Two-layer anti-counterfeiting device

Field of the invention

The invention relates to devices intended to discourage the counterfeiting of fiduciary documents (certificates, banknotes, etc.) or security documents such as identity documents, access cards to restricted areas, credit cards and so on.

State of the art There are known in particular from

EP 0 265 323 and GB 2 189 800 documents having printed areas which, exposed to UV radiation, produce, through the use of fluorescent pigments, two areas of contrasted colors (for example green-red) . The problem is that users are generally content to verify whether there is fluorescence or not, without authenticating the colors in themselves. This is a failing that well-equipped counterfeiters could exploit.

There is known from EP-I 179 808 a method for more precise identification of fraudulent documents. Thanks to the use of fluorescent pigments with carefully calibrated characteristics, when a document made secure in this way is subjected successively to two UV sources with different wavelengths, similar or dissimilar patterns of colors are obtained, enabling authentication .

FR-2 762 545 concerns a fiduciary document or the like, such as a banknote, passport, identity card, bank card, comprising a medium whereon are provided security prints. The security prints include: a first

print produced in ink of a first color invisible to the naked eye but fluorescent or phosphorescent; a second print covering the first and produced in ink of a second color visible or invisible to the naked eye but fluorescent or phosphorescent, the second print being produced so as to blur the first print, such that in neutral light or ultraviolet illumination, only said second print is visible, while the first print is revealed only in ultraviolet illumination and through a filter of the same color as that of the first print. In this technique, a perfect equivalence of colors, very difficult to obtain by a possible counterfeiter with different inks, is not requested. It is further necessary to have a particular filter to check possible counterfeited banknotes.

Summary of the invention

An object of the invention is to enable easy and reliable checking of the authentication of a document.

Another object of the invention is to call on a technology that is simple to use but difficult or even impossible for potential counterfeiters to reproduce.

The subject of the invention is a document authentication device, said document carrying at least two juxtaposed areas each printed using an ink containing fluorescent pigments. The composition of these inks is such that when the document is exposed to a first of two types of UV radiation of particular wavelength, the two areas appear with an identical color to the human eye, whereas when the document is exposed

to a second of two types of UV radiation (with another particular wavelength) , they appear with different colors. In this device, these at least two juxtaposed areas each cover, at least partially, at least one third area, also printed using an ink containing fluorescent pigments. The composition of the inks of these at least two areas is such that they form an opaque filter under one of the two types of UV radiation for the radiation emitted toward or retransmitted by the third area, so that this at least one third area remains invisible. This filter effect disappears or is attenuated when the document is exposed to the other of the two types of UV radiation, so that the third area appears at this time with a color different from those of the at least two other areas.

In a preferred embodiment, the patterns formed by the three areas do not appear separately from their background in ambient light.

In an advantageous embodiment, the composition of the inks of the at least two areas is such that, under the first type of UV radiation, they form an opaque filter for the part of that radiation able to reach the at least one third area.

The authentication device of the invention advantageously includes at least two third areas.

Another object of the invention is a security document that includes at least one authentication device as described above.

Brief description of the figures

The above and other aspects of the invention will be clarified in the detailed description of particular embodiments of the invention, which refers to the drawings of the figures, in which:

Fig. 1 is a view in section of a device of the invention .

Figs 2, 4, 5 are diagrammatic plan views of the device from fig. 1 seen under different types of illumination.

Fig. 3 is a diagrammatic plan view of the device from fig. 2 concealed in a background pattern.

Figs 6 and 7 are diagrammatic plan views, under two types of radiation, of another embodiment of the invention.

The figures are not drawn to scale. As a general rule, similar elements are indicated by identical references in the figures.

Detailed description of particular embodiments

Fig. 1 shows, in section, and with the thicknesses greatly exaggerated, the general embodiment of the device 1 of the invention. Two contiguous patterns 2, 4 printed using inks with different compositions each containing fluorescent pigments are applied to an appropriate support 6. One example of a composition for the color of the pattern 2 is [Red bi- fluo yellow/orange, SICPA Yellowish red 20, SICPA Transparent white 20, SICPA Bi-fluo yellow-orange 60] and for the pattern 4 [Red fluo yellow, SICPA Yellowish

red 20.0, SICPA Transparent white 75.0, SICPA Colorless fluo yellow 1.5, SICPA Colorless fluo yellow 2.0, SICPA

Colorless fluo red 1.5] . This support 6 can be a paper intended for the fabrication of paper money, authentic documents, plastic, etc. These patterns 2, 4 cover

(completely in the example shown) a third pattern 8, printed using an ink with a composition different from that forming the other two patterns, also including fluorescent pigments. In this instance the following composition can be used: White fluo red, Sun Chemical Covering white 50, SICPA Invisible fluo red 50]. Exposed to ambient light, as in fig. 2, the device 1 appears with any color (color A, rendered by dots) , for example in the form of a colored patch. The device can also be concealed in an abstract (see fig. 3) (here also of color A) or other pattern, printed on the support 6.

Fig. 4 shows what happens when a document provided with a device of the invention is subjected to the radiation (UVl) from an ultraviolet lamp 10 emitting in a first range of wavelengths: the two patterns 2, 4 appear to the human eye with an identical phosphorescent color B (here rendered symbolically by horizontal shading lines), the third pattern remaining invisible.

Fig. 5 shows what happens when the same document is subjected to the radiation (UV2) from a second ultraviolet lamp 10 emitting in a second range of wavelengths: each of the patterns 2, 4 appears with a different phosphorescent color (colors rendered by left or right oblique shading lines) . The third pattern appears with a third color (vertical shading lines) . The transition from a patch of uniform color to three areas

of different (and preferably violently contrasting) colors is evident proof for the user of the authenticity of the document, while the technology necessary for rendering the same effects is totally out of the reach of even a well-equipped counterfeiter.

To obtain the required effect, a technology is used that is relatively simple in itself but complex to implement :

It is first necessary to adjust the composition of the inks constituting the patterns 1 and 2 to obtain the same color under radiation UVl, which is already a difficult task for any counterfeiter.

Moreover, these inks must each include components blocking the passage of the radiation emitted by the pigments of the pattern 8 due to the effect of the excitation due to a precise type of radiation, in this instance UVl, but not blocking much or any of the radiation emitted by the same pattern 8 due to the effect of another light source (UV2), in such a fashion as to allow this pattern 8 to show through, as shown in figure 5. Additionally, this filter effect must be taken into consideration so as not to interfere with the balance of the colors obtained during the first test

(fig. 4), to which balance it can further contribute, where appropriate.

Potential counterfeiters are therefore confronted with a multitude of contradictory physical effects, which renders their task all the more difficult, for the greatest security of users. Another embodiment of the system of the invention is shown in figures 6 and 7. In the case

represented in fig. 6, the characteristics of the pigments have been chosen so that when the areas 1 and 2 appear with an identical color, in contrast to what happens in fig. 4, the pigments do not block much or any of the radiation emitted by the pattern 8 due to the effect of the light source (UV2), in such a manner as to allow this pattern 8 to show through. Two concentric areas of the different colors are therefore obtained. On the other hand, the characteristics have been selected here so that under the UVl type illumination the central patch 8 suddenly disappears, its radiation being blocked, while the colors of the areas 2 and 4 become different (see fig. 7) .

It will be obviously apparent to the person skilled in the art that the present invention is not limited to the examples illustrated and described above. The device of the invention can notably be fabricated separately from the support 6 and applied to the latter by any transfer process well known to the person skilled in the art. The invention comprises each of the new features and their combination. The presence of reference numbers cannot be considered as limiting. The use of the term "comprise" can in no way exclude the presence of elements other than those referred to. The use of the indefinite article "a" or "an" to introduce an element does not exclude the presence of a plurality of those elements. The present invention has been described with reference to specific embodiments, which have a purely illustrative value and must not be considered as limiting.