WO2021228943A1

WO2021228943A1 - Security element

Info

Publication number: WO2021228943A1
Application number: PCT/EP2021/062631
Authority: WO
Inventors: Martin EGGINGER; Stephan Trassl
Original assignee: Hueck Folien Gesellschaft M.B.H.
Priority date: 2020-05-12
Filing date: 2021-05-12
Publication date: 2021-11-18
Also published as: EP4149770A1; AT523060B1; AT523060A4

Abstract

The invention relates to a security element which comprises a substrate and an optically variable multilayer structure and which can be written by the action of a laser, the multilayer structure comprising a spacer layer and a phase change-material layer. The security element thus allows the generation of high-resolution two-color image information which is more difficult to reproduce.

Description

Security element

The invention relates to a security element, comprising a substrate and an optically variable multilayer structure, and a method for producing the same, as well as the use of the security element.

Data carriers, such as documents of value and the like, are provided with security elements to protect against forgery and to check authenticity. In the context of the present invention, data carriers are understood to mean in particular documents of value, such as bank notes, certificates and shares, as well as identification documents, e.g. passports and the like. Other items, such as packaging materials and branded items, are also often equipped with security elements that allow the authenticity to be checked and at the same time serve as protection against unauthorized reproduction.

Such security elements can for example be in the form of a security thread embedded in a bank note, a cover film for a bank note with a hole, an applied security strip, a self-supporting transfer element or also in the form of a feature area applied directly to a value document.

Documents of value generally include personalizing and / or individualizing information that enables the document to be assigned to a person and / or a group of people, objects and / or entities. Individualizing information can include, for example, a serial number or an indication of the issuing authority. The personalizing and / or individualizing information also represents a security feature.

Personalizing information is understood to mean information that can be assigned to a person. These can include, for example, image information, such as a passport photo, a fingerprint, etc., or alphanumeric character strings, such as a name, an address, a date of birth or the like.

Numerous methods for producing security elements for documents of value are known from the prior art. For example, US Pat. No. 6,022,429, US Pat. No. 6,264,296 and US Pat. No. 7,037,013 describe processes in which an inkjet print is applied to finished blanks, which is to be protected against mechanical and / or chemical damage and manipulation with a protective varnish or a protective film. With this method, information can be stored in one color in the value document by printing technology. The value documents produced in this way only have a relatively low level of security against manipulation because the printed information is printed completely close to the surface and the protective layer made of lacquer or a protective film usually does not form a material bond with the blank. This can thus be detached or removed and the printed matter can then be manipulated.

From DE 41 34539 A1 a value or identity card with colored image information is known. The image information is broken down into a light / dark component and a color component, the light / dark component intended for the visual impression being incorporated into the map in a high-resolution form. The colored image information is congruently superimposed on this portion, so that an integral overall impression is created. In order to ensure protection against forgery, one of the parts of the image information is incorporated into a card structure in a largely forgery-proof manner.

Laser thermal transfer systems have also received more attention in recent years. In a typical laser thermal transfer system, a donor web having a layer of infrared absorbing transfer medium is placed in contact with a receptor and the assembly is exposed to a pattern of IR radiation. The absorption of the IR radiation causes a rapid development of heat in the exposed areas, which in turn causes the transfer of the medium from the donor to the receptor in order to generate an image. This transfer can be the result of sublimation, ablation, film or mass transfer, for example.

In an ablation thermal transfer system, the exposed transfer medium is propelled from the donor to the receptor by the generation of a gas. Specific polymers are selected that decompose when exposed to heat to quickly generate a gas. The build-up of gas under or within the transfer medium acts as a propellant to transfer the medium to the receptor. Examples of laser ablation systems can be found, for example, in US 5,516,622, US 5,518,861 and US 5,326,619.

In a mass transfer system, the colorant and associated binder materials are transferred in a molten or semi-molten state upon exposure to the radiation source on a receptor. The thermal transfer medium adheres to the receptor surface with greater strength than to the donor surface, which leads to the physical transfer of the medium in the areas shown (e.g. JP 63319192 A, EP 745489 A, US 5,501,937 A).

The disadvantage of the known methods, however, is that the known security elements, which are produced by means of laser-addressable pigments or by means of laser ablation, are limited to one color. In addition to colored security elements, elements with viewing angle-dependent effects have played a role in recent years, since these cannot be reproduced even with the most modern copiers. The security elements are equipped with optically variable elements which give the viewer a different image impression from different viewing angles and, depending on the viewing angle, show a different color or brightness impression and / or a different graphic motif.

In the context of the present invention, the phrase “optically variable” or “optical variability” is understood to mean the change in an optical property that can be detected by a viewer of a security element or data carrier with a layer according to the invention viewed by the viewer. The variable optical properties are understood to mean in particular the properties of a color that people perceive as fundamental, namely hue, brightness and color saturation. The quality of the color effect on a viewer of a security element according to the invention can furthermore be described by values such as chroma, colourfulness (color intensity), chromaticity, depth of color, brilliance and gray cast. Furthermore, the security elements, data carriers or colored layers according to the invention can also be characterized by further optical properties, e.g. by their reflectivity.

The invention has the object of specifying a security element with an optically variable element which can provide two-color image information by means of laser action and thus provides better protection against manipulation or falsification. In particular, it should also be possible to be able to modify the optically variable element of the security element for the purpose of individualization.

This object is achieved by the security element, the production method and the use according to the independent claims. Advantageous further developments of the inventions are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into the content of this description. The inventions also include all meaningful and in particular all combinations of independent and / or dependent claims mentioned.

In a first aspect, the subject matter of the invention is a security element comprising a substrate and an optically variable multilayer structure, which is characterized in that the multilayer structure comprises a spacer layer and a phase change material layer.

The invention is based on the knowledge that, due to their changeable optical properties, phase change materials are extremely advantageously suitable as optically variable components of colored security elements. The functionality of phase change materials ("phase change materials", PCM) is based on the property of compounds to exist in different crystal structures or states of order, which can be reversibly transformed into one another and have different physical properties. Depending on the application, the structure of a PCM is converted from an amorphous to a crystalline state and vice versa, for example in the nanosecond range, using short, intense laser pulses.

The PCMs that can be used according to the invention include, for example, vanadium oxides (VOx), niobium oxides (NbOx) and compounds or alloys comprising Ge / Sb / Te (chalcogenides), Ge / Te, Ge / Sb, Ga / Sb, Ag / In / Sb / Te, In / Sb, In / Sb / Te, In / Se, Sb / Te, Te / Ge / Sb / S, Ag / Sb / Se, Sb / Se, Ge / Sb / Mn / Sn, Ag / Sb / Te, Au / Sb / Te or Al / Sb, especially the following compounds / alloys in every stable stoichiometry: GeSbTe, VOx, NbOx, GeTe, GeSb, GaSb, AglnSbTe, InSb, InSbTe, InSe, SbTe, TeGeSbS , AgSbSe, SbSe, GeSbMnSn, AgSbTe, AuSbTe and AlSb. Preferred PCMs include Ge ₂ Sb ₂ Te ₅ and Ag _{3 In} ₄ Sb ₇₆ Tei ₇ (known as AIST). Various stoichiometric forms of these materials are also possible, for example Ge _x Sb _y Te _z . Each of these materials can also comprise one or more dopants, such as C or N. Some of these materials have the property of being stable both in the amorphous and in the crystalline phase at room temperature. In addition to the materials mentioned, materials other than PCM can also be used.

The multilayer structure preferably further comprises a reflection-enhancing layer, the spacer layer being arranged between the reflection-enhancing layer and the phase change material layer.

Depending on the thickness of the spacer layer, this multi-layer structure results in a certain color that is changed when, for example, a laser acts on the phase change material and changes its state. This “switching” of the PCM layer makes it possible to generate high-resolution, two-color image information, motifs, etc., which allow authentication and make reproduction difficult.

According to a first preferred embodiment, the reflection-enhancing layer is arranged adjacent to the substrate. This essentially results in a structure of substrate / reflection-enhancing layer / spacer layer / phase change material layer. However, this structure can also comprise other or additional layers.

In this structure, the phase change material layer is closest to the viewer, ie he is looking at the phase change material layer (regardless of any transparent layers present on the phase change material layer). According to a second preferred embodiment, the

Phase change material layer arranged adjacent to the substrate. This essentially results in a structure of substrate / phase change material layer / spacer layer / reflection-enhancing layer. This structure can also include other or additional layers.

With this structure, the substrate, which is transparent in this case, is closest to the viewer, i.e. he is looking at the substrate (regardless of any transparent layers that may be present on the reflection-enhancing layer). This structure can be used, for example, in the case of documents of value with security windows.

The phase change material of the phase change material layer is preferably selected from VOx, NbOx and compounds or alloys of GeSbTe, GeTe, GeSb, GaSb, AglnSbTe, InSb, InSbTe, InSe, SbTe, TeGeSbS, AgSbSe, SbSe, GeSbMnSe and, preferably, AlSbTe, AgSbMnSe Ge ₂ Sb ₂ Te ₅ and Ag ₃ ln ₄ Sb Tei. The phase change material layer preferably has a thickness of about 7-35 nm.

The spacer layer can be a dielectric layer. Precisely defined optical interferences between the reflected or transmitted partial beams of incident light can be caused by dielectric coatings. In this way, incident light can be adjusted in almost any way in terms of transmission and reflection.

For the dielectric spacer layer of the thin-film element, dielectric materials with a refractive index less than or equal to _{1.65 come into question, e.g. aluminum oxide (Al 2} 0 ₃ ), metal fluorides, e.g. magnesium fluoride (MgF ₂ ), aluminum fluoride (AIF ₃ ), silicon oxide (SiO _x ) , Silicon dioxide (Si0 ₂ ), cerium fluoride (CeF ₃ ), sodium-aluminum fluoride (e.g. Na ₃ AIF ₆ or Na ₅ AI 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. The above-mentioned materials can be vapor-deposited or, especially if they are monomers and polymers, printed on.

For the dielectric spacer layer of the thin-film element, however, dielectric materials with a refractive index greater than 1.65 can also be used, e.g. zinc sulfide (ZnS), zinc oxide (ZnO), titanium dioxide (Ti0 ₂ ), carbon (C), indium oxide (In ₂ 0 ₃ ) , Indium tin oxide (ITO), tantalum pentoxide (Ta ₂ 0 ₅ ), cerium oxide (Ce0 ₂ ), yttrium oxide (Y ₂ 0 ₃ ), europium oxide (Eu ₂ 0 ₃ ), iron oxides such as iron (ll, lll) oxide (Fe ₃ 0 ₄ ) and iron (III) oxide (Fe ₂ 0 ₃ ), hafnium nitride (HfN), hafnium carbide (HfC), hafnium oxide (Hf0 ₂ ), lanthanum oxide (La ₂ 0 ₃ ), magnesium oxide (MgO), neodymium oxide (Nd ₂ 0 ₃ ), praseodymium oxide (Pr ₆ On), samarium _{oxide (Sm 2} 0 ₃ ), antimony trioxide (Sb ₂ 0 ₃ ), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), silicon monoxide (SiO), selenium trioxide ( Se ₂ 0 ₃ ), tin oxide (Sn0 ₂ ), tungsten trioxide (W0 ₃ ), high refractive index organic Monomers and / or high refractive index organic polymers. The above-mentioned materials can be vapor-deposited or, especially if they are monomers and polymers, printed on.

The spacer layer preferably has a thickness such that a 1/4 system is formed, and this is in the range of approximately 50-700 nm for the specified materials.

The reflection-enhancing layer, which ensures that the part of the light passing through the PCM layer is reflected again in order to produce the color impression for the viewer, is formed in advantageous configurations by an opaque reflector layer. A metallic layer is preferably used as the reflection-enhancing layer, which preferably comprises at least one metal selected from the group consisting of aluminum, gold, chromium, silver, copper, tin, platinum, nickel and their alloys, for example nickel / chromium or copper /Aluminum. It is also conceivable that the reflection-enhancing metallic layer contains a semiconductor such as silicon. Finally, it is also conceivable that the reflection-enhancing metallic layer is produced by applying a printing ink with metallic pigments, preferably from a metal from the aforementioned group.

If the security element is designed as a semitransparent element, e.g. to be able to be used in a see-through window of a document of value, the multi-layer structure is selected in such a way that the color impression obtained by the PCM can be seen through the see-through window. In addition, instead of an opaque reflector layer, a semitransparent metal layer or a transparent reflection-intensifying layer, the refractive index of which is different from that of the PCM layer, is used as the reflection-enhancing layer.

In principle, almost all vapor-deposited, transparent compounds can be used as a transparent reflection-enhancing layer, in particular also coating materials with a higher refractive index. For such reflection-enhancing layers designed as HRI (high refractive index) layers, dielectric materials with a refractive index greater than or equal to 1.65 come into question, such as zinc sulfide (ZnS), zinc oxide (ZnO), titanium dioxide (Tί0 ₂ ), carbon ( C), indium oxide (In ₂ 03), indium tin oxide (ITO), tantalum pentoxide (Ta20 ₅ ), cerium oxide (Ce02), yttrium oxide (Y2O3), europium oxide (Eu ₂ 0 ₃ ), iron oxides such as iron (II , lll) oxide (Fe ₃ 0 ₄ ) and iron (lll) oxide (Fe ₂ 0 ₃ ), hafnium nitride (HfN), hafnium carbide (HfC), hafnium oxide (Hf0 ₂ ), lanthanum oxide (La ₂ 0 ₃ ), magnesium oxide (MgO ), Neodymium oxide (Nd ₂ 0 ₃ ), praseodymium _{oxide (Pr 6} On), samarium _{oxide (Sm 2} 0 ₃ ), antimony trioxide (Sb ₂ 0 ₃ ), silicon carbide (SiC), silicon nitride (S13N4), silicon monoxide (SiO), selenium dioxide ( Se203), tin oxide (Sn02), tungsten trioxide (WO3), high refractive index organic monomers and / or high refractive index organic polymers. To produce reflection-enhancing layers designed as an HRI layer, the previously mentioned materials are either vapor-deposited or, especially when it comes to monomers and polymers, printed on

The layer thickness of the transparent reflection-enhancing layer is preferably in the range from 30 nm to 300 nm, particularly preferably in the range from 50 nm to 100 nm.

The reflection-enhancing layer is preferably vapor-deposited in a vacuum vapor deposition process.

A wide variety of vapor deposition processes are suitable for producing the layers. A methodical group forms the physical vapor deposition ("physical vapor deposition", PVD) with boat vaporization, vaporization by resistance heating, vaporization by induction heating or electron beam vaporization, sputtering (DG or AC) and arc vaporization. On the other hand, vapor deposition can also take the form of chemical vapor deposition (CVD), such as sputtering in reactive plasma or any other plasma-assisted vapor deposition. In principle, there is also the option of printing dielectric layers.

According to a further embodiment, the multilayer structure further comprises a cover layer. Cover layers serve, for example, as a protective layer against external mechanical or chemical effects or as an adhesive layer. For example, an adhesive varnish, such as a heat-sealing varnish, can be used for the top layer, it also being possible for a primer to be integrated into the top layer.

Flexible plastic films, also called carrier films, are preferably used as the substrate. This can be, for example, PI (polyimide), PP (polypropylene), MOPP (monoaxially stretched polypropylene), PE (polyethylene), PPS (polyphenylene sulfide), PEEK (polyetheretherketone), PEK (polyetherketone), PEI (polyetherimide), PSU ( Polysulfone), PAEK (polyaryletherketone), LCP (liquid crystal polymers), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PET (polyethylene terephthalate), PA (polyamide), PC (polycarbonate), COC (cyclo-olefin copolymers) , POM (polyoxymethylene), ABS (acrylonitrile butadiene styrene), PVC (polyvinyl chloride), PTFE (polytetrafluoroethylene), ETFE (ethylene tetrafluoroethylene), PFA (tetrafluoroethylene perfluoropropyl vinyl ether fluorocopolymer), MFA (tetrafluoromethylene perfluoropropyl vinyl ether), PVF copolymer Polyvinyl fluoride), PVDF (polyvinylidene fluoride), and EFEP (ethylene-tetrafluoroethylene-hexafluoropropylene-fluoroterpolymer) and / or mixtures and / or copolymers of these materials. The carrier substrate is preferably made from at least one of these materials.

The films preferably have a thickness of 5-700 µm, preferably 5-200 µm, particularly preferably 5-100 µm. According to a preferred embodiment of the invention, the security element forms a security strip, a security thread, a security tape, a patch or a transfer element for application to a security paper, document of value and the like.

In the case of security threads, a distinction is made between completely embedded threads (these are located completely within the document of value, e.g. the bank note) and partially embedded threads, so-called window threads, which appear in the window areas on the surface of the document of value, e.g. the paper.

A second aspect of the invention relates to a method for producing a security element in which an optically variable multilayer structure is formed on a substrate, the optically variable multilayer structure comprising a phase change material layer.

It is preferred that for the optically variable multilayer structure a transparent spacer layer is sandwiched between the phase change material layer and a reflection-enhancing layer.

A cover layer is preferably also formed on the multilayer structure.

According to a preferred embodiment, the phase change material layer is modified by the action of a laser, preferably flat in the form of motifs such as picture elements, numbers, letters, etc., in particular after application of the security element to a document of value.

For example, a passport lamination film can be individualized by laser writing. In another application, a consecutive serial number can be written in control marks, for example.

If the security element is required in the form of a window thread, it is not necessary to use this already modified. The personalization can also advantageously only be carried out after the thread has been introduced, e.g. into the bank note.

The subject of the invention according to a third aspect is the use of a security element described above to protect against forgery of documents of value and goods of any kind.

After the transfer of the security element to a document of value, the substrate can be peeled off from the multilayer structure of the security element or it can remain as a fixed component, for example as a protective layer. It goes without saying that the security element can also have further layers, such as those with other security features.

If the security element forms a semitransparent element and the substrate of the security element is not to be removed when it is applied to the value document, e.g. because it also serves as an adhesive or protective layer, the substrate is also optically transparent. In this case, a multilayer structure is provided in which the phase change material layer is arranged adjacent to the substrate.

The invention is explained in more detail below by means of the figures, which, however, do not represent a true-to-scale and proportionate representation of embodiments according to the invention, wherein

1 shows a schematic representation of the principle of PCM on the basis of an exemplary optically variable multilayer structure in a security element according to the invention in two different states, FIG

2 shows a schematic representation of the layer structure of an embodiment of the security element according to the invention, which is provided for use in a see-through window of a document of value.

In FIG. 1, the two different (crystal) states of a phase change material are each shown in a section of a security element according to an embodiment of the invention. The security element 1 has the same structure in the left and right figures, each corresponding to a different solid state of the PCM, and consists of an optically variable multilayer structure 2 which, for the sake of clarity, is essentially only the one required to achieve the inventive effect Shows elements or layers.

It goes without saying, however, that the specifically illustrated form is not restricted and that further layers can be present in the structure of the exemplary embodiments described, which serve additional functions or are required for other security features which are likewise present in the security element.

The multilayer structure 2 is formed on a substrate 3, which for example consists of a plastic film such as PE, PP or PTFE, with a thickness of 5-100 μm, and comprises a spacer layer 4 and a PCM layer 5.

The phase change material of the PCM layer 5 assumes a certain state at room temperature, which can be either a crystalline or an amorphous phase. In the illustrated embodiment, the state of the PCM is amorphous in the right figure, while it is crystalline in the left figure. When energy acts, in particular in the form of a laser beam 6, in particular in the form of a pulse, the phase change material switches from amorphous (disordered) to crystalline (ordered) or vice versa. This is illustrated in FIG. 1, where the amorphous phase is shown in the illustration on the right and the crystalline phase is shown in the illustration on the left. 1a shows, enlarged in a circular section, schematically the crystal structure of the “disordered” amorphous phase (right) and the “ordered” crystalline phase (left) of the PCM layer 5.

The phase change material of the PCM layer 5 is, for example, a vanadium oxide, a niobium oxide or a stoichiometric form of a compound or alloy of various combinations of Ge, Sb, Te, In and Ga as well as other elements such as Ag, Au, Al, Mn or S. Die PCM layer has a thickness of about 7-35 nm, for example.

The spacer layer 4 is preferably a dielectric layer, which, depending on the application, can be materials with a refractive index <1.65, such as SiO ₂ , or dielectrics with a refractive index greater than 1.65, such as ZnO. In order to achieve a particularly good result, the layer thickness of the transparent spacer layer 4 is selected such that a 1/4 system is formed when light is irradiated.

The multilayer structure 2 further comprises a reflection-enhancing layer 7 between the spacer layer 4 and the substrate 3, the reflection-enhancing layer 7 being arranged adjacent to the substrate 3 in the embodiment shown.

An opaque metallic layer such as Al or Pt, a semitransparent metal layer and an HRI layer such as ZnO can be used as the material for the reflection-enhancing layer 7.

The multi-layer structure 2 also comprises a cover layer 11, which can be designed, for example, as a protective layer against external influences.

If light, represented by its yellow component 8, its green component 9 and its blue component 10, falls on the security element 1, the light initially passes through the PCM layer 5 and becomes independent of the phase or the crystalline state of the phase change material reflected on the reflection-enhancing layer 7. When the reflected light passes through the PCM layer 5, however, depending on the phase of the material, a certain proportion of the light is absorbed.

While in the disordered state (amorphous phase - right) the green part 9 is absorbed and the PCM material appears magenta-red as a result, when the PCM layer 5 is transformed into the ordered state (crystalline phase - left) by the action of heat (e.g. laser pulse), it is transformed to a yellow color impression, since the blue light component 10 is absorbed here. Since the laser action can take place precisely and in a targeted manner, it is possible to bring about the phase transformation and thus the color change also locally selectively and to modify the PCM layer 5, for example in the form of colored motifs such as picture elements, numbers and letters. The modification can take place before the security element is applied to a value document or only afterwards, for example to individualize the same.

The representation of a security element modified in this way would correspond, for example, to the combination of the right and left images in FIG. 1 to form a single security element. In such a security element, there would be an area, for example in the form of a motif, in which the phase change material would be in an amorphous state and would appear, for example, magenta, and an area in which the phase change material is in a crystalline state and, for example, appear yellow would.

An alternative embodiment of the security element 1 according to the invention is shown in FIG. 2. The layer structure in this example differs from that from FIG. 1 in that it is not the reflection-enhancing layer 7 but rather the PCM layer 5 that is arranged adjacent to the substrate 3. The multilayer structure 2 thus has the same sequence as in Fig. 1, i.e. an arrangement in which the spacer layer 4 is present between the reflection-enhancing layer 7 and the PCM layer 5, but the substrate 3 is on the other side of the multilayer structure 2.

In this case, the substrate 3 is closest to the viewer and consequently transparent in order to make the color of the phase change material visible. In this case, the substrate 3 can also be designed as an adhesive or protective layer if it is not to be removed after the security element has been applied to a value document.

In such an application, a layer structure without a reflection-enhancing layer would also be possible, so that the security element appears to the viewer from both sides, for example as a colored stripe or thread, in the window.

Claims

PATENT CLAIMS

1. A security element comprising a substrate and an optically variable multilayer structure, characterized in that the multilayer structure comprises a spacer layer and a phase change material layer.

2. The security element according to claim 1, characterized in that the multilayer structure further comprises a reflection-enhancing layer, the spacer layer being arranged between the reflection-enhancing layer and the phase change material layer.

3. The security element according to claim 2, characterized in that the reflection-enhancing layer is arranged adjacent to the substrate.

4. Security element according to claim 2, characterized in that the phase change material layer is arranged adjacent to the substrate.

5. Security element according to one of claims 1 to 4, characterized in that the phase change material of the phase change material layer is selected from vanadium oxides (VOx), niobium oxides (NbOx) and compounds or alloys of GeSbTe, GeTe, GeSb, GaSb, AglnSbTe, InSb, InSbTe, InSe, SbTe, TeGeSbS, AgSbSe, SbSe, GeSbMnSn, AgSbTe, AuSbTe and AlSb.

6. Security element according to one of claims 1 to 5, characterized in that the spacer layer is a dielectric spacer layer.

7. Security element according to one of claims 1 to 6, characterized in that the reflection-enhancing layer is selected from an opaque metallic layer, a semitransparent metal layer and an HRI layer.

8. Security element according to one of claims 1 to 7, characterized in that the multilayer structure further comprises a cover layer.

9. Security element according to one of claims 1 to 8, characterized in that the substrate is selected from plastic films made of PI (polyimide), PP (polypropylene), MOPP (monoaxially stretched polypropylene), PE (polyethylene), PPS (polyphenylene sulfide), PEEK (Polyetheretherketone), PEK (polyetherketone), PEI (polyetherimide), PSU (polysulfone), PAEK (polyaryletherketone), LCP (liquid crystal polymers), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PET (polyethylene terephthalate), PA ( Polyamide), PC (polycarbonate), COC (cyclo-olefin copolymers), POM (polyoxymethylene), ABS (acrylonitrile-butadiene-styrene), PVC (polyvinyl chloride), PTFE (polytetrafluoroethylene), ETFE (ethylene tetrafluoroethylene), PFA (tetrafluoroethylene Perfluoropropyl vinyl ether fluorocopolymer), MFA (tetrafluoromethylene perfluoropropyl vinyl ether fluorocopolymer), PVF (polyvinyl fluoride), PVDF (polyvinylidene fluoride), and EFEP (ethylene-tetrafluoroethylene-flexafluoropropylene-fluoroterpolymer) and / or mixtures and / or co-polymers of these materials.

10. Security element according to one of claims 1 to 9, characterized in that the security element forms a security strip, a security thread, a security tape, a patch or a transfer element for application to a security paper, document of value and the like.

11. A method for securing a security element, characterized in that an optically variable multilayer structure is formed on a substrate, the optically variable multilayer structure comprising a phase change material layer.

12. The method according to claim 11, characterized in that a transparent spacer layer is sandwiched between the phase change material layer and a reflection-enhancing layer for the optically variable multilayer structure.

13. The method according to claim 11 or 12, characterized in that a cover layer is also formed on the multilayer structure.

14. The method according to any one of claims 11 to 13, characterized in that the phase change material layer is modified by the action of a laser, preferably flat in the form of motifs such as picture elements, numbers, letters, etc., in particular after application of the security element to a value document.

15. Use of a security element according to one of claims 1 to 10 to protect against forgery of documents of value and goods of any kind.