JPH0790287A - Powder for electrorheological fluid and electrorheological fluid using the same - Google Patents

Abstract

(57) [Abstract] [Purpose] A powder for electrorheological fluid that exhibits a high electrorheological effect with low power consumption over a wide temperature range, and a non-aqueous electrorheological material with a low initial viscosity and a high electrorheological effect. Provide fluid. [Structure] The carbonaceous powder is characterized by having a true spherical shape, and preferably, the true spherical shape is such that the deviation of the maximum diameter and the minimum diameter of the powder from the average diameter is A powder for an electrorheological fluid that is within 30%, and an electrorheological fluid in which the powder is dispersed in an oil medium having electrical insulation.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a powder for electrorheological fluid,
More specifically, the present invention relates to a powder for electrorheological fluid, which is made of carbonaceous powder having a spherical shape, and an electrorheological fluid in which the powder is dispersed in an oil medium having electrical insulation.

[0002]

2. Description of the Related Art An electrorheological fluid has a large viscoelastic property and can be reversibly changed by electric control, and the phenomenon that the apparent viscosity of the fluid greatly changes by applying an electric field is the Winslow effect. Has been known for a long time, and its application as a component for electrically controlling devices and parts such as clutches, valves, engine mounts, actuators, robot arms, etc. has been studied. However, the electrorheological fluid in the early stage is one in which powder such as starch is dispersed in mineral oil or lubricating oil, and the electrorheological effect is exhibited, but there is a drawback that the reproducibility is poor.

For this reason, many proposals have been made mainly for powders used as dispersoids for the purpose of obtaining a fluid having a high electrorheological effect and excellent reproducibility. For example, JP-A-53-93186 discloses a highly water-absorbing resin having an acid group such as polyacrylic acid, JP-B-60-3111 discloses an ion exchange resin, and JP-A-62-95397 discloses an alumina silicate. Is listed. These are all hydrophilic solid powders, which are made to contain water and dispersed in an insulating oily medium, and the powders are formed by the action of water when a high voltage is applied from the outside. It is said that the particles are polarized, and this polarization causes crosslinking in the direction of the electric field between the particles to increase the viscosity.

However, the water-containing electrorheological fluid using the water-containing powder cannot obtain a sufficient electrorheological effect in a wide temperature range and limits the use temperature and raises the temperature in order to prevent evaporation or freezing of water. Due to many problems such as increase in current used, instability due to migration of water, and corrosion of electrode metal when high voltage is applied, it was difficult to put into practical use.

In order to improve this problem, a non-aqueous electrorheological fluid which does not use water-containing particles has been proposed. For example,
In JP-A-61-216202, organic semiconductor particles such as polyacenequinone are formed, and in JP-A-63-97794 and JP-A-1-164823, a conductive thin film is formed on the surface of organic or inorganic solid particles, Furthermore, there is described a dielectric particle having an electrically insulating thin film formed thereon, that is, a thin film-coated composite particle that essentially requires a thin film having conductive / insulating electrical properties. Further, as the dispersoid powder having controlled electric characteristics, surface-treated metal particles, metal-coated inorganic powder and the like are known. However, all of the non-aqueous electrorheological fluids using these powders do not have a sufficient electrorheological effect at low power consumption, are difficult to industrially manufacture, and only function in an alternating electric field. However, it has not been put to practical use yet.

[0006]

SUMMARY OF THE INVENTION In order to solve this problem, the inventors of the present invention previously disclosed in Japanese Patent Application Laid-Open No. 3-47896 a carbonaceous fine powder having a specific particle size and an electric insulating oil having a specific viscosity. We have proposed a non-aqueous electrorheological fluid with high electrorheological effect and low power consumption. In order to further improve the electrorheological effect, it is necessary to increase the filling rate of the dispersoid powder. However, increasing the filling rate of the powder improves the initial viscosity of the fluid, and as a result, when the current is applied. There is a problem that the electrorheological effect becomes low. The present invention is improved to further improve the electrorheological effect without lowering the initial viscosity of the electrorheological fluid. That is, an object of the present invention is to provide a powder for electrorheological fluid that exhibits a high electrorheological effect with low power consumption over a wide temperature range, and a non-aqueous electrorheological fluid that has a low initial viscosity and a high electrorheological effect. To provide.

[0007]

The powder for electrorheological fluid of the present invention is a carbonaceous powder, and is characterized by having a true spherical shape.

Further, the powder for electrorheological fluid of the present invention is
In the spherical shape, the deviation of the maximum diameter and the minimum diameter of the carbonaceous powder from the average diameter is within 30% of the average diameter. Characterize.

Further, the powder for electrorheological fluid of the present invention is
The carbonaceous powder is a powder for electrorheological fluid according to any one of the above items, characterized in that the carbonaceous powder is made of a substance having no surface fusion property under carbonization reaction conditions.

The electrorheological fluid of the present invention is characterized in that a carbonaceous powder having a spherical shape is dispersed in an electrically insulating oily medium.

[0011]

[Function] In the electrorheological fluid, the initial viscosity is lowered,
Although it is desirable to increase the electrorheological effect, in the conventional powder for electrorheological fluid, when the filling rate of the powder is increased to improve the electrorheological effect, the initial viscosity also increases, and as a result, , It was difficult to obtain a high electrorheological effect, but by obtaining the electrorheological fluid using the spherical carbonaceous powder of the present invention, the number of particles present per unit volume increases because the particles are spherical. Even if the filling rate is improved, an effective electrorheological effect can be obtained without causing a sharp increase in viscosity, and further, the particle density of the amorphous particles, which is observed in the irregular fine particles, cannot be increased. This has an excellent effect that the consumption current is not increased due to the local voltage increase caused by the uniformity.

[0012]

The present invention will be described in detail below with reference to specific examples.

The powder for electrorheological fluid of the present invention is a carbonaceous powder and has a spherical shape. Suitable carbonaceous powder has a carbon content of 80 to 97% by weight. The amount is preferably 85 to 95% by weight. C / H ratio of carbonaceous powder (carbon / hydrogen atom ratio)
Is preferably 1.2 to 5, particularly preferably 2 to
It is 4.

It has been known for a long time that the electric resistance of the dispersed phase of the electrorheological fluid is generally in the semiconductor region [W.
M. Winslow: J. Appl. Physics
Vol. 20, p. 1137 (1949)], carbonaceous powder having a carbon content of less than 80% by weight and a C / H ratio of less than 1.2 is an insulator and exhibits an electrorheological effect. Almost no liquid is obtained. On the other hand, the carbon content exceeds 97% by weight,
In addition, a material having a C / H ratio of more than 5 is close to a conductor, exhibits an excessive current even when a voltage is applied, and a fluid exhibiting an electrorheological effect cannot be obtained.

Specific materials having the above C / H ratio suitable for the powder for electrorheological fluid of the present invention include thermosetting resins such as phenol resin, cellulose, unsaturated polyester, furan resin and melamine resin, Examples thereof include coal tar pitch, petroleum pitch, and pitch obtained by thermally decomposing polyvinyl chloride. For example, these materials may be molded into a spherical shape and used, for example, by crushing a pitch and making the material spherical by an emulsion method.

The true spherical carbonaceous powder used in the present invention has an average particle size of about 0.01 to 100 μm, preferably 0.1 to 20 μm, more preferably 0.5 to 5 μm.
The range is m.

The powder for electrorheological fluid of the present invention is required to have a true spherical shape. In the present invention, the true spherical shape means that the powder particles observed by an electron microscope have a true spherical shape. Preferably, the deviation of the maximum diameter and the minimum diameter of one powder particle from the average diameter is within 30% of the average diameter, and more preferably 20%.
Within. Further, when it is assumed that the powder particles are ideally smooth and have a perfect spherical shape, the unevenness that is the deviation from the surface is preferably within 10% of the average diameter and within 5% of the average diameter. It is more preferable that there is. Most preferably, the deviation between the maximum diameter and the minimum diameter of the powder particles with respect to the average diameter is within 10% of the average diameter, and the unevenness that is the deviation from the ideal true spherical surface has 3% of the average diameter. Within the powder particles. Here, the average diameter of one powder particle means the average value of the maximum diameter and the minimum diameter of the powder particle.

As a method for producing a spherical carbonaceous powder, in addition to a method in which the above-mentioned pitch is crushed into a spherical shape by an emulsion method, a thermosetting resin having a spherical shape is inertized with nitrogen, argon or the like. Examples include a method of carbonizing by heat treatment so as to maintain a spherical shape in a gas atmosphere.

As the raw material used for producing the powder for electrorheological fluid of the present invention, any of the above-mentioned substances can be preferably used, but it does not have a surface fusion property particularly under the carbonization reaction condition. Preference is given to using substances. In the present invention, the substance having no surface fusion property refers to a substance whose surface does not exhibit heat melting property under the heat treatment temperature condition in the carbonization reaction, for example, 100 to 500 ° C., spherical cellulose, highly crosslinked phenol. In addition to resins that have excellent heat resistance such as resins that do not exhibit heat melting properties, substances that have a certain degree of heat resistance, such as ordinary thermosetting resins, but whose surface softens due to heat treatment, Those subjected to a surface treatment that inhibits the surface fusion property are preferably used. As the surface treatment, for example, a thermosetting resin formed into a spherical shape is (1) surface-cured by a wet method, (2) surface-cured by a dry method, (3) surface-treated with a surfactant, (4) Examples of the method include forming a heat resistant coating of silica or a fluorine-based substance. As a specific example of the surface treatment, for example, as a wet method, a spherical resin is heat treated in an aqueous acid solution of hydrochloric acid, sulfuric acid, oxalic acid, or the like, and as a dry method, an infusibilizing treatment is performed in an oxygen atmosphere, As the activator treatment, dip and dry in a silicone-based surfactant.For the heat-resistant film formation method, disperse in ethyl silicate, coat the surface with ethyl silicate, and then coat the coated spherical resin in water with an acid catalyst. Examples of the method include dispersing and heating to cause a hydrolysis reaction of ethyl silicate to form a silica film on the surface.

As described above, by using a substance having no surface fusion property under the carbonization reaction condition as a raw material used for producing the powder for electrorheological fluid of the present invention, the powder during the carbonization reaction can be obtained. Since it is possible to prevent the fusion of the powder, the obtained powder has good uniformity, and further, there is an advantage that the steps of crushing and crushing after the carbonization reaction are unnecessary.

Next, the electrorheological fluid according to claim 4 of the present invention will be described in detail. The electrorheological fluid of the present invention is obtained by dispersing the powder for electrorheological fluid in an electrically insulating oily medium, wherein the electrorheological fluid is a dispersoid in the electrorheological fluid. The powder for use is contained in an amount of 1 to 60% by weight, preferably 20 to 50% by weight, and the oil medium as a dispersion medium is contained in an amount of 99 to 40% by weight, preferably 80 to 50% by weight. If the amount of the dispersoid is less than 1% by weight, the electroviscous effect is small, and if it exceeds 60% by weight, the initial viscosity when no voltage is applied is increased, which is not preferable.

The electrically insulating oily medium which is a dispersion medium preferably has a volume resistivity at 80 ° C. of 10 ¹¹ Ω · m or more, and more preferably 10 ¹³ Ω · m or more. For example, hydrocarbon oils, ester oils, aromatic oils, silicone oils and the like can be mentioned. Specifically, aliphatic monocarboxylic acids such as neocapric acid, aromatic monocarboxylic acids such as benzoic acid, adipic acid, Aliphatic dicarboxylic acids such as glutaric acid, sebacic acid, azelaic acid, phthalic acid,
Examples thereof include aromatic dicarboxylic acids such as isophthalic acid and tetrahydrophthalic acid, dimethylpolysiloxane, and methylphenylpolysiloxane. These can be used alone,
You may use it in combination of 2 or more type. Among these, silicone oils such as dimethylpolysiloxane and methylphenylpolysiloxane are preferably used from the viewpoint that they do not deteriorate even when they are used in direct contact with a material having rubber-like elasticity or various polymer materials.

The electrically insulating oily medium has a viscosity of 0.65 to 500 centistokes at 25 ° C.,
It is preferably 5 to 200 centistokes, more preferably 10 to 50 centistokes.
By using a dispersion medium having a suitable viscosity, it is possible to efficiently and stably disperse the powder which is a dispersoid. When the viscosity of the oily medium exceeds 500 centistokes, the initial viscosity of the electrorheological fluid increases and the change in viscosity due to the electrorheological effect decreases. If it is less than 0.65 centistokes, volatilization is likely to occur and the stability of the dispersion medium deteriorates.

In the electrorheological fluid of the present invention, other dispersoid powders and additives such as surfactants, dispersants, inorganic salts and the like may be used together or blended within a range not impairing the effects of the present invention. it can.

Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to the following examples.

Characteristic Evaluation (1) Measurement of Particle Size The particle size of the powder for electrorheological fluid is MIC manufactured by Nikkiso Co., Ltd.
It measured using the ROTRAC SPA / MK-II type | mold apparatus.

(2) Characteristics of electrorheological fluid The viscosity of the electrorheological fluid at the initial and 2 kV voltage application and the current density of the electrorheological fluid at 2 kV voltage application were measured by RDS-II type device manufactured by Rheometrics Far East Co. It was measured at room temperature (about 25 ° C.) and a shear rate of 350 / sec.

(Example 1) 500 g of a resol-type phenol resin (manufactured by Unitika) having a spherical shape was mixed with 1.5 g of oxalic acid in water, and the mixture was stirred vigorously to prepare 1
After heating to 00 ° C., filtration, washing and drying are performed. The powder thus obtained was carbonized at 600 ° C. for 5 hours in an argon atmosphere to obtain a carbonaceous spherical powder having no fusion and having a spherical shape. This was classified to obtain a powder for electrorheological fluid having an average particle size of about 3.2 μm.

FIG. 1 is a 2000 × electron micrograph of the powder for electrorheological fluid obtained in Example 1. It was confirmed that the powder was a spherical powder having a smooth surface. That is, the deviation of the maximum diameter and the minimum diameter of the obtained powder from the average diameter was within 10%, and the surface irregularities were within 3% of the average diameter.

True spherical carbonaceous powder 40 obtained in Example 1
A silicone oil having a viscosity of 10 centistokes at 25 ° C. as a dispersion medium (manufactured by Toshiba Silicone:
TSF451-10) was well dispersed in 60 wt% to obtain an electrorheological fluid, which was designated as Product 1 of the present invention.

The initial viscosity of the obtained electrorheological fluid, the viscosity when a voltage of 2 kV / mm was applied, and the current density were measured, and the results are shown in Table 1.

(Embodiment 2) A spherical divinylbenzene resin (manufactured by Sekisui Chemical Co., Ltd.) was used for 300 times in an oxygen atmosphere.
Heat treatment is performed at 8 ° C. for 8 hours to introduce oxygen into the resin to make it infusible. Further, by carbonizing at 550 ° C. for 4 hours under an ultrahigh pressure in an argon atmosphere, a powder for electrorheological fluid having a true spherical shape and an average particle diameter of about 3.2 μm without fusion was obtained.

True spherical carbonaceous powder 40 obtained in Example 2
An electrorheological fluid was obtained in the same manner as in Example 1 using% by weight, and the product 2 of the present invention was obtained. The obtained electrorheological fluid was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

(Example 3) Cellulose spheres having a spherical shape (Kanebo Co., Ltd.) were carbonized in an argon atmosphere at 530 ° C. for 5 hours to give a spherical shape with an average particle diameter of 4.2 μm. A powder for electrorheological fluid was obtained.

FIG. 2 is a 2000 × electron micrograph of the powder for electrorheological fluid obtained in Example 3. It was confirmed that the powder was a spherical powder having a smooth surface. That is, the deviation of the maximum diameter and the minimum diameter of the obtained powder from the average diameter was within 10%, and the surface irregularities were within 3% of the average diameter.

True spherical carbonaceous powder 40 obtained in Example 3
An electrorheological fluid was obtained in the same manner as in Example 1 using% by weight, and the product 3 of the present invention was obtained. The obtained electrorheological fluid was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

(Example 4) The crushed irregular-shaped pitch was dispersed in an oil bath, and formed into a spherical shape by an emulsion method, followed by filtration separation and heat treatment at 430 ° C for 1 hour to obtain a spherical shape. A powder for electrorheological fluid having an average particle diameter of about 3.5 μm having the above-mentioned shape was obtained.

True spherical carbonaceous powder 40 obtained in Example 4
An electrorheological fluid was obtained in the same manner as in Example 1 using% by weight, and the product of the present invention was obtained. The obtained electrorheological fluid was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

(Example 5) 500 g of a resole-type phenol resin (manufactured by Unitika) having a spherical shape is impregnated in ethyl silicate 28 (manufactured by Colcoat) to coat the surface of the resin with ethyl silicate. Disperse this in water with an acid catalyst (paratoluene sulfonic acid) and
Was subjected to a hydrolysis reaction of ethyl silicate to form a silica film on the resin surface, followed by filtration, washing and drying. The powder thus obtained was carbonized at 600 ° C. for 5 hours in an argon atmosphere to obtain a carbonaceous spherical powder having no fusion and having a spherical shape. This carbonaceous spherical powder was washed in an aqueous solution of hydrogen fluoride to remove excess silica attached to the surface, filtered, washed with water and dried. This was classified to obtain a powder for electrorheological fluid having an average particle size of about 3.2 μm.

True spherical carbonaceous powder 40 obtained in Example 5
An electrorheological fluid was obtained in the same manner as in Example 1 using% by weight, and the present invention product 5 was obtained. The obtained electrorheological fluid was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 1 A phenol resin powder having an irregular particle size and an average particle size of 3 μm obtained by pulverization and classification was used in Example 1.
The same treatment as above was performed to obtain an irregularly shaped carbonaceous powder for electrorheological fluid.

FIG. 3 is a 2000 × electron micrograph of the powder for electrorheological fluid obtained in Comparative Example 1. It was confirmed that the powder had an irregular shape.

Irregularly shaped carbonaceous powder 4 obtained in Comparative Example 1
An electrorheological fluid was obtained in the same manner as in Example 1 using 0% by weight, and was used as Comparative Product 1. The obtained electrorheological fluid was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 2 Pitch powder was crushed and classified to obtain an irregular-shaped pitch powder having an average particle diameter of 3.5 μm as a powder for electrorheological fluid.

FIG. 4 is a 2000 × electron micrograph of the powder for electrorheological fluid obtained in Comparative Example 2. It was confirmed that the powder had an irregular shape and had irregularities on the surface.

Irregularly shaped carbonaceous powder 4 obtained in Comparative Example 2
An electrorheological fluid was obtained in the same manner as in Example 1 using 0% by weight, and was used as Comparative product 2. The obtained electrorheological fluid was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 3) The bulk mesophase powder obtained by crushing the bulk mesophase obtained by heat-treating the pitch and classifying the bulk mesophase powder was used as a powder for electrorheological fluid.

FIG. 5 is a 2000 × electron micrograph of the powder for electrorheological fluid obtained in Comparative Example 3. It was confirmed that the powder had an irregular shape.

Irregularly shaped carbonaceous powder 4 obtained in Comparative Example 3
An electrorheological fluid was obtained in the same manner as in Example 1 by using 0% by weight to obtain Comparative Product 3. The obtained electrorheological fluid was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 4) 500 g of a resol type phenol resin S type (manufactured by Unitika) having a spherical shape,
Carbonization was carried out at 600 ° C. for 5 hours in an argon atmosphere to obtain an irregularly shaped carbonaceous powder in which partial fusion was observed. This was crushed to obtain a powder for electrorheological fluid having an average particle size of about 6.2 μm.

Irregularly shaped carbonaceous powder 4 obtained in Comparative Example 4
An electrorheological fluid was obtained in the same manner as in Example 1 by using 0% by weight to obtain Comparative product 4. The obtained electrorheological fluid was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0052]

[Table 1] As is clear from the results in Table 1, all of the electrorheological fluids of the products 1 to 5 of the present invention using the powder for electrorheological fluid of the present invention have sufficient viscosities when a voltage is applied and are compared with the initial viscosities. The viscosity was high when a voltage was applied, and a high electrorheological effect was exhibited. On the other hand, the electrorheological fluids of Comparative Products 1 to 4 using the irregularly shaped carbonaceous powder as the powder for electrorheological fluid have a small difference between the initial viscosity and the viscosity at the time of voltage application as compared with the examples, No electrorheological effect was obtained. Furthermore, the present invention product 1
In Nos. 5 to 5, even though the electrorheological effect was improved, the current density during voltage application did not remarkably increase, and the high electrorheological effect was obtained with low power consumption.

[0053]

Since the powder for electrorheological fluid of the present invention has the above constitution, it exhibits a high electrorheological effect over a wide temperature range with low power consumption. Furthermore, the non-aqueous electrorheological fluid using the same has a low initial viscosity and exhibits excellent electrorheological effect.

[Brief description of drawings]

FIG. 1 is a 2000 × electron microscope photograph of a true spherical electrorheological fluid powder made from the phenol resin of Example 1.

FIG. 2 is a 2000 × electron micrograph of a true spherical electrorheological fluid powder made from the cellulose spheres of Example 3.

FIG. 3 is a 2000-fold electron micrograph of a powder for irregular-shaped electrorheological fluid made of the phenol resin of Comparative Example 1 as a raw material.

FIG. 4 is a 2000 × electron micrograph of a powder for irregularly shaped electrorheological fluid, which is a pitch-crushed product of Comparative Example 2.

FIG. 5 is an electron micrograph (magnification: 2000) of a powder for irregularly shaped electrorheological fluid using the bulk mesophase of Comparative Example 3 as a raw material.

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[Procedure amendment]

[Submission date] February 21, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a 2000 × electron micrograph showing the particle structure of a powder for a spherical electrorheological fluid made from the phenol resin of Example 1 as a raw material.

FIG. 2 is a 2000 × electron micrograph showing a particle structure of a powder for a spherical electrorheological fluid made of the cellulose spheres of Example 3 as a raw material.

FIG. 3 is a 2000 × electron micrograph showing the particle structure of a powder for an irregular shaped electrorheological fluid made from the phenol resin of Comparative Example 1 as a raw material.

4 is a 2000 × electron micrograph showing the particle structure of a powder for irregularly shaped electrorheological fluid, which is a pitch pulverized product of Comparative Example 2. FIG.

5 is a 2000 × electron micrograph showing a particle structure of a powder for an irregular shaped electrorheological fluid that uses the bulk mesophase of Comparative Example 3 as a raw material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mari Miyano 3-1-1 Ogawahigashi-cho, Kodaira-shi, Tokyo Inside Bridgestone Corporation

Claims (4)

[Claims] 1. A powder for an electrorheological fluid, which is a carbonaceous powder and has a spherical shape. 2. The true spherical shape is such that the deviations of the maximum diameter and the minimum diameter of the carbonaceous powder from the average diameter are within 30% of the average diameter, respectively. The powder for electrorheological fluid described. 3. The powder for electrorheological fluid according to claim 1, wherein the carbonaceous powder is made of a substance having no surface fusion property under carbonization reaction conditions. 4. An electrorheological fluid, characterized in that a carbonaceous powder having a spherical shape is dispersed in an electrically insulating oily medium.