Micro-dome array capable of generating multi-colored retroreflective graphics, manufacturing method therefor, and system for generating pixelated graphics

Abstract

The disclosed method for manufacturing a micro-dome array comprises the steps of: forming an array of micro patterns; performing a reflow of a micro-pattern array so as to form micro-dome patterns; forming a mold having recessed-curved surfaces corresponding to an inverted shape of the micro-dome patterns; and forming a micro-dome array from the mold. The micro-dome array includes a base part and a protrusion part that includes micro domes protruding from a first surface of the base part, and a structural color is generated through retro-reflection on the convex surfaces of the micro domes.

Description

Micro dome array capable of generating multi-color retroreflective graphics, method for manufacturing the same, and system for generating pixelated graphics

[0001] The present invention relates to a microdome array capable of representing structural color through retroreflection. More specifically, the present invention relates to a microdome array capable of generating multi-color retroreflective graphics, a method for manufacturing the same, and a pixelated graphics generation system.

[0002] Structural color is an optical phenomenon resulting from wavelength-selective interference, diffraction, or scattering through light-matter interactions. Structural color can change color depending on the viewing angle and does not fade or discolor unless its structure is altered. Furthermore, because the color is purely derived from the structure, it does not cause chemical toxicity. This characteristic can be effectively utilized in fields such as paints, security applications such as anti-counterfeit patches, and cosmetics.

[0003] Conventional methods for expressing structural color primarily utilize nanostructures. These nanostructures are complex to manufacture and expensive. Recently, research is being conducted on expressing structural color through curved interfaces.

[0004] For example, a high-refractive-index material (microdome) with a convex surface and a diameter of tens of micrometers can produce structural color rings observed on the opposite side through multiple total internal reflections and interference of visible light at the convex surface.

[0005] When attempting to create two-dimensional graphics using these microdomes, methods such as embedding microspheres or directly printing microdomes have been attempted, but the manufacturing time is very long, and the density is limited to prevent adhesion of the microdomes, resulting in a decrease in resolution.

[0006] [Prior Art Literature]

[0007] [Patent Document]

[0008] 1. U.S. Patent Publication No. US2023-0185003

[0009] 2. Korean Patent Publication No. KR2020-0083237

[0010] 3. Chinese Patent Publication No. CN117980170

[0011] One object of the present invention is to provide a micro-dome array capable of generating high-resolution multi-color retroreflective graphics and capable of being manufactured in a simple and reliable manner.

[0012] Another object of the present invention is to provide a method for manufacturing the micro dome array.

[0013] Another object of the present invention is to provide a pixelated graphic generation system using a micro dome array.

[0014] However, the problem to be solved by the present invention is not limited to the problem mentioned above, and may be expanded in various ways without departing from the spirit and scope of the present invention.

[0015] According to exemplary embodiments of the present invention for achieving the above-described object, a method for manufacturing a micro-dome array includes the steps of forming an array of micro-patterns, reflowing the micro-pattern array to form micro-dome patterns, forming a mold having concave curved surfaces corresponding to inverse images of the micro-dome patterns, and forming a micro-dome array from the mold. The micro-dome array includes a base portion and a convex portion including micro-domes protruding from a first surface of the base portion, and structural color is generated through retroreflection on the convex surface of the micro-dome.

[0016] In one embodiment, the ratio of the height to the width of the micro patterns is 0.5 to 4.

[0017] In one embodiment, the angle between the curved surface of the micro dome pattern and the upper surface of the base substrate is greater than or equal to 60°.

[0018] In one embodiment, the microdome array comprises at least one selected from the group consisting of polydimethylsiloxane, polystyrene, polyester, polymethylmethacrylate, polyurethane, polyamide, polyethylene, polypropylene, and polycarbonate.

[0019] In one embodiment, reflow of the micro-pattern array is performed at 60°C to 200°C.

[0020] In one embodiment, the micro-pattern array is formed from a positive photoresist.

[0021] According to one embodiment, the step of forming the mold includes the steps of applying a resin composition onto the micro dome patterns, curing the resin composition, and separating the micro dome patterns and the base substrate from the cured product.

[0022] According to one embodiment, the step of forming the micro dome array includes the steps of applying a resin composition onto concave curved surfaces of the mold, curing the resin composition, and separating the mold from the cured product.

[0023] In one embodiment, the diameter of the micro domes on a plan view is 5 μm to 50 μm.

[0024] In one embodiment, the refractive index of the microdomes is 1.35 to 1.70.

[0025] In one embodiment, the base portion and the micro domes comprise the same material.

[0026] In one embodiment, the micro-patterns have a columnar shape and the micro-domes have a hemispherical shape.

[0027] According to one embodiment, the micro-patterns have a linear shape extending in one direction on a plan view, and the micro-domes have a hemi-cylinder shape.

[0028] According to one embodiment, the convex portion includes a first micro-dome and a second micro-dome having different radii of curvature, and a first structural color generated by light retroreflected from the convex surface of the first micro-dome and a second structural color generated by light retroreflected from the convex surface of the second micro-dome have different colors.

[0029] According to one embodiment, the micro-pattern array includes a first micro-pattern having a first width and a second micro-pattern having a second width smaller than the first width. The first micro-pattern and the second micro-pattern have the same height. The height of the first micro-dome pattern formed by reflow of the first micro-pattern is greater than the height of the second micro-dome pattern formed by reflow of the second micro-pattern.

[0030] A micro-dome array according to exemplary embodiments of the present invention includes a base portion and a convex portion including micro-domes protruding from a first surface of the base portion. The base portion and the convex portion comprise the same material. The micro-domes include a first micro-dome and a second micro-dome having different radii of curvature. A first structural color generated by light retroreflected from the convex surface of the first micro-dome and a second structural color generated by light retroreflected from the convex surface of the second micro-dome have different colors.

[0031] A pixelated graphics generation system according to exemplary embodiments of the present invention includes a micro-dome array including a first pixel area and a second pixel area. The first pixel area includes a plurality of first sub-pixel areas, and the second pixel area includes a plurality of second sub-pixel areas. A first micro-dome having a convex surface is disposed in at least one first sub-pixel area, and a second micro-dome having a convex surface having a different radius of curvature from the convex surface of the first micro-dome is disposed in at least one second sub-pixel area. A first structural color generated by light retroreflected from the convex surface of the first micro-dome and a second structural color generated by light retroreflected from the convex surface of the second micro-dome have different colors.

[0032] As described above, according to exemplary embodiments of the present invention, a single-step reflow process is used to simultaneously produce micro-domes with varying radii of curvature from micro-pillars of different diameters but uniform heights, thereby enabling the creation of multi-color structural color graphics by selecting desired color combinations. Furthermore, variations in brightness can be expressed by adjusting the spacing between the micro-domes.

[0033] The photolithography process for fabricating the above micro-pillars and the reflow process for converting them into micro-domes can be precisely controlled and are highly reproducible, allowing for consistent size and shape of the micro-domes. Consequently, structural color can be precisely generated over large areas with high reliability.

[0034] In addition, unlike structural colors by nanostructures that require periodic arrangement, since colors are expressed by a single micro dome structure, various colors and brightness can be expressed by mixing micro domes of different sizes in a small area or changing the density of the micro domes.

[0035] FIG. 1, FIG. 4 and FIG. 9 are plan views illustrating a method for manufacturing a micro dome array according to one embodiment of the present invention.

[0036] FIGS. 2, 5, 6, 7, 8, and 10 are cross-sectional views illustrating a method for manufacturing a micro dome array according to one embodiment of the present invention.

[0037] FIG. 3 is a plan view illustrating micro pillars in a method for manufacturing a micro dome array according to one embodiment of the present invention.

[0038] FIG. 11 is a cross-sectional view illustrating structural color generation of a micro dome array according to one embodiment of the present invention.

[0039] FIG. 12 is an enlarged cross-sectional view of a single microdome of a microdome array according to one embodiment of the present invention.

[0040] FIG. 13 is a schematic diagram illustrating a change in structural color according to compression of a micro dome array according to one embodiment of the present invention.

[0041] FIG. 14 is a plan view illustrating a micro pattern array in a method for manufacturing a micro dome array according to another embodiment of the present invention.

[0042] FIG. 15 is a perspective view illustrating micro dome patterns obtained from the micro pattern array of FIG. 14.

[0043] Figure 16 is a schematic diagram illustrating a method for manufacturing a micro dome array according to Example 1 of the present invention.

[0044] Figure 17 shows a scanning electron microscope (SEM) image (a) of a micropillar array (average diameter of micropillars: 13.5 μm, distance between pillars: 10 μm) of Example 1 and an SEM image (b) of a microdome pattern obtained after reflow.

[0045] Figure 18 shows an optical photograph (a) taken from the convex side, an optical photograph (b) taken from the flat side, and an enlarged photograph (c) taken from the flat side of the micro dome array (average diameter of micro pillars: 13.5 μm, distance between pillars: 10 μm) of Example 1.

[0046] Figure 19 shows optical photographs taken from the flat surface side when light was irradiated at an incident angle of 31° on the micro dome array of Example 1 (average diameter of micro pillars: 13.5 μm, distance between pillars: 10 μm).

[0047] Figure 20 shows SEM images of micro-pillars of various diameters (left) and micro-dome patterns formed therefrom (right) in Example 1.

[0048] Figure 21 is a photograph showing the structural color of the micro dome array obtained according to the diameter of the micro pillar in Example 1.

[0049] Figure 22 shows a stereoscopic image (a), an enlarged image (b) and a dot array (c) of the photomask in an enlarged area of ​​structural color graphics obtained through a combination of dots (transparent areas) and blank areas of different sizes in the photomask.

[0050] Figure 23 is a photograph showing the structural colors obtained from a single diameter micro dome (1:0, 0:1) and the structural colors obtained from a combination of multi-diameter micro domes (3:1, 1:1, 1:3).

[0051] Figure 24 shows an image (a) and an enlarged image (b) of a multi-color structural color graphic obtained by combining multi-diameter micro-domes.

[0052] Figure 25 shows an SEM photograph of the micro dome array of Example 2 (top), a structural color photograph by vertical irradiation (middle), and a structural color photograph by oblique irradiation (bottom).

[0053] Figure 26 shows a photograph (left) of a single structural color graphic generated by a micro dome array and a photograph of an enlarged area (right).

[0054] FIG. 27 is a plan view illustrating a micro dome array according to one embodiment of the present invention.

[0055] Figure 28 shows a pixelated graphic image using a micro dome array.

[0056] Hereinafter, a micro dome array and a manufacturing method thereof according to embodiments of the present invention will be described in detail with reference to the attached drawings. The present invention can be modified in various ways and can take various forms, and thus specific embodiments will be illustrated and described in detail in the text. However, this is not intended to limit the present invention to a specific disclosed form, but should be understood to include all modifications, equivalents, and substitutes included in the spirit and technical scope of the present invention. In the attached drawings, the dimensions of structures are illustrated larger than actual dimensions to ensure clarity of the present invention.

[0057] The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprise" or "have" indicate the presence of a feature, number, step, operation, component, or combination thereof described in the specification, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, or combinations thereof.

[0058] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0059] FIGS. 1, 4, and 9 are plan views illustrating a method for manufacturing a micro-dome array according to an embodiment of the present invention. FIGS. 2, 5, 6, 7, 8, and 10 are cross-sectional views illustrating a method for manufacturing a micro-dome array according to an embodiment of the present invention. Specifically, FIGS. 2, 5, 6, 7, 8, and 10 illustrate cross-sections taken along line I-I' of FIGS. 1, 4, and 9. FIG. 3 is a plan view illustrating micro-pillars in a method for manufacturing a micro-dome array according to an embodiment of the present invention.

[0060] Referring to FIGS. 1 and 2, a plurality of micro-patterns are formed on a base substrate (10). The micro-patterns can form a micro-dome pattern through a subsequent reflow process.

[0061] In one embodiment, the micro-patterns may be micro-pillars having a width (diameter, W1, W2) on a micro-level. For example, the ratio of the height to the width (aspect ratio, H1 / W1 or H2 / W2) of the micro-pillars may be 0.5 to 4 or 0.7 to 1.8. If the aspect ratio is too small, a lens-shaped pattern rather than a dome-shaped pattern may be obtained after reflow.

[0062] In one embodiment, the micro-pillars may include a plurality of patterns having different widths. For example, the micro-pillars may include a first micro-pillar (22) having a first width (W1) and a second micro-pillar (24) having a second width (W2) smaller than the first width (W1). The micro-pillars may be formed from the same photoresist film (photosensitive film). Therefore, the height (H1) of the first micro-pillar (22) and the height (H2) of the second micro-pillar (24) may be the same.

[0063] The first micro-pillars (22) and the second micro-pillars (24) may each be formed in multiple numbers to form a group. Alternatively, the first micro-pillars (22) may be dispersed between the second micro-pillars (24).

[0064] However, embodiments of the present invention are not limited thereto, and the micro-pillar array may include three or more micro-pillars having different widths, or may be composed of micro-pillars having a single width.

[0065] According to one embodiment, the micro-pillars may be micro-pillars having a circular shape in plan view. However, embodiments of the present invention are not limited thereto, and as illustrated in FIG. 3, in addition to a circular shape (a), the micro-pillars may have various shapes such as a square shape (b), an octagonal shape (c), etc. In addition, the micro-pillars may have different planar shapes. For example, the first micro-pillar (22) may have a square-shaped plane, and the second micro-pillar (24) may have a circular-shaped plane.

[0066] The above base substrate (10) may include various materials such as silicon, quartz, glass, and polymer, but it may be preferable to include a material with high heat resistance so that the substrate shape can be maintained during the reflow process.

[0067] The above micro-pillars can be formed through a photolithography process. For example, a photoresist composition is applied to the base substrate (10) to form a photosensitive film. Next, a portion of the photosensitive film corresponding to the micro-pillars is selectively exposed, or the portion corresponding to the micro-pillars is masked and the remaining portion is selectively exposed. Next, a developer is applied to the photosensitive film to remove portions not corresponding to the micro-pillars, thereby forming the micro-pillars.

[0068] In one embodiment, the photoresist composition may be of a positive type. When the photoresist composition is of a positive type, the solubility thereof increases upon exposure, so that the portion corresponding to the micro-pillars can be masked and the exposure process can be performed. When the photoresist composition is of a negative type, a cross-linking reaction may occur upon exposure, making it difficult to control shape deformation due to reflow.

[0069] The photoresist composition may include a polymer. For example, the photoresist composition may include a phenol resin, an epoxy resin, an acrylic resin, etc., and a commercially available positive photoresist composition may be used.

[0070] Referring to FIGS. 4 and 5, the micro-pillars are heated to form micro-dome patterns through reflow. A micro-dome pattern can be defined as a pattern that forms a dome shape by having a convex surface. For example, the micro-dome pattern can have a hemisphere shape, which has a circular shape in a plan view. In order to distinguish the dome pattern from a lens pattern, the dome pattern can be defined as having a three-dimensional shape defined by an overall convex curved surface and a flat lower surface, and a contact angle (the angle formed by the curved surface with respect to the base surface) of 60° or more.

[0071] When the above micro-pillars include first and second micro-pillars having different widths, the micro-dome patterns formed therefrom may also have different sizes. For example, the first micro-dome pattern (32) formed from the first micro-pillar (22) may have a first radius of curvature (R1), and the second micro-dome pattern (34) formed from the second micro-pillar (24) may have a second radius of curvature (R2) smaller than the first radius of curvature (R1).

[0072] Since the above micro dome pattern is formed through a reflow process, it may have a wider width than the micro pillar. Accordingly, the width (D1) of the first micro dome pattern (32) is larger than the width (W1) of the first micro pillar, and the width (D2) of the second micro dome pattern (34) is larger than the width (W2) of the second micro pillar. For example, the width of the micro dome pattern may be 1.1 to 1.3 times larger than the width of the micro pillar.

[0073] The above micro dome pattern may have a lower height than the micro pillar. In addition, micro dome patterns formed from micro pillars of different widths may have different heights. For example, the height (Ha) of the first micro dome pattern (32) may be greater than the height (Hb) of the second micro dome pattern (34).

[0074] For example, the heating temperature for the reflow process may be 60°C to 200°C. According to one embodiment, the heating temperature for the reflow process may be performed at a temperature that is 15°C to 35°C higher than the hard bake temperature of the micro pillar. For example, the reflow process may be performed at 125°C to 145°C. If the reflow process temperature is too low, a continuous curved surface may not be obtained, which may reduce the structural color intensity. In addition, if the reflow process temperature is excessive, the radius of curvature may increase, which may change the micro dome pattern into a microlens shape, and it is difficult to induce total internal reflection in the microlens structure.

[0075] Referring to FIGS. 6 and 7, a mold resin is coated on a base substrate (10) on which the micro dome patterns are formed and cured to form a mold (40) having concave curved surfaces (42, 44) corresponding to the micro dome patterns. After forming the mold (40), the base substrate (10) and the micro dome patterns (32, 34) can be removed.

[0076] In one embodiment, polydimethylsiloxane (PDMS) may be used as a material for forming the mold (40). However, embodiments of the present invention are not limited thereto, and various mold materials capable of transferring the shape of the micro dome patterns may be used.

[0077] Referring to FIGS. 8 to 10, a micro dome array (50) is obtained from the mold (40). For example, as illustrated in FIG. 8, a resin composition may be applied onto the surface of a mold having the concave curved surfaces (42, 44) and cured to obtain the micro dome array (50). However, embodiments of the present invention are not limited thereto, and after applying a resin composition onto a substrate, the shape of the mold (40) may be transferred by pressing the resin composition with the mold (40).

[0078] In one embodiment, the resin composition may be a composition for forming polydimethylsiloxane. However, embodiments of the present invention are not limited thereto, and various resin compositions having an appropriate refractive index, for example, a refractive index after curing of 1.35 to 1.70, may be used. For example, the microdome array (50) may include polydimethylsiloxane, polystyrene, polyester, polymethyl methacrylate, polyurethane, polyamide, polyethylene, polypropylene, polycarbonate, or a combination thereof.

[0079] According to one embodiment, the micro dome array (50) may include a base portion (50a) and a convex portion (50b). The base portion (50a) may have a two-dimensional film shape extending in a horizontal direction. The convex portion (50b) may include a plurality of micro domes that protrude from a first surface of the base portion (50a) and have convex surfaces (SS1, SS2). The base portion (50a) and the convex portion (50b) may be formed integrally by including the same material.

[0080] The second surface of the base portion (50a) may have a flat shape. That is, the second surface of the base portion (50a) may form a flat surface (a light-emitting surface of retroreflected light) of the micro dome array.

[0081] According to one embodiment, the convex portion (50b) may include a first micro dome (52) having a first radius of curvature (R1) and a second micro dome (54) having a second radius of curvature (R2) smaller than the first radius of curvature (R1).

[0082] Fig. 11 is a cross-sectional view illustrating the generation of structural color in a microdome array according to one embodiment of the present invention. Fig. 12 is an enlarged cross-sectional view illustrating a single microdome in a microdome array according to one embodiment of the present invention. Fig. 13 is a schematic diagram illustrating the change in structural color due to compression in a microdome array according to one embodiment of the present invention.

[0083] Referring to Fig. 11, the light entering the micro dome array (50) reaches the critical angle (=sin -1 When light is incident on the convex surfaces (SS1, SS2) of the micro-domes at an angle greater than (n1 / n2), where n1 = refractive index of the external medium and n2 = refractive index of the micro-dome, total reflection may occur. For example, when the external medium is air (refractive index = 1) and the micro-dome array is composed of PDMS (refractive index = 1.41), the critical angle may be 44.7°.

[0084] The totally reflected light may be re-incident on the convex surfaces (SS1, SS2), and thus, multiple total reflections may occur along the convex surfaces (SS1, SS2). The light incident on the light-emitting surface (ES) after repeated total reflections is emitted to the outside of the micro-dome array (50). As interference occurs between the light and light with different reflection counts, structural color may be observed in a ring shape along the periphery of the micro-domes when observed from the light-emitting surface (ES).

[0085] The color of the structural color may vary depending on the radius of curvature, refractive index, observation angle, refractive index of the surrounding medium, etc. of the micro-domes. For example, the structural color of the first light (SC1) emitted after being totally reflected by the first convex surface (SS1) of the first micro-dome (52) may be different from the structural color of the second light (SC2) emitted after being totally reflected by the second convex surface (SS2) of the second micro-dome (54). For example, the structural color of the first light (SC1) may have a color with a longer wavelength than the structural color of the second light (SC2). Therefore, the first area (A1) where the first micro-domes (52) are arranged and the second area (A2) where the second micro-domes (54) are arranged may generate different structural colors. Therefore, by combining micro-domes that generate different structural colors, a structural color graphic composed of multiple colors can be generated. In addition, a micro dome having a first structural color and a micro dome having a second structural color can be combined in the same or different ratios so that an external observer can perceive a third structural color different from the first structural color and the second structural color.

[0086] In this application, "structural color" is not limited to a color with saturation, and may include white or a color close to white. Furthermore, "first structural color," "second structural color," and the like do not imply a specific color, but are used to distinguish between different colors, and may refer to any color, including chromatic and achromatic colors.

[0087] Hereinafter, the specific shape of the first micro dome (52) will be described with reference to FIG. 12. The following description can be equally applied to the shape of the second micro dome (54).

[0088] The diameter (D1) of the first micro dome (52) may be defined as the diameter of a circular shape on a plan view, projected onto a base plane (BS) connecting the edges of the first convex surface (SS1). The base plane (BS) may correspond to the first surface of the base portion (50a). If the diameter of the first micro dome (52) is excessively large, multiple reflection peaks may occur in the visible range, making it difficult to display structural color. In addition, if the diameter of the first micro dome (52) is excessively small, the path through which total reflection can occur may be reduced, thereby reducing the brightness of the structural color. According to one embodiment, the diameter of the first micro dome (52) may be 5 ㎛ to 50 ㎛, 8 ㎛ to 30 ㎛, or 10 ㎛ to 25 ㎛.

[0089] According to one embodiment, the angle (θ1, contact angle) of the first convex surface (SS1) with respect to the base surface (BS) may be 60° or greater, preferably 70° or greater, and more preferably 80° or greater. For example, the contact angle may be 70° to 110° or 80° to 100°. If the contact angle is too small, a shape similar to a lens may be obtained, which may weaken the brightness of the structural color.

[0090] The above structural color may be well expressed when directional light (e.g., directional white light) is irradiated onto the microdome array, and may not be expressed when non-directional light, such as ambient light, is incident due to low interference intensity. Accordingly, the microdome array may be transparent in everyday environments and have structural color that appears when directional light is irradiated. Using these characteristics, the microdome array may be used to produce identification marks, such as anti-counterfeiting patterns.

[0091] In addition, when an external force is applied, the structural color may be selectively or sequentially changed depending on the height of the micro-domes. Referring to FIG. 13, a first structural color (SC1) may be generated by a first micro-dome, and a second structural color (SC2) may be generated by a second micro-dome having a smaller height than the first micro-dome. When the micro-dome array is compressed or pressed, the first micro-dome first contacts the lower floor, and the total reflection at the curved surface of the first micro-dome is reduced due to a change in the refractive index of the external medium (refractive index of air > refractive index of the flooring material (e.g., glass)), so that the first structural color (SC1) is not generated. In addition, when the compression progresses further, the second micro-dome may contact the lower floor, so that the second structural color (SC2) is not generated.

[0092] Fig. 14 is a plan view illustrating a micro pattern array in a method for manufacturing a micro dome array according to another embodiment of the present invention. Fig. 15 is a perspective view illustrating micro dome patterns obtained from the micro pattern array of Fig. 14.

[0093] Referring to FIG. 14, micro-patterns formed through photolithography may have a shape of a linear pattern extending in one direction on a plan view. In the micro-patterns, the width may be defined as the length of a short side. For example, the micro-pattern array may include a first micro-pattern (122) having a first width (W1) and a second micro-pattern (124) having a second width (W2) smaller than the first width (W1). The cross-sectional shapes of the first micro-pattern (122) and the second micro-pattern (124) may be substantially the same as the cross-sectional shapes of the first micro-pillar (22) and the second micro-pillar (24) illustrated in FIG. 2.

[0094] Referring to FIG. 15, a first micro dome pattern (132) and a second micro dome pattern (134) having a hemicylindrical shape can be formed from the first micro pattern (122) and the second micro pattern (124) through a reflow process. The cross-sections of the first micro dome pattern (132) and the second micro dome pattern (134) can be identical to the cross-sections of the first micro dome pattern (32) and the second micro dome pattern (34) illustrated in FIG. 5.

[0095] After forming a reverse mold from the first micro dome pattern (132) and the second micro dome pattern (134), a micro dome array having a convex portion of the same shape as the first micro dome pattern (132) and the second micro dome pattern (134) can be formed using the mold.

[0096] As described above, a micro-dome array having a cylindrical dome shape can also generate structural color. However, since the dome is not hemispherical, the structural color can be observed at the periphery of the curved surface along the length of the cylinder.

[0097] FIG. 27 is a plan view illustrating a micro dome array according to one embodiment of the present invention.

[0098] A micro dome array according to one embodiment of the present invention can be used to generate pixelated graphics (images).

[0099] Referring to FIG. 27, the micro dome array may include a first pixel area (P1) and a second pixel area (P2). The first pixel area (P1) may include a plurality of first sub-pixel areas (SP1), and the second pixel area (P2) may include a plurality of second sub-pixel areas (SP2). The first pixel area (P1) and the second pixel area (P2) may have the same area, and the first sub-pixel area (SP1) and the second sub-pixel area (SP2) may have different areas.

[0100] According to one embodiment, the first subpixel area (SP1) may have a larger area than the second subpixel area (SP2), and the number of the first subpixel areas (SP1) in the first pixel area (P1) may be smaller than the number of the second subpixel areas (SP2) in the second pixel area (P2). For example, the first pixel area (P1) may include first subpixel areas (SP1) arranged in an nxn matrix (n is a natural number greater than 2), and the second pixel area (P2) may include second subpixel areas (SP2) arranged in an mxm matrix (m is a natural number greater than n).

[0101] The first pixel area (P1) can display an achromatic color. For example, the first pixel area (P1) can display white, black, gray, or a combination thereof. At least one first micro dome (62) that generates a first structural color corresponding to white is arranged within the first pixel area (P1). A first sub-pixel area (SP1) in which the first micro dome (62) is not arranged can express black. A grayscale of the first pixel area (P1) or a grayscale of a certain area can be expressed by a combination of the first sub-pixel area (SP1) in which the first micro dome (62) is arranged and the first sub-pixel area (SP1) in which the first micro dome (62) is not arranged.

[0102] The second pixel area (P2) may include a chromatic color. At least one second micro-dome (64) that generates a second structural color corresponding to the chromatic color is arranged in the second pixel area (P2). The convex surface of the second micro-dome (64) may have a different radius of curvature from the convex surface of the first micro-dome (62). Accordingly, the second micro-dome (64) may generate a different structural color from the first micro-dome (62). For example, the diameter of the second micro-dome (64) in a plan view may be smaller than the diameter of the first micro-dome (62) in a plan view.

[0103] A plurality of second micro-domes (64) may be arranged in the second pixel area (P2). Micro-domes that generate different structural colors (having convex surfaces with different radii of curvature) may be arranged in the second pixel area (P2). In this way, by combining different structural colors in a unit pixel area, colors that are not generated by individual micro-domes can be expressed. For example, a second micro-dome that generates a second structural color and a third micro-dome that generates a third structural color may be arranged in the second pixel area (P2). The micro-domes that generate different structural colors may have different sizes. The second pixel area (P2) may include a second sub-pixel area (SP2) in which no micro-domes are arranged. The second sub-pixel area (SP2) in which the micro-domes are not arranged may express black.

[0104] According to embodiments of the present invention, a single-step reflow process is used to simultaneously produce micro-domes with varying radii of curvature from micro-pillars of different diameters but uniform heights, thereby enabling the creation of multi-color structural color graphics by selecting desired color combinations. Furthermore, variations in brightness can be expressed by adjusting the spacing between the micro-domes.

[0105] The photolithography process for fabricating the above micro-pillars and the reflow process for converting them into micro-domes can be precisely controlled and are highly reproducible, allowing for consistent size and shape of the micro-domes. Consequently, structural color can be precisely generated over large areas with high reliability.

[0106] In addition, unlike structural colors by nanostructures that require periodic arrangement, since colors are expressed by a single micro dome structure, various colors and brightness can be expressed by mixing micro domes of different sizes in a small area or changing the density of the micro domes.

[0107] By doing this, by pixelating the image to be created and extracting the primary color (RGB) value from each pixel, and based on this configuring each pixel with a micro dome and space of a specific size, an image with a high resolution almost identical to the image above can be reproduced.

[0108] Hereinafter, a method for manufacturing a microdome array and its effects according to exemplary embodiments will be described in detail through specific experimental examples. However, the above experimental examples are provided for illustrative purposes only, and the scope of the present invention is not limited to the contents provided in the above experimental examples.

[0109] Example 1

[0110] Fig. 16 is a schematic diagram illustrating a method for manufacturing a micro dome array according to Example 1 of the present invention. As illustrated in Fig. 16, a micro dome array was obtained through the following method.

[0111] The surface of a silicon wafer was treated with hexamethyldisilazane to make it hydrophobic. A positive photoresist (AZ12XT-20PL-10, AZ Electronic Materials) was spin-coated on the silicon wafer at 2,000 rpm for 10 seconds, followed by soft baking at 105°C for 180 seconds to obtain a photosensitive film with a thickness of 14 μm.

[0112] Subsequently, UV exposure was performed at 195 mW / cm2 through a photomask having a microdot array, and baking was performed at 90°C for 60 seconds. The exposed photosensitive film was developed with an alkaline solution (AZ300MIF, AZ Electronic Material) to form micropillar arrays with a height of 13.6 μm.

[0113] To reflow the micro-pillars, the wafer was heated to 135°C for 5 minutes on a hot plate to form a micro-dome pattern from the micro-pillars.

[0114] A mixture of PDMS prepolymer (Sylgard 184, Dow Corning) and a curing agent (weight ratio of prepolymer:curing agent = 10:1) was poured onto the above micro dome pattern and cured at 80°C for 4 hours in an oven. Subsequently, the PDMS mold (having the negative shape of the micro dome pattern) was treated with oxygen plasma for 300 seconds and treated with trichloro(1H,1H,2H,2H-perfluorooctyl)silane (Sigma-Aldrich) through deposition. The PDMS mixture (prepolymer + curing agent) was filled into the PDMS mold, cured, and then peeled off to obtain a PDMS micro dome array.

[0115] Figure 17 shows a scanning electron microscope (SEM) image (a) of a micropillar array (average diameter of micropillars: 13.5 μm, distance between pillars: 10 μm) of Example 1 and an SEM image (b) of a microdome pattern obtained after reflow.

[0116] Referring to Figure 17, it was confirmed that a dome-shaped pattern was obtained through the reflow process.

[0117] Figure 18 shows an optical photograph (a) taken from the convex side, an optical photograph (b) taken from the flat side, and an enlarged photograph (c) taken from the flat side of the micro dome array (average diameter of micro pillars: 13.5 μm, distance between pillars: 10 μm) of Example 1. To confirm the structural color, light was irradiated perpendicularly to the incident surface.

[0118] Referring to Fig. 18, when observed from the convex side of the micro dome array, no color appears, but when observed from the flat side, magenta appears, and it was confirmed that this color is generated by coloring formed at the periphery of each micro dome by retroreflection due to total internal reflection.

[0119] Figure 19 shows optical photographs taken from the flat surface side when light was irradiated at an incident angle of 31° on the micro dome array of Example 1 (average diameter of micro pillars: 13.5 μm, distance between pillars: 10 μm).

[0120] Referring to Figure 19, it was confirmed that the observed color changed depending on the angle at which the micro dome array was illuminated.

[0121] Figure 20 shows SEM images of micro-pillars of various diameters (left) and micro-dome patterns formed therefrom (right) in Example 1. Figure 21 shows images showing the structural colors of micro-dome arrays obtained according to the diameters of the micro-pillars in Example 1. The upper images in Figure 21 show the structural colors due to light irradiated perpendicular to the incident surface, and the lower images show the structural colors due to light irradiated at an incident angle of 31°.

[0122] Referring to FIGS. 20 and 21, it was confirmed that by adjusting the width of the micro pillars, micro dome patterns with different radii of curvature can be obtained, and from these, different structural colors can be obtained.

[0123] Figure 22 shows a stereoscopic image (a), an enlarged image (b) and a dot array (c) of the photomask in an enlarged area of ​​structural color graphics obtained through a combination of dots (transparent areas) and blank areas of different sizes in the photomask.

[0124] Referring to Figure 22, it was confirmed that multi-color structural color graphics can be generated by combining the dot sizes (diameters of micro pillars) of the photomask.

[0125] Figure 23 is a photograph showing structural colors (1:0, 0:1) obtained from a single diameter micro dome and structural colors (3:1, 1:1, 1:3) obtained from a combination of multi-diameter micro domes. Figure 24 shows an image (a) and an enlarged image (b) of a multi-color structural color graphic obtained from a combination of multi-diameter micro domes.

[0126] Referring to Figures 23 and 24, it was confirmed that color mixing was possible through a combination of micro domes of different diameters.

[0127] Example 2

[0128] A hemi-cylinder-shaped micro-dome array was obtained by carrying out the process in the same manner as Example 1, except that a linear micro-pattern array (with a line width gradually changing from 8 ㎛ to 22 ㎛ in increments of 0.5 ㎛) was used through a photolithography process.

[0129] Figure 25 shows an SEM photograph of the micro dome array of Example 2 (top), a structural color photograph by vertical irradiation (middle), and a structural color photograph by oblique irradiation (bottom).

[0130] Referring to Fig. 25, it was confirmed that a hemi-cylinder-shaped micro dome array that generates multi-color structural colors can be obtained by controlling the line width of the linear micro pattern.

[0131] Figure 26 shows a photograph (left) of a single structural color graphic generated by a micro dome array and a photograph of an enlarged area (right).

[0132] Referring to Fig. 26, it was confirmed that brightness can be expressed by controlling the density of micro-domes in a unit area (arranging 1, 4, 9, 16, and 25 micro-domes per unit area).

[0133] Figure 28 shows a pixelated graphic image using a micro dome array.

[0134] Specifically, the original image (top image) was pixelated and the RGB values ​​for each pixel were extracted. Based on the deviation of the RGB values, the pixels were classified into chromatic and achromatic pixels. For example, |RG| 2 +|GB| 2 + |BR| 2 If it is greater than 500, it is classified as a chromatic pixel. To generate a chromatic pixel, 128 x 128 ㎛ 2We used a 5 x 5 matrix with a size of , selected the size of the micro domes representing 11 different colors, and adjusted the density to properly match the RGB values, assuming linear correlation. To generate achromatic pixels, 128 x 128 ㎛ 2 A 4 x 4 matrix with a size of 17 levels of grayscale was used, and microdomes formed from micropillars with an average diameter of 26 μm were used to express 17 levels of grayscale. The original image (KAIST campus) was digitized into pixels of 210 x 215, and regenerated into 33,543 chromatic pixels and 11,607 achromatic pixels. Referring to Fig. 28, it was confirmed that high-resolution multi-color graphics can be generated through an embodiment of the present invention.

[0135] Although the present invention has been described with reference to exemplary embodiments thereof as described above, it will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below.

[0136] Structural color microparticles according to exemplary embodiments of the present invention can be used in decorative articles, display devices, signs, anti-counterfeiting marks, etc.

[0137] <Explanation of symbols>

[0138] 10: Base board

[0139] 22, 24: Micro pillars

[0140] 32, 34: Micro dome pattern

[0141] 40: Mold

[0142] 50: Micro Dome Array

[0143] 50a: Bass section

[0144] 50b: Convex part

[0145] 52, 54, 62, 64: Micro Dome

[0146] SS1, SS2: Convex surface

Claims

1. A step of forming an array of micro patterns on a base substrate through a photolithography process; A step of reflowing the above micro pattern array to form micro dome patterns; A step of forming a mold having concave curved surfaces corresponding to the inverse of the above microdome patterns; and comprising a step of forming a micro dome array from the mold; The above micro dome array includes a base portion and a convex portion including micro domes protruding from a first surface of the base portion, A method for manufacturing a microdome array, wherein structural color is generated through retroreflection on the convex surface of the microdome.

2. A method for manufacturing a micro dome array, wherein the ratio of the height to the width of the micro patterns in the first paragraph is 0.5 to 4.

3. A method for manufacturing a micro dome array, wherein the angle between the curved surface of the micro dome pattern and the upper surface of the base substrate in the first paragraph is 60° or more.

4. A method for manufacturing a micro dome array, wherein the micro dome array comprises at least one selected from the group consisting of polydimethylsiloxane, polystyrene, polyester, polymethyl methacrylate, polyurethane, polyamide, polyethylene, polypropylene, and polycarbonate.

5. A method for manufacturing a micro dome array, wherein the reflow of the micro pattern array in the first paragraph is performed at 60°C to 200°C.

6. A method for manufacturing a micro dome array according to claim 1, wherein the micro pattern array is formed from a positive photoresist.

7. In the first paragraph, the step of forming the mold is: A step of applying a resin composition onto the above micro dome patterns; a step of curing the resin composition; and A method for manufacturing a micro dome array, comprising the step of separating the micro dome patterns and the base substrate from a cured product.

8. In the first paragraph, the step of forming the micro dome array is: A step of applying a resin composition onto the concave curved surfaces of the mold; a step of curing the resin composition; and A method for manufacturing a micro dome array, comprising the step of separating the mold from the cured product.

9. A method for manufacturing a micro dome array, wherein the diameter of the micro domes on a plan view in the first paragraph is 5 µm to 50 µm.

10. A method for manufacturing a micro dome array, wherein the refractive index of the micro domes in the first paragraph is 1.35 to 1.

70.

11. A method for manufacturing a micro dome array, wherein the base portion and the micro domes comprise the same material in the first paragraph.

12. A method for manufacturing a micro dome array, wherein the micro patterns have a columnar shape and the micro domes have a hemispherical shape in the first paragraph.

13. A method for manufacturing a micro dome array, wherein the micro patterns have a linear shape extending in one direction on a plane, and the micro domes have a hemi-cylinder shape.

14. A method for manufacturing a microdome array in the first paragraph, wherein the convex portion includes a first microdome and a second microdome having different radii of curvature, and a first structural color generated by light retroreflected from a convex surface of the first microdome and a second structural color generated by light retroreflected from a convex surface of the second microdome have different colors.

15. Including a convex portion including a base portion and micro domes protruding from the first surface of the base portion, The base portion and the convex portion comprise the same material, A micro-dome array, wherein the micro-dome includes a first micro-dome and a second micro-dome having different radii of curvature, and a first structural color generated by light retroreflected from a convex surface of the first micro-dome and a second structural color generated by light retroreflected from a convex surface of the second micro-dome have different colors.

16. A micro dome array in claim 15, wherein the angle between the convex surface of the micro domes and the first surface of the base portion is 60° or more.

17. A microdome array in claim 15, wherein the diameters of the first microdome and the second microdome on a plan view are 5 µm to 50 µm, and the refractive index of the convex portion is 1.35 to 1.

70.

18. A micro dome array comprising a first pixel area and a second pixel area, The first pixel area includes a plurality of first subpixel areas, and the second pixel area includes a plurality of second subpixel areas, A first micro-dome having a convex surface is arranged in at least one first sub-pixel region, and a second micro-dome having a convex surface with a different radius of curvature from the convex surface of the first micro-dome is arranged in at least one second sub-pixel region. A pixelated graphic generation system, wherein a first structural color generated by light retroreflected from the convex surface of the first micro dome and a second structural color generated by light retroreflected from the convex surface of the second micro dome have different colors.

19. A pixelated graphics generation system in claim 18, wherein the first pixel area and the second pixel area have the same size, and the first subpixel area has a larger size than the second pixel area.

20. A pixelated graphic generation system in claim 19, wherein the first structural color is white and the second structural color is a chromatic color.

Images