JP2003270675A - Display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display element which has a memory property, a low driving voltage and quickly responds. <P>SOLUTION: The display element is provided with a pair of substrates arranged so as to face each other, a pair of electrodes formed on the substrates, and a mixture comprising a dielectric liquid and a plurality of dielectric particles charged between the substrates and has a cohesion state of the dielectric particles cohering between the substrates and a dispersion state of the dielectric particles being dispersed between the substrates as different display states, and the dielectric particles are electrified, and the dielectric constant of the dielectric liquid is made higher than that of the dielectric particles. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a display device using a mixture of a dispersion medium and dielectric particles.

[0002]

BACKGROUND ART In recent years, a reflective display element that does not require a polarizing plate or a backlight has attracted attention as a low power consumption portable display element. Under such circumstances, a bistable reflective display element capable of electrically switching between two display states having a memory property has been proposed. For example, Japanese Patent Application Laid-Open No. 10-148849 proposes a bistable display element using a liquid crystal composition composed of a liquid crystal and flat particles having an affinity for the liquid crystal.

Regarding the light transmittance of this element, a transparent state and a light scattering state can be formed by changing the voltage value of the electric signal applied to the element.

The transparent state was 9 with respect to the liquid crystal composition.
It is formed by applying a voltage of 0 to 140 V or more for several tens of milliseconds. In this case, the long axes of the liquid crystal molecules and the flat particles are oriented parallel to the electric field direction. On the other hand, the light scattering state is 7
It is formed by applying a voltage of 0 to 30 V or less for several seconds. In this case, the liquid crystal molecules and the flat particles are randomly aligned. Each state (transparent state, scattering state) is maintained even if the voltage application is released (has a memory property). In addition,
With the transition between the states, the orientation change of the particles in the major axis direction occurs, but the distribution state of the particles themselves in the in-plane direction of the electrode does not change.

It has been proposed by the inventor of the present application that a transparent state and a light blocking state be created by the movement of fine particles in liquid crystal.
01-75081. An alternating electric field is applied to the fine particles dispersed in the liquid crystal to move the fine particles in parallel to the substrate surface, and the movement direction is controlled by the presence or absence of the DC component of the electric field, and the magnitude and polarity of the DC components, whereby the fine particles are locally aggregated. It is to create a state (transparent state) and an evenly dispersed state (light blocking state). In this case also, the state after the voltage is released is maintained.

[0006]

However, the display element disclosed in Japanese Patent Laid-Open No. 10-148849 has the following two problems.

First, there is a problem that the driving voltage of the display element is high. 90 to 140 for forming a transparent state
A drive voltage of V or higher was required. On the other hand, a driving voltage of at least 70 to 30 V was required to form the scattered state. Secondly, there is a problem that the response time of the display element is long. The application time of the electric signal required to form the transparent state was several tens of milliseconds, but the application time of several seconds was required to form the scattering state. Further, the above-mentioned JP 2001-7
In the method of 5081, since the liquid crystal is a highly viscous medium, the moving speed of particles is as slow as 500 μm / sec or less, and a method of lowering the driving voltage as high as typically 80 V was not clear.

Therefore, an object of the present invention is to provide a bistable type using dielectric particles in which a driving voltage for forming a display state having a memory property is 30 V or less and a response speed is several tens of milliseconds or less. It is to provide a display element.

[0009]

According to the present invention, a pair of substrates arranged to face each other, a pair of electrodes formed on the substrate,
A dielectric liquid filled between the substrates and a mixture of a plurality of dielectric particles are provided, and an electric signal containing no DC component is applied between the electrodes to aggregate the dielectric particles between the substrates. A display element, wherein the agglomerated state and the dispersed state in which an electric signal containing a DC component is applied between the electrodes to disperse the dielectric particles between the substrates are different display states. The dielectric particles are charged dielectric particles, and the dielectric liquid is a polar liquid having a relative dielectric constant larger than that of the dielectric particles.

Further, according to the present invention, a pair of substrates arranged to face each other, a pair of electrodes formed on the substrate, a dielectric liquid filled between the substrates and a plurality of charged dielectric particles are provided. And a mixture state in which the dielectric particles are moved in a specific direction by a dielectrophoretic force and agglomerated between the substrates, and the dielectric particles are moved in a direction opposite to the specific direction by an electrophoretic force. In the display element, the dispersed state dispersed between the substrates is set to different display states, and the dielectric liquid is a polar liquid whose relative dielectric constant is larger than that of the dielectric particles. It is characterized by being.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The two states (aggregated state, dispersed state) and the electric signals for forming each state will be described with reference to FIGS.

FIG. 1 is a schematic view showing an example of a display device according to the present invention. In FIG. 1, 10 and 20 are substrates. Reference numeral 30 is a grid electrode, and 40 is a planar electrode. 50 is an electric signal applying means. Reference numeral 60 is a reflective layer. However, in FIG. 1, a mixture composed of a polar liquid and dielectric particles filled between the substrates, a spacer for maintaining a gap between the substrates, and the like are omitted. Further, in the following description, it is assumed that the dielectric constant of the dielectric particles is smaller than that of the polar liquid.

FIG. 2 is a schematic diagram of the distribution state of the dielectric particles observed when the display element of FIG. 1 in which the dielectric particles are dispersed is observed from the upper surface of the substrate 10. On the other hand, FIG. 3 is a schematic diagram of the distribution of dielectric particles observed when the display element of FIG. 1 in which the dielectric particles are in an aggregated state is observed from the upper surface of the substrate 10. As shown in FIG. 3, the dielectric particles in the agglomerated state are formed in the non-electrode forming region 80 adjacent to the grid electrode.
(Corresponding to the white square in FIG. 3) and its vicinity. 2 and 3, the dielectric particles 7
Only 0 and the grid electrode 30 are shown.

In the present invention, the dispersed state and the aggregated state are used as different display states. When the display element in which the dielectric particles are in an aggregated state is viewed with the naked eye, the color derived from the reflective layer can be observed. On the other hand, when the display element in which the dielectric particles are in a dispersed state is viewed with the naked eye, the color derived from the dielectric particles can be observed. For example, if the reflective layer is white and the dielectric particles are black, the aggregated state is white and the dispersed state is black.

It is also possible to use the display element as a transmissive type without providing a reflective layer. The agglomerated state of the dielectric particles can be used as a transparent state. Meanwhile, the dispersion state of the dielectric particles can be used as a light blocking state.

Next, the electric signal will be described.

An example of the electric signal that does not include the DC component is shown in FIG. The electric signal shown in FIG. 4 is an alternating voltage whose peak value on the positive side is equal to the peak value on the negative side.
Moreover, it is a rectangular wave with a duty ratio of 50%.

The duty ratio will be described with reference to FIG. FIG. 5 shows an electric signal in which the voltage value periodically changes, the horizontal axis represents time, and the vertical axis represents voltage. The duty ratio is τ / T (T = repetition period, τ
= Pulse width). The reason why the rectangular wave shown in FIG. 4 does not include a DC component is that the time average of the rectangular wave shown in FIG. 4 is substantially 0V.

When the rectangular wave shown in FIG. 4 is applied to the element in which the dielectric particles are in a dispersed state (see FIG. 2), the dielectric particles move horizontally within the surface of the substrate and reach the position farthest from the electrodes. An aggregated state (see FIG. 3) is formed. The aggregated state of the dielectric particles is retained (memory) even when the application of the electric signal is released.

If the peak value on the plus side of the electric signal not containing the DC component is equal to the peak value on the minus side,
The duty ratio is not limited to 50%.
It suffices that a desired aggregated state can be formed. For example, 30%
The duty ratio of 70% or less can be increased. Further, the waveform of the electric signal relating to the formation of the aggregation state is not limited to the rectangular wave, and may be a triangular wave, a sine wave, or a sawtooth wave.

On the other hand, examples of electric signals containing the DC component are shown in FIGS.

The electrical signal shown in FIG. 6 is a rectangular wave whose peak value on the plus side is equal to the peak value on the minus side and whose duty ratio is not 50%. The magnitude of the duty ratio in this case cannot be generally determined because it depends on the properties of the mixture and the like used, but it is less than 30% and / or 70%.
% Or more is preferable. More preferably, it is 10% or less and / or 80% or more.

The electrical signal shown in FIG. 7 is a rectangular wave in which a DC signal is superimposed on a rectangular wave having a plus side crest value equal to the minus side crest value and a duty ratio of 50%. The reason why the rectangular waves shown in FIGS. 6 and 7 include a DC component is that the time average of each electric signal is not 0V.

The electric signal shown in FIG. 8 is a DC signal itself, and the time average is not 0V.

When the electric signals shown in FIGS. 6 to 8 are applied to the element (FIG. 3) in which the dielectric particles show the agglomerated state, the dielectric particles are opposite to those when the agglomerated state is formed in the substrate surface direction. , The dielectric particles form a dispersed state (see FIG. 2) uniformly distributed between the substrates. The dispersed state of the dielectric particles is stored (memory) even when the application of the electric signal is released.
Has been done. The waveform of the electric signal for forming the dispersed state is not limited to the rectangular wave, but may be a triangular wave, a sine wave, or a sawtooth wave.

The details of the mechanism for storing the aggregated state and the dispersed state are unknown. However, it is assumed that the viscosity of the dispersion medium, the cohesive force between the dielectric particles, and the interaction between the dielectric particles and the substrate (electrode, substrate, etc.) play important roles. However, the memory mechanism is not limited to the above items.

The phenomenon of formation of two states (aggregated state and dispersed state) by applying an electric signal was discovered by the present inventor in the process of examining the electric field response of dielectric particles in a fluid.
As a result of diligent studies, the present inventors have found that the above phenomenon can be expressed at a low voltage by applying a short electric signal by adjusting the relative permittivity of a polar liquid as a fluid and dielectric particles. I found it. That is, it was found that the object of the present invention can be achieved.

The present inventor has also found that in order for the dielectric particles to move reversibly between the above two states at high speed, the dielectric particles must be charged.

The present inventor considers the driving force of the above phenomenon, that is, the driving force of the dielectric particle displacement, as follows.

When an electric signal containing the DC component is applied, that is, the driving force of the dielectric particles at the transition from the aggregation state to the dispersion state is mainly electrostatic Coulomb force, that is, electrophoresis. Believe in power. In fact, the mixture according to the invention (composed of charged dielectric particles and polar liquid) is packed between parallel plate electrodes and an electrical signal containing the DC component (for example as shown in FIG. 8). When a DC signal) is applied, the phenomenon that dielectric particles move toward one electrode is observed.

On the other hand, when an electric signal containing no DC component is applied, it is considered that the force that controls the driving of the dielectric particles is not the electrophoretic force. Because the time average of the signal is almost 0V, the time average of the electrostatic force acting on the dielectric particles becomes substantially zero. The present inventor believes that the driving force of the dielectric particles at the transition from the dispersed state to the aggregated state is mainly the dielectrophoretic force due to the nonuniformity of the electric field.

As is well known, the dielectrophoretic force F acting on another dielectric particle placed in a dielectric that is a dispersion medium is expressed by the following equation (1).

F∝ (ε _b −ε _s ) × grad (E ² ) (1) Formula (ε _b : relative permittivity of dielectric particles, ε _s : relative permittivity of dispersion medium, E: electric field The above formula (1) shows that the dielectric constant of the dielectric particles is different from the dielectric constant of the dispersion medium, and if a nonuniform electric field is applied at the same time, the dielectrophoretic force acts on the dielectric particles. The direction of the force depends on the sign of (ε _b −ε _s ). If (ε
_{If b-} ε _s ) <0, the dielectric particles are subjected to a force in the direction of weak electric field strength in the nonuniform electric field. In fact, the location in the device where the aggregated state of the dielectric particles (which satisfies (ε _b −ε _s ) <0 as described above) is formed in the non-uniform electric field formed between the substrates. It matches the region where the electric field strength is minimal (see FIG. 3). That is, when an electric signal that does not include the DC component is applied to the dielectric particles that are in a dispersed state, a dielectrophoretic force that acts toward a region where the electric field strength is weak acts on the dielectric particles. As a result, it is considered that the dielectric particles form an aggregated state in which they are aggregated in the region where the electric field strength is weak.

When the display element shown in FIG. 1 is filled with a mixture satisfying (ε _s ≈ε _b ), the dielectric particles are not aggregated or formed even when an electric signal shown in FIG. 4 is applied. It was difficult. For example, when a mixture of polymer beads having a relative dielectric constant of about 3 and silicone oil having a relative dielectric constant of about 3 was used, formation of an aggregated state of dielectric particles was not observed (see Comparative Example 1 described later). .

On the other hand, the larger the (ε _s −ε _b ) of the mixture filled in the display element of FIG. 1, the smaller the driving voltage of the electric signal (see FIG. 4) for forming the aggregated state was observed. (See Example 1 and Example 4 described later).
At the same time, it was observed that the application time of the electric signal was shortened. This also proves that the force acting on the dielectric particles when forming the aggregated state is the dielectrophoretic force of the above formula (1). On the other hand, when a voltage containing a DC component is applied, when the DC component exceeds a certain level, it is observed that the dielectric particles move in the direction opposite to the aggregation and form a state in which they are uniformly dispersed between the substrates. To be done. Since the electric field is non-uniform at this time as well, the dielectrophoretic force should work in the same way, but the electrostatic Coulomb force due to the charged electric charge becomes larger than that, and the charged dielectric particles are changed depending on the polarity. And is attracted toward one of the electrodes. At the same time, the dielectric particles tend to separate from each other due to the electrostatic repulsion between the charged particles or the volume exclusion effect, and it is presumed that a uniformly dispersed state can be obtained.

With non-charged particles, the aggregated state can be formed with a voltage containing no DC component, but the reverse movement, that is, the transition to the dispersed state does not occur. This also shows that the transition to the dispersed state is due to the Coulomb force.

As shown in the above equation (1), the dielectrophoretic force is proportional to the difference in the dielectric constant between the dielectric particles and the dielectric liquid that is the dispersion medium. Therefore, by increasing the dielectric constant of the dispersion medium, The drive voltage can be lowered. The present invention uses a polar liquid composed of polar molecules as the dispersion medium to increase the difference in dielectric constant.
Furthermore, since the polar liquid is often composed of low molecules, it is easy to obtain a liquid having low viscosity. By using the polar liquid with low viscosity, the dielectric particles are made to move easily, and the driving speed is increased.

Since the display element previously proposed in JP 2001-75081A uses liquid crystal, it is difficult to reduce the viscosity, which is an obstacle to speeding up and lowering the voltage. By using a polar liquid, the range of material selection was widened, and the degree of freedom in designing the dielectric constant and viscosity was increased. Further, since the charged dielectric particles are used, the transition to the dispersed state is performed by the action of electrophoresis. As a result, it becomes possible to increase the moving speed or decrease the driving voltage.

Next, the electrodes of the display element according to the present invention will be described. The electrode according to the present invention is not limited to the combination of the flat plate-shaped electrode and the grid-shaped electrode shown in FIG. There is no particular limitation as long as a non-uniform electric field required for forming two states (dispersion state and aggregation state) of the dielectric particles can be formed between the substrates. For example, as schematically shown in FIG. 9, even if the striped electrode 300 having both ends connected to each other is arranged so as to face the plate electrode 40, a nonuniform electric field is formed between the substrates. When the electric signal shown in FIG. 4 is applied between the electrodes shown in FIG. 9, the dielectric particles are aggregated in a region where the electric field strength is relatively small. This region corresponds to the non-electrode formation portion 310 of the substrate in which the stripe electrodes having both ends connected to each other are formed and the vicinity thereof. On the other hand, when the electric signals shown in FIGS. 6 to 8 are applied, the dispersed state of the dielectric particles is formed.

Since the dielectrophoretic force increases as the gradient of the electric field increases, at least one of the pair of electrodes for generating the electric field has a grid shape, a stripe shape, or the like having a size about the distance from the other electrode. It is preferable to make the electric field non-uniform by processing into the shape.

The electrode is not limited to a planar electrode, and an electrode having a three-dimensional shape may be used as long as a desired nonuniform electric field can be formed.

An insulating film may be provided on the electrode surface and the substrate surface relating to the present invention. The material of the insulating film is not particularly limited. For example, polyimide can be raised. Furthermore, the material of the substrate is not particularly limited, and may be a glass substrate or a plastic substrate. Furthermore,
The display element of the present invention may be composed of not only one pixel but also a plurality of pixels.

Next, the polar liquid relating to the present invention will be described.

The polar liquid referred to in the present invention means a liquid composed of polar molecules or a liquid containing polar molecules. Such a liquid has a relatively high dielectric constant due to the dipole moment of the molecule.

Examples of the polar liquid that can be used in the present invention include a dipolar aprotic solvent and a hydrogen-bonding polar solvent. Examples of the dipolar aprotic solvent include propylene carbonate, ethylene carbonate, N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide and hexamethylphosphoramide. it can. Examples of the hydrogen-bonding polar solvent include water and ethanol.
Also, a mixture of two or more kinds of dipolar aprotic solvents or a mixture of two or more kinds of hydrogen bonding polar solvents can be used as the polar solvent. Similarly, a mixture of dipolar aprotic solvent and hydrogen-bonding polar solvent can be used as the polar solvent.

However, if a desired display state can be formed,
The polar liquid usable in the present invention is not limited to the above dipolar aprotic solvent or hydrogen bonding polar solvent. If the relative permittivity is large (preferably 21 or more),
There is no limit to the type. For example, ionic liquid (provided that cross-linking between ions by molecular chains etc. has been performed)
Can also be used as the polar liquid according to the present invention. Further, the viscosity of the polar liquid is not particularly limited as long as it does not exert a viscous resistance that inhibits displacement of the dielectric particles on the dielectric particles. However, the viscosity of polar liquids is 1
It is preferably less than 7 cps.

Further, in the mixture according to the present invention, organic matter may be dissolved in the polar liquid. The organic material is not particularly limited as long as it can form a desired display state. For example, a substance having a relatively large relative permittivity (10 or more) can be given. Examples thereof include sugar chains and sugar chain derivatives (substances in which the hydroxyl groups of sugar chains are replaced with other organic molecules). Alternatively, a surfactant may be used. These organic substances are effective when it is necessary to adjust the dielectric constant, viscosity, or conductivity of the dispersion medium. In addition, the presence of the organic substance may improve the stability of the aggregated state of the dielectric particles. Although the details of this mechanism are unknown, it is presumed that it contributes to the generation of attractive force between the dielectric particles.

On the other hand, as described above, the dielectric particles according to the present invention need to have a relative permittivity different from that of the polar liquid and be charged.

The relative permittivity of the polar liquid is at least 5 or more higher than the relative permittivity of the dielectric particles. In order to increase the dielectrophoretic force acting on the dielectric particles, it is more preferable that the following expression (2) is satisfied.

(Relative permittivity of the polar liquid) − (Relative permittivity of the dielectric particles) ≧ 18 (2) Formula These conditions are satisfied, dissolution in the polar liquid and interelectrode gap The material and shape of the dielectric particles are not particularly limited as long as swelling that is larger than the gap does not occur. For example, a spherical dielectric particle made of an organic material can be used. However, it is preferable that the dielectric particles have the same shape, size, and material. Further, the dielectric particles may be colored. The concentration of the dielectric particles in the mixture is not particularly limited as long as a desired dispersed state and aggregated state can be formed. For example, the content of the dielectric particles in the mixture can be 0.5 to 90% by weight, and further 1 to 80% by weight.

There is no particular limitation on the method of charging the dielectric particles according to the present invention. If the desired charge can be imparted to the fine particles simply by dispersing the fine particles in the polar liquid relating to the present invention, it is not necessary to perform the charging treatment. For example, the dielectric particles used in the examples described below were automatically charged simply by dispersing them in a polar liquid. However, the charging treatment may be performed by modifying the surface of the fine particles. A known treatment can be applied to the surface modification. For example, an adsorption treatment of an ionic surfactant on the particle surface and a chemical bonding treatment of an ionic residue on the particle surface can be mentioned. Alternatively, the particles may be charged by contact charging. As a method of contact charging, a method of coating the particle surface with a substance different from the particle surface can be mentioned. Incidentally, the modification of the surface of the dielectric particles is not limited to imparting chargeability to the particles,
It may be performed in order to make the dielectric particles stably exist in the polar liquid.

The present invention will be described in detail below with reference to examples.

Example 1 In this example, the relative permittivity is 8
A mixture of ethylene carbonate of 9 (26 parts by weight) and propylene carbonate having a relative permittivity of 65 (10 parts by weight) (relative permittivity of about 80) was used as the polar liquid. Spherical (diameter 5 μm) black polymer beads (trade name KBS-505, manufactured by Sekisui Fine Chemical Co., Ltd.) having a relative dielectric constant of about 3 were used as the dielectric particles. In the case of this example, (relative permittivity of polar liquid) − (relative permittivity of dielectric particles) ≈73.

After mixing the polymer beads (10 parts by weight) with the polar liquid (40 parts by weight), ultrasonic treatment was carried out to uniformly disperse the polymer beads. This was used as a mixture for the display device in this example.

The display element according to this example has the same structure as the display element shown in FIG. In this embodiment, transparent glass substrates having a thickness of about 1 mm are used as the substrates 10 and 20. The gap between the substrates is 16 μm. Grid electrode 3
The 0 electrode and the plate electrode 40 are both ITO electrodes having a thickness of 100 nanometers. The size of the plate electrode 40 is 1
It is cm × 1 cm. On the other hand, the size of the region where the grid electrode is installed is 1 cm × 1 cm. The electrode width of the elongated electrodes forming the grid electrode is 10 μm. Further, the size of the quadrangle (corresponding to the white quadrangle arranged in FIG. 3) of the non-electrode forming portion formed by the grid of the grid electrode is 30 μm × 30 μm. 50 is an electric signal applying means. In this embodiment, the grid electrode is grounded. Further, in this embodiment, a white reflective layer is used as the reflective layer 60.

The result of changing the display state of the display element by applying an electric signal between the electrodes will be described below. The display state was observed from the upper surface of the substrate 10.

First, a rectangular wave having a Va of 5 V and a frequency of 1 kHz shown in FIG. 4 (hereinafter, referred to as signal 1) was applied to the display element showing black immediately after fabrication for 30 milliseconds. As a result, the display element showed a white state. Even if the application of the rectangular wave was released, the white state was preserved.

The movement of the polymer beads in the transition process from the black state to the white state was observed with a microscope. Prior to applying signal 1, the polymer beads were almost evenly dispersed in the microscope field. During the application of the signal 1, each polymer bead moved toward the non-electrode forming region adjacent to the adjacent grid electrode, and the polymer bead aggregated in the region and in the vicinity of the region. That is, the white state in this example corresponds to the aggregated state of the polymer beads. At the time when the application of the signal 1 was released, almost no polymer beads were present on the grid electrode. Even if the application of the signal 1 was released, the distribution state of the polymer beads was almost maintained.

Next, for the display element in the white state, Vd shown in FIG. 8 is +5 V DC voltage (hereinafter referred to as signal 2).
Was applied for 30 milliseconds. Then, the display element became black. Even if the application of the signal was released, the black state was preserved.

The movement of the polymer beads in the transition process from the white state to the black state was observed with a microscope.
Before applying the signal 2, the polymer beads were aggregated in the non-electrode forming region adjacent to the grid electrode and its vicinity. During the application of the signal 2, each polymer bead moved toward the neighboring grid-like electrode, and finally the polymer bead was dispersed between the element substrates. Even if the application of the signal 2 was released, the distribution state of the polymer beads was almost maintained.

Further, in this embodiment, the signal 1 and the signal 2 were alternately applied (application time of each signal was 30 milliseconds). As a result, a white state and a black state could be formed alternately. Then, each state was retained even after the application of each signal was released.

Next, in this example, a rectangular wave having a Va of 10 V and a frequency of 1 kHz shown in FIG. 4 (hereinafter referred to as signal 3) was applied to the element showing the black state for 10 milliseconds. As a result, the display element showed a white state. The white state was preserved even after the application of the rectangular wave was released. Next, Vd shown in FIG.
A DC voltage of 10 V (hereinafter referred to as signal 4) was applied for 10 milliseconds. Then, the display element became black. Even if the application of the signal was released, the black state was preserved. Further, in this embodiment, the signal 3 and the signal 4 were alternately applied (the application time of each signal was 10 milliseconds). As a result, a white state and a black state could be formed alternately. Then, each state was retained even after the application of each signal was released.

Comparative Example 1 The display element in this comparative example is the same as that in Example 1 except that the polar liquid is completely replaced with silicone oil having a relative dielectric constant of about 3. In the case of this comparative example, (relative permittivity of dispersion medium)-(relative permittivity of dielectric particles)
≈0.

The above signal 1 was applied to the display element in which the polymer beads were dispersed and which showed a black color, for 30 milliseconds. However, the display element remained black. Even when the signal 1 was applied for 1 second, it remained black. Next, FIG.
The signal with Va of 15 V shown in 1 was applied for 1 second. However, the display element remained black. The response of the polymer beads when each signal was applied was observed. as a result,
Little movement of the polymer beads was observed.

(Example 2) In this example, the same display element as in Example 1 was used. First, the display element was made white by applying the signal 1 to the display element showing a black state for 30 milliseconds. In the display element showing the white state, Va shown in FIG. 6 is 5 V and the duty ratio is 80
%, A rectangular wave with a frequency of 1 kHz (hereinafter referred to as signal 5)
Was applied for 30 milliseconds. As a result, the display element showed a black state. Even if the application of the rectangular wave 5 was released, the black state was preserved. When the signal 1 and the signal 5 were alternately applied (the application time of each signal was 30 milliseconds), a white state and a black state could be formed alternately. Moreover, the white state and the black state were preserved even after the application of each signal was released. When the distribution state of the polymer beads was observed, the white state and the black state of the display element also corresponded to the aggregated state and the dispersed state of the polymer beads in this example, respectively.

(Example 3) In this example, the same display element as in Example 1 was used. First, the display element was made white by applying the signal 1 to the display element showing a black state for 30 milliseconds. A rectangular wave (hereinafter, referred to as signal 6) having Vb of 8 V, Vc of 2 V, a duty ratio of 50% and a frequency of 1 kHz shown in FIG. 7 was applied to the display element showing the white state for 30 milliseconds. . Then, the display element became black. Even if the application of the signal 6 was released, the black state was preserved.

Further, in this embodiment, the signal 1 and the signal 6 were alternately applied (application time of each signal was 30 milliseconds). As a result, a white state and a black state could be formed alternately. Then, each state was retained even after the application of each signal was released.
When the distribution state of the polymer beads was observed, the white state and the black state of the display element also corresponded to the aggregated state and the dispersed state of the polymer beads in this example, respectively.

(Example 4) The display element of this example is the same as that of Example 1 except that the polar liquid was completely replaced with N-methyl-2-pyrrolidone having a relative dielectric constant of about 32. In the case of the present embodiment, (dielectric constant of polar liquid) − (dielectric constant of dielectric particles) ≈29.

First, as in Example 1, the signal 1 was applied to the display element showing the black state for 30 milliseconds. However, the display element remained in the black state. Next, the signal 3 is set to 1 on the display element showing the black state.
It was applied for 0 ms. However, the display element remained in the black state.

As described above, in this example, unlike Example 1, it was not possible to develop a white state by applying the signal 1 for 30 ms and the signal 3 for 10 ms. It is considered that this is because the dielectrophoretic force acting on the polymer beads of this example is smaller than the dielectrophoretic force of Example 1. This is because the magnitude of {(relative permittivity of polar liquid)-(relative permittivity of dielectric particles)} in this example is smaller than that in Example 1.

Next, for the display element showing the black state,
The signal 3 was applied for 70 milliseconds. As a result, the display element showed a white state. Subsequently, the signal 4 was applied for 70 milliseconds. As a result, the display element showed a black state.

Further, in this embodiment, the signal 3 and the signal 4 were alternately applied (the application time of each signal was 70 milliseconds). As a result, a white state and a black state could be formed alternately. Then, each state was retained even after the application of each signal was released.
When the distribution state of the polymer beads was observed, the white state and the black state of the display element also corresponded to the aggregated state and the dispersed state of the polymer beads in this example, respectively.

Next, in this embodiment, in the display element showing the black state, Va shown in FIG. 4 is 20 V and the frequency is 1
A rectangular wave of kHz (hereinafter referred to as signal 7) was applied for 30 milliseconds. As a result, the display element showed a white state. Even if the signal application was stopped, the white state was preserved. Subsequently, the DC voltage having a Vd of +20 V (hereinafter, referred to as signal 8) shown in FIG. 8 was applied to the display element in the white state for 30 milliseconds. Then, the display element became black. Even if the application of the signal was released, the black state was preserved.

Further, in this embodiment, the signals 7 and 8 were alternately applied (the application time of each signal was 30 milliseconds). As a result, a white state and a black state could be formed alternately. Then, each state was retained even after the application of each signal was released.
When the distribution state of the polymer beads was observed, the white state and the black state of the display element also corresponded to the aggregated state and the dispersed state of the polymer beads in this example, respectively.

(Embodiment 5) The display element according to this embodiment has the same structure as the display element shown in FIG. In this embodiment, transparent glass substrates having a thickness of about 1 mm are used as the substrates 10 and 20. The gap between the substrates is 16 μm. The flat plate-shaped electrode 40 and the striped electrode 300 connected to both ends are both 100 nm thick IT.
It is an O electrode. The size of the plate electrode 40 is 1 cm x 1
cm. On the other hand, the size of the region where the striped electrode 300 connecting both ends is 1 cm.
× 1 cm. The electrode width of the elongated electrode forming the electrode 300 is 10 μm. Further, the minimum width of the quadrangle of the non-electrode forming portion formed by the electrode 300 (corresponding to the white quadrangle arranged in FIG. 9) is 30 μm. 50 is an electric signal applying means. In this embodiment, the striped electrodes whose both ends are connected are grounded. In addition, in this embodiment, a white reflective layer is used as the reflective layer 60.

The mixture used in Example 1 was filled between the substrates of the above display device. Next, the signal 1 and the signal 2 were alternately applied (application time was 30 milliseconds each). As a result, a white state and a black state could be formed alternately. And
Each state was retained even when the application of the signal 1 and the signal 2 was released. Observation of the distribution state of the polymer beads revealed that the white state and the black state of the display element were
Each corresponded to the aggregated state and dispersed state of the polymer beads.

[0077]

As described above, according to the present invention, the driving voltage required to form a display state having a memory property is 3
It was possible to provide a bistable display element having a response speed of 0 V or less and a response speed of several tens of milliseconds or less, and a driving method thereof.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a display element according to the present invention.

FIG. 2 is a schematic diagram showing a dispersed state of dielectric particles.

FIG. 3 is a schematic diagram showing an aggregated state of dielectric particles.

FIG. 4 is a schematic diagram of an electric signal for forming an aggregated state.

FIG. 5 is an explanatory diagram of a duty ratio.

FIG. 6 is a schematic diagram of an electric signal for forming a dispersed state.

FIG. 7 is a schematic diagram of an electric signal for forming a dispersed state.

FIG. 8 is a schematic diagram of an electric signal for forming a dispersed state.

FIG. 9 is a schematic diagram showing an example of a display element according to the present invention.

[Explanation of symbols]

10, 20 substrate 30, 40, 300 electrodes 50 means for applying electric signal 60 reflective layer 70 Dielectric particles 80, 310 Electrode non-formation part

Claims (21)

[Claims] 1. A pair of substrates arranged to face each other, a pair of electrodes formed on the substrate, and a mixture of a dielectric liquid and a plurality of dielectric particles filled between the substrates, By applying an electric signal containing no DC component between the electrodes,
An aggregated state in which the dielectric particles are aggregated between the substrates,
A display device, which displays a different display state from a dispersed state in which the dielectric particles are dispersed between the substrates by applying an electric signal containing a DC component between the electrodes, wherein the dielectric particles are charged. A display element, which is a dielectric particle, wherein the dielectric liquid is a polar liquid having a relative dielectric constant larger than that of the dielectric particle. 2. A pair of substrates arranged to face each other, a pair of electrodes formed on the substrate, a mixture composed of a dielectric liquid filled between the substrates and a plurality of charged dielectric particles. Comprising: an aggregated state in which the dielectric particles are moved in a specific direction by a dielectrophoretic force and agglomerated between the substrates, and the dielectric particles are moved in a direction opposite to the specific direction by an electrophoretic force, A display element in which dispersed states dispersed between the display elements are different display states, wherein the dielectric liquid is a polar liquid having a relative dielectric constant larger than that of the dielectric particles. And display device. 3. The dielectrophoretic force is generated by applying an electric signal containing no DC component between the electrodes,
The display device according to claim 2, wherein the electrophoretic force is generated by applying an electric signal including a DC component between the electrodes. 4. The display element according to claim 1, wherein the relative dielectric constant of the polar liquid is larger than that of the dielectric particles by 5 or more. 5. The display device according to claim 1, wherein the relative dielectric constant of the polar liquid is 18 or more higher than the relative dielectric constant of the dielectric particles. 6. The display element according to claim 1, wherein the polar liquid has a viscosity of less than 17 cps. 7. The polar liquid according to claim 1, wherein the polar liquid contains a dipolar aprotic solvent as a constituent component.
The display element according to 1. 8. The display element according to claim 7, wherein the dipolar aprotic solvent is propylene carbonate. 9. The display device according to claim 7, wherein the dipolar aprotic solvent is ethylene carbonate. 10. The dipolar aprotic solvent is N-
8. Methyl-2-pyrrolidone
The display element according to 1. 11. The electric signal not containing the DC component is a pulse signal, the plus side pulse crest value is equal to the minus side pulse crest value, and the duty ratio is 30% or more.
It is 0% or less, The display element of Claim 1 or 3 characterized by the above-mentioned. 12. The duty ratio of the pulse signal is 50.
The display element according to claim 11, wherein the display element is%. 13. The electric signal containing the DC component is a pulse signal, the plus side peak value is equal to the minus side peak value, and the duty ratio is not 50%. Display element. 14. The duty ratio of the pulse signal is 30.
%, And / or 70% or more, the display element according to claim 13. 15. The duty ratio of the pulse signal is 10
% Or less and / or 80% or more, The display element according to claim 14. 16. The electric signal containing the DC component is a signal obtained by superimposing a DC signal on a pulse signal having a plus side peak value equal to a minus side peak value and a duty ratio of 50%. The display element according to claim 1 or 3. 17. The display element according to claim 1, wherein the electric signal containing the DC component is a DC signal. 18. The display according to claim 1, wherein a non-uniform electric field is formed between the substrates when an electric signal not containing the DC component and an electric signal containing the DC component are applied. element. 19. The display element according to claim 18, wherein a position where the aggregated state is formed is included in a region where the electric field strength is weak in the nonuniform electric field. 20. The display element according to claim 1, wherein the dispersed state is a state in which the dielectric particles are dispersed throughout the pair of electrodes. 21. The display element according to claim 1, wherein at least one of the pair of electrodes has a lattice shape or a stripe shape.