JPH06234512A - Electroviscous fluid - Google Patents

Abstract

(57) [Summary] [Purpose] To provide an electrorheological fluid with reduced viscosity (initial viscosity) when no voltage is applied. [Structure] Electric particles characterized by having a specific surface area of 40 m ² / g or less used as a dispersoid in an electrorheological fluid obtained by dispersing fine dielectric particles in an oil medium having excellent electric insulation. Viscous fluid. The average particle size of the particles is 0.5 to 40 μm, the ratio of particles exceeding 20 μm is 1% by weight or less, and the ratio of particles having a particle size of less than 1.6 μm is 3%.
It is preferably 0% by weight or less. C / H of carbonaceous powder
The (atomic ratio) is preferably 2.00 to 3.50.

Description

Detailed Description of the Invention

[0001]

[Industrial application] An electrorheological fluid is a fluid that exhibits a phenomenon in which the apparent viscosity of the fluid changes rapidly and reversibly when an electric field is applied to the fluid. Generally, it is an oily medium with excellent electrical insulation. It is constituted by dispersing fine particles which are a dielectric substance. The characteristics of this electrorheological fluid have been known for a long time, and its application to devices such as clutches, valves, and shock absorbers that require a strong force due to low electric output has been studied. The present invention relates to such an electrorheological fluid, in particular, an electrorheological fluid using novel fine particles having a dielectric property capable of realizing an excellent electrorheological effect.

[0002]

2. Description of the Related Art Electrorheological fluids that have been studied so far include, for example, U.S. Pat. Nos. 2,886,151 and 3,047.
No. 507 or JP-A Nos. 53-17585 and 53-
No. 93186, No. 61-44998, No. 61-259.
752, 62-95397, JP-A-1-2073.
No. 96 and the like, which are prepared by dispersing water-absorbing solid fine particles such as silica gel, starch, and cellulose in an oil medium having high electric insulation such as spindle oil, transformer oil, and chlorinated paraffin. Shows the above effect due to the polarization of water molecules adsorbed on the fine particle body.

However, in the electrorheological fluid using these powders, the electric conductivity of the particles is increased by the adsorbed water, and when the electric field is applied, the current flows too much and the energy efficiency is low. There are many problems in practical use, such as a change in performance over time due to desorption of water from fine particles, and extremely unstable temperature changes.

The requirements for a practical electrorheological fluid are (1) a large change in the viscosity of the fluid when a voltage is applied and when it is not applied, that is, the viscosity of the fluid is high when a voltage is applied and is not applied. Sometimes low, (2) low current value flowing in the fluid when voltage is applied, (3) good dispersibility of solid fine particles in the fluid and difficult to settle, (4) wide temperature range , (5) little deterioration of characteristics with time, and (6) good response of viscosity change when voltage is applied.

As a result of earnest studies from such a viewpoint, the present inventors proposed solid particles for electrorheological fluid which can exhibit excellent performance in Japanese Patent Laid-Open No. 3-279206. That is, by using the carbonaceous powder proposed in the above specification, an electrorheological fluid satisfying the above requirements can be obtained.

[0006]

The object of the present invention is to disperse a carbonaceous powder in an insulating oily medium by using a carbonaceous powder improved over the carbonaceous powder proposed in the above specification. An object of the present invention is to provide an electrorheological fluid whose viscosity (initial viscosity) when no voltage is applied is further reduced when the electrorheological fluid is prepared.

[0007]

Means for Solving the Problems As a result of further studies on the carbonaceous powder, the present inventors have found the requirements necessary for lowering the viscosity (initial viscosity) when no voltage is applied, and Arrived That is, in the present invention, the specific surface area of the carbonaceous powder used as the dispersoid in the electrorheological fluid obtained by dispersing the fine dielectric particles in an oil medium having excellent electrical insulation is 40 m ² / g or less. To provide an electrorheological fluid. The carbonaceous powder has an average particle size of 0.5 to 40 μm within a range of 2
The proportion of particles exceeding 0 μm is 1% by weight or less, and the particle size is 1.6.
The proportion of particles smaller than μm is preferably 30% by weight or less. The carbonaceous powder is selected from the group consisting of coal, coal-based tar, pitch, coal liquefaction, cokes, petroleum, petroleum-based tar, pitch, pitch obtained by polymerizing condensed aromatic ring compounds, and resins. The carbonaceous powder obtained by heat-treating the obtained organic compound is preferable. The carbonaceous powder has a carbonization degree (C / H), which is the ratio of the number of carbon atoms and hydrogen atoms by elemental analysis of the carbonaceous powder,
It is preferably 2.00 to 3.50.

[0008]

The present invention will be described in more detail below. In general, the properties required for an electrorheological fluid are that it exhibits a larger viscosity change under an external electric field, that the current flowing is as small as possible in terms of energy efficiency, that dispersoid particles do not settle in an oily medium, Furthermore, it is stable to long-term use and temperature, and has excellent responsiveness to the application of an electric field. Moreover, it is also an important requirement that the viscosity (initial viscosity) of the fluid when no voltage is applied is low. That is, a carbonaceous powder that achieves a fluid with a low initial viscosity is
In a fluid that requires a predetermined initial viscosity, the blending amount of the carbonaceous powder can be increased as compared with the carbonaceous powder of the fluid having a high initial viscosity, and as a result, a high electroviscosity change can be realized.

As a result of detailed examination of the characteristics of the carbonaceous powder required to satisfy the characteristics required for such an electrorheological fluid, it was found that the specific surface area of the carbonaceous powder used as fine particles of the dispersoid and the initial viscosity were It was found that there is a correlation and that the initial viscosity increases as the specific surface area increases.

When the particles having a high specific surface area are used, the initial viscosity of the fluid using such particles can be lowered by lowering the content ratio of the carbonaceous powder used as the dispersoid or by changing the particle diameter of the powder. It is necessary to increase. However, when the content rate is reduced, the viscosity change upon voltage application is reduced, the characteristics themselves are reduced, and when the particle size is increased, the sedimentation of particles in the fluid becomes faster,
Problems such as long-term use become impossible. Therefore, it is desirable that the specific surface area of the dispersoid particles be as small as possible. The specific surface area in this case is 40 m ² / g or less,
More preferably 20 m ² / g or less, further preferably 10 m ²
It is preferably less than / g. The specific surface area in this case means the BET specific surface area by nitrogen adsorption. As another characteristic, the average particle diameter of the carbonaceous powder is in the range of 0.5 to 40 μm, preferably in the range of 0.5 to 10 μm, and particularly preferably in the range of 0.5 to 4 μm. desirable. When the average particle size exceeds 40 μm, the sedimentation of the powder in the fluid becomes remarkable. On the other hand, the average particle size is 0.5 μm
If it is smaller, the viscosity when an electric field is not applied to the fluid is significantly increased and the electrorheological effect is reduced. Also,
It is desirable that the proportion of particles exceeding 20 μm is 1% by weight or less. Particles having a particle size of more than 20 μm settle rapidly in a fluid, and when left to stand, they quickly separate from the oily medium and form a cake that is difficult to redisperse. Further, the proportion of particles having a particle size of less than 1.6 μm is 30% by weight or less, preferably 20% by weight or less.
If it exceeds 30% by weight, the viscosity when an electric field is not applied to the fluid is remarkably increased and the electrorheological effect is reduced.

Another preferable characteristic of the carbonaceous powder for electrorheological fluid is C / H, which is the ratio of the number of carbon atoms and hydrogen atoms by elemental analysis, which indicates the degree of carbonization of the carbonaceous powder, is 2.00. ~ 3.50 (more preferably 2.20-3.0
0) is desirable. When the C / H value is less than 2.00, the carbonaceous powder does not function as a dielectric, and as a result, a sufficient electrorheological effect cannot be obtained. On the other hand, when the C / H value exceeds 3.50, an excessive current flows in the electrorheological fluid, which not only lowers the energy efficiency in practical use but also causes dielectric breakdown.

Further, in order to secure the stability of the electrorheological fluid at high temperature and in the long term, it is desirable to remove the low-boiling point organic components in the carbonaceous powder as much as possible. In particular, it is desirable that the amount of weight loss at room temperature to 200 ° C. when heated at 10 ° C./min under nitrogen flow by a thermobalance (TGA) is 0.5 wt% or less, preferably 0.3 wt% or less. . It is considered that such low boiling point organic components volatilize at repeated use and at high temperatures, and thus impair the stability of the electrorheological fluid.

Furthermore, the composition of the carbonaceous powder must be as homogeneous as possible. For example, coal tar pitches that are usually used as raw materials for carbonaceous powders contain impurities such as silica and alumina. Needless to say, it is preferable to remove such impurities in advance, but it is also desirable to previously remove free carbon (also known as free carbon) originally contained in coal tar pitch or the like. Free carbon is amorphous carbon fine particles with extremely advanced carbonization, which is said to be generated by the thermal decomposition of tar generated in a coke oven to 1000 ° C. or higher and the vapor phase thermal decomposition. Therefore, when such free carbon is contained in the carbonaceous powder, non-uniformity is brought about and the expected electrorheological effect cannot be obtained.

The carbonaceous powder having the characteristics described above is converted into silicon oil, spindle oil, chlorinated paraffin,
By dispersing in an electrically insulating oily medium such as transformer oil, it is possible to produce an electrorheological fluid having a low initial viscosity, an excellent electrorheological effect at a low current value, and temperature stability and long-term stability. It is possible.

Next, a specific method for producing carbonaceous powder will be described. Raw materials are coal, coal tar, coal pitch,
Coal liquefaction, cokes, petroleum, petroleum tar, petroleum pitch, resins or acenaphthylene, naphthalene,
A pitch obtained by polymerizing a condensed aromatic ring compound such as methylnaphthalene or anthracene, for example, naphthalene is converted into HF-
A naphthalene pitch polymerized with an acid catalyst such as BF ₃ is used. Here, when free carbon and ash are contained in the tar and pitch, it is preferable to remove them as necessary. Specifically, generally industrial methods such as a centrifugation method and a static separation method by adding various solvents can be applied. Further, when selecting these raw materials, it is necessary to select raw materials that do not increase the specific surface area in the subsequent heat treatment. Generally, it is desirable to select a material that melts and carbonizes during heat treatment. During the heat treatment, volatilization of the low molecular weight component produces pores, which increases the specific surface area. However, by using a meltable raw material, these pores are filled and it is possible to avoid an increase in the specific surface area. In the raw material which is not melted during the heat treatment, these pores are not filled and the specific surface area is increased. However, even in a sample having an increased specific surface area, it is possible to reduce the specific surface area by filling the pores by repeating impregnation of the raw material tar / pitch and the resins and the heat treatment during the heat treatment.

The raw material coal-based or petroleum-based tars or resins are carbonized by a method generally applied to such tars and pitches, such as heat treatment or solvent extraction, or a combination of these methods to promote C / H. You can control the value. Furthermore, the low boiling point organic components in the carbonaceous powder are heat treated.
It is possible to separately control the C / H value by newly providing solvent extraction conditions and a drying process.

Next, the particle size is controlled. Specifically, the particle size is controlled by removing particles larger than the target particle size by crushing, classifying, or the like. The particle size is preferably controlled by a jet crusher, more preferably a jet crusher of interparticle collision type in order to obtain particles having a specific surface area used for the electrorheological liquid of the present invention. As an inter-particle collision type jet crusher, for example, crushing is performed by collision of particles at the intersection of air jets such as air and nitrogen ejected from a plurality of nozzles and / or the opposing portion of air jets such as air and nitrogen. The method used is given.

By mixing the carbonaceous powder thus obtained with transformer oil, spindle oil, chlorinated paraffin, silicone oil, etc., the viscosity and current are stable even when a high voltage is applied, and the initial viscosity is low. An extremely stable fluid having excellent electrorheological characteristics can be obtained. The content of the carbonaceous powder is 1 to 60% by weight, preferably 20 to 5
It is 0% by weight, and the content of electrically insulating oil is 99-4.
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.

[0019]

EXAMPLES Next, the present invention will be specifically described based on examples. (Example 1) Coal tar containing no free carbon was heat-treated in a nitrogen atmosphere at 510 ° C for 3 hours using a 20 L autoclave. The resulting heat-treated product was extracted and filtered using tar-based medium oil (boiling range 120 to 250 ° C). The extraction / filtration residue was reheat-treated for 3 hours in a nitrogen gas stream at a temperature of 510 ° C. and 3 L / min for 3 hours using a batch type rotary reaction furnace having an internal volume of 2 L to obtain a carbonized product. After crushing such a carbonized product using an inter-particle collision type jet mill (manufactured by Nisshin Engineering Co., Ltd., model CJ-10), an air classifier (manufactured by Nisshin Engineering Co., Ltd.,
The average particle size was adjusted to 3.0 μm using Model TC-15M). At this time, particles larger than 10 μm were not detected,
The proportion of particles smaller than 1.6 μm was 4.9% by weight.
The carbonaceous powder thus obtained had a C / H value of 2.38 and a specific surface area of 5.1 m ² / g. The specific surface area was measured by a BET one-point method using nitrogen gas after drying 0.2 to 0.5 g of the sample at 200 ° C. for about 10 minutes using a flowsorb 2300 manufactured by Micromeritex. The particle size was measured by using a Coulter counter and an aperture tube of 50 μm. As a result of measurement by TGA (thermobalance), the low boiling point component of 200 ° C. or lower is 0.22.
% By weight. 36 parts by weight of the carbonaceous powder was uniformly dispersed with 64 parts by weight of 0.1 poise silicone oil at room temperature, which is an electrically insulating oily medium, to obtain an electrorheological fluid. The viscosity of this electrorheological fluid was measured using a double cylinder type rotational viscometer. The results are shown in Table 1 together with other examples.

Example 2 A fluid was prepared in the same manner as in Example 1 except that the powder prepared in the same manner as in Example 1 was adjusted except that the conditions of the air classifier were adjusted so that the average particle diameter was 2.2 μm. The viscosity was measured. At this time, particles larger than 10 μm were not detected, and the proportion of particles smaller than 1.6 μm was 17.0% by weight.
And the BET specific surface area was 7.3 m ² / g. The values of the initial viscosity are shown in Table 1.

(Example 3) The same carbonaceous powder as that used in Example 1 was again used in a batch type rotary reactor having an internal volume of 2 L at a temperature of 600 ° C. in a nitrogen stream of 3 L / min. A carbonized product that was reheat-treated for an hour was obtained. The carbonaceous powder thus obtained has an average particle size of 3.2 μm, particles having a particle size of more than 10 μm are not detected, and the ratio of particles having a particle size of less than 1.6 μm is 4.
The C / H value was 2.60, and the BET specific surface area was 36 m ² / g. The fluid was prepared in the same manner as in Example 1 and the viscosity was measured. The results are shown in Table 1.

(Comparative Example 1) The same carbonaceous powder as that used in Example 1 was again used in a batch type rotary reactor having an internal volume of 2 L at a temperature of 700 ° C. in a nitrogen stream of 3 L / min. It was reheat-treated for an hour to obtain a carbonized product. In the carbonaceous powder thus obtained, particles having an average particle size of 3.4 μm or more than 10 μm were not detected, and the ratio of particles having a particle size of less than 1.6 μm was 3.9.
% By weight, C / H value was 3.20, and BET specific surface area was 49 m ² / g. The fluid was prepared in the same manner as in Example 1 and the viscosity was measured. The results are shown in Table 1.

[0023]

[0024]

INDUSTRIAL APPLICABILITY The present invention has made it possible to apply carbonaceous fine particles, which have not been studied so far, to an electrorheological fluid. By using the carbonaceous fine particles according to the present invention, an extremely excellent electrorheological effect can be obtained. It has become possible to manufacture an electrorheological fluid having By using the carbonaceous powder, it became possible to obtain an electrorheological fluid having a lower initial viscosity. The present invention solves the problems of conventional electrorheological fluids and opens the way for industrial applications such as clutches, valves, and shock absorbers for electrorheological fluids.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a specific surface area of carbonaceous powder and an initial viscosity of an electrorheological fluid.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor ▲ Taka ▼ Ki 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba, Kawasaki Steel Corporation Technical Research Division (72) Inventor Hitomi Hitomi, Chiba-shi, Chiba 1 Kawasaki-cho, Kawasaki, Technical Research Division, Kawasaki Steel Co., Ltd. (72) Inventor Noriyoshi Fukuda, 1 Kawasaki-machi, Chuo-ku, Chiba City, Chiba Prefecture Technical Research Division, Kawasaki Steel Co., Ltd. (72) Takashi Maruyama No 3-1-1 Ogawa Higashicho, Kodaira, Tokyo (72) Inventor Takao Ogino 3-1-1 Ogawa Higashi, Kodaira, Tokyo (72) Inventor Tsubasa Saito 3-1-Ogawa Higashi, Kodaira, Tokyo 1

Claims (4)

[Claims] 1. A specific surface area of particles used as a dispersoid in an electrorheological fluid obtained by dispersing fine dielectric particles in an oil medium having excellent electric insulation is 40 m ² / g.
An electrorheological fluid characterized by being: 2. The average particle diameter of the particles is 0.5 to 40 μm, the proportion of particles exceeding 20 μm is 1% by weight or less, and the proportion of particles having a particle diameter of less than 1.6 μm is 30% by weight or less. Item 2. The electrorheological fluid according to Item 1. 3. The particles are coal, coal-based tar, pitch,
A carbonaceous powder obtained by heat-treating an organic compound selected from the group consisting of coal liquefaction, cokes, petroleum, petroleum tar, pitch, a pitch obtained by polymerizing a condensed aromatic ring compound, and resins. The electrorheological fluid according to claim 1. 4. The degree of carbonization (C / H), which is the ratio of the number of carbon atoms and hydrogen atoms by elemental analysis of the particles, is 2.00 to
The electrorheological fluid according to any one of claims 1 to 3, which is 3.50.