ES2320730T3 - AUTHENTICATION PROCEDURE FOR SENSITIVE DOCUMENTS. - Google Patents

Abstract

Procedure for authenticating documents such as banknotes, the procedure comprising: the integration into the document of at least one luminescent substance suitable for emitting light according to a determined frequency spectrum of response when the substance is exposed to a luminous radiation of excitation , the exposure of the document to a light excitation radiation, the excitation radiation being a laser radiation, the collection of the response of the document to said excitation radiation, each frequency response spectrum being essentially composed of at least one line, and the coding of the luminous response of the document to the excitation radiation, and the comparison of this response with a memorized expected response, characterized in that at least one luminescent substance comprises a medium that has no laser effect, said medium comprising a mixture of Europio complexes with u CN-PPP polymers (poly (2- (6 '' - cyano-6 '' - methyl-heptyloxy) -1,4-phenylene)).

Description

Document Authentication Procedure sensitive

The present invention relates to a procedure for authenticating sensitive documents such as fiduciary documents, as well as documents and means for implementing said procedure.
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Numerous means are known to secure and authenticate sensitive documents.

Such means may allow a Authentication of a document by any user: it is the case of the authentication means called "great public "who do not need any complex machine or device to allow document authentication.

Thus, it is known to integrate in the banknotes of bank security threads or watermarks, or even some luminescent substances that produce a particular light emission when the bill is exposed to excitation radiation determined (from an ultraviolet lamp, by example).

It is also known to provide some signs of security not readable by the general public; the detection of these signals need the use of a particular machine, such as a magnetic detector for example.

The signals of the latter type constitute a higher security level, since they are not directly accessible by the general public.

Numerous safety signs - large public or they do not use optical properties. In effect, they can be perceived the optical properties easily with the naked eye, or with some adapted sensors.

Generally, these optical signals use luminescence properties of adapted substances that, at be subjected to a certain excitation radiation, produce an emission according to a specific spectrum. The authentication of document in which these substances are integrated is made by comparing the spectrum of the response emitted with a expected spectrum, this comparison being able to intervene some electro-optical machines or not.

On the other hand, there are known attempts to make a document that includes an encoding made to from luminescent substances. Document FR 1 471 367 gives Know an example of such attempts.

The fact of anticipating substances luminescent intended not only to be detected, but also to form a specific code associated with the document, it should allow significantly increase the security level of the document.

But such attempts do not allow a effective coding of the document, particularly because of the large width of the emission peaks of the substances used; in In effect, it would be necessary to obtain an answer that includes some fine and distinct stripes to perform real coding.

WO 98/36376 A1 describes a authentication procedure of a document in which it is integrated a safety signal comprising layers that they include dye molecules and crystal molecules liquids that function as diffusion sites to produce a laser emission when the layers are subjected to a radiation of laser excitation

WO 00/46742 A1 describes a authentication procedure of a document in which it is integrated a safety signal comprising a structure of guide such as fibers and an amplifying means, such as a colorant or a rare earth ion, suitable for producing a laser emission When the structure is subjected to radiation of laser excitation, emits a response in the form of fine stripes to some predetermined wavelengths.

US 5,903,340 describes a authentication procedure of a document in which it is integrated a safety signal comprising a means amplifier, such as fibers, coated or impregnated with a dye or with any other appropriate material to emit light in Combination with diffuser particles. When the structure to a laser excitation radiation, emits a response characteristic in the form of fine stripes at wavelengths predetermined The authentic document is considered only if Detects a laser emission.

An objective of the invention is to enable said luminescent coding of sensitive documents.

Another object of the invention is also to avoid resort to onerous substances to manufacture and / or integrate into the document, in order not to excessively increase the document cost price.

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In order to achieve these goals, the invention proposes a document authentication procedure sensitive such as banknotes according to one of claims 1 or 5. The method comprises:

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document integration of at least one luminescent substance suitable for emitting light according to a given frequency spectrum of response when the substance is exposed to a light radiation of excitement.

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document exposure to a luminous radiation of excitation, and

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collecting the response of document to said excitation radiation,

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excitation radiation is a laser radiation,

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each frequency spectrum of answer is essentially composed of at least one line, Y

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the procedure includes also the coding of the luminous response of the document to the excitation radiation, and comparing this response with a expected response memorized.

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Other aspects of the procedure according to invention are as follows:

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each line of the response spectrum (s) have a width at half height less than a value of the order of 10 nm,

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the coding is done according to at least one of the following ways:

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spatial coding,

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coding on response frequencies,

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response intensity coding

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laser excitation radiation is obtained by a YAG laser that has a peak of emission close to 532 nm,

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at least one substance luminescent comprises a medium that has no effect To be,

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said medium comprises a mixture of Europium complexes with polymers of type CN-PPP (poly (2- (6'-cyano-6'-methyl-heptyloxy) -1,4-phenylene)),

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Europio ions are incorporate the polymer by synthesizing a family of complexes of Soluble Europium with ligands β-diketonates, and dissolving these complexes in a solvent in conjugation with the polymer,

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triplet energy level of the ligand is higher than the emission level of the Europium,

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the emission spectrum of polymer and the absorption spectrum of the complex are coated so less partially,

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at least one substance luminescent comprises a doped matrix-host with at least one rare earth ion,

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the coding is obtained in at least one of the following ways:

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using different dopants in the same matrix, and / or

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using the same dopant ion in matrices of different characteristics.

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Other aspects, objectives and advantages of the invention will become more clearly apparent from the reading the following description of preferred forms of embodiment of the invention.

In a first embodiment that does not form part of the invention, a banknote is made by integrating said bill a security marking made from fibers of silica doped by a laser dye.

Said doped fibers constitute a material whose pores have a size of the order of some tens to a few hundred angstroms, thus constituting a structure mesoscopic, and sorted, so that the structure formed by The pores are homogeneous.

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These fibers can be synthesized by spontaneous growth of fibers in an aqueous solution whose Molar composition is as follows:

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100 H2O

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0,0246 CTAB (being CTAB a cationic surface agent, for example of formula CH 3 (CH 2) 15 N (CH 3) 3 Br),

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2.92 HCl,

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0.00017 Rh6G (where Rh6G is a cationic dye such as rhodamine).

This first aqueous solution is stirred at then, and 0.05 mol of formula TBOS is added (C 4 H 9 O) 4 If without stirring the solution, so that the surface of a thin layer of TBOS is coated.

As explained in the article by Marlow et al ., "Doped mesoporous silica fibers: a new laser material" (Advanced Materials, 1999, 11, no. 8), spontaneous growth of silica fibers is observed after two days doped by rhodamine which constitutes a laser dye.

Proceed, after approximately five days, to the extraction of these fibers, and then to their dried

In one embodiment, the percentage by weight of dye in the fibers is thus of the order of 15%.

Fibers are obtained in this way whose physical characteristics (dimensions, being able the diameter of fibers obtained according to this procedure be of the order of 22 angstroms) and optical (absorption coefficient and birefringence) are homogeneous; these fibers constitute large waveguides benefits.

These fibers can be integrated into continuation on a banknote (or any sensitive document) by any known means, for example embedding the fibers in the plot of the paper, constituting a security thread in which doped fibers are integrated, and integrated in turn into the paper thickness, diluting these fibers in an ink or a varnish of ticket printing, etc.

The fibers integrated in the bill constitute an invisible safety signal for an observer, but Recognizable by a machine.

More precisely, the ticket on which the fibers have been integrated into the radiation of a laser source.

The energy of said incident radiation is It concentrates on a very fine frequency line. In a preferred mode In accordance with the invention, the laser is of the Nd: YAG type with a emission peak at 532 nm, at a frequency of 10 Hz.

Exciting fibers doped with said radiation laser, a light remission of laser type is observed by the same fibers, emitting rhodamine according to a much more marked peak that in the case of the exposure of a simple rhodamine solution at the same radiation.

This laser effect is the result of internal reflections of the photons inside the fibers in those that are imprisoned along their path in the fiber.

The exploitation of this laser effect, conjugate With an exposure to laser excitation radiation, it allows get some answers from the fibers in the form of stripes extremely thin, being the characteristic width of these stripes (width at half height) less than 10 nm.

The fibers are arranged on the bill so that an encoding is done. This coding can be done according to one or more of the following provisions:

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spatial coding: fibers are integrated in certain places selected from ticket, so that a geometric code (code of bars for example, or default graphic figure),

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coding on response frequencies: in this case several types of fibers in the bill, each fiber presenting a spectrum of Different response for a particular laser excitation. They may constitute for this some fibers from laser dyes different, whether or not they comprise rhodamine. This way you get, Illuminated the bill with some laser flashes, a luminous response according to certain discrete emission lines corresponding to the wavelengths of the emission stripes of the different dyes,

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intensity coding varying the amount of rhodamine (or any dye) that They comprise the different fibers integrated in the same bill. In In this case, the differences in dye concentration in different fibers cause differences in the intensities of response of these different fibers, which are centered by another side on the same wavelength.

This code is recognized by reading of the light signal emitted by the ticket, thanks to a set sensor adapted to collect and quantify the light emitted by the banknote in response to laser excitation, according to the stripes of expected frequency

Said sensor assembly may comprise a series of separating mirrors of which each one directs a part of the light emitted by the ticket to a sensor associated with a specific wavelength (for example a photoelectric diode in series behind a colored filter), or also a matrix sensor CCD type.

In all cases, the sensor assembly collects the light emitted by the ticket and produces electrical signals that translate the presence and intensity of light emission:

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for each length interval wave of a response spectrum that encompasses emission stripes of the different substances integrated in the ticket, and that it typically comprises therefore the visible and / or the infrared; each interval can thus have a width of the order of 5 to 10 nm; Y

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for each place of the ticket, presenting the sensor assembly some means of locating its position with respect to the surface of the bill, for example using an origin related to the edges of the bill or with a signal-origin integrated in the ticket, the bill surface can be divided into plots whose dimensions are adapted to the resolution of the sensor assembly and to manufacturing tensions.

To recognize the code, a memory that contains the expected response of the ticket is connected to the sensor set, and a comparator compares the captured signal and the expected signal

The great finesse of the spectra stripes response allows effective coding, which does not it was really the case with luminescent substances wide response spectrum

It is also possible to replace rhodamine with other materials whose response to a laser excitation was focused around a discrete line, or by a finite amount emission stripes; in particular, rhodamine may be replaced by nanocrystals doped by one or more land ions rare, or by conjugated polymers.

It is also possible to replace the fibers doped by doping paper or printing ink of the paper with pigments constituted by the assembly of semi-conductive organic elements with effect solid state laser.

In this second embodiment which is not part of the invention and which also provides a laser effect for the response to an incident radiation, it is therefore these organic elements that provide the laser effect. A more complete description of these organic elements can be found in the article by Tessler et al. "Lasers based on semiconducting organic materials" (Advanced Materials, 1999, 11 No. 5).

These organic elements semi-conductors can be made from a polymer of the type MEH-PPV (poly (2-methoxy-5- (2'-ethylhexyloxy) -1,4-phenylenevinylene)) or PPV (poly (p-phenylene vinyl)), and can be in solid state, preferably dispersed in a support-host of the glass type for example. Is It is also possible to further stimulate the laser effect by adding in the support-host diffuser particles, for example TiO_ {2}.

To define the polarization properties of said materials, you can also align the chains of polymers

These organic element assemblies can take the form of tubular structures that constitute guides of waves, or some stacks that can form some microcavities

Finally, the invention is put into practice without really exploit a "laser effect", that is a jump from the emitted energy in response to an excitation to concentrate this energy in discrete stripes, being the most important thing to obtain of the ticket an answer in the form of discrete stripes of a width typically less than about 10 nm.

Thus, in a third embodiment according With the invention, the authentication of bills is carried out:

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always by collecting and the analysis of the encoded response of the bills to a radiation from a laser source (this point being important for stimulate the substances integrated in the ticket only according to one or more spectral line (s) well certain (s)),

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but without exploiting an effect laser provided by these substances.

In this case, some molecules will be used synthetics embedded in the paper of the bill, or in an ink or a varnish, or also in an intermediate support such as a thread of security.

Examples of synthesis of these molecules can be found in the article by Mc Gehee et al. "Narrow band with luminescence from blends with energy transfer from semiconducting conjugated polymers to Europium complexes" (Advanced Materials, 1999, 11, No. 16).

Thus, a mixture of complexes can be used Europium with polymers of the CN-PPP type (poly (2- (6'-cyano-6'-methyl-heptyloxy) -1,4-phenylene)).

More precisely, the Europio ions are incorporate the polymer by synthesizing a family of complexes of Soluble Europium with ligands β-diketonates, dissolving these complexes in a solvent in conjugation with the polymer, and laminating at then a film from this double solution.

To get Europio complexes fluorescent, the energy level of ligand triplets must be higher than the Europio emission level.

In addition, to allow the transfer of polymer energy conjugated to ligands of the complex of Europium, the emission spectrum of the polymer and the spectrum of complex absorption should be coated at least partially.

Different molecules can thus be synthesized from CN-PPP, as set forth in the article by Mc Gehee et al . These molecules have the peculiarity of emitting according to very thin stripes (whose width at half height is less than 10 nm), in response to an ultraviolet light excitation.

By way of example, under the conditions mentioned above, four Europium complexes can be synthesized: Eu (acac) 3phen, Eu (mppd) 3phen, Eu (dbm) 3phen, and Eu (dnm) 3phen. The structure of these complexes is specified on page 1350 of the article by Mc Gehee et al .

In this variant embodiment of the invention, the narrowness of the source excitation stripes is used laser combined with the narrowness of the response stripes of the molecules so synthesized, to get an answer extremely well marked according to the Europio complexes used in combination with the CN-PPP; this allows to use a real coding, using in the same ticket different molecules whose response stripes to a certain excitation (for example a laser excitation close to the ultraviolet) are separated in a frequency band of the order of 5 nm.

Finally, it is also possible according to another variant of the invention integrate into the banknote (according to one in the ways set forth above) a substance comprising a host matrix that can be crystalline, doped by rare earth ions such as those used usually in lasers.

The use of the properties of luminescence of said substances. But it is not known to use them for the authentication of products such as tickets, with a exposure to laser excitation radiation (which constitutes an important element of the invention).

The fact of exciting said substance by means of a Extremely concentrated laser radiation on a thin line allows to obtain a response so concentrated in one or several stripes).

It is also possible according to the invention to proceed to a coding of the ticket response; this coding in this last variant of the invention can be carried out in several ways, separately or in combination:

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using some dopants different on the same matrix. They can be integrated in the banknote two different inks, one doped with a first ion of rare earths whose response to a laser excitation (which in turn concentrates around a visible wavelength, near infrared or ultraviolet), and the other doped with a second rare earth ion, different from the first, and whose length response wave to the same excitation is different,

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but also, using a same dopant ion on matrices of different characteristics (type of matrix, stoichiometry of the matrix ...) so that the response stripes in the different matrices are displaced in a width greater than the fineness of the stripes, and preferably at a width of the order of 10 nm.

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For example, some ions of Neodymium:

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on the one hand on a matrix of type YLF and get well, in response to a laser excitation of 800 nm wavelength, an emission line centered at 1,054 nm, and

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on the other hand, on a matrix YAG type and observe a line centered this time at 1,064 nm. Being the width at mid-height of the stripes in both cases of the order of 5 nm, it is understood that it is easy to distinguish the answers in the two matrices.

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This way you can combine one or several different dopants in one or several types of matrix, and integrate these different substances in the ticket in mixture or separately, so that an encoding of the response of the ticket to a laser radiation exposure.

Finally, it will be specified that it is possible obviously integrate several substances in the same ticket luminescent corresponding to any embodiment or to Any variant of the invention described above.

Claims (9)

1. Authentication procedure of documents such as banknotes, comprising the process:

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document integration of at least one luminescent substance suitable for emitting light according to a given frequency spectrum of response when the substance is exposed to a light radiation of excitement,

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document exposure to a light radiation of excitation, the radiation being excitation a laser radiation,

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collecting the response of document to said excitation radiation, each spectrum being frequency response essentially composed of at least a stripe, and

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response coding luminous of the document to the excitation radiation, and the comparison of this answer with an expected response memorized,

characterized because

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at least one substance Luminescent comprises a medium that has no laser effect, said medium comprising a mixture of Europium complexes with some CN-PPP type polymers (poly (2- (6'-cyano-6'-methyl-heptyloxy) -1,4-phenylene)).

2. Method according to claim 1, characterized in that the Europium ions are incorporated into the polymer by synthesizing a family of soluble Europium complexes with β-diketonate ligands, and dissolving these complexes in a solvent in conjugation with the polymer. 3. The method according to claim 2, characterized in that the triplet energy level of the ligand is higher than the emission level of the Europium. 4. Method according to one of claims 1 to 3, characterized in that the emission spectrum of the polymer and the absorption spectrum of the complex are at least partially coated. 5. Authentication procedure of documents such as banknotes, comprising the process:

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document integration of at least one luminescent substance suitable for emitting light according to a given frequency spectrum of response when the substance is exposed to a light radiation of excitement,

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document exposure to a light radiation of excitation, the radiation being excitation a laser radiation,

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collecting the response of document to said excitation radiation, each spectrum being frequency response essentially composed of at least a stripe, and

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response coding luminous of the document to the excitation radiation, and the comparison of this answer with an expected response memorized

characterized because

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at least one substance Luminescent comprises a medium that has no laser effect, said substance comprising a host matrix doped with at least one rare earth ion,

Y why

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authentication is carried out of documents without exploiting a laser effect provided by the substance.

Method according to claim 5, characterized in that the coding is obtained in at least one of the following ways:

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using some dopants different in the same matrix, and / or

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using the same dopant ion in a matrix of different characteristics.

7. Method according to one of the preceding claims, characterized in that each line of the specimen (s)
tro (s) of response has a width at half height less than a value of the order of 10 nm. Method according to one of the preceding claims, characterized in that the coding is carried out in at least one of the following ways:

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spatial coding,

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coding on response frequencies,

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intensity coding of reply.

Method according to one of the preceding claims, characterized in that the laser excitation radiation is obtained by means of a YAG laser having an emission peak near 532 nm.