JPS592908B2 - Electrochemical color display device and its driving method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a display device using an electrochemical coloring material (hereinafter abbreviated as EC material) that is electrochemically oxidized and reduced to reversibly color and fade, and a driving method thereof.

Inorganic or organic materials such as W03, MoO3, or viologen are known as EC materials.

When displaying various patterns using these EC materials as shown in Table 10, EC is placed between a display electrode consisting of a large number of segments that can be driven independently of each other and a common counter electrode.
An electrolyte containing the material is interposed, and the segments are selectively driven to form a coloring layer on their surfaces.

15 and below will be explained with reference to the drawings.

FIG. 1 is a wiring diagram for explaining the driving method of a conventional EC display device. Inside a display cell 1, a display electrode 2 consisting of a large number (seven in this case) of segments 2a to 2g is provided.
, and common counter electrodes 3 and 20 are arranged, with an electrolyte (not shown) containing an EC material interposed therebetween.

FIG. 2 shows a cross-sectional structure of the display cell 1, in which a counter substrate 7 having a counter electrode 3 and a display substrate 8 having a display electrode 2 are arranged in parallel with a spacer 9 in between.
An electrolyte 10 containing an EC material is interposed between them. 1
Reference numeral 1 denotes an insulating layer that covers the lead wire portion of the display electrode 2 .

The counter electrode 3 may be provided on the display substrate 8 side as shown in FIG. When displaying numbers with this device, the segments 2a-2g are arranged in a figure-eight pattern, as shown in FIG. If you want to switch from the state in which the segments 2b and 2c are colored and display the number ``1'' to the number ``2'', close the switch 4c in FIG. Turn the power switch 35 to the coloring direction to erase the color, then close the switches 2a, 2d, 2e, and 2g, and turn the power switch 5 to the coloring direction to erase the segments 2a, 2d, 2e.
, 2g to develop color. Even if the power switch 5 is in the open state, when the switches 4a to 4g are closed, current flows from the coloring segment to the decoloring segment and the memorization effect is eliminated, so all switches 4a to 4g are kept in the open state in the memorization state. . However, conventional display devices and their driving methods have many drawbacks as described below.

The first drawback is that when decoloring the display, the coloring that appears on the counter electrode side (referred to as reverse coloring) interferes with the display. For this purpose, an opaque screen (not shown) is placed between the display electrode 2 and the counter electrode 3 in FIG. 2, or the counter electrode 3 is placed in a peripheral area away from the display section in FIG. Measures are taken to hide this with the parting plate 12, but this increases the resistance between the electrodes and reduces responsiveness. The second drawback is that the coloring density of the coloring segments differs from one another, resulting in uneven shading.

The color density of a segment depends on the number of segments driven at the same time, the distance from the opposing electrode, the elapsed time in the memorized state, etc. Therefore, segments in the color state have various color densities based on their color history. This may make the display difficult to read. Generally, the electrode potentials of dark and light colored segments are different, so if these are wired outside the display cell, charge will move due to the difference in potential between dark and light colors, and the color development will be averaged out. I haven't gotten used to it. Incidentally, the unevenness of shading between segments is also a phenomenon observed in discolored segments. The third drawback is that power consumption is large.

Since EC display devices are driven by electrochemical reactions, they are essentially current-driven, and unavoidably consume more power than electric field-driven TN liquid crystal display devices, but conventional EC display devices In this case, the opposing electrode, which has nothing to do with the pattern to be displayed, is also turned on and off each time, which wastes a lot of power. A fourth drawback is the relatively short lifetime of the display cells.

There are various factors that can be considered to determine the lifespan of a display cell, and some of them are considered to be deterioration of the counter electrode and drift of the electrode potential. Each segment of the display electrode is selectively driven, whereas the counter electrode is driven every time, so it is driven more frequently and is more likely to deteriorate.

Therefore, the material or shape of the counter electrode is generally configured to be different from that of the display electrode. However, in either case, the counter electrode and the display electrode are not electrochemically equivalent, so products from side reactions (secondary reactions different from the redox reaction of EC) may occur in either one. It precipitates only on the electrode (eg, counter electrode) side, causing the electrode potential to drift in one direction, eventually making it impossible to drive. The purpose of the present invention is to eliminate the above-mentioned drawbacks in EC display devices at once. Therefore, in the present invention, counter electrodes are not particularly provided, and each segment of display electrodes is selectively distributed into two groups, and each segment of the display electrode is selectively divided into two groups. With the segment groups electrically connected, a voltage is applied between both groups to drive them, and the electrical connection of each segment group is maintained even in the memorized state after the drive voltage is removed.

FIG. 4 is a wiring diagram for explaining the structure and driving method of the display device of the present invention, in which a display electrode 2 consisting of segments 2a to 2g is arranged inside the display cell 1, and an EC
It is in contact with an electrolyte (not shown) containing the material.

Each segment is connected to the lead wire 2 via switches 4a to 4g.
Connected to either 0 or 21. When switching the display, segments that are in a colored state and should continue to be colored, and segments that are in a decolored state and should be newly colored are connected to one lead wire 20 and brought together as one segment group, and the segments are decolored. Connect the segments that are in the current state and should be continued to be decolored and the segments that are in the colored state and need to be newly decolored to the other lead wire 21 to combine them into the other segment group, and close the power switch 51 to combine both segment groups. A driving voltage is applied for a certain period of time. After the display switching is completed, the power switch 51 is opened, and the concentration of each segment group is maintained as it is. Therefore, even if there is uneven coloring in each segment group, the charge moves based on the difference in potential between shades, and the density is averaged. This eliminates the second drawback mentioned above. Since the display device of the present invention does not have a counter electrode, it is also clear that the first and fourth drawbacks caused by the counter electrode are eliminated. Furthermore, according to the drive method of the present invention, power consumption can also be significantly reduced. To color one segment of a certain area to a certain density or to return it to its original decolored state, a certain amount of charge Q must be moved, and if the driving voltage is V, then VQ
of energy is consumed. Now, if we consider switching the display by decoloring the colored segment a and coloring the decolored segment b, in the conventional method using counter electrodes, VQ is used for decoloring segment a, and VQ is used for coloring segment b. VQ, consuming a total of 2 VQ of energy. On the other hand, in the present invention, the switching is completed by simply moving the charge Q directly between the segments A and b, so that the energy consumption is VQ, which is half the energy of the conventional method. This eliminates the third drawback. However, with the driving method of the present invention, it is not possible to cause all segments to develop or decolor at the same time.

However, in the case of a time display device for a watch, for example, the segment arrangement as shown in FIG.
However, since it is impossible to display 18:88, there is always a segment in the erased state, and there is no problem.

The above embodiment is an example in which the display is driven only by segment type display electrodes, but if an auxiliary electrode is further provided and used in combination with this, the driving becomes easier.

When the segment groups of display electrodes are divided into a coloring segment group and a color-deleting segment group, it is clear that driving can be performed easily if the numbers of both groups are balanced, but if the numbers of both groups are extremely unbalanced, When it gets old, it becomes difficult to drive.
Sufficient density contrast may not be obtained. In such a case, if an auxiliary electrode is provided in advance and this is added to the small segment group and driven, satisfactory driving can be achieved.
The number of auxiliary electrodes is not limited to one, but two or more are provided, and only when the unbalance between both groups exceeds a certain limit, one or more auxiliary electrodes can be driven in accordance with the amount of unbalance. In this case, the auxiliary electrode may be provided at the edge of the display cell to hide it, as shown in FIG. It can be used for. The auxiliary electrodes used here are not always dedicated like the counter electrodes in the prior art, but are used from time to time in combination with a small group of display electrode segments. It is clear that the gist of the invention is not impaired and each of the aforementioned drawbacks of the prior art is largely eliminated. As described above, the present invention eliminates the problems caused by the opposing electrodes in the prior art, eliminates uneven density between segments, and provides an EC display device with low power consumption and long life. It is useful as a display device for watches, calculators, etc.

[Brief explanation of the drawing]

1 to 3 are a wiring diagram, a sectional structure diagram of a display cell, and an electrode arrangement diagram for explaining a driving method, respectively, in a conventional EC display device, and FIG. 4 is a diagram of a display device of the present invention. A wiring diagram for explaining the structure and driving method, and FIG. 5 is an electrode arrangement diagram in an embodiment of the present invention. 1...Display cell, 2...Display electrode, 3
......Counter electrode, 2a to 2g...Segments, 4a to 4g, 20, 21...Means for gathering into two segment groups, 51...Drive Means for connecting a power source, 6... Drive power source, 31, 32,
33, 34... Auxiliary electrode, 10... Electrolyte containing an electrochemical color forming material.

Claims (1)

[Scope of Claims] 1. A display electrode consisting of a large number of segments that can be driven independently of each other, an electrolyte containing an electrochemical coloring material that is electrochemically oxidized and reduced to develop and fade color by the display electrode, and An electrochemical color display device comprising means for selectively converging all of the segments into two segment groups, and means for applying a driving voltage between the two segment groups. 2. A display electrode consisting of a large number of segments that can be driven independently of each other; an electrolyte containing an electrochemical coloring material that is electrochemically oxidized and reduced to develop and erase color by the display electrode; and 2. An electrochemical color display device having means for assembling segments into one group and means for applying a driving voltage between the two segment groups is used, and the driving voltage is applied between the two segment groups to separate one group. A driving method for an electrochemical color display device, which is characterized in that after developing color and decoloring the other group, the drive voltage is removed and each group of segments is kept together until the next display switching.