Gravity-actuated display with patterned microcell arrays

Abstract

Gravity-actuated display systems are suitable for use as security markers, for example for incorporation into banknotes. The devices can be made to be very thin and flexible, yet robust enough to withstand the harsh conditions for incorporation into paper currency in general circulation. Because the displays are gravity-actuated, they do not require a power source or circuitry. Gravity-actuated displays can be fabricated using micro-embossing or photolithography, and can be filled and sealed using roll-to-roll techniques. The microcells can also be patterned to provide custom designs, such as official seals.

Description

[Background technology]

[0001] (Related Applications) This application claims priority to U.S. Provisional Patent Application No. 63 / 338,156, filed May 4, 2022. The entire contents of any patents, published applications, or other published works referenced herein are incorporated by reference.

[0002] Modern banknotes contain several technical features to make it difficult for criminals to duplicate them. Although such features add substantial cost to the printing process, they simultaneously deter counterfeiters and increase the public's confidence in the banknotes that will be exchanged for value. Banknotes of many countries contain such features as intaglio printing, watermarks, transparent windows, security ribbons, and microprinting. Depending on the value of the banknote, more expensive features such as holograms and RFID circuitry may be justified to deter unauthorized duplication. Naturally, such security features are also useful in verifying other items such as documents, artwork, clothing, sports memorabilia, historical documents, and software packaging.

[0003] One feature being considered as a high technology authenticity marker is the so-called gravity actuated dynamic security device. Such a device can be actuated by a user, i.e., a bank note holder, simply by flipping the device over, which generates a verification signal. The verification signature can be optical or audible, and since the device is gravity actuated, no additional power source is required. U.S. Pat. No. 10,921,579 ("the '579 patent") describes several alternative optical devices that may be used for gravity actuated dynamic security devices, including Janus particles in a capsule, particles of different densities (heavy and buoyant), fluids of different densities, and rolling spheres. The '579 patent does not provide details regarding the construction of such devices, but rather describes what appears to be the end product and benefits. For example, the sedimentation display example of the '579 patent is proposed to contain high density particles in a colored fluid, the high density particles being contained within one or more containers. However, the nature of the container, the method of producing such a container, and the method of filling such a container with the precipitation mixture are not provided. Furthermore, the final dimensions of the security device described in the '579 patent are not suitable for incorporation into, for example, a banknote. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Pat. No. 10,921,579 Summary of the Invention [Means for solving the problem]

[0005] Described herein is an improved gravity actuated dynamic security device suitable for incorporation into banknotes. In one aspect, the gravity actuated display comprises an array of microcells, each microcell having walls, a floor and a top opening, the floor of each microcell being optically transparent, and a tensile strength of at least 7 grams / cm.3 The display includes a first mixture comprising reflective particles having a higher density, a hydrocarbon solvent, and a first soluble dye, the first mixture disposed in at least some of the microcells in the array, and a light-transmissive sealing layer sealing the first mixture into at least some of the microcells. In one embodiment, the gravity-actuated display further comprises a first light-transmissive substrate coupled to the array of microcells. In one embodiment, the gravity-actuated display further comprises a second light-transmissive substrate coupled to the light-transmissive sealing layer. In one embodiment, the gravity-actuated display includes a 1×10 4The display does not include any layer having a conductivity higher than ohm·cm. In one embodiment, the gravity actuated display is less than 1 mm thick. In one embodiment, the gravity actuated display is less than 200 μm thick. In one embodiment, the gravity actuated display further comprises a second mixture comprising reflective particles, a hydrocarbon solvent, and a second soluble pigment, the second mixture disposed in at least some of the microcells different from at least some of the microcells in which the first mixture is disposed. In one embodiment, the first and second soluble pigments are different colors. In one embodiment, the reflective particles comprise silver, tungsten, gold, platinum, nickel, copper, tin, zinc, or indium. In one embodiment, the reflective particles are between 5 μm and 25 μm in their longest dimension. In one embodiment, the reflective particles are metal flakes or whiskers. In one embodiment, the first soluble pigment comprises an anthraquinone, a phthalocyanine, a naphthalene, an indole, an imidazole, or a thioindigo compound. In one embodiment, the hydrocarbon solvent comprises aliphatic molecules having a molecular weight of 100 g / mol to 300 g / mol. In one embodiment, the microcell walls and floor comprise an acrylate, vinyl ether, or epoxide. In one embodiment, the sealing layer comprises a polyvinyl alcohol, a polyvinyl pyrrolidone, a polyurethane, a polyisobutylene, or an acrylate. In one embodiment, the first mixture further comprises a surfactant. In one embodiment, the first mixture comprises 5-15% surfactant (weight surfactant / weight mixture), 20-50% reflective particles (weight particles / weight mixture), 1-8% soluble pigment (weight soluble pigment / weight mixture), and the remainder is the hydrocarbon solvent.

[0006] In another aspect, a gravity-actuated display includes an array of microcells, each microcell having walls, a floor, and an upper opening, the floor of each microcell being light-transmissive; and a 0.5 gram / cm 3The present invention includes a first mixture comprising reflective particles having a lower density, a hydrocarbon solvent, and a first soluble dye, the first mixture being disposed in at least some of the microcells in the array, and a light-transmissive sealing layer sealing the first mixture in at least some of the microcells. In one embodiment, the reflective particles comprise silica, zirconia, or alumina. In one embodiment, the gravity-actuated display has a 1×10 4 Does not include any layers with a conductivity higher than ohm·cm.

[0007] In another aspect, a magnetic gravity actuated display includes an array of microcells, each microcell having walls, a floor, and an upper opening, the floor of each microcell being optically transparent; and a 4 gram / cm 3 The array includes a first mixture comprising magnetic particles having a higher density, a hydrocarbon solvent, and a first soluble dye, the first mixture being disposed in at least some of the microcells in the array, and a light-transmissive sealing layer sealing the first mixture in at least some of the microcells. In one embodiment, the magnetic particles comprise nickel, iron, manganese, or oxides thereof. In one embodiment, the magnetic gravity actuated display has a resolution of 1×10 4 Does not include any layers with a conductivity higher than ohm·cm. [Brief description of the drawings]

[0008] [Figure 1A] FIG. 1A illustrates a cutaway side view of a gravity-actuated display in a first stable state whereby the high-density reflective particles have settled to the bottom of the multiple microcells, thereby allowing a viewer to observe the color of the hydrocarbon solvent with the compatible dye from above.

[0009] [Figure 1B] FIG. 1B illustrates the immediate effect of flipping the gravity-activated display of FIG. 1A over.

[0010] [Figure 1C] FIG. 1C illustrates the intermediate state of the high density reflective particles as they settle from the top surface to the bottom surface due to the different density of the reflective particles compared to the hydrocarbon solvent.

[0011] [Figure 1D] FIG. 1D illustrates the gravity-actuated display in a second stable state whereby the high-density reflective particles have again settled to the bottom of the multiple microcells, whereby the bottom surface of FIG. 1D corresponds to the top surface of FIG. 1A.

[0012] [Diagram 2] FIG. 2 illustrates a cutaway side view of an alternative embodiment in which some of the microcells contain a first mixture including a first dye, some of the microcells are empty, and some of the microcells contain a second mixture including a second dye.

[0013] [Diagram 3] FIG. 3 illustrates an example top view of a gravity-actuated display, where some of the microcells contain a first mixture including a first dye, some of the microcells are empty, and some of the microcells contain a second mixture including a second dye.

[0014] [Figure 4] FIG. 4 illustrates how a roll-to-roll process can be used to make a microcell for the present invention.

[0015] [Figure 5-1] 5A and 5B detail the production of a microcell for a gravity-actuated display system using photolithographic exposure through a photomask of a conductor film coated with a thermosetting precursor.

[0016] [Figure 5-2]Figures 5C and 5D detail an alternative embodiment in which microcells for gravity-actuated displays are fabricated using photolithography. In Figures 5C and 5D, a combination of top and bottom exposure is used, allowing walls in one lateral direction to be cured by top photomask irradiation and walls in another lateral direction to be cured by bottom irradiation through a light-transmitting substrate.

[0017] [Figure 6] 6A-6D illustrate steps for filling and sealing an array of microcells for use in a gravity-actuated display.

[0018] [Figure 7] Figure 7 is a microscope image of a layer of microcells filled with a mixture containing a blue dye. The cells are sealed with a light-transmitting sealing layer comprising polyisobutylene.

[0019] [Figure 8] 8A-8D illustrate an alternative embodiment of a gravity-activated display, which includes a top film with a base color and a logo cutout. When the base color matches the color of a hydrocarbon solvent containing a compatible dye, the logo is invisible in the default state (FIG. 8B). However, when the device is flipped over, the high-density reflective particles are allowed to settle to the top side, and the device is flipped over a second time, and the logo will "appear" temporarily as the high-density reflective particles have migrated to the surface adjacent to the top film (FIG. 8C). Over time, the high-density reflective particles will return to their initial position and the logo will disappear (FIG. 8D). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Improved gravity-actuated display systems are described herein that are suitable for use as security markers (e.g., incorporated into banknotes). Gravity display devices can be made to be very thin and flexible, yet robust enough to withstand the harsh conditions of paper currency in general circulation. Because the displays are gravity-actuated, they do not require a power source or circuitry. Gravity-actuated displays can be fabricated using micro-embossing or photolithography, and can be filled and sealed using roll-to-roll techniques. The microcells can also be patterned to provide custom designs, such as official seals.

[0021] The term "filled" in relation to a microcell (or microcells) means that a mixture is present within the microcell (or microcells). It does not necessarily mean that the entire volume of the microcell is occupied by the formulation. In other words, the term "filled" with reference to a microcell (or microcells) includes the concept of a partially filled microcell (or microcells) and a completely "filled" microcell (or microcells). Similarly, filling a microcell (or microcells) means that a formulation is added into the microcell (or microcells). It does not necessarily mean that a sufficient amount of the formulation is added into the microcell to occupy its entire volume. For example, a microcell may be "filled" with a mixture but leave a small amount of volume compared to the microcell, whereby the sealing layer occupies a small portion of the microcell, for example as shown in FIG. 1A.

[0022] A schematic of a gravity-activated display 10 is shown in Figs. 1A-1D. The display includes a plurality of microcells 11, which include walls 12 and a floor 13. The microcells 11 may be arranged as squares, honeycombs, circles, etc. The microcells are typically microembossed from a thermosetting material, however, they may be photolithographically produced, as described below. In the gravity-activated display 10 of Figs. 1A-1D, each microcell 11 is filled with a mixture including a dyed hydrocarbon solvent 14 and high-density reflective particles 15. The hydrocarbon solvent may be a branched or straight chain hydrocarbon or a combination thereof. For example, the hydrocarbon solvent comprises aliphatic molecules having a molecular weight of 100 g / mol to 300 g / mol. Suitable hydrocarbon solvents include the OPAR® series (Exxon Mobil), octane, nonane, decane, and dodecane, which may be purchased from chemical suppliers such as Sigma Aldrich. Typically, the reflective particles have a density of 7 grams / cm 3 Higher, e.g., 8 g / cm 3 Higher, e.g., 10 g / cm 3It has a higher density and is 5 μm to 25 μm in the longest dimension, for example, 10 μm to 20 μm in the longest dimension. The reflective particles can be metal flakes or whiskers, such as silver powder D1 (Ames Goldsmith, South Glens Falls, NY) or precipitated silver flakes (Sigma Aldrich, Milwaukee, WI). Other high-density reflective materials, such as tungsten, gold, platinum, nickel, copper, tin, zinc, or indium, can also be used. High-density alloys, such as brass and bronze, can also be used. Flaked brass and bronze can be purchased from craft suppliers, such as Wieland Chase (Montpelier, Ohio) or Advanced Metallics (https: / / www.advancedmetallics.com / ). In some cases, a dispersant or surfactant can be added to the mixture to reduce agglomeration between the metal flakes. For example, the hydrocarbon mixture may additionally contain SOLSPERSE® surfactant (Lubrizol, Corp., Wickliffe, OH) or TWEEN® surfactant (Sigma Aldrich). Other dispersants may be chemisorbed onto the surface of the metal, such as charged species, i.e., polyvinylpyrrolidone. In some embodiments, the metal particles / flakes are surface coated with compatible molecules that help the metal particles / flakes remain dispersed, such as polyvinyl alcohol, polyurethane, fatty acids, etc.

[0023] The light-transmitting sealing layer 16 may be constructed from, for example, polyvinyl alcohol, polyvinylpyrrolidone, polyurethane, polyisobutylene, acrylate, polyethylene, polyurethane, polycaprolactone, or polysiloxane. Although the gravity-actuated display 10 can be achieved with only the filled microcells 11 and the light-transmitting sealing layer 16, the gravity-actuated display typically also includes a first light-transmitting substrate 17 and a second light-transmitting substrate 18. The light-transmitting substrates 17, 18 may be constructed from any suitable light-transmitting film, however, films with good sealing properties, such as polyethylene, e.g., polyethylene terephthalate (PET), are preferred. Other suitable light-transmitting substrates may include films made from acrylates, methacrylates, polyvinylpyrrolidone, or polystyrene. Although not shown in FIGS. 1A-1D, gravity-actuated display 10 may include additional optically clear adhesive layers between light-transmissive substrates 17, 18 and microcell 11 and / or the light-transmissive seal layer.

[0024] The overall thickness of the gravity actuated display 10 can be 1 millimeter or less, for example 800 μm or less, for example 500 μm or less, for example 250 μm or less. For example, the gravity actuated display 10 can be 100 μm to 1 mm thick, for example 200 μm to 800 μm thick, for example 300 μm to 600 μm thick. Because the gravity actuated display 10 is very thin, the gravity actuated display 10 is very flexible and can be used like a ribbon, for example, to be incorporated into security documents and banknotes. Such a thin structure does not impair the appearance or performance when integrated into security documents and banknotes. In addition, because the gravity actuated display 10 is very thin, the user may not be able to feel any change in texture when the gravity actuated display 10 is integrated into security documents or banknotes. In some cases, the gravity activated display 10 may be held in place by other structures, which may include adhesives, threads, ribbons, staples, or the gravity activated display 10 may be pressed between protective transparent layers that extend outward beyond the edges of the gravity activated display 10. Suitable protective (barrier) layers include polyvinyl films, polyethylene films such as PET, polyimide films, and polyacrylate films. It is also possible that the gravity activated display 10 may be secured directly to a security document or other object using an adhesive layer, which may include, for example, polyisobutylene, acrylic, poly(ethylene) glycol, or silicone.

[0025] The function of the gravity-activated display 10 is illustrated in the transition from FIG. 1A to FIG. 1D. As shown, gravity (G) is toward the bottom of the page in all of FIG. 1A-FIG. 1D. The gravity-activated display starts in a stable display state, as shown in FIG. 1A. A viewer looking from above, as shown in FIG. 1A, would see the color of the dyed hydrocarbon solvent 14, since all of the intervening layers are light-transmitting. To activate the display, the user flips the gravity-activated display 10 over, as shown in FIG. 1B, and the viewer would momentarily see the color of the high-density reflective particles 15 present (now) on the top viewing surface. In other words, since both the light-transmitting sealing layer 16 and the light-transmitting substrate 18 are light-transmitting, the user would see light reflected from the high-density reflective particles 15. Shortly after turning over gravity-activated display 10, the high density reflective particles 15 will begin to settle with gravity and move towards the (now) bottom of gravity-activated display 10, as shown in FIG. 1C. Over time, the high density reflective particles 15 will settle to the (now) bottom substrate 17, and the user will see a very similar, if not identical, color of dyed hydrocarbon solvent 14 to the initial view in FIG. 1A. For the avoidance of doubt, it is assumed that the conductive layer (metal foil, carbon paste, a layer of conductive ceramic, etc., ITO or 1×10 4 It is not necessary to include a conductive layer (or some other layer having a conductivity higher than ohms·cm) in the gravity-actuated display 10. However, it is possible to prepare a gravity-actuated display 10 that includes one or more conductive layers. In some embodiments, the gravity-actuated display 10 may include high density reflective particles 15 that are electrically charged and move under a sufficient electric field, or that are magnetic and may be actuated with a magnetic field, or some combination of electric charge, magnetic charge, and gravity. Suitable magnetic, ferromagnetic, or antiferromagnetic particles may include high density reflective particles 15 comprising nickel, iron, iron oxide, manganese oxide, or lanthanum manganese oxide, and such particles may be doped with charge carriers or other materials to increase or decrease the magnetic or ferromagnetic response.

[0026] The amount of time between flipping the gravity-activated display 10 and the high-density reflective particles 15 returning to the bottom can be modified by including free polymers or rheology modifiers in the dyed hydrocarbon solvent 14. In some embodiments, the time between flipping the gravity-activated display 10 and the high-density reflective particles 15 returning to the bottom will be greater than 0.5 seconds, e.g., greater than 1 second, e.g., greater than 2 seconds, e.g., greater than 3 seconds, e.g., greater than 4 seconds. In some embodiments, the time between flipping the gravity-activated display 10 and the high-density reflective particles 15 returning to the bottom will be less than 20 seconds, e.g., less than 15 seconds, e.g., less than 10 seconds, e.g., less than 5 seconds. For example, the time between flipping the gravity-activated display 10 and the high-density reflective particles 15 returning to the bottom can be between 1 and 10 seconds, e.g., between 2 and 8 seconds, e.g., between 3 and 6 seconds. The viscosity of the dyed hydrocarbon solvent 14 may be greater than 0.8 centistokes (cSt) at 25°C, i.e., greater than 1.0 centistokes (cSt) at 25°C, i.e., greater than 1.2 centistokes (cSt) at 25°C, i.e., greater than 1.4 centistokes (cSt) at 25°C, i.e., greater than 1.6 centistokes (cSt) at 25°C.

[0027] As shown in FIG. 2, the patterned gravity-activated display 30 may include one or more microcells 31A containing a first dyed hydrocarbon solvent 34A and one or more microcells 31B containing a second dyed hydrocarbon solvent 34B. The patterned gravity-activated display 30 may also include one or more empty microcells 31C, which are not gravity-switched. Alternatively, the empty microcells 31C may be filled with a hydrocarbon solvent without the high-density reflective particles 15. Filling the non-switched microcells 31C may help seal the surrounding microcells 31A / 31B with a light-transmissive sealing layer 16. Filling the non-switched microcells 31C may also facilitate refractive index matching of interfaces across the patterned gravity-activated display 20, for example, when a user needs to see through the patterned gravity-activated display 20 (e.g., to view additional security markers). In some embodiments, the non-switched microcells 31C may also include a third dye or the first or second dye or some combination thereof. However, due to the absence of high density reflective particles 15, the dyed hydrocarbon solvent is visible in the non-switched microcell 31C at all times.

[0028] Any dye that is soluble in a hydrocarbon solvent is suitable for incorporation into the gravity-actuated display 10, including the patterned gravity-actuated display 20. Such dyes may include anthraquinone, phthalocyanine, naphthalene, indole, imidazole, or thioindigo compounds. Suitable dyes include so-called solvent dyes, such as Solvent Blue 89 HF, Solvent Green M HF, Solvent Purple RS HF, Solvent Red 175 HF, and Solvent Red KI HF, all available from Abbey Color (Philadelphia, PA). Thus, the dyed hydrocarbon solvents used in the present invention may include red, orange, yellow, green, blue, indigo, or violet. The color saturation of the dyed hydrocarbon solvent will depend on the amount of dye added to the hydrocarbon solvent. Adequate saturation can be achieved with as little as 0.5% soluble dye (weight dye / weight hydrocarbon mixture, including high density reflective particles 15); however, the dyed hydrocarbon mixture typically contains 1-8% soluble dye, e.g., 2-5% soluble dye. In some embodiments, the hydrocarbon mixture may additionally contain a surfactant, such as SOLSPERSE® surfactant (Lubrizol, Corp., Wickliffe, OH) or TWEEN® surfactant (Sigma Aldrich). In some embodiments, the dyed hydrocarbon mixture comprises 5-15% surfactant (weight surfactant / weight mixture), 20-50% reflective particles (weight particles / weight mixture), 1-8% soluble dye (weight soluble dye / weight mixture), and the remainder is the hydrocarbon solvent.

[0029] Certain microcells can be filled with a particular mixture of dyed hydrocarbon solvents, thus creating patterns in the patterned gravity-activated display 20, as shown in FIG. 3. Using a slot coating machine with adjustable feed channels, i.e., using only preferential microcell filling prior to sealing, as discussed below, it is possible to create various lines, shapes, logos, etc., in the array of microcells. In other embodiments not shown in the figures, separate segments of microcells can also be combined, with each separate segment filled with a differently dyed hydrocarbon fluid, creating patterns in the gravity-activated display. It is also possible to use microcell arrays with varying microcell widths or depths to create patterns that can be used as further indications of authenticity. For example, a microcell with a depth twice as deep as another microcell may take longer to return to a stable state after the gravity-activated display is flipped over. Alternatively, a microcell with a depth half as deep as another microcell may not achieve a saturated color state when in a stable state, since the high-density reflective particles are partially visible when they are at the bottom of the shallower microcells.

[0030] In another embodiment not shown in the figures, the high density reflective particles can be replaced with buoyant reflective particles that rise to the surface when the gravity-activated display is flipped over. Thus, while Figures 1A-1D show the reflective particles falling downward with gravity, the reflective particles would rise to the viewing surface in this embodiment. Thus, the stable default color of a gravity-activated display would typically be white or some other reflective color, and when the display is flipped over, the color of the dyed hydrocarbon solvent would be seen until such time that the buoyant reflective particles rise to the viewing surface. (For example, Figure 1B would represent the default state, while the state after a temporary flip would be represented by Figure 1A.) Suitable buoyant reflective particles would typically have a density of 0.5 grams / cm 3They have a lower density and may include silica, zirconia, or alumina. Suitable buoyant particles are available from Polysciences, Inc. (Warrington, PA).

[0031] In another embodiment illustrated in Figures 8A-8D, the gravity-activated display 10 or the patterned gravity-activated display 20 can be combined with a graphic overlayer 85, which masks a portion of the display from the viewer, creating the gravity-activated overlayer display 80. The graphic overlayer 85 is typically a thin film that can be constructed from a light-transmitting film such as PET, whereby a pattern, such as a corporate logo or identification number, is printed onto the film, for example, using screen printing or inkjet printing. In other embodiments, the graphic overlayer 85 can be physically cut from a colored film to partially mask the underlying gravity-activated display from the viewer. The desired pattern can be positive-type, meaning that the pattern itself is printed onto the film, or made from cut pieces that are adhered to it. The desired pattern can be negative-type, meaning that everything but the pattern is printed onto the film, or the shape of the pattern is cut out of the colored film. The printed pieces or cut colored film can be color-matched to the color of the reflective particles or the color of the soluble pigments. It should be understood that an optically clear adhesive layer (not shown) would typically be used to bond the graphic overlayer 85 to the underlying display. Additionally, while only one graphic overlayer 85 is shown in FIG. 8A, it is easy to apply a second graphic overlayer (not shown in FIG. 8A) to the bottom of the display, thus allowing the gravity-activated upper layer display 80 to change appearance each time it is flipped over. Additionally, the first and second graphic overlayers may include the same pattern or different patterns.

[0032] The mechanism of the gravity-activated top layer display 80 is detailed in Figures 8B-8D, which are top views of the device. As shown in Figure 8B, a logo 90 ("LOGO") is printed as a negative on a graphic top layer 85, which is made from a transparent film. The area surrounding the logo 90 is color matched to match the dyed hydrocarbon solvent 14. As a result, when the gravity-activated top layer display 80 is viewed from above, the logo 90 is invisible because the area surrounding the logo 90 is the same color as the dyed hydrocarbon solvent. (The logo 90 in Figures 8B and 8D is shaded slightly darker to aid in understanding. In actual practice, the logo 90 will be virtually invisible to the untrained eye.) To verify the authenticity of an item to which the gravity-activated top layer display 80 is attached, a user would turn the gravity-activated top layer display 80 over and wait a period of time.

[0033] Techniques for Constructing Microcells Microcells can be formed in either a batch-by-batch process or a continuous roll-to-roll process, as disclosed in U.S. Pat. No. 6,933,098. The latter provides a continuous, low-cost, high-throughput manufacturing technique for the production of compartments for use in a variety of applications, including gravity-activated displays. Microcell arrays suitable for use with the present invention can be produced using microembossing, as illustrated in FIG. 4. A male die 20 can be placed either above the web 24, as shown in FIG. 4, or below the web 24 (not shown). However, alternative arrangements are possible. See U.S. Pat. No. 7,715,088, which is incorporated herein by reference in its entirety. A conductive substrate can be constructed by forming a conductor film 21 on a polymeric substrate that serves as the backing for the device. A composition 22 comprising a thermoplastic, a thermoset, or a precursor thereof is then coated onto the conductor film. The thermoplastic or thermosetting precursor layer is embossed by a male die in the form of a roller, plate, or belt at a temperature above the glass transition temperature of the thermoplastic or thermosetting precursor layer.

[0034] The thermoplastic or thermosetting precursors for the preparation of the microcells can be multifunctional acrylates or methacrylates, vinyl ethers, epoxides, and oligomers or polymers thereof, etc. A combination of multifunctional epoxides and multifunctional acrylates is also very useful to achieve the desired physico-mechanical properties. Crosslinkable oligomers that confer flexibility, such as urethane acrylates or polyester acrylates, can be added to improve the bending resistance of the embossed microcells. The composition can include polymers, oligomers, monomers, and additives, or only oligomers, monomers, and additives. The glass transition temperature (or T) for this class of materials is g ) usually ranges from about -70°C to about 150°C, preferably from about -20°C to about 50°C. The microembossing process typically gIt is performed at higher temperatures. A heated male die or a heated housing substrate against which the die presses can be used to control the microembossing temperature and pressure.

[0035] As shown in FIG. 4, the mold is released while or after the precursor layer is cured, revealing an array of microcells 23. Curing of the precursor layer can be accomplished by cooling, solvent evaporation, cross-linking by radiation, heat, or moisture. If curing of the thermosetting precursor is accomplished by UV radiation, UV can be irradiated onto the transparent conductor film from the bottom or top of the web, as shown in the two figures. Alternatively, a UV lamp can be installed inside the mold. In this case, the mold must be transparent to allow the UV light to be irradiated onto the thermosetting precursor layer through the pre-patterned male mold. The male mold can be prepared by any suitable method, such as a diamond turning process or a photoresist process, followed by either etching or electroplating. A master template for the male mold can be manufactured by any suitable method, such as electroplating. For electroplating, a glass base is sputtered with a thin layer (typically 3,000 Å) of a seed metal, such as chrome Inconel. The mold is then coated with a layer of photoresist and exposed to UV. A mask is placed between the UV and the layer of photoresist. The exposed areas of the photoresist are hardened. The unexposed areas are then removed by washing them with a suitable solvent. The remaining hardened photoresist is dried and sputtered again with a thin layer of seed metal. The master is then ready for electroforming. A typical material used for electroforming is nickel cobalt. Alternatively, the master can be made from nickel by electroforming or electroless nickel deposition. The bed of the mould is typically around 50-400 microns. The master can also be made using other micro-engineering techniques including electron beam writing, dry etching, chemical etching, laser writing or laser interference as described in 'Replication techniques for micro-optics', SPIE Proc. Vol. 3099, pp. 76-82 (1997). Alternatively, the mould can be made by photomachining using plastics, ceramics or metals.

[0036] Prior to applying the UV-curable resin composition, the mold may be treated with a release agent to aid in the demolding process. The UV-curable resin may be degassed prior to dispensing and may optionally contain a solvent. The solvent, if present, evaporates easily. The UV-curable resin is dispensed over the male mold by any suitable means, such as coating, dipping, casting, etc. The dispenser may be moving or stationary. A conductor film is overlaid on the UV-curable resin. Pressure may be applied, as necessary, to ensure proper bonding between the resin and the plastic and to control the thickness of the microcell floor. Pressure may be applied using lamination rollers, vacuum molding, pressing devices, or any other similar means. If the male mold is metallic and opaque, the plastic substrate is typically transparent to the actinic radiation used to cure the resin. Conversely, the male mold can be transparent to actinic radiation and the plastic substrate can be opaque. To obtain good transfer of the molded features onto the transfer sheet, the conductor film needs to have good adhesion to the UV curable resin, and the UV curable resin should have good release properties with respect to the mold surface.

[0037] Photolithography Microcells can also be produced using photolithography. A photolithography process for fabricating a microcell array is illustrated in Figures 5A and 5B. As shown in Figures 5A and 5B, a microcell array 40 can be prepared by exposure to UV light (or alternatively other forms of radiation, e-beam, etc.) through a mask 46 of a radiation curable material 41a coated on a conductor electrode film 42 by known methods to form walls 41b corresponding to an image projected through the mask 46. The base conductor film 42 is preferably mounted on a supporting substrate base web 43, which may comprise a plastic material.

[0038] In photomask 46, in Fig. 5A, dark squares 44 represent opaque areas and the spaces between the dark squares represent transparent areas 45 of mask 46. UV is irradiated through transparent areas 45 onto radiation curable material 41a. Irradiation is preferably performed directly on radiation curable material 41a, i.e., UV does not pass through substrate 43 or base conductors 42 (top illumination). For this reason, neither substrate 43 nor conductors 42 need to be transparent to UV or other radiation wavelengths employed.

[0039] As shown in Figure 5B, the irradiated areas 41b are cured and the non-irradiated areas (protected by the opaque areas 44 of the mask 46) are then removed by a suitable solvent or developer to form the microcells 47. The solvent or developer is selected from those commonly used to dissolve or reduce the viscosity of radiation curable materials, such as methyl ethyl ketone (MEK), toluene, acetone, isopropanol, etc. Preparation of the microcells can be similarly accomplished by placing a photomask directly underneath the conductor film / substrate support web, in which case UV light is irradiated from the bottom through the photomask and the substrate needs to be transparent to the radiation.

[0040] (Image-wise exposure). Yet another alternative method for the preparation of the inventive microcell array by image-wise exposure is illustrated in Figures 5C and 5D. When opaque conductor lines are used, the conductor lines can be used as a photomask for exposure from the bottom. Durable microcell walls are formed by additional exposure from the top through a second photomask with opaque lines perpendicular to the conductor lines. Figure 5C illustrates the use of both top and bottom exposure principles to produce the inventive microcell array 50. The base conductor film 52 is opaque and patterned with lines. The radiation curable material 51a coated on the base conductor 52 and substrate 53 is exposed from the bottom through the conductor line pattern 52, which serves as the first photomask. A second exposure is performed from the "top" side through a second photomask 56 with a line pattern perpendicular to the conductor lines 52. The spaces 55 between the lines 54 are substantially transparent to UV light. In this process, the wall material 51b is cured sideways from the bottom up and perpendicularly from the top down, bonding to form integral microcells 57. The unirradiated areas are then removed by a solvent or developer as described above to reveal the microcells 57, as shown in FIG. 5D.

[0041] After the microcells are formed, they are filled with a suitable mixture of dyed hydrocarbon solvent and high-density reflective particles. Microcell arrays 60 can be prepared by any of the methods described above. As shown in cross-section in Figures 6A-6D, microcell walls 61 extend upward from an optically transparent substrate 63 to form open cells. Optionally, the microcells include a primer layer 62 to passivate the bottom of the microcell and prevent the high-density reflective particles from sticking to the cell floor and / or walls.

[0042] The microcells are then filled with a dyed hydrocarbon mixture 64 containing high density reflective particles 65. In some embodiments, the dyed hydrocarbon mixture 64 containing high density reflective particles 65 is sonicated prior to filling the microcells, which will result in a consistent mixture of the high density reflective particles 65 in the dyed hydrocarbon mixture 64. In some embodiments not shown in the figures, a desired amount of high density reflective particles 65 is dispersed within the microcells, and the dyed hydrocarbon mixture 64 is then filled into the various microcells. In some embodiments, filling the microcells with the high density reflective particles 65 is facilitated by light agitation. Filling can be done with a pipette, a gravity fill dispenser, or a squeegee. As shown in FIG. 6B, different microcells can contain different dyed hydrocarbon mixtures, as discussed above with respect to FIGS. 2 and 3. The microcells 60 are preferably partially filled to prevent overflow and unintentional mixing of the differently dyed hydrocarbon mixtures.

[0043] The microcells may be filled using a variety of techniques. In some embodiments, where multiple adjacent microcells are to be filled with the same mixture, blade coating may be used to fill the microcells to the depth of the microcell walls 61. In other embodiments, a slot die with positionable channels may be used to simultaneously fill multiple types of dyed hydrocarbon mixtures. In yet other embodiments, where different mixtures are to be filled into various nearby microcells, inkjet type microinjection may be used to fill the microcells. In yet other embodiments, a microneedle array or pipette may be used to fill an array of microcells in the correct order of the dyed hydrocarbon mixture.

[0044] After filling, the microcells are sealed by applying a polymer 66, which becomes a light-transmitting sealing layer, as shown in FIG. 6C. The light-transmitting sealing material may include polyvinyl alcohol, polyvinylpyrrolidone, polyurethane, polyisobutylene, or acrylate. In some embodiments, the sealing process may involve exposure to heat, dry hot air, or UV radiation. In most embodiments, the polymer 66 is compatible with the mixture 64, but will not be dissolved by the hydrocarbon fluid. Thus, the final microcell structure is able to resist leakage and to withstand bending without delamination of the light-transmitting sealing layer.

[0045] After the microcells 60 are filled, the sealed array can be laminated to a top light-transmitting substrate 67 using a thin layer of optically clear adhesive (OCA) 68. The light-transmitting substrate 67 can be a polyethylene film. Although not shown in FIGS. 6A-6D, a bottom light-transmitting substrate can also be added on the other side of the microcell array using another layer of OCA. In addition, the edges of the microcell array 60 can be sealed with a polymer such as polyurethane to prevent leakage of the hydrocarbon fluid. In an alternative embodiment, the filled and sealed microcell array can be encapsulated and sealed with a polyethylene film preform and the edges can be pinch sealed using heat or using a laser.

[0046] (Example 1 - Gravity-activated display with silver flakes) The microcell layer was prepared by microembossing polyethylene terephthalate (PET) as described above. A dyed hydrocarbon mixture was prepared by adding 30 grams of 10 μm silver flake (Sigma Aldrich) to 140 mL of Isopar® E along with 5 mL of Solsperse 19000 (Lubrizol) and 3 grams of Solvent Blue 89 HF (Abbey Color). The mixture was sonicated for 10 minutes, then the sonicated mixture was dispensed into the microcell using a pipette and the remaining dyed hydrocarbon mixture was removed from the top of the microcell using a rubber spatula. The filled microcell was overcoated with a light-transmitting sealant material of 1 part (by weight) polyurethane (HD2125; Hauthaway Corp.) to 4 parts polyvinyl alcohol (Z410; Mitsubishi Chemical) to 2 parts deionized water. A wet coating thickness of 8 mils (0.21032 mm) of sealing material was applied onto the top of the filled microcells, and the coated sealing material was subsequently dried to produce a light-transmitting sealing layer. A microscopic view of the filled and sealed microcell layer is shown in FIG. 7. The microcell walls (72) are spanned by a polyurethane sealing layer (74), and some of the silver flake particles (75) are visible through the polyurethane sealing layer (74). After the gravity-activated display is left standing, a blue color appears from above, as shown in FIG. 7. When the gravity-activated display is flipped over, the new viewing surface briefly glows due to the reflective silver particles in the viewing surface. The glowing surface begins to fade quickly, returning to the original blue color after 3 seconds.

[0047] (Example 2 - Gravity-activated display with bronze flakes) The microcell layer was prepared by microembossing polyethylene terephthalate (PET) as described above. A dyed hydrocarbon mixture was prepared by adding 15 grams of 50 μm bronze metal flake (Bravo Bronze, Lebanon, Tennessee) to 140 mL of Isopar® E along with 5 mL of Solsperse 19000 (Lubrizol) and 3 grams of Solvent Blue 89 HF (Abbey Color). The mixture was sonicated for 10 minutes, then the sonicated mixture was dispensed into the microcell using a pipette and the remaining dyed hydrocarbon mixture was removed from the top of the microcell using a rubber spatula. The filled microcell was overcoated with a light-transmitting sealant material of 1 part (by weight) polyurethane (HD2125; Hauthaway Corp.) to 4 parts polyvinyl alcohol (Z410; Mitsubishi Chemical) to 2 parts deionized water. A wet coating thickness of 8 mils (0.21032 mm) of sealant was applied onto the top of the filled microcells, and the coated sealant was subsequently dried to produce a light-transmitting sealant layer. When the gravity-activated display was flipped over, the new viewing surface momentarily became yellow and glowing due to the reflective bronze particles in the viewing surface. The glowing surface began to fade quickly, returning to the original blue color after 5 seconds. A subsequent sample was prepared using 1 gram of Solvent Blue 89 HF with 140 mL of Isopar® E, which had a lighter blue background color and showed a noticeable transition from glowing yellow to green to blue after the device was flipped over.

[0048] It will be apparent to those skilled in the art that numerous changes and modifications may be made in the specific embodiments of the invention described above without departing from the scope of the invention. Therefore, the whole of the foregoing description is to be interpreted in an illustrative sense, and not in a restrictive sense.

Claims

1. A gravity actuated display (10, 30, 80), comprising: an array of microcells (11), each microcell (11) having walls (12), a floor (13) and an upper opening, said floor (13) of each microcell being optically transparent; 7 grams / cm ３ a first mixture comprising reflective particles (15) having a higher density, a hydrocarbon solvent (14) and a first soluble dye, said first mixture being disposed in at least some of said microcells (11) in said array; a light-transmitting sealing layer (16) for sealing the first mixture into at least some of the microcells (11); A gravity-activated display.

2. 10. The gravity actuated display of claim 1, wherein the reflective particles (15) comprise silver, tungsten, gold, platinum, nickel, copper, tin, zinc, indium, or a bronze alloy.

3. 3. A gravity actuated display as claimed in claim 1 or 2, wherein the first mixture comprises 5-15% surfactant (weight surfactant / weight mixture), 20-50% reflective particles (weight particles / weight mixture), 1-8% soluble pigment (weight soluble pigment / weight mixture), and the remainder is a hydrocarbon solvent.

4. A gravity actuated display (10, 30, 80), comprising: an array of microcells (11), each microcell (11) having walls (12), a floor (13) and an upper opening, said floor (13) of each microcell being optically transparent; 0.5 grams / cm ３ a first mixture comprising reflective particles (15) having a lower density, a hydrocarbon solvent (14) and a first soluble dye, said first mixture being disposed in at least some of said microcells (11) in said array; a light-transmitting sealing layer (16) for sealing the first mixture into at least some of the microcells (11); A gravity-activated display.

5. 5. The gravity actuated display of claim 4, wherein the reflective particles (15) comprise silica, zirconia, or alumina.

6. A gravity-actuated display according to any one of claims 1 to 5, further comprising a first light-transmissive substrate (17) bonded to the array of microcells (11) and, optionally, a second light-transmissive substrate (18) bonded to the light-transmissive sealing layer (16).

7. The gravity-activated display is a 1×10 ４ A gravity actuated display according to any of claims 1-5, which does not include any layer having a conductivity higher than ohm-cm.

8. A gravity activated display according to any preceding claim, wherein the gravity activated display is less than 1 mm thick, optionally less than 200 μm thick.

9. 10. A gravity activated display as claimed in any preceding claim, further comprising a graphic overlayer (85), said graphic overlayer masking a portion of said gravity activated display from a viewer and being colour matched to said reflective particles (15) or said soluble pigments.

10. 6. A gravity-actuated display as claimed in any one of claims 1 to 5, further comprising a second mixture (34B) comprising the reflective particles (15), the hydrocarbon solvent (14) and a second soluble pigment, the second mixture (34B) being disposed in at least some of the microcells (31B) different from the at least some of the microcells (31A) in which the first mixture (34A) is disposed.

11. 11. The gravity actuated display of claim 10, wherein the first and second soluble dyes are different colors.

12. A gravity actuated display according to any preceding claim, wherein the reflective particles (15) are between 5 μm and 25 μm in their longest dimension.

13. A gravity actuated display according to any of claims 1 to 5, wherein the hydrocarbon solvent (14) comprises aliphatic molecules having a molecular weight between 100 g / mol and 300 g / mol.

14. 6. A gravity-actuated display as claimed in any one of claims 1 to 5, wherein the microcell walls (12) and floor (13) comprise an acrylate, a vinyl ether, or an epoxide, and the sealing layer (16) comprises a polyvinyl alcohol, a polyvinylpyrrolidone, a polyurethane, a polyisobutylene, or an acrylate.

15. A gravity actuated display according to any preceding claim, wherein the first mixture further comprises a surfactant.

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