JPH07305080A - Carbon fine powder for electroviscous fluid and its production - Google Patents

Abstract

PURPOSE:To obtain carbon fine powder for electroviscous fluid having high resistance and fine particle appearance and capable of providing excellent viscosity responsiveness to applied voltage and long-term stability by lowering initial viscosity in dispersing to a dispersing phase and to provide effective method for producing the fine powder. CONSTITUTION:This carbon fine powder for electroviscous fluid consists of amorphous shoot-like carbon fine powder containing carbon cluster and has 10-10<8>OMEGAcm electric specific resistance and 1-5wt.% of oxygen content. In the carbon fine powder, specific surface area of nitrogen absorption is preferably >=50m<2>/g. This method for producing the carbon fine powder comprises heating and vaporizing a carbon material in a system retained under 20-500Torr pressure by an inert atmosphere containing 1-20vol% oxygen and rapidly cooling and re-solidifying the vaporized carbon vapor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon fine powder used for solid fine particles forming a dispersed phase of an electrorheological fluid and a method for producing the same.

[0002]

2. Description of the Related Art An electrorheological fluid is a fluid having a special property in which fine dielectric particles are dispersed in a fluid having excellent electrical insulation properties.
An electrorheological effect is shown in which the apparent viscosity of a fluid increases with the application of an electric field. Therefore, it is expected to be useful as an energy absorbing material or a vibration isolating material for dampers, shock absorbers, engine mounts, etc.

Conventionally, cellulose, starch, silica gel, ion exchange resins, etc. have been used as the solid fine particles constituting the dispersed phase of the electrorheological fluid, and the electrorheological fluid using these is disclosed in JP-A-57-47234. Bulletin,
JP-A-61-259752, JP-A-1-2073
No. 95, etc. Also, JP-A-63-9
Japanese Patent No. 7694 describes a method of coating the surface of the solid fine particles with a polymer substance. However, since these solid fine particles are hydrophilic, there are many problems in practical use such as deterioration of performance stability over time due to adsorption of water and characteristic changes due to temperature.

From this point of view, carbonaceous powder has attracted attention as non-aqueous solid fine particles containing no water. For example, in Japanese Unexamined Patent Publication (Kokai) No. 5-70116, a carbon powder in a specific C / H ratio range obtained by heat-treating a raw material such as tar or resin is pulverized and classified in an atmosphere of low oxygen concentration and moisture concentration. The carbon powder is disclosed in JP-A-5-186786, and a carbonaceous material having a shape anisotropy obtained by a method of pulverizing a carbonaceous material and then pulverizing it.
Japanese Patent Publication No. 47896 discloses carbon powders each having an electric conductivity adjusted by coating an electrically insulating substance.

However, the mechanism of structure change is very complicated in the firing carbonization of tar and resin and the fibrization of carbonaceous material,
Not only strict control is required to adjust the electric resistivity in the treatment process, but also the process load for obtaining uniform fine particles for stable dispersion in the viscous fluid is not small. Moreover, since the carbon material is essentially a substance having low activity, a complicated process is required to secondarily treat the carbon material to make it highly active or to add a functional group to the surface.

The inventors of the present invention have proposed a novel carbonaceous fine powder for electrorheological fluid including a solution to the above problems, having an electric resistivity of 10 to 10 ⁸ Ωcm and a carbon content of 99% by weight or more. As an amorphous soot-like fine powder containing carbon clusters, and a manufacturing technique therefor, a carbon material is heated and vaporized in a system maintained at a pressure of 20 to 500 Torr by an inert atmosphere to rapidly vaporize vaporized carbon vapor. A method for cooling and resolidifying was previously proposed (Japanese Patent Application No. 5-3428).
No. 56).

[0007]

According to the above-mentioned prior art, an electrorheological fluid of high resistance, high purity and fine properties, which is provided with excellent viscous response to an applied voltage and long-term stability. It is possible to provide a carbon fine powder for use and an efficient production method thereof, but since carbon clusters having a specific property are contained as a carbon component, uniform dispersibility in the dispersed phase is insufficient, and the initial viscosity becomes high. There were issues to be improved.

The present inventor has conducted earnest research to solve the above problems, and as a result, the prior art (Japanese Patent Application No. 5-342856).
No.) soot-like carbonaceous fine powder containing a specific amount of oxygen has a low initial viscosity, and the viscous response can be further improved.

The present invention was developed based on this finding, and its purpose is to provide excellent dispersibility in a dispersed phase, excellent viscous response to an applied voltage, and long-term stability. It is an object of the present invention to provide a high resistance, fine carbon fine powder for electrorheological fluid and an efficient manufacturing method thereof.

[0010]

The carbon fine powder for electrorheological fluid according to the present invention for achieving the above object is made of amorphous soot-like carbon fine powder containing carbon clusters and has an electric resistivity of 10 to 10. ^The structural feature is that it has a property composition of ⁸ Ωcm and an oxygen content of 1 to 5% by weight.

The carbon clusters are composed of carbon molecules composed of C ₆₀ , C ₇₀ , C ₇₆ , C _78, etc. having a property in which several tens of carbon atoms are aggregated, and have a substantially specific electric resistance of 10 ⁹ Ωcm or more. It is a sexual substance. The carbon fine powder for electrorheological fluid according to the present invention is an amorphous soot-like carbon fine powder containing this carbon cluster, and has an electric resistivity of 10 or less.
It is characterized by having an amorphous crystalline property in the high resistance range of -10 ⁸ Ωcm and maintaining a composition with an oxygen content of 1-5% by weight. Further, when the particle properties are fine particles having a high surface area of 50 m ² / g or more, the nitrogen adsorption specific surface area is more effective.

In the present invention, the electrical resistivity is 10 to 10
The range of ⁸ Ωcm is a requirement for obtaining a practically sufficient electrorheological effect, and with an electrical resistivity of less than 10 Ωcm, a large current is required to obtain the electrorheological effect, leading to a decrease in energy efficiency. If it exceeds 10 ⁸ Ωcm, a suitable electrorheological effect cannot be obtained. Further, oxygen contained in soot-like carbon fine powder containing carbon clusters is a functional element that lowers the initial viscosity and improves dispersibility, and if the oxygen content is less than 1% by weight, the above function becomes insufficient, 5
When the content is more than weight%, the electric resistivity tends to decrease and the initial viscosity also increases. In addition to these requirements, it is preferable that the nitrogen adsorption specific surface area is 50 m ² / g or more from the viewpoint of dispersibility, and if it is less than 50 m ² / g, the sedimentation rate of the particles becomes faster and the particles aggregate in the dispersion medium. Sedimentation is likely to occur, and long-term dispersion stability is impaired.

The production method according to the present invention for obtaining the above-mentioned carbon fine powder for an electrorheological fluid comprises a carbon material of 20 to 500 Torr in an inert atmosphere containing 1 to 20% by volume of oxygen in an inert gas such as helium. A constitutional feature is that the vaporized carbon vapor is rapidly cooled and re-solidified by being vaporized by heating in a system maintained at a pressure.

The carbon material is vaporized in a temperature range of 4000 ° C. or higher using a heating means such as a resistance heating method, a laser heating method, an arc discharge method, a high frequency plasma method, and a plasma jet method. For this, it is preferable to apply an arc discharge method in which the carbon evaporation amount per unit power consumption is large. The carbon material used as a raw material is not limited in its tissue properties as long as it has high purity. However, when using the arc discharge method, it is desirable to use artificial graphite rods as electrodes.

Helium, argon, neon, krypton, etc. can be used as the inert atmosphere gas.
Among these, it is preferable to use helium, which has a high carbon evaporation rate. 1 to 2 oxygen is added to this inert atmosphere gas.
The content is 0% by volume, preferably 5 to 10% by volume. By heating and vaporizing the carbon material in an inert atmosphere system containing an oxygen amount in this range, it is possible to obtain an amorphous soot-like carbon fine powder containing carbon clusters having a composition containing 1 to 5% by weight of oxygen. Become.

The pressure in the system for heating and vaporizing is 20 to 50.
It is necessary to adjust the pressure reduction to the range of 0 Torr, and the electrical resistivity of the soot-like carbon fine powder obtained by setting these conditions is 10
It can be controlled between 10 ⁸ Ωcm. However, when the degree of pressure reduction is less than 20 Torr, the electrical resistivity is reduced to the same level as that of general carbon black, and when it exceeds 500 Torr, the evaporation amount of carbon is reduced and the production efficiency of soot-like fine powder is significantly reduced.

FIG. 1 shows an apparatus suitable for carrying out the manufacturing method according to the present invention. This apparatus is equipped with a gas supply line 6 connected from a helium cylinder 2 and an oxygen cylinder 3 via a valve 4 and a flow meter 5, respectively, and a vacuum pump 8 via a pressure adjusting valve 7 at the upper part for cooling and recovery of a bag filter structure. Water-cooled graphite electrode rods 12 and 13 connected to a power source 11 are set inside a decompression container 1 provided with a lead-out pipe 10 communicating with the device 9 with a gap between the end faces. The operation was performed by injecting helium gas mixed so that the oxygen amount became 1 to 20% by volume into the decompression container 1 to maintain the system decompression degree within the range of 20 to 500 Torr, and then between the graphite electrode rods 12 and 13. Arc discharge to heat the electrode, and the vaporized carbon vapor is guided to the cooling and recovery device 9 to rapidly cool and resolidify the soot-like carbon fine powder and collect the soot-like carbon fine powder.

The carbon fine powder thus obtained is an amorphous soot-like fine powder containing carbon clusters in the range of 1 to 30% by weight, and its composition is such that the oxygen content is 1 to 5% by weight and the carbon content is 90 to 95% by weight, nitrogen adsorption specific surface area of 50 m ² / g or more, and electric resistivity of 10 to 10 ⁸ Ωcm.

[0019]

The fine carbon powder for electrorheological fluid of the present invention has a high electric resistivity of 10 to 10 ⁸ Ωcm and 1 to 5% by weight of oxygen.
And a nitrogen specific surface area of 50 m ² / g or more and is composed of amorphous soot-like carbon fine powder containing carbon clusters having fine particle properties. In particular, a composition having an oxygen content of 1 to 5% by weight works effectively for lowering the initial viscosity when dispersed in the disperse phase and imparting excellent dispersibility and viscous response. Although this mechanism has not been clarified, when a certain amount of oxygen is bound to a special soot-like carbon made of amorphous material containing carbon clusters, the lipophilicity is further enhanced, and the dispersibility in electrically insulating oily fluid such as silicone oil is increased. Is supposed to be improved.

By virtue of the effect of reducing the initial viscosity due to the oxygen content and the function of the high electric resistivity and the nitrogen specific surface area, the viscous response to the applied voltage when dispersed in the electrically insulating oily medium is extremely high. Good, stable dispersibility over a long period of time and excellent electrorheological effect are exhibited.

Further, according to the manufacturing method of the present invention, the atmosphere in the system for heating and vaporizing the carbon material is an inert atmosphere containing 1 to 20% by volume of oxygen, and the pressure is controlled in the range of 20 to 500 Torr. It becomes possible to reproducibly obtain the carbon fine powder for electrorheological fluid having the above properties by a simple process.

[0022]

EXAMPLES Examples of the present invention will be described in detail below in comparison with comparative examples.

Examples 1 to 4 Using the apparatus shown in FIG. 1, the vacuum pump 8 was actuated to temporarily reduce the pressure in the system of the decompression container 1 to 0.01 Torr or less, and then the helium cylinder 2 and the oxygen cylinder 3 were removed. Introducing a fixed amount of He gas and O ₂ gas through a gas supply line,
Then, the pressure adjusting valve 7 was controlled to maintain the inside of the decompression container 1 at a predetermined degree of decompression. Continuously, power of 2 kw from the power source 11 was applied to the graphite electrode rod (carbon content 99.99% by weight, outer diameter 8 mm)
Then, arc discharge was generated between the electrodes.
In this state, the graphite electrode rod is incandescently heated and vaporized to become carbon vapor, which is sucked by the outlet pipe 10 and reaches the cooling and recovery device 9 to be rapidly cooled and re-solidified to be an amorphous soot-like carbon fine powder containing carbon clusters. Recovered.

The results and properties of the soot-like carbon fine powder thus obtained are shown in Table 1 in comparison with the oxygen content in helium gas and the degree of reduced pressure in the system. The oxygen content was measured by a CHN elemental analyzer [manufactured by Perkin Elmer Japan Co., Ltd., Model 2400], carbon, hydrogen,
The content rate of nitrogen was determined, and the balance was defined as the content rate of oxygen. In addition, the electrical resistivity value is in accordance with JIS K1469 "Method for measuring electrical resistivity of acetylene black", and the measurement pressure is 10
The measurement was performed by setting it to 2.2 kg / cm ² .

Then, each soot-like fine powder thus obtained was uniformly dispersed in a silicone oil (room temperature viscosity: 0.02 poise) as an electrically insulating oily medium in an amount ratio of 20% by weight to form an electrorheological fluid. A voltage of 2 kV / mm was applied to this electrorheological fluid at room temperature, and the viscosity change of the fluid and the current value flowing in the fluid were measured. Furthermore, the dispersed state after 50 days was observed. A B-type rotational viscometer was used to measure the viscosity, and the viscosity was measured when a direct current was applied between the electrodes. The obtained evaluation results are also shown in Table 1.

From the results shown in Table 1, the electrorheological fluid obtained by the production method of the present invention, in which the fine carbon powder satisfying the requirements of the invention is dispersed, has a low initial viscosity, and therefore has a large viscosity change before and after the application of a voltage. A stable low current circulated and a stable dispersed state was exhibited for a long period of time, and the sedimentation phenomenon of the powder was hardly observed.

[0027]

[Table 1]

COMPARATIVE EXAMPLE 1 A soot-like fine powder was prepared under the same conditions as in Example 1 except that the decompression container was set to a decompression degree of 98 Torr by an atmosphere system (oxygen content: 0% by volume) in which helium gas was not mixed with oxygen gas. Manufactured. The obtained soot-like fine powder was dispersed in silicone oil in the same manner as in the example to form an electrorheological fluid.
The results in this case are shown in Table 2.

Comparative Example 2 A pressure reduction degree of 131 Torr was set by an atmosphere system in which oxygen gas was mixed with helium gas and oxygen content rate was 38% by volume in a decompression container. A powder was produced. The obtained soot-like fine powder was dispersed in silicone oil in the same manner as in the example to form an electrorheological fluid. The results in this case are also shown in Table 2 in the same manner.

Comparative Example 3 A pressure reduction degree of 10 Torr was set by an atmosphere system in which oxygen gas was mixed with helium gas and oxygen content rate was 17% by volume in a decompression container. A powder was produced. The obtained soot-like fine powder was dispersed in silicone oil in the same manner as in the example to form an electrorheological fluid. The results in this case are also shown in Table 2 in the same manner.

Comparative Example 4 A pressure reduction degree of 650 Torr was set with an atmosphere system in which oxygen gas was mixed with helium gas and oxygen content was 20% by volume in the pressure reduction container. A powder was produced. The obtained soot-like fine powder was dispersed in silicone oil in the same manner as in the example to form an electrorheological fluid. The results in this case are also shown in Table 2 in the same manner.

[0032]

[Table 2] [Table Note] Measurement is impossible because the current value exceeds 3mA.

From the results shown in Table 2, in Comparative Example 1, since the soot-like carbon fine powder does not contain oxygen, the initial viscosity is high and the long-term stability of dispersion is also reduced. On the contrary, in Comparative Example 2, the oxygen content is too high and the electrical resistivity becomes low, so that it is not practical. In Comparative Example 3, the electrical resistivity is extremely reduced due to the low degree of decompression in the decompression container system, and in Comparative Example 4, the system internal pressure is too high, so that a sufficient electrorheological effect cannot be obtained.

[0034]

As described above, according to the present invention, the electric resistance is higher than that of the conventional carbon powder, the specific surface area is large,
It is possible to provide a non-aqueous carbon fine powder for electrorheological fluid that exhibits excellent dispersibility with a low initial viscosity. Therefore, the electrorheological fluid in which the carbon fine powder is dispersed can exhibit a viscous response and a stable dispersed state over a long period of time. Therefore, for example, an energy absorbing material such as a damper, a shock absorber, or an engine mount. It is also useful as an anti-vibration material.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating an apparatus for producing carbon fine powder for electrorheological fluid of the present invention.

[Explanation of symbols]

 1 Decompression Container 2 Helium Cylinder 3 Oxygen Cylinder 4 Valve 5 Flow Meter 6 Gas Supply Line 7 Pressure Adjustment Valve 8 Vacuum Pump 9 Cooling / Recovery Device 10 Outlet Pipe 11 Power Supply 12 Graphite Electrode Rod 13 Graphite Electrode Rod

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C10N 70:00

Claims (3)

[Claims] 1. An amorphous soot-like carbon fine powder containing carbon clusters, having an electric resistivity of 10 to 10.
A carbon fine powder for an electrorheological fluid, which has a property composition of 10 ⁸ Ωcm and an oxygen content of 1 to 5% by weight. 2. The carbon fine powder for electrorheological fluid according to claim 1, which has a nitrogen adsorption specific surface area of 50 m ² / g or more. 3. A carbon material is heated and vaporized in a system maintained at a pressure of 20 to 500 Torr by an inert atmosphere containing 1 to 20% by volume of oxygen, and the vaporized carbon vapor is rapidly cooled and resolidified. And a method for producing carbon fine powder for electrorheological fluid.