METHOD OF PERSONALIZING A SECURITY DOCUMENT

Abstract

 A method of personalizing a security document includes a formation of a personalized output image (5) by printing a two-dimensional pattern (6) consisting of a single continuous line (8). In this printing, at least one line parameter of each line unit (10) of the single continuous line (8) is varied in accordance with color values of the image units (9) in the personalized input image (4) to create a personalized output image having a unique appearance. If the printed personalized output image (5), in particular, the single continuous line (8) has an electrical conductivity above a given threshold value, the personalized output image (5) may form part of an RFID antenna (18) of the security document (10).

Description

Technical Field

[0001] The present disclosure generally relates to security features for security documents, in particular, personalizable security documents such as identification documents, driver's licenses and the like.

Background

[0002] Generally, in the market of physical identification documents, a variety of security features are included to increase the document's security. In some applications, a laser engraved image is considered vital, as the image features are engraved into a polycarbonate substrate rather than on the surface of the substrate. A laser engraved feature in a polycarbonate substrate may include a black and white (in particular, grayscale) image, a color image, or other special features.

[0003] There are also other approaches for providing security features for such identification documents. For example, EP 4 358 032 A1 discloses a method of generating a personalized output image for a security document. The method includes obtaining image information of a first image formed on one side of a page of the security document, and a personalized input image showing a portrait of a holder of the security document. On the basis of the two images, a personalized output image is calculated such that, when the personalized output image and the first image are viewed in transmission, the portrait of the holder of the security document appears.

[0004] The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior systems, without being limited to a particular type of security document.

Summary of the Disclosure

[0005] According to one aspect of the present disclosure, a method of personalizing a security document includes the steps of providing a personalizable security document including a substrate, providing a personalized input image formed by a plurality of image units, and providing a two-dimensional pattern consisting of a single continuous line formed by a plurality of line units. The method may further include a step of performing a registration between the input image and the two-dimensional pattern. The method further includes a step of determining at least one line parameter of each line unit of the single continuous line based on color values of the plurality of image units of the personalized input image, preferably after performing the registration, and printing the single continuous line onto the substrate in accordance with the at least one line parameters of the plurality of line units to form a personalized output image.

[0006] In another aspect of the present disclosure, a personalized security document has a substrate and a personalized image printed onto the substrate. The personalized image is formed as a two-dimensional pattern consisting of a single continuous line, preferably a double spiral consisting of a first spiral and a second spiral originating from a common origin at a center of the two-dimensional pattern, formed by plurality of line units. At least one line parameter of the plurality of line units varies along the single continuous line to form the personalized output image.

[0007] Other features and aspects of the present disclosure will be apparent from the following description and the accompanying drawings.

Brief Description of the Drawings

[0008] 

Fig. 1 shows a plan view of an exemplary personalized security document in accordance with the present disclosure;

Fig. 2 shows an input image in accordance with the present disclosure;

Fig. 3 shows a two-dimensional pattern consisting of a single continuous line in accordance with the present disclosure;

Fig. 4 shows an output image in accordance with the present disclosure;

Fig. 5 shows a diagram illustrating a determination of a line parameter of each line unit in accordance with the present disclosure;

Fig. 6 shows another output image in accordance with the present disclosure;

Fig. 7 shows a schematic cross-sectional view of an exemplary personalized security document in accordance with the present disclosure;

Fig. 8 shows a plan view of an RFID circuit in an exemplary personalized security document in accordance with the present disclosure; and

Fig. 9 shows an exemplary flow diagram of a method in accordance with the present disclosure.

Detailed Description

[0009] The following is a detailed description of exemplary embodiments of the present disclosure. The exemplary embodiments described herein are intended to teach the principles of the present disclosure, enabling those of ordinary skill in the art to implement and use the present disclosure in many different environments and for many different applications. Therefore, the exemplary embodiments are not intended to be, and should not be considered as, a limiting description of the scope of protection. Rather, the scope of protection shall be defined by the appended claims.

[0010] The present disclosure is based at least in part on the realization that security documents such as identification documents rely on a combination of different security features to prevent the falsification and forgery of the security document. The security of such documents can be increased if they are personalized to contain data of a holder of the security document. Additionally, features need to have a specific appearance and feel that allows a verifier to check the authenticity of the security document.

[0011] In some security documents, one security feature is a radio frequency identification (RFID) circuit that allows for performing RFID communications in order to read information on an RFID chip contained in the document. For example, such an RFID chip may hold biometric information of the holder of the security document. Generally, the RFID circuit is embedded in the security document and is not visible from the outside. This applies, in particular, to the RFID antenna of the RFID circuit.

[0012] Another security feature that is commonly used is the laser engraving of a primary or secondary portrait of the holder of the security document into the security document.

[0013] The present disclosure is based on the realization that the security of a security document can be increased further by linking an RFID antenna of the security document to a visual security feature. In particular, the visual security feature can be a personalized security feature, such that the antenna design is personalized.

[0014] Additionally, it has been realized that, while a primary portrait is produced by laser engraving, the look and feel of the resulting primary portrait is not visibly different from a regular black and white print. It has been realized that an additional security feature can be obtained by using a pattern when printing, for example, the primary or secondary portrait of the holder of the security document. The pattern is designed such that it resembles a double spiral, which is printed such that at least one line parameter varies along the double spiral. Here, the at least one line parameter may include a line width (thickness) of the line that forms the pattern, or an intensity, for example, a grayscale value of each line unit of the line forming the pattern. This results in a unique appearance of the primary or secondary portrait of the holder of the security document, which is not easily reproducible without having detailed information with respect to the printing parameters to be used.

[0015] The above-mentioned line pattern has the additional advantage that, when the line pattern is printed by laser engraving, the engraving process can be simplified, because the pattern is a single continous line, for example, a spiral or double spiral, that can be followed by the laser while varying laser parameters of the laser, for example, a laser power or the like, which allows for changing the width of the line during engraving. Another laser parameter that is used may be, for example, a laser speed or a beam width of the laser

[0016] In particular, due to the fact that the line pattern is a single continuous line, it becomes possible to use the line pattern as a part of an RFID antenna of the security document. It has been realized that this can be achieved in a variety of different ways, for example, by silkscreen printing of conductive ink, or 3D printing of a conductive polylactide (PLA), which allows for producing a line pattern having varying width or varying lightness.

[0017] Additionally, it has been realized that a laser-reactive material, which becomes conductive and, optionally, changes color based on laser irradiation can be used to form the line pattern, which may then form part of an RFID antenna.

[0018] Especially in case of printing the output image as a continuous line pattern by silkscreen printing, it has been realized that a halftoning mask in the form of the line pattern can be used to halftone the input image in order to create the silkscreens. Here, it has been realized that, especially in cases where the printing pattern is to be used as part of an RFID antenna, it may be necessary to adjust the values of the halftone mask to ensure that at least one line unit or pixel is always printed to form the continous pattern.

[0019] It has also been realized that it is advantageous to use a line pattern that is based on Fermat spirals, in particular, a double spiral having a common origin at a center of the line pattern, and end portions on opposite sides of the same. This may generate a unique look for the resulting output image, and may also facilitate connecting the line pattern to an RFID antenna in case this is to be implemented.

[0020] Fig. 1 shows a schematic plan view of an exemplary personalized security document 10 in accordance with the present disclosure. As shown in Fig. 1, security document 10 includes a substrate 1 having a substantially rectangular shape, but not limited to such a rectangular shape. Other shapes, for example, circular, elliptical, or polygonal shapes can also be used, depending on the application. Additionally, it should be understood that security document 10 does not need to be a separate card or sheet, but can also form part of a security document as a data page of a passport or the like.

[0021] As shown in Fig. 1, security document 10 is a personalized security document, which includes an image 2 of a holder of the security document as a primary portrait printed on a first side S1 of security document 10. Image 2 may be formed in an image region provided on substrate 1 in a known manner, for example, using a laser marking apparatus or the like.

[0022] As shown in Fig. 1, security document 10 includes a security feature 3 formed in substrate 1. In the exemplary embodiment, security feature 3 is a window having a rectangular shape, in which one or more security features such as a personalized output image 5, which will be described in more detail below, may be provided. It should be appreciated, however, that it is not necessary that personalized output image 5 of the present disclosure is part of a security feature such as the security feature 3 shown in Fig. 1. In other embodiments, personalized output image 5 may be formed in a portion of a surface of substrate 1, or on one of a plurality of substrate layers of the same, using the printing techniques that will be described in more detail in the following.

[0023] Fig. 7 shows a schematic cross-sectional view of personalized security document 10 in accordance with the present disclosure. As shown in Fig. 2, personalized security document 10 has substrate 1 having first side S1 and a second side S2 opposite to first side S1 in a thickness direction d of substrate 1. For example, substrate 1 is formed by stacking a plurality of substrate layers 31, 32, 33, 34, for example, polycarbonate or polyvinyl chloride (PVC) layers, and combining said substrate layers in an appropriate manner, for example, by lamination processes or the like. This is known the skilled person, such that a detailed description will be omitted herein.

[0024] Security feature 3 is formed in substrate 1 and extends through at least part of substrate 1 along thickness direction d. In the example shown in Fig. 7, security feature 3 extends from the uppermost substrate layer 31 to the bottom layer 34 of substrate 1. Here, additional secure elements (not shown) may be formed, for example, on substrate layers 33 and 34. In other embodiments, however, security feature 3 may only encompass first substrate layer 31 and second substrate layer 32, on which a layer of laser-engravable material 12, which will be described in more detail in the following, is provided. Layer of laser-engravable material 12 is configured to have a personalized output image 5 laser engraved in the same from first side S1 of substrate 1, as indicated by dashed lines in Fig. 7. Here, it will be appreciated that at least a portion of substrate layer 31 on top of substrate layer 32 is substantially transparent or at least semi-transparent for visible light, such that personalized output image 5 can be viewed from first side S1 in reflection, for example, under white light.

[0025] The material of layer of laser-engravable material 12 may have property such that it exhibits a color-change effect upon irradiation with laser light. As used herein, the "color-change effect upon irradiation with laser light" means that a laser light that is irradiated onto layer of laser-engravable material 12 changes at least one physical property of, for example, particles or pigments included in layer of laser-engravable material 12 in a predetermined manner, for example, depending on the intensity of the laser light, and/or other laser parameters. A particular example is the ink that is used in the Mirage security feature of HID. In this technology, each pixel in personalized output image 5 has a defined color value, depending, for example, on a digital grayscale value of a grayscale input image 4 (see Fig. 2). In this manner, for example, a grayscale portrait of a holder of security document 10, for example, a negative or positive image, can be formed in an upper surface of layer of laser-engravable material 12. Here, it will be appreciated that the present application is not limited to the Mirage ink described above, and can be applied to any known laser-engravable material that exhibits a color-change effect when irradiated with laser light.

[0026] Further, as will be described in more detail below, layer of laser-engravable material 12 may exhibit an additional change in its properties upon irradiation with laser light, namely, a change in conductivity from a low electrical conductivity to a high electrical conductivity upon irradiation with laser light. To this end, layer of laser-engravable material 12 may include, for example, silver (Ag) or copper (Co) nanowires, optionally, in addition to the pigments that exhibit the color-change effect. Examples for such conductive materials are, for example, the products LF-300 Paper, LF-350 PET, LF-380 HJT PV of the company Copprint Technologies Ltd. However, it should be noted that, in other embodiments, no conductive structures such as conductive nanowires need to be used, as long as the material that forms layer of laser-engravable material 12 and has, for example, a color-change effect is configured such that, or can be modified such that, in addition to the color-change effect, there is a change in electrical conductivity from low electrical conductivity to high electrical conductivity.

[0027] As used herein, the expression "low electrical conductivity" does not mean that the conductivity of the material has to be zero S/m, but that the electrical conductivity is too low for a current that allows an RFID antenna connected to a structure forming output image 5 to function. It will be appreciated that the threshold value for the RFID antenna to function may depend on the type of antenna, the dimensions of the structure forming output image 5, and the like. However, this threshold can be easily determined by the skilled person for a specific configuration. For example, in some RFID applications performing high-frequency (HF) communications, it has been found that the RFID circuit will be able to communicate in an electrical field strength of 0.8 A/m. In such a case, a conductivity of the structure forming output image 5 up to around 3-4 × 10⁷ S/m is considered to be a lower electrical conductivity. When the electrical conductivity of the structure forming output image 5 is higher than about 3-4 × 10⁷ S/m, the associated RFID circuitry is able to communicate with an RFID reader, and the structure forming output image 5 is considered to have a high electrical conductivity. Here, it will be appreciated that the conductivity of output image 5 can be easily measured using known methods such as a four-probe method and the like.

[0028] An exemplary embodiment of the present disclosure, in which personalized output image 5 is laser engraved in layer of laser-engravable material 12 will be described in the following. However, it will be appreciated that the methods and the resulting personalized documents disclosed herein are not limited to this particular embodiment.

[0029] Generally, a method of personalizing a security document 10 in accordance with present disclosure, as shown in Fig. 9, includes a step 110 of providing a personalized security document 10 including substrate 1. The method further includes a step 120 of providing a personalized input image 4 (see Fig. 2) formed by a plurality of image units (for example, pixels) 9.

[0030] In step S130, a two-dimensional pattern 6 consisting of a single continuous line 8 formed by a plurality of line units 10 (see Fig. 3) is provided.

[0031] In step 140, a registration of input image 4 and two-dimensional patterns 6 is performed. As will be described in more detail, this registration may include changing the resolution and/or aspect ratio of at least one of personalized input image 4 and two-dimensional pattern 6. In case the resolution of personalized input image 4 and two-dimensional pattern 6 is the same, the step of performing the registration may be limited to aligning personalized input image 4 and two-dimensional pattern 6, i.e., overlapping the same. In any case, after the registration, an association of line units 10 of single continuous line 8 with one or more of image units 9 in personalized input image 4 can be achieved, as will be described in more detail below.

[0032] In step 150, at least one line parameter of each line unit 10 of single continuous line 8 is determined based on color values of the plurality of image units 9 of personalized input image 4. Here, it will be appreciated that the at least one line parameter corresponds to (is associated with) one or more printing parameters that are used to print each line unit 10, which one or more printing parameters result the desired line parameters of the corresponding line unit. The at least one line parameter includes, for example, a line width w of single continuous line 8 (see Fig. 5), or a lightness or color value of the corresponding line unit. In case a laser is used to print output image 5, the one or more printing parameter are commonly used laser parameters used for laser-engraving, such as laser power, laser speed, repetition rate, beam width, etc. In case a printing apparatus is used, the one or more printing parameters are, for example, an ink amount, a width of a line forming a silkscreen to be used for the printing, a drop size or a number of drops in case of inkjet printing, a type of ink that is used for printing (i.e., different inks may be used to print single continuous line 8), etc.

[0033] After the at least one line parameter has been determined for each line unit 10, in step 160, single continuous line 8 is printed onto substrate 1 in accordance with the at least one line parameter of the plurality of line units 10 to form personalized output image 5, by appropriately varying/selecting the associated printing parameters of the printing apparatus. Here, it will be appreciated that the printing parameters and the size and/or number of line units 10 are selected such that, in case a conductive line pattern is to be produced, it is assured that successive printed line units 10 overlap at least to some extent, as shown in Figs. 4 and 5. If no conductive line pattern is to be produced, such an overlap is not absolutely necessary, i.e., there may be gaps between at least some successive line units 10.

[0034] As previously mentioned, in some embodiments, the disclosed method may include a further step of mapping one of personalized input image 4 and two-dimensional pattern 6 onto the other one of personalized input image 4 and two-dimensional pattern 6 prior to determining the at least one line parameter of each line unit 10. In other words, in particular in cases where personalized input image 4 and two-dimensional pattern 6 do not have the same resolution or aspect ratio, such a mapping may be useful for allowing the association of the line units 10 of single continuous line 8 with one or more image units 9 of personalized input image 4. For example, as shown in Fig. 2, input image 4 may be any appropriate image showing a portrait of a holder of security document 10, and may include image units or pixels 9 forming input image 4, which image units are associated with a specific resolution, i.e., number of image units or pixels per line, and number of lines forming input image 4.

[0035] On the other hand, two-dimensional pattern 6 may have a size, as well as an aspect ratio that is selected depending on the area in which output image 5 is to be provided, and, in particular, the number of line units 10 forming single continuous line 8 may be a predetermined number, which may be determined by an available resolution of the printing apparatus that is used. For example, a size of two-dimensional pattern 6 may be between 0.001 and 150 cm², preferably between 0.25 and 25 cm², and a total number of line units 10 may be between 10 and 10⁹, preferably between 10⁴ and 10⁶.

[0036] It should be appreciated that, in accordance with the present disclosure, it is not necessary that there is a 1 to 1 correspondence between image units 9 of personalized input image 4 and line units 10 of single continuous line 8. For example, as shown in Fig. 5, image units or pixels 9 of input image 4 may be arranged in a known manner as a plurality of lines, which are arranged next to each other in a vertical direction, whereas single continuous line 8 may be a curved line, and each line unit 10 may at least partially overlap a plurality of image units 9 in input image 4. In order to determine the at least one line parameter of each line unit 10 based on color values of the plurality of image units 9, an association of each line unit 10 to one or more image units 9 adjacent to or at least partially overlapping line unit 10 may be performed. In some embodiments, the color value of the image unit 9 that is closest to line unit 10, i.e., has the maximum overlap with the same, can be used to determine the at least one line parameter. In other embodiments, however, an average value of the color values of adjacent image units 9, for example, which overlap line unit 10 at least in part, may be used to determine the at least one line parameter. Other ways of associating each line unit 10 with one or more image units 9 will be readily apparent to the skilled person.

[0037] In some embodiments, the method further includes a step of converting input image 4 to a grayscale image prior to determining the at least one line parameter of each line unit 10. In particular, in cases where input image 4 is, for example, a color image, it may be advantageous to convert input image 4 into a grayscale image in a known manner. As a result, each image unit 9 of input image 4 has a lightness value between a minimum lightness value and a maximum lightness value (for example, between 0 and 255) as its color value. Based on this, in some embodiments, the at least one line parameter of each line unit 10 may be a line width w corresponding to the lightness values of one or more image units 9 associated with line unit 10. For example, as shown in Fig. 5, the lightness value of the image unit or pixel 9 that has the greatest overlap with a given line unit 10 could be associated with the same, and the at least one line parameter, in this case, the line width w (i.e., the printing parameters that are to be used in order to print line unit 10 with the required width w) may be appropriately determined. In a very simple example, if a laser engraving apparatus is used to engrave single continuous line 8, a beam width of the laser beam used to perform engraving is proportional to the line width w and may be varied in accordance with the lightness values of the one or more image units 9 associated with the line unit 10. In another example, if the laser power is proportional to the line- width w, the laser power may be varied in accordance with the lightness values of the one or more image units 9 associated with the line unit 10. In case an ink printing apparatus is used, it is immediately evident that, for example, an amount of ink that is used for printing a given line unit 10 is proportional to the thickness of the line, in particular, the line width of the same. Depending on the printing apparatus that is used, the skilled person will be easily capable of appropriately selecting printing parameters that result in a desired line width w of single continuous line 8.

[0038] As an alternative to varying the line width w of single continuous line 8, it is also possible to vary the at least one line parameter of each line unit 10 such that a lightness value corresponding to lightness values of one or more image units 9 associated with the line unit 10 is varied. In other words, personalized output image 5 may be formed as a grayscale image or an image that has a predefined color gradient depending on the variation of the at least one line parameter. For example, in case of the Mirage security feature of HID, a variation of, for example, a laser power may result in a change of a color of each line unit 10 from blue to golden in a continous manner. Of course, this is only one example, and the present disclosure it is not limited to this case. Different materials may produce different color changes. In particular, is should be immediately evident that the method disclosed herein, especially when varying line properties such as line width w and lightness, can also be applied in order to form personalized output image 5 directly in the material of substrate 1, for example, topmost substrate layer 31 in a known manner, as long as personalized output image 5 includes two-dimensional pattern 6 consisting of single continuous line 8 constructed in the manner disclosed herein.

[0039] Fig. 4 shows one example of personalized output image 5, in which the property of each line unit 10 that is changed depending on the lightness values of one or more image units 9 associated with line unit 10 is a line width. It can be seen from Fig. 4 that, with the method disclosed herein, the thickness (width) of single continuous line 8 varies along the same, depending on the lightness values in personalized input image 4 (see Fig. 2). In other words, darker regions in input image 4 result in broader lines in personalized output image 5. For example, as shown in the enlarged portion of Fig. 4, a line width may increase from a first width w1 to a second width w2 along line 8. Adjacent line sections that correspond to lighter parts of output image 5 have an even smaller line width w3. Here, it will be appreciated that pattern 6 should advantageously be formed such that distances between adjacent sections of line 8 are such that there is no overlap even if the adjacent sections have a maximum thickness.

[0040] Fig. 6 shows another example of personalized output image 5, in which the property of the line units 10 in single continuous line 8 that is changed based on the lightness values of the one or more image units 9 associated with each line unit 10 is a lightness value, resulting in formation of a grayscale image, where different portions of single continuous line 8 have different lightness values correspond to the lightness values of the associated one or more image units 9 in personalized input image 4 (again, see Fig. 2).

[0041] Also in the exemplary output images 5 shown in Figs. 4 and 5, single continuous line 8 may be formed by laser-engraving the same by varying one or more laser parameters in accordance with the at least one line parameters of the plurality of line units 10, the one or more laser parameters including one or more of laser power, pulse duration, laser speed, repetition rate, beam width, etc.

[0042] In the exemplary embodiment that is shown in Fig. 7, substrate 1 includes layer of laser-engravable material 12 embedded in substrate 1, preferably, as part of security feature 3. As already mentioned, layer of laser-engravable material 12 may exhibit at least one of: a color-change from a first chromatic color to a second chromatic color upon irradiation with laser light (such as, for example, in the Mirage security feature of HID); and a change in electrical conductivity from a low conductivity to a high conductivity of at least 3-4 × 10⁷ S/m, preferably more than 4 × 10⁷ S/m, upon irradiation with the laser light.

[0043] In other embodiments, however, single continuous line 8 may be printed onto substrate 1 by silkscreen printing or 3D printing in accordance with the at least one line parameters of the plurality of line units 10. Also in such cases, an ink or 3D printing material used to print single continuous line 8 may have an electrical conductivity of at least 3-4 × 10⁷ S/m, preferably more than 4 × 10⁷ S/m. In other words, the ink or 3D printing material may be suitable for forming a pattern that can be used to form part of an RFID antenna of a given RFID circuit, as will be described in more detail below.

[0044] In case a printing apparatus such as a silkscreen printing apparatus is used to print single continuous line 8, the method disclosed herein may include a further step of generating a halftone mask based on two-dimensional pattern 6, and a step of performing halftoning of input image 4 to determine the at least one line parameter of each line unit 10 of single continuous line 8. Here, preferably, the at least one line parameter of each line unit 10 is determined such that each line unit 10 has an electrical conductivity above a predefined threshold value, for example, 3-4 × 10⁷ S/m, preferably more than 4 × 10⁷ S/m.

[0045] As used herein, the expression "single continuous line" means any line pattern that extends from a start point to an end point in a continous manner. In other words, when printing single continuous line 8, no line unit 10 is omitted. In other words, each line unit 10 has a minimum property or value, such as a line width or an intensity.

[0046] Fig. 3 shows one example of single continuous line 8 in accordance with the present disclosure. In the example shown in Fig. 3, single continuous line 8 is a double spiral consisting of a first spiral 13 and a second spiral 14, preferably Fermat spirals, originating from a common origin O at a center of two-dimensional pattern 6. Such spirals are known to the skilled person, such that a detailed description will be omitted herein. In brief, the radial coordinate r of such spirals is θ for first spiral 13 and θ + π for second spiral 14. However, it will be appreciated that the double spiral shown, for example, in Figs. 3, 4 and 6 is only exemplary, and any other appropriate continuous line pattern can be used.

[0047] In the example shown in Fig. 3, first spiral 13 and second spiral 14 terminate on opposite sides of two-dimensional pattern 6 at a first end 15 and a second end 16, respectively. As will be described in more detail in the following, this allows for easily connecting an RFID antenna to first end 15 and second end 16 of the respective spirals.

[0048] As initially mentioned, in some embodiments, single continuous line 8 may have an electrical conductivity that is above a predetermined threshold value after formation of personalized output image 5. In such a case, personalized output image 5 can form part of an RFID antenna of an RFID circuit included in security document 10. This is illustrated in an exemplary manner in Fig. 8.

[0049] In Fig. 8, which is, for example, a plan view of second substrate layer 32 shown in Fig. 7, substrate 1 includes an RFID chip 20 and an open-circuit RFID antenna 18 connected to RFID chip 20 in a known manner. As shown in Fig. 8, open-circuit RFID antenna 18 includes antenna pads 22, 24 at opposite end portions of the same. The method disclosed herein further includes a step of printing single continuous line 8 onto substrate 1 to connect antenna pads 22, 24, with single continuous line 8 having an electrical conductivity of at least 3-4 × 10⁷ S/m, preferably more than 4 × 10⁷ S/m. As shown in Fig. 8, single continuous line 8 may be formed in layer of laser-engravable material 12 by varying one or more laser parameters, with opposing ends 15 and 16 of single continuous line 8 being connected to the respective antenna pads 22, 24 after formation of personalized output image 5. For example, layer of laser-engravable material 12 may be provided to partially overlap antenna pads 22, 24, such that an electrical connection to line pattern 8 after engraving can be assured. In such a manner, the RFID circuit is closed, and RFID chip 20 is capable of performing RFID communications. Here, it will be appreciated that detailed knowledge of, for example, the position of antenna pads 22, 24, as well as the manner in which personalized output image 5 is to be engraved, is necessary in order to be able to successfully engrave personalized output image 5 such that RFID chip 20 is functional. This makes it very difficult for unauthorized parties to forge security document 10.

[0050] It will be appreciated that, with the above-described methods, a personalized security document 10 can be obtained, which includes a substrate 1 and a personalized output image 5 printed onto substrate 1. As previously explained, personalized output image 5 is formed as a two-dimensional pattern 6 consisting of a single continuous line 8, preferably a double spiral consisting of a first spiral 13 and a second spiral 14 originating from a common origin O at a center of two-dimensional pattern 6, formed by a plurality of line units 10, where at least one line parameter of the plurality of line units 10 varies along the single continuous line 8 to form personalized output image 5.

Industrial applicability

[0051] With the above-described methods, a personalized security document 10 can be obtained, in which a personalized input image is printed onto a substrate of a security document 10 using a two-dimensional pattern 6 consisting of a single continuous line 8 formed by a plurality of line units 10. This allows for obtaining a personalized output image 5 having a unique appearance, due to at least one characteristic of the single continuous line varying along the same. In case the material forming single continuous line 8 is electrically conductive, the personalized output image 5 may also form part of an RFID antenna of security document 10, resulting in increased security due to the close link between the personalized output image 5 and the functionality of the RFID circuitry included in the security document 10.

[0052] It will be appreciated that the foregoing description provides examples of the disclosed systems and methods. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the general disclosure.

[0053] Recitation of ranges of values herein are merely intended to serve as a shorthand method for referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All method steps described herein can be performed in any suitable order, unless otherwise indicated or clearly contradicted by the context.

[0054] Although the preferred embodiments of the present disclosure have been described herein, improvements and modifications may be incorporated without departing from the scope of the following claims.

Claims

1. A method of personalizing a security document (10), comprising:

- providing a personalizable security document (10) including a substrate (1);

- providing a personalized input image (4) formed by a plurality of image units (9);

- providing a two-dimensional pattern (6) consisting of a single continuous line (8) formed by a plurality of line units (10);

- determining at least one line parameter of each line unit (10) of the single continuous line (8) based on color values of the plurality of image units (9) of the personalized input image (4); and

- printing the single continuous line (8) onto the substrate (1) in accordance with the at least one line parameters of the plurality of line units (10) to form a personalized output image (5).

2. The method of claim 1, further comprising:

- mapping one of the personalized input image (4) and the two-dimensional pattern (6) onto the other one of the personalized input image (4) and the two-dimensional pattern (6) prior to determining the at least one line parameter of each line unit (10).

3. The method of claim 1 or 2, further comprising:

- converting the input image (4) into a grayscale image prior to determining the at least one line parameter of each line unit (10).

4. The method of any one of claims 1 to 3, wherein each image unit (9) of the input image has a lightness value between a minimum lightness value and a maximum lightness value as its color value, and the at least one line parameter of each line unit (10) is at least one of: a line width (w) corresponding to the lightness values of one or more image units (9) associated with the line unit (10); and a lightness value corresponding to the lightness values of one or more image units (9) associated with the line unit (10).

5. The method of any one of claims 1 to 4, wherein the single continuous line (8) is laser engraved by varying one or more laser parameters in accordance with the at least one line parameters of the plurality of line units (10), the one or more laser parameters including one or more of laser power, pulse duration, laser speed, repetition rate.

6. The method of claim 5, wherein the substrate (1) includes a layer of laser-engravable material (12) embedded in the substrate (1), preferably, as part of a security feature (3) that extends at least in part through the substrate (1), the layer of laser-engravable material exhibiting at least one of: a color change from a first chromatic color to a second chromatic color upon irradiation with the laser light; and a change in electrical conductivity from a low conductivity to a high conductivity of at least 3-4 × 10⁷ S/m upon irradiation with the laser light.

7. The method of any one of claims 1 to 4, wherein the single continuous line (8) is printed onto the substrate (1) by silkscreen printing or 3D printing in accordance with the at least one line parameters of the plurality of line units (10).

8. The method of claim 7, wherein an ink or 3D printing material used to print the single continuous line (8) has an electrical conductivity of at least 3-4 × 10⁷ S/m.

9. The method of any one of claims 1 to 8, further comprising:

- generating a halftone mask based on the two-dimensional pattern (6); and

- performing halftoning of the input image (4) to determine the at least one line parameter of each line unit (10) of the single continuous line (8), preferably, wherein each line unit (10) has an electrical conductivity above a predefined threshold value.

10. The method of any one of claims 1 to 9, wherein the single continuous line (8) is a double spiral consisting of a first spiral (13) and a second spiral (14), preferably Fermat spirals, originating from a common origin (O) at a center of the two-dimensional pattern (6).

11. The method of claim 10, wherein the first spiral (13) and the second spiral (14) terminate on opposite sides of the two-dimensional pattern (6) at a first end (15) and a second end (16), respectively.

12. The method of any one of claims 1 to 11, wherein the substrate (1) includes an RFID chip (20) and an open-circuit RFID antenna (18) connected to the RFID chip (20), the open-circuit RFID antenna (18) including antenna pads (22, 24) at opposing end portions of the same, the method further comprising:

- printing the single continuous line (8) onto the substrate (1) to connect the antenna pads (22, 24), the printed single continuous line having an electrical conductivity of at least 3-4 × 10⁷ S/m.

13. The method of any one of claims 1 to 12, wherein a size of the two-dimensional pattern (6) is between 0.001 and 150 cm², preferably between 0.25 and 25 cm², and a number of line units (10) is between 10 and 10⁹, preferably between 10⁴ and 10⁶.

14. A personalized security document (10), comprising:

- a substrate (1); and

- a personalized image (5) printed onto the substrate,

- wherein the personalized image (5) is formed as a two-dimensional pattern (6) consisting of a single continuous line (8) formed by a plurality of line units (10), at least one line parameter of the plurality of line units (10) varying along the single continuous line (8) to form the personalized output image (5).

15. The personalized security document of claim 14, wherein the single continuous line (8) is a double spiral consisting of a first spiral (13) and a second spiral (14) originating from a common origin (O) at a center of the two-dimensional pattern (6).

Drawing