JPH1046182A - Electrorheological fluid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrorheological fluid which uses a relatively inexpensive compound, operates at room temperature, and can be used for a long time. An electrorheological fluid comprising an emulsion in which a modified silicone oil having a polar group is dispersed in a lower-viscosity insulating oil (eg, an unmodified silicone oil or a hydrocarbon-based insulating oil).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersed electrorheological fluid useful as an actuator for vibration absorption, torque transmission, servo control or the like in a mechanical system or as an optical element such as an optical shutter.

[0002]

2. Description of the Related Art An electrorheological fluid is a fluid whose viscosity changes instantaneously and reversibly (normally increases) when a voltage is applied.

[0003] Electrorheological fluids are broadly classified into dispersion systems and homogeneous systems. Many conventional electrorheological fluids are dispersion systems in which electropolarizable fine particles are dispersed in insulating oil. In a dispersed electrorheological fluid, when a voltage is applied, the fine particles dispersed in the insulating oil are polarized, and the polarized particles are arranged in a row in a row between the electrodes, impeding the flow of the insulating oil, which is a fluid. It shows the same behavior as increasing the viscosity. This dispersion-type electrorheological fluid has a large viscosity change and shows excellent performance in the short term, but has problems such as sedimentation of dispersed particles, exhaustion of electrodes, and destruction of particles itself, which is a major obstacle to practical application. It has become.

As a homogeneous electrorheological fluid, liquids such as a cholesteric liquid crystal mixture and a low-molecular liquid crystal are mainly used. In addition, a polar liquid such as nitromethane or nitrobenzene, or a ferroelectric polymer solution is used. Methods have also been proposed.

JP-A-6-220483 discloses a homogeneous electrorheological fluid comprising a polymer compound (eg, silicone) in which two or more liquid crystal groups (mesogen groups) are bonded to one molecular chain. Which shows a large change in viscosity comparable to a dispersion system upon application of a voltage.

[0006]

However, polymer liquid crystal compounds as described in the above publications are generally synthesized by introducing a liquid crystal functional group as a side chain into the polymer compound, and are synthesized in multiple steps. A process is required, and synthesis takes time. Therefore, this compound is very expensive. Also,
The liquid crystal compound has a problem that a sufficient electrorheological effect cannot be obtained unless the temperature is in a temperature range showing liquid crystallinity, the operating temperature range is limited, and the compound cannot be used at room temperature. Many applications of electrorheological fluids are operated at room temperature, and if they cannot be used at room temperature, their utility will be significantly poorer.

The present invention uses relatively inexpensive compounds,
An object of the present invention is to provide an electrorheological fluid that can be operated at room temperature and used for a long time.

[0008]

Means for Solving the Problems The present inventors have noticed that a commercially available emulsion obtained by dispersing a modified silicone oil in an insulating oil shows a large viscosity change at room temperature by applying a voltage, and generally, a liquid having a polar group It has been found that the above problem can be solved by an emulsion in which an organic polymer is dispersed in insulating oil.

Here, the present invention is an electrorheological fluid comprising an emulsion in which a liquid organic polymer having a polar group is dispersed in an insulating oil having a lower viscosity.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical example of a liquid organic polymer having a polar group is silicone oil (an alkylpolysiloxane liquid at room temperature, typically dimethylpolysiloxane).
Is a modified silicone oil modified by introducing a polar group into the molecular terminal and / or the side chain of the modified silicone oil. Examples of the polar group include an amino group, an epoxy group, an alkoxyl group, a fluorine-substituted alkyl group (eg, a trifluoromethyl group), a carboxyl group, and the like. These polar groups may be linked to the molecular chain of the polysiloxane via a suitable linking group. The organic polymer may have two or more polar groups.

Such a modified silicone oil is widely used industrially as a fiber treatment, a raw material for various silicone resins, and the like, and is commercially available at a relatively low price.
Specific examples include amino-modified silicone oil, epoxy-modified silicone oil, fluorine-modified silicone oil, carboxyl-modified silicone oil, and the like.
Examples of commercially available products include silicone oil KF-3 manufactured by Shin-Etsu Chemical.
93, KF-854, X-22-161A, X-22-162A, X-22-3637, KF-
101, FL-100, BY16-754, etc.

The liquid organic polymer having a polar group is not limited to silicone oil. For example, a liquid organic polymer obtained by introducing any of the above polar groups into a carbon-based organic polymer such as polyacrylic acid, polyethylene glycol, or polyvinyl alcohol can be used. Good. Hereinafter, a liquid organic polymer having a polar group will be described by using a modified silicone oil as a representative example.

The insulating oil in which the modified silicone oil is dispersed is not particularly limited as long as it does not cause conduction when a voltage is applied, but typical examples include silicone oil and hydrocarbon oil. A substantially non-polar insulating oil is used. That is, Si, C and H for silicone oil, and C and H for hydrocarbon oil.
Is preferred. When the insulating oil has polarity, it is easily compatible with the polar modified silicone oil,
It becomes difficult to form a desired emulsion.

Examples of the silicone oil that can be used as the insulating oil include dimethylpolysiloxane, methylhydrogenpolysiloxane, and the like. Some of the methyl groups are substituted with hydrocarbon groups such as phenyl and alkyl groups. Is also good. Examples of commercially available products include silicone oils KF-56, KF-96, and KF-99 manufactured by Shin-Etsu Chemical.

Specific examples of the hydrocarbon-based insulating oil include alkylnaphthalene, liquid paraffin, kerosene, xylene, toluene and the like.

The insulating oil used has a lower viscosity than the modified silicone oil dispersed therein. Thereby, the electrorheological fluid of the present invention in which the modified silicone oil is dispersed as a disperse phase in the insulating oil is obtained. The dispersion method is not particularly limited, for example, a method of dissolving both the modified silicone and the insulating oil in a common solvent capable of dissolving them and removing the solvent from the obtained solution by evaporation, the modified silicone oil and the insulating oil, Can be directly mixed.

The solvent can be removed by either a method of removing the solvent by heating under normal pressure or a method of evaporating under reduced pressure (with or without heating). It is not necessary to completely remove the solvent, and a part of the solvent may remain in the emulsion as long as the dispersion state can be stably maintained. Dispersion by mixing may be performed by mechanical stirring, ultrasonic waves, or the like.

If the emulsion contains water, the voltage cannot be applied effectively, and the obtained emulsion is dehydrated as necessary. The dehydration treatment may be separately applied to the modified silicone oil and the insulating oil before forming the emulsion. The dehydration treatment can be performed by heat dehydration, addition of a dehydrating agent, or the like. As the dehydrating agent, molecular sieves generally used for dehydrating an organic solvent are preferable.

The ratio between the modified silicone oil and the insulating oil is
There is no particular limitation as long as an emulsion in which the modified silicone oil is dispersed in the insulating oil is obtained, but usually the modified silicone oil is 1 to 70 based on the total amount of both.
%, The remaining amount of insulating oil is 30 to 99% by weight, preferably 5 to 50% by weight of modified silicone oil and 50 to 50% of insulating oil.
95% by weight. 1% by weight of modified silicone oil
When it is below, substantially no change in viscosity is obtained, and
Even at 70% by weight or more, it is difficult to obtain a change in viscosity.

The electrorheological fluid of the present invention comprises a modified silicone oil (organic polymer having a polar group) constituting a dispersed phase, a low-viscosity insulating oil constituting a dispersion medium, and a solvent which may be left in a small amount in some cases. In addition, if necessary, an additive component such as a nonionic surfactant may be contained.

In the present invention, the interaction between the modified silicone oil and the insulating oil has not been clarified, but neither the modified silicone oil alone nor the insulating oil alone shows the electrorheological behavior. It shows electrorheological behavior only when dispersed in insulating oil. Further, when a common solvent capable of dissolving both the modified silicone oil and the insulating oil is added to make the emulsion a homogeneous solution, a substantial electrorheological behavior cannot be obtained. Therefore, it is considered that the modified silicone oil dispersed in the insulating oil in the form of an emulsion contributes to the electrorheological behavior (viscosity change) by some action, for example, deformation and bonding of the emulsion particles.

In the present invention, when it is desired to obtain a large change in viscosity, it is preferable that the insulating oil has a low viscosity, while the modified silicone oil dispersed in the insulating oil has a high viscosity. That is, although the modified silicone oil has a higher viscosity than the insulating oil, the greater the difference in viscosity between the two, the larger the change in viscosity of the obtained electrorheological fluid tends to be. Preferably, the kinematic viscosity (Stokes viscosity) of the modified silicone oil at the operating temperature is at least three times, more preferably at least five times, the kinematic viscosity of the insulating oil. At this time, the kinematic viscosities of both are values in a ground state where no voltage is applied.

On the other hand, in applications where an absolute viscosity higher than the change in viscosity is required, it is easier to obtain the desired viscosity if the insulating oil has a relatively high viscosity. In that case, the ratio of the above kinematic viscosities may be less than three times.

The change in viscosity becomes particularly large when the modified silicone oil has an epoxy group, a carboxyl group or an amino group in the side chain. Further, the change in viscosity increases as the amount of polar groups present in the modified silicone oil increases. The proportion of the polar group in the modified silicone oil can be represented by the polar group equivalent or the acid value (when the polar group is an acid), which is an index of the molecular weight of each polar group. The proportion of groups will be higher).

The proportion of the polar group in the modified silicone oil used in the present invention is such that when the polar group is an epoxy group or an amino group, the epoxy equivalent or amino group equivalent is 40%.
00 g / mol or less (e.g., in the range of 200 to 4000 g / mol), and when the polar group is a carboxyl group, the acid value is 4000 mgKOH / g or less (e.g., in the range of 500 to 4000 mgKOH / g). It is preferable that the ratio be as follows.

[0026]

The present invention will be described below in detail with reference to examples. The measurement of the electrorheological effect, which is a basic property of the electrorheological fluid, was performed according to the following method. The viscosities (kinematic viscosities) described in the examples are all measured values at room temperature.

(Measurement of Base Viscosity and Electro-Rheological Effect) An electrode is connected to a rotor and a cup of a commercially available B-type viscometer [DVM-2, manufactured by Toki Sangyo Co., Ltd.] 500 V DC voltage was applied, and the viscosity before and after applying the voltage (base viscosity) was measured.

[0028]

Example 1 Commercially available modified silicone oil containing an epoxy group [KF-101 manufactured by Shin-Etsu Chemical; epoxy equivalent: 350 g / mol]
Kinematic viscosity 1800 cSt] 5 g and commercially available silicone oil-based insulating oil without polar group [KF-96 manufactured by Shin-Etsu Chemical; 21 cS
t] was dissolved in 30 g of hexane with stirring. The obtained solution was heated at 100 ° C. for 5 hours to evaporate hexane, and the remaining liquid was sufficiently stirred to obtain an emulsion in which the modified silicone oil was dispersed in the insulating oil. The change in viscosity is shown in Table 1.

[0029]

Example 2 5 g of the modified silicone oil containing an epoxy group (KF-101) used in Example 1 was obtained from a commercially available hydrocarbon insulating oil [alkylnaphthalene: Lion S made by Lion;
St] was mixed directly with 20 g and stirred to obtain an emulsion in which the modified silicone oil was dispersed in the insulating oil. The change in viscosity is shown in Table 1.

[0030]

Example 3 Fluorine-modified silicone oil containing a trifluoromethyl group [FL-100 manufactured by Shin-Etsu Chemical Co., Ltd .; existence ratio of polar group is unknown; 100 cSt] 3 g was the same hydrocarbon type as used in Example 2. The emulsion was directly mixed with 25 g of insulating oil and stirred to obtain an emulsion in which the modified silicone oil was dispersed in the insulating oil. The change in viscosity is shown in Table 1.

[0031]

Example 4 Modified silicone oil containing a carboxyl group [BY16-7 manufactured by Dow Corning Toray Silicone Co., Ltd.]
54; Acid value 1000 mgKOH / g; 3000 cSt] 10 g of insulating oil consisting of methylphenylpolysiloxane [KF-5 manufactured by Shin-Etsu Chemical Co., Ltd.]
6; 15 cSt] and stirred to obtain an emulsion in which the modified silicone oil is dispersed in the insulating oil. The change in viscosity is shown in Table 1.

[0032]

Example 5 Modified silicone oil containing epoxy polyether group [X-22-3667 manufactured by Shin-Etsu Chemical; epoxy equivalent: 38]
[00g / mol; 3000 cSt] 5 g was directly mixed with 15 g of the same hydrocarbon insulating oil used in Example 2 and stirred to obtain an emulsion in which the modified silicone oil was dispersed in the insulating oil. Was. The change in viscosity is shown in Table 1.

[0033]

Example 6 Modified silicone oil containing amino group
[KF-393 manufactured by Shin-Etsu Chemical; amino equivalent 360 g / mol; 60 cS
t] was directly mixed with 30 g of the same silicone oil-based insulating oil as used in Example 1 and stirred to obtain an emulsion in which the modified silicone oil was dispersed in the insulating oil. The change in viscosity is shown in Table 1.

[0034]

Comparative Example 1 Modified silicone oil used in Example 1
Table 1 shows the measurement results of the electrorheological effect of (KF-101).

[0035]

Comparative Example 2 The results of measuring the electrorheological effect of the insulating oil (KF-96) used in Example 1 are shown in Table 1.

[0036]

Comparative Example 3 The same operation as in Example 4 was performed except that an alkyl-modified silicone oil [KF-412 manufactured by Shin-Etsu Chemical; 500 cSt] was used as the modified silicone oil.

[0037]

Comparative Example 4 Modified Silicone Oil Containing Amino Group
[KF-865 manufactured by Shin-Etsu Chemical; amino equivalent: 4400 g / mol; 4400 c
St] was directly mixed with 30 g of the same silicone oil-based insulating oil as used in Example 1 and stirred. As a result, not an emulsion but a solution in which both components were uniformly compatible was obtained. Table 1 shows the measurement results of the change in viscosity of this solution.

[0038]

[Table 1]

As can be seen from Table 1, Examples 1 to 3 in which a modified silicone oil having a polar group was dispersed in an insulating oil.
Emulsion No. 6 has a large increase in viscosity when voltage is applied (approximately 1.5 times in Example 3 and more than 3 times in others), and shows a change in viscosity usable as an electrorheological fluid. On the other hand, whether the modified silicone oil as the disperse phase does not have a polar group (Comparative Example 3), or even if a modified silicone oil having a polar group is used, it is mixed homogeneously with the insulating oil to form a solution. Then (Comparative Example 4), the change in viscosity is small, and it cannot be used as an electrorheological fluid.

Each of the emulsions of Examples 1 to 6 and Comparative Example 3 maintained the emulsion state even after being left at 20 ° C. for one week, and was confirmed to be stable for a long period of time.

[0041]

The electrorheological fluid of the present invention operates at room temperature, can be easily and inexpensively manufactured, and exhibits a practically sufficient change in viscosity by applying a voltage. Further, unlike an electrorheological fluid of a dispersion system in which particles are dispersed, it is an emulsion in which a liquid is dispersed, and the dispersion state is stably maintained for a long time. The electrorheological fluid of the present invention can be applied to actuators such as valves, clutches, brakes, and torque converters, mechanical systems including vibration damping materials, and optical elements such as optical shutters that control light transmittance. .

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Claims (5)

[Claims] 1. An electrorheological fluid comprising an emulsion in which a liquid organic polymer having a polar group is dispersed in an insulating oil having a lower viscosity. 2. The electrorheological fluid according to claim 1, wherein said organic polymer is a silicone oil. 3. The electrorheological fluid according to claim 1, wherein said polar group is selected from the group consisting of an amino group, an epoxy group, an alkoxyl group, a fluorine-substituted alkyl group, and a carboxyl group. 4. The electrorheological fluid according to claim 1, wherein the insulating oil is selected from the group consisting of an aromatic hydrocarbon having no polar group and a silicone oil. 5. A mechanical system or optical element operated by an electrorheological fluid according to claim 1.