EP4065381A1

EP4065381A1 - Effect pigment, production method, value document and printing ink

Info

Publication number: EP4065381A1
Application number: EP20815714.9A
Authority: EP
Inventors: Michael Rahm; Manfred Heim; Raphael DEHMEL; Winfried HOFFMÜLLER
Original assignee: Giesecke and Devrient Currency Technology GmbH
Current assignee: Giesecke and Devrient Currency Technology GmbH
Priority date: 2019-11-27
Filing date: 2020-11-20
Publication date: 2022-10-05
Also published as: CN114728537A; CN114728537B; US20220403177A1; DE102019008289A1; WO2021104666A1

Abstract

The invention relates to a platelet-shaped magnetic effect pigment for use in a printing ink, comprising a layer structure with a magnetic layer and an optical functional layer, wherein the magnetic layer is based on a magnetic material with a columnar nanostructure and the magnetic columns each have a substantially uniform magnetic preferred direction that deviates from the platelet plane.

Description

Effect pigment, manufacturing process, document of value and printing ink

The invention relates to a platelet-shaped magnetic effect pigment for use in a printing ink, comprising a layer structure with a magnetic layer and at least one optical functional layer, where the magnetic layer is based on a magnetic material with a columnar nanostructure and the magnetic columns each have a largely uniform, have magnetic preferred direction deviating from the platelet plane. The invention further relates to a method for producing the platelet-shaped magnetic effect pigment, a printing ink containing the effect pigments and a document of value printed with the effect pigments.

Data carriers, such as value or identity documents, or other objects of value such as branded items, are often provided with security elements for protection that allow the authenticity of the data carrier to be checked and at the same time serve as protection against unauthorized reproduction. Security elements with viewing angle-dependent effects play a special role in securing authenticity, as these cannot be reproduced even with the most modern copiers. The security elements are equipped with optically variable elements that give the viewer a different image impression from different viewing angles and, for example, depending on the viewing angle, show a different color or brightness impression and / or a different graphic motif.

Thin-film systems which generate a viewing angle-dependent color impression for the observer by means of interference are known in the prior art. This optical effect can be used as an optically variable security serve selement. A large-area thin-film system can be crushed using various techniques. The size of the resulting flakes or platelets can be up to a few micrometers laterally, but the size is usually in a range from 2 µm to 100 µm. The vertical structure of a platelet is determined by the requirements placed on the interference layers and is usually as thin as possible, e.g. in a range from 200 nm to 800 nm. Such platelets come, for example, in optically variable colors (so-called OVI® color ) is used, which is used to provide a security element.

Also known is the possibility of applying the thin-film systems that produce a color impression to a ferromagnetic material. The pigment platelets thus have a magnetic moment. Magnetically orientable effect pigments are commercially available, for example, 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 days of optical effect layers and a magnetic layer embedded in between. With regard to the optical effect layers, metallic-reflective layers as well as color-shifting layer systems, e.g. with an absorber / dielectric / reflector structure, come into question. The embedded magnetic layer is usually not visible, but is necessary for aligning the pigments. In the prior art, it is also known to use such color pigments with a magnetic moment for providing optically variable security elements. For this purpose, the pigments are incorporated into a transparent binder . By means of a external magnetic field can die Alignment of the pigments can be influenced immediately after printing on a printing material. The binder is then cured, for example by means of UV radiation, in order to fix the orientation of the pigments. By skillfully setting the spatial course of the Pigmentaus directions, it is possible to equip the printed substrate with optical movement effects. Since the direction of magnetization of the pigments as a result of the shape anisotropy preferably runs along the direction of the largest dimension of the pigments, the magnetic moment of the particles is oriented perpendicular to the normal vector of the thin layers. 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.

As a consequence, the magnetic pigments can rotate about axes parallel to their magnetization, which are arranged perpendicular to the normal vector of the thin layers. With the use of the magnetic pigments known in the prior art, it can be assumed that the orientation of the pigments is essentially uniform in one direction, while it is essentially randomly distributed in another direction. This leads to a widening of the spruce reflection and to a reduced brilliance and sharpness of the optically variable effect.

The object of the present invention is to provide magnetic effect pigments which enable more extensive control of the spatial alignment in order to achieve a more attractive optical effect in this way.

This object is achieved on the basis of the combinations of features defined in the independent claims. Further developments of the invention are the subject of the subclaims.

Summary of the invention

1. (First aspect of the invention) Platelet-shaped magnetic effect pigment for use in a printing ink, comprising a layer structure with a magnetic layer and at least one optical functional layer, the magnetic layer being based on a magnetic material with a columnar nanostructure and the magnetic columns each have a largely uniform preferred magnetic direction deviating from the plane of the platelets.

2. (Preferred embodiment) Platelet-shaped magnetic effect pigment according to paragraph 1, wherein the largely uniform magnetic preferred direction of the magnetic columns is oriented essentially perpendicular to the platelet plane of the effect pigment.

3. (Preferred embodiment) Platelet-shaped magnetic effect pigment according to paragraph 1, the largely uniform magnetic preferred direction of the magnetic columns being inclined towards the platelet plane and the angle of inclination, measured starting from the perpendicular to the platelet plane, preferably in a range from 1 ° to 20 ° lies.

4. (Preferred embodiment) Platelet-shaped magnetic effect pigment according to one of paragraphs 1 to 3, the magnetic columns each having a size of less than 1000 nm, preferably less than 500 nm, further preferably less than 200 nm and particularly preferably less than 100 nm.

5. (Preferred embodiment) platelet-shaped magnetic effect pigment according to one of paragraphs 1 to 4, the largely uniform preferred magnetic direction of the magnetic columns being a uniaxial magnetic anisotropy, preferably a uniaxial magnetic crystal anisotropy or a uniaxial magnetic shape anisotropy.

6. (Preferred embodiment) Platelet-shaped magnetic effect pigment according to paragraph 5, the material of the magnetic layer being selected from the group consisting of BaFei ₂ 0i9, FePt, CoCrPt, CoPt, BiMn, a-Fe2C> 3 and Nd2Fei4B, and in particular the largely uniform one Magneti cal preferred direction of the magnetic columns is a uniaxial magnetic crystal anisotropy, or wherein the material of the magnetic layer is selected from the group consisting of iron, cobalt, nickel and an alloy of one or more of the aforementioned elements and in particular the largely uniform magnetic preferred direction of the magnetic columns is a uniaxial magnetic shape anisotropy.

7. (Preferred embodiment) Platelet-shaped magnetic effect pigment according to one of paragraphs 1 to 6, the columnar nanostructure of the magnetic material being obtainable by means of the glancing angle deposition (GLAD) technique or the oblique angle deposition (OAD) technique is.

8. (Preferred embodiment) Platelet-shaped magnetic effect pigment according to one of paragraphs 1 to 7, wherein the optical functional layer is a metallic layer, a color layer obtainable by printing, a layer on a reflective layer, a dielectric layer and an absor- The layer-based interference layer structure or a combination of two or more of the above-mentioned elements, for example an ink layer which is arranged above a metallic layer and which can be obtained by printing technology.

9. (Preferred embodiment) Platelet-shaped magnetic effect pigment according to any one of paragraphs 1 to 8, the effect pigment having a sandwich-like layer structure and the magnetic layer as a central layer both on the front side and on the rear side, each with an optical functional layer is provided, whereby the two optical functional layers are independent of one another from a reflective metallic layer, a color layer obtainable by printing, an interference layer structure based on a reflective layer, a dielectric layer and an absorbent layer or a combination of two or more of the aforementioned elements are selected, for example, an ink layer which is available in printing technology and is arranged above a reflective metallic layer.

10. (Preferred embodiment) platelet-shaped magnetic effect pigment according to paragraph 9, wherein the effect pigment has an asymmetrical layer structure with two differing optical functional layers, preferably two differing optical functional layers, each one on a reflective layer, one dielectric layer and one absorbent layer-based interference layer structure and differ in particular with regard to the material or the layer thickness of the dielectric layer and the effect pigment has the following layer sequence: absorbent layer - dielectric layer - reflective layer - magnetic layer - reflective layer - dielectric layer - absorbent layer. 11. (Preferred embodiment) Platelet-shaped magnetic effect pigment according to paragraph 9, the effect pigment having a symmetrical layer structure with two identical optical functional layers.

12. (Preferred embodiment) platelet-shaped magnetic effect pigment according to paragraph 11, the effect pigment having a symmetrical layer structure, the magnetic layer as a central layer being provided with an optical functional layer on both the front and the rear, the Both optical functional layers each have an interference layer structure based on a reflective layer, a dielectric layer and an absorbent layer, and the effect pigment has the following layer sequence: absorbent layer - dielectric layer - reflective layer - magnetic layer - reflective layer - dielectric layer - absorbent layer.

13. (Preferred embodiment) Platelet-shaped magnetic effect pigment according to Paragraph 8, the optical functional layer being an interference layer structure based on a reflective layer, a dielectric layer and an absorbing layer, and the effect pigment having the following layer sequence: absorbent layer - dielectric layer - reflective layer - dielectric layer - absorbent layer - magnetic layer.

14. (Preferred embodiment) platelet-shaped magnetic effect pigment according to paragraph 10, wherein the effect pigment has an asymmetrical layer structure, the magnetic layer on the front side with a reflective layer, a dielectric layer and an absorbent layer-based interference layer structure is provided and the magnetic layer is provided on the back with a reflective metallic layer, so that the effect pigment has the following layer sequence: absorbent layer - dielectric layer - reflective layer - magnetic layer - reflective metallic layer.

15. (Second aspect of the invention) A method for producing a platelet-shaped magnetic effect pigment according to one of paragraphs 1 to 14, comprising a) generating a magnetic layer based on a magnetic material with a columnar nanostructure, wherein the magnetic columns with a largely uniform magnetic preferred direction deviating from the plane of the magnetic layer are formed; b) the production of a layer structure having the magnetic layer and at least one optical functional layer; and c) comminuting the layer structure obtained in step b) to give individual platelet-shaped magnetic effect pigments.

16. (Third aspect of the invention) A method for producing a document of value, comprising

the printing of the value document substrate with a platelet-shaped magnetic effect pigment according to one of the paragraphs 1 to 14 containing first printing ink in a first area;

the alignment of the platelet-shaped magnetic effect pigments in the first printing ink printed in the first area by means of an external magnetic field;

the curing of the first printing ink printed in the first area. 17. (Preferred embodiment) Method according to paragraph 16, comprising

- The printing of the document of value substrate with a first platelet-shaped magnetic effect pigments according to one of paragraphs 1 to 14 contain the first printing ink in a first area;

- The printing of the document of value substrate with a second platelet-shaped magnetic effect pigments according to one of paragraphs 1 to 14 containing second printing ink in a second area adjoining the first area, the second effect pigments visually differing from the first effect pigments;

the alignment of the platelet-shaped magnetic effect pigments in the first and second printing inks respectively printed in the first area and in the second area by means of an external magnetic field;

the curing of the first and second printing inks respectively printed on in the first area and in the second area.

18. (Preferred embodiment) Method according to paragraph 16, comprising

- The printing of the document of value substrate with a conventional, platelet-shaped magnetic effect pigments containing second printing ink in a second area adjoining the first area, the conventional, platelet-shaped magnetic effect pigments having a preferred magnetic direction running along the plane of the platelets;

the alignment of the platelet-shaped magnetic effect pigments in the first and second printing inks respectively printed in the first area and in the second area by means of an external magnetic field; the curing of the first and second printing inks respectively printed on in the first area and in the second area, so that the two areas have an appearance that is clearly distinguishable from one another as a result of the different alignment of the two types of effect pigment.

19. (Fourth aspect of the invention) Value document, obtainable by the method according to one of paragraphs 16 to 18.

20. (Preferred embodiment) document of value according to paragraph 19, wherein the document of value is a bank note or an identification document.

21. (Fifth aspect of the invention) Printing ink comprising platelet-shaped magnetic effect pigments according to one of paragraphs 1 to 14. 22. (Preferred embodiment) Printing ink according to paragraph 21, wherein the

Printing ink comprises a binder, preferably a UV curing binder, an electron beam curing binder or a thermosetting binder.

Detailed description of the preferred embodiments

The platelet-shaped magnetic effect pigment according to the invention comprises a layer structure with a magnetic layer and at least one optical functional layer, the magnetic layer being based on a magnetic material with a columnar nanostructure and the magnetic columns each having a largely uniform preferred magnetic direction deviating from the platelet plane. Instead of the phrase “a magnetic one that deviates from the plane of the platelet Preferred direction ”is also used herein the phrase“ a magnetic preferred direction deviating from the perpendicular to the normal vector of the plate ”. The wording "largely uniform preferred direction" of the magnetic columns is to be understood in such a way that the individual magnetic columns of the effect pigment do not necessarily all have to point in exactly the same direction; ) distributed magnetic columns be oriented on average along exactly one direction. The magnetic columns preferably have a size of less than 1000 nm, more preferably less than 500 nm, even more preferably less than 200 nm and particularly preferably less than 100 nm The size of the magnetic columns is an average size and relates to the length of the column from one end to the opposite end. The largely uniform magnetic preferred direction of the magnetic columns is preferably oriented essentially perpendicular to the platelet plane of the effect pigment. According to one variant is the uniform preferred magnetic direction of the magnetic columns inclined towards the platelet plane, the angle of inclination starting from the perpendicular to the platelet plane preferably in a range of 1 ° to 20 °. The phrase "the angle of inclination starting from the perpendicular to the platelet plane" is synonymous with the formulation "the angle of inclination starting from the normal to the platelet plane". It is preferred that the uniform preferred magnetic direction of the magnetic columns in the columnar nanostructure is a uniaxial magnetic anisotropy, particularly preferably a uniaxial magnetic crystal anisotropy or a uniaxial magnetic shape anisotropy. The underlying magnetic material is in particular a ferromagnetic or ferrimagnetic material. The underlying magnetic material can, for example, be from the group consisting of BaFei ₂ 0i ₉ or Barrium ferrite, FePt, CoCrPt, CoPt, BiMn or Bismanol, a-Fe203 or Haema tit and (especially tetragonal) Nd2Fei4B can be selected.

The production of platelet-shaped magnetic effect pigments with a magnetic moment perpendicular to the plane of the platelet requires the production of a thin layer with a magnetic moment that is permanently perpendicular to the plane of the layer. Such a production represents a great technical challenge, especially if, in view of occupational safety, toxic substances such as toxic transition metals are to be avoided. By means of the manufacturing process according to the invention, magnetic layers with in particular a magnetic moment perpendicular to the plane of the layer can be advantageously produced, from which advantageous platelet-shaped magnetic effect pigments with in particular a magnetic moment perpendicular to the platelet plane can be obtained. The concept of the invention is based on the generation of a magnetic material with a columnar nanostructure, the magnetic columns each having a largely uniform preferred magnetic direction. Instead of the term “column”, the term “needle” is also used herein. Such a columnar nanostructure can be obtained in particular by means of the glancing angle deposition (GLAD) technique or the oblique angle deposition (OAD) technique. These are sub-variants of physical vapor deposition (PVD). As a rule, in PVD processes, the angles at which the gas particles impinge on the substrate to be vaporized are widely distributed around an average of about 90 °, because in this way the highest possible proportion of condensation on the substrate is achieved . In the case of the GLAD or the OAD technology, a narrow angle of incidence distribution is selected, the mean value of which deviates very significantly from the perpendicular angle of incidence and even approximates it. can run almost parallel to the substrate plane. It has been shown that special morphologies of the condensate often result in these configurations. Forests are formed, so to speak, consisting of needle-shaped structures, the needle-shaped structures being arranged almost parallel to each other, having high aspect ratios and all at a certain angle stand to the substrate surface. If a ferromagnetic or ferrimagnetic material is evaporated in this way, the direction of magnetization will be parallel to the longest direction of extension of the needle structures due to the shape anisotropy. Thus, a magnetic film can be produced whose direction of magnetization is at a fixed angle to the substrate plane. This angle can be influenced by the vapor deposition parameters and can, for example, also run almost perpendicular to the substrate plane.

Within the magnetic layer, the magnetic columns of the columnar nanostructure are preferably aligned in such a way that the axis of easy magnetization (also called “easy axis” in technical literature) is oriented perpendicular to the layer surface or layer plane.

Of course, on the basis of the method described above, the resulting magnetic layer can in principle be provided with any desired direction of magnetization, in particular with a direction of magnetization inclined to the plane of the layer. A perpendicular magnetization or a magnetization lying in the plane of the layer are special cases.

The magnetic layer obtained according to the production method described above can be combined on one side with an optical functional layer in order to create an optically variable magnetic layer in this way. to produce structure. Alternatively, the magnetic layer can be combined on both sides with an optical functional layer in each case in order to produce an optically variable magnetic layer structure in this way.

A preferred layer structure is a symmetrical layer structure with, for example, the sequence of layers: absorbent layer - dielectric layer - reflective layer - magnetic layer - reflective layer - dielectric layer - absorbent layer. With this layer structure, there is a color-shifting coating based on an absorber / dielectric / reflector thin-layer system on both sides with respect to the central magnetic layer. The individual layers can, for example, be vapor-deposited in a vacuum or applied by so-called sputtering.

Another preferred layer structure has the layer sequence absorbing layer - dielectric layer - reflective layer - dielectric layer - absorbing layer - magnetic layer. In this layer structure, the presence of the magnetic layer influences the reflectivity or the degree of reflection of the layer structure on one side. This influence is small if the magnetic columns are sufficiently small, e.g. have a size of less than 500 nm, preferably less than 200 nm and particularly preferably less than 100 nm.

Instead of an interference coating or a color-shifting thin-layer system, color layers available for printing, preferably translucent color layers, and / or purely reflective layers or metallic layers can also be used as an optical functional layer. Instead of a symmetrical layer structure, in which the color impression is independent of the viewing side, an asymmetrical layer structure can also be used. Since, according to the invention, the magnetic moment is particularly perpendicular to the layer plane, the visibility of the upper side and the lower side can be controlled in areas by means of external magnetic fields. In other words, flake-form magnetic effect pigments can be used which have a fixed magnetic north side and south side, but differ from one another with regard to the optical functional layer of these two sides. For example, optically variable magnetic effect pigments can be used which simultaneously have different color-changing effects on the top and bottom and whose magnetic moment is firmly defined relative to the top and bottom: north pole on the upper side with the first color-changing effect and south pole on the Bottom with the second color-changing effect. If you print these pigments on a transparent (value document) substrate and align them with an external magnetic field before the curing agent of the printing ink hardens, the viewer always sees the upper side of the pigments with the first color-shifting effect from one side and from the other side the underside of the pigments with the second color-shifting effect, which is different from the first color-shifting effect.

Furthermore, the magnetic layer of the invention-like external effect pigment can be combined, for example, on one or both sides with an optical functional layer, the optical functional layer having a metallic layer, in particular a reflective metallic layer, and a translucent or translucent colored layer . Appealing optical effects can be achieved by means of a metallic layer arranged between the magnetic layer and the colored layer. Furthermore, the magnetic layer of the effect pigment according to the invention can be combined, for example, on one or both sides with an optical functional layer, the optical functional layer being a dielectric layer, for example S1O2, and a metallic layer, in particular a reflective metallic layer, for example Al , having. By means of a combination of S1O2 and Al, golden shades, for example, can be achieved even without an additional absorbent layer and without an additional layer of color. With regard to the production method for the magnetic layer described above, there is fundamentally the risk that there is no optically smooth surface, so that the reflectivity of subsequent layers is impaired. This can be counteracted in that the further layers are not applied directly to the magnetic layer, but instead are first produced on a different substrate, for example a film such as a polyethylene terephthalate (PET) film. In a further step, a flexible adhesive layer can be applied to the magnetic layer and its rough surface can be leveled before the other layers are laminated or applied to the magnetic layer. In an optional step, the “other” substrate mentioned above can be removed from the structure obtained (so-called transfer lamination).

Alternatively, the lack of an optically smooth surface on the magnetic layer can be remedied by applying a leveling, smoothing intermediate layer, e.g. a suitable intermediate lacquer.

With regard to the production of the pigments according to the invention, there are various options. What all methods have in common is that initially A layer structure is produced above a carrier substrate, for example a carrier film such as a polyethylene terephthalate (PET) film, the layer structure having at least the magnetic layer and an optical functional layer. The layer structure is then detached from the carrier substrate and, if necessary, comminuted, for example by means of grinding, until particles with an adequate size distribution are obtained. For this purpose it is advantageous to arrange a further layer between the carrier substrate and the layer structure which can be removed in a controlled or selective manner, for example by dissolving in a suitable solvent. Since then, the effect pigments obtained can be mixed with a UV-curing binder to form a (screen) printing ink. The effect pigments are, in particular, two-dimensional, optically variable pigments and preferably have a magnetic moment that is oriented perpendicular to the plane of the effect pigment, corresponding to the perpendicular orientation of the individual magnetic columns in the columnar nanostructure. In the step of applying the ink to a printing material such as a security paper or a value document substrate by printing technology, an external magnetic field is expediently applied and the ink is cured, e.g. by UV radiation or the action of heat, so that the effect pigments become immobile.

The invention further relates to a method for producing a document of value, comprising

the printing of the document of value substrate with a first printing ink according to the invention, containing platelet-shaped magnetic effect pigments, in a first area;

the alignment of the platelet-shaped magnetic effect pigments in the first printing ink printed in the first area by means of an external magnetic field; the curing of the first printing ink printed in the first area.

Compared with the effect pigments according to the prior art with a magnetization running in the plane of the effect pigment, the magnetic effect pigments according to the invention align themselves in an externally applied magnetic field in such a way that the resulting security feature has a more brilliant effect and the light reflections look smoother because less light enters deviating directions is scattered. This optical effect is particularly advantageous in the case of a magnetization running perpendicular to the plane of the effect pigment.

A preferred method for producing a document of value comprises:

the printing of the document of value substrate with a first printing ink according to the invention containing first platelet-shaped magnetic effect pigments in a first area;

- The printing of the document of value substrate with a second printing ink according to the invention containing second platelet-shaped magnetic effect pigments in a second area adjoining the first area, the second effect pigments visually differing from the first effect pigments;

Another preferred method for producing a document of value comprises: the printing of the document of value substrate with a first printing ink containing the flake-form magnetic effect pigments according to the invention in a first area;

the curing of the first and second printing inks respectively printed in the first area and in the second area, so that the two areas have an appearance that is clearly distinguishable from one another due to the different alignment of the two types of effect pigment.

The striking jump in the appearance of the area bordering the area, which goes back to the different optically variable properties of the areas with the different types of effect pigment, represents a conspicuous and advantageous security feature.

Further advantages of the invention are explained below with the aid of the schematically greatly simplified figures, in the representation of which a true-to-scale and proportionate reproduction has been dispensed with in order to increase the clarity.

Show it: FIG. 1 shows a columnar nanostructure made of magnetic materi al above a substrate by means of glancing angle deposit (GLAD), the columns being oriented perpendicular to the substrate plane; FIG. 2 shows a columnar nanostructure of magnetic material produced above a substrate by means of glancing angle deposit (GLAD), the columns being inclined towards the substrate plane;

FIG. 3 shows an example of a magnetic layer of an effect pigment according to the invention;

FIG. 4 shows an example of a layer structure (section) from which platelet-shaped magnetic effect pigments according to the invention can be obtained by means of comminution;

FIG. 5 shows an example of a flake-form magnetic effect pigment according to the invention; and

FIG. 6 shows a conventional platelet-shaped magnetic effect pigment according to the prior art, the magnetic moment of which runs perpendicular to the normal vector of the thin layers.

FIG. 6 shows a conventional flake-form magnetic effect pigment 13 according to the prior art, the magnetic moment of which runs perpendicular to the normal vector of the thin layers. Such effect pigments 13 are commercially available under the trade name OVMI® from SICPA, have a platelet-shaped structure and are in the form of a layer composite, which has two layers of optical effect layers. th, for example each contains a color-shifting layer system with absorber / dielectric / reflector structure and a magnetic layer embedded in between. The optical effect layers each represent a colored area. The side areas of the pigment 13 are more or less uncolored. The magnetization of the magnetic pigment 13 is denoted by the symbol "m". If a magnetic field with a field strength with the symbol "H" is applied, the pigments 13 are aligned so that their magnetization is as parallel as possible to the field vector (see FIG. 6). As a consequence, the magnetic pigments 13 can rotate about axes parallel to their magnetization "m". The use of such magnetic pigments 13, for example when printing a document of value, thus leads to an essentially uniform alignment of the pigments 13 in one direction, while the alignment of the pigments 13 When looking at a document of value obtained in this way, a colored area of the pigment 13 does not always point upwards in the direction of the viewer Sharpness of the optically variable effect.

FIG. 5 shows an example of a platelet-shaped magnetic effect pigment 12 according to the invention, the magnetic moment "m" of which is oriented perpendicular to the platelet plane. If a magnetic field with a field strength with the symbol "H" is applied, the pigments 12 are oriented so that their magnetization is as parallel as possible to the field vector. Exactly as with the magnetic effect pigments 12 known in the prior art, one degree of freedom remains: the platelets can rotate about an axis which is arranged parallel to their magnetic moment without changing their potential energy in the magnetic field. In contrast to the magnetic pigments 13 known in the prior art, the rotation in the case of the pigments 12 according to the invention, however, no significant influence on the reflective properties of the pigments 12. The reflective properties can consequently be better controlled. In the case of the magnetic pigments 13 known in the prior art, the viewer sees a large number of small pigments, each with an essentially random brightness. The security elements obtained in this way consequently have a granular or, so to speak, "noisy" opushy texture. In contrast, homogeneously glossy surfaces can be produced using the pigments 12 according to the invention. In this way, so-called micromirror arching effects can be achieved, for example.

The flake-form magnetic effect pigment 12 according to the invention, shown in FIG. 5, has a sandwich-like layer structure with a special magnetic layer as a central layer, which is provided with an optical functional layer on both the front and the rear. The two opüschen functional layers are identical in the present example and are each formed by an interference layer structure with a reflective layer (e.g. an Al layer), a dielectric layer (e.g. a SiCb layer) and an absorbing layer (e.g. a Cr layer) . The effect pigment 12 thus has a symmetrical layer structure with the layer sequence: absorbent layer - dielectric layer - reflective layer - magnetic layer - reflective layer - dielectric layer - absorbent layer.

The production of the flake-form magnetic effect pigment 12 according to the invention according to FIG. 5 is described below with reference to FIGS. Figures 1 to 3 illustrate in particular the production of the magnetic layer. FIG. 1 shows a columnar nanostructure of magnetic material produced above a substrate 1 by means of glancing angle de position (GLAD), the columns 2 being oriented perpendicular to the substrate plane. For example, a-Fe2C> 3 (hematite) is used as the magnetic material.

The columnar nanostructure shown in FIG. 1 is provided after detachment from the substrate as a magnetic layer 5 for producing the effect pigments according to the invention (see FIG. 3). The arrows 6 shown in FIG. 3 each illustrate the magnetic moment of the individual magnetic columns within the nanostructure.

The magnetic layer 5 obtained is provided, according to FIG. 4, both on the front side and on the rear side by means of vapor deposition with a color-shifting interference layer structure, which has a reflective layer 9 (or 9 '), a dielectric layer 10 (or 10') and an absorbent layer 11 (or 11 '). FIG. 4 shows a section of the layer structure 7 obtained in this way, from which the flake-form magnetic effect pigments 12 according to the invention can be obtained by means of comminution.

According to a modification of the above-described production of an effect pigment according to the invention, the magnetic layer 5 shown in FIG. 3 is not based on the columnar nanostructure shown in FIG The columnar nanostructure shown in FIG. 2, in which the magnetic columns 4 are inclined towards the plane of the substrate 3. Furthermore, according to a further modification of the above exemplary embodiments, the columnar nanostructure of the magnetic material can be obtained instead of the glancing angle deposition (GLAD) technique by means of the oblique angle deposition (OAD) technique.

Claims

P a te n claims

1. Platelet-shaped magnetic effect pigment for use in a printing ink, comprising a layer structure with a magnetic layer and at least one optical functional layer, the magnetic layer being based on a magnetic material with a columnar nanostructure and the magnetic columns each having a largely uniform, of have the preferred magnetic direction deviating from the platelet level.

2. Platelet-shaped magnetic effect pigment according to claim 1, wherein the largely uniform preferred magnetic direction of the magnetic columns is oriented essentially perpendicular to the platelet plane of the effect pigment.

3. Platelet-shaped magnetic effect pigment according to claim 1, wherein the largely uniform preferred magnetic direction of the magnetic columns is inclined towards the platelet plane and the angle of inclination, measured starting from the perpendicular to the platelet plane, is preferably in a range from 1 ° to 20 °.

4. Platelet-shaped magnetic effect pigment according to one of claims 1 to 3, wherein the magnetic columns each have a size of less than 1000 nm, preferably less than 500 nm, more preferably less than 200 nm and particularly preferably less than 100 nm.

5. A platelet-shaped magnetic effect pigment according to any one of claims 1 to 4, wherein the substantially uniform magnetic preferential direction of the magnetic column is a uniaxial magnetic anisotropy, _V orzugs- wise is a uniaxial crystal magnetic anisotropy or a uniaxial shape magnetic anisotropy.

6. Platelet-shaped magnetic effect pigment according to claim 5, wherein the material of the magnetic layer is selected from the group consisting of BaFei ₂ 0i ₉ , FePt, CoCrPt, Co Pt, BiMn, a-Fe2C> 3 and Nd2Fei4B, and in particular the largely uniform one The preferred magnetic direction of the magnetic columns is a uniaxial magnetic crystal anisotropy, or the material of the magnetic layer is selected from the group consisting of iron, cobalt, nickel and an alloy of one or more of the above-mentioned elements and in particular the largely uniform magnetic preference direction of the magnetic columns is a uni-axial magnetic shape anisotropy.

7. Platelet-shaped magnetic effect pigment according to one of claims 1 to 6, wherein the columnar nanostructure of the magnetic material is obtainable by means of the glancing angle deposition (GLAD) technique or the oblique angle deposition (OAD) technique.

8. Platelet-shaped magnetic effect pigment according to one of claims 1 to 7, wherein the optical functional layer is a metallic layer, a color layer obtainable by printing, an interference layer structure based on a reflective layer, a dielectric layer and an absorbent layer, or a combination of two or more of the aforementioned An element is, for example, an ink layer that is available in printing technology and is arranged above a metallic layer.

9. Platelet-shaped magnetic effect pigment according to one of claims 1 to 8, wherein the effect pigment has a sandwich-like layer structure and the magnetic layer is provided as a central layer both on the front side and on the rear side with an optical function layer, the two optical functional layers being independently of one another from a reflective metallic layer, egg ner printing technology available color layer, one on a reflective Layer, a dielectric layer and an absorbing layer-based interference layer structure or a combination of two or more of the above-mentioned elements are selected, for example a color layer arranged above a reflective metallic layer from a printing technology point of view.

10. Platelet-shaped magnetic effect pigment according to claim 9, wherein the effect pigment has an asymmetrical layer structure with two optical functional layers which differ from one another, preferably two optical functional layers which differ from one another and which are each an interference layer structure based on a reflective layer, a dielectric layer and an absorbent layer and in particular with regard to the material or the layer thickness of the dielectric layer differ from one another and the effect pigment has the following layer sequence: absorbent layer - dielectric layer - reflective layer - magnetic layer - reflective layer - dielectric layer - absorbent layer.

11. Platelet-shaped magnetic effect pigment according to claim 9, wherein the effect pigment has a symmetrical layer structure with two identical optical functional layers.

12. Platelet-shaped magnetic effect pigment according to claim 11, wherein the effect pigment has a symmetrical layer structure, wherein the magnetic layer is provided as a central layer both on the front side and on the rear side with an optical functional layer each, the two optical functional layers each being an interference layer structure based on a reflective layer, a dielectric layer and an absorbent layer and the effect pigment being the following Layer sequence has: absorbent layer - dielectric layer - reflective layer - magnetic layer - reflective layer - dielectric layer - absorbent layer.

13. Platelet-shaped magnetic effect pigment according to claim 8, wherein the optical functional layer is an interference layer structure based on a reflective layer, an electrical layer and an absorbent layer, and the effect pigment has the following layer sequence: absorbent layer - dielectric layer - reflective layer - dielectric layer - absorbent layer - magnetic layer.

14. Platelet-shaped magnetic effect pigment according to claim 10, wherein the effect pigment has an asymmetrical layer structure, the magnetic layer being provided on the front side with an interference layer structure based on a reflective layer, a dielectric layer and an absorbing layer and the magnetic layer being provided on the rear side is provided with a reflective metallic layer so that the effect pigment has the following layer sequence: absorbing layer - dielectric layer - reflective layer - magnetic layer - reflective metallic layer.

15. A method for producing a platelet-shaped magnetic effect pigment according to any one of claims 1 to 14, comprising a) generating a magnetic layer based on a magnetic material with a columnar nanostructure, the magnetic columns being formed with a largely uniform preferred magnetic direction deviating from the plane of the magnetic layer; b) the production of a layer structure having the magnetic layer and at least one optical functional layer; and c) comminuting the layer structure obtained in step b) to give individual platelet-shaped magnetic effect pigments.

16. A method for producing a value document, comprising

the printing of the document of value substrate with a platelet-shaped magnetic effect pigment according to one of claims 1 to 14 contain the first printing ink in a first area;

the curing of the first printing ink printed in the first area.

17. The method of claim 16 comprising

- The printing of the value document substrate with a first platelet-shaped magnetic effect pigments according to one of claims 1 to 14 containing first printing ink in a first area;

- The printing of the document of value substrate with a second platelet-shaped magnetic effect pigments according to one of claims 1 to 14 containing second printing ink in a second area adjoining the first area, the second effect pigments visually differing from the first effect pigments; the alignment of the platelet-shaped magnetic effect pigments in the first and second printing inks respectively printed in the first area and in the second area by means of an external magnetic field;

18. The method of claim 16 comprising

the curing of the first and second printing inks respectively printed in the first area and in the second area, so that the two areas have an appearance that is clearly distinguishable from one another as a result of the different alignment of the two types of effect pigment.

19. Value document, obtainable by the method according to one of claims 16 to 18.

20. Document of value according to claim 19, wherein the document of value is a bank note or an identification document.

21. Printing ink comprising platelet-shaped magnetic effect pigments according to one of claims 1 to 14.

22. Printing ink according to claim 21, wherein the printing ink comprises a binder, preferably a UV-curing binder, a binder curing by means of electron beams, or a thermosetting binder.