RU2827751C1 - Method of producing dichroic security features for protecting valuable documents - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to protective devices for marking valuable documents. Method of making a security feature for protecting a valuable document, wherein said security feature exhibits a blue colour when viewed in transmitted light and a metallic yellow colour when viewed in an incident colour. Manufacturing method includes the following stages: a) printing a specific UV-curable ink on a transparent or partially transparent region of the substrate of the valuable document; b) heating the paint layer obtained at step a), at temperature from approximately 55 °C to approximately 100 °C for at least one second so that the paint layer exhibits a metallic yellow colour when viewed in an incident colour; and c) curing under the influence of radiation in UV and visible region of the ink layer obtained in step b), to form a security feature. Method of manufacturing according to the present invention enables to expediently obtain protective features exhibiting a blue colour when viewed in transmitted light and metallic yellow when viewed in incident colour and is especially useful for industrial printing of valuable documents.

EFFECT: high security of valuable documents from forgery and/or illegal reproduction.

24 cl, 17 tbl

Description

Field of technology to which the invention relates

The present invention relates to the field of methods for producing dichroic security features that exhibit a first colour when viewed in transmitted light and a second colour, different from the first colour, when viewed in incident light, for protecting valuable documents.

Prerequisites for the creation of an invention

With the continuous improvement in the quality of colour photocopies and printing work and in an attempt to protect security documents such as banknotes, valuable documents or cards, travel tickets or cards, tax stamps and product labels that do not have reproducible effects from counterfeiting, falsification or illegal reproduction, it has become common practice to include various security features in these documents.

Security features, for example for protected documents, can be broadly divided into "hidden" security features and "overt" security features. The security provided by hidden security features is based on the concept that such features are difficult to detect, usually requiring special equipment and knowledge to detect them, while "overt" security features are based on the concept that they are easily detectable by the naked human senses, for example, such features may be visible and/or detectable by tactile sensations and still difficult to produce and/or copy. However, the effectiveness of obvious security features depends to a large extent on their easy recognition as a security feature, since most users, and especially those who have no prior knowledge of the security features of the document or object protected by them, will only actually perform a security check based on the said security feature if they are actually aware of its existence and nature.

A special role in protecting valuable documents is played by dichroic security features, which display a first colour when viewed in incident light and a second colour, different from the first colour, when viewed in transmitted light. In order to provide a striking effect and attract the attention of a non-specialist, the first colour and the second colour must have an eye-catching appearance, such as blue, metallic yellow, purple and green, as well as a significant colour contrast (e.g. blue/metallic yellow, green/metallic yellow, purple/metallic yellow).

Such a dichroic security feature is disclosed in US Patent Application Publication No. US 20120242075 A1, which describes a transparent security element comprising a thin-film element with a multilayer structure and a carrier that appears gold when viewed in incident light and appears blue when viewed in transmitted light. The thin-film element comprises at least two semitransparent mirror layers and at least one dielectric separating layer located between at least two mirror layers. The process of manufacturing a transparent security element is time-consuming, since it involves thermal deposition, electron beam evaporation or sputtering of each of at least three layers contained in the thin-film element on the carrier.

International Patent Application Publication No. WO2011064162 A2 also describes a dichroic security or decorative element comprising a substrate and, on at least a portion of said surface of the substrate, a coating comprising plate-shaped transition metal particles whose longest edge length dimension is from 15 nm to 1000 nm and whose thickness is from 2 nm to 500 nm. Manual application of UV-curable paints comprising silver platelets and either a solvent-based carrier or a carrier comprising radical-curable monomers and a free-radical photoinitiator, wherein the weight ratio of silver platelets to carrier is 3:1.1, onto a transparent substrate provides security or decorative elements that exhibit a blue colour in transmitted light and a gold/copper or gold/bronze colour in reflected light. The high concentration of silver platelets in the paints used to produce the security or decorative element described in WO 2011064162 A2 worsens the mechanical resistance of the produced security or decorative element and, in addition, makes the process of producing said element expensive. In addition, the mechanical resistance of the security or decorative element described in WO 2011064162 A2 worsens due to the use of UV-radical-curing paints or solvent-based paints, which, as is well known to a person skilled in the art, provide cured coatings with limited mechanical resistance. Since mechanical resistance is an essential property of security elements and the manufacturing process described in WO 2011064162 A2 is labor-intensive and rather expensive, the technology described in that document is not suitable for the production of dichroic security elements, and especially for the industrial production of dichroic security elements on valuable documents.

Typically, high printing speeds of approximately 8,000 sheets/hour are required for industrial printing of security documents, with a significant number of security documents being created from each sheet. For illustrative purposes in the field of banknote printing, up to 55 security documents may be produced from a single sheet, each containing one or more security features. In order to be suitable for implementation on a production line, it is important that the process for producing each printed security feature present in a security document meets the high-speed requirements of industrial printing of security documents.

Thus, there remains a need for simple and economical methods of producing, at high speed (i.e., industrial speed), dichroic security features that exhibit a blue colour when viewed in transmitted light and a metallic yellow colour when viewed in incident light on valuable documents.

Brief description of the invention

Accordingly, the object of the present invention is to provide a simple and economical method for producing at high speed (i.e. industrial speed) a security feature for protecting a valuable document, wherein said security feature exhibits a blue colour when viewed in transmitted light and a metallic yellow colour when viewed in incident light. This is achieved by means of the method claimed in this document, wherein said method comprises the following steps:

a) printing, preferably by screen, rotogravure or flexographic printing, of UV and visible radiation-curable ink on a transparent or partially transparent area of the substrate of a document of value to provide a layer of ink;

b) heating the paint layer obtained in step a) at a temperature of from about 55°C to about 100°C for at least one second so that the paint layer exhibits a metallic yellow colour when viewed in incident light; and

c) curing under the influence of UV and visible radiation the paint layer obtained in step b) to form a security feature;

The paint, which is cured under the influence of radiation in the UV and visible range, contains:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii) ) from about 40% by weight to about 75% by weight of either a cycloaliphatic epoxide or a mixture of a cycloaliphatic epoxide and one or more UV-visible radiation-curable compounds other than a cycloaliphatic epoxide;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate; and optionally

vi ) up to 25% by weight of organic solvent;

and the mass percentage contentii) And vi) is calculated based on the total mass of UV-visible curable paint. The manufacturing method according to the present invention makes it possible to obtain security features exhibiting a blue color when viewed in transmitted light and a metallic yellow color when viewed in incident light on a valuable document in a reasonable manner, thereby meeting the high-speed requirements of industrial printing of valuable documents. The eye-catching appearance and the contrast between the blue color exhibited in transmitted light and the metallic yellow color exhibited in incident light make the security feature obtained by the method according to the present invention, noticeable, thereby attracting the attention of a non-specialist to the security feature and helping to find and recognize said security feature on a valuable document, as well as to authenticate the valuable document containing the security feature. Therefore, the manufacturing method according to the present invention provides dichroic security features with an eye-catching appearance and high recognition.

Preferably, the concentration of silver nanoplatelets in the UV-visible radiation-curable paint is from about 5 wt.% to about 20 wt.%, preferably from about 7.5 wt.% to about 17.5 wt.%, more preferably from about 10 wt.% to about 15 wt.%, wherein the weight percentage is calculated based on the total weight of the UV-visible radiation-curable paint. The concentration of silver nanoplatelets in the UV-visible radiation-curable paint used in the method according to the present invention is substantially lower than the concentrations of silver platelets used in paints known from the prior art. Therefore, the manufacturing method claimed in this document makes it possible to cost-effectively produce dichroic security features with optical effects similar to those known from the prior art, but with significantly improved mechanical resistance properties.

In an embodiment according to the present invention, the UV-visible radiation-curable paint used in the manufacturing method claimed and described herein is a cationically curable paint comprising:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii-1 ) from about 40 wt.% to about 75 wt.% of a cycloaliphatic epoxide;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate; and optionally

vi ) up to 25% by weight of organic solvent;

wherein the weight percentage of ii-1 ) and vi) is calculated based on the total weight of the UV-visible curable paint.

In a further embodiment according to the present invention, the UV-visible radiation-curable paint used in the manufacturing method claimed and described herein is a cationically curable paint comprising:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii-2 ) from about 40 wt.% to about 75 wt.% of a mixture of a cycloaliphatic epoxide and one or more cationically curable monomers other than a cycloaliphatic epoxide, wherein the ratio of the weight percentage (wt.%) of cycloaliphatic epoxide present in said paint to the weight percentage
(wt.%) of one or more cationically curable monomers other than a cycloaliphatic epoxide present in said paint exceeds approximately 1.1:1;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate; and optionally

vi ) up to 25% by weight of organic solvent;

wherein the weight percentage of ii-2 ) and vi) is calculated based on the total weight of the UV-visible curable paint.

The UV-visible radiation-curable paint used in the manufacturing method claimed and described herein may be a hybrid UV-visible radiation-curable paint comprising:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii-3 ) from about 40 wt.% to about 75 wt.% of a mixture of a cycloaliphatic epoxide and one or more radical-curable monomers and/or oligomers, wherein the ratio of the weight percentage (wt.%) of the one or more radical-curable monomers and/or oligomers present in said paint to the weight percentage (wt.%) of the cycloaliphatic epoxide present in said paint is below about 1.6:1;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate;

ix) one or more free radical photoinitiators; and optionally

vi ) up to 25% by weight of organic solvent;

wherein the weight percentage of ii-3 ) and vi) is calculated based on the total weight of the UV-visible curable paint.

In an alternative embodiment, the UV-visible radiation-curable paint used in the manufacturing method claimed and described herein may be a hybrid UV-visible radiation-curable paint comprising:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii-4 ) from about 40 wt.% to about 75 wt.% of a mixture of a cycloaliphatic epoxide, one or more cationically curable monomers other than a cycloaliphatic epoxide, and one or more radically curable monomers and/or oligomers,

wherein the ratio of the weight percentage (wt.%) of one or more radical-curable monomers and/or oligomers present in said paint and the sum of the weight percentage (wt.%) of cycloaliphatic epoxide present in said paint and the weight percentage (wt.%) of one or more cationically curable monomers other than cycloaliphatic epoxide present in said paint is below about 1.6:1, and

wherein the ratio of the weight percentage (wt.%) of the cycloaliphatic epoxide present in said paint to the weight percentage (wt.%) of one or more cationically curable monomers other than the cycloaliphatic epoxide present in said paint is greater than approximately 1.1:1;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate;

ix) one or more free radical photoinitiators; and optionally

vi ) up to 25% by weight of organic solvent; whereby the weight percentages of ii-4 ) and vi) are calculated on the basis of UV-visible curable paint.

Advantageously, the method claimed and described in this document, based on the use of a cationically curable paint under the influence of radiation in the UV and visible region, described in this document, or a hybrid curable paint under the influence of radiation in the UV and visible region, described in this document, provides security features with improved mechanical properties compared to similar security features known from the prior art, which are obtained from radical-curing paints under the influence of UV radiation or solvent-based paints, and in particular from radical-curing paints under the influence of UV radiation or solvent-based paints containing high concentrations of silver nanoplatelets.

In order to impart resistance to contamination to the valuable document and/or to protect the security feature from the physical and chemical influence of the environment, the manufacturing method claimed in this document preferably additionally includes steps f) and g) , performed after step c) :

f ) applying to the substrate, preferably by means of a printing process, a curable protective varnish to form a varnish layer;

g ) curing the varnish layer obtained in step f) to form a protective coating.

Detailed description

Definitions

To interpret the meaning of the terms discussed in the description and set out in the claims, the following definitions should be used.

In the context of this document, the singular form of an object refers to one or more objects and does not necessarily limit it to the singular.

In the context of the present document, the term "about" means that the stated amount or value may have a specific defined value or some other value adjacent to it. In general, the term "about" indicating a specific value is intended to indicate a range within ±5% of the value. As one example, the phrase "about 100" means a range of 100 ±5, i.e., a range from 95 to 105. Preferably, the range indicated by the term "about" means a range within ±3% of the value, more preferably ±1%. In general, when using the term "about", it can be expected that similar results or effects according to the present invention can be obtained in a range within ±5% of the stated value.

In the context of this document, the term "and/or" means that either all or only one of the elements of the specified group may be present. For example, "A and/or B" means "only A or only B, or both A and B". In the case of "only A", the term also covers the possibility of the absence of B, i.e. "only A but not B".

The term "comprising" in the context of the present document is non-exclusive and subject to change. Thus, for example, a solution containing compound A may contain other compounds in addition to A. However, the term "comprising" also covers, as does its specific embodiment, the more restrictive meanings of "consisting essentially of" and "consisting of", so that, for example, "a solution containing A, B and optionally C" may also (mainly) consist of A and B or (mainly) consist of A, B, and C.

When the present description refers to “preferred” embodiments/features, combinations of these “preferred” embodiments/features should also be considered as disclosed, insofar as the particular combination of “preferred” embodiments/features makes sense from a technical point of view.

In the context of this document, the term “one or more” means one, two, three, four, etc.

The term "UV-visible irradiation-curable" and "UV-visible irradiation-curing" refers to irradiation curing by photopolymerization, by exposure to radiation whose wavelength components are in the UV or UV-visible portion of the electromagnetic spectrum (typically from 100 nm to 800 nm, preferably 150-600 nm, and more preferably 200-400 nm).

It has been unexpectedly discovered that a method for producing a security feature for protecting a valuable document, in which said security feature exhibits a blue color when viewed in transmitted light and a metallic yellow color when viewed in incident light, said method comprising the following steps:

a) printing, preferably by screen, rotogravure or flexographic printing, of UV and visible radiation-curable ink on a transparent or partially transparent area of the substrate of a document of value to provide a layer of ink;

b) heating the paint layer obtained in step a) at a temperature of from about 55°C to about 100°C for at least one second so that the paint layer exhibits a metallic yellow colour when viewed in incident light; and

c) curing under the influence of UV and visible radiation the paint layer obtained in step b) to form a security feature;

The paint, which is cured under the influence of radiation in the UV and visible range, contains:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii ) from about 40% by weight to about 75% by weight of either a cycloaliphatic epoxide or a mixture of a cycloaliphatic epoxide and one or more UV-visible radiation-curable compounds other than a cycloaliphatic epoxide;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate; and optionally

vi ) up to 25% by weight of organic solvent;

wherein the mass percentage of ii ) and vi ) is calculated based on the total mass of the UV-visible curable paint, makes it possible to obtain dichroic security features with an eye-catching appearance and high recognition on valuable documents in a single printing step in a practical and cost-effective manner. The manufacturing method meets the high-speed requirements of industrial printing of valuable documents without affecting the optical properties exhibited by the dichroic security feature on the valuable document.

The security feature provided by the manufacturing method claimed in this document exhibits a blue color when viewed in transmitted light, i.e., when transmitted. For the purposes of the present invention, viewing in transmitted light means that the security feature is illuminated from one side, for example, when holding said security feature against daylight or in front of a light source, and viewed from the opposite side. Regardless of which side the security feature is viewed from in transmitted light, a blue color is observed. For the purposes of the present invention, a security feature exhibiting a blue color refers to a security feature exhibiting a blue color characterized by a C* chromaticity value (which corresponds to an indicator of color intensity or color saturation) above 20. An intense to very intense blue color is characterized by a C* chromaticity value above 30. The C* chromaticity value is calculated from the a* and b* values according to the CIELAB (1976) color space, where

The reported a* and b* values in transmitted light are measured using a Datacolor 650 spectrophotometer (settings: integrating sphere, diffuse illumination (D65 pulsed xenon) and 8° viewing angle, SP2000 analyzer with 256 dual diode array for the wavelength range 360-700 nm, transmission sampling aperture size 22 mm).

The security feature provided by the manufacturing method claimed in this document exhibits a metallic yellow color or a gold color when viewed in incident light, i.e., when reflected. In this patent application, the terms "metallic yellow color" and "gold color" are used interchangeably. For the purposes of the present invention, "viewed in incident light" means that the security feature is illuminated from one side and viewed from the same side. Regardless of which side the security feature is viewed from in incident light, a metallic yellow color is observed. For the purposes of the present invention, a security feature exhibiting a metallic yellow color or a gold color refers to a security feature exhibiting a yellow color characterized by a C* chromaticity value (which corresponds to an indicator of color intensity or color saturation) greater than 20, as calculated from the a* and b* values according to the CIELAB color space (1976), where

and the specified values a* and b* of the security feature were measured at an angle of 0° to the normal with an illumination angle of 22.5° using a goniometer (Goniospektrometer Codec WI-10 5&5 from Phyma GmbH Austria).

Step a) of the manufacturing method according to the present invention requires printing a UV-visible radiation-curable ink on a transparent or partially transparent area of the substrate of the valuable document to provide an ink layer. The manufacturing method according to the present invention claimed in this document makes it possible to obtain in a single printing step a security feature showing a metallic yellow colour in incident light and a blue colour, in particular an intense to very intense blue colour, in transmitted light. In the context of this document, the term "printing" refers to any printing process suitable for printing the UV-visible radiation-curable ink described in this document on the substrate of the valuable document. In particular, the term "printing" refers to a printing process selected from the group consisting of screen printing, rotogravure printing, flexographic printing, pad printing, inkjet printing and airbrushing. Preferably, the UV-visible curable ink is printed on a transparent or partially transparent area of the substrate of the valuable document by screen printing, rotogravure or flexographic printing, more preferably screen printing.

Screen printing (also referred to in the art as silk-screen printing) is a printing method that typically uses a woven mesh screen to support an ink stamping template. The attached template forms open mesh areas that transfer ink as a sharp-edged image onto a substrate. A squeegee is moved across the screen by the ink stamping template, causing the ink to pass the woven mesh threads in the open areas. An important characteristic of screen printing is that ink can be applied to a substrate at a greater thickness than with other printing methods. Consequently, screen printing is also preferred when ink deposits of about 10 to 50 µm or more are required, which cannot be (easily) achieved with other printing methods. Typically, the screen is made of a piece of porous, finely woven fabric called a mesh, stretched over a frame, such as aluminum or wood. Nowadays, most nets are made of artificial materials such as synthetic or steel threads. Preferred synthetic materials are nylon or polyester threads.

In addition to stencils made on the basis of a woven mesh based on synthetic or metallic threads, stencils made of a solid metal sheet with a grid of holes have been developed. Such stencils are obtained using a process that includes electrolytic formation of a metal stencil by forming in a first electrolytic bath a stencil frame on a matrix equipped with a separating agent, separating the formed stencil frame from the matrix and subjecting the stencil frame to electrolysis in a second electrolytic bath to deposit metal on said frame.

There are three types of screen printing machines, namely flat, cylinder and rotary screen printing machines. Flat and cylinder screen printing machines are similar in that they both use a flat screen and a three-stage reciprocating process to perform the printing operation. The screen is first moved into position over the substrate, then a squeegee is pressed against the mesh and pulled across the image area, and then the screen is lifted off the substrate to complete the process. With a flat machine, the substrate to be printed is usually placed on a horizontal printing platform parallel to the screen. With a cylinder machine, the substrate is mounted on a cylinder. Both flat and cylinder screen printing processes are intermittent processes and therefore have limited speeds, which are typically a maximum of 45 m/min for a web or 3,000 sheets/hour for a sheet fed process.

On the contrary, rotary screen printing machines are designed for continuous high-speed printing. The screens used on rotary screen printing machines are, for example, thin metal cylinders, which are usually produced using the electroforming process described in this document above, or are made of woven steel threads. The open-ended cylinders are closed at both ends and inserted into blocks at the side of the machine. During printing, ink is pumped into one end of the cylinder to maintain a constant supply of paint. The squeegee is fixed inside the rotating screen, and the squeegee pressure is maintained and adjusted to ensure good and consistent print quality. The advantage of rotary screen printing machines is the speed, which can easily reach 150 m/min in a web or 10,000 sheets/hour in a sheet-fed process.

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

As is known to those skilled in the art, the term "rotogravure printing" refers to a printing process as 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 engraved on the surface of a cylinder. The non-image areas are at a constant base level. Before printing, the entire printing plate (non-printable and printable elements) is coated and filled with ink. The ink is removed from the non-image area with a sponge or knife before printing so that the ink remains only in the cells. The image is transferred from the cells to the substrate under the influence of pressure, typically in the range of 2-4 bar, and the adhesion forces between the substrate and the ink. The term "rotary gravure printing" does not cover other gravure printing processes (also referred to in the art as engraved steel stamping processes or engraved copper plate printing), which are based, for example, on a different type of ink.

Flexographic printing methods preferably use a unit with a doctor blade chamber, an anilox roller, and a plate cylinder. The anilox roller preferably has small cells, the volume and/or density of which determines the degree of ink or varnish application. The doctor blade chamber is located opposite the anilox roller, filling the cells and simultaneously removing excess ink or varnish. The anilox roller transfers the ink to the plate cylinder, which ultimately transfers the ink to the substrate. Plate cylinders can be made of polymers or elastomer materials. Polymers are mainly used as a photopolymer in printing plates and sometimes as a seamless coating on the cylinder. Photopolymer printing plates are made of light-sensitive polymers that harden when exposed to ultraviolet (UV) light. Photopolymer printing plates are cut to the required size and placed in the UV exposure unit. One side of the printing plate is completely exposed to UV light to cure or harden the plate base. The printing plate is then turned over, the back side of the blank is placed on top of the uncured side, and the printing plate is further exposed to UV light. This hardens the printing plate in the image areas. The printing plate is then treated to remove uncured photopolymer from the non-image areas, which reduces the plate surface in these non-image areas. After treatment, the printing plate is dried and exposed to a further dose of UV light to cure the entire printing plate. The preparation of plate cylinders for flexographic printing is described in Printing Technology , J. M. Adams and P. A. Dolin, Delmar Thomson Learning, ^5th edition, pages 359-360.

In the context of the present document, "a transparent or partially transparent region of a substrate of a valuable document" refers to a region of the substrate of a valuable document, wherein said region is characterized by an average transmittance in the visible range of at least 50%, preferably at least 70%, 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 both the same material and different materials. The exclusion of one or more layers in a multilayer structure or the application of a transparent or partially transparent material to an opening in a substrate made of a material other than a transparent or partially transparent material makes it possible to obtain substrates for valuable documents, wherein the transparent or partially transparent region of the substrate and the remaining part of the substrate are made of different materials.

Substrate materials for security documents include, but are not limited to, 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, but not limited to, manila hemp, cotton fiber, flax fiber, wood pulp, and mixtures thereof. As is well known to those skilled in the art, cotton fiber and cotton/flax fiber mixtures are preferred for banknotes, while wood pulp is typically used for security documents other than banknotes. Typical examples of plastics and polymers include polystyrene, polycarbonate, polyolefins such as polyethylene (PE) and polypropylene (PP), including biaxially oriented polypropylene (BOPP), polyamides (PA), polyesters such as poly(ethylene terephthalate) (PET), glycol-modified polyethylene terephthalate (PETG), including poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate), poly(1,4-butylene terephthalate) (PBT), and poly(ethylene 2,6-naphthoate) (PEN), and polyvinyl chlorides (PVC). Typical examples of composite materials include, but are not limited to, multilayer structures or laminates of paper and at least one plastic or polymeric material, such as those described herein above. Suitable materials for the transparent or partially transparent area of the substrate include, but are not limited to, polystyrene, polycarbonate, polyolefins such as polyethylene (PE) and polypropylene (PP), including biaxially oriented polypropylene (BOPP), polyamides (PA), polyesters such as poly(ethylene terephthalate) (PET), glycol-modified polyethylene terephthalate (PETG), including poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate), poly(1,4-butylene terephthalate) (PBT), and poly(ethylene 2,6-naphthoate) (PEN), and polyvinyl chlorides (PVC). The transparent or partially transparent area of the substrate of the valuable document may carry a primer layer over which a UV-visible radiation-curable ink is printed. The primer layer can be produced by a UV/VIS curable varnish containing all of the ingredients of the UV/VIS curable paint described herein except for the silver nanoplatelets.

In step b) of the manufacturing method according to the present invention described herein, the paint layer obtained in step a) is heated at a temperature of about 55°C to about 100°C for at least one second, so that the paint layer exhibits a metallic yellow color when viewed in incident light. The step of heating at a temperature of about 55°C to about 100°C for at least one second allows the silver nanoplatelets contained in the paint layer to align at the boundary between the paint layer and air and at the boundary between the paint layer and the substrate, which leads to the expedient formation of a thin layer of silver nanoplatelets at said boundaries and the appearance of a metallic yellow color observed in incident light. The use of the specific UV-visible radiation-curable paint described herein prevents the formation of silver agglomerates in the paint layer during the heating step. The formation of silver agglomerates prevents the appearance of a blue colour in transmitted light. A comparison of the comparative test C1 with the test E1 according to the present invention proves that a minimum temperature of approximately 55°C is necessary during the heating step for the appearance of a metallic yellow colour in incident light and an intense blue colour in transmitted light within one second. Heating the ink layer at a temperature of 50°C for one second results in the appearance of a brown colour of low intensity in incident light, which is not noticeable to the layman and is therefore not suitable for a dichroic security feature for protecting a valuable document. The appearance of a metallic yellow colour within one second is achieved by heating the ink layer at a temperature of approximately 55°C to approximately 100°C (see, for example, tests E1 to E6 according to the present invention). Therefore, the manufacturing method according to the present invention, based on the combination of a specific UV-visible radiation-curable ink described in this document and a heating step at a temperature of from about 55°C to about 100°C of an ink layer printed preferably by screen printing, rotogravure or flexographic printing, and more preferably by screen printing, makes it possible to obtain ink layers showing a metallic yellow colour in incident light and a blue colour, especially an intense to very intense blue colour, in transmitted light during heating times of only one second. A time period of at least one second, necessary for the appearance of the metallic yellow colour, is compatible with the high-speed requirements of industrial printing of valuable documents.

Increasing the heating temperature from about 55°C to about 100°C and/or the heating time provides security features exhibiting high C* chromaticity values both in reflected light and in transmitted light, as confirmed, for example, by tests E1 to E6 and E31 to E39 according to the present invention. Preferably, in step b), the ink layer is heated at a temperature of from about 60°C to about 90°C for at least one second, more preferably at a temperature of from about 70°C to about 90°C for at least one second, and even more preferably at a temperature of about 80°C for at least one second. In order to meet the high-speed requirements of industrial printing of security documents, it is preferable that the heating time is lower than or equal to about ten seconds, more preferably lower than or equal to about six seconds, such as five seconds, four seconds, three seconds, two seconds and one second.

The heating step can be carried out by exposing the substrate carrying the paint layer obtained in step a) for at least one second to a temperature of from about 55°C to about 100°C provided by a heating element such as a hot air tunnel, an infrared dryer, a heating plate, a heating cylinder, a microwave oven, a photonic curing device or a combination thereof. Preferred heating elements include hot air tunnels, infrared dryers and combinations thereof.

In step c) of the manufacturing method according to the present invention claimed herein, the paint layer obtained in step b) is cured by exposure to UV-Vis radiation to form a security feature. In the context of the present document, the term "UV-Vis radiation curing" refers to radiation curing of the paint layer by photopolymerization, by exposure to radiation whose wavelength components are in the UV or in the UV-Vis part of the electromagnetic spectrum (typically from 100 nm to 800 nm, preferably 150-600 nm, and more preferably 200-400 nm). The cationically curable monomers are cured by cationic mechanisms consisting of activation by UV-Vis radiation of one or more photoinitiators, which release cationic species, such as acids, which in turn initiate the polymerization of the compound to form a cured binder. Radical-curable monomers and oligomers are cured by free-radical mechanisms consisting of activation by UV-Vis radiation of one or more photoinitiators, which release free radicals, which in turn initiate the polymerization process. Optionally, one or more photosensitizers may also be present. The photosensitizers are activated by one or more wavelengths emitted by a UV-Vis radiation source and achieve an excited state. The excited photosensitizer transfers energy to either one or more photoinitiators (in free-radical polymerization) or an electron (in cationic polymerization). Either process in turn initiates the polymerization process.

Preferably stagec)involves exposing the paint layer obtained at the stageb), the effects of UV and visible radiation emitted by a UV and visible radiation source selected from the group consisting of mercury lamps, preferably medium pressure mercury lamps, UV LED lamps and sequences thereof. As demonstrated, for example, by testsE29a And E29b, for the specific UV-visible radiation-curable paints described herein (for example, paints containing a diaryliodonium photoinitiator and a thioxanthone photosensitizer), a UV-visible radiation source, namely a UV-LED lamp or a mercury lamp, used in the stepc), does not affect the optical properties exhibited by the security feature obtained the manufacturing method described and claimed herein. Typical sequences include using one or more UV LED lamps in a first step to partially cure the UV-visible curable composition and one or more medium pressure mercury lamps in a second step. The mercury lamps preferably emit over a broad range of wavelengths in the range of UVA, UVB and UVC. Accordingly, a large selection of photoinitiators or photoinitiator/photosensitizer combinations is provided having an absorption spectrum matching at least one of the emission bands of the mercury lamp. UV LEDs have a more limited wavelength range, so that at industrial printing speeds only a limited selection of photoinitiators or photoinitiator/photosensitizer combinations are sufficiently effective. On the other hand, UV LEDs are less expensive, require less energy (in particular, they require much less demanding heat dissipation systems), are not prone to ozone formation, and have a much longer service life.

The UV-visible radiation-curable paint used in the manufacturing method according to the present invention comprises:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii) from about 40% by weight to about 75% by weight of either a cycloaliphatic epoxide or a mixture of a cycloaliphatic epoxide and one or more UV-visible radiation-curable compounds other than a cycloaliphatic epoxide;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate; and optionally

vi ) up to 25% by weight of organic solvent;

wherein the mass percentages of ii ) and vi ) are calculated based on the total mass of the UV-visible curable paint.

Preferably, the UV-visible radiation-curable ink is a UV-visible radiation-curable screen printing ink, a UV-visible radiation-curable rotogravure ink, or a UV-visible radiation-curable flexographic printing ink, more preferably a UV-visible radiation-curable screen printing ink. The viscosity of the UV-VIS radiation-curable paint used in the manufacturing method according to the present invention claimed herein is from about 50 mPa⋅s to about 2000 mPa⋅s at 25°C, as measured using a viscometer (model "DV-I Prime") equipped with a spindle S27 at 100 rpm, or a spindle S21 at 50 rpm for measuring viscosities of 500-2000 mPa⋅s, and a spindle S21 at 100 rpm for measuring viscosities equal to or less than 500 mPa⋅s. The viscosity of the UV-visible radiation-curable screen printing ink used in the manufacturing method according to the present invention claimed herein is from about 50 mPa⋅s to about 1000 mPa⋅s at 25°C, preferably from about 100 mPa⋅s to about 1000 mPa⋅s at 25°C.

The silver nanoplatelets contained in the UV-visible radiation-curable paint may be in the form of disks, regular hexagons, triangles, especially equilateral triangles and truncated triangles, especially truncated equilateral triangles, or mixtures thereof. They are preferably in the form of disks, truncated triangles, hexagons or mixtures thereof.

The average diameter of the silver nanoplatelets is in the range of 50-150 nm, preferably 60-140 nm, 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 said silver nanoplatelet and corresponds to the maximum dimension of said silver nanoplatelet when oriented parallel to the plane of the image obtained by transmission electron spectroscopy (TEM). In the context of this document, the term "average diameter of silver nanoplatelets" refers to the average diameter determined by transmission electron spectroscopy (TEM) using Fiji image analysis software based on the measurement of at least 300 randomly selected silver nanoplatelets, wherein the diameter of a silver nanoplatelet is the maximum dimension of said silver nanoplatelet oriented parallel to the plane of the image obtained by transmission electron spectroscopy (TEM). TEM analysis was performed on a dispersion containing 24.1 wt% silver nanoplatelets in isopropanol using a ZEISS EM 910 instrument in bright field mode at an electron beam acceleration voltage of 100 kV.

The average thickness of the silver nanoplatelets is in the range of 5-30 nm, preferably 7-25 nm, more preferably 8-25 nm, with a standard deviation of less than 50%, preferably less than 30%. The thickness of the silver nanoplatelet is the shortest dimension of said nanoplatelet and corresponds to the maximum dimension of said silver nanoplatelet when oriented perpendicular to the plane of the image obtained by transmission electron spectroscopy (TEM). In the context of this document, the term "average thickness of the silver nanoplatelets" refers to the average thickness determined by transmission electron spectroscopy (TEM) based on manual measurement of at least 50 randomly selected silver nanoplatelets oriented perpendicular to the plane of the TEM image, wherein the thickness of the silver nanoplatelet is the maximum dimension of said silver nanoplatelet when oriented perpendicular to the plane of the image obtained by transmission electron spectroscopy (TEM). TEM analysis was performed on a dispersion containing 24.1 wt% silver nanoplatelets in isopropanol using a ZEISS EM 910 instrument in bright field mode at an electron beam acceleration voltage of 100 kV.

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.

Preferably, the average diameter of the silver nanoplatelets is in the range of 70-120 nm with a standard deviation of less than 50%, the average thickness of said silver nanoplatelets is in the range of 8-25 nm with a standard deviation of less than 30%, and the average aspect ratio of said silver nanoplatelets exceeds 2.5.

The silver nanoplatelets used in the UV-Visible radiation-curable paint described herein are characterized by the highest absorption maximum at a wavelength of 560-800 nm, preferably 580-800 nm, most preferably 600-800 nm. The highest absorption maximum at a wavelength was measured in water at a concentration of about 5*10 ^-5 M (mol/L) silver using a Varian Cary 50 UV-Visible spectrophotometer. The absorption maximum has a full width at half maximum (FWHM) value in the range of 50-500 nm, preferably 70-450 nm, more preferably 80-450 nm. The molar extinction coefficient of silver nanoplatelets, as measured at the highest absorption maximum wavelength, exceeds 4000 L/(cm*mol _Ag ), in particular exceeds 5000 L/(cm*mol _Ag ), in particular exceeds 6000 L/(cm*mol _Ag ).

To prevent agglomeration and sedimentation of the silver nanoplatelets during storage, the silver nanoplatelets preferably contain one or more surface stabilizers.

A preferred embodiment according to the present invention is directed to a method for producing a security feature for protecting a valuable document, as claimed and described herein, wherein the silver nanoplatelets comprise a surface stabilizer of general formula ( I )

( I )

on their surface,

at the same time indicates a connection 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 independently of one another represent H, C ₁ -C ₈ alkyl or phenyl;

Y represents O or NR ⁸ ;

R ⁸ is H or C ₁ -C ₈ alkyl;

k1 is an integer in the range from 1 to 500,

k2 and k3 are independently equal to 0 or are integers in the range from 1 to 250;

k4 is 0 or 1,

k5 is an integer in the range 1 to 5.

Preferably, Y is O. Also preferably, k4 is 0.

The average molecular weight (Mn) of the surface stabilizer of the general formula ( I ) is preferably 1000-20000 [g/mol], and more preferably 1000-10000 [g/mol], most preferably 1000-6000 [g/mol].

If the stabilizer of formula ( I ) contains, for example, ethylene oxide units (EO) and propylene oxide units (PO), the order of (EO) and (PO) may be fixed (block copolymers) or may not be fixed (random copolymers).

Preferably, R ¹ is H or C ₁ -C ₁₈ alkyl, R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are independently of each other H, CH ₃ or C ₂ H ₅ , k1 is an integer in the range of 22-450, k2 and k3 are independently 0 or are integers in the range of 1 to 250, k4 is 0 or 1, and k5 is an integer in the range of 1 to 5.

More preferably, R ¹ is H or C ₁ -C ₄ alkyl, R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ independently of each other are H or CH ₃ , k1 is an integer in the range of 22-450, k2 and k3 are independently 0 or are integers in the range of 1 to 100, k4 is 0, k5 is an integer in the range of 1 to 4.

The most preferred surface stabilizer of general formula ( I ) has the general formula ( Ia )

Where

R ¹ represents H or a C ₁ -C ₈ alkyl group, especially H or CH ₃ , and

k1 is an integer in the range from 22 to 450, in particular from 22 to 150.

Preferred surface stabilizers are derived from MPEG thiols (poly(ethylene glycol) methyl ether thiols) with an average molecular weight (M _n ) of 2000 to 6000, such as, for example, MPEG 2000 thiol, MPEG 3000 thiol, MPEG 4000 thiol, MPEG 5000 thiol, MPEG 6000 thiol, PEG (O-(2-mercaptoethyl)-poly(ethylene glycol)) thiols with an average M _n of 2000 to 6000, such as, for example, PEG 2000 thiol, PEG 3000 thiol, PEG 4000 thiol, PEG 5000 thiol, PEG 6000 thiol.

In another preferred embodiment of the present invention, the silver nanoplatelets contained in the UV-VIS radiation-curable paint comprise a surface stabilizer which is a polymer or copolymer as described in WO200674969A1, which can be obtained by a process comprising the steps of:

d1) polymerization in a first step of one or more monomers with ethylene double bonds in the presence of at least one nitroxide ether with a structural element ,

where X is a group with at least one carbon atom and is such that the free radical X• obtained from X is capable of initiating polymerization; or

d2) polymerization in a first step of one or more monomers with ethylene double bonds in the presence of at least one stable free nitroxyl radical and a free radical initiator; wherein at least one monomer used in steps d1 ) or d2 ) is a C1 _{- C6} alkyl or hydroxy _C1 - _C6 alkyl ester of acrylic or methacrylic acid; and optionally

e) a second step comprising modifying the polymer or copolymer obtained in d1 ) or d2 ) by an intermolecular transesterification reaction, amidation, hydrolysis or anhydride modification or a combination thereof.

The monomer in step d1) or d2) is preferably selected from 4-vinylpyridine or pyridinium ion, 2-vinylpyridine or pyridinium ion, 1-vinylimidazole or imidazolinium ion, or

compounds of the formula CH ₂ =C(R _a )-(C=Z)-R _b ,

Where

R _a represents hydrogen or methyl;

R _b is NH ₂ , O ^- (Me ⁺ ), unsubstituted C ₁ -C ₁₈ alkoxy, C ₂ -C ₁₀₀ alkoxy interrupted by at least one N and/or O atom, or hydroxy-substituted C ₁ -C ₁₈ alkoxy, unsubstituted C ₁ -C ₁₈ alkylamino, unsubstituted di(C ₁ -C ₁₈ alkyl)amino, hydroxy-substituted C ₁ -C ₁₈ alkylamino or hydroxy-substituted di(C ₁ -C ₁₈ alkyl)amino, -O(CH ₂ ) _y NR ¹⁵ R ¹⁶ or -O(CH ₂ ) _y N ⁺ HR ¹⁵ R ¹⁶ An ^- , -N(CH ₂ ) _y NR ¹⁵ R ¹⁶ or -N(CH ₂ ) _y N ⁺ HR ¹⁵ R ¹⁶ An ^- ,

Where

An ^- is an anion of a monovalent organic or inorganic acid;

y is an integer between 2 and 10;

R ¹⁵ is a saturated or unsaturated straight or branched chain alkyl of 1 to 22 carbon atoms;

R ¹⁶ is a saturated or unsaturated straight or branched chain alkyl of 1 to 22 carbon atoms;

Me ⁺ is a monovalent metal atom or ammonium ion; and

Z represents oxygen or sulfur.

The second step e) is preferably an intermolecular transesterification reaction. In step e) the alcohol is preferably an ethoxylate of formula ( A )

Where

R _A is a saturated or unsaturated straight or branched chain alkyl of 1 to 22 carbon atoms or an alkylaryl or dialkylaryl of up to 24 carbon atoms and n is 1-150.

Preferably, step d1) or d2) is carried out twice and a block copolymer is obtained, wherein in the first or second stage of radical polymerization the monomer or mixture of monomers contains 50-100% by weight, based on the total amount of monomers, of a C ₁ -C ₆ alkyl ester of acrylic or methacrylic acid, and in the second or first stage of radical polymerization, respectively, the monomer or mixture of monomers with ethylene double bonds contains at least a monomer without a primary or secondary ester bond.

In the first stage of polymerization, the monomer or mixture of monomers contains 50-100% by weight based on the total amount of monomers of C ₁ -C ₆ alkyl ester of acrylic or methacrylic acid (the first monomer), and in the second stage of polymerization, the monomer or mixture of monomers with ethylene double bonds contains 4-vinylpyridine or pyridinium ion, 2-vinylpyridine or pyridinium ion, vinylimidazole 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 (the second monomer).

The nitroxyl ether is preferably a compound of formula ( O1 )

The surface stabilizer is preferably a copolymer which can be obtained by a method comprising the steps of:

d1) polymerizing in a first step a first monomer which is a _C1 - _C6 alkyl or hydroxy _C1 - _C6 alkyl ester of acrylic or methacrylic acid and a second monomer which is selected from 4-vinylpyridine or pyridinium ion, 2-vinylpyridine or pyridinium ion, 1-vinylimidazole or imidazolinium ion, 3-dimethylaminoethyl acrylamide, 3-dimethylaminoethyl methacrylamide, 3-dimethylaminopropyl acrylamide and 3-dimethylaminopropyl methacrylamide; in the presence of at least one nitroxyl ester with the structural element ;

And

e) a second step comprising modifying the polymer or copolymer obtained in d1 ) by an intermolecular transesterification reaction, wherein the alcohol in step e) is an ethoxylate of the formula

R _A -[O-CH ₂ -CH ₂ -] _n1 -OH ( A ),

Where

R _A is a saturated or unsaturated straight or branched chain alkyl of 1 to 22 carbon atoms or an alkylaryl or dialkylaryl of up to 24 carbon atoms and n1 is 1-150.

Preferably, a surface stabilizer obtained by the method described in this document is a copolymer of the following formula (III)

Where

R ¹¹ and R ¹² represent H or methyl,

R ¹³ , R _a and R _a' independently of each other represent H or methyl,

R _b is a saturated or unsaturated straight or branched chain alkyl of 1 to 22 carbon atoms,

R _b' is R _A -[O-CH ₂ -CH ₂ -] _n1 -O-,

R ¹⁴ is

Where

An ^- is an anion of a monovalent organic or inorganic acid;

y is an integer between 2 and 10;

R ¹⁵ is a saturated or unsaturated straight or branched chain alkyl of 1 to 22 carbon atoms,

R ¹⁶ is a saturated or unsaturated straight or branched chain alkyl of 1 to 22 carbon atoms,

R _A is a saturated or unsaturated straight or branched chain alkyl of 1 to 22 carbon atoms or an alkylaryl or dialkylaryl of up to 24 carbon atoms and n1 is 1-150,

m , n and p are independently integers from 1 to 200, and

o is an integer between 1 and 150.

More preferably, the surface stabilizer is a copolymer represented by formula ( III )

Where

R ¹¹ and R ¹² represent H or methyl,

m , n and p are independently integers from 1 to 200, and

o is an integer from 1 to 150. The order of monomers with indices m and n can be fixed (block copolymers) or not fixed (random copolymers).

Examples of preferred copolymers for use as stabilizers are the copolymers described in Example A3 and Example A6 of WO200674969A1.

To improve the stability of the optical properties of the silver nanoplatelets during storage or thermal exposure, the UV-visible irradiation-curable paint may additionally contain a stabilizer such as a compound of the general formula ( IIa ), ( IIb ), or ( IIc ).

The stabilizer may be a compound of the formulaR ²⁰ –X(IIa), Where R ²⁰ is a linear or branched C₁-C₂₅alkyl group or C₂-C₂₅an alkenyl group which may be substituted by one or more groups selected from -OH, -SH, -NH₂or -COOR¹⁹, Where R ¹⁹ represents a hydrogen atom or C₁-C₂₅alkyl group, andXrepresents -OH, -SH, -NH₂or -COOR^19', Where R ^19' represents a hydrogen atom, C₁-C₂₅alkyl group or C₂-C₂₅an alkenyl group which may be substituted by one or more groups selected from -OH, -SH, -NH₂or -COOR^19'', Where R ^19'' represents a hydrogen atom or C₁-C₂₅alkyl group.

Examples of compounds of formula ( IIa ) are 1-methylamine, 1-dodecylamine, 1-hexadecylamine, citric acid, oleic acid, D-cysteine, 1-dodecanethiol, 9-mercapto-1-nonanol, 1-thioglycerol, 11-amino-1-undecanethiol, cysteamine, 3-mercaptopropanoic acid, 8-mercaptooctanoic acid and 1,2-ethanedithiol.

The stabilizer may be a compound of formula ( IIb )

Where

R ^21a represents a hydrogen atom, a halogen atom, a C ₁ -C ₈ alkoxy group or a C ₁ -C ₈ alkyl group;

R ^21b represents a hydrogen atom or a group of the formula -CHR ²⁴ -N(R ²² )(R ²³ ), and

R ²² and R ²³ independently of one another represent a C ₁ -C ₈ alkyl, a hydroxy-C ₁ -C ₈ alkyl group or a group of the formula -[(CH ₂ CH ₂ )-O] _n2 -CH ₂ CH ₂ -OH, where n2 is from 1 to 5, R ²⁴ represents H or C ₁ -C ₈ alkyl.

Examples of compounds of formula ( IIb ) include, but are not limited to,

The stabilizer may be a "polyhydric phenol", i.e. a compound comprising an optionally substituted benzene ring and at least 2 hydroxy groups attached thereto. The term "polyhydric phenol" includes polyphenols such as, for example, tannic acid and polycyclic aromatic hydrocarbons which consist of condensed benzene rings wherein at least one benzene ring has at least 2 hydroxy groups attached thereto, such as, for example, 1,2-dihydroxynaphthalene. The "polyhydric phenol" may be substituted. Suitable substituents are described below.

In a preferred embodiment, the polyhydric phenolic stabilizer contained in the UV-VIS radiation-curable paint described herein is a polyhydric phenol of general group ( IIc )

Where

R ²⁵ in each case is the same or different and represents a hydrogen atom, a halogen atom, a C ₁ -C ₁₈ alkyl group, a C ₁ -C ₁₈ alkoxy group or a -C(=O)-R ²⁶ group;

R ²⁶ represents a hydrogen atom, a hydroxy group, a C ₁ -C ₁₈ alkyl group, an unsubstituted or substituted amino group, an unsubstituted or substituted phenyl group, or a C ₁ -C ₁₈ alkoxy group;

n3 is an integer in the range 1 to 4;

m3 is an integer in the range 2 to 4, and

the sum of integers m3 and n3 is 6.

In a more preferred embodiment, the polyhydric phenolic stabilizer contained in the UV-VIS radiation-curable paint is a polyhydric phenol of the general group ( IIc' )

Where

R ^25a and R ^25b independently of one another represent a hydrogen atom, a C ₁ -C ₁₈ alkyl group, a C ₁ -C ₁₈ alkoxy group or a group of the formula -C(=O)-R ²⁶ ;

R ²⁶ represents a hydrogen atom, a hydroxy group, a C ₁ -C ₁₈ alkyl group, an unsubstituted or substituted amino group, an unsubstituted or substituted phenyl group, or a C ₁ -C ₁₈ alkoxy group; and

m3 is an integer in the range from 2 to 4, in particular from 2 to 3. Particularly preferred are polyhydric phenols of the general formula ( IIc' ) with two hydroxy groups in the ortho position.

In an even more preferred embodiment, the polyhydric phenolic stabilizer contained in the UV-VIS radiation-curable paint is a polyhydric phenol of the general group ( IIc'' ):

Where

R ²⁵ represents a hydrogen atom or a group of the formula -C(=O)-R²⁶, Where R ²⁶ represents a hydrogen atom, C₁-C₁₈alkyl group or C₁-C₁₈an alkoxy group, an unsubstituted or substituted amino group, especially C₁-C₁₈alkyl group or C₁-C₈alkoxy group.

Polyhydric phenol of general formula ( IIc''' )

Where

R ²⁶ represents a hydrogen atom, a C ₁ -C ₁₈ alkyl group or a C ₁ -C ₁₈ alkoxy group, especially a C ₁ -C ₈ alkoxy group, is particularly preferred as a stabilizer. Examples of polyhydric phenols of the general formula ( IIc''' ) include, but are not limited to,

And

Additional polyhydric phenolic stabilizers include compounds having one of the following formulas:

Where R ²⁵ represents a hydrogen atom, C₁-C₁₈an alkyl group or a group of formula -C(=O)-R²⁶, Where R ²⁶ represents a hydrogen atom, a hydroxy group, C₁-C₁₈alkyl group or C₁-C₁₈an alkoxy group, an unsubstituted or substituted amino group, an unsubstituted or substituted phenyl group, especially C₁-C₁₈alkyl group or C₁-C₈alkoxy group. Examples of such polyhydric phenols include:

In a particularly preferred embodiment, the stabilizer is selected from compounds of formula ( IIb ), ( IIc ) and mixtures thereof.

A preferred embodiment according to the present invention relates to a method for producing security features as described and claimed herein, wherein the silver nanoplatelets carry one or more surface stabilizers of general formula ( I ) and one or more surface stabilizers of general formula ( III ), and the UV-visible radiation-curable paint comprises one or more stabilizers of general formula ( IIb ).

The dispersion of silver nanoplatelets used to produce the UV-Vis irradiation-curable paint used in the manufacturing method according to the present invention can be evaluated by using the following method:

(A) obtaining a solution containing a silver precursor, a compound of the formula

Where

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 independently of one another represent H, C ₁ -C ₈ alkyl or phenyl;

Y represents O or NR ⁸ ;

R ⁸ is H or C ₁ -C ₈ alkyl;

k1 is an integer in the range from 1 to 500;

k2 and k3 are independently equal to 0 or are integers in the range from 1 to 250;

k4 is 0 or 1; and

k5 is an integer between 1 and 5,

a polymer or copolymer that can be obtained by a process comprising the steps of:

D1) polymerization in a first step of one or more monomers with ethylene double bonds in the presence of at least one nitroxide ether with a structural element ,

where X is a group with at least one carbon atom and is such that the free radical X• obtained from X is capable of initiating polymerization; or

D2) polymerization in a first step of one or more monomers with ethylene double bonds in the presence of at least one stable free nitroxyl radical and a free radical initiator; wherein at least one monomer used in steps D1 ) or D2 ) is a C1 _{- C6} alkyl or hydroxy _C1 - _C6 alkyl ester of acrylic or methacrylic acid; and optionally

E) a second step comprising modifying the polymer or copolymer obtained in D1 ) or D2 ) by an intermolecular transesterification reaction, amidation, hydrolysis or anhydride modification or a combination thereof,

water and optionally antifoam;

( B1 ) obtaining a solution containing a reducing agent that contains at least one boron atom in a molecule and water;

( B2 ) adding the solution obtained in step ( A ) to the solution obtained in step ( B1 ) and adding one or more complexing agents;

( C ) adding a solution of hydrogen peroxide in water; and

( D ) optionally adding a stabilizer to the mixture obtained in step ( C ).

The silver precursor is a silver(I) compound selected from the group consisting of: _AgNO3 ; AgClO4; _Ag2SO4 ; _AgCl ; AgF; AgOH; _Ag2O ; AgBF4; _AgIO3 ; _AgPF6 ; _R200CO2Ag , ^R200SO3Ag , where R200 is unsubstituted or substituted _C1 - ^C18 alkyl, unsubstituted or substituted _C5 - _{C8 cycloalkyl} , ^{unsubstituted} or _{substituted C7} - _C18 aralkyl, unsubstituted or substituted _C6 - _C18 aryl, or unsubstituted or substituted _{C2 - C18} heteroaryl _; salts of Ag dicarboxylic, tricarboxylic, polycarboxylic acids, polysulfonic acids, P-containing acids and mixtures thereof, preferably from the group consisting of silver nitrate, silver acetate, silver perchlorate, silver methanesulfonate, silver benzenesulfonate, silver toluenesulfonate, silver trifluoromethanesulfonate, silver sulfate, silver fluoride and mixtures thereof, and more preferably silver nitrate.

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, ammonium borane and mixtures thereof. Sodium borohydride is most preferred.

One or more complexing agents are selected from the group of chlorine-containing compounds that are capable of releasing chloride ions under 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.

Non-limiting examples of complexing agents include ammonia, methylamine, dimethylamine, ethylamine, ethylenediamine, diethylenetriamine, ethylenediaminetetraacetic acid (EDTA), ethylenediamine-N,N′-disuccinic acid (EDDS), methylglycinediacetic 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, for example, trisodium salt of methylglycinediacetic acid (Na ₃ MGDA) and tetrasodium salt of EDTA.

The antifoam is a compound or composition capable of suppressing the formation of foam in a reaction mixture, such as, for example, the 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, K 3, K 7, K 8, N, Antifoam SE-15 from Sigma, Struktol SB-2080 and the like. The amount of the defoamer is in the range of 0.00001% to 5% by weight based on the total weight of the reaction mixture before adding hydrogen peroxide, preferably 0.0001% to 3% and more preferably 0.001% to 2% by weight.

The defoamer may be added to the solution obtained in step ( A ) and/or to the solution obtained in step ( B ).

The reaction of formation of silver nanoplatelets is carried out by gradual addition of a solution of silver precursor to a solution of reducing agent, while the temperature of both solutions is in the range from -3°C to 40°C, and the gradual addition is completed within 15 minutes to 24 hours.

The silver nanoplatelets may further be subjected to further purification and/or isolation methods such as decantation, (ultra)filtration, (ultra)centrifugation, reversible or irreversible agglomeration, phase transfer with an organic solvent, and combinations thereof. The silver nanoplatelet dispersion may comprise up to about 99 wt. % silver nanoplatelets, preferably from 5 wt. % to 99 wt. % silver nanoplatelets, more preferably from 5 wt. % to 90 wt. % silver nanoplatelets, wherein the wt. % is calculated based on the total weight of the dispersion.

The silver nanoplatelets used in this document are described in International Patent Application Publication No. WO2020224982A1.

A preferred embodiment according to the present invention is directed to a method for producing security features as described and claimed herein, wherein the UV-visible radiation-curable paint comprises a concentration of silver nanoplatelets of from about 5 wt.% to about 20 wt.%, preferably from about 7.5 wt.% to about 17.5 wt.%, more preferably from about 10 wt.% to about 15 wt.%, such as about 12.5 wt.%, wherein the weight percentage is calculated based on the total weight of the UV-visible radiation-curable paint. The concentration of silver nanoplatelets in the UV-visible radiation-curable paint used in the method according to the present invention is substantially lower than the concentrations of silver platelets used in paints known from the prior art. Therefore, the manufacturing method claimed in this document makes it possible to obtain, in a cost-effective manner, dichroic security features with optical effects similar to those known from the prior art, but with significantly improved mechanical resistance properties.

According to one embodiment, the UV-visible radiation-curable paint used in the manufacturing method claimed and described herein is a cationically curable paint (i.e., a paint containing exclusively cationically curable monomers and no radically curable monomers) and comprises:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii-1 ) from about 40 wt.% to about 75 wt.% of a cycloaliphatic epoxide;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate; and optionally

vi ) up to 25% by weight of organic solvent;

wherein the weight percentage of ii-1 ) and vi) is calculated based on the total weight of the UV-visible curable paint.

In an alternative embodiment according to the present invention, a UV-visible radiation-curable paint comprises:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii-5 ) from about 40 wt.% to about 75 wt.% of a mixture of a cycloaliphatic epoxide and one or more UV-visible radiation-curable compounds other than the cycloaliphatic epoxide;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate; and optionally

vi ) up to 25% by weight of organic solvent;

wherein the weight percentage of ii-5 ) and vi ) is calculated based on the total weight of the UV-visible curable paint. The one or more UV-visible curable compounds other than a cycloaliphatic epoxide may comprise vii) one or more cationically curable monomers other than a cycloaliphatic epoxide and/or viii) one or more radical-curable monomers and/or oligomers. If the one or more UV-visible curable compounds other than a cycloaliphatic epoxide comprise viii) one or more radical-curable monomers and/or oligomers, the UV-visible curable paint further comprises ix) one or more free-radical photoinitiators. Preferably, if the one or more UV-visible curable compounds other than a cycloaliphatic epoxide comprise vii) one or more cationically curable monomers other than a cycloaliphatic epoxide, the ratio of the weight percentage (wt%) of the cycloaliphatic epoxide present in said paint to the weight percentage (wt%) of the one or more cationically curable monomers other than a cycloaliphatic epoxide present in said paint is greater than about 1.1:1. It is also preferred that the one or more UV-visible curable compounds other than a cycloaliphatic epoxide comprise viii) one or more radical-curable monomers and/or oligomers, the ratio of the weight percentage (wt%) of the one or more radical-curable monomers and/or oligomers present in said paint, and the sum of the weight percentages of cationically curable monomers, including cycloaliphatic epoxide, present in said paint is below about 1.6:1, preferably below about 1.53:1, wherein the weight percentage (wt.%) is calculated based on the total weight of said paint.

Thus, in a preferred embodiment according to the present invention, the UV-visible radiation-curable paint used in the manufacturing method claimed and described herein is a cationically curable paint comprising:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii-2 ) from about 40 wt.% to about 75 wt.% of a mixture of a cycloaliphatic epoxide and one or more cationically curable monomers other than a cycloaliphatic epoxide;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate; and optionally

vi ) up to 25% by weight of organic solvent;

wherein the weight percentage of ii-2 ) and vi) is based on the total weight of the UV-VIS radiation-curable paint. Preferably, the ratio of the weight percentage (wt.%) of the cycloaliphatic epoxide present in said paint to the weight percentage (wt.%) of the one or more cationically curable monomers other than the cycloaliphatic epoxide present in said paint is greater than about 1.1:1, wherein the weight percentage (wt.%) is based on the total weight of said paint. More preferably, the cycloaliphatic epoxide present in the cationically curable paint is present in an amount of from about 20 wt.% to about 70 wt. % based on the total weight of said paint, and one or more cationically curable monomers other than a cycloaliphatic epoxide present in the cationically curable paint are present in an amount of from about 5 wt. % to about 20 wt. % based on the total weight of the UV-visible radiation-curable paint, provided that the ratio of the weight percentage (wt. %) of the cycloaliphatic epoxide present in said paint to the weight percentage (wt. %) of the one or more cationically curable monomers other than a cycloaliphatic epoxide present in said paint exceeds about 1.1:1.

In a further preferred alternative embodiment according to the present invention, the UV-Vis irradiation-curable paint is a hybrid paint (i.e., a paint containing both cationically curable monomers and radically curable monomers) comprising:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii-3 ) from about 40 wt.% to about 75 wt.% of a mixture of a cycloaliphatic epoxide and one or more radical-curable monomers and/or oligomers;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate;

ix) one or more free radical photoinitiators; and optionally

vi ) up to 25% by weight of organic solvent;

and the mass percentage contentii-3) And vi)calculated based on the total weight of the UV-Vis-curable paint. Preferably, the ratio of the weight percentage (wt.%) of one or more radical-curable monomers and/or oligomers present in the hybrid paint to the weight percentage (wt.%) of the cycloaliphatic epoxide present in said hybrid paint is below about 1.6:1, more preferably below about 1.53:1, wherein the weight percentage (wt.%) is calculated based on the total weight of said paint. In a more preferred embodiment, the hybrid paint comprises from about 25 wt.% to about 65 wt.% of a cycloaliphatic epoxide and from about 10 wt.% to about 40 wt.% of one or more radical-curable monomers and/or oligomers, with the proviso that the ratio of the weight percentage (wt.%) of the one or more radical-curable monomers and/or oligomers present in the hybrid paint and the weight percentage (wt.%) of the cycloaliphatic epoxide present in said hybrid paint is below about 1.6:1, preferably below about 1.53:1, wherein the weight percentage (wt.%) is calculated based on the total weight of said curable paint.

In an alternative preferred embodiment, the UV-visible radiation-curable paint used in the manufacturing method claimed and described herein is a hybrid paint (i.e., a paint containing both cationically curable monomers and radically curable monomers) comprising:

i ) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy;

ii-4 ) from about 40 wt.% to about 75 wt.% of a mixture of a cycloaliphatic epoxide, one or more cationically curable monomers other than a cycloaliphatic epoxide, and one or more radically curable monomers and/or oligomers;

iii ) one or more cationic photoinitiators;

iv ) a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride;

v ) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate;

ix) one or more free radical photoinitiators; and optionally

vi ) up to 25% by weight of organic solvent; whereby the weight percentages of ii-4 ) and vi) are calculated on the basis of UV-visible curable paint. Preferably, the ratio of the weight percentage (wt.%) of one or more radical-curable monomers and/or oligomers present in the hybrid UV-visible radiation-curable paint to the sum of the weight percentage (wt.%) of cycloaliphatic epoxide present in said hybrid UV-visible radiation-curable paint and the weight percentage (wt.%) of one or more cationically curable monomers other than cycloaliphatic epoxide present in said hybrid UV-visible radiation-curable paint is below about 1.6:1, more preferably below about 1.53:1, and the ratio of the weight percentage (wt.%) of cycloaliphatic epoxide present in said hybrid UV-visible radiation-curable paint, and the weight percentage (wt.%) of one or more cationically curable monomers other than a cycloaliphatic epoxide present in said hybrid UV/VIS radiation-curable paint is greater than about 1.1:1; wherein the weight percentage (wt.%) is based on the total weight of said curable paint. In a more preferred embodiment, the hybrid paint comprises from about 10 wt. % to about 65 wt. % of a cycloaliphatic epoxide, from 5 wt. % to about 20 wt. % of one or more cationically curable monomers other than a cycloaliphatic epoxide, and from about 10 wt. % to about 40 wt. % of one or more radical-curable monomers and/or oligomers, provided that the ratio of the weight percentage (wt.%) of the one or more radical-curable monomers and/or oligomers present in said paint to the sum of the weight percentage (wt.%) of cycloaliphatic epoxide present in said paint and the weight percentage (wt.%) of one or more cationically curable monomers other than cycloaliphatic epoxide present in said paint is below about 1.6:1, more preferably below about 1.53:1, and the ratio of the weight percentage (wt.%) of cycloaliphatic epoxide present in said paint to the weight percentage (wt.%) of one or more cationically curable monomers other than cycloaliphatic epoxide present in said paint, exceeds approximately 1.1:1, where the weight percentage (wt.%) is calculated based on the total weight of the hybrid paint.

Tests E15 - E19 according to the present invention demonstrate that similar optical properties can be obtained using a hybrid UV-VIS radiation-curable paint as described herein (i.e., a paint containing both cationically curable monomers and radically curable monomers) and a cationically curable paint (i.e., a paint containing exclusively cationically curable monomers and no radically curable monomers).

Advantageously, the method claimed and described in this document, based on the use of a cationically curable paint under the influence of radiation in the UV and visible region, described in this document, or a hybrid curable paint under the influence of radiation in the UV and visible region, described in this document, provides security features with improved mechanical properties compared to similar security features known from the prior art, which are obtained from radical-curing paints under the influence of UV radiation or solvent-based paints, and in particular from radical-curing paints under the influence of UV radiation or solvent-based paints containing high concentrations of silver nanoplatelets.

The UV-visible radiation-curable paint described herein comprises a cycloaliphatic epoxide, which is also known to those skilled in the art to be a cationically curable monomer. The cycloaliphatic epoxide described herein may be difunctional or polyfunctional. Preferably, the cycloaliphatic epoxide described herein comprises at least one cyclohexane group and at least two epoxy groups. Preferably, the cycloaliphatic epoxide is a compound of the general formula ( IV ):

wherein -L- represents a single bond or a divalent group containing one or more atoms. The cycloaliphatic epoxide of the general formula ( IV ) is optionally substituted by one or more linear or branched alkyl radicals containing from one to ten carbon atoms (such as methyl, ethyl, n -propyl, iso -propyl, n -butyl, iso -butyl, sec -butyl, tert -butyl, hexyl, octyl and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl, n -propyl and iso -propyl).

In the general formula ( IV ), the divalent group -L- may be a straight or branched chain alkylene group containing one to eighteen carbon atoms. Examples of said straight or branched chain alkylene group include, but are not limited to, a methylene group, a methylmethylene group, a dimethylmethylene group, an ethylene group, a propylene group, and a trimethylene group.

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

In the general formula ( IV ), -L- may be a divalent group containing one or more oxygen-containing bonding groups, wherein said oxygen-containing bonding groups are selected from the group consisting of - C(═O) - , - OC(═O)O - , - C(═O)O -, and - O - . Preferably, the cycloaliphatic epoxide is a cycloaliphatic epoxide of the general formula ( IV ), wherein -L- is a divalent group containing one or more oxygen-containing bonding groups, wherein said oxygen-containing bonding groups are selected from the group consisting of - C(═O) - , - OC(═O)O -, - C(═O)O -, and - O -, and more preferably a cycloaliphatic epoxide of the general formula ( IV-a ), ( IV-b ) or ( IV-c ), as defined below:

Where

L ¹ in each case may be the same or different and is a linear or branched alkyl radical containing from one to ten carbon atoms (such as methyl, ethyl,n-drank,iso-drank,n-butyl,iso-butyl,sec-butyl,rubs-butyl, hexyl, octyl and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl,n-drank andiso- propyl);

L ² in each case may be the same or different and is a linear or branched alkyl radical containing from one to ten carbon atoms (such as methyl, ethyl,n-drank,iso-drank,n-butyl,iso-butyl,sec-butyl,rubs-butyl, hexyl, octyl and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl,n-drank andiso-propyl); and

l1 and l2 are, independently of each other, integers in the range from 0 to 9, preferably in the range from 0 to 3;

Where

L ¹ in each case may be the same or different and is a linear or branched alkyl radical containing from one to ten carbon atoms (such as methyl, ethyl,n-drank,iso-drank,n-butyl,iso-butyl,sec-butyl,rubs-butyl, hexyl, octyl and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl,n-drank andiso- propyl);

L ² in each case may be the same or different and is a linear or branched alkyl radical containing from one to ten carbon atoms (such as methyl, ethyl,n-drank,iso-drank,n-butyl,iso-butyl,sec-butyl,rubs-butyl, hexyl, octyl and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl,n-drank andiso-propyl); and

l1 and l2 are, independently of each other, integers in the range from 0 to 9, preferably in the range from 0 to 3;

-L ³ - represents a single bond or a linear or branched divalent hydrocarbon group containing from one to ten carbon atoms, and preferably containing from 3 to 8 carbon atoms, such as alkylene groups including trimethylene, tetramethylene, hexamethylene and 2-ethylhexylene, and cycloalkylene groups such as 1,2-cyclohexylene group, 1,3-cyclohexylene group and 1,4-cyclohexylene group and cyclohexylidene group;

Where

L ¹ in each case may be the same or different and is a linear or branched alkyl radical containing from one to three carbon atoms, such as methyl, ethyl,n-drank andiso- sawn;

L ² in each case may be the same or different and is a linear or branched alkyl radical containing from one to three carbon atoms, such as methyl, ethyl,n-drank andiso- propyl; and

l1 and l2 are independently of each other integers in the range from 0 to 9, preferably in the range from 0 to 3.

Preferred cycloaliphatic epoxides of general formula ( IV-a ) include, but are not limited to, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate and 3,4-epoxy-4-methylcyclohexylmethyl-3,4-epoxy-4-methylcyclohexanecarboxylate.

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

A preferred cycloaliphatic epoxide of general formula ( IV-c ) is 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanemetadioxane.

Further cycloaliphatic epoxides include a cycloaliphatic epoxide of general formula ( V) and a cycloaliphatic epoxide of general formula (VI ), which are optionally substituted with one or more linear or branched alkyl groups containing from one to ten carbon atoms (such as methyl, ethyl, n -propyl, iso -propyl, n -butyl, iso -butyl, sec -butyl, tert -butyl, hexyl, octyl and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl, n -propyl and iso -propyl).

The cycloaliphatic epoxides described herein may be hydroxy modified or (meth)acrylate modified. Examples are commercially available under the names Cyclomer A400 (CAS: 64630-63-3) and Cyclomer M100 (CAS number: 82428-30-6) from Daicel Corp., or TTA 15 and TTA16 from TetraChem/Jiangsu.

The UV-visible radiation-curable paint described herein comprises one or more cationic photoinitiators. Preferably, the concentration of the one or more cationic photoinitiators in the cationic UV-visible radiation-curable paint described herein (i.e., the paint comprising exclusively cationic-curable monomers and not containing radical-curable monomers) is from about 1 wt. % to about 10 wt. %, preferably from about 1.1 wt. % to about 8 wt. %, more preferably from about 1.1 wt. % to about 6 wt. %, wherein the weight percentage is based on the total weight of the cationic UV-visible radiation-curable paint. Preferably, the concentration of one or more cationic photoinitiators in the hybrid UV-Vis-curable paint described herein (i.e., the paint containing both cationically curable monomers and radically curable monomers) is from 1 wt.% to about 6 wt.%, wherein the weight percentage is based on the total weight of the cationically curable UV-Vis-curable paint.

One or more cationic photoinitiators (also referred to in the art as photoacid generators) used in the UV-visible radiation-curable paint described herein 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, and even more preferably selected from the group consisting of sulfonium salts, iodonium salts and mixtures thereof.

One or more iodonium salts described herein have a cationic moiety and an anionic moiety, wherein the anionic moiety is preferably _BF4− ^, B( _C6F5 ) ₄₋ ^, _PF6− ^, _AsF6− , ^SbF6− or ^{CF3SO3− ,} more preferably _SbF6− ^, and wherein the cationic moiety is preferably an aromatic iodonium ion, more preferably _an iodonium ion containing two aryl groups _, wherein the two aryl groups may be independently substituted _with one or more alkyl groups (such as, for example, methyl, ethyl, isobutyl, tert- _butyl , 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. Particularly suitable iodonium salts for the present invention are commercially available 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.

One or more sulfonium salts described herein have a cationic moiety and an anionic moiety, wherein the anionic moiety is preferably BF ₄ ⁻ , B(C ₆ F ₅ ) ₄ ⁻ , PF ₆ ⁻ , (PF _6-h (C _j F _2j-1 ) _h ) ⁻ (wherein h is an integer from 1 to 5 and j is an integer from 1 to 4), AsF ₆ ⁻ , SbF ₆ ⁻ , CF ₃ SO ₃ ⁻ , a perfluoroalkyl sulfonate or pentafluorohydroxyantimonate, more preferably SbF ₆ ⁻ and 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 (such as, for example, methyl, ethyl, isobutyl, tert-butyl, etc.), one or more alkoxy groups, one or more aryloxy groups, one or more halogen-containing groups, one or more hydroxy groups, or a combination thereof. Suitable examples of sulfonium ions containing two or more aryl groups include, but are not limited to, triarylsulfonium ions, diphenyl[4-(phenylthio)phenyl]sulfonium ion, bis[4-(diphenylsulfonio)phenyl]sulfonium ion, triphenylsulfonium ions, and tris[4-(4-acetylphenyl)sulfanylphenyl]sulfonium ion. Suitable examples of sulfonium salts 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.

One or more oxonium salts described herein have a cationic moiety and an anionic moiety, wherein the anionic moiety is preferably _BF4− ^, B( _C6F5 ⁾ ₄₋ ^, _PF6− ^, _AsF6− , ^SbF6− _{or CF3SO3−} , more preferably _BF4− ^{and wherein} the cationic moiety is preferably _an aromatic oxonium ion, more preferably a pyrylium ion, preferably substituted with one or more aryl groups, wherein each of the one or more aryl groups may be independently substituted _with one or more alkyl groups (such as, for example, methyl, ethyl, isobutyl, tert-butyl, etc.), one or more alkoxy groups, one or more nitro groups, one or more halogen-containing groups, one or more hydroxy groups, or their combination. A particularly suitable oxonium salt for the present invention is 2,4,6-triphenylpyrylium tetrafluoroborate.

Other examples of photoinitiators used 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, J. V. Crivello & K. Dietliker, edited by G. Bradley and published in 1998 by John Wiley & Sons in association with SITA Technology Limited.

The one or more cationically curable monomers other than a cycloaliphatic epoxide described herein are selected from the group consisting of vinyl ethers, propenyl ethers, cyclic ethers such as epoxides, oxetanes and tetrahydrofurans, lactones, cyclic thioethers, vinyl thioethers, propenyl thioethers, hydroxyl-containing compounds and mixtures thereof, preferably selected from the group consisting of vinyl ethers and cyclic ethers such as epoxides, oxetanes and tetrahydrofurans, more preferably selected from the group consisting of vinyl ethers. Preferably, the ratio of the weight percentage (wt.%) of the cycloaliphatic epoxide present in the paint described herein to the weight percentage (wt.%) of one or more cationically curable monomers other than the cycloaliphatic epoxide present in said paint is greater than about 1.1:1, wherein the weight percentage (wt.%) is calculated based on the total weight of said paint.

It is known from the prior art that vinyl ethers accelerate curing and reduce tack, thereby limiting the risk of blocking and re-embossing when printed sheets are stacked immediately after printing and curing. They also improve the physical and chemical resistance of the printed security element and increase the flexibility of the printed and cured ink layer and its adhesion to the substrate, which is especially advantageous for printing on plastic and polymer substrates. Vinyl ethers also help to reduce the viscosity of the ink when strongly copolymerized with the ink binder.

Examples of preferred vinyl ethers include methyl vinyl ether, ethyl vinyl ether, n -propyl vinyl ether, n -butyl vinyl ether, iso -butyl 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, cyclohexanedimethanol divinyl ether, 4-(vinyloxymethyl)cyclohexyl methyl benzoate, phenyl vinyl ether, methyl phenyl vinyl ether, methoxyphenyl vinyl ether, 2-chloroethyl vinyl ether, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, 1,6-hexanediol monovinyl ether, ethylene glycol divinyl ether, ethylene glycol monovinyl ether, 1,4-butanediol divinyl ether, 1,6-hexanediol divinyl ether, 4-(vinyloxy)butyl benzoate, bis[4-(vinyloxy)butyl]adipate, bis[4-(vinyloxy)butyl]succinate, bis[4-(vinyloxymethyl)cyclohexylmethyl]glutarate, 4-(vinyloxy)bu til stearate, trimethylol propane trivinyl ether, propylene carbonate propenyl ether, diethylene glycol monovinyl ether, diethylene glycol divinyl ether, ethylene glycol butyl vinyl ether, dipropylene glycol divinyl ether, triethylene glycol divinyl ether, triethylene glycol methyl vinyl ether, triethylene glycol monobutyl vinyl ether, tetraethylene glycol divinyl ether, silt ether, Poly(tetrahydrofuran) divinyl ether, polyethyleneglycol methyl vinyl ether-520, divinyl ether pluriol-E200, tris[4-(vinyloxy)butyl] trimellitate, 1,4-bis(2-vinyloxyethoxy)benzene, 2,2-bis(4-vinyloxyethoxyphenyl)propane, bis[4-(vinyloxy)methyl]cyclohexyl]methyl] terephthalate, bis[4-(vinyloxy)methyl]cyclohexyl]methyl]isophthalate. Suitable vinyl ethers are marketed by BASF under the trade names EVE, IBVE, DDVE, ODVE, BDDVE, DVE-2, DVE-3, CHVE, CHDM-di, HBVE. One or more of the vinyl ethers described herein may be hydroxy modified or (meth)acrylate modified (e.g., VEEA, 2-(2-vinyloxyethoxy)ethyl acrylate from Nippon Shokubai (CAS: 86273-46-3)).

It is known from the prior art that oxetane compounds accelerate curing and reduce tack, thereby limiting the risk of blocking and overstamping when printed sheets are stacked immediately after printing and curing. They also help reduce the viscosity of the ink when strongly copolymerized with the ink binder.

Preferred examples of oxetanes include trimethylene oxide, 3,3-dimethyloxetane, trimethylolpropanoxetane, 3-ethyl-3-hydroxymethyloxetane, 3-ethyl-3-[(2-ethylhexyloxy)methyl]oxetane, 3,3-dicyclomethyloxetane, 3-ethyl-3-phenoxymethyloxetane, bis([1-ethyl(3-oxetanyl)]methyl)ether, 1,4-bis[3-ethyl-3-oxetanylmethoxy)methyl]benzene, 3,3-dimethyl-2( p -methoxyphenyl)oxetane, 3-ethyl-[(triethoxysilylpropoxy)methyl]oxetane, 4,4-bis(3-ethyl-3-oxetanyl)methoxymethyl]biphenyl and 3,3-dimethyl-2( p -methoxyphenyl)oxetane. One or more of the oxetanes described herein may be modified with a hydroxy or (meth)acrylate (e.g., UVi-Cure S170 from Lambson (CAS: 37674-57-0)).

Preferred examples of epoxy compounds include butanediol diglycidyl ether, butyl glycidyl ether, hexadecyl glycidyl ether, 2-ethylhexyl glycidyl ether, octyl glycidyl ether, decyl glycidyl ether, dodecyl glycidyl ether, tetradecyl glycidyl ether and mixtures thereof.

One or more radical-curing 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. The term "(meth)acrylate" in the context of the present invention refers to an acrylate as well as the corresponding methacrylate.

Preferred examples of the 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, 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.

Preferred examples of di(meth)acrylates include bisphenol-A-based di(meth)acrylates, alkoxylated (such as, for example, ethoxylated and propoxylated) bisphenol-A-based di(meth)acrylate, bisphenol-A-based 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.

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

Preferred examples of tetra(meth)acrylates include ditrimethylolpropane tetra(meth)acrylates, pentaerythritol tetra(meth)acrylates, alkoxylated (such as, for example, ethoxylated and propoxylated) pentaerythritol tetra(meth)acrylates and mixtures thereof, preferably selected from the group consisting of ditrimethylolpropane tetra(meth)acrylates, alkoxylated pentaerythritol tetra(meth)acrylates and mixtures thereof.

The radical-curing (meth)acrylate oligomers described herein are preferably selected from the group consisting of epoxy(meth)acrylates, (meth)acrylate-modified oils, (meth)acrylate-modified epoxidized oils, polyester(meth)acrylates, aliphatic or aromatic polyurethane(meth)acrylates, polyacrylic acid (meth)acrylates, polyacrylate ester (meth)acrylates and mixtures thereof, more preferably selected from the group consisting of epoxy(meth)acrylates, polyester(meth)acrylates, aliphatic or aromatic polyurethane(meth)acrylates and mixtures thereof.

The radical-curable oligomers described herein are preferably (meth)acrylate oligomers, which may be branched or substantially linear, and the (meth)acrylate functional group(s) may, respectively, be terminal groups and/or pendant groups linked to the oligomer chain. Preferably, the radical-curing oligomers are selected from the group consisting of (meth)acrylic oligomers, urethane (meth)acrylate oligomers, polyester (meth)acrylate oligomers, polyester-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.

Suitable examples of epoxy(meth)acrylate oligomers include, but are not limited to, aliphatic epoxy(meth)acrylate oligomers, particularly mono(meth)acrylates, di(meth)acrylates and tri(meth)acrylates, and aromatic epoxy(meth)acrylate oligomers. Suitable examples of aromatic epoxy(meth)acrylate oligomers include bisphenol-A-based (meth)acrylate oligomers such as bisphenol-A-based mono(meth)acrylates, bisphenol-A-based di(meth)acrylates and bisphenol-A-based tri(meth)acrylates, as well as alkoxylated (such as, for example, ethoxylated and propoxylated) bisphenol-A-based (meth)acrylate oligomers such as, for example, alkoxylated bisphenol-A-based mono(meth)acrylates, alkoxylated bisphenol-A-based di(meth)acrylates and alkoxylated bisphenol-A-based tri(meth)acrylates, preferably alkoxylated bisphenol-A-based di(meth)acrylates.

The one or more free radical photoinitiators are preferably selected from the group consisting of hydroxy ketones (e.g., alpha-hydroxy ketones), alkoxy ketones (e.g., alpha-alkoxy ketones), acetophenones, benzophenones, ketosulfones, benzyl ketals, benzoin ethers, phosphine oxides, phenyl glyoxylates, thioxanthones and mixtures thereof, more preferably selected from the group consisting of phosphine oxides, hydroxy ketones, thioxanthones and mixtures thereof. Preferably, the concentration of the one or more free radical photoinitiators in the hybrid UV/visible irradiation-curable paint described herein is from about 1 wt. % to about 6 wt. %, the percentage being based on the total weight of the hybrid UV/visible irradiation-curable paint.

Suitable examples of alpha-hydroxy ketones include, but are not limited to, (1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one), 1-hydroxycyclohexylphenyl 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].

Suitable examples of acetophenones include, but are not limited to, 2,2-diethoxyacetophenone and 2-methoxy-2-phenylacetophenone.

Suitable examples of benzophenones include, but are not limited to, benzophenone, polymeric derivatives of benzophenone, 2-methylbenzophenone, 3-methylbenzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, 4-phenylbenzophenone, 4-chlorobenzophenone, methyl 2-benzoyl benzoate, 4-(4-methylphenylthio)benzophenone, 4-hydroxybenzophenone laurate, and a mixture of 50% benzophenone and 50% 1-hydroxycyclohexylphenyl ketone.

Suitable ketosulfones include, but are not limited to, 1-[4-(4-benzoylphenylsulfanyl)phenyl]-2-methyl-2-(4-methylphenylsulfonyl)propan-1-one.

Suitable benzyl ketals include, but are not limited to, 2,2-dimethoxy-2-phenylacetophenone.

Suitable examples of benzoin ethers include, but are not limited to, 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.

Suitable examples of phosphine oxides include, but are not limited to, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, acyl substituted phosphine oxides, a mixture of diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide and 2-hydroxy-2-methylpropiophenone, a mixture of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and 2-hydroxy-2-methylpropiophenone, 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 ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate.

Suitable examples of thioxanthones include, but are not limited to, 2-methylthioxanthone, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 1-chloro-4-propoxythioxanthone, and polymeric derivatives of thioxanthone.

Suitable examples of phenylglyoxylates include, but are not limited to, methyl benzoyl formate, 2-[2-oxo-2-phenylacetoxyethoxy]ethyl 2-oxo-2-phenylacetate, and a mixture of 2-[2-oxo-2-phenylacetoxyethoxy]ethyl 2-oxo-2-phenylacetate and hydroxyphenylacetic acid 2-[2-hydroxyethoxy]ethyl ester.

Preferably, one or more free radical photoinitiators are phosphine oxides as described herein, and more preferably a mixture of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate.

The UV-visible radiation-curable paint described herein, in particular the cationic UV-visible radiation-curable paint described herein and the hybrid UV-visible radiation-curable paint described herein, comprisesiv) a polyvinyl chloride copolymer containing at least about 69 wt. % vinyl chloride. As shown, for example, by testsE17 - E20, E24 - E27according to the present invention and comparative testingC8, the UV/VIS curable paint shall comprise a polyvinyl chloride copolymer containing at least about 69% by weight of vinyl chloride, the weight percentage being calculated based on the total weight of the UV/VIS curable paint to obtain by the method of manufacturing, as claimed in this document, security features that exhibit a metallic yellow colour when viewed in incident light and a blue colour when viewed in transmitted light. UV-visible curable paints that do not contain a polyvinyl chloride copolymer (e.g. paintI25), provide security features with inconspicuous colors such as brown or dark brown, and also with a low C* chroma value when viewed in incident color and are therefore not suitable for use in the manufacturing method according to the present invention claimed herein. It is within the general knowledge of a person skilled in the art of paint formulation, taking into account the weight percentage of the remaining components of the paint, in particular the radical-curable oligomer, if present, and the printing process by which the inks for the formulation are printed, to select an adequate weight percentage of a polyvinyl chloride copolymer containing at least about 69 weight % vinyl chloride. The concentration of the polyvinyl chloride copolymer in the UV-visible radiation-curable paint is preferably below about 15 weight %, more preferably from about 2.9 weight % to about 12 weight %, even more preferably from about 4.9 weight % to about 11.6 weight %. %, and most preferably from about 6 wt. % to about 8.6 wt. %, wherein the weight percentage is calculated based on the total weight of the UV-visible curable paint.

The polyvinyl chloride copolymer should contain at least about 69 wt.%, preferably at least about 75 wt.% vinyl chloride. Test comparisonC7, carried out for comparative purposes, with testsE21 - E23according to the present invention, it is proved that the polyvinyl chloride copolymer should contain at least about 69 wt. %, preferably at least about 75 wt. % vinyl chloride, in order to obtain by the method of manufacturing, as stated in this document, security features that exhibit a metallic yellow colour when viewed in incident light.

In a preferred embodiment, the polyvinyl chloride copolymer is selected from the group consisting of a copolymer of vinyl chloride and vinyl acetate and a copolymer of vinyl chloride and a hydroxyacrylate, such as a copolymer of vinyl chloride, hydroxyalkyl acrylate and Z-alkylenedioic acid, a dialkyl ether copolymer, including a copolymer of vinyl chloride, 2-hydroxypropyl acrylate, 2-butenedioic acid ( Z )-, a dibutyl ether copolymer. The average molecular weight of the polyvinyl chloride copolymer is preferably from 3*10 ⁴ g/mol to about 8*10 ⁴ g/mol, as determined by size exclusion chromatography using polystyrene as a standard and tetrahydrofuran as a solvent. Particularly suitable examples of the polyvinyl chloride copolymer for the present invention are commercially available under the names Vinnol® H14/36, Vinnol® E15/40A and Vinnol® E22/48A from Wacker.

It has been surprisingly found that the use of a perfluoropolyether functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate as a surfactant in the UV-Vis irradiation-curable paint described herein is important for obtaining security features exhibiting a metallic yellow color when viewed in incident light. As confirmed, for example, by tests E7 and E8 according to the present invention and tests C2 - C5 carried out for comparative purposes, only UV-Vis irradiation-curable paints containing a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate provide security features exhibiting a metallic yellow color when viewed in incident light. The security features obtained as described in Tests C2 to C5 by using a UV-Visible radiation-curable paint comprising either a perfluoropolyether surfactant that does not contain a functional group selected from the group consisting of hydroxyl, acrylate and methacrylate (e.g. Paints I4 and I5 comprising a perfluoropolyether anionic surfactant and a perfluoropolyether nonionic surfactant, respectively) or a fluorosurfactant that does not contain a perfluoropolyether backbone in addition to a functional group selected from the group consisting of hydroxyl, acrylate and methacrylate (e.g. Paints I6 and I7 comprising a fluoroalkyl nonionic surfactant) exhibit a brown to dark brown colour in reflection that does not attract the attention of the layperson and is therefore not suitable for a dichroic security feature. a feature to protect a valuable document.

A perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate comprises a perfluoropolyether backbone and one or more, preferably two or more, terminal functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate and is characterized by an average molecular weight (Mn) below about 2000 [g/mol]. In the context of the present document, a perfluoropolyether backbone means the residue of a perfluoropolyether polymer containing 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), 1,1-difluoroethylene penta(oxyethylene), and a linear or branched hydrocarbon group, optionally fluorinated at the carbon atom connecting the spacer to the perfluoropolyether residue, containing one or more urethane groups, and optionally one or more cyclic groups, including saturated cyclic moieties (such as cyclohexylene) and aromatic cyclic moieties (such as phenylene). In a preferred embodiment, the perfluoropolyether surfactant is functionalized with one or more hydroxyl functional groups.

In another preferred embodiment, the perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate is a compound of general formula ( VII ) having an average molecular weight of from about 1200 [g/mol] to about 2000 [g/mol]

Where

f and e are independently integers chosen from 1, 2, and 3;

FG ¹ and FG ² independently of each other represent terminal functional groups selected from the group consisting of: -OH, -OC(O)CH=CH ₂ and -OC(O)C(CH ₃ )=CH ₂ ;

-S ¹ - represents a single bond or a spacer selected from:

Where

- J ¹ - selected from

Where

j ¹ is an integer in the range from 1 to 12, preferably from 4 to 10;

L ⁵ in each case may be the same or different and is a linear or branched alkyl radical containing from one to ten carbon atoms (such as methyl, ethyl,n-drank,iso-drank,n-butyl,iso-butyl,sec-butyl,rubs-butyl, hexyl, octyl and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl,n-drank andiso- propyl);

L ⁶ in each case may be the same or different and is a linear or branched alkyl radical containing from one to ten carbon atoms (such as methyl, ethyl,n-drank,iso-drank,n-butyl,iso-butyl,sec-butyl,rubs-butyl, hexyl, octyl and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl,n-drank andiso- propyl);

l ⁵ and l ⁶ are, independently of each other, integers in the range from 0 to 4, preferably in the range from 0 to 1; and

- J ³ - is selected from -O-, -CH ₂ -, -CH(CH ₃ )- and -C(CH ₃ ) ₂ -;

- J ² - selected from

a is an integer in the range from 1 to 6, preferably from 1 to 3; and

b is an integer from 1 to 6, preferably from 2 to 4;

-S ² - represents a single bond or a spacer selected from

Where

- J ⁴ - selected from

Where

j ⁴ is an integer in the range from 1 to 12, preferably from 4 to 10;

L ⁷ in each case may be the same or different and is a linear or branched alkyl radical containing from one to ten carbon atoms (such as methyl, ethyl, n -propyl, iso -propyl, n -butyl, iso -butyl, sec -butyl, tert -butyl, hexyl, octyl and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl, n -propyl and iso -propyl);

L ⁸ in each case may be the same or different and is a linear or branched alkyl radical containing from one to ten carbon atoms (such as methyl, ethyl, n -propyl, iso -propyl, n -butyl, iso -butyl, sec -butyl, tert -butyl, hexyl, octyl and decyl), and preferably containing from one to three carbon atoms (such as methyl, ethyl, n -propyl and iso -propyl);

l ⁷ and l ⁸ are, independently of each other, integers in the range from 0 to 4, preferably in the range from 0 to 1; and

- J ⁶ - is selected from -O-, -CH ₂ -, -CH(CH ₃ )- and -C(CH ₃ ) ₂ -;

- J ⁵ - selected from

where r is an integer in the range from 1 to 6, preferably from 1 to 3; and

w is an integer from 1 to 6, preferably from 2 to 4;

and where s and t are integers selected such that the average molecular weight of the compound of general formula ( VII ) is from about 1200 [g/mol] to about 2000 [g/mol].

Preferably, in the general formula ( VII ), FG ¹ and FG ² independently of each other represent -OC(O)CH=CH ₂ or -OC(O)C(CH ₃ )=CH ₂ ;

-S ¹ - represents , Where bhas the meaning ascribed to it in this document; and

-S ² - represents Where whas the meaning ascribed to it in this document.

Also preferably, in the general formula ( VII ), FG ¹ and FG ² represent -OH;

-S ¹ - represents a single bond or Where ahas the meaning given to it in this document;

-S ² - represents a single bond or Where rhas the meaning given to it in this document; and the amounto And rranges from 3 to 9.

Particularly suitable examples of the perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate for the present invention are commercially available under the names Fluorolink E10H, Fluorolink MD700, Fluorolink AD1700 and Fluorolink E-series from Solvay.

The concentration of the perfluoropolyether surfactant described herein in the UV-visible radiant-curable paint is preferably from about 0.05 wt. % to about 5 wt. %, preferably from about 0.075 wt. % to about 5 wt. %, more preferably from about 0.1 wt. % to about 2.5 wt. %, the weight percentage being based on the total weight of the UV-visible radiant-curable paint. As shown, for example, by Tests E9 through E14 according to the present invention, a concentration of a perfluoropolyether surfactant of from about 0.05 wt. % to about 2.5 wt. %, preferably from about 0.075 wt. % to about 2.5 wt. %, and more preferably from about 0.1 wt. % to about 2.5 wt. %, allows to obtain security features that exhibit a metallic yellow color when reflected with a high color value C*.

The UV/VIS radiation-curable paints described herein may contain up to 25% by weight of an organic solvent, the weight percentage being based on the total weight of the UV/VIS radiation-curable paint. The organic solvent has a boiling point greater than 100°C. Suitable organic solvents for use in the UV/VIS radiation-curable paints described herein include, but are not limited to, ethyl 3-ethoxypropionate, 2-methoxy-1-methylethyl acetate, propylene glycol monomethyl ether, triethylene glycol divinyl ether, cyclopentanone, cyclohexanone, n- butanol, cyclohexanol, ethylene carbonate, propylene carbonate, butylene carbonate, and mixtures thereof.

In a preferred embodiment according to the present invention, the UV-visible radiation-curable ink used in the manufacturing method according to the present invention, claimed and described herein, is solvent-free. The use of solvent-free ink in the industrial printing of valuable documents is of great interest, since it prevents the release of volatile organic components, which, as a rule, have a negative impact on the environment and are harmful to human health.

The cationic UV-visible curable paint described herein and the hybrid UV-visible curable paint described herein may further comprise one or more photosensitizers in combination with one or more photoinitiators described herein to achieve effective 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 are capable of efficient and rapid curing with UV LED light sources, such as thioxanthone derivatives, anthracene derivatives and naphthalene derivatives (such as 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 (such as Irgacure 784, sold by BASF). Particularly preferred are thioxanthone derivatives, including, but not limited to, isopropylthioxanthone (ITX), 1-chloro-2-propoxythioxanthone (CPTX), 2-chlorothioxanthone (CTX) and 2,4-diethylthioxanthone (DETX) and mixtures thereof. Alternatively, thioxanthone photosensitizers in oligomeric or polymeric form (e.g., Omnipol TX, sold by IGM Resins, Genopol* TX-2, sold by Rahn, or Speedcure 7010, sold by Lambson) can be used. When present, 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 percentage being based on the total weight of the UV-VIS-curable paint.

The UV-visible radiation-curable paint described herein may further comprise one or more antifoaming agents in an amount of less than about 2 wt.%, preferably less than about 1 wt.%.

In order to impart resistance to contamination to the valuable document and/or to protect the security feature from the physical and chemical influence of the environment, the manufacturing method claimed in this document preferably additionally includes steps f) and g) , performed after step c) :

f ) applying to the substrate, preferably by means of a printing process, a curable protective varnish to form a varnish layer;

g ) curing the varnish layer obtained in step f) to form a protective coating.

Examples of suitable curable protective varnishes for use in step f) and/or methods for applying said curable protective varnishes to a substrate and curing the varnish layer are described in International Patent Application Publication No. WO2020234211A1, International Patent Application Publication No. WO2013127715A2 and International Patent Application Publication No. WO2014067715A1.

Preferably, the valuable document is selected from banknotes, legal documents, tickets, checks, vouchers, revenue stamps, agreements, identity documents such as passports, identity cards, visas, driving licenses, bank cards, credit cards, transaction cards, access documents or cards, entrance tickets, public transport tickets, higher education certificates and academic degrees. More preferably, the valuable document is a banknote. The method for obtaining the security features claimed in this document can also be used to obtain a security feature directly on a valuable commercial product. The term "valuable commercial product" refers to packaging material, in particular for the pharmaceutical, cosmetic, electronic or food industries, which can be protected against counterfeiting and/or illegal reproduction, to guarantee the authenticity of the contents of the package, such as genuine medicines.

Examples

The present invention will now be described in more detail with reference to non-limiting examples. The following tests E1 to E40 and comparative tests C1 to C8 illustrate in more detail the production of security features according to the method using UV-visible radiation-curable screen printing security inks described herein.

A. Analytical methods

A-1. UV-Visible Spectroscopy

The UV and visible spectra of the dispersions were recorded on a Varian Cary 50 UV-Visible spectrophotometer at a dispersion concentration such that an optical density of 0.3 to 1.5 was achieved per 1 cm of optical path.

A-2. TEM Analysis

TEM analysis of dispersions and coatings was performed on a ZEISS EM 910 in bright field mode at an electron beam acceleration voltage of 100 kV. At least 2 representative images were recorded at different magnifications to characterize the dominant particle morphology for each sample.

Particle diameter was determined from TEM images as the maximum dimension of nanoplatelets oriented parallel to the image plane using Fiji image analysis software based on the measurement of at least 300 randomly selected particles.

Particle thickness was measured manually as the maximum dimension of nanoplatelets oriented perpendicular to the image plane from the TEM image based on the measurement of at least 50 randomly selected particles.

B. Preparation and characterization of Ag nanoplatelets

Silver nanoplatelets were prepared according to the procedure described in International Patent Application Publication No. WO2020224982A1, which is described in detail below.

B-1. Synthesis of raw materials

In a 1-liter 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 were added and the mixture was cooled to -1°C while stirring at 250 revolutions per minute (rpm, solution A).

In a 0.5 L double wall glass reactor equipped with an anchor stirrer, 132 g of deionized water and 4.8 g of MPEG-5000 thiol were mixed and the mixture was stirred for 10 minutes at room temperature. 72 g of the product from Example A3 of WO 2006074969 were added and the resulting mixture was stirred for another 10 minutes at room temperature to homogenize. 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, resulting in a viscous orange-brown solution. To this solution, 96 g of deionized water was added, followed by the addition of 3 g of Struktol SB2080 defoamer, pre-dispersed in 36 g of deionized water. The resulting mixture was cooled to 0°C while stirring at 250 rpm (solution B).

After this, solution B was dosed using a peristaltic pump at a constant rate over 2 h into solution A below the surface of the liquid. through a cooled (0°C) dosing tube, resulting in a dispersion of spherical silver nanoparticles. During pumping, solution A was stirred at 250 rpm.

After completion of dosing, the reaction mixture was heated to +5°C for 15 minutes and a solution of 862 mg KCl in 10 g deionized water was added in one portion, followed by the addition of 4 equal portions of 9.6 g ethylenediaminetetraacetic acid (EDTA) with a time interval of 10 minutes.

After adding the last portion of EDTA, the reaction mixture was stirred for 15 minutes at +5°C, then heated to 35°C for 30 minutes and stirred for 1 hour at this temperature. By this time, the evolution of hydrogen had ceased.

3.0 mL of 30% w/w ammonia in water was added followed by 5.76 g of solid NaOH and the mixture was stirred for 15 min at 35 °C. Then, 180 mL of 50% w/w hydrogen peroxide in water was dosed into the reaction mixture under the liquid surface using a peristaltic pump at a constant speed while stirring at 250 rpm for 4 h, maintaining the temperature at 35 °C. This resulted in a dark blue silver nanoplatelet dispersion, which was cooled to room temperature. 1.23 g of a compound of the formula was added

(a mixture of CAS 80584-88-9 and 80584-89-0) and the mixture was stirred for 1 h at room temperature.

B-2. Isolation and purification of Ag nanoplatelets

B-2a. First decantation

9.6 g of sodium dodecyl sulfate were added to the reaction mixture, and then approximately 25 g of anhydrous sodium sulfate powder was added in portions with stirring until the dispersion transmission color changed from blue to pink. The mixture was then kept without stirring at room temperature for 24 h, allowing the coagulated nanoplatelets to settle to the bottom of the reactor.

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

B-2b. Second decantation

Approximately 64 g of anhydrous sodium sulfate powder was added in portions with stirring until the dispersion transmission color changed from blue to yellowish-pink. The mixture was then kept without stirring at room temperature for 12 h, allowing the coagulated nanoplatelets to settle to the bottom of the reactor. 990 g of the supernatant was pumped out of the reactor using a peristaltic pump and 90 g of deionized water was added to the reactor. The resulting mixture was stirred for 30 min at room temperature, allowing the coagulated particles to redisperse.

B-2c. Ultrafiltration in water

The resulting Ag nanoplatelet dispersion was ultrafiltered using a Millipore Amicon 8400 ultrafiltration cell with a stirrer. The dispersion was diluted with deionized water to a weight of 400 g and ultrafiltered to a final volume of approximately 50 mL using a polyethersulfone (PES) membrane with a cutoff value of 300 kDa. The procedure was repeated a total of 4 times to obtain 60 g of the Ag nanoplatelet dispersion in water. After completion of the ultrafiltration, 0.17 g of the compound of formula

(a mixture of CAS 80584-88-9 and 80584-89-0) was added to the dispersion.

Ag content 28.9 wt.%; yield approximately 89% based on total silver; solids content (at 250°C) 33.5 wt.%; purity 86 wt.% silver based on solids content at 250°C.

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 ultrafiltration cell with a stirrer and diluted with isopropanol to a weight of 300 g. The dispersion was ultrafiltered to a volume of approximately 50 ml using a polyethersulfone (PES) membrane with a cutoff value of 500 kDa. The procedure was repeated a total of 4 times to obtain 72 g of the Ag nanoplatelet dispersion in isopropanol.

Ag content 24.1 wt.%; solids content (at 250°C) 25.7 wt.%; silver purity 93.5 wt.% based on solids content at 250°C.

The spectrum in the UV, visible and near IR regions was recorded in water at an Ag concentration of 9.8*10 ^-5 M. λ _max = 700 nm; extinction coefficient at maximum ε = 10200 l/(cm*mol Ag), FWHM = 340 nm.

The Ag nanoplatelets have an average particle diameter of 93±40 nm and an average particle thickness of 16±2.5 nm.

B-2e. Substitution of solvent with ethyl 3-ethoxypropionate

30 g of the Ag nanoplatelet dispersion after ultrafiltration in isopropanol was placed in a 100 mm round-bottomed flask and 9 g of ethyl 3-ethoxypropionate 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 the solvent was completely distilled off. The solid content was adjusted to 40% w/w by adding ethyl 3-ethoxypropionate to yield a silver nanoplatelet dispersion D1 .

B-2f. Replacement of solvent with Uvacure 1500 (7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3-carboxylate)

30 g of the Ag nanoplatelet dispersion after ultrafiltration in isopropanol was placed in a 100 mm round bottom flask and 6 g of Uvacure 1500 (Cytec) 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 the solvent was completely evaporated. The solid content was adjusted to 50% w/w by adding Uvacure 1500 to yield a silver nanoplatelet dispersion D2 .

C. Obtaining inks (I1 - I33) and their printed security features

Description of Ingredients of UV-Visible Curable Screen Printing Inks (I1-I33)

Table 1. Ingredients

Ingredient Trade name
(supplier) Chemical composition
(CAS number) Polyvinyl chloride copolymer Vinnol® H14/36 (Wacker) 85.6 wt.% PVC + 14.4 wt.% PVAc
(9003-22-9) Polyvinyl chloride copolymer Vinnol® E15/40A (Wacker) 84 wt.% PVC + 16 wt.% hydroxyacrylate
(53710-52-4) Polyvinyl chloride copolymer Vinnol® E22/48A (Wacker) 75 wt.% PVC + 25 wt.% hydroxyacrylate/dicarboxylic acid esters
(114653-42-8) Polyvinyl chloride copolymer Vinnol® H40/50 (Wacker) 63 wt.% PVC + 37 wt.% PVAc
(9003-22-9) Cycloaliphatic epoxide Uvacure 1500
(Allnex) 7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3-carboxylate
(2386-87-0) Simple vinyl ether CHVE (BASF) 1,4-bis[(vinyloxy)methyl]cyclohexane
(17351-75-6) Acrylic oligomer Ebecryl 2959 23 wt.% glycerol, propoxylated, esters with acrylic acid (52408-84-1) + 77 wt.% 4,4'-isopropylidenediphenol, oligomeric reaction products with 1-chloro-2,3-epoxypropane, esters with acrylic acid (55818-57-0) Acrylic monomer TMPTA (Allnex) 2,2-bis(acryloyloxymethyl)butyl acrylate
(15625-89-5) Antifoaming agent Tego Airex 900 (Evonik) Siloxanes and silicones, di-Me, reaction products with silicon dioxide (CAS not provided) Perfluoropolyether reactive surfactant Fluorolink E10H (Solvay) Tetrafluoroethylene, oxidized, oligomers, reduced, methyl esters, reduced, reaction products with ethylene oxide (162492-15-1)
Average molecular weight 1700 [g/mol] Perfluoropolyether reactive surfactant Fluorolink MD700 (Solvay) Perfluoropolyether urethane methacrylate
(CAS not submitted)
Average molecular weight 1500 [g/mol] Perfluoropolyether anionic surfactant Fluorolink F10
(Solvay) Perfluoropolyether functionalized with phosphate groups (200013-65-6)
Average molecular weight 600-900 [g/mol] Perfluoropolyether nonionic surfactant Fluorolink S10
(Solvay) Perfluoropolyether functionalized with silane groups (223557-70-8)
Average molecular weight 1750-1950 [g/mol] Fluoroalkyl nonionic surfactant Dynasyl F-8815 (Evonik) Fluoroalkyl functionalized with siloxane groups
(CAS not submitted)
Average molecular weight is not provided by the supplier Fluoroalkyl nonionic surfactant Dynasyl F-8261 (Evonik) 1H,1H,2H,2H-Perfluorooctyltriethoxysilane
(51851-37-7) Cationic photoinitiator Speedcure 976 (Lambson) 50 wt.% of a mixture of sulfonium, diphenyl[4-(phenylthio)
phenyl]-, (OC-6-11)-hexafluorantimonate(1-) (1:1) + sulfonium, (thiodi-4,1-phenylene)bis[diphenyl-, (OC-6-11)-hexafluorantimonate(1-) (1:2) (71449-78-0 and 89452-37-9) in 50% propylene carbonate (108- 32-7) Cationic photoinitiator Speedcure 976D (Lambson) 35 wt. % of a mixture of sulfonium, diphenyl[4-(phenylthio)phenyl]-, (OC-6-11)-hexafluoroantimonate(1-) (1:1) + sulfonium, (thiodi-4,1-phenylene)bis[diphenyl-, (OC-6-11)-hexafluoroantimonate(1-) (1:2) (71449-78-0 and 89452-37-9) in 65 wt. % oxirane, 2,2'-[1,4-butanediylbis(oxymethylene)]bis- (2425-79-8) Cationic photoinitiator DEUTERON UV 1242 (Deuteron) 50 wt.% bis(4-dodecylphenyl)iodonium hexafluoroantimonate (71786-70-4) + 50 wt.% oxirane, derivatives of mono[(C12-14-alkyloxy)methyl] (68609-97-2) Cationic photoinitiator 2,4,6-Triphenylpyryllium
tetrafluoroborate (Sigma-Aldrich) Pyrylium, 2,4,6-triphenyl-, tetrafluoroborate(1-)
(448-61-3) Radical photoinitiator Omnirad 2100
(IGM Resins) 92.5% ethylphenyl(2,4,6-trimethylbenzoyl)phosphinate + 7.5 wt. % phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide
(448-61-3) Sensitizer Speedcure CPTX (Lambson) 9H-Thioxanthen-9-one, 1-chloro-4-propoxy-
(142770-42-1) Ag nanoplatelets Variance D1 40 wt.% in ethyl 3-ethoxypropionate (763-69-9) Ag nanoplatelets Variance D2 50 wt.% in Uvacure 1500 (2386-87-0)

C1. Study of the influence of heating temperature on the optical properties exhibited by a security feature (comparative tests C1 and tests E1-E6 and E31-E39)

C1a. Obtaining paint I1

To evaluate the effect of heating temperature on the appearance of metallic yellow color and blue color exhibited by the security feature in incident and transmitted light, respectively, paint I1 was prepared as described below.

Table 2a. Composition of UV-Visible Curable Screen Printing Ink I1

Ingredient Trade name Amount of mass. % Polyvinyl chloride copolymer Vinnol® H14/36 7.3 Cycloaliphatic epoxide ^Uvacure® 1500 22 Simple vinyl ether CHVE 16 Radical curing oligomer Ebecryl 2959 4.4 Radical curing monomer TMPTA 9 Perfluoropolyether reactive surfactant Fluorolink E10H 1 Cationic photoinitiator Speedcure 976 5.8 Free radical photoinitiator Omnirad 2100 3.2 Ag nanoplatelets Variance D1 31.3 Cationically curable monomers 38 Radical curing monomers and oligomers 13.4 Solvent 21.7 Ag nanoplatelets (solid content) 12.5

The ingredients shown in Table 2a were mixed and dispersed at room temperature using Dispermat CV-3 for 10 minutes at 2000 rpm to yield 50 g of paint I1 . The silver nanoplatelet dispersion D1 contains 40 wt.% silver nanoplatelets and 60 wt.% ethyl 3-ethoxypropionate.

C1b. Acquisition of protective features

The UV-visible curable screen printing ink I1 was independently applied to sixteen pieces of transparent polymer substrate (PET Hostaphan® RN, 50 µm thick, sold by Pütz GmbH + Co. Folien KG) using a 160 thread/cm (405 mesh) screen. The printed pattern size was 5 cm x 5 cm.

After the printing step, sixteen pieces of printed substrate were independently placed on a heating plate (Huber PZ28-1) and heated for the time period specified in Table 2b below, at the temperatures specified in Table 2b below, then cured by exposing them twice at 100 m/min to UV-Vis radiation in a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W/ ^cm2 + mercury lamp 200 W/ ^cm2 ), to create the security features.

C1c. Results (optical properties) of security features

The optical properties of each of the security features obtained in item C1b were assessed independently in reflection, transmission and visually using the three tests described below. The results are presented in Table 2b .

Reflectance measurements were performed using a goniometer (goniospectrometer Codec WI-10 5&5 from Phyma GmbH Austria). The L*a*b* values of the printed security features were determined at an angle of 0° to the normal with an illumination angle of 22.5° on the side of the transparent polymer substrate that was printed. The C* values (chroma, corresponding to the color intensity or color saturation index) were calculated from the a* and b* values according to the CIELAB color space (1976), where:

The C* values (22.5/0° reflectance) are shown in Table 2b below.

Transmittance measurements were performed using a Datacolor 650 spectrophotometer (set to integrating sphere, diffuse illumination (D65 pulsed xenon) and 8° viewing angle, SP2000 analyzer with 256 dual diode array for the wavelength range 360-700 nm, 22 mm transmission sampling aperture). The C* values (8° transmission) are shown in Table 2b below.

Visual assessment was performed by observing each security feature with the naked eye in reflection from a diffuse source (e.g. light passing through a window without direct sunlight, the observer looks at the wall opposite the window). The following colors were observed:

- Colors from dark brown to brown with a matte appearance and no metallic effect;

- A gold colour (i.e. metallic yellow) with a glossy appearance and metallic effect. The metallic effect appears when the C* colour value in the reflection of 22.5/0° is above approximately 20.

A visual assessment was also carried out by observing each protective feature with the naked eye during transmission. The following colours were observed:

- Dull blue: the blue color is weak (but noticeable);

- Colour from blue (C* colour value at 8° transmittance greater than or equal to approximately 20) to dark blue (C* colour value at 8° transmittance greater than or equal to 30): intense to very intense blue colour.

As shown in Table 2b , the security features produced by the method according to the present invention (tests E1 to E6 and E31 to E39 ) exhibited a golden color in reflection and a blue to dark blue color in transmission, whereas the comparative security feature produced by the method not according to the present invention (test C1 ) exhibited a blue color in transmission but a brown color with a low chromaticity value in reflection, which is not eye-catching and is not suitable for a dichroic security feature.

As confirmed, for example, by tests E1 - E6 and E31 - E39 according to the present invention, security features with higher C* chromaticity values both in reflected light and in transmitted light can be obtained by increasing the heating temperature from about 55°C to about 100°C and/or the heating time in step b) of the manufacturing method according to the present invention.

Table 2b. Colour properties of security features obtained in comparative test C1 and tests E1 - E6 and E31 - E39 according to the present invention

C2. Study of the influence of surfactant on the optical properties exhibited by the security feature (comparative tests C2 - C5 and tests E7 - E8 according to the present invention)

To evaluate the influence of the surfactant on the optical properties exhibited by the protective feature, paints I2 - I7 were obtained.

C2a. Obtaining paints I2 - I7

Table 3a. Composition of UV-visible curable screen printing inks I2 - I7

Ingredient Trade name Amount of mass. % I2 I3 I4 I5 I6 I7 Polyvinyl chloride copolymer Vinnol® H14/36 7.3 Cycloaliphatic epoxide ^Uvacure® 1500 19.7 Simple vinyl ether CHVE 16 Radical curing oligomer Ebecryl 2959 4.4 Radical curing monomer TMPTA 9 Fluorinated surfactant Fluorolink E10H 2.5 Fluorolink MD700 2.5 Fluorolink F10 2.5 Fluorolink S10 2.5 Dynasyl F-8815 2.5 Dynasyl F-8261 2.5 Cationic photoinitiator Speedcure 976 5.8 Free radical photoinitiator Omnirad 2100 3.2 Antifoaming agent Tego ^® Airex 900 0.8 Ag nanoplatelets D1 31.3 Cationically curable monomers 35.7 Radical curing monomers and oligomers 13.4 Solvent 21.7 Ag nanoplatelets (solid content) 12.5

The ingredients presented in Table 3a were mixed and dispersed at room temperature using Dispermat CV-3 for 10 minutes at 2000 rpm to yield 50 g of each paint I2 - I7 .

C2b. Obtaining protective features

The UV-visible curable screen printing inks I2 to I7 were independently applied to six pieces of transparent polymer substrate (PET Hostaphan® RN, 50 µm thick, sold by Pütz GmbH + Co. Folien KG) using a 160 thread/cm (405 mesh) screen. The printed pattern size was 5 cm x 5 cm.

After the printing step, six pieces of printed substrate were independently placed on a heating plate (Huber PZ28-1) and heated for 10 seconds at 80°C, then cured by exposing them twice at 100 m/min to UV-Vis radiation in a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W/ ^cm2 + mercury lamp 200 W/ ^cm2 ), to create the security features.

C2c. Results (optical properties) of security features

The optical properties of the security features obtained in comparative tests C2 - C5 and tests E7 - E8 according to the present invention were independently assessed in reflection, transmission and visually using the tests described in paragraph C1c .

The reflective and transmitting colours and the C* values (reflectance 22.5/0° and transmittance 8°) exhibited by the security features obtained in comparative tests C2 to C5 and tests E7 to E8 according to the present invention are shown in Table 3b below.

Table 3b. Colour properties of security features obtained in comparative tests C2 - C5 and tests E7 - E8 .

C2 C3 C4 C5 E7 E8 Dye I4 I5 I6 I7 I2 I3 Fluorinated surfactant Fluorolink F10 Fluorolink S10 Dynasyl F-8815 Dynasyl F-8261 Fluorolink E10H Fluorolink MD700 C* (reflectance 22.5/0°) 6 15 7 14 23 26 C* (8° transmission) 24 28 27 28 26 27 Color (reflection) Dark brown Brown Dark brown Brown Gold Gold Color (transmission) Blue Blue Blue Blue Blue Blue

As shown in Table 3b , the security features obtained in tests E7 and E8 according to the present invention using a paint containing a perfluoropolyether surfactant functionalized with hydroxyl groups or methacrylate groups (Fluorolink E10H/ I2 and Fluorolink MD700/ I3 ) exhibited a gold color in reflection and a blue color in transmission. In comparison, the security features obtained by using an ink containing a perfluoropolyether anionic surfactant (Fluorolink F10/ I4 ), a perfluoropolyether nonionic surfactant (Fluorolink S10/ I5 ) or a fluorosurfactant not containing a perfluoropolyether backbone and a functional group selected from hydroxyl groups, acrylate groups and methacrylate groups (Dynasylan F8815/ I6 and Dynasylan F8261/ I7 ) exhibited a blue color in transmission but a dark brown to brown color with a low chroma value in reflection. The dark brown to brown color with a low chroma value in reflection does not attract attention and is therefore not suitable for a dichroic security feature for protecting a valuable document.

C3. Study of the influence of perfluoropolyether surfactant concentration on the optical properties exhibited by the security feature (comparative test C6 and tests
E9 - E14 according to the present invention)

To evaluate the effect of the concentration of a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate, and methacrylate on the optical properties exhibited by the security feature, paints I8 - I14 were prepared as described below.

C3a. Obtaining paint I8 - I14

Table 4a. Composition of UV-visible curable screen printing inks I8 - I14.

Ingredient Trade name Amount of mass. % I8 I9 I10 I11 I12 I13 I14 Polyvinyl chloride copolymer Vinnol® H14/36 7.3 Cycloaliphatic epoxide ^Uvacure® 1500 23 22.9 22.7 22.5 22.2 22 20.5 Simple vinyl ether CHVE 16 Radical curing oligomer Ebecryl 2959 4.4 Radical curing monomer TMPTA 9 Perfluoropolyether reactive surfactant Fluorolink E10H 0 0.1 0.3 0.5 0.8 1 2.5 Cationic photoinitiator Speedcure 976 5.8 Free radical photoinitiator Omnirad 2100 3.2 Ag nanoplatelets D1 31.3 Cationically curable monomers 39 38.9 38.7 38.5 38.2 38 36.5 Radical curing monomers and oligomers 13.4 Solvent 21.7 Ag nanoplatelets (solid content) 12.5

The ingredients presented in Table 4a were mixed and dispersed at room temperature using Dispermat CV-3 for 10 minutes at 2000 rpm to yield 50 g of each paint I8 - I14 .

C3b. Acquisition of protective features

UV-visible curable screen printing inks I8 to I14 were independently applied to seven pieces of transparent polymer substrate (PET Hostaphan® RN, 50 µm thick, sold by Pütz GmbH + Co. Folien KG) using a stencil with a size of 160 threads/cm (405 mesh). The printed pattern size was 5 cm x 5 cm. After the printing step, seven pieces of printed substrate were independently placed on a heating plate (Huber PZ28-1) and heated for 10 seconds at 80°C, then cured by exposing them twice at 100 m/min to UV-Vis radiation in a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W/ ^cm2 + mercury lamp 200 W/ ^cm2 ), to create the security features.

C3c. Results (optical properties) of security features

The optical properties of the security features obtained in comparative test C6 and tests E9 to E14 according to the present invention were independently assessed in reflection, transmission and visually using the tests described in paragraph C1c.

The reflective and transmitting colours and the C* chromaticity values (reflectance 22.5/0° and transmittance 8°) exhibited by the security features obtained in comparative test C6 and tests E9 to E14 according to the present invention are shown in Table 4b below.

Table 4b. Colour properties of security features obtained in comparative test C6 and tests E9 - E14 according to the present invention.

C6 E9 E10 E11 E12 E13 E14 Dye I8 I9 I10 I11 I12 I13 I14 Amount of surfactant 0 0.1 0.3 0.5 0.8 1 2.5 C* (reflectance 22.5/0°) 12 34 36 32 37 38 35 C* (8° transmission) 25 24 27 26 30 26 27 Color (reflection) Brown Gold Gold Gold Gold Gold Gold Color (transmission) Blue Blue Blue Blue Dark blue Blue Blue

As shown in Table 4b , the use of a concentration of the perfluoropolyether surfactant Fluorolink E10H from about 0.1 wt.% to about 2.5 wt.% makes it possible to obtain security features exhibiting a metallic yellow color with high chromaticity values in reflection and a color from blue to dark blue in transmission using the manufacturing method according to the present invention. In comparison, the security feature obtained in the comparative test C6 using an ink not containing Fluorolink E10H exhibits a color from dark brown to brown with a low chromaticity value in reflection. Such a color is not noticeable to a layman and cannot be used as a security feature for protecting a valuable document.

C4. Solvent effect study (solvent containing (compared to solvent-free paint) and/or the weight percentage of radical-curing monomers and oligomers present in the UV-VIS-curable paint (hybrid UV-VIS-curable paint (compared to a cationic UV-visible curable paint) on the optical properties exhibited by the security feature (tests E15 - E16 and E40 according to the present invention)

In order to evaluate whether the optical effects obtained by using a solvent-containing hybrid UV-Vis-curable paint can be reproduced by using a solvent-free hybrid UV-Vis-curable paint and a solvent-free cationic UV-Vis-curable paint, paints I1 , I15 and I16 were prepared.

C4a. Obtaining paints I15 and 16

Table 5a. Composition of UV-Vis-curable screen printing inks I15 - I16

Ingredient Trade name Amount of mass. % I15 I16 Polyvinyl chloride copolymer Vinnol® H14/36 7.3 Cycloaliphatic epoxide ^Uvacure® 1500 36.9 23.5 Simple vinyl ether CHVE 16 Radical curing oligomer Ebecryl 2959 0 4.4 Radical curing monomer TMPTA 0 9 Perfluoropolyether reactive surfactant Fluorolink E10H 2.5 Cationic photoinitiator Speedcure 976D 11.5 8.3 Free radical photoinitiator Omnirad 2100 0 3.2 Antifoaming agent Tego ^® Airex 900 0.8 Ag nanoplatelets D2 25 Cationically curable monomers 72.9 57.4 Radical curing monomers and oligomers 0 13.4 Solvent 0 0 Ag nanoplatelets (solid content) 12.5 12.5

The ingredients shown in Table 5a were mixed and dispersed at room temperature using Dispermat CV-3 for 10 minutes at 2000 rpm to yield 50 g each of paints I15 and I16 . I15 is a solvent-free cationic UV-Vis-curable paint, while I16 is a solvent-free hybrid UV-Vis-curable paint. Paint I1 , obtained in C1a , is a solvent-containing hybrid UV-Vis-curable paint. Silver nanoplatelet dispersion D2 contains 50 wt.% silver nanoplatelets and 50 wt.% Uvacure 1500 (cycloaliphatic epoxy).

C4b. Acquisition of protective features

UV-visible curable screen printing inks I1 , I15 and I16 were independently applied onto three pieces of transparent polymer substrate (PET Hostaphan® RN, 50 µm thick, sold by Pütz GmbH + Co. Folien KG) using a stencil with a size of 160 threads/cm (405 mesh). The printed pattern size was 5 cm x 5 cm. After the printing step, three pieces of printed substrate were independently placed on a heating plate (Huber PZ28-1) and heated for 10 seconds at 80°C, then cured by exposing them twice at 100 m/min to UV-Vis radiation in a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W/ ^cm2 + mercury lamp 200 W/ ^cm2 ), to create the security features.

C4c. Results (optical properties) of security features

The optical properties of the security features obtained in tests E15 , E16 and E40 according to the present invention were independently assessed in reflection, transmission and visually using the tests described in paragraph C1c .

The reflective and transmitting colours and the C* chromaticity values (reflectance 22.5/0° and transmittance 8°) exhibited by the security features are shown in Table 5b below.

Table 5b. Colour properties of security features obtained in tests E15 , E16 and E40 according to the present invention.

E15 E16 E40 Dye I15 I16 I1 Solvent free cationic paint Solvent free hybrid paint Solvent-based hybrid paint C* (reflectance 22.5/0°) 24 27 23 C* (8° transmission) 25 34 26 Color (reflection) Gold Gold Gold Color (transmission) Blue Dark blue Blue

As shown in Table 5b , the use of a solvent-containing hybrid ink ( I1 ), a solvent-free hybrid ink ( I16 ), or a solvent-free cationic ink ( I15 ) in the manufacturing method does not affect the optical properties of the security feature.

C5. Study of the influence of the ratio of the mass percentage of radical-curing monomers and oligomers present in the paint and the mass percentage of cation-curing monomers present in the paint on the optical properties of security features (tests E17 - E20 according to the present invention)

C5a. Obtaining paints I17 - I20

Table 6a. Composition of UV-Vis-curable screen printing inks I17 - I20

Ingredient Trade name Amount of mass. % I17 I18 I19 I20 Polyvinyl chloride copolymer Vinnol® H14/36 7.3 5.8 3.6 2.9 Cycloaliphatic epoxide ^Uvacure® 1500 33.8 26.6 16.7 13.4 Simple vinyl ether CHVE 16 12.7 7.9 6.3 Radical curing oligomer Ebecryl 2959 0 3.7 9.3 11.1 Radical curing monomer TMPTA 0 7.6 18.9 22.7 Perfluoropolyether reactive surfactant Fluorolink E10H 2.5 Cationic photoinitiator Speedcure 976D 8.3 7 4.2 3.3 Free radical photoinitiator Omnirad 2100 0 2 4.8 5.7 Antifoaming agent Tego ^® Airex 900 0.8 Ag nanoplatelets D1 31.3 Cationically curable monomers 55.2 43.9 27.3 22.1 Radical curing monomers and oligomers 0 11.3 28.2 33.8 Ratio of mass % of radical-curing mono- and oligomers and mass % of cation-curing monomers 0% 0.26:1 1.03:1 1.53:1 Solvent 18.8 Ag nanoplatelets (solid content) 12.5

The ingredients presented in Table 6a were mixed and dispersed at room temperature using Dispermat CV-3 for 10 minutes at 2000 rpm to yield 50 g of each paint I17 - I20 .

C5b. Acquisition of protective characteristics

UV-visible curable screen printing inks I17 - I20 were independently applied to four pieces of transparent polymer substrate (PET Hostaphan® RN, 50 µm thick, sold by Pütz GmbH + Co. Folien KG) using a stencil with a size of 160 threads/cm (405 mesh). The printed pattern size was 5 cm x 5 cm. After the printing step, four pieces of printed substrate were independently placed on a heating plate (Huber PZ28-1) and heated for 10 seconds at 80°C, then cured by exposing them twice at 100 m/min to UV-Vis radiation in a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W/ ^cm2 + mercury lamp 200 W/ ^cm2 ), to create the security features.

C5c. Results (optical properties) of security features

The optical properties of the security features obtained in tests E17 - E20 according to the present invention were independently assessed in reflection, transmission and visually using the tests described in paragraph C1c .

The reflective and transmitting colours and the C* chromaticity values (reflectance 22.5/0° and transmittance 8°) exhibited by the security features are shown in Table 6b below.

Table 6b. Colour properties of security features obtained in tests E17 - E20 according to the present invention.

E17 E18 E19 E20 Dye I17 I18 I19 I20 Ratio of mass % of radical-curing mono- and oligomers and mass % of cation-curing monomers 0 0.26:1 1.03:1 1.53:1 C* (reflectance 22.5/0°) 27 25 30 23 C* (8° transmission) 32 39 38 43 Color (reflection) Gold Gold Gold Gold Color (transmission) Dark blue Dark blue Dark blue Dark blue

Tests E17 - E20 according to the present invention show that similar optical effects can be obtained by using a cationically curable UV-Visible paint ( I17 ) or a hybrid UV-Visible curable paint ( I18 - I20 ) whose ratio of the mass percentage (wt%) of radical-curable mono- and oligomers to the mass percentage (wt%) of cationically curable monomers is below about 1.53:1.

C6. Study of the influence of the type of polyvinyl chloride copolymer on the optical properties exhibited by the security feature (comparative test C7 and tests E21 - E23 according to the present invention)

To evaluate the influence of the type of polyvinyl chloride copolymer on the optical properties exhibited by the security feature, paints I21 - I24 containing different polyvinyl chloride were prepared as described below.

C6a. Obtaining dyes I21 - I24

Table 7a. Composition of UV-Vis-curable screen printing inks I21 - I24

Ingredient Trade name Amount of mass. % I21 I22 I23 I24 Polyvinyl chloride copolymer Vinnol® H14/36 ^a) 7.3 Vinnol® E15/40A ^b) 7.3 Vinnol® E22/48A ^c) 7.3 Vinnol® H40/50 ^d) 7.3 Cycloaliphatic epoxide ^Uvacure® 1500 35.7 Radical curing oligomer Ebecryl 2959 4.4 Radical curing monomer TMPTA 9 Perfluoropolyether reactive surfactant Fluorolink E10H 2.5 Cationic photoinitiator Speedcure 976 5.8 Free radical photoinitiator Omnirad 2100 3.2 Antifoaming agent Tego ^® Airex 900 0.8 Ag nanoplatelets D1 31.3 Cationically curable monomers 35.7 Radical curing monomers and oligomers 13.4 Percentage of PVC in polyvinyl chloride copolymer [mass %] 85.6 84 75 63 Solvent 21.7 Ag nanoplatelets (solid content) 12.5

^a) polyvinyl chloride/polyvinyl acetate resin (85.6%/14.4%), K value 35±1, molecular weight 3-4·10 ⁴ Dalton (Wacker, size exclusion chromatography)

^b) polyvinyl chloride/polyhydroxyacrylate resin (84%/16%), K value 39±1, molecular weight 4-5·10 ⁴ Dalton (Wacker, size exclusion chromatography)

^c) polyvinyl chloride / (copolymer of dibutyl ester of acrylic acid / 1,2-propanediol / butenedioic acid) (75% / 25%), K value 48 ± 1, molecular weight 6-8 10 ⁴ Dalton (Wacker, size exclusion chromatography)

^d) polyvinyl chloride/polyvinyl acetate resin (63%/37%), K value 50±1, molecular weight 6-8·10 ⁴ Dalton (Wacker, size exclusion chromatography)

The ingredients presented in Table 7a were mixed and dispersed at room temperature using Dispermat CV-3 for 10 minutes at 2000 rpm to yield 50 g of each paint I21 - I24 .

C6b. Acquisition of protective characteristics

The UV-visible curable screen printing inks I21 - I24 were independently applied to four pieces of transparent polymer substrate (PET Hostaphan® RN, 50 µm thick, sold by Pütz GmbH + Co. Folien KG) using a 160 thread/cm (405 mesh) screen. The printed pattern size was 5 cm x 5 cm.

After the printing step, four pieces of printed substrate were independently placed on a heating plate (Huber PZ28-1) and heated for 10 seconds at 80°C, then cured by exposing them twice at 100 m/min to UV-Vis radiation in a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W/ ^cm2 + mercury lamp 200 W/ ^cm2 ), to create the security features.

C6c. Results (optical properties) of security features

The optical properties of the security features obtained in comparative test C7 and tests E21 - E23 according to the present invention were independently assessed in reflection, transmission and visually using the tests described in paragraph C1c .

The reflective and transmitting colours and the C* chromaticity values (reflectance 22.5/0° and transmittance 8°) exhibited by the security features are shown in Table 7b below.

Table 7b. Colour properties of security features obtained in comparative test C7 and tests E21 - E23 according to the present invention.

C7 E21 E22 E23 Dye I24 I21 I22 I23 Percentage of PVC in polyvinyl chloride copolymer [mass %] 63 85.6 84 75 C* (reflectance 22.5/0°) 16 31 30 28 C* (8° transmission) 20 35 43 32 Color (reflection) Brown Gold Gold Gold Color (transmission) Dull blue Dark blue Dark blue Dark blue

As shown in Table 7b , the polyvinyl chloride copolymer must contain at least about 69 wt.%, preferably at least about 75 wt.%, of vinyl chloride to provide a security feature that exhibits a metallic yellow color in reflection. The security feature obtained in Comparative Test C7 , made with an ink containing a polyvinyl chloride copolymer with a lower wt.% of vinyl chloride, exhibits a brown color in reflected light, which is not noticeable to the layman and cannot be used as a security feature to secure a valuable document.

C7. Study of the influence of the concentration of polyvinyl chloride copolymer on the optical properties of the security feature (comparative test C8 and tests E24 - E27 according to the present invention)

C7a. Obtaining paints I25, I27 - I30

Table 8a. Composition of UV-visible curable screen printing inks I25, I27 - I30

Ingredient Trade name Amount of mass. % I25 I27 I28 I29 I30 Polyvinyl chloride copolymer Vinnol® H14/36 0 4.9 7.3 8.6 11.6 Cycloaliphatic epoxide ^Uvacure® 1500 27 22.1 19.7 23.4 31.4 Simple vinyl ether CHVE 16 16 16 11 0 Radical curing oligomer Ebecryl 2959 4.4 Radical curing monomer TMPTA 9 Perfluoropolyether reactive surfactant Fluorolink E10H 2.5 Cationic photoinitiator Speedcure 976 5.8 Free radical photoinitiator Omnirad 2100 3.2 Antifoaming agent Tego ^® Airex 900 0.8 Ag nanoplatelets D1 31.3 Viscosity of paints [mPa•s] ^a) T = 25 °C 20 96 171 282 982 Cationically curable monomers 43 38.1 35.7 34.4 31.4 Radical curing monomers and oligomers 13.4 Solvent 21.7 Ag nanoplatelets (solid content) 12.5

^a) Viscosity was determined using a Brookfield viscometer (model "DVI-Prime") equipped with an S21 spindle at 100 rpm ( I25 , I27 - I29 ) or an S21 spindle at 50 rpm ( I30 ).

The ingredients presented in Table 8a were mixed and dispersed at room temperature using Dispermat CV-3 for 10 minutes at 2000 rpm to yield 50 g of each paint I25 , I27 - I30 .

C6b. Acquisition of protective characteristics

UV-visible curable screen printing inks I25 , I27 - I30 were independently applied to five pieces of transparent polymer substrate (PET Hostaphan® RN, 50 µm thick, sold by Pütz GmbH + Co. Folien KG) using a stencil with a size of 160 threads/cm (405 mesh). The printed pattern size was 5 cm x 5 cm. After the printing step, five pieces of printed substrate were independently placed on a heating plate (Huber PZ28-1) and heated for 10 seconds at 80°C, then cured by exposing them twice at 100 m/min to UV-Vis radiation in a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W/ ^cm2 + mercury lamp 200 W/ ^cm2 ), to create the security features.

C7c. Results (optical properties) of security features

The optical properties of the security features obtained in comparative test C8 and tests E24 - E27 according to the present invention were independently assessed in reflection, transmission and visually using the tests described in paragraph C1c .

The reflective and transmitting colours and the C* chromaticity values (reflectance 22.5/0° and transmittance 8°) exhibited by the security features are shown in Table 8b below.

Table 8b. Colour properties of security features obtained in comparative test C8 and tests E24 - E27 according to the present invention.

C8 E24 E25 E26 E27 Dye I25 I27 I28 I29 I30 The amount of polyvinyl chloride copolymer 0 4.9 7.3 8.6 11.6 C* (reflectance 22.5/0°) 3 21 25 27 23 C* (8° transmission) 32 23 28 32 28 Color (reflection) Dark brown Gold Gold Gold Gold Color (transmission) Dark blue Blue Blue Dark blue Blue

As shown in Table 8b , the security feature obtained in comparative test C8 by using an ink not containing Vinnol® H14/36 shows a dark brown colour with a low chromaticity value in reflection. Such a colour is not noticeable to the layman and cannot be used as a security feature for protecting a valuable document. The polyvinyl chloride copolymer Vinnol® H14/36 makes it possible to obtain a golden colour (i.e. metallic yellow) in reflected light. The amount of polyvinyl chloride copolymer had a strong influence on the viscosity of the ink, which for screen printing ink should preferably be from about 100 mPa•s to about 1000 mPa•s at 25°C, as in tests E24 to E27 .

C8. Study of the influence of cationic photoinitiators and UV-Visible curing system on the optical properties of security features (tests E28 - E30 according to the present invention)

C8a. Obtaining dyes I31 - I33

Table 9a. Composition of UV-Vis-curable screen printing inks I31 - I33

Ingredient Trade name Amount of mass. % I31 I32 I33 Polyvinyl chloride copolymer Vinnol® H14/36 7.3 Cycloaliphatic epoxide ^Uvacure® 1500 19.7 18.7 22.6 Simple vinyl ether CHVE 16 Radical curing oligomer Ebecryl 2959 4.4 Radical curing monomer TMPTA 9 Perfluoropolyether reactive surfactant Fluorolink E10H 2.5 Cationic photoinitiator Deuteron UV 1242 5.8 5.8 2,4,6-Triphenylpyryllium tetrafluoroborate 2.9 Free radical photoinitiator Omnirad 2100 3.2 Photosensitizer Speedcure CPTX 0 1 0 Antifoaming agent Tego ^® Airex 900 0.8 Ag nanoplatelets D1 31.3 Cationically curable monomers 38.6 37.6 38.6 Radical curing monomers and oligomers 13.4 Solvent 18.8 18.8 18.8 Ag nanoplatelets (solid content) 12.5

The ingredients presented in Table 9a were mixed and dispersed at room temperature using Dispermat CV-3 for 10 minutes at 2000 rpm to yield 50 g of each paint I31 - I33 .

C8b. Acquisition of protective features

UV-visible curable screen printing inks I31 - I33 were independently applied onto three pieces of transparent polymer substrate (PET Hostaphan® RN, 50 µm thick, sold by Pütz GmbH + Co. Folien KG) using a stencil with a size of 160 threads/cm (405 mesh). The printed pattern size was 5 cm x 5 cm. After the printing step, three pieces of printed substrate were independently placed on a heating plate (Huber PZ28-1) and heated for 10 seconds at 80°C, then cured by exposing them twice at 100 m/min to UV-Vis radiation in a dryer from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W/ ^cm2 + mercury lamp 200 W/ ^cm2 ), to create the security features.

The UV-visible curable screen printing ink I32 was applied to the fourth piece of transparent polymer substrate (PET Hostaphan® RN, 50 µm thick, sold by Pütz GmbH + Co. Folien KG) using a 405 thread/cm (160 mesh) screen. The printed pattern was 5 cm x 5 cm in size. After the printing step, the fourth piece of printed substrate was placed on a heating plate (Huber PZ28-1) and heated for 10 seconds at 80°C, then cured under a Phoseon Type FireLine UV-LED lamp (125 x 20 mm, 395 nm, 8 W/ ^cm2 ) for 2 seconds to create the security feature.

C8c. Results (optical properties) of security features

The optical properties of the security features obtained in tests E28 , E29a , E29b and E30 according to the present invention were independently assessed in reflection, transmission and visually using the tests described in paragraph C1c .

The reflective and transmitting colours and the C* chromaticity values (reflectance 22.5/0° and transmittance 8°) exhibited by the security features are shown in Table 9b below.

Table 9b.Color properties of security features obtained in testsE28,E29a,E29b And E30according to the present invention.

E28 E29a E29b E30 Curing system Hg lamps Hg lamps UV LED lamp Hg lamps Cationic photoinitiator Diaryliodonium Diaryliodonium + thioxanthone Diaryliodonium + thioxanthone Triphenylpyrilium Dye I31 I32 I32 I33 C* (reflectance 22.5/0°) 30 29 27 28 C* (8° transmission) 46 42 45 43 Color (reflection) Gold Gold Gold Gold Color (transmission) Dark blue Dark blue Dark blue Dark blue

As shown in Table 9b , the security features obtained in tests E28 , E29a and E30 according to the present invention using a paint containing a diaryliodonium photoinitiator ( I31 ), a diaryliodonium photoinitiator and a thioxanthone photosensitizer ( I32 ) or a triphenylpyrylium photoinitiator ( I33 ) and cured under standard mercury lamps, exhibit a golden color in reflection and a dark blue color in transmission with similar chromaticity values in both reflection and transmission. Curing with a UV-LED lamp or standard mercury lamps does not have any effect on the optical properties exhibited by the security feature, as confirmed by tests E29a and E29b .

Claims (65)

1. A method for obtaining a security feature for protecting a valuable document, characterized in that said security feature exhibits a blue color when viewed in transmitted light and a metallic yellow color when viewed in incident light, and said method includes the following steps: a) printing UV and visible radiation-curable ink on a transparent or partially transparent area of the substrate of a valuable document to provide an ink layer; b) heating the paint layer obtained in step a) at a temperature of from 55°C to 100°C for at least one second so that the paint layer exhibits a metallic yellow colour when viewed in incident light; and c) curing under the influence of radiation in the UV and visible region of the paint layer obtained in step b) to form a security feature; The paint, which is cured under the influence of radiation in the UV and visible range, contains: i) silver nanoplatelets, the average diameter of which is in the range of 50-150 nm with a standard deviation of less than 60%, the average thickness of which is in the range of 5-30 nm with a standard deviation of less than 50%, and the average aspect ratio of which exceeds 2.0, wherein the average diameter is determined by transmission electron microscopy, and the average thickness is determined by transmission electron microscopy; ii) from 40% by weight to 75% by weight of either a cycloaliphatic epoxide or a mixture of a cycloaliphatic epoxide and one or more UV-visible radiation-curable compounds other than a cycloaliphatic epoxide; iii) one or more cationic photoinitiators; iv) a polyvinyl chloride copolymer containing at least 69% by weight of vinyl chloride; v) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate and methacrylate; and optionally vi) up to 25% by weight of organic solvent; wherein the weight percentages of ii) and vi) are calculated based on the total weight of the UV-visible curable paint. 2. The method according to paragraph 1, characterized in that the printing at stage a) is screen, rotary gravure or flexographic printing. 3. The method according to claim 1 or 2, characterized in that the average diameter of the silver nanoplatelets is in the range of 70-120 nm with a standard deviation of less than 50%, the average thickness of the silver nanoplatelets is in the range of 8-25 nm with a standard deviation of less than 30%, and the average aspect ratio of the silver nanoplatelets exceeds 2.5. 4. The method according to any one of paragraphs 1-3, characterized in that the silver nanoplatelets contain a surface stabilizer of formula (I) on their surface. Where 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 independently of one another represent H, C ₁ -C ₈ alkyl or phenyl; Y represents O or NR ⁸ ; R ⁸ is H or C ₁ -C ₈ alkyl; k1 is an integer in the range from 1 to 500; k2 and k3 are independently equal to 0 or are integers in the range from 1 to 250; k4 is 0 or 1; and k5 is an integer in the range 1 to 5. 5. The method according to any one of paragraphs 1-4, characterized in that the silver nanoplatelets contain a surface stabilizer, which is a polymer or copolymer, which is obtained by a process including the steps of: d1) polymerization in a first step of one or more monomers with ethylene double bonds in the presence of at least one nitroxide ether with a structural element where X is a group with at least one carbon atom and is such that the free radical X• obtained from X is capable of initiating polymerization; or d2) polymerization in a first step of one or more monomers with ethylene double bonds in the presence of at least one stable free nitroxyl radical and free radical initiator; wherein at least one monomer used in steps d1) or d2) is a C ₁ -C ₆ alkyl or hydroxy C ₁ -C ₆ alkyl ester of acrylic or methacrylic acid; and optionally e) a second step comprising modifying the polymer or copolymer obtained in d1) or d2) by an intermolecular transesterification reaction, amidation, hydrolysis or anhydride modification or a combination thereof. 6. The method according to any one of paragraphs 1-5, characterized in that the paint cured under the influence of radiation in the UV and visible region contains one or more stabilizers selected from the group consisting of: compounds of formula (IIb) Where R ^21a represents a hydrogen atom, a halogen atom, a C ₁ -C ₈ alkoxy group or a C ₁ -C ⁸ alkyl group; R ^21b represents a hydrogen atom or a group of the formula -CHR ²⁴ -N(R ²² )(R ²³ ); R ²² and R ²³ independently of one another represent a C ₁ -C ₈ alkyl, a hydroxy-C ₁ -C ₈ alkyl group or a group of the formula -[(CH ₂ CH ₂ )-O] _n1 -CH ₂ CH ₂ -OH, where n1 is from 1 to 5; and R ²⁴ is H or C ₁ -C ₈ alkyl; And compound of formula (IIc) Where R ²⁵ in each case may be the same or different and represents a hydrogen atom, a halogen atom, a C ₁ -C ₁₈ alkyl group, a C ₁ -C ₁₈ alkoxy group or a -C(=O)-R ²⁶ group; R ²⁶ represents a hydrogen atom, a hydroxy group, a C ₁ -C ₁₈ alkyl group, an unsubstituted or substituted amino group, an unsubstituted or substituted phenyl group, or a C ₁ -C ₁₈ alkoxy group; n3 is an integer in the range 1 to 4; m3 is an integer in the range 2 to 4, and the sum of the integers m3 and n3 is 6. 7. The method according to any one of paragraphs 1-6, characterized in that the paint cured under the influence of radiation in the UV and visible region contains a concentration of silver nanoplatelets from 5 mass % to 20 mass %, wherein the mass percentage content is calculated based on the total mass of the paint cured under the influence of radiation in the UV and visible region. 8. The method according to any one of paragraphs 1-6, characterized in that the paint cured under the influence of radiation in the UV and visible region contains a concentration of silver nanoplatelets from 7.5 mass % to 17.5 mass %, wherein the mass percentage content is calculated based on the total mass of the paint cured under the influence of radiation in the UV and visible region. 9. The method according to any one of paragraphs 1-6, characterized in that the paint cured under the influence of radiation in the UV and visible region contains a concentration of silver nanoplatelets from 10 mass % to 15 mass %, wherein the mass percentage content is calculated based on the total mass of the paint cured under the influence of radiation in the UV and visible region. 10. The method according to any one of claims 1 to 9, characterized in that the one or more UV-visible curable compounds other than a cycloaliphatic epoxide comprise vii) one or more cationically curable monomers other than a cycloaliphatic epoxide, wherein the one or more cationically curable monomers are selected from the group consisting of vinyl ethers, propenyl ethers, cyclic ethers, lactones, cyclic thioethers, vinyl thioethers, propenyl thioethers, hydroxyl-containing compounds and mixtures thereof. 11. The method according to any one of claims 1 to 10, characterized in that one or more UV-visible curable compounds other than a cycloaliphatic epoxide contain viii) one or more radical-curable monomers and/or oligomers, and the UV-visible curable paint further contains ix) one or more free-radical photoinitiators. 12. The method according to any one of paragraphs. 1-11, characterized in that the paint cured under the influence of radiation in the UV and visible region contains a concentration of polyvinyl chloride copolymer from 2.9 mass % to 12 mass %, wherein the mass percentage content is calculated based on the total mass of the paint cured under the influence of radiation in the UV and visible region. 13. The method according to any one of paragraphs. 1-11, characterized in that the paint cured under the influence of radiation in the UV and visible region contains a concentration of polyvinyl chloride copolymer from 4.9 mass % to 11.6 mass %, wherein the mass percentage content is calculated based on the total mass of the paint cured under the influence of radiation in the UV and visible region. 14. The method according to any one of paragraphs. 1-11, characterized in that the paint cured under the influence of radiation in the UV and visible region contains a concentration of polyvinyl chloride copolymer from 6 mass % to 8.6 mass %, wherein the mass percentage content is calculated based on the total mass of the paint cured under the influence of radiation in the UV and visible region. 15. The method according to any one of paragraphs 1-14, characterized in that the polyvinyl chloride copolymer is selected from the group consisting of a copolymer of vinyl chloride and vinyl acetate and a copolymer of vinyl chloride and hydroxyacrylate. 16. The method according to any one of paragraphs 1-15, characterized in that the paint cured under the influence of radiation in the UV and visible range contains a concentration of perfluoropolyether surfactant from 0.05 mass % to 5 mass %, wherein the mass percentage content is calculated based on the total mass of the paint cured under the influence of radiation in the UV and visible range. 17. The method according to any one of paragraphs 1-15, characterized in that the paint cured under the influence of radiation in the UV and visible region contains a concentration of perfluoropolyether surfactant from 0.075 mass % to 5 mass %, wherein the mass percentage content is calculated based on the total mass of the paint cured under the influence of radiation in the UV and visible region. 18. The method according to any one of paragraphs. 1-15, characterized in that the paint cured under the influence of radiation in the UV and visible region contains a concentration of perfluoropolyether surfactant from 0.1 mass % to 2.5 mass %, wherein the mass percentage is calculated based on the total mass of the paint cured under the influence of radiation in the UV and visible region. 19. The method according to any one of paragraphs 1-18, characterized in that the paint cured under the influence of radiation in the UV and visible region does not contain a solvent. 20. The method according to any one of claims 1 to 19, characterized in that step c) comprises exposing the paint layer obtained in step b) to UV and visible radiation emitted by a UV and visible radiation source selected from the group consisting of mercury lamps, UV LED lamps and sequences thereof. 21. The method of claim 20, wherein the mercury lamps are medium pressure mercury lamps. 22. The method according to any one of claims 1 to 21, further comprising steps f) and g), performed after step c): f) applying a curable protective varnish to the substrate to form a varnish layer; and g) curing the varnish layer obtained in step f) to form a protective coating. 23. The method according to claim 22, wherein the application of the curable protective varnish to the substrate in step f) is carried out by means of a printing process. 24. The method according to any one of paragraphs 1-23, characterized in that the valuable document is selected from banknotes, legal documents, tickets, checks, vouchers, revenue stamps, agreements, identity documents such as passports, identity cards, visas, driver's licenses, bank cards, credit cards, transaction cards, access documents or cards, entrance tickets, tickets for travel on public transport, a certificate of higher education and academic titles.