RU2425757C1 - Method of important document counterfeit protection, counterfeit-proof important document, method to identify its authenticity and device to inspect authenticity of important document - Google Patents

Abstract

FIELD: printing industry. ^ SUBSTANCE: method of counterfeit protection of an important document includes application of a protective element onto the document surface, and the element is applied using a printing ink that contains an infrared absorber with full colour difference compared to the document base of not more than 7, capable of absorption of optical radiation in the range of wave lengths from 700 to 2500 nm and having an absorption band with half-width from 100 to 300 nm. ^ EFFECT: efficient method to protect an important document, and reliable inspection of its authenticity. ^ 10 cl, 8 dwg, 3 tbl

Description

The invention relates to valuable documents, methods for protecting valuable documents from counterfeiting and determining their authenticity, as well as to devices for controlling the authenticity of valuable documents.

Currently, various security features have been developed to prevent the falsification of bank cards, licenses, passports, and securities. It is widely known the use for this purpose of phosphors, liquid crystals, conductive and magnetic substances that are detected using special means.

Known security parameters suitable for identification by electronic means are described in documents US 4446204 A, 05/01/1984, US 4650319 A, 05.17.1987, US 5160171 A, 03.11.1992. These parameters are based on luminescence, magnetic properties or on the absorption of electromagnetic radiation in the invisible region of the spectrum. However, the application of some of these physical effects has disadvantages. For example, in the case of luminescence, the intensity of the measured radiation is usually low, therefore a very complex technology is required, including shielding from ambient radiation and from other effects of potential perturbations. Magnetic properties are less suitable as a protection parameter, since in this case mechanical contact between the banknote and the magnetic sensor (read head) is usually required. This is the main source of errors caused by jamming of wrinkled banknotes in the reader.

In addition, the document US 4650319A, 05.17.1987, describes the use of a single absorbing compound as a masking security element outside the visible region of the spectrum. The presence of a masking security element can be detected using publicly available CCD cameras (for example, door control cameras with sensitivity in the wavelength range from 300 to 1100 nm) and publicly available UV and IR filters sold in photo stores. In addition, generic compounds that absorb UV and IR radiation are used in many areas of modern technology, namely in certain electrophotographic developers, and thus they are also commercially available.

The basis of the present invention is the development of a security feature made by printing ink containing a substance that absorbs in the near infrared region of the spectrum and has improved protective capabilities, as well as a method for detecting it and an authentication device.

Substances absorbing in the near infrared are derivatives of phthalocyanine: monochlorinated aluminum phthalocyanine, monochlorinated halogenated aluminum phthalocyanine, cobalt phthalocyanine, as well as brominated copper phthalocyanine. Printing inks containing the above substances are recognized or detected using an infrared absorption detector operating in the near infrared region at wavelengths of 700-2500 nm.

There is a method of marking and identification of protected products (RU 2305119 C2, 08.27.2007), based on a mathematical algorithm for comparing the spectra of dyes or pigments by calculating coordinates in a special hyper-color space.

The mathematical algorithm considered in the known method has the following disadvantages. To describe the absorption spectra or luminescence of protective substances, optical density values are used. The zonal optical density values on genuine documents can vary widely. The spread of parameters of genuine products by the algorithm is not taken into account, which leads to a significant decrease in the accuracy of identification. To describe the absorption spectra or luminescence of protective substances, only the maxima of the absorption or luminescence lengths of protective substances are used and the shape of the absorption curves of these substances is not taken into account. The shape of the absorption curves, being “fingerprints” of protective substances, is more informative than the maximum absorption length. In addition, it does not allow us to consider cases of using a mixture of protective substances having closely spaced maxima of absorption or luminescence bands.

These shortcomings are eliminated by the claimed group of inventions that solve the following problems, ensuring the achievement of a technical result:

- development of an effective way to protect a valuable document,

- reliable control of the security element of authenticity, taking into account the spectral features of the compounds contained in the printing ink, such as the maximum and minimum absorption, the shape of the absorption curves, including for a mixture of protective substances with closely spaced absorption or luminescence bands,

- development of a method and device for authenticating a valuable document.

These tasks are solved using the objects presented in the independent claims. Preferred embodiments of the invention are given in the respective dependent claims.

In particular, the specified technical result is achieved due to the method of protection against counterfeiting of a valuable document, including applying to the document surface a security element made with a printing ink containing an IR absorber with a full color difference with respect to the document base of not more than 7, having the ability to absorb optical radiation in the wavelength range from 700 to 2500 nm and having at least one absorption band with a half-width from 100 to 300 nm.

Additionally, the result is achieved by the fact that the printing ink additionally contains a stabilizer, and the IR absorber is a compound selected from the group of derivatives of cyanines, pyrenes, thiopyrenes, indoanilines, squared, croconium, iminium, diiminium compounds, azulenes, dithiolenes and transition metal phthalocyanines, organic and organometallic azo compounds, and the stabilizer is a compound selected from the group: N-isopropyl-N'-phenyl-p-phenylenediamine, pyrocatechol, hydroquinone, 4-tert-butylcatechol, isfenol A.

In addition, the printing ink has the following composition, wt.%: IR absorber 5-15, stabilizer 2-4, desiccant 2-4, binder - the rest.

The result is also achieved by means of a valuable document protected from counterfeiting, using the proposed method described above and consisting of a banknote, excise stamp, passport, travel document, driver’s license, identity card, security paper, plastic card with a protective element deposited on the surface of the document in the form of a hidden protective marking.

In this case, the protective element can be made of offset or type-offset method.

The result is also achieved through a method of identifying the authenticity of the described valuable document, including irradiating the valuable document with test radiations at different wavelengths within the specified range, measuring diffuse reflection coefficients in the visible and / or near infrared optical spectrum, and calculating the derivative information according to an algorithm including determining a plurality of parameters from the measured diffuse reflection coefficients, and comparing it with predetermined reference values, the derivative inf rmacia is represented as a point in the multidimensional space of parameters, and reference values are presented in the form of a cluster describing the possible values of the parameters of genuine documents, while determining the coordinates of the cluster center — the centroid vector C and the covariance matrix Σ describing the shape of the cluster of reference values, and the comparison by measuring the distance from the measured point to the cluster.

The above method is implemented using another invention - a device for implementing the above method and includes a photometer for measuring the diffuse reflection coefficients of the samples under study, connected to a power source and an information processing unit, the photometer including a photodetector, lens and a block of radiation sources of different wavelengths, made with the possibility of inclusion in a pulsed mode and equipped with a conical diffuser located coaxially with the lens and installed between the radiation unit tels and the studied sample, and the lens is a fiber optic gradient lens.

In addition, the device may contain light emitting diodes as radiation sources, and the radiation wavelengths coincide with the maxima and minima of the reflection spectra of the protective element, and for identifying the authenticity protection element, the following data are stored in its memory:

- inverse covariance matrix Σ ^-1 ;

- the centroid vector C;

- response threshold.

As the IR absorber contained in the printing ink for the manufacture of security elements, in particular, cyanine-based organic compounds with absorption in the infrared range from 730 nm to 1100 nm, azulenes (730 nm), pyrilium and thiapirilium cations can be used (750 nm - 880 nm), iminium and diiminium compounds (720 nm - 1100 nm), hardened and croconium compounds (700 nm - 850 nm), transition metal dithiolenes (700 nm - 2500 nm), phthalocyanines (700 nm - 830 nm) ), organic and organometallic azo compounds (700 nm - 900 nm), indoanilines (700 nm - 800 nm). Absorbing in the near infrared region, phthalocyanine is manganese phthalocyanine, monochlorinated halogenated aluminum phthalocyanine, cobalt phthalocyanine, and brominated copper phthalocyanine. These phthalocyanines are absorbed at wavelengths of more than 700 nm and, in particular, in the near infrared region of the spectrum at wavelengths of 800-1100 nm, which greatly distinguishes them from copper phthalocyanine, which is usually used as a pigment. The formula of one of the representatives of phthalocyanine compounds - manganese phthalocyanine - is shown in figure 1.

Many classes of organic IR absorbers are known which, by their spectral properties in the near IR region (700 nm - 1500 nm), may be of interest for use in printing inks. [M.Simitani. Kagaku Kogyo. May 1986. P.379.]

These include cyanines with absorption in the IR region from 730 nm to 1100 nm, azulenes (730 nm), pyrilium and thiopyril cations (750 nm - 880 nm), iminium and diiminium compounds (720 nm - 1100 nm), squarilium (squarilium) and croconium (croconium) compounds (700 nm - 850 nm), (squarilia and croconium compounds can be called differently: quaternary salts of quadratic (or square) and croconic acids), as well as transition metal dithiolenes (700 nm - 1600 nm) , quinones / anthraquinones (750 nm - 800 nm), phthalocyanines (700 nm - 830 nm), organic and organometallic azo compounds (70 0 nm - 900 nm), indoanilines (700 nm - 800 nm).

However, most of these compounds are characterized by low thermal, light, and chemical resistance and, due to the noted features, cannot be useful for printing inks, which are aggressive media for organic compounds due to the radical reaction mechanism by which these inks cure.

Preferably, the printing ink additionally contains a stabilizer - a substance that reduces the rate of chemical processes that lead to aging (change in properties). The stabilizer can be selected from the group: N-isopropyl-N'-phenyl-p-phenylenediamine, pyrocatechol, hydroquinone, 4-tert-butylcatechol, bisphenol A.

Preferably, the printing ink has the following composition, wt.%: IR absorber 10-15, stabilizer 2-4, desiccant 2-4, binder - the rest.

Preferably, the security element of the valuable document is made by the printing method, in particular, offset or type-offset method.

Preferably, the inventive device as radiation sources contains LEDs, and the wavelengths of radiation coincide with the maxima and minima of the reflection spectra of the protective element.

The proposed method is characterized by an effective algorithm for identifying the type of authentication element based on the methods of multidimensional cluster analysis. Identification of the type of authenticity protection element is carried out by mathematically converting the values of reflection coefficients obtained by irradiating the authenticity protection element with test radiations with different wavelengths into a set of parameters describing the most characteristic features of the reflection spectrum; presentation of these parameters in the form of a point in multidimensional space, followed by determining whether this point belongs to one of the classes (clusters) that describe the parameters of the authenticity protection element on genuine products. A characteristic feature of the method is the description of the reference values in the form of clusters in multidimensional space, and clusters are formed on the basis of the results of measurements of a large number of genuine documents with protective markings, and in the general case they represent not one reference value, but a set of values describing the properties of a statistically significant sample of genuine documents with protective marking.

Known methods of statistical analysis can be used to mathematically describe the size and shape of clusters, for example, the method of calculating the covariance matrix and the centroid vector.

To assess whether the results of measurements of the authentication element belong to one of the clusters, criteria used in multivariate statistical analysis can be used, for example, the Mahalanobis distance, the Euclidean distance, the Minkowski distance, the Chebyshev distance, etc.

The list of figures of graphic images.

Figure 1 shows the formula of manganese phthalocyanine.

Figure 2 shows the photometer diagram, which shows a photodetector 1 with a lens 2 and several radiation sources 3 operating at different wavelengths, the diffuser 4, the sample under study - object 5.

Figure 3 - absorption spectrum of a protection element based on manganese phthalocyanine and spectra of radiation sources.

Figure 4 is a diagram of a cluster of reference values.

Figure 5 - absorption spectrum of an authenticity protection element based on manganese phthalocyanine with a set of absorption spectra of training samples describing the parameters of an authenticity protection element (technological variation) on genuine products.

Figure 6 shows the identification circuit of the security element.

7 is a reflection spectrum of a simulator of the authenticity protection element with a set of absorption spectra of training samples describing the parameters of the simulator of the authenticity protection element (technological variation) on falsified products.

On Fig - identification scheme of the simulator of the element of authentication.

The photometer of the inventive device (figure 2) includes a photodetector 1 with a lens 2 and several radiation sources 3 operating at different wavelengths. A lens 2 based on an optical fiber with a variable refractive index (gradient fiber) provides an image of the illuminated area on the sensitive area of the photodetector 1. A diffuser 4 is mounted coaxially with the lens 5 between the emitter unit 3 and the test sample 5. The diffuser 4 is a conical element made of a translucent polymer and provides diffuse illumination of the controlled object 5, which allows the correct detection of protective features when the detector is tilted relative to the counter liruemogo object.

The device operates as follows. LEDs 3 turn on in pulse mode. The radiation of the LEDs 3 passes through the diffuser 4 and irradiates the surface of the test sample 5. The radiation reflected from the test sample 5 enters the gradient lens 4 and is collected by it on the sensitive area of the photodetector 1.

LEDs operate independently of each other, reflected radiation is also registered independently. To separate the signals of the LEDs in the device, frequency modulation of radiation is used. Each of the LEDs 3 operates in a pulsed mode at a specific frequency. The switching frequencies of different LEDs vary. To determine the magnitude of the signal separately for each LED, the photodetector signal is divided into frequency components. This also eliminates spurious signals from external radiation sources.

After registration of emissions from different LEDs, the signal values are recorded and compared with the corresponding signal values obtained at the reference (calibration) object. Further, the values undergo mathematical processing, the results of which make a conclusion about the presence or absence of a quality protective feature at the controlled object.

An example implementation of the invention

To create a security feature, model inks were selected based on Huber 680280 GSI offset binder, 680272 desiccant and offset translucent white ink 2516 / 2514-82 in accordance with TU 2352-005-02424767-04. Recipes model paints are shown in table 1.

Table 1 Model Paint Components Amount, wt.% IR absorber: manganese phthalocyanine 13 13 13 10 13 10 13 13 13 Binder 680280 83 83 83 86 83 86 83 83 83 Desiccant 680272 2 2 2 2 2 2 2 2 2 Lemon acid 2 - one one - - - - - Stearic acid - - - - one one - - - N-isopropyl-N'-phenyl-p-phenylenediamine - - - - - - - 2 - 4-tert-butylcatechol (4TBK) - 2 one one one one - - - Hydroquinone - - - - - - 2 - - Catechol - - - - - - - - 2 Stabilization constant (K _st ) 0.8 More than 0.9 0.8 0.8 0.8 0.8 0.85 0.8 0.85

To determine the stability of the protective properties of an IR absorber with stabilizers from model inks, prints with different ink layer thicknesses from 1.4 g / m ² to 2.5 g / m ² were made on a Prüfbau MZ II laboratory sampler.

To determine the stability of the protective properties of the IR absorber in model formulations, a criterion is chosen - the stabilization constant (K _st ), which is determined by the formula:

where K _neg. - reflection coefficient of the IR absorber, measured over time;

To _neg. - reflection coefficient of the IR absorber, measured after receiving the print (specified).

A study of the dynamics of the values of the special protective feature of all model inks showed that the most critical period is 10-14 days from the moment of receipt of the prints, during which the greatest decrease in the value of the protective feature occurs (criterion (K _st ) - less than 0.8). Further, the process is stabilized.

For printing inks based on a binder 2516 / 2514-82, all the selected redox stabilizers, except hydroquinone, show approximately the same stabilizing effect (K _st not less than 0.85). Optimal in this group of stabilizers is 4TBK. For 4ТБК K _st is more than 0.9.

Different ratios with an IR absorber were investigated and the optimal one was chosen - 2:13. Tests of a valuable document containing a protective element with a stabilizer 4TBK, was carried out using the proposed device. The absorption spectrum of the IR absorber for the element of protection of authenticity is shown in Fig.3.

A characteristic property of the spectrum is the presence of an absorption band in the near infrared region at a wavelength of about 800 nm and a relatively high reflection level in the visible range and in a band above 1000 nm.

To identify the security element of authenticity, the reflection coefficients K ₁ , K ₂ and K ₃ measured at wavelengths λ ₁ = 600 nm, λ ₂ = 800 nm and λ ₃ = 1000 nm are used as primary data. Reflection coefficients are measured by irradiating the protective mark with test emissions. The spectra of radiation sources are also shown in figure 3.

To describe the characteristic features of the spectrum, a set of four parameters P is used. The parameters P are calculated from the reflection coefficients using the following formulas:

Each measured spectrum is described as a vector (point) P in a four-dimensional mathematical space (parameter space P):

P = p ₁ p ₂ p ₃ p ₄

The cluster of reference values is formed on the basis of the measurement results of the training sample according to the following scheme (figure 4).

The sample consists of 10 documents with protective marking with the maximum variation of the parameters within the permissible range (see table 2).

Table 2 shows the reflection spectra of the samples of the training sample.

table 2 Sample No. Reflection coefficients K ₁ K ₂ K ₃ one 0.55 0.21 0.87 2 0.52 0.18 0.79 3 0.51 0.13 0.74 four 0.52 0.15 0.81 5 0.48 0.13 0.80 6 0.40 0.08 0.73 7 0.42 0.09 0.71 8 0.40 0.05 0.63 9 0.52 0.23 0.92 10 0.54 0.17 0.88

After measuring the reflection coefficients according to formulas (2), the parameters P are calculated (see table 3).

Table 3 shows the values of the parameters P of the samples of the training sample.

Table 3 Sample No. Parameter Values P ₁ P ₂ P ₃ P ₄ one 2.62 0.63 0.24 1,52 2 2.89 0.66 0.23 1,50 3 3.92 0.69 0.18 1.77 four 3.47 0.64 0.19 1.93 5 3.69 0.60 0.16 2.46 6 5.00 0.55 0.11 4.13 7 4.67 0.59 0.13 3.22 8 8.00 0.63 0.08 4.60 9 2.26 0.57 0.25 1.74 10 3.18 0.61 0.19 2.00 Avg arithmetic. 3,969 0.617 0.175 2,487

Using the values of the parameters p, two matrices are calculated that describe the cluster of reference values:

1. Coordinates of the cluster center (vector-centroid C) - parameter values corresponding to the "average" security feature (the nominal value of the security feature). The components of the vector are the arithmetic mean values of the parameters p in the training set:

С=

C = from ₁ from ₂ from ₃ from ₄ = 3,969 0.617 0.175 2,487

2. The covariance matrix Σ describing the shape of the cluster of reference values:

The components of the matrix are calculated by the formula:

,

,

where m is the volume of the training sample (in this example, m = 10);

k is the index of the document in the training set;

i, j are the indices of the parameters ρ ₁ ... ρ ₄ ;

S _k = (p _ki -c _i ) (p _kj -c _j );

c - components of the vector C (coordinates of the center of the cluster of reference values).

For the values given in table 3, the covariance matrix has the following form:

2.4664 -2 · 10 ^-4 -0.078 1,5067 Σ = -0,0002 0.0016 4 · 10 ^-4 -0.017 -0.0777 0,0004 0.003 -0,053 1,5067 -0.017 -0,053 1,1209

For the convenience of further calculations, the inverse covariance matrix ∑ ^{-1 is} calculated:

22.97 -423.78 -112.72 -42.802 Σ ^-1 = -423.8 8963.8 3371.3 868,749 -112.7 3371.3 4534.7 418.92 -42.8 868.75 418.92 91,7859

To identify the element of protection of authenticity, the following data are recorded in the device memory:

- inverse covariance matrix Σ ^-1 ;

- the centroid vector C;

- response threshold.

In this example, the Mahalanobis distance D _{m is} used as a criterion for the presence of an authenticity protection element:

where (RC) ^T is the transposed vector of the difference of the vectors P and C.

An example of identification of an authentication security element on an authentic document with a set threshold of operation D _m0 = 4. The authentication element authentication is carried out in 7 steps (Fig.5, 6).

An example of identifying a simulator of an authenticity protection element with a set response threshold D _m0 = 4 (Figs. 7, 8).

Thus, the claimed invention allows to identify high-quality imitators of the element of protection of authenticity.

Compared with the known method for identifying security features by comparing reflection coefficients with reference values, the claimed invention provides a significant increase in the reliability of detection of an authenticity protection element.

The claimed invention can be implemented on low-cost, non-contact optical identification equipment operating at high speed.

Claims (10)

1. A method of protection against falsification of a valuable document, comprising applying to the document surface a security element made with printing ink containing an IR absorber with a full color difference with respect to the document base of not more than 7, having the ability to absorb optical radiation in the wavelength range from 700 to 2500 nm and having at least one absorption band with a half width of 100 to 300 nm. 2. The method of protection against counterfeiting of a valuable document according to claim 1, characterized in that the printing ink further comprises a stabilizer. 3. The method of protection against counterfeiting of a valuable document according to claim 2, characterized in that the IR absorber is a compound selected from the group: derivatives of cyanines, pyrenes, thiopyrenes, indoanilines, squarlium, croconium, iminium, diiminium compounds, azulenes, dithiolenes and transition metal phthalocyanines, organic and organometallic azo compounds, and the stabilizer is a compound selected from the group: N-isopropyl-N'-phenyl-p-phenylenediamine, pyrocatechol, hydroquinone, 4-tert-butylcatechol, bisphenol A. 4. The method of protection against counterfeiting a valuable document according to any one of claims 1 to 3, characterized in that the printing ink has the following composition, wt.%: IR absorber 5-15, stabilizer 2-4, desiccant 2-4, binder - rest. 5. Valuable document protected from counterfeiting by the method described in any one of claims 1 to 4, which is a banknote, excise stamp, passport, travel document, driver’s license, identity card, security paper, plastic card with a security element on it surface of the document in the form of hidden security marking. 6. Valuable document according to claim 5, characterized in that the protective element is made of offset or type-offset method. 7. A method for identifying the authenticity of a valuable document described in any of claims 5 or 6, including irradiating a valuable document with test radiations at different wavelengths within a specified range, measuring diffuse reflection coefficients in the visible and / or near infrared optical spectrum, calculating the derivative information on the algorithm, including determining the set of parameters from the measured diffuse reflection coefficients, and comparing it with predetermined reference values, the derived information being it as a point in the multidimensional space of parameters, and the reference values are presented in the form of a cluster describing the possible values of the parameters of genuine documents, while determining the coordinates of the center of the cluster — the centroid vector C and the covariance matrix ∑ describing the shape of the cluster of reference values, and the comparison is performed by measuring the distance from the measured point to the cluster. 8. A device for implementing the method described in claim 7, comprising a photometer for measuring diffuse reflection coefficients of the samples under study, connected to a power source and an information processing unit, the photometer including a photodetector, a lens, and a block of radiation sources of various wavelengths, configured to be turned on in a pulsed mode and equipped with a conical diffuser located coaxially with the lens and installed between the block of emitters and the sample under study, the lens being yaet a fiber optic gradient lens. 9. The device according to claim 8, characterized in that it contains LEDs as radiation sources, and the radiation wavelengths coincide with the maxima and minima of the reflection spectra of the protective element. 10. The device according to claim 8, characterized in that, for identifying an authenticity protection element, the following data are stored in its processing unit:
inverse covariance matrix ∑ ^-1 ;
centroid vector C;
trigger threshold.

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