DE3121523C2 - - Google Patents

Description

The invention relates to a security Authenticity features in the form of luminescent Substances and a method for determining authenticity.

Under the name "security" here Banknotes, check forms, stocks and stamps as well as ID cards, credit cards, check cards, Passports, tickets and other documents and Documents understood.

Securing securities against counterfeiting with luminescent substances is already known for a long time. Already in DE-PS 4 49 133 from 1925 and DE-PS 4 97 037 from the Years 1926 brought the introduction of luminescent Substances described in securities, where the luminophores with ultraviolet or others invisible rays are excitable and visible Emit area.

In US-PS 34 73 027 and 35 25 698 are luminophores and their use as coding colors the basis of rare earth doped Host lattice, which optionally coactivates are described, in which the suggestion in UV range and short-wave visible range and the emission in the visible or IR range take place, the emissions in the IR range to expand the usable spectral range be used.

DE-OS 29 03 073 describes a coactivated with neodymium and ytterbium Phosphor that u. a. can also be excited by infrared radiation is and also emits in the infrared wavelength range. This phosphor can e.g. B. for an optical card reader or the like are used and should stand out distinguish a high emission intensity. With this substance it is an oxysalt phosphor that acts as an activator Contains ytterbium and neodymions. With this combination will have high emissions activity near Reaches 980 nm, which allows a good adjustment to the sensitivity range a silicon photodetector is achieved.  

The rare earth luminophores described in DE-OS 25 47 768 are excited in the IR range and emit in the visible range.

The use of luminophores for protection of securities is also in DE-OS 15 99 011 described.

The state of the art in terms of protection of securities with luminescent substances can be summarized in that such Luminophores were selected whose emissions were in proportion large spectral distance from the excitation is done to ensure that the emission characteristics without the disturbing influence of the excitation light can be determined.

There are also numerous in the patent literature Suggestions for the modification of luminophores, for example by combining them with other substances or their coating and wrapping, for a variety of purposes including changing the spectral ranges made.

For example, the chemical is proposed Resistance of luminophores through To improve sheathing with certain substances. With fluorescent screens becomes multi-colored Representation of pictures a part of the phosphors covered with a barrier layer. In the  Manufacture of cathode ray tubes for color television receivers it is known the phosphors with pigments to coat the Increase contrast.

To improve the image of screen tubes it is also for color television receivers known, undesirable emissions of the phosphors suppressed by pigment coating. In this regard, for example, on the DE-OS 27 54 369 and the US-PS 41 52 483 pointed out will.

It is also known, for example from the GB-PS 14 84 471, the excitation area of a Luminophors by combination with a second Expand luminophore.

In DE-OS 21 02 120 is also the casing of luminophores with dielectric multiple coatings described to be part of the emission spectrum to suppress and that way to increase the intensity at other wavelengths.

DE-OS 15 99 011 has already proposed Luminophores used to hedge Identification cards and the like are used be covered with a foil to put on this way to avoid hedging can be seen with the naked eye.  

Finally, it is known from GB-PS 11 86 253 Records with luminescent substances partially with impermeable to the emission radiation To mask dyes to make certain Characters, such as letters, represent can.

When securing securities with authenticity features in the form of luminescent substances have the numerous proposed for different purposes No modifications of the luminophores Application found. As stated above the endeavor was to provide authenticity features for Rather, the selection of suitable securities Luminophores, their excitation and emission have a large spectral shift, for identification without interference from the excitation light as simple and safe as possible.

A major disadvantage of those used in securities Luminophores is therefore that Luminescence with standard devices can be determined and from the luminescence characteristics on the presence of certain Luminophore can be closed. However, it would be more advantageous if the luminescence is achieved using conventional means would not be detectable at all.  

The invention is based on the object Security with authenticity in the form of to create luminescent substances which the luminescence with usual means not is observable.

The invention is based on the knowledge that that this problem can be solved that the security with such luminophores is equipped, the emission is only spectral show near the excitation area so that the emission sets in the excitation light.

The invention relates to a security with luminescent authenticity features, the is characterized in that at least one Part of the luminescent features only excitable in a narrow wavelength range are and in this same or narrow also emit adjacent wavelength range.

The invention also relates to a method for determining the authenticity of luminescent Securities containing substances by excitation with electromagnetic radiation and observation of the excitation and / or Emission characteristics, characterized in that is that the excitation of the luminescent Substances spectrally close to the Emission takes place, which is evaluated, as well a device for performing the Procedure.  

In the case of the securities according to the invention luminescent substances used thus exploiting an effect of resonance fluorescence very similar to gases and therefore in the following with quasi-resonance luminescence referred to as.

Resonance fluorescence is that of luminescence phenomenon known from gases that excitation and emission at the same point in the spectrum respectively; it only occurs with low gases Pressure on, because with these the molecules relatively little interact. The one included in the suggestion Energy has no interaction with the surroundings no possibility, partially to flow into other processes. The emission therefore takes place with the same quantum energy, d. H. Wavelength or frequency, like the excitation.

Also rare earth metals that are "diluted" in the host lattice built in, show a similar Effect. Because the optically effective inner shells in the nuclear construction of rare earth metals outer shells are shielded, and because of the diluted installation in the host lattice the interaction with the environment is proportional low. This results in a lot narrowband excitation and emission lines of the Rare earth metal luminophores.  

The quasi-resonance luminescence of rare earth Luminophores is researched for Laser substances known. For example, on the US-PS 32 08 009 be pointed out in the one Solid state laser activated with trivalent ytterbium that is described at 914 to 974 µm is excited and emitted at 1015 µm.

When hedging securities with rare earth Luminophores have so far been preferred such luminophores are used in which the basic lattice and the doping were chosen in this way that in certain wavelength ranges, for example in the UV or IR range the excitation energy by means of "energy transfer" transferred to the rare earth metal ion becomes spectral and this the energy emitted far apart from the excitation.

In contrast, according to the invention Emission in the same narrow wavelength range like the excitation or in spectrally closely adjacent Wavelengths. An "energy transfer" is avoided. Spectrally separated emissions if they occur additionally, by special masking methods suppressed.

In order to achieve the effect according to the invention, the wavelength range, for example, through commercially available Dye filter or colored glasses cannot be dissolved be. Usually this condition is met if the range is about 100 nm wide, preferably about 50 nm and less.  

Suitable luminophores, which also without additional Measures show only quasi-resonance luminescence, can by appropriate choice of suitable Basic grids and active dopings are provided will.

According to the invention, however, one is not on the Selection of luminophores limited by home just show quasi-resonance luminescence because it Such luminophores can also be used according to the invention that are in addition to quasi-resonance luminescence one or more common luminescent emissions show if care is taken to ensure that these undesirable emissions are suppressed.

Suppressing unwanted emissions can be achieved by using masking substances take place that absorb in those wavelength ranges, where the luminophore is an undesirable Emission or an undesirable Suggestion allowed.

Particularly suitable masking substances Dyes and pigments. Preferably become the luminophores with the masking substances encased. One can see the characteristic substances but also by mixing luminescent material and produce masking substance. Another One possibility is to apply the characteristic substance in or on the security and subsequent coating with the masking substance; still a  Another possibility is the introduction of luminescent Doping in host substances, which due to their optical properties simultaneously take on the masking function can.

The safeguards from Securities with luminophores are either below normal lighting, UV lighting or IR lighting visible or with standard equipment make visible as long as it is possible the excitation light and the emission from each other to separate.

As for the property "quasi-resonance" no technical Application is known are also not for it suitable detection devices commercially available. Because of the lack of technical application the corresponding luminophores are also not commercially available. This represents an important one additional safety factor.

This increases the possibility of counterfeiting difficult.

When conventional luminophores are incorporated into securities care must be taken that both the Excitation area as well as the emission area not be disturbed by other additives. At the luminophores used according to the invention on the other hand only needs a narrow wavelength range be kept free in both the suggestion  as well as the emission. This is especially when using the luminophore as Color addition advantageous.

The used in the securities of the invention Rare earth metal luminophores are in the general solvent-resistant and comply all resistance tests prescribed for banknote colors. With less high demands in terms of durability, of course other substances too, not all of these usual requirements in banknote production meet, be used.

There are no filters when detecting the luminescence required the excitation light and emission spectrally separate from each other, d. H. the detection apparatus does not need such parts to contain from which one could conclude which substance is detected.

For the production of safety-related valuable persistence is the persistence the luminophores preferably so to choose briefly that due to the blind time and Recovery time from eye or photoelectric Proof ordering the emission after termination not to take the suggestion without special measures watch is. A further increase in security can be achieved if the quasi-resonance emission moved to invisible spectral ranges becomes.  

Because of the unusual verification procedure and Difficulty for outsiders the spectral range you can see the probability of Discovery of the security feature very low. For less vulnerable applications if necessary to simplify the test device therefore enough, luminophores with a slightly longer persistence and possibly somewhat higher luminescence intensity to use.

The invention is illustrated below by means of examples explained in more detail.

example 1

86 g yttrium oxide Y₂O₃, 7 g europium oxide Eu₂O₃, 40 g sodium carbonate Na₂CO₃, 40 g sulfur S and 20 g potassium phosphate K₃PO₄ were mixed intimately and in a corundum crucible annealed in air at 1100 ° C for four hours.

After cooling, the sintered product was ground, the resulting excess sodium polysulfide dissolved out with water, the residue made of europium-doped yttrium oxysulfide micronized in an agitator ball mill and recrystallized at 500 ° C.

It was obtained as a colorless powder of europium-activated yttrium oxysulfide with the composition Y _1.9 Eu _0.1 O ₂ S and an average grain size of 0.5 μm.

The product showed one under UV radiation red luminescence at 630 nm. This line group is not only with UV light, but also excitable in quasi-resonance.

In order to eliminate the UV excitability, that was Powder together with a UV absorbing Dye in the area of red luminescence however, is permeable, embedded in a synthetic resin.

For this purpose, in a heated kneader with 0.6 l useful content 200 g of the product with 34 g Isophorone diisocyanate, 17 g toluenesulfonamide, 10 g Melamine and 10 g permanent yellow GR 36 L (registered trademark from Hoechst) mixed. The temperature was slowly increased to 140 ° C, with a homogeneous mass arose after 10 minutes with an exothermic reaction with a temperature increase to 200 ° C to one brittle solid polymerized.

The product was kept at 180 ° C for a further 20 minutes held and then after cooling in a pencil mill to a fine yellow powder grind.

The pigment thus obtained showed with excitation UV light no luminescence, but was at 630 nm excitable in quasi-resonance.

The pigment is suitable for mixing in printing inks, the quasi-resonance luminescence is not is affected if one in the resonance range permeable dye, e.g. B. Hansa Yellow, Helio Orange, Permanent red or host violet used is (registered trademark of Hoechst).  

Example 2

100 g of europium-activated yttrium oxysulfide Y _1.9 Eu _0.1 O ₂ S, prepared according to Example 1, were mixed with 10 g of 2,4-dihydroxybenzophenone instead of the dyes mentioned.

When excited with UV light, this mixture showed no luminescence, but it was quasi-resonant excitable red luminescence at 630 nm.

This mixture is completely colorless and suitable is therefore in favor of colorless printing on securities.

Example 3

293 g of lanthanum oxide La₂O₃ and 39.4 g of ytterbium oxide Y₂O₃ were dissolved hot in concentrated nitric acid and precipitated with oxalic acid as oxalates.

The dried mixed oxalate was placed in a crucible transferred from high-purity aluminum oxide Al₂O₃ and Annealed for 24 hours at 1300 ° C.

The product, ytterbium-activated lanthanum oxide, had the composition (La _0.9 Yb _0.1 ) ₂ O ₃ and was colored pure white. After milling on a jet mill, the product was obtained with an average grain size of 1 μm.

The luminophore showed a quasi-resonant excitation Luminescence at 950 nm. In the UV range showed he also has a weak suggestion.  

200 g of the luminophore were then removed with 10 g of m-hydroxyphenyl benzoate C₁₃H₉O₃ mixed.

The mixture showed no luminescence when excited with UV light, but one in quasi-resonance excitable luminescence at 950 nm.

Since the quasi-resonance is only used in the IR and the visible areas of the optical spectrum the luminophore with everyone is not affected any dye or dye mixture combined are provided that the dyes or color mixtures are for the wavelength range from 900 nm to 1000 nm permeable. Color pigments with this property is available in all colors, including colorless and black.

Example 4

94 g calcium carbonate CaCO₃ and 5.8 g thulium oxide Tm₂O₃ were dissolved in hydrochloric acid HCl. With sodium hydroxide solution NaOH was adjusted to a pH of 10 and with a aqueous sodium tungstate solution.

The mixed tungstate obtained was 120 g Sodium tungstate Na₂WO₄ mixed in a crucible transferred from alumina and at four hours Annealed at 1100 ° C.

After cooling, the flux was mixed with water washed out.  

A white powder of the composition Na _0.03 Ca _0.94 Tm _0.03 WO ₄ with an average grain size of 2 μm was obtained.

This thulium activated calcium tungstate has a blue luminescence when excited with UV light at 480 nm and luminescence in the IR at 800 and 1700 nm. The emission at 1700 nm leaves also stimulate in quasi-resonance.

The luminescence at 480 and 800 nm could be by combination with a mixture of suitable absorbent dyes and an IR absorber suppress; a suitable such mixture consists, for example, of the Ni complex Bis-dithio-diketons as IR absorbers and one Dye mixture of 3 parts chrome yellow (registered Trademark of Siegle u. Co.), 3 parts of lithol ruby and 2 parts heliogen blue (registered trademark of BASF).

Since the luminescence that can be excited by quasi-resonance at 1700 nm in the middle IR range, can all be beyond the example given above organic dyes and pigments other than carbon black for suppressing of unwanted emissions.

With the exception of Quasi-resonance even if only the excitation area in the UV, for example using 2,4-dihydroxybenzophenone is suppressed. That is so far advantageous than a completely colorless Hedging substance is available.  

The securities according to the invention can with the luminophores in a variety of ways will. The luminophores can be found in the Printing inks, in paper or in a security thread be introduced.

It is particularly important that the Luminophores with a variety of dyes and pigments can be combined because only a narrow spectral range for excitation and emission must be kept free.

The luminophores can be used, for example, at Production of a dye stored in a resin will; you can also use the masking substances are encased and then be added to the printing ink. Can also the luminophores mixed with the masking substance added to the printing ink or with a Printing ink are shielded such that the Suppression of disturbing suggestions or Emissions from the printing ink itself becomes. Furthermore, it is possible that the characteristic substances inserted into or onto the paper the security thread film are applied. The masking substance can optionally also in a varnish. It also comes considering the ink containing the luminophore to coat the printed image obtained with a color, which contains the masking substance; e.g. B. by overprinting with a corresponding one Printing ink.  

The particular difficulty in proving the quasi-resonance is that the spectral ranges of excitation radiation and emitted luminescence radiation overlap. A separation by filters, as is generally the case usual, is therefore not possible. The possibilities of proof are therefore limited to essential to the evaluation of the cooldown (which, however, is particularly important for quasi-resonance difficult to measure) and the changed direction the luminescence radiation in relation to the Excitation light.

A suitable one for the proof of the cooldown Device is for example in DE-OS 15 24 711. With this device becomes the security to be checked in the characteristics area by a flash lamp of suitable radiation pulsatingly illuminated. The emitted luminescent radiation is broken down spectrally and the different spectral radiation areas are by means of a rotating slit diaphragm in time Order scanned. If quasi-resonance is not is present, you can with this device different cooldowns of the different Determine luminescence because that compared to the Luminescent light more intense by powers of ten Excitation light through optical filters from the detectors is shieldable.  

In the case of quasi-resonance, this is spectral Shielding not possible; a measurement with the device described in DE-OS 15 24 711 therefore fails because of the excitation light Residual current signal, which by the Response and clearing speed of the photoelectric Layer as well as from the RC time of the Measuring electronics is determined.

From the same publication it is also known that generated by a pulsed light source, in its intensity is also a time-dependent luminescence signal into a DC and an AC component to disassemble, the ratio of which is a measure of the Cooldown of a certain luminescent substance is.

A test procedure evaluating the changed Direction of the luminescent radiation in the ratio the excitation light can be used, for example, if the luminescent substances in a Layer of the security are stored optically is higher than the neighboring ones Layers. This condition is, for example through a glass fiber, a plastic fiber or fulfilled a plastic film. The light that in the higher refractive index can be initiated with a suitable opening angle do not leave the shift due to total reflection. If the higher refractive index layer with the invention Luminescent substances equipped, luminescence radiation is excited there, which because of their largely independent of the suggestion Directional distribution proportions outside the total reflection angle has and thus emerge from the shift can.  

These proportions may otherwise be conventional assembled test device determined will.

In Fig. 1, the test principle is shown on such securities. The excitation light is introduced into the longitudinal direction of the glass fibers 14 by the light sources 10 arranged on the side of the security 12 . The glass fibers contain a luminescent substance in a suitable concentration. The glass mass itself can also serve as a kind of "host lattice" for luminescent dopants. The emitted luminescence radiation is non-directional and, to a certain extent, emerges from the glass fiber when the critical angle of reflection is exceeded, as indicated by arrows 16 in the figure. This radiation can easily be measured in a suitable device 11 by means of photodiodes, the excitation radiation, which cannot leave the glass fiber due to the total reflection, being disregarded.

A particularly suitable device for testing a security according to the invention provided with printed feature substances is explained below with reference to FIG. 2.

A coding line 22 is applied to the security 20 in the form of individual fields and is equipped with a luminescent substance according to the invention.

A flash lamp 24 and an array of photodiodes 26 are separated from one another in the device by a light shield (not shown), the latter being arranged such that they can come to lie exactly above the coding fields in the feature area of the security 20 .

Furthermore, a claw 28 is located in the device on a gripper arm and can be used to grasp an edge of the security. The claw 28 is closed by a special electromagnet 29 . The claw 28 is itself attached to the gripping arm 27 , which can be moved in the longitudinal direction by means of a lifting magnet 25 .

When the security 20 is inserted through a slot into the test device, a positioning stop, for example a microswitch or a light barrier, is actuated, which triggers the start pulse for the following processes. The electromagnet 29 closes the claw 28 . The flash lamp 24 , which is located exactly above the coding line 22 , is actuated simultaneously. The claw 28 is moved by means of the lifting magnet 25 and the security area having the coding line is pulled away in a fraction of a second under the flash lamp 24 and brought under the photodiode array 26 such that the coding line of the security is detected by the photodiodes.

The luminescent radiation emitted by the fields 22 during the excitation by the flash lamp has a certain decay characteristic, ie the fields continue to shine for a very short period of time even after the excitation has ended. This "afterglow" is registered by the photodiodes 26 , since the flash lamp 24 and the photodiodes 26 are separated from one another by light protection. It is thus possible to determine the luminescence in spite of the wavelength lying in the same spectral range as the excitation light.

The flash lamp 24 can of course also be replaced by suitable light-emitting diodes. Instead of the claw 28 and the lifting magnet 25 , a transport device operating at a defined constant speed, for example a conveyor belt, can also be provided, with which the security 20 is moved under the flash lamp and the photodiode field. In this case, it is advantageous to use a plurality of photodiode arrays arranged one behind the other in the transport direction. In addition to the mere presence of luminescent radiation, the decay characteristic can also be determined from the ratio of the signals emitted by the photodiodes located one behind the other.

The devices or circuits described are of course not only suitable for the detection of one Quasi-resonance, in which the emission in the spectral range the suggestion, but also for proof any other luminescence with characteristic Cooldown.

Claims (18)

1. Security with luminescent substances as authenticity feature, characterized in that the luminescent substances can either be excited only in a narrow wavelength range of a maximum of 100 nm and also emit in this narrow wavelength range, or excitability and emission outside this narrow wavelength range of 100 nm are suppressed by masking substances . 2. Security according to claim 1, characterized in that the masking substances Dyes, color pigments and IR or UV absorbers or mixtures thereof. 3. Security according to claim 1 or 2, characterized characterized in that the luminescent substances mixed with the masking substances are. 4. Security according to claim 1 or 2, characterized characterized in that the luminescent substances coated with the masking substances are. 5. Security according to claim 1 or 2, characterized characterized in that the luminescent substances overprinted with the masking substances are. 6. Security according to claim 1, characterized in that the luminescent Authenticity features are printed.   7. Security according to claim 1, characterized in that that the luminescent Authenticity features in paper preparation are clogged. 8. Security according to claim 1 or 2, characterized characterized that the luminescent Authenticity features in an optical transparent layer of the security stored are optically higher refractive index than the neighboring material. 9. Security according to claim 8, characterized in that that the optically higher refractive index layer one or more glass fibers, Plastic fiber (s) or plastic film (s) is (are). 10. Method for determining the authenticity of luminescent Securities containing substances according to one or more of the preceding claims by excitation with electromagnetic radiation and observation of the excitation and / or emission characteristics, characterized, that the excitation of the luminescent Substances occur spectrally in the vicinity of the emission, which is evaluated. 11. The method according to claim 10, characterized in that the excitation radiation such in the optically higher refractive index Layer of the security is initiated that in which the excitation radiation is totally reflected and that from the totally reflective Emission radiation emerging from the surface is observed.   12. The method according to claim 10, characterized in that that in the spectral Area or closely adjacent area of excitation the decay behavior of the emission radiation is observed. 13. An apparatus for checking securities with authenticity features in the form of luminescent substances, characterized by a light source arranged in a housing and one or more photodetectors 26 arranged shielded from the light source 24 and a transport mechanism 25, 27, 28 which detects the security 20 within the decay time of the luminescent material is moved out of the area of the light source 24 and brings the feature area of the security 20 with the one or more photodetectors 26 to coincide. 14. The apparatus according to claim 13, characterized in that the light source is a flash lamp 24 or a light emitting diode field which approximately covers the feature area of the security 20 and that the photodetectors of the light source are arranged accordingly, so that several coding fields can be evaluated in the feature area. 15. The apparatus of claim 13 or 14, characterized characterized that the transport device the security continuously with constant defined speed at the speed synchronous controlled light source and the or the photodetectors.   16. The apparatus according to claim 13 or 14, characterized in that the transport device has an electromagnetically actuated claw 28 which grasps the security 20 and transported after exposure from the area of the light source 24 under the photodetectors 26 . 17. The apparatus according to claim 16, characterized in that the light source 24 and the transport device are controlled by a position switch actuated by the front edge of the security 20 . 18. The apparatus according to claim 15, characterized in that multiple photodetectors arranged one behind the other in the transport direction are.