EP1404526B1 - Non-falsifiable information carrier material, information carrier produced therefrom and test device therefor - Google Patents

Description

The invention relates to a tamper-proof information carrier material comprising a substrate and at least one photochromic substance, which can be converted by light irradiation from a first state to at least a second state, which is distinguishable spectroscopically from the first state, and to an information carrier and a device made therefrom for its examination.

Already in daily use one encounters numerous types of information carriers, for which there is a high need for counterfeit security. Examples are, in particular, banknotes, checks or other value documents whose substrate is made of paper, but also information carriers on thicker and stronger substrates, such as credit cards, check cards, ID cards or the like. The terms "information carrier material" and "information carrier" are therefore intended to be of all types of records to be protected against unauthorized imitation.

For counterfeiting of banknotes it is already known ( GB 2 272 861 A ) to print on the music paper an image both with permanently visible ink as well as with reversibly variable color photochromic ink between two states. For authenticity testing, the permanently visible optical image of the banknote is compared with the photochromic image in its two states, which are caused by suitable light irradiation. However, the resulting safety standard is not satisfactory, because with the sophisticated duplication methods available today, this printing technology is also accessible to counterfeiters.

U.S. Patent 5,470,690 relates to the optical storage of information by means of an optically switchable medium, which is in particular bacteriorhodopsin. To form a two-dimensional memory, the bacteriorhodopsin is placed in a polyvinyl alcohol solution, spread on a substrate and dried. The dried film containing thus produced bacteriorhodopsin molecules is used as a two-dimensional memory. To form a three-dimensional optical memory, the bacteriorhodopsin is embedded in a three-dimensional block of material.

The invention has for its object to provide an information carrier material with increased security against counterfeiting, produced therefrom information carrier and a device for their testing.

According to the invention, this is achieved with regard to the information carrier material in that the substrate is a paper or a thicker and stronger card-shaped substrate, the photochromic substance is embedded in the substrate and the substrate is sufficiently permeable to the light wavelengths used for the transfer from the first to the second state.

Since the photochromic substance is embedded in the substrate in the information carrier material according to the invention, a qualitatively good forgery would presuppose the counterfeiter himself produces or procures the substrate doped with the photochromic substance. The former is virtually impossible because of the high technical complexity, whereas the latter is also not possible for lack of general accessibility of such special substrates. The attempt to forgery by superficial application of the substance to the substrate can be easily determined because of the concomitant change in the surface condition, for example by optical methods.

The substrate is often a strongly absorbing or scattering material, preferably paper, cardboard, plastic or mixtures thereof. Sufficient permeability of the substrate is given if its transmission is between 0.001% and 80%, preferably between 0.01% and 30%. The first and second states of the photochromic substance may in particular be isomeric states.

In the case where the photochromic states are thermally stable for a long time, what is termed bistable, it is possible to permanently locally transfer the information carrier material to a second state by targeted light irradiation, which means an initialization according to a local pattern of two states. This local pattern can serve, in particular, as a code for information which can be used for checking the authenticity. Although the techniques required for this are known (cf., for example Science, Vol. 245, August 25, 1989, pages 843-845 . American Scientist, Vol. 82, July / August 1994, pages 348-355 . Computer, Vol. 25, November 1992, pages 56-67 ), but because of the necessary advanced laser method for counterfeiters are not manageable, whereas they can be carried out by authorized manufacturers in mass production with very low unit cost. An overview of possible photochromic materials can be found in Chemical Reviews, Vol. 100, No. 5 (May 2000 ).

An advantageous development consists in that at least one second state can be attributed to light irradiation in the first state and the substrate is sufficiently permeable to these light wavelengths. This makes it possible to delete at least parts of the pattern generated during initialization or a separately recorded pattern again and overwrite them with a pattern corresponding to a new information. Depending on the type of photochromic substance used, this erasable second state can be the same state as the second state used for initialization, but different second states can also be used. Because of this rewritability, it is not only possible to describe an information carrier made on the information carrier material from case to case with additional information, but also earlier information overwrite, ie replace with new information. If such an information carrier passes through several stations at which it is sighted, and places a corresponding endorsement on each viewing station, the path of the information carrier can be accurately followed by the various viewing stations.

The desired properties, in particular the good optical distinctness of the two photochromic states, can be found in particular in the case of the chromoproteins. Preferably, a bacterial chromoprotein is used. A particularly suitable and already scientifically well-studied substance is bacteriorhodopsin. It is known that this substance can be switched between isomeric states, for example, by one-photon, sequential one-photon or two-photon processes in which light in the green spectral range and light in the red spectral range is irradiated. It is known that with the wild-type bacteriorhodopsin and to a greater extent with some variants of bacteriorhodopsin, two thermally stable states are available. One is the stable initial state b _R and the other one, in order to reach the stable P or Q state which can be reached via intermediate states (cf. EP0655162B1 and " Popp et al., Photochemical Conversion of the O-intermediate to 9-cis Retinal Containing Products in Bacteriorhodopsin Films. Biophys. J., 65 (1993) 1449-1459 In this way, local regions of the bacteriorhodopsin in the substrate can be thermally permanently initialized.The districts that have been initialized into the Q state appear optically more transparent when illuminated with light in the red spectral region than the remaining districts remaining in the b _R state The light-dark pattern thus obtained thus forms a security feature for the information carrier material.

In a further embodiment of the inventive concept it is provided that the photochromic substance is located in the information carrier material to particles. In this case, each embedding location of a carrier particle can be operated as a localized storage element whose storage state is represented by the particular absorption state of the photochromic substance concentrated there. The localization on the particles can be effected, for example, by the photochromic material being applied to its surface or enclosed in its volume. Also, the particles themselves can be made of the / the photochromic substance / substances, optionally with the addition of suitable auxiliaries.

An advantageous embodiment is that the photochromic substance is embedded in embedded in the substrate particles or hollow bodies, whose Substance enclosing matrix or wall for the transfer of the first to the second state serving light wavelengths and the distinction of the two states serving light wavelengths is sufficiently transparent. In this case, the photochromic substance is protected by the inclusion in the hollow body. In particular, optimal conditions for the photochromic substance, for example its moisture content, can be set within the hollow bodies. Moreover, the optical properties of the matrix or wall can be optimized with respect to the optical processes of light absorption during initialization and the light irradiation during readout and possibly when deleting the states, eg low light scattering and high optical transparency of the matrix material.

An important embodiment is that the substrate is a paper. This paper can preferably be used for the production of banknotes, checks and all other value deeds.

According to the invention, an information carrier produced from the information carrier material according to the invention is characterized in that the substance transferred to the second state is located at at least one point of the information carrier.

The localized transfer of the photochromic substance into its second state can be carried out as an initialization step either on the information carrier material or on the information carrier produced therefrom. In both cases, the local position of this location / locations in the information carrier can be detected in a subsequent optical scanning process and thereby check the authenticity of the information carrier.

In an advantageous embodiment, it is further provided that a position information representing the location of the position / points in the information carrier is recorded on the information carrier in readable form. The recording of this position information on the information carrier can be done, for example, in the form of printed position information data or by storage in an inseparably connected to the information carrier, readable electronic memory. In the authenticity check, both the recorded position information can then be read out and the information determined by the pattern of the locations located in the second state can be scanned and correlated with one another. A method for the three-dimensional storage of information by means of bacteriorhodopsin is known in US 5,559,732 specified. However, it is in no case assumed that the bacteriorhodopsin is embedded in a limited translucent matrix. To enroll three-dimensional information into the information carrier claimed here is not provided.

In the important case of the formation of the information carrier as a security, for example, as a banknote, in addition to the printing, the storage in a designated in the security memory circuit is basically known (see. DE 196 30 648 A1 and EP 0 905 657 A1 ).

Fig. 1

eine Aufsicht auf eine Banknote, und

Fig. 2

einen zur Darstellung von Fig. 1 senkrechten Querschnitt mit einer schema- tischen Darstellung der Lichtverläufe beim Prüfvorgang.

In the following description, the invention is explained in more detail with reference to an illustrated in the drawing embodiment of a banknote. It shows:

Fig. 1

a top view of a banknote, and

Fig. 2

one for the representation of Fig. 1 vertical cross-section with a schematic representation of the light courses during the test procedure.

An in Fig. 1 illustrated banknote 1 consists of a banknote paper, which has been doped in its preparation with a photochromic substance, in the illustrated embodiment, bacteriorhodopsin. The doping can be carried out, for example, by adding the bacteriorhodopsin to the pulp used for producing the banknote paper before it is fed to the sieve. In this case, the banknote has a substantially constant doping density over its entire area. Alternatively, the doping can also take place in such a way that the pulp spread on the wire is doped only in places, so that the banknote paper and also the banknote 1 has localized area districts which can be distributed over the entire area either uniformly or irregularly. Preferably, the photochromic substance is not introduced directly into the paper pulp, but with the aid of carrier particles provided with the substance. The latter are preferably designed as small hollow bodies, in which the photochromic substance is enclosed and thereby protected against the surrounding paper pulp. In general, the doping of the banknote paper and the banknote 1 with the naked eye is not recognizable.

If the photochromic substance does not have two thermally stable states but returns to the initial state without exposure to light, the presence of the embedded photochromic substance, in dispersed or in or on particle bound form, can be used as a safety feature. In bacteriorhodopsin, the initial state designated as b _R and that in the green state by irradiation with light are suitable for this purpose or yellow-red spectral range can be generated M state. The transient generation of bacteriorhodopsin in the M-state can be detected with blue light, preferably in the range 400-415 nm.

If the photochromic substance has the property that it has at least two thermally long-term stable states, wherein it can be converted by light absorption from one state to the other, information can also be introduced into the information carrier material. For bacteriorhodopsin, the initial state designated as b _R and the Q state obtainable therefrom by the irradiation of light in the green spectral range and of light in the red spectral range are suitable for this purpose. In these spectral ranges, the paper pulp is sufficiently transparent to radiation. Thus, by passing the bill paper or bill 1 through a corresponding laser beam emitting laser array, localized locations can be transformed to the Q state. These places, which are invisible to the naked eye, are in Fig. 1 and 2 indicated by borders 2. While the schematic representations of Fig. 1 and 2 If only three such locations 2 are shown, any number of such locations, which is ≥ 1, may be provided in any desired location.

In connection with the initialization of the banknote 1 by creating the Q-state 2, the location of these locations 2, ie their location coordinate values on the banknote 1, is simultaneously recorded and this location information recorded on the banknote 1. The latter can be done for example in the form of an uncoded or coded imprint 3 on the banknote 1, which is optically readable, for example. In Fig. 1 For example, this print is exemplified by a series of decimal digits.

The places 2 formed by the initialization are optically distinguishable from the uninitialized remaining area of the banknote 1. In the case of bacteriorhodopsin, the Q state present at sites 2 is distinguished from the b _R state surrounding sites 2 in that low intensity light in the red spectral region absorbed only by the b _R state but not by the Q state, is irradiated. In this reading, the digits 2 appear more translucent than their surroundings. The light-dark pattern occurring as a result can be scanned in this way and the location information for the locations 2 can be read out therefrom.

In Fig. 2 a device suitable for this purpose is indicated schematically and designated by the reference numeral 5. An arrow 6 indicates the direction of the light irradiated for writing or reading. In Fig. 2 are needed in the case of bacteriorhodopsin green and red light rays irradiated on the same side of the banknote 1. Alternatively, however, it may be provided that, for example, the green light flat on the in Fig. 2 the lower side of the banknote 1 is irradiated, whereas the red light in the form of a collimated scanning beam is incident on the upper side of the banknote 1. In this case, the banknote 1 is offset transversely to the direction of this scanning beam in a scanning movement. The same applies to the blue light for detecting the M state, if there are no two thermally long-term stable states in the bacteriorhodopsin.

In the device 5, the position information characterizing the points 2 is reconstructed from the scanning result. At the same time, the device 5 also reads out the position information 3 recorded on the banknote 1. By comparing the reconstructed and the recorded position information, the authenticity of the banknote 1 is checked.

One according to the scheme of Fig. 2 The device which has been set up can also be used for initializing, ie for initially writing to, the banknote 1 or for later writing with additional information with previous deletion of previously recorded information. For initialization, light in the green and red spectral region is irradiated in the direction of the arrow 6, as is required for transferring from the b _R initial state into the Q state. To extinguish the Q state, light in the blue spectral region is irradiated in the direction of the arrow 6, whereby the Q state returns to the b _R initial state. The deleted areas can be described again.

The read, write and erase operations exemplified above allow for the identity of the information carrier material to be checked in general and, in specific embodiments, also as data memory for recording binary coded information. For this purpose, the information carrier material is assigned a predetermined raster of recording locations at which either the first or the second state of the photochromic substance is produced. The two possible states at these recording locations represent the two binary values "0" and "1". To secure a key can be formed from the recorded bit pattern, which is printed for example in optically readable form on the surface of the information carrier or stored in an embedded therein electronic circuit. In the case of paper, the raster of the recording sites is two-dimensional, while in the case of spatially extended information carriers it can be three-dimensional.

List of reference numbers

1

bill

2

Put

3

imprint

5

Tester

6

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Claims (8)

1. Counterfeitproof information carrier material, comprising a substrate and at least one photochromic substance, which can be converted by light radiation from a first state to at least one second state, which can be spectroscopically distinguished from the first state, characterized in that the substrate is a paper or a thicker and more solid substrate in the form of a card, the photochromic substance is embedded in the substrate, and the substrate is sufficiently transparent to the visible wave-lengths that serve to convert the photochromic substance from the first to the second state.
2. Counterfeitproof information carrier material in accordance with claim 1, characterized in that at least one second state can be converted back to the first state by light radiation, and the substrate is sufficiently transparent to these wavelengths.
3. Counterfeitproof information carrier material in accordance with claim 1, characterized in that the photochromic material is a bistable material.
4. Counterfeitproof information carrier material in accordance with claim 1 to 3, characterized in that the photochromic substance is a chromoprotein.
5. Counterfeitproof information carrier material in accordance with one of claims 1 to 4, characterized in that the photochromic substance in the information carrier material is localized on particles.
6. Counterfeitproof information carrier material in accordance with one of claims 1 to 5, characterized in that the substance that has been converted to the second state is localized in at least one point (2) of the information carrier (1).
7. Counterfeitproof information carrier material in accordance with claim 6, characterized in that a position information representing the local position of the point (2) in the information carrier is recorded in readable form on the information carrier.
8. Method for writing binary-coded information on an information carrier produced from an information carrier material in accordance with one of claims 1 to 5, characterized in that the two binary values "0" and "1" are recorded by the two states of the photochromic substance in a predetermined grid pattern.

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