Security feature

Abstract

A security feature for a security document, as well as a security document incorporating the security feature, is disclosed comprising a substrate with a first iridescent ink layer and a second iridescent ink layer, wherein the first iridescent ink layer and the second iridescent ink layer at least partially overlap each other; wherein the second iridescent ink layer includes a colour switching ink, and wherein, when viewed in reflection, the combination of the first iridescent ink layer and the second iridescent ink layer display a first image when viewed from a first viewing angle and display a second image when viewed from a second viewing angle.

Description

[0001] SECURITY FEATURE

[0002] TECHNICAL FIELD

[0003]

[0001] The present disclosure relates generally to security features such as those used in or on security documents, comprising a number of ink layers overprinted on one another, and methods of manufacturing such security features. More particularly, the present disclosure relates to security features for security documents or tokens such as bank notes or identification documents such as identity cards or passports, and the like.

[0004] BACKGROUND

[0005]

[0002] It is important that security documents, such as banknotes, credit cards, ID documents (including passports), land title, share and educational certificates, packaging materials for high-value goods, security labels and security cards, are difficult to replicate by counterfeiters and are provided with security features that allow for quick and easy authentication.

[0006]

[0003] Typically security documents, such as bank notes, are printed with security features in the form of watermarks, holograms, raised printing or with photo luminesce, iridescent or other suitable inks.

[0007]

[0004] Existing security documents with security features that use iridescent inks typically require authentication from both sides of the security document. They are also typically limited to displaying a single image.

[0008]

[0005] Any reference to or discussion of any document, act or item of knowledge in this specification is included solely for the purpose of providing a context for the present disclosure. It is not suggested or represented that any of these matters or any combination thereof formed at the priority date part of the common general knowledge, or was known to be relevant to an attempt to solve any problem with which this specification is concerned.

[0009] SUMMARY OF THE INVENTION

[0010]

[0006] In a first aspect, the present disclosure provides a security feature for a security document comprising: a substrate with a first iridescent ink layer and a second iridescent ink layer, wherein the first iridescent ink layer and the second iridescent ink layer at least partially overlap each other; wherein the second iridescent ink layer includes a colour switching ink, and wherein, when viewed in reflection, the combination of the first iridescent ink layer and the second iridescent ink layer display a first image when viewed from a first viewing angle and display a second image when viewed from a second viewing angle.

[0007] According to embodiments, the second iridescent ink layer displays at least one colour shift between a first colour and a second colour when viewed from the first viewing angle and second viewing angle, respectively.

[0011]

[0008] According to embodiments, the first iridescent ink layer is substantially invisible when viewed from the first viewing angle and visible when viewed from the second viewing angle.

[0012]

[0009] According to embodiments, the first iridescent ink layer and the second iridescent ink layer completely overlap each other.

[0013]

[0010] According to embodiments, the security feature is applied to a window region of the security document. The window region may include a half-window. The window region may include a full-window.

[0014]

[0011] According to embodiments, the second iridescent ink layer at least partially overlaps the window region.

[0015]

[0012] According to embodiments, the substrate has a first side and a second side and the first iridescent ink layer and the second iridescent ink layer are both printed on the first side or the second side of the substrate.

[0016]

[0013] According to embodiments, wherein the first iridescent ink layer and the second iridescent ink layer are printed on opposite sides of the substrate.

[0017]

[0014] According to embodiments, the first iridescent ink layer and the second iridescent ink layer form a design on the substrate. The design may comprise at least one of text, indicia, a portrait, a building, an object, a tree, a flower, and / or an animal.

[0018]

[0015] According to embodiments, the first iridescent ink layer includes a metallic ink or a pearlescent ink.

[0019]

[0016] According to embodiments, the first iridescent ink layer includes a colour switching ink.

[0020]

[0017] According to embodiments, the substrate comprises a plurality of opacifying layers.

[0021]

[0018] According to embodiments, the substrate includes at least one opacifying layer on a first side and / or a second side of the substrate.

[0022]

[0019] According to embodiments, one or more opacifying layers, at least partially overlap the first iridescent ink layer and / or the second iridescent ink layer.

[0020] According to embodiments, the substrate comprises a substantially transparent polymer film. According to embodiment, the substrate comprises an opaque polymer film. The opaque polymer film may be white.

[0023]

[0021] According to embodiments, the first iridescent ink layer and the second iridescent ink layer are printed on the substrate.

[0024]

[0022] According to embodiments, the first iridescent ink layer and the second iridescent ink layer are printed using Gravure printing or screen printing.

[0025]

[0023] According to embodiments, the second image is a distinct image that is not correlated with the first image.

[0026]

[0024] In a second aspect, the present disclosure provides a method of producing a security document, the method comprising the steps of: providing a substrate to a printing process, the substrate having a first side and a second side; printing a first iridescent ink layer on the first side or the second side and printing a second iridescent ink layer on the first side or the second side such that the first iridescent ink layer and the second iridescent ink layer at least partially overlap.

[0027]

[0025] According to embodiments, the method comprises printing at least one opacifying layer on the first side and / or the second side to form a base coat.

[0028]

[0026] According to embodiments, the method comprises printing at least one opacifying layer on the first side and / or second side to form a top coat.

[0029]

[0027] According to embodiments, opacifying layers on the first side and / or the second side of the substrate are absent in at least one region to form a full window or a half window. The first iridescent ink layer and the second iridescent ink layer may be printed in the region of the full window or half window.

[0030]

[0028] Another aspect of the present disclosure provides a security document comprising the security feature according to the first aspect.

[0031]

[0029] In this specification, the terms ‘comprises’, ‘comprising’, ‘includes’, ‘including’, or similar terms are intended to mean a non-exclusive inclusion, such that a method, system or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed.BRIEF DESCRIPTION OF THE DRAWINGS

[0032]

[0030] Various preferred aspects of the present disclosure will now be described, by way of examples only, with reference to the accompanying Figures, in which:

[0033]

[0031] Figure 1 illustrates a cross-sectional schematic diagram of a security document including a security feature, according to an aspect of the present disclosure, with a half window, and the first iridescent ink layer and second iridescent ink layer on the second side of the substrate;

[0034]

[0032] Figure 2 illustrates a cross-sectional schematic diagram of a security document including a security feature, according to a further aspect of the present disclosure, with a half window, the first iridescent ink layer and second iridescent ink layer on the second side of the substrate and regions omitted from the second iridescent ink layer;

[0035]

[0033] Figure 3 illustrates a cross-sectional schematic diagram of a security document including a security feature, according to another aspect of the present disclosure, with a half window, and the first iridescent ink layer and second iridescent ink layer on the first side of the substrate;

[0036]

[0034] Figure 4 illustrates a cross-sectional schematic diagram of a security document including a security feature, according to a further aspect of the present disclosure, with a half window, the first iridescent ink layer and second iridescent ink layer on the first side of the substrate and regions omitted from the second iridescent ink layer;

[0037]

[0035] Figure 5 illustrates a cross-sectional schematic diagram of a security document including a security feature, according to another aspect of the present disclosure, with a full window, and the first iridescent ink layer and second iridescent ink layer on the second side of the substrate;

[0038]

[0036] Figure 6 illustrates a cross-sectional schematic diagram of a security document including a security feature, according to a further aspect of the present disclosure, with a full window, the first iridescent ink layer and second iridescent ink layer on the second side of the substrate and regions omitted from the second iridescent ink layer;

[0039]

[0037] Figure 7 illustrates a cross-sectional schematic diagram of a security document including a security feature, according to another aspect of the present disclosure, with a full window, and the first iridescent ink layer and second iridescent ink layer on the first side of the substrate;

[0038] Figure 8 illustrates a cross-sectional schematic diagram of a security document including a security feature, according to a further aspect of the present disclosure, with a full window, the first iridescent ink layer and second iridescent ink layer on the first side of the substrate and regions omitted from the second iridescent ink layer;

[0040]

[0039] Figure 9 illustrates a cross-sectional schematic diagram of a security document including a security feature, according to another aspect of the present disclosure, without opacifying layers;

[0041]

[0040] Figure 10 illustrates a cross-sectional schematic diagram of a security document including a security feature, according to another aspect of the present disclosure, without opacifying layers and with regions omitted from the second iridescent ink layer; and

[0042]

[0041] Figure 11 illustrates a cross-sectional schematic diagram of a security document including a security feature with the first iridescent ink layer and the second iridescent ink layer on opposed sides of the substrate.

[0043] DEFINITIONS

[0044] Security Document

[0045]

[0042] As used herein, the term security document includes all types of documents of value and identification documents including, but not limited to the following: items of currency such as banknotes, credit cards, cheques, passports, identity cards, securities and share certificates, driver's licences, deeds of title, travel documents such as airline and train tickets, entrance cards and tickets, birth, death and marriage certificates, and academic transcripts.

[0046] Security Feature

[0047]

[0043] 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 banknote from counterfeiting, copying, alteration or tampering. Security devices or features may be provided in or on the substrate of the banknote 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 banknote; 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 variable devices (OVDs) such as diffractive devices including diffraction gratings, holograms and diffractive optical elements (DOEs). Printed security features are a subclass of security features which are applied by printing, particularlythe security inks mentioned above, but also include particular designs in inks, which otherwise would not be classed as security inks.

[0048] Substrate

[0049]

[0044] 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 windows and other more advanced security features. The substrate may thus be 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 such materials. In some embodiments, the substrate is a transparent polymeric material. A particularly suitable transparent substrate is polypropylene and in particular bi-axially oriented polypropylene (BOPP).

[0050]

[0045] In some embodiments, the substrate is an opaque polymeric substrate. The opaque polymeric substrate is opacified during manufacture of the film itself by inclusion of an opacifying additive into the polymer during extrusion. The polymer film is thus opacified due to its bulk properties rather than due to addition of opacifying layers. One such example of a suitable polymer film is a bi-axially oriented polypropylene (BOPP) which has titanium dioxide particles added during manufacture to create a white polymer film.

[0051]

[0046] In some embodiments, the substrate is from 60 to 100 microns thick, preferably from 65 to 90 microns thick.

[0052] Window

[0053]

[0047] One common security feature in polymeric banknotes produced for Australia and other countries is a transparent area or 'window'. Transparent polymeric substrates for banknotes are commonly opacified by the application of at least one pigmented opacification layer, and typically multiple overlying opacification layers on each side. In this scenario, a full window is provided by entirely omitting the opacifying layers on both sides of an area of the transparent substrate. A partly transparent or translucent area, hereafter referred to as a 'half-window', may also be formed by partially or completely omitting the opacification layers on one side only.

[0054]

[0048] Alternatively, a window may be produced by including a transparent polymeric substrate as an insert in a cut out section of an opaque substrate.

[0049] The term 'window' or 'window region' is used in this specification to refer to all the different types of full, and half windows as described above.

[0055] Opacification

[0056]

[0050] The opacified regions of bank notes produced on a transparent polymeric substrate typically comprise at least one printed opacification layer, with printed design features or security features then applied on top. Typically, multiple overlaid opacification layers are sequentially printed to provide a suitable pigment density for opacification. In other cases, as already noted, a polymer film is opacified during its manufacture by inclusion of an opacifying additive into the polymer melt for extrusion into film.

[0057]

[0051] The opacification layers or opacified film may comprise any opacifier which suitably opacifies the substrate, as perceived by a viewer. The opacifier is typically a pigment in the form of a particulate material, which is dispersed or bound in a polymeric matrix or binder. The pigment particles may optionally be coated or otherwise surface-modified to improve their dispersibility.

[0058]

[0052] The opacification layers may comprise a pigment that is substantially non-absorbent of visible light, but which opacifies the substrate by scattering and / or refracting visible light. Unless other colouring agents are also included, transparent substrates overlaid with opacification layers of sufficient combined thickness and pigment density will appear white to a viewer when viewed in natural light, since a wide range of visible light wavelengths are substantially reflected from the substrate as a result of light scattering by the pigment particles.

[0059]

[0053] Scattering (white) pigments generally have a high refractive index relative to the matrix in which they are dispersed. Furthermore, it will be appreciated that the particle size of the pigment affects scattering power. Refractive particles scatter light optimally when the primary particle size is approximately half the wavelength of the light. Since the human eye is most sensitive to yellow-green light, with a wavelength of around 550 nm, pigment particles with a particle size of 200-300 nm are considered optimal opacifiers in the art. The pigment particles may therefore have particle sizes predominantly in a range of from 150 nm to 500 nm, such as from 200 nm to 400 nm. Particles smaller than about 100 nm may be too small to effectively scatter visible light.

[0060]

[0054] A particularly suitable pigment for opacification of film substrates according to the present disclosure is particulate titanium dioxide, preferably with a high content of rutile phase (although anatase is also considered to be effective). Rutile titanium dioxide has a higher refractive index (2.73) compared with many other white pigments. Although titanium dioxideis thus preferred, other opacifier pigments such as antimony oxide, zinc oxide, calcium carbonate, magnesium silicate (talc) and the like may also be used.

[0061] Print processes

[0062]

[0055] For the traditional banknote industry, the typical print processes are sheet-fed offset and sheet-fed intaglio printing. Thus, a banknote substrate is supplied in sheets to an offset print press and then, separately, to an intaglio print press. Other print process types which are commonly found both inside and outside the security industry are letterpress, gravure, flexographic and ink jet. All of these print processes require particular types of substrate supply, print equipment and inks.

[0063]

[0056] Print processes in which a web of the substrate is fed through a print press comprising successive print units offer a number of advantages over sheet fed processes, in particular the greater speed of printing. The print process types which can run at the highest speeds, and therefore lowest costs, in a web-fed print process are flexographic and gravure printing.

[0064]

[0057] Although the term 'intaglio printing' can be used generically to cover all printing techniques in which an image is incised into a surface and the incised line or sunken area holds the ink for printing, in the art of security printing a distinction is made between gravure (also known as rotogravure) and intaglio (also known as line intaglio) print process types. The skilled person in the art of security printing would immediately understand that an intaglio print process for printing a security document involves high viscosity ink applied to lines incised into an intaglio print plate which is applied at great pressure to the substrate. Likewise, the skilled person in the art of security printing would immediately understand that a gravure print process for printing a security document refers to lower viscosity inks captured from a bath of ink by a cylinder with 'cells' engraved in the cylinder and applied to a substrate.

[0065] Iridescent ink

[0066]

[0058] An iridescent ink is a type of optically variable ink that typically displays rainbow like colours. The colours shift / change across the spectrum of the rainbow when viewed from different angles and under different lighting.

[0067]

[0059] Generally, the iridescent ink composition includes pearlescent or interference pigments. The pearlescent or interference pigments typically include mica particles coated with layers of metal oxides (such as titanium dioxide or iron oxide). The pigments are mixed with a binder, which is typically, a transparent or translucent varnish. When this ink is appliedto a substrate in a printing process, the mica particles cause interference of incident light and produces the colour changing effect.

[0068] Colour shifting ink

[0069]

[0060] A colour shifting ink is a type of optically variable ink, and typically a type of iridescent ink, that changes between two distinct colours when viewed from different angles.

[0070]

[0061] One example of a colour shifting ink composition 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, typically an organic pigment. The interference pigment and particles of the colour pigment may be mixed with a binder or resin to form the colour shifting ink composition, which is suitable for application to a substrate in a printing process.

[0071]

[0062] Specifically, 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), from about 0.5% to about 10% of an organic pigment, eg phthalocyanine blue, and from about 60% to 90% of transparent binder or resin. Preferably, the pearl lustre interference pigments have a particle size from about 5pm (microns) to about 200pm (microns).

[0072]

[0063] Advantageously, when applied to a transparent substrate, such an ink composition can exhibit unusual colour shifting properties. For instance, an area of the transparent substrate covered by the colour shifting ink composition can appear a metallic colour, eg gold or silver, when viewed in reflection at certain viewing angles, and may appear a distinct colour, eg blue or pink, when viewed at other viewing angles. Additionally, the colour shifting effects may vary depending upon whether the colour shifting ink composition is viewed against different backgrounds, eg a light colour, such as white, or a dark colour, such as black.

[0073]

[0064] Other examples include pearlescent or interference particles which are magnetically aligned during manufacture to produce specific reflection shapes and / or characteristics. One such security feature is known under the brand name Spark® and is supplied by Sicpa Holding SA. in Switzerland.DETAILED DESCRIPTION

[0074]

[0065] Figure 1 shows a schematic diagram of a security document 1 comprising a security feature 10 and a substrate 20, in the form of a transparent polymeric film. The substrate 20 has a first side 21 and a second side 22. The substrate 20 is coated with a plurality of opacifying layers 30 on each side of the substrate 20.

[0075]

[0066] The substrate 20 is preferably formed from a transparent polymeric material, In one example, the transparent polymeric material may be made up of at least one bi-axially oriented polymeric film. The substrate may comprise a single layer film of polymeric material. Alternatively, the substrate may comprise a laminate of two or more layers of polymeric material.

[0076]

[0067] The plurality of opacifying layers 30 may comprise any one or more of a variety of opacifying inks which can be used in the printing of banknotes or other security documents. For example, the layers of opacifying ink may comprise coatings comprising a pigment, such as those described under 'Opacification' above, dispersed within a binder or carrier. The binder is typically a heat-activated cross-linkable polymeric material, but can also be activated by other forms of radiation, such as UV (ultra violet).

[0077]

[0068] In this example, two opacifying layers 31 , 32 are printed on the first side 21 , and further three opacifying layers 33, 34 and 35 are printed on a second side 22 of the substrate 20. The number of opacifying layers provided on the first side 21 and the second side 22 of the substrate 20 may be different in other examples, and not necessarily limited to the same number of layers as illustrated in Figures 1 to 8. In this example, the first side 21 defines a front face of the substrate 20, while the second side 22 defines a back face of the substrate 20. In this example, opacifying layers 32, 33 and 34 each represent base coats while opacifying layers 31 and 35 represent top coats. In some examples, the plurality of opacifying layers 30, at least partially overlap the first iridescent ink layer 11 and / or the second iridescent ink layer 12.

[0078]

[0069] As illustrated, the opacifying layers 31, 32 are omitted in selected regions of the security document 1 , in order to form a window region 40. Although examples disclosed herein indicate that a window region is formed in the security document 1, it will be understood that the location and number of window regions are shown for illustration purposes only. In other examples, a plurality of window regions may be formed in the security document 1 in different locations, each of which includes one or more of the security features disclosed herein.

[0070] In this example, the security feature 10 is at least partially, or substantially formed in the window region 40 of the security document 1. In this example, the window region 40 is a half-window. The security feature 10 includes a first iridescent ink layer 11 and a second iridescent ink layer 12 on the second side 22 of the substrate 20. That is, the first iridescent ink layer 11 and the second iridescent ink layer 12 are both on the same side of the substrate. In other examples, the first iridescent ink layer 11 and the second iridescent ink layer 12 may be on opposite sides of the substrate 20.

[0079]

[0071] In this example, the first iridescent ink layer 11 and the second iridescent ink layer 12 are printed on the substrate 20 in the window region 40. The first iridescent ink layer 11 and the second iridescent ink layer 12 are printed such that they at least partially overlap one another. In this example, the second iridescent ink layer 12 entirely overlaps the first iridescent ink layer 11. In other examples, the first iridescent ink layer 11 may entirely overlap the second iridescent ink layer 12. In this example, the first iridescent ink layer 11 is printed with an iridescent ink and the second iridescent ink layer 12 is printed with a colour switching ink. In other examples, the first iridescent ink layer 11 may be printed with a metallic ink, a pearlescent ink, or a colour switching ink instead. In further examples, both the first iridescent ink layer 11 and the second iridescent ink layer 12 may be printed with colour switching inks.

[0080]

[0072] The first iridescent ink layer 11 and the second iridescent ink 12 layer are printed such that they form a design on the substrate 20. The design may be, for example, of text, indicia, a portrait, a building, an object, a tree, a flower, or an animal.

[0081]

[0073] In this example, the second iridescent ink layer 12 is printed with a colour shifting ink, and exhibits a colour shifting effect when viewed in reflection from the first side 21. The second iridescent ink layer displays at least one colour shift between a first colour and a second colour when viewed from the first viewing angle and second viewing angle, respectively. For example, a first colour, the colour of the pearlescent interference pigment such as gold or green, is seen at a first viewing angle. When the security document 1 is tilted or rotated, a second distinct colour, eg blue, is seen at a second viewing angle. The second colour is, typically, largely determined by the colour pigment but may be altered by other components of the colour shifting ink (such as other pigments (such as carbon black), the amount of interference pigment, etc.). When the second iridescent ink layer 12 is viewed in transmission, no colour changing effects can be seen, only the first colour is seen and an image formed by the colour shifting ink may be discernible as being a different shade of colour to the surrounding area.

[0074] In some examples, the second iridescent ink layer 12 may extend partly into an area surrounding the window region 40. These parts of the security feature that extend partly into the opacifying layers in the area surrounding the window region 40 exhibit no colour shifting effects whether viewed in reflection or transmission, but may appear a different shade from the second colour in the window region. In other words, these parts of the security feature appear the same colour at all viewing angles. The colour observed from the second iridescent ink layer 12 in the region surrounding the window may be a lighter shade of the second colour when viewed through one or more white opacifying layers. In other examples, the second iridescent ink layer 12 does not extend partly into an area surrounding the window region 40.

[0082]

[0075] The first iridescent ink layer is substantially invisible when viewed from the first viewing angle and visible when viewed from the second viewing angle. When the first iridescent ink layer 11 and the second iridescent ink layer 12 are viewed together in reflection (ie in combination), they display a first image when viewed from a first viewing angle. When viewed from a second viewing angle, they display a second image of a different colour. For example when viewed from the first viewing angle, the first iridescent ink layer 11 may be substantially invisible and the second iridescent ink layer 12 may exhibit a first colour. In this case, the image displayed is substantially of the second iridescent ink layer 12 as the first iridescent ink layer 11 is 'hidden' from the viewer. However, when the security device 1 is rotated and viewed from the second viewing angle, the first iridescent ink layer 11 is visible and the second iridescent ink layer 12 may exhibit a second colour distinct from the colour. In this case, the image displayed is a combination the first iridescent ink layer 11 and the second iridescent ink layer 12 as the first iridescent ink layer 11 is 'revealed' to the viewer. Preferably, the second image is a distinct image that is not correlated with the first image.

[0083]

[0076] Figure 2 is similar to the embodiment of Figure 1 , and like reference numerals refer to like elements. In this example, the second iridescent ink layer 12 includes regions 13 in which the ink is omitted to reduce the opacity in those regions. The second ink layer 12 may be printed in half tone to form the regions 13 where ink is omitted. The second ink layer being applied with gap regions 13 of Figure 2 may result in the first iridescent ink layer 11 being masked or less visible than in embodiments where the second ink layer 12 has been applied in the manner shown in Figure 1.

[0084]

[0077] Figure 3 is similar to the embodiment in Figure 1 , and like reference numerals refer to like elements. In this example, the first iridescent ink layer 11 and the second iridescent ink layer 12 of the security feature 10 are printed on the first side 21 of the substrate 20. The firstiridescent ink layer 11 and second iridescent ink layer 12 may provide substantially the same optical effect and / or appearance in Figures 1 and 3.

[0085]

[0078] Figure 4 is similar to the embodiment in Figure 3, and like reference numerals refer to like elements. In this example, the second iridescent ink layer 12 includes regions 13 in which the ink is omitted to reduce the opacity in those regions. The first iridescent ink layer 11 and second iridescent ink layer 12 may provide substantially the same optical effect and / or appearance in Figures 2 and 4.

[0086]

[0079] Figure 5 is similar to the embodiment in Figure 1 , and like reference numerals refer to like elements. In this example, the window region 40 is a full-window. The first iridescent ink layer 11 and second iridescent ink layer 12 may provide substantially the same optical effect in Figures 1 , 3 and 5. The difference between Figure 5 to Figures 1 and 3 is that the layers 11, 12 are provided in a full window rather than a half window. This may provide a difference in appearance when viewed in reflected light from the second side 22 of the security document 1 between these examples.

[0087]

[0080] Figure 6 is similar to the embodiment in Figure 5, and like reference numerals refer to like elements. In this example, the second iridescent ink layer 12 includes regions 13 in which the ink is omitted to reduce the opacity in those regions. The first iridescent ink layer 11 and second iridescent ink layer 12 may provide substantially the same optical effect in Figures 2, 4 and 6. The difference between Figure 6 to Figures 2 and 4 is that the layers 11, 12 are provided in a full window rather than a half window, which may provide a difference in appearance when viewed in reflected light from the second side 22 of the security document 1.

[0088]

[0081] Figure 7 is similar to the embodiment in Figure 3, and like reference numerals refer to like elements. In this example, the window region 40 is a full-window. Figure 7 is also similar to the embodiment in Figure 5, in the example of Figure 7 the first iridescent ink layer 11 and the second iridescent ink layer 12 of the security feature 10 are printed on the first side 21 of the substrate 20. The first iridescent ink layer 11 and second iridescent ink layer 12 may provide substantially the same optical effect and appearance in Figures 7 and 5.

[0089]

[0082] Figure 8 is similar to the embodiment in Figure 7, and like reference numerals refer to like elements. In this example, the second iridescent ink layer 12 includes regions 13 in which the ink is omitted to reduce the opacity in those regions. Figure 8 is also similar to the embodiment in Figure 6, in the example of Figure 8 the first iridescent ink layer 11 and the second iridescent ink layer 12 of the security feature 10 are printed on the first side 21 of thesubstrate 20. The first iridescent ink layer 11 and second iridescent ink layer 12 may provide substantially the same optical effect and appearance in Figures 8 and 6.

[0090]

[0083] Figures 9 and 10 are similar to the embodiments of Figures 7 and 8, respectively, and like reference numerals refer to like elements. In these examples, there are no opacifying layers 30 on each side of the substrate 20. The substrate 20 may be substantially transparent, as with other examples herein, such as being formed from a transparent polymeric material. The first iridescent ink layer 11 and second iridescent ink layer 12 in Figure 9 may provide substantially the same optical effect and appearance as the like features in Figures 5 and 7. The first iridescent ink layer 11 and second iridescent ink layer 12 in Figure 10 may provide substantially the same optical effect and appearance as the like features in Figures 6 and 8.

[0091]

[0084] Figure 11 is similar to the embodiment of Figure 7 and like reference numerals refer to like elements. This example shows the first iridescent ink 11 and second iridescent ink 12 in a full window region 40, but is equally applicable to other examples herein which do not have a full window region. In this example, the first iridescent ink 11 is printed on the second side of the substrate and the second iridescent ink 12 is printed on the first side of the substrate. In other words the first iridescent ink 11 and second iridescent ink 12 are on opposed sides of the substrate 20. The optical effect provided by the iridescent inks example of Figure 11 will be similar to that seen in the example of Figure 7. It is noted that any of the examples provided herein could employ first and second iridescent inks 11, 12 that are printed on opposed sides of the substrate or that are printed on the same side of the substrate. Where an opaque or substantially opaque substrate is used it may be preferable for the first and second iridescent inks to be printed on the same side of the substrate.

[0092]

[0085] According to the examples herein, the substrate 20 may be opaque or substantially opaque. For example, the substrate may be an opaque or substantially opaque polymeric substrate. One example of a suitable polymer film is a bi-axially oriented polypropylene (BOPP) which has titanium dioxide particles added during manufacture to create a white polymer film. The substrate 20 may be white or substantially white in colour. The examples of Figures 9 and 10, or any other example provided herein, may comprise an opaque or substantially opaque substrate 20, such as a substantially opaque polymer film. Where an opaque substrate is used, the security feature may not be viewed in transmission through the security document. The optical effects provided by the first iridescent ink layer 11 and second iridescent ink layer 12 will be visible in reflected light. A substantially opaque substrate may allow a small amount of visible light to pass through it and the optical effects may be visible in transmission in those instances. The optical effects of the iridescent ink layers will be similar on an opaque or substantially opaque substrate to those on a substantially transparentsubstrate. The effect may be reduced where an opaque or substantially opaque substrate is used compared to a substantially transparent film due to the opaque background of the substrate, such as a white substrate, creating diffuse scattering of the non-iridescent colour. The first iridescent ink layer 11 and second iridescent ink layer 12 are printed on the same side 21,22 of the opaque substrate 20 to provide the combined effects of the two layers 11, 12. This differs to examples where the substrate 20 is transparent or translucent in which the first iridescent ink layer 11 and second iridescent ink layer 12 may be printed on opposed sides 21 , 22 of the substrate 20 or on the same side.

[0093] Methods of printing a security feature on a substrate for a security document

[0094]

[0086] This disclosure also relates to methods of printing a security document with the inks disclosed herein. The inks may be applied to a substrate by any suitable technique, which in some embodiments is gravure printing, offset printing, and / or screen printing.

[0095]

[0087] In some embodiments, the inks may be printed onto a web of polymeric substrate in a print press comprising one or more print units through which the web is fed during a print run. It will be appreciated that different inks may be printed at multiple such print units along the web, for example inks with differing colouring agents or fluorescent compositions, . Furthermore, a wide variety of other conventional printing operations may be performed at other print units and stations along the web. Examples of such operations, for the specific case where the web is a transparent polymeric substrate, include surface treatment to improve adhesion (such as corona discharge treatment), printing of multiple successive opacification layers, gravure printing of design elements comprising one or more coloured inks, application and embossing of UV-curable lacquers to form optically active embossed features, and the like.

[0096]

[0088] The inks may be printed or otherwise applied at a suitable coat weight for the print technique of choice. It will be appreciated that the loading of the functional ink components in the resulting print layer will directly depend on the applied coat weight. For gravure printing, a suitable wet coat weight may be from about 2 g / m2 to 10 g / m2, for example approximately 6 g / m2. The printed ink may then be dried and / or cured on the substrate by conventional means, including via heating applied by a drying unit or via exposure to actinic illumination, for example UV-light. The resulting print layer may have a thickness of in the range of about 100 nm to about 3 microns, typically between 1 and 3 microns.

[0097]

[0089] It will be appreciated that the security feature enhances the security documents but also simplifies the authentication process for users.

[0090] It will be appreciated that the security feature allows for quick and easy visual verification and authentication from one side of the security document, that is, without requiring to be viewed in both reflection and transmission.

[0098]

[0091] It will be appreciated that the security feature displays two different images when viewed at two different angles for improved security.

[0099]

[0092] It will be appreciated that the security feature allows for quick and easy visual verification and authentication by changing the viewing angle.

[0100]

[0093] It will be appreciated that the security feature provides an improved security feature that is difficult to counterfeit.DRAWING REFERENCES

[0101]

Claims

CLAIMS1. A security feature for a security document comprising:a substrate with a first iridescent ink layer and a second iridescent ink layer,wherein the first iridescent ink layer and the second iridescent ink layer at least partially overlap each other;wherein the second iridescent ink layer includes a colour switching ink, andwherein, when viewed in reflection, the combination of the first iridescent ink layer and the second iridescent ink layer display a first image when viewed from a first viewing angle and display a second image when viewed from a second viewing angle.

2. The security feature according to claim 1, wherein the second iridescent ink layer displays at least one colour shift between a first colour and a second colour when viewed from the first viewing angle and second viewing angle, respectively.

3. The security feature according to claim 1 or claim 2, wherein the first iridescent ink layer is substantially invisible when viewed from the first viewing angle and visible when viewed from the second viewing angle.

4. The security feature according to any one of the preceding claims, wherein the first iridescent ink layer and the second iridescent ink layer completely overlap each other.

5. The security feature according to any one of the preceding claims, wherein the security feature is applied to a window region of the security document.

6. The security feature according to claim 5, wherein the window region includes a halfwindow.

7. The security feature according to claim 5, wherein the window region includes a fullwindow.

8. The security feature according to claims 5 to 7, wherein the second iridescent ink layer at least partially overlaps the window region.

9. The security feature according to any one of the preceding claims, wherein the substrate has a first side and a second side and the first iridescent ink layer and the second iridescent ink layer are both printed on either the first side or the second side of the substrate.

10. The security feature according to any one of claims 1 to 8, wherein the first iridescent ink layer and the second iridescent ink layer are printed on opposite sides of the substrate.

11. The security feature according to any one of the preceding claims, wherein the first iridescent ink layer and the second iridescent ink layer form a design on the substrate.

12. The security feature according to claim 11 , wherein the design comprises at least one of text, indicia, a portrait, a building, an object, a tree, a flower, an animal.

13. The security feature according to any one of the preceding claims, wherein the first iridescent ink layer includes a metallic ink or a pearlescent ink.

14. The security feature according to any one of claims 1 to 12, wherein the first iridescent ink layer includes a colour switching ink.

15. The security feature according to any one of the preceding claims, wherein the substrate comprises a plurality of opacifying layers.

16. The security feature according to claim 15, wherein the substrate includes at least one opacifying layer on a first side and / or a second side of the substrate.

17. The security feature according to claim 15 or claim 16, wherein one or more opacifying layers, at least partially overlap the first iridescent ink layer and / or the second iridescent ink layer.

18. The security feature according to any one of the preceding claims, wherein the first iridescent ink layer and the second iridescent ink layer are printed on the substrate.

19. The security feature according to claim 18, wherein the first iridescent ink layer and the second iridescent ink layer are printed using Gravure printing or screen printing.

20. The security feature according to any one of the preceding claims, wherein the second image is a distinct image that is not correlated with the first image.

21. A method of producing a security document, the method comprising the steps of:providing a substrate to a printing process, the substrate having a first side and a second side;printing a first iridescent ink layer on the first side or the second side and printing a second iridescent ink layer on the first side or the second side such that the first iridescent ink layer and the second iridescent ink layer at least partially overlap.

22. The method of claim 21, comprising printing at least one opacifying layer on the first side and / or the second side to form a base coat.

23. The method of claim 21 or 22, comprising printing at least one opacifying layer on the first side and / or second side to form a top coat.

24. The method of claim 22 or 23, wherein opacifying layers on the first side and / or the second side of the substrate are absent in at least one region to form a full window or a half window, and wherein the first iridescent ink layer and the second iridescent ink layer are printed in the region of the full window or half window.

25. A security document comprising the security feature of any one of claims 1 to 20.

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