Security document and system for checking the security document

Abstract

A security document (1) having a transparent window (2) comprising UV fluorescent inks (3, 3 ') and UV absorbing ink (4), characterised by that the UV absorbing ink (4) is positioned in a part of the transparent window (2), the first UV fluorescent ink (3) being positioned between the surface of the first side (A) of the transparent window (2) and the UV absorbing ink (4), the second UV fluorescent ink (3' ) is positioned between the surface of the second side (B) of the transparent window (2) and the UV absorbing ink (4) in such a way that the first and second UV fluorescent inks (3, 3' ) are positioned opposite each other on the part of the transparent window (2) not covered by the UV absorbing ink (4), and another part of the first and second UV fluorescent inks (3, 3' ) are positioned opposite each other on the part covered by the UV absorbing ink (4).

Description

[0001] Security document and system for checking the security document

[0002] The field of the invention

[0003] The present invention relates to security documents having a transparent window, which transparent window has UV- f Increscent properties .

[0004] The state of the art

[0005] Security documents must be equipped with security elements to make it di f ficult or prevent their forgery . The essence of the security elements is that the creation of imitations of the documents with them is impossible or requires special expertise and equipment . At the same time , it is advantageous i f the existence , originality and / or integrity of the security elements can be easily checked with the naked eye or with an easily accessible and easy-to-use device .

[0006] Patent document WO2022189815 Al describes a security document that includes a UV absorbing material in a window transparent to visible light . During the security document check, a UV fluorescent surface is placed behind the document and the transparent window is illuminated with UV light . In the part where the UV absorbing material is applied, UV light cannot pass through and a shadow appears on the UV fluorescent surface behind the window . Therefore , a UV light source and a UV fluorescent surface are needed for the control .

[0007] Patent document EP3317114 Bl describes a security document comprising a UV absorbing layer in a window transparent to visible light and a fluorescent ink over the UV absorbing layer . The security document is checked by illuminating both sides of the window separately with UV light , measuring the intensity of the fluorescent light produced by the instrument and comparing the measured values with a reference . This requires a UV light source , a detector capable of measuring fluorescence light intensity and a reference material .

[0008] Patent document EP1719637 Bl describes security documents that have a window that is transparent to visible light , which includes a UV absorbing material and a fluorescent ink over the UV absorbing layer . During the security document check, one side of the window is illuminated with UV light , revealing the fluorescent-coated area on that side , while the other side is illuminated with UV light , revealing the fluorescent-coated area on the other side . A single UV light source is therefore needed to check the document , but i f a multi-colour fluorescent pattern is to be displayed in the window, the individual colours must be printed in precise alignment with each other and the window, and in the case of a document with multiple layers , the layers must be very precisely aligned .

[0009] This is necessary because the colours of a multi-colour design on a single page are always printed separately on a single layer or printed on separate layers , and without accurate alignment the desired design will be distorted by overlapping ( getting over each other ) or getting too far from each other ( creating a gap in the design) .

[0010] It follows from the above that a security document is needed whose authenticity can be easily veri fied and the security element placed on it can be produced without the need for precise adj ustments .

[0011] Brief description of the invention It is the obj ect of the present invention to provide a security document free from disadvantages according to the state of the art .

[0012] The present invention is based on the recognition that by applying a UV absorbing print on one layer of a transparent window of a security document with a window transparent to visible light , and simple UV fluorescent prints on other layers of the window, the correct choice of the colour and fluorescence intensity of the UV fluorescent prints and the correct pattern of the UV absorbing print in the window, without precise alignment , will produce a multi-coloured fluorescent image on both sides of the window, which can be easily checked with a UV light source .

[0013] In view of the above , the present invention relates to a security document having a transparent window comprising UV fluorescent inks and UV absorbing inks , and characterised in that the UV absorbing ink is disposed on one part of the transparent window, the first UV fluorescent ink being disposed between the surface of the first side of the transparent window and the UV absorbing ink, the second UV fluorescent ink is positioned between the surface of the second side of the transparent window and the UV absorbing ink in such a way that a part of the first and second UV fluorescent inks are positioned opposite each other on the part of the transparent window not covered by the UV absorbing ink and another part of the first and second UV fluorescent inks are positioned opposite each other on the part of the transparent window covered by the UV absorbing ink .

[0014] The preferred embodiments of the invention are defined in the sub-claims . The invention also relates to a system for checking the security document , the system containing the above security document and a UV light source .

[0015] The invention is further described in detail with reference to the accompanying figures , which illustrate a preferred embodiment of the security document according to the invention .

[0016] In the figures

[0017] Figure 1 shows : a front view of side A of a preferred embodiment of the security document according to the invention;

[0018] Figure 2 shows : a cross-sectional view of a preferred embodiment of the security document according to the invention;

[0019] Figure 3 shows : a front view of another preferred embodiment of the security document according to the invention, illuminated by a UV light source , from the front (A) and back (B ) ;

[0020] Figure 4 shows : a cross-sectional view of a preferred embodiment of the security document according to the invention, comprising two UV absorbing inks and three UV fluorescent inks .

[0021] Detailed description of the invention

[0022] The essence of the security document according to the invention is that the security document comprises a transparent window, on one layer of which transparent window ( typically, but not exclusively, on the inside ) a UV absorbing ink of some form is applied, further, between the UV absorbing ink and the outer surfaces of the security document , di f ferent UV fluorescent inks are printed on one layer on each side of the transparent window, such that the part of the transparent window not covered by the UV absorbing ink and the part covered by the UV fluorescent ink are at least partially covered, and the UV fluorescent inks are at least partially covered each other in the plane of the security document. The resulting security element can be easily checked with a UV light source, because it will be illuminated by UV light in different colours on the parts covered by the UV absorbing ink and on the parts where the UV fluorescent inks are overlapping .

[0023] In the context of the present invention, the term "transparent" is understood to mean translucent to visible light, unless the light to which the term "transparent" is applied is explicitly mentioned. For example, by transparent window we mean that said window is translucent, i.e. transparent, to visible light, but this is not necessarily true for other lights, e.g. UV light

[0024] In the context of the present invention, a security document means any document, or paper that physically exists and that the counterfeiter could benefit from the forging, such as identity documents, passports, travel passes, concert tickets, airline tickets, bank notes, etc.

[0025] In the context of the present invention, a transparent window is that part of the security document that is substantially transparent to visible light, i.e., the part of the security document that is transparent to visible light can be seen through the security document under normal lighting conditions (e.g., natural daylight) . A security document may have more than one transparent window. When we talk about a transparent window, we mean a part of the document that is not limited to visible light by a non-transparent layer. In the context of the present invention, UV fluorescent ink means an ink containing a UV fluorescent substance which is colourless in visible light due to the transparent window required for the operation of the security element , i . e . an ink which emits light when exposed to UV light but is colourless in visible light .

[0026] In the context of the present invention, the plane of the security document is understood to be the plane substantially parallel to the first and second substantially parallel outer surfaces (A, B ) of the security document .

[0027] In the context of the present invention, the surface of the security document is understood to be the outer boundary of the outermost layer of the security document , i . e . , the layers on the security document are located below the surface of the security document .

[0028] In the context of the present invention, a directed light source is understood to be a light source having an angle of incidence of up to 45 ° , preferably up to 20 ° . Such light sources have a higher luminous intensity, so that the fluorescent light emission induced by UV light will be stronger .

[0029] In the context of the present invention, the term " light di f fraction" is used to refer to a layer on a security document , used primarily for security purposes , which is designed to break down the incident composite light into its components ( colours ) and reflect the broken down light in speci fic, di f ferent directions in space . A particularly useful form of this from a security point of view is the Di f fractive Optically Variable Imaging Device ( DOVID) , which breaks up and reflects light in such a way that the observer perceives some meaningful image .

[0030] In the context of the present invention, anti-Stokes pigments are pigments that emit radiation at a lower wavelength, typically but not exclusively visible , upon excitation at a higher wavelength, typically but not exclusively infrared .

[0031] In the context of the present invention, infrared fluorescent pigments are those pigments that emit higher wavelengths of infrared radiation upon excitation at lower wavelengths , typically, but not exclusively, visible .

[0032] In the context of the present invention, iridescent pigments are pigments that transmit the light falling on them in a predominant way ( transparent ) , but reflect a small part of it partially by splitting it into colours .

[0033] In the context of the present invention, metallic luster pigments are pigments that reflect light ( similar to metallic surfaces ) in a directed manner .

[0034] In the context of the present invention, pigments of varying colours depending on the direction of illumination and perception are pigments that reflect a predominant part of the light falling on them in such a way that the observer sees di f ferent colours depending on the direction of perception .

[0035] In the context of the present invention, photochromic pigments are pigments that reversibly change color upon exposure to electromagnetic ( typically, but not exclusively, ultraviolet ) irradiation . In the context of the present invention, thermochromic pigments are pigments that change colour in response to temperature changes . The process may be reversible or irreversible .

[0036] Figure 1 shows a front view of a preferred embodiment of the security document 1 according to the invention . The security document 1 has a transparent window 2 which is provided with a first UV fluorescent ink 3 and a UV absorbing ink 4 . Figure 2 shows the structure ( layering) of the transparent window 2 of the security document 1 shown in Figure 1 as a whole . The UV absorbing ink 4 is applied to a part of an inner layer of the transparent window 2 as shown in Figure 2 , the first UV fluorescent ink 3 and a second UV fluorescent ink 3 ' are applied to the outer layers of the transparent window 2 on both sides of the security document 1 in such a way that a layer of UV fluorescent ink is placed on both sides between the UV absorbing ink 4 and the outer surfaces of the security document 1 . Furthermore , a part of the first 3 and the second 3 ' UV fluorescent ink layer in the plane of the security document 1 is overlapped with each other in the part of the transparent window 2 not covered by the UV absorbing ink 4 , also should at least be partially covered on the part covered with the UV absorbing ink 4 .

[0037] The system with the security document 1 and the UV light source 5 is shown in Figure 2 . The authenticity of the security document 1 can be easily checked by using a UV light source 5 , in visible light the transparent window 2 is transparent , the first and second UV fluorescent ink 3 , 3 ' inside are not visible . But when illuminating the security document 1 with an UV light source 5 , the UV absorbing ink 4 forms a star as shown in Figure 1 . Furthermore , by illuminating the security document 1 on the front and back side separately, the individual UV fluorescent inks and also their blending can be seen where the first and the second UV fluorescent ink 3 , 3 ' overlap each other in the part not covered by the UV absorbing ink 4 . Here , a mixture of light emitted by the UV fluorescent inks will be detected, which will be perceived by the eye as a di f ferent colour than the light emitted by each UV fluorescent ink alone .

[0038] UV light cannot pass through the parts of the transparent window 2 covered with the UV absorbing ink 4 , the first UV fluorescent ink 3 on the side of the transparent window 2 facing the UV light source 5 is forced to emit light . Then the colour of the light coming from the first UV fluorescent ink 3 is visible on the parts covered by the UV absorbing ink 4 , but not the colour of the second UV fluorescent ink 3 ' on the opposite side .

[0039] UV light can pass through the parts of the transparent window 2 not covered by the UV absorbing ink 4 , forcing the first and second UV fluorescent ink 3 , 3 ' on either side of the transparent window to emit light . In these places , a third colour is created by mixing the di f ferent colours of light emitted by the first and second UV fluorescent ink 3 , 3 ' in the part of the transparent window 2 that does not contain any UV absorbing ink 4 .

[0040] Since the two sides of the transparent window 2 are printed with a first and a second UV fluorescent ink 3 , 3 ' both in di f ferent colours , the pattern in the transparent window 2 has the same shape on both sides , but they have di f ferent colours . For example , i f the first UV fluorescent ink 3 emits green light under UV irradiation and the second UV fluorescent ink 3 ' emits red light under UV irradiation, and the UV absorbing ink 4 forms a star, then one side of the transparent window ( left side in Figure 2 ) illuminated with UV light will show a red star in a yellow environment , and the other side ( right side in Figure 2 ) will show a green star in a yellow environment .

[0041] I f the fluorescence intensities of the first and second UV fluorescent ink 3 , 3 ' are very dif ferent , one may suppress the other, so that the shape formed by the UV absorbing ink 4 does not appear on both sides . As shown in the example above , i f the intensity of the first UV fluorescent ink 3 emitting green light is at least 50% higher than that of the second UV fluorescent ink 3 ' emitting red light , then when illuminated with UV light , the side facing the first UV fluorescent ink 3 ( left side in Figure 2 ) will be completely green, since the first UV fluorescent ink 3 with the colour green will suppress the light emitted by the second UV fluorescent ink 3 ' with the colour red . When the opposite side of the transparent window 2 ( right side in Figure 2 ) is illuminated with UV light , a red star appears against a green background .

[0042] No precise positioning is needed to create a shape with a di f ferent fluorescent colour on a fluorescent background, as it is created spontaneously as each layer is assembled . The information is given by the light emitted by the blending of the di f ferent UV fluorescent inks , so the essential element is to apply the UV fluorescent inks so that they partially overlap on the part not covered by the UV absorbing ink 4 and also on the part covered by the UV absorbing ink 4 . This does not require the exact matching of the UV fluorescent and the UV absorbing ink 4 , only the overlapping should be ensured and the colour combinations that will prove the authenticity of the security document 1 will be produced when exposed to the UV light 5 . Preferably, in the present invention, the UV fluorescent inks cover the entire surface of the transparent window 2 in the particular layer where they are placed . Thus , the fluorescent image of the two sides of the transparent window 2 , which is di f ferent on each side and composed of several colours , is obtained by the fact that in the parts of the window which are not filled with the security element of the UV absorbing ink 4 , UV light excites the di f ferent UV fluorescent inks , the light emitted by them is mixed, and the human eye observes their sum, a third colour . As this third colour is not applied separately, but is generated spontaneously at all points of the transparent window 2 that are not covered by the UV- absorbing ink 4 as a security element , there is no need for precise positioning, no unwanted overlaps or gaps can be generated in the pattern .

[0043] Of course , we do not exclude the possibility that the shape of the UV absorbing ink 4 could be an aesthetic pattern, a speci fic representation, or even a code , such as a series of numbers , or content to personalise the security document . We do not exclude the possibility that the UV absorbing ink 4 shows an abstract or accidental representation, but in this case it is more di f ficult to check the integrity of the UV absorbing ink 4 . The transparent window 2 with di f ferent UV fluorescence on both sides is di f ficult to copy because its UV absorbing nature and UV fluorescence nature are due to colourless inks that are not detected by the copier or scanner . Furthermore , such inks are special and are generally not available for the general public .

[0044] On the other hand, the present invention also covers cases where the transparent window 2 is large , even covering the entire surface of the security document 1 , or where several transparent windows 2 are located on the surface of the security document 1 . The shape of the transparent window 2 is irrelevant to the invention, it is a well-known element of the security documents 1 to the person skilled in the state of the art . Thus , the shape of the transparent window 2 can be a circle , square , rectangle as shown in Figure 1 , but also other more complex shapes such as the outline of a plant , animal , coat of arms , etc .

[0045] Below are presented the steps for a simple method of producing the security document 1 with a transparent window 2 according to Figure 1 . The security document 1 could be , for example , an identity card, which is created in a way which is known to the person skilled in the state of the art . The plastic-based security documents 1 with a transparent window 2 can be produced in several ways . The simplest way is a single-layer document . In this case , the base of the security document 1 is a transparent film on which the opaque (white ) part is printed . The printed elements of the document (beyond the transparent window 2 ) are placed on this layer . The area intended for the transparent window 2 will not be covered by the white print . The UV absorbing ink 4 is applied to one surface of the transparent window 2 , since the transparent window is made of a single layer of transparent film in this case . One of the first and second UV fluorescent inks 3 , 3 ' is applied directly to the UV absorbing ink 4 , and the other is applied directly to the surface of the transparent window 2 on the opposite side of the transparent window 2 . For the creation of more complex security documents 1 , it is possible and advisable to laminate this printed film with additional transparent layers to create the final structure . For laminated documents with several layers , it is advisable to print the first 3 and second 3 ' UV fluorescent inks on di f ferent layers than the UV absorbing ink 4 , thus avoiding fluorescence weakening caused by migration . The first and second UV fluorescent inks 3, 3' are applied to the transparent window 2 area using conventional printing techniques such as, but not limited to, screen, offset, flexo, inkjet, other digital printing technologies. The UV fluorescent component (so-called UV fluorescent pigment) of the first and second UV fluorescent inks 3, 3' can be chemically diverse, preferably but not exclusively doped or heat-treated inorganic metal oxides, organic substances containing UV-excitable conjugated electrons in their molecules (e.g. quinine) , lanthanide-chelate complexes. The concentration used is highly dependent on the fluorescence intensity desired and the migration of the substance, ranging from 1 to 30 mass percentage, typically between 5 and 20 mass percentage. The other components of the first and second UV fluorescent ink 3, 3' are subject to the expertise of a person skilled in the state of the art and are components normally used in the printing process, such as binders, stabilisers, etc .

[0046] The UV absorbing ink 4 is applied to the area of the transparent window 2 using traditional printing techniques such as, but not limited to, screen, offset, flexo, inkjet, other digital printing technologies. The UV absorbing ink 4 must be placed between the first and second UV fluorescent ink 3, 3' for the security feature to function properly, but if this condition is met, its position in the security document layers is optional. The UV absorbing component of the UV absorbing ink 4 can be chemically diverse, preferably but not exclusively benzoate, benzophenone, benzotriazole, formamidine, triazine, benzoxazine derivatives. The concentration used is strongly dependent on the absorption coefficient of the substance, ranging from 1 to 40 mass percentage, preferably from 2 to 20 mass percentage. The other components of the UV absorbing ink 4 are subject to the knowledge of a person skilled in the state of the art and are components normally used in the printing process, such as binders, stabilisers, etc.

[0047] The security document 1 is checked as shown in Figure 2. The security document 1 is illuminated from one direction with a UV light source 5. The light from the UV light source 5 passes through the transparent window 2 at points where it does not contain UV absorbing ink 4. At these points, it forces the first and second UV fluorescent inks 3, 3' on either side of the transparent window 2 to emit light. The first and second UV fluorescent inks 3, 3' emit different wavelengths of light due to the fluorescence caused by UV light. The mixing of these different wavelengths of light is detected by the observer as an additional colour. At the points of the transparent window 2 where it contains UV absorbing ink 4, the UV light cannot pass through, so only the first UV fluorescent ink 3 on the side of the window facing the UV light source 5 will emit light. The observer will then see a two-colour fluorescent image. When illuminated from opposite sides (not shown in Figure 2) , the shape shown in the image is the same, but since the other side of the security document 1 has a different second UV fluorescent ink 3' than the first side, the parts of the transparent window 2 printed with UV-absorbing ink 4 also have a different colour image. Thus, the existence of a transparent window 2 with different UV fluorescence on the two sides can be easily checked with a UV light source 5. A security document 1 can have more than one transparent window 2 with different UV fluorescence on the two sides. If the security document 1 has more than one transparent window 2, a transparent window 2 with different UV fluorescence on at least one side of the transparent window 2 is designed as a security feature. In other words, the arrangement is also within the scope of the present invention where the security document 1 has multiple transparent windows 2, including one that is not a transparent window 2 with different UV fluorescence on the two sides. Such an arrangement further increases the difficulty of counterfeiting.

[0048] Of course, we do not exclude the use of first and second UV fluorescent inks 3, 3' with a large difference in fluorescence intensity, so that different colours of fluorescent light appear in the transparent window 2 when illuminated from different sides, but only one side shows a multicoloured pattern (see Figure 3) . In Figure 3, the intensity of the first UV fluorescent ink 3 is 70% higher than the intensity of the second UV fluorescent ink 3' , so the second UV fluorescent ink 3' is only visible with the other UV light source 5 illuminated from side B on the parts of the transparent window 2 covered by the UV absorbing ink 4. The light emitted by the second UV fluorescent ink 3' is otherwise suppressed by the light emitted by the first UV fluorescent ink 3.

[0049] In addition, we do not exclude the use of more complex constructions in which multiple layers of UV absorbing ink 4 and at least a third 3' ’ UV fluorescent ink are used to provide a multi-colour fluorescent pattern, this preferred embodiment is illustrated in Figure 4.

[0050] Figure 4 illustrates an embodiment where there are multiple UV absorbing inks 4 on the security document 1 and at least a third UV fluorescent ink 3' ’ among the UV absorbing inks 4. Thus, when the security document 1 is illuminated with a UV light source 5, different colour combinations are visible for different pages due to the overlapping of some of the UV fluorescent inks. Furthermore, we do not exclude the use of a non-directed UV light source, but the fluorescence effect is stronger when using a directed light source.

[0051] In addition to the transparent window 2 with different UV fluorescence on both sides, the security document 1 can be equipped with secondary security elements, which are used to prevent and make it more difficult to counterfeit the security document. Depending on their type, these secondary security features may be placed in the transparent window 2 or in other parts of the security document 1. They can also be placed on the surface of the security document 1 or in its material, depending on the secondary security feature. Examples of such secondary security features are:

[0052] - a layer providing a phenomenon based on light diffraction;

[0053] - laser engraved elements (e.g. photo) ;

[0054] - other fluorescent security features not included in the window;

[0055] - anti-Stokes pigments;

[0056] - infrared fluorescent elements;

[0057] - iridescent pigments;

[0058] - pigments with metallic luster;

[0059] - pigments of varying colours depending on the direction of illumination and perception;

[0060] - photochromic pigments;

[0061] - thermochromic pigments. Examples

[0062] Example 1 : The security document 1 according to Figure 1 The security document 1 with the transparent window 2 according to Figure 1 is an ID card, created as a multilayered document as presented in the description . The transparent window 2 contains UV absorbing ink 4 in the shape of a star, which is screen printed on one of the inner layers of the transparent window 2 . The first and second UV fluorescent inks 3 , 3 ' were applied by of fset printing on the outer layers . The UV absorbing ink 4 contains benzoate derivative as a UV absorbing compound, and screen ink . The first and second UV fluorescent inks 3 , 3 ' contain UV fluorescent pigments (heat-treated inorganic metal oxide ) and of fset inks , where the first UV fluorescent ink 3 emits green light when exposed to UV light and the second UV fluorescent ink 3 ' emits yellow light when exposed to UV light .

[0063] Example 2 : The security document 1 according to Figure 3 The security document 1 with the transparent window 2 according to Figure 3 is a driver ' s license , created as a multilayer document as presented in the description . The transparent window 2 contains a UV absorbing ink 4 containing a negative image of a guilloche pattern . This was screen printed on an inner layer of the transparent window . The first and second UV fluorescent inks 3 , 3 ' were applied to the outer layers by of fset printing . The UV absorbing ink 4 contains formamidine as a UV absorbing compound, and a screen ink . The first and second UV fluorescent inks 3 , 3 ' contain UV fluorescent pigments ( lanthanide chelate complexes ) and of fset inks . The intensity of the first UV fluorescent ink 3 is 50% higher than that of the second UV fluorescent ink 3 ' . When the front side is illuminated with UV light , the intense fluorescence of the first UV fluorescent ink 3 suppresses the less intense fluorescence of the second UV fluorescent ink 3 ' , so the guilloche pattern does not appear and the whole window is monochrome . When the backside is illuminated, the less intense fluorescence of the second UV fluorescent ink 3 ' cannot suppress the intense fluorescence of the first UV fluorescent ink 3 , so the guilloche pattern appears .

[0064] Example 3 : The security document 1 according to Figure 4 The security document 1 with the transparent window 2 according to Figure 4 is a passport cover page , which was created as a multilayer document as presented in the description . We place UV absorbing inks 4 in the two inner layers of the transparent window 2 by screen printing . The first and second UV fluorescent inks 3 , 3 ' were applied to the outer layers by of fset printing . The UV absorbing inks 4 contain triazine as a UV absorbing compound, and screen ink . The first 3 and second 3 ' UV fluorescent inks contain UV fluorescent pigments ( lanthanide chelate complexes ) and of fset inks . In addition, a third 3" UV fluorescent ink is included in the transparent window 2 between the two layers of UV absorbing ink 4 .

[0065] The advantage of the solution according to the invention is that the multicoloured fluorescent pattern on the two sides of the transparent window is of di f ferent colours , no precise positioning is required for its design, because the colours on the same side are created by layering UV fluorescent inks and UV absorbing inks , no colour matching is required . The resulting window is completely transparent to the naked eye in visible light , its security properties can be easily checked with a UV light source .

Claims

Claims1. A security document (1) having a transparent window (2) comprising UV fluorescent inks (3, 3' ) and UV absorbing ink (4) , characterised by that the UV absorbing ink (4) is positioned in a part of the transparent window (2) , the first UV fluorescent ink (3) being positioned between the surface of the first side (A) of the transparent window (2) and the UV absorbing ink (4) , the second UV fluorescent ink (3' ) is positioned between the surface of the second side (B) of the transparent window (2) and the UV absorbing ink (4) in such a way that the first and second UV fluorescent inks (3, 3' ) are positioned opposite each other on the part of the transparent window (2) not covered by the UV absorbing ink (4) , and another part of the first and second UV fluorescent inks (3, 3' ) are positioned opposite each other on the part covered by the UV absorbing ink (4) .

2. The security document (1) according to claim 1, characterised by that the security document (1) is multilayered and the first and second UV fluorescent inks (3, 3' ) are arranged on different layers of the transparent window (2) of the security document (1) .

3. The security document (1) according to any one of claims 1 to 2, characterised by that the UV fluorescent inks (3, 3' ) cover substantially the entire surface of the transparent window ( 2 ) .

4. The security document (1) according to any one of claims 1 to 3, characterised by that the UV fluorescent inks (3, 3' ) differ in fluorescence intensity by up to 50%.

5. The security document according to any one of claims 1 to 4, characterised by that it has several transparent windows (2) .

6. The security document (1) according to any one of claims 2 to 5, characterised by that the transparent window comprises more than one layer of UV absorbing ink (4) , and the transparent window contains at least three different UV- fluorescent (3, 3', 3") inks arranged so that they at least partially overlap in the plane of the security document (1) .

7. The security document (1) according to any one of claims 1 to 6, characterised by that the security document (1) is an identity card, passport, driving licence, vehicle registration certificate, residence card, access card or transport pass.

8. The security document (1) according to any one of claims 1 to 7, characterised by that the security document (1) further contains at least one secondary security element.

9. The security document according to claim 8 (1) , characterised by that the secondary security feature is chosen from the following:- a layer providing a phenomenon based on light diffraction;- laser engraved elements (e.g. photo) ; fluorescent security features;- anti-Stokes pigments;- infrared fluorescent elements;- iridescent pigments;- pigments with metallic luster;- pigments of varying colours depending on the direction of illumination and perception;- photochromic pigments;- thermochromic pigments.

10. A system for security document verification, comprising a security document (1) and a UV light source (5) , characterised by that the security document (1) is a security document (1) according to any one of claims 1 to 9.

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