JP4700386B2 - Display element and manufacturing method thereof - 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 a semiconductor particle such as titanium oxide. is doing. 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. 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 driven at a low power consumption. It is another object of the present invention to provide a method for manufacturing a reflective display element that can generate color with low power consumption.

  As a result of various studies to solve the above problems, the present inventors have a display layer containing an electrochromic composition in which an organic electrochromic compound is supported on conductive or semiconductive fine particles on a transparent conductive substrate. In an electrochromic display element, at least a transparent conductive substrate is coated with a film containing conductive or semiconductive fine particles, and then a display layer created by a manufacturing method including a step of pressing and pressing is used for the electrochromic display element. Thus, it was found that the above problems can be solved.

  Conventionally developed EC display elements include an element in which an inorganic EC compound is formed by vapor deposition, an element in which an organic EC compound is dissolved in an electrolytic solution, and an element in which a polymer EC compound is applied. Compared with these EC display elements, an EC display element in which a display layer containing conductive or semiconductive fine particles carrying an organic EC compound is formed on a transparent conductive substrate can develop color with a small amount of charge. This is because charges from the substrate electrode can be injected into the organic EC compound very efficiently through the surface of conductive or semiconductive fine particles having a large specific surface area. Based on this principle, if the specific surface area is increased by increasing the number of conductive or semiconducting fine particles per unit area, the color development efficiency (color density per applied charge amount) can be expected to be improved. Here, the simplest method for increasing the number of conductive or semiconductive fine particles per unit area is to increase the thickness of the conductive or semiconductive fine particle layer.

However, it has been found that when the thickness of the conductive or semiconductive fine particle layer is greater than 15 μm, the durability is remarkably deteriorated, for example, cracks are generated. Further, it has been found that the thicker the conductive or semiconductive fine particle layer is, the worse the transparency of the layer is, so that the display performance such as white reflectance and contrast ratio is adversely affected.
Therefore, as a result of intensive studies by the present inventors, the number of conductive or semiconductive fine particles per unit area can be increased without being deteriorated by press-pressing and compressing the conductive or semiconductive fine particle layer. Was found to be possible.

Therefore, the display layer manufacturing method of the present invention is characterized by (1) an electrochromic display having a display layer containing an electrochromic composition in which an organic electrochromic compound is supported on conductive or semiconductive fine particles on a transparent conductive substrate. in the display layer manufacturing method for the device, the method comprising, after applying the least transparent conductive substrate containing a conductive or semi-conductive fine particles on the membrane, in that those comprising a step of pressure pressing the membrane.

  The above-mentioned problem is solved by (2) of the present invention, and the method for producing a display layer according to the above-mentioned item (1), wherein the pressure press treatment is 200 kgf / cm 2 to 10000 kgf / cm 2. .

  Furthermore, the above-mentioned problem is an electrochromic in which an organic electrochromic compound is supported on conductive or semiconductive fine particles produced by using the method described in (3), (1) or (2) of the present invention. The display element comprising the composition has a film thickness of 15 μm or less, and (4) the method for producing a display layer according to (1) or (2), or This is solved by a display device using the display element according to the item (3).

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 drive at a low voltage, and to drive at a low power consumption. In addition, an extremely excellent effect is provided that a method for manufacturing a reflective display element capable of developing color with low power consumption is provided.
More specifically, according to the present invention described in the above items (1) and (2), an electrochromic composition in which an organic electrochromic compound is supported on conductive or semiconductive fine particles on a transparent conductive substrate. In a display layer manufacturing method of an electrochromic display element having a display layer containing, a display including a step of applying a pressure press treatment to a film after coating a film containing conductive or semiconductive fine particles on at least a transparent conductive substrate By using the layer manufacturing method, there is provided a display element capable of displaying a high white reflectance and a high contrast ratio, capable of being driven at a low voltage and a high speed, and driven at a low power consumption. According to the described invention, a display layer comprising an electrochromic composition in which an organic electrochromic compound is supported on conductive or semiconductive fine particles Since the film thickness is 15 μm or less, a high white reflectance / high contrast ratio can be displayed, low voltage driving and high speed driving can be performed, and further low power consumption driving can be provided. According to the present invention described in item (4), a reflective display display that can display a high white reflectance and a high contrast ratio, can be driven at a low voltage and a high speed, and can be driven with low power consumption. An extremely excellent effect is provided.

Hereinafter, an example of a structure of a display element and an example of a manufacturing method in the present invention 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.
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.

  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 large specific surface area with respect to a smooth electrode surface, and can efficiently transfer charges.

  These conductive or semiconductive fine particles are dispersed in water or an organic solvent to form a paste, which is applied onto a transparent conductive substrate. A surfactant, a dispersant, a thickener and the like may be added to the paste as necessary. As the coating method, there are a screen printing method, a spin coating method, a squeegee method, a doctor blade method, a spray method, an ink jet method, and the like, and any of them may be used. In general, a screen printing method, a squeegee method, or the like is useful for forming a thick film.

A conductive or semiconductive fine particle paste is applied, dried, and then pressed. In order to perform the pressing process, it is most convenient to use a hot press apparatus. The pressure value to be applied is preferably in the range of 200 kgf / cm ² to 10,000 fkg / cm ² . If it is smaller than 200 kgf / cm ² , the effect is small, and if it is larger than 10000 fkg / cm ^{2, the} display layer may be damaged by pressure press treatment. By applying a pressure of about 1000 kgf / cm ^2, the film thickness of the conductive or semiconductive fine particle layer is compressed to about ½.

  The pressure press treatment may be performed while heating. By heating, the conductive or semiconductive fine particle layer can be pressurized and compressed more efficiently. The heating temperature is preferably about 100 to 300 ° C. However, when a plastic substrate is used as the transparent conductive substrate, it is necessary to set the heating temperature so as not to hinder the substrate.

  The step of heat-sintering the conductive or semiconductive fine particle layer can be performed after the pressure press treatment. In an EC display element using a conductive or semiconductive fine particle layer, charges are efficiently conducted by heating and sintering conductive or semiconductive fine particles. In the method for producing a display layer according to the present invention, an effect close to heat sintering can be obtained in the step of pressure press treatment. However, by further heat sintering, charge conductivity can be improved and better color development efficiency can be obtained. I can do it.

  The conductive or semiconductive fine particle layer may be subjected to pressure press treatment and compressed, and then a step of applying the conductive or semiconductive fine particle paste again and pressurizing and pressing may be included. As described above, the coloring efficiency increases as the number of conductive or semiconductive fine particles per unit area is increased. However, applying a conductive or semiconductive fine particle layer with a large film thickness at one time may cause problems in uniformity or damage during pressure pressing. Therefore, after applying and pressurizing the conductive or semiconductive fine particle layer with an appropriate film thickness, it is only necessary to apply and press again. The overcoating can be performed any number of times.

  The film thickness of the conductive or semiconducting fine particle layer after the pressure pressing is desirably 15 μm or less. As described above, when the film thickness is larger than this, the probability of deterioration due to cracks or film peeling increases.

  Examples of the organic EC compound used in the display device of the present invention include a viologen compound, a styryl compound, a phenothiazine compound, and the like. It is desirable to use Moreover, in order to carry | support on the microparticle surface, it is necessary 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 simplest method for supporting the organic EC compound is to dissolve the organic EC compound in water, alcohol, or an organic solvent and immerse the transparent conductive substrate having a conductive or semiconductive fine particle layer in this solution. The concentration of the solution is preferably about 0.01 mol / l to 1 mol / l. The immersion time is preferably about 10 minutes to 50 hours, more preferably about 1 hour to 24 hours.

  The 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.

  In order to fabricate a reflective display device using the display element of the present invention, a transparent conductive substrate having a conductive or semiconductive fine particle layer and a counter substrate are disposed via a spacer member, and an electrolyte is placed between the two substrates. Encapsulate. Further, as the white reflection part, a white reflection layer is formed on the counter substrate, or white pigment fine particles are dispersed in the electrolyte.

  As the counter substrate, a glass or plastic film coated with a transparent conductive thin film such as ITO, FTO or ZnO or a conductive metal film such as zinc or platinum is 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.

  Examples of the electrolyte include a solution system in which a lithium salt such as lithium perchlorate and lithium borofluoride is dissolved in an organic solvent such as acetonitrile and propylene carbonate, and a solid system such as a perfluorosulfonic acid polymer film. Solution systems have the advantage of high ionic conductivity. The solid system is suitable for producing a highly durable element without deterioration.

  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. Further, when the white pigment particles are dispersed in the electrolytic solution, the white pigment particles are dispersed in advance in the electrolytic solution and then injected into the display element. In this case, since no resin for fixing the white pigment particles is required, the ionic conductivity in the element is good, and the element can be driven at a low voltage.

  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 the conductive or semiconductive fine particles, titanium oxide fine particles (manufactured by Teika Co., Ltd.) having a primary particle diameter 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. Part of a glass substrate with a tin oxide transparent electrode film on its entire surface (area 1 cm ² ) is added with 15 wt% aqueous dispersion of titanium oxide fine particles and 30 wt% of polyethylene glycol # 500000 to the titanium oxide fine particles to form a titanium oxide paste. Prepared. This titanium oxide paste was applied to a thickness of about 10 μm by screen printing. Using an intermediate pressure hot press apparatus (manufactured by Tester Sangyo Co., Ltd.), pressure pressing was performed for 1 hour under the conditions of 1000 kgf / cm ² and a heating temperature of 300 ° C. The film thickness of the titanium oxide fine particle layer after the pressure press treatment was about 5 μm. The display substrate was sintered at 450 ° C. for 1 hour.

[Production of display substrate]
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 has a thickness of about 2 μm by spin coating on a glass substrate with a tin oxide transparent electrode film on 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 to sinter and sintering at 450 ° C. for 1 hour.

[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. Displayed by dispersing 35 wt% of titanium oxide particles (Ishihara Sangyo Co., Ltd.) with a primary particle size of 300 nm in a solution of 0.2 M perchloric acid chloride dissolved in propylene carbonate to prepare an electrolyte solution and sealing it in a cell. An element was produced.

[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 for 50 ms, only the portion having the fine particle layer of the display electrode was colored reddish purple. This color is due to the development of EC1. When a voltage of −1.0 V was applied for 50 ms, the reddish purple color disappeared and became white again.

[Example 4]
When the amount of applied charge and the change in reflectance at a wavelength of 550 nm were measured in the color development reaction of Example 3, the amount of applied charge necessary to obtain a reflectance of about 3% (contrast ratio 20) was 2 mC.

[Comparative Example 1]
A display element similar to that of Example 1 was produced except that a titanium oxide paste was applied to a thickness of about 5 μm on the display substrate and no pressure press treatment was performed. When the same measurement as in Example 4 was performed, the amount of applied charge necessary to achieve a reflectance of about 3% (contrast ratio 20) was 3.4 mC, which is a necessary charge as compared with the case where the pressing process was performed. The amount was great.

[Example 5]
The same titanium oxide paste as in Example 1 was prepared and applied to the display substrate to a thickness of about 10 μm. Pressurization was performed for 1 hour under the conditions of 1000 kg / cm 2 and a heating temperature of 300 ° C. The film thickness of the titanium oxide fine particle layer after pressurization was about 5 μm. The titanium oxide paste was again applied and pressure-pressed. The film thickness of the titanium oxide fine particle layer after the pressure press treatment was about 7 μm.
A display element similar to that in Example 1 was produced and evaluated in the same manner as in Example 4. As a result, the amount of applied charge necessary to obtain a reflectance of about 3% (contrast ratio 20) was 1.6 mC, and the color development reaction occurred with a smaller amount of charge than in Example 1.

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

Claims (4)

In a method for preparing a display layer of an electrochromic display element having a display layer containing an electrochromic composition in which an organic electrochromic compound is supported on conductive or semiconductive fine particles on a transparent conductive substrate, at least the conductive layer is conductive on the transparent conductive substrate Alternatively, a method for producing a display layer, comprising: applying a film containing semiconducting fine particles, and then subjecting the film to press-pressing.
  The display layer manufacturing method according to claim 1, wherein the pressure press treatment is 200 kgf / cm 2 to 10,000 kgf / cm 2.   The film thickness of the display layer containing an electrochromic composition in which an organic electrochromic compound is supported on conductive or semiconductive fine particles produced by using the method according to claim 1 or 2 is 15 μm or less. A characteristic display element. A display device using the method for manufacturing a display layer according to claim 1 or the display element according to claim 3.

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