JP4863184B2 - Electrophoretic display element - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a display element that is used when electrically rewritable display is performed, and in particular, display is performed by moving fine particles colored in a display color between a visible region and an invisible region by an electric field. This relates to the configuration of the electrophoretic display element.
[0002]
[Prior art]
As a typical configuration of a conventional electrophoretic display element, in a cell in which electrodes are provided on an upper substrate and a lower substrate, for example, a liquid that is colored black, and a color that is colored white, for example, is negative. When a positive potential is applied to the electrode provided on the upper substrate, the particles are adsorbed on the upper substrate side. Therefore, when viewed from the side of the upper substrate which is the viewing side of the electrophoretic display element, the electrophoretic display element appears white.
[0003]
Further, if no potential is applied to either the upper substrate or the lower substrate, the particles are dispersed in the liquid away from the upper substrate, and the upper substrate which is the viewing side of the electrophoretic display element When viewed from the side, most of the particles are covered with black liquid, and when viewed from the upper substrate side, they appear black. Therefore, by arranging a plurality of cells in a matrix or the like and appropriately arranging white display and black display, characters, figures, and the like can be displayed. (For example, see Patent Document 1)
[0004]
However, in the above configuration, since the white particles are mixed in the black liquid, the black liquid cannot be completely eliminated from between the white particles even when white display is performed. In addition, even when no potential is applied, it is impossible to completely eliminate those existing in the vicinity of the upper substrate of the particles.
[0005]
Therefore, the cells to be displayed in white become light black, and the cells to be displayed in black cannot be avoided from becoming light white. This causes a problem that the contrast is lowered and the display quality is lowered. In addition, it is unavoidable that white particles are stained with black liquid as the electrophoretic display element is used for a long time, which further reduces the contrast and further degrades the display quality. Yes.
[0006]
In order to solve this problem, each of the center electrode and the peripheral electrode is provided with a substantially flat plate-like substrate and the other substrate provided with a substantially hemispherical recess, The transparent liquid in which the colored particles are mixed is sealed. By switching the polarity between the central electrode and the peripheral electrode, the granular material is placed in either the central portion or the peripheral portion. Moving.
[0007]
Here, since the liquid is transparent and is stored in a substantially hemispherical concave portion of the other substrate, the shape thereof is a convex lens shape, and the light incident from above is focused in the central direction. Become. In the electrophoretic display element, the central electrode is provided in a range where light is focused.
[0008]
Here, when the electrophoretic display element is viewed from the front in a state where the particles are adsorbed to the central electrode, the central electrode portion appears to be enlarged on the entire surface of the convex lens. The entire surface of the lens can be seen with a colored color (for example, black), and when the particles are adsorbed to the peripheral electrode, the entire surface of the lens is colored with the colored central portion electrode (for example, white). The contrast is improved without causing color mixing with the liquid. (For example, see Patent Document 2)
[0009]
[Patent Document 1]
JP 2002-287179 A (paragraphs 10 to 62, FIGS. 1 and 2)
[Patent Document 2]
Japanese Patent Laid-Open No. 11-212499 (paragraphs 22 to 86, FIGS. 1a and 1b)
[0010]
[Problems to be solved by the invention]
The thing of patent document 2 certainly has a contrast higher than that of patent document 1 and the display quality is improved, but on the other hand, first, it is filled in a recess provided in the other substrate. In this part, the condition of (solid refractive index) <(liquid refractive index) is required, and the range of selection of materials for both the other substrate and liquid is narrow. There is a problem.
[0011]
Secondly, when such a transparent liquid is used, it is advantageous to use liquid crystals to obtain a brighter and higher contrast display. However, the refractive index of liquid crystals changes when driven. Therefore, the refractive index is the same as that of the other substrate, and it is difficult to adopt such a problem that the convex lens function cannot be obtained. It will cause problems that cannot be demonstrated.
[0012]
[Means for Solving the Problems]
The present invention provides an electrophoretic display element in which a plurality of display cells in which a dispersion medium and particles are sealed are gathered as specific means for solving the above-described conventional problems. On the upper surface of the upper substrate of the cell, there is provided a microlens that generates a focal point in the vicinity of the lower substrate near the center of the display cell when parallel rays are incident on the display cell from the normal direction . One of a pair of electrodes for moving the particles is provided in the central part of the lower substrate, and the other of the pair of electrodes for moving the fluid is provided on the lower substrate peripheral part of each display cell. By providing an electrophoretic display element provided and characterized in that the dispersion medium is a liquid crystal, it is possible to achieve a bright display with high contrast and solve the problem.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Below, this invention is demonstrated in detail based on embodiment shown in a figure. 1 and FIG. 2 shows an electrophoretic display element according to the present invention, and the figure shows a state of one cell S constituting the electrophoretic element 1, and an actual electrophoretic display. In the element 1, an arbitrary number of the cells S are arranged in the row and column directions, and characters, figures, etc. are displayed by selecting and driving appropriate ones from the cells S. is there.
[0014]
Each of the electrophoretic display elements 1 is formed as a flat plate, and a cell S is configured by allowing the upper substrate 2 and the lower substrate 3 to face each other at an appropriate interval, for example, 50 to 200 μm. In the gap between the substrates 2 and 3, for example, a liquid crystal 4 in which particles 5 charged to a positive potential are dispersed, that is, a dispersion medium is sealed. In this embodiment, the cell S is a square having a side of 450 μm. In the present invention, the upper substrate 2 refers to a substrate located on the viewing direction side of the electrophoretic display element 1.
[0015]
At this time, a transparent member is employed for the upper substrate 2, and the lower substrate 3 is provided with a colored film 3 a having a color that provides a high contrast with the particles 5. In the present invention, since the dispersion medium is the liquid crystal 4, the upper substrate 2 and the lower substrate 3 are formed with alignment films 2a and 3b for causing the liquid crystal 4 to be aligned. Two electrodes 3c and 3d for moving the body 5 to a predetermined position are also provided. Further, a shielding film 2b for concealing the grains 5 when retracted at the periphery of the cell S may be provided on the upper substrate 2 side.
[0016]
In the present invention, the microlens 6 is provided on the upper surface of the upper substrate 2, and in this embodiment, the acrylic resin is coated on the surface of the upper substrate 2 formed of PET resin. The glass or metal mold in which the female shape of the microlens 6 is formed on this portion is pressed while heating to transfer the shape, and the upper substrate 2 having the microlens 6 is obtained.
[0017]
If there is no problem in airtightness or durability when the liquid crystal 4 is sealed, the upper substrate 2 is made of an easily heat-molded member such as an acrylic resin and has an appropriate thickness. The lens shape may be transferred to one surface using the same mold as described above, and the upper substrate 2 and the microlens 6 may be integrated with the same material. .
[0018]
FIG. 3 shows in detail the cross-sectional shape of the microlens 6 formed as described above. The thickness of the lens portion of the microlens 6 when the pitch between the cells S is 450 μm is about 90 μm. The focal length was about 400 μm. Further, when the cell S is formed with the distance between the upper substrate 2 and the lower substrate 3 to which the microlens 6 is attached being about 200 μm, and completely diffused light is incident from the microlens 6 side, the lower substrate 3 It was confirmed that an area illuminated in a circular shape with a radius of 100 μm was produced on the surface of the film.
[0019]
That is, when the viewer views the electrophoretic display element 1, only the circular part having a radius of 100 μm, which is the central part of the lower substrate 3, can be seen by the microlens 6. You will not be able to see it. Therefore, it is sufficient that the particles 5 are present (see FIG. 1) and retreat (see FIG. 2) in the circular portion having a radius of 100 μm by driving.
[0020]
FIG. 4 shows another embodiment of the electrophoretic display element 1 according to the present invention. In this embodiment, the particles 5 are dark and opaque such as black, and the lower substrate 3 is transparent or It is supposed to be translucent. A light source 7 is provided below the lower substrate 3.
[0021]
In this way, each cell S of the electrophoretic display element 1 functions as a shutter that opens and closes the light from the light source 7, and the reflection of external light that changes depending on the presence or absence of the particles 5. Compared with the case where the light / dark difference (contrast) of display / non-display is obtained by the light quantity ratio of light, a much larger contrast can be obtained. In addition, since the light is artificially emitted, the display readability can be ensured even in the state where the outside light is insufficient at night.
[0022]
5 and 6 show still another embodiment of the present invention. In the previous embodiment, the so-called convex lens-shaped microlens 6 was adopted. However, the present invention limits the shape of the microlens 6. However, if it has an action of converging light within a predetermined range in the vicinity of the lower substrate 3, a diffraction grating, a Fresnel lens 8 or the like as shown in FIG. As shown, a so-called graded index lens 9 having a higher refractive index of the transparent member toward the center can be used.
[0023]
【Effect of the invention】
As described above, according to the present invention, there is provided an electrophoretic display element in which a plurality of display cells in which a dispersion medium and particles are sealed are assembled. By using an electrophoretic display element with a microlens that produces a focal point near the lower substrate near the center of the display cell when parallel rays are incident on the cell from the normal direction, the refractive index of the dispersion medium is used. Therefore, it is possible to focus the light in the cell without using the liquid crystal, and it is possible to adopt a liquid crystal as a dispersion medium and to achieve an extremely excellent effect of realizing a high-contrast and bright electrophoretic display element.
[0024]
In addition, with the above configuration, in selecting materials such as the upper substrate, the lower substrate, and the liquid crystal (dispersion medium), it is basically not restricted by optical characteristics such as a refractive index. In addition, it is possible to widen the degree of freedom and improve the performance, and at the same time, the cost is reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of an electrophoretic display element according to the present invention in a state in which particles are present at the center of a cell.
FIG. 2 is a cross-sectional view showing a state in which the granule of the same embodiment has retreated from the center of the cell.
FIG. 3 is an explanatory diagram showing in detail a cross-sectional shape of a microlens in the same embodiment.
FIG. 4 is a cross-sectional view showing another embodiment of the electrophoretic display element according to the present invention.
FIG. 5 is a cross-sectional view showing still another embodiment of the electrophoretic display element according to the present invention.
FIG. 6 is a cross-sectional view showing still another embodiment of the electrophoretic display element according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electrophoretic display element 2 ... Upper substrate 2a ... Alignment film 2b ... Shielding film 3 ... Lower substrate 3a ... Colored film 3b ... Alignment film 3c, 3d ... Electrode 4 ... Liquid crystal 5 ... ... Granule 6 ... Micro lens 7 ... Light source 8 ... Fresnel lens 9 ... Graded index lens

Claims (5)

An electrophoretic display element in which a plurality of display cells in which a dispersion medium and particles are sealed are assembled. An upper surface of an upper substrate of each display cell is parallel to the display cell from a normal direction. Is provided with a microlens that generates a focal point near the lower substrate near the center of the display cell,
One of a pair of electrodes for moving the particles is provided at the center of the lower substrate of each display cell,
An electrophoretic display element, wherein the lower substrate periphery of each display cell is provided with the other of a pair of electrodes for moving the particles, and the dispersion medium is a liquid crystal. The microlens is formed in a lens shape that allows only a predetermined range of the center of the display cell to be viewed when viewed from an angle within a range that can be displayed by the electrophoretic display element. The electrophoretic display element according to claim 1.   3. The electrophoretic display element according to claim 1, wherein the lens action of the microlens is mainly caused by refraction at an interface between the microlens and air.   4. The electrophoretic display element according to claim 3, wherein the microlens is formed of any one of a physical optical lens, a surface hologram, and a diffraction grating.   The electrophoretic display element according to claim 1, wherein the microlens is formed of any one of a volume hologram and a graded index lens.

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