JP2006276850A - Display element and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display element and a display device which have high image storage properties. <P>SOLUTION: The display element and display device are each characterized in that a display electrode, a counter electrode provided opposite to the display electrode at an interval, and an electrolyte arranged between both the electrodes are provided, a display layer containing an electrochromic composition carrying an organic electrochromic compound with conductive or semiconductive particulates is formed on the surface of the display electrode on the side of the counter electrode, and a insulating or semiconductive substance stick on surfaces of the conductive or semiconductive particulates. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display element, and more particularly to an element configuration of a display using an electrochromic display element.

  Electronic paper has been actively developed as an electronic medium to replace paper. The characteristics necessary for electronic paper compared to conventional displays such as CRTs and liquid crystal displays are reflective display elements, high white reflectance and high contrast ratio, high-definition display, display In other words, it has a memory effect, can be driven at a low voltage, is thin and light, and is inexpensive. In particular, white reflectance and contrast ratio equivalent to those of paper are required as display characteristics, and it is not easy to develop a display device having these characteristics. Examples of electronic paper technologies proposed so far include a reflective liquid crystal element, an electrophoretic element, a toner electrophoretic element, and the like, all of which have a low white reflectance.

Electrochromism is a phenomenon in which a reversible color change or a reversible color change occurs when a voltage is applied. An EC display element that utilizes the coloring / decoloring of an electrochromic (hereinafter sometimes abbreviated as EC) compound that causes such a phenomenon is a reflective display element, and is capable of high white reflectance. Since it is effective and can be driven at a low voltage, it is listed as a candidate for electronic paper. Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4 report an EC element in which an organic EC compound is supported on the surface of semiconductive fine particles such as titanium oxide. It is known that this EC element can be colored and decolored very efficiently due to the surface area effect of semiconducting fine particles, and has high repeated durability. However, the memory effect when no electric field is applied is about 20 minutes, and there is a problem in image retention performance.
Special table 2001-510590 gazette JP 2002-328401 A JP 2004-151265 A Japanese Patent Application No. 2004-265054

  The present invention has been made in view of the above-described state of the art and problems, and provides a display element and a display device that have high white reflectance, a memory effect, can be driven at a low voltage, and have high image retention. provide.

The reason why an EC composition in which an organic EC compound is supported on conductive or semiconductive fine particles has a problem in image retention performance is that the charge held by the colored organic EC compound is gradually leaked through the fine particles. Is mentioned. Therefore, the organic EC compound returns to the decolored state by releasing the electric charge. Thus, as a result of intensive studies by the present inventors, it has been found that by using conductive or semiconductive fine particles having an insulating or semiconducting substance attached to the surface, charge leakage is suppressed and image holding performance is improved. The present invention has been reached.
In the present invention, it has also been confirmed that the coloring voltage and coloring efficiency are not changed by attaching an insulating or semiconducting substance to the surface of the fine particles.

That is, the present invention is as follows.
(1) A display electrode, a counter electrode provided to face the display electrode at a distance from each other, and an electrolyte disposed between the two electrodes. An organic EC compound is applied to the conductive or semiconductive fine particles. A display element having a display layer containing a supported EC composition on the surface on the counter electrode side of the display electrode, wherein an insulating or semiconducting substance is attached to the surface of the conductive or semiconductive fine particles A display element.
(2) The display element according to (1), wherein the insulating or semiconductive substance attached to the conductive or semiconductive fine particles contains a metal oxide compound.
(3) The display element according to (1) or (2), wherein the insulating or semiconducting substance attached to the conductive or semiconductive fine particles contains aluminum oxide.
(4) The display element according to any one of (1) to (3), wherein a plurality of types of organic electrochromic compounds are supported on conductive or semiconductive fine particles.
(5) The display element according to any one of (1) to (4), wherein the display layer is formed in an arbitrary pattern.
(6) The display element according to any one of (1) to (5), wherein a white reflective layer is provided between a display electrode having a display layer and a counter electrode.
(7) The display element according to any one of (1) to (6), wherein the electrolyte contains fine pigment particles.
(8) The display element according to any one of (1) to (7), wherein a drive element is formed on a surface of the display electrode or the counter electrode.
(9) A display device using the display element according to any one of (1) to (8).

The invention of claim 1 has a display layer containing an electrochromic composition in which an organic electrochromic compound is supported on conductive or semiconductive fine particles having an insulating or semiconducting substance attached to the surface, thereby providing image retention performance. A high display element can be provided.
According to the second aspect of the present invention, by using a metal oxide compound as the insulating or semiconducting substance, the surface treatment of the fine particles can be facilitated, and a display element having high image holding performance can be provided at low cost.
According to the invention of claim 3, by using aluminum oxide as the insulating or semiconducting substance, a display element with very high image holding performance can be provided at low cost.
The invention of claim 4 can provide a display element capable of increasing the display color variation and displaying black with high visibility by using a plurality of types of organic EC compounds.

The invention according to claim 5 can provide a display element capable of displaying a high-definition image quality by forming the display layer in an arbitrary pattern.
The invention of claim 6 can provide a display element having a high white reflectance by providing a white reflective layer between a display electrode having a display layer and a counter electrode.
The invention of claim 7 can provide a display element that can be driven at a low voltage by containing pigment fine particles in the electrolyte.
In the invention of claim 8, by forming the drive element, the display element can be actively driven, and can correspond to a large area and high-definition display.
The invention of claim 9 can provide a reflective display having high image holding performance.

  The present invention comprises a display electrode, a counter electrode provided opposite to the display electrode at a distance, and an electrolyte disposed between both electrodes. Display element having a display layer containing an EC composition supporting selenium on the counter electrode side surface of the display electrode, wherein an insulating or semiconducting substance is attached to the surface of the conductive or semiconductive fine particles An example of the configuration is shown in FIG. 1 and will be described below. However, the structure of the display element of the present invention is not limited to FIG.

The display electrode is preferably a glass or plastic film coated with a transparent conductive thin film such as ITO, FTO, or ZnO. In particular, if a plastic film is used, a lightweight and flexible display device can be manufactured.
As the counter electrode, glass or plastic film coated with a transparent conductive thin film such as ITO, FTO or ZnO, or coated with a conductive metal film such as zinc or platinum can be used. In the case of using a substrate coated with a transparent conductive thin film such as ITO, FTO, or ZnO, electric charges can be efficiently transferred by forming conductive particles having a large specific surface area such as tin oxide fine particles and ITO fine particles.

The display layer contains conductive or semiconductive fine particles having an insulating or semiconductive substance on the surface and an organic EC compound.
As the conductive or semiconductive fine particles, for example, fine particles having an average primary particle diameter of about 5 to 50 nm made of titanium oxide, zinc oxide, tin oxide or the like are preferable, and 5 to 20 nm is more preferable. These have conductive or semiconducting properties, and can exchange charges with the electrode and the organic EC compound. Further, since the fine particles have an average primary particle size of about 5 to 50 nm, they can have a very large specific surface area with respect to a smooth electrode surface, and charge can be transferred efficiently. Further, since a transparent film can be formed, there is a great advantage as a display element.
The average primary particle size can be measured, for example, by observation with an electron microscope.

  Examples of the insulating or semiconducting substance attached to the surface include metal oxide compounds such as aluminum oxide, silicon oxide, and zirconium oxide, and organic compounds such as polymer films. Of these, surface treatment with a metal oxide compound is actually used for the purpose of controlling the dispersibility of particles, and is useful because it can be easily adhered to the surface of conductive or semiconductive fine particles. As the surface treatment method, there is a method of attaching an alkoxide precursor of a metal oxide compound by a sol-gel method. Moreover, in the display element of the present invention, when conductive or semiconductive fine particles are bonded to the electrode surface by sintering, a strong and conductive display layer can be formed. Therefore, surface treatment with a metal oxide compound rather than an organic compound Is more effective. In addition, as a result of the study of fine particles surface-treated with various metal oxide compounds, the present inventors have shown that the display element using fine particles surface-treated with aluminum oxide or aluminum oxide / zirconium oxide has the longest image retention time. It was. It seems to be caused by the high insulating property of aluminum oxide.

There is no restriction | limiting in particular as an organic EC compound, Although it can select suitably according to the objective, For example, a viologen type compound, a styryl type compound, a phenothiazine type compound etc. are mentioned. Among these, viologen compounds are particularly preferable because they are reductive color developing and can develop many colors depending on the molecular structure.
Examples of viologen compounds include:
1-Ethyl-1 '-(2-phosphonoethyl) -4,4'-bipyridinium dichloride,
1-p-cyanophenyl-1 '-(2-phosphonoethyl) -4,4'-bipyridinium dichloride,
Bis (2-phosphonylethyl) -4,4'-bipyridinium dichloride,
1-Ethyl-1'-acetic acid -4,4'-bipyridinium dichloride
Etc.
Examples of styryl compounds include
2- [2- [4- (dimethylamino) -5-carboxy-phenyl] ethenyl] -3,3-dimethylindolino [2,1-b] oxazolidine,
2- [2- [4- (dimethylamino) -5-carboxy-phenyl] -1,3-butadienyl] -3,3-dimethylindolino [2,1-b] oxazolidine,
2- [2- [4- (dimethylamino) phenyl] -1,3-butadienyl] -3,3-dimethyl-5-sulfonylindolino [2,1-b] oxazolidine
Etc.
Examples of phenothiazine compounds include
(2-Phenothiazin-10-yl-ethyl) -phosphinic acid,
3-Phenothiazin-10-yl-propionic acid,
3-Phenothiazin-10-yl-methanesuffonic acid
Etc.

Examples of the method for supporting the organic EC compound on the conductive or semiconductive fine particles include a method in which the organic EC compound is dissolved in water, alcohol, an organic solvent or the like and the conductive or semiconductive fine particles are immersed therein. Moreover, in order to carry | support on the fine particle surface, the organic EC compound needs to have an adsorption site. As the adsorption site, an acidic structure such as phosphonic acid, carboxylic acid, sulfonic acid, and salicylic acid is good. In particular, the phosphonic acid structure is the most useful structure because of its strong adsorption ability.
The thickness of the display layer is preferably from 0.1 to 50 μm, more preferably from 1 to 15 μm.

  Another feature of the display element of the present invention is that a plurality of types of organic EC compounds are supported on conductive or semiconductive fine particles. Organic EC compounds such as viologen compounds can produce various colors depending on their molecular structure. Since the display element of the present invention can easily carry a plurality of types of compounds, for example, a dark purple (substantially black) color can be developed by simultaneously carrying a blue color developing compound and a red color developing compound. There are advantages such as an increase in color variations and the ability to display black with high visibility.

  Another feature of the display element of the present invention is that the display layer made of the EC composition is formed in an arbitrary pattern. In the display element of the present invention, even when a display layer is provided on the entire surface of a substrate with a transparent electrode, only a part of the color can be developed by applying a voltage, but since the charge is slightly diffused, the color is developed. The image may be slightly blurred. Therefore, by patterning the display layer with high definition for each pixel in advance, it is possible to prevent blurring of the image due to charge diffusion and to obtain a sharp colored image.

Another feature of the display element of the present invention is that a white reflective layer is provided. Since the display layer of the display element of the present invention causes a reversible color change between a transparent state and a colored state, when it is a reflective display element, the whiteness of the element is determined by the characteristics of the white reflective layer. If a white reflective layer in which white particles are dispersed in a resin or the like is used, the reflective layer can be easily produced, and a high white reflectance similar to that of paper can be obtained. As the white particles, particles made of a general metal oxide can be applied, and specific examples include titanium oxide, aluminum oxide, zinc oxide, silicon oxide, cesium oxide, yttrium oxide and the like. Any resin may be used as long as it is transparent. Typical examples include acrylic resins, vinyl chloride resins, polyester resins, polyamide resins, polyolefin resins, and urethane resins.
The white reflective layer can be produced, for example, by applying to the surface of the counter electrode. Although there are various coating methods, the doctor blade method or the spin coating method is particularly simple and a reflective layer having a uniform film thickness can be produced.

As another method for obtaining a high white reflectance, there is a method in which pigment fine particles are dispersed in an electrolyte. The pigment fine particles are dispersed in advance in the electrolyte and then injected into the display element. In this method, since no resin for fixing the pigment fine particles is required, the conductivity in the element is good and the element can be driven at a low voltage. As the pigment fine particles, particles made of a general metal oxide can be applied as described above, and specific examples include titanium oxide, aluminum oxide, zinc oxide, silicon oxide, cesium oxide, yttrium oxide and the like.
Examples of the electrolyte include a solution system in which lithium salts such as lithium perchlorate and lithium borofluoride are dissolved in an organic solvent such as acetonitrile and propylene carbonate, and a solid system such as a perfluorosulfonic acid polymer film. There is. Solution systems have the advantage of high ionic conductivity. The solid system is suitable for producing a highly durable element without deterioration.

  Another feature of the display element of the present invention is that active driving can be performed by providing a driving element on the surface of the display electrode or the counter electrode. Control using an active drive element is indispensable for high-definition display on an A4 size screen. In the reflective display element of the present invention, active driving can be easily performed by providing an active driving element on the surface of the counter electrode.

  The display element of the present invention is a display unit of a mobile device such as a notebook computer, PDA, or mobile phone, electronic paper such as an electronic book or electronic newspaper, a bulletin board such as a signboard, a poster, or a blackboard, a copier, a rewritable paper that replaces printer paper. It can be used for electronic calculators, electronic POPs, etc.

  FIG. 2 is a schematic view showing an example of the display device of the present invention. As shown in FIG. 2, the display device 10 includes a display element 11, a housing 12, an information input unit 13, a drive circuit, an arithmetic circuit, an internal memory, and a power source that are not shown. The electrodes in the display element 11 of FIG. 2 form a dot matrix and can display an image as a whole by displaying ON a designated dot.

Hereinafter, the present invention will be described in detail based on examples.
Example 1
As conductive or semiconducting fine particles to which an insulating or semiconducting substance adhered, titanium oxide fine particles (manufactured by Teika Co., Ltd.) having an average primary particle size of 6 nm whose surface was treated with aluminum oxide were used.
Further, 1-Ethyl-1 ′-(2-phosphonoethyl) -4,4′-bipyridinium dichloride (hereinafter abbreviated as EPBp) was used as the organic EC compound.
The display electrode was produced as follows. A 20 wt% toluene dispersion of the surface-treated titanium oxide fine particles was applied to a part (area 1 cm ² ) of a glass substrate with a tin oxide transparent electrode film on the entire surface by spin coating so as to have a thickness of about 2 μm. And sintered at 450 ° C. for 1 hour. EPBp was dissolved in water to prepare a 0.04M solution, and the display substrate was immersed in this aqueous solution to adsorb EPBp on the surface of the fine particles.
The counter electrode has a thickness of about 2 μm by spin coating on a glass substrate on which a tin oxide transparent electrode film is attached to the entire surface of a 20 wt% aqueous dispersion of tin oxide particles (Mitsubishi Materials Corporation) having an average primary particle size of 30 nm. It was produced by applying the powder and sintering at 450 ° C. for 1 hour.

  The display electrode and the counter electrode were bonded to each other through a 75 μm spacer to produce a cell. By dispersing 35 wt% of titanium oxide particles (manufactured by Ishihara Sangyo Co., Ltd.) having an average primary particle size of 300 nm in a solution of 0.2 M lithium perchlorate dissolved in propylene carbonate, an electrolyte solution is prepared and enclosed in a cell. A display element was produced.

<Evaluation>
When the white reflectance was measured without applying a voltage, it showed a high value of about 60%. In addition, this measurement was performed by irradiating diffused light using a spectrocolorimeter (CM-3730d, manufactured by Konica Minolta).
When the display electrode was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.0 V was sufficiently applied, only a portion of the display electrode having the display layer developed reddish purple. This color is attributed to the development of EPBp. When a voltage of −4.0 V was sufficiently applied, the reddish purple color disappeared and became white again.
When the display electrode was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.0 V was sufficiently applied, only a portion of the display electrode having the display layer developed reddish purple. In this state, when it was left off from the power source and left to stand, the colored state was maintained even after 2 hours.

Example 2
Example 1 except that titanium oxide fine particles having an average primary particle size of 6 nm (manufactured by Teika Co., Ltd.) whose surface was treated with zirconium oxide were used as conductive or semiconductive fine particles to which an insulating or semiconducting substance adhered. A display element having the same configuration was manufactured.
<Evaluation>
When the display electrode of the display element was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.0 V was sufficiently applied, only a portion of the display electrode having the display layer developed reddish purple. This color is attributed to the development of EPBp. Next, when a voltage of −4.0 V was sufficiently applied, the reddish purple color disappeared and became white again.
Further, when the display electrode of the display element was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.0 V was sufficiently applied, only a portion of the display electrode having the display layer was colored reddish purple. In this state, when the display element was removed from the power source and left to stand, the colored state was maintained even after 1 hour 30 minutes.

Example 3
Titanium oxide fine particles with an average primary particle size of 6 nm (manufactured by Teika Co., Ltd.) whose surfaces were treated with aluminum oxide and zirconium oxide (composition ratio 3: 1) as conductive or semiconductive fine particles with insulating or semiconducting substances attached A display element having the same configuration as that of Example 1 was produced except that (2) was used.
<Evaluation>
When the display electrode of the display element was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.0 V was sufficiently applied, only a portion of the display electrode having the display layer developed reddish purple. This color is attributed to the development of EPBp. Next, when a voltage of −4.0 V was sufficiently applied, the reddish purple color disappeared and became white again.
Further, when the display electrode of the display element was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.0 V was sufficiently applied, only a portion of the display electrode having the display layer was colored reddish purple. In this state, when the display element was removed from the power source and left to stand, the colored state was maintained even after 2 hours.

Example 4
The same constitution as in Example 1 except that EPBp and 1-p-cyanophenyl-1 ′-(2-phosphonoethyl) -4,4′-bipyridinium dichloride (hereinafter abbreviated as “CNPhPBp”) were used as organic EC compounds. A display element was produced. Here, an aqueous solution for supporting the organic EC compound was prepared by mixing a 0.04M aqueous solution of EPBp and a 0.04M aqueous solution of CNPhPBp in a ratio of 1: 1.
<Evaluation>
When the white reflectance of the manufactured display element was measured without applying a voltage, it showed a high value of about 60%.
Next, when the display electrode of the display element was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.0 V was sufficiently applied, only a portion of the display electrode having the display layer was colored black. This color is attributed to the development of both EPBp and CNPhPBp. Next, when a voltage of −4.0 V was sufficiently applied, the black color disappeared and became white again.
Further, when the display electrode of the display element was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.0 V was sufficiently applied, only a portion of the display electrode having the display layer was colored black. In this state, when the display element was removed from the power source and left to stand, the colored state was maintained even after 2 hours.

Example 5
Titanium oxide particles having an average primary particle size of 300 nm (made by Ishihara Sangyo Co., Ltd.) were used as white particles, polyethylene was used as the resin, and methylcyclohexanone was used as the solvent. 1 g of polyethylene was dissolved in 10 ml of methylcyclohexanone, and 5 g of titanium oxide was further dispersed.
The above dispersion was applied to the counter electrode produced in Example 1 by spin coating (rotation speed: 3000 rpm, rotation time: 30 seconds). The film thickness was about 5 microns and showed the same white color as paper.
A cell was fabricated by bonding the display electrode having the display layer prepared in Example 1 and the counter electrode having the white reflective layer through a 75 μm spacer. An electrolyte solution in which 0.2 M of lithium perchlorate was dissolved in propylene carbonate was prepared and sealed in the cell. Thus, a display element was produced.
<Evaluation>
When the white reflectance of the manufactured display element was measured without applying a voltage, it showed a high value of about 60%.
Next, when the display electrode of the display element was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.2 V was sufficiently applied, only a portion of the display layer of the display electrode developed reddish purple. This color is attributed to the development of EPBp. Next, when a voltage of -4.2 V was sufficiently applied, the reddish purple color disappeared and became white again.
Further, when the display electrode of the display element was connected to the negative electrode and the counter electrode was connected to the positive electrode, and a voltage of 3.2 V was sufficiently applied, only a portion of the display layer of the display electrode developed reddish purple. In this state, when the display element was removed from the power source and left to stand, the colored state was maintained even after 2 hours.

Example 6
A 20 mass% toluene dispersion of titanium oxide fine particles surface-treated with aluminum oxide, which is the same as in Example 1, was applied to a part (area 1 cm ² ) of a glass substrate having a tin oxide transparent electrode film on the entire surface thereof. Applied) to a thickness of 2 μm. At this time, it was set as the linear display layer pattern which provided the space of 10 micrometers with respect to the line of width 100 micrometers. This substrate was sintered at 450 ° C. for 1 hour and immersed in a 0.04M aqueous solution of EPBp to produce a display electrode having EPBp supported on the surface.
A display element having the same configuration as in Example 1 was produced except that the above display electrode was used.
<Evaluation>
When the display electrode of the display element was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.0 V was sufficiently applied, only the line pattern portion having the display layer of the display electrode developed reddish purple. This color is attributed to the development of EPBp. Next, when a voltage of −4.0 V was sufficiently applied, the reddish purple color disappeared and became white again.

Comparative Example 1
A display element was prepared in the same manner as in Example 1 using titanium oxide fine particles (manufactured by Teika Co., Ltd.) having an average primary particle size of 6 nm that were not subjected to surface treatment as fine particles.
When the white reflectance was measured without applying a voltage, it showed a high value of about 60%. When the display electrode was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.0 V was sufficiently applied, only the portion having the fine particle layer of the display electrode developed reddish purple as in Example 1. However, when it was removed from the power source and left in this state, the color disappeared in about 20 minutes.

It is a figure which shows the structure of the display element of this invention. It is the schematic which shows an example of the display apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Display apparatus 11 Display element 12 Housing 13 Information input means

Claims (9)

  A display electrode, a counter electrode provided to face the display electrode at a distance from each other, and an electrolyte disposed between the two electrodes, and an organic electrochromic compound supported on conductive or semiconductive fine particles In a display element having a display layer containing an electrochromic composition on the surface on the counter electrode side of the display electrode, an insulating or semiconducting substance is attached to the surface of the conductive or semiconductive fine particles, Display element.   The display element according to claim 1, wherein the insulating or semiconducting substance attached to the conductive or semiconductive fine particles contains a metal oxide compound.   The display element according to claim 1, wherein the insulating or semiconducting substance attached to the conductive or semiconducting fine particles contains aluminum oxide.   The display element according to claim 1, wherein a plurality of types of organic electrochromic compounds are supported on conductive or semiconductive fine particles.   The display element according to claim 1, wherein the display layer is formed in an arbitrary pattern.   The display element according to claim 1, wherein a white reflective layer is provided between the display electrode having the display layer and the counter electrode.   The display element according to any one of claims 1 to 6, wherein the electrolyte contains fine pigment particles.   The display element according to claim 1, wherein a drive element is formed on a surface of the display electrode or the counter electrode.   A display device using the display element according to claim 1.

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