U.S. patent application number 13/201508 was filed with the patent office on 2011-12-08 for dielectric film, process for producing same, and transducer using same.
This patent application is currently assigned to TOKAI RUBBER INDUSTRIES, LTD.. Invention is credited to Shinji Iio, Jun Kobayashi, Yota Kokubo, Shigeaki Takamatsu, Shunsuke Taniguchi, Hitoshi Yoshikawa.
Application Number | 20110300393 13/201508 |
Document ID | / |
Family ID | 43758564 |
Filed Date | 2011-12-08 |
United States Patent
Application |
20110300393 |
Kind Code |
A1 |
Iio; Shinji ; et
al. |
December 8, 2011 |
DIELECTRIC FILM, PROCESS FOR PRODUCING SAME, AND TRANSDUCER USING
SAME
Abstract
A dielectric film which has high electrical resistance and
excellent durability and a process for producing the dielectric
film are provided. Also provided is a transducer which has large
displacement and excellent durability. The dielectric film includes
a three-dimensional crosslinked body that is synthesized from an
organic metal compound, a rubber polymer that is other than a
polydimethyl siloxane and has a functional group that is reactive
with the organic metal compound, and an inorganic filler that has a
functional group that is reactive with the organic metal compound.
The transducer is configured by interposing the dielectric film
between at least a pair of electrodes. The dielectric film may be
produced by preparing a first solution that contains a rubber
polymer and an inorganic filler in a solvent that is capable of
dissolving the rubber polymer and of chelating an organic metal
compound, then preparing a second solution by mixing the organic
metal compound into the first solution, and then removing the
solvent from the second solution to allow a crosslinking reaction
to proceed.
Inventors: |
Iio; Shinji; ( Aichi-ken,
JP) ; Takamatsu; Shigeaki; (Aichi-ken, JP) ;
Taniguchi; Shunsuke; (Aichi-ken, JP) ; Kokubo;
Yota; (Aichi-ken, JP) ; Yoshikawa; Hitoshi;
(Aichi-ken, JP) ; Kobayashi; Jun; (Aichi-ken,
JP) |
Assignee: |
TOKAI RUBBER INDUSTRIES,
LTD.
Aichi-ken
JP
|
Family ID: |
43758564 |
Appl. No.: |
13/201508 |
Filed: |
September 6, 2010 |
PCT Filed: |
September 6, 2010 |
PCT NO: |
PCT/JP2010/065200 |
371 Date: |
August 15, 2011 |
Current U.S.
Class: |
428/521 ;
524/566 |
Current CPC
Class: |
C08K 3/36 20130101; H02N
1/08 20130101; Y10T 428/31931 20150401; C08J 2313/00 20130101; H01L
41/183 20130101; C08J 3/20 20130101; C08K 5/098 20130101; C08J 3/24
20130101; C08K 5/0091 20130101; H04R 7/02 20130101; C08K 3/36
20130101; H04R 2307/027 20130101; H01L 41/37 20130101; H02N 1/006
20130101; C08L 13/00 20130101; C08K 5/098 20130101; C08L 21/00
20130101; H04R 2307/025 20130101 |
Class at
Publication: |
428/521 ;
524/566 |
International
Class: |
B32B 27/28 20060101
B32B027/28; C08L 9/02 20060101 C08L009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2009 |
JP |
2009-217208 |
Mar 19, 2010 |
JP |
2010-064002 |
Claims
1. A dielectric film that is to be interposed between at least a
pair of electrodes of a transducer, characterized by comprising a
three-dimensional crosslinked body that is synthesized from: an
organic metal compound, a rubber polymer that is other than a
polydimethyl siloxane and has a functional group that is reactive
with the organic metal compound, and an inorganic filler that has a
functional group that is reactive with the organic metal
compound.
2. The dielectric film according to claim 1, wherein the organic
metal compound is at least one compound selected from the group
consisting of metal alkoxide compounds, metal acylate compounds and
metal chelate compounds.
3. The dielectric film according to claim 1, wherein the inorganic
filler is silica.
4. The dielectric film according to claim 3, wherein the silica has
a pH of 8.5 or less.
5. The dielectric film according to claim 1, wherein the functional
group of the rubber polymer is at least one group selected from the
group consisting of a carboxyl group, a hydroxyl group, an amino
group, an amide, an epoxy group, a thiol and an ester.
6. The dielectric film according to claim 1, wherein the rubber
polymer is at least one polymer selected from the group consisting
of acrylonitrile-butadiene copolymers, hydrogenated nitrile
rubbers, acrylic rubbers, urethane rubbers, fluorine rubbers,
fluorosilicone rubbers, chlorosulfonated polyethylene rubbers,
chloroprene rubbers, ethylene-vinyl acetate copolymers and
chlorinated polyethylenes.
7. The dielectric film according to claim 1, wherein the organic
metal compound contains at least one element selected from the
group consisting of titanium, zirconium, aluminum, silicon, boron,
vanadium, manganese, iron, cobalt, germanium, yttrium, niobium,
lanthanum, cerium, tantalum, tungsten and magnesium.
8. The dielectric film according to claim 1, wherein the
three-dimensional crosslinked body is synthesized from a
composition that includes a plasticizer in addition to the organic
metal compound, the rubber polymer and the inorganic filler.
9. A process for producing a dielectric film as recited in claim 1,
comprising: a first solution preparing step that prepares a first
solution that contains the rubber polymer, the inorganic filler
and, optionally the plasticizer in a solvent that is capable of
dissolving the rubber polymer and of chelating the organic metal
compound, a second solution preparing step that prepares a second
solution by mixing the organic metal compound into the first
solution, and a crosslinking step that removes the solvent from the
second solution to allow a crosslinking reaction to proceed.
10. A transducer characterized by comprising a dielectric film as
recited in claim 1, and a plurality of electrodes that are arranged
via the dielectric film.
Description
TECHNICAL FIELD
[0001] The present invention relates to a dielectric film that is
suited for use in transducers such as actuators and sensors, to a
process for producing the same, and to a transducer using the
same.
BACKGROUND ART
[0002] Transducers can be actuators, sensors, electric power
generation elements, etc. that perform conversion between
mechanical energy and electrical energy. Alternatively, transducers
can be speakers, microphones, etc. that perform conversion between
acoustic energy and electrical energy. Polymer materials such as
dielectric elastomers are useful for configuring transducers that
are high in flexibility, small in size and light in weight.
[0003] An actuator may be configured by, for example, arranging a
pair of electrodes on both thickness direction sides of a
dielectric film that is formed of a dielectric elastomer. In an
actuator of this type, electrostatic attractive force between the
electrodes increases with an increase of the voltage that is
applied between the electrodes, so that the dielectric film that is
sandwiched between the electrodes is compressed in the thickness
direction and the thickness thereof is reduced. As a result of the
reduction of the film thickness, the dielectric film
correspondingly expands in the direction parallel with the
electrode plane. When the voltage that is applied between the
electrodes is reduced, on the other hand, electrostatic attractive
force decreases so that the compressive force that is acted on the
dielectric film in the thickness direction is reduced and the
thickness thereof increases as a result of the elastic restoring
force thereof. As a result of the increase of the film thickness,
the dielectric film correspondingly contracts in the direction
parallel with the electrode plane. Thus, the actuator can drive an
object to be driven by the expansion and contraction of the
dielectric film. As the dielectric film material, silicone rubbers,
acrylic rubbers, nitrile rubbers, urethane rubbers, etc. are used
(see, for example, Patent Documents 1 and 2).
PRIOR ART DOCUMENTS
Patent Documents
[0004] [Patent Document 1] Published Japanese Translation of PCT
application 2003-505865 [Patent Document 2] Published Japanese
Translation of PCT application 2001-524278
[Patent Document 3] Japanese Patent No. 3295023
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0005] Since a silicone rubber, for example, has a skeletal
structure that is composed of siloxane bonds, the electric
resistance thereof is high. For this reason, a dielectric film made
of such a silicone rubber hardly undergoes dielectric breakdown
even when a high voltage is applied thereto. A
polydimethylsiloxane-based silicone rubber, on the other hand, has
low polarity, namely has a small dielectric constant. Therefore,
when an actuator is configured using a dielectric film that is
composed of such a polydimethylsiloxane-based silicone rubber, the
electrostatic attractive force for an applied voltage is so small
that sufficient force and displacement are not obtainable.
[0006] On the other hand, when an actuator is configured using a
dielectric film that has a large dielectric constant, it is
possible to store a large amount of charges in a boundary between
the dielectric film and each electrode. It follows that the
electrostatic attractive force for an applied voltage is large. For
example, known acrylic rubber and nitrile rubber have a larger
dielectric constant than silicone rubber and, therefore, are suited
as a dielectric film. However, the electric resistance of acrylic
rubber, etc. is smaller than that of silicone rubber. Therefore,
when acrylic rubber or the like rubber is used as a dielectric
film, a current unavoidably flows through the dielectric film when
an applied voltage is high. Hence, charges are not sufficiently
accumulated in the film. Thus, in spite of the fact that acrylic
rubber or the like rubber has a large dielectric constant, the
electrostatic attractive force decreases so that it is impossible
to obtain a sufficient force and displacement. Further, when a
current flows through the dielectric film, there is a possibility
that the dielectric film is broken down due to the generated Joule
heat. Furthermore, there arises an additional problem that the
dielectric film undergoes dielectric breakdown due to its small
electric resistance.
[0007] The present invention has been made in view of the foregoing
circumstances and is aimed at the provision of a dielectric film
that has a large electric resistance and is excellent in durability
and of a method for producing the same. It is also an object of the
present invention to provide a transducer that uses such a
dielectric film and that has large displacement and excellent
durability.
Means for Solving the Problem
[0008] (1) A dielectric film according to the present invention is
a dielectric film that is to be interposed between at least a pair
of electrodes of a transducer. The dielectric film is characterized
by including a three-dimensional crosslinked body that is
synthesized from an organic metal compound, a rubber polymer which
is other than a polydimethyl siloxane and has a functional group
which is reactive with the organic metal compound, and an inorganic
filler which has a functional group that is reactive with the
organic metal compound.
[0009] The above-mentioned Patent Document 3 discloses a ceramic
composite rubber in which a rubber polymer and an organic metal
compound that has an organic functional group which is reactive
with the rubber polymer are chemically bonded to each other. The
ceramic composite rubber does not contain an inorganic filler that
is capable of forming a three-dimensional crosslinked body. Namely,
in the ceramic composite rubber, a metal oxide that is produced by
hydrolysis of an unreacted organic metal compound is merely
dispersed in the rubber.
[0010] In contrast to this, the three-dimensional crosslinked body
of the present invention contains an inorganic filler. Further,
each of the rubber polymer and inorganic filler has a functional
group that is capable of reacting with the organic metal compound.
Therefore, during synthesis of the three-dimensional crosslinked
body, reactions occur between the rubber polymer and the organic
metal compound and between the inorganic filler and the organic
metal compound, so that they are chemically bonded to each other.
Thus, the three-dimensional crosslinked body of the present
invention has such a structure in which the rubber polymer is
crosslinked with the organic metal compound and the inorganic
filler is incorporated in the thus formed crosslinkage.
[0011] In the three-dimensional crosslinked body of the present
invention, flow of electrons is interrupted by the inorganic filler
as well as by the metal oxide that is derived from the organic
metal compound. Accordingly, the electric resistance of the
three-dimensional crosslinked body is high. Namely, the electric
resistance of the dielectric film of the present invention is high.
Therefore, when a voltage is applied between a pair of electrodes
between which the dielectric film of the present invention is
interposed, an electric current does not easily flow through the
dielectric film. For this reason, a large amount of charges can be
stored in the dielectric film. As a consequence, electrostatic
attractive force increases so that large force and displacement are
obtainable in, for example, an actuator.
[0012] In addition, because an electric current does not easily
flow through the dielectric film, generation of Joule heat is
suppressed. For this reason, there is low possibility that the
dielectric film of the present invention is thermally broken down.
Additionally, the dielectric film of the present invention, which
has a high electric resistance, does not easily undergo insulation
breakdown. Thus, the dielectric film of the present invention has
excellent durability. Moreover, it is possible to apply a higher
voltage to the dielectric film of the present invention. Therefore,
with the dielectric film of the present invention, large force and
displacement are obtainable in, for example, an actuator.
[0013] The dielectric film of the present invention uses a rubber
polymer that is other than polydimethylsiloxane. Namely, the film
uses a rubber polymer that has higher polarity, in other words, a
larger dielectric constant, than that of the conventionally
employed polydimethylsiloxane-type silicone rubber. Therefore, with
the dielectric film of the present invention, large electrostatic
attractive force is generated even when an applied voltage is
relatively low. As a consequence, a desired force and displacement
are obtainable in, for example, an actuator that uses the
dielectric film of the present invention.
[0014] (2) A process for producing a dielectric film according to
the present invention, the process being suited for the production
of the above-described dielectric film according to the present
invention, includes a first solution preparing step that prepares a
first solution that contains the rubber polymer, the inorganic
filler and, optionally the plasticizer in a solvent that is capable
of dissolving the rubber polymer and of chelating the organic metal
compound, a second solution preparing step that prepares a second
solution by mixing the organic metal compound into the first
solution, and a crosslinking step that removes the solvent from the
second solution to allow a crosslinking reaction to proceed.
[0015] The organic metal compound hydrolyzes by reaction with water
and is polycondensed by dehydration or dealcoholation (sol-gel
reaction) to form a three-dimensional crosslinked body. The organic
metal compound is generally highly reactive with water and
difficult to handle. In the production process according to the
present invention, it is possible, by chelating the organic metal
compound, to suppress abrupt reaction thereof with water. Namely,
in the production process of the present invention, the solvent not
only can dissolve the rubber polymer and disperse the inorganic
filler but also serves to act as a chelating agent.
[0016] In the second solution preparing step, when the organic
metal compound is mixed into the first solution, in which the
rubber polymer is dissolved and the inorganic filler is dispersed,
the organic metal compound in the solution is chelated. Thus, the
hydrolysis of the organic metal compound is suppressed. In the
succeeding crosslinking step, the solvent is removed. Namely, the
chelating agent is removed. As a result, the dealcoholation of the
organic metal compound is accelerated so that the crosslinking by
polycondensation proceeds.
[0017] Thus, with the production process of the present invention,
the reaction speed of the organic metal compound can be lowered.
Therefore, it is possible to obtain a homogeneous dielectric film.
Further, since the solvent serves to function both as a solvent for
dissolving the rubber polymer and dispersing the inorganic filler
and as a chelating agent, it is not necessary to separately prepare
a solvent and a chelating agent. Therefore, the production step is
simplified and is practical. In the first solution preparing step,
a first solution, in which the rubber polymer is dissolved and the
inorganic filler is dispersed, is previously prepared.
Consequently, the dispersibility of the inorganic filler in the
second solution is improved so that a homogeneous dielectric film
is obtainable. Incidentally, a plasticizer may be mixed as needed.
Namely, the plasticizer may be or may not be contained in the first
solution.
[0018] (3) A transducer of the present invention is characterized
by including the above-described dielectric film according to the
present invention, and a plurality of electrodes that are arranged
via the dielectric film
[0019] The transducer of the present invention includes the
above-described dielectric film of the present invention. As
described previously, the dielectric film of the present invention
has a high electric resistance and, therefore, can store a large
amount of charges. For this reason, when the transducer of the
present invention is used, for example, as an actuator, large force
and displacement can be obtained. Further, there is low possibility
that the dielectric film of the present invention is thermally
broken down. Additionally, the dielectric film does not easily
undergo insulation breakdown. Thus, the dielectric film of the
present invention has excellent durability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is schematic cross-sectional view of an actuator
which is a first embodiment of a transducer according to the
present invention, wherein (a) shows an OFF state and (b) shows an
ON state.
[0021] FIG. 2 is schematic cross-sectional view of a capacitive
sensor which is a second embodiment of a transducer according to
the present invention.
[0022] FIG. 3 is schematic cross-sectional view of an electric
power generation element which is a third embodiment of a
transducer according to the present invention, wherein (a) shows an
expanded state and (b) shows a contracted state.
[0023] FIG. 4 is a front view of an actuator that is mounted on an
experimental device.
[0024] FIG. 5 is a V-V cross-sectional view of FIG. 4.
DESCRIPTION OF THE REFERENCE NUMERALS
[0025] 1: actuator (transducer), 10: dielectric film, 11a, 11b:
electrodes, 12: power source; [0026] 2: capacitive sensor
(transducer), 20: dielectric film, 21a, 21b: electrodes, 22:
substrate; [0027] 3: electric power generation element
(transducer), 30: dielectric film, 31a, 31b: electrodes; [0028] 5:
actuator, 50: dielectric film, 51a, 51b: electrodes; 52: upper
chuck, 53: lower chuck
DESCRIPTION OF EMBODIMENTS
[0029] Embodiments of the dielectric film, production process
thereof and transducer according to the present invention will be
described below. It should be noted that the dielectric film,
production process thereof and transducer according to the present
invention are not limited to the following specific embodiments but
may be embodied in various forms that can be modified or improved
by those skilled in the art without departing from the gist of the
present invention.
[0030] <Dielectric Film>
[0031] The dielectric film of the present invention includes a
three-dimensional crosslinked body that is synthesized from an
organic metal compound, a rubber polymer that has a functional
group which is reactive with the organic metal compound and which
is other than a polydimethyl siloxane, and an inorganic filler that
has a functional group which is reactive with the organic metal
compound.
[0032] (1) Organic Metal Compound
[0033] The kind of the organic metal compound is not specifically
limited. The organic metal compound may be liquid or solid.
Examples of the organic metal compound include metal alkoxide
compounds, metal acylate compounds and metal chelate compounds. One
compound that is selected from these compounds may be used singly.
Alternatively, two or more of these compounds may be used in
combination. It is desired that the organic metal compound contains
at least one element that is selected from the group consisting of
titanium, zirconium, aluminum, silicon, boron, vanadium, manganese,
iron, cobalt, germanium, yttrium, niobium, lanthanum, cerium,
tantalum, tungsten and magnesium.
[0034] The metal alkoxide compound is represented, for example, by
the following general formula (a):
M(OR).sub.m (a)
[In the formula (a), M represents an atom such as a metal, R
represents at least one of C.sub.1 to C.sub.10 alkyl groups, aryl
groups and alkenyl groups and may be the same or different, and m
is a valency of the atom M which is a metal or the like element].
The metal alkoxide compound may also be a polymer that has two or
more recurring units of [(MO).sub.n where n is an integer of 2 or
more] in the molecule thereof. By changing the number n, it is
possible to control compatibility with the rubber polymer, reaction
speed, etc. of the metal alkoxide compound. It is advisable,
therefore, to select a suitable polymer depending on the kind of
the rubber polymer.
[0035] Examples of the atom M such as a metal include titanium,
zirconium, aluminum, silicon, iron, copper, tin, barium, strontium,
hafnium and boron. Particularly, at least one atom that is selected
from titanium, zirconium and aluminum is preferably contained for
reasons of good reactivity. Specific examples of suitable metal
alkoxide include tetra-n-butoxy titanium, tetra-n-butoxy zirconium,
tetra-n-butoxy silane, acetoalkoxy aluminum diisopropylate,
tetra-1-propoxy titanium, tetraethoxy silane,
tetrakis(2-ethylhexyloxy) titanium and titanium butoxide dimer.
[0036] Examples of the metal acylate compound include polyhydroxy
titanium stearate and zirconium tributoxy monostearate.
[0037] Examples of the metal chelate compound include titanium
chelate compounds such as titanium
diisopropoxy-bis(acetylacetonate), titanium tetraacetylacetonate,
titanium dioctyloxy-bis(octylene glycolate), titanium
diisopropoxy-bis(ethylacetoacetate), titanium
diisopropoxy-bis(triethanolaminate) and titanium
dibutoxy-bis(triethanolaminate) and zirconium chelate compounds
such as zirconium tetraacetylacetonate, zirconium tributoxy
monoacetylacetonate, zirconium monobutoxy
acetylacetonate-bis(ethylacetoacetate) and zirconium
dibutoxy-bis(ethylacetoacetate).
[0038] (2) Rubber Polymer
[0039] The rubber polymer is other than polydimethylsiloxane and
has a functional group that is capable of reacting with the organic
metal compound. The rubber polymer may be liquid or solid. Examples
of the functional group that is capable of reacting with the
organic metal compound include a carboxyl group (--COOH), a
hydroxyl group (--OH), an amino group (--NH), an amide
(--CONR.sub.1R.sub.2), an epoxy group, a thiol (--SH) and an ester
(R.sub.3C(.dbd.O)OR.sub.4). It is preferred that the rubber polymer
has one or more of these functional groups.
[0040] It is desirable to use a rubber polymer that has high
polarity, namely a high dielectric constant, from the standpoint of
obtaining large displacement using a small applied voltage. For
example, a rubber polymer that has a dielectric constant of 2.8 or
more (measuring frequency of 100 Hz) is preferable. Examples of the
rubber polymer that has a high dielectric constant include
acrylonitrile-butadiene copolymers (NBR), hydrogenated nitrile
rubbers (H-NBR), acrylic rubbers, urethane rubbers, fluorine
rubbers, fluorosilicone rubbers, chlorosulfonated polyethylene
rubbers, chloroprene rubbers, ethylene-vinyl acetate copolymers and
chlorinated polyethylenes. It is desired that these rubbers be used
singly or as a mixture of two or more thereof. It is also preferred
that the rubber polymer have an unsaturated main chain because of
its less tendency to cause insulation breakdown even when applied
with a high voltage and of its weatherability.
[0041] (3) Inorganic Filler
[0042] The inorganic filler has a functional group that is capable
of reacting with the organic metal compound. Examples of the
functional group that is capable of reacting with the organic metal
compound include a hydroxyl group (--OH), a carboxyl group
(--COOH), an amino group (--NH), an amide (--CONR.sub.1R.sub.2), an
epoxy group, a thiol (--SH) and an ester
(R.sub.3C(.dbd.O)OR.sub.4), which are similar to the case of the
rubber polymer. It is preferred that the inorganic filler have one
or more of these functional groups. The inorganic filler may be
subjected to a surface treatment to increase the number of the
functional groups. By so doing, the reactivity of the inorganic
filler with the metal alkoxide can be improved.
[0043] Examples of the inorganic filler include silica, titanium
oxide, barium titanate, calcium carbonate, clay and talc. In
particular, silica is preferably used because the number of its
functional groups is large and because it is relatively
inexpensive.
[0044] There is a possibility that ionic impurities that remain in
the inorganic filler may reduce the electric resistance of the
dielectric film. It is, therefore, desired that an inorganic filler
that has as small an amount of ionic impurities as possible is
used. For example, silica that has been produced by certain methods
may contain sodium that is derived from the raw material. When such
sodium remains present in a large amount, there is a possibility
that sodium ions cause a reduction of the electric resistance.
Here, the residual amount of sodium is related to the pH of silica.
Namely, the pH value tends to increase with an increase of the
residual amount of sodium. Therefore, when silica is used, it is
desirable to choose silica that has as low a pH value as possible.
For example, a pH value of 10.5 or less is suitable. The pH value
is desirably 8.5 or less, more desirably 6.5 or less. As used
herein, the term "pH value" is intended to mean a value that is
measured by the following method. Silica is first dispersed in
water to prepare a dispersion that has a silica concentration of 4%
by mass. After dispersion is sufficiently stirred, the pH value of
the dispersion is measured with a pH meter.
[0045] (4) Other Additives
[0046] In the production of the three-dimensional crosslinked body
of the present invention, a catalyst, a reinforcing agent, a
plasticizer, an age resister, a coloring agent, etc. may be mixed
therein in addition to the organic metal compound, rubber polymer
and inorganic filler. For example, addition of a plasticizer can
improve the flexibility of the produced three-dimensional
crosslinked body, namely the flexibility of the dielectric film of
the present invention. As a consequence, the dielectric film of the
present invention can be easily stretched. When the plasticizer is
incorporated into the film, it is possible to obtain larger force
and displacement in an actuator, for example.
[0047] From the standpoint of its less tendency to reduce the
electric resistance of the dielectric film, the plasticizer to be
mixed is preferably one which is highly insulative and is sparingly
volatile. Examples of suitable plasticizers include tricresyl
phosphate, tris(2-ethylhexyl) trimellitate, chlorinated paraffin,
tris(n-octyl) trimellitate, tris(isononyl) trimellitate,
tris(isodecyl) trimellitate, dipentaerythritol esters and octyl
esters of pyromellitic acid.
[0048] <Production Process for Dielectric Film>
[0049] The production process for the dielectric film of the
present invention is not specifically limited. The dielectric film
may be produced by, for example, the methods that are shown in (1)
and (2) below.
(1) In a first method, a rubber polymer, an inorganic filler and an
organic metal compound are kneaded with rolls or a kneader
(kneading step), and the kneaded product is formed into a thin film
under predetermined conditions (film forming step). (2) In a second
method, a first solution that includes a solvent in which a rubber
polymer and an inorganic filler are contained is first prepared
(first solution preparing step). Into the first solution, an
organic metal compound, either as such or as a solution in a
predetermined solvent, is mixed so as to prepare a second solution
(second solution preparing step). Thereafter, the second solution
is applied to a substrate and dried under predetermined conditions
(film forming step).
[0050] In the second method, the rubber polymer and inorganic
filler may be previously kneaded with rolls or a kneader, and the
resulting kneaded mixture is subsequently added to the solvent to
prepare the first solution. By previously kneading the rubber
polymer together with the inorganic filler, the dispersibility of
the inorganic filler is improved. Alternatively, the first solution
may be prepared by mixing a solution of the rubber polymer in a
solvent with a dispersion of the inorganic filler in a solvent.
[0051] When the organic metal compound in the form of a solution in
a predetermined solvent is mixed, this solvent may be the same as
or different from the solvent that is used in the preparation of
the first solution. In the first method, a catalyst, a reinforcing
agent, a plasticizer, an age resister, a coloring agent, etc. may
be added in the kneading step as needed. In the second method, a
catalyst, a reinforcing agent, a plasticizer, an age resister, a
coloring agent, etc. may be added in the first solution preparing
step and second solution preparing step, as needed.
[0052] A mixing amount of the organic metal compound is preferably
0.5 part by mass or more and 40 parts by mass or less per 100 parts
by mass of the rubber polymer. When the amount is less than 0.5
part by mass, crosslinking does not proceed sufficiently so that
the three-dimensional crosslinked body is not easily produced. The
mixing amount is preferably 1.5 parts by mass or more. When the
amount exceeds 40 parts by mass, on the other hand, crosslinking
excessively proceeds so that there is a possibility that the
dielectric film becomes hard and the flexibility thereof is
deteriorated. The mixing amount is preferably 30 parts by mass or
less.
[0053] A mixing amount of the inorganic filler is preferably 1 part
by mass or more and 40 parts by mass or less per 100 parts by mass
of the rubber polymer. When the amount is less than 1 part by mass,
flow of electrons cannot be sufficiently interrupted so that the
effect of increasing the electric resistance is small. The mixing
amount is preferably 5 parts by mass or more. When the amount
exceeds 40 parts by mass, on the other hand, there is a possibility
that the dielectric film becomes hard and the flexibility thereof
is deteriorated. The mixing amount is preferably 30 parts by mass
or less.
[0054] When the plasticizer is mixed, the mixing amount thereof is
preferably 1 part by mass or more and 200 parts by mass or less per
100 parts by mass of a total amount of the rubber polymer and the
organic metal compound. When the amount is less than 1 part by
mass, the effect of improving the flexibility is low. The mixing
amount is preferably 5 parts by mass or more. When the mixing
amount exceeds 200 parts by mass, on the other hand, there is a
possibility that the compatibility of the plasticizer with the
rubber component is deteriorated and bleeding occurs. The mixing
amount is preferably 150 parts by mass or less.
[0055] The organic metal compound reacts with water in the air or
in the reaction system (rubber polymer, solution) to undergo
hydrolysis and polycondensation (sol-gel reaction). It is,
therefore, desirable to use the organic metal compound in a
chelated form using a chelating agent in order to suppress abrupt
reaction with water and to form a homogeneous film. In particular,
a metal alkoxide compound has high reactivity and, hence, is
desired to be used in a chelated form. A metal acylate compound, on
the other hand, is not so reactive as compared with the metal
alkoxide compound and, therefore, the necessity for chelating is
low.
[0056] When the organic metal compound is used in a chelated form,
it is advisable to adopt, for example, the following method. A
first solution that includes a predetermined solvent in which the
rubber polymer and the inorganic filler are contained is first
prepared (first solution preparing step). Into the first solution,
an organic metal compound in a chelated form is mixed so as to
obtain a second solution (second solution preparing step).
Thereafter, the second solution is applied to a substrate and dried
under predetermined conditions to remove the chelating agent and to
allow a crosslinking reaction to proceed (crosslinking step). By
these steps, a dielectric film in the form of a thin film is
produced.
[0057] Examples of the chelating agent include .beta.-diketones
such as acetyl acetone, benzoyl acetone and dibenzoylmethane,
.beta.-keto acid esters such as ethyl acetoacetate and ethyl
benzoylacetate, triethanolamine, lactic acid, 2-etylhexane-1,3-diol
and 1,3-hexanediol. The chelating agent is desirably used in an
amount of 10 parts by mass or more and 100,000 parts by mass or
less per 100 parts by mass of the organic metal compound. When the
amount is less than 10 parts by mass, the organic metal compound
cannot be sufficiently chelated. The mixing amount is preferably 50
parts by mass or more. When the amount exceeds 100,000 parts by
mass, it becomes difficult to remove the chelating agent and,
therefore, the drying, for example, must be performed excessively.
The mixing amount is preferably 8,000 parts by mass or less.
[0058] When the rubber polymer is capable of being dissolved in the
chelating agent, it is possible to use the chelating agent as a
solvent for the rubber polymer. In this case, it is advisable to
adopt the following method, for example. A first solution that
contains the rubber polymer and the inorganic filler in a solvent
that is capable of dissolving the rubber polymer and of chelating
the organic metal compound is first prepared (first solution
preparing step). Then, the organic metal compound is mixed into the
first solution to prepare a second solution (second solution
preparing step). Thereafter, the solvent is removed from the second
solution to allow a crosslinking reaction to proceed (crosslinking
step).
[0059] The solvent may consist only of the chelating agent or may
be a mixture of the chelating agent and other solvent. In the
crosslinking step, it is only necessary to apply the second
solution to a substrate and dry it. By so doing, a dielectric film
in the form of a thin film may be produced. A temperature of the
crosslinking step may be appropriately determined according to the
type of solvent in consideration of the reaction speed, etc. For
example, room temperature may be employed. However, a temperature
that is not lower than the boiling point of the solvent may be
desirably used. When the organic metal compound in a chelated form
is used, a catalyst, a reinforcing agent, a plasticizer, an age
resister, a coloring agent, etc. may be added in the first solution
preparing step and second solution preparing step. In one specific
embodiment in which a plasticizer is used, the production process
for the dielectric film may include the following three steps. At
first, a first solution that contains the rubber polymer, the
inorganic filler and the plasticizer in a solvent that is capable
of dissolving the rubber polymer and of chelating the organic metal
compound is prepared (first solution preparing step). Then, the
organic metal compound is mixed into the first solution to prepare
a second solution (second solution preparing step). Thereafter, the
solvent is removed from the second solution to allow a crosslinking
reaction to proceed (crosslinking step).
[0060] <Transducer>
[0061] The transducer of the present invention includes the
dielectric film according to the present invention, and a plurality
of electrodes that are arranged via the dielectric film. The
constitution and process for production of the dielectric film of
the present invention are as described above and the description
thereof is omitted here. In the transducer of the present
invention, it is desired that the preferred embodiments of the
dielectric film of the present invention be also employed.
[0062] A thickness of the dielectric film may be appropriately
determined according to, for example, the intended use thereof. For
example, when the transducer of the preset invention is used as an
actuator, it is preferred that the thickness of the transducer be
thin from the standpoint of compactness of the actuator, capability
of driving at a low voltage, large displacement, etc. In this case,
also in consideration of insulation breakdown, it is desired that
the thickness of the dielectric film be 1 .mu.M or more and 1,000
.mu.M (1 mm) or less, more preferably 5 .mu.m or more and 200 .mu.m
or less.
[0063] In the transducer of the present invention, the material for
the electrode is not specifically limited. It is possible to use,
for example, an electrode that is obtainable by applying a paste or
paint which is a mixture of: an electrically conductive material
formed by a carbonaceous material, such as carbon black or carbon
nanotubes, or a metal; and a binder such as oil or an elastomer.
Alternatively, an electrode may be used that is obtainable by
weaving a carbonaceous material or a metal into mesh. It is desired
that the electrode be expandable/contractible in conformity with
the expansion/contraction of the dielectric film. When the
electrode is expanded/contracted together with the dielectric film,
deformation of the dielectric film is not disturbed by the
electrode. As a consequence, when the transducer of the present
invention is used as an actuator, for example, desired displacement
may be easily achieved.
[0064] When the transducer of the present invention is designed
such that a plurality of the dielectric films and electrodes are
alternately laminated, it is possible to generate larger force.
Therefore, when such a laminated structure is employed, a high
output of an actuator, for example, can be obtained. By this, a
member to be driven can be driven with a larger force.
First Embodiment
[0065] As a first example of the transducer of the present
invention, description will be made of an embodiment embodying an
actuator. FIG. 1 shows a cross-sectional schematic view of an
actuator of the first embodiment, in which (a) shows an OFF state
and (b) shows an ON state.
[0066] As shown in FIG. 1, the actuator 1 includes a dielectric
film 10 and electrodes 11a and 11b. The dielectric film 10 is a
three-dimensional crosslinked body (dielectric film of the present
invention) that has been synthesized from tetrakis(2-ethylhexyloxy)
titanium (metal alkoxide compound), hydrogenated nitrile rubber
that has carboxyl groups (rubber polymer) and silica (inorganic
filler). The electrodes 11a and 11b are fixed to upper and lower
sides of the dielectric film 10, respectively. The electrodes 11a
and 11b are connected to a power source 12 through wires. The
actuator is turned from the OFF state to the ON state when a
voltage is applied between the paired electrodes 11a and 11b. Upon
the application of the voltage, the thickness of the dielectric
film 10 is reduced and, therefore, correspondingly expands in the
direction parallel with the planes of the electrodes 11a and 11b as
shown by the white arrows in FIG. 1(b). Thus, the actuator 1 can
output driving forces in the up-down direction and left-right
direction.
[0067] Here, the electric resistance of the dielectric film 10 is
high. When a high voltage is applied between the electrodes 11a and
11b, therefore, an electric current does not easily flow through
the dielectric film 10. For this reason, a large amount of charges
can be stored in the dielectric film 10. As a consequence, large
electrostatic attractive force is generated so that large force and
displacement are obtainable. In addition, because an electric
current does not easily flow through the dielectric film 10,
generation of Joule heat is suppressed. For this reason, there is
low possibility that the dielectric film 10 is thermally broken
down. Additionally, the dielectric film 10 does not easily undergo
insulation breakdown. Thus, the actuator 1 has excellent
durability. Incidentally, insulation breakdown strength of the
dielectric film 10 is improved when the dielectric film 10 is
arranged in the state where it is stretched in the
surface-extending direction thereof. In this case, since it is
possible to apply a higher voltage, large force and displacement
are obtainable.
Second Embodiment
[0068] As a second example of the transducer of the present
invention, description will be made of an embodiment embodying a
capacitive sensor. FIG. 2 shows a cross-sectional schematic view of
a capacitive sensor of the second embodiment. As shown in FIG. 2,
the capacitive sensor 2 includes a dielectric film 20, electrodes
21a and 21b and a substrate 22. The dielectric film 20 is a
three-dimensional crosslinked body (dielectric film of the present
invention) that has been synthesized from tetrakis(2-ethylhexyloxy)
titanium (metal alkoxide compound), hydrogenated nitrile rubber
that has carboxyl groups (rubber polymer) and silica (inorganic
filler). The dielectric film 20 is in the form of a strip that
extends in the left-right direction. The dielectric film 20 is
disposed on an upper surface of the substrate 22 via the electrode
21b. The electrodes 21a and 21b are each in the form of a strip
that extends in the left-right direction. The electrodes 21a and
21b are fixed to upper and lower sides of the dielectric film 20,
respectively.
[0069] The electrodes 21a and 21b are connected to wires (not
shown). The substrate 22 is an insulative flexible film and is in
the form of a strip that extends in the left-right direction. The
substrate 22 is fixed to a lower side of the electrode 21b.
[0070] The capacitance of the capacitive sensor 2 may be determined
from the following equation (I):
C=.di-elect cons..sub.0.di-elect cons..sub.rS/d (I)
[C: capacitance. .di-elect cons..sub.0: dielectric constant in
vacuum, .di-elect cons..sub.r: relative dielectric constant of the
dielectric film, S: area of electrode, d: inter-electrode
distance]. When the capacitive sensor 2 is pressed from above, for
example, the dielectric film 20 is compressed and is
correspondingly expanded in the direction parallel with the planes
of the electrodes 21a and 21b. When the film thickness, namely the
inter-electrode distance d is reduced, the capacitance between the
electrodes 21a and 21b increases. The amount and position of the
applied load may be thus detected by the change in the
capacitance.
[0071] Here, the electric resistance of the dielectric film 20 is
high. Therefore, even when the capacitance between the electrodes
21a and 21b becomes high as a result of application of a large
compression force, an electric current does not easily flow through
the dielectric film 20. For this reason, it is possible to
precisely detect the amount and position of the applied load. In
addition, because an electric current does not easily flow through
the dielectric film 20, generation of Joule heat is suppressed. For
this reason, there is low possibility that the dielectric film 20
is thermally broken down. Further, the dielectric film 20 does not
easily undergo insulation breakdown. Thus, the capacitive sensor 2
has excellent durability.
Third Embodiment
[0072] As a third example of the transducer of the present
invention, description will be made of an embodiment embodying an
electric power generation element. FIG. 3 shows a cross-sectional
schematic view of an electric power generation element of the third
embodiment, in which (a) shows an expanded state and (b) shows a
contracted state. As shown in FIG. 3, the electric power generation
element 3 includes a dielectric film 30 and electrodes 31a and 31b.
The dielectric film 30 is a three-dimensional crosslinked body
(dielectric film of the present invention) that has been
synthesized from tetrakis(2-ethylhexyloxy) titanium (metal alkoxide
compound), hydrogenated nitrile rubber that has carboxyl groups
(rubber polymer) and silica (inorganic filler). The electrodes 31a
and 31b are fixed to upper and lower sides of the dielectric film
30, respectively. The electrodes 31a and 31b are connected to wires
and the electrode 31b is grounded.
[0073] As shown in FIG. 3(a), when the electric power generation
element 3 is compressed to expand the dielectric film 30 in the
direction parallel with the planes of the electrodes 31a and 31b,
the thickness of the dielectric film 30 is reduced so that charges
are stored between the electrodes 31a and 31b. When the compressive
force is released thereafter, the dielectric film 30 contracts due
to the elastic restoring force thereof as shown in FIG. 3(b).
Therefore, the film thickness increases. In this case, charges are
discharged and electric power is generated.
[0074] Here, the electric resistance of the dielectric film 30 is
high. Therefore, even when the amount of compression is large, an
electric current does not easily flow through the dielectric film
30 so that a large amount of charges are stored between the
electrodes 31a and 31b. For this reason, it is possible to generate
a large amount of power. In addition, because an electric current
does not easily flow through the dielectric film 30, generation of
Joule heat is suppressed. For this reason, there is low possibility
that the dielectric film 30 is thermally broken down. Further, the
dielectric film 30 does not easily undergo insulation breakdown.
Thus, the electric power generation element 3 has excellent
durability.
EXAMPLES
[0075] The present invention will be next described in more
concretely by way of examples.
<Production of Dielectric Film>
[Dielectric Films of Examples 1 to 10]
[0076] Dielectric films of Examples 1 to 10 were produced from the
raw materials that are shown in Table 1. At first, a carboxyl
group-containing hydrogenated nitrile rubber (THERBAN (registered
trademark) XT8889 manufactured by LANXESS Inc.) and the specified
silica were kneaded with a roll kneader to prepare a rubber
composition. The thus prepared rubber composition was then
dissolved in acetyl acetone. Into the resulting solution,
tetrakis(2-ethylhexyloxy) titanium as an organic metal compound was
added to be mixed. Here, the acetyl acetone served not only as a
solvent for dissolving the carboxyl group-containing hydrogenated
nitrile rubber (rubber polymer) but also as a chelating agent for
the tetrakis(2-ethylhexyloxy) titanium (metal alkoxide compound).
The mixture solution was thereafter applied to a substrate, dried
and heated at 150.degree. C. for about 60 minutes to obtain each
dielectric film. Each of the dielectric films had a thickness of
about 40 .mu.m.
[0077] [Dielectric Films of Reference Examples 1 and 2]
[0078] Dielectric films of Reference Examples 1 and 2 were produced
from the raw materials that are shown in Table 1. The dielectric
films of Examples 1 to 10 differ from those of Reference Examples 1
and 2 in the presence or absence of silica. At first, a carboxyl
group-containing hydrogenated nitrile rubber (same as above) was
dissolved in acetyl acetone. Into the resulting solution,
tetrakis(2-ethylhexyloxy) titanium was added to be mixed. The
mixture solution was thereafter applied to a substrate, dried and
heated at 150.degree. C. for about 60 minutes to obtain each
dielectric film. Each of the dielectric films had a thickness of
about 40 .mu.m.
[0079] [Dielectric Films of Examples 11 to 16]
[0080] Dielectric films of Examples 11 to 16 were produced from the
raw materials that are shown in Table 2 in the same manner as that
for the production of the dielectric films of Examples 1 to 10
except that the kind of inorganic filler was changed. Each of the
dielectric films had a thickness of about 40 .mu.m.
[0081] [Dielectric Films of Examples 17 to 21]
[0082] Dielectric films of Examples 17 to 21 were produced from the
raw materials that are shown in Table 3 in the same manner as that
for the production of the dielectric films of Examples 1 to 10
except that a plasticizer was mixed. At first, a carboxyl
group-containing hydrogenated nitrile rubber (same as above) and
silica (b) that is described hereinafter were kneaded with a roll
kneader to prepare a rubber composition. The thus prepared rubber
composition was then dissolved in acetyl acetone. Into the
resulting solution, tetrakis(2-ethylhexyloxy) titanium and the
specified plasticizer were added to be mixed. The mixture solution
was thereafter applied to a substrate, dried and heated at
150.degree. C. for about 60 minutes to obtain each dielectric film.
Each of the dielectric films had a thickness of about 40 .mu.M.
[0083] [Dielectric Films of Examples 22 to 25]
[0084] Dielectric films of Examples 22 to 25 were produced from the
raw materials that are shown in Table 4 in the same manner as that
for the production of the dielectric films of Examples 1 to 10
except that the kind of the organic metal compound was changed.
Each of the dielectric films had a thickness of about 40 .mu.m.
[0085] [Dielectric Films of Comparative Examples 1 and 2]
[0086] Dielectric films of Comparative Examples 1 and 2 were
produced from the raw materials that are shown in Table 5. At
first, the specified raw materials were mixed and dispersed with a
roll kneader to prepare a rubber composition. The thus prepared
rubber composition was then shaped into a thin sheet, fed into a
mold, and subjected to press-crosslinking at 175.degree. C. for
about 30 minutes to obtain each dielectric film. Each of the
dielectric films had a thickness of about 50 .mu.m.
[0087] The kinds and mixing amounts of the raw materials that were
used are shown in Table 1 to Table 5. Silica shown in Tables 1, 3
and 4 are as follows. Silica (a): wet silica "Nipsil (registered
trademark) VN3", manufactured by Tosoh Silica Corporation, pH 5.5
to 6.5, specific surface area 240 m.sup.2/g
Silica (b): dry silica "AEROSIL (registered trademark) 380",
manufactured by Nippon Aerosil Co., Ltd., pH 3.7 to 4.7, specific
surface area 380 m.sup.2/g Silica (c): wet silica "Nipsil ER",
manufactured by Tosoh Silica Corporation, pH 7 to 8.5, specific
surface area 120 m.sup.2/g
[0088] Raw materials shown in Table 5 are as follows.
Silicone rubber: "DMS-V31" (manufactured by Gelest, Inc.) Nitrile
rubber: "Nipol (registered trademark) 1042" (manufactured by ZEON
CORPORATION) Methyl-H-siloxane: "TSF484" (manufactured by GE
Toshiba Silicones Co., Ltd.) Retarder: "Surfynol (registered
trademark) 61" manufactured by Nissin Chemical Industry Co., Ltd.
Platinum catalyst: "SIP6830.0" manufactured by Gelest, Inc.
Vulcanization aid: Zinc Oxide Grade 2 (manufactured by Mitsui
Mining & Smelting Co., Ltd) Stearic acid: "LUNAC (registered
trademark) S30" (manufactured by Kao Corporation) Tetraethylthiuram
disulfide: "Sanceler (registered trademark) TET-G" (manufactured by
SANSHIN CHEMICAL INDUSTRY CO., LTD.) N-Cyclohexyl-2-benzothiazyl
sulfenamide: "Sanceler (registered trademark) CZ-GS" (manufactured
by SANSHIN CHEMICAL INDUSTRY CO., LTD.) Sulfur: "SULFAX T-10"
manufactured by TURUMI CHEMICAL INDUSTRY CO., LTD.)
TABLE-US-00001 TABLE 1 (parts by mass) Raw materials Example 1
Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Rubber
polymer Carbixyl group-containing 100 100 100 100 100 100 100
hydrogenated nitrile rubber Organic metal Tetrakis
(2-ethylhexyloxy) 5 15 15 15 15 30 30 compound titanium Inorganic
filler Silica (a) [pH 5.5 to 6.5] 10 5 10 20 30 10 30 Silica (b)
[pH 3.7 to 4.7] -- -- -- -- -- -- -- Silica (c) [pH 7 to 8.5] -- --
-- -- -- -- -- Solvent Acetyl acetone (chelating agent) 643 655 683
740 797 743 857 Electric resistance of dielectric film [.OMEGA. cm]
6.0 .times. 10.sup.11 8.6 .times. 10.sup.11 1.5 .times. 10.sup.12
2.5 .times. 10.sup.12 1.3 .times. 10.sup.12 5.9 .times. 10.sup.12
1.7 .times. 10.sup.12 Maximum generated stress of actuator [MPa]
0.09 0.19 0.30 0.26 0.21 0.29 0.24 Maximum field strength of
actuator [V/.mu.m] 26 43 55 51 37 56 43 Reference Reference Raw
materials Example 8 Example 9 Example 10 Example 1 Example 2 Rubber
polymer Carbixyl group-containing 100 100 100 100 100 hydrogenated
nitrile rubber Organic metal Tetrakis (2-ethylhexyloxy) 15 30 15 5
15 compound titanium Inorganic filler Silica (a) [pH 5. 5 to 6.5]
-- -- -- -- -- Silica (b) [pH 3.7 to 4.7] 10 10 -- -- -- Silica (c)
[pH 7 to 8.5] -- -- 10 -- -- Solvent Acetyl acetone (chelating
agent) 683 743 683 587 627 Electric resistance of dielectric film
[.OMEGA. cm] 4.2 .times. 10.sup.12 5.9 .times. 10.sup.12 4.8
.times. 10.sup.11 2.5 .times. 10.sup.11 3.8 .times. 10.sup.11
Maximum generated stress of actuator [MPa] 0.60 0.78 0.28 0.08 0.14
Maximum field strength of actuator [V/.mu.m] 70 80 45 24 40
TABLE-US-00002 TABLE 2 (parts by mass) Raw materials Example 11
Example 12 Example 13 Example 14 Example 15 Example 16 Rubber
polymer Carbixyl group-containing 100 100 100 100 100 100
hydrogenated nitrile rubber Organic metal Tetrakis
(2-ethylhexyloxy) 15 15 15 15 15 15 compound titanium Inorganic
filler Barium titanate 10 -- -- -- -- -- Calcium carbonate -- 10 --
-- -- -- Titanium oxide -- -- 10 20 40 -- Clay -- -- -- -- -- 10
Solvent Acetyl acetone (chelating agent) 683 683 683 683 683 683
Electric resistance of dielectric film [.OMEGA. cm] 4.5 .times.
10.sup.11 5.1 .times. 10.sup.11 4.2 .times. 10.sup.11 5.3 .times.
10.sup.11 4.0 .times. 10.sup.12 3.2 .times. 10.sup.12 Maximum
generated stress of actuator [MPa] 0.69 0.43 0.68 0.80 0.69 0.43
Maximum field strength of actuator [V/.mu.m] 75 65 70 75 70 65
TABLE-US-00003 TABLE 3 (parts by mass) Raw materials Example 17
Example 18 Example 19 Example 20 Example 21 Rubber polymer Carbixyl
group-containing 95 90 95 95 90 hydrogenated nitrile rubber Organic
metal Tetrakis(2-ethylhexyloxy) 5 10 5 5 10 compound titanium
Inorganic filler Silica (b) [pH 3.7 to 4.7] 10 10 10 10 10
Plastiizer Tricresyl phosphate 25 50 -- -- -- Tris(2-ethylhexyl)
trimellitate -- -- 25 -- -- Chlorinated paraffin -- -- -- 25 50
Solvent Acetyl acetone (chelating agent) 806 806 806 806 806
Electric resistance of dielectric film [.OMEGA. cm] 2.2 .times.
10.sup.12 1.1 .times. 10.sup.12 2.9 .times. 10.sup.12 2.2 .times.
10.sup.12 5.9 .times. 10.sup.11 Maximum generated stress of
actuator [MPa] 0.23 0.31 0.22 0.23 0.45 Maximum field strength of
actuator [V/.mu.m] 50 65 50 55 70
TABLE-US-00004 TABLE 4 (parts by mass) Raw materials Example 22
Example 23 Example 24 Example 25 Rubber polymer Carbixyl
group-containing 100 100 100 100 hydrogenated nitrile rubber
Organic metal compound Polyhydroxytitanium stearate 15 30 -- --
Titanium butoxide dimer -- -- 15 -- Zirconium tetraacetyl acetonate
-- -- -- 7 Inorganic filler Silica (b) [pH 3.7 to 4.7] 10 10 10 10
Solvent Acetyl acetone (chelating agent) 683 857 683 651 Electric
resistance of dielectric film [.OMEGA. cm] 5.7 .times. 10.sup.12
6.3 .times. 10.sup.12 2.8 .times. 10.sup.12 3.2 .times. 10.sup.12
Maximum generated stress of actuator [MPa] 0.45 0.38 0.79 0.30
Maximum field strength of actuator [V/.mu.m] 65 55 80 50
TABLE-US-00005 TABLE 5 (parts by mass) Raw materials Comparative
Example 1 Comparative Example 2 Rubber polymer Silicone rubber 100
-- Nitrile rubber -- 100 Crosslinker Methyl-H-siloxane 1.5 --
Retarder Surfynol 61 0.03 -- Catalyst Platinum catalyst 0.01 --
Vulcanization aid Zinc oxide grade 2 -- 5 Processing aid Stearic
acid -- 1 Accelerator Tetraethylthiuram disulfide -- 2.1
N-Cyclohexyl-2-benzothiazyl sulfenamide -- 1 Sulfur -- 0.44
Electric resistance of dielectric film [.OMEGA. cm] 8.0 .times.
10.sup.14 2.0 .times. 10.sup.10 Maximum generated stress of
actuator [MPa] 0.05 0.06 Maximum field strength of actuator
[V/.mu.m] 120 18
[0089] <Measurement of Electric Resistance of Dielectric
Films>
[0090] The electric resistance of each of the dielectric films of
Examples, Reference Examples and Comparative Examples was measured
according to JIS K6911 (1995). The measurement results are
summarized in Table 1 to Table 5. As shown in Table 1 to Table 4,
any of the dielectric films of Examples has a high electric
resistance, namely has high insulative properties. For example,
with reference to Table 1, when comparison is made between
dielectric films in which the mixing amount of the metal alkoxide
compound is the same, the electric resistance of Example 1 is
higher than that of Reference Example 1 and the electric
resistances of Examples 2 to 5, 8 and 10 are higher than that of
Reference Example 2. Namely, it has been confirmed that the
dielectric films of Examples that contain silica (inorganic filler)
each have a higher electric resistance as compared with the
dielectric films of Reference Examples that do not contain silica.
Similarly, when comparison is made between Examples 11 to 16 in
Table 2 and Reference Example 2 in which the mixing amount of the
metal alkoxide compound is the same, the electric resistance of
Examples 11 to 16 is higher than that of Reference Example 2.
Namely, it has been confirmed that, irrespective of the kind of
inorganic filler, the dielectric films of Examples that contain an
inorganic filler each have a higher electric resistance as compared
with the dielectric films of Reference Examples that do not contain
an inorganic filler. In addition, each of the dielectric films of
Examples 17 to 21 in which a plasticizer was mixed has high
electric resistance. Incidentally, it is seen that the electric
resistance of the dielectric film in which the conventional
silicone rubber is used (Comparative Example 1) is high while the
electric resistance of the dielectric film in which nitrile rubber
is used (Comparative Example 2) is low, as shown Table 5.
[0091] The relationship between the pH value of silica and the
electric resistance will be next considered. When Examples 3, 8 and
10, for example, are compared, it is seen that the electric
resistance increases in the order of Example 10, Example 3 and
Example 8. This tendency is in conformity with the decrease of the
pH value of silica. Namely, the pH value of the silica in these
examples decreases in the order of Example 10, Example 3 and
Example 8. That is to say, the lower the pH value of silica (the
stronger the acidity of silica), the higher the electric
resistance.
[0092] The relationship between the mixing amount of silica and the
electric resistance will be next considered. When Examples 2 to 4,
for example, are compared, the electric resistance increased with
an increase of the mixing amount of silica (in the order of Example
2, Example 3 and Example 4). Incidentally, no additional increase
in the electric resistance was observed in Example 5 in which the
mixing amount of silica is the largest (30 parts by mass), in
contrast to Example 4 (20 parts by mass) and Example 3 (10 parts by
mass). The reason for this is considered that the insulation effect
attained by the addition of silica became saturated.
[0093] <Evaluation of Actuators>
[0094] Actuators were next prepared using each of the dielectric
films of Examples, Reference Examples and Comparative Examples and
their maximum generated stresses and maximum field strengths were
measured. Description will be first made of an experiment device
and an experiment method.
[0095] Actuators were prepared by bonding an electrode formed by a
mixture of an acrylic rubber with carbon black to each of the front
and back surfaces of each of the dielectric films of Examples,
Reference Examples and Comparative Examples. The prepared actuators
will be hereinafter referred to as "actuators of Examples", etc. in
correspondence with the types of the dielectric films. A front view
of an actuator mounted to an experiment device is shown in FIG. 4.
FIG. 5 is a V-V sectional view of FIG. 4.
[0096] As shown in FIG. 4 and FIG. 5, an upper end of an actuator 5
is held by an upper chuck 52, while a lower end of the actuator 5
is held by a lower chuck 53. The actuator 5 is mounted between the
upper chuck 52 and the lower chuck 53 in the state where the film
is stretched in the upper-lower direction beforehand (stretching
rate: 25%). A load cell (not shown) is disposed above the upper
chuck 52.
[0097] The actuator 5 includes a dielectric film 50 and a pair of
electrodes 51a and 51b. The dielectric film 50 in a free state is a
rectangular film that is 50 mm long, 25 mm wide and about 40 .mu.m
thick. The electrodes 51a and 51b are arranged so as to face each
other with the dielectric film 50 being sandwiched therebetween.
Each of the electrodes 51a and 51b in a free state is a rectangular
film that is 40 mm long, 25 mm wide and about 10 .mu.m thick. The
electrodes 51a and 51b are arranged in the state where they are
offset by 10 mm in the upper-lower direction. Namely, the
electrodes 51a and 51b overlap with each other through the
dielectric film 50 over the area of 30 mm length and 25 mm width. A
wire (not shown) is connected to a lower end of the electrode 51a.
Similarly, a wire (not shown) is connected to an upper end of the
electrode 51b. The electrodes 51a and 51b are connected to a power
source (not shown) through the wires.
[0098] When a voltage is applied between the electrodes 51a and
51b, electrostatic attractive force is generated between the
electrodes 51a and 51b so that the dielectric film 50 is
compressed. As a result, the thickness of the dielectric film 50
decreases and the dielectric film 50 expands in the stretching
direction (upper-lower direction). The expansion of the dielectric
film 50 causes a decrease of the stretching force in the
upper-lower direction. The reduction of the stretching force before
and after the application of the voltage, which was measured by the
load cell, represents a generated stress. The measurement of the
generated stress was continued while increasing the applied voltage
stepwise until the dielectric film 50 was broken down. The
generated stress just before the breakage of the dielectric film 50
represents the maximum generated stress. The value obtained by
dividing the voltage at that time by the thickness of the
dielectric film 50 represents the maximum field strength. The
measurement results of the maximum generated stress and maximum
field strength of each of the actuators of Examples, Reference
Examples and Comparative Examples are summarized in Table 1 to
Table 5.
[0099] As shown in Table 1 to Table 4, the maximum generated
stresses of the actuators of Examples are larger than those of the
actuators of Comparative Examples. It is also seen that the
generated stress of the actuator of Comparative Example 1 in which
the dielectric film made of a silicone rubber is used is small,
though the maximum field strength is very high. When comparison is
made between actuators in which the mixing amount of the metal
alkoxide compound is the same, the maximum generated stress of
Example 1 is larger than that of Reference Example 1 and the
maximum generated stresses of Examples 2 to 5, 8 and 10 are larger
than that of Reference Example 2. Similarly, when comparison is
made between Examples 11 to 16 in Table 2 and Reference Example 2
in which the mixing amount of the metal alkoxide compound is the
same, the maximum generated stresses of Examples 11 to 16 are
larger than that of Reference Example 2. The maximum generated
stress is also large in Examples 17 to 21 in which a plasticizer is
used.
[0100] As described above, the electric resistances of the
dielectric films of Examples are high. Therefore, the actuators of
Examples can store a large amount of charges. Further, the
dielectric films each also have high resistance to insulation
breakdown, so that breakage by Joule heat can be suppressed.
Therefore, it is possible to apply a high voltage to the actuators
of Examples. It is considered that the actuators of Examples could
output large force for the above reasons.
[0101] As described above, when Examples 3, 8 and 10 are compared,
there is seen a tendency that the lower the pH value of silica, the
higher the electric resistance. Similar to the tendency of the
electric resistance, the maximum generated stress and the maximum
filed strength increase in the order of Example 10, Example 3 and
Example 8.
INDUSTRIAL APPLICABILITY
[0102] The dielectric film of the present invention may be widely
used in transducers such as actuators, sensors, electric power
generation elements, etc. that perform conversion between
mechanical energy and electrical energy, as well as speakers,
microphones, noise cancellers etc. that perform conversion between
acoustic energy and electrical energy. Among them, the dielectric
film is suited for flexible actuators that are used, for example,
in artificial muscle for industrial, medical or rehabilitation
robots; in small pumps that are used for, for example, electronic
part coolers and medical purposes; and in medical instruments.
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