JP2007298713A - Electrochromic display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new electrochromic display of which the characteristics such as response speed, repeatability, chemical stability, tolerance to environmental conditions and so on are improved. <P>SOLUTION: An electrode active material layer 4 composed of a radical polymer, an electrolyte layer 6, and an electrolyte layer 5 are interposed between a pair of electrode substrates 1a, 1b, the electrode active material layer 4 is formed on the electrode substrate 1a, and the electrochromic layer 5 is formed on the electrode substrate 1b. The electrolyte layer 6 is constructed with an ion conductive polymer with white fine particles dispersed therein. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrochromic display.

Since the introduction of electronic paper (e-Paper) developed by E-Ink (Boston), USA, much attention has been focused on rewritable flexible thin film displays. This electronic paper is composed of an element with a very simple structure in which fine particles having a positive or negative charge are dispersed in an insulating liquid between two electrodes. It is a simple one that uses a change in reflectance after electrophoresis. Multi-color display can be achieved by using pigments with different colors of fine particles so that the charge to be charged is different from positive and negative. When fine particles are migrated in a liquid, the frictional resistance is large and the response speed is slow. In order to improve this, a method of moving charged fine particles in the air has been devised (for example, Patent Documents 1 to 6). However, such an element has the following problems.
(B) The drive voltage is too high.
(B) The lifetime of the device is short due to particle aggregation.
(C) The image quality (resolution, contrast, etc.) is insufficient.
(D) The economics of the manufacturing process is not good.

  On the other hand, electrochromic display (ECD) is a low-voltage drive display technology that has been known before the advent of electronic paper, and has attracted attention because its display characteristics are close to those written on paper. The application field was limited due to its slowness. However, since the above-mentioned technology has appeared and a new product called electronic paper has attracted attention on the market, the ECD type flexible thin film display has been reviewed again.

For example, a new type of ECD in which a viologen derivative is used as an electrochromic material and chemisorbed on nano-sized titanium oxide fine particles has been developed and used as electronic paper (Non-Patent Document 1). In addition, studies have been made to improve the response speed of ECD. For example, it is known that an attempt has been made to increase the speed by using an electrochromic material layer having a fine uneven structure on the surface and a film thickness of 100 nm or less. (Patent Document 7). Further, the speed is increased by using an electrochromic material having at least one metal oxide layer having micropores, wherein the pore size frequency distribution of the micropores has a plurality of peaks. The thing which aimed at is also known (patent document 8).
JP 2002-202532 A JP 2002-107771 A JP 2002-72256 A JP 2004-46056 A JP 2004-29700 A JP 2003-315846 A JP 2001-188264 A JP 2000-89257 A U. Bach, et al., Adv. Mater., 14, 845 (2002).

  However, the response speed of the conventional ECD has not reached the level of practical use, and in order to put the ECD into practical use, in addition to improving the response speed, repeatability, chemical stability, environmental resistance ( It was necessary to improve characteristics such as deterioration due to oxygen and moisture.

  Therefore, in view of the above problems, the present invention puts to practical use a flexible thin film display based on the ECD display principle, which can be used as a low voltage drive mobile thin film display that can be driven in combination with a paper-like battery as an electronic paper of a new concept. An object of the present invention is to provide a novel electrochromic display with improved characteristics such as response speed, repeatability, chemical stability, and environmental resistance.

  The present inventors have so far developed a new polymer material called a polymer containing a radical and applied it to various electronic devices. In particular, by utilizing the excellent redox property of a polymer containing radicals, a battery having an extremely fast charging speed or a nonvolatile memory element having a fast response speed has been successfully developed. The present inventors tried to improve the problems of the conventional ECD using the characteristics of the polymer containing such radicals. As a result, the response speed was improved by using the radical polymer as an electrode active material. The present invention has been found out that it is possible to construct an ECD that is fast and has high driving stability.

  The electrochromic display according to claim 1 of the present invention comprises an electrode active material layer, an electrolyte layer, and an electrochromic layer sandwiched between a pair of electrode substrates. An electrochromic display in which a material layer is formed and the electrochromic layer is formed on the other electrode substrate, wherein at least one of the electrode active material layer and the electrochromic layer is made of a radical polymer. And

  The electrochromic display according to claim 2 of the present invention is characterized in that, in claim 1, the electrode active material layer is made of a radical polymer.

  The electrochromic display according to claim 3 of the present invention is characterized in that, in claim 1 or 2, the electrochromic layer is made of a radical polymer.

  An electrochromic display according to a fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the electrolyte layer is made of an ion conductive polymer in which white fine particles are dispersed.

  According to the electrochromic display of the present invention, by using a novel electrode active material called a radical polymer in at least one of the electrode active material layer and the electrochromic layer, response speed, repeatability, chemical stability, environmental resistance Therefore, it is possible to provide a new type of electrochromic display that can be put into practical use as a flexible thin film display.

  Hereinafter, an embodiment of the electrochromic display of the present invention will be described.

  FIG. 1 is a cross-sectional view schematically showing the basic configuration of the electrochromic display of this embodiment. Reference numeral 1a denotes an electrode substrate, which includes a substrate 2a and an electrode layer 3a formed on the substrate 2a. ing. Reference numeral 1b denotes an electrode substrate that forms a pair with the electrode substrate 1a. The electrode substrate 1b includes a substrate 2b and an electrode layer 3b formed on the substrate 2b.

The substrates 2a and 2b are made of transparent glass. As a material of the substrates 2a and 2b, plastics can be used in addition to glass, and the material is not limited to a specific one as long as it is transparent or translucent. The electrode layers 3a and 3b are made of ITO (Indium Tin Oxide). As a material for the electrode layers 3a and 3b, in addition to ITO, ZnO, SnO ₂ or the like can be used, and any material can be used as long as it is transparent and conductive.

  An electrode active material layer 4 made of a radical polymer is formed on the electrode layer 3a of one electrode substrate 1a. The radical polymer used here is an organic polymer having unpaired electrons that are reversibly and rapidly oxidized and reduced. By constituting the electrode active material layer 4 from a radical polymer, oxidation and reduction in the electrode active material layer 4 are performed reversibly and rapidly, and as a result, the response speed and repeatability of the electrochromic display are improved.

  Examples of functional groups having unpaired electrons include 2,2,6,6-tetramethylpiperidinoxy radical (Chemical Formula 1), 3-carboxyprosyl radical (Chemical Formula 2), and 16-doxyl stearic acid radical (Chemical Formula 3). ), 4- (1-hydroxy-1-methylethyl) -2,2,5,5-tetramethyl-3-imidazolium-1-yloxy radical (chemical formula 4), galvinoxyl radical (chemical formula) as a phenoxy radical 5) Several different types of radical species are mentioned, such as the 2,2,2-diphenyl-1-picrylhydrazyl (DPPH) radical.

  By introducing such radical species into the polymer matrix, a radical polymer that forms the electrode active material layer 4 can be obtained. As a method for introducing radical species into a polymer matrix, it can be dispersed in a general-purpose organic polymer such as polystyrene, polymethylmethacrylate, epoxy resin, novolac resin, etc., but uniformity and stability at the molecular level. In view of the properties, handling properties, etc., a method in which radical species are covalently bonded to the polymer skeleton is preferably used. An example of a radical polymer in which a radical species is covalently bonded to a polymer skeleton is the poly (4-methacryloxy-2,2,6,6-tetramethylpiperidinoxyl-1-oxyl) radical , Poly (3,5-di (Nt-butylnitroxyl) styrene) radical (Chemical formula 8), poly (1- (Nt-butylnitroxyl) propyne) radical (Chemical formula 9), poly (N- t-butyl-N-acryloylnitroxyl) radical (Chemical Formula 10), poly (dianisylaminium acetylene) radical (Chemical Formula 11), poly (allyl proxyl) radical (Chemical Formula 12), poly (4- (2,2, 6,6-tetramethylpiperidinium) phenyleneacetylene) radical (Chemical Formula 13). By configuring the electrode active material layer 4 from the above radical polymer, characteristics such as response speed, repeatability, chemical stability, and environmental resistance can be improved. The radical polymer used in the present invention is It is not limited to those.

  Here, it is desirable that all radical polymers have 10% or more radicals per monomer unit, and 70% to 100% is appropriate. In the present invention, the radical polymer used for the electrode active material layer 4 is preferably a high molecular weight polymer. The molecular weight is preferably several thousand or more as the weight average molecular weight, but 10,000 to several hundred thousand is appropriate in consideration of film forming property and thermal stability. As described above, by using a radical polymer having a sufficiently high molecular weight, a simple film forming process by a wet method can be performed. The wet method is a known technique for forming a thin film of an organic polymer, and generally, a spin coating method, an ink jet method, and other various printing methods are known.

  An electrochromic layer 5 is formed on the electrode layer 3b of the other electrode substrate 1b. As the electrochromic material constituting the electrochromic layer 4, galvinoxyl radicals exhibiting electrochromic characteristics can be used in the above radical polymers, and viologen, phthalate esters, various conductive polymers ( (Polythiophene, polypyrrole, polyaniline, etc.), inorganic substances such as Prussian blue, rare earth diphthalocyanine and other metal complexes, and metal oxides such as tungsten trioxide and iridium oxide. Furthermore, a salt containing metal ions such as silver and bismuth can be used for monochrome display. The metal ion is reduced to become a zero-valent metal, and the fine particles are black and can be used for black and white display. In addition, a material suitable for the purpose of the electrochromic display can be appropriately selected and used.

  An electrolyte layer 6 made of an electrolyte is formed between the electrode active material layer 4 and the electrochromic layer 5. The electrolyte layer 6 is effective in separating charges so that the redox reaction between the electrode active material layer 4 and the electrochromic layer 5 does not interfere smoothly and the reverse reaction (so-called self-discharge) does not occur. Applied for purposes of In order to operate the electrochromic display stably and at high speed, a material having a high ion conductivity is preferably used for the electrolyte layer 6. Specifically, a material in which a supporting salt is uniformly supported in a liquid, solid, or semi-solid (gel) medium can be used. However, from a practical viewpoint, there is no risk of liquid leakage, and it is easy. Therefore, it is advantageous to use an ion-conducting polymer in which a supporting salt is supported on a gel-like medium because it has a higher ionic conductivity than a solid electrolyte and is advantageous for speeding up an electrochromic display. It is done.

  Examples of the polymer constituting this ion conductive polymer include polyvinylidene fluoride copolymer, polyacrylonitrile, and cellulose-based polysaccharides. Ion conductivity, mechanical strength, chemical stability, thermal stability, Considering adhesiveness to the substrate, a homopolymer or copolymer of a monomer having an ethylene oxide chain in the side chain as shown in Chemical formulas 14 to 16 is preferably used. Furthermore, the film strength of the electrolyte layer 6 can be improved by adding a crosslinking agent as shown in Chemical Formula 17 to the monomer and polymerizing the monomer.

  As the solvent to be impregnated into the polymer as described above, water having a high dielectric constant, ethylene carbonate, propylene carbonate and the like are suitable. In addition, as the supporting salt dissolved in these solvents, inorganic salts such as lithium perchlorate and potassium chloride, or organic salts such as tetramethylammonium tetrafluoroborate and tetraethylammonium chloride can be used.

  Moreover, in order to improve the reflectance of an electrochromic display, the electrolyte layer 6 is configured by dispersing white fine particles in the above-described ion conductive polymer. The white fine particles used here are preferably metal oxide white pigments such as titanium oxide.

  In the electrochromic display of this embodiment, for example, an electrode active material layer 4 is formed by spin coating a radical polymer on one electrode substrate 1a, and an electrochromic material is immobilized on the other electrode substrate 1b. It can be manufactured by a relatively simple process in which the layer 5 is formed and the electrolyte layer 6 is formed by sandwiching the electrolyte between the two electrode substrates 1a and 1b. In the case where the electrolyte layer 6 is composed of a liquid electrolyte, the electrolyte layer 6 can be easily formed by sandwiching a spacer having a thickness of 0.5 to 1 mm made of silicone rubber or the like between the electrodes. .

  As described above, in the electrochromic display of this example, the electrode active material layer 4 made of a radical polymer, the electrolyte layer 6, and the electrochromic layer 5 are sandwiched between the pair of electrode substrates 1a and 1b. Become. An electrode active material layer 4 is formed on the electrode substrate 1a, and an electrochromic layer 5 is formed on the electrode substrate 1b. A new type that can be put to practical use as a flexible thin film display with improved response speed, repeatability, chemical stability, environmental resistance, etc., by using a new electrode active material called radical polymer for the electrode active material layer 4 An electrochromic display can be provided.

  Further, since the electrolyte layer 6 is made of an ion conductive polymer in which white fine particles are dispersed, the reflectance of the electrochromic display can be improved. Moreover, compared with the case where a reflecting material is directly fixed to an electrode substrate, the process for fixing a reflecting material can be omitted, and the reflectance of an electrochromic display can be improved more easily.

  The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. In the above embodiment, the electrode active material layer is composed of a radical polymer. However, the present invention is not limited thereto, and the electrode active material layer is composed of a material other than the radical polymer, and the electrochromic layer is composed of a radical polymer. You may make it do.

  Hereinafter, the electrochromic display of the present invention will be described more specifically.

An electrochromic layer was formed by depositing Prussian blue (PB) on an ITO glass substrate electrode by an electrodeposition method. Specifically, in an iron ion-containing aqueous solution in which potassium ferricyanide, ferrous chloride, and hydrochloric acid are each dissolved at a concentration of 10 mM, an ITO glass substrate electrode (surface area of about 5 cm ² ) is used as a working electrode, a platinum wire is used as a counter electrode, and Ag / A blue PB film was deposited on the surface of the ITO glass substrate electrode by applying a constant current of 0.5 mA for 100 seconds using AgCl as a reference electrode.

Further, as a material constituting the electrode active material layer, a mixture (weight ratio 1: 1: 8) of radical polymer, polyvinylidene fluoride (PVDF), carbon powder (Showa Denko, VGCF) was used, and this was used as N-methylpyrrolidone. 140 mg of paste dispersed and dissolved in (NMP) at a concentration of 0.6 wt% is dropped onto an ITO glass substrate (surface area of about 5 cm ² ), uniformly applied with a glass rod, and vacuum-dried at 80 ° C. for 10 hours. Thus, an electrode active material layer was formed. The radical polymer used here is partially cross-linked poly (4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (PTMA), and its synthesis method is shown below.

  According to Chemical formula 18, poly (4-methacryloyloxy-2,2,6,6-tetramethylpiperidine), which is a precursor polymer obtained by polymerization using 2,2′-azobis (isobutyronitrile) as an initiator, was converted into dichloromethane. Into this, a dichloromethane solution of metachloroperbenzoic acid was added dropwise and reacted at room temperature for 1 hour to obtain a radical. After completion of the reaction, an aqueous potassium carbonate solution was added to separate the solution into two liquids. The organic layer was recovered and reprecipitated in hexane to obtain PTMA as a light orange powder. This PTMA was radicalized by 70 to 80% per mole, but the analysis results suggested that the remaining part formed a crosslinked structure.

And the electrolyte layer was formed by arrange | positioning the silicon rubber spacer (thickness 0.5mm) between said 2 ITO glass substrates, and pouring the paste-like composition which is an electrolyte solution composition into it. Here, as the electrolyte composition, a milky white liquid in which polyethylene glycol (PEG; M _w = 500,000), KPF ₆ , TiO ₂ , and propylene carbonate (PC) are dispersed and dissolved in a weight mixing ratio of 5: 20: 5: 100. (Organic solvent system) was used.

  When the voltage-current characteristics of the ECD element produced as described above were analyzed using an analyzer model 2400 manufactured by Keithley, the result shown in FIG. 2 was obtained. From this result, as shown in Chemical Formulas 19 and 20, it was presumed that the oxidation reaction of the radical polymer and the reduction reaction of PB became redox couples to cause electrochromism.

FIG. 3 shows changes over time in the initial current value when the ECD element is decolored and colored by applying −1.2 V and +0.5 V. When the initial value has a response time of time until the change _{90% (T 90), T} 90 of the erasing process and the coloring process 0.7 seconds, respectively, it was 2.1 seconds.

  FIG. 4 shows the cycle characteristics when erasing and coloring are repeated by alternately applying voltages of -1.2V and + 0.5V. As shown in this figure, no deterioration phenomenon was observed in the electrochromism in the repetition range of about 100 times.

  As described above, it was confirmed that by forming the electrode active material layer with a radical polymer, the ECD element is driven stably and has excellent cycle characteristics.

  As a material constituting the electrochromic layer, a material in which galvinoxyl radical (GALVI) is dispersed in polyvinylidene fluoride (PVDF) at a weight ratio of 1: 9 is used, and this is added to N-methylpyrrolidone (NMP) at 2 wt%. A solution dissolved in a concentration of% was applied on an ITO glass substrate and dried at 80 ° C. for 1 hour to form an electrochromic layer. The electrode active material layer and the electrolyte layer were formed in the same manner as in Example 1.

  The voltage-current characteristics of the ECD device fabricated as described above are as shown in FIG. When +3 V was applied to this ECD element, the color changed from yellow to reddish purple, and when −2 V was applied, the opposite color change was observed. This ECD characteristic was basically the same as that of Example 1.

  As in Example 2, the GALVI / PVDF dispersion film was an electrochromic layer. As a material for forming the electrode active material layer, poly (3-hexylthiophene-2,5-diyl) (P3HT) was used, dissolved in toluene at a concentration of 1.6 wt%, and spin-coated (1000 rpm × 10 seconds) Then, it was applied onto an ITO glass substrate by 6000 rpm × 50 seconds) and vacuum-dried at 80 ° C. for 1 hour. This was used as the electrode active material layer, and the electrolyte layer was the same as in Example 1.

  The voltage-current characteristics of the ECD element fabricated as described above are as shown in FIG. 6 and basically showed the same performance as in Example 2.

Comparative example

In the same manner as in Example 1, an electrochromic layer was formed of Prussian blue (PB) on an ITO glass substrate. Moreover, the electrode active material layer was also formed of PB in the same manner as the electrochromic layer. And the electrolyte composition was formed by arrange | positioning the silicon rubber spacer (thickness 0.5mm) between said two ITO glass substrates, and pouring the paste-like composition which is an electrolyte solution composition in it. Here, as the electrolyte composition, a milky white liquid (aqueous system) in which polyethylene glycol (PEG; M _w = 500,000), KCl, TiO ₂ , and water are dispersed and dissolved in a weight mixing ratio of 20: 20: 1: 100 is used. It was.

  The voltage-current characteristics of the ECD device fabricated as described above are as shown in FIG. 7, and redox peaks corresponding to oxidation and reduction of PB were observed.

  FIG. 8 shows cycle characteristics when ± 1.5 V is repeatedly applied alternately. As shown in this figure, the initial current value in the coloring process rapidly decayed. With the decay of the initial current ground, the color change of the electrochromic layer became unclear as the number of repetitions increased.

It is sectional drawing which shows typically the basic composition of the electrochromic display of this invention. It is the voltage-current characteristic (sweep speed of 10 mV / sec) of the ECD element of Example 1. The time-dependent change of the initial electric current value when -1.2V and + 0.5V of the ECD element of Example 1 are applied and it erases and colors is shown. The cycle characteristics when the voltage of -1.2V and + 0.5V of the ECD element of Example 1 are alternately applied to repeat decoloring and coloring are shown. It is the voltage-current characteristic (sweep speed of 10 mV / sec) of the ECD element of Example 2. It is the voltage-current characteristic (sweep speed of 10 mV / sec) of the ECD element of Example 3. It is the voltage-current characteristic (sweep speed of 100 mV / sec) of the ECD element of the comparative example. The cycle characteristics when the voltage of -1.5V and + 1.5V of the ECD element of the comparative example are alternately applied to repeat decoloring and coloring are shown.

Explanation of symbols

1a, 1b Electrode substrate 4 Electrode active material layer 5 Electrochromic layer 6 Electrolyte layer

Claims (4)

An electrode active material layer, an electrolyte layer, and an electrochromic layer are sandwiched between a pair of electrode substrates, the electrode active material layer is formed on one of the electrode substrates, and the electrode substrate on the other electrode An electrochromic display in which an electrochromic layer is formed, wherein at least one of the electrode active material layer and the electrochromic layer is made of a radical polymer. The electrochromic display according to claim 1, wherein the electrode active material layer is made of a radical polymer. 3. The electrochromic display according to claim 1, wherein the electrochromic layer is made of a radical polymer. The electrochromic display according to claim 1, wherein the electrolyte layer is made of an ion conductive polymer in which white fine particles are dispersed.

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