HK1209685B

HK1209685B - Optical effect layers showing a viewing angle dependent optical effect; processes and devices for their production; items carrying an optical effect layer; and uses thereof

Info

Publication number: HK1209685B
Application number: HK15110315.0A
Authority: HK
Inventors: Mathieu Schmid; Evgeny LOGINOV; Claude Alain Despland; Pierre Degott
Original assignee: Sicpa Holding Sa
Priority date: 2013-01-09
Filing date: 2014-01-07
Publication date: 2018-05-11

Description

Optical effect layer exhibiting viewing angle-dependent optical effect, process and apparatus for producing the same, article with optical effect layer, and use thereof

Technical Field

The invention relates to the field of protecting value documents and value goods against forgery and illegal copying. In particular, the present invention relates to an Optical Effect Layer (OEL) exhibiting a viewing angle dependent optical effect, a device and a process for the production thereof, an article carrying said OEL, and the use of said optical effect layer as an anti-counterfeiting device on a document.

Background

It is well known in the art to manufacture security elements, for example in the field of security documents, using inks, components or layers comprising oriented magnetic or magnetizable particles or pigments, in particular optically variable magnetic pigments. Coatings or layers comprising oriented magnetic or magnetizable particles are disclosed for example in US 2,570,856, US 3,676,273, US 3,791,864, US 5,630,877 and US 5,364,689. Coatings or layers comprising oriented magnetic color-shifting pigment particles that produce an attractive optical effect and are useful for protecting security documents are disclosed in WO 2002/090002 a2 and WO 2005/002866 a 1.

For example, security features for security documents can generally be classified as "implicit" security features on the one hand, and "explicit" security features on the other hand. The protection provided by the implicit security features relies on the concept of: that is, these features are difficult to detect, often requiring special equipment and knowledge to detect, while "explicit" security features rely on the concept of: that is, the human senses can easily detect these features without any assistance, for example, the features can be seen and/or detected by touch, but are still difficult to manufacture and/or copy. However, the effectiveness of explicit security features depends to a large extent on their easy recognizability as a security feature, since most users, in particular users who have no knowledge in advance of the security features of the relevant security documents or items, actually perform security checks based on the security features only at this point if they actually know the presence and nature of the security features.

Particularly attractive optical effects can be achieved if the security feature modifies its appearance in accordance with changes in viewing conditions (e.g. viewing angle). This effect can be achieved, for example, by the dynamic appearance-modifying optical device (DACOD) disclosed in EP-a 1710756, which is, for example, a concave fresnel-type reflective surface, or a convex fresnel-type reflective surface, relying on oriented pigment particles in a hardened coating. This document describes a way of obtaining an image of a printing plate containing magnetically charged pigments or debris by aligning the pigments in a magnetic field. After alignment in a magnetic field, these pigments or fragments exhibit a fresnel structure arrangement, for example a fresnel reflector. By tilting the image to alter the direction of reflection towards the viewer, the area that presents the maximum reflection to the viewer moves according to the alignment (alignment) of the flakes or pigments. An example of such a structure is the so-called "rolling bar" effect. This effect is used today for several security elements on banknotes, for example "50" for 50 rand banknotes in south africa. However, this rolling effect is generally only visible when the security document is tilted in a particular direction, i.e. up or down or sideways from the perspective of the viewer.

Although fresnel-type reflective surfaces are flat, they provide the appearance of a concave-convex reflective hemisphere. The fresnel-type reflective surface may be produced by exposing a wet coating comprising anisotropic reflective magnetic or magnetizable particles to the magnetic field of a single dipole magnet (magnet), which is placed above or below the plane of the coating, which has its own north-south axis parallel to said plane and is rotated about an axis perpendicular to said plane, as shown in figures 37A-37D in EP-a 1710756. The particles thus oriented are then fixed in position and orientation by hardening the coating.

Moving ring images are generated by exposing a wet coating comprising anisotropically reflective magnetic or magnetizable particles to the magnetic field of a dipole magnet, which images show a ring ("rolling ring") effect that appears to move with changing viewing angle. WO 2011/092502 discloses a moving ring image that can be acquired or generated by using a device for orienting particles in a coating. The disclosed device allows orienting magnetic or magnetizable particles with the aid of a magnetic field which is generated by a combination of a magnetizable soft sheet and a spherical magnet which has its own north-south axis perpendicular to the plane of the coating and which is arranged below said magnetizable soft sheet.

The moving ring images of the prior art are generally produced by aligning magnetic or magnetizable particles according to the magnetic field of only one rotating or static magnet. Since the degree of curvature of the magnetic field lines of only one magnet is typically relatively soft, i.e. has a low curvature, the changes in orientation of the magnetic or magnetizable particles on the surface of the OEL are also relatively soft. Further, when only a single magnet is used, the strength of the magnetic field rapidly decreases as the distance from the magnet increases. This results in difficulties in obtaining highly dynamic, well-defined features through the orientation of the magnetic or magnetizable particles, and may result in a "rolling ring" effect that presents a blurred ring edge. This problem is exacerbated as the "rolling ring" image size (diameter) increases when only a single stationary or rotating magnet is used.

There is therefore a need for a security feature which displays a dramatic dynamic ring effect covering a large area on a document with high quality, which security feature should be easy to verify regardless of the orientation of the security document, is difficult to manufacture on a large scale using equipment available to counterfeiters, and can be provided in a large number of possible shapes and forms.

Disclosure of Invention

It is therefore an object of the present invention to overcome the above-mentioned drawbacks of the prior art. This object is achieved by providing, for example on a document or other item, an optical effect layer which exhibits an apparent movement of image features dependent on viewing angle over an extended length, has good sharpness and/or contrast, and is easy to detect. The present invention provides an optical effect layer: for example as an improved explicit security feature that is easy to detect in the field of document security, or alternatively or additionally as an implicit security feature.

Optical Effect Layers (OELs) comprising security elements and security documents comprising said optical effect layers are disclosed and claimed herein. In particular, an Optical Effect Layer (OEL) is provided comprising a plurality of non-spherical magnetic or magnetizable particles, said particles being dispersed in a coating composition comprising a binder material, wherein in at least one annular region of the OEL at least a portion of the plurality of non-spherical magnetic or magnetizable particles are oriented: with its longest axis substantially parallel to the plane of the OEL, the annular region forming an optical image of an annular body surrounding a central region, wherein, in a cross-section perpendicular to the OEL and extending from the center of the central region, the longest axis of the oriented particles present in the annular region is tangent to an imaginary elliptical or circular negative or positive curvature. By orienting the non-spherical magnetic or magnetizable particles in this way, an optical effect of a ring-shaped body is generated to the observer.

Magnetic field generating devices useful for generating the optical effect layers described herein are also described and claimed herein. In particular, a magnetic field generating device for forming an optical effect layer is provided, the device being configured to receive a coating composition comprising a plurality of non-spherical magnetic or magnetizable particles and a binder material, and comprising one or more magnets configured to orient at least a portion of the plurality of non-spherical magnetic or magnetizable particles parallel to a plane of the optical effect layer in at least one annular region of the optical effect layer, the annular region forming an optical image of a closed annular body surrounding a central region, wherein, in a cross-section perpendicular to the OEL and extending from the center of the central region, the longest axis of the oriented particles present in the annular region forming the optical image of the annular body is tangent to a negative or positive curvature of an assumed ellipse or circle. The coating composition may be applied directly onto a support surface that is part of the apparatus and is formed from a solid member (e.g., a plate), or onto a substrate disposed on such a support surface, or alternatively, the substrate may serve as a support surface for the coating composition.

Processes for producing security elements, optical effect layers comprising security elements in the field of flat printing, and the use of optical effect layers for preventing forgery of security documents or for decorative applications are also described and claimed. In particular, the invention relates to a process for producing an Optical Effect Layer (OEL), comprising the steps of:

a) applying a coating composition comprising a binder and a plurality of non-spherical magnetic or magnetizable particles, said coating composition being in a first (fluid) state, on a substrate surface or a support surface of a magnetic field generating device,

b) exposing the coating composition in the first state to a magnetic field of a magnetic field generating means, preferably as defined in any of claims 8-12, to orient at least a part of the non-spherical magnetic or magnetizable particles in at least one annular region around a central region such that, in a cross-section perpendicular to the OEL and extending from the center of the central region, the longest axis of the particles present in the annular region is tangent to the negative or positive curvature of an assumed circle, and

c) hardening the coating composition to a second state so as to fix the magnetic or magnetizable non-spherical particles in the position and orientation in which they are used.

Further embodiments and aspects of the invention will become apparent from reading the dependent claims and the following description.

Various aspects of the invention may be summarized as follows:

1. an Optical Effect Layer (OEL) comprising a plurality of non-spherical magnetic or magnetisable particles, said particles being dispersed in a coating composition comprising a binder material,

wherein in at least one annular region of the OEL, at least a portion of the plurality of non-spherical magnetic or magnetizable particles are oriented: with its longest axis substantially parallel to the plane of the OEL, the annular region forming an optical image of a closed annular body surrounding a central region, wherein, in a cross-section perpendicular to the OEL and extending from the center of the central region, the longest axis of the oriented particles present in the annular region forming the image of the annular body is tangent to an assumed negatively or positively curved portion of an ellipse or circle.

2. The Optical Effect Layer (OEL) of item 1, wherein the OEL comprises an outer region located outside of a closed annular region, and the outer region surrounding the annular region comprises a plurality of non-spherical magnetic or magnetizable particles, wherein a portion of the plurality of non-spherical magnetic or magnetizable particles located within the outer region is oriented: with its longest axis substantially perpendicular to the plane of the OEL, or randomly oriented.

3. The Optical Effect Layer (OEL) of item 1 or 2, wherein the central region surrounded by the annular region comprises a plurality of non-spherical magnetic or magnetizable particles, wherein a portion of the plurality of non-spherical magnetic or magnetizable particles located within the central region is oriented: its longest axis is substantially parallel to the plane of the OEL, thereby creating a prominent optical effect within the central region of the annular body.

4. The Optical Effect Layer (OEL) of item 3, wherein at least a portion of the protruding peripheral shape is similar to the shape of the annular body.

5. The Optical Effect Layer (OEL) of item 4, wherein the annular bodies have an annular form and the protrusions have a solid circular or hemispherical shape.

6. The Optical Effect Layer (OEL) according to any one of the preceding items, wherein at least a portion of the plurality of non-spherical magnetic or magnetizable particles is comprised of non-spherical optically variable magnetic or magnetizable pigments.

7. The Optical Effect Layer (OEL) of item 6, wherein the non-spherical optically variable magnetic or magnetizable pigment is selected from the group consisting of magnetic thin film interference pigments, magnetic cholesteric liquid crystal pigments, and mixtures thereof.

8. A magnetic field generating device for forming an optical effect layer, the device being configured to receive a coating composition comprising a plurality of non-spherical magnetic or magnetizable particles and a binder material, and comprising one or more magnets configured to orient at least a portion of the plurality of non-spherical magnetic or magnetizable particles parallel to a plane of the optical effect layer in at least one annular region of the optical effect layer, the annular region forming an optical image of a closed annular body surrounding a central region, wherein, in a cross-section perpendicular to the OEL and extending from the center of the central region, the longest axis of the oriented particles present in the annular region forming the image of the annular body is tangent to a negatively curved or positively curved portion of an assumed ellipse or circle.

9. The magnetic field generating apparatus according to item 8, wherein

a) Comprises a support surface for receiving a coating composition, and the support surface is formed by:

a1) a plate to which the coating composition can be applied directly,

a2) a plate for receiving a substrate to which the coating composition may be applied,

or

a3) A magnet surface onto which the coating composition can be directly applied, or onto or over which a substrate onto which the coating composition can be applied can be disposed; or

b) Configured to receive a substrate on which the optical effect layer is to be disposed, the substrate replacing the support surface.

10. The magnetic field generating apparatus of item 9, the apparatus comprising a support surface or being configured to receive a substrate in place of the support surface, the apparatus further comprising

a) A bar dipole magnet and a pole piece, the bar dipole magnet being disposed below the support surface or the substrate replacing the support surface and having its own north-south axis perpendicular to the support surface/the substrate surface, wherein

a1) The pole piece is disposed below the bar dipole magnet and is in contact with one pole of the magnet, and/or

a2) Wherein the pole piece is spaced from and laterally surrounds the bar dipole magnet;

b) one or more pairs of strip dipole magnets positioned below the support surface and rotatable about an axis of rotation substantially perpendicular to the support surface, the magnets having their north-south axes substantially parallel to the support surface and their north-south magnetic axes substantially radial to the axis of rotation, and

b1) opposite magnetic north-south direction, or

b2) Same magnetic north-south direction

The one or more pairs of bar-shaped dipole magnets are respectively formed of two bar-shaped dipole magnets disposed substantially symmetrically about the rotation axis;

c) one or more pairs of bar dipole magnets positioned below the support surface and rotatable about an axis of rotation substantially perpendicular to the support surface, the magnets having i) their own north-south axes substantially perpendicular to the support surface, ii) their own north-south axes substantially parallel to the axis of rotation, and iii) opposite magnetic north-south directions, the one or more pairs of bar dipole magnets each formed by an assembly of two bar dipole magnets disposed substantially symmetrically about the axis of rotation;

d) three bar dipole magnets positioned below the support surface and arranged to be rotatable about a rotation axis substantially perpendicular to the support surface, wherein two of the three bar dipole magnets are located at opposite sides with respect to the rotation axis, the third bar dipole magnet is located on the rotation axis, and wherein i) each of said magnets has its own north-south axis substantially parallel to said support surface, ii) said two magnets spaced from said axis of rotation have their own north-south axes substantially radial with respect to said axis of rotation, iii) said two bar dipole magnets spaced from said axis of rotation have the same, i.e., a north-south direction that is asymmetric with respect to the rotation axis, and iv) the third bar dipole magnet located on the rotation axis has a north-south direction opposite to the north-south direction of the two spaced bar dipole magnets;

e) a dipole magnet located beneath the support surface or a substrate replacing the support surface, the dipole magnet being formed of a toroid having its own north-south magnetic axis extending radially from the center of the toroid toward the periphery;

f) one or more bar dipole magnets positioned below the support surface or a substrate replacing the support surface and rotatable about an axis of rotation substantially perpendicular to the support surface/the substrate surface, each of the one or more bar dipole magnets having its own north-south magnetic axis substantially parallel to the support surface/substrate surface, having its own north-south magnetic axis substantially radial to the axis of rotation, and the north-south directions of the one or more bar dipole magnets all being directed towards the axis of rotation or all being directed away from the axis of rotation; or

g) Three or more bar dipole magnets positioned below the support surface, all three or more magnets being statically positioned about a center of symmetry, each of the three or more bar dipole magnets having i) its own north-south axis substantially parallel to the support surface, ii) its own north-south magnetic axis aligned to extend substantially radially from the center of symmetry, and iii) the north-south directions of the one or more magnets all being directed toward or away from the center of symmetry.

11. The magnetic field generating device for forming an optical effect layer according to item 10, embodiment b2), c) or d), wherein, when the magnet is rotated around the rotation axis, time-dependent magnetic field lines substantially parallel to the support surface are generated in a region defining a ring shape and located within a central region, the central region being surrounded by and spaced from the ring shape.

12. The magnetic field-generating apparatus of item 12, wherein the annular body takes a ring-like form, and the central region surrounded by the annular body takes a solid circle or a hemisphere form.

13. A printing assembly comprising a magnetic field generating device as described in any of items 8-12.

14. Use of the magnetic field generating device of any of items 8 to 12 for generating an OEL as described in any of items 1 to 7.

15. A process for producing an Optical Effect Layer (OEL), comprising the steps of:

a) applying a coating composition comprising a binder and a plurality of non-spherical magnetic or magnetizable particles on a substrate surface or a support surface of a magnetic field generating device, the coating composition being in a first state,

b) exposing the coating composition in the first state to a magnetic field of a magnetic field generating means, preferably as defined in any of items 8-12, to orient at least a part of the non-spherical magnetic or magnetizable particles in at least one annular region around a central region such that, in a cross-section perpendicular to the OEL and extending from the center of the central region, the longest axis of the particles present in the annular region is tangent to the negative or positive curvature of an assumed circle, and

16. The process of clause 15, wherein the curing step c) is accomplished by UV-Vis light radiation curing.

17. The optical effect layer of any one of items 1-7, which is obtainable by the process of item 15 or item 16.

18. An optical effect coated substrate (OEC) comprising one or more optical effect layers according to any one of items 1-7 or 17 on the substrate.

19. A security document, preferably a banknote or an identity document, comprising an optical effect layer as described in any one of items 1 to 7 or 17.

20. Use of the optical effect layer recited in any of items 1-7 or 18 or the optical effect coating substrate recited in item 18 to protect a security document from counterfeiting or tampering, or for decorative applications.

Drawings

The Optical Effect Layer (OEL) and its production according to the present invention will now be described in more detail with reference to the accompanying drawings and specific embodiments, in which

Fig. 1 schematically shows the deformation of the annular body (fig. 1A) and the orientation of the non-spherical magnetic or magnetizable particles with respect to the substrate surface (not shown, in the figure below layer L) on which oel (L) is arranged, in a cross-section extending from the center of the central area surrounded by the annular area forming the optical effect of the annular body, the orientation of the non-spherical magnetic or magnetizable particles is tangential to the assumed negatively curved portion (fig. 1B) or positively curved portion (fig. 1C) of the ellipse. In fig. 1B and 1C, the orientation of the longest axis of the particle is tangent to the negative or positive curvature of the hypothetical ellipse in cross section. Thus, fig. 1B and 1C show the orientation of the particles in a cross-section perpendicular to the plane of the OEL and extending from the center of the central region of a portion of the annular region, thereby providing an optical effect from the inner side (side of the central region) to the outer side of the annular body.

Figure 2A shows a photograph of an OEL providing a dynamic optical effect of a ring-shaped body provided in accordance with one embodiment of the present invention. Figure 2B shows a photograph with highlighted OEL, in accordance with one embodiment of the present invention.

Fig. 3 schematically shows the structure of a magnetic field generating device for generating an OEL according to a first exemplary embodiment.

Fig. 4 schematically shows the structure of a magnetic field generating device for generating an OEL according to a second exemplary embodiment.

Fig. 5 schematically shows a structure of a magnetic field generating device for generating an OEL according to a third exemplary embodiment.

Fig. 6 schematically shows a structure of a magnetic field generating device for generating an OEL according to a fifth exemplary embodiment.

Fig. 7 schematically shows the structure of a magnetic field generating device for generating an OEL according to a sixth exemplary embodiment.

Fig. 8 schematically shows the structure of a magnetic field generating device for generating an OEL according to a seventh exemplary embodiment.

Fig. 9 schematically shows a structure of an apparatus for generating an OEL further including protrusions according to the first exemplary embodiment.

Fig. 10 schematically shows a structure of an apparatus for generating an OEL further including protrusions according to the second exemplary embodiment.

Fig. 11 schematically shows a structure of an apparatus for generating an OEL further including protrusions according to a third exemplary embodiment.

Fig. 12 schematically shows an optical effect coated substrate (OEC) comprising two separate Optical Effect Layer (OEL) assemblies (a and B) disposed on a substrate.

Fig. 13 shows an example of a ring shape surrounding one central area.

Figure 14A schematically illustrates the orientation of non-spherical magnetic or magnetisable particles in an annular security element of the invention; and

fig. 14B schematically shows the orientation of non-spherical magnetic or magnetizable particles in an annular security element of the invention, wherein the central area surrounded by the annulus is filled protrudingly.

Detailed Description

Definition of

The following definitions will be used to explain the meanings of the terms discussed in the description and recited in the claims.

As used herein, the indefinite articles "a" or "an" refer to one as well as to more than one and do not necessarily limit the noun to which they refer to a singular.

As used herein, the term "about" means that the quantity or value referred to can be the particular value specified, or other values in the vicinity thereof. In general, the term "about" indicating a particular value is intended to indicate a range within ± 5% of that value. For example, the phrase "about 100" indicates a range of 100 ± 5, i.e., a range from 95 to 105. In general, when the term "about" is used, it is contemplated that similar results or effects in accordance with the present invention may be achieved within a range of ± 5% of the indicated value.

As used herein, the term "and/or" means that all elements of the group or only one element may be present. For example, "a and/or B" shall mean "a only, or B only, or both a and B". In the case of "a only", the term also covers the possibility of missing B, i.e. "a only, but not B included".

The term "substantially parallel" indicates a degree of deviation from parallel alignment of less than 20 °, and the term "substantially perpendicular" indicates a degree of deviation from perpendicular alignment of less than 20 °. Preferably, the term "substantially parallel" indicates a degree of deviation from parallel alignment of no more than 10 °, and the term "substantially perpendicular" indicates a degree of deviation from perpendicular alignment of no more than 10 °.

The term "at least partially" is intended to indicate that the following property is achieved to some extent or completely. Preferably, the term indicates that the following properties are achieved by at least 50% or more, more preferably by at least 75%, even more preferably by at least 90%. The term may preferably indicate "completely".

The terms "substantially" and "substantially" are used to indicate that the following feature, attribute, or parameter is fully (completely) achieved or satisfied or has a substantial negative impact on the target result. Thus, the term "substantially" or "essentially" preferably means, for example, at least 80%, at least 90%, at least 95% or 100%, as the case may be.

As used herein, the term "comprising" is intended to mean a non-exclusive and open meaning. Thus, for example, a coating composition comprising compound a may comprise other compounds in addition to a. However, the terms "comprising" also cover the more restrictive meanings of "consisting essentially of …" and "consisting of …", so that, for example, "a coating component comprising compound a" can also consist (essentially) of compound a.

The term "coating composition" refers to any composition capable of forming an Optical Effect Layer (OEL) of the present invention on a solid substrate, and preferably, but not exclusively, may be applied by a printing process. The coating composition includes at least a plurality of non-spherical magnetic or magnetizable particles and a binder. These particles have anisotropic reflectivity due to their non-spherical shape.

As used herein, the term "optical effect layer" (OEL) indicates a layer comprising at least a plurality of oriented non-spherical magnetic or magnetizable particles and a binder, wherein the non-spherical magnetic or magnetizable particles are oriented within the binder.

As used herein, the term "optical effect coated substrate (OEC)" is used to indicate the product resulting from providing OEL on a substrate. The OEC may be composed of a substrate and an OEL, but may also include other materials and/or layers than OEL. The term OEC therefore also encompasses security documents such as banknotes.

The term "annular area" indicates an area of the OEL that recombines with itself and provides an optical effect or optical image of a ring-shaped body. This region takes the form of a closed loop around a central region. The "ring shape" may have the following shape: circular, oval, elliptical, square, triangular, rectangular, or any polygon. Examples of circular shapes include circular, rectangular or square (preferably with rounded corners), triangular, pentagonal, hexagonal, heptagonal, octagonal, and the like. Preferably, the region forming the loop does not intersect itself. The term "toroid" is used to indicate an optical effect obtained by: the non-spherical magnetic or magnetizable particles are oriented in the annular region to provide an optical image of the three-dimensional object to a viewer.

The term "security element" is used to indicate an image or graphical element that can be used for authentication purposes. The security elements may be explicit and/or implicit security elements.

The term "magnetic axis" or "north-south axis" indicates a theoretical line connecting the north and south poles of the magnet and extending through the north and south poles. The line does not have a specific direction. Conversely, the term "north-south direction" indicates a direction from north to south along the north-south or magnetic axis.

Detailed description of the invention

In one aspect, the present invention relates to an OEL generally disposed on a substrate to form an OEC. OEL comprises a plurality of non-spherical magnetic or magnetizable particles, which have anisotropic reflectivity due to their non-spherical shape. These particles are dispersed in the binder material and have a particular orientation for providing an optical effect. This orientation is achieved by orienting the particles in accordance with an external magnetic field, as will be described in more detail below.

In OELs, the non-spherical magnetic or magnetizable particles are dispersed in a coating composition comprising a hardened binder material that fixes the orientation of the non-spherical magnetic or magnetizable particles. The hardened binder material is at least partially transparent to electromagnetic radiation of one or more wavelengths in the range of 200nm to 2500 nm. Preferably, the hardened binder material is at least partially transparent to electromagnetic radiation of one or more wavelengths in the range of 200-800nm, more preferably 400-700 nm. Herein, the term "one or more wavelengths" indicates that the adhesive material may be transparent to only one wavelength within a given range of wavelengths, or may be transparent to multiple wavelengths within a given range. Preferably, the adhesive material is transparent to more than one wavelength within the given range, more preferably, to all wavelengths within the given range. Thus, in a more preferred embodiment, the hardened binder material is at least partially transparent to all wavelengths in the range of about 200 to about 2500nm (or 200-800nm, or 400-700 nm), and even more preferably, the hardened binder material is completely transparent to all wavelengths in these ranges.

Herein, the term "transparent" indicates that the transmission of electromagnetic radiation through the 20 μm hardened binder material layer present in the OEL (excluding non-spherical magnetic or magnetizable particles, but including all other optional components of the OEL, if present) is at least 80%, more preferably at least 90%, even more preferably at least 95%. This can be determined, for example, by determining the transmission of a sample of hardened binder material (excluding non-spherical magnetic or magnetizable particles) according to well-established test methods, such as DIN 5036-3 (1979-11).

The non-spherical magnetic or magnetizable particles described herein, due to their non-spherical shape, have anisotropic reflectivity with respect to incident electromagnetic radiation that is at least partially transparent to the hardened binder material. As used herein, the term "anisotropic reflectivity" indicates that the proportion of incident radiation from a first angle that is reflected by the particle into a particular (viewing) direction (second angle) depends on the orientation of the particle, i.e. a change in orientation of the particle relative to the first angle may result in a different magnitude of reflection towards the viewing direction.

Preferably, each of the plurality of non-spherical magnetic or magnetizable particles described herein has anisotropic reflectivity with respect to incident electromagnetic radiation in the complete wavelength range or certain portions between about 200 and about 2500nm, more preferably between about 400 and about 700nm, such that a change in orientation of the particle results in a change in the direction to which the particle reflects.

In the OEL of the present invention, the non-spherical magnetic or magnetizable particles are arranged in such a way as to form a dynamic ring-shaped security element.

Here, the term "dynamic" indicates that the appearance and light reflection of the security element changes depending on the viewing angle. In other words, the appearance of the security element is also different when viewed from different angles, i.e. the security element presents a different appearance (e.g. relative to a viewing angle of about 90 °, relative to the OEL plane, both viewed from a viewing angle of about 22.5 °). This behavior is caused by the orientation of the non-spherical magnetic or magnetizable particles with anisotropic reflectivity and/or the properties of the non-spherical magnetic or magnetizable particles themselves having a viewing angle dependent appearance (e.g. the optically variable pigments described below).

The term "toroid" indicates that non-spherical magnetic or magnetizable particles are arranged so that the OEL provides the viewer with a visual image of the enclosure recombined with itself to form an enclosed toroid surrounding a central region. The "toroid" may have a circular, elliptical, ellipsoidal, square, triangular, rectangular, or any polygonal shape. Examples of annular shapes include circular, rectangular or square (preferably with rounded corners), triangular, (regular or irregular) pentagonal, (regular or irregular) hexagonal, (regular or irregular) heptagonal, (regular or irregular) octagonal, any polygonal shape, and the like. Preferably, the annular body does not cross itself (for example in a double ring, or in a shape in which a plurality of rings such as olympic rings overlap each other). An example of a ring shape is also shown in fig. 13.

In the present invention, the optical image of the annular body is formed by the orientation of non-spherical magnetic or magnetizable particles. That is, the annular shape of the annular body is not achieved by applying (e.g. by printing) a coating composition comprising a binder material and non-spherical magnetic or magnetizable particles in the annular shape on a substrate, but by aligning the non-spherical magnetic or magnetizable particles according to a magnetic field in the annular region of the OEL. Thus, the annular region represents a portion of the entire area of the OEL, which, in addition to the annular region, also includes such portions: wherein the non-spherical magnetic or magnetizable particles are not aligned at all (i.e. have random orientation) or are aligned so as not to participate in forming the image of a ring-shaped body. In this portion that does not participate in the image forming the annular body, at least a portion of the particles are typically oriented such that their longest axis is substantially perpendicular to the plane of the OEL.

Preferably, the non-spherical magnetic or magnetizable particles are oblong or oblate ellipsoidal, platelet-shaped or needle-shaped particles or mixtures thereof. Thus, even per unit surface area (e.g., per μm)²) Is uniform over the entire surface of such particles, but due to its non-spherical shape, the reflectivity of the particles is also anisotropic, since the visible region of the particles depends onIn the direction of observation. In one embodiment, the non-spherical magnetic or magnetizable particles, which are anisotropically reflective due to their non-spherical shape, may further have an intrinsic anisotropic reflectivity, for example in optically variable magnetic pigments, due to the presence of multiple layers of different reflectivity and refractivity. In this embodiment, the non-spherical magnetic or magnetizable particles comprise non-spherical magnetic or magnetizable particles having intrinsic anisotropic reflectivity, such as non-spherical optically variable magnetic or magnetizable pigments.

Suitable examples of non-spherical magnetic or magnetizable particles described herein include, but are not limited to, particles containing: ferromagnetic or ferrimagnetic metals such as cobalt, iron or nickel; ferromagnetic or ferrimagnetic alloys of iron, manganese, cobalt, iron or nickel; ferromagnetic or ferrimagnetic oxides of chromium, manganese, cobalt, iron, nickel or mixtures thereof; and mixtures of the foregoing. The ferromagnetic or ferrimagnetic oxides of chromium, manganese, cobalt, iron, nickel or mixtures thereof may be pure or mixed oxides. Examples of magnetic oxides include, but are not limited to, such as hematite (Fe)₂O₃) Magnetite (Fe)₃O₄) Chromium dioxide (CrO)₂) Magnetic ferrite (MFe)₂O₄) Magnetic alumina (MR)₂O₄) Magnetic hexaferrite (MFe)₁₂O₁₉) Magnetic orthoferrite (RFeO)₃) Magnetic garnet M₃R₂(AO₄)₃Iron oxides of the type, wherein M represents divalent, R represents trivalent, A represents tetravalent metal ions, and "magnetic" represents ferromagnetic or ferrimagnetic properties.

Optically variable elements are known in the field of security printing. Optically variable elements (also referred to in the art as color shifting elements or goniochromatic elements) exhibit a color that is dependent on the angle of view or angle of incidence, and are used to prevent counterfeiting and/or illegal copying of banknotes and other security documents using common color scanning, printing and copying office equipment.

Preferably, at least a portion of the plurality of non-spherical magnetic or magnetizable particles described herein is comprised of non-spherical optically variable magnetic or magnetizable pigments. Such non-spherical optically variable magnetic or magnetizable pigments are preferably oblong or oblate ellipsoidal, platelet-shaped or needle-shaped particles or mixtures thereof.

The plurality of non-spherical magnetic or magnetizable particles may comprise non-spherical optically variable magnetic or magnetizable pigments and/or non-spherical magnetic or magnetizable particles not having optically variable properties.

As will be explained below, an optical image of the annular body is formed by orienting (aligning) the plurality of non-spherical magnetic or magnetizable particles in accordance with the field lines of the magnetic field, resulting in a highly dynamic viewing angle dependent appearance of the annular body. If at least a part of the plurality of non-spherical magnetic or magnetizable particles described herein is constituted by non-spherical optically variable magnetic or magnetizable pigments, an additional effect may be obtained, since the color of the non-spherical optically variable magnetic or magnetizable pigments is significantly dependent on the viewing angle or angle of incidence with respect to the plane of the pigments, resulting in an effect combined with a viewing angle dependent dynamic ring effect. As shown in fig. 2A and 2B, the use of magnetically oriented non-spherical optically variable pigments in the region of the OEL forming the image of the dynamic annular body according to the present invention enhances the visual contrast of the bright areas and improves the visual impact of the annular body in document security and decorative applications. The combination of the dynamic annular shape achieved using magnetically oriented non-spherical color shifting optically variable pigments and the observed color variation of the optically variable pigments results in the appearance of differently colored edges in the annular body that are easily verified by the naked eye. Thus, in a preferred embodiment of the invention, the optical image of the annular body is formed at least in part by magnetically orienting the non-spherical optically variable pigment.

In addition to the explicit security provided by the color-changing properties of the non-spherical optically variable magnetic or magnetizable pigments, which allows OECs (e.g., security documents) with OELs according to the present invention to be easily detected, identified and/or distinguished from possible counterfeits using the human sense without any assistance, e.g., because these features are visible and/or detectable, but still difficult to manufacture and/or reproduce, the OELs can be identified using the color-changing properties of the non-spherical optically variable magnetic or magnetizable pigments as a machine-readable tool. Thus, the optically variable properties of the non-spherical optically variable magnetic or magnetizable pigment can be simultaneously used as an implicit or semi-implicit security feature in a verification process for analyzing the optical (e.g. spectral) properties of the particles.

The use of non-spherical optically variable magnetic or magnetizable pigments can enhance the importance of OEL as a security feature in document security applications, as these materials (i.e., optically variable magnetic or magnetizable pigments) are dedicated to the security document printing industry and are not publicly sold.

As mentioned above, preferably at least a part of the plurality of non-spherical magnetic or magnetizable particles is constituted by non-spherical optically variable magnetic or magnetizable pigments. These may more preferably be selected from the group consisting of magnetic thin film interference pigments, magnetic cholesteric liquid crystal pigments and mixtures thereof.

Magnetic thin-film interference pigments are well known to the person skilled in the art and are disclosed, for example, in US 4,838,648, WO 2002/073250A 2, EP-A686675, WO 2003/000801A 2, US 6,838,166, WO 2007/131833A 1 and the documents related thereto. Since these pigments have magnetic characteristics, they can be machine-readable, so coating compositions comprising magnetic thin film interference pigments can be detected, for example, using a dedicated magnetic detector. Thus, the coating composition comprising the magnetic thin-film interference pigment can be used as an implicit or semi-implicit security element (authentication tool) for a security document.

Preferably, the magnetic thin-film interference pigments comprise pigments having a five-layer fabry-perot multilayer structure and/or pigments having a six-layer fabry-perot multilayer structure and/or pigments having a seven-layer fabry-perot multilayer structure. A preferred five-layer fabry-perot multilayer structure consists of an absorber/insulator/reflector/insulator/absorber multilayer structure, wherein the reflector and/or the absorber are also magnetic layers. The preferred six-layer Fabry-Perot multilayer structure is composed of absorber/insulator/reflectorA/magnetic/insulator/absorber multilayer structure. A preferred seven-layer fabry-perot multilayer structure consists of an absorber/insulator/reflector/magnetic/reflector/insulator/absorber multilayer structure, as disclosed for example in US 4,838,648; more preferably, it is composed of a seven-layer fabry-perot absorber/insulator/reflector/magnetic/reflector/insulator/absorber multilayer structure. Preferably, the reflector layer described herein is selected from the group consisting of metals, metal alloys and combinations thereof, preferably from the group consisting of reflective metals, reflective metal alloys and combinations thereof, more preferably from the group consisting of aluminum (Al), chromium (Cr), nickel (Ni) and mixtures thereof, more preferably aluminum (Al). Preferably, the insulator layer is independently selected from magnesium fluoride (MgF)₂) Silicon dioxide (SiO)₂) And mixtures thereof, more preferably magnesium fluoride (MgF)₂). Preferably, the getter layer is independently selected from the group consisting of chromium (Cr), nickel (Ni), metal alloys, and mixtures thereof. Preferably, the magnetic layer is preferably selected from the group consisting of nickel (Ni), iron (Fe), and cobalt (Co), alloys including nickel (Ni), iron (Fe), and/or cobalt (Co), and mixtures thereof. Particularly preferably, the magnetic thin film interference pigment comprises a chromium/magnesium fluoride (Cr/MgF)₂/Al/Ni/Al/MgF₂A seven-layer Fabry-Perot absorber/insulator/reflector/magnetic/reflector/insulator/absorber multilayer structure consisting of/Cr multilayer structures.

The magnetic thin film interference pigments described herein are typically manufactured by vacuum deposition of the different necessary layers on a web. After the desired number of layers are deposited (e.g., by PVD), the stack of layers is removed from the web by dissolving the release layer in a suitable solvent, or by stripping the material from the web. The material obtained in this way is then broken up into pieces which must be further processed by grinding, milling or any suitable method. The final product consists of flat chips with broken edges, irregular shapes and different aspect ratios. Further information on the preparation of suitable magnetic thin-film interference pigments can be found, for example, in EP-A1710756, which is incorporated herein by reference.

Suitable magnetic cholesteric liquid crystal pigments exhibiting optically variable characteristics include, but are not limited to, single layer cholesteric liquid crystal pigments and multilayer cholesteric liquid crystal pigments. These pigments are disclosed, for example, in WO 2006/063926 a1, US 6,582,781 and US 6,531,221. WO 2006/063926 a1 discloses monolayers and pigments obtained therefrom which have high brightness and colour change properties and which have other specific properties such as magnetisability. The disclosed monolayer and the pigment obtained by crushing the monolayer comprise a three-dimensionally crosslinked cholesteric liquid crystal mixture and magnetic nanoparticles. U.S. Pat. No. 6,582,781 and U.S. Pat. No. 6,410,130 disclose platelet-shaped cholesteric multilayer pigments comprising the sequence A¹/B/A²Wherein A is¹And A²May be the same or different and each comprise at least one cholesteric layer, and B is an interlayer, the absorption layer A of which¹And A²Some or all of the light transmitted and imparts magnetic properties to the interlayer. US 6,531,221 discloses platelet-shaped cholesteric multilayer pigments comprising the sequence a/B and, if desired, C, where a and C are absorber layers comprising pigments imparting magnetic properties and B is a cholesteric layer.

In addition to or consisting of non-spherical magnetic or magnetizable particles (which may or may not comprise or consist of non-spherical optically variable magnetic or magnetizable pigments), non-magnetic or non-magnetizable particles may also be comprised in the OEL in addition to or within the annular body security element and/or the annular body security element. These particles may be colour pigments, known in the art, with or without optically variable properties. Further, the particles may be spherical or non-spherical, and may have isotropic or anisotropic optical reflectivity.

In OEL, the non-spherical magnetic or magnetizable particles described herein are dispersed in a binder material. Preferably, the amount of non-spherical magnetic or magnetizable particles is from about 5 to about 40 weight percent, more preferably from about 10 to about 30 weight percent, based on the total dry weight of the OEL including the binder material, the non-spherical magnetic or magnetizable particles, and other optional ingredients of the OEL.

As previously mentioned, the hardened binder material is at least partially transparent to electromagnetic radiation of one or more wavelengths in the range of 200-. Thus, the binder material is at least in its hardened or solid state (also referred to below as second state) at least partially transparent to electromagnetic radiation of one or more wavelengths in the range of about 200nm to about 2500nm, i.e. in a wavelength range commonly referred to as the "spectrum" comprising the infrared part, the visible part and the UV part of the electromagnetic spectrum, so that the particles contained in the binder material in the hardened or solid state and their orientation-dependent reflectivity are perceivable by the binder material.

More preferably, the adhesive material is at least partially transparent in the visible spectral range between about 400nm and about 700 nm. Incident electromagnetic radiation, such as visible light entering the OEL through a surface thereof, may reach particles dispersed within the OEL and may be reflected therein, and the reflected light may again exit the OEL to produce a desired optical effect. OELs can also serve as an implicit security feature if the wavelength of the incident radiation is selected outside the visible range, e.g. in the near UV range, since it is then usually necessary to take technical measures to detect the (complete) optical effects produced by OELs under various illumination conditions including the selected invisible wavelengths. In this case, preferably the OEL and/or the annular region comprised therein comprises luminescent pigments which luminesce in response to selected wavelengths outside the visible spectrum comprised in the incident radiation. The infrared, visible and UV portions of the electromagnetic spectrum correspond approximately to the wavelength ranges between 700-2500nm, 400-700nm and 200-400nm, respectively.

If an OEL is to be provided on a substrate, the coating composition comprising at least the binder material and the non-spherical magnetic or magnetizable particles must take the form of: this form allows the coating composition to be processed, for example by printing, in particular copper gravure printing, screen printing, gravure printing, flexographic printing or roller coating, in order to apply the coating composition on a substrate, such as a paper substrate or a substrate described below. Further, after application of the coating composition on the substrate, the non-spherical magnetic or magnetizable particles are oriented by applying a magnetic field to align the particles along the field lines. In this case, the non-spherical magnetic or magnetizable particles are oriented in the annular region of the coating composition on the substrate in order to form an optical image of the annular body to an observer who observes the substrate from a direction perpendicular to the substrate plane. After or while performing the step of orienting/aligning the particles by applying the magnetic field, the particle orientation is fixed. It is therefore worth noting that the coating composition must have a first state, i.e., a fluid state or a paste state, in which the coating composition is sufficiently wet or soft so that the non-spherical magnetic or magnetizable particles dispersed in the coating composition are free to move, rotate and/or orient when exposed to a magnetic field, and must have a second hardened (e.g., solid) state in which the non-spherical particles are fixed or frozen in their respective positions and orientations.

Such first and second states are preferably provided using a particular type of coating composition. For example, the components of the coating composition other than the non-spherical magnetic or magnetisable particles may take the form of an ink or coating composition such as those used in security applications (e.g. banknote printing).

The first and second states described above may be provided using materials that: this material may increase in viscosity substantially in response to a stimulus such as a change in temperature or exposure to electromagnetic radiation. That is, when the fluent binder material is hardened or cured, the binder material transitions to a second state, i.e., a hardened or solid state, in which the particles are fixed in their current position and orientation, and can no longer move within the binder material, nor rotate therein.

As is well known to those skilled in the art, the composition included in an ink or coating composition that can be applied to a surface, such as a substrate, and the physical properties of the ink or coating composition are determined by the nature of the process used to transfer the ink or coating composition to the surface. Thus, the binder material included in the ink or coating composition described herein is generally selected from binder materials known in the art and is dependent upon the coating, or printing process used to apply the ink or coating composition, and the selected curing process.

In one embodiment, a polymeric thermoplastic adhesive material or a thermosetting adhesive material may be employed. Unlike thermosetting binder materials, thermoplastic resins can be repeatedly melted and solidified by heating and cooling without causing any significant change in properties. Typical examples of thermoplastic resins or polymers include, but are not limited to, polyamides, polyesters, polyoxymethylenes, polyolefins, polystyrenic resins, polycarbonates, polyarylates, polyimides, Polyetheretherketones (PEEK), Polyetherketoneketones (PEKK), polyphenylene resins (e.g., polyphenylene ethers, polyphenylene oxides, polyphenylene sulfides, etc.), polysulfones, and mixtures thereof.

After applying the coating composition on the substrate and orienting the non-spherical magnetic or magnetizable particles, the coating composition is hardened (i.e., converted to a solid state or solid state) in order to fix the orientation of the particles.

Hardening may be purely physical, for example, where the coating composition includes a polymeric binder material and a solvent, and is applied at an elevated temperature. The particles are then oriented at high temperature by applying a magnetic field, followed by evaporation of the solvent and finally cooling of the coating composition. This hardens the coating composition and orients the particles.

Alternatively or preferably, the "hardening" of the coating composition involves a chemical reaction, for example by curing, which cannot be reversed by a simple temperature increase (for example, to 80 ℃) that may occur during use of a typical security document. The term "cure" or "curable" indicates a process in which: this process involves a chemical reaction, crosslinking or polymerization of at least one component of the applied coating composition, by which process the coating composition becomes a polymeric material having a higher molecular weight than the starting substance. Preferably, curing results in the formation of a three-dimensional polymer network.

Such curing is typically initiated by applying an external stimulus to the coating composition (i) after applying the coating composition to the substrate surface or the support surface of the magnetic field generating means, (ii) after or while performing the orientation of the magnetic or magnetizable particles. Thus, preferably, the coating component is an ink or coating component selected from the group consisting of radiation curing components, thermal drying components, oxidative drying components, and combinations thereof. Particularly preferably, the coating component is an ink or coating component selected from the group consisting of radiation-curable components.

Preferred radiation curable components include those curable by UV visible radiation (hereinafter UV-Vis curing) or by electron beam radiation (hereinafter EB). Radiation curable components are well known in the art and can be found in the following standard textbooks: for example, the "Chemistry & Technology of UV & EB Formulation for Coatings, Inks & Paints (Chemistry and Technology of UV and EB formulations for Coatings, Inks and Paints, John Wiley and Sons, Inc. of SITATechnology Limited, 1997 and 1998, Vol. 7)" series.

According to a particularly preferred embodiment of the present invention, the ink or coating composition described herein is a UV-Vis curing composition. UV-Vis curing advantageously enables a very fast curing process, thus significantly reducing the preparation time of the OEL according to the present invention and of articles and documents comprising said OEL. Preferably, the UV-Vis curing component comprises one or more compounds selected from the group consisting of radically curable compounds, cationically curable compounds and mixtures thereof. Preferably, the UV-Vis curing component comprises one or more compounds selected from the group consisting of radical curing compounds, cationic curing compounds and mixtures thereof. Cationically curable compounds cure by a cationic mechanism, typically involving radiation activation by one or more photoinitiators that release cationic reactive species (e.g., acids), which in turn initiate curing to react and/or crosslink the monomers and/or oligomers, thereby hardening the coating composition. Free radical curable compounds cure by a free radical mechanism, typically involving radiation activation by one or more photoinitiators, to generate free radicals, which in turn initiate polymerization to harden the coating component.

The coating composition may further include one or more machine-readable materials selected from the group consisting of magnetic materials, luminescent materials, conductive materials, infrared absorbing materials, and mixtures thereof. As used herein, the term "machine-readable material" refers to a material that exhibits at least one particular property that is not perceptible to the naked eye, which material may be included in a layer in order to provide a way to authenticate the layer or an article comprising the layer using a particular device for authentication.

The coating composition may further comprise one or more colour components selected from the group consisting of organic and inorganic pigments and organic dyes, and/or one or more additives. The latter include, but are not limited to, compounds and materials used to adjust the physical, rheological, and chemical parameters of the coating composition, including, for example, viscosity (e.g., solvents, thickeners, and surfactants), consistency (e.g., anti-settling agents, fillers, and plasticizers), foam properties (e.g., defoamers), lubricating properties (waxes, oils), UV stability (photosensitizers and light stabilizers), adhesion properties, antistatic properties, storage stability properties (inhibitors), and the like. The additives described herein may be present in the coating composition in amounts and in forms well known in the art, including the so-called nanomaterial form, in which form at least one dimension of the additive is in the range of 1 to 1000 nm.

After or while applying the coating composition on the substrate surface or the support surface of the magnetic field generating means, the non-spherical magnetic or magnetizable particles are oriented using an external magnetic field which orients the particles according to the desired orientation mode. Thus, the permanent magnetic particles are oriented: its magnetic axis is aligned with the direction of the external magnetic field lines at the particle location. Magnetizable particles without an intrinsic permanent magnetic field are oriented by an external magnetic field so that their longest dimension is aligned with the magnetic field lines at the particle location. The above principle applies analogously also in the case of particles having a layer structure comprising layers having magnetic or magnetizable properties. In this case, the longest axis of the magnetic layer or the longest axis of the magnetizable layer is aligned with the direction of the magnetic field.

Upon application of a magnetic field, the non-spherical magnetic or magnetizable particles adopt an orientation in the layer of coating composition in such a way that: a visual appearance or optical image of the dynamic annular body is produced which can be seen from at least one surface of the OEL (see, for example, fig. 1 and 2). Thus, a dynamic toroid may be seen by an observer as a reflective region that exhibits a dynamic visual shifting effect as the OEL is rotated or tilted, the toroid appearing to move in a different plane than the rest of the plane of the OEL. After or while performing the orientation of the non-spherical magnetic or magnetizable particles, the coating composition is hardened to fix the orientation (e.g., irradiated with UV-Vis light in the case of a UV-Vis cured coating composition).

At a given direction of incident light (e.g. perpendicular), the highest reflectivity (i.e. specular reflection at non-spherical magnetic or magnetizable particles) area of the oel (l) comprising particles with a fixed orientation changes position with a change in viewing (tilt) angle: the annular bright area is seen at position 1 when the OEL (l) is viewed from the left, at position 2 when the OEL is viewed from the top, and at position 3 when the layer is viewed from the right. When changing the viewing direction from left to right, the ring-shaped bright area thus also appears to move from left to right. The opposite effect can also be obtained, i.e. the ring-shaped bright area appears to move from right to left when changing the viewing direction from left to right. Depending on the sign of the curvature of the non-spherical magnetic or magnetizable particles present in the ring-shaped body, which may be negative (see fig. 1B) or positive (see fig. 1C), the dynamic ring element may be observed to move towards the observer (in case of positive curvature, fig. 1C) or away from the observer (negative curvature, fig. 1B) for movements performed by the observer with respect to the OEL. Notably, the viewer position is above the OEL in fig. 1. This dynamic optical effect or optical image can be observed if the OEL is tilted, and due to the ring shape, this effect can be observed regardless of the direction of tilt of, for example, a bill on which the OEL is disposed. This effect is observed, for example, when a banknote with an OEL is tilted from left to right, while also tilting from top to bottom.

The region of the OEL forming the visual image of the annular body (i.e. the annular region of the OEL) comprises oriented non-spherical magnetic or magnetizable particles, thus forming an optical effect of at least one annular body (closed loop) surrounding one central region. In this region, the direction of the longest axis of the non-spherical magnetic or magnetizable particles, when viewed in cross-section in the direction extending from the center of the central region to the outer space of the annular region (from the boundary of the annular region with the central region to the boundary of the annular region with the region outside the annular region), is tangential to the assumed negative or positive curvature of the ellipse or circle. In this cross-sectional view of the annular region, the orientation of the particles is substantially parallel to the plane of the OEL in the vicinity of the center of the annular region, and in this cross-sectional view, gradually changes towards a less parallel (typically substantially perpendicular) direction (this direction towards the boundary of the annular region). This situation is illustrated in fig. 1, and further illustrated in fig. 14A and 14B. It is noted that the rate of change of orientation from a substantially parallel direction to a more perpendicular direction may be constant (the orientation of the non-spherical particles being tangential to the negative or positive curvature of the circle) or may vary along the width of the annular region (the orientation of the non-spherical particles being tangential to the negative or positive curvature of the ellipse).

In fig. 14A, an embodiment of an OEL comprising an annular region arranged on a support (S) and the orientation of non-spherical magnetic or magnetizable particles therein is shown. At the top, the optical image of the toroid is seen in the plan view of the OEL. At the bottom, a cross section in a direction extending from the center of the central region to the outer space of the annular region forming the optical image of the annular body is shown. In detail, an annular region (1) forming the optical effect of the annular body surrounds a central region (2). When viewed in a cross-section (3) of the outer space extending from the center (4) of the central region (2) to the annular region (shown at the bottom of the figure), the non-spherical magnetic or magnetizable particles (5) located in a region (represented by the grey box in which the particles (5) are located) from the border of the annular region with the central region to the border of the region outside the annular region with the annular body are oriented: its longest axis is tangent to the negative curve of the hypothetical ellipse or circle (6) in fig. 14A). Of course, orientations tangential to the assumed positive curvature of an ellipse or circle may also be achieved.

In fig. 14A, only non-spherical magnetic or magnetizable particles are shown in the region forming the optical image of the annular body. However, as will be apparent from the following, the particles may also be located within the central region (2) and outside the annular region forming the optical image of the annular body.

Preferably, in a cross-sectional view, the center of the assumed ellipse or circle (6) is located on a line (i.e. the perpendicular line to the bottom of fig. 14A) perpendicular to the OEL and extending approximately from the center of the area defining the ring-shaped body (i.e. the area from the border of the ring-shaped area with the central area to the border of the area outside the ring-shaped area with the ring-shaped body (indicated by the grey box showing the particle (5) in fig. 14A, also referred to as the "width" of the ring-shaped area)). In a further preferred embodiment, additionally or alternatively, the diameter of the assumed circle or the longest or shortest axis of the assumed ellipse is approximately equal to the width of the annular region, so that at the border of the annular region and the central region, and at the border of the annular region and the region outside the annular body, an orientation of the non-spherical particles substantially perpendicular to the plane of the OEL is achieved, which orientation gradually changes to a parallel orientation towards the center of the width of the annular region (i.e. the center of the grey box in fig. 14A). The central region surrounded by the annular region may not comprise magnetic or magnetizable particles, and in this case the central region may not be part of the OEL. This can be achieved by not providing the coating composition in the central region during the printing step.

However, alternatively or preferably, the central region is part of the OEL and is not ignored when the coating composition is provided on the substrate. This simplifies the fabrication of OELs because the coating composition can be applied over a larger area of the substrate surface. In this case, also non-spherical magnetic or magnetizable particles are present in the central region. These particles may have random orientations, providing no special effect, but only a small reflectivity. Preferably, however, the non-spherical magnetic or magnetizable particles present in the central region are substantially perpendicular to the plane of the Optical Effect Layer (OEL), so that substantially no reflection is provided in a direction perpendicular to the plane of the OEL when illuminated from the same side of the OEL.

The orientation of the non-spherical magnetic or magnetizable particles outside the annular region forming the optical image of the annular body may be substantially perpendicular to the plane of the OEL or may be randomly oriented. In one embodiment, the particles in the central region and the particles outside the annular region (i.e., the particles inside and outside the annular region) are oriented: substantially perpendicular to the plane of the OEL.

Fig. 1B shows a cross-section of a portion of the annular region (i.e., the width of the annular region) in a direction extending from the center of the central region to the outer boundary of the annular region. Here, non-spherical magnetic or magnetizable particles (P) in oel (l) are fixed in the binder material, said particles being tangent to the negative curvature of the surface of the hypothetical circle. Fig. 1C shows a similar cross-section, where the non-spherical magnetic or magnetizable particles in the OEL are tangent to the positive curvature of the surface of a hypothetical ellipse (circle in fig. 1 and 14).

In fig. 1, 14A and 14B, the non-spherical magnetic or magnetizable particles (P) are preferably dispersed throughout the volume of the OEL, whereas for the purpose of discussing the orientation of these particles within the OEL with respect to the surface of the support surface, preferably the substrate, it is assumed that these particles all lie within the same cross-sectional plane of the OEL. These non-spherical magnetic or magnetizable particles are shown graphically, each particle being represented by a short line representing its long axis. Of course, in reality and as shown in fig. 14A, some of the non-spherical magnetic or magnetizable particles may partially or completely overlap each other when viewed on the OEL.

The total amount of non-spherical magnetic or magnetizable particles in an OEL can be suitably selected depending on the desired application, but in order to constitute a surface coverage pattern that produces a visual effect, typically thousands of particles are required in a volume corresponding to 1 square millimeter of the surface of the OEL, e.g. about 1,000-10,000 particles.

The plurality of non-spherical magnetic or magnetizable particles which together produce the optical effect of the security element of the invention may correspond to all or only a subset of the total number of particles in the OEL. For example, the particles that produce the optical effect of the annular bodies may be combined with other particles contained in the binder material, which may be conventional or special color pigment particles.

As shown in fig. 2B, according to a particularly preferred embodiment of the present invention, the Optical Effect Layer (OEL) described herein may further provide an optical effect called "protrusion" caused by the reflective region in the central region surrounded by the annular region. The "protrusions" partially fill the central region, and there is preferably an optical image of the gap between the inner boundary of the toroid and the outer boundary of the protrusions. Optical imaging of such gaps can be achieved by orienting non-spherical magnetic or magnetizable particles in the region between the inner boundary of the annular region and the outer boundary of the protrusion substantially perpendicular to the plane of the OEL.

The protrusions provide an image of a three-dimensional object, such as a hemisphere, present in a central region surrounded by the annular body. The three-dimensional object appears to extend from the OEL surface toward the observer (similar to viewing an upright or inverted bowl, depending on whether the particle is along a negative or positive bend), or from the OEL surface away from the observer. In these cases, the OEL comprises non-spherical magnetic or magnetizable particles in a central region oriented substantially parallel to the OEL plane, thereby providing a reflective region.

An embodiment of such an orientation is shown in fig. 14B. As shown at the top of fig. 14B, the central region (2) is filled with protrusions. In a cross-sectional view along a line (3) extending from the center (4) of the central area (2) surrounded by the annular area providing the optical effect of the ring shaped body (1), the orientation in the annular area is the same as described above for fig. 14A. In the area forming the protrusion in the central region, the orientation of the non-spherical magnetic or magnetizable particles (5) is tangential to the positive or negative curvature of a hypothetical ellipse or circle, preferably with its own center, which lies on a line extending perpendicular to the cross-section and located approximately through the center (14) of the central region surrounded by the annular region (i.e. the perpendicular in fig. 14B) (at the bottom of fig. 14B, only the protrusion from the center to the outer region of the annular region is shown). Further, the diameter of the longest or shortest axis of the hypothetical ellipse or hypothetical circle is preferably about the same as the diameter of the protrusion, such that the longest axis of the non-spherical particle located at the center of the protrusion is oriented substantially parallel to the plane of the OEL and, at the boundary of the protrusion, substantially perpendicular to the plane of the OEL. Again, the speed of change of orientation may be constant (the orientation of the particle is tangential to the circle) or may vary (the orientation of the particle is along an ellipse) in this cross-sectional view.

Thus, the dynamic toroid is filled with center effect picture elements (i.e., "protrusions"), which may be solid circles or hemispheres, for example, in the case where the toroid forms a circle, or may have a triangular base in the case of a triangular loop. In these embodiments, the peripheral shape of the protrusions preferably follows the form of a ring (e.g., when the ring body is a ring, the protrusions are solid circles or hemispheres, and when the ring body is a hollow triangle, the protrusions may be solid triangles or triangular pyramids). According to one embodiment of the invention, at least a part of the peripheral shape of the protrusion is similar to the shape of the ring-shaped body, and preferably the ring-shaped body has the form of a ring and the protrusion has a solid circular or hemispherical shape. Further, the protrusions preferably occupy at least about 20%, more preferably at least about 30%, and most preferably at least about 50% of the area defined by the inner boundary of the annular body.

Preferably, the orientation of the non-spherical particles in the protrusions is the same as the orientation of the non-spherical particles in the annular region. That is, in the cross-sectional view described above and shown in the lower half of fig. 14B, in both the region forming the optical image of the annular body and the projected region, the particle is tangent to the negative curvature of an imaginary ellipse or circle in both the regions, or to the positive curvature of an imaginary ellipse or circle in both the regions, the imaginary ellipse or circle having respective centers located on a perpendicular line extending from about the center of the respective region (the center of the central region and the center of the width of the annular region), as shown in fig. 14B.

Another aspect of the invention described herein relates to a magnetic field generating device for generating an Optical Effect Layer (OEL) as described herein, said device comprising one or more magnets and being configured to receive a coating composition comprising non-spherical magnetic or magnetizable particles and a binder material or being configured to receive a substrate on which the coating composition comprising non-spherical magnetic or magnetizable particles and the binder material are arranged, whereby said orientation of the magnetic or magnetizable particles for forming the Optical Effect Layer (OEL) can be achieved. Since the non-spherical magnetic or magnetizable particles within the coating composition, which is in a fluid state in which the particles may rotate/orient before hardening the coating composition, are self-aligned along the field lines described above, the achieved individual orientation of the particles (i.e. in the case of magnetic particles, the magnetic axis of the particles, in the case of magnetizable particles, the largest dimension) at least on average coincides with the local direction of the magnetic field lines at the respective position of the particles. Alternatively, the magnetic field generating devices described herein may be used to provide a partial OEL, i.e., a security feature that displays one or more portions of a ring shape (e.g., 1/2 circles, 1/4 circles, etc.).

As shown for example in fig. 5, in one embodiment, a generally supporting surface over which a coating composition layer (L) is disposed in a fluid state (before hardening) and comprising a plurality of non-spherical magnetic or magnetizable particles (P)) is placed at a given distance (d) from the poles of a magnet (M) and exposed to the average magnetic field of the device.

Such a support surface of the magnetic field generating means may be part of a magnet that is part of the magnetic field generating means. In this embodiment, the coating composition may be applied directly to the support surface (magnet) on which the orientation of the non-spherical magnetic or magnetizable particles takes place. After or while performing the orientation, the adhesive material is transformed into a second state (e.g. by irradiation in the case of radiation-curable compositions) to form a hard film that is peelable from the support surface of the magnetic field generating means. Accordingly, OELs in the form of films or flakes can be produced in which the oriented/aligned non-spherical particles are fixed in a binder material (in this case, a polymeric material that is typically transparent).

Alternatively, the support surface of the magnetic field generating device of the present invention is formed by a thin plate (typically less than 0.5mm thick, for example 0.1mm thick) made of a non-magnetic material such as a polymeric material, or a metal plate made of a non-magnetic material such as aluminum. Such a plate forming the support surface is arranged above the magnet or magnets of the magnetic field generating means, as shown in fig. 5. Then, a coating composition may be applied onto the board (support surface), followed by performing orientation and hardening of the coating composition, thereby forming an OEL in the same manner as described above.

Of course, in both of the above-described embodiments (in which the support surface is part of the magnet, or is formed by a plate above the magnet), it is also possible to provide a substrate (for example made of paper or any other substrate described below) on which the coating composition is applied, on the support surface, followed by the orientation and hardening. It is noted that the coating composition may be provided on the substrate first, and then the substrate to which the coating composition has been applied may be placed on the support surface, or the coating composition may be applied on the substrate with the substrate already placed on the support surface. In either case, a layer L (i.e., an OEL) may be provided on the substrate, which is not shown in FIG. 5.

If the OEL is disposed on a substrate, the substrate can also serve as a support surface instead of a plate. Specifically, if the substrate is dimensionally stable, it is not necessary to provide, for example, a plate for receiving the substrate, but the substrate may be provided on or above the magnet without interposing a supporting plate therebetween. Thus, in the following description, the term "support surface" (particularly with respect to the orientation of the magnet relative thereto) may in such embodiments refer to the position or plane occupied by the substrate surface without the provision of an intermediate plate.

After the coating composition is provided on a support surface or substrate, which is provided on a separate support surface (plate or magnet) or acts as a support surface, the particles (P) are aligned with the magnetic field lines (F) of the magnetic field generating means.

If the support surface is formed by a plate arranged above the magnets of the magnetic field generating means, the distance (d) between the ends of the poles of the magnets and the surface of the support surface (or substrate if the substrate is to replace the support surface) on the side where the OEL is formed by particle orientation is typically in the range of 0 (i.e. the support surface is the surface of the magnets, without using any substrate) to about 5mm, preferably in the range of about 0.1 to about 5mm, and is selected to generate an appropriate dynamic ring element according to design requirements. The support surface may be a support plate preferably having a thickness equal to the distance (d), which allows a tight mechanical assembly of the magnetic field generating device.

According to the distance (d), dynamic annular bodies with different appearances can be generated by the same magnetic field generating device. Of course, if the coating composition is applied to the substrate before the particle orientation on the support surface is performed, and the OEL is formed on the opposite side of the substrate relative to the support surface, the thickness of the substrate will also affect the distance between the magnet and the coating composition (in particular, if the substrate acts as a support surface). Moreover, the substrate is typically very thin (e.g., about 0.1mm for a paper substrate for a banknote), so that this effect is practically negligible. However, if the influence of the substrate cannot be neglected, for example in case the substrate thickness is larger than 0.2mm, the substrate thickness influencing distance d may be taken into account.

According to one embodiment of the present invention, and as shown in fig. 3, the magnetic field generating means for generating OEL comprises a bar dipole magnet M disposed below the supporting surface formed by the plate or the substrate serving as the supporting surface and having its own north-south axis perpendicular to the supporting surface. The device further includes a pole piece Y disposed below the bar dipole magnet and in contact with one pole of the magnet. The pole pieces indicate structures composed of materials having high magnetic permeability, preferably about 2 to about 1,000,000 nA^-2(newtons per square ampere), more preferably from about 5 to about 50,000 na^-2And yet more preferably from about 10 to about 10,000N · a^-2Magnetic permeability therebetween. The pole pieces serve to guide the magnetic field generated by the magnet, as can also be taken from fig. 5. Preferably, the pole pieces described herein comprise or consist of an iron yoke (Y).

According to another embodiment of the present invention, and as shown in fig. 4, the magnetic field generating means for generating an OEL comprises a bar dipole magnet (M) magnetized in an axial direction (i.e. having its own north-south axis perpendicular to the support surface or substrate surface, if no support surface in the form of a plate is used) and arranged below the support surface, and additionally comprises a pole piece (Y), preferably an iron yoke, spaced from the bar dipole magnet and laterally surrounding the bar dipole magnet. It is noted that the pole pieces are only provided laterally in this embodiment, i.e. not above or below the magnets.

Alternatively, and as shown in fig. 5, the magnetic field generating means for generating the OEL comprises a bar dipole magnet magnetized in the axial direction (i.e. having its own north-south axis perpendicular to the support surface or substrate surface, if no support surface in the form of a plate is used) and arranged below the support surface, and in addition comprises a pole piece arranged below the bar dipole magnet and also surrounding the bar dipole magnet from the side. In this embodiment, the pole piece is also located below the magnet and in contact with the pole piece. Thus, the device of fig. 5 combines the pole pieces of fig. 3 and 4.

Fig. 5 shows a cross section of such a magnetic field generating device comprising a bar dipole magnet (M) magnetized in the axial direction (i.e. having its own north-south axis perpendicular to the support surface) and located below the support surface, and a pole piece (Y) consisting of a circular U-shaped iron yoke. The magnetic field lines (F) are bent downward on each side of the north-south axis of the bar dipole magnet (M) to form arc-shaped magnetic field line portions. The device in space and the three-dimensional field of the magnet (M) are rotationally symmetrical with respect to a central vertical axis (z). From the field lines, it can be deduced: if the coating composition comprising the non-spherical magnetic or magnetizable particles is placed directly on the support surface (or on the thin substrate) and the distance d is chosen as in fig. 5, the device shown in fig. 5 will result in an orientation of the non-spherical magnetic or magnetizable particles substantially parallel with respect to the surface of the OEL (i.e. the support surface of the device) in the area within the OEL corresponding to the space between the edge of the magnet and the pole piece. In the region of the OEL corresponding to the space directly above the magnet and the pole piece, the non-spherical magnetic or magnetizable particles will assume a substantially perpendicular orientation with respect to the surface of the OEL. Thus, the arrangement in fig. 5 will result in the formation of a ring-shaped body (ring) surrounding a central area, wherein the central area is not "filled out" and wherein no reflection, or only a few reflections, are seen.

As shown, for example, in fig. 6, according to another embodiment of the present invention, the magnetic field generating means for generating the OEL described herein comprises a dipole magnet located below the support surface, said dipole magnet taking the form of a toroid (a ring in fig. 6A, a triangle in fig. 6B, an n-polygon in fig. 6C, and a pentagon in fig. 6D) having its own north-south axis extending from the central region to the periphery of the toroid when viewed from the top (the side of the support surface). Fig. 6 shows a top view of such a dipole magnet, which is a ring body (hollow body) having its own north-south magnetic axis extending from the ring body to the periphery, or in other words, which is a ring body (hollow body) and magnetized in the axial direction.

According to another embodiment of the present invention, the magnetic field generating means for generating the OEL described herein comprises three or more bar dipole magnets arranged below the support surface (or substrate surface if no support surface in the form of a plate is used), all three or more magnets being arranged in a static manner around the center of symmetry, each of the three or more bar dipole magnets having i) its own north-south axis substantially parallel to the substrate or support surface, ii) its own north-south magnetic axis aligned to extend substantially radially from the center of symmetry, iii) the north-south directions of the three or more magnets all pointing towards or all away from the center of symmetry. Fig. 7 shows a top view of an associated magnetic orienting device according to an embodiment, wherein n magnets (in fig. 7, n-8) are arranged in a plane with their magnetic axes aligned in a radial direction from the midpoint (center of symmetry) of the magnet assembly (i.e., their extended north-south axes are grouped together substantially in the midpoint of the magnet assembly). When used in a device according to the invention, the magnetic axis is then parallel to the support surface. N magnets arranged in this manner may be used to create a ring shape in the form of an n-sided polygon (e.g., a regular octagon in fig. 7).

In the magnetic field generating devices for generating an OEL, which are depicted in a schematic way in fig. 3 to 7, a ring-shaped body is formed by orienting magnetizable or magnetic particles in accordance with a (static) ring-shaped magnetic field generating device in a ring-shaped region of the OEL. In other words, the optical effect of the toroid in the security element is achieved by orienting the particles substantially parallel to the support surface or substrate surface (if a substrate is used) and to the plane of the final OEL according to the field lines of the magnetic field generating means having a permanent (static) magnetic field, wherein the field lines extend parallel to the support surface at the location where the optical image of the toroid is formed. In a cross-section perpendicular to the OEL and extending from the center of the central region, the orientation of the non-spherical magnetic or magnetizable particles is thus substantially parallel to the plane of the OEL in the central part of the "width" of the annular region, and the longest axis of the oriented particles present in the annular region forming the optical image of the annular body is tangent to the assumed negative or positive curvature of the ellipse or circle, such that in this cross-sectional view a less parallel (typically substantially perpendicular) orientation of the particles is obtained at the width boundary of the annular region. Thus, in cross-sectional view, the orientation gradually changes along a line extending from the center of the central region to the outer region of the annular region. The speed of orientation change need not be constant over the width of the annular region forming the optical effect of the annular body in this cross-sectional view (as is the case if the orientation of the non-spherical magnetic or magnetizable particles is tangential to the assumed negative or positive curvature of the circle), but may vary over the width of the region forming the optical effect of the annular body. In the case where the particle orientation variation speed is not constant, the particle orientation follows the negative curvature or the positive curvature of the assumed ellipse.

Thus, in the arrangement shown in fig. 7, the ring shape of the annular region generally corresponds to the ring shape in the form of an arrangement of one or more magnets in the magnetic field generating means. For example, in fig. 6, magnetic field lines connecting north and south poles of the magnet extend in parallel in regions located above and below the ring magnet in the form of a ring. Thus, in these cases, the orientation of the non-spherical magnetic or magnetizable particles in the annular region forming the optical effect of the annular body can be achieved by providing the coating composition in the first state directly only on the support surface or on a substrate provided on the support surface, in these cases the orientation is parallel to the magnetic axis of the magnet of the magnetic field generating means, and no relative movement of the coating composition with respect to the magnet of the magnetic field generating means is required to achieve the desired particle orientation.

However, the desired orientation of non-spherical magnetic or magnetizable particles in the annular region of an OEL cannot be achieved only by a magnetic field generating device having such a static magnetic field. Conversely, movement of one or more magnets of the magnetic field generating device relative to a support surface or substrate surface (e.g., if a support surface in the form of a plate is not used) on which the coating composition is disposed (either directly or on the substrate) in the first state may also be employed. Further, unlike the "static" devices described above, the magnetic field generating device may also be constructed in such a way that: i.e. to achieve particle orientation inside the center surrounded by the annular region resulting in a "highlight" image. Such an apparatus for forming an annular body around or not around the protrusion will be described below.

According to one embodiment of the present invention, the magnetic field generating means for generating the OEL described herein comprises one or more bar dipole magnets positioned below the support surface (or substrate surface if a support surface in the form of a plate is not used). The one or more magnets are arranged to be rotatable about an axis of rotation substantially perpendicular to the support surface, the one or more bar dipole magnets having their own north-south axes substantially parallel to the support surface/substrate surface and having their own north-south axes substantially radial to the axis of rotation. Where the magnetic field generating means comprises two or more magnets, their north-south axes may have the same orientation relative to the axis of rotation (i.e. the north-south directions of all the magnets are directed towards the axis of rotation, as shown in fig. 8, or away from the axis of rotation), or may have different orientations relative to the axis of rotation, as shown in fig. 9. Here, "same" orientation or direction with respect to the rotation axis means that the orientation of the north-south direction of the magnet is symmetrical with respect to the rotation axis.

Alternatively, in order to achieve mechanical balance, two or more bar dipole magnets having similar moments of inertia may be symmetrically disposed (e.g., oppositely disposed) with respect to the rotation axis. For example, as shown in fig. 8, magnets having similar or identical sizes may be used symmetrically with respect to the rotation axis (z). The same magnetization pattern is produced in the oel (l) on the support surface by the magnet rotating about the axis of rotation when the north-south orientation of the second magnet with respect to the axis of rotation (i.e., pointing toward or away from the axis of rotation) is the same as the north-south orientation of the first strip dipole magnet.

If the magnetic field generating means comprise more than one magnet, it is particularly preferred that the magnets have approximately the same size and are arranged at equal distances from the axis of rotation. In this case, since the path of the magnet located below the support surface is almost the same when the magnet is rotated around the rotation axis, the desired orientation of the non-spherical magnetic or magnetizable particles in the annular region of the OEL can be achieved by providing the coating composition in the first state on the support surface of the magnetic field generating device and rotating the magnet around the rotation axis.

Fig. 8 shows an example of such a magnetic field generating device comprising two bar dipole magnets (M) which are rotatable in a plane about a mechanical axis (z). The bar dipole magnet has i) its own north-south axis in a plane, which is typically ii) substantially parallel to the support surface of the magnetic field generating means. In fig. 8, the magnets iii) have their own magnetic axes substantially radial with respect to the axis of rotation (z), wherein iv) the north-south directions are pointing in the same direction with respect to the axis of rotation (i.e. the north-south directions are symmetrical with respect to the axis of rotation, all pointing inwards towards the axis of rotation). Further, v) the magnets have about the same size and are arranged substantially symmetrically at positions about equidistant from the axis of rotation. The average magnetic field generated by the bar dipole magnet is rotationally symmetric with respect to said axis (z). As can be seen from the field lines in fig. 8, the device results in the formation of a ring-shaped element, which does not comprise protrusions, by forming a suitable magnetic field in a time-dependent manner when the magnet rotates about the axis of rotation, which element takes the form of a ring.

It is worth noting that the same orientation of the particles in the annular region would be obtained with the north-south direction of each of the two magnets in fig. 8 inverted (so that the north-south direction of each magnet points away from the axis of rotation). This is therefore an alternative embodiment of the magnetic field generating device of the present invention.

If the magnetic field generating means are constructed such that the distance of the magnet or magnets from the axis of rotation is fixed (for example, by providing a simple bar between the magnet and the axis forming the axis of rotation), and, in the case of two or more magnets, the magnets are of about the same size and are arranged at a position equidistant from the axis of rotation, it is necessary for the annular body to take the form of a ring (since the path of the magnet below the support surface of the magnetic field generating means follows a circle, the shape of the annular region is a circle). However, if it is desired to form an annular body other than a ring (e.g., oval, rectangular with rounded corners, skeletal or similar shape), this can be accomplished by constructing the device such that the path of the magnets under the support surface resembles the desired shape of the corresponding annular region. In such a case, it may be desirable to construct a device such that the distance of the magnet from the axis of rotation is altered when rotating about the axis of rotation (e.g., by providing a camshaft structure about which rotation will occur).

The above-described magnetic field generating means comprising a magnet arranged rotatable around an axis of rotation are designed to generate the optical effect of a ring-shaped body by orienting magnetic or magnetizable particles in a ring-shaped region of the OEL, wherein at least a part of the particles are oriented substantially parallel to the plane of the OEL, thereby providing reflection in a direction perpendicular to the plane of the OEL when illuminated from this direction (or under diffuse light), otherwise tangent to a supposed negative or positive curvature of a circle or ellipse, as described above. These devices provide an annular region surrounding a central region which may or may not contain non-spherical magnetic or magnetizable particles. If particles are contained in the central region, as described above, these particles are typically oriented perpendicular to the plane of the OEL (so that no or only little reflection of light occurs in this direction when illuminated from a direction perpendicular to the plane of the OEL), so that no "protrusion" is formed.

However, in a preferred aspect, the present invention also relates to a magnetic field generating device for generating an OEL further comprising a "protrusion" in a central area surrounded by an annular area. Such a device comprises a support surface for receiving a coating composition (directly or on a substrate) in a first state, the coating composition comprising non-spherical magnetic or magnetizable particles and a binder material, thereby creating the optical effect layer. The magnetic field generating means for generating the OEL described herein, which further comprises protrusions, comprises more than one magnet (e.g., 2, 3, 4 or more magnets) positioned below the support surface. They are rotatable about an axis of rotation substantially perpendicular to the support surface.

According to one such embodiment of the invention, the magnetic field generating means for generating an OEL further comprising protrusions comprises one or more pairs of strip-shaped dipole magnets. Magnets forming one or more pairs of magnets are disposed below the support surface and are rotatable about an axis of rotation substantially perpendicular to the support surface. Each of the one or more pairs of magnets is formed by an assembly of two bar dipole magnets disposed away from the axis of rotation. The bar dipole magnets in a given magnet pair have their own north-south axes that are radial with respect to the axis of rotation, and further have their own north-south directions that are asymmetric with respect to the axis of rotation, or point in different directions with respect to the axis of rotation (one pointing towards the axis of rotation and one pointing away from the axis of rotation). Preferably, the magnets forming the pair of magnets are disposed at positions approximately equal in distance from the rotation axis. As shown in fig. 9, the one or more pairs of strip dipole magnets (M) of the magnetic field generating device have i) their own magnetic axes substantially parallel to the support surface (in fig. 9, formed by a plate), ii) their own magnetic axes substantially radial with respect to the rotation axis (z), and iii) their own north-south directions in different directions with respect to the rotation axis (toward the rotation axis in the right-hand magnet of fig. 9, and away from the rotation axis in the left-hand magnet of fig. 9).

According to another embodiment of the present invention, the magnetic field generating means for generating an OEL further comprising protrusions comprises one or more pairs of such bar dipole magnets: they are disposed below a support surface formed by a plate or by a substrate serving as a support surface (i.e., a substitute support surface), and are rotatable about a rotation axis substantially perpendicular to the support surface. Each of the one or more pairs of magnets is formed by an assembly of two bar dipole magnets disposed away from the axis of rotation, preferably at approximately equal distances from the axis of rotation. The dipole magnets are preferably arranged directly opposite each other with respect to the rotation axis as a center. Further, as shown in fig. 10, unlike the above-described embodiment for forming an optical effect not including the protruded toroid, in this embodiment of the apparatus for forming a toroid surrounding the protrusion, the magnetic axis of the bar dipole magnet is not substantially parallel to the support surface or the substrate, but is substantially perpendicular to the support surface or the substrate.

A preferred embodiment of such a device is shown in fig. 10. As shown in fig. 10, the one or more pairs of strip dipole magnets (M) of the magnetic field generating means have i) their own north-south axis substantially perpendicular to the support surface or substrate, ii) their own north-south axis substantially parallel to the axis of rotation (z), and iii) opposite magnetic north-south directions (one upward and one downward in fig. 10).

As shown in fig. 11, another embodiment of the magnetic field generating device for generating an OEL further including a protrusion according to the present invention includes an assembly of three bar dipole magnets which are disposed below a supporting surface formed of a plate or a substrate serving as the supporting surface and which are rotatable about a rotation axis substantially perpendicular to the supporting surface. The magnetic axis of each of the three magnets is substantially parallel to the support surface. Two of the three bar dipole magnets are arranged on opposite sides with respect to the rotation axis, preferably at approximately equal distances from the rotation axis, have their own north-south axes substantially radial with respect to the rotation axis, and have the same north-south orientation (i.e. opposite or asymmetrical with respect to the rotation axis, one directed towards the rotation axis and one directed away from the rotation axis). The third bar dipole magnet is disposed between the other two magnets disposed away from the axis of rotation, and preferably the third magnet is disposed on the axis of rotation (i.e., the axis of rotation extends through the third magnet, preferably through its center). Each of the three magnets has its own north-south axis substantially parallel to the support surface, ii) two of the magnets spaced from the axis of rotation have their own north-south axis substantially radial to the axis of rotation, iii) two of the bar dipole magnets spaced from the axis of rotation have an asymmetric north-south direction (i.e., opposite to the axis of rotation), and iv) a third of the bar dipole magnets located on the axis of rotation has a north-south direction opposite to the north-south direction of the spaced two bar dipole magnets (see fig. 11).

As shown in fig. 11, three bar dipole magnets have their own magnetic axes substantially parallel to the support surface, the three bar dipole magnets have their own magnetic axes substantially radial to the rotation axis and substantially parallel to the support surface, two bar dipole magnets disposed away from the rotation axis have magnetic north-south directions (i.e., asymmetric north-south directions) opposite to the rotation axis, and a third bar dipole magnet is disposed on the rotation axis and has its own north-south direction pointing opposite to the north-south direction of the bar dipole magnet whose north-south direction points toward the rotation axis.

Similar to the static magnetic field generating devices described herein, the rotatable magnetic field generating devices described herein may further include one or more additional pole pieces.

Those skilled in the art will appreciate that the speed and number of revolutions per minute of the rotatable magnetic field generating means described herein may be adjusted in order to orient the non-spherical magnetic or magnetizable particles described herein, i.e. to make them tangent to the negative or positive curvature of an assumed circle.

The magnets of the magnetic field generating devices described herein may comprise or consist of any permanent (hard) magnetic material, for example, alnico, hexaferrite of barium or strontium, cobalt alloys, or rare earth iron alloys such as neodymium-iron-boron alloys. But particularly preferred are readily processable permanent magnetic composites comprising a permanent magnetic filler in a plastic or rubber type matrix, such as strontium hexaferrite (SrFe)₁₂O₁₉) Or neodymium-iron-boron (Nd)₂Fe₁₄B) And (3) powder.

Also described herein is a rotary printing assembly comprising magnetic field generating means for generating an OEL as described herein, said magnetic field generating means being mounted on and/or inserted on a printing cylinder as part of a rotary printing press. In this case, the magnetic field generating means are designed and adapted accordingly to fit the cylindrical surface of the rotary unit, so as to ensure a smooth contact with the surface to be imprinted.

Also described herein is a process for producing an OEL described herein, the process comprising the steps of:

a) applying a coating composition in a first (fluid) state comprising a binder material as described herein and a plurality of non-spherical magnetic or magnetizable particles on a support surface or preferably a substrate arranged on or acting as a support surface,

b) exposing the coating composition in the first state to a magnetic field of a magnetic field generating device to orient non-spherical magnetic or magnetizable particles in the substrate composition; and

c) the coating composition is hardened to a second state to fix the magnetic or magnetizable non-spherical particles in the position and orientation they adopt.

The applying step a) is preferably a printing process selected from the group consisting of copper gravure, screen printing, gravure, flexographic printing and roller coating, more preferably a printing process selected from the group consisting of screen printing, gravure printing and flexographic printing. These processes are well known to those skilled in the art and are described, for example, in "Printing Technology" by j.m. adams and p.a. dolin, fifth edition, published by delmr Thomson Learning.

Although the coating composition described herein comprising a plurality of non-spherical magnetic or magnetizable particles is still sufficiently wet or soft that the non-spherical magnetic or magnetizable particles therein can be moved and rotated (i.e., when the coating composition is in the first state), the coating composition will be exposed to a magnetic field to achieve particle orientation. The step of magnetically orienting the non-spherical magnetic or magnetizable particles comprises the steps of: when the applied coating is in a "wet" state (i.e. still fluid and less viscous, that is, in a first state), it is exposed to a determined magnetic field (which is generated above or over the support surface of the magnetic field generating means described herein) so as to orient the non-spherical magnetic or magnetizable particles along the field lines of the magnetic field so as to form a ring-shaped orientation mode. In this step, the coating composition is brought into sufficiently close proximity to or into contact with the support surface of the magnetic field generating means.

When the coating composition is brought close to the support surface of the magnetic field generating device and the OEL is to be formed on the side of the substrate, the side of the substrate with the coating composition may face the side of the device on which the magnet or magnets are arranged, or the side of the substrate without the coating composition may face the side on which the magnet is arranged. In the case where the coating composition is applied to only one surface of the substrate, or to both sides simultaneously, but the side to which the coating composition is applied is oriented to face the side on which the magnet is disposed, it is preferred not to establish direct contact with the support surface if the support surface is part of the magnet or is formed by a plate (the substrate is only brought sufficiently close to, but not in contact with, the magnet or plate of the device forming the support surface).

It is noted that the coating composition may actually be brought into contact with the support surface of the magnetic field generating means. Alternatively, a fine air gap may be provided, or an intermediate isolation layer. In a further and preferred alternative embodiment, a method may be performed such that the substrate surface without the coating composition may be in direct contact with one or more magnets (i.e., the magnets form a support surface).

If desired, an underlayer may be applied to the substrate before step a) is performed. This may improve the quality of the magnetic transfer particle-oriented image or enhance adhesion. An example of such a bottom layer can be found in WO 2010/058026 a 2.

The step of exposing the coating composition comprising the binder material and the plurality of non-spherical magnetic or magnetizable particles to the magnetic field (step b)) may be performed simultaneously with step a) or may be performed after step a). That is, steps a) and b) may be performed simultaneously or may be performed sequentially.

The process for producing the OEL described herein includes a step of hardening the coating composition (step c)), which may be performed concomitantly with or after step (b), in order to fix the magnetic or magnetizable non-spherical particles in the position and orientation they adopt, thereby transforming the coating composition into the second state. By this fixing, a solid coating or layer is formed. The term "hardening" refers to the following process: including drying or setting, reacting, curing, crosslinking, or polymerizing binder components of an applied coating composition that includes a selectively added crosslinking agent, a selectively added polymerization initiator, and selectively added further additives to form a substantially solid material that strongly adheres to the substrate surface. As mentioned above, the hardening step (step c)) may be performed using different devices or processes, depending on the binder material comprised in the coating composition comprising the plurality of non-spherical magnetic or magnetizable particles.

The hardening step may generally be any step that increases the viscosity of the coating composition so as to form a substantially solidified material that adheres to the support surface. The hardening step may involve a physical process based on evaporation of volatile components (e.g., solvent and/or water evaporation (i.e., physical drying)). Here, hot air, infrared rays, or a combination of hot air and infrared rays may be used. Alternatively, the hardening process may comprise a chemical reaction, such as a curing, polymerization or crosslinking process performed on a binder and optionally an initiator compound and/or optionally a crosslinking compound included in the coating composition. Such chemical reactions may be initiated by heating or IR irradiation as described above for the physical hardening process, but may preferably include initiating chemical reactions by radiation mechanisms including, but not limited to, ultraviolet-visible radiation curing (hereinafter UV-Vis curing) and electron beam radiation curing (E-beam curing); oxidative polymerization (an oxidized network, typically induced by the combined action of oxygen and one or more catalysts (e.g., cobalt-and manganese-containing catalysts)); a crosslinking reaction, or any combination thereof.

Radiation curing is a particularly preferred cure, with UV-Vis photoradiation curing even more preferred, as these techniques advantageously enable a very fast curing process, thus significantly reducing the manufacturing time of any article comprising an OEL as described herein. Moreover, radiation curing has the advantage that: after the coating composition is exposed to the curing radiation, the viscosity of the coating composition is allowed to increase momentarily, thereby minimizing any further movement of the particles. Thus, any loss of information after the magnetic orientation step is substantially avoided. Radiation curing by photopolymerization under the influence of actinic light having a wavelength component in the UV or blue part of the electromagnetic spectrum (typically 300nm to 500 nm; more preferably 380nm to 420 nm; UV-visible curing) is particularly preferred. The apparatus for UV-visible curing may include a high power Light Emitting Diode (LED) lamp, or an arc discharge lamp (e.g., a Medium Pressure Mercury Arc (MPMA) or metal vapor arc lamp) as the source of actinic radiation. The hardening step (step c)) may be performed simultaneously with step b) or may be performed after step b). However, the time from the end of step b) to the start of step c) is preferably relatively short to avoid any orientation failure or loss of information. In general, the time between the end of step b) and the beginning of step c) is less than 1 minute, preferably less than 20 seconds, further preferably less than 5 seconds, even more preferably less than 1 second. It is particularly preferred that there is substantially no time difference between the end of the orientation step b) and the beginning of the hardening step c), i.e. that step c) is performed immediately following step b) or already started while step b) is still in progress.

As mentioned above, step (a) (applied on the support surface, or preferably on the substrate surface provided on or acting as the support surface) may be performed simultaneously with step b) (effecting particle orientation by means of a magnetic field), or may precede step b), and further step c) (hardening) may be performed simultaneously with step b) (effecting particle orientation by means of a magnetic field), or may be performed after step b). Although possible for a particular type of device, in general the three steps a), b) and c) are not performed simultaneously. In addition, steps a) and b), and steps b) and c) may be performed in the following manner: they are performed partially simultaneously (i.e. the times at which each of these steps is performed partially overlap, so as to start the hardening step c), for example at the end of the orientation step b)).

To increase stain durability or chemical resistance and cleanliness, thereby increasing the circulation time of the security document, or to modify the aesthetic appearance (e.g. gloss) of the security document, one or more protective layers may be applied on top of the OEL. When present, the one or more protective layers are typically made of a protective lacquer. These protective lacquers may be transparent or may be slightly tinted or colored and may have greater or lesser gloss. The protective lacquer may be a radiation curable component, a thermal drying component, or any combination thereof. Preferably, the one or more protective layers are radiation curable components, more preferably UV-Vis curable components. The protective layer may be applied after the OEL is formed by step c).

The above process allows to obtain a substrate with an OEL that is capable of providing an optical appearance of a closed ring-shaped body surrounding a central area, wherein the non-spherical magnetic or magnetizable particles present in the ring area forming the closed ring-shaped body follow a negative curvature (see fig. 1B) or a positive curvature (see fig. 1C) of an imaginary ellipse or circle, depending on whether the magnetic field of the magnetic field generating means is applied to the set of coating layers comprising non-spherical magnetic or magnetizable particles from below or above. This orientation can also be expressed as the orientation of the longest axis of the non-spherical magnetic or magnetizable particles along the surface of a hypothetical semi-toroidal body lying in the plane of the optical effect layer, as shown in fig. 1. Further, depending on the type of device used, the central region surrounded by the annular body may comprise so-called "protrusions", i.e. regions comprising magnetic or magnetizable particles having an orientation substantially parallel to the substrate surface. In these embodiments, the orientation varies towards the surrounding toroid, when viewed in cross-section extending from the center of the central region to a region outside the closed toroid, along a negative or positive bend. Between the annular body and the "projection", there is preferably a region: wherein the particles are oriented substantially perpendicular to the substrate surface so as to show no or only a small reflection of light.

This is particularly useful in applications with the following features: i.e. where the OEL is formed by an ink (e.g. a security ink) or some other coating material and is permanently provided on a substrate such as a security document, for example by means of the above-mentioned printing.

In the above process, when an OEL is disposed on a substrate, the OEL can be disposed directly on the substrate to be permanently retained thereon (e.g., for banknote applications). However, in alternative embodiments of the present invention, the OEL may also be provided on a temporary substrate for production purposes, from which the OEL is then removed. This may for example facilitate the production of OEL, especially when the binder material is still in its fluid state. Thereafter, after hardening the coating composition for producing the OEL, the temporary substrate may be removed from the OEL. Of course, in these cases, the coating composition must take the form: i.e. to maintain physical integrity after the hardening step, for example in the case of forming a plastic-like or sheet-like material by hardening. Thus, a film-like transparent and/or translucent material may be provided which is constituted by such an OEL (i.e. substantially by oriented magnetic or magnetizable particles having anisotropic reflectivity, a hardened adhesive component for fixing the orientation of the particles and forming a film-like material such as a plastic film, and further optional components).

Alternatively, in another embodiment, the substrate may comprise an adhesion layer on the opposite side of the side on which the OEL is arranged, or an adhesion layer may be arranged on the OEL on the same side of the OEL, preferably after completion of the hardening step. In these examples, an adhesive label comprising an adhesive layer and an OEL is formed. Such labels can be attached to all types of documents or other goods or items without the need for a printing process or other process involving machinery and significant effort.

According to one embodiment, the OEC is manufactured in the form of a transfer foil which can be applied to a document or a commercial good by a separate transfer step. To this end, a release coating is provided on a substrate, and an OEL is then produced on the release coating in accordance with the description herein. One or more adhesion layers may be applied on the OEL thus produced.

The substrate described herein is preferably selected from the group consisting of paper or other fibrous materials such as cellulose, paper-containing materials, glass, ceramics, plastics and polymers, glass, composites, and mixtures or combinations thereof. Typical paper, paper-like or other fibrous materials are made from a variety of fibers including, but not limited to, abaca, cotton, flax, wood pulp and mixtures thereof. It is well known to those skilled in the art that cotton and cotton/flax blends are preferably suitable for use in banknotes, whereas wood pulp is commonly used for non-banknote security documents. Typical examples of plastics and polymers include polyolefins such as Polyethylene (PE) and polypropylene (PP), polyamides, polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polyvinyl chloride (PVC). Spunbonded fabric olefin fibres may also be used as a substrate, for example under the trade markA fiber product for sale. Typical examples of composite materials include, but are not limited to, multilayer structures or laminates comprising: paper and the at least one plastic or polymeric material mentioned above, and the plastic and/or polymeric fibers mentioned above integrated in the paper-like or fibrous material. Of course, the substrate may comprise further additives well known to the person skilled in the art, such as sizing agents, brighteners, processing aids, reinforcing agents or wet-strength agents, etc.

According to one embodiment of the present invention, an optical effect coated substrate (OEC) comprises more than one OEL on the substrate described herein, e.g., it may comprise two, three, etc. OELs. Here, one, two or more OELs may be formed using a single magnetic field generating device, using several identical magnetic field generating devices, or may be formed using several different magnetic field generating devices. Fig. 12 shows a cross-section of an exemplary OEC having dispersed therein a plurality of non-spherical magnetic or magnetizable particles (P) as described herein, which are disposed on a substrate. In cross-sectional view, the OEC described herein includes two (A and B) OELs disposed on a substrate. In a third dimension perpendicular to the cross-section shown in fig. 12, OELs a and B may or may not be connected to each other.

The OEC may include a first OEL and a second OEL, where both OELs are located on the same side of the substrate, or one of the OELs is located on one side of the substrate and the other OEL is located on the other side of the substrate. The first and second OELs may or may not be adjacent to each other if disposed on the same side of the substrate. Additionally or alternatively, one of the OELs may partially or completely overlap another OEL.

If more than one magnetic field generating means is used to generate the plurality of OELs, the magnetic field generating means for orienting the plurality of non-spherical magnetic or magnetizable particles to generate one OEL and the magnetic field generating means for generating another OEL may be positioned i) on the same side of the substrate so as to generate two OELs exhibiting a negative curvature (see fig. 1B) or a positive curvature (see fig. 1C), or ii) on opposite sides of the substrate so as to generate one OEL exhibiting a negative curvature and another OEL exhibiting a positive curvature. The magnetic orientation of the non-spherical magnetic or magnetizable particles used to generate the first OEL and the magnetic orientation of the non-spherical magnetic or magnetizable particles used to generate the second OEL may be performed simultaneously or sequentially, which may or may not include intermediate or partial curing of the binder material.

To further increase the security level of security documents, and their resistance to counterfeiting and illegal copying, the substrate may include printed, coated, or laser marked or laser punched indicia, watermarks, security threads, fibers, painted panels, luminescent compounds, window threads, foils, labels, and combinations thereof. Also to further increase the security level of the security documents, and their resistance to counterfeiting and illegal copying, the substrate may include one or more marking substances or taggants and/or machine readable substances (e.g., luminescent substances, UV/visible/IR absorbing substances, magnetic substances, and combinations thereof).

The OELs described herein can be used for decorative purposes, as well as for securing and authenticating security documents.

The present invention also encompasses articles and ornaments comprising OELs as described herein. The articles and decorations may include more than one optical effect layer as described herein. Typical examples of the articles and decorations include, but are not limited to, luxury goods, cosmetic sets, automobile parts, electronic/electric appliances, furniture, and the like.

An important aspect of the present invention relates to a security document comprising an OEL as described herein. The security document may comprise more than one optical effect layer as described herein. Security documents include, but are not limited to, documents of value and merchandise of value. Typical examples of value documents include, but are not limited to, banknotes, contracts, tickets, checks, payment certificates, printed tax stamps and tax labels, agreements and the like, identity documents such as passports, identity cards, visas, drivers' licenses, bank cards, credit cards, transaction cards, access cards or cards, admission tickets, public transportation tickets or certificates and the like. The term "commodity of value" refers to packaging material, in particular packaging material for the pharmaceutical, cosmetic, electrical or food industry, which should be protected against counterfeiting and/or illegal copying to ensure that the contents of the package, such as genuine drugs, are authentic. Examples of such packaging materials include, but are not limited to, labels such as certified brand labels, tamper evident labels, and sealing strips.

Preferably, the security document described herein is selected from the group consisting of banknotes, identity documents, authorization documents, drivers licenses, credit cards, access cards, transportation certificates, bank checks, warranty product labels, and the like. Alternatively, the OEL may be produced on a secondary substrate such as a security thread, security strip, foil, label, window or label, which is then transferred to the security document in a separate step.

Many modifications to the specific embodiments described above may be devised by those skilled in the art without departing from the spirit of the present invention. Such modifications are also encompassed by the present invention.

Further, all documents referred to throughout this specification are fully incorporated by reference as if fully set forth herein.

The invention will now be described by way of examples, which are not intended to limit the scope of the invention in any way.

Examples of the invention

Example 1

The magnetic field generating device according to fig. 5 was used to orient non-spherical optically variable magnetic pigments in a printed layer of UV-curing screen printing ink on black paper as a substrate.

The ink has the following formula:

epoxy acrylate oligomers	40％
		Trimethylolpropane triacrylate monomer	10％
Tripropylene glycol diacrylate monomer	10％
		Genorad 16(Rahn)	1％
Oxygen phase silica 200(Evonik)	1％

Irgacure 500(BASF)	6％
		Genocure EPD(Rahn)	2％
Non-spherical optically variable magnetic pigment (7 layers) ()	20％
		Propylene glycol methyl ether acetate	10％

(xi) green-blue optically variable magnetic pigment chips having a diameter d50 of about 15 μm and a thickness of about 1 μm, provided by JDS-Uniphase, Santa Roche, Calif.

The magnetic field generating device comprises a ground plate made of soft magnet, on which an axially magnetized NdFeB permanent magnet column with a diameter of 5mm and a thickness of 8mm is arranged, wherein the south pole is positioned on the soft magnet ground plate. A rotationally symmetrical U-shaped soft-magnetic yoke with an outer diameter of 16mm, an inner diameter of 12mm and a depth of 8mm is arranged on the north pole of the axially magnetized NdFeB permanent magnet column.

A paper substrate with an applied layer of UV-curing screen-printing ink was placed at a distance of 1mm from the poles and yoke of the ring permanent magnet. After performing the applying step, the magnetic orientation pattern of the optically variable pigments obtained in this way is then fixed by performing UV curing on the printed layer comprising the particles.

The resulting magnetically oriented image is given in fig. 2A.

Example 2

The magnetic field generating device according to fig. 9 was used to orient optically variable magnetic pigments in a printed layer of UV-curing screen printing ink with the formulation of example 1 on black paper as substrate.

The magnetic field generating device comprises two NdFeB magnets of 10mm size, 10mm width and 10mm height, which are 15mm apart from each other, having their own magnetization direction along the 10mm width. The magnets are radially aligned with respect to the axis of rotation so that their magnetization directions lie on the same line. The magnets are mounted on a plate that rotates at a speed of 300rpm (revolutions per minute). The paper substrate with the UV-cured screen-printed ink layer was placed 0.5mm from the magnet surface. After performing the applying step, the magnetic orientation pattern of the optically variable pigments obtained in this way is then fixed by performing UV curing on the printed layer comprising the particles.

The resulting magnetically oriented image is given in fig. 2B by three different views, which show the viewing angle dependent image variation.

Claims

wherein in at least one annular region of the OEL, at least a portion of the plurality of non-spherical magnetic or magnetizable particles are oriented: (ii) having its longest axis substantially parallel to the plane of the OEL, and wherein, in a cross-section perpendicular to the OEL and extending from the center of the central region, the longest axis of the oriented particles present in the annular region is tangent to the assumed negative or positive curvature of the ellipse or circle;

wherein the central region surrounded by the annular region comprises a plurality of non-spherical magnetic or magnetizable particles, wherein a portion of the plurality of non-spherical magnetic or magnetizable particles located within the central region is oriented: its longest axis is substantially parallel to the plane of the OEL, thereby forming a prominent optical effect within the central region of a ring-shaped body indicative of an optical effect obtained by: the non-spherical magnetic or magnetizable particles are oriented in the annular region to provide an optical image of the three-dimensional object to a viewer.

2. The Optical Effect Layer (OEL) of claim 1, wherein the OEL comprises an outer region located outside a closed annular region, and the outer region surrounding the annular region comprises a plurality of non-spherical magnetic or magnetizable particles, wherein a portion of the plurality of non-spherical magnetic or magnetizable particles located within the outer region is oriented: with its longest axis substantially perpendicular to the plane of the OEL, or randomly oriented.

3. The Optical Effect Layer (OEL) of claim 1, wherein at least a portion of the projected peripheral shape is similar to a shape of the annular body.

4. The Optical Effect Layer (OEL) of claim 3, wherein the annular bodies have an annular form and the protrusions have a solid circular or hemispherical shape.

5. The Optical Effect Layer (OEL) according to any one of the preceding claims, wherein at least a portion of the plurality of non-spherical magnetic or magnetizable particles consists of non-spherical optically variable magnetic or magnetizable pigments.

6. The Optical Effect Layer (OEL) of claim 5, wherein the non-spherical optically variable magnetic or magnetizable pigment is selected from the group consisting of magnetic thin film interference pigments, magnetic cholesteric liquid crystal pigments, and mixtures thereof.

7. A magnetic field generating device for forming an optical effect layer, the device being configured to receive a coating composition comprising a plurality of non-spherical magnetic or magnetizable particles and a binder material on a support surface or on a substrate, the device comprising one or more magnets located below the support surface, the magnets being arranged to be rotatable around a rotational axis substantially perpendicular to the support surface, the device being configured to orient at least a part of the plurality of non-spherical magnetic or magnetizable particles parallel to the plane of the optical effect layer in at least one annular region of the optical effect layer, wherein, in a cross-section perpendicular to the OEL and extending from the centre of a central region, the longest axis of the oriented particles present in the annular region is tangent to a negatively or positively curved portion of an assumed ellipse or circle, and to orient a part of the plurality of non-spherical magnetic or magnetizable particles in the central region, such that its longest axis extends substantially parallel to the plane of the OEL, thereby forming a prominent optical effect in the central region of a ring-shaped body indicative of an optical effect obtained by: the non-spherical magnetic or magnetizable particles are oriented in the annular region to provide an optical image of the three-dimensional object to a viewer.

8. The magnetic field generating apparatus according to claim 7, wherein

a1) a plate to which the coating composition can be applied directly,

or

9. The magnetic field generating device according to claim 7 or 8, the device comprising a support surface or being configured to receive a substrate in place of the support surface, wherein, upon rotation of the magnet about the rotation axis, time-dependent magnetic field lines substantially parallel to the support surface are generated in a region defining a ring shape and being located within a central region, the central region being surrounded by and spaced from the ring shape, the device comprising

a) One or more pairs of strip dipole magnets positioned below the support surface and rotatable about an axis of rotation substantially perpendicular to the support surface, the magnets having their own north-south axes substantially parallel to the support surface and having their own north-south magnetic axes substantially radial to the axis of rotation and the same magnetic north-south directions,

b) one or more pairs of bar dipole magnets positioned below the support surface and rotatable about an axis of rotation substantially perpendicular to the support surface, the magnets having i) their own north-south axes substantially perpendicular to the support surface, ii) their own north-south axes substantially parallel to the axis of rotation, and iii) opposite magnetic north-south directions, the one or more pairs of bar dipole magnets each formed by an assembly of two bar dipole magnets disposed substantially symmetrically about the axis of rotation; or

c) Three bar dipole magnets positioned below the support surface and arranged to be rotatable about a rotation axis substantially perpendicular to the support surface, wherein two of the three bar dipole magnets are located at opposite sides with respect to the rotation axis, the third bar dipole magnet is located on the rotation axis, and wherein i) each of said magnets has its own north-south axis substantially parallel to said support surface, ii) said two magnets spaced from said axis of rotation have their own north-south axes substantially radial with respect to said axis of rotation, iii) said two bar dipole magnets spaced from said axis of rotation have the same north-south orientation asymmetrical with respect to said axis of rotation, and iv) the third bar dipole magnet located on the rotation axis has a north-south direction opposite to the north-south direction of the two spaced bar dipole magnets.

10. The magnetic field generating device according to claim 9, wherein the annular region provides an optical image of an annular body, the annular body taking the form of a ring, and the central region surrounded by the annular region provides an optical image of a solid circle or hemisphere.

11. A printing assembly comprising a magnetic field generating device as claimed in any one of claims 7 to 10.

12. Use of a magnetic field generating device as defined in any of claims 7 to 10 for the generation of an OEL as defined in any of claims 1 to 6.

13. A process for producing an Optical Effect Layer (OEL), comprising the steps of:

b) exposing said coating composition in a first state to a magnetic field of a magnetic field generating means to orient at least a portion of the non-spherical magnetic or magnetizable particles in at least one annular region around a central region such that, in a cross-section perpendicular to and extending from the center of said central region, the longest axis of the particles present in said annular region is tangent to the negative or positive curvature of an assumed circle, and orienting a portion of said plurality of non-spherical magnetic or magnetizable particles in the central region such that their longest axis extends substantially parallel to the plane of the OEL, thereby forming a prominent optical effect in the central region of an annular body indicative of an optical effect obtained by: orienting the non-spherical magnetic or magnetizable particles in the annular region, thereby providing an optical image of the three-dimensional object to a viewer, an

14. The process according to claim 13, wherein the magnetic field generating device is a magnetic field generating device as defined in any one of claims 7-10.

15. The process according to claim 13 or 14, wherein the hardening step c) is done by UV-Vis light radiation curing.

16. The optical effect layer according to any one of claims 1-4, 6, obtained by the process of claim 13 or claim 14.

17. An optical effect coated substrate (OEC) comprising one or more optical effect layers according to any one of claims 1-6 or 16 thereon.

18. A security document comprising an optical effect layer as claimed in any one of claims 1 to 6 or 16.

19. A security document according to claim 18, which is a banknote or an identity document.

20. Use of an optical effect layer as described in any one of claims 1 to 6 or 16 or an optical effect coated substrate as described in claim 17 for protecting security documents against forgery or tampering, or for decorative applications.

21. The optical effect layer according to claim 5, obtained by the process of claim 13 or claim 14.