JP4700385B2 - Electrochromic display element - Google Patents

Description

  The present invention relates to a display element, and more particularly to an element configuration of a display using an electrochromic display element, and is applied to a reflective display and electronic paper.

  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 element utilizing the coloring / decoloring of an electrochromic (hereinafter sometimes abbreviated as EC) compound that causes such a phenomenon is a reflective display element, and has a high white reflectance, and a memory effect. And because it can be driven at a low voltage, it is listed as a candidate for electronic paper.

  Patent Literature 1 (Japanese Patent Publication No. 2000-506629), Patent Literature 2 (Japanese Patent Publication No. 2001-510590), Patent Literature 3 (Japanese Patent Publication No. 2003-511837), Patent Literature 4 (Japanese Patent Laid-Open No. 2002-328401) ), Patent Document 5 (Japanese Patent Publication No. 2004-537743), and Patent Document 6 (Japanese Patent Application No. 2004-265054) describe an EC element in which an organic EC compound is supported on the surface of semiconductor fine particles such as titanium oxide. is doing. It is known that this EC element can be efficiently colored and decolored by the surface area effect of semiconductor fine particles and has high repeated durability. However, these EC elements also require a large amount of charge compared to liquid crystal elements and electrophoretic elements, and there is a problem in power consumption.

JP 2000-506629 A Special table 2001-510590 gazette Japanese translation of PCT publication No. 2003-511837 JP 2002-328401 A Special table 2004-537743 gazette Japanese Patent Application No. 2004-265054

The present invention has been made in view of the above-described state of the art and problems, can display a high white reflectance and a high contrast ratio, can be driven at a low voltage, and can be developed with low power consumption. An object is to provide a reflective display element.

  As a result of various studies to solve the above problems, the present inventors have found that a display electrode made of a substrate with a transparent conductive film and a counter electrode made of a substrate with a conductive film are spaced from each other with the conductive film side facing each other. In the reflective display element in which the display layer including the electrochromic composition is disposed on the transparent conductive film of the display electrode, the above problem is achieved by adding a nanostructure to the display layer and further into the electrolyte. Has found that can be solved.

  The EC display element is composed of a display electrode in which the EC composition undergoes a color change due to oxidation or reduction reaction, a counter electrode that causes an oxidation-reduction reaction opposite to the display electrode, and an electrolyte that performs charge transfer between the display electrode and the counter electrode. . Among these, as an electrolyte for a general EC display element, a solution in which an ionic substance such as lithium perchlorate or lithium borofluoride is dissolved in an organic solvent such as acetonitrile or propylene carbonate is used. Thus, as a result of intensive studies by the present inventors on electrolytes, it has been found that the response can be accelerated by up to about 20% by adding nanostructures from 0.01 wt% to 10 wt% in these electrolytes. This phenomenon is attributed to the fact that the ionic substances are regularly arranged by agglomerating around the nanostructure, and the charge mobility of the electrolyte is increased due to electron hopping.

Therefore, the display element of the present invention is characterized in that (1) two conductive substrates, at least one of which is made of a transparent conductive substrate, are arranged with an interval between the conductive surfaces facing each other, and at least an oxidation reaction or an inside of the substrate It includes an electrochromic composition that develops and decolors by a reduction reaction, an electrolyte , and a nanostructure that is one of metal nanoparticles, metal oxide nanoparticles, and carbon nanostructures is added to the electrolyte. .

Furthermore above problems, the present invention (2), the display according to the first (1), characterized in that the electrochromic composition is a material carrying an organic electrochromic compound conductive or semi-conductive fine particles This is solved by an element and ( 3 ) a display device using the display element according to the item (1) or (2) .

As will be understood from the following detailed and specific description, according to the present invention, it is possible to display a high white reflectance and a high contrast ratio, to be driven at a low voltage, and to be capable of high-speed response. An extremely excellent effect of providing a type display element is exhibited.
More specifically, according to the present invention, two conductive substrates, at least one of which is made of a transparent conductive substrate, are disposed at a distance from each other with their conductive surfaces facing each other, and at least an oxidation reaction or reduction is performed inside the substrate. It contains an EC composition that develops and decolors upon reaction, and an electrolyte. By adding a nanostructure to the electrolyte, it can display a high white reflectance and a high contrast ratio, and can be driven at a low voltage. According to the present invention as set forth in the item ( 1 ), two conductive substrates, at least one of which is made of a transparent conductive substrate, are arranged with their conductive surfaces facing each other and spaced apart from each other. And an EC composition and an electrolyte that develop and discolor at least by an oxidation reaction or a reduction reaction inside the substrate, and a commercially available nanostructure is added to the electrolyte. Allows you to view the high white reflectance and high contrast ratio, and can be driven at a low voltage, is further provided high-speed response display device is low cost, according to the present invention of the first (2) above, wherein, at least one Including an EC composition, an electrolyte, wherein two conductive substrates each made of a transparent conductive substrate are disposed with a gap between the conductive surfaces facing each other, and the substrate is colored and decolored by at least an oxidation reaction or a reduction reaction inside the substrate, Furthermore, by adding a nanostructure in the electrolyte, and the EC composition is a material in which an organic EC compound is supported on conductive or semiconductive fine particles, a high white reflectance and a high contrast ratio can be displayed, and can be driven at a low voltage, there is provided a display device further high-speed response, according to the present invention of the first (3) above, wherein, you can display a high white reflectance and high contrast ratio And can be driven at a low voltage, excellent effect is exerted that the reflection type display displays showing yet high-speed response is provided.

Hereinafter, an example of a structure of a display element of the present invention and an example of a manufacturing method will be described in detail, and FIG. 1 illustrates an example of an element structure. However, the present invention is not limited to these examples.
In the present invention, the nanostructure added to the display layer is an element in which the size of nanosize is important, and the presence or absence of conductivity is not particularly limited. As for the size, the particle size or minor axis length is desirably 500 nm or less, and more desirably 30 nm or less. Examples of the type of nanostructure include metal nanoparticles, metal oxide nanoparticles, and carbon nanostructures. These are already commercially available and can be obtained at low cost. The metal nanoparticles may be any metal nanoparticle such as gold, silver, copper, nickel, or an alloy of a plurality of metals. Examples of the metal oxide nanoparticles include titanium oxide, tungsten oxide, molybdenum oxide, iridium oxide, zinc oxide, silicon oxide, aluminum oxide, and zirconium oxide. These metal oxides may also be composites. Furthermore, the metal nanoparticles and metal oxide nanoparticles do not necessarily have to be spherical, and may have a tube shape or a wire shape.

  The carbon nanostructure mainly includes fullerene, fullerene derivatives, carbon nanotubes, carbon nanohorns, carbon nanowires, and the like.

  As the EC composition in the display device of the present invention, any of an inorganic EC compound and an organic EC compound may be used. Conductive polymers can also be used because they exhibit electrochromism. Examples of the inorganic EC compound include tungsten oxide, molybdenum oxide, iridium oxide, and titanium oxide. Examples of the organic EC compound include viologen, rare earth phthalocyanine, and styryl. Examples of the conductive polymer include polypyrrole, polythiophene, and polyaniline.

  Further, as the EC composition in the display element of the present invention, it is particularly desirable to use a structure in which an organic EC compound is supported on conductive or semiconductive fine particles. Specifically, it has a structure in which ultrafine particles having a particle size of about 5 nm to 50 nm are sintered on the electrode surface and an organic EC compound having a polar group such as a hydroxyl group or a carboxyl group is adsorbed on the surface of the ultrafine particles. In this structure, electrons are efficiently injected into the organic EC compound by utilizing the large surface effect of the ultrafine particles, so that it responds faster than the conventional EC display element. Furthermore, since a transparent film can be formed as a display layer by using ultrafine particles, a high white reflectance can be obtained. Also, a plurality of types of organic EC compounds can be 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.

  As the conductive or semiconductive fine particles, titanium oxide, zinc oxide, tin oxide and the like are desirable. These materials have conductivity and semiconducting properties, and can exchange charges with the electrode and the organic EC compound.

  Examples of the organic EC compound include a viologen compound, a styryl compound, a phenothiazine compound, and the like, but it is desirable to use a viologen compound because it has a reduction coloring property and can develop many colors depending on a molecular structure. Adsorption sites include phosphonic acid (phosphonyl group), carboxylic acid (carboxyl group), sulfonic acid (sulfonyl group), salicylic acid (salicyl group) and other acidic structures, especially phosphonic acid structure has strong adsorption ability. Useful structure.

  The transparent conductive substrate 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 substrate, a glass or plastic film coated with a transparent conductive thin film such as NESA, ITO, FTO, or ZnO or a conductive metal film such as zinc or platinum is used. When a substrate coated with a transparent conductive thin film such as NESA, ITO, FTO, or ZnO is used, charge can be efficiently transferred by forming conductive particles having a large specific surface area such as tin oxide fine particles and ITO fine particles.

In order to produce a reflective display device using the display element of the present invention, a white reflective layer is formed on the counter substrate as a white reflective portion.
For the white reflective layer, the simplest production method is to disperse white pigment particles in a resin and apply it on a counter substrate. As the white pigment fine 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.

  As a method for driving the display device of the present invention, any method may be used as long as an arbitrary voltage and current can be applied. If a passive driving method is used, an inexpensive display device can be manufactured. Further, if the active driving method is used, high-definition and high-speed display can be performed. In the reflective display element of the present invention, active driving can be easily performed by providing an active driving element on a counter substrate.

Hereinafter, the present invention will be described specifically by way of examples.
[Example 1]
As conductive or semiconductive fine particles, titanium oxide fine particles (manufactured by Taika Co., Ltd.) having a primary particle size of 6 nm were used. Further, 1-Ethyl-1 ′-(2-phosphoethyl) -4,4′-bipyridinium dichloride (hereinafter abbreviated as EC1) was used as the organic EC compound. EC1 is known and can be prepared by known methods described in Solar Energy Materials and Sollar Cells, 57, (1999), 107-125.

[Production of display substrate]
The display substrate was produced as follows. Add 20 wt% of polyethylene glycol # 20000 to a 15 wt% aqueous dispersion of titanium oxide fine particles to a part (area 1 cm ² ) of a glass substrate with a tin oxide transparent electrode film on the entire surface, and add titanium oxide paste. Prepared. This titanium oxide paste was applied by spin coating so as to have a thickness of about 2 μm, and this display substrate was sintered at 450 ° C. for 1 hour.
EC1 was dissolved in water to prepare a 0.04M solution, and the display substrate was immersed in this aqueous solution for 24 hours to adsorb EC1 on the surface of the titanium oxide fine particles.

[Production of counter substrate]
The counter substrate is formed by applying a 20 wt% aqueous dispersion of tin oxide particles with a primary particle size of 30 nm (manufactured by Mitsubishi Materials Corporation) to a glass substrate with a tin oxide transparent electrode film on the entire surface thereof to a thickness of about 2 μm by spin coating. And sintered at 450 ° C. for 1 hour.
5 g of titanium oxide having a particle size of 0.3 microns (Taika Corporation, JR-301) and 1 g of polyethylene were dispersed in 10 ml of methylcyclohexanone.
The dispersion was applied to the counter substrate by a spin coating method to form a white reflective layer.

[Production of display element]
The display substrate and the counter substrate were bonded to each other through a 75 μm spacer to produce a cell.
An electrolyte was prepared by further dispersing 1 wt% of gold nanoparticles having a particle diameter of 3 nm in a solution of 0.2 M perchloric acid chloride dissolved in propylene carbonate. A display element was fabricated by enclosing the electrolyte in a cell.

[Example 2]
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.

[Example 3]
When the display substrate was connected to the negative electrode, the counter substrate was connected to the positive electrode, and a voltage of 3.0 V was applied, the color developed reddish purple in about 80 ms. When a voltage of -1.0 V was applied, the red purple color disappeared and became white again in 300 ms.

[Comparative Example 1]
A display element similar to that of Example 1 was produced except that the gold nanoparticles were not dispersed in the electrolyte. When the same measurement as in Example 3 was performed, it took about 100 ms for color development, and the display element in which gold nanoparticles were dispersed showed a faster response. In addition, it took about 350 ms to erase the color, and the display element in which the gold nanoparticles were dispersed showed faster response.

[Example 4]
A display element similar to that of Example 1 was produced except that 1 mol% of zinc oxide nanoparticles having a particle size of 10 nm were dispersed in the electrolyte instead of gold nanoparticles. When the same measurement as in Example 3 was performed, the time required for color development was about 90 ms, and a high-speed response was shown compared to a display element that was not dispersed.

[Example 5]
A display element similar to that of Example 1 was produced except that 1 wt% of fullerene was dispersed in the electrolyte instead of gold nanoparticles. When the same measurement as in Example 3 was performed, the time required for color development was about 80 ms, and a high-speed response was shown compared to a display element that was not dispersed.

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

Claims (3)

An electrochromic composition and electrolyte in which two conductive substrates at least one of which is made of a transparent conductive substrate are arranged with a space between the conductive surfaces facing each other and are colored and decolored by at least an oxidation reaction or a reduction reaction inside the substrate And a nanostructure which is any one of metal nanoparticles, metal oxide nanoparticles, and carbon nanostructures is added to the electrolyte. The display element according to claim 1, wherein the electrochromic composition is a material in which an organic electrochromic compound is supported on conductive or semiconductive fine particles. Display device characterized by using a display device according to claim 1 or 2.

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