EP4275911A1 - Safety element - Google Patents

Abstract

The present invention relates to a security element (1) with optical security features, suitable for arrangement on a flat support (2), comprising a moth-eye structure (3) and a layer for producing a first color-shifting effect (4), the security element further comprising a reflective layer (6), which reflective layer (6) is arranged at least in sections directly on the moth-eye structure (3) and the layer for producing a first color-shifting effect (4) overlaps at least in sections with the reflective layer (6) arranged on the moth-eye structure (3). is arranged.

Description

FIELD OF THE INVENTION

The present invention relates to a security element with optical security features, suitable for arrangement on a flat support, comprising a moth-eye structure and a layer for producing a first color shift effect.

STATE OF THE ART

Security elements are already known from the prior art, which have an optical element for producing a color-shifting effect in order to increase security against forgery.

The prior art already knows how to create a color-shifting effect using a liquid crystal layer (LC layer). Color shift effects between typical color pairs can be achieved here, for example from a green color impression to a blue color impression. However, a color shift effect from green to red cannot be achieved when using an LC layer.

Furthermore, the generation of color-shifting effects using interference layers is known in the prior art.

When using interference layers, color-shifting effects are achieved with a variety of colors.

So-called thin-film arrangements are also known in the prior art in order to be able to achieve a color-shifting effect.

For example, a color-shifting effect from the color impression of black to any color impression is also known, and such a color-shifting effect can be achieved by using moth-eye structures with diffractive behavior. The company Toppan ^®, for example, sells a moth-eye structure under the name Asterium ^® , which appears black when viewed at a steep angle and colored when tilted to a shallow angle.

From the EP 2 676 802 B1 Such a moth-eye structure is known, which is used as an absorber to vary the density of an image.

OBJECT OF THE INVENTION

One object of the invention is to provide a security element with optical security features, whereby a color-shifting effect is generated between atypical color pairs, thereby increasing the anti-counterfeit security of the security element.

PRESENTATION OF THE INVENTION

The object of the invention is achieved by a security element with optical security features, suitable for arrangement on a flat support, comprising a moth-eye structure and a layer for producing a first color shift effect, it being provided according to the invention that the security element further has a reflective layer, which reflective layer is arranged at least in sections directly on the moth eye structure and the layer to produce a first color shift effect overlaps at least in sections with that on the Moth eye structure arranged reflective layer is arranged.

Moth eye structures are used in the prior art due to their light-absorbing properties for anti-reflection and preventing reflections in many areas and are therefore already known in the prior art. Moth eye structures can be produced by various already known methods, such as embossing, etching and the like, for example on a lacquer base.

In principle, a moth eye structure is a microstructure with a (pseudo)periodic, for example conical or sinusoidal structure. The moth-eye structure can be arranged on a support in the form of a diffraction grating, with linear, circular gratings, but also cross gratings, for example, coming into consideration. Of course, it cannot be ruled out that the moth eye structure has a different structure.

The moth-eye structure is preferably formed with the aid of an embossed lacquer layer, which essentially consists of nitrocellulose, acrylates and their copolymers, polyamides and their copolymers, polyvinyl chlorides and their copolymers. The moth eye structure is preferably made from a crosslinkable or crosslinked lacquer.

In order to ensure that the moth eye structure absorbs light in the visible range, it is provided that the structure period is equal to or preferably smaller than the wavelength of the visible light, so that the reflection of the radiation is prevented as much as possible.

A moth eye structure, as used in the present invention, only appears to the viewer dark to almost black at a steep viewing angle, while at a flat viewing angle it has a diffractive optical effect due to an existing periodicity and therefore appears colored, i.e. has a diffraction color. The moth eye structure in question therefore shows a color shift effect from black to colored. The reflective layer basically serves to make the moth eye structure "visible" in a layer structure, i.e. to increase the difference in the refractive index to other layers. At a steep viewing angle, the reflective layer acts as an amplifier for the color-shifting effect caused by the layer for producing a first color-shifting effect, because at a steep viewing angle the reflected rays are swallowed by the moth-eye structure, whereby the coloring of the layer for producing a color-shifting effect becomes visible.

The moth eye structure according to the invention preferably has periodic structures so that the desired color shift effect can be created. However, it is also not excluded that aperiodic moth eye structures may be used if this is necessary or more advantageous for a particular effect to be achieved.

Of course, it is also possible to produce different diffraction colors in a single moth eye structure by varying the structural parameters of the moth eye structure, such as the structural period. For example, a special security element can be produced by the moth eye structure comprising an area with a certain periodicity (structure period) of the moth eyes and, next to this area, another area with a periodicity (structure period) different from this first periodicity. Comprehensive the moth eye structure The two different areas then appear dark to black in their entirety at a steep viewing angle, so the security element appears in the color of the layer to produce a first color shift effect, while the moth-eye structure has two different diffraction colors at a flat viewing angle, corresponding to the two areas different periodicity. This allows the security element to be designed to be even more forgery-proof.

A similar effect can also be achieved if, in addition to a moth's eye structure, a black or dark layer, e.g. made of black paint or metal oxides in the form of a so-called black metallization, is applied and both the moth's eye structure and the area with the dark or black layer are coated with a , in particular the same, layer to create a first color shift effect. In this case too, the two areas themselves appear dark to black at a steep viewing angle, overall due to the layer creating a first color-shifting effect in the color of this layer, while when tilted to a flat viewing angle, a different color effect is created because the moth-eye structure is one Has diffraction color, but the area with the dark or black layer does not. A dark layer is a layer with a reflectance for visible light at 525 nm of less than 20%, in particular less than 15%; a black layer is a layer with a reflectance for visible light of less than 12%, in particular less than 10%.

The production of a black layer using metal oxides in the form of black metallization is known from the prior art, for example from EP 1522606 A1 , where the production of a black aluminum layer is shown.

In principle, any layer that can be used to achieve a color-shifting effect can be considered as a layer for producing a first color-shifting effect. However, in connection with the present invention, a cholesteric LC layer or a cholesteric LC pigment layer, a layer with interference pigments or a thin-film arrangement is preferably used.

Color shift effect generally means that the color impression of the layer changes depending on the viewing angle. This means that in the present case the layer produces a different color impression at a steep viewing angle, i.e. at an angle of approximately 75°-90° to the surface of the security element, than at a flat viewing angle, i.e. at an angle of less than 75°, in particular less than 45°. The viewing angle is 90° if the security element is viewed normal to its plane and 0° if one were to look parallel to the plane of the security element.

By using LC layers, LC pigment layers, a layer with interference pigments or a thin-film arrangement, color-shifting effects can be achieved with already known color pairs. In this context, a color-shifting effect of green at a steep angle and blue at a shallow angle is known. However, LC layers or LC pigment layers cannot produce a color shift effect from blue in a steep viewing angle to green in a flat viewing angle or a color shift effect from green in a steep viewing angle to red in a flat viewing angle. This disadvantage is intended to be overcome with the present invention.

According to the invention it is provided that the layer for producing a first color shift effect overlaps at least in sections with the moth eye structure (and the one on it arranged reflective layer). The layer for producing a first color shift effect can therefore be arranged both completely and only in certain sections on the reflective layer arranged on the moth eye structure. Preferably, however, the reflective layer disposed on the moth eye structure is completely congruent with the layer for producing a first color shift effect. The effect according to the invention occurs in the overlapping area.

Overlapping does not mean that the moth-eye structure and the layer must be arranged directly adjacent to one another normal to the plane of the security element in order to produce a first color shift effect. This means that one or more layers can also be arranged between the moth-eye structure and the layer for producing a first color-shifting effect.

In principle, the layer for producing a first color shift effect can be applied on or above the moth-eye structure, that is to say on or above the structured surface of the moth-eye structure, or below the moth-eye structure, that is to say on or below the essentially flat surface of the moth-eye structure.

The layer to create an initial color shift effect requires an underlying dark to black absorber layer in order to create easily recognizable color impressions. In the present invention, the moth-eye structure serves as an absorber layer, with which the layer is arranged to overlap at least in sections to produce a first color shift effect.

This at least partially overlapping arrangement of the layer for generating a first color-shifting effect on the moth-eye structure according to the invention ensures that two color-shifting effects can be generated. At a steep angle The moth eye structure appears dark to almost black to an observer, while the layer for generating a first color shift effect appears green, for example, since wavelengths in the range of light that appear green are reflected. Due to the fact that the moth eye structure at this angle serves as an absorber for the layer to create a first color shift effect, a viewer at a steep angle has a green overall color impression, since the green of the layer to create a first color impression overlays the dark moth eye structure. However, if the viewer tilts the optical security element at a shallow angle, the moth-eye structure no longer acts as an absorber and appears black, but rather itself creates a color impression, for example red, due to the existing diffractive optical structure.

An unusual color-shifting effect according to the invention is now created because the layer arranged above the moth-eye structure to produce a first color-shifting effect appears, for example, blue at the same time when viewed at a flat angle. However, the underlying moth eye structure no longer acts as an absorber that appears black, so that the red color impression as the diffraction color of the moth eye structure is superimposed on the blue color impression of the layer to produce a first color shift effect, whereby the viewer essentially sees the diffraction color of the moth eye structure, i.e. essentially a red color impression has. What this essentially means in this context is that the color impression of the diffraction color predominates, but this diffraction color can be slightly overlaid by the color of the layer to produce a first color shift effect.

The layer arrangement according to the invention therefore enables, for example, the unusual color-shifting effect from green to red, which is achieved through the two color-shifting effects taking place at the same time. The color-shifting effect of the layer to produce a first color-shifting effect runs, for example, from green to blue, while at the same time the moth-eye structure enables a color-shifting effect from dark or black to red. However, due to the fact that the blue color impression of the layer for generating a first color shift effect is much weaker than the red of the moth's eye structure, it appears to the viewer as if only a single color shift effect occurs, namely one from green to red.

As mentioned, to create an initial color-shifting effect, the layer does not need to be applied directly to the moth's eye structure. The arrangement in the security element is determined in particular by the type of this layer for generating a first color shift effect. When using an LC layer, for example, the layer to produce a first color shift effect can first be arranged on a separate carrier, since the liquid crystals contained in the LC layer are first electrically and/or magnetically and/or along a structure or embossing of the carrier, e.g. on a film surface, must be aligned in order to be suitable for creating a color shift effect. The layer according to the invention is preferably aligned to produce a first color shift effect through the preferred direction of the carrier, which can in particular be a plastic film.

In order to be able to carry out the alignment as efficiently as possible, the liquid crystals are aligned separately, for example on a separate carrier which is suitable for alignment, and only then is the layer to produce a first color-shifting effect applied to the moth-eye structure, for example by means of an adhesive layer separate carrier can be removed or placed on the Layer can be left. A PET film is particularly suitable as a separate carrier. Of course, other films or carriers are not excluded from use.

In order to be able to apply the layer with liquid crystals to the moth eye structure after aligning the liquid crystals, a primer or an adhesive, such as a laminating adhesive or a lamination adhesive, must first be applied to the moth eye structure and / or the layer with liquid crystals in order to sufficiently fix the layer to be able to. However, the prerequisite is that the primer layer or the adhesive layer is also at least semi-transparent, since otherwise the double color-shifting effect according to the invention can no longer be achieved.

In a preferred embodiment of the invention it is provided that the security element further comprises a flat carrier. The moth-eye structure and the layer to create an initial color-shifting effect are usually flat layers. For reasons of stability, they are usually arranged on a flat support.

A support according to the invention can be any support that is suitable for having a moth-eye structure applied thereto. This is preferably a carrier made of plastic, for example PET (polyethylene terephthalate). Of course, the use of other suitable materials is not excluded. The carriers are, for example, transparent carrier films, preferably flexible plastic films, for example made of polyimide (PI), polypropylene (PP), monoaxially oriented polypropylene (MOPP), biaxially oriented polypropylene (BOPP), polyethylene (PE), polyphenylene sulfide (PPS), polyetheretherketone (PEEK ), polyether ketone (PEK), Polyethyleneimide (PEI), polysulfone (PSU), polyaryl ether ketone (PAEK), polyethylene naphthalate (PEN), liquid crystalline polymers (LCP), polyester, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyamide (PA), polycarbonate (PC), cycloolefin copolymers ( COC), polyoxymethylene (POM), acrylonitrile butadiene styrene (ABS), polyvinyl chloride (PVC) ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF) and ethylene tetrafluoroethylene hexafluoropropylene fluoroterpolymer (EFEP ) and/or mixtures and/or co-polymers of these materials in question. The carriers or carrier films can be transparent, translucent, semi-opaque or opaque.

The carrier can in particular be a film, but other carriers are not excluded from use.

It is preferably provided that the security element is protected by protective layers on one or both sides, for example by means of protective lacquer layers. For example, a moth-eye structure lying on the surface of the security element or a layer to create a color-shifting effect can be provided with a protective layer. And/or a protective lacquer layer can be arranged on the carrier in order to protect the carrier.

In one embodiment of the invention it is provided that the layer for producing a first color shift effect is an LC layer and/or an LC pigment layer in order to achieve a color shift effect between unusual color pairs particularly easily and cheaply.

Any LC layer or LC pigment layer known in the prior art that can be used to produce a color shift effect can be considered as an LC layer or LC pigment layer. This is any cholesteric LC layer or LC pigment layer. However, the prerequisite is that the layer is transparent in order to create the desired effect. In connection with the present invention, an LC layer is preferably used, which itself produces a first color shift effect from green in the steep viewing angle to blue in the flat viewing angle.

The advantage of using an LC pigment layer is that it does not have to be aligned before application. This means that an LC pigment layer can usually be applied to an adhesive or primer layer that does not, partially or completely flatten the moth eye structure, or can be applied directly to the reflective layer. If the adhesive or primer layer has a small thickness in relation to the moth's eye structure and the LC pigment layer also has a small thickness in relation to the moth's eye structure, then the LC pigment layer is not flat, but follows the elevations of the moth's eye structure.

In a further embodiment of the invention it is provided that the layer for producing a first color-shifting effect is a layer with interference pigments in order to produce particularly diverse color-shifting effects. If the layer for producing a first color shift effect is a layer with interference pigments, this layer comprises, on the one hand, the interference pigments and a carrier substance, namely a binder, which can absorb the interference pigments without impairing their function. It is necessary that this carrier substance is transparent.

The advantage of using a layer with interference pigments is that it does not have to be aligned before application. This means that a Layer with interference pigments can usually be applied to an adhesive or primer layer, which does not level the moth eye structure, partially or completely, or can be applied directly to the reflective layer. If the adhesive or primer layer has a small thickness in relation to the moth's eye structure and the layer with interference pigments also has a small thickness in relation to the moth's eye structure, then the layer with interference pigments is not flat, but follows the elevations of the moth's eye structure.

In one embodiment of the invention it is provided that the layer for producing a first color-shifting effect is a thin-film arrangement in order to produce particularly diverse color-shifting effects. The thin-film arrangement causes a color-shifting effect by means of thin-film interference.

A thin-film arrangement usually consists of at least two sub-layers: a dielectric layer and an absorber layer. An additional reflection layer on the other side of the dielectric layer, i.e. opposite the absorber layer with respect to the dielectric layer, reflects electromagnetic waves, such as light in the visible range, and thus increases the interference effect. The dielectric layer serves as a spacer layer, if necessary between the reflection layer and the absorber layer. The color shift effect occurs when viewing the interference coating from the side of the absorber layer, i.e. when light falls through the absorber layer onto the dielectric layer.

Dielectric materials with a refractive index less than or equal to 1.65, for example aluminum oxide (Al ₂ O ₃ ), are suitable for the dielectric layer of the thin-film arrangement. Metal fluorides, for example magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), silicon oxide (SiO _x ), silicon dioxide (SiO ₂ ), cerium fluoride (CeF ₃ ), sodium aluminum fluorides (for example Na ₃ AlF ₆ or Na ₅ Al ₃ F ₁₄ ), neodymium fluoride (NdF ₃ ), lanthanum fluoride (LaF ₃ ), samarium fluoride (SmF ₃ ), barium fluoride (BaF ₂ ), calcium fluoride (CaF ₂ ), lithium fluoride (LiF), low-refractive index organic monomers and/or low-refractive index organic polymers.

Dielectric materials with a refractive index greater than 1.65 are also suitable for the dielectric layer of the thin-film arrangement, for example zinc sulfide (ZnS), zinc oxide (ZnO), titanium dioxide (TiO ₂ ), carbon (C), indium oxide (In ₂ O ₃ ). , indium tin oxide (ITO), tantalum pentoxide (Ta ₂ O ₅ ), cerium oxide (CeO ₂ ), yttrium oxide (Y ₂ O ₃ ), europium oxide (Eu ₂ O ₃ ), iron oxides such as iron (II, III) oxide (Fe ₃ O ₄ ) and iron (III) oxide (Fe ₂ O ₃ ), hafnium nitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO ₂ ), lanthanum oxide (La ₂ O ₃ ), magnesium oxide (MgO), neodymium oxide (Nd ₂ O ₃ ), praseodymium oxide (Pr ₆ O ₁₁ ), samarium oxide (Sm ₂ O ₃ ), antimony trioxide (Sb ₂ O ₃ ), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), silicon monoxide (SiO), selenium trioxide (Se ₂ O ₃ ), tin oxide (SnO ₂ ), tungsten trioxide (WO ₃ ), high-index organic monomers and/or high-index organic polymers.

A metallic layer can be used as the absorber layer of the thin-film arrangement, which can be, for example, a pure metal layer or a layer containing metallic clusters. The absorber layer preferably comprises at least one metal from the group consisting of aluminum, gold, titanium, vanadium, cobalt, tungsten, niobium, iron, molybdenum, palladium, platinum, chromium, silver, copper, nickel, tantalum, tin and / or their alloys, for example gold/palladium, copper/nickel, copper/aluminum or chrome/nickel.

A metallic layer can optionally be used as the reflection layer of the thin-film arrangement, which preferably contains at least one metal selected from the group consisting of aluminum, gold, chromium, silver, copper, tin, platinum, nickel and their alloys, for example nickel/chrome or copper/aluminum . It is also conceivable that the reflection layer contains a semiconductor, such as silicon. Finally, it is also conceivable that the reflection layer is produced by applying a printing ink with metallic pigments, preferably made of a metal from the group mentioned above. The reflection layer is applied over the entire surface or in part by known methods, such as spraying, vapor deposition, sputtering, or, for example, as printing ink by known printing methods (gravure, flexo, screen, digital printing), by painting, roller application methods, slot nozzles, dipping (rolldip coating ) or curtain coating processes and the like are applied.

So-called HRI layers (high refractive index layers), which comprise a material with a refractive index greater than 1.5, can also be used as the reflection layer of the thin-film arrangement. Such HRI layers have, for example, dielectric materials with a refractive index of greater than or equal to 1.65, for example zinc sulfide (ZnS), zinc oxide (ZnO), titanium dioxide (TiO ₂ ), carbon (C), indium oxide (In ₂ O ₃ ), indium -Tin oxide (ITO), tantalum pentoxide (Ta ₂ O ₅ ), cerium oxide (CeO ₂ ), yttrium oxide (Y ₂ O ₃ ), europium oxide (Eu ₂ O ₃ ), iron oxides such as iron (II, III) oxide ( Fe ₃ O ₄ ) and iron (III) oxide (Fe ₂ O ₃ ), hafnium nitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO ₂ ), lanthanum oxide (La ₂ O ₃ ), magnesium oxide (MgO), neodymium oxide (Nd ₂ O ₃ ), praseodymium oxide (Pr ₆ O ₁₁ ), samarium oxide (Sm ₂ O ₃ ), antimony trioxide (Sb ₂ O ₃ ), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), silicon monoxide (SiO), selenium trioxide (Se ₂ O ₃ ), tin oxide (SnO ₂ ), tungsten trioxide (WO ₃ ), high-index organic monomers and/or high-index organic polymers. These materials can be either vapor deposited or printed (especially the monomers and polymers).

If, in turn, an LC layer or LC pigment layer or a layer with interference pigments is used, it is advantageous that an additional absorber layer is no longer required, but the function of the absorber layer is completely fulfilled by the moth eye structure used itself. The moth eye structure absorbs the radiation and thus prevents reflection, making the moth eye structure appear dark.

In one embodiment of the invention, an adhesive layer is provided to secure the layer to the moth eye structure or a support to produce a first color shift effect. The adhesive layer is advantageous in order to achieve particularly good results, since a base surface that is as flat as possible on which the layer is applied to produce a first color shift effect has a particularly advantageous effect. The adhesive layer usually levels the moth eye structure. Instead of an adhesive layer, a primer layer, i.e. an adhesion promoter layer, is also conceivable, which generally does not level the moth's eye structure, but follows the underlying shape of the moth's eye structure.

In a further embodiment of the invention it is provided that the reflective layer is a metallic layer in order to ensure particularly simple production. The metallic layer is therefore applied directly to the microstructures of the moth eye structure.

In a further embodiment of the invention it is provided that the reflective layer is an HRI layer in order to have a particularly wide range of applications to enable the present invention. The HRI layer is also applied directly to the microstructures of the moth eye structure.

The metallic layer or, if appropriate, the HRI layer serves to reinforce the diffraction generated by the moth-eye structure. The metallic layer or the HRI layer is so thin that the moth eye structure is not or hardly changed, i.e. the height and width of the microstructures are not or hardly changed. The metallic layer is applied so that its optical density is greater than 1, in particular greater than 1.5. The metallic layer or the HRI layer fulfills the very general purpose of creating a refractive index difference between the layers in order to be able to generate a reflection at all. This is particularly necessary because several layers are usually used to produce a security element and otherwise there would not be a sufficiently large difference in refractive index.

An adhesive layer can then be arranged on the metallic layer or the HRI layer in order to create a layer that is as flat as possible, on which the layer can then be arranged to create a first color shift effect. A flat adhesive layer is particularly advantageous if an LC layer is used as a layer to create a first color shift effect, since this must first be aligned on a separate layer and then applied to the adhesive layer.

The material used for the metallic layer is in particular metals selected from the group consisting of aluminum (Al), gold (Au), chromium (Cr), silver (Ag), copper (Cu), tin (Sn), platinum (Pt), Nickel (Ni) and their alloys, for example nickel/chrome or copper/aluminum in question. It is also conceivable that the metallic layer contains a semiconductor, such as silicon (Si). Finally, it is also conceivable that the metallic layer is produced by applying a printing ink with metallic pigments, preferably made of a metal from the group mentioned above.

In general, the reflective layer is applied over the entire surface or in part by known processes, such as spraying, vapor deposition, sputtering, or, for example, as printing ink using known printing processes (gravure, flexographic, screen, digital printing), by painting, roller application processes, slot nozzles, dipping. (rolldip coating) or curtain application processes (curtain coating) and the like are applied.

The same materials as those previously discussed in connection with the reflective layer of the thin-film arrangement can be considered as HRI layers in connection with the present invention.

Of course, it cannot be ruled out that another layer is used instead of the metallic or HRI layer, provided it is suitable for the application according to the invention.

In one embodiment of the invention it is provided that the security element is designed such that in a first viewing angle of the security element the moth-eye structure largely absorbs incident radiation and that the moth-eye structure largely diffracts incident radiation in a second viewing angle of the security element in order to produce a second color shift effect.

The moth eye structure used in connection with the present invention is a special moth eye structure which, on the one hand, acts as an absorber and on the other hand can serve as a diffractive structure. A corresponding moth eye structure, which acts as a diffractive structure at a certain viewing angle, is sold by the company Toppan under the name Asterium ^® .

At a first steep viewing angle, this means a viewing angle greater than 75°, the moth eye structure acts as an absorber and absorbs the wavelengths of visible light. The moth eye structure therefore appears dark to almost black to an observer at this angle.

However, in a flat viewing angle, i.e. a viewing angle of less than 75°, preferably less than 45°, the moth eye structure acts as a diffractive element, so that incident radiation is diffracted in a specific wavelength range, preferably the red wavelength range. This can ensure that the moth eye structure appears colored to the viewer at a flat viewing angle and no longer appears dark or almost black.

The moth eye structure therefore appears dark to almost black in a first viewing angle for a viewer at a steep viewing angle. The layer for producing a first color-shifting effect appears colored, for example green, to an observer at a steep angle. However, due to the fact that the layer for generating a first color-shifting effect is arranged at least in sections on the moth-eye structure, the viewer experiences a green color impression at a steep angle, since the moth-eye structure in this case acts as an absorber for the layer above it to generate a first color-shifting effect and the color impression of the layer to create a The first color shift effect is superimposed on the dark color impression of the moth eye structure.

In a second, flat viewing angle, the moth-eye structure no longer acts as an absorber, but in turn diffracts the incident radiation, so that a second color-shifting effect is created. Depending on the diffracted wavelength of the light, a different color effect is created. The layer for generating a first color-shifting effect, which is arranged at least in sections on the moth-eye structure, appears, for example, blue due to the first color-shifting effect, but since the underlying moth-eye structure no longer serves as an absorber, the color impression of blue is not strongly pronounced and that of the moth-eye structure The resulting color impression is superimposed on the color impression of the layer above to create a first color shift effect.

Since the layer for generating a first color shift effect only has to be arranged in sections on or overlapping with the moth's eye structure, this means that the double color shift effect can only occur in the areas in which the layer for generating a first color shift effect on or overlapping with the moth eye structure is arranged. In this case, the viewer therefore sees a color shift effect from green to red, while in sections in which only the moth eye structure is arranged, the viewer experiences a color impression from black to red.

Such a color effect from black to red is particularly advantageous because the red color impression of the moth's eye structure overlays the weak color impression of the layer above to produce a first color shift effect. This will result in approximately one Color-shifting effect between unusual color pairs is achieved, which cannot otherwise be achieved in this way.

In one embodiment of the invention it is provided that the security element is designed such that the layer for generating a first color shift effect has a first color impression in a first viewing angle and that the layer for generating a first color shift effect in a second viewing angle has a second color impression that is different from the first Color impression to create a color shift effect, e.g. from blue at a steep viewing angle to green at a flat viewing angle. At a flat viewing angle, the moth-eye structure does not act as an amplifier of the color-shifting effect of the layer for producing a first color-shifting effect, so that the color impression of the layer for producing a first color-shifting effect can be well superimposed on the color impression of the moth-eye structure generated by diffraction, whereby an unusual color-shifting effect can be produced overall .

Of course, it cannot be ruled out that the moth eye structure also diffracts into other wavelength ranges in order to achieve a color-shifting effect between other typical color pairs, such as from red to green.

In a further embodiment of the invention it is provided that the layer for producing a first color shift effect has a transmittance of greater than 10%, preferably greater than 50% and particularly preferably greater than 75%, in order to allow the desired radiation to pass through to the moth's eye structure.

In a further embodiment of the invention it is provided that the moth eye structure has microstructures a height in the range from 300 nm to 700 nm, preferably from 400 nm to 430 nm, and a structure period (also referred to as grating period) from 250 nm to 500 nm, preferably from 350 nm to 450 nm.

Microstructures at this height enable the specific property of the moth's eye structure so that at a steep angle it appears black and acts as an absorber for the layer to create a first color-shifting effect, while at a shallow angle they diffract light, creating a second color-shifting effect.

In principle, different variants of the order of the layers of the security element are conceivable:
In a first variant, the moth-eye structure and the layer for producing a first color-shifting effect are arranged on the same side of the carrier in order to enable particularly simple production of the security element.

A second variant of the invention provides that the moth-eye structure and the layer for generating a first color-shifting effect are arranged on different sides of the carrier, i.e. that the moth-eye structure is arranged on the first side and the layer for generating a first color-shifting effect is arranged on the second side of the carrier is, or vice versa. This has the advantage that the microstructures of the moth's eye structure provided with the reflective layer are additionally protected from external influences by the wearer from the visible side, i.e. the side comprising the layer for producing a first color shift effect.

In a further embodiment of the invention it is provided that the moth eye structure is between the first layer to produce a first color shift effect and a second layer is arranged to create a further color shift effect in order to enable a bilateral color shift effect between unusual color pairs.

The application of a layer on both sides to create a color-shifting effect enables the present invention to be widely used, for example in connection with banknotes or other documents of value. Banknotes or other valuable documents or data carriers are usually flat elements, each of which has two flat sides, whereby the security element can be arranged on one of these flat sides. The banknotes or other valuable documents can also be designed to be transparent in sections, in which case a security element with a color-shifting effect on both sides can then be arranged in this transparent section.

An arrangement in the transparent section of the banknote or the document of value or data carrier and the corresponding structure of the layers, namely comprising a moth-eye structure, on which a layer is arranged on both sides to produce a first color shift effect, makes it possible for the viewer, regardless of which flat side of the banknote or the document of value faces the viewer to create a double color-shifting effect according to the invention.

It is envisaged that the security element is used in particular in connection with data carriers or valuable documents, i.e. the security element is part of a valuable document or data carrier in order to increase the security against forgery. Of course, another application of the security element is not excluded.

Of course, it cannot be ruled out that a security element according to the invention has additional layers includes. These can be additional layers that create a color-shifting effect or other layers. Other layers that come into consideration are, for example, layers comprising machine-readable features, the machine-readable features being, in particular, magnetic codes, electrically conductive layers, electromagnetic wave-absorbing layers and/or re-emitting substances, additional colored lacquer layers, protective lacquer layers, adhesive layers, primer layers and/or film layers .

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be explained in more detail using exemplary embodiments. The drawings are exemplary and are intended to explain the idea of the invention, but are in no way intended to restrict or even exhaustively represent it.

• Fig. 1 eine perspektivische Ansicht eines Längsschnitts einer erfindungsgemäßen Mottenaugenstruktur,
• Fig. 2 eine perspektivische Ansicht eines Längsschnitts durch ein erfindungsgemäßes Sicherheitselement, wobei die Schicht zur Erzeugung eines ersten Farbkippeffekts noch nicht auf der Mottenaugenstruktur angeordnet ist,
• Fig. 3 eine perspektivische Ansicht eines Längsschnitts durch ein erfindungsgemäßes Sicherheitselement umfassend eine Mottenaugenstruktur sowie die darüber angeordnete Schicht zur Erzeugung eines ersten Farbkippeffekts,
• Fig. 4a einen Längsschnitt eines erfindungsgemäßen Sicherheitselements umfassend eine LC-Schicht mit ablösbarem Träger,
• Fig. 4b einen Längsschnitt eines erfindungsgemäßen Sicherheitselements umfassend eine LC-Schicht mit teilweise abgelöstem Träger,
• Fig. 5a-5d zeigen weitere Ausführungsformen eines erfindungsgemäßen Sicherheitselements mit einer Pigmentschicht als Schicht zur Erzeugung eines ersten Farbkippeffekts,
• Fig. 6 einen Längsschnitt eines erfindungsgemäßen Sicherheitselements mit mehreren Schichten, wobei die Mottenaugenstruktur und die Schicht zur Erzeugung eines ersten Farbkippeffekts auf unterschiedlichen Seiten angeordnet sind,
• Fig. 7 einen Längsschnitt eines erfindungsgemäßen Sicherheitselements mit zwei zusätzlichen Schutzlackschichten.

This shows:

• Fig. 1 a perspective view of a longitudinal section of a moth eye structure according to the invention,
• Fig. 2 a perspective view of a longitudinal section through a security element according to the invention, wherein the layer for producing a first color-shifting effect is not yet arranged on the moth-eye structure,
• Fig. 3 a perspective view of a longitudinal section through a security element according to the invention comprising a moth-eye structure and the layer arranged above it to produce a first color shift effect,
• Fig. 4a a longitudinal section of a security element according to the invention comprising an LC layer with a removable carrier,
• Fig. 4b a longitudinal section of a security element according to the invention comprising an LC layer with a partially detached carrier,
• Figs. 5a-5d show further embodiments of a security element according to the invention with a pigment layer as a layer for producing a first color shift effect,
• Fig. 6 a longitudinal section of a security element according to the invention with several layers, the moth-eye structure and the layer for producing a first color-shifting effect being arranged on different sides,
• Fig. 7 a longitudinal section of a security element according to the invention with two additional protective lacquer layers.

WAYS OF CARRYING OUT THE INVENTION

Fig. 1 shows the longitudinal section through a moth eye structure 3 according to the invention, made from, for example, plastic or a crosslinked or crosslinkable varnish, which is worn by the carrier 2. The carrier 2 thus has a moth-eye structure 3 on the first side. At carrier 2 the Fig. 1 This is a PET film.

Fig. 1 further shows the conical microstructures 7 of the moth-eye structure 3, which are arranged on the carrier 2 at periodic intervals in the form of a cross grid. The structure period (lattice period) is less than or equal to the wavelength of visible light to prevent reflection. On the microstructures 7 of the moth eye structure 3, a reflective layer 6 is arranged to enhance the diffraction effect, here a metallic layer.

Fig. 2 shows the longitudinal section of a moth-eye structure 3 before the layer is applied to produce a first color-shifting effect 4. Below is the carrier 2, which is provided with the moth-eye structure 3, which is coated with the metallic layer 6. Above, the layer for producing a first color shift effect 4 is shown in the form of a transparent cholesteric liquid crystal layer (LC layer), which is arranged on a separate carrier 8 for the purpose of aligning the liquid crystals.

In principle, four LC layers, LC pigment layers, layers comprising interference pigments or even thin layer structures can be considered as a layer for generating a first color shift effect.

The layer shown for generating a first color shift effect 4, for example, creates a color shift effect from green in a first viewing angle to blue in a second viewing angle. The separate carrier 8 can be a carrier 8 that remains on the layer for producing a first color-shifting effect 4 or one that is removed after the layer for producing a first color-shifting effect 4 has been applied to the moth-eye structure 3 (not shown). In the present case it is a separate carrier 8, which remains on layer 4.

In order to enable the layer 4 to be fixed on the moth-eye structure 3, an adhesive layer 9, here a laminating adhesive layer, is also applied to the reflective layer 6 in order to level the moth-eye structure 3 as much as possible. Layer 4 can then be applied as a flat layer to this layer, which is as leveled as possible, see Fig. 3 .

Fig. 3 shows the longitudinal section through a security element 1 according to the invention, which is made from Fig. 2 is available, wherein the security element 1 comprises a carrier 2, a moth-eye structure 3 and a layer for producing a first color shift effect 4. The layer for producing a first color-shifting effect 4 is fixed on the moth-eye structure 3 by means of an adhesive layer 9. The adhesive layer 9 must be at least semi-transparent in order to be able to obtain a double color-shifting effect according to the invention. The security element 1 is considered Fig. 3 from above.

The separate carrier 8 remains on the layer to produce a first color shift effect 4, so that it must in any case be a semi-transparent or transparent separate carrier 8 in order not to impair the function of the invention. However, the carrier 2 on which the moth-eye structure 3 is arranged is in the exemplary embodiment Fig. 4 designed as a detachable carrier 2.

In a first, steep viewing angle, for example vertically from above Fig. 3 , the moth eye structure 3 acts as an absorber layer for an observer and would therefore in principle appear dark to almost black. However, due to the fact that the layer for generating a first color-shifting effect 4 is arranged on the moth-eye structure 3 and the moth-eye structure 3 serves as an absorber in this area for the layer for generating a first color-shifting effect 4, the viewer experiences a green color impression here. If the viewer tilts it in Fig. 3 shown security element 1 to a flat viewing angle from above, the color impression changes from green to red. This occurs because the moth-eye structure 3 no longer acts as an absorber layer for the layer for generating a first color shift effect 4, but itself diffracts light into the red wavelength range , giving the viewer a red receives color impression. At the same time, layer 4 no longer appears green as in the steep viewing angle, but blue. However, since the moth-eye structure 3 arranged underneath no longer functions as an absorber, the blue color impression created by the layer 4 is only weakly pronounced and is overlaid by the red of the moth-eye structure 3. To the viewer, the security element therefore appears red at a flat angle.

Figs. 4a-4b show different structures of embodiments of a security element according to the invention.

Fig. 4a shows a longitudinal section through a security element according to the invention Fig. 3 , wherein the separate carrier 8 can be removed from the layer to produce a first color shift effect 4. Fig. 4a shows the separate carrier 8 still completely arranged on the moth-eye structure 3, while Fig. 4b represents the carrier 8 partially detached. The separate carrier 8 basically serves to ensure that the liquid crystal layer of the layer 4 can be aligned separately before it is applied to the moth-eye structure 3. The separate carrier 8 is then removed again because it is no longer needed.

Fig. 5a to 5d show further embodiments of a security element according to the invention, wherein the layer for producing a first color shift effect 4 is designed as a pigment layer.

Fig. 5a shows an embodiment of a security element 1 according to the invention, which in principle is like the security element 1 according to Fig. 1 is constructed. In contrast to Fig. 3 includes the security element of the Fig. 5a However, an LC pigment layer as a layer for producing a first color shift effect 4 and does not have a separate carrier 8. Advantageous of using an LC pigment layer is that this layer can be applied directly to the moth eye structure 3 or the layer(s) arranged thereon. The same applies if an interference pigment layer is used instead of an LC pigment layer.

According to the Fig. 5a the LC pigment layer is applied as a layer 4 to an adhesive layer 9, which was previously applied to the moth-eye structure 3, more precisely to its reflective layer 6, and levels the moth-eye structure 3. The LC pigment layer then forms a flat surface on the adhesive layer 9 following the structure of the moth eyes.

Fig. 5b shows a further embodiment of a security element 1 according to the invention, which in principle is like the security element 1 according to Fig. 1 is constructed. In contrast to the security element 1 according to the Fig. 5a only a thin primer layer 12 (adhesion promoter layer) is applied to the reflective layer 6, which does not level the moth-eye structure 3, but follows the underlying shape of the moth-eye structure 3. An LC pigment layer is then applied to the primer layer 12 as a layer for producing a first color shift effect 4, this being applied with such a layer thickness that it levels the structure of the primer layer 12.

Fig. 5c shows a further embodiment of a security element 1 according to the invention, which in principle is like the security element 1 according to Fig. 1 is constructed. In contrast to the security element 1 according to the Fig. 5b is applied to the primer layer 12, which is applied to the reflective layer 6 and which does not flatten the moth-eye structure 3, as a layer for producing a first Color shift effect 4 applied an LC pigment layer, which is applied with such a layer thickness that it does not level the structure of the primer layer 12, but follows it or the moth-eye structure 3.

Fig. 5d shows a further embodiment of a security element 1 according to the invention, which in principle is like the security element 1 according to Fig. 1 is constructed. In contrast to the security element 1 according to the 5a to 5c no adhesive layer 9 or primer layer 12 is applied to the reflective layer 6, as a result of which the structure of the moth eyes or the reflective layer 6 arranged thereon are not leveled. The LC pigment layer 4 is then applied directly to the reflective layer 6. The LC pigment layer, as a layer for generating a first color shift effect 4, also follows the structure of the underlying moth eyes in this case.

Fig. 6 shows another embodiment of the invention. The carrier 2 is here arranged between a moth-eye structure 3 and the layer for producing a first color shift effect 4, here a cholesteric liquid crystal layer. In order to achieve a desired double color shift effect, both the carrier 2 and the cholesteric liquid crystal layer 4 must be at least semi-transparent. In the embodiment according to Fig. 6 the microstructures 7 of the moth eye structure 3 are arranged on the side facing away from the carrier 2. The security element is viewed here again from above.

However, in order to make a color shift effect visible, it is necessary as in Fig. 6 shown that the moth eye structure 3 is again coated with a reflective layer 6, for example a metallic layer.

A security element according to the Fig. 5a-d and 6 can also be designed in such a way that the moth eye structure 3 has at least two areas with different periodicity of the moth eyes (not shown in the figures). Such an arrangement would have the effect that the moth-eye structure 3 appears dark to black everywhere at a steep viewing angle (the security element therefore appears in the color of the layer 4 to produce a first color shift effect), but at a flat viewing angle due to the different periodicity of the Areas in each area a different diffraction color is achieved. A similar effect (also not shown in the figures) can also be achieved if, in addition to a moth-eye structure 3, a black or dark layer, for example made of black paint or metal oxides in the form of a so-called black metallization, is applied. In this case too, the two areas appear dark to black at a steep viewing angle (or with layer 4 to create a first color-shifting effect in the color of this layer), while tilting to a flat viewing angle creates a different color effect because of the moth-eye structure 3 has a diffraction color, but the dark or black layer does not.

In Fig. 7 Another embodiment of the invention is shown, which is again viewed from above. Fig. 7 shows a carrier 2 on which a moth eye structure 3 is arranged. On the other side, i.e. opposite that of the moth eye structure 3, a protective lacquer layer 11 is applied. A metallic layer is applied as a reflective layer 6 on the moth eye structure 3. To level the moth eye structure 3, which includes the microstructures 7, an adhesive layer 9 is applied to the reflective layer 6. On this adhesive layer 9 is the cholesteric Liquid crystal layer arranged as layer 4 to create the first color shift effect. A separate carrier 8, as in Fig. 3 , has already been removed from layer 4 here. A protective lacquer layer 11 is again applied over layer 4. It goes without saying that the protective lacquer layers 11 are at least semi-transparent in order not to prevent an effect according to the invention.

Of course, the security elements 1 of the other embodiments can also be provided with a protective lacquer layer 11 on one or both sides. In particular, an otherwise exposed side of the security element 1 will be provided with a protective layer, for example in the form of a protective lacquer layer 11, in order to protect the security element 1 from external influences. That side of the security element 1 that is or is to be connected to a document of value generally does not require such a protective layer.

In all exemplary embodiments Fig. 1-7 A thin-film arrangement can also be used as a layer to create a first color-shifting effect 4.

REFERENCE SYMBOL LIST

1

Security element

2

carrier

3

Moth eye structure

4

Layer to create a first color shift effect

5

-

6

reflective layer

7

Microstructures

8th

Separate carrier

9

adhesive layer

10

-

11

Protective varnish layer

12

Primer layer

Claims (16)

Security element (1) with optical security features, suitable for arrangement on a flat support (2), comprising a moth-eye structure (3) and a layer for producing a first color-shifting effect (4), characterized in that the security element further comprises a reflective layer (6 ), which reflective layer (6) is arranged at least in sections directly on the moth-eye structure (3) and the layer for generating a first color shift effect (4) is arranged at least in sections overlapping with the reflective layer (6) arranged on the moth-eye structure (3). . Security element (1) according to claim 1, characterized in that the security element (1) further comprises a flat support (2). Security element (1) according to claim 1 or 2, characterized in that the layer for producing a first color shift effect (4) is an LC layer and/or an LC pigment layer. Security element (1) according to claim 1 or 2, characterized in that the layer for producing a first color shift effect (4) is a layer with interference pigments. Security element (1) according to claim 1 or 2, characterized in that the layer for producing a first color shift effect (4) is a thin-film arrangement. Security element (1) according to one of claims 1 to 5, characterized in that an adhesive layer (9) is provided to produce the layer for a first Attach the color-shifting effect (4) to the moth-eye structure (3) or a support (2). Security element (1) according to one of claims 1 to 6, characterized in that the reflective layer (6) is a metallic layer. Security element (1) according to one of claims 1 to 6, characterized in that the reflective layer (6) is an HRI layer. Security element (1) according to one of claims 1 to 8, characterized in that it is designed such that the moth-eye structure (3) largely absorbs incident radiation at a first viewing angle and that the moth-eye structure (3) largely diffracts incident radiation at a second viewing angle to create a second color-shifting effect. Security element (1) according to one of claims 1 to 9, characterized in that it is designed such that the layer for generating a first color-shifting effect (4) has a first color impression at a first viewing angle and that the layer for generating a first color-shifting effect (4) has a first color impression ( 4) in a second viewing angle has a second color impression that is different from the first in order to create a color shift effect. Security element (1) according to one of claims 1 to 10, characterized in that the layer for producing a first color shift effect (4) has a transmittance of greater than 10%, preferably greater than 50% and particularly preferably greater than 75%. Security element (1) according to one of claims 1 to 11, characterized in that the moth-eye structure (3) Microstructures (7) with a height in the range from 300 nm to 700 nm, preferably from 400 nm to 430 nm, and a structure period from 250 nm to 500 nm, preferably from 350 nm to 450 nm. Security element (1) according to claim 2, characterized in that the moth-eye structure (3) and the layer for producing a first color shift effect (4) are arranged on the same side of the carrier. Security element (1) according to claim 2, characterized in that the moth-eye structure (3) and the layer for producing a first color shift effect (4) are arranged on different sides of the carrier. Security element (1) according to one of claims 1 to 14 , characterized in that the moth-eye structure (3) is arranged between the layer for generating a first color-shifting effect and a second layer for generating a further color-shifting effect. Data carrier or document of value comprising a security element (1) according to one of claims 1 to 15.

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