JP2004062008A - Corner cube array and method of manufacturing the same - Google Patents

Abstract

An object of the present invention is to manufacture a micro corner cube array having minute and unit elements with high shape accuracy.
A method of manufacturing a corner cube array includes a step of preparing a base material having a concave portion on the surface, a step of forming a first portion having a convex shape corresponding to the concave portion, and a second portion having a predetermined surface. Providing a particle comprising: forming a corner cube including a predetermined surface of the particle by disposing a first portion of the particle in a recess of the base material such that a second portion is exposed on the base material; Forming.
[Selection diagram] Fig. 4

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a corner cube array suitably used in a display device and the like, and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, very small optical elements (micro optical elements), such as microlenses, micromirrors, and microprisms, have been developed and are being used in the fields of optical communication and display devices. The realization of such a micro-optical element is expected to further develop and enhance the fields of optical technology and display technology.
[0003]
As a display device using such a micro optical element, a reflective liquid crystal display device having a retroreflective plate is disclosed in, for example, US Pat. No. 5,182,663, JP-A-11-7008, and JP-A-2000-19490. No., etc. If a retroreflective plate is used, light can be reflected (that is, retroreflected) in the same direction as the light incident direction. For this reason, in the reflective liquid crystal display device, the reflected light of light emitted from the vicinity of the user selectively reaches the eyes of the user, and the reflected light of light emitted from a light source such as an external light or the sun is reflected. Light is prevented from reaching. Thereby, reflection of external light can be suppressed, and visibility can be improved. Further, in this reflective liquid crystal display device, since the reflection of external light is reduced by the retroreflective plate, it is not necessary to lower the reflectivity of the reflective plate to lower the intensity of the reflected light. This makes it possible to realize a bright and high-contrast display.
[0004]
Such a retroreflector is formed, for example, using a corner cube array. A corner cube has a shape that forms one corner of a cube, and typically has three surfaces orthogonal to each other. The reflection plate formed from such a corner cube array can reflect the light in the original direction regardless of the incident direction by reflecting the incident light on a plurality of reflection surfaces. Hereinafter, the configuration of a conventional reflective liquid crystal display device 80 including a retroreflective plate formed using a corner cube array will be described with reference to FIG.
[0005]
The reflective liquid crystal display device 80 includes a substrate 82 on which a corner cube array 83 is provided, a transparent substrate 81 located on the viewer side, and a polymer dispersed liquid crystal layer 84 sandwiched between these substrates 81, 82. And A metal reflection film 85 is formed on the corner cube array 83, and the light transmitted through the transparent substrate 81 and the polymer dispersion type liquid crystal layer 84 controlled to transmit light during black display is incident on the corner reflection array 85. It can reflect in the same direction as the direction. The concave portion of the corner cube array 83 is filled with a transparent flattening member 86, and a transparent electrode 87 is formed on the flattening member 86. On the liquid crystal layer side of the transparent substrate 81, a color filter layer 88 and a transparent electrode 89 are provided. In the reflective liquid crystal display device 80, the light transmittance (or scattering state) of the polymer dispersed liquid crystal layer 84 is controlled by controlling the voltage applied to the polymer dispersed liquid crystal layer 84 by the transparent electrodes 87 and 89. Thus, an image is displayed.
[0006]
The size L1 of the corner cube used in the display device 80 is preferably equal to or less than the pixel size L2. When the size L1 of the corner cube is larger than the pixel size L2, a pixel passing light incident on a predetermined corner cube may be different from a pixel passing light reflected by the corner cube. This causes problems such as color mixing. Therefore, for example, when the pixel size L2 is about 100 μm, the corner cube size L1 is preferably set to several tens μm or less.
[0007]
As a corner cube used in such a conventional reflective liquid crystal display device, a corner cube having a shape composed of only triangular pyramid-shaped concave portions or convex portions is known. If a triangular pyramid-shaped concave portion or convex portion is a corner cube, it is relatively easy to produce a size of several tens μm or less and high shape accuracy as described above.
[0008]
On the other hand, as a relatively large-sized retroreflective plate used in a road sign or the like, a retroreflective plate using a corner cube having a more complicated shape (corner cube reflector) is known. Hereinafter, the configuration of a corner cube reflector having a more complicated shape will be described with reference to FIGS. 6 (a) to 6 (c).
[0009]
As shown in FIGS. 6A and 6B, the corner cube reflector 90 has a structure including three substantially square reflecting surfaces S1, S2, and S3 substantially orthogonal to each other. The light incident on the corner cube reflector 90 is reflected on, for example, three surfaces S2, S3, and S1, as shown in FIG. 6C, and returns to the same direction as the incident direction. In the corner cube reflector 90, each of the substantially square reflecting surfaces S1, S2, and S3 corresponds to three surfaces having a common vertex among the six surfaces of the cube. As shown in FIG. 6A, the corner cube reflector 90 includes a convex portion 92 having the highest vertex indicated by a circle (a portion above a level defined by a middle point indicated by a cross) and a black circle. A concave portion 94 having the lowest point (a portion below a level defined by a middle point indicated by X). Hereinafter, such a corner cube is referred to as a cubic corner cube.
[0010]
A reflector formed using a cubic corner cube can reduce incident light more than a case using a corner cube formed only of a triangular pyramid-shaped concave or convex portion (hereinafter, referred to as a triangular pyramidal corner cube). Retroreflection can be performed efficiently. Hereinafter, the state of light reflection when each of the triangular pyramid-shaped corner cube and the cubic-shaped corner cube is used will be described with reference to FIGS.
[0011]
FIGS. 7A and 7B show a triangular pyramid-shaped corner cube 96, and FIGS. 7C and 7D show a cubic corner cube 98. As shown in FIG. 7B, in the triangular pyramid-shaped corner cube 96, the light A incident on the center of the corner cube is retroreflected as shown by the dotted line in the figure, but the light B incident on the corner is Is not retroreflected. That is, in the triangular pyramid-shaped corner cube 96, as shown in FIG. 7A, a non-retroreflective region 96a is formed at the corner. On the other hand, as shown in FIG. 7D, in the cube-shaped corner cube 98, even light incident on the corner is retroreflected. Therefore, in the cubic corner cube 98, a non-retroreflective area is not formed, and a retroreflective area on the reflective surface is widened, so that more incident light can be retroreflected.
[0012]
When a triangular pyramidal corner cube retroreflector is used in a reflective display device, part of the light transmitted through the liquid crystal layer during black display is not retroreflected but reflected in a direction different from the incident direction. Become. In this case, a part of the reflected light of the light emitted from a place distant from the user reaches the user's eyes, thereby lowering the contrast ratio. On the other hand, if a retroreflective plate formed from a cubic corner cube is used, incident light can be retroreflected with higher efficiency, so that the contrast ratio can be improved.
[0013]
However, it is not easy to produce a cubic corner cube with a fine size of, for example, 100 μm or less, which is suitably used in a reflection type display device. Hereinafter, a method of manufacturing a conventional cubic corner cube array will be described.
[0014]
(Pin binding method)
In the pin bundling method, a prism having three square surfaces orthogonal to each other is provided at the tip of a metal pin having a hexagonal prism shape, and a number of these prisms are bundled to form a prism assembly. A cubic corner cube is formed using one surface of each of the prisms provided on each of the three adjacent pins.
[0015]
However, in this method, since prisms formed on separate pins are collected to form a corner cube array, it is actually difficult to produce a small-sized corner cube. The size of a corner cube (dimension corresponding to L3 shown in FIG. 6B) which can be manufactured by this method is limited to about 1 mm, and it is difficult to form a cubic corner cube having a size of several tens of μm. .
[0016]
(Plate method)
In the plate method, a plurality of flat plates having two planes parallel to each other are superimposed, and a V-groove is cut at an equal pitch in a direction perpendicular to the planes at an end face of the superimposed flat plate to have a vertex angle of about 90 °. To form a continuous roof-shaped projection group. Next, by moving the top of the roof of the group of roof-shaped projections formed on each flat plate so as to coincide with the bottom of the V-groove formed on the adjacent flat plate, the gold for the cube-shaped corner cube array is moved. Make a mold.
[0017]
However, in this method, it is necessary to accurately rearrange and fix the flat plate on which the roof-shaped projections are formed so as to have an appropriate positional relationship with the adjacent flat plate. Therefore, it is difficult to form a fine cubic corner cube having a size of 100 μm or less.
[0018]
[Problems to be solved by the invention]
However, in recent years, a technique for producing a cubic corner cube array with a fine size has been developed. Such techniques are described, for example, in Applied Optics Vol. 35, No19, pp 3466-3470, "Precision crystal corner cube arrays for optical gratings formed by (100) silicon planes with a selective episode, a paper entitled" According to this paper, a fine corner cube array is produced by epitaxially growing a crystal from a silicon substrate.
[0019]
If a retroreflective plate is produced from the fine cubic corner cube obtained in this way, a high retroreflectivity can be realized. If this is used for a display device, color mixing can be prevented and the contrast ratio can be improved. However, in the above method, it is necessary to appropriately control the crystal growth, and there has been a problem that a fine cubic corner cube is manufactured by other methods.
[0020]
The present invention has been made to solve the above problems, and an object of the present invention is to provide a corner cube array having a fine unit structure, which is suitably used as a retroreflective plate of a display device, and a method of manufacturing the same. And
[0021]
[Means for Solving the Problems]
The method of manufacturing a corner cube array according to the present invention includes a step of preparing a base material having a concave portion on the surface, a first portion having a convex shape corresponding to the concave portion, and a second portion having at least one surface. Providing a particle comprising: a corner cube including the at least one surface by disposing the first portion in the recess such that the second portion is exposed on the base material. Forming.
[0022]
In a preferred embodiment, the at least one plane includes three planes orthogonal to each other.
[0023]
In a preferred embodiment, the concave portion has a triangular pyramid shape, and the particles have a cubic shape.
[0024]
In a preferred embodiment, the particle is a crystal, and the at least one plane is defined by a predetermined crystal plane of the crystal.
[0025]
In a preferred embodiment, the particles are made of sodium chloride.
[0026]
In a preferred embodiment, the size of the particles is 1 μm or more and 1000 μm or less.
[0027]
In a preferred embodiment, the method further includes a step of transferring the shape of the corner cube formed on the base material to another material.
[0028]
The corner cube array of the present invention includes a base material having a plurality of concave portions on the surface, and a plurality of convex portions each having a convex portion having a shape corresponding to each of the plurality of concave portions and arranged in each of the plurality of concave portions. Particles.
[0029]
In a preferred embodiment, each of the plurality of particles has at least one surface exposed on the base material, and a corner cube is formed by the at least one surface of an adjacent particle.
[0030]
In a preferred embodiment, the at least one plane includes three planes orthogonal to each other.
[0031]
In a preferred embodiment, the concave portion has a triangular pyramid shape, and the particles have a cubic shape.
[0032]
In a preferred embodiment, the particle is a crystal, and the at least one plane is defined by a predetermined crystal plane of the crystal.
[0033]
In a preferred embodiment, the particles are made of sodium chloride.
[0034]
The mold of the corner cube array of the present invention has a base material having a plurality of concave portions on its surface, and each has a convex portion having a shape corresponding to each of the plurality of concave portions, and is arranged in each of the plurality of concave portions. A plurality of particles, and a coating film provided on the base material on which the plurality of particles are arranged.
[0035]
The method for producing a corner cube array according to the present invention includes a step of preparing a base material, a step of preparing particles including a portion having at least one surface, and the portion protruding on the base material and the at least one surface. Forming a corner cube including the at least one surface by disposing the particles on the base material such that is exposed.
[0036]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a retroreflective plate formed using a fine cubic corner cube array manufactured as an embodiment of the present invention will be described with reference to the drawings.
[0037]
FIGS. 1A and 1B show a base material 10 used for manufacturing a retroreflective plate according to the present embodiment. As a base material, a metal plate such as nickel can be used. On the surface of the base material 10, a plurality of fine triangular pyramid-shaped concave portions 11 (one side of the triangular pyramid is, for example, about 50 μm) are alternately arranged with the flat portions 12 in three directions different from each other by 60 °. It is formed so that. Each of the triangular pyramid-shaped recesses has a shape defined by three surfaces of a right-angled isosceles triangle orthogonal to each other, and has a shape corresponding to a corner of the cube. Such a concave portion is formed by cutting a high-hardness pin having a triangular pyramid convex portion of a predetermined shape by cutting, and this pin is pressed many times at a predetermined pitch against a surface of a base metal plate. It can be formed by forming. Thus, a base material having a plurality of concave portions formed at predetermined positions is obtained.
[0038]
In addition, the concave portions provided in the base material may be formed to be completely separated from each other, or may be formed to partially overlap. However, preferably, each central portion of the concave portion is a honeycomb lattice point (a point corresponding to the vertex of each regular hexagon and the center of gravity of each regular hexagon when congruent regular hexagons are spread without gaps, or A plurality of parallel lines at equal intervals (predetermined intervals) extending in one direction, and a plurality of parallel lines at equal intervals and equal to the predetermined intervals extend in a second direction different from the first direction by 60 ° (Intersection point with).
[0039]
Next, particles to be arranged on the base material having the plurality of recesses as described above are prepared. The particles prepared here include a first portion having a convex shape corresponding to the concave shape of the base material and a second portion other than the first portion, and the second portion has a surface forming a corner cube. Has at least one face (facet). In the present embodiment, cubic sodium chloride crystals are used as such particles. Hereinafter, a method of obtaining the cubic sodium chloride crystal particles will be described in more detail.
[0040]
2A to 2C show a method of obtaining a plurality of minute cubic sodium chloride particles 20 having a uniform size (for example, 35 μm on one side) used in the present embodiment.
[0041]
First, as shown in FIG. 2A, cleaved sodium chloride particles (crystals) 21 are dispersed in a nonpolar liquid 22 in which sodium chloride does not dissolve (for example, tetrahydrofuran). The cleaved sodium chloride particles 21 can be obtained, for example, by boiling down saturated saline or mechanically pulverizing. Each of the sodium chloride particles 21 thus obtained has a cubic shape. The particles 21 need not be formed of sodium chloride, but may be formed of a material having a rock salt type crystal structure (for example, MgO or KCl).
[0042]
Next, as shown in FIG. 2B, the liquid (dispersion liquid) 22 in which the sodium chloride particles 21 are dispersed is supplied to a centrifugal separator 23, and the sodium chloride particles 21 in the dispersion liquid are centrifuged. Thereby, cubic sodium chloride particles 20 having a uniform size in each region in the liquid are obtained. As shown in FIG. 2C, by extracting the cubic sodium chloride particles 20 existing in a predetermined region with a Pasteur pipette or the like, sodium chloride particles 20 having a desired size can be obtained. Each of the thus obtained sodium chloride particles having substantially the same size has a cubic shape as described above, and has six square faces (facets). The six facets of the particle include three orthogonal planes.
[0043]
Next, as shown in FIG. 3, a dispersion is prepared by dispersing sodium chloride particles 20 having the same size in a nonpolar liquid (dispersion medium) in which sodium chloride does not dissolve, and the dispersion is poured onto the base material 10. Thereby, the sodium chloride particles 20 are arranged on the base material 10. More specifically, the particles 20 are arranged in the recesses 11 of the base material 10 by fitting the corners of the particles 20 into the recesses 11 of the base material 10. Since the particles 20 have corners corresponding to the shape (triangular pyramid shape) of the concave portion 11 of the base material 10, the particles 20 can be formed only by flowing the dispersion liquid on the base material 10. It is automatically arranged in a predetermined direction in the concave portion 11.
[0044]
As a method of disposing the particles dispersed in the liquid in the concave portion of the base material, for example, US Pat. Nos. 5,545,291, 5,783,856, 5,824,186 , 5,904,545, etc. may be used. That is, the base material in which the concave portion is formed is accommodated in a vessel in a state where the base material is inclined at a predetermined angle, and the dispersion liquid containing the sodium chloride particles 20 flows on the base material at a predetermined flow rate in the vessel. However, the base material is immersed in the dispersion liquid in the vessel, and the flow of the dispersion liquid is supplied onto the base material from an outlet provided near the base material. At this time, if the flow rate and the like of the dispersion liquid are appropriately set, the corners of the sodium chloride particles can be appropriately fitted into the triangular pyramid-shaped recess provided on the base material. Thereby, particles can be arranged in each concave portion.
[0045]
As shown in FIG. 4, in a state where the particles 20 are arranged in the concave portions of the base material 10, a portion 20 b of the cubic particles 20 (a second portion different from the first portion 20 a located in the concave portion) ) Protrudes on the base material 10, and the facets 25 formed in this portion 20b are exposed on the base material. That is, the particles 20 are partially arranged in the concave portions of the base material 10.
[0046]
Thus, the cubic corner cube array 40 can be formed. The corner cube, which is a unit element of the cubic corner cube array 40, is constituted by the facets 25 of the exposed portions 20b of the particles 20 described above. More specifically, a corner cube is formed by facets 25 of three adjacent cubic particles. Facets of three particles constituting the corner cube are arranged so as to be substantially orthogonal to each other.
[0047]
The sodium chloride particles are crystals, and the facets of the particles constituting the corner cube can be defined by a predetermined crystal plane of the crystals. For example, the above facets correspond to the {100} faces of sodium chloride crystals.
[0048]
The corner cube thus formed is fine, and each surface of the corner cube is formed of a flat crystal surface of sodium chloride, so that the shape accuracy is high. Therefore, it is suitable as a corner cube array for producing a retroreflective plate used for a display device.
[0049]
Although the size of the corner cube can be determined by the size of the particles (and the concave portions), the size of the corner cube must be smaller than the pixel size in order to obtain a retroreflector suitable for use in a reflective display device. Is desirable. However, when the size of the particles is too small, that is, when the size of the particles is equal to or smaller than the wavelength of light (visible light), there arises a problem that the corner cube array does not function as a retroreflective plate due to the influence of interference or the like. For this reason, the size of the particles is desirably 1 μm to 1000 μm.
[0050]
After providing a coating film that functions as a protective film by depositing a metal thin film such as silver on the corner cube array manufactured in the present embodiment, by taking the mold of the corner cube array by electroforming, A micro corner cube array mold can be manufactured. By transferring the corner cube array to a resin material or the like by transfer using a roller or the like using the mold formed in this manner, it is possible to mass-produce the corner cube array used in the display device.
[0051]
A retroreflective plate can be obtained by providing a thin film of a metal such as aluminum on the surface of the corner cube array manufactured as described above and forming a reflective region. The retroreflective plate thus obtained can be suitably used in, for example, a reflection type liquid crystal display device (for example, a polymer dispersion type liquid crystal display device shown in FIG. 5), an organic EL (electroluminescence) display, and the like. .
[0052]
Although the embodiment of the present invention has been described above, various methods can be adopted as a method of obtaining a base material having a concave portion, for example, as described in JP-A-7-205322. Photochemical techniques can also be used. That is, a mask having a plurality of equilateral triangular transmission areas (or light-shielding areas), wherein the transmittance or light-shielding rate of each transmission area (or light-shielding area) varies from the center of the transmission area (or light-shielding area) to the peripheral area. Exposure and development are performed using a gradually decreasing mask toward. This makes it possible to form a plurality of triangular pyramid-shaped protrusions having three isosceles triangular surfaces orthogonal to each other at predetermined positions on the substrate. This substrate is used as a mold to produce a substrate with reversed irregularities, and this can be used as a base material of the present embodiment.
[0053]
Further, in the present embodiment, the mode in which a part of the cubic particles is arranged in the triangular pyramid-shaped concave portion defined by the three surfaces of the right-angled isosceles triangle is described, but the particle includes a portion corresponding to the shape of the concave portion. As long as the shape of the concave portion and the shape of the particle are different, other shapes may be used. However, the particles need to have at least one facet for forming a corner cube in a portion other than the portion corresponding to the shape of the concave portion. It is preferable that at least one facet of the particle includes three surfaces orthogonal to each other.
[0054]
【The invention's effect】
As described above, according to the present invention, by arranging the particles on the base material, it is possible to form a corner cube including a predetermined surface of the particles. It is possible to fabricate an array of fine corner cubes (cubic corner cubes) composed of surfaces, or a mold thereof.
[Brief description of the drawings]
1A and 1B are diagrams for explaining a manufacturing process of a corner cube array according to an embodiment of the present invention, wherein FIG. 1A is a cross-sectional view of a base material, and FIG. 1B is a perspective view of the base material.
FIGS. 2A to 2C are diagrams for explaining a manufacturing process of the corner cube array according to the embodiment of the present invention, wherein FIGS.
FIG. 3 is still another view for explaining the manufacturing process of the corner cube array according to the embodiment of the present invention, and is a cross-sectional view showing a process of arranging particles on a base material.
FIG. 4 is still another view for explaining the manufacturing process of the corner cube array according to the embodiment of the present invention, and is a perspective view of the completed corner cube array.
FIG. 5 is a cross-sectional view illustrating a configuration of a conventional reflective liquid crystal display device.
6A and 6B are diagrams showing a cubic corner cube array, wherein FIG. 6A is a plan view, FIG. 6B is a side view showing a portion higher than a middle point, and FIG. 6C is a perspective view.
7A and 7B are diagrams showing a comparison between a triangular pyramid type corner cube and a cubic type corner cube; FIG. 7A is a plan view of the triangular pyramid type corner cube; FIG. (C) is a plan view of the cubic corner cube, and (d) is a perspective view of the cubic corner cube.
[Explanation of symbols]
Reference Signs List 10 base material 11 triangular pyramid concave portion 12 flat portion 20 minute cubic sodium chloride particles (crystal) of uniform size
21 Cleaved sodium chloride 22 Non-polar solvent 23 Centrifuge 40 Cube-shaped corner cube array

Claims (15)

A step of preparing a base material having a concave portion on the surface,
Preparing a first portion having a convex shape corresponding to the concave portion, and a particle comprising a second portion having at least one surface;
Forming the corner cube including the at least one surface by disposing the first portion in the recess such that the second portion is exposed on the base material. Array manufacturing method. The method of claim 1, wherein the at least one surface includes three planes orthogonal to each other. The method of claim 2, wherein the recess has a triangular pyramid shape, and the particles have a cubic shape. 4. The method according to claim 2, wherein the particles are crystals, and the at least one plane is defined by a predetermined crystal plane of the crystals. The method according to claim 4, wherein the particles are made of sodium chloride. The method for manufacturing a corner cube array according to claim 1, wherein the size of the particles is 1 μm or more and 1000 μm or less. The method for manufacturing a corner cube array according to claim 1, further comprising a step of transferring a shape of the corner cube formed on the base material to another material. A base material having a plurality of recesses on its surface,
A corner cube array comprising a plurality of projections each having a shape corresponding to each of the plurality of recesses and a plurality of particles arranged in each of the plurality of recesses. The corner cube array according to claim 8, wherein each of the plurality of particles has at least one surface exposed on the base material, and the at least one surface of the adjacent particles forms a corner cube. . The corner cube array according to claim 9, wherein the at least one surface includes three planes orthogonal to each other. The corner cube array according to claim 10, wherein the concave portion has a triangular pyramid shape, and the particles have a cubic shape. 12. The corner cube array according to claim 10, wherein the particles are crystals, and the at least one plane is defined by a predetermined crystal plane of the crystals. The corner cube array according to claim 12, wherein the particles are made of sodium chloride. A base material having a plurality of recesses on its surface,
A plurality of particles each having a convex portion having a shape corresponding to each of the plurality of concave portions, and arranged in each of the plurality of concave portions,
A corner cube array including a coating film provided on the base material on which the plurality of particles are arranged. A process of preparing a base material,
Providing particles comprising a portion having at least one surface;
Forming a corner cube including the at least one surface by disposing the particles on the base material such that the portion protrudes on the base material and the at least one surface is exposed. A method of manufacturing a corner cube array including the same.

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