EP3523136B1 - Method for producing a security element - Google Patents

Description

The present invention relates to security elements for secure documents, and their manufacturing methods.

The invention relates more particularly to security elements carrying liquid crystals.

Liquid crystals, especially cholesteric, are widely used in security elements for their goniochromatic properties. In order to improve the visibility of the color change effect with the angle of observation, they are generally placed in front of a dark background, in particular black.

Furthermore, tape security elements, also called security threads, are very often incorporated into secure documents such as banknotes.

These security elements conventionally comprise a substrate made of a thermoplastic material, for example PET, which can be metallized and provided with demetallized zones in the form of patterns appearing in transmitted light.

There is an interest in providing these security elements with liquid crystals in order to enhance security by creating optical effects visible to the naked eye.

However, the deposition of liquid crystals comes up against multiple problems, which are currently only solved through processes that are complex to implement, costly and impose certain limitations in terms of arrangement.

Thus, it is known to apply liquid crystals in the form of a solid by a transfer process, with the drawback of limiting the possibilities on the artistic level, and of imposing the presence of liquid crystals in the demetallized zones. This imparts a coloration in transmitted light which is unattractive, and the presence of liquid crystals in the demetallized areas increases the cost of security without providing any significant gain in terms of security or artistically.

The transfer process generates a loss of material and lamination steps, which make manufacturing more complex.

EP 1 744 904 discloses a substrate made of a biaxially oriented PET film coated with oriented liquid crystals. This type of structure does not offer complete satisfaction in terms of adhesion to the substrate.

Requirement US 2003189684 describes various methods for the orientation of liquid crystals.

Requirement US20070216518 discloses multilayer liquid crystal structures. The superposition of liquid crystals makes structures expensive, increasing the amount of liquid crystals to be used. Manufacturing by a transfer process is preferred.

Requirement EP2 073 986 also describes structures with superposition of liquid crystals.

JP 2009-98568 discloses a security element comprising an oriented film, of plastic material, capable of undergoing biaxial stretching and capable of carrying liquid crystals.

GB 2 527 763 discloses a sheet having an oriented polymeric film and capable of containing liquid crystals as well as an adhesive layer.

WO 2008/116796 relates to a security document comprising a plurality of polymeric films including a non-transparent film undergoing axial stretching. Adhesive layers can be applied to this film by printing. Furthermore, this film may include liquid crystals.

There is a need to further improve the liquid crystal security elements and their manufacturing processes, in particular to have security elements in which the liquid crystals adhere well to the substrate, are used fully and in a manner allowing a large wealth of optical effects.

The invention aims to meet this need, and it achieves it by means of a method of manufacturing a security element comprising an oriented plastic support and at least one layer of liquid crystals carried and oriented by the support, a primer adhesion being deposited before or after the stretching of the support at least in one direction, said stretching making it possible to bring the support to the oriented state and the liquid crystals being deposited by printing on this adhesion primer.

The term “adhesion primer” should be understood to mean any layer promoting adhesion. Thus this expression should not be understood in a limiting manner.

Thanks to the invention, the adhesion of liquid crystals is improved and the deposition of liquid crystals by printing offers multiple possibilities in terms of aesthetics and optical effects obtained.

The application of the liquid crystals can be carried out in any pattern, on well-defined areas, offering great flexibility in the arrangement. different means of securing within the element. It is possible to obtain a greater diversity of color change effects, without penalizing the transparency of the openings of a Cleartext, if necessary.

The invention makes it possible to avoid deposition of liquid crystals by transfer, which facilitates the implementation of the method.

Preferably, the adhesion primer is deposited before a step of stretching the support.

More preferably, the support is oriented in one direction, then the primer is deposited, and the support is then stretched in another direction.

The fact of applying the primer before stretching of the support allows the primer to accompany the stretching of the support and thus further improves the orientation of the liquid crystals.

The support preferably comprises PET, but other materials can be used.

The primer may require crosslinking before application of the liquid crystals, in particular when it comprises monomers. The method can thus comprise a step of crosslinking the adhesion primer, preferably after stretching of the support.

The adhesion primer may comprise a polyolefin (or polyalkene), preferably polyethylene, polyurethane, polyester, polyether, polycarbonate, polyacrylic or one of their copolymers, and preferably comprise a polyacrylic.

The adhesion primer may comprise, in particular before its deposition, at least one olefin (or alkene), urethane, ester, ether, carbonate or acrylic, preferably acrylic, monomer.

The application of the primer can be carried out by any means, and in particular by printing, coating, spraying or co-extrusion.

The printing of the liquid crystals can be carried out by any means and preferably by screen printing, gravure printing or flexography. The liquid crystals are deposited after stretching of the support.

The method may include printing on the adhesion primer two different inks, at least one of which comprises liquid crystals, better still both of which include liquid crystals, the liquid crystals preferably being cholesteric.

These two inks can be deposited without overlapping; the quantity deposited is thus limited to the quantity which is just useful.

The reflective haze effect ("Reflection Haze" hereinafter "Haze") of the cholesteric liquid crystal layer may be lower than that of a reference security element without the adhesion primer layer. . Diffusion haze in reflection causes a milky appearance, related to low intensity light scattering next to the main reflection, which corresponds to the reflection in the specular direction. The measurement can be performed according to ASTM D4039-09 (reapproved 2015) or ISO 13803: 2014. This allows visibility over a wider angular range of the goniochromatic effect and therefore masking of the background over a wider angular range.

A dark background can be provided under the liquid crystal layer, in particular on the opposite side of the support. As a variant, the dark background can be provided on the liquid crystal layer, in particular on the same side of the support. This dark background can be obtained by printing a dye, or a pigment (absorbent or interference). As a variant, the dark background is obtained by metallization, in particular under vacuum or electrochemically or by any other technique for depositing a metal, a metal oxide or a metal oxide salt. The dark background can also be carried by an additional support, preferably comprising PET, fixed to the support by any suitable means, in particular by lamination using an adhesive. Where appropriate, the additional support is preferably attached to the support on the side of the liquid crystal layer.

Preferably, the dark background is at least partially superimposed on the liquid crystal layer.

The dark background is preferably arranged in a marked manner relative to the printing of the liquid crystals; in particular, the dark background can be exactly superimposed on the liquid crystals.

The dark background can be achieved before or after the application of the liquid crystals.

The dark background may have a transmission rate of less than 80%, and is preferably opaque.

The adhesion primer is preferably transparent.

1. a. un support en matière thermoplastique étirée,
2. b. un primaire d'adhésion à la surface du support,
3. c. au moins une couche de cristaux liquides, notamment cholestériques, déposée par impression sur le primaire d'adhésion.

Another subject of the invention, according to another of its aspects, is a security element for a secure document, in particular obtained using a method according to the invention as defined above, comprising:

1. at. a support in stretched thermoplastic material,
2. b. an adhesion primer to the surface of the support,
3. vs. at least one layer of liquid crystals, in particular cholesteric, deposited by printing on the adhesion primer.

The security element may include printing of at least two liquid crystal inks, preferably without superimposition between them.

The adhesion of the liquid crystal layer on the support measured according to the Tesa test described below is preferably equal to 2.

Preferably, the liquid crystal layer is in the form of patterns, in particular alphanumeric.

The subject of the invention is also a method for authenticating a security element according to the invention, comprising the observation of the element so as to determine whether a goniochromatic effect is observed for incidences greater than or equal to 70 °. , and the step of generating information regarding the authenticity based at least on this observation.

The authentication method may include observing the element through a polarizing filter in order to demonstrate the orientation of the support and the adhesion primer and the step of generating information relating to the. authenticity on the basis of at least this observation.

• La figure 1 représente en vue de dessus un élément de sécurité selon l'invention,
• la figure 2 est une coupe longitudinale selon II-II de la figure 1,
• la figure 3 représente un détail de réalisation de l'élément,
• la figure 4 est une vue analogue à la figure 1 d'une variante de réalisation,
• la figure 5 est une coupe longitudinale de l'élément de la figure 4,
• la figure 6 est une vue analogue à la figure 3 d'une variante de réalisation de l'élément,
• la figure 7 illustre différentes étapes d'un exemple de procédé selon l'invention,
• la figure 8 représente un exemple d'article sécurisé incorporant un élément sécurisé selon l'invention, et
• la figure 9 est un schéma illustrant la mesure du « Haze » décrit ci-après.

The invention may be better understood on reading the description which follows, of non-limiting examples of its implementation, and on examining the appended drawing, in which:

• The figure 1 shows a top view of a security element according to the invention,
• the figure 2 is a longitudinal section along II-II of the figure 1 ,
• the figure 3 represents a detail of the realization of the element,
• the figure 4 is a view analogous to figure 1 an alternative embodiment,
• the figure 5 is a longitudinal section of the element of the figure 4 ,
• the figure 6 is a view analogous to figure 3 an alternative embodiment of the element,
• the figure 7 illustrates different steps of an example of a method according to the invention,
• the figure 8 represents an example of a secure article incorporating a secure element according to the invention, and
• the figure 9 is a diagram illustrating the measurement of the “Haze” described below.

In the drawing, the actual proportions have not always been observed for the sake of clarity.

We have represented on the figures 1 to 3 a security element 10 according to the invention, comprising a support 11, a bonding primer 12 and a liquid crystal layer 13 deposited by printing on the primer 12.

Layer 13 is formed by two prints 13a, 13b without superimposition between them, of different colors. In the example of figures 1 to 3 , the impressions 13a and 13b together do not cover the entire surface area of the face 11a of the support. Areas 14 which can be used by other securing means, such as for example a layer, in particular an ink, fluorescent or opaque, remain around the prints.

In the example of figures 4 to 6 , the prints 13a and 13b together cover the entire face 11a of the support.

In order to improve the visibility of the liquid crystals, the prints are advantageously carried out superimposed on an opaque background, preferably dark or reflecting, for example black.

By way of example, we have illustrated on the figure 6 the presence of a dark background in the form of an opaque layer 15 on the support 11, on the side opposite to the layer 13 of liquid crystals. The opaque layer 15 is for example an impression of a black ink or a metallization.

Layer 15 is produced, for example, after depositing layer 13 of liquid crystals.

According to an alternative embodiment of the figure 6 , the opaque layer 15 is present on the liquid crystal layer 13 on the same side of the support. The observation of the security element is then made from the side of the support opposite to the layer 13 of liquid crystals.

Support

The support is made of a stretchable thermoplastic material.

Preferably, the support is made of PET, polypropylene or polyethylene.

In order to improve the durability of the security element, an additional support, preferably comprising PET, is attached to the support by any suitable means, in particular by lamination using an adhesive.

The additional support is preferably attached to the support on the side of the liquid crystal layer. In a variant intended to improve the cohesion of the sandwich thus formed, the liquid crystal layer is preferably in the form of patterns, and for example covers less than 50% of the surface of the support. The adhesion between the support and the additional support is thus reinforced.

Liquid crystals

Preferably, the liquid crystals are cholesteric liquid crystals (CLC). Alternatively, the liquid crystals are nematic liquid crystals.

Many liquid crystal inks currently exist on the market and can be used. The ink can be a mixture of cholesteric and nematic liquid crystals, in a ratio chosen as a function of the desired color variation.

Primary membership

The adhesion primer increases the adhesion of the liquid crystals to the support without thereby preventing the support from participating by its intrinsic structure in the orientation of the liquid crystals.

The adhesion primer comprises one or more polymers.

The primer can be applied in the form of monomers, in particular olefin (or alkene), urethane, ester, ether, carbonate or acrylic, preferably acrylic, on the support and this application is then followed by crosslinking, for example by exposure to UV radiation

Preferably, the chemical nature of the primer is chosen so as to have the best affinity with the liquid crystal ink used. Thus, many liquid crystal inks being based on acrylate monomers, it is preferred to use a primer based on acrylate monomers as well.

The quantity of primer which is deposited is chosen so that the thickness of the deposit remains sufficiently low for the structure of the underlying support to remain active with respect to the orientation of the liquid crystals.

The thickness of the primer is thus preferably less than 1000 nm, better still less than 100 nm.

The fact of orienting the support with the primer already present on it can make it possible to orient the primer and thus allow a greater deposit of primer.

Other means of securing

The security element may include, in addition to the liquid crystals, any other security means chosen from those of first, second or third levels.

• motifs apparaissant en lumière transmise et formés par métallisation et/ou démétallisation,
• colorants, pigments luminescents, pigments interférentiels , notamment sous forme imprimée ou mélangée à au moins une couche constitutive de l'élément de sécurité,
• composés, colorants et/ou pigments photochromes ou thermochromes, notamment sous forme imprimée ou mélangée à au moins une couche constitutive de l'élément de sécurité,
• absorbeur ultraviolet (UV), notamment sous forme enduite ou mélangée à au moins une couche constitutive de l'élément de sécurité,
• structure multicouche interférentielle,
• une couche réfractive, biréfringente ou polarisante,
• une structure de diffraction,
• des moyens produisant un "effet de moiré", un tel effet pouvant par exemple faire apparaître un motif produit par la superposition de deux moyens de sécurité, par exemple par le rapprochement de lignes de deux moyens de sécurité,
• un filtre coloré.
• une sécurité lisible automatiquement, ayant des caractéristiques spécifiques et mesurables de luminescence (par exemple fluorescence, phosphorescence), d'absorption de la lumière (par exemple ultraviolet, visible ou infrarouge), d'activité Raman, de magnétisme, d'interaction micro-ondes, d'interaction aux rayons X ou de conductivité électrique.

It can be:

• patterns appearing in transmitted light and formed by metallization and / or demetallization,
• dyes, luminescent pigments, interference pigments, in particular in printed form or mixed with at least one constituent layer of the security element,
• photochromic or thermochromic compounds, dyes and / or pigments, in particular in printed form or mixed with at least one layer constituting the security element,
• ultraviolet (UV) absorber, in particular in coated form or mixed with at least one constituent layer of the security element,
• multilayer interference structure,
• a refractive, birefringent or polarizing layer,
• a diffraction structure,
• means producing a "moiré effect", such an effect being able for example to reveal a pattern produced by the superposition of two security means, for example by bringing together lines of two security means,
• a colored filter.
• an automatically readable security, having specific and measurable characteristics of luminescence (eg fluorescence, phosphorescence), light absorption (eg ultraviolet, visible or infrared), Raman activity, magnetism, micro interaction waves, X-ray interaction or electrical conductivity.

Security element

The security element according to the invention is advantageously a security thread, a foil, a patch or a variable data protection film. It may also be a card or a protective or tamper-evident film.

In the case of a security element consisting of a security thread, the latter can be integrated into windows in a security paper such as a bank note 30, as illustrated in figure 8 . The security element then extends from one edge 31 to the other 32 of the document.

When the security element is in the form of a wire, its width is for example between 1 and 10 mm and its thickness between 10 and 100 μm.

In the case of a foil, the security element is applied by transfer to the surface of a paper, film or card, for example.

The term “patch” denotes a film which does not cover the entire surface of the underlying substrate.

Manufacturing process

According to the invention, the method comprises, as illustrated in figure 7 , a step 21 of making a plastic film, for example by extrusion. This film can be monolayer or multilayer.

It undergoes at least one stretching step 22, which makes it possible to orient it in a first direction. This is for example a first stretch in the longitudinal direction (also called the running direction).

Next, the adhesion primer is applied in a step 23, then the film is stretched again, in a direction different from the first, for example in the transverse direction (also called the transverse direction), in a step 24.

Finally, the liquid crystals are deposited by printing in step 25, on the film thus bi-stretched and coated with the adhesion primer.

The orientation of the liquid crystals takes place during the evaporation of the solvent present in the ink used. This evaporation is preferably carried out by “airborne” drying (Air Flow in English), preferably horizontally to promote the orientation of the liquid crystals. Preferably, the ink is crosslinkable under UV, and the crosslinking which follows the deposition of the ink makes it possible to definitively fix this orientation.

Printing is preferably carried out with several liquid crystal inks, which are preferably deposited without overlap between them. The inks can be deposited in the form of solids or patterns. The term "pattern" denotes any pattern recognizable to the naked eye in particular, such as for example one or more alphanumeric characters, or the image of a subject such as a character, animal, object, landscape, plant or monument. . It may be a halftone raster pattern, preferably appearing in 3D due to a shading effect obtained by halftone reproduction of the pattern. It may be a repeating pattern arranged in a given direction, in a frame or preferably in a checkerboard arrangement.

Printing can be done by flexography, screen printing or gravure printing, among other printing techniques that can be used.

In a variant of the process, the film undergoes a double stretching in the running and transverse directions after application of the adhesion primer. This removal preferably takes place after a first stretching in the running direction.

• étirement sens marche,
• dépose du primaire,
• étirement sens travers,
• étirement sens marche.

We can thus have the following sequence:

• walking direction stretch,
• removal of the primary,
• crosswise stretch,
• stretch walking direction.

Authentication process

The authentication of a security element according to the invention can be carried out by observing the element so as to determine whether a goniochromatic effect is observed for incidences greater than or equal to 70 °, this effect being linked to the presence of liquid crystals.

It is then possible to generate information regarding the authenticity on the basis of at least this observation.

Authentication may include observing the element through a polarizing filter with a view to demonstrating the orientation of the support and the adhesion primer and the step of generating information relating to the authenticity on at least the basis of this observation.

The bi-orientation of the support can be verified by analyzing the birefringence of the film, in a conventional manner.

You can use a linear polarizer, such as a filter to put on the security element, which is rotated 90 ° to determine if you change from a dark appearance to a lighter appearance when rotating.

Examples

The “Tesa” test mentioned below is an adhesion test of a layer deposited on a substrate, in which an adhesive tape is applied to the layer of which it is sought to measure the cohesion and the adhesion to the substrate.

• 0 désigne une accroche totale au ruban donc adhésion nulle au substrat de la couche testée
• 1 désigne une accroche partielle au ruban et
• 2 désigne une absence d'accroche au ruban donc une meilleure adhésion au substrat de la couche testée.

A score of 0 to 2 is obtained depending on the proportion of the tested layer which remains attached to the tape after its removal:

• 0 designates total adhesion to the tape therefore zero adhesion to the substrate of the layer tested
• 1 designates partial adhesion to the tape and
• 2 denotes an absence of adhesion to the tape and therefore better adhesion to the substrate of the layer tested.

Examples 1 to 3 (comparative)

• cristaux liquides cholestériques: 5,29 g
• cristaux liquides nématiques: 3,11 g
• photoiniateur : 1,6 g

Several PET films are printed with liquid crystal ink formulated with a mixture of three products, namely:

• cholesteric liquid crystal: 5.29 g
• nematic liquid crystals: 3.11 g
• photoinator: 1.6 g

The mixture constitutes an ink with an acrylic base, comprising cholesteric and nematic liquid crystals.

The ratio chosen between cholesteric and nematic liquid crystals gives the color; here we get a change from blue to green-yellow with the angle of observation.

The liquid crystals are deposited to a thickness of 3 microns, on the coating bar.

Hot air blown drying is performed to align the liquid crystals. The ink is subjected to UV crosslinking.

Liquid crystals are observed against a dark background. Movie Treatment "Tesa" test Goniochromatic effect ** (1) Standard bi-oriented PET No 0 Benchmark effect (2) bi-oriented PET Chemical attack * 2 Strong deterioration: whitish appearance due to the translucency of the film (3) bi-oriented PET Plasma treatment 0 Identical to the reference effect * Chemical attack: treatment with an acid solution creating a surface micro-roughness
** Goniochromatic effect: the parameters observed are as follows: clear observation of the two colors, brightness of the colors and angle of the color change.

The plasma treatment does not provide optimal adhesion, but the alignment of the liquid crystals is correct.

The chemically etched PET film provides excellent adhesion, but the optical effect is degraded.

Examples 4 (comparative) and 5 to 7 (according to the invention)

The liquid crystal deposition is carried out as in Examples 1 to 3 by means of a commercially available liquid crystal ink. *** Offline: the application occurs after the PET film stretching steps. In-line: the application takes place during the manufacture of the film between at least two stages of stretching of the PET film. Movie Treatment "Tesa" test Goniochromatic effect (4) Standard bi-oriented PET No 0 Benchmark effect (5) Bi-oriented PET Polyacrylic primer applied offline *** 1 Improvement: increased range of viewing angles and grazing angle not viewing dark background (6) Bi-oriented PET Polyacrylic primer applied in line *** 2 Improvement: increased range of viewing angles and grazing angle not viewing dark background (7) Bi-oriented PET Copolyester primer applied in line *** 2 Improvement: increased range of viewing angles and grazing angle not viewing dark background

The goniochromatic effect is surprisingly preserved for Examples 5 to 7, despite the presence of an intermediate primer layer between the biaxially oriented PET support which allows alignment and the liquid crystal layer.

The alignment of the liquid crystals is modified by the presence of the adhesion primer. The modification of this alignment makes it possible to increase the visibility of the color change effect, and to give the liquid crystal layer a translucency which makes it possible to limit the visibility of the black background.

The degree of translucency can be determined by measuring the “Haze” in reflection according to ASTM D4039-09 and ISO13803. This is a measure of haze, i.e. milky opalescence, glossy or clear topcoat.

On quality surfaces (class A), an image of clear and shiny appearance is expected. Microstructures can cause a milky appearance. This effect is called diffusion veil or "Haze". If microscopic and fine defects are present on a very shiny surface, it leads to low intensity light scattering next to the main reflection. The predominant part is reflected in the specular direction, so the surface appears very bright and with image rendering, but it is covered with a milky cloudy haze.

The “Haze” of the layer of liquid crystals on a support according to the invention can be lower than that of the layer of liquid crystals on an untreated PET, which results in much less gloss than for the layer of liquid crystals on a support. standard. In addition, the reduction of the “Haze” increases the light diffusion of the liquid crystal layer and therefore allows the observation of the goniochromatic effect over a larger range of angles. Thus, surprisingly, at “grazing” angles the goniochromatic effect is maintained with a support according to the invention, whereas with a standard support, the liquid crystals are no longer visible and the dark background is observed, which is not desirable.

The “Haze”, measured according to the ISO 13803: 2014 standard, of the films (1) and (6) is respectively 274 and 79. Such a measurement is illustrated on the figure 9 on which the support to be measured 91 is illuminated at an angle α which is for example 20 ° for the aforementioned standard). The “Haze” is measured by means of the sensors 92 and corresponds to the intensity of the light rays 93, as opposed to the brightness which corresponds to the intensity of the specular ray 94 (angle -a).

In order to quantify the increase in the angular range of the goniochromatic effect, the maximum intensity over the wavelength range 400 - 700nm ("Intensity" in the table below) was measured at different angles of. observation for illumination at an angle of 50 °, on samples (1) and (6). All the intensity measurements indicated in the table below are given in arbitrary units corresponding to a given calibration, in particular the intensities of samples (1) and (6) were measured with the same calibration. Viewing angle (°) Sample intensity (6) Sample intensity (1) 10 50 10 20 100 20 30 200 100 40 400 400 50 400 1800 60 300 300 70 250 150 80 200 100

Note that for grazing observation angles, for example 10 °, 20 °, 70 ° and 80 °, the intensity of sample 6 is greater than that of sample 1, which reflects the visibility over a wider angular range of the goniochromatic effect of sample 6.

Claims (15)

1. Process for producing a security element comprising a support (11) made from oriented plastic and at least one layer of liquid crystals (13) borne and oriented by the support, an adhesion primer (12) being deposited before or after the support is stretched in at least one direction, said stretching making it possible to bring the support to the oriented state and characterized in that the liquid crystals are deposited by means of printing on this adhesion primer.
2. Process according to Claim 1, the adhesion primer (12) being deposited before a step of stretching the support (11) and/or the support comprising PET.
3. Process according to either of Claims 1 and 2, said process also comprising a step of crosslinking the adhesion primer, preferably after said stretching of the support.
4. Process according to any one of Claims 1 to 3, the adhesion primer comprising a polyolefin, a polyurethane, polyester, polyether, polycarbonate, polyacrylic or a copolymer thereof, the adhesion primer comprising in particular a polyacrylic and preferably comprising, in particular before the depositing thereof, at least one urethane, ester, ether, carbonate or acrylic monomer.
5. Process according to any one of the preceding claims, the printing of the liquid crystals being carried out by screen printing, photogravure or flexography.
6. Process according to any one of the preceding claims, the liquid crystals being deposited after stretching of the support.
7. Process according to any one of the preceding claims, comprising the printing on the adhesion primer of two different inks, at least one of which comprises cholesteric liquid crystals, better still both comprise cholesteric liquid crystals.
8. Process according to any one of the preceding claims, the haze effect of the layer of cholesteric liquid crystals being less than that of a reference security element without the layer of adhesion primer.
9. Process according to any one of the preceding claims, comprising a dark background under the layer of liquid crystals.
10. Process according to any one of the preceding claims, the adhesion primer being transparent.
11. Security element (10) for a secure document, in particular obtained by means of a process according to any one of the preceding claims, comprising:

    a. a support (11) made from stretched thermoplastic material,

    b. an adhesion primer (12) at the surface of the support, and characterized by

    c. at least one layer (13) of liquid crystals deposited on the adhesion primer by printing.
12. Security element according to Claim 11, comprising a printing of at least two liquid-crystal inks, which are preferably not superimposed on one another.
13. Security element according to Claim 11 or 12, the adhesion of the layer of liquid crystals on the support measured according to the Tesa test being equal to 2 and/or the layer of cholesteric liquid crystals is in the form of a pattern, in particular an alphanumeric pattern.
14. Security element according to any one of Claims 11 to 13, also comprising a dark background.
15. Process for authenticating a security element according to any one of Claims 11 to 14, comprising the observation of the element so as to determine whether a goniochromatic effect is observed for angles of incidence greater than or equal to 70°, and the step consisting in generating a piece of information concerning the authenticity on the basis at least of this observation, or comprising the observation of the element through a polarizing filter with a view to demonstrating the orientation of the support and of the adhesion primer, and the step consisting in generating a piece of information concerning the authenticity on the basis of at least this observation.

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