Gravity-operated display with patterned microcell array

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 on 4 May 2022. The entire content of any patent, published application, or other published work referenced herein is incorporated by reference. 【0002】 Modern banknotes include several technical features designed to make it difficult for criminals to counterfeit them. While such features add substantial costs to the printing process, they simultaneously deter counterfeiters and increase public confidence in banknotes that will be exchanged for their value. Banknotes in many countries include features such 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 circuits may be justified to deter counterfeiting. Naturally, such security features are also useful in verifying other items such as documents, works of art, clothing, sports memorabilia, historical documents, and software packaging. 【0003】 One feature being considered as a high-tech authenticity marker is the so-called gravity-operated dynamic security device. Such a device can be activated by a user, i.e., a banknote holder, simply by turning the device over, thereby generating a verification signal. The verification signature can be optical or audible, and since the device is gravity-operated, no additional power is required. U.S. Patent No. 10,921,579 (Patent Document 1) ("Patent No. '579") describes several alternative optical devices that may be used for gravity-operated dynamic security devices (including Janus particles in capsules, particles of different densities (heavy particles and buoyant particles), fluids of different densities, and rolling balls). Patent No. '579 does not provide details on the construction of such a device, but rather describes the end product and its potential benefits. For example, the precipitated display example of Patent No. '579 proposes containing high-density particles in a colored fluid, and the high-density particles are contained in one or more containers. However, the properties of the container, methods for producing such a container, and methods for filling such a container with a precipitated mixture are not provided. Furthermore, the final dimensions of the security device described in Patent No. 579 are not suitable for, for example, integration into banknotes. [Prior art documents] [Patent Documents] 【0004】 [Patent Document 1] U.S. Patent No. 10,921,579 [Overview of the Initiative] [Means for solving the problem] 【0005】 An improved gravity-actuated dynamic security device suitable for integration into banknotes is described herein. In one aspect, the gravity-actuated display is an array of microcells, each microcell having a wall, a floor, and an upper opening, the floor of each microcell being light-transmitting, and the array of microcells is 7 g / cm³.3 A first mixture comprising reflective particles having a higher density, a hydrocarbon solvent, and a first soluble dye, wherein the first mixture is placed in at least some of the microcells in an array, and includes a light-transmitting seal layer that seals the first mixture in at least some of the microcells. In one embodiment, the gravity-operated display further comprises a first light-transmitting substrate coupled to an array of microcells. In one embodiment, the gravity-operated display further comprises a second light-transmitting substrate coupled to the light-transmitting seal layer. In one embodiment, the gravity-operated display comprises 1 × 10⁻⁶ 4It does not contain any layer having a conductivity higher than ohms·cm. In one embodiment, the gravity-operated display is thinner than 1 mm. In one embodiment, the gravity-operated display is thinner than 200 μm. In one embodiment, the gravity-operated display further comprises a second mixture comprising reflective particles, a hydrocarbon solvent, and a second soluble dye, wherein the second mixture is disposed in at least some microcells different from at least some of the microcells in which the first mixture is disposed. In one embodiment, the first and second soluble dyes 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 have a maximum dimension of 5 μm to 25 μm. In one embodiment, the reflective particles are metal flakes or metal whisker crystals. In one embodiment, the first soluble dye comprises anthraquinone, phthalocyanine, naphsalen, indole, imidazole, or thioindigo compounds. 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 acrylates, vinyl ethers, or epoxides. In one embodiment, the sealing layer comprises polyvinyl alcohol, polyvinylpyrrolidene, polyurethane, polyisobutylene, or acrylates. In one embodiment, the first mixture further comprises a surfactant. In one embodiment, the first mixture comprises 5-15% surfactant (weight of surfactant / weight of mixture), 20-50% reflective particles (weight of particles / weight of mixture), and 1-8% soluble dye (weight of soluble dye / weight of mixture), with the remainder being a hydrocarbon solvent. 【0006】 In another aspect, the gravity-operated display is an array of microcells, each microcell having a wall, a floor, and an upper opening, and the floor of each microcell is light-transmitting, and the array of microcells is 0.5 g / cm³. 3A first mixture comprising reflective particles having a lower density, a hydrocarbon solvent, and a first soluble dye, wherein the first mixture is placed in at least some of the microcells in an array, and a light-transmitting seal layer seals the first mixture in at least some of the microcells. In one embodiment, the reflective particles are silica, zirconia, or alumina. In one embodiment, the gravity-operated display is 1 × 10⁻⁶ 4 It does not contain any layer having a conductivity higher than ohms·cm. 【0007】 In another aspect, the magneto-gravity operated display is an array of microcells, each microcell having a wall, a floor, and an upper opening, and the floor of each microcell is light-transmitting, with a density of 4 grams / cm³. 3 A first mixture comprising magnetic particles having a higher density, a hydrocarbon solvent, and a first soluble dye, wherein the first mixture is placed in at least some of the microcells in an array, and a light-transmitting seal layer seals the first mixture in at least some of the microcells. In one embodiment, the magnetic particles are made of nickel, iron, manganese, or an oxide thereof. In one embodiment, a magneto-gravity operated display is 1 × 10⁻⁶ 4 It does not contain any layer having a conductivity higher than ohms·cm. The present invention provides, for example, the following items: (Item 1) A gravity-operated display (10, 30, 80), wherein the gravity-operated display is An array of microcells (11), each microcell (11) having a wall (12), a floor (13), and an upper opening, wherein the floor (13) of each microcell is light-transmitting, and the array of microcells 7 grams / cm³ 3 A first mixture comprising reflective particles (15) having a higher density, a hydrocarbon solvent (14), and a first soluble dye, wherein the first mixture is disposed in at least some of the microcells (11) in the array, A light-transmitting seal layer (16) seals the first mixture into at least some of the microcells (11) and A gravity-operated display equipped with this feature. (Item 2) The gravity-operated display according to item 1, wherein the reflective particles (15) comprise silver, tungsten, gold, platinum, nickel, copper, tin, zinc, indium, or a bronze alloy. (Item 3) The first mixture comprises 5-15% surfactant (weight of surfactant / weight of mixture), 20-50% reflective particles (weight of particles / weight of mixture), and 1-8% soluble dye (weight of soluble dye / weight of mixture), with the remainder being a hydrocarbon solvent, as described in item 1 or 2. (Item 4) A gravity-operated display (10, 30, 80), wherein the gravity-operated display is An array of microcells (11), each microcell (11) having a wall (12), a floor (13), and an upper opening, wherein the floor (13) of each microcell is light-transmitting, and the array of microcells 0.5 grams / cm³ 3 A first mixture comprising reflective particles (15) having a lower density, a hydrocarbon solvent (14), and a first soluble dye, wherein the first mixture is placed in at least some of the microcells (11) in the array, A light-transmitting seal layer (16) seals the first mixture into at least some of the microcells (11) and A gravity-operated display equipped with this feature. (Item 5) The gravity-operated display according to item 4, wherein the reflective particles (15) comprise silica, zirconia, or alumina. (Item 6) A gravity-operated display according to any of items 1-5, further comprising a first light-transmitting substrate (17) coupled to an array of microcells (11), and optionally a second light-transmitting substrate (18) coupled to the light-transmitting sealing layer (16). (Item 7) The gravity-operated display is 1 × 10 4 A gravity-actuated display as described in any of items 1-5, which does not contain any layer having a conductivity higher than ohms·cm. (Item 8) The gravity-operated display described above has a thickness of less than 1 mm, and optionally less than 200 μm, as described in any of items 1-5. (Item 9) A gravity-actuated display according to any prior item, further comprising a graphic upper layer (85) wherein the graphic upper layer masks a portion of the gravity-actuated display from the viewer and is color-matched to the reflective particles (15) or the soluble dye. (Item 10) A gravity-operated display according to any one of items 1-5, further comprising a second mixture (34B) comprising the reflective particles (15), the hydrocarbon solvent (14), and a second soluble dye, wherein the second mixture (34B) is disposed in at least some of the microcells (31B) that are different from at least some of the microcells (31A) in which the first mixture (34A) is disposed. (Item 11) The gravity-operated display described in item 10, wherein the first and second soluble dyes are of different colors. (Item 12) The gravity-operated display according to any of items 1-5, wherein the reflective particles (15) have a maximum dimension of 5 μm to 25 μm. (Item 13) The gravity-operated display according to any of items 1-5, wherein the hydrocarbon solvent (14) comprises aliphatic molecules having a molecular weight of 100 g / mol to 300 g / mol. (Item 14) The gravity-operated display according to any one of items 1-5, wherein the microcell walls (12) and floor (13) comprise acrylate, vinyl ether, or epoxide, and the sealing layer (16) comprises polyvinyl alcohol, polyvinylpyrrolidene, polyurethane, polyisobutylene, or acrylate. (Item 15) [[ID=N0]] The gravity-operated display according to any of items 1-5, wherein the first mixture further comprises a surfactant. <I00001> 【0008】 Figure 1A illustrates a cut-away side view of a gravity-operated display in a first stable state, whereby high density reflective particles have settled to the bottom of a plurality of microcells, thereby enabling a viewer to observe the color of a hydrocarbon solvent containing a compatible dye from above. ​​【0009】 [Figure 1B] Figure 1B illustrates the immediate effect of flipping the gravity-operated display shown in Figure 1A upside down. 【0010】 [Figure 1C] Figure 1C illustrates the intermediate state of high-density reflective particles as they settle from the top surface to the bottom surface, due to the different densities of reflective particles compared to hydrocarbon solvents. 【0011】 [Figure 1D] Figure 1D illustrates the gravity-operated display in a second stable state, where the high-density reflective particles have settled again at the bottom of the multiple microcells, so that the bottom surface in Figure 1D corresponds to the top surface in Figure 1A. 【0012】 [Figure 2] Figure 2 shows a cross-section side view of an alternative embodiment in which some of the microcells contain a first mixture containing a first dye, some of the microcells are empty, and some of the microcells contain a second mixture containing a second dye. 【0013】 [Figure 3] Figure 3 illustrates an exemplary top view of a gravity-operated display, in which some of the microcells contain a first mixture containing a first dye, some of the microcells are empty, and some of the microcells contain a second mixture containing a second dye. 【0014】 [Figure 4] Figure 4 shows a method for producing microcells for the present invention using a roll-to-roll process. 【0015】 [Figure 5-1] Figures 5A and 5B detail the production of microcells for a gravity-operated display system using photolithography irradiation through a photomask of a conductive film coated with a thermosetting precursor. 【0016】 [Figure 5-2] Figures 5C and 5D detail an alternative embodiment in which a microcell for a gravity-operated display is fabricated using photolithography. In Figures 5C and 5D, a combination of top and bottom exposure is used, allowing one lateral wall to be cured by top photomask irradiation and the other lateral wall to be cured by bottom irradiation through a light-transmitting substrate. 【0017】 [Figure 6] Figures 6A-6D illustrate the steps of filling and sealing an array of microcells for use in a gravity-operated display. 【0018】 [Figure 7] Figure 7 is a microscopic image of a layer of microcells filled with a mixture containing a blue dye. The cells are sealed with a light-transmitting sealing layer containing polyisobutylene. 【0019】 [Figure 8] Figures 8A–8D illustrate an alternative embodiment of a gravity-operated display, which includes an upper film having a base color and a logo cutout. The logo is invisible in the default state when the base color matches the color of a hydrocarbon solvent containing a compatible dye (Figure 8B). However, when the device is turned over, high-density reflective particles are allowed to settle on the upper layer side, and when the device is turned over a second time, the logo will temporarily "appear" as the high-density reflective particles have moved to the surface adjacent to the upper film (Figure 8C). Over time, the high-density reflective particles will return to their initial positions, and the logo will disappear (Figure 8D). [Modes for carrying out the invention] 【0020】 An improved gravity-actuated display system is described herein, which is suitable for use as a security marker (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 banknotes in general circulation. Since the displays are gravity-actuated, they do not require a power supply or circuitry. Gravity-actuated displays can be fabricated using micro-embossing or photolithography and filled and sealed using a roll-to-roll technique. Microcells can also be patterned to provide custom designs such as official seals. 【0021】 The term “filled” in reference to a microcell (or multiple microcells) means that a mixture is present within the microcell (or multiple microcells). It does not necessarily mean that the entire volume of the microcell is occupied by the mixture. In other words, the term “filled” referring to a microcell (or multiple microcells) includes the concepts of a partially filled microcell (or multiple microcells) and a fully “filled” microcell (or multiple microcells). Similarly, filling a microcell (or multiple microcells) means that a mixture is added into the microcell (or multiple microcells). It does not necessarily mean that a sufficient amount of mixture is added into the microcell to occupy its entire volume. For example, a microcell may be “filled” with a mixture, but leave a small volume relative to the microcell, thereby allowing a sealing layer to occupy a small portion of the microcell, as shown, for example, in Figure 1A. 【0022】 An overview of the gravity-operated display 10 is shown in Figures 1A-1D. The display comprises a plurality of microcells 11, which include walls 12 and a floor 13. The microcells 11 can be arranged as squares, honeycomb, circles, etc. Microcells are typically micro-embossed from thermosetting materials, however, they can be produced by photolithography as described below. In the gravity-operated display 10 of Figures 1A-1D, each microcell 11 is filled with a mixture containing a stained hydrocarbon solvent 14 and high-density reflective particles 15. The hydrocarbon solvent can be branched-chain or straight-chain hydrocarbons or a combination thereof. For example, the hydrocarbon solvent comprises aliphatic molecules having molecular weights of 100 g / mol to 300 g / mol. Suitable hydrocarbon solvents include the OPAR® series (Exxon Mobil) and octane, nonane, decane, and dodecane, which can be purchased from chemical suppliers such as Sigma Aldrich. Typically, reflective particles have a density of 7 grams / cm³. 3 Higher, for example, 8 grams / cm³ 3 Higher, for example, 10 grams / cm³ 3These particles have a higher density, with a maximum dimension of 5 μm to 25 μm, for example, 10 μm to 20 μm. The reflective particles may be metal flakes or metal whisker crystals 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 may also be used. High-density alloys such as brass and bronze may 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, dispersants or surfactants may be added to the mixture to reduce agglomeration between the metal flakes. For example, the hydrocarbon mixture may also include SOLSPERSE® surfactant (Lubrizol, Corp., Wickliffe, OH) or TWEEN® surfactant (Sigma Aldrich). Other dispersants may be chemically adsorbed onto the surface of charged species, i.e., metals such as polyvinylpyrrolidene. In some embodiments, the metal particles / flaks are surface-coated with compatible molecules such as polyvinyl alcohol, polyurethane, or fatty acids, which help keep the metal particles / flaks dispersed. 【0023】 The light-transmitting seal layer 16 can be constructed from, for example, polyvinyl alcohol, polyvinylpyrrolidene, polyurethane, polyisobutylene, acrylate, polyethylene, polyurethane, polycaprolactone, or polysiloxane. While the gravity-operated display 10 can be achieved with only the filled microcells 11 and the light-transmitting seal layer 16, the gravity-operated display typically also includes a first light-transmitting substrate 17 and a second light-transmitting substrate 18. The light-transmitting substrates 17 and 18 can be constructed from any suitable light-transmitting film; however, films with excellent sealing properties, such as polyethylene, e.g., polyethylene terephthalate (PET), are preferred. Other suitable light-transmitting substrates may include films made from acrylate, methacrylate, polyvinylpyrrolidene, or polystyrene. Although not shown in Figures 1A-1D, the gravity-operated display 10 may include an additional optically transparent adhesive layer between the light-transmitting substrates 17, 18 and the microcells 11 and / or light-transmitting sealing 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, it is very flexible and can be used like a ribbon to be incorporated into security documents and banknotes, for example. Such a thin structure does not impair appearance or performance when integrated into security documents and banknotes. In addition, because the gravity-actuated display 10 is very thin, users may not even notice any change in texture when the gravity-actuated display 10 is integrated into security documents or banknotes. In some cases, the gravity-actuated display 10 may be held in place by other structures, which may include adhesives, threads, ribbons, and staples, or the gravity-actuated display 10 may be subjected to pressure between protective transparent layers, with the protective transparent layers extending outward beyond the edges of the gravity-actuated display 10. Suitable protective (barrier) layers include polyvinyl film, polyethylene film such as PET, polyimide film, and polyacrylate film. The gravity-actuated display 10 may also be directly attached to security documents or other objects using an adhesive layer, which may, for example, include polyisobutylene, acrylic, poly(ethylene) glycol, or silicone. 【0025】 The function of the gravity-operated display 10 is illustrated in the transition from Figure 1A to Figure 1D. As shown, gravity (G) is directed downwards in all of Figures 1A-1D. The gravity-operated display starts in a stable display state, as shown in Figure 1A. As shown in Figure 1A, a viewer looking from above will see the color of the stained hydrocarbon solvent 14, since all of the intervening layers are light-transmitting. To activate the display, the user turns the gravity-operated display 10 over, as shown in Figure 1B, and the viewer will then temporarily see the color of the high-density reflective particles 15 present on the top viewing surface (at this point). In other words, since both the light-transmitting seal layer 16 and the light-transmitting substrate 18 are light-transmitting, the user sees the light reflected from the high-density reflective particles 15. Shortly after the gravity-operated display 10 is turned over, the high-density reflective particles 15 will begin to sink due to gravity, as shown in Figure 1C, and will move toward the bottom of the gravity-operated display 10 (at this point). Over time, the high-density reflective particles 15 will sink toward the bottom substrate 17 (at this point), and the user will see the color of the stained hydrocarbon solvent 14, which is very similar, if not identical, to the initial image in Figure 1A. To avoid misunderstanding, a conductive layer (metal foil, carbon paste, conductive ceramic layer, etc., ITO or 1×10) is used. 4 It is not necessary to include any other layer having a conductivity higher than ohms·cm within 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, which are charged and move under a sufficient electric field, or are magnetic and can be actuated in conjunction with a magnetic field, or actuated in any 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 their magnetic or ferromagnetic response. 【0026】 The amount of time between turning over the gravity-operated display 10 and the high-density reflective particles 15 returning to the bottom can be modified by including a free polymer or rheological modifier in the stained hydrocarbon solvent 14. In some embodiments, the time between turning over the gravity-operated display 10 and the high-density reflective particles 15 returning to the bottom will be longer than 0.5 seconds, e.g., longer than 1 second, e.g., longer than 2 seconds, e.g., longer than 3 seconds, e.g., longer than 4 seconds. In some embodiments, the time between turning over the gravity-operated display 10 and the high-density reflective particles 15 returning to the bottom will be shorter than 20 seconds, e.g., shorter than 15 seconds, e.g., shorter than 10 seconds, e.g., shorter than 5 seconds. For example, the time between turning over the gravity-operated display 10 and the high-density reflective particles 15 returning to the bottom may be between 1 and 10 seconds, e.g., between 2 and 8 seconds, e.g., between 3 and 6 seconds. The viscosity of the stained hydrocarbon solvent 14 may be higher than 0.8 centistokes (cSt) at 25°C, i.e., higher than 1.0 centistoke (cSt) at 25°C, i.e., higher than 1.2 centistokes (cSt) at 25°C, i.e., higher than 1.4 centistokes (cSt) at 25°C, i.e., higher than 1.6 centistokes (cSt) at 25°C. 【0027】 As shown in Figure 2, the patterned gravity-actuated 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-actuated 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 hydrocarbon solvent without the high-density reflective particles 15. Filling the non-switching microcells 31C may help seal the surrounding microcells 31A / 31B with a light-transmitting seal layer 16. Filling the non-switching microcells 31C may also facilitate refractive index matching at interfaces traversing the patterned gravity-actuated display 20, for example, if a user needs to look through the patterned gravity-actuated display 20 (e.g., to view additional security markers). In some embodiments, the non-switching microcells 31C may also include a third dye or a first or second dye or some combination thereof. However, since high-density reflective particles 15 are not present, the stained hydrocarbon solvent is always visible in the non-switching microcell 31C. 【0028】 Any dye soluble in hydrocarbon solvents is suitable for incorporation into gravity-operated displays 10, including patterned gravity-operated displays 20. Such dyes may include anthraquinones, phthalocyanines, naphsalenes, indoles, imidazoles, 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 using a small amount of soluble dye (a gravimetric dye / gravimetric hydrocarbon mixture containing high-density reflective particles 15) of about 0.5%, however, the dyed hydrocarbon mixture typically contains 1-8% soluble dye, e.g., 2-5% soluble dye. In some embodiments, the hydrocarbon mixture may also 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 of surfactant / weight of mixture), 20-50% reflective particles (weight of particles / weight of mixture), and 1-8% soluble dye (weight of soluble dye / weight of mixture), with the remainder being a hydrocarbon solvent. 【0029】 Some microcells can be filled with specific mixtures of dyed hydrocarbon solvents, making it possible to generate patterns within the patterned gravity-operated display 20, as shown in Figure 3. By using a slot coating machine with adjustable feeding channels, i.e., using only preferred microcell filling prior to sealing, as discussed below, it is possible to generate various lines, shapes, logos, etc., within the array of microcells. In other embodiments not shown in the figures, it is also possible to combine separate segments of microcells, each separate segment being filled with a differently dyed hydrocarbon fluid to generate patterns within the gravity-operated display. It is also possible to use a microcell array with varying microcell widths or depths to generate patterns that can be used as further indicators of authenticity. For example, a microcell with a depth twice as deep as other microcells may take longer to return to a stable state after the gravity-operated display has been turned over. Alternatively, a microcell with a depth half as deep as other microcells may not achieve a saturated color state when stable, as the high-density reflective particles are partially visible when the high-density reflective particles are at the bottom of the shallower microcells. 【0030】 In another embodiment not shown in the figures, high-density reflective particles can be replaced with buoyant reflective particles that rise to the surface when the gravity-operated display is turned over. Thus, while Figures 1A-1D show reflective particles falling downwards due to gravity, in this embodiment, the reflective particles would rise to the viewing surface. Therefore, the stable default color of the gravity-operated display is typically white or some other reflective color, and when the display is turned over, the color of the dyed hydrocarbon solvent will be visible for a time such 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 inversion would be represented by Figure 1A.) Suitable buoyant reflective particles are typically 0.5 grams / cm³ 3These particles have a lower density and may contain 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-actuated display 10 or patterned gravity-actuated display 20 can be combined with a graphic top layer 85, which masks a portion of the display from the viewer and generates a gravity-actuated top layer display 80. The graphic top layer 85 is typically a thin film, which may be constructed from a light-transmitting film such as PET, thereby printing a pattern, such as a company logo or identification number, onto the film, for example, using screen printing or inkjet printing. In other embodiments, the graphic top layer 85 may be physically cut from a colored film to partially mask the underlying gravity-actuated display from the viewer. The desired pattern may be positive, meaning that the pattern itself is printed on the film or made from cut portions adhered to it. The desired pattern may be negative, meaning that everything other than the pattern is printed on the film or the shape of the pattern is cut from a colored film. The printed portion or cut colored film may be color-matched to the color of reflective particles or soluble dyes. It should be understood that an optically transparent adhesive layer (not shown) would typically be used to bond the graphic upper layer 85 to the lower layer display. In addition, while only one graphic upper layer 85 is shown in Figure 8A, it is easy to apply a second graphic upper layer (not shown in Figure 8A) to the bottom of the display, thus allowing the gravity-operated upper layer display 80 to change its appearance each time it is turned over. Furthermore, the first and second graphic upper layers may contain the same pattern or different patterns. 【0032】 The mechanism of the gravity-operated upper layer display 80 is detailed in Figures 8B-8D, which are top views of the device. As shown in Figure 8B, the logo 90 ("LOGO") is printed as a negative on the graphic upper layer 85, which is made from a transparent film. The area surrounding the logo 90 is color-matched to match the color of the dyed hydrocarbon solvent 14. As a result, when the gravity-operated upper 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 colored hydrocarbon solvent. (The logo 90 in Figures 8B and 8D is slightly darker and shaded to aid in understanding. In actual practice, the logo 90 would be virtually invisible to an untrained eye.) To verify the authenticity of an item to which the gravity-operated upper layer display 80 is attached, the user would turn the gravity-operated upper layer display 80 over and wait for a certain amount of time. 【0033】 (Techniques for constructing microcells) Microcells may be formed in either a batch-to-batch process or a continuous roll-to-roll process, as disclosed in U.S. Patent No. 6,933,098. The latter provides a continuous, low-cost, high-throughput manufacturing technique for producing compartments for use in a variety of applications, including gravity-operated displays. A microcell array suitable for use with the present invention may be produced using micro-embossing, as shown in Figure 4. A male mold 20 may be positioned either above or below the web 24 (not shown), as shown in Figure 4. However, alternative arrangements are also possible. See U.S. Patent No. 7,715,088 (which is incorporated herein in its entirety by reference). A conductive substrate may be constructed by forming a conductive film 21 on a polymer substrate that will serve as a backing for the device. A composition 22 comprising a thermoplastic, thermosetting material, or a precursor thereof is then coated onto the conductive film. The thermoplastic or thermosetting precursor layer is embossed by a male mold in the form of a roller, plate, or belt at a temperature higher than the glass transition temperature of the thermoplastic or thermosetting precursor layer. 【0034】 Thermoplastic or thermosetting precursors for the preparation of microcells may include polyfunctional acrylates or methacrylates, vinyl ethers, epoxides, and their oligomers or polymers. Combinations of polyfunctional epoxides and polyfunctional acrylates are also very useful for achieving desired physicomechanical properties. Crosslinkable oligomers that impart flexibility, such as urethane acrylates or polyester acrylates, may be added to improve the bending resistance of embossed microcells. The composition may consist of polymers, oligomers, monomers, and additives, or oligomers, monomers, and additives only. Glass transition temperature (or T) for this class of material. g The temperature typically ranges from about -70°C to about 150°C, preferably about -20°C to about 50°C. The micro-embossing process is typically T gThis process is carried out at higher temperatures. A heated male mold or a heated housing substrate pressed by the mold may be used to control the micro-embossing temperature and pressure. 【0035】 As shown in Figure 4, the mold is released during or after the curing of the precursor layer and shows an array of microcells 23. The curing of the precursor layer can be achieved by cooling, solvent evaporation, radiation crosslinking, heat, or moisture. If the curing of the thermosetting precursor is achieved by UV radiation, the UV can be irradiated onto the transparent conductive film from the bottom or top of the web, as shown in two figures. Alternatively, a UV lamp can be installed inside the mold. In this case, the mold must be transparent to allow UV light to be irradiated onto the thermosetting precursor layer through a pre-patterned male mold. The male mold can be prepared by any suitable method, such as a diamond swirling 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. With respect to electroplating, the glass substrate is sputtered with a thin layer (typically 3,000 Å) of seed metal such as chromium inconel. The mold is then coated with a layer of photoresist and exposed to UV. A mask is placed between the UV and the photoresist layer. The exposed areas of the photoresist are cured. The unexposed areas are then removed by washing them with a suitable solvent. The remaining cured photoresist is dried and sputtered again using 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 mold floor is typically about 50–400 microns. The master can also be made using other microengineering 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 mold can be made by photomachining using plastic, ceramic, or metal. 【0036】 Prior to applying the UV-curable resin composition, the mold may be treated with a release agent to assist in the demolding process. The UV-curable resin may be degassed prior to dispensing and may optionally contain a solvent. If present, the solvent evaporates readily. The UV-curable resin is dispensed throughout the male mold by any suitable means such as coating, dipping, or casting. The dispenser may be movable or stationary. A conductive film is layered on top of the UV-curable resin. Pressure may be applied as needed 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 forming, pressing devices, or any other similar means. If the male mold is metallic and impermeable, the plastic substrate is typically permeable to the chemical rays used to cure the resin. Conversely, the male mold can be permeable to chemical rays, and the plastic substrate can be impermeable. To obtain good transfer of molded features onto a transfer sheet, the conductive film must have good adhesion to the UV-curable resin, and the UV-curable resin should have good release properties to the mold surface. 【0037】 (Photolithography) Microcells can also be produced using photolithography. Photolithography processes for fabricating microcell arrays are illustrated in Figures 5A and 5B. As shown in Figures 5A and 5B, a microcell array 40 may be prepared by irradiation of a mask 46 with UV light (or alternatively, other forms of radiation, such as an electron beam) through a mask 46 of a radiation-curable material 41a coated on a conductive electrode film 42 by a known method to form walls 41b corresponding to an image projected through the mask 46. The base conductive film 42 is preferably mounted on a support substrate base web 43, which may comprise a plastic material. 【0038】 In Figure 5A, the photomask 46 has dark squares 44 representing opaque areas, and the spaces between the dark squares represent transparent areas 45 of the mask 46. UV light is irradiated onto the radiation-curable material 41a through the transparent areas 45. The irradiation is preferably carried out directly on the radiation-curable material 41a, i.e., the UV light does not pass through the substrate 43 or the base conductor 42 (top irradiation). For this reason, neither the substrate 43 nor the conductor 42 needs to be transparent to UV or any other radiation wavelength employed. 【0039】 As shown in Figure 5B, the irradiated area 41b is cured, and the unirradiated area (protected by the opaque area 44 of the mask 46) is then removed with a suitable solvent or developer to form a microcell 47. The solvent or developer is selected from those commonly used to dissolve radiation-curable materials or to reduce their viscosity, such as methyl ethyl ketone (MEK), toluene, acetone, and isopropanol. Microcell preparation can also be accomplished by placing a photomask directly beneath a conductive film / substrate support web, in which case UV light is irradiated from below through the photomask, and the substrate needs to be transparent to radiation. 【0040】 (Irradiation per image). Yet another alternative method for preparing the microcell array of the present invention by irradiation per image is illustrated in Figures 5C and 5D. When opaque conductive lines are used, the conductive lines can be used as a photomask for irradiation from the bottom. Durable microcell walls are formed by additional irradiation from the top through a second photomask having opaque lines perpendicular to the conductive lines. Figure 5C illustrates the use of both top and bottom irradiation principles to produce the microcell array 50 of the present invention. The base conductive film 52 is opaque and patterned with lines. The base conductor 52 and the radiation-curable material 51a coated on the substrate 53 are exposed from the bottom through the conductive line pattern 52, which serves as a first photomask. The second exposure is carried out from the "top" side through a second photomask 56 having a line pattern perpendicular to the conductive lines 52. The spaces 55 between the lines 54 are substantially transparent to UV light. In this process, the wall material 51b is cured laterally from bottom to top and then perpendicularly from top to bottom, joining together to form a single microcell 57. As shown in Figure 5D, the unirradiated areas are then removed with a solvent or developer, as described above, to reveal the microcell 57. 【0041】 After the microcells are formed, they are filled with a suitable mixture of a stained hydrocarbon solvent and high-density reflective particles. The microcell array 60 can be prepared by any of the methods described above. As shown in the cross-sections in Figures 6A-6D, the microcell walls 61 extend upward from the light-transmitting substrate 63, forming open cells. Optionally, the microcells include a primer layer 62 to passivate the bottom of the microcells and prevent the high-density reflective particles from adhering to the cell floor and / or walls. 【0042】 The microcells are then filled with a stained hydrocarbon mixture 64 containing high-density reflective particles 65. In some embodiments, the stained hydrocarbon mixture 64 containing high-density reflective particles 65 will be sonicated prior to filling the microcells to produce a consistent mixture of high-density reflective particles 65 in the stained 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 stained hydrocarbon mixture 64 is then filled into the various microcells. In some embodiments, filling the microcells with high-density reflective particles 65 is facilitated by light stirring. Filling can be done using a pipette, gravity-filling dispenser, or squeegee. Different microcells may contain different stained hydrocarbon mixtures, as discussed above with respect to Figures 2 and 3, as shown in Figure 6B. The microcells 60 are preferably partially filled to prevent overflow and unintentional mixing of the different stained hydrocarbon mixtures. 【0043】 Microcells can be filled using a variety of techniques. In some embodiments, when a large number of adjacent microcells are to be filled with the same mixture, blade coating can be used to fill the microcells to the depth of the microcell walls 61. In other embodiments, slot dies with positionable channels can be used to fill multiple types of stained hydrocarbon mixtures simultaneously. In yet another embodiment, when different mixtures are to be filled into various nearby microcells, inkjet-type microinjectors can be used to fill the microcells. In yet another embodiment, a microneedle array or pipette can be used to fill an array of microcells with stained hydrocarbon mixtures in the correct order. 【0044】 As shown in Figure 6C, after filling, the microcells are sealed by applying a polymer 66 that forms a light-transmitting sealing layer. The light-transmitting sealing material may include polyvinyl alcohol, polyvinylpyrrolidene, polyurethane, polyisobutylene, or acrylate. In some embodiments, the sealing process may involve exposure to heat, dry high-temperature air, or UV radiation. In most embodiments, the polymer 66 is compatible with the mixture 64 but will not dissolve in the hydrocarbon fluid. Thus, the final microcell structure is capable of withstanding leakage and bending without delamination of the light-transmitting sealing layer. 【0045】 After the microcells 60 are filled, the sealed array can be laminated onto an upper light-transmitting substrate 67 using a thin layer of optically transparent adhesive (OCA) 68. The light-transmitting substrate 67 may be a polyethylene film. Although not shown in Figures 6A-6D, a bottom light-transmitting substrate can also be added to the opposite side of the microcell array using another layer of OCA. In addition, the edges of the microcell array 60 may be sealed with a polymer such as polyurethane to prevent leakage of hydrocarbon fluid. In an alternative embodiment, the filled and sealed microcell array may be encapsulated and sealed with a polyethylene film preform, and the edges may be pinch-sealed using heat or a laser. 【0046】 (Example 1 - Gravity-operated display with silver flecks) The microcell layer was prepared by micro-embossing polyethylene terephthalate (PET) as described above. The stained hydrocarbon mixture was prepared by adding 30 grams of 10 μm silver flakes (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, and the sonicated mixture was then dispensed into the microcells using a pipette, while the remaining stained hydrocarbon mixture was removed from the top of the microcells using a rubber spatula. The filled microcells were overcoated with a light-permeable sealing material consisting of 1 part (by weight) polyurethane (HD2125; Hauthaway Corp.) to 4 parts polyvinyl alcohol (Z410; Mitsubishi Chemical) to 2 parts deionized water. A sealing material with a wet coating thickness of 8 mil (0.21032 mm) was applied to the top of the filled microcells, and the coated sealing material was subsequently dried to create a light-transmitting sealing layer. A micrograph of the filled and sealed microcell layer is shown in Figure 7. The microcell walls (72) are straddled by the polyurethane sealing layer (74), and some of the silver flake particles (75) are visible through the polyurethane sealing layer (74). After the gravity-operated display was left standing, blue appeared from above, as shown in Figure 7. When the gravity-operated display was turned over, the new viewing surface temporarily glowed due to the reflective silver particles on the viewing surface. The glowing surface began to fade rapidly, returning to its original blue color after 3 seconds. 【0047】 (Example 2 - Gravity-operated display with bronze flap) The microcell layer was prepared by micro-embossing polyethylene terephthalate (PET) as described above. The stained hydrocarbon mixture was prepared by adding 15 grams of 50 μm bronze metal flakes (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, and the sonicated mixture was then dispensed into the microcells using a pipette, while the remaining stained hydrocarbon mixture was removed from the top of the microcells using a rubber spatula. The filled microcells were overcoated with a light-permeable sealing material consisting 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 of sealing material with a thickness of 8 mil (0.21032 mm) was applied to the top of a filled microcell. The coated sealing material was then dried to create a light-transmitting sealing layer. When the gravity-operated display was turned over, the new viewing surface temporarily glowed yellow due to reflective bronze particles on the viewing surface. The glowing surface began to fade rapidly, returning to its original blue color after 5 seconds. A subsequent sample was prepared using 1 gram of Solvent Blue 89 HF with respect to 140 mL of Isopar® E, which had a paler blue base color and showed a noticeable transition from glowing yellow to green and then to blue after the device was turned over. 【0048】 It will be apparent to those skilled in the art that numerous changes and modifications can be made without departing from the scope of the invention, in the specific embodiments of the invention described above. Therefore, the entire preceding description should be interpreted as illustrative, not restrictive.

Claims

[Claim 1] A gravity-operated display (10, 30, 80), wherein the gravity-operated display is An array of multiple microcells (11), each microcell (11) having multiple walls (12), a floor (13), and an upper opening, the floor (13) of each microcell being light-transmitting, A first mixture, wherein the first mixture is 7 grams / cm³ ３ The first mixture comprises reflective particles (15) having a higher density than, a hydrocarbon solvent (14), and a first soluble dye, wherein the first mixture is placed in at least some of the plurality of microcells (11) in the array, A light-transmitting seal layer (16) seals the first mixture into at least some of the plurality of microcells (11), A graphic upper layer (85) that masks a portion of the gravity-operated display from the viewer, wherein the color of the graphic upper layer (85) matches the color of the reflective particles (15) or the color of the first soluble dye, and A gravity-operated display equipped with this feature. [Claim 2] The gravity-operated display according to claim 1, wherein the reflective particles (15) include silver, tungsten, gold, platinum, nickel, copper, tin, zinc, indium, or a bronze alloy. [Claim 3] The gravity-operated display according to claim 1, wherein the first mixture comprises 5% to 15% of a surfactant (weight of surfactant / weight of mixture), 20% to 50% of reflective particles (weight of particles / weight of mixture), and 1% to 8% of a soluble dye (weight of soluble dye / weight of mixture), with the remainder being a hydrocarbon solvent. [Claim 4] The gravity-operated display according to claim 2, wherein the first mixture comprises 5% to 15% of a surfactant (weight of surfactant / weight of mixture), 20% to 50% of reflective particles (weight of particles / weight of mixture), and 1% to 8% of a soluble dye (weight of soluble dye / weight of mixture), with the remainder being a hydrocarbon solvent. [Claim 5] A gravity-operated display (10, 30, 80), wherein the gravity-operated display is An array of multiple microcells (11), each microcell (11) having multiple walls (12), a floor (13), and an upper opening, the floor (13) of each microcell being light-transmitting, A first mixture, wherein the first mixture is present in an amount of 0.5 grams / cm³. ３ The first mixture comprises reflective particles (15) having a lower density than, a hydrocarbon solvent (14), and a first soluble dye, wherein the first mixture is placed in at least some of the plurality of microcells (11) in the array, A light-transmitting seal layer (16) seals the first mixture into at least some of the plurality of microcells (11), A graphic upper layer (85) that masks a portion of the gravity-operated display from the viewer, wherein the color of the graphic upper layer (85) matches the color of the reflective particles (15) or the color of the first soluble dye, and A gravity-operated display equipped with this feature. [Claim 6] The gravity-operated display according to claim 5, wherein the reflective particles (15) include silica, zirconia, or alumina. [Claim 7] The gravity-operated display according to any one of claims 1 to 6, further comprising a first light-transmitting substrate (17) coupled to an array of the plurality of microcells (11), and optionally a second light-transmitting substrate (18) coupled to the light-transmitting seal layer (16). [Claim 8] The gravity-operated display is 1 x 10 ４ A gravity-operated display according to any one of claims 1 to 6, which does not include any layer having a conductivity higher than ohms-cm. [Claim 9] The gravity-operated display according to any one of claims 1 to 6, wherein the gravity-operated display has a thickness of less than 1 mm, and optionally less than 200 μm. [Claim 10] The gravity-operated display according to any one of claims 1 to 6, further comprising a second mixture (34B), the second mixture (34B) comprising the reflective particles (15), the hydrocarbon solvent (14), and a second soluble dye, wherein the second mixture (34B) is disposed in at least some of the plurality of microcells (31B) which are different from at least some of the plurality of microcells (31A) in which the first mixture (34A) is disposed. [Claim 11] The gravity-operated display according to claim 10, wherein the first soluble dye and the second soluble dye are different colors. [Claim 12] The gravity-operated display according to any one of claims 1 to 6, wherein the reflective particles (15) have a maximum dimension of 5 μm to 25 μm. [Claim 13] The gravity-operated display according to any one of claims 1 to 6, wherein the hydrocarbon solvent (14) contains aliphatic molecules having a molecular weight of 100 g / mol to 300 g / mol. [Claim 14] The gravity-operated display according to any one of claims 1 to 6, wherein the plurality of walls (12) and the floor (13) of each microcell (11) comprise acrylate, vinyl ether, or epoxide, and the sealing layer (16) comprises polyvinyl alcohol, polyvinylpyrrolidene, polyurethane, polyisobutylene, or acrylate. [Claim 15] The gravity-operated display according to any one of claims 1 to 6, wherein the first mixture further comprises a surfactant.

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