JP2007121785A - Electrophoretic display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophoretic display device that eliminates a non-uniform electric field, displays a stable halftone or black color, has an improved memory property and a simple structure for color display, and prevents decrease in reflectance due to a transparent electrode. <P>SOLUTION: An electrophoretic dispersion liquid 3 having electrophoretic particles 4 dispersed therein is sealed in a space formed by a first substrate 1, a second substrate 2 and a barrier wall 6. A first electrode 5 and a second electrode 7 are connected through a resistant layer 9. When a voltage is applied on the first electrode 5, potential gradient toward the second electrode is generated in the resistance layer 9. This suppresses a non-uniform electric field in the electrophoretic dispersion liquid 3 and gives a uniform dispersion state of electrophoretic particles 4 in the electrophoretic dispersion liquid. Since the resistance layer 9 is colored, a color filter is unnecessary and favorable and bright color reproduction is attained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophoretic display device that changes a display state by changing a distribution state of electrophoretic particles in an electrophoretic dispersion.

  With the widespread use of portable personal computers and electronic notebooks, the demand for low power consumption and thin display devices is increasing. For example, a display function that integrates a display function and a coordinate input process using a thin display such as a liquid crystal display and can directly input the content displayed on the display by pressing with a pen or a finger has been commercialized.

  However, since many liquid crystals do not have so-called memory properties, it is necessary to continue voltage application to the liquid crystals during the display period. On the other hand, a liquid crystal having a memory property has not been put into practical use because it is difficult to ensure reliability when assumed to be used in various environments such as a portable personal computer.

  Thus, there is an electrophoretic display device 100B disclosed in Patent Document 1 as one of thin and light display systems having a memory property. As shown in FIGS. 5 (a) and 5 (b), this was injected into a gap between a pair of counter substrates 101 and 102 arranged in a state where a predetermined gap was opened and the counter substrate 101 and 102. An insulating electrophoretic dispersion 103 and a large number of electrophoretic particles 104 dispersed in the electrophoretic dispersion 103 are provided. Furthermore, a pixel electrode 105 disposed so as to be close to the electrophoretic dispersion liquid 103, a common electrode 106 disposed so as to partition the pixels, and insulating layers 107 and 108 covering these electrodes 105 and 106 are provided.

  In the display device described in Patent Document 2, a liquid crystal display device in which a conductive colored layer also serves as a pixel electrode has been proposed for the purpose of improving manufacturing yield.

  In the electrophoretic display device as described above, the color filter is the simplest method for colorization, and the color filter is formed on the counter substrate 101 or 102 side shown in FIG. There are two ways to do this. As for the former, since the cell is assembled so that the color filter and the pixel match, there is always a misalignment in manufacturing. Since misalignment causes color mixing between adjacent pixels, it is necessary to provide a black matrix for the alignment margin on the counter substrates 101 and 102 side. For this reason, it is difficult to obtain a high aperture ratio. In particular, when a high-definition pixel of 150 ppi or less is formed, or when a plastic substrate having a high thermal expansion coefficient is used, the aperture ratio is remarkably lowered and cannot be practically used.

  On the other hand, in the latter case, as shown in FIG. 7, a decrease in the aperture ratio can be suppressed by directly forming the color filters 109a, 109b, and 109c in the pixels. However, in such a cell configuration, residual DC that causes burn-in occurs.

  As a countermeasure, there is a method in which a transparent electrode is formed on an insulating layer, that is, a color filter, so that residual DC of the insulating layer does not accumulate.

Japanese Patent No. 3421494 JP-A-8-313726

  FIG. 6 shows equipotential lines when a voltage is applied between the pixel electrode 105 and the common electrode 106 of the conventional electrophoretic display device 100B. The dotted line represents an equipotential line. The electric field in the electrophoretic dispersion 103 is non-uniform because the equipotential lines are dense in the narrow space between the electrodes 105 and 106 and the electric field is strong because the equipotential lines are sparse in the center of the pixel. It can be seen that it is. For this reason, when displaying a halftone, it is difficult to control the position of the charged electrophoretic particles 104, and a stable gradation may not be displayed.

  When displaying black, a negative voltage is applied to the pixel electrode 105 to collect and display the electrophoretic particles 104 on the pixel electrode 105, but the electric field in the center direction of the pixel is very weak. Therefore, there is a problem that the charged electrophoretic particles 104 do not reach the center of the pixel and sufficient contrast cannot be obtained.

Furthermore, in a place where the electric field is strong, the polarization of the charged electrophoretic particles 104 and ions becomes very large. Therefore, when the voltage is lowered to 0 V, repulsion between the electrophoretic particles 104 and a counter electric field due to particle / ion attractive force are generated. In some cases, however, the memory performance is hindered.
Furthermore, with regard to colorization, the method of forming a transparent electrode on the above-described color filter complicates the structure, and there is a concern about a decrease in reflectance due to the transparent electrode.

  Therefore, the present invention suppresses the non-uniformity of the electric field in the electrophoretic dispersion, can display a stable halftone and black, can improve the memory property, and in colorization, An object of the present invention is to provide an electrophoretic display device having a simple structure and capable of preventing a decrease in reflectance due to a transparent electrode.

  The present invention holds a sealed electrophoretic dispersion liquid in which electrophoretic particles are dispersed between a first electrode and a second electrode, and applies a voltage between the first electrode and the second electrode. In the electrophoretic display device that moves the electrophoretic particles in the electrophoretic dispersion liquid and changes the distribution state thereof, the electrophoretic display device is connected to the first electrode and extends toward the second electrode. And a resistance layer in which a potential gradient is generated in the layer by a voltage applied between the first electrode and the second electrode, and the resistance layer is colored.

  The present invention also provides a first substrate and a second substrate that are arranged to face each other, a partition that secures a gap between the first substrate and the second substrate, and partitions pixels, the first substrate, An electrophoretic dispersion liquid filled with an electrophoretic particle in a sealed space constituted by a second substrate and the partition wall, a first electrode formed on the first substrate, and formed on the partition wall The electrophoretic particles are moved in the electrophoretic dispersion liquid and the distribution state thereof is changed by applying a voltage between the first electrode and the second electrode. In the electrophoretic display device, the potential gradient is formed in the layer by a voltage connected between the first electrode and extending toward the second electrode, and applied between the first electrode and the second electrode. A resistor layer formed of There are colored, and wherein the.

  According to the present invention, the resistive layer has a resistance layer connected to the first electrode and extending toward the second electrode, and the resistance layer has a potential toward the second electrode in the layer by a voltage applied to the first electrode. A gradient is formed. Accordingly, the potential difference can be reduced at a location where the distance from the resistance layer to the second electrode is short, and the potential difference can be increased at a location far away, so that the unevenness of the electric field in the electrophoretic dispersion liquid can be suppressed. For this reason, the distribution state of the electrophoretic particles in the electrophoretic dispersion liquid can be made substantially uniform, and a stable halftone display can be performed. Further, for example, since the optical level during black display can be lowered, the contrast can be improved. In addition, since there is no place where the electric field acts extremely strongly, the formation of a counter electric field due to the polarization of particles / ions can be suppressed, and the memory performance can be improved.

  Furthermore, since the resistance layer is colored, it is not necessary to provide a separate color filter, and it is possible to maintain good and bright color reproduction and simplify the manufacturing process.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, what attached | subjected the same code | symbol in the same drawing or a different drawing performs the same structure or the same effect | action, The duplication description is abbreviate | omitted suitably about these.

<Embodiment 1>
FIG. 1 shows a part of an electrophoretic display device (electrophoretic display element) 100 to which the present invention can be applied. FIG. 2 is a diagram schematically showing a longitudinal section of one pixel P in the electrophoretic display device 100 having a large number of pixels P. Note that symbol E in the figure indicates a human “eye”, and the figure indicates that the electrophoretic display device 100 is viewed from above. As shown in the figure, the electrophoretic display device 100 includes a first substrate 1 and a second substrate 2 disposed so as to face the first substrate 1. The first substrate 1 and the second substrate 2 are disposed so as to be parallel to each other while maintaining a predetermined gap. A partition wall 6 is provided between the first substrate 1 and the second substrate 2 to partition adjacent pixels P and P. The 2nd board | substrate 2 is comprised with light transmissive boards, such as transparent glass and a transparent film, for example. On the other hand, the 1st board | substrate 1 does not necessarily need to be transparent, and may be comprised with a film substrate, a metal substrate, etc.

  A display surface forming body 8 is formed on the surface of the first substrate 1 (the surface facing the second substrate 2). The display surface forming body 8 is made of a transparent material. As the material, for example, a plastic material such as acrylic resin, epoxy resin, silicone resin, or glass can be used. These may be mixed with inorganic oxide pigments and dyes such as titanium oxide, zinc oxide, and aluminum oxide to be colored and light scattered.

  A first electrode 5 is disposed under the display surface forming body 8. As the first electrode 5, an ITO film can be used, but a metal film such as an Al film may be used. The optimum size of the first electrode 5 depends on the pixel pitch, the height of the partition walls, and the like, but in this embodiment, the size seen from above is a square of 5 μm in length and width.

  As the partition wall 6, a generally used resist material, thermoplastic material, ultraviolet curable material, or the like can be used. The thickness of the partition wall 6 is usually about 5 to 30 μm. A second electrode 7 is formed on the surface of the partition wall 6. The second electrode 7 can be made of a metal film such as Al or Ti, or an ITO film.

  Further, a resistance layer (conductive film) 9 connected to the first electrode 5 is disposed so as to cover the display surface forming body 8. The resistance layer 9 includes a light transmissive material and a pigment material. As the light-transmitting material, an organic film such as polysilane, polysiloxane, or polyacetylene, or a composite, copolymer, or carbon-containing film thereof can be used. In addition, an inorganic film such as indium-tin oxide (ITO), a semiconductor film such as silicone, or a conductive filler (filler), for example, metal powder, carbon particles, or the like is blended in an epoxy resin, a polypropylene resin, or the like. An obtained conductive resin film or the like can also be used.

  Examples of dye materials include dyes such as azo, diazo, anthraquinone, anthracene, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, thioindigo, pyrocholine, fluorvin, and quinophthalone. Can be mentioned.

The resistance layer 9 is prepared by blending these pigment materials with the above light-transmitting materials so as to have a volume resistivity of 10 ⁶ to 10 ¹² Ω · cm and a film thickness of 1 to 200 nm in accordance with desired spectral characteristics. desirable. The resistance layer 9 is configured such that its volume resistivity is lower than that of the above-described electrophoretic dispersion liquid 3.

  An electrophoretic dispersion 3 is enclosed in a sealed space formed between the first substrate 1, the second substrate 2, and the four partition walls 6. The electrophoretic dispersion liquid 3 includes a liquid layer dispersion medium and charged electrophoretic particles 4 dispersed in the liquid layer dispersion medium. Here, as the liquid layer dispersion medium, water, methanol, ethanol, acetone, hexane, toluene, aromatic hydrocarbons such as benzene having a long-chain alkyl group, or other various oils alone or these A mixture of a surfactant and the like can be used.

  The electrophoretic particles 4 are organic or inorganic particles having a property of moving by electrophoresis due to a potential difference in a liquid layer dispersion medium. As the electrophoretic particles 4, for example, one or more of black pigments such as aniline black and carbon black, white pigments such as titanium dioxide and antimony trioxide, azo pigments, and other colored pigments may be used. it can.

  Furthermore, these pigments include electrolytes, surfactants, resins, rubbers, oil-based charge control agents, titanium-based coupling agents, aluminum-based coupling agents, silane-based coupling agents, etc., as necessary. A dispersant, a lubricant, a stabilizer and the like can be added. Further, in the present embodiment, a drive voltage generator (not shown) that generates a drive voltage is connected between the first electrode 5 and the second electrode 7.

  Next, the operation of the electrophoretic display device 100 configured as described above will be described. In the following description, the case where the electrophoretic particles 4 are positively charged is taken as an example, but conversely, even when the electrophoretic particles 4 are negatively charged, the direction of movement of the electrophoretic particles 4 is different. The same explanation can be made in consideration of the reverse.

  3A, 3B, and 3C are diagrams showing various signal waveforms for one pixel of the electrophoretic display device 100. FIG. Among these, (a) shows the potential of the first electrode 5, and (b) shows the potential (conductive film potential) at point A of the resistance layer 9 in FIG. And (c) shows an optical response. The horizontal axis common to (a), (b), and (c) indicates time. Among these, the period from time t1 to time t2 corresponds to the reset period, and the period from time t2 to time t3 corresponds to the writing period. The potential of the second electrode 7 is 0V.

  In the reset period, a reset voltage Vr is applied to the first electrode 5 in order to align the electrophoretic particles 4 at a predetermined position. At this time, the potential of the resistance layer 9 at the point A in FIG. 1 becomes a potential between the potential (0 V) of the second electrode 7 and the potential Vr of the first electrode 5 by resistance division.

  Thereafter, when the writing period starts, the writing voltage Vw is applied to the first electrode 5 at time t2, the potential of the resistance layer 9 also changes, and is lower than the potential Vw of the first electrode 5 due to resistance voltage division. It becomes a potential.

  After the completion of writing (time t3), the voltage of the first electrode 5 is reduced to 0V and the display state maintaining period is started. If the resistance of the resistance layer 9 is made sufficiently lower than the resistance of the liquid layer dispersion medium, residual DC will not accumulate, so an electric field in the reverse direction will not be generated immediately after dropping to 0 V, and the memory performance will not be impaired. .

  In such a configuration, the first electrode 5 and the second electrode 7 are connected via the resistance layer 9, and when a drive voltage is applied, a potential gradient is generated in the resistance layer 9, resulting in resistance voltage division. Thus, the potential of the resistance layer 9 becomes smaller as the potential is closer to the second electrode 7. The equipotential lines at this time are shown in FIG. Since the equipotential line interval between the first electrode 5 and the second electrode 7 is significantly wider than in the prior art (see FIG. 6), the electric field in the vicinity of the second electrode 7 of the partition 6 is reduced. Therefore, the electric field non-uniformity in the liquid layer dispersion medium is eliminated, and a stable halftone display can be obtained.

  In addition, since the first electrode 5 is formed in the central portion of the display pixel, a horizontal electric field is generated toward the center when displaying black, so that the particles reach the central portion and the contrast is remarkably increased. Can be improved.

  Furthermore, by making the electric field uniform, a counter electric field due to the polarization of particles and ions can be suppressed, and a sufficient memory property can be obtained.

<Embodiment 2>
FIG. 4 shows an electrophoretic display device 100A according to the second embodiment. This figure corresponds to FIG. 1 in the first embodiment described above. In the present embodiment, the first electrode 12 and the resistance layer 9 are connected via the contact portion 11. In such a configuration, since the resistance layer 9 has a simple planar shape, it can be formed to have a uniform layer thickness to reduce surface irregularities (steps). The problem of sticking to unevenness can be solved.

  In addition, the contact portion 11 is disposed substantially at the center of the pixel P. That is, it is arranged at a position farthest from each second electrode 7. As a result, the potential difference between the center portion of the pixel P and the second electrode 7 becomes the largest, and a horizontal electric field is generated toward the center during black display, so that the electrophoretic particles 4 reach the center portion. Contrast is greatly improved.

  The contact portion 11 is preferably made of a material lower than the resistance of the resistance layer 9, and a metal such as Al or Ti, ITO, or a conductive resin may be used. When the resistance of the contact part 11 is low, the potential drop at the contact part 11 can be suppressed, and the voltage can be applied to the liquid layer dispersion medium more efficiently than in the first embodiment. Further, when the contact portion 11 is made of metal, even if the diameter of the contact portion 11 is reduced, the resistance of the connection portion can be sufficiently reduced, so that the area of the effective portion for display is widened, and a bright and good display can be obtained. It is done.

  In the present embodiment, the first electrode 12 is further formed on the unevenness 13. The unevenness 13 can be formed, for example, by applying a photosensitive resin and then performing exposure and wet development. Moreover, the method of making a fine unevenness | corrugation in glass may be used. As the material of the first electrode 12 formed on the unevenness 13, a material having high reflectivity such as aluminum or silver is desirable. With such a configuration, the first electrode 12 can have a function of diffusing light. Since the distribution of the inclination angle of the unevenness 13 can be controlled, the viewing angle can be expanded and the external light can be reflected efficiently, a better display brighter than that of the first embodiment can be obtained.

  When the electrophoretic display device 100A described above is colored, the method using a color filter is the simplest. There are two types of color filters: a case where the color filter is formed on the substrate side and a case where the color filter is formed on the electrode. As for the former, since the cell is assembled so that the color filter and the pixel match, there is always a misalignment in manufacturing. Since misalignment causes color mixture between adjacent pixels, it is necessary to provide a black matrix for the alignment margin on the substrate side. For this reason, it is difficult to obtain a high aperture ratio. In particular, when a high-definition pixel of 150 ppi or more is formed, or when a plastic substrate having a high thermal expansion coefficient is used, the aperture ratio is remarkably lowered, which is not practical.

  FIG. 7 shows an example in which the latter, that is, a color filter is formed on an electrode. As shown in the figure, a decrease in the aperture ratio can be suppressed by forming the color filters 109a, 109b, and 109c directly in the pixel P. However, in such a cell configuration, residual DC that causes burn-in occurs.

  As a countermeasure, there is a method in which a transparent electrode is formed on an insulating layer, that is, a color filter, so that residual DC of the insulating layer does not accumulate. However, the structure is complicated, and there is a concern that the reflectance is lowered by the transparent electrode. Is done.

  Therefore, in the present embodiment, the resistance layer 9 formed on the first electrode 12 is also used as the colored layers 10a, 10b, and 10c. The colored layer is made of, for example, an ultraviolet curable acrylic resin resist in which a pigment of red, blue, green, cyan, or magenta is dispersed. The film thickness is usually about 0.5 to 4 μm, and a contact portion 11 is formed at the center of the pixel P.

  The display surface forming body 8 uses a transparent material. For example, a plastic material such as acrylic resin, epoxy resin, or silicone resin, or glass can be used.

  As described above, in the present embodiment, since the resistance layer 9 also serves as the color filters 10a, 10b, and 10c, there is no need to provide a separate color filter, and it is possible to maintain good and bright color reproduction and to maintain the manufacturing process. Simplification can be achieved.

FIG. 3 is a diagram schematically illustrating a vertical cross section of one pixel in the electrophoretic display device according to the first embodiment. 3 is a diagram showing equipotential lines in the driving state of the electrophoretic display device of Embodiment 1. FIG. 2 is a diagram illustrating various signal waveforms for one pixel of the electrophoretic display device of Embodiment 1, wherein (a) is a first electrode potential, (b) is a conductive film potential at point A, and (c) is an optical response. FIG. ing. FIG. 6 is a diagram schematically showing a vertical cross section of one pixel in an electrophoretic display device according to a second embodiment. (A), (b) is a figure which shows typically the longitudinal cross-sectional view of 1 pixel of the conventional electrophoretic display element. It is a figure which shows the equipotential line in the drive state of the conventional electrophoretic display apparatus. It is a figure explaining the color filter of the conventional electrophoretic display element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st board | substrate 2 2nd board | substrate 3 Electrophoretic dispersion liquid 4 Electrophoretic particle 5 1st electrode 6 Partition 7 Second electrode 8 Surface formation layer 9 Resistance layer 10a, 10b, 10c
Colored layer 11 Contact portion 100, 100B, 100C, 100D
Electrophoretic display device

Claims (11)

By holding an electrophoretic dispersion in a sealed state in which electrophoretic particles are dispersed between the first electrode and the second electrode, and applying a voltage between the first electrode and the second electrode, In the electrophoretic display device that moves the electrophoretic particles in the electrophoretic dispersion and changes the distribution state thereof,
A resistance layer connected to the first electrode and extending toward the second electrode, wherein a potential gradient is generated in the layer by a voltage applied between the first electrode and the second electrode The resistance layer is colored,
An electrophoretic display device. A first substrate, a second substrate, a partition that secures a gap between the first substrate and the second substrate, and partitions pixels; the first substrate, the second substrate, and the partition; An electrophoretic dispersion liquid in a state where electrophoretic particles are dispersed, a first electrode formed on the first substrate, and a second electrode formed on the partition wall. In the electrophoretic display device that moves the electrophoretic particles in the electrophoretic dispersion liquid by applying a voltage between the first electrode and the second electrode, and changes the distribution state thereof.
A resistance layer connected to the first electrode and extending toward the second electrode, wherein a potential gradient is formed in the layer by a voltage applied between the first electrode and the second electrode The resistance layer is colored,
An electrophoretic display device. The resistance layer and the second electrode are connected;
The electrophoretic display device according to claim 1 or 2. The first electrode is disposed in the center of the sealed space;
The electrophoretic display device according to claim 2 or 3. The resistance value of the resistance layer is lower than the resistance value of the electrophoretic dispersion,
The electrophoretic display device according to claim 1, wherein the electrophoretic display device is provided. The volume resistivity of the resistance layer is 10 ⁶ to 10 ¹² Ω · cm.
The electrophoretic display device according to claim 1, wherein the electrophoretic display device is an electrophoretic display device. The first electrode and the resistance layer are connected via a contact portion;
The electrophoretic display device according to claim 2, wherein the electrophoretic display device is an electrophoretic display device. The contact portion is disposed in the center of the sealed space;
The electrophoretic display device according to claim 7. The colored resistance layer includes a colored layer of at least one of red, blue, green, cyan, magenta, and yellow.
The electrophoretic display device according to any one of claims 5 to 8. A resistance value of the contact portion is lower than a resistance value of the resistance layer;
The electrophoretic display device according to claim 9. The contact portion is made of metal;
The electrophoretic display device according to claim 10.

Images