Uv-led curable viscous printing inks and printing processes

Abstract

The present invention relates to the field of viscous UV-LED radically curable inks for printing security features on substrates, in particular security documents, said inks comprising one or more radically curable (meth)acrylate compounds, one or more thioxanthone compounds, one or more amino containing synergists, one or more fillers and / or extenders, and one or more pigments of formula (I).

Description

UV-LED CURABLE VISCOUS PRINTING INKS AND PRINTING PROCESSESFIELD OF THE INVENTION

[0001] The present invention relates to the field of the protection of security documents against counterfeit and illegal reproduction. In particular, the present invention relates to the field of UV-LED radically curable viscous or pasty printing inks and processes for producing security features or patterns on substrates, in particular on security documents.BACKGROUND OF THE INVENTION

[0002] With the constantly improving quality of color photocopies and printings and in an attempt to protect security documents such as banknotes, value documents or cards, transportation tickets or cards, tax banderols, and product labels that have no reproducible effects against counterfeiting, falsifying or illegal reproduction, it has been the conventional practice to incorporate various security means in and on these documents. Typical examples of security means include security threads, windows, fibers, planchettes, foils, decals, holograms, watermarks, security inks comprising optically variable pigments, magnetic or magnetizable thin-film interference pigments, interference-coated particles, thermochromic pigments, photochromic pigments, luminescent compounds, infrared-absorbing compounds, ultraviolet-absorbing or magnetic compounds.

[0003] It is known in the art to apply inks on security documents in several printing steps, including different printing processes using low viscous inks such as screen printing inks, flexography printing inks and gravure printing inks as well as highly viscous or pasty inks such as offset printing inks, intaglio printing inks and letterpress printing inks.

[0004] Offset printing processes consist of indirect methods wherein an ink is first transferred from a printing plate to a blanket cylinder and onto a substrate. Offset printing processes are categorized in three distinct technologies, namely wet offset processes, waterless offset processes and dry offset processes. Wet offset processes take advantage of the difference in surface energy between the image area and the non-image area of the printing plate. The image area is oleophilic, whereas the non-image area is hydrophilic. Thus, oily inks used in the method tend to adhere to the image-area and to be repelled from the non-image area of the printing plate. Wet offset printing is typically carried out by feeding both a fountain solution (also referred in the art as dampening solution) and an oleophilic ink to the printing plate surface to allow the image areas to receive preferentially the ink and the non-image areas preferentially the fountain solution and then transferring the ink deposited on image areas onto a substrate via the printing cylinder. In waterless offset processes, the non-image areas are covered with a specific silicone rubber material having very low surface tension (about 20 mN / m) and repelling the ink. No water (and hence no fountain solution) is needed. Dry offset processes are methods wherein the blanket cylinder is covered with a metal- backed photopolymer forming reliefs carrying the motifs to be printed. The ink adheres to the reliefs and is then transferred to the substrate via the printing cylinder. In this case also, no fountain solution is required.

[0005] Intaglio printing is used in the field of security documents, in particular banknotes, and delivers the most consistent and high quality printing of fine lines. Moreover, intaglio printing confers the well-known and recognizable relief features, in particular the unmistakable touch feeling, to a printed document. The term "intaglio printing" as used in this application shall apply to the so-called "engraved steel die" or "copper plate" printing process which is well known to the skilled in the art. The following shall not apply to the alsowell-known rotogravure or gravure printing processes, which rely on a different type of inks, said gravure inks exhibiting very low viscosity values compared to intaglio inks.

[0006] During an intaglio printing processes, a rotating engraved steel cylinder or a printing cylinder carrying one or more plates engraved with a pattern or image to be printed is supplied with one or more inks, wherein said inks are applied to the engraved surface of the cylinder orthe plates and the engravings. The inked intaglio plate is brought into contact with a substrate, e.g. a paper, a composite or a plastic material in sheet form or web form and the ink is transferred under pressure from the engravings of the intaglio printing plate onto the substrate, forming a thick relief printing pattern on the substrate. The high pressure deforms the impression material, forcing the substrate to be printed into the engravings on the engraved cylinder. This results in the substrate picking up some ink and being embossed, corresponding to the engravings on the surface of the engraved cylinder.

[0007] Subsequently to the application of inks on substrates, the intaglio inks and offset inks have then to be cured or dried. This has been conventionally done either by the application of heat or, more commonly, by oxidative drying. Curing or drying of oxidatively drying inks is typically a slow process which results in a higher tendency of the oxidative inks, as compared to radiation curable inks, to produce set-off. Set off occurs when a printing ink which is not sufficiently dried or cured at least partially adheres to the back of a printed substrate placed on top of it during the stacking of printed substrates as it comes off the printing machines. This is a particular problem during the printing of features on security documents, especially banknotes, since said documents typically carry several overlapping or partially overlapping features which are applied in subsequent steps. If the previously applied feature, e.g. a background image or graphic pattern, has not yet sufficiently dried or cured, the whole multi-step printing process is not only delayed but also the so-obtained feature may still suffer from set off or marking due to set off on the machine during any subsequent printing or process operations. Furthermore, curing or drying of oxidatively drying inks has the substantial disadvantage that it is a relatively slow process, and documents correspondingly printed and stacked as sheets cannot usually be handled for further processing before a drying time period of one to several days. The curing of printed inks by radiation is known and widely introduced in the art of printing. Radiation curing allows a rapid, almost instantaneous curing / drying of the printed ink film, and hence opens the way to increased production speed. Due to its fast or almost immediate curing, printing with radiation curable inks allows reducing the time between printing and handling of the printed substrates and allows increasing the number of stacked sheets per pile. The presence of volatile organic compounds can be avoided with radiation curable inks. Radiation curable inks are also significantly more stable on the printing press than oxidatively drying inks, that may tend to start drying before their application on the substrate.

[0008] Radiation curing is usually carried out by using mercury lamps, in particular by medium-pressure mercury lamps. However, mercury lamps require a high amount of energy, need efficient and costly heat dissipation systems, are prone to ozone formation and have a limited lifespan. With the aim of providing solutions that are less costly, require less intervention and are more environmentally friendly, lamps and systems based on UV-LEDs have been developed for curing inks and coatings. Contrary to mediumpressure mercury lamps that have emission bands in the UV-A, UV-B and UV-C regions of the electromagnetic spectrum, UV-LED lamps emit radiation in the UV-A region. Moreover, current UV-LED lamps emit quasi monochromatic radiation, i.e. only emit at one wavelength, such as 365 nm, 385 nm, 395 nm or 405 nm.

[0009] Pigments are extensively used in security inks to allow the production of security features of thedesired shade. However, it is known in the art that yellow pigments may negatively impact the curing performance of UV curable inks (W. A. Green, Industrial Photoinitiators, Chapter 5.5.1 p. 131 , CRC Press, 2010 I P. Gloeckner et al, Radiation curing, Coatings and printing inks, Chapter 3.6.2, p. 106-110). Thus, yellow, orange or green inks whose hue and saturation rely on a high concentration of yellow pigments may suffer from an insufficient curing performance, leaving unreacted monomers / oligomers and yielding security features and documents (such as for example banknotes) comprising said feature with insufficient chemical and / or physical resistance. Alternatively and / or additionally, high doses of UV light may be required to fully cure said yellow, orange or green inks however said high doses are not always possible with currently available equipments. Full cure the UV curable inks (offset, intaglio or letterpress inks) is essential to avoid set-off of the uncured inks on the printing machines used for the next printing steps (such as on the printing cylinders of the intaglio printing machine in the case of offset inks, since intaglio printing processes are usually applied next to offset printing processes).

[0010] Thus, there remains a need for UV-LED radically curable printing inks having a high viscosity, in particular UV-LED radically curable offset printing inks, UV-LED radically curable intaglio printing inks and UV-LED radically curable letterpress printing inks, preferably UV-LED radically curable offset printing inks, and processes for printing security features on security documents at high speed (i.e. industrial speed), said UV-LED curable printing inks exhibiting good curing properties and efficiency even at a low radiation dose, as well as, subsequently to the curing of said inks, they allow to produce printed security features exhibiting good optical properties.SUMMARY OF THE INVENTION[Oil] Accordingly, it is an object of the present invention to overcome the deficiencies of the prior art as discussed above. This is achieved by the provision of using more than about 10 wt.% of one or more pigments of formula (I) in pasty UV-LED radically curable printing inks comprising one or more radically curable (meth)acrylate compounds, one or more thioxanthone compounds and one or more amino containing synergists and one or more fillers and / or extenders.

[0012] Described herein are UV-LED radically curable printing inks having a viscosity in the range of about 2.5 to about 25 Pa s at 40°C and 1000 s-1for printing a security feature on a substrate, said UV-LED radically curable printing ink comprising: i) from about 30 wt.% to about 80 wt.% of one or more radically curable (meth)acrylate compounds; ii) from about 2 wt.% to about 20 wt.% of one or more thioxanthone compounds, iii) from about 0.5 wt.% to about 15 wt.% of one or more amino containing synergists, iv) more than about 1 wt.% of one or more fillers and / or extenders, and v) more than about 10 wt.% of the one or more pigments of formula (I):wherein Am are each independently a hydrogen atom, an halogen atom, a methyl group, an ethyl group, a methoxy group or a ethoxy group, preferably a hydrogen atom, an halogen atom, a methyl group or an ethyl group and m are each independently an integer of 1 to 4, the weight percents being based on the total weight of the UV-LED radically curable printing ink.

[0013] The UV-LED radically curable printing inks described herein preferably have a viscosity in the range of about 2.5 to about 35 Pa s at 40°C and 1000 s-1.

[0014] The UV-LED radically curable printing inks described herein are being curable upon exposure to radiation having a wavelength in the range from 315 to 415 nm, preferably 350 to 415 nm.

[0015] Described herein are processes for printing one or more security features on a substrate by printing process, preferably an offset, intaglio or letterpress printing process, more preferably an offset printing process, said process comprising the steps of applying the UV-LED radically curable printing ink described herein so as to form an ink layer and exposing the ink layer to UV light, preferably by exposure to one or more wavelengths of between about 350 nm and about 415 nm, more preferably by exposure to UV light at 365 nm and / or 385 nm and / or 395 nm and / or 405 nm, emitted by a UV-LED light source; preferably said exposure is carried out at a dose of at least 50 mJ / cm2to cure said ink layer with the UV-LED light source.

[0016] Also described herein are security features consisting of cured ink layers made from the UV-LED radically curable printing inks described herein. Described herein are uses of the security features described herein for the protection of a security document, value document or article against counterfeiting or fraud and security documents, value documents or articles comprising the one or more printed security features described herein.

[0017] Also described herein are security documents comprising the substrate described herein and the one or more printed security features described herein.

[0018] Also described herein are uses of the one or more pigments of formula (I) described herein in an amount of at least about 10 wt.% for producing a UV-LED radically curable printing ink having a viscosity in the range of about 2.5 to about 25 Pa s at 40°C and 1000 s-1, said UV-LED radically curable printing ink being suitable for printing one or more security features on a security document by a printing process, preferably an offset, an intaglio or letterpress printing process, more preferably an offset printing process, said UV-LED radically curable printing ink comprising from about 30 wt.% to about 80 wt.% of the one or more radically curable (meth)acrylate compounds described herein and from about 2 wt.% to about 20 wt.% of the one or more thioxanthone compounds described herein, from about 0.5 wt.% to about 15 wt.% of the one or more amino containing synergists described herein and more than about 1 wt.% of the one or morefillers and / or extenders described herein, the weight percents being based on the total weight of the UV- LED radically curable printing ink.DETAILED DESCRIPTIONDefinitions

[0019] The following definitions clarify the meaning of the terms used in the description and in the claims.

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

[0021] As used herein, the term “about” means that the amount, value or limit 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. For example, the phrase “about 100” denotes a range of 100 ± 5, i.e. the range from 95 to 105. Generally, when the term “about” is used, it can be expected that similar results or effects according to the invention can be obtained within a range of ±5% of the indicated value. However, a specific amount, value or limit supplemented with the term "about" is intended herein to disclose as well the very amount, value or limit as such, i.e. without the "about" supplement.

[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 “one or more” means one, two, three, four, etc.

[0024] The term “comprising” as used herein is intended to be non-exclusive and open-ended. Thus, for instance an ink 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 “an ink comprising a compound A” may also (essentially) consist of the compound A.

[0025] 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.

[0026] The term "security document" refers to a document which is usually protected against counterfeit or fraud by at least one security feature. Examples of security documents include without limitation value documents and value commercial goods.

[0027] The descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable other persons skilled in the art to best use the present invention and various embodiments with various modifications as are suited to the particular use contemplated.

[0028] The present invention provides UV-LED radically curable printing inks having a high viscosity (referred therein as viscous or pasty inks), in particular UV-LED radically curable offset printing inks, UV- LED radically curable intaglio printing inks and UV-LED radically curable letterpress inks, for producing(printing) one or more security features on a substrate, preferably a security document, by a printing process, preferably an offset printing process, an intaglio printing process, or a letterpress printing process, more preferably by an offset printing process or an intaglio printing process. The present invention further provides printed security features consisting of cured ink layers made from the UV-LED radically curable printing inks described herein and security documents comprising the one or more printed security features described herein. The UV-LED radically curable printing inks described herein are being curable upon exposure to radiation having a wavelength in the range from 315 to 415 nm, preferably 350 to 415 nm.

[0029] According to one embodiment, the UV-LED radically curable printing inks described herein are applied by an offset printing step, wherein said offset printing may be a wet printing process or a dry offset printing process.

[0030] According to one embodiment, the UV-LED radically curable printing ink described herein is an intaglio printing ink and is applied by an intaglio printing step.

[0031] According to one embodiment, the UV-LED radically curable printing ink described herein is a letterpress printing ink and is applied by a letterpress printing step.

[0032] The one or more radically curable (meth)acrylate compounds of the UV-LED radically curable printing ink described herein undergo curing in the presence of the one or more thioxanthones described herein and the one or more amino containing synergists described herein and optionally one or more additional photoinitiators described herein by exposure to UV light, preferably by exposure to one or more wavelengths of between about 350 nm and about 415 nm, more preferably by exposure to UV light at 365 nm and / or 385 nm and / or 395 nm and / or 405 nm, emitted by a UV-LED light source; preferably said exposure is carried out at a dose of at least 50 mJ / cm2to cure said ink layer with the UV-LED light source. As known by the man skilled in the art, the UV-LED radically curable offset printing inks described herein could also be suitable for curing using medium-pressure mercury lamps.

[0033] The UV-LED radically curable printing ink described herein may also be exposed to UV light emitted by the UV-LED light source in a first step, and subsequently exposed to light by one or more mediumpressure mercury light sources in a second step. Mercury lamps advantageously emit on a wide range of wavelengths in the UV-A, UV-B and UV-C range.

[0034] The UV-LED radically curable offset printing ink described herein preferably has a viscosity in the range of about 2.5 to about 35 Pa s at 40°C and at a shear rate of 1000 s-1, preferably between about 2.5 Pa s and about 25 Pa s, more preferably between 2.5 Pa s and 10 Pa s, wherein said viscosity values are measured with a Haake Roto-Visco RV1 with a cone 2 cm 0.5°, linear speed increase 0-1000 sec1in 30 seconds.

[0035] The UV-LED radically curable intaglio printing ink described herein preferably has a viscosity in the range of about 2.5 Pa s and 35 Pa s, preferably between about 5 Pa s and about 30 Pa s, more preferably between about 10 Pa s and about 25 Pa s at 40°C and at a shear rate of 200 s-1, wherein said viscosity values are measured with 40°C and 1000 sec1with a Haake Roto Visco 1 rotational rheometer (C20 / 0.50).

[0036] The UV-LED radically curable letterpress printing ink described herein preferably has a viscosity in the range of about 2.5 Pa s and 35 Pa s, preferably between about 5 Pa s and about 30 Pa s, more preferably between about 10 Pa s and about 25 Pa s at 40°C and at a shear rate of 1000 s-1, wherein said viscosity values are measured with a Haake Roto-Visco RV1 with a cone 2 cm 0.5°, linear speed increase 0-1000 sec1in 30 seconds.

[0037] The UV-LED radically curable printing ink described herein comprises radically curable (meth)acrylate compounds. The radically curable (meth)acrylate compounds described herein are present in a total amount from about 30 wt.% to about 80 wt.%, preferably from about 40 wt.% to about 80 wt.%, the weight percents being based on the total weight of the UV-LED radically curable printing ink described herein.

[0038] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable offset printing ink and comprises the one or more radically curable (meth)acrylate compounds described herein in a total amount preferably from about 30 wt.% to about 80 wt.%, preferably from about 40 wt.% to about 80 wt.%, the weight percents being based on the total weight of the UV-LED radically curable offset printing ink described herein.

[0039] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable intaglio printing ink and comprises the one or more radically curable (meth)acrylate compounds described herein in a total amount preferably from about 30 wt.% to about 60 wt.%, preferably from about 30 wt.% to about 50 wt.%, the weight percents being based on the total weight of the UV-LED radically curable intaglio printing ink described herein.

[0040] 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 layer or coating.

[0041] Preferably, at least one of the one or more radically curable (meth)acrylate compounds described preferably consist of one or more radically curable (meth)acrylate oligomer and at least one of the one or more radically curable (meth)acrylate compounds described consist of a radically curable (meth)acrylate monomer. The term “(meth)acrylate” in the context of the present invention refers to the acrylate as well as the corresponding methacrylate.

[0042] The radically curable (meth)acrylate oligomers described herein are preferably selected from the group consisting of epoxy (meth)acrylates, (meth)acrylated oils, (meth)acrylated epoxidized oils, polyester (meth)acrylates, aliphatic or aromatic polyurethane (meth)acrylates, polyacrylic acid (meth)acrylates, polyacrylate esters (meth)acrylates and mixtures thereof, more preferably selected from the group consisting of epoxy (meth)acrylates, polyester (meth)acrylates, aliphatic or aromatic polyurethane (meth)acrylates and mixtures thereof.(043} The radically curable oligomers described herein are preferably (meth)acrylate oligomers which may be branched or essentially linear, and the (meth)acrylate functional group or groups, respectively, can be terminal groups and / or pendant side groups bonded to the oligomer backbone. Preferably, the radically curable oligomers are selected from the group consisting of (meth)acrylic oligomers, urethane (meth)acrylate oligomers, polyester (meth)acrylate oligomers, polyether based (meth)acrylate oligomers, epoxy (meth)acrylate oligomers and mixtures thereof, more preferably selected from the group consisting of polyester (meth)acrylate oligomers, epoxy (meth)acrylate oligomers and mixtures thereof.

[0044] Suitable examples of epoxy (meth)acrylate oligomers include without limitation aliphatic epoxy acrylates such as e.g. acrylated epoxy soybean oil, and aromatic epoxy acrylates. Suitable examples of aromatic epoxy acrylates include in particular the oligomeric products resulting from the reaction of bisphenol-A, epichlorhydrin and (meth)acrylic acid. Suitable compounds are commercially sold for example by IGM Resins under the trademark PHOTOMER® 3015 and 3016, by Arkema under the trademark Sartomer® CN104, by Allnex under the trademark Ebecryl® 1606 and 3720 or by AGI-DSM under thetrademarks NeoRad™ E10, AgiSyn™ 1010, 1020, 1030 and 3050 and have a functionality (i.e. the number of acrylate moieties per molecule) of two. Pendant hydroxy groups may be substituted with fatty acids to impart hydrophobic properties to the oligomers (AGI-DSM NeoRad™ E-20 or AgiSyn™ 3051). Since their viscosity may be very high, such oligomers may be diluted with one or more radically curable (meth)acrylate monomers such as those described herein.

[0045] Polyester (meth)acrylate oligomers are the reaction products of a difunctional or multifunctional polyol (such as polyethylene glycol, trimethylolpropane or pentaerythritol, optionally ethoxylated or propoxylated), an aliphatic or aromatic polyacid (such as succinic acid or terephthalic acid) and (meth)acrylic acid. Pendant hydroxy groups may be substituted with fatty acids to impart hydrophobic properties to the oligomers. Their functionality ranges from 2 to 6. Suitable compounds are commercially sold by Allnex under the trademark Ebecryl® 450, 657, 1657, 870, 1870, 873 and 875, by IGM Resins under the trademark PHOTOMER® 5450 or by AGI-DSM under the trademarks NeoRad™ P-41 , P-60, P-61 , P- 65, AgiSyn™ 705, 706 and 714).

[0046] The radically curable (meth)acrylate monomers described herein are preferably selected from the group consisting of mono(meth) acrylates, di(meth)acrylates, tri(meth)acrylates, tetra(meth)acrylates, penta(meth)acrylates, hexa(meth)acrylates and mixtures thereof, more preferably selected from the group consisting of di(meth)acrylates, tri(meth)acrylates, tetra(meth)acrylates, and mixtures thereof, and still more preferably selected from the group consisting of tri(meth)acrylates, tetra(meth)acrylates, and mixtures thereof.

[0047] Preferred examples of mono(meth)acrylates include 2(2-ethoxyethoxy)ethyl (meth)acrylate, 2- phenoxyethyl (meth)acrylate, C12 / C14 alkyl (meth)acrylate, C16 / C18 alkyl (meth)acrylate, caprolactone (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, nonylphenol (meth)acrylate, isobornyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, octyldecyl (meth)acrylate, tridecyl (meth)acrylate, methoxy polyethylene glycol) (meth)acrylate, polypropylene glycol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 1 ,3-butylene glycol di(meth)acrylate, 1 ,4-butanediol di(meth)acrylate, 1 ,6-hexanediol di(meth)acrylate, 3-methyl-1 ,5-pentanedioldi(meth)acrylate, alkoxylated di(meth)acrylate, esterdiol di(meth)acrylate as well as mixtures thereof.

[0048] Preferred examples of di(meth)acrylates include bisphenol A di(meth)acrylates, alkoxylated (such as for example ethoxylated and propoxylated) bisphenol A di(meth)acrylate, bisphenol A diglycidyl ether di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipropyleneglycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate as well as mixtures thereof.

[0049] Preferred examples of tri(meth)acrylates include trimethylolpropane tri(meth)acrylates, alkoxylated (such as for example ethoxylated and propoxylated) trimethylolpropane tri(meth)acrylates, alkoxylated (such as for example ethoxylated and propoxylated) glycerol tri(meth)acrylates, pentaerythritol tri(meth)acrylates, alkoxylated pentaerythritol tri(meth)acrylates, alkoxylated (such as for example ethoxylated and propoxylated) pentaerythritol tri(meth)acrylates as well as mixtures thereof.

[0050] Preferred examples of tetra (meth)acrylates include 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 asmixtures thereof.

[0051] The UV-LED radically curable printing ink described herein comprises from about 2 wt.% to about 20 wt.%, preferably about 3 wt.% to about 15 wt.%, more preferably about 3 wt.% to about 10 wt.%, of the one or more thioxanthone compounds described herein, the weight percents being based on the total weight of the UV-LED radically curable printing ink described herein.

[0052] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable offset printing ink and comprises the one or more thioxanthone compounds described herein in a total amount from about 2 wt.% to about 20 wt.%, preferably about 3 wt.% to about 15 wt.%, more preferably about 3 wt.% to about 10 wt.%, the weight percents being based on the total weight of the UV-LED radically curable offset printing ink described herein.

[0053] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable intaglio printing ink and comprises the one or more thioxanthone compounds described herein in a total amount from about 2 wt.% to about 20 wt.%, preferably about 3 wt.% to about 15 wt.%, more preferably about 3 wt.% to about 10 wt.%, the weight percents being based on the total weight of the UV-LED radically curable intaglio printing ink described herein.

[0054] The one or more thioxanthone compounds are preferably selected from the group consisting of 2- isopropyl-9H-thioxanthen-9-one (CAS 5495-84-1); 4-(1-methylethyl)-9H-thioxanthen-9-one (CAS 83846- 86-0); 2,4-diethyl-9H-thioxanthen-9-one (CAS 82799-44-8); 2-chloro-9H-thioxanthen-9-one (CAS 86-39-5); 1-chloro-4-propoxy-9H-thioxanthen-9-one (CAS 142770-42-1); 1 ,3-di[[a-[1-chloro-9-oxo-9H-thioxanthen-4- yl)oxy]acetylpoly[oxy(1-methylethylene)]]oxy]-2,2-bis[[a-[1-cloro-9-oxo-9H-thioxanthen-4- yl)oxy]acetylpoly[oxy(1-methylethylene)]]oxymethylpropane (CAS 1003567-83-6); a-[2-[(9-oxo-9H- thioxanthenyl)oxy]acetyl]-oj-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]-poly(oxy-1 ,4-butanediyl (CAS 813452-37-8); 2-[2-[1-[2-[[2-(9-oxothioxanthen-2-yl)oxyacetyl]amino]-3-[1-[2-(2-prop-2- enoyloxyethoxy)ethoxy]ethoxy]-2-[1-[2-(2-prop-2- enoyloxyethoxy)ethoxy]ethoxymethyl]propoxy]ethoxy]ethoxy]ethyl prop-2-enoate (CAS 1427388-03-1); a- [2-[(9-Oxo-9H-thioxanthenyl)oxy]acetyl]-oj-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]-poly(oxy-1 ,4- butanediyl) (CAS 813452-37-8); oligomeric and polymeric compounds thereof (CAS 515139-51-2 and 2055335-46-9); and mixtures thereof. The one or more thioxanthone compounds are more preferably selected from the group consisting of 2-isopropyl-9H- thioxanthen-9-one (CAS 5495-84-1); a-[2-[(9-oxo- 9H-thioxanthenyl)oxy]acetyl]-oj-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]-poly(oxy-1 ,4-butanediyl (CAS 813452-37-8); 2-[2-[1-[2-[[2-(9-oxothioxanthen-2-yl)oxyacetyl]amino]-3-[1-[2-(2-prop-2- enoyloxyethoxy)ethoxy]ethoxy]-2-[1-[2-(2-prop-2- enoyloxyethoxy)ethoxy]ethoxymethyl]propoxy]ethoxy]ethoxy]ethyl prop-2-enoate (CAS 1427388-03-1); 4- (1-methylethyl)-9H-thioxanthen-9-one (CAS 83846-86-0); 1-chloro-4-propoxy-9H-thioxanthen-9-one (CAS 142770-42-1); 1 ,3-di[[a-[1-chloro-9-oxo-9H-thioxanthen-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]]oxy]- 2,2-bis[[a-[1-chloro-9-oxo-9H-thioxanthen-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]]oxymethylpropane (CAS 1003567-83-6); oligomeric and polymeric compounds thereof (CAS 2055335-46-9); and mixtures thereof and still more preferably 2-isopropyl-9H-thioxanthen-9-one (CAS 5495-84-1); 4-(1-methylethyl)-9H- thioxanthen-9-one (CAS 83846-86-0); (1 ,3-di[[a-[1-chloro-9-oxo-9H-thioxanthen-4-yl)oxy]acetylpoly[oxy(1- methylethylene)]]oxy]-2,2-bis[[a-[1 -cloro-9-oxo-9H-thioxanthen-4-yl)oxy]acetylpoly[oxy(1- methylethylene)]]oxymethylpropane (CAS 1003567-83-6); and mixtures thereof.

[0055] A particularly suitable example of thioxanthone compounds is commercially available under the name Omnirad ITX from IGM Resins.

[0056] The UV-LED radically curable printing ink described herein comprises 0.5 wt.% to about 15 wt.%, preferably from about from about 1 wt.% to about 10 wt.% and still more preferably from about from about 1.5 wt.% to about 5 wt.%, of the one or more amino containing synergists described herein, the weight percents being based on the total weight of the UV-LED radically curable printing ink described herein. The one or more amino containing synergists described herein consist of compounds having an amino group.

[0057] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable offset printing ink and comprises the one or more amino containing synergists described herein in a total amount from about 0.5 wt.% to about 15 wt.%, preferably about 0.5 wt.% to about 10 wt.%, more preferably about 1 wt.% to about 5 wt.%, the weight percents being based on the total weight of the UV-LED radically curable offset printing ink described herein.

[0058] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable intaglio printing ink and comprises the one or more amino containing synergists described herein in a total amount from about 0.5 wt.% to about 15 wt.%, preferably about 0.5 wt.% to about 10 wt.%, more preferably about 1 wt.% to about 5 wt.%, the weight percents being based on the total weight of the UV-LED radically curable intaglio printing ink described herein.

[0059] The one or more amino containing synergists are preferably selected from the group consisting of aliphatic and aromatic tertiary amines. Aliphatic amines include without limitation N-methyldiethanolamine (CAS 105-59-9), triethanolamine (CAS 102-71-6) and tri-isopropanolamine (CAS 122-20-3).

[0060] Aromatic tertiary amines include without limitation ethyl 4-(dimethylamino)benzoate (CAS10287- 53-3); benzoic acid, 4-(dimethylamino)-, 2-ethylhexyl ester (CAS 21245-02-03); benzoic acid, 4- (dimethylamino)-, 3-methylbutyl ester (CAS 21245-01-2); benzoic acid, 2-(dimethylamino)ethyl ester (CAS 2208-05-1). However, such small molecules (having a molecular weight below about 400 g / mol) may be prone to migration and raise increasing EHS concerns.

[0061] For those reasons, amino containing synergists under an oligomeric form and having a higher molecular weight, in particular a molecular weight higher than 400 g / mol were developed and are suitable for the present invention. Suitable amino containing oligomeric synergists include without limitation benzoic acid, 4-(dimethylamino)-, 1 ,1 '-[(methylimino)di-2,1 -ethanediyl] ester (CAS 925246-00-0, sold as Esacure A198 by IGM Resins, molecular weight 414 g / mol); poly(oxy-1 ,2-ethanediyl), a-[4-(dimethylamino)benzoyl]- oj-[[4-(dimethylamino)benzoyl]oxy]- (CAS 71512-90-8, sold as Omnipol ASA by IGM Resins, molecular weight 510 g / mol); a mixture of oxirane, 2-methyl-, polymer with oxirane, 4-(dimethylamino)benzoate (CAS 1003557-17-2) and poly[oxy(methyl-1 ,2-ethanediyl)], a-hydro-oj-[[4-(dimethylamino)benzoyl]oxy]-, ether with 2,2-bis(hydroxymethyl)-1 ,3-propanediol (4:1) (CAS 1003567-84-7), sold as Speedcure 7040 by Arkema (molecular weight > 1000 g / mol); polymeric 4-dimethylaminobenzoic ester coinitiator sold under the trademark Genopol® AB-2 (CAS 1816296-43-1 , molecular weight 900 g / mol) by Rahn.

[0062] Another way of avoiding the migration problem is to synthesize amino containing synergists comprising one or more (meth)acrylate groups, such that the molecule reacts to form a part of the polymeric backbone and is no longer able to migrate. Such amino containing synergists are referred in the art as acrylated oligoamines, acrylated amine synergists or amino-modified (meth)acrylate monomers or oligomers. Usually, one or more pendant (meth)acrylate groups of the parent compound, such as a polyfunctional (meth)acrylate monomer, an epoxy (meth)acrylate oligomer or a polyether (meth)acrylateoligomer, are reacted with one or more secondary aliphatic or aromatic amines to generate a molecule comprising one or more tertiary aliphatic or aromatic amines and one or more (meth)acrylate groups. Suitable amino containing synergists are commercially sold e.g. by Allnex under the trademark EBECRYL® 80, 81 , 83, 85, 880, LEO 10551 , LEO 10552, LEO 10553, 7100, 7110, P104, P115, P116 and LED 03, by Arkema under the trademark SARTOMER® CN501 , CN550, CN UVA421 , CN3705, CN3715, CN3755, CN381 and CN386, by Rahn underthe trademark GENOMER* 5142, 5161 , 5271 and 5275, by IGM Resins under the trademark PHOTOMER® 4068, 4771 , 4780, 4967, 5006, 4775, 5662, 5850 and 5930) or by AGI- DSM under the trademarks NeoRad™ P-80, P-81 , P-82, P-85, AgiSyn™ 701 , 702, 703 and 3052.

[0063] Preferably, the one or more amino containing synergists are selected from the group consisting of benzoic acid, 4-(dimethylamino)-, 1 ,1 '-[(methylimino)di-2,1-ethanediyl] ester (CAS 925246-00-0, Esacure A198), mixture of oxirane, 2-methyl-, polymer with oxirane, 4-(dimethylamino)benzoate (CAS 1003557-17- 2) and poly[oxy(methyl-1 ,2-ethanediyl)], a-hydro-oj-[[4-(dimethylamino)benzoyl]oxy]-, ether with 2,2- bis(hydroxymethyl)-1 ,3-propanediol (4:1) (CAS 1003567-84-7) (Speedcure 7040), Ebecryl® 80 (Allnex), Genomer* 3457 and 3480 (Rahn), PHOTOMER®5662 (IGM Resins), NeoRad™ P-82 and AgiSyn™ 701 (AGI-DSM).

[0064] The UV-LED radically curable printing ink described herein further comprises one or more fillers and / or extenders in a total amount more than about 0.5 wt.%, preferably from about 1 wt.% to about 55 wt.%, more preferably from about 1 wt.% to about 40 wt.%, still more preferably from about 1 to about 35 wt.%, the weight percents being based on the total weight of the UV-LED radically curable printing ink.

[0065] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable offset printing ink and comprises the one or more fillers and / or extenders described herein in a total amount of more than or equal to about 0.5 wt.%, preferably from about 0.5 wt.% to about 10 wt.%, preferably from about 0.5 to about 5 wt.%, the weight percents being based on the total weight of the UV-LED radically curable offset printing ink described herein.

[0066] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable intaglio printing ink and comprises the one or more fillers and / or extenders described herein in a total amount more than or equal to about 0.5 wt.%, preferably from about 10 wt.% to about 55 wt.%, preferably from about 20 to about 55 wt.%, the weight percents being based on the total weight of the UV-LED radically curable intaglio printing ink described herein.

[0067] Preferably the one or more fillers an / or extenders are selected from the group consisting of talcs, micas (e.g. muscovites), montmorillonites, bentonites, wollastonites, halloysites, calcined clays, china clays, carbonates (e.g. calcium carbonate, magnesium carbonate), silicates (e.g. magnesium silicate, aluminum silicate), vermiculites, amorphous silica (e.g. fumed silica, precipitated silica, silica flour), wood flours (sawdust), natural fibers, synthetic fibers (such as carbon fibers or carbon nanotubes) and mixtures thereof; preferably selected from the group consisting of talcs, micas, wollastonites, calcined clays, carbonates, amorphous silica and mixtures thereof.

[0068] The UV-LED radically curable printing ink described herein further comprises more than about 10 wt.% (x > 10 wt.%) of the one or more pigments of formula (I) described herein, preferably in a total amount of more than or equal to about 10.5 wt.% (x > 10.5 wt.%), preferably from more than about 10 wt.% to less than or equal to about 55 wt.% (10 wt.% < x < 55 wt.%), preferably more than about 12.5 wt.% (x > 12.5 wt.%), more preferably in a total amount from more than about 12.5 to less than or equal to about 30 wt.% (12.5 wt.% < x < 30 wt.%), still more preferably in a total amount from more than about 12.5 to less than orequal to about 25 wt.% (12.5 wt.% < x < 25 wt.%), the weight percents being based on the total weight of the UV-LED radically curable intaglio printing ink described herein:wherein Am are each independently a hydrogen atom, an halogen atom, a methyl group, an ethyl group, a methoxy group or a ethoxy group, and m are each independently an integer of 1 to 4.

[0069] The pigments of formula (I) exist as tautomers having structures represented by, for example formulas (l-i) and (l-ii), wherein said tautomers are also encompassed in the present invention:(l-i) (l-ii)

[0070] According to a preferred embodiment, the pigments are of formula (I), wherein Am are each independently hydrogen atom, an halogen atom, a methyl group or an ethyl group, and m are each independently an integer of 1 to 4; more preferably Am are each independently a hydrogen atom, or an halogen atom, still more preferably a hydrogen atom or an halogen atom, wherein the halogen is fluorine, chlorine or bromine, preferably chlorine or bromine, more preferably bromine. A particularly suitable example of pigments of formula (I) described herein is commercially available under the name Paliotol® Yellow D0960 (CAS 30125-47-4) from BASF.

[0071] The UV-LED radically curable printing ink described herein may further comprise less than about 5 wt.%, preferably from about 0.1 wt.% to about 5 wt.%, more preferably from about 0.1 wt.% to about 4 wt.%, of one or more acyl phosphine oxide compounds, the weight percents being based on the total weight of the UV-LED radically curable printing ink described herein.

[0072] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable offset printing ink and comprises the one or more acyl phosphine oxide compounds described herein in a total amount less than about 5 wt.%, preferably from about 0.1 wt.% to about 5 wt.%, more preferably from about 0.1 wt.% to about 4 wt.%, the weight percents being based on the total weight of the UV-LED radically curable offset printing ink described herein.

[0073] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable intaglio printing ink and comprises the one or more acyl phosphine oxide compounds described herein in a total amount less than about 5 wt.%, preferably from about 0.1 wt.% to about 5 wt.%, more preferably from about 0.1 wt.% to about 4 wt.%, preferably from about 10 wt.% to about 55 wt.%, preferably from about 20 to about 55 wt.%, the weight percents being based on the total weight of the UV- LED radically curable intaglio printing ink described herein.

[0074] The one or more acyl phosphine oxide compounds are preferably selected from the group consisting of (1 ,4,6-trimethylbenzoyl)diphenylphosphine oxide (CAS 75980-60-8); 2,4,6-trimethylbenzoyl- ethoxylphenylphosphine oxide (CAS 84434-11-7); phenyl-bis(2,4,6-trimethylbenzoyl)phosphine oxide (CAS 162881-26-7); bis(1 ,6-dimethoxybenzoyl)(1 ,4,4-trimethylpentyl)phosphine oxide (CAS 145052-34- 2); ethyl (3-benzoyl-2,4,6-trimethylbenzoyl)(phenyl)phosphinate (CAS 1539267-56-5); a,a’,a”-1 ,2,3- propanetriyltris[oj-[[phenyl(1 ,4,6-trimethylbenzoyl)phosphinyl]oxy]-poly(oxy-1 ,2-ethanediyl) (CAS 1834525-17-5); and mixtures thereof. A particularly suitable example of acyl phosphine oxide compounds is commercially available under the name Speedcure TPO-L (CAS 84434-11-7) from Lamberti.

[0075] The UV-LED radically curable printing ink described herein may further comprise less than about 5 wt.%, preferably from about 0.1 wt.% to about 5 wt.%, more preferably from about 0.1 wt.% to about 4 wt.%, of one or more additional photoinitiators selected from the group consisting of alpha-hydroxyketones, acetophenones, ketosulfones, benzyl ketals, benzoin ethers, phenylglyoxylates and mixtures thereof, the weight percents being based on the total weight of the UV-LED radically curable printing ink described herein.

[0076] Suitable examples of alpha-hydroxyketones include without limitation 2-hydroxy-2- methylpropiophenone (CAS 7473-98-5); 2-hydroxy-4’-hydroxyethoxy-2-methylpropiophenone (CAS 106797-53-9); 2-hydroxy-1-[4-[4-(1-hydroxy-2-methylpropanoyl)phenoxy]phenyl]-2-methylpropan-1-one (CAS 474510-57-1); (l-hydroxycyclohexyl)phenylmethanone (CAS 947-19-3); 2-hydroxy-1-[4-[4-(1- hydroxy-2-methylpropanoyl)phenoxy]phenyl]-2-methylpropan-1 -one (CAS 71868-15-0); 1 -[2,3-dihydro-1 - [4-(1 -hydroxy-2-methyl-1 -oxopropyl)phenyl]-1 ,3,3-trimethyl-1 H-inden-5-yl]-2-hydroxy-2-methyl-1 - propanone (CAS 135452-43-6); ar-(1-hydroxy-2-methyl-1 -oxopropyl) (l-methylethenyl)-benzene homopolymer (CAS 163702-01-0,); a-(1 ,1-dimethyl-2-oxo-2-phenylethyl)-oj-hydroxy-poly(oxy-1 ,2- ethanediyl) (9CI) (CAS 554449-21-7); polymeric alpha-hydroxy-ketone (CAS 1842314-75-3).

[0077] Suitable examples of acetophenones include without limitation 2,2-diethoxyacetophenone; 2- ethylhexyl-4-dimethylaminobenzoate; and 2-methoxy-2-phenylacetophenone.

[0078] A suitable example of ketosulfone include without limitation 1-[4-(4- benzoylphenylsulfanyl)phenyl]-2-methyl-2-(4-methylphenylsulfonyl)propan-1-one.

[0079] A suitable example of benzyl ketals includes without limitation 2,2-dimethoxy-2- phenylacetophenone.

[0080] Suitable examples of benzoin ethers include without limitation benzoinmethyl ether; benzoinisopropyl ether; 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.

[0081] 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.

[0082] Suitable examples of aromatic ketones include without limitation benzophenone; 2- methylbenzophenone; 3-methylbenzophenone; 4-methyl benzophenone; 2,4,6-trimethyl benzophenone; mixture of 4-methyl benzophenone and 2,4,6-trimethyl benzophenone; 3,3'-dimethyl-4- methoxybenzophenone; 2-hydroxybenzophenone; 3-hydroxybenzophenone; 4-hydroxybenzophenone; 4- chlorobenzophenone; 4,4'-dichlorobenzophenone methyl ortho benzoylbenzoate; 4-phenyl benzophenone; 4-(4-methylphenylthio)-benzophenone; 4,4’-bis(dimethylamino)-benzophenone (Michler’s ketone); 4,4’- bis(diethylamino)-benzophenone; 4,4’-bis(ethylmethylamino)-benzophenone; and 4,4’-diphenoxy- benzophenone; 4,4’-bis(4-isopropyl-phenoxy)-benzophenone.

[0083] 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.

[0084] The UV-LED radically curable printing ink described herein may further comprise one or more waxes in a total amount preferably less than about 10 wt.%, more preferably from about 0.1 wt.% to about 5 wt.%, the weight percents being based on the total weight of the UV-LED radically curable printing ink.

[0085] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable offset printing ink and comprises the one or more waxes described herein in a total amount from about 0.1 wt.% to about 5 wt.%, preferably from about 0.1 wt.% to about 3 wt.%, more preferably from about 0.1 to about 2 wt.%, the weight percents being based on the total weight of the UV- LED radically curable offset printing ink described herein.

[0086] According to one embodiment, the UV-LED radically curable printing ink described herein is a UV- LED radically curable intaglio printing ink and comprises the one or more waxes described herein in a total amount from about 0.1 wt.% to about 5 wt.%, preferably from about 0.5 wt.% to about 7 wt.%, more preferably from about 1 to about 5 wt.%, the weight percents being based on the total weight of the UV- LED radically curable intaglio printing ink described herein.

[0087] Preferably the one or more waxes are selected from the group consisting of synthetic waxes, petroleum waxes, natural waxes, and mixtures thereof, more preferably the one or more waxes are selected from the group consisting of amide waxes, erucamide waxes, paraffin waxes, polyethylene waxes, polypropylene waxes, fluorocarbon waxes, polytetrafluoroethylene waxes, Fischer-Tropsch waxes, silicone fluids, bee waxes, candelilla waxes, montan waxes, carnauba waxes, rice bran waxes and mixtures thereof, still more preferably selected from the group consisting of paraffin waxes, polyethylene waxes, fluorocarbon waxes, polytetrafluoroethylene waxes, carnauba waxes and mixtures thereof.

[0088] The UV-LED radically curable offset printing ink described herein may further comprise one or more coloring agents, preferably coloring dyes and / or coloring pigments such as red dyes / pigments, green dyes / pigments, blue dyes / pigments, violet dyes / pigments to fine tune the shade of the security features described herein. The one or more coloring agents described herein may be added in a small amount (up to 15 wt.% depending on the dyes and / or pigments) provided that these coloring agents do not negativelyinterfere with the curing properties of the UV-LED radically curable offset printing inks described herein.

[0089] The UV-LED radically curable offset printing ink described herein may further comprise one or more machine readable materials selected from the group consisting of luminescent materials, magnetic materials, IR absorbing materials and mixtures thereof provided that the curing properties of the UV-LED radically curable offset printing inks described herein are not affected. As used herein, the term “machine readable material” refers to a material which exhibits at least one distinctive property which is detectable by a device or a machine, such as for example a CCD or CMOS sensor, a magnetic detector (when the machine readable materials have magnetic properties) or an IR-camera (when the machine readable materials have IR-absorbing properties), and which can be comprised in a security feature made from the UV-LED radically curable printing ink described herein so as to confer a way to authenticate said security feature by the use of a particular equipment for its detection and / or authentication. When present, the one or more machine readable materials described herein are preferably present in a total amount from about 1 wt.% to about 60 wt.%, preferably from about 5 wt.% to about 40 wt.%, the weight percents being based on the total weight of UV-LED radically curable printing ink.

[0090] The UV-LED radically curable offset printing ink described herein may further comprise one or more markers and / or taggants.

[0091] The UV-LED radically curable printing ink described herein may further comprise one or more UV- stabilizers in order to stabilize said ink in particular during its storage. Typical examples of suitable UV- stabilizers include without limitation, hydroquinone, hydroquinone monomethyl ether, 4-t-butylcatechol, 4- t-butyl-phenol, 2,6-di-t-butyl-4-methyl-phenol (BHT), pyrogallol, phenothiazine (PTZ), 2,4- diazabicyclo[2.2.2] octane (DABCO), copper (II) salts (such as e.g. copper (II) phenoxide, copper (II) acetylacetonate, copper (II) gluconate, copper (II) tartrate, copper (II) acetate, copper (II) carbamate, copper (II) thiocarbamate, copper (II) dithiocarbamate or copper (II) dimethyl dithiocarbamate), copper (I) salts (such as e.g. copper (I) chloride or copper (I) acetate), tris[N-(hydroxyl-KO)-N-(nitroso- KO)benzenaminato]-aluminum and mixtures thereof. When present, the one or more UV-stabilizers described herein are present in the UV-LED radically curable printing ink in a total amount from about 0.1 wt.% to about 5 wt.%, preferably in a total amount from about 0.5 wt.% to about 2 wt.%, the weight percents being based on the total weight of the UV-LED radically curable printing ink.

[0092] As known by those skilled in the art, the UV-LED radically curable printing ink described herein may further comprise one or more solvents and / or diluents. However, when present, said one or more solvents are present in a total amount of less than 5 wt.%, preferably of less than 2wt.%, the weight percents being based on the total weight of the UV-LED radically curable printing ink.

[0093] The UV-LED radically curable printing ink described herein may further comprise additives that include, but are not limited to, one or more of the following components as well as combinations of these: anti-settling agents, anti-foaming agents, surfactants and other processing aids known in the field of inks. Additives described herein may be present in the UV-LED radically curable printing ink described herein in amounts and in forms known in the art, including in the form of so-called nano-materials where at least one of the dimensions of the particles is in the range of 1 to 1000 nm.

[0094] The UV-LED radically curable printing ink described herein is typically prepared by a method comprising a step of dispersing, mixing and / or milling all the ingredients described herein. The one or more pigments of formula (I) described herein, the one or more thioxanthone compounds described herein, the one or more amine compounds described herein, the one or more acyl phosphine oxide compounds whenpresent and the optional one or more additional photoinitiators when present are added to the ink either during the dispersing / mixing / milling step of all other ingredients or may be added at a later stage (i.e. subsequently to the preparation of the printing ink vehicle).

[0095] As described herein, the process for producing the printed feature described herein comprises a step a) of applying the UV-LED radically curable printing ink, preferably the UV-LED radically curable offset printing ink or the UV-LED radically curable intaglio printing ink, more preferably the UV-LED radically curable offset printing ink, described herein by offset printing or by intaglio printings so as to form an ink layer, and b) of exposing the ink layer to UV light emitted by a UV-LED light source.

[0096] Should the UV-LED radically curable printing ink described herein be an intaglio printing ink, the process described herein comprises the steps of: a) inking an intaglio engraved printing plate with the UV- LED radically curable intaglio printing ink, b) wiping off any excess of the ink using a disposable fibrous material such as for example a paper or a tissue wiping system (“calico”), or a polymeric roll wiping system (“wiping cylinder”), b2) in case of the use of a wiping cylinder, cleaning said polymeric wiping cylinder with an alkaline aqueous wiping solution in combination with one or more mechanical means, c) printing the pattern or image with the intaglio engraved printing plate by applying the UV-LED radically curable intaglio printing ink onto a substrate such as those described herein, and d) curing the UV-LED radically curable intaglio printing ink as described herein.

[0097] According to one embodiment, said step described herein consists of exposing the ink layer to a light source or curing unit comprising a high-power light-emitting-diode lamp, wherein said exposure of the ink layer to UV light (curing step) is preferably carried out at a dose of at least 50 mJ / cm2. As described hereafter, the dose may be measured using a LEDCure™ radiometer (2.0 LLC) from EIT, Inc., U.S.A. Preferably, said step described herein consists of exposing the ink layer to a high-power light-emitting- diode lamp to one or more wavelengths between 350 and 415 nm. Typically, commercially available UV- LED sources use one or more wavelengths such as for example 365 nm, 385 nm, 395 nm and 405 nm. According to one embodiment, said curing step described herein consists of exposing the ink layer to a single wavelength between 350 and 415 nm, more preferably by exposure to UV light at 365 nm, 385 nm, 395 nm or 405 nm.

[0098] The process described herein is particularly suitable for producing one or more printed security features on a substrate that is suitable as substrate for a security document, a decorative element or a decorative object. The one or more printed features described herein may be continuous or discontinuous.

[0099] 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, fiberbased substrates, preferably substrates based on cellulosic fibers such as paper, cellulose, papercontaining materials, glasses, metals or metalized materials, ceramics, polymer-based substrates, composite materials (e.g. substrates obtained by the lamination of paper layers and polymer films), 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), polycarbonates (PC), polyvinyl chlorides (PVC), polyamides, polyesters such as poly(ethylene terephthalate) (PET), poly(1 ,4- butylene terephthalate) (PBT), polyethylene 2,6-naphthoate) (PEN) and polyvinylchlorides (PVC). Typicalexamples 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 document described herein can be printed with any desired signs, including any symbols, images and patterns. In one preferred embodiment the security features are printed on a substrate selected from offset papers and fiduciary papers. Offset paper is manufactured from wood-pulp cellulose with properties that make the paper suitable for offset printing, including dimensional stability, resistance to curling, high surface strength, a surface free from foreign particles and a high level of resistance to moisture penetration. Typically the basis weight of offset paper is of 30 g / m2to 250 g / m2, preferably of 50 g / m2to 150 g / m2.

[0100] Fiduciary paper (also referred in the art as security paper) is manufactured from lignin-free, cottonpulp cellulose. Compared to offset papers, additional properties of fiduciary papers include enhanced mechanical resistance (especially resistance to tearing and wearing), resistance to soiling and treatment against degradation by micro-organisms (bacteria, virus and fungi). The mechanical resistance of fiduciary papers may be enhanced by the introduction into the paper (cotton-based) pulp of synthetic fibers, and the anti-soiling performance may be improved by coating or printing an anti-soil polymeric layer prior to printing or applying the features of the banknote. Usually, the treatment with biocides is combined with the anti-soil treatment. Typically, the fiduciary paper has a basis weight between 50 and 150 g / m2, preferably between 80 and 120 g / m2.

[0101] Furthermore, the use of fiduciary paper instead of offset paper adds an additional element of anticounterfeiting protection, since fiduciary paper is manufactured on special paper-making machines that are only available to manufacturers of security paper, and since the supply chain is protected such as to prevent the fiduciary paperfrom being diverted to counterfeiters. To the contrary of ordinary writing papers, fiduciary papers do not contain optical brighteners. Said optical brighteners are used to confer a whiter, brighter appearance to ordinary writing papers, but at the same time exhibit a strong blue fluorescence when exposed to UV light, while fiduciary papers remain comparatively dark under similar irradiation. Papers devoid of optical brighteners are not available outside the security domain, which means that bright blue fluorescence under UV light is already a sign of counterfeit (Optical Document Security, Third Ed., 2005, Artech House, 3.2.5 p. 71).

[0001] Typical examples of decorative elements or decorative objects include without limitation luxury goods, cosmetic packaging, automotive parts, electronic / electrical appliances, furniture and fingernail articles.

[0002] 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 protected against 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 includewithout 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.

[0102] The security document, decorative element and decorative object described herein may further comprise one or more additional layers or coatings either below or on top of the printed security feature described herein. Should the adhesion between the substrate and the printed security feature described herein and consisting of a cured ink layer made from the UV-LED radically curable offset printing ink described herein be insufficient, for example, due to the substrate material, a surface unevenness or a surface inhomogeneity, an additional layer, coating or a primer between the substrate and the printed feature might be applied as known for those skilled in the art.

[0103] With the aim of further increasing the security level and the resistance against counterfeiting and illegal reproduction of security documents, the substrate may contain watermarks, security threads, fibers, planchettes, luminescent compounds, windows, foils, decals, coatings and combinations thereof.

[0104] The substrate described herein on which the UV-LED radically curable printing ink described herein is applied, may consist of an intrinsic part of a security document, or alternatively, the UV-LED radically curable printing ink described herein is applied onto an auxiliary substrate such as for example a security thread, security stripe, a foil, a decal or a label and consequently transferred to a security document in a separate step.

[0105] Also described herein are uses of the one or more pigments of formula (I) described herein, in the amounts described herein, for producing the UV-LED radically curable printing ink described herein.

[0106] 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.

[0107] Further, all documents referred to throughout this specification are hereby incorporated by reference in their entirety as set forth in full herein.EXAMPLE

[0108] The present invention is now described in more details with reference to non-limiting examples. The Examples below provide more details for the preparation of UV-LED radically curable printing pasty inks, in particular UV-LED radically curable offset and intaglio printing inks, and use of the pigments of the formula (I) described herein, the one or more thioxanthone compounds and the one or more amino containing synergists in said inks according to the invention and comparative data. Table 1-1. Offset printing ink vehicleTable 1-2. PigmentsTable 1-3. Photoinitiators

[0109] The offset printing ink vehicle was prepared by mixing all the ingredients of Table 1-1 with aSpeedMixer™ (DAC 150 SP CM31 from Hauschild Engineering) at room temperature for three minutes.

[0110] The viscosity value of the offset printing ink vehicle provided in Table 1-1 was measured at 40°C and 1000 s-1with a Haake Roto- Visco RV1 with a cone 2 cm 0.5°, linear speed increase 0-1000 sec1in 30 seconds.

[0111] UV-LED radically curable offset printing inks (E1-E4 and C1-C30) described in Table 2 were prepared by independently adding to the offset printing ink vehicle of Table 1-1 the pigments of Table 1-2, the photoinitiators of Table 1-3 and an optional filler (Calofort S / SM Lifford (precipitated calcium carbonate, stearate coating, average particle size 100-500 nm, CAS 471-34-1); and mixing with a SpeedMixer™ (DAC 150 SP CM31 from Hauschild Engineering) at room temperature for three minutes. Subsequently, theresulting pastes were independently ground on a SDY300 three roll mill in three passes (a first pass with a pressure of about 5 bars, a second and a third pass with a pressure of about 11 bars). The so-obtained pastes were independently ground on a SDY300 three roll mill in three passes (a first pass at a pressure of 5 bars, a second and a third pass at a pressure of 11 bars). The viscosity values of the UV-LED radically curable offset printing inks provided in Table 2 were independently measured at 40°C and 1000 s-1on a Haake Roto- Visco RV1 with a cone 2 cm 0.5°, linear speed increase 0-1000 sec1in 30 seconds.Table 2. UV-LED radically curable offset printing inks (E1-E4 and C1-C30)

[0112] Security features (4.5 cm x 23 cm) were prepared by independently applying the UV-LED radically curable offset printing inks of Table 2 on a fiduciary polymer substrate (Guardian™, CCL Secure) using a Prufbau at a pressure of 1000 N (T = 22°C, relative humidity = 54%). The so-obtained ink layers were independently cured with a LUV20 UV-LED irradiation source (1ST GmbH) at doses of about 60 mJ / cm2and about 125 mJ / cm2, respectively. The exact amount of the printed and cured ink layers was calculated for each sample by weighting the substrate before and after printing and curing. The weight of the printed and cured ink layers of all the printed features was 1 g / m2± 3%.

[0113] The irradiation dose was determined as described hereafter: the irradiation source (LUV20 385 nm, 1ST) was turned on at 25% of the maximum power. A LEDCure™ radiometer (EIT 2.0 LLC) was placed on the track of the irradiation apparatus designed to receive the samples to be irradiated. The LEDCure™ radiometer was irradiated with the irradiation source at different belt speeds in two passes. The track speed to obtain an irradiation of about 60 mJ / cm2in two passes was determined to be about 150 m / min (average of two measured values). The track speed to obtain an irradiation of about 125 mJ / cm2in two passes was determined to be about 74 m / min (average of two measured values).Curing properties and efficiency of the UV-LED radically curable offset printing inks E1-E4 and C1-C30

[0114] Curing data were acguired using a Bruker Vertex 80 FTIR spectrometer operating in Rapid Scan mode, eguipped with a LN-MCT detector (Liquid Nitrogen cooled Mercury Cadmium Telluride).

[0115] Layers of uncured ink were drawn on Specac Golden Gate Heated Diamond ATR Top-Plate (KRS- 5 lenses). The inks were independently applied using a 100 pm gauge in order to get an homogeneous uncured ink layer.

[0116] Samples were irradiated by using a HAMAMATSU LED system eguipped with a 365 and 385 nm, respectively, UV-LED source having a power of about 600 mW / cm2. The temperature of the ink layer during the measurement was room temperature (22-25°C) and the measurements were performed in normal air atmosphere. Exposure time was controlled using an Oriel Fast Shutter system 76995 with Opus driver. Every sample was measured three times and the results were averaged. Integration parameters were determined empirically, i.e. by trying to reach the most stable possible baseline.

[0117] ATR FT-IR spectra (from 3000 cm'1to about 700 cm-1) were recorded with a time resolution of 12 ms and a spectral resolution of 16 cm-1, before, during and after the LED exposure. An absorption band centered around 810 cm-1(CH=CH2 twisting mode) was chosen as the band of interest for the absorbance measurements, said band being the least influenced by the absorption bands corresponding to the pigments P1-P16.

[0118] A linear calibration was first established for each of inks E1-E4 and C1-C30 and under each illumination (365 nm and 385 nm) by measuring the absorbance at time t = 0 (no curing) and after a 90 second irradiation. At time t = 0 (i.e. before irradiation), the inks were fully uncured, whereas at t = 90seconds, the inks were considered to be fully dried and cured (i.e. the remaining absorbance at 810 cm-1was due to remaining acrylate double bonds). In a second step, a fresh sample of ink was exposed to a 320 millisecond irradiation, corresponding to a curing dose of 200 mJ / cm2(as determined by a Hamamatsu C9536-2 Power meter) and curing was followed till 3.5 seconds.

[0119] The absorbance of the band at 810 cm'1was converted into polymerization degree (PD) by using the following eguation:wherein Aaio(O) is the absorbance at 810 cm-1of the fresh sample of ink (uncured)A8W(90) is the absorbance at 810 cm-1of the sample after a 90 second irradiation (fully cured)Aaio (t) is the absorbance at 810 cm-1and a time t of the sample after a 350 millisecond irradiation

[0120] The curing properties are provided in Tables 3-1 to 3-3, wherein the degree of polymerization is reported as PDmax(%), meaning that the degree of polymerization was calculated at the end of the recording time (tmax = 3.5 seconds). Since there was a trigger time of about 1 second between the start of the measurement (t = 0) and the start of the irradiation and that the irradiation time was about 320 milliseconds, the start of the irradiation was at about t = 1 second, the end of the irradiation was at about t = 1 .32 seconds and the end of the recording was at about t = 3.5 seconds, meaning that there was about 2.18 seconds of dark cure between the end of irradiation and tmax (end of recording).

[0121] The polymerization rate (PR) was determined from the first derivative of the curve of degree of polymerization, i.e. determining the polymerization degree PD (%) for each recorded spectrum and applying the following equation:wherein PD(%)nis the polymerization degree calculated for the nthspectrumPD(%)n~1is the polymerization degree calculated for the (n-1)thspectrum At is the time resolution of the measurement (here 12 milliseconds)

[0122] The maximum polymerization rate (PRmax) disclosed in in Tables 3-1 to 3-3 corresponds to the maximum of the obtained curve. It is intentionally reported without unit for simplicity reasons.

[0123] Based on the obtained values, relative values of the curing rate for the UV-LED radically curable offset inks E1 and C1-C16 were determined from the maximum degree polymerization (PDmax(%)) and the maximum polymerization rate (PRmax) of example E2 and reported as “% of E2” in Tables 3-1 and 3-2 below. For inks E3, E4, C17-C30, the assessment was based on the performance of a pigment-free comparison standard (CS) and reported as “% of CS” in Table 3-3 below.

[0124] The assessment (“pass” or “fail”) in Tables 3-1 to 3-3 was done according to the following criteria:

[0125] Curing efficiency was also assessed for each security feature obtained as described herein, by placing a piece of blank substrate (i.e. an unprinted substrate) on the front side of the substrate carrying the printed and cured ink layer and by submitting the so-formed assembly to a counter-pressure of SOO- WOO bars at 65°C with an ORMAG Intaglio Proof Press.

[0126] In order to precisely determine the counter-pressure value, a Fujifilm Prescale HS film (having a sensitivity between 50 and 130 MPa) was passed at 25°C in the ORMAG Intaglio Proof Press. The opticaldensity ODmax was measured at ten randomly chosen points using a Techkon SpectroDens densitometer(illuminant: D65 at 10°, reference white: unused film, density filter: ISO E, CMYK mode, polarizing filter: auto). An average value was calculated and compared with the scale provided by Fujifilm. The calculated average value of ODmax corresponded to a pressure of about 92 MPa. Considering an error margin of ±10%, the pressure was finally calculated to be about 83-101 MPa, i.e. about 800-1000 bars.

[0127] The substrate carrying the printed and cured layer and the blank substrate were separated and the optical density of the blank substrate was checked for ink transfer (set-off). Two blanks were prepared to define the two possible extremes of the curing behavior. A first blank to define the maximal efficiency (100% curing efficiency) was obtained by measuring the optical density of a sample of an unprinted substrate, whereas the minimal efficiency (0% curing efficiency) was defined by measuring the optical density of a sample obtained by counterpressure of a fully uncured ink layer (no pass under the UV-LED lamp) directly after printing. The maximal optical density (corresponding to a curing efficiency of 0%) was defined as ODo, whereas the minimal optical density (corresponding to a curing efficiency of 100%) was defined as OD100. The curing efficiency (CE) was calculated with the following equation and is provided in:

[0128] The assessment of curing efficiency (“pass” or “fail”) was done according to the following criteria and is provided in Tables 3-1 to 3-3:Optical properties of security features made of the UV-LED radically curable offset printing inks E1-E4 and C1-C30

[0129] The optical density values ODmaxand ODyeiiow of the security features obtained from the UV-LED radically curable offset inks E1-E4 and C1-C30 were independently measured using a Techkon SpectroDens densitometer with the following parameters: CMYK mode, illuminant: D65 at 10°, density filter: ISO E, polarizing filter: auto. A white reference was set using a piece of unprinted substrate. On each security feature, measurements were performed at three randomly chosen places and an average value was calculated.

[0130] The assessment (“pass” or “fail”) was done according to the following criteria is provided in Tables 3-1 to 3-3:Table 3-1a)final assessment: “pass” only if all criteria are fulfilled

[0131] As shown in Table 3-1 , the UV-LED radically curable offset inks E1-E2 and security features obtained therefrom (i.e. inks comprising a pigment of formula (I) in the required concentration) were able to fulfill all criteria, i.e. they were at the same time fast to cure and providing yellow security features exhibiting good optical properties. The comparative inks C1-C2 (i.e. inks comprising the same amount of an alternative pigment) allowed the manufacture of security features exhibiting good optical properties, but suffered from insufficient curing properties making them unsuitable to prepare high-quality security features.Table 3-2C2 and E2 (from Table 3-1) were added for a comparison purposeTable 3-3

[0132] As shown in Table 3-2, all the comparative inks C1-C16 did not allow to manufacture high- quality security features because either said comparative inks suffered from insufficient curing properties (C2, C4-C8, C10, C12, C16) or security features obtained therefrom suffered from poor optical properties (C3, C9, C11 , C13, C14).

[0133] As shown in Table 3-3, the concentration of the pigments P4, P7, P10 and P15 was varied while the composition and the concentration of the ink vehicle and the photoinitiators blend were kept constant. In order to avoid viscosity changes that may impact the curing properties and / or the optical properties of the security features obtained from said inks, the varying amount of pigment was compensated by adding a varying amount of the additional filler (table 2) in such a way that the total amount of filler and pigment was maintained constant at 20 wt.%. A comparison standard (denoted CS in Table 3) was prepared in the same way as the inks according to the invention E3-E4 and the comparative inks C17-C30, but the total amount of filler and pigment was replaced by the filler only (no pigment). As shown in Table 3-3, the curing properties of the inks E3-E4 and the inks C17-C30 were compared to the curing properties of the pigment-free comparison standard (CS).

[0134] As shown in Table 3-3, replacing a portion of the pigment (P4, P7, P10 or P15) by the filler allowed an improvement of the curing efficiency; however this led to negative optical properties (i.e. the ODmax and the ODyeiiow decreased). Contrary to the use of the pigments P4, P10 and P15 in comparative inks C19-C30 and to the use of the pigment P7 (i.e. the pigment of formula (I)) at a too low concentration in comparative inks C17-C18, using the pigment P7 (i.e. the pigment of formula (I)) in the required amount (i.e. more than 10 wt.%, preferably at least 12.5 wt.%) allowed to obtain a combination of positive effects in terms of curing properties and the optical properties of security features obtained from said inks E3-E4.Table 4. UV-LED radically curable intaglio inks (E5-E6 and C31-C32)a)blue pigment was added in small amount to make the printed pattern more visible with the naked eye (as a consequence, the printed pattern is green instead of bright yellow)

[0135] The UV-LED radically curable intaglio inks of Table 4 were independently prepared by mixing all ingredients with a DAC 150 SP CM 31 speedmixer (Hauschild) at room temperature for three minutes at 2500 rpm. The resulting pastes were independently ground on a SDY200 three roll mill (Buhler) inthree passes at 25°C (a first pass at a pressure of 8 bars, a second and a third pass at a pressure of 11 bars).

[0136] The viscosity values of the UV-LED radically curable intaglio inks provided in Table 4 were independently measured with a Haake Roto Visco 1 rotational rheometer (C20 / 0.50; at 40°C and 1000 sec-1).

[0137] The UV-LED radically curable intaglio inks were independently applied on the printing plate of an Ormag intaglio proof-press with a polymer hand-inking roller at a temperature of 60°C. The printing plate comprised a set of “U”-shaped engravings of various depths (from about 20 pm to about 100 pm) and widths (from about 60 pm to about 500 pm) such as to mimic an intaglio printed feature on a banknote. The excess of the UV-LED curable intaglio inks was manually wiped off with a paper, then the UV-LED radically curable intaglio inks were independently applied in the form of a security feature on a blank sheet of standard cotton paper for banknote applications (Cotton Banknote Paper from Louisenthal; 17 cm x 14.5 cm).

[0138] The so-obtained printed security features were independently cured with an UV-LED lamp (LUV20 385 nm, 1ST GmbH) at doses of about 60 mJ / cm2and about 125 mJ / cm2, respectively.

[0139] The irradiation dose was determined in the same way as described for the UV-LED radically curable offset inks (E1-E4 and C1-C30).

[0140] The curing efficiency of the UV-LED radically curable intaglio inks E5-E6 and C31-C32 was assessed on the security features obtained therefrom according to the process described hereabove, wherein said features were submitted to a counterpressure test and to an abrasion test.

[0141] The counterpressure test was carried out according to the procedure described for the UV-LED radically curable offset inks (E1-E4 and C1-C30) at 60°C and at a pressure of 800-1000 bar. The processed samples were visually inspected and the results are provided in Table 5 according to the following scale:- “5”: no ink transfer visible, no damage to the printed sample I passed- “4”: slight ink transfer visible, minor damage to the printed sample I passed- “3”: moderate ink transfer visible, minor damage to the printed sample I passed- “2”: strong ink transfer visible, strong damage to the printed sample I failed- “1 very strong ink transfer visible, considerable damage to the printed sample I failed

[0142] The abrasion test was conducted as follows: the security features obtained from the UV-LED radically curable intaglio inks E5-E6 and C31-C32 were independently mounted inside an abrasion tester (Prufbau). A circular cut-out (diameter about 45 mm) of a blank piece of substrate (Cotton Banknote Paper from Louisenthal) was sticked using double-sided adhesive tape to a metallic weight of 610 g and said weight was placed upon the printed security feature, the surface of the blank piece of substrate being in contact with the printed surface of the security feature. A motor then moved the metallic weight back and forth on the printed surface 100 times while rotating it at each back and forth movement by about 22°. The processed samples were visually inspected and the results are provided in Table 5 according to the following scale:- “5”: no ink transfer visible, no damage to the printed sample I passed- “4”: slight ink transfer visible, minor damage to the printed sample / passed‘3”: moderate ink transfer visible, minor damage to the printed sample / passed‘2”: strong ink transfer visible, strong damage to the printed sample I failed‘1 very strong ink transfer visible, considerable damage to the printed sample / failedTable 5

[0143] As shown in Table 5, the comparative UV-LED radically curable intaglio inks C31-C32 did not allow to manufacture high-quality security features because said comparative inks suffered from an insufficient curing at both 60 and 125 mJ / cm2(see the poor results of the counterpressure and the abrasion tests).

[0144] Contrary to the comparative examples C31-C32, the UV-LED radically curable intaglio inks prepared according to the invention E5-E6 (i.e. inks comprising the pigment of formula (I) in the required amount) allowed to obtain high-quality security features, even when said inks were cured at the relatively low UV dose of 60mJ / cm2.

Claims

CLAIMS1 . A UV-LED radically curable printing ink for printing a security feature on a substrate, said UV- LED radically curable printing ink comprising: i) from about 30 wt.% to about 80 wt.% of one or more radically curable (meth)acrylate compounds; ii) from about 2 wt.% to about 20 wt.% of one or more thioxanthone compounds, iii) from about 0.5 wt.% to about 15 wt.% of one or more amino containing synergists, iv) more than about 0.5 wt.% of one or more fillers and / or extenders, and v) more than about 10 wt.% of one or more pigments of formula (I):wherein Am are each independently a hydrogen atom, an halogen atom, a methyl group, an ethyl group, a methoxy group or a ethoxy group, preferably a hydrogen atom, an halogen atom, a methyl group or an ethyl group and m are each independently an integer of 1 to 4, the weight percents being based on the total weight of the UV-LED radically curable printing ink.

2. The UV-LED radically curable printing ink according to claim 1 , wherein the halogen atom is bromine or chlorine, preferably chlorine.

3. The UV-LED radically curable printing ink according to claim 1 or 2 having a viscosity in the range of about 2.5 to about 35 Pa s at 40°C and 1000 s-1.

4. The UV-LED radically curable printing ink according to any one of claims 1 to 3, wherein at least one of the one or more radically curable (meth)acrylate compounds consists of one or more radically curable (meth)acrylate oligomers and at least one of the one or more radically curable (meth)acrylate compounds consists of radically curable (meth)acrylate monomers, said radically curable (meth)acrylate oligomers being selected from the group consisting of epoxy (meth)acrylates, (meth)acrylated oils, (meth)acrylated epoxidized oils, polyester (meth)acrylates, aliphatic or aromatic polyurethane (meth)acrylates, polyacrylic acid (meth)acrylates, polyacrylate esters (meth)acrylates and mixtures thereof, more preferably selected from the group consisting of epoxy (meth)acrylates, polyester (meth)acrylates, aliphatic or aromatic polyurethane (meth)acrylates and mixtures thereof, andsaid radically curable (meth)acrylate monomer being selected from the group consisting of mono(meth) acrylates, di(meth)acrylates, tri(meth)acrylates, tetra(meth)acrylates, penta(meth)acrylates, hexa(meth)acrylates and mixtures thereof.

5. The UV-LED radically curable printing ink according to any one of claims 1 to 4, further comprising one or more acyl phosphine oxide compounds, preferably selected from the group consisting of (1 ,4,6-trimethylbenzoyl)diphenylphosphine oxide; 2,4,6-trimethylbenzoyl- ethoxylphenylphosphine oxide); phenyl-bis(2,4,6-trimethylbenzoyl)phosphine oxide; bis(1 ,6- dimethoxybenzoyl)(1 ,4,4-trimethylpentyl)phosphine oxide; ethyl (3-benzoyl-2,4,6- trimethylbenzoyl)(phenyl)phosphinate; a,a’,a”-1 ,2,3-propanetriyltris[oj-[[phenyl(1 ,4,6- trimethylbenzoyl)phosphinyl]oxy]-poly(oxy-1 ,2-ethanediyl); and mixtures thereof.

6. The UV-LED radically curable printing ink according to any one of claims 1 to 5, wherein the or more fillers and / or extenders are selected from the group consisting of talcs, micas, montmorillonites, bentonites, wollastonites, halloysites, calcined clays, china clays, carbonates, silicates, vermiculites, amorphous silica, wood flours, natural fibers, synthetic fibers and mixtures thereof, more preferably selected from the group consisting of talcs, micas, wollastonites, calcined clays, carbonates, amorphous silica and mixtures thereof, the weight percents being based on the total weight of the UV-LED radically curable printing ink.

7. The UV-LED radically curable printing ink according to any one of claims 1 to 6, further comprising one or more waxes in a total amount preferably less than about 10 wt.%, preferably selected from the group consisting of synthetic waxes, petroleum waxes, natural waxes, and mixtures thereof, more preferably selected from the group consisting of paraffin waxes, polyethylene waxes, fluorocarbon waxes, polytetrafluoroethylene waxes, carnauba waxes, rice bran waxes and mixtures thereof, the weight percents being based on the total weight of the UV-LED radically curable printing ink.

8. The UV-LED radically curable printing ink according to any one of claims 1 to 7 which is an offset printing ink.

9. A printed security feature consisting of a cured ink layer made from the UV-LED radically curable printing ink recited in any one of claims 1 to 8.10 A security document, a decorative element or a decorative object comprising a substrate and one or more printed security features recited in claim 9.

11. A process for printing a feature on a substrate comprising the steps of: a) applying the UV-LED radically curable printing ink recited in any one of claims 1 to 8 by intaglio printing or by offset printing so as to form an ink layer, and b) exposing the ink layer to UV light emitted by a UV-LED light source.

12. The process according to claim 11 , wherein the ink is applied during step a) by an offset printing process.

13. The process according to claim 11 or 12, wherein step b) is carried out by exposing the ink layer one or more wavelengths of between about 350 nm and about 415 nm, more preferably by exposure to UV light at 365 nm and / or 385 nm and / or 395 nm and / or 405 nm.14 The process according to any one of claims 11 to 13 wherein step b) is carried out at a dose of at least 50 mJ / cm2.

15. A use of one or more pigments of formula (I) recited in claim 1 or 2 in a total amount of at least 10 wt.% for producing the UV-LED radically curable printing ink recited in any one of claims 1 to 8, said UV-LED radically curable printing ink being suitable for printing one or more security features on a security document, a decorative element or a decorative object.

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