DE102018004434A1 - Effect pigment, printing ink, security element, data carrier and manufacturing process - Google Patents

Abstract

The invention relates to a platelet-shaped magnetic effect pigment for use in a printing ink, wherein the effect pigment has a magnetic moment oriented essentially perpendicular to the platelet plane.

Description

The invention relates to a platelet-shaped magnetic effect pigment for use in a printing ink, a printing ink, a security element for securing a value document or a valuable article, a data carrier, in particular a banknote, and methods for producing the effect pigment and the security element.

Data carriers, such as valuables or identity documents, or other valuables, such as branded articles, are often provided with security elements for the purpose of security, which permit verification of the authenticity of the data carriers and at the same time serve as protection against unauthorized reproduction. Security elements with viewing-angle-dependent effects play a special role in the authentication of authenticity since they can not be reproduced even with the most modern copiers. The security elements are thereby equipped with optically variable elements that give the viewer a different image impression under different viewing angles and, for example, show a different color or brightness impression and / or another graphic motif depending on the viewing angle.

Thin-film systems which produce a viewing angle-dependent color impression on the viewer by means of interference are known in the prior art. This optical effect can serve as an optically variable security element. A large-area thin-film system can be comminuted by various techniques. The size of the resulting flakes or platelets can be laterally up to a few micrometers, but the size usually moves in a range of 2 .mu.m to 100 .mu.m. The vertical structure of a chip is given by the requirements of the interference layers and is usually as thin as possible, e.g. in a range of 200 nm to 800 nm. Such platelets are e.g. in optically variable color (so-called OVI® color) is used, which serves to provide a security element.

Also known is the possibility of applying the color impression producing thin-film systems to a ferromagnetic material. Thus, the pigment platelets have a magnetic moment. Magnetically orientable effect pigments are e.g. commercially available under the trade name OVMI® from SICPA (the abbreviation OVMI stands for the term "optically variable magnetic ink"). The pigments typically have a platelet-like structure and are in the form of a layer composite which often includes two layers of optical effect layers and a magnetic layer embedded therebetween. With respect to the optical effect layers, metallic reflecting layers as well as color shifting layer systems, e.g. with an absorber / dielectric / reflector structure, in question. The embedded magnetic layer is usually invisible, but is required to align the pigments.

It is also known in the prior art to use such color pigments, which have a magnetic moment, for the provision of optically variable security elements. For this purpose, the pigments are introduced into a transparent binder. Using an external magnetic field, the orientation of the pigments can be influenced immediately after printing on a substrate. Subsequently, the binder is cured, for example by means of UV irradiation, to fix the orientations of the pigments. By skillfully adjusting the spatial course of the pigment alignments, it is possible to provide the printed substrate with optical motion effects. Since the magnetization direction of the pigments is preferably along the direction of the largest dimension of the pigments due to the shape anisotropy, the magnetic moment of the particles is oriented perpendicular to the normal vector of the thin films. If a magnetic field with a field strength with the symbol "H" is applied, the pigments are aligned so that their magnetic moments are as parallel as possible to the field vector (see the attached 1 ).

As a consequence, the magnetic pigments can rotate about axes parallel to their magnetization with the symbol "m", which are arranged perpendicular to the normal vector of the thin films. In the use of the magnetic pigments known in the prior art, it can be assumed that the orientation of the pigments in one direction is substantially uniform, while it is essentially randomly distributed in another direction, thus not always showing a colored surface of the pigment upward ( see the attached 2 ). This leads to an expansion of the light reflection and to a reduced brilliance and sharpness of the optically variable effect.

The object of the present invention is to provide a method by which the control over the arrangement of the magnetic color pigments can be improved to allow a more attractive optical effect in this way.

This object is achieved on the basis of the feature combinations defined in the independent claims.

Further developments of the invention are the subject of the dependent claims.

Summary of the invention

1. 1. (First aspect of the invention) The platelet-shaped magnetic effect pigment for use in a printing ink, wherein the effect pigment has a magnetic moment substantially perpendicular to the platelet plane.
2. 2. (Preferred Embodiment) The platelet-shaped magnetic effect pigment according to clause 1, wherein the effect pigment has a layer structure with a magnetic layer arranged between two reflective layers.
3. 3. (Preferred Embodiment) Platelet-shaped magnetic effect pigment according to Clause 2, wherein at least one reflective layer, preferably each of the two reflective layers, additionally with a translucent color layer or with an interference layer or with at least one further layer, which leads to the production of a multilayer interference layer arrangement, combined.
4. 4. (Preferred Embodiment) The platelet-shaped magnetic effect pigment according to any one of Clauses 2 or 3, wherein the magnetic layer is based on a ferromagnetic or ferrimagnetic material having a high coercive force.
5. 5. (Preferred Embodiment) The platelet-shaped magnetic effect pigment according to any one of Clauses 2 to 4, wherein the magnetic layer is based on a rare earth metal and is preferably based on neodymium-iron-boron or samarium-cobalt.
6. 6. (Preferred Embodiment) The platelet-shaped magnetic effect pigment according to any one of Clauses 2 to 4, wherein the magnetic layer is on a Co / Cr alloy or on a layer structure based on the NiFe / TiCr / CoCr-TaPt configuration deposited on an Al / NiP Substrate, based.
7. 7. (Second aspect of the invention) Printing ink comprising platelet-shaped magnetic effect pigments according to any one of clauses 1 to 6.
8. 8. (Preferred embodiment) Printing ink according to clause 7, wherein the printing ink comprises a binder, preferably a UV-curing binder or a thermosetting binder.
9. 9. (Preferred embodiment) Printing ink according to clause 7 or 8, wherein the printing ink in addition to the platelet-shaped magnetic effect pigments according to one of the clauses 1 to 6 additionally conventional magnetically orientable effect pigments, e.g. commercially available under the trade name OVMI®.
10. 10. (Preferred embodiment) Security element for securing a value document or a valuable article, obtainable by printing application of the Printing ink according to one of the clauses 7 to 9 on a printing substrate.
11. 11. (Preferred Embodiment) Security element according to clause 10, wherein the printing substrate is a value document substrate, preferably a paper substrate, a polymer substrate, a paper / polymer composite substrate or a paper-like substrate.
12. 12. (Preferred embodiment) A security element according to clause 10 or 11, wherein for the viewer when viewing the security element, a viewing angle-dependent optical effect is perceptible based on the fixed in an external magnetic field and fixed in the cured binder pigments.
13. 13. (Preferred embodiment) A security element according to one of the clauses 10 to 12, wherein the pigments along the security element are present in regions in the form of patterns, characters or a coding.
14. 14. (Third aspect of the invention) Data carrier with a security element according to one of the clauses 10 to 13.
15. 15. (Preferred embodiment) Data carrier according to Clause 14, wherein the data carrier is a banknote or another value document, a passport, a document, payment card or an identity card.
16. 16. (Fourth aspect of the invention) A process for producing the platelet-shaped magnetic effect pigment according to any one of clauses 1 to 6, comprising
    • a) the step of producing a layer structure above a carrier substrate, the layer structure comprising a magnetic layer arranged between two reflective layers;
    • b) the step of detaching the layer structure from the carrier substrate;
    • optionally c) the step of comminution, eg by means of grinding, until particles with an adequate size distribution are obtained;
    • optionally d) the step of mixing the resulting particles with a UV-curing or thermosetting binder to a (screen) printing ink.
17. 17. (Fifth aspect of the invention) A method of manufacturing the security element according to any one of clauses 10 to 13, comprising printing the ink of any one of clauses 7 to 9 on a substrate, wherein an external magnetic field is applied in the step of applying the ink by printing and the color is cured, preferably by UV radiation or by heat, so that the particles become immobile.

Detailed Description of the Preferred Embodiments

The advantages of the invention are explained below with reference to the schematically greatly simplified figures, the representation of which has been dispensed with a representation true to scale and proportion, in order to increase the clarity.

• 1 die mögliche Magnetisierung (mit dem Formelzeichen „m“) eines OVMI®-Pigments und die daraus folgende Ausrichtung des Pigments in einem Magnetfeld (mit dem Formelzeichen „H“);
• 2 mögliche Ausrichtungen eines OVMI®-Pigments im Magnetfeld (mit dem Formelzeichen „H“) durch eine Rotation um eine Achse mit dem Formelzeichen „m“; und
• 3 die Rotation des OVMIOO-Pigments um die Flächennormale bei einer Magnetisierung, die parallel zur Flächennormale zeigt; dabei ändert sich die Intensität des optischen Reflexes nicht.

Show it:

• 1 the possible magnetization (with the symbol "m") of an OVMI® pigment and the consequent orientation of the pigment in a magnetic field (with the symbol "H");
• 2 possible alignments of an OVMI® pigment in the magnetic field (with the symbol "H") by a rotation about an axis with the symbol "m"; and
• 3 the rotation of the OVMIOO pigment around the surface normal at a magnetization parallel to the surface normal; At the same time, the intensity of the optical reflex does not change.

The present invention is a printing technology available security element based on platelet-shaped magnetic effect pigments whose magnetic moment is aligned substantially perpendicular to the platelet plane.

Similar to the magnetic pigments known in the prior art, the magnetic pigments according to the invention can be oriented in a static external magnetic field so that their magnetic moments are substantially parallel to the magnetic field lines. Just as with the magnetic pigments known in the art, one degree of freedom remains: the platelets can rotate about an axis that is parallel to their magnetic moment without changing their potential energy in the magnetic field. In contrast to the magnetic pigments known in the art, however, rotation in the case of the pigments according to the invention has no significant influence on the reflection properties of the pigments. The reflection properties can therefore be better controlled. In the case of the magnetic pigments known in the prior art, the viewer sees a large number of small pigments each having a substantially random brightness. The security elements obtained in this way consequently have a granular or a so-called "noisy" optical texture. In contrast, homogeneous surfaces can be produced by means of the pigments according to the invention. In this way, e.g. achieve so-called micromirroring effects.

There are various possibilities with regard to the preparation of the pigments according to the invention. All methods have in common that initially above a carrier substrate, e.g. a carrier film, a layer structure is produced, wherein the layer structure has a magnetic layer arranged between two reflective layers. The reflective layers may additionally be combined with translucent colors or with interference layers (or with further layers resulting in the creation of a multilayered interference layer arrangement). Subsequently, the layer structure is detached from the carrier substrate and optionally comminuted, e.g. by grinding until particles with an adequate size distribution are obtained. Thereafter, the resulting particles may be mixed with a UV-curing binder to form a screen printing ink. In the step of printing the ink onto a printing material, an external magnetic field is expediently applied and the ink is cured, e.g. by UV radiation or by heat, so that the particles become immobile.

In the following, preferred methods for producing the magnetic layers in pigments according to the invention are described.

• Es wird eine Schicht aus ferromagnetischem oder ferrimagnetischem Material, das eine hohe Koerzitivfeldstärke aufweist, auf ein Trägersubstrat aufgebracht. Diese Schicht wird mittels eines externen Magnetfelds senkrecht zur Schichtebene magnetisiert. Während der Magnetisierung kann es von Vorteil sein, die Temperatur der Schicht kurzzeitig deutlich zu erhöhen, z.B. mittels IR-Strahlung oder mittels Laserstrahlung), und/oder einen hohen Druck auf das Material auszuüben. In den weiteren Verarbeitungsschritten dürfen die Schichten und/oder Pigmente nur noch externen Magnetfeldern ausgesetzt werden, deren Feldstärke deutlich geringer als die Koerzitivfeldstärke der Magnetschicht ist.

First preferred production method:

• A layer of ferromagnetic or ferrimagnetic material having a high coercive force is applied to a carrier substrate. This layer is magnetized by means of an external magnetic field perpendicular to the layer plane. During the magnetization, it may be advantageous to increase the temperature of the layer for a short time significantly, for example by means of IR radiation or by means of laser radiation), and / or to exert a high pressure on the material. In the further processing steps, the layers and / or pigments may only be exposed to external magnetic fields whose field strength is significantly lower than the coercive field strength of the magnetic layer.

• Ein ferromagnetisches oder ferrimagnetisches Material mit einer sehr hohen Koerzitivfeldstärke wird mittels Zermahlen zerkleinert, bis eine Partikelgröße von weniger als 10 µm, vorzugsweise weniger als 1µm, vorliegt. Das Pulver wird in ein flüssiges Medium eingebracht, welches kontrolliert verfestigt werden kann, und die Mischung wird auf ein Trägersubstrat aufgebracht. Die Partikel werden dann mittels eines externen Magnetfelds so ausgerichtet, dass ihre Magnetisierungsrichtung jeweils senkrecht zur Substratebene angeordnet ist, und das flüssige Medium wird verfestigt, sodass die Partikel unbeweglich werden und die Magnetisierung der Schicht sozusagen eingefroren wird. Während des Ausrichtens mittels eines externen Magnetfelds kann es von Vorteil sein, die Temperatur der Schicht kurzzeitig deutlich zu erhöhen und/oder einen hohen Druck auf das Material auszuüben. In den weiteren Verarbeitungsschritten dürfen die Schichten und/oder Pigmente nur noch Magnetfeldern ausgesetzt werden, deren Feldstärke deutlich geringer als die Koerzitivfeldstärke der Magnetschicht ist.

Second preferred production method:

• A ferromagnetic or ferrimagnetic material having a very high coercive force is comminuted by grinding until a particle size of less than 10 μm, preferably less than 1 μm, is present. The powder is introduced into a liquid medium which can be solidified in a controlled manner and the mixture is applied to a carrier substrate. The particles are then aligned by means of an external magnetic field so that their magnetization direction is in each case arranged perpendicular to the substrate plane, and the liquid medium is solidified, so that the particles become immobile and the magnetization of the layer is frozen, so to speak. During the alignment by means of an external magnetic field, it may be advantageous to increase the temperature of the layer for a short time significantly and / or to exert a high pressure on the material. In the further processing steps, the layers and / or pigments may only be exposed to magnetic fields whose field strength is significantly lower than the coercive field strength of the magnetic layer.

• Eine Magnetschicht wird aus einem solchen Material erzeugt, bei dem die Formanisotropie nicht dominant ist, und das magnetische Moment vorzugsweise senkrecht zur Schichtebene angeordnet ist.

Third preferred production method:

• A magnetic layer is formed of such a material in which the shape anisotropy is not dominant, and the magnetic moment is preferably perpendicular to the layer plane.

The above-described first preferred manufacturing method and the second preferred manufacturing method are each based on the prior art production of rare earth magnets, e.g. Neodymium iron boron or samarium cobalt.

The third preferred manufacturing method described above is based on the prior art production of a hard disk (i.e., a magnetic storage medium of computer technology) in which thin films are perpendicularly polarized to the layer plane ("perpendicular recording"). Examples of materials which can be used include Co / Cr alloys or layer structures based on the NiFe / TiCr / CoCr-TaPt configuration, deposited on an Al / NiP substrate. The preparation may e.g. done by sputtering.

The use of the particles according to the invention makes it possible to realize optically variable patterns, the surfaces produced in this way having an extremely homogeneous and brilliant effect compared with the patterns known in the prior art. In addition, novel patterns can be produced which can not be realized on the basis of the pigments known hitherto in the art, e.g. Micromirror Wölbeffekte.

Furthermore, the particles according to the invention can additionally be mixed with particles according to the prior art. When the resulting mixture is exposed to an external magnetic field, the major planes of the two types of particles are locally perpendicular to each other so that the pattern thus produced is visible from widely different viewing angles. Thus, when tilting a security element produced in this way, firstly a change of viewing between two different optically variable patterns can be made visible; secondly, the two particle types can have a different color, so that a color change can be made visible.

Claims (17)

A platelet-shaped magnetic effect pigment for use in a printing ink, wherein the effect pigment has a magnetic moment substantially perpendicular to the platelet plane. Platelet-shaped magnetic effect pigment after Claim 1 wherein the effect pigment has a layer structure with a magnetic layer arranged between two reflective layers. Platelet-shaped magnetic effect pigment after Claim 2 in which at least one reflective layer, preferably each of the two reflective layers, is additionally combined with a translucent color layer or with an interference layer or with at least one further layer which leads to the production of a multilayer interference layer arrangement. Platelet-shaped magnetic effect pigment according to one of Claims 2 or 3 wherein the magnetic layer is based on a ferromagnetic or ferrimagnetic material having a high coercive force. Platelet-shaped magnetic effect pigment according to one of Claims 2 to 4 wherein the magnetic layer is based on a rare earth metal and is preferably based on neodymium iron boron or on samarium cobalt. Platelet-shaped magnetic effect pigment according to one of Claims 2 to 4 wherein the magnetic layer is based on a Co / Cr alloy or on a layer structure based on the NiFe / TiCr / CoCr-TaPt configuration deposited on an Al / NiP substrate. Printing ink comprising platelet-shaped magnetic effect pigments according to one of Claims 1 to 6 , Ink after Claim 7 wherein the printing ink comprises a binder, preferably a UV-curing binder or a thermosetting binder. Ink after Claim 7 or 8th , wherein the printing ink next to the platelet-shaped magnetic effect pigments according to one of Claims 1 to 6 in addition conventional magnetically orientable effect pigments which are commercially available under the trade name OVMI®. Security element for securing a value document or a valuable article obtainable by printing on the printing ink according to one of Claims 7 to 9 on a substrate. Security element after Claim 10 wherein the printing substrate is a value document substrate, preferably a paper substrate, a polymer substrate, a paper / polymer composite substrate or a paper-like substrate. Security element after Claim 10 or 11 in which, when the security element is viewed, the observer is able to perceive a viewing angle-dependent optical effect based on the pigments oriented in an external magnetic field and fixed in the hardened binder. Security element according to one of Claims 10 to 12 , wherein the pigments are present along the security element in regions in the form of patterns, characters or a coding. Disk with a security element according to one of Claims 10 to 13 , Disk after Claim 14 , wherein the data carrier is a banknote or other document of value, a passport, a document, a payment card or an identity card. Process for producing the platelet-shaped magnetic effect pigment according to one of the Claims 1 to 6 comprising: a) the step of producing a layer structure above a carrier substrate, the layer structure having a magnetic layer arranged between two reflective layers; b) the step of detaching the layer structure from the carrier substrate; optionally c) the step of comminution, eg by means of grinding, until particles with an adequate size distribution are obtained; optionally d) the step of mixing the resulting particles with a UV-curing or thermosetting binder to a (screen) printing ink. Method for producing the security element according to one of Claims 10 to 13 comprising the printing technology applying the printing ink according to one of Claims 7 to 9 on a substrate, wherein in the step of applying the ink by printing an external magnetic field is applied and the ink is cured, preferably by UV radiation or by heat, so that the particles are immobile.

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