JPH02255798A - Electroviscous fluid - Google Patents

Abstract

PURPOSE:To obtain an electroviscous fluid in which increase of consumed electric current is suppressed within a limit electric current in the range of used temperature by constructing dielectric granules from polyhydric alcohol- containing crystalline cellulose granules and covering surface thereof with a thin film having electrical insulation properties. CONSTITUTION:In an electroviscous fluid obtained by dispersing dielectric fine granules into an oily medium consisting of an amino modified or alcohol modified silicone oil, etc., granules constituted of crystalline cellulose granules containing a polyhydric alcohol as hydrophilic agent, whose surface is covered with an electrical insulating thin film of polyamide or epoxy resin, etc., and having two layer structure are used as the dielectric granules.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an electrorheological fluid that has a characteristic that its viscosity increases upon application of an electric field and can be used as a working fluid for, for example, clutches, dampers, valves, etc. It is.

(Background Art) Electrorheological fluids are known in which water-absorbing or hydrophilic solid particles are dispersed in an oily substance with high electrical insulation, or semiconductive particles are similarly dispersed in an oily substance. However, in the latter case, because the dispersed particles are semiconductors, current flows easily when a high electric field is applied from outside the fluid, and it requires technology to control the resistance value of the particles, so it is not stable. It was difficult to obtain electrorheological fluids.

On the other hand, the former configuration does not have such problems and is suitable for practical use, but when it is actually sealed in a mechanical device and used as a working fluid, it may be affected by the heat storage effect of the device itself and the environmental conditions. As a result, the temperature of the fluid changes reversibly, and various performances of the fluid are inevitably affected by this temperature change.

In particular, changes in shear stress and changes in current consumption when an external electric field is applied to a fluid have a large impact on the performance of mechanical equipment and peripheral equipment, and for this reason, it is difficult to stabilize fluid performance against temperature changes. This is a challenge in the practical application of electrorheological fluids.

To describe in more detail the change in the current consumption flowing through the electrorheological fluid due to temperature changes, the change in the current consumption is exponential, and the change in the current consumption due to temperature changes is exponential. When the temperature changes from about C to 100 DEG C., the current consumption on the high temperature side takes a value of 100 to 1000 times the current consumption on the low temperature side, resulting in a significant increase (see FIG. 1).

Therefore, normally used high-voltage power supplies that can supply approximately 10 KV cannot tolerate an increase in current within the operating temperature range of mechanical equipment. ) If a sufficiently large high-voltage power supply is provided, the high-voltage power supply device will become larger and, by extension, the space required for the entire system will become larger, resulting in space problems. Furthermore, if the current consumption of the electrorheological fluid becomes significantly excessive, a so-called dielectric breakdown condition may occur, and there is even a fear that the mechanical device itself that uses the electrorheological fluid may be destroyed.

By the way, the mechanism by which an electrorheological fluid increases its viscosity by applying an electric field is generally explained by the following electric double layer.

According to this explanation, water or a hydrophilic agent attached or adsorbed to the surface of solid particles dispersed in an oily substance constitutes an electric double layer, and when a high electric field is applied from the outside,
The movement of free ions is excited and polarization occurs within the solid particles. These polarized solid particles are arranged between two positive and negative electrode plates inserted into the electrorheological fluid, and form a quasi-condensing bond due to mutual electrostatic attraction, making them perpendicular to this bond. The flow of fluid in the direction creates a large resistance,
The shear force increases and a solidification phenomenon occurs.

Here, the solid particles have free ions in the electric double layer, so that current flows through them,
The amount of such particles is extremely small, and therefore, electrorheological fluids containing such particles as a dispersed phase are expected to be put into practical use as fluids that can achieve the effect of varying viscosity with a small amount of current. However, as the temperature of the fluid increases, the phenomenon of dissociation into free ions increases within the electric double layer, causing electrons to pass through the electric double layer and flow between the electrodes, resulting in a significant increase in current consumption. it is conceivable that.

As mentioned earlier, this increase in current is exponential, so it exceeds the output limit of the high-voltage power supply in the normal operating temperature range of the machine, and the machine itself and the power supply There is an inherent risk of destruction, which makes it difficult to put electrorheological fluids into practical use. In other words, in order for a mechanical device that uses an electrorheological fluid to be put into practical use, the amount of current flowing through the electrorheological fluid must always meet the consumption specified by the output capacity of the power source, at least within the operating temperature range of the mechanical device. An essential condition is not to exceed the maximum value of current (limit current, limit value).

Furthermore, when considering the efficiency of a mechanical device, it is desirable to obtain higher shear stress with lower current consumption when the applied voltage is constant.

(Problem to be solved) Under such circumstances, the problem to be solved by the present invention is to suppress the increase in current consumption to within the limit current even if the temperature changes, at least within the operating temperature range, and to An object of the present invention is to provide an electrorheological fluid that can obtain an efficient electrorheological effect (Winslow effect).

(Solution Means) In order to solve this problem, the present invention provides an electrorheological fluid in which dielectric fine particles are dispersed in an oily medium. It was constructed so that it had a two-layer structure in which the surface was covered with an electrically insulating thin film.

Further, in one embodiment of the present invention, a silicone oil containing at least one of an amino-modified silicone oil and an alcohol-modified silicone oil is used as the oily medium. The electrically insulating thin film was formed from polyamide or epoxy resin.

(Function/Effect) In other words, dielectric particles used in electrorheological fluids are generally hydrophilic substances (
For example, an aqueous salt solution, a surfactant, etc.), but in the present invention, such solid particles are crystalline cellulose, contain polyhydric alcohol as a hydrophilic agent, and
Furthermore, by forming an electrically insulating thin film on the surface of the solid particles, it was possible to maintain good polarization of the electric double layer while making it difficult for current to pass through the electric double layer.

Even if the temperature of the electrorheological fluid increases and the dissociation phenomenon of the hydrophilic agent into free ions increases, this can be estimated from within the electric double layer due to the presence of an electrically insulating thin film on the surface of the dielectric particles. This is thought to be because the free movement of ions is restricted within this thin film, which inhibits the passage of current.

On the other hand, polarization within the dielectric particles is effectively carried out by the presence of polyhydric alcohol within the electrically insulating thin film, and the Winslow effect can be effectively exerted. be.

Therefore, the current flowing through the electrorheological fluid can be effectively reduced, and its maximum current! (Amount of current consumption at the maximum operating temperature of the mechanical device) can be suppressed within the limit current amount specified by the output of the power supply device, and while using a power supply device with a normal output, it is possible to insulate the mechanical device. This made it possible to prevent destruction from occurring.

(Specific configuration) By the way, the crystalline cellulose used as the solid particles of the dielectric particles in the present invention has a large specific surface area and has good hygroscopicity. For example, methyl cellulose, methyl hydroxyethyl cellulose, etc. can be used. I can do it. Further, it is desirable that the particle size is as small as possible, and it is preferable to use particles with a particle size of several μm to several tens of μm.

Such crystalline cellulose has good water absorption properties and has lower hardness than silica gel, aluminum silicate, etc. that have been conventionally used as solid particles, so it can be used inside mechanical devices that use electrorheological fluids as working fluids. It is possible to reduce wear and maintain a good lifespan of mechanical equipment.

Further, as the polyhydric alcohol which is a hydrophilic agent to be adsorbed onto the crystalline cellulose, for example, ethylene glycol, propylene glycol, butanediol, etc. can be used, or a mixture thereof can also be used. The blending ratio of the crystalline cellulose and the polyhydric alcohol is preferably such that the polyhydric alcohol is in an amount of 5 to 15 parts by weight per 100 parts by weight of the crystalline cellulose. If the proportion of this polyhydric alcohol is less than 5 parts by weight, the thickening effect will be low, and if it exceeds 15 parts by weight, there will be a problem that power consumption will be too high.

Furthermore, the material of the electrically insulating thin film that covers the surface of the dielectric particles is not limited, and may be appropriately selected from suitable resins, inorganic compounds, and the like. However, in order to apply an electric field to the dielectric particles to generate polarization and exhibit a good Winslow effect, it is desirable that the film thickness be approximately 0.5 μm or less. In addition, when forming such a thin film on the surface of the dielectric particles, various known methods may be selected as appropriate depending on the material of the thin film to be formed, such as solution coating,
Various techniques such as powder coating, vapor deposition, surface reaction, surface polymerization, and interfacial polymerization can be used.

Among these, the interfacial polymerization method is widely applied for the production of microcapsules, and there are books on it (for example, "Microcapsules: Production Method, Properties, and Applications 1" by Tamotsu Kondo and Masumi Koishi, Sankyo Publishing Co., Ltd. ). When this method is used, the adsorption of polyhydric alcohol onto crystalline cellulose and the formation of an electrically insulating thin film on the crystal cell openings are performed in the same process. , which utilizes the polymerization reaction that occurs at the interface between the aqueous and oil phases.A water-soluble monomer dissolved in a hydrophilic substance (aqueous phase reactant) is included in the solid particles in advance, and the hydrophobic substance is dissolved in the solid particles. By adding a dissolved oil-soluble monomer (oil phase reactant) and mixing jiE1, a h' polymer thin film is formed on the surface of the two solid particles. This method can be called 1n-situ polymerization because the Monopa component necessary for the bipolymerization reaction is dispersed in advance at the location where the polymerization product is desired, and the particles are coated simultaneously with the entrainment of the polymerization reaction. By this method, it is possible to form a thin film of electrically angular material such as polyamide or neboxyl resin on the surface of dielectric particles.

The desired electrorheological fluid can be obtained by dispersing the dielectric particles obtained as described above in a predetermined oily medium that maintains electrical insulation properties. The oily medium 4, which is a dispersion medium, contains diphenyl chloride, butyl cepatate, and aromatic polycarboxylic acid higher alcohol so that the specific gravity is approximately equal to that of the dispersed phase (dielectric particles) in order to stabilize the suspended state. It is determined as appropriate from among known oils such as ester, ha-r7 phenyl alkyl ether, trans oil, chlorinated paraffin 1, fluorine thread oil 7, silicone oil, etc., but especially amino-modified silicone oil and alcohol-modified oil. When an oily medium made of silicone oil containing at least one of silicone oils is used, it is possible to bring out a high Winslow effect due to its excellent insulating properties. In this case, the degree of modification, blending ratio, etc. of each modified silicone oil will be determined as appropriate depending on the performance required for the intended electrorheological fluid.

In addition, in order to keep the dispersion medium (oil medium) and the dispersed phase (dielectric particles) in a stable suspended state, it is desirable to make the specific gravity of both U as close as possible, and from this point of view, the type and hardness of the oily medium and hydrophilic agent], the degree of hygroscopicity of the particles,
Furthermore, the 44 qualities of the electrically insulating thin film are determined as appropriate.

The mixing ratio of the predetermined oily medium and the dielectric particles is such that the dielectric particles are mixed with 100 parts by weight of the oily medium.
It is desirable that the amount is about 50 to 200 parts by weight. If the dielectric particles are less than 50 parts by weight, the Winslow effect will be low, and if it is blended in a layer exceeding 200 parts by weight,
This is because the viscosity before applying voltage is too high. More specific blending ratios may be determined as appropriate depending on the degree of Winslow effect required for mechanical devices using electrorheological fluids and the internal shape of the machine. By stirring each time for a predetermined period of time, the desired electrorheological fluid can be obtained.

The electrorheological fluid thus obtained has a structure in which dielectric particles having a two-layer structure, in which polyhydric alcohol-containing crystalline cellulose particles are covered with an electrically insulating thin film, are dispersed in an oily medium. And 1. The free movement of ions in dielectric particles, as estimated from the electric double layer theory, is restrained within the electrically insulating thin film, which prevents current from passing through the electric double layer, reducing current consumption. On the other hand, ions can move freely within the electrically insulating thin film, and polarization occurs when voltage is applied, producing a good Winslow effect.

(Examples) Below, some examples of the present invention will be shown to clarify the present invention more specifically, but the present invention will not be limited by the description of such examples. Needless to say, it is not something that can be accepted.

In addition to the following embodiments and the above-mentioned specific description, the present invention ζ, 2 may be modified in various ways based on the knowledge of those skilled in the art, without departing from the spirit of the present invention.
It should be understood that modifications, improvements, etc. may be made.

First, various dielectric particles to be used as the dispersed phase of an electrorheological fluid were prepared. The manufacturing method is shown below.

(1) Particles A Piperazine (diamine compound) was mixed with ethylene glycol to make a 2M solution, and in order to neutralize the acidic substance generated by interfacial polymerization, 2M NaOH was added to form an aqueous phase reactant. Terephthalic acid dichloride was mixed into a mixed solvent of chloroform/cyclohexane=1/3 to give a concentration of 0.04 M to prepare an oil phase reactant.

Commercially available crystalline cellulose (Avicel PH manufactured by Asahi Kasei Corporation) was added to the chloroform/cyclohexane mixed solvent 50-
After mixing and stirring 10g of MO6), add the aqueous phase reactant id, continue stirring, and after reaching a homogeneous state,
50 d of oil phase reactant was added to initiate interfacial polymerization.

After continuing stirring for about 2 hours to complete the polymerization reaction, about 6 hours
After standing for 7 hours, a solid substance was precipitated, and only the solvent was removed with decanethicillin. Further, the remaining monomer was removed by recycling the decanetisilin, and then filtration was performed. The resulting solid material was washed with solvent and further
Vacuum drying was performed at 0°C for 24 hours to obtain the desired product η.

The material thus obtained was observed by electron microscopy and E.
Nitrogen atoms were confirmed by PMA, and it was confirmed that there was a polyamide film layer on the surface.

;2) Particle B Hexamethylenetetomine was used as the diamine compound added to the aqueous phase reactant, and the other conditions were the same as the method for producing particles, and the surface of crystalline cellulose was formed by interfacial polymerization. Form an amide membrane and decant as well. The desired substance was obtained by filtration and vacuum drying.

(3) Particles C chloroform/cyclohexane-i/3 (7>
Crystalline cellulose was Log mixed in 50 d of the mixed solvent and stirred, then 1-added only ethylene glycol, and after thorough stirring, 50 d of the mixed solvent was further added and stirred.9 Then,. In the same manner as in the preparation method for particles, the solvent was removed and vacuum drying was performed at 50°C for 24 hours to obtain the target substance.

(4) Particles D 1.45 g of modified aliphatic polyamine (Adeka Hardener EH-220 manufactured by Asahi Denka Kogyo Co., Ltd.), which is a hardening agent for epoxy resin, was dissolved in 10 m of ethylene glycol to prepare a water phase reactant, while toluene Bisphenol A type epoxy compound (Adeka Resin EP 4200 manufactured by Asahi Denka Kogyo Co., Ltd.) in toad? , 42g dissolved,
It was used as an oil phase reactant.

10 g of crystalline cellulose and 50 g of toluene were mixed in a flask equipped with a cooling tube, stirred thoroughly while keeping the temperature at 60 "C, and dispersed for 10 minutes. Then, the above aqueous phase reactant 1 d was added, and stirring was continued. After continuing to reach a uniform state, add the above oil phase reactant 50II1.
Stirring was continued for 6 hours while maintaining the temperature of the dispersion at 60°C to perform a curing reaction of the epoxy resin and form an insulating organic polymer (epoxy resin) thin film on the surface of the crystalline cellulose.7 This dispersion was released. After cooling and standing to precipitate the fine powder and removing the clear liquid, add toluene and repeat the decantation operation, vacuum drying at 50"C for 24 hours to obtain the target substance. Ta.

(5) Particles E A solution of 10 d of ethylene glycol mixed with 1.9 g of piperazine, a diamine compound, was used as the water phase reactant, and the same oil phase reactant as that used for making the particles was used. According to the particle preparation method, an insulating organic polymer thin film was formed on the surface of crystalline cellulose by interfacial polymerization, followed by decantation and vacuum drying to obtain the desired material.

(6) Particles! ? Mix 10 g of crystalline cellulose in 50 ate of toluene, heat to 60°C, and then add 1 ml of ethylene glycol alone.
d was added and stirring continued. Furthermore, 50 d of toluene was added and stirred.

Thereafter, the solvent was removed and vacuum drying was performed at 50°C for 24 hours in the same manner as in the preparation of particles to obtain the desired substance.

Using each of the particles A to F produced above as dielectric particles, corresponding electrorheological fluids A to F were prepared. The formulation composition is summarized in Table 1 below. Note that the electrorheological fluid G is obtained using crystalline cellulose as the dielectric particles G.

−m For electrorheological fluids A, CSG, F, and G, the environmental conditions in which ordinary mechanical devices are placed are -20
The current density was measured in the temperature range from 'C to 100C.

The results are shown in FIGS. 2 and 3, respectively. At the same time, the shear stress of these electrorheological fluids was also measured, and the results are shown in FIGS. 4 and 5.

In addition, each measurement was performed by applying an electric field strength of 2.5 KV/ms between the inner cylinder and outer cylinder containing each electrorheological fluid.
Fluids C and F exceeded the maximum permissible current of the voltage supply device at 60"C and fluid G became unmeasurable. In contrast, fluids A and D according to the present invention Each of the fluids had a value below the maximum permissible current value of the voltage supply device over the entire temperature range of -20°C to 100°C, and it was possible to measure the shear stress thereof.

As is clear from FIGS. 2 and 3, for fluids A and D that meet the present invention, the amount of current consumption is below the limit current over the entire operating temperature range, and It has a lower current value than other fluids in the range,
The electrorheological effect is efficiently exhibited. Moreover, as can be seen from FIGS. 4 and 5, the shear stress obtained is comparable to that of other fluids.

Further, when the current density and shear stress were similarly measured using fluids B and E, the same results as fluids A and D were obtained, respectively.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the temperature of the electrorheological fluid and the current consumption in the -a electrorheological fluid. 2 and 3 are graphs showing the relationship between temperature and current density of various electrorheological fluids measured in Examples, respectively. FIG. 3 shows fluid channels F and G. Moreover, FIGS. 4 and 5 are graphs showing the relationship between the temperature of the electrorheological fluid and the shear stress obtained by measurement in Examples, respectively.
The figure shows fluids ASC and G, and FIG. 5 shows fluids F and G. Fig. 1 Temperature Fig. 3 A degree [°C] Fig. 2 Temperature [°C] Fig. 4 Temperature [°C]

Claims (3)

[Claims] (1) An electrorheological fluid comprising dielectric fine particles dispersed in an electrically insulating oily medium, wherein the dielectric particles are composed of crystalline cellulose particles containing polyhydric alcohol as a hydrophilic agent, and An electrorheological fluid characterized by having a two-layer structure whose surface is covered with an electrically insulating thin film. (2) The electrorheological fluid according to claim 1, wherein the electrically insulating oily medium comprises a silicone oil containing at least one of amino-modified silicone oil and alcohol-modified silicone oil. (3) Claim (1) or (2), wherein the electrically insulating thin film is formed of polyamide or epoxy resin.
The electrorheological fluid described.