Use of nanoparticles to tailor the refractive index of a polymer matrix layer and optimize micro-optical (MO) focusing

Abstract

The security device (100, 600, 700) comprises one or more graphical icon arrays (100a, 110b, 615, 715), one or more refractive graphical icon concentrator arrays (120, 605, 705), and an encapsulation layer (127, 600, 1005) comprising an organic resin and nanoparticles. Furthermore, the one or more refractive graphical icon concentrator arrays are disposed over the one or more graphical icon arrays such that portions of the one or more refractive graphical icon concentrator arrays form a composite image of portions of the one or more graphical icon arrays. Furthermore, the one or more refractive graphical icon concentrator arrays contact the encapsulation layer along a non-planar boundary.

Description

[Technical Field]

[0001] The present disclosure relates generally to improving the performance of security devices, such as micro-optical strips applied to or otherwise incorporated into security documents to provide anti-counterfeiting indicia. More specifically, the present disclosure relates to, but is not limited to, the use of nanoparticles to tailor the refractive index of a polymeric matrix (sometimes referred to as "goo") used to form one or more layers of a micro-optical security device to optimize micro-optical ("MO") focus. [Background technology]

[0002] The challenges of designing and manufacturing a particular micro-optical security device often involve negotiating trade-offs between achieving desired characteristics of the end product against the opportunities and constraints imposed by, for example, available manufacturing technologies and the laws of physics. For example, manufacturers of security documents (e.g., banknotes, checks, and other documents presenting the need for reliable indicia of authenticity) desire micro-optical security devices that are one or more of thin, durable, counterfeit-resistant, and visually appealing. At the same time, the properties of the materials used, in combination with the laws of physics used to construct the micro-optical security device, can impose constraints on the performance characteristics of the end product. As one non-limiting example, a lens made from a material with a low refractive index can be thicker than a lens of equivalent focal length made from a material with a high refractive index. As a further non-limiting example, the interaction between light waves and the constituent materials of the lens can cause chromatic aberration, causing the focal length of the lens to vary across different wavelengths of light.

[0003] In view of the above, tailoring the physical properties of materials (e.g., thickness and refractive index of components) for fabricating micro-optical security devices offers untapped opportunities to push the envelope in terms of achieving a larger set of desirable end-product properties (e.g., overall thickness, resistance to dirt) within the constraints imposed by the operation of the laws of physics for the selected materials. Summary of the Invention

[0004] The present disclosure illustrates, but is not limited to, system and method embodiments that use nanoparticles to adjust the refractive index of a polymer matrix to optimize micro-optical ("MO") focus, as well as micro-optical system embodiments that use low-RI materials in one or more constituent layers of the system.

[0005] In a first embodiment, a security device includes one or more image icon arrays, one or more refractive image icon concentrator arrays, and an encapsulation layer. Furthermore, the one or more refractive image icon concentrator arrays are disposed on the one or more image icon arrays such that a portion of the one or more refractive image icon concentrator arrays projects a composite image of a portion of the one or more image icon arrays. Furthermore, the one or more refractive image icon concentrator arrays contact the encapsulation layer along a non-planar boundary. Additionally, at least one of the one or more refractive image icon concentrator arrays and the encapsulation layer includes a mixture of an organic resin having a first refractive index and nanoparticles.

[0006] In a second embodiment, the security device includes one or more image icon arrays. and, One or more refractive image icon concentrator arrays and wherein the one or more refractive image icon concentrator arrays comprise a mixture of organic resin and nanoparticles. The one or more refractive image icon concentrator arrays are disposed above the one or more image icon arrays such that the portions of the one or more refractive image icon concentrator arrays project a composite image of the portions of the one or more image icon arrays. The mixture of organic resin and nanoparticles has a refractive index greater than 1.5.

[0007] In a third embodiment, a security document includes a substrate and a security device. The security device includes one or more image icon arrays, one or more refractive image icon concentrator arrays, and an encapsulation layer. Furthermore, the one or more refractive image icon concentrator arrays are disposed above the one or more image icon arrays such that a portion of the one or more refractive image icon concentrator arrays projects a composite image of a portion of the one or more image icon arrays. Furthermore, the one or more refractive image icon concentrator arrays contact the encapsulation layer along a non-planar boundary. Additionally, at least one of the one or more refractive image icon concentrator arrays and the encapsulation layer includes an organic resin having a first refractive index and a nanoparticle mixture.

[0008] In a fourth embodiment, a security document includes a substrate and a security device. The security device includes one or more image icon arrays. and, One or more refractive image icon concentrator arrays and wherein the one or more refractive image icon concentrator arrays comprise a mixture of organic resin and nanoparticles. The one or more refractive image icon concentrator arrays are disposed above the one or more image icon arrays such that the portions of the one or more refractive image icon concentrator arrays project a composite image of the portions of the one or more image icon arrays. The mixture of organic resin and nanoparticles has a refractive index greater than 1.5.

[0009] In a fifth embodiment, a security device includes one or more image icon arrays, one or more refractive image icon concentrator arrays, and a spacer layer disposed between the one or more image icon arrays and the one or more refractive image icon concentrator arrays. The spacer layer includes a mixture of organic resin and nanoparticles. Additionally, the one or more refractive image icon concentrator arrays are disposed above the one or more image icon arrays such that a portion of the one or more refractive image icon concentrator arrays projects a composite image of a portion of the one or more image icon arrays. Furthermore, the mixture of organic resin and nanoparticles has a refractive index greater than 1.5.

[0010] In a sixth embodiment, a security document includes a substrate, one or more image icon arrays, one or more refractive image icon concentrator arrays, and a spacer layer disposed between the one or more image icon arrays and the one or more refractive image icon concentrator arrays. The spacer layer includes a mixture of organic resin and nanoparticles. Additionally, the one or more refractive image icon concentrator arrays are disposed above the one or more image icon arrays such that a portion of the one or more refractive image icon concentrator arrays projects a composite image of a portion of the one or more image icon arrays. Furthermore, the mixture of organic resin and nanoparticles has a refractive index greater than 1.5.

[0011] In a seventh embodiment, a security device includes an image icon focusing element array, each image icon focusing element of the image icon focusing element array associated with a focal path, an image icon layer including one or more image icons associated with a first characteristic color and one or more image icons associated with a second characteristic color, and one or more regions between the image icons including a volume of substantially colorless material. Additionally, at a first viewing angle, a color is visible through each image icon focusing element, and the color visible through each image icon focusing element at the first viewing angle is based on one or more of the first characteristic color, the second characteristic color, or the substantially colorless material.

[0012] Other technical features may be readily apparent to those skilled in the art from the following drawings, descriptions, and claims.

[0013] Before proceeding with the detailed description below, it may be advantageous to provide 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," and their derivatives, mean inclusion without limitation. The term "or" is inclusive, meaning and / or. The phrase "associated with," and derivatives thereof, have meanings including "to include," "be included within," "interconnect with," "contain," "be contained within," "connect to or with," "couple to or with," "be communicable with," "cooperate with," "interleave," "juxtapose," "be proximate to," "be bound to or with," "have," "have a property of," "have a relationship to or with," and 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 that only one item in the list may be required. For example, "at least one of A, B, and C" includes any combination of A, B, C, A and B, A and C, B and C, and A, B, and C.

[0014] Definitions of other specific words and phrases are provided throughout this patent document, and those skilled in the art should understand that in many, if not most, cases, such definitions apply to prior and future uses of the words and phrases so defined.

[0015] For a more complete understanding of the present disclosure and its advantages, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: [Brief explanation of the drawings]

[0016] [Figure 1A] 1A-1C illustrate examples of a micro-optical security device and elements of a security document including a micro-optical security device, according to certain embodiments of the present disclosure. [Figure 1B] 1A-1C illustrate examples of a micro-optical security device and elements of a security document including a micro-optical security device, according to certain embodiments of the present disclosure. [Figure 1C] 1A-1C illustrate examples of a micro-optical security device and elements of a security document including a micro-optical security device, according to certain embodiments of the present disclosure. [Figure 2] 1A-D illustrate aspects of adjusting the optical properties of refractive image icon collection elements according to various embodiments of the present disclosure. [Figure 3] FIG. 10 illustrates aspects of chromatic aberration associated with the passage of different wavelengths of light through a refractive image icon collecting element. [Figure 4] 1A-1C illustrate examples of multiple image icon arrays positioned under refractive index-tuned image icon concentrating elements, according to some embodiments of the present disclosure. [Figure 5] 10A-10C illustrate aspects of visual effects in a composite image produced by a miniature optical security device, in accordance with certain embodiments of the present disclosure. [Figure 6] 1A-E illustrate examples of configurations of miniature optical security devices having nanoparticle-modified encapsulation layers according to various embodiments of the present disclosure. [Figure 7] 1A-E illustrate example configurations of miniature optical security devices having nanoparticle-modulated refractive image icon focusing elements, according to certain embodiments of the present disclosure. [Figure 8] 10A-10C illustrate examples of composite images including a combination of a characteristic color of a first image icon array associated with a first characteristic color and a characteristic color of a second image icon array associated with a second characteristic color, according to various embodiments of the present disclosure. [Figure 9A] FIG. 10 illustrates a manner in which a composite image is generated that includes a combination of a characteristic color of a first image icon array associated with a first characteristic color and a characteristic color of a second image icon array associated with a second characteristic color. [Figure 9B] FIG. 10 illustrates a manner in which a composite image is generated that includes a combination of a characteristic color of a first image icon array associated with a first characteristic color and a characteristic color of a second image icon array associated with a second characteristic color. [Figure 9C] FIG. 10 illustrates a manner in which a composite image is generated that includes a combination of a characteristic color of a first image icon array associated with a first characteristic color and a characteristic color of a second image icon array associated with a second characteristic color. [Figure 10A] 1A-1C illustrate examples of miniature optical security devices according to various embodiments of the present disclosure. [Figure 10B] 1A-1C illustrate examples of miniature optical security devices according to various embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0017] 1A-10B discussed below, and the various embodiments used to illustrate the principles of the present disclosure in this patent document, are merely for illustrative purposes and should not be construed in any way as limiting the scope of the present disclosure.

[0018] Figures 1A, 1B, and 1C illustrate examples of elements of a micro-optical security device and a security document including a micro-optical security device, according to certain embodiments of the present disclosure. For convenience, structural elements common to the examples of Figures 1A, 1B, and 1C are numbered similarly (e.g., substrate 105).

[0019] Referring to the non-limiting example of FIG. 1A, the micro-optical security device 100 and security document 101 can be constructed as a layered combination of some or all of the elements shown in the example example of FIG. 1A.

[0020] 1A, security document 101 includes a substrate 105 to which micro-optical security device 100 is attached. As used in this disclosure, the term "security document" encompasses documents that utilize a micro-optical security device to provide a visual indicia of authenticity (e.g., a composite image created by the spatial alignment of one or more image icon arrays with one or more refractive image icon focusing elements) to prevent document counterfeiting. Examples of security documents include, but are not limited to, banknotes, passports, tickets, collectible trading cards, and ID cards (e.g., driver's licenses).

[0021] According to certain embodiments, substrate 105 is a sheet of thin, flexible fibrous material, such as currency paper. According to some embodiments, substrate 105 is a thin, flexible sheet of polymeric film of biaxially oriented polypropylene (BOPP). In various embodiments, substrate 105 is a piece of synthetic paper material, such as TESLIN®. According to some embodiments, substrate 105 is a piece of polymeric card material, such as a polyethylene terephthalate (PET) blank of the type suitable for making credit cards and driver's licenses.

[0022] Referring to the non-limiting example of FIG. 1A, miniature optical security device 100 includes one or more image icon arrays (110a and 110b). According to various embodiments, one or more image icon arrays include colored regions of colored pigmented material (e.g., colored region 112) arranged in a predetermined pattern (e.g., as an icon design synthetically magnified by one or more refractive image icon concentrator arrays). According to various embodiments, colored region 112 includes a shaped volume of pigmented image material (e.g., a colored pigmented UV-curable polymer). In certain embodiments, colored region 112 has a width of about 1 μm or greater.

[0023] According to certain embodiments, each of the one or more graphical icon arrays 110 a and 110 b is formed as a separate layer. In some embodiments, the graphical icon array is formed by creating a layer structure of icons (e.g., embossing and curing a polymer matrix) to create holding structures, such as recesses or voids, for holding one or more pigmented polymeric materials, and then applying one or more pigmented polymeric materials to create colored regions (e.g., colored regions 112) that collectively define the array of graphical icons.

[0024] In various embodiments, for a given image icon array, the pigmented polymeric material used to create the colored region (e.g., colored region 112) is configured so that most or all of the colored region is filled with the characteristic colored polymeric material. As used in this disclosure, the term "characteristic color" encompasses a color associated with a specified wavelength of light or a range of wavelengths of light for which the focal length of the refractive image icon focusing element matches the depth of the image icon array within the micro-optical security device 100.

[0025] 1A, in certain embodiments according to the present disclosure, miniature optical security device 100 comprises two stacked image icon arrays (110a and 110b). Embodiments according to the present disclosure are not limited to two image icon arrays, and embodiments having fewer or more image icon arrays are within the intended scope of the present disclosure.

[0026] According to various embodiments, the refractive index of a polymer matrix used to create a retention structure (e.g., retention structure 114) for one or more pigment-containing materials in one image icon array (e.g., image icon array 110b) can be adjusted through the addition of nanoparticles to the matrix to improve the focusing of light on another image icon array (e.g., image icon array 110a).

[0027] In certain embodiments according to the present disclosure, the micro-optical security device 100 is attached to the substrate 105 by an adhesive bond between the bottom surface of the pictorial icon array (e.g., pictorial icon array 110a). In some embodiments, the micro-optical security device is attached to the substrate 105 as part of the manufacturing process of the substrate 105 (e.g., as a windowed security thread in a sheet of currency paper).

[0028] 1A, in certain embodiments, the micro-optical security device 100 includes an optical spacer 115. According to some embodiments, the optical spacer 115 includes a thin film of transparent material (e.g., polyester) onto which a polymeric matrix is applied, shaped (e.g., by embossing), and cured to create a retention structure (e.g., retention structure 114) for the refractive image icon focusing elements and / or pigment-containing material. In some embodiments, the optical spacer 115 is formed as a layer of polymeric matrix and is integrated with one or more of the refractive image icon focusing element arrays. According to various embodiments, the optical spacer 115 formed from the polymeric matrix ContainsThe optical properties of the micro-optical security device 100 (e.g., the quality of focusing the image icon or the arrangement of internal reflections within the security device) may be adjusted by varying the thickness of the optical spacer 115 and / or adjusting the concentration of nanoparticles within the polymer matrix used to form the optical spacer 115; According to certain embodiments, the optical spacer 115 is formed from a polymeric matrix suitable for use in forming the encapsulation layer 125 or the refractive focusing element 121. In various embodiments, the composition of the matrix used to form the optical spacer 115 is specifically formulated to be free of materials having polarizing elements such as iodine, bromine, chlorine, or sulfur.

[0029] Additionally, while in the non-limiting example of Figure 1A, miniature optical security device 100 is shown as including optical spacer 115, embodiments according to the present disclosure are not so limited. In certain embodiments, optical spacer 115 may be omitted. Furthermore, while in the non-limiting example of Figure 1A, optical spacer 115 is shown as being physically distinct from the refractive image icon light collection element array, embodiments according to the present disclosure are not so limited, and embodiments in which one or more of the refractive image icon light collection element arrays are formed by creating a structural variation in the refractive index of the material used to create optical spacer 115 are within the intended scope of the present disclosure.

[0030] 1A, in certain embodiments, miniature optical security device 100 comprises one or more refractive image icon concentrator arrays 120 disposed above one or more image icon arrays (e.g., image icon arrays 110a and 110b) such that a portion of the one or more refractive image icon concentrator arrays projects a composite image of a portion of the one or more image icon arrays. As discussed elsewhere in this disclosure, in certain embodiments, two or more composite images are generated, each composite image being associated with a characteristic color.

[0031] As shown in the non-limiting example of FIG. 1A, refractive image icon light collecting element array 120 includes a plurality of individual refractive light collecting elements (e.g., refractive light collecting elements 121) arranged in a predetermined pattern relative to at least one image icon array (e.g., image icon array 110a). In certain embodiments, the colored regions of the image icon array are substantially co-located in a plane defining the x- and y-axes of a coordinate system. In some embodiments, the centers of the refractive light collecting elements are at common x- and y-values as the image icons, but at different coordinates on the z-axis. In some embodiments, the composite image may appear to be in the plane of miniature-optical security device 100. In some embodiments, the center-to-center distance (i.e., pitch) of the refractive light collecting elements may be slightly different from the repeat distance of the image icons, and the composite image(s) may appear to be above or below the plane of miniature-optical security device 100. In various embodiments, the center of the refractive focusing element may be rotated slightly (eg, by less than 1 degree) relative to the image icon, creating orthoparallactic motion effects.

[0032] In certain embodiments, the refractive focusing element 121 comprises a volume of a hardened polymer matrix having at least one outer surface that defines a non-planar boundary between a region of a medium having a first refractive index and a region of a medium having a second refractive index. In the non-limiting example of FIG. 1A, the refractive focusing element 121 is shown as having a planar lower surface and a radially symmetric curved uppermost surface, although embodiments according to the present disclosure are not so limited. According to some embodiments, the refractive focusing element may be a lenticule of a lenticular array, or may be curved at its upper and lower surfaces, for example.

[0033] In some embodiments according to the present disclosure, the refractive focusing element 121 is formed from a polymer matrix that, when cured, has a refractive index of less than 1.5. Examples of materials for use in such a polymer matrix that have a refractive index of 1.5 or less include, but are not limited to, isodecyl acrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyester tetraacrylate, trimethylpropane triacrylate, and hexanediol diacrylate. Further examples of materials suitable for forming refractive concentrating elements 121 include substantially clear or transparent, colored or colorless polymers such as acrylic, acrylated polyester, acrylated urethane, epoxy, polycarbonate, polypropylene, polyester, and urethane. Further examples of materials that can be used to form a matrix to form refractive concentrating elements 121 include, but are not limited to, acrylate monomers, acrylate oligomers, O-phenylphenoxyethyl acrylate, phenylthioethyl acrylate, bis-phenylthioethyl acrylate, Kumil Examples of suitable acrylates include phenoxyl ethyl acrylate, biphenyl methyl acrylate, bisphenol A epoxy acrylate, fluorene-type acrylates, brominated acrylates, halogenated acrylates, melamine acrylates, and combinations thereof. According to certain embodiments, the composition of the matrix used to form the refractive concentrating element 121 is specifically formulated to be free of materials having polarizing elements such as iodine, bromine, chlorine, or sulfur. As used in this disclosure, the term "polarizing element" encompasses elements with polarizing properties greater than carbon.

[0034] In various embodiments according to the present disclosure, the refractive index of the material comprising the refractive concentrating element 121 can be adjusted or tuned by adding or adjusting the concentration of nanoparticles in the material mixture (e.g., polymer matrix) used to form the refractive concentrating element 121. According to some embodiments, the refractive index of the material comprising the refractive concentrating element can be adjusted by adding inorganic nanoparticles having a particle size of 100 nm or less to the mixture. Examples of inorganic nanoparticles that can be added to the material mixture include, but are not limited to, aluminum oxide, zirconium dioxide, titanium dioxide, zinc sulfide, or zinc telluride nanoparticles. According to certain embodiments, adding nanoparticles to the material mixture can increase the refractive index of the material mixture used to form the refractive concentrating element 121 from less than 1.5 to 1.7 or greater. In some embodiments, a refractive index greater than 1.7 is possible by adding nanoparticles to an organic resin.

[0035] 1A, in various embodiments according to the present disclosure, the miniature optical security device 100 further comprises a sealing layer 125. According to various embodiments, the sealing layer 125 includes a smooth or substantially planar top surface 127 and a non-planar bottom surface 129 that provides a substantially continuous, non-planar boundary between the sealing layer 125 and the refractive image icon focusing element array 120. According to some embodiments, the sealing layer 125 has a non-planar top surface that has fewer "pockets" than the boundary between the sealing layer 125 and the refractive image icon focusing element array 120.

[0036] In certain embodiments, sealing layer 125 protects one or more refractive image icon concentrating element arrays 120 and contributes to the robustness and durability of micro-optical security device 100 by eliminating the space between refractive concentrating elements (e.g., refractive concentrating elements 121) from accumulating dirt, grease, and other contaminants associated with the use and distribution of security documents. Additionally, in certain embodiments, sealing layer 125 allows for the use of additional layers of material, such as a top adhesive, without significantly affecting the focal length of the system.

[0037] According to various embodiments, the encapsulation layer 125 contacts the refractive concentrating elements of the refractive image icon concentrating element array (e.g., refractive image icon concentrating element array 120) along a non-planar boundary defined at least in part by the bottom surface 129 of the encapsulation layer 125. In certain embodiments, the encapsulation layer 125 is formed from a material having a refractive index that differs from the refractive index of the material used to create the refractive concentrating elements 121.

[0038] In various embodiments, the sealing layer 125 is formed from a polymeric matrix that, when cured, In some cases, the polymer matrix has a refractive index of less than 1.5. Examples of materials for use in such polymer matrices having a refractive index of 1.5 or less include, but are not limited to, isodecyl acrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyester tetraacrylate, trimethylolpropane triacrylate, and hexanediol diacrylate. Further examples of materials suitable for forming the sealing layer 125 include substantially clear or transparent, colored or colorless polymers such as acrylic, acrylated polyester, acrylated urethane, epoxy, polycarbonate, polypropylene, polyester, and urethane. Further examples of materials that can be used to form the matrix for forming the sealing layer 125 include, but are not limited to, acrylate monomers, acrylate oligomers, O-phenylphenoxyethyl acrylate, phenylthioethyl acrylate, bis-phenylthioethyl acrylate, Kumil Examples of suitable acrylates include phenoxyl ethyl acrylate, biphenyl methyl acrylate, bisphenol A epoxy acrylate, fluorene-type acrylate, brominated acrylate, halogenated acrylate, melamine acrylate, and combinations thereof. According to certain embodiments, the composition of the matrix used to form the sealing layer 125 is specifically formulated to be free of materials having polarizing elements such as iodine, bromine, chlorine, or sulfur.

[0039] According to certain embodiments, the encapsulation layer 125 may be formed from a material that provides a large difference in refractive index (e.g., a difference greater than 0.1) between the encapsulation layer 125 and the one or more refractive image icon concentrator arrays 120. According to certain embodiments, suitable low-RI materials for use in the encapsulation layer 125 include materials having an RI between 1.3 and 1.4, or materials having an RI less than 1.3. Examples of suitable low-RI materials include, but are not limited to, blends of fluorinated acrylates and fluorinated urethane acrylates, which have been measured to have refractive indices ranging from 1.3 to 1.135. Further examples of suitable low-RI materials include, but are not limited to, certain perfluoropolyether compounds, such as perfluoropolyether caprolactone diacrylate.

[0040] In various embodiments according to the present disclosure, the refractive index of the material comprising the encapsulation layer 125 can be adjusted or tuned by adding or adjusting the concentration of nanoparticles in the material mixture (e.g., polymer matrix) used to form the encapsulation layer 125. According to some embodiments, the refractive index of the material comprising the refractive light-collecting elements can be adjusted, for example, by adding inorganic nanoparticles having a particle size of 100 nm or less to the mixture. Examples of inorganic nanoparticles that can be added to the material mixture include, but are not limited to, aluminum oxide, zirconium dioxide, titanium dioxide, zinc sulfide, or zinc telluride nanoparticles. According to certain embodiments, adding nanoparticles to the material mixture can increase the refractive index of the material mixture used to form the encapsulation layer 125 from less than 1.5 to 1.7 or greater. In some embodiments, a refractive index greater than 1.7 is possible by adding nanoparticles to an organic resin. Depending on the relative values of the refractive indices between the encapsulation layer 125 and the one or more refractive image icon light-collecting element arrays 120, the shape of the interface between these two layers can be either convex or concave. 1A, if the material forming one or more refractive light-collecting element arrays 120 has a higher refractive index than the material forming encapsulation layer 125, the refractive light-collecting elements will have a convex shape. Similarly, if encapsulation layer 125 is formed from a material having a higher refractive index than one or more refractive image icon light-collecting element arrays 120, the refractive light-collecting elements will have a concave shape.

[0041] In the non-limiting example of FIG. 1A, the micro-optical security device 100 is shown incorporating a sealing layer 125, however, embodiments according to the present disclosure are not so limited and embodiments without a sealing layer 125 are also within the intended scope of the present disclosure.

[0042] 1B illustrates a further non-limiting example of a micro-optical security device 100 according to various embodiments of the present disclosure. Referring to the non-limiting example of FIG. 1B, according to some embodiments, the micro-optical security device 100 comprises an unencapsulated system (e.g., encapsulation layer 125 is omitted) in which nanoparticles 117 are incorporated into a matrix used to create the optical spacer 115. According to some embodiments, certain optical properties (e.g., the F-number (F#) and effective focal length of the refractive focusing element 121) can be tuned by adjusting the concentration of nanoparticles 117 in the matrix used to create the optical spacer 115.

[0043] 1C illustrates a further example of a micro-optical security device 100 according to various embodiments of the present disclosure. As shown in the non-limiting example of FIG. 1C, according to certain embodiments, the refractive index of the material comprising the encapsulation layer 125 may be greater than the refractive index of the material comprising the one or more refractive image icon concentrator arrays 120. According to certain embodiments, depending on the relative proportions of the refractive index of the encapsulation layer 125, the one or more refractive image icon concentrator arrays have a concave or plano-concave lens profile, as shown in FIG. 1C.

[0044] 2A-2D illustrate aspects of adjusting the optical properties of refractive image icon collecting elements according to various embodiments of the present disclosure.

[0045] As discussed elsewhere in this disclosure, the design and manufacture of micro-optical security devices often involves negotiating a trade-off between achieving a desired end product and constraints imposed by the materials of manufacture and the operation of the laws of physics on the selected materials. As one example, limited manufacturing tolerances for creating the refractive light-collecting elements and the graphical icon layer can impose limits on the accuracy with which the refractive light-collecting elements can properly focus on the graphical icon. As a further example, manufacturing tolerances can impose limits on the amount of visual information (e.g., detail within a single composite image or multiple different composite images) that can be placed in the focal area beneath the refractive light-collecting elements. In systems where the refractive index of the materials used to construct the refractive light-collecting elements is fixed, the laws of physics dictate that increasing the size of the design space beneath the refractive light-collecting elements (e.g., the graphical icon and the area of the graphical icon layer that can provide graphical information) requires increasing the thickness of the light-collecting elements. For many end products (e.g., banknotes), increasing the thickness of the light-collecting layer is undesirable because thicker banknotes may be more susceptible to damage or jamming in processing machinery (e.g., the bill acceptor on a vending machine).

[0046] As discussed with reference to the non-limiting examples of Figures 2A-2D, certain embodiments of the present disclosure enable designers and manufacturers of micro-optical security devices to treat the refractive index of one or more components of a micro-optical security device as a tunable parameter, thereby reducing the extent to which designers and manufacturers of micro-optical security devices are required to accept trade-offs between one desired performance characteristic (e.g., device thickness) in order to achieve another desired performance characteristic (e.g., increased visual information under a refractive focusing element).

[0047] 2A, a refractive light-collecting element 200 is shown having a height h1 and a width w1. According to certain embodiments, the refractive light-collecting element 200 is formed from a material including at least an organic resin. In some embodiments, the organic resin has a refractive index of less than 1.5. In various embodiments, the refractive index of the refractive light-collecting element can be increased by adding nanoparticles to the polymer matrix used to create the refractive light-collecting element 200.

[0048] According to some embodiments, increasing the refractive index of the refractive focusing element 200 can facilitate achieving one or more desired end-product properties without trading off other desired end-product properties. For example, adding nanoparticles to increase the refractive index of the refractive focusing element can create a thinner focusing element with the same focal length. For example, the refractive focusing element 205 can have the same width (w1) and focal length as the refractive focusing element 200, but with a reduced thickness (h2

[0049] In certain embodiments, increasing the refractive index of the refractive focusing element 200 can cause an increase in the available area beneath the refractive focusing element, thereby allowing more visual information to be provided beneath the refractive focusing element (e.g., by creating a pictorial icon array) without requiring an increase in the thickness of the focusing element or an increase in manufacturing tolerances for encoding the visual information. For example, a refractive focusing element 210 in which nanoparticles are added to the polymer matrix used to form the refractive focusing element has a higher refractive index. In this non-limiting example, the refractive focusing element 210 has the same thickness and focal length but a larger diameter (w2>w1) than the refractive focusing element 200, thereby allowing more visual information to be encoded beneath the refractive focusing element 210 than the refractive focusing element 200.

[0050] ​In many micro-optical security devices, imperfect focus (i.e., when the focal length of the refractive focusing element does not match the depth of the image icon at the target wavelength(s)) corresponds to poor contrast in the composite image provided by the micro-optical security device. According to certain embodiments, the focal length (f) of refractive focusing element 215, which has the same width and diameter as refractive focusing element 200, can be adjusted over a range of lengths (Δf) by changing the concentration of nanoparticles in the material mixture used to create refractive focusing element 215. For example, increasing the concentration of nanoparticles in the material mixture corresponds to an increase in the refractive index of refractive focusing element 215, thereby decreasing the focal length of refractive focusing element 215. Similarly, decreasing the concentration of nanoparticles in the material mixture corresponds to a decrease in the refractive index of refractive focusing element 215, thereby increasing the focal length of refractive focusing element 215.

[0051] 2A-2D illustrate optical tuning of a refractive light-collecting element by adjusting the concentration of nanoparticles in a material mixture, embodiments according to the present disclosure are not so limited. The properties of components of a micro-optical security device, such as a sealing layer (e.g., sealing layer 125 of FIG. 1A), an optical spacer (e.g., optical spacer 115 of FIG. 1A), or a retaining structure for an array of graphical icons (e.g., retaining structure 114 of FIG. 1A), can also be tuned by varying the concentration of nanoparticles in the material mixture to alter the refractive index of the component.

[0052] Although the exemplary examples of Figures 2A-2D have been described with reference to convex or plano-convex lenses, embodiments according to the present disclosure are not so limited, and optical tuning using nanoparticles is also possible with multiple lenses of other shapes (e.g., multiple convex lenses or multiple plano-convex lenses).

[0053] FIG. 3 illustrates aspects of chromatic aberration associated with different wavelengths of light passing through a refractive image icon concentrator.

[0054] Referring to the exemplary embodiment of Figure 3, a refractive light-collecting element 300 suitable for use in a micro-optical security device (e.g., micro-optical security device 100 of Figure 1A) is shown. In this exemplary embodiment, refractive light-collecting element 300 has a refractive index of approximately 1.5. Furthermore, in the embodiment of Figure 3, the refractive index of refractive light-collecting element 300 can be adjusted to higher values through the addition of nanoparticles to the material mixture used to form refractive light-collecting element 300.

[0055] In this example, dispersion effects within refractive focusing element 300 cause light of different wavelengths to focus at different focal lengths, resulting in chromatic aberration, or spherochromatic aberration. For example, a first light ray 305 of a color associated with wavelength λ passes through refractive focusing element 300 and is focused to a point at focal length f. Similarly, a second light ray 310 of a color associated with a longer wavelength λ (e.g., λ > λ) passes through refractive focusing element 300 and is focused to a point at focal length f, which is longer than focal length f.

[0056] In the context of micro-optical security devices, the aforementioned chromatic aberrations have the effect of reducing the contrast between colors in the composite image produced by the micro-optical system, which may be deemed undesirable by end-product users. Furthermore, as the refractive index of the refractive focusing element 300 is increased (e.g., by adding nanoparticles to the material mixture), the degree of chromatic aberration (e.g., the ratio of f2 to f1) may become more pronounced, depending on the change in dispersion within the matrix. In telescopes and cameras, chromatic aberrations can be managed by increasing the overall focal length of the focusing element to bring the focal lengths of different wavelengths closer together, but this approach is typically unacceptable in the context of micro-optical security devices and security documents, where thicker products are often not possible. Additionally, in certain embodiments, chromatic aberrations can be managed through the introduction of a second lens or a doublet formed from two materials with different dispersion characteristics.

[0057] 4 shows an example of an array of multiple image icons positioned beneath a refractive image icon focusing element, according to some embodiments of the present disclosure. According to certain embodiments of the present disclosure, nanoparticles can be used to adjust the refractive index of the refractive focusing element and / or other components of the micro-optical security device to reduce the chromatic aberration effect described with reference to FIG. 3 of the present disclosure, as well as to utilize the chromatic aberration effect to create composite images with surprising visual effects.

[0058] 4, refractive light-collecting element 400 is shown focusing first light rays 405 of a first wavelength λ1 onto first image icon array 415. According to certain embodiments, first image icon array 415 includes one or more features of color (e.g., colored region 112 of FIG. 1) associated with wavelengths equal to wavelengths within a particular wavelength range around first wavelength λ1. According to certain embodiments, in addition to refractive light-collecting element 400, the first light rays pass through other optical components of the micro-optical security device (e.g., spacer layer or encapsulation layer), which, in combination with refractive light-collecting element 400, provide a first effective focal length f1 for light of wavelength λ1. * According to a particular embodiment, f1 is set so that the first light ray 405 is focused on the first image icon array 415. * The value of can be adjusted by adjusting the concentration of nanoparticles in the refractive light-collecting element 400 and other components of the micro-optical security device.

[0059] 4, refractive light-collecting element 400 is shown to focus second light rays 410 at a second wavelength λ2 onto a second image icon array 420. According to certain embodiments, second image icon array 420 includes one or more features of colors associated with wavelengths equal to wavelengths within a specified wavelength range around second wavelength λ2. According to certain embodiments, in addition to refractive light-collecting element 400, the first light rays pass through other optical components of the micro-optical security device (e.g., a spacer layer or a sealing layer), which, in combination with refractive light-collecting element 400, provide a second effective focal length f2 for light of wavelength λ2.* It has.

[0060] According to some embodiments, the second image icon array 420 is located below the first image icon array 415, so that the second light beam 410 passes through an additional structure 419 (e.g., a spacer layer or a retaining structure) of the micro-optical security device. * The value of can be adjusted to ensure that the second light beam 410 is focused onto the second image icon array 420, for example, by adjusting the concentration of nanoparticles in the refractive focusing element 400 as well as the additional structure 419.

[0061] FIG. 5 illustrates aspects of the visual effects in a composite image created by a miniature optical security device according to certain embodiments of the present disclosure.

[0062] Referring to the non-limiting example of FIG. 5, a refractive focusing element 500 has an effective focal length f1 for light of wavelength λ1. * 1 through the components of the micro-optical security device to focus a first light ray 505 of a color associated with wavelength λ1 (e.g., blue) through the components of the micro-optical security device so as to focus the first light ray 510 of a color associated with wavelength λ2 (e.g., red) through the components of the micro-optical security device (including additional components 519) so that the second light ray 510 has an effective focal length f2 for light of wavelength λ2. * , and focus on the second image icon array 520.

[0063] Referring to the non-limiting example of FIG. 5, the effective focal length f1 for light of wavelength λ1 is * is the effective focal length f2 for light of wavelength λ2 * According to various embodiments, the above-mentioned f1 * and f2 *The difference in effective focal length between the first image icon array 515 and the second image icon array 520 represents a wavelength-based difference in F-number. In other words, the features of the first image icon array 515 in a first characteristic color associated with wavelength λ1 form a component of the first characteristic color of the composite image projected by the micro-optics system. Similarly, the features of the second image icon array 520 in a second characteristic color associated with wavelength λ2 form a component of the second characteristic color of the composite image projected by the micro-optics system.

[0064] Effective focal length f1 for light of wavelength λ1 * and the effective focal length f2 for light of wavelength λ2 * Due to this difference in layer height, image icons whose characteristic color is associated with light of wavelength λ1 are formed in the first image icon array 515 on a different layer than the second image icon array 520 containing image icons whose characteristic color is associated with light of wavelength λ2. All other factors being equal (e.g., both image icon arrays provide similar optical effects), the layer height difference between the first image icon array 515 and the second image icon array 520 described above causes the component of the composite image created by micro-optical security of the first characteristic color to exhibit a smaller change in position (Δ1) in response to a shift in viewing position than the change in position (Δ2) of the component of the second characteristic color. That is, in the non-limiting example of FIG. 5 , the red component of the composite image appears to move farther and faster in response to a change in viewing position than the blue component of the composite image (i.e., Δ2 > Δ1). Stated another way, the composite image from the first image icon array 515 appears to be on a shorter "lever arm" 550 compared to a longer "lever arm" 560 for the long-wavelength component of the composite image from the second image icon array 520. Thus, as an observer adjusts the viewing angle of the micro-optical security device, the longer wavelength components (e.g., red portions) of the composite image on the second image icon array 520 appear to move faster than the shorter wavelength components (e.g., blue portions) of the composite image on the first image icon array 515. According to certain embodiments, the relative "speed" of the different color components of the composite image can be an indication of the authenticity of the security feature.

[0065] While the non-limiting examples in Figures 3-5 illustrate aspects of the optical effects produced by micro-optical systems according to certain embodiments incorporating lenses described as convex or plano-convex lenses, embodiments according to the present disclosure are not so limited, and the examples in Figures 3-5 are applicable across embodiments using multiple lens shapes, including, but not limited to, concave or plano-concave lenses.

[0066] Figures 6A-6E show five example configurations a.)-e.) of micro-optical security devices having nanoparticle-tuned sealing layers according to various embodiments of the present disclosure. While particular embodiments are described with reference to the five embodiments shown in the illustrative examples of Figures 6A-6E, the present disclosure is not limited thereto, and additional configurations of micro-optical security devices having nanoparticle-tuned sealing layers are possible and within the contemplated scope of the present disclosure.

[0067] 6A-6E, a particular micro-optical security device according to the present disclosure includes a nanoparticle-modulated encapsulation layer 600. In some embodiments, the nanoparticle-modulated encapsulation layer 600 constitutes the topmost layer of the micro-optical security device (relative to the intended viewing location) and has a substantially planar top surface to resist the accumulation of dirt, grease, and other factors that could degrade the micro-optical security device's ability to generate a composite image. According to various embodiments, the nanoparticle-modulated encapsulation layer 600 is constructed from a material mixture including an organic resin (e.g., an acrylate monomer or acrylate oligomer) and one or more nanoparticles, the concentration of which in the material mixture modulates the refractive index of the nanoparticle-modulated encapsulation layer 600. In some embodiments, the concentration of the nanoparticles is selected to achieve a predetermined difference in refractive index between the nanoparticle-modulated encapsulation layer 600 and one or more refractive image icon concentrator arrays 605 along the non-planar boundary between the nanoparticle-modulated encapsulation layer 600 and one or more refractive image icon concentrator arrays 605. 6A-6E, the nanoparticle-modulated encapsulation layer 600 is constructed of a material having a higher refractive index than the refractive image icon focusing element 605, resulting in the refractive image icon focusing element 605 having a concave lens shape. Other embodiments according to the present disclosure in which the RI difference between the encapsulation layer 600 and the refractive image icon focusing element 605 necessitates a convex lens shape are possible and within the intended scope of the present disclosure.

[0068] As shown in the illustrative examples of FIGS. 6A-6E , a micro-optical security device according to certain embodiments of the present disclosure can include one or more refractive image icon focusing element arrays 605. According to certain embodiments, the one or more refractive image icon focusing element arrays include a set of structures defining one or more non-planar boundaries between regions of different refractive index to focus light of at least one wavelength onto image icons in the one or more image icon arrays 615. In some embodiments, the refractive focusing elements in the one or more refractive image icon focusing element arrays 605 are radially symmetric. In certain embodiments, the refractive focusing elements are axially or translationally symmetric (e.g., lenticules in a lenticular array). In some embodiments, the one or more refractive image icon focusing element arrays comprise two or more refractive image icon focusing element arrays (e.g., 605a and 605b). In certain embodiments, the use of multiple refractive image icon focusing element arrays may be desirable due to internal reflections, chromatic aberrations, or other unwanted visual effects. According to various embodiments, the refractive concentrating elements in one or more refractive image icon concentrating element arrays 605 have a diameter of 30 μm or greater. In various embodiments, the refractive image icon concentrating elements 605 have a diameter of 7.5 to 25 μm.

[0069] In various embodiments according to the present disclosure, the micro-optical security device having a nanoparticle-modulated encapsulation layer includes an optical spacer 610. According to some embodiments, the optical spacer 610 can be a sheet of material to which material for forming other elements of the micro-optical security device is applied and formed. In some embodiments, the optical spacer 610 is integrated with another component of the micro-optical security device (e.g., the refractive image icon condenser array). In certain embodiments, depending on, for example, the difference in refractive index along the non-planar boundary between the encapsulation layer and the refractive image icon condenser array, the optical spacer 610 serves to position one or more image icon arrays at the focal length of the refractive image icon condenser array.

[0070] As shown in the non-limiting examples of Figures 6A-6E, a miniature-optical security device according to certain embodiments of the present disclosure includes one or more image icon arrays 615 disposed (relative to an intended viewpoint) below one or more refractive image icon concentrator arrays 605 such that a portion of the one or more refractive image icon concentrator arrays 605 projects a composite image of a portion of the one or more image icon arrays 615. According to certain embodiments, the miniature-optical security device has two or more image icon arrays (615a and 615b). In certain embodiments, each of the image icon arrays includes a feature having a characteristic color, each of the image icon arrays is disposed at a depth or position within the miniature-optical security device relative to the one or more refractive image icon concentrator arrays 605, and the one or more refractive image icon concentrator arrays are associated with a wavelength-dependent effective focal length of the one or more refractive image icon concentrator arrays 605.

[0071] In various embodiments according to the present disclosure, the micro-optical security device with nanoparticle-modified sealing layer further comprises a machine-readable security device (Mr-SD) 620. In certain embodiments, Mr-SD 620 comprises a layer of magnetic ink, or another medium, that provides a characteristic emission or response spectrum to a highly secured validation standard when passed through a proprietary device, such as a banknote equipment manufacturer (BEM) machine.

[0072] According to various embodiments, a micro-optical security device having a nanoparticle-modulated encapsulation layer 600 has a device thickness of 50 microns or less. As used in this disclosure, the term "device thickness" encompasses the distance from the surface where light enters the optical device to the surface (opposite the adhesive layer) that provides the interface between the micro-optical security device and the substrate to which the micro-optical security device is attached.

[0073] 7A-7E show five configurations of a micro-optical security device that does not include a nanoparticle-modulated sealing layer, according to various embodiments of the present disclosure. Example While certain embodiments are described with reference to the five embodiments shown in the illustrative examples of Figures 7A-7E, the present disclosure is not limited thereto and additional configurations of micro-optical security devices are possible and within the contemplated scope of the present disclosure.

[0074] As shown in the illustrative examples of Figures 7A-7E, a micro-optical security device according to certain embodiments of the present disclosure may include one or more refractive image icon focusing element arrays 705. According to certain embodiments, the one or more refractive image icon focusing element arrays include a set of structures defining one or more non-planar boundaries between regions of different refractive index to focus light of at least one wavelength onto image icons in the one or more image icon arrays 715. In some embodiments, the refractive focusing elements in the one or more refractive image icon focusing element arrays 705 are radially symmetric. In certain embodiments, the refractive focusing elements are axially symmetric (e.g., lenticules in a lenticular array). In some embodiments, the one or more refractive image icon focusing element arrays comprise two or more refractive image icon focusing element arrays (e.g., 705a and 705b). In certain embodiments, the use of multiple refractive image icon focusing element arrays may be desirable due to internal reflections, chromatic aberrations, or other unwanted visual effects. According to various embodiments, the refractive concentrating elements in one or more refractive image icon concentrating element arrays 705 have diameters of 30 μm or greater. According to various embodiments, the refractive concentrating elements are formed from a material mixture including an organic resin and nanoparticles, which in combination have a refractive index greater than 1.5. According to some embodiments, the organic resin in the material mixture itself has a refractive index less than 1.5. In certain embodiments, the organic resin in the material mixture has a refractive index of 1.4 or less.

[0075] In various embodiments according to the present disclosure, a micro-optical security device that omits a nanoparticle-modulated sealing layer includes an optical spacer 710. According to some embodiments, the optical spacer 710 can be a sheet of material (e.g., polyester film) onto which material is applied to form other elements of the micro-optical security device. In some embodiments, the optical spacer 710 is integrated with another component of the micro-optical security device (e.g., a refractive image icon concentrator array). In certain embodiments, the optical spacer 710 serves to position one or more image icon arrays at the focal length of the refractive image icon concentrator array, for example, depending on the difference in refractive index along a non-planar boundary between the refractive image icon concentrator array and another medium (e.g., air).

[0076] As shown in the non-limiting examples of Figures 7A-7E, a miniature-optical security device according to certain embodiments of the present disclosure includes one or more image icon arrays 715 disposed (relative to an intended viewpoint) below one or more refractive image icon concentrator arrays 705 such that a portion of the one or more refractive image icon concentrator arrays 705 projects a composite image of a portion of the one or more image icon arrays 715. According to certain embodiments, the miniature-optical security device has two or more image icon arrays (715a and 715b). In certain embodiments, each of the image icon arrays includes a feature having a characteristic color, each of the image icon arrays is disposed at a depth or position within the miniature-optical security device relative to the one or more refractive image icon concentrator arrays 705, and the one or more refractive image icon concentrator arrays are associated with a wavelength-dependent effective focal length of the one or more refractive image icon concentrator arrays 705.

[0077] In various embodiments according to the present disclosure, the micro-optical security device, which does not include a nanoparticle-modified sealing layer, further comprises a machine-readable security device (Mr-SD) 720. In certain embodiments, Mr-SD 720 comprises a layer of magnetic ink, or another medium, which, when passed through a proprietary device, such as a banknote equipment manufacturer (BEM) machine, provides a characteristic emission or response spectrum to a highly secured validation standard.

[0078] According to various embodiments, micro-optical security devices that do not include a nanoparticle-modified sealing layer can have a device thickness of 20-30 microns. In some embodiments, micro-optical security devices that do not include a nanoparticle-modified sealing layer have a thickness of 20 microns or less. According to certain embodiments, micro-optical security devices that do not include a nanoparticle-modified sealing layer can have a device thickness of less than 15 microns.

[0079] FIG. 8 illustrates an example of a composite image 800 including permutations of a characteristic color of a first image icon array associated with a first characteristic color and a characteristic color of a second image icon array associated with a second characteristic color, according to various embodiments of the present disclosure.

[0080] Referring to the non-limiting example of FIG. 8, a composite image provided by a micro-optical security device (e.g., micro-optical security device 100 of FIG. 1) is depicted as it appears at a first viewing angle. According to certain embodiments, the micro-optical security device projecting composite image 800 includes a nanoparticle-tuned refractive image icon concentrator array (e.g., refractive image icon concentrator array 120 of FIG. 1A), with the refractive index of the concentrator elements tuned to focus light of a first wavelength onto a first layer including an image icon array associated with a first characteristic color (e.g., image icon array 110b of FIG. 1). In this illustrative example, the first characteristic color is blue, although embodiments having a different first characteristic color are possible and within the scope of the present disclosure. Similarly, the refractive index of the concentrator elements of the micro-optical security device providing the composite image shown in FIG. 8 is also tuned to focus light of a second wavelength onto a second layer including a second image icon array associated with a second characteristic color (e.g., image icon array 110a of FIG. 1). In this illustrative example, the second characteristic color is magenta, although embodiments having a different second characteristic color are possible and within the scope of this disclosure. Additionally, according to some embodiments, the image icon layer of the miniature optical security device that projects composite image 800 includes substantially colorless areas between the image icons (e.g., areas of transparent material that define the structure that holds the image icons).

[0081] As shown in FIG. 8 , a composite image 800 presented at a first viewing angle includes shades, or permutations, of the first characteristic color, the second characteristic color, and colorless regions. For example, composite image 800 includes region 801, which is the same shade of blue as the first characteristic color. Similarly, composite image 800 includes region 803, which is a lighter shade of blue than the first characteristic color. Furthermore, composite image 800 includes region 805, which is the same shade of magenta as the second characteristic color. Furthermore, composite image 800 includes region 807, which is a lighter shade of magenta than the second characteristic color. Furthermore, composite image 800 includes region 809, which is substantially colorless, as well as certain interstitial regions within the image icon layer. Additionally, composite image 800 includes region 811, which is a shade of purple associated with a blend of the first and second characteristic colors. 8, composite image 800 includes region 813, which is a shade of purple associated with the second characteristic color and a lighter shade of the first characteristic color (e.g., a lighter shade of blue in region 803). Similarly, composite image 800 includes region 815, which is a shade of purple associated with the lighter shade of the first characteristic color (e.g., a lighter shade of blue in region 803) and a lighter shade of the second characteristic color (e.g., a lighter shade of magenta in region 807). Finally, in certain embodiments, composite image 800 includes region 817, which is a shade of purple associated with the first characteristic color and a lighter shade of the second characteristic color (e.g., a lighter shade of magenta in region 807).

[0082] Thus, certain embodiments according to the present disclosure provide the unexpected result of employing a two-color icon structure to enable a single focusing element to provide at least nine colors for a composite image provided by a micro-optical system including the icon structure and the focusing element. More generally, in certain embodiments according to the present disclosure, a composite image provided by a security device over a first range of viewing angles can include at least nine colors by adjusting the positions of image icons associated with a first characteristic color and image icons associated with a second characteristic color within two image icon layers.

[0083] Additionally, in certain embodiments, additional colors beyond the at least nine colors provided by a single light-collecting element projecting light from a two or more layer graphic icon structure may be achieved by aggregating the output of multiple light-collecting elements whose color output has been modulated in accordance with various embodiments of the present disclosure. Micro-optical cell Micro-optical security devices including (e.g., micro-optical security devices 100 ), each micro-optical cell can output at least nine colors by adjusting the position and presence of the image icons within the two layers of the image icon structure. When used herein, the term "micro-optic cell" encompasses a three-dimensional portion of a micro-optic security device corresponding to a single light-gathering element, such as that shown in Figure 4 of the present disclosure. By configuring a first portion (e.g., one-third) of the micro-optic cell to output one color (e.g., a lighter shade of magenta in region 807 of Figure 8) of at least nine colors achievable with the two layers of the icon structure, and configuring a second portion of the micro-optic cell to output another color (e.g., magenta shown in region 805 of Figure 8) of at least nine colors, Micro-optical cellThe region will appear as a region of color that is a mixture of the colors output by the first and second portions of the micro-optical cells within that region. Thus, according to certain embodiments, the micro-optical cells can be made to appear as a region of color that is a mixture of the colors output by the first and second portions of the micro-optical cells within that region by interspersing cells that output different colors among the at least nine colors output by each micro-optical cell. This allows for extremely fine control over the colors provided by the color system.

[0084] 9A, 9B, and 9C illustrate ways of generating a composite image that includes a combination of a characteristic color of a first image icon array associated with a first characteristic color and a characteristic color of a second image icon array associated with a second characteristic color.

[0085] Referring to the non-limiting examples of Figures 9A, 9B, and 9C, in certain embodiments, the combination of a set of characteristic colors of an image icon may be achieved by adjusting the position of the image icon relative to the focal position of the image icon and colorless areas within the image icon layer.

[0086] 9A, a first subsection 900 of a micro-optical security device (e.g., micro-optical security device 100 of FIG. 1) is shown. According to certain embodiments, the micro-optical security device includes an encapsulation layer 901 (e.g., encapsulation layer 125 of FIG. 1), a plurality of focusing elements including focusing elements 903, 905, and 907, and an optical spacer 913 (e.g., optical spacer 115 of FIG. 1). In some embodiments according to the present disclosure, one or more of encapsulation layer 901, focusing elements 903, 905, and 907, or optical spacer 913 are constructed from a polymer matrix that includes nanoparticles to adjust the refractive index of that layer. Furthermore, in some embodiments according to the present disclosure, depending on the lens shape (e.g., convex or concave) selected for the concentrating elements 903, 905, and 907, the encapsulating layer 901 or one or more of the concentrating elements 903, 905, and 907 are constructed from a low-RI material, e.g., a material having an RI less than 1.4, a material having an RI between 1.30 and 1.35, or a material having an RI less than 1.3. In certain embodiments, one or more of the encapsulating layer 901, the concentrating elements 903, 905, and 907, or the optical spacer 913 are constructed from a polymer matrix that does not contain nanoparticles to adjust the refractive index of that layer.

[0087] 9A, the miniature optical security device further comprises a first array of graphical icons associated with a first characteristic color (in this illustrative example, blue, although other colors are possible and within the intended scope of the present disclosure) disposed within the first layer 909. Additionally, in some embodiments according to the present disclosure, the miniature optical security device comprises a second array of graphical icons associated with a second characteristic color (in this illustrative example, magenta, although other colors are possible and within the intended scope of the present disclosure). According to certain embodiments, the space between the graphical icons in the first layer 909 and the second layer 911 comprises a substantially colorless material (e.g., a polymer that does not contain color pigments).

[0088] According to certain embodiments, at a first viewing angle, each of the light-collecting elements 903, 905, and 907 focuses light entering the micro-optical security device onto regions within the first layer 909 and the second layer 911 along paths that converge at focal points 915, 917, and 919, respectively. Similarly, light exits the micro-optical security device from focal points 915, 917, and 919 along the same paths as shown. As discussed elsewhere in this disclosure, subtle adjustments to the position of the color-pigmented image icons relative to the paths taken by light arriving at the micro-optical security device in directions associated with the first viewing angle for each of the focal points 915, 917, and 919 (referred to herein as "focal paths") can permute the placement of colors provided in the composite image provided by the micro-optical system beyond the two characteristic colors used for the image icons in the first layer 909 and the second layer 911.

[0089] As a first example, when an image icon 921a associated with a first characteristic color and an image icon 921b associated with a second characteristic color are both on the same focal path of the light collection element, the component of the composite image provided by the light collection element 903 has a color that is a mixture of the first characteristic color and the second characteristic color. In this non-limiting example, mixing the first characteristic color (blue) with the second characteristic color (magenta) produces a deep purple color 923.

[0090] As a second example, when image icon 925a associated with a first characteristic color is offset from the focal path of the concentrating element and image icon 925b associated with a second characteristic color is on the focal path, the component of the composite image provided by concentrating element 905 has a color that is a mixture of the first characteristic color, a colorless area, and the second characteristic color. In this non-limiting example, offsetting image icon 925a relative to the focal path produces color 927 that is a pinkish shade of purple. Note that in this non-limiting example, the contribution of the first characteristic color to color 927 is primarily diluted by the offset of image icon 925a from the focal path, while the contribution of the second characteristic color is substantially unaffected.

[0091] As a third example, when image icon 929a associated with a first characteristic color is positioned on the focal path of the concentrating element and image icon 929b associated with a second characteristic color is offset from the focal path of the concentrating element, the component of the composite image provided by concentrating element 907 has color 931 that is a mixture of the first characteristic color, the second characteristic color, and the substantially colorless areas between the image icons in second layer 911. In this particular example, color 931 includes a bluish tint of purple. Note that in this illustrative example, the contribution of the first characteristic color is substantially unaffected, while the contribution of the second characteristic color to color 931 is diluted by the offset of image icon 929b from the focal path.

[0092] FIG. 9B provides a further illustrative example of achieving combination of a limited set of characteristic colors in a composite image, according to various embodiments of the present disclosure.

[0093] Referring to the non-limiting example of Figure 9B, a second subsection 991 of a micro-optical device is shown in Figure 9B. For ease of reference, the second subsection 991 utilizes the same structure as the first subsection 900 shown in Figure 9A. As shown in this illustrative example, the second subsection 991 includes an encapsulation layer 901, focusing elements 903, 905, and 907, and an optical spacer 913, which are equivalent structures to their corresponding embodiments described with reference to Figure 9A. Similarly, the second subsection 991 includes a first layer 909 and a second layer 911, which are equivalent structures to their corresponding embodiments in Figure 9A.

[0094] According to certain embodiments, by offsetting the image icon 933 associated with the first characteristic color from the focal path of the light collection element and not providing the image icon in the second layer 911, the component of the composite image provided by the light collection element 903 has a color 935 that is a combination of the first characteristic color and the substantially colorless material in the first layer 909. In this particular example, the color 935 is a lighter shade of the first characteristic color, which in this example comprises a light shade of blue.

[0095] In some embodiments according to the present disclosure, by omitting image icons near the focal path of light collection element 905 and offsetting image icon 937 from the focal path, the component of the composite image provided by light collection element 905 has color 939 that is a combination of the second characteristic color and the substantially colorless material in second layer 911. In this non-limiting example, color 939 is a lighter shade of the second characteristic color, which in this illustrative example comprises a light shade of pink.

[0096] In various embodiments according to the present disclosure, by offsetting both image icon 941 and image icon 941b associated with the first characteristic color from the path of light collection element 907, the component of the composite image provided by light collection element 907 has color 943 that is a combination of the first characteristic color, the second characteristic color, and the substantially colorless material in first layer 909 and second layer 911. In this non-limiting example, color 943 comprises the color lavender.

[0097] Referring to the non-limiting example of FIG. 9C , a third subsection 993 of a micro-optical device is shown in FIG. 9C . For ease of reference, the third subsection 993 utilizes the same structure as the first subsection 900 shown in FIG. 9A . As shown in this illustrative example, the third subsection 993 includes an encapsulation layer 901, focusing elements 903, 905, and 907, and an optical spacer 913, which are equivalent structures to the corresponding embodiments described with reference to FIG. 9A . Similarly, the third subsection 993 includes a first layer 909 and a second layer 911, which are equivalent to their corresponding embodiments in FIG. 9A .

[0098] Referring to the non-limiting example of FIG. 9C , according to certain embodiments, by positioning an image icon 945 associated with a first characteristic color on the focal path of the focusing element 903 and not positioning an image icon associated with a second characteristic color on or in close proximity to the focal path of the focusing element 903, the color 947 of the component of the composite image partially projected by the focusing element 903 is the first characteristic color.

[0099] According to various embodiments, by positioning an image icon 949 associated with a second characteristic color on the focal path of the focusing element 905 and not positioning an image icon associated with the first characteristic color on or in close proximity to the focal path of the focusing element 905, the color 951 of the focusing element 905's contribution to the composite image is the second characteristic color.

[0100] Similarly, in various embodiments according to the present disclosure, by not positioning a colored image icon on or in close proximity to the focal path of the focusing element 907, the contribution of the focusing element 907 to the composite image is substantially colorless, as is the area between the image icons on the first layer 909 and the second layer 911.

[0101] While the examples of Figures 8 and 9A-9C have described modulation between combinations of characteristic colors with reference to a micro-optical system using refractive light-collecting elements, embodiments according to the present disclosure are not so limited, and the color modulation effects described above may also be produced in systems using reflective light-collecting elements (e.g., the micro-optical security device 100 of Figure 1C). Additionally, while certain embodiments according to the present disclosure describe achieving micro-optical cell-level modulation of the colors the cells contribute to the composite image with reference to a system having a two-layered image icon structure and image icons associated with two characteristic colors, the present disclosure is not so limited. Embodiments including image icon structures with more than two layers and embodiments having image icons associated with three or more characteristic colors are within the intended scope of the present disclosure.

[0102] According to certain embodiments, further granularity in the micro-level colors output by a finite set of characteristic colors for an icon element can be achieved by adjusting the size of the image icon associated with each characteristic color. Note that, as used in this disclosure, the term "micro-level" encompasses colors observed through a single focusing element in the absence of a colored substrate. According to some embodiments, the size of the image icon associated with a particular characteristic color can be adjusted by one or more of changing the line width of the line icon, deleting a partial image icon, or doubling the image icon within the footprint of the image icon focusing element.

[0103] In some embodiments according to the present disclosure, further granularity of macro-level color may be observed in response to subtle variations in viewing angle, such that between micro-optical cells having similar image icon structures, a region may be observed that borders whether the image icon is within the focal path of the image icon focusing element, resulting in a region exhibiting an intermediate color between the colors associated with a combination of a first characteristic color and a second characteristic color. Note that, as used in this disclosure, the term "macro-level" encompasses the colors observed when viewing multiple micro-optical cells at once. Region 819 in FIG. 8 provides a non-limiting example of macro-level granularity in the colors observed when viewing multiple micro-optical cells of a micro-optical security device simultaneously. As shown in FIG. 8, in region 819, a visible color gradation (rather than a sharp boundary) including multiple shades of the characteristic color may be observed between two hues.

[0104] 10A and 10B show examples of miniature optical security devices according to certain embodiments of the present disclosure.

[0105] Referring to the non-limiting example of FIG. 10A, micro-optics Security Illustrated is an example of a device 1000. According to certain embodiments, micro-optics Security The device 1000 includes an encapsulation layer 1005 , an array of refractive concentrating elements 1010 , an optical spacer 1015 , and an image icon layer 1020 including a plurality of image icons 1025 .

[0106] According to certain embodiments, micro-optics Security The device 1000 may include a device capable of projecting a variety of composite images, including, but not limited to, micro-optical Security Images that appear above and / or below the plane of the device 1000 include color shift effects, optically variable effects, and synthetically magnified images of content in the icon layer 1020. 10A, the encapsulation layer 1005 is formed from a material having a higher refractive index than the material used to form the refractive concentrator array 1010. In some embodiments, the encapsulation layer 1005 is formed from a high refractive index material, such as an aromatic-functionalized acrylate with dispersed nano-zirconia nanoparticles. As one non-limiting example, in a particular embodiment, the encapsulation layer 1005 has a refractive index of approximately 1.6, and the encapsulation layer 1005 is formed as a UV-cured layer including a liquid blend of a zirconium dioxide acrylate monomer mixture, a blend of bisphenol fluorene diacrylate and o-phenylphenol ethyl acrylate, and a suitable photoinitiator.

[0107] According to various embodiments, the refractive concentrator array 1010 is formed from a material having a refractive index of 1.5 or less. Applying the lensmaker's equation, for a given lens radius, increasing the difference in refractive index between the material forming the encapsulation layer 1005 and the material comprising the refractive concentrator array 1010 can improve the micro-optical SecurityThe overall thickness of device 1000 can be reduced. In some embodiments, the difference in refractive index between the two materials described above is greater than 0.1. In particular embodiments, the difference in refractive index between the material used to form encapsulation layer 1005 and refractive concentrator array 1010 is between 0.1 and 0.15, and in some embodiments, the difference in refractive index is between 0.16 and 0.20. In various embodiments, the difference in refractive index is between 0.21 and 0.25, and in some embodiments, the difference in refractive index is 0.26 or greater.

[0108] As an illustrative example, in at least one embodiment, the refractive concentrator array 1010 is formed from a layer of a UV-curable fluorinated acrylic material blend having a refractive index of approximately 1.35, such as a mixture including one or more fluorourethane acrylates and a suitable photoinitiator. Security While not limiting compounds suitable for use as low-RI materials in device 1000, fluorinated acrylic materials offer certain manufacturing advantages, including, but not limited to, low tack, good adhesion to other acrylic materials, soil and chemical resistance, and a glass transition temperature high enough to avoid deformation or excessive stickiness of the layer during manufacturing. Further examples of materials suitable for refractive concentrator arrays include: Examples include, but are not limited to, silicone acrylates and silicone methacrylates.

[0109] As shown in the non-limiting example of FIG. 10A, micro-optics Security The device 1000 includes an optical spacer 1015 (e.g., optical spacer 115 of FIG. 1A). According to certain embodiments, the optical spacer 1015 is formed from a thin cross-section, substantially transparent film, such as 75 gauge polyethylene terephthalate (PET). According to various embodiments, the micro-optical SecurityDevice 1000 includes a graphical icon layer 1020 (e.g., graphical icon layer 615 of FIGS. 6A-6E ). In certain embodiments, graphical icon layer 615 includes a set of cast and cured retaining structures that are then filled with one or more characteristic colored UV-curable materials, which are cured to form a plurality of graphical icons (e.g., graphical icons 1025).

[0110] Skilled engineers are experts in micro-optics. Security It will be appreciated that the overall thickness of an embodiment of device 1000 may depend on a series of application-specific variables, including the visual effect to be produced by the system, the desired lens size, and the number of image icon layers. However, the refractive index difference between the encapsulating layer and the light-collecting elements allows for a device with a fully encapsulated spherical lens capable of projecting composite images with a variety of optical effects (including, but not limited to, color changes, multi-directional effects, or orthoparallax motion effects) with a single image icon layer to have an overall thickness of approximately 30 microns.

[0111] In the illustrative example of FIG. 10A, the micro-optical security device 1000 has been described with reference to a configuration in which the sealing layer 1005 comprises a material having a higher refractive index than the refractive focusing element array 1010, but embodiments according to the present disclosure are not limited thereto.

[0112] Figure 10B shows an embodiment of a micro-optical security device 1050 in which the relative positions of the high-RI and low-RI materials are reversed in the encapsulation layer 1005 and the refractive concentrator array 1010. For ease of cross-referencing, structural elements of the micro-optical security device 1050 that are common to the micro-optical security device 1000 of Figure 10A are similarly numbered.

[0113] In some embodiments, the refractive index difference between the encapsulation layer and the collection elements can be reversed, such that the encapsulation layer is formed from a low-RI material. In such embodiments, the shape of the collection elements similarly switches from concave to convex lenses, as shown in FIG. 10B . Additionally, in certain embodiments, the refractive collection element array 1010 comprises a transition region 1030 between the curved (i.e., concave or convex) lens surfaces of the collection elements and the optical spacer 1015. According to certain embodiments, the presence of the transition region 1030, which ensures a minimum thickness through the refractive collection element array 1010, reduces the likelihood of individual collection elements of the refractive collection element array 1010 "popping off" or otherwise separating from the overall system. By doing so, micro-optics Security Devices Improve the structural integrity of the 1050.

[0114] Similarly, in the exemplary embodiment of FIG. 10A, micro-optics Security Although device 1000 has been described with reference to an embodiment having a single layer icon structure, embodiments according to the present disclosure are not so limited. Security The device has a multi-layer icon structure (eg, as shown with reference to Figures 9A-9C herein).

[0115] An example of a security device according to certain embodiments of the present disclosure is a security device including one or more image icon arrays, one or more refractive image icon focusing element arrays, and a sealing layer, wherein the one or more refractive image icon focusing element arrays are disposed above the one or more image icon arrays such that a portion of the one or more refractive image icon focusing element arrays projects a composite image of a portion of the one or more image icon arrays, and the one or more refractive image icon focusing element arrays contact the sealing layer along a non-planar boundary.

[0116] An example security device according to certain embodiments of the present disclosure includes a security device in which at least one of the one or more refractive image icon focusing element arrays and the sealing layer comprises a mixture of an organic resin having a first refractive index and nanoparticles.

[0117] Examples of security devices according to some embodiments of the present disclosure include a security device in which at least one of the refractive image icon focusing element arrays and the sealing layer comprises a low refractive index material having a second refractive index, and the difference between the first refractive index and the second refractive index has a magnitude of 0.1 or greater.

[0118] Examples of security devices according to some embodiments of the present disclosure include security devices in which the low refractive index material has a refractive index between 1.3 and 1.4.

[0119] Examples of security devices according to some embodiments of the present disclosure include security devices in which the low refractive index material has a refractive index less than 1.3.

[0120] Examples of security devices according to some embodiments of the present disclosure include security devices in which the low refractive index material comprises a fluorinated acrylate or a fluorinated urethane acrylate.

[0121] Examples of security devices according to some embodiments of the present disclosure include security devices in which the low refractive index material comprises a perfluoropolyether compound.

[0122] Examples of security devices according to some embodiments of the present disclosure include security devices in which the mixture of nanoparticles includes one or more of aluminum oxide, zirconium dioxide, titanium dioxide, zinc sulfide, or zinc telluride nanoparticles.

[0123] Examples of security devices according to various embodiments of the present disclosure include security devices in which the organic resin comprises an acrylate monomer.

[0124] Examples of security devices according to various embodiments of the present disclosure include security devices in which the organic resin comprises an acrylate oligomer.

[0125] Examples of security devices according to certain embodiments of the present disclosure include those in which the organic resin is selected from the group consisting of phenoxybenzyl acrylate, O-phenylphenoxyethyl acrylate, phenylthioethyl acrylate, bis-phenylthioethyl acrylate, Kumil The security device includes one or more of phenoxyethyl acrylate, biphenyl methyl acrylate, bisphenol A epoxy acrylate, fluorene-type acrylate, brominated acrylate, halogenated acrylate, or melamine acrylate.

[0126] Examples of security devices according to certain embodiments of the present disclosure include security devices in which the organic resin comprises one or more of isodecyl acrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyester tetraacrylate, trimethylolpropane triacrylate, or hexanediol diacrylate.

[0127] Examples of security devices according to certain embodiments of the present disclosure include security devices in which the organic resin does not include a polarizing element.

[0128] Examples of security devices according to certain embodiments of the present disclosure include security devices that do not include a sealing layer.

[0129] Examples of security devices according to some embodiments of the present disclosure include security devices in which the encapsulating layer has a refractive index of 1.5 or greater.

[0130] Examples of security devices according to various embodiments of the present disclosure include security devices in which the encapsulating layer has a refractive index of 1.6 or greater.

[0131] Examples of security devices according to various embodiments of the present disclosure include a security device in which the refractive image icon focusing element array includes a transition region between the lens surface of the refractive image icon focusing element array and the spacer layer.

[0132] Examples of security devices according to various embodiments of the present disclosure include security devices in which the refractive image icon concentrating elements in one or more refractive image icon concentrating element arrays have diameters greater than 30 microns.

[0133] Examples of security devices according to various embodiments of the present disclosure include security devices in which the refractive image icon concentrating elements in the one or more refractive image icon concentrating element arrays have diameters of less than 30 microns.

[0134] An example security device according to certain embodiments of the present disclosure includes a security device comprising a spacer layer disposed between an array of refractive image icon concentrating elements and an array of image icons, the spacer layer including nanoparticles.

[0135] An example security device according to some embodiments of the present disclosure includes a security device comprising a spacer layer integrated with an array of refractive image icon concentrating elements.

[0136] Examples of security devices according to various embodiments of the present disclosure include security devices comprising two or more refractive image icon concentrator arrays that meet along one or more non-planar boundaries.

[0137] Examples of security devices according to some embodiments of the present disclosure include security devices, wherein the security device has a thickness of 50 microns or less.

[0138] Examples of security devices according to certain embodiments of the present disclosure include security devices, wherein the security device has a thickness of 20 microns or less.

[0139] Examples of security devices according to various embodiments of the present disclosure include security devices in which the security device has a thickness of 15 microns or less.

[0140] Examples of security devices according to some embodiments of the present disclosure include security devices comprising machine-readable security devices (Mr-SD).

[0141] An example of a security device according to certain embodiments of the present disclosure includes a security device having two or more image icon arrays, each of the image icon arrays including a feature having a characteristic color associated with the image icon array, each of the image icon arrays disposed at a relative depth to one or more refractive image icon focusing element arrays associated with wavelength-dependent focal lengths, the wavelength-dependent focal lengths associated with the characteristic color associated with the image icon array.

[0142] Examples of security devices according to various embodiments of the present disclosure include security devices in which a composite image includes shades of one or more characteristic colors that move at different speeds.

[0143] Examples of security devices according to some embodiments of the present disclosure include a security device comprising one or more image icon arrays and one or more refractive image icon focusing element arrays, wherein the one or more refractive image icon focusing element arrays comprise a mixture of organic resin and nanoparticles, the one or more refractive image icon focusing element arrays are disposed above the one or more image icon arrays, whereby a portion of the one or more refractive image icon focusing element arrays project a composite image of a portion of the one or more image icon arrays, and the organic resin and nanoparticle mixture has a refractive index greater than 1.5.

[0144] Examples of security devices according to certain embodiments of the present disclosure include security devices in which the organic resin has a refractive index of less than 1.5.

[0145] Examples of security devices according to various embodiments of the present disclosure include security devices in which the mixture of organic resin and nanoparticles has a refractive index greater than 1.6.

[0146] Examples of security devices according to some embodiments of the present disclosure include security devices in which the mixture of organic resin and nanoparticles has a refractive index greater than 1.7.

[0147] An example security document according to certain embodiments of the present disclosure includes a substrate attached to one or more security devices according to embodiments of the present disclosure.

[0148] Examples of security devices according to various embodiments of the present disclosure include a security device in which the composite image comprises an area of a third color, the third color comprising a permutation of at least one of the first characteristic color or the second characteristic color.

[0149] An example security device according to certain embodiments of the present disclosure includes a security device in which a composite image provided by the security device over a first range of viewing angles includes at least nine colors, the at least nine colors including permutations of a first characteristic color and a second characteristic color.

[0150] Examples of security devices according to various embodiments of the present disclosure include a security device in which each image icon focusing element of an array of image icon focusing elements includes an image icon focusing element associated with a focal path and an image icon layer including one or more image icons associated with a first characteristic color, one or more image icons associated with a second characteristic color, and one or more regions between the image icons including a volume of substantially colorless material, wherein for a given viewing angle, a color is visible through each image icon focusing element, and the color visible through each image icon focusing element at the first viewing angle is based on one or more of the first characteristic color, the second characteristic color, or the substantially colorless material.

[0151] Examples of security devices according to some embodiments of the present disclosure include a security device in which, in the absence of a colored substrate, when there is no image icon disposed on or offset from the focal path of the image icon focusing element, the color visible through the image icon focusing element at a first viewing angle is white, associated with a volume of substantially colorless material.

[0152] An example security device according to certain embodiments of the present disclosure includes a security device in which, in the absence of a colored substrate, when an image icon associated with a first characteristic color is offset from the focal path of the image icon focusing element, the color visible through the image icon focusing element at a first viewing angle has a component associated with a lighter shade of the first characteristic color, and in the absence of a colored substrate, when an image icon associated with a second characteristic color is offset from the focal path of the image icon focusing element, the color visible through the image icon focusing element at a first viewing angle has a component associated with a lighter shade of the second characteristic color.

[0153] An example security device according to certain embodiments of the present disclosure may include a security device in which, in the absence of a colored substrate, the colors visible through the image icon collecting element include a combination from a group of nine combinations of the first characteristic color and the second characteristic color, the group of nine combinations comprising: a first color (947) associated with an image icon associated with a first characteristic color disposed in the focal path of the image icon focusing element and an absence of an image icon associated with a second characteristic color disposed in or offset from the focal path of the image icon focusing element; a second color (951) associated with an image icon associated with the second characteristic color disposed in the focal path of the image icon focusing element and an absence of an image icon associated with the first characteristic color disposed in or offset from the focal path of the image icon focusing element; a third color including a white color associated with a substantially colorless material associated with an absence of any image icon disposed in or offset from the focal path of the image icon focusing element; a fourth color (935) associated with an image icon associated with the first characteristic color offset from the focal path of the image icon focusing element and an absence of an image icon associated with the second characteristic color disposed in or offset from the focal path of the image icon focusing element; a fifth color (939) associated with the absence of an image icon associated with a first characteristic color disposed in or offset from the focal path of the image icon focusing element; a sixth color (923) associated with an image icon associated with the first characteristic color disposed in the focal path of the image icon focusing element and an image icon associated with a second characteristic color disposed in the focal path of the image icon focusing element; a seventh color (931) associated with an image icon associated with the first characteristic color disposed in the focal path of the image icon focusing element and an image icon associated with the second characteristic color offset from the focal path of the image icon focusing element; an eighth color (927) associated with an image icon associated with the second characteristic color disposed in the focal path of the image icon focusing element and an image icon associated with the first characteristic color offset from the focal path of the image icon focusing element; and an image icon associated with the first characteristic color offset from the focal path of the image icon focusing element.and a ninth color (943) associated with the security device. An example of a security device according to a particular embodiment of the present disclosure includes a security device having a first image icon associated with a first characteristic color and a second image icon associated with a second characteristic color, wherein in the absence of a colored substrate, the ratio of the size of the first image icon to the size of the second image icon is such that the colors visible through the image icon focusing element include a tenth color that is not one of the nine combinations of the first and second characteristic colors.

[0154] Examples of security devices according to some embodiments of the present disclosure include security devices comprising one or more of refractive image icon focusing elements or reflective image icon focusing elements.

[0155] Examples of security devices according to various embodiments of the present disclosure include security devices in which the graphical icon collecting element comprises a mixture of organic resin and nanoparticles.

[0156] Examples of security documents according to various embodiments of the present disclosure include a security document comprising a substrate and a security device attached to the substrate. In some embodiments, the security device comprises one or more image icon arrays, one or more refractive image icon concentrator arrays, and an encapsulation layer comprising an organic resin and nanoparticles. In some embodiments, the one or more refractive image icon concentrator arrays are disposed above the one or more image icon arrays such that a portion of the one or more refractive image icon concentrator arrays forms a composite image of a portion of the one or more image icon arrays. In some embodiments, the one or more refractive image icon concentrator arrays contact the encapsulation layer along a non-planar boundary.

[0157] An example security document according to various embodiments of the present disclosure includes a security document comprising a substrate and a security device attached to the substrate. In some embodiments, the security device includes one or more image icon arrays and one or more refractive image icon concentrator arrays, where the one or more refractive image icon concentrator arrays include a mixture of organic resin and nanoparticles. In certain embodiments, the one or more refractive image icon concentrator arrays are disposed above the one or more image icon arrays such that a portion of the one or more refractive image icon concentrator arrays forms a composite image of a portion of the one or more image icon arrays. In some embodiments, the mixture of organic resin and nanoparticles has a refractive index greater than 1.5.

[0158] An example security document according to certain embodiments of the present disclosure includes a security document comprising a substrate and a security device attached to the substrate. In some embodiments, the security device comprises one or more image icon arrays, one or more refractive image icon concentrator arrays, and a spacer layer disposed between the one or more image icon arrays and the one or more refractive image icon arrays, the spacer layer comprising a mixture of organic resin and nanoparticles. In certain embodiments, the one or more refractive image icon concentrator arrays are disposed above the one or more image icon arrays such that a portion of the one or more refractive image icon concentrator arrays forms a composite image of a portion of the one or more image icon arrays. In some embodiments, the mixture of organic resin and nanoparticles has a refractive index greater than 1.5.

[0159] Nothing in this application should be construed as implying that any particular element, step, or function is an essential element required for inclusion in a claim. The scope of patented subject matter is defined solely by the claims. Moreover, none of the claims are intended to invoke 35 U.S.C. § 112(f) unless the precise words "means for" are followed by a participle.

Claims

1. A security device (100, 600, 700), one or more image icon arrays (110a, 110b, 615, 715); one or more refractive image icon concentrator arrays (120, 605, 705); a sealing layer (127, 600, 1005) comprising an organic resin and metal nanoparticles; a spacer layer (115, 610, 710, 1015) disposed between the refractive image icon concentrator array and the image icon array, the spacer layer comprising the organic resin and the metal nanoparticles; Equipped with the one or more refractive icon concentrator arrays are disposed above the one or more icon arrays such that the one or more refractive icon concentrator arrays form a composite image of the one or more icon arrays; the one or more refractive image icon concentrator arrays are disposed in a layer separate from the encapsulation layer and contact the encapsulation layer along a non-planar boundary; The metal nanoparticles contained in the sealing layer are dispersed throughout the sealing layer to affect the shape of the refractive image icon light collecting element; the one or more image icon arrays include a first image icon array and a second image icon array located below the first image icon array; the refractive index of the sealing layer and the refractive index of the spacer layer are adjusted by the metal nanoparticles so that a first light of a first wavelength incident on each light-collecting element of the one or more refractive image icon light-collecting element arrays is focused on a lower surface of the first image icon array, and a second light of a second wavelength different from the first wavelength incident on each light-collecting element of the one or more refractive image icon light-collecting element arrays is focused on a lower surface of the second image icon array; Security device.

2. A security device (100, 600, 700), one or more image icon arrays (110a, 110b, 615, 715); one or more layers of refractive icon arrays (120, 605, 705), the layers comprising a mixture of organic resin and metal nanoparticles; a sealing layer (127, 600, 1005) containing the organic resin and the metal nanoparticles; a spacer layer disposed between the refractive image icon concentrator array and the image icon array; (115, 610, 710, 1015) A spacer layer comprising the organic resin and the metal nanoparticles; Equipped with the one or more refractive icon concentrator arrays are disposed above the one or more icon arrays such that the one or more refractive icon concentrator arrays form a composite image of the one or more icon arrays; the one or more refractive image icon concentrator arrays are disposed in a layer separate from the encapsulation layer and contact the encapsulation layer along a non-planar boundary; the metal nanoparticles are dispersed throughout the layer of the one or more refractive icon concentrator arrays to affect the shape of the refractive icon concentrator elements; the one or more image icon arrays include a first image icon array and a second image icon array located below the first image icon array; the refractive index of the layer of the image icon light collecting element array, the refractive index of the sealing layer, and the refractive index of the spacer layer are adjusted by the metal nanoparticles so that a first light of a first wavelength incident on each light collecting element of the one or more refractive image icon light collecting element arrays is focused on a lower surface of the first image icon array, and a second light of a second wavelength different from the first wavelength incident on each light collecting element of the one or more refractive image icon light collecting element arrays is focused on a lower surface of the second image icon array; Security device.

3. 3. The security device of claim 1 or claim 2, wherein the metal nanoparticles comprise one or more of aluminum oxide, zirconium dioxide, titanium dioxide, zinc sulfide, or zinc telluride.

4. 3. The security device of claim 1 or claim 2, wherein the organic resin comprises an acrylate monomer.

5. 3. The security device of claim 1 or claim 2, wherein the organic resin comprises an acrylate oligomer.

6. 3. The security device of claim 1 or claim 2, wherein the organic resin comprises one or more of phenoxybenzyl acrylate, O-phenylphenoxyethyl acrylate, phenylthioethyl acrylate, bis-phenylthioethyl acrylate, cumylphenoxyethyl acrylate, biphenylmethyl acrylate, bisphenol A epoxy acrylate, fluorene-type acrylate, brominated acrylate, halogenated acrylate, or melamine acrylate.

7. 3. The security device of claim 1 or claim 2, wherein the organic resin comprises one or more of isodecyl acrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyester tetraacrylate, trimethylpropane triacrylate, or hexanediol diacrylate.

8. 3. A security device according to claim 1 or claim 2, wherein the organic resin does not contain a polarizing element.

9. 3. A security device according to claim 1 or claim 2, wherein the encapsulation layer has a refractive index of 1.5 or greater.

10. 3. A security device according to claim 1 or claim 2, wherein the encapsulating layer has a refractive index of 1.6 or greater.

11. 10. The security device of claim 1, wherein the refractive image icon concentrator elements of said one or more refractive image icon concentrator arrays have diameters greater than 30 microns.

12. 3. A security device as claimed in claim 1 or claim 2, wherein the spacer layer is integrated with an array of refractive image icon concentrators.

13. 3. A security device as claimed in claim 1 or claim 2, further comprising two or more refractive image icon concentrator arrays meeting along one or more non-planar boundaries.

14. 3. The security device of claim 1 or claim 2, wherein said security device has a thickness of 50 microns or less.

15. The security device of claim 1 or claim 2, further comprising a machine-readable security device (Mr-SD) (620, 720).

16. 3. The security device of claim 2, wherein the mixture has a refractive index greater than 1.

5. Chair.

17. 3. The security device of claim 2, wherein the organic resin has a refractive index of less than 1.

5. Chair.

18. A security document (101) comprising a security device according to claim 1.

19. A security document (101) comprising a security device according to claim 2.

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