JPH04227996A - Powder and electroviscous fluid - Google Patents

Abstract

PURPOSE:To obtain a powder improved in oxidation resistance, controllability of electrical properties and heat stability by uniformly dispersing a particulate dispersed phase of a low conductivity in a matrix phase of a medium conductivity. CONSTITUTION:A matrix phase comprising a carbonaceous material of a carbon content of 80-99.9wt.% having an electric conductivity of 10<-10> 10<-2>Scm<-1> and 70wt.% or below at least one particulate material selected between a semiconductor and an insulator each having an electric conductivity which is at most 1/10 time as high as that of the matrix phase and having a particle diameter of 1nm-10mum. The resulting mixture is granulated by spray drying to obtain a powder having a mean particle diameter of 0.1-100nm, a water content of 1wt.% or below and an electric conductivity of 10<-13>-10<2>Scm<-1>. 1-60wt.% this powder is dispersed in 99-40wt.% insulating oil of a viscosity of 0.65-1000cSt at 25 deg.C to obtain an electroviscous fluid.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a highly functional powder consisting of fine particle uniformly dispersed composite particles in which a fine particle dispersed phase of low conductivity is uniformly dispersed in a matrix phase of medium conductivity, and the powder thereof. The invention relates to an electrorheological fluid in which the electrolyte is dispersed in an oily medium with excellent electrical insulation properties.

0002

[Prior Art and Problems to be Solved by the Invention] Electrorheological fluids are fluids whose viscoelastic properties can be significantly and reversibly changed by electrical control. The phenomenon of large changes in apparent viscosity has long been known as the Winslow effect. However, early electrorheological fluids were made by dispersing starch or other substances in mineral oil or lubricating oil, and although this was sufficient to make us aware of the importance of the electrorheological effect, it lacked reproducibility.

[0003] For this reason, with the aim of obtaining a fluid with a high electrorheological effect and good reproducibility, many proposals have been made, centering on powders used as dispersoids. For example, as a powder, super absorbent resins with acid groups such as polyacrylic acid (JP-A No. 53-93186), ion exchange resins (JP-A No. 60-31211), alumina silicate (JP-A No. 62-Sho. No. 95397), etc. are known.

[0004] All of these electrorheological fluids are hydrophilic solid powder impregnated with water and dispersed in an insulating oily medium, and when a high voltage is applied from the outside, the powder becomes It is said that polarization occurs in the particles constituting the material, and this polarization causes crosslinking between the particles in the direction of the electric field, thereby increasing the viscosity.

[0005] However, these water-containing electrorheological fluids using water-containing powders have had serious problems in terms of practicality. In other words, water-containing electrorheological fluids have insufficient electrorheological effects over a wide temperature range, limitations on the operating temperature to prevent moisture evaporation or freezing, significant increases in current due to temperature increases, and stability problems due to moisture migration. There are many problems such as insufficient or melting corrosion of electrode metal when high voltage is applied.
It is difficult to put it into practical use as an electrorheological fluid.

[0006] As a method of improving the drawbacks of this water-containing electrorheological fluid, a non-aqueous electrorheological fluid using particle powder that does not contain water has also been proposed.

Such non-aqueous fluids include fluids using homogeneous single-phase particle powders consisting of organic semiconductor particles such as polyacenequinone, that is, homogeneous single-phase particles of an organic compound with electrical properties (semiconductivity) (Unexamined Japanese Patent Publication No. (No. 61-216202), dielectric particles with an electrically insulating thin film layer formed on the surface of an organic or inorganic solid particle, that is, a film with electrical properties (conductive/insulating) Fluid using powder of thin film-coated composite particles that requires a layer (Japanese Patent Laid-Open No. 1983-
No. 97694, Japanese Unexamined Patent Publication No. 1-164823), etc. are known.

However, non-aqueous electrorheological fluids that use homogeneous single-phase particles or thin-film-coated composite particle powders currently lack long-term stability of properties and are poor in restorability. Moreover, when an electric field is applied, the current flowing through the electrorheological fluid is large, resulting in large current consumption, and furthermore, industrial manufacturing is difficult, so it has not been put to practical use.

[0009] For this reason, there has been a demand for a powder that can be suitably used as a dispersoid for non-aqueous electrorheological fluids. Powders with controlled electrical properties include, in addition to the homogeneous single-phase particles and thin-film-coated composite particles mentioned above, carbon powders with different firing temperatures, surface-treated metal powders, and metal-coated powders. Inorganic powders are known, but the powders that have been used primarily for electrical properties have many problems, such as poor heat resistance and oxidation resistance, and difficulty in controlling electrical resistance and dielectric constant. These points have significantly hindered the expansion of its uses. Therefore, there has been a demand for the development of powders that have excellent functions.

The present invention was made in response to the above-mentioned needs, and an object of the present invention is to provide a highly functional powder that has excellent oxidation resistance and control of electrical properties and is suitably used as a dispersoid for electrorheological fluids. Another object of the present invention is to provide a novel electrorheological fluid that overcomes the drawbacks of conventional fluids as described above.

[0011]

[Means and effects for solving the problem] As a result of intensive studies to achieve the above object, the present inventors focused on the structure and electrical properties of particles, and created micro-composite particles of an unprecedented new concept. A powder was obtained and the present invention was completed.

That is, the present inventors further added fine particles having a lower electric conductivity to the matrix phase by, for example, mixing an organic compound with a high residual carbon content and a metal compound, pulverizing the mixture, and then carbonizing the mixture. In this case, the electrical conductivity of the matrix phase is set to 1.
The electrical conductivity of the matrix phase is set to 0-10 to 102 Scm-1, and the dispersed fine particles dispersed therein are
Formed from a semiconductor or insulator having an electrical conductivity of /10 or less, and furthermore, the amount of dispersed fine particles dispersed in the matrix phase is 70% (wt%, same hereinafter) as a whole.
By doing the following, it has excellent heat resistance and oxidation resistance, and
It was discovered that a highly functional powder whose electrical resistance and dielectric constant can be easily controlled can be obtained.

[0013] In addition, by using as a dispersoid a powder consisting of composite particles of a new structure in which a dispersed fine particle phase of low conductivity is uniformly dispersed in a matrix phase of medium conductivity, electric insulating properties can be obtained. By dispersing in an oily medium,
Fundamentally different from conventional homogeneous single-phase particles and thin film-coated composite particles, it is a highly functional electrorheological fluid that provides a high level of electrorheological effect over a wide temperature range and whose properties remain stable for a long time. However, the present inventors have discovered that an electrorheological fluid with excellent functions, such as a small current flowing when an electric field is applied, can be obtained, leading to the present invention.

Therefore, the present invention comprises composite particles having a uniform dispersion of fine particles in a matrix phase, and the electrical conductivity of the matrix phase is 10-10 to 10.
2Scm-1, the dispersed fine particles are made of at least one material selected from semiconductors and insulators, and the electrical conductivity thereof is 1/1 of the electrical conductivity of the matrix phase.
10 or less, and the amount of the dispersed fine particles dispersed in the composite particles is 70% or less as a whole, and the powder is dispersed in an oily medium having electrical insulation properties. Provides an electrorheological fluid.

[0015] The present invention will be described in more detail below. First, the powder of the first aspect of the present invention is such that the composite particles constituting the powder include fine particles of low conductivity in a matrix phase of medium conductivity. It consists of a uniformly dispersed micro-composite structure (sea-island structure).

[0016] Here, the electric conductivity of the matrix phase is medium conductivity, that is, 10-10 to 102 Scm-
1, preferably 10-10 to 100 Scm-1. The material for forming the matrix phase may be any organic material or inorganic material as long as it exhibits the electrical conductivity described above. Specifically, carbonaceous materials, carbide materials such as boron carbide and aluminum carbide, organic semiconductor materials such as polyaniline and polyacenequinone,
Examples include oxide semiconductor materials such as zinc oxide, potassium titanate, and barium titanate, but carbonaceous materials are preferred. Among them, carbon content 8
0-99.9% carbonaceous material is preferred, more preferably 90-99% carbonaceous material. Note that the remainder usually consists of hydrogen atoms, oxygen atoms, and nitrogen atoms.

On the other hand, the fine particles dispersed in the matrix phase are at least one material selected from semiconductors and insulators, but it is essential that the electrical conductivity thereof has a lower value than that of the matrix phase. 1/10 or less of that of the matrix phase, preferably 1/10 to 1/1
014, more preferably 1/103 to 1/1014. If this is larger than 1/10, effective composite particles cannot be obtained. Furthermore, the electrical conductivity of the fine particles is 10-2 Scm-1 or less, especially 10-6 Sc, while satisfying the above conditions.
It is preferable that it is m-1 or less.

Examples of the particulate material include oxides such as alumina, silica, boron oxide, titania, calcium oxide, iron oxide, tin oxide, and zinc oxide, and non-oxides such as silicon carbide, silicon nitride, and aluminum nitride. can be mentioned. Furthermore, when the matrix phase is a carbonaceous material, it is also possible to use a carbonaceous material with lower conductivity as the fine particles. Among the fine particle materials, preferred are silica, alumina, titania, and the like.

[0019] The size of the fine particles is 1 nm to 10 μm.
, preferably in the range of 2 nm to 5 μm. Even if the size is smaller than 1 nm or larger than 10 μm, the effect of the present invention cannot be obtained. In addition, the amount of fine particles dispersed in the composite particles is 0.1 to 70% as a whole, preferably 1 to 60%.
%. When the amount is less than 0.1%, the electrical conductivity of the composite particles is not controlled and becomes almost the same as that of the matrix phase with medium conductivity, so that the effects of the present invention cannot be obtained. If the amount exceeds 70%, the electrical properties of the composite particles become similar to those of fine particles with low conductivity, which is not preferable.

[0020] The average particle diameter of the composite particles of the present invention consisting of the above-mentioned matrix phase and dispersed fine particles is not particularly limited, but when used as a dispersoid of an electrorheological fluid as described below, it is preferably 0.1 to 100 μm, and more preferably 0.1 to 100 μm. Preferably it is in the range of 0.5 to 50 μm. If it is less than 0.1 μm, the initial viscosity becomes significantly large in the absence of an electric field and the viscosity change due to the electrorheological effect is small, and if it exceeds 100 μm, sufficient stability may not be obtained.

Further, the electrical conductivity of the powder made of the composite particles is not particularly limited, but the electrical conductivity measured by molding the powder is preferably 10-13 to 102 Scm-1, more preferably 10 -12 to 10-2 Scm-1.

Furthermore, the water content of the powder is preferably 1% or less, particularly preferably 0.5% or less. If the water content exceeds 1%, when used as an electrorheological fluid dispersoid, power consumption at high temperatures may increase due to the conductivity of water.

[0023] Note that indicators of the internal structure of the composite particles of the present invention, that is, the morphological state and physical specifications, can be easily specified by various analytical techniques shown in the Examples described later.

[0024] Here, as a method for producing the powder of composite particles of the present invention, a starting compound corresponding to a matrix phase with medium conductivity (hereinafter abbreviated as matrix phase compound) and fine particles with low conductivity are mixed. A method of mixing a starting compound (hereinafter abbreviated as a fine particle compound) and granulating this mixture by a method such as spray drying, a method of solidifying this mixture by a curing reaction, etc., and then granulating it using a ball mill etc. A method of heat-treating granulated powder at a higher temperature,
Alternatively, a method may be used in which the mixture is once heat-treated and then granulated. In order to produce the desired powder, the combination of starting compounds, their mixing method,
In manufacturing processes such as granulation methods or heat treatment methods (including heat treatment means and heat treatment atmosphere), the following (A
) to (C) can be adopted. (A) The matrix phase compound is in a liquid or solution state and encapsulates the fine particle compound, or is liquefied in the manufacturing process and is liquefied to encapsulate the fine particle compound, and then gelled by an appropriate method. Alternatively, it can be hardened and heat treated. Note that the fine particle compound is selected from a solid material in the manufacturing process. (B) When both the matrix phase compound and the fine particle compound are mixed in liquid or solution form to produce a powder, the fine particle compound gels or forms a precipitate faster than the matrix phase compound. A method in which the materials are selected from such materials, the ratio of the amounts of both compounds is selected, and the two compounds are mixed, gelled or hardened, granulated, and heat treated. (C) When both the matrix phase compound and the fine particle compound are mixed in solid form to produce a powder, the matrix phase compound becomes fluid during the production process to obtain the desired powder. and that the fine particle compound be in a solid state in all of the manufacturing processes, the two compounds are mixed, heat treated if necessary, and then granulated.

The powder of the present invention can be obtained by the production methods (A) to (C) above, but depending on the combination of starting compounds, the obtained powder may be heat-treated at a higher temperature, and the heat treatment temperature and heat treatment atmosphere may be changed. It is desirable to change the conductivity of the powder by controlling the To give an example of controlling the heat treatment atmosphere, an inert gas atmosphere is usually selected when it is desired that many carbides remain in the composite particles even after heat treatment, but in particular when it is desired to generate nitrides inside the composite particles, An atmosphere such as NH3 gas or N2 gas is selected.

As the starting compound corresponding to the matrix phase, at least one compound selected from organic compounds with a high residual carbon content such as phenol resin, furan resin, and polydimethylsilane resin can be used.

On the other hand, starting compounds corresponding to fine particles include metal alkoxides such as ethyl silicate, aluminum isopropoxide and titanium isopropoxide, organometallic complexes such as ferrocene, and organic compounds such as borate esters synthesized from diethanolamine and boric acid. At least one compound selected from esters consisting of compounds and inorganic acids, silica, alumina, titania, other insulating materials, semiconductor materials, etc. can be used.

[0028] Even when the organic compound with a high residual carbon content is combined with an organic compound such as tar or pitch that produces a carbon material with higher conductivity after carbonization,
The powder of the present invention can be obtained which consists of composite particles in which the former compound corresponds to fine particles and the latter compound corresponds to a matrix phase.

Furthermore, the composite particles of the present invention are not limited to the manufacturing method described above.

Next, the electrorheological fluid which is the second invention of the present invention uses the powder of the first invention as a dispersoid and disperses it in an oily medium (dispersion medium) having electrical insulation properties. be.

Examples of the dispersion medium include electrically insulating oils such as hydrocarbon oils, ester oils, aromatic oils, silicone oils, fluorosilicone oils, and phosphazene oils. These can be used alone or in combination of two or more. Among these electrical insulating oils, silicone oils such as polydimethylsiloxane and polymethylphenylsiloxane are superior in that they can be used even in direct contact with materials having rubber-like elasticity. Note that the electrical insulating oil of the present invention is not limited to these examples.

The viscosity of electrical insulating oil is 0.6 at 25°C.
The viscosity is preferably 5 to 1000 centistokes (cSt), more preferably 1 to 500 cSt. By using electrical insulating oil with this viscosity as a dispersion medium, the dispersoid can be suspended efficiently, but if the viscosity of the dispersion medium is too low, the volatile content will increase and the stability of the dispersion medium will deteriorate. Furthermore, if the viscosity of the dispersion medium is too high, the initial viscosity in the absence of an electric field will become too high, making effective electrical control of applied products difficult.

The ratio of the dispersoid to the dispersion medium constituting the electrorheological fluid of the present invention is such that the content of the dispersoid is 1 to 60%, preferably 5 to 50%, and the content of the dispersion medium is 40 to 60%. 99
%, preferably 50 to 95%. When the amount of dispersoid is less than 1%, the electrorheological effect is small, and 60
%, the initial viscosity in the absence of an electric field may become significantly large.

The electrorheological fluid of the present invention may contain other dispersoids, surfactants, dispersants, inorganic salts, and other additives as long as the effects of the present invention are not impaired.

[0035]

[Effects of the Invention] The powder of the present invention has excellent oxidation resistance, high thermal stability in the atmosphere, and is extremely easy to control electrical resistance and dielectric constant.

Therefore, this powder is effective as a dispersoid for electrorheological fluids, and is also suitable for use as an agent for imparting electrical properties to polymeric compounds.

Further, the effects of the electrorheological fluid of the present invention are listed below. i Over a wide temperature range, the level of electrorheological effects is high. ii The properties of the electrorheological fluid are stable over a long period of time. iii When an electric field is applied, the current flowing through the electrorheological fluid is small, resulting in low power consumption. iv The application of the electric field can be arbitrarily selected from either direct current or alternating current. v It is easy to manufacture industrially and is highly practical.

Therefore, the electrorheological fluid of the present invention can be effectively applied to electrical control of mechanical devices such as engine mounts, shock absorbers, valves, and clutches.

[0039]

[Examples] The present invention will be explained in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. In addition, in the following examples, the characteristics of the powder and the characteristics of the electrorheological fluid were measured by the following methods. Characteristic particle size of powder: MICROTRAC SPA manufactured by Nikkiso Co., Ltd.
/Measured with MK-II modelElectrical conductivity:Measured using the two-terminal method on a compacted powder Size of dispersed fine particles:Measured using an ultra-high resolution electron microscopeSilica weight ratio in composite particles:Silica was measured using hydrofluoric acid Extracted and measured by inductively coupled plasma method (ICP method) at 400°C Weight loss rate: TGD700 manufactured by Shinku Riko Co., Ltd.
Properties of electrorheological fluids measured by thermogravimetric analysis in air at a heating rate of 5°C/min using Rheometrics Far East Co., Ltd. RDS-II at a shear rate of 350°C.
Measured under the condition of /second

[Example 1] 60 g of a resol type phenol resin (resin manufactured by Sumitomo Jules Co., Ltd.), 30 g of a polysilicate ester (ethyl silicate 40 manufactured by Colcoat Co., Ltd.), and 10 g of toluenesulfonic acid are mixed and stirred vigorously. When gelatinization begins to proceed, finely grind the mixture in a mortar to form a powder. The powder thus obtained was heated under an argon atmosphere.
After raising the temperature to 625° C. at a heating rate of 5° C./min, it was heated for 1 hour and carbonized to obtain a powder having a specific gravity of 2.1 and consisting of spherical composite particles with an average particle size of 10 μm.

[0041] This composite particle has a carbonaceous material as a matrix phase and silica as a fine particle, and the electrical conductivities of the carbonaceous material and silica are 4 x 10-9 Scm-1 and 1 x
It was 10-14 Scm-1. The electrical conductivity of the powder was 3 x 10-12 Scm-1 as a whole. Further, the size of the dispersed silica was 60 nm, and the amount of silica dispersed in the composite particles was 29% as a whole. Further, the moisture content of this powder was measured when it was left at room temperature, and the result was 0.2%. Furthermore, the weight loss rate at 400° C. in air was measured as an index of the oxidation resistance of this powder. The results are shown in Table 1, and it is recognized from the results that this powder has excellent oxidation resistance.

As described above, it was confirmed that the composite particles constituting the powder obtained in this example had a composite particle structure in which silica was uniformly dispersed in the carbonaceous material, and fine particles were uniformly dispersed. This powder was found to have a high level of heat resistance.

[Example 2] Aluminum hydroxide powder 50
g is dispersed in 400 g of water, 100 g of a water-soluble phenol resin (resin manufactured by Sumitomo Jules Co., Ltd.) and 30 g of a 65% aqueous solution of toluenesulfonic acid are added thereto, followed by spray drying. The obtained powder was carbonized in the same manner as in Example 1 to obtain a powder having a specific gravity of 2.6 and consisting of spherical composite particles with an average particle size of 15 μm.

[0044] This composite particle has a carbonaceous material as a matrix phase and alumina as a fine particle, and the electrical conductivities of the carbonaceous material and alumina are 4 x 10-9 Scm-1 and 1 x 10-14 Scm-1 or less, respectively. there were. The electrical conductivity of the powder was 8 x 10-12 Scm-1 as a whole. In addition, the size of dispersed alumina was 0.8 μm, and the amount of alumina dispersed in the composite particles was 47% as a whole.
As in Example 1, it was found that the sample had a composite particle structure in which fine particles were uniformly dispersed. Further, the moisture content of this powder was measured when it was left at room temperature, and the result was 0.25%.

[0045] Furthermore, as shown in Table 1, the oxidation resistance of this powder was found to be extremely excellent, similar to that of the powder of Example 1.

[Comparative Example 1] The mixed aqueous solution containing 30% of the water-soluble phenol resin and 1% of toluenesulfonic acid used in Example 2 was dried by spray drying, and this powder was dried under an argon atmosphere at a heating rate of 5. After increasing the temperature to 625℃ at a rate of ℃/min, heating for 1 hour and carbonizing, the average particle size was 12μm and the electrical conductivity was 6×10.
A powder consisting of particles of carbonaceous material of −9 Scm−1 was obtained.

Table 1 shows the weight loss rate of this powder in air at 400°C. It can be seen that the oxidation resistance of the powders of Example 1 and Example 2 is clearly superior to that of this powder.

[0048]

[Table 1]

[Example 3] 50 g of the powder obtained in Example 1 was dispersed in 95 g of silicone oil (manufactured by Toshiba Silicone Corporation: TSF451-10) to produce an electrorheological fluid. Table 2 shows the properties as an electrorheological fluid.

First, the viscosity was 0.4 poise when measured at room temperature without an electric field, and the viscosity increased to 2.5 poise by applying a DC electric field of 2 KV/mm. Further, the current value at that time was 0.001 μA/cm 2 or less. Next, 100℃
The initial viscosity was 0.2 poise, and the viscosity increased to 3.0 poise by applying an electric field of 2 KV/mm, and the current value at that time was 0.1 μA/cm 2 .

Table 3 shows the changes in viscosity and current over time when a DC electric field of 2 KV/mm is applied at room temperature.
It is. As can be seen, this fluid remained effective even after being used for over 1000 hours.

Therefore, as shown by the above results, this electrorheological fluid has a high level of electrorheological effect over a wide temperature range, the current flowing when an electric field is applied is small, low power consumption, and long-term stability. It is recognized that it has features such as being extremely superior.

[Example 4] Using the powder obtained in Example 2, an electrorheological fluid was produced in the same manner as in Example 3. Table 2 shows the properties as an electrorheological fluid.

First, the viscosity when measured at room temperature without an electric field was 0.8 poise, and the viscosity increased to 8.13 poise by applying a DC electric field of 2 KV/mm. Further, the current value at that time was 12 μA/cm 2 . Next, the initial viscosity at 100°C is 0.3 poise, which increases to 7.9 poise by applying an electric field of 2 KV/mm, and the current value at that time is 96 μA.
/cm2.

As can be seen from the above results, the electrorheological fluid of this example has excellent properties similar to those of Example 3.

[Comparative Example 2] Using the powder of Comparative Example 1, a suspended fluid was obtained in the same manner as in Example 3. Table 2 shows the electrorheological properties of this fluid.

It can be seen that this fluid does not exhibit an electrorheological effect, and moreover, a large current flows due to a DC electric field. That is, it is shown that an effective electrorheological fluid cannot be obtained only from the matrix phase (in this case, carbonaceous material) that constitutes the composite particles of the present invention. Note that a satisfactory electrorheological fluid could not be obtained using only silica or alumina, which are one of the dispersed fine particles constituting the composite particles of the present invention.

[Comparative Example 3] Silica gel (Nipsil VN-3 manufactured by Nippon Silica Co., Ltd.)
An electrorheological fluid was obtained by dispersing 13 parts by weight of the mixture with a moisture content of 6% by weight in 87 parts by weight of silicone oil. Table 2 shows the electrorheological properties of this fluid.

The viscosity of this electrorheological fluid was 3.4 poise when measured at room temperature without an electric field, and the viscosity increased to 6.0 poise by applying a direct current electric field of 2 KV/mm. The current value at that time was 21 μA/cm2. Further, at 100° C., the current was too large to measure the electrorheological effect. Furthermore, when this fluid was used continuously for a long time, its effectiveness gradually decreased, and the effectiveness decreased to less than half after about 100 hours.

[0060]

[Table 2]

[0061]

[Table 3]

Claims (2)

[Claims] [Claim 1] Consisting of fine particle homogeneously dispersed composite particles in which fine particles are uniformly dispersed in a matrix phase, the matrix phase has an electrical conductivity of 10-10 to 102 Scm-1, and the dispersed fine particles are selected from semiconductors and insulators. and the electrical conductivity thereof is 1/10 or less of the electrical conductivity of the matrix phase, and the amount of the dispersed fine particles dispersed in the composite particles is 70% by weight or less as a whole. A powder characterized by: 2. An electrorheological fluid comprising the powder according to claim 1 dispersed in an oily medium having electrical insulation properties.