Abstract:
An optionally transferable optical system with a reduced thickness is provided. The inventive optical system is basically made up of a synthetic image presentation system in which one or more arrangements of structured image icons are substantially in contact with, but not completely embedded within, one or more arrangements of focusing elements. The focusing element and image icon arrangements cooperate to form at least one synthetic image. By way of the subject invention, the requirement for an optical spacer to provide the necessary focal distance between the focusing elements and their associated image icon(s) is removed. As a result, overall system thicknesses are reduced, suitability as a surface-applied authentication system is enabled, and tamper resistance is improved.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 61/525,239, filed Aug. 19, 2011, which is incorporated herein in its entirety by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention generally relates to an improved system for presenting one or more synthetic images, and more particularly relates to an optionally transferable optical system with a reduced thickness. 
       BACKGROUND AND SUMMARY OF THE INVENTION 
       [0003]    As described in detail in, for example, U.S. Pat. No. 7,333,268 to Steenblik et al., the focal length of focusing elements in micro-optic materials determines the optical separation of the focusing elements from an image icon array. In other words, the arrays in these micro-optic materials are positioned on either side of an optical spacer so as to align the focal point of each focusing element with its associated image icon(s). When the focal point lies on or within the image icon array, the synthetic image is in sharp focus. When, however, the focal point lies above or below the image icon array, the synthetic image is blurry and out of focus. 
         [0004]    By way of the present invention, the requirement for an optical spacer (i.e., a flexible transparent polymeric film-like material) to provide the necessary focal distance between the focusing elements and their associated image icon(s) is removed. As a result, overall system thicknesses are reduced, suitability as a surface-applied authentication system is enabled, and tamper resistance is improved. 
         [0005]    More specifically, the present invention provides an optionally transferable optical system with a reduced thickness, which basically comprises a synthetic image presentation system made up of one or more arrangements of structured image icons substantially in contact with, but not completely embedded within, one or more arrangements of focusing elements, wherein the one or more arrangements of image icons and the one or more arrangements of focusing elements cooperate to form at least one synthetic image of at least a portion of the image icons, wherein interstitial space between focusing elements in the one or more arrangements of focusing elements does not contribute to the formation of the at least one synthetic image. 
         [0006]    The phrase “substantially in contact”, as used herein, is intended to mean that either the top or bottom (e.g., apex or base) of the focusing elements is substantially in contact with or touches the image icons. 
         [0007]    Focusing elements contemplated for use in the present invention include refractive, reflective (e.g., concave reflective, convex reflective), hybrid refractive/reflective, and diffractive focusing elements. Examples of such focusing elements are described in U.S. Pat. No. 7,333,268 to Steenblik et al., U.S. Pat. No. 7,468,842 to Steenblik et al., and U.S. Pat. No. 7,738,175 to Steenblik et al., which are fully incorporated herein by reference as if fully set forth herein. Interstitial space between focusing elements in the arrangements used in inventive micro-scale systems is typically about 5 microns or less for systems with a total thickness of less than about 50 microns, while interstitial space in inventive macro-scale systems is typically greater in size, preferably about 5 millimeters or less for systems with a total thickness of less than or equal to 1 centimeter. It is noted that reflective focusing elements reflect incident light and may be metalized to obtain high focusing efficiency. For metallization, the profiles of the lens structures of the concave reflective or convex reflective arrangements may be provided with a reflecting metal layer (e.g., a vapor deposited metal layer). Instead of a fully opaque reflecting metal layer, a semitransparent (or partially metalized) metal layer, or a high refractive index layer can be provided. Furthermore, multiple layers of vapor deposited material may be used to provide reflectivity, for example, color-shifting interference coatings formed from dielectric layers, or from a combination of metal and dielectric layers such as metal/dielectric/metal may also provide the necessary reflectivity. 
         [0008]    Image icons contemplated for use in the present invention are structured image icons (i.e., image icons having a physical relief). In one exemplary embodiment, the image icons are optionally coated and/or filled voids or recesses (e.g., voids in a substantially planar structure, the voids optionally filled or coated with another material), while in another exemplary embodiment, the image icons are formed from raised areas or shaped posts (e.g., raised areas in a substantially planar structure). Examples of structured image icons are also described in U.S. Pat. No. 7,333,268 to Steenblik et al., U.S. Pat. No. 7,468,842 to Steenblik et al., and U.S. Pat. No. 7,738,175 to Steenblik et al. 
         [0009]    Unexpectedly and quite surprisingly, the present inventors have discovered that tailoring the focal length of the focusing elements in the inventive system serves to obviate the need for an optical spacer. It was found that the arrangement(s) of image icons may intersect the depth of focus of the arrangement(s) of focusing elements without the need for an optical spacer, resulting in a thinner, more streamlined system capable of presenting at least one synthetic image. Moreover, and as will be explained in more detail below, the present inventors have also discovered that when certain focusing element designs are used, it is possible to transfer the inventive system to a value document or product without a base film or carrier substrate forming any part of the transferred system. Both discoveries have resulted in a synthetic image presentation system having a decrease in cross-sectional thickness, a suitability as a surface-applied security feature, and a reduced risk of interlayer delamination. 
         [0010]    Other benefits realized by the subject invention include increased tamper resistance and projected images with improved contrast and clarity. As will be readily appreciated, optical systems lacking a tough optical spacer between the focusing elements and image icons are more difficult to remove intact from a final substrate once bonded. Moreover, the closer the focusing elements are to the image icons, the greater the contrast and clarity of the projected images. Without the additional thickness imposed by an optical spacer film (typically a biaxially-oriented optical spacer film) between focusing elements and image icons, there is less light scattering and birefringence. This results in images that appear sharper and have greater contrast. 
         [0011]    As alluded to above, various system size ranges are contemplated by the present invention. In addition to micro-scale systems, macro-scale systems are also contemplated. Such larger scale systems may constitute unitary or complete film structures, or may be formed with replaceable image icon arrangements. 
         [0012]    Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings. 
         [0013]    Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present disclosure may be better understood with reference to the following drawings. Components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. 
           [0015]    Particular features of the disclosed invention are illustrated by reference to the accompanying drawings which are cross-sectional side views of the following exemplary embodiments of the present invention: 
           [0016]    FIG.  1 —refractive optical system; 
           [0017]    FIG.  2 —transferable refractive optical system; 
           [0018]    FIG.  3 —concave reflective optical system; 
           [0019]    FIG.  4 —convex reflective optical system; 
           [0020]    FIG.  5 —transferable concave reflective optical system; 
           [0021]    FIG.  6 —diffractive optical system employing transmissive Fresnel lenses; and 
           [0022]    FIG.  7 —diffractive optical system employing reflective Fresnel lenses. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Exemplary embodiments of the inventive system will now be disclosed in connection with the drawings. There is no intent, however, to limit the present disclosure to the embodiments disclosed herein. On the contrary, the intent is to cover all alternatives, modifications and equivalents. For example, additional features or functionality, such as those described in U.S. Pat. No. 7,333,268 to Steenblik et al., U.S. Pat. No. 7,468,842 to Steenblik et al., and U.S. Pat. No. 7,738,175 to Steenblik et al., may also be included in the invention system. Such additional features or functionality may comprise textured surfaces for better adhesion to further layers, adhesion promoters, etc. The inventive system may also contain overt or covert information such as customized or personalized information in the form of serial numbers, bar codes, images, etc. that can be formed using traditional printing techniques or laser engraving systems. This added functionality would allow interaction between the synthetic images and the covert information. Additionally, information can be overprinted or printed on various layers at all stages of manufacture, or post manufacture. 
       Refractive System Embodiments 
       [0024]    In a first exemplary embodiment, which is best shown in  FIG. 1 , the inventive system is a refractive optical system  10  that further includes a support or carrier substrate  12 . In this embodiment, a synthetic image presentation system  14  is built on one side of the carrier substrate  12 . As will be readily appreciated, the carrier substrate  12  does not contribute to the optical functionality of the system. In other words, synthetic images will be presented regardless of the presence or opacity of the carrier substrate  12 . 
         [0025]    The synthetic image presentation system  14  in this first exemplary embodiment employs refractive focusing elements  16 , which each have a focal length such that a structured image icon  18  placed substantially in contact or close to its base intersects with a portion of its depth of focus, when viewed normal to the surface. Generally, these focusing elements have very low f-numbers (e.g., less than or equal to 1) and cylindrical, spheric or aspheric surfaces. 
         [0026]    The term “f-number”, as used herein, is intended to mean the ratio of a focusing element&#39;s focal length (real or virtual in the case of convex reflectors) to its effective lens diameter. 
         [0027]    The synthetic image presentation system  14  may be cast against the carrier substrate  12 . The materials forming carrier substrate  12  can be selected from plastics, cellulose, composites, polyamide (e.g., nylon  6 ), polycarbonate, polyester, polyethylene, polyethylene napthalate (PEN), polyethylene terephthalate (PET), polypropylene, polyvinylidene chloride films or sheets, mylar sheets, cellophane, paper, rag/cotton, combinations thereof, and the like. 
         [0028]    The arrangements of structured image icons and focusing elements of the synthetic image presentation system  14  may be formed from a variety of materials such as substantially transparent or clear, colored or colorless polymers such as acrylics, acrylated polyesters, acrylated urethanes, epoxies, polycarbonates, polypropylenes, polyesters, urethanes, and the like, using methods such as extrusion (e.g., extrusion embossing, soft embossing), radiation cured casting, and injection molding, reaction injection molding, and reaction casting. High refractive index, colored or colorless materials having refractive indices (at 589 nanometers, 20° C.) of more than 1.5, 1.6, 1.7, or higher, such as those described in U.S. Patent Application Publication No. US 2010/0109317 A1 to Hoffmuller et al., may also be used in the practice of the present invention. 
         [0029]    An exemplary method of manufacture is to form the icons as voids in a radiation cured liquid polymer (e.g., acrylated urethane) that is cast from an icon mold against a base film (i.e., carrier substrate  12 ), such as 75 gauge adhesion-promoted PET film, then to fill the icon voids with a submicron particle pigmented coloring material by gravure-like doctor blading against the polymeric icon surface, then to solidify the fill by suitable means (e.g., solvent removal, radiation curing, or chemical reaction), then to cast lenses against the filled icons by bringing the icon side of the base film against a lens mold filled with radiation curable polymer, and solidifying the polymer by application of ultraviolet (UV) light or other actinic radiation. 
         [0030]    For micro-scale systems used, for example, in the form of a security strip, thread, patch, or overlay:
       (a) the focusing elements have preferred widths (in the case of cylindrical focusing elements) and base diameters (in the case of non-cylindrical focusing elements) of less than about 50 microns (more preferably, less than about 25 microns, and most preferably, from about 5 to about 15 microns), preferred focal lengths of less than about 50 microns (more preferably, less than about 25 microns, and most preferably, from about 1 to about 5 microns), and preferred f-numbers of less than or equal to 1 (more preferably, less than or equal to 0.75);   (b) the structured image icons are either optionally coated and/or filled voids or recesses each preferably measuring from about 50 nanometers to about 8 microns in total depth, or raised areas or shaped posts each preferably measuring from about 50 nanometers to about 8 microns in total height;   (c) the carrier substrate has a preferred thickness ranging from about 10 to about 50 microns, more preferably, from about 15 to about 25 microns; and   (d) the total thickness of the inventive system is preferably less than about 50 microns (more preferably, less than about 45 microns, and most preferably, from about 10 to about 40 microns).       
 
         [0035]    In a second exemplary embodiment, which is best shown in  FIG. 2 , the inventive system is a transferable refractive optical system  20  that further includes a microstructure-bearing release liner  22 , which is made up of carrier substrate  24  and “lens mold” layer  26 .  FIG. 2  shows the system  20  during application to a paper substrate  28 . The refractive optical system  20  (with one or more adhesive layers) may be transferred to another surface as a transfer film using techniques including mechanical, chemical, thermal and photo-induced separation techniques. The concept of separation of desired components from a carrier substrate is known in the art of holographic foil transfer, whereby a film with a release coating (i.e., release liner) is provided with optical coatings and adhesives, such that the optical coatings and adhesives can be transferred to a final substrate with application of heat and pressure. This embodiment is particularly useful in applications requiring films with very thin cross-sectional thicknesses. 
         [0036]    By way of the present exemplary embodiment, the inventors made the surprising discovery that synthetic image presenting optics may in fact be successfully separated from a carrier film. As will be readily appreciated by those skilled in the art, the crest and trough geometry of focusing elements described herein means that the optical structure will be more resistant to release from a carrier film, as compared to smoother films or foils (e.g., holograms), which have lower surface areas and lower aspect ratios of microstructured features, making them easier to separate from a carrier film. Moreover, incorrect separation operations cause nonuniform stresses to be applied to the system being transferred, negatively impacting upon the ability of these systems to project synthetic images. The synthetic image presenting optics of the present invention rely on the focusing of light within the volume of the transferred structure and applied stress may cause distortions in the volume of the structure. By utilizing the techniques and optical structures described herein, these difficulties are overcome. 
         [0037]    Referring again to  FIG. 2 , synthetic image presentation system  30  is shown releasably coupled to the release liner  22  by way of “lens mold” layer  26 . The “lens mold” layer  26  is typically a curable resin (e.g., polyester acrylate) layer between 3 and 50 microns in thickness, while the carrier substrate  24  is typically a 15 to 50 micron UV transmissive film (e.g., a PET film). 
         [0038]    An optional stiffening layer  32  is shown on the arrangement of structured image icons of the synthetic image presentation system  30 . Process performance is enhanced by making system  30  have a higher stiffness or resistance to bending than the carrier substrate  24  and “lens mold” layer  26 . The stiffening layer  32  may be prepared from energy curable acrylates and has a preferred thickness between 1 and 10 microns. In addition to, or instead of, stiffening layer  32 , one or more sealing layers may be applied to the arrangement of structured image icons. Such a sealing layer may be prepared from energy curable acrylates (e.g., energy curable acrylates containing organic or inorganic fillers with pigmenting or reinforcing properties), solvent or water based coatings such as acrylics, epoxies, ethylene-vinyl acetates (EVAs), polyurethanes, polyvinyl alcohols (PVAs), and the like, and may have a thickness between 1 and 10 microns. 
         [0039]    Adhesive layer  34  is shown on the stiffened system  30  in  FIG. 2 . Adhesive layer  34  may be prepared from thermally activated adhesives (i.e., hot melt or heat seal adhesives), pressure sensitive adhesives, or any thermoset or thermoplastic adhesive system selected to provide bonding between these target surfaces including acrylics, cyanoacrylates, epoxies, polyimides, polyurethanes, polyvinyl acetates, rubber, and silicones. Adhesive layer  34  is preferably prepared from a tack free thermally activated adhesive, and has a preferred thickness between 1 and 100 microns. Common activation temperatures for thermally activated adhesives may range from about 70 to about 170 ° C., while for pressure activated adhesives, no additional heat is required to activate the adhesive. 
         [0040]    An exemplary method of manufacturing the transferable refractive optical system of the present invention comprises: 
         [0041]    forming a microstructure-bearing release liner comprising a “lens mold” layer adhered to a carrier film (e.g., a UV transmissive carrier film), wherein the “lens mold” layer is formed from a curable resin having a plurality of voids with negative lens geometries, the negative lens geometries being made by UV curing the resin against a rigid surface having positive lens geometries (i.e., a positive lens mold); and 
         [0042]    forming the transferable refractive optical system onto the “lens mold” layer of the microstructure-bearing release liner by:
       placing the “lens mold” layer of the microstructure-bearing release liner against a rigid icon mold while an optically functional UV curable liquid polymer (e.g., polyester acrylate) fills the plurality of voids of both the “lens mold” layer and the rigid icon mold, applying pressure with a nip roller to exclude excess liquid polymer, and simultaneously exposing the liquid polymer to UV radiation such that the UV curable polymer cures or hardens and can be lifted from the icon mold. As will be readily appreciated by those skilled in the art, the optically functional polymer must have sufficient adherence to the “lens mold” layer of the release liner to survive the process of lifting after the material is cured between the “lens mold” layer and the rigid icon mold and lifted from the icon mold;   filling the plurality of image icons with a material providing a contrast with the optically functional polymer (e.g., a UV curable flexographic printing ink) to form a filled image icon layer; optionally,   optionally applying one or more of a sealing layer, a stiffening layer, a pigmented or dyed layer, an opacifying layer, or combinations thereof to the filled image icon layer; and   applying one or more adhesive layers (e.g., tack free thermally activated adhesive layers) to the optionally sealed, stiffened, pigmented/dyed, and/or opacified, filled image icon layer.       
 
         [0047]    Once prepared, the transferable refractive optical system  20  may be handled like a traditional transfer foil, that is, the material can be wound and unwound from a roll and further converted into a suitable final shape such as a patch, thread, or sheet by converting methods common in the security printing and packaging industries. In order to transfer the synthetic image presentation system  30  from the release liner  22 , the adhesive side of the system  20  is placed in contact with a desired final substrate (e.g., paper substrate  28 ). Heat and/or pressure is applied causing the adhesive in adhesive layer  34  to bond securely to substrate  28 . Then, the release liner  22  with “lens mold” layer  26  is peeled away, leaving behind the desired synthetic image presentation system  30 . 
         [0048]    As will be readily appreciated from the above description, for reliable separation to occur using this technique, relative bond strengths must be controlled as follows: 
         [0049]    Strongest Bond Strengths:
       adhesive layer  34  to paper substrate  28     “lens mold” layer  26  to carrier substrate  24         
 
         [0052]    Mid-Range Bond Strength:
       cured optically functional polymer to positive lens mold       
 
         [0054]    Weakest Bond Strength:
       cured optically functional polymer to rigid icon mold.       
 
         [0056]    While bond strengths may be higher or lower depending on the process conditions and final product requirements, the relative interfacial bond strengths must be maintained in the aforementioned way. For example, if the cured optically functional polymer bonds very aggressively to the rigid icon mold, then this sets the minimum bond strength value, and all other bonds must be adjusted higher accordingly. 
       Reflective System Embodiments 
       [0057]    In a third exemplary embodiment, which is best shown in  FIG. 3 , the inventive system is a concave reflective optical system  36  that further includes a support or carrier substrate  38 . In this embodiment, a synthetic image presentation system  40  is built on one side of the carrier substrate  38 . 
         [0058]    The synthetic image presentation system  40  in this exemplary embodiment employs concave reflective focusing elements  42 , which each have a focal length such that a structured image icon  44  placed substantially in contact or close to its crest or highest point intersects with a portion of its depth of focus, when viewed normal to the surface. These reflective focusing elements are coated with a reflective material to obtain high focusing efficiency. For example, the focusing elements may be conformally coated with a reflective material such as aluminum, chrome, copper, gold, nickel, silver, stainless steel, tin, titanium, zinc sulfide, magnesium fluoride, titanium dioxide, or other material providing the desired level of reflectivity. This reflective material may be applied at thicknesses ranging from about 50 nanometers to about 2 microns using physical vapor deposition (PVD), chemical vapor deposition (CVD), or other suitable process. A protective coating may then be applied to protect the reflective layer. Protective coatings may be prepared from energy curable acrylates (e.g., energy curable acrylates containing organic or inorganic fillers with pigmenting or reinforcing properties), solvent or water based coatings such as acrylics, epoxies, EVAs, polyurethanes, PVAs, and the like, and applied at thicknesses ranging from about 1 to about 10 microns. 
         [0059]    Generally, these focusing elements have very low f-numbers, preferably, less than about 1, and more preferably, between about 0.25 and about 0.50, and cylindrical, spheric or aspheric surfaces. As noted above, f-number means the ratio of a focusing element&#39;s focal length to its effective lens diameter. For a spherical concave reflector, the focal length is equal to the radius of curvature divided by two. 
         [0060]    For reflective focusing elements with an f number greater than about 1, the optical separation required for focusing on an image icon layer is too large to be practical without employing the use of an optical spacer. For f-numbers less than about 0.25, the focal points of the reflectors will lie within the volume of the reflector (i.e., within the region bounded by the crest and the trough of the reflector) and will be out of focus with an image icon layer formed at its base. So f-numbers between about 1 and about 0.25 are preferred for the inventive system to present focused synthetic images without the use of an optical spacer. 
         [0061]    The synthetic image presentation system  40  may be formed against the carrier substrate  38  during formation of the structured image icons and focusing elements by the method of casting and releasing from microstructured molds using energy curable polymers. Suitable carrier substrates include those described in the first exemplary embodiment. Similarly, the arrangements of structured image icons and focusing elements of the synthetic image presentation system  40  can be formed from the materials identified above with respect to the first exemplary embodiment. 
         [0062]    The preferred dimensions for micro-scale systems are also the same as those identified for the first exemplary embodiment. For macro-scale systems used, for example, for signage or in the form of motor vehicle decals or wraps:
       (a) the focusing elements have preferred widths/base diameters ranging from about 1 to about 10 millimeters (mm), including (but not limited to) widths/base diameters ranging from about 250 microns to about 1 mm, and ranging from about 50 to about 250 microns, preferred focal lengths ranging from about 25 microns to about 5 mm (more preferably, from about 250 microns to about 1 mm), and preferred f-numbers of less than or equal to about 1 (more preferably, less than or equal to about 0.5);   (b) the structured image icons are either optionally coated and/or filled voids or recesses each preferably measuring from about 5 centimeters (cm) to about 1 micron in total depth, or raised areas or shaped posts each preferably measuring from about 5 cm to about 1 micron in total height;   (c) the carrier substrate has a preferred thickness ranging from about 25 microns to about 5 mm, more preferably, from about 250 microns to about 1 mm; and   (d) the total thickness of the inventive refractive optical system is preferably less than or equal to about 1 cm including (but not limited to) thicknesses: ranging from about 250 microns to about 1 cm; ranging from about 50 to about 250 microns; and of less than about 50 microns.       
 
         [0067]    Macro-scale reflective optical systems contemplated by way of the present invention may employ image icons formed using conventional printing techniques (e.g., traditional inkjet or laser printing). These systems are made up of one or more arrangements of reflective focusing elements (e.g., concave reflective, convex reflective, reflective diffractive) with dimensions as noted above (e.g., widths/base diameters ranging from about 1 to about 10 millimeters), and printed image icons substantially in contact with, but not completely embedded within, the one or more arrangements of focusing elements. The printed image icons have line widths of less than or equal to about 1 millimeter. As will be readily appreciated by those skilled in the art, when finer line widths are used, more detailed designs may be applied within the design space afforded by way of these relatively large focusing elements. 
         [0068]    In a fourth exemplary embodiment, which is best shown in  FIG. 4 , the inventive system is a convex reflective optical system  46  that further includes a support or carrier substrate  48 . The surface of each convex reflective focusing element  50  is such that it “bulges out” towards the viewer. These focusing elements are “shiny” in the sense that a bright spot of light  52  appears on the surface when it is illuminated by a distant light source. The bright spot of light  52  is called a “specular highlight”. 
         [0069]    When viewing system  46  with image icons situated above the convex reflective focusing elements, the viewer will either see that the specular highlights are blocked by the image icons, or that they are not blocked by the image icons. In other words, the arrangement of convex reflective focusing elements  50  when coupled with the arrangement of structured image icons  54  will form a pattern of blocked and non-blocked specular highlights. This pattern forms a synthetic image. 
         [0070]    Generally, these focusing elements also have very low f-numbers, preferably, less than about 1, and more preferably, between about 0.25 and about 0.50, and spheric or aspheric surfaces. 
         [0071]    In addition to focusing elements prepared by the methods described herein (as well as in U.S. Pat. No. 7,333,268 to Steenblik et al., U.S. Pat. No. 7,468,842 to Steenblik et al., and U.S. Pat. No. 7,738,175 to Steenblik et al.), macro-scale reflective focusing elements of the convex or concave type may also constitute separate discrete structures, or may be formed by casting from these discreet structures. For example, metallic ball bearings can be grouped together into a regular close-packed arrangement onto a flat surface, forming an arrangement of convex reflectors. By placing a transparency film over the top of the ball bearing arrangement, the transparency film having an arrangement of image icons with the same packing arrangement on its surface, the arrangement of image icons having a pitch scaled with respect to the pitch of the ball bearing arrangement, then a macro-scale synthetic image presentation system may be formed. 
         [0072]    Such a system of convex reflectors may be useful in a display or billboard installation, in which case the ball bearings (e.g., 3.18 mm diameter highly polished stainless steel) would be permanently bonded to a rigid, flat backing surface by way of, for example, an epoxy or by permanent welds. In this type of installation, image icons can be printed by traditional inkjet or laser printing (e.g., by large format inkjet billboard printing equipment) onto a suitable transparent, printable film or plastic sheeting (e.g., heavy gauge transparent billboard vinyl) and overlaid against the ball bearings with printed side facing the ball bearing arrangement. The printed arrangement may be secured against the ball bearings by way of a frame, or the printing may be covered by a semipermanent adhesive and then adhered to the arrangement of ball bearings. The printed overlay could then be removed and replaced as needed with new graphics as is typical with traditional billboard installations. 
         [0073]    In order to reduce the cost and weight of using the discreet reflective elements in the final display, an alternative approach is first to form one permanent arrangement of discreet convex reflective elements, as described above. Focal distance may then be tailored by filling the interstitial spaces of the arrangement to the desired level with an epoxy or mold release agent, and subsequently casting a polymer replica from this arrangement. By using techniques known in the art of macro-scale mold forming (e.g., vacuum forming, heat molding, resin casting, etc.), a rigid sheet having concave lens geometry may be formed and removed from the permanent mold. Once removed, the rigid sheet may be metalized with a reflective coating (e.g., by physical vapor deposition, solution deposition, electroplating, etc.) and is then ready for installation as a concave reflective synthetic image presentation system. By placing a printed graphic arrangement (as described above) in contact with the reflector arrangement, synthetic images may be formed, resulting in a large format display system. 
         [0074]    The dimensions of these arrangements may be modified as necessary depending on the required viewing distance. For example, a viewing distance of approximately 90 meters is estimated to require an individual reflector diameter of from about 8 mm to about 1 cm. 
         [0075]    Similar to the previously described system embodiments, synthetic image presentation system  56  may be cast against carrier substrate  48 , with the materials used and the system dimensions the same as those identified for the third exemplary embodiment. 
         [0076]    In a fifth exemplary embodiment, which is best shown in  FIG. 5 , the inventive system is a transferable concave reflective optical system  58  that further includes, among other layers, a release liner  60 , which is made up of carrier substrate  62  and release coating  64 . While  FIG. 5  relates to a transferable concave reflective optical system, the above described convex reflective optical system is also transferable. 
         [0077]      FIG. 5  shows the system  58  during application to a paper substrate  66 , with synthetic image presentation system  68  releasably coupled to release liner  60 . Typically, release coating  64  is a functional release coating, applied at a thickness of between 1 and 10 microns that allows bonding at ambient conditions and then release at the time of transfer using mechanical, chemical, thermal and photo-induced separation techniques. For example, when a heat and pressure activated release is desired, the carrier substrate  62  (e.g., a UV transmissive PET film layer with a thickness between 15 and 50 microns) would contain a coating that has good adhesion at ambient temperature, but softens and releases with the application of heat and pressure at the time of lamination in, for example, a desktop document laminator, or on an industrial foiling machine, which apply heat and pressure in a continuous web process. Examples of suitable functional release coatings include, but are not limited to, low surface energy materials such as polyethylene, polypropylene, silicone, or hydrocarbon waxes. Also suitable are pressure sensitive adhesives whose bond strengths weaken considerably at elevated temperatures, formulated with tackifying resins and monomers with the appropriate glass transition temperature (Tg), to provide release at the desired temperature. 
         [0078]    A reflective layer (e.g., a vapor deposited metal layer)  70 , optional protective coating  72 , and adhesive layer  74 , are shown on the arrangement of focusing elements  76 . The reflective layer is a conformally coated reflective layer prepared using aluminum, chrome, copper, gold, nickel, silver, stainless steel, tin, titanium, zinc sulfide, magnesium fluoride, titanium dioxide, or other material providing the desired level of reflectivity. This layer may be applied at thicknesses ranging from about 50 nanometers to about 2 microns using physical vapor deposition (PVD), chemical vapor deposition (CVD), or other suitable process. Optional protective coating  72 , which serves to protect the reflective layer, may be prepared from energy curable acrylates (e.g., energy curable acrylates containing organic or inorganic fillers with pigmenting or reinforcing properties), solvent or water based coatings such as acrylics, epoxies, EVAs, polyurethanes, PVAs, and the like, and is applied at thicknesses ranging from about 1 to about 10 microns, while the adhesive layer may be prepared from thermally activated adhesives (i.e., hot melt or heat seal adhesives), pressure sensitive adhesives, or any thermoset or thermoplastic adhesive system selected to provide bonding between these target surfaces including acrylics, cyanoacrylates, epoxies, polyimides, polyurethanes, polyvinyl acetates, rubber, and silicones, is preferably prepared from a tack free thermally activated adhesive (e.g., water-based polyurethane), and is applied at thicknesses ranging from about 1 to about 10 microns. 
         [0079]    An exemplary method of manufacturing the transferable reflective optical system of the present invention comprises:
       applying a curable resin material to a surface of a release liner (e.g., a smooth or non-structured carrier substrate having a functional release coating) and curing the surface against a rigid icon mold to form one or more arrangements of image icons in the form of voids within a surface of the curable resin material;   filling the voids with a material providing a contrast with the curable resin material to form a filled image icon layer;   applying a curable resin material to a surface of the filled image icon layer and curing the resin against a rigid surface having negative lens geometries (i.e., a negative lens mold) forming one or more arrangements of focusing elements on a surface of the curable resin material;   applying a conformal coating of metal or other reflective material to the focusing elements to form one or more arrangements of reflective focusing elements; optionally, applying one or more protective coating layers to the one or more arrangements of reflective focusing elements; and   applying one or more adhesive layers (e.g., tack free thermally activated adhesive layers) to the one or more optionally protective coated arrangements of reflective focusing elements.       
 
         [0085]    The resulting film-like structure can be handled/converted/transferred like a traditional transfer film. In other words, the structure may be brought into contact with a target substrate (e.g., currency paper, ID document, or product packaging), and upon the application of heat and pressure, the release liner can be completely peeled away, leaving only the synthetic image presentation system on the final substrate. 
         [0086]    An example of a continuous transfer process for transferring the inventive system to a target substrate employs a hot stamping machine available from Leonard Kurz Stiftung &amp; Co. KG (model number MHA 840). In this process, the system in the form of up to six film-like structures are placed in register (in cross direction (CD)) on a base paper, counter wheel pairs on the hot stamping machine apply pressure (550 Newtons (N)/wheel) to the film-like structures, which causes activation of the tack free thermally activated adhesive layers. The release liners are then separated from the underlying structures and rewound on common cylinders. Typical machine settings are: speed (100-120 meters/minute), temperature (135-160° C.). 
         [0087]    Generally speaking, in order for the reflective system to reliably transfer to a final substrate (e.g., paper), the adhesive bond strength between the substrate and the reflective system must be greater than the bond which holds the reflective system to the release liner. Typical bond strengths for such an arrangement may be in the range of 10 to 100 Newtons per square inch (N/in 2 ) for the bond between the reflective system and substrate, and in the range of 0.1 to 10 N/in 2  for the bond between the reflective system and release liner. 
       Diffractive System Embodiments 
       [0088]    In a sixth exemplary embodiment, the inventive system is an optionally transferable diffractive optical system. Diffractive focusing elements also provide for convergence of incident light and systems made using these focusing elements are thinner than the above described refractive and reflective systems with comparable f-numbers, with total diffractive optical system thicknesses ranging from about 3 to about 50 microns (preferably, from about 5 to about 10 microns). 
         [0089]    The inventive diffractive optical system employs diffractive focusing elements made using the same materials identified for the focusing elements used in the above described refractive and reflective systems. These diffractive focusing elements have preferred widths/base diameters of less than about 100 microns (more preferably, less than about 75 microns, and most preferably, from about 15 to about 50 microns). 
         [0090]    These diffractive focusing elements are selected from the group of diffractive Fresnel lenses, Fresnel zone plate lenses, and hybrid refractive/diffractive lenses, and combinations thereof. In an exemplary embodiment, diffractive Fresnel lenses are used, each such lens having a series of concentric annular rings with a common focus. The concentric rings lie in a common plane making each lens extremely flat compared to refractive lenses with similar f-numbers. The successive rings may have continuous curvature for maximum efficiency or the curvature may be approximated by any number of steps or phase levels. The simplest diffractive Fresnel lens approximation has only two steps and is known as a Fresnel Zone Plate or Binary Fresnel Lens. More complex approximations, in increased order of complexity, are quaternary, eight levels, sixteen levels, and analog. In a preferred embodiment, the diffractive Fresnel lens is an analog profile lens. 
         [0091]    The structured image icons used in the inventive diffractive optical system are similar to those used in the above described refractive and reflective systems. 
         [0092]    Diffractive focusing elements are known to be sensitive to wavelength changes and suffer from high chromatic aberration. In the inventive system, however, the diffractive focusing elements may be either transmissive (see diffractive optical system  78  in  FIG. 6 ) or reflective (see diffractive optical system  80  in  FIG. 7 ). In either system, the structured image icons intersect with the depth of focus of an associated diffractive focusing element (e.g., Fresnel lens), which is accomplished without the use of an optical spacer. 
         [0093]    The optionally transferable transmissive diffractive optical system  78  is produced using the same method and material construction as the first exemplary embodiment, except that the geometry of the refractive lens mold is replaced with a geometry suitable for producing a diffractive lens. This optical system can also be transferred from its carrier substrate using the technique detailed in the second exemplary embodiment. 
         [0094]    The optionally transferable reflective mode diffractive optical system  80  is produced using the same method and material construction as the third exemplary embodiment, except that the geometry of the reflective lens mold is replaced with a geometry suitable for producing a reflective style of diffractive lens, which is subsequently metalized. This optical system can likewise be transferred from its carrier substrate using the technique for reflective transfer detailed in the fifth exemplary embodiment. 
         [0095]    The present invention further provides fibrous and non-fibrous sheet materials that are made from or employ the inventive system, as well as documents made from these materials. The term “documents”, as used herein designates documents of any kind having financial value, such as banknotes or currency, bonds, checks, traveler&#39;s checks, lottery tickets, postage stamps, stock certificates, title deeds and the like, or identity documents, such as passports, ID cards, driving licenses and the like, or non-secure documents, such as labels. The inventive optical system is also contemplated for use with goods (consumer or non-consumer goods) as well as bags, packaging, or labels used with these goods. 
         [0096]    Other contemplated end-use applications for the inventive system include products for projecting larger dimension images such as advertising and multimedia displays (e.g., billboards, traffic and industrial safety signs, commercial displays for marketing or tradeshow purposes), products for enhancing a vehicle&#39;s appearance (e.g., decal, wrap), decorative wrap and wallpaper, shower curtains, artistic displays, and the like. 
         [0097]    Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.