JP3102054B2 - Powder and electrorheological fluid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a heterogeneous dispersion type composite in which fine particles having a low conductivity are dispersed in a medium matrix phase in a large amount on the surface side and less in the center side. The present invention relates to a highly functional powder composed of particles and an electrorheological fluid in which the powder is dispersed in an oil medium having excellent electrical insulation.

[0002]

2. Description of the Related Art Electrorheological fluids are fluids whose viscoelastic properties can be changed largely and reversibly by means of electric control. The phenomenon that the apparent viscosity changes greatly has long been known as the Winslow effect. However, the initial electrorheological fluid was made by dispersing starch or the like in mineral oil or lubricating oil, and was sufficient for recognizing the importance of the electrorheological effect, but lacked reproducibility.

[0003] For this reason, many proposals have been made mainly on powders used as dispersoids in order to obtain a fluid having a high electrorheological effect and good reproducibility. For example, as a powder, a superabsorbent resin having an acid group such as polyacrylic acid (JP-A-53-93186), an ion-exchange resin (JP-B-60-31111), and an alumina silicate (JP-A-62-93216). No. 95397).

[0004] Each of these electrorheological fluids contains a hydrophilic solid powder containing water and is dispersed in an insulating oily medium. When a high voltage is applied from the outside, the powder acts by the action of water. It is said that polarization occurs in the particles constituting and the polarization increases crosslinks between the particles in the direction of the electric field, thereby increasing the viscosity.

[0005] However, a hydrous electrorheological fluid using these hydrous powders has a serious problem in practical use. In other words, hydrous electrorheological fluids have insufficient electrorheological effects over a wide temperature range, limit the operating temperature to prevent evaporation or freezing of water, increase current significantly due to temperature rise, and maintain stability due to water transfer. There are many problems such as shortage or dissolution corrosion of the electrode metal when a high voltage is applied, and it is difficult to put it into practical use as an electrorheological fluid.

As a method for improving the drawbacks of the hydrous electrorheological fluid, a non-aqueous electrorheological fluid using a powder of particles containing no water has been proposed.

As such a non-aqueous fluid, a fluid using a powder of organic semiconductor particles such as polyacenequinone, that is, a powder of homogeneous single-phase particles composed of a uniform organic compound having electric characteristics (semiconductivity) (see Japanese Patent Application Laid-Open (JP-A) no. No. 61-216202),
On the conductive thin film layer formed on the surface of the organic or inorganic solid particles, dielectric particles further formed an electrically insulating thin film layer,
That is, a fluid using a powder of a thin film-coated type composite particle which essentially requires a film layer having electrical characteristics (conductivity / insulation) (JP-A-63
-97694, JP-A-1-164823) and the like.

However, any non-aqueous electrorheological fluid using a powder of a homogeneous single-phase particle or a thin film-coated composite particle has, at present, poor long-term stability and poor restorability. Furthermore, when an electric field is applied, the current flowing through the electrorheological fluid is large, so that the current consumption is large. Further, it is not practically used because industrial production is difficult.

For this reason, there has been a demand for a powder that can be suitably used as a dispersoid of a non-aqueous electrorheological fluid. In addition, as the powder having controlled electric characteristics, in addition to the above-described homogeneous single-phase particles and thin-film-coated composite particles, carbon powders having different firing temperatures, metal powders subjected to surface treatment, and metal-coated powders are used. Inorganic powders have been known, but powders that have been used mainly for their electrical properties have many problems such as poor heat resistance and oxidation resistance, and difficulty in controlling electrical resistance and dielectric constant. Due to the point, the expansion of the use has been significantly hindered. Therefore, development of a powder excellent in such a function has also been required.

SUMMARY OF THE INVENTION The present invention has been made to meet the above-mentioned demand, and an object of the present invention is to provide a highly functional powder which is excellent in oxidation resistance and control of electric characteristics and is preferably used as a dispersoid for an electrorheological fluid. Another object of the present invention is to provide a novel electrorheological fluid that overcomes the disadvantages of the conventional fluid as described above.

[0011]

The present inventors have made intensive studies to achieve the above object, and as a result, focused on the structure and electrical characteristics of the particles, and made up of microcomposite particles of a new concept, which has not existed before. The powder was obtained, and the present invention was completed.

That is, the present inventors further impregnated organic particles having a high residual carbon ratio with an organometallic compound, and then carbonized the particles so that fine particles having a lower electric conductivity were further introduced into the matrix phase on the surface side. many, constitute a powder of fine particles unevenly distributed composite particles obtained unevenly dispersed in small state toward the center, yet in this case, the electrical conductivity of the matrix phase 10 ^-10 to 10 ² Sc
m- ¹ range, and the dispersed fine particles dispersed therein are formed of a semiconductor or insulator material having an electric conductivity of 1/10 or less of the electric conductivity of the matrix phase,
Further, by setting the dispersion amount of the dispersed fine particles in the matrix phase to 40% (% by weight, the same applies hereinafter) or less as a whole, the heat resistance and the oxidation resistance are excellent, and the electric resistance and the dielectric constant are easily controlled. It has been found that a highly functional powder can be obtained.

[0013] Further, a powder composed of a heterogeneous finely dispersed composite particle having a new structure in which a low-conductive fine particle dispersed phase is non-uniformly dispersed in the conductive medium matrix phase is used as a dispersoid. By dispersing in an insulating oily medium, fundamentally different from conventional homogeneous single-phase particles and thin-film-coated composite particles, high-performance electrorheological fluids, that is, high-level electrorheological effects in a wide temperature range The present invention has been found to provide an electrorheological fluid having excellent functions, for example, the characteristics thereof are stable for a long time, and the current flowing when an electric field is applied is small.

Accordingly, the present invention comprises non-uniformly dispersed composite particles in which the fine particles are non-uniformly dispersed in the matrix phase in such a manner that the fine particles gradually decrease from the surface side toward the center side, and the electric conductivity of the matrix phase is 10%. ^{-10 ~10 2} Scm
^-1 , and the dispersed fine particles are formed of at least one material selected from a semiconductor and an insulator, and the electric conductivity thereof is 1/10 or less of the electric conductivity of the matrix phase. Provided are a powder characterized in that the dispersion amount in the composite particles is 40% by weight or less as a whole, and an electrorheological fluid obtained by dispersing the powder in an electrically insulating oily medium.

Hereinafter, the present invention will be described in more detail. First, as shown in the schematic diagram of FIG. 1, the composite particles 1 constituting the powder according to the first invention of the present invention are electrically conductive. Composed of a micro-composite structure (sea-island structure) in which fine particles 3 of low conductivity are dispersed in a large amount (densely) on the surface side and less (sparsely) in the center side in the matrix phase 2 It is. In this case, as an example of the non-uniform dispersion mode, the state shown in the schematic diagram of FIG. 2 is given. That is, as shown by A, B, and C in the schematic diagram of FIG. 2, the weight ratio of the dispersed fine particles is increased in the layer near the surface of the composite particle, and the weight ratio gradually increases toward the layer near the center through the layer near the middle. It is preferable that the structure is made macroscopically negative with a negative slope so as to decrease, and this means that the electric conductivity is reduced in the layer near the surface of the composite particle, and the electric conductivity gradually increases toward the layer near the center. This means that the structure is made macroscopically larger with a positive slope so as to increase.

[0016]

[0017] Here, the electrical conductivity of the matrix phase 2 is electrically conductive medium, i.e., 10 ^-10 to 10 ² Scm ^-1, preferably 10 ^-10 ~10 ⁰ Scm ^-1. As a material for forming the matrix phase, any organic material or inorganic material can be used as long as the material exhibits the electric conductivity. Specific examples include carbonaceous materials, carbide materials such as boron carbide and aluminum carbide, organic semiconductor materials such as polyaniline and polyacenequinone, and oxide semiconductor materials such as zinc oxide, potassium titanate, and barium titanate. Although preferred, carbonaceous materials are preferred. Among them, a carbon content of 80 to 9
Preferred is 9.9% carbonaceous material, more preferred is 90-99% carbonaceous material. The remainder is usually composed of hydrogen, oxygen and nitrogen atoms.

On the other hand, the fine particles 3 dispersed in the matrix phase 2 are at least one material selected from a semiconductor and an insulator, and it is an essential condition that the electric conductivity has a lower value than the matrix phase. And 1/10 or less of that of the matrix phase, preferably 1/1
0 to 1/10 ¹⁴ , more preferably 1/10 ³ to 1/1
It is ¹⁴ . If this is more than 1/10, effective composite particles cannot be obtained. Further, the electric conductivity of the fine particles satisfies the above condition, and is 10 ⁻² Scm ⁻¹ or less, particularly 10 ⁻⁶ Sc.
It is preferably at most m ⁻¹ .

Examples of the fine particle material include oxides such as alumina, silica, boron oxide, titania, calcium oxide, iron oxide, tin oxide, and zinc oxide, and non-oxides such as silicon carbide, silicon nitride, and aluminum nitride. Can be mentioned. Among them, preferred are silica, alumina, titania and the like.

The size of the fine particles is 1 nm to 1 μm,
Preferably, the range is 2 nm to 0.5 μm. The dispersion amount of the fine particles in the composite particles is 0.01 to
It is 40%, preferably 0.1 to 30%. 0.01%
If less, the effect of the present invention cannot be obtained and 40%
When the number is larger, it is not preferable because the production of the composite particles is hindered. When the composite particles of the present invention are formed such that the dispersion amount of the fine particles is large on the surface side and small on the center side, the dispersion amount on the surface side is 0.1 to 99%, particularly 1 to 95%, and the dispersion amount near the center is 0 to 0%. It is preferably 30%, particularly 0 to 25%, and the dispersion amount on the surface side is preferably about 1.5 times or more, particularly about 3 times or more the dispersion amount near the center.

The above matrix phase 2 and dispersed fine particles 3
In the composite particles 1 of the present invention, the average particle diameter is not particularly limited, but is preferably 0.1 to 100 μm, more preferably 0.5 to 50 μm when used as a dispersoid of an electrorheological fluid described later. It is. 0.1μ
If it is less than 100 m, the initial viscosity becomes remarkably large in the absence of an electric field, and the change in viscosity due to the electrorheological effect is small.
If it exceeds μm, sufficient stability may not be obtained.

The electric conductivity of the powder comprising the composite particles is not particularly limited, but the electric conductivity measured by molding the powder is preferably 10 ^-13 to 10 ² Scm ^-1 , and more preferably. Is 10 ⁻¹² to 10 ⁻² Scm ⁻¹ .

Further, the water content of the present powder is preferably 1% or less, particularly preferably 0.5% or less. When the water content exceeds 1%, when the electrorheological fluid is used as a dispersoid,
In some cases, power consumption at high temperatures increases due to conductivity by water.

The index of the internal structure of the composite particles of the present invention, that is, the morphological state and physical specifications can be easily specified by various analytical methods shown in Examples described later.

Here, as a method for producing the composite particles of the present invention, the following methods (A) to (D) can be mentioned in the case of composite particles in which fine particles are largely dispersed on the surface side of the matrix phase. . (A) Organic particles such as thermosetting resin such as phenolic resin, furan resin, polydimethylsilane resin, melamine resin, and epoxy resin, and resin obtained by subjecting a thermoplastic resin such as polyacrylonitrile to radiation treatment or infusibilization treatment are added to ethyl. Impregnated with compounds such as silicates, metal alkoxides such as aluminum isopropoxide and titanium isopropoxide, organometallic complexes such as ferrocene, organic compounds such as borate esters synthesized from diethanolamine and boric acid, and esters composed of inorganic acids and heat treatment. Later, carbonization method. (B) After attaching a compound such as a metal alkoxide, an organic metal complex, an ester of an organic compound and an inorganic acid to the surface of organic particles having a high residual carbon ratio, such as a phenol resin, a furan resin, and a polydimethylsilane resin, Further, a method of carbonizing fine particles coated with a liquid organic compound having a high residual carbon ratio by heat treatment. (C) On the surface of organic particles having a high residual carbon ratio, such as a phenol resin, a furan resin, and a polydimethylsilane resin, a compound having a high residual carbon ratio is formed on a compound such as a metal alkoxide, an organic metal complex, or an ester of an organic compound and an inorganic acid. A method in which a mixture of liquid organic compounds is attached, and then carbonized by heat treatment. (D) After heat-treating organic particles with a high residual carbon ratio, such as phenolic resin, furan resin and polydimethylsilane resin,
After attaching a compound that forms desired electrically conductive fine particles to the surface by a method such as a chemical vapor deposition method (CVD),
Furthermore, a method of carbonizing by heat treatment.

[0026]

[0027]

The composite particles of the present invention are not limited to the above-mentioned production method.

Next, an electrorheological fluid according to a second aspect of the present invention is obtained by using the powder of the first aspect as a dispersoid and dispersing the powder in an electrically insulating oily medium (dispersion medium). is there.

Here, examples of the dispersion medium include electric insulating oils such as hydrocarbon oil, ester oil, aromatic oil, silicone oil, fluorosilicone oil and phosphazene oil. These can be used alone or in combination of two or more. Among these electric insulating oils, silicone oils such as polydimethylsiloxane and polymethylphenylsiloxane are excellent in that they can be used even in a state of being in direct contact with a rubber-like elastic material. The electric insulating oil of the present invention is not limited to these examples.

The viscosity of the electric insulating oil is 0.6 at 25 ° C.
The viscosity is preferably 5 to 1000 centistokes (cSt), more preferably 1 to 500 cSt. The dispersoid can be efficiently suspended by using an electric insulating oil having this viscosity as a dispersion medium. However, if the viscosity of the dispersion medium is too low, the volatile content increases and the stability of the dispersion medium deteriorates. On the other hand, if the viscosity of the dispersion medium is too high, the initial viscosity in the absence of an electric field becomes too high, and it may be difficult to effectively control the applied products.

The content of the dispersoid in the electrorheological fluid of the present invention is from 1 to 60%, preferably from 5 to 50%, and the content of the dispersoid is from 40 to 50%. 99
%, Preferably 50 to 95%.
When the amount of the dispersoid is less than 1%, the electrorheological effect is small,
%, The initial viscosity in the absence of an electric field may be significantly increased.

The electrorheological fluid of the present invention may contain other dispersoids, surfactants, dispersants, and additives such as inorganic salts as long as the effects of the present invention are not impaired.

[0034]

The powder of the present invention has excellent oxidation resistance, high thermal stability in the atmosphere, and extremely easy control of electric resistance and dielectric constant. Therefore, the present powder is effective as a dispersoid of an electrorheological fluid, and is also suitable for applications such as an electrical property imparting agent for a polymer compound.

The effects of the electrorheological fluid of the present invention are listed below. i In a wide temperature range, the level of the electrorheological effect is high. ii The characteristics of the electrorheological fluid are stable for a long time. iii When an electric field is applied, the current flowing through the electrorheological fluid is small and the power consumption is small. iv The application of an electric field can be arbitrarily selected from DC and AC. v Easy industrial production method and full of practicality.

For this reason, the electrorheological fluid of the present invention is effectively applied to electrical control of mechanical devices such as engine mounts, shock absorbers, valves, clutches and the like.

[0037]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the following examples, the characteristics of the powder and the characteristics of the electrorheological fluid were measured by the following methods. Characteristic particle size of powder : MICROTRAC SPA / manufactured by Nikkiso Co., Ltd.
Measured by MK-II type Carbon content: Measured by a carbon analyzer manufactured by HORIBA, Ltd. Electric conductivity: Measured by a two-terminal method for compacts Size of dispersed fine particles: Measured by an ultra-high resolution electron microscope Composite particles Weight ratio of silica in the mixture: Extracted with silica using hydrofluoric acid and measured by inductively coupled plasma method (ICP method) Weight ratio of dispersed fine particles of each layer in composite particles: Measured by electron micrograph Heat generation peak temperature: Vacuum science and technology Characteristics of electro-rheological fluid measured by differential thermal analysis using TGD7000 manufactured by Co., Ltd. in the air at a heating rate of 5 ° C./min. Using RDS-II manufactured by Rheometrics Far East Co., Ltd., a shear rate of 350 / sec. Measured under conditions

Example 1 150 g of phenolic spheres (Univex S manufactured by Unitika Ltd.) as a thermosetting resin was added to 160 g of orthosilicate (ethyl silicate 28 manufactured by Colcoat Co., Ltd.).
After impregnation day and night, filter off. The treated phenol spheres are washed with ethanol, heated in 400 g of distilled water to which 4 g of toluenesulfonic acid is added at 40 ° C. for 8 hours, and then filtered. Then, it is dried in a vacuum oven at 80 ° C. for 8 hours. The silica-containing phenol spheres thus obtained were placed in an argon atmosphere at 600 ° C. at a rate of 5 ° C./min.
After heating up to 1 hour, carbonized, average particle size 37μ
Thus, a powder having a specific gravity of 1.45, which was composed of m spherical composite particles, was obtained.

The composite particles are made of a carbonaceous material (carbon content 9%).
0.6%) as a matrix phase and silica as a fine particle dispersed phase, and the electrical conductivity of the carbonaceous material and that of the silica were 6 × 10 ⁻⁹ Scm ⁻¹ and 1 × 10 ⁻¹³ Scm ⁻¹ , respectively. . The electric conductivity of the powder was 4 × 10 as a whole.
^-12 Scm ^-1 . The size of the dispersed silica is 2
0 nm, and the weight ratio of silica in the composite particles was 5.0% as a whole, but the weight ratio of silica in the near surface layer, near middle layer and near center layer of the composite particles was 8.7%, respectively. 2.5% and 0% were indicated. The water content of this powder measured at room temperature was 0.2%. Further, an exothermic peak temperature was measured as an index of the oxidation resistance of the powder. The results are shown in Table 1. From the results, it is recognized that the present powder has excellent oxidation resistance.

As described above, in the composite particles constituting the powder obtained in this example, the silica is unevenly dispersed in the carbonaceous material, and the dispersion manner is such that the silica gradually decreases from the particle surface toward the center. It was confirmed that the powder had a non-uniformly dispersed composite particle structure showing a desirable inclination mode, and that the powder had a high level of heat resistance.

Example 2 Using phenol spheres (Univex C-10 manufactured by Unitika Ltd.) and polysilicates (ethyl silicate 40 manufactured by Colcoat Co., Ltd.), which are thermosetting resins, in distilled water to which toluenesulfonic acid was added. In the same manner as in Example 1 except that the mixture was heated at 80 ° C. for 2 hours, a powder having a specific gravity of 1.46 composed of spherical composite particles having an average particle size of 5 μm was obtained.

The composite particles are made of a carbonaceous material (carbon content 9%).
1.4%) as a matrix phase and silica as a fine particle dispersed phase. The weight ratio of silica in the composite particles is 2.0% as a whole, and silica is present on the composite particle surface side as in Example 1. It had a fine particle heterogeneous dispersion type composite particle structure with a large number and a small inclination on the center side.

The electric conductivity of the powder was 5 as a whole.
× 10 ⁻¹² Scm ⁻¹ . The powder contained 0.15% of water when left at room temperature. Further, the oxidation resistance (exothermic peak) of the present powder is as shown in Table 1, and it was found that the heat resistance was extremely excellent similarly to the powder of Example 1.

Comparative Example 1 The phenol sphere used in Example 2 was heated to 600 ° C. at a rate of 5 ° C./min in an argon atmosphere as it was, and then heated and carbonized for 1 hour to obtain an average particle diameter of 5 μm. Electric conductivity 6 ×
A powder composed of carbonaceous material particles of 10 ^-9 Scm ^-1 was obtained.

The exothermic peak temperature of this powder in air is shown in Table 1. It can be seen that the oxidation resistance of the powders of Example 1 and Example 2 is clearly superior to that of the present powder.

[0046]

[Table 1]

Example 3 The powder of Example 1 was heat-treated in air at 400 ° C. for 3 hours. As a result, part of the carbon in the powder was removed by this heat treatment, the silica content in the powder was increased to 18%, and the specific gravity was 1.50. Further, the average particle size became 34 μm.

Example 4 500 g of phenolic spheres (Univex UA-30 manufactured by Unitika Ltd.) as a thermosetting resin were impregnated with 800 cc of acetone for 6 hours. After removing excess acetone from the phenol spheres swollen by decantation,
Add 500 cc of the orthosilicate used in Example 1 and stir for 18 hours. The phenol spheres thus treated are washed with ethanol, and mixed and stirred for 10 minutes in 1500 cc of distilled water to which 25 g of toluenesulfonic acid is added. Next, heat treatment is performed at 40 ° C. for 1 hour and at 90 ° C. for 1 hour. Next, filtration and washing are performed, and 80
Dry in a vacuum oven at 4 ° C. for 4 hours.

The silicic acid-containing phenol spheres thus obtained were subjected to 620 heating at a rate of 2 ° C./min in an argon atmosphere.
After raising the temperature to 0 ° C., the mixture is heated for 1 hour to perform a carbonization treatment. By this treatment, a powder having a specific gravity of 1.46 composed of composite particles having an average particle diameter of 17.3 μm was obtained. The weight ratio of silica in the composite particles was 6.0%.

Example 5 100 g of aluminum isopropoxide powder was mixed and stirred in 400 g of acetone for 4 hours, and the filtrate was collected with a fluted filter paper. The filtrate contained phenol spheres (a thermosetting resin). UNIVEX UA-3 manufactured by Unitika Ltd.
0) Impregnate 250 g for 24 hours. The phenol spheres thus treated are washed with isopropanol, washed with acetone and washed with ethanol, and further mixed and stirred for 10 minutes in 500 cc of distilled water to which 12.5 g of toluenesulfonic acid is added. Then, at 40 ° C. for 1 hour, 90
Heat treatment at 1 ° C. for 1 hour. Thereafter, the mixture is filtered, washed, and dried in a vacuum oven at 80 ° C. for 4 hours.

The aluminum hydroxide-containing phenol spheres thus obtained were heated at a rate of 5 ° C. in an argon atmosphere.
After heating to 615 ° C./min, the mixture is heated for 1 hour to perform carbonization. By this treatment, a powder having a specific gravity of 1.46, composed of composite particles having an average particle size of 17.2 μm, was obtained. The weight ratio of alumina in the composite particles was 2.0%.

Example 6 Powder 50 obtained in Example 1
g to silicone oil (Toshiba Silicone Co., Ltd .: TSF
451-10) was dispersed in 95 g to produce an electrorheological fluid. Table 2 shows the characteristics as an electrorheological fluid.

First, the viscosity measured at room temperature without an electric field was 0.4 poise, and the viscosity increased to 5.5 poise by applying a DC electric field of 2 KV / mm. The current value at that time was 0.03 μA / cm ² . Next, the initial viscosity at 100 ° C. is 0.2 poise, and the viscosity increases to 7.0 poise by applying an electric field of 2 KV / mm, and the current value at that time is 1.15.
μA / cm ² .

Table 3 shows the time-dependent changes in the viscosity and the current when a DC electric field of 2 KV / mm was applied at room temperature.
It is. As can be seen, the effect of this fluid was not changed when used for more than 1000 hours.

Therefore, as shown by the above results, this electrorheological fluid has a high level of electrorheological effect in a wide temperature range, a small current flows when an electric field is applied, a small power consumption, and a long-term stability. It is recognized that it has such features as being extremely excellent.

Example 7 An electrorheological fluid was produced in the same manner as in Example 6 using the powder obtained in Example 2. Table 2 shows the characteristics as an electrorheological fluid.

First, the viscosity measured at room temperature without an electric field was 0.6 poise, and the viscosity increased to 2.4 poise by applying a DC electric field of 2 KV / mm. The current value at that time was 0.001 μA / cm ² or less. Next, at 100 ° C
The initial viscosity was 0.2 poise, and the viscosity increased to 2.5 poise by application of an electric field of 2 KV / mm, and the current value at that time was 0.037 μA / cm ² .

As can be seen from the above results, the electrorheological fluid of this embodiment has excellent characteristics as in the case of the sixth embodiment.

Comparative Example 2 Using the powder of Comparative Example 1, a suspension fluid was obtained in the same manner as in Example 6. Table 2 shows the electrorheological characteristics of this fluid.

It can be seen that this fluid has no electrorheological effect, and that a large current flows due to the DC electric field.
That is, it is shown that an effective electrorheological fluid cannot be obtained only by the matrix phase (in this case, carbonaceous material) constituting the composite particles of the present invention. It should be noted that a satisfactory electrorheological fluid could not be obtained only with silica, which is one of the dispersed fine particles constituting the composite particles of the present invention.

Comparative Example 3 Silica gel (Nipsil VN-3 manufactured by Nippon Silica Co., Ltd.)
13 parts by weight of water adjusted to 6% by weight were dispersed in 87 parts by weight of silicone oil to obtain an electrorheological fluid. Table 2 shows the electrorheological characteristics of this fluid.

The viscosity of the electrorheological fluid measured at room temperature without an electric field was 3.4 poise, and the viscosity increased to 6.0 poise by applying a DC electric field of 2 KV / mm. The current value at that time was 21 μA / cm ² . At 100 ° C., the current was too large to measure the electrorheological effect. Furthermore, the effect of this fluid was gradually reduced after long-term continuous use, and the effect was reduced to less than half after about 100 hours.

[0063]

[Table 2]

[0064]

[Table 3]

Example 8 When the electrorheological effect was measured using the powder of Example 3 in the same manner as in Example 6, the viscosity was 0.5 poise when measured without an electric field and at room temperature. The viscosity increased to 4.8 poise when a DC electric field of 2 KV / mm was applied. The current value at that time was 0.001 μA / cm ² or less.

Next, the initial viscosity at 80 ° C. is 0.2 poise, the viscosity increases to 5.6 poise by applying a DC electric field of 2 KV / mm, and the current value at that time is 0.011 μA / c.
m ² . As can be seen from the results, the powder of Example 3 has excellent characteristics.

Example 9 Using the powder of Example 4 and measuring the electrorheological effect in the same manner as in Example 6, the viscosity was 0.5 poise when measured without an electric field and at room temperature. In addition, the viscosity increased to 13 poise by applying a DC electric field of 2 KV / mm. The current value at that time was ² μA / cm ² or less. As can be seen from the results, the powder of Example 4 has excellent characteristics.

Example 10 When the electrorheological effect was measured using the powder of Example 5 in the same manner as in Example 6, the viscosity was 0.5 poise when measured without an electric field and at room temperature. In addition, the viscosity increased to 9 poise by applying a DC electric field of 2 KV / mm. The current value at that time was 1.2 μA / cm ² . As can be seen from the results, the powder of Example 5 has excellent characteristics.

[Brief description of the drawings]

FIG. 1 shows a schematic view of a cross section of a composite particle of the present invention.

FIG. 2 is a schematic diagram showing the relationship between the weight ratio of each layer from the surface to the center of the composite particles and the dispersed fine particles.

[Explanation of symbols]

 1 Composite Particle 2 Matrix Phase 3 Dispersed Fine Particle

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ identification code FI (C10M 125/00 125: 02 125: 26) C10N 20:00 40:14 (58) Fields surveyed (Int.Cl. ⁷ , (DB name) C10M 171/06 H01B 1/20 C09K 3/00 C10M 125/00 C10N 40:14

Claims (2)

(57) [Claims] The present invention comprises a non-uniformly dispersed type composite particle in which fine particles are non-uniformly dispersed in a matrix phase from the surface side to the center side in a gradually decreasing manner, and the matrix phase has an electrical conductivity of 10 ^-10 to 10. ² Scm ^-1 , the dispersed fine particles are formed of at least one material selected from a semiconductor and an insulator, and the electric conductivity thereof is 1/10 or less of the electric conductivity of the matrix phase. A powder, wherein the dispersion amount of the fine particles in the composite particles is 40% by weight or less as a whole. 2. An electrorheological fluid comprising the powder according to claim 1 dispersed in an electrically insulating oily medium.