JPH0316910A - Fluid having electroviscous effect - Google Patents

Abstract

PURPOSE:To improve electroviscous effect by forming electrically insulating film on the surface of electrically conductive particles dispersed in an electrical]y insulating liquid by hydrolysis or polymerization of a metal alkoxide or its derivative. CONSTITUTION:An aqueous alcohol solution is prepared, which has 0.05 to 5mole% of metal alkoxide such as Si methoxide concentration, 0.1 to 10mole% of water concentration, and 1 to 100 of [H2O]/[alkoxide]. Electrically conductive fine particles of 0.01 to 500mum average particle size and more than 10<-10>OMEGA<-1>.cm<-1> such as Al, semiconductive Si or beta-Al2O3 particles are dispersed in the prepared aqueous alcohol solution to deposit the hydrolysate of the metal alkoxide or its derivative on the surface of the fine particles. Then, the particles are separated from the solution and dried below about 600 deg.C to give fine particles whose surfaces are coated with electrically insulating film in a thickness of 0.05 to 1mu. The fine particles are dispersed in an electrically insulating fluid such as silicone oil in a concentration of 5 to 50% by volume and an electric field is impressed to obtain the subject electroviscous fluid.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to electrorheological fluids.
The present invention relates to an electrorheological fluid characterized in that fine particles whose surfaces are uniformly coated with an electrically insulating film by a specific method are used as the particles dispersed in an electrically insulating liquid.

An electrorheological fluid is a liquid that exhibits the so-called electrorheological effect, in which its apparent viscosity changes rapidly and reversibly under the action of applied voltage (QFF, ON (voltage change)).

[Prior art]

An electrorheological fluid is made by dispersing conductive fine particles in an electrically insulating liquid, and the mechanism of its electrorheological effect is thought to be as follows.

That is, when a voltage is applied to an electrorheological fluid, the dispersed particles are polarized due to the action of the electric field generated between the electrodes, and further, they aggregate with each other due to electrostatic attraction based on the polarization, and as a result, the electrorheological effect occurs. be done.

Conventionally, electrorheological fluids have been developed based on this principle. As dispersed particles, particles containing an electrolyte solution, semiconductor particles, and the like are known.

By the way, good conductor particles such as metals and conductive carbon also
It is thought that they can be used as dispersed particles if a coating of an electrically insulating substance is provided on their surfaces to prevent short-circuits between the particles when they aggregate.

In addition, even in conventional electrorheological fluids, high resistivity is desirable in order to reduce power consumption, but
Since the resistivity may decrease depending on the type of electrically insulating liquid, the conductivity of the particles, or the magnitude of the applied voltage, coatings of electrically insulating materials like this51 are useful for expanding the optimal range of operating conditions. , is desirable.

[Problems with conventional technology]

However, the particles used in electrorheological fluids have a particle size of, for example, 0.7 to 0.00 μm due to the need to ensure long-term dispersion stability. It is difficult to uniformly coat the surface of fine particles with an appropriate thickness of an electrically insulating material without causing agglomeration, and in fact, an example of an electrorheological fluid made by dispersing such fine particles in an electrically insulating liquid is There is no known temperature.

[Structure of the invention]

The present invention has been made based on the above-mentioned circumstances, and its gist is that conductive fine particles are placed in an electrically insulating liquid. The electrorheological fluid is a dispersed electrorheological fluid, characterized in that the fine particles have an electrically insulating film formed on their surface by a hydrolysis/polymerization reaction of a metal alkoxide or a derivative thereof. .

The present invention will be explained in detail below.

The conductive fine particles used in the present invention refer to conductive fine particles that do not contain volatile substances such as electrolyte solutions, and the electrical conductivity thereof is usually /θ-10Ω-1-α-1 or more, preferably /0 -50-1·(lm-' or more.

Specifically, metals, semiconductors, conductive carbon, solid electrolytes, conductive resins, etc. can be used, but typical examples include aluminum, semiconductor silicon, graphite, β-alumina, etc. . The particle size of the conductive fine particles may be particularly limited as long as the particles can be stably dispersed in the electrically insulating liquid described below, but the average particle size may be 0.0/~
0.00 μm or more preferably 0.00 μm to /00 μm is used. The metal alkoxides or derivatives thereof used in the present invention are as follows:
adley, R. C. Mehrotra, D. P.
Co-authored by Gaur) Academic Press/9
Various alkoxides described in ``g.
Alkoxides such as Zr or derivatives thereof containing alkyl groups, vinyl groups, etc., Ba-Ti, Sr-
T i. , P b-T i , P b-T i
-Zr, Li-Nb and other complex alkoxides or derivatives thereof. Among the,
Lower alkoxides such as 81 methoxy, ethoxy, propoxy, and pyroxy are preferably used from the viewpoint of reaction rate, ease of handling, and availability on an industrial scale.

In addition, these alkoxides may be partially hydrolyzed and multimerized (.) as long as this does not cause any problem in coating the fine particles.

Hydrolysis of metal alkoxides is generally carried out by mixing an alcohol solution in which the alkoxide is dissolved and an alcohol aqueous solution, but by dispersing the fine particles in an alcohol aqueous solution and adjusting the hydrolysis rate appropriately, electrical insulation properties can be achieved. A coating can be deposited on the surface of the microparticles. The hydrolysis rate is usually adjusted by the molar ratio and concentration of alkoxide and water in the reaction system, the amount of catalyst (acid or alkali) added as necessary, and the like. Conditions for obtaining an electrically insulating film cannot be determined unconditionally because they vary depending on the type of fine particles, particle size distribution, and type of alkoxide, but, for example, Si.
(OC2H5)4, T i (○C2H5)
4, Zr(OC2H5)4, usually [:H20]/C alkoxide] is /~
/00, the concentration of alkoxide (mo1%) is o, o
t − s, the concentration of water (mol 1%) is selected from the range of 0.7 to /O. Further, this reaction can be repeated by further adding an alcohol solution of alkoxide, and the film thickness can be increased by increasing the number of reactions.

Although it is difficult to directly measure the thickness of the electrically insulating film, it can be calculated from the amount of fine particles added, the particle size, and the amount of alkoxide added.

The film thickness of the coating is usually selected from the range of QθS ~/μm,
An appropriate film thickness can be obtained by increasing/decreasing the particle/alkoxide ratio and the number of hydrolysis reactions.

The fine particles whose surfaces are coated with an electrically insulating material are separated from the alcohol solution by an appropriate method and dried to completely remove volatile components during coalescence. The temperature at this time is about 0.degree. C. or lower, preferably about /O.theta. to 300.degree. C. so as not to sinter the particles.

Next, electrically insulating liquids suitable for use in the present invention include silicone oil, transformer oil, engine oil, ester, dihydric alcohol, etc., which can stably disperse the above-mentioned fine particles and have high insulation resistance. be.

The amount of the fine particles is usually &vol% with respect to the electrically insulating liquid.
~O vol% is used, preferably /O vol
% to 110 vol%. As the dispersion method, general mixing and dispersion methods such as ball mill and ultrasonic dispersion can be used.

If an electric field is applied to a fluid made by dispersing conductive particles whose surfaces are coated with an electrically insulating substance in an electrically insulating liquid using this method, the electrically insulating coating will maintain the insulation between the particles. Therefore, the particles become polarized due to the movement of charges, and it becomes possible to exhibit the electrorheological effect by the above-mentioned mechanism.

The method for measuring the electrorheological effect is to use a coaxial double-cylinder rotational viscometer to apply a voltage between the inner and outer cylinders, find the increase in shear stress at the same shear rate (/42 sec-''), and calculate the viscosity change. It was converted to

Since the flow characteristics of electrorheological fluids can be controlled by applying voltage, it is expected that they will be used in computer-controlled mechatronics fields in the future. Here are some examples of specific applications. In the automobile industry, application parts such as clutches, torque converters, valves, shock absorbers, brake systems, and power steering are being considered. It is also being applied to various actuators in the field of industrial robots.

Hereinafter, the present invention will be specifically explained with reference to Examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof.

〔Example/〕

Aluminum powder (average particle size 3oμm)/! rg to ethanol λ Ku friend 9 u 9,! gwt% ammonia water 30.
gtji, distilled water. 2 +, 00g to the mixed solution, to which 66g of ethyl silicate and 9λ of ethanol! A mixed solution of Ajj was added and stirring was continued for 4 hours. Let this mixture stand, discard the supernatant, and remove the remaining particles.
It was vacuum dried for a period of time. When the obtained particles were observed using a scanning electron microscope and an energy dispersive X-ray analyzer, it was found that a silica 9 film was formed on the surface of the aluminum powder. Although it is difficult to directly measure the thickness of the coating, it is calculated by assuming that the particles are spheres with a diameter of 30 μm and that all the added ethyl silicate is deposited uniformly on the particle surface as silica. //μm.

The silica-coated aluminum powder io. o o
，! 9 Silicone oil (Toray silicone sH)
200/Ocs) 32.33fj and was dispersed and mixed using a plastic bowl.

For the electrorheological fluid of the present invention thus obtained, the shear stress at the same shear rate (/A2g-') was measured using a coaxial double cylinder rotational viscometer ( Inter-electrode distance M/mu, i&ss
As a result, 8°' (initial viscosity) 2.7 voids when no electric field is applied is /. When an electric field of lIKV-π'1 is applied, l3. ! Poise [Comparative example/] Aluminum powder (average particle size 3oμm) / 0.0
In addition to 32.33 fi of 0g silicone oil, the mixture was dispersed and mixed using a plastic ball mill. 0 to the resulting fluid
．． When an electric field of 'l KV-mm-' was applied, a short circuit occurred and no electrorheological effect was exhibited.

[Example 2] A silica film was formed on semiconductor silicon (average particle size 2 s μm) /YθOg in the same manner as in Example. When the film thickness of the film was calculated in the same manner as in Example 1, it was found to be θ. /
/μm.

The particles/0.0θg silicone oil/A, 3
9g and dispersed and mixed.

The thus obtained electrorheological fluid of the present invention was measured in the same manner as in Example 1 and found to have an initial viscosity of 0. When an electric field of /, A KV-mm-'' is applied to the g-boise, g.
It increased to g poise. /． The resistivity when applying KV-mm-' is λ. It was O×/09Ω·.

[Comparative Example 4] Semiconductor silicon (average particle size 4 S μm) / 0. 0
0g silicone oil/4. 0 3 g and dispersed and mixed.

The obtained fluid had an initial viscosity of 0.4 poise. gKV・m
When an electric field of m-' was applied, the voids increased to +,g, but
/ KV-run-'' was applied, causing a short circuit.The resistivity when applying 0.g KV-mm-' was K.K.
/θ7Ω.

[Example 3] Graphite (average particle size/0 μl)/t. 0
A sample of 0 g of silica was coated with silica in the same manner as in Example. When the film thickness of the coating was calculated in the same manner as in Example 1, it was o. It was Ogμm.

The particles j, o o g are mixed with silicone oil J3.
．． 3! ig and dispersed and mixed.

The thus obtained electrorheological fluid of the present invention was measured in the same manner as in Example 1, and the initial viscosity/. / Boise applies an electric field of 2,0 KV-mm-', then K. Otsu Poise has increased. The resistivity when applying :l, OKV·mm-' was 2#X/09Ω·snoring.

[Comparative Example 3] Graphite (average particle size/Oμm) h, oθg was mixed with silicone oil. 2 3.3 j In addition to 9, it was dispersed and mixed.

When an electric field of θH 2 KV-mm-' was applied to the obtained fluid, a short circuit occurred and no electrorheological effect was exhibited.

[Example G]

β-alumina (average particle size/Oμm)/k, 00g was coated with silica in the same manner as in Example. The thickness of the coating was calculated in the same manner as in Example 1 and was found to be 0.0 gμm.

The particles/θ: oog to silicone oil/g, 2
．． ! 1-g and dispersed and mixed.

The thus obtained electrorheological fluid of the present invention was measured at 2S°C, and as a result, the initial viscosity was /,0 voids. O
When an electric field of KV-mu-'' was applied, the resistance increased to /.!i poise.The resistivity at this time was 9.7 When the viscosity was 0.2 poise, when an electric field of u.OKV・mm-' was applied, it increased to Otsukpoise.The resistivity at this time was '7'.
, ? It was X/09Ω・α.

[Comparative example]

β-alumina (average particle size/Oμn-r)/o. 00g was added to silicone oil/Otsu, slIg and dispersed and mixed. The electrorheological fluid thus obtained was measured at 43°C and found to have an initial viscosity of θ. 2 voices are 2, O KV-m
When an electric field of m-' is applied, o. It increased to g poise.

The resistivity at this time was 1,×/09Ω·V. Also, as a result of measurement at 20°C, the initial viscosity was O. l Poise is Yu. When an electric field of oK■.ho-1 was applied, it increased to +, r poise. The resistivity at this time was 3.OX/09Ω·α.

〔Effect of the invention〕

As described above, the present invention provides an electrorheological fluid that exhibits a stable electrorheological effect over a wider temperature range than the compositions disclosed in the prior art.

[Brief explanation of the drawing]

Figure 1 is a graph showing the thickening effect of an electrorheological fluid according to an embodiment of the present invention due to an applied electric field, where the horizontal axis is the applied voltage (KV-mrrr-') and the vertical axis is the viscosity (poi).
se).

Claims (1)

[Claims] (1) An electrorheological fluid formed by dispersing conductive fine particles containing no volatile components in an electrically insulating liquid, in which the surface of the fine particles has an electrically insulating property due to the hydrolysis/polymerization reaction of a metal alkoxide or its derivative. An electrorheological fluid characterized by forming a film of.