JP2000258805A - Electrophoretic display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To embody a long-term stable memory characteristic without requiring switching control of an open state without depending upon electrode holding charges. SOLUTION: A colored insulative liquid 6 and colored electrostatic charge particles 7 dispersed in the colored insulative liquid 6 are held within the closed spaces enclosed by a transparent display substrate 1, a counter substrate 2 and partition walls 3. Transparent electrodes 4 are arranged on the transparent display substrate 1 of the respective closed spaces and counter electrodes 5 are arranged on the counter substrate 2. The transparent electrodes 4 and the counter electrodes 5 have fixing surfaces 13 where the colored electrostatic charge particles 7 gather thereon. Charge films 8 which stationarily electrostatically charge the surface charge of the polarity reverse from the polarity of the colored electrostatic charge particles 7 are arranged on the fixing surfaces 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophoretic display device.

[0002]

2. Description of the Related Art In recent years, with the development of information devices, needs for low power consumption and thin display devices have been increasing, and research and development of display devices meeting these needs have been actively conducted. Among them, the liquid crystal display device can electrically control the arrangement of liquid crystal molecules and change the optical characteristics of liquid crystal,
Active developments have been made and commercialized as display devices that can meet the above needs. However, these liquid crystal display devices have not yet sufficiently solved the difficulty in seeing characters on the screen due to the angle at which the screen is viewed or reflected light, and the burden on vision caused by flickering and low brightness of the light source. For this reason, research on a display device with a small burden on vision has been actively studied. In particular, a reflective display device is expected from the viewpoints of low power consumption, reduction of burden on eyes, and the like.

[0003] As one of them, an electrophoretic display device which performs display by moving colored charged particles in an absolutely green liquid is known (for example, US Patent No. 36681).
06 specification). FIG. 8 shows a cross-sectional view of the most typical electrophoretic display device.

In FIG. 8, the electrophoretic display device includes a dispersion layer composed of colored charged particles 7 and a colored insulating liquid 6, and a pair of electrodes 4 and 5 opposed to each other with the dispersion layer interposed therebetween. By applying a voltage to the dispersion layer via the electrode, the colored charged particles 7 are electrophoresed and fixed on the electrode biased to the opposite polarity to perform display. The display is performed by the color of the colored charged particles 7 and the color of the dyed insulating liquid. That is, the first migrating particles close to the observer
When the particles adhere to the surface of the second electrode, the color of the migrating particles is displayed, and when the particles adhere to the surface of the second electrode far from the observer, the color of the stained colored insulating liquid is displayed.

[0005]

However, the conventional electrophoretic display has the following problems.
FIG. 7 is an explanatory diagram showing the operation of the conventional display device. In FIG. 7, the display image holding performance (hereinafter, referred to as memory property) of the conventional electrophoretic device is determined by applying a voltage (see FIG. 7A), opening the circuit immediately after the voltage is applied, and charging the electrodes. Is held, and the colored charged fine particles are adsorbed by the Coulomb force of the electrode-holding charge (see FIG. 7B).

However, this memory property is such that when the circuit is short-circuited, the electrode holding charges are released and disappear (see FIG. 7).
(C)). Therefore, when writing an image by matrix driving, it is necessary to provide a semiconductor switching element for each pixel and independently perform ON / OFF control in an open state. Such an active matrix control has a problem that the structure is complicated and the manufacturing cost is significantly increased.

[0007] Further, in a state where the circuit is opened (FIG. 7)
(B)), the minute resistance of the electrode charge passing through the inside of the electrophoretic layer gradually progresses.
Even with E + 15 Ω · cm, the memory time was at most a dozen hours to a few tens hours, which was not sufficient.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has realized an electric memory which has realized a long-term stable memory function without requiring switching control in an open state irrespective of an electrode holding charge. An object is to provide a migration display device.

[0009]

That is, the present invention provides at least two electrodes, colored charged particles dispersed in an insulating liquid filled between the electrodes, and a fixing surface on which the colored charged particles gather. And means for migrating and fixing the charged particles on the fixing surface by applying a voltage between the electrodes, wherein a surface charge having a polarity opposite to that of the colored charged particles is applied to the fixing surface. An electrophoretic display device including a charged film that is constantly charged.

Preferably, the charged film is provided on a fixing surface on the electrode. Preferably, the charged film is formed of a ferroelectric material or an electret material. The volume resistivity of the insulating liquid is IE + 12Ω · cm
It is preferable to have the above values. It is preferable that the vertical movement type electrophoretic display device is provided with the two electrodes facing each other. It is preferable that the two electrodes are a horizontal movement type electrophoretic display device provided on the same surface.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrophoretic display device according to the present invention comprises at least two electrodes, charged particles dispersed in an insulating liquid, at least two fixing surfaces on which the charged particles are collected, Means for moving and gathering the charged particles on the fixing surface by applying a voltage to the fixing surface, wherein the fixing surface is provided with a charged film charged with a surface charge having a polarity opposite to that of the charged particles. And

The charged film which is a feature of the present invention includes a ferroelectric film or an electret film. It is desirable that a polar ion adsorbent such as alumina or silica be added to the insulating liquid. By adding a polar ion adsorbent, the ion concentration in the insulating liquid is kept low, and the volume resistivity is given as lE + 12 to lE + 15Ω · c.
The high insulation property of about m is maintained. Therefore, the decrease in the surface charge of the charged film due to ion adsorption can be ignored.

FIG. 1 is a schematic sectional view showing an embodiment of the electrophoretic display device of the present invention. FIG. 1 shows a configuration having two closed spaces corresponding to display segments. In the electrophoretic display device, the colored insulating liquid 6 and the colored charged particles 7 dispersed in the green colored liquid 6
Is held in a closed space surrounded by the transparent display substrate 1, the counter substrate 2, and the partition 3. A transparent display electrode 4 is disposed on the transparent display substrate 1 in each closed space, and a counter electrode 5 is disposed on the counter substrate 2, and a fixing surface on which the colored charged particles 7 gather on the transparent display electrode 4 and the counter electrode 5. The fixing film 13 is provided with a charged film 8 which is constantly charged with a surface charge having a polarity opposite to that of the colored charged particles 7.

Hereinafter, the operation principle of the electrophoretic display device of the present invention will be described with reference to FIG. In FIG. 3, the electrophoretic display device of the present invention includes two opposing substrates 1 and 2, a transparent display electrode 4 for display formed on a translucent upper transparent display substrate 1, Counter electrode 5 formed on lower counter substrate 2
And the colored insulating liquid 6 filled between the upper and lower electrodes, and the colored charged particles 7 (tentatively positively charged) dispersed in the colored insulating liquid 6, are provided on each electrode which is a feature of the present invention. It is constituted by a charged film 8 having a surface charge of a different polarity from the formed colored charged particles 7.

By connecting an external circuit 10 as shown in FIG. 3A and inducing a negative charge on the transparent display electrode 4 and a positive charge on the counter electrode 5, the positively charged colored charged particles 7 are converted to the transparent display electrode. 4 and is held and fixed on the surface 4, and the display surface exhibits the color of the colored particles.

In this state, when the external circuit 10 is switched to the open state as shown in FIG. 3B, the electric charges on the electrodes are held. The colored charged particles 7 maintain a state of being fixed on the transparent display electrode 4 without supplying energy from the outside by the electrostatic attraction of the retained charges.

Next, from this state, the external circuit 10 is connected as shown in FIG.
When the state is switched to the short state as shown in (c), the charges held on both electrodes are released, and the electrostatic attraction disappears. But,
Also in this state, the colored charged particles 7 are continuously held by the electrostatic attraction of the negative surface charge of the charged film 8 formed on the electrode surface, and can be maintained fixed on the transparent display electrode 4.

Therefore, even in a control such as a simple matrix drive in which the open state of the circuit cannot be effectively maintained, a good memory property can be exhibited. Further, since the surface charges on the charging film 8 are not released, a stable memory property can be realized for a long time.

The present invention is not limited to the configuration described above, but can be applied to any type of electrophoretic display device having a fixing surface. For example, a display device of the display electrode / shielding electrode type disclosed in JP-A-9-021149 as shown in FIG. 4 or a horizontal movement disclosed in JP-A-10-005727 as shown in FIG. In the type display device, the charged film 8 may be formed on the electrodes 24 and 25 as in the above-described configuration. FIG.
In the microcapsule type disclosed in Japanese Patent Application Laid-Open No. 1-086116, the same effect can be obtained by applying a charging treatment to the microcapsule coating to make the coating a charged film. Is possible.
In this case, the position of the fixing surface may be defined as the outer wall surface of the microcapsule coating.

In the present invention, the charged film is preferably formed of a ferroelectric material or an electret material. Examples of the ferroelectric material used in the present invention include inorganic compounds such as lead zirconate titanate (PZT), lanthanum-added lead zirconate titanate (PLZT), and barium titanate; polyvinylidene fluoride (PVDF); A copolymer of vinylidene and trifluoroethylene (PVDF /
Organic polymers such as PTrFE) are preferred. If a ferroelectric material is used, it is possible to form a very large surface charge of 100 to 20,000 nC / cm ² .

As the electret material used in the present invention, general dielectrics including inorganic materials such as glass can be cited, but from the viewpoint of mass productivity, an organic polymer material which can cope with a printing process is more preferable. For example, fluorine resins such as Teflon (Teflon-FEP, Teflon-TFE) are particularly excellent in terms of performance, and polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyvinyl chloride, polyethylene terephthalate, polyimide and the like are also suitable. is there. The electret film preferably has a surface charge density of 5 nC / cm ² or more, and can form a surface charge of about 50 nC / cm ^{2 at} the maximum.

Hereinafter, the electret material will be described in more detail. Electret (electric stone) is derived from its name because of its similarity to a magnet (magnet), and is a substance that semi-permanently freezes and retains polarization charges to form an electric field outside.

The origin of the electret lies in the formation of the polarization and its freezing. The polarization that can be frozen is as follows. 1. charge separation by microscopic or macroscopic displacement of ions contained in the dielectric; 2. Anisotropic orientation of an intramolecular permanent dipole constituted by a polar group or the like due to an external electric field; A typical example is the charge injection by corona discharge generated in a corona discharge electrode or a gap between an electrode and a dielectric.

The 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 the polarization charge due to corona discharge injection becomes a homo charge having the same polarity. According to the measurement using the thermal stimulation current (TSC), deep traps of electrons, holes, and ions existing in a mismatched portion such as a crystal grain boundary in the dielectric, particularly near the surface, cause the polarization charge to freeze. Is believed to be.

Various methods for forming electrets
There is. As a typical method, Heating the dielectric to near the softening or melting temperature,
Method of cooling while applying high electric field DC (thermo-elev
1. Crett method); Corona discharge on dielectric surface or dielectric breakdown voltage
Near high electric field DC (~ 10 ⁶ V / cm) at room temperature
2. Method (electro-electret method); High energy radiation (electron beam, γ
Irradiation method (radio-electret method); Method of applying high voltage DC during light irradiation (Photo
Reclet), 5. Method by mechanical deformation such as pressing and stretching (mechanical
No electret), and the like.

[0026]

The embodiments of the present invention will be described in detail with reference to the following examples.

Embodiment 1 In this embodiment, a case will be described in which the present invention is applied to the most general electrophoretic display device shown in FIG. FIG. 1 shows a configuration having two closed spaces corresponding to display segments. The colored insulating liquid 6, and the colored charged particles 7 dispersed in the colored insulating liquid 6,
It is held in a closed space surrounded by the display-side transparent substrate 1, the counter substrate 2 and the partition 3. A transparent display electrode 4 is provided on the display-side transparent substrate 1 in each closed space, and a counter electrode 5 is provided on the counter substrate 2.
Is disposed, and a charged film 8 according to the present invention is disposed on the transparent display electrode 4 and the counter electrode 5.

Hereinafter, the manufacturing process will be described. In this embodiment, as the charged film material, Teflon-
Using FEP), electret treatment was performed by corona discharge under high heat.

First, a transparent display electrode 4 is provided on a transparent display substrate 1.
The counter electrode 5 was formed on the counter substrate 2. As each substrate material, a material having high transmittance of visible light and high heat resistance is used. In addition to inorganic materials such as glass and quartz, polymer films such as polyethylene terephthalate (PET) and polyethersulfone (PES) can be used. In this embodiment, a glass substrate was used.

As the transparent display electrode 4, any conductive material that can be patterned may be used. In this embodiment, indium tin oxide (ITO) is formed to a thickness of 200 nm by a vacuum deposition method. The opposite electrode 5 may be made of a metal material other than the above-described materials. In this embodiment, the Al film is formed to a thickness of 200 nm by a vacuum evaporation method.

After each electrode is etched with Ar gas for 5 minutes to roughen the surface to improve the adhesion of the surface,
A Teflon-FEP transparent sheet having a thickness of 5 μm is superimposed on the electrode surface side of each substrate, and heated to 300 ° C. with a weight applied thereto via a glass substrate, and then heated to 300 ° C.
After the sheet was melted and cooled, a 5 μm thick Teflon-FEP film was formed on the electrode.

A segment-shaped resist pattern was formed on the electrode on which the Teflon-FEP film was formed, and continuous etching was performed with oxygen plasma and Ar plasma to remove the Teflon-FEP film and the electrode film other than the segment electrode pattern.

For the electretization treatment, the knife edge electrode attached to the XYZ displacement drive mechanism, the substrate on which the Teflon-FEP film and the electrode film were formed were placed in a thermostat. The knife edge electrode was arranged so as to face the surface of the Teflon-FEP film via a gap, and the distance between the two was adjusted to 200 μm. With the inside of the thermostat kept at 300 ° C., a voltage of 5 kV was applied between the electrode film and the knife edge electrode in the negative direction on the knife edge electrode side to generate a corona discharge between the electrodes. An XYZ displacement drive mechanism attached to the knife-edge electrode reciprocates the knife-edge electrode in a direction parallel to the substrate surface at a constant speed. The entire surface of the substrate is uniformly irradiated by corona discharge, and rapidly cooled by dry nitrogen to form an electret. Finished.

The obtained Teflon-FEP film has good transparency. When the surface potential was measured, a surface potential of about −35 V was observed for each electrode film. In addition, it was confirmed that the charged film 8 was formed on the counter electrode 5.

Next, the partition 3 is formed on the counter substrate 2.
A polymer resin is used as the partition wall material. The partition wall may be formed by any method. For example, a method of performing exposure and wet development after applying a photosensitive resin layer, a method of bonding a separately prepared partition, or a method of forming a mold on the surface of the light-transmitting second substrate is used. be able to. In the present embodiment, the partition walls 3 having a height of 50 μm were formed by repeating the application, exposure and wet development processes of the photosensitive polyimide varnish three times.

Subsequently, the colored insulating liquid 6 and the colored electrophoretic particles 7 were filled in the partition 3. Ultrafine particles of alumina and silica, which are polar ion adsorbents, were previously added to the colored insulating liquid 6 by 0.5 wt%.

As the green colored liquid 6, a dispersion liquid in which a dye is dispersed in an insulating liquid such as silicone oil, toluene, xylene, or high-purity petroleum is used. In this embodiment, a colored insulating liquid 6 in which an anthraquinone-based black dye is dispersed in silicone oil is used.

As the colored charged particles 7, pigment particles which can be charged in the colored green liquid 6 or particles obtained by dispersing a pigment powder in a resin are used. As the size of the particles, usually, the average particle size is 0. One having a size of about 1 μm to 50 μm is used. In this embodiment, a white pigment powder of titanium oxide is dispersed in a resin such as polyethylene or polystyrene.
Was used. It has been confirmed that the white charged particles 7 are positively charged in the colored insulating liquid 6.

Finally, the partition 3 and the transparent display substrate 1 were bonded together with an adhesive to obtain a display device having the structure shown in FIG.
Further, as Comparative Example 1, a display device having exactly the same configuration but not performing the electret treatment on the Teflon-FEP film was also prepared.

The two display devices thus obtained were driven by a drive circuit (not shown). First, a voltage of −50 V with respect to the counter electrode 5 was applied to the transparent display electrode 4 of the left cell, and a voltage of +50 V was applied to the right cell. In the cell on the left, positively charged white particles 7 dispersed in the insulating black liquid 6
Migrated and fixed to the display transparent electrode 4, and the cell exhibited white, which is the color of the fixed charged particles. In the cell on the right side, the positively charged white particles 7 migrate and fix to the counter electrode 5, and the cell contains the insulating liquid 6.
Black color. The response speed was 50 msec. The display device according to the first embodiment and the display device according to the first comparative example exhibited almost the same driving characteristics.

In the display device of Comparative Example 1, no change was observed even when the external circuit was opened in this state. However, in the observation after standing for 5 hours, a clear change in the coloration state was recognized, and detachment and diffusion of some of the colored charged particles 7 from the fixing surface were observed. Next, after returning to the initial color state again, when the external circuit was short-circuited and the transparent display electrode 4 and the counter electrode 5 were short-circuited, the color state was lost within a few minutes, and most of the colored charged particles were lost. 7 desorbed and diffused into the liquid.

Next, the external circuit of the display device of this embodiment was opened in this state, but no change was observed. Further, this state was maintained for 50 hours, but no change was observed. Then, the external circuit is short-circuited and the transparent display electrode 4
And the opposite electrode 5 was short-circuited, but no change was observed. Similarly, although this state was maintained for 50 hours, no change was observed at all, and it was confirmed that good memory properties were realized.

After that, when a driving voltage of the opposite polarity was applied to each cell, the display color was inverted at a response speed of 50 msec. Therefore, it was confirmed that the influence of the adsorption by the charged film on the driving characteristics was small. Was.

Example 2 In this example, lanthanum-added lead zirconate titanate (PLZT), which is an inorganic ferroelectric, was used as the charged film. FIG. 2 shows a schematic configuration diagram of the present embodiment. The configuration other than the charging film is exactly the same as that of the first embodiment. In the charged film, the dipole moments of the respective polarization domains of the ferroelectric phase are arranged in the same direction on the substrate side, and a negative surface charge is expressed on the surface of the charged film in contact with the migration layer.

Hereinafter, the manufacturing process of the PLZT charged film 8 will be described. The manufacturing process other than the charged film is the same as that of the first embodiment, and thus the description is omitted. Examples of the method for forming the PLZT thin film include a sol-gel method, a sputtering method, and a CVD method (chemical vapor deposition method). In this embodiment, the PLZT thin film is formed by the sputtering method.

First, a PLZT (lanthanum-added lead zirconate titanate) thin film is deposited to a thickness of 250 nm on a quartz glass substrate 1 or 2 on which a transparent display electrode 4 or a Pt counter electrode 5 is formed by a high frequency sputtering method. did. At this time, the composition of the deposited film is a stoichiometric composition ratio.

Subsequently, the deposited film was irradiated with light using a halogen lamp (lamp heating), and the temperature was set at 5 ° C.
Heat treatment at 50 to 650 ° C. for 1 minute. This allows
Only the film (amorphous) deposited on the substrate was heated to change to a perovskite type crystal structure to form a ferroelectric film.
The transmittance of the obtained PLZT film was about 70%.

Subsequently, a flat metal electrode is arranged on the PZT thin film formed on each substrate with a gap of 200 μm therebetween.
In a state where the PLZT thin film is heated to 90 ° C., the transparent display electrode 4 or the Pt counter electrode 5 is applied to the flat metal electrode by −lk.
A poling process was performed by applying a voltage of V to form a charged film 8.

Hereinafter, by the same process as in Example 1,
A display device having the configuration shown in FIG. 2 was obtained. The two display devices thus obtained were driven by a drive circuit (not shown).
First, a voltage of −50 V with respect to the counter electrode 5 was applied to the transparent display electrode 4 of the left cell, and a voltage of +50 V was applied to the right cell. In the cell on the left, the positively charged white particles 7 dispersed in the insulating black liquid 6 migrate and fix to the transparent display electrode 4, and the cell exhibits white, which is the color of the fixed charged particles. In the cell on the right side, the positively charged white particles 7 migrate and fix to the counter electrode 5, and the cell has a black color, which is the color of the insulating liquid 6. The response speed was 50 msec.

Next, the external circuit of the display device of this embodiment was opened in this state, but no change was observed. Further, this state was maintained for 50 hours, but no change was observed. Subsequently, the external circuit was short-circuited, and the transparent display electrode 4 and the counter electrode 5 were short-circuited, but no change was observed. Similarly, although this state was maintained for 50 hours, no change was observed at all, and it was confirmed that good memory properties were realized.

Embodiment 3 In this embodiment, a case will be described in which the present invention is applied to a horizontal movement type electrophoretic display device disclosed in Japanese Patent Application No. 10-005727.

FIG. 5 is a schematic sectional view of a display device according to the present invention. FIG. 5 shows a configuration having two closed spaces corresponding to one pixel. A white display electrode 25 is disposed on the entire pixel surface on the display substrate 1, and a black display electrode 24 is disposed on a part of the pixel surface via the green layer 14. The charge film 8 according to the present invention is formed on the upper surface of the black display electrode 24 and the upper surface of the insulating layer 14 on the white display electrode 25. The space surrounded by the display substrate 1, the counter substrate 2, and the partition 3 is filled with the transparent insulating liquid 26 and the black charged particles 27. In the horizontally moving type electrophoretic display device, the charged particles 27 are moved horizontally with respect to the display substrate 1,
The display is performed by collecting on the black display electrode 24 or the white display electrode 25 formed on the display substrate.

Black charged particles 27 in transparent insulating liquid 26
Is collected on the white display electrode 25 by applying a voltage to the electrode, and the observer (opposite substrate side) receives black charged particles 27.
And the black display electrode 24 is observed (displayed). On the other hand, when the polarity of the electrode is changed and the black charged particles 27 are collected on the black display electrode 24, the white display electrode 25 is exposed and the color changes. If the area of the white display electrode 25 is made larger than that of the black display electrode 24, the coloration of the white display electrode 25 is dominant. The color of the white display electrode 25 is formed by coloring the insulating layer 14, the white display electrode 25, the display substrate 1, and the like.

Hereinafter, a method of manufacturing the display device according to the present embodiment will be described. As the display substrate 1, a light-transmitting PET film having a thickness of 200 μm was used. ITO was formed as a white display electrode 25 on the display substrate 1 and patterned in a line shape. Next, titanium oxide fine particles were mixed as the insulating layer 14 on the white display electrode 25 to form a whitened PET film. Next, dark black titanium carbide was deposited as a black display electrode 24 and patterned in a line shape. The line width was 50 μm.

Next, a method for forming the charged film 8 according to the present invention will be described. In this example, polyvinylidene fluoride (PVDF), which is a polymer ferroelectric, was used as the charged film material. After dissolving the PVDF pellet in dimethylacetamide (DMA) solution to prepare a 10 wt% solution,
A 2 μm-thick PVDF thin film was formed and patterned on the insulating layer on the black display electrode 24 and the white display electrode 25 by a casting method.

A flat metal electrode is arranged on the PVDF thin film formed on the display substrate with a gap of 200 μm therebetween.
A poling (polarization) treatment was performed. That is, while the PLZT thin film is heated to 100 ° C., a voltage of + lkV is applied to the flat metal electrode to the black display electrode 24 and the white display electrode 25 for about 15 minutes, and after 15 minutes, the substrate temperature is returned to room temperature. The voltage was released to obtain a charged film 8 having a polarization which is considered to be due to the electric field orientation of the polar group in the PVDF thin film.

Next, the partition 3 was formed. The partition walls 3 were formed by applying a photosensitive thick film resist (trade name: SU-8, manufactured by 3M) under a condition of a film thickness of 50 μm, and then performing exposure and wet development. After forming a heat-fusible adhesive layer on the joint surface with the counter substrate 2, the partition walls were filled with the transparent insulating liquid 26 and the black charged particles 27. As the transparent insulating liquid 26, silicone oil was used. In the used silicone oil, ultra-fine particles of alumina and silica, which are polar ion adsorbents, are each 0.5 watts.
t% was added. The black charged particles 27 are a mixture of polystyrene and carbon and have a particle size of 1 μm to 2 μm.
The m-th thing was used. Next, the display substrate 1 of the opposite substrate 2
A heat-fusible adhesive layer pattern was formed on the surface to be bonded, and the positions of the partition wall 3 of the display substrate 1 and the adhesive layer of the counter substrate 2 were aligned and bonded in a heated state. A display circuit was completed by installing a drive circuit on the display sheet thus obtained.

On the other hand, a display device having a conventional structure was prepared in parallel as a comparative cell. A transparent polyimide thin film was formed in a thickness of 2 μm instead of the PVDF thin film, and the poling treatment was not performed on the polyimide thin film. The other materials used and the manufacturing process are exactly the same.

The two display devices thus obtained were driven by a drive circuit (not shown). The white display electrode 25 is set to the ground potential as a common electrode, and the black display electrode 2 is first set.
For -4, -50 V for the left pixel and +5 for the right pixel
A voltage of 0 V was applied. In the pixel on the left side, the black positively charged particles 27 migrated and fixed on the upper surface of the black display electrode to exhibit white. In the right pixel, the black positively charged particles 27 migrate and fix on the upper surface of the white display electrode 25 to exhibit black. The response speed was 50 msec. The display device according to the example of the present invention and the display device for comparison showed almost the same drive characteristics.

Regarding the comparative display device, no change was observed even when the external circuit was opened in this state. However, in observation after standing for 5 hours, some of the charged particles 27 were detached and diffused from the fixing surface, and a clear change in the color state was observed. Next, after returning to the initial color state again, when the external circuit was short-circuited and the black display electrode 24 and the white display electrode 25 were short-circuited, the color state was impaired within a few minutes and many charged particles were lost. 27 desorbed into the liquid and diffused into the pixel.

Next, with respect to the display device of this embodiment, the external circuit was opened in this state, but no change was observed. Further, this state was maintained for 50 hours, but no change was observed. Subsequently, the external circuit was short-circuited and the black display electrode 24 and the white display electrode 25 were short-circuited, but no change was observed. Similarly, although this state was maintained for 50 hours, no change was observed at all, and it was confirmed that good memory properties were realized.

[0062]

As described above, according to the present invention, a good memory property can be realized even in a control in which the open state of the circuit cannot be maintained effectively, such as a simple matrix drive control. In addition, since the surface charges on the charged film are not released, an electrophoretic display device capable of realizing stable memory properties for a long time can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of an electrophoretic display device of the present invention.

FIG. 2 is a schematic sectional view showing another embodiment of the electrophoretic display device of the present invention.

FIG. 3 is an explanatory diagram illustrating an operation principle of the electrophoretic display device of the present invention.

FIG. 4 is a schematic sectional view showing another embodiment of the electrophoretic display device of the present invention.

FIG. 5 is a schematic sectional view showing another embodiment of the electrophoretic display device of the present invention.

FIG. 6 is a schematic sectional view showing another embodiment of the electrophoretic display device of the present invention.

FIG. 7 is an explanatory diagram illustrating the operation principle of a conventional display device.

FIG. 8 is a schematic sectional view showing a conventional display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent display substrate 2 Counter substrate 3 Partition wall 4 Transparent display electrode 5 Counter electrode 6 Colored insulating liquid 7 Colored charged particle 8, 8a Charged film 9 Microcapsule 10 External circuit 11 Light shielding part 12 Polymer binder 13 Fixing surface 14 Insulating layer 24 Black display electrode 25 White display electrode 26 Transparent insulating liquid 27 Black charged particles

Claims (6)

[Claims] 1. A voltage is applied between at least two electrodes, colored charged particles dispersed in an insulating liquid filled between the electrodes, a fixing surface on which the colored charged particles gather, and the electrodes. This allows the charged particles to migrate to the fixing surface.
An electrophoretic display device comprising: a fixing film having a charging film that is constantly charged with a surface charge having a polarity opposite to that of the colored charged particles on the fixing surface. 2. The electrophoretic display device according to claim 1, wherein the charged film is provided on a fixing surface on the electrode. 3. The charge film according to claim 1, wherein the charge film is made of a ferroelectric material or an electret material.
The electrophoretic display device according to claim 1. 4. The insulating liquid has a volume resistivity of 1E + 1.
The electrophoretic display device according to claim 1, which has a value of 2 Ω · cm or more. 5. The electrophoretic display device according to claim 1, wherein the electrophoretic display device is a vertical movement type electrophoretic display device in which the two electrodes are provided to face each other. 6. The electrophoretic display device according to claim 1, wherein the two electrodes are a horizontally moving electrophoretic display device provided on the same surface.