EP4389449A1

EP4389449A1 - Personalizable security document and methods of manufacturing and personalizing the same

Info

Publication number: EP4389449A1
Application number: EP22315342.0A
Authority: EP
Inventors: Nipun Sharma; Manuel Alejandro FLORES FIGUEROA; Nathalie DESTOUCHES; Francis Vocanson
Original assignee: Centre National de la Recherche Scientifique CNRS; Universite Jean Monnet Saint Etienne; HID Global CID SAS
Current assignee: Centre National de la Recherche Scientifique CNRS; Universite Jean Monnet Saint Etienne; HID Global CID SAS
Priority date: 2022-12-21
Filing date: 2022-12-21
Publication date: 2024-06-26

Abstract

A personalizable security document (1) includes a laser-engravable film (2) formed on a layer (6) of the security document (1) as a functional layer, which can be irradiated with laser light of a specific wavelength to form a color image. The functional layer includes metallic nanoparticles (20) that can be excited with the laser light of a specific wavelength to promote a growth, reshaping, or reorganization of the nanoparticles, which results in a change in the color of the laser-engravable film (2) that can be observed, for example, in one or more observation modes. The laser-engravable film (2) is provided as a thin film in the nanometer range, which is very difficult to tamper with.

Description

Technical Field

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

Generally, in the market of physical identification documents, a variety of different security features is used. In some applications, a laser engraved image is considered vital, as the image features are obtained inside 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.
There are also other approaches for providing security features for such identification documents or other security documents, For example, WO 2015/083099 A1 discloses a security structure comprising a layer containing a binder and goniochromatic metal particles inside the binder.
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

According to one aspect of the present disclosure, a personalizable security documents comprises a substrate (i.e., a body) including a plurality of layers, and a laser-engravable film formed on a first layer of the plurality of layers. The laser-engravable film includes metallic nanoparticles distributed in a matrix (i.e., a base material) of the laser-engravable film. The laser-engravable film is configured to have an image laser-engraved in the same by varying one or more laser parameters of a laser. The metallic nanoparticles are configured to exhibit at least one of a change in size (for example, growth), a change in shape (e.g., anisotropy), and a change in organization upon irradiation with laser light of a specific wavelength from the laser. The at least one of a change in size, a change in shape, and a change in organization results in a color change of the laser-engravable film (in particular, the metallic nanoparticles) depending on the one or more laser parameters. Preferably, the laser-engravable film is included in a security feature formed in the substrate.
In another aspect of the present disclosure, a method of manufacturing a personalizable security document comprises the steps of providing a first layer of a substrate of the security document, applying a laser-engravable film onto the first layer, the laser-engravable film including metallic nanoparticles distributed in a matrix of the laser-engravable film, the metallic nanoparticles being configured to exhibit at least one of a change in size, a change in shape, and a change in organization upon irradiation with laser light of a specific wavelength, providing at least one second layer of the substrate on top of the first layer having the laser-engravable film formed on the same, and combining the at least one second layer with the first layer to form the personalizable security document.
In a further aspect, the present disclosure relates to a method of personalizing a security document, comprising the steps of providing a personalizable security document in accordance with the above aspect, and laser-engraving a personalized image in the laser-engravable film using a laser having the specific wavelength, by varying one or more laser parameters. The one or more laser parameters may include, for example, laser speed, laser power, repetition rate, line spacing, polarization. The personalized image is a color image that is formed using a known relation between the one or more laser parameters and a color of the laser-engravable film, in combination, for example, with techniques such as halftoning and/or gamut mapping.
Other features and aspects of the present disclosure will be apparent from the following description and the accompanying drawings.

Brief Description of the Drawings

Fig. 1 shows a schematic plan view of a personalizable security document in accordance with the present disclosure,
Fig. 2 shows a schematic cross-sectional view of the personalizable security document in accordance with the present disclosure,
Fig. 3 is a schematic cross-sectional view illustrating a process of personalizing the personalizable security document in accordance with the present disclosure,
Fig. 4 is a schematic plan view of a personalized security document in accordance with the present disclosure,
Fig. 5 is another schematic plan view of the personalized security document in accordance with the present disclosure,
Fig. 6 is a schematic plan view illustrating a process for determining a color palette to be used in the personalization of the security document in accordance with the present disclosure,
Fig. 7 is a schematic cross-sectional view of another embodiment of a personalizable security document in accordance with the present disclosure,
Fig. 8 is a schematic plan view of the personalizable security document of Fig. 7,
Fig. 9 is a schematic cross-sectional view illustrating a process for personalizing the security document of Fig. 7,
Fig. 10 is a schematic plan view of the personalized security document of Fig. 7,
Fig. 11 is a first plan view of a security feature in accordance with the present disclosure,
Fig. 12 is a second plan view of the security feature in accordance with the present disclosure,
Fig. 13 is a third plan view of the security feature in accordance with the present disclosure,
Fig. 14 is a schematic cross-sectional view of a laser-engravable film in accordance with the present disclosure,
Fig. 15 is another cross-sectional view of the laser-engravable film in accordance with the present disclosure,
Fig. 16 is a plan view of the laser-engravable film shown in Fig. 14,
Fig. 17 is a plan view of the laser-engravable film shown in Fig. 15, and
Fig. 18 is another plan view of the laser-engravable film of the present disclosure.

Detailed Description

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.
The present disclosure is based at least in part on the realization that the development of security features has become fundamental for secure applications such as ID documents, passports, banknotes, driver's licenses, etc. Printing processes-are generally very complex, thus making it difficult to replicate the documents without the proper tools. However, in recent years, modern digital printers and scanners have become accessible to the general public and are capable of replicating high-quality documents. As a consequence, developing anti-counterfeiting measures has gained immense attraction, and many different elements have been implemented to add an extra layer of protection. Color laser printing, for example, inside a polycarbonate substrate, is one solution to prevent counterfeiting. Here, it has been realized that one particularly secure way of printing a color image inside, for example, a polycarbonate substrate is to provide at least one thin inorganic film including metallic nanoparticles on one of the layers forming the substrate. Here, the metallic nanoparticles can be distributed in a film layer, for example, an inorganic film layer, or provided as a near coalescence metallic film on such a film layer. As used herein, both cases are referred to as the metallic nanoparticles being distributed in a matrix of a laser-engravable film, which is formed by the metallic nanoparticles and the material in or on which the metallic nanoparticles are provided. It will be appreciated that it is also contemplated to provide a plurality of such laser-engravable films stacked on top of each other.
In particular, it has been realized that the at least one film can be applied to the layer of the substrate via coating techniques such as a sol-gel process, physical or chemical vapor deposition, or other known methods to obtain at least one thin film with a thickness on the nanometer scale. Due to this, it becomes nearly impossible to replicate such a coating, in contrast to the dyes and inks that are used in conventional applications for forming laser images inside a polycarbonate substrate, where the thickness of said dyes and inks is in the micron range. In particular, the film thicknesses of the one or more films are critical parameters that must be known within a few nanometers to obtain the desired effects.
In addition, it has been realized that the provision of a functional layer including metallic nanoparticles encapsulated in, for example, an inorganic film enables the production of color gamuts that is a result of the reshaping and self-organization of the nanoparticles, changes in local density, crystal phase, or film thickness. This is in contrast to other technologies, where the color change is obtained by bleaching, burning, or activation of wavelength-specific layers of an applied ink or coating. In particular, due to the fact that the color change of the thin films disclosed herein is a result of the excitation of the nanoparticles at a specific wavelength, there is no need to use several lasers with different wavelengths. Instead, the functional layer including the metallic nanoparticles can be activated by a single laser wavelength, which may lie inside the window of the plasmon resonance of the metallic nanoparticles.
The present disclosure is also based at least in part on the realization that the use of metallic nanoparticles may have the additional effect that said particles also exhibit a color-change effect when viewed under different modes of observation, for example, in transmission or in reflection, or under different observation angles. In particular, this can be achieved in case the laser-engraving is provided in a clear window that extends through the substrate of the security document.
In addition, it has been realized that, with an appropriate calibration, it becomes possible to produce a full color image inside a substrate such as a polycarbonate substrate, both on a white (or other color) background or in a clear window. Here, various techniques such as halftoning and gamut mapping can be applied to print, for example, a color portrait of a holder of a security document with the methods disclosed herein. In some applications, it is possible to generate a multiplexed image, i.e., an image that is seen as a first image when viewed in a first observation mode, and as a second, different image when viewed in a second observation mode. This further increases the security, because it is even more difficult to replicate such a multiplexed image.
It has also been realized that it is advantageous to configure the film including the metallic nanoparticles in such a manner (for example, by selecting appropriate nanoparticles) that the nanoparticles can be excited with a wavelength in the visible range, for example, with a green laser. This further facilitates the personalization of the security document. In other embodiments, infrared (IR) lasers may also be used, for example, with a wavelength of 1064 nm.
Fig. 1 shows a plan view of an exemplary personalizable security document 1 in accordance with the present disclosure. As shown in Fig. 1, security document 1 includes a substrate 4, for example, a polycarbonate or PVC substrate having a substantially rectangular shape. In addition, as shown in Fig. 1, document 1 includes a security feature 3 formed in substrate 4, for example, in the shape of a rectangular window in which one or more security elements can be provided.
It will be appreciated that, after manufacturing, security document 1 may be a personalizable security document. As used herein, the expression "personalizable security document" indicates that the security document is intended to be processed further in order to personalize the same, i.e., include personalized information such as a portrait of the holder of the security document. To this end, security document 1 includes a laser-engravable film 2, which will be described in more detail below.
Fig. 2 shows a schematic sectional view of personalizable security document 1. As shown in Fig. 2, personalizable security document 1 comprises substrate 4 having first side S1 and a second side S2 opposite to first side S1 in a thickness direction d of substrate 4. For example, substrate 4 is formed by stacking a plurality of layers 5, 6 (for example, polycarbonate or PVC layers), and combining them in an appropriate manner, for example, by lamination processes or the like. This is known to the skilled person, such that a detailed description will be omitted herein.
As mentioned above, security feature 3 includes laser-engravable film 2, which is formed on a first layer 6 of the plurality of layers. Laser-engravable film 2 includes metallic nanoparticles 20 distributed (dispersed) in a base material (also referred to as "matrix") of laser-engravable film 2. For example, laser-engravable film 2 may comprise an inorganic base material, for example, a titania-based material, a silica-titania-based material, or other metal oxides such as ZnO, that includes the metallic nanoparticles 20. The metallic nanoparticles 20 may include at least one of Al, Ag, Cu and Au, and may have a size (in particular, an in-plane size) up to a few tens of nm prior to the personalization by irradiation with laser light. In some embodiments, a plurality of layers 6, each including laser-engravable film 2, may be provided and stacked on top of each other. This may allow for obtaining an increased contrast by forming the image in each of the films.
In some embodiments, laser-engravable film 2 has a thickness of between 5 nm and 400 nm, preferably between 50 nm and 350 nm, more preferably between 80 nm and 200 nm. Further, laser-engravable film 2 may be applied onto first layer 6 by known coating techniques such as a sol-gel process, chemical or physical vapor deposition, spraying and/or other chemical or electrochemical techniques or other known methods. An exemplary method of manufacturing personalizable security document 1 will be described later.
Laser-engravable film 2 is configured to have an image 9 (see, for example, Fig. 4) laser engraved in the same by varying one or more laser parameters of a laser 7. Metallic nanoparticles 20 are configured to exhibit at least one of a change in size (for example, growth) and a change in shape (e.g., anisotropy) upon irradiation with laser light of a specific wavelength from laser 7. As will be described in more detail below, the at least one of a change in size and a change in shape results in (contributes to) a color change of laser-engravable film 2, depending on the one or more laser parameters. In some cases, the irradiation with laser light additionally results in a change in the optical properties of the host material (matrix), which may also affect (contribute to) the color change.
In particular, laser-engravable film 2 may form a functional layer comprising metallic nanoparticles 20 and inorganic material. Metallic nanoparticles 20 are provided in a dielectric matrix of the inorganic film, for example, as a nanocomposite of TiO₂ and Ag particles. Initially, as shown, for example, in Figs. 14 and 16, which schematically show metallic nanoparticles 20, for example, when observed using scanning electron microscopy, laser-engravable film 2 includes small nanoparticles and ions, which are distributed in the inorganic matrix of the same. In other embodiments, as mentioned above, metallic nanoparticles 20 may be formed as a near coalescence film on a film layer (matrix) of inorganic material.
After manufacturing of personalizable security document 1, laser-engravable film 2 is configured in such a manner that metallic nanoparticles 20 inside the inorganic matrix have a resonance frequency window (an absorption window), in particular, a plasmon resonance frequency window, at a specific wavelength range. A specific laser wavelength inside this window can be used to irradiate laser-engravable film 2 using laser 7. As a result, an excitation of metallic nanoparticles 20 inside the inorganic matrix occurs, which, in particular, generates heat inside the layer and thereby promotes the change in size (for example, growth), change in shape, and/or reorganization (for example, self-organization) of the nanoparticles. This is schematically shown in Figs. 17 and 18. In particular, as laser parameters of laser 7 change, the temperature rise inside laser-engravable film 2 may form a regular array, as shown in Fig. 18. Generally, the more the temperature rises, the more the nanoparticles grow. It has been found that this change in the size of metallic nanoparticles 20 and/or the shape/arrangement of the same results in different observable colors (in some cases, together with changes in the host material), for example, when laser-engravable film 2 is viewed in reflection from first side S1 of substrate 4. This property can be used to form different colors in laser-engravable film 2 by varying the parameters of laser 7, allowing for the formation of image features that represent, for example, a portrait of a holder of security document 1.
Here, it will be appreciated that the relationship between the one or more laser parameters that are used to irradiate laser-engravable film 2 and the resulting colors may be non-trivial, and may not be known in advance. Therefore, in some embodiments, it is necessary to perform a calibration for a specific laser-engravable film 2, i.e., a specific combination of, for example, metallic nanoparticles 20 and inorganic material. To this end, as shown in Fig. 6, the one or more laser parameters of laser 7 may be continuously or stepwise varied to form a plurality of different images C₁, C₂, C₃, C₄, ..., C₁₆ in a reference laser-engravable film 2. The resulting colors in one or more observation modes can be measured in a known manner and stored in a memory in association with the corresponding laser parameters. In such a manner, a color palette can be generated for a given laser-engravable film 2, which can be used to print a desired image using said palette. For example, the image to be printed may be a full color portrait of the holder of the document. The color values of the input image can then be produced using the palette and, if necessary, known printing techniques such as halftoning and gamut mapping, depending on the number of available colors in the palette. Here, it will be appreciated that, for practical reasons, it may be contemplated that only a limited number of colors are used in the palette, for example, a number of sixteen as indicated in the example shown in Fig. 6. It will be appreciated, however, that this is not limiting the present disclosure.
After the calibration has been performed, a given input image can be formed in laser-engravable film 2 by appropriately varying the one or more laser parameters of laser 7 to generate image 9, which is shown, for example, in Fig. 4. In the example in Fig. 4, image 9 is a secondary image that corresponds to a primary image 8 that is printed on security document 1, for example, in a known manner. For example, image 9 may be an image that replicates the portrait of the holder of security document 1 that is formed as primary image 8 on security document 1.
In some embodiments, the specific wavelength at which the metallic nanoparticles 20 are excited may be a wavelength in the visible range, for example, between 400 nm and 600 nm, or about 530 nm. This allows for using a readily available laser having a wavelength in the visible range in order to form image 9. In other embodiments, an IR laser wavelength (for example, 1064 nm) can be used to form image 9.
In the embodiment shown in Fig. 2, first layer 6 is transparent at least in a region on which laser-engravable film 2 is formed. Here, it is preferable that the remaining layers, for example, a second layer 5 provided on top of first layer 6, are also transparent at least in the region in which laser-engravable film 2 is formed, such that laser-engravable film 2 is visible from both sides S1 and S2 of substrate 4. Fig. 4 shows a schematic plan view of personalized security document 1 with secondary image 9 formed in the above-described manner.
Here, it will be appreciated that, in some embodiments, metallic nanoparticles 20 may exhibit an additional color-change effect, after formation of image 9, when substrate 4 is viewed under different observation conditions, for example, in transmission and reflection, or under different observation angles in transmission or reflection. Such goniochromatic effects are known, and a detailed description will be omitted herein. However, it is important to emphasize that this goniochromatic effect is different from the above-described color change due to the excitation of the metallic nanoparticles 20 resulting in the change in size and/or change in shape of the same. If such a further goniochromatic effect is present, it can be seen, for example, in Fig. 5 that, by viewing image 9 under different observation conditions, the appearance of image 9 will change, resulting in a second image 9a. For example, second image 9a may be the portrait of the holder of security document 1 that has a different color when the observation angle is changed from the configuration shown in Fig. 4 to the configuration shown in Fig. 5 when document 1 is viewed from first side S1 under reflection. Alternatively, second image 9a may also be obtained by changing the observation mode such that, for example, image 9 is viewed in reflection in Fig. 4, and in transmission in Fig. 5. This may also result in, for example, an observed color change.
Fig. 7 shows another embodiment in accordance with the present disclosure, which differs from the embodiment shown in Fig. 2 in that another first layer 10 is not transparent, but opaque. For example, first layer 10 may be a white, non-transparent polycarbonate layer. In addition, laser-engravable film 2 may be used to form an image 12, which is not part of security feature 3. Also in this case, it will be appreciated that, with the methods disclosed herein, image 12 can be formed inside substrate 4, such that image 12 can be protected from outside influences and/or from being tampered with. Accordingly, as shown in Fig. 8, in the present embodiment, laser-engravable film 2 is provided in an image region 11 for forming image 12. As shown in Fig. 9, laser-engravable film 2 is again irradiated with laser light from laser 7 to form image 12, which can be observed from first side S1 of security document 1 as shown in Fig. 10. Here, it will be appreciated that the above-described embodiments can be combined, i.e., two or more laser-engravable films may be provided, for example, one as part of security feature 3, and another one in imaging area 11 for forming image 12.
From the above, it will be evident that image 12 may only be visible from first side S 1 of substrate 4, and not from second side S2 of the same. Nevertheless, the above-described goniochromatic effect can also be present in image 12. In the same manner, the appearance of image 12 can also change depending on whether the same is viewed from first side S1 in reflection or in transmission.
Figs. 11 to 13 indicate other embodiments, where laser-engravable film 2 is configured such that, in particular, a plurality of images are visible as part of security feature 3 depending on different observation conditions. For example, if metallic particles 20 exhibit the above-mentioned goniochromatic effect, a multiplexing of two images 9 and 9b may be possible, where first image 9 is visible under a first observation mode (for example, observation angle), and second image 9b is visible under a second observation mode (for example, observation angle). Here, it will be appreciated that the above-described calibration has to be performed in order to generate a multiplexed palette, i.e., by varying the laser parameters and measuring the two or more color values that can be observed in the two or more observation modes. In addition, the additional steps of halftoning and/or gamut mapping also have to be adapted to the multiplexed palette. By doing so, it becomes possible to, for example, map two different input images (in the examples shown in Figs. 11 and 12, the portrait of the holder and the letter T) to the multiplexed palette, and then print the images by varying the corresponding laser parameters. As a result, depending on the observation mode, either image 9 or image 9b can be seen.
It may also be possible to "hide" certain parts of image 9b depending on the observation modes by using the properties of metallic nanoparticles 20. For example, it may be possible to form a first part of image 9b using a first set of laser parameters, and form a second part of the same using a second set of laser parameters, such that, when the observation mode is changed, part of image 9b disappears, resulting in the exemplary image 9c shown in Fig. 13. It will be readily appreciated that the provision of such additional features results in an even higher security for personalized security document 1, because such complicated effects are much harder to reproduce by a counterfeiter.

Industrial applicability

With the above-described configurations, a cost-effective and secure solution for printing a color image, in particular, inside a polycarbonate substrate can be obtained. In particular, a single wavelength laser, preferably in the visible range, can be used to form the image, for example, in a matter of minutes (depending on the image size). The use of a laser allows for obtaining a high quality, due to the high resolution that is offered by the laser process. In addition, security can be further enhanced by selecting the properties of the metallic nanoparticles and the inorganic layer such that different images can be observed under different observation modes, and even multiplexing of images is possible.
An exemplary method of manufacturing a personalizable security document 1 in accordance with the present disclosure will be described in the following.
In a first step, first layer 6 of substrate 4 of security document 1 is provided. Then, laser-engravable film 2 is applied onto first layer 6, laser-engravable film 2 including metallic nanoparticles 20 distributed in the matrix of laser-engravable film 2 in the above-described manner. As also mentioned above, metallic nanoparticles 20 are configured to exhibit at least one of a change in size (for example, growth), a change in shape, and a change in organization upon irradiation with laser light of a specific wavelength.
After formation of laser-engravable film 2, at least one second layer 5 of substrate 4 is provided on top of first layer 6 having laser-engravable film 2 formed on the same. In a subsequent step, at least one second layer 5 is combined with first layer 6 to form personalizable security document 1. Here, it will of course be appreciated that any desired number of additional layers, either partially or fully transparent or opaque, can be added to first layer 6 and second layer 5 to obtain security document 1 (in particular, one or more protective layers can be added). Substrate 4, i.e., personalizable security document 1, can be formed, for example, by laminating the plurality of layers in a known manner.
In some embodiments, laser-engravable film 2 is applied onto first layer 6 using a coating technique such as a sol-gel process, chemical or physical vapor deposition, spraying and other chemical or electrochemical techniques, or other methods, which are known to the skilled person. Further, in some embodiments, the further steps of curing and/or stabilizing laser-engravable film 2 by heating and/or UV treatment may be included. For example, a heat treatment at temperatures between 40°C and 120°C may be performed, and/or a UV treatment with wavelengths between 200 and 300 nm, for example, about 254 nm, can also be performed. This results in the stabilization of the functional layer including metallic nanoparticles 20 and the inorganic matrix including the same.
After manufacturing personalizable security document 1 in the above manner, security document 1 can be personalized, for example, by performing the following steps.
An image 8 (or 9) is laser-engraved using laser 7 having the specific wavelength, by varying one or more laser parameters. The laser parameters include, for example, laser speed, laser power, repetition rate, line spacing, polarization. In this process, the above-described palette, which is generated in advance, may be used. The specific wavelength may be a wavelength in the visible range, for example, between 350 nm and 600 nm. For example, the wavelength may be 350 nm in case metallic nanoparticles 20 include Au, and it may be 530 nm in case metallic nanoparticles 20 include Ag. During the personalization, the nanoparticles may exhibit, for example, the above-mentioned growth, such that after forming the image said nanoparticles may have a size, for example, an in-plane size, on the order of 100 nm, for example, up to 130 nm, in particular, between 20 and 80 nm.
The result of the above-described personalization is an image that is a color image, which is formed inside substrate 4 of security document 1 in the above-described manner.
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.
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.
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

A personalizable security document (1) comprising:
a substrate (4) including a plurality of layers (5, 6, 10); and

a laser-engravable film (2) formed on a first layer (6, 10) of the plurality of layers (5, 6, 10), the laser-engravable film including metallic nanoparticles (20) distributed in a matrix of the laser-engravable film,

wherein the metallic nanoparticles (20) are configured to exhibit at least one of a change in size, a change in shape, and a change in organization upon irradiation with laser light of a specific wavelength from a laser (7), the at least one of a change in size, a change in shape, and a change in organization resulting in a color change of the laser-engravable film (2) such that an image (8, 9, 9a-9c, 12) can be laser engraved in the laser-engravable film (2) by varying one or more laser parameters of the laser (7).
The security document of claim 1, wherein the laser-engravable film (2) has a thickness between 80 nm and 200 nm, preferably between 100 nm and 180 nm.
The security document of claim 1 or 2, wherein the laser-engravable film (2) comprises an inorganic material, for example, a titania-based material, including the metallic nanoparticles (20).
The security document of any one of claims 1 to 3, wherein the metallic nanoparticles include at least one of Al, Ag and Au.
The security document of any one of claims 1 to 4, wherein the metallic nanoparticles have a size, for example, an in-plane size, between 1 nm and 100 nm, preferably between 5 nm and 40 nm, prior to irradiation with laser light.
The security document of any one of claims 1 to 5, wherein the specific wavelength is a wavelength that is absorbed by the metallic nanoparticles (20), for example, in a plasmon resonance window of the metallic nanoparticles (20).
The security document of claim 6, wherein the specific wavelength is in the visible or near infrared range, for example, between 350 nm and 1100 nm, preferably about 530 nm or about 1064 nm.
The security document of any one of claims 1 to 7, wherein the first layer (6) is transparent at least in a region on which the laser-engravable film (2) is formed, preferably, wherein the laser-engravable film (2) is visible from both sides (S1, S2) of the substrate (4).
The security document of any one of claims 1 to 8, further comprising a security feature (3) that is formed in the substrate (4),
wherein the laser-engravable film (2) is included in the security feature (3), and/or

wherein the laser-engravable film (2) is configured to form a primary image (8) that is not part of the security feature (3).
The security document of any one of claims 1 to 9, wherein the metallic nanoparticles (20) exhibit a color-change effect when the substrate (4) is viewed under different observation conditions, for example, in transmission and reflection, or under different observation angles in transmission or reflection.
The security document of any one of claims 1 to 10, wherein the first layer (6, 10) is a polycarbonate layer, preferably, wherein the plurality of layers (5, 6, 10) are polycarbonate layers, more preferably, wherein the substrate (4) is a polycarbonate substrate.
A method of manufacturing a personalizable security document (1), comprising:
providing a first layer (6, 10) of a substrate (4) of the security document (1);

applying a laser-engravable film (2) onto the first layer (6, 10), the laser-engravable film including metallic nanoparticles (20) distributed in a matrix of the laser-engravable film, the metallic nanoparticles (20) being configured to exhibit at least one of a change in size, a change in shape, and a change in organization upon irradiation with laser light of a specific wavelength;

providing at least one second layer (5) of the substrate (4) on top of the first layer (6) having the laser-engravable film (2) formed on the same; and

combining the at least one second layer (5) with the first layer (6, 10) to form the personalizable security document (1).
The method of claim 12, further comprising applying the laser-engravable film (2) by using a coating technique such as a sol-gel process, chemical or physical vapor deposition, spraying and other chemical or electrochemical techniques or other methods.
The method of claim 12 or 13, further comprising at least one of curing and stabilizing the laser-engravable film (2) by heating and/or UV treatment, for example, at temperatures between 10°C and 120°C and/or with wavelengths between 200 nm and 300 nm, for example, about 250 nm.
A method of personalizing a security document (1), comprising:
providing a personalizable security document (1) in accordance with any one of claims 1 to 13; and

laser engraving an image (8, 9, 9a-9c, 12) in the laser-engravable film (2) using a laser (7) having the specific wavelength, by varying one or more laser parameters,

wherein the image (8, 9, 9a-9c, 12) is a color image that is formed using a known relation between the one or more laser parameters and a color of the laser-engravable film (2), for example, in combination with techniques such as halftoning and/or gamut mapping.