HK1220663B

HK1220663B - Permanent magnet assemblies for generating concave field lines and process for creating optical effect coating therewith (inverse rolling bar)

Info

Publication number: HK1220663B
Application number: HK16108864.8A
Authority: HK
Inventors: Evgeny LOGINOV; Mathieu Schmid; Claude Alain Despland; Pierre Degott
Original assignee: Sicpa Holding Sa
Priority date: 2013-06-14
Filing date: 2014-06-13
Publication date: 2018-05-25

Description

Permanent magnet assembly for generating a concave field line and method for creating an optical effect coating therewith (counter-rolling bar)

Technical Field

The present invention relates to the field of protection of valuable documents and valuable commercial goods against counterfeiting and illegal reproduction. In particular, the present invention relates to a device and a method for producing an Optical Effect Layer (OEL) displaying a viewing angle dependent optical effect, an article (items) bearing said OEL and the use of said optical effect layer as an anti-counterfeiting means on a document.

Background

It is known in the art to use inks, compositions or layers comprising oriented magnetic or magnetizable particles or pigment particles, in particular also magneto-optically variable pigment particles, for the production of security elements, for example in the field of security documents. Coatings or layers comprising oriented magnetic or magnetizable pigment particles are for example described 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 magnetically color-shifting pigment particles, in particular leading to attractive optical effects for security document protection, have been disclosed in WO 2002/090002 a2 and WO 2005/002866 a 1.

For example, security features for security documents can be generally classified into "hidden" security features on the one hand and "overt" security features on the other hand. The protection provided by hidden security features relies on the concept that these features are difficult to detect, typically requiring specialized equipment and knowledge for detection, while "overt" security features rely on the concept of being easily detectable with unaided human senses, e.g. the features are visible and/or detectable via tactile senses, while still being difficult to generate and/or reproduce. However, the effectiveness of overt security features depends to a large extent on their ease of identification as security features, since most users, especially those who do not have prior knowledge of the security features with their security documents or items, will then actually perform security checks based only on the security features if they have actual knowledge of their presence and nature.

Particularly significant optical effects can be achieved if the security feature changes its appearance in the field of view to a change in viewing conditions, such as viewing angle. This effect can be obtained, for example, by Dynamic Appearance Changing Optical Devices (DACOD), such as concave and convex fresnel-type reflective surfaces, respectively, relying on oriented pigment particles in a hardened coating, as disclosed in EP 1710756 a 1. This document describes one way of obtaining a printed image containing pigment particles or flakes having magnetic properties by aligning the pigment particles in a magnetic field. After their alignment in the magnetic field, the pigment particles or flakes exhibit a fresnel structure arrangement, such as a fresnel reflector. By tilting the image and thereby changing the direction of reflection towards the viewer, the area showing the greatest reflection towards the viewer moves according to the alignment of the flakes or pigment particles.

While fresnel-type reflective surfaces are flat, they provide the appearance of a concave or convex reflective hemisphere. The fresnel-type reflective surface may be produced by exposing a wet coating comprising non-isotropic reflective magnetic or magnetizable pigment particles to the magnetic field of a single dipole magnet, wherein the latter are arranged above and below the plane of the coating, respectively, as shown in fig. 7B of EP 1710756 a1, for convex orientation. The pigment particles thus oriented are thus fixed in position and orientation by the hardened coating.

An example of such a structure is the so-called "rolling bar" effect (fig. 1), as disclosed in US 2005/0106367. The "rolling bar" effect is based on simulating the orientation of pigment particles across a curved (curved) surface of the coating. The viewer sees the specular reflection area moving away or toward the viewer as the image is tilted. So-called forward rolling bars comprise pigment particles oriented in a concave manner (fig. 2b) and follow a positively curved surface; the forward scroll bar moves with the sense of rotation of the tilt. The so-called negative rolling bar comprises pigment particles oriented in a convex manner (fig. 2a) and follows a negatively curved surface; the negative going scrollbar moves against the sense of rotation of the tilt. A hardened coating comprising pigment particles having an orientation following a concave curve (positive curved orientation) shows a visual effect characterized by an upward movement of the scroll bar (positive scroll bar) when the support is tilted backwards. Concave curvature refers to curvature as seen by an observer viewing the hardened coating from the side of the support bearing the hardened coating. A hardened coating comprising pigment particles having an orientation that follows convex curvature (orientation of negative curvature) exhibits a visual effect characterized by downward movement of the rolling bar (negative rolling bar) as the support bearing the hardened coating is tilted backwards (i.e. the top of the support is moved away from the viewer and the bottom of the support is moved towards the viewer). This effect is used today on several security elements on banknotes, such as on the "5" of a 5 euro banknote or the "100" of a 100 rand banknote in south africa.

For the optical effect layer printed on the substrate, the negative rolling bar effect (orientation of the pigment particles (P) in a convex manner, curve (V) of fig. 2a) is generated by exposing the wet coating to the magnetic field of a magnet disposed on the side of the substrate opposite the coating (fig. 3a), while the positive rolling bar effect (orientation of the pigment particles (P) in a concave manner, curve (W) of fig. 2b) is generated by exposing the wet coating to the magnetic field of a magnet disposed on the same side of the substrate as the coating (fig. 3 b). For a forward rolling bar, the position of the magnet facing the still wet coating may cause problems in the industrial process. If the magnet is in physical contact with the wet coating, it may interfere with the optical effect layer.

Therefore, there remains a need for a method to produce the security features of displaying a forward scrollbar while avoiding the disadvantages of the prior art.

Disclosure of Invention

It is therefore an object of the present invention to overcome the drawbacks of the prior art as discussed above. This is achieved by providing a magnetic field generating means that produces or forms positively curved magnetic field lines (in a concave manner). The present invention provides such magnetic field generating devices, and their use for producing optical effect layers exhibiting a positive rolling bar effect, as an improved method, for example in the field of document security. When the magnetic field generating means of the invention is applied on the side of the substrate opposite to the not yet hardened coating comprising non-spherical magnetic or magnetizable pigment particles, it may be adapted to produce a positive rolling bar effect.

In a first aspect of the invention, a magnetic field generating device is provided for producing an Optical Effect Layer (OEL) formed by a hardened coating, the magnetic field generating device being configured for receiving (recovering) a support surface carrying a coating composition, the coating composition comprising a plurality of non-spherical magnetic or magnetizable pigment particles and a binder material, and the magnetic field generating device being configured for orienting at least a part of the plurality of non-spherical magnetic or magnetizable pigment particles in an orientation forming a forward rolling bar effect, wherein the magnetic field generating device is located on a side of the support surface opposite to the side carrying the coating composition.

In a second aspect of the present invention, there is provided a method for producing an Optical Effect Layer (OEL), the method comprising the steps of: a) applying a coating composition comprising a binder and a plurality of non-spherical magnetic or magnetizable pigment particles on a support surface, 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 receiving the support surface, preferably one of the magnetic field generating means as defined in any one of claims 1 to 9, thereby orienting at least a part of the non-spherical magnetic or magnetizable pigment particles so as to form a positive rolling bar effect, and c) hardening the coating composition into a second state so as to fix the non-spherical magnetic or magnetizable pigment particles in their adapted position and orientation.

The invention also includes optical effect layers produced by the methods described herein, and security documents comprising such optical effect layers.

Drawings

Magnet generating devices and methods of using the same to produce Optical Effect Layers (OEL) exhibiting a forward rolling bar effect according to the present invention will now be described in more detail with reference to the accompanying drawings and specific embodiments

Fig. 1 schematically illustrates the "scroll bar" effect (prior art).

Fig. 2a schematically shows pigment particles that follow a tangent to a negatively curved magnetic field line in a convex manner.

Fig. 2b schematically shows pigment particles that follow a tangent to a positively curved magnetic field line in a concave manner.

Fig. 3a schematically shows a magnetic field generating device adapted to form negatively curved magnetic field lines in a convex manner according to the prior art.

Fig. 3b schematically shows a magnetic field generating device adapted to form positively curved magnetic field lines in a concave manner according to the prior art.

Fig. 4 schematically shows a magnetic field generating device adapted to form positively curved magnetic field lines in a concave manner according to the invention.

Fig. 5a to 5c schematically show a magnetic field generation device according to a first exemplary embodiment.

Fig. 5d shows an example of an optical effect produced by using the magnetic field generating device described in fig. 5a to 5c, as seen at different viewing angles.

Fig. 6a to 6c show a magnetic field generation device according to a second exemplary embodiment.

Fig. 6d shows an example of an optical effect produced by using the magnetic field generating device described in fig. 6a to 6c, as seen at different viewing angles.

Fig. 7a to 7d schematically show a magnetic field generation device according to a third exemplary embodiment.

Fig. 7e shows an example of an optical effect produced by using the magnetic field generating device described in fig. 7a to 7d, as seen at different viewing angles.

Fig. 8a to 8b schematically show a magnetic field generation device according to a fourth exemplary embodiment.

Fig. 9a to 9c schematically show a magnetic field generation device according to a fifth exemplary embodiment.

Fig. 9d shows an example of an optical effect produced by using the magnetic field generating device described in fig. 9a to 9c, as seen at different viewing angles.

Fig. 10a schematically shows an alternative magnetic field generating device according to the second exemplary embodiment shown in fig. 6a-6 c.

Detailed Description

Definition of

The following definitions are used to explain the meaning of the terms discussed in the specification and recited in the claims.

As used herein, the indefinite articles "a" or "an" indicate one and more than one, and do not necessarily limit their reference to a noun in the singular.

As used herein, the term "about" means that the quantity or value in question may be the particular value specified or some other value in the vicinity thereof. Generally, the term "about" denoting a value is intended to mean within ± 5% of the value. As one example, the phrase "about 100" means 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 according to the present invention may be obtained within a range of ± 5% of the indicated value.

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

The term "substantially parallel" means less than 20 ° from parallel alignment, while "substantially perpendicular" means less than 20 ° from perpendicular alignment. Preferably, the term "substantially parallel" means not more than 10 ° from parallel alignment, while the term "substantially perpendicular" means not more than 10 ° from perpendicular alignment.

The term "at least partially" is intended to mean that the following attributes are accomplished to some extent or completely. Preferably, the term means that the following properties are fulfilled by at least 50% or more, more preferably by at least 75%, even more preferably by at least 90%. It may be preferred that the term means "complete".

The terms "substantially" and "substantially" are used to indicate that a feature, attribute, or parameter is achieved or satisfied in its entirety (completely) or to the extent that it does not adversely affect the intended result. Thus, the term "substantially" or "essentially" preferably means, for example, at least 80%, at least 90%, at least 95%, or 100%, depending on the circumstances.

The term "comprising" as used herein is intended to be non-exclusive and open-ended. Thus, for example, a coating composition comprising compound a may comprise other compounds than a. However, the term "comprising" also covers the stricter meaning of "consisting essentially of" and "consisting of", so that for example "a coating composition comprising compound a" may also consist (essentially) of a compound.

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

The term "optical effect layer" (OEL) as used herein means a layer comprising at least a plurality of oriented non-spherical magnetic or magnetizable pigment particles and a binder, wherein the non-random orientation of the non-spherical magnetic or magnetizable pigment particles is fixed within the binder.

As used herein, the term "optical effect coated substrate (OEC)" is used to denote the product resulting from the provision of an OEL on a substrate. The OEC may be composed of a substrate and an OEL, but may also include other materials and/or layers in addition to the OEL. The term OEC thus also covers security documents such as banknotes.

The term "scrollbar" or "scrollbar effect" refers to an area within the OEL that provides an OEL optical effect or optical representation in the form of a cylindrical bar located laterally within the OEL, wherein the axis of the cylindrical bar is parallel to the plane of the OEL and a portion of the curved surface of the cylindrical bar is above the plane of the OEL. "scroll bar", i.e. a cylindrical bar shape, may be symmetrical or asymmetrical, i.e. the radius of the cylindrical bar may or may not be constant; when the radius of the cylindrical bar is not constant, the scroll bar has a tapered form.

The terms "convex manner" or "convex curvature" and the terms "concave manner" or "concave curvature" refer to the curvature of the fresnel surface across the OEL providing the optical effect or optical representation of the scrollbar. A fresnel surface is a surface that includes a microstructure in the form of a series of grooves with varying inclination angles. At the position where the OEL is generated, the magnetic field generating means causes the non-spherical magnetic or magnetizable pigment particles to follow the tangential orientation of the curved surface. The terms "convex manner" or "convex curvature" and the terms "concave manner" or "concave curvature" refer to the apparent curvature of a curved surface as seen by an observer viewing the Optical Effect Layer (OEL) from the side of the OEL carrying optical effect coated substrate (OEC). The curvature of the curved surface follows the magnetic field lines generated by the magnetic field generating means at the location where the OEL is generated. "convex curvature" refers to negatively curved magnetic field lines (as shown in FIG. 2 a); "concavely curved" refers to magnetic field lines that are positively curved (as shown in FIG. 2 b).

The term "security element" is used to denote an image or graphical element that can be used for authentication purposes. The secure element may be an overt and/or a covert secure element.

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

The present invention provides magnetic field generating means for producing an optical effect layer exhibiting a positive rolling bar effect, said magnetic field generating means advantageously being applied on the side of the support surface opposite to the side configured for receiving the coating composition or the substrate carrying the coating composition.

The "rolling bar" effect is based on the specific orientation of magnetic or magnetizable pigment particles in a coating on a substrate. The magnetic or magnetizable pigment particles in the binder material are aligned in an arcuate pattern relative to the substrate surface so as to create a contrast stripe across the image that appears to move as the image is tilted relative to the viewing angle. In particular, the magnetic field generating device described herein produces an Optical Effect Layer (OEL) comprising magnetic or magnetizable pigment particles aligned in a curved manner following a concave curvature (W) as shown in fig. 2b (also referred to in the art as a positive curved orientation). A hardened coating comprising pigment particles having an orientation following a concave curve (positive curve orientation) shows a visual effect characterized by a movement of the rolling bar following a tilting sensation.

In one aspect, the invention relates to a magnetic field generating device for producing an Optical Effect Layer (OEL) exhibiting a forward rolling bar effect, said device comprising two or more bar dipole magnets (M1, M2, etc.), optionally one or more pole pieces (Y1, Y2, etc.), optionally a magnetic plate (M6), and a support surface (K) arranged above the two or more bar dipole magnets, the optional one or more pole pieces and the optional magnetic plate. The support surface (K) is configured for receiving a coating composition comprising non-spherical magnetic or magnetizable pigment particles as described herein and a binder material as described herein, whereby said orientation of the magnetic or magnetizable pigment particles for Optical Effect Layer (OEL) formation is to be achieved. The support surface (K) is a substrate or a combination of a substrate and a non-magnetic plate.

In an embodiment, the magnetic field generating means comprises a pair of spaced apart bar dipole magnets and a third magnetic or magnetisable element, preferably a third dipole magnet or pole piece, wherein the dipole magnets have north-to-south axes aligned with each other, substantially parallel to the support surface and having the same magnetic north-south direction, wherein the dipole magnets are spaced along the north-south axis to provide a gap region between the dipole magnets, the magnetic field lines in the gap region are such that the magnetic or magnetizable pigment particles are oriented according to the field lines in the gap region to form a positive rolling bar effect, and wherein a third element is arranged with the pair of spaced dipole bar magnets to suitably disturb the magnetic field in the region of the gap between the spaced dipole bar magnets, to allow the magnetic or magnetizable particles in the coating composition to orient to behave as a positive rolling bar effect. In an embodiment, the third element is arranged in a gap region between the support surface and the pair of dipole magnets, or in a gap region between the pair of dipole magnets and aligned therewith, or in a gap region, wherein the pair of dipole magnets is arranged between the support surface and the third element.

In an embodiment, the third element is a third dipole magnet, and the third dipole magnet has a north-south axis aligned with the north-south axes of the pair of spaced-apart bar dipole magnets and has the same magnetic north-south direction.

In an embodiment, each of the pair of spaced apart bar dipole magnets has a pole facing the gap region, wherein the facing poles are spaced apart to form the gap region. In an embodiment, the facing poles are each positioned adjacent a respective opposing pole side of the third dipole magnet.

In an embodiment, a pair of bar dipole magnets is disposed at or outside of the perimeter of the coating composition and is configured to generate magnetic field lines in a gap region between the bar dipole magnets to create a forward rolling bar effect in the coating composition in the gap region.

In an embodiment, at least one of the pair of strip dipole magnets has a length along a north-to-south axis that is less than a space between the pair of strip dipole magnets along the north-to-south axis.

As shown for example in fig. 4, the magnetic field generating device (M) is disposed below the support surface (K) and is configured so as to form concave magnetic field lines (F).

According to an embodiment of the invention and as shown in fig. 5a to 5c, the magnetic field generating means comprises three bar dipole magnets (M1), (M2) and (M3) having their north-south axes substantially parallel to the support surface (K) and having the same magnetic north-south direction. The bar dipole magnet (M1) is disposed below the support surface (K) and above the pair of bar dipole magnets (M2) and (M3). The bar dipole magnets (M2) and (M3) are directly adjacent to the bar dipole magnet (M1) or spaced apart from the bar dipole magnet (M1). When the bar dipole magnets (M1), M2) and (M3) are spaced apart, the distance between (M1) and the bar dipole magnets (M2) and (M3) is less than or equal to the thickness (d1) of (M1). Preferably, the bar dipole magnets (M2) and (M3) are directly adjacent to the bar dipole magnet (M1). Preferably, the bar dipole magnet (M1) has a length (L1) comprised in the range from about 10mm to about 100mm, more preferably from about 20mm to about 40 mm; and a thickness (d1) in the range of from about 1mm to about 5mm, more preferably from about 2mm to about 4 mm; the bar dipole magnets (M2) and (M3) each have a length (L2), (L3) independently included in a range from about 1mm to about 10mm, a thickness (d2), (d3), more preferably from about 4mm to about 6mm, independently included in a range from about 1mm to about 10mm, and a distance (x), more preferably from about 10mm to about 30mm, independently included in a range from about 5mm to about 50mm, with the proviso that the sum of (L2), (L3), and (x) is less than or equal to the length (L1). Fig. 5a schematically shows a cross-sectional view parallel to the magnetic axis of the bar dipole magnet (M1) of the magnetic field generating device of fig. 5. Fig. 5b is another schematic representation of a cross-sectional view parallel to the magnetic axis of the bar dipole magnet (M1) of the magnetic field generating device of fig. 5, showing the magnetic field lines (F) produced by the magnetic field generating device. As shown in fig. 5b, the magnetic field lines (F) generated by the magnetic field generating device over the gap region included between the bar dipole magnets (M2) and (M3) are positively curved (concave manner). As shown in fig. 5a and 5b, the coating composition (C) was applied on the support surface (K) included in the gap region between the bar dipole magnets (M2) and (M3). Fig. 5c is another schematic representation of the magnetic field generating device of fig. 5, wherein the south and north poles of the magnetic strip dipole magnets (M1), (M2) and (M3) are represented by different colors, black for the south pole and gray for the north pole.

Fig. 5d is a picture at three different viewing angles of the optical effect of the scroll bar produced by using the magnetic field generating means described in fig. 5a to 5 c. A large edge indicates that this is the image side closer to the viewer, and a small edge indicates that this is the image side further away from the viewer. The three pictures represent the scroll bar as seen at three different tilt angles of the OEC or in other words at three different viewing angles with respect to the surface of the OEL: the picture in the center shows the scroll bar as seen at an orthogonal viewing angle, and the left and right pictures show the scroll bar as seen at an oblique viewing angle.

According to another embodiment of the present invention, and as shown in fig. 6a to 6c, the magnetic field generating means comprises three bar dipole magnets (M1), (M2) and (M3) having their north-south axes substantially parallel to the support surface (K) and having the same magnetic north-south direction. The pair of bar dipole magnets (M2) and (M3) are disposed below the support surface (K) and above the bar dipole magnet (M1). The bar dipole magnets (M2) and (M3) are directly adjacent to the bar dipole magnet (M1) or spaced apart from the bar dipole magnet (M1). When the bar dipole magnets (M1), (M2) and (M3) are spaced apart, the distance between (M1) and the bar dipole magnets (M2) and (M3) is less than or equal to the thickness (d1) of (M1). Preferably, the bar dipole magnets (M2) and (M3) are directly adjacent to the bar dipole magnet (M1). Preferably, the bar dipole magnet (M1) has a length (L1) comprised in the range from about 10mm to about 100mm, more preferably from about 20mm to about 40mm, and a thickness (d1) comprised in the range from about 1mm to about 5mm, more preferably from about 2mm to about 4 mm; the bar dipole magnets (M2) and (M3) have a length (L2), (L3) respectively independently included in the range from about 1mm to about 10mm, a thickness (d2), (d3) respectively independently included in the range from about 1mm to about 10mm, more preferably from about 4mm to about 6 mm; and a distance (x) included in the range of from about 5mm to about 50mm, more preferably from about 10mm to about 30mm, with the proviso that the sum of (L2), (L3), and (x) is less than or equal to length (L1). Fig. 6a schematically shows a cross-sectional view parallel to the magnetic axis of the bar dipole magnet (M1) of the magnetic field generating device of fig. 6. Fig. 6b is another schematic representation of a cross-sectional view parallel to the magnetic axis of the bar dipole magnet (M1) of the magnetic field generating device of fig. 6, showing the magnetic field lines (F) produced by the magnetic field generating device. As shown in fig. 6b, the magnetic field lines (F) generated by the magnetic field generating device above the gap region included between the bar dipole magnets (M2) and (M3) are positively curved (concave manner). As shown in fig. 6a and 6b, the coating composition (C) was applied over the support surface (K) included in the gap region between the bar dipole magnets (M2) and (M3). Fig. 6c is another schematic representation of the magnetic field generating device of fig. 6, wherein the north and south poles of the magnetic strip dipoles (M1), (M2) and (M3) are represented by different shades of gray. Also as in fig. 5d, fig. 6d is a picture at three different viewing angles of the optical effect of the scroll bar produced by using the magnetic field generating means described in fig. 6.

In the embodiments shown in fig. 5a to 5c and in fig. 6a to 6c, the bar dipole magnets (M2) and (M3) may be the same or different. When the bar dipole magnets (M2) and (M3) are different from each other, the bar dipole magnets (M2) and (M3) have different sizes (L2) and (L3) and/or (d2) and (d 3); or the bar dipole magnets (M2) and (M3) are made of different magnetic materials; or the bar dipole magnets (M2) and (M3) are different from a combination of different materials and different sizes.

The bar dipole magnets (M2) and (M3) may be made of a single bar dipole magnet. Or alternatively, the bar dipole magnets (M2) and (M3) may be made of a plurality of aligned bar dipole magnets embedded in a plastic support bracket and having the same magnetic north-south direction, as schematically shown in fig. 10.

According to another embodiment of the invention and as shown in fig. 7a to 7d, the magnetic field generating means comprise two bar dipole magnets (M4) and (M5) having their north-south axes substantially parallel to the support surface (K) and having the same magnetic north-south direction, and a pole piece (Y). Pole piece means a structure consisting of a material with high magnetic permeability, preferably at about 2N^.A^-2To about 1,000,000N^.A^-2Magnetic permeability (newtons per square ampere), more preferably about 5N^.A^-2To about 50000N^.A^-2And more preferably about 10N^.A^-2And about 10,000N^.A^-2In the meantime. The pole pieces serve to guide the magnetic field generated by the magnet. Preferably, the pole pieces described herein comprise or consist of an iron yoke (Y). The pair of strip dipole magnets (M4) and (M5) are disposed below the support surface (K), and the pole piece (Y) is disposed at the strip dipoleBetween the pole magnets (M4) and (M5). Bar dipole magnets (M4) and (M5) adjacent to the ends of the pole pieces (Y); or alternatively the bar dipole magnets (M4) and (M5) are arranged at a distance of less than 2mm, preferably comprised in the range from about 0.1mm to about 2mm, from the end points of the pole piece (Y). Preferably, the pole piece (Y) has a length (Y) comprised in the range from about 10mm to about 50mm, more preferably from about 15mm to about 25 mm; and a thickness (dY) included in a range from about 1mm to about 10mm, more preferably from about 3mm to about 6 mm. Preferably, the bar dipole magnets (M4) and (M5) have lengths (L4), (L5) independently included in a range from about 1mm to about 20mm, more preferably from about 3mm to 6mm, respectively. Preferably, the bar dipole magnets (M4) and (M5) have thicknesses (d4), (d5) independently included in a range from about 1mm to about 10mm, more preferably from about 3mm to about 6mm, respectively. Preferably the thickness (dY) of the pole piece (Y) and the thicknesses (d4) and (d5) of the bar dipole magnets (M4) and (M5) are chosen such that the thicknesses (d4) and (d5) are equal to the thickness (dY), or at most twice the thickness (dY). The bar dipole magnets (M4) and (M5) may be the same or different. When the bar dipole magnets (M4) and (M5) are different from each other, the bar dipole magnets (M4) and (M5) have different sizes (L4) and (L5) and/or (d4) and (d 5); or the bar dipole magnets (M4) and (M5) are made of different magnetic materials; or the bar dipole magnets (M4) and (M5) are different from a combination of different materials and different sizes. Preferably, the bar dipole magnets (M4) and (M5) are identical. When the bar dipole magnets (M4) and (M5) have different lengths, it is preferable that (L4) is larger than (L5), and (M4) has a length (L4) 2 to 4 times longer than the length (L5).

Fig. 7a schematically shows a cross-sectional view parallel to the magnetic axis of the bar dipole magnet (M4) of the magnetic field generating device of fig. 7, wherein the pole piece (Y) is disposed between the bar dipole magnets (M4) and (M5). Fig. 7b is another schematic representation of a cross-sectional view parallel to the magnetic axis of the bar dipole magnet (M4) of the magnetic field generating device of fig. 7, showing magnetic field lines (F) produced by the magnetic field generating device. As shown in fig. 7b, the magnetic field lines (F) generated by the magnetic field generating device above the pole piece (Y) included in the gap region between the bar dipole magnets (M4) and (M5) are positively curved (concave manner). As shown in fig. 7a and 7b, the coating composition (C) is applied on the support surface (K) in the area above the pole piece (Y). Fig. 7c schematically shows a top view of the magnetic field generating device of fig. 7. Fig. 7d is another schematic representation of the magnetic field generating device of fig. 7, wherein the north and south poles of the magnetic strip dipoles (M4) and (M5) are represented by different colors, black for the south pole and gray for the north pole. Also as in fig. 5d, fig. 7e is three pictures at different viewing angles of the scrolling strip optical effect produced by using the magnetic field generating means described in fig. 7.

According to another embodiment described herein and shown in fig. 8a, the magnetic field generating device of fig. 7a to 7d further comprises a non-engraved magnetic plate (M6) located between the assembly formed by the two bar dipole magnets (M4) and (M5) and the pole piece (Y) and the support surface (K) and having its north-south axis substantially perpendicular to the support surface (K).

According to another embodiment described herein and shown in fig. 9a to 9c, the magnetic field generating device of fig. 7a to 7d further comprises an engraved magnetic plate (M6) located between the assembly formed by the two bar dipole magnets (M4) and (M5) and the pole piece (Y) and the support surface (K) and having its north-south axis substantially perpendicular to the support surface (K).

Fig. 9a schematically shows a cross-sectional view parallel to the magnetic axis of the bar dipole magnet (M4) of the magnetic field generating device of fig. 9, comprising magnetic bar dipoles (M4) and (M5), pole pieces (Y), and an engraved magnetic plate (M6). Fig. 9b is another schematic representation of a cross-sectional view parallel to the magnetic axis of the bar dipole magnet (M4) of the magnetic field generating device of fig. 9, showing the magnetic field lines (F) produced by the magnetic field generating device. Fig. 9c is another schematic representation of the magnetic field generating device from a top view, with the engraving of the magnetic plates (M6) in the form of a and B labels. Also as in fig. 5d, fig. 9d is a picture at three different viewing angles of the optical effect of the scroll bar produced by using the magnetic field generating means described in fig. 9.

The bar dipole magnet (M1) of the magnetic field generating device described herein, (M1)M2), (M3), (M4), (M5) and the magnetic plate (M6) may comprise or consist of any permanent magnetic (hard magnetic) material, for example alnico, barium or strontium ferrite, cobalt alloys, or rare earth-iron alloys such as neodymium-iron-boron alloys. However, for the magnetic plate (M6), particularly preferred is an easy-to-handle permanent magnetic composite material comprising such as strontium ferrite (SrFe) in a plastic or rubber type matrix₁₂O₁₉) Or neodymium-iron-boron (Nd)₂Fe₁₄B) Powdered permanent magnetic filler.

The magnetic plate (M6) may be an engraved magnetic plate (as shown in fig. 9a to c) or a non-engraved magnetic plate (as shown in fig. 8 a). When the magnetic plate (M6) is an engraved magnetic plate, it may be produced by any method capable of providing the desired structure by material abrasion, such as by engraving or grinding of permanent magnetic plates, for example by physical, laser ablation or chemical means, or by material addition such as, for example, 3D printing. Examples of engraved magnetic plates have been disclosed in EP 1641624B1 and EP1937415B 1.

The surface of the magnetic field generating means facing the support surface (K) may have any shape, such as for example circular, oval, elliptical, square, triangular, rectangular or any polygonal shape.

As shown in fig. 5 to 9, a support surface (K) is typically positioned above the magnetic field generating means and exposed to the magnetic field of the means, above which support surface (K) a layer (C) of a coating composition is provided in a fluid state (before hardening) and comprising a plurality of non-spherical magnetic or magnetizable pigment particles (P). The support surface (K) is a substrate on which the coating composition (C) is applied, or a combination of a non-magnetic plate and a substrate. When the support surface (K) is a combination of a non-magnetic plate and a substrate, the non-magnetic plate is formed by a thin (typically less than 0.5mm thick, such as 0.1mm thick) plate made of a non-magnetic material, such as a polymer material, or a metal plate made of a non-magnetic material, such as for example aluminium. When present, the non-magnetic plates are an inherent part of the magnetic device of the present invention. The coating composition (C) is applied to the support surface (K), followed by orientation and hardening of the coating composition to form the OEL in the same manner as described above.

It is noted that when the support surface (K) comprises a combination of a substrate and a non-magnetic plate, the coating composition (C) may be disposed on the substrate before the substrate with the applied coating composition is placed on the non-magnetic plate, or the coating composition may be applied on the substrate at a point in time where the substrate has been placed on the non-magnetic plate.

When the support plate comprises a substrate (instead of a combination of a substrate and a non-magnetic plate), the substrate may also play the role of a support surface, instead of a plate. Especially if the substrate is dimensionally stable, it may not be necessary to provide, for example, a plate for receiving the substrate, but the substrate may be arranged on or above the magnet without a support plate interposed therebetween. In the following description, the term "support surface", especially with regard to the orientation of the magnets in this respect, may thus in such an embodiment relate to the position or plane occupied by the substrate surface, without the provision of an intermediate plate.

If the support surface is formed by a combination of a non-magnetic plate and a base plate, said non-magnetic plate is arranged above the magnets of the magnetic field generating means. The distance (h) between the extremity of the magnet and the substrate surface at the side where the coating composition (C) is applied and where the OEL is to be formed by the orientation of the pigment particles is equal to the sum of the thicknesses of the non-magnetic plate and the substrate. If the support surface is formed by a substrate, the distance (h) is equal to the thickness of the substrate. The distance (h) is typically in the range of between 0.05mm to about 5mm, preferably between about 0.1mm and about 5mm, as required by the design, and is selected so as to produce a suitable dynamic ticker element. If the support surface is formed by a combination of a non-magnetic plate and a substrate, the non-magnetic plate may be part of a mechanical solid component of the magnetic field generating means.

Depending on the distance (h), dynamic ticker-bodies with different shapes, such as e.g. different curvature, different ticker-width or different viewing saliency effects, can be produced with the same magnetic field generation means. The thickness of the substrate may contribute to the distance between the magnet and the coating composition. However, typically the substrate is very thin (such as about 0.1mm in the case of paper substrates for banknotes) so that this contribution can be neglected in practice. However, if the contribution of the substrate cannot be neglected, for example in case the thickness of the substrate is larger than 0.2mm, the thickness of the substrate may be considered to contribute to the distance (h).

After the coating composition (C) is disposed on the support surface (K), the magnetic or magnetizable pigment particles are aligned with the magnetic field lines (F) of the magnetic field generating means.

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

a) applying a coating composition (C) in a first (fluid) state comprising a binder material as described herein and a plurality of non-spherical magnetic or magnetizable pigment particles (P) on a support surface (K),

b) exposing the coating composition (C) in the first state to the magnetic field of a magnetic field generating means described herein and disposed on the side of the support surface (K) or of the substrate disposed on the support surface opposite to the side on which the coating composition (C) is disposed, such that at least a portion of the coating composition overlaps the sheet pole (Y) or the portion of the magnetic field generating means between the bar dipole magnets (M2) and (M3) to orient the non-spherical magnetic or magnetizable pigment particles in a concave manner within the coating composition; and

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

In step b), preferably the coating composition (C) is applied such that it overlaps the center of the sheet pole (Y), or in the middle of the magnetic field generating means between the bar dipole magnets (M2) and (M3).

The applying step a) is preferably a printing method selected from the group consisting of copperplate gravure, screen printing, gravure, flexo printing and roll coating, and more preferably selected from the group consisting of screen printing, gravure and flexo printing. These methods are well known to those skilled in the art and are described, for example, in the printing technology of j.m. adams and p.a. dolin, Delmar Thomson Learning, 5 th edition.

When the coating composition (C) comprising a plurality of non-spherical magnetic or magnetizable pigment particles (P) as described herein is still wet or sufficiently soft such that the non-spherical magnetic or magnetizable pigment particles therein can move and rotate (i.e. when the coating composition is in the first state), the coating composition is subjected to the magnetic field of the magnetic field generating means as described herein to achieve a positively curved orientation of the pigment particles following magnetic field lines that are curved in a concave manner. The step of magnetically orienting the non-spherical magnetic or magnetizable pigment particles comprises exposing the applied coating composition to a determined magnetic field generated at or above the support surface of the magnetic field generating device described herein when it is "wet" (i.e. still liquid and less viscous, i.e. in the first state), thereby orienting the non-spherical magnetic or magnetizable pigment particles along the magnetic field lines of the magnetic field so as to form an orientation pattern in the shape of stripes. As shown in fig. 5 to 9, the magnetic field generating means is positioned on the opposite side to the support surface (K) provided with the coating composition (C). As shown in fig. 5 to 9, the coating composition is applied such that it is positioned over a cross section of the magnetic field generating means parallel to the bar dipole magnet. The magnetic field generating means produce magnetic field lines that are curved in a concave manner, resulting in a positively curved orientation of the non-spherical magnetic or magnetizable pigment particles. In this step, the coating composition is brought sufficiently close to or into contact with the support surface of the magnetic field generating means.

Subsequently or simultaneously, with the application of the coating composition on the support surface of the magnetic field generating means, the non-spherical magnetic or magnetizable pigment particles are oriented by using external magnetic field generating means for orienting them according to the desired orientation pattern. Thereby, the permanent magnetic pigment particles are oriented such that their magnetic axes are aligned with the direction of the external magnetic field lines at the location of the pigment particles. Magnetizable pigment particles without an intrinsic permanent magnetic field are oriented by an external magnetic field such that the direction of their longest dimension is aligned with the magnetic field lines at the location of the pigment particles. The above applies analogously to the case in which the pigment particles should have a layer structure comprising a layer 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 magnetic field direction.

Subsequently or simultaneously, the orientation of the pigment particles is fixed using a step of orienting/aligning the pigment particles by applying a magnetic field. Notably, the coating composition must therefore have a first state, i.e., a liquid or paste-like state, in which the basecoat composition is wet or sufficiently soft such that the non-spherical magnetic or magnetizable pigment particles dispersed in the coating composition are freely movable, rotatable and/or orientable upon exposure to a magnetic field, and a second hardened (e.g., solid) state; in the second hardened state, the non-spherical pigment particles are fixed or held in their respective positions and orientations.

Such first and second states are preferably provided by using some type of coating composition. For example, the components of the coating composition other than the non-spherical magnetic or magnetizable pigment particles may take the form of an ink or coating composition, such as those used in security applications, for example for printing banknotes.

The first and second states described above may be provided by using a material that exhibits a large increase in viscosity in response to a stimulus such as a change in temperature or exposure to electromagnetic radiation. That is, when the fluid binder material is hardened or cured, the binder material transitions to a second state, a hardened or solid state, in which the pigment particles are fixed in their current position and orientation and are no longer able to move or rotate within the binder material.

As is well known to those skilled in the art, the components included in an ink or coating composition to be applied, for example, to 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 compositions described herein is generally selected among those known in the art, and depends on the coating or printing process used to apply the ink or coating composition, as well as the selected hardening process.

In one embodiment, a polymeric thermoplastic binder material or a thermosetting resin may be used. Unlike thermosetting resins, thermoplastic resins can be repeatedly melted and solidified by heating and cooling without producing any significant change in properties. Typical examples of the thermoplastic resin or polymer include, but are not limited to, polyamide, polyester fiber, polyacetal, polyolefin, styrene polymer, polycarbonate, polyarylate, polyimide, Polyetheretherketone (PEEK), Polyetherketoneketone (PEKK), polyphenylene-series resin (e.g., polyphenylene oxide (polyphenylene ether), polyphenylene oxide, polyphenylene sulfide), polysulfone, and a mixture thereof.

If desired, a primer layer may be applied to the substrate prior to step a). This may enhance the quality of the optical effect layer or promote adhesion. An example of such a primer layer can be found in WO 2010/058026a 2.

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

The method for producing the OEL described herein comprises, concomitantly to or following step b), a step of hardening (step c) the coating composition in order to fix the non-spherical magnetic or magnetizable pigment particles in their adapted position and orientation, thereby transforming the coating composition into the second state. By this fixation, a solid coating or layer is formed. The term "hardening" refers to the process of drying or setting, reacting, curing, crosslinking or polymerizing the binder component in the applied coating composition, which binder component comprises the optional presence of a crosslinking agent, the optional presence of a polymerization initiator, and the optional presence of further additives in such a way as to form a substantially solid material firmly adhered to the substrate surface. As previously mentioned, the hardening step (step c) may be performed by using different means or processes depending on the binder material comprised in the coating composition, which further comprises a plurality of non-spherical magnetic or magnetizable pigment particles.

The hardening step may generally be any step that increases the viscosity of the coating composition such that a substantially solid material is formed that adheres to the support surface. The hardening step may involve a physical process based on evaporation of volatile components such as solvents and/or evaporation of water (i.e. physical drying). Here, hot air, infrared rays, or a combination of hot air and infrared rays may also be used. Alternatively, the hardening process may comprise a chemical reaction, which is irreversible by a simple temperature increase (e.g. up to 80 ℃) that may occur during normal use of the security document, which chemical reaction may be curing, polymerization or crosslinking of the binder and optionally the initiator compound and/or optionally the crosslinking compound comprised in the coating composition. The term "curing" or "curable" refers to a chemical reaction, crosslinking or polymerization involving at least one component in the applied coating composition in such a way that it becomes a polymeric material having a greater molecular weight than the starting material. Preferably, curing causes the formation of a three-dimensional polymer network. Such curing is typically induced by applying an external stimulus to the coating composition: (i) subsequent to or simultaneous with its application to the substrate surface or support surface of the magnetic field generating means, and (ii) the orientation of the non-spherical magnetic or magnetizable pigment particles. Such chemical reactions may be initiated by thermal or infrared radiation, as outlined above for the physical hardening process, but may preferably include initiation of chemical reactions by a radiation mechanism, including but not limited to ultraviolet-visible radiation curing (hereinafter UV-Vis light curing) and electron beam radiation curing (E-beam curing); oxidative polymerization (oxidative reticulation, typically caused by the combined reaction of oxygen and one or more catalysts, such as cobalt-and manganese-containing catalysts); a crosslinking reaction, or any combination thereof. Thus, preferably, the coating composition is an ink or a coating composition selected from the group consisting of radiation curable compositions, thermal drying compositions, oxidative drying compositions, and combinations thereof. Particularly preferably, the coating composition is an ink or a coating composition selected from the group consisting of radiation curable compositions.

Radiation curing is particularly preferred, uv-vis radiation curing is even more preferred, as these techniques advantageously result in a very fast curing process and thus greatly reduce the set-up time of any article comprising an OEL as described herein. In addition, radiation curing has the advantage of producing a momentary increase in the viscosity of the coating composition upon exposure to curing radiation, thereby reducing any further movement of the pigment particles. Thereby, any loss of information after the magnetic orientation step can be substantially avoided. Radiation curing by photopolymerization under the influence of actinic light having a wavelength component in the ultraviolet or blue part of the electromagnetic spectrum (typically 300nm to 550 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, such as 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 subsequently to step b). However, the time from the end of step b) to the start of step c) is preferably relatively short to avoid any disorientation and information loss. Typically, the time between the end of step b) and the start 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 essentially no time gap between the end of step b) and the start of step c), i.e. step c) follows step b) immediately or has already started while step b) is still in progress.

Preferred radiation curable compositions include those curable by ultraviolet visible radiation (hereinafter referred to as UV-Vis curing) or by electron beam radiation (hereinafter referred to as EB curing). Radiation curable compositions are known in the art and can be found in standard textbooks, such as the series "Chemistry & Technology of UV & EB formulation for Coatings, Inks & Paints", published by John Wiley & Sons in combination with SITA science and Technology, Inc. on volume 7 of 1997 and 1998. Preferably, the UV-Vis curable composition comprises one or more compounds selected from the group consisting of radical curable compounds, cationic curable compounds and mixtures thereof. The cationically curable compound can be cured by a cationic mechanism, typically involving excitation by radiation of one or more photoinitiators that release cationic species such as acids, which in turn initiates curing to react and/or crosslink the monomers and/or oligomers, thereby hardening the coating composition. Free radical curable compounds are cured by a free radical mechanism, which typically includes excitation by one or more photoinitiator radiations, thereby generating free radicals, which in turn initiate polymerization to cure the coating composition.

As mentioned above, step a) (application on the support surface (K)) may be performed simultaneously with step b) or before step b) (orientation of the pigment particles by the magnetic field), and likewise step c) (hardening) may be performed simultaneously with step b) or subsequently to step b) (orientation of the pigment particles by the magnetic field). Although this is also possible for certain types of equipment, usually not all three steps a), b) and c) are performed simultaneously. Furthermore, steps a) and b), and steps b) and c) may be performed such that they are performed partially simultaneously (i.e. the times at which each of the steps is performed partially overlap, such that, for example, the hardening step c) already starts at the end of the orientation step b).

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

The magnetic field generating device and the method exemplified by the present invention are used to produce an Optical Effect Layer (OEL) exhibiting a forward rolling bar effect.

OELs include a plurality of non-spherical magnetic or magnetizable pigment particles that have a non-isotropic reflectivity due to their non-spherical shape. Non-spherical magnetic or magnetizable pigment particles are dispersed in the binder material and have a particular orientation for providing an optical effect. This orientation is achieved by orienting the non-spherical magnetic or magnetizable pigment particles according to an external magnetic field generated by the magnetic field generating means described herein.

Since the coating composition is in a fluid state and wherein the pigment particles are rotatable/orientable prior to hardening of the coating composition, the non-spherical magnetic or magnetisable pigment particles within the coating composition are self-aligned along the field lines as described above, whereby the respective orientation of the obtained pigment particles (i.e. their magnetic axis in case of magnetic particles, or their largest dimension in case of magnetisable pigment particles) coincides, at least on average, with the local direction of the magnetic field lines at the location of the pigment ions.

In OEL, non-spherical magnetic or magnetizable pigment particles are dispersed in a coating composition comprising a hardened binder material that fixes the orientation of the non-spherical magnetic or magnetizable pigment 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 200nm to 800nm, more preferably in the range of 400nm to 700 nm. Incident electromagnetic radiation, such as visible light, entering the OEL through its surface may reach the pigment particles dispersed inside the OEL and be reflected there, and the reflected light may again leave the OEL for producing the desired optical effect. Herein, the term "one or more wavelengths" means that the adhesive material may be transparent to only one wavelength within a given range of wavelengths, or may be transparent to several wavelengths within a given range. Preferably, the adhesive material is transparent to more than one wavelength within the given range, and more preferably transparent 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 200nm to about 2500nm (or 200nm to 800nm, or 400nm to 700nm), and even more preferably, the hardened binder material is substantially transparent to all wavelengths in these ranges.

In the present context, the term "transparent" means that the transmission of electromagnetic radiation through a 20 μm layer of hardened binder material (excluding non-spherical magnetic or magnetizable pigment particles, but including all other optional components, in the presence of such components) as present in an OEL is at least 80%, more preferably at least 90%, even more preferably at least 95%. This can be determined, for example, by measuring the transmission of a test piece of hardened binder material (excluding non-spherical magnetic or magnetizable pigment particles) according to accepted test methods, for example DIN 5036-3 (11 months 1979).

The OEL can also be used as a hidden security feature if the wavelength of the incident radiation is selected outside the visible range, e.g. in the near ultraviolet range, since then usual technical means would be necessary to detect the (complete) optical effect generated by the OEL under the respective illumination conditions comprising the selected non-visible wavelength. In this case, it is preferred that the OEL comprises luminescent pigment particles exhibiting luminescence 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 wavelength ranges between 700nm to 2500nm, 400nm to 700nm and 200nm to 400nm, respectively.

Due to their non-spherical shape, the non-spherical magnetic or magnetizable pigment particles described herein have a non-isotropic reflectivity with respect to incident electromagnetic radiation to which the hardened binder material is at least partially transparent. As used herein, the term "non-isotropic reflectance" means that the proportion of incident radiation from a first angle reflected by a pigment particle to a certain (viewing) direction (second angle) is a function of the orientation of the pigment particle, i.e. a change in orientation of the pigment particle relative to the first angle may result in a different magnitude of reflection to the viewing direction.

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

In the OEL described herein, non-spherical magnetic or magnetizable pigment particles are provided in such a way to form a dynamic positive rolling bar security element.

Herein, the term "dynamic" means that the appearance and light reflection of the security element varies according to the viewing angle. In other words, the appearance of the security element is different when viewed from different angles, i.e. the security element presents a different appearance (e.g. both relative to the plane of the OEL when viewed from a viewing angle of about 90 ° compared to a viewing angle of about 22.5 °). This behavior is caused by the orientation of non-spherical magnetic or magnetizable pigment particles with non-isotropic reflectivity.

Optically variable elements are known in the field of security printing. Optically variable elements (also known in the art as colourshifting or goniochromatic elements) exhibit a viewing angle or angle of incidence dependent colour and are used to avoid counterfeiting and/or illegal copying of banknotes and other security documents by commonly available colour scanning, printing and copying office equipment.

The plurality of non-spherical magnetic or magnetizable pigment particles may comprise non-spherical optically variable magnetic or magnetizable pigment particles and/or non-spherical magnetic or magnetizable pigment particles having non-optically variable properties.

Preferably, at least a portion of the plurality of non-spherical magnetic or magnetizable pigment particles described herein are comprised of non-spherical optically variable magnetic or magnetizable pigment particles. Preferably, the non-spherical magnetic or magnetizable pigment particles are prolate or oblate ellipsoidal, platelet-shaped or needle-shaped pigment particles, or mixtures thereof. Therefore, since it is notSpherical shape, i.e. intrinsic reflectivity per unit surface area (e.g. per μm)²) Is uniform throughout the surface of such pigment particles, the reflectivity of the pigment particles is non-isotropic, as the visible area of the pigment particles depends on the direction from which it is viewed. In one embodiment, the non-spherical magnetic or magnetizable pigment particles having a non-isotropic reflectivity due to their aspherical shape may further have an intrinsic non-isotropic reflectivity (such as for example in optically variable magnetic pigment particles) due to the presence of layers of different reflectivity and refractive index. In this embodiment, the non-spherical magnetic or magnetizable pigment particles comprise non-spherical magnetic or magnetizable pigment particles having an intrinsic non-isotropic reflectivity, such as non-spherical optically variable magnetic or magnetizable pigment particles.

Preferably, at least a portion of the plurality of non-spherical magnetic or magnetizable pigment particles are selected from the group consisting of magnetic thin film interference pigment particles, magnetic interference coated pigment particles, magnetic cholesteric liquid crystal pigment particles, and mixtures thereof.

Suitable examples of non-spherical magnetic or magnetizable pigment particles described herein include, but are not limited to, pigment particles comprising ferromagnetic or ferrimagnetic metals, such as cobalt, iron, 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 thereof. 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: iron oxides, such as hematite (Fe)₂O₃) Magnetite (Fe)₃O₄) Chromium dioxide (CrO)₂) Magnetic ferrite (MFe)₂O₄) Magnetic spinel (MR)₂O₄) Magnetic hexagonal ferrite (MFe)₁₂O₁₉) Magnetic orthoferrite (RFeO)₃) Magnetic garnet M₃R₂(AO₄)₃Wherein M represents divalent and R is trivalent, anda is for tetravalent metal ions and "magnetic" is for ferromagnetic or ferrimagnetic properties.

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

Magnetic thin film interference pigment particles are known to the person skilled in the art and are described, for example, in US 4,838,648; WO 2002/073250 a 2; EP 686675 a 1; WO 2003/000801 a 2; US6,838,166; WO 2007/131833a1 and documents related thereto. Due to their magnetic properties, they are machine readable and therefore coating compositions comprising magnetic thin film interference pigment particles can be detected, for example, with a specific magnetic detector. Thus, the coating composition comprising magnetic thin film interference pigment particles can be used as a covert or semi-covert security element (authentication tool) for a security document.

Preferably, the magnetic thin-film interference pigment particles comprise pigment particles having a five-layer Fabry-Perot (Fabry-Perot) multilayer structure, and/or pigment particles having a six-layer Fabry-Perot multilayer structure, and/or pigment particles having a seven-layer Fabry-Perot multilayer structure. A preferred five-layer fabry-perot multilayer structure is composed of an absorber/dielectric/reflector/dielectric/absorber multilayer structure, wherein the reflector and/or the absorber are also magnetic layers. The preferred six-layer fabry-perot multilayer structure is comprised of an absorber/dielectric/reflector/magneto/dielectric/absorber multilayer structure. A preferred seven-layer fabry-perot multilayer structure is constituted by an absorber/dielectric/reflector/magnetic/reflector/dielectric/absorber multilayer structure, such as disclosed in US 4,838,648; and more preferably a seven-layer fabry-perot absorber/dielectric/reflector/magnetic/reflector/dielectric/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 metalsAlloys and combinations thereof, and more preferably selected from the group consisting of aluminum (Al), chromium (Cr), nickel (Ni), and mixtures thereof, and still more preferably from aluminum (Al). Preferably, the dielectric layers are independently selected from the group consisting of magnesium fluoride (MgF)₂) Silicon dioxide (SiO)₂) And mixtures thereof, and more preferably magnesium fluoride (MgF)₂). Preferably, the absorber 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 comprising nickel (Ni), iron (Fe) and/or cobalt (Co) and mixtures thereof. It is particularly preferred that the magnetic thin film interference pigment particles comprise a mixture of Cr/MgF₂/Al/Ni/Al/MgF₂A seven-layer Fabry-Perot absorber/dielectric/reflector/magnetic/reflector/dielectric/absorber multilayer structure consisting of/Cr multilayer structures.

The magnetic thin film interference pigment particles described herein are typically manufactured by vacuum deposition of different desired layers onto a grid. After deposition of the desired number of layers, the stack of layers is removed from the grid, for example by PVD, by dissolving the release layer in a suitable solvent, or by stripping the material from the grid. The material thus obtained is then broken down into flakes which have to be further processed by grinding, milling or any suitable method. The resulting product consisted of flat flakes with broken edges, irregular shapes and different aspect ratios. Further information on the preparation of suitable magnetic thin-film interference pigment particles can be found, for example, in EP-A1710756, which is hereby incorporated by reference.

Suitable interference coated pigments comprising one or more magnetic materials include, but are not limited to, consisting of a substrate selected from the group consisting of a core (core) coated with one or more layers, wherein at least one of the core or one or more layers has magnetic properties. For example, suitable interference coated pigments comprise a core made of a magnetic material such as those described above, said core being coated with one or more layers made of metal oxides, and a structure consisting of a core made of a synthetic or natural cloudParent, phyllosilicate (e.g. talc, kaolin and sericite), glass (e.g. borosilicate), Silica (SiO)₂) Alumina (Al)₂O₃) Titanium oxide (TiO)₂) Graphite and mixtures thereof.

Pigment particles of suitable magnetic cholesteric liquid crystals exhibiting optically variable properties include, but are not limited to: single-layer cholesteric liquid crystal pigment particles and multilayer cholesteric liquid crystal pigment particles. Such pigment particles are disclosed, for example, in WO 2006/063926 a1, US6,582,781 and US6,531,221. WO 2006/063926 a1 discloses monolayers and pigment particles obtained therefrom having high brightness and color shift properties with additional special properties such as magnetization capability. The disclosed monolayer and pigment particles obtained therefrom by comminuting the monolayer comprise a three-dimensional crosslinked cholesteric liquid crystal mixture and magnetic nanoparticles. US6,582,781 and US6,410,130 disclose inclusion of sequence a¹/B/A²Platelet-shaped cholesteric multilayer pigment particles of (1), wherein A¹And A²May be the same or different and each comprises at least one cholesteric layer, while B is an absorbing layer A¹And A²An intermediate layer that transmits all or some of the light and imparts a magnetic property to the optical intermediate layer. US6,531,221 discloses platelet-shaped cholesteric multilayer pigment particles comprising the sequence a/B (and if desired C), wherein a and C are absorbing layers comprising pigment particles imparting magnetic properties and B is a cholesteric layer.

In addition to the non-spherical magnetic or magnetizable pigment particles (which may or may not comprise or consist of non-spherical optically variable magnetic or magnetizable pigment particles), non-magnetic or non-magnetized pigment particles may also be comprised in the positive rolling bar security element. These pigment particles may be colour pigment particles known in the art, with or without optically variable properties. Further, the pigment particles may be spherical or non-spherical, and may have isotropic or non-isotropic optical reflectance.

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

The total number of non-spherical magnetic or magnetizable pigment particles in an OEL can be appropriately selected according to the desired application; however, to construct a surface covering pattern that produces a visible effect, typically thousands of pigment particles, such as about 1,000 to 10,000 pigment particles, are required in a volume corresponding to one square millimeter of the OEL surface.

In addition to the covert security provided by the color-shifting properties of the non-spherical optically variable magnetic or magnetizable pigment particles, which allows the OEL or an OEC (e.g. a security document) carrying the OEL described herein to be easily detected, identified and/or authenticated from their possible counterfeiting with unaided human senses, for example because such features may be visible and/or detectable while still being difficult to produce and/or reproduce, the color-shifting properties of the non-spherical optically variable magnetic or magnetizable pigment particles may be used as a machine readable tool for OEL identification. Thus, the optically variable properties of the non-spherical optically variable magnetic or magnetizable pigment particles may simultaneously be used as a covert or semi-covert security feature in an authentication process, wherein the optical (e.g. spectral) properties of the pigment particles are analyzed.

The use of aspherical optically variable magnetic or magnetizable pigment particles enhances the significance of OEL as a security feature in security document applications, since such materials (i.e. optically variable magnetic or magnetizable pigment particles) are left to the security document printing industry and are not commercially available to the public.

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

The coating composition may further comprise 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 unique property, which is not perceptible by the naked eye, and which may be included in a layer so as to impart a way to authenticate the layer or an article comprising the layer through the use of a particular device for its authentication.

The coating composition may further comprise one or more coloring components selected from the group consisting of organic and inorganic pigments and organic dyes, and/or one or more additives. The latter include, without limitation, compounds and materials used to adjust the physical, rheological, and chemical parameters of the coating composition, such as viscosity (e.g., solvents, thickeners, and surfactants), consistency (e.g., anti-settling agents, fillers, and plasticizers), foaming characteristics (e.g., defoamers), lubricating characteristics (waxes, oils), ultraviolet light stability (photosensitizers and light stabilizers), adhesion characteristics, antistatic characteristics, storage stability (polymerization inhibitors), and the like. The additives described herein may be present in the coating composition in amounts and forms known in the art, including in the form of so-called nanomaterials, wherein at least one of the dimensions of the additives is in the range of 1nm to 1000 nm.

Also described herein are rotary printing assemblies that include one or more magnetic field generating devices for producing the OELs described herein that are mounted and/or inserted on a plate cylinder as part of a rotary printing press. In this case, the magnetic field generating device or devices are designed and adapted accordingly to the cylindrical surface of the rotary unit in order to ensure a smooth contact with the surface to be imprinted.

One or more protective layers may be applied on top of the OEL with the purpose of increasing the durability and hence the cycle life of the security certificates by dirt or chemical resistance and cleanliness, or with the purpose of modifying their aesthetic appearance (e.g. optical gloss). When present, the protective layer or layers are typically made of protective varnish (varnishes). These may be clear or lightly colored or tinted, and may have more or less gloss. The protective varnish may be a radiation curable composition, a thermally drying composition, or any combination thereof. Preferably, the one or more protective layers are radiation curable compositions, more preferably UV-Vis curable compositions. The protective layer may be applied after the formation of the OEL in step c).

In the above-described method, the OEL can be disposed directly on the substrate where it should be permanently retained (e.g., for banknote applications). Alternatively, the OEL may also be provided on a temporary substrate for production purposes, from which the OEL can be subsequently removed. This may facilitate production of OELs, for example, particularly when the adhesive material is still in a fluid state. Thereafter, after hardening the coating composition for the production of OELs, the temporary substrate may be removed from the OEL. Of course, in this case, the coating composition must be in a physically integrated form after the hardening step, such as for example in the case in which a plastic-like or sheet-like material is formed by hardening. Thus, a film-like transparent and/or translucent material consisting of the OEL itself (i.e. consisting essentially of a hardened adhesive component having a non-isotropic reflectivity for fixing the pigment particles in their orientation and forming a film-like material such as a plastic film, and further optional components) may be provided.

The method as described above may further comprise the step of adding an adhesive layer on the side opposite to the side where the OEL is provided, or an adhesive layer provided on the same side as the OEL and on top of the OEL, preferably after the hardening step has been completed. In this case, an adhesive label including an adhesive layer and an OEL is formed. Such labels can be attached to all kinds of documents or other articles or items without the need for printing or other processes involving machinery and considerable effort.

Alternatively, OECs are manufactured in the form of transfer foils, which can be applied to a document or article in a separate transfer step. For this purpose, the substrate is provided with a release coating on which the OEL is produced, as described herein. One or more adhesive layers may be applied over the OEL so 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, metals, composites and mixtures thereof 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, hemp, wood pulp, and blends thereof. As is well known to those skilled in the art, cotton and cotton/hemp blends are preferred for 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 poly (ethylene terephthalate) (PET), poly (butylene 1, 4-terephthalate) (PBT), poly (ethylene 2, 6-napthalate) (PEN), and polyvinyl chloride (PVC). Spunbonded olefin fibres, e.g. under the trade markThose sold may also be used as substrates. Metals include, but are not limited to, those used to make metal coins and those used to make metallized plastic polymer materials such as metallized security threads. Typical examples of composite materials include, but are not limited to, a multi-layer structure or laminate of paper, and at least one plastic or polymeric material such as those described hereinabove, and plastic and/or polymeric fibers contained in a paper-like or fibrous material such as those described hereinabove. Of course, the substrate may comprise further additives known to the person skilled in the art, such as sizing agents, brighteners, processing aids, reinforcing agents or moisture-reinforcing agents, etc

For the purpose of further increasing the level of security and preventing counterfeiting and illegal copying of security documents, the method described herein may further comprise the step of adding printed, coated or laser marked or laser perforated markings, watermarks, security threads, fibers, flakes (planchettes), luminescent compounds, windows, foils, decals and combinations thereof to the OEC. To further increase the level of security and to prevent the same purpose of counterfeiting and illegal copying of security documents, the method described herein may further comprise the step of adding one or more marking substances or markers and/or machine readable substances (e.g. luminescent substances, uv/visible/ir absorbing substances, magnetic substances and combinations thereof) to the OEC.

The OEL produced by the methods described herein may be used for decorative purposes as well as for protecting and authenticating security documents. Also described herein are articles and decorative objects comprising the OELs described herein. The articles and decorative objects may include more than one optical effect layer as described herein. Typical examples of articles and decorative objects include, but are not limited to luxury goods, cosmetic packages, automobile parts, electronic/electric appliances, furniture, and the like.

Also described herein are security documents comprising OELs produced using the magnetic field generating devices and methods described herein. The security document may comprise more than one optical effect layer as described herein. Security documents include, but are not limited to, valuable documents and valuable commercial goods. Typical examples of documents of value include, but are not limited to, banknotes, deeds, tickets, cheques, vouchers, tax stamps and tax labels, agreements and the like, identification documents such as passports, identification cards, visas, driver's licenses, bank cards, credit cards, transaction cards, access documents or cards, tickets, public transportation tickets or business cards and the like. The term "valuable commercial goods" refers to packaging materials, in particular for the pharmaceutical, cosmetic, electronic or food industry, which should be protected against counterfeiting and/or illegal copying in order to guarantee, for example, the packaging-like content of genuine medicaments. Examples of such packaging materials include, but are not limited to, labels, such as authenticating brand labels, tamper evidence labels, and seals.

Preferably, the security document described herein is selected from the group consisting of banknotes, identity documents, rights-conferring documents, driver's licenses, credit cards, access cards, transport titles (titles), bank checks and security product labels. Alternatively, the OEL may be produced on a secondary substrate, such as for example a security thread, a security strip, a foil, a decal, a window or a label, and thus transferred to the security document in a separate step.

Those skilled in the art will envision several modifications to the particular embodiments described above without departing from the spirit of the invention. Such modifications are encompassed by the present invention.

Moreover, all documents referred to throughout this specification are hereby incorporated by reference in their entirety as if fully set forth herein.

The invention will now be described by way of example, which however is not intended to limit its scope in any way.

Examples of the invention

On black paper as a substrate, the magnetic field generating device according to fig. 5 to 9 was used to orient the non-spherical optically variable magnetic pigment particles in the printed layer of the UV curable screen printing ink described in table 1. A paper substrate carrying an applied layer of UV curable screen printing ink described in table 1 was placed on a support surface (K) made of polyethylene. Following the application step, the thus obtained magnetically oriented pattern of optically variable pigment particles is fixed by a UV curable printed layer comprising pigment particles.

Table 1. the inks have the formula:

epoxy acrylate oligomers	40％
		Trimethylolpropane alkenoic acid ester monomer	10％
Tripropylene glycol diacrylate monomer	10％
		GENORAD 16(Rahn)	1％
AEROSIL 200(Evonik)	1％
		Irgacure 500(BASF)	6％
GENOCURE EPD(Rahn)	2％
		Non-spherical optically variable magnetic pigment particles (7 layers) ()	20％
DOWANOL PMA	10％

(. about.) green to blue optically variable magnetic pigment particles obtained from JDS-Uniphase of St.Roche, Calif. having a diameter d50 of about 20 μm and a thickness of about 1 μm in flake form.

Example 1

The magnetic field generating means comprises a bar dipole magnet (M1) disposed above the bar dipole magnet (as shown in fig. 5a by (M2) and (M3). The bar dipole magnet M1 has a length (L1) of 30mm and lengths (L2) and (L3) for the bar dipole magnets (M2) and (M3) of 2 mm. The thickness (d1) was 2mm, and the thicknesses (d2), (d3) were 5 mm. The distance (x) between the magnets (M2) and (M3) was 24 mm. The magnetic field generating device has a width (w) of 30mm, that is, the bar dipole magnet (M1) and the bar dipole magnets (M2 and M3) each have a width of 30 mm. The bar dipole magnet consists of NdFeB UH30 for (M1) and NdFeB N48 for M (2) and M (3) magnets. The distance h is 2 mm. A picture of the resulting optical effect layer is shown in fig. 5 d.

Example 2

The magnetic field generating means includes a bar dipole magnet (M1) disposed below the bar dipole magnet (as shown by (M2) and (M3) in fig. 6 a). The bar dipole magnet M1 has a length (L1) of 30mm and lengths (L2) and (L3) for the bar dipole magnets (M2) and (M3) are 2 mm. The thickness (d1) was 5mm, and (d2), (d3) was 5 mm. The distance (x) between the magnets (M2) and (M3) was 18 mm. The magnetic field generating device has a width (w) of 30mm, that is, the bar dipole magnet (M1) and the bar dipole magnets (M2 and M3) each have a width of 30 mm. The bar dipole magnet consists of NdFeB N42 for (M1) and NdFeB N48 for M (2) and M (3) magnets. The distance h is 2 mm. A picture of the resulting optical effect layer is shown in fig. 6 d.

Example 3 (symmetrical device)

The magnetic field generating means comprises a pole piece (Y) disposed between a pair of bar dipole magnets (as shown in fig. 7a by (M4) and (M5)). The pole piece (Y) has a Length (LY) of 21mm and a thickness (dY) of 5 mm. The bar dipole magnets (M4 and M5) had lengths (L4) and (L5) of 4mm, and thicknesses (d4) and (d5) of 5 mm. The magnetic field generating means had a width (w) of 30mm, i.e., the pole piece (Y) and the bar dipole magnets (M4 and M5) each had a width of 30 mm. The pole piece (Y) is made of pure ironAnd the pair of strip dipole magnets are comprised of NdFeB N48 magnets. The distance h is 3 mm. A picture of the resulting optical effect layer is shown in fig. 7 e.

Example 4 (asymmetric device)

The magnetic field generating means comprises a pole piece (Y) arranged between a pair of bar dipole magnets (as shown in fig. 8a by (M4) and (M5)). The pole piece (Y) has a Length (LY) of 21mm and a thickness (dY) of 5 mm. The bar dipole magnet (M4) has a length (L4) of 6mm, and the bar dipole magnet (M5) has a length (L5) of 3 mm. The bar dipole magnets (M4 and M5) had thicknesses (d4) and (d5) of 6 mm. The magnetic plate (M6) is arranged at a distance of 3mm from the pole piece (Y). The magnetic field generating means has a width (w) of 30mm, i.e. the pole piece (Y) and the bar dipole magnet each have a width of 30 mm. The pole piece (Y) is made of pure ironAnd the pair of strip dipole magnets are comprised of NdFeB N48 magnets. The magnetic plate (M6) is a plastic bonded magnet (plastic ferrite loaded with strontium hexaferrite). The distance h is 3 mm. A picture of the resulting optical effect layer is shown in fig. 8 d.

Example 5

The magnetic field generating means includes a pole piece (Y) disposed between a pair of bar dipole magnets (as shown in fig. 9a by (M4) and (M5)). The pole piece (Y) has a Length (LY) of 21mm and a thickness (dY) of 5 mm. The bar dipole magnet (M4) has a length (L4) of 6mm, and the bar dipole magnet (M5) has a length (L5) of 3 mm. The bar dipole magnets (M4 and M5) had thicknesses (d4) and (d5) of 6 mm. A magnetic plate (M6) with engravings in the form of a and B marks was placed at a distance of 3mm from the pole piece (Y). The magnetic field generating means has a width (w) of 30mm, i.e. the pole piece (Y) and the bar dipole magnet each have a width of 30 mm. The pole piece (Y) is made of pure ironAnd the pair of strip dipole magnets (M4 and M5) are composed of NdFeB N35 magnets. The magnetic plate (M6) is a plastic bonded magnet (plastic ferrite loaded with strontium hexaferrite) with a thickness of 1mm and an engraving depth of the a and B marks of 0.4 mm. The distance h is 3 mm. A picture of the resulting optical effect layer is shown in fig. 9 d.

Claims

1. A magnetic field generating device for producing an Optical Effect Layer (OEL) formed by a hardened coating, the magnetic field generating device being configured for receiving a support surface carrying a coating composition, the coating composition comprising a plurality of non-spherical magnetic or magnetizable pigment particles and a binder material, and the magnetic field generating device being configured for forming concave magnetic field lines for orienting at least a part of the plurality of non-spherical magnetic or magnetizable pigment particles in an orientation forming a forward rolling bar effect, wherein

The magnetic field generating means is located on the side of the support surface opposite to the side carrying the coating composition,

wherein the magnetic field generating means is

a) A bar dipole magnet (M1) and a pair of bar dipole magnets (M2) and (M3), said bar dipole magnets (M1), (M2) and (M3) having their north-south axes substantially parallel to said support surface and the same magnetic north-south direction,

a1) the bar dipole magnet (M1) is disposed below the support surface, and the pair of bar dipole magnets (M2) and (M3) are disposed below the bar dipole magnet (M1) and spaced apart from each other, or

a2) The pair of bar dipole magnets (M2) and (M3) are disposed below the support surface and spaced apart from each other, and the bar dipole magnet (M1) is disposed below the pair of bar dipole magnets (M2) and (M3); or

b) A pair of bar dipole magnets (M4) and (M5) having their north-south axes substantially parallel to said support surface and the same magnetic north-south direction, and a pole piece (Y) disposed between said bar dipole magnet (M4) and said bar dipole magnet (M5); or

c) A pair of bar dipole magnets (M4) and (M5), a pole piece (Y) and a magnetic plate (M6), said pair of bar dipole magnets (M4) and (M5) having their north-south axes substantially parallel to said support surface and the same magnetic north-south direction, said magnetic plate (M6) having its north-south axis substantially perpendicular to said support surface, said pole piece (Y) being disposed between said bar dipole magnet (M4) and said bar dipole magnet (M5); or

d) Wherein the magnetic field generating means comprises a pair of spaced apart bar dipole magnets and a third element, the third element being a third dipole magnet or pole piece, wherein the dipole magnets have north-south axes aligned with each other, substantially parallel to the support surface and having the same magnetic north-south direction, wherein the dipole magnets are spaced apart along the north-south axes so as to provide a gap region between the dipole magnets, the magnetic field lines in the gap region being such that the magnetic or magnetizable pigment particles are oriented in the gap region to form the positive rolling bar effect, and wherein the third element is arranged relative to the pair of spaced apart bar dipole magnets so as to disturb the magnetic field in the gap region between the spaced apart bar dipole magnets.

2. The magnetic field generating device according to claim 1, wherein the support surface is a substrate, or a combination of a non-magnetic plate and a substrate, on which the coating composition (C) is applied.

3. The magnetic field generating device according to claim 1, wherein in optional c) the surface of the magnetic plate (M6) facing the support surface comprises an engraving.

4. The magnetic field generating device of claim 1, wherein in optional d) the third element is the third dipole magnet, and

the third dipole magnet has a north-south axis aligned with the north-south axes of the pair of spaced-apart bar dipole magnets and has the same magnetic north-south direction; and the pair of spaced apart bar dipole magnets each having a pole facing the gap region, wherein the facing poles are spaced apart to form the gap region and are positioned adjacent to opposite sides of the third dipole magnet.

5. The magnetic field generating device according to any one of the preceding claims, wherein the pair of bar dipole magnets are disposed at or outside a perimeter of the coating composition and are configured to produce magnetic field lines in a gap region between the bar dipole magnets to create the forward rolling bar effect in the coating composition in the gap region.

6. The magnetic field generating device according to any one of claims 1 to 4, wherein at least one of the pair of bar dipole magnets has a length along the north-south axis that is less than a space between the pair of bar dipole magnets along the north-south axis.

7. The magnetic field generating device of claim 5, wherein at least one of the pair of bar dipole magnets has a length along the north-south axis that is less than a space between the pair of bar dipole magnets along the north-south axis.

8. A printing assembly comprising one or more magnetic field generating devices according to any one of claims 1 to 7.

9. Use of a magnetic field generating device according to any of claims 1 to 7 for producing an Optical Effect Layer (OEL).

10. A method 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 pigment particles on a support surface, the coating composition being in a first state,

b) exposing the coating composition in a first state to the magnetic field of a magnetic field generating device according to any one of claims 1 to 7 receiving the support surface, thereby orienting at least a part of the non-spherical magnetic or magnetizable pigment particles so as to form a positive rolling bar effect, the magnetic field generating device being located on the side of the support surface opposite to the side carrying the coating composition, and

c) hardening the coating composition to a second state to fix the non-spherical magnetic or magnetizable pigment particles in their adapted position and orientation.

11. The method of claim 10, comprising applying the optical effect layer to a security document.

12. The method of claim 11, wherein the security document is selected from the group consisting of a banknote, an identification document, a driver's license, a credit card, an access card, a transport title, a bank check, and a secure product label.