Single-sided micro-optic security device

Abstract

A security document (160, 200, 250, 275) or device (100) includes, a substrate (150, 201) having a first side, a coated surface disposed on the first side of the substrate, an icon layer (120, 205) disposed on the coated surface, the icon layer comprising a plurality of pigmented structures and a focusing layer (211) comprising a plurality of focusing elements (105). Each focusing element (121) of the plurality of focusing elements has a footprint, and the plurality of focusing elements projects a synthetic image (402) of portions of the icon layer in footprints of the plurality of focusing elements.

Description

SINGLE-SIDED MICRO-OPTIC SECURITY DEVICETECHNICAL 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 single-sided micro-optic security devices in which harvesting resistance is enhanced and the aggregate environmental impact is reduced through the elimination of plastic constructional substrates as well as casting or transfer substrates.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 security documents such as banknotes, passports (and other items presenting attractive duplication targets to counterfeiters and other malicious actors. This is due, without limitation to the facts that: a.) such microoptic 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] Many security documents, most notably, banknotes are produced in enormous production runs to support a nation’s requirements for paper currency and to provide new bills to replace bills offset through central banks’ routine retirement and destruction of currency notes which are no longer fit for circulation. In the United States alone, over two billion banknotes are retired and destroyed each year. Where banknotes and other security documents are built upon cellulosic (for example, linen currency paper) substrates, most of the material in the security document can either be recycled, or composted. However, certain components of security documents, such as applied security patches or threads of micro-optic security material, which are built upon extruded plastic substrates, or built using extruded plastic substrates (for example, carrier or transfer films) are not compostable or otherwise biodegradable. While such components comprise only a minor portion of the materials in an individual security document, over multi-million or multi-billion security document runs, their use produces large quantities of plastic. Disposal of large quantities of plastic presents environmental and technical challenges.

[0005] Additionally, in many cases, where a security device constructed upon an extruded polymeric substrate (for example, a thin section of PET or BOPP film) is adhered to a fibrous or cellulosic substrate, malicious actors can use solvents to weaken or degrade the adhesive attaching the security device to thesubstrate to the point where the sheer strength of the security device exceeds the strength of the adhesive bond between the security device and the substrate. This is due in part to the fact that, polymeric substrates typically structurally reinforce the security device. At this point, the security device can often be “harvested” or removed intact from the substrate. Harvested components can be used to make higher-quality forgeries.

[0006] Reducing plastic waste (both in finished security documents, and the materials used to manufacture same) and minimizing opportunities for harvesting remain a source of technical challenges and opportunities for improvement in the art.SUMMARY

[0007] The present disclosure illustrates embodiments of a single-sided micro-optic security device and methods for making same.

[0008] In a first embodiment, a security document includes a substrate having a first side, a coated surface disposed on the first side of the substrate, an icon layer disposed on the coated surface, the icon layer comprising a plurality of pigmented structures, and a focusing layer comprising a plurality of focusing elements, wherein each focusing element of the plurality of focusing elements has a footprint, and wherein the plurality of focusing elements projects a synthetic image of portions of the icon layer in footprints of the plurality of focusing elements.

[0009] In a second embodiment, a micro-optic security device includes an icon layer, the icon layer comprising a plurality of pigmented structures, an adhesive layer disposed on the icon layer, and a focusing layer comprising a plurality of focusing elements, wherein each focusing element of the plurality of focusing elements has a footprint, wherein the plurality of focusing elements projects a synthetic image of portions of the icon layer in footprints of the plurality of focusing elements, and wherein none of the icon layer or focusing layer comprise or contact a layer of extruded transparent or translucent polymer film.

[0010] In a third embodiment, a method of making a security document, includes - on a substrate having a coated surface, forming an icon layer on the coated surface, and forming a focusing layer comprising a plurality of focusing elements, wherein each focusing element of the plurality of focusing elements has a footprint, and wherein the plurality of focusing elements projects a synthetic image of portions of the icon layer in footprints of the plurality of focusing elements.

[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 arelationship 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 including a micro-optic security device;

[0016] FIGURES 2A-2C illustrate examples of security documents comprising reduced-plastic, single-sided security devices according to various embodiments of this disclosure;

[0017] FIGURE 3 illustrates an example of a method for producing security documents comprising reduced-plastic, single sided security devices according to various embodiments of this disclosure; and

[0018] FIGURES 4A and 4B illustrate an example portion of a security device in accordance with this disclosure.DETAILED DESCRIPTION

[0019] FIGURES 1 through 4B, 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] To provide context on the improvements provided by, and technical challenges overcome by, certain embodiments according to this disclosure FIGURE 1 illustrates an example of a known architecture for a micro-optic security device 100, which is incorporated in a security document 160.

[0022] Referring to the non-limiting example of FIGURE 1, micro-optic security device 100 comprises a focusing layer comprising a plurality of focusing elements 105 (including, for example, focusing element 107), and an arrangement of image icons 120 (including, for example, image icon 121. 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, change shapes, 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] 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. Variations on micro-optic security device 100 in which plurality of focusing elements 105 are reflective focusing elements (i.e., micro-mirrors) are also possible. 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 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 film 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. The individual image icons of arrangement of image icons 120 comprise regions of light cured material associated with the focal path of structuredlight (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. 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, an 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, 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] In certain embodiments, micro-optic security device 100 includes an optical spacer 110. 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. For many real -world embodiments of lens-icon micro-optic security devices, as well as other optically-variable security devices, such as holograms and patches of color changing material, a section of a clear polymer fdm (such as, PET or BOPP) is part of the structure. In addition to positioning image icons in, or around, the focal plane of the focusing layer, and providing a uniformly flat surface upon which to cast-cure focusing elements and icons upon, optical spacer 110 provides micro-optic security device 100 with sufficient structural integrity to facilitate mechanized and automated handling and storage, such as in reel-to-reel processes, without stretching or tearing. However, and as noted herein, while optical spacer 110 provides clear manufacturing and technical benefits, these benefits come at the cost of increased plastic use (particularly over large document runs), and absent mitigation measures (for example, stronger adhesives or creating failure points in micro-optic security device 100).

[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 icons120 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] Micro-optic security device 100 can include 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 FIGURE 1, 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] As discussed herein, certain embodiments according to the present disclosure, micro-optic systems which provide the same synthetic images as the system described with reference to FIG. 1, but omit both optical spacer 110, as well as plastic carrier substrates (such as described in U.S. Patent No. 10,890,692) for casting focusing elements or other structures of the lens-icon micro-optic system. In this regard, certain embodiments according to this disclosure can provide improved harvesting resistance and reduced plastic use.

[0033] FIGS. 2A-2C illustrate examples of security documents with reduced plastic, single-sided micro-optic security devices according to various embodiments of this disclosure. For consistency andconvenience of cross-reference, elements common to more than one of FIGS. 2A-2C are numbered similarly.

[0034] Referring to the non-limiting example of FIG. 2A, a first example of a security document 200 with a reduced-plastic single-sided micro-optic security feature according to various embodiments of this disclosure is shown. Skilled artisans will appreciate that, while the examples of FIGS. 2A-2B describe the single-sided construction techniques in the context of security documents, the “bottom up” constructional techniques described herein may also be used to construct security devices for attachment to other substrates, such as fibrous / cellulosic substrates or polymer substrates. This disclosure contemplates security features comprising the same structural features as the security documents described in this disclosure. As shown in the figure, security document 200 comprises a coated substrate 201. In this example, coated substrate 201 comprises a section of fibrous currency paper with a polymeric coating to enhance wear resistance and soiling of circulated banknotes. While this disclosure contemplates thicker and thinner embodiments, testing has shown that thicknesses between 0.05 to 0.075 mm work well. Depending on embodiments, the coating on coated substrate 201 can be applied as a wet film, which subsequently cures on the surface of the substrate. In some embodiments, the coating on coated substrate 201 can be forced into the pores and sub-surface structures of the fibrous coated substrate 201. In certain embodiments, the coating on coated substrate 201, once dried, does not completely fill in, or otherwise “smooth out” the natural grain, and “papery feel” of the fibrous component of coated substrate. Put differently, in contrast to polymeric substrates, which are smooth, even at micron- and sub-micron scales, coated substrate 201 can retain some of the inherent graininess and texture of the fibrous substrate. In the simplest possible terms, coated substrate can still “feel” like the paper from which it is made. Because it retains much of the surface variation and “tooth” (referring to the quality of paint to adhere more tenaciously to slightly rougher surfaces) of a fibrous substrate, coated substrate 201 can present different wetting and adhesion properties than much smoother, extruded polymeric film substrates.

[0035] Examples of coatings which may be applied to form a coated surface on coated substrate 201 include, without limitation, coatings built on aqueous dispersions of polyurethane and cellulose ester-based coatings.

[0036] In certain embodiments according to this disclosure, the coating(s) applied to coated substrate 201 not only provide a less porous surface upon which to build a micro-optic security device which omits layers comprising thin sections of plastic film, but can also tune the opacity of coated substrate 201 to enable passing UV curing light from one side of coated substrate 201 to a second side of coated substrate 201 for cast-curing material disposed on the second side of coated structure 201. In some embodiments, the coated substrate has a diffuse opacity of less than 85% when measured according to the Technical Association of the Pulp and Paper Industry (“TAPPI”) standard T425. However, embodiments in which coated substrate 201 is more translucent (for example, having a diffuse opacity of 70% or less, when measured according to TAPPI standard T425) are possible, and within the contemplated scope of this disclosure.

[0037] Referring to the non-limiting example of FIG. 2A, an icon layer 205, comprising a plurality of icon structures is formed on top of coated substrate 201. As discussed with reference to FIG. 1, icon layer 205 comprises a layer of cured polymeric “goo.” As used in this disclosure, “goo” encompasses the term of art within the field of banknote and security manufacture to refer to light-curable polymers (for example, polyacrylates) and embossable resins (for example, cast-curing resins manufactured by Crane Corporation or Giesecke and Devrient, GmbH) with sufficient viscosity to fill micron- scale relief structures of embossing molds when uncured, and sufficient strength to withstand removal from the embossing mold after curing and use in security documents. According to certain embodiments, icon layer 205 is formed by first applying a layer of uncured goo to a coated top surface of coated substrate 201, pressing an embossing tool defining retaining structures (for example, mesas, voids and posts to be filled or covered with pigmented icon material) of icon layer 205 onto the uncured goo layer, and then passing curing light (for example, UV light) through the backside of coated substrate 201 to cross-link and cure the goo.

[0038] As noted elsewhere in this disclosure, in embodiments where coated substrate 201 is a fibrous (i.e., paper) substrate to which a coating agent has been applied, the surface of coated substrate 201 has greater “tooth” or adhesive properties, due to surface variations not present in extruded polymeric films. As such, directly porting manufacturing techniques used for manufacturing icon and lens structures on extruded polymeric films (for example, optical spacer 110 in FIG. 1) frequently results in tearing or damaging of retaining structures with sub-micron scale features, given the relative strength of the adhesive bond between the underside of icon layer 205 (which is anchored in the surface variations of coated substrate) and adhesion between the embossing tool. Accordingly, “goos” with less surface tension and weaker adhesive properties than are typically used when cast-curing features anchored to extruded polymer films need to be used.

[0039] Once the retaining structures are formed, a layer of polymeric icon material in a contrasting color (or clear, if the retaining structures are pigmented) to the retaining structures is applied on top of the retaining structures such that the retaining structures are “just barely” filled or coated, such that, when viewed from above, the icon layer comprises contrasting regions of retaining structure colored material and fill material. In many embodiments, applying the contrasting polymeric icon material comprises applying a flood coat on top of the retaining structures, and doctor blading excess material off to create contrasting regions of retaining structure and pigmented icon material. Having filled the retaining structures, the uncured contrasting material of the icon layer is cured. The curing light can be passed through the underside of coated substrate 201 or from a light source directly facing the retaining structures of icon layer 205.

[0040] In contrast to embodiments in which separation between the icon layer and focusing layer of a micro-optic device is achieved by cast-curing an icon layer on a first side of a section of extruded polymeric film of a specified thickness, and cast curing the focusing layer on a second side of the section of extruded polymeric film, building up the constituent layers of a micro-optic film with sub-micron scale icon features, and small lenses (for example, having pitches of 35 microns or less) on a single side of a fibrous substrate, presents heightened challenges with respect to achieving good adhesion of smooth layers of goo on thelayers on top of the icon layer. Put differently, attempting to form a smooth layer of uncured goo at a uniform thickness on an icon layer formed on a coated fibrous substrate (for example, with a Mayer rod), is generally not possible. As shown in FIG. 2, to achieve a substantially uniform thickness differential between the focusing layers and icon layers of a security device which is “built up” on a single side of a fibrous substrate, one or more textured adhesion layers (207 and 209) of varying thickness are applied on top of icon layer 205. Textured adhesion layers 207 and 209 comprise cast-cured layers of a goo which has the same index of refraction as focusing layer 211. As shown in the figure, each of first textured adhesion layer 207 and second textured adhesion layer 209 has an embossed relief pattern defining texture elements. In this example, the textured elements of first adhesion layer 207 comprise hemispherical undulations, spaced at an element spacing 217. While texture elements comprise, hemispherical undulations are easy to form and can frequently spare manufacturers the expense of sourcing new embossing tools (molds for coarser pitch lenses can be used to create texture elements), there is no requirement that the texture elements of textured adhesion layers 207 and 209 be so shaped. Other texture elements, such as triangular ridges or square waves, are possible and within the contemplated scope of this disclosure. Curing light for forming textured adhesion layers 207 and 209 can, as with icon layer 205, be provided from underneath (i.e., through coated substrate 201) or facing textured adhesion layers 207 and 209. Additionally, in certain embodiments, the embossing tool use to create textured adhesion layers 207 and 209 may be translucent or comprise a light source, to facilitate both casting and curing by a single tool.

[0041] Referring to the explanatory example of FIG. 2A, a focusing layer 211 is formed on top of the top-most textured adhesion layer (in this example, second texture adhesion layer 209) by applying a layer of uncured goo on top of the top-most textured adhesion layer, embossing same with a tool defining a lens relief pattern, and curing same with ultraviolet light. In the explanatory example of FIG. 2A, focusing layer 211 comprises an array of refractive lenses which are disposed at an element spacing 215. For the purposes of this disclosure, when used with reference to lenses, the expression “element spacing” encompasses lens pitch. To simplify design and modelling the appearance and behavior or synthetic images projected by security document 200, focusing layer 211 can be formed using the same goo as textured adhesion layers 207 and 209, thereby that each of these layers have a common refractive index. However, it is possible to form focusing layer 211 from goos having different indices of refraction than the material used to form first and second adhesion layers 207 and 209 to create systems (for example, doublet lenses) with more complex optical behavior.

[0042] FIG. 2B illustrates a second example of a security document 250 with a reduced-plastic singlesided micro-optic security feature according to various embodiments of this disclosure is shown. Security document 250 builds on the example of security document 200 in FIG. 1 through the addition of a cast- cured polymeric seal layer disposed on top of focusing layer 211. Depending on the geometry of focusing layer 211, in particular, whether the focusing elements of focusing layer are convex or concave layer, seal layer 220 is formed from a goo having a different index of refraction than the lenses of focusing layer 211. Where the lenses of focusing layer 211 are concave (as shown in FIG. 2B) seal layer 220 is formed from agoo having a lower RI than that of focusing layer 211. Similarly, where the lenses of focusing layer 211 are convex, seal layer 220 is formed from a goo having a higher RI than that of focusing layer 211. The RI of both seal layer 220 and focusing layer 211 can be tuned upwards by adding nanoparticles to the uncured goo used to form these elements.

[0043] FIG. 2C illustrates a third example of a security document 275 with a reduced-plastic singlesided micro-optic security feature according to various embodiments of this disclosure is shown. While FIGS. 2A and 2B described examples of micro-optic security devices with refractive lenses which were built upon an icon layer as the first layer added to coated substrate 201, the present disclosure is not limited to such embodiments. As shown with reference to FIG. 2C, embodiments according to this disclosure include embodiments with reflective focusing elements, and in which the icon layer does not comprise the bottom-most layer (i.e., closest to coated substrate 201).

[0044] Referring to the illustrative example of FIG. 2C, a first textured adhesion layer 207 is formed on coated substrate 201. In some embodiments, first textured adhesion layer is cast-cured by embossing polymeric goo to define the texture elements (which, in this example, have a smaller element spacing than focusing elements of focusing layer 211) and cured using UV light passed through coated substrate 201.

[0045] While in the examples of FIGS. 2A and 2B, multiple textured adhesion layers were interposed between icon layer 205 and focusing layer 211, FIG. 2C illustrates that embodiments according to this disclosure do not require such a construction. As shown in FIG. 2C, focusing layer 211, comprising a layer of concave, reflectively coated (with a metallizing coating) lenses is formed by cast-curing the concave forms of the focusing elements in the same manner as first textured adhesion layer 207, and then metallizing same (for example, through vapor deposition of a reflective metal, such as aluminum or chromium).

[0046] Depending on the focal properties of the reflective focusing elements of focusing layer 211, a second textured adhesion layer 209 can be applied on top of focusing layer 211. As skilled artisans will appreciate, polymers metallized by vapor deposition both reflect and permit the passage of light through the metallized surface (which is why reflective sunglasses are so made). Accordingly, second textured adhesion layer 209 can, like the layers beneath it, be formed by embossing uncured goo on top of metallized focusing layer 211 and passing UV curing light up through coated substrate 201 to second textured adhesion layer 209.

[0047] As shown in FIG. 2C, an icon layer 205 can be formed on second textured adhesion layer 209. In some embodiments, icon layer 205 is formed by cast curing retaining structures defining the icon pattern, filling the retaining structures with pigmented icon material (for example, by doctor blading uncured tinted polymeric goo across the retaining structures), and then flood-curing same. Curing of the retaining structures and tinted icon material of icon layer 205 can be performed using light passed through coated substrate 201.

[0048] FIG. 3 illustrates operations of a method 300 for making security documents reduced-plastic single-sided micro-optic security features according to this disclosure. As already illustrated by the examples of FIGS. 2A-2C, there is no requirement that the operations described with reference to FIG. 3need to be performed in the order shown in the figure, and variations from the sequence shown in FIG. 3 to create different security document structures are within the contemplated scope of this disclosure.

[0049] Referring to the illustrative example of FIG. 3, at operation 305, a coated substrate having at least one coated surface (for example, coated substrate 201) is provided. In some embodiments, the coated substrate can be a dual sided coated substrate, where two opposite sides of the substrate are coated. According to various embodiments, the coated substrate provided at operation 305 is a fibrous substrate, and at least one of the coated surfaces retains some of the texture and microscopic surface variation which distinguishes fibrous substrates not seen in extruded polymeric films at the same levels of microscopic magnification.

[0050] At operation 310, an icon layer (for example, icon layer 205 in FIGS. 2A-2C) is formed on the at least one coated surface of the coated substrate. As discussed in this disclosure, the icon layer can be formed by cast-curing (i.e., embossing uncured material, and then exposing same to actinic UV light) uncured polymeric goo on top of the at least one coated surface, and then passing the curing light through the coated substrate.

[0051] At operation 315, a layer of focusing elements (for example, focusing layer 211 in FIGS. 2A- 2C) is formed. The focusing layer can be formed on top of the icon layer, or alternatively, can be formed on one or more textured adhesion layers disposed between the icon layer and focusing elements. As described in this disclosure, the focusing layer, can, like the layer(s) below it, be produced by cast-curing uncured polymeric goos using UV light either presented directly to the uncured goo, or passed through the coated substrate.

[0052] As described with respect to FIGURE 1, micro-optic security device 100 comprises a focusing layer comprising a plurality of focusing elements 105 (including, for example, focusing element 107), and an arrangement of image icons 120 (including, for example, image icon 121. 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, change shapes, or change colors) in response to shifts in viewing angle.

[0053] For example, FIGURES 4A and 4B illustrate an example portion 402 of a security device in accordance with this disclosure. The portion 402 of the security device can be a part of the micro-optic security device 100, and can include components of the micro-optic security device 100, such as focusing elements and image icons. In some embodiments, the portion 402 can be a thread of the micro-optic security device 100.

[0054] The portion 402 of the security device can, using the image icons, project various synthetic images within the footprints of the focusing elements. For instance, in the example of FIGURE 4A, varioussynthetic images 404 are visible. The synthetic images can form a pattern of image types, or, in some embodiemnts, each image can be of a selected type, without following a certain pattern. In some embodiemnts, each image may be different. That is, it will be understood that the synthetic images 402 shown in FIGURES 4A and 4B are merely examples, and the synthetic images can take any visual shape, can be of any color or combination of colors, and can be in any position on the portion 402 of the security device. In this example, the synthetic images are a combination of three types of images: shields, locks, and mobile devices.

[0055] These synthetic images 402 can dynamically react (for example, by appearing to move, change shapes, or change colors) in response to shifts in viewing angle. For instance, FIGURE 4A is the portion 402 of the security device at a first example viewing angle, and FIGURE 4B is the portion 402 of the security device at a second example viewing angle. As shown in FIGURE 4B, when the portion 402 of the security device is moved, or a viewer moves, the second viewing angle cause the synthetic images 404 to morph. In this example, the shapes of the synthetic images 404 viewed in corresponding areas of the portion 402 appear to morph to other shapes. For instance, in this example, a lock image viewed at the first viewing angle of FIGURE 4A may morph into a shield image when viewed at the second viewing angle of FIGURE 4B, a mobile device image viewed at the first viewing angle of FIGURE 4A may morph into a lock image when viewed at the second viewing angle of FIGURE 4B, and so on. As described above, it will be understood that the perceived position and / or color of the synthetic images 402 may also change when the viewing angle changes.

[0056] Examples of security documents according to embodiments of this disclosure include security documents comprising a substrate having a first side, a coated surface disposed on the first side of the substrate, an icon layer disposed on the coated surface, the icon layer comprising a plurality of pigmented structures, a focusing layer comprising a plurality of focusing elements, wherein each focusing element of the plurality of focusing elements has a footprint, and wherein the plurality of focusing elements projects a synthetic image of portions of the icon layer in footprints of the plurality of focusing elements.

[0057] Examples of security documents according to embodiments of this disclosure include security documents, wherein the substrate includes a second side, and a second coated surface disposed on the second side of the substrate.

[0058] Examples of security documents according to embodiments of this disclosure include security documents, wherein none of the icon layer or the focusing layer comprise or contact a layer of extruded transparent or translucent polymer film.

[0059] Examples of security documents according to embodiments of this disclosure include security documents, wherein the substrate is a fibrous substrate.

[0060] Examples of security documents according to embodiments of this disclosure include security documents, wherein the fibrous substrate has a diffuse opacity of less than 85% when measured according to TAPPI standard T425.

[0061] Examples of security documents according to embodiments of this disclosure include security documents, wherein the fibrous substrate has a diffuse opacity of less than 70% when measured according to TAPPI standard T425.

[0062] Examples of security documents according to embodiments of this disclosure include security documents comprising a textured adhesion layer disposed between the icon layer and the focusing layer.

[0063] Examples of security documents according to embodiments of this disclosure include security documents, wherein the icon layer is a structured icon layer, comprising at one or more of mesas, posts, or voids of cured light-curable polymer.

[0064] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices comprising an icon layer, the icon layer comprising a plurality of pigmented structures, an adhesive layer disposed on the icon layer, and a focusing layer comprising a plurality of focusing elements, wherein each focusing element of the plurality of focusing elements has a footprint, wherein the plurality of focusing elements projects a synthetic image of portions of the icon layer in footprints of the plurality of focusing elements, and wherein none of the icon layer or focusing layer comprise or contact a layer of extruded transparent or translucent polymer fdm.

[0065] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices comprising a textured adhesion layer disposed between the icon layer and the focusing layer.

[0066] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices, wherein focusing elements of the plurality of focusing elements are refractive focusing elements.

[0067] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices, wherein focusing elements of the plurality of focusing elements are reflective focusing elements.

[0068] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices, wherein the focusing layer or a seal layer comprises a first exterior surface of the micro-optic security device, and the first exterior surface does not contact a carrier substrate.

[0069] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices, wherein the adhesive layer has a diffuse opacity of less than 70% when measured according to TAPPI standard T425.

[0070] Examples of micro-optic security devices according to embodiments of this disclosure include micro-optic security devices, wherein the icon layer is a structured icon layer, comprising at one or more of mesas, posts, or voids of cured light-curable polymer.

[0071] Examples of methods of making security documents according to embodiments of this disclosure include methods comprising on a substrate having a coated surface, forming an icon layer on the coated surface, and forming a focusing layer comprising a plurality of focusing elements, wherein each focusing element of the plurality of focusing elements has a footprint, and wherein the plurality of focusingelements projects a synthetic image of portions of the icon layer in footprints of the plurality of focusing elements.

[0072] Examples of methods of making security documents according to embodiments of this disclosure include methods comprising subsequent to forming the icon layer and before forming the focusing layer, forming one or more textured adhesion layers.

[0073] Examples of methods of making security documents according to embodiments of this disclosure include methods, wherein the one or more textured adhesion layers have a first element spacing, wherein focusing elements of the focusing layer are spaced at a second element spacing, and wherein the first element spacing is greater than the second element spacing.

[0074] Examples of methods of making security documents according to embodiments of this disclosure include methods, wherein the icon layer is formed by applying a layer of uncured, light curable material to the coated surface, embossing the layer of uncured light curable material to define a plurality of relief structures within the icon layer, and curing the light curable material by passing light through the substrate.

[0075] Examples of methods of making security documents according to embodiments of this disclosure include methods, wherein the substrate is a fibrous substrate.

[0076] Examples of methods of making security documents according to embodiments of this disclosure include methods, wherein the substrate has a diffuse opacity of less than 85% when measured according to TAPPI standard T425.

[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 security document (160, 200, 250, 275) comprising: a substrate (150, 201) having a first side; a coated surface disposed on the first side of the substrate; an icon layer (120, 205) disposed on the coated surface, the icon layer comprising a plurality of pigmented structures; and a focusing layer (211) comprising a plurality of focusing elements (105), wherein each focusing element (121) of the plurality of focusing elements has a footprint, and wherein the plurality of focusing elements projects a synthetic image (402) of portions of the icon layer in footprints of the plurality of focusing elements.

2. The security document of claim 1, wherein none of the icon layer or the focusing layer comprise or contact a layer of extruded transparent or translucent polymer film.

3. The security document of claim 1, wherein the substrate is a fibrous substrate.

4. The security document of claim 3, wherein the fibrous substrate has a diffuse opacity of less than 85% when measured according to TAPPI standard T425.

5. The security document of claim 3, wherein the fibrous substrate has a diffuse opacity of less than 70% when measured according to TAPPI standard T425.

6. The security document of claim 1, further comprising a textured adhesion layer (207, 209) disposed between the icon layer and the focusing layer.

7. The security document of claim 1, wherein the icon layer is a structured icon layer, comprising at one or more of mesas, posts or voids of cured light-curable polymer.

8. A micro-optic security device (100), comprising: an icon layer (120, 205), the icon layer comprising a plurality of pigmented structures; an adhesive layer disposed on the icon layer; and a focusing layer (211) comprising a plurality of focusing elements (105), wherein each focusing element (121) of the plurality of focusing elements has a footprint, wherein the plurality of focusing elements projects a synthetic image (402) of portions of the icon layer in footprints of the plurality of focusing elements, and wherein none of the icon layer or focusing layer comprise or contact a layer of extruded transparent or translucent polymer film.

9. The micro-optic security device of claim 8, further comprising a textured adhesion layer (207, 209) disposed between the icon layer and the focusing layer.

10. The micro-optic security device of claim 8, wherein focusing elements (107) of the plurality of focusing elements are refractive focusing elements.

11. The micro-optic security device of claim 8, wherein focusing elements of the plurality of focusing elements are reflective focusing elements.

12. The micro-optic security device of claim 8, wherein the focusing layer or a seal layer (140) comprises a first exterior surface of the micro-optic security device, and the first exterior surface does not contact a carrier substrate.

13. The micro-optic security device of claim 8, wherein the adhesive layer has a diffuse opacity of less than 70% when measured according to TAPPI standard T425.

14. The micro-optic security device of claim 8, wherein the icon layer is a structured icon layer, comprising at one or more of mesas, posts or voids of cured light-curable polymer.

15. A method of making a security document(160, 200, 250, 275), the method comprising: on a substrate (150, 201) having a coated surface, forming an icon layer on the coated surface; and forming a focusing layer (211) comprising a plurality of focusing elements (105), wherein each focusing element (121) of the plurality of focusing elements has a footprint, and wherein the plurality of focusing elements projects a synthetic image (402) of portions of the icon layer in footprints of the plurality of focusing elements.

16. The method of claim 15, further comprising: subsequent to forming the icon layer and before forming the focusing layer, forming one or more textured adhesion layers (207, 209).

17. The method of claim 16, wherein the one or more textured adhesion layers have a first element spacing, wherein focusing elements of the focusing layer are spaced at a second element spacing, and wherein the first element spacing is greater than the second element spacing.

18. The method of claim 15, wherein the icon layer is formed by: applying a layer of uncured, light curable material to the coated surface; embossing the layer of uncured light curable material to define a plurality of relief structures within the icon layer; and curing the light curable material by passing light through the substrate.

19. The method of claim 15, wherein the substrate is a fibrous substrate.

20. The method of claim 19, wherein the substrate has a diffuse opacity of less than 85% when measured according to TAPPI standard T425.

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