SECURITY PAPER

Description

[0001] The present invention relates to a secure sheet, in particular intended for the production of a secure document.

[0002] A "secure document" means a means of payment, such as a banknote, a check or a restaurant voucher, an identity document, such as an identity card, a visa, a passport or a driving licence, a lottery ticket, a transport ticket or an entry ticket to cultural or sporting events.

[0003] The invention relates more particularly but not exclusively to security sheets intended for the production of banknotes.

[0004] In order to protect against attempts to falsify or counterfeit a secure document, it is desirable that the authentication and / or identification of the document can be done simply.

[0005] The watermark technique is very widely used in the field of security papers and paper money in particular, where it remains the historical first level of security, identifiable and recognizable by most users of banknotes, even the man in the street.

[0006] It has already been proposed by application WO2005 / 106118 to produce a secure sheet comprising a paper substrate provided with a watermark, with openings covered by a security film affixed to one side of the substrate. The openings are made outside the watermark, and visually complete the appearance of the latter. The security film may include de-metallizations contributing to the overall observable pattern.

[0007] US8465625 discloses an opening made by papermaking, having an irregular edge with fibers protruding into the opening in a manner visible to the naked eye. This opening can contribute to forming an overall pattern by cooperating with a watermark arranged around it. The opening can be covered by a film applied to one side of the paper substrate. The production of such an opening with an irregular edge is a complex papermaking operation to master, which makes it relatively more difficult to obtain detailed, reproducible and aesthetic renderings.

[0008] Patent DE102005022018 discloses a security document having two openings, one with a regular edge and the other with an irregular edge. The regular edge opening can be incorporated into a watermark.

[0009] Patent DE102014016249 discloses a security document comprising a through opening which can be combined with a security thread or a watermark, the opening being laser cut.

[0010] The invention aims to further improve security sheets, and in particular to provide security that is easily recognizable by the man in the street and offers numerous aesthetic possibilities, while being complex for a counterfeiter to reproduce.

[0011] The invention achieves this objective by providing, according to a first of its aspects, a security sheet as described in claim 1.

[0012] By "inside the watermark" is meant the connected surface bounded by a curve following the outermost contour of the watermark. Thus, a watermark in the shape of a circular ring will define a connected surface in the shape of a disc with an outer diameter equal to that of the ring.

[0013] The opening may extend inside the watermark and may or may not overlap a watermarked area, that is, the watermark itself. Using the example of a ring watermark, the opening may be inside the watermark without overlapping it if the opening is a hole with a diameter smaller than that of the inner circle of the ring. The watermarked area is the one whose thickness is different from the thickness of the vellum. This thickness may be less than that of the vellum for a light watermark, and greater for a dark watermark.

[0014] The outline of the watermark is the one that pre-exists before the cutting is carried out.

[0015] Cutting may or may not be done through a watermarked area. When cutting is done through a watermarked area, it means that part of the watermark is removed by the cutting operation.

[0016] Making the opening(s) inside the watermark makes any possible discrepancy between the expected position of the opening and that of the watermark, linked to manufacturing tolerances, more aesthetically acceptable.

[0017] Additionally, the watermark has varying paper thickness and creating a regular edge cut within it requires a high-performance cutting tool, making counterfeiting more difficult.

[0018] The opening may have various surfaces, being less than 1 mm 2< or greater than 1 mm 2< , for example extending almost to the outer contour of the watermark in which it is made.

[0019] By "regular edge" is meant an edge without long free fibers protruding in a manner visible to the naked eye in the opening, unlike the opening obtained by papermaking disclosed in the aforementioned patent US8465625. The regular edge is preferably an edge obtained by laser cutting, and this edge can be straight, curved, wavy or indented, the wavy or toothed being the result of cutting.

[0020] The invention also relates, according to a second of its aspects, to a security sheet as described in claim 11.

[0021] Preferably, the secure document is a banknote.

[0022] Preferably, the security film comprises a plastic backing. According to the first aspect, the security film comprises a transparent plastic backing.

[0023] The area of ​​the sheet where the opening overlaps the safety film is called the "window."

[0024] The invention, according to its first and second aspects, makes it possible to further secure the document against the risks of counterfeiting by proposing a combination making it possible to observe the watermark and the united security film synchronously, either in transmitted light or in reflected light.

[0025] The security element may have, in the area of ​​the opening, front and back faces with different appearances. This may include, in particular, a difference in brightness, contrast, color and / or shade, patterns of different size, contour and / or content, and / or different patterns. This difference in appearance is observable in transmitted or reflected light, preferably in reflected light. It is then observable according to at least one observation angle given to the front and at least one observation angle given to the back. It may be observable according to at least one illumination, in particular in visible, UV or IR light, illuminating the front and at least one illumination, in particular in visible, UV or IR light, illuminating the back.

[0026] Preferably, the front and back sides have different patterns. In this way, observation can be made in a differentiated manner by an asymmetry of appearance on the front and back.

[0027] This combination advantageously compensates for the lack of visibility of the window when the associated patterns are too busy, particularly due to printing, to be immediately identifiable by the man in the street. It is indeed customary not to overload the printing at the watermark level, and in particular to deprive the watermarked area of ​​printing.

[0028] The combination of the security film with the watermark, which is spontaneously more natural when viewed in transmitted light, makes it easier to locate the window.

[0029] Furthermore, especially when the aesthetics of the patterns and optical effects carried by the window are shimmering and visible, the observer is encouraged to pay more attention to the watermark and this becomes an indirect means of reinforcing the observer's attention to its authenticity.

[0030] Another advantage that can be provided by the invention is the lasting protection of the watermark by the security film, partial or total depending on the covering of the watermark by the film and the presence or absence of another protective film, affixed to the opposite side of the paper substrate, and called “counter-foil”.

[0031] Various optical effects can be obtained at the window level in particular.

[0032] Pattern effects appearing in negative writing in transmitted light, in particular as described in application EP0319157, and called “CLEARTEXT”, can be obtained.

[0033] The optical effect present in the window may be uniform, with “CLEARTEXT” effects visible in transmitted light, and present in reflected light different patterns and / or optical effects and / or colors on each of the faces.

[0034] Alternatively, the safety film can advantageously leave a transparent surface at the opening free from any visible optical effect.

[0035] The extent of the watermark as delimited by its outer contour may be greater by a factor of at least 1.1 than the extent of said at least one opening, better still at least 1.5, even better still by a factor of at least 10 or 20.

[0036] The opening may be of small size, and in particular constitute a micro-perforation. By "micro-perforation" we mean an opening whose extent is less than or equal to 1 mm 2< .

[0037] The at least one opening may be placed in the center of the watermark or elsewhere. A central arrangement can further enhance security, requiring precise positioning.

[0038] Preferably, the aperture is positioned relative to a nominal position on the secure document with an accuracy better than + / - 3 mm in the machine direction SM (i.e. in the direction of travel of the substrate in the paper machine) and in the transverse direction ST. If necessary, the measured deviation between the expected position of the aperture relative to the watermark and the observed position is measured, and it is checked whether this deviation satisfies a predefined statistical law. If so, this can constitute an additional indicator of the authenticity of the document.

[0039] The security film comprises at least one security element overlapping at least partially with the opening. Preferably, the security film completely covers the opening. The security element may or may not completely cover the opening. The security element may be an optically variable device, in particular a diffractive device.

[0040] The outline of the security element may be homothetic to that of the opening, or alternatively, it may be arbitrary. A homothetic outline can further enhance security, being more difficult to achieve. It can also make it easier to detect incorrect positioning of the security element relative to the outline of the opening.

[0041] The security film and the security element may completely cover the opening, being in particular 5 to 20% larger than the opening.

[0042] The security element can be optically variable in the area of ​​the opening. This is, for example, an optically variable device (or OVD for optically variable device in English) such as a lenticular, Moiré, diffractive security element, in particular of the first order (laser hologram, 3D hologram, echelon grating or blazed grating in English) or zero order, or such as a thin-film interference structure, in particular monolayer or multilayer (Bragg structures, volume holograms, liquid crystals, etc.). Such a device produces different visual effects when the angle of observation or illumination varies.

[0043] The security element may be a diffractive structure, and in particular a diffractive optical element of the digital hologram type DOE as described in application WO 2014 / 119296 on page 5. When such an optical element is illuminated, in particular by a collimated beam, it generates an interference pattern producing an image in a viewing plane, which is visible on a surface positioned in this plane, or visible in transmission from this plane. Such a diffractive optical element is computer-generated, being different from so-called rainbow, Fresnel or volume reflection holograms.

[0044] The security element may have, in the area of ​​the opening, a metal layer and at least one recess therein.

[0045] The outline of said at least one opening may be substantially homothetic to that of the watermark.

[0046] The outline of said at least one opening may be homothetic to a pattern of the watermark.

[0047] The watermark may be screened and / or shaded, or otherwise, for example electrotype.

[0048] Preferably, as mentioned above, the film completely covers said at least one opening.

[0049] The film may extend in a strip from one edge to the opposite edge of the sheet. Alternatively, the film is applied as a patch extending beyond the opening, which may also be superimposed on the watermark. When the film is a patch, it extends back from at least three edges of the document; when the document is rectangular, it is better to extend back from all edges of the document.

[0050] The width of the film may be less than the width of the watermark.

[0051] The outline of said at least one opening may be reproduced elsewhere on the sheet or on the security element. This increases security by making it more difficult to reproduce the secure sheet.

[0052] Said at least one window may extend into contact with a watermarked area of ​​thickness different from the vellum thickness of the sheet, in particular an area of ​​lower thickness. This may minimize the creation of excess thicknesses.

[0053] The watermark can be without a center of symmetry.

[0054] The invention also relates to a method of manufacturing a secure sheet according to the first aspect, as described in claim 10.

[0055] The opening is preferably made using a laser, but alternatively it can be made using a punch.

[0056] When the opening is carried out with a laser, the method may include optical acquisition of the watermark area, and real-time control of the laser based on this acquisition, so as to direct the laser using the watermark as a reference, to ensure a predefined positioning of the opening within the watermark. This makes it possible to maintain the appearance of the combined pattern formed by the watermark and the opening substantially constant, while taking into account the dispersion of positioning of the watermark within the sheet resulting from the papermaking process.

[0057] The reference pattern may be present on the security film, in particular in the form of printing, metallization or demetallization, and preferably in the form of partial demetallization after metallization (hereinafter “metallization / demetallization”).

[0058] The watermark may comprise several repeating elementary patterns and said at least one opening may have the same outline as one of said elementary patterns.

[0059] As stated above, the watermark can be of any type, for example, a shaded and / or halftone watermark. The reference pattern can be alphanumeric. In this case, the watermark can be an electrotype watermark.

[0060] The film at least partially overlaps the watermark.

[0061] The film may extend outside the watermark.

[0062] The watermark may be sandwiched between two films applied on either side of it, on the front and back sides of the paper substrate. These films may or may not cover the same surface of the paper substrate, and may or may not overlap exactly. In this case, at least one of these films covers the entire surface of the paper substrate. In one example, each of these films covers the entire surface of the paper substrate.

[0063] The invention also relates, according to another of its aspects, to a secure document as described in claim 9.

[0064] The secure sheet, or the document obtained from it, in particular the banknote, may include one or more additional security elements as defined below.

[0065] Some of these additional security features are detectable by eye, in daylight or artificial light, without the use of any special equipment. These security features include, for example, colored fibers or planchettes, printed or fully or partially metallized threads. These security features are called first-level security features.

[0066] Other types of additional security features are detectable only using a relatively simple device, such as a lamp emitting in the ultraviolet (UV) or infrared (IR) range. These security features include, for example, fibers, planchettes, strips, threads, or particles. These security features may or may not be visible to the naked eye, for example, being luminescent under illumination from a Wood lamp emitting at a wavelength of 365 nm. These security features are called second-level security features.

[0067] Other types of additional security features require a more sophisticated detection device for their detection. These security features are, for example, capable of generating a specific signal when subjected, simultaneously or not, to one or more external excitation sources. Automatic signal detection allows the document to be authenticated, if necessary. These security features include, for example, tracers in the form of active materials, particles or fibers, capable of generating a specific signal when these tracers are subjected to optronic, electrical, magnetic or electromagnetic excitation. These security features are called third-level security features.

[0068] The additional security element(s) present on and / or within the security sheet, in particular the security film and / or the paper substrate, may have first, second or third level security features.

[0069] Described but not claimed is a method for authenticating a secure sheet or a secure document, as defined above, in which at least one face of the sheet is observed in reflected light and in transmitted light, and information concerning the authenticity of the document is generated from this observation. In particular, the front and back faces can each be observed in reflected light and in transmitted light and said information generated from this observation. The observation can be made in the window. An overall pattern formed by the watermark, the opening(s) and at least one element of the security film can be compared with a reference pattern appearing elsewhere on the sheet or the document, this reference pattern being for example printed, formed by metallization and / or demetallization or by a hologram.

[0070] The invention may be better understood by reading the detailed description which follows, non-limiting examples of its implementation, as well as by examining the attached drawing, in which: there figure 1 represents an example of a secure document according to the invention, observed on the back side, the figure 2 represents the document of the figure 1 , observed on the front side, the figure 3A represents the watermark of the document figures 1 et 2 during the production of the secure sheet, before making the openings, the figure 3B represents the watermark of the figure 3A after completion of the openings, the figures 4A à 4C illustrate different stages of the production of a variant of security sheet according to the invention, the figures 5 And 6 represent an example of a secure document, observed respectively on the back and front sides, the figures 7A et 7B illustrate different stages of the production of the document sheet according to the figures 5 And 6 , there figure 8 represents another example of a secure document, and the figures 9A à 9D respectively represent a secure document according to an alternative implementation of the invention, observed respectively on the back in reflection, on the front in reflection, on the back in transmission and on the front in transmission.

[0071] We have represented at the figures 1 et 2 a first example of a secure document 1 produced in accordance with the invention.

[0072] This document 1 is for example a banknote, and may have a rectangular shape.

[0073] Document 1 comprises a paper substrate 10 having a watermark 11, which may be of any type.

[0074] This watermark 11 is represented in isolation at the figure 3A , in the appearance it may take after the manufacture of the paper substrate 10.

[0075] According to one aspect of the invention, the document 1 comprises at least one opening 12 made in the substrate 11.

[0076] This opening 12 is preferably made by cutting with a laser, which makes it possible to obtain a cut with a regular edge.

[0077] In the example considered, two openings 12 each in the shape of a star are thus made through the watermark 11, during the production of the document 1, as illustrated in figure 3B .

[0078] These openings 12 are located set back from the outer contour 13 of the watermark 11, being for example at a minimum distance d from this non-zero contour, for example greater than or equal to 3 mm.

[0079] To produce the opening(s) 12, the laser cutting installation may include an optical device for locating the watermark on the paper substrate, so as to use this watermark as a spatial reference for producing the opening(s). This makes it possible to take into account the positioning tolerances of the watermark on the sheet plane, which are unavoidable due to the manufacturing process thereof. The optical device comprises, for example, at least one camera filming the sheet and a computer for analyzing the image and recognizing the watermark. Then, the computer can control the laser to produce the opening(s) in a predefined area of ​​the watermark.

[0080] In accordance with the invention, the secure document 1 also comprises at least one film 15 applied to the paper substrate 10. This film 15 may be in the form, as illustrated, of a strip extending from one edge of the document to the opposite edge.

[0081] The film 15 may comprise a support made of thermoplastic material, such as PET for example. Preferably, the material of the support is transparent.

[0082] The film 15 carries at least one security element 20, in the form of at least one pattern formed by metallization / demetallization for example or alternatively by printing. In the example illustrated, the film 15 comprises two security elements 20 each in the form of a star produced by metallization / demetallization. The pattern of the security element 20 may correspond to the shape of the opening, for example to within a homothety. In particular, the security element may have a size greater than that of the opening 12 on which it is superimposed. Thus, in the event of a positioning tolerance of the film 15 relative to the opening 12, the security element 20 continues to fully close the opening, as illustrated.

[0083] The film 15 comprises a transparent region 21 in which the security element(s) 20 are produced, the film 15 being metallized, or alternatively printed, outside this region 21 in areas 22 not superimposed on the watermark 11. The area 21 is for example formed by demetallization of a layer of metal deposited on the film 15, for example by vacuum metallization or galvanic deposition. Alternatively, the area 21 can be obtained by printing. The two techniques can also coexist within the same film 15.

[0084] The film 15 is fixed to the paper substrate by an adhesive, heat-activated for example. It is for example applied by heat transfer.

[0085] Preferably, the film 15 is fixed after the openings 12 have been made.

[0086] The film 15 may have a sufficient width to allow it to completely cover the openings 12, as illustrated. The minimum distance k between the edge of an opening and the edge of the film 15 is preferably non-zero, in particular to ensure strength of the assembly, and for example greater than or equal to 3 mm.

[0087] The width of the film 15 ranges for example from 5 to 20 mm.

[0088] The film 15 at least partially covers the watermark. In the illustrated example, the covering is partial, the watermark overflowing on each side of the film 15.

[0089] It is useful for the film 15 to maintain a certain transparency in its region 21 which overlaps the watermark 11, so as not to affect the visibility of the latter in transmitted light.

[0090] In the area of ​​the opening(s) 12, the film may comprise a first-level security element as just described, formed by printing or by metallization / demetallization. Alternatively, the security element is diffractive, for example being made so as to produce an image when illuminated by a beam of light such as a laser beam. In one alternative, the film comprises a security element superimposed on the opening which is a second-level security.

[0091] When the secure document is viewed in reflected light from the reverse side, as in the figure 1 , the security elements 20 can be seen through the openings 12.

[0092] Areas 22 of film 15 are masked by the paper substrate. Watermark 11 is faintly visible. In transmitted light, watermark 11 becomes more visible.

[0093] When the secure document 1 is observed in reflected light on the front side, it can be seen as illustrated in figure 2 the areas 22 of the film 15 as well as the security elements 20. The openings 12 are masked by the security elements 20. The watermark 11 is weakly visible, but becomes more visible in transmitted light.

[0094] In variants not shown, the secure document 1 comprises a second film which covers the paper substrate on the side opposite the film 15. This can make it possible to improve the protection of the openings 12.

[0095] It has been represented on the figures 4A à 4C different stages of the production of a secure document variant 1.

[0096] On the figure 4A , we see a watermark 11 produced in the paper substrate 10 of the document. This watermark 11 is for example formed by the juxtaposition of a screened watermark 11a and a shaded watermark 11b.

[0097] There figure 4B illustrates the creation of an opening 12 within this watermark 11, at a distance from the edges of the watermark 11a.

[0098] A safety film 15 is attached to the paper substrate 10, as illustrated in the figure 4C This film 15 comprises a security element 20 which is positioned on the document so as to overlap with the opening 12 and at a distance from the edge thereof, so as to provide a margin 24 as illustrated.

[0099] The security element 20 may have a pattern formed by metallization / demetallization or by printing, or even by a combination of these two techniques, the outline of which has a link with that of the opening 12, for example is homothetic to it as illustrated.

[0100] The security element 20 may have text appearing in negative writing, for example letters as illustrated.

[0101] We can also observe on the figure 4C that the film 15 may have a transparent region 21 whose contour 26 matches that of the watermark 11, for example by leaving a gap 27. The transparent region 21 is for example formed by demetallization of the film 15. The zones 22 of the film 15 located on either side of the transparent region 21 may be opaque, being for example metallized, and may have patterns 29 in negative writing, for example the letters of the word “africa” in the example illustrated.

[0102] It has been represented on the figures 5 And 6 a secure document 1 containing a watermark 11 in the shape of a flower.

[0103] This watermark 11 is represented in isolation at the figure 7A .

[0104] Document 1 comprises an opening 12, for example in the shape of a hexagon, made in the central part of the watermark 11, as illustrated in figure 7B This opening 12 is preferably made by laser cutting, like the previous examples.

[0105] Document 1 includes a security film 15, which has as shown in the figure 6 a transparent region 21 with a security element 20 formed for example by printing or by metallization / demetallization of the film 15. This security element 20 has for example a contour homothetic to that of the opening 12, preferably being of larger dimensions.

[0106] The security element 20 advantageously complements, aesthetically and conceptually, the watermark 11, as can be seen in the figure 6 .

[0107] The security element 20 is visible through the opening 12 on the reverse side, as illustrated in the figure 5 .

[0108] On the figure 8 a secure document 1 is shown comprising an electrotype watermark 11, representing an alphanumeric pattern for example, for example the term "security" and an opening 12 made by laser, completing the pattern of the watermark 11, for example the letter "A". The watermark 11 and the opening 12 fully reproduce a reference sign 60 which appears elsewhere on the document 1, in this case "A security". A security film 15 is laminated onto the paper substrate 10 and covers the opening 12.

[0109] This film 15 can provide various optical effects to the document, such as a holographic, iridescent, metallic effect, etc. On the front side, the pattern of the opening 12 can thus appear with the effect provided by the security film 15.

[0110] We will now describe with reference to the figures 9A à 9D another example of a secure document 1 made in accordance with one aspect of the invention.

[0111] This document 1 comprises a paper substrate 10 provided with a watermark 11 which represents, for example, a frangipani flower and a butterfly.

[0112] An opening 12 is made through the watermark 11, preferably by laser cutting. This opening 12 completes or matches the contour of a part of the pre-existing watermark 11, in this case a petal of the flower.

[0113] The document 1 comprises a security film 15 which covers the watermark 11. This film 15 comprises a transparent region 21 whose contours substantially match the shape of the watermark 11, except in the opening 12 where the edge 30 of the transparent region may have, as illustrated, a shape which follows that of an opposite edge 31 of the opening 12, thus providing a transparent window 32 through the opening 12 between the edge 30 and the edge 31.

[0114] Film 15 is narrower than watermark 11 but wider than aperture 12, as illustrated, completely covering it.

[0115] A reference pattern 35 repeating that of the watermark 11 or a part of it, in this case the flower, may appear on the film 15. This reference pattern 35 may be produced by demetallization of a metallized region of the film 15 or by negative printing on the film 15.

[0116] Another pattern 40, for example reproducing identically or conceptually another part of the watermark, in this case the butterfly, can be reproduced elsewhere on the security film, for example by demetallization also, for example on the opposite side of the reference pattern 35 with respect to the watermark 11. On the figure 9A , we see the document 1 in reflection on the back. The watermark 11 is faintly visible. The film 15 is masked by the paper substrate 10. The region 22 of the film 15, for example metallized, is visible through the opening 12.

[0117] In transmitted light, as shown in figure 9C , the watermark 11 becomes clearly visible, as do the text or other patterns 35 and 40 in negative writing produced by demetallization of the film 15. The transparent window 32 becomes very bright.

[0118] Front side, in reflection, as illustrated in the figure 9B , the watermark 11 is faintly visible, as is the window 32. The film 15 is perfectly visible, and may present, for example, a metallic reflection effect, diffractive elements or a variable color depending on the angle of observation or illumination.

[0119] In transmitted light, as shown in figure 9D, window 32 becomes perfectly visible, as do watermark 11 and text and other motifs 35 and 40 in negative writing. The image created by the combination of the watermark and the opening, which recomposes a flower, can be compared to the reference motif 35; in an authentic document, the recomposed motif is identical in appearance or sufficiently close to that of the reference motif to be considered identical by the observer.

[0120] Of course, the invention is not limited to the examples which have just been described.

[0121] For example, one or more small openings, for example of an area less than or equal to 1 mm 2< , can be made through the watermark, then constituting one or more micro-perforations. Preferably, the security film is superimposed on at least one of these micro-perforations and has in the superposition zone a diffractive security element, allowing when a beam of light, in particular laser, is sent through the opening to generate an image by projection. Such a diffractive security element is described in application WO2014 / 199296. Alternatively, the security film is transparent in its zone which is superimposed on the micro-perforation.

[0122] The security film may still include a diffractive element that is superimposed on a larger opening in the paper substrate.

[0123] Security film may contain various security features, which may or may not have the same appearance on the front and back of the film. For example, security film may have different colored metallizations on its front and back sides.

[0124] The security film may have micro-reliefs created, for example, by embossing the plastic support of the film, and these micro-reliefs may be metallized where appropriate.

[0125] The security film can be in the form of a patch or as a variant of a film completely covering one side of the paper substrate.

[0126] Two plastic films, at least one of which is a security film, may cover the substrate on both sides and sandwich the opening(s) made through the paper substrate. In this case, these two films cover the entire surface of each side of the sheet.

[0127] The aperture may be given any shape, including polygonal, non-polygonal, alphanumeric, reproducing the shape of a watermark pattern or a pattern appearing elsewhere on the document or security film, for example a pattern printed on the paper substrate. The outline of the aperture may reproduce the shape of a country.

[0128] The invention makes it possible to bring together in a single limited area of ​​the document various securities, through the presence of the watermark, the opening and the security film, leaving more space on the document for security prints and other associated security elements.

[0129] The security film may comprise a lenticular array. This array may comprise microlenses cooperating with micro-patterns to form an image whose appearance varies with the direction of observation.

[0130] The lenticular grating may or may not be present in the area of ​​the film overlapping the aperture. For example, the lenticular grating is present on the film both in an area overlapping the aperture and elsewhere; alternatively, the lenticular grating is present only in the area of ​​the aperture, and the associated effect can be observed through the aperture.

[0131] The area(s) of the film bearing the lenticular network may complete the watermark pattern.

[0132] The expression "comprising a" must be understood in its usual sense as being synonymous with "comprising at least one", unless otherwise specified.

Claims

1. Security sheet, comprising: - at least one paper substrate (10), - at least one watermark (11) produced in the paper substrate (10), this watermark having an exterior outline (13), - at least one aperture (12) of regular edge, produced by ablation of the paper substrate, - at least one security film (15) that comprises a carrier made of transparent plastic material and that is at least partially superposed on the watermark (11) and on the aperture (12), the security film (15) being transparent in the region (21) superposed on the watermark (11), sheet characterized in that said at least one aperture (12) lies inside the watermark (11), such as bounded by its exterior outline, the security film (15) comprising at least one security element (20) that is at least partially superposed on the aperture (12), the width of the film (15) being smaller than the width of the watermark (11).

2. Security sheet according to Claim 1, the extent of the watermark (11) such as bounded by its exterior outline (13) being greater than the extent of said at least one aperture (12) by a factor at least equal to 1.1, better still at least equal to 1.5, and even better still at least equal to 10 or 20, said at least one aperture (12) especially being placed at the centre of the watermark (11).

3. Sheet according to either one of the two preceding claims, the outline of the security element (20) being homothetic with that of the aperture (12) and / or the security element (20) entirely covering the aperture, and especially being of extent greater by 5 to 20% with respect to the extent of the aperture, and / or the security element (20) being optically variable in the region of the aperture (12) and / or the security element (20) being an optically variable device, especially a diffractive device and preferably a DOE digital hologram and / or the security element (20) comprising, in the region of the aperture, a metal layer and at least one void therein and / or the security element having, in the region of the aperture, front and back faces of different appearances.

4. Sheet according to any one of the preceding claims, the outline of said at least one aperture (12) being substantially homothetic with that of the watermark (11) and / or the outline of said at least one aperture being homothetic with a pattern of the watermark.

5. Sheet according to any one of the preceding claims, the watermark (11) being stippled and / or shaded.

6. Sheet according to any one of the preceding claims, the film (15) entirely covering said at least one aperture (12) and / or the film extending in a strip from one edge to the opposite edge of the sheet or being applied in the form of a patch that covers the aperture and more.

7. Sheet according to any one of the preceding claims, the outline of said at least one aperture (12) being reproduced elsewhere on the sheet or on the security element and / or said at least one aperture (12) making contact with a watermarked region of thickness different from the thickness of the unwatermarked sheet.

8. Sheet according to any one of the preceding claims, the watermark (11) being without centre of symmetry and / or the watermark (11) being sandwiched between two plastic films.

9. Security document (1), especially a banknote, comprising a sheet such as defined in any one of the preceding claims.

10. Process for manufacturing a sheet according to any one of Claims 1 to 8, comprising steps consisting in producing a watermarked sheet of paper comprising at least one watermark, in cutting at least one aperture of regular edge in this watermark, especially using a laser or a die-cutter, and in at least partially obturating said aperture with a security film that also covers the watermark, the security film being transparent in the region (21) superposed on the watermark (11).

11. Security sheet, comprising: - at least one paper substrate, - at least one representation of a reference pattern (60; 35), taking the form of a print, of a metallization / de-metallization or of a hologram, - at least one watermark (11) produced in the paper substrate, this watermark representing said reference pattern (60; 35) in an incomplete form, - at least one aperture (12) of regular edge, produced by ablation of the paper substrate, this aperture completing the watermark and reproducing therewith the appearance and / or meaning of the reference pattern when the sheet is observed in transmitted light, - at least one security film that is at least partially transparent or translucent, this film being at least partially superposed on the aperture and at least partially on the watermark (11), the security film (15) being transparent in the region (21) superposed on the watermark (11).

12. Sheet according to Claim 11, the reference pattern (35) being present on the security film and / or the reference pattern (35) being present in the form of a demetallization.

13. Sheet according to either of Claims 11 and 12, the watermark comprising a plurality of repeating elementary patterns and said at least one aperture having the same outline as one of said elementary patterns, the watermark especially being a shaded and / or stippled watermark.

14. Sheet according to one of Claims 11 to 13, the reference pattern (60) being alphanumeric and / or the watermark being an electrotype watermark.

15. Sheet according to any one of Claims 11 to 14, the film (15) being at least partially superposed on the watermark and / or the film (15) extending beyond the watermark (11).