JP2004538586A - Anti-counterfeit marking of objects and method of identifying the marking - Google Patents

Abstract

The present invention relates to anti-counterfeit marking of objects such as check cards, bills, labels and the like. The anti-counterfeiting marking includes a transparent plastic film (1) having first and second surfaces, whereby a plurality of films are applied to the second surface. When viewed from the first surface, the colors of the plurality of films change depending on the viewing angle, and the plurality of films include an absorbing layer provided on the second surface, a spacer layer (3) overlapping the absorbing layer, and the spacer. It is formed from a mirror layer (2) overlapping the layer (3). In order to improve the identifiability of the authenticity of the marking by the device, the present invention comprises the absorbing layer with metal clusters (4).

Description

【Technical field】
[0001]
The invention relates to a forgery prevention marking according to the preamble of claim 1. The invention also relates to a method for identifying the marking by the device.
[Background Art]
[0002]
Patent Document 1 discloses a similar marking. This marking basically consists of a combination of a holographically structured film and a series of layers that appear different in color depending on the viewing angle. The series consists of an absorbing layer, a dielectric layer, and a reflecting layer. The layer thicknesses of the series of layers are each in the nanometer range. The proposed anti-counterfeiting marking is particularly used for identifying bills, check cards and the like. In such applications, the device must reliably and reliably check the authenticity of the marking. The above marking does not meet this requirement.
[Patent Document 1]
WO 01 / 53113A1 pamphlet [Disclosure of the Invention]
[Problems to be solved by the invention]
[0003]
It is an object of the present invention to provide a forgery prevention marking and a method for identifying the marking, which overcomes the disadvantages of the prior art. In particular, the present invention provides an anti-counterfeiting marking that can be reliably and reliably verified by an apparatus. It is a further object of the present invention to provide a method for identifying such anti-counterfeiting markings.
[Means for Solving the Problems]
[0004]
The above object is achieved by the features of claims 1 and 20. Preferred embodiments are shown in the features of claims 2 to 19 and claims 21 to 26.
[0005]
In the present invention, the absorption layer includes a metal cluster. As a result, a situation where the device can confirm the authenticity of the marking can be effectively obtained. The absorption layer formed of metal clusters produces a very characteristic absorption spectrum due to unexpected changes in refractive index and changes in absorbance with wavelength. For example, a specific peak caused by the metal cluster, and / or the movement of the peak, and / or the shape of the peak can be measured. Furthermore, the metal clusters, due to their extreme absorption coefficients, give rise to particularly high peak intensities in the absorption spectrum compared to conventional unstructured absorption layers. In conventional unstructured absorber layers, absorption is only slightly dependent on the angle in a wide angular range, as is well known. It has been found that the use of a structured absorber layer comprising metal clusters according to the invention essentially exhibits substantially stronger angle-dependent absorption. As a result, the absorption spectrum of the anti-counterfeiting marking according to the invention changes in an unexpected manner and can be confirmed by the device when measured at different angles. The above-described characteristics of the anti-counterfeiting marking enable the device to reliably and reliably verify authenticity.
[0006]
It has proven useful for the clusters to form discontinuous islands in at least one spatial direction of less than 100 nm, preferably of 5 to 35 nm. The thickness of the spacer layer, which is preferably dielectric, is appropriately selected such that the absorption of visible light incident on the cluster layer is maximized.
[0007]
As a further configuration feature, it is useful that the series of layers has an absorption of at least 60%, preferably 80%, particularly preferably 90% at a viewing angle of 45 ° in the wavelength range from 300 to 800 nm. It turns out that. This allows the device to reliably and reliably identify anti-counterfeiting markings.
[0008]
The cluster is preferably formed from one metal selected from gold, silver, platinum, palladium, tin, aluminum, copper, and indium.
[0009]
According to a further preferred embodiment, the cluster layer can not only be firmly adhered to the spacer layer, but also can be detachably adhered to the spacer layer. In addition, the spacer layer may be firmly adhered to the mirror layer, and may be detachably adhered to the mirror layer. These proposed configurations allow a reversible separation of the series of layers. On the other hand, in the opposite case, it is also possible for the series of layers to adhere reversibly at the proposed separation surface. This allows the anti-counterfeit marking to be visible only when reading.
[0010]
For the spacer layer, it has proven useful if its thickness is between 40 and 2000 nm. The spacer layer is a metal oxide, a metal nitrite, a metal oxynitrite, a metal carbide, in particular, a silicon oxide, a silicon carbide, silicon nitrite, tin oxide, tin nitrite, aluminum oxide, aluminum nitrite, a polymer, In particular, polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyurethane (PU), polyimide (PI), polystyrene (PS), polymethacrylate (PMA), polyvinyl alcohol (PVA), polyacrylate (PA), It may be made of one material selected from nitrocellulose (NC) and polyethylene terephthalate (PET).
[0011]
According to a further preferred embodiment, said membrane has a thickness of 5-100 μm. The membrane may be made from polyethylene terephthalate. In a particularly preferred embodiment, the first or second surface of the film is a structure that produces a holographic effect. The structure producing the holographic effect may be in the range of 0.1 to 1.0 μm. This preferred embodiment provides a holographically structured film with anti-counterfeit color marking. The authenticity of this marking can be identified by the device.
[0012]
According to a further feature of the configuration, the mirror layer may be applied to a carrier film. Further, for example, an adhesive layer can be applied to the carrier film by a lamination method. Thereby, the forgery prevention marking formed as described above can be attached to the object to be marked.
[0013]
The adhesive layer is conveniently made from either a pressure sensitive adhesive or a hot melt adhesive. The adhesive layer is effectively covered with a peelable protective film. Thus, the forgery prevention marking can be easily fixed to the object to be marked.
[0014]
According to a further preferred embodiment, the series of layers applied to the second surface may be a laminate of flakes contained in a transparent matrix. The laminate of flakes may float in a regular array, for example, in a transparent plastic matrix. The laminate of flakes may be applied to the membrane dispersed in a clear plastic varnish.
[0015]
The series of layers, starting for example from a cluster layer, is preferably applied directly to the surface of the film by a coating process. In this coating process, it is found to be effective if the film is wound up using a coating device and guided continuously or semi-continuously. On the other hand, in the case of discontinuous coating, for example, in the case of direct coating on a product, an increase in unit price is expected, and a coating method such as a vacuum coating method is relatively economically used in the continuous mode. In this case, a reflective film is particularly suitable. This is because if a reflective coating is used, the mirroring required to produce the characteristic color effect can be achieved at least in part by the surface to be marked.
[0016]
When the distance between the film and the cluster layer is less than 2 μm, the color forming the marking becomes visible. Therefore, the thickness of the spacer layer is preferably 20 to 2000 nm. In the three methods described above, they are advantageously applied in structured form. The structuring may be a structure present in the surface in the form of a string, a pattern (eg, a barcode), or a diagram (eg, a logo). However, an embossed structure may be used. In this case, the markings appear in different colors. By applying a thin, preferably polymeric, layer using a non-vacuum-based method, the above-described relief-shaped spacer layer can be easily fabricated.
[0017]
According to a further construction feature, an inert protective layer transparent to electromagnetic waves may be applied to the cluster layer. This protective layer is used to protect against mechanical damage and contamination. However, this protective layer affects the characteristic color spectrum in a specific manner. As a result, security against counterfeiting of the markings is increased due to the increased complexity of the layer structure.
[0018]
The protective layer may be made from one of the following materials that are transparent to electromagnetic waves: polymers, metal oxides, metal nitrites, metal oxynitrites, metal carbides, metal fluorides, especially Silicon oxide, silicon carbide, silicon nitrite, tin oxide, tin nitrite, aluminum oxide, aluminum nitrite. These materials are substantially chemically inert and do not react to moisture.
[0019]
According to a further architectural feature, the series of layers produced is produced, at least to some extent, by thin-layer technology. In this case, PVD, CVD, or the like is particularly suitable. Alternatively, a series of layers may be deposited using a solution by a wet chemical method. For this, reference is made to WO 98/48275, the disclosure of which is incorporated herein by reference.
[0020]
According to a further preferred embodiment, the membrane coated with a series of layers is processed to form an adhesive or laminate label. For this purpose, the membrane is provided on one of two sides, an adhesive layer or a double-sided adhesive film or a laminate layer. According to an exemplary application, the layer system thus produced is then applied to a siliconized substrate with the adhesive layer on the bottom. The layer system can then be drilled or cut into the desired shape without affecting the stability of the siliconized substrate. The excess can then be stripped off, so that the layer system in a sticky or stackable form can be applied to the various products in an automated form from dispensing edges.
[0021]
Said anti-counterfeiting markings can in particular be used on membranes for processing check cards, banknotes, for example labels for valuables or their packaging and the like. In this case, a spacer layer having a predetermined thickness is applied to the mirror layer adhered to the film. Further, a metal cluster layer is applied to the spacer layer. Since such a marking is permanently visible, it has high anti-counterfeiting properties.
[0022]
The anti-counterfeit marking may also have a spacer layer of a predetermined thickness applied to the cluster layer adhered to the film and a mirror layer provided thereon. Since such markings are permanently visible through the membrane, they are also highly anti-counterfeit.
[0023]
The anti-counterfeiting marking may also include a mirror layer adhered to the film and a spacer layer of a predetermined thickness. Such markings are initially invisible. The cluster layer may be applied to a further film as a substrate, for verification purposes or to make the markings visible. It may be located at a predetermined distance from the first layer.
[0024]
The film to be marked can be, for example, a plastic (eg, polycarbonate, polyurethane, polyethylene, polypropylene, polyacrylate, polyimide, polyvinyl chloride, polyepoxide, polyethylene terephthalate, etc.) or a metal (eg, aluminum, gold, silver, copper) , Iron, stainless steel, etc.).
[0025]
If the film to be marked is already made of a material that reflects electromagnetic waves (eg, metal) or is coated with such a material, the mirror layer can be formed by the film itself.
[0026]
Since the film to be marked can be printed before being coated, the optical effect of the marking layer system can be affected by interaction with the printing ink in an unpredictable manner. According to the invention, it is found to be an advantageous form if the layer reflects electromagnetic waves and the cluster layer exhibits a reflection of less than 50% over at least part of the visible spectrum.
[0027]
In general, additional information can be recorded on the marking surface by using a printing method. As a result, it is also possible to obtain a unique marking. Such customization of the marking can also be achieved by subsequent printing of the marked surface with more widely used printing methods (laser printers, ink jet printers, etc.).
[0028]
The membrane to be marked may also comprise a hologram. The marking may be effective if all the marking layers together absorb less than 90% of the incident light, so that the underlying hologram structure can still be easily detected. Further, the above markings may also be provided directly on or near the surface of the embossed hologram. As a result, the hologram has anti-counterfeiting properties and is readable by the device.
[0029]
Further, the present invention provides a method for identifying anti-counterfeiting markings by the device. The method includes the steps of: a) recording the spectrum of light reflected on the anti-counterfeiting marking at a predetermined viewing angle; and b) (i) the location of one or more absorption peaks characteristic of the marking within a predetermined spectral range. And / or (ii) measuring values for determining shape and / or (iii) intensity; and c) replacing the values of (i)-(iii) measured in step b with predetermined corresponding values. Comparing; and d) identifying the marking using the comparison result.
[0030]
The measurement of the value for determining the characteristic absorption peak is performed within a predetermined spectral range according to step b. Here, the spectral region in which the absorption peak characteristic of the marking is expected is appropriately selected. If no absorption peak occurs within this predetermined spectral range, further steps for identification may be omitted. Steps c and b provide high identification security.
[0031]
It has proven useful to record the spectrum at a viewing angle of 5 ° to 50 ° (based on the normal to the surface), preferably at 15 ° to 40 °. Particularly pronounced absorption peaks are observed in this range. Further, it is useful to use the symmetry of the absorption peak as a function of detecting the presence of the absorption peak caused by the cluster layer. The absorption spectrum produced by the cluster layer is partly clearly asymmetrically formed.
[0032]
As another discriminating function, the absolute intensity of the absorption peak is measured. This is significantly higher than the absorption peak of a series of layers made according to the prior art.
[0033]
The light illuminated by the marking may be generated by an incandescent, laser, fluorescent, light emitting diode, or xenon lamp. In this case, the reflected light is particularly suitable for measuring the absorption spectrum. To enhance the security of identification, reflection spectra at various viewing angles may be recorded to identify the marking.
[0034]
Further, in order to ensure the authenticity of the marking, the marking may be identified only when the measured values (i) to (iii) are within a predetermined value range around the corresponding value.
[0035]
For further architectural features of the method of the invention, reference is made to the preceding description relating to anti-counterfeiting markings.
BEST MODE FOR CARRYING OUT THE INVENTION
[0036]
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings.
[0037]
In the markings shown in FIGS. 1 to 5, the mirror layer that reflects electromagnetic waves is indicated by reference numeral 2. For example, this layer can be a thin film of aluminum. However, the mirror layer 2 may also be a layer formed of metal clusters and is applied to the film 1. The membrane 1 can be a membrane to be marked. The inert spacer layer is shown at 3. The cluster layer is indicated by reference numeral 4.
[0038]
2 and 5, the second film for visualizing the marking is denoted by reference numeral 5.
[0039]
In FIG. 3 to FIG. 5, the adhesive layer or laminate layer provided for further processing of the film marked for preventing forgery is indicated by 6. The change in reflected light that produces a characteristic color spectrum compared to the incident light is shown in FIGS. 3 and 4 as a gray step change in the arrow.
[0040]
In the markings shown in FIGS. 1 and 3, the cluster layer 4 is applied to the spacer layer 3. In this case, the spacer layer 3 is applied to the mirror layer 2. 1 and 3, the mirror layer is applied to the film 1.
[0041]
In FIG. 4, a cluster layer 4 is applied to the film 1 first, then a spacer layer 3, then a mirror layer 2, and finally an adhesive or laminate layer 6 is applied.
[0042]
In the markings shown in FIGS. 2 and 5, only the optically transparent spacer layer 3 is applied to the mirror layer 2, the latter being applied to the film 1. This marking is initially invisible. The marking is visible only when it comes into contact with the second film 5 having a surface coated with a cluster layer 4 formed of metal clusters. Next, a color effect that can be observed through the transparent film 5 occurs. The membrane 5 is effectively made of a transparent material (eg, a plastic such as polycarbonate, polyurethane, polyethylene, polypropylene, polyacrylate, polyvinyl chloride, polyepoxide, polyterephthalate, etc.).
[0043]
The function of the marking is as follows.
[0044]
When light from a light source such as an incandescent lamp, a laser, a fluorescent lamp, a xenon lamp or the like is illuminated on any of the markings shown in FIGS. 1, 3 and 4, this light is reflected by the mirror layer 2. Interaction between the reflected light and the cluster layer 4 formed of metal clusters causes some incident light to be absorbed. This reflected light has a characteristic spectrum that depends on the number of parameters (for example, the optical constant of the layer structure or the shape of the cluster). This marking appears in color. The coloring serves as a check to prevent forgery of the authenticity of the marking. The color impression thus obtained depends on the angle and can be perceived either roughly by the naked eye or by a reader (preferably a spectrometer) operating in reflection mode. Such a reader can, for example, record the coloring of markings from two different angles. This recording may be performed using a detector with two light sources, properly tilted and properly connected, or two readers measuring samples illuminated from two different angles from the two corresponding angles. It is performed using.
[0045]
For the parameters to be maintained for the interaction to take place, reference is made to US Pat. No. 5,611,998 and WO 99/47702, the disclosures of which are incorporated herein.
[0046]
FIG. 6A shows a film with a continuously coated anti-counterfeit mark. This film is partially wound up on a roll.
[0047]
FIG. 6B illustrates a method of making an adhesive label made from the film of FIG. 6A using anti-counterfeit marking.
[0048]
The spectrum of the anti-counterfeit marking of FIG. 1 shown in FIG. 7 was measured using a Perkin Elmer Lambda UV / VIS spectrometer with a reflection insert. FIG. 7 shows that longer wavelength peaks move toward shorter wavelengths as the viewing angle increases. In addition, stationary peaks characteristic of the silver cluster used can be observed. When the viewing angle is less than 45 °, the peak intensity of this marking is about 1 OD, which corresponds to an absorbance of 90%.
[0049]
FIG. 8 shows the quantitative evaluation of the spectrum of FIG. 7, in each case at two different wavelengths. At the wavelength considered, the changed absorbance is observed as a function of viewing angle. The absorption pattern is characteristic of the authenticity of the marking.
[0050]
9 and 10 show the difference of the cluster layer according to the present invention when compared with a conventional absorption layer formed of a metal layer. The spectrum shown in FIG. 9 was measured for a forgery prevention marking having a 75 μm-thick film made of polyethylene terephthalate. A gold layer having a thickness of 100 nm is applied to this film as a mirror layer. The mirror layer is covered with a 270 nm-thick spacer layer made of MgF ₂ . The spacer layer is covered with a layer made of a metal gold cluster and having a thickness of 0 to 12 nm. Each of the above layers was applied to the film by a vacuum coating method. In each case, measurements were taken at a viewing angle of 18 °.
[0051]
For comparison, FIG. 10 shows the absorption spectrum of an absorption layer made of gold, calculated using the above parameters.
[0052]
9 and 10, it can be seen that in this case, particularly, the cluster layer having a film thickness in the range of 2.5 to 5 nm shows a characteristic absorption peak that shifts to a higher wavelength. This absorption peak is significantly broadened, and becomes asymmetric in the case of a cluster layer having a thickness of 5 nm. For a cluster thickness of 8 nm, the absorption peak is the same as the wavelength in the calculated spectrum, but still significantly higher. For larger cluster layers, the absorption peak is similar to the absorption peak of the calculated spectrum. This illustrates the fact that in the example shown, starting at a film thickness of about 12 nm, the coating density of the clusters is so high that the formed cluster layer acts at least as an optically continuous metal layer. ing.
[0053]
The anti-counterfeiting marking proposed in the present invention can be identified with high reliability by the device. For this purpose, the marking is illuminated, for example, with an incandescent lamp. The absorption spectrum of the light reflected from the marking is measured, for example, at a viewing angle of 18 °. For this purpose, a spectral range between 500 and 700 nm is advantageously observed. The absolute intensity of the absorption peak that may occur there is determined. Further, the maximum spectral position is determined. Further, the symmetry of the absorption peak is determined using a predetermined reference point. The determined value is compared to a predetermined range of values determined using a standard to identify the marking.
[0054]
The measurements may be taken at different viewing angles to increase the certainty of the identification.
[0055]
FIG. 11A shows a sample of five stripes (gold clusters formed on an aluminum oxide spacer layer formed on an aluminum mirror) to demonstrate the analysis of the device evaluation. At about 45 °, all five stripes exhibit a bluish color. The difference between the stripes is whether or not the stripes are barely or not visible in the gray-step mode.
[0056]
FIG. 11B shows the measured spectra of the five stripes of FIG. 11A, which were measured using a manually operated two-channel spectrometer. If the data for fringe 3 is stored as the original, fringes 1, 2, 4, and 5 are detected as counterfeits in software-assisted evaluation of the data from the two-channel spectrometer.
[Brief description of the drawings]
[0057]
FIG. 1 is a schematic cross-sectional view of a first marking that is continuously visible. FIG. 2 is a schematic cross-sectional view of a first marking that is not continuously visible and a second film that is suitable or provides visibility for confirmation. 3 is a schematic cross-sectional view of a continuously visible first marking that can be laminated or adhered. FIG. 4 is a schematic cross-sectional view of another continuously visible second marking that can be laminated or adhered. FIG. 6A is a schematic cross-sectional view of a first marking that is not continuously visible, stackable or bondable, and a second film that is suitable or provides visibility for confirmation. FIG. 6B shows an adhesive label made from the strip of FIG. 6A. FIG. 7 shows the absorption spectrum of anti-counterfeiting markings at various viewing angles. FIG. 8 shows the absorption spectrum at various wavelengths. Fig. 9 shows the quantitative evaluation of the spectrum shown in Fig. 7. Fig. 9 shows the measurement of the absorption spectrum of anti-counterfeit marking using metal cluster layers of different thicknesses. Fig. 10 shows the use of metal layers of different thicknesses. FIG. 11A shows a calculated absorption spectrum of the markings. FIG. 11A shows five anti-counterfeiting markings applied to an aluminum substrate, which cannot be clearly distinguished by eyes. Figure showing measured absorption spectrum of anti-counterfeit marking of book [Explanation of symbols]
[0058]
REFERENCE SIGNS LIST 1 film 2 mirror layer 3 spacer layer 4 cluster layer 5 second film 6 adhesive layer

Claims (26)

Forgery prevention marking of objects such as check cards, bills, labels, etc.
A transparent film (1) made of plastic, having first and second surfaces;
A series of layers provided on the second surface, the colors appearing differently depending on a viewing angle;
An absorbing layer (4), a spacer layer (3) overlapping the absorbing layer (4), and a mirror layer (2) overlapping the spacer layer (3), forming the series of layers;
Anti-counterfeiting marking, characterized in that said absorbing layer comprises metal clusters (4). The anti-counterfeiting marking according to claim 1, characterized in that the clusters (4) form discontinuous islands of less than 100 nm, preferably 5-35 nm, in at least one spatial direction. The thickness of the spacer layer (3), which is preferably dielectric, is selected such that absorption of light incident on the cluster layer (4) is maximized. Anti-counterfeiting marking as described. 2. The series of layers, characterized in that they have a maximum absorption of at least 60%, preferably 80%, particularly preferably 90%, at a viewing angle of 45 [deg.] In the wavelength range from 300 to 800 nm. 3. The forgery prevention marking according to any one of 3. The cluster (4) is formed from one kind of metal selected from gold, silver, platinum, palladium, tin, aluminum, copper, and indium. Anti-counterfeit marking. The anti-counterfeit marking according to any of the preceding claims, characterized in that said cluster layer (4) is rigidly or removably adhered to said spacer layer (3). 7. Anti-counterfeit marking according to any of the preceding claims, characterized in that the spacer layer (3) is rigidly or detachably adhered to the mirror layer (1). The forgery prevention marking according to any one of claims 1 to 7, wherein the spacer layer (3) has a thickness of 40 to 2000 nm. The spacer layer (3) is made of metal oxide, metal nitrite, metal oxynitrite, metal carbide, particularly silicon oxide, silicon carbide, silicon nitrite, tin oxide, tin nitrite, aluminum oxide, aluminum nitrite. , Polymers, especially polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyurethane (PU), polyimide (PI), polystyrene (PS) or polymethacrylate (PMA), polyvinyl alcohol (PVA), polyacrylate ( The forgery-preventive marking according to any one of claims 1 to 8, wherein the marking is made of one material selected from PA), nitrocellulose (NC), and polyethylene terephthalate (PET). The forgery prevention marking according to any one of claims 1 to 9, wherein the film (1) has a thickness of 5 to 100 µm. The forgery-preventive marking according to any of claims 1 to 10, wherein the membrane is made of polyethylene terephthalate. The anti-counterfeit marking according to claim 1, wherein the first or second surface of the film has a structure that produces a holographic effect. 13. The forgery-preventive marking according to any of the preceding claims, wherein the structure producing the holographic effect is in the range of 0.1 to 1.0 [mu] m. The forgery prevention marking according to any of the preceding claims, wherein an adhesive layer is applied to the mirror layer (2). The anti-counterfeit marking according to any of the preceding claims, wherein the mirror layer (2) is applied to a carrier film (6). The anti-counterfeiting marking according to claim 1, wherein an adhesive layer is applied to the carrier film. 17. The anti-counterfeiting marking according to any of the preceding claims, wherein the adhesive layer is made of either a pressure sensitive adhesive or a hot melt adhesive. The forgery prevention marking according to any one of claims 1 to 17, wherein the adhesive is covered with a peelable protective film. 19. The anti-counterfeit marking of any of claims 1 to 18, wherein the series of layers applied to the second surface is a laminate of flakes contained in a transparent matrix. A method for identifying a forgery prevention marking according to any one of claims 1 to 19, by an apparatus,
a) recording a spectrum of light reflected on the anti-counterfeiting marking at a predetermined viewing angle;
b) measuring a value within a predetermined spectral range for determining (i) the position and / or (ii) the shape and / or (iii) the intensity of one or more absorption peaks characteristic of said marking. When,
c) comparing said values (i) to (iii) measured in step b with predetermined corresponding values;
d) identifying the marking according to the comparison result. The method according to claim 20, characterized in that the spectra are recorded at a viewing angle of between 5 and 50, preferably between 15 and 40. 22. The method according to claim 20, wherein the symmetry of the absorption peak is used as a feature for detecting the presence of an absorption spectrum caused by the cluster (4). 23. The method according to any of claims 20 to 22, wherein the absolute intensity of the absorption peak is measured. 24. The method according to any of claims 20 to 23, wherein the marking is identified only when the measured values (i) to (iii) are within a predetermined value range around the corresponding value. the method of. The method according to any of claims 20 to 24, wherein the light illuminated by the marking is generated by an incandescent lamp, a laser, a fluorescent lamp, a light emitting diode or a xenon lamp. The method according to any of claims 20 to 25, wherein the markings are identified by recording the reflection spectra at different viewing angles.

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