JPH0742473B2 - Electrorheological liquid - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrorheological liquid whose viscosity is increased by applying a voltage.

[Prior Art] An electrorheological liquid is a suspension in which finely divided dielectric solids are dispersed in a non-conductive oil, and extremely rapidly under the action of a sufficiently strong electric field. It is a liquid whose viscosity increases reversibly.

To change the viscosity, not only an electric field of direct current but also an electric field of alternating current can be used, the required current is very small, and a small amount of electric power gives a large change in viscosity from a liquid to an almost fixed state. For example, a clutch,
Electrorheological liquids have been studied as components for controlling devices and parts such as valves, shock absorbers, vibrators, various anti-vibration rubbers, actuators, robot arms, and damping materials.

Conventionally, as solid particles that are one of the components of the electrorheological liquid, U.S. Patent Nos. 2,417,850, 3,047,507, 3,
397,147, 3,970,573, 4,129,513, or Japanese Patent Publication No. 60-31211, German published patent 3,427,499
As disclosed in the publication No. 3, cellulose, starch, silica gel, ion exchange resins, lithium polyacrylate, etc., which have been made to absorb water from the surface and made into fine particles, and other components, such as a liquid phase, are halogenated. It is known to use diphenyl, butyl sebacate, hydrocarbon oil, chlorinated paraffin, silicone oil, etc., but an electrorheological liquid of extremely high performance and high stability, which is of poor practicality and has practical value, is still available. not exist.

The properties required for a practical electrorheological liquid are a large electrorheological effect over a wide temperature range, low power consumption when an electric field is applied, low viscosity when the electric field is removed, and a dispersed phase. Is that it does not settle down and maintains stable characteristics for a long time.

However, as described above, in the dispersed phase in which water is absorbed in order to promote the expression of the electrorheological effect, the current flowing between the particles also increases, which causes a large problem in power consumption. In particular, this tendency becomes stronger as the temperature rises, and the upper limit of the operating temperature of the electroviscous liquid using the conventional dispersed phase is 70-
If it is used at a high temperature of about 80 ° C or higher, current will flow excessively and power consumption will become extremely high, and the power of expressing the electrorheological effect and deterioration of responsiveness will occur over time, such as in the engine room of an automobile. It was not possible to apply it to devices and parts used in high temperature atmosphere.

Further, the water-based electrorheological liquid containing the dispersed phase in which water is absorbed as described above does not exhibit the electrorheological effect due to the solidification of water at a low temperature of 0 ° C. or lower.

[Problems to be Solved by the Invention] As described above, a water-based electrorheological liquid whose dispersed phase needs to contain water in order to function as an electrorheological liquid has an essential problem in the temperature range and durability associated with water evaporation. It has been a reason why the liquid has not been put to practical use for a long time.

Therefore, the advent of a practical non-aqueous electrorheological liquid that does not require water in the dispersed phase has been awaited. As such a non-aqueous liquid, a liquid having substantially no water or a dispersed phase disclosed in U.S. Pat. No. 4,687,589 or JP-A-63-97694 and JP-A-64-6093 has a multilayer structure. Liquids have also been proposed, but due to problems such as small electrorheological effect, large power consumption, and functioning only in an alternating electric field, an electrorheological liquid that is practical and has sufficient properties is currently developed. It is hard to say that it has been done.

When an electric field is applied as one of the expression mechanisms of a non-aqueous electrorheological liquid, interfacial polarization occurs due to the movement of electrons or holes in the dispersed phase particles, the dispersed phase particles attract each other, form a bridge of particles, and increase the viscosity. It is possible to raise it. From this, the inventors have paid attention to a so-called low-temperature treated carbon material, which has a high concentration of radicals (unpaired electrons) necessary for interfacial polarization due to the movement of electrons or holes, and is used as a dispersed phase of a non-aqueous electrorheological liquid. I considered doing. As a result, the application of a direct current and an alternating electric field shows a high electrorheological effect in a wide temperature range, but it has led to the development of an electrorheological liquid that consumes less power and can maintain a high electrorheological effect for a long period of time.

[Means for Solving the Problems] The present invention exhibits a high electrorheological effect over a wide temperature range by applying a DC or AC electric field, but has low power consumption and is capable of maintaining a high electrorheological effect for a long period of time. For the purpose of providing a liquid, a dispersed phase of 1 to 60% by weight of carbonaceous fine powder having an average particle size of 0.01 to 100 microns, and an electrical insulating oil having a viscosity of 0.65 to 500 centistokes (cSt) at room temperature 99
This problem was solved by an electrorheological liquid characterized by consisting of ~ 40% by weight liquid phase.

The carbonaceous fine powder suitable as the dispersed phase of the electrorheological liquid in the present invention preferably has a carbon content of 80 to 97% by weight, and particularly preferably 90 to 95% by weight. The C / H ratio (carbon / hydrogen atom ratio) of the carbonaceous fine powder is preferably 1.2 to 5, and particularly preferably 2 to 4.

It has long been known that the electric resistance of the dispersed phase of an electrorheological liquid is generally in the semiconductor region (WM Winslow: J.
Appl. Physics 20 1137 (1949), carbonaceous fine powder having a carbon content of 80% by weight or less and a C / H ratio of 1.2 or less is an insulator, and a liquid exhibiting an electrorheological effect is hardly obtained.

On the other hand, those having a carbon content of 97% by weight or more and a C / H ratio of 5 or more are close to a conductor and show an excessive current even when a voltage is applied, and a liquid showing an electrorheological effect cannot be obtained.

Specifically, the above C / H suitable as a dispersed phase of an electrorheological liquid
As carbonaceous fine powder having a ratio, coal tar pitch,
Finely pulverized petroleum pitch, pitch obtained by thermally decomposing polyvinyl chloride, fine powder consisting of various mesophases obtained by heat-treating those pitch or tar components, that is, an optical difference formed by heating. Fine powder obtained by dissolving and fractionating pitch components in spherical solvent (spherulite or mesophase small spheres) and then finely pulverizing it. Bulk raw mesophase by heat treatment of pitch raw material (eg published in Japan) Patent Sho 59-30887
No.), finely crushed pits, finely crushed partially crystallized pits, carbonized thermosetting resin such as fail resin at low temperature, pyrolyzed polyacrylonitrile, etc. Carbon fine powder is exemplified,
Further, coal such as anthracite, bituminous coal and heat-treated products thereof are finely pulverized, and a mixture of a hydrocarbon-based vinyl polymer such as polyethylene, polypropylene or polystyrene and a chlorine-containing polymer such as polyvinyl chloride or polyvinylidene chloride is used. Examples thereof include carbon spheres obtained by heating under pressure, or finely pulverized carbon spheres.

Among these, carbonaceous fine powder having a high aromatic radical concentration of 10 ¹⁸ / g or more and an electric resistance of 10 ⁵ Ωcm or more is
It is preferred in the sense that it exhibits a high electrorheological effect with low power consumption.

From this point of view, among the above specific examples, it is particularly preferable to use carbonaceous fine powder obtained by separating optically anisotropic small spheres produced by heat treatment of coal tar pitch from pitch components.

The outline of the production method of the carbonaceous fine powder obtained from this coal tar pitch is described below. Coal tar pitch from 350 to 5
When heat-treated at 00 ° C., spherical optically anisotropic small spheres (spherulites or mesophase small spheres) grow from the components of coal tar pitch. (JD Brooks and GH Taylor,
Garbon 3 , 185 (1965)) The size of this spherulite is determined by the heating temperature and the heating time, but when the desired size is reached, heating is stopped and residual coal is used with a solvent such as quinoline or tar oil. This spherulite can be separated by dissolving tar pitch and filtering.

The spherulite is a spherical carbonaceous fine powder having a graphite-like structure. As disclosed in JP-A-60-25364, a part of the coal tar pitch component (for example, β-resin) remains on the surface of the spherulites when the spherulites are separated, but if necessary. The spherulites can be removed by heat treatment (calcination) at 200 to 600 ° C. in an inert gas atmosphere,
It is also possible to change the electrical resistance and radical concentration of spherulites.

The particle size of the spherulites can be controlled by the heating time and the heating temperature of the coal tar pitch, and finer particles can be obtained by pulverizing with a jet mill or the like. In addition to coal tar pitch as a raw material, a petroleum pitch or a tar component having a similar structure can be treated in the same manner to obtain a carbonaceous fine powder suitable for use in the present invention.

The water content of the carbonaceous fine powder thus obtained is at most 1% by weight or less, and although the water content is almost unrelated to the electrorheological effect, the concentration of aromatic radicals in the fine powder is Since it is considered that the electro-viscous effect is high due to the interfacial polarization due to the movement of electrons or holes, the electro-viscous effect is exhibited in a wide temperature range and the electro-viscous effect is maintained for a long time by using the fine powder as a dispersed phase. A viscous liquid that can be maintained can be obtained.

If the spherulites are used, the carbonaceous fine powder has optical anisotropy, and therefore the electrical conductivity also shows anisotropy, which means that the electrorheological liquid having the fine powder as a dispersed phase exhibits low power consumption. It is thought to be related.

On the other hand, in these carbonaceous fine powders, the C / H ratio changes and the conductivity changes by changing the calcination temperature and the like. That is, as the C / H ratio increases, the electrorheological effect also increases,
At the same time, current consumption also increases. Therefore, it is necessary to set the electric resistance of the carbonaceous fine powder so that the consumption current and the electrorheological effect have optimum points. In this sense, the most preferable electric resistance of the carbonaceous fine powder is 10 ⁷ to 10 ¹⁰ Ω · cm.

Furthermore, the inventor has found that as a method of maintaining the electrorheological effect to some extent and reducing only the current consumption, it is effective to coat a part or all of the surface of the particles in the carbonaceous fine powder with an electrically insulating thin film. . This method is particularly effective for carbonaceous fine powders having a high C / H ratio and a high carbon content.

Here, as the electrically insulating thin film, whether it is organic or inorganic, it suffices if the thin film can be formed on the surface of the carbonaceous fine powder to a thickness of 1/10 or less of the particle diameter, but the optimum thickness of the thin film is the carbonaceous material. It depends on the conductivity of the fine powder. That is, when the electrical conductivity of the carbonaceous fine powder is high, it is better that the insulating thin film is relatively thick. Conversely, when the electrical conductivity of the fine powder is low, the insulating thin film is relatively thin. It is necessary to maintain the viscous effect and reduce the current when voltage is applied.

Such an electrically insulative thin film is coated on a powder from a polymer solution, hybridization in which small-diameter particles are dry-blended and melted on the surface of the powder, surface treatment such as silane treatment, sputtering vacuum deposition, from a monomer. An electrically insulating substance formed by polymerization or the like is used as a synthetic polymer substance such as polymethylmethacrylate, polystyrene, polyvinyl acetate, polyvinyl chloride, polyvinylidene fluoride, epoxy resin or phenol resin, methyltrimethoxysilane, Phenyltrimethoxysilane, hexamethyldisilazane, silane treating agents such as trimethylchlorosilane, modified silicone oil or silicone surfactant having dimethylpolysiloxane or phenylmethylpolysiloxane structure having a carboxyl group or hydroxyl group as the main chain, silica, Lumina, inorganic compounds such as rutile can be mentioned as typical examples. Created in this way,
By using the carbonaceous fine powder coated with the electrically insulating thin film as the dispersed phase of the electrorheological liquid, an electrorheological liquid exhibiting a high electrorheological effect but consuming less electricity can be obtained.

The preferred particle size for the dispersed phase of the electrorheological liquid is 0.01 to 10
It is in the range of 0 micron, preferably 0.1 to 20 micron, more preferably 0.5 to 5 micron, and the particle size distribution is preferably as sharp as possible. If it is less than 0.01 micron, the initial viscosity is remarkably increased in the absence of an electric field and the change in viscosity due to the electrorheological effect is small, and if it exceeds 100 micron, sufficient stability as a dispersed phase of a liquid cannot be obtained.

The volume resistivity at 80 ° C is 10
It is preferably ¹¹ Ω · cm or more, particularly preferably 10 ¹³ Ω.
・ It is preferably cm or more. Specifically, hydrocarbon oil,
Examples thereof include ester oils, aromatic oils, halogenated hydrocarbon oils such as perfluoropolyether and polytrifluoro-chloroethylene, phosphazene oils and silicone oils. These can be used alone or in combination of two or more. Among these electrical insulating oils, silicone oils such as polydimethylsiloxane, polymethylphenylsiloxane, and polymethyltrifluoropropylsiloxane can be used even when they are in direct contact with rubber-like elastic materials and many polymer materials. Excellent in terms.

The viscosity of the electric insulating oil at 25 ° C. is 0.65 to 500 centistokes (cSt), preferably 5 to 200 cSt, more preferably 10 to 50 cSt. If the viscosity of the liquid phase is too low, the volatile content increases and the stability of the liquid phase deteriorates. If the viscosity of the liquid phase is too high, the initial viscosity in the absence of an electric field will be high and the change in viscosity due to the electrorheological effect will be small.
In addition, the dispersed phase can be efficiently suspended by using an electrically insulating oil having a moderately low viscosity as the liquid phase.

The ratio of the dispersed phase and the liquid phase constituting the electrorheological liquid of the present invention is such that the content of the dispersed phase composed of the carbonaceous fine powder is 1 to 60.
% By weight, preferably 20 to 50% by weight, and the content of the liquid phase consisting of the electrically insulating oil is 99 to 40% by weight, preferably 80% by weight.
~ 50% by weight. If the amount of the dispersed phase is less than 1% by weight, the electrorheological effect is small, and if it exceeds 60% by weight, the initial viscosity in the absence of an electric field becomes significantly large.

The electroviscous liquid of the present invention may be used in combination or blended with other disperse phases and additives such as a surfactant, a dispersant and an inorganic salt, within a range that does not significantly impair the effects of the present invention.

The present invention will be specifically described below with reference to examples.

[Example 1] Coal tar pitch was heat-treated at 450 ° C in an inert atmosphere to grow spherulites, and then extraction with oil in tar and extraction were repeated to remove pitch components, and at 350 ° C in a nitrogen stream. Heat treated (calcination) again, fine carbonaceous powder consisting of spherulites (carbon content: 93.78 wt%, C / H ratio: 2.35, electric resistance: 1.79 × 10 ⁹ Ω ・
cm, electron spin concentration: 3.28 × 10 ¹⁹ Ω ・ cm, water content: 0.4
Wt%) was obtained. Silicone oil with a viscosity of 20 cSt at 25 ° C, which is a liquid phase component, is 40% by weight of a carbonaceous derivative having an average particle diameter of 14 microns obtained by classifying this fine carbon powder (TSF451-20 manufactured by Toshiba Silicone Co., Ltd.). It was well dispersed to 60% by weight to obtain an electrorheological liquid as a suspension.

[Example 2] Heat treatment (calcination) in a nitrogen stream in Example 1 was performed at 450 ° C.
Was carried out to obtain a carbonaceous fine powder composed of spherulite. A silicone oil having a viscosity of 20 cSt at 25 ° C, which is a liquid phase component, is 40% by weight of carbonaceous fine powder having an average particle size of 16 microns (other characteristics are shown in Table 1) obtained by classifying this fine carbonaceous powder. (TSF451-20 manufactured by Toshiba Silicone Co., Ltd.) was well dispersed in 60% by weight to obtain an electrorheological liquid as a suspension.

[Example 3] 44% by weight of carbonaceous fine powder having an average particle diameter of 4 microns obtained by pulverizing and classifying a carbonaceous fine powder produced by the same method as in Example 2 was used as a liquid phase component 25 Viscosity at ℃
20cSt silicone oil (manufactured by Toshiba Silicone Co., Ltd .: TSF451-
20) 60% by weight was well dispersed to obtain an electrorheological liquid as a suspension.

Example 4 A carbonaceous fine powder (various characteristics are shown in Table 1) was prepared in the same manner as in Example 1 except that the calcination temperature was set to 200 ° C. A viscous liquid was obtained.

Example 5 A carbonaceous fine powder (various characteristics are shown in Table 1) was prepared in the same manner as in Example 1 except that the calcination temperature was set to 500 ° C., and the same formulation as in Example 1 was used. A viscous liquid was obtained.

Example 6 A carbonaceous fine powder (various characteristics are shown in Table 1) was prepared in the same manner as in Example 1 except that the calcination temperature was set to 600 ° C., and the same formulation as in Example 1 was used. A viscous liquid was obtained.

[Example 7] The carbonaceous fine powder obtained in Example 2 was heated under reflux at 80 ° C for 6 hours in a xylene solution of phenyltrimethoxysilane and then filtered to obtain a fine powder having the surface treated with silane. This fine powder 40
60% by weight of a liquid phase component of a silicone oil having a viscosity of 20 cSt at 25 ° C. (TSF451-20 manufactured by Toshiba Silicone Co., Ltd.)
It was well dispersed to a weight percentage to obtain an electrorheological liquid as a suspension.

Example 8 The carbonaceous fine powder obtained in Example 6 was heated and refluxed at 80 ° C. for 6 hours in a xylene solution of methyltrimethoxysilane, and then filtered.
A fine powder whose surface was silanized was obtained. 40% by weight of this fine powder was well dispersed in 60% by weight of a liquid phase component of silicone oil having a viscosity of 20 cSt at 25 ° C. (TSF451-20 manufactured by Toshiba Silicone Co., Ltd.) to obtain an electrorheological liquid as a suspension. It was

[Example 9] Commercially available phenol resin micro beads 60
Heat treatment was carried out at 0 ° C. to obtain a carbonaceous fine powder having an average particle size of about 8 μm (characteristics are shown in Table 1). Using this fine powder,
An electroviscous liquid was obtained with the same formulation as in Example 1.

[Example 10] 40% by weight of the carbonaceous fine powder of Example 2 was used to obtain a viscosity at 25 ° C.
40% by weight of an oil consisting of 10 cSt trifluorochloroethylene polymer and a naphthenic hydrocarbon oil with a viscosity of 5.2 cSt at 25 ° C 20
The wt% was mixed and dispersed to obtain an electroviscous liquid as a suspension.

Comparative Example 1 40% by weight of commercially available sodium polyacrylate fine powder was well dispersed in 60% by weight of the same silicone oil as in Example 1 to obtain an electrorheological liquid.

Comparative Example 2 13% by weight of commercially available silica gel fine powder was dispersed in 87% by weight of the same silicone oil as in Example 1 to obtain an electroviscous liquid.

Table 1 shows the characteristic values of the dispersed phases of Examples 1, 2, 4 to 6 and 10 and Comparative Examples 1 and 2.

In Table 1, carbon weight% and C / H ratio were obtained from elemental analysis values. The aromatic radical concentration was determined as the electron spin concentration. The electron spin concentration is measured by an electron spin resonance (ESR) device under the conditions of a central magnetic field of 331 mT (millitesla) and a microwave frequency of 9.233 GHz (gigahertz). Was used as a standard substance to determine the spin concentration. The electric resistance was measured by pressing the powder. The water content is Karl Fishe
It was measured from volatile matter at 250 ° C by method r).

The electrorheological effect was measured for each of the electrorheological liquids obtained in Examples 1 to 10 and Comparative Examples 1 and 2. The electroviscous effect is obtained by using a double cylinder type rotational viscometer, and applying a DC voltage between the inner and outer cylinders, the same shear rate (375sec ^-1 ), temperature
It was evaluated by shearing forces at 25 ° C and 80 ° C, and at the same time, the current density flowing between the inner and outer cylinders was measured. (Inner cylinder radius: 34 mm, outer cylinder radius: 36 mm, inner cylinder height: 20 mm) Shear force To when no electric field is applied to Table 2, DC electric field 2 KV /
The shearing force T when mm is applied, its difference T-To, and the current density when a DC electric field of 2 KV / mm is applied are shown.

In Table 2, the difference T-To obtained by subtracting the shear force To when the electric field is not applied from the shear force T when the electric field (2 KV / mm) is applied represents the magnitude of the electrorheological effect of the liquid. That is, a liquid having a large T-To in Table 1 exhibits a large electrorheological effect. The current density (μA / cm ² ) is related to the electric power required to develop the electric field (2 KV / mm).

[Operation] As is clear from Table 2, in Examples 1, 2 and 4 in which fine powder containing almost no water was used as the dispersed phase, high temperature (80
Comparative Example 1 in which a fine powder containing a large amount of water was used as the dispersed phase, although the electrorheological effect was exhibited at a low current density even at (.degree. C.).
Requires a large current density. In particular, in Example 2, at a lower current density than Comparative Example 1, a larger electrorheological effect than in Comparative Example 1 was obtained.

Further, when viewed from the data at room temperature (25 ° C.), in Examples 7 and 8 in which the carbonaceous fine powder coated on the particle surface was used as the dispersed phase, Example 2 in which the uncoated carbonaceous fine powder was used as the dispersed phase
Although the current is significantly reduced compared to Nos. 6 and 6, the electrorheological effect does not drop much.

The thermosetting resin carbide of Example 9 also exhibits the electrorheological effect like the mesophase spherules, and has the characteristic of a non-aqueous system having a high spin concentration.

On the other hand, although the silica of Comparative Example 2 exhibits an electrorheological effect as shown in Table 2, no radicals are detected as shown in Table 1 and it is understood that the silica is an aqueous electrorheological liquid.

When an AC electric field of 2 KV / mm was applied to the liquid of Example 1, T was 522 g · cm and current density was 66 μA / cm ^{2 at} 25 ° C.
Met. As described above, the electrorheological liquid containing the carbonaceous fine powder as a dispersed phase also functions with alternating current, and an electrorheological effect slightly lower than that of direct current can be obtained.

Next, for the electrorheological liquids of Example 1 and Comparative Example 1, the change in electrorheological effect before and after heat treatment at high temperature (120 ° C., 50 hours) was measured by a rotational viscometer at 25 ° C. Shown in FIGS.

FIG. 1 shows the electric field strength (horizontal axis: KV / mm) and torque before heat treatment (○ mark) and after heat treatment (△ mark) of the electrorheological liquid of Example 1 at high temperature (120 ° C., 50 hours). FIG. 2 is a diagram showing the relationship with (vertical axis: g · cm), and FIG. 2 is a diagram showing the results of similar measurements performed on the electrorheological liquid of Comparative Example 1.

As shown in FIG. 1, in Example 1, the electrorheological effect does not change even if continuous heating at a high temperature (120 ° C.) is performed, but Comparative Example 1
Then, as shown in FIG. 2, the power of exerting the electrorheological effect after the heat treatment is reduced.

FIG. 3 shows the case where an electric field of 1.5 KV / mm was applied to the electrorheological liquid of Example 2 (circle) and the case where no electric field was applied (Δ).
Fig. 4 shows the relationship between the torque (vertical axis: g · cm) of the rotational viscometer and the measured temperature (horizontal axis: ° C) in Fig. 4, and Fig. 4 shows the same measurement for the electrorheological liquid of Comparative Example 1. In these figures, the non-aqueous liquid of Example 2 functions from −50 ° C. to 200 ° C., while the aqueous liquid of Comparative Example 1 shows 0 ° C.
Below, the electrorheological effect is not shown, and at 90 ° C or higher, it can be seen that the current flows too much to measure the electrorheological effect.

[Advantages of the Invention] An electrorheological liquid that exhibits a high electrorheological effect over a wide temperature range but consumes less power and can maintain a high electrorheological effect for a long period of time can be obtained.

[Brief description of drawings]

FIG. 1 shows the electric field strength (horizontal axis: KV / mm) and torque before heat treatment (○ mark) and after heat treatment (△ mark) of the electrorheological liquid of Example 1 at high temperature (120 ° C., 50 hours). FIG. 2 is a diagram showing the relationship with (vertical axis: g · cm), and FIG. 2 is a diagram showing the results of similar measurements performed on the electrorheological liquid of Comparative Example 1. FIG. 3 shows the case where an electric field of 1.5 KV / mm was applied to the electrorheological liquid of Example 2 (circle) and the case where no electric field was applied (Δ).
Fig. 4 shows the relationship between the torque (vertical axis: g · cm) of the rotational viscometer and the measured temperature (horizontal axis: ° C) in Fig. 4, and Fig. 4 shows the same measurement for the electrorheological liquid of Comparative Example 1. It is a figure which shows a result.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C10M 101: 02) C10N 20:02 20:06 AZ 40:14 (72) Inventor Yoshiki Fukuyama Tokyo 3-5-8-104 Ogawa Higashi-cho, Kodaira-shi, Tokyo (72) Tsubasa Saito 1265-2 Kamiirai, Tokorozawa, Saitama Prefecture (56) References JP-A-63-97694 (JP, A) JP-A-64-6093 (JP, A)

Claims (3)

[Claims] 1. An average particle size of 0.01 to 100 microns and a carbon content of 8
0 to 97% by weight and C / H ratio (carbon / hydrogen atom ratio) 1.2 to 5
An electrorheological liquid comprising a dispersed phase of 1 to 60% by weight of carbonaceous fine powder and a liquid phase of 99 to 40% by weight of electric insulating oil having a viscosity of 0.65 to 500 centistokes at room temperature. 2. Optically anisotropic small spheres produced by heat treatment of coal tar pitch or petroleum pitch by carbonaceous fine powder are separated from pitch components and then heated to 200 to 600 ° C. in an inert atmosphere. The electrorheological liquid according to claim 1, which is obtained by processing. 3. The electrorheological liquid according to claim 1, wherein the carbonaceous fine powder is coated with an electrically insulating thin film.