JPH0353224A - Electrophoretic display element - Google Patents

Abstract

PURPOSE:To prevent the flocculation of electrophoretic particles by oscillating at least either of a dispersion medium and the electrophoretic particles by driving an oscillating device when a voltage is impressed to an electrode. CONSTITUTION:A cell 1 is oscillated by the oscillation of a PZT ultrasonic oscillator 20, by which dispersion media 14 and the electrophoretic particles 13 are oscillated as well when an oscillator driving circuit 21 is driven simultaneously with the inversion driving of an electrophoretic display element driving circuit 15. The electrophoretic particles 13 stuck to the electrode 12b are liberated form the electrode 12b by the energy of this oscillation and are attracted to the electrode 12a. The PZT ultrasonic oscillator 20 is driven for a prescribed period of time and while the liberated electrophoretic particles are diffused into the cell space, the particles are attracted to the electrode 12a. Consequently, the electrophoretic particles 13 attracted to the electrode 12a are stuck uniformly to the entire surface of the electrode 12a and the red display of the electrophoretic particles 13 is visible from a viewing side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophoretic display element used in various displays and the like.

[Prior Art] Electrophoretic display elements are known that perform display using the charging phenomenon of cocolloid particles. This electrophoretic display element is
A dispersion system in which electrophoretic particles are separated into a dispersion medium is sealed between a pair of substrates, at least one of which is transparent, and display is performed by applying a DC voltage to an electrode formed on the inner surface of the substrate. It is. Considering the case where the electrophoretic particles are positively charged in the dispersion medium, the electrophoretic particles gather on the negative electrode side when a voltage is applied. Therefore, the unique color of the electrophoretic particles can be seen from the outside of the front substrate provided with the negative electrode. If the direction of voltage application is reversed, the electrophoretic particles will gather at the opposite electrode, and the color of the electrophoretic particles will disappear from the outside of the front substrate. This allows display to be performed.

[Problems to be Solved by the Invention] In order to ensure the display of an electrophoretic display element, it is necessary to ensure the movement of electrophoretic particles to each electrode. However, since electrophoretic particles are dispersed in a dispersion medium, they may aggregate or settle over time. In this case, the concentration of electrophoretic particles within the cell becomes uneven, which tends to cause uneven display.

In order to prevent such problems,
No. 1930 discloses an electrophoresis system in which the inside of the cell is divided into a plurality of small sections so that the dispersion medium flows when the electrophoretic particles move, and the aggregation of the electrophoretic particles is prevented by convection and sliding. A display element is disclosed.

However, when electrophoretic particles are drawn to one electrode by applying a voltage, some of the electrophoretic particles may remain attached to the surface of the other electrode or the inner peripheral surface of the cell other than the electrode and not be drawn. When this happens, display quality deteriorates.

Furthermore, electrophoretic display elements in which one of a pair of opposing electrodes is a full-surface electrode and the other is a striped electrode have also been developed in recent years. However, in such an electrophoretic display element, when the electrophoretic particles are moved from the striped electrode to the entire surface electrode, the electrophoretic particles do not spread sufficiently, making it impossible to completely cover the entire surface electrode with the electrophoretic particles. This may become difficult and display quality may deteriorate. When roughly moving from a full surface electrode to a striped electrode, electrophoretic display elements located close to the striped electrode are quickly released from the full surface electrode, but electrophoretic display elements located far away take a longer time to be released. Since the length is longer, movement becomes slower, resulting in a problem of lower responsiveness.

The present invention was made in view of these circumstances, and
The purpose is to prevent agglomeration of electrophoretic particles and to improve display quality and responsiveness.

[Means for Solving the Problems] The electrophoretic display element of the present invention includes a pair of substrates that are spaced apart and facing each other, at least one of which is transparent, and an electrode formed on the inner surface of each substrate. a dispersion system in which electrophoretic particles are introduced between a pair of substrates and are dispersed in a dispersion medium; a vibrating device provided in contact with or apart from the cell;
It is characterized in that it is configured to vibrate at least one of the electrophoretic particles and the electrophoretic particles by driving the vibrating device when a voltage is applied to at least the electrodes.

As the pair of substrates constituting the cell, glass substrates, resin substrates, etc. can be used as in the past. At least one of them is a transparent substrate, and the outside of the transparent substrate becomes the display side of the electrophoretic display element. Both substrates can also be transparent substrates.

A pair of substrates are generally opposed to each other with a spacer of a predetermined thickness interposed therebetween, and the edges are sealed with epoxy resin or the like to form a cell space. In this cell space, the electrophoretic particles are divided into fB! A dispersion system consisting of a medium is enclosed.

Here, as the dispersion medium, a halogen compound such as tetrachlorethylene is used as in the conventional case. Furthermore, various organic pigments or inorganic pigments can be used as the electrophoretic particles. It is desirable that the dispersion medium and the electrophoretic particles have similar specific gravity.

Further, a surfactant or the like may be mixed, or the dispersion medium itself may be colored with a dye or the like.

The electrodes are provided on opposing surfaces of a pair of substrates forming a cell space. The shape is not particularly limited and can be selected from various shapes depending on the purpose, such as a full surface electrode, a striped electrode, or a mesh electrode. It may be a transparent electrode or an opaque electrode.

In the case of transparent electrodes, P from materials such as ITO and tin dioxide can be used.
It can be formed by a common method such as a VD method or a photo-etching method.

The vibrating device that is a feature of the present invention is capable of vibrating at least one of a dispersion medium and electrophoretic particles, and is a mechanical vibrating device that uses ultrasonic vibrators, various piezoelectric materials, electromagnets, etc. It can be selected from a device that vibrates or a device that vibrates electromagnetically using an alternating electric field. In the case of a mechanically vibrating device such as an ultrasonic vibrator, it is usually used in contact with a cell. The desired location is the center of the cell, but a plurality of them may be provided at the ends.

Note that the frequency and intensity of vibration are variously selected depending on the shape of the cell, the material, the type of dispersion medium, the type and size of the electrophoretic particles, etc.

The vibrating device is activated at least when a voltage is applied to the electrodes. For example, it vibrates for 0.5 to 2 seconds when switching the display. In addition, it is possible for children to apply weak vibrations continuously or intermittently.

[Operations and Effects of the Invention] In the electrophoretic display element of the present invention, the vibrating device is driven at least when voltage is applied. This causes at least one of the dispersion medium and the electrophoretic particles to vibrate. Due to this vibration, the electrophoretic particles attached to the electrode or the inner surface of the cell are subjected to mechanical force and become easily separated. Therefore, the electrophoretic particles left attached are liberated by vibrational energy and are attracted to an electrode having a potential opposite to that of the electrophoretic particles. This improves display quality.

In addition, the electrophoretic particles that had been aggregated are also redistributed by receiving vibrational energy. Therefore, the concentration of electrophoretic particles becomes uniform, and display quality is also improved.

Furthermore, in an electrophoretic display element in which a striped electrode and a full surface electrode face each other, when electrophoretic particles gathered on the striped electrode are moved to the full surface electrode, the electrophoretic particles are spread and destroyed by vibration energy. Therefore, it adheres with sufficient spread.

This improves display quality. Furthermore, when moving from the entire surface electrode to the striped electrode, electrophoretic particles located far from the striped electrode are also liberated from the entire surface electrode at approximately the same time as electrophoretic particles located close to the striped electrode due to vibration energy. Vibration energy also causes damage. Therefore, the time required for each electrophoretic particle to be attracted to the striped electrode is approximately the same, improving responsiveness.

Therefore, according to the electrophoretic display element of the present invention, aggregation is prevented, display quality is improved with excellent light transmission characteristics such as responsiveness and contrast, and display quality can be maintained for a long time.

[Example] Hereinafter, this will be explained in detail using examples.

(Example 1) FIG. 1 shows the electrophoretic display element of this example.

This electrophoretic display element is composed of a cell 1 and a vibrating device 2 held in the cell 1.

Cell 1 is a transmission type electrophoretic display element, and spacer 11
a pair of substrates 10a facing each other with a gap between them;
10b, transparent electrodes 12a and 12b formed on the entire opposing surfaces of the substrates 10a and 10b, respectively, and the substrate 10.
The electrophoretic particles 13 and dispersion medium 14 sealed between a and 10b, and the cell 1 connected to transparent electrodes 12a and 12b.
and an electrophoretic display element drive circuit 15 that drives the electrophoretic display element drive circuit 15.

Substrates 10a and 10b are each formed from soda lime glass with a thickness of 1.6 mm. On the opposing surfaces of the substrates IQa and 10b, transparent electrodes 12a and 12b made of an ITO film with a thickness of 500.degree. C. are formed over the entire surface, respectively. The transparent electrodes 12a, 12b are formed by a vapor deposition method. A spacer 11 made of a polyester film with a thickness of 100 μm is arranged at the peripheral edge between the substrates 10a and 10b, and the spacer 11 and the periphery of the substrates 10a and 1ob are bonded and sealed with an epoxy resin adhesive.

In the cell space surrounded by the pair of substrates 10a and 10b and the spacer 11, organic pigments (as electrophoretic particles 13)
A dispersion medium 14 (a mixture of tetrachloroethylene and xylene) in which rRedBRNJ (manufactured by Nippon Ciba Geigy Co., Ltd.) is dispersed is enclosed. and a pair of transparent substrates 12a
, 12b are connected to an electrophoretic display element drive circuit 15 and configured to apply a DC voltage.

The vibration device 2 includes a PZT ultrasonic vibrator 20 and a vibrator drive circuit 21, and the PZT ultrasonic vibrator 20 is held in contact with the center of the outer surface of one substrate 10b. This PZT ultrasonic vibrator 20 has a vibration frequency of 10 to 1
It is possible to vibrate in the range of 00K, but in this example, it is 30K.
It is designed to vibrate within a range of ~55K, and the driving power at this time is several watts to several tens of watts.

The operation of the electrophoretic display element of this example configured as described above will be explained. First, the electrophoretic rib display element drive circuit 15 is driven, and a state in which the electrophoretic particles 13 are attached to the transparent electrode 10b side is set as an initial state. In this electrophoretic display element, the substrate 10a is on the viewing side, and in this state, the color of the dispersion medium 14 itself is visible from the viewing side. Next, the polarity of the voltage applied to the electrophoretic display element drive circuit 15 is reversed.

Then, the electrophoretic particles 13 that had been attached to the electrode 12b are released from the electrode 12b and begin to move toward the electrode 12a.

However, some electrophoretic particles 13 may remain attached to the electrode 12b. Therefore, as shown in FIG. 2, the vibrator drive circuit 2-1 is driven simultaneously with the inversion drive of the electrophoretic display element drive circuit 15.

Then, the cell 1 vibrates due to the vibration of the PZT ultrasonic vibrator 20, and the dispersion 114 and electrophoretic particles 13 also vibrate.

Due to the energy of this vibration, the electrophoretic particles 13 attached to the electrode 12b are also released from the electrode 12b, and
drawn to. Note that the PZT ultrasonic transducer 20 is driven for about 1.2 seconds, and the liberated electrophoretic particles are attracted to the electrode 12a while spreading in the cell space.

As a result, the electrophoretic particles 1 attracted to the electrode 12a
3 is uniformly adhered to the entire surface of the electrode 12a, and the red display of the electrophoretic particles 13 can be seen from the viewing side.

Therefore, according to the electrophoretic display element of this embodiment, almost all the electrophoretic particles 13 contribute to display and are uniformly attached to the entire surface of the electrode 12a, so that the display quality is excellent.

(Example 2) FIG. 3 shows an electrophoretic display element of a second example. This electrophoretic display element is similar to Example 1 except that the electrodes 12b formed on the substrate 10b are striped. The same is true.

The operation of the electrophoretic display element of this example will be explained.

As in Example 1, it is assumed that electrophoretic particles 13 are attached to the electrode 12b. When the electrophoretic display element drive circuit 15 is reversely driven, the electrophoretic particles 13 are released from the electrodes 12b and begin to move. At the same time, the vibrator drive circuit 21 is driven, and the electrophoretic particles 13 left behind attached to the electrodes 12b and the electrophoretic particles 13 attached to the surface of the substrate 10b between the electrodes 12b are absorbed by the vibration energy. It is released by Then, the liberated electrophoretic particles 13 are expanded into the cell space by the vibration energy, and the influence of adhering in a stripe pattern is eliminated. Therefore, the electrophoretic particles 13 adhere uniformly to the entire surface of the electrode 12a, resulting in improved display quality.

Next, when the electrophoretic display element drive circuit 15 is reversely driven again, the electrophoretic particles 13 attached to the electrode 12a are released and begin to move toward the electrode 12b. Here, in the conventional electrophoretic display element, as shown in FIG. 4, the electrophoretic particles (A) closest to the striped electrode 12b are liberated first, and then the electrophoretic particles (A), C, and II are released in the order of Mm. . Therefore, the time required to reach the striped electrode 12b is different, causing a problem in response. However, in the electrophoretic display element of this example, the PZT ultrasonic transducer 2
Due to the drive of 0, it receives vibration energy and produces A, Mouth, Ha,
The two electrophoretic particles 13 are released almost simultaneously. Therefore, the time taken to reach the striped electrode 112b is almost the same, and excellent responsiveness is exhibited.

In these embodiments, the vibrating device @2 was provided on the electrode 12b side, but the present invention is not limited to this. It can also be provided in sections.

Further, a plurality of vibration devices may be provided.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the structure of an electrophoretic display element according to an embodiment of the present invention, and FIG. 2 is a time chart of the electrophoretic display element drive voltage and the drive voltage of the PZT ultrasonic transducer according to embodiment 1. , FIG. 3, and FIG. 4 are explanatory views showing the operation of the electrophoretic display element of the second embodiment, respectively. 1... Cell 2... Vibration device 10... Substrate 11... Spacer 12... Electrode
13... Electrophoretic particles 14... Dispersion medium 15... Electrophoretic display element drive circuit 20... PZT ultrasonic vibrator 21... Vibrator drive circuit

Claims (1)

[Claims] (1) A pair of substrates facing each other at a distance, at least one of which is transparent, an electrode formed on the inner surface of each substrate, and electrophoretic particles sealed between the pair of substrates. A cell comprising a dispersion system dispersed in a dispersion medium, a vibrating device provided in contact with or apart from the cell, and driving the vibrating device when a voltage is applied to at least the electrode. An electrophoretic display element, characterized in that the electrophoretic display element is configured to vibrate at least one of the dispersion medium and the electrophoretic particles.