JPH0718283A - Electroviscous fluid - Google Patents

Abstract

PURPOSE:To provide an electroviscous fluid which has excellent electroviscous characteristics such as an excellent response due to the much more stable viscosity or electric current under applied voltage than the conventional ones and a low electric current under applied voltage. CONSTITUTION:An electroviscous fluid is obtd. by using, as fine dielectric particles, a carbonaceous powder which provides an extract having an extinction of 2.5 or lower at a certain wavelength in the range of 400-500nm when the powder is extracted with the same wt. of toluene at its b.p. for 10min or longer.

Description

Detailed Description of the Invention

[0001]

[Field of Industrial Application] An electrorheological fluid is a fluid whose apparent viscosity changes rapidly and reversibly by applying a voltage to the fluid, that is, a fluid showing the so-called Winslow effect.
Generally, it is obtained by dispersing dielectric particles in an oil medium having excellent electric insulation. The characteristics of this electrorheological fluid have been known for a long time, and are expected to be applied to clutches, valves, vibration absorbers and the like. The present invention relates to an electrorheological fluid that exhibits an excellent electrorheological effect by using a specific carbonaceous powder as dielectric fine particles.

[0002]

2. Description of the Related Art Generally, electrorheological fluids are required to have a large viscosity change when a low voltage is applied in terms of energy efficiency, and at the same time, a small amount of current flows at the same time. Does not settle in the interior, the characteristics do not deteriorate during long-term use (for example, decrease in viscosity change, increase in current value), small change in characteristics due to operating temperature, excellent responsiveness to voltage application, and voltage The viscosity and the current value do not change with time during application, and the viscosity of the fluid when no voltage is applied (hereinafter referred to as initial viscosity) is as low as possible.

That is, if a large change in viscosity can be realized under an external electric field of low current, the energy efficiency of various devices using electrorheological fluid can be improved. Also,
Solid particles that can achieve electrorheological fluid with low initial viscosity are
In an electrorheological fluid that requires a predetermined initial viscosity, it is possible to increase the blending amount of solid fine particles in the fluid as compared with the solid fine particles of an electrorheological fluid having a high initial viscosity, and as a result, a high electrorheological change can be realized. Furthermore, if the viscosity and current value fluctuate during voltage application, it becomes difficult to control a device (apparatus) that uses the electrorheological fluid, and a sufficient change in viscosity cannot be obtained, which poses a practical problem.

Conventionally, as such an electrorheological fluid, water such as silica gel, starch and cellulose, and highly dielectric liquid such as alcohol are absorbed in an oil medium having high electric insulation such as transformer oil, spindle oil and chlorinated paraffin. With dispersed solid particles (US Pat. No. 2,886,151,
Nos. 3047507 and JP-A-53-175
No. 85, No. 53-93186, No. 61-44998.
No. 61-259752, 62-95397,
JP-A-1-207396, etc.), or various polymers are coated on the surface in order to improve the deterioration of characteristics during long-term use and the deterioration of performance at high temperature, which are caused by using solid particles that have absorbed water. And the like (Japanese Patent Application Laid-Open Nos. 47-17674 and 63-97694) are disclosed. Despite these suggestions,
It is hard to say that an electrorheological fluid that is practical and has sufficient performance has been developed.

[0005]

On the other hand, as the dielectric particles which can satisfy the performance required for the electrorheological fluid, the degree of carbonization (carbon atoms and hydrogen in the elemental analysis, which does not require a high dielectric liquid such as water) is required. The use of carbonaceous powder in which the ratio of the number of atoms = C / H) is controlled is disclosed in JP-A-3-279206. Such a carbonaceous powder is basically
An organic compound such as coal-based tar, coal-based pitch, coal liquefaction, petroleum-based tar, petroleum-based pitch, and resins is used as a raw material, and the raw material is heated in an autoclave, kiln, electric furnace, etc. at a maximum temperature of 300 to 800 ° C. After the heat treatment of 1), the product obtained by the heat treatment is pulverized and classified.

It is also disclosed in Japanese Patent Laid-Open No. 3-279206 that the carbonaceous powder having the following characteristics is desirable. That is,
C / H is 1.70 to 3.50, or further the result of gravimetric analysis by a thermobalance (TGA) is 40 in a nitrogen atmosphere.
Weight loss in the range of 0 to 600 ° C is 0.5 to 1
It is desirable that the content is 3.0% by weight, the maximum particle size is 50 μm or less, and the average particle size is 0.5 to 40 μm. Therefore, the heat treatment step and the crushing / classifying step are adjusted so as to realize the above characteristics.

The electrorheological fluid prepared by using the above-mentioned carbonaceous powder exhibits a large viscosity change at a low voltage and, at the same time, has a small amount of current flowing at that time. Although it exhibits excellent electrorheological characteristics in terms of solving the instability with respect to temperature and the instability with respect to temperature, etc., depending on the manufacturing method and selection of raw materials, fluctuations in viscosity and current values occur during voltage application There are cases where problems such as stable electrorheological effect cannot be stably exhibited and low response to voltage application, and there is room for improvement.

An object of the present invention is to solve the above-mentioned problems of the prior art. For example, the fluctuation of viscosity during voltage application is smaller than that of the prior art and the response is excellent, and the current value during voltage application is small. An object of the present invention is to provide an electrorheological fluid having excellent electrorheological characteristics.

[0009]

[Means for Solving the Problems] The mechanism of manifestation of the electrorheological effect has not been fully clarified. However, it is generally considered that polarization is generated on the particle surface by the application of an external electric field, and the polarized particles attract each other by electrostatic attraction, resulting in an increase in apparent viscosity. Here, according to the study by the present inventors, the degree of this polarization depends on the electrical characteristics such as the dielectric constant and the electric conductivity of the carbonaceous powder, and these electrical characteristics are C of the above-mentioned carbonaceous powder. / H, weight loss due to TGA (content of low boiling point material), particle size, and other characteristics of the carbonaceous powder are closely related.

That is, in the electrorheological fluid, when the carbonaceous powder to be used has uniform characteristics of each powder (particle), the degree of polarization of each carbonaceous powder and the state of dispersion in the oily medium. Is uniform, the characteristics of the electrorheological fluid are stable, the viscosity and the like do not change during the application of voltage, and the response is also good. However, if the characteristics of the carbonaceous powders vary, the polarization state and conductivity of the carbonaceous powders differ from each other. for that reason,
Each carbonaceous powder interacts with each other during the application of a voltage, resulting in a change in the polarization state and the conductive state of each, and as a result, the viscosity and the current value change with time even when the same voltage is applied,
Poor responsiveness will occur. Further, when the variations in these characteristics are large, the electrorheological effect cannot be exhibited.

Therefore, in order to realize an electrorheological fluid having excellent responsiveness, stability of current and viscosity when a voltage is applied, and the like, it is necessary to individually add C to the carbonaceous powder.
It is necessary to realize an entirely homogeneous carbonaceous powder having no variation in characteristics such as weight loss due to / H and TGA.
As a result of earnest studies on the factors of the variation in the characteristics of the carbonaceous powder, the present inventors have found that the absorbance of the extraction solution obtained by solvent-extracting the carbonaceous powder and the subtle difference in the characteristics such as C / H of the carbonaceous powder. Therefore, it has been found that by preparing an electrorheological fluid using a carbonaceous powder having the above-mentioned absorbance within a predetermined range, it is possible to realize an electrorheological fluid with a small viscosity fluctuation when a voltage is applied, and the present invention is realized. completed.

That is, the present invention is an electrorheological fluid obtained by dispersing dielectric fine particles in an oil medium having excellent electric insulation, wherein the dielectric fine particles are:
A carbonaceous powder having an absorbance of 2.5 or less at any wavelength of 400 to 500 nm of a solution obtained by mixing with toluene at a weight ratio of 1: 1 and extracting at a boiling point for 10 minutes or more, An electrorheological fluid is provided.

[0013]

[Structure] The electrorheological fluid of the present invention will be described in detail below. The electrorheological fluid of the present invention is an electrorheological fluid obtained by dispersing dielectric fine particles in an insulating oily medium, and is a carbonaceous powder obtained by subjecting tar pitch or the like to heat treatment and then pulverizing and classifying. Is used as dielectric fine particles, especially as carbonaceous powder,
Toluene and carbonaceous powder were mixed at a weight ratio of 1: 1,
400 to 50 of the solution obtained by extracting at the boiling point for 10 minutes or more
A carbonaceous powder having an absorbance (-log I / I ₀ ) of 2.5 or less at any wavelength of 0 nm is used.

As described above, in an electrorheological fluid that uses carbonaceous powder, the viscosity may change when a voltage is applied, and this variation in viscosity causes variations in the characteristics of individual carbonaceous powder powders. to cause. Here, as a result of repeated investigations by the inventors of the viscosity fluctuation of the electrorheological fluid,
The variation in the characteristics of the carbonaceous powder, that is, the variation in the viscosity when a voltage is applied, is 40
It has a correlation with the absorbance at any wavelength of 0 to 500 nm, and by preparing an electrorheological fluid using a carbonaceous powder having this absorbance of 2.5 or less, there is little fluctuation in viscosity when a voltage is applied, which is excellent. It was found that an electrorheological fluid with different characteristics could be obtained.

More specifically, the absorbance is measured as follows. First, carbonaceous powder and toluene are mixed at a weight ratio of 1: 1 and extraction is performed at the boiling point of toluene for 10 minutes or more. If the extraction temperature is low or the extraction time is less than 10 minutes, the extraction rate will be poor and it will not be possible to obtain an effective absorbance for the preparation of the electrorheological fluid. Although there is no particular limitation, even if the extraction time is 30 minutes or more, the change in the extraction rate is extremely small, which is disadvantageous in terms of time.

After the extraction is completed, the carbonaceous powder and the extract are separated by filtration. Then 400-500 of the separated extract
Absorbance is measured by an absorptiometer at any wavelength in nm. In the carbonaceous powder carbonized to the extent that electrorheological characteristics are exhibited, the toluene-soluble component in the powder is a collection of aromatic compounds. Therefore, by measuring the absorbance in the above wavelength range, the relative amount can be grasped.
The measurement wavelength of the absorbance is preferably around 450 nm.

In the electrorheological fluid of the present invention, the electrorheological fluid is prepared by using carbonaceous powder having an absorbance of 2.5 or less at any wavelength of 400 to 500 nm measured as described above, preferably around 450 nm. Prepare. With such a configuration, it is possible to realize an electrorheological fluid that has a small change in viscosity when a voltage is applied and is excellent in responsiveness.

The electrorheological fluid of the present invention basically uses a carbonaceous powder having such characteristics, but preferably has a C / H value of 1.70 to 3.50, more preferably. 2.00 to 3.50, especially 2.20 to 3.00
More preferably, the amount of weight loss by TGA in the temperature range of 400 to 600 ° C. under a nitrogen atmosphere is 0.5 to 13.0 wt%, preferably 0.5 to 6.0 wt%. A carbonaceous powder is used. This can be achieved by appropriately setting the temperature and time of each heat treatment in the carbonaceous powder manufacturing process.

By using a carbonaceous powder having a C / H in the range of 1.70 to 3.50, sufficient electrorheological characteristics can be obtained when an electrorheological fluid is prepared, and further,
It is possible to realize an electrorheological fluid having a small current value when a voltage is applied and good energy efficiency. Also, C /
H in the range of 2.00 to 3.50, and further 2.20 to 3.
With the range of 00, this characteristic becomes more remarkable.

The average particle size of the carbonaceous powder used is preferably 0.5 to 40 μm, more preferably the average particle size 2
It is preferable to use a carbonaceous powder having a particle size of ˜40 μm, and particularly an average particle size of 2 to 10 μm. By using the carbonaceous powder having an average particle diameter in the above range, the carbonaceous powder can be uniformly and satisfactorily dispersed in the oil solvent without settling when the electrorheological fluid is prepared. Better results can be obtained in that the initial viscosity can be suitably reduced.

The method for producing such carbonaceous powder will be described below. Usually, as the raw material of the carbonaceous powder used in the present invention, coal-based tar, coal-based pitch, coal liquefaction, petroleum-based tar, petroleum-based pitch and the like, polyvinyl chloride, thermoplastic resins such as polyvinyl alcohol and the like. Organic compounds such as thermosetting resins such as phenol resin can be used. In addition, examples of other raw materials include polymers of condensed polycyclic aromatic compounds such as acenaphthylene, naphthalene, methylnaphthalene, anthracene, and phenanthrene, and monomers and polymers such as naphthacene. Also,
A compound obtained by polymerizing acenaphthylene, hydrogenated pyrene or the like by heat treatment can also be used. Examples of these polymers include polymers produced by using an acid catalyst such as HF-BF ₃ . These raw materials may be used alone as a starting material for the carbonaceous powder, or may be used as a mixture of two or more kinds.

When free carbon and ash are contained in the tar, it is preferable to remove them if necessary. Specifically, a generally industrially practiced removal method such as centrifugal separation or static separation by adding various solvents can be applied. Furthermore, coal tar pitches
Although it contains impurities such as silica and alumina, it is preferable to remove such impurities in advance.

Then, such a raw tar pitch is
An autoclave, a kiln, a fluidized bed, an electric furnace or the like is used alone or in combination, and heat-treated at a maximum temperature of 300 to 800 ° C., preferably 300 to 500 ° C., and the C / H value of the obtained carbonaceous powder, preferably, The amount of weight loss by TGA in a nitrogen atmosphere at 400 to 600 ° C. is adjusted to the above-mentioned target value.

Various methods can be used for this heat treatment depending on the raw material. For example, when the raw material organic compound is a liquid such as coal tar pitch, it is carried out as follows. That is, first, the raw material tar pitch is subjected to a primary heat treatment at 300 to 800 ° C. in a non-oxidizing atmosphere such as a nitrogen stream using an autoclave or the like. After this heat treatment, the heat-treated product obtained is further subjected to 300 times in a non-oxidizing atmosphere such as under a nitrogen stream using a rotary kiln or the like.
Secondary heat treatment is performed in the temperature range of up to 800 ° C. In this method, the raw material tar pitch, which is usually a liquid, is solidified by the primary heat treatment and the weight reduction amount due to C / H or TGA is roughly adjusted, and further, the weight reduction amount due to C / H or TGA is caused by the subsequent heat treatment. Finally adjust.

Between the primary heat treatment and the secondary heat treatment,
If necessary, an extraction step may be provided to dissolve and remove unnecessary components. The extraction solvent is exemplified by tar-medium oil and the like.

The heat treatment may be carried out not only in the above-mentioned primary and secondary heat treatments but also in three or more times, or the carbonaceous powder may be produced by one heat treatment instead of plural times.
The heat treatment may be carried out by either a batch method or a continuous method. Further, if necessary, a crushing / classifying step before the heat treatment, an extraction step for removing unnecessary components, and the like may be provided.

Next, the carbonaceous powder thus obtained is pulverized and classified to bring the average particle size of the carbonaceous powder to the above-mentioned target value. This crushing / classifying step can be carried out using an ordinary crushing and classifying device.For example, a jet mill, a hammer mill, a ball mill and a wind classifier, an apparatus and a method generally used industrially such as sieving can be used. Available.

Further, if necessary, the carbonaceous powder obtained by pulverizing and classifying may be reheated and / or depressurized. By performing this reheating treatment / decompression treatment, the low boiling point component existing on the powder surface can be effectively controlled and removed, and the surface is homogeneous and more stable while maintaining the main characteristics such as C / H. It becomes possible to manufacture a carbonaceous powder capable of realizing an electrorheological fluid having excellent electrorheological characteristics.

If the reheating treatment and / or the depressurizing treatment are carried out at an excessively high temperature, the main characteristics of the carbonaceous powder may be changed, and the current value when a voltage is applied when using an electrorheological fluid may increase. Therefore, the reheat treatment and / or the depressurization treatment is usually performed at a temperature not higher than the maximum temperature of the heat treatment before pulverization / classification.

The carbonaceous powder thus obtained is dispersed in an electrically insulating oily medium such as transformer oil, spindle oil, chlorinated paraffin or silicon oil to prepare the electrorheological fluid of the present invention. Such an electrorheological fluid of the present invention is an extremely stable electrorheological fluid having a small current value even when a high voltage is applied, stable viscosity and current, low initial viscosity, and excellent electrorheological characteristics. As described above.

The content of the carbonaceous powder in the electrorheological fluid of the present invention is 1 to 60% by weight, preferably 20 to 50% by weight, and the content of the electrically insulating oily medium is 99 to 4%.
It is 0% by weight, preferably 80 to 50% by weight. If the amount of carbonaceous powder is less than 1% by weight, the electrorheological effect is small, and 6
If it exceeds 0% by weight, the initial viscosity in the absence of an electric field becomes remarkably large and the fluidity deteriorates.

[0032]

EXAMPLES The present invention will be described in more detail with reference to specific examples of the present invention. The present invention is not limited to the examples below.

Example Using coal tar pitch having a softening point of 250 ° C. as a raw material, various carbonaceous powders were obtained by the following steps. Each heat treatment was performed in a non-oxidizing atmosphere with nitrogen inflow. The average particle size of the carbonaceous powder was measured using a Coulter counter and an aperture tube having a diameter of 50 μm.

[0034]

Each carbonaceous powder was mixed with toluene in a weight ratio of 1: 1 and extracted at the boiling point of toluene for 30 minutes,
The extract was obtained by performing filtration.

When the absorbance at 450 nm (-log I / I ₀ ) of each carbonaceous powder extract was measured using an absorptiometer,
It was as shown in the table below.

Then, about 40% by weight of each carbonaceous powder is uniformly dispersed in silicone oil having a viscosity of 0.1 P (poise),
An electrorheological fluid was obtained. A voltage of 2 kV / mm was applied to the obtained electrorheological fluid at room temperature using a double cylinder type rotational viscometer to measure the viscosity every 12 seconds at 25 points under a shear rate of 366 / sec.

From the viscosity measurement results, a single regression line of the viscosity change was calculated, and the deviation from the regression of each measurement point, that is, the sum of squares of deviations (σ _E ) was calculated to measure the fluctuation of the viscosity. .

FIG. 1 shows the relationship between the calculated fluctuation of the viscosity with time and the absorbance of the extract of the carbonaceous powder used.
As shown in FIG. 1, the electrorheological fluid of the present invention using a carbonaceous powder having an absorbance of the extract liquid at 450 nm of 2.5 or less has a fluctuation in viscosity of 5 or less which causes no practical problem. It can be seen that the electrorheological fluid is excellent in responsiveness with little fluctuation in viscosity and current value when a voltage is applied. From the above results, the effect of the present invention is clear.

[0040]

INDUSTRIAL APPLICABILITY As described in detail above, the present invention uses a carbonaceous powder having an absorbance of 2.5 or less at 400 to 500 nm of an extract when the carbonaceous powder is extracted with toluene under predetermined conditions. According to the present invention, it is possible to realize a carbonaceous powder capable of realizing an electrorheological fluid exhibiting excellent responsiveness and excellent electrorheological characteristics with little fluctuation in viscosity and current value during voltage application.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the absorbance of a carbonaceous powder toluene extract at 450 nm and the viscosity fluctuation.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C10N 40:04 40:08 40:14 70:00 (72) Inventor Taku Hara Oka Chiba Chiba Kawasaki Steel Co., Ltd., Chuo-ku, Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Noriyoshi Fukuda No. 1 Kawasaki-machi, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor ▲ Kaoru Takagi, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba, Kawasaki Steel Corporation Technical Research Division (72) Inventor Takayuki Maruyama 3-1-1 Ogawa-Higashicho, Kodaira-shi, Tokyo (72) Inventor Saito Tsubasa 3-1-1 Ogawahigashi-cho, Kodaira-shi, Tokyo (72) Inventor Takao Ogino 3-1-1 Ogawa-higashi-cho, Kodaira-shi, Tokyo

Claims (1)

[Claims] 1. An electrorheological fluid obtained by dispersing dielectric fine particles in an oil medium having excellent electrical insulation, wherein the dielectric fine particles are mixed with toluene at a weight ratio of 1: 1 to obtain a boiling point. An electrorheological fluid characterized by using a carbonaceous powder having an absorbance of 2.5 or less at any wavelength of 400 to 500 nm of a solution obtained after extraction for 10 minutes or more.