WO2010139427A1

WO2010139427A1 - Security element comprising a magnetic fluid

Info

Publication number: WO2010139427A1
Application number: PCT/EP2010/003257
Authority: WO
Inventors: Alexander Bornschlegl; Christoph Mengel
Original assignee: Giesecke & Devrient Gmbh
Priority date: 2009-06-05
Filing date: 2010-05-28
Publication date: 2010-12-09
Also published as: RU2011153088A; RU2497198C2; EP2437945A1; DE102009023982A1

Abstract

The invention relates to a security element (30) that provides a visual impression which can be modified using an external magnetic field. The security element (30) contains a plurality of core-shell particles (40). According to the invention, the core of the core-shell particles (40) contains a magnetic fluid (44) and a non-magnetic phase (46) which is movably arranged within the magnetic fluid (44) and can be visually distinguished from the magnetic fluid (44).

Description

SECURITY ELEMENT WITH A MAGNETIC FLUID

The invention relates to a security element with a variable by a magnetic field visual impression. The invention further relates to a method for producing such a security element, a security arrangement with such a security element, a correspondingly equipped data carrier and a verification device for such a security element.

Data carriers, such as valuables or identity documents, but also other valuables, such as branded goods, are often provided with security elements for the purpose of security, which permit verification of the authenticity of the data carrier and at the same time serve as protection against unauthorized reproduction. The security elements can be embodied, for example, in the form of a security thread embedded in a banknote, a covering film for a banknote with a hole, an applied security strip, a self-supporting transfer element or else in the form of a feature area printed directly on a value document.

Security elements with a changeable visual impression, which can be interactively influenced by a user, have a particularly high security against counterfeiting, since interactively triggerable optical effects can not be reproduced with copiers.

From document WO 03/089250 A2 a security element is known, which consists at least partially of a material that is optically changeable by an electric or magnetic field. For this purpose, the optically variable material preferably comprises a multiplicity of particles which can be changed in their position or orientation by means of the electric or magnetic field. The preparation of the optically modifiable material, in which the particles are enclosed in microcapsules and the micro-particles

BESTÄTIGUNG8KOPIE Capsules are brought by means of a swelling agent in a swollen state, however, is relatively expensive.

Proceeding from this, the object of the invention is to further improve a security element of the aforementioned type and, more particularly, to provide a security element with an attractive appearance and high security against forgery which can be produced easily and cost-effectively, the visual appearance of which can also be interactively influenced during the authenticity check.

This object is achieved by the security element having the features of the main claim. A method for producing such a security element, a security arrangement with such a security element, a correspondingly equipped data carrier and a verification device for such a security element are specified in the coordinated claims. Further developments of the invention are the subject of the dependent claims.

According to the invention, a generic security element comprises a plurality of core-shell particles, the core of the core-shell particles containing a magnetic fluid and a non-magnetic phase visually distinguishable from the magnetic fluid, which are movably disposed within the magnetic fluid is. These measures create an interactive human feature that can be verified by external magnetic fields, as explained in more detail below.

The core-shell particles thereby form microcapsules which, like pigments, are introduced into an ink and coated with the printing processes customary in the security printing sector, in particular screen printing or intaglio printing. can be printed. The widespread use of devices that contain sufficiently strong magnets to trigger the authenticity feature, such as mobile phones, headphones or point-of-sale security systems at the point of sale, ensures that simple verification of the security element is possible even in normal cash transactions.

In a preferred embodiment, the magnetic fluid and the non-magnetic phase have different colors. This also includes the possibility that one of the two components, typically the non-magnetic phase, is transparent. Since the non-magnetic phase is movably disposed within the magnetic fluid, its relative position can be changed by the external magnetic field, and therefore a change in the visual appearance of the security element due to the different colors can be achieved.

Advantageously, the change of the visual impression of the security element by the external magnetic field is reversible, so that after removal of the external magnetic field, the original visual impression is restored. In principle, however, designs are also possible in which a permanent change in the visual appearance is generated by the external magnetic field, which is initially retained even after removal of the external magnetic field, and only by a further stimulus, for example a temperature increase or a magnetic clear signal can be deleted again.

The magnetic fluid may be liquid or gaseous, with currently preferred fluids being liquid at room temperature (T w 300 K) for ease of encapsulation. In an advantageous variant of the invention, the magnetic fluid is a ferrofluid. Ferrofluids are stable suspensions of surface-modified magnetic nanoparticles having a diameter of the order of 10 nm. The surface modification is usually carried out with detergents, so that the nanoparticles form a stable suspension without agglomeration in an aqueous or organic carrier liquid. The nanoparticles may in particular consist of iron, cobalt or magnetite (Fe.sub.3O.sub.4).

The typical density of ferrofluids is about 0.9 g / cm ³ to 1.2 g / cm ³ . An external magnetic field induces magnetic forces between the nanoparticles of the ferrofluid, resulting in an increase in viscosity. Also, the ferrofluid in the magnetic field behaves as if it had a much higher density, an effect called increasing the virtual density. In this way, non-magnetic phases, which have a much higher density than the ferrofluid, can float on the ferrofluid when an external magnetic field is applied while sinking without an external magnetic field. This effect is also used within the scope of the invention for changing the relative position of the nonmagnetic phase.

In a further advantageous variant of the invention, the magnetic fluid is a liquid at room temperature, magnetic ionic liquid, hereinafter also referred to as RTMIL (Room Temperature Magnetic Ionic Liquid). Ionic liquids are salts with a low melting point, which may also be below room temperature. In contrast to ferrofluids, which usually have a black or brown inherent color, the RTMILs used according to the invention are advantageously transparent or have a different color from brown and black Own color on or are colored in a desired color. In addition, due to the ionic structure, RTMILs have a very low vapor pressure. Their physical and chemical properties can be widely adjusted as desired.

With particular advantage, RTMILs are used which, in addition to their magnetic properties, exhibit luminescence in order to easily integrate another authenticity feature in the security element.

The RTMILs used preferably have one or more of the following properties: they are transparent or colored, have a high magnetic moment, are stable to water, are immiscible with water and are physiologically harmless.

Examples of the RTMILs which can be used in the invention are: bmimpFeCU] (1-butyl-3-methylimidazolium tetrachloroferrate), [PR ₄ ] [FeCb] with the trihexyl (tetradecyl) phosphonium cation [PR ₄ ] ⁺ , [PR ₄ Ia [CoCU], [PR ₄ I ₂ [MnCl ₄ ], [PR ₄ J ₃ [GdCl ₆ ], [C ₆ IrUm] ₅ [Dy (SCN) ₈ ] with the 1-hexyl-3-methylimidazolium cation [C ₆ mim]), [C ₆ mim] ₄ [Dy (SCN) 7 (H2θ)] and [C ₆ HTo] ₃ [Dy (SCN) ₆ (H ₂ O) _2].

The latter three compounds have, in addition to their magnetic properties, a strong luminescence in the yellow spectral range, which is due to a characteristic emission of dysprosium (IΙI) ion.

According to another advantageous variant of the invention, the magnetic fluid is a magnetor ideological fluid. Magnetorheological fluids are suspensions of small magnetically polarisable particles, for example of carbonyl iron powder, which are finely dispersed in a carrier liquid. shares are. Compared with ferrofluids, the particles are larger by about one to three orders of magnitude in magnetorheological fluids and typically have a diameter of about 1 .mu.m to 10 .mu.m. As carrier liquids mostly mineral oil and synthetic oils, glycol and water are used. Magnetorheological fluids are typically dark gray in color. Their density is higher than that of ferrofluids and is usually between about 2 g / cm ³ and about 4 g / cm ³ .

The non-magnetic phase of the core-shell particles may be solid, liquid or gaseous, with their density in all cases advantageously different from the density of the magnetic fluid.

In the case of a gaseous non-magnetic phase, this is preferably formed by air or nitrogen.

In a further advantageous variant, the non-magnetic phase is liquid at room temperature and is immiscible with the magnetic fluid. Suitable non-magnetic liquid phases include, for example, high boiling point hydrocarbons or high boiling point synthetic esters, silicone oils or fluorinated silicone oils.

Also conceivable is a variant in which the nonmagnetic phase is liquid at room temperature and separated from the magnetic fluid by a flexible membrane. Regardless of whether the nonmagnetic phase liquid at room temperature is miscible with the magnetic fluid or not, this variant can be realized with advantage by enclosing the nonmagnetic phase and / or the magnetic fluid in a thin flexible membrane and so forth are separated from each other. In this case, the flexible membrane can be produced, for example, by a (chemical) surface modification of the non-magnetic phase or of the magnetic fluid.

According to a further, likewise advantageous variant of the invention, the non-magnetic phase is solid at room temperature. The non-magnetic phase can be based, for example, on aluminum, copper, titanium dioxide, polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK), glass, ceramic or silicon. Also conceivable is a nonmagnetic phase based on effect pigments, in particular liquid crystal, pearlescent or interference pigments, which are very particularly preferably of translucent design. For solid non-magnetic phases, it is desirable to modify the surface to impart desired properties to the phase, such as a colored or optically variable appearance, or a polarizing reflection.

The solid non-magnetic phases do not have to be homogeneous, so they may contain other particles. The surface of the solid non-magnetic

Phases are preferably poorly wettable by the magnetic fluid. This property can also be generated or reinforced by a surface modification.

In preferred embodiments, the solid non-magnetic phase is in the form of one or more floats, which are preferably spherical, elliptical or lenticular. The floats may consist of several layers and also have holes or holes and be hollow or spongy. The core-shell particles may also be provided with several different types of floats which differ in color, density, material and / or size. In this way, multi-stage effects can be generated in which, for example, depending on the strength of the magnetic field other floats dominate the visual impression of the security element, or in which an increasing number of floats are driven up with increasing magnetic field strength and thus cause a stronger color.

The solid nonmagnetic phase can also consist of a flexible substance and be gelatinous or gelatinous, for example. In this case, the non-magnetic phase can be flexibly applied to the inside of the sleeve and thus ensure a particularly uniform visual appearance.

In a further development, in addition to the magnetic fluid and the non-magnetic phase, the core of the core-shell particles may contain magnetic particles whose visual appearance differs from the magnetic fluid and the non-magnetic phase.

Such magnetic particles preferably have one or more of the following properties: they are poorly wettable by the magnetic fluid, for example generated by a modified surface, have a multi-layered structure, have a colored surface, are spherical, elliptical or lenticular formed, they have a size between about 0.2 microns and 10 microns and they are formed on the basis of iron, nickel, soft ferrites, magnetite or a magnetic oxide. In expedient developments, the core of the core-shell particles contains further magnetic fluids and / or non-magnetic phases whose magnetic properties and / or their visual appearance differ from the first magnetic fluid and the first nonmagnetic phase. As a result, for example, two fluids with different degrees of magnetic properties can be used, or a combination of a magnetic fluid, a magnetic solid and a non-magnetic phase. The combination of several different non-magnetic floats and the provision of additional magnetic particles within the core has already been mentioned above.

The shell of the core-shell particles preferably consists of a highly transparent encapsulation material for a specific frequency range of the electromagnetic spectrum. The frequency range of the transparency is preferably in the visible spectral range. In order to ensure the required optical and mechanical properties, the material of the shell, the wall thickness and, if polymers are used, their degree of crosslinking can also be suitably selected. Advantageous materials for the shell are, for example, gelatin, modified gelatin, in particular with chemical post-crosslinking, PMMA and other polyacrylates, which are particularly suitable because of their high transparency, polyurethanes, polyamides, melamine / formaldehyde, silicones, but also inorganic oxidic materials, such as such as silicates, titanium, hafnium or iron oxides.

The diameter of the core-shell particles is advantageously between about 1 .mu.m and about 100 .mu.m, in particular between about 1 .mu.m and about 80 .mu.m. The wall thickness of the core-shell particles is typically between 5% and 25%, preferably between 10% and 20%, of the diameter of the core-shell particles.

The shell of the core-shell particles may be constructed of one or more layers to adjust desired properties, such as surface wettability, as desired. In addition, additives may be incorporated in the layer or layers of the shell material, which serve further purposes, for example, laser-markable dyes, UV absorbers, luminescent or other feature substances.

In preferred embodiments, the core-shell particles are present in a feature layer applied to a support. The security element can also contain an information-bearing background layer over which the feature layer with the core-shell particles is applied. The background layer advantageously contains a spatially varying, visually recognizable information and / or exhibits spatially varying magnetic properties.

Such embodiments are particularly suitable when at least one of the two components "magnetic fluid" and "non-magnetic phase" is transparent. By changing the position of the non-magnetic phase within the magnetic fluid by the external magnetic field, a respective different subregion of the background layer can be made visible. If the information of the background layer is produced with hard or soft magnetic colors, its position and arrangement can be used to specify a preferred orientation of the core / shell particles, as described in more detail below. The invention also comprises a method for producing a security element, in which

Core-shell particles whose core contains a magnetic fluid and a non-magnetic phase visually distinguishable from the magnetic fluid, which is movably disposed within the magnetic fluid, and

a plurality of such core-shell particles are disposed in the security element to impart to the security element a visual impression variable by an external magnetic field.

In an advantageous embodiment, the core-shell particles are introduced into a binder and printed on a carrier.

The invention further comprises a security arrangement for securing security papers, value documents, data carriers and the like with a security element of the type described and with a verification element with a magnetic motif area in which magnetic material in the form of patterns, lines, characters or an encoding is present. With particular advantage, the magnetic motif region is magnetized essentially perpendicular to the plane of the verification element. The motif represented by the magnetic motif area can be openly visible or can not be recognized even without aids, for example by covering with a dark printing layer.

The invention further comprises a data carrier, in particular a value document, such as a banknote, a passport, a document, an identity card or the like, which is provided with a security element of the type described or with a security arrangement of the type described.

The substrate material for the data carrier is any kind of paper, in particular cotton paper. Of course, it is also possible to use paper which contains a proportion of polymeric material in the range of 0 <x <100% by weight.

Furthermore, it is basically conceivable that the substrate material of the data carrier a plastic film, for. B. a polyester film is. The film may also be monoaxially or biaxially stretched. The stretching of the film, inter alia, leads to it receiving polarizing properties that can be used as another security feature.

It may also be expedient if the substrate material of the data carrier is a multilayer composite which has at least one layer of paper or of a paper-like material. Such a composite is characterized by an extremely high stability, which is for the durability of the ^" data carrier of great advantage.

It is also conceivable, however, to use a multilayer, paper-free composite material as the substrate material. These materials can be used to advantage in certain climatic regions of the world.

All materials used as substrate material may have additives that serve as a mark of authenticity. It is primarily to think of luminescent, which are preferably transparent in the visible wavelength range and in the non-visible wavelength range by a suitable tool, for. B. emitting a UV or IR radiation Radiation source, can be excited to produce a visible or at least detectable with auxiliary luminescence. Other security features can also be used to advantage if they do not impair the contemplation of the security element according to the invention or at least do not significantly affect it.

The security element can, in particular if it is present on a transparent or translucent substrate, also be arranged in or above a window area or a through opening of the data carrier.

If the data carrier contains both a security element according to the invention and an associated verification element, these are advantageously geometrically arranged on the data carrier such that the security element can be brought over the verification element by bending or folding the data carrier.

The invention further comprises a verification means for checking the authenticity of a security element of the type described with a mapπretischen ^~ Mötivbereich7irTdern magnetic MäteriaTirf star shape Vorf Mu is present lines, characters or a code, and which is magnetized substantially perpendicular to the plane of the subject area to pass through the Magnetic field of the magnetic motif area to change the visual impression of the security element.

Since, for example, ferrofluids contain soft magnetic nanoparticles, the core-shell particles according to the invention can also be read out by machine, like conventional soft magnetic colors. The core-shell particles also have a high light fastness, since no photosensitive substances are used to prepare the designs according to the invention are required. The core-shell particles may, in addition to the magnetic properties in the foreground in the foreground, also have other properties that can be used for the authenticity check. Examples are the above-mentioned luminescence of certain magnetic ionic liquids or the provision of additives in the shell of the core-shell particles.

Further exemplary embodiments and advantages of the invention are explained below with reference to the figures, in the representation of which a representation in terms of scale and proportions has been dispensed with in order to increase the clarity.

Show it:

1 is a schematic representation of a banknote with a security element according to the invention,

FIG. 2 shows the security element of FIG. 1 together with a verification element, in which (a) security element and verification element are spatially separated, and in (b) the security element rests on the verification element, FIG.

3 shows a verification element in the form of a motif magnet,

4 shows a cross section through a security element according to a

Embodiment of the invention, wherein the security element is shown in the left half without magnetic field and in the right half of the image with external magnetic field, 5 shows a variant of core-shell particles according to the invention, in which the non-magnetic phase is formed by a multiplicity of fixed floating bodies, left without, right with magnetic field,

6 shows a further variant of core-shell particles according to the invention, in which the core-shell particles additionally contain magnetic particles with a blue inherent color in addition to the magnetic fluid and a non-magnetic phase from a multiplicity of solid, red floating bodies,

7 shows a security element according to an embodiment of the

Invention in which a feature layer is combined with the core-shell particles having an information-bearing background layer, wherein (a) the security element without external magnetic field, (b) the security element with a left side magnetic field and (c) the security element with a FIG. 8 shows a security element similar to the security element of FIG.

7, in which an information component of the background layer is applied with a hard magnetic ink, and

9 shows a banknote with a security arrangement according to the invention comprising a security element and a verification element arranged mirror-inverted to the center line.

The invention will now be explained using the example of security elements for banknotes. 1 shows a schematic representation of a banknote 10 with a security element 12 printed directly onto the banknote paper, whose visual impression is reversible by an external magnetic field can be changed. The interactive change of the visual impression serves to prove the authenticity of the security element 12 and the banknote 10 provided therewith, so that the security element 12 represents a reversible, interactively triggerable human feature.

It is understood that the invention is not limited to printed security elements and bank notes, but can be used with all types of security elements, for example labels on goods and packaging or in the security of documents, ID cards, passports, credit cards, health cards and like. In bank notes and similar documents come in addition to printed elements, for example, transfer elements, security threads or security strips and supervisory elements in addition to see-through elements in question.

With reference to FIG. 2, the verification of the security element 12 can take place with the aid of a simple magnet 20, which can be, for example, a component of a mobile phone, a headphone or earphone or a consumer protection system at the point of sale. By the strong

^~ Dissemination of such magnetic field generating device is a simple verification of the security element 12 is possible in the normal len cash transactions.

In the situation illustrated in FIG. 2 (a), the security element 12 and the magnet 20 serving as an external verification element are initially clearly separated from one another spatially. In the embodiment of Fig. 2 (a), the security element 12 in this case shows a homogeneous appearance and appears as a continuous dark or black area. The magnetization of the magnet 20 is indicated by the indicated magnetic field lines 22 in FIG. 2 (a). When the magnet 20 is brought close to the security element from below, for example by placing the security element 12 on the magnet 20, as shown in FIG. 2 (b), the visual appearance of the security element 12 changes significantly. In particular, the color of the security element 12 changes as a result of the influence of the magnetic field 22 in the region 24 above the magnet 20, a color change from black to red taking place in the exemplary embodiment of FIG.

If the magnet 20 is moved back and forth under the security element 12, the red area 24 with the magnet 20 also moves accordingly. When the user removes the magnet 20 again from the security element 12, the red area 24 disappears and the original homogeneous appearance of FIG. 2 (a) returns. Due to the characteristic color change of the security element 12, its authenticity can be verified interactively by the user in a simple manner.

Instead of using a simple magnet 20, the verification of the security element 12 3 ^~~ may also be effected with a motif magnet 26, as shown in Fig. ^~~ Def Mo ^{"tivfrϊägner26} is irTFörm vorTMüsternyOnien, Zeicherföder a coding design and forms in the embodiment shown the letter" H In this case, the magnetic north pole represents the upper side of the magnet and the magnetic south pole represents the underside of the magnet, so that the magnetization of the motif magnet indicated by the magnetic field lines 28 is substantially perpendicular to the plane of the magnetic material In the general case, the magnetization can also be reversed or formed by a more complex sequence of magnetic north and south poles, for which the magnetic material of the motif magnet is magnetized in particular magnetic rare earth alloys, such as samarium-cobalt or neodymium-iron-boron alloys, in addition to conventional magnetic materials.

The construction of security elements according to the invention and the occurrence of the reversible change in the visual appearance will now be explained in more detail with reference to the cross-sectional illustration of FIG. 4. In this case, the left half of the figure shows a security element 30 without magnetic field or in a region away from the magnet 20, while the right half shows a section of a portion of the security element 30, which is disposed directly above the magnet 20.

In the area of the security element 30, a feature layer 34 is printed on the banknote paper 32 of the banknote, which contains a multiplicity of core-shell particles 40 in a binder 36. The core-shell particles 40 have a multi-part structure and typically have a diameter between 1 .mu.m and 100 .mu.m, in the exemplary embodiment of about 60 .mu.m.

The shell 42 of the core-shell particles 40 consists of a transparent in the visible spectral range encapsulation material, in the embodiment of PMMA. The wall thickness of the shell is generally between 5% and 25% of the capsule diameter, for example about 15%.

Essential to the present invention is the structure of the core of

Core-shell particles. This includes, according to the invention, a magnetic fluid 44 and a non-magnetic phase 46 visually distinguishable from the magnetic fluid, which is movably disposed within the magnetic fluid. In the exemplary embodiment of FIG. 4, the core contains, as the magnetic fluid 44, a ferrofluid with a black inherent color. The non-magnetic phase 46 is formed in the embodiment shown by a at room temperature (300 K) liquid phase, which is not mixable with the ferrofluid 44 bar. It also has a higher density than the ferrofluid and a different visual appearance from the ferrofluid. For example, the non-magnetic liquid phase may be constituted by a high boiling point hydrocarbon, a high boiling point synthetic ester, a silicone oil or a fluorinated silicone oil.

Without an external magnetic field, a state occurs in the core-shell particles 40 of the feature layer, in which the non-magnetic liquid phase 46 collects in the lower region of the core-shell particles 40, as in the left half of FIG. 4 shown schematically. The visual appearance of the security element 30 in plan view is dominated in this case by the black inherent color of the ferrofluid 44, the security element appears evenly black to the viewer 38.

On the other hand, in the region of the magnet 20, the magnetic field 22 attracts the ferrofluid 44, so that the non-magnetic liquid phase 46 is displaced from the lower part of the core and pressed to the top of the core-shell particle 40, as in the right half of FIG Fig. 4 shown schematically. In this area, therefore, the observer 38 perceives, in plan view, the inherent color of the non-magnetic liquid phase 46. After removal of the magnet 20, the non-magnetic liquid phase 46 decreases again so that reversibly the original, black appearance of the left half of the image is restored. FIG. 5 shows a variant of core-shell particles 50 according to the invention, in which the nonmagnetic phase is not liquid, but is formed by a plurality of solid floating bodies 52. For the floats 52, a variety of suitable materials is considered, as explained in more detail above. In the exemplary embodiment of FIG. 5, the floating bodies 52 have a red inherent color in order to produce a striking contrast to the black inherent color of the ferrofluid 44.

Without an external magnetic field, the state shown schematically in the left-hand half of FIG. 5, in which the solid floats 52 collect in the lower part of the core-shell particles 50, so that the visual appearance of the security element in supervision of the black Intrinsic color of ferrofluid 44 is dominated.

In the right-hand half of FIG. 5, the situation is schematically shown with a magnet 20 arranged below the security element. The magnetic field 22 of the magnet attracts the ferrofluid 44 so that the non-magnetic floats 52 are displaced from the lower part of the core and pressed against the top of the core-shell particles 50. In the area of the magnet 20, the appearance of the security element in supervision is therefore determined by the red inherent color of the floating bodies 52, so that a striking contrast to the black-colored area outside of the magnet 20 results.

After removal of the magnet 20, the non-magnetic floating bodies 52 sink again so that reversibly the original black appearance of the left half of the image is restored. In the embodiment shown in FIG. 6, in addition to the magnetic fluid 44 and a non-magnetic phase of a plurality of solid red floating bodies 52, the core-shell particles 54 additionally contain magnetic particles 56 having a blue inherent color. The magnetic particles 56 have a size of about 5 microns and are formed for example of iron, nickel, soft ferrites, magnetite or magnetic oxides. They may have a modified surface to ensure poor wetting of the magnetic particles by the magnetic fluid and / or to produce the desired intrinsic color.

Without external Magrietfeld adjusts the state shown schematically in the left part of the figure in FIG. 6, in which the fixed floats 52 and the magnetic particles 56 are in the lower part of the core-shell particle 54. The visual appearance of the security element in supervision is dominated by the black color of ferrofluid 44 in this state.

The situation is shown schematically in the middle part of FIG. 6 with a magnet 20 arranged below the security element. The magnetic field 22 of the magnet attracts the ferrofluid 44 and the magnetic particles 56 so that the non-magnetic floats 52 are displaced from the lower part of the core and pressed against the top of the core-shell particle 50. The appearance of the security element in supervision is thus determined by the red inherent color of the float 52 in this magnetic position.

On the other hand, when the user brings the magnet 20 over the core-shell particles as shown in the right-hand part of Fig. 6, the comparatively large magnetic particles 56 are strongly attracted to the magnet 20 and brought to the top of the core-shell particles so that the visual appearance is now dominated by the blue inherent color of the magnetic particles 56.

The core-shell particles according to the invention can also be used in combination with information-carrying printing layers. In this case, the different visual impression of the security element can be achieved by the fact that the core-shell particles, depending on the strength and / or orientation of the magnetic field, release the view of different partial views of the information-bearing printed layers.

By way of illustration, FIG. 7 shows a security element 60 in which a feature layer 62 with core-shell particles 70 is combined with an information-bearing background layer 64. The background layer 64 contains spatially varying information, for example a spatially varying color information, which is schematically represented in FIG. 7 by the alternating information components "A" and "B". For example, the information components "A" may be a red print and the information components "B" may be a blue print, or the information components "A" may represent a graphic symbol and the information components "B" may be a text information.

The feature layer 62 includes a plurality of core-shell particles 70, the core of which contains a ferrofluid 44 having a black inherent color, a transparent, non-magnetic float 72, or a transparent, non-magnetic and ferrofluid-immiscible liquid. Without an external magnetic field, the state shown schematically in FIG. 7 (a) occurs, in which the fixed floats 72 are located in the lower part of the core-shell particles 70. Because of the laterally uniform distribution of the ferrofluid 44, the feature layer 62 for a viewer 66 appears overall opaque, as indicated by the arrows 68, which do not penetrate to the background layer 64. In supervision neither the information components "A" nor the information components "B" are recognizable for the viewer 66, the security element 60 shows a uniformly black appearance.

If a lateral magnetic field is now applied by a magnet 20 from the left, as illustrated in FIG. 7 (b), the magnetic field of the magnet 20 attracts the ferrofluid 44, while the non-magnetic floating bodies 72 displace from the left part of the core and are pressed to the right side of the core-shell particles 70. Since the floats 72 are transparent, they provide the observer 66 with a view of the information components "B" of the background layer 64, as indicated by the arrows 74.

If the lateral magnetic field is removed again, the opaque state of the feature layer 62 of FIG. 7 (a) reversibly sets.

On the other hand, when a lateral magnetic field is applied from the right by the magnet 20, as shown in Fig. 7 (c), the magnetic field of the magnet 20 pulls the ferrofluid 44 to the right, thereby displacing the non-magnetic floats 72 from the right part of the core and pressed to the left side of the core-shell particles 70. The transparent floats 72 then provide the viewer 66 with the view of the information components "A" as indicated by the arrows 76. Here too After removal of the magnetic field reversibly, the opaque state of the feature layer 62 shown in FIG. 7 (a) again arises.

The appearance of the feature layer 62 of the security element 60 can thus be interactively and reversibly changed by the user from an opaque, uniformly black state to a view of only the information components "A" or to a view of only the information components "B". As mentioned above, the information components "A" and "B" stand for any information, for example different color areas or for alphanumeric information, such as the denomination or the serial number of a banknote.

It is understood that the shutter effect described with reference to FIG. 7 shows the advantages of the invention even in a relatively simple embodiment. Contains the sub-base layer 64 instead of two pieces of information "A" and "B" only information, eg. B. in the form of the letter "C", this information is not visible in supervision without applied magnetic field to the viewer 66, since the feature layer 62 as shown in FIG.

7 (a) appears opaque to the viewer 66 as a whole. If, on the other hand, a lateral magnetic field from the left or right is applied by means of a magnet 20, the observer 66 is shown looking at the background layer 64 having the information "C", as shown in FIG. 7 (b) or FIG Venetian blind effect of such an embodiment combines a high degree of protection against forgery with a very appealing appearance for the observer.

The information of the background layer can also be applied with magnetic colors, for example to specify which partial information is visible without an external magnetic field. For illustration, FIG. 8 shows a safety a feature layer 62 containing a plurality of core-shell particles 70 of the type described in connection with FIG. 7.

The feature layer 62 is combined with an information-bearing background layer 82 having spatially varying information with information components "A" and "B" to which the information component "B" having a hard magnetic ink 84 is applied.

Without an external magnetic field, the state shown schematically in Fig. 8 (a) occurs, in which the remanent magnetic field of the hard magnetic ink areas 84 attracts the ferrofluid 44 and displaces the non-magnetic floats 72 from the right portion of the core and to the left side the core-shell particle 70 pushes. The transparent floats 72 thus release the view of the information components "A" without an external magnetic field (arrows 76).

Now, when a lateral magnetic field is applied by a magnet 20 from the left as illustrated in FIG. 8 (b), the magnetic field of the external magnet 20 exceeds the magnetization of the hard magnetic color regions 84, and the ferrofluid 44 becomes inside the core-shell particles 70 pulled to the left while the non-magnetic floats 72 are pressed to the right side of the core-shell particles 70. The transparent floats 72 now reveal the information components "B" (arrow 74).

When the magnet 20 is brought under the feature layer 62 as shown in Fig. 8 (c), the magnetic field of the magnet 20 pulls down the ferrofluid 44 and urges the non-magnetic floats 72 to the top the core-shell particles 70. Due to the laterally uniform distribution of the ferrofluid 44, the feature layer 62 then appears opaque to an observer (arrows 68), so that neither the information components "A" nor the information components "B" can be seen from above and the Safety element 80 appears evenly black.

Correspondingly, the arrangement of the magnet 20 under the feature layer 62 of FIG. 7 would result in the ferrofluid 44 being pulled down and the laterally uniform distribution of the ferrofluid 44 making the feature layer 62 opaque to the viewer 66.

The same effect can be achieved by bringing the magnet 20 over the feature layer, since the ferrofluid 44 within the core-shell particles 70 is pulled upwards uniformly and then also blocks the view of the background layer 82 due to its laterally uniform distribution ,

In the embodiments described so far, the verification of the security element takes place in each case with a separately present verification device in the form of an external magnet 22 or 26. However, it is also possible to provide a verification element on the banknote itself for the verification of a security element applied to a banknote. so that the security element and the verification element form an associated security arrangement, as explained with reference to the exemplary embodiment of FIG. 9.

In the banknote 90 shown in FIG. 9 (a), the denomination "10" is applied to the front of the sheet with a hard magnetic ink 92. As security element 94, on the back of the banknote, a feature layer 96 containing a plurality of core-shell particles 50 of the type described in connection with FIG. 5.

In the unfolded state and without an external magnetic field, the feature layer 96 of the security element appears as a uniformly black area when viewed from the back of the banknote. In addition to the already described in Fig. 5 possibility of verification by an external magnet, however, the security element 94 can be triggered by simply folding the banknote 90, the denomination imprint 92 serves as a verification element.

For this, the security element 94 is arranged mirror-symmetrically relative to the denomination imprint 92 with respect to the center line 98 of the banknote 90, so that the feature layer 96 comes to lie above the denomination imprint 92 by folding the note around the center line 98, as shown in FIG. 9 (b)

In this state, the ferrofluid 44 of the core-shell particles 50 is attracted by the remanent magnetic field of the denomination hard magnetic imprint 92, and the non-magnetic red floating bodies 52 are pressed to the top of the core-shell particle 50. In the feature layer 96, therefore, the denomination "10" appears in red against a black background. When the banknote 90 is unfolded again, the representation of the denomination "10" disappears, and the security element 94 shows, as before, a homogeneous black appearance.

Claims

Patent claims

A security element having a visual impression variable by an external magnetic field, comprising a plurality of core-shell particles, characterized in that the core-shell particle core comprises a magnetic fluid and a visibly distinguishable from the magnetic fluid, contains non-magnetic phase, which is movably disposed within the magnetic fluid.

2. Security element according to claim 1, characterized in that the magnetic fluid and the non-magnetic phase have different colors.

3. Security element according to claim 1 or 2, characterized in that the change of the visual impression of the security element by the external magnetic field is reversible.

4. Security element according to at least one of claims 1 to 3, characterized in that the magnetic fluid is liquid at room temperature.

5. The security element according to at least one of claims 1 to 4, characterized in that the magnetic fluid is a ferrofluid.

6. The security element according to at least one of claims 1 to 4, characterized in that the magnetic fluid is a liquid at room temperature, magnetic ionic liquid.

7. A security element according to at least one of claims 1 to 4, characterized in that the magnetic fluid is a magnetorheological fluid.

8. The security element according to at least one of claims 1 to 7, characterized in that the non-magnetic phase is liquid at room temperature and immiscible with the magnetic fluid.

9. A security element according to at least one of claims 1 to 7, character- ized in that the non-magnetic phase is solid at room temperature, and preferably based on aluminum, copper, titanium dioxide, polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK), glass , Ceramics or silicates or effect pigments, such as liquid crystal, pearlescent or iriodin pigments.

10. Security element according to claim 9, characterized in that the surface of the solid, non-magnetic phase is modified and in particular has a colored or an optically variable appearance.

11. A security element according to claim 9 or 10, characterized in that the solid, non-magnetic phase is in the form of one or more floats, which are in particular spherical, elliptical or lenticular.

12. A security element according to at least one of claims 1 to 11, characterized in that the core in addition to the magnetic fluid and the non-magnetic phase contains magnetic particles whose visual appearance differs from the magnetic fluid and the non-magnetic phase.

13. The security element according to claim 1, characterized in that the core contains further magnetic fluids and / or nonmagnetic phases whose magnetic properties and / or their visual appearance differ from the first magnetic fluid and the first magnetic fluid non-magnetic phase is different.

14. The security element according to at least one of claims 1 to 13, characterized in that the shell of the core-shell particle is transparent in the visible spectral range.

15. A security element according to at least one of claims 1 to 14, characterized in that the core-shell particles are present in a deposited on a carrier feature layer.

16. A security element according to claim 15, characterized in that the security element contains an information-bearing background layer over which the feature layer is applied with the core-shell particles.

17. A security element according to claim 16, characterized in that the background layer contains a spatially varying, visually recognizable information and / or having spatially varying magnetic properties.

18. Method for producing a security element, in which

Core-shell particles whose core is a magnetic fluid and a visibly distinguishable from the magnetic fluid, contains non-magnetic phase, which is movably disposed within the magnetic fluid, and

19. The method according to claim 18, characterized in that the core-shell particles are introduced into a binder and printed on a support.

20. Security arrangement for securing security papers, documents of value, data carriers and the like having a security ^element according to claim 1 and having a verification element with a magnetic motif area in which magnetic material in the form of patterns, lines, characters or a Coding is present.

21. Safety arrangement according to claim 20, characterized in that the magnetic motif area is magnetized substantially perpendicular to the plane of the verification element.

22. A data carrier with a security element according to one of claims 1 to 17 or a security arrangement according to one of claims 20 to 21.

23. A data carrier according to claim 22, characterized in that the security element and the verification element are geometrically arranged on the disk, that the security element can be brought by bending or folding of the data carrier via the verification element.

24. A data carrier according to claim 22 or 23, characterized in that the security element is arranged in or over a window area or a through opening of the data carrier.

25. A data carrier according to claim 22, wherein the data carrier is a banknote or another value document, a passport, a document or an identity card.

26. Verification device for checking the authenticity of a security element according to one of claims 1 to 17, with a magnetic motif area in which magnetic material in the form of patterns, lines, characters or a coding exists, and which is magnetized substantially perpendicular to the plane of the motif area in order to change the visual impression of the security element by the magnetic field of the magnetic motif area.