AU2016102127A4 - Optically variable moire security device - Google Patents

Abstract

Abstract A security device for a security document and a method for producing the security device a provided, wherein the security device includes at least two opposing layers, a bottom layer including a reflective surface and a top layer including a pattern, the first and top layers separated by a region transparent to light to produce an optically variable effect due to a moire interference occurring between the pattern and a reflection of the pattern by the reflective surface. Figure 1 100' 125' 120' 110' Figure 2

Description

2016102127 16 Dec 2016 1 OPTICALLY VARIABLE MOIRE SECURITY DEVICE Technical Field [0001] The invention relates generally to security documents in which optical security devices are used as an anti-counterfeiting measure, and in particular to the configuration of such optical security devices.

Background of Invention [0002] Security devices are applied to security documents or similar articles, such as identity cards, passports, credit cards, bank notes, cheques and the like and may take the form of diffraction gratings and similar optically detectable microstructures. Such security devices are difficult to falsify or modify, and are easily damaged or destroyed by any attempts to tamper with the document. Often security devices are designed to be overt features of the document, such that they are observable with the naked eye. This type of public or primary security device enables members of the public to perform some degree of authentication of the document, without the use of any additional viewing apparatus.

[0003] The ever increasing sophistication of counterfeiting operations requires continuous improvement in the design of security devices for protecting documents against forgery. Accordingly, alternative and improved security devices are constantly under development.

[0004] Some alternative security devices make use of moire effects. Moire effects produce a visual perception that occurs when viewing a pattern comprising a series of lines or dots is superimposed on another pattern, where the series of lines or dots differ in relative size, angle, or spacing between the superimposed patterns. Superimposing two similar patterns gives rise to a third pattern referred to as the “moire pattern” which when observed from different angles will vary thereby generating an optical effect that is perceived as an animation effect. 2016102127 16 Dec 2016 2 [0005] Conventional means of producing moire patterns, for example, by printing least one of the patterns to be superimposed over the other on a transparent substrate, often gives rise to registration errors. That is, the superimposed patterns must be substantially perfectly aligned to give rise to a desired moire pattern. Any malalignment between superimposed patterns may give rise to undesirable optical effects and degrade the quality of the resulting moire pattern. Such registration issues cause difficulties in manufacturing security features based on moire effects due to the prominence of pattern placement or registration errors.

[0006] It would be desirable to provide an improved security devices for application to a security documents for authentication which ameliorates at least some of the drawbacks of the prior art.

[0007] A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

Definitions

Security Document or Token [0008] As used herein the term security document 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.

[0009] The invention is particularly, but not exclusively, applicable to security documents 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. The diffraction gratings and optically variable devices described herein may also have application in other products, such as packaging. 3 2016102127 16 Dec 2016

Substrate [0010] As used herein, the term substrate refers to the base material from which 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 plastic material, or of two or more polymeric materials.

[0011] The use of plastic or polymeric materials in the manufacture of security documents pioneered in Australia has been very successful because polymeric banknotes are more durable than their paper counterparts and can also incorporate new security devices and features. One particularly successful security feature in polymeric banknotes produced for Australia and other countries has been a transparent area or “window”.

Transparent Windows and Half Windows [0012] 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.

[0013] 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.

[0014] A partly transparent or translucent area, hereinafter referred to as a “halfwindow,” may be formed in a polymeric security document which has opacifying 4 2016102127 16 Dec 2016 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 viewed clearly through the half-window.

[0015] 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.

Opacifying Layers [0016] 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 Lj<L0 where L0 is the amount of light incident on the document, and Lj is the amount of light transmitted through the document. An opacifying layer may 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. 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 [0017] 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 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 structures; optically 2016102127 16 Dec 2016 5 variable devices (OVDs) such as diffractive devices including diffraction gratings, holograms and diffractive optical elements (DOEs).

Embossable Radiation Curable Ink [0018] The term embossable radiation 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 by radiation to fix the embossed relief structure. The curing process does not take place before the radiation 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 radiation curable ink is preferably curable by ultraviolet (UV) radiation. Alternatively, the radiation curable ink maybe cured by other forms of radiation, such as electron beams or X-rays.

[0019] 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.

[0020] In one particularly preferred embodiment, the transparent or translucent ink preferably comprises an acrylic based UV curable clear embossable lacquer or coating, [0021] Such UV curable lacquers can be obtained from various manufacturers, including Kingfisher Ink Limited, product ultraviolet type UVF-203 or similar. Alternatively, the radiation curable embossable coatings maybe based on other compounds, e.g. nitro-cellulose.

[0022] 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 arrays. However, they may also be embossed with larger relief structures, such as non-diffractive optically variable devices. 6 2016102127 16 Dec 2016 [0023] 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.

[0024] Preferably, in order to be suitable for Gravure printing, the radiation curable ink 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.

[0025] With some polymeric substrates, it may be necessary to apply an intermediate layer to the substrate before the radiation curable ink 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 crosslinker, 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 acetyl acetone; melamines; and carbodi-imides.

Summary of Invention [0026] According to an aspect of the present invention, there is provided a security device for a security document, the security device including at least two opposing layers, a bottom layer including a reflective surface and a top layer including a pattern, the bottom and top layers separated by a region transparent to light to produce an optically variable effect due to a moire interference occurring between the pattern and a reflection of the pattern by the reflective surface.

[0027] In a preferred embodiment, the security device is formed on a substrate. The substrate may be substantially planar in form and have two opposing surfaces, for example, an upper and a lower surface. The two opposing surfaces may be 7 2016102127 16 Dec 2016 substantially parallel. In this embodiment, the bottom layer is applied to a first opposing surface of the substrate, i.e. the lower surface, and the top layer is formed on or in the opposing surface, i.e. the upper surface. When viewing the security device, the bottom layer must be orientated to the underside of the security device so that the pattern lies on the upper surface, in order for light to be transmitted through the top layer and reflected by the bottom layer such that the moire pattern can be viewed by an observer. Accordingly, the terms “top”, “bottom”, “upper” and “lower” refer to the orientation of the security device when the desired moire effect is viewed by an observer.

[0028] The region separating the bottom layer and the top layer which is transparent to light may comprise at least part of the substrate. That is, the inherent thickness of the substrate may determine the magnitude of the separation between the bottom layers and the top layer. For example, if the substrate has a thickness of approximately 70 microns, then this would dictate the magnitude of the separation between the two layers forming the optically variable moire security device.

[0029] The bottom layer of the security device includes a reflective surface. The reflective surface can be formed in any one or more of a number of ways. For example, the reflective surface may be formed by printing with metallic ink. Alternatively, the reflective surface is formed by adhesion of a transfer foil to the first opposing surface of the substrate. In another embodiment, the bottom layer is a reflective surface embossed with one or more diffractive structures. In yet another embodiment, the bottom layer is a reflective surface embossed with one or more surface relief structures and printed with metallic ink.

[0030] In certain embodiments of the invention, the pattern formed in or on the top layer includes regions which block the transmission of light.

[0031] The pattern itself may include at least two regions, wherein a first region has a different periodicity to a second region. Alternatively or additionally, the pattern includes at least two regions, each region including a plurality of lines, dots, polygons, or a combination thereof wherein a first region has lines, dots or polygons of a first thickness which is different to a second thickness of lines, dots or polygons in a second grid region. 8 2016102127 16 Dec 2016 [0032] In some embodiments the pattern is formed in a grid.

[0033] In a particular form of the present invention, the substrate on or in which security device is formed, is formed from a polymer.

[0034] According to another aspect of the present invention, there is provided a method of manufacturing a security device for a security document, the method comprising the steps of: providing a substrate having two opposing surfaces; applying a bottom layer to a first opposing surface of the substrate, the bottom layer including a reflective surface; and applying a top layer to a second opposing surface of the substrate, the top layer including a pattern; wherein the bottom layer and the top layer are separated by a region transparent to light to produce an optically variable effect due to a moire interference occurring between the pattern and a reflection of the pattern by the reflective surface.

[0035] In alternative forms of the invention, the pattern may be formed by printing. More particularly, the pattern may be formed by printing with at least one optically variable ink, or at least one reflective ink.

[0036] In a particular form of the present invention, the substrate which is provided is formed from a polymer.

Brief Description of Drawings [0037] Embodiments of the invention will now be described with reference to the accompanying drawings. It is to be understood that the embodiments are given by way of illustration only and the invention is not limited by this illustration. In the drawings: [0038] Figure 1 is a schematic cross section view of a security device according to an embodiment of the present invention.

[0039] Figure 2 is a schematic cross section view of a security device according to another embodiment of the present invention.

[0040] Figure 3 is a schematic showing the angles of constructive interference producing the moire effect according to an embodiment of the present invention. 9 2016102127 16 Dec 2016 [0041] Figure 4 is a schematic showing the angles of destructive interference producing the moire effect according to another embodiment of the present invention.

[0042] Figure 5 is a plan view of a security device formed with a pattern having two regions according to an embodiment.

[0043] Figure 6 is a plan view of a security device formed with a pattern having two regions according to another embodiment.

[0044] Figure 7 A is a plan view showing the effect of observing the security device in Figure 6 when the patterns within the numeral “5” are constructively interfering while the patterns outside the numeral “5” are destructively interfering.

[0045] Figure 7B is a plan view showing the reverse effect of Figure 7A.

[0046] Figure 8 is a flowchart showing a method according to the present invention.

Detailed Description [0047] Referring firstly to Figure 1, there is shown a cross section of the security device 100 in accordance with an embodiment. The security device 100 includes two layers. A bottom layer 110 and a top layer 120. The bottom layer 110 and the top layer 120 are to be substantially opposing as shown.

[0048] The bottom layer 110 includes a reflective surface 115. The reflective surface 115 can be formed in any one or more of a number of ways. For example, the bottom layer 110 may include a reflective surface 115 formed by printing with metallic ink. Alternatively, the bottom layer 110 includes a reflective surface 115 formed by adhesion of a transfer foil to the first opposing surface of the substrate, a reflective surface embossed with one or more diffractive structures, or a reflective surface embossed with one or more surface relief structures and printed with metallic ink.

[0049] The top layer 120 includes pattern 125 formed in the upper surface. Referring now to Figure 2, a similar result can be achieved by forming the pattern 125 comprising top layer 120' as a separate layer. For example, in an embodiment, wherein the security device 100' is formed on a substrate, the substrate having two 10 2016102127 16 Dec 2016 opposing surfaces, the top layer pattern 125' may be formed in the substrate, e.g. by embossing the pattern into the substrate (as shown in Figure 1), or on the substrate, e.g. by printing the pattern with ink (as shown in Figure 2). The ink may, for example, be an optically variable ink, or a reflective ink.

[0050] Referring back to Figures 1 and 2, the bottom layer 110, 110' including a reflective surface 115, 115' and the top layer 120,120' including a pattern 125, 125', are separated by a region 130, 130’ that is transparent to light. This region 130, 130' produces an optically variable moire effect due to interference occurring between the pattern 125, 125' in the top layer 120, 120' being reflected by the reflective surface 115,115' in the bottom layer 110,110'. That is, to an observer, a moire pattern is formed and varies with the angle of observation.

[0051] The reference to “bottom” and “top” is to be understood in the context of the orientation of the security device is orientated when viewed by an observer. That is the bottom layer 110 bearing the reflective surface 115 must be on the underside so that light is transmitted though the top layer 120 and reflected by the reflective surface 115 to give rise to the desired moire effect.

[0052] As already surmised, various versions of such an optically variable moire security device are envisaged, with the bottom layer and the top layer taking various forms to achieve a similar result.

[0053] In one exemplary embodiment, the reflective surface 115 may itself include a diffraction grating. That is, the bottom layer is a reflective surface embossed with one or more diffractive structures. Such a diffraction grating is configured to operate in the zero order mode, i.e. where no diffraction occurs and the diffractive structure acts as a reflective surface.

[0054] The thickness t of the region 130 between the bottom layer and the top layer is generally determined by the thickness of the substrate. For example, where the security document is a bank note, e.g. a polymer bank note, the thickness of the substrate will typically be around 70 microns. This thickness twill dictate the thickness of any lines, dots or polygons forming the pattern and the periodicity of the lines or dots that is required to produce the optical moire effect. 2016102127 16 Dec 2016 11 [0055] Referring now to Figure 3, there is shown in the schematic sense how the moire effects is observed as a result of constructive interference. That is, whether the light reflected by the reflective surface on the bottom layer and through the top layer 310, 320 will interfere constructively will depend on the thickness t between the bottom layer 330 and the top layer 340, the thickness of any lines 350, dots or polygons forming the pattern and the angle of observation. If the reflected light is exactly in phase, then constructive interference occurs and the pattern is observed as white by an observer 360.

[0056] Likewise for destructive interference which is illustrated in Figure 4 in relation to a pattern which has half the spatial frequency of the pattern shown in Figure 3. The pattern itself is formed by lines or dots which block the transmission of light through the top layer 440. In this case, if the reflected light is out of phase, then destructive interference occurs and the pattern is observed as black by an observer 460.

[0057] The pattern may include at least two regions. The regions are distinguished in that either the first region has a different periodicity to the second region and/or that where the pattern comprises a series of lines, dots, or polygons or a combination thereof, the line, dots or polygons of the first regions are of a different thickness to the lines, dots or polygons of a second grid region. This concept is illustrated in Figure 5. Figure 5 shows a pattern 500 revealing the numeral “5”. The pattern 500 is constructed from two gridded regions 510, 520. In the first region 510, located within the numeral “5”, the lines 530 have twice the thickness and twice the periodicity of the lines 540 in the second region 520 which is located outside of the numeral “5”. For example, if the security device formed by pattern 500 were to have a size of 15 x 15mm and the lines are 60 microns wide with a spacing of 30 microns in the first region 510, and 30 microns thick with a spacing of 15 microns in the second region 520 an optical effect such as that shown in Figure 5 could be produced.

[0058] Referring now to Figure 6, there is shown the reverse scenario to Figure 5,

i.e. where the lines in the first region 610 within the numeral “5” have twice the thickness and periodicity of the lines in the second region 620 outside of the numeral ii£"H 12 2016102127 16 Dec 2016 [0059] Referring now to Figures 7 A and 7B, Figure 7A illustrates the effect of observing the device 700 when the lines within the numeral “5” cause the reflected light to constructively interfere while the lines outside the numeral “5” destructively interfere resulting in the numeral “5” being observed in white with a black surround. Conversely, Figure 7B illustrates the effect of observing the device 700' when the lines within the numeral “5”cause the reflected light to destructively interfere while the lines outside the numeral “5” cause the reflected light to constructively interfere resulting in the numeral “5” being observed in black with a white surround. Switching between the scenarios illustrated in Figures 7A and 7B involves changing the angle of observation.

[0060] In certain embodiments, it is envisaged that the security device could comprise a double-sided security device, having a reflective surface or layer positioned in between two top layers including a pattern. In this case, the reflective surface of layer would be reflective on both sides, with the pattern bearing top layers spaced from the reflective surface sufficiently to produce an optically moire effect on both sides of the device. This way, the moire interference could be observed on both sides of the device.

[0061 ] Referring finally to Figure 8, there is shown a flowchart illustrating the steps of a method for manufacturing a security device for a security document. The method 800 includes at step 810, providing a substrate having two opposing surfaces. At step 820, the method involves applying a bottom layer to a first opposing surface of the substrate, the bottom layer including a reflective surface. At step 830 the method involves applying a top layer to a second opposing surface of the substrate, the top layer including a pattern. The configuration of the pattern and the separation of the pattern bottom layer from the top layer is determined so as to provide a region transparent to light to produce an optically variable effect due to a moire interference occurring between the pattern and a reflection of the pattern by the reflective surface provided on the bottom layer.

[0062] The pattern may be formed by printing. More particularly, the pattern may be formed by printing with at least one optically variable ink, or at least one reflective ink. The pattern may be printed directly onto the substrate. 2016102127 16 Dec 2016 13 [0063] It is an advantage of the present invention that the optically variables moire security device so formed is a self-registering or self-aligning moire pattern thereby ameliorating the difficulties in manufacturing moire patterns manufactured in the conventional manner.

[0064] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[0065] While the invention has been described in conjunction with a limited number of embodiments, it will be appreciated by those skilled in the art that many alternative, modifications and variations in light of the foregoing description are possible. Accordingly, the present invention is intended to embrace all such alternative, modifications and variations as may fall within the spirit and scope of the invention as disclosed.

[0066] The present application may be used as a basis or priority in respect of one or more future applications and the claims of any such future application may be directed to any one feature or combination of features that are described in the present application. Any such future application may include one or more of the following claims, which are given by way of example and are non-limiting in regard to what may be claimed in any future application.

Claims (5)

1. The claims defining the invention are as follows

   1. A security device for a security document, the security device including at least two opposing layers, a bottom layer including a reflective surface and a top layer including a pattern, the bottom layer and the top layer are separated by a region transparent to light to produce an optically variable effect due to a moire interference occurring between the pattern and a reflection of the pattern by the reflective surface.
2. 2. A security device according to claim 1, wherein the security device is formed on a substrate, the substrate having two opposing surfaces, wherein the bottom layer is applied to a first opposing surface of the substrate.
3. 3. A security device according to claim 2, wherein the top layer is formed on or in a second opposing surface of the substrate.
4. 4. A security device according to claim 2 or 3, wherein the region transparent to light comprises at least part of the substrate
5. 5. A security device according to any one of claims 2 to 4, where the bottom layer and the top layer are separated by a distance determined by a thickness of the substrate.