Processes for producing optical effects layers

Abstract

The invention relates to the field of the protection of security documents such as for example banknotes and identity documents against counterfeit and illegal reproduction. In particular, the present invention provides processes for producing optical effect layers (OELs) comprising at least a first motif and a second motif being at least partially adjacent to each other, each of said motifs independently comprising magnetically oriented platelet-shaped magnetic or magnetizable pigment particles.

Description

PROCESSES FOR PRODUCING OPTICAL EFFECTS LAYERSFIELD OF THE INVENTION

[0001] The present invention relates to the field of processes for producing optical effect layers (OELs) comprising magnetically oriented platelet-shaped magnetic or magnetizable pigment particles. In particular, the present invention provides processes for magnetically orienting platelet-shaped magnetic or magnetizable pigment particles in more than one coating layers so as to produce OELs and the use of said OELs as anti-counterfeit means on security documents or security articles as well as decorative purposes.BACKGROUND OF THE INVENTION

[0002] It is known in the art to use inks, compositions, coatings or layers containing oriented magnetic or magnetizable pigment particles, particularly also optically variable magnetic or magnetizable pigment particles, for the production of security elements, e.g. in the field of security documents. Coatings or layers comprising oriented magnetic or magnetizable pigment particles are disclosed for example in US 2,570,856; US 3,676,273; US 3,791 ,864; US 5,630,877; and US 5,364,689. Coatings or layers comprising oriented magnetic color-shifting pigment particles, resulting in particularly appealing optical effects, useful for the protection of security documents, have been disclosed in WO 2002 / 090002 A2 and WO 2005 / 002866 A1 .

[0003] Security features, e.g. for security documents, can generally be classified into “covert” security features on the one hand, and “overt” security features on the other hand. The protection provided by covert security features relies on the principle that such features are difficult to detect, typically requiring specialized equipment and knowledge for detection, whereas “overt” security features rely on the concept of being easily detectable with the unaided human senses, e.g. such features may be visible and / or detectable via the tactile sense while still being difficult to produce and / or to copy. However, the effectiveness of overt security features depends to a great extent on their easy recognition as a security feature.

[0004] Magnetic or magnetizable pigment particles in printing inks or coatings allow for the production of magnetically induced images, designs and / or patterns (also referred in the art as “Optical Effect Layers (OELs”) through the application of a correspondingly structured magnetic field, inducing a local orientation of the magnetic or magnetizable pigment particles in the not yet hardened (i.e. wet) coating, followed by the hardening of the coating. The result is a fixed and stable magnetically induced image, design or pattern. Materials and technologies for the orientation of magnetic or magnetizable pigment particles in coating compositions are known. The magnetically induced images in question can only be produced by having access to both, the magnetic or magnetizable pigment particles or the corresponding ink, and the particular technology employed to print said ink and to orient said pigment in the printed ink.

[0005] With the aim of optimizing and increasing the counterfeiting resistance of security documents, in particular banknotes, striking and sophisticated magnetically induced images and optical effects layers (OELs) have been developed. Said OELs are obtained by using specific magnetic assemblies and advantageously exhibit a dynamic appearance upon tilting. Examples of such dynamic OELsinclude reflection zone bars moving as the OEL is tilted, loop-shaped bodies moving as the OEL is tilted, loop-shaped bodies having a varying shape as the OEL is tilted, bright areas and dark areas moving as the OEL is tilted. WO 2012 / 104098 A1 discloses OELs comprising more than one magnetically induced images. WO 2012 / 104098 A1 discloses an OEL comprising two areas, each one exhibiting a reflection zone bar moving as the OEL is tilted, one of said bar moving away the observer upon tilting of the OEL and the other said bar moving towards the observer upon tilting of the OEL.

[0006] Processes for producing OELs comprising at least two areas made of a single cured layer, comprises i) applying on the substrate a UV curable ink comprising magnetic or magnetizable particles so as to form a coating layer; ii) exposing the coating layerto the magnetic field of a magnetic-field-generating device, thereby orienting the pigment particles, iii) curing one or more first areas of the coating layer to a second state so as to fix the magnetic or magnetizable particles in their adopted positions and orientations, said curing being performed by selectively irradiating the coating layer with a radiation source; iv) exposing the coating layer to the magnetic field of a magnetic-field-generating device thereby re-orienting the magnetic or magnetizable particles which are comprised in the coating layer still being in a wet, liquid state and not yet-cured due to the selective curing of step iii) and v) curing the coating layer so as to fix the magnetic or magnetizable particles in their new adopted positions and orientations.

[0007] It is known in the art of curing a coating or ink composition for producing OELs with the help of a UV radiation source, that the characteristics and the construction of the UV irradiation source and the precise exposure conditions of the coating or ink composition to the UV radiation source are crucial for obtaining a high-resolution image and a fast curing of the composition. However, known methods for selective curing suffer from several drawbacks.

[0008] A method includes the use of fixed photomasks including one or more voids corresponding to a pattern to be formed as a part of an image on the coating layer being carried by the fixed substrate is disclosed. However, the disclosed method may result in the potential creation of shadow effects on the coating layer due to the constraints that a) the photomask may not touch the not yet cured ink layer, but must be disposed at a certain distance from it, and that b) the UV-source is necessarily an extended light source. All of these resulting in low-resolution images and require operation at low printing speeds due to the need for keeping in a fixed constellation the substrate, the photomask, and the UV-source during the exposure time. Alternatively, a fixed photomask may be used with a coating layer being carried by a moving substrate. Said method may also result in the production of shadow effects on the coating layer and / or image blurring due to a substrate movement at industrial speeds during exposition to irradiation, without any possibility to implement a variable image information during printing. Alternatively, a moving photomask may be used with a moving substrate. However, said method may also result in the production of shadow effects on the coating layer resulting in a low-resolution imaging and would be highly complex to implement.

[0009] Another method uses laser beams. However, said method is known to require highly special equipments and high costs.

[0010] Another method uses LED Light Emitting Diode (LED) arrays. However, this method may suffer from unnecessary losses of light density resulting in longer curing times and degrading the printing performance.[Oil] Processes for producing OELs comprising at least two areas made of two different inks involve several passes on a printing press such as disclosed in EP 2 433 798 B1 . Said processes comprise i) applying on a substrate a first UV curable ink comprising magnetic or magnetizable pigment particles so as to form a first coating layer; ii) exposing the first coating layer to the magnetic field of a magnetic-field- generating device, thereby orienting the pigment particles, iii) curing the first coating layer to a second state so as to fixthe pigment particles in their adopted positions and orientations, iv) removing the substrate carrying the first coating from the printing press and re-introducing in said press so as to v) apply a second UV curable ink comprising magnetic or magnetizable pigment particles so as to form a second coating layer; vi) exposing the second coating layer to the magnetic field of a magnetic-field-generating device, thereby orienting the pigment particles, and vii) curing the second coating layer to a second state so as to fix the pigment particles in their adopted positions and orientations. Due to the requirement of several passes in the printing press, said processes require a tedious and time-consuming alignment of the substrate priorto the second application step. Since said alignment is highly difficult to control and achieve, a significant amount of optical effect layers suffering from a poor and unacceptable register are obtained thus leading to a high amount of wasted substrates and inks.

[0012] Alternatively, OELs comprising at least two areas made of two different inks may be produced with processes comprising i) applying on a substrate a first UV curable ink comprising magnetic or magnetizable pigment particles so as to form a first coating layer; ii) applying on the substrate a second UV curable ink comprising magnetic or magnetizable pigment particles so as to form a second coating layer, iii) exposing the coating layers to the magnetic field of a magnetic-field-generating device, thereby orienting the pigment particles, iv) curing the first and second coating layers to a second state so as to fix the pigment particles in their adopted positions and orientations. However, said method is extremely complex to be implemented since it implies printing the two inks in a liquid state and requires the printing of the second ink while the first ink is still liquid without disturbing it thus allowing only the preparation of spaced apart coating layers.

[0013] A need remains for improved and controlled processes for producing eye-catching optical effect layers (OELs) for security printers at industrial speed, wherein said so-produced OELs are easily authenticated by the man in the street while said processes are highly difficult to be implemented on a mass-scale production by counterfeiters and the illicit market.SUMMARY OF THE INVENTION

[0014] Accordingly, it is an object of the present invention to overcome the deficiencies of the prior art as discussed above. This is achieved by the provision of a process for producing an optical effect layer (OEL) on a substrate (x10), said optical effect layer (OEL) comprising a first motif comprising magnetically oriented platelet-shaped magnetic or magnetizable pigment particles oriented according to a first magnetic pattern and a second motif comprising magnetically oriented platelet-shaped magnetic or magnetizable pigment particles oriented according to a second magnetic pattern, said process comprising: a first set of steps consisting ofa’) applying onto the first side of the substrate (x10) a first radiation curable coating composition, preferably a first UV-Vis-curable curable coating composition, comprising the platelet-shaped magnetic or magnetizable pigment particles so as to form a first coating layer (x20’) on said first side of the substrate (x10), said coating composition being in a first state, b’) exposing the first radiation curable coating composition of step a’) to a magnetic field of a magnetic assembly (x30’) so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles, the magnetic assembly (x30’) being positioned on the second side of the substrate (x10); c’) at least partially curing the radiation curable coating composition of step b’) to a second state so as to fix the platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and so as to produce the first motif; and a second set of steps consisting of a”) applying onto the second side of the substrate (x10) and in register a second radiation curable coating composition, preferably a second UV-Vis-curable curable coating composition, comprising platelet-shaped magnetic or magnetizable pigment particles so as to form a second coating layer (x20”) on said second side of the substrate (x10), said coating composition being in a first state, and at least a part of the second coating layer (x20”) being adjacent to at least a part of the first coating layer (x20’) b”) exposing the second radiation curable coating composition of step a”) to a magnetic field of a magnetic assembly (x30”), said magnetic assembly (x30”) being the same as the magnetic assembly (x30’) used in step b’) and being positioned on the first side of the substrate (x10) and the magnetic field in step b”) being substantially the same as the magnetic field in step b’) so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles; and c”) at least partially curing the second radiation curable coating composition of step b”) to a second state so as to fix the platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and so as to produce the second motif, wherein the magnetic field of the magnetic assembly (x30’) in step b’) and the magnetic field of the magnetic assembly (x30”) in step b”) are symmetric with respect to a mirror plane which is parallel to the substrate (x10).

[0015] Also described herein are processes for producing OELs comprising the first motif comprising the platelet-shaped magnetic or magnetizable pigment particles oriented according to the first magnetic pattern described herein, the second motif comprising the platelet-shaped magnetic or magnetizable pigment particles oriented according to the second magnetic pattern described herein, and a third motif comprising the platelet-shaped magnetic or magnetizable pigment particles oriented according to a third magnetic pattern, wherein the first, second and third magnetic patterns are different from each other, wherein at least a part of the third motif is adjacent to at least a part of the first motif and in proper register and / or adjacent to at least a part of the second motif and in proper register (i.e. the third motif is at least partially adjacent to and in proper register with the first motif and / or at least partially adjacent to and in proper register with the second motif), and wherein said processes comprise the first set of steps a’), b’) and c’) described herein, the second set of steps a”), b”) and c”) described herein and athird set of steps a’”), b’”) and c’”), said third step a’”) being carried out subsequently to and continuously with step c”).

[0016] Also described herein are optical effect layers (OELs) produced by the process described herein and security documents as well as decorative elements and objects comprising one or more optical OELs described herein.

[0017] Also described herein are methods of manufacturing a security document or a decorative element or object, comprising a) providing a security document or a decorative element or object, and b) providing an optical effect layer obtained by the process described herein, so that it is comprised by the security document or decorative element or object.

[0018] The present invention provides processes advantageously allowing the manufacture of eyecatching optical effect layers (OELs) which are easily authenticated by the man in the street. In particular and thanks to the use of magnetic fields in steps b’) and b”) being substantially symmetric with respect to a mirror plane which is parallel to the substrate (x10), the so-produced OELs comprising the first and second motifs described herein having specific magnetic orientation patterns exhibit a continuous effect at one first viewing angle, said effect originating from the first and second magnetic patterns and consisting of a continuous image extending continuously from the first motif to the second motif, wherein the effect splits upon tilting and recombines to form the same effect upon tilting to come back to the first viewing angle; this highly dynamic effect resulting from the perfect register of not only the applied first and second motifs but also the effect originated from the first and second magnetic patterns allows an easy authentication due to the continuity of said effect at one angle and to the split and recombination upon tilting while combining a high level of counterfeit resistance due to the sophisticated in register adjacent motifs. Thanks to the controlled process described herein and the so-obtained optical effect layers (OELs), authentication of said overt security features allows an observer to easily discriminate against imitations (visually similar result obtained with a different process) as well as against poor reproduction (obtained with the same process but less well controlled).BRIEF DESCRIPTION OF DRAWINGS

[0019] Figs 1-9 provided therein schematically illustrates the present invention and are not true to scale. The optical effect layers (OELs) described herein and their production are now described in more detail with reference to the drawings and to particular embodiments, whereinFig. 1 schematically illustrates the combination of a first motif comprising platelet-shaped magnetic or magnetizable pigment particles oriented according to a first magnetic pattern and a second motif comprising platelet-shaped magnetic or magnetizable pigment particles oriented according to a second magnetic pattern, wherein the first and second motifs are on opposite sides of the substrate (110); furthermore, Fig. 1 schematically illustrate said OEL, wherein the first motif (120’) comprises plateletshaped magnetic or magnetizable pigment particles (P’) oriented according to a first magnetic pattern and the second motif (120”) comprises platelet-shaped magnetic or magnetizable pigment particles (P”) oriented according to a second magnetic pattern, wherein said first and second magnetic patterns are substantially symmetric with respect to a mirror plane which is parallel to the substrate (110).Fig. 2 schematically illustrates a platelet-shaped pigment particle.Fig. 3 schematically illustrates a process for producing an optical effect layer (OEL) on a substrate (310) comprising the first set of steps (1) and the second set of steps (2) according to the present invention while both orientation steps b’) and b”) consist of one-step orientation steps, wherein a substrate (310) carrying on its first side a first coating layer (320’) obtained by screen printing (340’) (step a’)) is exposed to a magnetic field of a magnetic assembly (330’) so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles (step b’)) and wherein the first coating layer (320’) is at least partially cured with a first curing unit (350’) (step c’)), wherein the magnetic assembly (330’) is positioned on the second side of the substrate (i.e. the side lacking the first coating layer (320’)), and wherein subsequently to and continuously with step c’), the substrate (310) carrying on its second side the second coating layer (320”) obtained by screen printing (340”) (step a”)) is exposed to a magnetic field of a magnetic assembly (330”) so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles (step b”) .wherein the second coating layer (320”) is at least partially cured with a second curing unit (350”) (step c”)), wherein the magnetic assembly (330”) is positioned on the first side of the substrate (i.e. the side comprising the first coating layer (320’) in a cured state). Figs 4A-1 and 4A-2 illustrate industrial one-step magnetic orientation steps b) (being steps b’) and b”)), wherein the coating layer (420) is exposed to the magnetic field of a magnetic assembly (430) being either mounted on a rotating magnetic cylinder with the coating layer (420) facing the environment (Fig. 4A-1) or placed outside a rotating cylinder with the coating layer (420) facing said magnetic assembly (430) (Fig. 4A-2).Fig. 4B illustrates an industrial one-step magnetic orientation step b) (b) being b’) and / or b”)), wherein the coating layer (420) is exposed to the resultant magnetic field of a first magnetic assembly (430-a) and of a second magnetic assembly (430-b), wherein said first magnetic assembly (430-a) is mounted on a rotating magnetic cylinder and said second magnetic assembly (430-b) is placed outside the rotating magnetic cylinder.Fig. 5-1 schematically illustrates a process for producing an optical effect layer (OEL) on a substrate (510) comprising the first set of steps (1) and the second set of steps (2) according to the present invention, wherein said process was used in Examples E1-E4 provided therein and wherein both orientation steps b’) and b”) consist of two-steps magnetic orientation steps, wherein a substrate (510) carrying on its first side a first coating layer (520’) obtained by screen printing (540’) (step a’)) is first exposed to a first magnetic field of a magnetic assembly (53O’-a) (step b’-1)) and then subsequently exposed to the magnetic field of a second magnetic field of a magnetic assembly (53O’-b) (step b’-2)) so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles (step b’)) and wherein the coating layer (520’) is at least partially cured with a first curing unit (550’) (step c’)), wherein the magnetic assemblies (53O’-a and 53O’-b) are positioned on the second side of the substrate (i.e. the side lacking the first coating layer (520’)), and wherein subsequently to and continuously with step c’), the substrate (510) carrying on its second side a second coating layer (520”) obtained by screen printing (540”) (step a”)) is first exposed to the magnetic field of a first magnetic field of a magnetic assembly (530”-a) (step b”-1)) and then subsequently exposed tothe magnetic field of a second magnetic field of a magnetic assembly (530”-b) (step b”-2)) so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles (step b”)) and wherein the second coating layer (520”) is at least partially cured with a second curing unit (550”) (step c”)), wherein the magnetic assemblies (530”-a and 530”-b) are positioned on the first side of the substrate (i.e. the side comprising the first coating layer (520’) in a cured state).Fig. 5-2 illustrates an industrial two-steps magnetic orientation step b) (b) being b’) and / or b”)), wherein the coating layer (520) is first exposed to the magnetic field of a first magnetic assembly (530-a) and subsequently to the magnetic field of a second magnetic assembly (530-b), said second magnetic assembly (530-b) being placed on a rotating magnetic cylinder, and wherein the coating layer (520) is at least partially cured with a curing unit (550) (step c)). Fig. 5-3 illustrates an industrial two-steps magnetic orientation step b) (b) being b’) and / or b”)), wherein the coating layer (520) is first exposed to the magnetic field of a first magnetic assembly (530-a) and subsequently to the resultant magnetic field of a second magnetic assembly (530-b) and of a third magnetic assembly (530-c), said second magnetic assembly (530-b) being mounted on a rotating magnetic cylinder and said third magnetic assembly (530- c) being positioned outside said rotating magnetic cylinder, and wherein the coating layer (520) is at least partially cured with a curing unit (550) (step c)).Fig. 6 schematically illustrates a process for producing an optical effect layer (OEL) on a substrate (610) comprising the first set of steps (1) and the second set of steps (2) according to the present invention, wherein both orientation steps b’) and b”) consist of two-steps magnetic orientation steps, wherein a substrate (610) carrying on its first side a first coating layer (620’) obtained by screen printing (640’) (step a’)) is first exposed to the magnetic field of a first magnetic assembly (63O’-a) (step b’-1)) and then subsequently exposed to the resultant magnetic field of a second magnetic assembly (63O’-b) and of a third magnetic assembly (63O’-c) (step b’-2)) so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles (step b’)) and wherein the coating layer (620’) is at least partially cured with a first curing unit (650’) (step c’)), wherein the magnetic assemblies are positioned on the second side of the substrate (i.e. the side lacking the first coating layer (620’)), and wherein subsequently to and continuously with step c’), the substrate (610) carrying on its second side a second coating layer (620”) obtained by screen printing (640”) (step a”)) is first exposed to the magnetic field of a first magnetic assembly (630”-a) (step b”-1)) and then subsequently exposed to the resultant magnetic field of a second magnetic assembly (630”-b) and of a third magnetic assembly (630”-c) (step b”-2)) and wherein the second coating layer (620”) is at least partially cured with a second curing unit (650”) (step c”)), wherein the magnetic assemblies are positioned on the first side of the substrate (i.e. the side comprising the first coating layer (620’) in a cured state).Fig. 7 schematically illustrates a magnetic assembly (730) for bi-axially orienting the pigment particles and used in the Examples provided therein.Fig. 8 schematically illustrates a magnetic assembly (830) used in Examples E1-E2 provided therein and suitable for producing a motif exhibiting a dynamic movement of a reflective bar which splits when the motif is tilted.Fig. 9 schematically illustrates a magnetic assembly (930) used in Examples E3-E4 provided therein and suitable for producing a motif exhibiting a dynamic movement of a multi-loop-shaped body which splits when the motif is tilted.

[0020] The distances provided in the Figures are only illustrative and not true to scale.DETAILED DESCRIPTIONDefinitions

[0021] The following definitions are to be used to interpret the meaning of the terms discussed in the description and recited in the claims.

[0022] As used herein, the indefinite article "a" indicates one as well as more than one and does not necessarily limit its referent noun to the singular.

[0023] As used herein, the term “at least” is meant to define one or more than one, for example one or two or three.

[0024] As used herein, the term “about” means that the amount or value in question may be the specific value designated or some other value in its neighborhood. Generally, the term “about” denoting a certain value is intended to denote a range within ± 5% of the value. As one example, the phrase “about 100” denotes a range of 100 ± 5, i.e. the range from 95 to 105. Generally, when the term “about” is used, it can be expected that similar results or effects according to the invention can be obtained within a range of ±5% of the indicated value.

[0025] As used herein, the term “and / or” means that either all or only one of the elements of said group 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 “only A”, the term also covers the possibility that B is absent, i.e. “only A, but not B”.

[0026] The term “comprising” as used herein is intended to be non-exclusive and open-ended. Thus, for instance a coating composition comprising a compound A may include other compounds besides A. However, the term “comprising” also covers, as a particular embodiment thereof, the more restrictive meanings of “consisting essentially of’ and “consisting of’, so that for instance “a fountain solution comprising A, B and optionally C” may also (essentially) consist of A and B, or (essentially) consist of A, B and C.

[0027] The term “optical effect layer (OEL)” as used herein denotes a coating or layer that comprises oriented platelet-shaped magnetic or magnetizable pigment particles and a binder, wherein said plateletshaped magnetic or magnetizable pigment particles are oriented by a magnetic field and wherein the oriented platelet-shaped magnetic or magnetizable pigment particles are fixed / frozen in their orientation and position (i.e. after hardening / curing) so as to form a magnetically induced image.

[0028] The term "coating composition" refers to any composition which is capable of forming an optical effect layer (OEL) on a solid substrate and which can be applied preferably but not exclusively by a printing method. The coating composition comprises the platelet-shaped magnetic or magnetizable pigment particles described herein and the binder described herein.

[0029] As used herein, the term “wet” refers to a coating layer which is not yet cured, for example a coating in which the platelet-shaped magnetic or magnetizable pigment particles are still able to change their positions and orientations under the influence of external forces acting upon them.

[0030] As used herein, the term “indicia” shall mean discontinuous layers such as patterns, including without limitation symbols, alphanumeric symbols, motifs, letters, words, numbers, logos and drawings.

[0031] The term “curing” is used to denote a process wherein the viscosity of a coating composition in a first physical state which is not yet hardened (i.e. wet) is increased so as to convert it into a second physical state, i.e. a hardened or solid state, where the platelet-shaped magnetic or magnetizable pigment particles are fixed / frozen in their current positions and orientations and can no longer move nor rotate.

[0032] The term "security document" refers to a document which is usually protected against counterfeit or fraud by at least one security feature. Examples of security documents include without limitation value documents and value commercial goods.

[0033] The term “security feature” is used to denote an image, pattern or graphic element that can be used for authentication purposes.

[0034] Where the present description refers to “preferred” embodiments / features, combinations of these “preferred” embodiments / features shall also be deemed as disclosed as long as this combination of “preferred” embodiments / features is technically meaningful.

[0035] The present invention provides processes for producing optical effect layers (OELs) being suitable as security features against counterfeit or fraud and comprising magnetically oriented plateletshaped magnetic or magnetizable pigment particles on substrates. As shown in Fig. 1 , said OELs comprise a first motif (in the form of a cured first coating layer 120’) comprising platelet-shaped magnetic or magnetizable pigment particles oriented according to a first magnetic pattern and a second motif (in the form of a cured second coating layer 120”) comprising platelet-shaped magnetic or magnetizable pigment particles oriented according to a second magnetic pattern, the first and second magnetic patterns being substantially symmetric with respect to a mirror plane which is parallel to the substrate (x10) and wherein said first and second motifs are at least partially adjacent to each other (i.e. the second motif is adjacent to at least a part of the first motif) and in proper register.

[0036] By “first and second magnetic patterns being substantially symmetric with respect to a mirror plane which is parallel to the substrate (x10)” it is intended that the field lines (F1) describing the magnetic field at the surface of the substrate (x10), on the area corresponding to the first motif, and the field lines (F2) describing the magnetic field at the surface of the substrate, on the area corresponding to the second motif, irrespective of their direction, are related to one another by a symmetry operation consisting of a mirror reflection on the plane of the substrate, optionally followed by one or more of the following operations: a translation on the plane of the substrate, a rotation about an axis perpendicular to the substrate, a mirror reflection on a plane perpendicular to the substrate. By “field line”, it is intended an imaginary line tangent to the magnetic field at any given point, and by “irrespective of their direction” it is intended taking into account only the orientation in space of the field lines but not their direction (N- S or S-N). While the reflection on the horizontal plane does not change the shape of the magnetically induced pattern as viewed from a perpendicular observation / illumination direction, it does change the apparent direction of movement of the pattern as the OEL is tilted. Thus, in the case when F1 and F2 are related by a reflection on the plane of the substrate, the OEL exhibits a continuous effect as viewed from a perpendicular direction, with said effect appearing to break apart when the OEL is tilted. When afurther symmetry operation of translation / rotation / reflection is introduced, as described above, the OEL exhibits an effect which has the corresponding additional symmetry, as viewed from a perpendicular direction, and the symmetry breaks upon OEL tilting.

[0037] As shown in Fig. 1 , the first and second motifs (in the form of cured first and second coating layers x20” and x20”) may independently consist of single sub-motifs or may, as shown in Fig. 1 , consist of more than one sub-motifs, said more than one sub-motifs independently forming the first and second motifs, respectively.

[0038] As described herein, the first magnetic pattern of the first motif and the second magnetic pattern of the second motif are obtained by independently exposing the first radiation curable coating composition of step a’) and the second radiation curable coating composition of step a”) to substantially the same magnetic field so as to form the first and second coating layers (x20’ and x20”), respectively. The substantially same magnetic field is preferably obtained by using a same magnetic assembly (same x30’ and x30”) during steps b’) and b”). For example, the process used to prepare the OEL of Example E1 provided therein uses a same magnetic assembly (x30) while the magnetic field is applied on opposite sides of the substrate(x10) in the orientation step b’) and orientation step b”) (see Fig. 5-1) thus leading to two magnetic patterns being substantially symmetric with respect to a mirror plane which is parallel to the substrate (x10). Since the process described herein is a continuous process wherein step a”) is carried out directly after step c’), for embodiments using “a same magnetic assembly” during an industrial process using rotating cylinders, it is meant that a first magnetic assembly (x30’) is used during step b’) and a second magnetic assembly (x30”) is used during step b”), wherein said assemblies are two individual objects and not “the” same object used twice.

[0039] The process described herein comprises at least two sets of steps, i.e. a first set comprising steps a’), b’) and c’) and at least a second set comprising steps a”), b”) and c”). The process described herein is thus a continuous process meaning that the second set of steps is carried out directly after the first set (in other words, the step a”) of the second set is carried out subsequently and directly after step c’) of the first set while the substrate carrying the first coating layer (x20’) is not removed from the printing machine, i.e. is continuously fed, to carry out the second set of steps. In other words, the multi-sets of steps process described herein is a continuous process using a single machine, said machine allowing the application, preferably printing, of coating composition, the exposure of said compositions to magnetic fields and the at least partial curing of said compositions. An example of such a single machine allowing the multi-sets of steps described herein is disclosed in US 2021 / 0316545, said machine comprising in the following order: at least a first printing unit, a first orientation unit, a first curing unit, a second printing unit to downstream apply compositions, a second orientation unit and a second curing unit. As mentioned therein, the process described herein allows the preparation of OELs comprising the first motif and the second motif described herein, said OELs exhibiting a continuous effect as observed by the naked eye at one first viewing angle (as obtained by the use of magnetic fields being symmetric with respect to a mirror plane which is parallel to the substrate (x10)), and said effect originating from the first and second magnetic patterns and consisting of a continuous image extending continuously from the first motif to the second motif, wherein said effect splits upon tilting and recombines to form the same continuous image upon tilting to come back to the first viewing angle; this highly dynamic effectresults from the perfect register of not only the applied first and second motifs but also originated from the first and second magnetic patterns.

[0040] The OEL is seen by an observer at a first viewing angle as a continuous image extending continuously from one motif to the other described herein, wherein said continuous image may or may not be centrally aligned in said OEL, i.e., may or may not be centrally aligned within the combination of the first and second motifs described herein.

[0041] Should the first and / or second motifs described herein independently consist of sub-first-motifs and sub-second-motifs (as shown for example in Fig. 1), the continuous effect / image results from the combination of a plurality or of all sub-motifs.

[0042] Fig. 1 schematically shows the first and second magnetic pattern of an OEL produced by the process described herein, wherein said OEL exhibits a single bar at one first viewing angle and two bars moving in opposite direction when the OEL is tilted; wherein said effect is based on pigment particles orientations independently imitating a curved surface across the coating layers. The OEL exhibiting two bars moving in opposite directions upon tilting comprises the first and second motifs described herein (in the form of the first cured coating layer 120’ and the cured second coating layer 120” on the substrate 110). Thanks to the symmetry of the first and second magnetic patterns with respect to a mirror plane which is parallel to the substrate (110), an observer sees at viewing angles being different from the one at which both bars appear as a single bar one as a bright bar moving in one direction upon tilting and the other as a bright bar moving in the opposite direction upon tilting. In other words, the observer sees one bright bar moving away from said observer upon tilting of the OEL and another one bright bar moving towards said observer upon tilting of the OEL. The observation of a bar which moves away or towards the observer upon tilting of the OEL originates from the specific magnetic orientation patterns of the pigment particles. Two patterns are shown in Fig. 1 : a magnetic orientation pattern comprising particles oriented according to a concave fashion and following a positively curved surface is shown in Fig. 1 for motif 120’ and a magnetic orientation pattern comprising particles oriented according to a convex fashion and following a negatively curved surface is shown in Fig. 1 , motif 120”. The terms “convex fashion” or “convex curvature” and the terms “concave fashion” or “concave curvature” refer to the apparent curvature of the curved surface as seen by an observer (Fig. 1) viewing the OEL from the side of the substrate (110) carrying the first coating layer (120’) (as shown by the eye in Fig. 1). The curvature of the curved surface follows the magnetic field lines produced by the magnetic field-generating device at the position where the OEL is produced. A “convex curvature” refers to a negatively curved magnetic field line (as shown in Fig 1 , motif 120”); a “concave curvature” refers to a positively curved magnetic field line (as shown in Fig 1 , motif 120’). A convex curvature leads to a visual effect characterized by a downward movement of the bright bar when the OEL is tilted backwards and a concave curvature (positive curve orientation) leads to a visual effect characterized by a upward movement of the bright bar when the OEL is tilted backwards.

[0043] The OEL described herein comprises the first and second motifs (i.e. the first and second cured coating layers 120’ and 120”) on opposite sides of the substrate (110), wherein said substrate (110) is preferably transparent, and wherein said first and second motifs are at least partially adjacent to each other (i.e. the second motif is adjacent to at least a part of the first motif) and in proper register so thatan observer sees the OEL as a continuous feature at a first viewing angle in a see-through observation mode or in a transparency observation mode. By “adjacent”, it means that the first and second motifs (first coating layer (x20’) and second coating layer (x20”) have their projections on each side of the substrate (110) (see dotted line in Fig. 1) being contiguous (i.e. they share at least one region together and have a common border). The projections of first and second motifs on each side of the substrate (110) are at least partially adjacent (i.e. the second motif is adjacent to at least a part of the first motif) and in proper register, preferably at least partially juxtaposed and in proper register or at least partially interlaced and in proper register. The first and second motifs may be continuous or discontinuous.

[0044] The process described herein comprises at least two independent steps a’) and a”) consisting of applying onto the first side of the substrate (x10) the first radiation curable coating composition so as to form the first coating layer (x20’) (step a’) and consisting of applying onto the second side of the substrate (x10) (i.e. the side of the substrate(x10) lacking the first coating layer (x20’)) and in register the second radiation curable coating composition so as to form the second coating layer (x20”) (step a”), wherein said first and second radiation curable coating compositions are in a first physical state which allows their application as layers and which are in a not yet hardened (i.e. wet) state wherein the platelet-shaped magnetic or magnetizable pigment particles can move and rotate within the binder material. The process described herein comprises at least two independent steps b’) and b”) consisting of independently exposing the first and second radiation curable coating compositions of step a’) and step a”) to a magnetic field so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles and forming the first and second coating layers (and forming the first and second motifs), the so-obtained first and second motifs having specific magnetic orientation patterns in register, i.e. the process described herein allows to control the position the magnetic assemblies (x30’ and x30”) during step b’) and step b”) so that the effect / image of the OELs described herein is observed at one first viewing angle as an image extending continuously from the first motif to the second motif thus wherein said image splits upon tilting and recombines to form the same effect upon tilting to come back to the first viewing angle thus allowing an easy authentication due to the continuity of said effect at one viewing angle resulting from the perfect register of not only the applied first and second motifs but also the effect originated from the first and second magnetic patterns.

[0045] As mentioned therein, the first and second coating layers (x20’ and x20”) (and the first and second motifs, respectively) are at least partially adjacent to each other (i.e. the second motif is adjacent to at least a part of the first motif) and in proper register, meaning that not only the radiation curable coating composition is applied without or with a very limited (smaller than 1 mm, preferably smaller than 0.5 mm, more preferably smaller than or equal to 0.2 mm) misalignment and misplacement between the second coating layer (x20”) and the first coating layer (x20’) but also that the provided first magnetic pattern and second magnetic patterns of the obtained OEL appear to the naked eye as a continuous layer (i.e. no breakup image) at one first viewing angle. Said register is allowed by the claimed continuous process. According to one embodiment, the first and second coating layers (x20’ and x20”) are within a register of ± 1 mm, preferably ± 0.5 mm and more preferably ± 0.2 mm. Said in register is allowed by the claimed continuous process using a single machine.

[0046] Preferably, said steps a’) and a”) are independently carried out by a printing process, preferablyindependently selected from the group consisting of screen printing, rotogravure printing, flexography printing and intaglio printing (also referred in the art as engraved copper plate printing and engraved steel die printing), more preferably selected from the group consisting of screen printing, rotogravure printing and flexography printing and still more preferably by screen printing.

[0047] Screen printing (also referred in the art as silkscreen printing) is a stencil process wherein an ink is transferred to a surface through a stencil supported by a fine fabric mesh of silk, mono- or multifilaments made of synthetic fibers such as for example polyamides or polyesters or metal threads stretched tightly on a frame made for example of wood or metal (e.g. aluminum or stainless steel). Alternatively, the screen-printing mesh may be a chemically etched, a laser-etched, or a galvanically formed porous metal foil, e.g. a stainless steel foil. The pores of the mesh are blocked in the non-image areas and left open in the image area, the image carrier being called the screen. Screen printing might be of the flat-bed or rotary type. Screen printing is further described for example in The Printing ink manual, R.H. Leach and R.J. Pierce, Springer Edition, 5thEdition, pages 58-62 and in Printing Technology, J.M. Adams and P.A. Dolin, Delmar Thomson Learning, 5thEdition, pages 293-328.

[0048] Rotogravure (also referred in the art as gravure) is a printing process wherein the image elements are engraved into the surface of a cylinder. The non-image areas are at a constant original level. Prior to printing, the entire printing plate (non-printing and printing elements) is inked and flooded with ink. Ink is removed from the non-image by a wiper or a blade before printing, so that ink remains only in the cells. The image is transferred from the cells to the substrate by a pressure typically in the range of 2 to 4 bars and by the adhesive forces between the substrate and the ink. The term rotogravure does not encompass intaglio printing processes (also referred in the art as engraved steel die or copper plate printing processes) which rely for example on a different type of ink. More details are provided in “Handbook of print media”, Helmut Kipphan, Springer Edition, page 48 and in The Printing ink manual, R.H. Leach and R.J. Pierce, Springer Edition, 5thEdition, pages 42-51.

[0049] Flexography preferably uses a unit with a doctor blade, preferably a chambered doctor blade, an anilox roller and plate cylinder. The anilox roller advantageously has small cells whose volume and / or density determines the ink application rate. The doctor blade lies against the anilox roller, and scraps off surplus ink at the same time. The anilox roller transfers the ink to the plate cylinder which finally transfers the ink to the substrate. Specific design might be achieved using a designed photopolymer plate. Plate cylinders can be made from polymeric or elastomeric materials. Polymers are mainly used as photopolymer in plates and sometimes as a seamless coating on a sleeve. Photopolymer plates are made from light-sensitive polymers that are hardened by ultraviolet (UV) light. Photopolymer plates are cut to the required size and placed in an UV light exposure unit. One side of the plate is completely exposed to UV light to harden or cure the base of the plate. The plate is then turned over, a negative of the job is mounted over the uncured side and the plate is further exposed to UV light. This hardens the plate in the image areas. The plate is then processed to remove the unhardened photopolymer from the nonimage areas, which lowers the plate surface in these nonimage areas. After processing, the plate is dried and given a post-exposure dose of UV light to cure the whole plate. Preparation of plate cylinders for flexography is described in Printing Technology, J. M. Adams and P.A. Dolin, Delmar ThomsonLearning, 5thEdition, pages 359-360 and in The Printing ink manual, R.H. Leach and R.J. Pierce, Springer Edition, 5thEdition, pages 33-42.

[0050] The first and second radiation curable coating compositions are independently applied during steps a’) and a”) thus forming the first coating layer (x20’) and the second coating layer (x20”), respectively. The first and second radiation curable coating compositions independently comprise a binder and the platelet-shaped magnetic or magnetizable pigment particles described herein. As shown in Figs 1 , 3, 5 and 6, the first radiation curable coating composition is applied during step a’) on the first side of the substrate (x10) thus forming the first coating layer (x20’) and the second radiation curable coating composition is applied on the second side of the substrate (i.e. the side of the substrate lacking the first coating layer (x20’) in register during step a”) thus forming the second coating layer (x20”).

[0051] According to one embodiment, the first radiation curable coating composition exhibits a color and the second radiation curable coating composition exhibits the same color with the naked eyes. According to one embodiment, the first and second radiation curable coating compositions have different binders but comprise the same platelet-shaped magnetic or magnetizable pigment particles so that they exhibit the same color with the naked eyes. According to another embodiment, the first and second radiation curable coating compositions are the same, i.e. they comprise the same binder and comprise the same platelet-shaped magnetic or magnetizable pigment particles.

[0052] According to one embodiment, the first radiation curable coating composition exhibits a first color and the second radiation curable coating composition exhibits a second color, said second color being different color from the first color as observed with the naked eyes. OELs comprising the first and second motifs of different colors not only exhibit an eye catching effect due to its dynamic effect (continuous effect observed at one first viewing angle, wherein said effect splits upon tilting and recombines to form the same effect upon tilting to come back to the first viewing angle) but also combine a high level of counterfeit resistance due to the sophisticated adjacent motifs of different colors.

[0053] According to one embodiment, the first and second radiation curable coating compositions comprise the same platelet-shaped magnetic or magnetizable pigment particles but comprise a different binder, the binder of the first composition comprising a dye and / or a colorant so that the compositions exhibit a different color with the naked eyes. According to one embodiment, the first and second radiation curable coating compositions comprise the same platelet-shaped magnetic or magnetizable pigment particles but comprise a different binder, the binder of the second composition comprising a dye and / or a colorant so that the compositions exhibit a different color with the naked eyes. According to one embodiment, the first and second radiation curable coating compositions comprise the same plateletshaped magnetic or magnetizable pigment particles but comprise a different binder, the binder of the first composition comprising a dye and / or colorant and the binder of the second composition comprising a dye and / or a colorant having a different color so that the compositions exhibit a different color with the naked eyes. For optically variable platelet-shaped magnetic or magnetizable pigment particles, i.e. pigments exhibiting a different color upon tilting (i.e. exhibiting a face color and a different angle color), “different colors” refer to different face colors or different angle colors or different face and angle colors. According to one embodiment, the first radiation curable coating composition comprises optically variable platelet-shaped magnetic or magnetizable pigment particles having a first face color and a firstangle color and the second radiation curable coating composition comprises optically variable plateletshaped magnetic or magnetizable pigment particles having a second face color and a second angle color, wherein the first face color is different from the second face color and the first angle color is different from the second angle color. According to one embodiment, the first radiation curable coating composition comprises optically variable platelet-shaped magnetic or magnetizable pigment particles having a first face color and a first angle color and the second radiation curable coating composition comprises optically variable platelet-shaped magnetic or magnetizable pigment particles having a second face color and a second angle color, wherein the first face color is the same as the second face color and the first angle color is different from the second angle color. According to one embodiment, the first radiation curable coating composition comprises optically variable platelet-shaped magnetic or magnetizable pigment particles having a first face coIor and a first angle color and the second radiation curable coating composition comprises optically variable platelet-shaped magnetic or magnetizable pigment particles having a second face color and a second angle color, wherein the first face color is different from the second face color and the first angle color is the same as the second angle color.

[0054] The first and second coating compositions described herein as well as the first coating layer (x20’) and the second coating layer (x20”) described herein comprise the platelet-shaped magnetic or magnetizable pigment particles described herein. In contrast to needle-shaped pigment particles which can be considered as quasi one-dimensional particles, platelet-shaped pigment particles are quasi two- dimensional particles due to the large aspect ratio of their dimensions. As shown in Fig. 2, plateletshaped pigment particle can be considered as a two-dimensional structure wherein the dimensions X and Y are substantially larger than the dimension Z. Platelet-shaped pigment particles are also referred in the art as oblate particles or flakes. Such pigment particles may be described with a main axis X corresponding to their longest dimension crossing the pigment particle and a second axis Y perpendicular to X and corresponding to the second longest dimension crossing the pigment particle. In other words, the XY plane roughly defines the plane formed by the first and second longest dimensions of the pigment particle, the Z dimension being ignored.

[0055] The platelet-shaped magnetic or magnetizable pigment particles described herein have, due to their non-spherical shape, non-isotropic reflectivity with respect to incident electromagnetic radiation for which the hardened / cured binder material is at least partially transparent. As used herein, the term “non- isotropic reflectivity” denotes that the proportion of incident radiation from a first angle that is reflected by a particle into a certain (viewing) direction (a second angle) is a function of the orientation of the particles, i.e. that a change of the orientation of the particle with respect to the first angle can lead to a different magnitude of the reflection to the viewing direction.

[0056] In the first and second motifs of the OELs described herein, the platelet-shaped magnetic or magnetizable pigment particles described herein are dispersed in the first and second coating layer (x20’ and x20”), respectively, said layers comprising a hardened binder material that fixes the orientation of the platelet-shaped magnetic or magnetizable pigment particles. The binder material is at least in its hardened or solid state (also referred to as second state herein), at least partially transparent to electromagnetic radiation of a range of wavelengths comprised between 200 nm and 2500 nm, i.e. within the wavelength range which is typically referred to as the “optical spectrum” and which comprisesinfrared, visible and UV portions of the electromagnetic spectrum. Accordingly, the particles contained in the binder material in its hardened or solid state and their orientation-dependent reflectivity can be perceived through the binder material at some wavelengths within this range. Preferably, the hardened binder material is at least partially transparent to electromagnetic radiation of a range of wavelengths comprised between 200 nm and 800 nm, more preferably comprised between 400 nm and 700 nm. Herein, the term “transparent” denotes that the transmission of electromagnetic radiation through a layer of 20 pm of the hardened binder material as present in the OEL (not including the platelet-shaped magnetic or magnetizable pigment particles, but all other optional components of the OEL in case such components are present) is at least 50%, more preferably at least 60 %, even more preferably at least 70%, at the wavelength(s) concerned. This can be determined for example by measuring the transmittance of a test piece of the hardened binder material (not including the platelet-shaped magnetic or magnetizable pigment particles) in accordance with well-established test methods, e.g. DIN 5036-3 (1979-11).

[0057] The platelet-shaped magnetic or magnetizable pigment particles described herein are defined as having, due to their non-spherical shape, non-isotropic reflectivity with respect to an incident electromagnetic radiation for which the cured binder material is at least partially transparent. As used herein, the term “non-isotropic reflectivity” denotes that the proportion of incident radiation from a first angle that is reflected by a particle into a certain (viewing) direction (a second angle) is a function of the orientation of the particles, i.e. that a change of the orientation of the particle with respect to the first angle can lead to a different magnitude of the reflection to the viewing direction. Preferably, the plateletshaped magnetic or magnetizable pigment particles described herein have a non-isotropic reflectivity with respect to incident electromagnetic radiation in some parts or in the complete wavelength range of from about 200 to about 2500 nm, more preferably from about 400 to about 700 nm, such that a change of the particle’s orientation results in a change of reflection by that particle into a certain direction. As known by the man skilled in the art, the magnetic or magnetizable pigment particles described herein are different from conventional pigments, in that said conventional pigment particles exhibit the same color and reflectivity, independent of the particle orientation, whereas the magnetic or magnetizable pigment particles described herein exhibit either a reflection or a color, or both, that depend on the particle orientation.

[0058] The first and second radiation curable coating compositions described herein as well as the first and second coating layers (x20’, x20”) described herein independently comprise the platelet-shaped magnetic or magnetizable pigment particles described herein preferably in an amount from about 1 wt.% and about 40 wt.%, preferably between about 3 wt.% and about 35 wt.%, more preferably between about 5 wt.% and about 30 wt.%, the weight percentages being based on the total weight of the radiation curable coating composition or the coating layer.

[0059] Suitable examples of platelet-shaped magnetic or magnetizable pigment particles described herein include without limitation pigment particles comprising a magnetic metal selected from the group consisting of cobalt (Co), iron (Fe), and nickel (Ni); a magnetic alloy of iron, manganese, cobalt, nickel or a mixture of two or more thereof; a magnetic oxide of chromium, manganese, cobalt, iron, nickel or a mixture of two or more thereof; or a mixture of two or more thereof. The term “magnetic” in reference tothe metals, alloys and oxides is directed to ferromagnetic or ferrimagnetic metals, alloys and oxides. Magnetic oxides of chromium, manganese, cobalt, iron, nickel or a mixture of two or more thereof may be pure or mixed oxides. Examples of magnetic oxides include without limitation iron oxides such as hematite (Fe2Os), magnetite (FesC ), chromium dioxide (CrC>2), magnetic ferrites (MFe2C>4), magnetic spinels (MR2O4), magnetic hexaferrites (MFei2Oi9), magnetic orthoferrites (RFeCh), magnetic garnets MSR2(AO4)3, wherein M stands for two-valent metal, R stands for three-valent metal, and A stands for four-valent metal.

[0060] Examples of platelet-shaped magnetic or magnetizable pigment particles described herein include without limitation pigment particles comprising a magnetic layer M made from one or more of a magnetic metal such as cobalt (Co), iron (Fe), or nickel (Ni); and a magnetic alloy of iron, cobalt or nickel, wherein said magnetic or magnetizable pigment particles may be multilayered structures comprising one or more additional layers. Preferably, the one or more additional layers are layers A independently made from one or more selected from the group consisting of metal fluorides such as magnesium fluoride (MgF2), silicon oxide (SiO), silicon dioxide (SiC>2), titanium oxide (TiC>2), and aluminum oxide (AI2O3), more preferably silicon dioxide (SiC>2); or layers B independently made from one or more selected from the group consisting of metals and metal alloys, preferably selected from the group consisting of reflective metals and reflective metal alloys, and more preferably selected from the group consisting of silver (Ag), aluminum (Al), chromium (Cr), and nickel (Ni), and still more preferably aluminum (Al); or a combination of one or more layers A such as those described hereabove and one or more layers B such as those described hereabove. Typical examples of the platelet-shaped magnetic or magnetizable pigment particles being multilayered structures described hereabove include without limitation A / M multilayer structures, A / M / A multilayer structures, A / M / B multilayer structures, A / B / M / A multilayer structures, A / B / M / B multilayer structures, A / B / M / B / A / multilayer structures, B / M multilayer structures, B / M / B multilayer structures, M / A / M multilayer structures, B / A / M / A multilayer structures, B / A / M / B multilayer structures, B / A / M / B / A multilayer structures, B / A / M / A / B multilayer structures, B / A / B / A / M / A / B / A / B multilayer structures, A / B / A / B / A / M / A / B / A / B / A multilayer structures, wherein the layers A, the magnetic layers M and the layers B are chosen from those described hereabove.

[0061] The UV-Vis radiation curable coating composition described herein may comprise plateletshaped optically variable magnetic or magnetizable pigment particles, and / or platelet-shaped magnetic or magnetizable pigment particles having no optically variable properties. Preferably, at least a part of the platelet-shaped magnetic or magnetizable pigment particles described herein is constituted by platelet-shaped optically variable magnetic or magnetizable pigment particles. In addition to the overt security provided by the colorshifting property of the optically variable magnetic or magnetizable pigment particles, which allows easily detecting, recognizing and / or discriminating an article or security document carrying an ink, coating composition, or coating layer comprising the optically variable magnetic or magnetizable pigment particles described herein from their possible counterfeits using the unaided human senses, the optical properties of the optically variable magnetic or magnetizable pigment particles may also be used as a machine readable tool for the recognition of the OEL. Thus, the optical properties of the 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 and thus increase the counterfeiting resistance.

[0062] The use of platelet-shaped optically variable magnetic or magnetizable pigment particles in coating layers for producing an OEL enhances the significance of the OEL as a security feature in security document applications, because such materials are reserved to the security document printing industry and are not commercially available to the public.

[0063] As mentioned above, preferably at least a part of the platelet-shaped magnetic or magnetizable pigment particles is constituted by platelet-shaped optically variable magnetic or magnetizable pigment particles. These are more preferably selected from the group consisting of platelet-shaped magnetic thin-film interference pigment particles, platelet-shaped interference coated pigment particles.

[0064] Magnetic thin film interference pigment particles are known to those skilled in the art and are disclosed e.g. in US 4,838,648; WO 2002 / 073250 A2; EP 0 686 675 B1 ; WO 2003 / 000801 A2; US 6,838,166; WO 2007 / 131833 A1 ; EP 2 402 401 B1 ; WO 2019 / 103937 A1 ; EP 3 587 500 A1 , EP 3 587 501 A1 , EP 3 587 502 A1 , EP 3 587503 A1 , WO 2020 / 006286 A1 , WO 2020 / 131700 A1 , US 2021 / 0101402, US 2021 / 038812, US 2022 / 0282094, and in the documents cited therein. Preferably, the magnetic thin film interference pigment particles comprise pigment particles having a five-layer 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 and / or pigment particles having a nine-layer Fabry-Perot multilayer structure and / or pigment particles having an elevenlayer Fabry-Perot multilayer structure and / or pigment particles having a multilayer structure combining one or more multilayer Fabry-Perot structures.

[0065] Preferred five-layer Fabry-Perot multilayer structures consist of absorber / dielectric / reflector / dielectric / absorber multilayer structures wherein the reflector and / or the absorber is also a magnetic layer, preferably the reflector and / or the absorber is a magnetic layer comprising nickel, iron and / or cobalt, and / or a magnetic alloy comprising nickel, iron and / or cobalt and / or a magnetic oxide comprising nickel (Ni), iron (Fe) and / or cobalt (Co).

[0066] Further preferred five-layer Fabry-Perot multilayer structures consist of dielec- tric / reflector / magnetic / reflector / dielectric multilayer structures.

[0067] Preferred six-layer Fabry-Perot multilayer structures consist of absorb- er / dielectric / reflector / magnetic / dielectric / absorber multilayer structures.

[0068] Preferred seven-layer Fabry Perot multilayer structures consist of absorb- er / dielectric / reflector / magnetic / reflector / dielectric / absorber multilayer structures such as disclosed in US 4,838,648.

[0069] Preferred nine-layer Fabry-Perot multilayer structures consist of dielec- tric / absorber / dielectric / reflector / magnetic / dielectric / absorber / dielectric multilayer structures.

[0070] Preferred eleven-layer Fabry-Perot multilayer structures consist of absorb- er / dielectric / absorber / dielectric / reflector / magnetic / reflector / dielectric / absorber / dielectric / absorber multilayer structures.

[0071] Preferably, the reflector layers described herein are independently made from one or more selected from the group consisting of metals and metal alloys, preferably selected from the groupconsisting of reflective metals and reflective metal alloys, more preferably selected from the group consisting of aluminum (Al), silver (Ag), copper (Cu), gold (Au), platinum (Pt), tin (Sn), titanium (Ti), palladium (Pd), rhodium (Rh), niobium (Nb), chromium (Cr), nickel (Ni), and alloys thereof, even more preferably selected from the group consisting of aluminum (Al), chromium (Cr), nickel (Ni) and alloys thereof, and still more preferably aluminum (Al). Preferably, the dielectric layers are independently made from one or more selected from the group consisting of metal fluorides such as magnesium fluoride (MgF2), aluminum fluoride (AIF3), cerium fluoride (CeFs), lanthanum fluoride (LaFs), sodium aluminum fluorides (e.g. NasAIFe), neodymium fluoride (NdFs), samarium fluoride (SmFs), barium fluoride (BaF2), calcium fluoride (CaF2), lithium fluoride (LiF), and metal oxides such as silicon oxide (SiO), silicium dioxide (SiC>2), titanium oxide (TiC>2), aluminum oxide (AI2O3), more preferably selected from the group consisting of magnesium fluoride (MgF2) and silicon dioxide (SiC>2) and still more preferably magnesium fluoride (MgF2). Preferably, the absorber layers are independently made from one or more selected from the group consisting of aluminum (Al), silver (Ag), copper (Cu), palladium (Pd), platinum (Pt), titanium (Ti), vanadium (V), iron (Fe) tin (Sn), tungsten (W), molybdenum (Mo), rhodium (Rh), Niobium (Nb), chromium (Cr), nickel (Ni), metal oxides thereof, metal sulfides thereof, metal carbides thereof, and metal alloys thereof, more preferably selected from the group consisting of chromium (Cr), nickel (Ni), metal oxides thereof, and metal alloys thereof, and still more preferably selected from the group consisting of chromium (Cr), nickel (Ni), and metal alloys thereof. Preferably, the magnetic layer comprises nickel (Ni), iron (Fe) and / or cobalt (Co); and / or a magnetic alloy comprising nickel (Ni), iron (Fe) and / or cobalt (Co); and / or a magnetic oxide comprising nickel (Ni), iron (Fe) and / or cobalt (Co). When magnetic thin film interference pigment particles comprising a seven-layer Fabry-Perot structure are preferred, it is particularly preferred that the magnetic thin film interference pigment particles comprise a seven-layer Fabry-Perot absorber / dielectric / reflector / magnetic / reflector / dielectric / absorber multilayer structure consisting of a Cr / MgF2 / AI / M / AI / MgF2 / Cr multilayer structure wherein M is Ni, Fe or Co.

[0072] The magnetic thin film interference pigment particles described herein may be multilayer pigment particles being considered as safe for human health and the environment and being based for example on five-layer Fabry-Perot multilayer structures, six-layer Fabry-Perot multilayer structures, seven-layer Fabry-Perot multilayer structures, nine-layer Fabry-Perot multilayer structures, eleven-layer Fabry-Perot multilayer structures and pigment particles having a multilayer structure combining one or more, or two or more, multilayer Fabry-Perot structures, wherein said pigment particles include one or more magnetic layers comprising a magnetic alloy having a substantially nickel-free composition including about 40 wt.% to about 90 wt.% iron, about 10 wt.% to about 50 wt.% chromium and about 0 wt.% to about 30 wt.% aluminum. Typical examples of multilayer pigment particles being considered as safe for human health and the environment can be found in EP 2 402 401 B1 whose content is hereby incorporated by reference in its entirety.

[0073] Suitable interference coated pigment particles comprising one or more magnetic materials include without limitation structures consisting of a substrate selected from the group consisting of a core coated with one or more layers, wherein at least one of the core or the one or more layers have magnetic properties. For example, suitable interference coated pigment particles comprise a core madeof a magnetic material such as those described hereabove, said core being coated with one or more layers made of one or more metal oxides, or they have a structure consisting of a core made of synthetic or natural micas, layered silicates (e.g. talc, kaolin and sericite), glasses (e.g. borosilicates), silicon dioxides (SiC>2), aluminum oxides (AI2O3), titanium oxides (TiC>2), graphites and mixtures of two or more thereof, said core being coated with one or more magnetic materials. Furthermore, one or more additional layers such as coloring layers may be present.

[0074] The platelet-shaped magnetic or magnetizable pigment particles of the first and second coating layers described herein preferably have a size d50 between about 2 |j.m and about 50 |j.m (as measured by direct optical granulometry).

[0075] The platelet-shaped magnetic or magnetizable pigment particles described herein may be surface treated so as to protect them against any deterioration that may occur in the coating composition and coating layer and / or to facilitate their incorporation in said coating composition and coating layer; typically corrosion inhibitor materials and / or wetting agents may be used.

[0076] Further, subsequently to the independent applications of the first and second radiation curable coating compositions described herein so as to form the first coating layer (x20’) and the second coating layer (x20”) (step a’) and step a”)) described herein, said first and second radiation curable coating compositions of step a’) and step a”) are independently exposed to the magnetic field of a magnetic assembly (x30’, x30”, respectively) so as to independently magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles (step b’) and step b”), respectively).

[0077] The process described herein comprises the at least two independent steps b’) and b”) consisting of exposing the first and second radiation curable coating compositions described herein to the magnetic field of a magnetic assembly (x30’) or magnetic assembly (x30”), respectively, so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles. The magnetic assembly (x30’) used in step b’) and the magnetic assembly (x30”) used in step b”) are same assemblies such as for example two same individual objects when used during an industrial process using rotating cylinders, i.e. so that the first and second magnetic patterns are symmetric magnetic orientation patterns with respect to a mirror plane.

[0078] During the magnetic orientation step b’) and step b”) described herein, the substrate (x10) may be independently disposed on a non-magnetic supporting plate (x70) which is made of one or more nonmagnetic materials.

[0079] As described hereafter, “x30”’ and “x30”” independently either refer to single magnets or refer to assemblies (x30) comprising two or more magnets or refer to assemblies comprising one or more magnets and an engraved magnetic plate, or refer to assemblies comprising one or more magnets and a soft magnetic plate or refers to an assembly comprising a magnet and one or more pole pieces or comprising two or more magnets and one or more pole pieces, said magnetic assemblies (x30’ and “x30”) being selected according to the design of the magnetic orientation patterns of the first and second motifs of the OELs to be produced. Should the magnetic assemblies (x30’ and “x30”) comprise more than one components, the platelet-shaped magnetic or magnetizable pigment particles are exposed to the resultant magnetic field of said more than one components.

[0080] According to one embodiment, the process described herein comprises the magnetic orientationstep b’) and the magnetic orientation step b”) consisting both of a one-step magnetic orientation step, wherein the substrate (x10) carrying on its first side the first coating layer (x20’) is exposed to the magnetic field of the magnetic assembly (x30’) and wherein the substrate (x10) carrying on its second side the second coating layer (x20”) is exposed to the magnetic field of the magnetic assembly (x30”) and wherein both magnetic assemblies (x30’ and x30”) are same assemblies, in particular two same individual objects, so as to produce the first and second magnetic patterns being symmetric with respect to a mirror plane which is parallel to the substrate (x10).

[0081] According to one embodiment, the process described herein comprises the magnetic orientation step b’) and the magnetic orientation step b”) consisting both of a one-step magnetic orientation step, wherein the substrate (x10) carrying on its first side the first coating layer (x20’) is exposed to the magnetic field of the magnetic assembly (x30’) being positioned on the first side of the substrate (i.e. the side comprising the first coating layer (x20’) in a wet state) and wherein the substrate (x10) carrying on its second side the second coating layer (x20”) is exposed to the magnetic field of the magnetic assembly (x30”) being positioned on the second side of the substrate (i.e. the side lacking the first coating layer (x20’) and comprising the second coating layer (x20”) in a wet state) and wherein both magnetic assemblies (x30’ and x30”) are same assemblies, in particular two same individual objects, so as to produce the first and second magnetic patterns being symmetric with respect to a mirror plane which is parallel to the substrate (x10).

[0082] According to one embodiment and as shown in Fig. 3 (not true to scale), the process described herein comprises the first set of steps (1) and the second set of steps (2), wherein both the magnetic orientation step b’) of the first set of steps (1) and the magnetic orientation step b”) of the second set of steps (2) independently are one-step magnetic orientation steps, wherein the substrate (310) carrying on its first side the first coating layer (320’) is exposed to the magnetic field of the magnetic assembly (330’) being positioned on the second side of the substrate (i.e. the side lacking the first coating layer (320’)) and wherein the substrate (310) carrying on its second side the second coating layer (320”) is exposed to the magnetic field of the magnetic assembly (330”) being positioned on the first side of the substrate (i.e. the side comprising the first coating layer (320’) in a cured state) and wherein both magnetic assemblies (330’ and 330”) are same assemblies, in particular two same individual objects, so as to produce the first and second magnetic patterns being symmetric with respect to a mirror plane which is parallel to the substrate (310).

[0083] Fig. 4A-1 (not true to scale) illustrates a process wherein the orientation step b) (being b’) and / or b”) consists of a one-step magnetic orientation step, wherein the radiation curable coating composition described herein is exposed to the magnetic field of a single magnetic assembly (430), wherein said magnetic assembly (430) is mounted on a rotating magnetic cylinder. Fig. 4A-2 (not true to scale) illustrates a process wherein the orientation step b) (being b’) and / or b”)) consists of one-step magnetic orientation step, wherein the radiation curable coating composition described herein is exposed to the magnetic field of a single magnetic assembly (430), wherein said magnetic assembly (430) is arranged in the vicinity of a rotating cylinder.

[0084] As described herein, the process allows the preparation of OELs wherein both the first motif and second motif exhibit in combination at one first viewing angle a continuous effect / image, said effectoriginating from the first and second magnetic orientation patterns and said effect consisting of a image extending continuously from the first motif to the second motif (see for Example E1 wherein the effect due to the specific combination of the first and second motifs consists of a single bar at one first viewing angle, wherein said bar split into two bars moving in opposite direction when the OEL is tilted, i.e. at viewing angles being different from the first viewing angle and see for Example E3, wherein the effect due to the specific combination of the first and second motifs consists of a multi-loop-shaped body at one first viewing angle, wherein said multi-loop-shaped body split into multiple circle segments when the OEL is tilted).

[0085] According to one embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic movement upon tilting said OEL and one or more indicia, wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly (x30) comprising a bar dipole magnet and an engraved magnetic plate, wherein said engraved magnetic plate comprises one or more engravings having the shape of the one or more indicia, wherein the engraved magnetic plate is placed above the bar dipole magnet. The engraved magnetic plate described herein is preferably made from a permanent magnetic powder material and a polymer. The engraved magnetic plate (x30) described herein may typically be produced by an injection molding process or by metal or laser engraving. Preferred permanent magnetic powder materials include cobalt, iron and their alloys, chromium dioxide, generic magnetic oxide spinels, generic magnetic garnets, generic magnetic ferrites including the hexaferrites such as calcium-, strontium-, and barium- hexaferrite (CaFe12019, SrFe12019, BaFe12019, respectively), generic alnico alloys, generic samarium-cobalt (SmCo) alloys, and generic rare-earth- iron-boron alloys (such as NdFeB), as well as the permanent-magnetic chemical derivatives thereof (such as indicated by the term generic) and mixtures thereof. Plates made of a composite material comprising a polymer and a permanent magnetic powder are obtainable from many different sources, such as from Bomatec, Hbri, CH, ARNOLD® Magnetic Technologies (Plastiform®) or from Materiali Magnetici, Albairate, Milano, IT (Plastoferrite).

[0086] According to one embodiment, the process described herein comprises both steps b’) and b”) consisting of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in US 8,025,952 and EP 1 819 525 B1 and WO 2022 / 049024 A1 , wherein this effect is so- called Venetian-blind” effect. Fig. 5A-B of US 7,047,883 discloses a magnetic assembly comprising two spaced apart magnets 84 placed on a magnetic base 62 with their North poles facing the substrate. Fig. 9B of US 7,047,883 discloses a magnetic assembly comprising a magnet 140 and the substrate comprising the coating layer being placed with an offset position relatively the magnet axes. Fig. 9C of US 7,047,883 discloses a magnetic assembly comprising two magnets 142 and one magnet 142' having a diamond-shaped cross section, wherein the two magnets 142 have their North pole facing the substrate while the intervening magnet 142' has its South pole facing the substrate. Fig. 9D of US 7,047,883 discloses a magnetic assembly comprising two magnets 144, and one magnet 144' having roof-shaped, hexagonal, rounded, trapezoidal, or other cross-sections, wherein the two magnets 144 have their North pole facing the substrate while the intervening magnet 144' has its South pole facing the substrate. Fig. 9E of US 7,047,883 discloses a magnetic assembly comprising five magnets, the firstmagnet 142 being a diamond-shaped magnet with its North pole facing the substrate, the second magnet 146 being a rectangular magnet with its South pole facing the substrate, the third magnet 148 being a magnet with rounded top having its North pole facing the substrate, the fourth magnet 150 being a roof-shaped and having its South pole facing the substrate and the fifth magnet 152 being also a roofshaped magnet and having its North pole facing the substrate. Fig. 4A1 of WO 2022 / 049024 A1 discloses a magnetic assembly comprising a bar dipole magnet and the particles are exposed to the magnetic field (magnetic field lines shown as lines with arrows pointing from the North Pole to the South Pole) of the magnetic assembly in one or more areas (shown as a dotted rectangle A) wherein the magnetic field is substantially homogeneous and wherein the magnetic field lines are substantially parallel to each other in said one or more areas. Fig. 4A2 of WO 2022 / 0490241 A discloses a magnetic assembly comprising two bar dipole magnets (M1 , M2) having a same magnetic direction and an iron yoke (Y) and the particles are exposed to the magnetic field (magnetic field lines shown as lines with arrows pointing from the North Pole to the South Pole) of the magnetic assembly in one or more areas (shown as a dotted rectangle A) wherein the magnetic field is substantially homogeneous and wherein the magnetic field lines are substantially parallel to each other in said one or more areas. Fig. 6A-B of WO 2022 / 049024 A1 discloses a magnetic assembly comprising a rectangular assembly comprising two bar dipole magnets (M1 , M2) and two pole pieces (P1 , P2) and the particles are exposed to the magnetic field (magnetic field lines shown as lines with arrows pointing from the North Pole to the South Pole) of the magnetic assembly in one or more areas (shown as a dotted rectangle A) wherein the magnetic field is substantially homogeneous and wherein the magnetic field lines are substantially parallel to each other in said area.

[0087] According to one embodiment shown for example in Fig. 8 (examples E1-E2, magnetic assembly (830) used during step b’) and step b”)), the process described herein allows the preparation of OELs wherein both the first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a bright reflective horizontal bar moving in a vertical direction (up / down) when the OEL is tilted around a horizontal axis; wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a bar dipole magnet having a magnetic axis oriented to be substantially parallel to a substrate and substantially parallel to the machine feed direction. This effect is the so-called “rolling bar” effect, as disclosed in US 2005 / 0106367. A “rolling bar” effect is based on pigment particles orientation imitating a curved surface across the coating. The observer sees a specular reflection zone which moves away or towards the observer as the OEL is tilted.

[0088] According to another embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic along of the OEL being a bright reflective vertical bar moving in a horizontal direction (left / right) when the OEL is tilted around a vertical axis; wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a bar dipole magnet having a magnetic axis oriented to be substantially parallel to the substrate and substantially perpendicular to the machine feed direction. This effect is the so-called “rolling bar” effect, as disclosed in US 2005 / 0106367.

[0089] According to another embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement of the OEL being a bright reflective vertical bar moving in a horizontal (left / right) direction when the OEL is tilted around a horizontal axis; wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2020 / 160993 A1. Figs 2-5 of WO 2020 / 160993 A1 disclose magnetic assemblies comprising a) at least one dipole magnet (x40) being a square-shaped or rectangle-shaped dipole magnet having its magnetic axis oriented to be substantially parallel to a substrate and b) a combination of n sets of spaced apart bar dipole magnets (x30-a1 , x30-a2) with n being an integer equal to or bigger than 1 , wherein each of said bar dipole magnets (x30-a1 , x30-a2) has its North-South magnetic axis substantially parallel to the substrate surface, wherein, for each set of said n sets, the bar dipole magnets (x30-a1 , x30-a2) have their North pole pointing in a same direction and are substantially parallel to each other; wherein the vector sum H1 of the magnetic axes of the bar dipole magnets (x30-a1 , x30-a2) and the vector sum H2 of the at least one dipole magnet (x40) form an angle a in the range from about 5° to about 175° or in the range from about 185° to about 355°; wherein the combination of n sets of spaced apart bar dipole magnets (x30-a1 , x30-a2) is placed below or above the at least one dipole magnet (x40), and wherein the at least one dipole magnet (x40) and the combination of n sets of spaced apart bar dipole magnets (x30-b1 , x30-b2) are essentially centered with respect to one another.

[0090] According to another embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement of the OEL being a bright reflective horizontal bar moving in a vertical direction (up / down) when the OEL is tilted around a horizontal axis ; wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2014 / 198905 A2. Figs 5-9 of WO 2014 / 198905 A2 disclose magnetic assemblies comprising: 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 axis substantially parallel to the substrate and the same magnetic North-South direction, wherein a1) said bar dipole magnet (M1) is disposed below the substrate and said pair of bar dipole magnets (M2) and (M3) are disposed below the bar dipole magnet (M1) apart from each other; or a2) said pair of bar dipole magnets (M2) and (M3) are disposed below the substrate and apart from each other, and said bar dipole magnet (M1) is disposed below said pair of bar dipole magnets (M2) and (M3); or b) a pair of bar dipole magnets (M4) and (M5) and a pole piece (Y), said pair of bar dipole magnets (M4) and (M5) having their North-South axis substantially parallel to the substrate and the same magnetic North-South direction, said pole piece (Y) being 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 axis substantially parallel to the substrate and the same magnetic North-South direction, said magnetic plate (M6) having its North-South axis substantially perpendicular to the substrate, said pole piece (Y) being disposed between said bar dipolemagnet (M4) and said bar dipole magnet (M5). Particularly suitable magnetic assemblies are those shown in Figs 5c, 6c and 7d of WO 2014 / 198905 A2.

[0091] According to one embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a pattern of bright areas and dark areas moving when the OEL is tilted; wherein said at least one of steps b’) and b”) consists of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2013 / 167425 A1 and WO 2021 / 083809 A1. Disclosed magnetic assemblies of WO 2021 / 083809 A1 comprise at least one dipole magnet (x41) having a magnetic axis oriented to be substantially parallel to the substrate and a combination comprising at least four additional dipole magnets (x31) having their North poles pointing in a same direction and having their magnetic axes oriented to be substantially parallel to the substrate, wherein each of the additional dipole magnets (x31) is arranged on an intersection of at least two substantially parallel straight lines oci (i = 1 , 2, ...) and at least two substantially parallel straight lines ft (j = 1 , 2, ...), the straight lines eq and ft forming a grid, wherein at least two additional dipole magnets (x31) are disposed on one of the straight lines eq and at least two other additional dipole magnets (x31) are disposed on another one of the straight lines oq , wherein the magnetic axes of the additional dipole magnets are oriented substantially parallel to the substantially parallel straight lines oq, wherein the at least one dipole magnet (x41) is disposed below the combination comprising at least four dipole magnets (x31). According to one embodiment, each straight line oq and a vector H of the magnetic axis of the at least one dipole magnet (x41) is substantially parallel or substantially perpendicular with respect to each other and the OEL exhibits a dynamic movement being a pattern of bright areas and dark areas moving when the substrate carrying said OEL is tilted, said pattern of bright areas and dark areas moving in the same direction as the tilting direction. According to another embodiment, each straight line oq and a vector H of the magnetic axis of the at least one dipole magnet (x40) is substantially non-parallel and substantially non-perpendicular with respect to each other OEL, preferably wherein each straight line oq and the vector sum H of the magnetic axis of the at least one dipole magnet (x41) form an angle y in the range from about 20° to about 70° or in the range from about 110° to about 160° or in the range from about 200° to about 250°, or in the range from about 290° to about 340°; and the OEL exhibits a dynamic movement being a pattern of bright areas and dark areas moving not only in a diagonal direction when the substrate carrying said OEL is tilted around a vertical / longitudinal axis but also moving in a diagonal direction when the substrate carrying said OEL is tilted around a horizontal / latitudinal axis (in other words, the optical effect layer OEL described herein provides the optical impression of a plurality of dark and a plurality of bright spots that are moving when the substrate carrying said OEL is tilted around two perpendicular axes, i.e. horizontal / latitudinal axis and vertical / longitudinal axis. Suitable magnetic assemblies are those shown in Figs 6-8 of WO 2021 / 083809 A1.

[0092] According to one embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a pattern of bright areas and dark areas moving when the OEL is tilted; wherein said at least one of steps b’) and b”) consists of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2021 / 083808 A1. Disclosedmagnetic assemblies of WO 2021 / 083808 A1 comprise at least one dipole magnet (x41) having a magnetic axis oriented to be substantially parallel to the substrate and a combination comprising at least four additional dipole magnets (x31) having their North poles pointing in a same direction and having their magnetic axes oriented to be substantially parallel to the substrate, wherein each of the additional dipole magnets (x31) is arranged on an intersection of at least two substantially parallel straight lines cq (i = 1 , 2, ...) and at least two substantially parallel straight lines ft (j = 1 , 2, ...), the straight lines cq and ft forming a grid, wherein at least two additional dipole magnets (x31) are disposed on one of the straight lines eq and at least two other additional dipole magnets (x31) are disposed on another one of the straight lines ai , wherein the magnetic axes of the additional dipole magnets (x31) are oriented substantially parallel to the substrate, straight lines ai, wherein the at least one dipole magnet (x41) is disposed below the combination comprising at least four first dipole magnets (x31), wherein, on each straight line i, and on each straight line ft, neighboring additional dipole magnets (x31) have their North pole pointing in an opposite direction, wherein each straight line ai and a vector H of the magnetic axis of the at least one dipole magnet (x41) is substantially non-parallel and substantially non-perpendicular with respect to each other OEL, preferably wherein each straight line ai and the vector sum H of the magnetic axis of the at least one dipole magnet (x41) form an angle y in the range from about 20° to about 70° or in the range from about 110° to about 160° or in the range from about 200° to about 250°, or in the range from about 290° to about 340°; and the OEL exhibits a dynamic movement being a pattern of bright areas and dark areas moving not only in a diagonal direction when the substrate carrying said OEL is tilted around a vertical / longitudinal axis but also moving in a diagonal direction when the substrate carrying said OEL is tilted around a horizontal / latitudinal axis (in other words, the optical effect layer OEL described herein provides the optical impression of a plurality of dark and a plurality of bright spots that are moving when the substrate carrying said OEL is tilted around two perpendicular axes, i.e. horizontal / latitudinal axis and vertical / longitudinal axis). Suitable magnetic assemblies are those shown in Figs 5-7 of WO 2021 / 083808 A1.

[0093] According to one embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a loop-shaped body moving when the OEL is tilted; wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2014 / 108404 A2. The disclosed magnetic assemblies of WO 2014 / 108404 A2 comprise either a) at least one dipole magnet having a magnetic axis oriented to be substantially perpendicular to the substrate and one or more pole pieces, said one or more pole pieces being disposed below the at least one dipole magnet and in contact with the dipole magnet and / or being spaced apart from and laterally surrounding the at least one dipole magnet (see for example Figs 3-5 of WO 2014 / 108404 A2); b) the at least one dipole magnet being a loop-shaped magnet having a radial magnetization (i.e. having its magnetic North-South axis radially extending from the center of the loopshaped magnet to the periphery) (see for example Fig. 6 of WO 2014 / 108404 A2); or c) the at least one dipole magnet being three or more dipole magnets disposed in a loop-shaped arrangement having a radial magnetization (i.e. each of said three or more dipole magnets has its magnetic axis oriented to be substantially parallel to the substrate and has its magnetic axis aligned such as to be substantiallyradially extending from the center of symmetry of the loop-shaped arrangement, wherein the North- South directions of said three or more dipole magnets point either all towards or all away from the center of symmetry (see for example Fig. 7 of WO 2014 / 108404 A2). WO 2014 / 108404 A2 also disclose spinneable magnetic assemblies comprising a) at least two bar dipole magnets having their magnetic axis substantially parallel to the substrate and having either the same magnetic direction (Fig. 9) or an opposite magnetic direction (see Fig 11 of WO 2014 / 108404 A2) or comprising b) at least two bar dipole magnets having their magnetic axis substantially perpendicular to the substrate and having an opposite magnetic direction (see Fig. 10 of WO 2014 / 108404 A2).

[0094] According to one embodiment shown for example in Fig. 9 (examples E3-E4, magnetic assembly (930) used during step b’) and step b”)), the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a multi-loop-shaped body moving when the OEL is tilted; wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2014 / 108303 A2. Disclosed magnetic assemblies of WO 2014 / 108303 A2 comprise one of the following: a) at least one dipole magnet being a loop-shaped magnet defining a loop and having a magnetic axis oriented to be substantially perpendicular to the substrate and a pole piece (x60) being disposed below the at least one dipole magnet and within the loop of said at least one dipole magnet and having one or more protrusions disposed within the loop of the at least one dipole magnet (see for example Figs 3-5 of WO 2014 / 108303 A2); or b) at least one dipole magnet having a magnetic axis oriented to be substantially perpendicular to the substrate, an additional dipole magnet having a magnetic axis oriented to be substantially perpendicular to the substrate and two or more pole pieces, wherein said at least one dipole magnet and additional magnet have the same magnetic direction and are provided in different distances from substrate, wherein said two or more pole pieces are arranged in the space between the magnets and in contact therewith and wherein at least one of the two or more pole pieces form one or more loop-shaped projections surrounding a central area in which the at least one dipole magnet is arranged (see for example Fig. 6 of WO 2014 / 108303 A2); or c) at least one dipole magnet having a magnetic axis oriented to be substantially perpendicular to the substrate, a plate-like-shaped pole piece being disposed below and in contact with the at least one dipole magnet, and one or more loop-shaped pole pieces being disposed on top the at least one dipole magnet, wherein a central pole piece of said one or more loop-shaped pole pieces is in contact with the at least one dipole magnet, and wherein said plate-like-shaped pole piece may comprise one or more protrusions spaced apart and laterally surrounding the at least one dipole magnet (see for example Figs 7 of WO 2014 / 108303 A2). WO 2014 / 108303 A2 also disclose spinneable magnetic assemblies comprising a) at least two bar dipole magnets having their magnetic axis substantially perpendicular to the substrate (see Figs 8-10 and 13-14 of WO 2014 / 108303 A2) or comprising b) at least four bar dipole magnets having their magnetic axis substantially parallel to the substrate (see Figs 11 , 12 and 15 of WO 2014 / 108303 A2).

[0095] According to one embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a loop-shaped body having a size that varies when the OEL is tilted; wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2017 / 064052 A1 , WO 2017 / 080698 A1 and WO 2017 / 148789 A1. Disclosed magnetic assemblies of WO 2017 / 064052 A1 , WO 2017 / 080698 A1 and WO 2017 / 148789 A1 comprise one of the following:- a) at least one dipole magnet (x40) being either a single bar dipole magnet having a North-South magnetic axis substantially parallel to a substrate or a combination of two or more bar dipole magnets having a resulting North-South magnetic axis substantially parallel to the substrate and b) a loop-shaped magnetic-field generating device (x30) being either a single loop-shaped dipole magnet having a North- South magnetic axis substantially perpendicular to the substrate or a combination of two or more dipole magnets disposed in a loop-shaped arrangement and having a resulting North-South magnetic axis substantially perpendicular to the substrate (see for example Figs 1-4 of WO 2017 / 064052 A1), or- a) at least one dipole magnet (x40) being either a single dipole magnet having a magnetic axis substantially parallel to the substrate or a combination of two or more bar dipole magnets, each of the two or more bar dipole magnets having a magnetic axis substantially parallel to the substrate and having a same magnetic field direction, b) a loop-shaped magnetic-field generating device (x31) being either a single loop-shaped dipole magnet having a magnetic axis substantially perpendicular to the substrate or a combination of two or more dipole magnets disposed in a loop-shaped arrangement, each of the two or more dipole magnets having a magnetic axis substantially perpendicular to the substrate and having a same magnetic field direction, and c) a single dipole magnet (x32) having a magnetic axis substantially perpendicular to the substrate or two or more dipole magnets, each of the two or more dipole magnets having a magnetic axis substantially perpendicular to the substrate and having a same magnetic field direction and / or one or more pole pieces (see for example Figs 1-12 of WO 2017 / 080698 A1), or- a) at least one dipole magnet (x40) being either a single bar dipole magnet having a magnetic axis substantially parallel to the substrate or a combination of two or more bar dipole magnets, each of the two or more bar dipole magnets having a magnetic axis substantially parallel to the substrate and having a same magnetic field direction, b) a loop-shaped magnetic-field generating device (x31) being either a single loop-shaped magnet or a combination of two or more dipole magnets (x31), disposed in a loopshaped arrangement, the loop-shaped magnetic-field generating device having a radial magnetization, and c) a single dipole magnet (x32) having a magnetic axis substantially perpendicular to the substrate or a single dipole magnet having a magnetic axis substantially parallel to the substrate (x32), or two or more dipole magnets (x32), each of said two or more dipole magnets (x32) having a magnetic axis substantially perpendicular to the substrate, wherein the North pole of said single dipole magnet (x32) or the North pole of at least one of said two or more dipole magnets (x32) is pointing towards the substrate when the North pole of the single loop-shaped magnet (x31) or of the two or more dipole magnets (x31) forming the loop-shaped magnetic-field generating device is pointing towards the periphery of said loop-shaped magnetic-field generating device, or wherein the South pole of said singledipole magnet (x32) or the South pole of at least one of said two or more dipole magnets (x32) is pointing towards the substrate when the South pole of the single loop-shaped magnet (x31) or of the two or more dipole magnets (x31) forming the loop-shaped magnetic-field generating device is pointing towards the periphery of said loop-shaped magnetic-field generating device (x31) (see for example Figs 1-14 of WO 2017 / 148789 A1).

[0096] According to one embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a loop-shaped body having a shape that varies when the OEL is tilted; wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2018 / 054819 A1 . In particular, the disclosed magnetic assembly of WO 2018 / 054819 A1 comprises a loop-shaped magnetic-field generating device (x31) being either a single loop-shaped magnet (x31) or a combination of two or more dipole magnets (x31) disposed in a loop-shaped arrangement, the loop-shaped magnetic-field generating device (x31) having a radial magnetization; and a single dipole magnet (x32) having a magnetic axis substantially perpendicular to the substrate surface or two or more dipole magnets (x32), each of said two or more dipole magnets (x32) having a magnetic axis substantially perpendicular to the substrate surface, wherein the single dipole magnet (x32) or the two or more dipole magnets (x32) are located partially within, within or above the loop defined by the single loop-shaped magnet (x31) or partially within, within or above the loop defined by the two or more dipole magnets (x31) disposed in the loop-shaped arrangement, and wherein the South pole of said single dipole magnet (x32) or the South pole of each of said two or more dipole magnets (x32) is pointing towards the substrate surface when the North pole of the single loop-shaped magnet (x31) or of the two or more dipole magnets (x31) forming the loop-shaped magnetic-field generating device (x31) is pointing towards the periphery of said loop-shaped magnetic-field generating device (x31) or the North pole of said single dipole magnet (x32) or the North pole of each said two or more dipole magnets (x32) is pointing towards the substrate surface when the South pole of the single loop-shaped magnet (x31) or of the two or more dipole magnets (x31) forming the loop-shaped magnetic-field generating device (x31) is pointing towards the periphery of said loop-shaped magnetic-field generating device (x31).

[0097] According to one embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a moon crescent moving and rotating when the OEL is tilted; wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2019 / 215148 A1. Disclosed magnetic assemblies of WO 2019 / 215148 A1 comprise a) a first magnetic-field generating device (x30) having its North-South magnetic axis substantially perpendicular to the substrate surface and having length L1 , b) a second magnetic-field generating device (x40) having its North-South magnetic axis substantially perpendicular to the substrate and having a length L3, and c) a flat pole piece (x50) lacking any protrusions or projections extending outside the surface of said pole piece and having a length L5, wherein the first magnetic-field generating device and the second magnetic-field generating device have a same magnetic field direction, wherein the first magnetic-field generating device faces the substrate and isdisposed above the flat pole piece), wherein the second magnetic-field generating device faces the environment and is disposed below the flat pole piece, wherein the length L1 of the first magnetic-field generating device is smaller than the length L3 of the second magnetic-field generating device, wherein the length L1 of the first magnetic-field generating device is smaller than the length L5 of the flat pole piece, and wherein the length L3 of the second magnetic-field generating device is smaller than the length L5 of the pole piece (see for example Figs 1-12 of WO 2017 / 148789 A1).

[0098] According to one embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a loop-shaped body surrounded by a substantially loop-shaped body having their shape and / or their brightness varying when the OEL is tilted; wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2020 / 193009 A1. Disclosed magnetic assemblies of WO 2020 / 193009 A1 comprise a) a combination of three or more first dipole magnets (x31-ai), each of said first dipole magnets having its center disposed on a loop in a plane parallel to the substrate, wherein said first dipole magnets (x31-ai) have their magnetic axes oriented to be substantially parallel to the substrate and b) at least one second dipole magnet (x41) having its magnetic axis oriented to be substantially perpendicular to the substrate and being arranged to have a projection of its center on the substrate be located at a projection point within the loop, wherein the at least one second dipole magnet (x41) is disposed above the combination of three or more first dipole magnets (x31-ai), wherein angles eq are formed between each of the vectors Cx41Cx31-ai(Cx41Cx31-al, Cx41Cx31-a2, Cx41Cx31-a3) and the vector hx31-ai(hx3 ! -a !, hx31-a2, hx31-a3, ...) of the magnetic axis of the respective first dipole magnet magnets (x31-ai), wherein all of the angles eq, when measured in a counterclockwise direction, are in a range from about 20° to about 160° or in a range from about 200° to about 340°, and wherein each of the first dipole magnets (x31-ai) is disposed at a first distance (Y), said first distance (Y being on the substrate between the projection point and the center of the first dipole magnet (x31-ai) (see for example Figs 2- 9 of in WO 2020 / 193009 A1).

[0099] According to one embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a change from dark to light of two areas when the OEL is tilted (effect so-called flip-flop); wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in Figs 1 , 3 and 6 of US 2005 / 0106367.

[0100] According to one embodiment, the process described herein allows the preparation of OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a comet-shaped spot rotating around said center of rotation upon tilting said OEL, wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2019 / 038371 A1 , WO 2019 / 038370 A1 and WO 2019 / 038369 A1. Disclosed magnetic assemblies of WO 2019 / 038371 A1 , WO 2019 / 038370 A1 and WO 2019 / 038369 A1 comprise at least one of the following:- a) first magnetic-field generating device (x30) and b) a second magnetic-field generating device (x40),wherein said first magnetic-field generating device (x30) and said second magnetic-field generating device (x40) have mutually skew magnetic axes, wherein said first magnetic-field generating device (x30) has its magnetic axis substantially perpendicular to the axis of spinning and said second magnetic- field generating device (x40) has its magnetic axis substantially perpendicular to the axis of spinning and wherein the projection of the magnetic axis of the first magnetic-field generating device (x30) and the projection of the magnetic axis of the second magnetic-field generating device (x40) along the axis of spinning onto a plane perpendicular to the axis of spinning form an angle (Q) either in the range from about 5° to about 175° or in the range from about -5° to about -175°, and wherein the first magnetic- field generating device (x30) comprises a bar dipole magnet having its North-South magnetic axis substantially perpendicular to the axis of spinning, or two or more bar dipole magnets, each of said two or more bar dipole magnets having its North-South magnetic axis substantially perpendicular to the axis of spinning and all of said two or more bar dipole magnets having a same magnetic field direction, or a loop-shaped dipole magnet having its North-South magnetic axis substantially perpendicular to the axis of spinning, or a disc-shaped dipole magnet being nested inside a loop-shaped dipole magnet, each of the disc-shaped dipole magnet and the loop-shaped dipole magnets having their North-South magnetic axis substantially perpendicular to the axis of spinning and having a same magnetic field direction, or two or more nested loop-shaped dipole magnets, each of said two or more nested loop-shaped dipole magnets, having its North-South magnetic axis substantially perpendicular to the axis of spinning and all of said two or more nested ring-shaped magnets having a same magnetic field direction; and wherein the second magnetic-field generating device (x40) comprises a disc-shaped dipole magnet having its North-South magnetic axis substantially perpendicular to the axis of spinning, or a loop-shaped dipole magnet having its North-South magnetic axis substantially perpendicular to the axis of spinning, or a bar dipole magnet having its North-South magnetic axis substantially perpendicular to the axis of spinning;- a first magnetic-field generating device (x30) and b) a second magnetic-field generating device (x40), wherein the first magnetic-field generating device (x30) comprises at least one pair of two bar dipole magnets (x31) at least partially or fully embedded in a supporting matrix (x32), each of said bar dipole magnets (x31) having its North-South magnetic axis substantially parallel to the axis of spinning, said two bar dipole magnets (x31) of the at least one pair having opposite magnetic field directions and being arranged in a symmetric configuration around the axis of spinning along a line (a), and the second magnetic-field generating device (x40) comprises b1) a disc-shaped dipole magnet (x41) having its North-South magnetic axis substantially perpendicular to the axis of spinning, b2) a loopshaped dipole magnet (x41) having its North-South magnetic axis substantially perpendicular to the axis of spinning, b3) a bar dipole magnet (x41) having its North-South magnetic axis substantially perpendicular to the axis of spinning and arranged on the axis of spinning, and / or b4) at least one pair of two bar dipole magnets (x41), each of said bar dipole magnets (x41) having its North-South magnetic axis substantially parallel to the axis of spinning, said two bar dipole magnets (x41) of the at least one pair having opposite magnetic field directions and being arranged in a symmetric configuration around the axis of spinning along a line (P), wherein the projection of the line (a) where the bar dipole magnetsprojection of the magnetic axis of the second magnetic-field generating device (x40) form along the axis of spinning onto a plane perpendicular to the axis of spinning an angle (Q) either in the range from about 5° to about 175° or in the range from about -5° to about -175°; or- a magnetic-field generating device (x30) comprising a disc-shaped dipole magnet (x31) having its North-South magnetic axis substantially perpendicular to the axis of spinning, or a loop-shaped, preferably a ring-shaped, dipole magnet (x31) having its North-South magnetic axis substantially perpendicular to the axis of spinning, or a bar dipole magnet (x31) having its North-South magnetic axis substantially perpendicular to the axis of spinning and arranged on the axis of spinning, wherein the disc-shaped dipole magnet (x31), the loop-shaped, preferably the ring-shaped, dipole magnet (x31) or the bar dipole magnet (x31) of the magnetic-field generating device (x30) comprises at least one pair of indentations (I) and / or at least one pair of voids (V) and / or at least one pair of protrusions (P), wherein the indentations (I) of the at least one pair, the voids (V) of the at least one pair and / or the protrusions (P) of the at least one pair are located: symmetrically about the axis of spinning, and asymmetrically with respect to a mirror plane which is perpendicularto the North-South magnetic axis of the disc-shaped dipole magnet (x31), the loop-shaped, preferably the ring-shaped, dipole magnet (x31) or the bar dipole magnet (x31) of the magnetic-field generating device (x30) and which contains the axis of spinning.

[0101] According to one embodiment, the process described herein allows the preparation of OELs, wherein both steps b’) and b”) consist of independently exposing the radiation curable coating composition to the resultant magnetic field of a combination of a magnetic assembly described hereafter for bi-axially orienting pigment particles and a soft magnetic plate comprising one or more indentations (I) and / or one or more voids (V) and / or one or more protrusions (P). The soft magnetic plate described herein comprises one or more soft magnetic materials, i.e. materials having a low coercivity and a high permeability p. Their coercivity is lower than 1000 Am-1as measured according to IEC 60404-1 :2000, to allow for a fast magnetization and demagnetization. Suitable soft magnetic materials have a maximum relative permeability / ZRmax of at least 5, where the relative permeability / ZR is the permeability of the material p relative to the permeability of the free space po ( / ZR = p / po) (Magnetic Materials, Fundamentals and Applications, 2ndEd., Nicola A. Spaldin, p. 16-17, Cambridge University Press, 2011). Soft magnetic materials are described, for example, in the following handbooks: (1) Handbook of Condensed Matter and Materials Data, Chap. 4.3.2, Soft Magnetic Materials, p. 758-793, and Chap. 4.3. 4, Magnetic Oxides, p. 811-813, Springer 2005; (2) Ferromagnetic Materials, Vol. 1 , Iron, Cobalt and Nickel, p. 1-70, Elsevier 1999; (3) Ferromagnetic Materials, Vol. 2, Chap. 2, Soft Magnetic Metallic Materials, p. 55-188, and Chap. 3, Ferrites for non-microwave Applications, p. 189-241 , Elsevier 1999; (4) Electric and Magnetic Properties of Metals, C. Moosbrugger, Chap. 8, Magnetically Soft Materials, p. 196-209, ASM International, 2000; (5) Handbook of modern Ferromagnetic Materials, Chap. 9, High- permeability High-frequency Metal Strip, p. 155-182, Kluwer Academic Publishers, 2002; and (6) Smithells Metals Reference Book, Chap. 20.3, Magnetically Soft Materials, p. 20-9 - 20-16, Butterworth- Heinemann Ltd, 1992. The soft magnetic plate described herein may either be a plate made of one or more metals, alloys or compounds of high magnetic permeability (hereafter referred as “soft magnetic metal plate”) or a plate made of a composite comprising soft magnetic particles dispersed in a nonmagnetic material (hereafter referred as “soft magnetic composite plate”). According to oneembodiment, the soft magnetic metal plate described herein is made of one or more soft magnetic metals or alloys easily workable as sheets or threads. Preferably, the soft magnetic metal plate described herein is made from one or more materials selected from the group consisting of iron, cobalt, nickel, nickel-molybdenum alloys, nickel-iron alloys (permalloy or supermalloy-type materials), cobaltiron alloys, cobalt-nickels alloys iron-nickel-cobalt alloys (Fernico-type materials), Heusler-type alloys (such as Cu2MnSn or Ni2MnAI), low silicon steels, low carbon steels, silicon irons (electrical steels), ironaluminum alloys, iron-aluminum-silicon alloys, amorphous metal alloys (e.g. alloys like Metglas®, ironboron alloys), nanocrystalline soft magnetic materials (e.g. Vitroperm®) and combinations thereof, more preferably selected from the group consisting of iron, cobalt, nickel, low carbon steels, silicon irons, nickel-iron alloys and cobalt-iron alloys and combinations thereof.

[0102] Fig. 4B illustrates a process wherein the orientation step b) (steps b’) and / or b”)) independently consist of one-step magnetic orientation steps, wherein an assembly comprising the substrate (410) comprising the coating layer (420) described herein is placed on a first magnetic assembly (430-a) and said assembly is concomitantly moved in the vicinity of a static second magnetic assembly (430-b), wherein said first magnetic assembly (430-a) is mounted on a transferring device being a rotating magnetic cylinder and the second magnetic assembly (430-b) is arranged in vicinity of said rotating magnetic cylinder. According to one embodiment shown for example in Fig. 4B, the process described herein allows the preparation of OELs, wherein both step b) (steps b’) and / or b’)’) independently consist of placing the substrate (410) carrying the radiation curable coating composition in the form of the coating layer (420) on a first magnetic assembly (430-a) providing a first magnetic field vector component, said first magnetic assembly being mounted on a rotating magnetic cylinder thereby subjecting the platelet-shaped magnetic or magnetizable pigment particles to said first magnetic field vector component and concomitantly moving said substrate (410) carrying the coating layer (420) and said first magnetic assembly (430-a) in the vicinity of a static second magnetic assembly (430-b), said second magnetic assembly (430-b), providing a second magnetic field vector component, thereby subjecting the platelet-shaped magnetic or magnetizable pigment particles to a time-dependent resultant magnetic field formed by the first and second magnetic field vector components so as to bi- axially orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles. According to one embodiment, the ratio of the magnetic flux density of the first magnetic assembly (430- a) and the magnetic flux density of the static second magnetic assembly (430-b) is less than about 4.0, preferably less than about 1 .9 and more preferably between about 1 .5 and about 0.5. The first magnetic assembly (430-a) onto which the substrate (410) carrying the coating layer (420) is exposed preferably selected from the magnetic assemblies described hereabove for mono-axially orienting pigment particles and the soft magnetic plates described hereabove. The second magnetic assembly (430-b) is preferably selected from the magnetic assemblies described hereabove for bi-axially orienting pigment particles. Such processes are disclosed in WO 2019 / 14142 A1 and WO 2019 / 141453 A1.

[0103] According to one embodiment shown for example in Fig. 5-1 and used in the Examples E1-E4 provided therein, the process described herein comprises the first set of steps (1) and the second set of steps (2), wherein the magnetic orientation step b’) of the first set of steps (1) and the magnetic orientation step b”) of the second set of steps (2) independently consist of two-steps magneticorientation steps, said steps consisting of the two following ones: a first orienting step (b’-1 and b”-1 , respectively) to bi-axially orient the platelet-shaped magnetic or magnetizable pigment particles such as described herein followed by a second orienting step to re-orient (b’-2 and b”-2, respectively) the platelet-shaped magnetic or magnetizable pigment particles such as described herein, wherein the substrate (510) carrying on its first side the first coating layer (520’) is exposed to the magnetic field of a magnetic assembly (53O’-a) and subsequently to the magnetic field of a magnetic assembly (53O’-b), said both magnetic assemblies (53O’-a and 53O’-b) being positioned on the second side of the substrate (i.e. the side lacking the first coating layer (520’)) and wherein the substrate (510) carrying on its second side the second coating layer (520”) is exposed to the magnetic field of a magnetic assembly (530”-a) and subsequently to the magnetic field of a magnetic assembly (530”-b), both magnetic assemblies (530”-a and 530”-b) being positioned on the first side of the substrate (i.e. the side comprising the first coating layer (520’) in a cured state) and wherein the magnetic assemblies 53O’-a and 530”-a are same assemblies, in particular two same individual objects, and the magnetic assemblies 53O’-b and 530”-b are same assemblies, in particular two same individual objects, so as to produce the first and second magnetic patterns being symmetric with respect to a mirror plane which is parallel to the substrate (510).

[0104] Fig. 5-2 (not true to scale) illustrates a process wherein the orientation step b (being steps b’) and b”)) consist of two-steps magnetic orientation steps, wherein the radiation curable coating composition described herein is first exposed to the magnetic field of a first magnetic assembly (530-a) and subsequently exposed to the magnetic field of a second magnetic assembly (530-b), wherein said second magnetic assembly (530-b) is mounted on a rotating magnetic cylinder. Fig. 5-3 (not true to scale) illustrates a process wherein the orientation step (being steps b’) and b”)) consists of two-steps magnetic orientation steps, wherein the radiation curable coating composition described herein is exposed to the magnetic field of a magnetic assembly (530-a), and subsequently exposed to the resultant magnetic field of a second magnetic assembly (530-b) and a third magnetic assembly (530-c), wherein said second magnetic assembly (530-b) is mounted on a rotating magnetic cylinder and the third magnetic assembly (530-c) is arranged in vicinity of said rotating magnetic cylinder. Suitable processes wherein the orientation steps b) consist of two-steps magnetic orientation steps are disclosed in WO 2015 / 086257 A1.

[0105] According to one embodiment shown for example in Fig. 6, the process described herein comprises the first set of steps (1) and the second set of steps (2), wherein the magnetic orientation step b’) of the first set of steps (1) and the magnetic orientation step b”) of the second set of steps (2) independently being two-steps magnetic orientation steps, said steps independently consisting of the two following ones: a first orienting step (b’-1 and b”-1 , respectively) to bi-axially orient the plateletshaped magnetic or magnetizable pigment particles such as described herein followed by a second orienting step to re-orient (b’-2 and b”-2, respectively) the platelet-shaped magnetic or magnetizable pigment particles such as described herein, wherein the substrate (610) carrying on its first side the first coating layer (620’) is exposed to the magnetic field of the magnetic assembly (63O’-a) and subsequently to the resultant magnetic field of the magnetic assembly (63O’-b) and of the magnetic assembly (630’- c), said magnetic assemblies (63O’-a, 63O’-b, 63O’-c) being positioned on the second side of the substrate (i.e. the side lacking the first coating layer (620’)) and wherein the substrate (610) carrying onits second side the second coating layer (620”) is exposed to the magnetic field of the magnetic assembly (630”-a) and subsequently to the resultant magnetic field of the magnetic assembly (630”-b) and of the magnetic assembly (630”-c), the magnetic assemblies (630”-a, 630”-b and 630”-c) being positioned on the first side of the substrate (i.e. the side comprising the first coating layer (620’) in a cured state) and wherein the magnetic assemblies 63O’-a and 630”-a are same assemblies, in particular two same individual objects, the magnetic assemblies 63O’-b and 630”-b are same assemblies, in particular two same individual objects, and the magnetic assemblies 63O’-c and 630”-c are same assemblies, in particular two same individual objects, so as to produce the first and second magnetic patterns being symmetric with respect to a mirror plane which is parallel to the substrate (610).

[0106] The first orienting step (b-1) to bi-axially orient the platelet-shaped magnetic or magnetizable pigment particles such as described herein is preferably carried out with the magnetic assemblies described hereafter and the second orienting step (b-2) to re-orient the pigment particles is preferably carried out with the magnetic assemblies described hereabove.

[0107] Contrary to a mono-axial orientation wherein platelet-shaped magnetic or magnetizable pigment particles are orientated in such a way that only their main axis is constrained by the magnetic field, carrying out a bi-axial orientation means that the platelet-shaped magnetic or magnetizable pigment particles are made to orientate in such a way that their two main axes are constrained. In contrast to needle-shaped pigment particles which can be considered as one-dimensional particles, plateletshaped pigment particles have an X-axis and a Y-axis defining a plane of predominant extension of the particles. In other words, platelet-shaped pigment particles may be considered to be two-dimensional particles due to the large aspect ratio of their dimensions as can be seen in Fig. 2. As shown in Fig. 2, a platelet-shaped pigment particle can be considered as a two-dimensional structure wherein the dimensions X and Y are substantially larger than dimension Z. Platelet-shaped pigment particles are also referred in the art as oblate particles or flakes. Such pigment particles may be described with a main axis X corresponding to the longest dimension crossing the pigment particle and a second axis Y perpendicular to X which also lies within said pigment particles. Carrying out a bi-axial orientation leads to platelet-shaped magnetic or magnetizable pigment particles having two main axes constrained, i.e. bi-axially oriented neighboring platelet-shaped magnetic pigment particles are close to each other in space and are essentially parallel to each other. Put another way, bi-axial orientation aligns the planes of the platelet-shaped magnetic or magnetizable pigment particles so that the planes of said pigment particles are oriented to be essentially parallel relative to the planes of neighboring (in all directions) platelet-shaped magnetic or magnetizable pigment particles.

[0108] Bi-axially oriented platelet-shaped magnetic or magnetizable pigment particles described herein consist of platelet-shaped magnetic or magnetizable pigment particles forming a sheet-like structure with their X and Y axes preferably substantially parallel to the substrate (x10) surface and are planarized in said two dimensions.

[0109] According to another embodiment, the magnetic assembly described hereafter allow to bi- axially orient the platelet-shaped magnetic or magnetizable pigment particles described herein such that the platelet-shaped magnetic or magnetizable pigment particles have a first axis within the X-Y planesubstantially parallel to the substrate (x10) surface and a second axis being substantially perpendicular to said first axis at a substantially non-zero elevation angle to the substrate surface.

[0110] According to another embodiment, the magnetic assembly described hereafter allows to bi- axially orient the platelet-shaped magnetic or magnetizable pigment particles described herein such that the platelet-shaped magnetic or magnetizable pigment particles have their X-Y plane substantially parallel to an imaginary spheroid surface.[OHl] Suitable magnetic assemblies for bi-axially orienting the platelet-shaped magnetic or magnetizable pigment particles described herein are provided hereafter as non-limiting examples.

[0112] According to one embodiment shown for example in Fig. 7 (examples E1-E4, magnetic assembly (730) used during steps b’) and b”)), wherein said steps b’) and b”) independently consist of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO 2021 / 239607 A1 . The disclosed magnetic assemblies of WO 2021 / 239607 A1 comprise: a) at least a first set (S1) and a second set (S2), each of the first and second sets (S1 , S2) comprising: i) one first bar dipole magnet (x31) having a first thickness (L1), a first length (L4) and a first width (L5), and having its magnetic axis oriented to be substantially parallel to the substrate, and ii) two second bar dipole magnets (x32aand x32b) having a second thickness (L2), a second length (L6) and a second width (L7), the two second bar dipole magnets (x32a, x32b) having their uppermost surfaces flush with each other, and having their magnetic axes oriented to be substantially perpendicular to the substrate, wherein the first bar dipole magnet (x31) of the first set (S1) has a magnetic direction opposite to the magnetic direction of the first bar dipole magnet (x31) of the second set (S2), the first bar dipole magnets (x31) of the first and second sets (S1 , S2) are spaced apart by a first distance (d1), the first bar dipole magnet (x31) of the first set (S1) has substantially the same thickness (L1), first length (L4) and first width (L5) as the first bar dipole magnet (x31) of the second set (S2), and the two second bar dipole magnets (x32aand x32b) of the first set (S1) have substantially the same second thickness (L2), second lengths (L6) and second widths (L7) as the two second bar dipole magnets (x32aand x32b) of the second set (S2), wherein the first bar dipole magnet (x31) and the second bar dipole magnets (x32aand x32b) of each of the first and second sets (S1 , S2) are aligned to form a column, in that the first bar dipole magnet (x31) of the first and second sets (S1 , S2) is respectively placed between and spaced apart from the second bar dipole magnets (x32aand x32b) by a second distance (d2), the first width (L5) and the second length (L6) being substantially the same, the North pole of one second bar dipole magnet (x32aand x32b) of each of the first and second sets (S1 , S2) pointing towards the first plane and the North Pole of the first bar dipole magnet (x31) pointing towards said one, and the South pole of the other of the second bar dipole magnet (x32aand x32b) of each of the first and second sets (S1 , S2) pointing towards the first plane and the South Pole of the first bar dipole magnet (x31) pointing towards said other; and b) a first pair (P1) of third bar dipole magnets (x33aand x33b) having a third thickness (L3), a third length (L8) and a third width (L9) and having their magnetic axes oriented to be substantially parallel to the substrate, the second width (L7) of the two second bar dipole magnets (x32aand x32b) of the first and second sets (S1 , S2) having substantially the same value as the third width (L9) of the third bar dipole magnets (x33aand x33b), each of the third bar dipole magnets (x33aand x33b) being aligned with onesecond bar dipole magnet (x32aand x32b) of the first set (S1) and one second bar dipole magnet (x32aand x32b) of the second set (S2) so as to form two lines, the third bar dipole magnets (x33aand x33b) being placed between and spaced apart from the respective second bar dipole magnets (x32aand x32b) by a third distance (d3), the North poles of the third bar dipole magnets (x33a and x33b) respectively pointing towards one of the second bar dipole magnets (x32aand x32b) when the North Poles of said ones of the second bar dipole magnets (x32aand x32b) point towards the substrate or the South poles of the third bar dipole magnets (x33aand x33b) respectively pointing towards one of the second bar dipole magnets (x32aand x32b) when the South Poles of said ones of the second bar dipole magnets (x32aand x32b) pointing towards the substrate.

[0113] According to one embodiment, the process described herein comprises the steps b’) and b”) independently consisting of exposing the radiation curable coating composition to a magnetic assembly such as those described in EP 2 157 141 A1 . The disclosed magnetic assemblies of EP 2 157 141 A1 provide a magnetic field that changes its direction while the platelet-shaped magnetic or magnetizable pigment particles move through said assemblies, forcing the platelet-shaped magnetic or magnetizable pigment particles to rapidly oscillate until both main axes become parallel to the substrate, i.e. the platelet-shaped magnetic or magnetizable pigment particles oscillate until they come to a stable sheetlike formation with their X and Y axes parallel to the substrate to the substrate and are planarized in said two dimensions. As shown in Fig. 5 of EP 2 157 141 , the magnetic assembly comprises a linear arrangement of at least three magnets that are positioned in a staggered fashion or in zigzag formation, said at least three magnets being on opposite sides of a feedpath where magnets at the same side of the feedpath have the same polarity, which is opposed to the polarity of the magnet(s) on the opposing side of the feedpath in a staggered fashion. The arrangement of the at least three magnets provides a predetermined change of the field direction as platelet-shaped magnetic or magnetizable pigment particles in a coating composition move past the magnets (direction of movement: arrow). According to one embodiment, the magnetic assembly comprises a) a first magnet and a third magnet on a first side of a feedpath and b) a second magnet between the first and third magnets on a second opposite side of the feedpath, wherein the first and third magnets have a same polarity and wherein the second magnet has a complementary polarity to the first and third magnets. According to another embodiment, the magnetic assembly further comprises a fourth magnet on the same side of the feedpath as the second magnet, having the polarity of the second magnet and complementary to the polarity of the third magnet.

[0114] According to one embodiment, the process described herein comprises the steps b’) and b”) independently consisting of exposing the radiation curable coating composition to a magnetic assembly consisting of a linear permanent magnet Halbach array, i.e. assemblies comprising a plurality of magnets with different magnetization directions and cylinder devices. A detailed description of Halbach permanent magnets was given by Z.Q. Zhu and D. Howe (Halbach permanent magnet machines and applications: a review, IEE. Proc. Electric Power Appl., 2001 , 148, p. 299-308). The magnetic field produced by such a Halbach array has the properties that it is concentrated on one side while being weakened almost to zero on the other side. Linear Halbach arrays are disclosed for example in WO 2015 / 086257 A1 and WO 2018 / 019594 A1 and Halbach cylinder devices are disclosed in EP 3 224 055B1.

[0115] According to one embodiment, the process of orienting the platelet-shaped magnetic or magnetizable pigment particles described herein steps b’) and b”) independently consists of exposing the radiation curable coating composition to spinning magnetic assemblies at an appropriate speed. Examples of spinning magnetic assemblies are assemblies comprising one or more disc-shaped spinning magnets or magnetic assemblies that are essentially magnetized along their diameter, magnetic assemblies consisting of spinning magnets or magnetic- field generating devices are described in US 2007 / 0172261 A1 , said spinning magnets or magnetic-field generating devices generating radially symmetrical time-variable magnetic fields, allowing the bi-axial orientation of pigment particles. These magnetic assemblies are driven by a shaft (or spindle) connected to an external motor. CN 102529326 B discloses examples of magnetic assemblies comprising spinning magnets that might be suitable for bi-axially orienting pigment particles. In a preferred embodiment, suitable magnetic assemblies are shaft-free disc-shaped spinning magnetic assemblies constrained in a housing made of non-magnetic, preferably non-conducting, materials and are driven by one or more magnet-wire coils wound around the housing. Examples of such shaft-free disc-shaped spinning magnetic assemblies are disclosed in WO 2015 / 082344 A1 , WO 2016 / 026896 A1 and WO2018 / 141547 A1 .

[0116] Also described herein are the following combinations of sets of steps:- the first set of steps comprising the step b’) and the second set comprising step b”), independently consisting both of one-step magnetic orientation steps as described herein; and- the first set of steps comprising the step b’) and the second set comprising step b”), independently consisting of the two-steps magnetic orientation steps as described herein, preferably the two-steps magnetic orientation steps independently comprising the first orienting step to bi-axially orient the platelet-shaped magnetic or magnetizable pigment particles followed by the second orienting step to reorient the platelet-shaped magnetic or magnetizable pigment particles described herein.

[0117] Subsequently to or partially simultaneously with, preferably partially simultaneously with, the steps of orienting the platelet-shaped magnetic or magnetizable pigment particles described herein (step b’) and step b”)), the orientation of the platelet-shaped magnetic or magnetizable pigment particles is independently fixed or frozen (step c’) and step c”)) by curing. The first and second coating compositions must thus noteworthy have a first state, i.e. a liquid or pasty state, wherein the compositions are not yet hardened and wet or soft enough, so that the platelet-shaped magnetic or magnetizable pigment particles dispersed in the compositions are freely movable, rotatable and orientable upon exposure to a magnetic field, and a second hardened (e.g. solid or solid-like) state, wherein the platelet-shaped magnetic or magnetizable pigment particles are fixed or frozen in their respective positions and orientations.

[0118] Such a first and second state is preferably provided by using a certain type of coating compositions. For example, the components of the first and second radiation curable coating composition other than the platelet-shaped magnetic or magnetizable pigment particles may take the form of an ink or coating composition such as those which are used in security applications, e.g. for banknote printing. The aforementioned first and second states can be provided by using a material that shows an increase in viscosity in reaction to a stimulus such as for example a temperature change oran exposure to an electromagnetic radiation. That is, when the fluid binder material is hardened or solidified, said binder material converts into the second state, i.e. a hardened or solid state, where the platelet-shaped magnetic or magnetizable pigment particles are fixed in their current positions and orientations and can no longer move nor rotate within the binder material. As known to those skilled in the art, ingredients comprised in an ink or coating composition to be applied directly or indirectly onto a substrate and the physical properties of said ink or coating composition must fulfil the requirements of the process used to transfer said ink or coating composition. Consequently, the binder material comprised in the coating compositions described herein is typically chosen among those known in the art and depends on the coating or printing process used to apply the ink or coating composition and the chosen hardening process.

[0119] The curing steps described herein (step c’) and step c”)) independently involve a chemical reaction, for instance curing, which is not reversed by a simple temperature increase (e.g. up to 80°C) that may occur during a typical use of a security document. The term “curing” or “curable” refers to processes including the chemical reaction, crosslinking or polymerization of at least one component in the applied coating composition in such a manner that it turns into a polymeric material having a greater molecular weight than the starting substances. Preferably, the curing causes the formation of a stable three-dimensional polymeric network. Such a curing is generally induced by applying an external stimulus to the compositions (i) after its application (step a’) and step a”)) and (ii) subsequently to or partially simultaneously with the orientation (step b’) and step b”)) of at least part of the platelet-shaped magnetic or magnetizable pigment particles (step c’) and step c”)). Advantageously the curing steps (step c’) and step c”)) of the first and second coating layers (x20’ and x20”) described herein is independently carried out partially simultaneously with the orientation (step b’) and step b”)) of at least a part of the platelet-shaped magnetic or magnetizable pigment particles (step c’) and step c”)). Radiation curing, in particular UV-Vis curing, advantageously leads to an instantaneous increase in viscosity of the first and second radiation curable coating compositions after exposure to the irradiation, thus preventing any further movement of the pigment particles and in consequence any loss of information after the magnetic orientation steps. Preferably, the curing steps (step c’) and c”)) are independently carried out by irradiation with UV-visible light (i.e. UV-Vis light radiation curing) or by E- beam (i.e. E-beam radiation curing), more preferably by irradiation with UV-Vis light since UV-Vis curing advantageously allows very fast curing processes and hence drastically decreases the preparation time of the OEL described herein, documents and articles and documents comprising said OEL.

[0120] Preferably, the first or second radiation curable coating compositions, preferably the first and second UV-Vis-curable curable coating compositions, independently comprise one or more compounds selected from the group consisting of radically curable compounds and cationically curable compounds. The compositions described herein may be hybrid systems and comprise a mixture of one or more cationically curable compounds and one or more radically curable compounds. Cationically curable compounds are cured by cationic mechanisms typically including the activation by radiation of one or more photoinitiators which liberate cationic species, such as acids, which in turn initiate the curing so as to react and / or cross-link the monomers and / or oligomers to thereby harden the coating composition. Radically curable compounds are cured by free radical mechanisms typically including the activation byradiation of one or more photoinitiators, thereby generating radicals which in turn initiate the polymerization so as to harden the coating composition. Depending on the monomers, oligomers or prepolymers used to prepare the binder comprised in the first and second radiation curable coating compositions described herein, different photoinitiators might be used. Suitable examples of free radical photoinitiators are known to those skilled in the art and include without limitation acetophenones, benzophenones, benzyldimethyl ketals, alpha-aminoketones, alpha-hydroxyketones, phosphine oxides and phosphine oxide derivatives, as well as mixtures of two or more thereof. Suitable examples of cationic photoinitiators are known to those skilled in the art and include without limitation onium salts such as organic iodonium salts (e.g. diaryl iodoinium salts), oxonium (e.g. triaryloxonium salts) and sulfonium salts (e.g. triarylsulphonium salts), as well as mixtures of two or more thereof. Other examples of useful photoinitiators can be found in standard textbooks. It may also be advantageous to include a sensitizer in conjunction with the one or more photoinitiators in order to achieve efficient curing. Typical examples of suitable photosensitizers include without limitation isopropyl-thioxanthone (ITX), 1-chloro- 2-propoxy-thioxanthone (CPTX), 2-chloro-thioxanthone (CTX) and 2,4-diethyl-thioxanthone (DETX) and mixtures of two or more thereof. The one or more photoinitiators comprised in the UV-Vis-curable coating compositions are preferably present in a total amount from about 0.1 wt-% to about 20 wt-%, more preferably about 1 wt-% to about 15 wt-%, the weight percents being based on the total weight of the first and second radiation curable coating compositions, respectively.

[0121] The first and second radiation curable coating compositions described herein may further independently comprise one or more additives including without limitation compounds and materials which are used for adjusting physical, rheological and chemical parameters of the composition such as the viscosity (e.g. solvents and surfactants), the consistency (e.g. anti-settling agents, fillers and plasticizers), the foaming properties (e.g. antifoaming agents), the lubricating properties (waxes), UV reactivity and stability (photosensitizers and photostabilizers) and adhesion properties, etc. Additives described herein may be present in the coating compositions described herein in amounts and in forms known in the art, including in the form of so-called nano-materials where at least one of the dimensions of the particles is in the range of 1 to 1000 nm.

[0122] The first and second radiation curable coating compositions described herein may be independently prepared by dispersing or mixing the platelet-shaped magnetic or magnetizable pigment particles described herein and the one or more additives when present in the presence of the binder material described herein, thus forming liquid compositions. When present, the one or more photoinitiators may be added to the composition either during the dispersing or mixing step of all other ingredients or may be added at a later stage, i.e. after the formation of the liquid coating composition.

[0123] The process for producing the OEL described herein comprises partially simultaneously with step b) (step b’ and / or b”)) or subsequently to step b) (step b’ and / or b”), preferably partially simultaneously, a curing step c) (step c’) and c”)) of the radiation curable coating compositions. The step of curing the coating compositions allows the platelet-shaped magnetic or magnetizable pigment particles to be fixed in their adopted positions and orientations in a desired pattern to form the OEL, thereby transforming the radiation curable coating composition to a second state. However, the time from the end of orientation step b) (step b’) and / or b”)) to the beginning of the curing step c) (step c’)and c”)) is preferably relatively short in order to avoid any de-orientation and loss of information. Typically, the time between the end of step b) (step b’) and / or b”)) and the beginning of step c) (step c’ and c”) is less than 1 minute, preferably less than 20 seconds, further preferably less than 5 seconds. It is particularly preferable that there is essentially no time gap between the end of the orientation step b) (step b’ and / or b”) and the beginning of the curing step c) (step c’) and c”)), i.e. that step c) follows immediately after step b) or already starts while step b) is still in progress (partially simultaneously). By “partially simultaneously”, it is meant that both steps are partly performed simultaneously, i.e. the times of performing each of the steps partially overlap. In the context described herein, when curing is performed partially simultaneously with the step c), it must be understood that curing becomes effective after the orientation so that the platelet-shaped magnetic or magnetizable pigment particles orient before the complete or partial curing of the OEL. As mentioned herein, the curing step c)) (step c’) and c”)) may be performed by using different means or processes depending on the binder material comprised in the coating composition that also comprises the platelet-shaped magnetic or magnetizable pigment particles.

[0124] The curing steps generally may be any step that increases the viscosity of the radiation curable coating composition such that a substantially solid material adhering to the substrate is formed. The curing steps may involve a physical process based on the evaporation of a volatile component, such as a solvent, and / or water evaporation (i.e. physical drying). Herein, hot air, infrared or a combination of hot air and infrared may be used. Alternatively, the curing steps may include a chemical reaction, such as a curing, polymerizing or cross-linking of the binder and optional initiator compounds and / or optional cross-linking compounds comprised in the radiation curable coating composition. Such a chemical reaction may be initiated by heat or IR irradiation as outlined above for the physical hardening processes, but may preferably include the initiation of a chemical reaction by a radiation mechanism including without limitation Ultraviolet-Visible light radiation curing (hereafter referred as UV-Vis curing) and electronic beam radiation curing (E-beam curing); oxypolymerization (oxidative reticulation, typically induced by a joint action of oxygen and one or more catalysts preferably selected from the group consisting of cobalt-containing catalysts, vanadium-containing catalysts, zirconium-containing catalysts, bismuth-containing catalysts and manganese-containing catalysts); cross-linking reactions or any combination thereof.

[0125] Radiation curing is particularly preferred, and UV-Vis light radiation curing is even more preferred, since these technologies advantageously lead to very fast curing processes and hence drastically decrease the preparation time of any article comprising the OEL described herein. Moreover, radiation curing has the advantage of producing an almost instantaneous increase in viscosity of the coating composition after exposure to the curing radiation, thus minimizing any further movement of the particles. In consequence, any loss of orientation after the magnetic orientation step can essentially be avoided. Particularly preferred is radiation-curing by photo-polymerization, under the influence of actinic light having a wavelength component in the UV or blue part of the electromagnetic spectrum (typically 200 nm to 650 nm; more preferably 200 nm to 420 nm). Suitable curing units (x50) for the curing steps (step c’) and step c”)) may comprise a high-power light-emitting-diode (LED) lamp, or an arc discharge lamp, such as a medium-pressure mercury arc (MPMA) or a metal-vapor arc lamp, as the source of theactinic radiation. On the contrary to medium-pressure mercury lamps that have emission bands in the UV-A, UV-B and UV-C regions of the electromagnetic spectrum, UV-LED lamps emit radiation in the UV-A region and / or visible (Vis) region, e.g. in the range from about 350 nm to about 470 nm. Moreover, current UV-LED and Vis-LED lamps emit quasi monochromatic radiation, i.e. only emit at one wavelength, such as 365 nm, 385 nm, 395 nm, 405 nm or 450 nm. Preferably, at least one of the steps c’) and c”), more preferably steps c’) and c”), described herein are carried out by exposing the first coating layer (x20’) and the second coating layer (x20”), respectively, to UV light with the LED curing unit (x50), preferably to one or more wavelengths between about 355 nm and about 415 nm, more preferably by exposure to UV light at 365 nm and / or 385 nm and / or 395 nm, emitted from the LED curing unit (x50)

[0126] Also described herein are alternative processes for producing the OELs described herein, wherein the first and second coating layers are applied on the same side or on opposite sides of the substrate and wherein the first and second magnetic patterns are symmetric with respect to a mirror plane which is parallel to the substrate (x10) and wherein said OELs are obtained by using different magnetic assemblies in step b’) and step b”) with both magnetic assemblies being positioned on the side lacking the coating layers when the first and second coating layers are applied on the same side. OELs comprising the first and second coating layers (x20’ and x20”) on the same side of the substrate (x10) may be produced by exposing the first and second radiation curable coating compositions to the following magnetic assemblies (said assemblies being preferably positioned on the side lacking the first and second coating layers):- for OELs wherein both the first and second motifs in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a bright reflective horizontal bar moving in a vertical direction (up / down) when the OEL is tilted around a horizontal axis, a) a magnetic assembly consisting of a dipole magnet having a magnetic axis oriented to be substantially parallel to the substrate as shown in Fig. 8 may be used in one step and b) a magnetic assembly such as those disclosed in Figs 5-9 of WO 2014 / 198905 A2, in particular Figs 5c, 6c and 7d of WO 2014 / 198905 A2 may be used in the other step;- for OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement of the OEL being a bright reflective vertical bar moving in a horizontal (left / right) direction when the OEL is tilted around a horizontal axis, a) a magnetic assembly such as those disclosed in WO 2020 / 160993 A1 (for example those shown in Figs 2-5 of WO 2020 / 160993 A1) and described herein may be used in one step and b) the same magnetic assembly as used in the one step except that in Fig. 2 and 4 of WO 2020 / 160993 A1 , the value of the angle p is changed to p’ = 180° - p, in Fig. 3, the value of the angle a is changed to a’ = -a, and in Fig. 5, the magnetization of the magnets 531 -a1 , 531 -a2, 531 -b1 and 531 -b2 is inverted (N->S, and S->N) may be used in the other step;- for OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a loop-shaped body having a size that varies when the OEL is tilted; a) a magnetic assembly such as those disclosed in WO 2017 / 064052 A1 (for example those shown in Figs 1-4 of WO 2017 / 064052 A1) and described herein may be used in one step andb) the same magnetic assembly as used in the one step except that the magnetization of the magnet(s) (x30) in Figs. 1-4 of WO 2017 / 064052 A1 is inverted (N->S, and S->N) may be used in the other step;- for OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a loop-shaped body having a size that varies when the OEL is tilted; a) a magnetic assembly such as those disclosed in WO 2017 / 080698 A1 (for example those shown in Figs 1-12 of WO 2017 / 080698 A1) and described herein may be used in one step and b) the same magnetic assembly as used in the one step except that in Figs. 1-12 of WO 2017 / 080698 A1 , the magnetization of the magnets (x31 and x32) is inverted (N->S, and S->N) may be used in the other step;- for OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a loop-shaped body having a size that varies when the OEL is tilted; a) a magnetic assembly such as those disclosed in WO 2017 / 148789 A1 (for example those shown in Figs 1-14 of WO 2017 / 148789 A1) and described herein may be used in one step and b) the same magnetic assembly as used in the one step except that in Figs. 1-14 of WO 2017 / 148789 A1 , the magnetization of the magnets (x31 and x32) is inverted (N->S, and S->N) may be used in the other step;- for OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a pattern of bright areas and dark areas moving when the OEL is tilted, a) a magnetic assembly such as those disclosed in WO 2021 / 083809 A1 (for example those shown in in Figs 6-8 of WO 2021 / 083809 A1) and described herein may be used in one step and b) the same magnetic assembly as used in the one step except that in Figs 6-8 of WO 2021 / 083809 A1 the least one dipole magnet (x41) is replaced by a magnetic assembly such as those disclosed in Figs 5-9 of WO 2014 / 198905 A2 (in particular Figs 5c, 6c and 7d of WO 2014 / 198905 A2) and the magnetization of the magnets (x31) is inverted (N->S, and S->N) may be used in the other step;- for OELs wherein both first motif and second motif in combination exhibit a dynamic motion upon tilting said OEL, said dynamic movement being a pattern of bright areas and dark areas moving when the OEL is tilted, a) a magnetic assembly such as those disclosed in WO 2021 / 083808 A1 (for example those shown in Figs 5-7 of WO 2021 / 083808 A1) and described herein may be used in one step and b) the same magnetic assembly as used in the one step except that in Figs 6-8 of WO 2021 / 083809 A1 the least one dipole magnet (x41) is replaced by a magnetic assembly such as those disclosed in Figs 5-9 of WO 2014 / 198905 A2 (in particular Figs 5c, 6c and 7d of WO 2014 / 198905 A2) and the magnetization of the magnets (x31) is inverted (N->S, and S->N) may be used in the other step.

[0127] Prior to the curing step c’), the first coating layer (x20’) may be subjected to customization so as to produce OELs further exhibiting one or more indicia, wherein said customization step is carried out after the orientation step b’) and prior to the curing step c’) respectively. Prior to the curing step c”), the second coating layer (x20”) may be subjected to customization so as to produce OELs further exhibiting one or more indicia, wherein said customization step is carried out after the orientation step b”) and prior to the curing step c”) respectively. Preferably, prior to the curing steps c’) and c”) , the first coating layer (x20’) and the second coating layer (x20”) may be independently subjected to customization so as to produce OELs further exhibiting one or more indicia, wherein said customization step is carried out after the orientation steps b’) and b”), respectively, and prior to the curing steps c’) and c”), respectively and wherein the so-obtained indicia extend across both the first and second motifs. The customization step is preferably carried out by applying a liquid coating composition on top of the coating layer which is still in a wet state (a wet-on-wet process), said application being carried out by a contactless fluid microdispensing process such as disclosed in WO 2021 / 259527 A1.

[0128] The present invention provides the processes to produce the OELs described herein on the substrate (x10) described herein. The substrate described herein is preferably selected from the group consisting of papers or other fibrous materials (including woven and non-woven fibrous materials), such as cellulose, paper-containing materials, glasses, metals, ceramics, plastics and polymers, metalized plastics or polymers, at least partially opacified plastics or polymers, composite materials and mixtures or combinations of two or more thereof. Typical paper, paper-like or other fibrous materials are made from a variety of fibers including without limitation abaca, cotton, linen, wood pulp, and blends thereof. As is well known to those skilled in the art, cotton and cotton / linen blends are preferred for banknotes, while wood pulp is commonly used in non-banknote security documents. Typical examples of plastics and polymers include polyolefins such as polyethylene (PE) and polypropylene (PP) including biaxially oriented polypropylene (BOPP), polyamides, polyesters such as poly(ethylene terephthalate) (PET), poly(1 ,4-butylene terephthalate) (PBT), poly(ethylene 2,6-naphthoate) (PEN) and polyvinylchlorides (PVC). Spunbond olefin fibers such as those sold under the trademark Tyvek® may also be used as substrate. Typical examples of metalized plastics or polymers include the plastic or polymer materials described hereabove having a metal disposed continuously or discontinuously on their surface. Typical examples of metals include without limitation aluminum (Al), chromium (Cr), copper (Cu), gold (Au), silver (Ag), alloys thereof and combinations of two or more of the aforementioned metals. The metallization of the plastic or polymer materials described hereabove may be done by an electrodeposition process, a high-vacuum coating process or by a sputtering process. Opacified polymers have been developed with the aim of mimicking the appearance and some properties of conventional paper-based substrates for security document and consist of polymeric transparent substrates which are surface treated typically on one or on both of their sides with opacifying layers so as to form opacified polymer based substrates. Typical examples of composite materials include without limitation multilayer structures or laminates of paper and at least one plastic or polymer material such as those described hereabove as well as plastic and / or polymer fibers incorporated in a paper-like or fibrous material such as those described hereabove. Of course, the substrate can comprise further additives that are known to the skilled person, such as fillers, sizing agents, Whiteners, processing aids,reinforcing or wet strengthening agents, etc. When the OELs produced according to the present invention are used for decorative or cosmetic purposes including for example fingernail lacquers, said OEL may be produced on other type of substrates including nails, artificial nails or other parts of an animal or human being.

[0129] According to one embodiment, the substrate (x10) described herein is a transparent substrate preferably selected from the group consisting of transparent polyolefins (such as polyethylene (PE) and polypropylene (PP) including biaxially oriented polypropylene (BOPP)), transparent polyamides, transparent polyesters (such as polyethylene terephthalate) (PET), poly(1 ,4-butylene terephthalate) (PBT), polyethylene 2,6-naphthoate) (PEN) and transparent polyvinylchlorides (PVC), more preferably biaxially oriented polypropylene; or a partially opacified substrate, in particular an at least partially opacified transparent polymer, preferably selected from the group consisting of transparent polyolefins (such as polyethylene (PE) and polypropylene (PP) including biaxially oriented polypropylene (BOPP)), transparent polyamides, transparent polyesters (such as poly(ethylene terephthalate) (PET), poly(1 ,4- butylene terephthalate) (PBT), polyethylene 2,6-naphthoate) (PEN) and transparent polyvinylchlorides (PVC), more preferably biaxially oriented polypropylene. According to one embodiment, the OELs described herein are present on a banknote and are present on a transparent substrate such as those described herein and preferably in the form of a window or a foil or on an at least partially opacified substrate such as those described herein, preferalby in the non-opacified areas, preferably in the form of a non-opacified area in the form of a window or a foil.

[0130] The substrate (x10) described herein may be in the form of webs, sheets, thread reels, film reels, labels of the roll or label stocks, preferably sheets.

[0131] Should the OEL produced according to the present invention be on a security document, and with the aim of further increasing the security level and the resistance against counterfeiting and illegal reproduction of said security document, the substrate may comprise printed, coated, or laser-marked or laser-perforated indicia, watermarks, security threads, fibers, planchettes, luminescent compounds, windows, foils, decals and combinations of two or more thereof. With the same aim of further increasing the security level and the resistance against counterfeiting and illegal reproduction of security documents, the substrate may comprise one or more marker substances or taggants and / or machine readable substances. According to one embodiment, the substrate (x10) comprises a printed pattern, preferably an offset printed pattern, wherein at least one of the radiation curable coating compositions of steps a’) and a”) is applied at least partially on top of said printed pattern and the process described herein comprises a step of printing an ink on the substrate (x10) described herein, wherein said step occurs prior to step a’) and step a”) described herein, as the case may be.

[0132] If desired, a primer layer may be applied to the substrate (x10) prior to the step a’) and / or prior to step a”). This may enhance the quality of the OEL described herein or promote adhesion. Examples of such primer layers may be found in WO 2010 / 058026 A2.

[0133] With the aim of increasing the durability through soiling or chemical resistance and cleanliness and thus the circulation lifetime of an article, a security document or a decorative element or object comprising the OEL obtained by the process described herein, or with the aim of modifying their aesthetical appearance (e.g. optical gloss), one or more protective layers may be applied on top of theOEL. When present, the one or more protective layers are typically made of protective varnishes. These may be transparent or slightly colored or tinted and may be more or less glossy. Protective varnishes may be radiation curable compositions, thermal drying compositions or any combination thereof. Preferably, the one or more protective layers are radiation curable compositions, more preferable UV- Vis curable compositions. The protective layers are typically applied after the formation of the OEL.

[0134] The process described herein may further comprise a step of embossing the OEL described herein using for example an embossing dye or an intaglio printing plate as disclosed in WO 2012 / 025206 A2 and WO 2019 / 233624 A1 .

[0135] The OEL described herein may be used in combination with holograms, microlenses and / or micromirrors as described in WO 2020 / 244805 A1 , EP 3 254 863 A1 , US 2008 / 0160226, US 2005 / 0180020 and EP 2 284 017 A1 , said holograms, microlenses and / or micromirrors being applied at a position spaced apart from the OEL or at least partially on top or below the OEL.

[0136] The present invention further provides optical effect layers (OELs) produced by the process according to the present invention.

[0137] Alternatively, in another embodiment an adhesive layer may be present. Therefore, an adhesive layer may be applied after the curing step of the last set of steps described herein has been completed. Such an article may be attached to all kinds of documents or other articles or items without printing or other processes involving machinery and rather high effort. Alternatively, the substrate described herein comprising the OEL described herein may be in the form of a transfer foil, which can be applied to a document or to an 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.

[0138] Also described herein are substrates (x10) comprising more than one, i.e. two, three, four, etc. OELs obtained by the process described herein, each of said OELs independently comprising the first and second motifs described herein in the form of the first and second coating layers (x20’, x20”). The process for producing more than one OEL on the substrate (x10) described herein may comprise a first set of steps a’), b’) and c’) to produce the first motif of a first OEL, a second set of steps a”), b”) and c”) to produce the second motif of the first OEL, a third set of steps a’”), b’”) and c’”) to produce the first motif of the second OEL and a fourth set of steps a””), b””’) and c””) to produce the second motif of the second OEL. Alternatively, the process for producing more than one OEL on the substrate (x10) described herein may comprise a first set of steps a’), b’) and c’) to produce the first motif of a first OEL, a second set of steps a”), b”) and c”) to produce the first motif of the second OEL, a third set of steps a’”), b’”) and c’”) to produce the second motif of the first OEL and a fourth set of steps a””), b’”’) and c””) to produce the second motif of the second OEL.

[0139] Also described herein are articles, in particular security documents, decorative elements or objects, comprising the OEL produced according to the present invention. The articles, in particular security documents, decorative elements or objects, may comprise more than one (for example two, three, etc.) OELs produced according to the present invention.

[0140] As mentioned hereabove, the OEL produced according to the present invention may be used for decorative purposes as well as for protecting and authenticating a security document.

[0141] Typical examples of decorative elements or objects include without limitation luxury goods, cosmetic packaging, automotive parts, electronic / electrical appliances, furniture and fingernail articles.

[0142] Security documents include without limitation value documents and value commercial goods. Typical examples of value documents include without limitation banknotes, deeds, tickets, checks, vouchers, fiscal stamps and tax labels, agreements and the like, identity documents such as passports, identity cards, visas, driving licenses, bank cards, credit cards, transactions cards, access documents or cards, entrance tickets, public transportation tickets or titles and the like, preferably banknotes, identity documents, right-conferring documents, driving licenses and credit cards. The term “value commercial good” refers to packaging materials, in particular for cosmetic articles, nutraceutical articles, pharmaceutical articles, alcohols, tobacco articles, beverages or foodstuffs, electrical / electronic articles, fabrics or jewelry, i.e. articles that shall be protected against counterfeiting and / or illegal reproduction in order to warrant the content of the packaging like for instance genuine drugs. Examples of these packaging materials include without limitation labels, such as authentication brand labels, tamper evidence labels and seals. It is pointed out that the disclosed substrates, value documents and value commercial goods are given exclusively for exemplifying purposes, without restricting the scope of the invention.

[0143] Alternatively, the OEL may be produced onto an auxiliary substrate such as for example a security thread, security stripe, a foil, a decal, or a window and consequently transferred to a security document in a separate step.

[0144] The skilled person can envisage several modifications to the specific embodiments described above without departing from the spirit of the present invention. Such modifications are encompassed by the present invention.

[0145] Further, all documents referred to throughout this specification are hereby incorporated by reference in their entirety as set forth in full herein.EXAMPLES

[0146] The present invention is now described in more details with reference to non-limiting examples. The Examples below provide more details for the processes according to the present invention and suitable magnetic assemblies for the production of optical effects layers (OELs).

[0147] The OELs obtained by the process of Examples E1-E4 were prepared on a laboratory equipment according to processes comprising two sets of steps, wherein both orientation steps b’) and b”) are shown in Fig. 5-1 to mimic an industrial process comprising two sets of two-steps magnetic orientation steps as shown in Fig. 5-2. The exact register of the first and the second motifs (i.e. of the first and second cured coating layers (x20’ and x20”) was ensured by using screens comprising, in addition to the motifs to be printed, guiding marks.

[0148] Examples E1-E4 were independently prepared by using the first and second UV-curable screen printing inks of Table 1 , wherein the first ink was applied during steps a’) on a first side of a transparent substrate (x10) (polymeric BOPP substrate, Guardian™ from CCL) so as to form the first coating layer (x20’) and the second UV-curable screen printing ink was applied during steps a”) on the second side of the substrate (x10), i.e. the lacking the first coating layer (x20’).

[0149] The first UV-curable screen printing ink was applied (step a’)) onto the first side of substrate (x10), said application being carried out by hand screen printing using a first T90 screen (x40’) so as to form the first coating layer (x20’) having a thickness of about 20 |j.m and having a shape as shown in Table 2.

[0150] The second UV-curable screen printing ink was applied (step a”)) on the second side of the substrate (10) in exact register with the first coating layer (x20’) applied in step a’), said application being carried out by hand screen printing using a second T90 screen (x40”) so as to form the second coating layer (x20”) having a thickness of about 20 |j.m and having a shape as shown in Table 2.Two-step orientation steps with the two motifs being on opposite sides of the substrate (Fig. 5-1)

[0151] The substrate (510) carrying coating layer (520’) was moved (see grey arrow) above a static magnetic assembly (53O’-a) (step b’-1)) and was subsequently placed above a magnetic assembly (53O’-b) (step b’-2). The so-obtained magnetic orientation pattern of the platelet-shaped magnetic pigment particles was then, partially simultaneously with the orientation step b’-2), (i.e. while the substrate (510) carrying the first coating layer (520’) was still in the magnetic field of the magnetic assembly (53O’-b), fixed by exposing for about 1.5 seconds to UV-curing the layer comprising the pigment particles using a first UV-LED-lamp (550’) from Phoseon (Type FireFlex 50 x 75 mm, 395 nm, 8 W / cm2) (step c’)). The substrate (510) was flipped / rotated and the second UV-curable screen printing ink was applied (step a”)) onto the opposite side of the first coating layer (520’) so as to form the second coating layer (520”) in exact register with said first coating layer (520’). The substrate (510) carrying the first and second coating layers (520’ and 520”) was moved (see grey arrow) above a static magnetic assembly (530”-a) (step b”-1)) with the first coating layer (520’) facing the static magnetic assembly (530”-a) and was subsequently placed above a magnetic assembly (530”-b) (step b”-2) with the first coating layer (520’) facing the magnetic assembly (530”-b). The so-obtained magnetic orientation pattern of the platelet-shaped magnetic pigment particles was then, partially simultaneously with theorientation step b”-2), (i.e. while the substrate (510) carrying the first and second coating layers (520’ and 520”) was still in the magnetic field of the magnetic assembly (530”-b), fixed by exposing for about 1 .5 seconds to UV-curing the layer comprising the pigment particles using a second UV-LED-lamp (550”) from Phoseon (Type FireFlex 50 x 75 mm, 395 nm, 8 W / cm2) (step c”)).Table 1(*) green-to-blue colorshifting magnetic pigment particles having a flake shape (platelet-shaped pigment particles) of diameter d50 of about 11 |j.m and thickness about 1 |j.m.(**) magenta-to-blue colorshifting magnetic pigment particles having a flake shape (platelet-shaped pigment particles) of diameter d50 of about 11 |j.m and thickness about 1 |j.m.(***) gold-to-green colorshifting magnetic pigment particles having a flake shape (platelet-shaped pigment particles) of diameter d50 of about 11 |j.m and thickness about 1 |j.m.Magnetic assembly of Fig. 7

[0152] The magnetic assembly (730) used to bi-axially orient the pigment particles according to the process of the present invention is disclosed in Fig. 3A of WO 2021 / 239607 A1 . The magnetic assembly (730) consists of (630-a) when used in the first step b-1 of Fig. 6 and consists of (630-c) when used in the second step b-2 of Fig. 6.

[0153] The magnetic assembly (730) comprised a) a first set (S1) comprising a first bar dipole magnet (731 -a) and two second bar dipole magnets (732-a and 732-d), a second set (S2) comprising a first bar dipole magnet (731 -b) and two second bar dipole magnets (732-b and 732-e), a third set (S3) comprising a first bar dipole magnet (731 -c) and two second bar dipole magnets (732-c and 732-f),and b) a first pair (P1) of third bar dipole magnets (733-a and 733-b) and a second pair (P2) of third bar dipole magnets (733-c and 733-f).

[0154] The uppermost surface of the first bar dipole magnet (731 -a, 731 -b and 731 -c) of the first,second and third sets (S1 , S2, S3), of the second bar dipole magnets (732-a to 732f) of the first, second and third sets (S1 , S2, S3) and of the third bar dipole magnets (733-a to 733-d) of the first and second pairs (P1 and P2) were flush with each other.

[0155] The third bar dipole magnet (733-a) of the first pair (P1) was aligned with the second bar dipole magnet (732-a) of the first set (S1), with the second bar dipole magnet (732-b) of the second set (S2), with the third bar dipole magnet (733-c) of the second pair (P2) and with the second bar dipole magnet (732-c) of the third set (S3) so as to form a line. The third bar dipole magnet (733-b) was aligned with the second bar dipole magnet (732-d) of the first set (S1), with the second bar dipole magnet (732-e) of the second set (S2), with the third bar dipole magnet (733-d) of the second pair (P2) and with the second bar dipole magnet (732-f) of the third set (S3) so as form a line. For each line described herein, the third bar dipole magnets (733-a, 733-b, 733-c and 733-d) and the second bar dipole magnets (732-a to 732- f) were spaced apart by a third distance (d2) of 2 mm. The first bar dipole magnet (731 -a) of the first set (S1) and the first bar dipole magnet (731 -b) of the second set (S2), and the first bar dipole magnet (731 - c) of the third set (S3) were spaced apart by a distance (d3) of 24 mm.

[0156] The first bar dipole magnets (731-a, 731-b and 731-c) of the first, second and third sets (S1 , S2, S3) had the following dimensions: first length (L1) of 60 mm, first width (L2) of 40 mm and first thickness (L3) of 5 mm. Each of the second bar dipole magnets (732-a to 732-f) of the first, second and third set (S1 , S2, S3) had the following dimensions: second length (L4) of 40 mm, second width (L5) of 10 mm and second thickness (L6) of 10 mm. Each of the third bar dipole magnets (733-a to 733-d) of the first and second pairs (P1 , P2) had the following dimensions: third length (L7) of 20 mm, third width (L8) of 10 mm and third thickness (L9) of 10 mm.

[0157] The first bar dipole magnet (731-a) ofthe first set (S1) and the second bar dipole magnets (732- a and 732-d) of the first set (S1) were aligned to form a column; and the first bar dipole magnet (731-b) of the second set (S2) and the second bar dipole magnets (732-b and 732-e) of the second set (S2) were aligned to form a column; and the first bar dipole magnet (731-c) of the third set (S3) and the second bar dipole magnets (732-c and 732-f) of the third set (S3) were aligned to form a column. For each set (S1 , S2, S3) and each column described herein, the first bar dipole magnets (731-a, 731-b and 731-c) and the two second bar dipole magnets (732-a and 732-d; 732-b and 732-e; and 732-c and 732- f, respectively) were spaced apart by a second distance (d1) of 2 mm.

[0158] The first bar dipole magnets (731-a, 731-b and 731-c) of the first, second and third sets (S1 , S2, S3) had their magnetic axis oriented to be substantially parallel to the substrate (710), wherein the first bar dipole magnet (731-a) of the first set (S1) had its magnetic direction opposite to the magnetic direction of the first bar dipole magnet (731-b) of the second set (S2), and the first bar dipole magnet (731-b) of the second set (S2) had its magnetic direction opposite to the magnetic direction of the first bar dipole magnet (731-c) of the third set (S3). The first bar dipole magnet (731-a) of the first set (S1) and first bar dipole magnet (731-b) of the second set (S2), as well as the first bar dipole magnet (731 - b) of the second set (S2) and the first bar dipole magnet (731-c) of the third set (S3), were spaced apart by a first distance (d3) of 24 mm (corresponding to the sum of the third length (L7) and the two third distances (d2)).

[0159] The two second bar dipole magnets (732-a to 732-f) of the first, second and third set (S1 , S2,S3) had their magnetic axis oriented to be substantially perpendicular to the substrate (710) surface. The South pole of the second bar dipole magnet (732-a) of the first set (S1), the South pole of the second bar dipole magnet (732-e) of the second set (S2) and the South pole of the second bar dipole magnet (732-c) of the third set (S3) pointed towards the substrate (710). The North pole of the second bar dipole magnet (732-d) of the first set (S1), the North pole of the second bar dipole magnet (732-b) of the second set (S2) and the North pole of the second bar dipole magnet (732-f) of the third set (S3) pointed towards the substrate (710). The North pole of the first bar dipole magnet (731 -a) of the first set (S1) pointed towards the second bar dipole magnet (732-d) of the first set (S1), the North pole of the second bar dipole magnet (731 -b) of the second set (S2) pointed towards the first bar dipole magnet (732-b) of the second set (S2) and the North pole of the first bar dipole magnet (731 -c) of the third set (S3) pointed towards the second bar dipole magnet (732-f) of the third set (S3). The South pole of the third bar dipole magnet (733-a) of the first pair (P1) pointed towards the second bar dipole magnet (732- a) of the first set (S1), said second bar dipole magnet (732-a) having its South pole pointing towards the substrate (710); the South pole of the third bar dipole magnet (733-d) of the second pair (P1) pointed towards the second bar dipole magnet (732-e) of the second set (S2), said second bar dipole magnet (732-e) having its South pole pointing towards the substrate (710); the North pole of the third bar dipole magnet (733-b) of the first pair (P1) pointed towards the second bar dipole magnet (732-d) of the first set (S1), said second bar dipole magnet (732-d) having its North pole pointing towards the substrate (710); and the North pole of the third bar dipole magnet (733-c) of the second pair (P2) pointed towards the second bar dipole magnet (732-b) of the second set (S2), said second bar dipole magnet (732-b) having its North pole pointing towards the substrate (710).

[0160] The first bar dipole magnets (731-a, 731-b and 731-c) of the first, second and third sets (S1 , S2, S3) and the second bar dipole magnets (732-a to 732-f) of the first, second and third sets (S1 , S2, S3) were made of NdFeB N42; the third bar dipole magnets (733-a, 733-b, 733-c and 733-d) of the first and second pairs (P1 , P2) were made of NdFeB N48. All the magnets (731-a to 731-c, 732-a to 732-f and 733-a to 733-d) were embedded in a non-magnetic supporting matrix (not shown) made of POM having the following dimensions: 200 mm x 120 mm x 12 mm.Magnetic assembly of Fig. 8

[0161] The magnetic assembly (830) comprised a bar dipole magnet (830-1) and a holding case (870). The bar dipole magnet (830-1) had a length and a width of about 30 mm and a thickness of about 8.5 mm. The North-South magnetic axis of the bar dipole magnet (830-1) was parallel to the substrate (810) surface, parallel to its length (L1) and parallel to the machine feed direction (shown by the arrow in Fig. 8). The bar dipole magnet (830-b1) was made of NdFeB BMnPi 80 / 48.

[0162] The holding case (870) was made of a hollow top part with a curved surface and a bottom lid. The hollow top part had a length of about 40 mm, a width of about 40 mm, a thickness of about 15.1 mm and was made of PPS. The bottom lid had a length of about 35 mm, a width of about 35 mm, a thickness of about 3 mm and was made of POM. The curved surface was suitable to match the surface of a rotating magnetic cylinder of an industrial printing press. The hollow top part was suitable for receiving the bar dipole magnet (830-1).

[0163] The distance (h) between the top surface of the bar dipole magnet (830-1) and the bottomsurface of the substrate (810) was about 3.35 mm.Magnetic assembly of Fig. 9

[0164] The magnetic assembly (930) comprised a first disc-shaped dipole magnet (930-1), a second disc-shaped dipole magnet (930-2), a disc-shaped pole piece (960-1), a square-shaped wedge (980-1), and a holding case (970).

[0165] The holding case (970) was made of a hollow top part with a curved surface and a bottom lid. The hollow top part had a length and a width of about 40 mm, a thickness of about 15.1 mm and was made of PPS. The bottom lid had a length and a width of about 35 mm, a thickness of about 3 mm and was made of POM.

[0166] The first disc-shaped dipole magnet (930-1) had a diameter of about 6 mm and a thickness of about 2 mm. The North-South magnetic axis of the disc-shaped dipole magnet (930-1) was perpendicular to the substrate (910) surface and perpendicular to its diameter, with its North pole pointing toward the substrate (910). The disc-shaped dipole magnet (930-1) was made of NdFeB N45.

[0167] The second disc-shaped dipole magnet (930-2) had a diameter of about 10 mm and a thickness L4 of about 1 mm. The North-South magnetic axis of the second disc-shaped dipole magnet (930-2) was perpendicular to the substrate (910) surface and perpendicular to its diameter, with its North pole pointing toward the substrate (910). The disc-shaped dipole magnet (930-2) was made of NdFeB N35.

[0168] The disc-shaped pole piece (960-1) had a diameter of about 30 mm and a thickness of about 2 mm. The disc-shaped pole piece (960-1) was made of steel 140HV.

[0169] The square-shaped wedge (980-1) had a side-length of about 29.9 mm and a thickness of about 6 mm. The square-shaped wedge (980-1) was made of polyethylene.

[0170] The first disc-shaped dipole magnet (930-1) was disposed on top and direct contact with the second disc-shaped dipole magnet (930-2), the second disc-shaped dipole magnet (930-2) was disposed on top and direct contact with the disc-shaped pole piece (960-1), and the disc-shaped pole piece (960-1) was disposed on top and direct contact with the square-shaped wedge (980-1). The first disc-shaped dipole magnet (930-1), the second disc-shaped dipole magnet (930-2), the disc-shaped pole piece (960-1) and the square-shaped wedge (980-1) were centrally aligned.

[0171] The distance (h) between the top surface of the first disc-shaped dipole magnet (930-1) and the bottom surface of the substrate (910) was about 0.34 mm.Table 2The OEL having the shape of a hot balloon (see E1-E2), i.e. the combination of the first motif and second motif shown in Table 2 had the following dimensions: height of about 20 mm and length of about 18 mm. The OEL having the shape of an hourglass (see E3-E4), i.e. the combination of the first motif and second motif shown in Table 2 had the following dimensions: length of about 20 mm and height of about 20 mm.

[0172] The claimed process allows the production of OELs comprising the first and second motifs described herein in a perfect register not only in terms of the printed first and second motifs but also in terms of the effect originated from the first and second magnetic patterns, wherein said OELs are easily authenticable by the man in the street thanks to their effect on the whole surface of the OELs, said effect consisting of an image at one first viewing angle (for example 0°), said effect originating from the firstand second magnetic patterns and consisting of a continuous image extending continuously from the first motif to the second motif, wherein the effect splits upon tilting and recombines to form the same effect upon tilting to come back to the first viewing angle, i.e. at viewing angles being different from the first viewing angle such as for example-45oand +45°; or in other words thanks to the jointly visible motifs as observed by the man in the street due to the lack of any breakup of said OELs at one first viewing angle and thanks to the eye-catching effect obtained by dynamic split and recombination upon tilting.

[0173] E1 and E2 exhibits an easily authenticable by the man in the street eye-catching effect due to the jointly visible motifs exhibiting one single bar at a viewing angle of 0°, wherein said bar splits into two bars when the OEL is tilted, wherein said two bars recombined to form a single bar upon tilting to a viewing angle of 0°. E2 further exhibits an eye-catching effect obtained by the two different colors of the first and second motifs, one being a colorshift from green-to-blue and the other being a colorshift from magenta-to-blue.

[0174] E3 and E4 exhibits an easily authenticable by the man in the street eye-catching effect due to the jointly visible motifs exhibiting one single double ring at a viewing angle of 0°, wherein said ring splits into circle segments when the OEL is tilted at -45° or at +45°, wherein said circle segments recombined to form the single double ring upon tilting to a viewing angle of 0°. E4 further exhibits an eye-catching effect obtained by the two different colors of the first and second motifs, one being a colorshift from green-to-blue and the other being a colorshift from magenta-to-blue.

[0175] The OELs E1-E4 obtained by the claimed process are highly suitable as an enhanced security feature for demanding end-use application due to their high dynamicity in terms of the split and the recombination of the continuous effect (a single bar or a single double ring) at one viewing angle, said effect originating from the process allowing a perfect register.

[0176] The following items also form part of the present disclosure:Item 1. A process for producing an optical effect layer (OEL) on a substrate (x10) having a first side and a second side, said optical effect layer (OEL) comprising a first motif comprising magnetically oriented platelet-shaped magnetic or magnetizable pigment particles oriented according to a first magnetic pattern and a second motif comprising magnetically oriented platelet-shaped magnetic or magnetizable pigment particles oriented according to a second magnetic pattern, said process comprising: a first set of steps consisting of a’) applying onto the first side of the substrate (x10) a first radiation curable coating composition, preferably a first UV-Vis-curable curable coating composition, comprising the platelet-shaped magnetic or magnetizable pigment particles so as to form a first coating layer (x20’) on said first side of the substrate (x10), said coating composition being in a first state, b’) exposing the first radiation curable coating composition of step a’) to a magnetic field of a magnetic assembly (x30’) so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles, the magnetic assembly (x30’) being positioned on the second side of the substrate (x10);c’) at least partially curing the radiation curable coating composition of step b’) to a second state so as to fix the platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and so as to produce the first motif; and a second set of steps consisting of a”) applying onto the second side of the substrate (x10) and in register a second radiation curable coating composition, preferably a second UV-Vis-curable curable coating composition, comprising platelet-shaped magnetic or magnetizable pigment particles so as to form a second coating layer (x20”) on said second side of the substrate (x10), said coating composition being in a first state, and at least a part of the second coating layer (x20”) being adjacent to at least a part of the first coating layer (x20’) b”) exposing the second radiation curable coating composition of step a”) to a magnetic field of a magnetic assembly (x30”), said magnetic assembly (x30”) being the same as the magnetic assembly (x30’) used in step b’) and being positioned on the first side of the substrate (x10) and the magnetic field in step b”) being substantially the same as the magnetic field in step b’) so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles; and c”) at least partially curing the second radiation curable coating composition of step b”) to a second state so as to fix the platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and so as to produce the second motif, wherein the magnetic field of the magnetic assembly (x30’) in step b’) and the magnetic field of the magnetic assembly (x30”) in step b”) are symmetric with respect to a mirror plane which is parallel to the substrate (x10).Item 2. The process according to item 1 , wherein at least one of step b’) and step b”) is a one-step magnetic orientation step to mono-axially orient the platelet-shaped magnetic or magnetizable pigment particles, or is a two-steps orientation step comprising a first orienting step to bi-axially orient the platelet-shaped magnetic or magnetizable pigment particles followed by a second orienting step to re-orient the plateletshaped magnetic or magnetizable pigment particles.Item 3. The process according to item 2, wherein step b’) and / or step b”) independently are two-steps orientation steps comprising the first orienting step to bi-axially orient the platelet-shaped magnetic or magnetizable pigment particles followed by the second orienting step to re-orient the platelet-shaped magnetic or magnetizable pigment particles.Item 4. The process according to any one of items 1 to 3, wherein the step b’) and / or the step b”) are two-steps orientation steps comprising the first orienting step to bi-axially orient the platelet-shaped magnetic or magnetizable pigment particles followed by the second orienting step to -re-orient the platelet-shaped magnetic or magnetizable pigment particles and wherein the first orienting step is carried out to bi-axially orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles to i) have both their X-axis and Y-axis substantially parallel to the substrate (x10) surface, or ii) have a first axis within the X-Y plane substantially parallel to the substrate (x10) surface and a second axis being perpendicular to said first axis at a substantially non-zero elevation angle to the substrate (x10) surface, or iii) have their X-Y plane parallel to an imaginary spheroid surface.Item 5. The process according to any one of items 1 to 4, wherein the first radiation curable coating composition and the second radiation curable coating composition exhibit different colors.Item 6. The process according to any of items 1 to 5, wherein steps a’) and a”) are independently carried out by a printing process selected from the group consisting of screen printing, rotogravure, flexography printing and intaglio printing, preferably by screen printing.Item 7. The process according to any one of items 1 to 6, wherein the step c’) is carried out partially simultaneously with step b’) and / or step c”) is carried out partially simultaneously with step b”).Item 8. The process according to item 7, wherein the step c’) is carried out by exposure to UV-Vis light radiation with a LED curing unit (x50) and / or the step c”) is carried out by exposure to UV-Vis light radiation with a LED curing unit (x50).Item 9. The process according to any one of items 1 to 8, wherein at least a part of the platelet-shaped magnetic or magnetizable pigment particles is constituted by platelet-shaped optically variable magnetic or magnetizable pigment particles.Item 10. The process according to any one of items 1 to 9, wherein the substrate (x10) is selected from the group consisting of papers or other fibrous materials, paper-containing materials, glasses, metals, ceramics, polymers, metalized polymers, at least partially opacified polymers, composite materials and mixtures or combinations thereof.Item 11 . The process according to item 10, wherein the substrate (x10) is a transparent substrate.Item 12. The process according to any one of items 1 to 11 , wherein the substrate (x10) comprises a printed pattern, preferably an offset printed pattern, and wherein at least one of the radiation curable coating compositions of steps a’) and a”) is applied at least partially on said printed pattern.Item 13. The process according to any one of items 1 to 12, wherein the first coating layer (x20) and the second coating layer (x20’) are within a register of ± 1 mm, preferably ± 0.5 mm and more preferably ± 0.2 mm.

Claims

CLAIMS1 . A process for producing an optical effect layer (OEL) on a substrate (x10) having a first side and a second side, said optical effect layer (OEL) comprising a first motif comprising magnetically oriented platelet-shaped magnetic or magnetizable pigment particles oriented according to a first magnetic pattern and a second motif comprising magnetically oriented platelet-shaped magnetic or magnetizable pigment particles oriented according to a second magnetic pattern, said process comprising: a first set of steps consisting of a’) applying onto the first side of the substrate (x10) a first radiation curable coating composition, preferably a first UV-Vis-curable curable coating composition, comprising the platelet-shaped magnetic or magnetizable pigment particles so as to form a first coating layer (x20’) on said first side of the substrate (x10), said coating composition being in a first state, b’) exposing the first radiation curable coating composition of step a’) to a magnetic field of a magnetic assembly (x30’) so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles, the magnetic assembly (x30’) being positioned on the second side of the substrate (x10); c’) at least partially curing the radiation curable coating composition of step b’) to a second state so as to fix the platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and so as to produce the first motif; and a second set of steps consisting of a”) applying onto the second side of the substrate (x10) and in register a second radiation curable coating composition, preferably a second UV-Vis-curable curable coating composition, comprising platelet-shaped magnetic or magnetizable pigment particles so as to form a second coating layer (x20”) on said second side of the substrate (x10), said coating composition being in a first state, and at least a part of the second coating layer (x20”) being adjacent to at least a part of the first coating layer (x20’) b”) exposing the second radiation curable coating composition of step a”) to a magnetic field of a magnetic assembly (x30”), said magnetic assembly (x30”) being the same as the magnetic assembly (x30’) used in step b’) and being positioned on the first side of the substrate (x10) and the magnetic field in step b”) being substantially the same as the magnetic field in step b’) so as to magnetically orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles; and c”) at least partially curing the second radiation curable coating composition of step b”) to a second state so as to fix the platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and so as to produce the second motif, wherein the magnetic field of the magnetic assembly (x30’) in step b’) and the magnetic field of the magnetic assembly (x30”) in step b”) are symmetric with respect to a mirror plane which is parallel to the substrate (x10),wherein at least a part of the second coating layer (x20”) and the first coating layer (x20’) have their projections on each side of the substrate (x10) and at least a part of the second coating layer (x20”) and the first coating layer (x20’) is adjacent to at least a part of the first coating layer (x20’), which means their projections on each side of the substrate (x10) are contiguous.

2. The process according to claim 1 , wherein at least one of step b’) and step b”) is a one-step magnetic orientation step to mono-axially orient the platelet-shaped magnetic or magnetizable pigment particles, or is a two-steps orientation step comprising a first orienting step to bi-axially orient the plateletshaped magnetic or magnetizable pigment particles followed by a second orienting step to reorient the platelet-shaped magnetic or magnetizable pigment particles.

3. The process according to claim 2, wherein step b’) and / or step b”) independently are two-steps orientation steps comprising the first orienting step to bi-axially orient the platelet-shaped magnetic or magnetizable pigment particles followed by the second orienting step to re-orient the platelet-shaped magnetic or magnetizable pigment particles.

4. The process according to any one of claims 1 to 3, wherein the step b’) and / or the step b”) are two-steps orientation steps comprising the first orienting step to bi-axially orient the plateletshaped magnetic or magnetizable pigment particles followed by the second orienting step to -reorient the platelet-shaped magnetic or magnetizable pigment particles and wherein the first orienting step is carried out to bi-axially orient at least a part of the platelet-shaped magnetic or magnetizable pigment particles to i) have both their X-axis and Y-axis substantially parallel to the substrate (x10) surface, or ii) have a first axis within the X-Y plane substantially parallel to the substrate (x10) surface and a second axis being perpendicular to said first axis at a substantially non-zero elevation angle to the substrate (x10) surface, or iii) have their X-Y plane parallel to an imaginary spheroid surface.

5. The process according to any one of claims 1 to 4, wherein the first radiation curable coating composition and the second radiation curable coating composition exhibit different colors.

6. The process according to any of claims 1 to 5, wherein steps a’) and a”) are independently carried out by a printing process selected from the group consisting of screen printing, rotogravure, flexography printing and intaglio printing, preferably by screen printing.

7. The process according to any one of claims 1 to 6, wherein the step c’) is carried out partially simultaneously with step b’) and / or step c”) is carried out partially simultaneously with step b”).

8. The process according to claim 7, wherein the step c’) is carried out by exposure to UV-Vis light radiation with a LED curing unit (x50) and / or the step c”) is carried out by exposure to UV-Vis light radiation with a LED curing unit (x50).

9. The process according to any one of claims 1 to 8, wherein at least a part of the platelet-shaped magnetic or magnetizable pigment particles is constituted by platelet-shaped optically variable magnetic or magnetizable pigment particles.

10. The process according to any one of claims 1 to 9, wherein the substrate (x10) is selected from the group consisting of papers or other fibrous materials, paper-containing materials, glasses,metals, ceramics, polymers, metalized polymers, at least partially opacified polymers, composite materials and mixtures or combinations thereof.11 . The process according to claim 10, wherein the substrate (x10) is a transparent substrate.

12. The process according to any one of claims 1 to 11 , wherein the substrate (x10) comprises a printed pattern, preferably an offset printed pattern, and wherein at least one of the radiation curable coating compositions of steps a’) and a”) is applied at least partially on said printed pattern.

13. The process according to any one of claims 1 to 12, wherein the first coating layer (x20’) and the second coating layer (x20”) are within a register of ± 1 mm, preferably ± 0.5 mm and more preferably ± 0.2 mm.

14. The process according to any one of claims 1 to 13, wherein the process is a continuous process using a single machine, continuous meaning that the second set of steps is carried out directly after the first set of steps, or, in case the process comprises a third set of steps, that the third set of steps is carried out directly after the second set of steps.

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