UV-vis curable security INKS comprising tags and security features obtained thereof

Abstract

The present invention relates to the technical field of security features comprising taggants by means of Surface-Enhanced Raman Spectroscopy (SERS) and their detection. Furthermore, the present invention relates to the field of UV-Vis curable security inks comprising SERS tags for printing security features on substrates, in particular on security documents or articles, wherein said inks comprise one or more surface enhanced Raman spectroscopy (SERS) tags, one or more radiation curable compounds, and one or more photoinitiators and wherein said inks lack a vinyl ether containing compound.

Description

UV-VIS CURABLE SECURITY INKS COMPRISING TAGS AND SECURITY FEATURES OBTAINED THEREOF FIELD OF THE INVENTION

[0001] The present invention relates to the technical field of security features comprising taggants by means of Surface-Enhanced Raman Spectroscopy (SERS) and their detection. Furthermore, the present invention relates to the field of UV-Vis curable security inks comprising SERS tags for printing security features on substrates, in particular on security documents or articles. BACKGROUND OF THE INVENTION

[0002] With the constantly improving quality of color photocopies and printings and in an attempt to protect security articles and documents 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 features on or in these documents.

[0003] Security features, e.g. for security documents and articles, can be classified into “overt” and “covert” security features. Overt security features are 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, whereas covert security features typically require specialized equipment and knowledge for their detection.

[0004] Machine readable inks, such as for example magnetic inks, luminescent inks and infrared (IR) absorbing inks, have been widely used in the field of security documents, in particular for banknotes printing, to produce covert security features.

[0005] Machine readable inks comprising taggants of the SERS type or of SERRS type (referred therein as SERS tags and SERRS tags) have been developed for securing security articles and documents. Surface-enhanced Raman scattering is referred as SERS and surface-enhanced resonance Raman scattering is referred as SERRS. SERS and SERRS tags possess a unique characteristic surface enhancement feature, (i.e. respectively a surface-enhanced Raman scattering feature or a surface-enhanced resonance Raman scattering feature), that allows using a standard Raman spectrometer for its detection and authentication.

[0006] As well known by the person skilled in the art, SERS and SERRS tags comprise aggregates of nanoparticles presenting a plasmonic surface and Raman active reporter molecules adsorbed on the surface of the nanoparticles. Surface enhanced Raman scattering is a laser-based optical spectroscopy that, for molecules or other materials, generates a fingerprint-like vibrational spectrum with features that are much narrower than typical fluorescence. The nanoparticles presenting a plasmonic surface are responsible for the generation of the electric field required for the Raman amplification, while the Raman active reporter molecules provide the unique vibrational fingerprint of the SERS taggant.

[0007] SERS tags comprise a metal or other enhancing surface which electromagnetically couple to incident electromagnetic radiation and create a locally amplified electromagnetic field that leads to 102- to 109-fold or greater increases in the Raman scattering of a SERS active molecule situated on or nearthe enhancing surface. The output in a SERS experiment is the fingerprint-like Raman spectrum of the SERS active molecule.

[0008] SERS tags and other types of optical detection tags can be fabricated in various sizes, shapes and with some control over selected configuration elements.

[0009] Raman spectra are obtained by measuring the intensity distribution of Raman scattered photons, received from a sample including a substance of interest and illuminated by a light source, as a function of wavelength. Quantitative determination is based on the concentration of the substance of interest being proportional to the integrated intensity of its characteristic Raman bands.

[0010] As mentioned hereabove, machine readable inks comprising SERS taggants have been developed for securing security articles and documents. For example, EP 0806460 A1 discloses security inks, in particular an oxidative drying ink, containing a SERS-active metal aggregate containing a Raman active compound. WO 91 / 11492 A1 discloses security inks such as lithography, letterpress printing, intaglio printing and screen printing inks comprising a Raman active compound and WO 2010 / 135354 A1 also discloses inks such as lithography, letterpress printing, intaglio printing and screen printing inks.

[0011] During a conventional printing process of security documents, in particular banknotes, several inks are independently applied in sequences through a multi-step printing process. The fast drying properties of UV-Vis curable inks advantageously lead to the production of security feature not suffering from low surface curing properties, thus avoiding any delay of the subsequent printing steps.

[0012] However, the prior art fails to disclose formulation details and fails to disclose UV-Vis curable security inks.

[0013] Therefore, a need remains for UV-Vis curable security inks comprising SERS tags, wherein security features obtained thereof may be easily and unambiguously authenticated. SUMMARY OF THE INVENTION

[0014] Accordingly, it is an object of the present invention to overcome the deficiencies of the prior art. This is achieved by the provision of a UV-Vis radiation curable printing ink comprising: i) one or more surface enhanced Raman spectroscopy (SERS) tags in a total amount from about 0.01 wt.% to about 1 wt.%, preferably from about 0.02 wt.% to about 1 wt.%, preferably the one or more surface enhanced Raman spectroscopy (SERS) tags are nanoparticles and more preferably at least one of said one or more SERS tags comprises gold (Au) as SERS-enhancing material; ii) one or more radiation curable compounds in a total amount from about 50 wt.% to about 95 wt.%, preferably from about 60 wt.% to about 95 wt.%; and iii) one or more photoinitiators in a total amount from about 1 wt.% to about 20 wt.%, preferably from about 2 wt.% to about 15 wt.%, wherein said UV-Vis radiation curable printing ink lacks a vinyl ether containing compound, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

[0015] Also described herein are security features made from the UV-Vis radiation curable printing inks described herein and security articles comprising a substrate and a radiation cured coating obtained by UV-Vis radiation curing of the UV-Vis radiation curable printing ink described herein.

[0016] Also described herein are methods for producing the security articles described herein, wherein said methods comprising the steps of: a. printing, preferably by a printing process selected from the group consisting of screen printing, flexography printing or a contactless fluid microdispensing technology, the UV-Vis radiation curable printing ink recited in any one of claims 1 to 10, on the substrate, and b. UV-Vis radiation curing the UV-Vis radiation curable printing ink, preferably with one or more light sources selected from the group consisting of mercury lamps, UV-LED lamps and sequences thereof, so as to form one or more security features.

[0017] Also described herein are methods to authenticate the one or more security features described herein and the security articles described herein, said method comprising the steps of: a. providing the security article described herein and comprising the one or more security features described herein made of a radiation cured layer made of the UV-Vis radiation curable printing ink described herein; b. illuminating the one or more security features with visible and / or near IR light and measuring the SERS spectrum, and c. comparing the SERS spectrum obtained in step b with a pre-recorded reference Raman spectrum.

[0018] The UV-Vis curable security inks comprising SERS tags described herein allow the printing and preparation of security features for security articles that might be advantageously and unambiguously authenticated by means of Raman spectroscopy. Said unambiguous authentication relates to the absence of detection issues that may occur due to saturation phenomena of SERS signal of security features. Advantageously, the present invention allows the fast production of circulation resistant security features due to a reduced drying time and due to their good chemical and physical resistances. BRIEF DESCRIPTION OF DRAWINGS Figs 1 to 6 show Raman shifts of printed features consisting of cured layers independently made of UV- Vis radiation curable printing inks (E1-E21 and C1-C22). Fig.1 shows Raman shifts of a printed feature consisting of a cured layer made of a UV-Vis radiation curable inkjet printing ink (E1), said feature being applied either by an inkjet printing process with different ink coverages (25%, 50% and 75%) and by hand-coating (HC). Figs 2-1 to 2-6 and Fig. 6-1 show Raman shifts of printed features consisting of cured layers independently made of UV-Vis radiation curable inkjet printing inks (E1-E6 in Figs 2-1 to 2-6 and E20 in Fig.6-1). Figs 3-1 to 3-12 show Raman shifts of printed features consisting of cured layers independently made of comparative UV-Vis radiation curable inkjet printing inks (C1-C12). Figs 4-1 to 4-13 and Fig. 6-2 show Raman shifts of printed features consisting of cured layers independently made of UV-Vis radiation curable screen printing inks (E7-E19 in Figs 4-1 to 4-13 and E21 in Fig 6-2). Figs 5-1 to 5-10 show Raman shifts of printed features consisting of cured layers independently made of comparative UV-Vis radiation curable screen printing inks (C13-C22), wherein the Raman shiftsΔν̃are reported in wavenumbers in cm-1(Δν =̃ [(1 / ^0)- (1 / ^1)], with ^0 being the laser excitation wavelength and ^1 being the Raman spectrum wavelength). DETAILED DESCRIPTION Definitions

[0019] The following definitions are to be used to interpret the meaning of the terms discussed in the description and recited in the claims.

[0020] As used herein, the article "a / an” indicates one as well as more than one, and does not necessarily limit its referent noun to the singular.

[0021] As used herein, the term “at least one” is meant to define one or more than one, for example one or two or three.

[0022] 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”.

[0023] As used herein, the term “about” means that the amount or value in question may be the specific value designated or some other value in its neighborhood. Generally, the term “about” denoting a certain value is intended to denote a range within ± 5% of the value. As one example, the phrase “about 100” denotes a range of 100 ± 5, i.e. the range from 95 to 105. Preferably, the range denoted by the term “about” denotes a range within ± 3% of the value, more preferably ± 1 %. Generally, when the term “about” is used, it can be expected that similar results or effects according to the invention can be obtained within a range of ±5% of the indicated value.

[0024] The term “comprising” as used herein is intended to be non-exclusive and open-ended. Thus, for instance a solution 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 solution comprising A, B and optionally C” may also (essentially) consists of A and B, or (essentially) consists of A, B and C.

[0025] The term "security article" refers to an article which is usually protected against counterfeit or fraud by one or more security features.

[0026] The term “security feature” is used to denote an image, pattern or graphic element that can be used for authentication purposes.

[0027] 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.

[0028] The term “UV-Vis curable” and “UV-Vis curing” refers to radiation-curing by photo- polymerization, under the influence of an irradiation having wavelength components in the UV or in the UV and visible part of the electromagnetic spectrum (typically 100 nm to 800 nm, preferably between 150 and 600 nm and more preferably between 200 and 470 nm).

[0029] The present invention provides UV-Vis radiation curable printing inks, preferably selected from the group consisting of UV-Vis radiation curable screen printing inks, UV-Vis radiation curableflexography printing and UV-Vis radiation curable contactless fluid microdispensing inks, more preferably selected from the group consisting of UV-Vis radiation curable screen printing inks and UV- Vis radiation curable contactless fluid microdispensing inks, still more preferably selected from the group consisting of UV-Vis radiation curable screen printing inks and UV-Vis radiation curable inkjet printing inks. Upon application and curing of said -Vis radiation curable printing inks, one or more security features can be manufactured.

[0030] Typically, UV-Vis radiation curable printing inks suitable for screen printing processes have a viscosity in the range from about 500 mPa s to about 2500 mPa s, preferably in the range from about 600 mPa s to about 1500 mPa s at 25˚C (using for example a Brookfield machine “RVDV-I Prime”, spindle 27 at 100 rpm).

[0031] Screen printing (also referred in the art as silkscreen printing) is a printing technique that typically uses a screen made of woven mesh to support an ink-blocking stencil. The attached stencil forms open areas of mesh that transfer ink as a sharp-edged image onto a substrate. A squeegee is moved across the screen with ink-blocking stencil, forcing ink past the threads of the woven mesh in the open areas. A significant characteristic of screen printing is that a greater thickness of the ink can be applied to the substrate than with other printing techniques. Screen-printing is therefore also preferred when ink deposits with the thickness having a value between about 10 to 50 µm or greater are required which cannot (easily) be achieved with other printing techniques. Generally, a screen is made of a piece of porous, finely woven fabric called mesh stretched over a frame of e.g. aluminum or wood. Currently most meshes are made of man-made materials such as synthetic or steel threads. Preferred synthetic materials are nylon or polyester threads.

[0032] In addition to screens made on the basis of a woven mesh based on synthetic or metal threads, screens have been developed out of a solid metal sheet with a grid of holes. Such screens are prepared by a process comprising of electrolytically forming a metal screen by forming in a first electrolytic bath a screen skeleton upon a matrix provided with a separating agent, stripping the formed screen skeleton from the matrix and subjecting the screen skeleton to an electrolysis in a second electrolytic bath in order to deposit metal onto said skeleton.

[0033] There are three types of screen printing presses, namely flat-bed, cylinder and rotary screen printing presses. Flat-bed and cylinder screen printing presses are similar in that both use a flat screen and a three-step reciprocating process to perform the printing operation. The screen is first moved into position over the substrate, the squeegee is then pressed against the mesh and drawn over the image area, and then the screen is lifted away from the substrate to complete the process. With a flat-bed press the substrate to be printed is typically positioned on a horizontal print bed that is parallel to the screen. With a cylinder press the substrate is mounted on a cylinder. Flat-bed and cylinder screen printing processes are discontinuous processes, and consequently limited in speed which is generally at maximum 45 m / min in web or 3’000 sheets / hour in a sheet-fed process.

[0034] Conversely, rotary screen presses are designed for continuous, high speed printing. The screens used on rotary screen presses are for instance thin metal cylinders that are usually obtained using the electroforming method described hereabove or made of woven steel threads. The open-ended cylinders are capped at both ends and fitted into blocks at the side of the press. During printing, ink ispumped into one end of the cylinder so that a fresh supply is constantly maintained. The squeegee is fixed inside the rotating screen and squeegee pressure is maintained and adjusted to allow a good and constant print quality. The advantage of rotary screen presses is the speed which can easily reach 150 m / min in web or 10’000 sheets / hour in a sheet-fed process.

[0035] Screen printing is further described for example in The Printing Ink Manual, R.H. Leach and R.J. Pierce, Springer Edition, 5thEdition, pages 58-62, in Printing Technology, J. M. Adams and P.A. Dolin, Delmar Thomson Learning, 5thEdition, pages 293-328 and in Handbook of Print Media, H. Kipphan, Springer, pages 409-422 and pages 498-499.

[0036] Typically, UV-Vis radiation curable printing inks suitable for flexography printing processes have a viscosity in the range from 50 mPa s and about 2000 mPa s at 25°C, preferably in the range from about 600 mPa s to about 1500 mPa s at 25˚C (using for example a Brookfield machine “RVDV-I Prime”, spindle 27 at 100 rpm).

[0037] Flexography printing methods preferably use a unit with a chambered doctor blade, an anilox roller and plate cylinder. The anilox roller advantageously has small cells whose volume and / or density determines the ink or varnish application rate. The chambered doctor blade lies against the anilox roller, filling the cells and scraping off surplus ink or varnish at the same time. The anilox roller transfers the ink to the plate cylinder which finally transfers the ink to the substrate. Plate cylinders can be made from polymeric or elastomeric materials. Polymers are mainly used as photopolymer in plates and sometimes as a seamless coating on a sleeve. Photopolymer plates are made from light-sensitive polymers that are hardened by ultraviolet (UV) light. Photopolymer plates are cut to the required size and placed in an UV light exposure unit. One side of the plate is completely exposed to UV light to harden or cure the base of the plate. The plate is then turned over, a negative of the job is mounted over the uncured side and the plate is further exposed to UV light. This hardens the plate in the image areas. The plate is then processed to remove the unhardened photopolymer from the non-image areas, which lowers the plate surface in these non-image areas. After processing, the plate is dried and given a post-exposure dose of UV light to cure the whole plate. Preparation of plate cylinders for flexography is described in Printing Technology, J. M. Adams and P.A. Dolin, Delmar Thomson Learning, 5thEdition, pages 359-360.

[0038] Contactless fluid microdispensing processes includes processes preferably selected from the group consisting of spray coating, aerosol jet printing, electrohydrodynamic printing, slot die coating, Laser Induced Forward Transfer (LIFT) printing and inkjet printing, more preferably by an inkjet printing process.

[0039] Spray coating is a technique involving forcing the composition through a nozzle whereby a fine aerosol is formed. A carrier gas and electrostatic charging may be involved to aid in directing the aerosol at the surface that is to be printed. Spray printing allows to print spots and lines. Suitable compositions for spray printing typically have a viscosity between about 10 mPa.s and about 1 Pa.s (25°C, 1000 s-1). Resolution of spray coating printing lies in the millimeter range. Spray printing is described for example in F. C. Krebs, Solar Energy Materials & Solar Cells (2009), 93, page 407.

[0040] Aerosol jet printing (AJP) is an emerging contactless direct write approach aimed at the production of fine features on a wide range of substrates. AJP is compatible with a wide material range and freeform deposition, allows high resolution (in the order of about 10 micrometers) coupled with arelatively large stand-off distance (e.g. 1-5 mm), in addition to the independence of orientation. The technology involves aerosol generation using either ultrasonic or pneumatic atomizer to generate an aerosol from compositions typically having a viscosity between about 1 mPa.s and about 1 Pa.s (25°C, 1000 s-1). Aerosol jet printing is described for example in N. J. Wilkinson et al., The International Journal of Advanced Manufacturing Technology (2019) 105:4599–4619.

[0041] Electrohydrodynamic inkjet printing is a high resolution inkjet printing technology. Electrohydrodynamic inkjet printing technology makes use of externally applied electric fields to manipulate droplets sizes, ejection frequencies and placement on the substrate to get higher resolution than convention inkjet printing, while keeping a high production speed. The resolution of electrohydrodynamic inkjet printing is about two orders of magnitude higher than conventional inkjet printing technology; thus, it can be used for the orienting of nano- and micro-scale patterns. Electrohydrodynamic inkjet printing may be used both in DOD or in continuous mode. Compositions for electrohydrodynamic inkjet printing typically have a viscosity between about 1 mPa s and about 1000 mPa s (25°C, 1000 s-1). Electrohydrodynamic inkjet printing technology is described for example P.V. Raje and N.C. Murmu, International Journal of Emerging Technology and Advanced Engineering, (2014), 4(5), pages 174-183.

[0042] Slot die-coating is a 1-dimensional coating technique. Slot-die coating allows for the coating of stripes of material which is well suited for making a multilayer coating with stripes of different materials layered on top of each other. The alignment of the pattern is produced by the coating head being translated along the direction perpendicular to the direction of the web movement. A slot die-coating head comprises a mask that defines the slots of the coating head through which the slot-die coating ink is dispersed. An example of a slot-die coating head is illustrated in F. C. Krebs, Solar Energy Materials & Solar Cells (2009), 93, page 405-406. Suitable compositions for slot die-coating typically have a viscosity between about 1 mPa s and about 20 mPa s (25°C, 1000 s-1).

[0043] Laser Induced Forward Transfer (LIFT) printing is a direct-writing technique based in the action of a laser to print a small fraction of material from a thin donor layer onto a receiving substrate. Solid donor films have been used since its origins, but the same principle of operation works for ink liquid films, too. LIFT is a nozzle-free printing technology that can be used for two- and three-dimensional printing and which has almost no restrictions in the particle size and the viscosity of the ink to be printed. In LIFT, a laser pulse creates an impulse inside a thin film of material that results in the formation of a liquid jet. Compositions for LIFT printing typically have a viscosity between about 1 mPa s and about 100 Pa s (25°C, 1000 s-1). Examples of LIFT applications have been described for example by J. Marcos Fernandez-Pradas and Perre Serra, Crystals (2020) 10(8), page 651, and by M Jalaal et al., J. Fluid Mech. (2019), 880, pages 497-513.

[0044] According to one embodiment, the UV-Vis radiation curable printing inks described herein is printed by an inkjet printing process, preferably a continuous inkjet (CI) printing process or a drop-on- demand (DOD) inkjet printing process, more preferably a drop-on-demand (DOD) inkjet printing process. Drop-on-demand (DOD) printing is a non-contact printing process, wherein the droplets are only produced when required for printing, and generally by an ejection mechanism rather than by destabilizing a jet. Depending on the mechanism used in the printhead to produce droplets, the DODprinting is divided in piezo impulse, thermal jet, valve jet (viscosity between about 1 mPa.s and about 1 Pa.s (25°C, 1000 s-1)) and electrostatic process.

[0045] The light source required to cure the UV-Vis radiation curable printing inks described herein are selected from the group consisting of mercury lamps (preferably medium-pressure mercury lamps), UV- LED lamps and sequences thereof. Typical sequences include the use of one or more UV-LED lamps in a first step to partially cure the UV-Vis radiation composition and one or more medium-pressure mercury lamps in a second step. Mercury lamps advantageously emit on a wide range of wavelengths in the UV-A, UV-B and UV-C range.

[0046] The UV-Vis radiation curable printing ink described herein lacks a vinyl ether containing compound. By “lacking” it is meant that the UV-Vis radiation curable printing ink described herein comprises 0 wt.-% of a vinyl ether containing compound, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

[0047] The UV-Vis radiation curable printing inks described herein comprise the one or more surface enhanced Raman spectroscopy (SERS) tags in a total amount from about 0.01 wt.% to about 1 wt.%, preferably from about 0.02 wt.% to about 1 wt.%, more preferably from about 0.04 wt.% to about 0.6 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

[0048] According to one embodiment, the one or more surface enhanced Raman spectroscopy (SERS) tags are incorporated in the UV-Vis radiation curable printing inks described herein in the form of a dispersion, including for example a dispersion comprising an alkyd-based resin, wherein said dispersion comprise from about 10 wt.% to about 30 wt-%, for example 20 wt.% of said surface enhanced Raman spectroscopy (SERS) tags.

[0049] SERS tags are aggregates of nanoparticles presenting a plasmonic surface and having Raman active reporter molecules adsorbed on their surface. The SERS tags presenting a plasmonic surface are responsible for the generation of the electric field required for the Raman signal or Raman scattering amplification, while the Raman active reporter molecule provides the unique vibrational fingerprint of the SERS tag. Typically, the aggregates present an external coating layer which a) isolates the SERS tag from the external medium thereby, preventing the Raman active reporter molecules from leaching out from the SERS tag and protecting the SERS tag from contaminations of the external medium that may give rise to vibrational noise, b) increases the stability of the SERS tag, and c) provides a convenient surface for further chemical functionalization. To date, polymers and silica have been employed as external coating layers. External coating layers include silica and polymers, such as poly(ethylene imine) (PEI), poly(styrene-alt-maleic acid) sodium salt (PSMA), poly(diallyldimethylammonium chloride) (PDADMAC).

[0050] Preferred Raman active reporter molecules include fully conjugated molecules comprising an aryl group substituted by one or more substituents selected from NR1R2, –SH, —≡, —≡N and —N═, preferably from –NR1R2and –SH, and / or an N-containing heteroaryl group and / or a S-containing heteroaryl group, wherein the residues R1and R2are independently of each other selected from –H and alkyl, preferably from –H and C1-C4-alkyl. As known by the person skilled in the art of organic chemistry, a fully conjugated molecule is a molecule having a conjugated electrons system extending over theentire molecule. A conjugated electrons system is a system of connected p orbitals with delocalized electrons.

[0051] As well known by the person skilled in the art “an aryl group” is a group derived from a monocyclic or polycyclic aromatic hydrocarbon compound by removal of one hydrogen atom from a ring carbon atom. Examples of aryl groups include without limitation phenyl, naphthyl, anthracenyl, phenanthryl and pyrenyl.

[0052] An N-containing heteroaromatic compound is an aromatic compound containing at least one nitrogen heteroatom as part of the cyclic conjugated π system. As part of the cyclic conjugated π system, the N-containing heteroaromatic compound may further contain one or more oxygen atoms. Examples of N-containing heteroaryl groups include without limitation imidazolyl, pyrazolyl, triazolyl, tetrazolyl, benzoimidazolyl, indazolyl, benzotriazolyl, pyridinyl, pyrimidinyl, pyridazinyl, triazinyl, quinolinyl, isoquinolinyl, diazanaphthyl, quinazolinyl, cinnolinyl, phthalazinyl, quinoxalinyl, purinyl, aza-phenanthryl, diaza-phenanthryl, aza-anthracenyl, diaza-anthracenyl, aza-pyrenyl, diazapyrenyl, oxazolyl, isoxazolyl, oxadiazolyl, benzoxazolyl, benzisoxazolyl and benzoxadiazolyl.

[0053] A S-containing heteroaromatic compound is an aromatic compound containing a sulfur heteroatom as part of the cyclic conjugated π system. As part of the cyclic conjugated π system, the S- containing heteroaromatic compound may further contain one or more nitrogen atoms. Examples of S- containing heteroaryl groups include without limitation thiophenyl, thiazolyl, isothiazolyl, thiadiazolyl, benzothiophenyl, benzothiazolyl, benzoisothiazolyl, benzothiadiazolyl, imidazothiazolyl and imidazothiadiazolyl.

[0054] Preferred Raman active reporter molecules include, but are not restricted to: - a fully conjugated compound consisting of an aryl group substituted by one or more substituents selected from —NR1R2, —SH, —≡, —≡N and —N═, preferably from —NR1R2and —SH, which is connected directly or via a linker —L1— to an aryl group substituted by one or more substituents selected from the list comprising an amino group (—NH2), an N-alkyl amino group, an N,N-dialkyl-amino group, a thiol group, an ethynyl group, a cyano group and an isocyanide group, a N-containing heteroaryl group, or a S-containing heteroaryl group, wherein the substituents R1and R2have the meanings defined herein the group Y is selected from O, S, NH; the linker —L1— is selected from —CR8═CR9—, —N=N—, —≡—, —CR10═CR11—o-C6H4—, —CR10═CR11—m-C6H4—, —CR10═CR11—p-C6H4—,e su s uens – are seece rom y rogen, a y, a oxy, a y o, ormy, cyano, nitro, halide, hydroxycarbonyl, and alkoxycarbonyl; - a fully conjugated compound consisting of an N-containing heteroaryl group, which is connected directly or via a linker —L1— to an N-containing heteroaryl group, or a S-containing heteroaryl group, wherein the linker —L1— is selected from —CR8═CR9—, —N=N—, —≡—, —CR10═CR11—o-C6H4—, —CR10═CR11—m-C6H4—, —CR10═CR11—p-C6H4—,e su s uens – are seece rom y rogen, a y, a oxy, a y o, ormy, cyano, nitro, halide, hydroxycarbonyl and alkoxycarbonyl; - a fully conjugated compound consisting of a S-containing heteroaryl group, which is connected directly or via a linker —L1— to an S-containing heteroaryl group, whereinthe linker —L1— is selected from —CR8═CR9—, —N=N—, —≡—, —CR10═CR11—o-C6H4—, —CR10═CR11—m-C6H4—, —CR10═CR11—p-C6H4—,and the substituents R8– R15are selected from hydrogen, alkyl, alkoxy, alkylthio, formyl, cyano, nitro, halide, hydroxycarbonyl and alkoxycarbonyl; and - a fully conjugated compound consisting of an aryl group substituted by one or more, preferably at least two, substituents selected from —NR1R2, —SH, —≡, —≡N and —N═, preferably from —NR1R2and — SH, an N-containing heteroaryl group optionally substituted by one or more substituents selected from –NR3R4, –SH, —≡, —≡N and —N═, or a S-containing heteroaryl group optionally substituted by one or more substituents selected from –NR5R6, –SH, —≡, —≡N and —N═, connected directly to a hydrogen atom, wherein the substituents R1and R2have the meanings defined herein and the substituents R3– R6are independently of each other selected from –H and alkyl, preferably from –H and C1-C4-alkyl.

[0055] The aryl group substituted by one or more substituents selected from —NR1R2, —SH, —≡, — ≡N and —N═, preferably from —NR1R2and —SH, may contain one or more further substituents preferably selected from: hydroxy, alkyl, alkoxy, alkylthio, formyl, nitro, halide, hydroxycarbonyl, alkoxycarbonyl and O-containing heteroaryl group, and more preferably selected from: alkyl, alkoxy, alkylthio, halides and O-containing heteroaryl group.

[0056] The N-containing heteroaryl group and the S-containing heteroaryl group may contain one or more further substituents preferably selected from: amino, N-alkyl amino, N,N-dialkyl-amino, thiol, hydroxy, alkyl, alkoxy, alkylthio, formyl, cyano, isocyanide, ethynyl, nitro, halide, hydroxycarbonyl, alkoxycarbonyl and O-containing heteroaryl group, preferably from alkyl, alkoxy, alkylthio, halides and O-containing heteroaryl group.

[0057] Examples of O-containing heteroaryl groups include, but are not restricted to furanyl, benzofuranyl, isobenzofuranyl, oxazolyl, isoxazolyl, benzoxazolyl and oxadiazolyl.

[0058] A preferred Raman active reporter compound is a compound of general formula (I), whereinA1, B1and C1are independently of each other selected from N, CR16and CR17, with the proviso that only one of A1, B1and C1is N; A2, B2and C2are independently of each other selected from N, CR18and CR19, with the proviso that only one of A2, B2and C2is N;E1, D1, E2, D2, R16, R17, R18and R19are independently of each other selected from: hydrogen, amino, N-alkyl amino, N,N-dialkyl-amino, thiol, hydroxy, alkyl, alkoxy, alkylthio, formyl, cyano, isocyanide, alkynyl, nitro, halide, hydroxycarbonyl, alkoxycarbonyl and O-containing heteroaryl group, preferably from hydrogen, alkyl, alkoxy, alkylthio, halides and O-containing heteroaryl group; and X is a single bond or a linker —L2— selected from —CR8═CR9—, —N=N—, —≡—, — CR10═CR11—o-C6H4—, —CR10═CR11—m-C6H4—, —CR10═CR11—p-C6H4—, —CR10═CR11—o-C6H4—and– hydroxycarbonyl, and alkoxycarbonyl.

[0059] Preferably, the residues A1and A2are N in the general formula (I). More preferably, the residues A1and A2are N and the substituents E1, D1, E2, D2, R16, R17, R18and R19are hydrogen in general formula (I).

[0060] Raman active reporter molecules include without limitation: 2-mercaptopyridine; benzenethiol; mercaptobenzoic acid; 4-nitrobenzenethiol; 3,4-dicholorobenzenethiol; 3-fluorothiophenol; 4- fluorothiophenol; 3-5-bis(trifluoromethyl)benzenethiol; 4-mercaptophenol; biphenyl-4-thiol, 7-mercapto- 4-methylcoumarin, 1-(4-hydroxyphenyl)-1H-tetrazole-5-thiol, 2-fluorothiophenol, 2-naphthalenethiol, 4- (((3-mercapto-5-(2-methoxyphenyl)-4H-1,2,4-triazol-4-yl)imino)methyl)phenol, (2-trifluoromethyl) benzenethiol, 4-aminothiophenol, 1-naphthalenethiol, 1,1',4,1"-terphenyl-4-thiol, biphenyl-4,4'-dithiol, thiosalicylic acid, 4-(((3-mercapto-5-(2-pyridinyl)-4H-1,2,4-triazol-4-yl)imino)methyl)-1,2-benzenediol, 4- (((3-mercapto-5-(2-pyridinyl)-4H-1,2,4-triazol-4-yl)imino)methyl)benzoic, 2,3,4,6- tetrafluorobenzenethiol, (5-(4-methoxyphenyl)-1,3,4-oxidazole-2-thiol), (E)-1,2-di(pyridin-4-yl)ethene, 5- (pyridin-4-yl)-1,3,4-oxadiazole-2-thiol, and 1,4-bis((E)-2-(pyridin-4-yl)vinyl)benzene.

[0061] Typically, SERS tags are nanoparticles. Within the meaning of the present invention, the term “nanoparticle” is defined as a single particle having a size corresponding to the maximum physical dimension (e.g.: length, diameter, etc.) in the range from 20 ± 5 nm to 160 ± 5 nm, preferably from 40 ± 5 nm to 140 ± 5 nm. The SERS tags used in the present invention has a plasmonic surface i.e. the nanoparticle has an outer surface capable of enhancing the Raman scattering of a Raman active molecule. The outer surface of the nanoparticle is made of any known SERS-enhancing material. Preferably, the SERS-enhancing material is selected from: gold (Au), silver (Ag), copper (Cu), aluminum (Al), palladium (Pd), platinum (Pt) or a mixture or alloy thereof, and more preferably is gold (Au). The SERS tags used in the present invention may be solid or hollow, and preferably solid. A solid nanoparticle may be made of a single material i.e. the SERS-enhancing material of the outer surface of the nanoparticle, or of more materials i.e. the material(s) of the core of the nanoparticle may be different from the SERS-enhancing material of the outer surface of the nanoparticle. A hollow nanoparticle is a nanoparticle whose core is a void space. The nanoparticle may have any shape capable of being produced. Preferably, at least one of the one or more SERS tags is a solid Au nanoparticle, wherein said nanoparticle preferably has a shape selected from the group consisting of a sphere, spheroid, rod, disk, prism and cube, more preferably selected from a sphere and a spheroid, and even more preferably a spheroid shape.

[0062] The UV-Vis radiation curable printing ink described herein may be a cationically curable printing ink (i.e. comprises cationically curable compounds), a radically curable ink (i.e. comprises radically curable compounds), or a hybrid curable inks (i.e. comprises cationically curable compounds andradically curable compounds). Cationically UV-Vis radiation curable printing inks are cured by cationic mechanisms consisting of the activation by UV-Vis light of one or more cationic photoinitiators, which liberate cationic species, such as acids, which in turn initiate the polymerization of the cationically curable monomers so as to form a cured binder, exhibit increased adhesion and mechanical resistance when compared to free-radically UV-Vis radiation curable coatings. Radically UV-Vis radiation curable printing inks are cured by free radical mechanisms consisting of the activation of one or more free radical photoinitiators able to liberate free radicals upon the action of radiation, in particular of UV-Vis light, which in turn initiate the polymerization of the radically curable monomers and / or oligomers so as to form a cured layer. Hybrid UV-Vis radiation curable printing inks comprise cationically curable compounds and radically curable compounds, cationic photoinitiators and free radical photoinitiators.

[0063] The UV-Vis radiation curable printing ink described herein comprises the one or more radiation curable compounds in a total amount from about 50 wt.% to about 95 wt.%, preferably from about 60 wt.% to about 95 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink. The radiation curable compounds may be cationically curable compounds and radically curable compounds.

[0064] Cationically curable compounds are preferably selected from the group consisting of propenyl ethers, cyclic ethers (such as epoxides, oxetanes, glycidyl ethers and tetrahydrofuranes), lactones, cyclic thioethers, propenyl thioethers, silanes, and mixtures thereof; more preferably selected from the group consisting of propenyl ethers, cyclic ethers (such as epoxides, oxetanes and tetrahydrofuranes), lactones, silanes, and mixtures thereof; and still more preferably cyclic ethers such as epoxides, oxetanes and mixtures thereof.

[0065] According to one embodiment, the cationically curable compounds are selected from the group consisting of epoxides, oxetanes and mixtures thereof, preferably cycloaliphatic epoxides, oxetanes and mixtures thereof.

[0066] According to one embodiment, the UV-Vis radiation curable printing ink described herein comprises at least one cycloaliphatic epoxide, wherein said cycloaliphatic epoxide may be difunctional or polyfunctional. The UV-Vis radiation curable printing ink described herein comprising the at least one cycloaliphatic epoxide described herein may further comprise one or more cationically curable epoxysiloxane compounds such as those described herein.

[0067] According to one embodiment, the UV-Vis radiation curable printing ink described herein comprises at least one of the cycloaliphatic epoxide described herein and at least one oxetane described herein. The UV-Vis radiation curable printing ink described herein comprising the at least one cycloaliphatic epoxide described herein and the at least one oxetane described herein may further comprise one or more cationically curable epoxysiloxane compounds such as those described herein.

[0068] As well known by the person skilled in the art, a cycloaliphatic epoxide is a cationically curable monomer containing at least a substituted or unsubstituted epoxycyclohexyl residue:

[0069] Preferably, the cycloaliphatic epoxide described herein comprises at least one cyclohexane ring, and at least two epoxide groups. Preferred cycloaliphatic epoxides comprise more than one (i.e. at least two) cyclohexane groups and preferably have the structural formula (II): wherein –X–or more atoms. The cycloaliphatic epoxide of general formula (II) is optionally substituted by one or more linear or branched alkyl radicals containing from one to ten carbon atoms (such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl, n-propyl, and i-propyl).

[0070] According to one embodiment, –X– is a divalent hydrocarbon group which may be a straight- or branched-chain alkylene group comprising from one to eighteen carbon atoms, wherein examples of said straight- or branched-chain alkylene group include without limitation methylene group, methylmethylene group, dimethylmethylene group, ethylene group, propylene group, and trimethylene group.

[0071] According to one embodiment, –X– is a divalent alicyclic hydrocarbon group or cycloalkydene group such as 1,2-cyclopentylene group, 1,3-cyclopentylene group, cyclopentylidene group, 1,2- cyclohexylene group, 1,3-cyclohexylene group, 1,4-cyclohexylene group, and cyclohexylidene group.

[0072] According to one embodiment, –X– is a divalent group comprising one or more oxygen- containing linkage groups, wherein said oxygen-containing linkage groups are selected from the group consisting of –C(═O)–, –OC(═O)O–, –C(═O)O–, and –O–. Preferably, the cycloaliphatic epoxide is a cycloaliphatic epoxide of general formula (II), wherein –X– is a divalent group comprising one or more oxygen-containing linkage groups, wherein said oxygen-containing linkage groups are selected from the group consisting of –C(═O)–, –OC(═O)O–, –C(═O)O–, and –O–, and more preferably a cycloaliphatic epoxide of general formula (II-a), (II-b), or (II-c), as defined below:(II-a) wherein X1 can be the same, or different in each occurrence and is a linear or branched alkyl radical containingfrom one to ten carbon atoms (such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl, n-propyl, and i-propyl); X2 can be the same, or different in each occurrence and is a linear or branched alkyl radical containing from one to ten carbon atoms (such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl, n-propyl, and i-propyl); and l1 and l2 are independently of each other integers comprised between 0 and 9, preferably comprised between 0 and 3, and more preferably 0;(II-b) wherein X1 can be the same, or different in each occurrence and is a linear or branched alkyl radical containing from one to ten carbon atoms (such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl, n-propyl, and i-propyl); X2 can be the same, or different in each occurrence and is a linear or branched alkyl radical containing from one to ten carbon atoms (such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl, n-propyl, and i-propyl); and l1 and l2 are independently of each other integers comprised between 0 and 9, preferably comprised between 0 and 3, and more preferably 0; –X3– is a single bond or a linear or branched divalent hydrocarbon group containing from one to ten carbon atoms, and preferably containing from three to eight carbon atoms, such as alkylene groups including trimethylene, tetramethylene, hexamethylene, and 2-ethylhexylene, and cycloalkylene groups such as 1,2-cyclohexylene group, 1,3-cyclohexylene group, and 1,4-cyclohexylene group, and cyclohexylidene group;(II-c) wherein X1can be the same, or different in each occurrence and is a linear or branched alkyl radical containing from one to three carbon atoms, such as methyl, ethyl, n-propyl, and i-propyl; X2 can be the same, or different in each occurrence and is a linear or branched alkyl radical containing from one to three carbon atoms, such as methyl, ethyl, n-propyl, and i-propyl; and l1 and l2 are independently of each other integers comprised between 0 and 9, preferably comprised between 0 and 3, and more preferably 0.

[0073] Preferred cycloaliphatic epoxides of general formula (II-a) include, but are not limited to: 3,4- epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-6-methyl-cyclohexylmethyl-3,4- epoxy-6-methylcyclohexanecarboxylate, 3,4-epoxy-2-methyl-cyclohexylmethyl-3,4-epoxy-2-methyl- cyclohexanecarboxylate, and 3,4-epoxy-4-methyl-cyclohexylmethyl-3,4-epoxy-4- methylcyclohexanecarboxylate.

[0074] Preferred cycloaliphatic epoxides of general formula (II-b) include, but are not limited to: bis(3,4- epoxycyclohexylmethyl)adipate, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, bis(3,4- epoxycyclohexylmethyl)oxalate, bis(3,4-epoxycyclohexylmethyl)pimelate, and bis(3,4- epoxycyclohexylmethyl)sebacate.

[0075] A preferred cycloaliphatic epoxide of general formula (II-c) is 2-(3,4-epoxycyclohexyl-5,5-spiro- 3,4-epoxy)cyclohexane-meta-dioxane.

[0076] Further cycloaliphatic epoxides include a cycloaliphatic epoxide of general formula (III-a) and a cycloaliphatic epoxide of general formula (III-b), which are optionally substituted by one or more linear or branched alkyl groups containing from one to ten carbon atoms (such as methyl, ethyl, n-propyl, i- propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl, n-propyl, and i-propyl)

[0077] The cycloaliphatic epoxides described herein may be hydroxy modified or (meth)acrylate modified.

[0078] According to one embodiment, the UV-Vis radiation curable printing inks described herein comprise the at least one cycloaliphatic epoxide described herein and further comprise at least one linear epoxide. The use of linear epoxides other than the cycloaliphatic epoxides in the inks described herein aids in accelerating curing and reducing tackiness, as well as in reducing the viscosity of the ink, while strongly co-polymerizing. Preferred examples linear epoxides include, but are not limited to, cyclohexane dimethanol diglycidylether, poly(ethyleneglycol) diglycidyl ether, poly(propyleneglycol) diglycidyl ether, butanediol diglycidyl ether, hexanediol diglycidyl ether, bisphenol-A diglycidyl ether, neopentylglycol diglycidylether, trimethylolpropane triglycidyl ether, glycerol triglycidyl ether, pentaerythritol tetraglycidyl ether, butyl glycidyl ether, p-tert-butyl phenyl glycidyl ether, hexadecyl glycidyl ether, 2-ethyl-hexyl glycidyl ether, octyl glycidyl ether, decyl glycidyl ether, dodecyl glycidyl ether, tetradecyl glycidyl ether, C12 / C14-alkyl glycidyl ether, C13 / C15-alkyl glycidyl ether and mixtures thereof. Suitable linear epoxide are commercially sold by EMS Griltech under the trademark Grilonit®including for example RV 1802,RV 1806, RV 1907.41, RV 1812, V 51-31 and V51-63, or by Huntman under the trademark Araldite®DY including for example DY-C, DY-D, DY-E, DY-G, DY-F, DY-H, DY-K, DY-P, DY-31, DY-3601.

[0079] Oxetane compounds are known in the art to accelerate curing and reduce tackiness, thus limiting the risk of blocking and set-off when the printed sheets are put in stacks just after printing and curing. They also help reducing the viscosity of the ink while strongly co-polymerizing. Preferred examples of oxetanes include trimethylene oxide, 3,3-dimethyloxetane, trimethylolpropane oxetane, 3- ethyl-3-hydroxymethyl oxetane, 3-ethyl-3-[(2-ethylhexyloxy) methyl]oxetane, 3,3-dicyclomethyl oxetane, 3-ethyl-3-phenoxymethyl oxetane, bis ([1-ethyl(3-oxetanyl)]methyl) ether, 1,4-bis [3-ethyl-3-oxetanyl methoxy)methyl]benzene, 3,3-dimethyl-2(p-methoxy-phenyl)-oxetane, 3-ethyl-[(tri-ethoxysilyl propoxy)methyl]oxetane, 4,4-bis(3-ethyl-3-oxetanyl)methoxymethyl]biphenyl and 3,3-dimethyl-2(p- methoxy-phenyl) oxetane. The one or more oxetanes described herein may be hydroxy modified or (meth)acrylate modified. When present, the one or more oxetanes described herein are preferably present in a total amount from about 0.1 wt.% to about 25 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

[0080] As described therein for UV-Vis radiation curable printing inks comprising the at least one cycloaliphatic epoxide described herein or for inks comprising both the at least one cycloaliphatic epoxide described herein and the at least one oxetane described herein, said inks may further comprise one or more cationically curable epoxysiloxane compounds. Preferred examples of epoxysiloxane compounds are 3-glycidyloxypropyltrimethoxysilane (Dynasylan®GLYMO) and 3- glycidyloxypropyltriethoxysilane (Dynasylan®GLYEO).

[0081] Cationic photoinitiators (also referred in the art as photo-acid generators) are preferably onium salts. The onium salts described herein are preferably selected from the group consisting of azonium salts, oxonium salts, iodonium salts, sulfonium salts and mixtures thereof, more preferably selected from the group consisting of oxonium salts, iodonium salts, sulfonium salts and mixtures thereof, and still more preferably selected from the group consisting of iodonium salts, sulfonium salts and mixtures thereof.

[0082] The one or more iodonium salts described herein have a cationic moiety and an anionic moiety, wherein the anionic moiety is preferably BF4−, B(C6F5)4−, PF6−, (PF6-m(CnF2n-1)m)−(where m is an integer from 1 to 5, and n is an integer from 1 to 4), AsF6−, SbF6−or CF3SO3−perfluoroalkyl sulfonate or pentafluorohydroxyantimonate, more preferably SbF6−, PF6−or B(C6F5)4−and wherein the cationic moiety is preferably an aromatic iodonium ion, more preferably a iodonium ion comprising two aryl groups, wherein the two aryl groups may be independently substituted by one or more alkyls groups (such as for example methyl, ethyl, isobutyl, tertbutyl, etc.) one or more alkoxy groups, one or more nitro groups, one or more halogen containing groups, one or more hydroxy groups or a combination thereof. Particularly suitable examples of iodonium salts for the present invention are commercially available under the name WPI-113, WPI-116 and WPI-124 from FUJIFILM Wako Chemicals.

[0083] The one or more sulfonium salts described herein have a cationic moiety and an anionic moiety, wherein the anionic moiety is preferably, BF4−, B(C6F5)4−, PF6−, (PF6-m(CnF2n-1)m)−(where m is an integer from 1 to 5, and n is an integer from 1 to 4), AsF6−, SbF6−, CF3SO3−, perfluoroalkyl sulfonate or pentafluorohydroxyantimonate, more preferably SbF6−or PF6−and wherein the cationic moiety is preferably an aromatic sulfonium ion, more preferably a sulfonium ion comprising two or more aryl groups, wherein the two or more aryl groups may be independently substituted by one or more alkyls groups (such as for example methyl, ethyl, isobutyl, tertbutyl, etc.) one or more alkoxy groups, one or more aryloxyl groups, one or more halogen containing groups, one or more hydroxy groups or a combination thereof. Particularly suitable examples of sulfonium salts for the present invention are commercially available under the name SpeedCure 992 and SpeedCure 976 from Lambson.

[0084] Radically curable compounds are cured by free radical mechanisms consisting of the activation by energy of one or more photoinitiators which liberate free radicals which in turn initiate the polymerization so as to form a binder. Preferably, the radically curable compounds are selected from the group consisting of (meth)acrylates, preferably selected from the group consisting of epoxy (meth)acrylates, (meth)acrylated oils, polyester and polyether (meth)acrylates, aliphatic or aromatic urethane (meth)acrylates, silicone (meth)acrylates, acrylic (meth)acrylates and mixtures thereof.

[0085] Suitable examples of (meth)acrylates include tri(meth)acrylates, tetra(meth)acrylates and mixtures thereof.

[0086] In addition to the radically curable compounds being tri(meth)acrylates, tetra(meth)acrylates and mixtures thereof, the UV-Vis radiation curable printing ink described herein may further comprises one or more radically curable diluents preferably selected from the group consisting of mono(meth)acrylates, di(meth)acrylates and mixtures thereof.

[0087] Suitable examples of mono(meth)acrylates include without limitation alkyl (meth)acrylates, cycloalkyl (meth)acrylates, benzyl (meth)acrylates, phenyl (meth)acrylates (including phenoxyalkyl(meth)acrylates such as phenoxyethyl acrylate), cyclic trimethylolpropane formal acrylate, tetrahydrofurfuryl acrylate, aliphatic urethane (meth)acrylates and alkoxylated (in particular ethoxylated or propoxylated) compounds thereof.

[0088] Suitable examples di(meth)acrylates ethylene glycol diacrylate; ethylene glycol dimethacrylate; 1,4-butanediol diacrylate; 1,4-butanediol dimethacrylate; 1,3-butanediol diacrylate; 1,3-butanediol dimethacrylate; 2-methyl-1,3-propanediol diacrylate; 3-methyl-1,5-pentanediol diacrylate); 2-butyl-2- ethyl-1,3-propanediol diacrylate; 1,6-hexanediol diacrylate; 1,6-hexanediol dimethacrylate; neopentyl glycol diacrylate; neopentyl glycol dimethacrylate; 1,9-nonanediol diacrylate; 1,9-nonanediol dimethacrylate; 1,10-decaanediol diacrylate; 1,10-decaanediol dimethacrylate; alkoxylated (in particular ethoxylated and propoxylated) 1,6-hexanediol diacrylates; propoxylated neopentyl glycol diacrylate; ethoxylated 2-methyl-1,3-propanediol diacrylate; tricyclodecanedimethanol diacrylate); diethylene glycol diacrylate; diethylene glycol dimethacrylate; dipropylene glycol diacrylate; triethylene glycol diacrylate; triethylene glycol dimethacrylate; tripropylene glycol diacrylate; tripropylene glycol dimethacrylate; tetraethylene glycol diacrylate; tetraethylene glycol dimethacrylate; polyethylene glycol 200 / 400 / 600 diacrylates; polyethylene glycol 200 / 400 / 600 dimethacrylate; ethoxylated (EO2 / EO3 / EO4 / EO10) bisphenol A diacrylates; and ethoxylated (EO2 / EO3 / EO4 / EO10) bisphenol A dimethacrylate.

[0089] Suitable examples of tri(meth)acrylates include without limitation trimethylolpropane triacrylates, trimethylolpropane trimethacrylates, alkoxylated (in particular ethoxylated or propoxylated) trimethylolpropane triacrylates, alkoxylated (in particular ethoxylated or propoxylated) trimethylolpropane trimethacrylates, alkoxylated (in particular ethoxylated or propoxylated) glycerol triacrylates, pentaerythritol triacrylates, alkoxylated (in particular ethoxylated or propoxylated) pentaerythritol triacrylates and mixtures thereof, preferably selected from the group consisting of trimethylolpropane triacrylates, alkoxylated (in particular ethoxylated or propoxylated) trimethylolpropane triacrylates, alkoxylated (in particular ethoxylated or propoxylated) glycerol triacrylates, pentaerythritol triacrylates and mixtures thereof.

[0090] Suitable examples of tetra(meth)acrylates include without limitation ditrimethylolpropane tetra(meth)acrylates, pentaerythritol tetra(meth)acrylates, alkoxylated (such as for example ethoxylated and propoxylated) pentaerythritol tetra(meth)acrylates and mixtures thereof, preferably selected from the group consisting of ditrimethylolpropane tetra(meth)acrylates, alkoxylated pentaerythritol tetra(meth)acrylates, as well as mixtures thereof.

[0091] Free radical photoinitiators are preferably selected from the group consisting of hydroxyketones (e.g. alpha-hydroxyketones), alkoxyketones (e.g. alpha-alkoxyketones), acetophenones, benzophenones, ketosulfones, benzyl ketals, benzoin ethers, coumarins, camphorquinones, phosphine oxides, phenylglyoxylates, and mixtures thereof, more preferably selected from the group consisting of phosphine oxides, hydroxyketones, and mixtures thereof.

[0092] Suitable examples of alpha-hydroxyketones include without limitation (1-[4-(2-hydroxyethoxy)- phenyl]-2-hydroxy-2-methyl-1-propan-1-one); 1-hydroxycyclohexyl phenyl ketone; 2-hydroxy-2-methyl- 1-phenylpropan-1-one; 2-hydroxy-2-methyl-1-(4-tert-butyl)phenylpropan-1-one; 2-hydroxy-1-[4-[[4-(2- hydroxy-2-methylpropanoyl)phenyl]methyl]phenyl]-2-methylpropan-1-one; 2-hydroxy-1-[4-[4-(2-hydroxy-2-methylpropanoyl)phenoxy]phenyl]-2-methylpropan-1-one; and oligo[2-hydroxy-2-methyl-1- [4-(1-methylvinyl)phenyl]propanone].

[0093] Suitable examples of acetophenones include without limitation 2,2-diethoxyacetophenone and 2-methoxy-2-phenylacetophenone.

[0094] Suitable examples of benzophenones include without limitation benzophenone; polymeric benzophenone compounds; 2-methylbenzophenone; 3-methylbenzophenone; 4-methylbenzophenone; 2,4,6-trimethylbenzophenone; 3,3′-dimethyl-4-methoxybenzophenone; 4-phenylbenzophenone; 4- chlorobenzophenone; methyl-2-benzoylbenzoate; 4-(4-methylphenylthio)benzophenone; 4- hydroxybenzophenone laurate, and a mixture of 50% benzophenone and 50% 1-hydroxycyclohexyl phenyl ketone.

[0095] A suitable example of ketosulfone include without limitation 1-[4-(4- benzoylphenylsulfanyl)phenyl]-2-methyl-2-(4-methylphenylsulfonyl)propan-1-one.

[0096] A suitable example of benzyl ketals includes without limitation 2,2-dimethoxy-2- phenylacetophenone.

[0097] Suitable examples of benzoin ethers include without limitation 2-ethoxy-1,2- diphenylethanone; 2-isopropoxy-1,2-diphenylethanone; 2-isobutoxy-1,2-diphenylethanone; 2-butoxy- 1,2-diphenylethanone; 2,2-dimethoxy-1,2-diphenylethanone; and 2,2-diethoxyacetophenone.

[0098] Suitable examples of coumarins include without limitation 3-(4-dodecylbenzoyl)-5,7- dimethoxy-2H-1-benzopyran-2-one and 3-(4-C10-C13-benzoyl)-5,7-dimethoxy-2H-1-benzopyran-2- one.

[0099] A suitable example of camphorquinone includes without limitation 1,7,7-trimethyl- bicyclo[2.2.1]heptane-2,3-dione.

[0100] Suitable examples of phosphine oxides include without limitation 2,4,6- trimethylbenzoyldiphenylphosphine oxide; ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate ; phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; bis(2,6-dimethoxybenzoyl)-2,4,4- trimethylpentylphosphine oxide; mixtures of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and 2- hydroxy-2-methylpropiophenone, a mixture of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and 2-hydroxy-2-methylpropiophenone; and a mixture of ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate and 2-hydroxy-2-methylpropiophenone.

[0101] Suitable examples of phenylglyoxylates include without limitation methyl benzoylformate; 2-[2- oxo-2-phenyl-acetoxy-ethoxy]ethyl 2-oxo-2-phenylacetate; and a mixture of 2-[2-oxo-2-phenyl-acetoxy- ethoxy]ethyl 2-oxo-2-phenylacetate and oxy-phenyl-acetic acid 2-[2-hydroxy-ethoxy]-ethyl ester.

[0102] Other examples of useful photoinitiators can be found in standard textbooks such as "Chemistry & Technology of UV & EB Formulation for Coatings, Inks & Paints", Volume III, "Photoinitiators for Free Radical Cationic and Anionic Polymerization", 2nd edition, by J. V. Crivello & K. Dietliker, edited by G. Bradley and published in 1998 by John Wiley & Sons in association with SITA Technology Limited.

[0103] The UV-Vis radiation curable printing inks described herein comprise the one or more photoinitiators described herein in a total amount from about 1 wt.% to about 20 wt.%, preferably from about 2 wt.% to about 15 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink. For UV-Vis radiation curable printing ink described herein consisting ofcationically curable inks, said inks comprise the one or more cationic photoinitiators described herein in a total amount from about 1 wt.% to about 20 wt.%, preferably from about 2 wt.% to about 15 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink. For UV-Vis radiation curable printing ink described herein consisting of radically curable inks, said inks comprise the one or more free radical photoinitiators described herein in a total among from about 1 wt.% to about 20 wt.%, preferably from about 2 wt.% to about 15 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink. For UV-Vis radiation curable printing ink described herein consisting of hybrid curable inks, said inks comprise a combination of the one or more cationic photoinitiators and the one or more free radical photoinitiators described herein in a total amount from about 1 wt.% to about 20 wt.%, preferably from about 2 wt.% to about 15 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

[0104] Optionally, one or more photosensitizers may also be present. Photosensitizers are activated by one or more of the wavelengths emitted by the UV-Vis light source and reach an excited state. The excited photosensitizer either transfer energy to the one or more photoinitiators (in free-radical polymerization) or an electron (in cationic polymerization). Either process in turn initiates the polymerization process. The UV-Vis radiation curable printing ink described herein may further comprise one or more photosensitizers in conjunction with the one or more photoinitiators described herein in order to achieve efficient curing. Suitable examples of photosensitizers are known to those skilled in the art (e.g. in Industrial Photoinitiators, W. A. Green, CRC Press, 2010, Table 8.1 p.170). Preferably, the one or more photosensitizers are selected from the group consisting of thioxanthone compounds, naphthalene compounds, anthracene compounds, titanocene compounds, and mixtures thereof; more preferably are selected from the group consisting of thioxanthone compounds (including without limitation isopropyl-thioxanthone (ITX), 1-chloro-2-propoxy-thioxanthone (CPTX), 2-chloro-thioxanthone (CTX) and 2,4-diethyl-thioxanthone (DETX) and mixtures thereof and oligomeric or polymeric forms thereof), anthracene compounds (such as 9,10-diethoxyanthracene and 9,10-dibutyloxyanthracene, and mixtures thereof. When present, the one or more photosensitizers are preferably present in a total amount from about 0.1 wt.% to about 5 wt.% and still more preferably about 0.2 wt.% to about 1 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

[0105] According to one embodiment, the UV-Vis radiation curable printing ink described herein is a cationically curable printing ink (i.e. comprises cationically curable compounds) and the one or more radiation curable compounds, i.e. the one or more cationically curable compounds (preferably the cationically curable compounds being selected from the group consisting of epoxides, oxetanes and mixtures thereof, preferably cycloaliphatic epoxides, oxetanes and mixtures thereof) described herein and the one cationically curable epoxysiloxane compounds described herein, when present, are present in a total amount from about 50 wt.% to about 95 wt.%, preferably from about 60 wt.% to about 95 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

[0106] According to one embodiment, the UV-Vis radiation curable printing ink described herein is a radically curable printing ink (i.e. comprises radically curable compounds), and the one or more radiation curable compounds, i.e. the one or more tri(meth)acrylates and tetra(meth)acrylates described herein and the one or more reactive diluents described herein, when present, are present in a total amountfrom about 50 wt.% to about 95 wt.%, preferably from about 60 wt.% to about 95 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

[0107] According to one embodiment, the UV-Vis radiation curable printing ink described herein is a hybrid curable ink (i.e. comprises cationically curable compounds and radically curable compounds), and the one or more radiation curable compounds, i.e. the one or more cationically curable compounds (preferably the cationically curable compounds are selected from the group consisting of epoxides, oxetanes and mixtures thereof, preferably cycloaliphatic epoxides, oxetanes and mixtures thereof) described herein and the one cationically curable epoxysiloxane compounds described herein, when present, the one or more radiation curable compounds, i.e. the one or more tri(meth)acrylates and tetra(meth)acrylates described herein and the one or more reactive diluents described herein, when present, are present in a total amount from about 50 wt.% to about 95 wt.%, preferably from about 60 wt.% to about 95 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

[0108] The UV-Vis radiation curable printing inks described herein, in particular the cationically or hybrid UV-Vis radiation curable screen printing inks described herein, may further comprise one or more polyhydroxy compounds. For embodiments wherein the radiation curable coating composition comprises the one or more polyhydroxy compounds described herein, said one or more polyhydroxy compounds are preferably present in a total less than or equal to about 15 wt.%, more preferably in a total amount from about 1 wt.% to about 15 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink. Polyhydroxy compounds are known in the art to improve adhesion to substrates known to exhibit poor adhesion properties, such as plastic or polymer substrates that become increasingly popular in the field of security documents, in particular banknotes.

[0109] The one or more polyhydroxy compounds described herein preferably comprise more than two hydroxyl groups and may be linear, branched or hyperbranched (also referred in the art as dendritic). Preferably, the one or more polyhydroxy compounds described herein are trifunctional, tetrafunctional compounds, hexafunctional compounds or multifunctional compounds.

[0110] The one or more polyhydroxy compounds described herein are preferably selected from the group consisting of polyhydroxy derivatives of aliphatic or aromatic polyethers, polyhydroxy derivatives of polyesters, polyhydroxy derivatives of polycarbonates, glycerol, trimethylolpropane, di- trimethylolpropane, pentaerytritol, dipentaerytritol and mixtures thereof.

[0111] The one or more polyhydroxy compounds described herein may be at least partially alkoxylated. The one or more polyhydroxy compounds described herein may therefore have alkoxylated units, preferably ethoxylated and / or propoxylated units. According to a preferred embodiment, the one or more polyhydroxy compounds described herein are selected from the group consisting of trifunctional compounds, preferably glycerols and trimethylolpropanes, tetrafunctional compounds, preferably di- trimethylolpropanes and pentaerytritols, hexafunctional compounds, preferably dipentaerytritols, and mixtures thereof, wherein said compounds, preferably said trimethylolpropanes, pentaerytritols and dipentaerytritols, may be alkoxylated (ethoxylated and / or propoxylated).

[0112] The UV-Vis radiation curable printing inks described herein, in particular the UV-Vis radiation curable screen printing inks described herein, may further comprise one or more fillers or extenderspreferably selected from the group consisting of carbon fibers, talcs, mica (muscovite), wollastonites, calcinated clays, China clays, kaolins, carbonates (e.g. calcium carbonate, sodium aluminum carbonate), silicates (e.g. magnesium silicate, aluminum silicate), sulfates (e.g. magnesium sulfate, barium sulfate), titanates (e.g. potassium titanate), alumina hydrates, silica, fumed silica, montmorillonites, graphites, anatases, rutiles, bentonites, vermiculites, zinc whites, zinc sulfides, wood flours, quartz flours, natural fibers, synthetic fibers and combinations thereof. When present, the one or more fillers or extenders are preferably present in a total amount from about 0.1 wt.% to about 20 wt.%, more preferably in a total amount from about 0.1 wt.% to about 10 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

[0113] The UV-Vis radiation curable printing inks described may further comprise one or more solvents to fine-tune the viscosity of said inks. Preferred solvents are polar aprotic solvents exhibiting a high boiling point such as carbonates. Preferred carbonates are alkylene carbonates (e.g. ethylene carbonates, propylene carbonates and butylene carbonates). Particularly preferred are propylene carbonates, which have a high boiling point and a favorable ecotoxicity profile. When present, the one or more solvents are present in a total amount less than about 5 wt.% and more preferably less than about 2.5 wt.%, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

[0114] The UV-Vis radiation curable printing ink described herein may further comprise one or more coloring components selected from the group consisting of organic pigment particles, inorganic pigment particles, and organic dyes, and / or one or more additives. The latter include without limitation compounds and materials that are used for adjusting physical, rheological and chemical parameters of the coating composition such as the viscosity (e.g. thickeners and surfactants), the consistency (e.g. anti-settling agents and plasticizers), the foaming properties (e.g. antifoaming agents), the lubricating properties (waxes, oils), UV stability (photostabilizers), the adhesion properties, the antistatic properties, the storage stability (polymerization inhibitors) etc. Additives described herein may be present in the coating composition in amounts and in forms known in the art, including so-called nano-materials where at least one of the dimensions of the additive is in the range of 1 to 1000 nm.

[0115] According to one embodiment, the UV-Vis radiation curable printing inks described herein are UV-Vis radiation curable inkjet printing inks described herein, preferably cationically UV-Vis radiation curable inkjet printing inks such as those described herein. The cationically UV-Vis radiation curable inkjet printing inks preferably comprise: i) the one or more of cationically curable compounds described herein, preferably compounds selected from the group consisting of the cyclic ethers (more preferably cyclic ethers selected from the group consisting of the cycloaliphatic epoxides described herein), the oxetanes described herein and mixtures thereof, ii) the one or more cationic photoinitiators described herein, preferably selected from the group consisting of iodonium salts, sulfonium salts and mixtures thereof; iii) optionally the one or more cationically curable epoxysiloxane compounds; iii) optionally the one or more photosensitizers, preferably selected from the group consisting of thioxanthone compounds, anthracene compounds and mixtures thereof; andiv) optionally the one or more solvents wherein the one or more of cationically curable compounds (i) + optional iii)) are preferably present in a total amount from about 50 wt.% to about 95 wt.%, more preferably in a total amount from about 60 wt.% to about 95 wt.% and the one or more cationic photoinitiators (ii)) are preferably in a total amount from about 1 wt.% to about 20 wt.%, more preferably in a total amount from about 2 wt.% to about 15 wt.%, the weight percents being based on the total weight of the cationically UV-Vis radiation curable inkjet printing ink.

[0116] According to one embodiment, the UV-Vis radiation curable printing inks described herein are UV-Vis radiation curable inkjet printings ink described herein, preferably hybrid UV-Vis radiation curable inkjet printing ink such as those described herein. The hybrid UV-Vis radiation curable inkjet printing inks preferably comprise: i) the one or more of cationically curable compounds described herein, preferably compounds selected from the group consisting of the cyclic ethers (more preferably cyclic ethers selected from the group consisting of the cycloaliphatic epoxides described herein), the oxetanes described herein and mixtures thereof; ii) the one or more cationic photoinitiators described herein, preferably selected from the group consisting of iodonium salts, sulfonium salts and mixtures thereof, iii) one or more radically curable compounds described herein, preferably selected from the group consisting of aliphatic epoxy (meth)acrylate compounds, more preferably selected from the group consisting of the tri(meth)acrylates, the tetra(meth)acrylates and the mixtures thereof described herein; iv) one or more free radical photoinitiators described herein, preferably selected from the group consisting of phosphine oxides, hydroxyketones, and mixtures thereof; v) optionally the one or more cationically curable epoxysiloxane compounds; and vi) optionally the one or more solvents, wherein the one or more of cationically curable compounds (i) + optional v)) and the one or more radically curable compounds (iii)) described herein are preferably present in a total amount from about 50 wt.% to about 95 wt.%, more preferably in a total amount from about 60 wt.% to about 95 wt.%; the one or more cationic photoinitiators (ii)) and the one or more free radical photoinitiators (iv)) are preferably in a total amount from about 1 wt.% to about 20 wt.%, more preferably in a total amount from about 2 wt.% to about 15 wt.%, the weight percents being based on the total weight of the hybrid UV-Vis radiation curable inkjet printing ink.

[0117] According to one embodiment, the UV-Vis radiation curable printing inks described herein are UV-Vis radiation curable screen printing inks described herein, preferably cationically UV-Vis radiation curable screen printing inks such as those described herein. The cationically UV-Vis radiation curable screen printing inks preferably comprise: i) the one or more of cationically curable compounds described herein, preferably compounds selected from the group consisting of the cyclic ethers (more preferably cyclic ethers selected from the group consisting of the cycloaliphatic epoxides described herein), the oxetanes described herein and mixturesthereof; ii) the one or more cationic photoinitiators described herein, preferably selected from the group consisting of iodonium salts, sulfonium salts and mixtures thereof; iii) optionally the one or more polyhydroxy compounds described herein; iv) optionally the one or more fillers or extenders described herein; v) optionally the one or more solvents described herein; and iii) optionally the one or more photosensitizers, preferably selected from the group consisting of thioxanthone compounds, anthracene compounds and mixtures thereof, wherein the one or more of cationically curable compounds (i)) are preferably present in a total amount from about 50 wt.% to about 95 wt.%, more preferably in a total amount from about 60 wt.% to about 95 wt.% and the one or more cationic photoinitiators (ii)) are preferably in a total amount from about 1 to about 20 wt.%, more preferably in a total amount from about 2 wt.% to about 15 wt.%, the weight percents being based on the total weight of the cationically UV-Vis radiation curable inkjet printing ink.

[0118] According to one embodiment, the UV-Vis radiation curable printing inks described herein are UV-Vis radiation curable screen printing inks described herein, preferably hybrid UV-Vis radiation curable screen printing inks such as those described herein. The hybrid UV-Vis radiation curable screen printing inks preferably comprise: i) the one or more of cationically curable compounds described herein, preferably compounds selected from the group consisting of the cyclic ethers (more preferably cyclic ethers selected from the group consisting of the cycloaliphatic epoxides described herein), the oxetanes described herein and mixtures thereof, ii) the one or more cationic photoinitiators described herein, preferably selected from the group consisting of iodonium salts, sulfonium salts and mixtures thereof, iii) one or more radically curable compounds described herein, preferably selected from the group consisting of aliphatic epoxy (meth)acrylate compounds, more preferably selected from the group consisting of the tri(meth)acrylates, the tetra(meth)acrylates and the mixtures thereof described herein; iv) one or more free radical photoinitiators described herein, preferably selected from the group consisting of phosphine oxides, hydroxyketones, and mixtures thereof; v) optionally the one or more polyhydroxy compounds described herein; vi) optionally the one or more fillers or extenders described herein; vii) optionally the one or more solvents described herein; and viii) optionally the one or more photosensitizers, preferably selected from the group consisting of thioxanthone compounds, anthracene compounds and mixtures thereof, wherein the one or more of cationically curable compounds (i) + optional v)) and the one or more radically curable compounds (iii)) described herein are preferably present in a total amount from about 50 wt.% to about 95 wt.%, more preferably in a total amount from about 60 wt.% to about 95 wt.%; the one or more cationic photoinitiators (ii)) and the one or more free radical photoinitiators (iv)) are preferably in a total amount from about 1 wt.% to about 20 wt.%, more preferably in a total amount from about 2 wt.% to about 15 wt.%,the weight percents being based on the total weight of the cationically UV-Vis radiation curable screen printing ink.

[0119] The UV-Vis radiation curable printing inks described herein may be prepared by dispersing or mixing all the ingredients described herein thus forming liquid compositions. Alternatively, for the UV- Vis radiation curable screen printing inks described herein, the one or more photoinitiators and the optional one or more photosensitizers may be added to the composition either during the dispersing or mixing step of all other ingredients or may be added at a later stage, i.e. after the formation of the liquid coating composition.

[0120] Also described herein are uses of the UV-Vis radiation curable printing inks described herein for manufacturing one or more security features on a security article and security articles obtained thereof.

[0121] Also described herein are method for producing the security articles and security articles obtained thereof.

[0122] The UV-Vis radiation curable printing inks described herein may be i) applied on a substrate such as those described herein by the printing process, preferably selected from the group consisting of screen printing, flexography printing or a contactless fluid microdispensing technology (preferably an inkjet printing) described herein, preferably by the screen printing process or the inkjet printing process described herein, and ii) UV-Vis radiation curing said ink, preferably with the one or more light sources selected from the group consisting of mercury lamps, UV-LED lamps and sequences thereof described herein, so as to form one or more security features on the substrate described herein.

[0123] As mentioned hereabove, the one or more security features described herein may be used for protecting and authenticating a security article or a decorative element.

[0124] The shape of the one or more security features is not limited and may be any desired signs, including any symbols, images and patterns. According to one embodiment, said one or more security features consist of one or more indicia. As used herein, the term “indicia” shall mean continuous and discontinuous layers consisting of distinguishing markings or signs or patterns. Preferably, the one or more indicia (x30) described herein are selected from the group consisting of 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. Examples of codes include encoded marks such as an encoded alphanumeric data, a one-dimensional barcode, a two-dimensional barcode, a QR-code, datamatrix and IR-reading codes.

[0125] With the aim of further increasing the security level and the resistance against counterfeiting and illegal reproduction of security article, 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.

[0126] With the aim of increasing the durability through soiling or chemical resistance and cleanliness and thus the circulation lifetime of security documents or with the aim of modifying their aesthetical appearance (e.g. optical gloss), one or more protective layers may be applied on top of the security features or security document described herein provided that protective layers do not negatively interfere with the Raman spectrum of interest of the security features described herein.

[0127] The one or more security features described herein may be provided directly on a substrate on which it shall remain permanently (such as for banknote applications). Alternatively, the one or more security features may also be provided on a temporary substrate for production purposes, from which the one or more security features are subsequently removed. Thereafter, after printing and curing of the UV-Vis radiation curable security inks described herein for the production of the one or more security features, the temporary substrate may be removed from the one or more security features.

[0128] Alternatively, in another embodiment an adhesive layer may be present on the one or more security features or may be present on the substrate comprising said features, said adhesive layer being on the side of the substrate opposite to the side where the one or more security features are provided or on the same side as the one or more security features and on top of said features. Therefore, an adhesive layer may be applied to the one or more security features or to the substrate, said adhesive layer being applied after the curing step has been completed. Such an article may be attached to all kinds of documents or other articles or items without printing or other processes involving machinery and rather high effort. Alternatively, the substrate described herein comprising the one or more security features described herein may be in the form of a transfer foil, which can be applied to a document or to an article in a separate transfer step. For this purpose, the substrate is provided with a release coating, on which the one or more security features are produced as described herein. One or more adhesive layers may be applied over the so produced features.

[0129] As used herein, the term ”substrate” includes any security article substrate onto which one or more ink printed security features can be applied. Security article substrates include without limitation, papers or other fibrous materials such as cellulose, paper-containing materials, glasses, metals, ceramics, plastics and 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 well known by the person skilled in the art, cotton and cotton / linen blends are preferred for banknotes, while wood pulp is commonly used in non-banknote security documents. Typical examples of plastics and polymers include polyolefins, such as polyethylene (PE) and polypropylene (PP), polyamides, polyesters such as poly(ethylene terephthalate) (PET), poly(1,4-butylene terephthalate) (PBT), poly(ethylene 2,6- naphthoate) (PEN) and polyvinylchlorides (PVC). Typical examples of composite materials include without limitation multilayer structures or laminates of paper and at least one plastic or polymer material, such as those described hereabove. The substrate of the security article described herein can be printed with any desired signs, including any symbols, images and patterns. The substrate described herein should preferably not emit any luminescence and / or Raman signal that may interfere with the properties of the one or more surface enhanced Raman spectroscopy (SERS) tags in the inks described herein. In case the substrate exhibits any luminescence properties and / or Raman signal, said properties should be smaller than 25000 au.

[0130] Typical examples of decorative elements or objects include without limitation luxury goods, cosmetic packaging, automotive parts, electronic / electrical appliances, furniture and fingernail articles.

[0131] As used herein, the term “security article” refers to a article having a value such as to render it potentially liable to attempts at counterfeiting or illegal reproduction and which is usually protectedagainst counterfeit or fraud by one or more security features. Security articles include without limitation value articles or documents and value commercial goods. Typical examples of value articles or documents include without limitation banknotes, deeds, tickets, checks, vouchers, fiscal stamps and tax labels, agreements and the like, identity documents such as passports, identity cards, visas, bank cards, credit cards, transaction cards, access documents, academic diploma or titles and the like, entrance tickets, public transportation tickets or titles, agreements and the like. The term “value commercial good” refers to packaging materials, in particular for cosmetic articles, nutraceutical articles, pharmaceutical articles, alcohols, tobacco articles, beverages or foodstuffs, electrical / electronic articles, fabrics or jewelry, i.e. articles that shall be protected against counterfeiting and / or illegal reproduction in order to warrant the content of the packaging like for instance genuine drugs. Examples of these packaging materials include without limitation labels, such as authentication brand labels, tamper evidence labels and seals. It is pointed out that the disclosed substrates, value documents and value commercial goods are given exclusively for exemplifying purposes, without restricting the scope of the invention.

[0132] Also described herein are methods to authenticate the one or more security features and the security article described herein. With the aim of authenticating the one or more security features and the security article described herein, the Raman spectrum of said one or more security features is measured and acquired prior its circulation and use and recorded as the reference Raman spectrum. The method authenticating the one or more security features and the security article described herein comprises the steps of: a) providing the security article described herein and comprising the one or more security features described herein made of the cured layer made of the UV-Vis radiation curable printing ink described herein; b) illuminating the one or more security features with visible and / or near IR light and measuring the SERS spectrum, and c) comparing the SERS spectrum obtained in step b) with a pre-recorded reference Raman spectrum.

[0133] The skilled person can envisage several modifications to the specific embodiments described above without departing from the spirit of the present invention. Such modifications are encompassed within the present invention.

[0134] Further, all documents referred to throughout this specification are hereby incorporated by reference in their entirety as set forth in full herein.EXAMPLES

[0135] The present invention is now described in more details with reference to non-limiting examples. The Examples below provide more details for the production of UV-Vis radiation curable printing inks, in particular UV-Vis radiation curable inkjet printing inks and UV-Vis radiation curable screen printing inks, comprising surface enhanced Raman spectroscopy (SERS) tags and the production and authentication of security features made with said inks.

[0136] Examples and Comparative Examples of UV-Vis radiation curable inkjet printing ink (E1-E6 and E20 in Tables 1A-1 and 1C-1; C1-C12 in Table 1A-2) and of UV-Vis radiation curable screen printing ink (E7-E19 and E21 in Tables 1B-1 and 1C-2; C13-C22 in Table 1B-2) were prepared as described herein.

[0137] Examples E1-E21 and Comparative Examples C1-C22 were prepared by applying the UV-Vis radiation curable printing inks on a polymeric substrate (Guardian®from CCL) as a 5 cm x 10 cm rectangle (E1-E6 and E20 (Table 1A-1 and 1C-1) and C1-C12 (Table 1A-2)) or as a 6 cm x 10 cm rectangle (E7-E19 and E21 (Table 1B-1 and 1C2) and C13-C22 (Table 1A-2)).

[0138] Examples E1-E21 and Comparative Examples C1-C22 were cured immediately after application using: Hg lamp (TECHNIGRAPH AKTIPRINT MINI (UN50049); 80 W / cm; one pass at 12 m / min, dose: 222 mJ / cm2) (E1, E3, E5, E6-14, E17-E21; C1, C3-C8, C9-a), C10-a), C11-C16, C17-a), C18, C19-a), C21, C22) or LED LUV20 lamp (IST, 385 nm, 40 m / min; two passes, dose 1080 mJ / cm2) (E2, E4, E15, E16; C2, C- 9b), C10-b), C17-b), C19-b), C20). Preparation of a dispersion comprising SERS tags

[0139] A gold colloid used to prepare the SERS tag comprised in the UV-Vis radiation curable inks of the Examples and Comparative Examples was prepared according to the method described in WO 2021 / 009090 A1 Example I.3, “Preparation of 90 nm gold colloid stock solution”.

[0140] The gold colloid suspension (160 ml; 0.25 g / lt Au) was stirred under vigorous magnetic agitation in a mixing reactor. A 1 mmol solution (0.1 ml) of (E)-1,2-di(pyridine-4-yl)ethene (97%; CAS Nr: 13362- 78-2) in ethanol was added rapidly. After about 20 seconds, the aggregation process was stopped by the addition of a polymer solution in water. The mixture was stirred for 15 minutes, concentrated by ultrafiltration to 1 g and rinsed several times with a NaOH solution.

[0141] The resulting aggregate was coated with silica using the Stöber method, said method being well known by the man skilled in the art and is disclosed for example in US 7723100 B2.

[0142] A linseed-based alkyd resin was added to obtain a dispersion of SERS tags in the alkyd resin and the residual solvents (water and ethanol) was removed under vacuum. The so-obtained dispersion comprising about 20 wt.% of SERS was used as such for the printing inks (Table 1A-1, 1A-2, 1B-1, 1B- 2, 1C-1 and 1C-2).Preparation of the UV-Vis radiation curable printing inks

[0143] The UV-Vis radiation curable inkjet printing inks E1-E6 and E20 and C1-C12 were independently prepared by mixing the ingredients listed in Tables 1A-1, 1A-2 and 1C-1 for 20 minutes at room temperature and at 1000 rpm using a Dispermat (LC220-12). The viscosities of the inks provided in Tables 1A-1, 1A-2 and 1C-1 were independently measured at 45°C using an Anton Paar viscometer (model QC300, spindle B-SC4-21 at 250 rpm).

[0144] The UV-Vis radiation curable screen printing ink E7-E19, E21 and C13-C22 were independently prepared by mixing the ingredients listed in Tables 1B-1, 1B-2 and 1C-2 for 10 minutes at 2000 rpm using a Dispermat CV-3. The viscosities of the inks provided in Tables 1B-1, 1B-2 and 1C-2 were independently measured at 25°C on a Brookfield viscometer (model "DV-I Prime", spindle S27 at 100 rpm). Preparation of the printed security features

[0145] The evaluation of the UV-Vis radiation curable inkjet printing inks E1-E6 and E20 and C1-C12 was performed on ink layers applied by hand-coating to facilitate the screening of said inks.

[0146] Fig.1 disclosed the Raman shifts spectra of the UV-Vis radiation curable inkjet printing ink E1 applied by inkjet printing using a Ricoh Gen5 inkjet printing head (2 dpd, ink coverage of (a) 25%, (b) 50% and (c) 75%) and by hand-coating (K Hand Coater from ERICHSEN, HC 0 bar, layer thickness of about 4 μm, (HC)). After curing, the Raman shift spectra of the samples were measured as described hereafter. Fig.1 shows that the inkjet printed security features and the hand-coated sample resulted in comparable spectra, in particular for inkjet printed ink coverage of about 50%.

[0147] The examples E2-E6 and E20 (Tables 1A-1 and 1C-1) and C1-C12 (Table 1A-2) were all prepared by hand-coating application using a HC 0 bar.

[0148] The UV-Vis radiation curable screen printing inks E7-E19, E21 and C13-C22 were independently applied by hand screen printing using a 77T screen so as to form a layer having a thickness of about 22 μm. Measurement of the SERS spectra

[0149] The Raman shift spectra of the Examples E1-E21 and of the Comparative Examples C1-C22 were measured using a Raman spectrophotometer from Wasatch Photonics (laser type: 100 mW single mode; wavelength: 785 nm) using an integration time of 800 msec and a 4.3 mW laser power.

[0150] The Raman shift spectra were measured immediately after the curing step (t0; black curves in Figs 1 to 6).

[0151] The substrates carrying the coating layers were individually arranged between two glass plates (15 cm x 20 cm x 0.3 cm; 220 g each) and stored for 48 hours in an oven at 50°C (relative humidity 10%) to mimic the conditions of a printed sheet in a substrates pile during the printing process on an industrial press.

[0152] The Raman shift spectra were measured (t48; grey curves in Figs 2 to 6) and compared with the spectra measured immediately after curing (t0; black curves in Figs 2 to 6).

[0153] As illustrated in Figs 2-1 to 2-6 for the examples E1-E6 and in Fig.6-1 for E20 (inkjet printing inks from Tables 1A-1 and 1C-1) and in Figs 4-1 to 4-13 for the examples E7-E19 and in Fig.6-2 for E21 (screen printing inks from Tables 1B-1 and 1C-2), the spectra at t48 (grey curves) were similar to the spectra at t0 (black curves) and in particular, no saturation (intensity ≥ 65’000) of the signal was observed.

[0154] On the other hand, as illustrated in Figs 3-1 to 3-12 for the comparative examples C1-C12 (inkjet printing inks from Table 1A-2) and in Figs 5-1 to 5-10 for the comparative examples C13-C22 (screen printing inks from Table 1B-2), the spectra at t48 (grey curves) showed spectra saturation, that is the measured intensity reached values ≥ 65’000, at least in part of the measured range, therefore preventing a definite authentication of the SERS tags. List of compounds in Tables 1A-C CAB-381-0.5 (Eastman™): cellulose acetate butyrate [CAS Nr 9004-36-8] DPGDA (dipropylene glycol diacrylate) (Cytec): 1,1′-[oxybis(methyl-2,1-ethanediyl)-2-propenoic acid ester [CAS Nr 57472-68-1] Dynasylan®GLYMO (EVONIK Industries): glycidoxypropyltrimethoxysilane [CAS Nr 2530-83-8] GENOMER* 1120 (Rahn): 3,3,5-trimethylcyclohexyl-2-propenoic acid ester [CAS Nr 86178-38-3] MIRAMER M4004 ((Rahn): α-hydro-ω-[(1-oxo-2-propen-1-yl)oxy]-, ether with 2,2-bis(hydroxymethyl)- 1,3-propanediol poly(oxy-1,2-ethanediyl) (polyetherpolyol tetraacrylate) [CAS Nr 51728-26-8] MIRAMER M410 (DiTMPTA; polyetherpolyol tetraacrylate) ((Rahn): 1,1’-[2-[[2,2-bis[[(1-oxo-2-propen- 1-yl)oxy]methyl] butoxy] methyl]-2-ethyl-1,3-propanediyl] -2-propenoic acid ester [CAS Nr 94108-97-1] Photomer®3016-20G (IGM Resins) : bisphenol A epoxyacrylate [CAS Nr 55818-57-0] and glyceryl [4 PO] triacrylate (GPTA) [CAS Nr 52408-84-1] Polyol R4631 (Perstorp): polymer of 2,2-bis(hydroxymethyl)-1,3-propanediol, 2-methyloxirane and oxirane [CAS Nr 30374-35-7] UviCure S105ES (Lambson): 7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3- carboxylat) [CAS Nr 2386-87-0] UviCure S130 (Lambson): 3-ethyl-3-hydroxymethyl oxetane [CAS Nr 3047-32-3] ANTHRACURE®UVS 1331 (Kawasaki Kasei Chemicals Ltd): 9,10-dibutoxy-anthracene [CAS Nr 76275-14-4] CHIVACURE®1176 (CHITEC Technology): diphenyl(4-phenylthio)phenylsulfonium hexafluoroantimonate [CAS Nr 71449-78-0] and thiodi-4,1-phenylene)bis(diphenylsulfonium) bis- hexafluoroantimonate [CAS Nr 89452-37-9] in propylene carbonate [CAS Nr 108-32-7] IRGACURE®290 (IGM): tris-[4-[(4-acetylphenyl)thio]phenyl]sulfonium tetrakispentafluorophenyl borate [CAS Nr 1203809-92-0] GENOCURE* DETX (Rahn): 2,4-diethyl-thioxanthone [CAS Nr 82799-44-8] GENOCURE* ITX (Rahn):2-isopropyl-9H-thioxanthen-9-one [CAS Nr 5495-84-1] Omnirad 1173 (IGM): 2-hydroxy-2-methyl-1-phenylpropan-1-one [CAS Nr 7473-98-5]SpeedCure TPO-L (Lambson): 2,4,6-trimethylbenzoyl-ethoxylphenylphosphine oxide [CAS Nr 84434- 11-7] SpeedCure CPTX (Lambson): 1-chloro-2-propoxy-thioxanthone [CAS Nr 142770-42-1] SpeedCure 976 (Lambson): bis[4-(diphenylsulfonium)phenyl] sulfide bis-hexafluoroantimonate [CAS Nr 89452-37-9)] and 4-(phenylthio)phenyldiphenylsulfonium hexafluoroantimonate [CAS Nr 71449-78-0] in propylene carbonate [CAS Nr 108-32-7] SpeedCure 992 (Lambson): [CAS 68156-13-8, 74227-35-3, 108-32-7] mixture of diphenyl[(phenylthio)phenyl]-sulfonium hexafluorophosphate and S,S′-(thiodi-4,1-phenylene)bis[S,S- diphenyl-sulfonium bis-hexaflurorophosphate in propylene carbonate [CAS Nr 108-32-7] WPI 113 (FUJIFILM Wako Chemicals): bis(C10-14-alkylphenyl)iodonium hexafluorophosphate [CAS Nr 868698-33-3] WPI 116 (FUJIFILM Wako Chemicals): bis(decylphenyl)iodonium hexafluoroantimonate [CAS Nr 149759-20-6] WPI 124 (FUJIFILM Wako Chemicals): bis(decylphenyl)iodonium tetrakispentafluorophenyl borate [CAS Nr 1791428-74-4] AEROSIL®200 (Evonik): hydrophilic fumed silica [CAS Nr 7631-86-9] BYK-UV 3510 (BYK): polyether-modified polydimethylsiloxane GENORAD* 16 (Rahn): stabilizer TEGO®Airex 900 (Evonik): defoamer TEGO®Rad 2300 (Evonik): levelling agent Propylene carbonate (Brenntag Scheizerhall): [CAS Nr 108-32-7] UCAR Ester EEP (DOW): ethyl-3-ethoxypropionate [CAS 763-69-9] DVE-3-TEDGE (BASF): triethyleneglycol divinyl ether [CAS Nr 765-12-8] DVE-2 (BASF): diethyleneglycol divinyl ether [CAS Nr 764-99-8] CHDVE (BASF): 1,4-bis[(ethenyloxy)methyl]-cyclohexane [CAS Nr 17351-75-6] VEEA (Nippon Shokubai): 2-[2-(ethenyloxy)ethoxy]-2-propenoic acid ethyl ester [CAS Nr 86273-46-3]Table 1A-1 (Raman shifts shown in Figs 2-1 to 2-6) UV-Vis radiation curable inkjet printing inks E1 E2 E3 E4 E5 E6 Irradiation source Hg LED Hg LED Hg Hg UviCure S105ES 57.5 57 57.5 57 50.5 30.5 Dynasylan®GLYMO 35 35 15 35 35 35 UviCure S130 20 20 Photomer®3016-20G 6 6 BYK-UV 3510 0.5 0.5 0.5 0.5 0.5 0.5 dispersion comprising the SERS tags 1 1 1 1 1 1 SpeedCure 976 6.0 6.0 6.0 6.0 6.0 SpeedCure 992 6.0 Omnirad 1173 1.0 1.0 ANTHRACURE®UVS 1331 0.5 0.5 Viscosity / mPa s 11.5 10 15.3 10.8 13.5 9.8Table 1A-2 (Raman shifts shown in Figs 3-1 to 3-12) UV-Vis radiation curable inkjetprinting inksC1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12Irradiation source Hg LED Hg Hg Hg Hg Hg Hg Hg C9a) Hg Hg Hg LED C10a) C9b) LED C10b) UviCure S105ES 57.5 57 57.5 57.5 57.5 57.5 50 37.5 50 60.5 50.5 30.5 Dynasylan®GLYMO 15 15 30 15 15 15 22.5 15 22 22 15 15 DVE-3-TEDGE 20 20 5 20 20 20 20 20 20 DVE-2 20 CHDVE 20 VEEA 20 UviCure S130 20 20 Photomer®3016-20G 6 6 BYK-UV 3510 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 dispersion comprising the SERStags1 1 1 1 1 1 1 1 1 1 1 1SpeedCure 976 6 6 6 6 6 6 6 6 6 ANTHRACURE®UVS 1331 0.5 CHIVACURE®1176 6 WPI 116 6 WPI 124 2.5 SpeedCure CPTX 0.5 0.5 Omnirad 1173 1 1 Viscosity / mPa s 11.2 10.8 11.3 8.9 12.3 11 8.6 7.2 10.6 10.2 11.3 9.3Table 1B-1 (Raman shifts shown in Figs 4-1 to 4-13) UV-Vis radiation curable E7 E8 E9 E10 E11 E12 E13 E14 E15 E16 E17 E18 E19 screen printing inks Irradiation source Hg Hg Hg Hg Hg Hg Hg Hg LED LED Hg Hg Hg UviCure S105ES 79.2 78.7 73.7 80.7 74.2 81.2 80.7 77.2 78.7 80.2 54.6 54.1 49.1 UviCure S130 5 5 5 Polyol R4631 10 10 10 10 10 10 10 10 10 10 10 10 10 MIRAMER M4004 20 20 20 AEROSIL®200 2 2 2 2 2 2 2 2 2 2 2 2 2 TEGO®Airex 900 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Propylene carbonate 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 dispersion comprising the 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 SERS tags SpeedCure 976 4 4 4 4 4 4 4 4 SpeedCure 992 2.5 2.5 Omnirad 1173 4.6 4.6 4.6 WPI 113 2 WPI 116 2.5 WPI 124 6 GENOCURE* ITX 0.5 0.5 0.5 0.5 ANTHRACURE®UVS 1331 0.5 0.5 Viscosity / mPa s 1095 1087 792 1045 760 1053 1090 1097 1089 1034 1100 1090 810Table 1B-2 (Raman shifts shown in Figs 5-1 to 5-10) UV-Vis radiation curable C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 screen printing inks Irradiation source Hg Hg Hg Hg Hg C17a) Hg Hg C19a) LED Hg Hg LED C17b) LED C19b) UviCure S105ES 58.7 73.7 56.7 56.7 60.2 57.2 56.7 58.7 35.6 32.1 DVE-3-TEDGE 20 5 20 20 20 20 20 20 DVE-2 20 CHDVE 20 Polyol R4631 10 10 10 10 10 10 10 10 10 10 MIRAMER M4004 20 20 AEROSIL®200 2 2 2 2 2 2 2 2 2 2 TEGO®Airex 900 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Propylene carbonate 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 dispersion comprising the 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 SERS tags SpeedCure 976 4 4 6 6 4 WPI 116 2.5 2.5 IRGACURE®290 6 WPI 124 6 6 Omnirad 1173 4.6 4.6 GENOCURE* ITX 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 ANTHRACURE®UVS 1331 0.5 Viscosity / mPa s 560 1030 580 600 590 612 593 576 622 625 5Table 1C-1 (Raman shifts shown in Fig.6-1) UV-Vis radiation curable inkjet E20 printing ink Irradiation source Hg DPGDA 41.8 GENOMER* 1120 31 MIRAMER M410 20 GENORAD* 16 1 TEGO®Rad 2300 0.1 dispersion comprising the SERS tags 1 SpeedCure TPO-L 5 GENOCURE* DETX 0.1 Viscosity / mPa s 6.7 Table 1C-2 (Raman shifts shown in Fig.6-2) UV-Vis radiation curable screen E21 printing ink Irradiation sourceHgDPGDA 36.4 MIRAMER M410 20 GENOMER* 1120 27 GENORAD* 16 1 TEGO®Rad 2300 0.1 CAB-381-0.5 3.6 UCAR Ester EEP 6.4 dispersion comprising the SERS 0.5 tags Omnirad 1173 5 Viscosity / mPa s 309

[0155] As illustrated in Figs 2-1 to 2-6 for E1-E6 and in Fig.6-1 for E20 (layers made of UV-Vis radiation curable inkjet printing inks from Tables 1A-1 and 1C-1) and in Figs 4-1 to 4-13 for E7-E19 and in Fig.6- 2 for E21 (layers made of UV-Vis radiation curable screen printing ink from Tables 1B-1 and 1C-2), UV- Vis radiation curable printing inks according to the present invention comprising SERS tags and lacking any vinyl ether containing compounds (contrary to the comparative examples C1-C22) resulted in cured ink layers displaying Raman shift spectra at t48 (grey curves), i.e. spectra measured after substrate storage for 48 hours in at 50°C and 10% relative humidity, being substantially identical or very similar with the Raman shift spectra at t0, i.e. measured immediately after curing, and showing no signal saturation, i.e. no signal ≥ 65’000 units.

[0156] Comparative Examples C1-C22 (Figs 3-1 to 3-12 and 5-1 to 5-10) made of UV-Vis radiation curable printing inks comprising SERS tags and one or more vinyl ether compounds resulted in cured ink layers displaying Raman shift spectra at t48 (grey curves) showing signal saturation, i.e. signal being ≥ 65’000 units at least in part of the spectrum. Variation of the vinyl ether compounds concentration, e.g. as in C1 and C3 (Figs 3-1 and 3-3) or in C13-C14 (Figs 5-1 to 5-2), or variation of the vinyl ether component, as e.g. as in C1, C4-C6 (Figs 3-1, 3-4, 3-5 and 3-6) or in C13, C15-C16 (Figs 5-1 , 5-3 and 5-4), or variation of the photoinitiators, as e.g. in C1, C7, C9-C10 (Figs 3-1, 3-7, 3-9 and 3-10) or in C13, C17-C22 (Figs 5-1 and 5-5 to 5-10), or variation of the irradiation source as e.g. in C9-b), C10-b), C17- b) C19-b) and C20 (Figs 3-9 b), 3-10 b), 5-5 b), 5-7b and 5-8), did not solve the problem, that is the signals remained saturated.

Claims

CLAIMS 1. A UV-Vis radiation curable printing ink comprising: i) one or more surface enhanced Raman spectroscopy (SERS) tags in a total amount from about 0.01 wt.% to about 1 wt.%, preferably from about 0.02 wt.% to about 1 wt.%, preferably the one or more surface enhanced Raman spectroscopy (SERS) tags are nanoparticles and more preferably at least one of said one or more SERS tags comprises gold (Au) as SERS-enhancing material; ii) one or more radiation curable compounds in a total amount from about 50 wt.% to about 95 wt.%, preferably from about 60 wt.% to about 95 wt.%; and iii) one or more photoinitiators in a total amount from about 1 wt.% to about 20 wt.%, preferably from about 2 wt.% to about 15 wt.%, wherein said UV-Vis radiation curable printing ink lacks a vinyl ether containing compound, the weight percents being based on the total weight of the UV-Vis radiation curable printing ink.

2. The UV-Vis radiation curable printing ink according to claim 1, wherein the one or more SERS tags are present in the form of a dispersion, preferably a dispersion comprising an alkyd-based resin and about 10 wt.% to about 30 wt-%, for example 20 wt.% of said surface enhanced Raman spectroscopy (SERS) tags, the weight percents being based on the total weight of the dispersion.

3. The UV-Vis radiation curable printing ink according to claim 1 or 2 being selected from the group consisting of screen printing inks, flexography printing inks and contactless fluid microdispensing technologies inks.

4. The UV-Vis radiation curable printing ink according to any one of claims 1 to 3, wherein the one or more radiation curable compounds are cationically curable compounds selected from the group consisting of propenyl ethers, cyclic ethers, lactones, cyclic thioethers, propenyl thioethers, silanes and mixtures thereof, preferably cyclic ethers and more preferably epoxides, oxetanes and mixtures thereof, and the one or more photoinitiators are one or more cationic photoinitiators being onium salts, preferably being selected from the group consisting selected from the group consisting of oxonium salts, iodonium salts, sulfonium salts and mixtures thereof.

5. The UV-Vis radiation curable printing ink according to claim 4, wherein the cationically curable compounds selected from the group consisting of epoxides, oxetanes and mixtures thereof, preferably cycloaliphatic epoxides, oxetanes and mixtures thereof.

6. The UV-Vis radiation curable printing ink according to claim 4 or 5, further comprising one or more radically curable compounds selected from the group consisting of tri(meth)acrylates, tetra(meth)acrylates and mixtures thereof and one or more one or more free radical photoinitiators selected from the group consisting of hydroxyketones, alkoxyketones, acetophenones, benzophenones, ketosulfones, benzyl ketals, benzoin ethers, coumarins, camphorquinones, phosphine oxides, phenylglyoxylates, and mixtures thereof, preferably selected from the group consisting of phosphine oxides,hydroxyketones, and mixtures thereof.

7. The UV-Vis radiation curable printing ink according to claim 4 or 5 being a cationically UV-Vis radiation curable screen printing ink and further comprising one or more polyhydroxy compounds and / or one or more fillers or extenders and / or one or more solvents and / or one or more photosensitizers.

8. The UV-Vis radiation curable printing ink according to claim 6 being a hybrid UV-Vis radiation curable screen printing ink and further one or more polyhydroxy compounds one or more fillers or extender and / or one or more solvents and / or one or more photosensitizers.

9. The UV-Vis radiation curable printing ink according to claim 4 or 5 being a cationically UV-Vis radiation curable inkjet printing ink and further comprising one or more cationically curable epoxysiloxane compounds and / or one or more photosensitizers and / or one or more solvents.

10. The UV-Vis radiation curable printing ink according to claim 6 being a hybrid UV-Vis radiation curable inkjet printing ink and further comprising one or more cationically curable epoxysiloxane compounds and / or one or more solvents.

11. A use of the UV-Vis radiation curable printing ink recited in any one of claims 1 to 10 for manufacturing one or more security features on a substrate.

12. A security feature made from the UV-Vis radiation curable printing ink recited in any one of claims 1 to 10.

13. A security article comprising a substrate and a radiation cured coating obtained by UV-Vis radiation curing of the UV-Vis radiation curable printing ink recited in any one of claims 1 to 10, wherein the substrate is preferably selected from the group consisting of papers or other fibrous materials, paper-containing materials, glasses, metals, ceramics, plastics and polymers, composite materials and mixtures or combinations of two or more thereof.

14. A method for producing the security article recited in claim 13, comprising the steps of: a. printing, preferably by a printing process selected from the group consisting of screen printing, flexography printing or a contactless fluid microdispensing technology, the UV- Vis radiation curable printing ink recited in any one of claims 1 to 10, on the substrate, and b. UV-Vis radiation curing the UV-Vis radiation curable printing ink, preferably with one or more light sources selected from the group consisting of mercury lamps, UV-LED lamps and sequences thereof, so as to form one or more security features.

15. A method to authenticate the one or more security features recited in claim 12 and the security article recited in claim 13, comprising the steps of: a. providing the security article recited in claim 13 and comprising the one or more security features recited in claim 12 made of a radiation cured layer made of the UV-Vis radiation curable printing ink recited in any one of claims 1 to 10; b. illuminating the one or more security features with visible and / or near IR light and measuring the SERS spectrum, and c. comparing the SERS spectrum obtained in step b with a pre-recorded reference Raman spectrum.

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