JPH06243718A - Composite dielectric fine grain and electric viscous fluid using same - Google Patents

Abstract

PURPOSE:To obtain the fluid showing a high electroviscous effect stably by coating the surface of a fine grain, which is changed to the carbonaceous material by burning, with the insulating fine grains, and burning it to obtain the composite dielectric fine grains, and dispersing these composite fine grains in the insulating liquid. CONSTITUTION:The surface of fine grains of the organic high polymer material such as phenol resin, which is changed to the carbonaceous material by burning, is coated with the insulating fine grains such as SiO2, Si3N4 to obtain the composite dielectric fine grains. These obtained compound dielectric fine grains are dispersed in the electrically insulating liquid such as silicone oil and ester group oil at 5-50 capacity %. High electroviscous effect is thereby obtained stably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to composite dielectric fine particles and an electrorheological fluid using the same, and more particularly to an electrorheological fluid capable of stably obtaining a high electrorheological effect. Such an electrorheological fluid is useful for an electrically controllable vibration damping device, power transmission device, or the like.

An electrorheological fluid is an action (OF) of an applied electric field.
It is a fluid that exhibits a so-called electrorheological effect in which its shear stress (apparent viscosity) changes rapidly and reversibly by F, ON (change of electric field).

[0003]

2. Description of the Related Art Generally, an electrorheological fluid is made by dispersing polarizable fine particles in an electrically insulating liquid, and the mechanism of manifesting the electrorheological effect is considered as follows. That is, when an electric field is applied to the electrorheological fluid, the dispersed fine particles are polarized, and further an electrostatic attractive force based on the polarization forms a chain-like aggregate structure, and as a result, the electrorheological effect is exhibited.

Conventionally, as an electrorheological fluid based on such a principle, many fluids using dispersed particles such as water or particles adsorbing a polar solvent other than water are known. Further, as one of fluids using particles containing no adsorbing component as dispersed particles, one using composite dielectric fine particles in which conductive fine particle surfaces are coated with an insulating layer (T. Sasada e
t. al: Proc. 17th Japan Con
g. Mater. Res. , 288 (1974), JP-A-63-97694, and JP-A-3-137196).

[0005]

However, in a fluid using particles in which water or a solvent other than water is adsorbed, power consumption increases at high temperatures, and the adsorbed components volatilize when exposed to high temperatures for a long time. However, there is a problem that the electrorheological effect is reduced. Further, in the case of the fluid using the conventional composite dielectric particles, the insulating layer is formed by the chemical reaction on the surface of the conductive particles, but with this method, the aggregation between the composite dielectric particles and the nonuniformity of the insulating layer film thickness are caused. Therefore, it is difficult to arbitrarily control the thickness of the insulating layer to be generated. In addition, there is a limit in terms of the particle size of usable particles, and there are problems in terms of electrorheological effect and dispersion stability. The present invention has been made to solve the above problems, and an object of the present invention is to produce an electrorheological fluid capable of stably obtaining a high electrorheological effect.

[0006]

SUMMARY OF THE INVENTION The object of the present invention, however, is to provide a composite dielectric prepared by baking composite particles in which the surfaces of the carbonaceous particles are covered with insulating particles in an inert atmosphere. Body particles and an electrorheological fluid obtained by dispersing the composite dielectric particles in an electrically insulating liquid,
More easily achieved.

The present invention will be described in detail below. The composite fine particles used in the present application can be obtained by coating the surface of the fine particles that become carbonaceous by firing with insulating fine particles. As the fine particles that become carbonaceous by firing (hereinafter referred to as “fine particles”), organic polymer materials can be used, and specifically, phenolic resins, polyacetals, polyethylene oxides, polycarbonates, polyesters, epoxy resins, polyethylenes. , Polyvinyl acetate, polymethylmethacrylate, polyacrylonitrile, polybutadiene, polyisobutylene and the like. These fine particles become carbonaceous when fired in an inert atmosphere. The inert atmosphere is an atmosphere composed of vacuum or a rare gas and a gas having poor reactivity, and examples of the gas used include argon and nitrogen.

The particle size of "fine particles" is 0.1-10.
Particles of 0 μm can be used. Average particle size 0.1μ
Particles of m or less have a large viscosity due to an increase in the specific surface area of the particles when no electric field is applied, and the ratio of the viscosity when an electric field is applied and when there is no electric field becomes small. Further, particles larger than the average particle diameter of 100 μm are likely to cause particle sedimentation. The insulating fine particles used for coating the “fine particles” have a resistivity of 10 ⁹ Ωcm.
As described above, it is more preferable to use a substance having a resistivity of 10 ¹⁰ Ωcm or more and having a high strength against dielectric breakdown. In addition, it is necessary to use the above-mentioned insulating fine particles that do not lose the insulating property even if fired in an inert atmosphere, and an inorganic insulating material is preferably used. Specifically, specifically, SiO ₂ , Si ₃
Examples thereof include N ₄ , Al ₂ O ₃ , Ta ₂ O _{5 and the} like.

[0009] In the composite fine particles of the present invention, it is possible to control the thickness of the insulating eight layers by changing the particle diameter of the insulating fine particles used, the average particle diameter of the insulating particles (d _i ) Is determined from the average particle diameter (d _c ) of the “fine particles”, the strength of the insulating fine particles against dielectric breakdown (E _frac ), and the applied electric field (E) using the following equation (1) as a guide.

[0010]

[Equation 1]

If the average particle size of the insulating fine particles is smaller than d _i , dielectric breakdown occurs when an electric field is applied. Moreover, when the average particle diameter of the insulating fine particles is much larger than d _i , a sufficient electrorheological effect cannot be obtained. Therefore, the average particle size of the insulating fine particles is preferably equal to or slightly larger than d _i . The particle size distribution of the insulating fine particles is preferably uniform in order to achieve uniform coating.

The amount M _i of insulating fine particles required to coat 1 kg of “fine particles” with insulating fine particles is _{calculated from} the particle diameters d _c and d _{i of} each particle and the specific gravities ρ _c and ρ _{i as} follows. (2)
Calculated by the formula.

[0013]

[Equation 2]

If the amount of the insulating fine particles is less than this, the insulation may be incomplete and may cause dielectric breakdown. On the other hand, if it is more than this, the coated fine particles agglomerate with each other, and the viscosity in the absence of an electric field increases, which is not preferable.

The method of coating the "fine particles" with insulating fine particles is not particularly limited as long as they are uniformly coated.
Heteroaggregation method (Polymer processing, 38 (7), pp.322
-328 (1989)) and the mechanofusion method (crushing, No. 33, pp. 66-71 (1989)) and the like can be used. Further, in order to bond the insulating fine particles more firmly to the surface of the “fine particles”, it is possible to add a small amount of a compound that forms an insulating layer by a chemical reaction on the surface of the “fine particles”.

By firing the composite fine particles obtained by the above method, the insulating fine particles coating the surface of the "fine particles" and the "fine particles" are firmly bonded and the "fine particles" are changed to carbonaceous material so as to have conductivity. To give composite dielectric fine particles. The firing temperature varies depending on the type of “fine particles” and insulating fine particles used, but is generally 300 ° C. to 1000 ° C.
C is preferred. When the firing temperature is low, the "fine particles" are not carbonized and the conductivity is low, so that a sufficient electrorheological effect cannot be obtained. Further, since the insulating fine particles do not bond firmly, there is a problem in durability. If the firing temperature is too high, the composite dielectric fine particles will sinter with each other and the viscosity will increase when no electric field is applied, which is not preferable.

The composite dielectric fine particles thus obtained are dispersed in the electrically insulating liquid so as to have a content of 5 to 50 vol%. Electrically insulating liquid has a resistivity of 10 ⁹ Ω
cm or more, more preferably a liquid having an insulating property of 10 ¹⁰ Ωcm or more, and examples thereof include silicone oil, ester oil, and mineral oil. Specifically, dimethylpolysiloxane, dioctyl phthalate, dibutyl phthalate, Examples thereof include diisononyl phthalate, trioctyl trimellitate, triisodecyl trimellitate, dibutyl adipate, butyl stearate, paraffinic mineral oil, and naphthenic mineral oil.

When the composite dielectric fine particles are dispersed in the electrically insulating liquid, the content is preferably 5 to 50% by volume. The composite dielectric fine particles are 5
If it is less than vol%, a sufficient electrorheological effect cannot be obtained. On the other hand, if it is more than 50 vol%, the viscosity in the absence of an electric field increases, and the ratio of the viscosity when an electric field is applied to the viscosity in an electric field becomes small, such being undesirable.

A method such as a ball mill or a paint shaker can be used as a method for dispersing the composite dielectric fine particles in the electrically insulating liquid. In addition, additives such as a dispersant can be used if necessary. Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

[0020]

【Example】

[Example 1] Phenolic resin particles having an average particle size of 10 µm and a specific gravity of 1.27 ("UNIVEX C1" manufactured by Unitika Ltd.)
0 ") 100 g is dispersed in 5 L of water, and pH is adjusted with hydrochloric acid.
Adjusted to 4. This dispersion has an average particle size of 45 nm and SiO 2.
₂ 6.34 g of silica sol (Cataloid SI-45P, manufactured by Catalysts & Chemicals Industry Co., Ltd.) having a concentration of 40 wt% was added, and the pH was readjusted to 4 and stirred for 30 minutes. As a result, the phenolic resin particles and the silica sol particles caused heterocoagulation, and the surface of the phenolic resin particles was uniformly covered with a single particle layer of silica sol.

The dispersion was allowed to stand for 12 hours to allow the particles to settle, the supernatant was discarded, the residue was sufficiently dried, and the phenol resin particles were carbonized by firing at 700 ° C. in nitrogen. In this way, particles were obtained in which the inside of the particles was conductive carbonaceous particles and the surface of which was uniformly coated with insulating silica sol particles.

The specific gravity of the obtained particles was 1.63.
Silicone oil (Toray Dow Corning Silicone Co., Ltd. “SH200”)
Ball mill dispersed in 10 cs "specific gravity 0.934),
The sample was used for measuring the electrorheological effect. The characteristics of the sample when an electric field is applied are the shear rate of 365 s ^-1 when a voltage is applied between the inner and outer cylinders using a coaxial double cylinder type rotational viscometer.
Measurement of shear stress (distance between electrodes 1mm, temperature 2
5 ° C). The result is shown in FIG. As is clear from FIG. 1, the shearing force greatly increases due to the increase of the applied electric field.

Comparative Example 1 Aluminum particles having an average particle size of 2.8 μm (“AC-500”, manufactured by Toyo Aluminum Co., Ltd.)
5 ″) was dispersed in 500 ml of water, heated with stirring and treated at 70 ° C. for 4 hours. In this way, particles whose surface was covered with an insulating layer of boehmite were obtained.

The specific gravity of the obtained particles was 2.93.
The particles were dispersed in the same silicone oil as that used in Example 1 so that the amount of particles was 30 vol%, and used as a sample for measuring an electrorheological effect, and the measurement was performed in the same manner as in Example 1. The measurement result is shown in FIG.
Shown in.

[0025]

According to the present invention, an electrorheological fluid that stably exhibits a high electrorheological effect can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing an electrorheological effect on an applied electric field of electrorheological fluids of Examples and Comparative Examples of the present invention. The horizontal axis represents the applied electric field (KV · mm ⁻¹ ), and the vertical axis represents the shear stress (P
a).

Claims (2)

[Claims] 1. Composite dielectric fine particles obtained by firing composite fine particles in which the surface of fine particles that become carbonaceous by firing is coated with insulating fine particles in an inert atmosphere. 2. An electrorheological fluid obtained by dispersing the composite dielectric particles according to claim 1 in an electrically insulating liquid.