WO2013188518A1

WO2013188518A1 - Micro-optic material with improved abrasion resistance

Info

Publication number: WO2013188518A1
Application number: PCT/US2013/045372
Authority: WO
Inventors: Jonathan D. GOSNELL; Caroline B. KENNEDY; Gregory R. Jordan
Original assignee: Visual Physics, Llc
Priority date: 2012-06-13
Filing date: 2013-06-12
Publication date: 2013-12-19

Abstract

A micro-optic material that demonstrates improved abrasion resistance while continuing to provide optimal optical performance is provided. An outermost layer of the micro-optic material is prepared from a formulation utilizing an effective amount of one or more nanocomposites {e.g., a silica-polymer nanocomposite, an alumina-polymer nanocomposite). The inventive material, which offers easily recognized dynamic optical effects, is suitable for use in high wear end-use applications, such as rigid ID cards, which have heightened performance requirements.

Description

MICRO-OPTIC MATERIAL WITH IMPROVED ABRASION RESISTANCE

RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Patent Application Serial No.

61/659,080, filed June 13, 2012, which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

[0002] The present invention generally relates to a micro-optic material with improved abrasion resistance, and more particularly relates to a micro-optic security device that demonstrates improved abrasion resistance while continuing to provide optimal optical performance.

BACKGROUND AND SUMMARY OF THE INVENTION

[0003] Micro-optic film materials projecting synthetic images generally comprise (a) a light-transmitting polymeric substrate, (b) an arrangement of micro-sized image icons located on or within the polymeric substrate, and (c) an arrangement of focusing elements {e.g., microlenses). The image icon and focusing element arrangements are configured such that when the arrangement of image icons is viewed through the arrangement of focusing elements, one or more synthetic images are projected. These projected images may show a number of different optical effects. Material constructions capable of presenting such effects are described in U.S. Patent No. 7,333,268 to Steenblik et al., U.S. Patent No. 7,468,842 to Steenblik et al., U.S. Patent No. 7,738,175 to Steenblik et al., U.S. Patent No. 7,830,627 to Commander et al., U.S. Patent No. 8,149,51 1 to Kaule et al.; U.S. Patent Application Publication No. 2010/0177094 to Kaule et al.; U.S. Patent Application Publication No. 2010/0182221 to Kaule et al.; European Patent No. 2162294 to Kaule et al.; and European Patent Application No. 08759342.2 (or European Publication No. 2164713) to Kaule.

[0004] The arrangements of focusing elements and image icons used in these micro- optic film materials are formed from a variety of materials such as substantially transparent or clear, colored or colorless polymers such as acrylics, acrylated polyesters, acrylated urethanes, epoxies, polycarbonates, polypropylenes, polyesters, urethanes, and the like, using a multiplicity of methods that are known in the art of micro-optic and microstructure replication, including extrusion {e.g., extrusion embossing, soft embossing), radiation cured casting, and injection molding, reaction injection molding, and reaction casting.

[0005] These film materials may be used as security devices for authentication of banknotes, secure documents and products. For banknotes and secure documents, these materials are typically used in the form of a strip or thread and either partially embedded within the banknote or document, or applied to a surface thereof. For passports or other identification (ID) documents, these materials could be used as a full laminate or embedded as an anti- counterfeit feature in polycarbonate passports.

[0006] MOTION^® micro-optic security devices, which are described in U.S. Patent No.

7,333,268, have found increasingly widespread usage in applications that require authentication and counterfeit resistance, in such forms as security threads in banknotes and as security seals or labels for product packaging. To meet the production and performance needs for these industries, specific blends of ultraviolet (UV) curable monomers and oligomers {e.g., acrylate- functional UV curable monomers and oligomers) have been utilized in the formation of precision microstructures {i.e., focusing elements and image icons) such that a rigid microstructured master can be replicated quickly and inexpensively by casting from its surface.

[0007] High wear end-use applications for these micro-optic security devices require heightened performance requirements. For example, rigid identification (ID) cards have high standards for abrasion resistance and require that personalization data remain secure and legible even after many thousands of slides into and out of a wallet, against other cards. Film based over-laminates are sometimes applied to card surfaces to protect the underlying data and these must be wear and abrasion resistant in addition to providing some level of secure authentication.

[0008] MOTION^® micro-optic security devices are desired for use in such high wear end- use applications where these devices provide an even greater level of security and authentication due to the easily recognized dynamic optical effects. However, past attempts to utilize MOTION^® security devices on the upper surfaces of ID cards have shown that the device's upper exposed surface is degraded prematurely during normal usage. Furthermore, as the outermost layer undergoes wear and degradation, the optical security effects are diminished or eliminated. When the outermost layer is an exposed arrangement or array of microlens, it is thus desirable to make this layer from materials that are much more resistant to scratching and abrasion than those that have been used in the past. Likewise, when the outermost layer is an embedding layer {e.g., sealing or protective layer) which embeds the arrangement or array of microlens, again it is desirable to make this layer from a highly abrasion resistant material.

[0009] The present invention therefore provides a micro-optic material suitable for use in such high wear end-use applications. The inventive micro-optic material has an upper surface that demonstrates improved abrasion resistance while still maintaining the optical performance required for a synthetic image magnification system. Because this upper surface has optical performance requirements and must be produced at high rates of speed, among a number of other constraints and physical requirements, the selection of a highly abrasion resistant material that is suitable for use in preparing the outermost layer or microlenses of these micro-optic materials has required extensive research and development efforts. The term "outermost layer", as used herein, is intended to mean the focusing element {e.g., microlens) layer or layer that embeds the focusing element layer and not layers added to the micro-optic material to facilitate its incorporation onto or within a final substrate {e.g., dissolvable adhesive layers).

[0010] As a result of these efforts, the present inventors have found a class of formulating materials that give surprisingly dramatic increases in the level of abrasion resistance, scratching, or resistance to friction induced degradation of the layers from which the materials are composed. When used as a lens material, the resulting microlenses still function in accordance with standard performance requirements, and when used as an embedding layer provides a uniform refraction of light without significant dispersion or loss of focus. In all cases, the result is a durable micro-optic material that demonstrates greatly improved abrasion resistance and optimal optical performance.

[0011] The present invention more specifically provides a formulation suitable for use in preparing arrangements or arrays of focusing elements {e.g., microlenses) for micro-optic materials, as well as layers embedding focusing element arrangements, the formulation comprising an effective amount of one or more nanocomposites. The term "nanocomposite", as used herein, is intended to mean a nanoparticle-polymer nanocomposite {e.g., a silica-polymer nanocomposite, an alumina-polymer nanocomposite), which is a composite having nanoparticles (average particle size of less than about 100 nanometers (nm), preferably from about 20 to about 50 nm) uniformly dispersed in a polymer medium. The nanoparticles are preferably non-agglomerated nanoparticles.

[0012] The inventive formulation preferably comprises from about 10 to about 90 % by wt, based on the total weight of the formulation, of one or more nanocomposites, more preferably from about 15 to about 75 % by wt, and most preferably from about 25 to about 50 % by wt.

[0013] In one such exemplary embodiment, the inventive formulation is a radiation- curable formulation that is substantially solvent-free and water-free {i.e., substantially 100 % solids formulation) and that adheres well to a target surface. As used herein, the term "substantially 100 % solids" means that the formulation contains substantially no volatile organic compounds ("VOCs"), and has essentially zero emissions of VOCs, and contains substantially no water.

[0014] If used to prepare arrangements or arrays of focusing elements for micro-optic materials, the inventive radiation-curable formulation is preferably a 100 % solids formulation. In other words, VOCs and water are not present in the formulation at all. In this exemplary embodiment, one or more monomeric diluents are used in the formulation to control viscosity {i.e., reduce viscosity levels to less than about 250 centipoise (cps)) and flow so as to render the formulation useable in a high speed manufacturing process {i.e., manufacturing speeds of greater than 20 meters per minute). The monomeric diluent(s) also serves to increase the flexibility of the focusing elements. The present inventors have discovered that monomeric diluent(s) quantities of less than or equal to about 75 % by wt., based on the total weight of the formulation, control viscosity and flow, and provide flexibility to the focusing elements, without serving to adversely impact upon the abrasion resistance demonstrated by the focusing elements. In this contemplated embodiment, the formulation has a preferred refractive index ranging from about 1.5 to about 1.7.

[0015] If used to prepare layers embedding focusing element arrangements, the inventive formulation may be either a 100 % solids formulation, or it may contain some solvent {i.e., VOCs and/or water). For formulations containing some solvent, the solvent would have to be fully evaporated before curing so as to reduce or eliminate the possibility of blistering or other defects. One or more monomeric diluents are used in the formulation in quantities at or below the level noted above to control viscosity and flow so as to render the formulation useable in a high speed manufacturing process. In this contemplated embodiment, the formulation has a preferred refractive index ranging from about 1.35 to about 1 .49.

[0016] The present invention further provides a micro-optic material with improved abrasion resistance in which an outermost layer of the micro-optic material is prepared from a formulation comprising an effective amount of one or more nanocomposites {e.g., one or more silica-polymer nanocomposites, one or more alumina-polymer nanocomposites).

[0017] The inventive micro-optic material, in an exemplary embodiment, comprises one or more optionally embedded arrangements of focusing elements, and one or more arrangements of image icons, wherein the arrangement(s) of image icons and the arrangement(s) of focusing elements cooperate to form at least one synthetic image of at least a portion of the image icons, wherein when the arrangement(s) of focusing elements is an outermost layer of the micro-optic material, the arrangement(s) of focusing elements is prepared from a formulation comprising an effective amount of one or more nanocomposites, and wherein when the arrangement(s) of focusing elements is embedded by an embedding layer, and the embedding layer constitutes an outermost layer of the micro-optic material, the embedding layer is prepared from a formulation comprising an effective amount of one or more nanocomposites.

[0018] By way of example, the micro-optic material may comprise one or more arrangements of exposed refractive microlenses prepared from the formulation described above.

[0019] By way of another example, the micro-optic material may comprise one or more arrangements of embedded microlenses, the embedding layer constituting an outermost layer of the micro-optic material that is prepared from the formulation described above.

[0020] The inventive micro-optic material may be, in yet another example, an optionally transferable micro-optic material with a reduced thickness, which basically comprises one or more arrangements of image icons substantially in contact with one or more optionally embedded arrangements of focusing elements, wherein an outermost layer of the micro-optic material is prepared from the formulation described above.

[0021] The present invention also provides a method of increasing the abrasion resistance of an outermost layer of a micro-optic material, the method comprising: using a formulation comprising an effective amount of one or more nanocomposites to prepare the outermost layer, the outermost layer being selected from the group of one or more arrangements of focusing elements or a layer embedding one or more arrangements of focusing elements.

[0022] Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings. [0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Particular features of the disclosed invention are illustrated by reference to the accompanying drawings in which:

FIG. 1 (a) is a series of three photomicrographs of images projected by a prior art embedded lens construct which has been subjected to 0, 50 and 100 weighted sandpaper strokes, respectively, the images no longer visible in the last photomicrograph after the construct has been subjected to 100 weighted sandpaper strokes;

FIG. 1 (b) is a series of three photomicrographs of images projected by the inventive micro-optic material which has also been subjected to 0, 50 and 100 weighted sandpaper strokes, respectively, the images continuing to be visible in the last photomicrograph after the material has been has been subjected to 100 weighted sandpaper strokes;

FIG. 2 is a series of three photomicrographs (150x magnification) of exposed, refractive microlens layers, of which FIG. 2(a) is an untouched exposed microlens layer prior to abrasion, FIG. 2 (b) is a prior art exposed microlens layer after being subjected to 100 weighted 3M™ Lapping Film Sheet stokes, and FIG. 2(c) is an exposed microlens layer of the present invention after also being subjected to 100 weighted 3M™ Lapping Film Sheet stokes; and

FIG. 3(a) is a cross-sectional graphical depiction of untouched and abraded prior art exposed microlens layers, which FIG. 3(b) is a cross-sectional graphical depiction of untouched and abraded exposed microlens layers of the present invention, with color shaded regions indicating the amount or degree of abrasion.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The formulation of the present invention is used to prepare transparent microlens and/or embedding layers with improved abrasion and scratch resistance. Other contemplated uses include, but are not limited to, applying the formulation to a surface of a security document {e.g., banknote) or coin and embossing and/or micro-embossing structures in the applied formulation in the form of, for example, holographic and diffraction patterns, fine line elements, micro texts, etc.

[0026] While embodiments of the inventive formulation described herein utilize silica nanocomposites, the invention is not so limited. The present invention also contemplates nanocomposites that utilize other inorganic nanoparticles such as alumina, zirconia, and the like, or inorganic-organic hybrid heterogeneous nanoparticles such as carboxy hydroxy, amino, or thio functionalized inorganic nanoparticles. For nanocomposites utilizing nanosilica particles, these nanocomposites may include nanosilica in both a fumed silica and colloidal silica state.

[0027] Suitable silica nanocomposites include silica-polymer nanocomposites containing at least about 10 % by wt. silica nanoparticles uniformly dispersed in a polymer medium. Suitable polymers for use in these silica-polymer nanocomposites include, but are not limited to, polymers derived from acrylates including aliphatic urethane acrylates, alkylmethacrylates, aromatic acrylates, ester acrylates, methacrylates, acrylics, acrylic acids, amides, carbonates, cellulose derivatives, epoxy resins, esters, arylethers, imides, olefins, polyesters, acrylated polyesters, polypropylenes, silicone resins, styrenes, sulfones, arylsulfones, ethersulfones, urethanes, acrylated urethanes, vinyls, vinyl derivatives, vinyl alcohols, and derivatives, combinations, and/or copolymers thereof.

[0028] In exemplary embodiments of the silica nanocomposite, nanosized silica is used as a filler for UV (or electron beam (EB)) curable acrylates. Such silica nanocomposites are sold under the trade designation UVHC8600 by Momentive of Columbus, OH (Momentive) and under the trade designation NANOCRYL^® C140 by Evonik Nanoresins GmbH, Geesthacht, Germany (Evonik).

[0029] In addition to employing an effective amount of one or more nanocomposites, the inventive formulation, as noted above, may also include monomeric diluents {e.g., functional acrylate monomers), as well as polymer resins, other fillers, anti-foaming agents, dispersing agents, antiblocking agents, and the like.

[0030] In an exemplary embodiment, the inventive formulation comprises an effective amount of one or more silica-UV curable acrylate polymer nanocomposites, one or more functional acrylate monomers, and one or more photoinitiators. Preferably, the inventive formulation comprises: (a) from about 25 to about 50 % by wt, based on the total weight of the formulation, of a silica-UV curable acrylate polymer nanocomposite;

(b) from about 25 to about 75 % by wt., based on the total weight of the formulation, of one or more functional acrylate monomers selected from the group of aliphatic urethane acrylate, dipropylene glycol diacrylate, 1-6-hexanediol diacrylate, isodecyl acrylate, tetrahydrofurfuryl (meth)acrylate, trimethylolpropane triacrylate and combinations thereof; and

(c) from about 1 to about 10 % by wt., based on the total weight of the formulation, of one or more photoinitiators selected from the group of free-radical photoinitiators, for example, aromatic carbonyl compounds such as benzophenone, other phenone, hydroxyketone, phosphine oxide free-radical forming derivatives, and combinations thereof.

[0031] After UV curing and casting of the inventive formulation from a rigid microstructured master, crosslinked polyacrylate nanocomposite layers with improved properties (e.g., scratch, abrasion and heat resistance) are obtained. Here, the acrylate polymer is covalently bonded to the silica.

[0032] The micro-optic material of the present invention has an outermost layer that is prepared from the above described formulation. In an exemplary embodiment, the inventive micro-optic material basically comprises one or more optionally embedded arrangements of focusing elements, and one or more arrangements of image icons, where the one or more arrangements of image icons and the one or more arrangements of focusing elements cooperate to form at least one synthetic image of at least a portion of the image icons. When the arrangement(s) of focusing elements is an outermost layer of the micro-optic material, the arrangement(s) of focusing elements is prepared from the inventive formulation. When the arrangement(s) of focusing elements is embedded by an embedding layer, and the embedding layer constitutes an outermost layer of the micro-optic material, the embedding layer is prepared from the inventive formulation.

[0033] The inventive micro-optic material may be prepared (to the extent not inconsistent with the teachings of the present invention) in accordance with the materials, methods and techniques disclosed in U.S. Patent No. 7,333,268 to Steenblik et al. , U.S. Patent No. 7,468,842 to Steenblik et al., U.S. Patent No. 7,738,175 to Steenblik et al., and U.S. Patent Application Publication No. 2010/0308571 A1 to Steenblik et al., all of which are fully incorporated herein by reference as if fully set forth herein. As described in these references, arrays of focusing elements and image icons can be formed from a variety of materials such as substantially transparent or clear, colored or colorless polymers such as acrylics, acrylated polyesters, acrylated urethanes, epoxies, polycarbonates, polypropylenes, polyesters, urethanes, and the like, using a multiplicity of methods that are known in the art of micro-optic and microstructure replication, including extrusion {e.g., extrusion embossing, soft embossing), radiation cured casting, and injection molding, reaction injection molding, and reaction casting. High refractive index, colored or colorless materials having refractive indices (at 589 nm, 20°C) of more than 1.5, 1 .6, 1.7, or higher, such as those described in U.S. Patent Application Publication No. US 2010/0109317 A1 to Hoffmuller et al., may also be used. As also described, embedding layers can be prepared using gels, lacquers, molded polymers, etc.

[0034] In one contemplated embodiment, the micro-optic material comprises one or more arrangements of exposed refractive microlenses prepared from the inventive formulation, while in another contemplated embodiment, the micro-optic material comprises one or more arrangements of embedded microlenses, the embedding layer constituting an outermost layer of the micro-optic material that is prepared from the inventive formulation.

[0035] In yet another contemplated embodiment, the micro-optic material is an optionally transferable micro-optic material with a reduced thickness ("thin construction"), which basically comprises one or more arrangements of image icons substantially in contact with one or more optionally embedded arrangements of focusing elements, wherein an outermost layer of the micro-optic material is prepared from the formulation comprising an effective amount of one or more silica nanocomposites.

[0036] When the micro-optic material is a transferable micro-optic material, such a thin construction may be manufactured by first casting an icon layer on a first transfer film layer. Recesses in the icon layer are then backfilled with a curable pigment and then a lens layer is cast on top of the filled icons. This structure eventually has adhesive added and is transferred using known techniques, ending up as a thin (film-free) structure applied to, for example, paper.

[0037] In another such embodiment, a layer of polymer resin is applied to the filled icons prior to the application of the lens layer. This resin layer, which can act as an optical spacer, is applied using an additional microstructured tool thereby forming a microstructured layer of known thickness over the icon structure. When the lens structure is then cast onto this microstructured spacer layer, the polymer resin fills in any voids in the microstructured layer, resulting in a lens layer uniformly separated from the icon layer. The resulting structure is thinner than those structures that incorporate an optical spacer in the form of a film, yet can be processed and applied using a thin foil transfer approach. The thin structure has advantages in bank note thickness and in improved tamper resistance in ID applications.

[0038] The inventive micro-optic materials may be used in the form of very thin threads, strips, ribbons, or patches that are partially embedded in, or mounted on a surface of a security document. Such security documents include, but are not limited to, those documents having one or more through-holes, the inventive micro-optic material positioned in the through-hole(s).

[0039] Aspects of the present invention will now be further illustrated by reference to the following non-limiting working examples.

EXAMPLES

[0040] Micro-optic film samples were fabricated as set forth below.

Example 1

[0041] Two embedded lens micro-optic film materials were prepared by forming the icons as voids in a radiation cured liquid polymer {i.e., acrylated urethane) by casting from an icon mold against a 75 gauge adhesion-promoted polyethylene terephthalate (PET) film {i.e., base film or optical spacer), then forming the lenses from the radiation cured liquid polymer on an opposite face of the base film in correct alignment or skew with respect to the icons, then filling the icon voids with a submicron particle pigmented coloring material by gravure-like doctor blading against the film surface, and solidifying the fill by application of UV light. A lower refractive index embedding layer was then cast against the lens layer. The lower refractive index embedding layer for the first or prior art micro-optic film material was prepared using Formula A below, while the lower refractive index embedding layer for the second or inventive micro-optic film material was prepared using Formula 1 below.

Formula A

2 parts benzophenone photoinitiator, which is sold by

Lamberti SpA, Gallarate Varese, Italy (Lamberti)

25 parts tetrahydrofurfuryl (meth)acrylate, which is sold

under the trade designation SR-285 by Sartomer

Company of Exton, PA., USA. (Sautomer) 25 parts isodecyl acrylate, which is sold under the trade

designation SR-395 by Sartomer

Formula 1

4 parts benzophenone photoinitiator, which is sold by

Lamberti

25 parts tetrahydrofurfuryl (meth)acrylate, which is sold

under the trade designation SR-285 by Sartomer

25 parts isodecyl acrylate, which is sold under the trade

designation SR-395 by Sartomer

50 parts UVHC8600 UV-curable, silica-modified coating

(Momentive)

[0042] Abrasion testing was performed on each embedded micro-optic film material using a Sutherland Rub Abrasion Testing Apparatus (Sutherland 2000) in accordance with ASTM D 5264. As shown in FIG. 1 , after abrasion with a one pound (1 lb) weight and sandpaper (600 grit, 100 strokes), the images projected by the first or prior art micro-optic film material are no longer visible after 100 strokes (see last frame in FIG. 1 (a)), while the images projected by the second or inventive micro-optic film material are only marginally compromised after 100 strokes (see last frame in FIG. 1 (b)).

Example 2

[0043] Two thin transfer structures with exposed refractive microlenses were prepared by casting an icon layer (using an acrylated urethane) on a first transfer film layer, then casting a pigment fill onto the icon layer, solidifying the fill by application of UV light, and then casting a lens layer on top of the filled icons. The lens layer for the first or prior art thin transfer structure was prepared using an acrylated urethane, which is available from Lord Corporation, World Headquarters, 1 1 1 Lord Drive, Cary, NC 2751 1 -7923 USA, under the product designation U107, while the lens layer for the second or inventive thin transfer structure was prepared using Formula 2 below.

Formula 2

4 parts benzophenone photoinitiator (Lamberti)

17 parts trimethylolpropane triacrylate, which is sold

under the trade designation SR-351 by Sartomer 33 parts 1-6-hexanediol diacrylate, which is sold under

the trade designation SR-238 by Sartomer

17 parts aliphatic urethane acrylate, which is sold under

the trade designation CN9026 by Sartomer

25 parts NANOCRYL^® C140 nanocomposite (Evonik)

[0044] Abrasion testing was performed on each thin transfer structure again using a

Sutherland Rub Abrasion Testing Apparatus (Sutherland 2000) in accordance with ASTM D 5264. A magnified (150x) image of the microlens layer of the thin transfer structure is shown in the first frame of FIG. 2 (FIG. 2(a)). After abrasion with a two pound (2 lb) weight and a 3M™ Lapping Film Sheet (9 micron grade, 100 strokes), synthetic images were no longer visible from the first or prior art thin transfer structure due to damage to the microlenses, while the images projected by the second or inventive thin transfer structure remained uncompromised due to only a few light scratches in the microlens layer. The second frame in FIG. 2 (FIG. 2(b)) shows the lens layer in the first or prior art structure after 100 strokes, while the third frame in FIG. 2 (FIG. 2(c)) shows the lens layer in the second or inventive structure after 100 strokes. As readily apparent from FIG. 2, there is a great deal less destruction of the inventive lens layer from a top down view.

[0045] In FIG. 3(a), a cross-sectional comparison between the un-abraded and abraded first or prior art structure is shown, while in FIG. 3(b), a cross-sectional comparison between the un-abraded and abraded second or inventive structure is shown. The difference in cross- sectional heights (which is shown as colored regions) was measured as 2.8 microns for FIG. 3(a) and as 0.8 microns for FIG. 3(b), which clearly shows the marked improvement in abrasion resistance demonstrated by the inventive micro-optic material.

Examples 3 and 4

[0046] Micro-optic materials in which the lens layer or embedding layer were prepared using either Formula 3 or Formula 4 below were also made. These samples also demonstrated greatly improved abrasion resistance.

Formula 3

4 parts benzophenone photoinitiator (Lamberti)

25 parts phenoxydiethylene glycol acrylate, which is sold by

Sigma-Aldrich Corporation, St. Louis, MO., USA dipropylene glycol diacrylate, which is sold under

the trade designation SR-508 by Sartomer

UVHC8600 UV-curable, silica-modified coating

(Momentive)

benzophenone photoinitiator (Lamberti)

SR-351 trimethylolpropane triacrylate (Sartomer)

SR-508 dipropylene glycol diacrylate (Sartomer)

NANOCRYL^® C140 nanocomposite (Evonik)

[0047] While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the exemplary embodiments.

[0048] We claim:

Claims

1. A formulation comprising an effective amount of one or more nanocomposites, wherein the formulation is used to prepare outermost layers of micro-optic materials, the outermost layers being selected from the group of one or more arrangements of focusing elements and layers embedding one or more arrangements of focusing elements, the outermost layers demonstrating improved abrasion resistance.

2. The formulation of claim 1 , wherein the one or more nanocomposites are selected from the group of inorganic nanoparticle-polymer nanocomposites, inorganic-organic hybrid heterogeneous nanoparticle-polymer nanocomposites, and combinations thereof.

3. The formulation of claim 2, wherein the one or more nanocomposites are inorganic nanoparticle-polymer nanocomposites selected from the group of silica nanoparticle- polymer nanocomposites, alumina nanoparticle-polymer nanocomposites, zirconia nanoparticle- polymer nanocomposites, and combinations thereof.

4. The formulation of claim 2, wherein the one or more nanocomposites are inorganic-organic hybrid heterogeneous nanocomposites selected from the group of carboxy hydroxyl functionalized inorganic nanoparticle-polymer nanocomposites, amino functionalized inorganic nanoparticle-polymer nanocomposites, thio functionalized inorganic nanoparticle- polymer nanocomposites, and combinations thereof.

5. The formulation of claim 1 , which is a radiation-curable, substantially 100 % solids formulation that comprises one or more nanoparticle-radiation curable polymer nanocomposites, one or more functional monomers, and one or more photoinitiators.

6. The formulation of claim 5, which comprises one or more silica-ultraviolet curable acrylate polymer nanocomposites, one or more functional acrylate monomers, and one or more photoinitiators.

7. The formulation of claim 6, which comprises:

(a) from about 25 to about 50 % by wt, based on the total weight of the formulation, of a silica-ultraviolet curable acrylate polymer nanocomposite;

(b) from about 25 to about 75 % by wt., based on the total weight of the formulation, of one or more functional acrylate monomers; and

(c) from about 1 to about 10 % by wt., based on the total weight of the formulation, of one or more free-radical photoinitiators.

8. The formulation of claim 7, wherein the one or more functional acrylate monomers is selected from the group of aliphatic urethane acrylate, dipropylene glycol diacrylate, 1 -6-hexanediol diacrylate, isodecyl acrylate, tetrahydrofurfuryl (meth)acrylate, trimethylolpropane triacrylate and combinations thereof.

9. A micro-optic material having an outermost layer that is prepared from a formulation comprising an effective amount of one or more nanocomposites, the outermost layer being selected from the group of one or more arrangements of focusing elements and layers embedding one or more arrangements of focusing elements, the outermost layer demonstrating improved abrasion resistance.

10. The micro-optic material of claim 9, wherein the formulation is a radiation- curable, substantially 100 % solids formulation that comprises one or more nanoparticle- radiation curable polymer nanocomposites, one or more functional monomers, and one or more photoinitiators.

1 1 . The micro-optic material of claim 10, wherein the formulation comprises a silica- ultraviolet curable acrylate polymer nanocomposite, one or more functional acrylate monomers, and one or more photoinitiators.

12. The micro-optic material of claim 1 1 , wherein the formulation comprises:

13. The micro-optic material of claim 12, wherein the one or more functional acrylate monomers is selected from the group of aliphatic urethane acrylate, dipropylene glycol diacrylate, 1-6-hexanediol diacrylate, isodecyl acrylate, tetrahydrofurfuryl (meth)acrylate, trimethylolpropane triacrylate and combinations thereof.

14. The micro-optic material of claim 9, which comprises one or more optionally embedded arrangements of focusing elements, and one or more arrangements of image icons, wherein the one or more arrangements of focusing elements and the one or more arrangements of image icons cooperate to form at least one synthetic image of at least a portion of the image icons, wherein when the one or more arrangements of focusing elements is an outermost layer of the micro-optic material, the one or more arrangements of focusing elements is prepared from a formulation comprising an effective amount of one or more nanocomposites, and wherein when the one or more arrangements of focusing elements is embedded by an embedding layer, and the embedding layer constitutes an outermost layer of the micro-optic material, the embedding layer is prepared from a formulation comprising an effective amount of one or more nanocomposites.

15. The micro-optic material of claim 14, which is an optionally transferable micro- optic material with a reduced thickness, which comprises one or more arrangements of image icons substantially in contact with one or more optionally embedded arrangements of focusing elements, wherein an outermost layer of the micro-optic material is prepared from the formulation comprising an effective amount of one or more nanocomposites.

16. The micro-optic material of claim 14 or 15, wherein the micro-optic material still forms at least one synthetic image of at least a portion of the image icons after the outermost layer is subjected to 100 strokes from a one pound weight and 600 grit sandpaper in accordance with the test method defined in ASTM D5264.

17. The micro-optic material of claim 14 or 15, wherein the micro-optic material still forms at least one synthetic image of at least a portion of the image icons after the outermost layer is subjected to 100 strokes from a two pound weight and 9 micron grade abrasive sheet in accordance with the test method defined in ASTM D5264.

18. The micro-optic material of claim 17, wherein the outermost layer lost less than about 2.8 microns in thickness after being subjected to 100 strokes from a two pound weight and 9 micron grade abrasive sheet in accordance with the test method defined in ASTM D5264.

19. The micro-optic material of claim 18, wherein the outermost layer lost from about 0.8 to less than about 2.8 microns in thickness after being subjected to 100 strokes from a two pound weight and 9 micron grade abrasive sheet in accordance with the test method defined in ASTM D5264.

20. A security document, which includes one or more security devices selected from the group of one or more micro-optic materials of claim 9 partially embedded therein and/or mounted on a surface thereof, one or more surface structures prepared from the formulation of claim 1 , and combinations thereof.

21 . A method of increasing the abrasion resistance of an outermost layer of a micro- optic material, the method comprising: using a formulation comprising an effective amount of one or more nanocomposites to prepare the outermost layer, the outermost layer being selected from the group of one or more arrangements of focusing elements or a layer embedding one or more arrangements of focusing elements.