HK1178192A - Crystalline colloidal array of particles bearing reactive surfactant - Google Patents

Description

Crystalline colloidal array of particles with reactive surfactant

Technical Field

The present invention relates to crystalline colloidal arrays, and more particularly, to periodic arrays of particles having a reactive surfactant covalently bonded thereto.

Background

Radiation diffractive materials based on crystalline colloidal arrays have been used for various purposes. Crystalline Colloidal Arrays (CCAs) are three-dimensional ordered arrays of monodisperse colloidal particles. The particles are generally composed of a polymer, such as polystyrene. Colloidal dispersions of these particles can self-assemble into ordered arrays (crystalline structures) with lattice spacings comparable to the wavelengths of ultraviolet, visible, or infrared radiation. The crystalline structure has been used to filter a narrow band of selected wavelengths from a broad spectrum of incident radiation while allowing propagation of adjacent radiation wavelengths. Alternatively, CCAs are manufactured to diffract radiation for use as colorants, markers, optical switches, optical limiters (optical limiters), and sensors.

Many of these devices have been created by dispersing particles in a liquid medium, whereby the particles self-assemble into an ordered array. The position of the particles in the array can be fixed by interpolymerization of the particles or by introducing a solvent that swells and locks the particles together.

Other CCAs are prepared from dispersions of similarly charged monodisperse particles in a carrier comprising a non-reactive surfactant. The dispersion is applied to a substrate, and the carrier is evaporated to produce an ordered periodic array of particles. The array is mounted in place by coating the array with a curable polymer such as an acrylic polymer, polyurethane, alkyd polymer, polyester, silicone-containing polymer, polysulfide, or epoxy-containing polymer. Methods for producing the above CCAs are disclosed in U.S. Pat. No. 6,894,086, which is incorporated herein by reference. Alternatively, the particles may have a core-shell structure, where the core is made of a material such as those described above for unitary particles and the shell is made of the same polymer as the material of the core, the particle shell polymer being different from the material of the core for a particular array of core-shell particles. Such core-shell particles and methods for their preparation are disclosed, for example, in U.S. patent application publication No. US2007/0100026, which is incorporated herein by reference.

Of these arrays of unitary or core-shell particles, the structure diffracts radiation following bragg's law, where radiation meeting the bragg condition is reflected and adjacent spectral regions that do not meet the bragg condition propagate through the device. The wavelength of the reflected radiation is determined in part by the effective refractive index of the array and the interparticle spacing within the array.

Disclosure of Invention

The present invention includes a method of preparing a crystalline colloidal array comprising dispersing a monomer in an emulsion comprising a reactive surfactant, polymerizing the monomer to produce monodisperse polymeric particles, wherein the reactive surfactant is covalently bonded to the polymeric particles, and applying the dispersion to a substrate whereby the particles are self-aligned into an ordered periodic array.

The present invention also includes a crystalline colloidal array comprising an ordered periodic array of polymeric particles, each of said particles having a surface comprising a polymeric material and a reactive surfactant covalently bonded to the surface of the particle, and a matrix surrounding the array of polymeric particles.

Detailed Description

For the purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

Moreover, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1-10" is intended to include all sub-ranges therebetween and to include the recited minimum value of 1 and the recited maximum value of 10, that is, to have a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in the present application, the use of "or" means "and/or" unless specifically stated otherwise, even though "and/or" may be explicitly used in certain instances.

The term "polymer" is meant to include homopolymers, copolymers, and oligomers. The term "metal" includes metals, metal oxides, and metalloids. The term "injection" and related terms (such as injection) relate to permeation from a liquid phase.

The present invention includes Crystalline Colloidal Arrays (CCAs) and methods of making crystalline colloidal arrays, wherein the CCAs diffract radiation in the visible and/or non-visible electromagnetic spectrum. The CCA includes an ordered periodic array of particles housed in a polymer matrix. The array includes a plurality of particle layers and satisfies bragg's law:

mλ=2ndsinθ

where m is an integer, n is the effective refractive index of the array, d is the spacing between layers of particles, and λ is the wavelength of rays reflected at an angle θ from the plane of the layers of particles. The CCA was prepared on a substrate as described below. As used herein, a "wavelength" of diffracted radiation includes a band of the electromagnetic spectrum surrounding that wavelength. For example, for a wavelength of 600 nanometers (nm), 595-605 nm may be included. The reflected radiation may be in the visible spectrum or invisible spectrum (infrared or ultraviolet). As used herein, if a periodic array of particles is said to bragg diffract radiation or reflect radiation according to bragg's law, it means that at least some of the incident radiation is diffracted by the crystalline structure of the array, thereby producing some reflected radiation that complies with bragg's law.

In the present invention, at least some of the particles have an effective amount of a reactive surfactant covalently bonded thereto. By "effective amount" is meant that there is at least a minimum amount of material sufficient to achieve the desired effect, including at least a minimum of defects in the CCA due to uneven distribution of surfactant. The phrase "reactive surfactant" generally refers to any surfactant (e.g., a non-reactive surfactant (non-reactive surfactant), a non-migratory surfactant, etc.) that is capable of immobilizing itself to the surface of the particle, for example, by forming a covalent bond. Generally, the bond between the reactive surfactant(s) and the particle surface(s) is strong enough to prevent separation and migration therebetween. In contrast, "non-reactive surfactant" refers to a surfactant that adsorbs (as opposed to being immobilized, reacting, or bonded) to the surface of the particle. By "particle surface", it is meant the outermost surface, including the outer surface of particles having a unitary structure or the outermost surface of particles having a core-shell structure, both as described below.

As used herein, a particle having a "unitary structure" means that the particle has a generally uniform structure without a constituent structure (e.g., a non-core-shell structure), although the composition may vary throughout the unitary particle, such as may occur when a solvent or matrix diffuses therein. Suitable materials for the unitary particles include polymers such as polystyrene, polyurethane, acrylic polymers, alkyd polymers, polyesters, siloxane-containing polymers, polysulfides, epoxy-containing polymers, and polymers derived from epoxy-containing polymers, and inorganic materials such as metal oxides (e.g., alumina, silica, or titanium dioxide) or semiconductors (e.g., cadmium selenide) or composites of these materials. "core-shell structure" refers to the preparation of the core from a component different from the shell component. Suitable components for the core of the particles include the above-listed materials for unitary particles. Suitable components for the shell include organic polymers (e.g., polystyrene, polyurethane, acrylic polymers, alkyd polymers, polyesters, silicone-containing polymers, polysulfides, epoxy-containing polymers, or polymers derived from epoxy-containing polymers), which may be crosslinked, the particle shell component being different from the material of the core. The shell material may be non-film-forming (e.g., crosslinked), meaning that the shell material remains around each particle core without forming a film of the shell material, such that the core-shell particles remain as discrete microparticles within the polymer matrix. As described above, the CCA of a core-shell particle may include at least three general regions, including a matrix, a particle shell, and a particle core. Alternatively, the shell material may be film-forming, such that the shell material forms a film around the core. The core material and the shell material may have different refractive indices. In addition, the refractive index of the shell may vary as a function of shell thickness in the form of a refractive index gradient through the shell thickness. The refractive index gradient may be caused by a gradient in the composition of the shell material through the shell thickness. For generally spherical particles, the core has a diameter of 85-95% or 90% of the total particle size, and the shell has the remainder of the particle size and a radial thickness dimension.

In one embodiment of the invention, the unitary particles are prepared by emulsion polymerization. Monomers (e.g., styrene, acrylates) and optionally initiators (e.g., sodium persulfate) are dispersed in an emulsion containing a reactive surfactant to produce a unitary particle. The monomers dispersed in the emulsion may include a single compound or a plurality of compounds, and may include crosslinking monomers such as divinylbenzene. The monodispersion of charged particles is prepared by purifying the monodispersion from the dispersion by removing undesirable materials such as unreacted monomers, small polymers, water, initiators, unbound surfactants, free salts, and coarse residue (agglomerated particles) by techniques such as ultrafiltration, dialysis, or ion exchange. Ultrafiltration is particularly suitable for purifying charged particles. The repulsive force of the charged particles can be mitigated if the particles are in a dispersion containing other materials such as salts or by-products; thus, the particle dispersion is purified to substantially contain only the charged particles, which then readily repel each other and form a regular ordered array on a substrate as described below.

In another embodiment, the core-shell particles are prepared via emulsion polymerization in two stages. In the first stage, the precursor monomers of the core (optionally with initiator) and surfactant are dispersed in an emulsion comprising surfactant. The core precursor monomer is polymerized to produce a dispersion of particle cores. The shell monomer is added to the dispersion of core particles containing the reactive surfactant, whereby the shell monomer polymerizes onto the core particles, binding the reactive surfactant to the shell. The particle core may be prepared in an emulsion comprising the non-reactive surfactant or both reactive and non-reactive dual surfactants. However, the polymerization of the shell monomer onto the core particle is carried out in an emulsion comprising a reactive surfactant. The core-shell particles are purified as described above with respect to the unitary particle purification to produce a dispersion of charged core-shell particles, which are then formed into an ordered array on a substrate as described below.

In preparing the unitary or core-shell particles, at least a portion of the outer surface (exterior surface) of any of the particles has a reactive surfactant bonded thereto. Unlike conventional particles in which non-reactive surfactants are adsorbed to the surface, the particles of the present invention include a reactive surfactant that is covalently bonded to at least a portion of the particle surface and remains on the particle surface during and after formation of the array. Arrays prepared with particles synthesized with reactive surfactants as described above show a significant reduction in defects if compared to arrays prepared with particles stabilized with absorbing (non-reactive) surfactants. When the particles are further processed to become CCAs, the benefits of using reactive surfactants to prepare the particles in the emulsion polymerization of monomers are described in detail below.

Certain reactive surfactants are molecules with long hydrophobic segments and short ionized and/or polar groups. The hydrophobic segment preferably adsorbs onto the particle surface during and after particle polymerization. The hydrophilic moiety extends into the aqueous phase of the dispersion. The reactive surfactant also contains a reactive group on the hydrophobic segment that can be covalently bonded to the particle surface. For example, the reactive group on the hydrophobic segment may include a carbon double bond. Alternatively, the reactive group may be present on the hydrophilic portion. One example of a reactive group on the hydrophilic moiety is an amine. In certain embodiments of the invention, the reactive group on the reactive surfactant is also present in the monomer(s) so that the reactive surfactant is more readily bonded to the particle surface during the polymerization reaction.

Reactive surfactants suitable for use in the present invention include any surfactant having a reactive group on a hydrophobic segment, which is capable of covalently bonding to the surface of the particle. The length and composition of the hydrophobic segment of the reactive surfactant may be selected to substantially correspond to the surface chemistry of the particle. Non-limiting examples of hydrophobic segments include C_10-20Alkyl chains, alkylaryl segments, and polypropoxy units. The hydrophilic group may be anionic, cationic, or nonionic. Suitable anionic functional groups include, for example, sulfonate, phosphonate, and carboxylate ions. Suitable cationic functional groups include, for example, ammonium ions. Suitable nonionic surfactants generally include surfactants that exhibit an ethoxy group hydrophilicity.

The reactive group may be selected based on the reactive species of the particle monomer. For example, acrylate reactive groups may be selected for particles composed of polymerized vinyl, acrylic, and/or styrenic monomers. Typical reactive surfactants include polyethylene glycol monomethacrylate, polyethylene glycol acrylate, phosphate esters of poly (propylene glycol) monomethacrylate, phosphate esters of poly (propylene glycol) monoacrylate, phosphate esters of poly (ethylene glycol) monomethacrylate, phosphate esters of poly (ethylene glycol) monoacrylate, poly (propylene glycol) monomethacrylate sulfate, poly (propylene glycol) monoacrylate sulfate, poly (ethylene glycol) monomethacrylate sulfate, poly (ethylene glycol) monoacrylate sulfate, allyloxypolyethoxy phosphate, allyloxypolypropoxy sulfate, and allyloxypolypropoxy phosphate. In particular embodiments of the invention, the reactive surfactant may comprise 1 to 40 ethyleneoxy or propoxy units. Other suitable reactive surfactants include polymerizable surfactants having a hydrophilic portion comprising an allylamine sulfonate moiety, an allylamine sulfate moiety, or an allylamine phosphate moiety, and a hydrophobic portion selected from-R or the formula RO- (CH)₂CH₂O)_nWherein R is alkyl or alkyl-substituted phenyl, wherein the alkyl has 1 to 20 carbon atoms, such as 10 to 18 carbon atoms, and n is an integer from 2 to 100, such as 2 to 15, as disclosed in U.S. patent application publication No. 2009/0163619, which is incorporated herein by reference. The hydrophilic portion and the hydrophobic portion may be linked with a covalent bond. Combinations of the above reactive surfactants may be used to prepare the particles.

Particle arrays

In one embodiment of the invention, excess starting materials, by-products, solvents, etc., are removed from the dispersion, as described above. The application of the particle dispersion to a substrate and the electrostatic repulsion of the charged particles causes the particles to self-assemble into an ordered array. The particle dispersion applied to the substrate may comprise 10-70vol.% charged particles, such as 30-65vol.% charged particles. The dispersion may be applied to the substrate to a desired thickness by dipping, spraying, brushing, rolling, curtain coating, flow coating, or die-coating. The wet coating thickness may be 4-50 microns, such as 20 microns. The dispersion coated on the substrate is allowed to dry, after which the material may comprise substantially only the particles, which have self-assembled into a bragg array and accordingly diffract radiation.

It has been found that non-reactive surfactants tend to remain adsorbed on the particle surface even after ultrafiltration or dialysis of the particle dispersion. Upon drying to make the array, the non-reactive surfactant may accumulate in discrete locations of the array and, as described below, may create defects in the final product. In contrast, the reactive surfactants used in the present invention remain bound to the particle surface and are unable to migrate or accumulate to an extent that would produce inhomogeneities in the resulting particle array. In one embodiment, at least 30% of the reactive surfactant present in the dispersion binds to the particles and remains bound to the particles in the CCA when the dispersion is coated to the substrate.

Base body

A dry array of particles (unitary or core-shell) on a substrate can be immobilized in a matrix by coating the array of particles with a fluid curable matrix composition comprising monomers and/or other polymer precursor materials, such as disclosed in U.S. patent No. 6,894,086, to interpenetrate the array of particles with the curable matrix composition. The curable matrix composition may be applied to the dried array of particles via dipping, spraying, brushing, roller coating, gravure coating, curtain coating, flow coating, slot-die coating, or ink-jet coating. By coated is meant that the curable matrix composition at least substantially covers the entirety of the array and at least partially fills the interstitial spaces between the particles.

The matrix material may beThe material for the particles may also be an organic polymer such as polystyrene, polyurethane, acrylic polymer, alkyd polymer, polyester, silicone-containing polymer, epoxy-containing polymer, and/or a polymer derived from an epoxy-containing polymer. In one embodiment, the matrix material is a water soluble or hydrophilic acrylic polymer. Monomers suitable for preparing a water soluble or hydrophilic matrix include, but are not limited to, ethoxylated trimethylolpropane triacrylate, polyethylene glycol (600) diacrylate, polyethylene glycol (400) diacrylate, polyethylene glycol (200) diacrylate, and acrylic acid, followed by curing the matrix composition to produce an organic matrix. Other monomers suitable for preparing a water soluble or hydrophilic polymer matrix may include polyethylene glycol (1000) diacrylate, methoxypolyethylene glycol (350) monoacrylate, methoxypolyethylene glycol (350) monomethacrylate, methoxypolyethylene glycol (550) monoacrylate, ethoxylated₃₀Bisphenol A diacrylate, 2- (2-ethoxyethoxy) ethyl acrylate, acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, polyethylene glycol (600) dimethacrylate, polyethylene glycol (400) dimethacrylate, ethoxylated₃₀Bisphenol a dimethacrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

As detailed below, the array of particles contained in the matrix may be fabricated on a substrate that is used as a temporary support or on a substrate required for the end use of the CCA. By temporary support is meant that the substrate is used to support the preparation of the CCA of the present invention, which is subsequently removed therefrom in a self-supporting form, e.g., a self-supporting film or comminuted particulate matter. The application goals and final forms of CCA are not limited to those described in this application.

In one embodiment, the CCA of the present invention is non-gelatinous and substantially solid. By non-gelatinous, it is meant that the CCA does not contain a fluidizing material, such as water, and is not a hydrogel, nor is it made from a hydrogel. In certain embodiments, the CCA of the present invention comprises substantially only the particles and a matrix with some possible residual solvent and, thus, is substantially solid. The volume ratio of particles to the matrix in the CCA is generally from about 25:75 to about 80: 20.

Imaging

In this CCA, an image may be produced using actinic radiation as described below. In one embodiment, the array of particles is contained within a curable matrix, such as by pre-arranging similarly charged particles in a periodic array on a substrate and coating the array of particles with a curable matrix composition. The periodic array of particles is coated by applying a curable matrix composition to the array by spraying, brushing, roll coating, gravure coating, screen coating, flow coating, slot-die coating, or ink jet coating (as disclosed in U.S. Pat. No. 6,894,086) or by embedding the array of particles into a coating composition on a substrate.

A first portion of the matrix-coated array is exposed to actinic radiation to cure the matrix composition in the exposed portion. The remaining portion of the array that is not exposed to actinic radiation is treated to change the inter-particle spacing in the remainder of the array. After changing the inter-particle spacing of the particles, the array is exposed to actinic radiation to cure the remainder of the matrix. The first exposed portion of the CCA diffracts radiation at a different wavelength band than the remaining portion. For example, the first portion may be exposed to actinic radiation by using a mask or by focusing laser radiation. In one embodiment, when the matrix composition is curable with Ultraviolet (UV) radiation, such as an acrylate-based composition, the actinic radiation used to cure the matrix composition includes UV radiation.

In another embodiment, a first portion of the matrix-coated array is exposed to actinic radiation to cure the curable matrix in the exposed portion. The remaining unexposed portions are altered in a manner that interferes with the array and prevents the remaining portions from diffracting radiation. The ordered periodic array of particles can be disrupted by a variety of techniques including, for example, by applying a solvent to the array that at least partially dissolves the particles, overheating the unexposed portion to destroy the particles, or by mechanically disrupting the particles.

Substrate

The substrate may be a flexible material such as a metal sheet or foil (e.g., aluminum foil), paper or a film (or sheet) of polyester or polyethylene terephthalate (PET), or a non-flexible material such as glass or plastic. By "flexible" is meant that the substrate can be subjected to mechanical stresses, such as bending, stretching, compression, and the like, without significant irreversible change. One suitable substrate is a microporous sheet material. Some examples of microporous sheet materials are disclosed in U.S. patent nos. 4,833,172, 4,861,644, and 6,114,023, the disclosures of which are incorporated herein by reference. Commercially available microporous sheets are by nameSold by PPG Industries, Inc. Other suitable flexible substrates include natural leather, synthetic leather, finished natural leather, finished synthetic leather, suede, vinyl nylon, ethylene-vinyl acetate copolymer foam (EVA foam), Thermoplastic Polyurethane (TPU), fluid-filled balloons, polyolefins and polyolefin blends, polyvinyl acetate and copolymers, polyvinyl chloride and copolymers, polyurethane elastomers, synthetic fabrics, and natural fabrics.

In certain embodiments, the flexible substrate is a compressible substrate. "compressible substrate" and like terms refer to a substrate that is capable of undergoing a compressive deformation and returning to substantially the same shape once the compressive deformation ceases. The term "compressive deformation" refers to a mechanical stress that at least temporarily reduces the volume in at least one direction. As noted above, the CCA of the present invention may be applied to a compressible substrate. The compressible substrate has a compressive strain of, for example, 50% or greater, such as 70%, 75%, or 80% or greater. Specific examples of compressible substrates include those comprising foam and air, liquid, and/or plasma filled polymeric balloons. The "foam" may be an open cell foam and/or a closed cell foam comprising a polymer or natural material. By "open cell foam" is meant that the foam comprises a plurality of interconnected air cavities and by "closed cell foam" is meant that the foam comprises discrete closed cells. Examples of foams include, but are not limited to, polystyrene foams, polyvinyl acetate and/or copolymers, polyvinyl chloride and/or copolymers, poly (meth) acrylimide (imide) foams, polyvinyl chloride foams, polyurethane foams, thermoplastic polyurethane foams, and polyolefin foams and polyolefin blends. Polyolefin foams include, but are not limited to, polypropylene foams, polyethylene foams, and ethylene vinyl acetate ("EVA") foams. "EVA foam" may comprise open cell foam, and/or closed cell foam. The EVA foam may comprise a planar sheet or plate or a molded EVA foam, such as a midsole. Different types of EVA foam have different types of surface porosity. Molded EVA foam may comprise a dense surface or "skin" while a planar sheet or plate may exhibit a porous surface.

The polyurethane substrates of the present invention include aromatic, aliphatic, and hybrid (hybrid examples are silicone polyether or polyester urethane and silicone carbonate urethane) polyester or polyether-based thermoplastic polyurethanes. "Plastic" means any of the common thermoplastic or thermoset synthetic materials, including thermoplastic olefins ("TPOs") such as polyethylene and polypropylene and blends thereof, thermoplastic polyurethanes, polycarbonates, sheet molding compounds, reaction-injection molding compounds, acrylonitrile-based feedstocks, nylons, and the like. A specific plastic is TPO, which comprises polypropylene as well as EPDM (ethylene propylene diene monomer).

The CCA may be applied to the article in a variety of ways. In one embodiment, the CCA is prepared on a substrate and then removed from the substrate and comminuted into a particulate form, such as in the form of flakes. The comminuted material can be incorporated as an additive into a coating composition for coating an article. It is beneficial to minimize haze in coating compositions containing the comminuted feedstock. Reduced haze may be achieved by reducing the refractive index difference between the matrix and the CCA particles. However, a reduction in the refractive index difference generally reduces the refracted ray intensity. Thus, when a minimum haze is required and the refractive index difference is reduced, strength can be maintained by increasing the material thickness, i.e., by increasing the number of particle layers in the array, as compared to materials in which the matrix refractive index and particles differ more from one another.

Coating composition

In one embodiment, the coating composition comprises a "hard coat," such as an alkoxylate. The alkoxylate may be further mixed and/or reacted with other compounds and/or polymers known in the art. Particularly suitable compositions comprise siloxanes formed by at least partial hydrolysis of an organoalkoxysilane such as one of the above formulas. Examples of suitable alkoxylate-containing compounds and methods for their preparation are disclosed in U.S. Pat. Nos. 6,355,189, 6,264,859, 6,469,119, 6,180,248, 5,916,686, 5,401,579, 4,799,963, 5,344,712, 4,731,264, 4,753,827, 4,754,012, 4,814,017, 5,115,023, 5,035,745, 5,231,156, 5,199,979, and 6,106,605, which are incorporated herein by reference.

In certain embodiments, the alkoxylate comprises a glycidyloxy [ (C)₁-C₃) Alkyl radical]III (C)₁-C₄) Alkoxysilane monomer and tetrakis (C)₁-C₆) A combination of alkoxysilane monomers. Glycidyloxy [ (C) groups suitable for use in the coating composition of the present invention₁-C₃) Alkyl radical]III (C)₁-C₄) The alkoxysilane monomer includes glycidoxymethyltriethoxysilane, α -glycidoxyethyltrimethoxysilane, α -glycidoxyethyltriethoxysilane, β -glycidoxyethyltrimethoxysilane, β -glycidoxyethyltriethoxysilane, α -glycidoxy-propyltrimethoxysilane, α -glycidoxypropyltriethoxysilane, β -glycidoxypropyltrimethoxysilane, β -glycidoxypropyltriethoxysilane, γ -glycidoxypropyltrimethoxysilane, and hydrolysates thereof, and/or mixtures of the foregoing silane monomers. In thatThe coating composition of the present invention may be reacted with a glycidyloxy group [ (C)₁-C₃) Alkyl radical]III (C)₁-C₄) Suitable tetra (C) s in combination with alkoxysilanes₁-C₆) The alkoxysilane includes, for example, materials such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetrapropoxysilane, tetrahexoxysilane, and mixtures thereof.

In certain embodiments, glycidyloxy [ (C) present in a coating composition for use in the present invention₁-C₃) Alkyl radical]III (C)₁-C₄) Alkoxysilane and tetrakis (C)₁-C₆) The weight ratio of the alkoxysilane monomer is glycidyloxy [ (C)₁-C₃) Alkyl radical]III (C)₁-C₄) Alkoxysilane to tetra (C)₁-C₆) The alkoxysilane is from 0.5:1 to 100:1, such as from 0.75:1 to 50:1 and, in some cases, from 1:1 to 5: 1. In certain embodiments, the alkoxylate is at least partially hydrolyzed before it is combined with other components of the coating composition, such as the polymer-surrounded color-imparting particles. The above hydrolysis reaction is disclosed in U.S. Pat. No. 3 at column 3, lines 7-28, the citation of which is incorporated herein by reference. In certain embodiments, the amount of water required for hydrolysis of the hydrolyzable alkoxylate(s) is provided. For example, in certain embodiments, water is present in an amount of at least 1.5 moles of water per mole of hydrolyzable alkoxylate. In certain embodiments, it may be sufficient if the atmospheric humidity is sufficient.

In certain embodiments, a catalyst is provided to catalyze the hydrolysis and condensation reactions. In certain embodiments, the catalyst is an acidic material and/or a material different from the acidic material that generates an acid upon exposure to actinic radiation. In certain embodiments, the acidic material is selected from an organic acid, an inorganic acid, or mixtures thereof. Non-limiting examples of such materials include acetic acid, formic acid, glutaric acid, maleic acid, nitric acid, hydrochloric acid, phosphoric acid, hydrofluoric acid, sulfuric acid, or mixtures thereof.

Any material that generates an acid upon exposure to actinic radiation may be used as a hydrolysis and condensation catalyst in the coating compositions of the present invention, such as Lewis and/or Bronsted acids. Non-limiting examples of acid generating compounds include onium salts and iodosyl (iodosyl) salts, aromatic diazonium salts, metallocenium salts, o-nitrobenzaldehyde, polyoxymethylene polymers disclosed in U.S. Pat. No. 3,991,033, o-nitromethanol esters, o-nitrophenyl acetals, their polyesters disclosed in U.S. Pat. No. 3,849,137, and end-capped derivatives disclosed in U.S. Pat. No. 4,086,210, sulfonic acid esters, or N-sulfonyloxy derivatives of aromatic alcohols, aromatic amides or imides containing a carbonyl group in the alpha or beta position relative to the sulfonic acid ester group, aromatic oxime sulfonates, benzoquinone diazides, and resins containing benzoin groups in the chain, such as those disclosed in U.S. Pat. No. 4,368,253. Examples of these radiation activated acid catalysts are also disclosed in U.S. Pat. No. 5,451,345.

In certain embodiments, the acid generating compound is a cationic photoinitiator, such as an onium salt. Non-limiting examples of such materials include diaryliodonium salts and triarylsulfonium salts, which can be used as the saltCD-1012 and CD-1011 are commercially available from Sartomer Company. Other suitable onium salts are disclosed in U.S. Pat. No. 5,639,802, column 8, line 59 to column 10, line 46. Examples of the above onium salts include 4, 4' -dimethyldiphenyliodonium tetrafluoroborate, phenyl-4-octyloxyphenyliodonium hexafluoroantimonate, lauryldiphenyliodonium hexafluoroantimonate, [4- [ (2-tetradecanol) oxy group]Phenyl radical]Phenyliodonium hexafluoroantimonate, and mixtures thereof.

The amount of catalyst used in the coating composition of the present invention may vary widely and depends on the particular material used. All that is required is the amount required to catalyze and/or initiate the hydrolysis and condensation reactions, e.g., a catalytic amount. In certain embodiments, the acidic material and/or acid generating material is used in an amount of 0.01 to 5 weight percent, based on the total weight of the composition.

Applications of

The CCAs prepared according to the present invention may be used in marking devices, including securities, articles and/or their packaging, as well as credentials, especially anti-counterfeiting devices. Non-limiting examples of securities include currency, credit cards, certificates of acceptance, collectibles and trading cards, contracts, deeds or registries (e.g., of cars), soft decals, tickets (e.g., for travel, competitions or parks), stamps, coins, stamps, checks and drafts, stationery (standationary), lottery tickets, chips and/or tokens, regulators (e.g., evidence), key fobs, keys, vests and tracking items, and as part of bar codes. Articles or article packaging may include aircraft parts, automotive parts such as vehicle identification numbers, pharmaceuticals and personal care products, recording media, apparel and footwear, electronics, batteries, ophthalmic devices, wine, food, printing inks and printing consumables, writing instruments, luxury items such as luggage and handbags, sporting goods, software and software packaging, anti-counterfeit seals, artwork (including original art), building materials, munitions, toys, fuel, industrial equipment, biological materials and living goods, jewelry, books, antiques, security items (e.g., fire extinguishers and filtration devices), carpets and other furniture, chemicals, medical devices, pigments and coatings, and windows and transparencies. Examples of credentials carrying a CCA prepared in accordance with the present invention include driver's licenses, identification cards (government, corporate, and educational) passports, visas, marriage certificates, hospital bracelets, and diplomas. These examples are not intended to be limiting but are merely examples with the CCA arrangement of the present invention. The above applications are not intended to be limiting.

Alternatively, the CCA may be prepared in the form of a film, which is then applied to an article via, for example, an adhesive.

Alternatively, the article itself may be used as a substrate (such as an electronics housing or directly on an article such as sporting equipment, apparel, optical lenses, eyeglass frames, apparel including shoes, etc.) by applying the array of particles directly to the housing of the article and coating the array with a matrix composition and then curing it to fix the array.

The CCA of the present invention may be used to authenticate an article, such as to authenticate a document certificate or device or to determine the origin of the article. If an article carrying the CCA exhibits properties such as diffracting certain wavelengths of radiation at a particular intensity level, a document, such as a security card, carrying the CCA of the present invention would be deemed authentic. A "security card" includes a certificate or device that certifies the identity of its carrier or allows access to a device, such as in the form of a badge. The security card may identify the card carrier (e.g. an optical identification card or passport) or may serve as a certificate or means indicating that the carrier will allow access to the security device. For example, a security card that appears authentic may be authenticated by having diffractive properties. Counterfeit security cards may not exhibit this property. Likewise, a consumer of a commodity (such as a pharmaceutical product) provided in a package with an optically variable security device of the present invention can verify its authenticity by testing the diffractive properties of the package. An improper response of the package would be considered counterfeit, and a package exhibiting this property would be considered authentic. Other consumer products may include the CCA of the present invention, such as on an article housing (e.g., an electronic device) or on the surface of an article of clothing (e.g., a shoe).

The CCA may additionally be at least partially covered with a coating composition in a multilayer structure. In one embodiment, the CCA surface is coated with a "hardcoat" coating composition as described above. In another embodiment, the CCA is coated with an anti-reflective coating, such as a multilayer anti-reflective stack. The antireflective coating may be formed from a dielectric material, for example a metal oxide deposited by sputtering, such as Zn₂SnO₄，In₂SO₄，SnO₂，TiO₂，In₂O₃，ZnO，Si₃N₄And/or Bi₂O₃。

The following examples are given to demonstrate the general principles of the invention. The invention is not limited to the specific embodiments given. All parts are by weight unless otherwise stated.

Examples

Example 1

A dispersion of polystyrene particles in water was prepared via the following method. 3.5 grams of sodium bicarbonate from Aldrich Chemical Company, Inc., 3.5 grams of Sipomer PAM 200 from Rhodia, and 4.5 grams of CD552 (methoxypolyethylene glycol (550) monomethacrylate) from Sartomer, 0.1 gram of Sodium Styrene Sulfonate (SSS) from Aldrich Chemical Company, Inc. was mixed with 2000 grams of deionized water and added to a 5-liter flask equipped with a thermocouple, heating mantle, stirrer, reflux condenser, and nitrogen inlet. The mixture was sparged with nitrogen for 45 minutes with stirring and then completely blanketed with nitrogen. Then, 300 g of the styrene monomer mixture was added with stirring. The mixture was then heated to 70 ℃ and held constant for 30 minutes. Next, sodium persulfate from Aldrich Chemical Company, inc. (9.6 grams in 70 grams of deionized water) was added to the mixture with stirring. The mixture temperature was maintained at 70 ℃ for about 2 hours. Thereafter, a pre-emulsified mixture of 380 grams deionized water, 3.0 grams ReasoapSR-10 from Adeak, 270 grams styrene, 1.2 grams SSS, and 0.5 grams sodium persulfate was added to the flask with stirring. The temperature of the mixture was maintained at 70 ℃ for 2 hours. A pre-emulsified mixture of 380 grams deionized water, 3.0 grams Reasoap SR-10 from Adeak, 135 grams styrene, 135 grams methyl methacrylate, 9 grams ethylene glycol dimethacrylate, 1.2 grams SSS, and 0.5 grams sodium persulfate was then added to the flask with stirring. The temperature of the mixture was maintained at 70 ℃ for a further 2 hours. The resulting dispersion was filtered through a 1 micron filter bag.

The polymer dispersion was further ultrafiltered using a 4-inch ultrafiltration jacket with a 2.41-inch polyvinylidene fluoride membrane, both available from PTI Advanced Filtration, inc. oxnard, CA, and pumped using a peristaltic pump at a flow rate of about 170 milliliters per second. Deionized water (2882 g) was added to the dispersion after 2882 g of the ultrafiltrate had been removed. This exchange was repeated several times until 7209 grams of ultrafiltrate had been replaced with 7209 grams of deionized water. Additional ultrafiltrate was then removed until the solids content of the mixture was 42.6 weight percent. The material was coated to a 2 mil thick polyethylene terephthalate (PET) substrate via a slot-die coater from Frontier Industrial Technology, inc., Towanda, PA and dried at 210 degrees fahrenheit for 60 seconds to a dry thickness of about 6 microns. The resulting CCA diffracted radiation at 370nm with a 95% reflectance measured using a Cary 500 spectrophotometer, available from Varian, inc. No visible defect in CCA was observed.

Example 2

Example 1 shows the experiment was repeated except that CD552 was replaced with Sartomer's CD550 (methoxypolyethylene glycol (350) monomethacrylate).

The resulting CCA diffracted radiation at 423 nm with a reflectivity of 85%. No visible defect in CCA was observed.

Comparative examples

A dispersion of polystyrene (latex) particles containing a non-reactive surfactant was prepared via the following method. Sodium bicarbonate (2.5 grams) was mixed with 2400 grams of deionized water and charged to a 5-liter reaction kettle equipped with a thermocouple, heating mantle, stirrer, reflux condenser, and nitrogen inlet. The mixture was sparged with nitrogen for 30 minutes with stirring and then blanketed with nitrogen. Aerosol MA80-I (20.0 g) from Cytec industries, Inc. and 4.0 g Brij 35 (polyoxyethylene (23) lauryl ether), 1.0 g SSS in 144 g deionized water was added to the mixture with stirring. The mixture was heated to about 50 ℃ using a heating mantle. Styrene monomer (500 g) was added to the kettle with stirring. The reaction mixture was heated to 65 ℃. Sodium persulfate (6 grams in 100 grams of deionized water) was added to the mixture with stirring. The temperature was maintained at about 65 ℃ for 4 hours with stirring. A mixture of water (300 g), Brij 35(1 g), styrene (80 g), methyl methacrylate (115 g), ethylene glycol dimethacrylate (10 g), and SSS (0.5 g) was added to the reaction mixture with stirring. The mixture temperature was maintained at 65 ℃ for about four more hours. The resulting polymer dispersion was filtered through a 1 micron filter bag. The polymer dispersion was then ultrafiltered using a 4-inch ultrafiltration chamber with a 2.41-inch polyvinylidene fluoride membrane and pumped using a peristaltic pump at a flow rate of about 170 milliliters per second. Deionized water was added continuously to the dispersion until 11349 grams of ultrafiltrate had been replaced with 11348 grams of deionized water. Additional ultrafiltrate was then removed until the solids content of the mixture was 42.0 wt%. The material was coated to a 2 mil thick polyethylene terephthalate (PET) substrate via a slot-die coater from FrontierIndustrial Technology, inc and dried at 180 degrees fahrenheit for 40 seconds to a dry thickness of about 10 micrometers. The resulting CCA diffracted radiation at 396nm with a reflectivity of 97.0%. The CCA had many visible defects with an average density of 20 defects per square inch of film.

While the invention has been described with respect to the above preferred embodiments, obvious modifications and variations can be made without departing from the spirit and scope of the invention. The scope of the invention is to be determined by the appended claims and their equivalents.

Claims (21)

1. A method of preparing a crystalline colloidal array comprising:

dispersing a monomer in an emulsion comprising a reactive surfactant;

polymerizing the monomer to produce monodisperse polymeric particles, wherein the reactive surfactant is covalently bonded to the polymeric particles, and

the dispersion is applied to a substrate whereby the particles are self-aligned into an ordered periodic array.

2. The method of claim 1, wherein the polymeric particle comprises polystyrene, acrylic polymers, polyurethanes, alkyds, polyesters, silicones, polysulfides, and/or epoxy polymers.

3. The method of claim 1, wherein the reactive surfactant comprises a reactive group that is bonded to the polymeric particles, the reactive group comprising an acrylate group, an allylsulfonate group, an allylsulfate group, and/or an allylphosphate group.

4. The method of claim 3, wherein the reactive surfactant comprises at least one of polyethylene glycol monomethacrylate, polyethylene glycol acrylate, phosphate ester of poly (propylene glycol) monomethacrylate, phosphate ester of poly (propylene glycol) monoacrylate, phosphate ester of poly (ethylene glycol) monomethacrylate, phosphate ester of poly (ethylene glycol) monoacrylate, poly (propylene glycol) monomethacrylate sulfate, poly (ethylene glycol) monoacrylate sulfate, allyloxypolyethoxy phosphate, allyloxypolypropoxy sulfate, and allyloxypolypropoxy phosphate.

5. The method of claim 1, wherein at least 30% of the reactive surfactant is bound to the particle.

6. The method of claim 1, further comprising coating the array of particles with a curable matrix composition and curing the matrix composition to fix the array of particles within the matrix.

7. The method of claim 1, wherein the particles have a unitary structure.

8. The method of claim 1, wherein a first monomer is dispersed in the first stage emulsion and polymerized to produce a particle core and wherein a second monomer is dispersed in the emulsion and polymerized on the particle core, thereby producing a core-shell particle.

9. The method of claim 8, wherein the polymerized monomers are crosslinked and non-film-forming.

10. A crystalline colloidal array comprising an ordered periodic array of polymeric particles, each of said particles having a surface comprising a polymeric material and a reactive surfactant covalently bonded to the surface of the particle and a matrix surrounding the array of polymeric particles.

11. The crystalline colloidal array of claim 10 wherein the polymeric particles comprise polymers including polystyrene, acrylic polymers, polyurethanes, alkyds, polyesters, silicones, polysulfides, and/or epoxy polymers.

12. The crystalline colloidal array of claim 10 wherein the polymeric particles have a unitary structure.

13. The crystalline colloidal array of claim 10 wherein the polymeric particles each comprise a core comprising a first polymer and a shell comprising a second polymer, wherein said first and second polymers are non-film-forming and are different from each other.

14. The crystalline colloidal array of claim 10 wherein the reactive surfactant comprises a reactive group that bonds to the polymeric particles, wherein the reactive group comprises an acrylate group, an allylsulfonate group, an allylsulfate group, and/or an allylphosphate group.

15. The crystalline colloidal array of claim 14 wherein the reactive surfactant comprises at least one of polyethylene glycol monomethacrylate, polyethylene glycol acrylate, phosphate ester of poly (propylene glycol) monomethacrylate, phosphate ester of poly (propylene glycol) monoacrylate, phosphate ester of poly (ethylene glycol) monomethacrylate, phosphate ester of poly (ethylene glycol) monoacrylate, poly (propylene glycol) monomethacrylate sulfate, poly (propylene glycol) monoacrylate sulfate, poly (ethylene glycol) monoacrylate sulfate, allyloxypolyethoxy phosphate, allyloxypolypropoxy sulfate, and allyloxypolypropoxy phosphate.

16. An article bearing the crystalline colloidal array of claim 10.

17. The article of claim 16, wherein said crystalline colloidal array constitutes packaging for said article.

18. The article of claim 16, wherein the article comprises currency.

19. The article of claim 16, wherein the article comprises an identification credential.

20. A film comprising the crystalline colloidal array of claim 10.

21. A coating composition comprising the crystalline colloidal array of claim 10.