AT509792A1 - SECURITY ELEMENTS WITH METALLIC MAGNETIC LAYERS - Google Patents

Description

Safety elements with metallic magnetic layers

The invention relates to security elements with metallic magnetic layers and an associated measurement method for checking the authenticity.

Security elements having layers with machine-readable magnetic properties are known.

These layers are made essentially by the application of a magnetic pigment paint or varnish.

Such security elements are known, for example, from EP 0 310 707 B or EP 0 516 790 B.

Security elements with magnetic coding are known, for example, from EP 1 488 935 A2.

The verification of such a magnetic feature is carried out by a hysteresis, on the one hand only the presence of the material can be detected (eg bitwise coding: 1 = magnetic, 0 = non-magnetic), or on the other magnetic characteristics such as remanence and / or coercive force and / or susceptibility be determined as a value, whereby an even clearer demarcation is possible.

Disadvantage of these security elements with magnetic layers of magnetic pigment paints or varnishes is that the magnetic layers, in order to obtain a verifiable measurement, and because of the size of the pigment particles, usually have a relatively high layer thickness of a few pm, this results in a difference in thickness between the magnetic-coated and non-magnetic-coated areas of the security element. On the other hand, this difference in thickness creates problems in embedding the security element in the form of a thread in a document of value, since the paper formation can be hindered by an excessive thickness of the thread.

This difference in thickness in turn leads to problems in the stacking and / or packaging of value documents, since the value document on the 2 lit *

Places where such a thread is embedded, overall slightly thicker. In addition, the magnetic pigment paints or lacquers usually have a dark coloration (black or brown), which is clearly visible through the paper surface. This optical disadvantage is usually attempted to be remedied by, for example, metallic cover layers or admixture of metallic particles.

The object of the invention was to provide a security element having magnetic features, wherein the layer having magnetic properties is thinner than the known magnetic pigment layers and does not impair the visual appearance of the security element.

The invention therefore relates to a security element with magnetic properties, characterized in that the magnetic layer consists of a thin magnetic metal layer, which can be verified by means of a magneto-optical process.

The magnetic metal layer is applied to a carrier substrate.

As carrier substrates, for example carrier films are preferably flexible plastic films, for example of PI, PP, MOPP, PE, PPS, PEEK, PEK, PEI, PSU, PAEK, LCP, PEN, PBT, PET, PA, PC, COC, POM, ABS, PVC , PTFE, ETFE (ethylene tetrafluoroethylene), PFA (tetrafluoroethylene)

Perfluoropropyl vinyl ether fluorocopolymer), MFA (tetrafluoromethylene-perfluoropropyl vinyl ether fluorocopolymer), PTFE (polytetrafluoroethylene), PVF (polyvinyl fluoride), PVDF (polyvinylidene fluoride), and EFEP (ethylene-tetrafluoroethylene-hexafluoropropylene fluoropolymer).

The carrier films preferably have a thickness of 5 to 700 μm, preferably 5 to 200 μm, more preferably 5 to 50 μm.

Furthermore, non-magnetic metal foils, for example Al, Cu, Sn or stainless steel foils with a thickness of 5-200 μm, preferably 10 to 80 μm, particularly preferably 20-50 μm, may also serve as the carrier substrate. The 3

Films can also be surface-treated, coated or laminated, for example with plastics, or painted.

Further, as carrier substrates and pulp-free or cellulose-containing paper, thermally activated paper or composites with paper, for example composites with plastics having a basis weight of 20 - 500 g / mz, preferably 40 - 200 g / ma. be used.

The carrier substrate may already have coatings or layers which may be applied over the whole area or partially.

In particular, the carrier substrate may already have a layer with a structured lacquer layer. The lacquer layer may be a radiation-curable lacquer layer or a thermoplastic lacquer layer mixed with stabilizers into which a structure, for example a surface relief, a diffraction structure, a diffraction grating, microlenses, a kinegram or a hologram is embossed by known methods. The structure is then stabilized, for example by electromagnetic radiation, or by curing the thermoplastic lacquer layer, which is improved by the stabilizers.

A thin layer of magnetic metal is now applied to the carrier substrate. Particularly suitable magnetic metal layers are ferromagnetic iron, nickel or cobalt layers and their alloys or compounds (for example iron oxides). However, it is also possible to use known hard-magnetic alloys based on samarium or neodymium, as well as other ferromagnetic materials known to those skilled in the art.

The thickness of the magnetic metal layer is dependent on the metal used and is generally 1 to 200 nm, preferably 5 to 100 nm. 4 4

• ·

The magnetic metal layer can be applied over the entire surface or partially.

The application of the metal layer can be carried out in the usual way, for example by known PVD or CVD methods, by sputtering and the like. Depending on the process, a full-area layer or a non-continuous layer, for example a layer formed from metallic clusters, can be applied by these methods.

For example, known demetallization processes or etching processes are suitable for applying a partial layer. Such methods are described, for example, in DE 197 39 193 A or EP 1 332 238 A, the contents of which are incorporated here.

Compared to the usual layers consisting of magnetic pigment paints or coatings, magnetic metal layers have the advantage that they can be made substantially thinner with similar magnetic properties. As a result, they can be integrated much more advantageously in the layer structure of a security element as an additional security feature.

In addition, these thin magnetic metal layers do not have the troublesome dark coloration of the conventional magnetic layers and a generally well-reflecting, glossy surface, and are therefore more visually appealing. The magnetic metal layers are therefore not at first glance of non-magnetic metal layers e.g. distinguishable from aluminum or chrome, making the magnetic layer much harder to detect and falsify.

In one embodiment, a plurality of optionally different magnetic metal layers may also be arranged along the entire surface and / or partially alongside one another and / or one above the other. Even with several ♦ · ♦ f 5 ♦ · ♦ f 5

The layer thickness of the magnetic layer remains significantly lower than in the case of a coating with conventional magnetic pigment paints. 5 Additional partial or full-surface layers can subsequently be applied to the magnetic metal layer.

In particular, it is possible to apply further metal layers. These layers may consist, for example, of Al, Cu, Cr, Sn, Pd, Au, Ag, Zn, Pt, Ti, In. In a preferred embodiment, for the magnetic metal layer and the further metal layer, two metals are optically very similar, e.g. Sn and Ni. If, for example, the magnetic layer 15 is applied partially and the further metal layer over the entire surface, the machine-readable magnetic code resulting from the arrangement of the magnetic regions is not optically recognizable, but can be detected beyond doubt by means of a suitable measurement. If a metal layer is used which produces a distinctly different visual impression, e.g. a reddish colored Cu layer, the contrast with a silvery Ni layer results in an interesting visually perceptible optical effect, in that the Ni layer is recognizable as distinct from the Cu layer, but the machine readability of the feature is not without aids can be detected.

In addition, the structure may also have further layers with possibly functional properties, such as, for example, dye and lacquer layers with optical, optically variable or electrically conductive properties.

Thus, for example, a lacquer layer may be applied, which may be unstructured or structured, for example embossed. Optically active 30 * *. • • * # # • • • • • • •. • • • • • • • * * * * * * *

Security features such as holograms, kinegrams, diffraction structures, diffraction gratings, surface reliefs, microlenses and the like may be introduced into the lacquer layer.

As color or lacquer layers, a wide variety of compositions can be used in each case. The composition of the individual layers may in particular vary according to their purpose, that is to say whether the individual layers serve exclusively for decorative purposes or should be a functional layer or whether the layer should be both a decorative corn and a functional layer.

These layers may be pigmented or unpigmented. As pigments, it is possible to use all known pigments, such as, for example, titanium dioxide, zinc sulfide, kaolin, ITO, ATO, FTO, aluminum, chromium oxides and silicon oxides, and also colored pigments. In this case, solvent-based coating systems and systems without solvents can be used.

Preferably, the pigments are incorporated in acrylate polymer dispersions having a molecular weight of from 150,000 to 300,000, in acrylate-urethane dispersions, acrylate-styrene or PVC-containing dispersions or in solvent-containing dispersions of this type.

The optical properties of the layer can be visualized by visible dyes or pigments, luminescent dyes or pigments which fluoresce or phosphoresce in the visible, in the UV region or in the IR region, effect pigments, such as liquid crystals, pearlescent, bronzes and / or multilayers Color change pigments and heat-sensitive colors or pigments influence. These can be replaced individually or in all possible combinations.

An electrically conductive coating may be a metallic or non-metallic or a polymeric conductive coating, wherein as II ·· * " Substantially all of the abovementioned metallic layers can be considered as starting from the metallic electrically conductive layers.

But it can also with carbon black, graphite or silver pigmented dispersions or solutions in Ethylenacrylatcopoiymer. Nitrocellulose, PVB, PA, acrylate or PVC or their copolymers.

The pigment content may be up to 90%, preferably the binder content may be 20-70%.

The electrically conductive polymers may be, for example, polyacetylene, poly-p-phenylene, polypyrroles, polythiophenes, poly-p-phenylenevinylene, low molecular weight macrocyclic semiconductors, organopolysilanes, polysulfur nitride and / or polyanilines and / or derivatives thereof. Polyaniline or polythiophenes are preferably used as electrically conductive polymers.

In a further embodiment, the security substrate having the security features may be laminated against another carrier substrate. Optionally, this further carrier substrate may also have security features.

The security element can be provided on one or both sides with a full-surface or partial protective lacquer layer. The protective lacquer layer can be unpigmented or pigmented.

Furthermore, the security element can be provided on one or both sides with an adhesive coating, for example a hot or cold seal adhesive coating or a self-adhesive coating. This improves anchorage in or on the support of the value document.

The security features according to the invention, if appropriate after appropriate assembly (for example into threads, tapes, strips,

" · • · · 8th

Patches or other formats) as security features for at least partial embedding in or for application to data carriers, in particular value documents such as identity cards, cards, banknotes or labels, seals and the like, but also in or on packaging materials for sensitive goods, such as pharmaceuticals, cosmetics, data carriers, used electronic components and the like.

In particular, the security elements according to the invention are suitable for at least partially closing an opening in a value document. In this case, the security elements can at least partially close off a complete opening as security elements embedded in the substrate of the value document, but also be visible on a surface in the region of a recess of the substrate.

Furthermore, the opening or the recess can also be at least partially closed by applying the security element to at least one surface of the value document.

Advantageously, then any adhesive coating is partially recessed in the region of the opening. If there is a thickening in the document of value around the aperture, the adhesive coating can be applied thinner in the area of this thickening.

In a further embodiment, the security element may be formed as a transfer element, wherein after the application to the object to be secured, the carrier substrate is withdrawn. If appropriate, the release capability can be adjusted by a known release layer applied to the carrier substrate.

Suitable release layers are known poorly adhering compositions, for example those based on cycloolefin copolymers, nitrocellulose, acrylates, polyvinyl chloride, ethylene acrylate copolymers or styrene acrylates in a suitable solvent. To adjust the adhesion, preferably chlorinated polyolefins are added. Furthermore, even very thinly applied polyamide, polyethylene, • · · ·

Fluoropolymer wax layers or silicone coatings are used as the release layer.

The verification of the magnetic metal layer is carried out by known measuring methods of magnetic properties, such as hysteresis or susceptibility. In particular, due to the thin layers and the associated very weak magnetization, the verification can advantageously be carried out by a magneto-optical measurement taking advantage of the magneto-optical Kerr effect (MOKE).

In a preferred embodiment, the magneto-optical measurement can be carried out by means of an RDS measurement (reflectance difference spectroscopy) using the magneto-optical Kerr effect (RD-MOKE). This method is particularly expedient if the layer thickness of the magnetic metal layer is chosen so thin that it can no longer be detected with the usual magnetic measuring methods.

The measurement principle and the physical principles of the RDS measurement are described, for example, in P. Weightman et al., Reports on Progress in Physics 68 (2005), p. 1251 et seq. The evaluation of morphological and magnetic information from an RD-MOKE measurement on nickel layers is explained in detail, for example, in R, Denk et al., Physical Review B 79 (2009), p. 073407 et seq. For such a measurement, the security feature, or in particular the magnetic metal layer in the structure of the security feature, must be optically accessible, but the metal layer may well be covered by one or more transparent or semitransparent layer (s). In any case, the prerequisite is that enough light is reflected from the magnetic metal layer so that an evaluable signal can be detected in the measuring system. In this way, pigmented magnetic layers can generally not be detected, since not enough light is reflected by the dark coloration and the light scattering on the pigments. · ·

10

In an RD-MOKE measurement, the security element is irradiated with defined polarized light (for example linearly or elliptically polarized light) and the relative change in the polarization properties of the reflected light compared to the incident light is determined.

The measurement can be carried out at a defined wavelength or over a broad spectral range.

Subsequently, an external magnetic field is applied, for example by placing a permanent magnet under the security element, or by an electromagnet generating a field at the location of the sample.

Upon application of the external magnetic field, there is a marked change in the polarization of the reflected light due to the magnetization of the magnetic layer in the external magnetic field compared to a measurement without an external field. Even when the magnetic field is reversed, there is a significant change in the measured signal.

The amount of change depends on the strength of the magnetic field, the material used and the thickness of the metallic magnetic layer. Magnetic fields of 0 - 2 T are usually used for the measurement, but magnetic fields with strengths below 1 T are preferred, in order to realize a simple measurement setup.

These changes are used for the qualitative and quantitative verification of the magnetic characteristic.

The size of the measuring spot is dimensioned so that a local evaluation of the magneto-optical signal is possible even on narrow security elements in the form of threads. Focusing is possible by using a lens or a lens system in the beam path or by integration into a confocal microscope. Such a construction is described in Koopmans et al., Applied Physics Leiters 69 (6) (1996), page 782 et seq. Typical spot sizes are in the range of 0.05 to 10 mm, preferably 0.1 to 2

mm, but may be significantly lower when using a confocal microscope.

In a preferred embodiment, the magnetic metal layer is so thin that there is no more coherent layer, but so-called clusters. These clusters generally have a size, ie a characteristic spatial extent in one of the spatial directions, in the range of 1-50 nm, preferably 1-10 nm, so that the magnetic properties differ significantly from the properties of the bulk material due to the small size. Such cluster layers show no signal in a conventional magnetic measurement, since the change of the magnetization by the external magnetic field is too small.

With a very sensitive measurement setup, such as However, the RDS method described above, even this low magnetization can still be clearly detected. Also, due to the measured spectrum, the presence of clusters instead of a continuous layer can be detected. The security against counterfeiting is thus again significantly higher than a coherent layer.

Non-magnetic metal layers generally exhibit an RDS signal in a MOKE or RD-MOKE measurement, however, which does not change when an external magnetic field is applied or changed. The measuring method therefore distinguishes reliably between magnetic and non-magnetic metal layers.

In Fig. 1, the measuring structure is shown schematically in a provided with the security element according to the invention value document.

FIGS. 2 and 3 show the construction of a value document with the security element fastened thereon in the form of a thread or ribbon. »« *

1. a document of value with a security element 7 according to the invention 2. the incident light beam 3. the reflected light beam 4. the magnetic field lines 5. a device for generating a magnetic field in the orthogonal direction to the surface of the security element, for example an electromagnet 6. a carrier substrate or Value document on which the security element is affixed 7. the security element 8. the measuring area 9. a transparent UV lacquer layer 10. the magnetic metal layer 11. a heat-seal adhesive layer 12. an embossing

For simplicity, the adhesive layer with which the structure is fixed to the value document, not shown in Fig. 1. Such a layer is provided between the magnetic metal layer 10 and the value document 6. The carrier film on which the layers of the security element 7 were produced was removed after the transfer of the layers to the value document and is therefore also not shown in FIGS. 1 to 3.

The security element 7 is irradiated with defined polarized light, for example linearly polarized light 2 (electric field Ein). The reflected light 3 (electric field Eout) is detected and the change in the polarization state (ψ) and the phase relationship of the two orthogonal components (Δ) are determined , From this, the normalized difference of the light reflection along two orthogonal polarization directions, ie the RDS signal, is determined:

- = tan4VÄ = 2 --- r * + ry ^ ~ 2Θ = 2θ + 2ΐε

The last relation holds for small complex angles of change Θ, where the real part of Θ corresponds to the rotation of the polarization Θ, and the imaginary part of Θ corresponds to the 5 ellipticity ε.

In general, the RDS signal results only from the optical anisotropy of the surface of the measured layer. However, if the sample is acted upon by a suitable device 5 with a magnetic field 4 along a direction 10 orthogonal to the surface, an additional change in the RDS signal results due to the magneto-optical Kerr effect in the case of magnetic materials. Δτ = (Ar \ r \ r / ((*> anisotropic magnetic + w \ r / n [(H - (Hl · 2 r / magnetic 15

From the difference of two measurements with opposite aligned magnetic field one can determine the magnetic RD-MOKE signal. With exclusively non-magnetic layers, the signal does not change upon reversal of the magnetic field. The result of such a measurement is shown in FIG. 4, where the real part of the RDS signal Ar / r is plotted as a function of the photon energy. Two measuring curves can be seen, which were measured with the applied magnetic field in different directions (Bup or Bd0Wn). The measurements at low photon energies (2-3 eV) show a significant difference, i. the measured nickel layer shows magnetic properties. In the case of a non-magnetic layer, the two traces would be identical. The oscillations in the measured curves result from interference effects in the overlying UV varnish and do not carry any significant information, except that with the help of appropriate modeling from the number and position of the oscillations on the thickness of the UV varnish can be deduced. * · * ·

• 1 r * * · • 1 jp · · ·

Example 1:

On a web-shaped carrier substrate made of PET with a thickness of 36 .mu.m was applied by means of an anilox roller a release-capable UV coating layer based on polyester acrylate with a thickness of 4 pm. This lacquer layer was provided with a hologram embossing on the surface facing away from the substrate. Such a method is described in EP 1 310 381 A.

Subsequently, a nickel layer was deposited by DC sputtering in a vacuum film coater. The thickness of the nickel layer was 30 nm.

The assembly was finally provided with a 20 pm thick heat sealing lacquer layer, applied to the value document under pressure at a temperature of about 180 ° C and the support substrate withdrawn.

FIG. 4 shows the spectrum of an RD-MOKE measurement on the security element from Example 1.

Example 2:

On a carrier substrate made of PET with a thickness of 12 μm, a layer of a highly pigmented printing ink was first applied partially by gravure printing. Thereafter, a partial nickel layer was deposited by electron beam vapor deposition in a continuous process. The thickness of the nickel layer was 100 nm.

Following the paint application was removed together with the overlying metal layer by means of a washing process again.

As a further metal layer, a full-surface 30 nm thick aluminum layer was vapor-deposited, likewise by electron beam vapor deposition.

The coated carrier substrate was then laminated by means of a laminating adhesive against another, 12 pm thick, PET film.

The structure was provided on both sides with a heat sealing lacquer layer with a thickness of 10 pm and then cut in the form of a thread.

This thread was introduced into the paper in the papermaking process such that the thread was partially covered by paper fibers.

In this case, the thread was embedded so that once the front of the thread on which the Ni layer is optically accessible, on the one surface of the paper and once the back of the thread on which the Al layer is optically accessible, on the opposite Surface of the paper came to lie open, so as swinging window thread.

Claims (18)

1) Security element with magnetic properties, characterized in that the security element contains at least one magnetic metal layer, and that the security element can be verified by means of a magneto-optical method. 2) A security element according to claim 1, characterized in that the thickness of the magnetic metal layer is 1 - 200 nm. 3) Security element according to one of claims 1 or 2, characterized in that the magnetic metal layer is present as a full-surface or partial layer or as a layer formed from clusters. 4) A security element according to any one of claims 1 to 3, characterized in that the magnetic metal layer consists of ferromagnetic iron, nickel or cobalt layers and their alloys or compounds or of alloys with these metals. 5) A security element according to any one of claims 1 to 3, characterized in that the magnetic metal layer consists of hard magnetic alloys based on samarium or neodymium. 6) Security element according to one of claims 1 to 5, characterized in that the magnetic metal layers are applied by a PVD or CVD method. 7) Security element according to one of claims 1 to 6, characterized in that the security element has one or more other full-surface or partial non-magnetic metal layers. * * *. ≪ * * * «» * * * # # ** «* * * * * * * * * * * * * * τ * I 4 Security element according to one of claims 1 to 7, characterized in that the security element has one or more further full-area or partial layers with optically, optically variable, optically active and / or electrically conductive properties, 9) Security element according to one of claims 1 to 8, characterized in that the security element is provided on one or both sides with a partial or full-surface protective lacquer layer. 10) Security element according to one of claims 1 to 9, characterized in that the security element is provided with a full-surface or partial heat-sealing, cold-sealing or self-adhesive layer. 11) Security element according to one of claims 1 to 10, characterized in that it is laminated against another carrier substrate. 12) A method for machine verification of the security element, characterized in that a magneto-optical measuring method is applied. 13) Method according to claim 12, characterized in that the magneto-optical measuring method utilizes the magneto-optical Kerr effect. 14) Method according to one of claims 12 or 13, characterized in that the magneto-optical measuring method distinguishes between magnetic and non-magnetic metal layers. ι • • • • · · · · · • • • • • • • • • • • • • • • 15) Method according to one of claims 12 to 14, characterized in that a local measurement is carried out at a measuring spot. 5 16) A method according to claim 15, characterized in that the size of the measuring spot is 0.1 to 10 mm. 17) Method according to one of claims 12 to 16, characterized in that the measurement takes place at a wavelength or 10 spectrally resolved. 18) Use of the security elements according to one of claims 1 to 11, optionally after packaging as security features for at least partial embedding in or for application to documents of value, 15 data carriers, seals, labels or packaging.