WO2015087275A1

WO2015087275A1 - Security structure

Info

Publication number: WO2015087275A1
Application number: PCT/IB2014/066804
Authority: WO
Inventors: Jacques MACHIZAUD; Marcel CAMUS
Original assignee: Arjowiggins Security
Priority date: 2013-12-13
Filing date: 2014-12-11
Publication date: 2015-06-18
Also published as: FR3014741A1

Abstract

The invention relates to a security structure (10) comprising a plurality of lenses, said plurality of lenses comprising a first assembly of converging lenses (11) and a second assembly of diverging or converging lenses (12), the lenses (11) of the first assembly having substantially the same focal length and said focal length being different from that of the lenses (12) of the second assembly so as to create a pre-defined pattern of light transmitted by simply focusing the light from the first set of lenses (11) on a projection surface (P).

Description

Security structure

The present invention relates to security structures used to secure documents against counterfeit attempts.

In order to guard against the counterfeiting of secure documents, it is known to produce structures comprising lenses of small dimensions giving optical effects easily recognizable by the man in the street.

"Secure document" means a means of payment, such as a bank note, a check or a restaurant ticket, an identity document, such as an identity card, a visa, a passport or a passport. driver's license, a lottery ticket, a ticket or a ticket to cultural or sporting events.

DE 10 2010 048 262 A1 discloses a substrate carrying a plurality of optical elements forming an image consisting of light spots arranged in a predefined pattern, when illuminated by a light source. The optical elements may be refractive or reflective, and of different focal lengths. Light spots can be above and below a surface, respectively, to give a fluctuating image impression. The optical elements may be Fresnel lenses. The fluctuating optical image effect can be relatively difficult to visualize, and require a precise arrangement of the optical elements.

It is also known to make security structures with lenticular arrays associated with specific impressions, in order to produce movement, depth and / or stereoscopic effects. The company CRANE markets under the brand MOTION ^® .

Such security structures exploit an optical structure whose face is exposed to the air, so that the difference between the refractive indices of the air and the material of the structure produces the refraction of the light rays sought.

Publications FR 2 952 194, WO 2007/133613, US 2008/0182084, US 2005/0180020 and US 2008/0160226 are still known from various examples of safety structures comprising optical structures.

FR 2 952 194 discloses a reflective surface formed of mirrors made by metallization of an embossed surface. The metal layer defining the reflective surface may have been demetallized. The mirrors may be concave mirrors towards the observer, of diameter for example between 50 and 70 microns. The mirrors serve, for example, to give the observer an enlarged or reduced image of a pattern. A Fresnel lens can be made to enlarge the image given by a mirror.

WO 2007/133613 discloses a substrate having a lenticular array with lenses having at their base a diameter of less than 50 microns and a pattern spatially coordinated with images produced by the lenticular array.

US 2008/0182084 teaches canceling the effect of lenses by applying an adhesive to their surface. In one example, the structure comprises a substrate carrying on one side a lenticular array with areas coated with varnish and on the other a diffraction structure and micro-images. The lenses have a diameter of between 10 and 150 microns.

US 2005/0180020 discloses a multilayer structure having a lenticular array capable of receiving printing. The lenses have a diameter less than 50 microns.

US 2008/0160226 discloses a microlens array of about 20 microns in diameter, associated with micro-images to create a moire effect.

There is a need for relatively easy structures to produce and easy to integrate into a substrate, while having optical properties difficult to imitate although easy to recognize for the man in the street.

The invention meets this need by virtue of a security structure comprising a plurality of lenses, said plurality comprising a first set of convergent lenses and a second set of convergent or divergent lenses, the lenses of the first set having substantially the same focal length and this focal length being different from that of the lenses of the second set so as to show a predefined pattern of light transmitted by the only focusing of the light from the first set of lenses on a projection surface.

This pattern can appear in positive or negative.

By "substantially the same focal length", it should be understood that the focal lengths are sufficiently close to a nominal value for the desired effect to be observed. Preferably, the focal lengths of the lenses of the first set are equal to a nominal value fi to + 10%, better to within 5%. For the purposes of the present invention, convergent lenses are considered to have a positive focal length while diverging lenses have a negative focal length. Thus, in a particular case according to the invention, where the lenses of the second set are divergent, the lenses of the first set may have in absolute value the same focal length as the lenses of the second set, ie fi = -f ₂ , but the lenses will nonetheless be considered to have different focal lengths because of the opposite signs.

In reflected light, the observation of the lenses does not allow the observer to easily discern the pattern because the lenses have substantially all the same appearance to the naked eye for the man in the street; the aforementioned pattern is thus not or hardly visible in reflected light.

All lenses in the second set may be divergent. As a variant, all the lenses of the second set are convergent. The lenses of the second set may have the same nominal focal length f ₂ , within ± 10%, better within 5%.

In the case where the lenses of the first set are convergent and those of the second set are divergent, fl and f2 can be equal in absolute values but of opposite sign.

In the case where the two sets have convergent lenses, the nominal value of the focal length f1 of the lenses of the first set is preferably different from that of the second set f2 by at least +/- 15%.

Preferably, all the lenses are Fresnel lenses, which allows them to be made with the same thickness irrespective of their focal length.

Preferably, at least a portion of the lenses is covered by a semi-reflective metal layer. The advantage of this layer is to allow to obtain a visual effect in reflection by creating a metal interface between the lenses and a protective varnish covering them.

The transmission coefficient of the metal layer is preferably between 10 and 60%, preferably between 15 and 30%, in order to allow transmission visualization through the metal layer. The semi-reflective metal layer may be perforated to define at least one negative writing pattern, for example an alphanumeric pattern, visible in transmitted light or reflected light.

The lenses can be made by embossing, in particular by thermo-embossing or by embossing followed by ultraviolet crosslinking. In particular, the lenses can be formed by hollow embossing, that is to say with a tool in relief, or by embossing in relief, that is to say with a recessed tool, a varnish, which can be a resin. The lenses may include an epoxy or acrylic resin or a thermoplastic material such as PET or polyester, among others.

Preferably, the lenses are formed by embossing a varnish. The latter can be applied in the fluid state on a support before embossing. The varnish may be colorless or colored, and optionally incorporate a luminescent agent, in particular a fluorescent agent.

The lenses can thus be embossed in relief especially in the case where one seeks to achieve convergent or hollow lenses, especially in the case where one seeks to achieve divergent lenses in a varnish and covered with a semi-layer reflective metallized on their side turned for example towards the observation side in reflected light. The semi-reflecting layer can thus be located between the observation face and the lens material.

If necessary, the lens array is embossed in a lacquer and the semi-reflecting layer is applied in the hollow of the patterns, on the side of the concave face.

The focal length of the convergent lenses of the first set may be between 10 and 30 cm. The projection surface can thus be located substantially at this distance from the security document during the observation of the pattern formed by projection.

Convergent lenses may be plano-convex or biconvex or meniscus.

The divergent lenses can be plane-concave or biconcave or meniscus.

The opening diameter of the lenses may be between 0.1 and 3 mm The lenses can be arranged on a support with a regular distribution in the two directions of this support other than the thickness or with a random distribution.

The support may be at least partially transparent or translucent. The support may for example be or comprise a film of a transparent or translucent thermoplastic material, for example polyester or PET. The interface between the support and the lens material is preferably flat.

The aforesaid support may constitute, where appropriate, the material in which the lenses are formed. When the lens material is attached to the support, it can be directly in contact with it or not.

The thickness of the support is for example between 5 and 100 μιτι, preferably 20 and 30 μιη. The support may have a constant thickness. The support can make it possible to manipulate the lenses during the fixation of the security structure in or on the document to be secured.

As mentioned above, a preferred embodiment implements lenses each in the form of a Fresnel lens, the base of which is not necessarily circular. To achieve the lens, it is possible from a volume representing the conventional lens, for example convex plane, whose focal length is to be reproduced, to subdivide this volume into equally spaced slices in the plane of the lens and to remove the portions. slices that have a constant thickness.

The lenses can completely cover one side of the support, or alternatively cover only partially. The lenses may or may not extend from one edge to the other of the support, depending on the length and / or the width of the support. The support may have one or more zones devoid of lenses and one or more areas covered by the lenses.

The semi-reflecting layer may be covered with a smoothing varnish, in particular intended to allow the application, preferably printing, of one or more ancillary elements. In addition, the smoothing varnish can protect the lenses coated with the semi-reflective layer. This smoothing varnish may be colorless or colored. In order to maintain the refractive power of the lenses, the refractive index of the various media constituting the security structure must be taken into account. Preferably, the lenses are coated with a protective varnish whose refractive index is different from the refractive index of the material constituting the lenses. In order to maintain the laws of refraction at the surface between the lenses and the surrounding medium (s), it is necessary to have a non-zero difference between the refractive indices of these media. Preferably, the difference between these indices is greater than 0.05.

In addition, with respect to the convergent lenses, to maintain the convergent nature of the lens, it is desirable that the index of the varnish remains lower than that of the lens material. For the same reasons it is desirable that the refractive index of the varnish deposited on a divergent lens is less than that of the material of the divergent lens to maintain its divergence optical property.

Advantageously, it is also planned to modify the type of lens from convergent to divergent or vice versa by covering the lens with a varnish of refractive index greater than that of the material of the lens. It is thus possible to obtain a security structure according to the invention from only convergent lenses on which a partial deposition of a varnish is obtained whose refractive index is greater than that of the lens material thus forming the second set of divergent lenses and therefore the pattern. It is understood that a similar effect can be obtained from divergent lenses on which a partial deposition of a varnish is obtained whose refractive index is greater than that of the lens material thus forming the first set of convergent lenses and so the motive. By "partial removal" means a removal of varnish on some of the lenses but not all.

The protective varnish can also be used as a heat-sealing varnish. The lenses can be arranged at regular intervals or not. The thickness of the lenses is for example between 1 and 30μπι, better 2 and

15 μπι.

The structure may comprise one or more ancillary elements, in particular visible on the side of the face to be observed in reflected light, superimposed at least partially on lenses and in particular on the semi-reflecting layer, at a distance or not from the latter.

These ancillary elements can be formed by printing, for example a macro-printing or a holographic printing, by metallization or demetallization. The ancillary elements may be metallic. A metal pattern disposed in front of a metal semi-reflective layer is particularly attractive when it is made of a different metal because it can be an immediately recognizable security.

The auxiliary element can correspond for example to an alphanumeric character, sign, logo, symbol, character or object.

An ancillary element may be carried on the support for example by a printing process such as offset, intaglio, laser, inkjet, micro-lithography, gravure printing or screen printing.

An additional element can be printed with colored or non-colored inks, visible to the naked eye, under ultraviolet (UV) and / or infrared (IR), opaque, fluorescent, phosphorescent, thermochromic, photochromic, translucent and / or transparent, among others.

The security structure according to the invention is preferably coated on at least its face opposite the face carrying the lenses of a heat-sealable varnish, in particular to facilitate the adhesion of the structure to a substrate of a security document. incorporating, in particular a security paper.

The heat-sealable varnish can furthermore make it possible to standardize the surface of the external faces of the security structure. The heat-sealable varnish can be a protective layer. The heat-sealable varnish may partially or completely cover the surface of the outer faces of the security structure. The heat-sealable varnish can come into contact with the semi-reflecting layer. The heat-sealable varnish may also come into contact with the lens material when the semi-reflective layer is perforated; in this case, the lenses may have their refractive power modified; the luminous points of the pattern observed on the projection surface may not come from lenses covered by the heat-sealable varnish.

The security structure according to the invention may thus comprise one or more adhesive layers on the surface, facilitating its incorporation into a document, in particular its adhesion to a fibrous paper mass.

The security structure may constitute a security thread, a security film (foil) or a patch. Preferably, the security structure is a security thread. The security structure may have a width greater than or equal to 4 mm, better 5 mm, better still 6 mm, for example between 6 and 8 mm, better still between 6 and 10 mm. According to another of its aspects, the subject of the invention is also a security element, in particular a security thread, film or patch, to be integrated in a document to be secured, in particular a document comprising a papermaker's substrate, comprising a security structure. security according to the invention.

The invention also relates to a secure document, comprising a security structure according to the invention. The pattern defined by the first set of lenses, for example alphanumeric, may be reproduced elsewhere on the document.

The document, and / or the security structure according to the invention that it comprises, may comprise one or more additional security elements as defined below.

Among the additional security features, some are detectable to the eye, daylight or artificial light, without the use of a particular device. These security elements comprise for example colored fibers or boards, fully or partially printed or metallized wires. These security features are said to be first-class.

Other types of additional security elements are detectable only with a relatively simple apparatus, such as a lamp emitting in the ultraviolet (UV) or infrared (IR). These security elements comprise, for example, fibers, boards, strips, wires or particles. These security elements may be visible to the naked eye or not, being for example luminescent under a lighting of a Wood lamp emitting at a wavelength of 365 nm. These security elements are said to be second level.

Other types of additional security elements require for their detection a more sophisticated detection device. These security elements are for example capable of generating a specific signal when they are subjected, simultaneously or not, to one or more external excitation sources. The automatic detection of the signal makes it possible to authenticate, if necessary, the document. These security elements comprise, for example, tracers in the form of active materials, particles or fibers capable of generating a specific signal when these tracers are subjected to optronic, electrical, magnetic or electromagnetic excitation. These security elements are said to be third level. The additional security element (s) present in the document, and / or the security structure that it comprises, may have first, second or third level security features.

Another subject of the invention, according to another of its aspects, is a method of authenticating a document according to the invention, comprising the step of exposing the lenses to a light source on one side so as to make appear in transmission by projection on a surface the pattern formed by the focusing of the light by the lenses of the first set of lenses.

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

FIG. 1 represents a front view of an example of a secure document incorporating a security structure according to the invention,

FIG. 2 illustrates the transmitted light formation of an image, FIG. 3 represents in cross section and schematically an example of a structure according to the invention,

FIG. 4 represents a front view of an example of distribution of the lenses of the first and second sets, and

- Figure 5 illustrates the realization of a negative write pattern in the semi-reflective layer.

FIG. 1 shows a document 1, comprising a substrate 2 and a security structure 10 according to the invention.

The document 1 is for example a banknote, which may include other security elements, for example a security thread 4, incorporated into windows.

The substrate 2 is for example a paperboard substrate, based on cellulose and / or synthetic fibers, and may comprise a watermark.

According to the invention, the security structure 10 comprises a first set of lenses 11 and a second set of lenses 12, having different optical properties of the first lenses, in particular a different focal length.

The first lenses 11 are convergent and produce, when illuminated for example by a quasi-point source S or a parallel beam of light, an image I formed of image light spots, on a projection surface P placed in the plane focal image. The light passing through the lenses 12 does not focus on the projection surface P, and does not prevent the observer from viewing the pattern M formed by the light spots coming from the lenses 11, in this case the letters AW which appear in positive.

Preferably, the light source used for the projection is a white light source, preferably directive, in particular emitting a collimated or slightly divergent parallel light beam, as emitted for example by a flashlight.

The lenses 11 define a hidden pattern in the lenses 12, because of the difficulty for the man of the street to distinguish the distribution of the lenses 11 within the set of lenses 11 and 12 when the document 1 is observed in reflected light.

There may be lenses 11 or groups of lenses 11 completely surrounded by lenses 12, as illustrated in FIG. 4. The lenses 11 are preferably arranged like the pixels of the pattern to be reproduced, and have their optical axis perpendicular to the plane of the document 1 .

Preferably, the lenses 11 and 12 are Fresnel lenses, as illustrated in FIG.

The lenses 12 may be convergent, or divergent, preferably divergent. This can reduce the amount of stray light in the projection plane.

The lenses 11 or 12 may be made in a layer 14 of a polymeric material deposited on a support 15.

The lenses 11 and 12 are preferably covered by a semi-reflective metal layer 16, which may have perforations 17 so as to define a raster negative write pattern, for example the letters AWS as illustrated in FIG. 5.

The opening diameter D of a lens 11 or 12 is for example between 1 and 3 mm.

This diameter D is measured parallel to the observation face, between the outer sides of the extreme ridges of the lens, as illustrated in FIG.

Each lens 11 or 12 may be a complete Fresnel lens, that is to say with a circular base, or a portion of Fresnel lens, that is to say with a truncated circular base. The lenses 11 and 12 may include ridges that constrict each other away from the center of the lens, as illustrated. The height h of the streaks is for example between 1 and 10 microns, each lens 11 or 12 advantageously having a constant thickness h.

The semi-reflecting layer 16 is preferably a layer of a metal deposited by a known metallization technique, for example by vacuum deposition. The recesses 17 formed in the semi-reflecting layer 16 may be formed by laser or by chemical etching of the metallic reflective layer, after application of a protective varnish, which may be left in place or removed after the etching step.

The laser demetallization can result from a modification of the crystalline phase of the metal layer by passing it to an amorphous phase, thus transparent. This conversion can be carried out thanks to a Nd YAG type laser which generates a punctually very high temperature generating the vitrification (liquefaction) of the metal at the point of impact of the laser, then the laser moving, the metal then returns to ambient temperature. quasi-instantaneous manner (which corresponds to quenching in metallurgy) making it possible to freeze the latter in the amorphous or partially amorphous state.

The polymeric material of the lenses 1 1 or 12 is for example a varnish and the Fresnel lenses are formed by embossing in relief of this varnish. The latter is for example an epoxy or acrylic resin.

A heat-sealable varnish 18 advantageously covers, as illustrated, the lenses 11 and 12, to improve the holding of the security structure 10 in the document 1.

The varnish 18 may also cover the face of the support 15 opposite to the lenses.

Of course, the invention is not limited to the illustrated examples.

The lenses 11 and 12 may be made differently, and for example be embossed directly in the support 15.

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

The intervals of values are understood by default included limits.

Claims

A security structure (10) comprising a plurality of lenses, said plurality having a first set of convergent lenses (11) and a second set of diverging or converging lenses (12), the lenses (11) of the first set having substantially the same same focal length and this focal length being different from that of the lenses (12) of the second set so as to show a predefined pattern (M) in light transmitted by the only focusing of the light from the first set of lenses (1 1) on a projection surface (P).

2. Structure according to claim 1, the lenses (12) of the second set being divergent.

3. Structure according to claim 1, the lenses (12) of the second set being convergent.

4. Structure according to any one of the preceding claims, the lenses (11,12) being Fresnel lenses.

5. Structure according to any one of the preceding claims, at least a portion of the lenses being covered by a semi-reflective metal layer (16).

6. Structure according to the preceding claim, the metal layer (16) having a transmission coefficient between 10 and 60%, preferably between 15 and

30%.

7. Structure according to one of claims 5 and 6, the semireflective metal layer (16) being apertured to define at least one negative writing pattern (17).

8. Structure according to any one of the preceding claims, the focal length (fl) of the convergent lenses of the first set being between

+10 and +30 cm.

9. Structure according to any one of the preceding claims, the lenses (11, 12) being arranged on a support (15) with a regular distribution or random in both directions.

10. Structure according to any one of the preceding claims, the lenses (11, 12) being covered at least partially by a varnish (18), including heat sealing.

11. Structure according to claim 10, the varnish (18) having a refractive index n _ve put different from that of the material material constituting the lenses, the difference | n _V emis - iimateriaul between the refractive indices being preferably greater than or equal to at 0.05.

12. Security element (10), in particular security wire or patch, to be integrated in a document to be secured, in particular a document comprising a paperboard substrate.

13. secure document (1), comprising a structure (10) for security as defined in any one of claims 1 to 12, including a passport, an identity card, a driver's license, a playing card or interactive collector, a means of payment, in particular a payment card, a bank note, a voucher or a voucher, a secure label, a transport card, a loyalty card, a service card, a card subscription or a specific payment method such as a chip or a wafer used in particular in casinos.

14. Document according to claim 13, the pattern (M) defined by the first set of lenses (1 1) being reproduced elsewhere on the document (1).

15. A method of authenticating a document (1) as defined in one of claims 13 or 14, comprising the step of exposing the lenses (11, 12) to a light source (S) of a side so as to show in transmission the pattern formed by the lenses (11) of the first set of lenses by projection on a surface. (P)