Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/30—Identification or security features, e.g. for preventing forgery
  • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
  • B42D25/373—Metallic materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/30—Identification or security features, e.g. for preventing forgery
  • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
  • B42D25/378—Special inks
• • G—PHYSICS
  • G07—CHECKING-DEVICES
  • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
  • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
  • G07D7/06—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using wave or particle radiation
  • G07D7/12—Visible light, infrared or ultraviolet radiation
  • G07D7/1205—Testing spectral properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/20—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof characterised by a particular use or purpose
  • B42D25/21—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof characterised by a particular use or purpose for multiple purposes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/20—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof characterised by a particular use or purpose
  • B42D25/23—Identity cards
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/20—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof characterised by a particular use or purpose
  • B42D25/24—Passports
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/20—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof characterised by a particular use or purpose
  • B42D25/29—Securities; Bank notes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/30—Identification or security features, e.g. for preventing forgery
  • B42D25/355—Security threads
• • G—PHYSICS
  • G07—CHECKING-DEVICES
  • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
  • G07D2207/00—Paper-money testing devices

Definitions

• the present invention lies in the technical field of the manufacture and verification of security documents and relates to a method for identifying a security mark.
• Valuable documents are generally protected against unauthorized and often illegal duplication by special markings. It has long been known to treat valuable documents for this purpose with luminescent substances that exhibit specific emission characteristics.
• the printed matter US 7762468 B2 Figure 1 shows an authentication method that uses a combination of two luminescent substances with different decay times.
• the second, slower-decaying luminescent substance is only detected once the luminescence of the first luminescent substance has already faded.
• the US 2014/0001351 A1 reveals two luminescent materials blended together in a security feature.
• the object of the present invention is to enable reliable, secure, and rapid identification of the marking of a valuable document using luminescent substances with complex time behavior. Furthermore, the invention aims to allow the use of a variety of different luminescent substances with non-exponential time behavior.
• a document of value bearing a security mark is shown.
• the term "document of value” refers to any item requiring protection against unauthorized or unlawful duplication, such as banknotes, checks, shares, tokens, identity cards, credit cards, and passports, as well as labels, seals, packaging, or other items used for security purposes.
• the security mark of the document of value can be assigned to at least one freely definable (binary) property of the document of value, wherein the property is present upon identification (presence of the security mark) and not present upon non-identification (absence of the security mark).
• the security mark can be assigned to the property of "authenticity" as an authenticity mark or feature to distinguish documents of value from counterfeits. It is also conceivable that the security mark could assign documents of value to a specific class or group, such as the denomination or country of origin of banknotes.
• the security marking is designed in the form of at least two luminescent substances (hereinafter also referred to as luminescent materials).
• the luminescent materials can be incorporated into or applied to the security document in a variety of ways.
• the luminescent materials can be added to a paper or plastic material used to manufacture the security document or to a printing ink used to print on the security document. It is also conceivable to provide the luminescent materials as, for example, an invisible coating on the security document.
• the luminescent materials can also be provided on or in a carrier material, for example, made of plastic, which is embedded in a paper or plastic material used to manufacture the security document.
• the carrier material can, for example, be in the form of a security or identification thread, a twill fiber, or a planchette.
• the carrier material can also be attached to the security document, for example, in the form of a plaque, for instance, to implement a product security measure. In principle, any shape of the carrier material is possible.
• the at least two luminescent substances of the security marking can be excited together by a (same) excitation pulse (e.g., a flash of light).
• a (same) excitation pulse e.g., a flash of light.
• the time courses of the intensities of the emitted radiation from the luminescent substances excited by the excitation pulse are different from one another, with at least one luminescent substance exhibiting a non-monoexponential time course of the intensity of the emitted radiation.
• the safety marking contains at least two luminescent substances in a definable or defined ratio in combination (preferably in the form of a mixture). This means that each luminescent substance is present in the safety marking in a definable or defined relative proportion, based on the total amount of luminescent substances.
• the safety marking can therefore be uniquely identified based on the ratio (mixing ratio) of the luminescent substances.
• each luminescent substance contributes the intensity of its emitted luminescence radiation to the total intensity of the radiation emitted simultaneously by the excited luminescent substances of the security marking.
• total intensity here and subsequently refers to the summed intensity of the luminescence radiation from the combined luminescent substances contained in the security marking, all excited by the same excitation pulse and detected at the same time.
• the security marking is designed in such a way that, for identification of the security marking, the quantity ratio (mixing ratio) of the luminescent substances can be determined by an analysis of the time course of the total intensity of the emitted luminescence radiation (excited by an excitation pulse) based on the time courses of the intensities of the luminescence radiation of the luminescent substances (excited by the same excitation pulse).
• the use of at least one luminescent substance with a non-mono-exponential time course of the emitted radiation intensity has the particular advantage that a large number of potentially suitable substances are available, and improved counterfeit protection can be achieved through specific selection. Furthermore, a relatively large difference in the rise and/or fall-off behavior of the luminescent substances can be achieved, allowing for reliable and secure identification of the security mark. If the excitation light is re-emitted with an (anti-)Stokes shifted wavelength due to intrinsic conversion processes, a clear separation of the excitation and emission radiation is readily possible using suitable filtering techniques.
• the at least two luminescent substances are selected such that the intensity of the emitted radiation of each luminescent substance lies within a range of 5% to 95%, preferably 10% to 90%, and particularly preferably 15% to 85%, of the total intensity of the luminescent substances.
• This allows for a particularly accurate analysis of the time course of the total intensity of the security marking based on the time courses of the intensities of the luminescent radiation emitted by the respective luminescent substances, which contributes to an improvement in the reliability of the identification of the security feature.
• the at least two luminescent substances are each selected such that the decay time, i.e., in particular the time between the end of the excitation pulse and reaching an intensity of 1/e of the intensity at the end of the excitation pulse, lies in the range of 100 ns to 100 ms, preferably 10 ⁇ s to 5 ms.
• the decay time i.e., in particular the time between the end of the excitation pulse and reaching an intensity of 1/e of the intensity at the end of the excitation pulse
• the decay time i.e., in particular the time between the end of the excitation pulse and reaching an intensity of 1/e of the intensity at the end of the excitation pulse
• the decay time i.e., in particular the time between the end of the excitation pulse and reaching an intensity of 1/e of the intensity at the end of the excitation pulse.
• the at least two luminescent substances have overlapping, and in particular identical, excitation spectra, which enables targeted and relatively strong excitation of the luminescent substances by a comparatively narrowband excitation pulse (flash of light).
• the at least two luminescent substances have overlapping emission spectra, which significantly increases the counterfeit protection of the security feature.
• the analysis of emitted radiation, which is more difficult, has been further improved in a beneficial way.
• the at least two luminescent substances are configured such that the time profiles of the intensities of the emitted radiation have a Bray-Curtis distance greater than 0.10, preferably greater than 0.20, and particularly preferably greater than 0.25.
• This measure can also increase the accuracy of the analysis of the time course of the total intensity of the emitted luminescence radiation of the luminescent substances of the security marking based on the time courses of the intensities of the luminescence radiation emitted by the luminescent substances, which contributes to a further improvement in the reliability of the identification of the security feature.
• the luminescent substances used for the security marking of the valuable document can generally be freely selected, provided that they can be excited together by a single excitation pulse and that the time courses of the emitted radiation from the luminescent substances are distinct, with at least one luminescent substance exhibiting a non-monoexponential time course of the intensity of the emitted radiation.
• Excitation and emission of the luminescent substances can occur in the UV, visible, and/or infrared (IR) range.
• luminescent substances can be used that are excited in the UV range and emit in the UV or visible spectral range.
• luminescent substances can be used that are excited in the IR range and emit in the IR range or emit in the visible range (up-converter).
• luminescent substances are advantageous if they exhibit a particularly strong non-monoexponential decay behavior after excitation.
• luminescent substances that each comprise a host lattice doped with at least one dopant selected from the rare-earth metals and transition metals (or their ions).
• Suitable inorganic host lattices include, for example, oxides, borates, gallates, phosphates, garnets, perovskites, sulfides, oxysulfides, apatites, vanadates, tungstates, glasses, tantalates, niobates, halides, oxyhalides, especially fluorides, silicates or aluminates.
• host lattices such as YAG, ZnS, YGG, YAM, YAP, AlPO 5 , zeolites, Zn 2 SiO 4 , YVO 4 , CaSiO 3 , KMgF 3 , Y 2 O 2 S, La 2 O 2 S, Ba 2 P 2 O 7 , Gd 2 O 2 S, NaYW 2 O 6 can be used as host lattices , SrMoO 4 , MgF 2 , MgO, CaF 2 , Y 3 Ga 5 O 12 , KY(WO 4 ) 2 , SrAl 12 O 19 , ZBLAN, LiYF 4 , YPO 4 , GdBO 3 , BaSi 2 O 5 or SrBeO 7 can be used.
• host lattices such as YAG, ZnS, YGG, YAM, YAP, AlPO 5 , zeolites, Zn 2 SiO 4 , YVO 4 ,
• Suitable dopants include, for example, the rare earth elements La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or Bi, Pb, Ni, Sn, Sb, W, Tl, Ag, Cu, Zn, Ti, Mn, Cr and V (or their ions).
• Luminescent substances with a strongly non-monoexponential time response of the emitted radiation intensity can be realized through various mechanisms.
• energy transfer processes between different dopants, especially rare-earth dopants, multiple time constants can intrinsically occur in both the rise and fall phases.
• Such energy transfer processes are known, for example, for the dopant ion combinations Yb/Er, Nd/Yb, Yb/Tm, Cr/Tm, Tm/Ho, Er/Tm, Er/Ho, Yb/Ho, Cr/Ho, Fe/Tm, Mn/Tm, Cr/Er, Fe/Er, Cr/Nd, Cr/Nd, Cr/Yb, and especially in combination with other dopants.
• the use of such dopant ion combinations is preferred.
• the precise time behavior of these substances is highly sensitive to both the host lattice used (due to the fine splitting of the energy states involved) and the respective dopant ion concentrations. This is caused by a relative change in the coupling rates compared to competing loss processes, such as non-radiative recombination of the ions involved.
• luminescent substances with complex intrinsic energy transfer processes can exhibit intensity profiles with strongly non-monoexponential time behavior, whereby the luminescence intensity can continue to increase even after the excitation phase has ended.
• the combination of such substances with classical substances that exhibit a monotonically decreasing time behavior after excitation allows for the targeted adjustment of the overall intensity of the luminescent substances over time. This can include not only decreasing emission phases but also increases, plateaus, local maxima, and/or minima.
• the safety marking comprises a combination of at least one luminescent substance with non-monoexponential time behavior and at least one luminescent substance with monoexponential time behavior. exhibits the time behavior of the intensity of the emitted luminescence radiation.
• the security marking can comprise a combination of at least two luminescent substances, each with different non-monoexponential time behavior of the intensity of the emitted luminescent radiation.
• luminescent materials in which several different transitions of a dopant ion, which are energetically very similar but have different lifetimes, contribute to emission in a narrow wavelength range. These luminescent materials also often exhibit non-monoexponential time behavior. Examples include Pr and Er.
• luminescent materials can exhibit non-monoexponential behavior due to randomly occurring or intentionally induced inhomogeneities during production, such as an inhomogeneous particle size distribution or an inhomogeneous distribution of dopants. This can occur, for example, when grains with faster time responses (i.e., faster decay and/or faster rise times) and grains with slower time responses (i.e., slower decay and/or slower rise times) are formed. Their differing properties are averaged during the relevant macroscopic measurement, in which a relatively large number of individual grains are generally excited and measured simultaneously. This results in the individual emission time structures of the individual grains overlapping in such a way that an overall non-monoexponential time response can emerge.
• a person skilled in the art can determine whether a luminescent substance exhibits monoexponential time behavior by simply measuring its time-dependent luminescence. This involves measuring the intensity over time during the decay phase and fitting an exponential curve to the decay curve.
• the coefficient of determination, R2 can be used as a measure of the goodness of fit, with the decay curve being considered "non-exponential" if R2 ⁇ 0.98.
• the signal-to-noise ratio at the beginning of the decay curve should be at least 50 to prevent a fit with a goodness of R2 ⁇ 0.98 being obtained by chance for a monoexponential decay curve.
• the invention relates to a method for identifying (i.e., detecting the presence or absence of) the security marking of a security document designed as described above.
• the method comprises the following steps:
• I ⁇ sub>i ⁇ /sub>(t) definable or defined time courses of the intensities of the luminescence radiation emitted by the luminescent substances (excited by the same excitation pulse)
• c ⁇ sub> i ⁇ /sub> represents linear coefficients to be fitted.
• the running index i refers to the luminescent substances
• n indicates the number of luminescent substances
• t represents time.
• the time courses I ⁇ sub>i ⁇ /sub> (t) of the intensities of the luminescent substances can be determined for each luminescent substance by excitation with the same excitation pulse and (preliminarily) detecting the luminescence radiation.
• the linear coefficients c ⁇ sub> i ⁇ /sub> are determined.
• the linear coefficients c ⁇ sub>i ⁇ /sub> each represent the relative contribution of a single luminescent substance to the linear combination I (t) over a given time course I ⁇ sub>i ⁇ /sub>(t). From the linear coefficients c ⁇ sub>i ⁇ /sub>, the relative proportion of each luminescent substance, relative to the total amount of luminescent substances in the security marking, and thus the ratio (e.g., mixing ratio) of the luminescent substances in the security marking, can be determined.
• Identifying i.e., recognizing the presence or absence of the security marking based on the linear coefficients c i .
• the adaptation of the linear combination I(t), consisting of a sum of the previously known time profiles I i (t) weighted with the linear coefficients c i , to the total intensity I(t) of the simultaneously emitted luminescence radiation advantageously enables a particularly simple, reliable and very fast determination of the quantity ratio (e.g. mixing ratio) of the luminescent substances in the security marking, thereby enabling a reliable identification of the security marking.
• the quantity ratio e.g. mixing ratio
• the linear coefficients c ⁇ sub> i ⁇ /sub> are determined such that absolute deviations of the linear combination I(t) from data points of the detected time course of the total intensity are minimized.
• the linear coefficients c ⁇ sub>i ⁇ /sub> are determined by the least squares method such that the sum of the squared deviations of the linear combination I(t) from data points of the detected total intensity is minimized.
• the least squares method is familiar to those skilled in the art in the field of statistical analysis of data sets, so further explanation is unnecessary here. It should merely be added that this is a standard statistical method for determining a regression curve for a data set with the smallest possible deviation of the data points from the regression curve.
• step iv) comprises the following sub-steps:
• the ratio Mi is determined by the ratio of the linear coefficient c i to the sum of at least one, preferably all, linear coefficients c i (e.g., c 1 / (c 1 + c 2 )).
• the ratios Mi indicate the quantitative ratio (e.g., mixing ratio) of the luminescent substances in the safety marking.
• the partial steps iv-1) to iv-4) advantageously enable a simple and reliable identification of the security marking based on the linear coefficients c i .
• step v) which comprises the following sub-steps:
• the coefficient of determination R2 is used as the measure G.
• the coefficient of determination R2 is familiar to those skilled in the art in the field of statistical analysis of data sets, so further explanation is unnecessary here. It should merely be added that the coefficient of determination R2 is a standard statistical method with which the quality of a linear approximation can be determined.
• sub-step v-4) Identify the security mark if all ratios M i have been rated with the attribute "ratio accepted” and in addition the measure G has been rated with the attribute "measure accepted”, or do not identify (i.e. detect the absence of) the security mark if at least one ratio M i has been rated with the attribute "ratio not accepted” and/or the measure G has been rated with the attribute "measure not accepted”.
• Step v) in particular in conjunction with sub-steps iv-1) to iv-4), can further improve the reliability of the identification of the security marking in a particularly advantageous way.
• more data points for detecting the overall intensity are acquired in a first period immediately following the switching off of the excitation pulse than in a second period immediately following the first period, wherein the first and second periods are of equal length.
• an overall intensity as a function of time i.e., the linear combination I(t)
• the linear combination I(t) is a combination of the time-dependent intensities I ⁇ sub>i ⁇ /sub>(t) of the luminescent substances with the linear coefficients c ⁇ sub> i ⁇ /sub> of the luminescent substances.
• the proportions of the luminescent substances are determined.
• a defined ratio and defined proportions of the luminescent substances result from the given, desired linear combination I(t).
• the respective time-dependent intensities I ⁇ sub>i ⁇ /sub> (t) of the luminescent substances and, if applicable, the respective linear coefficients c ⁇ sub>i ⁇ /sub> are considered and/or evaluated.
• a database containing the time-dependent intensity profiles I ⁇ sub>i ⁇ /sub>(t) allows for the definition of a combination of luminescent substances.
• the relative proportion of each luminescent substance can be defined using the linear coefficients c ⁇ sub>i ⁇ /sub>.
• camouflage agents reduce the luminescence intensity of the luminescent substance, specifically by a constant factor over time. Therefore, depending on the amount of camouflage agent, the linear coefficient c ⁇ sub> i ⁇ /sub> results in a different relative proportion for each luminescent substance.
• Fig. 1 In which the measured time profiles of the intensities of the emitted luminescence radiation from two different luminescent substances A and B are illustrated as examples.
• the intensity I is plotted against time t (in arbitrary time and
• the data points are plotted (intensity units).
• the measured data points are each connected by a solid data line.
• the luminescence radiation of the two luminescent materials A and B is simultaneously excited by a single, identical excitation pulse (flash of light).
• the duration and intensity of the excitation pulse are illustrated by the dashed lines.
• the duration of the flash of light is in the range of 10 ⁇ s to 10 ms and is, for example, 40 ⁇ s.
• the time-dependent intensity profiles of the two luminescent substances differ significantly, with both exhibiting non-monoexponential emission behavior.
• the Bray-Curtis difference between the time-dependent intensity profiles of the two luminescent substances is 0.25, which reflects a low and therefore favored correlation between the two emission profiles.
• the total intensity measurements are taken at defined time points. These measurements can be taken at equidistant or non-equidistant times, the latter being advantageous because, for example, with limited storage resources in the detection sensor, a reduced data set can be selected without significantly degrading the accuracy.
• more measurement points are preferably taken during time periods in which the intensity profiles of the base substances differ significantly, whereas fewer measurement points are taken during the decay phase long after excitation, when the luminescence has already largely subsided.
• the formula (A) used for linear fitting is a linear combination of (sampled) basis vectors Ii(t).
• the running index i identifies the luminescent substances.
• the basis vectors Ii(t) are definable or defined (previously known) time profiles of the luminescent substances used and preferably result from previously determined temporal intensity measurements of the luminescent substances.
• the basis vectors Ii(t) are each weighted by the associated linear coefficients ci.
• the basis vectors Ii(t) correspond to the previously known time profiles IA(t) and IB(t) of the two luminescent substances A and B, as described in Fig. 1 shown.
• the determined linear coefficients c ⁇ sub>i ⁇ /sub> are combined as a 2-tuple (c ⁇ sub>1 ⁇ /sub> , c ⁇ sub> 2 ⁇ /sub> ) and converted into a scale-independent value, a ratio M ⁇ sub> i ⁇ /sub>.
• the ratio of the first linear coefficient c ⁇ sub>1 ⁇ /sub> to the sum of the two linear coefficients c ⁇ sub>1 ⁇ /sub> and c ⁇ sub> 2 ⁇ /sub> is calculated.
• the ratio M ⁇ sub>1 ⁇ /sub> or M ⁇ sub>2 ⁇ /sub> lies within a corresponding, definable or defined (predetermined) range of values W ⁇ sub>1 ⁇ /sub> or W ⁇ sub>2 ⁇ /sub>, respectively.
• the ranges W ⁇ sub> 1 ⁇ /sub> and W ⁇ sub>2 ⁇ /sub> each define a range of variation around the known values.
• the proportions of the luminescent substances A and B in the security marking are determined.
• the attribute "ratio accepted" is assigned if the ratio lies within the corresponding value range, or the attribute "ratio not accepted” if the ratio lies outside the corresponding value range.
• the ratios M1 and M2 lie within the corresponding value ranges W1 and W2 , meaning that, within the margin of error, the correct, i.e., previously known, proportions of the two luminescent substances A and B were determined, each relative to the total amount of luminescent substances A and B, or the previously known ratio (mixing ratio) A/B.
• the goodness of fit of the linear combination I(t) to the time course of the total intensity of the two luminescent substances A and B is determined.
• the coefficient of determination R2 is used, preferably if the coefficient of determination R2 is above the threshold of 0.9, preferably above the threshold of 0.95. In the present case, a coefficient of determination R2 of 0.977 is obtained.
• the security mark is thus uniquely identified (i.e., present) because the ratios M1 and M2 have been assigned the attribute "ratio accepted” and the goodness of fit is above the desired threshold.
• the requirement of both conditions allows for particularly high reliability in identifying the security mark.
• the proportions of substances A, B, and C are, in that order, 20%, 50%, and 30%, respectively, based on the total amount of luminescent substances.
• the mixing ratio A/B/C is therefore 20%/50%/30%.
• the combined intensity was measured with a signal-to-noise ratio of approximately 20.
• the measurement data are in Fig. 4
• the linear coefficients c1 , c2, and c3 are shown, fitted using the least squares method. A good fit of the fit curve to the data points is evident despite the visually noticeable noise component.
• the evaluation yields relative proportions of the luminescent substances A, B, and C, in that order, of 18.8%, 50.7%, and 30.5%, respectively, based on the total amount of luminescent substances.
• ratios M 1 , M 2 it is checked whether the ratios lie within a corresponding, definable or defined (predetermined) range of values W 1 , W 2 , corresponding to the ranges of variation of the known mixture proportions; i.e., the distance of the mixture tuple (c 1 /(c 1 +c 2 +c 3 ), c 2 /(c 1 +c 2 +c 3 )) to the reference coordinates formed from the original mixture composition is determined.
• a tolerance range for example elliptically shaped, is defined in an ab-plane (see Fig. 5 This can vary in extent depending on the shape of the temporal intensity behavior in different directions.
• Fig. 5 The measured mixture tuple is represented by the filled circle, the target value (previously known mixture tuple) by the empty circle.
• the attribute "ratio accepted” is assigned if the ratio is within the corresponding range of values, or the attribute "ratio not accepted” is assigned if the ratio is outside the corresponding range of values.
• the two ratios M 1 , M 2 lie within their respective value ranges W 1 , W 2 , whereby, within the scope of the dispersion, the correct, i.e., previously known, relative proportions of the two luminescent substances A, B, each relating to the total amount of luminescent substances A, B, C, were determined.
• the security marking has the previously known composition, thus identifying the security marking.
• Fig. 6 The upper figure shows the following.
• differently normally distributed noise components were added to the measurement points of a decay curve of a mixture of two luminescent substances with monoexponential decay behavior.
• An evaluation was performed using a linear fitting method according to the present invention and a non-linear fitting method known in the prior art.
• Fig. 6 The lower figure illustrates the evaluation in a diagram where the relative proportion of a luminescent substance is plotted against the noise level.
• the determination of the relative proportion according to the invention shows a lower susceptibility to noise compared to the prior art method.
• the non-linear method there is an approximately linear relationship between the spread of the determined proportion and the noise level within the considered noise level interval.
• linear fitting method shows stability with a spread of 0.05 (absolute) of the proportion.
• FIG. 7 Figure 1 shows the time behavior of a monoexponentially decaying luminescent substance, which could, for example, be used for counterfeiting.
• FIG. 8 Figure 1 shows a security document 1, for example in the form of a banknote, which has an identification thread 2 with a security feature 3.
• the security feature 3 can be designed as described above.
• the invention offers significant advantages over prior art evaluation methods with non-linear fitting, in which decay times are used as model parameters in addition to the amplitudes of the temporal intensity spectra.
• the method according to the invention with its predetermined temporal behavior (especially decay curves) for the luminescent substances used in combination, enables a much faster and more stable evaluation (i.e., faster convergence behavior of the fitting routine) for both clean and noisy intensity measurements.
• Quantitative evaluation results in a computation time reduction of approximately three orders of magnitude compared to prior art non-linear fitting, which illustrates the increase in efficiency with regard to evaluation speed.
• a fast evaluation method is essential, for example, for analysis on high-speed banknote processing machines with banknotes moving at speeds of up to 12 m/s, since these essentially determine the processing speed.

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• 2016
  • 2016-09-14 DE DE102016011180.1A patent/DE102016011180A1/de active Pending
• 2017
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