Laser-assisted Tagant implantation

Abstract

Laser-assisted methods embed luminescent taggant particles into the surface of a substrate, providing a covert method of assessing the authenticity of articles so treated.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the benefit of U.S. Application No. 17 / 579,785, filed on January 20, 2022, and U.S. Provisional Application No. 63 / 141,034, filed on January 25, 2021.

[0002] (Field of the Invention) This technical field relates to methods of surface - treating solid substrates, and more particularly, to methods of fusing particles to the surface of solid substrates.

Background Art

[0003] A valuable item is any item that is valuable enough that there is a question as to whether the item is genuine. Particularly when the face value of an item is high, there is an economic incentive for bad actors to counterfeit such items as coins and other currencies, casino tokens, commemorative coins, and subway tokens. To thwart the counterfeiting process, systems are put in place to detect which items are pure in a process known as authentication.

[0004] The authentication of valuable items can be based on the detection of covert or overt aspects of the valuable item. Overt aspects are recognizable to the human eye, and some tend to be relatively easy for malicious actors to detect and defeat, with notable exceptions being materials with surface holograms or angle - dependent reflectivity. Covert aspects require custom equipment to detect and are not immediately obvious to an observer. These include spectral, magnetic, polarization, and similar properties of specially designed materials.

[0005] Phosphors are known materials that provide luminescent emission that can be detected to provide security or identification information in various technical fields. Therefore, it is desirable to find a new method for incorporating such materials into valuable items.

[0006] Furthermore, other desirable features and characteristics of this disclosure will become apparent when the following detailed description and the attached claims are read in conjunction with the attached drawings and the present background art. [Overview of the project]

[0007] A method for surface treatment of a solid substrate comprises applying or arranging a composition containing luminescent tagant particles onto the surface of the solid substrate, and fusing at least a portion of the particles on the surface with a laser beam. In various embodiments, the method includes directing the laser beam so that it is incident on at least some of the particles on the surface, or near at least some of the particles, or on at least a portion of the surface on which some of the particles are present. Here, the laser beam has sufficient power to fuse at least a portion of the incident particles onto the surface of the solid substrate. In one embodiment, the luminescent tagant particles include rare earth elements or transition metal compounds, or both. In various embodiments, the solid substrate is metallic or nonmetallic, and if metallic, it may be iron or nonferrous. In exemplary embodiments, the solid substrate is in the form of a coin, a coin blank, or any such precursor.

[0008] In other exemplary embodiments, the solid substrate may be a metal or other 3D printed part. In yet another exemplary embodiment, the solid substrate may be a plastic such as a polymer that can function as a conduit for polymer currency, driver's licenses, and other high-value objects.

[0009] The incident laser beam can be directed to fuse the article to the entire surface of a solid substrate or to a smaller area of ​​the surface. For example, the laser beam can be directed to a particle-loaded surface to form grooves or other features that immobilize the luminescent particles. The method may include further steps of subjecting the metal surface to mechanical treatment such as cleaning, rinsing, air drying, or ultrasonic treatment to remove particles that were not fused to the surface by the directed laser beam.

[0010] In another embodiment, the valuable article comprises a metal substrate and a luminescent tagant composition fused (or closely bound or embedded) to the surface of the substrate by laser energy. The tagant composition contains a phosphor, in addition to the host material, which may include transition metals or rare earth elements or combinations thereof.

[0011] A method for authenticating valuable articles is also provided, which includes detecting the emission of light and its distinctive characteristics using a dedicated detector. The light arises from emission provided by the excitation of luminescent tagant particles incorporated into the surface of the valuable article. The tagant particles are incorporated in regular, irregular, or random patterns. The patterns correspond to patterns of features created by laser treatment of the surface containing the tagant particles.

[0012] In one embodiment, the tagants are incorporated into a pattern containing information about the authenticity of an article, and the information can be encoded using specific locations of tagant particles within the pattern. Examples of patterns include barcode-like patterns, 2D matrix-like codes, or helices with a constant or variable pitch.

[0013] In this method, the features forming the pattern may, as necessary, have dimensions of approximately 0.1 to 100 microns, 1 to 100 microns, or 10 to 100 microns (i.e., length or width measured on a two-dimensional plane of the substrate surface), and a surface roughness of approximately 0.05 to 10 microns, in order to provide appropriate constraint to the Tagant particles and to support the detection and authentication process. [Brief explanation of the drawing]

[0014] This disclosure is explained below in conjunction with the following diagrams, where similar numbers indicate similar elements. [Figure 1A] This figure shows an image of an actual linear grid region on a silver substrate. [Figure 1B]This figure shows an image of an actual helical lattice region on a silver substrate. [Figure 2] This figure shows a silver blank with a laser-patterned area, which is held in a holder for handling during experimental work. [Figure 3] This figure shows data obtained from silver blank #1, demonstrating the presence of tagant in the laser-patterned area after cleaning. [Figure 4] This figure shows data obtained from silver blank #2, demonstrating that no tagant is present in the laser-patterned area after cleaning. [Modes for carrying out the invention]

[0015] The following "Modes for Carrying Out the Invention" are essentially illustrative and are not intended to limit the present disclosure or its uses and applications. Furthermore, they are not intended to be limited by any theory presented in the aforementioned background art or the detailed description below.

[0016] Base material In this instruction, luminescent particles are placed on the surface of a substrate before undergoing a laser embedding process. The substrate can take various forms depending on its end application. The substrate can be made from any material suitable for the laser-assisted embedding process. The substrate may be metallic or nonmetallic, and if metallic, it may be ferrous or nonferrous.

[0017] Non-metallic substrates include glass and ceramics, as well as polymer materials that may be thermoplastic or thermosetting. Glass may be a glass object or a part of an object having a glass-based component or a different material (e.g., a thermoplastic matrix incorporating a glass component or insert). For example, glass objects can range from standard glass bottles (marked for recycling purposes or brand protection) to specialized containers such as medical vials (e.g., for pharmaceutical company track-and-trace regulations). Thermoplastic substrates include polyester, polyolefin (BOPP), polyamide, cellulose-based materials, polystyrene, polyacrylic, thermoplastic polyurethane (TPU), polypropylene, polyethylene, polylactic acid, and polycarbonate. Thermosetting materials include epoxy, polyurethane, melamine, formaldehyde resin, amino resin, glass-reinforced plastic, and carbon fiber-reinforced plastic.

[0018] Suitable metal substrates include ferrous metals, non-ferrous metals, and combinations thereof. Suitable ferrous metals include iron, steel, and other alloys. Suitable non-ferrous substrates include gold, silver, platinum, copper and copper alloys, aluminum and aluminum alloys, titanium and titanium alloys, and other similar base metals and combinations thereof.

[0019] Valuable goods Coins, coin blanks, tokens, medals, gaming chips, commemorative coins, and other similar valuable items such as "paper" currency are made from a wide variety of base materials. Often, they are metals or metal alloys and are typically in disk form. Some are bullion coins made from precious metals such as platinum, gold, and silver. Valuable items used as currency have a polymer base, and their economic value is derived not from the value of the materials from which they are made, but rather from the value placed on them by the issuing authority, whether government or private entity. As yet another example, there are collectible coins issued by various groups, which are collectibles that are valuable either by virtue of their material or rarity, or both. Other valuable items serve security functions such as ID cards, driver's licenses, and passports.

[0020] The base material can take the form of a coin or other valuable items such as currency, tokens, chips, and medals. In one embodiment, the base material forms a disk that is a coin blank or precursor. The blank is further modified by embossing, edging, and similar modifications specific to the casting process.

[0021] The base material may be solid or may be formed of several layers and formed by several concentric radial structures. The base material can also be formed from molten powder particles such as those used in 3D printing processes for metal parts.

[0022] Various types of particles can be incorporated onto or within the surface interface of such valuable articles. Here, the surface interface means the actual surface of the article and at least a part of the interior of an object adjacent to the surface. At least some luminescent particles that are "fused to the surface" by a laser beam are indeed constrained on the surface, while other particles are expected to be found to be at least partially constrained beneath the surface of the article and embedded in the so-called surface interface. They function to alter the electromagnetic or optical characteristics of the valuable article, thereby enabling the identification of non-genuine articles. "Electromagnetic or optical characteristics" refers to all significant parameters that describe the emission, reflection, refraction, or dispersion of light from a single or a group of luminescent particles.

[0023] Luminescence Luminescence is either fluorescence or phosphorescence. When luminescent pigment molecules are preferably excited by light energy of a specific wavelength, they enter an excited energy state and then return to the original equilibrium state by emitting part of the absorbed energy as light. The emitted light is typically light of a wavelength different from that of the absorbed light. The luminescence process is characterized by the emission wavelength but also by a specific time constant that represents the speed at which the aggregate of luminescent particles returns to the ground state, equilibrium state.

[0024] Fluorescence is a phenomenon that occurs when a substance absorbs radiation of a specific wavelength or wavelength group and re-emits photons of a different wavelength. Typically, there are two types of molecules that exhibit fluorescence and are thus considered luminescent tags or tagant particles, namely, organic compounds having a high degree of conjugated unsaturation and an extended p-cloud structure, or inorganic compounds in which it is relatively easy to elevate electrons to higher empty energy levels (usually d-levels or f-levels) and the molecule can be excited to higher vibrational and rotational energy states. The spectrum of the emitted light is called the emission spectrum. Due to the conservation of energy, the emitted light is almost always of a longer wavelength.

[0025] Tagant The term "tagant" refers to particles or chemical compositions that are difficult to replicate or detect and can be identified based on physical properties such as luminescence. Similar to fingerprints, tagants can help identify valuable items such as currency, passports, or driver's licenses. As used herein, tagants are used in a variety of security applications, providing a covert aspect to the authentication process by providing luminescent material to valuable items such as bullion coins. This term is used herein to describe the role of phosphors or luminescent particles embedded on a substrate using the laser-assisted methods described.

[0026] Luminescent Tagant particles As used herein, luminescent particles are considered to be solid particles having a substantially spherical or other nearly three-dimensional regular or irregular shape that emit visible light under the influence of electromagnetic radiation. That is, particles can emit photoluminescence, in particular fluorescence. When they are exposed to and absorb radiation including ultraviolet, visible light, or near-infrared and infrared radiation, they are induced to emit visible or invisible light. These particles are also known as phosphors, and there is a great deal of literature and disclosures describing in detail the properties and behavior of this class of materials.

[0027] Phosphors are typically doped organic or inorganic materials such as oxides, sulfides, halides, garnets, phosphates, selenides, and oxysulfides. They are typically crystalline to enhance the photoluminescence process.

[0028] The selection of dopants broadens to include most transition and rare earth elements. Phosphors often contain a combination of dopants, one or more of which provide initial absorption, and one or more different dopants which provide emission.

[0029] Non-limiting examples include doped ZnS, doped Y2O3, doped Y2O3S, doped YAG, and doped Y3Al5O 12Examples of dopants include, but are not limited to, Cu, Er, Yb, Nd, Eu, Ho, Tm, and Dy.

[0030] Luminescent Tagant particles also affect a wide range of electromagnetic radiation when they interact with it. Polarization, reflection, and wavelength dispersion are well-known phenomena that can be used to provide components for authentication processes based on Tagant particles.

[0031] Deposition of Tagant particles on the substrate surface In the embodiments, the Tagant particles are deposited / coated onto the surface of the substrate before laser treatment, or otherwise positioned. In the embodiments, the Tagant particles are uniformly distributed on the surface with a uniform thickness, i.e., with a thickness variation of + / - 10% across the entire substrate. In the embodiments, a Tagant composition comprising the Tagant particles and optionally a carrier is prepared and applied to the surface of the substrate to form a Tagant layer before or during laser treatment. Suitable carriers include liquid solvents or gels that can be evaporated before laser treatment to achieve a substantially uniform distribution of Tagant particles across the entire substrate with a substantially uniform thickness. The Tagant composition can be deposited by spraying, brushing, pipetting, spin coating, or any similar method. In other embodiments, it should be understood that the Tagant particles can be deposited non-uniformly to provide areas of Tagant particles and areas without Tagant particles on the surface of the substrate. In a further embodiment, the tagant is deposited on the surface of the substrate via transfer from a solid carrier which is preferably in close contact with the surface of the substrate on which the tagant is deposited (similar to attaching a label having an adhesive surface to the substrate on which the tagant is embedded). In this embodiment, the tagant particles can be filled into a solid carrier (for example, the tagant is embedded in paper or an adhesive layer as a solid carrier). After laser treatment, the tagant particles are transferred to the surface of the substrate, and then the solid carrier is removed. A suitable material for the solid carrier can maintain the functionality of the tagant base on the primary substrate after the removal of the solid carrier. For example, the solid may be a label made of paper and / or an organic adhesive, which burns upon laser irradiation and leaves a residue that can be easily washed off the surface of the substrate, or can be washed off the surface of the substrate. Alternatively, an ink containing tagant particles is deposited on the surface of the solid carrier and deposited on the surface of the substrate before laser treatment.

[0032] Laser-assisted implantation of Tagant particles Tagant particles are incorporated into a solid substrate by a laser embedding process. In one embodiment, a laser beam having sufficient energy and power and an appropriate wavelength is directed to incident on the substrate, either directly onto or at least near the Tagant particles placed on the substrate. The energy of the laser beam interacts with the Tagant particles and the substrate surface to create features on the surface. These features are in the form of patterns incised into the surface (and also below the actual surface of the surface interface as defined above) by the action of the laser beam. Once the laser beam is directed onto the surface with the pattern of features, the Tagant particles are fused or embedded in the surface of the article. The pattern characteristics depend in part on the properties of the substrate, the type of laser used, and the particle size distribution of the Tagant particles intended to be embedded in the surface of the substrate. Regular or random patterns of dots, straight lines or curves are just a few examples of suitable structures. At least some of the Tagant particles are trapped or immobilized in the substrate, either directly or near the surface features.

[0033] The term “fused” is used herein to refer to the embedding process described above. This term means that at least a portion of the Tagant particles are embedded in or closely bound to a surface or resulting surface feature. As shown in the examples, the particles are bonded to such an extent that they cannot be removed or dislodged by wiping, rinsing, air drying, and sonication. Furthermore, the embedded Tagant particles are also resistant to the industry standard tape test, a test commonly used to check coating adhesion. The industry standard tape test involves repeatedly applying and removing a highly adhesive piece of tape from the test surface. The surface is tested before and after the tape treatment to evaluate any changes in the surface properties of the subject (in this case, the presence of Tagant particles as determined by measurements with a Tagant-specific detector). This teaching is not limited by any theory of laser-matter interaction, but it is considered that the embedding can be viewed, at least in part, as a mechanical property in which localized surface strain resulting from the interaction between the laser beam and the substrate captures the Tagant particles through clamping or pinning.

[0034] The laser embedding process can be considered a mechanical surface manipulation performed in such a way as not altering the chemical properties of the Tagant particles subjected to laser treatment. When the substrate is a soft metal (such as gold, silver, or platinum), a relatively moderate laser power density is sufficient to distort the surface of the substrate without damaging the luminescent Tagant particles. The laser may degrade or otherwise alter the luminescence properties of at least some of the Tagant particles. When the laser beam is irradiated as shown in the Examples section, at least some of the particles will withstand the treatment and emit enough light to be detectable.

[0035] A wide range of lasers and laser writing conditions can be used and adapted to the type of material substrate used. While not limited to continuous-wave lasers, preferred examples include pulsed lasers with pulse widths ranging from microseconds to femtoseconds. Pulse repetition is important because it determines the amount of energy deposited at a given location on the substrate material surface, and subsequently how fine a pattern can be generated on the surface. The preferred size of features present in the pattern (whether regular or random) depends on the Tagant particle size, as the goal is to trap, embed, or constrain particles on the surface. Typically, the repetition rate correlates with the speed at which the laser beam moves from one spot to another. Exemplary ranges are several Hz to kHz for pulse repetition rates and approximately 3000 mm / s to approximately 1 mm / s for laser beam speeds on the surface. The laser wavelength is selected to optimize its interaction with the substrate material so that a preferred pattern feature size is obtained through efficient absorption and heat dissipation. A preferred example is a laser emitting at 1.06 microns.

[0036] For illustrative purposes, grooves or other regular features can be fabricated on the surface of a solid substrate, as shown in the figures and detailed in the Examples section. For example, linear and helical lattice regions can be fabricated having a lattice half-period of about 1 to 50 microns and a surface roughness of about 0.05 to 10 microns. Larger Tagant particles can be trapped between the lattice lines, while smaller particles can be trapped within the rough surface of the lattice region along the lines or at the bottom of the spaces between the lines. Thus, small Tagant particles of less than 1 micron can be trapped within regular or random patterns. [Examples]

[0037] Laser-assisted embedding of Tagant particles into a silver blank is shown in the figure. The Tagant was doped YAG powder, a proprietary Tagant manufactured by Honeywell International (Morris Plains, New Jersey). The diameter of the Tagant particles was approximately 2 microns. A nanosecond pulsed laser with a laser wavelength of approximately 1 micron was used. The writing speed was several tens of millimeters per second, and no significant effort was spent optimizing the roughness of the surface features or the resolution of the pattern. Two pattern types were studied: a linear grid with lines separated by only 50 microns and 100 microns (exemplified in Figure 1A), and a helical pattern with column spacings of 50 microns and 100 microns (exemplified in Figure 1B). The surface roughness of the patterned areas was estimated to be on the order of microns.

[0038] Using a proprietary detection system developed by Honeywell International (Morris Plains, New Jersey), Tagant was excited, and fluorescence was recorded to evaluate the presence or absence of Tagant on the surface in areas that were laser-modified or not. The system includes an excitation source that matches the absorption of Tagant, and a detector that corresponds to the fluorescence emission of Tagant.

[0039] The surface cleaning procedure consisted of vigorously wiping the lens tissue by hand after immersing it in isopropyl alcohol, followed by ultrasonic cleaning (also known as ultrasonic treatment) in isopropyl alcohol for 5 minutes, and then air drying using an air balloon.

[0040] The first blank, defined here as Blank #1, was initially coated with Tagant and then laser-patterned. The actual blank is shown in Figure 2. The Tagant was deposited in a layer estimated to be several tens of microns thick without expending significant effort to achieve a uniform thickness or uniform distribution on the surface. The blanks were tested for the presence of Tagant on their surfaces before and after laser patterning, and after cleaning. On the laser-patterned surface, a fluorescence signal was detected after cleaning. On the unpatterned surface, no fluorescence signal was detected after cleaning.

[0041] This is shown in Figure 3, which displays detector fluorescence data as the detector moves along lines crossing three different grids in the direction indicated by the arrows drawn in Figure 2. The silver blank #1, which remains patterned and is not yet cleaned, shows a Tagant signal in both the patterned and unpatterned regions, but after cleaning, the fluorescence signal is present only in the laser-patterned region.

[0042] The second demonstration addressed the possibility that the Tagant only superficially adhered to the patterned area due to sample handling and cleaning, and that the cleaning procedure was not sufficiently thorough.

[0043] The second blank (defined here as blank #2) was first laser patterned, and then coated with Tagant in the same manner as described above. The same measurements as those for blank #1 were repeated, and the results are shown in Figure 4.

[0044] Initially, luminescence signals were present in both the laser-patterned and unpatterned areas. After cleaning, no luminescence signals were observed in the laser-patterned areas, and, as expected, no luminescence signals were observed in the unpatterned areas either. Essentially, the Tagant particles did not simply adhere to the laser-patterned areas; rather, laser patterning was required while the Tagant particles were on the surface in order to embed them.

[0045] These findings demonstrate that laser patterning of surfaces pre-treated with Tagant particles facilitates the embedding of Tagant particles into surfaces that can withstand significant cleaning efforts, including ultrasonic treatment.

[0046] While the detailed description above presents at least one exemplary embodiment, it should be understood that a vast number of variations exist. It should also be understood that the exemplary embodiments are merely examples and are not intended to limit the scope, applicability, or configuration of this disclosure in any way. Rather, the aforementioned "Modes for Carrying Out the Invention" will provide those skilled in the art with a convenient roadmap for carrying out the exemplary embodiments of this disclosure. It should be understood that various modifications can be made to the function and configuration of the elements described in the exemplary embodiments without departing from the scope of this disclosure as set forth in the attached "Claims." The present invention includes the following embodiments. [1] A method for surface treatment of a solid substrate, A composition containing luminescent tagant particles is placed on the surface of the substrate, A method comprising fusing at least a portion of the particles on the surface with a laser beam. [2] The method according to [1], comprising directing a laser beam to incident on at least a portion of the surface on which a portion of the particles are present. [3] The method according to [1], wherein the laser beam has sufficient power to fuse at least a portion of the incident particles to the surface of the solid substrate. [4] The method according to [1], wherein the laser beam is directed to confine the particles to an area smaller than the entire surface of the substrate. [5] The method according to [1], wherein the laser beam is directed onto the particles and the surface to generate a feature containing the luminescent particles within the surface. [6] The method according to [1], wherein the laser beam is directed onto the particles and the surface to generate localized surface strain that pins, clamps, or otherwise restrains the luminescent tagant particles on the surface. [7] The method according to [1], further comprising mechanically removing particles that have not been fused to the surface by the directed laser beam. [8] A valuable article comprising a substrate and a luminescent tagant composition confined within the surface interface of the substrate using laser energy. [9] The valuable article according to [8], wherein the Tagant composition comprises a transition metal and / or a rare earth element.

[10] Valuable articles as described in [9], selected from the group consisting of coins, coin blanks, tokens, medals, game chips, commemorative coins, and currency.

Claims

1. A method for surface treatment of a solid substrate, A composition containing luminescent tagant particles is placed on the surface of the solid substrate, By directing a laser beam so as to incident on at least a portion of the surface of the solid substrate where some of the luminescent tagant particles are present, at least a portion of the luminescent tagant particles are fused onto the surface of the solid substrate. To remove the luminescent tagant particles that were not fused to the surface by the directed laser beam. Includes, The laser beam has sufficient power to fuse at least a portion of the incident luminescent tagant particles to the surface of the solid substrate, The laser beam is directed onto the luminescent tagant particles and onto the surface of the solid substrate to generate localized surface strain that pins, clamps, and / or fuses the luminescent tagant particles to the surface of the solid substrate. method.

2. A method for authenticating a valuable article obtained by a surface treatment method for a solid substrate according to claim 1, wherein light emission resulting from the excitation of luminescent tagant particles fused by the laser beam is detected, and the luminescent tagant particles are incorporated into a regular pattern or random structure containing information used to evaluate the authenticity of the article.

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