DE102018004430A1 - Method for producing a value document, value document and printing device - Google Patents

Abstract

The invention relates to a method for producing a value document, in particular a banknote, comprising
a) providing a value document substrate;
b) printing the value document substrate with an ink based on magnetically orientable effect pigments or OVMI® pigments;
c) as long as the printed ink is still liquid, orienting or aligning the magnetically orientable effect pigments by alternately applying at least two non-parallel magnetic fields;
d) the curing of the color matrix surrounding the magnetically oriented effect pigments in the printed ink, so that the effect pigments are immobilized in the aligned state.

Description

The invention relates to a method for producing a value document, in particular a banknote, a document of value obtainable by the method and a printing device for carrying out the method.

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) 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. a) das Bereitstellen eines Wertdokumentsubstrats;
2. b) das Bedrucken des Wertdokumentsubstrats mit einer auf magnetisch orientierbaren Effektpigmenten bzw. OVMI®-Pigmenten basierenden Druckfarbe;
3. c) solange die aufgedruckte Druckfarbe noch flüssig ist, das Orientieren bzw. Ausrichten der magnetisch orientierbaren Effektpigmente durch abwechselndes Anlegen mindestens zweier nichtparalleler magnetischer Felder;
4. d) das Aushärten der die magnetisch orientierten Effektpigmente umgebenden Farbmatrix in der aufgedruckten Druckfarbe, sodass die Effektpigmente im ausgerichteten Zustand immobilisiert werden.

1. (First aspect of the invention) A method for producing a value document, in particular a banknote, comprising

1. a) providing a value document substrate;
2. b) printing the value document substrate with an ink based on magnetically orientable effect pigments or OVMI® pigments;
3. c) as long as the printed ink is still liquid, orienting or aligning the magnetically orientable effect pigments by alternately applying at least two non-parallel magnetic fields;
4. d) the curing of the color matrix surrounding the magnetically oriented effect pigments in the printed ink, so that the effect pigments are immobilized in the aligned state.

The value document substrate provided in step a) is in particular a paper substrate, a plastic substrate, a film / paper / foil composite substrate (see, for example, US Pat WO 2006/066431 A1 ) or a paper / foil / paper composite substrate (see eg WO 2004/028825 A2 ).

According to a variant, the value document substrate provided in step a) is a film substrate for producing security strips, security threads or security patches or security labels which are used to secure value documents, e.g. Banknotes that are suitable

In step d), the curing can be carried out in particular by means of UV radiation, thermal radiation or laser radiation.

2. (Preferred embodiment) Method according to clause 1, wherein in step c) the orientation or alignment of the magnetically orientable effect pigments is carried out by alternately applying at least two non-parallel magnetic fields.

3. (Preferred embodiment) Method according to clause 1 or 2, wherein in step c) the field lines of all magnetic fields in the vicinity of the effect pigments lie in the same plane.

4. (Preferred embodiment) Method according to one of the clauses 1 to 3, wherein in step c) at least one magnetic field undergoes a continuous rotation.

5. (Preferred embodiment) Method according to one of the clauses 1 to 4, wherein in step c) the different magnetic fields follow each other periodically or the different magnetic fields are applied in random temporal patterns one after the other.

6. (Preferred embodiment) Method according to one of the clauses 1 to 5, wherein in step c) the orientation or alignment of the magnetically orientable effect pigments takes place by alternately applying at least two nonparallel magnetic fields in rapid time sequence, preferably in a temporal sequence in one Range of 1 sec to 1/200 sec, more preferably in a range of 1/10 sec to 1/50 sec.

7. (Preferred embodiment) Method according to one of the clauses 1 to 6, wherein in step c) the temporal variation of a magnetic field takes place by a mechanical movement of a permanent magnet.

8. (Preferred embodiment) Method according to one of the clauses 1 to 6, wherein in step c) the temporal variation of a magnetic field is effected by an alternating drive of different electromagnets whose fields would overlap during simultaneous operation.

9. (Preferred embodiment) Method according to one of the clauses 1 to 6, wherein in step c) the temporal variation of a magnetic field is controlled by a time-variable control of a plurality of electromagnets with overlapping fields, e.g. with phase shift between the individual magnets, takes place.

10. (Preferred Embodiment) Method according to one of the clauses 1 to 6, wherein in step c) the temporal variation of a magnetic field is effected by a combination of two or all of the measures defined in clauses 7 to 9.

11. (Preferred Embodiment) Method according to one of the clauses 1 to 6, wherein in step c) the temporal variation of a magnetic field by a superposition of a static magnetic field, e.g. is generated by a stationary permanent magnet and / or electromagnet, on the one hand and a time-varying magnetic field according to one of the clauses 7 to 10 on the other hand.

12. (Preferred embodiment) Method according to one of the clauses 1 to 11, wherein in step c) the orientation or alignment of the magnetically orientable effect pigments takes place within a selected area of the printed ink, wherein the selected area is in particular in shape a pattern, in the form of characters or in the form of an encoding.

13. (Preferred embodiment) Method according to one of the clauses 1 to 12, wherein in step d) curing takes place within a selected area of the printed ink, the selected area being in particular in the form of a pattern, in the form of characters or in the form of an encoding is present.

14. (Second aspect of the invention) Value document, in particular a banknote, obtainable by the method according to one of the clauses 1 to 13.

The value document may further be in particular a paper banknote, polymer banknote or composite film banknote, or an identity card or a passport data page.

15. (Third aspect of the invention) Printing apparatus for performing the method according to any one of clauses 1 to 13, comprising means for providing a value document substrate, means for printing the value document substrate with magnetically orientable effect pigments or OVMI® pigments Printing ink, means for alternately applying at least two non-parallel magnetic fields, and means for curing the color matrix surrounding the magnetically-oriented effect pigments.

16. (Preferred Embodiment) A printing apparatus according to clause 15, wherein the printing apparatus is a screen printing apparatus.

Detailed Description of the Preferred Embodiments

In the present specification, the abbreviation OVMI® pigments is used instead of the term "magnetically orientable effect pigments".

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 auf die in der nachstehenden Beschreibung Bezug genommene „Formel (1)“.

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 to the "formula (1)" referred to in the following description.

The subject of the present invention is a technique which improves the control over the arrangement of the magnetic color pigments and thus enables a more attractive optical effect. This technique is based on a time-varying magnetic field.

• Fall 1: Änderung der Magnetisierung: die Richtung der Magnetisierung des Pigments ändert sich mit dem Magnetfeld.
• Fall 2: Umorientierung: in diesem Fall ändert sich die Magnetisierungsrichtung nicht; die Ausrichtung des gesamten Pigments folgt dem Magnetfeld.

In general, a free-moving particle with the magnetization "m" in the magnetic field "H" tries its potential energy "Epot" according to the 3 minimized by aligning it so that its magnetic moment runs as parallel as possible to the magnetic field (see compass needle). When the direction of the magnetic field is changed, depending on the field strength "H", the coercive force "Hc" of the magnetic material of the pigment, and the viscosity of the surrounding medium, there are two possibilities how the pigment may behave:

• Case 1: Change of magnetization: the direction of the magnetization of the pigment changes with the magnetic field.
• Case 2: reorientation: in this case, the magnetization direction does not change; the alignment of the entire pigment follows the magnetic field.

Combinations of the above two cases are also conceivable. In systems according to the prior art, there is a combination of the aforementioned influencing variables, in which essentially only changes in the magnetization in the pigment level occur: due to the shape anisotropy, a reorientation is energetically more favorable than a magnetization direction outside the pigment plane. In any case, the pigment is thus oriented so that its normal vector is substantially perpendicular to the magnetic field line.

Considering a pigment that is alternately exposed in rapid time to the action of two nonparallel magnetic fields, it will be understood that the most energetic state is that in which the plane of the pigment coincides with the plane subtended by the two magnetic field vectors. In this state, the pigment only has to change its direction of magnetization in the pigment plane during the magnetic field change (case 1), or rotate around its normal vector (case 2). When the pigment according to the prior art floats in a viscous medium, these rotations are the path of least resistance compared to rotation about an axis in the pigment plane.

Neither the change in the magnetization in the pigment plane nor the rotation around the normal vector change the reflection direction of the pigment, which is why no influence on the optical effect of the security element is to be expected.

Thus, by alternately applying two non-parallel magnetic fields, the reflection direction of the pigments can be clearly defined, which on the one hand increases the brilliance and sharpness of the reflection, on the other hand enables optically variable effects which are otherwise impossible (e.g., orthoparallactic motion effects, 3D relief effects).

It is irrelevant here whether two or more different magnetic fields are applied one after the other as long as the field lines of all the fields in the vicinity of the pigment lie in the same plane. Also possible is a continuous rotation of a magnetic field.

It is also irrelevant whether the various fields follow each other periodically, or whether they are created one after the other in random time patterns. The order of the created fields does not always have to be the same.

1. 1. Mechanische Bewegung eines Permanentmagnets.
2. 2. Alternierende Ansteuerung verschiedener Elektromagnete, deren Felder sich bei gleichzeitigem Betrieb überlagern würden.
3. 3. Zeitlich variable Ansteuerung mehrerer Elektromagnete mit sich überlagernden Feldern, z.B. mit Phasenversatz zwischen den einzelnen Magneten.
4. 4. Kombinationen zweier oder aller Fälle 1., 2., 3.
5. 5. Superposition eines statischen Magnetfelds, z.B. erzeugt durch ruhende Permanentmagnete und/oder Elektromagnete, und des zeitlich variablen Magnetfelds gemäß 1., 2., 3. oder 4.

The temporal variation of the magnetic field can be done, for example, by:

1. 1. Mechanical movement of a permanent magnet.
2. 2. Alternating control of various electromagnets whose fields would overlap in simultaneous operation.
3. 3. Time-variable control of several electromagnets with overlapping fields, eg with phase offset between the individual magnets.
4. 4. Combinations of two or all cases 1., 2., 3.
5. 5. Superposition of a static magnetic field, for example generated by stationary permanent magnets and / or electromagnets, and the time-variable magnetic field according to 1, 2, 3 or 4.

All methods can either be "global", ie all pigments of a security element, or "local", ie only pigments within limited parts of the security element.
Particularly attractive is the possibility to produce very finely structured magnetic fields with microelectronic devices with a high number of very small electromagnets.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2006/066431 A1 [0011]
• WO 2004/028825 A2 [0011]

Claims (16)

Method for producing a value document, in particular a banknote, comprising a) providing a value document substrate; b) printing the value document substrate with an ink based on magnetically orientable effect pigments or OVMI® pigments; c) as long as the printed ink is still liquid, orienting or aligning the magnetically orientable effect pigments by alternately applying at least two non-parallel magnetic fields; d) the curing of the color matrix surrounding the magnetically oriented effect pigments in the printed ink, so that the effect pigments are immobilized in the aligned state. Method according to Claim 1 , wherein in step c) the orientation or alignment of the magnetically orientable effect pigments is carried out by alternately applying at least two non-parallel magnetic fields. Method according to Claim 1 or 2 , wherein in step c) the field lines of all magnetic fields in the vicinity of the effect pigments lie in the same plane. Method according to one of Claims 1 to 3 , wherein in step c) at least one magnetic field undergoes a continuous rotation. Method according to one of Claims 1 to 4 , wherein in step c) the different magnetic fields follow each other periodically or the different magnetic fields are applied in random time patterns one after the other. Method according to one of Claims 1 to 5 , wherein in step c) the orientation or alignment of the magnetically orientable effect pigments by alternately applying at least two non-parallel magnetic fields in rapid time sequence, preferably in a time sequence in a range of 1 sec to 1/200 sec, more preferably in one Range from 1/10 sec to 1/50 sec. Method according to one of Claims 1 to 6 , wherein in step c), the temporal variation of a magnetic field by a mechanical movement of a permanent magnet takes place. Method according to one of Claims 1 to 6 , wherein in step c), the temporal variation of a magnetic field by an alternating control of different electromagnets whose fields would be superimposed during simultaneous operation takes place. Method according to one of Claims 1 to 6 , wherein in step c), the temporal variation of a magnetic field by a time-variable control of a plurality of electromagnets with overlapping fields, eg with phase offset between the individual magnets, takes place. Method according to one of Claims 1 to 6 , wherein in step c) the temporal variation of a magnetic field by a combination of two or all of the in the Claims 7 to 9 defined measures. Method according to one of Claims 1 to 6 , wherein in step c) the temporal variation of a magnetic field by a superposition of a static magnetic field, which is generated for example by a stationary permanent magnet and / or electromagnet, on the one hand and a time-variable magnetic field according to one of Claims 7 to 10 on the other hand. Method according to one of Claims 1 to 11 , wherein in step c) the orientation or alignment of the magnetically orientable effect pigments takes place within a selected area of the printed ink, wherein the selected area is present in particular in the form of a pattern, in the form of characters or in the form of a coding. Method according to one of Claims 1 to 12 , wherein in step d) the curing takes place within a selected area of the printed ink, wherein the selected area is present in particular in the form of a pattern, in the form of characters or in the form of an encoding. Security document, in particular a banknote, obtainable by the method according to one of Claims 1 to 13 , Printing device for carrying out the method according to one of Claims 1 to 13 apparatus comprising means for providing a value document substrate, means for printing the value document substrate with an ink based on magnetically orientable effect pigments or OVMI® pigments, means for alternately applying at least two non-parallel magnetic fields, and means for curing the the magnetic matrix surrounding the magnetically oriented effect pigments. Printing device after Claim 15 wherein the printing device is a screen printing device.

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