WO2012143185A1

WO2012143185A1 - Method and device for monitoring security features in security documents

Info

Publication number: WO2012143185A1
Application number: PCT/EP2012/054473
Authority: WO
Inventors: Gustav Martin BARTEL; Jakob Kuen
Original assignee: Bundesdruckerei Gmbh
Priority date: 2011-04-19
Filing date: 2012-03-14
Publication date: 2012-10-26
Also published as: EP2700056A1; CN103493109A; DE102011002181A1; EP2700056B1; CN103493109B

Abstract

The invention relates to a method for examining a security feature in security documents or materials, which security feature turns electroluminescent in an excited state. For this purpose, the electroluminescence of the security feature is initially excited by means of a stimulator. Subsequently, the distance between stimulator and electroluminescent security feature, and the intensity of the emission generated by the electroluminescence are measured. Lastly, the measured intensity is adjusted on the basis of the measured distance in order to generate an intensity value that is scaled to a predetermined basic distance and is distance-adjusted. The invention further relates to a device for carrying out said method.

Description

Method and device for checking

Security features in security documents

The invention relates to a method and a device for checking security features in security documents, wherein the security features comprise at least one electromechanical security feature.

Security documents such as banknotes, personal ^¬ documents, credit cards and the like. are usually provided with certain authenticity features to make it difficult to counterfeit such documents. To counteract the growing technical skills of potential counterfeiters, more and more complex authenticity features have been developed in recent years. For example, it is known to incorporate fluorescent pigments into structural features of banknote printing. Furthermore, special luminescent substances, for example with electroluminescence, are used. Such authenticity features are difficult to imitate in terms of their chemical composition. In addition, it is difficult to determine what is being analyzed in detail during the verification process and how it is being evaluated.

For the production of security documents, a wide variety of printing processes, such as offset printing, Letterset ^¬ pressure, offset coating, flexographic printing, screen printing, thermal sublimation tion, gravure and non-contact printing methods can be used. In order to ensure that the security features have been applied with appropriate quality to the security documents, it is necessary to ^{carry out} appropriate quality controls during the production process. The quality controls should promptly errors be recorded in order to be able to make corrections as soon as possible, thereby reducing the ^rejection quota. Therefore, in the following, security documents are understood as precursors to documents which, for example, occur as materials provided with security features in the production process.

DE 10 2005 000 698 AI deals with a method for testing a value document. In this method, the distance between a detector arrangement and a measuring point is determined in order to regulate the measured value, for example in order to normalize the measured value. The sensor at the measuring point can be a fluorescence sensor.

From DE 103 26 698 Al a method for testing the electrical conductivity or magnetic properties of security elements in security documents is known. The test takes place during the manufacturing process of the

Security document. The test may take place when the security element is connected to the substrate of the security document, or immediately thereafter, before the substrate is further processed or stored. Due to this so-called in-line test, a substantially greater test density of the material produced can be achieved compared to an off-line test.

DE 10 2008 047 636 A1 shows a device for checking the authenticity of a security document, which has at least one security feature that is electroluminescent at an excitation frequency in a high-voltage alternating field. The

Apparatus includes a sensor unit, which an excitation ^¬ module, a condenser and a detector unit beinhal ^¬ tet. The security document is passed through the sensor unit moves, the luminescent light collected by the condenser system and directed to the detector unit, which detects the luminescent light and spectrally evaluated. The excitation module has a slot-shaped opening which ^engages over the ^{path of} movement of the security document to be checked with its opposite boundary surfaces.

The problem with checking a safety feature electroluminescent at an excitation frequency in a high-voltage alternating field is that depending on the

Distance of the security feature from the exciter different intensities of the emission signal can be measured. Even with the same intensity, a smaller intensity value of the emission signal is measured by the exciter at a large distance of the security feature than at a smaller distance. In the previously known solutions no Berücksichti ^¬ supply of the distance of the security feature from the stimulator is done. For this reason, it can lead to strong intensity fluctuations in the measurement, which leads to problems in the evaluation. In a series production, the distance between the exciter and the surface to be examined, which contains the security feature, varies in some cases so considerably that the measurement values for the intensity of the emission vary by up to 400%. If such distance-related disturbance variables are ignored, this leads among other things to the fact that the actual intensity-influencing errors may not be recognized or error-free products are erroneously identified as being defective.

The object of the present invention is thus to provide a method and a device with which the verification of a security feature electroluminescent at an excitation frequency in a high-voltage alternating field is more reliable than in the case of the hitherto known ten solutions can be done. In particular, a method is also to be made available which can be integrated into the production process of a security document in order to be able to reject faulty documents in a timely manner or to be able to initiate appropriate corrective measures for error correction.

To achieve the object of the invention, a method according to the appended claim 1 and a device according to the appended claim 10 are used.

The inventive method for checking electroluminescent security features in security documents preferably comprises the following steps: First, an alternating electric field is generated with the aid of an exciter. Through the alternating electric field, a security document is moved through. The distance between the exciter and the electroluminescent security feature is measured.

Furthermore, the emission caused by the electroluminescence is measured. The intensity value of the measured emission is corrected in dependence on the measured distance, for example by applying a predetermined correla ^¬ tion factor or by recourse to a table of values stored in distance-corrected values, which were determined empirically. The distance-corrected intensity value of the emission thus sets one to a predetermined base distance

normalized value.

One advantage of the solution according to the invention is that the fluctuations in intensity of the measured emission signal that have hitherto occurred due to the influence of the distance between the exciter and the electroluminescent security feature can be compensated or corrected. In comparison with experienced test improves the reliability of the measurement signal. When integrating the method into the production process of a security document, reliable data is thus available promptly, on the basis of which a sorting out of defective products can already take place. Any fluctuations in the production process can be compensated immediately. This also minimizes the effort of a final quality control.

According to a particularly preferred embodiment, the measuring of the distance is performed by a triangulation measurement by means of LED. For the realization of the distance sensor is in particular ^¬ sondere an LED with a large point of light, for example, of about 2 mm, has proven advantageous. By a triangulation measurement of the distance to the to be tested safety docu ^¬ ment can be determined very accurately. Thus, the distance between the exciter and the surface of the security document is known because the position of the distance sensor and the exciter are fixed in the test device. The triangulation sensor preferably used for the measurement operates with an infrared LED in a non-visible wavelength range of about 890 nm.

In an advantageous embodiment, the alternating electric field is generated by at least one electrode pair. The type of excitation remains constant during the novel process, ie, there is no adjustment of Anre ^¬ supply strength. Basically, the person skilled in different types of excitation and devices for the realization are known, which he can select depending on the application.

In typical excitation arrangements, due to the electrode configuration in the exciter and the electroluminescence, the typical security document phosphors show a mathematically describable correlation between the distance security feature exciter and the measured intensity of the luminescence. This correlation can be described by an exponential function with a negative coefficient. It has proved to be useful if the assessment of the gemes senen emission by means of the formula given below

, PD intensity measured _ offset _ corrected * C * Q

FD Intensity corrected = =

d * e ^{~ as} - with

s_mon measured distance value

PD_intensity measured / corrected intensity value

a, b, c, d Constants based on empirical data

(determined with different samples)

Preferably, a zugehöri ^¬ ger distance value is detected for each intensity reading. This may be an absolu ^¬ th value or a relative indication with respect to a base distance which is set under optimum conditions between the security document to be tested and stuff and Anre ^¬ supply source. In practical tests, it has been shown that a particularly good compensation of the intensity fluctuations caused by a different distance can be achieved by the formula given above. In this way, meaningful measurement values are available on the basis of which it can be checked with high reliability whether the security feature has the corresponding properties.

It is advantageous if the security document is moved through the alternating electric field at a maximum speed of 150 m / min. Up to such a speed the measurements can be realized very well. However, it should not be limited to such a maximum speed.

According to a further advantageous embodiment, the values for distance measurement are recorded with a measuring frequency of at least 1 kHz.

In a preferred embodiment, a signal is output if the distance-compensated emission is outside of predefined values. This informs the operating personnel that the security feature no longer possesses the required properties that it must have to verify the security document. In this context, it has also proven to be expedient if the security document is provided with a corresponding marking, by means of which it can immediately be recognized as defective in a later quality control and sorted out.

Furthermore, it is advantageous if the inventive Ver ^¬ go into the production process of a security document is incorporated, whereby it expires after the application of the electroluminescence neszierenden security feature. The PRODUCTION PLANNING ^¬ process may be, for example, a screen printing process. A gängi ^¬ ger application of the method according to the invention are the special papers produced in paper mills, which are manufactured for the production of banknotes. Corresponding safety markings are printed on these papers. The printing is done denominationsabhängig. Usually 4, 5 or 6 tracks are printed at the same time. The Verdruc ^¬ effect is preferably in Endlossiebdruck. After done Printing and verification of the security feature will be the

Paper webs cut to banknote size.

The inventive device for checking security features, which comprise at least one electroluminescent security feature, includes an exciter for generating an alternating electric field, a detector for detecting and evaluating the emission caused by the electroluminescence. The device according to the invention is characterized in that it additionally has a distance sensor for detecting the distance between the exciter and the electroluminescent security feature. The distance sensor is preferably designed as a triangulation sensor. Furthermore, the device also comprises a processing unit for processing the data detected by the detector and the distance sensor for generating a distance-compensated signal.

A common application for the device according to the invention is the screen printing application of electroluminescent

Security features. The device according to the invention is preferably located behind the drying sections.

In the described application, as a rule, up to six pressure marks are simultaneously printed. In order to be able to test these pressure traces simultaneously and independently of one another, six exciters, detectors and distance sensors are preferably used in each case. The emission values detected by the detectors are detected together with the respective distance from the processing unit. From the detected data is determined by the processing unit using the specified to together ^¬ menhang with the process description, the compensation formula standoff-compensated emission. Further advantages, details and developments of the invention will become apparent from the following description of a preferred imple mentation form, with reference to the drawing.

The sole FIGURE shows the dependence of the intensity of the emission caused by the electroluminescence on the distance between the exciter and the electroluminescent security feature. To determine this relationship, a constant sample was measured at least 10 times in the example shown. A calibration of the system took place in the selected example to a nominal distance of 1.5 mm (corresponds to 100%). It was measured at intervals of 1.0 mm, 1.25 mm, 1.5 mm, 1.75 mm and 2.0 mm. This corresponds roughly to the usual

Spacing variations, such as occur in the application described above, the processing of specialty papers produced in paper mills for banknote printing.

The a-curve shown in the figure can be taken from the considerable fluctuations in intensity. At a distance of 1.0 mm, the intensity value is about 225%. At a distance of 2.0 mm just 40% are measured. Through this strong fluctuations can cause problems in verifying the security feature, since in Abhängigkei, decided by the intensity of the emission, which must exceed a minimum threshold in the relevant color area if the security feature with the required quality ^¬ ty to the security document or its precursor was placed ^¬. This may happen that due to a larger distance between security feature and Anre ^¬ ger too low intensity is measured and as a result, evaluates the quality of the security feature as not suffi ^¬ accordingly and thus erroneously be faulty offsort becomes. In the opposite case, it may happen that at a smaller distance otherwise faulty security feature is rated as sufficient, since the intensity ^exceeds the required minimum threshold by the smaller distance. Faulty security documents can thus not be detected promptly, during the production process, and must be determined with greater effort by a quality control downstream of the production.

The measurements were repeated with the inventive distance compensation switched on. By Abstandskompensa ^¬ tion a measured intensity value is smaller at a large distance - in the example 1.75 mm and 2 - increased in nomina ^¬ lem distance (1.5 mm) divided by 1 and at a low

Distance - in the example 1.25 mm and 1.0 mm - reduced. The result of these measurements can be seen from the b-curve in the figure. The hitherto occurring without distance compensation intensity fluctuations can be largely compensated. The intensity value only fluctuates in the range between 90 and 100%. Thus, a high-quality signal is available, by means of which reliable verification of the quality of the security feature can take place.

In the event that the distance-compensated intensity of the emission is outside the predetermined values, an audible or visual warning signal can be output. The security documents identified as defective can be provided with a corresponding marking so that they can subsequently be sorted out as rejects. The operating ^¬ personnel can initiate corrective actions in response to the warning signal to adjust, for example, the addition of the electroluminescent pigments. In practice, there is currently a manual intervention in the Printing process, for example, the level of the screen is checked, cleaned the screen or corrected any imbalances in the printing. Likewise, however, an automatic ^¬ catalyzed correction is possible, so that in response to the determined ^¬ detected measured value - in particular if it is outside predetermined limits - to be applied in the production process subsequent to security documents amount of the security feature is adjusted.

The person skilled in the art will recognize that implementation of the details of the excitation source for excitation of the luminescence is not important. Likewise, the nature of the to be tested

Security documents or materials of minor importance.

Claims

claims

A method of verifying an electroluminescent security feature in a security document or material upon excitation, comprising the steps of:

- exciting the electroluminescence of the security feature with the aid of an exciter;

Measuring the distance between the stimulator and the electroluminescent safety feature;

Measuring the intensity of the emission caused by the electroluminescence;

- Correcting the measured intensity as a function of the measured distance, one to a predetermined

Basis distance normalized, distance corrected intensity value to form.

2. The method according to claim 1, characterized in that the measuring of the distance is effected by a triangulation measurement.

3. The method of claim 1 or 2, characterized in that the excitation of the electroluminescent security feature takes place at least at an excitation frequency in an alternating electric field through which the security ^¬ document is moved through. Method according to one of claims 1 to 3, characterized in that the evaluation of the measured intensity by means of the following formula:

π _{Γ T} PD Intensity measured offset corrected * C * e ^{~ &} * ^h

FD Intensity corrected = =

- d * e ^on

With

s_mon measured distance value

PD_intensity measured / compensated intensity value a, b, c, d Constants based on empirical data

A method according to claim 3, characterized in that the security document is moved at a maximum speed of 150 m / min by the alternating electric field.

A method according to claim 5, characterized in that the values for the distance measurement are recorded with a measuring frequency of at least 1 kHz.

Method according to one of claims 1 to 6, characterized in that a signal is output when the

normalized intensity value is outside predetermined limits.

8. The method according to any one of claims 1 to 7, characterized in that it is integrated into the production process of a security ^¬ document, wherein it expires after the application of an electroluminescent security feature.

9. The method according to claim 8, characterized in that the amount of electroluminescent security feature to be applied is adjusted for subsequent in the production process safety documents, depending on the normier ^¬ th intensity value, especially if this is outside the predetermined limits.

10. The method according to claim 8 or 9, characterized in that it is a screen printing process in the production process.

11. Device for checking an electroluminescent security feature in security documents or

materials, with an exciter for generating an electric alternating field for exciting the electroluminescent de security feature, a detector for detecting an intensity value of the caused by the electroluminescence emission, characterized in that it further comprises a distance sensor for detecting the distance between the exciter and electroluminescent security feature and a processing unit which applies the detected intensity value to a correction factor formed in consideration of the detected distance to form a distance-corrected intensity value.