JP2010109121A - Dielectric film, actuator using the same, sensor, and transducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dielectric film that is flexible, having a large relative dielectric constant and dielectric breakdown strength, as well as providing an actuator, sensor, and to provide a transducer that have superior electric field response, and is superior in durability. <P>SOLUTION: A dielectric film which is installed among multiple electrodes in any one among an actuator, sensor, and transducer, is provided with elastomer containing copolymer of vinyl acetate. Furthermore, each of the actuator, sensor, and transducer is constructed by providing a dielectric film provided with elastomer containing copolymer of vinyl acetate and multiple electrodes arranged using the dielectric films in between. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a dielectric film suitable for an actuator, a sensor, and a transducer, and an actuator, sensor, and transducer using the dielectric film.

  In recent years, actuators using polymer materials such as a conductive polymer, an ion conductive polymer (ICPF), and a dielectric elastomer have been proposed. Since this type of actuator is highly flexible, lightweight, and easy to downsize, its use in various fields such as artificial muscles, medical instruments, and fluid control has been studied. For example, Patent Documents 1 and 2 introduce electrostrictive actuators in which a dielectric film made of a dielectric elastomer is held between a pair of electrodes.

In the electrostrictive 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. On the other hand, when the applied voltage 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. As described above, the electrostrictive actuator drives the drive target member by extending and contracting the dielectric film.
Special table 2003-506858 JP-T-2001-524278

  A dielectric film made of a dielectric elastomer is used not only for an electrostrictive actuator but also for a sensor, a transducer, and the like. The following three can be cited as characteristics required for dielectric films used in these electrostrictive actuators and the like. First, the relative dielectric constant is large. When the relative dielectric constant of the dielectric film is large, a large amount of charge can be stored at the interface with the electrode. Thereby, for example, the driving force and displacement amount of the actuator can be increased. Second, the dielectric breakdown strength is high. When the dielectric breakdown strength of the dielectric film is large, a large voltage can be applied. Therefore, the driving force and displacement amount of the actuator can be increased, and the durability is improved. Third is flexibility. When the dielectric film is highly flexible, the electric field response is excellent and the deterioration is small even if the expansion and contraction is repeated. Thereby, the driving force and displacement amount of the actuator can be increased, and the durability is improved.

  As the dielectric film of the electrostrictive actuator, as shown in Patent Documents 1 and 2, silicone rubber, isoprene rubber having a high dielectric breakdown strength, nitrile rubber having a high relative dielectric constant, or the like is used. .

  The former elastomers with low polarity such as silicone rubber and isoprene rubber have high electrical resistance and high dielectric breakdown voltage. Further, even when a large voltage is applied, the dielectric film has high durability because it generates little heat. However, the relative dielectric constant of silicone rubber and isoprene rubber is small. For this reason, the electrostatic attraction with respect to the applied voltage is small, and the electric field response is poor. For example, when an actuator is configured, it is difficult to obtain a desired force and displacement.

  The latter elastomer having a large relative dielectric constant such as nitrile rubber has a large electrostatic attraction with respect to an applied voltage. Therefore, the electric field response is good. However, an elastomer having a large relative dielectric constant is highly polar because it has a structure that causes polarization in an electric field to give a large dipole moment. Highly polar elastomers have low electrical resistance and low dielectric breakdown voltage. That is, if the electric resistance is small, a weak current flows in a high electric field, and Joule heat is generated. For this reason, at a dielectric breakdown voltage or higher, heat generation increases due to further reduction in electrical resistance accompanying heat generation, which may lead to breakdown.

  Thus, according to the conventional elastomer, it was impossible to achieve both electric field response and dielectric breakdown strength. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a flexible dielectric film having a large relative dielectric constant and dielectric breakdown strength. Another object of the present invention is to provide an actuator, a sensor, and a transducer that use such a dielectric film and have excellent electric field response and durability.

  (1) In order to solve the above-mentioned problem, the dielectric film of the present invention is characterized in that it is made of an elastomer containing a vinyl acetate copolymer interposed between a plurality of electrodes in any of an actuator, a sensor, and a transducer. (Corresponding to claim 1).

  The elastomer constituting the dielectric film of the present invention includes a vinyl acetate copolymer. That is, the polymer content of the elastomer may be only a vinyl acetate copolymer, or may be a blend of a vinyl acetate copolymer and another polymer. The “vinyl acetate copolymer” is a copolymer of vinyl acetate and other monomers. Vinyl acetate has a highly polar acetyl group in the side chain. For this reason, although it depends on the type of other monomers and the content ratio of vinyl acetate units, the relative dielectric constant of the vinyl acetate copolymer is relatively large. Therefore, according to the dielectric film of the present invention including the vinyl acetate copolymer, the electrostatic attraction with respect to the applied voltage is large. Therefore, the dielectric film of the present invention has a good electric field response.

  Further, the crystallinity of the vinyl acetate copolymer and the glass transition temperature (Tg) can be adjusted by changing the content ratio of the vinyl acetate unit. Therefore, desired flexibility, relative dielectric constant, etc. can be realized by adjusting the content ratio of the vinyl acetate unit to a suitable range according to the application. For example, when a crystalline polymer such as polyethylene is included, if the content ratio of vinyl acetate units is too small, the crystallinity of the vinyl acetate copolymer increases. For this reason, flexibility falls. In addition, the polarity of the vinyl acetate copolymer decreases, and the relative dielectric constant decreases. On the other hand, if the content ratio of the vinyl acetate unit is too large, the Tg of the vinyl acetate copolymer increases. For this reason, flexibility falls. On the other hand, when Tg is high, the side chain of the vinyl acetate unit is difficult to be oriented in the electric field direction, so that the relative dielectric constant becomes small.

  The volume resistivity of the vinyl acetate copolymer is relatively large. For this reason, the dielectric breakdown voltage is relatively high. Therefore, the dielectric breakdown strength of the dielectric film of the present invention containing the vinyl acetate copolymer is large. That is, even when a large voltage is applied, heat generation in the dielectric film is small. Therefore, the dielectric film of the present invention is excellent in durability. Thus, the dielectric film of the present invention has both electric field response and dielectric breakdown strength. Therefore, it is useful for actuators, sensors, and transducers.

  (2) Moreover, the actuator of this invention is equipped with the dielectric film which consists of an elastomer containing the copolymer of vinyl acetate, and the some electrode arrange | positioned through this dielectric film, The application between these electrodes The dielectric film expands and contracts according to the voltage (corresponding to claim 5).

  The actuator of the present invention includes the dielectric film of the present invention. For this reason, according to the actuator of the present invention, a large force and displacement can be obtained with a relatively small applied voltage. In addition, the dielectric breakdown strength of the dielectric film is large. In addition, since the dielectric film is flexible, it does not easily deteriorate even if the expansion and contraction is repeated. For this reason, the actuator of this invention is excellent in durability and stability.

  (3) In addition, the sensor of the present invention includes a dielectric film made of an elastomer containing a vinyl acetate copolymer, and a plurality of electrodes arranged via the dielectric film. Deformation is detected based on a change in capacitance (corresponding to claim 6).

  The sensor of the present invention includes the dielectric film of the present invention. Since the relative dielectric constant of the dielectric film is large, the capacitance is increased. Therefore, the detection sensitivity of the sensor of the present invention is high. In addition, the dielectric breakdown strength of the dielectric film is large. In addition, since the dielectric film is flexible, it does not easily deteriorate even if the expansion and contraction is repeated. For this reason, the sensor of this invention is excellent in durability and stability.

  (4) Further, the transducer of the present invention includes a dielectric film made of an elastomer containing a vinyl acetate copolymer, and a plurality of electrodes arranged via the dielectric film (claims). Corresponds to item 7).

  The transducer of the present invention includes the dielectric film of the present invention. According to the transducer of the present invention, since the relative dielectric constant of the dielectric film is large, more electric charges can be stored at the interface with the electrode. In addition, the dielectric breakdown strength of the dielectric film is large. In addition, since the dielectric film is flexible, it does not easily deteriorate even if the expansion and contraction is repeated. For this reason, the transducer of the present invention is excellent in durability and stability.

  According to the present invention, it is possible to provide a flexible dielectric film having a large relative dielectric constant and dielectric breakdown strength. In addition, it is possible to provide an actuator, a sensor, and a transducer that have excellent electric field responsiveness and excellent durability.

  Hereinafter, the dielectric film of the present invention, and the actuator, sensor, and transducer using the same will be described in detail.

<Dielectric film>
The dielectric film of the present invention comprises an elastomer containing a vinyl acetate copolymer. As described above, the polymer content of the elastomer may be only a vinyl acetate copolymer, or may be a blend of a vinyl acetate copolymer and another polymer. In any case, the content of vinyl acetate units in the elastomer is desirably larger than 20% by mass when the total polymer content of the elastomer is 100% by mass. In the case of 20% by mass or less, the crystallinity of the vinyl acetate copolymer becomes high and the flexibility is lowered. In addition, the polarity of the vinyl acetate copolymer decreases, and the relative dielectric constant decreases. The content of vinyl acetate units is preferably 30% by mass or more. On the other hand, the content ratio of the vinyl acetate unit is desirably 85% by mass or less when the entire polymer content of the elastomer is 100% by mass. When it is larger than 85% by mass, the Tg of the vinyl acetate copolymer becomes high and the flexibility is lowered. Further, when the Tg is high, the side chain of the vinyl acetate unit is difficult to be oriented in the electric field direction, so that the relative dielectric constant of the vinyl acetate copolymer is reduced. It is preferable that the content ratio of the vinyl acetate unit is 80% by mass or less. In addition, content rates, such as a vinyl acetate unit, can be measured by the mass spectrometry (Mass Spectrometry), for example.

  When blending other polymers, for example, acrylonitrile-butadiene copolymer rubber (NBR), hydrogenated nitrile rubber (H-NBR), hydrin rubber, urethane rubber, chloroprene rubber, chlorinated polyethylene, polyvinyl chloride having a high relative dielectric constant Chlorosulfonated polyethylene, acrylic rubber, fluorine rubber, etc., isoprene rubber (IR), natural rubber, styrene butadiene rubber (SBR), butyl rubber, ethylene-propylene-diene rubber (EPDM), etc. having high dielectric breakdown strength One or more are preferred.

  Examples of the monomer other than vinyl acetate constituting the vinyl acetate copolymer include ethylene, butadiene, acrylic acid ester, and vinyl chloride. Of these, one kind may be used alone, or two or more kinds may be used in combination. Of these, ethylene is preferred for the following reasons. That is, ethylene has a low polarity, and compatibility with other polymers is improved by using it together with a highly polar vinyl acetate. Further, since ethylene has high crystallinity, the vinyl acetate copolymer has a good balance between rigidity and flexibility.

  When the vinyl acetate copolymer is an ethylene-vinyl acetate copolymer, the mass ratio of ethylene units to vinyl acetate units is 60:40 to 15:85 (ethylene units: vinyl acetate units). It is desirable. That is, when the content ratio of the vinyl acetate unit in the ethylene-vinyl acetate copolymer is less than 40% by mass, the crystallinity of the ethylene-vinyl acetate copolymer increases, and the flexibility decreases. In addition, the polarity of the ethylene-vinyl acetate copolymer is lowered and the relative dielectric constant is reduced. On the other hand, when the content ratio of the vinyl acetate unit is greater than 85% by mass, the Tg of the ethylene-vinyl acetate copolymer increases and the flexibility decreases. On the other hand, when Tg is high, the side chain of the vinyl acetate unit is difficult to be oriented in the electric field direction, so that the relative dielectric constant of the ethylene-vinyl acetate copolymer becomes small.

  The dielectric film of the present invention comprises a copolymer of vinyl acetate, or a raw material polymer blended with a copolymer of vinyl acetate and other polymers as necessary, with a crosslinking agent, vulcanization accelerator, processing aid, plasticizer. An elastomer composition may be prepared by adding an agent, an anti-aging agent, a colorant, and the like as necessary, and the elastomer composition may be crosslinked to produce. Specifically, as a first method, first, a crosslinking agent, a processing aid, and the like are added to a raw material polymer and kneaded to prepare an elastomer composition. Next, the prepared elastomer composition is molded, filled in a mold, and press-crosslinked under predetermined conditions. Further, the elastomer composition prepared in the same manner as in the first method may be cross-linked after being extruded into a film or tube. As a second method, first, the raw material polymer is dissolved in a predetermined solvent. A cross-linking agent or the like is added to this solution, and the mixture is stirred and mixed to prepare an elastomer composition. Next, the prepared elastomer composition is applied on a substrate, dried to evaporate the solvent, and then crosslinked.

  As the crosslinking agent, it is desirable to use one or more selected from organic peroxides. In this case, a crosslinking aid may be used in combination. When organic peroxide is used, the remaining amount of impurities is small. For this reason, the electrical resistance of the obtained elastomer is increased, and the dielectric breakdown strength can be further increased. Examples of the organic peroxide include α, α′-di (t-butylperoxy) diisopropylbenzene, 1,1-di (t-butylperoxy) cyclohexane, dicumyl peroxide, and 2,5-dimethyl-2. , 5-di (t-butylperoxy) hexane and the like.

  When an actuator, a sensor, or a transducer is configured using the dielectric film of the present invention, at least a pair of electrodes may be disposed with the dielectric film of the present invention interposed therebetween. Hereinafter, embodiments of actuators, sensors, and transducers using the dielectric film of the present invention will be described.

<Actuator>
FIG. 1 is a schematic cross-sectional view of an actuator according to this embodiment. (A) shows an OFF state, and (b) shows an ON state. As shown in FIG. 1, the actuator 10 includes a dielectric film 20 and electrodes 30a and 30b. The electrodes 30a and 30b are fixed to the front and back of the dielectric film 20, respectively. The electrodes 30a and 30b are connected to the power supply 40 via a conducting wire. When switching from the off state to the on state, a voltage is applied between the pair of electrodes 30a and 30b. By applying the voltage, the film thickness of the dielectric film 20 is reduced, and accordingly, as shown by the white arrow in FIG. Thereby, the actuator 10 outputs the driving force in the horizontal and vertical directions in the figure.

  Here, the dielectric film 20 is made of an elastomer containing a vinyl acetate copolymer. The relative dielectric constant of the dielectric film 20 is large. Therefore, according to the actuator 10, a desired force and displacement amount can be obtained even when the applied voltage is relatively small. Further, the dielectric breakdown strength of the dielectric film 20 is large. In addition, since the dielectric film 20 is flexible, it does not easily deteriorate even if the expansion and contraction is repeated. For this reason, the actuator 10 is excellent in durability and stability.

  Also in the actuator of the present invention, it is desirable to adopt the above-described preferred embodiment of the dielectric film 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. In order to further increase the amount of displacement of the actuator, it is desirable to attach the dielectric film in a state of extending in the surface extending direction.

  The material of the electrode disposed on the surface of the dielectric film 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. As a result, the output of the actuator is increased, and the driven member can be driven with a greater force.

<Sensor>
As an example of a sensor using the dielectric film of the present invention, an embodiment of a capacitive sensor will be described. FIG. 2 is a schematic cross-sectional view of the capacitive sensor according to this embodiment. As shown in FIG. 2, the capacitive sensor 11 includes a dielectric film 21, electrodes 31 a and 31 b, and a base material 41. The dielectric film 21 has a strip shape extending in the left-right direction. The dielectric film 21 is disposed on the upper surface of the base material 41 via the electrode 31b. The electrodes 31a and 31b have a strip shape extending in the left-right direction. The electrodes 31a and 31b are fixed to the front and back of the dielectric film 21, respectively. Conductive wires (not shown) are connected to the electrodes 31a and 31b. The base material 41 is an insulating flexible film and has a strip shape extending in the left-right direction. The base material 41 is fixed to the lower surface of the electrode 31b.

The capacitance (capacitance) of the capacitance type sensor 11 can be obtained by the following equation (I).
C = ε ₀ ε _r S / d (I)
[C: capacitance, ε ₀ : dielectric constant in vacuum, ε _r : relative dielectric constant of dielectric film, S: electrode area, d: distance between electrodes]
For example, when the capacitive sensor 11 is pressed from above, the dielectric film 21 is compressed and extends in the longitudinal direction accordingly. As the film thickness d decreases, the capacitance between the electrodes 31a and 31b increases. The magnitude, position, etc. of the applied load are detected by this capacitance change. Here, the dielectric film 21 is made of an elastomer containing a vinyl acetate copolymer. Since the relative dielectric constant of the dielectric film 21 is large, the capacitance is large. Therefore, the detection sensitivity of the capacitive sensor 11 is high. Further, the dielectric breakdown strength of the dielectric film 21 is large. In addition, since the dielectric film 21 is flexible, it does not easily deteriorate even if the expansion and contraction is repeated. For this reason, the capacitive sensor 11 is excellent in durability and stability. In the sensor of the present invention, it is desirable to adopt the above-described preferred embodiment of the dielectric film of the present invention.

<Transducer>
An embodiment of a power generation transducer will be described as an example of a transducer using the dielectric film of the present invention. FIG. 3 is a schematic cross-sectional view of the power generation transducer in the present embodiment. (A) shows the time of expansion, and (b) shows the time of contraction. As shown in FIG. 3, the power generation transducer 12 includes a dielectric film 22 and electrodes 32a and 32b. The electrodes 32a and 32b are fixed to the front and back of the dielectric film 22, respectively. Conductive wires are connected to the electrodes 32a and 32b, and the electrode 32b is grounded.

  As shown in FIG. 3A, when the power generation transducer 12 is compressed and the dielectric film 22 is extended in a direction parallel to the surfaces of the electrodes 32a and 32b, the film thickness of the dielectric film 22 is reduced, and the distance between the electrodes 32a and 32b is reduced. The charge is stored in Thereafter, when the compressive force is removed, the dielectric film 22 contracts due to the elastic restoring force of the dielectric film 22, and the film thickness increases. At that time, electric charges are released and electric power is generated. Here, the dielectric film 22 is made of an elastomer containing a vinyl acetate copolymer. Since the dielectric constant of the dielectric film 22 is large, a large amount of charges can be stored at the interface with the electrodes 32a and 32b. Further, the dielectric breakdown strength of the dielectric film 22 is large. In addition, since the dielectric film 22 is flexible, it is not easily deteriorated even if the expansion and contraction is repeated. For this reason, the power generation transducer 12 is excellent in durability and stability. In the transducer according to the present invention, it is desirable to employ the above-described preferred embodiment of the dielectric film according to the present invention.

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

<Manufacture of dielectric film>
[Example 1]
First, 100 parts by mass of ethylene-vinyl acetate copolymer A (“Levaprene (registered trademark) 450” manufactured by LANXESS, ethylene unit: vinyl acetate unit = 55: 45 (mass ratio, the same applies hereinafter)) and a processing aid. 2 parts by weight of stearic acid (“LUNAC (registered trademark) S30” manufactured by Kao Corporation) and an organic peroxide as a crosslinking agent, α, α′-di (t-butylperoxy) diisopropylbenzene (Nippon Yushi ( 6.4 parts by mass of “Perbutyl (registered trademark) P-40” manufactured by Co., Ltd.) and triallyl isocyanurate as a crosslinking assistant (“TAIC (registered trademark) M-60” manufactured by Nippon Kasei Co., Ltd.) 1.2 An elastomer composition was prepared by mixing parts by mass with a roll kneader. The prepared elastomer composition was filled in a mold and press-crosslinked at 170 ° C. for about 15 minutes to obtain a dielectric film. The obtained dielectric film was referred to as Example 1. Two types of dielectric films were manufactured with different thicknesses. One thickness was 0.5 mm, and the other thickness was 0.2 mm (hereinafter, the same applies to Examples 2 to 4 and Comparative Examples 1 to 3).

[Example 2]
A dielectric film was produced in the same manner as in Example 1 except for the type of ethylene-vinyl acetate copolymer. That is, ethylene-vinyl acetate copolymer B (“Levaprene 600HV” manufactured by LANXESS, ethylene unit: vinyl acetate unit = 40: 60) having a different vinyl acetate unit content from Example 1 was used. The obtained dielectric film was referred to as Example 2.

[Example 3]
A dielectric film was produced in the same manner as in Example 1 except for the type of ethylene-vinyl acetate copolymer. That is, ethylene-vinyl acetate copolymer C (“Levaprene 800HV” manufactured by LANXESS, ethylene unit: vinyl acetate unit = 20: 80) having a different content of vinyl acetate units from Example 1 was used. The obtained dielectric film was referred to as Example 3.

[Example 4]
As the polymer component, 50 parts by mass of the same ethylene-vinyl acetate copolymer B as in Example 2 and 50 parts by mass of hydrogenated nitrile rubber (“Zetpol (registered trademark) 0020” manufactured by Nippon Zeon Co., Ltd.) are used. did. A dielectric film was manufactured in the same manner as in Example 1 except for the above. The obtained dielectric film was referred to as Example 4.

[Comparative Example 1]
A dielectric film was produced in the same manner as in Example 1 except for the type of ethylene-vinyl acetate copolymer. That is, ethylene-vinyl acetate copolymer D (“Levaprene 900HV” manufactured by LANXESS, ethylene unit: vinyl acetate unit = 10: 90) having a different content of vinyl acetate units from Example 1 was used. The obtained dielectric film was referred to as Comparative Example 1.

[Comparative Example 2]
In place of the ethylene-vinyl acetate copolymer, a dielectric film was manufactured using nitrile rubber (“NIPOL (registered trademark) DN202” manufactured by Nippon Zeon Co., Ltd.). That is, first, 100 parts by mass of nitrile rubber, 1 part by mass of stearic acid (same as above) as a processing aid and 10 parts by mass of magnesium oxide (“# 150” manufactured by Kyowa Chemical Industry Co., Ltd.) and sulfur (Tsurumi) as a crosslinking agent 0.5 parts by mass of “Sulfax T-10” manufactured by Chemical Industry Co., Ltd., and tetraethylthiuram disulfide as a vulcanization accelerator (“Sunseller (registered trademark) TET-G” manufactured by Sanshin Chemical Industry Co., Ltd.) 2 Part by mass and 1 part by mass of N-cyclohexyl-2-benzothiazylsulfenamide (“Sunceller CZ-G” manufactured by the same company) were mixed in a roll kneader to prepare an elastomer composition. The prepared elastomer composition was filled in a mold and press-crosslinked at 150 ° C. for about 15 minutes to obtain a dielectric film. The obtained dielectric film was referred to as Comparative Example 2.

[Comparative Example 3]
A dielectric film was produced using isoprene rubber (“NIPOL IR2200” manufactured by Nippon Zeon Co., Ltd.) instead of the ethylene-vinyl acetate copolymer. That is, first, 100 parts by mass of isoprene rubber, 2 parts by mass of stearic acid (same as above) as a processing aid, 2.5 parts by mass of sulfur (as above) of a crosslinking agent, and N-cyclohexyl-2-yl as a vulcanization accelerator. 1 part by mass of benzothiazylsulfenamide (same as above) was mixed with a roll kneader to prepare an elastomer composition. The prepared elastomer composition was filled in a mold and press-crosslinked at 150 ° C. for about 15 minutes to obtain a dielectric film. The obtained dielectric film was referred to as Comparative Example 3.

<Evaluation method>
The manufactured dielectric film was evaluated according to five items: flexibility, relative dielectric constant, volume resistivity, electric field strength at break, and maximum displacement rate. Hereinafter, each evaluation method will be described.

[Flexibility]
The dielectric film (film thickness 0.5 mm) was subjected to a tensile test according to JIS K6251 (2004), and the elongation at break (E _b ) was determined. The shape of the test piece was dumbbell No. 2. The larger the elongation at cutting, the higher the flexibility.

[Relative permittivity]
The relative dielectric constant of the dielectric film (film thickness 0.5 mm) was measured. For measurement of relative permittivity, each dielectric film is placed in a sample holder (Solartron, type 12962A), and a dielectric constant measurement interface (manufactured by the company, type 1296) and a frequency response analyzer (made by the company, type 1255B) are used in combination. And measured (frequency 100 Hz).

[Volume resistivity]
The volume resistivity of the dielectric film (film thickness 0.5 mm) was measured according to JIS K6271 (2008) (applied voltage 100 V). “SME-8411” manufactured by Toa Denpa Kogyo Co., Ltd. was used as the electrode.

[Electric field strength and maximum displacement rate at breakdown]
An actuator was configured using the manufactured dielectric film (film thickness 0.2 mm), and the displacement of the actuator with respect to the applied voltage was measured. Below, an experimental apparatus and an experimental method are demonstrated.

  Electrodes made by mixing carbon black and acrylic rubber were attached to the upper and lower surfaces of the dielectric film to form an actuator. FIG. 4 shows a top view of the manufactured actuator. FIG. 5 shows a VV cross-sectional view in FIG.

As shown in FIGS. 4 and 5, the actuator 5 includes a dielectric film 50 and a pair of electrodes 51 a and 51 b. The dielectric film 50 has a circular thin film shape with a diameter of 70 mm. The dielectric film 50 is disposed in a state of being stretched in the biaxial direction at a stretch rate of 50%. Here, the stretching ratio is a value calculated by the following formula (II).
Stretch rate (%) = {√ (S ₂ / S ₁ ) −1} × 100 (II)
[S ₁ : Dielectric film area before stretching (natural state), S ₂ : Dielectric film area after biaxial stretching]
The pair of electrodes 51a and 51b are arranged to face each other in the vertical direction with the dielectric film 50 interposed therebetween. The electrodes 51a and 51b have a circular thin film shape with a diameter of about 27 mm, and are arranged substantially concentrically with the dielectric film 50, respectively. A terminal portion 510a protruding in the diameter increasing direction is formed on the outer peripheral edge of the electrode 51a. The terminal portion 510a has a rectangular plate shape. Similarly, a terminal portion 510b protruding in the diameter increasing direction is formed on the outer peripheral edge of the electrode 51b. The terminal portion 510b has a rectangular plate shape. The terminal portion 510b is disposed at a position facing the terminal portion 510a by 180 °. Terminal portions 510a and 510b are each connected to power supply 52 via a conducting wire.

  When a voltage is applied between the electrodes 51a and 51b, an electrostatic attractive force is generated between the electrodes 51a and 51b, and the dielectric film 50 is compressed. Thereby, the thickness of the dielectric film 50 becomes thin and extends in the diameter expansion direction. At this time, the electrodes 51a and 51b are also integrated with the dielectric film 50 and extend in the diameter increasing direction. A marker 530 is attached to the electrode 51a in advance. The displacement of the marker 530 was measured by the displacement meter 53 and used as the displacement amount of the actuator 5.

From the measured displacement, the displacement rate of the dielectric film 50 was calculated by the following equation (III). The maximum value of the displacement rate was taken as the maximum displacement rate.
Displacement rate (%) = (displacement amount / radius of electrode) × 100 (III)
Further, the applied voltage was increased until the dielectric film 50 was broken, and the electric field strength when the dielectric film 50 was broken was obtained.

<Evaluation results>
The evaluation results of the dielectric film are shown in Table 1 together with the composition of the dielectric film.

  As shown in Table 1, the dielectric films of Examples 1 to 4 had a large volume resistivity in addition to a large elongation at break and a high relative dielectric constant. For this reason, in the actuator using the dielectric films of Examples 1 to 4, it was possible to increase the applied voltage and obtain a large amount of displacement. That is, when the dielectric films of Examples 1 to 4 were used, good electric field responsiveness was obtained. Moreover, when the dielectric films of Examples 1 to 3 were compared, the elongation at break and the relative dielectric constant tended to increase as the content of vinyl acetate units in the elastomer increased. The dielectric film of Example 4 contained a hydrogenated nitrile rubber having a large relative dielectric constant in addition to the ethylene-vinyl acetate copolymer, so that the elongation at break and the relative dielectric constant were higher.

  On the other hand, the dielectric film of Comparative Example 1 using an ethylene-vinyl acetate copolymer having a vinyl acetate unit of 90% by mass had a large volume resistivity but a small elongation at break and a relative dielectric constant. Moreover, since the dielectric film of Comparative Example 2 uses nitrile rubber, the volume resistivity is small although the relative dielectric constant is large. For this reason, the maximum electric field strength is small, and a sufficient amount of displacement cannot be obtained. Moreover, since the isoprene rubber is used for the dielectric film of Comparative Example 3, although the volume resistivity is large, the relative dielectric constant is small. For this reason, the maximum electric field strength increased, but a sufficient amount of displacement could not be obtained.

  From the above, it was confirmed that the dielectric film of the present invention is flexible and has a high relative dielectric constant and high dielectric breakdown strength. In addition, according to the dielectric film of the present invention, it was confirmed that an actuator with good electric field response can be configured.

  The dielectric film of the present invention is suitable for flexible actuators used in, for example, artificial muscles for industrial, medical, and welfare robots, small pumps for cooling electronic components, medical devices, and the like. The actuator using the dielectric film 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. In addition to a sensor such as a capacitive sensor and a power generation transducer, it is also suitable for a flexible transducer that emits light, generates heat, and develops color.

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 cross-sectional schematic diagram of the capacitance-type sensor which is one Embodiment of this invention. It is a cross-sectional schematic diagram of the electric power generation transducer which is one Embodiment of this invention, Comprising: (a) shows at the time of expansion | extension, (b) shows the time of contraction. It is a top view of the actuator used for the evaluation experiment. It is VV sectional drawing in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10: Actuator 20: Dielectric film 30a, 30b: Electrode 40: Power supply 11: Capacitance type sensor 21: Dielectric film 31a, 31b: Electrode 41: Base material 12: Power generation transducer 22: Dielectric film 32a, 32b: Electrode 5: Actuator 50: Dielectric film 51a, 51b: Electrode 52: Power source 53: Displacement meter 510a, 510b: Terminal part 530: Marker

Claims (7)

  A dielectric film comprising an elastomer including a vinyl acetate copolymer interposed between a plurality of electrodes in any of an actuator, a sensor, and a transducer.   2. The dielectric film according to claim 1, wherein a content ratio of the vinyl acetate unit in the elastomer is more than 20 mass% and 85 mass% or less when the polymer content of the elastomer is 100 mass%.   The dielectric film according to claim 1, wherein the vinyl acetate copolymer is made of a monomer containing ethylene and vinyl acetate. The vinyl acetate copolymer is an ethylene-vinyl acetate copolymer,
4. The mass ratio of ethylene units to vinyl acetate units in the ethylene-vinyl acetate copolymer is 60:40 to 15:85 (ethylene units: vinyl acetate units). 5. Dielectric film. A dielectric film made of an elastomer containing a vinyl acetate copolymer;
A plurality of electrodes disposed via the dielectric film,
An actuator in which the dielectric film expands and contracts according to the voltage applied between the electrodes. A dielectric film made of an elastomer containing a vinyl acetate copolymer;
A plurality of electrodes disposed via the dielectric film,
A sensor that detects deformation based on a change in capacitance between the electrodes. A dielectric film made of an elastomer containing a vinyl acetate copolymer;
A plurality of electrodes disposed via the dielectric film;
A transducer comprising:

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