JP2006215473A - Electrophoretic display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophoretic display device which is driven and conducts a display with a low voltage, and in which a displayed image is stably retained for a long period of time. <P>SOLUTION: The electrophoretic display device 101 is equipped with a first substrate 1 and a second substrate 2 in positions opposite to each other, is constructed with a first electrode 3 disposed on the inside of the first substrate 1, a second electrode 5 disposed on the inside of the second substrate 2, charged films 7 formed so as to cover the insides of the first electrode 3 and the second electrode 5, and an insulating liquid 10 having a plurality of charged particles 6 dispersed therein and arranged in a gap between the opposing charged films 7, and further stably retains the displayed picture for a long period of time by forming protrusions 9 to generate a difference of electric field density on a fixing surface 4 formed with the charged films 7. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophoretic display device, and more particularly to an apparatus for performing display by moving charged particles in a liquid.

  2. Description of the Related Art Conventionally, an electrophoretic display device has been proposed in which chargeable particles are arranged between a pair of opposing substrates and display is performed based on the movement of these particles by application of a voltage. In this electrophoretic display device, since it is desired to realize a function of stably holding a display state for a long time, a device using a charged film such as an electret film having an excellent charge holding function ( Patent Document 1) has been proposed.

  FIG. 6 is a cross-sectional view showing an example of a conventional electrophoretic display device using an electret film. The electrophoretic display device 104 shown in FIG. 6 includes two opposing substrates 21 and 22, a spacer 29 that separates the pixels between the substrates, and electrodes 23 and 25 provided inside the substrates 21 and 22. The electret film 27 having a stationary charge provided so as to cover these two electrodes, and the colored liquid 30 encapsulated inside the electret film 27 and dispersed with the positively charged charged particles 26 are formed. Is done.

  In the electrophoretic display device 104, for example, when a negative voltage is applied to the electrode 25, the color of the colored liquid 30 is visually recognized by the movement of the charged particles 26 in the vicinity of the electrode 25. On the other hand, when the voltage application is stopped, the electrification property of the electret film 27 keeps the attractive force between the charged particles 26 and the electret film 27, and the charged particles 26 stay in the vicinity of the position where the voltage particles moved when the voltage is applied. To do. Thereby, a threshold value can be set between the voltage value when moving the charged particles 26 and the voltage value when retaining the charged particles 26, and the display holding time when no voltage is applied is kept long by the attractive force generated by the electret film 27. Improvements have been made.

  In addition, an electrophoretic display device is also proposed in which a transparent display electrode is formed between two opposing transparent display substrates and a partition wall, and transparent display electrodes are provided on the inner sides between these substrates (Patent Document 2). reference). In this case, these two transparent display electrodes are each covered with a charged film having a regular charge (for example, negative charge), and further, a colored insulating liquid in which, for example, positively charged colored charged particles are dispersed is disposed inside. It is configured to be enclosed. Then, by inducing a negative charge on one of the transparent display electrodes and a positive charge on the other, the colored charged particles are fixed on the electrode side on which the negative charge is induced. Thereafter, even when the electrostatic attractive force disappears by opening or shorting both transparent display electrodes, the colored charged particles are continuously maintained by the electrostatic attractive force of the surface charge of the charged film. This realizes a stable memory characteristic for a long time even in a case where the open state of the circuit cannot be effectively maintained as in the case of simple matrix driving.

US Pat. No. 3,612,758 JP 2000-258805 A

  However, as described in Patent Documents 1 and 2, there is a conventional electrophoretic display device in which two electrodes arranged at opposite positions are covered with a charged film having surface charges of the same polarity. Therefore, when the display holding time when voltage is not applied is to be extended, the electric fields formed by the charged films at the opposite positions work to cancel each other, so that there is a gap between the charged film and the charged particles. In order to generate a sufficient attractive force, a large surface potential is required.

  Further, when a charged film such as an electret film is patterned into a shape such as a pixel unit or a pattern without covering the entire electrodes, a large electric field is generated at the outer peripheral portion of the patterned charged film. However, the electric field generated on the surface of the charged film inside the outer peripheral portion is smaller than that in the outer peripheral portion. That is, even in a charged film such as an electret film, the generation of an electric field is not uniform depending on the position, and when moving charged particles on a substrate subjected to patterning as described above, the voltage is low and constant. There is a problem that the threshold value of the voltage cannot be applied.

  Therefore, the present invention provides an electrophoretic display device capable of displaying an image at a low voltage and capable of holding the image display for a long time even when no voltage is applied. It is the purpose.

  The present invention covers a set of electrodes at least one of which is divided for each pixel, charged particles dispersed in an insulating liquid disposed between the electrodes, and the set of electrodes, And a set of charged films that form a fixing surface for fixing the charged particles made of a material, and the charged particles are moved to one of the set of fixing surfaces by applying a voltage between the electrodes. In the electrophoretic display device in which the charged particles are fixed to the respective fixing surfaces when the voltage between the electrodes is not applied, the charged film causes a difference in electric field density on the fixing surface. It has a difference generating part.

  According to the electrophoretic display device of the present invention, a charged film that covers a pair of electrodes and forms a fixing surface for fixing charged particles that move when a voltage is applied is provided on the fixing surface. Since the difference generating portion is generated, an image can be driven and displayed at a low voltage, and a display image can be held for a long time even when no voltage is applied.

<First Embodiment>
Hereinafter, an electrophoretic display device which is a particle movement type display device according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic sectional view showing an example of the configuration and display state of the electrophoretic display device according to the first embodiment, FIG. 2 is an explanatory view showing a first example of a recess formed in the electret film, and FIG. It is explanatory drawing which shows the 2nd example of the recessed part formed in an electret film | membrane.

  An electrophoretic display device 101 shown in FIG. 1 has a first substrate 1 and a second substrate 2 facing each other, a first electrode 3 disposed on the inner side of the first substrate 1, and an inner side of the second substrate 2. The charged electrode 7 formed so as to cover the inside of the first electrode 3 and the second electrode 5, and a plurality of charged particles 6 dispersed and opposed to each other. And an insulating liquid 10 disposed in the gap of the film 7. The electrophoretic display device 101 is referred to as a vertical electrophoretic display device by performing image display by moving the charged particles 6 up and down between the first electrode 3 and the second electrode 5.

  The set of the two substrates 1 and 2 and the electrodes 3 and 5 is sufficient if at least one of them is made of a transparent material having a substantially high light transmittance. In this embodiment, the visible light transmittance is high. Glass is used for the first substrate 1 and indium tin oxide (ITO) having a high visible light transmittance is used for the first electrode 3. The second electrode 5 is made of aluminum, and the second substrate 2 is made of glass. In addition, at least one of the first electrode 3 and the second electrode 5 may be divided for each pixel, and in the present embodiment, the second electrode 5 is divided for each pixel.

The insulating liquid 10 is a non-polar solvent having a high insulating property, which is colored with a blue dye. The charged particles 6 exhibit good charging characteristics in a dispersion medium such as the insulating liquid 10. TiO ₂ is used. The particle size of the charged particles 6 is usually about 0.01 to 50.0 [μm], preferably about 0.1 to 10.0 [μm]. Further, it is desirable that a polar ion adsorbent such as alumina or silica is added to the insulating liquid 10, and alumina is used in this embodiment. By adding this polar ion adsorbent, the ion concentration in the insulating liquid 10 is kept low, and a high insulating property of about 1E + 12 [Ω · cm] to 1E + 15 [Ω · cm] is maintained as the volume resistivity. Therefore, a decrease in the surface charge of the electret film due to ion adsorption can be ignored.

  For the charged film 7, for example, an electret film made of an electret material or a dielectric material (particularly a ferroelectric material) that spontaneously polarizes is used so that a steady charged state is maintained. This electret film freezes and holds the polarization charge over a long period of time, so that one surface is charged with a positive charge, the other surface is charged with a negative charge, and an electric field is generated outside thereof. . Due to this property, the charged particles 6 are attracted only by the attractive force of the charged film 7 even when no voltage is applied to the first electrode 3 and the second electrode 5, and the state where the charged particles 6 are held as they are continued. In the present specification, since the electret material is used as the material of the charged film 7, the charged film 7 is hereinafter referred to as the electret film 7.

  As shown in FIG. 1, the electret film 7 has a plurality of concave portions (difference generating portions) 9 which are through holes respectively reaching the first electrode 3 or the second electrode 5 from the surface thereof. By having the concave portion 9 which is the through hole, the electret film 7 has not only an end portion located on the outer periphery thereof but also an angular end portion in the surface thereof. Originally, there is a difference in the electric field density in the vicinity of the end portion of the electret film 7 and the electric field density is increased, so that the electric field strength in the vicinity of the concave portion 9 is increased. Due to this property, even if the surface charge density of the electret film 7 without the recess 9 is low, a strong electric field is generated in the vicinity of the recess 9 by forming the recess 9 in the surface of the electret film 7. As a result, the attractive force applied to the charged particles 6 increases. In addition, when the voltage is applied to the first electrode 3 and the second electrode 5, the charged particles 6 move in the vicinity thereof, and the charged particles 6 are distributed and held in the vicinity of the surface of the electret film 7. The vicinity of the surface is the fixing surface 4.

  The recesses 9 are formed on the surface of each electret film 7 so as to form stripes at equal intervals. The size of the recesses 9 is such that the charged particles 6 do not fit into the opening width of the recesses 9. The opening width is shorter than the diameter of the charged particles 6. This is because, if the charged particles 6 are fitted in the recesses 9, the influence of the attractive force or repulsive force generated by each electrode does not easily reach the charged particles 6 and prevents the movement and fixing from being performed smoothly. Because. Further, the interval between the recessed portions 9 provided side by side (that is, the width of each electret film 7) is formed to be approximately the diameter of the charged particles 6.

  Next, the operation of the electrophoretic display device 101 shown in FIG. 1 will be described.

  In the electrophoretic display device 101, the first electrode is applied to the charged particles 6 arranged in the gap between the first substrate 1 and the second substrate 2 arranged opposite to each other by a voltage application unit (not shown). An image is displayed by applying a voltage to 3 and the second electrode 5 and moving the charged particles 6.

  For example, when the first electrode 3 is set to the ground potential and a voltage having the same polarity as the charged particles 6 and higher than the threshold is applied to the second electrode 5, as shown in the pixel Aa in FIG. Since it moves to the vicinity of the 1st electrode 3, the color of the charged particle 6 is visually recognized from an observer (upward view in FIG. 1). Here, the threshold value refers to a boundary value of a voltage necessary for generating an attractive force stronger than the attractive force of the electret film 7. Further, when a voltage having a polarity opposite to that of the charged particles 6 is applied to the second electrode 5, the charged particles 6 move to the vicinity of the second electrode 5 as shown in the pixel Ba of FIG. The blue color of the insulating liquid 10 is visually recognized by the observer.

  Further, the attractive force generated by the electret film 7 described above will be described in more detail. When one charged particle 6 is fixed and held in one of the recesses 9 on the pixel Ba side shown in FIG. 6 receives a strong attractive force in the direction of the arrow L1 and a weak repulsive force in the direction of the arrow L2. When these forces are added together, the charged particles 6 are fixed and held on the concave portions 9, that is, the fixing surface 4, because they act as attractive forces with respect to the charged particles 6 as a whole. At this time, since the interval between the adjacent concave portions 9 is set to be approximately the diameter of the charged particles 6, the charged particles 6 are fixed on the entire surface of the electret film 7 (fixing on the second electrode 5 side in the pixel Ba shown in FIG. 1). The entire surface 4) is attracted with a substantially uniform force and is held at a high density.

  On the other hand, when a voltage equal to or lower than the threshold is applied to the first electrode 3 and the second electrode 5 or when no voltage is applied, the charged particles 6 that have been moved in the vicinity of the respective electrodes have the recesses 9. It is held in a state of being attracted to the concave portion 9 as it is by the attractive force acting in the vicinity of. As a result, the display image when the voltage is applied immediately before is held for a long time (semi-permanent).

  When the surface of the electret film 7 is charged with a charge having a polarity opposite to that of the charged particles 6, the charged particles 6 are attracted to the surface of the electret film 7 sandwiched between the recesses 9. For this reason, when the concave portions 9 are arranged at a distance of about the diameter of the charged particles 6, the concave portions 9 are dense and substantially uniform on the entire fixing surface 4 as in the case of FIG. Thus, the charged particles 6 are attracted.

  Incidentally, the arrangement shape of the recesses 9 in the electrophoretic display device 101 shown in FIG. 1 is shown in FIG. 2 as viewed from above.

  In FIG. 2, a plurality of concave portions 9 each having an elongated rectangular shape are regularly arranged in a stripe shape with an equal interval of approximately the diameter of the charged particles 6. As another example of the arrangement shape, as shown in FIG. 3, a plurality of circular recesses 9 regularly form a regular triangle having sides with a length approximately equal to the diameter of the charged particles 6. There is also a thing arranged in. When the charged particles 6 fixed to the electret film 7 are attracted and arranged in the concave portions 9 having the arrangement shape as shown in FIG. 2 or FIG. Thus, the display contrast becomes better.

  Next, a manufacturing method of the electrophoretic display device in the present embodiment will be described.

  Examples of the electret material include all dielectric materials including an inorganic material such as glass. From the viewpoint of mass productivity, an organic polymer material that can cope with a printing process is more preferable. Fluorine resins such as Teflon (registered trademark) (Teflon-FEP, Teflon-TFE) are particularly excellent in terms of performance, and other polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyvinyl chloride, polyethylene terephthalate, polyimide, etc. Is preferred.

  Hereinafter, the electret material will be described in more detail.

The origin of electrets lies in the formation of polarization and its freezing. As freezing polarization,
1. Charge separation by microscopic or macroscopic displacement of ions contained in the dielectric,
2. Anisotropy orientation by an external electric field of an intramolecular permanent dipole composed of a polar group, etc.
3. Charge injection by corona discharge generated in the gap between the corona discharge electrode or electrode and dielectric,
The one by is representative.

  Polarization charge due to ionic charge separation or dipole orientation becomes a hetero charge having a polarity different from that of the external electric field application electrode, and polarization charge due to corona discharge injection becomes a homo charge having the same polarity. According to the measurement by thermally stimulated current (TSC), deep traps of electrons, holes, ions, etc. present in mismatched parts such as grain boundaries inside the dielectric, particularly near the surface, cause polarization charge freezing. It is thought that

There are various methods for forming electrets. As a representative method,
1. A method of heating the dielectric to the softening temperature or near the melting temperature and cooling it while applying a high electric field DC (thermo-electret method),
2. A method of applying corona discharge to the dielectric surface or applying a high electric field DC (˜10 ⁶ V / cm) close to a dielectric breakdown voltage at room temperature (electro-electret method),
3. Method of radiating high-energy radiation (electron beam, γ-ray) to insulator in vacuum (radio electret method),
4). A method of applying high voltage DC during light irradiation (photo electret),
5. Method by mechanical deformation by pressurization / stretching (mechano / electret),
Etc.

  In addition, among these methods, when the treatment is performed by the thermo-electret method, the electret film 7 may be immersed in a nonpolar solvent, more preferably a solvent used during driving.

  It should be noted that any method may be used to form the recess 9 that causes a difference in charge density in the electret film 7. For example, when performing the above-described electret treatment, a part of the surface may be covered, and the coating may be removed after the treatment so that the charge for the coating is reduced.

  Alternatively, the electret material 7 may be partially formed in the electret film 7 by performing a process of forming the electret on a local portion of the electret material. You may form the said through-hole as the recessed part 9 by performing the electret process after patterning in the shape in which the through-hole was formed.

  In addition, when providing a region having a low surface charge density on the electret material as the recess 9, a layered region made of another substance that is difficult to be charged is formed on the surface of the electret material or in a place such as the inside. It is good also as an area | region where a surface charge density is low by performing electretization after that. Examples of the other substances mentioned above include metals, or materials that do not form a large polarization under electret processing conditions, or have a volume resistivity that is less problematic than electret films, and the charge disappears in a short time. Any material such as a resin or an inorganic material may be used as long as it is a material that would end up. Further, after the entire surface has been electretized, it may be partially heated and cooled to partially reduce the surface charge density, but is not limited thereto.

  As described above, according to the electrophoretic display device 101 according to the first embodiment, the difference in the electric field density in the electret film 7 that forms the fixing surface 4 that covers the first electrode 3 and the second electrode 5. Since the concave portion 9 to be generated is provided, the charged particles 6 can be attracted even when no voltage is applied or the electrode is short-circuited, so that the display image can be held for a long time (semi-permanent).

  Further, according to the electrophoretic display device 101 according to the first embodiment, since the concave portion 9 is provided on the fixing surface 4 formed by the electret film 7, the attractive particles 6 are attracted with a small surface charge density. Will be able to. Further, since the attractive force can be made uniform in the plane, there is no region having a threshold larger than necessary, and the image display by the electrophoretic display device 101 can be driven at a lower voltage.

  Further, according to the electrophoretic display device 101 according to the first embodiment, since the concave portions 9 are arranged on the fixing surface 4 formed by the electret film 7 so as to be uniform, the surface charge density is uniform with a minute surface charge density. Attractive force can be exerted on the charged particles, and the range of electret material selection can be expanded.

  Further, according to the electrophoretic display device 101 according to the first embodiment, when the recess 9 is provided in the electret film 7, the recess 9 is sized so that the charged particles 6 do not fit therein. Since the electret film 7 sandwiched between the concave portions 9 has a diameter equal to or smaller than the diameter of the charged particles 6 and is approximately equal to the diameter of the charged particles 6, the charged particles 6 can be held densely on the entire surface of the electret film 7. become.

  Further, according to the electrophoretic display device 101 according to the first embodiment, the recessed portion 9 is disposed as a recess or a through hole, and the embedded member is provided in the recessed portion 9, so that the charged particles 6 are fitted into the recessed portion 9. You can prevent that.

  In the first embodiment, the electrophoretic display device 101 has been described without providing a member that separates the pixels Aa and Ba. However, the configuration may be such that the pixels and the predetermined space are separated by a partition wall or the like. To do.

  In the first embodiment, the electrophoretic display device 101 has been described as being an upper and lower type electrophoretic display device. However, the electrophoretic display device 101 may be a horizontal electrophoretic display device. It is good also as a display apparatus which is not contained in the above-mentioned type | mold which moves a diagonally. Here, the horizontal electrophoretic display device is formed by arranging a plurality of electrodes on one substrate (for example, the center and the periphery of a pixel) without arranging electrodes on opposite substrates like the electrophoretic display device 101. An electrophoretic display device that displays images by moving charged particles in the horizontal (horizontal) direction.

<Second Embodiment>
Next, an electrophoretic display device according to a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a schematic side view showing an example of the configuration and display state of the electrophoretic display device according to the second embodiment. However, the same reference numerals are given to components common to FIG. 1, and the description of FIG. 1 is used.

  In the electrophoretic display device 102 shown in FIG. 4, at least two kinds of charged particles 6a and 6b having different optical characteristics and charging characteristics are dispersed, and a transparent insulating liquid 10 having a high visible light transmittance is sealed. ing. The charged particles 6a are white and charged positively, the charged particles 6b are black and charged negatively, and the surface of the electret film 7 on the fixing surface 4 side is charged positively. The electrophoretic display device 101 shown in FIG. 1 is different from the electrophoretic display device 101 described above, and the other configuration is the same as that of the electrophoretic display device 101. The electrophoretic display device 102 is a vertical electrophoretic display device, similar to the electrophoretic display device 101.

  In the electrophoretic display device 102, when the first electrode 3 is set to the ground potential and a positive voltage equal to or higher than the threshold value is applied to the second electrode 5, the white charged particles 6a are the first as shown in the pixel Ab of FIG. Since it moves to the vicinity of one electrode 3, the observer sees the white color of the charged particles 6a.

  When a negative voltage equal to or higher than the threshold value is applied to the second electrode 5, the black charged particles 6 b move to the vicinity of the first electrode 3 as shown in the pixel Bb of FIG. Shows the black color of the charged particles 6b.

On the other hand, when a voltage equal to or lower than the threshold is applied, or when no voltage is applied, the charged particles 6a and 6b do not move because they are not affected by the first electrode 3 or the second electrode 5.
At this time, the white charged particles 6a charged to the positive polarity continue to be attracted to the concave portion 9 of the electret film 7, and the black charged particles 6b charged to the negative polarity continue to be attracted to the fixing surface 4 of the electret film. As a result, the display state of the pixel is stably maintained for a long time regardless of whether the color is white or black.

  As described above, according to the electrophoretic display device 102 according to the second embodiment, the concave portion 9 is provided in the electret film 7 covering the first electrode 3 and the second electrode 5, and at least the optical characteristics and the charging characteristics are provided. Since the insulating liquid 10 having a high visible light transmittance in which two or more different types of charged particles 6a and 6b are dispersed is sealed, an electrophoretic display device including a plurality of types of charged particles having different polarities is also used. The display image can be held for a long time.

  In addition, according to the electrophoretic display device 102 according to the second embodiment, the electret film 7 is formed because the charged particles 6a charged to the positive polarity and the charged particles 6b charged to the negative polarity are arranged between the opposing substrates. The concave portion 9 formed on the concave portion 9 generates an attractive force substantially equal to that of the charged particle 6b having the same polarity as that of the charged particle 6b having a polarity different from the surface charge, and can hold the charged particle 6b for a long time. it can.

  In the second embodiment, the electrophoretic display device 102 has been described without providing a member that separates the pixels Ab and Bb. However, the configuration may be such that the pixels and the predetermined space are separated by a partition wall or the like. And

  Further, in the second embodiment, the electrophoretic display device 102 has been described as being a vertical electrophoretic display device. However, the electrophoretic display device 102 may be a horizontal electrophoretic display device. It is good also as a display apparatus which is not contained in the above-mentioned type | mold which moves a diagonally.

<Third Embodiment>
Next, an electrophoretic display device according to a third embodiment of the present invention will be described with reference to FIG. FIG. 5 is a perspective view illustrating an example of the configuration and display state of the electrophoretic display device according to the third embodiment. However, the same code | symbol is attached | subjected about the structure which is common in FIG.1 and FIG.4, and description of FIG.1 and FIG.4 is used.

  The electrophoretic display devices 101 and 102 in FIG. 1 and FIG. 4 described above are vertical electrophoretic display devices that perform display by moving the charged particles 6 to the opposing substrate sides (that is, moving them up and down). Although described, in the present invention, the arrangement of these electrodes is not particularly limited. Therefore, in this embodiment, an example of a horizontal electrophoretic display device will be described below with reference to FIG.

  As shown in FIG. 5, in the electrophoretic display device 103, the second electrode 5 and the insulating layer 11 are provided on the second substrate 2, and the first electrode 3 that also serves as a partition is provided between the pixels. . On the inner side surface of the first electrode 3 and the surface of the insulating layer 11 on the second electrode 5, an electret film 7 having a recess 9 is disposed. On the inner side surface portion of the first electrode 3, the recesses 9 are provided in a stripe shape extending vertically, and on the second electrode 5, the recesses 9 are provided in a lattice shape. A transparent insulating liquid 10 in which a plurality of charged particles 6 are dispersed is sealed in a space surrounded by the electret film 7 and the first substrate 1.

  In the electrophoretic display device 103 having the above-described configuration, when the first electrode 3 is set to the ground potential and a positive voltage higher than the threshold value is applied to the second electrode 5, the positive polarity is obtained as shown in the pixel Ac in FIG. The charged charged particles 6 move to the vicinity of the side surface of the first electrode 3. At this time, when the charged particles 6 are black and the electret film 7 and the concave portion 9 are white, white is visually recognized by the observer.

  Further, when a negative voltage equal to or higher than the threshold value is applied to the second electrode 5, the charged particles 6 move to the vicinity of the surface of the second electrode 5 as shown by the pixel Bc in FIG. 5. Thereby, when the charged particles 6 are black, the observer sees the black of the charged particles 6.

  On the other hand, when a voltage equal to or lower than the threshold is applied or when no voltage is applied, the charged particles 6 are not affected by the first electrode 3 or the second electrode 5 and are attracted to the vicinity of the recess 9 of the electret film 7 as they are. Therefore, the display state until immediately before is stably held for a long time.

  As described above, according to the electrophoretic display device 103 according to the third embodiment, the electret film 7 that covers the first electrode 3 that also serves as the partition wall that separates the pixels and the second electrode 5, respectively. Therefore, the horizontal electrophoretic display device 103 can be driven at a low voltage, and the display image can be long even when no voltage is applied or when the electrodes are short-circuited. It can be held over time.

  In the third embodiment, in the electrophoretic display device 103, only one type of charged particle 6 colored black is moved between the first electrode 3 and the second electrode 5 provided in the horizontal direction. As described above, two types of charged particles of different colors may be charged with different polarities, arranged and moved.

  In the first to third embodiments described above, it has been described that glass is used for the first substrate 1 and the second substrate 2, but a material that requires light transmission is used. When used, in addition to plastic films such as polyethylene terephthalate (PET), polycarbonate (PC) and polyethersulfone (PES), glass, quartz, etc. can be used, and when light transmission is not required Colored materials such as polyimide (PI), metals such as stainless steel, and the like can be used. Needless to say, when a metal is used as the substrate, it is necessary to provide an insulating layer between the substrate and the wiring and electrodes.

  In the first to third embodiments, it has been described that indium tin oxide and aluminum are used for the first electrode 3 and the second electrode 5, but the first electrode 3 and the second electrode 5 can be patterned. Any conductive material may be used. For example, a metal such as titanium (Ti), aluminum (Al), or copper (Cu), an oxide such as indium tin oxide (ITO), carbon or silver paste, or an organic conductive film can be used. Of these first electrode 3 and second electrode 5, it is necessary to use one having a high visible light transmittance, such as indium tin oxide, which is disposed on a substrate having at least a high light transmittance.

  In the first to third embodiments, when the simple matrix driving is adopted as the driving method, the first electrode 3 or the second electrode 5 may be formed in a line shape connecting a plurality of pixels. In addition, it is not particularly limited which material these electrodes are formed using, for example, even if the electrode is patterned using a known photolithography technique after forming a conductive film, It may be printed using conductive ink.

In the first to third embodiments, TiO ₂ is used as the charged particles 6. However, any material that exhibits good charging characteristics in a dispersion medium such as the insulating liquid 10 is used. For example, inorganic pigments and organic pigments such as TiO ₂ , Al ₂ O ₃ , and carbon black can be used, and further, resins, resins containing pigments, resins dyed with dyes Etc. can also be used.

  In the first to third embodiments, the description has been made on the assumption that isoparaffin is used for the insulating liquid 10. However, other nonpolar solvents having high insulating properties such as silicone oil and xylene and toluene are also used. Also good. Further, as the colored insulating liquid 10, those obtained by coloring these liquids with a dye can be used.

  In the first to third embodiments, the polar ion adsorbent is added to the insulating liquid 10. However, a charge control agent is added to the insulating liquid 10. May be. As such a charge control agent, for example, a metal complex salt of a monoazo dye, salicylic acid, an organic quaternary ammonium salt, a nigrosine compound, or the like can be used. Further, a dispersing agent for preventing aggregation of the charged particles 6 and maintaining a dispersed state may be added to the insulating liquid 10. As such a dispersing agent, polyvalent metal phosphates such as calcium phosphate and magnesium phosphate, carbonates such as calcium carbonate, other inorganic salts, inorganic oxides, organic polymer materials, and the like can be used.

  In the first to third embodiments, the recess 9 is described as being a through hole. However, the recess 9 can be provided on the electret film 7 such as a through hole. There are cases where the space itself is indicated and cases where a material other than the electret film 7 is embedded in the space. Furthermore, when the former concave portion 9 is a space, there are a case where the concave portion 9 is a space penetrating the electret film 7 and a case where the concave portion 9 is not penetrated but has a recess. The state in which the material other than the electret film 7 is embedded in the latter concave portion 9 refers to a state in which the embedded member is filled in the concave portion 9 having the above-described space, but a part of the concave portion 9 (for example, The embedded member may be in a state where the member is disposed in the recess 9 so that the member is disposed on the bottom of the recess 9).

  In addition to the above, a mode in which a material other than the electret film 7 is applied in the form of spots on the surface of the electret film 7 is present, and the electric field density on the surface of the electret film 7 is different. If it can form, it will not specifically limit. The material embedded in the recess 9 or the material applied as the recess 9 is, for example, a material having a lower charge density than the electret film 7, a material having a non-chargeable charge density of substantially zero, or an electret. A material having a polarity opposite to that of the film 7 is preferable.

  In the first to third embodiments, the description has been given on the assumption that the shape of the recess 9 is an elongated linear rectangle. However, the shape is not particularly limited, and may be a geometric pattern or a design. May be. Further, the arrangement shape of the concave portions 9 is not limited in the same manner, and may be the above-described stripe shape, spot shape, lattice shape, concentric circular shape, or the like. All of the arrangement shapes are included in the claims of the present application. In addition, in the case where the concave portions 9 are irregularly arranged, the size in which the charged particles 6 do not fit into the concave portions 9 and the shapes arranged at a distance of about the diameter of the charged particles 6 are included. In some cases, the charged particles 6 are attracted onto the electret film 7 with high density.

  In the first to third embodiments, another insulating layer that is not substantially charged between the electret film 7 and each electrode or between the electret film 7 and the insulating liquid 10 is provided. You may arrange. In such a case, the contact between each electrode and the charged particles or insulating liquid is effectively prevented, which is more preferable.

  In the first to third embodiments, the description has been made on the assumption that the electret film 7 has a plurality of recesses 9. However, if at least one recess 9 is provided, the effect of the present invention is achieved.

  In the first to third embodiments, the description has been made on the assumption that the insulating liquid 10 and the charged particles 6 are arranged in the space forming each pixel. You may make it arrange | position by including in a microcapsule.

Example 1
Here, Example 1 will be described below as a specific example for implementing the first embodiment described above. In the first embodiment, a specific example of a vertical electrophoretic display device will be described with reference to FIG.

  In this example, polymethylmethacrylate (hereinafter referred to as PMMA) was used as the material for the electret film, and electretization was performed by applying a strong electric field in a high-temperature nonpolar solvent.

  Then, a second electrode 5 made of aluminum and a wiring (not shown) are formed on the second substrate 2 made of a glass substrate having a thickness of 1.1 [mm] by using a known photolithography technique. The second electrode 5 is divided into 200 [μm] × 200 [μm] square pixels. In addition, on the first substrate 1 made of a glass substrate having a thickness of 1.1 [mm], indium tin oxide is used to form the first electrode 3 serving as an electrode common to all pixels and a wiring (not shown).

  Thereafter, PMMA dissolved in chloroform is spin-coated on the first electrode 3 and the second electrode 5, and then the solvent is removed to form a PMMA film having a thickness of 1 [μm].

  Next, stripe-shaped openings having a line width of 1 [μm] and a pitch of 3 [μm] are formed in the PMMA film by using a photolithography technique. First, a mask having a desired shape is formed on the PMMA film using a resist, and then the PMMA film in the mask opening is removed by dry etching using oxygen plasma, and then the mask is also removed.

  Next, electret processing of the PMMA film is performed. The first substrate 1 is opposed to a flat counter substrate (not shown) having a counter electrode at a distance of 300 [μm], and these are immersed in silicone oil in a container having a temperature control function. Further, a voltage applying means is connected to the first electrode 3 on the first substrate 1 and the ITO substrate on the counter substrate. Then, the above-described silicone oil is heated and held at 140 [° C.], and a voltage of 3 [kV] (minus on the first electrode 3 side) is applied between the counter electrode and the first electrode 3 for 10 minutes. Thereafter, the temperature of the silicone oil is lowered to room temperature while the voltage is applied, and the electretization process ends when the voltage is turned off.

  The extracted PMMA film maintained good transparency, and when the surface potential was measured, the surface potential of about +10 [V] was observed with respect to the first electrode 3, and the electret film was formed on the first electrode 3. It is formed.

  Similarly, electretization is also performed on the PMMA film on the second electrode 5 to obtain an electret film having a surface potential of about +10 [V].

  Subsequently, the colored insulating liquid 10 and charged particles 6 are filled between the first substrate 1 and the second substrate 2 and sealed.

  As the insulating liquid 10, a colored dispersion liquid in which a dye is dispersed in the insulating liquid is used. In Example 1, an insulating liquid 10 in which an anthraquinone black dye is dispersed in isoparaffin is used. As the charged particles 6, white particles having an average particle diameter of 3 [μm] in which titanium oxide powder is dispersed in polystyrene were used in Example 1. The white charged particles 6 are positively charged in the insulating liquid 10. The insulating liquid 10 is previously added with 0.5 [wt%] of ultrafine particles of alumina and silica, which are polar ion adsorbents, in advance. Further, a voltage application device (not shown) is connected to obtain the electrophoretic display device 101.

  Here, as a comparative example for the electrophoretic display device 101, the above-described PMMA film on the second electrode 5 is patterned in the same shape as the pixel electrode, and further covers the surfaces of the first electrode 3 and the second electrode 5, respectively. A display device having substantially the same configuration except that the recess 9 is not formed in the electret film 7 is prepared.

  In the display device of this comparative example and the electrophoretic display device 101, when the first electrode 3 is set to the ground potential and −30 [V] is applied to the second electrode 5, the charged particles 6 are in the vicinity of the second electrode 5. It moves and the black which is the color of the insulating liquid 10 is observed from the 1st board | substrate 1 side. Conversely, when +30 [V] is applied to the second electrode 5, the charged particles 6 move to the vicinity of the first electrode 3, and white, which is the color of the charged particles 6, is observed from the first substrate 1 side.

  And about the display apparatus of a comparative example, even if an external circuit is made into an open state in this state, a change is not seen. Furthermore, no change is seen even if it is held for 50 hours in this state. Subsequently, when the external circuit is short-circuited and the first electrode 3 and the second electrode 5 are short-circuited, a slight change is seen in the display state, and the charged particles 6 near the center of the pixel electrode are detached and diffused in the liquid. is doing. From this, in this comparative example, since the surface charge of the electret film 7 is small, it is considered that the attractive force is insufficient at the central portion of the electret film 7.

  Further, in the electrophoretic display device 101 according to the first embodiment, no change is seen even when the external circuit is opened in the white display state. Furthermore, no change is seen even if it is held for 50 hours in this state. Subsequently, even when the external circuit is short-circuited and the display transparent electrode 4 and the counter electrode 5 are short-circuited, no change is observed. It can be seen that (memory) is realized.

(Example 2)
Here, Example 2 will be described below as a specific example for implementing the above-described third embodiment. In Example 2, a specific example of a horizontal electrophoretic display device will be described with reference to FIG.

  In the present embodiment, a second electrode 5 having a side of 100 [μm] made of aluminum and a second substrate 2 made of a glass substrate having a thickness of 1.1 [mm] are formed using a known photolithography technique. A wiring or the like (not shown) is formed. On this second electrode 5, an insulating layer 11 made of an acrylic resin containing titanium oxide fine particles is coated. And the 1st electrode 3 which also serves as a partition is formed in the boundary part of each pixel using the plating method. Copper is used as the material of the first electrode 3.

  Further, the insulating layer 11 on the first electrode 3 and the second electrode 5 is covered with a PMMA film by the same spin coat method as in the first embodiment. Thereafter, the PMMA film on the side wall of the partition wall and the insulating layer 11 is patterned by the same method, and the PMMA film at the position where the recess 9 is formed is removed.

  Next, a counter substrate (not shown) provided with a counter electrode is opposed to a surface of the second substrate 2 including the second electrode 5 and the like at a distance of 300 [μm]. Thereafter, in the same manner as in Example 1, the PMMA film is electretized. At this time, a negative voltage is applied to both the first electrode 3 and the second electrode 5, and the PMMA films near the two electrodes of the first electrode 3 and the second electrode 5 are both electretized.

  Next, each pixel is filled with an insulating liquid 10 and charged particles 6. The insulating liquid 10 is made of transparent and highly insulating isoparaffin (trade name: Isopar, manufactured by Exxon), and the charged particles 6 are made of polystyrene-polymethylmethacrylate containing carbon black having a particle size of about 3 [μm]. A polymer resin is used. To the isoparaffin, 0.5 [wt%] each of ultrafine particles of alumina and silica which are polar ion adsorbents are added. The charged particles 6 are positively charged in the insulating liquid 10.

  Next, a first substrate 1 made of transparent polyethylene terephthalate and having a thickness of 50 [μm] is disposed on the first electrode 3 that also serves as a partition wall. Then, voltage application means (not shown) is connected to obtain the electrophoretic display device 103.

  The electrophoretic display device 103 manufactured by the above method applies a voltage between the first electrode 3 and the second electrode 5 to cause the charged particles 6 to move to the electret film 7 on the side surface of the first electrode 3, Image display is performed by moving between the electret film 7 on the surface of the second electrode 5.

  Then, by applying the positive voltage exceeding the threshold value to the second electrode 5 with the first electrode 3 set to the ground potential, the charged particles 6 move to the vicinity of the side surface portion of the first electrode 3, thereby displaying white. By applying a negative voltage exceeding the threshold value to the electrode 5, the charged particles 6 spread so as to cover the second electrode 5 and display black. On the other hand, when a voltage lower than the threshold is applied, the charged particles 6 do not move, and an external circuit (not shown) is short-circuited, and the first electrode 3 and the second electrode 5 are short-circuited. After 50 hours, the display state did not change and good memory performance was realized.

(Example 3)
Next, as a specific example for implementing the first to third embodiments described above, Example 3 will be described below. In Example 3, a specific example of a method for forming a recess will be described.

  In the present embodiment, an electrophoretic display device is obtained by using the same method as in the second embodiment except for the method of forming the electret film 7 having the recess 9.

  The electret film 7 is formed by spin-coating a PMMA solution in which silica fine particles having a diameter of about 1 [μm] are dispersed on the first electrode 3 and the second electrode 5, and then performing the same process as in Example 2. An electretization process is performed. However, since the silica fine particles have a property that is difficult to be charged, the silica fine particles are not largely charged as compared with PMMA when the electretization treatment is performed. As a result, the silica fine particles are positioned. Differences in electric field density occur at locations where

  Therefore, compared with the case where the recessed part 9 is formed as a through-hole etc., the recessed part 9 can be formed more easily by the formation method mentioned above. In the electrophoretic display device obtained in this embodiment, the same effects as those in Embodiment 2 can be obtained.

  As described above, the electrophoretic display device according to the present invention is useful when a display image is held for a long time, and is particularly suitable for an electrophoretic display device that requires a reduction in driving power.

It is a schematic sectional drawing showing the example of a structure and display state of the electrophoretic display apparatus concerning 1st Embodiment. It is explanatory drawing which shows the 1st example of the recessed part formed in an electret film | membrane. It is explanatory drawing which shows the 2nd example of the recessed part formed in an electret film | membrane. It is a schematic side view which shows the example of a structure and display state of the electrophoretic display device concerning 2nd Embodiment. It is a perspective view which shows the example of a structure and display state of the electrophoretic display device concerning 3rd Embodiment. It is sectional drawing which shows the example of the conventional electrophoretic display apparatus using an electret film | membrane.

Explanation of symbols

3 electrodes (first electrode)
4 Fixing surface 5 Electrode (second electrode)
6 Charged particles 6a Charged particles (white charged particles)
6b Charged particles (Black charged particles)
7 Charged membrane (electret membrane)
9 Recess 10 Insulating liquid 101, 102, 103 Electrophoretic display device

Claims (9)

A set of electrodes at least one of which is divided for each pixel, charged particles dispersed in an insulating liquid disposed between the electrodes, and covering each of the set of electrodes, are made of a dielectric material. A pair of charged films forming a fixing surface for fixing the charged particles, and applying a voltage between the electrodes moves the charged particles to one of the set of fixing surfaces, In the electrophoretic display device for fixing the charged particles to the respective fixing surfaces when the voltage between them is not applied,
The charged film has a difference generating portion that causes a difference in electric field density on the fixing surface.
An electrophoretic display device. The difference occurrence portion is formed of a recess formed in the charged film so as to be recessed from the fixing surface.
The electrophoretic display device according to claim 1. The recess is formed through the charged film.
The electrophoretic display device according to claim 2. An embedded member embedded in the recess and having a charging property different from that of the charged film;
The electrophoretic display device according to claim 2 or 3. The embedded member is made of a non-chargeable material,
The electrophoretic display device according to claim 4. The embedded member is made of a material having a polarity opposite to that of the charged film.
The electrophoretic display device according to claim 4. The recess is formed in a shape in which the charged particles do not fit,
The electrophoretic display device according to any one of claims 2 to 6. The charged film has a plurality of recesses, and the plurality of recesses are formed to have a uniform arrangement shape on the fixing surface.
The electrophoretic display device according to claim 2, wherein the electrophoretic display device is an electrophoretic display device. The charged film is formed of an electret material.
The electrophoretic display device according to claim 1, wherein the electrophoretic display device is provided.

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