JP2009173691A - Dielectric material and actuator using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dielectric material and an actuator that can provide a large displacement amount with a relatively small application voltage. <P>SOLUTION: The dielectric material comprises an elastomer and ferroelectric inorganic fine particles dispersed in the elastomer. The surfaces of the ferroelectric inorganic fine particles are subjected to a coupling treatment. The actuator 1 is composed of a dielectric film 20 made of the above dielectric material, a plurality of electrodes 21a, 21b disposed through the dielectric film 20 interposed therebtween. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an actuator that expands and contracts by a change in applied voltage to drive a member to be driven, and a dielectric material suitable for constituting the actuator.

In the fields of industrial and nursing robots, medical equipment, micromachines, etc., the need for highly flexible, small and lightweight actuators is increasing. As such an actuator material, for example, various polymers such as a conductive polymer, an ion conductive polymer (ICPF), and a dielectric elastomer have been proposed. In particular, an actuator using a dielectric elastomer is useful because it can be easily miniaturized and manufactured at low cost. For example, Patent Documents 1 and 2 introduce an actuator in which a dielectric film made of a dielectric elastomer is held between a pair of electrodes.
Special table 2003-506858 JP-T-2001-524278

  In the actuator, when the voltage applied between the electrodes is increased, the electrostatic attractive force between the electrodes is increased. For this reason, the dielectric film sandwiched between the electrodes is compressed from the film thickness direction, and the film thickness of the dielectric film is reduced. As the film thickness decreases, the dielectric film extends in a direction parallel to the electrode surface. Further, when the voltage applied between the electrodes is reduced, the electrostatic attractive force between the electrodes is reduced. For this reason, the compressive force from the film thickness direction to the dielectric film is reduced, and the film thickness is increased by the elastic restoring force of the dielectric film. As the film thickness increases, the dielectric film shrinks in the direction parallel to the electrode surface. Thus, the actuator drives the member to be driven by extending and contracting the dielectric film.

  As the dielectric film of the actuator, acrylic rubber, urethane rubber, silicone rubber or the like is used as shown in Patent Documents 1 and 2 above. When these conventional materials are used, a large voltage must be applied to increase the displacement of the actuator. For example, when acrylic rubber is used, since the Young's modulus of acrylic rubber is small, only a relatively small force can be obtained. In addition, repeated expansion and contraction increases creep and durability is not sufficient.

  This invention is made | formed in view of such a situation, and makes it a subject to provide the dielectric material which can obtain a big displacement with a comparatively small applied voltage, when an actuator is comprised. It is another object of the present invention to provide an actuator having a large displacement even with a relatively small applied voltage by using such a dielectric material.

  (1) In order to solve the above problems, the dielectric material of the present invention includes an elastomer and ferroelectric inorganic fine particles dispersed in the elastomer, and the surface of the ferroelectric inorganic fine particles is subjected to a coupling treatment. (Corresponding to claim 1).

  That is, the dielectric material of the present invention is formed by dispersing ferroelectric inorganic fine particles whose surfaces are subjected to coupling treatment in an elastomer. A functional group is imparted to the surface of the ferroelectric inorganic fine particles by the coupling treatment. For this reason, the ferroelectric inorganic fine particles have high compatibility with the elastomer and are integrated with the elastomer. Here, the ferroelectric inorganic fine particles are fine particles made of an inorganic material having a relatively large relative dielectric constant. Therefore, the dielectric constant of the dielectric material of the present invention containing the ferroelectric inorganic fine particles is larger than that of the elastomer alone. Therefore, when an actuator is configured using the dielectric material of the present invention, a large electrostatic attraction is generated even when the applied voltage is relatively small, and a large displacement can be obtained. In addition, a larger displacement can be obtained by increasing the applied voltage.

  The dielectric material of the present invention includes ferroelectric inorganic fine particles, that is, fine particles made of an inorganic material. For this reason, the strength of the dielectric material of the present invention is higher than that of a material composed only of the base material elastomer. Therefore, the dielectric material of the present invention is difficult to creep even after repeated expansion and contraction and is not easily broken. Further, when an actuator is configured, a larger force can be output. Thus, according to the dielectric material of the present invention, an actuator having a large displacement and excellent durability and stability can be configured.

  (2) Moreover, the actuator of this invention is equipped with the dielectric film which consists of the dielectric material of the said invention, and the some electrode arrange | positioned through this dielectric film, and is applied between these electrodes. The dielectric film expands and contracts due to a change in the applied voltage (corresponding to claim 6).

  The actuator of the present invention includes a dielectric film made of the dielectric material of the present invention. For this reason, according to the actuator of the present invention, a large amount of displacement can be obtained with a relatively small applied voltage. In addition, since the dielectric film is difficult to creep even after repeated expansion and contraction, the actuator of the present invention is excellent in durability and stability.

Hereinafter, the dielectric material of the present invention and the actuator using the same will be described in detail.
<Dielectric material>
As described above, the dielectric material of the present invention includes an elastomer and ferroelectric inorganic fine particles whose surfaces are coupled.

1. Elastomer The elastomer may be appropriately selected from rubber and thermoplastic elastomer. Among these, acrylic rubber, silicone rubber, ethylene-propylene copolymer (EPM), ethylene-propylene-diene terpolymer (EPDM), natural rubber, butyl rubber (IIR), isoprene from the viewpoint of high elongation at break. It is desirable to use one or more selected from rubber, acrylonitrile-butadiene copolymer (NBR), hydrogenated nitrile rubber (H-NBR), hydrin rubber, chloroprene rubber, fluororubber, urethane rubber, and styrene-butadiene rubber. Among them, acrylic rubber, silicone rubber, EPM, EPDM, natural rubber, IIR, isoprene rubber, H, because of the good compatibility with the ferroelectric inorganic particles subjected to the coupling treatment and the greater displacement amount can be obtained. -NBR is preferred.

2. Ferroelectric inorganic fine particles The ferroelectric inorganic fine particles may be fine particles made of an inorganic material having a relatively high relative dielectric constant. For example, an inorganic material having a relative dielectric constant of 80 or more may be selected. Specifically, it is desirable to use one or more selected from titanium oxide, barium titanate, lithium titanate, strontium titanate, lead zirconate titanate, bismuth titanate, tantalum oxide, and the like. In particular, titanium oxide and barium titanate are preferred because they have good compatibility with the elastomer and are relatively inexpensive.

  The surface of the ferroelectric inorganic fine particles is subjected to coupling treatment. Examples of the coupling treatment include surface treatment with a silane coupling agent, a titanate coupling agent, an aluminum coupling agent, and the like. Of these, surface treatment with a silane coupling agent is preferred because there are many types of functional groups and it is easy to obtain compatibility between the ferroelectric inorganic fine particles and the elastomer. Silane coupling agents are considered to be compatible with elastomers from the group of compounds having alkyl groups, epoxy groups, vinyl groups, amino groups, alkoxy groups, acetoxy groups, mercaptoalkyl groups, chlorine atoms, etc. as functional groups. And may be selected as appropriate. A silane coupling agent may be used individually by 1 type, and 2 or more types may be mixed and used for it. For example, when at least one selected from the group of compounds having an alkyl group is used, the compatibility and bonding properties with a relatively low polarity elastomer are good. Specific examples include ethyltrimethoxysilane, dimethyldimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, hexyltrimethoxysilane and the like.

  For the surface treatment with the silane coupling agent, a known method such as a dry method or a wet method may be employed. In the case of performing the dry method, the silane coupling agent may be added directly to the powder composed of the ferroelectric inorganic fine particles or dissolved in a predetermined solvent and mixed, and then dried. Moreover, when performing by a wet method, the powder which consists of ferroelectric inorganic fine particles may be added and stirred in the aqueous solution which melt | dissolved the silane coupling agent, and a solid substance should just be dried. Alternatively, a powder composed of ferroelectric inorganic fine particles may be dispersed in a predetermined solution in advance, and a silane coupling agent may be added thereto and stirred to dry the solid.

  From the viewpoint of reducing the compatibility with the elastomer and the effect on the expansion and contraction of the elastomer when a voltage is applied, the particle diameter of the ferroelectric inorganic fine particles is preferably 1 nm or more and 500 nm or less. Particularly, 5 nm to 100 nm is preferable. In this specification, the maximum length of the ferroelectric inorganic fine particles is adopted as the particle diameter. Further, the particle shape of the ferroelectric inorganic fine particles is not particularly limited. In order to improve the bondability with the elastomer and reduce the influence on the expansion and contraction and dielectric breakdown of the elastomer, it is desirable to employ spherical particles. “Spherical” includes not only true spheres and substantially true spheres, but also elliptic spheres, oval spheres (a shape in which a pair of opposing hemispheres are connected by a cylinder), partial spheres, spheres with different radii for each part, water droplet shapes, etc. included.

  The content of the ferroelectric inorganic fine particles is not particularly limited. For example, 20 parts by weight or more is desirable with respect to 100 parts by weight of the elastomer. This is because when the content of the ferroelectric inorganic fine particles is less than 20 parts by weight, the effect of improving the relative dielectric constant and strength cannot be obtained sufficiently. More preferably, it is 50 parts by weight or more. On the other hand, the content of the ferroelectric inorganic fine particles is desirably 400 parts by weight or less with respect to 100 parts by weight of the elastomer. This is because if the content of the ferroelectric inorganic fine particles exceeds 400 parts by weight, the rigidity becomes high, and the amount of expansion and contraction may be reduced or the strength may be reduced. More preferably, it is 200 parts by weight or less.

3. Production Method The dielectric material of the present invention can be produced by crosslinking a rubber composition containing the polymer constituting the elastomer and the ferroelectric inorganic fine particles. The polymer used may be solid or liquid. A crosslinking agent, a vulcanization accelerator, a processing aid, a plasticizer, an antiaging agent, a reinforcing agent, a coloring agent, and the like may be added to the rubber composition as necessary. As a first production method, first, a powder of ferroelectric inorganic fine particles, a crosslinking agent, and the like are added to a polymer and kneaded to prepare a rubber composition. Next, the prepared rubber composition is molded, filled in a mold, and press-crosslinked under predetermined conditions. The rubber composition prepared in the same manner as in the first production method may be crosslinked after being extruded into a film or tube. As a second production method, first, a powder of a ferroelectric inorganic fine particle, a crosslinking agent, or the like is added to a polymer solution obtained by dissolving a polymer in a predetermined solvent, and the mixture is stirred and mixed to prepare a rubber composition. Next, the prepared rubber composition is applied on a substrate, dried to evaporate the solvent, and then crosslinked.

A dielectric film can be manufactured from the dielectric material of the present invention to constitute an actuator. In this case, at least a pair of electrodes may be disposed so as to sandwich the dielectric film. Hereinafter, an actuator using the dielectric material of the present invention, that is, an embodiment of the actuator of the present invention will be described.
<Actuator>
FIG. 1 is a schematic cross-sectional view of the actuator of this embodiment. (A) shows an OFF state, and (b) shows an ON state. As shown in FIG. 1, the actuator 1 includes a dielectric film 20 and electrodes 21a and 21b. The dielectric film 20 is made of the dielectric material of the present invention. The electrodes 21a and 21b are fixed to the front and back of the dielectric film 20, respectively. The electrodes 21a and 21b are connected to the power source 22 through conductive wires. When switching from the off state to the on state, a voltage is applied between the pair of electrodes 21a and 21b. As the voltage is applied, the thickness of the dielectric film 20 is reduced, and as much as that, the dielectric film 20 extends in a direction parallel to the surfaces of the electrodes 21a and 21b, as indicated by white arrows in FIG. Thereby, the actuator 1 outputs the driving force in the horizontal and vertical directions in the figure.

  The dielectric film 20 is made of the dielectric material of the present invention, that is, a dielectric material in which ferroelectric inorganic fine particles are dispersed in an elastomer. Here, the ferroelectric inorganic fine particles have high compatibility with the elastomer and are integrated with the elastomer. The relative dielectric constant of the dielectric film 20 is larger than that of the elastomer alone. Therefore, according to the actuator 1, a large amount of displacement can be obtained even if the applied voltage is relatively small. In addition, the dielectric film 20 is difficult to creep even after repeated expansion and contraction. Therefore, the actuator 1 is excellent in durability and stability.

  Also in the dielectric film of the actuator of the present invention, it is desirable to employ the above-described preferred embodiment of the dielectric material of the present invention. Further, the thickness of the dielectric film may be appropriately determined according to the use of the actuator. For example, the thickness of the dielectric film is desirably thinner from the viewpoints of downsizing the actuator, driving at a low potential, and increasing the amount of displacement. In this case, it is desirable that the thickness of the dielectric film be 1 μm or more and 1000 μm (1 mm) or less in consideration of dielectric breakdown properties and the like. A more preferable range is 5 μm or more and 200 μm or less. Further, when the dielectric film is attached in a state extending in the surface extending direction, the dielectric breakdown strength of the dielectric film is improved, and a larger displacement amount can be obtained.

  The material of the electrode is not particularly limited. For example, a conductive material made of carbon material such as carbon black or carbon nanotube or a conductive material made of metal and a paste or paint mixed with oil or elastomer as a binder, or an electrode made by knitting carbon material or metal in a mesh shape, etc. Can be used. It is desirable that the electrode can expand and contract according to the expansion and contraction of the dielectric film. When the electrode expands and contracts together with the dielectric film, the deformation of the dielectric film is not easily disturbed by the electrode, and a desired amount of displacement is easily obtained.

  Further, when a laminated structure in which a plurality of dielectric films and electrodes are alternately laminated, a larger force can be generated. Thereby, the output of the actuator is increased, and the drive target member can be driven with a greater force.

  Next, the present invention will be described more specifically with reference to examples.

<Manufacture of dielectric film>
(1) Production of Dielectric Film of Example First, ferroelectric inorganic fine particles were produced by silane coupling treatment. 50 g of titanium oxide powder (“TTO-55N” manufactured by Ishihara Sangyo Co., Ltd., particle size: 30 nm to 50 nm) is dispersed in a mixed solvent of ethanol (195 ml) -water (10 ml), and 2 g of ethyltrimethoxysilane is added, and ultrasonic waves are added. The treatment was performed for 1 hour. Then, it left still for 15 hours. The precipitate was dried to obtain ferroelectric inorganic fine particles whose surface was modified with an ethyl group.

  Next, 100 parts by weight of an acrylic polymer solution (“Paracron (registered trademark) ME-2000” manufactured by Negami Kogyo Co., Ltd., solid concentration 20%), 50 parts by weight of the manufactured ferroelectric inorganic fine particles, and a crosslinking agent (Chemchula) 37.6 parts by weight of “Adiprene BL16” manufactured by the company) was added, and sonicated with stirring for 1 hour. The obtained rubber composition was applied onto a substrate by a bar coating method and air-dried. Thereafter, the film was crosslinked by heating at 165 ° C. for 1 hour to obtain a film-like dielectric film having a thickness of about 150 μm. The obtained dielectric film was used as the dielectric film of the example.

(2) Production of Dielectric Film of Comparative Example A dielectric film was produced in the same manner as the dielectric film of the above example except that the ferroelectric inorganic fine particles were not blended to obtain a dielectric film of Comparative Example 1. Further, the titanium oxide powder was directly added to the acrylic polymer solution without surface treatment, and a dielectric film was produced in the same manner as described above to obtain a dielectric film of Comparative Example 2. The thicknesses of the dielectric films of Comparative Examples 1 and 2 were both about 150 μm.

<Actuator evaluation>
An actuator was configured using each manufactured dielectric film, and the displacement of the actuator was measured.

(1) Experimental apparatus and experimental method First, an experimental apparatus and an experimental method will be described. Electrodes were formed on the upper and lower surfaces of the dielectric films of Examples and Comparative Examples by applying conductive paste in which carbon nanotubes were dispersed in oil to form actuators. Hereinafter, the manufactured actuators are referred to as the actuators of Examples and Comparative Examples 1 and 2, respectively, corresponding to the types of dielectric films. FIG. 2 shows a top view of the manufactured actuator. FIG. 3 is a cross-sectional view taken along the line III-III in FIG.

2 and 3, the actuator 3 includes a dielectric film 30 and a pair of electrodes 31a and 31b. The dielectric film 30 has a circular thin film shape with a diameter of 75 mm. The dielectric film 30 is disposed in a state of being stretched in the biaxial direction at a stretch rate of 100%. Here, the stretching ratio is a value calculated by the following equation (1).
Stretch rate (%) = {√ (S / S ₀ ) −1} × 100 (1)
[S ₀ : Dielectric film area before stretching (natural state), S: Dielectric film area after stretching]

  The pair of electrodes 31a and 31b are arranged so as to face each other in the vertical direction with the dielectric film 30 interposed therebetween. The electrodes 31 a and 31 b have a circular thin film shape with a diameter of about 27 mm, and are arranged substantially concentrically with the dielectric film 30. A terminal portion 310a protruding in the diameter increasing direction is formed on the outer peripheral edge of the electrode 31a. The terminal portion 310a has a rectangular plate shape. Similarly, a terminal portion 310b projecting in the diameter increasing direction is formed on the outer peripheral edge of the electrode 31b. The terminal portion 310b has a rectangular plate shape. The terminal portion 310b is disposed at a position facing the terminal portion 310a by 180 °. Each of the terminal portions 310a and 310b is connected to the power source 4 through a conducting wire.

  When a voltage is applied between the electrodes 31a and 31b, an electrostatic attractive force is generated between the electrodes 31a and 31b, and the dielectric film 30 is compressed. As a result, the thickness of the dielectric film 30 is reduced and extends in the diameter expansion direction. At this time, the electrodes 31a and 31b are also integrated with the dielectric film 30 and extend in the diameter increasing direction. A marker 50 is previously attached to the electrode 31a. The displacement of the marker 50 was measured by the displacement meter 5 and used as the displacement amount of the actuator 3.

(2) Experimental results Next, experimental results will be described. In FIG. 4, the displacement rate with respect to the applied voltage in each actuator of an Example and a comparative example is shown. The displacement rate was calculated by the following formula (2). The vertical axis in FIG. 4 indicates the displacement rate as a multiple of the reference value a.
Displacement rate (%) = (displacement amount / radius of electrode) × 100 (2)

  As shown in the graph of FIG. 4, according to the actuator of the example, a large amount of displacement was obtained even when the applied voltage was small, as compared with the actuator of Comparative Example 1 having a dielectric film made of an elastomer alone. Further, the displacement amount of the actuator of the comparative example 2 including the dielectric film containing the titanium oxide powder not subjected to the silane coupling treatment is the displacement amount of the actuator of the comparative example 1 including the dielectric film not including the titanium oxide powder. Almost unchanged. Thus, according to the dielectric material of the present invention in which the ferroelectric inorganic fine particles subjected to the coupling treatment are dispersed in the elastomer, it is confirmed that an actuator having a large displacement can be configured even when the applied voltage is relatively small. It was.

  The dielectric material of the present invention is useful for, for example, artificial muscles for industrial, medical, and welfare robots, small pumps for cooling electronic components, medical devices, etc., and actuators used for medical instruments. The actuator using the dielectric material of the present invention can be used as a substitute for all actuators such as a mechanical actuator such as a motor and a piezoelectric element actuator.

It is a cross-sectional schematic diagram of the actuator which is one Embodiment of this invention, Comprising: (a) shows an OFF state, (b) shows an ON state, respectively. It is a top view of the actuator used for the evaluation experiment. It is III-III sectional drawing in FIG. It is a graph which shows the displacement rate with respect to the applied voltage in each actuator of an Example and a comparative example.

Explanation of symbols

1: Actuator 20: Dielectric film 21a, 21b: Electrode 22: Power supply 3: Actuator 30: Dielectric film 31a, 31b: Electrode 310a, 310b: Terminal part 4: Power supply 5: Displacement meter 50: Marker

Claims (6)

An elastomer,
Ferroelectric fine particles dispersed in the elastomer,
A dielectric material characterized in that the surface of the ferroelectric inorganic fine particles is subjected to a coupling treatment.   The dielectric material according to claim 1, wherein the coupling treatment is a surface treatment with a silane coupling agent.   The dielectric material according to claim 1, wherein the ferroelectric inorganic fine particles have a relative dielectric constant of 80 or more.   The dielectric material according to any one of claims 1 to 3, wherein a particle diameter of the ferroelectric inorganic fine particles is 1 nm or more and 500 nm or less.   The elastomer is acrylic rubber, silicone rubber, ethylene-propylene copolymer, ethylene-propylene-diene terpolymer, natural rubber, butyl rubber, isoprene rubber, acrylonitrile-butadiene copolymer, hydrogenated nitrile rubber, hydrin rubber. 5. The dielectric material according to claim 1, wherein the dielectric material is one or more selected from chloroprene rubber, fluororubber, urethane rubber, and styrene-butadiene rubber. A dielectric film made of the dielectric material according to any one of claims 1 to 5,
A plurality of electrodes disposed via the dielectric film;
An actuator in which the dielectric film expands and contracts by a change in voltage applied between the electrodes.

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