- or half-tone patches of area no less than 1 cm 2 ,. According to Mak and Yip, Type 1 images can be formed by surface undulations due to slight elevations in the top surface resulting from an embossed 5 or cast pattern on the rear. Other authors disagree with this analysis and state that the key insight is that the image of a single surface step is neither a dark line nor a bright line but is bright on one side and dark on the other. This kind of mirror corresponds to what may be considered to be a 'true' Makyoh mirror. Type 2 mirrors can be considered to be simplified versions of Type 1 as 10 they do not have a concave upper surface, as such they are not able to work over a large range of screen mirror separations. For Type 2 images the key parameter for successful imaging is the distance between the mirror surface and the screen. This arises because the surface of the mirror is flat, yet the pattern is formed from nonzero surface gradients. Increasing the distance increases the lateral shift of 15 the image points due to the image surface gradients and also increases the overall contrast and sensitivity of the method. The optimum distance will produce a high enough contrast for realisable viewing whilst preserving a good correspondence between the image and mirror topography. Type 3 mirrors are similar to Type 1 in that the image can be observed at 20 any distance. With Type 3 mirrors however, the projected image can be unmagnified. Other workers have proposed that Type 3 mirrors are likely to be produced by a two layer system comprising a lower reflecting mirror containing partially scattering regions (the relief might be acid etched directly onto the reflecting surface) to produce greyscale dark patches. Therefore the dark patches 25 are not due to surface undulations causing divergence of reflected rays of light, but rather local scattering or absorption. Some Type 3 mirrors have embossed rear patterns that are different from the pattern projected on the screen. Therefore, the upper surface of these mirrors cannot have been formed from the transfer of the rear pattern. 30 As shown in figure 1, a security element 100 incorporating a Makyoh mirror-like effect, is configured to reflect light 114 towards a viewing screen 110. Preferably, the incident light 114 is composed of parallel light, or at least substantially parallel light. An example source 116 of such light is the sun. The 7 viewing screen 110 can be any suitable viewing screen, for example a projector screen, or even a wall. Alternatively, the viewing screen 110 can be a recording medium, for example film or a digitising screen. It is envisioned that there is a wide variety of screen types suitable for use with the security element. 5 The security element 100 includes a reflective surface 104 located on a reflective layer 102. For the following discussion, a layer may include one or more surfaces. To distinguish surfaces, a top surface is a surface located nearer the reflecting layer, and a bottom surface is a surface located away from the reflecting layer. The 10 reflective surface of the reflective layer is the surface configured to receive and reflect incident light. Also, for the purposes of this description, the term 'smooth' when used to describe a reflective surface refers to the surface having a profile which may be described as substantially 'mirror-like', for example a flat profile or a convex profile. 15 Included on, or in communication with, the reflective surface 104 are image element regions 106. Image element regions 106 are configured to alter the properties of the reflective surface 104 within the region of the reflective surface 104 encompassed by the image element regions 106. For example, as described in reference to particular embodiments of the invention, the image element 20 regions 106 may represent changes in profile from the nominal profile of the reflective surface 104 (as shown in the embodiments according to figures 2 to 10), or alternatively may alter the reflective properties of the reflective surface 104, for example by absorption or scattering of the incident light (as shown in the embodiments according to figures 14a and 14b). 25 The image element regions 106 are substantially or wholly invisible to, or at least difficult to discern by, a user when the reflective surface 104 is inspected directly by the user under normal viewing conditions. The image element regions 106 are configured to affect the reflected light such that the resulting image 112 corresponds to the arrangement of the image element regions 106 on the 30 reflective surface 104. According to an embodiment, in reference to figures 2 to 4, a security element 200, 300, 400, which is used in the same manner as described in reference to figure 1, is provided including a reflective layer 202, 302, 402, a 8 backing layer 208, 308, 408 including a substrate, and a reflective surface 204, 304, 404, wherein the reflective surface 204, 304, 404 is located on the opposite side of the reflective layer 202, 302, 402 to the backing layer 208, 308, 408. The reflective surface 204, 304, 404 profile is substantially smooth except in image 5 element regions 206, 306, 406. The image element regions 206, 306, 406 represent protrusions (as shown in the figures) and/or depressions (not shown) from the nominal profile of the reflective surface 204, 304, 404. According to this embodiment, the light source 116 and the viewing screen 110 are configured to interact with the top surface side of the security element 200, 300, 400. 10 According to figure 2, the nominal profile of the reflective surface 204 is an outwardly curved profile forming a convex reflective surface 202. According to figure 3, the reflective surface 304 is flat forming a planar reflective surface 304. According to figure 4, the security element 400 of figure 3 is configured to 15 be flexed, such that the reflective surface 404 can be formed into a temporary convex reflective surface 404, similar to the security element 200 of figure 2. According to another embodiment, in reference to figures 5 to 7, a security element 500, 600, 700, which is used in the same manner as described in reference to figure 1, is provided including a reflective layer 502, 602, 702, a 20 shaping layer 520, 620, 720 including a shaping surface 518, 618, 718, a backing layer 508, 608, 708 including a substrate, and a reflective surface 504, 604, 704, wherein the reflective surface 504, 604, 704 is located on the opposite side of the reflective layer 502, 602, 702 to the backing layer 508, 608, 708, and wherein the shaping layer 520, 620, 720 is located between the reflective layer 502, 602, 702 25 and the backing layer 508, 608, 708, and wherein the shaping surface 518, 618, 718 is the surface of the shaping layer 520, 620, 720 in contact with the reflective layer 502, 602, 702. The reflective surface 504, 604, 704 profile is substantially smooth except at image element regions 506, 606, 706. The image element regions 506, 606, 706 represent protrusions (as shown in the figures) and/or 30 depressions (not shown) from the nominal profile of the reflective surface 504, 604, 704. The image element regions 506, 606, 706 correspond to image element forming regions 522, 622, 722 of the shaping layer 520, 620, 720. According to the present embodiment, the reflective layer 502, 602, 702 is of uniform thickness 9 such that the reflective surface 504, 604, 704 profile corresponds to the shaping surface 518, 618, 718 profile. Further according to the present embodiment, the light source 116 and the viewing screen 110 are configured to interact with the top surface side of the security element 500, 600, 700. 5 Preferably, according to the present embodiment, the reflective layer is not visible from the bottom surface of the backing layer 508, 608, 708. According to figure 5, the nominal profile of both the reflective surface 504 and the shaping surface 518 is an outwardly curved profile forming a convex reflective surface 504 and shaping surface 518. 10 According to figure 6, the reflective surface 604 is flat forming a planar reflective surface 604. According to figure 7, the security element 700 of figure 6 is configured to be flexed, such that the reflective surface 704 can be formed into a temporary convex reflective surface 704, similar to the security element 500 of figure 5. 15 According to another embodiment, in reference to figures 8 to 10, a security element 800, 900, 1000, which is used in the same manner as described in reference to figure 1, is provided including a reflective layer 802, 902, 1002, a shaping layer 820, 920, 1020 including a shaping surface 818, 918, 1018, a backing layer 808, 908, 1008 including a substrate, and a reflective surface 804, 20 904, 1004, wherein the reflective surface 804, 904, 1004 is located on the side of the reflective layer 802, 902, 1002 closest to the backing layer 808, 908, 1008, and wherein the shaping layer 820, 920, 1020 is located between the reflective layer 802, 902, 1002 and the backing layer 808, 908, 1008, and wherein the shaping surface 818, 918, 1018 is the surface of the shaping layer 820, 920, 1020 25 in contact with the reflective layer 802, 902, 1002. The backing layer 808, 908, 1008 and the shaping layer 820, 920, 1020 are transparent, or at least translucent, such that incident light reflected off the reflective surface 804, 904, 1004 is viewable on a viewing screen 110. The reflective surface 804, 904, 1004 profile is substantially smooth except at image element regions 806, 906, 1006. 30 The image element regions 806, 906, 1006 represent protrusions and/or depressions from the nominal profile of the reflective surface 804, 904, 1004. The image element regions 806, 906, 1006 correspond to image element forming regions 822, 922, 1022 of the shaping layer 820, 920, 1020. According to the 10 present embodiment, the light source 116 and the viewing screen 110 are configured to interact with the bottom surface side of the security element 800, 900, 1000. According to figure 8, the nominal profile of the reflective surface 804, 904, 5 1004 is an outwardly curved profile forming a convex reflective surface 804, 904, 1004, while the nominal profile of the shaping surface is an inwardly curved profile forming a concave shaping surface 818, 918, 1018. According to figure 9, the reflective surface 904 is flat forming a planar reflective surface 904. The shaping layer 920 can be nominally of zero thickness 10 except at image element regions, and therefore the shaping surface 918 only corresponds to depressions in the reflective surface 904. According to figure 10, the security element 1000 of figure 9 is configured to be flexed, such that the reflective surface 1004 can be formed into a temporary convex reflective surface 1004, similar to the security element 800 of figure 8. 15 The image element regions 106 according to the embodiments shown in figures 2 to 10 can correspond to a surface profile as shown in figure 11. The image element region 1100 includes a right-handed step 1104 and a left-handed step 1106. Each step includes a convex portion 1108 and a concave portion 1110. The effect of each step 1104, 1106 is to alter the substantially parallel 20 incident light into focussed and unfocused regions. Referring to figure 12, a plot of the intensity of reflected light 1200 across the image is shown, showing the effect of the image element region 1100 of figure 11. As can be seen, each step 1104, 1106 corresponds to a maximum 1202 and a minimum 1204 in the reflected light intensity. These maxima 1202 25 and minima 1204 correspond to bright portions and dark portions of the resulting image when viewed on a viewing screen 110. Therefore, an image represented on the reflective surface by image element regions1100, will be visible as outlines of the image element regions on the viewing screen, where each line consists of a bright part 1202 and a dark part 1204. 30 In the embodiments where the reflective surface 102 includes a convex profile (see, for example, figures 2, 4, 5, 7, 8, and 10), the effect of the convex profile is to cause the reflected light rays to naturally spread apart. These embodiments correspond in operation to Type 1 magic mirrors. Therefore, the 11 image magnification increases with increasing separation between the reflective surface 102 and the screen. The image intensity in these embodiments decreases with increasing distance, and therefore there exists a practical limit where there is insufficient contrast to make out the lines. 5 In the embodiments where the reflective surface 102 includes a flat profile (see, for example, figures 3, 6, and 9), the reflected rays 1302 are substantially parallel except for rays 1302 originating from the image element regions 1304. These embodiments correspond to Type 2 magic mirrors. Therefore, as shown in figure 13, there is an optimal viewing distance 1300 corresponding to the focusing 10 point of the rays 1302. Away from this optimal viewing distance 1300, the image clarity and contrast will decrease. Figures 14a and 14b show an alternative embodiment wherein the image element regions 1404 correspond to regions of different reflectivity when compared to the non-image element regions of the reflective surface. In this 15 instance, the image element regions 1404 correspond to darkening regions, which may be ink regions. This embodiment corresponds to Type 3 magic mirrors. In general, the image element regions 1404 are configured to have different reflective properties when compared to the reflective surface. The image element regions 1404 therefore correspond to direct change (for example 20 reduction) in the reflected light. To avoid the image element regions 1404 being clearly visible upon inspection of the security element 1400, the security element 1400 includes a further partially reflective layer 1408 positioned between the reflective surface 1402 and the light source and viewing screen. The embodiment of figure 14a 25 includes a partially reflective layer 1408 located on the opposite side of the substrate 1406 to the reflective surface 1402, while the embodiment of figure 14b includes a partially reflective layer 1408 positioned on the same side of the substrate 1406 as the reflective surface 1402 such that the reflective surface is located between the substrate 1406 and the partially reflective layer 1408. 30 The effect of the partially reflective layer 1408 is to minimise the visibility of the image element regions 1404, such that they are only clearly visible as dark areas on a viewing screen.

12 The reflective surfaces 1402 according to the present embodiment can be flat, as shown in figures 14a and 14b. Therefore, there is no magnification in image as the screen to reflective surface 1402 distance is increased. Furthermore, as the surface profile of the reflective surface 1402 is flat, there is 5 no optimal viewing distance. However, as with all projections, there is a limit to the separation distance between the reflective surface and the screen, as the contrast of the image decreases with increasing distance. According to figure 15, a security document 1500 including a substrate, and further including a security element 1502 as described with reference to 10 figures 1 to 14b, and optionally one or more secondary elements 1504. The security element 1502 may be formed integrally with the security document 1500, or it may be prepared separately and incorporated into the security document. The secondary elements can be selected from any appropriate security elements, including but not limited to: micromirror reflective or refractive elements; Fourier 15 plane elements; flat elements arranged to provide a mirror reflection of a user to the user; lenslet elements of a lenslet array; and diffractive elements. A method of forming a security element according to the first three embodiments discussed includes providing a substrate including a first surface and a second surface. A security element can be formed onto the substrate by 20 applying onto the first surface an embossable layer, for example by printing an embossable material such as a UV curable ink onto the substrate. In respect of the first embodiment discussed, the embossable layer is composed of a reflective material. In respect of the third embodiment discussed, the embossable layer is completely, or at least substantially, transparent. 25 After, or during, application of the embossable layer, the embossable layer is embossed using standard techniques to form an outward facing surface with a substantially smooth profile except in locations corresponding to image element regions. The image element regions can correspond to either or both of depressions and protrusions from the nominal surface profile. The nominal profile 30 of the outward facing surface can be either convex or flat. If required, the embossable layer may be cured (e.g. UV cured) or set during or after the embossing procedure.

13 In regard to the embodiments including a shaping layer, a reflective layer is then applied to the outwards facing surface of the embossable layer. With respect to the embodiments shown in figures 5, 6 and 7, the reflective layer should be applied such that the thickness of the reflective layer is substantially uniform. If 5 required, the reflective layer can optionally undergo a curing or setting step. In regard to the embodiment shown in figure 14a, a reflective layer is applied to the second surface. Image element regions are applied to the first surface, and may correspond to printed ink, laser etching, embossing, UV casting. A partially reflective layer is then applied, for example by printing, to the 10 first surface, such that the partially reflective layer covers the image element regions, and preferably such that the outwards facing surface of the partially reflective layer is substantially or completely flat. In regard to the embodiment shown in figure 14b, a reflective layer is applied to the first surface such that the outwards facing surface of the reflective 15 layer is substantially or completely flat. Image element regions are applied to the outwards facing surface of the reflective layer, and may correspond to printed ink, laser etching, embossing, or UV casting. A partially reflective layer is then applied, for example by printing, to the outwards facing surface of the reflective layer, such that the partially reflective layer covers the image element regions, 20 and preferably such that the outwards facing surface of the partially reflective layer is substantially or completely flat. In general, the image element regions are configured to be positioned and shaped according to the desired projected image. Further modifications and improvements may be made without departing 25 from the scope of the present invention.

Claims (5)

1. A security element including a reflective layer, wherein the reflective layer includes a reflective surface, wherein the reflective surface includes image element regions configured to produce an image upon reflection of incident light, 5 and wherein the image element regions are substantially undetectable to a user upon direct inspection.

2. A security element as claimed in claim 1 wherein the reflective surface is outwardly curved or flat and wherein the image element regions correspond to perturbations of the reflective surface. 10

3. A security element as claimed in claim 2 including a shaping layer, wherein the shaping layer includes a shaping surface in contact with the reflective layer, and including perturbations corresponding to the image element regions such that the reflective surface profile corresponds to the shaping surface profile.

4. A security element as claimed in claim 1 wherein the image element 15 regions correspond to changes in reflectivity of the reflective surface and including a partially reflective surface applied to the reflective surface.

5. A method of manufacturing a security device including the steps of: a) providing a substrate including a first surface and a second surface; and 20 b) applying to the first surface a reflective layer; wherein the reflective layer includes a substantially mirror-like reflective surface, and wherein the reflective surface includes one or more image element regions configured to alter the reflective properties of the reflective layer. 25 SECURENCY INTERNATIONAL PTY LTD WATERMARK PATENT & TRADE MARK ATTORNEYS UIP1285AUOO