ELECTROCHROMIC DISPLAY ELEMENT

Abstract: Disclosed is an electrochromic display element having an electrochromic material layer (3) and an ion-conductive material layer (4) being in contact therewith, characterized in that said electrochromic layer (3) comprises a transistion metal oxide and said ion-conductive material layer (4) com­ prises a light-transmissive organic polymeric resin and an inorganic ion-conductive material.

Description: The invention relates to an electrochromic display element. In the prior art, in an electrochromic display element employing a transition metal oxide in the electrochromic material layer, it has been known to use a liquid ion-conductive material or a solid ion-conductive material as the ion-conductive material layer which is formed in contact with the electrochromic material layer. As the liquid ion-conductive material, there have been used, for example, electrolytes composed principally of acids with greater cation mobility such as sulfuric acid for the purpose of accelerating the color forming and extinguishing response speed and obtaining good contrast. However, when these are employed over a long term, there is involved the problem that elecrolytes are liable to be leaked out from the electrochromic display element. For this reason, in manufacturing of electrochromic display elements, electrolytes are required to be sealed liquid tight, whereby there is also involved another problem that manufacturing steps become cumbersome to lower working efficiency. On the other hand, as solid ion-conductive materials, there have been used inorganic ionoconducive materials such as silicon dioxide (SiO₂), magnesium fluoride (MgF₂), calcium fluoride (CaF₂), etc. or organic ion-conductive materials such as perfluorosulfonic acid resin, styrenesufonic acid resin, acrylic resin, etc. However, the former involves the problem that short-circuit is liable to occur between a transparent electrode and a counter-electrode through the pin holes existing in the ion-conductive material layer and the electrochromic material layer. Also, it can be manufactured with poor productivity and therefore is not suitable for practical application. On the other hand, when an organic ion-conductive material such as a polymeric resin is employed, there is the problem that it is poorly contacted at the interface with the electrochromic material layer, whereby ion migration at the interface does not proceed smoothly. Further, there is another problem that small migration speed of cations in an organic ion-conductive material makes speed of color forming and extinguishing response slower, as will take about 2 seconds. Further, in the electrochromic display element of the prior art, regardless of whether the ion-conductive material may be liquid or solid, hydrogen is generally liable to be generated by the side reactions. For this reason, a metal oxide such as stannic oxide (SnO₂) or indium oxide (In₂O₃) used as a transparent electrode is reduced with hydrogen to metallic Sn or metallic In. Accordingly, when used over a long term, there is involved the problem that the display portion of the electrochromic display element is unevenly discolored to brown or black by the metallic Sn or the metallic In formed by reduction, whereby display function is lowered. An object of this invention is to provide an electrochromic display element which may overcome the above problems, is free from occurrence of short-circuit between electrodes, good in close contact with the electrochromic material layer, rapid in color forming and extinguishing response speed and not lowered in display function without generation of hydrogen during usage over a long term According to the invention there is provided an electrochromic display element having an electrochromic material layer and an ion-conductive material being in contact therewith, wherein said electrochromic layer comprises a transistion metal oxide selected from the group consisting of tungsten oxide (WO₃), molybdenum oxide (MoO₃) and titanium oxide (TiO₂), and said ion-conductive material layer comprises a light-transmissive organic polymeric resin and an inorganic ion-conductive material, said organic polymeric resin being at least one of the resins selected from the group consisting of polystyrene, polyvinyl chloride, a vinyl chloride/vinyl acetate copolymer, polyvinyl acetate, polyvinyl acetal, phenol resin, epoxy resin, alkyd resin, acrylic resin, polyacrylonitrile, butadiene type synthetic rubber and polyolefin, and said inorganic ion-conductive material being at least one selected from the group consisting of lithium fluoride (LiF), lithium iodide (LiI), lithium hydroxide (LiOH), lithium perchlorate (LiClO₄), sodium fluroide (NaF), sodium iodide (NaI), sodium hydroxide (NaOH) and sodium perchlorate (NaClO₄), and containing polyethylene glycol for improving the responsiveness. Also, the electrochromic display element of this invention may be one wherein said ion-conductive material layer further contains a pigment. In the following, this invention will be described in further detail: In the drawing: Fig. 1 shows a schematic constitutional illustration of the electrochromic display element according to this invention. There is shown in Fig. 1 an embodiment, wherein a transparent electrode (2), an electrochromic material layer (3), an ion-conductive material layer (4) and a counter-electrode (5) are provided on a substrate (1), respectively. The material constituting the electrochromic material layer according to this invention is one of the following transition metal oxides: tungsten oxide (WO₃), molybdenum oxide (MoO₃), and titanium oxide (TiO₂). The materials constituting the ion-conductive material layer according to this invention, which may have a layer thickness of from 0.1 to 100 µm, are an organic polymeric resin and an inorganic ion-conductive material. The organic polymeric resin having transparency on fabrication into a film is selected from polystyrene, polyvinyl chloride, a vinyl chloride/vinyl acetate copolymer, polyvinyl acetate, polyvinyl acetal, phenol resin, epoxy resin, alkyd resin, acrylic resin, polyacrylonitrile, butadiene type synthetic rubber and polyolefin. There may be employed one kind or two or more kinds selected from the group consisting of these resins. The inorganic ion-conductive material contains Li⁺ or Na⁺ which participates in color formation and extinction and is selected from lithium fluoride (LiF), lithium iodide (LiI), lithium hydroxide (LiOH), lithium perchlorate (LiClO₄), sodium fluoride (NaF), sodium iodide (NaI), sodium hydroxide (NaOH) and sodium perchlorate (NaClO₄), and one kind or two or more kinds selected from the group consisting of these materials may be used. The above inorganic ion-conductive material may be formulated preferably in an amount of 0.01 to 1000 % by weight, more preferably 20 to 100 % by weight, based on the organic polymeric resin. When the amount of the inorganic ion-conductive material formulated is less than 0.01 % by weight, contrast during color formation may be lowered to make display function bad, while at a level exceeding 1000 % by weight, film forming characteristic as a composite material may be lowered to give difficultly an ion-conductive material layer with a uniform composition. The ion-conductive material layer according to this invention further contains polyethylene glycol(PEG) plasticizer. This not only improves the flexibility of the organic polymeric resin film, but also the color forming and extinguishing response. The plasticizer used in this invention may also include tricresyl phosphate (TCP), tributyl phosphate (TBP), triethyl phosphate (TED), trioctyl phosphate (TOP), trisdichloropropyl phosphate (CRP), tributoxyethyl phosphate (TBPX), methylacetyl ricinoleate (MAR), octyldecyl phthalate, butyllauryl phthalate (BLP), butylphthalyl butylglycolate (BPBG), butylbenzyl phthalate (BBP), dilauryl phthalate (DLP), dibutyl phthalate (DBP), cyclohexyl phthalate (DCHP), diethyl phthalate (DEP), diisobutyl phthalate (DIBP), diisodecyl phthalate (DIDP), dioctyl phthalate (DOP), dioctyl adipate (DOA), diisodecyl adipate (DIDA), octyldecyl adipate (ODA), dibutyl sebacate (DBS), tributyl citrate, acetyltributyl citrate, triethyl citrate, acetyltriethyl citrate, di-2-ethylhexyl maleate (DOM), dibutyl fumarate. One or more of these may be used ; a mixture of BPBG and PEG, for example. The amount of the plasticizer may appropriately be within the range of from 1 to 100 % by weight, preferably 5 to 70% by weight, based on the polymeric resin. When the amount of the plasticizer formulated is lower than 1 % by weight, no improvement in response characteristic of the element can be observed, whereby no effect of addition of the plasticizer can be exhibited. On the other hand, when it is added in excess of 100 %, formation into a thin film is difficult. In this invention, addition of the PEG plasticizer improves flexibility of the polymeric resin film and makes migration of the inorganic ionic material in the polymeric matrix to improve the ion-conductivity, thereby enabling formation of an electrochromic element excellent in response characteristic. The ion-conductive material layer according to this invention may further contain a pigment for the purpose of improving the display function and imparting a beautifying effect. The pigment to be used in this invention may be exemplified by white pigments such as titanium dioxide (TiO₂), aluminum oxide (Al₂O₃), magnesium oxide (MgO), zirconium oxide (ZrO₂), yttrium oxide (Y₂O₃), tantalum pentaoxide (Ta₂O₅) and silicon dioxide (SiO₂), and coloring pigment such as nickel titanium yellow, cadmium yellow, chromium yellow, cadmium red, molybdenum orange and colcothar. One kind or two or more kinds selected from the group consisting of these may be employed. Among them, it is particularly preferable to use a white pigment from the standpoint of the beautifying effect. The above pigment may be formulated preferably in an amount of 5 to 50 % by weight, more preferably 10 to 30 % by weight, based on the organic polymeric resin. When the amount of the pigment formulated is less than 5 % by weight, the color of the background can be thinly seen through to give no sufficient beautifying effect. On the other hand, at a level exceeding 50 % by weight, the film forming characteristic and ion-conductivity of the ion-conductive material layer may be lowered. Other materials to be used may include those conventionally used in electrochromic display elements. As the substrates, there may be employed, for example, transparent materials such as glasses, polyesters, etc. As the transparent electrode and the counter-electrode, there may be employed, for example, In₂O₃ , SnO₂, Au, etc. The electrochromic display element constituted by use of the above materials may be prepared according to, for example, the following procedures: Namely, a transparent electrode is first formed on a substrate by using a conventional method such as sputtering. Then, on the aforesaid transparent electrode is formed an electrochromic material layer by using a method such as vapor deposition. For formation of an ionoconducive material layer, first an organic polymeric resin and an inorganic ion-conductive material are formulated in predetermined amounts, or optionally with further addition of a pigment thereto, to prepare a dispersed and mixed product. The mixture may be diluted with an appropriate solvent, if necessary, or an organic polymeric resin previously diluted with an organic solvent may be used so as to control its viscosity, and then ready for coating on an electrochromic material layer by using, for example, the spinning coating method, the dipping method, the roller coating method or the spray coating method. When a solvent is used, for the purpose of removing the solvent remaining in the thin film, it is preferred to apply a heating treatment at a temperature range of from 50 to 150 o C. As the solvent to be used for controlling the viscosity of the above ion-conductive material, there may be included non-aqueous solvents such as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), toluene, xylene, cresol, ethylcellosolve acetate, butylcellosolve acetate, propylene carbonate, acetonitrile, dimethylacetamide, N-methylpyrrolidone, and dimethylformamide, and one kind or two or more kinds selected from the group consisting of these solvents may be employed. The above organic solvent may be formulated in an amount, which may preferably be selected suitably depending on the use as well as the preparation method during film formation of the composition of this invention, and it may be preferably employed in an amount so that the resin concentration may be within the range from 2 to 20 % by weight. Next, a counter-electrode is formed on the ion-conductive material layer by using a method such as sputtering similarly as in formation of the transparent electrode, to give the electrochromic display element. Since the ion-conductive material layer is formed according to a coating method, the electrochromic display element is free from generation of pin holes and the like, and therefore free from occurrence of short-circuit between electrodes. Also, due to good close contact between the electrochromic material layer and the ion-conductive material layer, response of color forming and extinguishing is rapid. Further, since color formation and exinction are effected by inorganic ions such as Li⁺ or Na⁺ in the ion-conductive material layer, there is no generation of hydrogen during usage over a long term, thus having an advantage of substantially no lowering of display function. Moreover, the electrochromic display element has good response characteristic by adding PEG to the above-mentioned ion-conductive material layer. The electrochromic display element having the advantages as mentioned above can also be prepared, in manufacturing thereof, to have a uniform thin film ion-conductive material layer according to a simple step. This invention will be described in a greater detail by the following Examples. Examples 1 to 5 On glass plates were prepared patternized transparent conductive films, on which there were provided tungsten oxide films to the thickness of 0.3 µm by the vapor deposition method. On these films, the compositions as shown in Examples 1 to 5 in Table 1, after being sufficiently dispersed, were coated by a spinner. Then, the coated products were dried under heating at 150 o C for 2 hours for removal of the organic solvents remaining in the solid electrolyte layers. Subsequently, counterelectrodes were provided by vapor deposition of gold. Additionally preparing three kinds of comparative examples as shown in Table 1, eight kinds of the electrochromic elements thus obtained were tested for actuation characteristics to give the results which are also shown in Table 1. Each of the elements obtained was found to be a display element which was good in response characteristic by driving at a low voltage. The response time is a time required before reaching the contrast ratio of 3 when a voltage of 1.5 V was applied. Comparative Examples 1 to 3 employ the composite materials as solid electrolytes without addition of a plasticizer. Examples 6 to 10 Prepared were electrochromic display elements according to this invention and comparative electrochromic display elements as shown in Table 2 in the same manner as in Examples 1 to 5 and Comparative Examples 1 to 3, except that MoO₃ was used in place of WO₃ for the electrochromic material layer. The electrochromic elements thus obtained were tested for actuation characteristics to give the results which are also shown in Table 2. Each of the elements obtained was found to be a display element which was good in response characteristic by driving at a low voltage. The response time is a time required before reaching the contrast ratio of 3 when a volage of 1.5 V was applied. Comparative Examples 4 to 6 employ the composite materials as solid electrolytes without addition of a plasticizer.

Claims: An electrochromic display element having an electrochromic material layer (3) and an ion-conductive material layer (4) being in contact therewith, wherein said electrochromic layer (3) comprises a transition metal oxide selected from the group consisting of tungsten oxide (WO₃), molybdenum oxide (MoO₃) and titanium oxide (TiO₂), and said ion-conductive material layer (4) comprises a light-transmissive organic polymeric resin and an inorganic ion-conductive material, said organic polymeric resin being at least one of the resins selected from the group consisting of polystyrene, polyvinyl chloride, a vinyl chloride/vinyl acetate copolymer, polyvinyl acetate, polyvinyl acetal, phenol resin, epoxy resin, alkyd resin, acrylic resin, polyacrylonitrile, butadiene type synthetic rubber and polyolefin, and said inorganic ion-conductive material being at least one selected from the group consisting of lithium fluoride (LiF), lithium iodide (LiI), lithium hydroxide (LiOH), lithium perchlorate (LiClO₄), sodium fluoride (NaF), sodium iodide (NaI), sodium hydroxide (NaOH) and sodium perchlorate (NaClO₄), and containing polyethylene glycol for improving the responsiveness. The electrochromic display element according to claim 1, wherein said organic polymeric resin is polystyrene, polyvinyl acetate or acrylic resin. The electrochromic display element according to claim 2, wherein said acrylic resin is polymethylmethaclyrate or a methyl methacrylate/methacrylic acid copolymer. The electrochromic display element according to any preceding claim, wherein said inorganic ion-conductive material is formulated in an amount of 0.01 to 1000 % by weight based on the organic polymeric resin. The electrochromic display element according to claim 4, wherein said inorganic ion-conductive material is formulated in an amount of 20 to 100 % by weight based on the organic polymeric resin. The electrochromic display element according to any preceding claim, wherein said ion-conductive material layer further contains a pigment. The electrochromic display element according to claim 6, wherein said pigment is at least one selected from the group consisting of white pigments such as titanium dioxide (TiO₂), aluminium oxide (Al₂0₃), magnesium oxide (MgO), zirconium oxide (ZrO₂), yttrium oxide (Y₂0₃), tantalum pentaoxide (Ta₂0₅) and silicon dioxide (Si0₂), and coloring pigment such as nickel titanium yellow, cadmium yellow, chromium yellow, cadmium red, molybdenum orange and colcothar. The electrochromic display element according to claim 7, wherein said pigment is titanium dioxide (Ti0₂), zirconium oxide (Zr0₂) or yttrium oxide (Y₂0₃). The electrochromic display element according to claim 7 or 8, wherein said pigment is formulated in an amount of 5 to 50 % by weight based on the organic polymeric resin. The electrochromic display element according to claim 9, wherein said pigment is formulated in an amount of 10 to 30 % by weight based on the organic polymeric resin. The electrochromic display element according to any preceding claim, wherein said ion-conductive material further contains at least one plasticizer selected from the group consisting of tricresyl phosphate (TCP), tributyl phosphate (TBP), triethyl phosphate (TED), trioctyl phosphate (TOP), trisdichloropropyl phosphate (CRP), tributoxyethyl phosphate (TBPX), methylacetyl ricinoleate (MAR), octyldecyl phthalate, butyllauryl phthalate (BLP), butylphthalyl butylglycolate (BPBG), butylbenzyl phthalate (BBP), dilauryl phthalate (DLP), dibutyl phthalate (DBP), cyclohexyl phthalate (DCHP), dibutyl phthalate (DEP), diisobutyl phthalate (DIBP), diisodecyl phthalate (DIDP), dioctyl phthalate (DOP), dioctyl adipate (DOA), diisodecyl adipate (DIDA), octyldecyl adipate (ODA), dibutyl sebacate (DBS), tributyl citrate, acetyltributyl citrate, triethyl citrate, acetyltriethyl citrate, di-2-ethylhexyl maleate (DOM), and dibutyl fumarate. The electrochromic display element according to any preceding claim, wherein the amount of said polyethylene glycol is within the range of from 1 to 100 % by weight based on the polymeric resin. The electrochromic display element according to claim 12, wherein the amount of said polyethylene glycol is within the range of from 5 to 70 % by weight based on the polymeric resin.

Inventors: MIYAMURA, MASATAKA, NAKAJIMA, YUKO, SAKAMOTO, MASANORI
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1983
Main classification: G02F1
IPC codes: G02F1