Hidden machine-readable micro-optical feature embedded in lens layer

Abstract

A micro-optical device comprising: an optical spacer layer (110) having a first side and a second side; an icon layer (120) comprising a plurality of image icons of a first color disposed on a first side of the optical spacer layer; and a focusing layer (105) comprising a plurality of refractive focusing elements (107) disposed on the second side of the optical spacer layer. The plurality of refractive focusing elements project a composite enlarged image of the plurality of image icons, and the image icon of the first color projects a portion of the composite enlarged image having the first color. In addition, the refractive focusing element is doped with a machine readable tracer that emits a characteristic signal at a first frequency in the ultraviolet spectrum.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to enhancing the security of safety documents, such as currency, passports, and other documents that include surface-applied micro-optic security devices. More specifically, the present disclosure provides machine-readable features embedded within the lens layer of a micro-optic device to provide enhanced detectability and consistent signal strength at a machine reader. BACKGROUND

[0002] Enhancing the security of passports, currency, and other documents (referred to herein as "security documents") by incorporating difficult-to-reproduce authenticity indicia as structural features is a perennial topic of technical challenge and opportunity for improvement in the field of security document design. More specifically, security document designers and difficult-to-reproduce security feature designers are tasked with, for example, balancing a set of competing technical and practical goals, including but not limited to optical performance requirements (e.g., the system provides bright, clear, and visible optically variable effects, thereby increasing user engagement and visible authenticity indicia), machine readability requirements (e.g., the system has one or more latent features whose presence or absence can be reliably detected by a specialized device), and manufacturing goals (e.g., the system that meets the optical performance and machine readability requirements can be produced using industry-standard machinery).

[0003] One specific example of the technical challenge posed by the competing and often mutually exclusive design goals of achieving machine readability and providing a clear composite image is the use of many micro-optic devices that project a composite image by cooperatively magnifying the contents of an icon layer through a set of focusing elements (e.g., lenses or mirrors). Such devices are most often implemented in some variation of a three-layer structure, specifically including: an icon layer as a bottom layer, an optical spacer layer (e.g., a section of transparent material of appropriate thickness to ensure that the icon layer is in the focal plane of the focusing layer), and a focusing layer. Typically, such micro-optic devices are attached icon-side down to a substrate (e.g., a sheet of currency paper) such that the adhesive holding the device to the substrate is on the underside of the icon layer (farthest from the focusing elements), and the focusing layer is on the outside of the security document (i.e., closest to the observer). When machine-readable ("MR") features are provided in such a micro-optic system, the MR features are typically embedded beneath the icon layer (e.g., in an opaque "camouflage jacket" of white or light-colored pigments), or the MR feature material is embedded within or around the material of the icon layer. This approach buries the MR component beneath the spacer and focusing layers, trading off machine readability for optical performance, as while the MR component is in a location that has little impact on the ability of the system to project a composite image, the signal provided by the MR component can be attenuated or distorted in its passage through the optical spacer and focusing layers to a reading device on the outside of the security document.

[0004] Alternatively, positioning the MR components in higher layers of the security device (e.g. in the focusing layer or the optical spacer layer) can generally improve machine readability, but can reduce optical performance, as many MR components either have a color (and thus can significantly interfere with the image projected by the system) or affect the focusing properties of the focusing layer (e.g. by changing the refractive index of the lens material).

[0005] While for many applications, e.g. very thin micro-optics used as authenticity markers on certain banknotes (e.g. with a device thickness of 50 microns or less), the attenuation of the signal is manageable, in other applications, e.g. thicker, cheaper micro-optical security devices used on consumer goods (e.g. difficult-to-reproduce authenticity markers used on product labels of Swiss watches or French wine), the attenuation effect can be more pronounced.

[0006] Therefore, optimizing machine readability and image sharpness in micro-optical systems that make use of a focusing layer remains a technical challenge and opportunity for improvement in this technical field. SUMMARY

[0007] The present disclosure sets forth embodiments of a moisture resistant harvest-embossed security device and a method of manufacturing the same.

[0008] In a first embodiment, a method comprises providing an optical spacer layer having a first side and a second side; forming an icon layer comprising a plurality of image icons of a first color on the first side of the optical spacer layer; and forming a focusing layer comprising a plurality of refractive focusing elements on the second side of the optical spacer layer, wherein the plurality of refractive focusing elements project a composite magnified image of the plurality of image icons, wherein the image icons of the first color project a portion of the composite magnified image having the first color, and wherein a refractive focusing element of the plurality of refractive focusing elements is doped with a machine-readable tracer that emits a characteristic signal at a first frequency in the ultraviolet spectrum.

[0009] In a second embodiment, a micro-optical device comprises an optical spacer layer having a first side and a second side; an icon layer comprising a plurality of image icons of a first color disposed on the first side of the optical spacer layer; and a focusing layer comprising a plurality of refractive focusing elements disposed on the second side of the optical spacer layer. The plurality of refractive focusing elements project a composite magnified image of the plurality of image icons, and the image icons of the first color project a portion of the composite magnified image having the first color. Additionally, a refractive focusing element is doped with a machine-readable tracer that emits a characteristic signal at a first frequency in the ultraviolet spectrum.

[0010] Other technical features can be readily apparent to one skilled in the art from the following figures, descriptions, and claims.

[0011] Before undertaking the DETAILED DESCRIPTION below, it can be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term “coupled” and its derivatives refer to any direct or indirect communication between two or more elements, regardless of the nature of the connection. The terms “comprise,” “comprises” and “comprising” and the like are used in a non-limiting sense and encompass the terms “consist of, “consists of, and “consisting of.” The term “or” is inclusive, meaning and / or. The phrase “associated with,” as well as derivatives thereof, can mean in connection with, included with, interconnect with, contain, be contained within, connected to or with, coupled to or with, be communicable with, cooperate with, interleave, be proximate to, be bound to or with, have a property of, have an attribute of, have a relationship to or with, or the like. The phrase “at least one of,” as used throughout this patent document, does not necessarily

[0012] Definitions for other certain words and phrases are provided throughout this patent document. Those of ordinary skill in the art will understand that in many, if not most instances, such definitions apply to prior as well as future uses of such defined words and phrases. BRIEF DESCRIPTION OF DRAWINGS

[0013] For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings in which like parts are marked with like numerals:

[0014] Figure 1 Examples of machine-readable micro-optics in accordance with various embodiments of the present disclosure are shown; and

[0015] Figure 2 Operations of an example method for fabricating a device in accordance with various embodiments of the present disclosure are shown. DETAILED DESCRIPTION

[0016] The following discussion of Figures 1 to 2 The principles of the present disclosure are described herein with reference to various embodiments. Such examples are presented by way of explanation of the present disclosure, not limitation. As such, many changes and modifications will become apparent to those skilled in the art upon reading of the present disclosure, which is intended to cover any and all such changes and modifications.

[0017] While the present disclosure has been described with reference to various embodiments, it will be understood that various changes and modifications can be suggested to one skilled in the art and it is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.

[0018] Figure 1An example of a machine-readable optical security device 100 according to certain embodiments of the present disclosure is shown, which is incorporated into a security document 160.

[0019] With reference to Figure 1 By way of non-limiting example, the optical security device 100 includes a plurality of focusing elements 105 (including, for example, focusing element 107) and an image icon arrangement 120 (including, for example, image icon 121). According to various embodiments, each focusing element of the plurality of focusing elements 105 has a footprint in which one or more image icons of the image icon arrangement 120 are positioned. Collectively, the focusing elements of the plurality of focusing elements 105 magnify a portion of the image icon 120 to produce a magnification effect (also referred to as a “synthetic magnified image” or more simply, a “synthetic image”), in which the individual microscopic image icons are collectively magnified by the plurality of focusing elements 105 to produce an image that dynamically reacts (e.g., by appearing to move or change color) in response to a change in viewing angle. Given the small scale and strict manufacturing tolerances of the constituent structures of the optical security device that provide the synthetic magnification effect, many malicious actors are unable to produce counterfeit versions of the optical security device 100. Thus, in many cases, the optical security device 100 is a trusted visual indicia of authenticity of a security document (e.g., security document 160).

[0020] According to certain embodiments, the plurality of focusing elements 105 includes a planar array of micro-optical focusing elements. In some embodiments, the focusing elements of the plurality of focusing elements 105 include micro-optical refractive focusing elements (e.g., plano-convex lenses or GRIN lenses). In some embodiments, the refractive focusing elements of the plurality of focusing elements 105 are fabricated from a photocured resin having a refractive index in the range of 1.35 to 1.7 and having a diameter in the range of 5 pm to 200 pm. In various embodiments, the focusing elements of the plurality of focusing elements 105 include reflective focusing elements (e.g., very small concave mirrors) having a diameter in the range of 5 pm to 50 pm. While the focusing elements of the plurality of focusing elements 105 are shown in this illustrative example to include circular plano-convex lenses, other refractive lens geometries (e.g., bi-convex lenses) are also possible and within the contemplated scope of the present disclosure. Suitable materials for forming the plurality of focusing elements 105 include, but are not limited to, substantially transparent, colored, or colorless polymers such as acrylic resins, acrylate polyesters, acrylate polyurethanes, epoxy resins, polycarbonates, polypropylenes, and the like. Various methods of providing the focusing element layer can include extrusion, radiation-cured casting, injection molding, reaction injection molding, or reaction casting.

[0021] The focusing elements of the plurality of focusing elements 105 (mirrors and refractive lenses) can be characterized by an F# which can be adjusted as needed to modify the synthetic image and its optical effects. Suitable F numbers can be adjusted to be less than 10, or in some embodiments less than about 4, or in some embodiments less than 2 or 1, taking into account the desired thickness of the security film or security device. The synthetic image can also be modulated by the relative arrangement and alignment of the focusing element array and the array of image elements, and each array has a respective period of repetition. The periods of repetition of the respective arrays can be adjusted so that their ratio is equal to 1, slightly higher than 1, or slightly lower than 1; although ratios much higher than 1 and much lower than 1 can also be considered. The base diameter of the focusing elements (equivalent to the base width of a cylindrical lens) can also be adjusted as needed, and within the scope of the present disclosure, these base diameters can have the following ranges: 200 pm to 500 pm; 50 pm to 200 pm; less than 50 pm (e.g., less than about 45 pm, or a range of about 10 pm to about 40 pm). The focusing elements can be further modified by adjusting the focal length so that the focal length allows for viewing of the image elements in the array of image elements through the focusing elements and the projection of the synthetic image. Focal lengths of less than 50 pm are suitable, e.g., less than 45 pm, e.g., a range of about 10 pm to about 30 pm.

[0022] Additionally, the cured photocurable material (e.g., a polyacrylate resin) forming the plurality of focusing elements 105 can include particles or molecules of a machine-readable tracer or additive. As used in the present disclosure, the term “machine-readable” encompasses a material or arrangement of materials that exhibits one or more properties that are latent to the human eye under daylight, but become apparent or detectable under conditions provided by a machine. Examples of machine- readability include, but are not limited to, upconversion (where a particle receives light energy of a first wavelength and emits light at a second wavelength that is shorter than the first wavelength). Other examples of machine-readable additives include magnetically readable compounds.

[0023] As Figure 1As shown in illustrative examples of FIG. 1, the image icon arrangement 120 includes a set of image icons (including image icon 121) positioned at predetermined locations within the footprint of focusing elements of the plurality of focusing elements 105. According to various embodiments, individual image icons in the image icon arrangement 120 include regions of photo-cured material associated with the focusing path of structured light (e.g., collimated UV light) passing through the plurality of focusing elements 105 from a projection point associated with one or more predetermined ranges of viewing angles. In some embodiments, individual image icons in the image icon arrangement 120 are not provided within a structured image icon layer. As used in this disclosure, the term“structured image layer” encompasses a layer of material (e.g., a photo-curable resin) that has been imprinted or otherwise formed to include structures (e.g., recesses, posts, grooves, or mesas) for positioning and retaining image icon material. According to various embodiments, individual image icons in the image icon arrangement 120 are provided within a structured image layer that includes one or more of voids, mesas, or posts that act as retention structures to retain micro- and nano- volumes of colored material. In some embodiments, the image icon arrangement 120 includes single-color icons. In other embodiments, the image icons of the image icon arrangement 120 include icons of two or more colors.

[0024] Although Figure 1 Although not shown in FIG. 1, in certain embodiments, the relief structure of the icon layer, rather than a contrasting gap-filling substance retained within the embossed relief structure, can be used as the image icons. In such embodiments, the imprinted material can be colored and translucent, and variations in the thickness of the relief structure can create contrast points that can be projected through the plurality of focusing elements 105 to provide a composite image.

[0025] As Figure 1 As shown in illustrative examples of FIG. 1, in certain embodiments, the optical security device 100 includes an optical spacer layer 110. According to various embodiments, the optical spacer layer 110 includes a film of substantially transparent material that is used to position the image icons in the image icon arrangement 120 within or around the focal plane of focusing elements of the plurality of focusing elements 105. In certain embodiments according to this disclosure, the optical spacer layer 110 includes a manufacturing substrate on which one or more layers of photo-curable material can be applied to form one or more of the image icon arrangement 120 or the plurality of focusing elements 105.

[0026] According to various embodiments, the optical security device 100 includes one or more regions of light-cured protective material that occupy the spaces between the image icons in the image icon arrangement 120. In some embodiments, the image icon arrangement 120 is first formed (e.g., by selectively curing and removing a liquid light-curable material on the optical spacing layer 110), then a layer of transparent light-curable material is applied to fill the spaces between the image icons in the image icon arrangement 120, then over-cure is performed to form a protective layer that protects the image icons from moving from their locations within the footprint of the focusing elements in the plurality of focusing elements 105. In certain embodiments, the light-curable material used to form the image icon arrangement 120 is a pigmented ultraviolet (UV) -curable polymer.

[0027] In some embodiments, the image icon arrangement 120 is secured to a second substrate 130 that serves to protect and secure the image icon arrangement 120 and provides an interface for attaching the optical security device 100 to a substrate 150 as part of a security document 160. In some embodiments, the optical security device 100 is secured to the substrate 150 during manufacture of the substrate in a papermaking machine, such as a Fourdrinier papermaking machine. According to some embodiments, the optical security device 100 is secured to the substrate 150 by an adhesive layer between the image icon arrangement 120 and the top surface of the substrate 150.

[0028] In certain embodiments according to the present disclosure, the optical security device 100 includes a sealing layer 140. According to certain embodiments, the sealing layer 140 includes a thin (e.g., 2 pm to 50 pm thick) layer of substantially transparent material that interfaces with the focusing elements in the plurality of focusing elements 105 on a lower surface, and includes an upper surface that has less variation in curvature (e.g., achieved by a smooth surface treatment, or by having a radius of curvature of its surface that is greater than the radius of curvature of the focusing elements) than the plurality of focusing elements 105. According to various embodiments, the upper surface of the sealing layer 140 is formed of a thermoplastic material that can be ultrasonically welded to a surface containing a cellulosic substance.

[0029] As Figure 1As shown in non-limiting examples, in some embodiments, the optical security device 100 may be attached to a substrate 150 to form a secure document 160. According to various embodiments, the substrate 150 comprises a sheet of material having at least one surface comprising a cellulosic substance, such as wood pulp, cotton fiber, linn fiber, flax fiber, sisal fiber, hemp fiber, abaca fiber, oak fiber, sage fiber, bamboo fiber, or kenaf fiber. In some embodiments, the substrate 150 is a mixture of cotton and linn fibers, such as those used in U.S. banknotes. For example, the substrate 150 may be made from a fiber mixture comprising 65%-80% cotton fiber and 20%-35% linn fiber. In some embodiments, the relative proportions of cotton and linn fibers may result in the substrate comprising 65%-100% cotton fiber and 0-35% linn fiber.

[0030] Although Figure 1 An example of an optical security device 100 is provided, but this disclosure is not limited thereto. Other optical security devices also fall within the scope of this disclosure, such devices comprising at least one surface containing a thermoplastic polymer and including micron- and nano-scale optical structures that are difficult to replicate (e.g., holograms, devices that provide thin-film effects, devices that produce diffraction-based optical effects); these devices also embed machine-readable features that do not affect the optical properties of the transparent layer above the icon layer. Additionally, certain embodiments of this disclosure may include... Figure 1 Structures not explicitly shown include, for example, a contrast coating or "camouflage" coating made of a light-shielding material to enhance the contrast of icon layer 120. In some embodiments, the contrast material may be a thin layer of white or light-colored pigment. Alternatively, the contrast coating may be a reflective material such as aluminum, zinc, or copper.

[0031] Figure 1 Operations of example methods for forming machine-readable micro-optical security devices according to various embodiments of this disclosure are described. It should be noted that references... Figure 2 The operations described do not necessarily need to be performed in the described order, and depending on the manufacturing process used, some operations may be omitted or performed in a different order. As an illustrative example, in a thin spacer layer micro-optical system, steps related to providing the optical spacer layer can be omitted. As a further illustrative example, the icon structure can be formed by directional curing, wherein curing light passes through a focusing element layer on one side of the device to form an icon structure including a cured coloring material region on the opposite side of the device.

[0032] refer to Figure 2 An illustrative example, in operation 205, in the optical spacer layer (e.g., Figure 2An icon layer (e.g., in the optical spacer layer 110) is formed on one side of the icon layer. Figure 1 The icon layer 120 is shown in some embodiments. In some embodiments, the icon layer is formed by casting curing, wherein an initially smooth, transparent or substantially colorless radiation-curable resin (e.g., polyacrylate) is placed on an optical spacer layer at a uniform thickness (e.g., using a Mayer rod), and then an embossed pattern is imprinted using one or more tools to define a set of retention structures for colored materials in the resin layer. The imprinted uncured material of the initial layer is then radiation-cured (e.g., by flooding the imprinted material with ultraviolet light or other forms of radiation to cure and crosslink the resin). In some embodiments, an uncured coloring photocurable material of a first color is subsequently applied to at least a portion of the micro-optical structure such that the uncured material fills the retention structure formed by the imprinting tool. The uncured coloring photocurable material of the first color is then exposed to curing radiation (e.g., ultraviolet light), and excess uncured coloring material is scraped off from the retention structure. Depending on whether multiple colors are used in the icon layer, multiple fillings and curings of the coloring material may be performed. Additionally, in some embodiments, the coloring material may be applied and cured in sections, wherein only a portion of the device receives the coloring material and the curing light. According to some embodiments, this method can produce closely aligned icon structures with multicolor patterns while avoiding image degradation associated with the scraper, which results in uncured coloring material being "smeared" onto the icon layer.

[0033] In some embodiments, instead of filling the negative spaces (i.e., wells) created in the icon layer by the embossing tool with coloring material, the coloring material is applied to the positive areas (i.e., the tabletop) formed by the embossing tool and then cured. In such embodiments, the step of smoothing the icon layer as part of operation 205 can be avoided.

[0034] like Figure 1 As shown, in operation 210, a focus element array (e.g., Figure 2The uncured resin of the focusing element array 105 is doped with one or more compounds that provide machine readability, while providing a concentration that does not affect the native optical properties of the material used to form the focusing element array, and simultaneously provides a reliable machine response. According to various embodiments, a volume of uncured acrylate resin is doped with an upconversion tracer (e.g., Honeywell's Lumilux MRG-100) at a concentration of 0.1% to 0.6% of the total mixture weight. As used herein, the term "upconversion" refers to a chemical substance absorbing light energy in a first frequency range and emitting light energy in a second, higher frequency range. For Lumilux, this upconverter absorbs light in the infrared portion of the EV spectrum and emits light in the ultraviolet portion of the spectrum. According to some embodiments, the machine-readable tracer is provided as a suspension in the radiation-curable lens material, and when the lens material is doped with a machine-readable compound, the tracer is kept suspended in the uncured lens material by adding a surfactant.

[0035] Those skilled in the art will understand that Lumilux is merely one non-limiting example of a machine-readable additive that can be provided to uncured lens material according to various embodiments of this disclosure. Other additives of similar concentration (e.g., strontium aluminum-based pigments) can also be used to dope uncured lens material and obtain similar results.

[0036] refer to Figure 1 An illustrative example, in operation 215, is the formation of a focused element layer (e.g., Figure 2 The focusing layer 105 in the image is used. According to various embodiments, the focusing layer is formed by applying an uncured lens material layer (e.g., by spreading a layer of uniform thickness using a Mayer rod) formed in operation 210 to the side of the optical substrate opposite to the icon layer side, and imprinting the uncured material to form an embossed structure that provides a curved interface between the lens material and a material with a different refractive index (RI). In some embodiments, the material with a different refractive index is air, and the embossed structure forms multiple convex lenses. In some embodiments, the material with a different refractive index is a sealing layer (e.g., ...). Figure 1 Figure 1 (Seal layer 140). In embodiments where the RI of the seal layer is higher than that of the lens, uncured lens material can be imprinted to form multiple concave lenses.

[0037] In some embodiments, after imprinting, the uncured and doped lens material is immersed in photochemical radiation (e.g., ultraviolet light) to initiate the curing and cross-linking of the resin. Depending on the design and whether a sealing layer is specified, another layer of transparent material may be applied to the top of the lens.

[0038] According to various embodiments, operations 205-215 can produce a micro-optic security device having a characteristic machine-readable signal that can be detected on quality control equipment (typically output pass-fail signals) and production equipment, such as that used by the United States Bureau of Engraving, which outputs a qualitative measure of signal strength, where the mid-value of the response curve is indicative of a "pass" and the upper and lower tails (i.e., saturated signals) are indicative of a failure or excess doping.

[0039] As described elsewhere in this disclosure, by doping the machine-readable compound optically neutral into the upper layer (i.e., the lens layer) of the micro-optic system, certain embodiments according to the present disclosure have the technical advantage of providing reliable machine-readability in micro-optic devices that are thicker (e.g., greater than 70 microns in total thickness) than can be achieved by applying machine-readable components in the camouflage coating layer below the icon layer.

[0040] An example of a micro-optic device according to certain embodiments of the present disclosure includes a micro-optic device comprising: an optical spacer layer having a first side and a second side; an icon layer comprising a plurality of image icons of a first color disposed on the first side of the optical spacer layer; and a focusing layer comprising a plurality of refractive focusing elements disposed on the second side of the optical spacer layer. The plurality of refractive focusing elements project a composite magnified image of the plurality of image icons, and the image icons of the first color project portions of the composite magnified image having the first color. Additionally, the machine-readable tracer is doped into the refractive focusing elements, the tracer emitting a characteristic signal at a first frequency in the ultraviolet spectrum.

[0041] An example of a micro-optic device according to certain embodiments of the present disclosure includes a micro-optic device wherein the machine-readable tracer is a phosphorescent up-converter that absorbs light energy at a second frequency in the infrared spectrum.

[0042] An example of a micro-optic device according to certain embodiments of the present disclosure includes a micro-optic device wherein the machine-readable tracer is a strontium aluminate-based pigment.

[0043] An example of a micro-optic device according to certain embodiments of the present disclosure includes a micro-optic device wherein the machine-readable tracer is provided as a suspension in a radiation-curable polymer.

[0044] An example of a micro-optic device according to certain embodiments of the present disclosure includes a micro-optic device wherein the machine-readable tracer is added at a concentration of 0.1% to 0.6% of the weight of the mixture of the tracer and the radiation-curable polymer.

[0045] An example of a micro-optic device according to certain embodiments of the present disclosure includes a micro-optic device that includes a surfactant to maintain the machine-readable tracer in suspension prior to curing.

[0046] Examples of micro-optical devices according to certain embodiments of the present application include micro-optical devices wherein the device does not include a background coating applied to the icon layer.

[0047] Examples of micro-optical devices according to certain embodiments of the present application include micro-optical devices wherein the micro-optical security device has a thickness of 75 microns or greater.

[0048] Examples of methods for manufacturing micro-optical devices according to various embodiments of the present disclosure include methods comprising: providing an optical spacer layer having a first side and a second side; forming an icon layer comprising a plurality of image icons of a first color on the first side of the optical spacer layer; and forming a focusing layer comprising a plurality of refractive focusing elements on the second side of the optical spacer layer, wherein the plurality of refractive focusing elements project a composite magnified image of the plurality of image icons, wherein the image icons of the first color project a portion of the composite magnified image having the first color, and wherein a refractive focusing element of the plurality of refractive focusing elements is doped with a machine-readable tracer that emits a characteristic signal at a first frequency in the ultraviolet spectrum.

[0049] Examples of methods for manufacturing micro-optical devices according to various embodiments of the present disclosure include methods wherein the machine-readable tracer is a phosphorescent up-converter that absorbs light energy at a second frequency in the infrared spectrum.

[0050] Examples of methods for manufacturing micro-optical devices according to various embodiments of the present disclosure include methods wherein the machine-readable tracer is a strontium aluminate-based pigment.

[0051] Examples of methods for manufacturing micro-optical devices according to various embodiments of the present disclosure include methods wherein the machine-readable tracer is provided as a suspension in a radiation-curable polymer.

[0052] Examples of methods for manufacturing micro-optical devices according to various embodiments of the present disclosure include methods wherein the machine-readable tracer is added at a concentration of 0.1% to 0.6% of the weight of the mixture of the tracer and the radiation-curable polymer.

[0053] Examples of methods for manufacturing micro-optical devices according to various embodiments of the present disclosure include methods further comprising adding a surfactant to keep the machine-readable tracer suspended prior to curing.

[0054] Examples of methods for manufacturing micro-optical devices according to various embodiments of the present disclosure include methods wherein the device does not include a background coating applied to the icon layer.

[0055] Examples of methods for manufacturing micro-optic devices according to various embodiments of the present disclosure include methods in which the micro-optic security device has a thickness of 75 microns or greater.

[0056] While the present disclosure has been described by various embodiments, various changes and modifications could be suggested by those skilled in the art. It is the intention that the present disclosure encompass such changes and modifications as fall within the scope of the claims.

Claims

1. A micro-optical security device, comprising: an optical spacer layer (110) having a first side and a second side; an icon layer (120) comprising a plurality of image icons of a first color disposed on the first side of the optical spacer layer; and a focusing layer (105) comprising a plurality of refractive focusing elements (107) disposed on the second side of the optical spacer layer, wherein the plurality of refractive focusing elements project a composite magnified image of the plurality of image icons, wherein the image icons of the first color project portions of the composite magnified image having the first color, and wherein a refractive focusing element of the plurality of refractive focusing elements is doped with a machine-readable tracer that emits a characteristic signal at a first frequency in the ultraviolet spectrum. the machine-readable tracer is a phosphorescent up-converter that absorbs light energy at a second frequency in the infrared spectrum.

2. The micro-optical security device of claim 1, wherein, the machine-readable tracer is a strontium aluminate-based pigment.

3. The micro-optical security device of claim 1, wherein, the machine-readable tracer is provided as a suspension in a radiation-curable polymer.

4. The micro-optical security device of claim 1, wherein, the machine-readable tracer is added at a concentration of 0.1% to 0.6% by weight of the mixture of tracer and radiation-curable polymer.

5. The micro-optical security device of claim 4, wherein, 6. The micro-optical security device of claim 4, further comprising a surfactant to maintain the machine-readable tracer in suspension prior to curing. the device does not include a background coating applied to the icon layer.

7. The micro-optical security device of claim 1, wherein, the micro-optical security device has a thickness of 75 microns or greater.

8. The micro-optical security device of claim 1, wherein, 9. A method of making a micro-optical security device, the method comprising: providing an optical spacer layer having a first side and a second side; forming an icon layer (205) comprising a plurality of image icons of a first color on the first side of the optical spacer layer; and forming a focusing layer (210, 215) comprising a plurality of refractive focusing elements on the second side of the optical spacer layer, wherein the plurality of refractive focusing elements project a composite magnified image of the plurality of image icons, wherein the image icons of the first color project portions of the composite magnified image having the first color, and wherein a refractive focusing element of the plurality of refractive focusing elements is doped with a machine-readable tracer that emits a characteristic signal at a first frequency in the ultraviolet spectrum. the machine-readable tracer is a phosphorescent up-converter that absorbs light energy at a second frequency in the infrared spectrum.

10. The method of claim 9, wherein, the machine-readable tracer is a strontium aluminate-based pigment.

11. The method of claim 9, wherein, the machine-readable tracer is provided as a suspension in a radiation-curable polymer.

12. The method of claim 9, wherein, the machine-readable tracer is added at a concentration of 0.1% to 0.6% by weight of the mixture of tracer and radiation-curable polymer.

13. The method of claim 12, wherein, 14. The method of claim 12, further comprising adding a surfactant to maintain the machine-readable tracer in suspension prior to curing. the device does not include a background coating applied to the icon layer.

15. The method of claim 9, wherein, the micro-optical security device has a thickness of 75 microns or greater.

16. The method of claim 9, wherein, ​

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