AU2010247266A1

AU2010247266A1 - Method of manufacturing a security element for a security document

Info

Publication number: AU2010247266A1
Application number: AU2010247266A
Authority: AU
Inventors: Xavier Borde; Julien Gillot
Original assignee: Oberthur Technologies SA
Current assignee: Oberthur Fiduciaire SAS
Priority date: 2009-05-13
Filing date: 2010-04-26
Publication date: 2011-12-08
Anticipated expiration: 2030-04-26
Also published as: CA2761781C; AU2010247266B2; CA2761781A1; BRPI1012206A2; EP2429825A1; FR2945551B1; ZA201108805B; EP2429825B1; WO2010130910A1; CN102448730B; RU2011150515A; RU2530419C2; FR2945551A1; CN102448730A; PL2429825T3

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

/FR20lU/ bU'/Ub 1 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, in other words that comprises an image that can be observed in transmitted light, or even reflected light 10 in a translucent area of a substrate of the security element. In the field of valuable documents, and particularly bank notes, it is known that one or several security elements of a varied nature can be 15 added in order to protect these documents from counterfeit. There are different types of security elements, particularly including "first level" security elements. Conventionally, a first level security element is 20 difficult to make while remaining easily identifiable by anyone, simply by looking at it carefully. A see-through type security element comprises a substrate on which complementary patterns are printed on each side, arranged in an approximately translucent 25 or even transparent area of the substrate, positioning one relative to the other so as to form a final composition that can be observed in transmitted light or even in reflected light when the area is sufficiently translucent. The translucent area 30 enabling through vision is frequently called "see through", and for example is made by local /FR2010/050786 2 modifications to paper properties during manufacturing (fibre density, grammage, etc.). In particular, it is known that the translucent area can be formed by the application of a product that 5 makes the substrate transparent. In particular, the state of the art includes a 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 10 composition that makes the area transparent. The disadvantage of this technique is that wetting of the substrate gives a greasy and tacky appearance that spoils the aesthetics of the security document even after drying. 15 The transparentising composition also tends to migrate to the surface of the substrate which makes the translucent area look deformed and irregular, like an ugly stain. The purpose of the invention is to overcome this 20 disadvantage by disclosing a method of making a security element comprising a substrate with a particularly aesthetic translucent area, while remaining very simple and inexpensive to implement. To achieve this, the purpose of the invention is 25 a method for manufacturing a security element for a security document, the security element comprising a substrate delimiting first and second opposite sides, in which a translucent area is formed in the substrate by applying a product that transparentises the 30 substrate, characterised in that the method includes the following steps to form this translucent area: /FR2010/050786 3 - a first step to apply a product that makes the substrate impermeable on a first area of the first side surrounding a second area of the first side devoid of this impermeabilising product, the impermeabilising 5 product preventing impregnation of the substrate by the product that makes the area transparent in the first peripheral area, then - a second step to apply the transparentising product on at least the second area so as to impregnate 10 the substrate to make it translucent in this area, the first and second areas forming first and second patterns respectively forming an image that can be observed from the two sides of the substrate. The first area forms a peripheral border around 15 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 translucent or even transparent. 20 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. The contour of the translucent area may then be 25 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 30 area, and secondly prevents this transparentising product from migrating in the substrate close to the -/FR2010/050786 4 first area. This has the effect of reducing the blurred aspect of the stain. An impermeabilising product is a product that is impermeable to a liquid at least for a given time. 5 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 area for a predefined time, after which the efficiency 10 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 substrate. 15 Preferably, the impermeabilising product is a product that is opaque to light and is thus a "covering" product. In both cases, the two areas together form a contrasting image due to the presence of two distinct 20 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 area corresponding to the translucent area containing 25 the transparentising product. 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 30 second side so as to form the second pattern on the second side.

'/FR2010/050786 5 Thus, the second pattern can be observed perfectly from the second side in transmitted or reflected light. This second pattern stands out from the uniform substrate particularly due to its 5 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 appears more opaque on the second side adjacent to this 10 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 side thus corresponds to the negative of the image that 15 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 areas together define a contrast in the image that is 20 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 visible than the second pattern and this contrast is 25 inverted by observation from the second side (referred 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 30 (due to impregnation of the entire thickness of the substrate).

-/FR20l0/05078b 6 Preferably, the impermeabilising product is an ink that can be used in offset printing, silkscreen printing, flexography, letter press, gravure printing and metal plate engraving. 5 Preferably, the impermeabilising product is an ink selected from among an iridescent ink, an ink with variable optical effect, a magnetic ink with variable optical effect, an ink with metallic effect for example such as a silver-based ink and a liquid crystal ink. 10 Preferably, 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. Obviously, the efficiency of impregnation of the 15 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 when it dries) but also on the nature of the substrate 20 (fibre impregnation capacity, grammage, surface calendering, porosity, etc.). Preferably, the transparentising product comprises security tracers, for example fluorescent particles, particles with a reaction at a predefined 25 wavelength and / or thermochromic particles. Optical effects and additional securities can thus be obtained due to the presence of such particles. Preferably, the method comprises a step to dry the transparentising product by irradiation under light 30 in the ultraviolet or infrared spectrum or by the '/FR2010/050786 7 emission of a hot air flow. Thus, due to drying, the transparentising product is fixed onto the substrate. Preferably, the substrate is made from a material essentially comprising natural and / or synthetic 5 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 ink to form a touch-sensitive mark in the second area. 10 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 to the touch, unlike the case in which the substrate is 15 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. Preferably, the transparent non-penetrating ink 20 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 particles react to exposure to light in the ultraviolet 25 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. Preferably, the transparentising product is 30 applied on the substrate by silkscreen printing, /FR20l0/050786 8 flexography, offset, metal plate engraving, letter press and / or gravure printing. Furthermore, the method preferably comprises a step to form a third pattern of the image on the second 5 side of 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 10 the other patterns. Preferably, the third pattern completes 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. Preferably, the second internal area is 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 25 by 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.

/FR2010/050786 9 Another purpose of the invention is a security element, characterised in that 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 '/FR2010/050786 19 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 Zl only very 5 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. 25

Claims

1. Method for manufacturing a security element (14) for a security document (10), the security element 5 (14) comprising a substrate (12) delimiting first (Fl) and second (F2) opposite sides, in which a translucent area (Z2) is formed in the substrate (12) by applying a product (24) that transparentises the substrate (12), characterised in that the method includes the following 10 steps to form this translucent area (Z2): - a first step to apply a product (20) that makes the substrate (12) impermeable on a first area (Z1) of the first side (Fl) surrounding a second area (Z2) of the first 15 side (Fl), devoid of this impermeabilising product (20), the impermeabilising product (20) preventing impregnation of the substrate (12) by the transparentising product (24) in the first area (Z1), then 20 - a second step to apply the transparentising product (24) on at least the second area so as to impregnate the substrate (12) to make it translucent in this area (Z2), the first area (Zi) and the second area (Z2) forming the 25 first pattern (18) and the second pattern (22) respectively forming an image that can be observed from the two sides (Fl, F2) of the substrate (12).

2. Method according to the previous claim, in 30 which the impermeabilising product is opaque to light. /FR2010/050786 21

3. Method according to claim 1 or 2, in which the impermeabilising product (20) is an ink that can be used in offset printing, flexography, silkscreen printing, letter press, gravure printing and metal 5 plate engraving.

4. Method according to any one of the previous claims, in which the impermeabilising product (20) is an ink chosen from among an iridescent ink, an ink with variable optical effect, a magnetic ink with variable 10 optical effect, an ink with metallic effect and a liquid crystal ink.

5. Method according to any one of the previous claims, in which the transparentising product (24) is an ink with a high wetting capacity, for example 15 comprising monomers with low surface tension, resins and / or photoinitiators or an acrylic ink.

6. Method according to the previous claim, in which the transparentising product (24) comprises security tracers, for example fluorescent particles, 20 reaction type particles reacting at a predefined wavelength and / or thermochromic particles.

7. Method according to any one of the previous claims, comprising a step to dry the transparentising product (24) by irradiation by light in the ultraviolet 25 or infrared spectrum or by emission of a hot air flow.

8. Method according to any one of the previous claims, comprising a metal plate engraving step with a transparent and non-penetrating ink or with no ink to form a touch sensitive mark in the second area (Z2). 30

9. Method according to the previous claim, in which the transparent non-penetrating ink preferably '/FR2010/050786 22 comprises security tracers, for example fluorescent particles, reaction type particles reacting at a predefined wavelength, and / or thermochromic particles. 5 10. Method according to any one of the previous claims, in which the transparentising product (24) is applied on the substrate (12) by silkscreen printing, flexography, offset, metal plate engraving, letter press and / or gravure printing.

10

11. Method according to any one of the previous claims, comprising a step to form a third pattern (26) of the image on the second side (F2), positioned relative to the second area (Z2) so that it can be observed from the first side (Fl) due to translucence 15 of the second area (Z2).

12. Method according to the previous claim, in which the third pattern (26) completes the first pattern (18) and the second pattern (22) to form a final image that can be observed from the two sides 20 (Fl, F2).

13. Method according to the previous claim, in which the third pattern (26) comprises a coded message (30) on the second side (F2) and the second area (Z2) comprises means (32) of decoding the message capable of 25 revealing the coded message (30) by observation from the first side (Fl) at least in transmitted light.

14. Method according to any one of the previous claims, in which the substrate (12) is made from a material essentially comprising natural and / or 30 synthetic fibre-based paper, porous paper and / or cardboard. /FR2010/050786 23

15. Method according to any one of the previous claims, in which the second area (Z2) is made sufficiently translucent to enable observation in reflected light from one of the sides (Fl) of a third 5 pattern (26) extending on the other of the sides (F2) by positioning relative to the second area (Z2).

16. Security element (14), characterised in that it is obtained using a manufacturing method according to any one of the previous claims. 10

17. Security document (10) such as a banknote, comprising a security element (14), characterised in that the security element (14) complies with the previous claim.