JPH0133810B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel electrochromic display element that reversibly develops and fades color through redox reactions caused by voltage application.

Electrochromic display (below)
ECD (abbreviated as ECD) utilizes a mechanism in which an oxidation or reduction reaction occurs on a transparent display electrode by applying a voltage, forming a colored pattern, and by applying a reverse voltage, the colored pattern is erased by a reverse reaction. There is.

ECDs that generate and erase colors using this mechanism can consume about the same amount of power as liquid crystals, which have traditionally been used as light-receiving display elements, and can display vivid colors without viewing angle dependence. It is attracting attention because it has many excellent features such as being easier to view, having a memory function, a wide operating temperature range, and the ability to easily make a large screen.

Typical ECD materials that have been proposed include organic compounds such as viologen derivatives (4,4'-bipyridine derivatives) and inorganic compounds such as tungsten oxide (WO ₃ ) and molybdenum oxide (M ₀ O ₃ ). be.

Among these, viologen derivatives provide a more vivid color display than inorganic compounds, and have the advantage that various colors can be selected by selecting the derivative.

However, at present, it is difficult to use organic compounds.
ECDs have not yet reached the level of practical use due to their short repeated display life and insufficient memory life.

Here, the coloring and decoloring reaction of the viologen derivative at the electrode is thought to follow the following equation.

That is, the viologen derivative ( ) is reduced by applying a negative voltage to become a colored radical cation ( ), forms a salt with the counter ion X ^- , becomes insoluble in water, and precipitates on the electrode surface. When the voltage application is stopped in this state, the colored state is maintained as it is and exhibits a memory effect. When decoloring, applying a voltage in the opposite direction causes oxidation and returns to the state of (), resulting in a colorless, uniform solution state.

At this time, if side reactions other than the above reaction formula or () are further reduced in the oxidation-reduction reaction at the electrode and proceed to a second reduced state, the repeated display life will be adversely affected.

In addition, a major feature of ECD is that it has memory characteristics, and once it is written, it can be displayed without consuming power, but at present, if the memory state is kept for a long time, it becomes difficult to erase the color due to the reverse reaction, so it is stable. It becomes difficult to repeat colors. The reason why decoloring becomes difficult by maintaining this memory state is that the radical cation salt in (2) gradually crystallizes on the electrode surface, and the rate of oxidation reaction decreases even when a reverse voltage is applied. It is believed that this is because

This phenomenon in which decoloring becomes difficult causes colored matter to gradually accumulate without being completely decolorized when displaying and decoloring are repeated, and also causes the memory time to be long when displaying using a memory effect. As the color increases, it becomes impossible to erase the color sufficiently, which is a very unfavorable result for ECD.

In this way, the color-changing and fading materials used in ECD include:
Becoming insoluble and depositing on the electrode surface when coloring,
There are many restrictions on material selection, as it is required to satisfy many factors, such as not causing side reactions during color development and fading, and not causing crystallization in the memory state.

Furthermore, the response speed for color development upon voltage application is currently several hundred milliseconds, and even faster response is required. The reason why the response speed is not so fast is that in order for the coloring/eliminating material that exists as a solution to develop color on the electrode surface when voltage is applied, the coloring/eliminating material with a relatively large molecular weight (for example, viologen derivatives) must diffuse. This is thought to be due to a reaction mechanism that is rate-limited by diffusion, in which it is necessary to reach the electrode surface. Therefore, in order to achieve high-speed response, it is desired to develop an EC display element with a mechanism different from the conventional mechanism.

The present invention realizes high-speed response through a coloring mechanism different from conventional ones by forming a polymer electrochromic material having a functional group in the main chain of the polymer on the display electrode in the form of a film. In addition, the present invention provides an ECD element that has a long repeated display life and stable memory performance.

The ECD element according to the present invention is one in which a polymer EC material represented by the following general formula is formed in the form of a film on a transparent display electrode.

Here, R represents a C ₁ to C ₁₀ alkylene group, a phenylene group such as phenylene, tolylene, diphenylene, or diphenylenemethane, and X represents a viologen, tetrathiofulvalene, leuco dye, which develops and disappears when voltage is applied. Indicates functional groups such as thionine, phthalocyanine, and porphyrin. n is a positive integer indicating the degree of polymerization.

These polymeric EC materials are obtained by the condensation reaction of diols or diamines with color-producing and fading functional groups and dicarboxylic acids or diisocyanates, and the synthesis route will be shown using viologen as an example.

The polymer EC material thus obtained is dissolved in a solvent selected from dimethylformamide, dimethylacetamide, dimethyl sulfoxide, methanol, methyl ethyl ketone, etc., and coated on a transparent display electrode using a spinner method, screen printing method, doctor blade method, etc. The ECD device shown in the drawing was constructed by forming a film.

In the figure, 1 is a substrate, 2 is a display electrode, 3 is a counter electrode, 4 is a spacer, 5 is an electrolyte solution, 6 is a white background, and 7 is a polymer EC film.

Here, the material of the transparent display electrode 2 is SnO ₂ ,
In ₂ O ₃ , a metal thin film, etc. are used, and the material of the counter electrode 3 is gold platinum, carbon, etc.
As the material for the white background 6, porous ceramic or porous white plastic is used. Electrolyte material 5 includes LiCl, Kcl, NaCl, KBr, K ₂ SO ₄ ,
Salts or complexes such as Fe, Co, Cr, Mn, Ni, Cu, etc. are added to a solution in which a supporting electrolyte such as KClO ₄ , KBF ₄ , K ₃ PO ₄ , KOAc, etc. is dissolved at a concentration of ¹ ×10 -5 to 1 mol/. It is used in addition. Adjusted like this
When a voltage is applied to the ECD element with the display electrode side negative and the counter electrode, a current indicating that a reduction reaction is occurring on the display electrode is observed, and at the same time, the polymer EC film on the display electrode is colored. The reaction rate was several times faster than that of conventional solution-type ECD devices. Furthermore, the color was immediately erased by applying a voltage in the opposite direction.

The reaction mechanism here is that electrons injected from the display electrode side move through the polymer EC membrane and reduce the color-forming groups to produce color, while at the same time the opposite electrode absorbs Fe in the electrolyte solution.
It is thought that salts or complexes such as The feature that differs from conventional solution-type ECD devices is that the reaction rate was conventionally slow because it was limited by the diffusion rate of the coloring material with a relatively large molecular weight, whereas the device of the present invention has a fast membrane. One example is that high-speed response can be obtained because the rate is determined by the movement of charges inside. Furthermore, since the color-forming group is formed in the form of a film on the display electrode, it has stable memory performance, and there is no need to utilize differences in solubility during color development and decolorization, and any color-forming and decolorizing group can be selected. , and the reaction at the counter electrode is carried out with metal ions such as iron in the electrolyte solution, which is characterized by the ability to prevent deterioration of the color-developing and fading groups.

The polymer EC film material used here has film formability,
Adhesive strength with the electrode surface, transparency, hydrophilicity for good contact with electrolyte components, moderate interaction of EC color forming groups in the polymer chain to achieve high-speed response, etc. However, the selection of polyester derivatives, polyurethane derivatives, and polyamide derivatives can be made depending on the target performance.

As described above, in the ECD device using the polymer EC film according to the present invention, compared to the conventional solution type,
The different reaction mechanisms at the electrodes enable high-speed response, and because the color-developing and color-developing groups are fixed on the display electrodes, stable memory performance can be obtained. It has many advantages, such as being able to select one another and extending the life of repeated display because no reaction takes place at the counter electrode.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited thereto.

Example 1 Viologen diol was synthesized from 4,4'-bipyridine and 4-bromo-1-butanol, and polyester was synthesized by interfacial polycondensation of this with isophthalic acid chloride. This was dissolved in dimethylformamide and converted to SnO ₂ using the doctor blade method.
A 3μ film was formed on the transparent electrode. As an electrolyte solution, 0.05 mol/K ₂ SO ₄ and 0.05 mol/FeCl ₂ were used.
An ECD cell was constructed using an aqueous solution containing .
Note that gold paste was used as the counter electrode, and a porous ceramic plate was used as the white background material. this
When we investigated the response speed of color development by applying a pulse voltage between the display electrode side of the ECD element as a negative electrode and the counter electrode, we found that it was 2 msec, compared to 150 msec in the conventional solution type using heptyl viologen. Reflection D density reached 0.8. The color was erased in 2 msec by applying a pulse voltage in the opposite direction. A life of more than 3 months was obtained by repeatedly displaying a coloring pulse width of 5 msec and a decoloring pulse width of 5 msec. Furthermore, 5m
A life of more than 3 months was obtained by repeatedly displaying the memory state by applying a sec pulse voltage, holding it in the memory state for 1 minute, and then adding a 5 msec erasing pulse.

Example 2 Viologen diol synthesized in Example 1 and 2,
Polyurethane was synthesized from 4-tolylene diisocyanate and used to perform ECD in the same manner as in Example 1.
The element was constructed. When the response speed was examined by applying a pulse voltage between the display electrode and the counter electrode with the display electrode as negative, the reflection D density reached 0.8 in 2 msec. The decoloring response speed due to voltage application in the opposite direction was 3 msec. Coloring pulse width 5msec, decoloring pulse width 5m
A life of more than 3 months was obtained by repeatedly displaying sec.
Furthermore, after applying a coloring pulse voltage of 5 msec, maintaining the memory state for 1 minute, and then applying a decoloring pulse of 5 msec for repeated display, a life of more than 3 months was obtained.

Example 3 Polyamide was synthesized from viologen diamine hydrochloride synthesized from 4,4'-bipyridine and 4-bromo-1-butylamine hydrochloride and adipic acid chloride, and using this polyamide was synthesized in the same manner as in Example 1. E.C.D.
The element was constructed. When the response speed was examined by applying a pulse voltage between the display electrode and the counter electrode with the display electrode as negative, the reflection D density reached 0.8 in 2 msec. The decoloring response speed due to voltage application in the opposite direction was 2 msec. Coloring pulse width 5msec, decoloring pulse width 5m
A life of more than 3 months was obtained by repeatedly displaying sec.
Furthermore, after applying a coloring pulse voltage of 5 msec, maintaining the memory state for 1 minute, and then applying a decoloring pulse of 5 msec for repeated display, a life of more than 3 months was obtained.

[Brief explanation of drawings]

The figure is an example of an ECD element according to the present invention,
In the figure, 1 is a substrate glass, 2 is a display electrode, 3 is a counter electrode, 4 is a spacer, 5 is an electrolyte solution, and 6
7 shows the white background material, and 7 shows the polymer EC film.

Claims (1)

[Claims] 1. In an electrochromic display that utilizes a coloring and fading reaction caused by the application of a voltage, a polymer electrochromic material having a functional group that develops and fades color in the main chain of the polymer is coated in advance on a display electrode. An electrochromic display element characterized in that it is formed into a shape. 2. The electrochromic device according to claim 1, characterized in that a polyester derivative represented by the following general formula is used as the polymer electrochromic material having a functional group that develops and fades color in the main chain of the polymer. Display element. (However, R indicates an alkylene group or a phenylene group, and X indicates a functional group that develops and discolors upon application of voltage. n is a positive integer and indicates the degree of polymerization.) 3. The functional group that develops and discolors is the main group of the polymer. 2. The electrochromic display element according to claim 1, wherein a polyurethane derivative represented by the following general formula is used as the polymer electrochromic material in the chain. (However, R represents an alkylene group or a phenylene group, and X represents a functional group that develops and fades color upon application of voltage. n is a positive integer indicating the degree of polymerization.) 4. The functional group that develops and fades color is the main group of the polymer. 2. The electrochromic display element according to claim 1, wherein a polyamide derivative represented by the following general formula is used as the polymer electrochromic material in the chain. (However, R represents an alkylene group or a phenylene group, and X represents a functional group that develops and fades color upon application of voltage. n is a positive integer and represents the degree of polymerization.)