CZ32585U1 - An identifier for marking and identification of paper documents using X-ray fluorescence - Google Patents

Description

Technical field

The technical solution relates to an identifier for marking and identifying archival paper documents by means of X-ray fluorescence.

BACKGROUND OF THE INVENTION

The current practice in archives and similar institutions is that documents are marked with the use of a classic metal or self-inking stamp with defined data, such as the name of the institution, the name of the archives, etc. but this marking is not usually applied to all leaves. The obvious and proven advantage of this procedure is its overall simplicity and time, technological and investment demands. On the other hand, this established procedure has its significant disadvantages, namely the visual dominance of such marking, often leading to a decrease in the aesthetic value of the document. Commonly used stamp inks are relatively easy to remove, which again can be evaluated as an advantage, for example, in the restoration of valuable carelessly marked archival materials, but also the disadvantage of easy removal of the imprint in case of theft of a valuable document.

With the advancement of digital technologies, electronic reading elements such as bar and checkerboard QR codes or purely electronic identification elements such as RFID elements and various other chips with contactless reading appear more and more frequently. Probably the most widespread are systems based on barcodes or QR codes with optical reading. These systems are now widely distributed in a wide range of fields. In archive practice, a barcode is sufficient to accurately describe the type of document and its classification. Technical equipment for reading and printing codes is not capital intensive, but the disadvantage of the system is again the visibility of the brand and its easy copying. The identification code can be copied and printed again in a very simple way. Codes thus have virtually no protective role. RF tags represent the technological evolution of barcodes in the form of contactless reading. They are also less disturbing in visual terms, a common form of white sticker of the order of centimeters.

However, not all of the above-described systems are primarily intended for identifying archival records in the event of a stolen document being lost or captured, but for simple sequencing and identification of a number of documents grouped together, for example, in archive boxes. If the archival document is of interest to dishonest conduct, it is difficult for the perpetrators to remove the marks described above trivially and subsequently identify the original owner.

The general solution to this problem is to mark the archived item in a way that is not apparent during normal viewing and thus escapes the attention of the perpetrator of the theft, but in case of capture it will allow reading the code and proving the original owner. The situation is to some extent similar to that of the protection of valuables and goods against counterfeiting. However, in the case of archive material, not only the distinction between original and counterfeit is required, but the mark on the archive document should carry at least a brief piece of information unambiguously identifying the owner.

For this purpose, many solutions for creating and reading short hidden codes based on a very wide range of technology principles have been described. By far the most popular principle is the use of fluorescence. For example, US 9836634 B2, US 8408468 B2 and US 6203069 B1 disclose various modifications of conventional barcodes but which are invisible when viewed under normal conditions and visualized by fluorescence under UV irradiation or

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IR source. US 8895072 B2 discloses a more sophisticated procedure based on the creation of short codes using quantum dots with a layered structure made up of differently fluorescent materials, the actual code being manifested by different emission fluorescence spectra.

Microdots as in US 4243734 A may also be used for the purpose described, and their location on the archives may be nationwide or local. In case of local application, the marking system must be supplemented with information leading to finding a microdot. A principle similar system based on mixtures of differently sized and differently colored microspheres is described in US 4767205 A.

US 5760394 A further describes the production of short codes useful for identifying lysic objects using long life element isotopes. Information content coding is done by setting specific proportions of selected isotopes, reading is performed using mass spectrometry, which, however, usually requires destructive sample preparation for analysis and is therefore not suitable for archival documents.

For obvious reasons, only non-destructive reading methods are applicable to the described application. US 20030178561 A1 then describes a system analogous to the previous one, however, where the unnatural ratios of the light element isotopes serve to alter the FTIR vibration spectra of the label forming chemicals and encode the information with these changes.

X-ray fluorescence or XRF appears to be very promising for the non-contact reading of codes based on the elemental composition of the label. While this method cannot distinguish isotopes of elements, but only different elements, it can still provide sufficient capacity for creating short codes and comfortable non-destructive reading. The general procedure for establishing the relationship between the XRF spectrum and the code value is described in the "Digital Equivalent Data System for XRF Labeling of Objects" (NASA). However, the publication is very general and does not include any description of the actual implementation. A more detailed implementation is described, for example, in US 6477227 B1, describing a system for identifying and demonstrating the origin of physical objects by means of a tag having a specific element composition that is identified by an XRF analyzer. The identification mark or marking element with a specific element composition is evenly dispersed throughout the volume of the final product, so it is necessary to use a large amount of the identification mark to its total volume. By means of the elemental composition and the relative frequency of representation is then created, respectively. code read. A disadvantage of said patent is that it does not address the compatibility of the brand with the article being marked. It is therefore evident that this system cannot be applied to all types of materials since it does not take into account the possible interactions between the mark and the article to be labeled, in particular because the patent does not address the chemical form of the mark. A similar principle with minor technical differences is used by a number of other solutions described for example in WO 2016014895 A1, WO 2016157185 A1, CA2617843 A1, etc. The disadvantages of these solutions lie in particular in that they completely ignore the quantitatively nonlinear phenomena accompanying XRF measurements.

However, the practical implementation of XRF codes has been hindered by numerous problems caused by various physical phenomena involved in XRF measurements, which in turn limit the reproducibility of the measured spectra and increase the error rate of reading the codes, respectively. limit the number of reliably executable codes. X-ray intensity alone can be measured very accurately, and routine work can produce errors of less than 1% without much effort, but comparable accuracy in quantitative analysis can only be achieved using non-linear calibration functions. Negative roles decreasing the accuracy of quantitative analysis include eg inter-element interactions (DOI: 10.1021 / ac60337a027), secondary fluorescence (DOI: 10.1002 / xrs.848), reabsorption and scattering (DOI: 10.1118 / 1.598612), sample inhomogeneity (DOI: 10.1002 / xrs 1300070406) or its particulate nature (DOI: 10.1002 / xrs.534). While scientific literature, especially those with an analytical focus, pays due attention to these problems, patent resources at least those aimed at using XRF coding - are, of course, more optimistic and generally ignore the problem.

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The object of the invention is to create an identifier for the identification of paper documents by means of X-ray fluorescence, which would help to prove the origin of paper documents, especially when stolen, whose marking would not visually interfere with archival documents. spectra imperceptible where there would be no interference between the identifier signal and the background signal of the paper document.

The essence of the technical solution

The task is solved by an identifier for marking and identifying paper documents by X-ray fluorescence comprising a marking element with a specific element composition with a specific frequency of representation of the individual elements constituting the identification code.

The actual coding is based on the variable relative frequency of representation of several selected chemical elements, which are not present in the archives and there is no danger of interference with the natural background of the paper document. The code is then read by XRF spectrometry. In the XRF spectrum, each code, respectively. marking element a unique qualitative expression, ie indicating the presence of individual elements manifested by the presence of the signal in a characteristic position, and quantitative, ie indicating the frequency of the relative representation of the element manifested by the signal intensity.

Thus, in order to generate the codes of the marking elements, it is first necessary to prepare the coding mixture in the form of a colloidal dispersion, for which precious elements not commonly found in archival paper documents, such as lanthanides and actinoids, are preferably used. Preferably, stable compounds are used, in particular oxides or carbonates, sulphates, aluminates or silicates of suitable elements. These stable compounds are white or faint colors, ie yellowish, pinkish or light blue. The coding mixtures are preferably formulated as colloidal dispersions, further suppressing their color appearance. The prepared colloidal dispersions of the individual compounds are mixed in specified ratios to form a crude coding mixture bearing one particular code value from many possible combinations, expressed as the ratio of peak heights in the XRF spectrum. However, due to the high concentration of the coding mixture, the XRF spectrum in this raw coding mixture is different from the spectrum of the future labeling element created by the coding mixture. In addition, transition metals may be used for the coding mixture.

A suitable application formulation adapted to the particular deposition technique is prepared from the raw coding mixture. A conventional method is to introduce the raw coding mixture into a colorless base of printing inks based on polyacrylates, cellulose nitrates, polyurethanes, polyesters or alkyd resins or into another suitable matrix at a concentration of 1 to 10% by weight. Suitable printing techniques may be pad printing, screen printing, flexographic printing or inkjet printing. The matrices used must, of course, meet higher requirements for archival stability and be compatible with the coding mixture used. In particular, separation of the components from the coding mixture during storage or application must be prevented, thereby "tuning" the set value of the code. The dispersions must therefore be well stabilized. Thin deposits of micrometer thickness produced by such formulations are almost colorless and semitransparent. They are not visually visible when applied to ordinary paper documents. A certain risk of visibility is due to the different gloss of the printed pad, but this can be corrected by the addition of conventional matting agents such as amorphous silica.

When using printing techniques, a more sophisticated deposition procedure may also be used, in which several printing formulations containing only one component of the code are prepared and the resulting marking element is assembled by reprinting several single component formulations. In addition to printing techniques, however, it is also possible to use simple manual application by transmission

U1 of the prefabricated marking element by pressure from the support washer. In particular, the inkjet printing method of marking elements, which, in combination with the instrument recognition of the original, enables a number of more sophisticated methods for positioning the marking elements and allows, in some cases, the elimination of the location element, is a particular application possibility. For example, a small, concentrated marker element can be applied to selectively selected locations of the original, i.e., a " overprinting the first letter on the page with a marking element, etc. Inkjet further allows the entire paper document to be covered with a small dot matrix containing a sufficient amount of coding mixture so that the entire paper document becomes one large marking element.

The applied marking element is visually imperceptible. It is therefore advisable to add an auxiliary element with a locating function to enable the identification element to be found. The location element may take the form of a simple, suitably shaped geometric pattern, such as an arrow, a border, a deliberate cross, and the like, providing information about the position of the marking element. The location element is again created by printing onto the surface of the paper document. The location element is also visually imperceptible and visualized by fluorescence emission after excitation. Preferably, the so-called up-conversion fluorescence induced by excitation with an infrared laser is used. Up-conversion pigment is a chemical compound that, when irradiated with high-intensity infrared radiation, generates fluorescence in the visible region of the spectrum. It is therefore photoluminescence generated by radiation of lower energy than the radiation generated. The advantage of this arrangement is that the location element is not identifiable in the UV irradiation commonly used to make the fluorescent security elements visible. Together, the labeling element and the location element form an identifier, which is also an object of the present invention.

The object of the technical solution is therefore a complex identifier for marking paper archived documents with visually imperceptible marks carrying short multi-bit codes. The identifier makes it possible to easily and efficiently place an identification code on a paper document or archive material, namely a marking element that is not visually visible under visible or UV or IR radiation. This marking element is semi-transparent, so it can be placed anywhere in the paper document, its position is not easily recognizable and does not interfere with the viewing of the original graphic content. The location of the marking element for measurement and decoding purposes is then solved by a so-called localization element located in the immediate vicinity of the marking element in such a way that once the fluorescent emission location element is visible, the position of the marking element can be determined and readily interpreted. After irradiating the paper document with the NIR source, ie the near infrared region, the location element is localized by the upconversion pigments and subsequently the measuring aperture of the XRF spectrometer can be applied and the XRF spectrum measured.

The labeling element is based on a combination of at least two elements from the group of lanthanides and / or actinoids and / or transition metals. These include, for example, niobium, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, therbium, dysprosium, holmium, erbium, thulium, yterbium, lutecium, lanthanum, actinium, thorium, ruthenium. These elements can be accurately identified and their content quantified with certain limitations by X-ray fluorescence or XRF. Elements are selected which ensure a natural absence in the protected paper document, whether due to the absence of paper material, the absence of ink, the colors used in the illuminations, etc., or optionally in the materials used to finish the archive paper document. The elements used and their compounds are not visible at the concentrations at which they are applied to the document by visual observation, even under UV or IR irradiation. Moreover, in these low amounts, they have no negative effect on the protected document itself.

Coding is based on different ratios of the frequency of occurrence of selected elements in coding mixtures and their identification, both qualitative and quantitative. E.g. let us have five different elements providing individual non-overlapping emission peaks in the XRF spectrum. The elements are labeled A, B, C, D, E and they form the individual variables of the described code, ie five variables. Amount

32585 U1 of the deposited material in the marking element limits the number of signal levels each variable can acquire. The lower limit is the noise accompanying the measurement, respectively. minimum signal value safely distinguishable above noise. In accordance with generally accepted practices, we assume three times the noise intensity. The upper limit depends on the optical properties of the labeling element, since the labeling element containing too much coding mixture will be visible, as well as the extent of the linear XRF concentration response, where too much coding mixture will interfere with each other and the signal will not be proportional to concentration. The examples below are visually unnoticeable and provide a sufficient signal-to-noise ratio and a sufficient linear range of signal intensity-concentration dependence to reliably differentiate up to four signal levels. In this case, we have a code with five variables taking four values, ie 5 ⁴ = 625 combinations.

In order to distinguish the so-called equisignal combinations or combinations with the same relative height of individual peaks, eg code (A = 1, B = 1, C = 1, D = 1, E = 1) from code (A = 2, B = 2, C = 2, D = 2, E = 2), an internal standard must be built into the system against which the other signal values will be compared. For the code described above, this means that one of the positions is used exclusively for the internal standard, so we have 4 ⁴ = 256 combinations left. The resulting code value can then be accurately assigned to the site or archive, which indicates the paper documents in this way, without this being apparent to the uninformed user. In this way, paper documents can be tagged with a view to their subsequent identification, for example after possible theft and proof of their origin on capture, without in any way impairing the visual integrity of the paper document. Thus, the paper document is not damaged from an aesthetic point of view, and in particular, any offender cannot determine whether and where the marking element, i.e. the identification code, is located.

Suppression of undesirable quantitatively nonlinear phenomena in XRF measurements is a key feature and advantage of the present invention and is achieved in several ways. In particular, the deposition of marking elements by material printing techniques plays a key role, which not only ensures the actual application of the coding mixture in a prescribed ratio, but also accurately measures their total quantity and ensures the prescribed area concentration, which are essential to ensure a stable and reproducible XRF response. Furthermore, it is primarily the textural properties, in particular the particle size in the coding mixture and the aggregation of the coding compounds, which are set at the stage of production of the raw coding mixtures by grinding to desired size by so-called pearl milling techniques. When designing liquid printing formulations for various printing techniques, concentrations are carefully selected to provide an optimum area and volume concentration of the coding mixture in the dried marking element so that the intended values of the coding variables are maintained and that the marking element contains an optimal amount of coding mixture that provides the signal to noise ratio, but does not affect the signal intensity by the concentration-nonlinear phenomena described above.

Advantages of the method of marking and identifying paper documents by X-ray fluorescence according to the present invention are that it helps to prove the origin of paper documents, especially when stolen, their marking does not visually interfere with archival documents, so that they are not destroyed. Due to the characteristics of the identifier of the present invention, there is no risk of interference between the identifier signal and the background signal of the paper document.

Example of technical solution implementation

Example 1 - Preparation of the starting coding mixture

To form the initial coding, the following mixtures of oxides of the lanthanides and transition metals - La2C> 3 S1112O3 CID ₂ () 3, Dy ₂ O 3 and the weight ratio of the backfill nbtk following is 38.22 wt%. % lanthanum oxide, 23.54 wt. % Samarium oxide, 17.29 wt. oxide

% Gadolinium, 16.42 wt. % dysprosium oxide and 4.53 wt. niobium pentoxide. Subsequently, the dry mixture should be sufficiently homogenized. This mixture is so-called "equisignal", meaning that the main peaks of all metals present have the same (+/- 2%) height. By reducing the content of oxides La, Sm Gd and Dy while maintaining the amount of Nb, additional codes can then be prepared which will have lower peaks compared to Nb acting as an internal standard.

60 g of Dowanol PM (2-methoxypropanol) are introduced into the beaker and 40 g of the starting lanthanide oxide coding mixture are added with stirring, and 4 g of Dispperbyk 103, a 50% solution of ion-free polymer in 2-methoxypropyl acetate, are added. . Then 30 g of glass ballotin with a diameter of 0.6 to 0.8 mm are added to the beaker. With a flat glass stirrer of 5 cm diameter, the suspension is ground to a stable dispersion at a speed of at least 2000 rpm. Filter the glass ballot through a polypropylene filter cloth. The average particle size is 190 to 200 nm and the prepared dispersion is stable for use as a coding mixture.

Example 2 - Screen printing of the marking element

3 g of a stock coding mixture of metal oxides forming the identification code of the marking element according to Example 1 are dispersed in 10 g of a clear base for a polyacrylate-based screen printing lacquer. The resulting formulation is thoroughly homogenized and screen-printed onto paper documents for marking. The printed pattern of the marking element has a circle shape of 8 mm diameter and is not visually perceptible after the solvents have evaporated. This quantity is sufficient to label a minimum of 500 sheets, with the XRF spectra of all printouts measured with the DELTA Professional ED-XRF handheld spectrometer showing a high degree of compliance - the total integral of the area under the spectra varies within ± 10% of mean. , which allows reliable resolution of the four signal levels in each variable of the code printed.

Example 3 - application of the location element by screen printing and formation of the identifier g by 4 wt. of polyvinyl butyral in ethanol is mixed with 300 mg of an upconversion fluorescent pigment, i.e. any pigment with an IR excitation of 950 to 1000 nm and a mean particle size in the range of 20 to 200 microns. The resulting formulation is thoroughly homogenized and screen-printed onto paper documents of the archival documents previously labeled with the tagging element in such a way that the location element has a 2 mm annulus shape surrounding the previously deposited tagging element and forms an identifier with each other. The locating element with visible green light emission upon excitation by a powerful near-IR emitting source, typically a 980 nm laser, 500 mW, serves to accurately target the XRF analyzer's measurement aperture.

Example 4 - application of the marking element by pad printing

3 g of the stock coding mixture of metal oxides forming the identification code of the marking element according to Example 1 are dispersed in 10 g of clear polyacrylate-based tampon lacquer base. The resulting formulation is thoroughly homogenized and applied by pad printing onto paper documents of the archival documents to be marked. The printed pattern of the marking element has a circle shape of 8 mm diameter and is not visually perceptible after the solvents have evaporated. This quantity is sufficient to label a minimum of 1000 sheets, with the XRF spectra of all prints showing a high match - the total integral of the spectra varies by no more than ± 10% from the mean and the relative peak height deviations do not exceed 5%. code printed this way.

Example 5 - Combined application of the marker element and the location element by pad printing

3 g of the stock coding mixture of metal oxides forming the identification code of the marking element according to Example 1 are dispersed in 10 g of a clear base for a tampon lacquer on polyacrylate.

32585 U1 prepares suspensions of an upconversion fluorescent pigment, i.e. any pigment with an IR excitation of 950 to 1000 nm and a mean particle size in the range of 20 to 200 microns in an amount of 300 mg in 10 g of the same lacquer colorless ink base. Both mixtures are applied by a pad printing technique on a paper document. Preferably, a two-color machine can be used for direct printing of both components. The marking element has a circle shape with a diameter of 8 mm, the location element has a shape of a 2 mm annulus surrounding the marking element. Locating element with visible green light emission after excitation by a powerful near-IR emitting source, typically a 980 nm laser, 500 mW. After the location element is visible, it is possible to attach a handheld XRF device and measure the response of the marker element located inside the location element. The quantitative and qualitative parameters of the marking element are identical to the previous case.

Example 6 - inkjet marking element application

A printing formulation is prepared by mixing 4 mL of a 50% by weight stock solution of polysiloxane resin in xylene. with 4 mL of the metal oxide storage coding mixture forming the identification code of the labeling element prepared according to Example 1 and 2 mL of alpha-terpineol. Printing is performed with a piezoelectric print head and 10 µL droplets are placed in a regular 100-micrometer square grid, the printed pattern having a 1 cm square shape. When one such layer is deposited in the XRF spectrum, the emission peaks of the marking element are just discernible, therefore the three layers provide the lowest safely distinguishable signal level. Thus, for a code working with four signal levels, twelve overprints, or more, are applied, thereby increasing the number of distinguishable signal levels. The XRF spectra of all prints show a very high degree of match - the total integral of the area under the spectra varies by no more than ± 5% from the mean and the relative height deviations of each peak do not exceed 2%, allowing up to twenty signal levels The deposited coding material material was too large and visible, and without deviations of the XRF signal from linearity were observed.

Example 7 - transfer film

The label element is prepared by introducing 3 g of the metal coding stock mixture forming the label element identification code of Example 1 into a medium consisting of 5 g of microcrystalline wax and 15 mL of a mixture of aliphatic hydrocarbons boiling at 178-191 ° C. A non-stick paper, such as non-porous glazed paper or siliconized paper, is subjected to screen printing using a round-shaped marking element of 8 mm diameter and dried by evaporating the solvents. The printed motif is transferred to the material to be marked by locally applying pressure to the foil, for example by means of a metal trowel or a book cube.

The XRF spectra of all transferred marking elements measured by the DELTA Professional ED-XRF spectrometer show a high level of compliance - the total integral of the area under the spectra varies by + - 10% from the mean value and relative peak height deviations do not exceed 5%. in each variable of the code printed this way.

Industrial applicability

An identifier for marking and identifying paper documents by means of X-ray fluorescence according to this invention can be used in particular for invisible and non-destructive marking of archival paper documents useful especially in the case of theft.

Claims (3)

An identifier for marking and identifying paper documents by X-ray fluorescence comprising a label element having a specific element composition with a specific frequency of individual elements constituting an identification code, characterized in that the label element is a coding mixture in the form of a colloidal dispersion of at least two chemically inert lanthanide compounds and / or non-paper actinides and / or transition metals and a colorless polyacrylate-based ink composition comprised of 1 to 10% by weight, when applied to the paper document, the marking element is colorless, semitransparent and identifiable by X-ray fluorescence, and an identifier it further comprises a locating element arranged adjacent to the marking element which is constituted by a fluorescent-generating pigment after irradiation with infrared radiation or a laser having a wavelength of 800 to 10 00 m. Identifier according to claim 1, characterized in that the lanthanide and / or actinoid and / or transition metal compounds are oxides and / or carbonates and / or sulphates and / or aluminates and / or silicates. Identifier according to claim 1 or 2, characterized in that the lanthanides are selected from the group of: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, yterbium, lutecium, the actinoids are selected from: actinium, thorium and transition metals are selected from: niobium and ruthenium.