WO2020126065A1 - Security element active in the thz range and method for production thereof - Google Patents

Abstract

The invention relates to a security element for producing security documents, such as bank notes, checks or the like, wherein a first layer is arranged in a first plane (10) in a dielectric (6) which is transparent to THz radiation, said first layer being formed from a layer material which is opaque to THz radiation and forming a first periodic or quasi-periodic line lattice structure (8) consisting of parallel longitudinal slots (20) which produce gaps in the first layer and being invisible to the naked eye, wherein a width of the longitudinal slots (20) is not greater than 1/5 of the period (p), preferably not greater than 1/10 of the period (p), wherein a second layer is arranged in a second plane (12) in the dielectric (10), which second plane is parallel to the first plane (10), said second layer also being formed from a layer material which is opaque to THz radiation and forming a second line lattice structure (14), which is inverse to the first line lattice structure (8).

Description

I work in THz-Bere

Security element and procedure

de ssen manufacture

The invention relates to a security element acting in the THz area for the production of ID cards, cards, passports or documents of value, such as banknotes, checks or the like, which has a lattice structure which cannot be seen with the naked eye, e.g. is formed by a metal layer. The invention further relates to a method for producing such a security element. Finally, the invention further relates to a document of value with such a security element.

Security elements are used to secure documents of value such as banknotes, checks or the like against counterfeiting. There are basically two types of security elements here: hidden security elements that are not easily recognizable for a user of the document of value and usually a mechanical one

Subjected to authenticity checks and open security elements that are recognizable to a user. Holograms are an example of open security elements. However, it is also known to design a security feature in such a way that it is both an open security feature, i.e. a security feature that can be recognized by a user, and a concealed security feature that can usually only be checked with the machine by the unarmed eye and possibly by a user not even noticeable. In addition to holograms, the prior art according to DE 102015009584 A1, for example, combines open security features based on metallized sawtooth structures or color shift inscriptions or embossed structures, which are coated with a thin metal layer, with lattice structures acting in the THz region. These lattice structures have a period of approx. 20 gm - 100 gm and consist of metallized Strips spaced by narrow slits. Such structures can also be overlaid with metallic relief structures. The disadvantage is that the narrow slits in the metal film have to be realized by an additional etching step or by laser demetallization. Since these slots preferably have a width of approx. 1 gm, this process is challenging in industrial production.

In general, security elements for documents of value must meet several requirements. On the one hand, they should be difficult or impossible to reproduce with simple means, i. H. the effort for a one-off production should be as high as possible. On the other hand, production in series production, on the other hand, should involve as little effort as possible.

The invention is therefore based on the object to provide a THz radiation detectable and thus concealed security element which has even more favorable properties in the THz area and requires little additional effort in series production. It should also be particularly advantageous to combine with open security features.

The invention is defined in the independent claims. The dependent claims relate to preferred further developments.

There is provided a security element for producing documents of value, such as bank notes, checks or the like, which has a lattice structure which cannot be seen with the naked eye and which is arranged in a dielectric, opaque layer for THz radiation, preferably a metal layer, is formed, the first layer lying in a first plane and having, for example, a layer thickness between 6 nm and 1 pm. In the first layer there are transparent, adjacent longitudinal slots formed. The first layer is embedded in a dielectric that is transparent to THz radiation. The longitudinal slots are arranged next to one another periodically or quasi-periodically with a period, for example between 8 pm and 200 pm. The width of the longitudinal slots is not greater than 1/5, preferably 1/10, of the period. The slots are preferably at least 5 times as long as the period. A second layer is further arranged in the dielectric in a second plane, which is parallel to the first plane. This is also formed from a layer material which is opaque for THz radiation and has a second line grating structure. This is designed vertically to the first line grid structure and offset by half a period. As a result, the second line grid structure forms longitudinal webs which, when viewed from above, exactly fill the gaps left by the first longitudinal slots in the first layer.

It is thus particularly provided to form the second line grid structure from parallel longitudinal webs, one of the longitudinal webs of the second layer being underneath each of the longitudinal slots of the first layer. The superimposed pairs of longitudinal slots and longitudinal webs each have essentially the same width (i.e. within the scope of manufacturing tolerances, which can be 5-10%, for example), so that the gap filling mentioned is realized.

In a particularly preferred embodiment, the distance between the first and second levels is between 50 nm and 100 pm, particularly preferably between 500 nm and 5 pm. The period is more preferably in the same interval.

Quasi-periodic means that the grating period fluctuates around an average. This fluctuation can preferably last up to half a period, particularly preferably be up to 1/10 period. With quasi-periodic arrangement, periodic structures are covered in particular, in which the period fluctuates due to production. Such quasi-periodic arrangements of slit structures also have an increased TM transmission in the THz range.

In a preferred embodiment, the first and / or the second layer comprises a color shift coating. This improves visual recognition - in addition to the machine evaluability that takes place in the THZ area.

Furthermore, the combinations known from DE 102015009584 Al with security features that are visible to the naked eye are possible. In particular, hologram structures, sub-wavelength gratings with periods between 200 ran and 500 nm, sawtooth structures etc. come into question here. The disclosure content of DE 102015009584 A1 is fully incorporated here with regard to this.

The method for producing a security element generates the security element described. For this purpose, a first layer is arranged in a dielectric transparent to THz radiation in a first plane, which is formed from a layer material that is opaque for THz radiation. It has a periodic or quasi-periodic, first line grid structure made up of parallel longitudinal slots, which cannot be seen with the naked eye, and which produce longitudinal slots in the first layer. A width of the longitudinal slots is not greater than 1/5 of the period, preferably not greater than 1/10 of the period. A second layer is arranged in the dielectric in a second plane, which is parallel to the first plane, and is also formed from a layer material that is opaque for THz radiation. In the second shift a second line grid structure is formed. It is inverted to the first line grid structure and offset by half a period. This in turn ensures that the longitudinal webs, which are formed in the second layer, exactly fill the longitudinal slots in plan view.

The configurations of the security element already mentioned can of course also be implemented in further developments of the method.

Finally, a value document is also provided, which is provided with a security element of the properties mentioned.

The security element according to the invention can be checked in the THz range, since the slot structure is transparent for THz radiation with TM polarization, but opaque for TE polarization or vice versa. Due to the slit structure, the security feature acts as a polarizer that transmits THz radiation with one polarization. If the incident THz radiation is appropriately polarized, a large proportion of this polarization component passes through the security element. The security element can therefore be subjected to a machine authenticity check very easily. A THz radiation source and a THz detector are used for this. Ideally, the THz radiation is polarized, and the security element can also be recognized with unpolarized THz radiation. In this case, a polarizer that acts as an analyzer is then mandatory in front of the detector. The authenticity check can be carried out with a measurement in transmission as well as in reflection. In the exemplary case of transmission, the security element acts as a polarizer, which transmits the THz radiation with TM polarization. If the THz radiation is correspondingly linearly polarized, this component largely passes through the security element and is rization of the analyzer completely detected. If the polarization directions of the radiation source and detector are perpendicular to each other, the trivial case of a hole in the security element can be excluded. This could also be checked visually. If the security feature is rotated, a vertically polarized THz radiation is rotated as it passes through the security element and the analyzer with horizontal polarization can receive the THz signal. By taking two or more different polarization directions, the contrast can be enhanced. The machine authenticity check can thus be carried out both with a parallel orientation of the polarization of the beam source and detector and with a crossed orientation. The rotation of the security feature is a rotation of the security feature in the plane, which is defined by the longitudinal slots lying next to one another periodically or quasi-periodically.

The slit structure cannot be seen with the naked eye, at least for an inexperienced observer and / or in a mere plan view, since the width of the longitudinal slits is not greater than 1/5 of the period. If you lower this upper limit, the slit structure is very difficult or even impossible for an experienced observer who is looking for the slit structure and / or when using special viewing techniques (for example, certain tilting and turning of the security element) . It is particularly preferred that the width of the longitudinal slots is not greater than 1/10 of the period, since the slot structure then creates a particularly well-concealed security feature.

Due to the double structure, which under the slots that are formed in the first layer, longitudinal webs that exactly match the slot width see, the transmission and reflection properties are improved in the THz range.

In a further development, the security element is designed such that the layer comprises a plurality of fields, between which a longitudinal direction of the longitudinal slots differs. The fields therefore have an individual angular orientation of their directions of the longitudinal slots. Such individual fields appear differently bright depending on the rotational position and / or orientation to the THz detector.

The design of the lattice structure in the layer is practically imperceptible to the naked eye. Thus, a potential counterfeiter receives no indication of the presence of such a security feature. The layer differs in reflection and transmission from a layer that is formed without the longitudinal slots. In particular, it is possible to combine the security element with a visually visible structure, e.g. in that the areas of the layer lying between the longitudinal slots are additionally provided with a further security feature which is visible to the naked eye. In this way, the security element has hidden properties that can be seen with THz radiation and additional properties that can be seen with the naked eye, i. H. open security features. The additional security feature perceptible to the naked eye can be, in particular, a metallized hologram, a subwavelength grating with periods from 200 nm to 500 nm, a sawtooth structure and / or a color shift coating.

The manufacturing method according to the invention can be designed in such a way that the described preferred configurations and embodiments of the security element are manufactured. It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the specified combinations but also in other combinations or on their own without departing from the scope of the present invention.

The invention is explained in more detail below by way of example with reference to the accompanying drawings, which also disclose features essential to the invention. Show it:

1 is a schematic representation of a banknote with a security element,

2A to 2D sectional views through the security element of FIG.

1 in various embodiments,

3A to 7B curves to illustrate the effect of the security element of FIGS. 2A to 2D on radiation in the THz range,

8 shows a plan view of an embodiment of the security element with fields of different longitudinal orientation of a structure influencing THz radiation, and FIG. 9 shows various embodiments of a field for coding hidden information with one of the security elements of FIGS. 2A to 2D. 1 shows a top view of a bank note 2 which is provided with a security element 4. In all embodiments, the security element 4 is designed in such a way that it filters radiation in the THz range in a certain way and at the same time is designed such that it cannot be seen by the unarmed eye. The security element 4 thus already provides a covert Si security feature that can be read out with a corresponding detector. So that the security element 4 cannot be perceived visually as far as possible with regard to the structures that make the effect effective in the THz area, so as not to give a potential counterfeiter an indication of the presence of a structure effective in the THz area, the THz structure is in the visible wavelength range almost opaque or at least not recognizable. This does not rule out that the structure is combined or overlaid with a visually transparent structure, as is the case in the embodiments of FIGS. 2B to 2D. The security element 4 can be exposed on both sides (for example when used as a fixed element spanning) and also on one side. It can also be completely embedded in the substrate transparent to THz radiation. Examples of the substrate or the dielectric are paper or plastic.

FIGS. 2A to 2D show a sectional view of the security element 4, which has a dielectric 6 arranged on a carrier (not designated in more detail). In the dielectric 6 transparent for THz radiation, a first line grating structure 8 is embedded, which is constructed from a THz radiation-absorbing coating, which is located in a first plane 10. A second line grating structure 14 is located in the dielectric 6 in a second plane 12 lying parallel to it by a distance h, which is also constructed from a material absorbing THz radiation, preferably from the same material as the first line grating structure 8. The first and the second line grating structure 8, 14 form a bi-layer grating 16. The first and the second line grating structure 8, 14 are formed inverted to each other. The first line grid structure 8 consists of metallic strips 18 which are spaced apart from one another by longitudinal slots 20. This structure is arranged according to a period p. For this purpose, the second line grid structure 14 is inverted. It has longitudinal slots 24 at those locations in which the first line grid structure 8 has the strips 18 and strips 22 at the locations of the longitudinal slots 20. The layer which forms the strips 18 has, for example, a thickness T1, the layer which the strips 22 forms a thickness t2. The strips 18, 22, and thus the line grating structures 8, 14, have a refractive index n and are completely surrounded by the dielectric 6, which preferably and optionally above and below the line grating structures 8, 14 has the same refractive index n. The refractive indices in the dielectric 6 can also vary.

As can be seen, the inverted shape which the second line grid structure 14 has for the first line grid structure 8 has the consequence that the width d of the strips 18 of the first line grid structure 8 corresponds exactly to the width of the longitudinal slots 24 of the second line grid structure 14. The same applies analogously to the width s of the longitudinal slots 20 of the first line grating structure 8 and the strips 22 of the second line grating structure 14. The inverted line grids are also relatively shifted by half a period in the plane 10 or 12 in such a way that a top view of the security element 4 2A (according to the direction of sight in Fig. 2A from top to bottom) a gap-free layer by the stripes fen and 22 is formed.

2A shows that a plane wave falls on the security element 4 at an azimuth angle ph and an elevation angle th. This incident radiation S is partly transmitted as transmitted radiation T tiert and partially reflected as reflected radiation R. The properties of this effect on radiation in the THz range are explained in more detail below with reference to FIGS. 3 to 7.

The embodiments of FIGS. 2B to 2D differ from those of FIG. 2A by the configuration of the strips 18. They are used to additionally generate a visually perceptible effect. Despite this visually perceptible effect, the structure effective in the THz area cannot be recognized. The covert security feature is therefore retained. In this context it is expressly referred to

Reference is made to DE 102015009584 A1, the disclosure content of which is fully incorporated here with regard to the combination of a structure effective in the THz range and a visually perceptible structure.

The structure described above for authenticity detection in the THz area is preferably produced on film substrates and can then be applied, for example, to bank notes 2. However, a metallic reflecting surface is not very attractive to an observer. It is possible to overprint this area. However, it is advantageous to overlay this structure with other security features based on film elements.

Known metallized security features, such as holograms, micromirror arrangements or metallic sub-wavelength grids, are primarily human features that are difficult to check authentically by machine. By superimposing these structures with the THz feature described above, a mechanical check of these structures in the THz area is possible.

An overlay with various known metallized Si security features is therefore advantageous. Such an overlay can with embossed holograms, as shown schematically in Fig. 2B. 2B, the strips of the first line grating structure 8 consist of a hologram structure 26. It is opaque for THz radiation, so that the hidden security property of the security element 4 is retained. Such holograms consist of grating arrangements with periods of approximately 500 nm to 1500 nm. In known embossed holograms, the grating profile has a sinusoidal shape or a rectangular shape with pitch of approximately 100 nm to 300 nm. The structure is metallized over the entire surface. Aluminum, silver or copper with layer thicknesses of approximately 30 nm to 80 nm are preferably used as metals. In this case, the overlay with the THz structure described above means that narrow periodic regions of the embossed hologram or mirror strip lie on the lower level 12. Since the period of the hologram grating is significantly smaller than the grating period of the THz structure, there is no additional interaction in the THz area with this structure. Because the period of the hologram is orders of magnitude smaller than the wavelength of the THz radiation. There is therefore a comparable transmission in the THz range as in the bi-layer grating 16 described above.

In Fig. 2C, the stripes include a color shift coating 28, which can optionally also be applied to the stripes of the second line grid structure 14. The color shift coatings 28, 30 produce a visually perceptible effect. Since they comprise a metal layer or another coating opaque for THz radiation, the effect of the security element 4 as a concealed security feature is also preserved here. The color shift structure consists, for example, of a semi-transparent chrome layer, a dielectric spacer layer, preferably made of silicon dioxide, and a metallic mirror layer located underneath, e.g. B. aluminum. This layer structure is finally designed as a bi-layer structure 16. det. The area of the underlying structure is small compared to the total area. Therefore, the visual impression of these security features is hardly affected by the overlay with the THz structure.

In FIG. 2D, the strips of the first line grid structure 8 are designed as a sawtooth structure 32. So there is an overlay with a saw tooth structure such. B. Fresnel structures. Known sawtooth arrangements have a lateral extent between 1 mhi and 10 mha at a height between approximately 0.3 mih and 4 mih. Such arrangements are used to create movement and spatial effects in reflection. They are either covered with a simple metal layer or they are vapor-coated with a so-called color shift structure in order to additionally create a color effect. The metallized structure is interrupted by the periodic arrangement of the longitudinal slots 20, below which the strips 22 lie on the lower plane. In the THz range, only this combination has an effect on the transmission, since the interaction with the sawtooth structure 32 itself is low.

The superimposition can also be carried out with (optical) sub-wavelength structures. These are 1-dimensional or 2-dimensional periodic gratings with periods between 100 nm and 500 nm, which are metallized. It should be mentioned that so-called metallic moth eye structures, which can serve as an absorbent background, can also be overlaid with the structure explained above. In addition, the metallized ridges are raised instead of recessed as in the above drawings. The transmission in the THz range is identical in this vertically mirrored arrangement. Furthermore, the above-mentioned THz radiation-absorbing coatings are not restricted to a simple metal layer or color shift structures. Other multilayer layers can also be used, as long as they are opaque to THz radiation - either in combination or due to an absorbent component or a layer.

The effect of the security element 4 on radiation in the THz range, that is to say on radiation between, for example, 1 and 12 THz, is explained below using the example of the security element in FIG. 2A. Since the visually perceptible structures of the stripes of the first line grid structure 8 in the embodiments according to FIGS. 2B to 2D have no effect on the effect in the THz range, the embodiments also apply analogously to this.

The following calculations refer to an aluminum grid with a rectangular cross-section. The refractive index of the surrounding dielectric is n = 1.4. 3A-C show the spectral transmission for TM- (Fig.

3A) and TE polarizations (FIG. 3B) and the degree of polarization for a bi-layer grating 16 with webs of different widths s = 2; 4; 6 gm with constant period d = 50 gm. For the frequency 1 THz the transmission with TM polarization is 32%, 43% and 49% for the web width s = 2 gm, 4 gm and 6 gm. For TE polarization the transmission for these web widths is almost zero. The thickness tl = t2 of the coating was 50 nm, the distance between the planes h = 2 gm. The contrast of the transmission between TM and TE polarization is shown in FIG. 3C). The calculated degree of polarization (TTM - TTE) / (TTM + TTE) is plotted here as a function of frequency.

The more these values differ from zero, the stronger the polarization effect of the bi-layer grating 16. It can be seen that the grating in the entire frequency range shown has pronounced polarization properties.

The influence of the height distance h on the transmission behavior in the THz range is now explained. 4A-C show the transmission with perpendicular incidence for an aluminum grid with a period d = 50 gm, s = 2 pm, f = 50 nm for the height spacings 0.5 gm, 1 gm, 1.5 gm and 2 gm The other parameters are identical to those of Figures 3A-C. Again, the figure labeled A shows the transmission for TM polarization, the figure labeled B shows the transmission for TE polarization, and the figure labeled C shows the contrast. Here it can be seen that a variation in the height distance h does not have a significant effect on the transmission behavior in the THz range. The polarization properties are hardly influenced. This means that the process window in series production is not critical with regard to this parameter.

Now the influence of the grating period on the transmission in the THz range is examined. 5A-C shows the transmission for gratings with the periods d = 25 gm, 50 gm, 75 gm and 100 gm. The ratio of the gap width to the period is constant and is s = 0.04 * d. 5A and 5B that the spectral characteristic of the transmission is shifted towards low frequencies for increasing periods. Fig.

5C it can be seen that the polarizing effect of the grating is very good for these periods in the entire spectral range shown. This shows that the transmission characteristic can be adjusted for the desired frequency band by the appropriate choice of the grating period. It should also be mentioned that the transmission or polarization properties shown here are hardly influenced if the lattice profile deviates from the ideal rectangular shape. Therefore, Position of such grids does not have to meet high requirements in order to fulfill the desired transmission or polarization effect in the THz range. The figures here are based on a height of h = 1.8 pm and a thickness of the metal layer (here Al) of t = 50 nm.

6 shows the calculated spectral reflection of a bi-layer grating 16, a simple wire grating and a smooth 60 nm thick aluminum film - in the visible spectral range. All structures are embedded in a dielectric with a refractive index of 1.52. The vertically incident light is unpolarized. The zero-order reflection for both grating types averages around 73% compared to 82% of a smooth 60 nm thick aluminum layer, which is also embedded in a dielectric with n = 1.52. For larger periods, the difference between the reflection on the bilayer grating 16 and a smooth surface is increasingly reduced. This means that a bi-layer grating 16 with periods d> 50 pm can hardly be distinguished from a viewer by a smooth metallic surface. This is all the less the case when such bi-layer gratings 16 are overlaid with other structures such as hologram gratings.

Finally, a metallized embossed hologram, which is overlaid with a bi-layer grating 16, was experimentally analyzed. The structure corresponds schematically to the drawing of Fig. 2B. The structure comprises a 60 nm thick aluminum film, which is embedded in UV lacquer between two PET films. The embossed hologram consists of grids of different azimuthal orientations with periods between 500 nm and 2 pm. The profile shape is sinusoidal. The parameters of the bi-layer grating are: d = 50 pm, h = 1.8 pm, s = 2 pm and 1 = 60 nm. FIG. 7A shows the spectral transmission in the range from 0.1 to 3 THz for TM and TE polarization. The degree of polarization was calculated from this and shown in FIG. 7B. The structure is in here embedded a UV-curable embossing lacquer with a refractive index of 1.4. The measurement confirms the previously presented properties of the bi-layer grating 16. The unexpected high transmission is also present for superimposed grating structures. The blocking effect for TE polarization is slightly lower for this sample. However, this is due to small defects in the sample through which the THz radiation penetrates unhindered. Nevertheless, the degree of polarization of the sample is high. The bi-layer grating 16 superimposed in the hologram can be reliably detected.

As mentioned earlier, the overlays come from the

DE 102015009584 Al (there for another concealed security feature) also comes into question here. The superimposition of a motif with the THz structure described above is explained using the example of FIG. 8. The motif "butterfly" with the number "25" is formed against a background by a metallic embossed hologram. Here, the entire area is overlaid with a bi-layer grid 16. The longitudinal slots 20, 24 are oriented horizontally in the background 34 and vertically in the surfaces 36-42. This security element 4 shows in the THz area a different transmission in the areas 34 on the one hand and 36-42 on the other. The subject in the THz range can be detected accordingly with a location-resolving detector.

Furthermore, this approach can be used to encode information that can be automatically evaluated in the THz area. An example is the coding of the denomination or the value of banknotes, e.g. B. 5, 10, 20, 50 and 100. These numerical values (or other values) can be encoded by differently oriented areas of bi-layer gratings, preferably with areas rotated by 90 °. An example with four fields 46, which are set against a background 48 with a horizontal longitudinal slot direction. FIG. 9 shows a plurality of coding fields 50-56 with a vertical longitudinal slot direction.

The security element 4 can be manufactured on an industrial scale by known methods. The essential steps in the positioning are: a) embossing the structure in UV varnish on foils,

b) full-surface directional metal vapor deposition, the flanks of the webs not being covered with metal,

c) lamination with cover film.

The basic principle corresponds to that of the above

DE 102015009584 Al, the advantage now being achieved that no metal has to be removed in the recessed longitudinal slots 20. The longitudinal slots 20 are formed by the corresponding embossed structure as depressions, and the metal is also deposited in the depressions in order to form the strips 22 there.

As already explained in the general part of the description, the security element can simply be subjected to an authenticity check by examining its polarization properties for radiation in the THz spectral range. Possible devices are shown in FIGS. 13 and 14 of DE 102015009584 A1. The security feature 4 acts as a polarizer that transmits THz radiation with TM polarization. If the THz radiation is correspondingly linearly polarized, this component largely passes through. In order to direct linearly polarized radiation with TM polarization onto the security element 4, the THz source can be followed by a polarizer; this can be omitted if the THz source already emits the corresponding polarized radiation. After passing through the security element 4 z. B. an analyzer is provided, which filters the direction of polarization accordingly for the THz detector. By picking up a signal The contrast can be enhanced in two or more different polarization directions, ie the device is first set in the configuration with the same orientation of source radiation and detector and then with an orthogonal orientation to one another. If the security element has 4 areas with differently oriented slot structures, a spatially resolving detector measures different intensities for the individual areas. This increases the reliability of the authentication of this feature.

For the authenticity check of the security element 4 described above, a THz radiation source and a THz detector are used, which are arranged opposite one another. The security element 4 is located in between and is preferably irradiated approximately vertically. The radiation from the THz beam source is preferably linearly polarized and the detector is also sensitive to polarization. The security element 4 is arranged in such a way that TM polarization is present for at least one area of the bi-layer grating 16 and the THz radiation reaches the detector there almost unimpeded. In contrast, the transmission for the lattice areas is blocked in TE polarization. In an alternative arrangement, the polarization directions of radiation source and detector are perpendicular to one another. So the trivial case of a hole in the security element can be excluded, through which the THz radiation would also pass unhindered. If the THz grating is rotated, a perpendicularly polarized THz radiation is rotated as it passes through and the analyzer with horizontal polarization can receive the THz signal. By recording a signal in two or more different directions of polarization, the contrast can be further enhanced. The THz analysis can be carried out at a single frequency or in a single frequency band as well as for several frequencies or separate frequency bands. The latter two embodiments refine the authenticity check.

Reference list

2 banknote

4 security element

6 dielectric

8 first line grid structure

10 first level

12 second level

14 second line grid structure

16 bi-layer grids

18, 22 strips

20, 24 longitudinal slots

26 hologram

28, 30 color shift layer

32 sawtooth structure

34, 56 background

36-44, 46, 50-56 box

S, T, R radiation

h distance

P period

tl, t2 thickness

n, nM refractive index

th elevation angle

ph azimuth angle

s, d width

Claims

Patent claims 1. Security element for the production of documents of value, such as bank notes, checks or the like, wherein in a transparent for THz radiation dielectric (6) in a first level (10) is arranged a first layer, which consists of a for THz radiation opaque layer material is formed and forms a periodic or quasi-periodic first line grating structure (8), which cannot be seen with the naked eye, from parallel longitudinal slots (20) which create gaps in the first layer, the width of the longitudinal slots (20) not greater than 1/5 of the period (p), preferably not greater than 1/10 of the period (p), d a d u r c h g e k e n n z e i c h n e t that a second layer is arranged in the dielectric (10) in a second plane (12) which is parallel to the first plane (10), which is also formed from a layer material opaque for THz radiation and forms a second line grating structure (14), which is inverse to the first line grid structure (8). 2. Security element according to claim 1, characterized in that the second line grating structure (14) is formed from parallel longitudinal webs (22), wherein under each of the longitudinal slots (20) of the first line grating structure (8) one of the longitudinal webs (22) of the second Line grid structure (14) and the overlying longitudinal slots (20, 24) and longitudinal webs (18, 22) each have essentially the same width (d, s), so that the longitudinal webs (24) of the second line grid structure (14) in plan view on the first level (10) cover the longitudinal slots (20) in the first line grid structure (8). 3. Security element according to claim 1 or 2, characterized in that a distance (h) between the first and second levels (10, 12) is between 50 nm and 100 pm. 4. Security element according to one of claims 1 to 3, characterized in that the period (p) is between 10 pm and 100 mpt. 5. Security element according to one of claims 1 to 4, characterized in that the first and / or second line grating structure (8, 14) a multilayer coating opaque for THz radiation, in particular a color shift coating (28, 30), exhibit. 6. A method for producing a security element for the production of documents of value, such as banknotes, checks or the like, wherein in a dielectric transparent for THz radiation (6) in a first plane (10) a first layer is arranged, which consists of a for THz Radiation opaque layer material is formed and is provided with a periodic or quasi-periodic, first line grating structure (8), which cannot be seen with the naked eye, of parallel longitudinal slots (20) producing gaps in the first layer, the width of the longitudinal slots (20 ) is not greater than 1/5 of the period (p), preferably not greater than 1/10 of the period (p), d a d u r c h g e k e n n z e i c h n e t that A second layer is arranged in the dielectric (6) in a second plane (12) which is parallel to the first plane (10), which is also formed from a layer material opaque for THz radiation and provided with a second line grating structure (14) which is inverse to the first line grid structure (8). 7. The method according to claim 6, characterized in that the second line grid structure (14) is formed from parallel longitudinal webs (22), the first line grid structure under each of the longitudinal slots (20). ture (8) one of the longitudinal webs (22) of the second line grid structure (14) is arranged and the overlying longitudinal slots (20, 24) and longitudinal webs (18, 22) each have essentially the same width (d, s), so that the longitudinal webs (24) of the second line grid structure (14) cover the longitudinal slots (20) in the first line grid structure (8) in a plan view of the first plane (10). 8. The method according to claim 6 or 7, characterized in that a distance (h) between the first and second levels (10, 12) is between 50 nm and 100 pm. 9. The method according to any one of claims 6 to 8, characterized in that the period (p) is between 10 pm and 100 pm. 10. The method according to any one of claims 6 to 9, characterized in that the first and / or second line grid structure (8, 14) have a color shift coating (28, 30). 11. Value document with a security element according to one of claims 1 to 5.