Note: Descriptions are shown in the official language in which they were submitted.
ZQOQ322
The present invention relates to an electroviscous fluid which
increases its viscosity when an electric potential difference is
applied thereto.
The electroviscous fluid is a suspension composed of a finely
divided dielectric solid dispersed in an electrically nonconductive
oil. The viscosity of the fluid increases swiftly and reversibly
under the influence of an electric field applied thereto and the
fluid turns to a plastic or solid state when the influence is
sufficiently strong.
An electric field to be applied for changing the viscosity of
the fluid can be not only that of a direct current but also that of
an alternating current, and the electric power requirement is very
small making it possible to give a wide range of viscosity
variation from liquid state to almost solid state with a small
consumption of electric power.
The electroviscous fluid has been studied with an expectation
that it can be a system component to control such apparatus or
parts as a alutch, valve, shock absorber, vibrator,
vibration-isolating rubber, actuator, robot arm or a damper, for
example.
Hitherto, electroviscous fluids using such solid particulates
as cellulose, starch, silica gel, ion exchange resin and lithium
polyacrylate which have been absorbed water from the surface and
,2 0 ~ ~5 3 ~
pulverized (USP 2,417,850, USP 3,047,507, USP 3,397,147,
USP 3,970,573, USP 4, 129,513, Japanese Patent Publication Tokkosho
60-31211 and DE 3,427,499) as one component and using such liquid as
diphenylhalide, dibutyl sebacate, hydrocarbon oils, chlorinated paraffin
5 and silicone oils as the other component were proposed.
However, they are not satisfactory in practical usages, and an
electroviscous fluid practically usable with excellent pelrollllance and
stability has not been known.
Characteristics requested for an electroviscous fluid usable
practically are: exhibiting an enhanced electroviscous effect covering a
wide range of temperature; a small electric power consumption for
imposing electric field; a low viscosity when electric field is removed;
and long term stability without the deposition of the dispersed
particulates.
However, those dispersed particulates containing water to attain
the enhanced electroviscous effect have a problem of requiring a large
electric current through the particulates which results in an excessive
consumption of electric power. The tendency is enhanced especially with
the increase of the temperature, and the upper limit of the temperature at
which the conventional electroviscous fluids using such dispersed phases
can be used practically is said to be around 70-80C. When the
electroviscous fluid is used at temperatures higher than the limit, a large
consumption of electric power occurs due to the excessive flow of electric
current as well as a decreased performance and delayed response of the
electroviscous effect as the time proceeds. Accordingly, it has been
virtually impossible to use the electroviscous fluid with constituents
mentioned above when operating
t~
Z~OQ3Z2
~ _ under such high temperature circumstances.
Furthermore, the electroviscous fluids using the particulates
containing water for the purpose of enhancing the electroviscous
effect do not show the electroviscous effect at temperatures under
0C, because the water freezes at temperatures under 0C.
As explained above, the conventional electroviscous fluids
using the particulates containing water as the dispersed phase for
the purpose of enhancing the electroviscous effect havean essential
defect that the temperature range for use is limited and th~t they
have a limited lifetime due to the evaporation of water.
From the above mentioned reasons, there has been desired the
development of an electroviscous fluid using anhydrous solid
particulates as the dispersed phase which is expected to be capable
of showing a higher electroviscous effect at high temperatures with
a lessened electric power consumption together with a long lifetime.
USP 4,678,589, Japanese Patent Provisional Publication
Tokkaisho 63-97694 and Japanese Patent Provisional Publication
Tokkaisho 64-6093 proposed an electroviscous fluid containing no
water or an electroviscous fluid using particulates with multi-
layer structure as the dispersed phase. However, there are still
problems with these such as a ~lle.r electroviscous effect, larger
consumption of electric power, or the problem that it can be used
only under the alternating electric current.
The mechanism of the electroviscous effect in anhydrous system
is supposed that the application of an electric potential
difference induces interfacial polarization due to the movement of
2QOQ322
~lectrons in each particulate, the mutual attraction among theelectronically polarized particulates, the formation of bridges
among the particulates and elevation of viscosity of the fluid
dispersing such particulates therein.
Accordin~ly, the present invention provides an electro-
viscous fluid comprising
1-60% by weight of a dispersed phase of carbonaceous particulates
having average particle size of 0.01-100 micrometer, and 99-40% by
weight of a continuous liquid phase of an electric insulating oil
having a viscosity of 0.65-500 centistokes at room temperature.
Thus, the inventors of the present invention
paid attention to a low temperature treated carbonaceous material
which has a high concentration of stable radical (unpaired
electron), and examined the availability for the dispersed phase of
an electroviscous fluid, and developed an electroviscous fluid
showing a high electroviscous effect with smaller electric power
consumption in a wide range of temperatures under the application
of a direct current or an alternating current.
A preferred feature of the present invention is to provide an
electroviscous fluid which uses anhydrous solid particulates as the
dispersed phase and can exhibit a greater electroviscous effect
with less electric power consumption in a wide range of
temperatures and can be used for a long period of time.
Preferred embodiments of the invention will now be discussed
by way of example only with reference to the figures attached
herewith wherein:
Fig.1 is a graph showing the relationship between the
magnitude of electric field (abscissa: KV/mm) and torque (ordinate:
g cm) for the electroviscous fluid of Example 1 before (o mark) and
ZQOQ32Z
after (~ mark) subjecting it to a high temperature heat-treatment
at 120C for 50 hours;
Fig.2 is a graph showing the result of the
same measurement for the electroviscous fluid of Comparative
Example 1;
Fig.3 is a graph showing the relationship between the
temperature (abscissa: C) and torque (ordinate: g cm) for the
electroviscous fluid of Example 2 when an electric potential
difference of 1.5 KV/mm was applied (o mark) and with no
application of the electric potential difference (~ mark); and Fig.4
is a graph showing the result of the same measurement for the
electroviscous fluid of Comparative Example 1.
A ~e~ Z feature of the invention is the provision of an electroviscous
fluid capable of exhibiting an excellent electroviscous effect even
at a high temperature with a low electric power consumption
together with maintaining the improved electroviscous effect for a
long period of time.
The problem has been solved through an electroviscous fluid
comprising 1-60% by weight of a dispersed phase of carbonaceous
particulates having average particle size of 0.01-100 micrometer,
and 99-40% by weight of a continuous liquid phase of an electric
insulating oil having a viscosity of 0.65-500 centistokes at room
temperature.
Preferably~ the carbonaceous particulates
suitable for the dispersed phase of the electroviscous fluid is to
have a carbon content of 80-97 % by weight, more preferably 90-95%
by weight, the C/H ratio (atomic ratio of carbon/hydrogen) of 1.2-
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~`~5, preferably 2-4, and the average particle size 0.01-100
micrometer.
It is well known that the electric resistance of particulates
generally used as the dispersed phase of electroviscous fluid is
in the area of semiconductor [Winslow: J. Appl. Physics 20 1137
(1949)] Carbonaceous particulates having the carbon content of
under 80% by weight and the C/H ratio of under 1.2 are insulating
material and do not show the electroviscous effect when applied as
the dispersed phase.
On the other hand, carbonaceous particulates having the carbon
content of over 97% by weight and the C/H ratio of over 5.0 show a
nearly equal property as that of an conductor and an excessive
electric current flows when an electric potential difference is
applied thereon thus giving no practically usable electroviscous
fluid.
Practically, carbonaceous particulates which are preferably
used as the dispersed phase in the electroviscous fluid of the
present invention include the so-called low temperature treated
carbonaceous particulates such as; pulverized particulates of coal
tar pitch, petroleum pitch and a pitch obtained by thermal
decomposition of polyvinylchloride; particulates composed of
various carbonaceous mesophases obtained by heat treatment of raw
pitches or tar components, that is, particulates obtained by a
solvent removal of pitch component from the pitch containing
optical anisotropic spherules (mesophase spherules) obtained by
above mentioned heat treatment; particulates obtained by
pulverization of above mentioned various carbonaceous mesophase
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-spherules; particulates obtained by heat treatment of raw pitches
to be converted to bulk-mesophases (Japanese Patent Provisional
Publication Tokkaisho 59-30887) and then pulverized; particulates
obtained by pulverization of partially crystallized pitch;
particulates obtained by low temperature carbonization of
thermosetting resin such as phenolic resin; particulates comprising
pyrolized polyacrylonitrile. In addition to the above,
particulates obtained by pulverization of anthracite, bituminous
coal and the like; carbonaceous particulates obtained by heating
under pressure a mixture of vinyl hydrocarbon polymers such as
polyethylene, polypropylene or polystyrene with chlorine-containing
polymers such as polyvinylchloride or polyvinylidene-chloride, and
pulverized products of thus obtained carbonaceous particulates are
preferably used.
In order to obtain a high electroviscous effect with less
electric power consumption, those carbonaceous particulates having
a high aromatic spin radical concentration of 1018/g or more and a
high volume resistivity of 105n cm or more are preferable.
From this standpoint, the carbonaceous particulates obtained
by heat treatment of coal tar pitch to produce optically
anisotropic spherules (mesophase spherules) followed by removing
pitch component therefrom are most preferable among the above
mentioned carbonaceous particulates.
An outlined process for preparing such carbonaceous
particulates from coal tar pitch is described hereunder. Coal tar
pitch is heat-treated at 350-500C to allow optically anisotropic
spherules of spherical shape (mesophase spherules) come to grow [J.
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--D. Brooks and G. H. Taylor; Carbon 3, 185 (1965)] . Since the size
of mesophase spherule depends on the heating temperature and length
of heating time, terminate the heating at a stage when the
mesophase spherule grow to a size desired. The mesophase spherule
is separated therefrom by dissolving remained coal tar pitch with a
solvent and filtering off.
The mesophase spherule has a structure similar to liquid
crystal, and is a spherical carbonaceous particulate. A part of
coal tar pitch component (e.g. ,B-resin), which vaporized at the
temperature of 400-600C in an inert gas, tends to remain on the
surface of mesophase spherule when it is separated as described in
(Japanese Patent Provisional Publication Tokkaisho 60-25364), but
the pitch component can be removed, if necessary, by heat-treating
it at 200-600C under an inert gas atmosphere, which improves the
electric resistance and aromatic spin radical concentration of the
mesophase spherule.
The particle size of mesophase spherule is controlled by
adjusting the length of heating time and heating temperature of the
coal tar pitch, and the size can be reduced by pulverization.
2 0 As to the raw material other than coal tar pitch, petroleum
pitches having similar structures can be treated in the same manner
to produce carbonaceous particulates suitable for usage in the
present invention.
The water content in those carbonaceous particulates are less
than 1% by weight and gives no influence to the electroviscous
effect. It is supposed that the high aromatic spin radical
concentration of the carbonaceous particulates induces interfacial
200Q322
polarization of the particulates to give the electroviscous effect.
Accordingly, using such carbonaceous particulates as the dispersed
phase, an electroviscous fluid exhibiting a high electroviscous
effect in a wide temperature range for a long period time can be
obtained.
As the above mentioned carbonaceous particulates composed of
mesophase spherule have an optical anisotropy, they show anisotropy
in the electric conductivity too and supposed to be the reason that
the electroviscous fluid using such carbonaceous particulates as
the dispersed phase show a low electric power consumption.
The C/H ratio of the carbonaceous particulates varies in
accordance with the heat treating temperature and the electric
conductivity of the particulates varies accordingly. With the
increase of the C/H ratio, the electroviscous effect increases
together with the electric power consumption. Therefore, it is
necessary to set the value of electric resistance of the
carbonaceous particulates to give a proper balance of the
electroviscous effect and the electric power consumption. From
this standpoint, the most preferable value of the volume
resistivity of the carbonaceous particulates is in the range of
107-1olOQ.Cm
Further, it has been found that it is effective to coat the
surface of the above mentioned carbonaceous particulates with an
electric insulating thin layer partly or wholly in order to obtain
a high level electroviscous effect with less electric power
consumption.
As the electric insulating thin layer, it is desirable to form
200Q322
-~a thin layer of organic or inorganic insulating material on the
surface of the carbonaceous particulates with a thickness of less
than one tenth of the diameter of the particulate.
The most preferable thickness of the thin layer is decided
depending on the electric conductivity of the carbonaceous
particulate. When the electric conductivity of the carbonaceous
particulate is comparatively higher, a comparatively thicker layer
is recommended. On the contrary, when the electric conductivity of
the carbonaceous particulate is comparatively lower, a
comparatively thinner layer is recommended in order to maintain a
high level electroviscous effect with less electric power
consumption.
Such electric insulating thin layer can be formed on the
surface of the carbonaceous particulates with methods such as;
coating of a solution of high molecular weight compound on the
particulates; the hybridization method wherein micro particles of
electric insulating material are mixed with the carbonaceous
particulates by dry method and melted on the surface of the
carbonaceous particulates; surface treatments of the carbonaceous
particulates such as the silane treatment; vacuum deposition by
sputtering; polymerization of monomer on the surface of the
carbonaceous particulates.
The preferable value of the volume resistivity of the electric
insulating layer is 101Q cm or more.
As to the electric insulating material, synthetic high
molecular weight materials such as polymethylmethacrylate,
polystyrene, polyvinylacetate, polyvinylchloride,
2QOQ3Z2
~~polyvinylidenefluoride, epoxy resin, phenol resin, melamine resin;
silane coupling agents such as methyltrimethoxysilane,
phenyltrimethoxysilane, hexamethyldisilazane,
trimethylchlorosilane; modified silicone oils having a main chain
of dimethylpolysiloxane or phenylmethylpolysiloxane structure and
carboxyl group or hydroxyl group; and inorganic compounds such as
silica, alumina, rutile are mentioned.
By the use of such carbonaceous particulates coated with
electric insulating thin layer as the dispersed phase, an
electroviscous fluid having a high electroviscous effect with less
electric power consumption can be obtained.
The particle size suitable for the dispersed phase of the
electroviscous fluid is in the range of 0.01-100 micrometer,
preferably in the range of 0.1-20 micrometer, and more preferably
in the range of 0.5-5 micrometer. When the size is smaller than
0.01 micrometer, initial viscosity of the fluid under no imposition
of electric field becomes extremely large and the change in
viscosity due to the electroviscous effect is small. When the size
is over 100 micrometer, the dispersed phase can not be held
sufficiently stable in the liquid.
As the electric insulating oil to constitute the liquid phase
of an electroviscous fluid, oils having a volume resistivity of
lO11Q cm or more, especially having a volume resistivity of
1013Q cm or more are preferable. For example, hydrocarbon oils,
ester oils, aromatic oils, halogenated hydrocarbon oils such as
perfluoropolyether and polytrifluoromonochloroethylene, phosphazene
oils and silicone oils are mentioned. They may be used alone or in
ZQOC~3Z2
~a combination of more than two kinds. Among these oils, such
silicone oils as polydimethylsiloxane, polymethylphenylsiloxane and
polymethyltrifluropropylsiloxane are preferred, since they can be
used in direct contact with materials such as rubber and various
kinds of polymers.
The desirable viscosity of the insulating oil is in the range
of 0.65-500 centistokes (cSt) at 25C, preferably in the range of
5-200 cSt, and more preferably in the range of 5-50 cSt. When the
viscosity of the liquid phase is too small, stability of the liquid
phase becomes inferior due to an increased content of volatile
matters, and a too high viscosity of the liquid brings about an
heightened initial viscosity under no imposition of electric field
to result in a decreased changing range of viscosity by the
electroviscous effect. When an electric insulating oil having an
appropriate low viscosity is employed as the liquid phase, the
liquid phase can suspend a dispersed phase efficiently.
With regard to the ratio of the dispersed phase to the liquid
phase constituting the electroviscous fluid according to the
present invention, the content of the dispersed phase composed of
the aforementioned carbonaceous particulates is 1-60% by weight,
preferably 20-50% by weight, and the content of the liquid phase
composed of the aforementioned electrical insulating oils is 99-40%
by weight, preferably 80-50% by weight. When the dispersed phase
is less than 1% by weight, the electroviscous effect is too small,
and when the content is over 60% an extremely large initial
viscosity under no imposition of electric field appears.
It may be possible to incorporate or compound water and other
2QOQ322
- _ additives including surface active agents, dispersing agents,
antioxidant and stabilizing agent into the electroviscous fluid of
the present invention being within a range not deteriorating the
effects of the present invention.
Embodiments of the present invention will be illustrated
with reference to the following non-limiting Examples.
Example 1
A coal tar pitch was heat treated at 450C in an inert gas
(nitrogen) to make grow mesophase spherule in it, then the
remaining pitch component was removed by repeated extractions with
a tar middle oil and filtrations. Then the filter cake was
calcined at 350C in an inert gas (nitrogen) to obtain carbonaceous
particulates composed of mesophase spherule. The assay was carbon
content: 93.78% by weight, C/H ratio: 2.35, electric resistance
1.79 x 109 Q cm, electron spin concentration: 3.28 x 1019/9, and
water content: 0.4% by weight. The carbonaceous particulates were
sieved to obtain particulates having an average particle size of 14
micrometer. The carbonaceous particulates being 4096 by weight were
dispersed in a liquid phase component being 609~ by weight of a
silicone oil (Toshiba-Silicone co.: TSF 451-20 ~) having 20 cSt
viscosity at 25C to prepare an electroviscous fluid in a
suspension form.
Example 2
Carbonaceous particulates composed of mesophase spherule were
prepared by the same method with that of Example 1 except that the
calcination was done at 450C. Characteristics of the particulates
are shown in Table 1. The carbonaceous particulates were sieved to
l3
2QOQ32Z
- obtain particulates having an average particle size of 16
micrometer. The carbonaceous particulates being 40% by weight were
dispersed in a liquid phase component being 60% by weight of a
silicone oil (Toshiba-Silicone co.: TSF 451-20 ~) having 20 cSt
5 viscosity at 25C to prepare an electroviscous fluid in a
suspension form.
Example 3
Carbonaceous particulates composed of mesophase spherule
prepared by the same method with that of Example 2 were pulverized
10 with a jet mill and sieved to obtain carbonaceous particulates
having an average particle size of 4 micrometer. The carbonaceous
particulates being 40% by weight were dispersed in a liquid phase
component being 60% by weight of a silicone oil (Toshiba-Silicone
co.:TSF 451-20 ~) having 20 cSt viscosity at 25C to prepare an
15 electroviscous fluid in a suspension form.
Example 4
Carbonaceous particulates composed of mesophase spherule were
prepared by the same method with that of Example 1 except that the
calcination was done at 200C. Characteristics of the particulates
20 are shown in Table 1. Using the particulates, an electroviscous
fluid in a suspension form was prepared in the same manner as that
of Example 1.
Example 5
Carbonaceous particulates composed of mesophase spherule were
25 prepared by the same method with that of Example 1 except that the
calcination was done at 500C. Characteristics of the particulates
are shown in Table 1. Using the particulates, an electroviscous
14
2QOQ322
fluid in a suspension form was prepared in the same manner as that
of Example 1.
Example 6
Carbonaceous particulates composed of mesophase spherule were
prepared by the same method with that of Example 1 except that the
calcination was done at 600C. Characteristics of the particulates
are shown in Table 1. Using the particulates, an electroviscous
fluid in a suspension form was prepared in the same manner as that
of Example 1.
Example 7
The same carbonaceous particulates as used in Example 2 were
treated with xylene solution of phenyltrimethoxysilane under reflux
at 80C for 6 hours, then sieved to obtain surface-coated
particulates. The surface-coated carbonaceous particulates being
40% by weight were dispersed in a liquid phase component being 60%
by weight of a silicone oil (Toshiba-Silicone co.:TSF 451-20 ~)
having 20 cSt viscosity at 25C to prepare an electroviscous fluid
in a suspension form.
Example 8
The same carbonaceous particulates as used in Example 2 were
treated with xylene solution of methyltrimethoxysilane under reflux
at 80C for 6 hours, then sieved to obtain surface-coated
particulates. The surface-coated carbonaceous particulates being
40% by weight were dispersed in a liquid phase component being 60%
by weight of a silicone oil (Toshiba-Silicone co.: TSF 451-20 ~)
having 20 cSt viscosity at 25C to prepare an electroviscous fluid
in a suspension form.
- 2Q00322
Example 9
Commercially available microbeads of phenolic resin were
calcined at 600C in nitrogen gas to obtain carbonaceous
particulates having an average particle size of 8 micrometer.
Characteristics of the particulates are shown in Table l. Using
the particulates, an electroviscous fluid in a suspension form was
prepared in the same manner as that of Example l.
Example lO
40% by weight of the same carbonaceous particulates as used in
Example 2 were dispersed in a liquid phase component composed of
40% by weight of polytrifluoro-monochloroethylene having lO cSt
viscosity at 25C and 20% by weight of naphthenic hydrocarbon oil
having 5.2 cSt viscosity at 25C to prepare an electroviscous fluid
ln a suspenslon form.
Comparative Example l
40% by weight of commercially available sodium polyacrylate
powder was dispersed in 60% by weight of the silicone oil as used
in Example l to prepare an electroviscous fluid. Characteristics
of the sodium polyacrylate powder are shown in Table l.
Comparative Example 2
13% by weight of a fine powder of silica-gel ~Nippon Silica
Co.: NIPSIL VN-3 ~) was dispersed in 87% by weight of the silicone
oil as used in Example l to prepare an electroviscous fluid.
Characteristics of the silica-gel are shown in Table l.
In Table l, the carbon content (weight percent) and the C/H
ratio (the atomic ratio of carbon to hydrogen) were obtained from
elemental analysis. The concentration of aromatic radical are
16
ZQ00322
~~represented by the electron spin concentration. The electron spin
concentration was measured by comparing the peak strength at half
band width of under 1 mT with a known concentration standard, using
ESR (electron spin resonance) apparatus in conditions of magnetic
flux density at center part: 331 mT (millitesra), frequency of
microwave: 9.233 GHz (gigahertz). The electric resistance was
measured for pressure compacted powder. The water content was
measured from volatile loss at 250C by Karl-Fisher method.
Table 1
Carbon C/H Electron Volume Water Particle
content ratio Spin conc. resistivity content size
wt.% /9 Q cm wt.%
Example 1 93.78 2.35 3.28xlO191.79xlO9 0.4 14
Example 2 93.4 2.44 4.36xlO194.73x108 0.3 16
Example 4 92.3 1.59 2.39xlO197.34xlO9 0.4 19
Example 5 94.1 2.54 7.12xlO196.55x107 0.5 16
Example 6 94.4 3.10 3.93xlO194.50x105 0.8 19
Example 9 91.4 2.70 0.63xlO197.50x108 0.9 8
Comp.Ex.1 - - trace 3.22xlO9 9.5 10
Comp.Ex.2 - - not 4 2x106 6.7 0 016
detected
Each of the electroviscous fluids prepared in Examples 1-10
~000322
~and Comparative Examples l-2 were subjected to measurements of the
electroviscous effect. The electroviscous effect was measured with
a double-cylinder type rotary viscometer to which a direct current
was applied with an electric potential difference between the outer
and inner cylinder, and the effect was evaluated with shearing
force under the same shearing speed (375 sec~l) at 25 or 80C,
together with measurement of electric current density between the
inner and outer cylinders. (radius of inner cylinder: 34mm, radius
of outer cylinder: 36mm, height of inner cylinder: 20mm)
In Table 2, To is the shearing force under no application of
electric potential difference, T is the shearing force under
application of electric potential difference of 2 KV/mm, T-To is
the difference of T and To and the current density is the value
under application of electric potential difference of 2KV/mm.
The value of T-To indicates the magnitude of electroviscous
effect of the fluid. That is, a fluid showing a large T-To in
Table 2 exhibits an enhanced electroviscous effect. And the value
of the current density (~A/cm2) concerns an electric power required
to apply the electric potential difference (2KV/mm).
Z5
18
2C~00322
Table 2
25C 80C
Current Current
To T T-To Density To T T-To Density
g cm g cm g cm ~A/cm2 g cm g cm g cm ~A/cm2
Example 185 621 53610.00 53534 48120.00
Example 267 699 63249.90 441017 973110.00
Example 3154913 75920.40
Example 475 292 2173.20 49339 2909.30
Example 576 946 870130.30
Example 6761050 9744183.70
Example 780 698 61826.10
Example 895 999 9041074.80
Example 981 205 1240.90
Example 10110985 87529.70
Comp.Ex.1169402 2330.30 79825 746266.00
Comp.Ex.2250403 1537.90
It is noticeable that the electroviscous fluids of the
Examples 1, 2 and 4 using carbonaceous particulates with little
19
;~QOC~3Z2
- water content show enough electroviscous effect under a high
temperature condition (80C) with a small increase of electric
current compared to the case under normal temperature (25C),
whereas the Comparative Example l using particulates with high
water content shcws a tremendous increase of electric current under
a high temperature condition (80C) compared to the case under
normal temperature (25C). Especially, Example 2 shcws a higher
electroviscous effect with a smaller electric current compared to
the Comparative Example l at 80C.
Viewing the data at 25C, the Example 7 using surface coated
carbonaceous particulates shcw~ the same electroviscous effect with
about a half of electric current compared to the Example 2 using
the same carbonaceous particulates without surface coating. In the
same manner, the Example 8 using surface coated carbonaceous
particulates shows about the same electroviscous effect with one
forth of electric current compared wlth the Example 6 using the same
carbonaceous particulates without surface coating.
The carbonaceous particulates obtained by calcination of a
thermosetting resin used in the Example 9 showed the electroviscous
effect in the same manner as the carbonaceous mesophase spherules,
thus indicating the characteristics of nonaqueous system having a
high electron spin concentration.
On the contrary, the silica used in the Comparative Example 2
showed no electron spin concentration as can be seen in Table l,
thus proving that the electroviscous fluid of the Comparative
Example 2 is an aqueous system electroviscous fluid, though it
showed the electroviscous effect as can be seen in Table 2.
~(~00322
When an alternating current with electric potential difference
of 2 KV/mm was applied to the electroviscous fluid of the Example
1, the value of T at 25C was 522 g-cm and the current density was
66 ~A/cm2. The results indicate that the electroviscous fluid
using the carbonaceous particulate as the dispersed phase can act
with alternating current, though the electroviscous effect
therefrom was a little smaller than the case applying the direct
current.
Fig.1 is a graph showing the relationship between the
magnitude of electric field (abscissa: KV/mm) and torque (ordinate:
g cm) for the electroviscous fluid of Example 1 before (o mark) and
after (~ mark) subjecting it to a high temperature heat-treatment
at 150C for 50 hours. Fig.2 is a graph showing the result of the
same measurement for the electroviscous fluid of Comparative
Example 1.
As can be seen from Fig.1, the electroviscous fluid of Example
1 shows no change for the electroviscous effect even after a
continuous high temperature treatment. Whereas the electroviscous
fluid of Comparative Example 1 show a decrease in the
electroviscous effect after the high temperature treatment as can
be seen in Fig.2.
Fig.3 is a graph showing the relationship between the
temperature (abscissa: C) and torque (ordinate: g cm) for the
electroviscous fluid of Example 2 when an electric potential
difference o~ 1.5 KV/mm was applied (o mark) and with no
application of the electric potential difference (~ mark). Fig.4
is a graph showing the result of the same measurement for the
21
2QOC~3Z2
~electroviscous fluid of Comparative Example 1.
As can be seen from Fig.3, the electroviscous fluid of Example
2 can be used from -50C to 200C. Whereas the electroviscous
fluid of Comparative Example 1 shows no electroviscous effect under
0C as can be seen in Fig.4, and the electroviscous effect over
90C could not be measured because of the need for too much
electric current.
