EP1182048A1 - Method for authentification of sensitive documents - Google Patents

Abstract

Method for authenticating sensitive documents comprises incorporating at least one luminescent material in the document, exposing the document to laser excitation radiation to generate a response in the form of an emission spectrum comprising at least one line; coding the response; and comparing the response with an expected response in memory.

Description

The present invention relates to a method for authenticating sensitive documents such as fiduciary documents, as well as documents and means for implementing such a method.

We know many ways to secure and authenticate sensitive documents.

Such means may authorize authentication of a document by any user; this is the case for authentication means known as “large public ”, which do not require any complex machine or device to allow document authentication.

It is thus known to integrate into banknotes wires of security or watermarks, or luminescent substances producing a particular light emission when the ticket is exposed to a given excitation radiation (from an ultraviolet lamp for example).

It is also known to provide unreadable security signs by the general public; the detection of these signs requires the implementation of a particular machine, such as a magnetic detector for example.

The signs of the latter type constitute a level of security higher because they are not directly accessible to the general public.

And many safety signs - general public or not - use optical properties. Indeed the optical properties are easily perceptible to the human eye, or to suitable sensors.

Generally, these optical signs use the properties of luminescence of suitable substances which, when subjected to radiation of given excitation, produce in return a emission according to a spectrum determined. And the authentication of the document to which these substances are integrated is done by comparison of the spectrum of the response sent with a expected spectrum, this comparison can involve machines electro-optical or not.

We also know of attempts to produce a document comprising coding made from luminescent substances. The document FR 1 471 367 discloses an example of such an attempt.

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

But such attempts do not allow coding efficient document, especially because of the large width of the emission peaks of the substances used; it would indeed be necessary get a response with fine and distinct lines to achieve real coding.

An object of the invention is to allow such coding to be carried out luminescent of sensitive documents.

Another object of the invention is to avoid further resorting to this. expensive substances to manufacture and / or integrate into the document, in order to not to excessively increase the cost price of the document.

• L'intégration au document d'au moins une substance luminescente apte à émettre de la lumière selon un spectre fréquentiel de réponse déterminé lorsque la substance est exposée à un rayonnement lumineux d'excitation,
• L'exposition du document à un rayonnement lumineux d'excitation, et
• Le recueil de la réponse du document audit rayonnement d'excitation,

caractérisé en ce que :

• le rayonnement d'excitation est un rayonnement laser,
• chaque spectre fréquentiel de réponse est essentiellement composé d'au moins une raie, et
• le procédé comporte également le codage de la réponse lumineuse du document au rayonnement d'excitation, et la comparaison de cette réponse à une réponse attendue mémorisée.

In order to achieve these aims, the invention proposes a method for authenticating sensitive documents such as banknotes, the method comprising:

• The integration into the document of at least one luminescent substance capable of emitting light according to a frequency spectrum of response determined when the substance is exposed to excitation light radiation,
• Exposing the document to exciting light radiation, and
• Collection of the document's response to this radiation of excitement,

characterized in that:

• the excitation radiation is laser radiation,
• each frequency response spectrum is essentially composed of at least one line, and
• the method also includes coding the light response of the document to excitation radiation, and comparing this response to an expected response stored.

• chaque raie du ou des spectre(s) de réponse a une largeur à mi-hauteur inférieure à une valeur de l'ordre de 10nm,
• le codage est réalisé selon au moins une des manières suivantes :
  • codage spatial,
  • codage sur les fréquences de réponse,
  • codage en intensité de réponse.
• au moins une substance luminescente comprend des fibres dopées présentant un effet laser,
• les fibres sont des fibres de silice dopées avec un colorant laser,
• les fibres sont obtenues par croissance spontanée dans une solution aqueuse du type
  • 100 H2O,
  • 0.0246 CTAB (CTAB étant un agent de surface cationique, par exemple de formule CH3(CH2)15N(CH3)3Br),
  • 2.92 HCI,
  • 0.00017 Rh6G (Rh6G étant de la rhodamine)
  à laquelle on a ajouté après agitation 0.05 mole de TBOS de formule (C4H90)4Si,
• le rayonnement d'excitation laser est obtenu par un laser de type YAG présentant un pic d'émission vers 532 nm,
• au moins une substance luminescente comprend des éléments organiques semi-conducteurs présentant un effet laser à l'état solide,
• au moins un élément organique semi-conducteur est réalisé à partir d'un polymère de type MEH-PPV ou PPV,
• au moins une substance luminescente comprend un milieu ne présentant pas d'effet laser,
• ledit milieu comprend un mélange de complexes d'Europium avec des polymères du type CN-PPP (poly(2-(6'-cyano-6'-méthyl-heptyloxy)-1,4-phénylène)),
• les ions d'Europium sont incorporés au polymère en synthétisant une famille de complexes d'Europium solubles avec des ligands □-dicétonates, et en dissolvant ces complexes dans un solvant en conjugaison avec le polymère,
• le niveau d'énergie de triplets du ligand est supérieur au niveau d'émission de l'Europium,
• le spectre d'émission du polymère et le spectre d'absorption du complexe se recouvrent au moins partiellement,
• au moins une substance luminescente comprend une matrice-hôte dopée avec au moins un ion de terres rares,
• le codage est obtenu par au moins une des manières suivantes :
  • en utilisant des dopants différents sur une même matrice,
  • et/ou en mettant en oeuvre un même ion dopant sur des matrices de caractéristiques différentes.

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

• each line of the response spectrum (s) has a width at half height less than a value of the order of 10 nm,
• coding is carried out in at least one of the following ways:
  • spatial coding,
  • coding on the response frequencies,
  • response intensity coding.
• at least one luminescent substance comprises doped fibers having a laser effect,
• the fibers are silica fibers doped with a laser dye,
• the fibers are obtained by spontaneous growth in an aqueous solution of the type
  • 100 H2O,
  • 0.0246 CTAB (CTAB being a cationic surfactant, for example of the formula CH3 (CH2) 15N (CH3) 3Br),
  • 2.92 HCI,
  • 0.00017 Rh6G (Rh6G being rhodamine)
  to which 0.05 mole of TBOS of formula (C4H90) 4Si was added after stirring,
• the laser excitation radiation is obtained by a YAG type laser having an emission peak around 532 nm,
• at least one luminescent substance comprises organic semiconductor elements exhibiting a laser effect in the solid state,
• at least one organic semiconductor element is produced from a polymer of the MEH-PPV or PPV type,
• at least one luminescent substance comprises a medium having no laser effect,
• said medium comprises a mixture of Europium complexes with polymers of the CN-PPP type (poly (2- (6'-cyano-6'-methyl-heptyloxy) -1,4-phenylene)),
• Europium ions are incorporated into the polymer by synthesizing a family of soluble Europium complexes with □-diketonates ligands, and by dissolving these complexes in a solvent in conjugation with the polymer,
• the energy level of ligand triplets is higher than the emission level of Europium,
• the emission spectrum of the polymer and the absorption spectrum of the complex overlap at least partially,
• at least one luminescent substance comprises a host matrix doped with at least one rare earth ion,
• the coding is obtained by at least one of the following ways:
  • using different dopants on the same matrix,
  • and / or by using the same doping ion on matrices with different characteristics.

Other aspects, aims and advantages of the invention will appear better on reading the following description of preferred embodiments of the invention.

In a first embodiment, there is developed according to the invention a bank note by integrating into said note a security marking carried out at from silica fibers doped with a laser dye.

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

• 100 H2O,
• 0.0246 CTAB (CTAB étant un agent de surface cationique, par exemple de formule CH3(CH2)15N(CH3)3Br),
• 2.92 HCI,
• 0.00017 Rh6G (Rh6G étant un colorant cationique tel que la rhodamine).

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

• 100 H2O,
• 0.0246 CTAB (CTAB being a cationic surfactant, for example of the formula CH3 (CH2) 15N (CH3) 3Br),
• 2.92 HCI,
• 0.00017 Rh6G (Rh6G being a cationic dye such as rhodamine).

This first aqueous solution is then stirred, then added 0.05 mole of TBOS of formula (C4H9O) 4Si without stirring the solution, so as to cover the surface with a thin layer of TBOS.

As explained in the article by Marlow et al. "Doped mesoporous silica fibers: a new laser material ”(Advanced Materials, 1999, 11, N ° 8), on observes after two days a spontaneous growth of silica fibers doped with rhodamine which constitutes a laser dye.

After about five days, we collect these fibers, then drying them.

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

And in this way we obtain fibers whose characteristics physical (dimensions, fiber diameter obtained by this process can be around 22 angstroms) and optical (absorption coefficient and birefringence) are homogeneous; these fibers constitute guides efficient waveforms.

We can then integrate these fibers into a banknote (or all sensitive document) by any known means, for example by drowning the fibers in the weft of the paper, constituting a security thread to which are integrated doped fibers, and itself integrated into the thickness of the paper, diluting these fibers in a ticket printing ink or varnish, etc.

Fibers incorporated in the ticket constitute an invisible security sign to an observer, but recognizable by machine.

More precisely, according to the invention, the ticket is exposed to which the fibers have been integrated into the radiation from a laser source.

The energy of such incident radiation is concentrated in a line very fine frequency. In a preferred embodiment of the invention, the laser is of the Nd: YAG type with an emission peak at 532 nm, a frequency 10Hz.

By exciting the fibers doped with such laser radiation, we observes a laser type light reemission by the fibers themselves, the rhodamine emitting according to a much more marked peak than in the case exposure of a simple rhodamine solution to the same radiation.

This laser effect results from the internal reflections of the photons inside fibers of which they are trapped throughout their journey in the fiber.

And the exploitation of this laser effect, combined according to the invention with a exposure to laser excitation radiation, provides responses from the fibers in the form of extremely fine lines, the characteristic width of these lines (width at half height) being less at 10 nm.

• codage spatial : les fibres sont intégrées en certains endroits choisis du billet, de manière à réaliser un code géométrique (code à barres par exemple, ou figure graphique prédéterminée),
• codage sur les fréquences de réponse : on intègre dans ce cas plusieurs types de fibres dans le billet, chaque fibre ayant un spectre de réponse différent pour une excitation laser donnée. On pourra pour cela constituer des fibres à partir de colorants laser différents, comprenant ou non la rhodamine. De la sorte, on obtient en illuminant le billet avec des flash laser une réponse lumineuse selon certaines raies discrètes d'émission qui correspondent aux longueurs d'onde des raies d'émission des différents colorants,
• codage en intensité par variation de la quantité de rhodamine (ou de tout colorant) que comprennent différentes fibres intégrées dans le même billet. Dans ce cas, les différences de concentration de colorant dans les différentes fibres entraínent des différences dans les intensités de réponse de ces différentes fibres, qui sont par ailleurs centrées sur la même longueur d'onde,

And according to the invention, the fibers are placed in the ticket so as to carry out coding.
This coding can be carried out according to one or more of the following dimensions:

• spatial coding: the fibers are integrated in certain selected places of the ticket, so as to produce a geometric code (bar code for example, or predetermined graphic figure),
• coding on the response frequencies: in this case several types of fibers are integrated into the ticket, each fiber having a different response spectrum for a given laser excitation. This can be done by making fibers from different laser dyes, including or not rhodamine. In this way, by illuminating the ticket with laser flashes, a light response is obtained according to certain discrete emission lines which correspond to the wavelengths of the emission lines of the different dyes,
• intensity coding by varying the amount of rhodamine (or any dye) that different fibers include in the same ticket. In this case, the differences in dye concentration in the different fibers cause differences in the response intensities of these different fibers, which are moreover centered on the same wavelength,

Such a code is recognized by reading the light signal emitted by the ticket, thanks to a sensor assembly adapted to collect and quantify the light emitted by the ticket in response to the excitation of the laser, according to the lines expected frequency.

Such a sensor assembly may include a series of mirrors separators each of which directs 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 color filter), or a sensor CCD type matrix.

• pour chaque intervalle de longueur d'onde d'un spectre de réponse qui englobe les raies d'émission des différentes substances intégrées au billet - et qui comprend donc typiquement le visible et/ou l'infra-rouge ; chaque intervalle peut ainsi avoir une largeur de l'ordre de 5 à 10 nm,
• et pour chaque endroit du billet - l'ensemble de capteur ayant des moyens de repérage de sa position par rapport à la surface du billet, par exemple en utilisant une origine liée aux bords du billet ou à un signe-origine intégré au billet - la surface du billet peut ainsi être divisée en parcelles dont les dimensions sont adaptées à la résolution de l'ensemble de capteur et aux contraintes de fabrication.

In all cases, the sensor assembly collects the light emitted by the bill and produces electrical signals which reflect the presence and intensity of light emission:

• for each wavelength interval of a response spectrum which includes the emission lines of the various substances integrated into the ticket - and which therefore typically includes the visible and / or the infrared; each interval can thus have a width of the order of 5 to 10 nm,
• and for each place on the ticket - the sensor assembly having means for locating its position relative to the surface of the ticket, for example by using an origin linked to the edges of the ticket or with an origin sign integrated into the ticket - ticket area can thus be divided into plots whose dimensions are adapted to the resolution of the sensor assembly and to manufacturing constraints.

To recognize the code, a memory containing the answer expected from the ticket is connected to the sensor assembly, and a comparator compares the signal received and the expected signal.

The great fineness of the lines of the response spectra allows to perform effective coding, which was not really the case with luminescent substances with a broad response spectrum.

It is also possible to substitute rhodamine for other materials whose response to laser excitation would be focused around a discrete line, or a finite number of emission lines; we can particular replace rhodamine with nanocrystals doped with one or several rare earth ions, or by conjugated polymers.

It is still possible to replace doped fibers in the ticket by doping the paper or a printing ink of the paper with pigments made from the assembly of organic semiconductor elements solid state laser effect.

In this second embodiment of the invention which provides also a laser effect for the response to incident radiation, these are so these organic elements that provide the laser effect. We will find a more complete description of such organic elements in the article of Tessler et al. "Lasers based on semiconducting organic materials" (Advanced Materials, 1999, 11, No. 5).

These organic semiconductor elements can be produced at from a polymer of the MEH-PPV type (poly (2-methoxy-5- (2'-ethyl-hexyloxy) -1,4-phenylenevinylene)) or PPV (poly (p-phenylenevinylene)), and may be in the solid state, preferably dispersed in a host support of the glass type for example. It is also possible to further stimulate the effect laser by adding diffusing particles into the host support, by example of TiO2.

To define the polarization properties of such materials, we can further align the polymer chains.

And these assemblages of organic elements can take the form of tubular structures which constitute waveguides, or stacks that can form microcavities.

Finally, it is also possible to implement the invention without exploit a real “laser effect”, ie a jump in the energy emitted in response to an excitation to concentrate this energy in discrete lines, the important thing is to be able to get a response from the ticket in the form of lines discrete with a width typically less than about 10nm.

• toujours par recueil et analyse de la réponse codée des billets à un rayonnement d'une source laser (ce point étant important pour ne stimuler les substances intégrées au billet que selon une ou des raie(s) spectrale(s) bien déterminée(s)),
• mais sans exploiter un effet laser fourni par ces substances.

Thus, in an alternative embodiment of the invention, the authentication of tickets is carried out:

• always by collecting and analyzing the coded response of the banknotes to radiation from a laser source (this point being important for stimulating the substances incorporated in the banknote only according to one or more well-defined spectral line (s) )
• but without exploiting a laser effect provided by these substances.

In this case, we will use synthetic molecules integrated in the ticket paper, or in ink or varnish, or in a intermediate support such as a safety wire.

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

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

More specifically, Europium ions are incorporated into the polymer by synthesizing a family of soluble Europium complexes with □ -diketonates ligands, by dissolving these complexes in a solvent conjugation with the polymer, then laminating a film from this double dissolution.

To obtain fluorescent Europium complexes, the level energy of ligand triplets must be greater than the emission level of europium.

In addition, to allow energy transfer from the conjugated polymer to the ligands of the Europium complex, the emission spectrum of the polymer and the absorption spectrum of the complex must overlap at least partially.

We can thus synthesize different molecules from CN-PPP, as explained in the article by Mc Gehee et al. These molecules have the peculiarity of transmitting according to very fine lines (whose width at mid-height is less than 10nm), in response to ultraviolet light excitation.

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

In this variant embodiment of the invention, the narrowness is used excitation lines of the laser source combined with the narrowness of the lines of response of the molecules thus synthesized, to obtain a response extremely well marked according to the Europium complexes put in works in combination with CN-PPP; this makes it possible to implement a real coding, using in the same ticket different molecules including the response lines to a given excitation (for example an excitation laser near the ultraviolet) are separated by a frequency band of around 5 nm.

Finally, it is also possible according to another variant of the invention of integrating into the bank note (according to one of the modes mentioned above) a substance comprising a host matrix which may be crystalline, doped with rare earth ions such as those commonly used in lasers.

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

Exciting such a substance with laser radiation extremely concentrated on a fine line allows to obtain a response also concentrated on one or more skate (s).

• en utilisant des dopants différents sur une même matrice. On pourra ainsi intégrer au billet deux encres différentes, l'une dopée avec un premier ion de terres rares dont la réponse à une excitation laser (qui est elle-même concentrée autour d'une longueur d'onde du visible, du proche infra rouge ou de l'ultraviolet), l'autre dopée avec un deuxième ion de terres rares, différent du premier, et dont la longueur d'onde de réponse à la même excitation est différente,
• mais également en mettant en oeuvre un même ion dopant sur des matrices de caractéristiques différentes (type de matrice, stoechiométrie de la matrice...) de sorte que les raies de réponse sur les différentes matrices sont décalées d'une largeur supérieure à la finesse des raies, et de préférence à une largeur de l'ordre de 10 nm.

And it is possible according to the invention to carry out an encoding of the response of the ticket; in the latter variant of the invention, this coding can be carried out in several ways, separately or in combination:

• using different dopants on the same matrix. We will thus be able to integrate two different inks into the ticket, one doped with a first rare earth ion whose response to a laser excitation (which is itself concentrated around a wavelength of visible, near infrared or ultraviolet), the other doped with a second rare earth ion, different from the first, and whose response wavelength to the same excitation is different,
• but also by using the same doping ion on matrices of different characteristics (type of matrix, stoichiometry of the matrix, etc.) so that the response lines on the different matrices are offset by a width greater than the fineness lines, and preferably at a width of the order of 10 nm.

• d'une part sur une matrice de type YLF et obtenir ainsi, comme réponse à excitation laser de longueur d'onde 800 nm, une raie d'émission centrée sur 1054 nm,
• et d'autre part sur une matrice de type YAG et observer une raie centrée cette fois sur 1064 nm. La largeur à mi-hauteur des raies étant dans les deux cas de l'ordre de 5 nm, on comprend qu'il est aisé de distinguer les réponses sur les deux matrices.

We can for example use Neodymium ions:

• on the one hand on a YLF type matrix and thus obtain, as a response to laser excitation of wavelength 800 nm, an emission line centered on 1054 nm,
• and on the other hand on a YAG type matrix and observe a line centered this time on 1064 nm. The width at mid-height of the lines being in the two cases of the order of 5 nm, we understand that it is easy to distinguish the responses on the two matrices.

It is thus possible to combine one or more different dopants on one or more types of matrix, and integrate these different substances into the ticket mixed or separately, so as to code the response of the ticket to exposure to laser radiation.

Finally, we specify that it is obviously possible to integrate into a same ticket several luminescent substances corresponding to any which embodiment or any variant of the invention described above.

Claims (16)

Method for authenticating sensitive documents such as banknotes, the method comprising: The integration into the document of at least one luminescent substance capable of emitting light according to a frequency spectrum of response determined when the substance is exposed to excitation light radiation, Exposing the document to exciting light radiation, and Collection of the document's response to this radiation of excitement characterized in that : the excitation radiation is laser radiation, each frequency response spectrum is essentially composed of at least one line, and the method also includes coding the light response of the document to excitation radiation, and comparing this response to an expected response stored. Method according to claim 1, characterized in that each line of the response spectrum (s) has a width at half height less than a value of the order of 10nm. Method according to one of the preceding claims, characterized in that the coding is carried out in at least one of the following ways: spatial coding, coding on the response frequencies, response intensity coding. Method according to one of claims 1 to 3, characterized in that at least one luminescent substance comprises doped fibers having a laser effect. Method according to the preceding claim, characterized in that the fibers are silica fibers doped with a laser dye. Method according to the preceding claim, characterized in that the fibers are obtained by spontaneous growth in an aqueous solution of the type 100 H2O, 0.0246 CTAB (CTAB being a cationic surfactant, for example of the formula CH3 (CH2) 15N (CH3) 3Br), 2.92 HCI, 0.00017 Rh6G (Rh6G being rhodamine), to which was added after stirring 0.05 mole of TBOS of formula (C4H9O) 4Si. Method according to one of claims 4 to 6, characterized in that the laser excitation radiation is obtained by a YAG type laser having an emission peak around 532 nm. Method according to one of the preceding claims, characterized in that at least one luminescent substance comprises organic semiconductor elements exhibiting a laser effect in the solid state. Method according to the preceding claim, characterized in that at least one organic semiconductor element is produced from a polymer of the MEH-PPV or PPV type. Method according to one of the preceding claims, characterized in that at least one luminescent substance comprises a medium having no laser effect. Method according to the preceding claim, characterized in that the said medium comprises a mixture of Europium complexes with polymers of the CN-PPP type (poly (2- (6'-cyano-6'-methyl-heptyloxy) -1,4 phenylene)). Method according to the preceding claim, characterized in that the Europium ions are incorporated into the polymer by synthesizing a family of soluble Europium complexes with □-diketonates ligands, and by dissolving these complexes in a solvent in conjugation with the polymer. Method according to the preceding claim, characterized in that the energy level of the ligand triplets is higher than the emission level of the Europium. Method according to one of claims 11 to 13, characterized in that the emission spectrum of the polymer and the absorption spectrum of the complex overlap at least partially. Method according to one of the preceding claims, characterized in that at least one luminescent substance comprises a host matrix doped with at least one rare earth ion. Method according to the preceding claim, characterized in that the coding is obtained by at least one of the following ways: using different dopants on the same matrix, and / or by using the same doping ion on matrices with different characteristics.