JPS5832197B2 - electrorheological fluid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrorheological fluid made by dispersing ferroelectric powder and silicon dioxide fine powder in highly electrically insulating oil.

Here, an electrorheological fluid is a fluid that exhibits a phenomenon in which the apparent viscosity of a fluid changes rapidly and reversibly by applying an electric field to the fluid, that is, an electrorheological effect, and is a fine powder with specific properties. It is constructed by dispersing it in an oil with excellent electrical insulation properties, that is, a dispersion medium.

Conventionally, electrorheological fluids are composed of cellulose, starch, and silica gel, which are made into fine powders that adsorb an appropriate amount of water as powders, and other constituents of electrorheological fluids, such as dispersion media, are diphenyl chloride and sebacin. Dibutyl acid, trans oil, and halafine chloride were used.

However, an electrorheological fluid with extremely high performance that can be used in flow control valves, power transmission clutches, etc., withstands continuous use for long periods of time, and is highly stable (and has a practical value) has not yet been found. .

This is mainly due to the following three reasons.

First of all, the powder, which is one of the components of the electrorheological fluid, is treated in advance by a method that adsorbs an appropriate amount of water, and since the water adsorbed to the powder greatly contributes to the electrorheological effect, the electrorheological The reproducibility of the effect is poor, and it is extremely problematic in practice.

This is because it is technically difficult to artificially control the amount of moisture adsorbed in the powder and the bonding state between the powder and moisture.

Further, since the electrorheological effect depends on the moisture adsorbed to the powder, it cannot exhibit an extremely large viscous effect, which also hinders its practical use.

Second, when a high electric field (0.5 to 3 Kv/mrn) is applied to a dispersed insulating oil in the form of powder that has absorbed water, dielectric breakdown is extremely likely to occur.

Dielectric breakdown prevents stable continuous use over long periods of time.

If the adsorbed water content of the powder is reduced in order to improve the dielectric breakdown resistance, the electrorheological effect will be significantly reduced.

Therefore, it is technically difficult to simultaneously improve the electrorheological effect and dielectric breakdown resistance of an electrorheological fluid whose component is a powder that has absorbed water, and this is a major practical obstacle.

Thirdly, the specific gravity of powder, which is one of the constituent elements of electrorheological fluid, is conventionally 1.5 or more, whereas the specific gravity of insulating oil, which is a dispersion medium, is approximately 0.8 to 1.5. Since it is in the range of
It is difficult to maintain a uniform and stable dispersion state (the powder settles due to the difference in specific gravity).

The sedimentation of the powder reduces the performance of the electrorheological fluid and the pump,
This may cause problems during transportation in the piping section.

As mentioned above, although electrorheological fluids have the remarkable property that the viscosity of the fluid can be adjusted electrically, it has been extremely difficult to create electrorheological fluids that have high performance and can withstand long-term practical use. It was considered difficult.

In view of the above-mentioned current situation, the present invention was completed as a result of intensive research by the present inventors in order to improve the deficiencies of electrorheological fluids. It provides an electrorheological fluid that is characterized by having good ferroelectric properties and being stably dispersed in insulating oil. The particle size is several tenths to several giants of the particle size of barium titanate, and 0.5 to 3
Silicon dioxide-based fine powder adsorbing moisture of about 0 weight coefficient, such as silicon dioxide (Si02) or magnesium aluminate silicate (A1203・M, ?0・2Si02・XH20)
) etc. are added at a ratio of 1 to 10 parts of silicon dioxide-based fine powder to 100 parts of ferroelectric powder, and after thorough stirring, the mixture is dispersed in highly electrically insulating oil. be.

When preparing the electrorheological fluid of the present invention, it is important to adsorb the silicon dioxide fine powder over a long period of time under slow moisture absorption conditions so that the amount of water on the surface of the powder is as small as possible. be.

The features of the electrorheological fluid of the present invention are as follows.

First, the electrorheological effect is greater than that of conventional electrorheological fluids using powders such as cellulose and silica gel.

In general, the mechanism of viscosity increase in the electrorheological effect is based on the bridging of powder between electrodes when an electric field is applied due to the dielectric properties of powder. Specifically, dielectric powder is dispersed in insulating oil. When an electric field is applied, the dielectric powder undergoes induced polarization, and when the dielectric constant of the powder is greater than that of the dispersion medium, a force is applied perpendicular to the electric field and in a direction opposite to the electric field strength. receive.

As a result, the particles move to a location where the electric field strength between the electrodes is high, and since the electric field strength at that location becomes even greater, the particles gather in a geometric progression.

Therefore, electrostatic action between the powders is involved, and a band-shaped bridge is formed between the electrodes.

This crosslinking by the powder generates an attractive force called the so-called Janson and Rahbek effect on the electrode surface, which acts as resistance to flow parallel to the electrode surface and as a shearing force against displacement of the electrode surface.

One of the advantages of the electrorheological effect of the electrorheological fluid of the present invention than that of conventional electrorheological fluids using cellulose, silica gel, etc. is that cellulose, silica gel, etc. have properties as dielectric materials by adsorbing water. However, since the powder used in the present invention is a ferroelectric substance, its dielectric properties are higher than those of cellulose or silica gel that have absorbed water. This results in a marked increase in the electrorheological effect.

The other is the powder that is a component of the electrorheological fluid according to the present invention, which is a mixture of ferroelectric powder and fine powder several tenths of the size of the ferroelectric powder. Therefore, when a crosslink is formed by powder, finer powder (silicon dioxide powder) gathers around the contact point between relatively large powder (corresponding to ferroelectric powder), and a large The fine powder fills the voids in the contact area of the powder, forming an extremely densely packed crosslinked structure, and as a result, the attractive force between the electrodes increases and the electrorheological effect increases. be.

Furthermore, the water-containing powder in the electrorheological fluid according to the present invention is only silicon dioxide-based fine powder that has adsorbed a small amount of water, and its weight distribution in the fluid is small. One of its characteristics is that even if the fluid changes slightly, it has little effect on the performance of the electrorheological effect, and the reproducibility of the performance of the fluid is good.

The second feature is that it has extremely good dielectric breakdown resistance compared to conventional electrorheological fluids.

This is because the water in the electrorheological fluid of the present invention is only absorbed by about 0.5 to 3 weight φ of the silicon dioxide powder added in a small amount, so the amount of water retained in the electrorheological fluid of the present invention is approximately 6 Therefore, the electrical insulation properties are significantly improved.

The third feature is that the powder is extremely stably dispersed in the insulating oil, eliminating problems such as settling and agglomeration of the powder.

When silicon dioxide-based fine powder is sufficiently stirred and mixed with insulating oil, it becomes a viscous grease-like structure, and the ferroelectric powder is stably dispersed over a long period of time despite the difference in specific gravity.

Next, the present invention will be explained in detail by way of examples.

Example 1 Ferroelectric materials A and B, 2 as ferroelectric powders according to the present invention
An electrorheological fluid containing magnesium aluminate silicate as a silicon oxide powder and dibutyl phthalate as an insulating oil is shown below.

The properties of the constituent powder are as follows.

Ferroelectric A Main component Barium titanate content density of about 90 coefficients 5 to 69/cri Dielectric constant 1200 Average particle size 20 to 200μ Ferroelectric B Main component Barium titanate content density of about 90 coefficients 5 to 6 g /cnl Dielectric constant 2000 Average particle size 20-200μ Magnesium silicate aluminate density 2.297cri Average particle size 2μ The blending ratio of the powder and dispersion medium is shown below.Next, the electrorheological fluid of the present invention Table 1 shows a comparison of the performance of the conventional electrorheological fluid and the conventional electrorheological fluid.

A conventional electrorheological fluid was prepared by dispersing cellulose powder adsorbed with an appropriate amount of water in dibutyl sebacate.

The blending ratio is as follows.

Conventional electrorheological fluid Cellulose 50 parts (water content 5.0% by weight) Dibutyl sebacate ioo part The electrorheological effect was measured using a coaxial double cylinder rotational viscometer and applying an electric field between the inner and outer cylinders. The same shear rate of (
Shear stress at 160 sec 1) (gW/cr?t
).

As is clear from Table 1, the electrorheological fluid of the present invention is superior to the conventional electrorheological fluid.

Example 2 5i0 was prepared as silicon dioxide-based fine powder in the same manner as in Example 1.
The case where 2 is used is shown below.

Formulation Example 3 Ferroelectric (B) 15 parts Ferroelectric (C) 35 parts Silicon dioxide 4 parts (moisture content 1.0 parts by weight) Dibutyl sebacate 50 parts The properties of the powder are as follows.

Ferroelectric C main component barium titanate (Contains about 90 sections) Density 5-6 g/cni Dielectric constant soo.

Average particle size 20-200μ Silicon dioxide density 2.2jilcrd average particle size 1
．． 5μ Electrorheological effect of the fluid [increase in shear stress gW/CTL
)] are shown in Table 2.

Claims (1)

[Scope of Claims] 1. Barium titanate with a particle size of about 20 to 200 μm, several milliseconds to several hundredths of the particle size of the barium titanate, and a weight of 0.5 to 3.0 μm. Adsorbed moisture to the extent of 2
An electrorheological fluid made by dispersing silicon oxide fine powder in insulating oil. 2. The electrorheological fluid according to claim 1, which is used in a ratio of 1 to 10 parts of silicon dioxide-based fine powder to 100 parts of titanium-dispersed barium powder. Silicon dioxide (SiOz) or magnesium silicate aluminate (A1203, 0.2
The electrorheological fluid according to claim 1 or 2, which uses Si02.XH20).