JPH01248182A - Electrophoretic display device - Google Patents

Abstract

PURPOSE:To stably maintain the effect of preventing sticking of electrophoretic particles over a long period of time by providing thin film layers consisting of fluoroplastic on the electrode pattern surfaces of an electrode plate. CONSTITUTION:The thin film layers 8 consisting of the fluoroplastic are provided on the electrode pattern surfaces 2, 4 of the electrode plate. Such thin film layers 8 consisting of the fluoroplastic can be formed by chemically and securely bonding said layers to the electrode surfaces by using a fluorosilane coupling agent and the thicknesses thereof are formed <=several 100Angstrom , more preferably <=100Angstrom thickness. Such treatment structure on the electrode surfaces can be easily formed on the electrode surfaces stably to the required thickness without being affected by the various sizes of the display region and has the exceptionally high effect of preventing the sticking of the electrophoretic particles. The degradation in the contrast and the unequal display, etc., are adequately prevented by combination use of the treating means and porous spacers for division of the dispersion system. The electrophoretic display device having a long life and good operation stability is thus obtd.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a display device using electrophoretic particles, and more specifically, to forming a thin fluororesin layer on the surface of a display driving electrode. The present invention relates to an electrophoretic display device that can maintain good contrast by preventing electrophoretic particles from adhering to the electrode surface.

"Prior art" This type of electrophoretic display device using electrophoretic particles is
As shown in FIG. 3, two transparent glass plates 1 each have a required display electrode pattern 2.4 formed on their opposing surfaces using a suitable transparent conductive material such as indium tin oxide.
．． 3, and a sealing member 6 which also serves as a spacer is disposed on the outer periphery in order to encapsulate a dispersion system 5 formed by dispersing electrophoretic particles in a liquid dispersion medium into the gap between the opposing sides. A voltage for display driving is applied to the N-pole pattern 2.4 to move electrophoretic particles to the electrode pattern 2.4.
By applying an electric field to the dispersion system 5 to change the distribution state of the electrophoretic particles so that they can be adsorbed and separated from the electrophoretic particles 4, the optical characteristics of the dispersion system 5 are changed to perform a desired display operation. .

When the dispersion system 5 is enclosed in a continuous phase with the sealing member 6 provided at the end as described above, the dispersion system 5 may be enclosed in a continuous phase due to unevenness in the electric field strength due to uneven spacing between the electrode patterns 2, 4, etc. The electrophoretic particles move in a direction parallel to the electrode pattern surface, causing a bias in the concentration distribution of the electrophoretic particles. Therefore, if this electrophoretic display device is used repeatedly for a long time, the concentration of the electrophoretic particles may become uneven in some places. There is a problem that the display becomes uniform and display unevenness occurs. Therefore, as a means to solve the above-mentioned disadvantages, as shown in FIG. Structures in which the phase is divided into small sections into discontinuous phases are also known.

Such electrophoretic display devices have been intensively researched due to their characteristics such as wide viewing angle, long-term memory, and low power consumption, but they are mainly due to the dispersibility of electrophoretic particles in liquid dispersion medium. There are many studies related to the stabilization of distributed systems, and as a result of these studies, memory performance, response speed, lifespan, etc. are considered. However, studies on the dispersibility of electrophoretic particles, the stability of the dispersion system, etc. alone are insufficient to increase the overall lifespan of electrophoretic display devices. For example, even in the case of a split-type electrophoretic display device in which the dispersion system is configured using a porous spacer as described above (in a discontinuous split type with small sections), the electrode pattern Electrophoretic particles gradually adhere to the display, resulting in a decrease in contrast, making it impossible to demonstrate its original performance as an electrophoretic display, and studies regarding the treatment of the electrode surface have not yet been sufficient.

That is, in the electrode pattern 2.4, a transparent conductive film such as indium tin oxide is used as a NES film, but all such conductive films are metal oxides, and their surface tension is extremely large, and therefore, even for electrophoretic particles such as pigment particles, which have a steric aggregation prevention function using a surfactant, their steric structure is destroyed by collision of the electrophoretic particles against the electrode pattern surface every time a display operation is performed due to the action of an electric field. Therefore, it is not easy to prevent electrophoretic particles from adhering to the electrode pattern surface.

Therefore, as a method to prevent electrophoretic particles from adhering to the electrode pattern surface, an organic layer made of a polyimide thin film with a thickness of 50 Å or less is formed on the electrode pattern surface.
The electrophoretic particles used are pure titanium oxide without surface treatment, and a repulsive force is created between the hydrophilicity of the surface of the pure titanium oxide and the hydrophobicity of the thin organic layer of polyimide. There is a technique disclosed in Publication No. 59-171931.

``Problems to be Solved by the Invention'' However, in the above-mentioned means for preventing the adhesion of electrophoretic particles to the surface of an electrode pattern, the organic solution made of polyimide is coated using a spinner at high speed. It is quite difficult to stably form the electrode pattern, and the coating process on the surface of the electrode pattern having a large display area becomes even more difficult. In addition, since it is necessary to use pure titanium oxide without surface treatment as electrophoretic particles, it is essential to mix several types of surfactants in order to control the charge of titanium oxide and stabilize its operation. However, even with such a structure, the effect of preventing electrophoretic particles from adhering to the display decreases after about 10,000 display changes, and even when compared with the conventional structure, it cannot be said to be remarkable.

[Means for Solving the Problems] The present invention provides an electrophoretic method that can suitably eliminate the situation in which contrast is reduced due to the adhesion phenomenon of electrophoretic particles to the electrode pattern surface as described above, and can satisfactorily increase the display life. The present invention provides a display device.

Therefore, according to the present invention, a dispersion system containing electrophoretic particles is sealed between a pair of opposing electrode plates, at least one of which is transparent, via a spacer, and a display driving voltage is applied to both types of electrode plates. In an electrophoretic display device that performs a desired display operation by adsorbing and separating the electrophoretic particles to the transparent electrode plate side under the action of It is constructed in such a way that layers are provided. Such a thin film layer of fluororesin can be formed by chemically bonding firmly to the electrode surface using a fluorosilane coupling agent, and its thickness is several hundred Å or less, preferably 100 Å. It is formed below.

Such a treatment structure for the electrode surface can be easily formed on the electrode surface in a stable manner to the required thickness regardless of the size of the display area, and is more effective in preventing electrophoretic particles from adhering than conventional structures. Furthermore, by combining such treatment means with a porous spacer for dividing the dispersed system, reduction in contrast and display unevenness can be suitably prevented, resulting in a long service life. It is possible to provide an electrophoretic display device with good operational stability.

"Function" The fluorine resin thin film layer suitably lowers the surface tension of the electrode surface and prevents electrophoretic particles from adhering to it, while the thickness of the fluorine resin thin film layer is preferably several hundred angstroms or less. By forming the electrode pattern to a thickness of 100 Å or less, it is possible to reliably perform the required electrophoretic display operation without impairing the transparency and conductivity of the electrode pattern.

"Example" Hereinafter, the electrophoretic display device according to the present invention will be described in more detail with reference to the example shown in the drawings. In FIG. 1, 1 and 3 are transparent glass plates, 2 and 4 are transparent glass plates, Required electrode patterns are formed separately on the opposing surfaces using transparent conductive materials such as indium tin oxide, and 6 is an end sealing member which is sealed in the gap between the picture electrode patterns 2 and 4. The system 5 can be configured as a wide continuous phase as it is, or can be divided into small sections of a discontinuous phase by using a porous spacer 7 having a large number of through holes. Reference numeral 8 indicates a thin film layer of a fluororesin made of a fluorosilane coupling agent formed on the surface of each electrode pattern 2.4, and the thickness thereof is several hundred Å or less, preferably 100 Å or less.

- In the example, a transparent glass plate 1.3 on which an electrode pattern 2.4 was formed with indium tin oxide was coated with 2% of a fluorosilane coupling agent represented by the general formula % as shown in FIG. After chemically bonding the fluororesin thin film layer 8 on the surface of each electrode pattern 2.4 by immersing it in a methanol solution 9 for about 30 minutes, it is heat-treated at 140°C for 1 hour to form a layer with a thickness of about 30-40°C.
Human thin layer 8. I got it.

The inter-electrode gap of the surface-treated electrode was maintained at 90 μm, and a dispersion system prepared using 40 cc of toluene, 2 g of titanium #, 0.4 g of surfactant, and 0.7 g of blue dye was placed between the electrodes. After encapsulating, it will be displayed on for 1 second,
When we repeated a display test using a rectangular wave drive voltage of ±100V with the off display for the next 1 second, no titanium oxide adhered to the electrode pattern and no decrease in contrast was observed even after 10' continuous switching operations. Ta. For comparison, a similar repeated display test was conducted on electrodes without the above-mentioned electrode surface treatment, and the result was 105.
At the stage of continuous switching operations, titanium oxide began to adhere to the electrode pattern, and a decrease in contrast was observed.

Therefore, it was confirmed that the fluororesin thin film layer on the electrode surface had a significant display life promoting effect.

The sealing member 6 can be formed into a desired shape using various sheet materials such as film materials, or an epoxy resin adhesive in which particles of alumina, silica, etc. having a relatively uniform particle size are dispersed.

In addition, when the dispersion system 5 is configured to be divided into small sections into discontinuous phases, the porous spacer 7 for this purpose is as follows:
In addition to swellable materials that can be appropriately composed of rubber members such as silicone rubber and fluorine-based rubber, it is also suitable to use various polymers with shape memory functions such as transpolyisoprene rubber, nobornene-based polymers, or ethylene-propylene-based synthetic rubbers. be.

When forming the porous spacer 7 using a shape memory member, after the dispersion system 5 is injected, the porous spacer 7 is formed by heating means such as heat or by applying an external stimulus such as ultraviolet rays. By restoring the thickness of the dispersion system 5, it is possible to construct a dispersion system 5 divided into small sections in the form of a discontinuous phase. Such a porous spacer 7 can be formed directly on one electrode pattern 2 by screen printing or spraying using the previously described shape memory polymer so that a large number of through holes can be formed. , or after forming a large number of required through-holes by punching or drilling using a sheet of silicone rubber, etc., the thickness is reduced to less than the required gap for handling as a conductive electrode by means such as hot pressing. It can be shaped as desired.

The shape of each through hole of the porous spacer 7 can be arbitrarily determined, such as a square shape, a slit shape, a circular shape, a rectangular shape, a polygonal shape, etc., and the arrangement thereof can also be provided regularly or irregularly. Can be done. The thickness of the porous spacer 7 can be appropriately selected in consideration of the recovery rate of the swellable material used, such as silicone rubber or shape memory polymer, the composition of the dispersion medium, the gap between the two electrode plates, etc. Yes, but generally 20μm to 1mm
It can be determined according to the degree.

As the electrophoretic particles used in the dispersion system 5, in addition to various well-known colloidal particles, various organic/inorganic pigments, dyes, metal powders, fine powders of glass or resin, etc. can be appropriately used. In addition, as a dispersion medium for the dispersion system, in addition to water, alcohols, hydrocarbons, halogenated hydrocarbons, etc., various natural or synthetic oils can be optionally used6. electrolytes and surfactants,
In addition to metal soap, in addition to a charge control agent consisting of particles of resin, rubber, oil, varnish, compound, etc., dispersants, lubricants, stabilizers, etc. can be appropriately added according to conventional methods. Furthermore, the charges of electrophoretic particles can be unified to positive or negative,
In addition to the means for increasing the Zeke potential and the means for uniformly stabilizing dispersion, it is also possible to appropriately adjust the adsorption of electrophoretic particles to the transparent electrode pattern 2.4 and the viscosity of the dispersion medium.

"Effects of the Invention" As described above, the electrophoretic display device according to the present invention is configured such that a thin film layer of fluororesin made of a fluorosilane coupling agent is provided on the electrode pattern surface of the electrode plate. It is possible to provide an electrophoretic display device with excellent display life by suitably lowering the surface tension of the surface to prevent adhesion of electrophoretic particles while maintaining good contrast.

Since the fluororesin thin film layer can be chemically bonded thinly and firmly to the electrode pattern surface, it is possible to significantly improve the durability of long-term display operation without impairing transparency and conductivity.

It is not affected by the size of the display area (a thin film layer of fluororesin can be uniformly formed on the surface of the electrode pattern to the required thickness, so it is suitable for large-area display devices, and electrophoretic particles The anti-adhesion effect can be stably maintained over a long period of time.

By using the above-mentioned electrode bag surface treatment structure and a porous spacer in combination, an electrophoretic display device with even better contrast and high characteristics can be provided.

[Brief explanation of the drawing]

FIG. 1 is a conceptual cross-sectional diagram of essential parts of an electrophoretic display device according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of bonding a thin film layer of fluororesin to an electrode pattern surface by a chemical method. , Fig. 3 is a conceptual cross-sectional diagram of main parts of a conventional dispersion type continuous phase electrophoretic display device, and Fig. 4 shows a conventional dispersion type segmented electrophoretic display device equipped with a porous spacer. It is a conceptual main part cross-sectional configuration diagram. ■, 3: Transparent glass plate 2.4: Electrode pattern 5: Dispersion system 6: End sealing member 7: Porous spacer 8: Fluorine resin thin film layer 1 Fig. λ 2 Fig. 3C No. 40 (1

Claims (4)

[Claims] (1) A dispersion system containing electrophoretic particles is enclosed between a pair of opposing electrode plates, at least one of which is transparent, via a spacer, and the electrophoretic particles are placed under the action of a display driving voltage applied to both electrode plates. In an electrophoretic display device in which a desired display operation is performed by attracting and separating a substance from the transparent electrode plate side, a thin film layer of fluororesin is provided on the electrode pattern surface of the electrode plate. An electrophoretic display device featuring: (2) The electrophoretic display device according to claim 1, wherein the fluororesin thin film layer is a fluorosilane coupling agent. (3) The electrophoretic display device according to claim (2), wherein the fluororesin thin film layer is formed to have a thickness of 100 Å or less. (4) The electrophoretic display device according to any one of the preceding claims, wherein the spacer comprises a porous spacer that divides the dispersed system into small sections of a discontinuous phase.