AU2010247266B2

AU2010247266B2 - Method of manufacturing a security element for a security document

Info

Publication number: AU2010247266B2
Application number: AU2010247266A
Authority: AU
Inventors: Xavier Borde; Julien Gillot
Original assignee: Oberthur Fiduciaire SAS
Current assignee: Oberthur Fiduciaire SAS
Priority date: 2009-05-13
Filing date: 2010-04-26
Publication date: 2014-03-27
Anticipated expiration: 2030-04-26
Also published as: WO2010130910A1; FR2945551A1; RU2530419C2; CN102448730B; AU2010247266A1; RU2011150515A; BRPI1012206A2; CA2761781C; CA2761781A1; EP2429825A1; FR2945551B1; PL2429825T3; CN102448730A; ZA201108805B; EP2429825B1

Abstract

A translucent area (Z2) is formed in the element (14) by applying a substance (24) that transparentizes its substrate (12). Thus, the method includes a step of applying a substance (20) that impermeabilizes the substrate (12) over a first area (Z1) on a first side (F1) of the substrate, surrounding a second area (Z2) devoid of the impermeabilizing substance (20). The impermeabilizing substance (20) prevents impregnation of the substrate (12) by the transparentizing substance (24) in the first area (Z1). The method then includes a step of applying the transparentizing substance (24) to at least the second area (Z2) so as to impregnate the substrate (12) in order to make it translucent in this area (Z2). The first (Z1) and second (Z2) areas form first (18) and second (22) patterns respectively, making up an image that can be observed from both sides (F1, F2) of the substrate (12).

Description

I METHOD OF MANUFACTURING A SECURITY ELEMENT FOR A SECURITY DOCUMENT This invention relates to the technical field of 5 security elements for valuable documents or security documents. It is more particularly applicable to manufacturing a see-through type security element, that comprises an image that can be observed in transmitted light, or even reflected light in a translucent area of 10 a substrate of the security element. In the field of valuable documents, and particularly bank notes, one or several security elements of a varied nature can be added in order to protect these documents from counterfeit. There are 15 different types of security elements, particularly including "first level" security elements. Conventionally, a first level security element is difficult to make while remaining easily identifiable by anyone, simply by looking at it carefully. 20 A see-through type security element comprises a substrate on which complementary patterns are printed on each side, arranged in an approximately translucent or even transparent area of the substrate, positioning one relative to the other so as to form a final 25 composition that can be observed in transmitted light or even in reflected light when the area is sufficiently translucent. The translucent area enabling through vision is frequently called "see through", and for example is made by local 30 modifications to paper properties during manufacturing (fibre density, grammage, etc.).

z In particular, the translucent area can be formed by the application of a product that makes the substrate transparent. In particular, the state of the art includes a 5 method of manufacturing a watermark, particularly like that described in document GB 1 489 084, in which the translucent area is formed by the application of a composition that makes the area transparent. The disadvantage of this technique is that 10 wetting of the substrate gives a greasy and tacky appearance that spoils the aesthetics of the security document even after drying. The transparentising composition also tends to migrate to the surface of the substrate which makes the 15 translucent area look deformed and irregular, like an ugly stain. An advantage of the invention is to overcome this disadvantage by disclosing a method of making a security element comprising a substrate with a 20 particularly aesthetic translucent area, while remaining very simple and inexpensive to implement. To achieve this, the invention provides a method for manufacturing a security element of a security document, the security element comprising a substrate 25 having first and second opposite faces, in which a translucent area is formed in the substrate by applying a product that transparentises the substrate, the substrate being made from a paper based material, and the method including the following steps to form the 30 translucent area: 3 (a) applying an impermeabilising product to a first area of the first face that makes the substrate impermeable, wherein the first area surrounds a second area of the first face, said second area remaining 5 devoid of the impermeabilising product, such that the impermeabilising product prevents impregnation of the substrate by the transparentising product in the first area, then (b) impregnating the second area with the 10 transparentising product to make the second area translucent, wherein the first area forms a first pattern and the second areas forms a second pattern, the first and second patterns forming an image that can be observed 15 from the first and second faces of the substrate, said impermeabilising product being an iridescent ink, an ink with variable optical effect, a magnetic ink with variable optical effect, an ink with metallic effect or a liquid crystal ink. 20 The first area forms a peripheral border around the second area that prevents impregnation of the substrate by the transparentising product. "Peripheral" means an area that extends around the second area. "Transparentising" means making 25 translucent or even transparent. Obviously, the first area may include more or less complex nesting in the second area, the important requirement being that the contour around the entire part of the second area is delimited by the first area. 30 The contour of the translucent area may then be clearly delimited due to the presence of the first area that surrounds the translucent area and that, due to its previously applied impermeabilising product, firstly prevents the transparentising product from extending beyond the limits of the second predefined 5 area, and secondly prevents this transparentising product from migrating in the substrate close to the first area. This has the effect of reducing the blurred aspect of the stain. An impermeabilising product is a product that is 10 impermeable to a liquid at least for a given time. Thus, when the transparentising product is applied onto an area of the substrate covered by the impermeabilising product, the transparentising product does not penetrate into the substrate adjacent to this 15 area for a predefined time, after which the efficiency of the impermeabilising product may reduce. It is then necessary to dry the transparentising product before the end of this predefined time so as to prevent late impregnation of the transparentising product into the 20 substrate. The impermeabilising product may be a product that is opaque to light and is thus a "covering" product. In both cases, the two areas together form a 25 contrasting image due to the presence of two distinct covering and transparentising products. The image observed in reflected or transmitted light from the first side comprises a dark area corresponding to the first area containing the covering product and a light 30 area corresponding to the translucent area containing the transparentising product.

b This contrast is inverted when the image is observed from the second side in transmitted or reflected light. The transparentising product impregnates the substrate from the first side to the 5 second side so as to form the second pattern on the second side. Thus, the second pattern can be observed perfectly from the second side in transmitted or reflected light. This second pattern stands out from 10 the uniform substrate particularly due to its diaphanous appearance caused by impregnation of the transparentising product in the substrate. On the other hand, the first pattern is difficult to observe from the second side because the substrate 15 appears more opaque on the second side adjacent to this area due to the presence of the covering product on the first side, particularly by observation in transmitted light. The image that can be observed from the second 20 side thus corresponds to the negative of the image that can be observed from the first observation side, and this is clearly visible by observation in transmitted light. The result is thus that the first and second 25 areas together define a contrast in the image that is inverted as a function of the observation side of the image. While the image is observed from the first side (referred to as the front), the first pattern is more 30 visible than the second pattern and this contrast is inverted by observation from the second side (referred 6 to as the back) because the first pattern is almost invisible from this side (due to the opacity of the substrate in this area) while the second pattern is at least as visible as by observation from the first side 5 (due to impregnation of the entire thickness of the substrate). The impermeabilising product may be an ink that can be used in offset printing, silkscreen printing, flexography, letter press, gravure printing and metal 10 plate engraving. The transparentising product may be an ink with a high wetting capacity, for example comprising monomers with low surface tension, resins and / or photoinitiators or an acrylic ink. 15 Obviously, the efficiency of impregnation of the substrate by the product depends not only on the properties of the transparentising product (its wettability, its viscosity, the quantity deposited and the duration between application of the product and 20 when it dries) but also on the nature of the substrate (fibre impregnation capacity, grammage, surface calendering, porosity, etc.). The transparentising product may comprise security tracers, for example fluorescent particles, 25 particles with a reaction at a predefined wavelength and / or thermochromic particles. Optical effects and additional securities can thus be obtained due to the presence of such particles. The method may comprise a step to dry the 30 transparentising product by irradiation under light in the ultraviolet or infrared spectrum or by the emission I of a hot air flow. Thus, due to drying, the transparentising product is fixed onto the substrate. In some embodiment, the paper based material may be made from a material essentially comprising natural 5 and / or synthetic fibre-based paper, porous paper and / or cardboard. Also, possibly and in one embodiment of the invention, the method comprises a metal plate engraving step with transparent non-penetrating ink or with no 10 ink to form a touch-sensitive mark in the second area. This makes it possible to add another effect to the image composed of the first and second patterns, thus producing touch sensations. Metal plate engraving with ink can form a more pronounced relief detectable 15 to the touch, unlike the case in which the substrate is difficult to deform. In the case of a deformable substrate, metal plate engraving with no ink (currently referred to as die stamping) may be sufficient to form a pronounced relief detectable to the touch. 20 The transparent non-penetrating ink may comprises security tracers, for example fluorescent particles, particles with a reaction at a predefined wavelength and / or thermochromic particles. In a manner known in itself, the fluorescent 25 particles react to exposure to light in the ultraviolet spectrum by producing a short term fluorescence reaction during this exposure. Conventionally, the colour of the thermochromic particles varies reversibly as a function of the temperature. 30 The transparentising product may be applied on the substrate by silkscreen printing, flexography, 8 offset, metal plate engraving, letter press and / or gravure printing. Furthermore, the method may comprises a step to form a third pattern of the image on the second side of 5 the substrate, positioned relative to the second area so that it can be observed from the first side due to the translucence of the second area. As a variant, the third pattern is not necessarily formed by fixed positioning, but by free positioning relative to the 10 other patterns. The third pattern may complete the first and second patterns to form a final image that can be observed from the two sides in transmitted light, and even also in reflected light. 15 Furthermore, in one embodiment of the invention, the third pattern comprises a message coded on the second side, and the second area comprises means of decoding the message capable of revealing the coded message by observation from the first side at least in 20 transmitted light. The second internal area may be made sufficiently translucent to enable observation in reflected light from one of the sides of the substrate of a third pattern extending on the other of the sides by 25 positioning relative to the internal area. Thus, the see-through effect can also be observed in reflected light and this facilitates checking the authenticity of the security document, particularly for cases in which the persons who are making the checks do 30 not have the time or skills to check this authenticity.

Another purpose of the invention is a security element, wherein it is obtained using a manufacturing method according to the invention. Finally, the purpose of the invention is a 5 security document such as a banknote comprising a security element, characterised in that the security element complies with the invention. Other advantages and characteristics of the invention will become clear after reading the following 10 description given with reference to the appended drawings in which: - Figures 1A and 1B show top and bottom views respectively of a security document comprising a security element according to a first embodiment of the 15 invention; - Figures 2A and 2B show top and bottom views respectively of a security document comprising a security element according to a second embodiment of the invention along section 3-3 in Figure 2A; 20 - Figure 3 shows a sectional view of the security document in Figures 2A and 2B; - Figures 4A and 4B show top and bottom views respectively of a security document comprising a security element according to a third embodiment; 25 - Figures 5A and 5B show top and bottom views respectively of a security document comprising a security element according to a fourth embodiment; - Figures 6A and 6B show top and bottom views respectively of a security document comprising a 30 security element according to a fifth embodiment in observation orthogonal to the plane of the security -/FR2010/050786 10 document and Figures 6C and 6D show the same views as Figures 6A and 6B but in grazing observation; - Figures 7 to 10 show steps in a method for manufacturing a security document comprising a security 5 element according to a sixth embodiment. Figures 1A and 1B show a security document comprising a security element according to the first embodiment. This security document is denoted by the general reference 10. 10 The security document 10 comprises a substrate 12 delimiting opposite first F1 and second F2 sides. In this example, the security document 10 is a page of a passport. As a variant, the security document may be a banknote or any other valuable document. 15 This security document 10 comprises a security element 14 formed on part of the substrate 12. This security element 14 comprises a first area Z1 forming a first pattern 18 extending on the first side F1 of the substrate 12. This first pattern 18 is formed by a 20 deposit of an impermeabilising product 20. Preferably, the impermeabilising product 20 is also opaque to light and is referred to as a covering product 20 in the remainder of the description. Obviously, as a variant, the impermeabilising product 20 may be more or less 25 opaque or even translucent, without going outside the scope of the invention. For example, the covering product 20 is applied on the substrate 12 by silkscreen printing, flexography, offset and / or metal plate engraving, 30 letter press and / or gravure printing. Thus, the covering product 20 is preferably an ink that can be /IFR2010U/050'/86 11 used in offset printing, flexography, silkscreen printing, letter press, gravure printing and metal plate engraving. Furthermore, the covering product 20 is 5 preferably an ink chosen from among iridescent ink, an ink with variable optical effect, a magnetic ink with variable optical effect, an ink with metallic effect such as a silver-based ink and a liquid crystal ink. Furthermore, the security element 14 comprises a 10 second area Z2 which forms a second pattern 22 and is devoid of any covering product 20. This area Z2 is translucent, in other words it allows light to pass through. This second area Z2 is formed by application of a 15 transparentising product 24. The transparentising product 24 may possibly be applied beyond the second area Z2, partly on the first area Z1. More specifically, the covering product 20 prevents impregnation of the substrate 12 by the 20 transparentising product 24 in the first area Zl. For example, the transparentising product 24 is an ink with high wetting capacity, comprising monomers with low surface tension, resins and / or photoinitiators or an acrylic ink. For example, a 25 transparentising product that may be suitable comprises a composition like that described in document GB 1 489 084. The transparentising product 24 is preferably applied by silkscreen printing. As a variant, the 30 transparentising product 24 may be applied by any other known printing technique.

*1 fR2U IU/ U5U-/8b 12 The first area Z1 is referred to as a peripheral area in the remainder of the description, in opposition to the second area Z2 said to be internal because the area Z1 surrounds said to be internal second area Z2. 5 In this first embodiment, the first area Z1 has a generally oval shape and the second area Z2 is in the general shape of a flower. In the example described, the security element 14 comprises a third pattern 26 printed on the second side 10 F2 of the substrate 12. This third pattern 26 completes the image formed by the first pattern 18 and the second pattern 22. The third pattern 26 extends onto a third area Z3 of the substrate 12. This third pattern 26 is printed by positioning outside the first 15 pattern 18 and the second pattern 22. The image obtained can be observed from the two sides F1 and F2 of the substrate 12 in transmitted light and at least partly in reflected light. Preferably, the second area Z2 is made 20 sufficiently translucent to enable observation in reflected light from the two sides F1 and F2. Thus, the internal area Z2 is sufficiently translucent to enable observation of the third pattern 26 in reflected light and no longer only in transmitted 25 light from the first side F1 (as can be seen in Figure 2A). The first pattern 18 of the image resulting from application of the covering product 20 can easily be observed in reflected light from the first side F1 but 30 it is more difficult to observe from the second side F2 in reflected light.

-/FR2010/050786 13 Thus, the contrast between an area of the substrate 12 devoid of any product and the area Zi is relatively small because the substrate 12 outside the area Z2 is relatively opaque when observed from side 5 F2. The first and second areas Z1 and Z2 define a contrast between them in the image, that is inverted depending on the side F1, F2 from which the image is observed in transmitted light, and possibly also in 10 reflected light in the case in which the second internal area Z2 is sufficiently translucent. However, while the contrast is relatively sharp in observation by transmitted light from the two sides F1 and F2, the contrast is not as visible when the 15 image is observed from the second side F2 (in other words from side F2 on which there is no covering product) in reflected light. Figures 2A to 6B show second to fifth embodiments of a security document 10 comprising a security element 20 14. In these embodiments, elements corresponding to the first embodiment have similar references in the figures and in the description. These various embodiments increase the security level of the document comprising the security element. 25 In the second embodiment illustrated by figures 2A and 2B, the first area Z1 also extends partly to the centre of the second area Z2. The first area Z1 follows the contours of the second area Z2. Furthermore, in this embodiment, the third 30 pattern 26 is partly printed in the second translucent area Z2.

-/FR2010/050786 14 Preferably, the second area Z2 is made sufficiently translucent to enable observation of a third pattern 26 on side F2 in reflected light from side F1, by positioning it outside and inside the 5 second area Z2. It can be observed in reflected light from the two sides F1, F2 of the substrate 12. Figure 3 shows layers of material applied on the substrate 12 to form areas Z1, Z2 and Z3. Thus, area 10 Z1 comprises a layer of covering product 20, area Z2 comprises a layer of transparentising product 22 that impregnates the substrate 12 over its entire thickness without impregnating the substrate 12 adjacent to area Z1. Finally, area Z3 also comprises a layer of product 15 28 such as ink. In the third embodiment shown in Figures 4A, 4B, the security document 10 is a banknote. The security element 14 may for example be generally rectangular in shape forming a vertical strip in the note 10. 20 The security element 14 comprises a first peripheral area Z1 in the general shape of a strip and a second internal translucent area Z2 delimiting a second pattern 22. In the example shown in the figures, the second pattern 22 comprises twice the back-to-front 25 number "100" and a stylised sun. The area Z3 represents a third pattern 26 and comprises the number "100" the right way round, the central "0" of the number 100 forming a sun positioned to be complementary to the sun on side F1 of the substrate 12. 30 In the fourth embodiment shown in figures 5A, 5B, the third pattern 26 comprises a coded message 30 on -/FR2010/050786 15 the second side F2 and the second area Z2 comprises means 32 of decoding the message, that could reveal the coded message 30 by observation from the first side F1 at least in transmitted light. 5 In this example, it can be seen that the third pattern 26 is an encrypted message "OA" that is difficult to perceive in observation in transmitted and / or reflected light from the second side F2 of the substrate 12, with the naked eye. Conversely, in 10 observation from the first side Fl, the message 30 is revealed by see-through due to the presence of decoding means in area Z2. For example, the message 30 is coded by a known steganography technique that consists of coding 15 information in background by isolated variations, for example by lines modulated at a predefined frequency. The third pattern 26 is preferably made by offset printing. For example, the decoding means 32 comprise lines 20 modulated at a frequency approximately equal to the message dissimulation frequency. Preferably, the lines are printed and / or formed in relief. In this illustrated example, the decoding means 32 comprise a relief 31 forming a repetition of lines 25 with a predefined height and frequency approximately equal to the frequency used for coding the message. For example, this relief 31 can be made by the conventional die stamping technique. Die stamping is made and positioned relative to 30 the offset printing of the side F2 of the substrate 12 and forms a steganographic decoding pattern, capable of '/FR2010/050786 16 revealing data hidden on the second side F2 of the substrate 12. For example, the relief 31 is made by metal plate engraving with a transparent non-penetrating ink to 5 form another touch sensitive mark in the second area Z2. The transparent non-penetrating ink preferably comprises security tracers, for example fluorescent particles, reaction type particles reacting at a 10 predefined wavelength, and / or thermochromic particles. Figures 6A and 6B show a security document 10 comprising a security element 14 according to a fifth embodiment of the invention. 15 In this fifth embodiment, the third pattern 26 comprises at least a latent image 34 on the first side F1, particularly in the first area Zl. In particular, it can be seen that the letters B and C form the first 34A and second 34B latent images. 20 The third pattern 26 comprises a third latent image 34C formed on the second side F2 in the second area Z2. These latent images 34A to 34C are formed by deformation with or without ink. Conventionally, a latent image is obtained by 25 printing by metal plate engraving and is only visible at a certain inclination of the document, for example in grazing observation. Depending on the observation angle, the image appears with more or less contrast with the background. 30 In the example described, the latent images are made using a printing in relief method. The security e/ MeU.LU/ UbU'/b 17 element 14 comprises a first network of lines 36 extending along a predefined orientation and a second network of lines 38 extending along another orientation, for example oblique (as in the illustrated 5 example) or perpendicular, thus forming a sharp break between the two networks 36 and 38. For example, the second network 38 forms a pattern of the latent image that can comprise information (in this example, the information contains 10 letters B and C) and the first network 36 forms the background of the latent image. Thus, as can be seen in Figures 6A and 6B, the latent image is not seen in orthogonal observation but rather in grazing observation as shown in Figures 6C 15 and 6D in which the pattern of the latent image is clearly visible. We will now describe the main steps of a method of making a security document 10 comprising a security element 14, with reference to Figures 7 to 10. 20 The patterns of the security element 14 shown in these figures have shapes different from the patterns in the other embodiments but the manufacturing method is applicable for making the security element for any of the previously described embodiments. 25 The third pattern 26 of the image delimited by the third area Z3 on the second side F2 of the substrate 12 is formed initially, and optionally. This third area Z3 is formed by flexography printing, metal plate engraving, silkscreen printing, letter press or 30 gravure printing, but preferably by offset printing.

'/FR2010/050786 18 The third pattern 26 represents a sun inscribed inside a star. The third pattern may be printed in many colours. Then, during a second step shown in Figure 8, 5 area ZI is formed on the first side F1 of the substrate 12 by application of a covering product 20 on area Z1. This first area Z1 is oval in shape delimiting a second internal area Z2 devoid of any covering product inside it. 10 During a third step shown in Figure 9, the transparentising product 24 is applied on at least the internal area Z2 so as to impregnate the substrate 12 to make it translucent in this area. The first area Z1 and second area Z2 form a first 15 pattern 18 and a second pattern 22 respectively, that are complementary to form an image observable at least by transmitted light and preferably by reflected light from the two sides F1 and F2 of the substrate 12. Since the area Z1 comprises covering product 20 20 that prevents impregnation of the substrate 12 by the transparentising product 24, it is possible to spread significantly onto the first area Z1 during this application without this spreading being visible. During this step, when the transparentising 25 product 24 has impregnated the entire thickness of the substrate 12, the third pattern 26 appears in transmitted light or even in reflected light when observed from the first side Fl. The method also comprises a step to dry the 30 transparentising product 24 by irradiation by light in the ultraviolet or infrared spectrum or by emission of a hot air flow. The fact of applying the transparentising product 24 by spreading onto the first area Z1 only very S slightly modifies the appearance of the covering product 18 on the first side Fl. A slight modification of the golden appearance of the covering product 18 can be observed if the covering product is for example an iridescent ink. 10 Thus, it is possible that application of the transparentising product 24 on the covering product 20 will slightly tarnish its golden appearance. This also provides a means of producing additional new optical effects. 15 Obviously, the embodiments that have just been described are in no way limitative and they may be modified in any desirable way without going outside the scope of the invention. In particular, application of the 20 transparentising product using printing techniques different from those mentioned preferentially in the description will fall within the scope of the invention. It is to be understood that, if any prior art 25 publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. In the claims which follow and in the preceding 30 description of the invention, except where the context requires otherwise due to express language or necessary 4eU implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition 5 of further features in various embodiments of the invention.

Claims

1. Method for manufacturing a security element of a security document, the security element comprising 5 a substrate having a first and a second opposite faces, in which a translucent area is formed in the substrate by applying a product that transparentises the substrate, the substrate being made from a paper based material, the method including the following steps to 10 form the translucent area: (a) applying an impermeabilising product to a first area of the first face that makes the substrate impermeable, wherein the first area surrounds a second area of the first face, said second area remaining 15 devoid of the impermeabilising product, such that the impermeabilising product prevents impregnation of the substrate by the transparentising product in the first area, then (b) impregnating the second area with the 20 transparentising product to make the second area translucent, wherein the first area forms a first pattern and the second area forms a second pattern, the first and second patterns forming an image that can be observed 25 from the first and second faces of the substrate, said impermeabilising product being an iridescent ink, an ink with variable optical effect, a magnetic ink with variable optical effect, an ink with metallic effect or a liquid crystal ink. 30

2. Method according to claim 1, in which the impermeabilising product is opaque to light.

3. Method according to claim 1 or 2, in which 5 the impermeabilising product is an ink that can be used in offset printing, flexography, silkscreen printing, letter press, gravure printing and metal plate engraving. 10

4. Method according to any one of claims 1 to 3, in which the transparentising product is an ink with a high wetting capacity, for example comprising monomers with low surface tension, resins and / or photoinitiators or an acrylic ink. 15

5. Method according to claim 4, in which the transparentising product comprises security tracers, for example fluorescent particles, reaction type particles reacting at a predefined wavelength and / or 20 thermochromic particles.

6. Method according to any one of claims 1 to 5, further comprising a step of drying the transparentising product by irradiation by light in the 25 ultraviolet or infrared spectrum or by emission of a hot air flow.

7. Method according to any one of claims 1 to 6, further comprising a metal plate engraving step with a 30 transparent and non-penetrating ink or with no ink to form a touch sensitive mark in the second area.

8. Method according to claim 7, in which the transparent non-penetrating ink preferably comprises security tracers, for example fluorescent particles, 5 reaction type particles reacting at a predefined wavelength, and / or thermochromic particles.

9. Method according to any one of claims 1 to 8, in which the transparentising product is applied on the 10 substrate by silkscreen printing, flexography, offset, metal plate engraving, letter press and / or gravure printing.

10. Method according to any one of claims 1 to 9, 15 further comprising a step of forming a third pattern of the image on the second face, positioned relative to the second area such that it can be observed from the first face due to the translucence of the second area. 20

11. Method according to claim 10, in which the third pattern completes the first pattern and the second pattern to form a final image that can be observed from the first and second faces. 25

12. Method according to claim 11, wherein the third pattern comprises a coded message on the second face and the second area comprises means of decoding the message capable of revealing the coded message by observation from the first face at least in transmitted 30 light.

13. Method according to any one of claims 1 to 12, wherein the paper based material is a material essentially comprising natural and / or synthetic fibre-based paper, porous paper and / or cardboard. 5

14. Method according to any one of claims 1 to 13, wherein the second area is made sufficiently translucent to enable observation in reflected light from one of the faces of a third pattern extending on 10 the other of the faces by positioning relative to the second area.

15. Security element, wherein the security element is obtained using a manufacturing method 15 according to any one of claims 1 to 14.

16. Security document such as a banknote, comprising a security element, wherein the security element complies with claim 15. 20

17. Method for manufacturing a security element for a security document substantially as hereinbefore described with reference to the accompanying drawings. 25

18. Security element or a security document comprising a security element, substantially as hereinbefore described with reference to the accompanying drawings.