JPH03249737A - Display liquid for electrophoresis display device and electrophoresis display device using the same - Google Patents

Abstract

PURPOSE:To obtain the long-life display liquid which can keep dispersing fine particles without separating these particles from a dispersion medium in the display liquid for a long period of time by using the fine particles which are treated with a coupling agent having a long chain alkyl group on the surfaces. CONSTITUTION:The fine particles which are treated with the coupling agent having the long chain alkyl group on the surface are used in the display liquid for the electrophoresis display device consisting of the fine particles and the dispersion medium varying in color therefrom. The fine particles are exemplified by titanium dioxide, etc., as the fine particles indicating white, chromium yellow, etc., as the fine particles indicating yellow, molybdate orange, etc., as the fine particles indicating orange, red oxide, etc., as the fine particles indicating red, mangenese violet, etc., as the fine particles indicating purple, ultramarine, etc., as the fine particles indicating blue, emerald green, etc., as the fine particles indicating green, and carbon black, etc., as the fine particles indicating black. The long-life display liquid which can keep dispersing the fine particles without separating the same from the dispersion medium is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a display liquid for an electrophoretic display device and an electrophoretic display device using the display liquid.

(Prior Art) In an electrophoretic display device, two substrates, at least one of which is transparent, are arranged facing each other with a required distance between them via a spacer to form a sealed space, and fine particles of different colors are placed in this sealed space. Display liquids dispersed in different dispersion media are filled to form a display panel, and an electric field is applied to this display panel to obtain a display, and the transparent substrate surface serves as the display surface.

The display liquid for electrophoretic display devices that is filled in the sealed space contains a dispersion medium such as xylene or isoparaffin, fine particles such as titanium dioxide, a dye to provide a color contrast with the fine particles, a dispersant such as a surfactant, and the like. Consists of additives such as charge-imparting agents.

By applying an electric field to this display liquid, the fine particles in the display liquid move toward the transparent plate, and the color of the fine particles appears on the surface. By applying an electric field in the opposite direction to this, the fine particles move to the back side and the color of the dispersion medium appears on the surface.

In this way, electrophoretic display devices can obtain a desired display by controlling the direction of the electric field, the display liquid is made of relatively easily available and low-cost materials, and the viewing angle is as wide as that of ordinary printed matter. Since it has low power consumption and has memory properties, it is attracting attention as an inexpensive display device.

In addition, as a means of adding electric fields of the electronic swimming display device, the method of applying a voltage between the electrodes formed on the pair of substrate surface, the colonion generator and this ion shown in the Special Opening 62-34187. There is a method in which an electrostatic latent image is formed on one substrate surface using a write electrode consisting of a control electrode that controls the flow of the liquid, and an electric field is generated between this electrostatic latent image and a transparent electrode on the other substrate surface. used.

As fine particles in a display liquid for an electrophoretic display device, an inorganic pigment with a high refractive index such as titanium dioxide is generally used.

A dispersant such as an ionic surfactant is added to disperse these inorganic pigments in the display liquid without separating them from the dispersion medium.

(Problems to be Solved by the Invention) These inorganic pigments have a very large difference in specific gravity from the dispersion medium in the display liquid and will separate due to sedimentation. The amount of ionic surfactant added must be increased.

However, especially in an electrophoretic display device that applies an electric field using charging of corona ions, the electric field is applied through the insulating substrate on the back side, so the conductivity of the display liquid must be made low. Therefore, the amount of ionic surfactant added must be as small as possible.

The present invention provides a long-life display liquid in which fine particles can continue to be dispersed in the display liquid for a long period of time without being separated from the dispersion medium, and an electrophoretic display device using this display liquid.

(Means for Solving the Problems) The present invention provides a display liquid for an electrophoretic display device consisting of fine particles and a dispersion medium of a different color. It is characterized by its use.

The fine particles used in the present invention include inorganic pigments such as titanium dioxide and zinc oxide that exhibit white color, and inorganic pigments such as chrome yellow cadmium yellow that exhibit yellow color, insoluble azo compounds such as Fast Yellow, and chromophthal. Condensed azo compounds such as yellow,
Organic pigments such as azo complex salts such as benzimidacylon azo yellow, condensed polycyclics such as flavance yellow, and nitro compounds such as naphthol yellow, as well as inorganic pigments such as molybdate orange, benzimidasilone, etc. Organic pigments such as azo complex salts such as Dacylon Azo Orange and condensed polycyclics such as Perinone Orange, inorganic pigments such as Benkara, Cadmium Red, dyeing lakes such as Madarake, and Lake Red. Organic pigments such as soluble azo compounds such as Naphthol Red, insoluble azo compounds such as Naphthol Red, condensed azo compounds such as Chromophthal Scarlet, condensed polycyclics such as Thioindigo Bordeaux, etc., and manganese violet etc. Inorganic pigments such as dye lakes such as rhodamine lake, and organic pigments such as condensed polycyclics such as dioxazine violet, as well as inorganic pigments such as navy blue and ultramarine blue, phthalocyanines such as phthalocyanine blue, alkali blue, etc. Organic pigments that exhibit green color include inorganic pigments such as emerald green, azo complex salts such as nickel azo yellow, phthalocyanines such as phthalocyanine green, and nitroso compounds such as pigment green. Examples include inorganic pigments such as carbon black and iron black, and organic pigments such as aniline black. These pigments can be used alone or in combination of two or more. The fine particles only need to be opaque.

Coupling agents having long-chain alkyl groups include propyltrimethoxysilane, butyltrimethoxysilane,
Alkoxysilanes such as hexyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, octadecyltrimethoxysilane, propyldodecyltrichlorosilane, butyltrichlorosilane, hexyltrimethoxysilane, decyltrichlorosilane, Chlorosilanes such as dodecyltrichlorosilane, hexadecyltrichlorosilane, octadecyltrichlorosilane, trifluoropropyltrimethoxysilane, trifluoropropyltrichlorosilane, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltrichlorosilane, heptadecafluorodecyltrichlorosilane Fluorosilanes such as methoxysilane, heptadecafluorodecyltrichlorosilane, isopropyl triisostearoyl titanate,
Examples include titanates such as isopropyltrioctanoyl titanate. These coupling agents can be used alone or in combination of two or more.

By treating the fine particles with a coupling agent, a coating layer of the coupling agent is formed on the surface of the fine particles.

It is desirable that the treatment amount of the coupling agent having a long-chain alkyl group be equal to or larger than the specific surface area of the fine particles.

When the amount of the coupling agent treated is less than the specific surface area of the fine particles, the dispersibility of the fine particles treated with the coupling agent is comparable to that of the untreated fine particles, and no significant improvement is observed. Methods for treating fine particles with a coupling agent include: a dry method in which a coupling agent solution is sprayed with dry air or nitrogen gas while the particles are forcibly stirred with a blender, etc., a dry method in which the particles are dispersed in water or a solvent, and the particles are dispersed in a slurry state. Examples include a wet method in which a coupling agent solution is added to the heated particles, a spray method in which a coupling agent solution is sprayed while vigorously stirring particles that have been heated in advance, and there are no particular limitations.

As a dispersion medium having a color different from that of the fine particles, a highly insulating organic solvent in which a dye having a color different from that of the fine particles is dissolved is used.

Here, as the dye, an oil-soluble dye that can be dissolved in an organic solvent is used.
Azo compounds such as (trade name manufactured by Orient Chemical Co., Ltd.)
First Orange G (BASF
Azo compounds such as Oil Red 5B (trade name manufactured by Orient Chemical Co., Ltd.) show a red color, while oil violet #730 (trade name manufactured by Orient Chemical Co., Ltd.) shows a purple color. ), anthraquinones such as Macrolex Blue RR (product name manufactured by Bayer) are blue-colored, and anthraquinones such as Sumiplast Green G (product name manufactured by Sumima Kagaku Co., Ltd.) are green-colored. Among anthraquinones, azo compounds such as Oil Brown GR (trade name, manufactured by Orient Chemical Co., Ltd.) exhibit a brown color, and azo compounds such as Sudan Black X60 (trade name, manufactured by BASF Corporation) exhibit a black color. It is mentioned as a typical example.

Examples of highly insulating organic solvents with low conductivity include benzene,
Aromatic hydrocarbons such as toluene, xylene, and naphthenic hydrocarbons, aliphatic hydrocarbons such as hexane, cyclohexane, kerosene, and paraffin hydrocarbons, and halogenated compounds such as chloroform, trichloroethylene, trichlorotrifluoroethylene, and ethyl bromide. Examples include hydrocarbons. These organic solvents can be used alone or in combination of two or more.

In some cases, in order to supplement the dispersibility of the fine particles in the dispersion medium, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, etc. that can be dissolved in the dispersion medium may be used. Dispersants such as fluorosurfactants, block polymers, and graft polymers can be used alone or in combination of two or more.

As an example of an electrophoretic display device using such a display liquid, FIG. 1 shows a cross-sectional view of an electrophoretic display device that utilizes charging of corona ions. The transparent substrate 1 has length and width of 500 mm,
It is a glass plate with a thickness of 3 mm, and a transparent conductive film 2 is formed over the entire surface on one side. A polyethylene terephthalate film with a thickness of 100 μm is used as the back substrate 4, and is placed opposite to the transparent substrate 1 by adhesive fixation via a spacer 3 to form a space 5. After filling this space 5 with the display liquid for an electrophoretic display device of the present invention, the space 5 is sealed to obtain an electrophoretic display panel.

On the other hand, the gold-plated tungsten wire (corona wire) 7,
Corona ions generated by applying a positive or negative voltage of about 3 to 10 KV are controlled by the control electrode 8, and the ions are selectively charged on the back substrate 4 of the electrophoretic display panel to form an electrostatic latent image 9. to form. An electric field is generated between the charged part of the ions and the transparent electrode 2, whereby the fine particles in the display liquid move toward the transparent substrate, and the color of the fine particles appears on the surface. Since no electric field is generated in the uncharged portion of the ions, the color of the dispersion medium appears on the surface.

In this way, an image corresponding to the electrostatic latent image 9 formed on the rear substrate 4 is formed on the transparent substrate. When an electric field in the opposite direction is applied, the particles that had been moving toward the transparent substrate move toward the back substrate, so the image formed on the transparent substrate disappears and the entire surface becomes the color of the dispersion medium. In this way, the electrophoretic display device can obtain a desired display by controlling the direction of the electric field.

Formation of such an electrostatic latent image is described in Japanese Patent Application Laid-Open No. 62-34187.
A writing electrode consisting of a corona ion generator shown in the above publication and a control electrode for controlling the flow of the ions can be used.

The present invention will be explained below with reference to Examples.

The characteristic values in the following examples were measured by the following method.

(1) Reaction rate of coupling agent The solution after the surface treatment was subjected to solid-liquid separation at 3000 rpm for 15 minutes using a tabletop centrifuge (CT5DL model, newly manufactured by Hitachi), and then passed through a 0.2 μm filter to remove the supernatant liquid. was fractionated. Column: 5ilicone using a gas chromatograph (G-3000 type, newly manufactured by Hitachi)
DC55010%/Unipoint HP, injection temperature: 220°C, oven temperature: 220°C, detection temperature = 22
The amount of coupling agent (unreacted amount) in this supernatant liquid was measured at 0° C., and the ratio to the initial treated amount (used amount) was calculated as the reaction rate.

(2) Dispersibility (average particle size) The display liquid of the present invention was diluted approximately 200 times, the particle size distribution was measured using a submicron particle analyzer (model N4, manufactured by C0ULTER), and the average particle size was calculated from this. Calculated.

Example 1 34 g of titanium tetraisobutoxide was weighed into a No. 11 beaker containing 500 ml of isopropyl alcohol, and sufficiently dissolved and mixed using a magnetic stirrer. 5.4 g of distilled water was added to this mixed solution, and stirring was continued for one day at room temperature to obtain a suspension containing titanium dioxide fine particles having a particle diameter of 400 nm. This suspension was centrifuged at 3000 r using a tabletop centrifuge (CT5DL model, newly manufactured by Hitachi).
pm, solid-liquid separation was performed for 15 minutes, and the precipitate was heated at 100°C for 15 minutes.
Approximately 8 g of titanium dioxide fine particles were obtained by vacuum drying for hours.

100 m of isopropyl alcohol in a 200 m beaker
l% Octadecyltriethoxysilane (Product name: T
0.682 g (SL8185, manufactured by Toshiba Silicone ■) and 0.098 g of distilled water were weighed out and stirred for about 15 minutes, then 1 g of the above titanium dioxide fine particles was added, and stirring was continued for 1 hour at room temperature. As a result of measuring the unreacted amount of the coupling agent in this solution, it was below the detection limit of a gas chromatograph, indicating that almost 100% of the coupling agent had reacted. This solution was mixed using a tabletop centrifuge (CT5DL model, newly manufactured by Hitachi) for 3
Solid-liquid separation was performed at 000 rpm for 15 minutes, and the precipitate was
Approximately 1 g of surface-treated titanium dioxide fine particles were obtained by vacuum drying at 0° C. for 1 hour. IR of this fine particle
As a result of measuring the spectrum, as shown in FIG. 2, a characteristic peak (indicated by an arrow in the figure) of the coupling agent used was observed.

Add 0.2 g of surface-treated titanium dioxide fine particles to 10 ml of isoparaffinic hydrocarbon (trade name: Isoba G1 manufactured by Exxon Chemical Co., Ltd.), and add it to 10 ml of isoparaffinic hydrocarbon (product name: Isoba G1 manufactured by Exxon Chemical Co., Ltd.).
A dispersion liquid was prepared by mixing for 10 minutes using a Nippon Seiki Seisakusho (model 300, new model). The average particle diameter of this dispersion was measured and found to be 505 nm. In addition, this dispersion liquid is 1
Even after leaving it for a week, no clear supernatant portion was formed.

In addition, isoparaffinic hydrocarbons (product name: Isopa G
1 (manufactured by Exxon Chemical) 10ml with di2 as a charge imparting agent.
- 10 mg of sodium ethylhexyl sulfosuccinate (manufactured by Tokyo Kasei Kogyo ■, hereinafter abbreviated as AOT) and anthraquinone blue dye (trade name: Macrolex Blue RR,
After thoroughly dissolving and mixing, 0.2 g of titanium dioxide fine particles subjected to the above surface treatment were added and mixed and dispersed for 10 minutes with an ultrasonic homogenizer (model US-300, manufactured by Nippon Seiki Seisakusho). , a display liquid was prepared.

On the other hand, a Pyrex glass plate with a thickness of 3 mm was used as a transparent substrate, and a transparent conductive film (ITO film) was formed on one side of the plate. A polyethylene terephthalate film with a thickness of 100 μm was used as the back substrate, and an epoxy resin adhesive (product name: Araldite) was attached to the transparent substrate via nylon beads (product name: 5P-500, manufactured by Toshi ■) used as spacers. Rapid (manufactured by Ciba Geigy) were used to bond them in a facing arrangement to form spaces at intervals of about 100 μm. Fill this space with the display liquid prepared above using a syringe, and seal the open part of the border between the transparent substrate and the back substrate with an epoxy resin adhesive (product name: DP-110, Jujutsu 3M side leg). An electrophoretic display panel was prepared by stopping the process. A corona ion generator using a gold-plated tungsten wire and a write electrode consisting of a control electrode that controls the flow of these ions selectively charge ions onto the back substrate of the electrophoretic display panel to create an electrostatic latent image. When this is formed, the titanium dioxide fine particles in the corresponding portions electrophores toward the transparent substrate, resulting in a clear white display on the transparent substrate that is identical to the electrostatic latent image formed on the back substrate. Obtained.

Additionally, the number of rewrites possible has been significantly increased, making it possible to extend the lifespan.

Example 2 100ml of isopropyl alcohol in a 200ml beaker
．． Octadecyldimethyl [3-(trimethoxysilyl)]
propyl] ammonium chloride (product name: AY43
Weigh out 0.127 g of 0.121 (manufactured by Tou μ Silicone ■) and 0.014 g of distilled water, stir for about 15 minutes, and then 1 g of the titanium dioxide fine particles obtained in Example 1 before surface treatment.
was added and stirring was continued for 1 hour at room temperature. Regarding this solution, the reaction rate of the coupling agent was calculated by the above method, and as a result, 86% of the treated amount was reacted. This solution was mixed using a tabletop centrifuge (model CT5DL, newly manufactured by Hitachi).
Solid-liquid separation was performed at 3000 rpm for 15 minutes, and the precipitate was
Approximately 1 g of surface-treated titanium dioxide fine particles were obtained by vacuum drying at 00° C. for 1 hour.

Add 0.2 g of surface-treated titanium dioxide fine particles to 10 ml of isoparaffinic hydrocarbon (product name: Isoba G1 manufactured by Exxon Chemical Co., Ltd.),
-300 model, manufactured by Nippon Seiki Seisakusho Co., Ltd.) for 10 minutes to prepare a dispersion liquid. The average particle diameter of this dispersion was measured and found to be 531 nm. Moreover, even if this dispersion was allowed to stand for one week, no transparent supernatant portion was formed.

In addition, isoparaffinic hydrocarbons (product name: Isoba G
1 exon chemical side leg) di2 as a charge imparting agent to 10 ml.
- 10 mg of sodium ethylhexyl sulfosuccinate (manufactured by Tokyo Kasei Kogyo ■, hereinafter abbreviated as AOT) and anthraquinone blue dye (trade name: Macrolex Blue RR,
After thoroughly dissolving and mixing, 0.2 g of titanium dioxide fine particles subjected to the above surface treatment were added and mixed and dispersed for 10 minutes with an ultrasonic homogenizer (model US-300, manufactured by Nippon Seiki Seisakusho). , a display liquid was prepared.

As a result of fabricating an electrophoretic display device using these display liquids in the same manner as in Example 1 and examining its display characteristics, it was found that a clear and clear white display was obtained on the transparent substrate, and furthermore, the number of times it could be rewritten was reduced. It was found that the performance was significantly improved, making it possible to extend the lifespan.

Example 3 In a 200 ml beaker, 100 ml of isoparaffinic hydrocarbon (trade name: Isoba G1 manufactured by Exxon Chemical ■) and isopropyl triisostearoyl titanate (trade name: Blenact KRTTS) were added.

Weighed out 0.50 g (manufactured by Ajinomoto) and 0.009 g of distilled water, stirred for about 15 minutes, added 1 g of titanium dioxide fine particles obtained in Example 1 before surface treatment, and incubated at room temperature for 1 hour. I continued to eat. As a result of calculating the reaction rate of the coupling agent for this solution using the above method, it was found that 70% of the throughput amount
was reacting.

Transfer this solution to a tabletop centrifuge (CT5DL model, manufactured by Hitachi, Ltd.)
Solid-liquid separation was performed at 3000 rpm for 15 minutes using
By vacuum drying the precipitate at 160°C for 1 hour, approximately 1
Titanium dioxide fine particles subjected to the surface treatment of g were obtained.

Add 0.2 g of surface-treated titanium dioxide fine particles to 10 ml of isoparaffinic hydrocarbon (trade name: Near Isopa G1 manufactured by Exxon Chemical Co., Ltd.), and add it to 10 ml of isoparaffinic hydrocarbon (trade name: Near Isopa G1 manufactured by Exxon Chemical Co., Ltd.), and add it to 10 ml of isoparaffinic hydrocarbon (trade name: Near Isopa G1 manufactured by Exxon Chemical Co., Ltd.).
A dispersion liquid was prepared by mixing for 10 minutes using a Nippon Seiki Seisakusho (model 300, new model). The average particle diameter of this dispersion was measured and found to be 458 nm. In addition, this dispersion liquid is 1
Even after leaving it for a week, no clear supernatant portion was formed.

In addition, isoparaffinic hydrocarbons (product name: Isoba G
1 (manufactured by Exxon Chemical ■) 10ml as a charge imparting agent,
10 mg of sodium 2-ethylhexylsulfosuccinate (manufactured by Tokyo Kasei Kogyo ■, hereinafter abbreviated as AOT) and anthraquinone blue dye (trade name: Macrolex Blue RR)
After thoroughly dissolving and mixing 100 mg of titanium dioxide fine particles, which had been subjected to the above surface treatment, 0.2 g of titanium dioxide fine particles
was added and mixed and dispersed for 10 minutes using an ultrasonic homogenizer (model US-300, manufactured by Nippon Seiki Seisakusho) to prepare a display liquid. As a result of fabricating an electrophoretic display device using these display liquids in the same manner as in Example 1 and examining its display characteristics, it was found that a clear and clear white display was obtained on the transparent substrate, and furthermore, the number of times it could be rewritten was reduced. It was found that the performance was significantly improved, making it possible to extend the lifespan.

Example 4 Titanium dioxide fine particles 5 obtained in Example 1 before surface treatment
Put g into an aluminum oxide vat and heat it in a Matsufuru furnace (
EP-31 model (manufactured by Yamato Kagaku) was heated to 600°C to produce a 600°C fired product. 100ml of isopropyl alcohol in a 200ml beaker. Weigh out 0.17 g of octadecyltriethoxysilane (trade name: TSL8185, manufactured by Toshiba Silicone ■) and 0.025 g of distilled water, stir for about 15 minutes, and then 1 g of the above 600°C calcined product.
was added and the accumulation was continued for 1 hour at room temperature.

Regarding this solution, the reaction rate of the coupling agent was calculated by the above method, and as a result, 67% of the treated amount was reacted.

Transfer this solution to a tabletop centrifuge (CT5DL model, manufactured by Hitachi, Ltd.)
using 3000 rpm.

Solid-liquid separation was performed for 15 minutes, and the precipitate was vacuum-dried at 100° C. for 1 hour to obtain about 1 g of surface-treated titanium dioxide fine particles.

Add 0.2 g of surface-treated titanium dioxide fine particles to 10 ml of isoparaffinic hydrocarbon (trade name: Isoba G1 manufactured by Exxon Chemical Co., Ltd.), and add it to 10 ml of isoparaffinic hydrocarbon (product name: Isoba G1 manufactured by Exxon Chemical Co., Ltd.).
A dispersion liquid was prepared by mixing for 10 minutes using a Nippon Seiki Seisakusho (model 300, new model). The average particle diameter of this dispersion was measured and found to be 652 nm. In addition, this dispersion liquid is 1
Even after leaving it for a week, no clear supernatant portion was formed.

In addition, isoparaffinic hydrocarbons (product name: Isoba G
1 (manufactured by Exxon Chemical ■) and di2 as a charge imparting agent.
- Ethylhexyl sulfosuccinic acid) (manufactured by Tokyo Kasei Kogyo@)) and 100 mg of anthraquinone blue dye (trade name: Macrolex Blue RR, manufactured by Bayer AG) were added to the solution. After dissolving and mixing, titanium dioxide fine particles subjected to the above surface treatment are added.
2 g was added and mixed and dispersed for 10 minutes using an ultrasonic homogenizer (model US-300, manufactured by Nippon Seiki Seisakusho) to prepare a display liquid. As a result of fabricating an electrophoretic display device using these display liquids in the same manner as in Example 1 and examining its display characteristics, a clear and vivid white display was obtained on the transparent substrate.
Furthermore, it was found that the number of rewrites possible was significantly increased, making it possible to extend the lifespan.

Comparative Example 1 0.2 g of titanium dioxide fine particles obtained in Example 1 before surface treatment were added to 10 ml of isoparaffinic hydrocarbon (trade name: Isoba G1 manufactured by Exxon Chemical Co., Ltd.), and the mixture was heated using an ultrasonic homogenizer (US-300 model, Japan). Seiki Manufacturing Co., Ltd.) for 10 minutes to prepare a dispersion. As a result of measuring the average particle diameter of this dispersion, it was found to be large, approximately 1000 to 3000 nm, and if left for a while, a transparent supernatant part appeared at the top of the solution, and if left for a week, most of the solution became transparent and particles has settled to the bottom.

In addition, isoparaffinic hydrocarbons (product name: Isoba G
1 (manufactured by Exxon Chemical ■), 10 mg of sodium diterethylhexyl sulfosuccinate (manufactured by Tokyo Chemical Industry ■, hereinafter abbreviated as AOT) as a charge imparting agent and anthraquinone blue dye (trade name: Macrolex Blue RR,
After thoroughly dissolving and mixing, 0.2 g of titanium dioxide fine particles before surface treatment were added and mixed and dispersed for 10 minutes using an ultrasonic homogenizer (model US-300, manufactured by Nippon Seiki Seisakusho). A display liquid was prepared. An electrophoretic display device was fabricated using these display liquids in the same manner as in Example 1, and the display characteristics thereof were examined. As a result, a white display was obtained on the transparent substrate immediately after fabrication, but as time passed, particles formed. The white color becomes lighter due to sedimentation,
Particles have accumulated at the bottom of the electrophoresis display panel.

Comparative Example 2 To 10 ml of isoparaffin hydrocarbon (trade name: Isoba G1 manufactured by Exxon Chemical Co., Ltd.) was added 0.2 g of the titanium dioxide fine particles obtained in Example 4 and baked at 600°C before surface treatment, and the mixture was heated using an ultrasonic homogenizer (US- 300, manufactured by Nippon Seiki Seisakusho Co., Ltd.) for 10 minutes to prepare a dispersion liquid. An attempt was made to measure the average particle diameter of this dispersion, but it could not be done because the particles settled immediately after mixing. Therefore,
I tried dispersing again using an ultrasonic homogenizer, but no matter how many times I tried dispersing, the particles immediately settled.

In addition, isoparaffinic hydrocarbons (product name: Isoba G
1 (manufactured by Exxon Chemical ■), 10 mg of sodium diterethylhexyl sulfosuccinate (manufactured by Tokyo Chemical Industry ■, hereinafter abbreviated as AOT) as a charge imparting agent and anthraquinone blue dye (trade name: Macrolex Blue RR,
After thoroughly dissolving and mixing, 0.2 g of titanium dioxide fine particles before surface treatment were added and mixed and dispersed for 10 minutes using an ultrasonic homogenizer (model US-300, manufactured by Nippon Seiki Seisakusho). A display liquid was prepared. An electrophoretic display device was fabricated using these display liquids in the same manner as in Example 1, and its display characteristics were examined. As a result, a slight white display was obtained on the transparent substrate immediately after fabrication.
Sedimentation of particles was severe, causing the white display to fade and particles to accumulate at the bottom of the electrophoretic display panel.

(Effects of the Invention) The present invention provides a long-life display liquid in which the conductivity does not decrease, the fine particles do not lose their charge for a long period of time, and can continue to be dispersed without separating from the dispersion medium. ,
An electrophoretic display device using this display liquid can provide a stable display for a long period of time, and is highly reliable with a greatly increased number of rewrites.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an electrophoretic display device, and FIG. 2 is an IR diagram of titanium dioxide fine particles subjected to surface treatment according to Example 1.
It is a spectrum. Explanation of symbols 1 Transparent substrate 2 Transparent conductive film 3 Spacer
4 Rear substrate 6 Adhesive 7 Corona wire 8 Control electrode 5 Wave number (m-1) Fig.

Claims (1)

[Claims] 1. A display liquid for an electrophoretic display device comprising fine particles and a dispersion medium of different colors, characterized in that fine particles whose surfaces are treated with a coupling agent having a long-chain alkyl group are used. Display liquid for electrophoretic display devices. 2. A display panel in which two substrates, at least one of which is transparent, are disposed facing each other with a required distance between them to form a sealed space, and the sealed space is filled with the display liquid according to claim 1, and a display panel. and means for applying an electric field to the electrophoretic display device.