JP2534169B2 - Electrorheology-fluid composition - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrorheological fluid composition, and more specifically, to a gel state in which the viscosity can be remarkably changed by an electric voltage, and further, no fluidity is exhibited. Electro-rheological fluid composition that can be applied to clutches, valves, dampers, brakes, shock absorbers, actuators, etc. It is about.

[0002]

BACKGROUND OF THE INVENTION Electrorheological fluids are electrorheological fluids,
It is also called an electrically responsive fluid, and it is usually in a liquid state and shows fluidity, but when a high voltage is applied, the viscosity rises significantly, and it changes to a gel state that does not show fluidity at all. It is a functional fluid.

As such a fluid, a certain polymer solution and a suspension in which various particles are dispersed have been proposed so far, but the former has a small increase rate of viscosity with respect to an applied voltage and is an electrorheological fluid. Since it does not exhibit a sufficient function, the latter particle dispersion fluid has been mainly studied so far.

Particle-dispersed electrorheological fluids exhibit a relatively good increase in viscosity due to voltage application, that is, the Winslow effect, as compared with polymer solution systems. So far, silica having a specific amount of surface silanol groups has been oily. A fluid composition dispersed in a medium (Japanese Examined Patent Publication No. 45-10048), a composition dispersed an ion-exchange resin that adsorbs water (Japanese Patent Laid-Open Publication No. 48-17806), barium titanate and silica fine powder. Dispersed composition (Japanese Patent Publication No. 58-32197), water-containing phenol resin dispersion system (JP-A-58-17)
9259), a composition in which crystalline zeolite is dispersed (JP-A-63-185812), and a composition in which cellulose, starch, soybean casein, etc. are dispersed are also known.

Although these known electrorheological fluid compositions change in viscosity depending on the applied voltage, the rate of change is not yet sufficient. Further, although an electrorheological fluid that can change from a fluid state to a gel state with strength capable of transmitting power by applying a voltage is desired, a gel that can change to a gel when a voltage is applied is desired. Is extremely thixotropic and highly viscous even when no voltage is applied, or one that has sufficient fluidity when no voltage is applied cannot be gelated even if an electric voltage is applied, or is satisfactory. It has not been possible to obtain such characteristics.

Furthermore, the above composition essentially requires adsorbed moisture, and therefore its operating temperature range is from 0 ° C to 80 ° C.
However, it could not be used for a long time at a high temperature, and was applicable only to a very limited use. In order to solve this problem, an electrorheological fluid which does not essentially require the presence of water has been proposed, but it has various drawbacks and no practical one has been obtained.

For example, Japanese Patent Application Laid-Open No. 61-216202 proposes an electrorheological fluid in which an organic semiconductor such as poly (acene-quinone) polymer is dispersed. However, the fluid has high conductivity and power consumption is high. There is a problem such as the size of the magnetic field and the generation of Joule heat, and the electrorheological effect is not sufficient, which makes it difficult to put into practical use.

Further, in Japanese Patent Laid-Open No. 64-6093,
An electrorheological fluid has been proposed in which dielectric particles having an electrically insulating thin film formed on the surface of conductive particles are dispersed in an oil medium. In this method, although many kinds of metals, alloys, carbon black and others are listed as conductive particles, in practice, only metal such as aluminum or conductive carbon-containing plastic is used, and the electrical insulating property is improved. As for the thin film, only a specific one is specifically used. According to the technical contents specifically shown, this method shows an electrorheological effect in a system in which water does not exist, but the electrorheological effect is not exhibited in a DC electric field, and therefore, the method disclosed in JP-A-1-26071.
As disclosed in Japanese Patent No. 0, the electrorheological effect is exhibited only under an AC voltage or a DC pulse voltage.
Further, the use of metal particles is extremely difficult to use fine particles, and the use of particles having a high specific gravity and a large particle diameter markedly impairs the storage stability of the electrorheological fluid and promotes the oxidation of the metal particles. There is a possibility that it cannot be said to be a practical composition.

Japanese Unexamined Patent Publication (Kokai) No. 2-169025 discloses an electrorheological fluid containing carbon fine particles coated with an electrically insulating thin film as a dispersed phase. This system is also expected to exhibit an electrorheological effect in a system in which there is no adsorbed water, but the carbon fine particles and the electrically insulating thin films of various organic polymers, inorganic oxides, etc. originally have interfacial affinity. In the electrorheological fluid that is lacking and is premised to be used under shear stress, peeling of the electrically insulating thin film during long-term use becomes a problem, and it is a fluid that is difficult to put into practical use.

[0010]

As described above, there has been a demand for an electrorheological fluid that does not essentially require adsorbed moisture, has a wide operating temperature range, and can be used stably for a long period of time. Up to now, the one satisfying the required characteristics has not been obtained.

The present invention is essentially a system that does not require water, is capable of exhibiting an electrorheological effect, has low conductivity of fluid, consumes less power, and operates in both DC and AC electric fields. The present invention intends to obtain an electrorheological fluid composition comprising fine particles and having good storage stability, which is possible and can withstand long-term use under shear stress.

[0012]

The present invention SUMMARY OF], in electrorheological fluid with solid particles are dispersed in the electrically insulating medium, solid particles in the semi-conductor oxide particles on the surface, chemical liquid using a metal alkoxide The above problems have been solved by an electrorheological fluid composition characterized in that an electrically insulating oxide layer formed by the phase method is formed.

In the above-mentioned Japanese Patent Laid-Open No. 64-6093, indium oxide and ferric oxide are listed as the conductive particles, and silica and alumina are listed as the electrically insulating thin film. I have mentioned,
Only those having a layer of aluminum oxide formed on the surface of metal aluminum particles are specifically mentioned as having an oxide, and the oxide was used for both the conductive particles and the electrically insulating thin film. Nothing is specifically mentioned, what kind of technical function it can perform, or it is not recognized at all.

However, according to the present invention, when solid particles having a combination of particles made of a semiconductor oxide and an electrically insulating layer made of an oxide formed on the solid particles are adopted, Japanese Unexamined Patent Publication No. 64-6093 and JP-A 1-2-2
No. 60710, a new electrorheological fluid composition having a new function that works with an AC or DC pulse, but does not have the disadvantage that it hardly works with a DC, and can also work effectively with a DC. It is a product developed. The present invention is different from the inventions of the electrorheological fluids described in both of the above publications in that the functions and functions are different.

Further, according to the present invention, the electrically insulating oxide layer is formed by a chemical liquid phase method using a metal alkoxide as a raw material in order to exert an excellent electrorheological effect and to keep the conductivity of the fluid low. I am supposed to. JP-A-64-
As in 6093 JP, but thin good adhesion is obtained to again to form an aluminum oxide thin film by reacting the surface of the metallic aluminum particles, electrically insulating oxide provided on a semi-conductor oxide particles Since the oxide forming the layer is different in substance from the oxide forming the particles, the electrically insulating oxide layer is usually formed separately from the particles. Is preferably one having good adhesion. The chemical liquid phase method will be described later.

[0016] and is that semi conductor oxide particles used in the present invention is an oxide particles showing a semiconductive, something like the following may be exemplified.

As the semiconductive oxide, SnO ₂ , Zn
O, CdO, MnO, FeO, CoO, Cu ₂ O, Mn
Fe ₂ O ₄ , NiFeO ₄ , NbO, NbO ₂ , Ti ₂
O ₃ , Ti ₃ O ₅ , Ti ₄ O ₇ , Ti ₅ O _{9 and the} like are exemplified.

Further, an oxide semiconductor doped with an impurity metal ion to increase the conductivity is also useful, and the following are exemplified. Nb, Ta-doped TiO ₂ , Al-doped ZnO, La, Ta-doped BaTiO ₃ ,
Sb-doped SnO ₂ , Li-doped NiO,
Ba ₂ -doped Bi ₂ O ₃ and Mg-doped Cr ₂
O _3, LaCrO ₃ doped with Sr.

[0019] These semi-conductor oxide, under use as an electrorheological fluid, less likely to change its physical properties over time, is suitable. These semi-conductor oxide particles, fine particles are preferable from the viewpoint of storage stability of the electrorheological fluid, the average particle diameter 0.01μ~50μ
m, more preferably particles of 0.05 μm to 30 μm are used.

[0020] These semi-conductor oxide particles formed monkey electrically insulating oxide layer on the surface, be amorphous glass in ceramics crystalline, or may be of other state, but the Those in either state are preferable. Such electrically insulating oxides include Si
O ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , MgO, Ca
Oxides of single metals such as O, Ga ₂ O ₂ , HfO ₂ , CuO, MgAl ₂ O ₄ , LiNbO ₃ , KNbO ₃ ,
In addition to metal oxides composed of multiple components such as mullite, various single and
A multi-component glass is exemplified.

[0021] These electrically insulating oxide thin film is formed on a semi-conductor oxide particle surface, a substance is both oxide constituting the material (core material) and thin film constituting the particles, sufficient strength It has a surface affinity for expressing. This is preferable in the electrorheological fluid that is premised on use under shear stress, and effectively contributes to exhibiting a stable electrorheological effect for a long period of time.

The thickness of these electrically insulating oxide thin films is preferably as thin as possible within a range that does not significantly increase the conductivity of the electrorheological fluid and does not reduce the dielectric breakdown voltage, and is usually 0.5 μm or less. , And more preferably 0.2 μm or less.

When the electrically insulating oxide thin film has a low dielectric constant, it is necessary to make the film extremely thin in order to exert the electrorheological effect. This extremely thin film thickness causes a decrease in the dielectric breakdown voltage of the electrorheological fluid, an increase in the dielectric constant during long-term use under shear stress, and the like. Therefore, a more preferable electrically insulating oxide thin film has a relative dielectric constant of 5 or more, and examples of such oxides include Al ₂ O ₃ , TiO ₂ , CuO, and ZrO.
₂ , Cr ₂ O ₇ , BaTiO _{3 and the} like are exemplified. When these oxides having a high relative dielectric constant are used, the electrorheological effect is exhibited even if the film thickness is made relatively thick, and the above problems are avoided.

[0024] The electrically insulating oxide thin film as a method for forming on a semi-conductor particle surface was coated electrically insulating oxide fine powder, heating, fixation methods, electrically insulating oxide layer from a homogeneous solution There are various methods such as a method for forming an oxide layer from a vapor phase such as PVD (physical vapor deposition method) and CVD (chemical vapor deposition method), but the formed film becomes too thick. The chemical liquid phase method is preferable as a method that can form a thin and uniform film without being formed and is excellent in productivity.

The chemical liquid phase method uses a uniform solution of a compound containing a constituent metal element of an electrically insulating oxide, such as a metal salt or an organic metal compound, as a starting material and involves chemical changes such as concentration and drying. Method to form a solid layer containing the constituent metal element of the oxide, or to form a solid layer containing the constituent metal element of the oxide by utilizing reactions such as formation of an insoluble compound by addition of a precipitant, hydrolysis, polycondensation, etc. A method of forming a solid layer for heating and then converting the solid layer into an oxide layer by heating will be described.

Among the chemical liquid phase methods, the method using a metal alkoxide as a starting material is excellent in the uniformity of the formed film, the affinity of the interface and the productivity, and is a particularly preferable method. As a method of forming an oxide film on the powder surface using this metal alkoxide, the journal of Powder Engineering, Vol. 27, No. 1
70 (1990), J. Materials Sc
ience. Vol. 22, pp. 1677 (1987),
It is possible to apply a method such as the Journal of the Ceramic Society of Japan, Volume 96, page 698 (1988).

That is, specifically describing the method,
A method in which a powder having adsorbed water is dispersed in an organic solvent that is not miscible with water, and the metal alkoxide is hydrolyzed by water on the surface of the powder. The powder is dispersed in an organic medium that is miscible with water. And a method of hydrolyzing the metal alkoxide by adding metal alkoxide and adding water thereto.

[0028] By the above method, the semi-conductor oxide particle surface solid layer formed on, by a heat treatment at a suitable temperature, electrically insulating oxide layer which firmly adheres to the core substance is formed . When a metal alkoxide is used, an oxide, hydrated oxide, or hydroxide layer is formed after hydrolysis, but even when an oxide layer is formed, it is used in an electrorheological fluid. Heat treatment is performed at an appropriate temperature to eliminate the influence of adsorbed moisture. By this heat treatment, hydrated oxides and hydroxides are converted into oxides that do not contain a large amount of water that affects the electrorheological effect. The temperature in the heat treatment, without causing the solid phase reaction with semi <br/> conductor oxide particles and the surface of the electrically insulating oxide layer, also appropriately be set in a range of temperature at which adsorbed moisture is removed, 40 An example is a range of 0 ° C to 1000 ° C.

The electric insulating medium used in the electrorheological fluid of the present invention is not particularly limited as long as it is a high-boiling substance having an electric insulating property, and commonly used petroleum-based lubricants and transformer oils. , Silicone oil, dibutyl sebacate, chlorinated paraffin, alkyl bromide, alkyl ester of aromatic polycarboxylic acid, halophenyl alkyl ester, halophenyl alkyl ether, fluorine oil and the like.

The amount of the solid particles forming an electrically insulating oxide layer on a semi-conductor oxide particles on the surface to the electrically insulating medium is preferably 10 to 50% by volume. 10% by volume
When it is less than the above, the rate of change in viscosity upon application of voltage is small, and the properties as an electrorheological fluid are poor. When it exceeds 50% by volume, the viscosity in the normal state when no voltage is applied is high and a thixotropic behavior is exhibited, which is unsuitable.

As a method for dispersing the solid particles in an electrically insulating medium, a usual method can be used.
It can be dispersed with a ball mill, attritor, three rolls, bees, etc.

[0032]

[Action] electrorheological fluid of the present invention, due to the use of solid particles electrically insulating oxide layer on a semi-conductor oxide particle surface is formed, conventionally specifically known on the metal particle surface Unlike the case of using solid particles having an electrically insulating oxide thin film layer formed thereon or solid particles having an electrically insulating synthetic resin thin film layer on a conductive synthetic resin particle, an electrorheological effect is exhibited even in a DC electric field. . This effect occurs action mechanism is not clear, grain boundary layer capacitors electrically insulating on efficiency good Ku semiconductors particle surface in the same mechanism and storing charge in the dielectric layer surrounding the grains of electrically conductive It is considered that charges are accumulated in the oxide layer, a strong dielectric polarization interaction occurs in the electric field, and a good electrorheological effect is exhibited. As a result, an electrorheological effect can be obtained in a system in which adsorbed water does not exist, so that the defects associated with the existence of water do not occur. In addition, since the solid particles consist entirely of oxide, the electrorheological fluid containing it does not change with time of the conductive particles, and there is no problem of interface peeling between the surface layer and the conductive particles. To be done.

[0033]

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. Example 1 50 g of SnO ₂ powder having a BET specific surface area of 50.9 m ² / g and an average particle size of 4.0 μm determined by centrifugal sedimentation method was dispersed in 100 g of methanol, and 4 g of tetramethoxysilane was added thereto. The mixture was stirred at room temperature for 24 hours. Then, a solution prepared by dissolving 1.9 g of water in 10 g of methanol was added,
The reaction was continued for another 24 hours. The dispersed particles are collected by suction filtration, and dried at 50 ° C. to obtain S
SnO ₂ powder coated with iO ₂ was obtained.
Weight increase rate for SnO ₂ ingredients at _1. 3%, BET specific surface area of the resulting powder 55.3m ² / g, X-ray diffraction pattern was quite equal to the SnO ₂ ingredients.

The obtained SiO ₂ -coated SnO ₂ particles were used as a silicone oil TSF-4 manufactured by Toshiba Silicone Co., Ltd.
51-100 was dispersed with milk bees to prepare an electrorheological fluid in which 30% by volume of the solid particles were dispersed.

The water content in the obtained electrorheological fluid was determined by the weight loss rate from room temperature to 200 ° C. in thermogravimetric analysis and was found to be 0.5%. In this electrorheological fluid, the usual electrorheological effect was obtained. It did not contain enough water to affect

The rheology of this electrorheological fluid was measured using a diaphragm type rheometer. This is an apparatus for measuring the viscoelasticity of a sample from a vibration displacement when a sample liquid is inserted in a gap between a fixed base and a diaphragm parallel to the fixed table and the diaphragm is vibrated with a constant force.

Dynamic measurement was carried out at a measurement frequency of 45 Hz, the sample film thickness was set to 150 μm, and 0 to 0.23 kV / m
The electrorheological behavior when a DC electric field of m was applied was investigated. As a result of the viscoelasticity measurement, the dispersion system used here was always G ₁ <0.2G ₂ (G
₁ : Storage elastic modulus, G ₂ : Loss elastic modulus), and the elastic efficiency was found to be very small. Therefore, all the experimental results will be represented by the absolute value of the complex elastic modulus | η * |.
| Η * | is represented by the following equation.

| Η * | = | G * | / ω = [(G ₁ ) ² + (G ₂ ) ² ] ^0.5 / ω (where | G * | is the absolute value of the complex elastic modulus and ω is the angular frequency) ) | Η * | before applying an electric field is almost constant irrespective of shear stress, and at the time of shear stress of 1.4 × 10 ² Pa (where Pa is Pascal), | η * | = 1.9 Pa · S
(However, Pa · S is Pascal · second)
3.2 Pa · S by applying a voltage of 0.23 kV / mm
And showed a good electrorheological effect. Also,
The current value when this DC voltage was applied was 0.2 μA / cm ² . Example 2 50 g of the same SnO ₂ powder as in Example 1 was added at 70 ° C. and 85 RH%.
Left in the atmosphere of 5 to absorb 51.3 g of Sn
O ₂ was obtained. Stearylamine concentration 0.002
14.4 g of titanium tetraisopropoxide dispersed in 100 ml of a mol / liter n-hexane solution was added and hydrolyzed with water adsorbed on the surface of SnO ₂ . 40 ° C
After reacting for 3 hours, the powder is separated by suction filtration,
Sn baked at 600 ° C for 1 hour and coated with a TiO ₂ layer
O ₂ particles were prepared. The weight increase rate with respect to SnO ₂ of the raw material was 5.7%, and the BET specific surface area of the obtained powder was 2
It was 5.4 m ² / g. Further, the X-ray diffraction pattern was such that a slight pattern of TiO ₂ (anatase) was found in the raw material SnO ₂ .

The obtained particles were dispersed in a silicone oil TSF-451-100 manufactured by Toshiba Silicone Co., Ltd. with a dairy bee to prepare an electrorheological fluid in which 25% by volume of the above solid particles were dispersed. When this electrorheological fluid was evaluated with the diaphragm type rheometer of Example 1, the shear stress was 1 × 1.
It was | η * | = 2Pa · S before applying an electric field at 0 ² Pa, but it increased to | η * | = 4.7Pa · S by applying a DC voltage of 0.23 kV / mm, which is good. It showed a strong electrorheological effect. The current value when this voltage was applied was 3 μA / cm ² . Comparative Example 1 The SnO ₂ powder used in Examples 1 and ₂ was dispersed in the same silicone oil without any treatment to prepare an electrorheological fluid containing 30% by volume of SnO ₂ . Examples 1, 2
As a result of evaluation with a diaphragm type rheometer in the same manner as above, | η * | at a shear stress of 1.0 × 10 ² Pa before applying an electric field
= 2.2 Pa · S, but 0.23 kV / mm
Was increased to 10 Pa · S by applying the DC voltage of
A current as high as 00 μA / cm ² flows, and it cannot be used as an electrorheological fluid. Example 3 The electrorheological fluid prepared in Example 2 was evaluated with a double cylindrical tube type rheometer with a distance between electrode plates of 1 mm. The results are shown in FIG. The vertical axis represents shear stress σ (Pa), and the horizontal axis represents shear rate dγ / dt (S ^-1 ). In the state where no electric field is applied (0. kVmm ^-1 ), the behavior was close to Newtonian fluidity, but when the voltage of 2 kV / mm was applied, the behavior of Bingham fluid was exhibited and 1.9 × 10 ³ Pa.
An excellent electrorheological effect indicating a high yield stress of was found.

[0040]

EFFECTS OF THE INVENTION According to the present invention, an electrorheological effect is produced in a system essentially not requiring water, it can be operated in both a direct current and an alternating electric field, and its viscosity can be remarkably changed by voltage. It has excellent voltage responsiveness and can withstand long-term use under shear stress. Therefore, the electrorheological fluid of the present invention is extremely effective for use in clutches, valves, dampers, shock absorbers, actuators, etc., and has industrial very practical utility.

[Brief description of drawings]

FIG. 1 is a graph showing the evaluation results of an electrorheological fluid prepared in Example 2 by a rheometer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C10N 10:10 C10N 10:14 10:14 10:16 10:16 20:06 A 20:06 40 : 04 40:04 40:14 40:14 9329-3J F16D 35/00 631D

Claims (2)

(57) [Claims] 1. A electrorheological fluid with solid particles are dispersed in the electrically insulating medium, solid particles in the semi-conductor oxide particles on the surface of an electrically insulating made of chemical liquid phase method using a metal alkoxide An electrorheological fluid composition, wherein a conductive oxide layer is formed. 2. A pre-Symbol electrorheological fluid composition according to claim 1, wherein the semi-conductor oxide particles electrically insulating oxide layer formed on the surface is characterized in that it consists of a relative dielectric constant of 5 or more electrical insulator Stuff.