WO 2012/062871 PCT/EP2011/069868 1 OPTICALLY VARIABLE SECURITY DEVICE FOR A VALUABLE DOCUMENT 5 DESCRIPTION The present invention concerns the technical field of security elements for valuable documents such as fiduciary or similar documents. 10 By < fiduciary document > in the meaning of the invention is meant all documents such as banknotes, cheques, bank cards used to transmit a sum of money. By < similar document >> is meant all documents issued by a State administration to certify the 15 identity of a person, the person's right to drive a vehicle e.g. in particular an identity card, passport, driving licence, etc. By this expression is also meant any document used to authenticate an item of value such as a label affixed to a luxury garment. Also meant is 20 any document used to authenticate the payment of a tax such as an excise stamp. In the field of valuable documents, in particular banknotes, it is known to affix one or more security components of varied type to protect these documents 25 against forgery.
WO 2012/062871 PCT/EP2011/069868 2 There is currently a strong demand for valuable documents comprising one or more security components that are easily identifiable on careful examination with the naked eye, but which are particularly complex 5 to reproduce. Said security components are also designated as « first level security components. In general, said security component produces an optical effect entailing one or more optical animations, such as contrasting effects, colour 10 changes, optical illusions, etc. From the state of the art, in particular from international application WO 01/036213, an optical security component is known comprising a film embossed with a first zone producing a rainbow effect in a first 15 orientation of the component relative to an illuminating direction, and a second zone producing a coloured effect of a first colour in a first orientation of the component then of a different second colour in an orientation perpendicular to this first 20 orientation. The complex production of said component generally lies in a combination of several print techniques that are difficult to reproduce using reprography equipment available to the general public (scanner, laser or 25 colour inkjet printers, etc.) and/ or using standard printers' equipment. The state of the art can also be illustrated by the documents commented upon below. EP 1 902 855 describes a security document 30 comprising a foil area with a first region of a first colour and a second region of a second colour. Underneath or beyond these, there extends a security means such as a hologram. Therefore the hologram is partly visible through the first and second regions of 35 different colours.
WO 2012/062871 PCT/EP20111/069868 3 WO 2008/154541 relates to an authentication product such as a label. A first part of this product comprises an inked intaglio print with a latent image, whilst the second is formed by a hologram. 5 US 6,088,161 relates to a substrate having a surface with diffractive submicron relief structures. This surface is formed of a series of parallel but non contiguous tracks. The diffraction effect is homogeneous in each track but different on contiguous 10 tracks. Finally, WO 95/23350 describes a diffractive surface with elements of shiny appearance which "light up" in turn, depending on the direction of observation. These elements are included in a hologram. 15 The objective of the present invention is to propose a security device, for example of first level, improving upon the properties of already known components whilst being difficult to reproduce in order to guarantee most difficult forgery. 20 For this purpose, the subject of the invention is in particular a security device comprising a substrate and thereupon a security component for a valuable document comprising at least first and second zones respectively reproducing first and second optical 25 effects each able to have at least two characteristic aspects as per different observation configurations of the component, characterized in that it comprises an image at least partly in relief obtained by deformation of said component and of said substrate on which said 30 component is affixed, this image comprising at least one first and one second graphic elements and extending at least in part in the two zones, and in that at least the said first and second graphic elements of the image are respectively revealed in the first and second zones WO 2012/062871 PCT/EP2011/069868 4 with at least one of the two aspects becoming visible of the first and second optical effects respectively. The image, the effects and the relief play a combined role. Therefore, according to the invention, 5 the image acts in synergy with the generated optical effects to produce a play of light and shadow, even of colours, by concentrating, scattering or diffracting the light derived from a light source. The invention proposes taking advantage of the 10 light variations obtained to obscure, partly or fully reveal security data according to different configurations of observation of the component. Therefore, depending on the optical configuration of observation of the component, one of the optical 15 effects is preferably combined with one of the parts of the image to produce a switch-on or switch-off effect of the part concerned. In one preferred embodiment of the invention, the image is configured so that the first and second 20 elements are concealed when the other of the two aspects of the first and second optical effects respectively becomes visible. Therefore, the visibility of a first aspect related to one of the optical effects allows the 25 revealing of one of the graphic elements, whereas the onset of the appearance of a second aspect allows the disappearance or masking thereof. By changing the observation configuration, it is then possible to reveal or to hide a data item contained for example in 30 the graphic element under consideration. In one preferred embodiment of the invention, in one same observation configuration, the first graphic element is revealed and the second graphic element is concealed. The data contained in the graphic elements WO 2012/062871 PCT/EP2011/069868 5 can therefore be partly revealed in one same observation configuration. The aforementioned relief allows combined use of the optical effects by locally modifying their optical 5 reflection and scattering properties. For example, the relief is determined by relief parameters chosen from among a relief shape, relief depth, spatial frequency, etc. Preferably, the relief depth is between 5 and 150 10 micrometres and the relief is obtained by deformation of the substrate (embossing). A security device of the invention may further comprise one or other of the characteristics according to which: 15 - one of the optical effects has at least three different characteristic aspects, a third graphic element of the image is revealed when this third aspect becomes visible in at least one of the two zones; 20 - the relief is formed by printing of dry embossing type; - the relief is formed by embossing during a hot or cold transfer step of stamping foil having zones respectively producing first and second 25 optical effects; - the image is formed at least in part by a simple or multiple latent image; - at least one of the optical effects acting in at least one priority direction, the image 30 comprises at least one halftone screen oriented in a discernible direction substantially coinciding with the priority direction of action of the optical effect; - the image comprises a background, the background 35 has a halftone screen oriented in a first WO 2012/062871 PCT/EP2011/069868 6 discernible direction and at least one of the graphic elements has a halftone screen oriented in a second discernible direction; - the screening of the background and the 5 screening of the graphic element are oriented in the same discernible direction and are offset from each other in a direction perpendicular to the discernible direction; - since the halftone screens are periodic of 10 identical period, the screens are offset from one another by at least one half-period; - the graphic element has at least two halftone screens oriented in two different discernible directions; 15 - the halftone screens of the image are formed in relief; - at least one of the optical effects is generated by a diffraction grating having at least one priority direction of diffraction; 20 - at least one of the effects produces at least one characteristic rainbow aspect; - at least one of the effects produces at least one characteristic metallized aspect (aluminium, copper, gold ...). 25 - at least one of the effects produces a first coloured aspect of a first colour and a second coloured aspect of a second colour; - at least one of the effects is generated by a colour subtraction filter by diffraction; 30 - at least one of the effects is generated by a volume hologram producing an animation effect capable of simulating movement of part of the image in relation to an observation configuration of the component; WO 2012/062871 PCT/EP2011/069868 7 - the part of the image able to move is positioned with reference to another part of the image so that the two parts complement one another in one orientation of the component; 5 - the two zones of the structure together form a repeat pattern, e.g. alternately arranged. A further subject of the invention is a valuable document such as a banknote comprising a security device according to the invention. 10 BRIEF DESCRIPTION OF THE FIGURES Other characteristics and advantages of the invention will become apparent in the light of the following description given with reference to the 15 appended drawings in which: - Figure 1 illustrates a valuable document such as a banknote comprising a security component according to a first embodiment of the invention; - Figures 2A and 2B illustrate the security 20 component in Figure 1 from two different viewing angles; - Figure 2C gives a detailed view of part of the image; - Figures 3A to 3C illustrate the security component 25 according to a second embodiment of the invention from three different viewing angles respectively; - Figure 3D gives a detailed view of part of the image; - Figure 4 illustrates the security components 30 according to a third embodiment of the invention; and - Figures 5A to 5C illustrate the security component according to a fourth embodiment of the invention from three different viewing angles respectively. 35 WO 2012/062871 PCT/EP2011/069868 8 DETAILED DESCRIPTION OF AT LEAST ONE PREFERRED EMBODIMENT OF THE INVENTION Figure 1 illustrates a valuable document. This valuable document carries the general reference 10. In 5 the described example, the valuable document 10 is a banknote. As a variant, the document 10 may be a passport, a driving licence or any other document which may need to be secured. The document 10 comprises a substrate 12 in a 10 material essentially comprising paper for example, or plastic or a mixture of both. Evidently, the invention is not limited to any particular material for the substrate. The material of the substrate may also have a multilayer structure and may, when applicable, 15 comprise several layers laminated together. As illustrated in Figure 1, the document 10 also comprises a security component 16 according to a first embodiment of the invention. The component 16 according to this first embodiment is illustrated in detail in 20 Figures 2A and 2B. According to the invention, the security component 16 comprises first Zl and second Z2 zones respectively producing first and second optical effects. The first and second optical effects are each able to have at 25 least two characteristic aspects according to different observation configurations of the component 16. In the illustrated example, the two aspects are clearly differentiated enabling an observer easily to distinguish between them. 30 in the meaning of the invention, an observation configuration is defined by a set of observation parameters e.g. the orientation of a component 16 relative to a direction of observation, a relative position of a light source, the size of the source, the WO 2012/062871 PCT/EP2011/069868 9 emission wavelengths of the source, the power of emission, etc. For example, the first effect offers a first aspect in first and second observation configurations 5 (Figure 2A) and a second aspect in a third observation configuration (Figure 2B) . For example, the first and second configurations respectively correspond to directions of observation 24A, 24B separated by an angle of a quarter turn, e.g. inclined at an angle of 10 450 relative to a plane comprising the component 16. The third configuration corresponds to a grazing observation angle schematized by reference 24C. In the example described and illustrated in the Figures, the optical effects vary in particular 15 depending on predefined orientations of the component 16 in relation to a light source S, schematically illustrated as a sun in the Figures, and more specifically in relation to a direction of illumination (not indicated in the Figures). 20 Evidently, the light source S may emit a directive or scattered beam. Although the invention is not limited thereto, the source is particularly well adapted for use with scattered visible polychromatic light (e.g. white) illuminating the security component. 25 Evidently, as a variant, the light source S may comprise a spectrum having a wavelength outside the visible range (conventionally defined between 0.4 and 0.7 micrometres) ; for example the ultraviolet spectrum having a wavelength of less than 0.4 micrometres, or 30 the infrared spectrum with a wavelength of more than 0.7 micrometres. In this case, it is generally necessary to use a specific detector to observe the optical security. For example, each of the optical effects acts in 35 at least one priority direction whose orientation WO 2012/062871 PCT/EP2011/069868 10 depends for example on the main direction of illumination of the source S. In the described example, the first optical effect associated with zone Z1 is generated by a diffraction 5 grating producing at least one first characteristic rainbow aspect in at least one grazing observation direction 24C (Figure 2B) and at least one second non diffracting aspect, for example dull grey, in at least one other direction of observation, for example in 10 direction 24A or 24B (Figure 2A). Preferably therefore, the first optical effect has at least one priority direction of action which, for a diffraction grating, is related in particular to the direction of an order of diffraction of this grating. 15 The direction of observation 24C in this example is determined in particular by the direction of illumination of the component 16 and substantially coincides for example with a direction following an order of diffraction of the grating. 20 Therefore, the diffraction grating preferably has at least one priority direction of diffraction which determines the direction of observation 24A and 24B of the rainbow aspect of the first effect. This direction of diffraction is itself defined for example in 25 relation to the reference direction of illumination of the source S. In manner known per se, a diffraction grating is generally formed by a regular arrangement of identical diffracting elements. Each of the elements diffracts 30 the incident light in all directions and each beam diffracted in one direction interferes with the other rays diffracted in the same direction. The grating allows chromatic dispersion to be produced responsible for the rainbow aspect observable in at least one 35 direction of observation.
WO 2012/062871 PCT/EP2011/069868 11 In the described example, the grating comprises a plurality of lines extending in a longitudinal direction which determines the priority direction of diffraction. 5 In this first embodiment the second effect associated with zone Z2 produces a first coloured aspect of a first colour observable in one of the configurations, and a second coloured aspect of a second colour observable in the other of the 10 configurations. In the described example the first colour is green and the second colour is red. Preferably, the second optical effect associated with the second zone Z2 is generated by a colour subtraction filter via diffraction. This second optical 15 effect is produced for example by a diffraction grating structure having predefined grating parameters so that the diffractive structure is configured to separate an incident polychromatic light into at least one pair of adjacent reflected beams separated by an angle and of 20 contrasting colours. With respect to this second optical effect with colour change, the diffractive grating preferably has two priority directions of action corresponding to each of the contrasting colours. In addition, the beams of 25 red and green colour are preferably spaced apart by an angle e.g. an angle of 900. In other words, to observe the change in colour of zone Z2, the component 16 must be rotated by a quarter turn, or a quarter turn rotation must be made from the 30 direction of observation 24A of the component 16 towards the direction of observation 24B (Figure 2A). In addition, the second optical effect has a third aspect for example that is non-diffractive in a third observation configuration corresponding to the grazing 35 angle observation 24C (Figure 2B).
WO 2012/062871 PCT/EP2011/069868 12 By diffraction grating parameter is meant for example a number of lines per unit length, a physical profile of the grating structure, the orientation of the grating lines, etc. 5 According to the invention, the security component 16 comprises an image 8 which extends at least partly in the two zones Z1 and Z2. In the entirety of this application, by "image in relief obtained by deformation of the component and of 10 the substrate on which the said component is affixed" is meant a graphic illustration formed of a single or several graphic elements which, in this latter case, may be separated from each other. In this example, the component 16 has a general 15 parallelepiped shape and the zones Zl and Z2 extend over the entire surface of the component 16. However, as a variant, the zones ZI and Z2 may only occupy part of the surface of the component 16. In the examples described in this application, the 20 first and second zones Z1 and Z2 are arranged together to form an alternate pattern, for example oblique hatched lines as illustrated in the different Figures. In the example illustrated in the Figures, the zones Z1 and Z2 are adjacent. However, in one variant not 25 illustrated in the Figures, the zones Z1 and Z2 can be distanced apart or they may partly overlap. Evidently, in another variant, the arrangement of the zones Zl and Z2 may be varied: for example, the zones may form concentric discs, interleaving of geometric shapes, 30 etc. According to the invention, the image 18 is structurally configured to act with the first and second optical effects. Therefore, according to the invention, the image 18 acts so that at least first 20 35 and second 22 graphic elements of the image 18 are WO 2012/062871 PCT/EP2011/069868 13 revealed in the first and second zones Zi and Z2 respectively. The revealing of the elements 20 and 22 is notably related to the onset of the visibility of at least one of the two aspects of the first and second 5 optical effects respectively. For example, the graphic elements 20 or 22 comprise alphanumeric characters. In one variant not illustrated, the graphic elements comprise micro lettering, geometric figures, drawings, portraits, etc. 10 In the described example, to act with the optical effects, the image 18 is formed at least partly in relief. Preferably, the relief of the image 18 is determined by relief parameters chosen from among a relief shape, relief depth, spatial frequency, etc. 15 Under these conditions this relief, in addition to be being visually perceptible, is also perceptible by touch which reinforces the security of the component. For example, the relief is formed by printing of dry embossing type. For this embossing it is possible 20 to use conventional ink-free intaglio printing to obtain dry embossing. Therefore, the deformation of the surface using a die etched with different halftone screens, different screen lines, with resist (non-screened zones) or 25 latent image (e.g. screen perpendicular to the global background screen) allows incident light rays to be reflected in very different manner than if they were to strike a planar element. By means of these deformations, the zones Zl and 30 Z2 can be made more matt (less shiny) through the use of dry embossing, and it is hence possible to reinforce the switch-off/switch-on effect of the optical effects in synergy. Preferably, the image 18 comprises at least one 35 screen oriented in a discernible direction chosen in WO 2012/062871 PCT/EP2011/069868 14 relation to at least one of the priority directions of action of the optical effect under consideration, to obtain optical synergy. For example, the discernible direction substantially coincides with at least one of 5 the priority directions of the optical effect under consideration. Persons skilled in the art will have no difficulty in finding a relative orientation of the screen of the image in relation to one of the priority directions of 10 action of the optical effect under consideration offering optimal optical synergy. For example, the image 18 is formed at least in part by a latent image, preferably of simple type. The latent image is arranged with reference to the first 15 optical effect for example. The orientation of the screened part is 900 for example from the screen of the diffraction grating producing the first optical effect or optionally parallel to this screen. In the first embodiment illustrated in Figures 2A 20 and 2B, the image 18 is formed by a relief of the type having a positive-negative effect. For example, the image 18 is generated by an etched intaglio die (not illustrated) or an embossing die or any other etched tool. As a variant, the image may comprise a non 25 screened background and at least one of the graphic elements may have at least one screened part oriented in a discernible direction. In the example, the background or the background of the image 18 is screened whereas the graphic 30 elements 20 and 22 are not screened as illustrated in Figure 2C. To form this image 18, the etched die comprises a screened part to form the background and a non-screened part of substantially planar surface to form the graphic elements. The screen of the background 35 defines a discernible direction of orientation 25 of WO 2012/062871 PCT/EP2011/069868 15 this screen corresponding to the orientation of the lines 23 of the screen. In this first embodiment, the first graphic element 20 forms a first chain of < TECH w characters 5 extending in the first zone Zl and the second graphic element 22 forms a second chain of < DCBE w characters extending in the second zone Z2. The background screening is formed for example by a plurality of etched lines, and is such as illustrated 10 in detail in Figure 2C; and the discernible direction 25 of this screening corresponds to the orientation of the lines 23. Preferably, this discernible direction is substantially aligned with the priority direction of action of the optical effect under consideration. 15 According to a first orientation of the component 16 illustrated in Figure 2A, the first zone Zl has a dull non-diffracting aspect whereas the second zone Z2 has a coloured aspect of a first colour e.g. green. The first chain of characters 20 is not visible in this 20 orientation whereas the second chain 22 is revealed by the coloured aspect of the second optical effect and gives the impression of lighting up. When an observer makes a quarter turn rotation along its plane as illustrated in Figure 2A, in 25 direction 24B, the positions of the source S and of the component 16 remaining unchanged, the first zone Zi maintains its dull, non-diffracting aspect. On the other hand, the second zone Z2 changes colour in clearly marked manner, for example changing from green 30 to red, hence the characters < DCBE > remain visible but change colour from green to red. When the direction of observation, corresponding to the grazing angle 24C for example, coincides with one of the priority directions of the first optical 35 effect, the background screen combines it action with WO 2012/062871 PCT/EP2011/069868 16 the first optical effect (Figure 2B). The first optical effect, in this grazing direction of observation, produces a rainbow aspect which will have the effect of revealing the first chain of characters 20 << TECH * 5 (Figure 2B) through the particular relief structure of the image 18 in zone Zi. The first graphic element 20 of the image 18 then becomes visible through the action of the screened background when the rainbow aspect becomes visible, 10 whereas the second graphic element 22 of the image 18 is hard to perceive with the naked eye and is practically invisible. Preferably, the image 18 is configured so that the first 20 and second 22 elements are concealed when the 15 other of the two aspects, of the first and second optical effects respectively, becomes visible. Therefore in this first embodiment, the first element 20 is obscured with the onset of the visibility of the non-diffracting aspect of the first optical 20 effect, and the same applies to the second element 22 which is also obscured with the extinguishing of the colour of the second optical effect. In addition, in this first embodiment, in one same observation configuration e.g. the one illustrated in 25 Figure 2B, the first graphic element 20 is revealed and the second graphic element 22 is concealed contrary to the observation configurations illustrated in Figure 2A. Figures 3A to 3D illustrate an optical component 30 16 according to a second embodiment. In these Figures, elements similar to Figures 1 to 2C carry the same references. In this second embodiment, the image is a multiple latent image. For example, the image 18 comprises a WO 2012/062871 PCT/EP2011/069868 17 background 28 having a screen oriented in a first discernible direction 30 (Figure 3D). In addition, preferably, one of the graphic elements has at least one screen oriented in a 5 discernible direction. Therefore, at least one of the graphic elements 20 or 22 has a screen oriented in a second discernible direction 32 different from the first direction 30. In one variant not illustrated in the Figures, the 10 screen of the background 28 and the screen of the graphic elements 20 or 22 are oriented in one same discernible direction and are offset from each other in a direction substantially transverse to this discernible direction. For example, the screens are 15 periodic having the same period, and the offset between the two screens corresponds to a half-period. In the example illustrated in Figure 3D, the graphic element 22 comprises a first screened part 22A oriented in a second discernible direction 32 different 20 from the first 30 and a second screened part 22B oriented in a third discernible direction 34 different from the first 30 and second 32 discernible directions 32. In addition, the second 32 and third 34 directions are perpendicular to one another. 25 For example, the second graphic element 22 comprises a first chain of characters c DCBE > and a second chain of characters q TECH >. Therefore, in this embodiment, the background 28 of the image 18 has a screen oriented in a first discernible direction 30, 30 the first chain < DCBE > has a screen oriented in a second discernible direction 32, and the second chain < TECH > has a screen oriented in the third discernible direction 34. In addition, preferably, the second optical effect 35 associated with the zone Z2 acts in at least two WO 2012/062871 PCT/EP2011/069868 18 priority directions. These directions are spaced apart by an angle of a quarter turn for example. For example, in the observation configuration illustrated in Figure 3A, defined in particular by a 5 direction of observation 26A, the first optical effect of the zone Zl has a rainbow aspect and the second optical effect of zone Z2 has a non-diffracting dull aspect. In this configuration, the first graphic element 10 20 « DCBE of the first zone Zl is revealed through the appearing of the rainbow aspect of the first optical effect. For example, the first graphic element 20 e DCBE > has a screen oriented in a discernible direction corresponding to one of the priority 15 directions of the second optical effect. On the other hand, the second graphic element 22 is concealed through the appearing of the non-diffracting dull aspect of the second optical effect. In a second observation configuration illustrated 20 in Figure 3B, defined in particular by direction 26B, the second optical effect has a first coloured aspect of a first colour e.g. green. The first chain of characters < DCBE > of the graphic element 22, having a screen oriented in the second discernible direction 32 25 substantially coinciding with the first priority direction of action of the second optical effect, is revealed. On the other hand, the other chain of characters « TECH w of this same graphic element 22 is obscured since it has a screen oriented in the third 30 discernible direction 34 which does not coincide with the priority direction of the second optical effect. Finally, in a third observation configuration illustrated in Figure 3C, defined in particular by the observation direction 26C, the second optical effect 35 has a second coloured aspect of a second colour e.g.
WO 2012/062871 PCT/EP2011/069868 19 red. The first graphic element 20 of the image 18 present in zone ZI is still obscured since the first optical effect in this direction of observation still has a non-diffracting dull aspect. On the other hand, 5 in this configuration, the second chain of characters < TECH of the second graphic element 22 is revealed by the red colouring of the second optical effect. A third embodiment is illustrated in Figure 4. In this third embodiment, the image 18 comprises a third 10 graphic element 28. This third graphic element 28 can be printed for example by offset, flexography, serigraphy, typography, intaglio with or without ink, etc. The third graphic element 28 is invariant irrespective of the observation configuration of the 15 component 16. Preferably, this third graphic element 28 is arranged with reference to the other graphic elements so that it complements the other graphic elements 20 or 22 for example to provide information. For example, this Figure illustrates the graphic 20 element 22 and the graphic element 28 positioned with reference to each other in the second zone Z2. A fourth embodiment of the invention is illustrated in Figures 5A to 5C. In this fourth embodiment, the first zone ZI may for example have one 25 of the above-described optical effects e.g. the first optical effect. As a variant, the first zone Zl may comprise the second above-described optical effect. In this embodiment, the second zone Z2 generates a volume hologram producing an animated effect capable of 30 simulating movement of part of the image in relation to the orientation of the component 16. For example, as illustrated in Figure 5A, in a first orientation, the first graphic element 20 becomes visible and the chain of characters e TECH > is WO 2012/062871 PCT/EP2011/069868 20 revealed through the rainbow aspect f or example of the first optical effect. In a second orientation of the component 16 illustrated in Figure 5B, the second graphic element 22 5 is revealed. This second graphic element 22 gives the impression of moving by varying the tilt angle of the component 16 as per the arrows indicated in the Figure. Preferably, as illustrated in Figure 5C, the part of the image capable of moving is positioned with 10 reference to another part of the image so that the two parts come to complement each other in one orientation of the component. Therefore, in this orientation, the graphic element 20 is revealed simultaneously with the graphic element 22 and the two elements come to 15 complement each other by slightly tilting the component 16. A description will now be given of the main functioning aspects of a component according to the invention with reference, for example, to the first 20 embodiment of the invention illustrated in Figures 2A to 2C. An observer wishes to authenticate a valuable document i.e. the banknote 10. To do so, the observer rotates the banknote 10 so as to observe various 25 aspects produced by the optical effects. According to the aspect generated by the optical effects, graphic elements become visible or disappear with the movements caused by the observer. The observer can then rapidly authenticate the valuable document all the easier since 30 the changes in aspect of the optical effects are clearly apparent. Also, on account of the complexity entailed in producing a said valuable document, the forging thereof is made difficult. Although the invention has been described using 35 examples with reference to the accompanying Figures, WO 2012/062871 PCT/EP2011/069868 21 numerous modifications can evidently be envisaged by persons skilled in the art without however departing from the scope of the present invention. Other optical effects can be used as part of the 5 invention. For example, at least one of the effects may produce a characteristic metallized aspect e.g. of aluminium, copper or gold type. 10