JP2617959B2 - Electrorheological fluid - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrorheological fluid whose viscosity can be controlled by a voltage, and more particularly to an electrorheological fluid containing water-free fine particles as components. And actuators such as shock absorbers.

[Prior art] Fluid in which water-containing fine particles such as silica, starch and ion exchange resin are dispersed in an electrically insulating oily medium such as trans oil, chlorinated paraffin, silicone oil, etc., has a large and instantaneous and reversible viscosity change upon application of a voltage. I do. This phenomenon has been known for a long time as the Winslow effect.
Applications to oscillators and the like have been studied.

It is believed that the Winslow effect occurs because the electric double layer formed by the water on the surface of the particles is polarized by an external electric field and cross-links are generated between the particles along the direction of the electric field due to electrostatic attraction. Conventionally, as a method for enhancing the Winslow effect, for example, a method in which fine particles of a strongly acidic or strongly basic ion exchange resin are dispersed in a higher ester of an aromatic carboxylic acid (see JP-A-50-92278), A dispersion in which hydrophilic solid particles are dispersed in a halogenated diaryl compound (see JP-A-58-501178), and a dispersion in which aluminum silicate particles are dispersed in silicone oil using an amino group-containing polysiloxane as a dispersant (Japanese Patent Laid-Open No. Sho 62) −95397) has been proposed.

[Problems to be Solved by the Invention] All of the electrorheological fluids proposed so far disperse water-absorbing solid fine particles in an insulating oily medium, and the polarization of an electric double layer formed by water on the surface of the particles. It utilizes the phenomenon.

By the way, conventional electrorheological fluids using solid fine particles that have absorbed water have insufficient stability due to water migration, dissolution of electrode metal due to application of high voltage, gas generation due to electrolysis of water, and the amount of current due to temperature rise. There are a number of problems attributable to the presence of water, such as an increase.

The present inventors have considered that there is a possibility that a new electrorheological fluid may be obtained if there is another method that can easily generate a polarization charge on the particle surface other than the presence of water in order to solve the above problem. It has been achieved by repeating many experiments with inorganic solid particles having excellent heat resistance with respect to the polarization of the system particles.

[Means for Solving the Problems] The present invention makes use of the excellent dielectric polarizability of metals and solves the problems of metals, for example, the problems of dielectric breakdown and easy sedimentation. The present invention relates to a new electrorheological fluid having excellent performance and durability. That is, fine particles having a three-layer structure in which a conductive thin film layer is formed on the surface of an inorganic solid particle and an insulating thin film layer is further formed on the surface thereof are dispersed in an oil medium having excellent electrical insulation properties. Fluid.

As the inorganic solid particles used in the present invention, those having a small specific gravity are preferable, and silicon, boron, aluminum,
Preferred examples include particles or composite compound particles mainly composed of a lightweight element itself of Group II, III and IV of the periodic table such as magnesium and beryllium, or a compound such as an oxide, nitride or carbide thereof ( However, aluminum and magnesium alone are excluded because they are conductors themselves). Particularly, silicon, boron, silica, boron nitride and the like are preferable particles having a small specific gravity.

The shape of these particles is preferably as round as possible, spherical or elliptical, and spherical is most preferable.

The particle size is preferably from several μm to several tens μm, and a smaller particle size is particularly preferable from the viewpoint of preventing settling of particles and sliding wear. However, if it is less than 1 μm, the formation of crosslinks between particles is weak, which is not preferable. As for the particle size distribution, those which are as close to monodisperse as possible tend to exhibit stable electrorheological properties.

The conductive thin film layer of the present invention is formed such that when a particle having the layer on the surface is placed under an electric field, a large dielectric polarization occurs on the particle surface, and a highly conductive one is preferable. The electrical resistance must be at most 10 ⁵ Ω · cm.

Examples of such a conductive thin film material include a metal, a metal compound, an organic conductor, and carbon. Methods such as chemical plating, vapor deposition, solution or powder coating, surface reaction, and surface polymerization are used for forming a thin film. The thickness of the conductive layer is generally sufficient if it is several μm. In particular, metal plating and evaporation, surface reaction of metal compounds such as copper sulfide, a highly conductive substance obtained by a surface polymerization reaction such as polypyrrole and polyacetylene, even with a thickness of about 0.1 μm,
It shows a sufficient dielectric polarization effect for the purposes of the present invention.

It is preferable that the conductive layer covers the particle surface as uniformly as possible and covers the entire surface of the particle. When a conductive layer is formed by coating with a conductive substance or by surface polymerization, secondary particles are generally easily generated, but it is preferable to suppress as much as possible by adjusting conditions.

Next, the electrically insulating thin film layer is a thin film layer formed of an organic and inorganic electrically insulating substance formed on the conductive thin film. By providing this electrically insulating thin film layer, the polarization charge generated in the conductive thin film on the surface of the particles placed under an electric field easily causes charge neutralization by contact between the particles,
By forming a conductive path between the electrodes, it is possible to prevent a dielectric breakdown accompanying sparks from occurring.

Organic and inorganic insulating materials that can be used for such purposes include polyvinyl chloride, polyamide, polyacrylonitrile, organic synthetic polymer materials such as polyvinylidene fluoride, wax, asphalt, organic natural polymer materials such as varnish, Representative examples include inorganic compounds such as silica, alumina, titanium oxide, and barium titanate.

Generally, the volume or surface electrical resistance is 10 ₈ Ω or 10 ₈
It is preferable to use a substance having a dielectric breakdown strength and a dielectric constant as large as possible that are Ωcm or more.

The thickness of the insulating thin film layer is preferably as thin as possible unless dielectric breakdown occurs, but is preferably 1 μm or less, more preferably 0.5 μm or less from the viewpoint of abrasion resistance and uniformity.

For forming the insulating thin film layer, a known coating method such as solution or powder coating, surface polymerization, vapor deposition, and surface reaction can be applied. In this case, as in the case of forming the conductive thin film layer, it is preferable to coat the entire surface with a uniform thickness, but it is necessary to prevent generation of secondary particles during the coating as much as possible. Examples of such a coating method include various methods introduced in Industrial Technology Library 25 "Microcapsule" (by Asashi Kondo, Nikkan Kogyo Shimbun), or insulation by oxidizing or nitriding the surface of the conductive thin film layer. A method of forming a metal oxide film by adsorbing a metal alkoxide on the surface and then hydrolyzing or thermally decomposing the metal alkoxide to form a metal oxide film can be used as a preferable method.

A three-layer structure particle in which two layers of the conductive layer and the insulating layer are laminated on the surface of an inorganic solid particle requires a considerable adhesive force between these layers in practical use. In many cases, physical or chemical treatments such as oxidation and etching of the resin, and the use of binding aids such as coupling agents and anchor coating agents are effective.

The oily medium used in the present invention is diphenyl chloride, butyl sebacate, aromatic polycarboxylic acid higher alcohol ester, halophenyl alkyl ether, trans oil, paraffin chloride, which has been used in conventional electrorheological fluids.
As long as it has high electrical insulation and dielectric breakdown strength, is chemically stable, and has a specific gravity close to that of the dispersed fine particles, of course, any of fluorine-based oil and silicone-based oil can be used.

The mixing weight ratio of the derivative fine particles of the present invention to the oil medium is selected in the range of 5:95 to 60:40, preferably 10:90 to 50:50. Additives can be used in the mixed electrorheological fluid for the purpose of dispersion stability, rust prevention, oxidation prevention and the like as long as the electric insulation properties are not significantly reduced.

[Effects] The electrorheological fluid of the present invention solves the biggest drawbacks of the conventional ones: problems such as poor long-term stability due to the presence of water, elution of electrodes, and a decrease in temperature dependence of electrorheological characteristics. It is durable even at high temperatures, and enables the realization of various electromechanical actuators such as valves, clutches, and shock absorbers that are compact and can be easily electrically controlled.

[Example] Hereinafter, the present invention will be described in more detail with reference to an example. The electrorheological characteristics in this example are sealed in a gap (1.0 mm) between a cylinder having an inner diameter of 40 mm having the same central axis and a rotor having an outer diameter of 38 mm. The sample fluid was subjected to shearing at a predetermined speed, and the shearing stress and current generated when a constant alternating current (50 cycles) voltage was applied were evaluated.

 The amounts of the components shown in the examples are on a weight basis.

Example 1 A spherical silica particle (average particle size: 5 μm) was subjected to a sensitizing agent [Okuno Pharmaceutical Co., Ltd., TMP Sensitizer] treatment, water washing, an activator (the same as above, TMP activator) treatment, and a water washing process. Thereafter, an electroless plating treatment was performed at 90 ° C. for 30 minutes with stirring using a nickel electroless plating solution (same as above, Top Nicolon), and a nickel layer having an average thickness of 0.2 μm was applied to the particle surface.

Next, the particles were immersed in a toluene solution of 1% by weight of isopropoxyaluminum, and the excess solution was removed by filtration. Then, the particles were gently stirred in a large amount of ethanol containing 0.5% by weight of water, and the surface of the particles was treated with isopropoxyaluminum. An aluminum oxide film as a hydrolyzate was formed.

After the particles were separated by filtration, the particles were heat-treated at 300 ° C. for 30 minutes in a nitrogen atmosphere to improve the film strength.

By repeating a series of steps of forming an aluminum oxide film three times, the average thickness of this insulating film was 0.3 μm, and a surface insulating thin film layer having high dielectric breakdown strength could be formed.

The silica particles having a three-layer structure thus obtained were dispersed in dimethyl silicone oil at a particle concentration of 30% by weight to obtain an electrorheological fluid.

Table 1 shows the relationship between the applied voltage, the shear stress (increment), and the current density.

Example 2 The electrorheological fluid of Example 1 was continuously sheared at 120 ° C. for 24 hours at a shear rate of 200 sec ⁻¹ while applying a voltage of 2.0 KV. Two
The shear stress at room temperature before and after heating for 4 hours and the shear stress during heating at 120 ° C. are almost constant as described below, and it can be seen that this electrorheological fluid exhibits an extremely stable electrorheological effect.

Generated shear stress [g / cm ² ] Before heating (room temperature): 1.8 After heating (〃): 1.8 During heating (120 ° C.): 2.0 For comparison, the silica used in Example 1 was left in a wet state to absorb water. After humidity control at a rate of 9% by weight, the conventional electrorheological fluid similarly dispersed at a particle concentration of 30% by weight in dimethyl silicone oil showed almost no shear stress when heated at 70 ° C. for 3 hours.

Example 3 Nickel was electrolessly plated on a spherical alumina (δAl ₂ O ₃ ) surface having an average particle diameter of 5 μm in the same manner as in Example 1 to form a nickel conductive thin film layer of about 0.2 μm.

After treating the particles with a silane coupling agent (Toshiba Silicone Co., Ltd., RSL8370), 24 parts of styrene, 16 parts of divinylstyrene and 1 part of dibenzoyl peroxide were mixed with 100 parts of the particles, and 5 parts of gum arabic were dissolved. Pour into 500 parts of water while stirring at high speed.
Polymerization was carried out for hours. The obtained particles have a thickness of about 0, almost uniformly.
Coated with 3μm polymer thin film, 4 × 10 ¹³ Ω ・ c
m electrical resistance.

25 parts of these particles are made of fluorinated oil (Dupont, KRYTOX 1
43A Y) Dispersed in 75 parts and evaluated for electrorheological properties. Table 2 shows the results.

In addition, this fluid also showed a stable electrorheological effect in a voltage application heating test at 120 ° C. for 24 hours.

[Effects of the Invention] As described above, since the electrorheological fluid of the present invention essentially does not contain water, it can withstand high-temperature use, has good long-term stability, and has a valve, clutch, and vibration. It is highly practical in actuators such as elements and vibration absorbing elements.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C10N 40:16

Claims (1)

(57) [Claims] A fine particle having a three-layer structure comprising a conductive thin film layer formed on the surface of an inorganic solid particle and an insulating thin film layer formed on the surface thereof is dispersed in an oil medium having excellent electrical insulation. An electrorheological fluid comprising: