Processes for producing optical effect layers

Abstract

The invention provides a process for producing novel optical effect layers (OELs).

Description

[0001] 273 983 t8

[0002] PROCESSES FOR PRODUCING OPTICAL EFFECT LAYERS

[0003] FIELD OF THE INVENTION

[0004] The invention relates to the field of security printing processes, as well as security features produced using such security printing processes. In particular, the invention relates to optical effect layers (OELs), and the use of such OELs as anticounterfeit features on security documents or security articles, as well as for decorative purposes.

[0005] BACKGROUND OF THE INVENTION

[0006] 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 US2,570,856; US3,676,273; US3,791 ,864; US5,630,877; and US5, 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 W02002 / 090002A2 and W02005 / 002866A1 .

[0007] 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.

[0008] Magnetic or magnetizable pigment particles in printing inks or coatings allow for the production of magnetically induced images, designs and / or patterns, which are referred to 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.

[0009] With the aim of optimizing and increasing the counterfeiting resistance of security documents, in particular banknotes, striking and sophisticated magnetically induced images and 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 OELs include 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. W02012 / 104098A1 discloses OELs comprising more than one magnetically induced images, each image having a different magnetic orientation pattern. W02012 / 104098A1 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.

[0010] 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 to form a coating layer; ii) exposing the coating layer to the magnetic field of a magnetic assembly, thereby orienting the pigment particles, iii) curing one or more first areas of the coating layer to a second state 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 assembly 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 to fix the magnetic or magnetizable particles in their new adopted positions and orientations.

[0011] A need remains for improved and controlled processes for producing eye-catching OELs for security printers at industrial speed, wherein said so-produced OELs are easily authenticated by the person in the street while said processes are highly difficult to be implemented on a mass-scale production by counterfeiters and the illicit market.

[0012] SUMMARY OF THE INVENTION

[0013] In a first aspect, the invention provides a process for producing an optical effect layer (OEL) on a substrate, said OEL comprising a first motif comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color, oriented according to a magnetic pattern and a second motif comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color, oriented according to said same magnetic pattern, which first and second motifs together form a composite motif, said process comprising: a) applying onto the substrate a first radiation-curable coating composition, preferably a first UV- Vis-curable coating composition, comprising the first optically variable platelet-shaped magnetic or magnetizable pigment particles at a concentration of [A] to form a first coating layer on said substrate, said first 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 to magnetically orient at least a part of the first optically variable platelet-shaped magnetic or magnetizable pigment particles according to said magnetic pattern; c) at least partially curing the first radiation-curable coating composition of step b) to a second state to fix the first optically variable platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and to produce the first motif; a’) applying, at least partially overlapping the first motif in an overlap zone, a second radiation- curable coating composition, preferably a second UV-Vis-curable coating composition, comprising the second optically variable platelet-shaped magnetic or magnetizable pigment particles at a concentration of [B] to form a second coating layer, said second coating composition being in a first state; b’) exposing the second radiation-curable coating composition of step a’) to a magnetic field of a magnetic assembly to magnetically orient at least a part of the second optically variable platelet-shaped magnetic or magnetizable pigment particles in the overlap zone, according to said same magnetic pattern; c’) at least partially curing the second radiation-curable coating composition of step b’) to a second state to fix the second optically variable platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and to produce the second motif; wherein steps b) and b’) are carried out in magnetic register and at least partly in , the first and second coating layers have different colors at at least one viewing angle, the ratio of [A] / [B] is from about 1.83 to about 5.5, and the sum of the numerical values of [A] + [B] is less than about 25.

[0014] In a second aspect, the invention provides an OEL comprising:

[0015] (i) a first motif composed of a first coating layer comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color and being comprised in the first coating layer at a concentration of [A], wherein the first optically variable platelet-shaped magnetic or magnetizable pigment particles are permanently oriented according to a predetermined magnetic pattern; ii) a second motif, at least partially overlapping the first motif in an overlap zone, composed of a second coating layer comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color and being comprised in the second coating layer at a concentration of [B], wherein the second optically variable platelet-shaped magnetic or magnetizable pigment particles are permanently oriented according to said same predetermined magnetic pattern in the overlap zone; wherein the first motif and the second motif together form a composite motif, and wherein the magnetic patterns of the first and second motifs are in magnetic register, the first and second coating layers have different colors at at least one viewing angle, the ratio of [A] / [B] is from about 1 .83 to about 5.5, and the sum of the numerical values [A] + [B] is less than about 25.

[0016] DETAILED DESCRIPTION

[0017] BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Fig. 1 depicts the creation of a composite motif (C) from a first motif (A) and a second motif (B) according to the invention, the first (210) and second (210’) coating layers overlapping each other.

[0019] Fig. 2A depicts schematically an embodiment of the process of the invention in which both steps of magnetic orientation (b) and b’)) are one-step magnetic orientation steps and are carried out with a single magnetic assembly (230 and 230’).

[0020] Fig. 2B depicts schematically an embodiment of the process of the invention in which both steps of magnetic orientation (b) and b’)) are two-step magnetic orientation steps and are carried out with a first (230-1 and 230- T) and second (230-2 and 230-2’) magnetic assemblies.

[0021] Fig. 3 depicts schematically a platelet-shaped pigment particle.

[0022] Fig. 4A depicts schematically an embodiment of a one-step magnetic orientation step b) (b) being b) and b’)) of the process of the invention (see Fig. 2A) in which the step b) and b’) are carried out with a single magnetic assembly (230).

[0023] Figs. 4B-4C depict schematically embodiments of a two-step magnetic orientation in the process of the invention in which the step b) and b’) consists of a two-step orientation b) consisting of b-1) and b-2), b’) consisting of b’-1) and b’-2)(see Fig.2B) with the use of a first (230-1 and 230-T) and second (230- 2 and 230-2’) magnetic assemblies;

[0024] Fig. 4D depicts schematically an industrial embodiment of the process of the inventio shown in Fig. 4A. Fig. 4E depicts schematically an industrial embodiment of the process of the invention shown in Fig.

[0025] 4B.

[0026] Fig. 5 schematically illustrates a top view of a static magnetic assembly (230-1 or 230-1 ’) as used in the steps b-1) and b’-1) and / or b-2) and b’-2) (bi-axial orientation) of the method of the invention.

[0027] Fig. 6 illustrates schematically a magnetic assembly (230-2 or 230-2’) used in the process of the invention.

[0028] Fig. 7 illustrates schematically a magnetic assembly (230-2 or 230-2’) used in the process of the invention.

[0029] Fig. 8 illustrates schematically a magnetic assembly (230-2 or 230-2’) used in the process of the invention.

[0030] Fig. 9 shows the a* and b* color values measured for Example E1 and Comparative Example C1 , as well as for single layers of inks A1 and A’1 .

[0031] The distances provided in the Figures are only illustrative and are not true to scale.

[0032] Definitions

[0033] As used herein, the article "a" indicates one as well as more than one and does not necessarily limit its referent noun to the singular.

[0034] As used herein, the term “about” means that the amount or value in question may be the value designated or some other value about the same. The phrases are intended to convey that similar values within a range of ± 5% of the indicated value promote equivalent results or effects according to the invention.

[0035] The term “UV” (ultraviolet) as used herein is intended to mean irradiation having a wavelength component in the UV part of the electromagnetic spectrum; typically from 200 nm to 420 nm.

[0036] The term “UV-VIS” as used herein is intended to mean irradiation having a wavelength component in the ultraviolet and / or visible part of the electromagnetic spectrum; typically from 200 nm to 800 nm.

[0037] As used herein, the term “at least one” is meant to define one or more than one, for example one or two or three.

[0038] 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”.

[0039] 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.

[0040] 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.

[0041] The term “acrylate” encompasses molecules bearing acrylate and / or (meth)acrylate moieties.

[0042] The term “optical effect layer (OEL)” as used herein denotes a coating or layer that comprises oriented optically variable platelet-shaped magnetic or magnetizable pigment particles and a binder, wherein said optically variable platelet-shaped magnetic or magnetizable pigment particles are oriented by a magnetic field and wherein the oriented optically variable platelet-shaped magnetic or magnetizable pigment particles are fixed / frozen in their orientation and position (i.e. after hardening / curing) to form a magnetically induced image.

[0043] The term "coating composition" refers to any composition which is capable of forming an OEL on a solid substrate and which can be applied preferably but not exclusively by a printing method. The coating composition comprises the optically variable platelet-shaped magnetic or magnetizable pigment particles and a binder.

[0044] 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.

[0045] The term “security feature” is used to denote an image, pattern or graphic element that can be used for authentication purposes.

[0046] The inventors have created novel OELs that enable easy authentication of security items, in particular documents, using the naked eye, while being producible in a cost-efficient manner. The OELs are made using a process in which a first radiation-curable coating composition, preferably a first UV-Vis-curable coating composition, comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles of a first color is applied, preferably printed, and a second radiation-curable coating composition, preferably a second UV-Vis-curable coating composition, comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles of a second color, is applied to at least partially overlap the first coating composition and in which the concentration of pigment particles is higher in the first coating layer than in the second coating layer, to create visually appealing composite motifs, which can be readily evaluated by the naked eye to authenticate documents or articles bearing the OELs.

[0047] The invention provides processes for producing OELs that are suitable as security features against counterfeit or fraud and which comprise magnetically oriented optically variable platelet-shaped magnetic or magnetizable pigment particles on a substrate. As depicted schematically in Figs 1 , 2A and 2B, the OELs comprise a first motif (in the form of a cured first coating layer 210) comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color, oriented according to a magnetic pattern and a second motif (in the form of a cured second coating layer 210’) comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles of a second color, applied to at least partially overlap the first coating layer (210) , and in which the pigment particles are oriented according to the same magnetic pattern. The expression “register” as used herein is defined as follows:

[0048] “Print Register” means that when two or more component motifs of a Designed Motif are applied and together form a composite motif, the composite motif reproduces the Designed Motif with a deviation of less than 1 mm, preferably less than 0.5 mm, more preferably less than or equal to 0.2 mm, in any direction in the plane of the substrate.

[0049] “Designed Motif’ means a motif as designed, which motif can be broken down into component motifs. “Magnetic register” means the magnetic patterns of step b) and step b’) are superposed on the plane of the substrate with an alignment that deviates by less than 1 mm preferably less than 0.5 mm, more preferably less than or equal to 0.2 mm, between the two magnetic patterns in any direction in the plane of the substrate.

[0050] The expression “overlap” means that, for at least a portion of the first and / or second motif, an imaginary line perpendicular to and passing through a coating layer would pass through both the first coating layer and the second coating layer.

[0051] The expression “same magnetic pattern” means that the pattern results from magnetic assemblies having identical size, magnetic properties, magnetic field strength, and materials, and that the orientations in steps b) and b’) are carried out under as similar conditions as possible, with respect to order and sequence of steps (e.g. one-step or two-step), distance of the substrate from the magnetic assembly and time of exposure to the magnetic assembly and timing and sequence of the curing steps. The process of the invention comprises at least two sets of steps, i.e. a first set comprising steps a), b) and c) in which a first motif is created comprising the first optically variable platelet-shaped magnetic or magnetizable pigment particles of a first color oriented according to a magnetic pattern, and a second set comprising steps a’), b’) and c’), in which a second motif is created comprising the second optically variable platelet-shaped magnetic or magnetizable pigment particles of a second color oriented according to the same magnetic pattern. The first motif and the second motif are printed so that at least a portion of the first motif is overlapped by the second motif in an overlap zone. The overlap may be partial or total.

[0052] Fig. 1 depicts the creation of a composite motif (C) of a hot air balloon on a substrate (220), formed from a first motif (A) of the first coating layer (210) and from a second motif (B) of the second layer (210’). As shown in Fig. 1 , the first (210), and second (210’) coating layers are all applied on the same side of the substrate (220).

[0053] In one embodiment, the first motif and the second motif are printed in print register.

[0054] The magnetic pattern of the first and second motifs are the same, and the orientations of both coating layers (210 and 210’) are carried out in magnetic register according to the same magnetic pattern.

[0055] The process of the invention is preferably a continuous process being carried out with a single machine and the substrate carrying the first coating layer (210) is not removed from the machine between steps a) and c’), the machine allowing the application, preferably printing, of coating compositions, the exposure of the compositions to magnetic fields and the at least partial curing of the compositions, said process allowing the preparation of OELs comprising the first motif and the second motif (optionally additional motifs).

[0056] References to features and preferred features of steps a), b), and c), are understood to apply equally and independently to steps a’), b’), and c’).

[0057] Some exemplary embodiments are described with reference to the Figures.

[0058] Referring to Fig. 2A: step a): a screen (290) having the first motif is used to print the first radiation-curable coating composition comprising the first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color onto the substrate (220), to form the first coating layer (210); step b): the first coating layer (210) is exposed to the magnetic field of a magnetic assembly (230) to orient at least a part of the particles in a specific and predetermined magnetic pattern; step c): the first coating layer (210) having specifically oriented particles is at least partially cured by exposure to radiation of a curing unit (250) to form an at least partially cured first coating layer (210) in the form of the first motif. In a preferred embodiment, the curing is carried out without removing the substrate (220) from the influence of the magnetic assembly (230), i.e. step c) is carried out partially simultaneously with, step b); step a’): a screen (290’) having the second motif is used to print the second radiation-curable coating composition comprising the second optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color, to at least partially overlap the first coating layer (210) in an overlap zone, to form the second coating layer (210’); step b’): the second coating layer (21 O’) is exposed to the magnetic field of a magnetic assembly (230’) to orient at least a part of the particles in the overlap zone in the same specific and predetermined magnetic pattern as in step b); step c’): the second coating layer (210’) having specifically oriented pigment particles is at least partially cured by exposure to radiation of a curing unit (250’) to form an at least partially cured second coating layer (210’) in the form of the second motif. In a preferred embodiment, the curing is carried out without removing the substrate (220) from the influence of the magnetic assembly (230’), i.e. step c’) is carried out partially simultaneously with step b’).

[0059] The orientation steps b) and b’) are carried out in magnetic register.

[0060] Referring to Fig. 2B, which illustrates an embodiment in which magnetic orientation is carried out with a first step of bi-axial orientation followed by a second step of orientation according to a predetermined magnetic pattern: step a): a screen (290) having the first motif is used to print the first radiation-curable coating composition comprising the first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color onto the substrate (220), to form the first coating layer (210); step b-1): the first coating layer (210) is exposed to the magnetic field of a first magnetic assembly (230- 1) to bi-axially orient the pigment particles; step b-2): the first coating layer (210) is exposed to the magnetic field of a second magnetic assembly (230-2) to re-orient at least a part of the particles according to a specific pattern; step c): the first coating layer (210) having specifically oriented particles is at least partially cured by exposure to radiation of a curing unit (250) to form an at least partially cured first coating layer (210) in the form of the first motif. In a preferred embodiment, the curing is carried out without removing the substrate (220) from the influence of the second (230-2) magnetic assembly, i.e. step c) is carried out partially simultaneously with, step b-2); step a’): a screen (290’) having the second motif is used to print the second radiation-curable coating composition comprising optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color to at least partially overlap the first coating layer (210) in an overlap zone, to form the second coating layer (210’); step b’1): the second coating layer (210’) is exposed to the magnetic field of a first magnetic assembly (230-1 ’) to bi-axially orient the particles; step b’2): the second coating layer (210’) is exposed to the magnetic field of a second magnetic assembly (230-2’) to re-orient at least a part of the particles in the overlap zone according to the same specific pattern as in step b-2); step c’): the second coating layer (210’) having specifically oriented particles is at least partially cured by exposure to radiation of a curing unit (250’) to form an at least partially cured second coating layer (210’) in the form of the second motif. In a preferred embodiment, the curing is carried out without removing the substrate (220) from the influence of the second (230-2’) magnetic assembly, i.e. step c’) is carried out partially simultaneously with, step b’-2).

[0061] The orientation steps b-2) and b’-2) are carried out in magnetic register.

[0062] The first (210) and second (210’) coating layers are applied to the same side of the substrate (220).

[0063] The first coating layer (210) comprises the first optically variable platelet-shaped magnetic or magnetizable pigment particles and the second coating layer (210’) comprises the second optically variable platelet-shaped magnetic or magnetizable pigment particles, wherein both the first (210) and second (210’) coating layers are optically variable layers and exhibit a different color at least at one viewing angle. Optically variable (also referred in the art as goniochromatic or colorshifting) layers are known to exhibit a viewing-angle or incidence-angle dependent color. The optically variable layer imparts a different color impression at different viewing angles. By “different color impression”, it is meant that the element exhibits a difference of at least one parameter of the CIELAB(1976) system, preferably exhibits a different “L*” value, a different “a*” value, or a different “b*” value or exhibits two or three different values chosen among “a*”, “b*” and “L*”values at different viewing angles, preferably exhibits a different “a*” and / or a different “b*” values.

[0064] As described herein, the first (210) and second (210’) coating layers exhibit a different color at least at one viewing angle. According to one embodiment, the first (210) and the second (210’) coating layers have different colors when both are viewed at a same grazing angle. According to one embodiment, the first (210) and the second (210’) coating layers have different colors when both are viewed at a same orthogonal angle. According to one embodiment, the first (210) and the second (210’) coating layers have different colors when both are viewed at a same grazing angle and different colors when both are viewed at a same orthogonal angle. The term “grazing angle” refers to a viewing angle of about 0° ± about 15° with respect to the plane of the item under observation and “orthogonal angle” (also referred in the art as incidence view or as face view or face-on) refers to a viewing angle of about 90° ± about 15° with respect to the plane of the item under observation.

[0065] In addition to the overt security provided by the color-shifting property which allows easy detection, recognition and / or discrimination of an article or security document carrying an ink, coating composition, or coating layer comprising the optically variable magnetic or magnetizable pigment particles from their possible counterfeits using the unaided human senses, the colorshifting optical properties may also be used as a machine-readable tool for the recognition of the OEL. Thus, the optically variable optical properties 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.

[0066] The first (210) and second (210’) coating layers comprising the first and second optically variable platelet-shaped magnetic or magnetizable particles, respectively, can further differ in several ways, for example:

[0067] 1 . they may comprise different sized optically variable platelet-shaped magnetic or magnetizable pigment particles;

[0068] 2. they may comprise different shaped optically variable platelet-shaped magnetic or magnetizable pigment particles;

[0069] 3. they may have different coating compositions in terms of binders and / or additives; or

[0070] 4. any combination of 1-3.

[0071] Preferably, steps a) and a’) are independently carried out by a printing process, preferably independently selected from the group consisting of screen-printing, rotogravure printing, flexography printing and intaglio printing (also referred to 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.

[0072] The first and second radiation-curable coating compositions as well as the first (210) and second (210’) coating layers as well as the first and second motifs comprise the optically variable platelet-shaped magnetic or magnetizable pigment particles. 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. 3, the plateletshaped pigment particle has an X-axis and an Y-axis defining a plane of predominant extension of the particles and can be considered as having a two-dimensional structure wherein the dimensions X and Y are substantially larger than the dimension Z. In other words, the platelet-shaped pigment particle may be considered to be a two-dimensional particle due to the large aspect ratio of their dimensions as can be seen in Fig. 3. Platelet-shaped pigment particles are also referred to 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.

[0073] The first and second radiation-curable coating compositions are independently applied during steps a) and a’) thus forming the first coating layer (210) and the second coating layer (210’), respectively. The optically variable platelet-shaped magnetic or magnetizable pigment particles have, due to their platelet 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. Optically variable platelet-shaped magnetic or magnetizable pigment particles are typically described by the two main colors observed at a grazing viewing and at an orthogonal viewing angle.

[0074] The first and second optically variable platelet-shaped magnetic or magnetizable pigment particles have different colors when both are viewed at least at one same viewing angle, preferably when both are viewed at a same grazing angle and / or when both are viewed at a same orthogonal angle.

[0075] According to one embodiment, the first optically variable platelet-shaped magnetic or magnetizable pigment particles, the first coating layer (210) and the first motif exhibit a colorshift upon variation of the viewing angle (e.g. from an orthogonal view to a grazing view) from a color impression CI1 to a color impression CI2 and the second optically variable platelet-shaped magnetic or magnetizable pigment particles, the second coating layer (210’) and the second motif exhibit a colorshift upon variation of the viewing angle (e.g. from an orthogonal view to a grazing view) from a color impression Cl 11 to a color impression CII2, wherein there is no identical or similar color impressions to the naked eye.

[0076] According to one embodiment, the first optically variable platelet-shaped magnetic or magnetizable pigment particles, the first coating layer (210) and the first motif exhibit a colorshift upon variation of the viewing angle (e.g. from an orthogonal view to a grazing view) from a color impression CI1 to a color impression CI2 and the second optically variable platelet-shaped magnetic or magnetizable pigment particles, the second coating layer (210’) and the second motif exhibit a colorshift upon variation of the viewing angle (e.g. from an orthogonal view to a grazing view) from a color impression Cl 11 to a color impression CII2, wherein the color impression CI2 looks identical or similar to the color impression CII1 to the naked eye.

[0077] According to one embodiment, the first optically variable platelet-shaped magnetic or magnetizable pigment particles, the first coating layer (210) and the first motif exhibit a colorshift upon variation of the viewing angle (e.g. from an orthogonal view to a grazing view) from a color impression CI1 to a color impression CI2 and the second optically variable platelet-shaped magnetic or magnetizable pigment particles, the second coating layer (210’) and the second motif exhibit a colorshift upon variation of the viewing angle (e.g. from an orthogonal view to a grazing view) from a color impression Cl 11 to a color impression CII2, wherein the color impression CI1 looks identical or similar to the color impression CII2 to the naked eye.

[0078] According to one embodiment, the first optically variable platelet-shaped magnetic or magnetizable pigment particles, the first coating layer (210) and the first motif exhibit a colorshift upon variation of the viewing angle (e.g. from an orthogonal view to a grazing view) from a color impression CI1 to a color impression CI2 and the second optically variable platelet-shaped magnetic or magnetizable pigment particles, the second coating layer (210’) and the second motif exhibit a colorshift upon variation of the viewing angle (e.g. from an orthogonal view to a grazing view) from a color impression Cl 11 to a color impression CII2, wherein the color impression CI1 looks identical or similar to the color impression CII2 to the naked eye and the color impression CI2 looks identical or similar to the color impression CII1 to the naked eye.

[0079] The following are some examples of optically variable platelet-shaped magnetic or magnetizable pigment particles that may be used in the process and OELs of the invention, preferably the left column pigment particles are paired with its corresponding right column pigment particles:

[0080] In the at least partially cured first (210) and second (210’) coating layers and as well in the first and second motifs of the OELs of the invention, the optically variable platelet-shaped magnetic or magnetizable pigment particles are dispersed and comprised in the first coating layer (210) and the second coating layer (210’), respectively. The first (210) and second (210’) coating layers comprise, independently, a cured binder material that fixes the orientation of the optically variable platelet-shaped magnetic or magnetizable pigment particles. The binder material is at least in its cured or solid state (also referred to as second state herein), and is at least partially transparent to electromagnetic radiation of a range of wavelengths comprised between 200 nm and 2,500 nm, i.e. within the wavelength range which is typically referred to as the “optical spectrum” and which comprises infrared, visible and UV portions of the electromagnetic spectrum. Accordingly, the particles contained in the binder material in its cured or solid state and their orientation-dependent reflectivity can be perceived through the binder material at some wavelengths within this range. Preferably, the cured 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 optically variable 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 cured binder material (not including the optically variable platelet-shaped magnetic or magnetizable pigment particles) in accordance with well-established test methods, e.g. DIN 5036-3 (1979-11).

[0081] The first radiation-curable coating composition, as well as the first coating layer (210) as well as the first motif comprise the first optically variable platelet-shaped magnetic or magnetizable pigment particles preferably at a concentration [A] of about 9 to about 20 wt%, more preferably about 12 to about 18 wt%, based on the total weight of the first coating composition, the first coating layer and the first motif, respectively.

[0082] The second radiation-curable coating composition, as well as the second coating layer (210’) as well as the second motif comprise the second optically variable platelet-shaped magnetic or magnetizable pigment particles preferably at a concentration [B] of about 3 to about 10 wt%, more preferably about 5 to about 8 wt%, based on the total weight of the second coating composition, the first coating layer and the first motif, respectively.

[0083] The sum of the numerical values of concentrations [A] and [B] is less than about 25, preferably less than about 24. The sum of the numerical values of concentrations [A] plus [B] is preferably greater than about 14 and less than about 25 (i.e. between about 14 and about 25, 14 and 25 being excluded), more preferably greater than about 14 and less than about 24 (i.e. between about 14 and about 24, 14 and 24 being excluded).

[0084] The ratio of the concentration [A] of the first optically variable platelet-shaped magnetic or magnetizable pigment particles in the first coating composition to the concentration [B] of the second optically variable platelet-shaped magnetic or magnetizable pigment particles in the second coating composition is from about 1 .83 to about 5.5, preferably about 2 to about 4, more preferably about 2.3 to about 3.3.

[0085] The first and second optically variable platelet-shaped magnetic or magnetizable pigment particles independently comprise 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 to the 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.

[0086] Examples of first and second optically variable platelet-shaped magnetic or magnetizable pigment particles 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 optically variable 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.

[0087] The use of optically variable platelet-shaped 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.

[0088] The first and second optically variable platelet-shaped magnetic or magnetizable pigment particles are more preferably independently selected from the group consisting of optically variable platelet-shaped magnetic thin-film interference pigment particles or of platelet-shaped interference coated pigment particles.

[0089] Magnetic thin film interference pigment particles are known to those skilled in the art and are disclosed e.g. in US4,838,648; W02002 / 073250A2; EP0686675B1 ; W02003 / 000801A2; US6,838,166; WO2007 / 131833A1 ; EP2402401 B1 ; WO2019 / 103937A1 ; EP3587500A1 , EP3587501A1 ,

[0090] EP3587502A1 , EP3587503A1 , W02020 / 006286A1 , W02020 / 131700A1 , US2021 / 0101402,

[0091] US2021 / 038812, US2022 / 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 eleven-layer Fabry-Perot multilayer structure and / or pigment particles having a multilayer structure combining one or more multilayer Fabry-Perot structures. 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). Further preferred five-layer Fabry-Perot multilayer structures consist of dielectric / reflector / magnetic / reflector / dielectric multilayer structures. Preferred six-layer Fabry-Perot multilayer structures consist of absorb- er / dielectric / reflector / magnetic / dielectric / absorber multilayer structures. Preferred seven-layer Fabry Perot multilayer structures consist of absorber / dielectric / reflector / magnetic / reflector / dielectric / absorber multilayer structures such as disclosed in US 4,838,648. Preferred nine-layer Fabry-Perot multilayer structures consist of dielectric / absorber / dielectric / reflector / magnetic / dielectric / absorber / dielectric multilayer structures. Preferred eleven-layer Fabry-Perot multilayer structures consist of absorb- er / dielectric / absorber / dielectric / reflector / magnetic / reflector / dielectric / absorber / dielectric / absorber multilayer structures. Preferably, the reflector layers are 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, 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.

[0092] The magnetic thin film interference pigment particles 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 EP2402401 B1 whose content is hereby incorporated by reference in its entirety.

[0093] 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 made of 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.

[0094] The optically variable platelet-shaped magnetic or magnetizable pigment particles preferably have a size dso between about 2 |j.m and about 50 |j.m (as measured by direct optical granulometry).

[0095] The optically variable platelet-shaped magnetic or magnetizable pigment particles may be surface treated 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.

[0096] In one embodiment, the optically variable platelet-shaped pigment particles are magnetic. In another embodiment, the optically variable platelet-shaped pigment particles are magnetizable.

[0097] Subsequently to each application of either the first and second radiation-curable coating compositions to form the first (210) and second (210’) coating layers, the coating compositions of steps a) and a’) are exposed to the magnetic field of a magnetic assembly (230) to magnetically orient at least a part of the optically variable platelet-shaped magnetic or magnetizable pigment particles in the overlap zone (step b) and b’)).

[0098] The magnetic orientation in step b) and b’) may be a single-step as shown for example in Fig. 4A or a multi-step, for example a two-step, (as shown for example in Fig. 4B-4C). If one-step orientation is used in step b), one-step orientation must be used in step b’). If two-step orientation is used in step b), two-step orientation must be used in step b’).

[0099] Single-step orientation means that the applied coating composition comprising the optically variable platelet-shaped magnetic or magnetizable pigment particles is subjected to the influence of a magnetic assembly (230) in step b) before curing in step c), and / or steps b’) and c’) resulting in orientation of the pigment particles according to a predetermined magnetic pattern.

[0100] Fig. 4A illustrates a process wherein the orientation step b) (i.e. b) and b’)) consists of a one-step orientation step, wherein the radiation curable coating composition described herein is exposed to the magnetic field of a single magnetic assembly (230). The position of the magnetic assembly (230) in Fig. 4A is only illustrative and the magnetic assembly may be placed on the opposite side of the substrate (220) depending on the choice and the design of the magnetic orientation pattern to be produced. Fig. 4D illustrates a method for carrying out steps b) (i.e. b) and b’)) and c) (i.e. c) and c’)) on an industrial printing press, wherein the orientation step b) (i.e. b) and b’)) consists of a one-step orientation step, wherein the radiation curable coating composition described herein is exposed to the magnetic field of a single magnetic assembly (230), wherein said magnetic assembly (230) is mounted on a rotating magnetic cylinder (the curved arrows denote the direction of rotation of the cylinder (A)).

[0101] Two-step orientation means that the applied coating composition comprising the optically variable platelet-shaped magnetic or magnetizable pigment particles is first subjected to the influence of a first magnetic assembly (230-1 , 230-1 ’) and subjected to the influence of a second magnetic assembly (230- 2, 230-2’) in step b) before curing in step c), and steps b’) and c’). The first orientation step is a bi-axial orientation with a magnetic assembly (230-1 , 230-1 ’) such as those described herein and the second orientation step consists of re-orienting the optically variable platelet-shaped magnetic or magnetizable pigment particles according to the predetermined magnetic pattern with a magnetic assembly (230-2, 230-2’) such as those described herein. Contrary to a mono-axial orientation wherein platelet-shaped magnetic or magnetizable pigment particles are oriented 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. 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 optically variable plateletshaped magnetic or magnetizable pigment particles so that the planes of said pigment particles are oriented to be substantially parallel relative to the planes of neighboring (in all directions) pigment particles.

[0102] According to one embodiment, the magnetic assembly bi-axially orients the optically variable plateletshaped magnetic or magnetizable pigment particles such that the pigment particles form a sheet-like structure with their X and Y axes preferably substantially parallel to the substrate (220) surface and are planarized in said two dimensions. According to another embodiment, the magnetic assembly described hereafter bi-axially orients the optically variable platelet-shaped magnetic or magnetizable pigment particles such that the pigment particles have a first axis within the X-Y plane substantially parallel to the substrate (220) surface and a second axis being substantially perpendicular to said first axis at a substantially non-zero elevation angle to the substrate surface. According to another embodiment, the magnetic assembly described hereafter bi-axially orients the optically variable platelet-shaped magnetic or magnetizable pigment particles such that the pigment particles have their X-Y plane substantially parallel to an imaginary spheroid surface.

[0103] During a bi-axial orientation step, the substrate carrying the coating layer is moved through the inhomogeneous magnetic field of the magnetic assembly so that the pigment particles are exposed to a magnetic field which is at least time-varying in direction thus bi-axially orienting at least part of said pigment particles while the coating composition is still in a wet (i.e. not yet hardened) state.

[0104] According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif comprises bi-axially oriented platelet-shaped magnetic or magnetizable pigment particles; wherein step b) and step b’) consists of exposing the radiation-curable coating composition to a magnetic assembly such as those described in EP2157141A1 . The disclosed magnetic assemblies of EP2157141A1 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 sheet-like formation with their X and Y axes parallel to the substrate to the substrate and are planarized in said two dimensions. According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif comprises bi-axially oriented platelet-shaped magnetic or magnetizable pigment particles; wherein step b) and step b’) consists 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 EP3224055B1.

[0105] According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif comprises bi-axially oriented platelet-shaped magnetic or magnetizable pigment particles; wherein said at least one of steps b) and b’) 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 assemblies are described in US2007 / 0172261 A1 , said spinning magnets or magnetic assemblies generating radially symmetrical time-variable magnetic fields, allowing the biaxial 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 WO2015 / 082344A1 , WO2016 / 026896A1 and WO2018 / 141547A1.

[0106] According to one embodiment, the process of the invention allows the preparation of OELs, wherein step b) and step b’) consists of exposing the radiation-curable coating composition to the resultant magnetic field of a combination of a magnetic assembly described hereabove 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 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-1 as measured according to IEC 60404-1 :2000, to allow for a fast magnetization and demagnetization. Suitable soft magnetic materials have a maximum relative permeability pR max of at least 5, where the relative permeability pR is the permeability of the material p relative to the permeability of the free space pO (pR = p / pO) (Magnetic Materials, Fundamentals and Applications, 2nd Ed., 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 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 non-magnetic material (hereafter referred as “soft magnetic composite plate”). According to one embodiment, the soft magnetic metal plate is made of one or more soft magnetic metals or alloys easily workable as sheets or threads. Preferably, the soft magnetic metal plate 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), cobalt-iron 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), iron-aluminum alloys, iron-aluminum-silicon alloys, amorphous metal alloys (e.g. alloys like Metglas®, iron-boron 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.

[0107] Fig. 4B illustrates a process wherein the orientation step b) (i.e. b) and b’)) consists of a two-step orientation step, wherein the radiation curable coating composition described herein is first exposed to the magnetic field of a first magnetic assembly (230-1) and subsequently exposed to the magnetic field a second magnetic assembly (230-2). The position of the magnetic assemblies (230-1 and 230-2) in Fig. 4B is only illustrative and may be placed on the opposite side of the substrate (220) depending on the choice and the design of the magnetic orientation pattern to be produced. Fig. 4E illustrates a method for carrying out steps b) (i.e. b) and b’)) and c) (i.e. c) and c’)) on an industrial printing press, wherein the orientation step b) (i.e. b) and b’)) consists of a two-step orientation step, wherein the radiation curable coating composition described herein is first exposed to the magnetic field of a first magnetic assembly (230-1) and subsequently exposed to the magnetic field of a second magnetic assembly (230-2), wherein said second magnetic assembly (230-2) is mounted on a rotating magnetic cylinder (the curved arrows denote the direction of rotation of the cylinder (A)).

[0108] Fig. 4C illustrates a process wherein the orientation step b) (i.e. b) and b’)) consists of a two-step orientation step, wherein the radiation curable coating composition described herein is first exposed to the magnetic field of a first magnetic assembly (230-1) and subsequently exposed to the magnetic field a second magnetic assembly (230-2). In this embodiment, the radiation curable coating is maintained under the influence of the magnetic field of the first magnetic assembly (230-1) while it is exposed to the magnetic field of the second magnetic assembly (230-2). The position of the magnetic assemblies (230-1 and 230-2) in Fig. 4C is only illustrative and may be placed on the opposite side of the substrate (220) depending on the choice and the design of the magnetic orientation pattern to be produced. The optically variable platelet-shaped magnetic or magnetizable pigment particles are aligned according to predetermined magnetic patterns, determined by the design of the magnetic assembly.

[0109] In a preferred embodiment, the optically variable platelet-shaped magnetic or magnetizable pigment particles are subjected to a two-step magnetic orientation, comprising step b-1) (i.e. b-1) and b’-1)) in which a first magnetic assembly (230-1 , 230-1 ’) is used to substantially bi-axially orient the pigment particles (preferably parallel to the plane of the substrate), and step b-2) (i.e. b-2) and b-2’)) in which the pigment particles are re-oriented and subjected to a second magnetic assembly (230-2, 230-2’) designed to have a specific and predetermined magnetic alignment pattern. The combination of a biaxial orientation followed by a design-specific alignment pattern results in a more visually striking effect than if the coating composition is simply subjected to a step of design-specific alignment. Such a two- step orientation is shown schematically in steps b-1) and b-2), and steps b’-1) and b’-2) of Fig. 2B. In step b-1) and b’-1) the first coating composition (210, 210’) is subjected to the influence of the magnetic field of the magnetic assembly (230-1 or 230- T), which has, for example, a structure as shown in Fig. 5. This results in bi-axial orientation of the pigment particles. In step b-2) and b’-2), the bi-axially-oriented pigment particles are brought underthe influence of the magnetic field of the second magnetic assembly (230-2 or 230-2’), resulting in a design-specific pattern.

[0110] As described hereafter, “230”, “230”’, “230-1 ”, “230-1 ”’, “230-2” and “230-2”’ independently either refer to single magnets or refer to assemblies 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 assembly being selected according to the design of the magnetic pattern of the motifs.

[0111] According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and / or second motif bears one or more indicia, wherein step b) and b’) consists of exposing the radiation-curable coating composition to magnetic assemblies comprising an engraved magnetic plate (230 or 230’), wherein said engraved magnetic plate (230 or 230’) comprises one or more engravings and / or protrusions having the shape of indicia. The engraved magnetic plate is preferably made from a permanent magnetic powder material and a polymer. The engraved magnetic plate 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 (CaFe12O19, SrFe12O19, BaFe12O19, 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).

[0112] According to one embodiment, the magnetic orientation in step b) and b’) is carried out by exposing the radiation-curable coating composition to a magnetic assembly such as those disclosed in US8,025,952 and EP1819525B1 and W02022 / 049024 A1 , wherein this effect is so-called “Venetian-blind” effect.

[0113] According to another embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif exhibits a dynamic motion upon tilting said OEL, said dynamic motion 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 step b) and b’) consists of exposing the radiation-curable coating composition to a magnetic assembly such as those disclosed in W02020 / 160993A1 .

[0114] According to another embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif exhibits 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 step b) and step b’) consists of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO2014 / 198905A2. According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif exhibits a dynamic motion upon tilting said OEL, said dynamic movement being a nested multi-loop-shaped body moving when the OEL is tilted; wherein step b) and step b’) consists of exposing the radiation-curable coating composition to a magnetic assembly such as those disclosed in W02014 / 108303A2.

[0115] According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif exhibits 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 step b) and step b’) consists of exposing the radiation-curable coating composition to a magnetic assembly such as those disclosed in W02017 / 064052A1 , W02017 / 080698A1 and WO2017 / 148789A1 .

[0116] According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif exhibits a dynamic motion upon tilting said OEL, said dynamic movement being one or more loop-shaped bodies having a shape that varies when the OEL is tilted; wherein step b) and step b’) consists of exposing the radiation-curable coating composition to a magnetic assembly such as those disclosed in WO2018 / 054819A1 .

[0117] According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif exhibits a dynamic motion upon tilting said OEL, said dynamic movement being a moon crescent moving and rotating when the OEL is tilted; wherein step b) and step b’) consists of exposing the radiation-curable coating composition to a magnetic assembly such as those disclosed in WO2019 / 215148A1.

[0118] According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif exhibits a dynamic motion upon tilting said OEL, said dynamic movement being a loop-shaped body surrounded by one or more loop-shaped bodies having their shape and / or their brightness varying when the OEL is tilted; wherein step b) and step b’) consists of exposing the radiation-curable coating composition to a magnetic assembly such as those disclosed in W02020 / 193009A1.

[0119] According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif exhibits a dynamic movement being a pattern of bright areas and dark areas moving when the OEL is tilted; wherein the step b) and step b’) consists of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in WO2013 / 167425A1 and W02021 / 083809A1.

[0120] According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif exhibits a dynamic movement being a pattern of bright areas and dark areas moving when the OEL is tilted; wherein step b) and step b’) consists of exposing the radiation curable coating composition to a magnetic assembly such as those disclosed in W02021 / 083808A1 .

[0121] According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif exhibits 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 step b) and step b’) consists of exposing the radiation-curable coating composition to a magnetic assembly such as those disclosed in Fig. 2, 3 and 6 of US2005 / 0106367.

[0122] According to one embodiment, the process of the invention allows the preparation of OELs wherein the first and second motif exhibits a dynamic motion upon tilting said OEL, said dynamic movement being at least one comet-shaped spot rotating around said center of rotation upon tilting said OEL, wherein step b) and step b’) consists of exposing the radiation-curable coating composition to a magnetic assembly such as those disclosed in WO2019 / 038371 A1 , W02019 / 038370A1 and WO2019 / 038369A1.

[0123] At least partially curing the first and second radiation-curable coating compositions in the form of the first (210) and second (210’) cured layers (steps c) and c’)) results in fixing the optically variable plateletshaped magnetic or magnetizable pigment particles. Subsequently to or partially simultaneously with, preferably partially simultaneously with the step or steps of orienting the optically variable plateletshaped magnetic or magnetizable pigment particles (step b) and step b’)), the orientation of the pigment particles is fixed or frozen (step c) and step c’)) by at least partially curing. The first radiation-curable coating compositions therefore have a first state, i.e. a liquid or pasty state, wherein the composition is not yet hardened and wet or soft enough, so that the pigment particles dispersed in the compositions are freely movable, rotatable and orientable upon exposure to a magnetic field, and a second hardened / cured (e.g. solid or solid-like) state, wherein the pigment particles are fixed or frozen in their respective positions and orientations.

[0124] Such a first and second state is preferably provided by using a certain type of coating composition. For example, the components of the first radiation-curable coating composition other than the optically variable 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 an exposure to an electromagnetic radiation. That is, when the fluid binder material is at least partially cured or solidified, said binder material converts into the second state, i.e. an at least partially cured or solid state, where the 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 fulfill the requirements of the process used to transfer said ink or coating composition. Consequently, the binder material comprised in the coating compositions 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.

[0125] Preferably, the first or second radiation-curable coating compositions, preferably the first and second UV-Vis-curable coating compositions, independently comprise one or more compounds selected from the group consisting of radically-curable compounds and cationically-curable compounds. The coating compositions may be hybrid systems and comprise a mixture of one or more cationically-curable compounds and one or more radically-curable compounds.

[0126] The first and second radiation-curable coating compositions 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 may be present in the coating compositions in amounts and in forms known in the art, including in the form of so-called nanomaterials where at least one of the dimensions of the particles is in the range of 1 to 1000 nm.

[0127] The first and second radiation-curable coating compositions may be independently prepared by dispersing or mixing the optically variable platelet-shaped magnetic or magnetizable pigment particles and / or the one or more additives when present in the presence of the binder material, thus forming liquid compositions. When present, 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.

[0128] The process for producing the OEL of the invention comprises partially simultaneously with step b) and step b’) or subsequently to step b) and step b’), preferably partially simultaneously, a step of curing step c) and step c’) of the first and second radiation-curable coating compositions. The step of curing the first (210) and second (210’) coating compositions allows the optically variable 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 first and second radiation-curable coating compositions to a second state. The time from the end of step b) and / or step b’) to the beginning of step c) and / or step 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) and / or step b’) and the beginning of step c) and / or step c’) is less than 1 minute, preferably less than 20 seconds, further preferably less than 5 seconds. It is particularly preferable that there be essentially no time gap between the end of the orientation step b) and / or step b’) and the beginning of the curing step c) and / or step c’), i.e. that step c) and / or step c’) follow immediately after step b) and / or step b’) or already start while step b) and / or 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 of the invention, when curing is performed partially simultaneously with the step b) and / or step b’), it must be understood that curing becomes effective after the orientation so that the optically variable platelet-shaped magnetic or magnetizable pigment particles orient before the complete or partial curing of the OEL. As mentioned herein, the curing steps c) and c’) may be performed by using different means or processes depending on the binder material comprised in the first coating composition and the second coating composition that also comprise the optically variable platelet-shaped magnetic or magnetizable pigment particles.

[0129] 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 at least partially curing steps c) and c’) involve a chemical reaction, such as a curing, polymerizing or crosslinking of the binder and optional initiator compounds and / or optional cross-linking compounds comprised in the radiation-curable coating composition, 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. The chemical reaction by a radiation mechanism include without limitation Ultraviolet-Visible light radiation curing (hereafter referred as UV-Vis curing) and electronic beam radiation curing (E-beam curing). Preferably, the curing step (step c and / or step c’) is 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.

[0130] 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 of the invention. 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. Preferably, radiation curing is 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. 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 for the curing steps (steps c and 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 the actinic radiation. On the contrary to mediumpressure 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’) is carried out by exposing the first coating layer (210) and the second coating layer (21 O’), respectively, to UV light with an LED curing unit, 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. In a preferred embodiment, the first and second radiation-curable coating compositions comprise polyacrylates, and at least one photoinitiator, and curing is carried out using UV-Vis light.

[0131] The orientations of both first (210) and second coating layers (210’) in steps b) and b’) are carried out in magnetic register. When the orientation of the optically variable platelet-shaped magnetic or magnetizable pigment particles is carried out in magnetic register, the result is that a third color is observable, said third color being different from the color of the first coating layer alone and the color of the second coating layer alone. A misregistration (i.e. deviation of more than 1 mm in the magnetic patterns of step b) and step b’)) between the first (210) and second (210’) layers does not result in the formation of the third color, thus allowing an observer to conclude that the OEL is a fake or counterfeit one.

[0132] The invention provides processes to produce the OELs of the invention on a substrate. The substrate 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 polyethylene terephthalate) (PET), poly(1 ,4-butylene terephthalate) (PBT), polyethylene 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 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 invention are used for decorative or cosmetic purposes including for example fingernail lacquers, said OEL may be produced on other type of substrates including finger and toe nails, artificial nails or other parts of an animal or human being. The substrate (220) may be in the form of a web, sheet, thread reel, film reel, labels of the roll or label stocks, preferably a web or sheet.

[0133] Should the OEL produced according to the 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 (220) comprises a printed pattern, preferably an offset printed pattern, wherein the radiation-curable coating composition of steps a) and is applied at least partially on top of said printed pattern and the process of the invention comprises a step of printing an ink on the substrate (220), wherein said step occurs prior to step a).

[0134] If desired, a primer layer may be applied to the substrate (220) prior to step a). This may enhance the quality of the OEL or promote adhesion. Examples of such primer layers may be found in W02010 / 058026A2.

[0135] 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 of the invention, or with the aim of modifying their aesthetic appearance (e.g. optical gloss), one or more protective layers may be applied on top of the OEL. When present, the one or more protective layers are typically made of 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 preferably UV-Vis-curable compositions. The protective layers are typically applied after the formation of the OEL.

[0136] The process of the invention may further comprise a step of embossing the OEL of the invention using, for example, an embossing dye or an intaglio printing plate as disclosed in W02012 / 025206A2 and WO2019 / 233624A1.

[0137] The OEL of the invention may be used in combination with holograms, microlenses and / or micromirrors as described in W02020 / 244805A1 , EP3254863A1 , US2008 / 0160226, US2005 / 0180020 and EP2284017A1 , said holograms, microlenses and / or micromirrors being applied at a position spaced apart from the OEL or least partially on top or below the OEL.

[0138] The invention further provides OELs produced by the process according to the invention.

[0139] The OEL of the invention may be provided directly on a substrate (220) on which it shall remain permanently (such as for banknote applications). Alternatively, an OEL comprising the first and second motifs on the same side of the substrate may also be provided on a temporary substrate for production purposes, from which the OEL is subsequently removed. This may for example facilitate the production of the OEL, particularly while the binder material is still in its fluid state. Thereafter, after curing the radiation-curable compositions for the production of the OEL, the temporary substrate may be removed from the OEL. Alternatively, in another embodiment an adhesive layer may be present. An adhesive layer may be applied after the curing step of the second set of steps 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 comprising the OEL of the invention 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. Also described herein are substrates comprising more than one, i.e. two, three, four, etc. OELs obtained by the process of the invention, each of said OELs independently comprising the first and second motifs in the form of the first (210) and second (210’) layers.

[0140] Also described herein are methods of manufacturing a security document or article or a decorative element or article, comprising a) providing a security document or article or a decorative element or object, and b) producing the optical effect layer (OEL) with the process described herein, so that the optical effect layer (OEL) is comprised by or on the security document or article or the decorative element or the object.

[0141] Also described herein are a products, in particular security documents and articles, decorative elements and objects comprising the OEL produced according to the invention. The products, in particular security documents and articles, and the decorative elements and objects, may comprise more than one (for example two, three, etc.) OELs produced according to the invention.

[0142] As mentioned hereabove, the OEL produced according to the invention may be used for decorative purposes as well as for protecting and authenticating a security document.

[0143] Typical examples of decorative elements or objects include without limitation luxury goods, cosmetic packaging, automotive parts, electronic / electrical appliances, furniture, fingernail and toenail articles and lacquers. 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.

[0144] Alternatively, the OEL may be produced onto an auxiliary substrate such as for example a security thread, security stripe, a foil, a decal, a window or a label and consequently transferred to a security document in a separate step.

[0145] The skilled person can envisage several modifications to the specific embodiments described above without departing from the spirit of the invention. Such modifications are encompassed by the invention. Further, all documents referred to throughout this specification are hereby incorporated by reference in their entirety as set forth in full herein.

[0146] Preferred embodiments of the invention

[0147] 1 . A process for producing an optical effect layer (OEL) on a substrate, said OEL comprising a first motif comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color, oriented according to a magnetic pattern and a second motif comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color, oriented according to said same magnetic pattern, which first and second motifs together form a composite motif, said process comprising: a) applying onto the substrate a first radiation-curable coating composition, preferably a first UV- Vis-curable coating composition, comprising the first optically variable platelet-shaped magnetic or magnetizable pigment particles at a concentration of [A] to form a first coating layer on said substrate, said first 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 to magnetically orient at least a part of the first optically variable platelet-shaped magnetic or magnetizable pigment particles according to said magnetic pattern; c) at least partially curing the first radiation-curable coating composition of step b) to a second state to fix the first optically variable platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and to produce the first motif; a’) applying, at least partially overlapping the first motif in an overlap zone, a second radiation- curable coating composition, preferably a second UV-Vis-curable coating composition, comprising the second optically variable platelet-shaped magnetic or magnetizable pigment particles at a concentration of [B] to form a second coating layer, said second coating composition being in a first state; b’) exposing the second radiation-curable coating composition of step a’) to a magnetic field of a magnetic assembly to magnetically orient at least a part of the second optically variable platelet-shaped magnetic or magnetizable pigment particles in the overlap zone, according to said same magnetic pattern; c’) at least partially curing the second radiation-curable coating composition of step b’) to a second state to fix the second optically variable platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and to produce the second motif; wherein steps b) and b’) are carried out in magnetic register, the first and second coating layers have different colors at at least one viewing angle, the ratio of [A] / [B] is from about 1 .83 to about 5.5, and the sum of the numerical values [A] + [B] is less than about 25.

[0148] 2. A process for producing an optical effect layer (OEL) on a substrate, said OEL comprising a first motif comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color, oriented according to a magnetic pattern and a second motif comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color, oriented according to said same magnetic pattern, which first and second motifs together form a composite motif, said process comprising: a) applying onto the substrate a first radiation-curable coating composition, preferably a first UV-Vis- curable coating composition, comprising the first optically variable platelet-shaped magnetic or magnetizable pigment particles at a concentration [A] of about 9 to about 20 wt%, preferably about 12 to about 18 wt%, based on the total weight of the first coating composition, to form a first coating layer on said substrate, said first 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 to magnetically orient at least a part of the optically variable platelet-shaped magnetic or magnetizable pigment particles according to said magnetic pattern; c) at least partially curing the first radiation-curable coating composition of step b) to a second state to fix the first optically variable platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and to produce the first motif; a’) applying, at least partially overlapping the first motif in an overlap zone, a second radiation- curable coating composition, preferably a second UV-Vis-curable coating composition, comprising the second optically variable platelet-shaped magnetic or magnetizable pigment particles, to form a second coating layer, said second coating composition being in a first state; b’) exposing the second radiation-curable coating composition of step a’) to a magnetic field of a magnetic assembly to magnetically orient at least a part of the second optically variable platelet-shaped magnetic or magnetizable pigment particles in the overlap zone, according to said same magnetic pattern; c’) at least partially curing the second radiation-curable coating composition of step b’) to a second state to fix the second optically variable platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and to produce the second motif; wherein steps b) and b’) are carried out in magnetic register, the first and second coating layers have different colors at at least one viewing angle, the ratio of [A] / [B] is from about 1 .83 to about 5.5, and the sum of the numerical values [A] + [B] is less than about 25.

[0149] 3. A process for producing an optical effect layer (OEL) on a substrate, said OEL comprising a first motif comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color, oriented according to a magnetic pattern and a second motif comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color, oriented according to said same magnetic pattern, which first and second motifs together form a composite motif, said process comprising: a) applying onto the substrate a first radiation-curable coating composition, preferably a first UV-Vis- curable coating composition, comprising the first optically variable platelet-shaped magnetic or magnetizable pigment particles at a concentration [A] of about 9 to about 20 wt%, preferably about 12 to about 18 wt%, based on the total weight of the first coating composition, to form a first coating layer on said substrate, said first 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 to magnetically orient at least a part of the optically variable platelet-shaped magnetic or magnetizable pigment particles according to said magnetic pattern; c) at least partially curing the first radiation-curable coating composition of step b) to a second state to fix the first optically variable platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and to produce the first motif; a’) applying, at least partially overlapping the first motif in an overlap zone, a second radiation- curable coating composition, preferably a second UV-Vis-curable coating composition, comprising the second optically variable platelet-shaped magnetic or magnetizable pigment particles at a concentration [B] of about 3 to about 10 wt%, preferably about 5 to about 8 wt%, based on the total weight of the second coating composition, to form a second coating layer, said second coating composition being in a first state; b’) exposing the second radiation-curable coating composition of step a’) to a magnetic field of a magnetic assembly to magnetically orient at least a part of the second optically variable platelet-shaped magnetic or magnetizable pigment particles in the overlap zone, according to said same magnetic pattern; c’) at least partially curing the second radiation-curable coating composition of step b’) to a second state to fix the second optically variable platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and to produce the second motif; wherein steps b) and b’) are carried out in magnetic register, the first and second coating layers have different colors at at least one viewing angle, the ratio of [A] / [B] is from about 1 .83 to about 5.5, and the sum of the numerical values [A] + [B] is less than about 25.

[0150] 4. An OEL comprising:

[0151] (i) a first motif composed of a first coating layer comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color and being comprised in the first coating layer at a concentration of [A], wherein the first optically variable platelet-shaped magnetic or magnetizable pigment particles are permanently oriented according to a predetermined magnetic pattern; ii) a second motif, at least partially overlapping the first motif in an overlap zone, composed of a second coating layer comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color and being comprised in the second coating layer at a concentration of [B], wherein the second optically variable platelet-shaped magnetic or magnetizable pigment particles are permanently oriented according to said same predetermined magnetic pattern in the overlap zone; wherein the first motif and the second motif together form a composite motif, and wherein the magnetic patterns of the first and second motif are in magnetic register, the first and second coating layers have different colors at at least one viewing angle, the ratio of [A] / [B] is from about 1 .83 to about 5.5, and the sum of the numerical values [A] + [B] is less than about 25.

[0152] 5. An OEL comprising:

[0153] (i) a first motif composed of a first coating layer comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color and being comprised in the first coating layer at a concentration [A] of about 9 to about 20 wt%, preferably about 12 to about 18 wt%, based on the total weight of the first coating composition, wherein the first optically variable platelet-shaped magnetic or magnetizable pigment particles are permanently oriented according to a predetermined magnetic pattern; ii) a second motif, at least partially overlapping the first motif in an overlap zone, composed of a second coating layer comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color and being comprised in the second coating layer at a concentration of [B] , wherein the second optically variable platelet-shaped magnetic or magnetizable pigment particles are permanently oriented according to said same predetermined magnetic pattern in the overlap zone; wherein the first motif and the second motif together form a composite motif, and wherein the magnetic patterns of the first and second motif are in magnetic register, the first and second coating layers have different colors at at least one viewing angle, the ratio of [A] / [B] is from about 1 .83 to about 5.5, and the sum of the numerical values [A] + [B] is less than about 25.

[0154] 6. An OEL comprising:

[0155] (i) a first motif composed of a first coating layer comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color and being comprised in the first coating layer at a concentration [A] of about 9 to about 20 wt%, preferably about 12 to about 18 wt%, based on the total weight of the first coating composition, wherein the first optically variable platelet-shaped magnetic or magnetizable pigment particles are permanently oriented according to a predetermined magnetic pattern; ii) a second motif, at least partially overlapping the first motif in an overlap zone, composed of a second coating layer comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color and being comprised in the second coating layer at a concentration [B] of about 3 to about 10 wt%, preferably about 5 to about 8 wt%, based on the total weight of the second coating composition, wherein the second optically variable platelet-shaped magnetic or magnetizable pigment particles are permanently oriented according to said same predetermined magnetic pattern in the overlap zone; wherein the first motif and the second motif together form a composite motif, and wherein the magnetic patterns of the first and second motif are in magnetic register, the first and second coating layers have different colors at at least one viewing angle, the ratio of [A] / [B] is from about 1 .83 to about 5.5, and the sum of the numerical values [A] + [B] is less than about 25.

[0156] 7. The process or OEL of any one preceding embodiment, wherein the ratio [A] / [B] is about 2 to about 4, more preferably about 2.3 to about 3.3.

[0157] 8. The process or OEL of any one preceding embodiment, wherein, after curing in step c’), a third color is observable, said third color being different from the color of the first coating layer alone and the color of the second coating layer alone.

[0158] 9. The process or OEL of any one preceding embodiment, wherein steps a) and a’) are carried out in print register, and the first motif and the second motif are in print register.

[0159] 10. The process or OEL of any one preceding embodiment, wherein the first and second radiation- curable coating compositions are UV-Vis-curable coating compositions. The process or OEL of any one preceding embodiment, wherein step b) and step b’) comprise a first step b-1 or b’-1 of bi-axially orienting the optically variable platelet-shaped magnetic or magnetizable pigment particles, and a second step b-2 or b’-2 of re-orienting the optically variable platelet-shaped magnetic or magnetizable pigment particles according to a predetermined magnetic pattern. The process or OEL of any one preceding embodiment, wherein the first and second coating layers have different colors when both are viewed from at least one of orthogonal or grazing angle. The process or OEL of any one preceding embodiment, wherein the first and second coating layers have different colors when both are viewed from the same orthogonal angle. The process or OEL of any one preceding embodiment, wherein the first and second coating layers have different colors when both are viewed from the same grazing angle. The process or OEL of any one preceding embodiment, wherein the first and second coating layers have different colors when both are viewed from both same orthogonal and same grazing angles. The process or OEL of any one preceding embodiment, wherein the first and second coating layers comprise optically variable platelet-shaped magnetic or magnetizable pigment particles having the colors listed below, preferably wherein the left column pigment is matched with its corresponding right column pigment: The process or OEL of any one preceding embodiment, wherein the first radiation-curable coating composition comprises optically variable platelet-shaped magnetic or magnetizable pigment particles at about 9 to about 20 wt%, preferably about 12 to about 18 wt%, based on the total weight of the first coating composition. The process or OEL of any one preceding embodiment, wherein the second radiation-curable coating composition comprises optically variable platelet-shaped magnetic or magnetizable pigment particles at about 3 to about 10 wt%, preferably about 5 to about 8 wt%, based on the total weight of the second coating composition. The process or OEL of any one preceding embodiment, wherein the sum of the numerical values of concentrations [A] plus [B] is less than 24 wt%. The process or OEL of any one preceding embodiment, wherein the first and second motif exhibit a dynamic motion upon tilting the OEL, said dynamic motion 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. The process or OEL of any one preceding embodiment, wherein steps b) and b’) consists of exposing the radiation-curable coating composition to a magnetic assembly such as those disclosed in Figs. 2-5 of W02020 / 160993A1 . The process of any one preceding embodiment, wherein step b) and / or step b’) comprises a first step b-1) and b’-1) of bi-axially orienting the optically variable platelet-shaped magnetic or magnetizable pigment particles, and a second step b-2) and b’-2) of re-orienting the optically variable platelet-shaped magnetic or magnetizable pigment particles according to the magnetic pattern. The process orOEL of any one preceding embodiment, wherein the first radiation-curable coating composition comprises the first optically variable platelet-shaped magnetic or magnetizable pigment particles at about 9 to about 20 wt%, preferably about 12 to about 18 wt%, based on the total weight of the first coating composition and wherein the second radiation-curable coating composition comprises the second optically variable platelet-shaped magnetic or magnetizable pigment particles at about 3 to about 10 wt%, preferably about 5 to about 8 wt%, based on the total weight of the second coating composition. The process or OEL of embodiment 23, wherein the first radiation-curable coating composition comprises the first optically variable platelet-shaped magnetic or magnetizable pigment particles about 12 to about 18 wt%, based on the total weight of the first coating composition and wherein the second radiation-curable coating composition comprises optically variable platelet-shaped magnetic or magnetizable pigment particles at about 5 to about 8 wt%, based on the total weight of the second coating composition. The process or OEL according to any one preceding embodiment, wherein the magnetic thin film interference pigment particles are selected from the group consisting of five-layer Fabry-Perot multilayer structure pigment particles, six-layer Fabry-Perot multilayer structure pigment particles, seven-layer Fabry-Perot multilayer structure pigment particles, nine-layer Fabry-Perot multilayer structure pigment particles, eleven-layer Fabry-Perot multilayer structure and / or a multilayer Fabry-Perot structure pigment particles, and mixtures thereof The process or OEL of any one preceding embodiment, wherein at least one of the steps c) and c’) is carried out by UV-Vis light radiation curing and / or wherein the steps c) and c’) is carried out partially simultaneously with the step b) and b’) . The process or OEL of any one preceding embodiment, wherein at least one of the steps c) and c’) is carried out by exposing the first coating layer (210) and the second coating layer (211), respectively, to UV light with an LED curing unit. The process or OEL of any one preceding embodiment, wherein after curing in step c’), a third color is observable, said third color being different from the color of the first coating layer alone and the color of the second coating layer alone. The process or OEL of any one preceding embodiment, wherein the first (210) and second (21 O’) coating layers exhibit a difference of at least one parameter of the CIELAB(1976) system, preferably a different “L*” value, and / or a different “a*” value, and / or a different “b*” value or exhibits two or three different values chosen among “a*”, “b*” and “L*”values at different viewing angles, more preferably exhibit a different “a*” and / or a different “b*” value. EXAMPLES

[0160] Ingredients for the inks used in the Examples and Comparative Examples are listed in Table 1. The composition of the inks used in the Examples and Comparative Examples are shown in Tables 2 and 3. Inks used as the first coating layer [210, step a)] are designated with an A, and inks used as the second coating layer [210’, step a’)] are designated with an A’.

[0161] The OELs of Examples E1-E8 and the Comparative Examples C1-C10, were prepared according to the steps illustrated schematically in Fig. 2B. The Examples E1-E4 and the Comparative Examples C1-C4 were prepared as illustrative examples of the invention (E1-E4) and as comparative examples (C1-C4) when the register condition for the orientation steps b) and b’) was not satisfied. Examples E5-E8 and Comparative Examples C5-C10 allow the determination of optimum concentration ranges for the optically variable platelet-shaped magnetic pigment particles in the second coating layer (210’).

[0162] The screen (290) used to print the UV curable screen-printing inks A1-A3 disclosed in Table 2 [step a)] and the screen (290’) used to print in register the UV curable screen-printing inks A’1-A’11 disclosed in Tables 2 and 3 [step a’)] are shown in Tables 4 and 6. Together, the component images of the screens of step a) and step a’) form a composite image of a square or of a hot air balloon. The register for the printing of the first coating layer [210, step a)] and of the second coating layer [210’, step a’)] was ensured by using screens having guiding marks, in addition to the motif to be printed.

[0163] The magnetic assembly (230-1) illustrated in Fig. 5 was used to bi-axially orient the optically variable platelet-shaped magnetic pigment particles in the coating layers (210 and 210’) of the UV curable screen-printing inks described in Tables 2 and 3 (steps b-1) and b’-1)). The magnetic assemblies (230- 2) illustrated in Figs. 6-8 were used to design-specifically re-orient the optically variable platelet-shaped magnetic pigment particles in the coating layers (210 and 210’) of the UV curable screen-printing inks described in Tables 2 and 3 (step b-2 and b’-2).

[0164] The substrate (220) used for all the Examples and Comparative Examples was a fiduciary paper (from Louisenthal).

[0165] The production of samples E1-E8 and the Comparative Examples C1-C10 is described with reference to Fig. 2B. The first UV curable screen-printing ink, comprising the first optically variable platelet-shaped magnetic pigment particles [inks A1 -A3, step a)] was applied onto the substrate by screen-printing using a first 90T screen (290) to form the first uncured coating layer (210) having a thickness of about 20 |j.m. The substrate (220) carrying the first uncured coating layer (210) was moved above the magnetic assembly (230-1) (being the magnetic assembly 230-1 of Fig. 5) (step b-1)) and was subsequently placed on the second magnetic assembly (230-2) (step b-2)). The so-obtained design-specific magnetic orientation pattern of the optically variable platelet-shaped magnetic pigment particles was then fixed by exposing for about 3 seconds to UV light to cure the coating layer (210) comprising the pigment particles, while the first coating layer (210) was still under the influence of the second magnetic assembly (230-2), using a UV-LED-lamp (250) from Phoseon (Type FireFlex 50 x 75 mm, 395 nm, 8 W / cm2), in step c), to form the first cured coating layer (210).

[0166] The second UV curable screen-printing ink comprising the second optically variable platelet-shaped magnetic pigment particles [inks A’1-A’11 , step a’)] was applied in register with the first cured coating layer (210) applied in step a) onto the substrate on top of the first coating layer (210) by screen-printing using a second 90T screen (290’) to form the second uncured coating layer (21 O’) having a thickness of about 20 |j.m.

[0167] The substrate (220) carrying the second uncured coating layer (210’) was moved above the magnetic assembly (230- T) (being the magnetic assembly 230-1 of Fig. 5) (step b’-1) and was subsequently placed on the second magnetic assembly (230-2’) (step b’-2). The so-obtained magnetic orientation pattern of the optically variable platelet-shaped magnetic pigment particles was then fixed by exposing for about 3 seconds to UV-light to cure the second coating layer (21 O’) comprising the pigment particles, while the substrate (220) and coating layer (210) were still under the influence of the second magnetic assembly (230-2’), using a UV-LED-lamp (250’) from Phoseon (Type FireFlex 50 x 75 mm, 395 nm, 8 W / cm2), in step c’), to form the second cured coating layer.

[0168] For Examples E1 to E4 the orientation steps b-2) and b’-2) were carried out in magnetic register, that is with a linear deviation of < 0.5 mm, whereas for Comparative Examples C1 to C4, the orientation steps b-2) and b’-2) were deliberately carried out off-register, as follows [numbers designate the approximate linear deviation of the orientation step b-2) from b’-2)]: C1 : 6 mm; C2: 1 mm; C3: 2-4 mm and C4: 3-4 mm.

[0169] *d5o of about 11 pm, thickness of about 1 pm

[0170] OELs of the Examples E1-E4 were prepared according to the process of the invention schematically illustrated in Fig. 2B, in magnetic register for the orientation steps b) and b’), in particular for the reorientation steps b-2) and b’-2). The resulting OELs provide the impression of a third optically variable color, different from the optical variable color of the first ink applied in step a) and from the second ink applied in step a’).

[0171] The results are summarized in Table 5.

[0172] For example, E1 displayed a single moving rolling bar effect with a silverish rose color at orthogonal viewing angle and a gold rose color at grazing viewing angle, in particular in the center of the rolling bar effect.

[0173] The OELs of E2-E4 also provided the impression of a third optically variable color, different from the optical variable color of the first ink applied in step a) and from the second ink applied in step a’).

[0174] OELs of Comparative Examples C1-C4 were prepared with the same process and the same inks as the corresponding Examples E1-E4, but the orientation steps b) and b’), in particular the pattern-specific orientation steps b-2) and b’-2), were performed, deliberately, in a slightly off-register manner. As a consequence, the resulting OELs do not provide the impression of a third optically variable color, different from the optical variable color of the first ink applied in step a) and from the second ink applied in step a’) and in addition two distinct visual effects are observed.

[0175] For instance, C1 displayed two separate moving rolling bar effects, one with a magenta-to-green color similar to the variable color of the first ink applied in step a), and one with green-to-blue color similar to the variable color of the second ink applied in step a’).

[0176] OELs for Examples E5-E8 and of Comparative Examples C5-C10 (Table 6) were prepared according to the process schematically illustrated in Fig. 2B to look at the effect of concentration of the optically variable platelet-shaped magnetic pigment particles in the second coating layer (210’). Contrary to E5-E8, when the concentration of the optically variable platelet-shaped magnetic pigment particles in the second coating layer (210’) was below about 3 wt% only the color of the first layer was observed (C5). When the concentration of the optically variable platelet-shaped magnetic pigment particles in the second coating layer (210’) was above about 9 wt% only the color of the second layer was observed (C6-C10).

[0177] (*) For Comparative Example C10, the ink A2 was used in step a’) i.e. to apply the second coating layer.

[0178] The OELs of Example E1 and of Comparative Example C1 were used to measure the different optically variable colors.

[0179] Two OELs comprising only one coating layer were independently prepared according to the process schematically illustrated in Fig. 2B using the ink A1 or the ink A’1 (steps a) to c) using the magnetic assembly 230-2 of Fig. 6 for the step b-2) on the same fiduciary paper substrate.

[0180] The OEL of E1 showed a single bright rolling bar effect, while the OEL of C1 showed two less bright rolling bar effects as a result of the off-register orientation steps b) and b’). The OELs of the samples prepared with the ink A1 and with the ink A’1 showed a single bright rolling bar effect resulting from the single coating layer.

[0181] The colors in the center of the OELs, i.e. in the center of the rolling bar effect, of E1 , C1 , A1 and A’1 were measured at 0° to the normal with an illumination angle of 22.5°, using a goniometer (Goniospektrometer Codec WI-10 5&5 by Phyma GmbH Austria). The a* and b* values are represented graphically in Fig. 9.

[0182] Ink A1 , when oriented and cured, yields a rolling bar having the color represented in Fig. 9 by point A1 , and ink A’1 , when oriented and cured, yields a rolling bar having the color represented in Fig. 9 by point A’1 . Example E1 uses these same inks for the first (210) and second (210’) coating layers. In Example E1 (1stcoating layer ink A1 , 2ndcoating layer ink A’1), where the orientation steps b) and b’) were carried out in register, a single rolling bar is observed, and the color of the rolling bar is represented in Fig. 9 as point E1. This color is a third color, clearly different from the colors of the rolling bars of individual inks used to make E1 (A1 and A’1).

[0183] In Comparative Example C1 (1stcoating layer ink A1 , second coating layer ink A’1), where the orientation steps b) and b’) were deliberately carried out off-register, two rolling bars are observed. The colors of the rolling bars are represented in Fig. 9 as points C1 and CT. The point designated C1 represents the color of the first rolling bar in Comparative Example C1. The point CT represents the color of the second rolling bar in Comparative Example C1 . The a* and b* values of these colors are similar to those of the constituent coating layers separately (A1 and A’1), and indeed points CT and A’1 are indistinguishable to the naked eye, as are points C1 and A1. Importantly, no third color is observed in Comparative Example C1 .

[0184] Magnetic assemblies

[0185] Static magnetic assembly for bi-axial orientation

[0186] The static magnetic assembly (230-1) used to bi-axially orient the optically variable platelet-shaped magnetic pigment particles according to the method of the present invention [steps b-1) and b’-1)] was the magnetic assembly disclosed in WO2021 / 239607A, and is shown in detail in Fig. 5.

[0187] Referring to Fig.5, the static magnetic assembly (230-1) comprised a) a first set (S1) comprising a first bar dipole magnet (531 -a) and two second bar dipole magnets (532-a and 532-d), a second set (S2) comprising a first bar dipole magnet (531 -b) and two second bar dipole magnets (532-b and 532-e), a third set (S3) comprising a first bar dipole magnet (531 -c) and two second bar dipole magnets (532-c and 532-f),and b) a first pair (P1) of third bar dipole magnets (533-a and 533-b) and a second pair (P2) of third bar dipole magnets (533-c and 533-f).

[0188] The uppermost surface of the first bar dipole magnet (531 -a, 531 -b and 531 -c) of the first, second and third sets (S1 , S2, S3), of the second bar dipole magnets (532-a to 532f) of the first, second and third sets (S1 , S2, S3) and of the third bar dipole magnets (533-a to 533-d) of the first and second pairs (P1 and P2) were flush with each other.

[0189] The third bar dipole magnet (533-a) was aligned with the second bar dipole magnet (532-a) of the first set (S1), with the second bar dipole magnet (532-b) of the second set (S2), with the third bar dipole magnet (533-c) and with the second bar dipole magnet (532-c) of the third set (S3) to form a line. The third bar dipole magnet (533-b) was aligned with the second bar dipole magnet (532-d) of the first set (S1), with the second bar dipole magnet (532-e) of the second set (S2), with the third bar dipole magnet (533-d) and with the second bar dipole magnet (532-f) of the third set (S3) to form a line. For each line, the third bar dipole magnets (533-a, 533-b, 533-c and 533-d) and the second bar dipole magnets (532- a to 532-f) were spaced apart by a third distance (d2) of 2 mm. The first bar dipole magnet (531 -a) of the first set (S1) and the first bar dipole magnet (531 -b) of the second set (S2), and the first bar dipole magnet (531 -c) of the third set (S3) were spaced apart by a distance (d3) of 24 mm.

[0190] The first bar dipole magnets (531 -a, 531 -b and 531 -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 (532-a to 532-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 (533-a to 533-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.

[0191] The first bar dipole magnet (531 -a) of the first set (S1) and the second bar dipole magnets (532-a and 532-d) of the first set (S1) were aligned to form a column; and the first bar dipole magnet (531-b) of the second set (S2) and the second bar dipole magnets (532-b and 532-e) of the second set (S2) were aligned to form a column; and the first bar dipole magnet (531 -c) of the third set (S3) and the second bar dipole magnets (532-c and 532-f) of the third set (S3) were aligned to form a column. For each set (S1 , S2, S3) and each column, the first bar dipole magnets (531 -a, 531-b and 531 -c) and the two second bar dipole magnets (532-a and 532-d; 532-b and 532-e; and 532-c and 532-f, respectively) were spaced apart by a second distance (d1) of 2 mm.

[0192] The first bar dipole magnets (531 -a, 531-b and 531 -c) of the first, second and third sets (S1 , S2, S3) had their magnetic axis oriented to be substantially parallel to the substrate (220) surface (“first plane P”), wherein the first bar dipole magnet (531-a) of the first set (S1) had its magnetic direction opposite to the magnetic direction of the first bar dipole magnet (531-b) of the second set (S2), and the first bar dipole magnet (531-b) of the second set (S2) had its magnetic direction opposite to the magnetic direction of the first bar dipole magnet (531-c) of the third set (S3). The first bar dipole magnet (531-a) of the first set (S1) and first bar dipole magnet (531-b) of the second set (S2), as well as the first bar dipole magnet (531-b) of the second set (S2) and the first bar dipole magnet (531-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)).

[0193] The two second bar dipole magnets (532-a to 532-f) of the first, second and third set (S1 , S2, S3) had their magnetic axis oriented to be substantially perpendicular to the substrate (220) surface. The South pole of the second bar dipole magnet (532-a) of the first set (S1), the South pole of the second bar dipole magnet (532-e) of the second set (S2) and the South pole of the second bar dipole magnet (532- c) of the third set (S3) pointed towards the plane of the substrate (220). The North pole of the second bar dipole magnet (532-d) of the first set (S1), the North pole of the second bar dipole magnet (532-b) of the second set (S2) and the North pole of the second bar dipole magnet (532-f) of the third set (S3) pointed towards plane of the substrate (220). The North pole of the first bar dipole magnet (531-a) of the first set (S1) pointed towards the second bar dipole magnet (532-d) of the first set (S1), the North pole of the second bar dipole magnet (531-b) of the second set (S2) pointed towards the first bar dipole magnet (532-b) of the second set (S2) and the North pole of the first bar dipole magnet (531-c) of the third set (S3) pointed towards the second bar dipole magnet (532-f) of the third set (S3). The South pole of the third bar dipole magnet (533-a) of the first pair (P1) pointed towards the second bar dipole magnet (532-a) of the first set (S1), said second bar dipole magnet (532-a) having its South pole pointing towards the plane of the substrate (220); the South pole of the third bar dipole magnet (533-d) of the second pair (P1) pointed towards the second bar dipole magnet (532-e) of the second set (S2), said second bar dipole magnet (532-e) having its South pole pointing towards the plane of the substrate (220); the North pole of the third bar dipole magnet (533-b) of the first pair (P1) pointed towards the second bar dipole magnet (532-d) of the first set (S1), said second bar dipole magnet (532-d) having its North pole pointing towards the plane of the substrate (220); and the North pole of the third bar dipole magnet (533-c) of the second pair (P2) pointed towards the second bar dipole magnet (532-b) of the second set (S2), said second bar dipole magnet (532-b) having its North pole pointing towards the plane of the substrate (220).

[0194] The first bar dipole magnets (531 -a, 531 -b and 531 -c) of the first, second and third sets (S1 , S2, S3) and the second bar dipole magnets (532-a to 532-f) of the first, second and third sets (S1 , S2, S3) were made of NdFeB N42; the third bar dipole magnets (533, 533-b and 533-c) of the first and second pairs (P1 , P2) were made of NdFeB N48. All the magnets (531 -a to 531 -c, 532-a to 532-f and 533-a to 533- 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.

[0195] Magnetic assembly of Fig. 6

[0196] The magnetic assembly (230-2) used to prepare the OEL of Examples E1-E2 and Comparative Examples C1-C2 is illustrated in Fig. 6. The magnetic assembly (230-2) of Fig. 6 comprised a bar dipole magnet (630-2-1) and a holding case (670). The bar dipole magnet (630-2-1) 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 (630-2-1) was parallel to the substrate (220) surface, parallel to its length (L1) and parallel to the machine feed direction (shown by the arrow in Fig. 6). The bar dipole magnet (630-2-1) was made of NdFeB BMnPi 80 / 48.

[0197] The holding case (670) 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 (630-2-1).

[0198] The distance (h) between the top surface of the bar dipole magnet (630-2-1) and the surface of the bottom substrate (220) was about 3.35 mm.

[0199] Magnetic assembly of Fig. 7

[0200] The magnetic assembly (230-2) used to prepare the OEL of Examples E3-E4 and Comparative Examples C3-C4 is illustrated in Fig. 7. The magnetic assembly (230-2) of Fig. 7 comprised a first discshaped dipole magnet (730-2-1), a second disc-shaped dipole magnet (730-2-2), a disc-shaped pole piece (760), a square-shaped wedge (780), and a holding case (770).

[0201] The holding case (770) 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.

[0202] The first disc-shaped dipole magnet (730-2-1) 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 (730-2-1) was perpendicular to the substrate (220) surface and perpendicular to its diameter, with its North pole pointing toward the substrate (220). The disc-shaped dipole magnet (730-2-1) was made of NdFeB N45. The second discshaped dipole magnet (730-2-2) 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 (730-2-2) was perpendicular to the substrate (220) surface and perpendicular to its diameter, with its North pole pointing toward the substrate (220). The disc-shaped dipole magnet (730-2-2) was made of NdFeB N35. The disc-shaped pole piece (760- had a diameter of about 30 mm and a thickness of about 2 mm. The disc-shaped pole piece (760) was made of steel 140HV. The square-shaped wedge (780) had a side-length of about 29.9 mm and a thickness of about 6 mm. The square-shaped wedge (780) was made of polyethylene.

[0203] The first disc-shaped dipole magnet (730-2-1) was disposed on top and direct contact with the second disc-shaped dipole magnet (730-2-2), the second disc-shaped dipole magnet (730-2-2) was disposed on top and direct contact with the disc-shaped pole piece (760), and the disc-shaped pole piece (760) was disposed on top and direct contact with the square-shaped wedge (780). The first disc-shaped dipole magnet (730-2-1), the second disc-shaped dipole magnet (730-2-2), the disc-shaped pole piece (760) and the square-shaped wedge (780) were centrally aligned.

[0204] The distance (h) between the top surface of the first disc-shaped dipole magnet (730-2-1) and the bottom surface of the substrate (220) was about 0.34 mm.

[0205] Magnetic assembly of Fig. 8

[0206] The magnetic assembly (230-2) used to prepare the OEL of Examples E5-E8 and Comparative Examples C5-C10 is illustrated in Fig. 8. The magnetic assembly (230-2) comprised a non-magnetic matrix (880) carrying 64 disc-shaped dipole magnets (830-2-2) and 64 disc-shaped dipole magnets (830-2-3), a square-shaped non-magnetic wedge (860), a bar dipole magnet (830-2-1) and a holding case (870).

[0207] 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 non-magnetic matrix (880) carrying the 64 disc-shaped dipole magnets (830-2-2) and the 64 discshaped dipole magnets (830-2-3), the square-shaped non-magnetic wedge (860) and the bar dipole magnet (830-2-1).

[0208] The 64 disc-shaped dipole magnets (830-2-2) and the 64 disc-shaped dipole magnets (830-2-3) had a diameter L6 of about 2 mm, a thickness of about 2 mm. The North-South magnetic axis of the discshaped dipole magnets (830-2-2) and of the disc-shaped dipole magnets (830-2-3) was perpendicular to the substrate (220) surface and perpendicular to their diameter L6, the 64 disc-shaped dipole magnets (830-2-2) having their North pole pointing toward the substrate, and the 64 disc-shaped dipole magnets (830-2-3) having their South pole pointing toward the substrate. The disc-shaped dipole magnets (830-2-2 & 830-2-3) were made of NdFeB N48.

[0209] The non-magnetic matrix (880) had a length L4 and a width L5 of about 29.9 mm and a thickness of about 2 mm. The non-magnetic matrix (880) comprised 128 voids for receiving the 64 disc-shaped dipole magnets (830-2-2) and the 64 disc-shaped dipole magnets (830-2-3). The non-magnetic matrix (880) was made of POM.

[0210] Each of the 64 first dipole magnets (830-2-2), in particular the center of each of them, was arranged on the intersection of a grid comprising eight parallel straight lines ai (i = 1 , ... , 8; a1 to a8) and eight parallel straight lines pi (I = 1 , ... , 8; pi to p8); each of the 64 first dipole magnets (830-2-3), in particular the center of each of them, was arranged on the intersection of a grid comprising eight parallel straight lines yi (i = 1 , ... , 8; y1 to y8) and eight parallel straight lines 8i (i = 1 , ... , 8; 81 to 88); the eight parallel straight lines ai (a1 to a8) and the eight parallel straight lines yi (y1 to y8) were parallel with each other and arranged in an alternating staggered manner; the eight parallel straight lines pi (pi to p8) and the eight parallel straight lines Si (81 to 88) were parallel with each other and arranged in an alternating staggered manner, as illustrated in Fig. 8.

[0211] The square-shaped non-magnetic wedge (860) had a length and a width of about 29.5 mm and a thickness of 0.22 mm and was made of an adhesive film made of PVC / acrylic film.

[0212] The bar dipole magnet (830-2-1) had a length L1 and a width L2 of about 29.9 mm and a thickness of about 6.9 mm. The North-South magnetic axis of the bar dipole magnet (830-2-1) was parallel to the substrate (220) surface and parallel to its length L1. The bar dipole magnet (830-2-1) was made of NdFeB BMnPi 80 / 48.

[0213] The distance (h) between the non-magnetic matrix (880) surface and the surface of the substrate (220) was about 1.1 mm.

Claims

CLAIMS1 . A process for producing an optical effect layer (OEL) on a substrate, said OEL comprising a first motif comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color, oriented according to a magnetic pattern and a second motif comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color, oriented according to said same magnetic pattern, which first and second motifs together form a composite motif, said process comprising: a) applying onto the substrate a first radiation-curable coating composition, preferably a first UV-Vis-curable coating composition, comprising the first optically variable platelet-shaped magnetic or magnetizable pigment particles at a concentration of [A] to form a first coating layer on said substrate, said first 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 to magnetically orient at least a part of the first optically variable plateletshaped magnetic or magnetizable pigment particles according to said magnetic pattern; c) at least partially curing the first radiation-curable coating composition of step b) to a second state to fix the first optically variable platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and to produce the first motif; a’) applying, at least partially overlapping the first motif in an overlap zone, a second radiation-curable coating composition, preferably a second UV-Vis-curable coating composition, comprising the second optically variable platelet-shaped magnetic or magnetizable pigment particles at a concentration of [B] to form a second coating layer, said second coating composition being in a first state; b’) exposing the second radiation-curable coating composition of step a’) to a magnetic field of a magnetic assembly to magnetically orient at least a part of the second optically variable platelet-shaped magnetic or magnetizable pigment particles in the overlap zone, according to said same magnetic pattern; c’) at least partially curing the second radiation-curable coating composition of step b’) to a second state to fix the second optically variable platelet-shaped magnetic or magnetizable pigment particles in their adopted positions and orientations and to produce the second motif; wherein steps b) and b’) are carried out in magnetic register, the first and second coating layers have different colors at at least one viewing angle, the ratio of [A] / [B] is from about 1 .83 to about 5.5, and the sum of the numerical values [A] + [B] is less than about 25.

2. The process according to claim 1 , wherein the ratio [A] / [B] is about 2 to about 4, more preferably about 2.3 to about 3.3.

3. The process according to claim 1 or 2, wherein steps a) and a’) are carried out in print register.

4. The process according to claim 1 , 2 or 3, wherein step b) and step b’) comprises a first step b-1) and b’-1) of bi-axially orienting the optically variable platelet-shaped magnetic or magnetizable44pigment particles, and a second step b-2) and b’-2) of re-orienting the optically variable plateletshaped magnetic or magnetizable pigment particles according to the magnetic pattern.

5. The process according to any one preceding claim, wherein the first and second coating layers have different colors when both are viewed at a same orthogonal angle and / or when both are viewed at a same grazing angle.

6. The process according to any one preceding claim, wherein the first radiation-curable coating composition comprises the first optically variable platelet-shaped magnetic or magnetizable pigment particles at about 9 to about 20 wt%, preferably about 12 to about 18 wt%, based on the total weight of the first coating composition.

7. The process according to any one preceding claim, wherein the second radiation-curable coating composition comprises the second optically variable platelet-shaped magnetic or magnetizable pigment particles at about 3 to about 10 wt%, preferably about 5 to about 8 wt%, based on the total weight of the second coating composition.

8. The process according to any one preceding claim, wherein the first radiation-curable coating composition comprises the first optically variable platelet-shaped magnetic or magnetizable pigment particles at about 9 to about 20 wt%, preferably about 12 to about 18 wt%, based on the total weight of the first coating composition and wherein the second radiation-curable coating composition comprises the second optically variable platelet-shaped magnetic or magnetizable pigment particles at about 3 to about 10 wt%, preferably about 5 to about 8 wt%, based on the total weight of the second coating composition.

9. The process according to claim 8, wherein the first radiation-curable coating composition comprises the first optically variable platelet-shaped magnetic or magnetizable pigment particles at about 12 to about 18 wt%, based on the total weight of the first coating composition and wherein the second radiation-curable coating composition comprises the second optically variable platelet-shaped magnetic or magnetizable pigment particles at about 5 to about 8 wt%, based on the total weight of the second coating composition.

10. The process according to any one preceding claim, wherein said process is a continuous process being carried out with a single machine and the substrate carrying the first coating layer (210) is not removed from said single machine between steps a) and c’).

11. The process according to any one preceding claim, wherein the first optically variable plateletshaped magnetic or magnetizable pigment particles and the second optically variable plateletshaped magnetic or magnetizable pigment particles are selected from the group consisting of magnetic thin-film interference pigment particles, interference coated pigment particles comprising a magnetic material and mixtures thereof.

12. The process according to claim 11 , wherein the magnetic thin film interference pigment particles are selected from the group consisting of five-layer Fabry-Perot multilayer structure pigment particles, six-layer Fabry-Perot multilayer structure pigment particles, seven-layer Fabry-Perot multilayer structure pigment particles, nine-layer Fabry-Perot multilayer structure pigment particles, eleven-layer Fabry-Perot multilayer structure and / or a multilayer Fabry-Perot structure pigment particles, and mixtures thereof.4513. The process according to any one preceding claim, wherein both steps c) and c’) are carried out by UV-Vis light radiation curing and / or wherein both steps c) and c’) are carried out partially simultaneously with the step b) and b’), respectively.

14. The process according to claim 13, wherein at least one of the steps c) and c’), preferably both steps c) and c’), is carried out by exposing the first coating layer (210) and the second coating layer (210’), respectively, to UV light with an LED curing unit.

15. An OEL comprising:(i) a first motif composed of a first coating layer comprising first optically variable platelet-shaped magnetic or magnetizable pigment particles having a first color and being comprised in the first coating layer at a concentration of [A], wherein the first optically variable platelet-shaped magnetic or magnetizable pigment particles are permanently oriented according to a predetermined magnetic pattern; ii) a second motif, at least partially overlapping the first motif in an overlap zone, composed of a second coating layer comprising second optically variable platelet-shaped magnetic or magnetizable pigment particles having a second color and being comprised in the second coating layer at a concentration of [B], wherein the second optically variable platelet-shaped magnetic or magnetizable pigment particles are permanently oriented according to said same predetermined magnetic pattern in the overlap zone; wherein the first motif and the second motif together form a composite motif, and wherein the magnetic patterns of the first and second motif are in magnetic register, the first and second coating layers have different colors at at least one viewing angle, the ratio of [A] / [B] is from about 1 .83 to about 5.5, and the sum of the numerical values [A] + [B] is less than about 25.46

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