EP4000940A1

EP4000940A1 - Security document in which a window comprises an ovm part and a photochromic or thermochromic material part

Info

Publication number: EP4000940A1
Application number: EP20306425.8A
Authority: EP
Inventors: Christophe Duriez; Leonardus Segeren
Original assignee: Idemia France SAS
Current assignee: Idemia France SAS
Priority date: 2020-11-20
Filing date: 2020-11-20
Publication date: 2022-05-25

Abstract

Security document (20) comprising a body (21), in which a cavity extends in at least a part of a thickness of the body from at least on side (22), and the body comprising a window (10) embedded in the cavity, the window (10) comprising at least an OVM part (11) and a chromic material part (12), at least a portion of the OVM part (11) being superimposed with at least a portion of the chromic material part (12).

Description

Technical field

The present invention relates to a security document.
It relates more particularly to security features to authenticate a security document.
It relates more specifically to a security document comprising a body including a cavity extending in at least a part of a thickness of the body from one side of the body, and in which a window is embedded.

Background of the invention

Nowadays identity documents are to be checked against counterfeiting and falsification in a fast and easy way, either manually or visually or automatically, i.e. by means of external devices.
A way of facilitating authentication of a security document is to incorporate a transparent and/or translucent window in a design of such a security document, which allows the usage of a "z-direction", i.e. a direction along a thickness of the window, to enhance the security level.
A goal of the present invention is to provide a security document in which the window limits risks of reproduction or falsification, and which provides an easy way to inspect the authenticity of the security document.

Summary of the invention

Accordingly, the invention provides a security document comprising a body, the body comprising at least one side and a cavity extending in at least a part of a thickness of the body from the side, and the body comprising a window embedded in the cavity, the window comprising at least an OVM part and a chromic material part, at least a portion of the OVM part being superimposed with at least a portion of the chromic material part.
Thus, security level of such a window can be drastically improved, whilst giving enhanced visual appearance and design identity to an inspector and a user or document providing authority, owing to a careful design of the window.
Such a window permits to take advantage of a depth, i.e. thickness, of the document (i.e. z-axis or z-direction).
The window can extend over only a part of the thickness of the body, or cross the entire thickness.
Such a window is further advantageously combined with other security features using a surface of the body.
For example, it can be combined with at least another security feature inside the bulk of the body, either above and/or below the OVM part, or even the window. For example, such another security feature can be a security artwork on one transparent layer.
The OVM part here designates a part of the window, which comprises an OVM.
An OVM is an optically variable material, i.e. a material which shows colour shifting effects depending on a colour of a background on which it is placed.
Thus, the OVM part is of a first colour when on a white background, and of a second colour, different from the first colour, when on a black background.
Here, "colour" includes any hue of colour, including colourless, as well as transparency or translucency.
Besides, a "white" background here means a background which is white or of any bright colour, while a "black" background here means a background which is black or of any dark colour.
In addition, an OVM is often UV fluorescent.
Document FR 3 080 325 describes for example such an optically variable material.
Such a material has appeared to be very interesting for securing and/or authenticating a product in order to fight against counterfeits or production of forgeries.
In an exemplary embodiment, the optically variable material comprises a given concentration of an active substance comprising one or more fluorescent compound (s), particularly of the family of 4,4-difluoro-4-bora-3a, 4a-diaza- s-indacenes or from the difluoroborane p-diketonate family (BF2bdks).
For example, the OVM part comprising the optically variable material also comprises a polymer in which the OVM is incorporated.
For example, the OVM part forms a layer of the window.
A chromic material part here designated a part of the window, which comprises a material the colour of which changes from a first colour to a second colour, which is different from the first one, under an external stimulus, which can be chemical or physical.
For example, without exposure, the chromic material part is of the first colour, and when the chromic material part is subjected to an exposure, it is of the second colour.
Here, "colour" includes any hue of colour, including colourless, as well as transparency or translucency.
Such changes are often reversible, which means that the change of colour can be repeated and reproduced.
Here, the changes of colour are preferably reversible.
According to an example embodiment, the colour change of the chromic material occurs gradually in time, typically in the order of seconds or minutes. Then, the chromic material often is time dependent in its colours changes.
According to one example embodiment, the chromic material part comprises at least one of a thermochromic material or a photochromic material.
A thermochromic material is a chromic material which is sensitive to temperature, while a photochromic material is a material which is sensitive to light; the light being for example general visible light (i.e. a light comprising at least one wavelength comprised between about 400 nm and 700 nm), or UV light (ultraviolet, for wavelength smaller than 400 nm, for example between 100 nm and 400 nm), or IR light (infrared, for wavelength greater than 700 nm, for example between 700 nm and 11 000 nm).
For example, an exposure source can be a finger (the temperature of which is generally higher than the temperature of a surface of the window), or a lamp.
According to one interesting example embodiment, the chromic material turns colourless and transparent under exposure.
Such result can for example be achieved owing to a thermochromic or a photochromic ink.
Such a thermochromic ink is for example water-based or solvent-based, and can use an active principle of liquid crystal type or of leuco-derivative type. Liquid crystal based inks are sensitive to small changes in temperature, but are relatively expensive and difficult to manufacture. Thermochromic materials therefore most often use leuco-derivatives, the complete colour change of which requires a variation of three degrees or more. These compounds are for example encapsulated in gelatine droplets of a diameter of about 10 µm to 20 µm, and of a thickness of about 1 µm to 2 µm. This microencapsulation allows thermochromic substances to be trapped in sealed microspheres which can then be incorporated into aqueous mixtures such as inks, without reacting with their other components. Document WO 0104221 describes an example of such a thermochromic ink.
Such a photochromic ink can comprise, for example, a spiropyran material, which changes between colourless to colour, reversible.
According to an interesting example embodiment, the chromic material part forms a pattern.
A pattern here includes at least one data, for example, a letter, and/or a number, and/or a symbol, and/or a picture, and/or any other element.
For example, the chromic material part has smaller apparent surface than the OVM part.
According to the invention, at least a portion of the OVM part is superimposed with at least a portion of the chromic material part.
Here, superimposed means that one of the parts is above or below another of the parts, and the part which is below the other part appears covered by this other part from a viewer's point of view, for example if an inspector checks the security document.
According to one example embodiment, the window comprises an additional pattern.
Such additional pattern designates personalized data which further enhances personalisation of the security document, and therefore further improves its security.
According to one example embodiment, at least a portion of the chromic material part is superimposed with at least a portion of the additional pattern.
Such additional pattern can be engraved or printed.
Such additional pattern is often black coloured, in particular when it is engraved. When it is printed it can be of any colour, as desired and possible.
According to one example embodiment, the window comprises a laser sensitive part in which the additional pattern is engraved.
A laser sensitive part here designates a part of the window comprising a material in which any pattern can be engraved, for example by means of a laser.
For example, the laser sensitive part can be mainly transparent, and preferably colourless.
For example, the laser sensitive part is formed of a layer.
According to one example embodiment, the window comprises at least a transparent part.
The transparent part is possibly colourless.
For example, the transparent part is formed of a layer.
As stated above, the OVM part changes colour depending on the background colour on which it is set.
Such background can be either an independent device, for example like a mat or a board, or it can be part of the security document.
The background comprises at least one colour.
According to one example embodiment, the security document comprises at least one background. Thus, the security document comprises at least one configuration in which at least a portion of the OVM part is superimposed with the background.
Integration of both the window and the background into the security document can be done in a so-called "asymmetric way"; for example, the window is integrated in the cavity of body, whereas the background can have a different size, and/or geometry, and/or position in the security document.
According to one example embodiment, the body comprises the background.
According to an example, they can be of different sizes, and/or geometries, and/or positions in the body, and the body can be folded so that the window can be superimposed with the background in at least one configuration of the security document.
Otherwise, for example, the background can be positioned in the bottom of the cavity, under the window or backside the window.
In this respect, the body can comprise lenses, like a lenticular lens, on top of the window; for example lenses on top of the document can work together with the chromic, OVM, pattern or a combination of these. Magnification, for example Moire magnification, would facilitate the authentication, and improve the security of the document. In addition, these lenses enable localized engraving under different angles, for multiple patterns to be inspected. These patterns may include data, including personal data.
Functionalities for at least the OVM part and/or the chromic material part can then be quickly integrated, without relying fully on a background for the window as generated by a handling of an inspector of the security document's authenticity.
According to another example, the window comprises the background.
According to a more specific example, the chromic material part forms at least a portion of the background.
For example, the chromic material part is positioned under the OVM part so that under exposure the chromic material part changes colour, inducing a change of colour of the OVM part.
Such configuration can be combined with a background set in the document, even in the window, or formed of an independent device.
According to one interesting embodiment, the security document can comprise a booklet, like for example a passport.
In such an embodiment, the body in which the window is embedded is for example any sheet, for example the first sheet, of the booklet, and the background is formed, for example, on a backside of a front cover of the security document booklet.
Security documents, like for example an identity card or a passport, can be rapidly authenticated by the colour combinations and changings in one window, either by an inspector directly or by simple additional tools like a mobile phone flashlight, a light source, or a document scanner.
The incorporation of dedicated materials, like inks, in certain positions and locations in the window which contains an OVM permits the above and creates security features that can be authenticated, either complemented through personalization (by adding printed or engraved additional patterns) or not, that respond to induced temperature elevation, or visible, UV or IR or high-intensity light stimulation.

Brief description of the drawings

Additional features and advantages of the present invention are described in, and will be apparent from, the description of the presently preferred embodiments which are set out below with reference to the drawings in which:

Figure 1 diagrammatically shows a cross-section of a security document according to a first example embodiment of the invention;
Figure 2 illustrates the changes of colour of a window like the one of the embodiment of figure 1;
Figure 3 diagrammatically shows a cross-section of a security document according to a second example embodiment of the invention;
Figure 4 illustrates the changes of colour of a window like the one of the embodiment of figure 3;
Figure 5 diagrammatically shows a cross-section of a security document according to a third example embodiment of the invention;
Figure 6 illustrates the changes of colour of a window of a forth example embodiment of the invention; and
Figure 7 illustrates the changes of colour of a window of a fifth example embodiment of the invention.

Detailed description of the invention

Figure 1 shows a diagrammatic cross-section of a security document 20, for example an identity document.
The security document 20 comprises a body 21, like a sheet or a card body.
The body 21 comprises a front side 22 and a back side 23.
For example, the front side 22 designates a side of the body, which comprises a portrait of a person to who the security document 20 belongs, and/or personal data.
The body 21 further comprises a cavity 24 extending from the front side 22.
The cavity can extend on only a part of the thickness of the body, or go through the entire thickness of the body 21.
Here the cavity extends until the back side 23, so that the cavity crosses the entire thickness of the body 21.
However, in practice, the body 21 is set between two transparent and/or translucent layers on either side therefore, one on top and the other below; such transparent/translucent layers are usually called overlays and they cover the internal layers, here referred to as the body, and their security feature.
In addition, lenses, like for example a lenticular lens, can be sit on top of at least one of these two overlays, for example the top overlay.
Thus, the thickness of the body 21 is here defined by a corresponding dimension between the front side 22 and the back side 23.
The security document 20 further comprises a window 10.
The window 10 is embedded in the cavity 24 which is formed in the body 21, and extends on at least a part of the thickness of the body.
The window 10, in the cavity 24, extends in the body 21 from the front side 22.
In the illustrated embodiment, the window 10 extends through an entire thickness of the body 21, until the back side 23.
Therefore, the window 10 here goes through the body 21.
However, it could extend on only a part of the thickness of the body, and/or from anyone of the sides (front side or back side).
The window 10 according to one example embodiment of the invention comprises mainly an OVM part 11 and a chromic material part 12.
The OVM part 11 here designates a part of the window which comprises an OVM.
An OVM refers to an optically variable material, for example like the one described in document FR 3 080 325 .
Such material can be incorporated in polycarbonate foils, e.g. by compounding and film extrusion.
The OVM is a material which shows colour shifting effects depending on a colour of a background.
In addition, such OVM can be UV fluorescent and then emits one single colour.
For example, the OVM part 11 is of a first colour (for example diagrammatically represented in white in figure 2) when on a white background 30, and of a second colour (for example diagrammatically represented by hatchings in figure 2) when on a black background 30.
Here, a white background represents a background 30 which is white or of any bright colour, while a black background represents a background 30 which is black or of any dark colour.
For example, the OVM part 11 comprises one specific OVM in polycarbonate.
For example, such an OVM-in-polycarbonate OVM part 11 is blue when on white background and red when on black background.
Here, the OVM part 11 is formed of a layer.
Here, the OVM part 11 comes out on the front side 22. In other word, a surface of the OVM part 11 substantially forms a part of the front side 22.
A chromic material part 12 here designates a part of the window which comprises a material the colour of which changes from a first colour to a second colour, under an external stimulus, which can be chemical or physical.
Such changes are often reversible.
Here, the changes of colour are preferably reversible and occur gradually in time, typically in the order of seconds or minutes.
Here, the chromic material of part 12 is for example sensitive to temperature or light (which can be general visible light, or UV light, of IR light).
For example, an exposure source can be a warm finger, or a lamp, a UV lamp or an IR lamp.
Therefore, the chromic material of part 12 is for example a thermochromic material or photochromic material.
More particularly, the chromic material of part 12 is for example a thermochromic or photochromic ink.
For example, without exposure, the chromic material of part 12 is of the first colour (for example black), and when the chromic material of part 12 is subjected to an exposure, like a thermal or light exposure for example, it is of the second colour (for example colourless and transparent, which is here considered as a colour).
According to the invention, at least a portion of the OVM part 11 is superimposed with at least a portion of the chromic material part 12.
Here, superimposed means that one of the parts is above or below another of the parts, and the part which is below the other part appears covered by this other part from a viewer's point of view, for example if an inspector checks the authentication of the security document.
Here, the chromic material part 12 is below the OVM part 11.
More specifically, at least in this example, only a portion of the OVM part 11 covers the chromic material part 12, and another portion of the OVM part 11 surrounds the chromic material part 12.
For example, the chromic material part 12 has a smaller apparent surface than the OVM part 11.
The chromic material part 12 is for example formed of a pattern. A pattern here includes at least one data, for example, a letter, and/or a number, and/or a symbol, and/or a picture, and/or any other element.
Figure 2 illustrates the changes of colour of the window 10, like the one of figure 1. In this figure, the OVM part 11 is represented by a larger circle than the chromic material part 12 to facilitate illustration of the changes. However, a cross section of the window 10 can be of any shape, preferable rectangle, square, oval or circular for example. The chromic material part 12 can also be of any shape as mentioned above, and preferable represents a pattern.
Then, for example, in figure 2a), the window 10 is placed on top of a white background 30.
The window 10 is in a first configuration which is considered as the natural configuration.
From figure 2a) to figure 2b), the window 10 is subjected to an exposure, in particular a thermal exposure, like a temperature elevation, or a light exposure, for example a higher intensity of light, and for example of visible light, or UV, or IR. In figure 2b), the window 10 is still on top of a white background 30.
In figure 2c), the window 10, while under the exposure, is placed on top of a black background 30.
From figure 2c) to figure 2d), the window 10 is subjected to a removal of the exposure. In figure 2d), the window 10 is still on top of a black background 30.
As mentioned above, OVM part 11 is for example of a first colour (for example diagrammatically represented in white) when on a white background, and of a second colour (for example diagrammatically represented by hatchings) when on a black background.
And for example, the chromic material of part 12 comprises a thermochromic material or photochromic material which is black in a said natural state (without exposure) and colourless transparent under exposure, in a said excited state.
The colours of the chromic material in either natural state or excited state can be different, depending on the requirement of the contemplated application.
In the present example, as illustrated in figure 2a), the window 10 appears of the second colour (for example represented by hatchings) where the OVM part 11 is superimposed with the chromic material part 12 which is there black, while it still appears of the first colour (represented in white) around the chromic material part 12, where the OVM part 11 is superimposed with the white background 30.
From figure 2a) to figure 2b), the window 10 is subjected to an exposure, in particular a thermal or a light exposure.
For a thermal exposure, the chromic material is preferably a thermochromic material, and for a light exposure, the chromic material is preferably a photochromic material.
A thermochromic exposure is for example a use of someone's finger, which is considered as naturally warm enough to generate a thermal heat of the chromic material.
A light exposure, also said phosphorescence, is for example a use of a light, for example of a different intensity, for example a flash light, or a UV or IR light by a UV or IR lamp.
Then, under exposure, as illustrated in figure 2b), while the whole window 10 is still on a white background 30, the chromic material part 12 turns from its original colour, for example here black, to a second colour, for example here colourless transparent.
As a consequence, the entire OVM part 11 appears superimposed with the white background 30 and therefore turns entirely of the first colour.
Still under exposure, the window 10 can be moved to a black background 30 as illustrated in figure 2c).
Considering the chromic material part 12 is still colourless transparent, the window 10 now appears superimposed entirely with the black background, and then the OVM part 11 entirely appears of its second colour (for example red, diagrammatically represented by hatchings).
If the exposure is removed, after a time depending on the reaction time of the chromic material of part 12 for example, the chromic material returns to its natural colour, for example here from colourless transparent to black.
The colour of the OVM part 11 depends on whether it is superimposed with the chromic material part 12 or with the background 30.
In figure 2d), as both the background 30 and the chromic material part 12 are black, the window 10 is of the colour of the OVM part 11 which is of the second colour (represented by hatchings), either where it is superimposed with the chromic material part 12 or with the background 30.
Thus, it can be noticed from this example illustrated in Figure 2 that the chromic material part 12 also plays the role of a background.
Therefore, there can be at least two levels of security, here:

A first security level in which for example a finger of someone is used to authenticate the document holder; and
A second security level in which an external, independent device, for example a lamp emitting light, or even specifically a UV or IR lamp, is used to identify other security features, like for example to make appear or disappear patterns formed by the chromic material part 12.

Referring back to figure 1, the window 10 can also comprise a laser sensitive part 13.
A laser sensitive part here designates a part of the window 10 comprising a material in which any additional pattern can be engraved, for example by means of a laser. Therefore, it is usually mainly transparent, and for example colourless.
In the illustrated embodiment, the laser sensitive part 13 is formed of a layer.
In addition, it is here positioned between the OVM part 11 and the chromic material part 12.
According to another example embodiment, not illustrated here, the OVM layer 11 may also be laser sensitive; hence, the OVM part 11 can include at least a part of a pattern which can be laser engraved. In such case, the OVM part 11 and the laser sensitive part 13 may, in practice, be formed of a same layer. Such can be said "laserable OVM PC".
As illustrated in figure 1, the window 10 can also comprise a transparent part 14.
In addition, the transparent part 14 can be colourless.
In the illustrated embodiment, the transparent part 14 is formed of a layer.
In addition, the transparent part 14 is here positioned under the chromic material part 12. In other words, the chromic material part 12 is placed between the transparent part 14 and the OVM part 11, and even here between the transparent part 14 and the laser sensitive part 13.
Here, a surface of the transparent part 14 substantially forms a part of the back side 23.
According to another embodiment not illustrated here, the window may also comprise printings, for example printed on any of the parts of the window. For example, such printings can represent any data.
Figures 3 and 4 illustrate an example embodiment integrating personalization data to enhance the security level. This can also enable certain designs executed in different technologies and principles to enhance security.
Same features bear same numeral references as in figures 1 and 2.
In this illustrated example, an additional pattern 15 is engraved in the laser sensitive layer 13. However, the additional pattern 15 could be engraved in the OVM part 11, as mentioned above.
As it is engraved, such additional pattern 15 is generally black coloured.
For illustration only, the additional pattern 15 comprises a word "XX-X".
Figures 4a) to 4d) correspond respectively to figures 2a) to 2d).
However, in addition, in figures 4b) and 4c), as the chromic material part 12 is there transparent, the additional pattern 15 becomes visible.
In figures 4a) and 4d), as the chromic material part 12 is there black, the additional pattern 15 is hidden.
The described example relies on a naturally black chromic material part, and a commonly black written additional pattern 15, however same is valid for any colours, providing that a contrast between the colour of the additional pattern 15 and the colour of chromic material part 12 is low enough for at least a human eye can't distinguish one from the other, the chromic material being in any of its natural state or excited state, depending on when the additional pattern might appear or disappear.
However, the additional pattern 15 being usually black laser engraving, it may be difficult to inspect on a black background.
In addition to, or instead of engraved additional pattern 15, same would occur in case of an additional pattern added behind the window 10, such as being printed on a back side of the window 10 or on any other support, or even for example on a following sheet of a booklet if the security document 20 comprises a booklet, like a passport.
Figure 5 shows another example embodiment comprising personalization data like in figure 3.
Same features bear same numeral references as in figure 3.
The embodiment of figure 5 differs from the embodiment of figure 3 in that the order of the part in this embodiment is different: mainly, it comprises two layers of transparent part 14 between which the chromic material part 12 is positioned.
Furthermore, the window 10 of figure 5 comprises a laser sensitive part 13 formed of a layer forming a back layer of the window 10.
Thus, both transparent part 14 surrounding the chromic material part 12 are positioned between the OVM part layer and the laser sensitive part 13.
However, the additional pattern 15 here remains superimposed with the chromic material part 12, as in figure 3. Notwithstanding, in figure 3, the additional pattern 15 is above the chromic material part 12, while in figure 5, the additional pattern 15 is below the chromic material part 12, and the chromic material part 12 is between the OVM part 11 and the additional pattern 15.
Complementary security can also be achieved by lateral personalization combined with thermochromic or photochromic materials and OVM in ordered layers in the thickness direction of the body.
In figures 6 and 7, same elements bear same numeral references.
Figure 6 shows an embodiment in which the window 10 is set on a white background 30. At least a portion of the OVM part 11 appears of the first colour. The chromic material part 12 comprises for example a black ink, which is IR sensitive, which forms a pattern which is here diagrammatically represented by "X-X". Therefore, under an IR lamp, only the pattern, here "X-X", becomes visible. In this example, it appears white. For example, in this case, the window 10 can comprise a coloured zone, for example black, to ease the identification of the pattern represented by the chromic material part 12 under IR. Such coloured zone can be formed by an additional pattern 15 for example, placed below the chromic material part 12.
In such example, the OVM part 11 can also be below the additional pattern 15.
Figure 7a) to 7d) show an example embodiment in which personalisation is also realised by engravings.
In figure 7a), the window 10 is set on a white background 30. The OVM part 11 appears of the first colour, at least around the chromic material part 12.
In figure 7b), the window 10 is set on a black background 30. The OVM part 11 appears of the second colour, at least around the chromic material part 12. This would be a first level of authentication for example, in which only a different background hue (bright/dark) is used.
At a second level of authentication, the chromic material part 12 can comprise, for example, at least a pattern of IR sensitive ink, drawing for example here "X-X" in black under exposure, for example under an IR lamp, as illustrated in figure 7c).
Furthermore, the window 10 can also comprise a laser engraved additional pattern 15, here for example representing "T", as illustrated in figure 7d). In this embodiment, when a main part of the chromic material part 12 becomes transparent under exposure, it lets appear the additional pattern 15, which can thus be over or below the chromic material part 12.
Considering figure 7c) and 7d), the chromic material part 12 can therefore comprise both a portion comprising a chromic material which turn transparent, and even colourless, under exposure, and a portion comprising IR ink.
The embodiments illustrated in figure 6 and 7 also show that the chromic material part 12 can be over the OVM part 11, unlike illustrated in the embodiments of figures 1 to 5 where the chromic material part 12 is under the OVM part 11.
Similarly, the additional pattern 15 can be set above or below the OVM part 11 and/or the chromic material part 12, depending on the desired effect.
If necessary, the window can also comprise at least one transparent layer on top, for example an overlay as mentioned above, to form a part of the front side of the body, to provide a smooth surface and/or protect the window, for example the OVM part or the chromic material part, depending on which one is on top.

Claims

Security document (20) comprising a body (21), the body comprising at least one side (22) and a cavity extending in at least a part of a thickness of the body from the side (22), and the body comprising a window (10) embedded in the cavity, the window (10) comprising at least an OVM part (11) and a chromic material part (12), at least a portion of the OVM part (11) being superimposed with at least a portion of the chromic material part (12).
Security document (20) according to claim 1, wherein the chromic material part (12) comprises at least one of a thermochromic material or a photochromic material.
Security document (20) according to anyone of claims 1 or 2, wherein the chromic material part (12) forms a pattern.
Security document (20) according to anyone of claims 1 to 3, wherein the window (10) comprises an additional pattern (15).
Security document (20) according to claim 4, wherein the window (10) comprises a laser sensitive part (13) in which the additional pattern (15) is engraved.
Security document (20) according to anyone of claims 4 or 5, wherein at least a portion of the chromic material part (12) is superimposed with at least a portion of the additional pattern (15).
Security document (20) according to anyone of claims 1 to 6, wherein it comprises at least one background (30), the security document (20) comprising at least one configuration in which at least a portion of the OVM part (11) is superimposed with the background (30).
Security document (20) according to claim 7, wherein the body (21) comprises the background (30).
Security document (20) according to anyone of claims 7 or 8, wherein the window (10) comprises the background (30).
Security document (20) according to anyone of claims 7 to 9, wherein the chromic material part (12) forms at least a portion of the background (30).