Security inks and machine-readable security features

Abstract

The present invention relates to the field of security inks suitable for printing machine-readable security features on substrates, security documents or articles, and machine-readable security features made from said security inks, and security documents comprising machine-readable security features made from said security inks. In particular, the present invention provides security inks comprising one or more IR-absorbing materials, said security inks having the following optical properties: a brightness L of about 80 or greater; * , saturation C below about 15 * and enables the creation of machine-readable security features having a reflectance at 900 nm of about 60% or less.

Description

Detailed Description of the Invention

[0001]

[0001] The present invention relates to the field of security inks suitable for printing machine-readable security features on a substrate, in particular a security document or article.

[0002] [Background of the invention]

[0002] Due to the ever-improving quality of color copying and printing, and to protect security documents such as banknotes, value documents or cards, transportation tickets or cards, tax strips, and product labels that do not have a reproducible effect from counterfeiting, alteration or illegal duplication, it has become conventional practice to incorporate various security features into these documents.

[0003]

[0003] Security features, for example for security documents, can be classified into "overt" and "covert" security features. Overt security features are easily detectable by unaided human senses, e.g., such features may be detectable by sight and / or touch, yet may be difficult to produce and / or copy, whereas covered security features typically require specialized equipment and knowledge for their detection.

[0004]

[0004] Machine-readable inks, such as magnetic inks, luminescent inks and infrared (IR) absorbing inks, are widely used in the field of security documents, especially in banknote printing, to create hidden security features. In the field of security and protection of valuable documents and valuable goods from counterfeiting, alteration and illegal duplication, it is known in the art to apply machine-readable security inks by various printing processes, including printing processes using high viscosity or paste-like inks, such as offset printing, letterpress and intaglio printing (also called in the art engraved steel die or copperplate printing), printing processes using liquid inks, such as rotogravure printing, flexography, screen printing and inkjet printing.

[0005]

[0005] Security features including infrared (IR) absorbing materials are widely known and used in security applications. IR absorbing materials commonly used in the field of security are based on the absorption of electromagnetic radiation by electronic transitions in the spectral range between 780 nm and 1400 nm (a range defined by the CIE (Commission Internationale de l'Eclairage)), this part of the electromagnetic spectrum is usually called the NIR region. For example, IR absorbing features are implemented in banknotes used by automated currency processing machines in banking and sales applications (automated teller machines, vending machines, etc.) to recognize the determined currency and verify its authenticity, in particular to distinguish it from copies made by color copiers. IR absorbing materials include organic compounds, inorganic materials, and glasses that contain a substantial amount of IR absorbing atoms, ions, or molecules. Typical examples of IR absorbing compounds include carbon black, quinone-diimmonium or ammonium salts, polymethines (e.g. cyanines, squaraines, croconines), phthalocyanine or naphthalocyanine type (IR absorbing π systems), dithiolenes, quaterylene diimides, metal salts, metal oxides and metal nitrides, among others.

[0006]

[0006] Due to its strong absorption in the visible range, carbon black is not a preferred security material, since said strong absorption limits the freedom to realize the design of security documents that are protected against counterfeiting or illegal copying.

[0007]

[0007] Ideally, a security feature comprising an infrared (IR) absorbing material for authentication purposes should not absorb in the visible range (400 nm to 700 nm), e.g. to enable its use in all kinds of visible pigmented inks and also in marks that are invisible or only partially visible to the naked eye, and at the same time exhibit strong absorption in the infrared or near infrared range, e.g. to enable its easy recognition by standard currency processing equipment.

[0008]

[0008] Organic NIR absorbers are generally of limited use in security applications due to their inherent poor thermal stability, poor light fastness and the complexity of their manufacture.

[0009]

[0009] Inorganic IR-absorbing compounds exhibiting improved properties are disclosed in WO 2007 / 060133 A2, which discloses an intaglio printing ink comprising an IR-absorbing material consisting of a transition element compound, the IR absorption of which is the result of electronic transitions within the d-shell of atoms or ions of the transition element.

[0010]

[0010] Therefore, there remains a need for a liquid security ink containing one or more IR absorbing materials for printing machine-readable security features which has advantages over the prior art and which is as suitable as, or even better than, known absorbers in terms of absorbing IR radiation, while at the same time having high chemical stability and high reflectance in the visible range.

[0011] [overview]

[0011] It is therefore an object of the present invention to overcome the above-mentioned deficiencies of the prior art.

[0012] In a first aspect, the present invention provides a security ink for printing a machine-readable security feature, said security ink comprising one or more IR absorbing materials, said IR absorbing materials being one or more transition elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu, and phosphate ions (PO4 3- ), hydrogen phosphate ion (HPO4 2- ), pyrophosphate ion (P2O7 4- ), metaphosphate ion (P3O9 3- ), polyphosphate ion, silicate ion (SiO4 4- ), condensed polysilicate ion; titanate ion (TiO3 2- ), condensed polytitanate ion, vanadate ion (VO4 3- ), condensed polyvanadate ion, molybdate ion (MoO4 2-), condensed molybdate ion, tungstate ion (WO4 2- ), condensed polytungstate ion, niobate ion (NbO3 2- ), fluorine ion (F - ), chloride ion (Cl - ), sulfate ion (SO4 2- ), hydroxide ion (OH - ) and mixtures thereof; The security ink has a viscosity of about 10 mPa s to about 3000 mPa s at 25° C. (the viscosity value is measured by the method described herein); The security ink has the following optical properties: a lightness L of about 80 or more (preferably about 85 or more, more preferably about 90 or more); * , chroma C of about 15 or less (preferably about 10 or less) * and enables the production of machine-readable security features having a reflectance at 900 nm of about 60% or less (preferably about 55% or less, and more preferably about 45% or less).

[0013]

[0013] A security ink prepared from the security ink described herein has the following optical properties: a brightness L of about 80 or more (preferably about 85 or more, more preferably about 90 or more); * , chroma C of about 15 or less (preferably about 10 or less) * and a reflectance at 900 nm of about 60% or less (preferably about 55% or less, more preferably about 45% or less).

[0014]

[0014] Also described and claimed in this specification is a method for generating a machine-readable security feature as described herein, said method comprising step a) of applying the security ink as described herein to a substrate, preferably by a printing process selected from the group consisting of screen printing, flexographic printing, rotogravure printing and inkjet printing.

[0015]

[0015] Also described and claimed herein is a security document that includes the machine-readable security features described herein.

[0016]

[0016] A method for authenticating a security document as described herein, comprising: a) providing a security document as described herein, comprising a machine-readable security feature made with the ink as described herein; b) illuminating the machine-readable security feature with at least one wavelength, or illuminating the machine-readable security feature with at least two wavelengths, one of the at least two wavelengths being in the visible range and another of the at least two wavelengths being in the IR range; c) detecting an optical characteristic of the machine-readable security feature by sensing light reflected or transmitted by said machine-readable security feature at at least one wavelength, or detecting an optical characteristic of the machine-readable security feature by sensing light reflected or transmitted by said machine-readable security feature at at least two wavelengths, one of said at least two wavelengths being in the visible range and another of said at least two wavelengths being in the IR range; d) determining the authenticity of the security document from the detected optical characteristics of the machine-readable security feature; Also described and claimed herein is a method comprising:

[0017]

[0017] The security ink described herein for printing the machine-readable security features described herein exhibits the following advantages over intaglio printing inks containing IR-absorbing compounds described in WO 2007 / 060133 A2:

[0018] The viscosity of the inks (10-3000 mPa s at 25° C.) is much lower than the typical viscosity of intaglio printing inks, making them printable by a wide variety of printing methods (in particular inkjet, flexographic, rotogravure and screen printing), thus offering more freedom and options to the security printer.

[0019] Intaglio printing designs are typically made up of lines with different heights and different widths, which may adversely affect the machine readability of the security feature or may require sophisticated IR detectors or strict design limitations on line height, width and spacing. The security inks described herein may be printed as flat areas with a security ink layer of approximately constant thickness, making machine readability of said security feature easier and faster.

[0020] The optical properties of the machine-readable security features made with the security inks described herein (luminosity L of about 80 or greater) * , chroma C below about 15 * , reflectance at 900 nm of about 60% or less), and in particular as a result of their colourless properties, the machine-readable security features can be located anywhere on the security document and can have any desired shape without interfering with the overall design of the document. Security features can for example be printed as codes (such as 1D codes or QR codes) that are identical within a given series (if printed with a printing method requiring a fixed printing design such as flexography, rotogravure or screen printing) or suitable for serialization (if printed with inkjet). Such designs are usually not appreciated by designers of banknotes or security documents due to their poor visual appearance.

[0021] The optical properties of the machine-readable security features made with the security inks described herein (luminosity L of about 80 or greater) * , chroma C below about 15 *As a result of this, the machine-readable security features formed with the colorless security ink, if the ink layer is thin enough, are transparent enough to be printed in windows, such as the increasingly common windows on banknotes, without affecting the visual appearance of the window while allowing readability in transmission.

[0022] Depending on the printing method (especially by rotogravure and screen printing), thick layers of the security inks described herein with high loadings of one or more IR absorbing compounds described herein can be achieved, resulting in strong machine-readable signals that make high speed sorting very reliable even when the overall area of ​​the security feature is small.

[0023] A machine-readable security feature made with the security inks described herein may be printed onto a substrate at an early stage, for example before any further printing steps. If the subsequently printed ink is IR transparent (e.g. offset printed, intaglio or iridescent ink), the ink may be used to further conceal the machine-readable security feature described herein within the overall design of the security document and / or to protect it from wear, for example due to distribution, thus extending the life of the security feature. This is particularly useful when the machine-readable security feature is printed as a code for the reasons described herein above. [Brief description of the drawings]

[0024] [Figure 1]FIG. 1 shows reflectance curves in the visible and NIR range of machine-readable security features produced by the printing process with a water-based heat-drying flexographic security ink (E1), a solvent-based heat-drying rotogravure security ink (E2), and a solvent-based heat-drying screen-printed security ink (E3), and a UV-Vis curable screen-printed security (E4) as described in the experimental part, said security inks independently comprising copper hydroxide phosphate Cu2PO4(OH) with phosphocite crystal structure as IR absorbing material.

[0025] [Detailed Description] The following definitions are used to interpret the meaning of the terms discussed in the description and recited in the claims.

[0026]

[0019] As used herein, the article "a" denotes one and more than one and does not necessarily limit the referent noun to the singular.

[0027]

[0020] As used herein, the term "about" means that the amount or value in question may be the specified value, or some other value that is approximately the same. The phrase is intended to convey that similar values ​​within ±5% of the indicated value will promote the same results or effects according to the present invention.

[0028]

[0021] As used herein, the term "and / or" or "or / and" means that either all or only one of the members of the group may be present. For example, "A and / or B" is intended to mean "only A, or only B, or both A and B."

[0029]

[0022] As used herein, the term "at least" is intended to define one or more than one, for example, one or two or three.

[0030]

[0023] The term "security document" refers to a document that is typically protected against counterfeiting or fraud by at least one security feature. Examples of security documents include, without limitation, value documents and value articles.

[0031]

[0024] The term "ultraviolet" (UV) is used to refer to the spectral range between 100 and 400 nm, "visible" (Vis) is used to refer to the spectral range between 400 and 700 nm, "infrared" (IR) is used to refer to the spectral range of wavelengths between 780 nm and 15000 nm, and near infrared (NIR) is used to refer to the spectral range of wavelengths between 780 nm and 1400 nm (the ranges are defined by the CIE (Commission Internationale de l'Eclairage) and cited in Sliney DH, Eye (the Scientific Journal of the Royal College of Ophthalmologists, 2016, 30(2), pp. 222-229)).

[0032]

[0025] The present invention provides a security ink comprising one or more IR absorbing materials as described herein for printing a machine-readable security feature. As used herein, the term "machine-readable security feature" refers to an element that exhibits at least one characteristic property detectable by a device or machine and that may be included in a layer, thereby providing a way to authenticate said layer or an article comprising said layer by the use of a specific instrument for its authentication. The machine-readable property of the security feature as described herein is embodied by one or more absorbing materials as described herein, which are included in the security ink as described herein.

[0033]

[0026] The machine-readable security features comprising one or more IR-absorbing materials described herein advantageously exhibit high reflectance in the visible range and low reflectance in the infrared or near infrared range, thus enabling efficient authentication and recognition by standard equipment and standard detectors, including those equipped with high speed banknote sorters, since such detectors rely on the difference in reflectance at selected wavelengths in the Vis and IR ranges. In particular, the security inks described herein provide a colorless or slightly colored machine-readable security feature, i.e., having the following optical properties: a lightness L of about 80 or more (preferably about 85 or more, more preferably about 90 or more). * , chroma C of about 15 or less (preferably about 10 or less) * and enables the production of a colored machine-readable security feature having a reflectance at 900 nm of about 60% or less (preferably about 55% or less, more preferably about 45% or less). * and saturation C * The L of machine-readable security features is defined according to CIELAB (1976). * a * b * It is calculated from the measurement of the value of a * and b * are color coordinates in Cartesian two-dimensional space (a * = color value along the red / green axis, b * = color value along the blue / yellow axis), L * a * b * The values ​​are obtained independently with a spectrophotometer DC 45IR from Datacolor (measurement geometry: 45 / 0°; spectrum analyzer: proprietary dual channel holographic grating. A 256-photodiode linear array is used for both reference and sample channels; light source: full bandwidth LED illumination). The substrate must have a higher IR reflectance than the machine-readable security feature in order not to affect the measured value (this is true for most colorless security substrates). From each data point, the C * and the h value was calculated.

[0034]

number

[0035]

[0027] As described herein, the reflectance at 900 nm of the machine-readable security features described herein can be measured with a spectrophotometer DC45IR from Datacolor, with 100% reflectance being measured using the device's internal standard.

[0036]

[0028] The present invention further provides the use of one or more IR absorbing materials as described herein as machine-readable compounds in a security ink as described herein for printing a machine-readable security feature on a substrate as described herein, preferably by a printing process selected from the group consisting of screen printing, flexographic printing, rotogravure printing, and inkjet printing (preferred inkjet printing processes include flextensional inkjet processes).

[0037] The security inks described herein have a viscosity of from about 10 mPa s to about 3000 mPa s. In particular, suitable viscosity ranges depend on the printing method used to produce the machine-readable security features described herein, with screen printing inks having a viscosity of about 50 mPa s to about 3000 mPa s at 25° C., flexographic printing inks having a viscosity of about 50 mPa s to about 500 mPa s at 25° C., rotogravure printing inks having a viscosity of about 50 mPa s to about 1000 mPa s at 25° C., and inkjet printing inks having a viscosity of about 10 mPa s to about 50 mPa s at 25° C. The viscosity measurements of security inks with viscosity values ​​of 100 mPa s to 3000 mPa s are carried out with a Brookfield viscometer (model “RVDV-I Prime”), the spindle and rotation speed (rpm) being adapted according to the following viscosity ranges: spindle 21 at 100 rpm for viscosity values ​​of 100 to 500 mPa s; spindle 22 at 500 rpm for viscosity values ​​of 500 to 2000 mPa s; Viscosity measurements of security inks with viscosity values ​​from 10 mPa s to 100 mPa s were performed at 25 °C and 1000 s with a TA Instruments rotational viscometer DHR-2 with cone-plane geometry and a diameter of 40 mm, using a spindle 27 at 100 rpm for viscosity values ​​from 2000 mPa s to 3000 mPa s; and at 50 rpm for viscosity values ​​from 1000 mPa s to 3000 mPa s. -1 It is held.

[0038]

[0030] The one or more IR absorbing materials described herein are preferably present in the security ink described herein in an amount of from about 5 to about 60% by weight, more preferably from about 10 to about 35% by weight, the weight percentage being based on the total weight of the security ink.

[0039]

[0031] One or more IR absorbing materials described herein are independently characterized by having a particular particle size. As used herein, the term "size" refers to a statistical property of the IR absorbing materials described herein. As known in the art, each of the one or more IR absorbing materials may be independently characterized by measuring the particle size distribution (PSD) of a sample. Such a PSD typically describes the amount of particles in a sample (relative to total number, total weight or total volume) as a function of a size-related property of the individual particles. A commonly used size-related property that describes individual particles is the "circle equivalent" (CE) diameter, which corresponds to the diameter of a circle having the same area as the orthogonal projection of the material. In this application, the following values ​​are reported:

[0040] d(v,50) (hereafter abbreviated as d50) is the value of the CE diameter in microns that separates the PSD into two parts of equal cumulative volume, the lower part representing 50% of the cumulative volume of all particles corresponding to particles with a CE diameter smaller than d50, and the upper part representing 50% of the cumulative volume of particles corresponding to particles with a CE diameter larger than d50. D50 is also known as the median of the volume distribution of the particles, d(v,98) (hereafter abbreviated as d98) is the value of the CE diameter in microns that separates the PSD into two parts with different cumulative volumes, such that the lower part represents 98% of the cumulative volume of all particles, corresponding to particles with a CE diameter smaller than d98, and the upper part represents 2% of the cumulative volume of particles with a CE diameter larger than d98.

[0041]

[0032] The one or more IR absorbing materials described herein each have a median particle size (d50 value) of about 0.01 μm to about 50 μm, more preferably about 0.1 μm to about 20 μm, even more preferably about 1 μm to about 10 μm, and / or a particle size (d98 value) of about 0.1 μm to about 100 μm, more preferably about 1 μm to about 50 μm, even more preferably about 5 μm to about 40 μm. To measure the PSD, various experimental methods are available, including, but not limited to, sieve analysis, electrical conductivity measurements (using a Coulter Counter), laser diffraction (e.g., Malvern Mastersizer), acoustic spectroscopy (e.g., Quantachrome DT-100), fractional sedimentation analysis (e.g., CPS device), and direct optical particle size distribution. The d50 and d98 provided herein were measured by laser diffraction under the following conditions: Instrument: (Cilas 1090); Sample preparation: According to ISO standard 13320, IR absorbing material was added to distilled water until the laser obscuration reached an operating level of 13-15%.

[0042]

[0033] The one or more IR absorbing materials described herein are suitable for producing machine-readable security features. The one or more IR absorbing materials described herein comprise one or more transition element compounds, whose infrared absorption is the result of electronic transitions in the d-shell of transition element atoms or ions. The one or more IR absorbing materials described herein comprise one or more transition elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. Preferably, the one or more IR absorbing materials described herein comprise one or more transition elements selected from the group consisting of Fe, Ni, and Cu, more preferably Fe and Cu, and even more preferably Cu. The one or more IR absorbing materials described herein comprise one or more transition elements selected from the group consisting of phosphate ions (PO4 3- ), hydrogen phosphate ion (HPO4 2- ), pyrophosphate ion (P2O7 4- ), metaphosphate ion (P3O9 3- ), polyphosphate ion, silicate ion (SiO44- ), condensed polysilicate ion; titanate ion (TiO3 2- ), condensed polytitanate ion, vanadate ion (VO4 3- ), condensed polyvanadate ion, molybdate ion (MoO4 2- ), condensed molybdate ion, tungstate ion (WO4 2- ), condensed polytungstate ion, niobate ion (NbO3 2- ), fluorine ion (F - ), chloride ion (Cl - ), sulfate ion (SO4 2- ), hydroxide ion (OH - ) one or more anions selected from the group consisting of:

[0043]

[0034] Preferably, the one or more IR absorbing materials described herein contain one or more transition elements selected from the group consisting of Fe and Cu, and phosphate ions (PO4 3- ), hydrogen phosphate ion (HPO4 2- ), pyrophosphate ion (P2O7 4- ), metaphosphate ion (P3O9 3- ), fluorine ion (F - ), chloride ion (Cl - ), sulfate ion (SO4 2- ) and hydroxide ion (OH - ), such as copper(II) fluoride (CuF2), copper hydroxyfluoride (CuFOH), copper hydroxide (Cu(OH)2), copper phosphate hydrate (Cu3(PO4)2 * 2H2O), anhydrous copper phosphate (Cu3(PO4)2), basic copper(II) phosphate (e.g. Cu2PO4(OH), Cu3(PO4)(OH)3, "cornetite", Cu5(PO4)3(OH)4, "pseudomalachite", CuAl6(PO4)4(OH)8·5H2O, "turquoise", etc.), copper(II) pyrophosphate (Cu2(P2O7) *3H2O), anhydrous copper(II) pyrophosphate (Cu2(P2O7)), copper(II) metaphosphate (Cu(PO3)2, more correctly written as Cu3(P3O9)2), iron(II) fluoride (FeF2 * 4H2O), anhydrous iron(II) fluoride (FeF2), iron(II) phosphate (Fe3(PO4)2 * 8H2O, "vivisite"), lithium iron(II) phosphate (LiFePO4, "triphylite"), sodium iron(II) phosphate (NaFePO4, "maricite"), iron(II) silicate (Fe2SiO4, "ferrooliticite"; FexMg2xSiO4, "olivine"), iron(II) carbonate (FeCO3, "ankerite", "siderite"), and the like. More preferably, the one or more IR absorbing materials described herein contain Cu as a transition element, as well as phosphate ions (PO4 3- ), hydrogen phosphate ion (HPO4 2- ), pyrophosphate ion (P2O7 4- ), metaphosphate ion (P3O9 3- ), polyphosphate ion and hydroxide ion (OH - ), and even more preferably phosphate ions (PO4 3- ), hydrogen phosphate ion (HPO4 2- ), pyrophosphate ion (P2O7 4- ), metaphosphate ion (P3O9 3- ), polyphosphate ion and hydroxide ion (OH - According to a preferred embodiment, at least one of the one or more IR absorbing materials described herein is Cu2PO4(OH) (CAS No: 12158-74-6), preferably Cu2PO4(OH) having a phosphocite crystal structure.

[0044]

[0035] The security inks described herein may be UV curable inks or thermally dry inks. According to one embodiment, the security inks described herein are UV curable inks or solvent-based thermally dry inks, since said inks advantageously exhibit low reflectance in the infrared or near infrared range.

[0045]

[0036] The security inks described herein are particularly suitable for application to substrates such as those described herein by a printing process selected from the group consisting of a screen printing process, a flexographic printing process, a rotogravure printing process, and an inkjet printing process (preferred inkjet printing processes include flextensional inkjet processes).

[0046]

[0037] Screen printing (also known in the art as silk screen printing) is a printing technique that uses a screen, typically made of woven mesh, to support an ink-blocking stencil. The attached stencil forms open areas of the mesh that transfer ink as a distinct image onto the substrate. A squeegee moves across the screen with the ink-blocking stencil, forcing the ink through the threads of the woven mesh in the open areas. Generally, the screen is made of a porous, finely woven piece of fabric called mesh that is stretched over, for example, an aluminum or wood frame. Currently, most meshes are made of man-made materials such as synthetic or steel threads. The preferred synthetic materials are nylon or polyester threads.

[0047] In addition to screens made on the basis of a woven mesh based on synthetic or metallic threads, screens have been developed from solid metal sheets with a grid of holes. Such screens are made by a process that includes electrolytically forming a metal screen by forming a screen skeleton on a matrix with a release agent in a first electric bath, peeling the formed screen skeleton from the matrix and subjecting said skeleton to electrolysis in a second electric bath in order to deposit metal on the screen skeleton.

[0048]

[0039] There are three types of screen printing presses: flatbed, cylinder and rotary screen printing presses. Flatbed and cylinder screen printing presses are similar in that they both use a flat screen and a three-stage reciprocating process to perform the printing operation. First the screen is moved into position over the substrate, then the squeegee is pressed against the mesh and pulled over the image area, and then the screen is lifted off the substrate to complete the process. In a flatbed press, the substrate to be printed is typically positioned on a horizontal printing bed parallel to the screen. In a cylinder press, the substrate is mounted on a cylinder. Flatbed and cylinder screen printing processes are discontinuous processes, resulting in limited speeds, typically up to 45 m / min for web or 3000 sheets / hour for sheet-fed processes.

[0049]

[0040] Rotary screen presses, on the other hand, are designed for continuous high-speed printing. The screens used in rotary screen presses are thin metal cylinders, for example, usually obtained using the electroforming method described herein above, or made of woven steel threads. The open-ended cylinders are capped at both ends and fitted into blocks on the sides of the press. During printing, ink is pumped into one end of the cylinder, thus maintaining a constant fresh supply. The squeegee is fixed inside the rotary screen, and the squeegee pressure is maintained and adjusted to allow good and consistent printing quality. The advantage of rotary screen presses is the speed, which can easily reach 150 m / min for webs, or 10,000 sheets / hour for sheet-fed processes.

[0050]

[0041] Screen printing is further described, for example, in The Printing Ink Manual, RH Leach and RJ Pierce, eds., Springer, 5th ed., pp. 58-62, Printing Technology, JM Adams and PA Dolin, Delmar Thomson Learning, 5th ed., pp. 293-328, and Handbook of Print Media, H. Kipphan, Springer, pp. 409-422 and pp. 498-499.

[0051]

[0042] Screen printing security inks are known in the art to require low viscosity. Typically, security inks suitable for screen printing processes have a viscosity in the range of about 50 mPa s to about 3000 mPa s at 25°C (e.g. using a Brookfield instrument "RVDV-I Prime", spindle 21 at 100 rpm, spindle 27 at 100 rpm, or spindle 27 at 50 rpm) in the range of about 50 mPa s to about 3000 mPa s, preferably in the range of about 100 mPa s to about 2500 mPa s, more preferably in the range of about 200 mPa s to about 2000 mPa s.

[0052]

[0043] The screen-printed security ink enables the production of machine-readable security features (i.e. dried or cured security ink layers) as described herein, which typically have values ​​of from about 3 μm to about 10 μm when a thermally dried screen-printed security ink is used, and typically have values ​​of from about 10 μm to about 30 μm when a UV-curable screen-printed security ink is used.

[0053]

[0044] The flexographic printing method preferably uses a unit with a chambered doctor blade, an anilox roller and a plate cylinder. The anilox roller advantageously has small cells whose volume and / or density determine the application rate of the protective varnish. The chambered doctor blade rests on the anilox roller and fills the cells while simultaneously scraping off the excess protective varnish. The anilox roller transfers the ink to the plate cylinder, which finally transfers the ink to the substrate. The plate cylinder may be made of a polymeric or elastomeric material. Polymers are mainly used as photopolymers for plates and occasionally as seamless coatings on sleeves. Photopolymer plates are made of photosensitive polymers that are hardened by ultraviolet (UV) light. The photopolymer plate is cut to the required size and placed in a UV light exposure unit. One side of the plate is fully exposed to UV light to harden or cure the base of the plate. The plate is then flipped over, the negative of the job is mounted on the uncured side and the plate is further exposed to UV light. This hardens the plate in the image areas. The plate is then treated to remove unhardened photopolymer from the non-image areas, which lowers the plate surface in these non-image areas. After treatment, the plate is dried and then exposed to a post-exposure dose of UV light to harden the entire plate. Preparation of plate cylinders for flexographic printing is described in Printing Technology, JM A Dams and PADolin, Delmar Thomson Learning, 5th Edition, pages 359-360.

[0054]

[0045] Flexographic security inks are known in the art to require low viscosity. Typically, security inks suitable for flexographic processes have a viscosity in the range of about 50 mPa s to about 500 mPa s at 25°C (e.g. using a Brookfield instrument "RVDV-I Prime", spindle 21 at 100 rpm).

[0055]

[0046] The flexographic security ink enables the production of the machine-readable security features described herein (i.e. the dried or cured security ink layer) which typically have a value of about 1 to about 6 μm when a thermally dried flexographic security ink is used, and typically have a value of about 2 to about 13 μm when a UV curable flexographic security ink is used.

[0056] The term rotogravure printing refers to the printing process described, for example, in "Handbook of print media", edited by Helmut Kipphan, Springer, p. 48. As known by those skilled in the art, 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 original level. Before printing, the entire printing plate (non-printing and printing elements) is inked and saturated with ink. The ink is removed from the non-image areas by a wiper or blade before printing, so that ink remains only in the cells. The image is transferred from the cells to the substrate by pressure, typically in the range of 2-4 bar, and by adhesive forces between the substrate and the ink. The term rotogravure printing does not encompass, for example, intaglio printing processes (also called engraved steel die or copperplate printing processes in the art), which rely on different types of ink.

[0057]

[0048] Rotogravure security inks are known in the art to have low viscosity. Typically, security inks suitable for the rotogravure printing process have a viscosity in the range of about 50 mPa s to about 1000 mPa s at 25°C (e.g. using a Brookfield equipment model "RVDV-I Prime", spindle 21 at 100 rpm or spindle 27 at 100 rpm).

[0058]

[0049] The rotogravure printing security inks enable the production of machine-readable security features (i.e., dried or cured security ink layers) described herein that typically have values ​​of from about 1 μm to about 10 μm when thermally dried rotogravure printing security inks are used, and typically have values ​​of from about 2 μm to about 18 μm when UV-curable rotogravure printing security inks are used.

[0059]

[0050] Flextensional inkjet printing is inkjet printing using a flextensional inkjet printhead structure. Typically, a flextensional transducer includes a body or substrate, a flexible membrane with an aperture defined therein, and an actuator. The substrate defines a reservoir for holding a supply of flowable material, and the flexible membrane has a peripheral edge supported by the substrate. The actuator may be piezoelectric (i.e., includes a piezoelectric material that deforms when a voltage is applied) or may be thermally activated, for example, as described in U.S. Pat. No. 8,226,213. Thus, when the material of the actuator deforms, the flexible membrane bends, causing the ejection of a quantity of flowable material from the reservoir through the aperture. A flextensional printhead structure is described in U.S. Pat. No. 5,828,394, which discloses a fluid ejector including one wall including a resilient membrane with an aperture defining a nozzle, and an element responsive to an electrical signal for bending the membrane to eject a droplet of fluid from the nozzle. Flextensional printhead structures are described in U.S. Pat. No. 6,394,363, which disclose, for example, the use of excitation of a surface layer incorporating nozzles arranged on one surface layer with addressability to form a liquid ejection array and are operable at high frequencies with a wide range of liquids. Flextensional printhead structures are also described in U.S. Pat. No. 9,517,622, which describes a droplet forming device comprising a film member configured to vibrate to eject liquid held in a liquid holding unit, the nozzles being formed in the film member. The device further comprises a vibration unit for vibrating the film member; and a drive unit for selectively applying ejection and agitation waveforms to the vibration unit. Flextensional printhead structures are also described in U.S. Pat. No. 8,226,213, which describes a method of actuating a thermal bending actuator having an active beam fused to a passive beam. The method includes passing a current through the active beam, resulting in a thermoelastic expansion of the active beam relative to the passive beam and bending of the actuator.

[0060] Flextensional inkjet printing security inks are known in the art to have very low viscosities. Typically, security inks suitable for flextensional inkjet printing processes have viscosities in the range of about 10 mPa s to about 50 mPa s (e.g., measured at 25° C. and 1000 s using a TA Instruments rotational viscometer DHR-2 with cone-plane geometry and 40 mm diameter). -1 Used in.

[0061]

[0052] The thickness of the machine-readable security features described herein (i.e., the dried or cured security ink layer) produced by flextensional inkjet printing depends essentially on the particle size of the one or more IR-absorbing compounds and is preferably from about 0.05 μm to about 10 μm (dried or cured ink layer), more preferably from about 0.1 μm to about 5 μm, and even more preferably from about 0.5 μm to about 2 μm.

[0062]

[0053] According to one embodiment, the security ink described herein is a UV curable ink comprising one or more photoinitiators, said one or more photoinitiators preferably in an amount of from about 0.1% to about 20% by weight, more preferably from about 1% to about 15% by weight, the weight percentage being based on the total weight of the security ink.

[0063]

[0054] Preferably, the UV-Vis curable security ink described herein comprises one or more UV curable compounds, which are monomers and oligomers selected from the group consisting of radically curable compounds and cationically curable compounds. The security ink described herein may be a hybrid system and comprise a mixture of one or more cationically curable compounds and one or more radically curable compounds. The cationically curable compounds are cured by a cationic mechanism, which typically involves the activation by radiation of one or more photoinitiators, which liberate cationic species, such as acids, which then initiate the curing to react and / or crosslink the monomers and / or oligomers, thereby curing the security ink. The radically curable compounds are cured by a free radical mechanism, which typically involves the activation by radiation of one or more photoinitiators, which then generate radicals which then initiate the polymerization, thereby curing the security ink.

[0064]

[0055] Preferably, the UV-Vis curable security inks described herein comprise one or more cationically curable oligomers (also referred to in the art as prepolymers) selected from the group consisting of oligomeric (meth)acrylates, vinyl ethers, propenyl ethers, cyclic ethers such as epoxides, oxetanes, tetrahydrofurans, lactones, cyclic thioethers, vinyl and propenyl thioethers, hydroxyl-containing compounds, and mixtures thereof. More preferably, the UV-Vis curable security inks described herein comprise one or more oligomers selected from the group consisting of oligomeric (meth)acrylates, vinyl ethers, propenyl ethers, cyclic ethers such as epoxides, oxetanes, tetrahydrofurans, lactones, and mixtures thereof. Representative examples of epoxides include, but are not limited to, glycidyl ethers, β-methyl glycidyl ethers of aliphatic or cycloaliphatic diols or polyols, glycidyl ethers of diphenols and polyphenols, glycidyl esters of polyhydric phenols, 1,4-butanediol diglycidyl ether of phenolformalhedhyde novolacs, resorcinol diglycidyl ethers, alkyl glycidyl ethers, glycidyl ethers including copolymers of acrylic esters (e.g., styrene-glycidyl ethers), glycidyl ethers of glycidyl ethers of styrene-glycidyl ethers, ... Examples of suitable epoxides include glycidyl methacrylate or methyl methacrylate-glycidyl acrylate), polyfunctional liquid and solid novolac glycidyl ether resins, polyglycidyl ethers and poly(β-methylglycidyl) ethers, poly(N-glycidyl) compounds, poly(S-glycidyl) compounds, epoxy resins in which glycidyl or β-methylglycidyl groups are bonded to different types of heteroatoms, glycidyl esters of carboxylic and polycarboxylic acids, limonene monoxide, epoxidized soybean oil, bisphenol-A and bisphenol-F epoxy resins. Examples of suitable epoxides are disclosed in EP 2125713. Suitable examples of aromatic, aliphatic or cycloaliphatic vinyl ethers include, without limitation, compounds having at least one, preferably at least two, vinyl ether groups in the molecule.Examples of vinyl ethers include, but are not limited to, triethylene glycol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether, 4-hydroxybutyl vinyl ether, propenyl ether of propylene carbonate, dodecyl vinyl ether, tert-butyl vinyl ether, tert-amyl vinyl ether, cyclohexyl vinyl ether, 2-ethylhexyl vinyl ether, ethylene glycol monovinyl ether, butanediol monovinyl ether, hexanediol monovinyl ether, 1,4-cyclohexanedimethanol monovinyl ether, diethylene glycol monovinyl ether, ethylene glycol di ... Examples of hydroxy-containing compounds include, but are not limited to, polyester polyols such as polycaprolactone or polyester adipate polyols, glycols and polyether polyols, castor oil, hydroxy-functional vinyl and acrylic resins, cellulose esters such as cellulose acetate butyrate, and phenoxy resins. Further examples of suitable cationically curable compounds are disclosed in EP 2125713 and EP 0119425.

[0065] According to one embodiment of the present invention, the UV-Vis curable security ink described herein comprises one or more radically curable oligomeric compounds selected from (meth)acrylates, preferably selected from the group consisting of epoxy (meth)acrylates, (meth)acrylated oils, polyester (meth)acrylates, aliphatic or aromatic urethane (meth)acrylates, silicone (meth)acrylates, amino (meth)acrylates, acrylic (meth)acrylates, and mixtures thereof. The term "(meth)acrylate" in the context of the present invention refers to acrylates and the corresponding methacrylates. The components of the UV-Vis curable security inks described herein may be formulated with additional vinyl ethers and / or monomeric acrylates such as trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PTA), tripropylene glycol diacrylate (TPGDA), dipropylene glycol diacrylate (DPGDA), hexanediol diacrylate (HDDA), and the like, and their polyethoxylated equivalents such as polyethoxylated trimethylolpropane triacrylate, polyethoxylated pentaerythritol triacrylate, polyethoxylated tripropylene glycol diacrylate, polyethoxylated dipropylene glycol diacrylate, and polyethoxylated hexanediol diacrylate.

[0066]

[0057] Alternatively, the UV-Vis curable security inks described herein may be hybrid inks and prepared from a mixture of radically curable and cationically curable compounds such as those described herein.

[0067]

[0058] As mentioned above, UV-Vis curing of monomers, oligomers requires the presence of one or more photoinitiators and can be carried out in several ways. As mentioned herein and known to those skilled in the art, the UV-Vis curable security inks described herein that are cured and hardened on substrates such as those described herein comprise one or more photoinitiators, optionally with one or more photosensitizers, said one or more photoinitiators and optional one or more photosensitizers being selected according to their / their (one or more) absorption spectrum in relation to the emission spectrum of the radiation source. Depending on the penetration of the electromagnetic radiation through the substrate, hardening of the security ink can be obtained by increasing the exposure time. However, depending on the substrate material, the exposure time is limited by the substrate material and its sensitivity to the heat generated by the radiation source.

[0068] Depending on the monomers, oligomers or prepolymers used in the UV-Vis curable security inks described herein, various photoinitiators may be used. Suitable examples of free radical photoinitiators are known to those skilled in the art and include, but are not limited to, acetophenone, benzophenone, benzil dimethyl ketal, alpha-amino ketones, alpha-hydroxy ketones, phosphine oxides and phosphine oxide derivatives, and mixtures of two or more thereof. Suitable examples of cationic photoinitiators are known to those skilled in the art and include, but are not limited to, onium salts, such as organic iodonium salts (e.g. diaryliodonium salts), oxonium (e.g. triaryloxonium salts) and sulfonium salts (e.g. triarylsulfonium salts), and mixtures of two or more thereof. Other examples of useful photoinitiators can be found in standard textbooks such as "Chemistry & Technology of UV & EB Formulation for Coatings, Inks & Paints", Vol. 3, "Photoinitiators for Free Radical Cationic and Anionic Polymerization", 2nd Edition, by JV Crivello & K. Dietliker, edited by G. Bradley, published in 1998 by John Wiley & Sons in collaboration with SITA Technology Limited. It may also be advantageous to include a sensitizer in conjunction with one or more photoinitiators to achieve efficient curing. Typical examples of suitable photosensitizers include, without limitation, isopropyl-thioxanthone (ITX), 1-chloro-2-propoxy-thioxanthone (CPTX), 2-chloro-thioxanthone (CTX) and 2,4-diethyl-thioxanthone (DETX), and mixtures of two or more thereof.

[0069]

[0060] According to one embodiment, the UV-Vis curable security ink described herein is a UV-Vis curable screen printed security ink comprising one or more photoinitiators as described herein, one or more UV curable compounds that are monomers and oligomers as described herein, and optional additives or components as described herein.

[0070]

[0061] According to one embodiment, the UV-Vis curable security ink described herein is a UV-Vis curable flexographic security ink comprising one or more photoinitiators as described herein, one or more UV curable compounds that are monomers and oligomers as described herein, and optional additives or components as described herein.

[0071]

[0062] According to one embodiment, the UV-Vis curable security ink described herein is a UV-Vis curable rotogravure security ink, said UV-Vis curable rotogravure security ink comprising one or more photoinitiators as described herein, one or more UV curable compounds that are monomers and oligomers as described herein, and optional additives or components as described herein.

[0072]

[0063] According to one embodiment, the UV-Vis curable security ink described herein is a UV-Vis curable inkjet printed security ink, preferably a flextensional inkjet printed security ink, said UV-Vis curable flextensional inkjet printed security ink comprising one or more photoinitiators as described herein, one or more UV curable compounds which are monomers and oligomers as described herein, and optionally additives or components as described herein.

[0073] According to one embodiment, the security ink described herein is a heat-drying ink comprising one or more solvents selected from the group consisting of organic solvents, water and mixtures thereof, said one or more solvents being preferably in an amount of about 10% to about 90% by weight, the weight percentage being based on the total weight of the security ink. Heat-drying security inks comprise security inks that are dried by hot air, infrared radiation or a combination thereof. Heat-drying security inks typically comprise about 10% to about 90% by weight of solids remaining on the print substrate and about 10% to about 90% by weight of one or more solvents that evaporate as a result of drying.

[0074]

[0065] Preferably, the organic solvent described herein is selected from the group consisting of alcohols (e.g., ethanol), ketones (e.g., methyl ethyl ketone), esters (e.g., ethyl acetate, propyl acetate, and isopropyl acetate), glycol ethers, and glycol ether esters (e.g., butyl glycol acetate and dipropylene glycol monomethyl ether), and mixtures thereof.

[0075]

[0066] According to one embodiment, the heat-drying security ink described herein comprises a water-based heat-drying security ink comprising one or more resins selected from the group consisting of polyester resins, polyether resins, polyurethane resins (e.g., carboxylated polyurethane resins), polyurethane alkyd resins, polyurethane-acrylate resins, poly(meth)acrylate resins, polyether urethane resins, styrene acrylate resins, polyvinyl alcohol resins, poly(ethylene glycol) resins, polyvinylpyrrolidone resins, polyethyleneimine resins, modified starches, cellulose esters or ethers (e.g., cellulose acetate and carboxymethyl cellulose), copolymers, and mixtures thereof.

[0076]

[0067] According to one embodiment, the heat-drying security ink described herein comprises a solvent-based heat-drying security ink comprising one or more resins selected from the group consisting of nitrocellulose, methylcellulose, ethylcellulose, cellulose acetate, polyvinyl butyral, polyurethane, poly(meth)acrylate (including but not limited to poly(meth)acrylate polymers and copolymers soluble in alkaline solutions), polyamide, polyester, polyvinyl acetate, vinyl chloride copolymer, rosin-modified phenolic resins, phenolic resins, maleic resins, styrene-acrylic resins, polyketone resins, and mixtures thereof.

[0077]

[0068] According to one embodiment, the thermal drying security ink described herein is a thermal drying screen printed security ink, said thermal drying screen printed security ink comprising one or more solvents described herein, one or more resins described herein, and optional additives or components described herein.

[0078]

[0069] According to one embodiment, the thermal drying security ink described herein is a thermal drying flexographic printing security ink, said thermal drying screen printing security ink comprising one or more solvents described herein, one or more resins described herein, and optional additives or components described herein.

[0079]

[0070] According to one embodiment, the heat-drying security ink described herein is a heat-drying rotogravure printing security ink, said heat-drying screen printing security ink comprising one or more solvents described herein, one or more resins described herein, and optional additives or components described herein.

[0080]

[0071] According to one embodiment, the thermal drying security ink described herein is a thermal drying inkjet printed security ink, preferably a flextensional inkjet printed security ink, said thermal drying ink comprising one or more solvents as described herein, one or more resins as described herein, and optionally additives or components as described herein.

[0081]

[0072] The security inks described herein may further comprise one or more fillers or extenders, provided that these potential additional fillers or extenders do not detrimentally interfere with the absorption characteristics in the IR / NIR range of the spectrum of the subject of the machine-readable security feature, and do not adversely interfere with the optical characteristics described herein (such as a brightness L of about 80% or more) of the machine-readable security feature described herein. * , chroma C below about 15 * and reflectance at 900 nm of about 60% or less). The one or more fillers or extenders described herein are preferably selected from the group consisting of carbon fiber, talc, mica (muscovite), wollastonite, calcined clay, china clay, kaolin, carbonates (e.g. calcium carbonate, sodium aluminum carbonate), silica and silicates (e.g. magnesium silicate, aluminum silicate), sulfates (e.g. magnesium sulfate, barium sulfate), titanates (e.g. potassium titanate), hydrated alumina, silica, fumed silica, montmorillonite, graphite, anatase, rutile, bentonite, vermiculite, zinc white, zinc sulfide, wood flour, quartz flour, natural fibers, synthetic fibers, and combinations thereof. Alternatively, and the optical properties described herein (brightness L of about 80% or more) of the machine-readable security features described herein may be selected from the group consisting of carbon fiber, talc, mica (muscovite), wollastonite, calcined clay, china clay, kaolin, carbonates (e.g. calcium carbonate, sodium aluminum carbonate), silica and silicates (e.g. magnesium silicate, aluminum silicate), sulfates (e.g. magnesium sulfate, barium sulfate), titanates (e.g. potassium titanate), hydrated alumina, silica, fumed silica, montmorillonite, graphite, anatase, rutile, bentonite, vermiculite, zinc white, zinc sulfide, wood flour, quartz flour, natural fibers, synthetic fibers, and combinations thereof. * , chroma C below about 15 *Microspheres or hollow spheres made of polymers (e.g., polystyrene or PMMA) or made of glass may be used as one or more fillers or extenders, with the aim of not reducing the reflectance at 900 nm (reflectance at 900 nm of about 60% or less). When present, the one or more fillers or extenders are preferably present in an amount of about 0.01 to about 10% by weight, preferably about 0.1 to about 5% by weight, the weight percentage being based on the total weight of the security ink.

[0082] The security inks described herein may further comprise one or more colorants (pigments or dyes), provided that said one or more colorants do not detrimentally interfere with the absorption characteristics in the IR / NIR range of the spectrum of the subject of the machine-readable security feature, and do not detrimentally interfere with the optical characteristics described herein (lightness L of about 80% or more) of the machine-readable security feature described herein. * , chroma C below about 15 * and reflectance at 900 nm of about 60% or less. Alternatively, the colorant(s) may be used as a shading additive, i.e., an additive to offset slight color shifts induced by the IR absorbing compound(s) or to better match the color of the substrate or underlying layer.

[0083]

[0074] The security inks described herein may further comprise one or more pearlescent pigments and / or one or more cholesteric liquid crystal pigments. Typical examples of pearlescent pigments include, but are not limited to, interference coating pigments consisting of a core made of synthetic or natural mica, other layered silicates (e.g. talc, kaolin and sericite), glass (e.g. borosilicate), silicon dioxide (SiO2), aluminum oxide (Al2O3), aluminum oxide / hydroxide (boehmite), and mixtures thereof, coated with one or more layers made of metal oxides (e.g. titanium oxide, zirconium oxide, tin oxide, chromium oxide, nickel oxide, copper oxide, iron oxide and iron oxide / hydroxide). The structures described herein above are described, for example, in Chem. Rev. 99 (1999), G. Pfaff and P. Reynders, pp. 1963-1981 and WO 2008 / 083894 A2. Typical examples of these interference coated pigments include, but are not limited to, silicon oxide cores coated with one or more layers made of titanium oxide, tin oxide and / or iron oxide; natural or synthetic mica cores coated with one or more layers made of titanium oxide, silicon oxide and / or iron oxide, in particular mica cores coated with alternating layers made of silicon oxide and titanium oxide; borosilicate cores coated with one or more layers made of titanium oxide, silicon oxide and / or tin oxide; titanium oxide cores coated with one or more layers made of iron oxide, iron oxide / hydroxide, chromium oxide, copper oxide, cerium oxide, aluminum oxide, silicon oxide, bismuth vanadate, nickel titanate, cobalt titanate and / or antimony-doped, fluorine-doped or indium-doped tin oxide; aluminum oxide cores coated with one or more layers made of titanium oxide and / or iron oxide. Cholesteric liquid crystal pigments are based on liquid crystals in the cholesteric phase that exhibit a molecular order in the form of a helical superstructure perpendicular to the long axis of the molecules. The helical superstructure is the origin of a periodic refractive index modulation throughout the liquid crystal material, which on the one hand results in the selective transmission / reflection of light of defined wavelengths (interference filter effect).Cholesteric liquid crystal polymers can be obtained by subjecting one or more crosslinkable substances (nematic compounds) with a chiral phase to alignment and orientation. The specific situation of helical molecular arrangement results in a cholesteric liquid crystal material that exhibits the property of reflecting circularly polarized light components in a defined wavelength range. In particular, by changing the nature of the chiral components and the ratio of nematic to chiral compounds, the pitch can be adjusted by varying selectable factors including temperature and solvent concentration. Crosslinking under the influence of UV radiation freezes the pitch in a predefined state by fixing the desired helical morphology, so that the color of the resulting cholesteric liquid crystal material is no longer dependent on external factors such as temperature. The cholesteric liquid crystal material can then be formed into a cholesteric liquid crystal pigment by subsequently powdering the polymer to the desired particle size. Examples of films and pigments made from cholesteric liquid crystal materials and their preparation are disclosed in U.S. Pat. No. 5,211,877; U.S. Pat. No. 5,362,315 and U.S. Pat. No. 6,423,246 and European Patent Application Publication No. 1213338; ​​European Patent Application Publication No. 1046692 and European Patent Application Publication No. 0601483, the disclosures of each of which are incorporated herein by reference.

[0084]

[0075] The security inks described herein may comprise one or more further IR absorbers known in the art. The role of said further IR absorbers may be to slightly modify the reflectance profile of the machine-readable security feature, for example to fully suit the specifications of a detection system. Preferably, said one or more further IR absorbers are selected from the group consisting of doped tin oxide, doped indium oxide, reduced tungsten oxide, tungsten bronze and mixtures thereof. If present, the amount of one or more further IR absorbers is between about 0.5% and about 25% by weight, the weight percentage being relative to the total weight of the security ink. If present, the ratio between one or more further IR absorbers and the sum of all IR absorbers is preferably between about 0.1% and about 30% by weight, more preferably between about 1% and about 15% by weight.

[0085] According to one embodiment, one of the one or more additional IR absorbers is a doped tin oxide, which is preferably doped with antimony (antimony tin oxide, ATO), and the antimony is present in an amount of about 0.5 to about 20 mol %, preferably about 2 to about 18 mol %.

[0086] According to another embodiment, one of the one or more further IR absorbers is doped indium oxide, preferably doped with tin (indium tin oxide, ITO), the tin being present in an amount of about 1 to about 30 mol %, preferably about 5 to about 15 mol %. Preferably, reduced indium tin oxide is used as the one or more further IR absorbers. The level of reduction is preferably about 0.1 mol % to about 5 mol %, more preferably about 0.5 mol % to about 1 mol %, a level of reduction of 1 mol % meaning that oxygen atoms have been removed from 1% of the indium tin oxide units.

[0087] According to another embodiment, one of the one or more further IR absorbers is reduced tungsten oxide and / or one of the one or more further IR absorbers is tungsten bronze. Reduced tungsten oxide has the general formula W y O z where the ratio z / y is greater than 2 and less than 3, preferably greater than 2.2 and less than 2.99, more preferably greater than 2.7 and less than 2.9. Such compounds are described, for example, in H. Takeda and K. Adachi, J. Am Ceram. Soc., 90

[12] , 2007, pp. 4059-4061, U.S. Patent Application Publication No. 2006 / 0178254 and U.S. Patent Application Publication No. 2007 / 0187653.

[0088]

[0079] Tungsten bronzes are non-stoichiometric compounds obtained from stoichiometric tungsten oxide WO3 or metal tungstates MWO4. x W y O zThe tungsten bronzes of M x W y O z are described, for example, in U.S. Patent Application Publication No. 2006 / 0178254 and U.S. Patent Application Publication No. 2007 / 0187653. U.S. Patent Application Publication No. 2006 / 0178254 discloses M x W y O z where 0.001 ≦ x / y ≦ 1 and 2.2 ≦ z / y ≦ 3.0. x W y O z U.S. Patent Application Publication No. 2007 / 0187653 discloses M x W y O z where 0.001 ≦ x / y ≦ 1.1 and 2.2 ≦ z / y ≦ 3.0. x W y O z M is at least one element selected from the group consisting of H, He, alkali metals, alkaline earth metals, rare earth elements, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi, and I, preferably Na, Cs, Rb, K, Tl, In, Ba, Li, Ca, Sr, Fe, and Sn.

[0089]

[0080] The tungsten bronzes of the formula M x WO3 are described, for example, in U.S. Patent Application Publication No. 2006 / 0178254 and U.S. Patent Application Publication No. 2007 / 0187653. In the formula, M is a metal element, such as an alkali metal, an alkaline earth metal, or a rare earth metal, and 0 < x < 1. Such a compound with M = K is also described in C. Guo et al., ACS Appl. Mater. Interfaces, 3, 2011, pages 2794 - 2799, and it has been shown to exhibit strong absorption beyond 900 nm. x WO3

[0090]

[0081] The formula M E A G W (1-G) O J E A G W (1-G) O JTungsten bronzes of the formula (I) are described, for example, in U.S. Patent Application Publication No. 2007 / 0187653, wherein M is one or more elements selected from H, He, alkali metals, alkaline earth metals, rare earth metals, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi, and I; A is one or more elements selected from Mo, Nb, Ta, Mn, V, Re, Pt, Pd, and Ti; W is tungsten; O is oxygen; and <E≦1.2であり;0<G≦1であり;2≦J≦3である。

[0091] US Patent Application Publication No. 201 / 0248225 describes, for example, x Cs y WO z where x+y≦1 and 2≦z≦3. Such compounds have been shown to be strong absorbers in the range of 1200-1750 nm.

[0092]

[0083] The security inks described herein may further comprise one or more luminescent compounds, for example to provide the security feature with improved counterfeit resistance.

[0093]

[0084] The security inks described herein may further comprise one or more marker substances or taggants.

[0094]

[0085] The security inks described herein may further comprise one or more additives, including, without limitation, compounds and materials used to adjust the physical, rheological and chemical parameters of the security ink, such as consistency (e.g. anti-settling agents and plasticizers), foaming properties (e.g. defoamers and degassing agents), lubricating properties (waxes), UV stability (light stabilizers), adhesion properties, surface properties (wetting agents, oleophobic and hydrophobic agents), drying / curing properties (curing accelerators, sensitizers, crosslinkers), etc. The additives described herein may be present in the security inks described herein in any amount and form known in the art, including the form of so-called nanomaterials, where at least one of the dimensions of the additive is in the range of 1-1000 nm.

[0095]

[0086] The present invention further provides a method for producing the security ink described herein, and the security ink obtained therefrom. The security ink described herein may be prepared by dispersing or mixing one or more of the IR absorbing materials described herein, and all other ingredients to form said ink. If the security ink described herein is a UV-VIS curable security ink, the one or more photoinitiators may be added to the composition during the dispersing or mixing step of all other ingredients, or may be added at a later stage, i.e. after the formation of the ink. The varnishes, binders, resins, compounds, monomers, oligomers, resins and additives are typically selected from among those known in the art and described above, depending on the printing process used to apply the security ink described herein to the substrate described herein.

[0096]

[0087] The security inks described herein are preferably applied to the substrates described herein to produce machine-readable security features by a printing process selected from the group consisting of a screen printing process, a rotogravure printing process, a flexographic printing process and an inkjet printing process (preferred inkjet printing processes include flextensional inkjet processes).

[0097]

[0088] The present invention further provides a method for producing a machine-readable security feature as described herein, and the resulting machine-readable security feature, comprising the step a) of applying a security ink as described herein to a substrate as described herein, preferably by a printing process selected from the group consisting of screen printing, flexographic printing, rotogravure printing and inkjet printing (preferred inkjet printing processes include flextensional inkjet processes).

[0098]

[0089] After the printing step, a step b) is performed of drying and / or curing the security ink in the presence of UV-VIS radiation and / or air or heat, thereby forming a machine-readable security feature as described herein on the substrate, said step of drying and / or curing being performed after step a). The time between step a) (i.e. step a) of applying, preferably by a printing process) and step b) (i.e. step b) of drying and / or curing) is preferably from about 0.1 seconds to about 10 seconds, more preferably from about 0.2 seconds to about 5 seconds, even more preferably from about 0.5 seconds to about 2 seconds.

[0099]

[0090] The present invention further provides a machine-readable security feature made with the security ink described herein on a substrate described herein.

[0100]

[0091] The substrate described herein is preferably selected from the group consisting of paper or other fibrous materials (including woven and nonwoven fibrous materials), such as cellulose, paper-containing materials, glass, metal, ceramic, plastics and polymers, metallized plastics or polymers, composite materials, and mixtures or combinations of two or more thereof. Typical paper, paper-like or other fibrous materials are made from a variety of fibers, including, but not limited to, hemp, cotton, linen, wood pulp, and blends thereof. As is well known to those skilled in the art, cotton and cotton / linen blends are preferred for banknotes, while wood pulp is commonly used in security documents other than banknotes. Typical examples of plastics and polymers include polyolefins, such as polypropylene (PP), including polyethylene (PE) and biaxially oriented polypropylene (BOPP), polyamides, polyesters, such as poly(ethylene terephthalate) (PET), poly(1,4-butylene terephthalate) (PBT), poly(ethylene 2,6-naphthoate) (PEN), and polyvinyl chloride (PVC). Spunbond olefin fibers, such as those sold under the trademark Tyvek®, may also be used as the substrate. Typical examples of metallized plastics or polymers include the plastic or polymer materials described above having metals disposed continuously or discontinuously on the surface. Typical examples of metals include, but are not limited to, aluminum (Al), chromium (Cr), copper (Cu), gold (Au), silver (Ag), alloys thereof, and combinations of two or more of the above-mentioned metals. Metallization of the plastic or polymer materials described above may be performed by an electrodeposition process, a high vacuum coating process, or by a sputtering process. Typical examples of composite materials include, but are not limited to, multi-layer structures or laminates of paper and at least one plastic or polymer material, such as those described above, as well as plastic and / or polymer fibers incorporated in paper-like or fibrous materials, such as those described above. Of course, the substrate may include further additives known to those skilled in the art, such as, for example, fillers, sizing agents, brighteners, processing aids, reinforcing or wet strength agents.

[0101]

[0092] With a view to further increasing the security level of the security document and its resistance to counterfeiting and illegal duplication, the substrates described herein may contain printed, coated or laser marked or laser drilled indicia, watermarks, security threads, fibers, planchets, luminescent compounds, windows, foils, decals, primers and combinations of two or more thereof, provided that these potential additional features or elements do not detrimentally interfere with the absorption characteristics in the IR / NIR range of spectrum of interest of the machine-readable security feature and do not detrimentally interfere with the optical characteristics described herein (brightness L of about 80% or more) of the machine-readable security feature described herein. * , chroma C below about 15 * and reflectance at 900 nm of about 60% or less).

[0102]

[0093] One or more protective layers may be applied onto the machine-readable security feature or security document described herein in order to increase the durability or chemical resistance to fouling and cleanability and thus the circulation life of the security document, or to modify its aesthetic appearance (e.g. optical gloss). If present, the one or more protective layers are typically made of a protective varnish, which may be clear or slightly pigmented or tinted and may also have more or less gloss. The protective varnish may be a radiation curable composition, a heat drying composition or any combination thereof. Preferably, the one or more protective layers are made of a radiation curable composition, more preferably a UV-Vis curable composition.

[0103]

[0094] The machine-readable security features described herein may be provided directly on the substrate on which the security feature is to remain permanently (e.g. in banknote applications). In some cases, the machine-readable security features described herein may be produced on an auxiliary substrate, such as a security thread, a security stripe, a foil, a decal, a window or a label, and subsequently transferred to the security document in a separate step. Alternatively, the machine-readable security features may also be provided on a temporary substrate for production purposes, from which the machine-readable security features are subsequently removed. Then, after hardening / curing of the security ink described herein for the production of the machine-readable security features, the temporary substrate may be removed from the machine-readable security features.

[0104]

[0095] Alternatively, in another embodiment, an adhesive layer may be present on the machine-readable security feature or on the substrate comprising the machine-readable security feature described herein, said adhesive layer being on the substrate opposite to the side on which the machine-readable security feature is provided or on the same side of the machine-readable security feature as the machine-readable security feature. Thus, an adhesive layer may be applied to the machine-readable security feature or to the substrate, said adhesive layer being applied after a drying or curing step is completed. Such an article may be attached to all kinds of documents, or other articles or goods, without printing or other processes involving machines and somewhat high labor. Alternatively, the substrate described herein comprising the machine-readable security feature described herein may be in the form of a transfer foil that can be applied to the document or article in a separate transfer step. For this purpose, the substrate is provided with a release coating on which the machine-readable security feature is generated as described herein. On top of the machine-readable security feature so generated, one or more adhesive layers may be applied.

[0105]

[0096] Also described herein are substrates, security documents, decorative elements and objects comprising two or more machine-readable security features as described herein, i.e. two, three, four etc. Also described herein are articles, in particular security documents, decorative elements or objects, comprising machine-readable security features as described herein.

[0106]

[0097] As mentioned above, the machine-readable security features described herein may be used for protection and authentication of security documents or decorative elements.

[0107]

[0098] Typical examples of decorative elements or objects include, without limitation, luxury goods, cosmetic packaging, automobile parts, electronic / electrical products, furniture, and nail articles.

[0108]

[0099] The security document includes, without limitation, valuable documents and valuable goods. Typical examples of valuable documents include, without limitation, banknotes, certificates, vouchers, cheques, vouchers, revenue stamps and tax marks, contracts, etc., identity documents such as passports, ID cards, visas, driver's licenses, bank cards, credit cards, transaction cards, access documents or cards, admission tickets, public transport tickets, graduation certificates or title deeds, etc., preferably banknotes, identity cards, title documents, driver's licenses and credit cards. The term "valuable goods" refers to packaging materials for items that should be protected against counterfeiting and / or illegal copying, in particular cosmetics, dietary supplements, medicinal products, alcohol, tobacco products, beverages or foodstuffs, electrical / electronic products, textiles or jewelry, i.e., to ensure the contents of the package, such as genuine drugs. Examples of these packaging materials include, without limitation, labels, such as authentication brand labels, tamper-proof labels and seals. It is pointed out that the disclosed substrates, valuable documents and valuable goods are given for illustrative purposes only and do not limit the scope of the present invention.

[0109]

[0100] A machine-readable security feature comprising one or more IR absorbing materials as described herein may consist of a pattern, image, indicia, logo, text, numbers, or a code (such as a barcode or QR code).

[0110]

[0101] The present invention further provides a method for authenticating a security document comprising the steps of: a) providing a security document as described herein comprising a machine-readable security feature made with a security ink as enumerated herein; b) illuminating the machine-readable security feature with at least one wavelength in the IR range (preferably 780nm - 3000nm, more preferably 780nm - 1600nm, even more preferably 800nm ​​- 1000nm); c) detecting an optical property of the machine-readable security feature by sensing light reflected by and / or transmitted through said machine-readable security feature at at least one wavelength, wherein said at least one wavelength is in the IR range (preferably 780nm - 3000nm, more preferably 780nm - 1600nm, even more preferably 800nm ​​- 1000nm); and d) determining authenticity of the security document from the detected optical property of the machine-readable security feature.The present invention also provides a method for authenticating a security document, comprising the steps of: a) providing a security document as described herein, comprising a machine-readable security feature made with a security ink as enumerated herein; b) illuminating the machine-readable security feature with at least two wavelengths, one of the at least two wavelengths being in the visible range (400-700 nm) and another of the at least two wavelengths being in the IR range (preferably 780 nm-3000 nm, more preferably 780 nm-1600 nm, even more preferably 800-1000 nm); and c) illuminating the machine-readable security feature with at least two wavelengths, one of the at least two wavelengths being in the visible range (400-700 nm) and another of the at least two wavelengths being in the IR range (preferably 780 nm-3000 nm, more preferably 780 nm-1600 nm, even more preferably 800-1000 nm). The present invention further provides a method comprising the steps of: detecting an optical property of a machine-readable security feature by sensing light reflected by and / or transmitted through said machine-readable security feature at two wavelengths, one of said at least two wavelengths being in the visible range and another of said at least two wavelengths being in the IR range (preferably 780nm - 3000nm, more preferably 780nm - 1600nm, even more preferably 800nm ​​- 1000nm); and d) determining the authenticity of the security document from the detected optical property of the machine-readable security feature.

[0111]

[0102] Authentication of the machine-readable security features described herein and made with the security inks described herein may be performed by using an authentication device comprising one or more light sources, one or more detectors, an analog-to-digital converter and a processor. The machine-readable security features are simultaneously or successively illuminated by one or more light sources, one or more detectors detect the light reflected by or transmitted through said machine-readable security features and output an electrical signal proportional to the light intensity, and an analog-to-digital converter converts said signal into digital information which is compared by the processor to reference values ​​stored in a database. The authentication device then outputs a positive signal of authenticity (i.e. the machine-readable security feature is genuine) or a negative signal (i.e. the machine-readable security feature is fake).

[0112] According to one embodiment, the authentication device comprises a first source (e.g. VIS LED) emitting at a first wavelength in the visible range, a second source (e.g. IR LED) emitting at a second wavelength in the IR range, and a broadband detector (e.g. photomultiplier tube). The first and second sources emit light at time intervals, causing the broadband detector to output separate signals corresponding to the VIS and IR emissions, respectively. These two signals can be compared separately (VIS signal with a VIS reference value, IR signal with an IR reference value). Alternatively, these two signals can be converted into a difference (or ratio) value, which can be compared to a difference (or ratio) reference value stored in a database. The signals can be read out in reflection and / or transmission.

[0113]

[0104] According to another embodiment of the detector unit, with the aim of increasing the operating speed, said detector may comprise two detectors specifically adapted to the emission wavelengths of the first and second sources (for example a Si photodiode for the visible range and an InGaAs photodiode for the IR range). The first and second sources emit light simultaneously and the two detectors simultaneously detect the light reflected by or transmitted through the security feature, and the two signals (or their difference or ratio) are compared with reference values ​​stored in a database.

[0114]

[0105] According to another embodiment, with the aim of increasing resistance to counterfeiting, the authentication device comprises sources emitting light at multiple (i.e. two, three, etc.) wavelengths in the VIS range and multiple (i.e. two, three, etc.) wavelengths in the IR range. The sources are activated sequentially and the light reflected by or transmitted through the machine-readable security feature is detected by a broadband detector (e.g. a photomultiplier tube). The signals corresponding to the multiple emission wavelengths are then processed into a complete spectrum, which is compared to a reference spectrum stored in a database.

[0115]

[0106] According to another embodiment, with the aim of increasing the resistance to counterfeiting and increasing the operating speed, the authentication device comprises a broadband continuous light source (e.g. a tungsten, tungsten halogen or xenon lamp), a collimation unit, a diffraction grating and a detector array. The diffraction grating is placed in the light path after the machine-readable security feature, and the light reflected by or transmitted through said machine-readable security feature is focused on the grating by a collimation unit (usually made of a series of lenses and / or adjustable slits). The detector array is made of a number of detector elements, each of which is sensitive to a specific wavelength. In this way, signals corresponding to the light intensity at a number of wavelengths are obtained simultaneously, which are processed as a complete spectrum and compared with a reference spectrum in a database.

[0116]

[0107] In another embodiment, for the purpose of obtaining a two-dimensional image of the machine-readable security feature described herein, the detector may be a CCD or CMOS sensor. In this case, the detectable wavelength range is from about 400 nm to about 1100 nm (this is the upper detection limit for silicon sensors). The machine-readable security feature is sequentially illuminated with at least two wavelengths, one of which is in the visible range and the other one in the IR range accessible to the CCD or CMOS detector. Alternatively, the CCD or CMOS sensor may be equipped with a filter layer so that the individual pixels of the sensor are sensitive to different limited regions of the visible and IR spectrum. In this case, it is possible to simultaneously obtain a two-dimensional image of the machine-readable security feature with at least two wavelengths, one in the visible range and one in the IR range accessible to the CCD or CMOS detector. The two-dimensional image is then compared to a reference image stored in a database.

[0117]

[0108] Optionally, the authentication device may comprise one or more light diffusing elements (e.g., condensers), one or more lens assemblies (e.g., focusing or collimating lenses), one or more slits (adjustable or non-adjustable), one or more reflective elements (e.g., mirrors, particularly semi-transparent mirrors), one or more filters (e.g., polarizing filters), and one or more fiber optic elements.

[0118]

[0109] Those skilled in the art may envision several modifications to the specific embodiments described above without departing from the spirit of the present invention. Such modifications are encompassed by the present invention.

[0119]

[0110] Additionally, all documents referenced throughout this specification are incorporated by reference in their entirety as if fully set forth herein.

[0120] [Example]

[0111] The invention will now be described in more detail with reference to non-limiting examples. The following examples provide further details regarding the preparation and use of security inks for printing machine-readable security features, said security inks independently comprising an IR-absorbing material consisting of copper hydroxide phosphate Cu2PO4(OH) (CAS-Nr. 12158-74-6) having a phosphocite crystal structure, a particle size d50 of 2.0-2.6 μm and a particle size d98 of 7.5-12.0 μm. The d50 and d98 values ​​were determined using a laser diffraction method (instrument: (Cyrus 1090); sample preparation: the IR-absorbing material was added to distilled water until the laser obscuration reached an operational level of 13-15% and measurements were carried out according to ISO standard 13320.

[0121]

[0112] Four different security inks were prepared and applied to a substrate. a) Water-based heat-drying flexographic security ink (Example E1); b) Solvent-based heat-drying rotogravure security ink (Example E2); c) a solvent-based heat-drying screen-printed security ink (Example E3); and d) UV-Vis curable screen printing security ink (Example E4).

[0122] I. Preparation of Security Inks and Fabrication of Security Features A. Water-based heat-drying flexographic security ink (Example E1) A.1. Preparation of Water-Based, Heat-Drying, Flexographic Security Ink (E1)

[0113] An ink vehicle as described in Table 1A was prepared by adding 429 g of the described acrylic resin to a solution containing 239 g of water, 214 g of ethanol and 26 g of ammonia and stirring until the resin was completely dissolved. Then 21 g of defoamer, 57 g of wetting agent and 14 g of dispersant were added. The mixture so obtained was dispersed at room temperature using a Dispermat (FT) at 1500 rpm for 10 minutes.

[0123]

[0114] 300 g of the IR absorbing compound copper hydroxide phosphate was added to 700 g of the ink vehicle described in Table 1A and dispersed at 1500 rpm for 10 minutes. The mixture was then dispersed at 2000 rpm for 5 minutes, resulting in 1 kg of heat-dried flexographic security ink E1 (Table 1B).

[0124]

[0115] The viscosity values ​​reported in Table 1B were measured at 25°C on approximately 15 g of security ink using a Brookfield viscometer (Model "RVDV-I Prime", spindle 21, 100 rpm).

[0125] [Table 1]

[0126] [Table 2]

[0127] A.2. Creation of Printed Machine-Readable Security Features Using Thermally Dryable Flexographic Security Ink E1

[0116] Anilox roller (55l / m, 20cm 3 / m 2 The security ink E1 was printed on a PET substrate (corona-treated, 19 μm thick) at a speed of 30 m / min by an experimental pilot flexographic printing unit (Flexo Norbert Schlafli Engler Maschinen) with a 300 mm diameter flexographic printer, resulting in the formation of a machine-readable security feature in the form of a dry coating with a thickness of 3-5 μm. After printing, the security feature was dried online with hot air at 90° C.

[0128] B. Solvent-Based Thermally Dryable Rotogravure Security Ink (Example E2) B.1. Preparation of Solvent-Based Thermally Dryable Rotogravure Security Ink (E2)

[0117] The components of the ink vehicle listed in Table 2A were mixed and dispersed using a Dispermat (FT) at 2500 rpm for 30 minutes at room temperature.

[0129]

[0118] 300 g of the IR absorbing compound copper hydroxide phosphate was added to 700 g of the ink vehicle described in Table 2A and dispersed at 1500 rpm for 10 minutes, resulting in 1 kg of hot-drying rotogravure security ink E2 described in Table 2B.

[0130]

[0119] The viscosity values ​​reported in Table 2B were measured at 25°C on 15 g of security ink using a Brookfield viscometer (model "RVDV-I Prime", spindle 21, 100 rpm).

[0131] [Table 3]

[0132] [Table 4]

[0133] B.2. Creation of Printed Machine-Readable Security Features Using Solvent-Based Thermally Dryable Rotogravure Security Ink E2

[0120] The security ink E2 was printed at a speed of 30 m / min on a PET substrate (corona treated, thickness 19 μm) by an experimental pilot printing unit (Gravure Norbert Schlafli Engler Maschinen) equipped with a cylinder with a gravure printing speed of 54 l / cm and a cell depth of 60 μm, resulting in the formation of a machine-readable security feature in the form of a dry coating with a thickness of 3-5 μm. After printing, the security feature was dried online with hot air at 90° C.

[0134] C. Solvent-Based Heat-Drying Screen Printing Security Ink (Example E3) C.1. Preparation of Solvent-Based Thermally Dryable Screen Printable Security Ink (E3)

[0121] The components of the ink vehicle listed in Table 3A were mixed and dispersed using a Dispermat (FT) at 1000 rpm for 15 minutes at room temperature.

[0135]

[0122] 120 g of the IR absorbing compound copper hydroxide phosphate was added to 880 g of the ink vehicle described in Table 3A and dispersed at 1200 rpm for 10 minutes, resulting in 1 kg of hot-dry screen printing security ink E3 described in Table 3B.

[0136]

[0123] The viscosity values ​​reported in Table 3B were measured at 25°C on approximately 15g of security ink vehicle using a Brookfield Viscometer (Model "RVDV-I Prime", spindle 27, 100 rpm).

[0137] [Table 5]

[0138] [Table 6]

[0139] C.2. Creation of Printed Machine-Readable Security Features Using Thermally Dryable Screen Printed Security Ink E3

[0124] Using a 90 threads / cm screen (230 mesh), security ink E3 was applied to a piece of trust paper (BNP paper from Louisenthal, 100 g / m 2 The printed pattern had a size of 6 cm x 10 cm. After printing, the security feature was dried in a hot air dryer at a temperature of about 50 °C for about 1 minute.

[0140] D. UV Curable Screen Print Security Ink (Example E4) D.1. Preparation of UV-curable screen printing security ink (E4)

[0125] Using a Dispermat (FT), the components of the ink vehicle listed in Table 4A were mixed and dispersed at 1000-1500 rpm for 15 minutes at room temperature.

[0141]

[0126] 120 g of the IR absorbing compound copper hydroxide phosphate was added to 880 g of the ink vehicle described in Table 4A and dispersed at 1200 rpm for 10 minutes, resulting in 1 kg of UV curable screen printing security ink E4 described in Table 4B.

[0142]

[0127] The viscosity values ​​reported in Table 4B were measured at 25°C on approximately 15 g of security vehicle using a Brookfield Viscometer (Model "RVDV-I Prime", spindle 27, 100 rpm).

[0143] [Table 7]

[0144] [Table 8]

[0145] D.2. Creation of Printed Machine-Readable Security Features Using UV-Curable Screen Printing Security Ink E4

[0128] Using a 90 threads / cm screen (230 mesh), security ink E4 was applied to a piece of trust paper (BNP paper from Louisenthal, 100 g / m 2 , 14.5 cm × 17.5 cm) resulting in the formation of a machine-readable security feature in the form of a hardened coating with a thickness of about 20 μm. The printed pattern had a size of 6 cm × 10 cm. After the printing step, it was cured under a curing unit from IST Metz GmbH (two lamps: iron-doped mercury lamp 200 W / cm 2 + Mercury lamp 200W / cm 2 ), and the security features were cured by exposing them twice to UV-Vis light at a speed of 100 m / min.

[0146] II. Results: Optical properties of printed machine-readable security features

[0129] The effect of the IR absorbing material present in the security inks E1 to E4 according to the invention on the visible color of the printed machine-readable security features is shown in Fig. 1 as a function of their L * , C * and h values, but L * indicates the brightness of the printed sample, and C * denotes its chroma (or the saturation of a color) and h denotes its hue angle.

[0147]

[0130] L * , C * and the h value is the L of a printed machine-readable security feature according to CIELAB (1976). * a * b * is derived independently from measurements of a * and b * are color coordinates in Cartesian two-dimensional space (a * = color value along the red / green axis, b * = color value along the blue / yellow axis). * a * b *The values ​​were measured independently on a Datacolor spectrophotometer DC45IR (measurement geometry: 45 / 0°; spectrum analyzer: proprietary dual channel holographic grating. A 256-photodiode linear array was used for both reference and sample channels; light source: full bandwidth LED illumination). The substrate had a higher IR reflectance than the security features in order not to affect the measurements. From each data point, the C * and the h value was calculated.

[0148]

number

[0149] [Table 9]

[0150] The reflectance spectra of each printed machine-readable security feature made with security inks E1-E4 were measured independently between 400 nm and 1100 nm with a Datacolor DC45. 100% reflectance was measured using the device's internal standard. The reflectance values ​​(%) at selected wavelengths are shown in Table 6A and the reflectance curves are shown in Figure 1.

[0151] [Table 10]

[0152] [Table 11]

[0153]

[0132] As shown in Tables 6A-B, the machine-readable printed security features made from security inks E1-E4 exhibited significant differences between the maximum reflectance in the Vis range and the minimum reflectance (i.e. maximum absorption) in the IR range, especially in the NIR range. The reflectance values ​​and profiles shown make it possible to suit high speed detection of said security features (i.e. machine-readable characteristics) with standard detectors such as those that characterize high speed banknote sorters, since such detectors rely on differences in reflectance at selected wavelengths in the Vis and IR ranges of interest. The L of the machine-readable printed security features made from security inks E1-E4 according to the present invention * a * b * The values ​​correspond to a light green colour. Thus, the machine-readable printed security features made from the security inks E1-E4 according to the invention exhibited a clear light colour in the Vis range whilst also exhibiting a sufficiently strong absorption in the IR range, especially in the NIR range.

Claims

1. A security ink for printing a machine-readable layer, said security ink comprising Cu 2 PO 4 (OH) having a phosphocite crystal structure, said security ink being selected from a screen printing ink having a viscosity of 50-3000 mPas at 25° C., a flexographic printing ink having a viscosity of 50-500 mPas at 25° C., a rotogravure printing ink having a viscosity of 50-1000 mPas at 25° C., and an inkjet printing ink having a viscosity of 10-50 mPas at 25° C.; The security ink has the following optical properties: a lightness L of 80 or more ＊ , chroma C below 15 ＊ and a reflectance at 900 nm of 60% or less. Security Ink.

2. 10. The security ink of claim 1, which is a UV curable ink comprising one or more photoinitiators.

3. 3. The security ink according to claim 1 or 2, which is a heat-drying ink comprising one or more solvents selected from the group consisting of organic solvents, water and mixtures thereof.

4. 4. The security ink according to claim 1, further comprising one or more pearlescent pigments and / or one or more cholesteric liquid crystal pigments.

5. 5. A security ink according to any one of claims 1 to 4, further comprising one or more further IR absorbing compounds selected from the group consisting of doped tin oxide, doped indium oxide, reduced tungsten oxide, tungsten bronze and mixtures thereof.

6. A security ink according to any one of claims 1 to 5, having the following optical properties: lightness L of 80 or more ＊ , chroma C below 15 ＊ and a machine-readable layer having a reflectance at 900 nm of 60% or less.

7. A security document comprising a machine-readable layer according to claim 6.

8. The following optical properties: Brightness L of 80 or more ＊ , chroma C below 15 ＊ and a method for producing a machine-readable layer having a reflectance at 900 nm of 60% or less, comprising: A method comprising the step a) of applying a security ink according to any one of claims 1 to 5 to a substrate.

9. 9. The method of claim 8, further comprising a step b) of drying and / or curing said security ink in the presence of UV-Vis radiation and / or air or heat, thereby forming said machine-readable layer on said substrate, said step of drying and / or curing being performed after said step a).

10. 10. The method of claim 8 or 9, wherein the substrate is selected from the group consisting of paper or other fibrous materials, paper-containing materials, glass, metals, ceramics, plastics and polymers, metallized plastics or polymers, composite materials, and mixtures or combinations thereof.

11. 1. A method for authenticating a security document, comprising: a) providing a security document according to claim 7, comprising a machine-readable layer according to claim 1 made with a security ink according to any one of claims 1 to 5; b) illuminating the machine-readable layer with at least one wavelength in the IR range; c) detecting an optical property of the machine-readable layer by sensing light reflected by or transmitted through the machine-readable layer at at least one wavelength, one of the at least one wavelength being in the IR range; and d) determining the authenticity of the security document from the detected optical properties of the machine-readable layer. The method includes:

12. step b) comprises illuminating the machine-readable layer with at least two wavelengths, one of the at least two wavelengths being in the visible range and another of the at least two wavelengths being in the IR range; and 12. The method of claim 11 , wherein step c) comprises detecting an optical property of the machine-readable layer by sensing light reflected by or transmitted through the machine-readable layer at at least two wavelengths, one of the at least two wavelengths being in the visible range and another of the at least two wavelengths being in the IR range.

Images