JPH02141730A - Electrophoretic image display device - Google Patents

Abstract

PURPOSE:To prevent the sepn. of a dispersion medium and dispersion particles over a long period of time by using a liquid contg. the colloidal particles of the metal oxide obtd. by converting the colloidal particles of a hydrophilic metal oxide by a surfactant to a lipophilic property and migrating the same into an org. solvent as a liquid electrophoretic dispersion. CONSTITUTION:Chemical bonding takes place between the part of the positive charge of the colloidal particles of the hydrophilic metal oxide in a hydrosol and the dissociation group of the surfactant and the surfactant chemically absorbs its lipophilic group on the colloidal particles of the metal oxide toward a soln. side when a proper volume of the surfactant is added to the hydrosol. The colloidal particles of the metal oxide, therefore, has the lipophilic property and flocculate. The flocculated colloidal particles migrate into an org. solvent phase when the proper org. solvent is added thereto an the mixture is stirred. The colloidal particles of the metal oxide obtd. in such a manner are dispersed as primary particles and the colloidal particles having 0.03 to 0.3mum grain size are easily obtd. The liquid electrophoretic dispersion which does not generate the sepn. of the dispersion and the particles over a long period of time is utilized in this way and the long-term reliability is greatly improved.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an electrophoretic image display device.

(Prior Art) As shown in FIG. form a space,
This sealed space is filled with an electrophoretic dispersion liquid 4, and is equipped with means (not shown) for applying an electric field to the electrophoretic dispersion liquid, and the transparent substrate serves as a display surface.

An electrophoretic dispersion is a mixture of a solvent as a dispersion medium, colored fine particles as dispersed particles, a dye, a stabilizer, etc. For example, a white pigment Ti as colored fine particles is mixed in xylene.
e. As the dye, a mixture of a blue dye and a surfactant is used.

By applying an electric field to the electrophoretic dispersion filled in the sealed space, the electrophoretic dispersion moves toward the transparent substrate and the color of the particles appears on the display surface. By applying an electric field in the opposite direction, the particles move toward the opposing substrate, and the color of the colored dispersion appears on the display surface.

In this way, electrophoretic image display devices can obtain a desired display by controlling the direction of the electric field, and because the display also has memory properties, it is possible to reduce power consumption and obtain a high-contrast display. .

Although not shown, a method for applying an electric field is a method of applying a voltage between electrodes formed on a pair of substrate surfaces, as shown in Japanese Patent Laid-Open No. 62-34187.
An electrostatic latent image is formed on one substrate surface by a coro ion generator and a write electrode consisting of a control electrode that controls the flow of ions, and an electrostatic latent image is formed between this electrostatic latent image and a transparent electrode on the other substrate surface. A method of generating an electric field, etc. is used.

Since an electrophoretic dispersion liquid consists of a dispersion medium and dispersed particles, there is a problem in that the difference in specific gravity between them causes separation of the dispersion medium and dispersed particles due to sedimentation or flotation, which significantly impairs display quality.

In order to prevent this, there is a method of substantially matching the specific gravity of the dispersion medium and the dispersed particles, as shown in Japanese Patent Publication No. 51-46396, for example.

Another method is to use dispersed particles having a particle size (average particle size, hereinafter the same) of 0.3 μm or less. With particle sizes of this size, the diffusion force due to Brownian motion is greater than that of gravity, resulting in a so-called colloidal solution that can be stably dispersed over a long period of time. Particles having a particle size of 0.03 μm or less are not preferable because they have a low light scattering ability and a low display ability. Therefore, the particle size is preferably about 0.03 to 0.3 μm.

(Problems to be Solved by the Invention) A method for substantially matching the specific gravity of a dispersion medium and dispersed particles disclosed in Japanese Patent Publication No. 51-46396 is such that the temperature coefficient of the specific gravity of a liquid is 1 to 2 digits higher than that of a solid. Since it is an order of magnitude larger, it is extremely difficult to always keep the specific gravity the same considering temperature fluctuations.

Furthermore, even if you try to disperse so-called ultrafine particles with a particle size of about 0.03 to 0.3 μm in a dispersion medium using ordinary dispersion means such as a paint shaker, stirrer, homogenizer, or ultrasonic homogenizer, secondary aggregation occurs. Because of the strength, it was difficult to completely disperse down to the primary particles and obtain a colloidal solution.

The present invention provides an electrophoretic image display device in which a dispersion medium and dispersed particles do not separate for a long period of time.

(Means for Solving the Problems) The present invention provides an electrophoretic dispersion liquid for an electrophoretic image display device that includes (A) a dispersion medium, and (B) a basic aqueous solution added to a metal salt aqueous solution or a metal alkoxide. It is recommended to use a product containing metal oxide colloid particles obtained by converting hydrophilic metal oxide colloid particles obtained by hydrolysis into lipophilic particles using a surfactant and then transferring them into an organic solvent. This is a characteristic feature.

As the metal salt, chlorides, nitrates, etc. of titanium, zirconium, etc. are used.

As the base, sodium hydroxide, aqueous ammonia, ammonium hydrogen carbonate, sodium carbonate, etc. are used.

Titanium tetrabutoxide or the like is used as the metal alkycoside.

When a basic aqueous solution is added to a metal salt aqueous solution or when a metal alkylcoside is hydrolyzed, a hydrosil containing hydrophilic metal oxide colloidal particles is obtained.

When an appropriate amount of a surfactant is added to this hydrosil, a chemical bond occurs between the positive 1-carrying portion of the hydrophilic metal oxide colloid particles in the hydrosil and the dissociative group of the surfactant, and the surfactant is Chemically adsorbed onto the metal oxide colloid particles with the lipophilic groups facing the solution side. Therefore, the metal oxide colloid particles become lipophilic and aggregate. When a suitable aqueous solvent is added and stirred, the metal oxide colloid particles are transferred into the organic solvent phase.

The metal oxide colloid particles thus obtained are dispersed as primary particles, and particles having a particle size of 0.03 to 0.3 μm can be easily obtained.

The metal oxide colloid particles can be used in a dispersed state in a Ja-containing solvent, or the organic solvent can be evaporated to dryness and used as a metal oxide powder.

As the surfactant, almost any surfactant can be used as long as it is soluble in water, but sodium dodecylbenzenesulfonate, sodium dioctylsulfosuccinate, etc. are preferred.

Examples of organic solvents include toluene, xylene, cyclohexane, benzene, n-hexane, carbon tetrachloride, and n-hexane, which are insoluble in water.
- Pentane etc. can be used.

As a dispersion medium for the electrophoretic dispersion liquid, xylene, halogenated hydrocarbon, paraffin such as hexane, etc. are used.

Example 1 While stirring 100 ml of a T t C1a aqueous solution with a concentration of 1 m o 1/1, 100 ml of a Nag CO3 aqueous solution with a concentration of 1.25 mol/1 was slowly added, and the mixture was left stirring for 30 minutes to reduce the particle size to about 50 nm. A colloidal solution of hydrophilic Tie was obtained.

Next, in order to convert it into a lipophilic colloidal solution, an aqueous solution (concentration of 0.10 mol/j) of sodium dodecylbenzenesulfonate (hereinafter abbreviated as DBS) as a surfactant was added until the colloid particles were completely aggregated. D-
The amount of BS aqueous solution is 160ml! Met. After adding 100 ml of xylene to this and stirring thoroughly, it was left standing for one day and night. This operation moved the colloidal particles into xylene.

The xylene in which the colloidal particles were dispersed was taken out.

10 ml of Kounouchi was collected, and 300 mg of the dye Macrolex Blue RR (manufactured by Bayer AG) was added thereto to prepare a dispersion liquid 1. Another 10mj! The product was fractionated and xylene was distilled off under reduced pressure to obtain a Tie powder. This powder is D
Dry for 30 minutes at 180℃, which is below the decomposition temperature of BS.
After removing the water molecules hydrated with rOz, it was dispersed in 10 ml of xylene, and 300 mg of Microlex Blue RR was added as a dye to prepare a dispersion liquid 2.

Element 1.2 was prepared by injecting the dispersion liquid 1.2 into an electrophoresis cell prepared by adhering two glass substrates with transparent conductive films using a 100IIH polyethylene phthalate film as a spacer. these elements at 0.5 Hz
As a result of measuring the characteristics when driven with a bipolar pulse of voltage 50V and duty of 50%, the response speed was 9.
0.60m5ec.

The contrast is 4.5.5.1, respectively, and the conduction current is 3.2X10-'A/crt, respectively! , 5.6XIO-
“It was A/crrl.

Further, as a result of leaving these elements for one month, no phase separation such as sedimentation or floating was observed.

Example 2 0.3 mol/j in 100 ml of an ethanol solution of titanium tetrabutoxide with a concentration of 0.1 m o I/1
After mixing 100 ml of an ethanol solution of water with a concentration of I and stirring for 5 minutes, HCI was added dropwise until the pH reached 3.85. As a result, a colloidal solution of water-resistant Tie with a particle size of about 1100 nm was obtained.

Next, in order to convert it into a lipophilic colloidal solution, sodium dioctyl sulfosuccinate was added as a surfactant until the colloid particles aggregated, and the ethanol was evaporated in a dryer, followed by heat treatment at 150°C for hr to hydrate. The water molecules present were removed. T i O obtained in this way,
A dispersion liquid was prepared by dispersing 1 g of the particles in 10 ml of xylene and adding 300 mg of Microlex Blue as a dye. Using this dispersion, we created an electrophoresis cell similar to the one before and measured its characteristics, and found that the response speed was 135 m5ec.
, contrast 8.5, conduction current 2.8 x 10A
/crd. Moreover, no phase separation such as sedimentation or flotation was observed even after leaving it for one month.

(Effects of the Invention) According to the present invention, an electrophoretic dispersion liquid in which separation of particles from the dispersion liquid does not occur for a long period of time can be used, and the long-term rental property of an electrophoretic image display device can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an electrophoretic image display device. Explanation of No. 6-1, 2 Substrate 3 Spacer 4 Electrobed dynamic dispersion liquid

Claims (1)

[Claims] 1. A sealed space is formed by arranging two substrates, at least one of which is transparent, facing each other with a required distance between them via a spacer;
In an electrophoretic image display device that is equipped with means for filling this sealed space with an electrophoretic dispersion liquid and applying an electric field to the electrophoretic dispersion liquid, the electrophoretic dispersion liquid is (A) a dispersion liquid, and (B). ) Hydrophilic metal oxide colloidal particles obtained by adding a basic aqueous solution to a metal salt aqueous solution or by hydrolyzing a metal alkoxide are converted to lipophilic by a surfactant, and then transferred into an organic solvent. Particle size obtained by
An electrophoretic image display device comprising metal oxide colloid particles of 0.3 μm.