Obvious Security Features

Abstract

The present invention relates to the field of methods for producing eye-catching overt security features exhibiting color-shifting properties as an anti-counterfeiting measure and for decorative purposes on security documents or security articles. In particular, the overt security feature comprises: a) a substrate (x10), a color constant layer (x20) comprising magnetically oriented platelet-shaped magnetic or magnetizable pigment particles, and an optically variable layer (x30) comprising a cholesteric liquid crystal polymer (CLCP) reflecting light in the visible spectral range, the platelet-shaped magnetic or magnetizable pigment particles of the color constant layer (x20) having substantially the same elevation angle α.

Description

Detailed Description of the Invention

[0001] [Field of the Invention]

[0001] The present invention relates to the field of overt security features on substrates, security documents, security articles, and decorative articles. In particular, the present invention provides an eye-catching overt security feature that exhibits color shifting properties as an anti-counterfeiting measure and decorative purpose on a security document or security article.

[0002] [Background of the invention]

[0002] With the ever-improving quality of color photocopying and printing, it has become conventional practice to incorporate various security elements into security documents and articles, such as banknotes, value documents or cards, transport tickets or cards, tax tickets, and product labels, which do not have reproducible effects, in an attempt to protect these documents and articles from counterfeiting, alteration, or illegal duplication. Typical examples of security elements include security threads, windows, fibers, planchets, foils, stickers, holograms, watermarks, optically variable pigments, magnetic or magnetizable thin film interference pigments, interference coated particles, thermochromic pigments, photochromic pigments, security inks containing luminescent, infrared absorbing, ultraviolet absorbing, or magnetic compounds.

[0003]

[0003] For example, security features for security documents can be generally classified into "covert" security features on the one hand, and "overt" security features on the other hand. The protection offered by covert security features depends on the notion that such features are difficult to detect and typically require special equipment and knowledge for detection, whereas "overt" security features rely on the notion that they are easily detectable by the unaided human senses, e.g., such features may be visible and / or detectable via touch, while still being difficult to make and / or copy. However, the effectiveness of an overt security feature depends to a large extent on its eye-catching effect as a security feature and its easy recognition, since most users, especially those without prior knowledge of the security features of the document or article protected by said features, will actually make a security check based on said security feature only if they are actually aware of the presence and nature of said security feature.

[0004]

[0004] Optically variable security features (also referred to in the art as goniochromatic features) have a color shift that is manifested by a change in lightness and / or saturation and / or hue with a change in observation angle (also referred to in the art as viewing angle) between grazing angle and face angle, and are commonly used to protect security documents and articles against counterfeiting and / or illegal duplication by available color scanning, printing, and copying office equipment.

[0005] Typically, the security feature comprises an ink containing flake-like multi-layer interference pigments.

[0006]

[0006] Other security features based on cholesteric liquid crystal materials have been developed. Materials with a liquid crystal structure with a chiral phase, also known as cholesteric liquid crystal materials, are known and used as optically variable security features. Cholesteric liquid crystal polymers exhibit molecular order in the form of a helical superstructure perpendicular to the longitudinal axis of their molecules. The helical superstructure results in a periodic refractive index modulation throughout the liquid crystal material, which in turn results in the selective transmission / reflection of light of a determined wavelength (interference filter effect). Cholesteric liquid crystal polymers can be obtained by aligning and orienting one or more crosslinkable substances (nematic compounds) with a chiral phase. The specific circumstances of the helical molecular arrangement result in cholesteric liquid crystal materials that exhibit the property of reflecting a circularly polarized component within a determined wavelength range, said circularly polarized light being left-handed or right-handed depending on the meaning of the rotation of the molecular helix. The range of wavelengths reflected by a cholesteric liquid crystal polymer is determined by the geometry of its periodic refractive index modulation, i.e. the pitch of the molecular helix, as known to those skilled in the art. The pitch (i.e. the distance over which a full 360° rotation of the helical configuration is completed) can be specifically tuned by varying selectable factors including temperature and solvent concentration, by varying the nature of the chiral component(s) and the ratio of nematic and chiral compounds. The pitch of the material can finally be frozen by a crosslinking (polymerization) reaction so that the color of the resulting cholesteric liquid crystal polymer is no longer dependent on external factors such as temperature.

[0007]

[0007] US Patent No. 6,423,246 discloses a security feature comprising an optically variable pigment prepared by milling a cholesteric liquid crystal polymer film, the pigment exhibiting a color shift from a first color to a second color upon tilting of the security feature.

[0008]

[0008] WO 2015 / 055504 A1 discloses an optically variable security element based on a single stiffening layer comprising a cholesteric liquid crystal polymer.

[0009]

[0009] The range of color shifts of cholesteric liquid crystal polymers available for security documents may be limited, and it may be advantageous to modify the reflection properties and thereby increase the range of available colors, with the aim of increasing the color gamut of the optically variable security feature. As mentioned above, the reflected light from a cholesteric liquid crystal polymer depends on the pitch of the helical structure of the polymer and thereby on the nature and concentration of the chiral component(s). In particular, adding an appropriate amount of the chiral component(s) to the precursor mixture results in a color shift modification to shorter wavelengths. However, it is not easy or cost-effective to customize cholesteric liquid crystal materials during production for each specific application and each desired color shift effect. Moreover, fine-tuning the color shift properties of cholesteric liquid crystal polymers is a delicate step, often resulting in a significant waste of time and / or material.

[0010]

[0010] Thus, there remains a need for eye-catching, multi-coloured overt security features, especially for highly demanding applications requiring high counterfeit resilience, thus allowing easy, direct and unambiguous authentication by the human eye without external devices or tools. Said overt security features need to be prepared by a method that is reliable, predictable in a controlled manner, easy to implement and should be able to function at high production speeds.

[0011] [Summary of the invention]

[0011] Therefore, the present invention aims to overcome the deficiencies of the prior art. a) a substrate (x10) made of a material selected from the group consisting of transparent materials, light absorbing materials, and combinations thereof; b) a color-constant layer (x20) containing magnetically oriented platelet-shaped magnetic or magnetizable pigment particles; c) an optically variable layer (x30) comprising a cholesteric liquid crystal polymer (CLCP) reflecting light in the visible spectral range, the optically variable layer (x30) being on top of the color constant layer (x20) and thus forming a first area consisting of a superposition of the optically variable layer (x30) and the color constant layer (x20), This is achieved by providing an overt security feature in which the platelet-shaped magnetic or magnetisable pigment particles of the colour constant layer (x20) have substantially the same elevation angle α, said elevation angle |α| having a value of between about 10° and about 45° (10°≦angle |α|≦45°), preferably between about 15° and about 40° (15°≦angle |α|≦40°), more preferably between about 15° and about 35° (15°≦angle |α|≦35°).

[0012]

[0012] The elevation angles |α| provided in this specification consist of average values ​​obtained either i) using a conoscopic scatterometer as described below, said value being averaged over at least about 1000 platelet-shaped magnetic or magnetizable pigment particles, or ii) using a microscope as described below, said value being averaged over at least 10, in particular 10 to 20, platelet-shaped magnetic or magnetizable pigment particles.

[0013]

[0013] The first area of ​​the overt security feature exhibits at least three different colors when viewed through the optically variable layer (x30) at different viewing / observation angles, one of said angles being a grazing angle (e.g. 10°, 20°, 30°, etc.) and another one being a face angle (approximately 90°), provided that if the substrate is transparent, the overt security feature must be placed on a light absorbing background.

[0014]

[0014] The colour constant layer (x20) described in this specification comprises uniaxially oriented platelet shaped magnetic or magnetisable pigment particles, or biaxially oriented platelet shaped magnetic or magnetisable pigment particles, said particles exhibiting a metallic colour (more preferably silver).

[0015]

[0015] The optically variable layer (x30) described in this specification is preferably obtained from a cholesteric liquid crystal polymer precursor composition comprising one or more nematic compounds, one or more chiral dopants, one or more photoinitiators, and one or more solvents.

[0016] The overt security features described herein are particularly suitable for protecting security documents, security articles, and decorative articles from counterfeiting, fraud, or illegal duplication.

[0017] Also described herein are security documents, security articles, and decorative articles that include one or more of the overt security features described herein, as well as methods for producing the same, and security documents, security articles, and decorative articles obtained therefrom. A method for producing an overt security feature described herein includes the steps of: a) applying onto a surface of a substrate (x10) a radiation curable coating composition comprising platelet-shaped magnetic or magnetisable pigment particles, said radiation curable coating composition being in a first liquid state so as to form a layer; b) exposing the layer obtained in step a) to magnetic field lines of a magnetic field generating device, said magnetic field lines forming an elevation angle |γ| with the substrate (x10) surface, said angle |γ| having a value of about 10° to about 45° or about 135° to about 170° so as to orient the platelet-shaped magnetic or magnetizable pigment particles; c) partially simultaneously with or subsequent to step b), at least partially curing the layer in a curing unit to at least partially fix the position and orientation of the platelet-shaped magnetic or magnetizable pigment particles, so that the platelet-shaped magnetic or magnetizable pigment particles have the same elevation angle α of about 10° to about 45° (10°≦angle |α|≦45°), preferably about 15° to about 40° (15°≦angle |α|≦40°), more preferably about 15° to about 35° (15°≦angle |α|≦35°), to form a color-constant layer (x20); d) applying a cholesteric liquid crystal polymer precursor composition at least partially onto the color-constant layer (x20) and / or at least partially onto the substrate (x10) surface; e) heating the layer obtained in step d); f) hardening of the layer obtained in step e) so as to obtain an optically variable layer (x30); Includes.

[0018]

[0018] Also described in this specification is a method of manufacturing a security document, security article, or decorative article, comprising: a) providing a security document, security article, or decorative article, and b) providing one or more overt security features described herein on or included by the security document, security article, or decorative article. [Brief description of the drawings]

[0019] [Figure 1A] 1A-1E and 2A-2B illustrate several embodiments of the present invention. [Figure 1B] 1A-1E and 2A-2B illustrate several embodiments of the present invention. [Figure 1C] 1A-1E and 2A-2B illustrate several embodiments of the present invention. [Figure 1D] 1A-1E and 2A-2B illustrate several embodiments of the present invention. [Figure 1E] 1A-1E and 2A-2B illustrate several embodiments of the present invention. [Figure 2A] 1A-1E and 2A-2B illustrate several embodiments of the present invention. [Figure 2B] 1A-1E and 2A-2B illustrate several embodiments of the present invention. [Figure 3A]FIG. 3A shows diagrammatically a platelet-shaped magnetic or magnetisable pigment particle having a major axis X and a major axis Y. [Figure 3B] Fig. 3B shows a schematic representation of uniaxially oriented platelet-shaped particles, where the platelet vectors (vectors parallel to the particle's main axis X) of adjacent platelet-shaped magnetic or magnetizable pigment particles are substantially parallel to each other. Fig. 3C shows a schematic representation of biaxially oriented platelet-shaped particles, where the platelet vectors (vectors parallel to the particle's main axis X) of adjacent platelet-shaped magnetic or magnetizable pigment particles are parallel to each other and the second platelet vectors (vectors parallel to the particle's main axis Y) of adjacent platelet-shaped magnetic or magnetizable pigment particles are substantially parallel to each other. [Figure 3C] Fig. 3B shows a schematic representation of uniaxially oriented platelet-shaped particles, where the platelet vectors (vectors parallel to the particle's main axis X) of adjacent platelet-shaped magnetic or magnetizable pigment particles are substantially parallel to each other. Fig. 3C shows a schematic representation of biaxially oriented platelet-shaped particles, where the platelet vectors (vectors parallel to the particle's main axis X) of adjacent platelet-shaped magnetic or magnetizable pigment particles are parallel to each other and the second platelet vectors (vectors parallel to the particle's main axis Y) of adjacent platelet-shaped magnetic or magnetizable pigment particles are substantially parallel to each other. [Figure 4] FIG. 4 shows a schematic cross-section of a substrate (410) supporting a color constant layer (420) comprising magnetically oriented platelet-shaped magnetic or magnetizable pigment particles, the platelet-shaped magnetic or magnetizable pigment particles having substantially the same elevation angle |α| (i.e. the absolute values ​​of +α and -α are the same in each color constant layer (x20)). [Figure 5A1]5A1-A2 show schematic diagrams of a suitable magnetic field generating device for biaxially oriented platelet-shaped magnetic or magnetizable pigment particles contained in a layer on a substrate. The magnetic field generating device includes nine magnet subassemblies (M1-M9) arranged in a row with alternating north-south magnetic directions, and the substrate supporting the layer containing the platelet-shaped magnetic or magnetizable pigment particles is tiled at an elevation angle γ, and the particles are exposed to the magnetic field of the magnetic field generating device. [Figure 5A2] 5A1-A2 show schematic diagrams of a suitable magnetic field generating device for biaxially oriented platelet-shaped magnetic or magnetizable pigment particles contained in a layer on a substrate. The magnetic field generating device includes nine magnet subassemblies (M1-M9) arranged in a row with alternating north-south magnetic directions, and the substrate supporting the layer containing the platelet-shaped magnetic or magnetizable pigment particles is tiled at an elevation angle γ, and the particles are exposed to the magnetic field of the magnetic field generating device. [Figure 6] FIG. 6 shows a cross-section of an overt security feature of the present invention in which an optically variable layer (630) overlies a constant color layer (620), optionally including a substrate (610) and a light absorbing background (640) if the substrate (610) does not consist of one or more light absorbing materials, and a method of authenticating said feature by varying the viewing / observation angle β. [Figure 7] FIG. 7 shows a top view of an overt security feature of the present invention comprising a substrate (710) with an optically variable layer (730) partially overlying a color constant layer (720), and how said feature can be authenticated by varying the viewing / observation angle β.

[0020] [Detailed Description] definition The following definitions are used to interpret the meaning of the terms described and claimed herein.

[0021]

[0020] As used herein, the article "a" denotes one and more than one and does not necessarily limit its associated noun to the singular.

[0022] As used herein, the term "at least one" is intended to define one or more than one, for example, 1, 2, or 3.

[0023]

[0022] As used herein, the terms "about" and "substantially" mean that the amount or value in question may be the specified particular value or some other value in its vicinity. In general, the terms "about" and "substantially" referring to a value refer to a range within ±5% of the value. As an example, the phrase "about 100" refers to a range of 100 ±5, i.e., a range of 95 to 105. In general, when the term "about" is used, it is expected that similar results or effects of the present invention can be obtained within a range of ±5% of the indicated value.

[0024] The term "substantially parallel" means at least 1 mm from parallel alignment. 2 or for at least about 100 particles.

[0025]

[0024] As used herein, the term "and / or" means that all or only one of the elements of the group may be present. For example, "A and / or B" means "A only, or B only, or both A and B." In the case of "A only," the term also encompasses the possibility that B is not present, i.e., "A only and not B."

[0026]

[0025] As used herein, the term "comprise" means non-exclusive and non-limiting. Thus, for example, a coating composition comprising compound A may contain other compounds in addition to A. However, the term "comprise" also encompasses the more restrictive meanings of "consisting essentially of" and "consisting of" as specific embodiments thereof, so that, for example, a "mixture comprising A, B, and optionally C" may also consist (substantially) of A and B, or may consist (substantially) of A, B, and C.

[0027]

[0026] The term "visible spectral range" refers to the range from 400 nm to 700 nm.

[0028]

[0027] The term "coating composition" refers to any composition capable of forming a layer on a solid substrate and preferably, but not exclusively, capable of being applied by a printing method. The coating composition comprises the platelet-shaped magnetic or magnetizable pigment particles described herein and the binder described herein.

[0029]

[0028] As used herein, the term "wet" refers to a coating layer that is not yet at least partially cured, e.g., a coating in which platelet-shaped magnetic or magnetizable pigment particles are still able to change their position and orientation under the influence of external forces acting on them.

[0030]

[0029] The term "security document" refers to a document that is typically protected against counterfeiting or fraud by at least one security feature. Examples of security documents include, but are not limited to, documents of value and items of commercial value.

[0031]

[0030] The term "security feature" is used to denote an image, pattern, or graphic element that can be used for authentication purposes.

[0032]

[0031] Where the present description refers to "preferred" embodiments / features, combinations of these "preferred" embodiments / features are also considered to be disclosed to the extent that such combinations of "preferred" embodiments / features make technical sense.

[0033]

[0032] The overt security feature described herein comprises a substrate (x10) as described herein, a color constant layer (x20) comprising magnetically oriented platelet shaped magnetic or magnetizable pigment particles as described herein, and an optically variable layer (x30) comprising a cholesteric liquid crystal polymer (CLCP) that selectively reflects light in the visible spectral range as described herein.

[0034]

[0033] The color constant layer (x20) refers to a coating layer comprising magnetically oriented platelet shaped magnetic or magnetizable pigment particles, said particles being oriented by a magnetic field and the oriented particles being fixed / stopped in their orientation and position (i.e. after curing) to form a magnetically induced layer.

[0035]

[0034] The optically variable layer (x30) overlies the color constant layer (x20) in a first area consisting of a superposition of the optically variable layer (x30) and the color constant layer (x20). Alternatively, the overt security feature described herein may further comprise a second area consisting of only the optically variable layer (x30), said second area preferably surrounding the first area described herein when viewed through the optically variable layer (x20). Figure 7 shows an example of an overt security feature comprising a first area consisting of the mark "A" and a second area consisting of the area around the mark "A".

[0036]

[0035] The eye-catching overt security feature described herein allows an observer to easily and conveniently authenticate the overt security feature because a first area of ​​the overt security feature exhibits at least three different colors (as shown by the eye in the figure) when viewed with the naked eye through an optically variable layer (x20) at different viewing / observation angles, one at a grazing angle (e.g. 10°, 20°, 30°, etc.) and another at a face angle (approximately 90°). However, if the substrate is transparent, the overt security feature must be placed on a permanent light-absorbing background.

[0037]

[0036] The color shifting property of an overt security feature comprising a cholesteric liquid crystal polymer is considered to be an overt security feature that is ostensibly easily recognizable. Advantageously, any one of them can be easily distinguished, recognized, and / or differentiated by the unaided human senses from possible counterfeits of said security feature or a security document or article comprising said security feature, for example, such a feature can be seen and / or distinguished while still being difficult to manufacture and / or copy. Furthermore, the property of reflecting circularly polarized light of a cholesteric liquid crystal polymer may be used as a semi-latent feature that can be seen or distinguished with the aid of a polarizing filter. In other words, the property of reflecting circularly polarized light of a cholesteric liquid crystal polymer may be used as an authentication tool for the recognition of a security feature comprising a cholesteric liquid crystal polymer, or a security document, security article, decorative article comprising said security feature.

[0038] The overt security feature described herein includes a substrate (x10) of a material selected from the group consisting of a transparent material, a light absorbing material, and combinations thereof.

[0039]

[0038] Preferred substrates made of one or more transparent materials include, but are not limited to, transparent polyolefins such as polyethylene (PE) and polypropylene (PP), including biaxially oriented polypropylene (BOPP), transparent polyamides, transparent polyesters such as poly(ethylene terephthalate) (PET), poly(1,4-butylene terephthalate) (PBT), poly(ethylene 2,6-naphthoate) (PEN) and transparent polyvinyl chloride (PVC), more preferably transparent polyesters such as PET.

[0040]

[0039] "Light absorbing substrate" refers to a substrate that absorbs at least 50%, preferably at least 60%, of the intensity of one or more portions of the visible portion of the electromagnetic spectrum (visible spectrum). The light absorbing substrate may be a continuous layer or may be a discontinuous layer in the form of a mark or pattern. Preferably, the light absorbing substrate is a dark substrate, more preferably a black substrate. When the substrate described herein is a light absorbing substrate, no further additional layers or coatings are required to easily observe the color shifting properties of the overt security feature without any machine or device. When the substrate is not a light absorbing substrate, an additional light absorbing background (x40), preferably a dark background (x40), more preferably a black background (x40), may be present, the dark background (x40) may be permanent or non-permanent.

[0041]

[0040] Preferred substrates of one or more absorbent materials include, but are not limited to, those selected from the group consisting of paper or other fibrous materials (including woven and nonwoven fibrous materials), such as cellulose, paper-containing materials, glass, metals, ceramics, plastics, and polymers, metallized plastics or polymers, composite materials, and mixtures or combinations of two or more thereof. Typical paper, paper-like, or other fibrous materials are made of a variety of fibers, including, but not limited to, abaca, cotton, linen, wood pulp, and blends thereof. As is 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.

[0042] The light-absorbing substrate may comprise a transparent substrate containing one or more layers (eg, printer layers) of light-absorbing material.

[0043]

[0042] When the substrate (x10) is made of one or more transparent materials, the overt color shifting properties of the overt security feature are observed by placing the transparent material on a non-permanent light absorbing background as described herein.

[0044]

[0043] It is pointed out that these substrate materials are given only for the purpose of illustration, without limiting the scope of the present invention. In general, any substrate (not necessarily flat, and may be uneven) whose surface is not soluble or only slightly soluble in the solvent(s) used in the cholesteric liquid crystal polymer precursor composition is suitable for the purpose of the present invention.

[0045] According to one embodiment shown in Figures 1A and 1B, the overt security feature described herein comprises a transparent substrate (x10), with a color-constant layer (x20) and an optically variable layer (x30) either located on the same side of said transparent substrate (x10) (see Figure 1A) or on opposite sides (see Figure 1B). As described herein, a non-permanent light-absorbing background may be used to observe the color-shifting properties of the security feature by placing said non-permanent light-absorbing background on the opposite side of the optically variable layer (x30).

[0046]

[0045] According to other embodiments shown in Figures 1C, 1D, and 1E, the overt security feature described in this specification comprises a transparent substrate (x10) and a permanent light-absorbing background (x40), with a color-constant layer (x20) and an optically variable layer (x30) either located on the same side of the transparent substrate (x10) (see Figures 1C and 1D) or on opposite sides (see Figure 1E).

[0047]

[0046] According to another embodiment shown in Figure 2A, the overt security feature described in this specification includes a light-absorbing substrate (x10), and a color-constant layer (x20) and an optically variable layer (x30) are placed on the same side of the light-absorbing substrate (x10).

[0048]

[0047] According to another embodiment shown in Figure 2B, the overt security feature described in this specification comprises a light-absorbing substrate (x10) and a permanent light-absorbing background (x40), and a color-constant layer (x20) and an optically variable layer (x30) are placed on the same side of the light-absorbing substrate (x10).

[0049]

[0048] The optically variable layer (x30) is on top of the color constant layer (x20), thus forming the first area described herein. According to one embodiment, the optically variable layer (x30) is partially on top of the color constant layer (x20) and comprises two areas: a first area where the optically variable layer (x30) is on top of the color constant layer (x20) (superposition of the two layers) and a second area consisting of only the optically variable layer (x30). "On top of" is not limited to direct contact; for example, as shown in Figure 1B, the optically variable layer (x30) is at least partially on top of the color constant layer (x20), but is not in direct contact since a substrate (x10) is present between the two layers (x20 and x30).

[0050]

[0049] According to one embodiment, for example shown in Figures 1A, 1C, 1D, 2A and 2B, the optically variable layer (x30) is at least partially in direct contact with the color constant layer (x20), and both layers are located on the same side of the substrate (x10). According to another embodiment, for example shown in Figures 1B and 1E, the optically variable layer (x30) is at least partially in direct contact with the color constant layer (x20), and both layers are located on opposite sides of the substrate (x10).

[0051]

[0050] The optically variable layer (x30) and the color constant layer (x20) may be independently continuous or discontinuous layers. The color constant layer (x20) and / or the optically variable layer (x30) may independently be in the form of one or more indicia, said indicia consisting of the color constant layer (x20) and the indicia consisting of the optically variable layer (x30) may have the same shape or different shapes. As used herein, the term "indicium" / "indicia" refers to continuous and discontinuous layers consisting of markings or signs or identifying patterns. Examples of indicia include codes, coded marks (e.g. coded alphanumeric data, one-dimensional barcodes, two-dimensional barcodes, QR codes, data matrices, and IR readable codes), symbols, alphanumeric symbols, motifs, geometric patterns (e.g. circles, triangles, and regular or irregular polygons), letters, words, numbers, logos, drawings, portraits, and combinations thereof.

[0052] The overt security feature described herein comprises a colour constant layer (x20) in which platelet shaped magnetic or magnetisable pigment particles are oriented according to a specific orientation pattern.

[0053]

[0052] The thickness of the color constant layer (x20) described in this specification is preferably from about 5 μm to about 30 μm, preferably from about 5 μm to about 20 μm, more preferably from about 5 μm to about 15 μm (measured using an Extramess Inductive Digital Comparator 2001 (manufactured by Mahr Corporation)).

[0054]

[0053] As mentioned herein, the method described herein for producing an overt security feature comprises a step c) of at least partially curing the layer comprising a radiation curable coating composition with particles to a second state, wherein the platelet-shaped magnetic or magnetisable pigment particles are fixed in their current position and orientation and can no longer move or rotate within said layer. According to one embodiment, said step c) is carried out by exposing said layer to one or more wavelengths from about 365 nm to about 470 nm, preferably from about 365 nm to about 405 nm, in a UV-Vis Light Emitting Diode (LED) curing unit.

[0055]

[0054] As used herein, "at least partially curing the layer" means that the platelet-shaped magnetic or magnetizable pigment particles are fixed / stopped in the adopted position and orientation of the pigment particles and can no longer move or rotate (referred to in the art as "pinning" the particles).

[0056]

[0055] As mentioned herein, the color constant layer comprises magnetically oriented platelet-shaped magnetic or magnetizable pigment particles in the at least partially cured layer. Preferably, the platelet-shaped magnetic or magnetizable pigment particles described herein are present in an amount of about 2% to about 25% by weight, preferably about 3% to about 20% by weight, more preferably about 4% to about 15% by weight, and even more preferably about 4% to about 10% by weight, the weight percentage being based on the total weight of the at least partially cured color constant layer. Preferably, the platelet-shaped magnetic or magnetizable pigment particles described herein are present in an amount of about 2% to about 25% by weight, preferably about 3% to about 20% by weight, more preferably about 4% to about 15% by weight, and even more preferably about 4% to about 10% by weight, the weight percentage being based on the total weight of the radiation curable coating layer described herein.

[0057]

[0056] The platelet-shaped magnetic or magnetisable pigment particles described herein are defined as having an anisotropic reflectivity to incident electromagnetic radiation to which the cured binder material is at least partially transparent due to the non-spherical shape of the pigment particles. The binder material is at least partially transparent to electromagnetic radiation in the range of wavelengths comprised between 200 nm and 2500 nm, i.e. in a wavelength region typically referred to as the "optical spectrum" and including the infrared, visible and UV portions of the electromagnetic spectrum, at least in its cured or solid state (also referred to herein as the second state). Thus, the non-spherical magnetic or magnetisable pigment particles contained in the binder material in its cured or solid state and their orientation-dependent reflectivity can be sensed through the binder material at several wavelengths within this range. Preferably, the cured binder material is at least partially transparent to electromagnetic radiation in the range of wavelengths comprised between 200 nm and 800 nm, more preferably between 400 nm and 700 nm. As used herein, the term "transparent" indicates that the transmission of electromagnetic radiation through a 20 μm layer of the cured binder material, as present in the OEL (not including platelet-shaped magnetic or magnetizable pigment particles, but including all other optional components of the OEL, if such components are present), is at least 50%, more preferably at least 60%, even more preferably at least 70% at the wavelength(s) of interest. This can be determined, for example, by measuring the transmittance of a test piece of the cured binder material (not including platelet-shaped magnetic or magnetizable pigment particles) according to established test methods, for example DIN 5036-3 (1979-11). As used herein, the term "anisotropic reflectance" indicates that the proportion of incident radiation from a first angle that is reflected by the particles in a certain (viewing / viewing) direction (second angle) is a function of the orientation of the particles, i.e., a change in the orientation of the particles relative to the first angle may result in a different magnitude of reflection in the viewing / viewing direction. In contrast to needle-shaped pigment particles, which can be considered one-dimensional particles, platelet-shaped pigment particles have an X-axis and a Y-axis that define the major plane of development of the particle (FIG. 3A).In other words, as shown in Figure 3A, platelet shaped pigment particles may be considered to be two-dimensional particles due to the large aspect ratio of their dimensions, with dimensions X and Y being substantially larger than dimension Z. Platelet shaped pigment particles are also referred to in the art as flattened particles or flakes. Such pigment particles can be described with a major axis X corresponding to the longest dimension intersecting the pigment particle, and a second major axis Y perpendicular to X that is also within said pigment particle.

[0058]

[0057] The color constant layer described herein comprises magnetically oriented platelet-shaped magnetic or magnetizable pigment particles in the at least partially cured layer described herein, said platelet-shaped magnetic or magnetizable pigment particles having a specific orientation angle in the color constant layer (x20) corresponding to an elevation angle |α|. The platelet-shaped magnetic or magnetizable pigment particles in the at least partially cured color constant layer (x20) are oriented as described herein at an elevation angle |α| as described herein and shown in Figure 4, where |α| represents the absolute value of +α and -α. In other words, as shown in Figure 4, the platelet-shaped magnetic or magnetizable pigment particles in the at least partially cured color constant layer (x20) have the same angle +α or have the same angle -α.

[0059]

[0058] The platelet-shaped magnetic or magnetizable pigment particles of the color constant layer (x20) have substantially the same elevation angle |α|, said elevation angle |α| having a value of about 10° to about 45° (10°≦angle |α|≦45°), preferably about 15° to about 40° (15°≦angle |α|≦40°), more preferably about 15° to about 35° (15°≦angle |α|≦35°). As described herein, the elevation angle |α| provided herein consists of an average value obtained i) using a conoscopic scatterometer as described below, said value being averaged over at least about 1000 platelet-shaped magnetic or magnetizable pigment particles, or ii) using a microscope as described below, said value being averaged over at least 10, in particular 10 to 20 platelet-shaped magnetic or magnetizable pigment particles.

[0060]

[0059] For example, as shown in Fig. 4, the platelet-shaped magnetic or magnetizable pigment particles are oriented as described above at an elevation angle α as described herein. In other words, the elevation angle α is formed by the main axis X of the platelet-shaped magnetic or magnetizable pigment particles and the two-dimensional surface of the substrate (410), said elevation angle |α| having a value as described herein.

[0061]

[0060] The orientation of the platelet-shaped magnetic or magnetisable pigment particles described herein is obtained in step b) described herein, said orientation being carried out so as to orient said particles described herein uniaxially or biaxially. In contrast to uniaxial orientation (Fig. 3B), in which the particles are oriented such that only their main axis is constrained by the magnetic field, carrying out a biaxial orientation means that the particles are oriented such that the two main axes X and Y of the particles are constrained (Fig. 3C). That is to say, each platelet-shaped magnetic or magnetisable pigment particle can be considered to have a major axis in the plane of the pigment particle and a minor axis perpendicular to the plane of the pigment particle. The axes Y and Y of the platelet-shaped magnetic or magnetisable pigment particles are respectively oriented according to the magnetic field. Effectively, this results in adjacent platelet-shaped magnetic pigment particles spatially close to each other, so as to be substantially parallel to each other. In other words, biaxial orientation aligns the faces of the platelet shaped magnetic or magnetizable pigment particles such that the faces of said pigment particles are oriented substantially parallel (in all directions) to the faces of adjacent platelet shaped magnetic or magnetizable pigment particles.

[0062]

[0061] For embodiments in which the platelet-shaped magnetic or magnetizable pigment particles are uniaxially oriented, for example as shown in Figure 3B, the orientation of the platelet-shaped pigment particles is defined by a platelet vector, which is a vector parallel to the particle's major axis X, and the platelet vectors of adjacent platelet-shaped magnetic or magnetizable pigment particles are substantially parallel to each other; that is, only the major axes X of adjacent platelet-shaped magnetic or magnetizable pigment particles are substantially parallel to each other (in other words, adjacent platelet-shaped magnetic or magnetizable pigment particles have substantially the same elevation angle α).

[0063]

[0062] For example, as shown in Figure 3C, for an embodiment in which the platelet-shaped magnetic or magnetizable pigment particles are biaxially oriented, the orientation of the platelet-shaped pigment particles is defined by a platelet vector that is a vector parallel to the primary axis X of the particle, the platelet vectors of adjacent platelet-shaped magnetic or magnetizable pigment particles are parallel to each other, and is further defined by a second platelet vector that is a vector parallel to a second axis Y of the particle, the platelet vectors of adjacent platelet-shaped magnetic or magnetizable pigment particles are parallel to each other, and the second platelet vectors of said adjacent platelet-shaped magnetic or magnetizable pigment particles are parallel to each other. For example, as shown in Figure 3C, for embodiments in which the platelet-shaped magnetic or magnetizable pigment particles are biaxially oriented, the platelet vectors of adjacent platelet-shaped magnetic or magnetizable pigment particles are parallel to each other, and not only are the primary axes X of adjacent platelet-shaped magnetic or magnetizable pigment particles substantially parallel to each other, but the secondary axes Y of adjacent platelet-shaped magnetic or magnetizable pigment particles are substantially parallel to each other. For example, as shown in Figure 3C, for embodiments in which the platelet-shaped magnetic or magnetizable pigment particles are biaxially oriented, the platelet-shaped magnetic or magnetizable particles are substantially parallel to each other.

[0064]

[0063] For example, according to one embodiment shown in Figures 1, 2, 4, and 5, the overt security feature described in this specification includes a color constant layer (x20) incorporating magnetically oriented platelet-shaped magnetic or magnetizable pigment particles, the platelet-shaped magnetic or magnetizable pigment particles having substantially the same elevation angle |α|.

[0065] Alternatively, the overt security feature described herein may comprise two or more zones comprising platelet-shaped magnetic or magnetisable pigment particles, the platelet-shaped magnetic or magnetisable pigment particles of one zone having substantially the same elevation angle |α| (the platelet-shaped magnetic or magnetisable pigment particles in the at least partially cured colour constant layer (x20) have the same angle +α or have the same angle -α) and the platelet-shaped magnetic or magnetisable pigment particles of a second zone having substantially the same additional elevation angle |α'| (the platelet-shaped magnetic or magnetisable pigment particles in the at least partially cured colour constant layer (x20) have the same angle +α' or have the same angle -α'), said elevation angle |α| and said additional elevation angle |α'| being different from each other and / or not coplanar. The two or more zones may consist of a single colour constant layer (x20) or may consist of two or more independent colour constant layers (x20, x20' etc.).

[0066] Suitable examples of the platelet shaped magnetic or magnetizable pigment particles described herein include, but are not limited to, magnetic metals selected from the group consisting of cobalt (Co), iron (Fe), and nickel (Ni); magnetic alloys of iron, manganese, cobalt, nickel, or mixtures of two or more thereof; magnetic oxides of chromium, manganese, cobalt, iron, nickel, or mixtures of two or more thereof; or color constant pigment particles comprising a mixture of two or more thereof. The term "magnetic" in relation to metals, alloys, and oxides covers ferromagnetic or ferrimagnetic metals, alloys, and oxides. The magnetic oxides of chromium, manganese, cobalt, iron, nickel, or mixtures of two or more thereof may be pure or mixed oxides. Examples of magnetic oxides include, but are not limited to, hematite (Fe 2 O 3 ), magnetite (Fe 3 O 4 ), chromium dioxide (CrO 2 ), magnetic ferrite (MFe 2 O 4 ), magnetic spinel (MR 2 O 4 ), magnetic hexaferrite (MFe 12 O 19 ), magnetic orthoferrite (RFeO 3 ), magnetic garnet M 3 R 2 (A.O. 4 ) 3 In this case, M represents a divalent metal, R represents a trivalent metal, and A represents a tetravalent metal.

[0067]

[0066] Examples of platelet shaped magnetic or magnetisable pigment particles described herein include, but are not limited to, colour constant pigment particles comprising a magnetic layer M consisting of one or more of the following: a magnetic metal, such as cobalt (Co), iron (Fe), or nickel (Ni); and a magnetic alloy of iron, cobalt, or nickel, said magnetic or magnetisable pigment particles may be a multi-layer structure comprising one or more additional layers. Preferably, the one or more additional layers are magnesium fluoride (MgF 2 ), silicon oxide (SiO), silicon dioxide (SiO2 ), titanium dioxide (TiO 2 ), and aluminum oxide (Al 2 O 3 ); or a layer B independently consisting of one or more compounds selected from the group consisting of metals and alloys, preferably selected from the group consisting of reflective metals and reflective metal alloys, more preferably selected from the group consisting of aluminum (Al), chromium (Cr), and nickel (Ni), even more preferably aluminum (Al); or a combination of one or more layers A such as those described above and one or more layers B such as those described above. Typical examples of platelet shaped magnetic or magnetisable pigment particles which are said multilayer structures include, but are not limited to, 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, B / A / M / A multilayer structures, B / A / M / B multilayer structures, B / A / M / B / A / multilayer structures, B / A / B / M / B / A / B multilayer structures, where layer A, magnetic layer M and layer B are selected from those mentioned above, preferably B / M / B multilayer structures and A / B / M / B / A multilayer structures, where A is a layer such as those described herein.

[0068]

[0067] The platelet shaped magnetic or magnetisable pigment particles described herein preferably exhibit a metallic colour, more preferably a silver colour.

[0069]

[0068] The platelet shaped magnetic or magnetisable pigment particles described herein preferably have a size d50 (measured by direct optical granulometry) of from about 2 μm to about 50 μm, preferably from about 5 μm to about 30 μm.

[0070]

[0069] The platelet shaped magnetic or magnetizable pigment particles described in this specification may be surface treated to protect the radiation curable compositions and layers from any deterioration that may occur to the radiation curable compositions and layers and / or to promote incorporation of the pigment particles into said compositions and layers; typically corrosion inhibitor materials and / or wetting agents may be used.

[0071] The method described herein comprises the step of preparing a color-constant layer (x20) as described herein. The method comprises the step a) of applying to the surface of a substrate (x10) as described herein a radiation curable coating composition comprising platelet-shaped magnetic or magnetisable particles as described herein, the radiation curable coating composition being in a first liquid state allowing its application as a layer and still in an at least partially uncured (i.e. wet) state, the pigment particles being able to move and rotate within the layer. As the radiation curable coating composition described herein is provided on the surface of the substrate (x10), the radiation curable coating composition comprises at least a binder material and magnetic or magnetisable pigment particles, the composition being in a form allowing its processing in a desired printing or coating device. Preferably, the step a) is carried out by a printing process, more preferably selected from the group consisting of screen printing, gravure printing and flexographic printing.

[0072] Depending on the printing process selected for producing the color-constant layer (x20) and the optically variable layer (x30) of the overt security features described herein, suitable viscosity values ​​of the radiation-curable coating composition comprising platelet-shaped magnetic or magnetizable pigment particles are used: screen printing inks have a viscosity of about 50 mPas to about 3000 mPas at 25° C., flexographic inks have a viscosity of about 50 mPas to about 2000 mPas at 25° C., gravure inks have a viscosity of about 50 mPas to about 1000 mPas at 25° C. and for security inks with viscosity values ​​of 100 mPas to 3000 mPas the viscosity measurements are carried out with a Brookfield viscometer (model “RVDV-I The viscosity measurements for security inks with viscosity values ​​of 10 mPas to 100 mPas are carried out at 25 °C, 1000 s. -1 The viscosity is measured at 25° C. in a TA Instruments rotational viscometer DHR-2 with a cone shape and a diameter of 40 mm, or at 25° C. in a DIN 4″ cup.

[0073]

[0072] The method described herein further comprises a step b) of exposing the layer obtained in step a) to magnetic field lines of a magnetic field generating device, said magnetic field lines forming an elevation angle |γ with the |substrate (x10) surface, said elevation angle |γ| having a value of about 10° to about 45° (10°≦|γ|≦45°), preferably about 15° to about 40° (15°≦|γ|≦40°), more preferably about 15° to about 35° (15°≦|γ|≦35°) so as to orient the platelet-shaped magnetic or magnetizable pigment particles (for example by tiling the substrate (x10) supporting the layer containing the particles in the magnetic field as shown in Fig. 5A1). Step b) described herein is carried out so as to orient the platelet-shaped magnetic or magnetizable pigment particles described herein uniaxially or biaxially.

[0074] According to one embodiment, step b) is performed to uniaxially orient at least a portion of the platelet shaped magnetic or magnetisable pigment particles described herein. Suitable magnetic field generating devices for uniaxially orienting the platelet shaped magnetic or magnetisable pigment particles described herein are not limited.

[0075]

[0074] Examples of magnetic field generating devices suitable for uniaxially orienting particles are disclosed in U.S. Patent No. 7,047,883 and co-pending application PCT / EP2021 / 073863.

[0076]

[0075] Figures 5A-B of US Patent No. 7,047,883 disclose a magnetic field generating device consisting of two spaced apart magnets 84 mounted on a magnetic base 62 with the north poles of the magnets facing the substrate. Figure 9B of US Patent No. 7,047,883 discloses a magnetic field generating device consisting of a magnet 140, with the article mounted at an offset position relative to the magnet axis. Figure 9C of US Patent No. 7,047,883 discloses a magnetic field generating device consisting of two magnets 142, one magnet 142' having a diamond-shaped cross section, both magnets 142 having their north poles facing the substrate, while the intervening magnet 142' has their south poles facing the substrate. Figure 9D of US Patent No. 7,047,883 discloses a magnetic field generator consisting of two magnets 144, one magnet 144' having a roof-shaped, hexagonal, round, trapezoidal or other cross-section, two magnets 144 having a north pole facing the substrate while the intervening magnet 144' has a south pole facing the substrate. Figure 9E of US Patent No. 7,047,883 discloses a magnetic field generator consisting of five magnets, the first magnet 142 being a diamond-shaped magnet with its north pole facing the substrate, the second magnet 146 being a rectangular magnet with its south pole facing the substrate, the third magnet 148 being a magnet with a rounded top end with its north pole facing the substrate, the fourth magnet 150 being roof-shaped with its south pole facing the substrate, and the fifth magnet 152 also being a roof-shaped magnet with its north pole facing the substrate.

[0077]

[0076] Figure 4A1 of co-pending application PCT / EP2021 / 073863 discloses a magnetic field generator consisting of a bar dipole magnet, where particles are exposed to the magnetic field of the magnetic field generator herein (magnetic field lines shown as lines with arrows pointing from the north pole to the south pole) in one or more areas (shown as a dotted rectangle A), where the magnetic field is substantially homogeneous and the magnetic field lines are substantially parallel to each other in said one or more areas. Figure 4A2 of co-pending application PCT / EP2021 / 073863 discloses a magnetic field generator consisting of an assembly including two bar dipole magnets (M1, M2) with the same magnetic direction and an iron yoke (Y), where particles are exposed to the magnetic field of the magnetic field generator herein (magnetic field lines shown as lines with arrows pointing from the north pole to the south pole) in one or more areas (shown as a dotted rectangle A), where the magnetic field is substantially homogeneous and the magnetic field lines are substantially parallel to each other in said one or more areas. Figures 6A-B of co-pending application PCT / EP2021 / 073863 disclose a magnetic field generating device consisting of a rectangular assembly including two bar dipole magnets (M1, M2) and two pole pieces (P1, P2), wherein particles are exposed to the magnetic field (magnetic field lines shown as lines with arrows pointing from the north pole to the south pole) of the magnetic field generating device in one or more areas (shown as dotted rectangle A), the magnetic field being substantially homogenous and the magnetic field lines being substantially parallel to each other in said areas.

[0078] According to one embodiment, step b) is performed to biaxially orient the platelet shaped magnetic or magnetisable pigment particles described herein. Suitable magnetic field generating devices for biaxially orienting the platelet shaped magnetic or magnetisable pigment particles described herein are not limited.

[0079]

[0078] Examples of magnetic field generating devices suitable for orienting particles in a uniaxial direction are disclosed in co-pending application PCT / EP2021073983, International Publication No. 2018 / 019594 A1, International Publication No. 2016 / 083259 A1, International Publication No. 2021 / 239607 A1, and co-pending application EP2178995.3.

[0080]

[0079] Figure 4B1 of International Application PCT / EP2021073983 (see also WO2018 / 019594A1) discloses a magnetic field generating device consisting of a linear arrangement of at least four magnets (M1-M4) located in a staggered or zigzag configuration, where the particles are exposed to the magnetic field (magnetic field lines shown as lines with arrows pointing from the north pole to the south pole) of the magnetic field generating device in one or more areas (shown as dotted rectangles A, A'), where the magnetic field is substantially homogenous and the magnetic field lines are substantially parallel to each other in said one or more areas. EP2157141A1 discloses a similar suitable magnetic field generating device in Figure 5, where the magnetic field generating device consists of a linear arrangement of at least three, preferably at least four, magnets located in a staggered or zigzag configuration. FIG. 4B2 of international application PCT / EP2021073983 (see also WO 2018 / 019594A1) discloses a magnetic field generator consisting of two dipole magnets (M1, M2) with opposite magnetic directions, where the particles are exposed to the magnetic field (magnetic field lines shown as lines with arrows pointing from the north pole to the south pole) of the magnetic field generator in one or more areas (shown as dotted rectangles A, A'), where the magnetic field is substantially homogeneous and the magnetic field lines are substantially parallel to each other in said one or more areas. FIG. 4B3 of international application PCT / EP2021073983 (see also WO 2018 / 019594A1) discloses a magnetic field generator consisting of two dipole magnets (M1, M2) with the same magnetic direction. As shown in FIG. 4B3, platelet-shaped magnetic or magnetizable pigment particles in a coating layer (410) on a substrate (420) are exposed to a magnetic field (magnetic field lines shown as lines with arrows pointing from the north pole to the south pole) of a magnetic field generating device (430) in one or more areas (shown as dotted rectangle A), the magnetic field being substantially homogeneous and the magnetic field lines being substantially parallel to each other in said one or more areas, and the substrate (420) supporting the coating layer (410) is positioned in said one or more areas at an angle α as described herein.Figure 4B4 of International Application PCT / EP2021073983 (see also WO 2018 / 019594A1) discloses a magnetic field generating device consisting of a Halbach array including five dipole magnets (M1-M5), wherein particles are exposed to the magnetic field (magnetic field lines shown as lines with arrows pointing from the north pole to the south pole) of the magnetic field generating device in one or more areas (shown as a dotted parallelepiped A), the magnetic field being substantially homogeneous and the magnetic field lines being substantially parallel to each other in said one or more areas. FIG. 4B5 of International Application PCT / EP2021073983 (see also WO 2016 / 083259A1) discloses a magnetic field generating device consisting of a Halbach cylinder assembly including four structures, each including a magnet bar (M1-M4) surrounded by a magnet wire coil (not shown), and particles are exposed to the magnetic field (magnetic field lines shown as lines with arrows pointing from the north pole to the south pole) of the magnetic field generating device in one or more areas (shown as dotted rectangle A), the magnetic field being substantially homogenous and the magnetic field lines being substantially parallel to each other in said one or more areas. FIG. 4B6 of International Application PCT / EP2021073983 (see also WO 2021 / 239607A1) discloses a magnetic field generating device consisting of an assembly of eight bar dipole magnets (M1-M8), said assembly including a first set including a first bar dipole magnet (M4) and two second bar dipole magnets (M1, M6), a second set including a first bar dipole magnet (M5) and two second bar dipole magnets (M3; M8), and a first pair of third bar dipole magnets (M2, M7), wherein particles are exposed to the magnetic field of the magnetic field generating device (magnetic field lines shown as lines with arrows pointing from the north pole to the south pole) in one or more areas (shown as dotted rectangle A), the magnetic field being substantially homogenous and the magnetic field lines being substantially parallel to each other in said one or more areas. Figures 5A1-3 of international application PCT / EP2021073983 disclose a magnetic field generating device consisting of an assembly including nine bar dipole magnets (M1-M5) arranged in a row with alternating N-S magnetic directions, wherein particles are exposed to the magnetic field (magnetic field lines shown as lines with arrows pointing from the N pole to the S pole) of the magnetic field generating device in one or more areas (shown as a dotted parallelepiped A), the magnetic field being substantially homogeneous and the magnetic field lines being substantially parallel to each other in said one or more areas.

[0081]

[0080] The method described herein further comprises a step c) of at least partially curing the layer in a curing unit, either partially simultaneously with step b) or subsequently, preferably partially simultaneously with step b), to at least partially fix the position and orientation of the particles to have the same elevation angle |α| of about 10° to about 45° (10°≦angle |α|≦45°), preferably about 15° to about 40° (15°≦angle |α|≦40°), more preferably about 15° to about 35° (15°≦angle |α|≦35°), so as to form the color-constant layer (x20) described herein. By "partially simultaneously" it is meant that both steps are performed partially simultaneously, i.e. the number of times each of the steps is performed partially overlaps. In the context described herein, it must be understood that if the curing is performed partially simultaneously with the orientation step b), the curing is effective after the orientation, so that the particles have time to orient before the complete or partial curing of the color-constant layer (x20). When step b) described herein is followed by step c), the time between said steps is preferably from about 0.1 seconds to about 1.5 seconds, more preferably from about 0.1 seconds to about 0.5 seconds.

[0082] According to one particularly preferred embodiment of the present invention, the radiation coating composition described herein is a UV-Vis curable coating composition. UV-Vis curing advantageously allows for a very fast curing process and therefore significantly reduces the preparation time of the color-constant layer (x20) described herein. Preferably, the UV-Vis curable coating composition comprises one or more compounds selected from the group consisting of radically curable compounds and cationically curable compounds. The UV-Vis curable coating composition described herein may be a hybrid system, comprising a mixture of one or more cationically curable compounds and one or more radically curable compounds. The cationically curable compounds are cured by a cationic mechanism, typically involving the activation by irradiation of one or more photoinitiators that liberate cationic species, such as acids, which then react and / or crosslink monomers and / or oligomers, thereby initiating curing to solidify the coating composition. The radically curable compounds are cured by a free radical mechanism, typically involving the activation by irradiation of one or more photoinitiators, thereby generating radicals that then initiate polymerization to solidify the coating composition. Depending on the monomers, oligomers, or prepolymers used to prepare the binder included in the UV-Vis curable composition described herein, different photoinitiators may be used. Suitable examples of free radical photoinitiators are known to those skilled in the art and include, but are not limited to, acetophenone, benzophenone, benzil dimethyl ketal, α-amino ketone, α-hydroxy ketone, phosphine oxide, and phosphine oxide derivatives, as well as mixtures of two or more thereof. Suitable examples of cationic photoinitiators are known to those skilled in the art and include, but are not limited to, onium salts, such as organic iodonium salts (e.g., diaryliodonium salts), oxonium (e.g., triaryloxonium salts), and sulfonium salts (e.g., triarylsulfonium salts), as well as mixtures of two or more thereof.Other examples of useful photoinitiators can be found in standard textbooks such as "Chemistry & Technology of UV & EB Formulation for Coatings, Inks & Paints", Vol. III, "Photoinitiators for Free Radical Cationic and Anionic Polymerization", 2nd Edition by JV Crivello & K. Dietliker, edited by G. Bradley, published in 1998 by John Wiley & Sons in association with SITA Technology Limited. To achieve efficient curing, it may also be advantageous to include a photosensitizer in conjunction with one or more photoinitiators. Typical examples of suitable photosensitizers include, but are not limited to, isopropyl-thioxanthone (ITX), 1-chloro-2-propoxy-thioxanthone (CPTX), 2-chloro-thioxanthone (CTX), and 2,4-diethyl-thioxanthone (DETX), as well as mixtures of two or more thereof. The one or more photoinitiators included in the UV-Vis curable coating composition are preferably present in a total amount of from about 0.1% to about 20% by weight, more preferably from about 1% to about 15% by weight, the weight percentages being based on the total weight of the UV-Vis curable coating composition.

[0083] According to one embodiment, the radiation curable compositions described herein are UV-Vis LED curable compositions, i.e. compositions that are curable upon exposure to one or more wavelengths between about 365 nm and about 470 nm emitted by a UV-LED light source, more preferably by exposure to UV light at about 365 nm and / or 385 nm and / or 395 nm. When only the UV-Vis LED curable composition comprises a radically curable monomer / oligomer, said composition typically comprises one or more photoinitiators that can be activated by one or more radically curable photoinitiators and / or photosensitizers absorbing in said wavelength range. Preferably, the photoinitiators absorbing in said range are selected from the group consisting of phosphine oxides, phosphine oxide derivatives, thioxanthones, and mixtures thereof. When a photosensitizer is present, it is preferably selected from the group consisting of thioxanthones (which may function as photoinitiators and photosensitizers, as known to those skilled in the art), as described above, and the one or more photoinitiators are preferably selected from the group consisting of phosphine oxides, phosphine oxide derivatives, α-aminoketones, benzophenones, and mixtures thereof. When a Nourish Type II photoinitiator such as thioxanthones and / or benzophenones is used, the radiation curable composition may further comprise an amine-containing compound such as Esacure A198 (IGM Resins, CAS1793103-51-1), Speedcure 7040 (Lambson, CAS1182751-31-0), or an amine-modified polyether acrylate such as Ebecryl® 80 (Allnex, CAS143748-77-0). When the UV-LED curable composition comprises a cationically curable monomer (either as part or as the whole of a radiation curable monomer / oligomer), said composition preferably comprises one or more iodonium salts such as those described above and one or more thioxanthones.

[0084]

[0083] The radiation curable coating compositions described herein may further comprise one or more marking substances or taggants and / or one or more machine-readable materials, provided that their presence does not significantly affect the observation of the color shifting properties of the overt security features described herein. The materials may be selected from the group consisting of magnetic materials (different from the non-spherical magnetic or magnetizable pigment particles described herein), luminescent materials, conductive materials, and infrared absorbing materials. As used herein, the term "machine-readable material" refers to a material that exhibits at least one characteristic property that is not detectable by the naked eye and that can be included in a layer so as to provide a method of authenticating the layer or an article containing the layer by the use of a specific device.

[0085]

[0084] The radiation curable coating compositions described herein may further comprise one or more additives, provided their presence does not significantly affect the observed color shifting properties of the overt security features described herein. Such additives include, but are not limited to, compounds and materials used to adjust the physical, rheological, and chemical parameters of the coating composition, such as viscosity (e.g., solvents, thickeners, and surfactants), consistency (e.g., anti-settling agents, fillers, and plasticizers), foaming properties (e.g., defoamers), lubricity (waxes, oils), UV stability (light stabilizers), adhesion, antistatic properties, storage stability (polymerization inhibitors), etc. The additives described herein may be present in the coating composition in amounts and forms known in the art, including so-called nanomaterials, where at least one of the dimensions of the additive is in the range of 1 to 1000 nm.

[0086]

[0085] The overt security features described herein include the optically variable layer (x30) described herein.

[0087]

[0086] According to one embodiment, the thickness of the optically variable layer (x30) described herein is from about 1 μm to about 10 μm, preferably from about 2 μm to about 8 μm, and more preferably from about 2 μm to about 6 μm (as measured using an Extramess Inductive Digital Comparator 2001 (manufactured by Mahr Corporation)).

[0088]

[0087] Preferably, the optically variable layer (x30) is obtained from a cholesteric liquid crystal polymer precursor composition comprising at least one nematic compound, at least one chiral dopant, at least one photoinitiator, and one or more solvents.

[0089]

[0088] The cholesteric liquid crystal precursor composition comprises (i) one or more nematic compounds A and (ii) one or more chiral dopant compounds B capable of generating a cholesteric state of the cholesteric liquid crystal precursor composition upon heating. The pitch of the available cholesteric state depends on the relative ratio of the nematic and chiral dopant compounds. The (total) concentration of the one or more nematic compounds A in the cholesteric liquid crystal precursor composition for use in the present invention is about 4 to about 30 times, preferably about 4 to about 25 times, the (total) concentration of the one or more chiral dopant compounds B. The one or more chiral dopant compounds B are preferably present in an amount of about 0.1% to about 30% by weight, more preferably about 0.1% to about 20% by weight, even more preferably about 3% to about 10% by weight, the weight percentage being based on the total weight of the cholesteric liquid crystal precursor composition. The one or more nematic compounds A are preferably present in an amount of about 20% by weight to about 50% by weight, more preferably about 30% by weight to about 45% by weight, the weight percentage being based on the total weight of the cholesteric liquid crystal precursor composition.

[0090] Both the nematic compound(s) A and the chiral dopant compound(s) B may comprise at least one compound comprising at least one polymerizable group. For example, all of the nematic compounds A and all of the chiral dopant compounds B may comprise at least one polymerizable group. The at least one polymerizable group may be, for example, a compound capable of being polymerized by free radical polymerization, in particular, for example, a compound of the formula H 2 It may also contain groups capable of participating in (preferably activated) unsaturated carbon-carbon bonds, such as acrylates having C=CH-C(O)-O.

[0091] Nematic (precursor) compounds A suitable for use in cholesteric liquid crystal precursor compositions are known in the art and, when used alone (i.e., without chiral dopant compounds), place themselves in a state characterized by their birefringence. Non-limiting examples of nematic compounds A suitable for use in the present invention are described, for example, in WO 93 / 22397 A1, WO 95 / 22586 A1, EP 0847432 B1, U.S. Patent No. 6,589,445, and U.S. Patent Application Publication No. 2007 / 0224341. The entire disclosures of these documents are incorporated herein by reference.

[0092] A preferred class of nematic compounds A for use in the present invention comprises one or more polymerizable groups per molecule, which may be the same or different from one another. Examples of polymerizable groups include groups capable of participating in free radical polymerization, in particular groups containing a carbon-carbon double or triple bond, such as, for example, acrylate, vinyl or acetylene moieties. Acrylate moieties are particularly preferred as polymerizable groups.

[0093] The nematic compound A used in the present invention may further comprise one or more optionally substituted aromatic groups, preferably phenyl groups. Examples of optional substituents of the aromatic groups include those described herein as examples of substituents on the phenyl ring of the chiral dopant compound of formula (I), such as, for example, alkyl and alkoxy groups.

[0094]

[0093] Examples of groups that may optionally be present to link the polymerizable group and the aryl (e.g., phenyl) group in the nematic compound A include those exemplified herein for the chiral dopant compound B of formula (I) (including those of formulas (IA) and (IB) described below). For example, the nematic compound A may include A in formula (I) (and formulas (IA) and (IB)), typically linked to an optionally substituted phenyl group. 1 and A 2 may include one or more groups of the formulae (i) to (vi) shown below as examples.

[0095]

[0094] Non-limiting examples of nematic compounds suitable for use in the present invention include, but are not limited to, the following compounds: 2-methoxybenzene-1,4-diylbis[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)benzoate]; 4-{[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)benzoyl]oxy}-2-methoxyphenyl 4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)-2-methylbenzoate; 2-methoxybenzene-1,4-diyl Bis[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)-2-methyl-benzoate];2-Methylbenzene-1,4-diylbis[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)-2-methyl-benzoate];4-{[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)benzoyl]oxy}-2-methylphenyl 4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)-3-methoxybenzoate;2-Methylbenzene-1,4-diylbis[ 4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)benzoate];2-Methylbenzene-1,4-diylbis[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)-3-methoxy-benzoate];4-{[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)-3-methoxybenzoyl]oxy}-2-methyl-phenyl 4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)-3,5-dimethoxybenzoate;2-Methylbenzene-1,4-diyl Bis[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)-3,5-dimethoxy-benzoate];2-Methoxybenzene-1,4-diylbis[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)-3,5-dimethoxybenzoate];4-{[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)-3-methoxybenzoyl]oxy}-2-methoxyphenyl 4-({[4-(acryloyloxy)-butoxy]carbonyl}oxy)-3,5-dimethoxybenzoate;4-({4-[4-(acryloyloxy)butoxy]benzoyl}oxy)-3-methylphenyl 4-[4-(acryloyloxy)butoxy]-2-methylbenzoate;4-({4-[4-(acryloyloxy)butoxy]benzoyl}oxy)-3-methylphenyl 4-[4-(acryloyloxy)butoxy]-3-methylbenzoate;2-Methylbenzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-2-methylbenzoate};4-({4-[4-(acryloyloxy)butoxy]-2-methylbenzene 4-({4-[4-(acryloyloxy)butoxy]-3,5-dimethylbenzoyl}oxy)-3-methylphenyl 4-[4-(acryloyloxy)butoxy]-2,5-dimethylbenzoate;2-Methylbenzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-2,5-dimethylbenzoate};2-Methylbenzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]benzoate};4-({4-[4-(acryloyloxy)butoxy]-3,5-dimethylbenzoyl}oxy)-3-methylphenyl 4-[4-(acryloyloxy)butoxy]-2,5-dimethyl Benzoate;2-Methylbenzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-3,5-dimethylbenzoate};2-Methoxybenzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-3,5-dimethylbenzoate};4-({4-[4-(acryloyloxy)butoxy]-3-methylbenzoyl}oxy)-2-methoxyphenyl 4-[4-(acryloyloxy)butoxy]-3,5-dimethylbenzoate;2-Methoxybenzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-3,5-dimethylbenzoate 4-({4-[4-(acryloyloxy)butoxy]benzoyl}oxy)-3-methoxyphenyl 4-[4-(acryloyloxy)butoxy]-3-methylbenzoate;4-({4-[4-(acryloyloxy)butoxy]benzoyl}oxy)-3-methoxyphenyl 4-[4-(acryloyloxy)butoxy]-2,5-dimethylbenzoate;2-Methoxybenzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-2-methoxybenzoate};2-Methoxybenzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-3,5-dimethoxybenzoate};2-Methoxybenzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-3-methoxybenzoate};2-Ethoxybenzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]benzoate};2-Ethoxybenzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-2-methylbenzoate};2-(Propan-2-yloxy)benzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]benzoate};4-({4-[4-(acryloyloxy)butoxy]benzoyl}oxy)-2-(propane -2-yloxy)phenyl 4-[4-(acryloyloxy)butoxy]-2-methylbenzoate; 2-(propan-2-yloxy)benzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-2-methylbenzoate}; 2-(propan-2-yloxy)benzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-2,5-dimethyl-benzoate}; 2-(propan-2-yloxy)benzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-3,5-dimethyl-benzoate}; and 2-(propan-2-yloxy)benzene-1,4-diylbis{4-[4-(acryloyloxy)butoxy]-3,5-dimethoxy-benzoate}. ;

[0096]

[0095] The one or more chiral dopant compounds B used in the present invention preferably contain at least one polymerizable group. Suitable examples of the one or more chiral dopant compounds B include those of formula (I): [ka] During the ceremony: R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R8 are each independently C 1 ~C 6 Alkyl and C 1 ~C 6 Represents alkoxy; A 1 and A 2 each independently represent a group of formulae (i) to (vi): (i) -[(CH 2 ) y -O] z -C(O)-CH=CH 2 ; (ii) -C(O)-D 1 -O-[(CH 2 ) y -O] z -C(O)-CH=CH 2 ; (iii) -C(O)-D 2 -O-[(CH 2 ) y -O] z -C(O)-CH=CH 2 ; (iv) -[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 ; (v) -C(O)-D 1 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 ; (vi) -C(O)-D 2 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 ; D 1 is the formula [ka] represents a group. D 2 is the formula [ka] represents a group. m, n, o, p, q, r, s, and t each independently represent 0, 1, or 2; y represents 0, 1, 2, 3, 4, 5, or 6; If y is equal to 0, then z is equal to 0, and if y is equal to 1 through 6, then z is equal to 1.

[0097] In one embodiment, the one or more chiral dopant compounds B may comprise one or more isomannide derivatives of formula (IA): [ka] During the ceremony: R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each independently C 1 ~C 6 Alkyl and C 1 ~C 6 Represents alkoxy; A 1 and A 2 each independently represent a group of formulae (i) to (vi): (i) -[(CH 2 ) y -O] z -C(O)-CH=CH 2 ; (ii) -C(O)-D 1 -O-[(CH 2 )yO] z -C(O)-CH=CH 2 ; (iii) -C(O)-D 2 -O-[(CH 2 )yO] z -C(O)-CH=CH 2 ; (iv) -[COO-(CH 2 ) y-O] z -C(O)-CH=CH 2 ; (v) -C(O)-D 1 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 ; (vi) -C(O)-D 2 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 ; D 1 is the formula [ka] represents a group. D 2 is the formula [ka] represents a group. m, n, o, p, q, r, s, and t each independently represent 0, 1, or 2; y represents 0, 1, 2, 3, 4, 5, or 6; If y is equal to 0, then z is equal to 0, and if y is equal to 1 through 6, then z is equal to 1.

[0098] In one exemplary embodiment of the compound of formula (IA) (and of the compound of formula (I)), R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each independently C 1 ~C 6 In an alternative embodiment, R in formula (IA) (and in formula (I)) represents alkyl. 1 , R 2 , R 3 , R 4 , R 5 , R6 , R 7 , and R 8 are each independently C 1 ~C 6 Represents alkoxy.

[0099] In another exemplary embodiment of the compounds of Formula (I) and Formula (IA), A 1 and A 2 each independently represents a group represented by the formula -[(CH 2 ) y -O] z -C(O)-CH=CH 2 R represents the group 1 , R 2 , R 3 , and R 4 are each independently C 1 ~C 6 and m, n, o, and p each independently represent 0, 1, or 2. In still other embodiments, A in Formula (I) and Formula (IA) 1 and A 2 each independently represents a group represented by the formula -[(CH 2 ) y -O] z -C(O)-CH=CH 2 R represents the group 1 , R 2 , R 3 , and R 4 are each independently C 1 ~C 6 represents alkoxy; and m, n, o, and p each independently represent 0, 1, or 2.

[0100] In another embodiment of the compounds of formula (IA) (and of formula (I)), A 1 and A 2 each independently represents a group of the formula -C(O)-D 1 -O-[(CH 2 ) y -O] z -C(O)-CH=CH 2 and / or formula -C(O)-D 2 -O-[(CH 2 ) y -O] z-C(O)-CH=CH 2 represents a group represented by the formula: 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each independently C 1 ~C 6 In an alternative embodiment, A1 and A2 in formula (IA) (and in formula (I)) each independently represent a group of the formula -C(O)-D 1 -O-[(CH 2 ) y -O] z -C(O)-CH=CH 2 and / or a group of the formula -C(O)-D 2 -O-[(CH 2 ) y -O] z -C(O)-CH=CH 2 represents a group represented by the formula: 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each independently C 1 ~C 6 Represents alkoxy.

[0101] In another embodiment of the compounds of formula (IA) (and formula (I)), A 1 and A 2 each independently represents a group of the formula -C(O)-D 1 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 and / or formula -C(O)-D 2 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 represents a group represented by the formula: 1 , R 2 , R 3 , R 4, R 5 , R 6 , R 7 , and R 8 are each independently C 1 ~C 6 In an alternative embodiment, A in formula (IA) (and in formula (I)) represents alkyl. 1 and A 2 each independently represents a group of the formula -C(O)-D 1 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 and / or formula -C(O)-D 2 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 represents a group represented by the formula: 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each independently C 1 ~C 6 Represents alkoxy.

[0102]

[0101] In other embodiments, the one or more chiral dopant compounds B may comprise one or more isosorbide derivatives represented by formula (IB): [ka] During the ceremony: R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each independently C 1 ~C 6 Alkyl and C 1 ~C 6 Represents alkoxy; A 1and A 2 each independently represent a group of formulae (i) to (vi): (i) -[(CH 2 )yO] z -C(O)-CH=CH 2 ; (ii) -C(O)-D 1 -O-[(CH 2 )yO] z -C(O)-CH=CH 2 ; (iii) -C(O)-D 2 -O-[(CH 2 )yO] z -C(O)-CH=CH 2 ; (iv) -[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 ; (v) -C(O)-D 1 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 ; (vi) -C(O)-D 2 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 ; D 1 is the formula [ka] represents a group. D 2 is the formula [ka] represents a group. m, n, o, p, q, r, s, and t each independently represent 0, 1, or 2; y represents 0, 1, 2, 3, 4, 5, or 6; If y is equal to 0, then z is equal to 0, and if y is equal to 1 through 6, then z is equal to 1.

[0103] In one embodiment of the compound of formula (IB), R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each independently C 1 ~C 6 represents alkyl; and m, n, o, and p each independently represent 0, 1, or 2. In an alternative embodiment, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each independently C 1 ~C 6 represents alkoxy; and m, n, o, and p each independently represent 0, 1, or 2.

[0104] In another embodiment of the compound of formula (IB), A 1 and A 2 each independently represents a group represented by the formula -[(CH 2 ) y -O] z -C(O)-CH=CH 2 R represents the group 1 , R 2 , R 3 , and R 4 are each independently C 1 ~C 6 and m, n, o, and p each independently represent 0, 1, or 2. In still other embodiments, A in formula (IB) 1 and A 2 each independently represents a group represented by the formula -[(CH 2 ) y -O] z -C(O)-CH=CH 2 R represents the group 1, R 2 , R 3 , and R 4 are each independently C 1 ~C 6 represents alkoxy; and m, n, o, and p each independently represent 0, 1, or 2.

[0105] In another embodiment of the compound of formula (IB), A 1 and A 2 each independently represents a group of the formula -C(O)-D 1 -O-[(CH 2 ) y -O] z -C(O)-CH=CH 2 and / or of the formula -C(O)-D 2 -O-[(CH 2 ) y -O] z -C(O)-CH=CH 2 R represents the group 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each independently C 1 ~C 6 and m, n, o, and p each independently represent 0, 1, or 2. In an alternative embodiment, A in formula (IB) 1 and A 2 each independently represents a group of the formula -C(O)-D 1 -O-[(CH 2 ) y -O] z -C(O)-CH=CH 2 and / or a group of the formula -C(O)-D 2 -O-[(CH 2 ) y -O] z -C(O)-CH=CH 2 R represents the group 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7, and R 8 are each independently C 1 ~C 6 represents alkoxy; and m, n, o, and p each independently represent 0, 1, or 2.

[0106] In another embodiment of the compound of formula (IB), A 1 and A 2 each independently represents a group of the formula -C(O)-D 1 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 and / or formula -C(O)-D 2 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 R represents the group 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are each independently C 1 ~C 6 and m, n, o, and p each independently represent 0, 1, or 2. In an alternative embodiment, A in formula (IB) 1 and A 2 each independently represents a group of the formula -C(O)-D 1 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 and / or a group of the formula -C(O)-D 2 -O-[COO-(CH 2 ) y -O] z -C(O)-CH=CH 2 R represents the group 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8are each independently C 1 ~C 6 represents alkoxy; and m, n, o, and p each independently represent 0, 1, or 2.

[0107]

[0106] Non-limiting examples of chiral dopant compound B of formula (I) for use in the present invention include, but are not limited to, the following compounds: 2,5-bis-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}-3-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol; 2-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}-3-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}-3-methoxybenzoyl)- 2,5-Bis-O-(4-{[4-(acryloyloxy)-benzoyl]oxy}-benzoyl)-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-butoxy]-benzoyl})-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-[4-(acryloyloxy)-2-methylbenzoyl] ... ,5-Bis-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}-benzoyl)-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-benzoyl]oxy}-3-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)-benzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-benzoyl]oxy}-3 -Methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-2-methylbenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methylbenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methylbenzoyl]oxy}-2-methoxybenzoyl)-1,4 :3,6-Dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-2,5-dimethylbenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-Dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)-2,5-dimethylbenzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)- 2-O-(4-{[4-(acryloyloxy)-2-methoxy-5-methylbenzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methylbenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methylbenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol 2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methylbenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}benzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}benzoyl)-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-3-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2,5-dimethyl 2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-methylbenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}-3-methylbenzoyl)-1,4:3,6-dianhydro-D-mannitol; ... 2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-ethoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-ethoxybenzoyl]oxy}benzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-ethoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-ethoxybenzoyl]oxy}benzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4- (acryloyloxy)benzoyl]oxy}-2-ethoxy-5-methylbenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-ethoxybenzoyl]oxy}benzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-ethoxy-5-methylbenzoyl)-5-O-(4-{[4-(acryloyloxy)-5-ethoxy-2-methylbenzoyl]oxy}benzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)-3-ethoxybenzoyl]oxy}benzoyl)-5-O-(4-{[4-(acryloyloxy)-2-methylbenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2-O-(4-{[4-(acryloyloxy)-2,5-dimethylbenzoyl]oxy}-2-ethoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-2-methylbenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol 2,5-Bis-O-(4-{[4-(acryloyloxy)-2,5-dimethylbenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol 2,5-Bis-O-(4-{[4-(acryloyloxy)-2-ethoxybenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-2-ethoxybenzoyl]oxy}-3-methylbenzoyl)-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-2-ethoxybenzoyl]oxy}-3-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-2-ethoxybenzoyl]oxy}-3-methoxybenzoyl)-1,4:3,6-dianhydro-D-mannitol ;2,5-Bis-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}-3-methoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;D-glucitol 1,4:3,6-dianhydro-bis[4-[[4-[[[4-[(1-oxo-2-propenyl)oxy]butoxy]carbonyl]oxy]benzoyl]oxy]benzoate];2,5-Bis-O-(4-{[4-(acryloyloxy)-benzoyl]oxy}-3-methoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-3-methoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2,5-bis-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-methoxybenzoyl)-5 -O-(4-{[4-(acryloyloxy)-2-methylbenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3 ... 2-O-(4-{[4-(acryloyloxy)-2,5-dimethylbenzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methylbenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)-2,5-dimethylbenzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methylbenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol 2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methylbenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methylbenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2,5-Bis-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-3-methoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D -glucitol;2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}benzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}benzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2,5-dimethylbenzoyl)-5-O-(4-{[4-(acryloyloxy; 2-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-methylbenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}-3-methylbenzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)-2-methoxy-5-methylbenzoyl]oxy}-2-methyl 2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-ethoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-ethoxybenzoyl]oxy}benzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-ethoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-ethoxybenzoyl]oxy}benzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-ethoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-ethoxybenzoyl]oxy}benzoyl)-1,4:3,6-dianhydro-D-glucitol 2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-ethoxy-5-methylbenzoyl)-5-O-(4-{[4-(acryloyloxy)-5-ethoxy-2-methylbenzoyl]oxy}benzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)benzoyl]oxy}-2-ethoxy-5-methylbenzoyl)-5-O-(4-{[4-(acryloyloxy)-5-ethoxy-2-methylbenzoyl]oxy}benzoyl)-1,4:3,6-dianhydro-D-glucitol 2-O-(4-{[4-(acryloyloxy)-2,5-dimethylbenzoyl]oxy}-2-ethoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-2-methylbenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2-O-(4-{[4-(acryloyloxy)-2,5-dimethylbenzoyl]oxy}-2-ethoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-2-methylbenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-2,5-dimethylbenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-2-ethoxybenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2,5-Bis-O-(4-{[4-(acryloyloxy)-2-methoxybenzoyl]oxy}-2-ethoxybenzoyl)-1,4:3,6-dianhydro- D-glucitol;2,5-bis-O-(4-{[4-(acryloyloxy)-2-ethoxybenzoyl]oxy}-2-methoxybenzoyl)-1,4:3,6-dianhydro-D-glucitol;2,5-bis-O-(4-{[4-(acryloyloxy)-2-ethoxybenzoyl]oxy}-3-methylbenzoyl)-1,4:3,6-dianhydro-D-glucitol;2,5-bis-O-(4-{[4-(acryloyloxy)-2-ethoxybenzoyl]oxy}-3-methoxybenzoyl)-1,4:3,6-diam ... 2,5-Bis-O-[4-(acryloyloxy)benzoyl]-1,4:3,6-dianhydro-D-glucitol;2,5-Bis-O-[4-(acryloyloxy)benzoyl]-1,4:3,6-dianhydro-D-mannitol;2,5-Bis-O-(4-{[4-({[4-(acryloyloxy)-butoxy]carbonyl}oxy)benzoyl]oxy}-benzoyl)-1,4:3,6-dianhydro-D-glucitol;2,5-Bis-O-(4-{[4-({[4-(acryloyloxy)-butoxy]carbonyl}oxy)benzoyl]oxy}-benzoyl)-1,4:3,6-dianhydro-D-glucitol 2,5-Bis-O-(4-{[4-({[6-(acryloyloxy)-hexyloxy]carbonyl}oxy)benzoyl]oxy}-benzoyl)-1,4:3,6-dianhydro-D-glucitol; 2,5-Bis-O-(4-{[4-({[6-(acryloyloxy)-hexyloxy]carbonyl}oxy)benzoyl]oxy}-benzoyl)-1,4:3,6-dianhydro-D-glucitol; and 2,5-Bis-O-[4-({[4-(acryloyloxy)-butoxy]carbonyl}oxy)benzoyl]-1,4:3,6-dianhydro-D-glucitol.

[0108]

[0107] The cholesteric liquid crystal precursor composition includes one or more solvents. Suitable solvents are known to those skilled in the art and include, but are not limited to, low viscosity, slightly polar aprotic organic solvents such as methyl ethyl ketone (MEK), acetone, cyclopentanone, cyclohexanone, ethyl acetate, ethyl 3-ethoxypropionate, and mixtures of two or more thereof. The one or more solvents included in the cholesteric liquid crystal precursor composition, when present, are preferably present in an amount of about 30% to about 70% by weight, more preferably about 40 to about 60% by weight, the weight percentage being based on the total weight of the cholesteric liquid crystal precursor composition.

[0109] According to one embodiment, the cholesteric liquid crystal precursor composition described herein further comprises one or more photoinitiators, and the cholesteric liquid crystal precursor composition is solidified during step f) by UV-visible light irradiation. Non-limiting examples of many photoinitiators suitable for the cholesteric liquid crystal precursor composition described herein include 1-hydroxy-cyclohexyl-phenyl-ketone and mixtures of 1-hydroxy-cyclohexyl-phenyl-ketone with one or more benzophenones (e.g., about 1:1), 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, and 2-hydroxy-1-[4-[4-(1-hydroxy-2-methylpropanoyl)phenoxy]phenyl]-2-methylpropan-1-one (e.g., available from IGM under the name ESACURE KIP160). α-Hydroxyketones such as methylbenzoyl formate and a mixture of oxy-phenylacetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester and oxy-phenylacetic acid 2-[2-hydroxy-ethoxy]-ethyl ester; benzyl dimethyl ketals such as α,α-dimethoxy-α-phenylacetophenone; 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-butan-1-one, 2-di Also included are α-amino ketones such as methylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one, and 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone; phosphine oxides and phosphine oxide derivatives such as diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide; phenyl-bis(2,4,6-trimethylbenzoyl)-phosphine oxide, and thioxanthone derivatives such as those described herein.When present, the one or more photoinitiators included in the cholesteric liquid crystal precursor composition are preferably present in an amount of about 0.01% to about 10% by weight, more preferably about 0.05% to about 7% by weight, the weight percentages being based on the total weight of the cholesteric liquid crystal precursor composition.

[0110]

[0109] The cholesteric liquid crystal precursor compositions described herein may further comprise one or more additives, including, but not limited to, compounds and materials used to adjust the physical, rheological, and chemical parameters of the composition, such as consistency (e.g., anti-settling agents and plasticizers), foamability (e.g., defoamers and degassing agents), lubricity (waxes), radiation sensitizers, UV stability (light stabilizers), adhesion, surface properties (wetting agents, oleophobic and hydrophobizing agents), etc., provided that said additives do not negatively inhibit or interfere with the formation of the helix and / or the formation of the polymer. The additives described herein may be present in one or more inks described herein in amounts and forms known in the art, including in the form of so-called nanomaterials, where at least one of the dimensions of the additive is in the range of 1-1000 nm. When present, the one or more additives included in the cholesteric liquid crystal precursor composition are preferably present in an amount of about 0.01% to about 5% by weight, the weight percentage being based on the total weight of the cholesteric liquid crystal precursor composition.

[0111]

[0110] The method described herein comprises the steps for preparing an optically variable layer (x30) as described herein. The method comprises a step d) of applying a cholesteric liquid crystal polymer precursor composition as described herein to form a layer on top of the color constant layer (x20) and / or on the surface of the substrate (x10). Preferably, said step d) is carried out by a printing process, preferably selected from the group consisting of screen printing, gravure printing and flexographic printing, more preferably selected from the group consisting of flexographic printing and gravure printing.

[0112]

[0111] When the overt security feature described herein includes a second area consisting only of an optically variable layer (x30) described herein, step d) consists of applying a cholesteric liquid crystal polymer precursor composition described herein to form a layer on top of the color constant layer (x20) and at least partially on the surface of the substrate (x10).

[0113] Following step d) of applying the cholesteric liquid crystal precursor composition described herein to form the layer described herein, the method includes step e) of heating the composition. During step e), the applied composition / layer is heated to bring it into a cholesteric liquid crystal state having specific optical properties. The term "specific optical properties" is understood as a liquid crystal state having a specific pitch (selective reflection band) that selectively reflects a specific wavelength range. To that end, the cholesteric liquid crystal precursor composition is heated and one or more solvents contained in the composition are evaporated, resulting in the promotion of the desired cholesteric liquid crystal state. The temperature used to evaporate the solvent and promote the formation of the liquid crystal state depends on the components of the cholesteric liquid crystal precursor composition and is preferably from about 45°C to about 150°C, more preferably from about 45°C to about 120°C, even more preferably from about 50°C to about 115°C. Typically, the heating step described herein uses a suitable heating source, including, but not limited to, conventional heating means such as a hot plate, an oven, a stream of hot air, and a radiation source. The required heating time depends on several factors, such as, for example, the components of the cholesteric liquid crystal precursor composition described herein, the type of heating device, and the strength of the heating (energy output of the heating device). Typically, the applied cholesteric liquid crystal precursor composition is heated for a period of about 1 second to about 45 seconds.

[0114]

[0113] Following the heating step e) as described herein, the method comprises a step f) of solidifying the layer obtained in step d) to form an optically variable layer (x30) as described herein. Preferably, the solidifying step f) is carried out by irradiation, including infrared radiation, UV-visible radiation, electron beam (E-beam) radiation, X-rays, gamma radiation, and ultrasonic radiation. More preferably, the solidifying step f) is carried out by UV-visible (UV / VIS) radiation. The UV-visible radiation may be carried out in the presence of one or more photoinitiators included in the cholesteric liquid crystal precursor composition as described herein.

[0115]

[0114] The overt security features described herein further comprise a discontinuous layer that changes the position of the selective reflection zone of the optically variable layer, said layer being disposed below the optically variable layer. The discontinuous layer described herein may be in the form of one or more indicia and may comprise one or more polymerizable monomers, each of which may be comprised of a composition comprising one or more ether functional groups (C-0-C-) per polymerizable group. WO 2015 / 067683 A1 discloses suitable resins including organic resins (such as polyacrylates, polymethacrylates, polyvinyl ethers, polyvinyl esters, polyesters, polyethers, polyamides, polyurethanes, polycarbonates, polysulfones, phenolic resins, epoxy resins, and mixed forms of these resins), mixed inorganic / organic resins such as silicones (e.g. polyorganosiloxanes), and water-based resins. When the discontinuous layer that changes the position of the selective reflection band of the optically variable layer is present in an overt security feature as described herein, the feature is prepared by applying and solidifying / curing the discontinuous layer prior to application of the cholesteric liquid crystal polymer precursor composition as described herein.

[0116]

[0115] Also described herein are security documents, security articles, and decorative articles that include one or more of the overt security features described herein.

[0117]

[0116] Typical examples of decorative articles include, but are not limited to, luxury goods, cosmetic packaging, automotive parts, electronic / electrical devices, furniture, and nails. Alternatively, the overt security features described herein may be included on an auxiliary substrate, such as, for example, a label, and thus transferred to the decorative article in a separate step.

[0118]

[0117] Security documents include, but are not limited to, valuable documents and goods of commercial value. Typical examples of valuable documents include, but are not limited to, banknotes, deeds, tickets, checks, certificates, revenue stamps and tax labels, contracts, etc., identity documents such as passports, identity cards, visas, driver's licenses, bank cards, credit cards, transaction cards, access documents or cards, entrance tickets, public transport tickets, academic diplomas or entitlements, etc., preferably banknotes, identity documents, entitlement documents, driver's licenses, and credit cards. The term "goods of commercial value" refers in particular to packaging materials for cosmetics, nutritional supplements, medicines, alcohol, tobacco articles, beverages or food, electrical / electronic articles, textiles or jewelry, i.e., articles that are protected against counterfeiting and / or illegal duplication to guarantee the package contents, such as genuine medicines. Examples of these packaging materials include, but are not limited to, labels, such as authentication brand labels, tamper-evident labels, and seals. It is pointed out that, without limiting the scope of the present invention, the disclosed substrates, security documents, and decorative articles are given solely for illustrative purposes.

[0119]

[0118] Alternatively, the overt security features described in this specification may be contained on a secondary substrate, such as a security thread, security strip, foil, sticker, window or label, and therefore transferred to the security document or article in a separate step.

[0120]

[0119] Also described herein are methods of manufacturing a security document, security article, or decorative article, and the resulting security document, security article, and decorative article, the methods including a) providing a security document, security article, or decorative article, and b) providing one or more overt security features, such as those described herein, on or included by the security document, security article, or decorative article. For example, the method comprises the steps of providing a security document, security article or decorative article comprising a substrate such as those described herein; applying a radiation curable coating composition comprising platelet-shaped magnetic or magnetisable pigment particles as described herein onto the substrate (x10) surface of the security document, security article or decorative article to form a layer; exposing the layer to magnetic field lines of a magnetic field generating device to orient the platelet-shaped magnetic or magnetisable pigment particles as described herein; partially simultaneously with or subsequent to the orienting step, at least partially curing the layer in a curing unit to at least partially fix the position and orientation of the platelet-shaped magnetic or magnetisable pigment particles such that the platelet-shaped magnetic or magnetisable pigment particles have the same elevation angle |α| having a value as described herein to form a colour-constant layer (x20) as described herein; applying a cholesteric liquid crystal polymer precursor composition as described herein; heating the layer as described herein; and solidifying the layer to obtain an optically variable layer (x30) as described herein.

[0121]

[0120] The substrates (x10) described herein may further comprise additional security elements such as organic and / or inorganic pigments, dyes, flakes, optically variable elements, magnetic pigments, and the like.

[0122]

[0121] In order to improve the durability or chemical resistance during contamination and the cleanliness and thus the cycling life of the overt security feature described herein, or to modify its aesthetics (e.g. optical gloss), one or more protective layers may be applied over the optically variable layer (x30). The one or more protective layers, if present, typically consist of a protective varnish. The protective varnish may be a radiation curable composition, a thermal drying composition, or any combination thereof. Preferably, the one or more protective layers are a radiation curable composition, more preferably a UV-Vis curable composition. The protective layer is typically applied after formation of the overt security feature.

[0123]

[0122] The overt security features described herein may be provided directly on a substrate (x10) which will remain permanently. Alternatively, the overt security features may be provided on a temporary substrate for manufacturing purposes, from which the overt security features are subsequently removed.

[0124] Alternatively, one or more adhesive layers may be present, said one or more adhesive layers being on the side of the overt security feature opposite to the side of the optically variable layer (x30). Thus, one or more adhesive layers may be applied, said one or more adhesive layers being applied after the solidifying step f) is completed. Such an object can be attached to any kind of document or other article or item without printing or other processes involving machines and rather high efforts. Alternatively, the overt security feature described herein may be in the form of a transfer foil and can be applied to the document or article in a separate transfer step. For this purpose, the overt security feature is provided with a release coating.

[0125]

[0124] The combination of the optically variable layer (x30) described herein and the color constant layer (x20) with a specific orientation pattern of magnetic or magnetisable pigment particles in the form of magnetically oriented platelets described herein allows the overt security feature described herein to be easily and conveniently authenticated by the naked eye by a layperson without requiring any device by tilting said feature and observing that a first area consisting of the superposition of the optically variable layer (x30) and the color constant layer (x20) described herein exhibits at least three different colors at different viewing / observation angles when said feature is observed through the optically variable layer (x30), provided that the overt security feature is placed on a permanent light absorbing background if the substrate is transparent.

[0126]

[0125] At least one viewing / observation angle, preferably two viewing / observation angles, are required to be grazing angles, allowing easy and convenient authentication. Figures 6 and 7 show different viewing / observation angles and a method (see steps i)-iii) of tilting and rotating a substrate (x10) supporting an optically variable layer (x30), a color constant layer (x20) and optionally a light absorbing background (x40) for authenticating an overt security feature described herein, said feature being observed through the optically variable layer (x30) (as shown by the eye). Figure 7 shows an overt security feature comprising a first area (see the "A" mark) and a second area (area around the "A" mark) as described herein, where the shape of the color constant layer (720, the "A" letter) differs from the shape of the optically variable layer (730, rectangular) to better illustrate the rotation of the feature performed during step ii).

[0127]

[0126] Authentication of the overt security features described herein by their optical properties is conveniently performed under typical lighting conditions (i.e. everyday lighting, including both non-directional light resulting from light diffusion or multiple reflections and directional light originating from the sun or artificial light sources). Direct lighting (i.e. lighting originating from a point source that strikes the security feature at a given angle and is reflected at the same angle back to the observer's eye) should best be avoided, as it produces specular reflections, making it difficult / impossible to observe color. Observation is preferably performed according to the following four situations (see, for example, FIG. 7): Situation A: the overt security feature is placed at arm's length horizontally and observed at a grazing angle |β|, said grazing angle |β| corresponding approximately to the elevation angle |α| of the magnetically oriented platelet-shaped magnetic or magnetisable pigment particles in the colour constant layer (x20). At this angle, a first area ("A" in Fig. 7) consisting of the superposition of the colour constant layer (x20) and the optically variable layer (x30) of the overt security feature shows a first colour (e.g. blue for the examples E1-E4 described below) and a second area consisting only of the optically variable layer (x30) (the area around "A" in Fig. 7) shows the same colour; then a layperson tilts the substrate (x10) supporting both layers (x20 and x30) so that it is held vertically so that the overt security feature faces the eye of the observer in Figs. 6-7 (see step i)); Situation B: the overt security feature is held vertically towards the observer's eye, the observation angle β' is then about 90°. At this angle, the first area shows the second color (e.g. silver for the embodiments E1-E4 described below) and the second area shows the third color (e.g. green for the embodiments E1-E4 described below); the layperson then rotates the substrate (x10) supporting both layers (x20 and x30) and performs a 180° rotation on an axis perpendicular to the substrate (x10) so that the overt security feature is held vertically towards the observer's eye (see step ii) of Figures 6-7), and the indicia "A" made of the color-constant layer (x20) in Figure 7 appears upside down due to the rotation. Situation C: At this angle β', the first area shows a third color (e.g. green for examples E1-E4 described below) and the second area shows the same color; the layperson then tilts the substrate (x10) supporting both layers (x20 and x30) so that the overt security feature is held horizontal (see step iii) in Figures 6-7). Situation D: The overt security feature is held horizontally and viewed again at grazing angle β, where the first area shows the second color (e.g., silver for Examples E1-E4 described below) and the second area shows the first color (e.g., blue for Examples E1-E4 described below).

[0128]

[0127] As described above, a layperson can observe at least three different colors (blue, silver and green for embodiments E1 to E4 described below) in the first area (marked "A" in Figure 6) consisting of a superposition of an optically variable layer (x30) and a constant color layer (x20), and therefore can easily and conveniently authenticate the overt security feature by observing at two different viewing / observation angles (β and 90°).

[0129]

[0128] Alternatively, it is possible to start the visual observation from any situation and in any direction (i.e. clockwise or counterclockwise). However, situation A described here is particularly easy to observe since, at the observation angle β (grazing angle), the color of the color constant layer (x20) is seen by the naked eye and in the absence of any device as being substantially the same as the color of the optically variable layer (x30) (i.e. the influence of the magnetic pigment particles in the color constant layer (x20) is very limited). EXAMPLES

[0130] The present invention will now be described in more detail with reference to the following non-limiting examples. Examples E1-E4 and C1-C2 were carried out using a coating composition comprising the platelet shaped magnetic or magnetisable pigment particle curable composition provided in Table 1, and a cholesteric liquid crystal polymer precursor composition provided in Table 2. [Table 1]

[0131]

[0130] The coating composition containing magnetic particles was prepared by first mixing all the ingredients listed in Table 1 except the magnetic particles provided in Table 1 and dispersing them using Dispermat (Model LC-2) at room temperature for 20 minutes at 1500 rpm. Then, platelet shaped magnetic pigment particles were added to obtain 100 g of coating composition and further dispersed at room temperature for 15 minutes at 1500 rpm. The coating composition containing magnetic particles in Table 1 has a viscosity suitable for screen printing, gravure printing and flexographic printing, and therefore the application method used therein mimicked the screen printing, gravure printing and flexographic printing processes. [Table 2]

[0132]

[0131] A cholesteric liquid crystal polymer precursor composition was prepared by injecting a solvent (cyclohexanone), LC monomer (Lumogen S250), and chiral dopant (Lumogen S750) in a 200 ml bottle, and placed in an ultrasonic bath at 40°C for about 30 minutes to dissolve the components in the solvent. The mixture was then poured into a Dispermat (model LC-2), and photoinitiator was added and dispersed at 2000 rpm for 20 minutes. Finally, surfactant (BYK361N) was added and mixed at 1500 rpm for 5 minutes.

[0133]

[0132] The cholesteric liquid crystal polymer precursor compositions of Table 2 have viscosities suitable for flexographic and gravure printing, and therefore the application methods used therein mimicked the flexographic and gravure printing processes.

[0134]

[0133] Upon heating and curing the cholesteric liquid crystal polymer precursor compositions of Table 2, layers made therefrom exhibited a blue to green color shift upon tilt. In other words, an optically variable layer (x30) without the presence of a color constant layer (x20) exhibited a blue to green color shift upon tilt and viewing between grazing and face angles.

[0135] For each sample, the following methods were used to prepare Examples E1-E4 and C1-C2: a) the coating composition containing magnetic particles provided in Table 1 was applied onto a piece of transparent PET substrate (Hostaphan, 20 cm x 7.5 cm, thickness: 50 μm) (x10) to form a layer (dimensions 18 cm x 4 cm), said steps being carried out on a semi-automatic laboratory coater (K101 Controlled Coater, RK Print) using a coating bar HC4 (nominal thickness 36 μm); b) exposing the layer (x10) obtained in step a) to the magnetic field of a magnetic field generator as described herein below so as to biaxially orient the platelet-shaped magnetic or magnetizable pigment particles as shown in FIG. 5A1, tilting the substrate (x10) supporting the layer (x20) at an elevation angle γ with respect to the magnetic field lines; Following step b), c) the layer obtained in step b) is at least partially cured to fix the position and orientation of the particles so that they have the same elevation angle γ of about 0° to about 50° as provided in Table 3, thus forming a color-constant layer (x20), said layer being first cured by UV-LED lamps (Phoseon Firefly, 395 nm, 4 W / cm) placed at a depth of 1 cm. 2 ) for about 2 seconds and then cured while removed from the magnetic field generator equipped with a mercury UV dryer (Technigraf Aktiprint Mini 18-2, two medium pressure mercury lamps, total power 80 W / cm, one pass at a constant speed of 90 mm / s corresponding to an exposure time of about 0.5 seconds); the thickness of the color-constant layer (x20) so obtained was about 25 μm; d) The cholesteric liquid crystal polymer precursor composition of Table 2 was applied onto the color constant layer (x20) using the same hand coater and coating bar HC1 described in step a) above to form a layer (dimensions 18 cm x 4 cm) (theoretical wet thickness 8 μm); e) the layer obtained in step d) was heated using a hot air dryer at a temperature of 50° C. for 30 seconds to evaporate the solvent and generate a cholesteric liquid crystal state; and f) The substrate (x10) supporting the color constant layer (x20) and the layer obtained in step e) was hardened by moving said substrate (x10) under the same mercury UV dryer as described above for step d) with the same parameters, so as to obtain an optically variable layer (x30; the thickness of the optically variable layer (x30) thus obtained was about 4 μm).

[0136] The thickness of 25 μm for the color constant layer (x20) was chosen to select the d50 value of the pigment particles (20 μm and 12 μm, respectively) to ensure that the orientation of the pigment particles was not inhibited, thus allowing for a comparison of the results, but said value is not the preferred value for end use applications.

[0137]

[0136] Examples E1-E4 and Comparative Examples C1-C2 contained a first area consisting of a superposition of a color constant layer (x20) and an optically variable layer (x30).

[0138] Magnetic field generating device (Figure 5A1-A2)

[0137] The magnetic assembly shown in Figures 5A1-A2 was used to orient pigment particles biaxially. The magnetic assembly included nine magnet subassemblies (M1-M9), each consisting of 18 identical magnets (NdFeBN45) with height L4 (40 mm), width L3 (10 mm), and thickness L5 (3 mm) (see Figure 5A2). Each assembly (M1-M9) was assembled by stacking three groups of six magnets vertically (i.e., each assembly (M1-M9) had height L1 = 3 x L4 (120 mm), width L2 = 6 x L5 (18 mm), and thickness L3 = 10 mm). The magnets were assembled such that the magnetic axis of each identical magnet was parallel to its thickness (L5), and the magnetic axis of each assembly (M1-M9) was parallel to their width (L2) and perpendicular to the plane formed by the dimensions L1 and L3.

[0139]

[0138] The magnetic assemblies (M1-M9) are embedded in a non-magnetic holder (not shown) made of polyoxymethylene (POM) and are arranged at a fixed interval L6 of 20 mm, with their magnetic axes pointing perpendicular to the plane formed by the dimensions L1 (120 mm) x L7 (250 mm) of the magnetic field generator, or in opposite directions, as shown in Figure 5A1. The generated magnetic field lines are substantially perpendicular to the plane L1 x L7 of the magnetic field generator, and therefore generate a substantially homogeneous magnetic field as long as the substrate supporting the layer containing the particles is moved at about half the height of the magnetic field generator.

[0140]

[0139] The substrate supporting the as yet uncured layer containing the particles was placed in a rotatable holder containing a polar coordinate ruler showing the elevation angle γ between the magnetic field lines and the holder, then moved at half the height of the magnetic field generator (L8 = 1 / 2L1) with an approximate speed of 10 cm / s, the distance L9 between the plane of the magnetic field generator L1 x L7 and the closest edge of the layer containing the particles is about 1 cm to orient the particles biaxially substantially parallel to each other in the plane of the generated magnetic field lines. The elevation angle γ (provided in Table 3) was set by rotating the holder and measuring the angle precisely using the polar coordinate ruler.

[0141]

[0140] The thicknesses of the color constant layer (x20) and the optically variable layer (x30) were measured using an Extramess inductive digital comparator 2001 (Mahr Corporation). [Table 3]

[0142] The measured elevation angle α of the magnetic pigment particles in the color constant layer (x20) was independently obtained using a conoscopic scatterometer as described in FIG. 4A of WO 2019 / 038371 A1 (obtained from Eckhardt Optics LLC, 5430 Jefferson Ct, White Bear Lake, MN 55110; http: / / eckop.com). The elevation angle α of the platelet-shaped magnetic or magnetizable pigment particles in the color constant layer (x20) was measured at approximately 1 mm. 2 The measurements were made directly on the layer surface after step d), i.e. the reported values ​​corresponded to an average value of about 1000 particles. The measured elevation angles α provided in Table 3 are the average values ​​of about 10 measurements at different positions of the color-constant layer (x20).

[0143] Optical microscope images were obtained by using a binocular microscope (Olympus BX51, magnification x100, illumination through a lens using an Olympus TH4-200 illuminator, camera: Nikon D7100) on one microtome slice of the sample (slice plane perpendicular to the substrate surface and coating layer thickness and perpendicular to the tilt axis). The substrate (x10) supporting the color constant layer (x20) was first embedded independently in epoxy resin (Technicol 9461) and left to dry at room temperature for 24 hours before cutting and polishing the microtome slice to produce a sample with the following dimensions: 10 mm x 10 mm x 30 mm. Measurements of the elevation angle α of the magnetic pigment particles were performed using the software Adobe illustrator CC (version 23.0.2). The values ​​of the elevation angle α reported in Table 3 were averaged for approximately 10 to 20 particles for each elevation angle.

[0144] The optical properties of the thus obtained Examples E1-E4 and C1-C2 were evaluated by the naked eye, without any other equipment, and are given in Table 4 (FIGS. 6 and 7 show how the observations were carried out). Examples E1-E4 and C1-C2 were observed under the commonly found lighting conditions mentioned above, in particular in a room illuminated by four rectangular neon lamps. A non-permanent black background (x40) (Leneta N2A-2, Leneta Company Inc. Mahwah, USA) was placed under the substrate (x10). Visual observations (shown by the eye in the figure) were made through the optically variable layer (x30).

[0145]

[0144] As described above, four situations A to D were evaluated and are shown in Figures 6 to 7 as situations A to D: Situation A: the observed security feature is held horizontally and visual observation is performed at a first observation angle β (grazing angle), said angle β approximately corresponding to the elevation angle α of the platelet-shaped magnetic or magnetisable pigment particles with respect to the plane of the substrate (x10) in the colour-constant layer (x20); Situation B: the overt security feature was tilted vertically so that it was then facing directly towards the observer's eye and visual observation was made at an observation angle β' of approximately 90° relative to the substrate surface (face angle); Situation C: The overt security feature was rotated 180° while maintaining the same vertical position, the axis of rotation was perpendicular to the substrate (x10) and the observation angle β' was the same as in situation B (face angle); and Situation D: The overt security feature was again positioned horizontally and viewed at angle β (grazing angle).

[0146]

[0145] Alternatively, it is possible to start visual observation from any situation and in any direction. However, situation A is particularly easy to observe because at grazing angles the color of the first area nearly matches the color of the second area (i.e. there is a very limited contribution from the magnetic pigment particles in the color constant layer (x20)). Therefore, it is easier to start from situation A.

[0147]

[0146] The observed colour of the first area consisting of the superposition of the colour constant layer (x20) and the optically variable layer (x30) is reported for each situation in Table 4 for Examples E1 to E4 and Comparative Examples C1 to C2.

[0148] [Table 4] Comparative Example C1 did not exhibit at least three different colors when viewed at different viewing / viewing angles (when viewed through the optically variable layer (x30) at different viewing / viewing angles).

[0149]

[0148] Comparative Example C2 showed at least three different colors when viewed at different viewing / viewing angles (when viewed through the optically variable layer (x30) at different viewing / viewing angles), but the viewing / viewing angle β (grazing angle) was too high, thus making the feature unsuitable for easy and convenient authentication. Moreover, the color at face angle (90°) in situation B was the green color observed in situation C, rather than the expected silver (Examples E1-E4).

[0150]

[0149] Contrary to Comparative Examples C1-C2, Examples E1-E4 comprising a color constant layer in which platelet-shaped magnetic or magnetizable pigment particles have an elevation angle |α| of about 10° to about 45° (10°≦angle |α|≦45°), preferably about 15° to about 40° (15°≦angle |α|≦40°), more preferably about 15° to about 35° (15°≦angle |α|≦35°), showed at least three different colors (blue, silver, and green) when observed at two different observation / viewing angles, and the viewing / viewing angle β (grazing angle) was small enough to enable easy and convenient authentication of the overt security feature with the naked eye and in the absence of any device.

[0151]

[0150] Examples E1 to E4 were also observed through the color constant layer (x20) while the non-permanent black background (x40) was placed under the optically variable layer (x30). When observed through the color constant layer (20) and at the same different viewing / observation angles provided in Table 4, only a single color (gray) was observed.

[0152] Similar Examples E1'-E4' and Comparative Examples C1'-C2' were prepared as above, except that the dimensions of the optically variable layer (x30) (dimensions 18 cm x 6 cm) were greater than the dimensions of the color constant layer (x20) (dimensions 18 cm x 4 cm); thus forming a feature consisting of a superposition of the color constant layer (x20) and the optically variable layer (x30) and including a first area (dimensions: 18 x 4 cm) located approximately in the center of the length of the substrate (x10) and a second area including two zones of approximately 18 x 1 cm on either side of the first area. Upon visual observation of the above examples, the observed colors of the first areas in the four situations A to D were the same as those described in Table 4, and the observed colors of the second areas were: blue for situations A and D, and green for situations B and C. In the absence of the color constant layer (x20), the optically variable layer (x30) appeared green and the second color was red at face angles for Examples E1-E4 and Comparative Examples C1-C2.

Claims

1. An overt security feature, comprising: a) a substrate (x10) made of a material selected from the group consisting of a transparent material, a light-absorbing material, and combinations thereof; b) a color-constant layer (x20) containing magnetically oriented platelet-shaped magnetic or magnetizable pigment particles; c) an optically variable layer (x30) comprising a cholesteric liquid crystal polymer selectively reflecting light in the visible spectral range, the optically variable layer (x30) being above said color constant layer (x20), thus forming a first area consisting of a superposition of said optically variable layer (x30) and said color constant layer (x20); Including, the platelet-shaped magnetic or magnetizable pigment particles of the color constant layer (x20) have substantially the same elevation angle α, the elevation angle |α| having a value between 10° and 45° (10°≦angle |α|≦45°); Overt security features.

2. 10. The overt security feature of claim 1, wherein the cholesteric liquid crystal polymer of the optically variable layer (x30) is obtained from a cholesteric liquid crystal polymer precursor composition comprising one or more nematic compounds, one or more chiral dopants, one or more photoinitiators, and one or more solvents.

3. An overt security feature according to claim 1 or 2, wherein the optically variable layer (x30) has a thickness of between 1 μm and 10 μm.

4. 3. An overt security feature according to claim 1 or 2, wherein said color constant layer (x20) is a layer obtained from a radiation curable coating composition comprising said platelet-shaped magnetic or magnetizable pigment particles, one or more radiation curable oligomers, one or more radiation curable monomers, and one or more photoinitiators.

5. 3. An overt security feature according to claim 1 or 2, wherein the platelet-shaped magnetic or magnetisable pigment particles exhibit a metallic colour.

6. 6. The overt security feature of claim 5, wherein said platelet-shaped magnetic or magnetizable pigment particles exhibit a silver color.

7. An overt security feature according to claim 1 or 2, wherein the platelet-shaped magnetic or magnetisable pigment particles have a size d50 between 2 μm and 50 μm.

8. 3. The overt security feature of claim 1 or 2, wherein the platelet-shaped magnetic or magnetisable pigment particles are present in an amount of 2% to 25% by weight, the weight percentage being based on the total weight of the colour constant layer.

9. An overt security feature according to claim 1 or 2, wherein the constant colour layer (x20) has a thickness of between 5 μm and 30 μm.

10. 3. An overt security feature according to claim 1 or 2, wherein the colour constant layer (x20) is in the form of one or more indicia and / or the optically variable layer (x30) is in the form of one or more indicia, said one or more indicia being the same or different.

11. 3. An overt security feature according to claim 1 or 2, further comprising a second area consisting solely of said optically variable layer (x30).

12. A security document, security article or decorative article comprising one or more overt security features according to claim 1 or 2.

13. 3. A method of manufacturing an overt security feature according to claim 1 or 2, comprising the steps of: a) applying a radiation curable coating composition comprising platelet-shaped magnetic or magnetizable pigment particles onto a surface of a substrate (x10), said radiation curable coating composition being in a first liquid state so as to form a layer; b) exposing the layer obtained in step a) to magnetic field lines of a magnetic field generator, said magnetic field lines forming an elevation angle |γ| with the substrate (x10) surface, said elevation angle |γ| having a value between 10° and 45° so as to orient the platelet-shaped magnetic or magnetizable pigment particles; c) partially simultaneously with or subsequent to step b), at least partially curing said layer in a curing unit to at least partially fix the position and orientation of said platelet-shaped magnetic or magnetizable pigment particles, so that the platelet-shaped magnetic or magnetizable pigment particles have the same elevation angle α between 10° and 45° (10°≦angle |α|≦45°), thereby forming a color-constant layer (x20); d) applying a cholesteric liquid crystal polymer precursor composition at least partially onto the color-constant layer (x20) and / or at least partially onto the surface of the substrate (x10); e) heating the layer obtained in step d); f) solidifying the layer obtained in step e) to obtain the optically variable layer (x30); A method comprising:

14. 14. The method of claim 13, wherein step a) is performed by a printing process selected from the group consisting of screen printing, gravure printing, and flexography, and wherein step d) is performed by a printing process selected from the group consisting of flexography and gravure printing.

15. 14. The method of claim 13, wherein step c) is carried out by exposing the layer to one or more wavelengths between 365 nm and 405 nm emitted by a UV-Vis LED curing unit.

Images