WO2004062942A1

WO2004062942A1 - Waveguide safety device

Info

Publication number: WO2004062942A1
Application number: PCT/FR2003/003923
Authority: WO
Inventors: Thierry Dumery
Original assignee: Banque De France
Priority date: 2003-01-03
Filing date: 2003-12-29
Publication date: 2004-07-29
Also published as: FR2849708A1; OA13016A; EP1578617A1; FR2849708B1

Abstract

The inventive safety device comprises a transparent substance layer (4) having a refraction index and a thickness suitable for forming a waveguide and containing at least one type of a photoluminescent product. One of the faces of said waveguide layer is provided with a light-extraction pattern (10) which locally disrupts a waveguide effect.

Description

Waveguide safety device

The present invention relates to a security device which can be affixed to or incorporated into an object in order to ensure first level or second level security against fraudulent reproduction of the object in question.

BACKGROUND OF THE INVENTION It is known that in order to avoid fraudulent reproduction of an object, in particular documents such as banknotes, or bank cards, it is necessary that the object includes at least one security device which, for to be effective, must be difficult to reproduce while being easily identifiable.

The security device may be intended to provide first level security, that is to say be visually identifiable without the use of a tool, or second level security, that is to say by using an identification tool such as an ultraviolet lamp or an infrared sensor. We know, in particular documents US-A-6,057

082 and PE-A-401 466, various security devices using light scattering properties. In particular, security devices are known in the form of stamps or tapes comprising holograms. Experience has shown that the signs produced by holograms are generally too complicated to be memorized by the general public, especially since the different colors of the hologram are only visible if the hologram is exposed to a light source. punctual, which is generally not the case in public places where first level control is carried out. In practice, it is therefore sufficient to deceive a consumer of average attention, that the object fraudulently reproduced includes any hologram or even simply a shiny part having strong reflections. reliable, even if the sign produced is significantly different from the sign used on the authentic security device. In addition, holograms are expensive to produce and have a fragile structure. OBJECT OF THE INVENTION

An object of the invention is to propose a security element which can be easily memorized and analyzed at least during a first level control. BRIEF DESCRIPTION OF THE INVENTION With a view to achieving this object, there is provided, according to the invention, a security device comprising a layer of transparent material having an index of refraction and a thickness suitable for forming a waveguide and containing at least one photoluminescent product, one of the faces of this waveguide layer comprising a light extraction pattern locally interrupting the waveguide effect.

Thus, whatever the shape of the light source, that is to say point or diffuse, the light which penetrates into the layer in waveguide excites the photoluminescent product from which the luminescent emission cannot escape of the waveguide layer only by the light extraction pattern and is therefore perceived by an observer according to the sign formed by the outline of this pattern. In particular, by providing a photoluminescent product emitting in the visible range, it is possible to provide first level control by observing not only the outline of the light extraction pattern, but the color of this pattern. It is also possible to carry out a second level control by providing either a photoluminescent product excited by ultraviolet radiation by means of an appropriate lamp, or a photoluminescent product emitting in a non-visible range such as infrared, the analysis being then performed with the corresponding sensor, i.e. a combination of these two tools.

According to an advantageous version of the invention, the security device comprises at least one transparent layer in contact with one face of the waveguide layer and having a refractive index lower than the refractive index of the guide layer wave. Thus, the waveguide effect is enhanced so that a stronger intensity of the light emitted through the light extraction pattern is obtained, and further extraction of light by soiling which is avoided would be applied to the external surface of the security device when the object carrying this security device is used, these soiling generally having a refractive index suitable for extracting the light at the location of the soiling.

According to other advantageous aspects of the invention, the light extraction pattern is produced either in the form of a relief pattern or in the form of a pattern produced by means of a transparent product having a higher refractive index. the refractive index of the waveguide layer.

According to yet another advantageous aspect of the invention, the waveguide layer comprises at least one zone comprising a first photoluminescent product and at least one adjacent zone comprising a second photoluminescent product forming a light cascade with the first photoluminescent product. A color is thus obtained at the level of the light extraction pattern which does not correspond to any natural color of photoluminescent product so that the difficulty of reproducing the safety device is increased.

BRIEF DESCRIPTION OF THE DRAWINGS Other characteristics and advantages of the invention will appear on reading the following description of different particular embodiments nonlimiting of the invention, in relation to the attached figures among which:

FIG. 1 is a partial perspective view of a bank note equipped with a security device according to the invention,

- Figure 2 is a very enlarged sectional view of a first embodiment of the security device according to the invention before its application on a banknote, - Figure 3 is a sectional view similar to that of Figure 2 of a second embodiment of the security device according to the invention,

FIG. 4 is a sectional view similar to that of FIG. 2 of a third embodiment of the security device according to the invention applied to a bank note,

- Figure 5 is a perspective view similar to that of Figure 1 of a fourth embodiment of the invention, - Figure 6 is a perspective view similar to that of Figure 1 of a fifth embodiment realization of the invention,

DETAILED DESCRIPTION OF THE INVENTION The security device according to the invention is illustrated in the form of a stamp 1 fixed by bonding to a bank note 2. The stamp 1 includes a security sign 3, here in the form of the symbol of the euro.

With reference to FIG. 2, the security device according to the first embodiment of the invention comprises a layer of transparent material 4, for example a flexible synthetic material having a refractive index of the order of 1.5, in which is incorporated a photoluminescent product emitting in the visible range, and having a suitable thickness to form a waveguide, for example a thickness about 10 μm. The waveguide layer 4 is covered with a transparent varnish layer 5 having a refractive index lower than the refractive index of the waveguide layer 4. The varnish layer 5 is for example made at by means of a transparent varnish loaded with ultrafine particles of silica (of the order of a few nanometers) so that the varnish has a refractive index close to 1. On its lower face the layer in waveguide 4 is also in contact with a layer of varnish 6 also having a refractive index lower than the refractive index of the waveguide layer 4, for example a layer of varnish analogous to the layer of varnish 5. The layers of Varnishes 5 and 6 essentially have the function of reinforcing the waveguide effect of the waveguide layer 4. In order not to unduly increase the total thickness of the safety device, these layers have a very small thickness for example of the order of microm to be . In this first embodiment, the security device further comprises a layer of material of white color 7, for example a layer of varnish having a thickness of the order of a micrometer loaded with particles of titanium. A layer of adhesive 8 is in contact with the layer of white material 7. The adhesive is preferably a hot-melt adhesive which allows the hot fixing of the stamp 1 on the banknote 2. The thickness of the layer of adhesive is adapted to allow the attachment of the security device on the object for which it is intended. In the case of a banknote, the thickness of this layer is typically of the order of 2 to 3 μm.

In the first illustrated embodiment, the underside of the waveguide layer 4 further comprises a light extraction pattern formed by a series of elements 9 in the form of curvilinear grooves joined together to form a relief pattern interrupting the waveguide effect and the outline of which forms the safety sign 3. In the illustrated embodiment, the grooves 9 are V-shaped, the sides of which form with the faces of the waveguide layer 4 an angle suitable for returning the light flowing in the waveguide to the upper surface of the waveguide layer 4 according to a angle allowing the light contained in the waveguide to be extracted. The layer of white matter reinforces this extraction and increases the contrast of the security sign with respect to the adjacent area.

In addition, the sawtooth relief thus obtained is a diffractive relief so that the light rays coming from the outside reaching the relief pattern 10 do not remain trapped in the waveguide layer 4 but are returned to the outside with a wavelength equal to the distance between crests of the relief pattern 10. When it is desired to avoid a visible effect of the diffractive effect of the relief pattern 10 relative to the photoluminescent emission, it suffices therefore to produce the grooves 9 with a width at least equal to 1 μm, for example of the order of 2 μm so as not to modify the surface appearance of the safety device too much, the diffractive effect obtained is then in the infrared domain and therefore does not interfere with first level control. On the contrary, it makes it possible to ensure a second level control by verifying that the security sign 3 is visible when the security device is analyzed by means of an infrared sensor.

In practice, the security device according to this first embodiment is preferably produced by first depositing the layer of varnish 5 on a support film suitably coated with a material allowing separation of the security device from the support film during placement on a banknote. The layer of varnish 5 is deposited on the support film by any suitable printing means, for example by screen printing. The material forming the waveguide layer 4 is then deposited on the varnish layer 5 according to a constant thickness. The transparent varnish layer 6 is then deposited on the waveguide layer 4, also at a constant thickness, then the relief pattern 10 is produced, for example by embossing. Note in this regard that the relief pattern 10 illustrated in Figure 2 has four grooves 9 only so as not to load the figure. Given the very small width of the grooves 9, the actual pattern will include a large number of grooves so that the sign produced is perceptible to the naked eye. After embossing the relief pattern 10, the layer of varnish 6 is covered with the layer of titanium varnish 7 then the layer of adhesive 8. The security device according to the invention is then ready to be fixed on an object to be authenticated .

With reference to FIG. 3, the security device comprises, as before, a waveguide layer generally designated at 4 surrounded by layers of varnish 5 and 6 with a low refractive index, the underside of the security device being as previously provided with a layer of adhesive 8. In this embodiment, the waveguide layer 4 has different zones 4.1 and 4.2 adjacent to each other and containing different photoluminescent materials forming between them a light cascade. Furthermore, in this embodiment, the light extraction pattern 11 is produced by means of a material having a refractive index greater than the refractive index of the waveguide layer 4. By way of example, the light extraction pattern 11 can be produced by means of a varnish containing zinc sulfide so that the refractive index of the pattern produced is close to 1.8.

As in the first embodiment, the security device according to this embodiment is preferably produced by depositing the different layers on a support film, starting with the layer of varnish 5. The zones 4.1 and 4.2 are produced by deposits successive of the materials constituting them. The light extraction pattern 11 can be produced by conventional printing techniques, by vacuum deposition or by any other technique allowing the application of a layer according to a defined contour.

With reference to FIG. 4, the safety device comprises, as in the previous embodiments, a waveguide layer 4 covered on its upper face by a layer of varnish 5 having a refractive index lower than the refractive index of the waveguide layer 4. In this embodiment, a reflective layer 12 is applied to the face of the waveguide layer opposite to the varnish layer 5. This reflective layer 12 is example obtained by vacuum deposition of an aluminum layer. As before, the security device is fixed to the bank note 2 by means of an adhesive layer 14 in which a white pigment has been incorporated.

In this embodiment, the light extraction pattern 13 having a structure identical to the light extraction pattern 10 is this time made on the upper surface of the security device.

This embodiment is obtained by first producing a stamp not comprising a light extraction pattern. The stamp is obtained by successively depositing on a support film the varnish layer 5 which is covered with the waveguide layer 4 then the reflective layer 12 and finally the white adhesive layer 14. The stamp thus obtained is transferred to a document and it is only after the transfer that the stamp is subjected to an embossing effecting the light extraction pattern 13. This embossing is for example carried out by hot calendering between rollers, one of which has a safety sign produced in intaglio. This embodiment makes it possible to manufacture a large number of security devices in advance, which makes it possible to use mass production means, then to personalize the security device according to the application. In the case of a bank note, this allows in particular to carry out a security sign corresponding to the serial number of the bank note.

In the previous embodiments, the extraction pattern is adjacent to the upper or lower face of the waveguide layer and appears on the upper surface of the security device. Figures 5 and 6 illustrate two embodiments in which the extraction pattern appears on the lateral face of the waveguide layer.

In the case of FIG. 5, the security device according to the fourth embodiment comprises a cutout 16 in the form of € made over the entire thickness of the layer in waveguide 1 so that the internal lateral faces 16 in look at each other form the light extraction pattern locally interrupting the waveguide effect. In the case of FIG. 6, the safety device according to the fifth embodiment is produced by cutting a sheet of material in waveguide according to a shape of € 17, and application of this shape on the support 2 of so that it is the side faces 18 of the device itself which form the pattern of extrac- tion of light. In this embodiment, the extraction pattern can also be produced by studs slightly spaced from one another and visually forming a complete pattern. The studs themselves can have various shapes including points, bars ...

Of course, the invention is not limited to the embodiments described and it is possible to make variant embodiments without departing from the scope of the invention as defined by the claims.

In particular, different combinations of the layers described can be produced in relation to each of the illustrated embodiments. By way of example, the layer of varnish 6 and the layer of white material 7 of the first embodiment may be replaced by a reflective analogous to the reflective layer 12 of the third embodiment.

It will also be noted that the light extraction pattern, whether this is a relief pattern or a pattern produced by means of a material having a refractive index greater than the refractive index of the guide layer. wave, can be made indifferently adjacent to the upper surface or to the lower surface of the waveguide layer. The light extraction motif made of a material with a high refractive index can, like the relief motif, be produced in the form of a series of separate lines or dots to avoid an edge effect when the security sign comprises solid areas . One or more of the transparent layers may contain a dye to modify the color of the light emitted by the photoluminescent product.

Different color combinations can also be made using photoluminescent materials of different colors in different areas of the color. che in waveguide, and associate different areas with different light extraction patterns so that they appear in different colors.

It is also possible to combine a first level security control and a second level security control by incorporating into the waveguide layer different photoluminescent materials emitting at different wavelengths which can be excited and / or controlled. separately. Although in the case of a relief light extraction motif, this has been illustrated by a sawtooth motif, it is possible to provide a relief motif having any configuration suitable for carrying out light extraction, for example example a staircase pattern or a factory roof pattern, that is to say a pattern formed by grooves whose walls have different inclinations, or a pattern formed by dots or perforations of various shapes, made of mechanically or using a laser, each point or each perforation may have a cylindrical, conical or stepped wall.

Although the security device according to the invention has been described in the form of a stamp intended to be affixed to a document, this device can also be produced in the form of a ribbon or a wire which is fixed to the object to be authenticated or incorporated into it, in particular in the case of a bank note or a document printed on a paper support. When the object to be identified comprises a thin support, the security device can also be produced directly on the object to be authenticated by successive deposition of layers and, if necessary, embossing of the layer as a waveguide. This applies in particular to a bank note produced from a transparent film, the note itself then being formed from the guide layer wave and comprising at least one unprinted zone to allow light to penetrate into the waveguide layer so that the extraction pattern is formed either by the edge of the banknote itself or by a pattern produced on the 'one side of the ticket.

Claims

1. safety device, characterized in that it comprises a layer of transparent material (4) having a refractive index and a thickness suitable for forming a waveguide, and containing at least one photoluminescent product, one of the faces of this layer

(4) in waveguide comprising a light extraction pattern (10, 11, 13, 16, 18) locally interrupting the waveguide effect.

2. Safety device according to claim 1, characterized in that the light extraction pattern (11) is made of a material having a refractive index greater than the refractive index of the waveguide layer ( 4).

3. Safety device according to claim 1, characterized in that the light extraction pattern (10, 13) is a relief pattern.

4. Safety device according to claim 3, characterized in that the relief pattern is diffractive.

5. Safety device according to claim 4, characterized in that the relief pattern is formed of elements (9) having a width at least equal to a micrometer.

6. Safety device according to claim 1, characterized in that it comprises a white color layer (7) extending over one face of the waveguide layer (4) opposite the extraction pattern of light (10).

7. Safety device according to claim 1, characterized in that it comprises at least one transparent layer (5, 6) in contact with one face of the waveguide layer (4) and having a refractive index in - lower than the refractive index of the guide layer wave (4).

8. Safety device according to claim 1, characterized in that it comprises a reflective layer (12) extending on one side of the waveguide layer (4).

9. Safety device according to claims 6 and 7 taken in combination, characterized in that it comprises a transparent layer (6) interposed between the layer of white material (7) and the waveguide layer (4).

10. Safety device according to claims 6 and 8 taken in combination, characterized in that the reflective layer (12) is interposed between the white material layer (14) and the waveguide layer (4).

11. Safety device according to claim

1, characterized in that the waveguide layer (4) comprises at least one zone (4.1) comprising a first photoluminescent product and at least one adjacent zone

(4.2) containing a second photoluminescent product forming a light cascade with the first photoluminescent product.