Patent Application
20070211317
The present invention relates to a security element for security papers, value documents and the like, having a thin-film element, with color-shift effect, that exhibits a reflection layer, an absorber layer and a spacing layer disposed between the reflection layer and the absorber layer. The present invention also relates to a security paper, a value document and a method for manufacturing such a security element.
Value documents, such as banknotes, stocks, bonds, certificates, vouchers, checks, valuable admission tickets and other papers that are at risk of counterfeiting, such as passports and other identitification documents, are normally provided with various security features to increase their counterfeit security. The security features can be developed, for example, in the form of a security thread embedded in a banknote, an applied security strip or a self-supporting transfer element, such as a patch or a label that, after its manufacture, is applied to a value document. According to the present invention, security paper is understood to be the not yet circulatable precursor to the value document.
Furthermore, it is known to use security features having multi-layer thin-film elements that likewise display a color-shift effect. As security features were used, for example, foils coated with cholesteric liquid crystals in which the color impression for the viewer changes with the viewing angle, and when the security feature is tilted, shifts for example from green to blue, from blue to magenta or from magenta to green. The color impression of these liquid crystal-coated foils can also be influenced after completion of the foil by means of stretching. The color effect is based on interference effects due to multiple reflections in the different sub-layers of the thin-film element and is described in detail in, for example, publication EP 0 395 410 B1. Such color changes upon tilting a security feature are referred to in the following as color-shift effects.
As the layer that is mainly responsible for the color effect, the thin-film elements include an ultra-thin dielectric layer that is typically disposed between an absorber layer and a reflection layer. The key technological challenge here is the manufacture of the dielectric layer, which is just a few hundred nanometers thick.
Currently, the thin dielectric layers are normally produced through a complex physical vapor deposition process. Particularly in the large-area coatings required in the security paper and banknote segment, the precision requirements are extraordinarily high, such that such coatings can be carried out in only a few locations worldwide.
Based on that, the object of the present invention is to specify a generic security element that is easier and cheaper to manufacture compared with the background art.
This object is solved by the security element having the features of the main claim. A security paper for the manufacture of security documents, a value document having such a security element and a manufacturing method for such a security element are the subject of the coordinated claims. Developments of the present invention are the subject of the dependent claims.
According to the present invention, the spacing layer in a security element of the kind mentioned above is formed by an ultra-thin foil having a thickness below 1.0 μm. The ultra-thin foil preferably exhibits a thickness of about 250 nm to about 750 nm, preferably of about 400 nm to about 600 nm. Such foils are already commercially available today and are used mainly as dielectric foils for capacitors.
According to an advantageous development of the present invention, the ultra-thin foil constitutes a stretched polyester foil, preferably a monoaxially, sequentially biaxially or simultaneously biaxially stretched polyalkylene terephthalate foil. In particular, the foil can be a biaxially stretched polyethylene terephthalate (PET) foil. Here, the stretching of the PET foils increases their stability and heat resistance and improves further properties of the foils, such as their dimensional stability.
In preferred embodiments, the reflection layer of the thin-film element is formed by an opaque metal layer. Here, particularly metal coatings comprising aluminum, silver, nickel, copper, iron, chrome or gold, as well as other strongly reflective metals may be used.
Instead of as a substantially opaque element, the security element can also be formed as a semitransparent see-through security element. In this case, as the reflection layer, instead of an opaque reflection layer, an absorber layer, a semitransparent metal layer or a transparent reflection layer is used whose refractive index is different from that of the ultra-thin foil. For such a transparent reflection layer, practically all vapor-depositable, transparent compounds may be used, especially also higher-index coating materials such as ZrO2, ZnS, TiO2 and ITO (indium tin oxide), whose refractive index differs from that of the foil by more than 0.2, preferably even by more than 0.5. The layer thickness of such a transparent reflection layer preferably lies in the range from 30 nm to 300 nm, particularly preferably between about 50 nm and about 60 nm.
As absorber layers, metal layers comprising materials such as chrome, iron, gold, copper aluminum or titanium that are preferably applied in a thickness of about 4 nm to about 20 nm can advantageously be used. Also compounds such as nickel-chrome-iron, or rarer metals such as vanadium, palladium or molybdenum can be used. Further suitable materials include, for example, nickel, cobalt, tungsten, niobium, aluminum, metal compounds such as metal fluorides, metal oxides, metal sulfides, metal nitrides, metal carbides, metal phosphides, metal selenides, metal silicides and compounds thereof, as well as carbon, germanium, cermet, iron oxide and the like.
The absorber layer and the reflection layer are preferably applied to the ultra-thin foil in a vacuum evaporation method. Here, a wide variety of evaporation methods can be used for coating the foil.
Physical vapor deposition (PVD) methods such as boat evaporation, evaporation by resistance or induction heating, AC and DC sputtering, and electron beam or arc evaporation form one group. As a further group, CVD (chemical vapor deposition) methods such as reactive plasma sputtering or other plasma-assisted vapor deposition methods may be used.
In an advantageous development of the present invention, it is provided that the absorber layer and/or the spacing layer exhibits gaps in the form of patterns, characters or codes in which no color-shift effect is perceptible. Alternatively or additionally, the reflection layer, too, can exhibit gaps in the form of patterns, characters or codes that appear as transparent or semitransparent areas in the thin-film element. The gaps can be applied as, for example, graphic designs or as positive or negative lettering, for instance in the form of a serial number or another individualizing mark, and further increase the counterfeit security of the security element.
To obtain a double-sided thin-film element having a color-shift effect that is visible from both sides, the thin-film element can exhibit a second absorber layer on the side of the reflection layer facing away from the spacing layer and, disposed between the second absorber layer and the reflection layer, a second spacing layer comprising an ultra-thin foil having a thickness below 1.0 μm.
For this second ultra-thin foil, the explanations given above for the first ultra-thin foil apply accordingly. In an advantageous embodiment, the first and second spacing layer are formed from foils of differing thickness such that different color-shift effects are perceptible from the two sides of the security element.
Further, it can be provided that the thin-film element exhibits at least one further layer having an additional security feature, especially a layer provided with magnetic, electrically conductive, luminescent or optically variable substances. For example, a magnetic metal layer suitable and intended for machine-readable codes and comprising nickel, iron, cobalt or a suitable alloy can be disposed between the reflection layer and a substrate of the security element in such a way that it remains invisible for the viewer and does not negatively impact the described optical effects.
To facilitate the further processing of the coated ultra-thin foil, the thin-film element is advantageously applied on a substrate, for example a transparent substrate foil. The transparency and/or color of the substrate are expediently coordinated with the properties of the thin-film element and the desired appearance of the security element. For example, a transparent substrate is suitable for see-through security elements or for security elements that are provided with gaps and whose information content is intended to be visible also in transmitted light. In some embodiments it can be provided that the substrate is removed, for example via suitable release layers, after the application of the security element to its destination.
Since the color impression of the security element depends on the local thickness of the foil, thickness variations in the foil can result in a non-uniform color impression. To compensate for this effect, the thin-film element can be stretched in some areas upon application to the substrate in order to compensate for thickness variations in the unstretched foil. The compensation can occur, for instance, with the aid of a control loop in which the thickness or the color impression of the foil is detected during the application of the foil and the magnitude of the elongation is regulated accordingly.
The elongation can also be used specifically to vary the color in that the foil is laminated, for example, along the direction of application with slowly increasing or decreasing elongation such that a continuous color transition is created.
According to a further advantageous development of the present invention, the thin-film element is provided with an areal diffraction pattern to form a color-shift hologram in which the color-shift effect is combined with a holographic effect. For this, the thin-film element is preferably disposed on a substrate that already exhibits an areal diffraction pattern. Alternatively to this, it is also possible to subsequently emboss the diffraction pattern in the thin-film element.
For example, the substrate can be formed by an embossing lacquer layer that is provided with a diffraction pattern and that forms a component of the finished security element. The diffraction pattern of the embossing lacquer layer is evaporated with a reflector, and the semitransparent thin-film element having the layer structure semitransparent metal/ultra-thin foil/semitransparent metal can be affixed on top of this. The absorber layer of such a color-shift hologram typically exhibits a transmission of between 25% and 75%.
An alternative layer structure for a security element provided with diffraction patterns is as follows: A substrate provided with diffraction patterns is provided with a semitransparent metal layer, on top of which an adhesive layer is applied. On top of the adhesive layer, an absorber is applied, then the ultra-thin foil and then a reflection layer.
Each of the above-described security elements can be designed, for example, in the form of a security strip, a security thread, a security band, an individual tag-shaped element (patch) or a transfer element for application to a security paper, value document or the like. In addition, the security element can be present in the form of pigments that are manufactured, for example, by grinding the thin-film structure according to the present invention. With suitable binders, these pigments can also be further processed into printing inks.
The present invention also includes a security paper for manufacturing security documents, such as banknotes, identification cards and the like, that is furnished with a security element of the kind described above. The security paper can especially include at least one through window area or a hole that is covered with the security element. In this case, advantageously, a security element is used whose reflection layer is provided with gaps, or a security element whose color-shift effects are visible from both sides.
The present invention further includes a value document, for example a banknote, that is furnished with an above-described security element. The value document can likewise include a window area covered with the security element or a hole covered therewith.
The security element, security paper or value document described can also be used for securing goods of any kind.
According to the present invention, for manufacturing a security element for security papers, value documents and the like that includes a thin-film element, with color-shift effect, that exhibits a reflection layer, an absorber layer and a spacing layer disposed between the reflection layer and the absorber layer, it is provided that the spacing layer is formed by an ultra-thin foil having a thickness below 1.0 μm that is coated on opposing main surfaces with the reflection layer and the absorber layer. The reflection layer and/or the absorber layer are preferably vapor deposited on the ultra-thin foil. Here, the reflection layer can be designed as described above, i.e. advantageously as an opaque metal layer, as a semitransparent metal layer, as a transparent reflection layer or as an absorber layer.
In a development of the method, gaps in the form of patterns, characters or codes are introduced into the thin-film element, preferably into the absorber and/or reflection layer. This can occur particularly in the manner described below with the aid of oil.
For further processing, the thin-film element is expediently applied to a substrate, for example a transparent substrate foil. Alternatively, the coated ultra-thin foil can be applied directly to a security paper or a value document. As mentioned, it can be advantageous to stretch the foil in some areas upon application to a substrate or an object to compensate for thickness variations in the foil.
Further exemplary embodiments and advantages of the present invention are explained below by reference to the drawings, in which a depiction to scale and proportion was omitted in order to improve their clarity.
Shown are:
The invention will now be explained using a banknote as an example.
In the exemplary embodiment, the banknote 10 exhibits a through, diecut opening 18 that, on the front side of the banknote, is completely covered by the color-shift transfer element 16. Alternatively, the opening could also have already been worked in when the paper was manufactured. The color-shift transfer element 16 is formed in the manner described below as a semitransparent see-through security element that, in the see-through area 18, displays a color-shift effect from both sides of the banknote.
First, the general layer structure of security elements according to the present invention is explained with reference to the cross-sectional illustrations in
The security element 20 in
The thin-film element 22 in
The security elements according to the present invention can be provided with gaps 42 in the form of patterns, characters or codes, as shown in the security element 40 in
To prevent metal vapor deposits on the masking tape, said tape is evaporated with oil prior to each inlet into the evaporation zone. After passing the evaporation zone, the deposited oil is removed from the masking tape again by a heater such that no thick and uneven oil film can accumulate on the masking tape. For further details of the manufacture of metal-free strips in metal evaporation, reference is made to publication EP 0 756 020 B1, whose disclosure in this respect is incorporated in the present application.
In a further alternative method, immediately prior to the evaporation step with metal, the foil can be printed on with a volatile oil at the sites at which gaps are to appear in the metal layer. During the evaporation step with metal, the oil evaporates at the coated sites on the foil such that no metal vapor settles there.
Alternatively, the gaps can also be created according to the method described in publication EP 1 023 499 B1. Its disclosure in this respect is likewise incorporated in the present application.
In the areas of the gaps 42 in the otherwise opaque reflection layer 26, the thin-film element is transparent or semitransparent such that, in these areas, the viewer is presented with a striking contrast to the surrounding color-shift effect. For example, the patterns, characters or codes can light up brightly in transmitted light when the thin-film element 22 is applied to a transparent substrate 34.
For this,
A further exemplary embodiment having a color-shift effect that is visible from both sides is illustrated in
In manufacturing such a double-sided thin-film element 60, the first ultra-thin foil 74 can be laminated with its absorber layer ahead on a transparent substrate foil and the second foil 76 then laminated with its reflection layer ahead on top of the first foil 74.
Alternatively, the two ultra-thin foils 74 and 76 can each be laminated with the reflection layer ahead onto opposing main surfaces of a substrate foil. In this case, the substrate foil must not be transparent, but instead can be, for example, suitably colored such that its own color stands out in some areas in gaps in the reflection layers 66 and 68.
These double-sided thin-film elements, particularly with the same color effect on the opposing main surfaces, are especially well suited for further processing into pigments. For this, the thin-film elements are ground into the desired pigment size and, if applicable, further processed into printing inks.
The security element 80 of the exemplary embodiment shown in
The security element 90 of the exemplary embodiment shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 032 565.0 | Jul 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/06378 | 6/15/2005 | WO | 12/20/2006 |
