JPS642924B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to electrochromism (hereinafter abbreviated as EC) that utilizes electrochromism, a phenomenon in which light absorption characteristics change depending on the application of voltage or electric current.
This invention relates to display devices, and in particular to reflective EC display devices, which enables display backgrounds with good contrast and thinner devices.

An EC display device is usually mainly composed of a display electrode, a counter electrode, and an electrolyte, and the EC substance is either provided as a thin film on a transparent conductive layer as part of the display electrode, or dissolved in the electrolyte. There is. As EC substances, inorganic EC substances such as tungsten oxide, molybdenum oxide, titanium oxide, and silver iodide, and organic EC substances such as viologen compounds are known. In addition, electrolytes include mixtures of sulfuric acid and glycerin, lithium perchlorate, potassium bromide, and other electrolytes dissolved in water or organic solvents such as propylene carbonate, cellosolve acetate, carbitol acetate, and γ-butyrolactone. It is used.

There are two types of EC display devices: transmissive and reflective.
Generally, reflective devices are being considered that provide a certain background and display using colored EC materials. In this case, an insoluble white substance such as titanium oxide or barium sulfate is usually dispersed and mixed into the electrolyte to provide a background for the display. Mixing such a white substance serves as a good background for the colored state of the EC substance and can increase the contrast.
It also has the role of hiding electrodes other than display electrodes. However, during long-term use, the dispersed substances often settle or agglomerate, resulting in uneven concentration, which poses a problem in the practical application of EC display devices. Furthermore, in this method, there are limits to the type and amount of substances that can be dispersed and mixed, and in order to apply it to an actual device, it becomes necessary to thicken the electrolyte layer.

The present invention provides an electrolytic solution layer between electrodes, which is formed by impregnating an electrolytic solution into a porous body that retains a pigment and a polymer substance showing wettability to the electrolytic solution in a porous space. The present invention solves the above-mentioned problems and provides a display device that provides a better display background and high contrast without dispersing a white substance into an electrolytic solution. Furthermore, since the display device of the present invention allows the electrolyte layer to be made thin, a thin device can be provided, which promotes the practical use of EC display devices.

The porous body in the present invention serves both the role of providing a display background and the role of impregnating an electrolyte to form an electrolyte layer. Examples of the material for this porous body include various resins, metals, ceramics, and glass, and its shape includes those with fine pores created by stretching, nonwoven fabric, net fabric, and net fabric. However, from the viewpoint of ease of handling, chemical resistance to electrolyte components, and heat resistance, materials made of halogen-containing polymers or polyolefins are suitable. Among others, polytetrafluoroethylene, polyvinylidene fluoride,
Porous bodies made of polyethylene or polypropylene were suitable.

A pigment and a polymer substance that exhibits wettability with respect to an electrolytic solution are held within the porous spaces of the porous body. In this case, the pigment is used to provide a display background, and the polymeric substance has the role of fixing the pigment to the porous body and at the same time improving the wettability of the porous body to the electrolyte. Examples of pigments include titanium white, zinc white, lead white, lithopone, titanium yellow, cobalt blue, vermilion, cadmium red, Bengara, iron black, silica, alumina, talc, gypsum, calcium carbonate, barium sulfate, and carbon black. Examples include powders of graphite, iron, shell, lead, tin, aluminum, and various organic pigments. These pigments can be used singly or in combination, and if necessary, dyes, fluorescent agents, etc. can be added to enhance the effect as a display background.

The polymer substance is not particularly limited as long as it shows wettability to the electrolyte and does not dissolve in the electrolyte, but if an organic solvent solution or aqueous solution with high surface tension is used as the electrolyte In particular, water-soluble polymers with good wettability were most suitable.

When this water-soluble polymer is dissolved in the electrolytic solution, it may be made insolubilized by crosslinking. Examples of water-soluble polymers include polyvinyl alcohol, polyethylene oxide, polyethylene glycol, polyvinylpyrrolidone, polyethyleneimide, polyacrylic acid, polyacrylamide, polyvinylamine, and the like.

In order to retain pigments and polymeric substances within the porous space of a porous body, the pigment is dispersed in a polymeric substance solution and then mechanically rubbed or press-fitted into the porous body. Suction from one side or vacuum impregnation may be used. Alternatively, only the pigment may be held in the porous space in the same manner and then impregnated with the polymeric substance solution. Furthermore, the pigment and the low-molecular polymerizable substance may be held in the porous space, and then the polymeric substance may be produced within the porous space by a polymerization reaction of the polymerizable substance. When it is necessary to crosslink and insolubilize a polymeric substance, a crosslinking reaction using a crosslinking agent, irradiation with ionizing radiation, irradiation with plasma, etc. may be used.

The EC display device of the present invention provides a clear display background with a high contrast in the colored state of the EC substance, and can withstand long-term use. The color tone of the display background is not limited to white, but can be arbitrarily colored by selecting the type of pigment, and furthermore, the effect of adding dyes, fluorescent agents, etc. can also be expressed at the same time.

In the EC display device of the present invention, when a halogen-containing polymer or polyolefin is used as the material for the porous body, its strength is particularly high, so it is easy to handle, strong against vibrations, and has chemical resistance against electrolytes. It also has excellent heat resistance and can withstand long-term use without breaking or discoloring. Also, the thickness of the porous body should be set to 0.1 mm, for example.
Even if it is extremely thin as below, it has a great effect as a display background, and the layer thickness of the electrolyte used by impregnating this porous body can be made that thinner, so the amount of electrolyte is small. This also reduces the electrical resistance of the electrolyte layer, which is economically advantageous. The advantage of being able to reduce the thickness also leads to a reduction in the overall thickness of the device, and the EC display device of the present invention is particularly useful as a display device that requires reduction in size and weight. Taking advantage of these features, the EC display device of the present invention can be used for display parts of watches, desk computers, measuring instruments, control panels, road signs, guide boards, and the like.

EXAMPLES The present invention will be explained and illustrated in more detail with reference to Examples below, but the scope of the present invention is not limited by these Examples.

Example 1 Polyvinyl alcohol PVA-217 (manufactured by Kuraray)
The same weight of titanium white pigment Taipei CR-90 (manufactured by Ishihara Sangyo) as the aqueous solution was added to a 2% aqueous solution and uniformly dispersed and mixed. This mixed solution was prepared using polytetrafluoroethylene as a material with an average pore size of 5.0 μm and a porosity of 85
%, mechanically rubbed from both sides of a porous membrane Fluoropore FP-500 (manufactured by Sumitomo Electric) sheet with a thickness of 80 μm.
By drying, a sheet-like porous body containing a white pigment and polyvinyl alcohol in porous spaces was obtained.

This porous body was impregnated with an electrolytic solution of lithium perchlorate dissolved in γ-butyrolactone at a concentration of 1.0 M, and incorporated as an electrolytic solution layer in an EC display device using tungsten oxide as the EC material. this
In EC display devices, the increase in electrical resistance of the electrolyte layer due to the inclusion of a porous material is only a few percent, and when a voltage is applied, it is displayed in blue against a white background.
It was an unprecedentedly clear display. The amount of titanium white pigment retained in the porous material is approximately ^per square meter of sheet area.
A weight of 20 g or more was sufficient to hide the underlying electrodes and provide a white display background.

Furthermore, when a porous material obtained by adding a small amount of fluorescent agent together with a white pigment was incorporated into an EC display device, the whiteness of the display background was even more excellent due to its whitening effect.

Example 2 Titanium yellow pigment Taipei Yellow TY-70 (manufactured by Ishihara Sangyo) was added to a 1% aqueous solution of polyethylene oxide PEO-3 (manufactured by Seitetsu Kagaku Kogyo) in the same weight as the aqueous solution and uniformly dispersed and mixed. This mixed solution is made from polytetrafluoroethylene with an average pore size.
It was mechanically rubbed on both sides of a porous membrane Fluoropore FT-500 (manufactured by Sumitomo Electric) sheet with a size of 5.0 μm, porosity 82%, and thickness 350 μm, sealed with a polyethylene sheet, irradiated with a 6 Mrad electron beam, and then dried. A sheet-like porous body containing yellow pigment and crosslinked polyethylene oxide in porous spaces was obtained. When this porous body was incorporated into an EC display device, it was displayed against a yellow background, giving the same good results as in Example 1.

Claims (1)

[Scope of Claims] 1. An electrolytic solution layer is provided between the electrodes by impregnating a porous body with a pigment and a polymeric material showing wettability to the electrolyte in a porous space and impregnating the electrolyte. An electrochromic display device characterized by: 2. The electrochromic display device according to claim 1, wherein the porous body is made of a halogen-containing polymer. 3. The electrochromic display device according to claim 1, wherein the porous body is made of polyolefin. 4. The electrochromic display device according to claim 1, wherein the polymeric substance is a water-soluble polymer. 5. The electrochromic display device according to claim 1, wherein the polymeric substance is a crosslinked water-soluble polymer.