JP2006267828A - Electrochromic display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection type display element which can perform display with high white reflectivity and a high contrast ratio, can be driven with a low voltage at a high speed, and can be manufactured at a low cost. <P>SOLUTION: Disclosed is the display element characterized in that two conductive substrates at least one of which is made of a transparent conductive substrate are arranged at an interval having conductive surface sides opposite each other, at least an electrochromic composition which colors and decolorizes by an oxidizing reaction or reducing reaction and an electrolyte are included inside the substrates, and a nanostructure is added in the electrolyte. <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, 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), an EC element in which an organic EC compound is supported on the surface of a metal oxide such as titanium oxide. Reporting. It is known that this EC element can be developed and discolored very efficiently due to the surface area effect of the metal oxide and has high repeated durability. In order to obtain a high white reflectance in the EC element, it is necessary to provide a white reflective layer. So far, the white reflective layer has been generally prepared by a method of forming a film containing white pigment particles on the counter electrode or dispersing the white pigment particles in the electrolyte. However, in order to form a film containing white pigment particles on the counter electrode, it is necessary to disperse the white pigment particles in a binder, which increases material costs and work costs. Even when the white pigment particles are dispersed in the electrolyte, it is difficult to adjust the dispersion conditions, and particularly when a solid electrolyte is used, the operation becomes difficult, leading to an increase in cost.

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, can be driven at a high speed, and can be manufactured at a low cost. 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 a reflective display element in which an electrochromic composition is disposed and provided on a transparent conductive film of the display electrode, an organic electrochromic compound is supported on conductive or semiconductive fine particles and used. The present inventors have found that the above-mentioned problems can be solved by using white pigment particles having a primary particle size larger than the conductive or semiconductive fine particles in the display layer.

  Therefore, the reflective display element of the present invention has the following features: (1) 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 arranged with a distance from each other with the conductive film side facing each other. Alternatively, a display layer containing an EC composition in which an organic EC compound is supported on semiconductive fine particles and white pigment particles having a primary particle size larger than that of the conductive or semiconductive fine particles is provided on the transparent conductive film of the display electrode. Is a reflective display element.

  In addition, the above-mentioned problem is (2) of the present invention, the primary particle size of the conductive or semiconductive fine particles supporting the organic electrochromic compound is 50 nm or less, or the minor axis length is 50 nm or less, and the white pigment particles This is solved by the reflective display element described in the item (1), wherein the primary particle size of the liquid crystal is 200 nm or more.

  Further, the above-mentioned problem is that (3) of the present invention, a layer containing conductive or semiconductive fine particles and white pigment particles is formed on the transparent conductive film of the display electrode in the first step, and the organic layer is formed in the second step. A method of forming a display layer by immersing a display electrode in a solution containing an electrochromic compound, wherein the display layer is the reflective display element according to the item (1) or (2). This is solved by a method for forming a display layer, which is a display layer. Further, the above object is to use the reflective display element according to (4), the item (1) or the item (2), or the method for producing a display layer according to the item (3). This is solved by a display device characterized by the fact that

As will be understood from the following detailed and specific description, according to the present invention, high white reflectance and high contrast ratio can be displayed, low voltage driving and high speed driving can be performed, and manufacturing can be performed at low cost. A reflective display element is provided.
That is, according to the present invention described in the items (1) and (2), an electrochromic composition in which an organic electrochromic compound is supported on conductive or semiconductive fine particles and a size larger than the conductive or semiconductive fine particles. By having a display layer containing white pigment particles with a primary particle size, high white reflectance and high contrast ratio can be displayed, low voltage drive and high speed drive can be made, and a reflective display that can be manufactured at low cost. According to the present invention described in the above item (3), a layer containing conductive or semiconductive fine particles and white pigment particles is formed on the transparent conductive film of the display electrode in the first step. A reflective display element that can be manufactured at low cost by forming a display layer in a method of immersing the display electrode in a solution containing an organic electrochromic compound in the second step According to the present invention described in item (4), an electrochromic composition in which an organic electrochromic compound is supported on conductive or semiconductive fine particles and a primary particle size larger than that of the conductive or semiconductive fine particles. By providing a display layer containing white pigment particles, a reflective display that can display high white reflectance and high contrast ratio, can be driven at low voltage and high speed, and can be manufactured at low cost is provided. An extremely excellent effect is exhibited.

Hereinafter, an example of the structure of the display element of the present invention will be described in detail with reference to FIG. However, the structure of the display element of the present invention is not limited to FIG.
The display layer is composed of conductive or semiconductive fine particles carrying an organic EC (electrochromic) compound and white pigment particles having a primary particle size larger than that of the conductive or semiconductive fine particles. Here, the conductive or semiconducting fine particles carrying the organic EC compound exist as display portions that develop and decolor by transferring charges from the electrodes. On the other hand, the white pigment particle exists as a white reflection part for scattering and reflecting external light. The reflective display element of the present invention reduces the material cost by including the display part and the white reflection part in the same layer.

  As the means for producing the display layer in the reflective display element of the present invention, a layer containing conductive or semiconductive fine particles and white pigment particles is formed on the transparent conductive film of the display electrode in the first step, The method of immersing the display electrode in a solution containing an organic EC compound in the process is the simplest, and since the display part and the white reflection part are completed in two processes, it can be manufactured at low cost. Here, since two types of particles of conductive or semiconductive fine particles and white pigment particles are mixed in the display layer, it is considered that the organic EC compound is also adsorbed to the white pigment particles. However, as a result of intensive studies by the present inventors, if the particle diameter of the conductive or semiconductive fine particles is about one digit smaller than that of the white pigment particles, the specific surface area becomes about one digit larger. It turned out that it became adsorbed only to fine particles. Therefore, the display part and the white reflection part can be easily manufactured by the above-described manufacturing method.

A configuration example of the reflective display element of the present invention will be described below.
The conductive or semiconductive fine particles are preferably fine particles having a particle diameter of about 5 nm to 50 nm made of titanium oxide, zinc oxide, tin oxide or the like. These materials have conductivity and semiconducting properties, and can exchange charges with the electrode and the organic EC compound. Further, fine particles having a particle diameter of about 5 nm to 50 nm can have a very large specific surface area with respect to a smooth electrode surface, and can efficiently transfer and receive charges.

  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. Moreover, in order to carry | support on the microparticle surface, it is necessary to have an adsorption site. 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 reflective display element of the present invention can also carry a plurality of types of organic EC compounds 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 white pigment 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. It is known that if the primary grain is 200 nm or more, the external light is favorably scattered in white and can be used as a white reflection part.

  Examples of the substrate include glass or plastic film. In particular, if a plastic film is used, a lightweight and flexible display device can be manufactured. Any general-purpose material such as ITO, FTO, or ZnO can be used as the transparent electrode.

  As a driving method of the reflective display element 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 the counter electrode.

  When the image of the display layer having the above structure was evaluated, it was found that the white reflection was almost the same as that of the medium having the white reflection layer on the counter electrode and the medium in which the white pigment particles were dispersed in the electrolyte. High contrast ratio.

Hereinafter, the present invention will be described specifically by way of examples.
[Example 1]
As the conductive or semiconductive fine particles, a 15 wt% aqueous dispersion of titanium oxide fine particles having a primary particle diameter of 18 nm (HPW-18NR, manufactured by Catalyst Kasei Kogyo Co., Ltd.) was used. As the white pigment fine particles, a 15 wt% aqueous dispersion of titanium oxide fine particles having a primary particle diameter of 400 nm (HPW-400C manufactured by Catalyst Chemical Industry Co., Ltd.) was used. These were prepared according to the following formulation to obtain a titanium oxide paste.
HPW-18NR 10g
HPW-400C 1.8g
1 ml of ethanol
Concentrated nitric acid 0.5ml
Polyethylene glycol 0.5g

In addition, 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.
[Preparation of display electrode]
The display electrode was produced as follows. The titanium oxide paste 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. . EC1 was dissolved in water to prepare a 0.04M solution, and the display electrode was immersed in this aqueous solution to adsorb EC1.

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 (manufactured by Mitsubishi Materials Corporation) having a 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. An electrolyte solution in which 0.2 M of perchloric acid chloride was dissolved in propylene carbonate was prepared and sealed in a cell to produce a display element.

[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 electrode was connected to the negative electrode, the counter electrode was connected to the positive electrode, and a voltage of 3.0 V was applied for 1 second, only the portion having the fine particle layer of the display electrode developed reddish purple. This color is due to the development of EC1. When a voltage of −1.0 V was applied for 1 second, the reddish purple color disappeared and became white again.

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

Claims (4)

  An electrochromic in which 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 arranged facing each other with the conductive film side facing each other, and conductive or semiconductive fine particles carry an organic electrochromic compound A reflective display element comprising a display layer containing a composition and white pigment particles having a primary particle size larger than that of the conductive or semiconductive fine particles on the transparent conductive film of the display electrode.   The primary particle size of the conductive or semiconductive fine particles supporting the organic electrochromic compound is 50 nm or less, or the minor axis length is 50 nm or less, and the primary particle size of the white pigment particles is 200 nm or more. The reflective display element according to claim 1.   A layer containing conductive or semiconductive fine particles and white pigment particles is formed on the transparent conductive film of the display electrode in the first step, and the display electrode is immersed in a solution containing the organic electrochromic compound in the second step. A method for forming a display layer, wherein the display layer is a display layer in the reflective display element according to claim 1. A display device using the reflective display element according to claim 1 or the method for producing a display layer according to claim 3.

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