EP2225417B1 - Safety structure comprising nematic liquid crystals - Google Patents

Description

The present invention relates to security structures intended to be incorporated in objects to be secured, for example valuable documents such as banknotes, tickets or coupons, packaging or security documents such as for example passports or identity cards.

It is known to introduce in paper security threads comprising a plastic support, for example polyester, coated with a metal deposit, partially demetallized so as to form a text visible in transvision.

It is also known to use coatings having birefringence properties, for example comprising so-called nematic liquid crystals.

Requirement WO 02/085642 discloses the use in safety structures of a coating having birefringence properties and may include nematic liquid crystals.

The patent WO 96/06220 discloses a method of manufacturing paper having localized areas of low opacity.

There is a need to benefit from new, more complex security structures, bringing increased security.

• une première région au moins partiellement réfléchissante d'opacité réduite,
• une deuxième région au moins partiellement réfléchissante de plus forte opacité que la première,
• un revêtement présentant des propriétés de biréfringence, par exemple comportant des cristaux liquides nématiques, recouvrant au moins partiellement les première et deuxième régions. Ce revêtement peut avoir été déposé par une technique d'impression.

The invention thus has, according to one of its aspects, a safety structure comprising:

• a first at least partially reflective region of reduced opacity,
• a second at least partially reflective region of greater opacity than the first,
• a coating having birefringence properties, for example having nematic liquid crystals, at least partially covering the first and second regions. This coating may have been deposited by a printing technique.

The invention offers new effects through the use of said coating, preferably nematic liquid crystals, superimposed on regions of varying opacity.

This variation in opacity makes it possible to observe the coating differently, in particular the nematic liquid crystals, depending on whether the coating covers the first region of reduced opacity or the second region of greater opacity.

By "at least partially reflective", one must understand that one observes a reflection of specular type, as opposed to a diffuse reflection.

Specular reflection may be more or less important depending on the angle of vision.

The reflective quality and the specular reflection limit may be chosen so as to obtain sufficient visibility of the liquid crystals through the polarizing filter.

In an exemplary implementation, the first region of reduced opacity is semi-reflective, like a one-way mirror, while the second region of higher opacity is reflective. In reflection, the first and second regions both appear reflective, which contributes to the visibility of the pattern (s) formed by the coating, in particular the layer of nematic liquid crystals; these patterns may not be precisely positioned relative to the first and second regions without having a significant impact on their visibility, unlike for example a nematic liquid crystal print on a structure having reflective zones metallized and demetallised transparent areas.

The first and second regions can be obtained for example by a deposit of variable thickness of a metal, for example aluminum.

In another exemplary embodiment, the structure comprises a deposit of a first material defining the first region of reduced opacity, being covered with a deposit of a second material in the second region of greater opacity.

The second region of higher opacity can completely surround the first region.

The first region may define patterns that repeat at regular intervals or not, these first patterns defining windows and / or text.

The opacity difference between the first and second regions, when the structure is observed in transvision (examination of the transmitted light), may depend on the manner in which the first and second regions are made, this opacity difference being adjusted to allow a contrast easily visible by transvision in the light of the day.

In the case in particular of producing the patterns by association of at least one aluminum-based reflective layer, the opacity gap between the opacity region low and that of opacity stronger, measured spectrophotometer (ISO 2471 substrate), can be between 5 to 80 units, preferably 35-40.

Other technologies for obtaining reflective material while being transparent or of low opacity, are known to those skilled in the art, such as the use of materials having a large difference in refractive index with their associated support (polymer film type polyester for example). Such materials are well known, for example in the realization of transparent holographic security. These are, for example, metal salts of general formula TiO (x) or such as Zinc sulphide (ZnS). It is also possible to use iridescent "Iriodin" pigments (produced by Merck), given that the opacity depends on the quantity of pigments deposited.

The coating, in particular the nematic liquid crystal layer, may form at least one pattern, for example a plurality of repeating patterns on the structure. The coating may for example comprise an impression of nematic liquid crystals in the form of at least one pattern. These patterns may for example define text or a logo or simple geometric shapes and may have a variable positioning vis-à-vis the area or areas of reduced opacity.

Another object of the invention is, according to another of its aspects, an object, in particular a document, incorporating a security structure as defined above.

The security structure may for example form a security thread extending from one edge to the other of the document.

The document may comprise a fibrous substrate, for example a substrate comprising paper fibers.

• observer en réflexion la structure, notamment sous une lumière non polarisée, l'observation s'effectuant sans filtre polarisant, notamment sans filtre à polarisation linéaire et/ou circulaire,
• observer la structure en réflexion au travers d'un filtre polarisant. Le cas échéant, le procédé peut également comporter l'étape consistant à observer la structure en transvision.

The invention also relates to a method for authenticating a security structure as defined above, comprising the following steps:

• observe in reflection the structure, in particular in a non-polarized light, the observation being carried out without polarizing filter, in particular without linear and / or circular polarization filter,
• observe the structure in reflection through a polarizing filter. If necessary, the method may also include the step of observing the structure in transvision.

The authenticity of the structure can be concluded by observing, through the polarizing filter, the coating having birefringence properties, in particular the liquid crystals, when the regions of the coating covering the zones of low opacity contrast with those covering the zones of high opacity.

It can also be concluded as to the authenticity if the liquid crystals are not apparent in transvision and only patterns are observed formed by the regions of different opacities.

Authentication can be performed with the naked eye, in visible or non-visible light, in particular U.V or I.R, natural or artificial, with or without magnification.

• la figure 1 représente de manière schématique, en vue de face, un exemple de structure de sécurité selon l'invention,
• la figure 2 est une coupe transversale selon II-II de la figure 1,
• la figure 3 est une coupe transversale selon III-III de la figure 1,
• la figure 4 est une coupe transversale selon IV-IV la figure 1,
• la figure 5 représente la structure de la figure 1 dans des conditions d'observation rendant les cristaux liquides nématiques observables,
• la figure 6 est une vue analogue à la figure 4 d'une variante de réalisation,
• la figure 7 représente un document incorporant une structure de sécurité selon l'invention, et
• la figure 8 représente de façon schématique en vue de dessus une variante de réalisation de la structure de sécurité.

The invention will be better understood on reading the following detailed description, non-limiting examples of implementation thereof, and on examining the appended drawing, in which:

• the figure 1 shows schematically, in front view, an example of a security structure according to the invention,
• the figure 2 is a cross section along II-II of the figure 1 ,
• the figure 3 is a cross section along III-III of the figure 1 ,
• the figure 4 is a cross section along IV-IV the figure 1 ,
• the figure 5 represents the structure of the figure 1 under observation conditions making the nematic liquid crystals observable,
• the figure 6 is a view similar to the figure 4 an alternative embodiment,
• the figure 7 represents a document incorporating a security structure according to the invention, and
• the figure 8 schematically shows in top view an alternative embodiment of the security structure.

In the figures, the actual proportions of the various elements represented have not always been respected, for the sake of clarity of the drawing.

The structure 10 shown on the Figures 1 to 5 comprises a transparent or translucent support 11, for example made of a thermoplastic film, for example polyester, PVC, PP, an aromatic polyamide or aramid, or others and on this support a deposit 12 of a metal, alloy or metal oxide, for example aluminum, copper, zinc, gold, platinum, ...

The deposit 12 presents in the example considered a variable thickness, thus defining a first region 14 of smaller thickness and reduced opacity and a second region 15 of greater thickness and greater opacity.

The thickness of the thinned layer 13 defining the first region 14 is chosen so as to give the structure, in this region 14, a semi-reflective or reflective character according to the angle of observation, that is to say whose reflectivity varies according to the angle of observation but the proportion of reflected light is less than 100%, while the thickness of the deposit 12 in the second region 15 gives the structure in this second region a character reflective opaque.

As an indication, the thickness of the thinned layer 13 is for example between 5 and 50 nm and the thickness of the deposit 12 in the second region 15 is for example between 100 and 300 nm.

The first region 14 may be in various ways on the structure, for example in the form of "windows" 24 repeating at regular intervals along the structure 10, as illustrated. The first region 14 can still form at least one text or logo.

In the example considered, the second region 15 completely surrounds the first region 14, but it could be different and the first region 14 could extend to at least one longitudinal edge of the structure 10.

The structure 10 also comprises a coating of a birefringent material, in this case a layer of nematic liquid crystals, in the form of patterns 18 which are repeated at regular intervals along the structure and whose positioning relative to the first region 14 is predefined, so that the patterns 18 cover both the first region 14 and the second region 15.

The nematic liquid crystals used are for example those produced by the company MERCK, adapted to conventional printing techniques, as disclosed in the application WO 2004/025337 .

When the structure 10 is observed in transvision, the nematic liquid crystals are not apparent, and only the patterns 24 which contrast with the second opaque region 15 are observed.

When the structure 10 is observed in reflection, with a linear and / or circular polarization filter, the patterns 18 appear in front of a background that appears substantially plain, since the patterns 24 reflect the light and are not visible, or are only few, and are substantially confused with the second region 15 also reflective. The zones of low opacity may have a reflectivity different from the high opacity zones, so the nematic liquid crystals may have a contrast of observation substantially different depending on the zones, through the polarizing filter.

The invention is not limited to a particular way of obtaining the first and second regions, and it can for example, as illustrated in FIG. figure 6 depositing on the support 11 a first reflecting material 20 whose opacity is sufficiently low to define the first region 14 and, at the sites of greater opacity, depositing a second reflecting material 21 on the first material 20.

The first material is for example a metal such as aluminum and the second material is for example an oxide such as TiO _x or ZnS, deposited under vacuum.

The security structure 10 may be in the form of a security thread which for example is integrated in a document 30, which comprises for example a fibrous substrate, by a known technique of incorporation of a security thread.

The security structure 10 may be disposed along its entire length on the surface of the document 30, or may be partially buried in the fibrous substrate.

The document 30 may comprise other security elements, such as for example a watermark.

The security structure 10 can still be in the form of a patch, as shown in FIG. figure 8 , Such a patch being for example intended to be glued on one side of the object to be secured in a transparent or translucent region thereof.

The invention is not limited to the illustrated examples. The reflective zones of low opacity can for example be made using an interference pigment, for example of titanium-based mica-coated plate or titanium oxide-coated glass plate, and the zones Reflective with higher opacity can be achieved using an ink, for example based on aluminum powder, the two types of patterns being printed at the mark one of the other.

In particular, the shape of the security structure can be modified and the first and second regions of different opacities can be made differently.

The security structure can be applied to objects other than paper, for example a packaging, a packaging device, a drug blister, an optical disk, etc.

The expression "having one" shall be understood as being synonymous with "having at least one", unless the opposite is specified.

Claims (16)

1. A security structure (10) comprising:

   - a first region (14) that is at least partially reflective and of low opacity;

   - a second region (15) that is at least partially reflective and of higher opacity than the first region;

   - a layer (18) of a coating presenting birefringence properties, covering the first and second regions, at least in part.
2. A structure according to claim 1, the coating (18) including nematic liquid crystals.
3. A structure according to claim 1 or claim 2, the first region (14) of low opacity being semi-reflective.
4. A structure according to any one of claims 1 to 3, the second region (15) of higher opacity being reflective.
5. A structure according to any preceding claim, the first and second regions being obtained by depositing varying thicknesses of a metal.
6. A structure according to any one of claims 1 to 5, the first region being obtained by depositing an interference pigment.
7. A structure according to any one of claims 1 to 6, the first region including a layer presenting a large difference of refractive index relative to an associated medium.
8. A structure according to any one of claims 1 to 7, the first region presenting a reflective characteristic that depends on an angle of observation.
9. A structure according to any preceding claim, the second region (15) completely surrounding the first region (14).
10. A structure according to any preceding claim, the first region (14) defining patterns (24) that repeat at regular intervals.
11. A structure according to any preceding claim, comprising, in the second region (15), a deposit of a first material (20), and a deposit of a second material (21) on the first.
12. A structure according to any preceding claim, the coating (18) comprising printing nematic liquid crystals in the form of at least one pattern.
13. A structure according to any preceding claim, the coating layer presenting birefringence properties that define patterns (18) that repeat on the structure.
14. A structure according to any one of claims 1 to 13, the difference in opacity between the region of low opacity and the region of higher opacity lying in a range of 5 to 80, better 35 to 40 (standard: ISO 2471).
15. An article selected from a document (30), packaging, a packaging device, in particular a blister pack for medication, or an optical disk, the article incorporating a security structure (10) as defined in any preceding claim.
16. A method of authenticating a security structure as defined in any one of claims 1 to 14, the method comprising the following steps:

    observing the structure in reflection, in particular in non-polarized light, the observation being performed without a polarizing filter, in particular without any filter presenting linear and/or circular polarization; and

    observing the structure in reflection through a polarizing filter.

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