JP2599963B2 - Electrorheological fluid with excellent high temperature stability, responsiveness and thickening effect - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an electrorheological fluid whose viscosity can be controlled by applying an electric field (voltage). The present invention relates to an electrorheological fluid which has a rapid and reversible change in viscosity from a low temperature range to a high temperature range, and is stable for a long time and has a large viscosity increasing effect.

(Prior art) An electro-rheological fluid (Electro-Rheological Fluid, Electrviscu) in which the viscosity of a fluid changes by application of an electric field (voltage)
It is called s Fluid, etc., and is also called ER fluid for short. ) Is known for a long time. That is, the ER fluid was already discovered at the end of the 19th century (Duff, AW,
physical Review Vol. 4, No. 1, (1896) 23).

Initial work on ER fluids focused on liquid-only systems and was ineffective. afterwards,
Moving from studies of liquid-only systems to studies of solid-dispersed fluids, considerable electrorheological effects have been obtained. For example, Winslow proposed an ER fluid using paraffin and silica gel powder and water to make the system slightly conductive (Winslow, WM, J. of Applied physics, Vol. 20).
(1949) 1137). According to Winslow's research, the electrorheological effect of the ER fluid is called the ER effect or the Winslow effect.

On the other hand, the mechanism of the onset of the thickening effect (ER effect) in the ER fluid is also being elucidated. For example, Klass describes that each particle, which is a dispersoid in the ER fluid, has a two-layer dielectric polarization (Indu
ced Polarization of the Double Layer) and attributed this to the main cause (Klass, DL, et al., J. of App
lied Physics, Vol. 38, No. 1 (1967) 67).

Explaining this from an electric double layer, the ions adsorbed around the dispersoid (such as silica gel) are uniformly arranged on the outer surface of the dispersoid when E (electric field) = 0. However, when E (electric field) = finite value, the ion distribution is shifted, and the particles mutually exert an electrostatic action within the electric field. In this way, each particle forms a bridge (crosslink) between the electrodes, and develops a shear resistance against stress, that is, an ER effect.

Various proposals have been made for the above-mentioned solid particle dispersion ER fluid from the viewpoints of improving the viscosity characteristics of the ER fluid and improving the stability while taking into account the mechanism of developing the ER effect. For example, a method using a silicon dioxide-based fine powder in which a ferroelectric powder and a small amount of water are adsorbed (JP
No. 53-17585), a high molecular weight dispersant having a functional group is used to stabilize a dispersion system composed of silica gel having a water content of 1 to 15 wt% as a disperse phase and silicone oil as a liquid phase. (Japanese Patent Application Laid-Open No. 61-44998) and the like have been proposed.

(Problems to be Solved by the Invention) However, despite various proposals, conventional ER fluids have a point of responsiveness (responsiveness) of rapid and reversible viscosity change by application of an electric field (voltage), and ER effect. Reproducibility, small thickening effect, stable maintenance of ER effect for a long time,
However, it is not yet sufficient. In particular, since water is used for these ER fluids, the difficulty is that water evaporates more and more in the high-temperature region above 80 ° C and the thickening effect decreases. Is changing and unstable.

The present inventors have conducted intensive studies to solve the above-mentioned problems of the ER fluid, and as a result, it has been possible to stably maintain the ER effect up to a high temperature region of 100 ° C. by replacing water with a polyhydric alcohol so far. In addition, it has just been proposed that even in a system using water, the stability of the ER effect and the thickening effect can be drastically improved by adding an inorganic acid or an organic acid thereto.

The present invention provides a solid particle dispersion ER over a wide temperature range.
It is an object of the present invention to further stabilize the ER effect of the fluid by using the above-mentioned polyhydric alcohol and acid in combination and to increase the thickening effect.

[Configuration of the invention]

(Means for Solving the Problems) To summarize the present invention, the present invention provides an electric insulating liquid as a dispersion medium, porous solid particles as a dispersoid, an acid selected from inorganic acids and organic acids, An electrorheological fluid (ER) with excellent high-temperature stability, responsiveness and thickening effect characterized by being composed of a polyhydric alcohol, or characterized by further adding a dispersant to these components.
Fluid).

 Hereinafter, the configuration of the present invention will be described in detail.

The electrically insulating liquid as the dispersion medium used in the ER fluid of the present invention may be any liquid as long as it is electrically insulating, and is not particularly limited.

Examples of this kind of electrically insulating liquid include mineral oil and synthetic lubricating oil, and more specifically, naphthenic mineral oil, paraffinic mineral oil, polyalphaolefin, polyalkylene glycol, silicone, diester, polyolester, phosphorus ester Examples include acid esters, silicon compounds, fluorine compounds, polyphenyl ethers, and synthetic hydrocarbons. The viscosity range of these electrically insulating liquids is preferably 5 to 300 cp at 40 ° C.

As the porous solid particles as a dispersoid used in the ER fluid of the present invention, conventional ones are used and there is no particular limitation.

Examples of such porous solid particles include silica gel, water-containing resin, diatomaceous earth, alumina, silica-alumina, zeolite, ion-exchange resin, and cellulose.

These porous solid particles usually have a particle size of 10 nm to 200 μm.
m is used in a ratio of 0.1 to 50% by weight. If it is less than 0.1 wt%, the ER effect is small, and if it exceeds 50 wt%, the dispersibility deteriorates, which is not preferable.

The dispersant used in the ER fluid of the present invention is used for making the dispersion state of the porous solid particles in the dispersion medium uniform and stable, and therefore, a conventional dispersant is used.

Examples of this type of dispersant include sulfonates,
Phenates, phosphonates, succinimides, amines, nonionic dispersants, and more specifically magnesium sulfonate, calcium sulfonate, calcium phenate, calcium phosphonate, polybutenyl succinimide, sorbitan monooleate, sorbitan sesquis There are oleates and the like. These are usually 0.1-10 wt%
Is used. However, the dispersant need not be used when the dispersibility of the solid particles is good.

Next, the “polyhydric alcohol” component and the “acid” component, which are the most significant features of the components of the ER fluid of the present invention, will be described.

As described above, the present inventors have found that the ER effect can be improved by using each of these components alone. That is, conventional ER fluids, typically
If "polyhydric alcohol" is used instead of "water" of the ER fluid composed of mineral oil, water, and solid particles, especially in the high temperature range (80 ℃
Above), the ER effect can be improved. In addition, each time an “acid” component is added to a conventional ER fluid (in this case, used together with water), the thickening effect can be stably improved.

The present invention aims at a synergistic effect by using these two components in combination.

As the above-mentioned “polyhydric alcohol” component, dihydric alcohol and trihydric alcohol are useful, and ethylene glycol, glycerin, propanediol, butanediol, hexanediol and the like are used.

Examples of the above-mentioned "acid" component include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, perchloric acid, chromic acid, phosphoric acid, and boric acid, or acetic acid, formic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, and oxalic acid. And organic acids such as malonic acid. In addition, these "polyhydric alcohol" components are usually 1 to 30% by weight, particularly preferably 2 to 15% by weight, based on the porous solid particles.
%, And the "acid" component is typically from 0.01 to
It is used in a proportion of 5% by weight, particularly preferably 0.1 to 2% by weight. 1wt% in the usage ratio of "polyhydric alcohol" component
If it is less than 30 wt%, the ER effect is small, and if it exceeds 30 wt%, the current easily flows, which is not preferable. On the other hand, if the content of the “acid” component is less than 0.01 wt%, the ER effect is small,
On the other hand, when the content exceeds 5 wt%, it is not preferable because current is easily supplied and power consumption increases.

In the present invention, in the combination use of the "polyhydric alcohol" component and the "acid" component, for example, a system of ethylene glycol and acetic acid is preferable in order to apply a high voltage to exhibit a high viscosity effect.

(Operation) The technical configuration of the present invention in which "polyhydric alcohol" and "acid" are used in combination with the ER fluid of the solid particle dispersion system enables the response (sensitivity) of viscosity change over a wide temperature range up to a high temperature range. Excellent effects such as reproducibility, stability over time, and a thickening effect (magnification of thickening when an electric field is applied to an electric field of 0) can be exhibited.

The present inventors have not sufficiently clarified the mechanism by which these excellent effects are expressed, but speculate as follows.

In a conventional ER fluid, typically an ER fluid composed of mineral oil, water, and solid particles, the cause of the ER effect is considered as follows. That is, the water adsorbed on the solid particles forms a thin water film, and is dielectrically polarized in the electric field by its polarity,
It is stretched in the direction of the electric field and begins to form bridges with each other. The bridge is completed between the electrodes and the viscosity increases in the direction perpendicular to the electric field.
Appears as an ER effect.

Therefore, the thickness of water is extremely important for the ER effect. However, since water has a low molecular weight and is easily evaporated, the thickness of water easily fluctuates due to changes in the external environment, particularly, in external temperature. This is the cause of the instability of the ER effect.

In the present invention, a polyhydric alcohol such as ethylene glycol or glycerin is used as a polar liquid that has a strong affinity for solid particles instead of water and is susceptible to an electric field. Alcohol has a higher molecular weight than water, is less likely to evaporate, and is stably adsorbed on solid particles up to a high temperature, so that a stable film with a small variation in film thickness is formed on the surface of the solid particles. In the present invention, the stability of this film is further strengthened than the "acid" component present in the system, and as a result, an ER fluid having a large thickening effect that is stable over a wide temperature range up to a high temperature region can be obtained. It is considered something.

In the ER fluid system of the present invention, water has been referred to in the above description of (action), but it is a matter of course that water may be used as long as the ER effect is not inhibited.

〔Example〕

Hereinafter, the present invention will be described in detail based on examples,
The present invention is not limited to these examples.

(Examples 1 to 4) / (Comparative Examples 1 to 6) (i) Preparation of ER fluid (a) Contains 7 wt% of ethylene glycol (accordingly,
Silica gel component: 93 wt%), silica gel with a diameter of about 1 μm, dispersant (succinimide), and mineral oil: 6: 4: 90
The mixture (weight ratio) is referred to as (A) fluid.

(B) Contains 7 wt% of water (therefore, the silica gel component
A mixture of silica gel having a diameter of about 1 μm, a dispersant (succinimide), and mineral oil at a weight ratio of 6: 4: 90 (weight ratio) is defined as a fluid (B).

Various ER fluids shown in Table 1 below were prepared using the fluids (A) and (B).

(Ii) Experimental conditions and evaluation items of ER fluid The following items were evaluated for the ER fluid at 40 ° C and 90 ° C using a rotational viscometer capable of applying a voltage.

● when changing the reactive ...... field from 0 to ^{1.4 × 10 6 (V / m} ), the viscosity was evaluated by either stabilize many seconds.

● Reproducibility: Evaluated by the change rate (%) of the viscosity when the electric field is 1.4 × 10 ⁶ (V / m) when the electric field is repeatedly cycled from 0 to 1.4 × 10 ⁶ (V / m) → 0. did.

● Stability: When the electric field was kept constant at 1.4 × 10 ⁶ (V / m), evaluation was made based on the amount of change (%) in viscosity over time (measurement time: 1 hour).

● Thickening effect …… The electric field is 1.4 × 10 compared to when the electric field is 0
Evaluation was made based on the magnification of the viscosity when ⁶ (V / m).

(Iii) Results The results are shown in Table 2.

[Effect of the Invention] The electrorheological fluid (ER fluid) of the present invention has extremely good stability in a wide range of the stoichiometric range up to a high temperature range, and has a large thickening effect. Further, the ER fluid of the present invention is remarkably excellent in response (sensitivity) and reproducibility as compared with the conventional fluid.

Therefore, the ER fluid of the present invention is useful for, for example, a control device utilizing a change in viscosity, and can significantly improve the control accuracy thereof, particularly, the control accuracy under high temperature use.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C10M 125: 26 125: 22 125: 20 125: 18 129: 32 129: 08 133: 16) C10N 30 : 02 30:04 30:08 40:16 (56) References JP-A-1-278598 (JP, A) JP-A-1-278599 (JP, A) JP-A-49-36704 (JP, A)

Claims (2)

(57) [Claims] 1. An electrorheological material having excellent high-temperature stability, responsiveness and thickening effect, comprising an electrically insulating liquid as a dispersion medium, porous solid particles as a dispersoid, an acid and a polyhydric alcohol. fluid. 2. It is excellent in high-temperature stability, responsiveness and thickening effect, comprising an electrically insulating liquid as a dispersion medium, porous solid particles as a dispersoid, an acid, a polyhydric alcohol and a dispersant. Electrorheological fluid.