Micro-optic security devices with absolute registration and methods for manufacturing same using semi-collimated curing light

Abstract

A micro-optic security device (450) includes an array of focusing elements (410) configured to focus light rays incident towards a first side of the micro-optic security device. The security device further includes a first array of icon elements (495) disposed on the first side of the micro-optic security device. Views of image icons of the first array of icon elements are projected through the array of focusing elements to viewpoints within a first range of viewing angles, and the views of the image icons of the first array of image icons are not telecentric. Uncured material is cured through light going through the focusing elements, cured parts being image icons, uncured parts being removed. The light is semi-collimated, which means that some rays are parallel to each other and others not. Telecentric means magnification does not change with depth.

Description

MICRO-OPTIC SECURITY DEVICES WITH ABSOEUTE REGISTRATION AND METHODS FOR MANUFACTURING SAME USING SEMI-COLLIMATED CURING EIGHTTECHNICAL FIELD

[0001] The present disclosure relates to improvements in micro-optic security devices and methods of making same. More specifically, the present disclosure relates to security devices with absolute registration and methods of manufacturing same using semi-collimated curing light.BACKGROUND

[0002] Manufacturing passports, banknotes, and other documents (referred to herein as “security documents”) whose constructional features include hard-to-reproduce indicia of the documents’ authenticity against counterfeiting remains an ongoing source of technical challenges and opportunities for improvement in the field of security document design.

[0003] The design and manufacture of security documents and security features with hard-to- reproduce indicia of authenticity requires finding an optimum balance between competing, and often contrary performance and design goals. For example, in the currency space, it is important that security features provide visual effects which are engaging, appear consistent across a run of security documents, and are extremely difficult for malicious actors to duplicate. Achieving these performance goals is most readily attainable through small batch manufacturing, and specialized tooling for large runs of documents. At the same time, it is also important security documents with the aforementioned security features be made at great scale, as small runs of security documents such as banknotes and passports are of limited, if any, practical value. Still further, it is desirable that the designs of security features can be readily changeable, for example, to restrict the pool of documents from which authentic security features can be harvested to produce inauthentic copies. For example, if a series of banknotes utilize a common or highly similar security feature across multiple denominations, the opportunities for malicious actors to repurpose security features from older, or low-denomination notes to make multiple forgeries of the same note, or up-cycled forgeries (i.e., a forgery of a high value note using a security device harvested from a lower denomination note) are increased. Unsurprisingly, this is undesirable.

[0004] Micro-optic security devices which provide optically variable effects (for example, floating or sunken images, images which appear three-dimensional, or dynamic movement in response to changes in viewing angle) through the orchestrated magnification and projection of micro- or nano-scale icon features through an array of focusing elements (for example, micro-mirrors or micro-reflectors) strike an excellent balance between the competing performance and manufacturing criteria discussed above.

[0005] In many cases, the performance of such micro-optic systems can be improved through tightening the registration between icons of the icon layer and the lenses of the system. As used in this disclosure, the expression “tightening the registration between icons of the icon layer and the lenses of the system,” encompasses increasing the extent to which icon material is positioned in relation to the lens. With increased registration control, it is possible for lens-icon systems to project increasingly complex (forexample, with greater or smoother changes in the projected image across a range of viewing angles) or choreographed (for example, making a specific image appear at a specific viewing angle) images.

[0006] While it is possible to achieve perfect, or near-perfect registration of icon material to predetermined locations within the footprints of focusing elements by performing through-the-lens curing of radiation curable material (for example, UV-curable polymers) in the focal plane of the focusing elements of an array of focusing elements using collimated light (for example, from a laser light source), this approach presents can present challenges in terms of manufacturing throughput. This is because collimated curing light (for example, laser energy) is typically only available in narrow, highly focused beams. Because of this limited beam width of most, if not all, commercially practical sources of collimated curing energy, only a small portion of the footprint may be imaged by the beam, which can slow down the rate at which the icon layer is formed.

[0007] Accordingly, developing faster, higher-throughput methods for producing tightly registered icon layers using through-the-lens curing of radiation curable material remains a source of technical challenges and opportunities for improvement in the art.SUMMARY

[0008] The present disclosure relates to a security document with methods of manufacturing security devices with absolute registration using semi-collimated curing light, and micro-optic security devices produced according to such methods.

[0009] In a first embodiment, a method includes applying a first volume of uncured radiation-curable material to a first side of a micro-optic device, the micro-optic device comprising an array of focusing elements, the array of focusing elements comprising a plurality of focusing elements configured to focus light rays incident towards the first side. The method further includes controlling an external light source disposed at a first viewpoint to direct rays of semi-collimated light towards the array of focusing elements, converting part of the first volume of uncured radiation-curable material into image icons of cured radiation- curable material on the first side of the micro-optic device, leaving a remaining part of the first volume of uncured radiation-curable material as a second volume of radiation-curable material and removing the second volume of uncured radiation-curable material from the first side of the micro-optic device. Views of the image icons are projected through the array of focusing elements to viewpoints within a first range of viewing angles. The first viewpoint is within the first range of viewing angles, and the rays of semicollimated light comprise a first component of parallel rays of light and a second component comprising rays of light which are not parallel to the first component.

[0010] In a second embodiment, a micro-optic security device includes an array of focusing elements, the array of focusing elements comprising a plurality of focusing elements configured to focus light rays incident towards a first side of the micro-optic security device. The security device further includes a first array of icon elements disposed on the first side of the micro-optic security device. Views of image icons of the first array of icon elements are projected through the array of focusing elements to viewpoints withina first range of viewing angles, and the views of the image icons of the first array of image icons are not telecentric.

[0011] Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims.

[0012] Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term “couple” and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and / or. The phrase “associated with,” as well as derivatives thereof, means to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.

[0013] Definitions for other certain words and phrases are provided throughout this patent document. Those of ordinary skill in the art should 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 THE DRAWINGS

[0014] 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 reference numerals represent like parts:

[0015] FIGURE 1 illustrates an example of a security document according to some embodiments of this disclosure;

[0016] FIGURE 2 illustrates an example of a security device according to various embodiments of this disclosure;

[0017] FIGURE 3 illustrates aspects of curing image icon material with collimated and semicollimated light according to various embodiments of this disclosure;

[0018] FIGURES 4A and 4B illustrate aspects of curing image icon material with collimated and semicollimated light according to various embodiments of this disclosure; and

[0019] FIGURE 5 illustrates an example of a method for forming image icons using semi-collimated cure light according to certain embodiments of this disclosure.DETAILED DESCRIPTION

[0020] FIGURES 1 through 5, discussed below, and the various embodiments used to describe the principles of the present disclosure are by way of illustration only and should not be construed in any wayto limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged security document.

[0021] Although the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as falling within the scope of the claims.

[0022] FIG. 1 illustrates an example of a security document according to certain embodiments of this disclosure.

[0023] Referring to the non-limiting example of FIGURE 1, an example of a security document 100 according to various embodiments of this disclosure is shown. In this illustrative example, security document 100 is a currency note, though other embodiments (for example, tickets, passports, identification papers, etc.) are within the contemplated scope of this disclosure. According to some embodiments, security document 100 comprises a polymeric or a fibrous substrate 105. In embodiments in which substrate 105 is fibrous, it can be formed from a wet web of fibrous material (for example, wood pulp, cotton fiber, linen fiber, flax fiber, sisal fiber, hemp fiber, Abaca fiber, Kozo fiber, Mitsumata fiber, bamboo fiber, Kenaf fiber and or synthetic fiber), which is laid down (for example, in a Fourdrinier process) at a first, baseline fiber density. Regions of the web in which the first fiber density is not altered while the web is wet (for example, through the use of wire rolls, electrotypes, or other watermarking tools) prior to pressing, drying and in some embodiments, calendaring, form bulk regions 110 of security document 100. As used in this disclosure, the expression “bulk region” encompasses a portion of a fibrous substrate embodying one or more of a baseline fiber density, baseline light absorption, or baseline caliper thickness. Put differently, as used in this disclosure, the expression “bulk region” encompasses portions of a finished fibrous substrate in which the locations of the constituent fibers are not deliberately altered (for example, through the use of embossed wirecloth or electrotypes) as part of the papermaking process.

[0024] As shown in the explanatory example of FIG. 1, security document 100 further comprises one or more security features 115 adhered to the surface of security document 100. Security feature 115 comprises a thin section of material with one or more optical structures, such as structures comprising an embossed or cast-cured outer surface that provides an optically variable effect. Examples of optical structures provided on security feature 115 include, without limitation, micro-lenses, diffractive structures, and micro-optic icons. Examples of optically variable effects provided by the optical structures of security feature 115 include, without limitation, color shift effects, and synthetic images, characterized by the synthetic projection of portions of image icons across an array of image icons by focusing elements of an array of focusing elements, wherein the scale ratio (i.e., the ratio of the repeat period of the focusing elements to the repeat period of the image icons) is approximately 1.000.

[0025] Security document 100 may comprise one or more functional watermarks 120. According to various embodiments, functional watermarks 120 comprise one or more regions in which the fiber density of fibrous substrate 105 is deliberately altered (either increased or decreased) from the fiber density in bulk region 110 to form a visible pattern of light (i.e., allowing more light to pass in transmission through thefibrous substrate than bulk region 110) and / or dark (i.e., less light to pass in transmission through the fibrous substrate than bulk region 110) elements. Additionally, at least a portion of functional watermark 120 can be covered by part of security feature 115, wherein security feature 115 is maintained in contact with functional watermark 120 by an adhesive bond. According to various embodiments, functional watermark 120 contacting security feature 115 comprises one or more light or dark elements with edges that are substantially perpendicular to one or more peel directions 125 of security feature 115. As used in this disclosure, the expression “peel direction” encompasses a direction in which the separation of security feature 115 is propagated in a direction generally corresponding a local minimum of the separation line. By lifting security feature 115 away from fibrous substrate 105 in a peel direction 125 substantially perpendicular to a separation line between security feature 115 and fibrous substrate 105, the total peeling force applied to fibrous substrate 105 is minimized. All other things being equal, malicious actors may be reasonably expected to attempt to harvest security feature 115 by separating security feature 115 from fibrous substrate 105 along peel direction 125, in order to minimize the force applied to security feature 115. Depending on its shape, security feature 115 may present more than one peel direction.

[0026] FIG. 2 illustrates constructional aspects of a micro-optic security device (for example, security feature 115 in FIG. 1) comprising part of a security document according to various embodiments of this disclosure.

[0027] Referring to the non-limiting example of FIG. 2, optical security device 200 comprises a plurality of focusing elements 205 (including, for example, focusing element 207), and an arrangement of image icons 220 (including, for example, image icon 221). According to various embodiments, each focusing element of plurality of focusing elements 205 has a footprint, in which one or more image icons of arrangement of image icons 220 is positioned. Further, image icons of arrangement of image icons 220 can be formed by through-the-lens curing of uncured material disposed in the footprints of arrangement of focusing elements 205. Collectively, the focusing elements of plurality of focusing elements 205, magnify portions of image icons 220 to produce a synthetic magnification effect (also referred to as “synthetic image”) wherein the individually microscopic image icons are collectively magnified by the plurality of focusing elements 205 to produce an image which dynamically reacts (for example, by appearing to move, or change colors) in response to shifts in viewing angle. Given the small scale and tight manufacturing tolerances of the constituent structures of optical security device providing a moire magnification effect, many malicious actors are not able to produce counterfeit versions of optical security device 200. However, the persistent incentives for malicious actors to produce security documents imply that, for producers of legitimate security documents there is a similarly durable demand to develop better and harder-to-reproduce security features, in order to stay ahead of criminal ingenuity. As it is foreseeable that forgers and other malicious actors may, eventually, be able to produce simple micro-optic systems which provide synthetic images of an icon layer, it is important that legitimate actors be able to produce devices with icon layers supporting features beyond the design and manufacturing capabilities of illegitimate actors.

[0028] Image icons 220 can comprise a plurality of sets of icons, wherein each set of icons occupies regions within focusing elements’ footprints associated with predetermined viewing angles. Orchestrating the appearance of visual effects with predetermined viewing angles (i.e., that a first image is projected when the security device is viewed head-on, and a second image is projected when the security device is viewed from an off-axis viewing angle) is premised on achieving precise control over each icon’s position within the footprint of each focusing element. From a technical standpoint, attaining such registration is very challenging. Because of the technical challenges associated with producing a visual effect which is orchestrated over a predetermined range of viewing angles, optical security device 200 is, in many cases, a trusted visual indicium of a security document’s (for example, security document 260) authenticity.

[0029] According to certain embodiments, plurality of focusing elements 205 comprises a planar array of micro-optic focusing elements. In some embodiments, the focusing elements of plurality of focusing elements 205 comprise micro-optic refractive focusing elements (for example, plano-convex or GRIN lenses). Refractive focusing elements of plurality of focusing elements 205 are, in some embodiments, produced from light cured resins with indices of refraction ranging from 1.35 to 1.7, and have diameters ranging from 5pm to 200pm. In various embodiments, the focusing elements of plurality of focusing elements 205 comprise reflective focusing elements (for example, very small concave mirrors), with diameters ranging from 5pm to 50pm. While in this illustrative example, the focusing elements of plurality of focusing elements 205 are shown as comprising circular plano-convex lenses, other refractive lens geometries, for example, lenticular lenses, are possible and within the contemplated scope of this disclosure .

[0030] As shown in the illustrative example of FIG. 2, arrangement of image icons 220 comprises a set of image icons (including image icon 221), positioned at predetermined locations within the footprints of the focusing elements of plurality of focusing elements 205. According to various embodiments, the individual image icons of arrangement of image icons 220 comprise regions of light cured material associated with the focal path of semi-collimated light passing through plurality of focusing elements 205 from a projection point associated with a first viewpoint within a predetermined range of viewing angles. In some embodiments, the individual image icons of arrangement of image icons 220 are not provided within a structured image icon layer. As used in this disclosure, the term “structured image layer” encompasses a layer of material (for example, a light-curable resin) which has been embossed, or otherwise formed to comprise structures (for example, recesses, posts, grooves, or mesas) for positioning and retaining image icon material. According to various embodiments, the individual image icons of arrangement of image icons 220 are provided within a structured image layer, the structured image layer comprising one or more of voids, mesas, or posts, which act as retaining structures to hold micro- and nano-scale volumes of colored material.

[0031] As shown in the illustrative example of FIGURE 2, in certain embodiments, optical security device 200 includes an optical spacer 210. According to various embodiments, optical spacer 210 comprises a film of substantially transparent material (for example, polyethylene terephthalate (“PET”) or Biaxially- Oriented Polypropylene (“BOPP”)) which operates to position image icons of arrangement of image icons220 in or around the focal plane of focusing elements of plurality of focusing elements 205. In certain embodiments according to this disclosure, optical spacer 210 comprises a manufacturing substrate upon which one or more layers of light curable material can be applied, to form one or more of arrangement of image icons 220 or plurality of focusing elements 205.

[0032] According to various embodiments, optical security device 200 comprises one or more regions of light-cured protective material which occupy the spaces between the image icons of arrangement of image icons 220. In some embodiments, the arrangement of image icons 220 is first formed (for example, by selectively curing and removing liquid light-curable material on optical spacer 210), and then a layer of clear, light-curable material is applied to fill spaces between the image icons of arrangement of image icons 220 and then flood-cured to create a protective layer, which protects the image icons from being moved from their positions within the footprints of focusing elements of plurality of focusing elements 205. In certain embodiments, the light-curable material used to form arrangement of image icons 220 is a pigmented, ultraviolet (UV)-curable polymer. Examples of suitable radiation (for example, UV-radiation) curable polymers for forming arrangement of image icons 220 include, without limitation, isodecyl acrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyester tetraacrylate, trimethylolpropane triacrylate, and hexanediol diacrylate.

[0033] In some embodiments, arrangement of image icons 220 is affixed to a second substrate 230, which operates to protect and secure arrangement of image icons 220 and provide an interface for attaching optical security device 200 to a substrate 250 as part of security document 260. In some embodiments, optical security device 200 is affixed to substrate 250 during the manufacture of substrate in a paper-making machine, such as a Fourdrinier machine. According to some embodiments, optical security device 200 is affixed to substrate 250 by a layer of adhesive between the arrangement of image icons and a top surface of substrate 250.

[0034] In certain embodiments according to this disclosure, optical security device 200 comprises a seal layer 240. According to certain embodiments, seal layer 240 comprises a thin (for example, a 2pm to 50pm thick) layer of substantially clear material which interfaces on a lower surface, with focusing elements of the plurality of focusing elements 205 and comprises an upper surface with less variation in curvature (for example, by being smooth, or by having a surface whose local undulations are of a larger radius of curvature than the focusing elements) than the plurality of focusing elements 205.

[0035] While FIGURE 2 provides one example of an optical security device according to various embodiments, the present disclosure is not so limited.

[0036] FIGURE 3 provides a high-level overview of some methods, apparatus, and technical benefits of certain embodiments according to the present disclosure.

[0037] Referring to the non-limiting example of FIGURE 3, image 300 shows two sections of microoptic security device (i.e., first section 305A & second section 305B) during manufacture. In this illustrative example, both sections 305A and 305B are shown with their arrays of focusing elements (for example, first array of focusing elements 310A and second array of focusing elements 310B) facing the viewer. While, inthis explanatory example, first and second arrays of focusing elements 310A and 31 OB are arrays of lenticular (sometimes referred to as “cylindrical”) refractive focusing elements, embodiments according to this disclosure are not so limited, and the methods of selective exposing uncured radiation curable material in an icon layer using semi-collimated light described herein can be practiced using spherical, aspherical, gradient index, and Fresnel-type refractive lenses. Additionally, while doing so may require modifications of techniques used with refractive focusing elements (for example, a temporary, or sacrificial array of focusing elements may be required, or the range of angles of incidence of curing light may be restricted, and uncured radiation curable material may need to be applied in small localized passes, rather than in a flood coat), the techniques described herein can also be practiced to create image icons for micro-optic security devices with reflective focusing elements.

[0038] While not visible in image 300, sections 305A and 305B each comprise first side 315A and second side 315B, which are disposed in, or near, the focal plane of the lenses of each of focusing element arrays 310A and 310B. Sides 315A and 315B are, in this example, coated with a thin layer of uncured, pigmented radiation-curable material, such as isodecyl acrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyester tetraacrylate, trimethylolpropane triacrylate, and hexanediol diacrylate.

[0039] As shown with reference to first section 305 A, image icons occupying portions of each lens’s footprints perfectly registered to predetermined viewing angles can be formed by directing collimated light energy (typically, ultraviolet light from a laser beam) from a location comprising a viewpoint at a predetermined viewing angle. As used in this disclosure, the expression “collimated” refers to light which is transmitted as a beam of substantially parallel rays, wherein the beam exhibits little to no divergence in width away from the source. Focusing elements of first array of focusing elements 310A focus the light energy to locations in their footprints on first side 315A, causing the radiation-curable material in these locations to cure by undergoing light-initiated cross-linking which transforms uncured radiation curable material (which typically has a gooey, thick, gel-like consistency) to dots of structurally stable solid material adhered to first section 305 A, which remains adhered after the uncured radiation-curable material on first side 315A is removed. Further examples of methods and apparatus for forming icon structures using through-the-lens U.S. Patent Publication No. 2022 / 0297463, the contents of which are incorporated by reference herein in their entirety.

[0040] While through-the-lens curing by selective exposure to collimated light energy provides exceptional registration accuracy of icon material to viewing angles and overall control of the image(s) of the icon layer as projected by the finished micro-optic security device, the characteristics of curing icon material with collimated light include: a.) the limited beam widths of collimated light sources mean that only a limited portion of the each footprint can be cured on a single exposure pass; and b.) the parallelism of the rays of curing light produce an image which appears telecentric. As used in this disclosure, the expression “telecentric” refers to a view whose scale or magnification does not change with depth. While neither a.) nor b.) are undesirable features, the fact remains that they may not be all the features manufacturers desire. Put differently, creating icon structures with narrow beams of collimated light is likecoloring with a fine-liner pen - perfectly possible, but potentially not as efficient as coloring with a chiseltipped marker. For applications (for example, printing large runs of banknotes) where scale is of great importance, the limited exposure area provided by many collimating beams can present an undesirable manufacturing bottleneck. Similarly, while telecentric views may be visually striking and unique, designers and users of security documents may desire the option of security features which project images having different depth vs. perceived scale relationships. Thus, while there is nothing “wrong,” with using collimated light for creating precisely registered icon elements via through-the-lens curing, it is nonetheless desirable to expand the range of design and manufacturing options available to legitimate manufacturers of security documents and security devices for same.

[0041] As described in greater detail herein, by creating image icons by passing semi-collimated light through an array of focusing elements to selective cure parts of a layer of uncured radiation curable material, it is possible to both increase the coverage of the curing light within the footprints of the focusing elements (making it easier to cure all of the uncured material associated with a desired range of viewing angles in a single, or at a minimum, fewer passes than necessary with collimated light), and obtain images which do not appear to present telecentric views.

[0042] Referring to the illustrative example of FIG. 3, certain embodiments according to this disclosure enable broader exposure of uncured radiation curable material and the creation of icon structures which do not present telecentric views by partially relaxing the extent to which the rays of curing light projected upon the focusing elements are fully parallel. As shown in FIG. 3, the rays of collimated light are, by definition, parallel to one another and strike the plane of first section 305A at a single angle of incidence. By contrast, the rays of semi-collimated light 325 are substantially coplanar but vary in the angles of incidence with which they strike the plane of second section 305B. As used in this disclosure, the expression “semi-collimated light” encompasses light which comprises at least two components: a first component of parallel rays of light and a second component of rays of light which are not parallel to the first component. According to certain embodiments, the second component can comprise rays which are not parallel to one another, but are co-planar to the first component, or are parallel to each other. In some embodiments, the expression “semi-collimated light” more generally encompasses light that impinges upon the plane of an array of focusing elements at a predetermined, non-zero (i.e., not collimated light) range of angles of incidence.

[0043] FIGS. 4A and 4B provide an additional example of the use of semi -collimated curing light for through-the-lens curing of icon material according to various embodiments of this disclosure and illustrate the differences between curing with semi-collimated and collimated light sources. For consistency and convenience of cross-reference, elements common to both FIGURES 4A and 4B are numbered similarly.

[0044] Referring to the illustrative example of FIG. 4A, an unfinished first section 400 of a microoptic security device is shown. First section 400 comprises a spacer layer 405 (for example, optical spacer 210 in FIGURE 2) atop which an array of focusing elements 410 is disposed. In this explanatory example, the focusing elements of array of focusing elements 410 are spherical lenses, but embodiments accordingto the present disclosure are not so limited, and can include, without limitation, cylindrical lenses, Fresnel lenses, aspherical lenses, and reflective lenses. Each focusing element of array of focusing elements 410 is associated with a footprint (shown in the figures as FPi, FP2 and FP3).

[0045] As shown in FIG. 4A, a volume of uncured radiation-curable material 415 is applied as a layer on the underside of spacer layer 405. As applied (for example, with a Mayer rod or squeegee), the uncured radiation-curable material typically has a gel-, or goo-like consistency with sufficient wettability to coat the underside of spacer layer 405 at a consistent depth.

[0046] As noted elsewhere in this disclosure, image icons, or small volumes of cured radiation-curable material can be formed in targeted, or predetermined locations within the footprints of the constituent focusing elements of array of focusing elements 410. Once formed, the image icons can project images, including optically variable images, through array of focusing elements 410. Further, the viewing angles at which the projected images appear to a user holding security device comprising first section 400 correspond to angles from which the curing light is directed towards the array of focusing elements. In this way, precise angular control over the range of viewing angles at which particular items image content is projected by the finished security device can be achieved. Put differently, the structural properties of the light rays directed upon the focusing elements to form image icons are largely determinative of the structural properties of the light rays projected through the array of focusing elements by the finished security device.

[0047] Referring to the illustrative example of FIG. 4A, rays of collimated curing light 420 are shown as being directed at first section 400 from a collimated light source 425. Collimated light source 425 is disposed at a first viewpoint, and causes parallel rays of curing light 420 to impinge upon array of focusing elements 410 at a first angle of incidence 61, whereupon the rays of light are refracted by the focusing elements and directed to locations within the footprints of the focusing elements, causing portions of uncured radiation-curable material 415 to cure and adhere to spacer layer 405, forming image icons (for example, image icon 430). The remaining uncured radiation-curable material 415 can be washed off or reexposed from a different angle until a full icon array has been generated.

[0048] As noted elsewhere in this disclosure, the structure of the light rays projected by a finished multi-lens / multi-icon micro-optic security device produced with an icon structure produced by through-the- lens curing is dependent on the structure of the light rays used to cure the icon layer. Thus, because the icons were formed with rays of collimated curing light emanating from light source 425, the so-cured icons of first section 400 of the finished micro-optic security device project substantially parallel rays of light when viewed through array of focusing elements 410, resulting in a generally telecentric image. As noted elsewhere in this disclosure, while telecentric views of an icon layer are not undesirable, they may not be the only image views desired by users and designers of micro-optic security.

[0049] FIG. 4B illustrates an example of curing uncured icon material in a layer of radiation-curable material according to various embodiments of this disclosure. Referring to the illustrative example of FIG. 4B, prior to exposing uncured radiation-curable material 415, second section 450 is structurally identical tofirst section 400, and likewise comprises an array of focusing elements 410 disposed above a spacer layer 405.

[0050] However, in the illustrative example of FIG. 4B, the curing light 499 for forming image icons is semi-collimated, rather than fully collimated, as shown in the example of FIG. 4A. As used in this disclosure, the expression “semi-collimated light” encompasses a transmission of light rays in which part of the light rays are parallel to one another, but in which not all of the light rays are parallel to one another. Thus, semi-collimated light is structured light, but less rigidly structured than collimated light. In some embodiments, semi-collimated light can be produced by passing all or part of a beam fully collimated light through a moving diffuser to ensure that not all of the rays of light are mutually parallel.

[0051] As shown in FIG. 4B, rays of semi-collimated curing light 499 are transmitted from a light source 497 disposed at a first viewpoint. Unlike collimated curing light 420 in FIG. 4A, the constituent rays of curing light 499 are not fully parallel and exhibit a variation in incident angle (62) to second section 450. Curing light 499 impinges upon the focusing elements of array of focusing elements 410, which focus the incident light energy to predetermined locations within the footprints of the focusing elements of array of focusing elements 410 associated with a range of viewing angles, which includes curing light 499. The received light energy causes portions of uncured radiation-curable material 415 to cure and form image icons (for example, image icons 495) in portions of the focusing elements’ footprints associated with a predetermined range of viewing angles which includes the viewpoint of light source 497. Thus, through- the-lens curing with semi -collimated light preserves the registration control of collimated light but provides additional features. As shown in FIG. 4B and exaggerated for emphasis, by using light with some spread in directionality, image icons (for example, image icon 495) can be formed across a larger area of each focusing elements’ footprint than with purely collimated light. In other words, slightly relaxing the parallelism and structure of the curing light by using semi-collimated light, allows designers and manufacturers of optical to, in effect, “paint with a broader brush” with respect to creating icon layers via through-the-lens curing of uncured radiation-curable material.

[0052] Additionally, because the structure of the light rays of the image projected through the lens array of a lens-layer / icon-layer micro-optic security device is dependent on the structure of the light passed through the lens array to cure and form the icon layer, producing an icon layer using semi-collimated light can produce a micro-optic device in which the rays of light projected from the icon layer through the array of focusing elements to provide an image have a different structure than that produced using purely collimated light. Put more simply, the image projected from icons formed using semi-collimated light can look different than similar images formed using only collimated light.

[0053] Referring to the illustrative example of FIG. 4B, because the rays of light of curing light 499 exhibit an angular variation 02, so too, do rays of light projected from the formed icons back up through array of focusing elements 410. Thus, in FIG. 4B, light rays projected back up through array of focusing elements 410 exhibit a similar angular variation to the light rays of curing light 499. In this regard, whenviewed from the viewpoint of light source 497, second section 450 does not project a telecentric view of the icon material.

[0054] FIGURE 5 illustrates operations of an example method 500 for creating tightly registered icon layers of a multi-lens / multi-icon micro-optic device using semi-collimated light, according to various embodiments of this disclosure. The operations of method 500 can be performed on a static section of unfinished micro-optic material comprising an array of focusing elements, or as part of a reel-to-reel manufacturing process on a moving web of unfinished micro-optic material.

[0055] Referring to the illustrative example of FIG. 5, at operation 505, a first volume (for example, volume of uncured radiation-curable material 415 in FIG. 4B) of uncured radiation-curable material is applied to a first side of an unfinished micro-optic device (for example, second section 450 in FIG. 4B). The unfinished micro-optic device comprises, at a minimum, an array of focusing elements, and a first side defining a plane which can physically support the first volume of uncured radiation-curable material, and which can selectively focus incident light upon locations in the first volume of uncured radiation-curable material within predetermined locations within the footprints of the focusing elements of the array of focusing elements. The first volume of uncured radiation-curable material can be applied to the first side using a Mayer rod, a squeegee, or any other suitable method of forming athin coat of low-viscosity material.

[0056] At operation 510, an external light source (for example, light source 497 in FIG. 4B) located at a first viewpoint within a predetermined range of viewing is controlled to direct rays of semi-collimated light (for example, curing light 499) towards the array of image icons. In some embodiments, semicollimated light can be obtained by passing a rotating, or otherwise moving diffuser into a beam of collimated light, thereby de-collimating some, but not all, of the rays of light in the beam to create angular variation within the stream of light directed towards the array of focusing elements. According to some embodiments, the semi-collimated light comprises a first component, consisting of rays of light which are parallel to each other, and a second component, comprising rays of light not parallel to each other. The semi-collimated light can exhibit a predetermined degree of angular variation (for example, 62 in FIG. 4B) in terms of angles of incidence towards the micro-optic security device.

[0057] The semi-collimated light can be focused by the array of focusing elements to locations within the footprints of focusing elements of the array of focusing elements associated with viewing angles encompassing the viewpoint of the source of semi-collimated curing light. The semi-collimated curing light cures uncured radiation-curable material in the areas of focus, creating image icons, which can be projected by the array of focusing elements to provide an image visible at viewing angles encompassing the viewpoint of the light source. In some embodiments, the rays of light of the projected image retain aspects of the structure of the curing light. Thus, where the curing light is not fully collimated, the projected image does not have a telecentric (i.e., characterized by parallelism in the rays of light providing the image) view.

[0058] At operation 515, a second volume, comprising a subset of the first volume (because some of the first volume was cured and formed into image icons), of uncured radiation-curable material removed from the first side, leaving only cured image icons disposed in locations in the focusing elements’ footprintsassociated with ranges of view angles that include the viewpoint of the source of semi-collimated curing light.

[0059] Multiple iterations of operations 505-515 can be performed to create an icon layer with multiple projected images or containing image icons of multiple colors. Additionally, operations 505-515 can be performed in conjunction with curing operations using collimated light, to create hybrid images with telecentric and non-telecentric components. As noted elsewhere, embodiments according to this disclosure enlarge the palette of design and manufacturing tools available to designers and manufacturers of legitimate security devices.

[0060] Examples of methods according to the present disclosure include methods comprising applying a first volume of uncured radiation-curable material to a first side of a micro-optic device, the micro-optic device comprising an array of focusing elements, the array of focusing elements comprising a plurality of focusing elements configured to focus light rays incident towards the first side, controlling an external light source disposed at a first viewpoint to direct rays of semi-collimated light towards the array of focusing elements, converting part of the first volume of uncured radiation-curable material into image icons of cured radiation-curable material on the first side of the micro-optic device, leaving a remaining part of the first volume of uncured radiation-curable material as a second volume of radiation-curable material, and removing the second volume of uncured radiation-curable material from the first side of the micro-optic device, wherein views of the image icons are projected through the array of focusing elements to viewpoints within a first range of viewing angles, wherein the first viewpoint is within the first range of viewing angles, and wherein the rays of semi-collimated light comprise a first component of parallel rays of light and a second component comprising rays of light which are not parallel to the first component.

[0061] Examples of methods according to the present disclosure include methods, wherein views of the image icons within the first range of viewing angles are not telecentric.

[0062] Examples of methods according to the present disclosure include methods, wherein the views of the image icons comprise a synthetic image.

[0063] Examples of methods according to the present disclosure include methods, wherein the first volume of uncured radiation-curable material is applied to spaces in a retaining structure disposed on the first side of the micro-optic device.

[0064] Examples of methods according to the present disclosure include methods, wherein the first range of viewing angles is a predetermined range of viewing angles.

[0065] Examples of methods according to the present disclosure include methods, wherein each focusing element of the array of focusing elements has a footprint, and wherein the image icons are registered to predetermined locations within the footprints of the focusing elements of the array of focusing elements.

[0066] Examples of methods according to the present disclosure include methods, wherein the microoptic device comprises a section of web in a roll-to-roll process, and wherein the first volume of uncured radiation-curable material is moving relative to the external light source.

[0067] Examples of methods according to the present disclosure include methods, wherein the section of web is relative to the external light source at a rate of 75 feet per minute or greater.

[0068] Examples of methods according to the present disclosure include methods, wherein the uncured radiation-curable material comprises one or more of isodecyl acrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyester tetraacrylate, trimethylolpropane triacrylate, and hexanediol diacrylate.

[0069] Examples of methods according to the present disclosure include methods, wherein the external light source projects light rays having an angle of incidence between 0 and 180 degrees to the array of focusing elements.

[0070] Examples of micro-optic security devices according to the present disclosure include microoptic security devices comprising an array of focusing elements, the array of focusing elements comprising a plurality of focusing elements configured to focus light rays incident towards a first side of the microoptic security device and a first array of icon elements disposed on the first side of the micro-optic security device, wherein views of image icons of the first array of icon elements are projected through the array of focusing elements to viewpoints within a first range of viewing angles, and wherein the views of the image icons of the first array of image icons are not telecentric.

[0071] Examples of micro-optic security devices according to the present disclosure include microoptic security devices, wherein image icons of the first array of image icons are formed by through-the-lens curing of uncured radiation-curable material using semi-collimated light.

[0072] Examples of micro-optic security devices according to the present disclosure include microoptic security devices, wherein the views of the first array of image icons comprise a synthetic image.

[0073] Examples of micro-optic security devices according to the present disclosure include microoptic security devices, wherein the first range of viewing angles is a predetermined range of viewing angles.

[0074] Examples of micro-optic security devices according to the present disclosure include microoptic security devices, wherein each focusing element of the array of focusing elements has a footprint, and wherein the image icons are registered to predetermined locations within the footprints of the focusing elements of the array of focusing elements.

[0075] Examples of micro-optic security devices according to the present disclosure include microoptic security devices, wherein the micro-optic device comprises a section of web in a roll-to-roll machine.

[0076] Examples of micro-optic security devices according to the present disclosure include microoptic security devices, wherein the image icons of the first array of image icons are formed from one or more of radiation-cured isodecyl acrylate, radiation-cured dipropylene glycol diacrylate, radiation-cured tripropylene glycol diacrylate, radiation-cured polyester tetraacrylate, radiation-cured trimethylolpropane triacrylate, and radiation-cured hexanediol diacrylate.

[0077] Although the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as falling within the scope of the claims.

[0078] The present disclosure should not be read as implying that any particular element, step, or function is an essential element, step, or function that must be included in the scope of the claims. Moreover, the claims are not intended to invoke 35 U.S.C. § 112(f) unless the exact words “means for” are followed by a participle.

Claims

WHAT IS CLAIMED IS:

1. A method comprising : applying (505) a first volume of uncured radiation-curable material to a first side of a micro-optic device (450), the micro-optic device comprising an array of focusing elements (410), the array of focusing elements comprising a plurality of focusing elements configured to focus light rays incident towards the first side; controlling (510) an external light source disposed at a first viewpoint to direct rays of semicollimated light towards the array of focusing elements, converting part of the first volume of uncured radiation-curable material into image icons (495) of cured radiation-curable material on the first side of the micro-optic device, leaving a remaining part of the first volume of uncured radiation-curable material as a second volume of uncured radiation-curable material; and removing (515) the second volume of uncured radiation-curable material from the first side of the micro-optic device, wherein views of the image icons are projected through the array of focusing elements to viewpoints within a first range of viewing angles, wherein the first viewpoint is within the first range of viewing angles, and wherein the rays of semi-collimated light comprise a first component of parallel rays of light and a second component comprising rays of light which are not parallel to the first component.

2. The method of claim 1, wherein the views of the image icons within the first range of viewing angles are not telecentric.

3. The method of claim 1, wherein the views of the image icons comprise a synthetic image.

4. The method of claim 1, wherein the first volume of uncured radiation-curable material is applied to spaces in a retaining structure disposed on the first side of the micro-optic device.

5. The method of claim 1, wherein the first range of viewing angles is a predetermined range of viewing angles.

6. The method of claim 1, wherein each focusing element of the array of focusing elements has a footprint, and wherein the image icons are registered to predetermined locations within the footprints of the focusing elements of the array of focusing elements.

7. The method of claim 1, wherein the micro-optic device comprises a section of web in a roll-to-roll process, andwherein the first volume of uncured radiation-curable material is moving relative to the external light source.

8. The method of claim 7, wherein the section of web is relative to the external light source at a rate of 75 feet per minute or greater.

9. The method of claim 1, wherein the first and second volumes of uncured radiation-curable material comprises one or more of isodecyl acrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyester tetraacrylate, trimethylolpropane triacrylate, and hexanediol diacrylate.

10. The method of claim 1 , wherein the external light source proj ects light rays having an angle of incidence between 0 and 180 degrees to the array of focusing elements.

11. A micro-optic security device (450) comprising: an array of focusing elements (410), the array of focusing elements comprising a plurality of focusing elements configured to focus light rays incident towards a first side of the micro-optic security device; and a first array of icon elements (495) disposed on the first side of the micro-optic security device, wherein views of image icons of the first array of icon elements are projected through the array of focusing elements to viewpoints within a first range of viewing angles, and wherein the views of the image icons of the first array of icon elements are not telecentric.

12. The micro-optic security device of claim 11 , wherein image icons of the first array of image icons are formed by through-the-lens curing of uncured radiation-curable material using semi-collimated light.

13. The micro-optic security device of claim 11, wherein the views of the first array of image icons comprise a synthetic image.

14. The micro-optic security device of claim 11, wherein the first range of viewing angles is a predetermined range of viewing angles.

15. The micro-optic security device of claim 11 , wherein each focusing element of the array of focusing elements has a footprint, and wherein the image icons are registered to predetermined locations within the footprints of the focusing elements of the array of focusing elements.

16. The micro-optic security device of claim 11, wherein the micro-optic device comprises a section of web in a roll-to-roll machine.

17. The micro-optic security device of claim 11, wherein the image icons of the first array of image icons are formed from one or more of radiation-cured isodecyl acrylate, radiation-cured dipropylene glycol diacrylate, radiation-cured tripropylene glycol diacrylate, radiation-cured polyester tetraacrylate, radiation-cured trimethylolpropane triacrylate, and radiation-cured hexanediol diacrylate.

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