EP2094504B1 - Security element with metallisation - Google Patents

Abstract

The present invention relates to a security element (20) for security papers, value documents and the like, having a substrate (22) and an opaque metallization 24, 26) arranged on the substrate. According to the invention in the security element is provided, that the metallization (24, 26) comprises a first opaque metal layer (24) and a second opaque metal layer (26) arranged above the first metal layer (24), and that the two metal layers (24, 26) have substantially the same tone of color in the visible spectral region.

Description

The invention relates to a security element for security papers, documents of value and the like having a substrate and an opaque metallization arranged on the substrate. The invention further relates to an associated manufacturing method, a security paper and a data carrier with such a security element.

Valuables, such as branded goods or documents of value, are often provided with security elements for the purpose of protection, which allow verification of the authenticity of the object of value and at the same time serve as protection against unauthorized reproduction.

A number of these security elements, such as hologram strips or so-called hologram patches, contain thin opaque metal coatings, typically having a thickness between 10 nm and about 100 nm. Due to the good availability, the excellent reflection properties, the relatively good chemical resistance and the low price, aluminum is used predominantly for the metal coatings of banknote holograms, security threads and the like.

WO 2003/091042 shows a security element with two layers of different metal.

Banknotes may be subject to severe mechanical and sometimes chemical stress during their circulation. It was observed that the thin aluminum coatings of the security elements can corrode and thus be severely damaged, whereby the optical impression of the banknote is greatly changed. Chemically highly resistant metals, such as gold, palladium or platinum, are generally considerably too expensive for use in security elements. Other chemically better resistant metals than aluminum are less expensive, but optically less brilliant and therefore visually less appealing.

Proceeding from this, the object of the invention is to avoid the disadvantages of the prior art. In particular, a security element of the type mentioned with improved circulation resistance and / or increased counterfeit security should be specified.

This object is achieved by the security element having the features of the main claim. A corresponding manufacturing method and a security paper and a data carrier, which are equipped with such a security element, are specified in the independent claims. Further developments of the invention are the subject of the dependent claims.

According to the invention, it is provided in a generic security element that the metallization comprises a first opaque metal layer and a second opaque metal layer arranged above the first metal layer, and that the two metal layers have substantially the same color shade in the visible spectral range. Complete color matching of the metal layers is not required. As explained in more detail below, it is sufficient for the purpose of the invention if the hues of the two metal layers are so similar to each other that they appear the same at cursory viewing.

In an advantageous embodiment of the invention, the two metal layers differ significantly in their chemical and / or mechanical resistance. Increased circulation resistance is achieved, in particular, when the second metal layer is chemically and / or mechanically more resistant than the first metal layer.

Despite their substantially the same hue, the metal layers may differ in their reflectivity, the arrangement of the metal layers for a good visual impression is advantageously chosen so that the first metal layer reflects more than the second metal layer.

The layer thickness of thin layers is usually expressed in terms of optical density, which is a measure of the attenuation experienced by light as it passes through the thin layer. The optical density OD is the decadic logarithm of the quotient of 100 and the transmission (in percent), ie OD = log (100 / T). For example, an optical density of 1.0 corresponds to a weakening of the light to one-tenth of the original illuminance, an optical density of 2.0 to one-hundredth of a weakening.

For the purposes of the invention, "opaque" is to be understood as meaning an optical density of at least 0.5, preferably of at least 0.7, particularly preferably of at least 1.0.

According to an advantageous embodiment of the invention, the Schichtdikken the two metal layers are chosen so that their optical density is substantially equal. For example, the optical densities of the two metal layers may differ by less than 0.3, in particular by less than 0.2.

While good reflection properties and good corrosion resistance can already be obtained from an optical density of about 0.5, the optical density of the two metal layers is preferably greater than 1.0, in particular greater than 1.2. The two metal layers are suitably coordinated so that the optical density of the opaque Metallization, so the two metal layers together, between 1.5 and 5.0, preferably between 1.5 and 3.0.

Within the scope of the invention, a layer of a corrosion-resistant metal, in particular a platinum layer, a palladium layer or a chromium layer, is advantageously considered for the second metal layer. At present, the use of a chromium layer is particularly preferred because this material combines low cost, high durability, and relatively good reflective properties. The second metal layer is therefore preferably a chromium layer, in particular with a thickness of about 25 nm or more.

Because of its excellent reflective properties, the use of aluminum layers, in particular with a thickness of about 15 nm or more, is preferred for the first metal layer.

Particularly advantageous is the combination of a chromium layer as the second metal layer with an aluminum layer as the first metal layer, since chromium and aluminum both have a substantially flat reflection spectrum in the visible spectral range and therefore both cause a white color impression. In this way, the advantages of the high reflectivity of the aluminum and the high resistance of the chromium can be combined. In a substantially intact aluminum layer, the visual impression of the metallization of the security element is determined by the high-gloss aluminum layer.

If the aluminum layer receives imperfections or cracks due to heavy wear, the chromium layer with its essentially the same color tone takes on the light reflection. The lower reflectivity of the chromium layer falls practically in the case of heavily used banknotes with the naked eye not up. The characteristic appearance of the metallization of the security element thus remains even with heavy wear.

According to a development of the invention, a spacer layer is provided between the two metal layers, which in particular forms an electrical and / or chemical insulation layer. The spacer layer is advantageously formed by a transparent printing layer or a transparent vapor-deposited layer. In an expedient embodiment, the spacer layer is formed by a ceramic layer, in particular an SiO _x layer, an Al ₂ O ₃ layer, an MgF ₂ layer, or else by an organic layer. Alternatively or additionally, the spacer layer can form a barrier layer against the permeation of gases and vapors, in particular of oxygen and hydrogen.

In particularly preferred embodiments of the invention, the security element has a diffraction structure in the form of a relief structure. The diffraction structure advantageously comprises an embossed embossing lacquer layer and at least a partial region of the metal layers. If it is desired to visually emphasize certain partial regions of the diffraction structure, the first metal layer can advantageously be present only in these partial regions. The security element then contains first areas in which the first metal layer is visible and second areas in which the second metal layer is visible. Although the visual impression in the two areas is naturally very similar due to the substantially same color shade, nuances in the appearance of the partial areas can be perceived with different reflection properties of the metal layers.

In addition to diffraction structures, the security element can also be scattering structures (matt structures), antireflective topographies, refractive structures, Zero order gratings, blazed gratings, optically variable topographies using micromirrors and / or retroreflective structures.

In two advantageous embodiments, the two metal layers have recesses in the form of patterns, characters or a coding, which pass through both metal layers. In the region of the recesses, the security element can then be transparent or translucent, or it can emerge an information arranged below the metallization.

The security element preferably represents a security thread, a security strip, a security tape or a patch.

The invention also includes a method for producing a security element for security papers, documents of value and the like, in which a substrate is provided, a first opaque metal layer is arranged on the substrate, and a second opaque metal layer is arranged over the first metal layer in the visible spectral range has substantially the same color as the first metal layer.

The two metal layers are preferably applied by means of a vacuum coating process. In a particularly advantageous method, an aluminum layer is applied as first metal layer and a chromium layer as second metal layer.

Between the first and second metal layers, a spacer layer may be applied, which is conveniently printed or vapor deposited in a vacuum coating process.

In a development of the method according to the invention, the security element is provided with a diffraction structure in the form of a relief structure. In this case, an embossing lacquer is applied to the substrate, the embossing lacquer is embossed in the form of a desired diffraction structure, and the first and second metal layers are applied successively, optionally with the interposition of a spacer layer, to the embossed lacquer layer.

In the metal layers can be introduced through both metal layers through recesses in the form of patterns, characters or a coding, in particular with that of the document WO 99/13157 A1 known washing process.

The invention further includes a security paper for the production of value documents or the like and a data carrier, in particular a value document, such as a banknote, an identity card or the like. The security paper or the data carrier are equipped according to the invention with a security element of the type described.

Further embodiments and advantages of the invention will be explained below with reference to the figures, the representation has been dispensed to scale and proportionate reproduction in order to increase the clarity.

Fig. 1

eine schematische Darstellung einer Banknote mit erfindungsgemäßen Sicherheitselementen, und

Fig. 2 bis 6

Querschnitte durch Sicherheitselemente nach verschiedenen Ausführungsbeispielen der Erfindung.

Show it:

Fig. 1

a schematic representation of a banknote with security elements according to the invention, and

Fig. 2 to 6

Cross sections through security elements according to various embodiments of the invention.

The invention will now be explained using the example of security elements for banknotes. Fig. 1 shows a schematic representation of a banknote 10, which is provided with two high-cycle resistance metallized security elements according to the invention. The first security element represents a security thread or a security strip 12, the second security element is formed by a glued transfer element 14 of any shape.

The layer structure of inventive security elements and the effect of the invention will now be described with reference to the cross-sectional views of FIGS. 2 to 6 described in more detail, wherein in each case only the layers essential for the invention are shown. Of course, depending on the intended application, the finished security elements will contain other layers known to those skilled in the art, such as adhesive layers, protective layers, primers or the like.

The security element 20 of Fig. 2 comprises, as a substrate, a plastic film 22 on which two opaque metal layers 24 and 26 are vapor-deposited one above the other, which have substantially the same color shade in the visible spectral range. In the exemplary embodiment, the first metal layer 24 is formed by a thin aluminum layer, the second metal layer 26 by a thin chromium layer.

The layer thicknesses of the two metal layers are chosen so that the optical density of the aluminum layer and the chromium layer is about 1.5 each.

The vapor-deposited chromium layer 26 and the aluminum layer 24 both have an almost flat reflection spectrum in the visible spectral range and thus appear with a white color impression. The reflectivity of the chromium layer 26 is about 50%, however, less than the reflectivity of the aluminum layer 24, which is about 90%, so that the chromium layer alone appears slightly darker than the aluminum layer with the same hue.

The metallized substrate is preferably applied to a security paper with the metallized side so that the substrate film 22 faces the viewer.

The chrome layer 26 is then completely covered by the opaque aluminum layer 24 as seen by the viewer, so that the overall visual impression of the security element is given only by the high-gloss aluminum layer 24. Depending on the embodiment, the substrate 22 may remain on the already applied security element or, preferably, be removed.

During the circulation of the banknotes provided with the security element 20, the partial corrosion of the thin aluminum layer 24 may occur in the case of particularly high stress, for example in tropical countries or in the case of strong perspiration. The aluminum layer, which is less resistant to the highest stresses, can thereby obtain light-permeable cracks and defects.

According to the invention, the chemically and mechanically significantly more resistant chromium layer 26 assumes the light reflection in these light-transmissive areas. Although the reflectivity of the chromium layer 26 is slightly lower than that of the aluminum layer 24, especially in mechanical and / or chemical However, bank notes that are heavily stressed are hardly noticeable to the observer by the change of reflective metal in some areas. In particular, the basic visual impression of the security element, namely its metallic appearance and the color impression of the metallization, is maintained even with heavy wear.

An increased circulation resistance can be obtained in a wide range of layer thicknesses for the two metal layers 24, 26. Layer thicknesses from an optical density of about 0.5 are suitable for the first metal layer facing the observer, but optical densities of 1.0 or more are generally selected for a very good visual impression and high reflection.

The second, highly resistant metal layer also leads from an optical density of 0.5 already to a significant increase in circulation resistance of the security element. When using chromium layers, optical densities above 1.0 have been proven for good corrosion protection. However, if very expensive metals, such as platinum or palladium, are used for the corrosion-resistant second metal layer, the second metal layer is formed with the minimum necessary layer thickness for cost reasons, so that optical densities well below 1.0 are also possible.

In the context of the invention, the thicknesses of the two metal layers are advantageously matched to one another such that the optical density of the metal layers together is above 1.5, in particular in the range from 1.5 to 3.0. In the embodiment of Fig. 2 the optical densities of the metal layers add up to OD _ges = OD _Al + OD _Cr = 1.5 + 1.5 = 3.0.

In the further embodiment of the Fig. 3 between the two metal layers 24, 26 of the security element 30, an electrically and optionally also chemically insulating, transparent spacer layer 32 is arranged. The spacer layer 32 can in particular prevent local element formation and thus accelerated corrosion by pitting.

Suitable spacer layers are transparent print layers, transparent layers applied in a vacuum coating process, such as layers of SiO _x , with x between 1.5 and 2, Al ₂ O ₃ or MgF ₂ , but also organic coatings. The layer thickness of the spacer layer 32 plays only a minor role and may be between about 10 nm and several micrometers.

Instead of or in addition to their electrical insulation, the spacer layer 32 can also be designed as a barrier layer against the permeation of gases and vapors, in particular of oxygen and hydrogen.

Fig. 4 shows as another embodiment of the invention provided with a metallized hologram security element 40. In this case, an embossing lacquer layer 44 was printed on a carrier film 42 and embossed the desired diffraction structure of the hologram in the form of a relief structure.

In order to obtain the described advantages of increased circulation resistance, a first metal layer 46 made of aluminum and a second metal layer 48 made of chromium are applied as hologram metallization. Between the two metal layers 46, 48, a spacer layer 50 may be provided. Due to the variable surface topography of the relief structure, the Spacing layer 50 may be able to follow the surface topography of the first metal layer 46. In particular, ceramic, transparent vapor deposition layers, such as SiO _x , Al ₂ O ₃ or MgF ₂ , with layer thicknesses of 10 nm or more are suitable for this purpose. Even thin, the surface topography following organic coatings can be used.

In further embodiments, the security elements according to the invention may also contain negative information in the form of patterns, characters or codes, which are formed by corresponding recesses in the metallization. For illustration shows Fig. 5 a security element 60 in which a substrate 62 is provided with a metallization 64 formed by an aluminum layer 66, a transparent ceramic spacer layer 68, and a chromium layer 70.

The metallization 64 may also form the metal coating of a diffractive structure, such as a hologram. In this case, the substrate 62 comprises in addition to a carrier film in particular also an embossed lacquer layer, such as in Fig. 4 shown.

Coming back to Fig. 5 , 64 recesses 72 in the form of the desired negative information, for example in the form of negative writing are introduced into the metallization 64, wherein the recesses 72 extend through the two metal layers 66, 70 and the ceramic spacer layer 68. The demetallized areas 72 can be produced, for example, by a washing process, as is known from the document WO 99/13157 A1 is known.

Another embodiment of the invention is in Fig. 6 illustrated. The security element 80 shown there corresponds in its layer structure largely the security element 60 of Fig. 5 , but with the difference that the chromium layer 70 is applied as a first metal layer and an aluminum layer 66 as a second metal layer and that now recesses 82 are provided which are present only in the aluminum layer 66. This security element is viewed from the aluminum layer 66 side.

In this variant according to the invention, the second metal layer 70 is applied to the first metal layer only in partial areas. In this novel security element 80, due to the different reflectivities of the two metal layers 66, 70 in the areas with or without recesses 82, nuanced visual appearances can be perceived. Although the visual impression in the two areas is very similar in design terms, the subtle differences between certain design elements, in particular holograms ( Fig. 4 ), emphasized and highlighted.

With increasing wear of the security element 80, the recognizability of the nuanced appearances formed by the shape and position of the recesses 82 generally decreases and can ultimately disappear completely under extreme wear. However, the increased circulation resistance of the security element 80 is ensured by the highly resistant chromium layer 70 even at maximum wear.

Claims (16)

1. A security element for security papers, value documents and the like, having a substrate and an opaque metallization arranged on the substrate, wherein the metallization comprises a first opaque metal layer having an optical density of at least 0.5 and a different second opaque metal layer arranged above the first metal layer and having an optical density of at least 0.5, wherein the two metal layers have substantially the same tone of color in the visible spectral region and differ significantly in their chemical and/or mechanical durability.
2. The security element according to claim 1, characterized in that the second metal layer is chemically and/or mechanically more durable than the first metal layer.
3. The security element according to claim 1 or 2, characterized in that the metal layers differ in their reflectivity and the first metal layer reflects more strongly than the second metal layer.
4. The security element according to at least one of claims 1 to 3, characterized in that the optical density of the two metal layers is larger than 1.0, preferably larger than 1.2, respectively.
5. The security element according to at least one of claims 1 to 4, characterized in that the second metal layer is a chrome layer having a thickness of about 25 nm or more, and that the first metal layer is an aluminum layer having a thickness of about 15 nm or more.
6. The security element according to at least one of claims 1 to 5, characterized in that between the metal layers a spacing layer is provided, which forms an electrical and/or chemical isolation layer.
7. The security element according to at least one of claims 1 to 6, characterized in that the security element comprises a diffraction structure in form or a relief structure.
8. The security element according to at least one of claims 1 to 7, characterized in that the metal layers comprise gaps reaching through both metal layers and being in the form of patterns, characters or a code.
9. A method of producing a security element for security papers, value documents and the like, in which a substrate is provided, a first opaque metal layer having an optical density of at least 0.5 is arranged on the substrate, and a second different opaque metal layer having an optical density of at least 0.5 is arranged above the first metal layer, which second metal layer has substantially the same tone of color in the visible spectral region as the first metal layer and differs significantly from the first metal layer in its chemical and/or mechanical durability.
10. The method according to claim 9, characterized in that the two metal layers are applied with an optical density of more than 1.0, preferably of more than 1.2.
11. The method according to claim 9 or 10, characterized in that the two metal layers are applied by means of a vacuum coating process.
12. The method according to at least one of claims 9 to 11, characterized in that a chrome layer is applied as second metal layer and that an aluminum layer is applied as first metal layer.
13. The method according to at least one of claims 9 to 12, characterized in that a spacing layer is applied between the first and the second metal layer and that the spacing layer is printed or vapor deposited in a vacuum coating process.
14. The method according to at least one of claims 9 to 13, characterized in that the security element is provided with a diffraction structure in form of a relief structure.
15. A security paper for the manufacturing of value documents or the like, which is provided with a security element according to at least one of claims 1 to 8.
16. A data carrier, in particular a value document, such as a bank note, an identity card or the like, which is provided with a security element according to one of claims 1 to 8.

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