JP2862548B2 - Electric field responsive fluid composition - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an electric field responsive fluid having excellent electric field response characteristics, and more particularly, to an electric field responsive fluid having a shape anisotropy and a high crystallinity. High performance electric field responsive fluid composition. And it is useful as an electromechanical actuator for a shock absorber, a clutch, a torque converter and the like.

U.S. Pat. No. 2,417,850 to Winslow discloses finely divided solids such as starch,
A technology in which lime or a derivative thereof, gypsum, flour, gelatin or the like is dispersed in a non-conductive liquid, for example, olive oil or mineral oil, to increase the flow resistance if a potential difference is applied to the suspension. Is disclosed. This effect is called the Winslow effect.

An increase in flow resistance due to the application of an electric field was initially interpreted as an increase in viscosity, and a substance exhibiting such an effect was called an electrorheological fluid. However, subsequent studies have shown that the increase in flow resistance is not only due to the increase in viscosity as in Newtonian fluids, but also to Bingham plasticity induced by an applied electric field. A suspension exhibiting a strong Winslow effect is an electric field responsive fluid (electrorheological fluid)
It has come to be called.

Some proposals have already been made as a method for enhancing the Winslow effect, for example, a method in which fine particles of a strongly acidic ion exchange resin are dispersed in a higher ester of an aromatic carboxylic acid or a method in which a hydrophilic diaryl compound is used. And those in which conductive solid particles are dispersed (JP-A-58-501178). Each of these is obtained by dispersing solid fine particles holding water in an insulating oily substance, and the following electric double layer theory is the most promising mechanism for expressing the Winslow effect. That is, water existing on the particle surface dissociates on the solid surface to form an electric double layer, and the electric double layer causes the movement of free ions by an external electric field to cause polarization. The polarized particles are mutually bonded by electrostatic attraction, and cross-linking of the particles occurs in the direction of the electric field. It is theorized that this becomes resistance to shearing force in the direction perpendicular to the electric field and increases the viscosity. Therefore, in order to avoid such a problem caused by water, a method using an organic semiconductor such as an aromatic condensed polycyclic system (Japanese Patent Application Laid-Open No. 61-216202) discloses a method of disposing a metal in an intermediate layer in a three-layer structure. A method using particles (JP-A-63-97694) and a method using crystallized zeolite dried at a temperature higher than the use conditions (JP-A-63-185812) have been proposed. The first two examples attempt to replace polarization by water with electron transfer within the particle, and in the last example,
It is intended to be polarized by water, and the amount of water is reduced by the amount of dehydration at a high temperature, so that a decrease in polarization cannot be avoided. In addition, regarding the behavior of polarized and ionized water under a high electric field, the same problems as in the prior art cannot be eliminated.

Further, none of these methods take into account the effect of water crosslinking, and in particular, since the polarization is not determined by electron transfer, the shape anisotropy seems to be negative (see JP-A-63-97694). Page 2, left column, lower 5 lines).

The electric field responsive fluid using solid fine particles holding water as described above has poor stability due to migration and decomposition of water on the particle surface,
There are many problems related to the presence of water, such as promotion of ionization by application of a high electric field, an increase in current accompanying the application of the electric field, and an anxiety of a temperature characteristic that progresses in a chain with a further increase in temperature. In addition, there is an essential problem that sufficient electric field response is not exhibited when water is eliminated. Furthermore, if the response characteristic is low, the applied voltage must be increased in order to obtain a certain effect, and problems such as arc resistance, insulation, durability, and safety associated with the high voltage are caused.

(Problems to be Solved by the Invention) An object of the present invention is to provide an electric field responsive fluid composition which avoids many problems due to the presence of water and has excellent electric field response.

(Means for Solving the Problems) The present invention has a shape anisotropy selected from crystalline organic fibers such as gypsum, niobate, asbestos, polyimide, and polyamide, or ferroelectric oxide fibers, and has a degree of crystallinity. Substances with high levels (except those treated with alkylamines)
As a dispersed phase or a part of a dispersed phase in an electrically insulating oily medium.

The material having a shape anisotropy used in the present invention and having high crystallinity includes gypsum, titanate, niobate,
Examples include inorganic whiskers such as asbestos and crystalline organic fibers such as polyimide and polyamide. Ferroelectric oxide fibers such as titanate and niobate are particularly preferable. Regarding the shape anisotropy, the ratio of length to thickness is 2
Those having a molecular weight of from 1000 to 1000 are preferable, and those having a molecular weight of from 5 to 500 are particularly effective in terms of orientation, response and the like. Further, if the length is too long from the viewpoint of dispersibility, response, practicality, etc.
It is preferably as small as possible at 0 μm or less, more preferably about 200 μm or less. Considering these points and whisker productivity and practicality, the general formula MO
Metal titanate whisker represented by iO ₂ (however, M
Is an element selected from Group IIa and b metals, and n is 1
≤ n ≤ 4). Preferred examples of M include Be, Mg, Ca, Sr, B
a, Zn, Cd, Hg and the like can be mentioned.

As a method for producing a metal titanate having shape anisotropy,
In addition to the flux method described below as a reference example, a powder made of hydrous titanium dioxide needle-like particles, or a needle-like anatase-type dioxide elongated in one a-axis direction obtained by heat-treating this powder. Japanese Patent Application Laid-Open No. 57-88030 discloses a firing method characterized by mixing a powder of titanium particles and a barium compound and firing the mixture. Also, the ratio of fiber length to fiber diameter is at least
10 hydrated potassium titanate is; and _{(K 2 O · aTiO 2 ·} bH 2 O where to a from 2 13, b is 0 to a at 6, b is not always required to be an integer) fibers or fiber length Titanium dioxide hydrate having a fiber diameter ratio of at least 10 (TiO ₂ · cH ₂ O;
However, c is not more than 5 and does not necessarily have to be an integer.) The production method by a hydrothermal method in which the fiber is reacted with a solution containing a divalent metal ion in a closed vessel or under hydrothermal conditions, and the ratio of the fiber length to the fiber diameter is at least 10 hydrated potassium titanate is _{(K 2 O · dTiO 2 ·} eH 2 O; however d = 2 to 13, e is 0 to at 6, d, e need not necessarily be an integer) fibers or fibers Titanium dioxide hydrate having a ratio of length to fiber diameter of at least 10 (TiO ₂ · fH ₂ O; f is not more than 5 and is not necessarily an integer) Fiber is usually mixed with a solution containing divalent metal ions. The reaction is carried out at a temperature from room temperature to the boiling point under pressure and then heat-treated at a temperature of 400 ° C. or more and a melting temperature, preferably 500 ° C. to 1100 ° C. (Referred to as the step reaction method) It is.

Furthermore the general formula _{K 2 -lHlTi 2 O 5 · gH} 2 O ( where l is 0 to 2) crystalline fibrous material 2 potassium titanate or its hydrated derivative represented by, Ba, Sr, Pb, Ca , Manufacture by reacting one or more aqueous solutions selected from the group consisting of oxides, hydroxides, inorganic acid salts, and metal salts of organic acid salts of divalent metals such as Mg, Zn, and Ni under contact. The method is disclosed as another example of the hydrothermal method (JP-A-62-21799).

The metal tin whisker whiskers thus obtained are fine fibrous crystals having a fiber length of about 1 to 30 μm, a fiber diameter of about 0.1 to 1 μm, and a high dielectric constant (3
00-3000), the polarization is oriented along the crystal axis developed in the fiber length direction, and a large dipole can be formed. Therefore, regardless of the presence or absence of water, the system in which the whiskers of the present invention are dispersed can always have polarized fine particles, and the fiber axis is oriented along the electric field. Is very strong and a state similar to that of a rigid rod-like shape is produced, and a very effective electric field response behavior can be exhibited.

The oily medium that can be used in the present invention can be arbitrarily selected from mineral oil having an electrical insulating property, vegetable oil, and synthetic oil, but is preferably synthetic oil in view of meeting various requirements.
Examples include polyolefins, alkyl esters,
There are diester type, polyphenylene type, polyether type, silicon type, perfluoropolyether type, phosphazene type, s-triazine type and the like.

On the other hand, substances that can be used in combination with the above substances as a part of the dispersed phase include finely divided silica gel, alumina, synthetic zeolite, zinc oxide, titanium oxide, potassium titanate, sodium titanate, barium titanate, strontium titanate and the like. Other examples include organic pigments and carbon.

In addition, the substantially anhydrous state described in the present specification refers to a specific or each dispersed phase in which the dispersed phase is 0.1 mmHg.
It was dried under constant vacuum at 100 ° C. for 2 days to a constant weight.
It is in a state of being treated with a synthetic zeolite which has been dried by heating at a temperature of ° C.

In the present invention, the disperse phase may be used in any ratio within a range in which the mixed composition with the oily medium has a desired fluidity in a target temperature range, and a preferable ratio is a volume ratio of the disperse phase of 0.1 to 50. %, More preferably 1 to 40%.

(Effects of the Invention) The electric field responsive fluid of the present invention has the greatest drawbacks of the conventional ones: poor long-term stability due to the presence of water, elution of electrodes and other metal members due to application of an electric field, and electric field response characteristics. In addition, it is possible to solve the problems such as the temperature dependence of the compound, and to compensate for the decrease in the electric field response effect due to the formation of the cross-links lost by making it anhydrous, by using the effect of high shape anisotropy.

The evaluation of the electric field response characteristic in the present invention was performed by using a sample fluid sealed in a gap (2 mm) between a cylindrical electrode having an inner diameter of 22.85 mm and a rotor electrode having an outer diameter of 18.85 mm having the same central axis as shown in FIG. The measurement was performed by measuring a change in viscosity when a predetermined DC voltage was applied.

The fluid composition of the present invention exhibits a large electric field response characteristic regardless of the presence or absence of water, and it has been confirmed that this effect is similarly exhibited in a substantially anhydrous system.

(Examples) Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.

Reference Example 1 Powdered titanium oxide (TiO ₂ ) 56 g, anhydrous potassium carbonate 27.6
g, 14.9 g of potassium chloride as a flux is uniformly mixed, filled into a cylindrical mold having a diameter of 100 mm, and pressure molded (200 kgf / cm
² ) The fired product was fired at 1100 ° C for 2 hours, and gradually cooled to 950 ° C at a cooling rate of 20 ° C / hr. After cooling, the mixture is poured into water 3 and the fibrous substance is suspended and separated by stirring.
After washing with water and drying at 110 ° C., 65 g of a product was obtained. The product was a potassium tetratitanate fiber having a composition formula of K ₂ O.4TiO ₂ , a fiber length of 14 μm, and a fiber diameter of 0.5 μm. 1N sulfuric acid was added to the 5% aqueous dispersion to adjust the pH to 1 or less,
After stirring for one hour, leaving overnight, washing with water, washing with ethanol, and drying, a hydrated titania fiber was obtained.

The thus obtained hydrated titania fibers 5.1 g, barium hydroxide _{[Ba (OH) 2 · 8H 2} O ] 18.4g and those were mixed homogeneously sodium chloride 3.3g 10g (Ti / Ba / Na = 1 / 1/1)
Into a cylindrical mold with a diameter of 25mm and press molding (20kgf / cm ² )
This was heated and baked in a Matsufuru furnace at 600 ° C. for 2 hours, separated by wet defibration in boiling water, washed with water, and dried in a 110 ° C. constant-temperature dryer for 5 hours. The product obtained is 4.2 g,
As a result of X-ray diffraction, only perovskite type BaTiO ₃ fiber was obtained. When this sample was observed with an electron microscope, it was found to be a homogeneous whisker having a fiber length of 10 μm and a fiber diameter of 0.3 to 0.5 μm.

Reference Example 2 A whisker (BaTiO ₃₎ composed of a mixed phase of barium tetratitanate or the like instead of barium titanate single phase in the same manner as in the reaction of Reference Example 1 except that barium chloride was used instead of barium hydroxide. : BaTi ₃ O ₇ : BaTi ₄ O ₉ = 1: 4: 5)
I got Further, a single phase of barium tetratitanate was obtained by setting the firing temperature to 1000 ° C.

Example 1 Perovskite-type BaTiO ₃ whiskers (fiber length about 10 μm, fiber diameter 0.3 to 0.3 mmHg, vacuum dried at 100 ° C. for 48 hours)
0.5 μm synthesized according to Reference Example 1) 33 parts by volume
Otsuka Phosphorol NF-46 [fluoroalkoxyphosphonitrile manufactured by Otsuka Chemical Co., Ltd.] [H (CF ₂ CF ₂ ) ₂ CH ₂ O] ₃ [C dehydrated with synthetic zeolite heated and dried at 00 ° C.
F ₃ CF ₂ CH ₂ O] ₃ [PN] ₃ ｝]
Degassed and mixed at 0.5 mmHg for 2 hours. The viscosity of the fluid thus prepared was 75 centipoise at 30 ° C. and had good fluidity at room temperature. This fluid is sealed in a gap of 2 mm between a cylindrical outer electrode having an inner diameter of 22.85 mm having the same central axis as shown in FIG. 1 and an inner rotor electrode having an outer diameter of 18.85 mm, and a DC voltage of 0 to 1000 V is applied by a step. Meanwhile, the change in the viscosity was directly read and recorded by a viscometer. 30 of this fluid
The electric field response behavior at ℃ is expressed by the magnification
It was shown to.

Even when a low voltage was applied, the viscosity increased greatly, and the viscometer, which had been used to evaluate a conventional electric field responsive fluid, greatly exceeded the measurement limit, and the value at 500 V / mm could not be measured accurately. FIG. 2 also shows the viscosity change rates of the fluids of 16 parts by volume and 13 parts by volume of the BaTiO ₃ whiskers prepared in the same manner.

Comparative Example 1 The viscosity change rate of a fluid prepared using 33 parts by volume of BaTiO ₃ powder (high dielectric type, average particle size 1.5 μm) as in Example 1 is shown in FIG. 2 for comparison. FIG. 2 clearly shows the effect of the whisker.

Examples 2 to 9 The viscosity change rates of the various electric field responsive fluids prepared and measured in the same manner as in Example 1 are shown, and the viscosities of the electric field strengths of 250 V / mm and 500 V / mm, assuming that the viscosity at an applied voltage of 0 is 1 as in FIG. Change rate of the first
It is shown in the table. * 1 in the table indicates that ASME / ASLE Lubrication Confe by Carl E. Snyder and others.
triazine oils disclosed in rence (Ohio) 1970.10.13-15.

* 2 is a phosphazene-based oil described in JP-A-61-275332.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a viscosity measurement system for an electric field responsive fluid,
FIG. 2 is a graph showing the relationship between the applied voltage and the rate of increase in viscosity of the electric field responsive fluids of the example and the comparative example.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ identification code FI C10N 30:00 40:14 (58) Investigated field (Int.Cl. ⁶ , DB name) C10M 125/00 C10N 40:14

Claims (5)

(57) [Claims] 1. A dispersed phase comprising a material having a shape anisotropy selected from gypsum, asbestos, polyimide, polyamide or ferroelectric oxide fiber and having a high degree of crystallinity (excluding those treated with an alkylamine). Alternatively, an electric field responsive fluid composition suspended as a part of a dispersed phase in an electrically insulating oily medium. 2. The length of a substance having shape anisotropy is about 200 μm.
2. The composition according to claim 1, wherein the ratio of length to thickness is in the range of 5 to 500. 3. The material having shape anisotropy is Ti, Zr, Nb, Ta.
2. The composition according to claim 1, wherein the substance is a ferroelectric oxide fiber based on an oxide of the above. 4. The material having shape anisotropy is BaTiO ₃ , MgTi
_{O 3, SrTiO 3, CaTiO 3} , BaTi 3 O 7, BaTi 4 O 9 than at least one ferroelectric oxide fibers in a composition according to claim 3 which is selected. 5. A finely divided silica gel as a part of a dispersed phase,
2. The composition according to claim 1, wherein alumina, synthetic zeolite, zinc oxide, titanium oxide, potassium titanate, sodium titanate, barium titanate or strontium titanate are used in combination.