JPS6129485B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to an image display device that utilizes color development and fading phenomena based on electrochemical redox reactions. 2. Description of the Related Art In recent years, attention has been paid to devices that display images by externally supplying electricity to a substance that develops and fades in color through an electrochemical redox reaction. That is, this display device basically consists of a display electrode, a hidden counter electrode, and a coloring medium (mainly composed of a coloring/eliminating substance, an electrolyte, an inert solvent, etc.) in contact with these electrodes. . When the display electrode is set to the (-) polarity and energized, "writing" is performed, and when the polarity is reversed, "erasing" is performed. Such a device is called an electrochromy device, and unlike conventional display devices (such as fluorescent display tubes, gas discharge tubes, plasma display devices, or LEDs), it is a non-emissive (passive) display, so it cannot be used in bright places. It has the advantage that it looks reasonably good, and your eyes won't get tired even if you look at it for a long time. Also, unlike the same non-emissive type liquid crystal display device, it has advantages such as no viewing field dependence and display with high image contrast. Furthermore, such an element can be provided with a function of storing an image once displayed even if the driving power is turned off. However, many problems remain in putting such devices into practical use. For example, such devices generally have poor cyclic durability. That is, when a series of display cycles of "writing"-"memory"-"erasing" is repeated, poor coloring, coloring side reactions, uneven coloring, electrode deterioration, etc. tend to occur. The reason for this has not yet been clarified, but it is believed that during the display cycle described above, the transfer of electrons and the accompanying chemical reactions do not take place reversibly at the fused interface between the electrode and the coloring/decolorizing medium. There is a relationship. In electrochromy elements, when a reduction reaction occurs on the display electrode, an oxidation reaction occurs on the counter electrode, and when an oxidation reaction occurs on the display electrode, a reduction reaction occurs on the counter electrode. Ideally, this is done alternately and evenly on the display electrode and the counter electrode, but as mentioned above, if the colored species on the display electrode exists for a long time, this balance will be disrupted, resulting in unerased areas, poor emission, or This is thought to cause electrode contamination. Further, the electrode surface is generally likely to be partially contaminated due to the presence of impurities in the coloring/decoloring medium. Once the electrode surface becomes contaminated, the coloring is not uniform and uneven coloring occurs, resulting in poor visibility. In addition, excessive transient current flows when voltage is applied, or the electrode surface becomes contaminated and the potential distribution becomes partially high, causing water decomposition and the formation of H ₂ or O ₂ bubbles. arise. Furthermore, when a viologen bromide type coloring and erasing substance is used, an anodic reaction of B ions occurs, forming a deep yellow colored precipitate on the electrode surface, which significantly impairs the display effect. Alternatively, in some types of color-developing and color-developing substances, the colored species generated by energization tends to bleed, resulting in poor display effects. Although many proposals have been made to improve the various drawbacks as described above, at present no image display device has been obtained that has solved all of the above drawbacks. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a novel image display device that solves all of the various drawbacks mentioned above. That is, a first object of the present invention is to provide an image display device that does not cause failures in coloring or decoloring even when the number of times of display is large. A second object of the present invention is to provide an image display device that does not cause uneven color development even when the number of times of display increases. A third object of the present invention is to provide an image display device that does not cause side reactions or electrode deterioration even when the number of times of display increases. A fourth object of the present invention is to provide an image display device in which a displayed image is less likely to bleed. The present invention, which achieves the above-mentioned objects, is a reaction product of a silane coupling agent and an electrochemical coloring/discoloring substance having a group in its molecule that is active toward the reactive substituent of the silane coupling agent. An image display device includes a first electrode and a first substrate on which a layer of an object is formed, a layer of an electrolyte, and a second electrode placed opposite to the first electrode. The structure, operation, etc. of the image display device of the present invention will be explained in detail below. The basic structure of the display device of the present invention is as shown in FIG. 1, in which a display electrode 1 and a counter electrode 2 are arranged in a cell 3 made of glass or the like, and both electrodes 1 and 2 are connected to a power source 4. The cell 3 is filled with a color-developing medium 5 made of an electrolyte or an inert solvent capable of dissolving a color-developing substance. The electrodes within the cell 3 can be arranged arbitrarily according to the specifications of the device. That is, the display electrode 1 and the counter electrode 2 may be provided on two opposing substrates 6 and 7 as shown in FIG. 2a, or may be provided on the same substrate 6 as shown in FIG. 2b. In addition, in Figure 2 a and b above,
Reference numeral 6 is an opaque or transparent substrate, 7 is a transparent substrate, and 8 is a spacer frame. The three members 6, 7, and 8 constitute a cell 3 that accommodates the coloring/decoloring medium 5. 9 is a blinding plate for hiding the counter electrode. The material for electrodes 1 and 2 is Pt, which is chemically stable.
Metals such as Pd and Au, or metal compounds such as SnO ₂ , In ₂ O ₃ and TiO ₂ can be preferably used. Alternatively, carbon electrodes may be used. Selection of these materials and arrangement within the cell may be made arbitrarily according to the specifications of the device. The image display device of the present invention is characterized in that the color-developing substance is chemically fixed near the electrodes.
However, the term "near the electrode" as used herein refers not only to the surface of the electrode, but also to a portion of the substrate or spacer, etc., located at a position where electrons can be exchanged with the electrode. The immobilization of the coloring/eliminating substance is achieved by chemically creating some type of bond using reactive substituents or active sites that the electrode surface or substrate and the coloring/eliminating substance have, respectively. Among chemical bonds, covalent bonding is common. Specifically, OH groups exist on the surface of oxide electrodes such as SnO ₂ , In ₂ O ₃ , TiO ₂ , and the like. Therefore, in the present invention, this OH group can be used as it is. In addition, when metal electrodes or carbon electrodes are used, the oxide surfaces of these electrodes may be used, or the surfaces may be activated, or functional groups (COOH
group, C═O group, NO ₂ group, etc.) may be introduced. Preferably, the coloring/discoloring substance has a reactive substituent or the like in its molecule in advance. However, even substances without reactive substituents may be used as long as a reaction is carried out to introduce a suitable group. Further, the following method is used to fix the color-developing and fading substance. 1. Interposing a binder between the two, a. Fixing the binder on the electrode surface, substrate, etc., and then reacting the binder with a color-changing and decolorizing substance. b. Providing a reaction product between the color-developing and decolorizing substance and the binder. The reaction product is prepared in advance and fixed on the electrode surface, substrate, etc. In particular, when this method is used, various compounds that can chemically bond inorganic materials (electrodes, substrates, etc.) and organic materials (coloring and fading substances) can be used as binders.
Typically, organosilicon compounds are used. Among the organosilicon compounds, the silane coupling agents shown in the table below are preferably used.

[Table] The following is an example of a case in which a binder as described above is fixed in advance on the surface of an electrode or a substrate, and then a coloring/discoloring substance is bonded to the binder. However, RSiX ₃ contains a binder (R; non-reactive substituent, etc.)
X: reactive substituent or active site), S: electrode or substrate surface), Y: reactive substituent that is pre-existing on the electrode surface or substrate surface or introduced by appropriate treatment etc., A indicates a molecule of a color-developing substance. Note that even if R ₂ SiX ₂ or R ₃ SiX is used as the binder, the color-developing and fading substance is fixed in substantially the same manner. As mentioned above, the effect can be observed even if the color-developing and fading substance is fixed only in the vicinity of the display electrode or in the vicinity of both the display electrode and the counter electrode. The electrochemical coloring/decolorizing substance used in the present invention is not particularly limited, and a wide range of redox-reactive substances can be selected. The most typical example is a pyridinium compound having a quaternary ammonium salt structure. Some of them are 1,1'-dimethyl-4,4'-bipyridinium dibromide 1,1'-diethyl-4,4'-bipyridinium dibromide
Dibromide 1,1'-diheptyl-4,4'-bipyridinium dibromide 1,1'-dibenzyl-4,4'-bipyridinium dibromide 1,1'-di(4-amino)benzyl-4,4 ′−
Bipyridinium dibromide 1,1'-di(4-carboxy)benzyl-4,
4'-Bipyridinium dibromide N,N'-di(P-cyanophenyl)-4,4'-
Bipyridinium dichloride 2,2'-(diethyl)-bipyridinium dichloride N,N'-diethyl-2,7'-diazapyrenium dichloride N-benzyl-4-cyano-pyridinium bromide N-benzyl-3-amino-quinolium・Bromide N-benzyl-4-amino-pyridinium bromide Also, as a redox indicator, Safranin T Neutral red indigo monosulfonic acid diphenyl amine diphenyl amine P-sulfonic acid P-nitro - Diphenyl, amine, diphenyl, amine-2,3'-dicarboxylic acid, diphenyl, amine-2,2'-dicarboxylic acid, etc. The solvent used in the present invention is generally water, but other solvents include methyl alcohol, ethyl alcohol, ethylene glycol, propylene carbonate, benzene, chloroform, acetonitrile, nitrobenzene, ethylene glycol monomethyl ether acetate, carbon tetrachloride, Examples include non-aqueous solvents such as formic acid, pyridine, tetrahydrofuran, dioxane, dimethylformamide, and dimethyl sulfoxide, and mixtures of water and these non-aqueous solvents. Electrolytes include lithium chloride, potassium chloride, sodium chloride, potassium bromide, potassium sulfate, potassium acetate, potassium phosphate, ammonium sulfate, ferrous sulfate, ammonium phosphate, lithium perchlorate, zinc ammonium sulfate, magnesium ammonium sulfate. -Metal salts such as ferrous ammonium sulfate can be preferably used. In addition to these electrolytes, auxiliary agents such as a carboxylic acid (for example, formic acid, acetic acid, tartaric acid, etc.) or a complexing agent such as complexan, and a buffer solution for adjusting pH may be added. Alternatively, in the present invention, a coloring and fading substance that is not fixed in the electrode or the cell container may be further contained in the cell solution consisting of an electrolyte, an inert solvent, and the like. In addition, in the color developing and decoloring device of the present invention, when storing the color developing and decoloring medium in which these components are dissolved in a suitable housing, the dissolved oxygen concentration in the medium may be adjusted to 5 ppm or less. desirable. By reducing the amount of dissolved oxygen in the medium, it is possible to extend the memory life and at the same time obtain better results in terms of lifetime. Next, the driving method of such a device is as follows. That is, first, writing to the display electrode 1 occurs when a DC voltage is applied from the outside 4 so that the display electrode 1 becomes negative and the counter electrode 2 becomes positive, and second, the memory effect occurs when the external voltage 4 is cut off and the circuit is opened. (The writing on the display electrode 1 continues.) Thirdly, the polarity of the applied voltage is reversed from that during writing, and a DC voltage is applied from the outside 4 so that the display electrode 1 side is positive and the counter electrode 2 side is negative. Therefore, there are three driving steps: erasing the writing on the display electrode 1. Note that writing may be performed with the display electrode 1 side facing forward. The third is a typical drive pulse application method, 1
0 represents a write step, 11 represents a memory step, and 12 represents an erase step. The driving method described above is the simplest two-pole constant voltage method, but other known methods include the two-pole constant current method and the three-pole constant potential drive method. The three-electrode constant potential method uses a reference electrode in addition to the display electrode 1 and counter electrode 2 to detect the drive of the potential of the display electrode and automatically adjust the applied voltage to keep the potential of the display electrode 1 constant. This is a drive system designed to maintain In the present invention, any of these methods can be used for driving. As described above, by chemically fixing the color-developing and fading substance, an excellent image display device with no image bleeding and improved durability over repeated use can be obtained. In other words, the coloring species is hard to bleed, and at the same time, the cycle of coloring and erasing is carried out in a well-balanced manner without going through the process of diffusion ← → precipitation by the coloring and erasing substance during the "writing" - "memory" - "erasing" cycle. be able to. Therefore, even if the number of times of display increases, an image display device that does not cause defects in color development/decolorization, uneven color development, electrode deterioration, etc. can be obtained. Furthermore, good results can be obtained in terms of response or color development efficiency. Regarding the configuration and effects of the image display device of the present invention,
This will be explained in more detail in the following examples. Example 1 SnO ₂ electrode formed on a glass substrate (resistance value 15
Ω/cm ² , size 2 mm×3 mm) were used as the display electrode and counter electrode. Next, a color developing and fading substance having the following formulation was fixed. Gamma for the OH group on the surface of the SnO ₂ electrode
Amino-propyltriethoxysilane (binder)
reacted. Next, for the NH ₂ group side of the binder,
1,1'-di(4-carboxy)benzyl-4,
The COOH group of 4'-bipyridinium dibromide was reacted in the presence of dicyclohexylcarbodiimide (hereinafter referred to as DCC). Further, after performing the above processing, a cell as shown in FIG. 2b was constructed.
This cell was filled with an aqueous solution of KBr (0.3 mol/). Then, apply a DC power supply between the display electrode and the counter electrode -2V (2sec) → OV (0.5sec) → +2V
It was driven by applying a potential cycle (2 sec), and the durability was checked by repeating coloring → memory → decoloring. The device had a cyclic durability of approximately 5 x 10 degrees. The repeated durability referred to here is an evaluation based on the number of times the process of coloring → memory → decoloring is repeated using the above-mentioned driving method, until there is no fading or uneven coloring on the electrode. . In Examples 2 to 9 below, display devices similar to those of this example were constructed, and their repeated use durability was checked in the same manner. The results are summarized in the table below. Example 2 A color-developing and fading substance was fixed on a TiO ₂ electrode having the same shape as in Example 1 according to the following formulation. That is,
Gamma glycidoxypropyltrimethoxysilane (binder) was reacted with the OH groups on the TiO ₂ surface.
Also, binder

[Formula] The base side was reacted with 1,1'-di(4-amino)benzyl-4,4'-bipyridinium dibromide in the presence of DCC. Example 3 Using a Pt electrode, beta-
(3,4-Epoxychlorohexyl)ethyltrimethoxysilane was reacted, and then the NH ₂ group of Safranin T was bonded to the cyclohexane ring side of the binder. Example 4 First, gamma-chloropropyltrimethoxysilane and 4,4'-dipyridine were reacted to form a bond between the binder and the color-developing and fading substance. Thereafter, the conjugate was immobilized on the surfaces of the same electrode and electrode substrate as in Example 1 in the presence of DCC. Example 5 The results were almost the same as in Example 1, except that the color-developing and erasing substance was not fixed on the electrode surface but on the electrode substrate. Comparative Example 1 For the same SnO ₂ electrode used in Example 1,
Cells were constructed without any treatment to fix the color-developing and fading substance. In the cell, 1,1'-dimethyl-4,4'-bipyridinium dipromide (concentration 0.1 mol/)
A color developing and decoloring medium consisting of and KBr (concentration 0.3 mol/) was enclosed. Repeated use durability was checked in the same manner as in Example 1. The results are compared with the results of Examples 1 to 5 and are shown in the table below. Comparative Example 2 Example 1 was obtained by carrying out the same procedure as Comparative Example 1 except for using 1,1'-di(4-amino)benzyl-4,4'-bipyridinium and dibromide as the color developing and fading substance. A comparison with the results of ~5 is shown in the table below. Comparative Example 3 Used when creating the image display device of Example 1
_-NH2 group and 1,1'- in the binder in the presence of DCC
A comparative image display device was prepared in exactly the same manner as in Example 1, except that the reaction of di(4-carboxy)benzyl-4,4'-bipyridinium dibromide with the -COOH group was omitted. This comparative image display device was checked for durability in repeated use in the same manner as in Example 1. The results are compared with the results of Examples 1 to 5 and are shown in the table below.

【table】

【table】 [Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram of an example of the configuration of an electrochemical coloring/decolorizing device, Fig. 2 a and b are cross-sectional views showing an example of electrode arrangement, and Fig. 3 is a signal waveform diagram showing an example of a drive signal. be. 1 is a display electrode, 2 is a counter electrode, 3 is a cell, 4 is a power source, 5 is a coloring/decolorizing medium, 6 is a substrate, 7 is a transparent substrate, 8 is a spacer, 9 is a blinding plate, 10 is a writing step, 11 is memory step, 12
is the erase step.

Claims (1)

[Claims] 1 A first electrode on which a layer of a reaction product of a silane coupling agent and an electrochemical coloring/decolorizing substance having a group in its molecule that is active toward the reactive substituent of the silane coupling agent is formed. An image display device comprising: a first substrate; an electrolyte layer; and a second electrode disposed to face the first electrode.