RU2417898C2 - Method of documents protection by magnetic nanoparticles - Google Patents

Abstract

FIELD: printing industry.

SUBSTANCE: invention relates to methods to protect documents made on paper, cardboard, etc. with application of dyes, ink, etc. by means of application of texts, symbols, codes, manually or with the help of any printing device, onto their surface. Method is based on adding nanoparticles of ferromagnetic material or ferromagnetic material mixture with previously specified magnetic resonant properties. At the same time the document authenticity is verified at EPR spectrometre by comparison of magnetic resonance curve type of separate symbols or other document fragments with reference dye curve, which is produced at the moment of its manufacturing.

EFFECT: increased extent of documents counterfeit protection, at the same time authenticity check is carried out using complex measurement procedure and is characterised by high security.

1 dwg, 1 tbl

Description

The invention relates to methods for protecting documents made on paper, cardboard, etc. using dyes, inks, etc., by applying to their surface texts, symbols, codes, made by hand or using any printing device.

Numerous methods are known to prevent counterfeiting of original documents or the creation of illegal copies thereof. Initially, protection was carried out using special grades of paper (parchment, papyrus) and assuring them with various seals or creating a watermark system on paper. Further development of this direction can be traced on the example of an increase in the number of degrees of protection of bank notes: for this purpose watermarks are used, the inclusion of colored fibers, metallized stripes in the composition of the paper, the application of inscriptions in the form of microholes and the use of complex micro-blocking, holographic signs that change color when illuminated under different angles of incidence of light. The main disadvantages of these methods are: their easy distinguishability, localization on separate parts of the document, high complexity of application, requiring the use of special equipment. In addition, these protective measures can easily be violated or distorted on the protected document, which will lead to the problem of recognition of its authenticity.

Also known is a method based on the use of magnetic codes recorded on magnetic media, which is a special strip of magnetic material that is applied to the surface of credit cards, certificates, travel tickets, etc. The main disadvantage of this method is the low mechanical strength of the magnetic strip: when bending, stretching in the strip, integrity violations occur, leading to demagnetization and loss of information. The recorded information is a code consisting of some characters that can be lost during demagnetization in an external electromagnetic field or stolen due to the prevalence of reading devices. In addition, magnetic protection when using this method is localized only on parts of the document, thereby allowing, in principle, to change the content of its other parts.

Closest to the proposed method is the method described in [1]. It consists in introducing into the constituent parts of the paper (security document) ferromagnetic components that are added to the paint, as a result of which they acquire magnetic properties. Diagnostics of the presence of ferromagnetic components and their topographic distribution is carried out using detectors built into the appropriate devices, or special visualizers such as Magnetoscope 2. These detectors operate on the basis of the Faraday effect - rotation of the plane of polarization of light as it passes through a magnetic medium.

The disadvantages of the prototype are:

- localization of protective equipment only on certain fragments of the document, which leaves the possibility of changing the content or appearance of all its unprotected parts;

- the complexity of the procedure for the production of the document: the application of protection by the proposed method is a separate process operation, performed in several stages;

- degradation over time of the magneto-optical characteristics of the material, which reduces the amplitude of the signal recorded by means of readers.

The aim of the present invention is to eliminate the disadvantages of the prototype, complicating the possibility of falsification of documents.

This goal is achieved by introducing into the composition of the dye, which is used to apply the text of the document, all its attributes, including titles, state or company symbols, nanoparticles of ferromagnetic materials with pre-set magnetic resonance properties. As a result, any fragment of a document or protected text can be verified for authenticity by examining the electronic magnetic resonance of its individual characters. The verification is carried out by comparing the type of the curve of the ferromagnetic resonance from the fragment of the document with the reference curve, which is obtained during the manufacturing process of the dye, and this information is confidential, and the type of dye has unique properties. These properties are changed by changing the concentration of nanoparticles in the dye, using mixtures of nanoparticles of various ferromagnetic materials, or changing the chemical composition of the dye itself.

The proposed method creates a fundamentally new quality of document protection, not available in other cases. Indeed, when using the proposed method, the protection area extends to the entire area of the document. The proposed method, in addition, can be used in combination with any other methods of protection. It is distinguished by simplicity, because it does not require the use of special equipment or the use of additional technological operations, so this method is notable for low cost. In addition, the protection of the document in accordance with the claimed method is characterized by increased secrecy, because it is only possible to establish the presence of protection using a rather complicated measuring procedure using magnetic resonance spectrometers, and can only be performed in specialized laboratories by specially trained personnel.

An analysis of the level of development of technology by the applicant, including a search by patent and scientific and technical sources of information and identification of sources containing information about analogues of the claimed technical solution, did not find sources characterized by signs that are identical or identical to all the essential features of the claimed method. The selection from the list of identified analogues of the prototype as the closest in the totality of the features of the analogue made it possible to establish a number of distinguishing features of the method of protecting documents described in the claims with respect to the technical solution proposed by the applicant. Therefore, the claimed method meets the criterion of "novelty."

An additional search conducted by the applicant did not reveal known solutions containing signs that match the distinctive features of the claimed method from the prototype. Therefore, for a specialist, the claimed technical solution does not follow explicitly from previously known solutions, because the essential features of the patented method do not arise as a result of the conversion of known methods. The claimed technical solution is also not based on a change in the quantitative sign (s), the presentation of such signs in conjunction or a change in the type of known analogues and prototype. Therefore, the claimed method meets the criterion of "inventive step".

In this work, we chose the toners used in laser printers of ordinary personal computers, namely, dyes from Canon and Hewlett-Packard (HP), as the medium containing nanoparticles of magnetic materials. They contain iron oxide nanoparticles, but different manufacturers have size, concentration, etc. nanoparticles in the composition of the dye are different. Using a standard personal computer printing device, the same text was reproduced on identical sheets of paper using toners from these companies.

Electron magnetic resonance (EMR) measurements were carried out at room temperature on an X-band EPR spectrometer (frequency ≈9.1 GHz) Varian E-4. A sample in the form of a narrow paper strip printed with the letter “I” - in fact, a straight line segment, evenly colored with toner - was lowered to the bottom of a quartz ampoule, which was placed in the resonator of the spectrometer. The orientation of the plane of the paper strip was either perpendicular or parallel to the quasistationary magnetic field. The external magnetic field was varied in the range of 0-6 kG. The effective resonance field was determined as the arithmetic mean of the maximum and minimum of the curve of the first derivative of the absorbed power in units of magnetic field induction. The line width ΔB was determined as the distance between the maximum and minimum on the curve of the first derivative of the intensity of the absorbed power in units of magnetic field induction.

The drawing shows the EMR spectra of toner samples. All spectra consist of a single intense resonance line with the parameters given in the table.

The electron magnetic resonance spectra of the image of the letter “I” were obtained using toners from Canon and HP. The lines shifted to the region of low (high) magnetic fields are obtained for the orientation of the paper plane parallel to (perpendicular) to the external magnetic field.

Such an EMR signal is typical for superparamagnetic nanoparticles of iron oxides [2, 3]. In the HP sample, the width of the EMR signal is noticeably larger, and the resonance field is smaller than in the Canon sample. This difference reaches its maximum value for the orientation of the samples parallel to the direction of the induction vector of the quasistationary magnetic field. The difference in the shape of the resonance curves is caused by the difference in the sizes of magnetic particles in different dyes.

Sample Type ΔB _pp , T Effective resonance "Canon" box perpendicular to paper 0.123 0.358 "Canon", box parallel to paper 0.113 0.320 "HP" box perpendicular to paper 0.177 0.352 "HP, box parallel to paper" 0.168 0.239

Thus, the shape of the EMR spectra allows one to unambiguously distinguish dyes by their characteristic features by the concentration and size of the magnetic nanoparticles contained in them.

Literature

1. I.A. Pavlov, A. B. Potapov. Verification of the authenticity of documents, securities and banknotes. M .: Technosphere. 2006, p. 86.

2. Yu.A. Koksharov, S.P. Gubin, I.D. Kosobudsky, M. Beltran, Y. Khodorkovsky, A.M. Tishin. Low temperature electron paramagnetic resonance anomalies in Fe-based nanoparticles, J. Appl. Phys., V. 88, N1, (2000), pp. 587-592.

3. Yu.A. Koksharov, S.P. Gubin, I.D.Kosobudsky, G.Yu.Yurkov, D.A. Bankratov, L.A. Ponomarenko, M.G. Mikheev, Y. Khodorkovsky, M. Beltran, A.M. Tishin. Electron-paramagnetic-resonance spectra near spin-glass transition in iron-oxide nanoparticles. Phys. Rev. B.63 (2001), pp. 12407-12410.

Claims (1)

A method of protecting documents with magnetic nanoparticles, namely, that a dye in the form of ink, paint, pastes, etc. is applied to the surface of a paper or paper substitute, the dye is made from materials with magnetic properties, characterized in that nanoparticles are added to the dye ferromagnetic material or a mixture of ferromagnetic materials with predetermined magnetic resonance properties, and the authenticity of the document is checked on an EPR spectrometer by comparing the form of the magnetic resonance curve nyh characters or other fragments of the document with a reference dye curve, which is obtained at the time of manufacture.

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