JP2705235B2 - Driving method of electrophoretic display element - Google Patents

Description

The present invention relates to a method for driving an electrophoretic display element.

[Prior Art] An electrophoretic display element is a device in which a dispersion layer in which particles are dispersed in an insulating liquid is sealed between a pair of glass substrates having transparent electrodes, and the particles in the dispersion layer are Utilizing that has a surface charge, the particles are moved by electrophoresis to visualize the signal.

As a conventional electrophoretic display, for example, the one shown in FIG. 4 is known (Japanese Patent Application Laid-Open No. 62-299824). In FIG. 4, A indicates the viewing side, but a pair of substrates 1a and 1b are arranged so as to face each other, and at least the viewing side substrate 1a is transparent and the respective substrates 1a and 1b face each other. The transparent electrode layers 2a and 2b are provided on the surface. Substrate to form cell between substrates 1a and 1b
Spacers 5 are fixed to the inner surfaces of the peripheral edges of 1a and 1b. The dispersion layer is obtained by dispersing positively or negatively charged dispersed particles 3 in a dispersion medium 4 made of an insulating liquid, and is formed by being injected into a cell formed between the substrates 1a and 1b.

When a DC voltage is applied between the transparent electrode layers 2a and 2b, the dispersed particles 3 positively or negatively charged in the dispersion medium 4 are shown in the right half or the left half of FIG. 4, depending on the polarity of the voltage. As described above, it migrates and attaches to one of the electrodes. As shown in the right half of FIG. 4, when the dispersed particles 3 adhere to the transparent electrode layer 2a on the viewing side, the display element displays the color of the dispersed particles 3, and the dispersed particles 3 are dispersed in the dispersion medium 4. When dispersed or as shown in the left half of FIG. 4, the opposite electrode layer
When the dispersed particles 3 adhere to 2b, the substrate on the viewing side becomes the dispersion medium 4
Is displayed.

Thus, in the conventional electrophoretic display element, when no voltage is applied to the electrode layer, the dispersed particles are dispersed in the dispersion medium, and the display-side substrate displays the color of the dye of the dispersion medium,
When a voltage is applied to the electrode layer, the dispersed particles adhere to the display portion on which the electrode layer is formed, and the color of the dispersed particles is displayed. The display element is of a reflective type, and is transmitted as it is. It could not be used as a type display element.

[Problems to be Solved by the Invention] Therefore, in order to use a conventional electrophoretic display element as a transmissive display element, a transparent dispersion medium is used, and one of the transparent electrode layers is formed in a mesh shape or a stripe shape. Alternatively, a proposal has been made in which one of the transparent substrates is saw-toothed and a transparent electrode layer is formed on a surface parallel to the light traveling direction (Japanese Utility Model Application No. 63-7602).
1, Jpn. 63-79064, Jpn. 63-86709). In these proposals, when the dispersed particles are attached to a mesh-shaped or striped transparent electrode layer, light passing between the transparent electrode layers on which the dispersed particles are accumulated passes through the transparent dispersion medium, and the transmission-type display is performed. Becomes possible.

However, in the above proposal in which one of the transparent electrode layers has a mesh shape or a stripe shape, if the aperture ratio of the electrode pattern is increased in order to improve the transmittance of light in a transmission state, an electric field is not generated in the cell when a voltage is applied. There is a problem in that the particles become uniform, and the dispersed particles do not spread uniformly on the entire surface of the electrode in a colored state, thereby deteriorating the light shielding ratio at the time of coloring. In order to increase the response speed in the transmission state, it is necessary to apply a high voltage.However, a current flows through the electrode due to excessive charge, and the charge is reduced. Therefore, there is a problem that the dispersed particles are released from the striped or mesh-shaped electrode and exude from the electrode, thereby lowering the transmittance of incident light.

The present invention has been made to solve the above-described problems in a transmission state or a light-shielding state of a transmission type electrophoretic display element in which a transparent electrode layer formed on one transparent substrate has a mesh shape or a stripe shape. With an excellent response speed, the dispersed particles uniformly adhere to the entire electrode layer in the colored state to obtain a good light-shielding state, and the dispersed particles are released from the striped or mesh-shaped transparent electrode layer even in the transmission state. It is an object of the present invention to provide a driving method of a transmissive electrophoretic display element which adheres without causing a good transmission state.

[Means for Solving the Problems] A driving method of a transmissive electrophoretic display element according to the present invention includes a method of driving a transparent substrate disposed opposite to two transparent substrates and a surface of the transparent substrate opposite to each other. A transparent electrode layer formed on one side and formed on the entire surface and the other on a mesh or stripe shape; a spacer fixed to a peripheral portion of the transparent substrate to form a cell between the transparent substrates; A method for driving a transmissive electrophoretic display element comprising a highly insulating dispersion medium encapsulated therein and dispersed particles dispersed in the dispersion medium, wherein the mesh-shaped or striped transparent electrode layer is After applying the first DC high voltage so that the polarity is opposite to the polarity of the charging of the dispersed particles, the second DC low voltage is applied and held to obtain the transmission state of the display element, and the display element is formed on the entire surface. The polarity of the transparent electrode layer is opposite to the polarity of the charging of the dispersed particles. After applying the first high DC voltage, as it is summarized in that to obtain a colored state of the display element is held by applying a second low DC voltage.

In the present invention, the first direct current high voltage applied to the mesh-like or striped transparent electrode layer or the transparent electrode layer formed on the entire surface has a sufficient response speed to obtain a transmission state or a colored state of the display element. Must be obtained. This high DC voltage can be increased by 20 depending on the thickness of the cell gap.
An appropriate value is selected between 0 and 500V. The application time of the first DC high voltage is a time sufficient for the dispersed particles to migrate in the dispersion medium and reach the vicinity of the mesh-shaped or striped transparent electrode layer or the transparent electrode layer formed on the entire surface, It is appropriately selected from 0.5 seconds to 1 minute according to the cell gap.

The second direct current low voltage may be any voltage that does not cause charge-up of the dispersed particles and is sufficient to cause the dispersed particles to be adsorbed on the mesh-like or striped transparent electrode layer or the transparent electrode layer formed on the entire surface. , Is preferably about half or less of the first DC high voltage. After applying the first high DC voltage, the second low DC voltage may be applied after temporarily holding the DC voltage between the first high DC voltage and the second low DC voltage.

Regardless of whether the electrophoretic display element is in the transmissive state or in the colored state, a DC voltage is applied in the same voltage application pattern only by changing the positive and negative polarities of the transparent electrode layer.

[Operation] When the first direct current high voltage is applied so that the polarity of the mesh-like or striped transparent electrode film is opposite to the polarity of the charging of the dispersed particles, the first direct current high voltage is applied to the high-voltage, so that it is dispersed in the dispersion medium. Alternatively, the dispersed particles adhered to the entire surface electrode migrate quickly during the dispersion and reach the mesh-like or stripe-like transparent electrode layer at a quick response speed.

Subsequently, when a second direct current low voltage was applied so that the polarity of the mesh or striped transparent electrode layer was opposite to the polarity of the charging of the dispersed particles, the mesh or the striped transparent electrode layer was reached. Since the dispersed particles adhere to the transparent electrode layer without causing charge-up, a transmission state having an excellent transmittance can be obtained without deteriorating the responsiveness and without releasing the dispersed particles.

When the first DC high voltage is applied so that the polarity of the entire surface transparent electrode layer is opposite to the polarity of the charging of the dispersed particles, since the high voltage is applied, the first DC high voltage is dispersed in the dispersion medium or is striped or meshed. Alternatively, the dispersed particles adhering to the striped transparent electrode layer migrate quickly in the dispersion medium and reach the entire transparent electrode layer at a high response speed.

Subsequently, when a second DC low voltage is applied so that the polarity of the entire surface transparent electrode layer is opposite to the polarity of the charging of the dispersed particles,
The dispersed particles that have reached the entire transparent electrode layer quickly adhere to the transparent electrode layer without causing charge-up,
An excellent colored state can be obtained without deteriorating the response.

Embodiment A preferred embodiment of the present invention will be described below with reference to the drawings. The present invention is not construed as being limited by the description of the embodiments described below.

FIG. 1 is a diagram showing a change in voltage over time of a driving method according to an embodiment of the present invention and a driving method according to a comparative example;
FIG. 2 is a diagram showing a change in transmittance with the passage of time when a display element is driven in the embodiment and the comparative example of the present invention shown in FIG. 1, and FIG. 3 is a transmission type electricity to which the present invention is applied. It is sectional drawing of a migration display element.

First, the transmission type electrophoretic display device shown in FIG. 3 will be described. In the figure, arrows indicate the direction of incidence of light, and A indicates the viewing side. The two transparent substrates 1a and 1b are soda-lime glass (manufactured by Asahi glass) having a thickness of 1.8 mm, and are arranged so as to face each other with a desired gap.

On opposing surfaces of the respective transparent substrates 1a and 1b,
Transparent electrode layers 2a and 2b made of ITO are formed with a thickness of 1500 °. The transparent electrode layer 2a on the viewing side is formed on the entire surface of the transparent substrate 1a, while the transparent electrode layer 2b on the light source side is in the form of a stripe, the line width is 400 μm, and the distance between the lines is 1000 μm. It is formed by patterning using a technique.

A spacer 5 made of a 100 μm-thick polyester film (manufactured by Toray Industries Inc.) is fixed to the inner surfaces of the peripheral portions of the transparent substrates 1a and 1b so as to form cells between the substrates. A sealant 6 made of an epoxy adhesive is adhered to the outer periphery of the spacer 5 and the transparent substrates 1a and 1b.

A dispersion particle 3 and a dispersion medium 4 are sealed in the cell. Pigment violet B manufactured by Ciba-Geigy Japan
Which is negatively charged in the dispersion medium 4. Xylene / tetrachloroethylene (manufactured by Nacalai Tesque) was used as the dispersion medium 4.

Using this transmissive electrophoretic display element, it was driven into a transmissive state and a colored state by the driving method shown in FIG.

That is, first, as an example of the present invention, the first DC high voltage is 300 V between the transparent electrodes 2a and 2b, and the application time is set so that the polarity of the stripe-shaped transparent electrode film 2b is opposite to the polarity of the charging of the dispersed particles 3. For 10 seconds. Subsequently, the second direct current low voltage of 10 V is applied between the transparent electrodes 2 a and 2 b so that the polarity of the stripe-shaped transparent electrode film 2 b is opposite to the polarity of the charging of the dispersed particles 3.
When a voltage of 0 V was applied and held, a transmission state of the display element was obtained. The transmittance of the display element was measured until the transmission state was maintained after the first DC voltage was applied.

Subsequently, the first DC high voltage was applied between the transparent electrodes 2a and 2b at 300 V and the application time was set to 10 seconds so that the polarity of the entire surface transparent electrode layer 2a was opposite to the polarity of the charging of the dispersed particles 3. .
Subsequently, the second direct current low voltage of 100 V was applied between the transparent electrodes 2a and 2b so that the polarity of the transparent electrode layer 2a on the entire surface was opposite to the polarity of the charging of the dispersed particles 3. 3 adhered to the entire surface of the transparent electrode layer 2a, and a colored state of the display element was obtained. The transmittance of the display element while the light-shielded state was maintained after the application of the first DC voltage was measured as before.

Next, the transmission type electrophoretic display device shown in FIG. 3 was driven into a transmission state and a colored state by the conventional driving methods shown in Comparative Examples 1 and 2 in FIG. The first
As shown in FIG.
In the comparative example 2, a low voltage was applied, and a direct current of 100 V was applied.

That is, the transparent electrodes 2 a-2 b are arranged such that the polarity of the stripe-shaped transparent electrode film 2 b is opposite to the polarity of the charging of the dispersed particles 3.
In the meantime, in Comparative Example 1, a DC voltage of 300 V was applied and in Comparative Example 2, a DC voltage of 100 V was applied and held, thereby obtaining a transmission state.

After the transmittance was measured until the transmission state was obtained after the application of the voltage, Comparative Example 1 applied DC 300 V and Comparative Example 2 so that the polarity of the entire surface electrode film 2 a was opposite to the polarity of the charging of the dispersed particles 3. Then, a colored state was obtained by applying and maintaining a direct current of 100 V.
As before, the transmittance until the colored state was obtained after voltage application was measured.

In the transmission state and the colored state after the application of the first DC high voltage obtained by the driving method of the method of the present invention shown in Example 1 and the driving methods of the conventional methods shown in Comparative Examples 1 and 2,
FIG. 2 shows the change in transmittance with time.

As shown in FIG. 2, the response speed of Comparative Example 1 was very high because of the high voltage, but the charge-up occurred due to excessive charge, and the dispersed particles were released from the electrode, and the transmission in the transmission state occurred. The ratio is low, and the light blocking ratio in the colored state is low. Further, Comparative Example 2 had a low voltage, so that the response speed was slow and the transmittance and the light-shielding ratio were excellent, but a completely transparent state or a colored state was obtained.
It is taking almost twice as long.

On the other hand, in Example 1, which is an example of the present invention, the response speed was superior to Comparative Example 1 of high voltage, and both the transmittance in the transmission state and the light-shielding rate in the colored state were different from those of Comparative Example 1. It was as excellent as the above, and the effect of the present invention was confirmed.

In this embodiment, the second DC low voltage is applied immediately after the first DC high voltage is applied. However, after the first DC high voltage is applied, the first DC high voltage and the second DC high voltage are applied. The same result can be obtained by temporarily holding at the intermediate DC voltage of the DC low voltage of No. 2 and then applying the second DC low voltage.

[Effects of the Invention] In the method for driving a transmissive electrophoretic display element of the present invention, a transparent electrode layer is formed on the entire surface of one transparent substrate, and the transparent electrode layer is formed in a mesh or stripe on the other transparent substrate. In the method for driving a formed transmissive electrophoretic display element, a first direct current high voltage is applied such that the polarity of the mesh-like or striped transparent electrode layer is opposite to the polarity of charging of the dispersed particles. Thereafter, a second direct current low voltage is applied and held to obtain a transmission state of the display element, and the first electrode is formed such that the polarity of the transparent electrode layer formed on the entire surface is opposite to the polarity of the charging of the dispersed particles. After applying a high DC voltage, a second DC low voltage is applied and maintained to obtain a colored state of the display element. In the colored state, the dispersed particles uniformly adhere to the entire surface electrode. In addition to obtaining a good light-shielding state with a high light-shielding rate, Even in this case, since the dispersed particles adhere to the striped or mesh-shaped transparent electrode layer without being separated, there is an excellent effect that a good transmission state having a high transmittance can be obtained at a high response speed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in voltage over time of the driving method of the present invention and the driving method of the comparative example, and FIG. 2 is a diagram showing the display element of FIG. 3 according to the present invention and the comparative example of FIG. FIG. 3 is a graph showing a change in transmittance with time over time when the driving is performed.
FIG. 1 is a sectional view of a transmission type electrophoretic display device to which the present invention is applied, and FIG. 4 is a sectional view of a conventional electrophoretic display device. 1a and 1b: transparent substrate, 2a and 2b: transparent electrode layer,
3 dispersion medium, 4 dispersion particles, 5 spacer

Claims (1)

(57) [Claims] 1. A transparent substrate disposed opposite to two substrates,
A transparent electrode layer formed on opposing surfaces of the two transparent substrates, one formed over the entire surface and the other formed in a mesh or stripe shape, and the transparent electrode layer is formed to form cells between the transparent substrates. A method for driving a transmissive electrophoretic display element comprising: a spacer fixed to a peripheral portion of a substrate; a highly insulating dispersion medium sealed in the cell; and dispersed particles dispersed in the dispersion medium. After applying a first DC high voltage so that the polarity of the mesh-like or striped transparent electrode layer is opposite to the polarity of the charging of the dispersed particles, a second DC low voltage is applied and held. After obtaining a transmission state of the display element and applying a first DC high voltage so that the polarity of the transparent electrode layer formed on the entire surface is opposite to the polarity of charging of the dispersed particles, the second DC low voltage is applied. It is characterized in that a voltage is applied and held to obtain a colored state of the display element. For driving a transmissive electrophoretic display device.