WO2025199507A1

WO2025199507A1 - Micro-optic security device with enhanced focusing layer geometry

Info

Publication number: WO2025199507A1
Application number: PCT/US2025/021026
Authority: WO
Inventors: Howard Gao; Benjamin E. BLEIMAN; Samuel M. Cape
Original assignee: Crane and Co Inc
Current assignee: Crane and Co Inc
Priority date: 2024-03-22
Filing date: 2025-03-21
Publication date: 2025-09-25
Anticipated expiration: 2026-09-22

Abstract

A micro-optic security device (100) includes a focusing layer (108, 202). The focusing layer includes a plurality of refractive focusing elements (105, 201) with circular bases (205) and an interstitial planar region (207), wherein the interstitial planar region comprises a flat surface between the circular bases of the plurality of refractive focusing elements. The micro-optic security device further includes an icon layer (122), comprising sections of material in focal footprints of the refractive focusing elements of the focusing layer.

Description

MICRO-OPTIC SECURITY DEVICE WITH ENHANCED FOCUSING EAYER GEOMETRY

TECHNICAL FIELD

[0001] The present disclosure relates to micro-optic security devices which are configured to synthetically magnify image content in an icon layer through the choreographed operation of a plurality of lenses. More specifically, the present disclosure relates to such micro-optic security devices which embody an enhanced focusing layer geometry.

BACKGROUND

[0002] Hardening 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] Micro-optic security features, utilizing multi-layer optical structures which magnify micro- or nano- scale features in an icon layer to visible scales through the combined operation of a plurality of micro- or nano- scale focusing elements are a leading option for providing reliable indicia of authenticity on banknotes, passports (also known as “security documents” and other items presenting attractive duplication targets to counterfeiters and other malicious actors. This is due, without limitation to the facts that: a.) such micro-optic features can present characteristic images whose presence (and equally importantly, absence) readily catches the eye of end users; and b.) by virtue of the tiny size of the lenses and icons providing the image content, manufacturing such micro-optic features present significant manufacturing challenges and tooling requirements which are insurmountable to counterfeiters.

[0004] However, for micro-optic security features to be effective as a bulwark against circulation of counterfeit security documents and inauthentic goods, the characteristic visual effects (for example, synthetic images which appear to float above, or lie below the plane of the device, or devices which change appearance, or move unexpectedly (for example, orthogonally to a tilt direction) in responses to changes in viewer perspective), they have to be seen. Put differently, to perform well, the image content projected by the focusing layer - icon layer system has to look good, in the sense that the characteristic, authenticating image feature is simultaneously, appears bright, exhibits good contrast between light and dark areas, and lines and the synthetically magnified image appears in focus.

[0005] Irrespective of the technical challenges associated with its designing and manufacture, a microoptic security feature which appears dull, out-of-focus, or exhibits limited contrast is more likely to be overlooked by end users, and thus, the presence or absence of characteristic visual features is similarly likely to go unnoticed, stripping the micro-optic security feature of much of its utility as an end-user accessible indicia of authenticity.

[0006] Thus, ensuring the image quality of synthetic images and other optically variable effects by micro-optic security features remains a source of technical challenges and opportunities for improvement in the art. SUMMARY

[0007] The present disclosure illustrates embodiments of a micro-optic security device with enhanced focusing layer geometry.

[0008] In a first embodiment, a micro-optic security device includes a focusing layer. The focusing layer includes a plurality of refractive focusing elements with circular bases and an interstitial planar region, wherein the interstitial planar region comprises a flat surface between the circular bases of the plurality of refractive focusing elements. The micro-optic security device further includes an icon layer, comprising sections of material in focal footprints of the refractive focusing elements of the focusing layer.

[0009] In a second embodiment, a method of making a micro-optic security device includes forming a focusing layer. The focusing layer includes a plurality of refractive focusing elements with circular bases and an interstitial planar region, wherein the interstitial planar region comprises a flat surface between the circular bases of the plurality of refractive focusing elements. The method further includes forming an icon layer, comprising sections of material in focal footprints of the refractive focusing elements of the focusing layer.

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

[0011] Before undertaking the DETAIEED 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.

[0012] 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

[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 reference numerals represent like parts:

[0014] FIGURE 1 illustrates an example of a security document including micro-optic device according to various embodiments of this disclosure; [0015] FIGURE 2 provides an explanatory example of an enhanced lens geometry according to various embodiments of this disclosure;

[0016] FIGURES 3A through 3D provide laser confocal microscope images comparing the differences between density maximizing lens architectures, and enhanced lens architectures according to various embodiments of this disclosure;

[0017] FIGURES 4A through 4F provide comparison data of the contrast, brightness and focus of images projected by density-maximizing lens architectures and enhanced lens architectures according to various embodiments of this disclosure; and

[0018] FIGURE 5 illustrates operations of an example method for making a micro-optic security device with an enhanced lens geometry according to various embodiments of this disclosure.

DETAILED DESCRIPTION

[0019] 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 way to 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.

[0020] 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.

[0021] FIGURE 1 illustrates an example of a micro-optic security device 100, which is incorporated in a security document 160, according to embodiments of this disclosure.

[0022] Referring to the non-limiting example of FIGURE 1, micro-optic security device 100 comprises a focusing layer 108 comprising a plurality of focusing elements 105 (including, for example, focusing element 107), and an icon layer 122 having an arrangement of image icons 120 (including, for example, image icon 121). As discussed in greater detail with reference to the overhead view provided by FIG. 2, the focusing layer 108 further comprises one or more interstitial planar regions between the focusing elements. According to various embodiments, each focusing element of plurality of focusing elements 105 has a footprint, in which one or more image icons of arrangement of image icons 120 is positioned. Collectively, the focusing elements of plurality of focusing elements 105, magnify portions of image icons 120 to produce a magnification effect (also referred to as a “synthetically magnified image” or more briefly, a “synthetic image”) wherein the individually microscopic image icons are collectively magnified by the plurality of focusing elements 105 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 the synthetic magnification effect, many malicious actors are not able to produce counterfeit versions of micro-optic security device 100. Accordingly, micro-optic security device 100 is, in many cases, a trusted visual indicium of a security document’s (for example, security document 160) authenticity. [0023] According to certain embodiments, plurality of focusing elements 105 comprises a planar array of refractive focusing elements. In some embodiments, the focusing elements of plurality of focusing elements 105 comprise micro-optic refractive focusing elements (for example, plano-convex or GRIN lenses). Refractive focusing elements of plurality of focusing elements 105 are, in some embodiments, produced from cured light curable resins (for example, by cast-curing), wherein the cured resin has an index of refraction ranging from 1.35 to 1.7. Additionally, the individual focusing elements have circular bases, wherein the circular bases have diameters ranging from 5pm to 200pm. Materials suitable for forming plurality of focusing elements 105 include, without limitation, substantially transparent, colored or colorless polymers such as acrylics, acrylated polyesters, acrylated urethanes, epoxies, polycarbonates, polypropylenes, and the like. Various methods of providing the layer of focusing elements 108 can include extrusion, radiation cured casting, injection molding, reaction injection molding or reaction casting.

[0024] The focusing elements of plurality of focusing elements 105 (can be characterized by an F#, which may be adjusted as desired to modify the synthetic image and its optical effect. Suitable F numbers, in view of the desired thickness of the security fdm or security device, 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. The synthetic image can also be modulated by the relative arrangements and alignments of the array of focusing elements to the array of image elements and each array has respective repeat periods. The repeat periods of the respective arrays may be adjusted such that their ratios are equal to 1 , slightly above or slightly below 1 ; though ratios substantially above and substantially below 1 are also contemplated. Base diameters of the focusing elements may also be adjusted as desired and it is within the scope of the present disclosure that these base diameters could have ranges of 200 pm to 500 pm; 50 pm to 200 pm; less than 50 pm (such as less than about 45 pm or ranging from about 10 pm to about 40 pm). The focusing elements may further be modified by adjusting the focal lengths such that the focal lengths allow for image elements in the array of image elements to be viewed through the focusing element and project a synthetic image. Focal lengths of less than 50 pm are suitable, such as less than 45 pm, such as ranging from about 10 pm to about 30 pm.

[0025] As shown in the illustrative example of FIGURE 1, arrangement of image icons 120 comprises a set of image icons (including image icon 121), positioned at predetermined locations within the footprints of the focusing elements of plurality of focusing elements 105. According to various embodiments, the individual image icons of arrangement of image icons 120 comprise regions of light cured material associated with the focal path of structured light (for example, collimated UV light) passing through plurality of focusing elements 105 from a projection point associated with one or more predetermined ranges of viewing angles. In some embodiments, the individual image icons of arrangement of image icons 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 (for example, a light-curable resin) which has been embossed, or otherwise formed to comprise retaining 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 120 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. In some embodiments, arrangement of image icons comprises icons of a single color. In other embodiments, image icons of arrangement of image icons 120 comprise icons of two or more colors.

[0026] While not shown in FIG. 1, in certain embodiments, the relief structures of the icon layer 122, rather than contrasting interstitial material retained within the embossed relief structures may operate as the image icons. In such embodiments, the embossed material may be pigmented and semi-opaque, and the variances in thickness of the relief structures may create points of contrast which can be projected through plurality of focusing elements 105 to provide a synthetic image.

[0027] As shown in the illustrative example of FIGURE 1, in certain embodiments, micro-optic security device 100 includes an optical spacer 110. According to various embodiments, optical spacer 110 comprises a fdm of substantially transparent material which operates to position image icons of arrangement of image icons 120 in or around the focal plane of focusing elements of plurality of focusing elements 105. In certain embodiments according to this disclosure, optical spacer 110 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 120 or plurality of focusing elements 105. Alternatively, optical spacer 110 can be formed as a “flat” layer of the same, or similar light-curable transparent resin as used to form one or more of arrangement of image icons 120 or focusing elements 105.

[0028] According to various embodiments, micro-optic security device 100 comprises one or more regions of light-cured protective material which occupy the spaces between the image icons of arrangement of image icons 120. In some embodiments, the arrangement of image icons 120 is first formed (for example, by selectively curing and removing liquid light-curable material on optical spacer 110), and then a layer of clear, light-curable material is applied to fill spaces between the image icons of arrangement of image icons 120 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 105. In certain embodiments, the light-curable material used to form arrangement of image icons 120 is a pigmented, ultraviolet (UV)-curable polymer.

[0029] In some embodiments, arrangement of image icons 120 is affixed to a second substrate 130, which operates to protect and secure arrangement of image icons 120 and provide an interface for attaching micro-optic security device 100 to a substrate 150 as part of security document 160. In some embodiments, micro-optic security device 100 is affixed to substrate 150 during the manufacture of substrate in a papermaking machine, such as a Fourdrinier machine. According to some embodiments, micro-optic security device 100 is affixed to substrate 150 by a layer of adhesive between the arrangement of image icons and a top surface of substrate 150.

[0030] In certain embodiments according to this disclosure, micro-optic security device 100 comprises a seal layer 140. According to certain embodiments, seal layer 140 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 105 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 105. According to various embodiments, the upper surface of seal layer 140 is formed from a thermoplastic material which can be ultrasonically welded to a surface comprising a cellulosic material.

[0031] As shown in the non-limiting example of FIGURE 1, in certain embodiments, micro-optic security device 100 can be attached to substrate 150, to form a security document 160. According to various embodiments, substrate 150 comprises a sheet of material with at least one surface. Substrate 150 can be a polymeric substrate (for example, a section of PET or BOPP film). Alternatively, or additionally, substrate 150 can be a fibrous substrate comprising cellulosic material, such as wood pulp, cotton fiber, linen fiber, flax fiber, sisal fiber, hemp fiber, Abaca fiber, Kozo fiber, Mitsumata fiber, bamboo fiber or Kenaf fiber. In some embodiments, substrate 150 is a blend of cotton and linen fibers, such as used for U.S. banknotes. For example, substrate 150 may be made of a fiber blend which contains between 65-80% cotton fibers and between 20-35% linen fibers. In some embodiments, the relative proportions of cotton and linen fibers may be such that the substrate contains 65-100% cotton fibers and between 0 to 35% linen fibers.

[0032] While FIGURE 1 provides one example of a micro-optic security device 100 according to various embodiments, the present disclosure is not so limited. Additionally, certain embodiments according to this disclosure may include structures not explicitly shown in FIG. 1, such as a contrast or “camo” coat of opacifying material applied to enhance the contrast of image icons 120. In some embodiments, the contrasting material can be a thin layer of white or light-colored pigment. Alternatively, the contrast coat may be a layer of a reflective material, such as, aluminum, zinc, or copper.

[0033] FIG. 2 illustrates aspects of an enhanced focusing layer geometry according to embodiments of this disclosure. Referring to the non-limiting example of FIG. 2, cross sectional, and overhead views of a rectangular section 200 of a focusing layer 202 according to various embodiments of this disclosure. For convenience of cross reference, elements common to both the cross-sectional and overhead views of rectangular section 200 of the focusing layer are numbered similarly. As shown in the figure, focusing layer 202 comprises a plurality of refractive focusing elements (for example, focusing element 201). Each refractive focusing element has a lensing portion 203, which provides a curved interface between the high refractive index material of the focusing element, and the low (i.e., 1) refractive index of the surrounding air. Each refractive focusing element has a circular base (for example, circular base 205) where the curved lensing portion meets the interstitial planar region 207 (shaded with dots in the overhead view) of the focusing layer.

[0034] Historically, the dominant paradigm, as informed by theory and intuition, in focusing layer design has been to minimize, to the greatest extent possible, the area of planar interstitial space between refractive focusing elements, even at the cost of cramming focusing elements together so closely as to “pinch” the perimeter of the focusing elements’ bases into a substantially hexagonal shape. The theoretical motivations for maximizing the packing density of focusing elements were twofold. First, planar interstitial region 207 has historically been understood as being optically analogous to a pointing error in a cut gemstone (i.e., where two facets fail to meet along a single line, but instead, converge upon the edges of an interstitial region bridging the facets). Based on this theory, interstitial space between refractive elements was understood to have the primary effect of diminishing the brightness and contrast of image icon content as projected through the focusing elements. Additionally, while there was some understanding that increasing the packing density would cause some distortion by pinching otherwise circular lens bases into a hexagonal shape. However, the effects of this distortion around the base were understood to be minimal, as the distortion was understood to be confined to the periphery of the lenses, and would, in theory at least, only degrade focus at significantly off-axis (i.e., more parallel than perpendicular to the surface of the micro-optic security device) viewing angles.

[0035] The intuitive motivation for maximizing the packing density of focusing elements, even at the expense of circularity of lens bases, was that interstitial space between lenses created a space for trapping dirt (sometimes referred to as “crudding”) and other substances, which could be expected to also degrade the brightness and contrast of image icon content as projected through the focusing elements.

[0036] While theory and intuition are correct in that densely packing lenses does, inter alia, create distortion at off-axis viewing angles, and slightly improve the brightness and contrast of projected images by reducing the area of a focusing area not contributing in some manner (even if out of focus due to distortions from dense lens packing) to the projection of synthetic images, Applicants have found that significantly better overall performance can be achieved with lens packing geometries which reject the theoretical and intuitive motivations towards packing the lenses together with an eye to maximizing the percentage of a focusing layer’s surface area given over to focusing elements, and minimizing the percentage of the focusing layer’s surface area dedicated to interstitial planar regions. As discussed herein, by relaxing the packing density of focusing elements to ensure the circularity of refractive focusing elements’ bases and increasing the fractional area of interstitial planar regions by as much as 50-100%, significant gains in image sharpness and focus, including at on-axis viewing angles can be realized, with little or no loss of image brightness. Additionally, and as discussed herein, brightness and contrast losses associated with potentially increased crudding in the expanded interstitial planar region between lenses can be mitigated through the use of an anti-viscid agent, including, without limitation, anti-viscid agents such as described in U.S. Patent No. 11,912,057, which is incorporated herein by reference.

[0037] Referring again to the illustrative example of FIG. 2, the area of section rectangular 200 has a height h, and a width w, defining a total area of h x w, within which eighteen (18) whole focusing elements are disposed. As used in this disclosure a “whole focusing element” comprises a focusing element whose base is not crossed by a line defining a rectangular area comprising a plurality of rows of focusing elements. In this example, the bases of the eighteen focusing elements (shown in white) shown cover a first percentage of the total area (h x w) of the rectangular section 200 of the focusing layer 202. The interstitial planar region 207 (shown with dotted shading) covers a second percentage of the rectangular section 200 of the focusing layer 202. The first and second percentages, plus, where applicable, a percentage of the measured area accounting for measurement errors should add up to one hundred percent.

[0038] Skilled artisans will appreciate that the relative percentages of a measurement area of a focusing layer comprising bases of focusing elements and planar interstitial space can be manipulated by one or more of: a.) defining the measurement area to reduce the number of focusing elements; and b.) gerrymandering the shape of the perimeter of the measurement area to maximize or minimize the size of the interstitial planar region. Skilled artisans will also appreciate that, in the simplified example of FIG. 2, the rectangular section 200 of the focusing layer 202 comprises only whole focusing elements, while, in many foreseeable embodiments, rectangular sample sections of a focusing layer will likely necessarily include some partial bases of focusing elements, wherein the circular perimeter of the base is cut off by one or more sides of the rectangle segment over which the relative areal percentages of focusing element bases and interstitial planar regions are being calculated.

[0039] To obtain meaningful measurements of the relative percentages of area within a measurement space given over to the bases of focusing elements and interstitial planar regions, in which the effects of variations in sample region placement do not cause significant variation in the measured percentages, this disclosure recommends that a measurement segment meet the following criteria: be rectangular in shape; and comprise at least fifty whole refractive focusing elements arrayed in at least five rows within the measurement segment.

[0040] By measuring the areas of whole and partial refractive focusing element bases in a segment satisfying the above-described criteria, an “honest slice” measurement which overwhelmingly reflects the lens packing density in the sample area can be obtained.

[0041] To illustrate the structural differences of lens geometries according to embodiments of this disclosure, a laser confocal microscope image of a lens layer embodying a conventional, high-density lens geometry is provided as FIG. 3A and a laser confocal microscope image of a lens layer embodying an enhanced lens geometry according to various embodiments ofthis disclosure is provided as FIG. 3B. FIGS. 3C and 3D provide cross-sectional views of the micro-optic devices shown in FIGS. 3A and 3B. For convenience of cross reference, elements common to more than one of FIGS. 3A-3D are numbered similarly.

[0042] Referring to FIG. 3A, an electron microscope image of a first focusing layer 301 according to a high-density lens geometry is shown in the figure. In this example, first focusing layer 301 is part of a micro-optic security device with an overall film thickness of 30 to 50 pm. The lenses in this example have a measured base diameter of 28.5 pm, and a honeycomb-shaped interstitial planar region 305 having a generally constant width of 1.5 pm. To accommodate the honeycomb shape of interstitial planar region 305, the bases of the focusing elements (for example, focusing element 310) are hexagonally shaped. In this example, over a rectangular measurement segment comprising at least fifty whole focusing elements, approximately 90.5% of the area of the measurement segment was covered by whole or partial focusing element bases. [0043] Referring to FIG. 3B, a laser confocal microscope image of a second focusing layer 351 embodying an example of an enhanced lens geometry according to embodiments of this disclosure. Here again, second focusing layer is part of a micro-optic security device with an overall fdm thickness of 30 to 50 pm. In contrast to first focusing layer 301, the focusing elements in this image (for example, focusing element 360) have circular bases, with a measured base diameter of 24.5 pm. Additionally, in contrast to the honeycomb structure shown in FIG. 3 A the boundaries between second interstitial planar region 355 and the focusing elements do not include any straight lines defining the second interstitial planar region 355. Instead, the width of second interstitial planar region 355 varies across second focusing layer 351, with a measured minimum of 1.5 pm. In the example of FIG. 3B, over a rectangular measurement segment comprising at least fifty whole focusing elements, approximately 80% of the area of the measurement segment was covered by whole or partial focusing element bases. Rather than maximizing the packing density of focusing elements, the micro-optic device comprising the image layer shown in FIG. 3B “relaxes” the packing density to preserve the circularity of the lenses’ bases.

[0044] FIG. 3C shows, in cross-sectional view, the micro-optic system comprising first focusing layer 301. As shown in the figure, interstitial planar region 305 is consistently narrow (i.e., ~1.5pm) across the cut line of the cross section.

[0045] FIG. 3D shows, in cross-sectional view, the micro-optic system comprising second focusing layer 351. As shown in the figure, and consistent with the overhead view provided in FIG. 3B, the width of second interstitial planar region 355 varies across the cut line, from a minimum of ~1.5pm to a maximum of approximately ~3-4pm.

[0046] FIGS. 4A through 4F provide image data and spatial brightness data within a common color channel illustrating, the performance differences between first focusing layer 301 in FIGS. 3 A and 3C and the second focusing layer 351 in FIGS. 3B and 3D. For convenience of cross-reference, elements common to more than one of FIGS. 4A-4F are numbered similarly.

[0047] Referring to the example of FIG. 4A, a screenshot from Blender an image of a first icon layer as projected through a focusing layer with the same lens geometry as first focusing layer 301 as FIG. 3 A is shown in the figure. The background of the screenshot shows the image projected to the camera from the focusing layer. Circle 401 calls out a linear sampling line over which brightness values in the red channel of the image color space are mapped to points along the sample line by graph 403. Graph 403 shows the brightness in the red channel drop, at first transition 405a, from the slightly below the third bar on the y- axis to the second bar. At second transition 407a, the measured brightness in the red channel rises back to slightly below the third bar on the y axis. The measured difference between the highest brightness (measured on a scale from 0 to 1) in the red channel and lowest measured brightness (also measured on a scale from 0 to 1) in the red channel across the sample line showed a contrast difference of 0.18.

[0048] FIG. 4B shows the same measurement but performed on a micro-optic security device with the same lens geometry as second focusing layer 351 in FIG. 3B. As shown by graph 409, the brightness once again drops again at first transition 405b and returns to its original levels at second transition 407b. In this example, the measured difference between the highest brightness in the red channel and the lowest brightness in the red channel in FIG. 4B is 0.33, indicating an 88% improvement in measured contrast between the systems shown in FIGS. 4A and 4B. Additionally, the highest measured brightness values shown in FIG. 4B are higher than those in FIG. 4A, indicating that the losses in image brightness predicted by design theory are non-existent or negligible in lens architectures according to embodiments of this disclosure. Still further, the slopes in transitions 405b and 407b are shown in graph 409 to be steeper than the slopes observed in graph 403 at transition points 405a and 405b, indicating that lens architectures according to embodiments of this disclosure provide an across-the-board improvement (i.e., focus, brightness, and contrast) relative to maximum-density lens architectures in which lens bases are pinched into honeycomb shapes.

[0049] Like FIGS. 4A and 4B, FIGS. 4C and 4D comprise Blender screenshots showing and analyzing, in a common color channel, brightness data from a pair of micro-optic security devices having a common icon layer but embodying different lens geometries. Referring to the example of FIG. 4C, a camera image of icon layer content projected through a focusing layer with the lens geometry of first focusing layer 301 in FIG. 3 A is shown, with circle 411 showing the region across which the sample line was drawn. First graph 413 indicates that, with a maximum -density lens architecture, brightness values in the red channel drop and rebound along a relatively smooth curve along the sample line. The measured difference between the brightest value in the red channel and the darkest value in the red channel in the example of FIG. 4C was 0.08.

[0050] FIG. 4D shows image data and red channel brightness data from a micro-optic security device with a second focusing layer 351 in FIG. 3B. Graph 415 shows the variance in brightness in the red channel over the sample line. As shown in FIG. 4D, the brightest values in graph 415 are greater than the lowest values in graph 413, with a contrast difference of 0.14, or 69% more than the 0.08 contrast difference achieved with the density maximizing lens geometry of first focusing layer 301. The higher peak brightness value in graph 415 indicate that enhancing the lens geometry by utilizing an enhanced lens geometry does not make projected images darker. Further, as shown by the comparatively steep downward line at third transition 417, the transitions between light areas and dark areas are less soft-edged (i.e., they occur across shorter sections of the sample line), indicating that enhancing the lens geometry according to embodiments of this disclosure provides tighter focus. Here, again, micro-optic security devices embodying the enhanced lens geometry of second focusing layer 351 in FIG. 3B outperform equivalent interstitial space -minimizing lens geometries.

[0051] Additionally, as exemplified by the size difference in first instance of 412A of the word “secure” in FIG. 4C relative to its counterpart second instance in 412B, where enhancing a focusing layer’s lens geometry is effected by reducing the diameters of the lenses to ensure circularity at the lenses’ bases (which does not necessarily require retooling or redesigning an existing icon layer), the curvature of the lenses is necessarily increased, resulting in greater magnification. For micro-optic security devices which provide a “motion” effect, such as a transition between two images, or orthoparallactic (i.e., perpendicular to the direction of change of viewing angle, such as an image which appears to move right-to-left in response to up-and-down tilting of the device), enhancing the focusing layer geometry as discussed herein has the added effect of increasing the “motion” in the visual effects provided by the micro-optic security device.

[0052] FIGS. 4E and 4F are Blender images of a comparison test on the projection properties of the high-density first focusing layer 301 of FIG. 3 A versus the enhanced lens geometry of second focusing layer 351 of FIG. 3B.

[0053] FIG. 4E is a Blender screenshot showing image data of an icon layer, as projected through first focusing layer 301 in FIG. 3 A. Circle 421 identifies the location of the test line along which brightness data in the red channel was obtained and graph 423 shows brightness values in the red color channel measured along the color line. As shown in FIG. 3A, the values of graph 423 move as a relatively smooth curve in a value range bounded by the second and third horizontal hash lines. A difference of 0.17 in brightness values between the brightest point along the test line and the darkest point along the test line was observed.

[0054] FIG. 4F is a Blender screenshot showing image data of the same icon layer as FIG. 4E, as projected through second focusing layer 351 in FIG. 3B. Again, circle 421 identifies the test line along which the brightness data shown in graph 425 was obtained. A difference of 0.27 (or an increase of 59% compared to graph 423) between the brightest point and darkest points of the data plotted in graph 425 was observed, indicating improved contrast. Additionally, the peak red channel brightness values for graphs 425 and 423 are equivalent, indicating no loss of brightness due to relaxing the lens geometry to ensure sufficient room in the planar interstitial region to accommodate fully circular lens bases. Also, in contrast to graph 423, graph 425 shows steep-sloped transitions (for example, transition 427) between regions of dissimilar brightness which are not present in graph 423, indicating that second focusing layer 351 provides sharper focus than first focusing layer 301. Once again, the enhanced lens geometry embodied by second focusing layer 351 outperforms the more familiar lens geometry of first focusing layer 301.

[0055] FIG. 5 illustrates operations of an example method 500 for creating a micro-optic security device with an enhanced lens geometry according to various embodiments of this disclosure. It should be noted that the operations described with reference to FIG. 5 do not necessarily need to be performed in the order described, and that, depending on the manufacturing process utilized, certain operations may be omitted or performed in a different sequence.

[0056] Referring to the illustrative example of FIG. 5, at operation 505, a focusing layer comprising both a plurality of refractive focusing elements with circular bases and an interstitial planar region (for example, second focusing layer 351 in FIG. 3B) is formed. The focusing layer can be formed by cast-curing, by embossing a layer of uncured polymeric material with a die having the relief pattern of the focusing elements and interstitial planar region, and then curing same to create a stable layer of refractive focusing elements. According to various embodiments, the interstitial planar region does not include any straight lines defining spaces between focusing elements (i.e., the bases of the focusing elements are circular, and not pinched towards the hexagonal forms of cells of a honeycomb or other polygonal grid). In some embodiments, bases of the refractive focusing elements cover less than 90% of the total area of the sample segment. In some embodiments for a sample segment of the focusing layer comprising at least fifty whole refractive focusing elements, in which the sample segment has a total area, bases of the refractive focusing elements cover no more than 85% of the total area. In some embodiments, bases of the refractive focusing elements cover no more than 80% of the total area. In some embodiments, bases of the refractive focusing elements cover no more than 70% of the total area of the sample segment. Depending on the desired thickness of the end product and the optical characteristics of the projected image (i.e., all other things being equal, longer focal lengths provide more “motion” in response to changes in viewing angle), the focusing layer can be formed on a sheet of clear material providing an optical spacer.

[0057] At operation 505 an icon layer, comprising sections of material (often, pigmented light-curable polymer) disposed in the footprints of the refractive focusing elements is formed. Icon layers according to embodiments of this disclosure can be formed in a plurality of ways, including, without limitation, by printing icons onto the underside of the focusing layer, or, in embodiments utilizing an optical spacer, printing icons onto the side of the optical spacer opposite to the side supporting the focusing layer. In some embodiments, the icon layer can be formed by cast curing a plurality of retaining structures defining wells, posts, and mesas for locating icon material, and then filling the retaining structures with pigmented material. In some embodiments, icon layers can be applied using digital tooling techniques, which do not rely on retaining structures to position icon material, wherein a layer of uncured pigmented material is disposed on either the underside of the focusing layer and selectively cured by passing collimated or semi-collimated light through the focusing layer to create image icons.

[0058] In certain embodiments, at operation 515, an anti-viscid agent, such as described in U.S. Patent No. 11,912,057 is applied to at least part of an exterior surface of the focusing layer. In certain embodiments, the applied anti-viscid agent does not affect the focal properties (for example, F#, focal length or refractive index) of focusing elements of the focusing layer.

[0059] While this disclosure describes improvements in the geometry of focusing elements with reference to examples and microscope images of embodiments using refractive lenses, the present disclosure is not so limited. Skilled artisans will appreciate that the improvements in focus quality of images projected by micro-optic security devices without little to no loss of image brightness attained by ensuring sufficient interstitial space can also be realized in other focusing structures in which interstitial space can be provided, such as systems with reflective lenses.

[0060] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices comprising a focusing layer. The focusing layer comprising a plurality of refractive focusing elements with circular bases and an interstitial planar region, wherein the interstitial planar region comprises a flat surface between the circular bases of the plurality of refractive focusing elements. The micro-optic security device also comprises an icon layer, comprising sections of material in focal footprints of the refractive focusing elements of the focusing layer. [0061] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices comprising an optical spacer disposed between the focusing layer and the icon layer.

[0062] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices, wherein a boundary of the interstitial planar region does not include any straight lines defining spaces between refractive focusing elements.

[0063] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices, wherein, for a rectangular segment of the focusing layer comprising at least fifty whole refractive focusing elements, having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 85% of the total area of the rectangular segment.

[0064] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices wherein, for a rectangular segment of the focusing layer comprising at least fifty whole refractive focusing elements, having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 80% of the total area of the rectangular segment.

[0065] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices wherein, for a rectangular segment of the focusing layer comprising at least fifty whole refractive focusing elements, having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 70% of the total area of the rectangular segment.

[0066] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices comprising an anti-viscid agent disposed on an exterior portion of a first side of the focusing layer.

[0067] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices wherein the anti-viscid agent is disposed on an exterior portion of the plurality of refractive focusing elements.

[0068] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices, wherein the anti-viscid agent does not affect a focal length of focal elements of the plurality of refractive focusing elements.

[0069] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices, wherein the icon layer does not contain retaining structures for holding uncured pigmented image icon material.

[0070] Examples of methods of making a micro-optic security device according to embodiments of this disclosure include methods comprising forming a focusing layer. The focusing layer comprising a plurality of refractive focusing elements with circular bases and an interstitial planar region, wherein the interstitial planar region comprises a flat surface between the circular bases of the plurality of refractive focusing elements. The method also includes forming an icon layer, comprising sections of material in focal footprints of the refractive focusing elements of the focusing layer.

[0071] Examples of methods of making a micro-optic security device according to embodiments of this disclosure include methods, wherein the focusing layer is formed on a first side of an optical spacer, and the icon layer is formed on a second side of the optical spacer.

[0072] Examples of methods of making a micro-optic security device according to embodiments of this disclosure include methods, wherein a boundary of the interstitial planar region does not include any straight lines defining spaces between refractive focusing elements.

[0073] Examples of methods of making a micro-optic security device according to embodiments of this disclosure include methods, wherein, for a rectangular segment of the focusing layer comprising at least fifty whole refractive focusing elements, and having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 85% of the total area of the rectangular segment.

[0074] Examples of methods of making a micro-optic security device according to embodiments of this disclosure include methods, wherein, for a rectangular segment of the focusing layer comprising at least fifty whole refractive focusing elements, and having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 80% of the total area of the rectangular segment.

[0075] Examples of methods of making a micro-optic security device according to embodiments of this disclosure include methods, wherein, for a rectangular segment of the focusing layer comprising at least fifty whole refractive focusing elements, and having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 70% of the total area of the rectangular segment.

[0076] Examples of methods of making a micro-optic security device according to embodiments of this disclosure include methods comprising applying an anti-viscid agent disposed on an exterior portion of a first side of the focusing layer.

[0077] Examples of methods of making a micro-optic security device according to embodiments of this disclosure include methods, wherein the anti-viscid agent is applied on an exterior portion of the plurality of refractive focusing elements.

[0078] Examples of methods of making a micro-optic security device according to embodiments of this disclosure include methods, wherein the anti-viscid agent does not affect a focal length of focal elements of the plurality of refractive focusing elements.

[0079] Examples of methods of making a micro-optic security device according to embodiments of this disclosure include methods, wherein the icon layer does not contain retaining structures for holding uncured pigmented image icon material. [0080] 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.

[0081] 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 micro-optic security device (100), comprising: a focusing layer (108, 202), the focusing layer comprising: a plurality of refractive focusing elements (105, 201) with circular bases (205) and an interstitial planar region (207), wherein the interstitial planar region comprises a flat surface between the circular bases of the plurality of refractive focusing elements; and an icon layer (122), comprising sections of material in focal footprints of the refractive focusing elements of the focusing layer.

2. The micro-optic security device of claim 1, further comprising an optical spacer (110) disposed between the focusing layer and the icon layer.

3. The micro-optic security device of claim 1, wherein a boundary of the interstitial planar region does not include any straight lines defining spaces between refractive focusing elements.

4. The micro-optic security device of claim 1, wherein, for a rectangular segment (200) of the focusing layer comprising at least fifty whole refractive focusing elements, having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 85% of the total area of the rectangular segment.

5. The micro-optic security device of claim 1 , wherein, for a rectangular segment (200) of the focusing layer comprising at least fifty whole refractive focusing elements, having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 80% of the total area of the rectangular segment.

6. The micro-optic security device of claim 1, wherein, for a rectangular segment (200) of the focusing layer comprising at least fifty whole refractive focusing elements, having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 70% of the total area of the rectangular segment.

7. The micro-optic security device of claim 1, further comprising an anti -viscid agent disposed on an exterior portion of a first side of the focusing layer.

8. The micro-optic security device of claim 7, wherein the anti -viscid agent is disposed on an exterior portion of the plurality of refractive focusing elements.

9. The micro-optic security device of claim 8, wherein the anti-viscid agent does not affect a focal length of focal elements of the plurality of refractive focusing elements.

10. The micro-optic security device of claim 1, wherein the icon layer does not contain retaining structures for holding uncured pigmented image icon material.

11. A method of making a micro-optic security device (100), the method comprising: forming a focusing layer (108, 202), the focusing layer comprising: a plurality of refractive focusing elements (105, 201) with circular bases (205) and an interstitial planar region (207), wherein the interstitial planar region comprises a flat surface between the circular bases of the plurality of refractive focusing elements; and forming an icon layer (122), comprising sections of material in focal footprints of the refractive focusing elements of the focusing layer.

12. The method of claim 11, wherein the focusing layer is formed on a first side of an optical spacer (110), and the icon layer is formed on a second side of the optical spacer.

13. The method of claim 11, wherein a boundary of the interstitial planar region does not include any straight lines defining spaces between refractive focusing elements.

14. The method of claim 11, wherein, for a rectangular segment (200) of the focusing layer comprising at least fifty whole refractive focusing elements, and having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 85% of the total area of the rectangular segment.

15. The method of claim 11, wherein, for a rectangular segment (200) of the focusing layer comprising at least fifty whole refractive focusing elements, and having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 80% of the total area of the rectangular segment.

16. The method of claim 11, wherein, for a rectangular segment (200) of the focusing layer comprising at least fifty whole refractive focusing elements, and having a total area: bases of the whole refractive focusing elements and bases of partial refractive focusing elements within the rectangular segment cover no more than 70% of the total area of the rectangular segment.

17. The method of claim 11, further comprising applying an anti -viscid agent disposed on an exterior portion of a first side of the focusing layer.

18. The method of claim 17, wherein the anti -viscid agent is applied on an exterior portion of the plurality of refractive focusing elements.

19. The method of claim 18, wherein the anti-viscid agent does not affect a focal length of focal elements of the plurality of refractive focusing elements.

20. The method of claim 11, wherein the icon layer does not contain retaining structures for holding uncured pigmented image icon material.