UV-VIS radiation curable security inks for creating dichroic security features

Abstract

The present invention provides a UV-Vis radiation curable security ink for producing a security feature for securing a valuable document, the security feature exhibiting a blue color when viewed in transmitted light and a metallic yellow color when viewed in incident light. The UV-Vis radiation curable security ink comprises a cationically curable or hybrid curable ink vehicle and a compound represented by the general formula (I): TIFF2023547688000073.tif33149 [In the formula, residue R A is a C2-C4 alkyl group substituted with a hydroxy group; residue R B is selected from C1-C4 alkyl groups and C2-C4 alkyl groups substituted with hydroxy groups; Cat + Na + , K. + , Cs + and Rb + The silver nanoplatelets have a surface stabilizer, which is a cation selected from the group consisting of:

Description

Detailed Description of the Invention

[0001] [Field of the Invention] The present invention relates to the technical field of security inks for producing dichroic security features for securing value documents, wherein said dichroic security features exhibit a first color when viewed in transmitted light and a second color, different from the first color, when viewed in incident light.

[0002] [Background of the invention] With the ever-increasing quality of color copying and printing, it has been conventional practice to incorporate various security features in an attempt to protect security documents such as banknotes, value documents or cards, transport tickets or cards, tax banderoles, and product labels without reproducible consequences to counterfeiting, falsifying, or illegal duplication.

[0003] For example, security features for security documents can generally be categorized as "covert" and "overt" security features. The protection offered by covert security features relies on the notion that such features are difficult to detect, typically requiring specialized equipment and knowledge for detection, whereas "overt" security features are easily detectable by unaided human senses, e.g., they are visible and / or detectable by touch, yet are difficult to fabricate and / or copy. However, the effectiveness of overt security features relies heavily on their easy recognition as security features, since most users, especially those without prior knowledge of the security features of a document or item secured thereby, will only actually conduct a security check based on the security feature once they have actual knowledge of its existence and nature.

[0004] A special role in securing valuable documents is played by dichroic security features, which exhibit a first color when viewed in transmitted light and a second color different from the first when viewed in incident light. To provide a striking effect and attract the public's attention, the first and second colors must have an appealing visual appearance, such as blue, metallic yellow, magenta, and green, and a significant color contrast (blue / metallic yellow, green / metallic yellow, violet / metallic yellow).

[0005] The dichroic security features, which exhibit a blue color in transmitted light and a metallic yellow color in incident light, are obtained from inks containing silver platelets.

[0006] WO 2011064162 describes solvent-based inks and UV radical-curable inks containing silver platelets for producing dichroic security or decorative elements that exhibit a gold / copper color in reflection and a blue color in transmission. The inks contain a high concentration of silver platelets, characterized by a silver platelet to binder weight ratio of 3:1.1. The high concentration of silver platelets in the inks used to obtain the security or decorative elements described in WO 2011064162 is detrimental to the mechanical resistance of the resulting security or decorative elements and, in addition, makes the production process for the elements expensive. Furthermore, the mechanical resistance of the security or decorative elements described in WO 2011064162 is compromised by the use of UV radical-curable inks or solvent-based inks, which, as is well known to those skilled in the art, provide cured coatings with limited mechanical resistance. Since mechanical resistance is an essential property for a security element and the manufacturing process described by WO2011064162 is tedious and rather expensive, the inks and manufacturing process described therein are not suitable for the industrial production of dichroic security features with acceptable mechanical resistance on value documents.

[0007] WO 2013186167 describes the use of a UV-curable ink containing silver platelets, a radically curable binder, and a significant amount of organic solvent to coat the surface of a holographic structure. The coated holographic structure exhibits a strongly saturated blue color in transmitted light and a low-saturation yellow color in reflected light on the embossed surface. Although the UV-curable ink described in WO 2013186167 contains a lower concentration of silver platelets than the UV-radiation radically curable ink described in WO 2011064162, the ink is still not suitable for the industrial production of dichroic features on valuable documents. This is because, on the one hand, the increased amount of organic solvent is environmentally unfriendly and requires an additional air-drying step before the UV-curing step, and, on the other hand, the coating obtained with the ink has limited mechanical resistance and low saturation in reflected light.

[0008] Typically, industrial printing of value documents requires high printing speeds of around 8,000 sheets / hour, with each sheet producing a significant number of value documents. By way of example, in the field of banknote printing, up to 55 value documents, each containing one or more security features, can be produced from a single sheet. To be suitable for production line implementation, it is essential that the production process for each printable security feature present on a value document meets the high speed requirements of industrial printing of value documents.

[0009] Thus, there remains a need for a stable security ink for producing dichroic security features on value documents at high speeds (i.e., industrial speeds) that have improved mechanical resistance and that exhibit a blue color when viewed in transmitted light and a metallic yellow color when viewed in incident light.

[0010] [Summary of the Invention] It is therefore an object of the present invention to provide a UV-Vis radiation cationically curable security ink and a UV-Vis radiation hybrid curable security ink for producing at high speed (i.e. industrial speed) dichroic security features on value documents that have improved mechanical resistance and that exhibit a blue color in transmitted light and a metallic yellow color in incident light. This is achieved by the claimed UV-Vis radiation curable security ink, which comprises: a) about 7.5 wt-% to about 20 wt-% of silver nanoplatelets having an average diameter in the range of 50-150 nm with a standard deviation of less than 60%, an average thickness in the range of 5-30 nm with a standard deviation of less than 50%, and an average aspect ratio greater than 2.0, wherein the average diameter is determined by transmission electron microscopy and the average thickness is determined by transmission electron microscopy, and the silver nanoplatelets are represented by the general formula (I): [ka] [In the formula, residue R A is a C2-C4 alkyl group substituted with a hydroxy group; residue R B is selected from C1-C4 alkyl groups and C2-C4 alkyl groups substituted with a hydroxy group; Cat + Na + , K. + , Cs + and Rb + a surface stabilizer, wherein the stabilizer is a cation selected from the group consisting of: b) perfluoropolyether surfactants functionalized with at least hydroxy groups; c) about 3 wt.-% to about 12 wt.-% polyvinyl chloride copolymer containing at least 69 wt.-% vinyl chloride; d) d1) about 25 wt-% to about 55 wt-% of an alicyclic epoxide, and about 1 wt-% to about 10 wt-% of a cationic photoinitiator; or d2) about 30 wt.-% to about 65 wt.-% of a mixture of a cycloaliphatic epoxide and a radically curable compound, about 1 wt.-% to about 6 wt.-% of a cationic photoinitiator, and about 1 wt.-% to about 6 wt.-% of a free radical photoinitiator; and optionally e) vinyl ethers having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the alicyclic epoxide of e1) d); e2) vinyl ethers having less than about 5 wt. % of one vinyloxy residue; e3) less than about 10 wt. % of an epoxide other than a cycloaliphatic epoxide; e4) oxetanes having two oxetanyl residues in an amount of less than about 20 wt. %; e5) oxetanes having one oxetanyl residue in an amount of less than about 3.5 wt.-%; and e6) a mixture of e1) and / or e2) and / or e3) and / or e4) and / or e5) a cationically curable compound selected from the group consisting of where the weight percentage is based on the total weight of the UV-Vis radiation curable security ink.

[0011] A further aspect according to the present invention is a method of making a security feature for securing a value document, said security feature exhibiting a blue color when viewed in transmitted light and a metallic yellow color when viewed in incident light, said method comprising the steps of: A) printing a UV-Vis radiation curable security ink as claimed herein onto a transparent or partially transparent area of ​​a value document substrate, preferably by screen printing, rotogravure printing, or flexographic printing, to provide an ink layer; and B) UV-Vis curing of the ink layer obtained in step A) to form the security feature. The present invention relates to a method, including:

[0012] [Detailed explanation] (definition) The following definitions are used to interpret the meaning of terms discussed in the specification and recited in the claims.

[0013] As used herein, the article "a / an" indicates one as well as more than one and does not necessarily limit the referent noun to the singular.

[0014] As used herein, the term "about" means that the amount or value in question may be the specific value specified or another value nearby it. Generally, the term "about" used to denote a value is intended to indicate a range of ±5% of that value. As an example, the phrase "about 100" indicates a range of 100 ±5, i.e., a range of 95 to 105. Preferably, the range indicated by the term "about" indicates a range of ±3%, more preferably ±1%, of the value. Generally, when the term "about" is used, it can be expected that similar results or effects according to the present invention can be obtained within a range of ±5% of the indicated value.

[0015] As used herein, the term "and / or" means that all or only one of the elements of a stated group may be present. For example, "A and / or B" means "A only, or B only, or both A and B." In the case of "A only," the term also encompasses the possibility that B is not present, i.e., "A only and not B."

[0016] As used herein, the term "comprising" is intended to be non-exclusive and open-ended. Thus, for example, a solution containing compound A may contain other compounds in addition to A. However, the term "comprising" also encompasses the more restrictive meanings of "consisting essentially of" and "consisting of," in certain embodiments thereof; thus, for example, a "solution comprising A, B, and optionally C" may consist (essentially) of A and B, or may consist (essentially) of A, B, and C.

[0017] When "preferred" embodiments / features are referred to in this specification, combinations of these "preferred" embodiments / features are also disclosed insofar as a particular combination of "preferred" embodiments / features makes technical sense.

[0018] As used herein, the term "one or more" means one, two, three, four, etc.

[0019] The terms "UV-Vis curable" and "UV-Vis curing" refer to radiation curing by photopolymerization under the influence of radiation having wavelength components in the UV or UV and visible portions of the electromagnetic spectrum (typically 100 nm to 800 nm, preferably 150 to 600 nm, more preferably 200 to 400 nm).

[0020] Surprisingly, a) about 7.5 wt-% to about 20 wt-% of silver nanoplatelets having an average diameter in the range of 50-150 nm with a standard deviation of less than 60%, an average thickness in the range of 5-30 nm with a standard deviation of less than 50%, and an average aspect ratio greater than 2.0, wherein the average diameter is determined by transmission electron microscopy and the average thickness is determined by transmission electron microscopy, and the silver nanoplatelets are represented by the general formula (I): [ka] [In the formula, residue R A is a C2-C4 alkyl group substituted with a hydroxy group; residue R B is selected from C1-C4 alkyl groups and C2-C4 alkyl groups substituted with a hydroxy group; Cat + Na + , K. + , Cs + and Rb + is a cation selected from the group consisting of having a surface stabilizer of; b) perfluoropolyether surfactants functionalized with at least hydroxy groups; c) polyvinyl chloride copolymers containing from about 3 wt-% to about 12 wt-% of at least 69 wt-% vinyl chloride; d) d1) about 25 wt-% to about 55 wt-% of an alicyclic epoxide, and about 1 wt-% to about 10 wt-% of a cationic photoinitiator; or d2) about 30 wt.-% to about 65 wt.-% of a mixture of a cycloaliphatic epoxide and a radically curable compound, about 1 wt.-% to about 6 wt.-% of a cationic photoinitiator, and about 1 wt.-% to about 6 wt.-% of a free radical photoinitiator; and optionally e) vinyl ethers having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the alicyclic epoxide of e1) d); e2) vinyl ethers having less than about 5 wt. % of one vinyloxy residue; e3) less than about 10 wt. % of an epoxide other than a cycloaliphatic epoxide; e4) oxetanes having two oxetanyl residues in an amount of less than about 20 wt. %; e5) oxetanes having one oxetanyl residue in an amount of less than about 3.5 wt.-%; and e6) a mixture of e1) and / or e2) and / or e3) and / or e4) and / or e5) a cationically curable compound selected from the group consisting of It has been discovered that a UV-Vis radiation-curable security ink, comprising the formula (I), where the weight percentages are based on the total weight of the UV-Vis radiation-curable security ink, has improved mechanical resistance and enables convenient and cost-effective production of security features that exhibit a blue color in transmitted light and a metallic yellow color in incident light. The combination of specific silver nanoplatelets having a surface stabilizer of general formula (I) described herein with the specific ink vehicle described herein allows the silver nanoplatelets contained in the ink layer obtained by printing the security ink according to the present invention to migrate favorably from the ink layer mass at the ink layer-air interface and the ink layer-substrate interface and align at the interfaces to form a thin reflective layer, thereby producing a metallic yellow color in reflected light and a blue color in transmitted light, regardless of the thickness of the printed ink layer. The favorable production of a metallic yellow color in reflected light and a blue color in transmitted light cannot be achieved with inks described in the prior art. The cationically curable or hybrid curable binder contained in the claimed UV-Vis radiation-curable security ink provides high mechanical resistance to the dichroic security feature obtained from the ink. The attractive visual appearance and contrast between the blue color shown in transmitted light and the metallic yellow color shown in incident light highlight security features made with inks according to the present invention, thereby drawing the public's attention to the security feature, helping them to locate and recognize the security feature on value documents, and to authenticate value documents containing the security feature. The UV-Vis radiation curable inks according to the present invention have outstanding storage stability. Therefore, the UV-Vis radiation curable security inks according to the present invention meet the high-speed requirements of industrial printing of value documents and provide dichroic security features with attractive visual appearance, high value recognition, and high mechanical resistance.

[0021] Security features made with the claimed UV-Vis radiation curable security inks exhibit a blue color when viewed in transmitted light, i.e., transmission. For purposes of this invention, viewing in transmitted light means illuminating the security feature from one side, for example, by holding the security feature facing sunlight or in front of a light source, and viewing from the other side. The blue color is observed regardless of the side on which the security feature is viewed in transmitted light. For purposes of this invention, a security feature exhibiting a blue color is one that has a chroma value C greater than 20. * This refers to a security feature that exhibits a blue color characterized by its color intensity or color saturation (corresponding to a measure of color intensity or color saturation). An intense to very intense blue color has a saturation value C greater than 30. * It is characterized by the saturation value C * is based on the CIELAB (1976) color space. * and b * is calculated from the value, where

number

[0022] The above a in transmitted light * and b * The values ​​are measured using a Datacolor 650 spectrophotometer (parameters: integrating sphere, diffuse illumination (pulsed xenon D65) and 8° field of view, analyzer SP2000, dual 256 diode array, wavelength range 360-700 nm, transmitted light sampling aperture size 22 mm).

[0023] Security features made with the claimed UV-Vis radiation curable security inks exhibit a metallic yellow or gold color when viewed in incident or reflected light. In this patent application, the terms "metallic yellow" and "gold" are used interchangeably. For purposes of the present invention, "viewed in incident light" means that the security feature is illuminated from the surface printed with the claimed security ink and viewed from the same side. For purposes of the present invention, security features exhibiting a metallic yellow or gold color are defined as a * and b * saturation value C greater than 20 calculated from the value * refers to a security feature that exhibits a yellow color characterized by a color intensity or color saturation (corresponding to a measure of color intensity or color saturation),

number

[0024] The claimed UV-Vis radiation curable security inks described herein are preferably selected from screen printing security inks, rotogravure security inks, and flexographic security inks. Preferably, the claimed UV-Vis radiation curable security inks are characterized by a viscosity of about 50 mPas to about 2000 mPas, measured at 25°C using a Brookfield viscometer (model "DV-I Prime") equipped with a 100 rpm spindle S27 for measuring viscosities between 500 and 2000 mPas, or a 50 rpm spindle S21, or a 100 rpm spindle S21 for measuring viscosities below 500 mPas. The claimed UV-Vis radiation curable screen printing security inks are characterized by a viscosity of about 50 mPas to about 1000 mPas at 25°C, preferably about 100 mPas to about 1000 mPas at 25°C.

[0025] As known to those skilled in the art, the term rotogravure printing refers to a printing process described, for example, in Handbook of Print Media, Helmut Kipphan, Springer Edition, page 48. Rotogravure printing is a printing process in which image elements are imprinted onto the surface of a cylinder. The non-image areas are at a constant original level. Before printing, the entire printing plate (non-printing and printing elements) is inked and flooded with ink. Before printing, the ink is removed from the non-image with a wiper or blade, so that the ink remains only in the cells. The image is transferred from the cells to the substrate by pressure, typically in the range of 2-4 bar, and by the adhesive forces between the substrate and the ink. The term rotogravure printing does not include, for example, intaglio printing processes (also known in the art as engraved steel die or copperplate printing processes), which rely on different types of ink.

[0026] The flexographic printing process preferably uses an apparatus equipped with a chambered doctor blade, an anilox roller, and a plate cylinder. The anilox roller advantageously has small cells, the volume and / or density of which determine the ink or varnish application speed. The chambered doctor blade faces the anilox roller, filling the cells while simultaneously scraping off excess ink or varnish. The anilox roller transfers the ink to the plate cylinder, which ultimately transfers the ink to the substrate. The plate cylinder can be made of a polymer or elastomeric material. Polymers are primarily used as photopolymer plates, sometimes as seamless coatings on sleeves. Photopolymer plates are made from photosensitive polymers that are cured by ultraviolet (UV) light. The photopolymer plate is cut to the required size and placed in a UV light exposure device. One side of the plate is fully exposed to UV light to harden or cure the base of the plate. The plate is then inverted, a negative of the job is placed on the uncured side, and the plate is further exposed to UV light. This hardens the image areas of the plate. The plate is then processed to remove the unhardened photopolymer from the non-image areas, lowering the plate surface in these non-image areas. After processing, the plate is dried and a post-exposure dose of UV light cures the entire plate. Preparation of plate cylinders for flexographic printing is discussed in Printing Technology, JM Adams and PA Dolin, Delmar Thomson Learning, 5 th Edition, pages 359-360.

[0027] As known to those skilled in the art, screen printing (also known in the art as silkscreen printing) is a printing technique that uses a screen, typically made of a woven mesh, to support an ink-blocking stencil. The attached stencil forms open areas in the mesh, which transfer ink onto the substrate as a sharp-edged image. A squeegee, along with the ink-blocking stencil, moves across the screen, forcing the ink through the open areas and past the woven mesh threads. An important feature of screen printing is its ability to apply ink to a substrate at thicknesses greater than other printing techniques. Screen printing is therefore also preferred when ink deposition thicknesses of approximately 10 to 50 μm or greater are required that cannot be easily achieved with other printing techniques. Typically, screens are made from a single sheet of porous, finely woven fabric, called mesh, stretched over a frame, e.g., aluminum or wood. Currently, most meshes are made from synthetic or man-made materials such as steel threads. Preferred synthetic materials are nylon or polyester threads.

[0028] In addition to screens made based on woven meshes based on synthetic or metal yarns, screens have been developed from solid metal sheets having a grid of holes. Such screens are prepared by a process that includes electrolytically forming a metal screen by forming a screen skeleton on a substrate containing a separating agent in a first electrolytic bath, stripping the formed screen skeleton from the substrate, and subjecting the screen skeleton to electrolysis in a second electrolytic bath to deposit metal on the skeleton.

[0029] There are three types of screen printers: flatbed, cylinder, and rotary screen printers. Flatbed and cylinder screen printers are similar in that they both use a flat screen and a three-step regression process to perform the printing operation. The screen is first moved into position above the substrate, then a squeegee is pressed against the mesh and pulled over the image area, and the screen is then lifted off the substrate to complete the process. In a flatbed press, the substrate to be printed is placed on a horizontal print bed, typically parallel to the screen. In a cylinder press, the substrate is mounted on a cylinder. Flatbed and cylinder screen printing processes are discontinuous processes and, as a result, are generally limited to a maximum of 45 m / min for web or 3,000 sheets / hour for sheet-fed processes.

[0030] Rotary screen presses, on the other hand, are designed for continuous, high-speed printing. The screens used in rotary screen presses are thin metal cylinders, for example, usually obtained using the electroforming method described above or made of woven steel threads. The open cylinder is capped at both ends and fitted into a block on the side of the press. During printing, ink is pumped into one end of the cylinder, thus maintaining a constant fresh supply. A squeegee is fixed inside the rotating screen, and the squeegee pressure is maintained and adjusted to allow good and consistent printing quality. The advantage of rotary screen presses is the speed that can easily be achieved: 150 m / min for web or 10,000 sheets / hour for sheet-fed processes.

[0031] Screen printing is further described in, for example, The Printing Ink Manual, RH Leach and RJ Pierce, Springer Edition, 5 th Edition, pages 58-62, Printing Technology, JM Adams and PA Dolin, Delmar Thomson Learning, 5 thEdition, pages 293-328 and Handbook of Print Media, H. Kipphan, Springer, pages 409-422 and pages 498-499.

[0032] More preferably, the UV-Vis radiation curable security inks claimed and described herein are screen printing security inks. Such UV-Vis radiation curable screen printing security inks are particularly useful for the industrial production of dichroic security features on value documents, as they allow for very high speed printing of dichroic security features having a large thickness of at least about 4 μm.

[0033] The claimed UV-Vis radiation curable ink described herein comprises: a) about 7.5 wt-% to about 20 wt-%, preferably about 7.5 wt-% to about 15 wt-%, and more preferably about 10 wt-% to about 12.5 wt-% silver nanoplatelets having an average diameter in the range of 50 to 150 nm with a standard deviation of less than 60%, an average thickness in the range of 5 to 30 nm with a standard deviation of less than 50%, and an average aspect ratio greater than 2.0, wherein the average diameter is determined by transmission electron microscopy and the average thickness is determined by transmission electron microscopy, and the silver nanoplatelets have a surface stabilizer of the general formula (I): [ka] [In the formula, residue R A is a C2-C4 alkyl group substituted with a hydroxy group; residue R B is selected from C1-C4 alkyl groups and C2-C4 alkyl groups substituted with hydroxy groups; Cat + Na + , K. + , Cs + and Rb + is a cation selected from the group consisting of:

[0034] The silver nanoplatelets described herein having a surface stabilizer of general formula (I) are readily dispersible in the vehicle of the claimed UV-Vis radiation-curable security ink. Upon printing, the silver nanoplatelets described herein migrate from the ink layer bulk of the claimed UV-Vis radiation-curable security ink to the ink layer-air interface and the ink layer-substrate interface, aligning themselves to form thin layers of silver nanoplatelets at said interfaces, thereby leading to the advantageous development of a metallic yellow color observed under incident light. The properties of the claimed UV-Vis radiation-curable security ink are particularly advantageous because, on the one hand, the time required for development of the metallic yellow color is compatible with the high-speed requirements of industrial printing of valuable documents, and, on the other hand, enable the production of dichroic security features using inks containing as little as 7.5 wt.-% silver nanoplatelets, which dramatically reduces production costs, especially for dichroic security features having a large thickness of at least about 4 μm. Depending on the thickness of the fabricated dichroic security feature and the composition of the ink vehicle, the amount of silver nanoplatelets in the UV-Vis radiation curable security ink can be adjusted to rapidly develop a metallic yellow color in reflected light without affecting the blue hue and saturation in transmitted light.

[0035] The silver nanoplatelets contained in the UV-Vis can be in the form of a disk, a regular hexagon, a triangle, particularly an equilateral triangle, and a truncated triangle, particularly an equilateral triangle, or a mixture thereof, preferably in the form of a disk, a truncated triangle, a hexagon, or a mixture thereof.

[0036] The average diameter of the silver nanoplatelets is in the range of 50-150 nm, preferably 60-140 nm, and more preferably 70-120 nm, with a standard deviation of less than 60%, preferably less than 50%. The diameter of a silver nanoplatelet is the longest dimension of the silver nanoplatelet and corresponds to the largest dimension of the silver nanoplatelet when oriented parallel to the plane of a transmission electron microscopy (TEM) image. As used herein, the term "average diameter of silver nanoplatelets" refers to the average diameter determined by transmission electron microscopy (TEM) using Fiji image analysis software based on measurements of at least 300 randomly selected silver nanoplatelets oriented parallel to the plane of the transmission electron microscopy (TEM) image, where the diameter of the silver nanoplatelet is the largest dimension of the silver nanoplatelet oriented parallel to the plane of the transmission electron microscopy (TEM) image. TEM analysis was performed using a ZEISS EM910 instrument in brightfield mode with an e-beam accelerating voltage of 100 kV. A dispersion of silver nanoplatelets in isopropanol at an appropriate concentration, preferably lower than 24.1 wt-%, was used to perform the TEM analysis.

[0037] The average thickness of the silver nanoplatelets ranges from 5 to 30 nm, preferably 7 to 25 nm, and more preferably 8 to 25 nm, with a standard deviation of less than 50%, preferably less than 30%. The thickness of a silver nanoplatelet is the shortest dimension of the nanoplatelet and corresponds to the maximum thickness of the silver nanoplatelet. As used herein, the term "average thickness of silver nanoplatelets" refers to the average thickness determined by transmission electron microscopy (TEM) based on manual measurements of at least 50 randomly selected silver nanoplatelets oriented perpendicular to the plane of the TEM image, where the thickness of the silver nanoplatelet is the maximum thickness of the silver nanoplatelet. TEM analysis was performed using a ZEISS EM910 instrument in bright-field mode at an e-beam accelerating voltage of 100 kV. A dispersion of silver nanoplatelets in isopropanol at an appropriate concentration, preferably less than 24.1 wt.%, was used to perform the TEM analysis.

[0038] The average aspect ratio of the silver nanoplatelets (defined as the ratio of the average diameter to the average thickness) is greater than 2.0, preferably greater than 2.2, and more preferably greater than 2.5.

[0039] Preferably, the average diameter of the silver nanoplatelets is in the range of 70 to 120 nm with a standard deviation of less than 50%, the average thickness of the silver nanoplatelets is in the range of 8 to 25 nm with a standard deviation of less than 30%, and the average aspect ratio of the silver nanoplatelets is greater than 2.5.

[0040] The silver nanoplatelets used in the UV-Vis radiation curable inks described herein are characterized by a highest wavelength absorption maximum between 560 and 800 nm, preferably between 580 and 800 nm, and most preferably between 600 and 800 nm. The highest wavelength absorption maximum is approximately 5 times that of silver in water. * 10 -5 The measurements were performed using a Varian Cary 50 UV-visible spectrophotometer at a concentration of 1000 mol / L. The absorption maximum has a full width at half maximum (FWHM) value in the range of 50-500 nm, preferably 70-450 nm, and more preferably 80-450 nm. The molar extinction coefficient of the silver nanoplatelets measured at the highest wavelength absorption maximum is 4000 mol / cm. * mol Ag ) and especially 5000 L / (cm * mol Ag ) and especially 6000L / (cm * mol Ag ) is greater than.

[0041] The silver nanoplatelets contained by the claimed UV-Vis radiation curable inks have a surface stabilizer of the general formula (I): [ka] [In the formula, residue R A is a C2-C4 alkyl group substituted with a hydroxy group; residue R Bis selected from C1-C4 alkyl groups and C2-C4 alkyl groups substituted with hydroxy groups; Cat + Na + , K. + , Cs + and Rb + Without being bound by theory, it is believed that the surface stabilizers of general formula (I) help to prevent aggregation and precipitation of the silver nanoplatelets in the claimed security inks, as well as to facilitate migration of the silver nanoplatelets from the ink layer mass obtained in the claimed security inks to the ink layer-air interface and the ink layer-substrate interface.

[0042] The cation Cat in the general formula (I) + is preferably Na + , K. + and Cs + is selected from the group consisting of:

[0043] The surface stabilizer of general formula (I) can be present in an amount of about 0.4% to about 5%, preferably about 0.5% to about 3%, more preferably about 0.5% to about 1.5%, and especially preferably about 0.5% to about 1% by weight percent (wt-%) of the silver nanoplatelets.

[0044] The term "C1-C4 alkyl group" as used herein means a saturated, linear or branched, monovalent hydrocarbon group of one to four carbon atoms (C1-C4). Examples of C1-C4 alkyl groups include methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, isopropyl, -CH(CH3)2), 1-butyl (n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2-butyl (s-Bu, s-butyl, -CH(CH3)CH2CH3), and 2-methyl-2-propyl (t-Bu, t-butyl, -C(CH3)3).

[0045] The term "hydroxy-substituted C2-C4 alkyl group" means a linear or branched alkyl group having 2 to 4 carbon atoms that is substituted with a hydroxy group (-OH). The C2-C4 alkyl group can be substituted with one or two hydroxy groups.

[0046] In the general formula (I), the residue R A may be a C2-C4 alkyl group substituted with two hydroxy groups, and the residue R B can be a C1-C4 alkyl group.

[0047] In a preferred embodiment according to the invention, the residue R A and R B are each independently a C2-C4 alkyl group substituted with a hydroxy group, preferably one hydroxy group. Thus, in one embodiment according to the invention, the residue R A and R B are independently selected from the group consisting of -CH2CH2OH, -CH2CH(OH)CH3, -CH2CH2CH2OH, -CH(CH3)(CH2OH), -CH2CH(OH)CH2CH3, -CH2CH2CH(OH)CH3, -CH2CH2CH2CH2OH, -CH(CH3)CH(OH)CH3, -CH(CH2OH)CH2CH3, -CH(CH3)CH2CH2OH, -CH2CH(CH2OH)CH3, -CH2C(CH3)(OH)CH3, -CH2CH(CH3)CH2(OH), -CH2C(OH)(CH3)2, -CH2C(CH3)(CH2OH), more preferably selected from the group consisting of -CH2CH2OH, -CH2CH(OH)CH3, and -CH2CH2CH2OH. A and R B may be the same or different.

[0048] Examples of dithiocarbamate salts of general formula (I) include, but are not limited to, sodium bis(2-hydroxyethyl)dithiocarbamate, potassium bis(2-hydroxyethyl)dithiocarbamate, cesium bis(2-hydroxyethyl)dithiocarbamate, sodium bis(3-hydroxypropyl)dithiocarbamate, potassium bis(3-hydroxypropyl)dithiocarbamate, cesium bis(3-hydroxypropyl)dithiocarbamate, sodium bis(4-hydroxybutyl)dithiocarbamate, potassium bis(4-hydroxybutyl)dithiocarbamate, and cesium bis(4-hydroxybutyl)dithiocarbamate.

[0049] To prevent aggregation and precipitation of the silver nanoplatelets upon storage, the silver nanoplatelets may have an additional surface stabilizer on their surface.

[0050] In a preferred embodiment, the silver nanoplatelets have on their surface an additional surface stabilizer of general formula (II): [ka] [In the formula, R 1 is H, C1-C 18 alkyl, phenyl, C1-C8 alkylphenyl, or CH2COOH; R 2 , R 3 , R 4 , R 5 , R 6 and R 7 are each independently H, C1-C8 alkyl, or phenyl; Y is O or NR 8 and; R 8 is H or C1-C8 alkyl; k1 is an integer ranging from 1 to 500; k2 and k3 are each independently 0 or an integer ranging from 1 to 250; k4 is 0 or 1; and k5 is an integer ranging from 1 to 5. Preferably, in general formula (II), Y represents O. Also preferably, in general formula (II), k4 is 0.

[0051] The surface stabilizer of general formula (II) preferably has an average molecular weight (Mn) of 1,000 to 20,000 [g / mol], more preferably 1,000 to 10,000 [g / mol], and most preferably 1,000 to 6,000 [g / mol].

[0052] If the surface stabilizer of Formula (I) contains, for example, ethylene oxide units (EO) and propylene oxide units (PO), the order of the (EO) and (PO) can be fixed (block copolymer) or not (random copolymer).

[0053] Preferably, in general formula (II), R 1 is H or C1-C 18 alkyl, and R 2 , R 3 , R 4 , R 5 , R 6 and R 7 are each independently H, CH3, or C2H5, k1 is an integer ranging from 22 to 450, k2 and k3 are each independently 0 or an integer ranging from 1 to 250, k4 is 0 or 1, and k5 is an integer ranging from 1 to 5. More preferably, in general formula (II), R 1 is H or C1-C4 alkyl, and R 2 , R 3 , R 4 , R 5 , R 6 and R 7 are each independently H or CH3, k1 is an integer ranging from 22 to 450, k2 and k3 are each independently 0 or an integer ranging from 1 to 100, k4 is 0, and k5 is an integer ranging from 1 to 4.

[0054] The most preferred surface stabilizers of general formula (II) have the general formula (IIa): [ka] [In the formula, R 1 is H or a C1-C8 alkyl group, in particular H or CH3, k1 is an integer ranging from 22 to 450, especially from 22 to 150.

[0055] Preferred surface stabilizers of general formula (II) have an average molecular weight (M n ) with MPEG thiol (poly(ethylene glycol) methyl ether thiol), an average M of 2000-6000 n and the like.

[0056] The silver nanoplatelets contained in the security ink may further comprise a surface stabilizer which is a polymer or copolymer as described in WO200674969, which can be obtained by a process comprising the following steps: i-1) In a first step, one or more ethylenically unsaturated monomers are polymerized in the presence of at least one nitroxyl ether having the following structural elements: [ka] where X represents a group having at least one carbon atom, such that a free radical X· derived from X is capable of initiating polymerization; or i-2) In the first step, at least one stable free nitroxyl radical is produced. [ka] and polymerizing one or more ethylenically unsaturated monomers in the presence of a free radical initiator; wherein at least one monomer used in step i-1) or i-2) is a C1-C6 alkyl or hydroxy C1-C6 alkyl ester of acrylic or methacrylic acid; and optionally ii) A second step which comprises modifying the polymer or copolymer prepared in i-1) or i-2) by transesterification, amidation, hydrolysis or anhydride modification or a combination thereof.

[0057] The monomer of step i-1) or i-2) is preferably a 4-vinyl-pyridine or pyridinium-ion, a 2-vinyl-pyridine or pyridinium-ion, a 1-vinyl-imidazole or imidazolinium-ion, or a compound of formula CH═C(R a )-(C=Z)-R b wherein R a is hydrogen or methyl; R b is NH2, O - (Me + ), unsubstituted C1-C 18 Alkoxy, C2-C interrupted by at least one N and / or O atom 100 Alkoxy or hydroxy substituted C1-C 18 Alkoxy, unsubstituted C1-C 18 Alkylamino, unsubstituted di(C1-C 18 alkyl)amino, hydroxy-substituted C1-C 18 Alkylamino or hydroxy substituted di(C1-C 18 alkyl)amino, -O(CH2) y NR 15 R 16 , or -O(CH2) y N + HR 15 R 16 An - , -N(CH2) y NR 15 R 16 , or -N(CH2) y N+ HR 15 R 16 An - and where An - is a monovalent anion of an organic or inorganic acid; y is an integer from 2 to 10; R 15 is a saturated or unsaturated, linear or branched chain alkyl of 1 to 22 carbon atoms; R 16 is a saturated or unsaturated, linear or branched chain alkyl of 1 to 22 carbon atoms; Me + is a monovalent metal atom or an ammonium ion; Z is oxygen or sulfur.

[0058] The second step ii) is preferably a transesterification reaction. In step ii) the alcohol is preferably of formula R c -[O-CH2-CH2-] c -OH ethoxylates, c is a saturated or unsaturated, linear or branched chain alkyl of 1 to 22 carbon atoms, or alkylaryl or dialkylaryl of up to 24 carbon atoms, and c is 1 to 150.

[0059] Preferably, step i-1) or i-2) is carried out twice to obtain a block copolymer, wherein in the first or second radical polymerization step the monomer or monomer mixture contains 50 to 100% by weight of C1-C6 alkyl esters of acrylic or methacrylic acid, based on the total weight of the monomers, and in the second or first radical polymerization step, respectively, the ethylenically unsaturated monomer or monomer mixture contains at least one monomer without a first or second ester bond.

[0060] In the first polymerization step, the monomer or monomer mixture contains 50 to 100% by weight of a C1-C6 alkyl ester of acrylic or methacrylic acid (first monomer) based on the total weight of the monomers, and in the second polymerization step, the ethylenically unsaturated monomer or monomer mixture contains 4-vinyl-pyridine or pyridinium ion, 2-vinyl-pyridine or pyridinium ion, vinyl-imidazole or imidazolinium ion, 3-dimethylaminoethyl acrylamide, 3-dimethylaminoethyl methacrylamide or the corresponding ammonium ion, 3-dimethylaminopropyl acrylamide or the corresponding ammonium ion, or 3-dimethylaminopropyl methacrylamide or the corresponding ammonium ion (second monomer).

[0061] Preferably, the nitroxyl ether has the structure: [ka] It has.

[0062] The surface stabilizer is preferably a copolymer obtainable by a process comprising the following steps: i-2) In the first step, the next structural element [ka] polymerizing a first monomer which is a C1-C6 alkyl or hydroxy C1-C6 alkyl ester of acrylic or methacrylic acid, and a second monomer selected from 4-vinyl-pyridine or pyridinium ions, 2-vinyl-pyridine or pyridinium ions, 1-vinyl-imidazole or imidazolinium ions, 3-dimethylaminoethyl acrylamide, 3-dimethylaminoethyl methacrylamide, 3-dimethylaminopropyl acrylamide, and 3-dimethylaminopropyl methacrylamide, in the presence of at least one nitroxyl ether having the formula: ii) a second step comprising the modification by transesterification of the polymer or copolymer prepared in i-1), wherein the alcohol of step ii) is of formula R c -[O-CH2-CH2-] c -OH ethoxylates, c is a saturated or unsaturated, linear or branched chain alkyl of 1 to 22 carbon atoms, or alkylaryl or dialkylaryl of up to 24 carbon atoms, and c is 1 to 150.

[0063] Preferably, the surface stabilizer obtained by the processes described herein is a copolymer of formula (III): [ka] [In the formula, R 17a , R 17b and R 17c are each independently H or methyl; R 18a and R 18b is H or methyl; R 19a is a saturated or unsaturated, linear or branched chain alkyl of 1 to 22 carbon atoms; R 19b is R c -[O-CH2-CH2-] c -O-; R 19c teeth [ka] , -C(=O)-NH-(CH2) y NR 15 R 16 , or -C(=O)-NH-(CH2) y N + HR 15 R 16 An - and; where An - is a monovalent anion of an organic or inorganic acid; y is an integer from 2 to 10; R 15 is a saturated or unsaturated, linear or branched chain alkyl of 1 to 22 carbon atoms; R 16 is a saturated or unsaturated, linear or branched chain alkyl of 1 to 22 carbon atoms; R c is a saturated or unsaturated, linear or branched chain alkyl of 1 to 22 carbon atoms, or alkylaryl or dialkylaryl of 24 or fewer carbon atoms, and c is 1 to 150; y1, y2, and y3 are each independently an integer of 1 to 200.

[0064] More preferably, the surface stabilizer is a copolymer represented by formula (III-a): [ka] [In the formula, R 18a and R 18b is H or methyl; y1, y2, and y3 are each independently an integer of 1 to 200; and c is an integer between 1 and 150. The order of the monomers with the subscripts y1 and y2 may be fixed (block copolymer) or not (random copolymer).

[0065] Examples of preferred copolymers for use as surface stabilizers are the copolymers described in Examples A3 and A6 of WO200674969.

[0066] To improve the stability of the optical properties of the silver nanoplatelets upon storage or exposure to heat, the silver nanoplatelets may have an additional surface stabilizer of general formula (IV): [ka] [In the formula, R 9is a hydrogen atom or a group of formula -CHR 11 -N(R 12 )(R 13 ) group; R 10 is a hydrogen atom, a halogen atom, a C1-C8 alkoxy group, or a C1-C8 alkyl group; R 11 is H or C1-C8 alkyl; R 12 and R 13 are each independently a C1-C8 alkyl, a hydroxy C1-C8 alkyl group, or a group of the formula -[(CH2CH2)-O] n1 -CH2CH2-OH group, and n1 is 1 to 5.

[0067] Examples of compounds of formula (IV) include, but are not limited to: [ka] There is.

[0068] The dispersion of silver nanoplatelets used to prepare the claimed UV-Vis radiation curable security ink can be obtained by using a method comprising the following steps: 1) Silver precursor, a compound of formula (II) [ka] [In the formula, R 1 is H, C1-C 18 alkyl, phenyl, C1-C8 alkylphenyl, or CH2COOH; R 2 , R 3 , R 4 , R 5 , R 6 and R 7 are each independently H, C1-C8 alkyl, or phenyl; Y is O or NR 8 and; R 8is H or C1-C8 alkyl; k1 is an integer ranging from 1 to 500; k2 and k3 are each independently 0 or an integer ranging from 1 to 250; k4 is 0 or 1; k5 is an integer ranging from 1 to 5], A polymer or copolymer obtainable by a process comprising the steps of: [i-1) In the first step, the structural element [ka] (wherein X represents a group having at least one carbon atom such that the free radical X· derived from X is capable of initiating polymerization). or polymerizing one or more ethylenically unsaturated monomers in the presence of at least one nitroxyl ether having the formula: i-2) In the first step, at least one stable free nitroxyl radical is produced. [ka] and polymerizing one or more ethylenically unsaturated monomers in the presence of a free radical initiator; wherein at least one monomer used in step i-1) or i-2) is a C1-C6 alkyl or hydroxy C1-C6 alkyl ester of acrylic or methacrylic acid; and optionally ii) a second step comprising modifying the polymer or copolymer prepared in i-1) or i-2) by transesterification, amidation, hydrolysis or anhydride modification, or a combination thereof; preparing a solution comprising water and, optionally, an antifoaming agent; 2) preparing a solution containing a reducing agent containing at least one boron atom in the molecule and water; 3) adding the solution obtained in step 1) to the solution obtained in step 2) and adding one or more complexing agents; 4) adding a solution of hydrogen peroxide in water; and 5) Adding one or more surface stabilizers to the mixture from step 4).

[0069] Silver precursors are AgNO3; AgClO4; Ag2SO4; AgCl; AgF; AgOH; Ag2O; AgBF4; AgIO3; AgPF6; R 200 CO2Ag, R 200 SO3Ag (where R 200 is unsubstituted or substituted C1-C 18 Alkyl, unsubstituted or substituted C5-C8 cycloalkyl, unsubstituted or substituted C7-C 18 Aralkyl, unsubstituted or substituted C-C 18 Aryl or unsubstituted or substituted C2-C 18 Heteroaryl); a silver(I) compound selected from the group consisting of dicarboxylic acids, tricarboxylic acids, polycarboxylic acids, polysulfonic acids, Ag salts of P-containing acids, and mixtures thereof, preferably silver nitrate, silver acetate, silver perchlorate, silver methanesulfonate, silver benzenesulfonate, silver toluenesulfonate, silver trifluoromethanesulfonate, silver sulfate, silver fluoride, and mixtures thereof, more preferably silver nitrate.

[0070] The reducing agent is selected from the group consisting of alkali or alkaline earth metal borohydrides such as sodium borohydride, alkali or alkaline earth metal acyloxyborohydrides such as sodium triacetoxyborohydride, alkali or alkaline earth metal alkoxy or aryloxyborohydrides such as sodium trimethoxyborohydride, aryloxyboranes such as catecholborane, and amine-borane complexes such as diethylanilineborane, tert-butylamineborane, morpholineborane, dimethylamineborane, triethylamineborane, pyridineborane, ammoniaborane, and mixtures thereof. Sodium borohydride is most preferred.

[0071] The complexing agent(s) are selected from the group consisting of chlorine-containing compounds capable of liberating chloride ions under the reaction conditions, such as metal chlorides, alkyl or aryl ammonium chlorides, phosphonium chlorides; primary or secondary amines and the corresponding ammonium salts, such as methylamine or dimethylamine; ammonia and the corresponding ammonium salts; and aminocarboxylic acids and their salts, such as ethylenediaminetetraacetic acid.

[0072] Non-limiting examples of complexing agents include ammonia, methylamine, dimethylamine, ethylamine, ethylenediamine, diethylenetriamine, ethylenediaminetetraacetic acid (EDTA); ethylenediamine N,N'-disuccinic acid (EDDS); methylglycine diacetic acid (MGDA); diethylenetriaminepentaacetic acid (DTPA); propylenediaminetetraacetic acid (PDTA); glutamic acid N,N-diacetic acid (N,N-dicarboxymethylglutamic acid tetrasodium salt (GLDA)); nitrilotriacetic acid (NTA), and any salts thereof; N-hydroxyethylethylenediaminetriacetic acid (HEDTA), triethylenetetraaminehexaacetic acid (TTHA), N-hydroxyethyliminodiacetic acid (HEIDA), dihydroxyethylglycine (DHEG), ethylenediaminetetrapropionic acid (EDTP) and their derivatives, such as the trisodium salt of methylglycine diacetic acid (NaMGDA) and the tetrasodium salt of EDTA.

[0073] The antifoaming agent is a compound or composition capable of suppressing foam formation in the reaction mixture, such as commercially available TEGO® Foamex 1488, 1495, 3062, 7447, 800, 8030, 805, 8050, 810, 815N, 822, 825, 830, 835, 840, 842, 843, 845, 855, 860, 883, K3, K7, K8, N, Sigma's Antifoam SE-15, Struktol SB-2080, etc. The amount of antifoaming agent ranges from 0.00001% to 5% by weight, preferably from 0.0001% to 3%, more preferably from 0.001% to 2% by weight, based on the total weight of the reaction mixture before the addition of hydrogen peroxide.

[0074] The antifoaming agent can be added to the solution prepared in step 1) and / or the solution prepared in step 2).

[0075] The silver nanoplatelet formation reaction is carried out by gradually adding the silver precursor solution to the reducing agent solution, while the temperature of both solutions ranges from -3°C to 40°C, and the gradual addition is completed within 15 minutes to 24 hours.

[0076] The silver nanoplatelets obtained in steps 4) and / or 5) can be subjected to further purification and / or isolation methods such as decantation, (ultra)filtration, (ultra)centrifugation, reversible or irreversible coagulation, phase transfer with organic solvents, and combinations thereof. The dispersion of silver nanoplatelets can contain up to about 99 wt-% silver nanoplatelets, preferably 5 wt-% to 99 wt-% silver nanoplatelets, more preferably 5 wt-% to 90 wt-% silver nanoplatelets, where wt-% is based on the total weight of the dispersion.

[0077] Starting from the silver nanoplatelets obtained by purification and / or isolation, the silver nanoplatelets having a surface stabilizer of general formula (I) can be prepared: i) CS2 in the presence of silver nanoplatelets in the presence of A R B Reaction of NH with an amine followed by treatment with a base, ii) CS2 in the presence of silver nanoplatelets and a base is reacted with CS2 according to the formula R A R B reacting with amines of NH, or iii) CS2 is dissolved in the solution of formula R A R B Reaction of NH with an amine, followed by treatment with a base, gives the dithiocarbamate of general formula (I), which is then reacted with silver nanoplatelets It can be prepared by

[0078] The base is selected from alkali metal hydroxides, alkali metal alkoxides, and mixtures thereof, wherein the alkali metal is selected from sodium, potassium, and cesium. Preferred examples of bases used in the preparation process include, but are not limited to, NaOH, KOH, CsOH, RbOH, NaOCH2CH3, KOCH2CH3, CsOCH2CH3, and mixtures thereof.

[0079] The silver nanoplatelets described herein are disclosed in European Patent Application No. 20206698.1, filed November 10, 2020 by BASF SE, entitled "Composition Comprising Silver Nanoplatelets."

[0080] The claimed UV-Vis radiation-curable security inks contain b) at least a hydroxy-functionalized perfluoropolyether surfactant. Surprisingly, it has been found that the use of at least a hydroxy-functionalized perfluoropolyether surfactant as a surfactant in the UV-Vis radiation-curable inks described herein is essential for producing security features that exhibit a metallic yellow color when viewed in incident light. As evidenced, for example, by Tables 4c and 5c, only UV-Vis radiation-curable inks containing at least a hydroxy-functionalized perfluoropolyether surfactant provide security features that exhibit a metallic yellow color when viewed in incident light. Security features produced with UV-Vis radiation-curable inks that lack surfactant (e.g., as in Ink C16) or that contain perfluoropolyether surfactants lacking hydroxy functionality (e.g., as in Inks C7-C9), or surfactants lacking a perfluoropolyether backbone in addition to hydroxy functionality (e.g., as in Inks C10-C15), exhibit a brown to dark brown color in reflected light, which is inconspicuous to the average person and therefore unsuitable for dichroic security features for securing valuable documents.

[0081] The at least hydroxy-functionalized perfluoropolyether surfactant comprises a perfluoropolyether backbone and one or more, preferably two or more, terminal hydroxy functional groups, and is characterized by an average molecular weight (Mn) of less than about 2000 g / mol. As used herein, perfluoropolyether backbone refers to the residue of a perfluoropolyether polymer comprising randomly distributed repeating units selected from perfluoromethyleneoxy (-CF2O-) and perfluoroethyleneoxy (-CF2-CF2O-). The perfluoropolyether residue is linked to the terminal functional group directly or via a spacer selected from methylene(oxyethylene), 1,1-difluoroethylene-(oxyethylene), methylene-di(oxyethylene), 1,1-difluoroethylene-di(oxyethylene), methylene-tri(oxyethylene), 1,1-difluoroethylene-tri(oxyethylene), methylene-tetra(oxyethylene), 1,1-difluoroethylene-tetra(oxyethylene), methylene-penta(oxyethylene), and 1,1-difluoroethylene-penta(oxyethylene).

[0082] Preferably, the perfluoropolyether surfactant functionalized with at least a hydroxy group is a compound of general formula (V) having an average molecular weight of about 800 [g / mol] to about 2000 [g / mol] [ka] [wherein e1 and e4 are each independently an integer of 0 to 6, preferably 0 to 4; e2 and e3 are selected so that the average molecular weight is about 800 [g / mol] to about 2000 [g / mol].] In a preferred embodiment, the sum of the integers e1 and e4 is 3 to 9.

[0083] Preferably, the perfluoropolyether surfactants described herein are present in the UV-Vis radiation curable ink in an amount of from about 0.025 wt-% to about 5 wt-%, preferably from about 0.05 wt-% to about 2.5 wt-%, and more preferably from about 0.05 wt-% to about 1.0 wt-%, where the weight percentage is based on the total weight of the UV-Vis radiation curable ink.

[0084] The claimed UV-Vis radiation curable security ink contains c) about 3 wt-% to about 12 wt-% polyvinyl chloride copolymer containing at least 69 wt-% vinyl chloride, preferably at least 75 wt-% vinyl chloride. UV-Vis radiation curable security inks that do not contain polyvinyl chloride copolymer have unattractive colors such as brown or dark brown when viewed in incident light, and low chroma values ​​C * and as a result is not suitable for use in making security features that exhibit a metallic yellow color in incident light.

[0085] Preferably, the polyvinyl chloride copolymer contains up to 90 wt-% vinyl chloride.

[0086] Preferably, the polyvinyl chloride copolymer containing at least 69 wt-% vinyl chloride is present in the claimed security inks in an amount of from about 4.9 wt-% to about 11.6 wt-%, most preferably from about 6 wt-% to about 8.6 wt-%, the weight percentages being based on the total weight of the UV-VIS radiation curable ink.

[0087] Preferably, the polyvinyl chloride copolymer is selected from the group consisting of vinyl chloride-vinyl acetate copolymer and vinyl chloride-hydroxyacrylate copolymer, such as vinyl chloride-hydroxyalkyl acrylate-Z-alkylenedioic acid, dialkyl ester copolymer, such as vinyl chloride-2-hydroxypropyl acrylate-2-butenedioic acid (Z)-, dibutyl ester copolymer. The polyvinyl chloride copolymer preferably has a molecular weight of 3 or less as determined by size exclusion chromatography using polystyrene as a standard and tetrahydrofuran as a solvent. * 10 4 g / mol~about 8 * 10 4 Particularly suitable examples of polyvinyl chloride copolymers for the present invention are commercially available from Wacker under the names Vinnol® H14 / 36 and Vinnol® E22 / 48A.

[0088] In an embodiment according to the present invention, the claimed UV-Vis radiation curable security ink is a cationically curable ink (i.e., an ink containing exclusively cationically curable monomers and no radically curable monomers) comprising d1) about 25 wt-% to about 55 wt-% of a cycloaliphatic epoxide, and about 1 wt-% to about 10 wt-% of a cationic photoinitiator; and optionally e) e1) vinyl ethers having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the cycloaliphatic epoxide of d); e2) vinyl ethers having one vinyloxy residue in an amount of less than about 5 wt.%, preferably less than or equal to about 4.1 wt.%; e3) less than about 10 wt. % of an epoxide other than a cycloaliphatic epoxide; e4) oxetanes having two oxetanyl residues in an amount of less than about 20 wt. %; e5) oxetanes having one oxetanyl residue in an amount of less than about 3.5 wt.-%, preferably less than or equal to about 3.3 wt.-%; and e6) a cationically curable compound selected from the group consisting of mixtures of e1) and / or e2) and / or e3) and / or e4) and / or e5). wherein the weight percentages are based on the total weight of the UV-Vis radiation curable security ink. Thus, an embodiment in accordance with the present invention relates to a UV-Vis radiation cationically curable security ink for producing a security feature that exhibits a blue color when viewed in transmitted light and a metallic yellow color when viewed in incident light, said ink comprising: a) about 7.5 wt-% to about 20 wt-% silver nanoplatelets having an average diameter in the range of 50-150 nm with a standard deviation of less than 60%, an average thickness in the range of 5-30 nm with a standard deviation of less than 50%, and an average aspect ratio greater than 2.0, wherein the average diameter is determined by transmission electron microscopy and the average thickness is determined by transmission electron microscopy; The silver nanoplatelets have a surface stabilizer of the general formula (I): [ka] [In the ceremony residue R A is a C2-C4 alkyl group substituted with a hydroxy group; residue R B is selected from C1-C4 alkyl groups and C2-C4 alkyl groups substituted with a hydroxy group; Cat + Na + , K. + , Cs + and Rb + is a cation selected from the group consisting of: b) perfluoropolyether surfactants functionalized with at least hydroxy groups; c) about 3 wt.-% to about 12 wt.-% polyvinyl chloride copolymer containing at least 69 wt.-% vinyl chloride; d1) about 25 wt-% to about 55 wt-% of an alicyclic epoxide, and about 1 wt-% to about 10 wt-% of a cationic photoinitiator; and optionally e) vinyl ethers having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the alicyclic epoxide of e1) d); e2) vinyl ethers having one vinyloxy residue in an amount of less than about 5 wt.%, preferably less than or equal to about 4.1 wt.%; e3) less than about 10 wt. % of an epoxide other than a cycloaliphatic epoxide; e4) oxetanes having two oxetanyl residues in an amount of less than about 20 wt. %; e5) oxetanes having one oxetanyl residue in an amount of less than about 3.5 wt.-%, preferably less than or equal to about 3.3 wt.-%; and e6) a cationically curable compound selected from the group consisting of mixtures of e1) and / or e2) and / or e3) and / or e4) and / or e5). Including, Weight percentages are based on the total weight of the UV-Vis radiation curable security ink.

[0089] In an alternative embodiment according to the present invention, the claimed UV-Vis radiation curable security ink is a hybrid curable ink (i.e., an ink containing both cationically curable and radically curable monomers) and comprises d2) about 30 wt-% to about 65 wt-% of a mixture of a cycloaliphatic epoxide and a radically curable compound, about 1 wt-% to about 6 wt-% of a cationic photoinitiator, and about 1 wt-% to about 6 wt-% of a free radical photoinitiator; and optionally e): e1) vinyl ethers having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the cycloaliphatic epoxide of d); e2) vinyl ethers having one vinyloxy residue in an amount of less than about 5 wt.%, preferably less than or equal to about 4.1 wt.%; e3) less than about 10 wt. % of an epoxide other than a cycloaliphatic epoxide; e4) oxetanes having two oxetanyl residues in an amount of less than about 20 wt. %; e5) oxetanes having one oxetanyl residue in an amount of less than about 3.5 wt.-%, preferably less than or equal to about 3.3 wt.-%; and e6) a cationically curable compound selected from the group consisting of mixtures of e1) and / or e2) and / or e3) and / or e4) and / or e5). wherein the weight percentages are based on the total weight of the UV-Vis radiation curable security ink. Thus, an embodiment according to the present invention relates to a UV-Vis radiation hybrid curable security ink for producing security features that exhibit a blue color when viewed in transmitted light and a metallic yellow color when viewed in incident light, said ink comprising: a) about 7.5 wt-% to about 20 wt-% silver nanoplatelets having an average diameter in the range of 50-150 nm with a standard deviation of less than 60%, an average thickness in the range of 5-30 nm with a standard deviation of less than 50%, and an average aspect ratio greater than 2.0, wherein the average diameter is determined by transmission electron microscopy and the average thickness is determined by transmission electron microscopy; The silver nanoplatelets have a surface stabilizer of the general formula (I): [ka] [In the ceremony residue R A is a C2-C4 alkyl group substituted with a hydroxy group; residue R B is selected from C1-C4 alkyl groups and C2-C4 alkyl groups substituted with a hydroxy group; Cat + Na + , K. + , Cs + and Rb + is a cation selected from the group consisting of: b) perfluoropolyether surfactants functionalized with at least hydroxy groups; c) polyvinyl chloride copolymers containing from about 3 wt-% to about 12 wt-% of at least 69 wt-% vinyl chloride; d2) about 30 wt.-% to about 65 wt.-% of a mixture of a cycloaliphatic epoxide and a radically curable compound, about 1 wt.-% to about 6 wt.-% of a cationic photoinitiator, and about 1 wt.-% to about 6 wt.-% of a free radical photoinitiator; and optionally e): e1) vinyl ethers having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the cycloaliphatic epoxide of d); e2) vinyl ethers having one vinyloxy residue in an amount of less than about 5 wt.%, preferably less than or equal to about 4.1 wt.%; e3) less than about 10 wt. % of an epoxide other than a cycloaliphatic epoxide; e4) oxetanes having two oxetanyl residues in an amount of less than about 20 wt. %; e5) oxetanes having one oxetanyl residue in an amount of less than about 3.5 wt.-%, preferably less than or equal to about 3.3 wt.-%; and e6) a cationically curable compound selected from the group consisting of mixtures of e1) and / or e2) and / or e3) and / or e4) and / or e5). where the weight percentages are based on the total weight of the UV-Vis radiation curable security ink. If the claimed hybrid inks contain only cycloaliphatic epoxides described herein as cationically curable monomers, the ratio of the weight percentage (wt-%) of the radically curable compounds to the weight percentage (wt-%) of the cycloaliphatic epoxide is preferably less than 1.6:1, more preferably less than 1:1, and even more preferably less than 0.5:1. If the claimed hybrid inks contain both cycloaliphatic epoxides described herein and cationically curable compounds described herein as cationically curable monomers, the ratio of the weight percentage (wt-%) of the radically curable compounds to the sum of the weight percentage (wt-%) of the cycloaliphatic epoxide and the weight percentage (wt-%) of the cationically curable compounds is preferably less than 1.6:1, more preferably less than 1:1, and even more preferably less than 0.5:1.

[0090] Advantageously, the claimed UV-Vis radiation cationically curable security inks and the claimed UV-Vis radiation hybrid curable security inks provide security features with improved mechanical resistance properties compared to security features known in the art obtained from UV radically curable inks or solvent-based inks, in particular from UV radically curable inks or solvent-based inks containing high concentrations of silver nanoplatelets.

[0091] The claimed security ink comprises: d1) about 25 wt-% to about 55 wt-% of a cycloaliphatic epoxide, and about 1 wt-% to about 10 wt-% of a cationic photoinitiator; or d2) about 30 wt-% to about 65 wt-% of a mixture of a cycloaliphatic epoxide and a radically curable compound, about 1 wt-% to about 6 wt-% of a cationic photoinitiator, and about 1 wt-% to about 6 wt-% of a free-radical photoinitiator, the weight percentages being based on the total weight of the UV-Vis radiation curable security ink.

[0092] As known to those skilled in the art, cationically curable monomers cure via a cationic mechanism consisting of activation of one or more photoinitiators by UV-Vis light, which liberates cationic species, such as acids, which then initiate polymerization of the monomers to form a cured binder.

[0093] As is well known to those skilled in the art, cycloaliphatic epoxides contain at least a substituted or unsubstituted epoxycyclohexyl residue: [ka] It is a cationically curable monomer containing

[0094] Preferably, the cycloaliphatic epoxides described herein contain at least one cyclohexane ring and at least two epoxide groups. More preferably, the cycloaliphatic epoxides have the general formula (VI): [ka] [wherein -L- represents a single bond or a divalent group containing one or more atoms]. The alicyclic epoxide of general formula (VI) may optionally be substituted with one or more linear or branched alkyl groups containing 1 to 10 carbon atoms (e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), preferably alkyl groups containing 1 to 3 carbon atoms (e.g., methyl, ethyl, n-propyl, and i-propyl).

[0095] In general formula (VI), the divalent group -L- can be a straight or branched chain alkylene group containing 1 to 18 carbon atoms. Examples of the straight or branched chain alkylene group include, without limitation, methylene, methylmethylene, dimethylmethylene, ethylene, propylene, and trimethylene.

[0096] In general formula (VI), the divalent group -L- can be a divalent alicyclic hydrocarbon group or a cycloalkydene group, such as 1,2-cyclopentylene, 1,3-cyclopentylene, cyclopentylidene, 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, and cyclohexylidene.

[0097] In general formula (VI), -L- can be a divalent radical containing one or more oxygen-containing linking groups, said oxygen-containing linking groups being selected from the group consisting of -C(-O)-, -OC(=O)O-, -C(=O)O-, and -O-. Preferably, the cycloaliphatic epoxide is of general formula (VI), wherein -L- is a divalent radical containing one or more oxygen-containing linking groups, said oxygen-containing linking groups being selected from the group consisting of -C(=O)-, -OC(=O)O-, -C(=O)O-, and -O-, more preferably an cycloaliphatic epoxide of general formula (VI-a), (VI-b), or (VI-c) as defined below. [ka] [In the formula, L 1 may be the same or different in each occurrence and is a linear or branched alkyl group containing 1 to 10 carbon atoms (e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), preferably containing 1 to 3 carbon atoms (e.g., methyl, ethyl, n-propyl, and i-propyl); L 2 may be the same or different in each occurrence and is a linear or branched alkyl group containing 1 to 10 carbon atoms (e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), preferably containing 1 to 3 carbon atoms (e.g., methyl, ethyl, n-propyl, and i-propyl); l1 and l2 are each independently an integer of 0 to 9, preferably 0 to 3; [ka] [In the formula, L 1 may be the same or different in each occurrence and are linear or branched alkyl groups containing 1 to 10 carbon atoms (e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), preferably containing 1 to 3 carbon atoms (e.g., methyl, ethyl, n-propyl, and i-propyl); L 2 may be the same or different in each occurrence and are linear or branched alkyl groups containing 1 to 10 carbon atoms (e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), preferably containing 1 to 3 carbon atoms (e.g., methyl, ethyl, n-propyl, and i-propyl); l1 and l2 are each independently an integer of 0 to 9, preferably an integer of 0 to 3; -L 3 - is a single bond or a linear or branched divalent hydrocarbon radical containing 1 to 10 carbon atoms, preferably 3 to 8 carbon atoms, such as alkylene radicals, e.g., trimethylene, tetramethylene, hexamethylene, and 2-ethylhexylene, and cycloalkylene radicals, e.g., 1,2-cyclohexylene, 1,3-cyclohexylene, and 1,4-cyclohexylene, and cyclohexylidene; [ka] [In the formula, L 1 may be the same or different in each occurrence and is a linear or branched alkyl group containing 1 to 3 carbon atoms, e.g., methyl, ethyl, n-propyl, and i-propyl; L 2 may be the same or different in each occurrence and is a linear or branched alkyl group containing 1 to 3 carbon atoms, e.g., methyl, ethyl, n-propyl, and i-propyl; l1 and l2 each independently represent an integer of 0 to 9, preferably 0 to 3.

[0098] Preferred cycloaliphatic epoxides of general formula (VI-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.

[0099] Preferred cycloaliphatic epoxides of general formula (VI-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.

[0100] A preferred cycloaliphatic epoxide of general formula (VI-c) is 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane.

[0101] Further cycloaliphatic epoxides include those of general formula (VII-a) and those of general formula (VII-b), which may optionally be substituted with one or more linear or branched alkyl groups containing 1 to 10 carbon atoms (e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, hexyl, octyl, and decyl), preferably those containing 1 to 3 carbon atoms (e.g., methyl, ethyl, n-propyl, and i-propyl). [ka]

[0102] The cycloaliphatic epoxides described herein can be hydroxy-modified or (meth)acrylate-modified. Examples are commercially available from Daicel Corp. under the names Cyclomer A400 (CAS: 64630-63-3) and Cyclomer M100 (CAS No.: 82428-30-6), or from TetraChem / Jiangsu under the names TTA 15 and TTA16 46.

[0103] The cationic photoinitiators (also referred to in the art as photoacid generators) used in the claimed UV-Vis radiation curable inks are onium salts, 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, even more preferably selected from the group consisting of sulfonium salts, iodonium salts and mixtures thereof.

[0104] The iodonium salts described herein have a cationic portion and an anionic portion, where the anionic portion is preferably BF4 - , B(C6F5)4 - , PF6 - , AsF6 - , SbF6 - or CF3SO3 - , more preferably SbF6 - wherein the cationic moiety is preferably an aromatic iodonium ion, more preferably an iodonium ion containing two aryl groups, each of which may be independently substituted with one or more alkyl groups (e.g., 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, preferably one or more alkyl groups. Iodonium salts particularly suitable for the present invention are commercially available and known under the names DEUTERON UV 1240, DEUTERON UV 1242, DEUTERON UV 2257, DEUTERON UV 1250, and DEUTERON UV 3100 (all available from DEUTERON), OMNICAT 250, OMNICAT 440, and OMNICAT 445 (all available from IGM Resins), SpeedCure 937, SpeedCure 938, and SpeedCure 939 (all available from Lambson).

[0105] The sulfonium salts described herein have a cationic portion and an anionic portion, where the anionic portion is preferably BF4 - , B(C6F5)4 - , PF6 - , (PF 6-h (C j F 2j-1 ) h ) - (where h is an integer from 1 to 5, and j is an integer from 1 to 4), AsF6 - , SbF6 - , CF3SO3 - , perfluoroalkylsulfonates or pentafluoro-hydroxyantimonates, more preferably SbF6 - wherein the cationic moiety is preferably an aromatic sulfonium ion, more preferably a sulfonium ion containing two or more aryl groups, wherein the two or more aryl groups may be independently substituted with one or more alkyl groups (e.g., methyl, ethyl, isobutyl, tertbutyl, etc.), one or more alkoxy groups, one or more aryloxy groups, one or more halogen-containing groups, one or more hydroxy groups, or combinations thereof. Suitable examples of sulfonium ions containing two or more aryl groups include, without limitation, triarylsulfonium ion, diphenyl[4-(phenylthio)phenyl]sulfonium ion, bis[4-(diphenylsulfonio)phenyl]sulfonium ion, triphenylsulfonium ion, and tris[4-(4-acetylphenyl)sulfanylphenyl]sulfonium ion. Examples of sulfonium salts that are particularly suitable for the present invention are commercially available under the names SpeedCure 976, SpeedCure 976D, and SpeedCure 992 (all available from Lambson), ESACURE 1187, OMNICAT 270, OMNICAT 320, OMNICAT 432, and OMNICAT 550 (all available from IGM Resins).

[0106] The oxonium salts described herein have a cationic portion and an anionic portion, where the anionic portion is preferably BF4 -, B(C6F5)4 - , PF6 - , AsF6 - , SbF6 - or CF3SO3 - , more preferably BF4 - wherein the cationic moiety is preferably an aromatic oxonium ion, more preferably a pyrylium ion, preferably substituted with one or more aryl groups, which may be substituted independently with one or more alkyl groups (e.g., methyl, ethyl, isobutyl, tertbutyl, etc.), one or more alkoxy groups, one or more nitro groups, one or more halogen groups, one or more hydroxy groups, or combinations thereof. An oxonium salt particularly suitable for the present invention is 2,4,6-triphenylpyrylium tetrafluoroborate.

[0107] Other examples of useful cationic 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.

[0108] The radically curable compounds described herein are selected from radically curable monomers, radically curable oligomers, and mixtures thereof.

[0109] The radically curable monomers described herein are selected from the group consisting of mono(meth)acrylates, di(meth)acrylates, tri(meth)acrylates, tetra(meth)acrylates and mixtures thereof, preferably from the group consisting of tri(meth)acrylates, tetra(meth)acrylates and mixtures thereof. In the context of the present invention, the term "(meth)acrylate" refers to the acrylate as well as the corresponding methacrylate.

[0110] 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 trimethylolpropaneformal(meth)acrylate, nonylphenol(meth)acrylate, isobornyl(meth)acrylate, isodecyl(meth)acrylate, lauryl(meth)acrylate, stearyl(meth)acrylate, octyldecyl(meth)acrylate, and the like. (meth)acrylate, tridecyl (meth)acrylate, methoxypoly(ethylene 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-pentanediol di(meth)acrylate, alkoxylated di(meth)acrylate, ester diol di(meth)acrylate, and mixtures thereof.

[0111] Preferred examples of di(meth)acrylates include bisphenol A di(meth)acrylate, alkoxylated (e.g., 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, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, and mixtures thereof.

[0112] Preferred examples of tri(meth)acrylates include trimethylolpropane tri(meth)acrylate, alkoxylated (e.g., ethoxylated and propoxylated) trimethylolpropane tri(meth)acrylate, alkoxylated (e.g., ethoxylated and propoxylated) glycerol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, alkoxylated pentaerythritol tri(meth)acrylate, alkoxylated (e.g., ethoxylated and propoxylated) pentaerythritol tri(meth)acrylate, and mixtures thereof.

[0113] Preferred examples of tetra(meth)acrylates include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, alkoxylated (e.g., ethoxylated and propoxylated) pentaerythritol tetra(meth)acrylate, and mixtures thereof, preferably selected from the group consisting of ditrimethylolpropane tetra(meth)acrylate, alkoxylated pentaerythritol tetra(meth)acrylate, and mixtures thereof.

[0114] As used herein, the term "radically curable oligomer" refers to a radically curable (meth)acrylate oligomer, which may be branched or linear in nature and may have terminal and / or pendant (meth)acrylate functional group(s). Preferably, the radically curable oligomer is 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.

[0115] Suitable examples of epoxy (meth)acrylate oligomers include, without limitation, aliphatic epoxy (meth)acrylate oligomers, particularly mono(meth)acrylates, di(meth)acrylates, and tri(meth)acrylates, as well as aromatic epoxy (meth)acrylate oligomers. Suitable examples of aromatic epoxy (meth)acrylate oligomers include bisphenol-A (meth)acrylate oligomers, such as bisphenol-A mono(meth)acrylate, bisphenol-A di(meth)acrylate, and bisphenol-A tri(meth)acrylate, and alkoxylated (e.g., ethoxylated and propoxylated) bisphenol-A (meth)acrylate oligomers, such as alkoxylated bisphenol-A mono(meth)acrylate, alkoxylated bisphenol-A di(meth)acrylate, and alkoxylated bisphenol-A tri(meth)acrylate, preferably alkoxylated bisphenol-A di(meth)acrylate.

[0116] The free radical photoinitiator used in the present invention is preferably selected from the group consisting of hydroxyketones (e.g., alpha-hydroxyketones), alkoxyketones (e.g., alpha-alkoxyketones), acetophenones, benzophenones, ketosulfones, benzil ketals, benzoin ethers, phosphine oxides, phenyl glyoxylates, thioxanthones, and mixtures thereof, more preferably selected from the group consisting of phosphine oxides, hydroxyketones, thioxanthones, and mixtures thereof.

[0117] Suitable alpha-hydroxy ketones 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].

[0118] Suitable acetophenones include, without limitation, 2,2-diethoxyacetophenone, and 2-methoxy-2-phenylacetophenone.

[0119] Suitable benzophenones include, without limitation, benzophenone, polymeric benzophenone derivatives, 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.

[0120] Suitable ketosulfones include, without limitation, 1-[4-(4-benzoylphenylsulfanyl)phenyl]-2-methyl-2-(4-methylphenylsulfonyl)propan-1-one.

[0121] Suitable benzyl ketals include, without limitation, 2,2-dimethoxy-2-phenylacetophenone.

[0122] Suitable 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.

[0123] Suitable phosphine oxides include, without limitation, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, ethylphenyl(2,4,6-trimethylbenzoyl)phenylphosphinate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, substituted acyl-phosphine oxides, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and 2-hydrobenzoyl- a mixture of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and 2-hydroxy-2-methylpropiophenone; a mixture of ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate and 2-hydroxy-2-methylpropiophenone; and a mixture of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and ethylphenyl(2,4,6-trimethylbenzoyl)phenylphosphinate.

[0124] Suitable thioxanthones include, without limitation, 2-methylthioxanthone, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 1-chloro-4-propoxythioxanthone, and polymeric thioxanthone derivatives.

[0125] Suitable phenyl glyoxylates include, without limitation, methyl benzoyl formate, 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.

[0126] Preferably, the free radical photoinitiator is a mixture of phosphine oxides described herein, more preferably a mixture of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and ethylphenyl(2,4,6-trimethylbenzoyl)phenylphosphinate.

[0127] The claimed UV-Vis radiation curable security ink e1) vinyl ethers having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the cycloaliphatic epoxide of d); e2) vinyl ethers having one vinyloxy residue in an amount of less than about 5 wt.%, preferably less than or equal to about 4.1 wt.%; e3) less than about 10 wt. % of an epoxide other than a cycloaliphatic epoxide; e4) oxetanes having two oxetanyl residues in an amount of less than about 20 wt. %; e5) oxetanes having one oxetanyl residue in an amount of less than about 3.5 wt.-%, preferably less than or equal to about 3.3 wt.-%; and e6) a mixture of e1) and / or e2) and / or e3) and / or e4) and / or e5); wherein the weight percent is based on the total weight of the UV-Vis radiation curable security ink. Preferably, the cationically curable compound is selected from the group consisting of e1) vinyl ethers having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the cycloaliphatic epoxide of d); e3) less than about 10 wt. % of an epoxide other than a cycloaliphatic epoxide; e4) an oxetane having two oxetanyl residues in an amount of less than about 20 wt.%; or e6) a mixture of e1) and / or e3) and / or e4) where the weight percentages are based on the total weight of the UV-Vis radiation curable security ink.

[0128] In certain embodiments according to the present invention, the cationically curable compound consists of e1) a vinyl ether having two vinyloxy residues in an amount less than 50% of the weight percent (wt-%) of the cycloaliphatic epoxide of d); or e6) a mixture of e1) and e2); a mixture of e1) and e3); a mixture of e1) and e4); a mixture of e1) and e5); a mixture of e1), e2) and e3); a mixture of e1), e2) and e4); a mixture of e1), e2) and e5); a mixture of e1), e3) and e4); a mixture of e1), e3) and e5); or a mixture of e1), e4) and e5), wherein the weight percentages are based on the total weight of the UV-Vis radiation curable security ink. In a more specific embodiment of the present invention, the cationically curable compound is selected from the group consisting of e1) a vinyl ether having two vinyloxy residues in an amount less than 50% of the weight percent (wt-%) of the cycloaliphatic epoxide of d); and e6) a mixture of e1) and e3); a mixture of e1) and e4); and a mixture of e1), e3) and e4), where the weight percent is based on the total weight of the UV-Vis radiation curable security ink. For example, as evidenced by Table 2c, a security ink according to the present invention containing a mixture of a cycloaliphatic epoxide and a vinyl ether having two vinyloxy residues as cationically curable monomers, and having a ratio of vinyl ether wt-% to cycloaliphatic epoxide wt-% less than about 0.5, provides a dichroic security feature that exhibits a metallic yellow color when viewed in incident light and a blue color when viewed in transmitted light. A metallic yellow color when viewed in incident light cannot be achieved with inks containing a mixture of a cycloaliphatic epoxide and a vinyl ether having two vinyloxy groups as cationically curable monomers with a ratio of vinyl ether wt.% to cycloaliphatic epoxide wt.% of 0.5 or more, as shown, for example, in Table 2c. Such inks provide dark brown to brown and low chroma features in reflected light, which are not noticeable to the average person and are therefore not suitable for dichroic security features to secure valuable documents.Preferably, the vinyl ether having two vinyloxy residues is present in an amount of 49%, 48%, 47%, 46%, 45% or less of the weight percent (wt-%) of the cycloaliphatic epoxide; the wt-% being based on the total weight of the UV-Vis radiation curable security ink.

[0129] Therefore, a preferred embodiment according to the present invention is a) about 7.5 wt-% to about 20 wt-% silver nanoplatelets having an average diameter in the range of 50-150 nm with a standard deviation of less than 60%, an average thickness in the range of 5-30 nm with a standard deviation of less than 50%, and an average aspect ratio greater than 2.0, wherein the average diameter is determined by transmission electron microscopy and the average thickness is determined by transmission electron microscopy; The silver nanoplatelets have a surface stabilizer of the general formula (I): [ka] [In the formula, residue R A is a C2-C4 alkyl group substituted with a hydroxy group; residue R B is selected from C1-C4 alkyl groups and C2-C4 alkyl groups substituted with a hydroxy group; Cat + Na + , K. + , Cs + and Rb + is a cation selected from the group consisting of: b) perfluoropolyether surfactants functionalized with at least hydroxy groups; c) about 3 wt.-% to about 12 wt.-% polyvinyl chloride copolymer containing at least 69 wt.-% vinyl chloride; d) d1) about 30 wt-% to about 55 wt-% of an alicyclic epoxide, and about 1 wt-% to about 10 wt-% of a cationic photoinitiator; or d2) about 35 wt.-% to about 65 wt.-% of a mixture of a cycloaliphatic epoxide and a radically curable compound, about 1 wt.-% to about 6 wt.-% of a cationic photoinitiator, and about 1 wt.-% to about 6 wt.-% of a free radical photoinitiator; and optionally e) a vinyl ether having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the cycloaliphatic epoxide of e1) d); and e6) a mixture of vinyl ethers having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the cycloaliphatic epoxides of e1) d) and e3) an epoxide other than a cycloaliphatic epoxide in an amount less than about 10 wt-%; e1) a mixture of vinyl ethers having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the cycloaliphatic epoxide of d) and e4) an oxetane having two oxetanyl residues in an amount less than about 20 wt-%; or e1) a mixture of vinyl ethers having two vinyloxy residues in an amount less than 50% by weight (wt-%) of the cycloaliphatic epoxide of d), e3) an epoxide other than a cycloaliphatic epoxide in an amount less than about 10 wt-%, and e4) an oxetane having two oxetanyl residues in an amount less than about 20 wt-%. a cationically curable compound selected from the group consisting of For security inks comprising:

[0130] In an alternative embodiment, the cationically curable compound comprises e3) an epoxide other than a cycloaliphatic epoxide in an amount of less than about 10 wt-%; or e6) a mixture of e3) and e1); a mixture of e3) and e2); a mixture of e3) and e4); a mixture of e3) and e5); a mixture of e3), e1) and e2); a mixture of e3), e1) and e4); a mixture of e3), e1) and e5); a mixture of e3), e2) and e4); a mixture of e3), e2) and e5); or a mixture of e3), e4) and e5), wherein the weight percentages are based on the total weight of the UV-Vis radiation curable security ink. In a more specific embodiment of the present invention, the cationically curable compound consists of e3) an epoxide other than a cycloaliphatic epoxide in an amount less than about 10 wt-%; or e6) a mixture of e1) and e3); a mixture of e3) and e4), or a mixture of e1), e3) and e4), wherein the weight percentages are based on the total weight of the UV-Vis radiation curable security ink.

[0131] In an alternative embodiment, the cationically curable compound comprises e4) an oxetane having two oxetanyl residues in an amount of less than about 20 wt-%; or e6) a mixture of e4) and e1); a mixture of e4) and e2); a mixture of e4) and e3); a mixture of e4) and e5); a mixture of e4), e1) and e2); a mixture of e4), e1) and e3); a mixture of e4), e1) and e5); a mixture of e4), e2) and e3); a mixture of e4), e2) and e5); or a mixture of e3), e4) and e5), wherein the weight percentages are based on the total weight of the UV-Vis radiation curable security ink. In a more specific embodiment of the present invention, the cationically curable compound consists of e4) an oxetane having two oxetanyl residues in an amount of less than about 20 wt-%; or e6) a mixture of e4) and e1); a mixture of e4) and e3); or a mixture of e1), e3) and e4), wherein the weight percentages are based on the total weight of the UV-Vis radiation curable security ink.

[0132] As known to those skilled in the art, vinyl ethers are cationically curable monomers containing at least a vinyloxy (CH═CH—O—) residue. Vinyl ethers are known in the art to accelerate curing and reduce tack, thereby limiting the risk of blocking and set-off when printed sheets are stacked immediately after printing and curing. They also improve the physical and chemical resistance of printed security elements and enhance the flexibility of the printed and cured ink layer and its adhesion to the substrate, which is particularly advantageous for printing plastic and polymer substrates. Vinyl ethers also help reduce the viscosity of the ink while copolymerizing strongly with the ink vehicle.

[0133] As used herein, "vinyl ether having one vinyloxy residue" means a cationically curable monomer having one vinyloxy residue. Examples of vinyl ethers having one vinyloxy residue include methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, ethylhexyl vinyl ether, octadecyl vinyl ether, dodecyl vinyl ether, isopropyl vinyl ether, tert-butyl vinyl ether, tert-amyl vinyl ether, cyclohexyl vinyl ether, cyclohexanedimethanol monovinyl ether, 4-(vinyloxymethyl)cyclohexylmethylbenzoate, phenyl vinyl ether, methylphenyl vinyl ether, methoxyphenyl vinyl ether, 2-chloroethyl vinyl ether, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, 1,6-hexanediol diol monovinyl ether, ethylene glycol monovinyl ether, 4-(vinyloxy)butylbenzoate, 4-(vinyloxy)butyl stearate, diethylene glycol monovinyl ether, ethylene glycol butyl vinyl ether, triethylene glycol methyl vinyl ether, triethylene glycol monobutyl vinyl ether, and polyethylene glycol-520 methyl vinyl ether. Suitable vinyl ethers having one vinyloxy residue are sold by BASF under the names EVE, IBVE, DDVE, ODVE, BDDVE, CHVE, HBVE. Vinyl ethers having one vinyloxy residue may be hydroxy-modified or (meth)acrylate-modified (for example: VEEA, 2-(2-vinyloxyethoxy)ethyl acrylate (CAS: 86273-46-3) from Nippon Shokubai).

[0134] As used herein, "vinyl ether having two vinyloxy residues" refers to a cationically curable monomer containing two vinyloxy (CH=CH-O-) residues linked through a divalent group containing one or more atoms.

[0135] Preferably, the vinyl ether having two vinyloxy residues is a compound having 2 to 20 carbon atoms and two vinyloxy (CH2=CH-O-) residues linked via a divalent group containing, optionally, one or more oxygen atoms. More preferably, the vinyl ether having two vinyloxy residues used in the claimed UV-Vis radiation curable security ink is a compound of the general formula (VIII): [ka] [In the formula, -F- is: -(CH2) f1 -, -(CH2) f2 -(O(CH2) f2 ) f3 -, [ka] wherein f1 is an integer from 1 to 10; f2 is an integer from 2 to 4; f3 is an integer from 1 to 3; f4 and f5 are each independently an integer of 2 to 6.

[0136] Preferably, -F- is: -(CH2) f2 -(O(CH2) f2 ) f3 - and [ka] wherein f2 and f3 have the meanings defined herein. More preferably, -F- is: -(CH2)2-(O(CH2)2) f3 - and [ka] wherein f3 is an integer of 1 to 3, preferably 1 to 2.

[0137] Preferred examples of vinyl ethers having two vinyloxy residues include, but are not limited to, cyclohexanedimethanol divinyl ether, 1,4-butanediol diol divinyl ether, 1,6-hexanediol diol divinyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, dipropylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, poly(tetrahydrofuran) divinyl ether, bis[4-(vinyloxy)butyl]adipate, bis[4-(vinyloxy)butyl]succinate, bis[4-(vinyloxymethyl)cyclohexylmethyl]glutarate, 2,2-bis(4-vinyloxyethoxyphenyl), bis[4-(vinyloxy)methyl]cyclohexyl]methyl]terephthalate, and bis[4-(vinyloxy)methyl]cyclohexyl]methyl]isophthalate. Suitable vinyl ethers having two vinyloxy residues are sold by BASF under the names BDDVE, DVE-2, DVE-3, and CHDM-di.

[0138] As known to those skilled in the art, an epoxide is a compound having at least one epoxy residue. [ka] The use of epoxides in UV-Vis radiation curable inks helps accelerate cure, reduce tack, and lower the viscosity of the ink, while copolymerizing tightly with the ink vehicle. Preferred examples of epoxides other than the cycloaliphatic epoxides described herein include, but are not limited to, cyclohexanedimethanol diglycidyl ether, poly(ethylene glycol) diglycidyl ether, poly(propylene glycol) diglycidyl ether, butanediol diglycidyl ether, hexanediol diglycidyl ether, bisphenol-A diglycidyl ether, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, glycerol triglycidyl ether, pentaerythritol tetraglycidyl ether, butyl glycidyl ether, p-tert-butylphenyl glycidyl ether, hexadecyl glycidyl ether, 2-ethyl-hexyl glycidyl ether, octyl glycidyl ether, decyl glycidyl ether, dodecyl glycidyl ether, tetradecyl glycidyl ether, C 12 / C 14 -Alkyl glycidyl ether, C 13 / C 15 - alkyl glycidyl ethers and mixtures thereof. Suitable epoxides other than cycloaliphatic epoxides are sold under the trademark Grilonit® (e.g. Grilonit® V51-63 or RV 1806) by EMS Griltech.

[0139] As is well known to those skilled in the art, oxetane is at least an unsubstituted or substituted oxetanyl residue, preferably an unsubstituted or substituted 3-oxetanyl residue: [ka] As used herein, "oxetane having one oxetanyl residue" refers to a cationically curable monomer having one substituted or unsubstituted oxetanyl residue. Preferably, the oxetane having one oxetanyl residue is of the general formula (IX): [ka] [In the formula, R 20 is selected from -H, phenyl, o-methoxy-phenyl, m-methoxy-phenyl and p-methoxy-phenyl; R 21 is selected from —H, methyl, and ethyl; R 22 -H, methyl, ethyl, -CH2-OR 23 Selected from; R 23 is -H, C1-C8-alkyl, phenyl, benzyl, [ka] where g1 is an integer from 2 to 8.

[0140] Preferred examples of oxetanes having one oxetanyl residue include trimethylene oxide, 3,3-dimethyloxetane, trimethylolpropaneoxetane, 3-ethyl-3-[(2-ethylhexyloxy)methyl]oxetane, 3-ethyl-3-phenoxymethyloxetane, 3,3-dimethyl-2(p-methoxy-phenyl)-oxetane, 3-ethyl-[(tri-ethoxysilylpropoxy)methyl]oxetane, and 3,3-dimethyl-2(o-methoxy-phenyl)oxetane.

[0141] As used herein, "oxetane having two oxetanyl residues" refers to a cationically curable monomer containing two substituted or unsubstituted oxetanyl residues linked via a divalent group containing one or more atoms. Preferably, the oxetane having two oxetanyl residues is a compound having 2 to 20 carbon atoms and, optionally, two oxetanyl residues linked via a divalent group containing one or more oxygen atoms. Even more preferably, the oxetane having two oxetanyl residues is a compound of the general formula (X): [ka] [In the formula, -G- is a bond, -O-(CH2) g2 - [ka] represents g2 is an integer from 2 to 8; g3 is an integer from 1 to 3; g4 is an integer between 1 and 4.

[0142] Preferred examples of oxetanes having two oxetanyl residues include 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene, 4,4-bis(3-ethyl-3-oxetanyl)methoxymethyl]biphenyl, bis[1-ethyl(3-oxetanyl)]methyl ether, 1,2-bis[(3-ethyl-3-oxetanylmethoxy)methyl]ethane, 1,3-bis[(3-ethyl-3-oxetanylmethoxy)methyl]propane, ethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, ethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, diethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, triethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, and tetraethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether.

[0143] The claimed UV-Vis radiation curable security inks may contain up to about 25 wt-% organic solvent, where the weight percent is based on the total weight of the UV-Vis radiation curable ink. The solvent has a boiling point greater than 100°C. Suitable organic solvents for use in the UV-Vis radiation curable inks described herein include, without limitation: ethyl-3-ethoxypropionate, 2-methoxy-1-methylethyl acetate, propylene glycol monomethyl ether, cyclopentanone, cyclohexanone, n-butanol, cyclohexanol, ethylene carbonate, propylene carbonate, butylene carbonate, and mixtures thereof.

[0144] In a preferred embodiment according to the present invention, the UV-Vis radiation curable security ink is solvent-free. The use of solvent-free inks in industrial printing processes of valuable documents is of great interest as it prevents the release of volatile organic components which usually have a negative impact on the environment and are harmful to human health.

[0145] The claimed UV-Vis radiation curable security ink may further comprise one or more photosensitizers in addition to one or more photoinitiators described herein to achieve efficient curing. Suitable examples of photosensitizers are known to those skilled in the art (e.g., Industrial Photoinitiators, W.A. Green, CRC Press, 2010, Table 8.1 p. 170). Preferred photosensitizers are those that can achieve efficient and fast curing under UV-LED light sources, such as thioxanthone derivatives, anthracene derivatives, and naphthalene derivatives (e.g., 9,10-diethoxyanthracene sold as Anthracure UVS-1101 and 9,10-dibutyloxyanthracene sold as Anthracure UVS-1331, both sold by Kawasaki Kasei Chemicals Ltd.), and titanocene derivatives (e.g., Irgacure 784 sold by BASF). Particularly preferred are thioxanthone derivatives, 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. Alternatively, the thioxanthone photosensitizers may be used in oligomeric or polymeric form (e.g., Omnipol TX sold by IGM Resins, Genopol TX sold by Rahn). * TX-2, or Speedcure 7010 sold by Lambson. When present, the one or more photosensitizers are preferably present in an amount of from about 0.1 wt-% to about 2 wt-%, more preferably from about 0.2 wt-% to about 1 wt-%, the weight percentages being based on the total weight of the UV-Vis radiation curable ink.

[0146] The claimed UV-Vis radiation curable inks may further comprise one or more anti-foaming agents in an amount of less than about 2 wt-%, preferably less than about 1 wt-%.

[0147] Another aspect of the present invention is a method of making a security feature for securing a value document, said security feature exhibiting a blue color when viewed in transmitted light and a metallic yellow color when viewed in incident light, said method comprising the steps of: A) printing a claimed UV-Vis radiation curable security ink onto a transparent or partially transparent area of ​​a value document substrate to provide an ink layer, preferably by screen printing, rotogravure printing, or flexographic printing; and B) UV-Vis curing of the ink layer obtained in step A) to form the security feature. The present invention relates to a method, including:

[0148] The claimed manufacturing process of the present invention allows access to a security feature that exhibits a metallic yellow color in incident light and a blue color, especially an intense to very intense blue color, in transmitted light in a single printing step. As used herein, the term "printing" refers to any printing process suitable for printing the UV-Vis radiation curable ink described herein onto a value document substrate. In particular, the term "printing" refers to a printing process selected from the group consisting of: screen printing, rotogravure printing, flexography, pad printing, inkjet printing, and spray printing. Preferably, the UV-Vis radiation curable security ink is printed onto a transparent or partially transparent area of ​​the value document substrate by screen printing, rotogravure printing, or flexography, more preferably by screen printing.

[0149] As used herein, a "transparent or partially transparent region of a value document substrate" refers to a region of a value document substrate characterized by an average transmittance in the visible range of at least 50%, preferably at least 70%, and more preferably at least 90%. The transparent or partially transparent region of the substrate and the remaining region of the substrate can be made of the same material or different materials. Deletion of one or more layers in a multi-layer structure or application of a transparent or partially transparent material to an aperture in a substrate made of a different material from the transparent or partially transparent material provides a value document substrate in which the transparent or partially transparent region of the substrate and the remaining region of the substrate are made of different materials.

[0150] Materials for the value document substrate include, without limitation, paper or other fibrous materials, such as cellulose, paper-containing materials, plastics and polymers, composite materials, and mixtures or combinations thereof. Typical paper, paper-like, or other fibrous materials are made from a variety of fibers, including, without limitation, abaca, cotton, linen, wood pulp, and blends thereof. As is known to those skilled in the art, cotton and cotton / linen blends are preferred for banknotes, while wood pulp is typically used for non-banknote security documents. Typical examples of plastics and polymers include polystyrene, polycarbonate, polyolefins such as polyethylene (PE) and polypropylene (PP), e.g., biaxially oriented polypropylene (BOPP), polyamide (PA), polyesters such as poly(ethylene terephthalate) (PET), polyethylene terephthalate glycol-modified (PETG), e.g., poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate), poly(1,4-butylene terephthalate) (PBT), and poly(ethylene 2,6-naphthoate) (PEN), and polyvinyl chloride (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 listed above. Suitable materials for the transparent or partially transparent regions of the substrate include, but are not limited to, polystyrene, polycarbonate, polyolefins such as polyethylene (PE) and polypropylene (PP), such as biaxially oriented polypropylene (BOPP), polyamide (PA), polyesters such as poly(ethylene terephthalate) (PET), polyethylene terephthalate glycol-modified (PETG), such as poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate), poly(1,4-butylene terephthalate) (PBT), and poly(ethylene 2,6-naphthoate) (PEN), and polyvinyl chloride (PVC). The transparent or partially transparent regions of the value document substrate may have a primer layer onto which a UV-Vis radiation curable ink is printed.The primer layer can be obtained by UV-Vis curing a varnish containing all the components of the UV-Vis radiation curable ink described herein except for the silver nanoplatelets.

[0151] In step B) of the claimed manufacturing process of the present invention, the ink layer obtained in step A) is subjected to UV-Vis curing to form the security feature. As used herein, the term "UV-Vis curing" refers to radiation curing of the ink layer by photopolymerization under the influence of radiation having wavelength components in the UV or UV and visible portions of the electromagnetic spectrum (typically 100 nm to 800 nm, preferably 150 to 600 nm, more preferably 200 to 400 nm). Cationically curable monomers cure via a cationic mechanism consisting of UV-Vis light activation of one or more photoinitiators, which liberate cationic species, such as acids, that in turn initiate polymerization of the compound to form a cured binder. Radically curable monomers and oligomers cure via a free-radical mechanism consisting of UV-Vis light activation of one or more photoinitiators, which liberate free radicals that then initiate the polymerization process. Optionally, one or more photosensitizers may also be present. The photosensitizer is activated by one or more of the wavelengths emitted by the UV-Vis light source and reaches an excited state. The excited photosensitizer transfers energy to one or more photoinitiators (in the case of radical polymerization) or electrons (in the case of cationic polymerization), either of which then initiates the polymerization process.

[0152] Preferably, step B) comprises exposing the ink layer obtained in step A) to UV-Vis light emitted by a UV-Vis light source selected from the group consisting of a mercury lamp, preferably a medium-pressure mercury lamp, a UV-LED lamp, and sequences thereof. A typical sequence involves partial curing of the UV-Vis radiation composition using one or more UV-LED lamps in a first step and one or more medium-pressure mercury lamps in a second step. Mercury lamps are advantageous because they emit light over a wide range of wavelengths in the UV-A, UV-B, and UV-C ranges. Therefore, there is a wide selection of photoinitiators or photoinitiator / photosensitizer combinations with absorption spectra that match at least one of the emission bands of mercury lamps. UV-LEDs have a more limited wavelength range, so only a limited selection of photoinitiators or photoinitiator / photosensitizer combinations are efficient enough at industrial printing speeds. On the other hand, UV-LEDs are less expensive, require less energy (especially requiring a much less heat dissipation system), are less prone to ozone formation, and have a much longer lifetime.

[0153] In order to provide the valuable document with soil resistance and / or to protect the security features against physical and chemical attacks from the environment, the claimed manufacturing process preferably further comprises steps C) and D) performed after step B): C) applying a curable protective varnish to the substrate, preferably by a printing process, to form a varnish layer; D) The varnish layer obtained in step C) is cured to form a protective coating.

[0154] Examples of suitable curable protective varnishes for use in step C) and / or methods of applying said curable protective varnishes to a substrate and curing the varnish layer are described in WO2020234211, WO2013127715 and WO2014067715.

[0155] Preferably, the valuable document is selected from banknotes, certificates, tickets, cheques, receipts, revenue stamps, contracts, identity documents such as passports, identity cards, visas, driver's licenses, bank cards, credit cards, transaction cards, access documents, and cards, admission tickets, public transport tickets, academic diplomas, and academic titles. More preferably, the valuable document is a banknote. The claimed security ink can also be used to create security features directly on value commercial good. The term "value commercial good" relates to packaging material that can be protected against counterfeiting and / or illegal copying to ensure the contents of the package, such as genuine medicines, in particular in the pharmaceutical, cosmetic, electronics, or food industries. [Example]

[0156] The present invention will now be described in more detail with reference to the following non-limiting examples. The following Examples E1-E48 and Comparative Examples C1-C21 provide more details regarding the preparation of the UV-Vis radiation curable screen printing security inks described herein and the optical properties of the resulting security features.

[0157] (A. Analysis method) (A-1.UV-Vis spectroscopy) UV-Vis spectra of the dispersions were recorded on a Varian Cary 50 UV-visible spectrophotometer with the dispersions concentrated to achieve an optical density of 0.3–1.5 at a light path of 1 cm.

[0158] (A-2.TEM analysis) TEM analysis of the dispersions and coatings was performed on a ZEISS EM 910 instrument in bright field mode at an e-beam acceleration voltage of 100 kV. At least two representative images were recorded at different magnification scales to characterize the predominant particle morphology of each sample.

[0159] The average diameter of the silver nanoplatelets was determined by transmission electron microscopy (TEM) using Fiji image analysis software based on measurements of at least 300 randomly selected silver nanoplatelets oriented parallel to the plane of the transmission electron microscopy image (TEM), where the diameter of the silver nanoplatelet is the largest dimension of the silver nanoplatelet oriented parallel to the plane of the transmission electron microscopy image (TEM).

[0160] The average thickness of the silver nanoplatelets was determined by transmission electron microscopy (TEM) based on manual measurements of at least 50 randomly selected silver nanoplatelets oriented perpendicular to the plane of the TEM image, where the thickness of the silver nanoplatelets is the maximum thickness of the silver nanoplatelets.

[0161] B. Preparation and Characterization of Ag Nanoplatelet Dispersions D1-D10 (B-1. Synthesis of raw materials) In a 1 L double-walled glass reactor equipped with an anchor stirrer, 365 g of deionized water was cooled to +2° C. 13.62 g of sodium borohydride was added, and the mixture was cooled to −1° C. while stirring at 250 revolutions per minute (RPM, Solution A).

[0162] In a 0.5 L double-walled glass reactor equipped with an anchor stirrer, 132 g of deionized water and 4.8 g of MPEG-5000-thiol were combined and the mixture was stirred for 10 minutes at room temperature. 72 g of the product from Example A3 of WO2006074969 was added, and the resulting mixture was stirred for an additional 10 minutes at room temperature for homogenization. A solution of 30.6 g of silver nitrate in 30 g of deionized water was added in one portion, and the mixture was stirred for 10 minutes to obtain an orange-brown viscous solution. 96 g of deionized water was added to this solution, followed by 3 g of Struktol SB 2080 antifoamant, previously dispersed in 36 g of deionized water. The resulting mixture was cooled to 0°C while stirring at 250 RPM (Solution B).

[0163] Solution B was then added subsurface to Solution A via a chilled (0 °C) addition tube at a constant rate over 2 h using a peristaltic pump, resulting in a dispersion of spherical silver nanoplatelets. Solution A was stirred at 250 RPM during pumping.

[0164] After the addition was complete, the reaction mixture was warmed to +5°C within 15 min and a solution of 862 mg of KCl in 10 g of deionized water was added in one portion, followed by the addition of 9.6 g of ethylenediaminetetraacetic acid (EDTA) in four equal portions at 10 min time intervals.

[0165] After addition of the final portion of EDTA, the reaction mixture was stirred for 15 min at +5° C., then warmed to 35° C. over 30 min and stirred at this temperature for 1 h, at which point hydrogen evolution was complete.

[0166] 3.0 mL of a 30% w / w solution of ammonia in water was added, followed by 5.76 g of solid NaOH, and the mixture was stirred for 15 min at 35°C. 180 mL of 50% w / w aqueous hydrogen peroxide was then added subsurface to the reaction mixture at a constant rate of 250 RPM using a peristaltic pump over 4 h, while maintaining the temperature at 35°C. This resulted in a deep blue dispersion of silver nanoplatelets, which was cooled to room temperature. 1.23 g of the formula [ka] (a mixture of CAS 80584-88-9 and 80584-89-0) was added and the mixture was stirred for 1 h at room temperature.

[0167] B-2. Isolation and Purification of Ag Nanoplatelets (B-2a. First Decantation) 9.6 g of sodium dodecyl sulfate was added to the reaction mixture, followed by approximately 25 g of anhydrous sodium sulfate powder, which was gradually added with stirring until the color of the dispersion changed from blue to pink in transmitted light. The mixture was then kept at room temperature without stirring for 24 h, allowing the solidified nanoplatelets to settle to the bottom of the reactor.

[0168] 890 g of the supernatant was pumped from the reactor using a peristaltic pump, and 890 g of deionized water was added to the reactor. The mixture in the reactor was stirred for 1 h at room temperature to redisperse the coagulated particles.

[0169] (B-2b. Second Decantation) Approximately 64 g of anhydrous sodium sulfate powder was added in small increments with stirring until the color of the dispersion in transmitted light changed from blue to yellowish pink. The mixture was then kept at room temperature without stirring for 12 hours, allowing the coagulated nanoplatelets to settle to the bottom of the reactor. 990 g of the supernatant was pumped from the reactor using a peristaltic pump, and 90 g of deionized water was added to the reactor. The resulting mixture was stirred at room temperature for 30 minutes to redisperse the coagulated particles.

[0170] (B-2c. Submerged Ultrafiltration) The resulting dispersion of Ag nanoplatelets was subjected to ultrafiltration using a Millipore Amicon 8400 stirred ultrafiltration cell. The dispersion was diluted with deionized water and ultrafiltered to a final volume of approximately 50 mL using a polyethersulfone (PES) membrane with a 300 kDa cutoff. The procedure was repeated four times to obtain a total of 60 g of dispersion of Ag nanoplatelets in water. After ultrafiltration was completed, 0.17 g of the formula [ka] (a mixture of CAS 80584-88-9 and 80584-89-0) was added to the dispersion. Ag content 28.9% w / w; yield about 89% based on total silver; solids (250°C) 33.5% w / w; silver purity based on solids at 250°C 86% w / w.

[0171] (B-2d. Ultrafiltration in isopropanol) The dispersion was further ultrafiltered in isopropanol. 60 g of the Ag nanoplatelet dispersion obtained after ultrafiltration in water was placed in a Millipore Amicon 8400 stirred ultrafiltration cell and diluted to a weight of 300 g with isopropanol. The dispersion was ultrafiltered to a volume of approximately 50 mL using a polyethersulfone (PES) membrane with a 500 kDa cutoff. This procedure was repeated four times in total to obtain 72 g of Ag nanoplatelet dispersion in isopropanol. Ag content 24.1% w / w; solids (250°C) 25.7% w / w; silver purity based on solids at 250°C 93.5% w / w. UV-Vis-NIR spectrum in water, 9.8 * 10 -5 The Ag concentration was recorded in M. max =700nm; maximum extinction coefficient ε=10200L / (cm * mol Ag), FWHM = 340 nm. Number average particle diameter 93±40 nm, number average particle thickness 16±2.5 nm.

[0172] (B-3 Preparation of Dispersion D1) a) Synthesis of diethanolamine dithiocarbamic acid sodium salt (sodium bis(2-hydroxyethyl)dithiocarbamate) 60 g ethanol, 10.5 g diethanolamine, and 4.0 g sodium hydroxide granules were placed in a 100 mL round-bottom flask under an argon atmosphere. The mixture was stirred until the sodium hydroxide dissolved and then cooled to +2°C. While maintaining the temperature of the reaction mixture at 0 to +5°C, 7.6 g of carbon disulfide was added dropwise with stirring over 1 h. The mixture (yellowish suspension) was then stirred for 30 min at 0 to +5°C, then warmed to 23°C and stirred for 1 h.

[0173] b) Surface modification of Ag nanoplatelets 50 g (12.85 g solid) of the Ag nanoplatelet dispersion obtained as described in item B-2d was placed in a 250 mL round-bottom flask under an argon atmosphere. 1.09 g of the suspension obtained in step a) (0.27 g diethanolamine dithiocarbamic acid sodium salt) was added in one portion, and the mixture was stirred for 24 h at 23 °C under argon.

[0174] c) Solvent exchange To the dispersion obtained in step b) was added 15.0 g of ethyl 3-ethoxypropionate (CAS No.: 763-69-9). The resulting mixture was concentrated on a rotary evaporator at a pressure of 40 mbar and a bath temperature of 40° C. until no further solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by adding ethyl 3-ethoxypropionate (corresponding to a calculated total solids content of 40.9% w / w).

[0175] (B-4 Preparation of Dispersion D2) a) Surface modification of Ag nanoplatelets 50 g (12.85 g solid) of the Ag nanoplatelet dispersion obtained as described in item B-2d was placed in a 250 mL round-bottom flask at 23 °C under an argon atmosphere. 0.46 g of a 5% w / w solution of carbon disulfide in absolute ethanol was added, and the mixture was stirred for 5 min, followed by the addition of 0.62 g of a 5% w / w solution of diethanolamine in absolute ethanol. After stirring the mixture for 1 h at 23 °C, 0.49 g of a 5% w / w solution of potassium ethoxide in absolute ethanol was added, and stirring was continued for 30 min.

[0176] b) Solvent exchange To the dispersion obtained in step a) was added 15.0 g of ethyl 3-ethoxypropionate (CAS No.: 763-69-9). The mixture obtained was concentrated on a rotary evaporator at a pressure of 40 mbar and a bath temperature of 40° C. until no further solvent was distilled off. The weight of the dispersion obtained was adjusted to 32.1 g by adding ethyl 3-ethoxypropionate (corresponding to a calculated total solids content of 40.2% w / w).

[0177] (B-5 Preparation of dispersion liquid D3) a) Synthesis of diethanolamine dithiocarbamic acid potassium salt 16 g ethanol, 2.7 g diethanolamine, and 9.0 g of a 24% w / w solution of potassium ethoxide in ethanol were added under an argon atmosphere, and the mixture was stirred until the potassium ethoxide dissolved, then cooled to +2°C. 1.95 g of carbon disulfide was added dropwise with stirring over 1 h, and the temperature of the reaction mixture was maintained at 0 to +5°C. The mixture (yellowish suspension) was then stirred for 30 min at 0 to +5°C, then warmed to 23°C, and stirred for 1 h.

[0178] b) Surface modification of Ag nanoplatelets 50 g (12.85 g solid) of the Ag nanoplatelet dispersion obtained as described in item B-2d was placed in a 250 mL round-bottom flask under an argon atmosphere. 0.675 g of the suspension obtained in step a) (0.128 g of diethanolaminedithiocarbamic acid potassium salt) was added in one portion, and the mixture was stirred for 24 h under argon at 23 °C.

[0179] c) Solvent exchange To the dispersion obtained in step b) was added 15.0 g of ethyl 3-ethoxypropionate (CAS No.: 763-69-9). The mixture obtained was concentrated on a rotary evaporator at a pressure of 40 mbar and a bath temperature of 40° C. until no further solvent was distilled off. The weight of the dispersion obtained was adjusted to 32.1 g by adding ethyl 3-ethoxypropionate (corresponding to a calculated total solids content of 40.4% w / w).

[0180] (B-6 Preparation of Dispersion D4) a) Surface modification of Ag nanoplatelets 50 g (12.85 g solid) of the Ag nanoplatelet dispersion obtained as described in item B-2d was placed in a 250 mL round-bottom flask under an argon atmosphere at 23 °C. 1.37 g of a 5% w / w solution of carbon disulfide in absolute ethanol was added, and the mixture was stirred for 5 min, followed by the addition of 1.86 g of a 5% w / w solution of diethanolamine in absolute ethanol. After stirring the mixture for 1 h at 23 °C, 1.48 g of a 5% w / w solution of potassium ethoxide in absolute ethanol was added, and stirring was continued for 30 min.

[0181] b) Solvent exchange To the dispersion obtained in step a) was added 15.0 g of ethyl 3-ethoxypropionate (CAS No.: 763-69-9). The mixture obtained was concentrated on a rotary evaporator at a pressure of 40 mbar and a bath temperature of 40° C. until no further solvent was distilled off. The weight of the dispersion obtained was adjusted to 32.1 g by adding ethyl 3-ethoxypropionate (corresponding to a calculated total solids content of 40.6% w / w).

[0182] (B-7 Preparation of Dispersion D5) a) Surface modification of Ag nanoplatelets 50 g (12.85 g solid) of the Ag nanoplatelet dispersion obtained as described in item B-2d was placed in a 250 mL round-bottom flask at 23 °C under an argon atmosphere. 0.46 g of a 5% w / w solution of carbon disulfide in absolute ethanol was added, and the mixture was stirred for 5 min, followed by the addition of 0.62 g of a 5% w / w solution of diethanolamine in absolute ethanol. After stirring the mixture for 1 h at 23 °C, 0.99 g of a 5% w / w solution of cesium hydroxide monohydrate in absolute ethanol was added, and stirring was continued for 30 min.

[0183] b) Solvent exchange To the dispersion obtained in step a) was added 15.0 g of ethyl 3-ethoxypropionate (CAS No.: 763-69-9). The resulting mixture was concentrated on a rotary evaporator at a pressure of 40 mbar and a bath temperature of 40° C. until no further solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by adding ethyl 3-ethoxypropionate (corresponding to a calculated total solids content of 40.3% w / w).

[0184] (B-8 Preparation of Dispersion D6) a) Surface modification of Ag nanoplatelets 50 g (12.85 g solid) of the Ag nanoplatelet dispersion obtained as described in item B-2d was placed in a 250 mL round-bottom flask at 23 °C under an argon atmosphere. 0.91 g of a 5% w / w solution of carbon disulfide in absolute ethanol was added, and the mixture was stirred for 5 min, followed by the addition of 1.24 g of a 5% w / w solution of diethanolamine in absolute ethanol. After stirring the mixture for 1 h at 23 °C, 1.97 g of a 5% w / w solution of cesium hydroxide monohydrate in absolute ethanol was added, and stirring was continued for 30 min.

[0185] b) Solvent exchange To the dispersion obtained in step a) was added 15.0 g of ethyl 3-ethoxypropionate (CAS No.: 763-69-9). The mixture obtained was concentrated on a rotary evaporator at a pressure of 40 mbar and a bath temperature of 40° C. until no further solvent was distilled off. The weight of the dispersion obtained was adjusted to 32.1 g by adding ethyl 3-ethoxypropionate (corresponding to a calculated total solids content of 40.6% w / w).

[0186] (B-9 Preparation of Dispersion D7) a) Synthesis of diethanolamine dithiocarbamic acid cesium salt 16 g of ethanol, 2.7 g of diethanolamine, and 4.3 g of cesium hydroxide monohydrate were placed in a 100 mL round-bottom flask under an argon atmosphere, and the mixture was stirred until the cesium hydroxide dissolved and then cooled to +2 °C. 1.95 g of carbon disulfide was added dropwise with stirring over 1 h, and the temperature of the reaction mixture was maintained between 0 and +5 °C. The mixture (yellowish suspension) was then stirred for 30 min at 0 to +5 °C, then warmed to 23 °C, and stirred for 1 h.

[0187] b) Surface modification of Ag nanoplatelets 50 g (12.85 g solid) of the Ag nanoplatelet dispersion obtained as described in item B-2d was placed in a 250 mL round-bottom flask under an argon atmosphere. 0.40 g of the suspension obtained in step a) (0.128 g of diethanolaminedithiocarbamic acid cesium salt) was added in one portion, and the mixture was stirred for 24 h at 23 °C under argon.

[0188] c) Solvent exchange To the dispersion obtained in step b) was added 15.0 g of ethyl 3-ethoxypropionate (CAS No.: 763-69-9). The resulting mixture was concentrated on a rotary evaporator at a pressure of 40 mbar and a bath temperature of 40° C. until no further solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by adding ethyl 3-ethoxypropionate (corresponding to a calculated total solids content of 40.4% w / w).

[0189] (B-10 Preparation of Dispersion D8) a) Surface modification of Ag nanoplatelets 50 g (12.85 g solid) of the Ag nanoplatelet dispersion obtained as described in item B-2d was placed in a 250 mL round-bottom flask at 23 °C under an argon atmosphere. 1.37 g of a 5% w / w solution of carbon disulfide in absolute ethanol was added, and the mixture was stirred for 5 min, followed by the addition of 1.86 g of a 5% w / w solution of diethanolamine in absolute ethanol. After stirring the mixture for 1 h at 23 °C, 2.96 g of a 5% w / w solution of cesium hydroxide monohydrate in absolute ethanol was added, and stirring was continued for 30 min.

[0190] b) Solvent exchange To the dispersion obtained in step a) was added 15.0 g of ethyl 3-ethoxypropionate (CAS No.: 763-69-9). The resulting mixture was concentrated on a rotary evaporator at a pressure of 40 mbar and a bath temperature of 40° C. until no further solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by adding ethyl 3-ethoxypropionate (corresponding to a calculated total solids content of 40.9% w / w).

[0191] (B-11 Preparation of Dispersion D9) a) Surface modification of Ag nanoplatelets 50 g (12.85 g solid) of the Ag nanoplatelet dispersion obtained as described in item B-2d was placed in a 250 mL round-bottom flask under an argon atmosphere at 23 °C. 0.91 g of a 5% w / w solution of carbon disulfide in absolute ethanol was added, and the mixture was stirred for 5 min, followed by the addition of 1.24 g of a 5% w / w solution of diethanolamine in absolute ethanol. After stirring the mixture for 1 h at 23 °C, 0.986 g of a 5% w / w solution of potassium ethoxide in absolute ethanol was added, and stirring was continued for 30 min.

[0192] b) Solvent exchange To the dispersion obtained in step a), 15.0 g of 7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3-carboxylate (CAS number: 2386-87-0) was added. The resulting mixture was concentrated on a rotary evaporator at a pressure of 40 mbar and a bath temperature of 40 °C until no further solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by adding 7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3-carboxylate (corresponding to a calculated total solids content of 40.4% w / w).

[0193] (B-12 Preparation of Dispersion D10) a) Surface modification of Ag nanoplatelets 50 g (12.85 g solid) of the Ag nanoplatelet dispersion obtained as described in item B-2d was placed in a 250 mL round-bottom flask at 23 °C under an argon atmosphere. 0.91 g of a 5% w / w solution of carbon disulfide in absolute ethanol was added, and the mixture was stirred for 5 min, followed by the addition of 1.24 g of a 5% w / w solution of diethanolamine in absolute ethanol. After stirring the mixture for 1 h at 23 °C, 1.97 g of a 5% w / w solution of cesium hydroxide monohydrate in absolute ethanol was added, and stirring was continued for 30 min.

[0194] b) Solvent exchange To the dispersion obtained in step a), 15.0 g of 7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3-carboxylate (CAS number: 2386-87-0) was added. The resulting mixture was concentrated on a rotary evaporator at a pressure of 40 mbar and a bath temperature of 40 °C until no further solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by adding 7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3-carboxylate (corresponding to a calculated total solids content of 40.6% w / w).

[0195] C. Preparation of Examples (E1-E48), Comparative Examples (C1-C21) and Their Printed Security Features (Description of ingredients used in preparing inks according to the invention (E1 to E48) and inks prepared for comparative purposes (C1 to C21)) [Table 1] TIFF0007730899000044.tif208149 TIFF0007730899000045.tif207149 TIFF0007730899000046.tif106149

[0196] (C1. Effect of the cation (Na) of the surface stabilizer on the optical properties of the security function obtained with the security inks (E1 to E7) of the present invention + , K. + and Cs + ) Study of the impact of (C1a. Preparation of Inks E1 to E7) The components listed in Table 1a below were mixed separately and dispersed at room temperature for 10 minutes at 2000 rpm using a Dispermat CV-3 to obtain 50 g of inks E1 to E7. [Table 2] TIFF0007730899000048.tif59149

[0197] (C1b. Preparation of security features) The UV-Vis radiation-curable screen printing inks E1-E7 were applied individually to transparent polymer substrate pieces (PET Hostaphan® RN, 50 μm thick, provided by Putz GmbH + Co. Folien KG) using a 160 threads / cm screen (405 mesh). The printed patterns measured 5 cm x 5 cm. 10 seconds after the printing step, the printed substrate pieces were exposed twice to UV-Vis light under a dryer from IST Metz GmbH at a speed of 100 m / min (2 lamps: iron-doped mercury lamp 200 W / cm). 2 + mercury lamp 200W / cm 2 ) which independently hardened at room temperature to create the security feature.

[0198] (C1c. Security function results (optical properties)) The optical properties of each security feature obtained in item C1b were evaluated independently in reflected light, transmitted light, and visually using the three tests described below, and the results are summarized in Table 1c.

[0199] The reflected light measurements were performed using a goniometer (Goniospektrometer Codec WI-10 5&5 by Phyma GmbH Austria). * a * b * The values ​​were determined on the printed side of a transparent polymer substrate at an illumination angle of 22.5° at 0° to the normal. * The values ​​(corresponding to a measure of chroma, color intensity or color saturation) are a * and b * Calculated from the values:

number

[0200] C * The values ​​(reflected light 22.5 / 0°) are shown in Table 1c below.

[0201] Transmitted light measurements were performed using a Datacolor 650 spectrophotometer (parameters: integrating sphere, diffuse illumination (pulsed xenon D65) and 8° field of view, analyzer SP2000, dual 256 diode array, wavelength range 360-700 nm, transmitted light sampling aperture size 22 mm). * The values ​​(transmitted light 8°) are shown in Table 1c below.

[0202] The visual evaluation consisted of observing each security feature with the naked eye in reflected light on the printed surface of a transparent polymer substrate using a diffuse source (e.g., light coming through a window rather than direct sunlight, observer facing the wall opposite the window). The following colors were observed: Dark brown to brown, matte appearance with no metallic effect; Gold (i.e. metallic yellow), with a glossy appearance and metallic effect. The metallic effect has a chroma value C of greater than approximately 20 in reflected light at 22.5 / 0°. * It appears in.

[0203] The visual evaluation also involved viewing each security feature with the naked eye in transmitted light. The following colors were observed: Dull blue: the blue is weak (but visible); Blue (saturation value C of approximately 20 or more at 8° transmitted light) * ) ~ dark blue (chroma value C of 30 or more at 8° transmitted light * ): The blue color is intense to very intense.

[0204] As shown in Table 1c, the security features obtained with the inks of the present invention (Examples E1 to E7) exhibit a gold color and a blue to dark blue color in transmitted light. [Table 3]

[0205] As evidenced by Table 1c, security inks E1 to E7 according to the present invention containing Ag nanoplatelets stabilized with diethanolamine dithiocarbamic acid sodium salt, diethanolamine dithiocarbamic acid potassium salt, or diethanolamine dithiocarbamic acid cesium salt exhibited a gold color in reflected light and a blue color in transmitted light, as well as large chroma values ​​C in both reflected and transmitted light. * Provides security features that indicate

[0206] C2. Study of the influence of the ratio of the wt-% of vinyl ether with two vinyloxy residues to the wt-% of cycloaliphatic epoxide (Comparative Inks C1 to C6 and Inventive Inks E1, E8 to E23) Comparative inks C1 to C6 and inventive inks E1, E8 to E23 were prepared to evaluate the effect of the ratio of the wt-% of vinyl ether with two vinyloxy residues to the wt-% of cycloaliphatic epoxide on the optical properties of the security features.

[0207] (C2a. Preparation of Inks C1 to C6, E1, and E8 to E23) The components listed in Tables 2a-1, 2a-2, and 2a-3 were mixed and dispersed at room temperature for 10 minutes at 2000 rpm using a Dispermat CV-3 to obtain inks C1 to C6, E1, and E8 to E23 at a yield of 50 g each. [Table 4] [Table 5] [Table 6]

[0208] (C2b. Preparation of security features) The UV-Vis radiation curable screen printing inks C1 to C6 and E1, E8 to E23 were applied independently to transparent polymer substrate strips (PET Hostaphan® RN, 50 μm thick, provided by Putz GmbH + Co. Folien KG) using a 160 threads / cm screen (405 mesh). The printed patterns measured 5 cm x 5 cm. 10 seconds after the printing step, the printed substrate strips were independently cured by exposure to UV-Vis light at room temperature under a dryer from IST Metz GmbH twice at a speed of 100 m / min (two lamps: iron-doped mercury lamp 200 W / cm). 2 + mercury lamp 200W / cm 2 ) security features.

[0209] (C2c. Security Function Results (Optical Properties)) The optical properties of the security features obtained in item C2b were evaluated independently in reflected light, transmitted light and visually using the tests described in item C1c.

[0210] The color in reflected and transmitted light of security features prepared with comparative inks C1 to C6 and inks E1, E8 to E23 of the present invention, and C * The values ​​(reflected 22.5 / 0° and transmitted 8°) are shown in Table 2c (below).

[0211] As shown in Table 2c, the security features obtained from inks E1, E8-E23 of the present invention, which have a ratio of the wt-% of vinyl ether having two vinyloxy residues to the wt-% of cycloaliphatic epoxide less than 0.5, exhibit a gold color in reflected light and a blue to dark blue color in transmitted light, regardless of the cation used in the stabilizer. In comparison, the security features obtained from comparative inks C1-C6, which have a ratio of the wt-% of vinyl ether having two vinyloxy residues to the wt-% of cycloaliphatic epoxide greater than or equal to 0.5, exhibit a blue to dark color in transmitted light but a dark brown to brown color with low chroma values ​​in reflected light. The dark brown to brown color with low chroma values ​​in reflected light is not noticeable to the average person and is therefore not suitable for a dichroic security feature for securing valuable documents. [Table 7]

[0212] C3. Study of the effect of the weight percentage of radically curable monomers and oligomers present in the solvent (solvent-containing vs. solvent-free inks) and / or UV-Vis radiation curable inks (UV-Vis radiation hybrid curable inks vs. UV-Vis radiation cationically curable inks) on the resulting optical properties exhibited by the security feature (Examples E24-E27) Ink E24 was prepared to evaluate whether the optical effects obtained with solvent-containing UV-Vis radiation hybrid curable inks could be reproduced with solvent-containing UV-Vis radiation cationically curable inks.

[0213] In order to evaluate whether the optical effects obtained by using solvent-containing UV-Vis radiation cationic or hybrid curable inks can be reproduced with solvent-free UV-Vis radiation cationic or hybrid curable inks, inks E25, E26 and E27 were prepared.

[0214] (C3a. Preparation of Inks E24 to E27) The components listed in Table 3a were mixed and dispersed at room temperature for 10 minutes at 2000 rpm using a Dispermat CV-3 to obtain 50 g of each of inks E24 to E27. [Table 8]

[0215] (C3b. Preparation of security functions) UV-Vis radiation-curable screen printing inks E24 to E27 were applied individually to transparent polymer substrate pieces (PET Hostaphan® RN, 50 μm thick, provided by Putz GmbH + Co. Folien KG) using a 160 threads / cm screen (405 mesh). The printed patterns measured 5 cm x 5 cm. 10 seconds after the printing step, the printed substrate pieces were cured individually by exposing them to UV-Vis light at room temperature twice at a speed of 100 m / min under a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W / cm). 2 + mercury lamp 200W / cm 2 ), creating security features.

[0216] (C3c. Security Function Results (Optical Properties)) The optical properties of the security features obtained in item C3b were evaluated independently in reflected light, transmitted light and visually using the tests described in item C1c.

[0217] The color of the security features prepared with inks E24 to E27 of the present invention in reflected and transmitted light and C * The values ​​(reflected 22.5 / 0° and transmitted 8°) are shown in Table 3c (below). [Table 9]

[0218] As shown in Table 3c, security features of similar optical properties can be accessed by using a solvent-containing cationically curable ink (E24), a solvent-free hybrid curable ink (E27), or a solvent-free cationically curable ink (E25-E26).

[0219] C4. Study of the influence of surfactants on the optical properties exhibited by security features (Comparative inks C7 to C15 and ink E28 of the invention) Comparative inks C7-C15 and inventive ink E28 were prepared to evaluate the effect of surfactants on the optical properties exhibited by the security features.

[0220] (C4a. Preparation of Inks C7 to C15 and E28) The ingredients listed in Table 4a were mixed and dispersed at room temperature for 10 minutes at 2000 rpm using a Dispermat CV-3 to obtain 50 g of each of inks C7 to C15 and E28. [Table 10]

[0221] (C4b. Preparation of security features) The UV-Vis radiation-curable screen printing inks C7 to C15 and E28 were applied independently to a transparent polymer substrate strip (PET Hostaphan® RN, 50 μm thick, provided by Putz GmbH + Co. Folien KG) using a 160 threads / cm screen (405 mesh). The printed pattern measured 5 cm x 5 cm. 10 seconds after the printing step, the printed substrate strip was dried by exposing it twice to UV-Vis light at a speed of 100 m / min under a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W / cm). 2 + mercury lamp 200W / cm 2 ) independently hardened to create security features.

[0222] (C4c. Security Function Results (Optical Properties)) The optical properties of the security features in item C4b were evaluated independently in reflected light, in transmitted light, and visually using the test described in item C1c.

[0223] The colours in reflected and transmitted light and C shown by security features prepared with inks C7-C15 and E28 * The values ​​(reflected light 22.5 / 0° and transmitted light 8°) are shown in Table 4c below. [Table 11]

[0224] As shown in Table 4c, security features obtained from an ink of the present invention (E28) containing a hydroxy-functionalized perfluoropolyether surfactant (Fluorolink E10H) exhibit a gold color in reflected light and a deep blue color in transmitted light. In comparison, security features obtained from inks containing hydroxy-functionalized perfluoropolyether surfactants (Fluorolink MD700 / C7, Fluorolink F10 / C8, or Fluorolink S10 / C9), or surfactants lacking both a perfluoropolyether chain and a hydroxy group, such as BYK 330 (C10), BYK 371 (C11), TEGO RAD 2300 (C12), TEGO RAD 2700 (C13), Dynasylan F8815 (C14), and Dynasylan F8261 (C15), exhibit a dull blue to deep blue color in transmitted light, but a dark brown to brown color with low chroma values ​​in reflected light. Dark brown to brown colors with low saturation values ​​in reflected light are not noticeable and are therefore not suitable for dichroic security features to secure valuable documents.

[0225] C5. Study of the influence of the concentration of perfluoropolyether surfactants containing hydroxy groups on the optical properties exhibited by the security features (Comparative ink C16 and inks E29 to E33 of the invention) Ink C16 and inks E29 to E33 of the present invention were prepared to evaluate the effect of the concentration of perfluoropolyether surfactant functionalized with one or more hydroxy groups on the optical properties exhibited by the security feature. E32 is the same as E3 and is included for comparison purposes.

[0226] (C5a. Preparation of Inks C16 and E29 to E33) The ingredients listed in Table 5a were mixed and dispersed at room temperature for 10 minutes at 2000 rpm using a Dispermat CV-3 to obtain 50 g of each of the inks C16 and E29 to E33. [Table 12]

[0227] (C5b. Preparation of security features) The UV-Vis radiation curable screen printing inks C16 and E29 to E33 were applied independently to transparent polymer substrate strips (PET Hostaphan® RN, 50 μm thick, provided by Putz GmbH + Co. Folien KG) using a 160 threads / cm screen (405 mesh). The printed patterns measured 5 cm x 5 cm. 10 seconds after the printing step, the printed substrate strips were cured independently twice by exposure to UV-Vis light under a dryer from IST Metz GmbH at a speed of 100 m / min (two lamps: iron-doped mercury lamp 200 W / cm). 2 + mercury lamp 200W / cm 2 ) security features were created.

[0228] (C5c. Security Feature Results (Optical Properties)) The optical properties of the security features obtained in item C5b were evaluated independently in reflected light, transmitted light and visually using the tests described in item C1c.

[0229] The color of security features prepared with inks C16 and E29-E33 in reflected and transmitted light and C * The values ​​(reflected 22.5 / 0° and transmitted 8°) are shown in Table 5c below. [Table 13]

[0230] As shown in Table 5c, the use of perfluoropolyether surfactant Fluorolink E10H in an amount of about 0.05 wt-% to about 5 wt-% ensures the creation of security features that exhibit a metallic yellow color with a high chroma value in reflected light and a deep blue color in transmitted light (inks E29 to E33). In comparison, the security feature obtained with an ink that does not contain Fluorolink E10H (comparative ink C16) exhibits a dark brown to brown color with a low chroma value in reflected light. Such a color is not noticeable to the average person and cannot be used as a security feature to secure valuable documents.

[0231] C6. Study of the influence of the type of polyvinyl chloride copolymer on the optical properties exhibited by the security feature (Comparative ink C17 and inks E34-E35 of the invention) To evaluate the effect of the type of polyvinyl chloride copolymer on the optical properties exhibited by the security feature, comparative ink C17 and inventive inks E34-E35 were prepared as described below. E34 is the same as E19 and was used for comparative purposes.

[0232] (C6a. Preparation of Inks C17 and E34 to E35) The ingredients listed in Table 6a were mixed and dispersed at room temperature for 10 minutes at 2000 rpm using a Dispermat CV-3 to obtain 50 g of each of inks C17 and E34 to E35. [Table 14]

[0233] (C6b. Preparation of security features) The UV-Vis radiation-curable screen printing inks C17 and E34-E35 were applied independently to a transparent polymer substrate (PET Hostaphan® RN, 50 μm thick, provided by Putz GmbH + Co. Folien KG) using a 160 threads / cm screen (405 mesh). The printed patterns measured 5 cm x 5 cm. 10 seconds after the printing step, the printed substrate pieces were independently exposed twice to UV-Vis light at a speed of 100 m / min under a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W / cm). 2 + mercury lamp 200W / cm 2 ) hardened to create a security feature.

[0234] (C6c. Results of security features (optical properties)) The optical properties of the security features obtained in item C6b were evaluated independently in reflected light, transmitted light and visually using the tests described in item C1c.

[0235] The color in reflected and transmitted light and C of security features prepared using inks C17 and E34-E35 * The values ​​(reflected 22.5 / 0° and transmitted 8°) are shown in Table 6c below. [Table 15]

[0236] As evidenced by the optical properties of the security features shown in Table 6c, the polyvinyl chloride copolymer must contain at least about 69 wt-%, preferably at least about 75 wt-%, vinyl chloride to provide a security feature that exhibits a metallic yellow color in reflected light (Inventive Inks E34-E35). The security feature obtained with comparative ink C17, which contains a polyvinyl chloride copolymer with a lower wt-% vinyl chloride, exhibits a blue color in transmitted light but a brown color in reflected light, which is not noticeable to the average person and cannot be used as a security feature to secure valuable documents.

[0237] C7. Study of the influence of other cationically curable monomers (Comparative Inks C18-C21 and Inventive Inks E36-E48) To evaluate the effect of cationically curable monomers on the optical properties exhibited by the security features, inks C18-C21 and E36-E48 were prepared as described below.

[0238] (C7a. Preparation of Inks C18 to C21 and E36 to E48) The components listed in Tables 7a-1 and 7a-2 were mixed and dispersed at room temperature for 10 minutes at 2000 rpm using a Dispermat CV-3 to obtain 50 g of each of inks C18 to C21 and E36 to E48.

[0239] (C7b. Preparation of security features) The UV-Vis radiation-curable screen printing inks C18 to C21 and E36 to E48 were applied independently to a transparent polymer substrate strip (PET Hostaphan® RN, 50 μm thick, provided by Putz GmbH + Co. Folien KG) using a 160 threads / cm screen (405 mesh). The printed patterns measured 5 cm x 5 cm. 10 seconds after the printing step, the printed substrate strip was exposed to UV-Vis light twice at a speed of 100 m / min under a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W / cm). 2 + mercury lamp 200W / cm 2 ) independently cured to create a security feature.

[0240] (C7c. Security Feature Results (Optical Properties)) The optical properties of the security features obtained in item C7b were evaluated independently in reflected light, transmitted light and visually using the tests described in item C1c.

[0241] The colours in reflected and transmitted light and C of security features prepared using inks C18-C21 and E36-E48* The values ​​(reflected light 22.5 / 0° and transmitted light 8°) are shown in Table 7c.

[0242] A comparison of the optical properties of the security features obtained with inks E8, E14 and E15 with those of the security features obtained with inks E36 to E38 shows that the structure of the vinyl ether containing two vinyloxy residues does not have any influence on the optical properties of the security feature.

[0243] As shown by Table 7c, inks containing vinyl ethers with one vinyloxy residue, such as HBVE, in amounts of 6.1 wt-% or more (comparative inks C18 and C19) provide security features that are deep blue in transmitted light but brown in reflected light, which is unacceptable as a dichroic security feature for securing valuable documents. However, small amounts of vinyl ethers with one vinyloxy residue in the claimed security inks do not affect the optical properties of the security feature obtained with said inks, as shown by experiments performed with ink E39.

[0244] The presence of less than about 3.5 wt-% of an oxetane with one functional oxetanyl residue, such as Curalite™ OX TMPO, in a UV-Vis radiation curable ink does not affect the optical properties of the security feature obtained with said ink, as shown, for example, by experiments carried out with inks C20, C21, E40 to E44. The use of an oxetane with two oxetanyl residues, such as Curalite™ OXPLUS, in a UV-Vis radiation curable ink does not have a detrimental effect on the optical properties of the security feature obtained with said ink, as shown, for example, by experiments carried out with inks E45 to E48 of the present invention. [Table 16] [Table 17]

Table 18

Claims

1. 1. A UV-Vis radiation curable security ink for producing a security feature that exhibits a blue color when viewed in transmitted light and a metallic yellow color when viewed in incident light, said ink comprising: a) about 7.5 wt-% to about 20 wt-% silver nanoplatelets having an average diameter in the range of 50-150 nm with a standard deviation of less than 60%, an average thickness in the range of 5-30 nm with a standard deviation of less than 50%, and an average aspect ratio greater than 2.0, wherein the average diameter is determined by transmission electron microscopy and the average thickness is determined by transmission electron microscopy; The silver nanoplatelets have a surface stabilizer of the general formula (I) 【Chemical 1】 [In the formula, residue R Ａ is a C substituted with a hydroxy group ２ -C ４ is an alkyl group; residue R Ｂ is C １ -C ４ C substituted with alkyl and hydroxy groups ２ -C ４ alkyl groups; Cat ＋ is Na ＋ , K. ＋ , Cs ＋ and Rb ＋ is a cation selected from the group consisting of: b) a perfluoropolyether surfactant functionalized with at least hydroxy groups; c) from about 3 wt-% to about 12 wt-% of a polyvinyl chloride copolymer containing at least 69 wt-% vinyl chloride; d) d1) about 25 wt-% to about 55 wt-% of a cycloaliphatic epoxide, and about 1 wt-% to about 10 wt-% of a cationic photoinitiator; or d2) about 30 wt-% to about 65 wt-% of a mixture of a cycloaliphatic epoxide and a radically curable compound, about 1 wt-% to about 6 wt-% of a cationic photoinitiator, and about 1 wt-% to about 6 wt-% of a free-radical photoinitiator; and optionally e) e1) a vinyl ether having two vinyloxy residues in an amount less than 50% by weight percent (wt-%) of the cycloaliphatic epoxide of d); e2) vinyl ethers having one vinyloxy residue in an amount of less than about 5 wt. %; e3) less than about 10 wt-% of an epoxide other than a cycloaliphatic epoxide; e4) oxetanes having two oxetanyl residues in an amount less than about 20 wt-%; e5) oxetanes having one oxetanyl residue in an amount less than about 3.5 wt-%; and e6) a mixture of e1) and / or e2) and / or e3) and / or e4) and / or e5) a cationically curable compound selected from the group consisting of wherein the weight percent is based on the total weight of the UV-Vis radiation curable security ink.

2. 10. The UV-Vis radiation curable security ink of claim 1, wherein said security ink is selected from a screen printed security ink, a rotogravure printed security ink, and a flexographic printed security ink.

3. 3. The UV-Vis radiation curable security ink of claim 1, wherein the average diameter of the silver nanoplatelets is in the range of 70 to 120 nm with a standard deviation of less than 50%, the average thickness of the silver nanoplatelets is in the range of 8 to 25 nm with a standard deviation of less than 30%, and the average aspect ratio of the silver nanoplatelets is greater than 2.

5.

4. 4. The UV-Vis radiation curable security ink of claim 1, wherein the surface stabilizer of general formula (I) is present in an amount of about 0.4% to about 5% by weight percent (wt-%) of the silver nanoplatelets of a).

5. The residue R Ａ and R Ｂ are each independently substituted with a hydroxy group ２ -C ４ The UV-Vis radiation curable security ink according to any one of claims 1 to 4, wherein the alkyl group is an alkyl group.

6. 6. The UV-Vis radiation curable security ink according to any one of claims 1 to 5, wherein the silver nanoplatelets have a further surface stabilizer of general formula (II) 【Chemistry 2】 [In the formula, 【Chemistry 3】 indicates a bond with silver; R １ is H, C １ -C １８ Alkyl, phenyl, C １ -C ８ Alkylphenyl, or CH ２ COOH; R ２ , R ３ , R ４ , R ５ , R ６ and R ７ are independently H, C １ -C ８ alkyl, or phenyl; Y is O or NR ８ and R ８ is H or C １ -C ８ is alkyl; k1 is an integer ranging from 1 to 500; k2 and k3 are each independently 0 or an integer ranging from 1 to 250; k4 is 0 or 1; k5 is an integer ranging from 1 to 5.

7. 7. The UV-Vis radiation curable security ink according to any one of claims 1 to 6, wherein the silver nanoplatelets have a further surface stabilizer of general formula (III): 【Chemistry 4】 [In the formula, R １７ａ , R １７ｂ and R １７ｃ are each independently H or methyl; R １８ａ and R １８ｂ is H or methyl; R １９ａ is a saturated or unsaturated, linear or branched chain alkyl having 1 to 22 carbon atoms; R １９ｂ is R ｃ -[O-CH ２ -CH ２ -] ｃ -O-; R １９ｃ teeth 【Chemistry 5】 , -C(=O)-NH-(CH ２ ) ｙ NR １５ R １６ , or —C(═O)—NH—(CH ２ ) ｙ N ＋ HR １５ R １６ An － and where An － is a monovalent organic or inorganic acid anion; y is an integer from 2 to 10; R １５ is a saturated or unsaturated, linear or branched chain alkyl having 1 to 22 carbon atoms; R １６ is a saturated or unsaturated, linear or branched chain alkyl having 1 to 22 carbon atoms; R ｃ is saturated or unsaturated, linear or branched chain alkyl having 1 to 22 carbon atoms, or alkylaryl or dialkylaryl having up to 24 carbon atoms; c is 1 to 150; y1, y2 and y3 are each independently an integer of 1 to 200.

8. 8. The UV-Vis radiation curable security ink according to any one of claims 1 to 7, wherein the silver nanoplatelets have a further surface stabilizer of general formula (IV): 【Chemistry 6】 [During the ceremony R ９ is a hydrogen atom or a group of the formula -CHR １１ -N(R １２ ) (R １３ ) group; R １０ is a hydrogen atom, a halogen atom, C １ -C ８ an alkoxy group, or C １ -C ８ is an alkyl group; R １１ is H or C １ -C ８ is alkyl; R １２ and R １３ are independent of each other and C １ -C ８ Alkyl, hydroxy C １ -C ８ an alkyl group or a group of the formula -[(CH ２ CH ２ ) -O] ｎ１ -CH ２ CH ２ -OH group, and n1 is 1 to 5.

9. 9. The UV-Vis radiation curable security ink according to any one of claims 1 to 8, wherein the UV-Vis radiation curable security ink comprises a perfluoropolyether surfactant in an amount of about 0.025 wt-% to about 5 wt-%, the weight percentage being based on the total weight of the UV-Vis radiation curable security ink.

10. 10. The UV-Vis radiation curable security ink of any one of claims 1 to 9, wherein said security ink comprises d1) about 25 wt-% to about 55 wt-% of a cycloaliphatic epoxide, and about 1 wt-% to about 10 wt-% of a cationic photoinitiator.

11. 10. The UV-Vis radiation curable security ink according to any one of claims 1 to 9, wherein the security ink comprises d2) about 30 wt-% to about 65 wt-% of a mixture of a cycloaliphatic epoxide and a radically curable compound, about 1 wt-% to about 6 wt-% of a cationic photoinitiator, and about 1 wt-% to about 6 wt-% of a free-radical photoinitiator; and the radically curable compound is selected from a radically curable monomer, a radically curable oligomer, and mixtures thereof.

12. 12. A UV-Vis radiation curable security ink according to any one of claims 1 to 11, wherein the cationically curable monomer is a vinyl ether having two vinyloxy residues in an amount less than 50% by weight percent (wt-%) of the cycloaliphatic epoxide of e1)d).

13. 13. The UV-Vis radiation curable security ink of any one of claims 1 to 12, further comprising: g) up to about 25 wt-% organic solvent, the weight percentage being based on the total weight of the UV-Vis radiation curable security ink.

14. 1. A method of making a security feature that secures a valuable document, said security feature exhibiting a blue color when viewed in transmitted light and a metallic yellow color when viewed in incident light, said method comprising the steps of: A) printing the UV-Vis radiation curable security ink according to any one of claims 1 to 13 onto a transparent or partially transparent area of ​​a substrate of a value document, preferably by screen printing, rotogravure printing or flexographic printing, to provide an ink layer; and B) UV-Vis curing the ink layer obtained in step A) to form the security feature. A method comprising:

15. 15. The method of claim 14, wherein the valuable document is selected from banknotes, certificates, tickets, cheques, receipts, revenue stamps, contracts, identity documents such as passports, identity cards, visas, driver's licenses, bank cards, credit cards, transaction cards, access documents and cards, admission tickets, public transport tickets, diplomas and degrees.

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