Printing process

Abstract

The invention provides a novel security feature and a method for making it.

Description

[0001] PRINTING PROCESS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of security printing processes, as well as security features produced using such security printing processes.

[0004] BACKGROUND OF THE INVENTION

[0005] With the constantly improving quality of color photocopies and printing, and in an attempt to protect security documents and articles such as banknotes, value documents or cards, transportation tickets or cards, tax banderols, and product labels that have no reproduceable effects against counterfeiting, falsifying or illegal reproduction, it has been the conventional practice to incorporate various security elements in these documents and articles.

[0006] Security features can generally be classified into "covert” security features on the one hand, and “overt” security features on the other hand. The protection provided by covert security features relies on the concept that such features are difficult to detect, typically requiring specialized equipment and knowledge for detection, whereas “overt” security features rely on the concept of being easily detectable with the unaided human senses, e.g. such features may be visible and / or detectable via the tactile senses while still being difficult to produce and / or to copy. However, the effectiveness of overt security features depends to a great extent on their eye-catching effect and their easy recognition as a security feature, because most users, and particularly those having no prior knowledge of the security features of a document or article secured therewith, will only then actually perform a security check based on said security feature if they have actual knowledge of their existence and nature.

[0007] Optically variable inks provide first-line recognizability not only by a person, but in some cases also facilitate machine-readability. One example of optically variable inks is the class of compounds called cholesteric liquid crystal polymers. When illuminated with light, the cholesteric liquid crystal structure reflects light of a certain color which depends on the material in question and varies upon changing the viewing angle by, for example, tilting the security feature. The cholesteric liquid crystal material itself is colorless and the observed color is the result of a physical reflection effect of the cholesteric helical structure that is adopted by the liquid crystal precursor composition at a given temperature. See, e.g., J.L. Fergason, Molecular Crystals, Vol. 1 , pp. 293-307 (1966). Materials having 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 show a molecular order in the form of a helical superstructure perpendicular to the longitudinal axes of its molecules. The helical superstructure provides for a periodic refractive index modulation throughout the liquid crystal material, which in turn results in a selective transmission / reflection of determined wavelengths of light (interference filter effect). Cholesteric liquid crystal polymers can be obtained by subjecting one or more polymerizable nematic monomers and one or more chiral monomers to alignment and orientation. The particular situation of the helical molecular arrangement leads to cholesteric liquid crystal materials exhibiting the property of reflecting a circularly polarized light component within a determined wavelength range, wherein said circularly polarized light may be left-handed or right-handed, depending on the sense of rotation of the molecular helices. 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 helices, as known to the skilled man. The pitch (i.e. the distance over which a full rotation of 360° of the helical arrangement is completed) can be tuned in particular by varying selectable factors including the temperature and solvents concentration, by changing 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, such that the color of the resulting cholesteric liquid crystal polymer is independent of external factors such as temperature.

[0008] United States patent no. 10,611 ,919 describes security features made using cholesteric liquid crystal compositions in which the liquid crystal monomers comprise polymerizable groups. A precursor solution comprising nematic monomers and chiral monomers in a solvent is deposited on a substrate, heated to remove the solvent, and then polymerized using UV-VIS-light. The resulting cholesteric liquid crystal polymer (CLCP) reflects light at a wavelength that varies depending on the angle of viewing. The authors disclose that the wavelength of reflected light can be shifted to longer wavelengths if the CLCP layer is deposited on a resin layer comprising polyether moieties. To enhance the security of such CLCP features, there is an ongoing need to increase the palette of complexity that is available with CLCP printing, both in design and color.

[0009] SUMMARY OF THE INVENTION

[0010] In a first aspect, the invention provides a method for producing a security feature on a substrate, wherein the security feature comprises a primer gradient layer, optionally in the form of one or more indicia, and a layer comprising a cholesteric liquid crystal polymer, optionally in the form of one or more indicia, the method comprising the steps:

[0011] (1) providing a first UV-VIS-curable primer composition A, which, when cured and in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of Ai;

[0012] (2) providing a second UV-VIS-curable primer composition B, which, when cured and in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of A2, wherein AAr= A2 - A1 10 nm;

[0013] (3) applying the first UV-VIS-curable primer composition A to the substrate in a first zone and the second UV-VIS-curable primer composition B in a second zone, wherein there is an intermediate zone between the first and second zones, wherein the first UV-VIS-curable primer composition A and the second UV- VIS-curable primer composition B are mixed in the intermediate zone, wherein in the intermediate zone, when proceeding from the first zone to the second zone, the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner, and the concentration of the second UV-VIS- curable primer composition B increases in a continuous manner;

[0014] (4) curing the first and second UV-VIS-curable primer compositions A and B using UV-VIS light, to produce the primer gradient layer;

[0015] (5) applying at least partially to the primer gradient layer a cholesteric liquid crystal precursor composition comprising at least one nematic liquid crystal monomer, at least one chiral liquid crystal monomer, at least one UV-VIS-photoinitiator and at least one solvent, the nematic liquid crystal monomers and chiral liquid crystal monomers being capable of copolymerizing to form a cholesteric liquid crystal polymer;

[0016] (6) heating to remove the at least one solvent; and

[0017] (7) polymerizing the cholesteric liquid crystal precursor composition using UV-VIS-light to produce the layer comprising the cholesteric liquid crystal polymer; wherein the face reflection wavelength of the cholesteric liquid crystal polymer is Ai in the first zone and A2 in the second zone, and varies from A1 to A2 in a continuous manner in the intermediate zone.

[0018] In a second aspect, the invention provides a security feature comprising:

[0019] (1 ) the substrate described herein;

[0020] (2) the primer gradient layer described herein on the surface of the substrate, which may optionally be in the form of one or more indicia;

[0021] (3) the layer comprising the cholesteric liquid crystal polymer described herein on the surface of the primer gradient layer, which layer comprising the cholesteric liquid crystal polymer may optionally be in the form of one or more indicia; wherein the primer gradient layer comprises a first primer A, which, when in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of A1, a second primer B, which, when in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of A2, wherein AAr = A2 - A1 > 10 nm, and the primer gradient layer comprises the following zones: a first zone comprising 100% primer A, a second zone comprising 100% primer B, and an intermediate zone between the first and second zones, wherein in the intermediate zone, when proceeding from the first zone to the second zone, the concentration of primer A decreases in a continuous manner, and the concentration of primer B increases in a continuous manner, and the face reflection wavelength of the cholesteric liquid crystal polymer is A1 in the first zone and A2 in the second zone, and varies from A1 to A2 in a continuous manner in the intermediate zone.

[0022] DETAILED DESCRIPTION

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1a depicts a printing method that can be used to apply the first UV-Vis curable primer composition A (referred to hereinafter as “primer composition A”) and the second UV-Vis curable primer composition B (referred to hereinafter as “primer composition B”) directly to the substrate.

[0025] Figure 1 b depicts a printing method that can be used to apply primer composition A and primer composition B indirectly to the substrate using a blanket.

[0026] Figure 2 depicts a lateral-view of an inking roller schematically. Part 1 shows the application of primer composition A and primer composition B to the inking roller. Part 2 shows the concentration gradient that results when primer composition A and primer composition B are mixed.

[0027] Figure 3a depicts a face-on view of a preferred embodiment of the method of the invention, in which an underlying layer of primer gradient is laid down and cured, followed by the printing overtop of a waveform indicium using the cholesteric liquid crystal precursor composition. Figure 3b is a photo of the security feature resulting from the pro cess depicted in Figure 3a.

[0028] Figure 4a depicts face-on view of a preferred embodiment of the method of the invention, in which a three-stripe indicium is printed using the primer gradient, cured, and a cholesteric liquid crystal precursor composition is printed overtop thus forming the layer comprising a cholesteric liquid crystal polymer (referred to hereinafter as “CLCP layer”) to completely cover the indicium.

[0029] Figure 4b depicts a face-on view of a security feature resulting from the process depicted in Figure 4a. Figure 5a depicts a preferred embodiment of a security feature of the invention in cross-section view. Figure 5b depicts a preferred embodiment of a security feature of the invention in cross-section view.

[0030] Definitions

[0031] As used herein, the article "a" indicates one as well as more than one and does not necessarily limit its referent noun to the singular.

[0032] As used herein, the term “about” means that the amount or value in question may be the value designated or some other value about the same. The phrases are intended to convey that similar values within a range of ± 5% of the indicated value promote equivalent results or effects according to the invention.

[0033] The term “UV” (ultraviolet) as used herein is intended to mean irradiation having a wavelength component in the UV part of the electromagnetic spectrum; typically from 200 nm to 420 nm.

[0034] The term “UV-VIS” as used herein is intended to mean irradiation having a wavelength component in the ultraviolet and / or visible part of the electromagnetic spectrum; typically from 200 nm to 800 nm.

[0035] As used herein, the term “at least one” is meant to define one or more than one, for example one or two or three.

[0036] As used herein, the term “and / or” means that either all or only one of the elements of said group may be present. For example, “A and / or B” shall mean “only A, or only B, or both A and B”. In the case of “only A”, the term also covers the possibility that B is absent, i.e. “only A, but not B”.

[0037] The term “comprising” as used herein is intended to be non-exclusive and open-ended. Thus, for instance a coating composition comprising a compound A may include other compounds besides A. However, the term “comprising” also covers, as a particular embodiment thereof, the more restrictive meanings of “consisting essentially of’ and “consisting of’, so that for instance “a fountain solution comprising A, B and optionally C” may also (essentially) consist of A and B, or (essentially) consist of A, B and C.

[0038] The term "security document" refers to a document which is usually protected against counterfeit or fraud by at least one security feature. Examples of security documents include without limitation value documents and value commercial goods.

[0039] The term “security feature” is used to denote an image, pattern or graphic element that can be used for authentication purposes.

[0040] Where the present description refers to “preferred” embodiments / features, combinations of these “preferred” embodiments / features shall also be deemed as disclosed as long as this combination of “preferred” embodiments / features is technically meaningful.

[0041] The term “acrylate” encompasses molecules bearing acrylate and / or (meth)acrylate moieties. The term "continuous”, with respect to concentration, wavelength or color, means showing a change over distance that is gradual and going from high to low in one direction (or low to high in the opposite direction) in a curvilinear or linear fashion, without abrupt discontinuities.

[0042] The term "aliphatic polyurethane” refers to polyurethanes based on compounds in which the isocyanate groups are directly attached to aliphatic carbons.

[0043] The term "aromatic polyurethane” refers to polyurethanes based on compounds in which the isocyanate groups are directly attached to aromatic carbons.

[0044] The term "face reflection wavelength” means the wavelength of reflected light from a surface, when observed at an angle that is substantially perpendicular to the surface.

[0045] The term "lateral view” with respect to a cylinder or roller means a view that is perpendicular to the longitudinal axis of the cylinder or roller.

[0046] Abbreviations

[0047] PU polyurethane

[0048] CLCP cholesteric liquid crystal polymer

[0049] The inventors have created a novel security feature using cholesteric liquid crystal polymers, as defined by the claims. The invention makes use of the fact that the reflection color of a CLCP layer is influenced by the primer base on which the CLCP layer is polymerized. The various features will be described in more detail.

[0050] Substrate

[0051] The security feature described herein comprises a substrate made of a material selected from the group consisting of transparent materials, light-absorbing and light-reflecting materials and combinations thereof.

[0052] Preferred substrates made of one or more transparent materials include without limitation transparent polyolefins such as polyethylene (PE) and polypropylene (PP) including biaxially oriented polypropylene (BOPP), transparent polyamides, transparent polyesters such as polyethylene terephthalate) (PET), poly(1 ,4-butylene terephthalate) (PBT), polyethylene 2,6-naphthoate) (PEN) and transparent polyvinylchlorides (PVC), more preferably transparent polyesters such as PET.

[0053] “Light-absorbing substrates” refers to substrates that absorb at least 50%, preferably at least 60% of the intensity of one or more portions of the visible part of the electromagnetic spectrum (visible spectrum). Said light-absorbing substrates may be a continuous layer or may be a discontinuous layer in the form of an indicium or a pattern. Preferably, the light-absorbing substrate is a dark substrate, more preferably a black substrate. Should the substrate described herein be a light-absorbing substrate, no further additional layer or coating is required to easily observe without any machine or device the colorshifting properties of the overt security feature. Should the substrate not be a light-absorbing substrate, an additional light-absorbing background, preferably a dark background and more preferably a black background may be present, wherein said dark background may be permanently present or non-permanently present. Preferred substrates made of one or more light-absorbing materials include without limitation those selected from the group consisting of papers or other fibrous materials (including woven and non-woven fibrous materials), such as cellulose, paper-containing materials, glasses, metals, ceramics, plastics and polymers, 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 from a variety of fibers including without limitation abaca, cotton, linen, wood pulp, and blends thereof. As is well known to those skilled in the art, cotton and cotton / linen blends are preferred for banknotes, while wood pulp is commonly used in non-banknote security documents.

[0054] Light-absorbing substrates may consist of transparent substrates comprising a layer (for example a printed layer) made of one or more light-absorbing materials. Should the substrate be made of one or more transparent materials, the overt color-shifting properties of the overt security feature are observed by disposing it on a non-permanent light-absorbing background as described herein. The substrate materials mentioned herein are given exclusively for exemplifying purposes, without restricting the scope of the invention. In general, any substrate (which may not necessarily be flat and may be uneven) whose surface is not soluble, or only slightly soluble, in solvent(s) used in the cholesteric liquid crystal polymer precursor composition, or the components of the primer compositions, is a suitable substrate for the purposes of the present invention. As mentioned above, the substrate may advantageously have a dark or black surface or background onto which the primer compositions are applied. Without wishing to be bound by any theory, it is speculated that in the case of a dark or black background the light transmitted by the cholesteric liquid crystal polymer is largely absorbed by the background, whereby any residual backscattering from the background does not disturb the perception of the cholesteric liquid crystal polymer's own reflection with the unaided eye. In contrast, on a substrate with a light or white surface or background the reflection color of the cholesteric liquid crystal polymer is less visible when compared with a black or dark background, due to the strong backscattering from the background. However, even in the case of a light or white background, a cholesteric liquid crystal polymer can be recognized with the help of a circular polarization filter because it selectively reflects only one of the two possible circular polarized light components, in accordance with its chiral helical structure. The background may be in the form of one or more indicia in dark color or black, in which case once the primer gradient layer and CLCP layer are applied, the one or more indicia will appear as a more intense CLCP reflection and the non-dark or non-black portions will appear as a less intense CLCP reflection.

[0055] It is contemplated and included in the present invention to cover the surface of the substrate with a primer background layer (preferably continuous) prior to carrying out the steps of the method described herein. This is done, for example, by applying a UV-VIS-curable primer composition to the surface of the substrate, followed by curing with UV-light, to form the primer background layer. This is particularly desirable when there are areas where no primer gradient layer will be applied (i.e. in the case the primer gradient layer is applied as indicia, and only party covers the surface), as it avoids the potentially negative impact of the substrate (which is routinely surface-treated at the manufacturing plant) on the alignment of the cholesteric liquid crystal compounds. In an embodiment depicted in Fig. 4a and 4b, the optional primer background layer is made of the cured UV-VIS-curable primer composition A. Alternatively, the optional primer background layer may be made of the cured UV-VIS-curable primer composition B. Alternatively, the optional primer background layer may be made of a third cured UV- VIS-curable primer composition, distinct from UV-VIS-curable primer composition A and UV-VIS- curable primer composition B. The primer background layer is usually applied by a printing process selected from the group consisting of flexography printing processes, gravure printing processes and screen-printing processes, followed by curing with UV-light. Alternatively, the primer background layer may be applied using a roll-to-roll coating process such as metering rod-coating, slot-die coating, air knife coating or curtain coating, followed by curing with UV-light. Preferably, the primer background layer is transparent or translucent.

[0056] The substrate according to the present invention may further comprise additional security elements, such as organic and / or inorganic pigments, dyes, flakes, optically variable elements, magnetic pigments, etc. With the aim of further increasing the security level and the resistance against counterfeiting and illegal reproduction of security documents, the substrate described herein may contain printed, coated, or laser-marked or laser-perforated indicia, watermarks, security threads, fibers, planchettes, luminescent compounds, windows, foils, decals, primers and combinations of two or more thereof, provided that these potential additional features or elements do not negatively interfere with the optical properties of the overt security feature described herein.

[0057] The security feature described herein comprises the primer gradient layer described herein and the layer comprising a cholesteric liquid crystal, designated as CLCP layer, described herein, wherein the primer gradient layer and the CLCP layer may independently be in the form of one or more indicia and wherein said one or more indicia may the same for both layers or may be different. As used herein, the term “indicium'7“indicia” shall mean continuous and discontinuous layers consisting of distinguishing markings or signs or patterns. Examples of indicia include codes, encoded marks (e.g. encoded alphanumeric data, a one-dimensional barcode, a two-dimensional barcode, a QR-code, datamatrix and IR-reading 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.

[0058] Primer compositions

[0059] The invention makes use of two (or more) primer compositions:

[0060] 1 . A first UV-VIS-curable primer composition A, designated primer composition A, which, when cured and in contact with a CLCP polymerized thereon results in a face reflection wavelength of the CLCP of Ai; and

[0061] 2. A second UV-VIS-curable primer composition B, designated primer composition B, which, when cured and in contact with a CLCP polymerized thereon results in a face reflection wavelength of the CLCP of A2; wherein Ai < A2, and AAr= A2- Ai > 10 nm.

[0062] The general requirements for the first UV-VIS-curable primer composition A and primer composition B are:

[0063] 1 . UV-VIS-curable;

[0064] 2. Miscible and / or compatible with each other; 3. AAr> 10 nm

[0065] In a preferred embodiment, AAr > 15 nm, more preferably AAr > 20 nm, more particularly preferably AAr > 25 nm. The bigger the value of AAr, generally the more striking the resulting security feature, and the greater the range of colors reflected from the CLCP layer.

[0066] The primer compositions A and B are UV-VIS-curable, including radically-curable components, cationically-curable, or mixtures of both. Radically-curable components are preferred.

[0067] Preferably the first and second primer compositions A and B independently comprise one or more oligomeric UV-VIS-curable components. Oligomeric, for the purposes of this description, is meant to include molecules having two or more repeating units.

[0068] Preferred radically-curable components for use in the invention are acrylates. For the purposes of this description, the expression acrylates is intended to include (meth)acrylates, and formulae that include one or more acrylate moieties extend to the corresponding formulae in which one or more acrylate moieties are replaced with one or more (meth)acrylate moieties.

[0069] In a preferred embodiment, the first UV-VIS-curable primer composition A and the second UV-VIS- curable primer composition are acrylate-based. In a particularly preferred embodiment, both primer composition A and primer composition B, comprise at least one acrylate oligomer.

[0070] Acrylates for use in the invention include those having acrylate functionalities of 1 , 2, 3 and greater. It is preferred to use one or more oligomeric acrylates, having an acrylate functionality of 2, 3 or 4. Oligomers for use in the invention include epoxy-based acrylates, such as bisphenol A epoxy resin endcapped with acrylate groups, acrylated oligoamine resins, polyether-based acrylate resins, polyester- based acrylate resins, polyurethane-based acrylate resins, and mixtures of these.

[0071] The primer compositions A and B may additionally independently comprise one or more monomeric acrylates having acrylate functionalities of 1 , 2 or greater. Some examples include hexamethylene diacrylate (HDDA), 4-(1-oxo-2-propenyl)-morpholine, pentaerythritol reaction product with acrylic acid, di(trimethylolpropane) tetraacrylate, trimethylolpropane triacrylate, and mixtures of these.

[0072] The primer A and B compositions additionally independently comprise at least one photoinitiator. For radically-curable components, the photoinitiator must be suitable for initiating radical curing. For cationically-curable components (such as epoxy-terminated oligomers and / or monomers). The photoinitiator must be suitable for initiating cationic curing. If a hybrid system is used (radical / cationic), both types of photoinitiator must be used.

[0073] In a preferred embodiment, the UV-VIS-curable primer compositions A and B are based on (meth)acrylates, and a radical photoinitiator is used. Examples include a-hydroxyketones such as 1- hydroxy-cyclohexyl-phenyl-ketone and a mixture (e.g., at or about 1 :1 ) of 1-hydroxy-cyclohexyl-phenyl- ketone and one or more of benzophenone, 2-hydroxy-2-methyl-1-phenyl-1 -propanone, and 2-hydroxy- 1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1 -propanone; phenylglyoxylates such as methylbenzoylformate and a mixture of oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester and oxy-phenyl-acetic 2-[2-hydroxy-ethoxy]-ethyl ester; benzyldimethyl ketals such as alpha, alpha-dimethoxy-alpha-phenylacetophenone; a-aminoketones such as 2-benzyl-2-(dimethylamino)-1- [4-(4-morpholinyl)phenyl]-1-butanone and 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1- propanone; phosphine oxide and phosphine oxide derivatives such as diphenyl (2,4,6- trimethylbenzoyl)-phosphine oxide; phenyl bis(2,4,6-trimethylbenzoyl) supplied by IGM Resins; and also thioxanthone derivatives such as Speedcure ITX (CAS 142770-42-1), Speedcure DETX (CAS 82799-44-8), Speedcure CPTX (CAS 5495-84-1-2 or CAS 83846-86-0) supplied by Lambson. In a preferred embodiment, 2-hydroxy-1 -[4-[4-(2-hydroxy-2-methylpropionyl)phenoxy]phenyl]-2- methylpropanone is used as photoinitiator.

[0074] The UV-VIS curable primer compositions A and B may additionally independently comprise fillers, such as, for example, talcs, micas (e.g. muscovites), montmorillonites, bentonites, wollastonites, halloysites, calcined clays, china clays, carbonates (e.g. calcium carbonate, magnesium carbonate), silicates (e.g. magnesium silicate, aluminum silicate), vermiculites, amorphous silica (e.g. fumed silica, precipitated silica, silica flour), wood flours (sawdust), natural fibers, synthetic fibers (such as carbon fibers or carbon nanotubes) and mixtures thereof; preferably selected from the group consisting of talcs, micas, wollastonites, calcined clays, carbonates, amorphous silica and mixtures thereof.

[0075] In a preferred embodiment, the UV-VIS curable primer compositions A and B have viscosities of from 10 to 40 Pas, more preferably 15 to 35 Pas, more particularly preferably 20 to 30 Pas, determined at 25°C and 500 s1.

[0076] In a particularly preferred embodiment, the UV-VIS curable primer compositions A and B comprise acrylate monomers and oligomers and have viscosities of from 10 to 40 Pas, more preferably 15 to 35 Pas, more particularly preferably 20 to 30 Pas, determined at 25°C and 500 s-1.

[0077] The UV-VIS curable primer compositions A and B may additionally independently comprise other additives, such as, but not limited to, UV stabilizers, waxes, co-initiators, anti-settling agents, antifoaming agents, surfactants and other processing aids known in the field of printing inks.

[0078] Preferably, the different components of the UV-VIS-curable primer compositions A and B are chosen in such a way that once polymerized, the primer gradient layer is transparent or translucent, so as not to negatively impact the visual aspect of the CLOP layer.

[0079] In a preferred embodiment, the UV-VIS curable primer compositions A and B independently comprise at least one polyether acrylate oligomer.

[0080] In a preferred embodiment, the UV-VIS curable primer compositions A and B independently comprise an oligomer that is an amine-modified acrylate, more preferably an amine-modified acrylate together with glycerol propoxylate triacrylate and trimethylolpropane triacrylate.

[0081] In a particularly preferred embodiment, the UV-VIS curable primer compositions A and B independently comprise an oligomer mixture that is at or about 77 wt% amine-modified acrylate in admixture with at or about 15 wt% glycerol propoxylate triacrylate, and at or about 8 wt% trimethylolpropane triacrylate, based on the total weight of the oligomer mixture.

[0082] In another particularly preferred embodiment, the UV-VIS curable primer compositions A and B independently comprise at or about 25-80 wt%, preferably at or about 30-75 wt% of an oligomer that is an amine-modified acrylate, based on the total weight of the primer composition, more preferably an amine-modified acrylate together with glycerol propoxylate triacrylate and trimethylolpropane triacrylate. In a preferred embodiment, the UV-VIS curable primer compositions A and B independently comprise a polyurethane acrylate oligomer, preferably at or about 10-60 wt%, more preferably at or about 15-55 wt%, based on the total weight of the first and second primer composition A and B, respectively. In a preferred embodiment, the first UV-VIS-curable primer composition A comprises less than at or about 20 wt%, based on the total weight of the first UV-VIS-curable primer composition A, of aliphatic polyurethane acrylate oligomer with an acrylate functionality of less than 3, and the second UV-VIS- curable primer composition B comprises greater than or equal to at or about 20 wt% aliphatic polyurethane acrylate oligomer with an acrylate functionality of less than 3, based on the total weight of the UV-VIS curable primer compositions A and B, respectively.

[0083] Cholesteric liquid crystal polymer (CLCP)

[0084] The cholesteric liquid crystal precursor composition comprises (i) one or more nematic compounds and (II) one or more chiral liquid crystal monomers which are capable of giving rise to a cholesteric liquid crystal state of the cholesteric liquid crystal precursor composition upon heating. The pitch of the obtainable cholesteric liquid crystal state depends on the relative ratio of the one or more nematic compounds. The (total) concentration of the one or more nematic compounds in the cholesteric liquid crystal precursor composition for use in the present invention is at or about 4 to at or about 30, preferably at or about 4 to at or about 25, times the (total) concentration of the one or more chiral liquid crystal monomers. The one or more chiral liquid crystal monomers are preferably present in an amount from at or about 0.1 wt% to at or about 30 wt%, more preferably from at or about 0.1 wt% to at or at or about 20 wt%, and still more preferably from at or about 3 wt% to at or about 10 wt%, the weight percents being based on the total weight of the cholesteric liquid crystal precursor composition. The one or more nematic compounds are preferably present in an amount from at or about 20 wt% to at or about 50 wt%, more preferably in an amount from at or about 30 wt% to at or about 45 wt%, based on the total weight of the cholesteric liquid crystal precursor composition.

[0085] Both the one or more nematic compounds and the one or more chiral liquid crystal monomers comprise at least one polymerizable group. For example, all of the one or more nematic compounds and all of the one or more chiral liquid crystal monomers may comprise at least one polymerizable group. The at least one polymerizable group may, for example, comprise a group which is able to take part in a free radical polymerization and in particular, an unsaturated carbon-carbon bond such as for example an acrylate group with formula H2C=CH-C(0)-0 or H2C=C(CH3)-C(O)-O.

[0086] Nematic (precursor) compounds which are suitable for use in the cholesteric liquid crystal precursor composition are known in the art; when used alone (i.e., without chiral liquid crystal monomers) they arrange themselves in a state characterized by its birefringence. Non-limiting examples of nematic compounds that are suitable for use in the present invention are described in, e.g., WO 93 / 22397 A1 , WO 95 / 22586 A1, EP 0 847432 B1 , US 6,589,445, US 2007 / 0224341 . The entire disclosures of these documents are incorporated herein by reference.

[0087] A preferred class of nematic compounds for use in the present invention comprises one or more polymerizable groups, identical or different from each other, per molecule. Examples of polymerizable groups include groups that are capable of taking part in a free radical polymerization, and in particular, groups comprising a carbon-carbon double or triple bond such as for example an acrylate moiety, a vinyl moiety or an acetylenic moiety. Particularly preferred as polymerizable groups are acrylate moieties. The nematic compounds for use in the present invention further may comprise one or more optionally substituted aromatic groups, preferably phenyl groups. Examples of the optional substituents of the aromatic groups include those which are set forth herein as examples of substituent groups on the phenyl rings of the chiral liquid crystal monomers of formula (I) such as for example alkyl and alkoxy groups.

[0088] Examples of groups which may optionally be present to link the polymerizable groups and the aryl (e.g., phenyl) groups in the nematic compounds include those which are exemplified herein for the chiral liquid crystal monomers of formula (I) (including those of formula (IA) and formula (IB) set forth below). For example, the nematic compounds may comprise one or more groups of formulae (I) to (vi) which are indicated below as examples for A1 and A2 in formula (I) (and formulae (IA) and (IB)), typically bonded to optionally substituted phenyl groups.

[0089] Non-limiting specific examples of nematic compounds which are suitable for use in the present invention include without limitation the following compounds: 2-methoxybenzene-1 ,4-diyl bis[4-({[4- (acryloyloxy)butoxy]carbonyl)oxy)benzoate]; 4-{[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)benzoyl]oxy}-

[0090] 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-diyl bis[4- ({[4-(acryloyloxy)butoxy]carbonyl}oxy)-2-methyl-benzoate]; 4-{[4-({[4-

[0091] (acryloyloxy)butoxy]carbonyl}oxy)benzoyl]oxy}-2-methylphenyl 4-({[4-(acryloyloxy)butoxy]carbonyl}- oxy)-3-methoxybenzoate; 2-methylbenzene-1 ,4-diyl bis[4-({[4-(acryloyloxy)butoxy]- carbonyl}oxy)benzoate]; 2-methylbenzene-1 ,4-diyl bis[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-diyl bis[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)-3,5-di-methoxybenzoate]; 4-{[4-({[4-

[0092] (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-diyl bis{4-[4- (acryloyloxy)butoxy]-2-methylbenzoate}; 4-({4-[4-(acryloyloxy)butoxy]-2-methylbenzoyl}oxy)-3- methylphenyl 4-[4-(acryloyl-oxy)butoxy]-2,5-dimethylbenzoate; 2-methylbenzene-1 ,4-diyl bis{4-[4- (acryloyloxy)butoxy]-2,5-dimethylbenzoate} 2-methylbenzene-1 ,4-diyl bis{4-[4-(acryloyl- oxy)butoxy]benzoate); 4-({4-[4-(acryloyloxy)butoxy]-3,5-dimethylbenzoyl}oxy)-3-methylphenyl 4-[4- (acryloyloxy)butoxy]-2,5-dimethylbenzoate; 2-methylbenzene-1 ,4-diyl bis{4-[4-(acryloyloxy)butoxy]- 3,5-dimethylbenzoate); 2-methoxybenzene-1 ,4-diyl bis{4-[4-(acryloyloxy)butoxy]-3,5- dimethylbenzoate}; 4-({4-[4-(acryloyloxy)butoxy]-3-methylbenzoyl}oxy)-2-methoxyphenyl 4-[4- (acryloyl-oxy)butoxy]-3,5-dimethylbenzoate; 2-methoxybenzene-1,4-diyl bis{4-[4-(acryloyloxy)butoxy]-

[0093] 3-methylbenzoate); 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-

[0094] (acryloyloxy)-butoxy]-2,5-dimethylbenzoate; 2-methoxybenzene-1,4-diyl bis{4-[4-(acryloyloxy)butoxy]- 2-methoxybenzoate}; 2-methoxybenzene-1 ,4-diyl bis{4-[4-(acryloyloxy)butoxy]-3,5- dimethoxybenzoate}; 2-methoxybenzene-1 ,4-diyl bis{4-[4-(acryloyloxy)butoxy]-3-methoxybenzoate}; 2- ethoxybenzene-1 ,4-diyl bis{4-[4-(acryloyloxy)butoxy]benzoate}; 2-ethoxybenzene-1 ,4-diyl bis{4-[4- (acryloyloxy)butoxy]-2-methylbenzoate}; 2-(propan-2-yloxy)benzene-1 ,4-diyl bis{4-[4- (acryloyloxy)butoxy]benzoate}; 4-({4-[4-(acryloyloxy)butoxy]benzoyl}oxy)-2-(propan-2-yloxy)phenyl 4- [4-(acryloyl-oxy)butoxy]-2-methylbenzoate; 2-(propan-2-yloxy)benzene-1 ,4-diyl bis{4-[4- (acryloyloxy)butoxy]-2-methylbenzoate}; 2-(propan-2-yloxy)benzene-1 ,4-diyl bis{4-[4- (acryloyloxy)butoxy]-2,5-dimethyl-benzoate}; 2-(propan-2-yloxy)benzene-1 ,4-diyl bis{4-[4- (acryloyloxy)butoxy]-3,5-dimethyl-benzoate}; and 2-(propan-2-yloxy)benzene-1 ,4-diyl bis{4-[4- (acryloyloxy)butoxy]-3,5-dimethoxy-benzoate}. In a preferred embodiment, the nematic monomer is 2-methylbenzene-1 ,4-diyl bis[4-({[4- (acryloyloxy)butoxy]carbonyl}oxy)benzoate]. The one or more chiral liquid crystal monomers for use in the present invention preferably comprise at least one polymerizable group. Suitable examples of the one or more chiral liquid crystal monomers include those of formula (I): wherein:

[0095] Ri, R2, Rs, R4, Rs, Re, Rz and Re each independently denote Ci-Ce alkyl and Ci-Ce alkoxy;

[0096] A1 and A2 each independently denote a group of formula (i) to (vi):

[0097] Di denotes a group of formula D2denotes a group of formula m, n, o, p, q, r, s, and t each independently denote 0, 1 , or 2; y denotes 0, 1 , 2, 3, 4, 5, or 6; z equals 0 if y equals 0 and z equals 1 if y equals 1 to 6.

[0098] In one embodiment, the one or more chiral liquid crystal monomers may comprise one or more isomannide derivatives of formula (IA):

[0099] (IA) wherein:

[0100] Ri, R2, RS, RS. RS, Re, R? and Rs each independently denote Ci-Ce alkyl and Ci-Ce alkoxy;

[0101] Ai and Az each independently denote a group of formula (i) to (vi):

[0102] (i) -[(CH2)y-O]z-C(O)-CH=CH2;

[0103] (ii) -C(O)-Di-O-[(CH2)y-O]z-C(O)-CH=CH2;

[0104] (iii) -C(O)-D2-O-[(CH2)y-O]z-C(O)-CH=CH2;

[0105] (iv) -[COO-(CH2)y-O]z-C(O)-CH=CH2;

[0106] (v) -C(O)-Di-O-[COO-(CH2)y-O]z-C(O)-CH=CH2;

[0107] (vi) -C(O)-D2-O-[ COO- (CHz)y-O]z-C(O)-CH=CHz;

[0108] Di denotes a group of formula:

[0109] D2denotes a group of formula: m, n, o, p, q, r, s, and t each independently denote 0, 1 , or 2; y denotes 0, 1 , 2, 3, 4, 5, or 6; z equals 0 if y equals 0 and z equals 1 if y equals 1 to 6.

[0110] In one exemplary embodiment of the compounds of formula (IA) (and of compounds of formula (I)), Ri, R2, RS, R4, RS, Re, Rz and Rs each independently denote Ci-Ce alkyl. In an alternative embodiment, Ri, R2, RS, R4, RS, Re, Rz and Rs in formula (IA) (and in formula (I)) each independently denote Ci-Ce alkoxy. In another exemplary embodiment of the compounds of formula (I) and of formula (IA), Ai and A2 each independently denote a group of formula -[(CH2)y-O]z-C(O)-CH=CH2; Ri, R2, R3 and R4 each independently denote Ci-Ce alkyl; and m, n, 0, and p each independently denote 0, 1 , or 2. In yet another embodiment, A1 and A2 in formula (I) and formula (IA) each independently denote a group of formula -[(CH2)y-O]z-C(O)-CH=CH2; Ri, R2, Rs and R4 each independently denote Ci-Ce alkoxy; and m, n, 0, and p each independently denote 0, 1 , or 2.

[0111] In another embodiment of the compounds of formula (IA) (and of formula (I)), A1 and A2 each independently denote a group of formula -C(O)-Di-O-[(CH2)y-O]z-C(O)-CH=CH2 and / or of formula - C(O)-D2-O-[(CH2)y-O]z-C(O)-CH=CH2; and Ri, R2, R3, R4, Rs, Re, Rz and Rs each independently denote Ci-Ce alkyl. In an alternative embodiment, A1 and A2 in formula (IA) (and in formula (I)) each independently denote a group of formula -C(O)-Di-O-[(CH2)y-O]z-C(O)-CH=:CH2 and / or a group of formula -C(O)-D2-O-[(CH2)y-O]z-C(O)-CH=CH2; and Ri, R2, R3, R4, Rs, Re, Rz and Rs each independently denote Ci-Ce alkoxy.

[0112] In another embodiment of the compounds of formula (IA) (and of formula (I)), A1 and A2 each independently denote a group of formula -C(O)-Di-O-[COO-(CH2)y-O]z-C(O)-CH=CH2 and / or of formula — C(O)-D2-O— [COO- (CH2)y-O]z-C(O)-CH=CH2; and Ri, R2, Rs, R4, Rs, Re, Rz and Rs each independently denote Ci-Ce alkyl. In an alternative embodiment, A1 and A2 in formula (IA) (and in formula (I)) each independently denote a group of formula -C(O)-Di-O-[COO-(CH2)y-O]z-C(O)-CH=CH2 and / or of formula -C(O)-D2-O-[COO- (CH2)y-O]z-C(O)-CH=CH2; and R-i, R2, Rs, R4, Rs, Rs, Rz and Rs each independently denote Ci-Ce alkoxy.

[0113] In another embodiment, the one or more chiral liquid crystal monomers may comprise one or more isosorbide derivatives represented by formula (IB):

[0114] (IB) wherein:

[0115] R1, R2, R3, R4, Rs, Re, Rz and Rs each independently denote Ci-Ce alkyl and Ci-Ce alkoxy;

[0116] A1 and A2 each independently denote a group of formula (i) to (vi):

[0117] (i) -[(CH2)y-O]z-C(O)-CH=

[0118] (ii) -C(O)-Di-O-[(CH2)y-O]

[0119] (iii) -C(O)-D2-O-[(CH2)y-O

[0120] (iv) -[COO-(CH2)y-O]z-C(O

[0121] (v) -C(O)-Di-O-[COO-(CH

[0122] (vi) -C(O)-D2-O-[ COO- (

[0123] Di denotes a group of formula:

[0124] D2 denotes a group of formula: m, n, 0, p, q, r, s, and t each independently denote 0, 1 , or 2; y denotes 0, 1 , 2, 3, 4, 5, or 6; z equals 0 if y equals 0 and z equals 1 if y equals 1 to 6.

[0125] In one embodiment of the compounds of formula (IB), R1, R2, R3, R4, Rs, Re, Rz and Rs each independently denote Ci-Ce alkyl; and m, n, 0, and p each independently denote 0, 1 , or 2. In an alternative embodiment, Ri, R2, R3, R4, Rs, Rs, R7 and Rs in formula (IB) each independently denote Ci- Cs alkoxy; and m, n, o, and p each independently denote 0, 1 , or 2.

[0126] In another embodiment of the compounds of formula (IB), A1 and A2 each independently denote a group of formula -[(CH2)y-O]z-C(O)-CH=CH2; R1, R2, R3 and R4 each independently denote Ci-Cs alkyl; and m, n, 0, and p each independently denote 0, 1 , or 2. In yet another embodiment, A1 and A2 in formula (IB) each independently denote a group of formula -[(CH2)y-O]z-C(O)-CH=CH2; R1, R2, R3 and R4 each independently denote Ci-Cs alkoxy; and m, n, 0, and p each independently denote 0, 1 , or 2. In another embodiment of the compounds of formula (IB), A1 and A2 each independently denote a group of formula -C(O)-Di-O-[(CH2)y-O]z-C(O)-CH=CH2 and / or of formula -C(O)-D2-O-[(CH2)y-O]z-C(O)- CH=CH2j RI, R2, 3, R4, Rs, Rs, R7 and Rs each independently denote Ci-Cs alkyl; and m, n, 0, and p each independently denote 0, 1 , or 2. In an alternative embodiment, A1 and A2 in formula (IB) each independently denote a group of formula -C(O)-Di-O-[(CH2)y-O]z-C(O)-CH=CH2 and / or a group of formula -C(O)-D2-O-[(CH2)y-O]z-C(O)-CH=CH2; Ri, R2, R3, R4, Rs, Rs, R7 and Rs each independently denote Ci-Cs alkoxy ; and m, n, 0, and p each independently denote 0, 1 , or 2.

[0127] In another embodiment of the compounds of formula (IB), A1 and A2 each independently denote a group of formula -C(O)-Di-O-[COO-(CH2)y-O]z-C(O)-CH=CH2 and / or of formula — C(O)-D2-O-[COO- (CH2)y- O]Z-C(O)-CH=CH2; RI, R2, R3, R4, Rs, Rs, R7 and Rs each independently denote Ci-Cs alkyl; and m, n, o, and p each independently denote 0, 1 , or 2.

[0128] In an alternative embodiment, A1 and A2 in formula (IB) each independently denote a group of formula -C(O)-Di-O-[COO-(CH2)y-O]z-C(O)-CH=CH2 and / or a group of formula -C(O)-D2-O-[COO- (CH2)y-O]z- C(O)-CH=CH2; RI, R2, R3, 4, Rs, Rs, R7 and Rs each independently denote Ci-Cs alkoxy ; and m, n, 0, and p each independently denote 0, 1 , or 2. Non-limiting examples of chiral liquid crystal monomers of formula (I) for use in the present invention include without limitation 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}-benzoyl)- 1,4:3,6-dianhydro-D-mannitol; 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]-1 ,4:3,6-dianhydro-D-mannitol; 2,5-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-

[0129] (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-

[0130] (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)-3- methylbenzoyl]oxy}-2-methoxybenzoyl)-1 ,4:3,6-dianhydro-D-mannitol; 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-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-

[0131] (acryloyloxy)benzoyl]oxy}-3-methoxybenzoyl)-1 ,4:3,6-dianhydro-D-mannitol; 2-O-(4-{[4-(acryloyloxy)-

[0132] 2-methoxybenzoyl]oxy}-2,5-dimethylbenzoyl)-5-O-(4-{[4-(acryloyloxy)-3-methoxybenzoyl]oxy}-3- methylbenzoyl)-1 ,4:3,6-dianhydro-D-mannitol; 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)-2-methoxy-5-methylbenzoyl]oxy}-2-methylbenzoyl)-5-O-(4-{[4- (acryloyloxy)-5-methoxy-2-methylbenzoyl]oxy}-3-methylbenzoyl)-1,4:3,6-dianhydro-D-mannitol; 2-0- (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-ethoxybenzoyl]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)-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];

[0133] 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)-

[0134] 3-methylbenzoyl]oxy}-2-methoxybenzoyl)-1 ,4:3,6-dianhydro-D-glucitol; 2-0-(4-{[4-(acryl- oyloxy)benzoyl]oxy}-2-methoxybenzoyl)-5-O-(4-{[4-(acryloyloxy)-2,5-dimethylbenzoyl]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-methoxy-5-methylbenzoyl]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-

[0135] (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-methoxy- benzoyl]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)- 3-methoxybenzoyl]oxy}-3-methylbenzoyl)-1,4:3,6-dianhydro-D-glucitol; 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-methylbenzoyl)-5-O-(4-{[4-(acryloyloxy)-5-methoxy-2-methylbenzoyl] oxy}-3- methylbenzoyl)-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)-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)-3-ethoxybenzoyl]oxy}benzoyl)-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-(ac-ryloyloxy)-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-dianhydro-D-glucitol; 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)-3-methoxybenzoyl]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. In a preferred embodiment, the chiral liquid crystal monomer is D-Glucitol 1 ,4:3,6-dianhydro-bis[4-[[4- [[[4-[(1-oxo-2-propenyl)oxy]butoxy]carbonyl]oxy]benzoyl]oxy]benzoate]. The cholesteric liquid crystal precursor composition comprises one or more solvents. Suitable solvents are known to those skilled in the art and include without limitation low-viscosity, slightly polar and aprotic organic solvents, such as for example methyl ethyl ketone (MEK), acetone, cyclopentanone, cyclohexanone, ethyl acetate, ethyl 3-ethoxypropionate, and mixtures of two or more thereof. Cyclohexanone is particularly preferred.

[0136] The one or more solvents are preferably present in an amount from at or about 30 wt% to at or about 70 wt%, more preferably from at or about 40 to at or about 60 wt%, based on the total weight of the cholesteric liquid crystal precursor composition.

[0137] The CLCP precursor composition described herein further comprises one or more photoinitiators. Nonlimiting examples of the many suitable photoinitiators for the cholesteric liquid crystal precursor composition described herein include a-hydroxyketones such as 1-hydroxy-cyclohexyl-phenyl-ketone and a mixture (e.g., at or about 1 :1) of 1-hydroxy-cyclohexyl-phenyl-ketone and one or more of benzophenones, 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 (sold for example by IGM Resins under the name ESACURE® KIP 160); phenylglyoxylates such as methylbenzoylformate and a mixture of oxyphenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester and oxy-phenyl-acetic 2-[2-hydroxy- ethoxy]-ethyl ester; benzyldimethyl ketals such as alpha, alpha-dimethoxy-alpha-phenylacetophenone; a-aminoketones such as 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-butan-1-one, 2- dimethylamino-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 oxide and phosphine oxide derivatives such as diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide; phenyl-bis(2,4,6-trimethylbenzoyl)- phosphine oxide and also thioxanthone derivatives such as those described herein.

[0138] The one or more photoinitiators are preferably present in an amount from at or about 0.01 wt% to at or about 10 wt%, more preferably from at or about 0.05 wt% to at or about 7 wt%, based on the total weight of the cholesteric liquid crystal precursor composition.

[0139] In a preferred embodiment, the CLCP precursor composition comprises 2-hydroxy-1-[4-[4-(1-hydroxy- 2-methylpropanoyl)phenoxy]phenyl]-2-methylpropan-1-one as photoinitiator, preferably at or about 0.7- 2.5 wt%, more preferably at or about 0.8-1 .5 wt%, based on the total weight of the CLCP precursor composition.

[0140] The cholesteric liquid crystal precursor composition described herein may further comprise one or more optional additives, provided that said one or more additives do not negatively disturb or interfere with the formation of the helix and / or the formation of the polymer, said one or more additives including without limitation compounds and materials which are used for adjusting physical, rheological and chemical parameters of the composition such as the consistency (e.g. anti-settling agents and plasticizers), foaming properties (e.g. antifoaming agents and deaerators), lubricating properties (waxes), radiation sensitizers, UV stability (photostabilizers), adhesion properties, surface properties (wetting agents, hydrophilisizing and hydrophobisizing agents), etc. When present, the one or more additives comprised in the cholesteric liquid crystal precursor composition are preferably present in an amount from at or about 0.01 wt% to at or about 5 wt%, based on the total weight of the cholesteric liquid crystal precursor composition.

[0141] In a preferred embodiment, the cholesteric liquid crystal precursor composition comprises 2- methylbenzene-1 ,4-diyl bis[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)benzoate] as nematic monomer and D-glucitol 1 ,4:3,6-dianhydro-bis[4-[[4-[[[4-[(1-oxo-2- propenyl)oxy]butoxy]carbonyl]oxy]benzoyl]oxy]benzoate] as chiral monomer, preferably at or about SO- 45 wt% 2-methylbenzene-1 ,4-diyl bis[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)benzoate] as nematic monomer, and at or about 0.7-2.5 wt% D-Glucitol 1,4:3,6-dianhydro-bis[4-[[4-[[[4-[(1-oxo-2- propenyl)oxy]butoxy]carbonyl]oxy]benzoyl]oxy]benzoate] as chiral monomer, based on the total weight of the cholesteric liquid crystal precursor composition.

[0142] In another preferred embodiment, the cholesteric liquid crystal precursor composition comprises 2- methylbenzene-1 ,4-diyl bis[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)benzoate] as nematic monomer and D-glucitol 1 ,4:3,6-dianhydro-bis[4-[[4-[[[4-[(1-oxo-2- propenyl)oxy]butoxy]carbonyl]oxy]benzoyl]oxy]benzoate] as chiral monomer, and 2-hydroxy-1-[4-[4-(1- hydroxy-2-methylpropanoyl)phenoxy]phenyl]-2-methylpropan-1-one as photoinitiator.

[0143] In another preferred embodiment, the cholesteric liquid crystal precursor composition comprises at or about 30-45 wt% 2-methylbenzene-1 ,4-diyl bis[4-({[4-(acryloyloxy)butoxy]carbonyl}oxy)benzoate] as nematic monomer, and at or about 0.7-2.5 wt% D-Glucitol 1,4:3,6-dianhydro-bis[4-[[4-[[[4-[(1-oxo-2- propenyl)oxy]butoxy]carbonyl]oxy]benzoyl]oxy]benzoate] as chiral monomer, and 2-hydroxy-1-[4-[4-(1- hydroxy-2-methylpropanoyl)phenoxy]phenyl]-2-methylpropan-1-one as photoinitiator at or about 0.7- 2.5 wt%, more preferably at or about 0.8-1 .5 wt%, based on the total weight of the cholesteric liquid crystal precursor composition.

[0144] Examples of embodiments of the method of the invention

[0145] The method of the invention comprises a step of applying the first UV-VIS-curable primer composition A to the substrate in a first zone and the second UV-VIS-curable primer composition B in a second zone, wherein there is an intermediate zone between the first and second zones, wherein the first UV- VIS-curable primer composition A and the second UV-VIS-curable primer composition B are mixed in the intermediate zone, wherein in the intermediate zone, when proceeding from the first zone to the second zone, the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner, and the concentration of the second UV-VIS-curable primer composition B increases in a continuous manner.

[0146] The first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B can be mixed using any method that gives a continuous gradient, in which the concentration of primer composition A decreases in a continuous manner proceeding in one direction, and the concentration of primer composition B increases in a continuous manner proceeding in the same direction.

[0147] One method is to apply primer composition A at a first zone of an application device, and apply primer composition B at a second zone of the application device, in such a way that where the first and second zone abut, mixing of the two primer compositions A and B occurs.

[0148] In a preferred embodiment, step (3) is carried out using a printing method comprising the following steps:

[0149] (3i) applying the first UV-VIS-curable primer composition A at a first end of a first roller and applying the second UV-VIS-curable primer composition B at the second end of the first roller. The primer compositions A and B may optionally be separated by a separator when applied to the first roller. The primer compositions may optionally be transferred from the first roller to one or more intermediate rollers so as to ensure even distribution of the primer compositions;

[0150] (3ii) applying a second roller to the first roller or to at least one of the optional intermediate rollers, to spread the primer compositions, wherein the second roller is capable of axial reciprocating motion to cause mixing of the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B at an interface, resulting in a concentration gradient, wherein the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner and the concentration of primer composition B increases in a continuous manner, proceeding axially from the first end of the first roller, or the one or more of the intermediate rollers, if used, to the second end;

[0151] (3iii) transferring the primer compositions in the form of the gradient to a plate cylinder, which bears one or more indicia;

[0152] (3iv) transferring the one or more indicia from the plate cylinder to the substrate, either directly, or indirectly using a blanket.

[0153] In a preferred embodiment, step (3) is carried out using an offset printing method

[0154] Offset printing processes consist of indirect methods wherein an ink is transferred from a plate cylinder carrying a printing plate to a blanket cylinder and subsequently onto a substrate. Offset printing processes are categorized in three distinct technologies, namely wet offset processes, waterless offset processes and dry offset processes. Wet offset processes take advantage of the difference in surface energy between the image area and the non-image area of the printing plate. The image area is oleophilic, whereas the non-image area is hydrophilic. Thus, oily inks used in the method tend to adhere to the image-area and to be repelled from the non-image area of the printing plate. Wet offset printing is typically carried out by feeding both a fountain solution (also referred in the art as dampening solution) and an oleophilic ink to the printing plate in such a way that the image areas preferentially receive the ink and the non-image areas preferentially the fountain solution and then transferring the ink deposited on image areas onto a substrate via the blanket cylinder. In waterless offset processes, the non-image areas of the printing plate are covered with a specific silicone rubber material having very low surface tension (about 20 mN / m) and repelling the ink. No water (and hence no fountain solution) is needed. Dry offset processes are methods wherein the printing plate is made of a metal-backed photopolymer forming reliefs carrying the motifs to be printed (for this reason, it is also called letterpress offset). The ink adheres to the reliefs and is then transferred to the substrate via the blanket cylinder. In this case also, no fountain solution is required.

[0155] In one embodiment, the printing process in steps (1) - (3) is a dry offset printing process wherein the printing plate of the plate cylinder is made from a metal-baked photopolymer bearing reliefs to form the indicia and the process includes indirectly transferring the first and second primer compositions A and B in the form of a gradient from the plate cylinder to the substrate using a blanket cylinder.

[0156] In a preferred embodiment, the invention provides a method for producing a security feature on the substrate described herein, wherein the security feature comprises the primer gradient layer described herein, which may optionally be in the form of one or more indicia, and the layer comprising a cholesteric liquid crystal polymer described herein, which may optionally be in the form of one or more indicia, the method comprising the steps: (1) providing the first UV-VIS-curable primer composition A described herein, which, when cured and in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of Ai;

[0157] (2) providing the second UV-VIS-curable primer composition B described herein, which, when cured and in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of A2, wherein AAr= A2 - A1 10 nm;

[0158] (3) applying the first UV-VIS-curable primer composition A to the substrate in a first zone and the second UV-VIS-curable primer composition B in a second zone, wherein there is an intermediate zone between the first and second zones, wherein the first UV-VIS-curable primer composition A and the second UV- VIS-curable primer composition B are mixed in the intermediate zone, wherein in the intermediate zone, when proceeding from the first zone to the second zone, the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner, and the concentration of the second UV-VIS- curable primer composition B increases in a continuous manner, wherein the application of the first UV- VIS-curable primer composition A and the second UV-VIS-curable primer composition B is carried out by:

[0159] (3i) applying the first UV-VIS-curable primer composition A at a first end of a first roller and applying the second UV-VIS-curable primer composition B at the second end of the first roller, optionally transferring the primer compositions from the first roller to one or more intermediate rollers so as to ensure even distribution of the primer compositions;

[0160] (3ii) applying a second roller to the first roller or to at least one of the optional intermediate rollers, to spread the primer compositions, wherein the second roller is capable of axial reciprocating motion to cause mixing of the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B at an interface, resulting in a concentration gradient, wherein the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner and the concentration of primer composition B increases in a continuous manner, proceeding axially from the first end of the first roller, or the one or more of the intermediate rollers, if used, to the second end;

[0161] (3iii) transferring the primer compositions in the form of the gradient to a plate cylinder, which bears one or more indicia;

[0162] (3iv) transferring the one or more indicia from the plate cylinder to the substrate, either directly, or indirectly using a blanket;

[0163] (4) curing the first and second UV-VIS-curable primer compositions using UV-VIS light, to produce the primer gradient layer;

[0164] (5) applying at least partially to the primer gradient layer the cholesteric liquid crystal precursor composition described herein and comprising at least one nematic liquid crystal monomer, at least one chiral liquid crystal monomer, at least one UV-VIS-photoinitiator and at least one solvent, the nematic liquid crystal monomers and chiral liquid crystal monomers being capable of copolymerizing to form the cholesteric liquid crystal polymer;

[0165] (6) heating to remove the at least one solvent; and

[0166] (7) polymerizing the cholesteric liquid crystal precursor composition using UV-VIS light to produce the layer comprising the cholesteric liquid crystal polymer; wherein the face reflection wavelength of the cholesteric liquid crystal polymer is Ai in the first zone and A2 in the second zone, and varies from A1 to A2 in a continuous manner in the intermediate zone.

[0167] Steps (4) and (7) are preferably carried out with one or more light sources so at to cure the composition, wherein the one or more light sources are preferably selected from the group consisting of arc discharge lamp such as mercury lamps (preferably medium-pressure mercury lamps), UV-VIS-LED lamps and sequences thereof described herein.

[0168] Two embodiments of this process are described in more detail referring to Figures 1a and 1b.

[0169] Figure 1a depicts a printing apparatus schematically in an end-on view. The curved arrows designate the direction of rotation of the various rollers:

[0170] (3i) the first UV-VIS-curable primer composition A is applied at a first end of a first roller (1) and the second UV-VIS-curable primer composition B is applied at the second end of the first roller (1), where the application of the primer compositions A and B is indicated by the solid arrow. The two primer compositions A and B may be separated during application to the first roller (1) using a separator (not shown). Optionally, one or more intermediate rollers may be provided (not shown), with the primer compositions being transferred from the first roller (1) to the one or more intermediate rollers sequentially. The intermediate rollers improve the even distribution of the primer compositions;

[0171] (3ii) a second roller (2) is applied to the first roller (1), or to the one or more intermediate rollers (not shown) to spread the primer compositions A and B, wherein the second roller (2) is capable of axial reciprocating motion to cause mixing of primer composition A and primer composition B at an interface, resulting in a concentration gradient on roller (1 ), wherein the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner and the concentration of the second UV-VIS- curable primer composition B increases in a continuous manner, proceeding axially from the first end of the first roller (1) to the second end, or in the case where one or more intermediate rollers are used the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner and the concentration of primer composition B increases in a continuous manner, proceeding axially from the first end of the intermediate roller to the second end;

[0172] (3iii) the primer compositions are transferred to a plate cylinder (3), which bears one or more indicia; (3iv) the one or more indicia are transferred from the plate cylinder (3) to the substrate (4) directly, with an impression cylinder (5) applying the required pressure between the substrate (4) and the plate cylinder (3).

[0173] In Figure 1 b, the transfer occurs indirectly via a blanket cylinder (6), which is typical of offset printing processes. Figure 1b depicts a printing apparatus schematically in an end-on view. The curved arrows designate the direction of rotation of the various rollers:

[0174] (3i) the first UV-VIS-curable primer composition A is applied at a first end of a first roller (1) and the second UV-VIS-curable primer composition B is applied at the second end of the first roller (1), where the application of the primer compositions A and B is indicated by the solid arrow. The two primer compositions A and B may be separated during application to the first roller (1) using a separator (not shown). Optionally, one or more additional intermediate rollers may be provided (not shown), with the primer compositions being transferred from the first roller (1) to the one or more intermediate rollers. The intermediate rollers improve the even distribution of the primer compositions; (3ii) a second roller (2) (“oscillating roller”) is applied to the first roller (1), or to the one or more intermediate rollers (not shown) to spread the primer compositions A and B, wherein the second roller (2) is capable of axial reciprocating motion to cause mixing of primer composition A and primer composition B at an interface, resulting in a concentration gradient on roller (1), wherein the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner and the concentration of the second UV-VIS-curable primer composition B increases in a continuous manner, proceeding axially from the first end of the first roller (1) to the second end, or in the case where one or more intermediate rollers is used the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner and the concentration of primer composition B increases in a continuous manner, proceeding axially from the first end of the intermediate roller to the second end;

[0175] (3iii) the primer compositions are transferred to a plate roller (3), which bears one or more indicia;

[0176] (3iv) the one or more indicia are transferred from the plate roller (3) to a blanket or offset cylinder (6), which then applies the one or more indicia to the substrate (4), with an impression roller (5) applying the required pressure between the substrate (4) and the blanket cylinder (6).

[0177] The disposition of primer compositions A and B on the first roller (1) is depicted in Figure 2. In step 1, a schematic lateral view of roller (1 ) is shown, with the first UV-VIS-curable primer composition A applied at the right-hand side and the second UV-VIS-curable primer composition B applied at the left-hand side. In step 2, the gradient of primer compositions from A to B on roller 1 is depicted after the action of the spreading and reciprocating second roller (2) (not depicted).

[0178] The method of the invention has many variations, some of which will now be described, with reference to Figures 3 to 5.

[0179] As mentioned previously, the substrate is preferably dark or black or has a precoat that is dark or black, as in the absence of a dark or black background, the intensity of the reflected light is less. This effect can also be used to add complexity to the security feature. For example, prior to using the method of the invention, the substrate may bear one or more indicia in the form of dark / black regions and light regions. Once a primer gradient layer is applied and subsequently a CLCP layer is applied, the one or more dark / black indicia on the substrate will appear as intense CLCP reflection regions (dark / black regions) and less intense CLCP reflection regions (light regions).

[0180] It is within the scope of the invention to apply a primer background layer prior to step (3). Preferably, the primer background layer is continuous (i.e. it covers the substrate surface in an unbroken manner) and is made either of the first UV-VIS-curable primer composition A in cured form or of the second UV- VIS-curable primer composition B in cured form, or a third UV-VIS-curable primer composition, distinct from first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B, in cured form. The primer gradient layer described herein is then applied, in the form of one or more indicia, overtop of the primer background layer.

[0181] Variation 1

[0182] A first variation is described with reference to Figures 3a and 3b. Figure 3a shows the process schematically. Step 1 is a lateral view of roller (1), with the first UV-VIS-curable primer composition A applied at the right-hand end, and the second UV-VIS-curable primer composition B is applied at the left-hand end. The second roller (2) (not depicted) spreads and mixes the primer compositions to give a gradient. The primer composition gradient is then applied to a plate cylinder (not depicted), which in turn transfers the gradient in the form of a rectangle indicium (7), to the substrate (4) (black or dark), as depicted in Step 2. The primer composition gradient rectangle (7) is cured by UV-VIS-light. For the purposes of this illustration, the primer compositions are depicted as if they have a color, whereas in practice they are usually transparent or translucent, and do not appear different from one another to the naked eye.

[0183] In step 3 of Figure 3a, the cholesteric liquid crystal precursor composition is printed overtop of the primer gradient rectangle (7) with a method selected from flexography printing, gravure printing, screenprinting or ink-jet printing, in this case in the form a wave indicium (8). The cholesteric liquid crystal precursor composition is heated to evaporate the solvent and polymerized by UV-VIS-light.

[0184] The resulting security feature is illustrated in face-on view in Figure 3b, wherein Ai indicates a zone in which the face reflection wavelength of the wave indicium is Ai , A2 indicates a zone in which the face reflection wavelength of the wave indicium is A2, and An indicates an intermediate or gradient zone in which the face reflection wavelength of the wave indicium varies in a continuous gradient from A1 to A2, going from right to left. The background is black or dark in this case because the substrate has a black surface, and the CLCP layer is only present in the wave indicium.

[0185] The security feature resulting from Variation 1 is depicted schematically in cross-section view in Figure 5a, where (4) designates the substrate, (7) the primer gradient layer and (8) designates the CLCP layer, which is in the form of an indicium.

[0186] Variation 2

[0187] A second variation is described with reference to Figures 4a and 4b. Figure 4a depicts the process schematically. Step 1 is a lateral view of roller (1), with the first UV-VIS-curable primer composition A is applied at the left-hand end and the second UV-VIS-curable primer composition B is applied at the right-hand end. The second roller (2) (not depicted) spreads and mixes the primer compositions to give a gradient. The primer gradient is then applied to the plate cylinder (3) (not depicted), which in turn transfers the gradient to the substrate (4) (black or dark) in the form of a three-stripe indicium (7), as depicted in Step 2. Previously, and in order to cancel the potentially negative impact of the substrate on the alignment of the liquid crystal compounds in areas where the primer gradient is not present, a layer of the first UV-VIS-curable composition A was applied on the whole substrate (4) surface and cured. Alternatively, the substrate may be covered with a cured layer of the second UV-VIS-curable composition B which is cured before applying the primer gradient. The primer composition gradient three-stripe indicium (7) is cured by UV-VIS-light. For the purposes of this illustration, the primer compositions are depicted as if they have a color, whereas in practice they are usually transparent or translucent, and do not appear different from one another to the naked eye.

[0188] In step 3 of Figure 4a, the cholesteric liquid crystal precursor composition is printed overtop of the primer gradient three-stripe indicium (7) (invisible in step 3 of Figure 4a) with a method selected from flexography printing, gravure printing, screen-printing or ink-jet printing, in this case in the form a rectangle (8) that covers over the three-stripe indicium (7) and the primer A-coated substrate (4). The cholesteric liquid crystal precursor composition is heated to evaporate the solvent and polymerized by UV-VIS-light.

[0189] The resulting security feature is shown in Figure 4b, where Ai indicates areas where the face reflection wavelength of the CLCP is Ai , and A2 indicates areas where the face reflection wavelength of the CLCP is A2 and An indicates an intermediate or gradient zone on the three-stripe indicium in which the face reflection wavelength of the three-stripe indicium varies in a continuous gradient from Ai to A2, going from left to right. The color gradient appears only in the three-stripe indicium. The background has a face reflection wavelength of Ai in this case because the CLCP layer covers both the background and the three-stripe indicium, and the background is covered with the first UV-VIS-curable primer composition A before application of the one or more indicia and the CLCP layer.

[0190] The security feature resulting from Variation 2 is depicted schematically in cross-section view in Figure 5b, where (4) designates the substrate (7) the primer gradient layer in the form of a three-stripe indicium, (8) designates the CLCP layer, which is in the form of a rectangle that covers over the indicium in the primer gradient layer, and (9) the primer background layer which is made of the first UV-VIS-curable primer composition A in cured form.

[0191] Security feature

[0192] The invention provides a security feature obtainable by or made by the method of the invention.

[0193] In one aspect, the invention provides a security feature comprising:

[0194] (1) the substrate described herein;

[0195] (2) the primer gradient layer described herein on the surface of the substrate, which may optionally be in the form of one or more indicia;

[0196] (3) the layer comprising a cholesteric liquid crystal polymer, as described herein, at least partially on the surface of the primer gradient layer, and which may optionally be in the form of one or more indicia; wherein the primer gradient layer comprises a first primer A, which, when in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of Ai, a second primer B, which, when in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal composition of A2, wherein AAr= A2 - Ai > 10 nm, and the primer gradient layer comprises the following zones: a first zone comprising 100% primer A, a second zone comprising 100% primer B, and an intermediate zone between the first and second zones, wherein in the intermediate zone, when proceeding from the first zone to the second zone, the concentration of primer A decreases in a continuous manner, and the concentration of primer B increases in a continuous manner, and the reflectance wavelength of the cholesteric liquid crystal composition is Ai in the first zone and A2 in the second zone, and varies from Ai to A2 in a continuous manner in the intermediate zone.

[0197] Preferred examples of the various components of the security feature are as stated for the method of the invention.

[0198] Two examples of security features of the invention are illustrated schematically in Figures 5a and 5b. The security feature resulting from Variation 1 is depicted schematically in cross-section view in Figure 5a, where (4) designates the substrate, (7) the primer gradient layer, which is a gradient of concentration from primer A to primer B, and (8) designates the CLCP layer, which is in the form of one or more indicia.

[0199] The security feature resulting from Variation 2 is depicted schematically in cross-section view in Figure 5b, where (4) designates the substrate, (7) the primer gradient layer, (8) designates the CLCP layer, which is in the form of a rectangle that covers over the one or more indicia in the primer gradient layer, and (9) the primer background layer which is made of the first UV-VIS-curable primer composition A in cured form.

[0200] Preferred embodiments of the invention

[0201] 1. A method for producing a security feature on a substrate, wherein the security feature comprises a primer gradient layer, which may optionally be in the form of one or more indicia, and a layer comprising a cholesteric liquid crystal polymer, which may optionally be in the form of one or more indicia, the method comprising the steps:

[0202] (1) providing a first UV-VIS-curable primer composition A, which, when cured and in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of i ;

[0203] (2) providing a second UV-VIS-curable primer composition B, which, when cured and in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of A2, wherein AAr = A2 - A1 > 10 nm;

[0204] (3) applying the first UV-VIS-curable primer composition A to the substrate in a first zone and the second UV-VIS-curable primer composition B in a second zone, wherein there is an intermediate zone between the first and second zones, wherein the first UV-VIS-curable primer composition A and the second UV- VIS-curable primer composition B are mixed in the intermediate zone, wherein in the intermediate zone, when proceeding from the first zone to the second zone, the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner, and the concentration of the second UV-VIS- curable primer composition B increases in a continuous manner;

[0205] (4) curing the first and second UV-VIS-curable primer compositions using UV-VIS light, to produce the primer gradient layer;

[0206] (5) applying at least partially to the primer gradient layer a cholesteric liquid crystal precursor composition comprising at least one nematic liquid crystal monomer, at least one chiral liquid crystal monomer, at least one UV-VIS-photoinitiator and at least one solvent, the nematic liquid crystal monomers and chiral liquid crystal monomers being capable of copolymerizing to form a cholesteric liquid crystal polymer;

[0207] (6) heating to remove the at least one solvent; and

[0208] (7) polymerizing the cholesteric liquid crystal precursor composition using UV-VIS light to produce the layer comprising the cholesteric liquid crystal polymer; wherein the face reflection wavelength of the cholesteric liquid crystal polymer is A1 in the first zone and A2 in the second zone, and varies from A1 to A2 in a continuous manner in the intermediate zone; wherein the substrate optionally comprises a primer background layer underneath the primer gradient layer, preferably made of either the cured UV-VIS curable primer composition A or the cured UV-VIS- curable primer composition B. 2. A security feature comprising:

[0209] (1) a substrate;

[0210] (2) a primer gradient layer on the surface of the substrate, which may optionally be in the form of one or more indicia;

[0211] (3) a layer comprising a cholesteric liquid crystal polymer, at least partially on the surface of the primer gradient layer, and which may optionally be in the form of one or more indicia; wherein the primer gradient layer comprises a first primer A, which, when in contact with the cholesteric liquid crystal polymer polymerized thereon results in a face reflection wavelength of the cholesteric liquid crystal polymer of Ai, a second primer B, which, when in contact with the cholesteric liquid crystal polymer polymerized thereon results in a face reflection wavelength of the cholesteric liquid crystal polymer of A2, wherein AAr= A2 - A1 > 10 nm, preferably AAr> 15 nm, more preferably AAr> 20 nm, still more preferably AAr> 25 nm, and the primer gradient layer comprises the following zones: a first zone comprising 100% primer A, a second zone comprising 100% primer B, and an intermediate zone between the first and second zones, wherein in the intermediate zone, when proceeding from the first zone to the second zone, the concentration of primer A decreases in a continuous manner, and the concentration of primer B increases in a continuous manner, and the face reflection wavelength of the cholesteric liquid crystal polymer is A1 in the first zone and A2 in the second zone, and varies from A1 to A2 in a continuous manner in the intermediate zone, the substrate optionally comprising a primer background layer, underneath the primer gradient layer, preferably made of either primer A or primer B.

[0212] 3. Embodiment 1 or 2, wherein the first UV-VIS-curable primer composition A and the second UV- VlS-curable primer composition B independently further comprise one or more oligomeric UV-VIS- curable components, preferably one or more oligomeric acrylates.

[0213] 4. Embodiment 1 , 2 or 3, wherein the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B independently comprise acrylates having acrylate functionalities of 1 , 2, 3 and greater.

[0214] 5. Any one preceding embodiment, wherein the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B independently comprise at least one oligomer selected from epoxy-based acrylates, such as bisphenol A epoxy resin end-capped with acrylate groups, acrylated oligoamine resins, polyether-based acrylate resins, polyester-based acrylate resins, polyurethane-based acrylate resins, and mixtures of these.

[0215] 6. Any one preceding embodiment, wherein the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B independently comprise one or more monomeric acrylates having acrylate functionalities of 1 , 2 or greater, preferably wherein the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B independently comprise at least one monomeric acrylate selected from hexamethylene diacrylate (HDDA), 4-(1-oxo-2-propenyl)- morpholine, pentaerythritol reaction product with acrylic acid, di(trimethylolpropane)tetraacrylate, trimethylolpropane triacrylate, and mixtures of these.

[0216] 7. Any one preceding embodiment, wherein the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B independently comprise 2-hydroxy-1-[4-[4-(2-hydroxy-2- methylpropionyl)phenoxy]phenyl]-2-methylpropanone, as photoinitiator.

[0217] 8. Any one preceding embodiment, wherein the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B independently comprise at least one polyether acrylate oligomer.

[0218] 9. Any one preceding embodiment, wherein the first UV-VIS-curable primer composition A and the second UV-VIS-curable composition B independently comprise an oligomer that is an amine- modified acrylate, more preferably an amine-modified acrylate together with glycerol propoxylate triacrylate and trimethylolpropane triacrylate.

[0219] 10. Any one preceding embodiment, wherein the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B independently comprise a polyurethane acrylate oligomer, preferably at at or about 10-60 wt%, more preferably at at or about 15-55 wt%, the weight percents being based on the total weight of the primers A and B, respectively.

[0220] 11. Any one preceding embodiment, wherein the first UV-VIS-curable primer composition A comprises less than at or about 20 wt%, based on the total weight of the primer composition, of aliphatic polyurethane acrylate oligomer with an acrylate functionality of less than 3, and the second UV-VIS- curable primer composition B comprises greater than or equal to at or about 20 wt% aliphatic polyurethane acrylate oligomer with an acrylate functionality of less than 3, the weight percents being based on the total weight of the UV-VIS curable primer compositions A and B, respectively.

[0221] 12. Any one preceding embodiment, wherein the UV-VIS curable primer compositions A and B have viscosities of from 10 to 40 Pas, more preferably 15 to 35 Pas, more particularly preferably 20 to 30 Pas, determined at 25°C and 500 S’1.

[0222] EXAMPLES

[0223] Production of a security feature of the invention

[0224] To prepare the security feature depicted in Fig. 3b, step (3) was performed using a wet offset process, such as the one depicted in Fig. 1b.

[0225] Referring to Fig. 1 b, 3a and 3b, primer compositions A (Ai , green) and B (A2, gold), as described herein, were applied to a first roller (1) being a fountain roller (i.e. a roller simultaneously fed with a fountain solution), with a separator (not shown in Fig. 3a) in the middle of the fountain roller, such that the first UV-VIS-curable primer composition A was on the right-hand end of the fountain roller and the second UV-VIS-curable primer composition B was on the left-hand side of the fountain roller, as shown by step 1 of Figure 3a. The primer compositions were transferred to multiple intermediate rollers (also called distributing rollers) (not shown in Fig. 1b). A second roller (2) being an axially reciprocating roller was applied to one of the distributing rollers to mix the primer compositions in an intermediate zone, resulting in a gradient from the first UV-VIS-curable primer composition A to the second UV-VIS-curable primer composition B, as represented by step 2 of Figure 3a. The gradient was transferred to a plate cylinder (3) bearing a rectangle indicium, the indicium was transferred to a blanket cylinder (6) and then to a transparent self-adhesive biaxially-oriented polypropylene film (4). The printed primer composition gradient was cured using a mercury UV-VIS-curing device (GEW E2C UV-curing system, total power 140 W / cm, one pass at a constant speed of 60 m / min corresponding to an exposure time of about 0.1 sec) to generate the primer gradient layer.

[0226] A cholesteric liquid crystal precursor composition was then printed overtop of the primer gradient layer by a flexographic method, in the form of a wave, as represented by step 3 of Figure 3a. The applied cholesteric liquid crystal precursor composition was then dried in a hot air oven at a temperature of 70°C for 15 seconds to evaporate the solvent and generate the cholesteric liquid crystal state. Finally, the still liquid cholesteric liquid crystal precursor composition layer was polymerized using the mercury UV-VIS-curing device described above with the same settings to generate a CLCP layer. The self- adhesive transparent film bearing the primer gradient layer and the CLCP layer was then applied to a black leneta card, to give a black background.

[0227] The resulting security feature is shown in Figure 3b, wherein Ai indicates a zone in which the face reflection color of the wave indicium is green, A2 indicates a zone in which the face reflection color of the wave indicium is gold, and An indicates an intermediate or gradient zone in which the face reflection color of the wave indicium varies in a continuous gradient from green to gold, going from right to left. The background is black.

[0228] Examples of primer compositions for use in the method of the invention

[0229] The following primer compositions exemplify those that can be used in the method of the invention. When in contact with a CLCP polymerized thereon, each of the cured primers induces a particular reflection wavelength in the CLCP layer. Different primer composition pairs may be chosen as the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B to achieve the desired effect in the final security feature. In general, the bigger the difference in reflection wavelength between two primers (AAr), the more striking the effect when used in the method of the invention.

[0230] Ingredients used in the Examples are listed in Table 1. Primer compositions

[0231] Primer compositions 1-21 were prepared using the ingredients listed in Tables 2 and 3, as follows: The ingredients were mixed and dispersed at room temperature using a high-speed mixer (DISPERMAT LC-2), for 20 minutes at 1 ,500 rpm. The viscosities of the primer compositions 20 and 21 were determined at 25°C using a Brookfield viscosimeter (model "RVDV-I Prime”), spindle 21 at 100 rpm for 20 and spindle 28 at 100 rpm for 21. The measured viscosities and the absence of fillers in primer compositions 20 and 21 make them particularly suited to printing with flexography or rotogravure processes.

[0232] The viscosities of primer compositions 1-19 were determined at 25°C and 500s-1using an Anton Paar MCR92 portable viscosimeter. The measured viscosity as well as the presence of fillers in these primer compositions makes them suitable for offset printing.

[0233] Table 2. Composition of primer compositions 1-19 (amounts are in wt%, based on the total weight of the primer composition), with viscosity and selective reflection data, when CLCP layer is applied overtop

[0234] 1F = functionality

[0235]

[0236] Cholesteric liquid crystal polymer (CLCP) precursor composition

[0237] The cholesteric liquid crystal precursor composition was prepared using the ingredients listed in Table 4, as follows: the solvent was poured in a 200 ml bottle, the nematic monomer and the chiral monomer were added and the bottle was kept in an ultrasonic bath for about 30 minutes at 40°C in order to dissolve the ingredients in the solvent. The mixture was then poured in a high-speed mixer (Dispermat LC-2), the photoinitiator was added and dispersed for 20 minutes at 2000 rpm. Finally, the surfactant was added and mixing was continued for a further 5 minutes at 1500 rpm.

[0238] The viscosity of the cholesteric liquid crystal precursor composition was measured at 25°C using a DIN 4” cup, the values being converted to mPas using a viscosity conversion table provided by Saint Clair Systems (Washington, USA). The measured viscosity indicates that the exemplified cholesteric liquid crystal precursor composition is suitable for printing with flexography or gravure processes.

[0239] Optical samples

[0240] Optical samples were made to evaluate the face reflection wavelength of a CLCP layer deposited overtop of the cured primer compositions using primer compositions 1-21 and the cholesteric liquid crystal precursor composition, as follows: a) The primer compositions 1-21 were independently applied vertically on black / white Leneta cards (Leneta Inc., Form N2C-2, 194 x 260mm) using a semi-automatic laboratory coater (K101 Control Coater, RK Print) equipped with a coating bar HC0 (nominal thickness 4pm) to form a rectangle of approx. 18 cm x 4 cm. The so-obtained primer composition layers were independently cured using a mercury UV-curing device (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 sec) to generate the cured primer layer.

[0241] The result was a series of cards with a cured primer compositions 1-21 applied thereto. b) The cholesteric liquid crystal precursor composition (Table 4) was then independently applied overtop of the primer layers obtained in step a) using the same semi-automatic coater equipped with a coating bar HC1 (theoretical thickness 6 pm), as a rectangle of approximately 18cm x 4cm centered on the black part of the Leneta card. The applied cholesteric liquid crystal precursor composition was then dried in a hot air oven at a temperature of 50°C for 30 seconds to evaporate the solvent and generate the cholesteric liquid crystal state. Finally, the still liquid cholesteric liquid crystal layer was polymerized using the mercury UV-curing device described at step a) with the same settings to generate a cholesteric liquid crystal polymer (CLCP) layer overtop of the primers 1-21 .

[0242] Optical properties of samples

[0243] The following optical properties were independently recorded for each of the cards: a) Maximum wavelength [nm] of selective reflection at face angle: a UV-Vis spectrum (360 - 700 nm) was recorded using a Datacolor 650 spectrophotometer (parameters: integration sphere, diffuse illumination (pulse xenon D65) and 10° viewing, analyzer SP2000 with dual 256 diode array for the wavelength range 360-700 nm, emission aperture 9 mm, detection aperture 5 mm) with a precision of ± 5 nm. The maximum wavelength of selective reflection (i.e. the wavelength at which the reflection reached its maximum value) was derived therefrom and is reported in Tables 2 and 3. b) Reflectance [%]: the amount of light reaching the detector at the maximum wavelength of selective reflection obtained under a) was compared to the amount of emitted light at the same wavelength, determined using a white reflecting calibration standard. Since the CLCP layer completely absorbs one of the two circularly polarized components, the maximal possible reflectance is 50%. Reflectance is an indication of the “brightness” of the obtained color shift, i.e. a high reflectance results in bright, saturated colors whereas a low reflectance results in a dull appearance. The reflectance values were measured with the same device and the same observation parameters as the maximum wavelength of selective reflection under item a) and reported in Table 5, below. c) Color shifting properties: the CLCP layers were independently assessed for their color shifting behavior by first holding them vertically in front of the observer’s eye and then slowly changing the observation angle from face angle (about 90°) to grazing angle (20-30°), noting down only the colors observed at both extremes. The results are reported in Table 5, below.

[0244] Results

[0245] The data in Tables 2 and 3 demonstrate that, for the CLCP system chosen, reflection wavelengths of 560-600 nm are obtainable, merely by changing the composition of the underlying primer layer. One can use, for example, any two of the primer compositions exemplified (having a difference of reflection wavelength of > 10 nm) to use in the method of the invention as the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B.

Claims

CLAIMS1. A method for producing a security feature on a substrate, wherein the security feature comprises a primer gradient layer, optionally in the form of one or more indicia, and a layer comprising a cholesteric liquid crystal polymer (CLCP), optionally in the form of one or more indicia, the method comprising the steps:(1 ) providing a first UV-VIS-curable primer composition A, which, when cured and in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of Ai;(2) providing a second UV-VIS-curable primer composition B, which, when cured and in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of A2, wherein AAr= A2 - A1 > 10 nm;(3) applying the first UV-VIS-curable primer composition A to the substrate in a first zone and the second UV-VIS-curable primer composition B in a second zone, wherein there is an intermediate zone between the first and second zones, wherein the first UV-VIS-curable primer composition A and the second UV- VIS-curable primer composition B are mixed in the intermediate zone, wherein in the intermediate zone, when proceeding from the first zone to the second zone, the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner, and the concentration of the second UV-VIS- curable primer composition B increases in a continuous manner;(4) curing the first and second UV-VIS-curable primer compositions using UV-VIS light, to produce the primer gradient layer;(5) applying at least partially to the primer gradient layer a cholesteric liquid crystal precursor composition comprising at least one nematic liquid crystal monomer, at least one chiral liquid crystal monomer, at least one UV-VIS-photoinitiator and at least one solvent, the nematic liquid crystal monomers and chiral liquid crystal monomers being capable of copolymerizing to form a cholesteric liquid crystal polymer (CLCP);(6) heating to remove the at least one solvent; and(7) polymerizing the cholesteric liquid crystal precursor composition using UV-VIS light to produce the layer comprising the cholesteric liquid crystal polymer; wherein the face reflection wavelength of the cholesteric liquid crystal polymer is A1 in the first zone and A2 in the second zone, and varies from A1 to A2 in a continuous manner in the intermediate zone.

2. The method of claim 1 , wherein the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B independently comprise (meth)acrylate monomers and oligomers.

3. The method of claim 1 or 2, wherein the primer gradient layer is in the form of one or more indicia.

4. The method of claim 1, 2 or 3, wherein the layer comprising the cholesteric liquid crystal polymeris in the form of one or more indicia.

5. The method according to any one of claims 1 to 4, wherein the application of the UV-VIS curable primer compositions in step (3) is carried out by a printing process.

6. The method according to any one of claims 1 to 5, wherein the application of the UV-VIS curable primer compositions in step (3) is carried out by a process comprising the following steps:(3i) applying the first UV-VIS-curable primer composition A at a first end of a first roller and applying the second UV-VIS-curable primer composition B at the second end of the first roller, optionally transferring the primer compositions from the first roller to one or more intermediate rollers;(3ii) applying a second roller to the first roller or to at least one of the optional intermediate rollers, to spread the primer compositions, wherein the second roller is capable of axial reciprocating motion to cause mixing of the first UV-VIS-curable primer composition A and the second UV-VIS-curable primer composition B in an intermediate zone, resulting in a concentration gradient, wherein the concentration of the first UV-VIS-curable primer composition A decreases in a continuous manner and the concentration of primer composition B increases in a continuous manner, proceeding axially from the first end of the first roller, or the one or more intermediate rollers, if used, to the second end of the first roller, or the one or more intermediate rollers, if used;(3iii) transferring the first and second primer compositions A and B in the form of the gradient to a plate cylinder, which optionally bears one or more indicia;(3iv) transferring the one or more indicia from the plate cylinder to the substrate, either directly, or indirectly using a blanket.

7. The method according to claim 5 or 6, wherein the printing process in step (3) is an offset printing process.

8. The method according to any one of claims 1 to 7, wherein the application of the cholesteric liquid crystal precursor composition in step (5) is a printing process preferably selected from the group consisting of flexography printing processes, gravure printing processes and screen-printing processes.

9. The method according to any one of claims 1 to 8, wherein the first UV-VIS-curable primer composition A comprises less than at or about 20 wt% of an aliphatic polyurethane with a functionality of less than 3, and the second UV-VIS-curable primer composition B comprises aliphatic polyurethane with a functionality of less than 3 at a concentration of greater than or equal to at or about 20 wt%, the weight percents being based on the total weight of the first and second primer compositions A and B, respectively.

10. The method of according to any one of claims 1 to 9, wherein the second UV-VIS-curable primer composition B comprises at least one aliphatic polyurethane acrylate oligomer with an acrylate functionality of less than 2.5.

11. The method according to any one of claims 1 to 10, wherein the second UV-VIS-curable primer composition B comprises at least one aliphatic polyurethane acrylate oligomer at a polyurethane concentration of at or about 20 wt% or greater, based on the total weight of the second UV-VIS-curable primer composition B.

12. A security feature obtained or obtainable by the method of any one of claims 1 to 11 .

13. A security feature comprising:(1 ) a substrate;(2) a primer gradient layer on the surface of the substrate, which may optionally be in the form of one or more indicia;(3) a layer comprising a cholesteric liquid crystal polymer, at least partially on the surface of the primer gradient layer, and which may optionally be in the form of one or more indicia; wherein the primer gradient layer comprises a first primer A, which, when in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal polymer of Ai , a second primer B, which, when in contact with the cholesteric liquid crystal polymer results in a face reflection wavelength of the cholesteric liquid crystal composition of A2, wherein AAr = A2 - A1 > 10 nm, and the primer gradient layer comprises the following zones: a first zone comprising 100% primer A, a second zone comprising 100% primer B, and an intermediate zone between the first and second zones, wherein in the intermediate zone, when proceeding from the first zone to the second zone, the concentration of primer A decreases in a continuous manner, and the concentration of primer B increases in a continuous manner, and the reflectance wavelength of the cholesteric liquid crystal composition is A1 in the first zone and A2 in the second zone, and varies from A1 to A2 in a continuous manner in the intermediate zone.

14. The security feature of claim 13, wherein the primer gradient layer is in the form of one or more indicia.

15. The security feature of claim 13 or 14, wherein the layer comprising the cholesteric liquid crystal polymer is in the form of one or more indicia.