Polymer Actuators and Sensors

Abstract

To provide a polymer actuator including a dielectric elastomer layer in which decrease in a dielectric breakdown voltage is suppressed and a dielectric constant is improved.SOLUTION: A polymer actuator includes a dielectric elastomer layer and two electrodes disposed on both surfaces of the dielectric elastomer layer. The dielectric elastomer layer is formed of a cured product of a composition containing a resin component containing polyrotaxane and a diene-based polymer having a hydroxyl group, and a (meth) acrylic polymer having, in a side chain, a cyclic carbonate structure or a cyano group and a linear or branched hydrocarbon chain.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to polymer actuators and sensors, and more particularly to polymer actuators and sensors that include a dielectric elastomer layer. [Background technology]

[0002] Polymer actuators having a dielectric elastomer layer containing polyrotaxane have been known as polymer actuators with large displacements (for example, JP 2017-66318 A (Patent Document 1)). However, conventional polymer actuators having a dielectric elastomer layer containing polyrotaxane do not necessarily have sufficiently high output, and there has been a demand for higher output.

[0003] In general, improving the dielectric constant of a polymer actuator having a dielectric elastomer layer is considered effective for increasing the output. Furthermore, incorporating a high-dielectric-constant filler, such as barium titanate or titania, is considered effective for improving the dielectric constant of the dielectric elastomer layer. However, since many high-dielectric-constant fillers are made of ceramics with high elastic moduli, incorporating such high-dielectric-constant fillers into a dielectric elastomer layer improves the dielectric constant of the dielectric elastomer layer. However, incorporating such high-dielectric-constant fillers into a dielectric elastomer layer significantly increases the elastic modulus, resulting in a problem of reduced displacement of the polymer actuator during operation. For this reason, there has been a demand for a technology that improves the dielectric constant of a polymer actuator having a dielectric elastomer layer while maintaining the flexibility of the dielectric elastomer layer.

[0004] Furthermore, Japanese Patent Laid-Open Publication No. 2018-59042 (Patent Document 2) discloses a dielectric elastomer material containing a copolymer having polar groups such as carbonate groups introduced into its side chains, and states that the introduction of the polar groups increases the dielectric constant of the dielectric elastomer material. However, dielectric elastomer materials containing copolymers having only polar groups such as carbonate groups introduced into their side chains do not necessarily have a sufficient improvement in dielectric constant. Furthermore, because copolymers having only polar groups such as carbonate groups introduced into their side chains tend to aggregate and phase separate in the dielectric elastomer material, the dielectric breakdown voltage is lower than that of dielectric elastomer materials that do not contain copolymers having polar groups such as carbonate groups introduced into their side chains. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-66318 [Patent Document 2] Japanese Patent Application Publication No. 2018-59042 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the problems associated with the above-mentioned conventional technology, and aims to provide a polymer actuator and sensor having a dielectric elastomer layer that suppresses a decrease in breakdown voltage and improves the dielectric constant. [Means for solving the problem]

[0007] As a result of extensive research to achieve the above-mentioned object, the inventors have discovered that by blending a (meth)acrylic polymer having a cyclic carbonate structure or a cyano group and a linear or branched hydrocarbon chain in its side chain with a dielectric elastomer layer made of a resin component containing a polyrotaxane and a diene-based polymer having a hydroxyl group, it is possible to suppress a decrease in the breakdown voltage of the dielectric elastomer layer and improve the dielectric constant, thereby completing the present invention.

[0008] That is, the present invention provides the following aspects.

[0009] [1] A polymer actuator comprising a dielectric elastomer layer and two electrodes arranged on both sides of the dielectric elastomer layer, wherein the dielectric elastomer layer is made of a cured product of a composition containing a resin component including a polyrotaxane and a diene-based polymer having a hydroxyl group, and a (meth)acrylic polymer having a cyclic carbonate structure or a cyano group and a linear or branched hydrocarbon chain in its side chain.

[0010] [2] The polymer actuator according to [1], wherein the (meth)acrylic polymer further has a polyalkylene glycol chain on the side chain.

[0011] [3] The (meth)acrylic polymer is represented by the following formula (1):

[0012] [ka]

[0013] (In the above formula, R 1 represents a hydrogen atom or a methyl group, and R 2 represents an alkylene group, and D represents a cyclic carbonate structure or a cyano group. and a repeating unit represented by the following formula (2):

[0014] [ka]

[0015] (In the above formula, R 3 represents a hydrogen atom or a methyl group, and R 4 represents a linear or branched hydrocarbon chain. The polymer actuator according to [1] or [2], which contains a repeating unit represented by the following formula:

[0016] [4] A sensor comprising the polymer actuator according to any one of [1] to [3].

[0017] Although the reason why the present invention makes it possible to suppress a decrease in the breakdown voltage of a dielectric elastomer layer and improve its dielectric constant is not entirely clear, the inventors speculate as follows: Cyclic carbonate structures and cyano groups have large dielectric polarization, resulting in a high dielectric constant. However, when a (meth)acrylic polymer having only cyclic carbonate structures or only cyano groups in its side chains is blended into a dielectric elastomer layer, the large dielectric polarization of the cyclic carbonate structures or cyano groups tends to cause aggregation between the cyclic carbonate structures or the cyano groups, reducing the dispersibility of the (meth)acrylic polymer in the resin component containing the polyrotaxane and the diene-based polymer having hydroxyl groups, reducing the uniformity of the dielectric elastomer layer, thereby reducing the breakdown voltage and destabilizing the operation of elements such as actuators and sensors. On the other hand, when a (meth)acrylic polymer having a cyclic carbonate structure or a cyano group and a hydrocarbon chain in the side chain is blended, the hydrocarbon chain in the side chain is hydrophobic and has a high affinity with the hydroxyl-containing diene polymer, which is the hydrophobic component in the resin component, so the (meth)acrylic polymer is uniformly dispersed in the resin component containing the polyrotaxane and the hydroxyl-containing diene polymer. As a result, a highly uniform dielectric elastomer layer is formed, which is thought to suppress a decrease in breakdown voltage and improve the output and sensitivity of elements such as actuators and sensors.

[0018] Furthermore, when a (meth)acrylic polymer having only cyclic carbonate structures or only cyano groups in the side chain is blended, as described above, the cyclic carbonate structures or the cyano groups tend to aggregate, canceling out polarization within the aggregate structure. Furthermore, even when an electric field is applied to the dielectric elastomer layer, the (meth)acrylic polymer is less likely to orient in the direction of the applied electric field. As a result, some of the cyclic carbonate structures or cyano groups no longer contribute to improving the dielectric constant, making it difficult to sufficiently improve the dielectric constant of the dielectric elastomer layer. On the other hand, when a (meth)acrylic polymer having a cyclic carbonate structure or a cyano group and a hydrocarbon chain in the side chain is blended, the hydrocarbon chain suppresses the aggregation of the cyclic carbonate structures or the cyano groups, maintaining the large dielectric polarization of the cyclic carbonate structure or the cyano group. Therefore, when an electric field is applied to the dielectric elastomer layer, the (meth)acrylic polymer is presumably oriented in the direction of the applied electric field, improving the dielectric constant. Furthermore, when a polyalkylene glycol chain is introduced into the side chain in addition to the cyclic carbonate structure or the cyano group and the hydrocarbon chain, the action of the polyalkylene glycol chain, which has high mobility and is likely to induce large polarization, can further suppress aggregation between the cyclic carbonate structures or between the cyano groups, and it is therefore presumed that the dielectric constant is further improved. [Effects of the Invention]

[0019] According to the present invention, it is possible to obtain a polymer actuator and a sensor that are provided with a dielectric elastomer layer in which a decrease in breakdown voltage is suppressed and the dielectric constant is improved. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a photograph showing a fluorescent light reflected on the surface of the cured film obtained in Example 3. [Figure 2] 1 is a photograph showing a fluorescent light reflected on the surface of the cured film obtained in Example 6. [Figure 3] 1 is a photograph showing a fluorescent light reflected on the surface of the cured film obtained in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in detail below based on preferred embodiments thereof.

[0022] The polymer actuator of the present invention comprises a dielectric elastomer layer and two electrodes arranged on both sides of the dielectric elastomer layer, and the dielectric elastomer layer is made of a cured product of a composition containing a resin component including a polyrotaxane and a diene-based polymer having a hydroxyl group, and a (meth)acrylic polymer having a cyclic carbonate structure or a cyano group and a linear or branched hydrocarbon chain in its side chain.

[0023] (Polyrotaxane) Polyrotaxane is a molecular assembly having a structure in which a rod-shaped molecule (axial molecule) penetrates a hole in a ring-shaped molecule, with bulky moieties (terminal groups) attached to both ends of the rod-shaped molecule. By incorporating such a polyrotaxane into a dielectric elastomer layer, the dielectric constant of the dielectric elastomer layer can be improved while suppressing a decrease in the breakdown voltage, thereby enabling the output of the actuator to be improved. Furthermore, a dielectric elastomer layer containing the polyrotaxane is less likely to become worn because the polyrotaxane serves as a dynamic crosslinking point, preventing the crosslinking point from being broken by deformation. This results in excellent reversibility (reversible responsiveness) and stability of the operation. In the present invention, there are no particular limitations on the type of polyrotaxane, and conventionally known polyrotaxanes can be used.

[0024] The ring-shaped molecule is not particularly limited, and examples thereof include cyclodextrins (e.g., α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin), crown ethers, cyclophanes, calixarenes, cucurbiturils, and cyclic amides. These ring-shaped molecules may be used alone or in combination. Furthermore, such ring-shaped molecules may have a substituent or a side chain. Among these ring-shaped molecules, cyclodextrins having caprolactone chains as graft chains are preferred from the viewpoint of obtaining appropriate flexibility and dielectric constant. Furthermore, cyclodextrins modified with hydrocarbon groups (e.g., alkyl groups or aryl groups) are preferred from the viewpoints of improving the moisture resistance of the dielectric elastomer layer, making it difficult for water molecules to be mixed into the dielectric elastomer layer, thereby suppressing the occurrence of hydrolysis reactions and deterioration of insulating properties, and ensuring the dispersibility and solubility of the polyrotaxane in the resin component.

[0025] The axial molecule is not particularly limited, and examples thereof include polyethylene glycol, polypropylene glycol, polyethylene, polypropylene, polyisoprene, polyisobutylene, polybutadiene, polylactic acid, polytetrahydrofuran, polydimethylsiloxane, polyvinyl alcohol, and polyvinyl methyl ether. These axial molecules may be used alone or in combination of two or more. Among these axial molecules, polyethylene glycol and polypropylene glycol are preferred because they have a low glass transition temperature and allow the ring-shaped molecule to move smoothly.

[0026] Furthermore, the bulky terminal group is not particularly limited, and examples thereof include a dinitrophenyl group, a cyclodextrin group, an adamantane group, a trityl group, a fluorescein group, a pyrene group, a substituted benzene ring, a polycyclic aromatic ring, and a steroid group. These terminal groups may be used alone or in combination of two or more. Among these terminal groups, the dinitrophenyl group, the cyclodextrin group, the adamantane group, the trityl group, the fluorescein group, and the pyrene group are preferred, with the adamantane group being more preferred, from the viewpoints of being easily introduced into the terminal of the axial molecule and having sufficient bulk to prevent the ring-shaped molecule from coming off.

[0027] (Diene polymer) The diene polymer (diene rubber) used in the present invention is a diene polymer having a hydroxyl group, and the hydroxyl group may be present at the end of the diene polymer or may be present on a side chain by a graft reaction or the like.

[0028] Examples of the diene polymers (diene rubbers) include homopolymers of dienes such as butadiene, isoprene, and chloroprene (for example, butadiene rubber, isoprene rubber, and chloroprene rubber) and copolymers (butadiene copolymers such as styrene-butadiene rubber and acrylonitrile-butadiene rubber, and isoprene copolymers such as styrene-isoprene rubber and acrylonitrile-isoprene rubber). Examples of copolymerizable monomers in the diene copolymers include (meth)acrylate, styrene, and acrylonitrile.

[0029] Among these diene polymers, hydrophobic diene polymers such as butadiene rubber, isoprene rubber, butadiene copolymers, and isoprene copolymers are preferred, from the viewpoint of avoiding the introduction of moisture due to moisture absorption, which promotes a decrease in the breakdown voltage, and butadiene rubber and isoprene rubber are more preferred.

[0030] ((Meth)acrylic polymer) The (meth)acrylic polymer used in the present invention has a cyclic carbonate structure or a cyano group and a linear or branched hydrocarbon chain in its side chain. The cyclic carbonate structure and the cyano group are groups exhibiting high dielectric properties (hereinafter, these are also collectively referred to as "highly dielectric functional groups"). By incorporating a (meth)acrylic polymer having such a highly dielectric functional group in its side chain into a dielectric elastomer layer, the dielectric constant of the dielectric elastomer layer is improved. However, because cyclic carbonate structures and cyano groups tend to aggregate with each other, a dielectric elastomer layer incorporating a (meth)acrylic polymer having only a cyclic carbonate structure or only a cyano group in its side chain is prone to aggregation and phase separation of the (meth)acrylic polymer. The (meth)acrylic polymer used in the present invention has the hydrocarbon chain introduced therein, which has a high affinity with the diene polymer having a hydroxyl group, which is a hydrophobic component in the resin component. This prevents aggregation of cyclic carbonate structures or cyano groups, and allows the polymer to be highly dispersed in the resin component containing the polyrotaxane and the diene polymer having a hydroxyl group, thereby forming a highly uniform dielectric elastomer layer and preventing a decrease in the breakdown voltage.

[0031] The (meth)acrylic polymer used in the present invention preferably further has a polyalkylene glycol chain in its side chain. By further introducing a polyalkylene glycol chain as a side chain of the (meth)acrylic polymer, aggregation of cyclic carbonate structures or cyano groups is suppressed, dispersibility of the (meth)acrylic polymer in the resin component containing the polyrotaxane and the diene polymer having a hydroxyl group is improved, and a more uniform dielectric elastomer layer is formed, thereby further suppressing a decrease in breakdown voltage.

[0032] The highly dielectric functional group is a cyclic carbonate structure or a cyano group, and the cyclic carbonate structure may be an alkylene carbonate structure such as an ethylene carbonate structure.

[0033] The (meth)acrylic polymer used in the present invention contains a repeating unit containing such a highly dielectric functional group, for example, a repeating unit represented by the following formula (1):

[0034] [ka]

[0035] The repeating unit has the following structure:

[0036] In the formula (1), R 1 represents a hydrogen atom or a methyl group. 2 represents an alkylene group, examples of which include a methylene group, an ethylene group, a propylene group, etc. D represents the highly dielectric functional group (the cyclic carbonate structure or a cyano group), and examples of the cyclic carbonate structure include alkylene carbonate structures such as an ethylene carbonate structure.

[0037] The hydrocarbon chain may be linear or branched, saturated or unsaturated. Examples of such hydrocarbon chains include alkyl groups, alkenyl groups, and alkadienyl groups having 3 to 30 carbon atoms (preferably 3 to 20, more preferably 4 to 18). Examples of the alkyl group include propyl, butyl, isobutyl, hexyl, octyl, 2-ethylhexyl, decyl, dodecyl, and stearyl (octadecyl). Examples of the alkenyl group include hydrocarbon groups having 4 to 30 carbon atoms (preferably 4 to 20, more preferably 4 to 18 carbon atoms) and one C═C bond per molecule, such as crotyl, methallyl, prenyl, isopentenyl, octenyl, decenyl, dodecenyl, and oleyl (octadecenyl). Examples of the alkadienyl group include hydrocarbon groups having two C=C bonds in one molecule and having 4 to 30 carbon atoms (preferably 4 to 20 carbon atoms, more preferably 4 to 18 carbon atoms), such as a butadienyl group, a sorbyl group (hexadienyl group), an octadienyl group, a decadienyl group, a dodecadienyl group, and an octadecadienyl group.

[0038] The (meth)acrylic polymer used in the present invention contains a repeating unit containing such a hydrocarbon chain, for example, a repeating unit represented by the following formula (2):

[0039] [ka]

[0040] The repeating unit has the following structure:

[0041] In the formula (2), R 3 represents a hydrogen atom or a methyl group. 4 represents the linear or branched hydrocarbon chain, which may be saturated or unsaturated, and examples thereof include alkyl and alkenyl groups having 3 to 30 carbon atoms (preferably 3 to 20, more preferably 4 to 18).

[0042] Examples of the polyalkylene glycol chain include a polyethylene glycol chain and a polypropylene glycol chain. Among these, a polyethylene glycol chain is preferred from the viewpoint of high chain mobility and not interfering with the movement of the highly dielectric functional group.

[0043] The degree of polymerization of the alkylene glycol in the polyalkylene glycol chain is preferably 4 to 100, more preferably 4 to 80, even more preferably 4 to 50, still more preferably 4 to 20, and particularly preferably 4 to 10. If the degree of polymerization of the alkylene glycol is less than the lower limit, aggregation of cyclic carbonate structures or cyano groups cannot be sufficiently suppressed, and therefore the dielectric constant does not improve sufficiently and a decrease in breakdown voltage tends not to be sufficiently suppressed. On the other hand, if the degree of polymerization exceeds the upper limit, the mobility of the polyalkylene glycol chain decreases, and the movement of the highly dielectric functional group tends to be hindered.

[0044] The (meth)acrylic polymer used in the present invention has a repeating unit containing such a polyalkylene glycol chain, for example, a repeating unit represented by the following formula (3):

[0045] [ka]

[0046] It is preferable that the polymer further has a repeating unit represented by the following formula:

[0047] In the formula (3), R 5 represents a hydrogen atom or a methyl group. AO represents an alkyleneoxy group, such as an ethyleneoxy group or a propyleneoxy group. Among these, an ethyleneoxy group is preferred from the viewpoint of increasing the dielectric constant relative to the amount added because it has a large polarization despite its small molecular weight. 6 represents an alkyl group, examples of which include a methyl group and an ethyl group. p represents the degree of polymerization of the alkyleneoxy group and is preferably 4 to 100, more preferably 4 to 80, even more preferably 4 to 50, still more preferably 4 to 20, and particularly preferably 4 to 10. If p is less than the lower limit, aggregation of cyclic carbonate structures or cyano groups cannot be sufficiently suppressed, so the dielectric constant does not improve sufficiently and the decrease in breakdown voltage tends not to be sufficiently suppressed. On the other hand, if p exceeds the upper limit, the mobility of the polyalkylene glycol chain decreases, hindering polarization of the high dielectric functional group, so the dielectric constant tends to be difficult to improve.

[0048] Furthermore, the (meth)acrylic polymer used in the present invention may contain other (meth)acrylic monomer units in addition to the repeating unit containing the highly dielectric functional group, the repeating unit containing the hydrocarbon chain, and the repeating unit containing the polyalkylene glycol chain, provided that the effects of the present invention are not impaired. Examples of such other (meth)acrylic monomer units include (meth)acrylic monomer units having a hydroxyl group in the side chain, such as hydroxyalkyl (meth)acrylate units such as hydroxymethyl (meth)acrylate units and hydroxyethyl (meth)acrylate units.

[0049] The degree of polymerization of the (meth)acrylic monomer in the (meth)acrylic polymer used in the present invention (i.e., the total number of repeating units containing the highly dielectric functional group, repeating units containing the hydrocarbon chain, repeating units containing the polyalkylene glycol chain, and other (meth)acrylic monomer units) is preferably 3 to 10,000, more preferably 5 to 1,000, and particularly preferably 5 to 100. If the degree of polymerization of the (meth)acrylic monomer is below the lower limit, the (meth)acrylic polymer tends to easily bleed out from the dielectric elastomer layer. On the other hand, if it exceeds the upper limit, the (meth)acrylic polymer does not disperse uniformly within the dielectric elastomer layer, and therefore the dielectric constant does not improve sufficiently and the decrease in breakdown voltage tends not to be sufficiently suppressed.

[0050] In the (meth)acrylic polymer used in the present invention, the molar ratio (highly dielectric functional group unit:hydrocarbon chain unit) of the repeating unit containing the highly dielectric functional group (hereinafter also referred to as "highly dielectric functional group unit") to the repeating unit containing the hydrocarbon chain (hereinafter also referred to as "hydrocarbon chain unit") is preferably 2:98 to 90:10, more preferably 5:95 to 80:20, and particularly preferably 10:90 to 70:30. If the ratio of highly dielectric functional group unit:hydrocarbon chain unit is less than the lower limit, the amount of highly dielectric functional group introduced tends to be small, making it difficult to improve the dielectric constant. On the other hand, if the ratio exceeds the upper limit, aggregation between cyclic carbonate structures or cyano groups cannot be sufficiently suppressed, so the dielectric constant does not sufficiently improve and the decrease in breakdown voltage tends to be insufficiently suppressed.

[0051] In the (meth)acrylic polymer used in the present invention, the molar ratio of the highly dielectric functional group unit to the repeating unit containing the polyalkylene glycol chain (hereinafter also referred to as "polyalkylene glycol chain unit") (highly dielectric functional group unit:polyalkylene glycol chain unit) is preferably 2:98 to 90:10, more preferably 5:95 to 80:20, and particularly preferably 10:90 to 70:30. If the ratio of highly dielectric functional group unit:polyalkylene glycol chain unit is less than the lower limit, the amount of highly dielectric functional group introduced tends to be small, making it difficult to improve the dielectric constant. On the other hand, if the ratio exceeds the upper limit, it is not possible to sufficiently suppress aggregation between cyclic carbonate structures or between cyano groups, so the dielectric constant does not improve sufficiently and the decrease in breakdown voltage tends to be insufficiently suppressed.

[0052] In the composition for forming the dielectric elastomer layer, the content of the (meth)acrylic polymer is preferably 5 to 60 parts by mass, more preferably 10 to 40 parts by mass, per 100 parts by mass of the resin component for forming the dielectric elastomer layer. If the content of the (meth)acrylic polymer is less than the lower limit, the effects of the highly dielectric functional group and the hydrocarbon chain are not sufficiently obtained, and for example, the dielectric constant is not sufficiently improved and the decrease in breakdown voltage tends not to be sufficiently suppressed. On the other hand, if the content exceeds the upper limit, the (meth)acrylic polymer tends to undergo phase separation.

[0053] Furthermore, in the composition for forming the dielectric elastomer layer, the content of the (meth)acrylic polymer is preferably 5 to 5,000 parts by mass, more preferably 100 to 3,000 parts by mass, relative to 100 parts by mass of the polyrotaxane. If the content of the (meth)acrylic polymer is less than the lower limit, the effects of the highly dielectric functional group and the hydrocarbon chain are not sufficiently obtained, and for example, the dielectric constant is not sufficiently improved and the decrease in breakdown voltage tends to be insufficiently suppressed. On the other hand, if the content exceeds the upper limit, the (meth)acrylic polymer tends to undergo phase separation.

[0054] The method for synthesizing such a (meth)acrylic polymer is not particularly limited, and examples thereof include a method in which a heterocyclic (meth)acrylate containing one oxygen atom in a cyclic structure (e.g., glycidyl (meth)acrylate), a (meth)acrylic monomer containing the hydrocarbon chain, and, if necessary, a (meth)acrylic monomer containing the polyalkylene glycol chain, and another (meth)acrylic monomer are heated in the presence of lithium bromide in a carbon dioxide atmosphere to copolymerize the (meth)acrylate while converting the cyclic structure containing one oxygen atom to a cyclic carbonate structure; and a method in which a (meth)acrylic monomer containing the cyclic carbonate structure or a (meth)acrylate containing a cyano group, a (meth)acrylic monomer containing the hydrocarbon chain, and, if necessary, a (meth)acrylic monomer containing the polyalkylene glycol chain, and another (meth)acrylic monomer are heated in a nitrogen atmosphere to copolymerize the (meth)acrylate.

[0055] The reaction conditions for these synthesis methods are not particularly limited, and conventionally known reaction conditions can be appropriately adopted, and it is preferable to adopt optimized reaction conditions.

[0056] (Other resin components) The composition for forming the dielectric elastomer layer may optionally contain a polysiloxane-containing block copolymer or a polysiloxane-free polymer. The polysiloxane is not particularly limited, but examples thereof include polydimethylsiloxane, polymethylphenylsiloxane, and modified polydimethylsiloxane. The polysiloxane-containing block copolymer is not particularly limited, but examples thereof include polycaprolactone-polysiloxane block copolymer, polyadipate-polysiloxane block copolymer, and polyethylene glycol-polysiloxane block copolymer. The polysiloxane-free polymer is not particularly limited, but examples thereof include polypropylene glycol, polytetramethylene glycol, polycarbonate, polycaprolactone, polyethylene adipate, polybutylene adipate, and polypropylene glycol monobutyl ether.

[0057] The dielectric elastomer layer of the present invention can be formed by curing a composition containing at least the resin component including the polyrotaxane and the diene polymer having a hydroxyl group, the (meth)acrylic polymer, and, if necessary, a block copolymer containing polysiloxane or a polymer not containing polysiloxane. Therefore, the composition preferably contains a crosslinking agent if necessary.

[0058] Such a crosslinking agent can be appropriately selected depending on the resin components contained in the composition, such as the polyrotaxane, the diene polymer having a hydroxyl group, the block copolymer containing the polysiloxane, and the polymer not containing the polysiloxane, and is not particularly limited, and examples thereof include aliphatic polyols, aliphatic polyethers, aliphatic polycarbonates, and block copolymers thereof, each having a functional group. Examples of the functional group include an isocyanate group, a blocked isocyanate group, and an epoxy group.

[0059] The method for forming the dielectric elastomer layer is not particularly limited, and examples thereof include a method in which the composition is coated by a known film-forming method such as spin coating, slit die coating, screen printing, or inkjet printing, and then cured.

[0060] The polymer actuator of the present invention comprises a dielectric with an electrode layer, which consists of such a dielectric elastomer layer and two electrodes arranged on both sides of the dielectric elastomer layer. There are no particular restrictions on the shape of the dielectric with an electrode layer, and examples include a cylindrical shape formed by multiple spiral wounds, or a curtain-like shape formed by bending and folding the dielectric in a wavy pattern.

[0061] The electrodes are not particularly limited, and known electrodes used in conventional actuators can be used. Examples include conductive polymer films made of silicone, natural rubber, resin, etc., in which conductive particles such as noble metals (e.g., silver nanowires, etc.) and carbon (e.g., carbon black, carbon nanotubes, graphene, etc.) are dispersed.

[0062] The sensor of the present invention is equipped with the polymer actuator of the present invention. [Example]

[0063] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0064] (Synthesis Example 1) <Synthesis of (meth)acrylic polymer> 0.4 g of 2-cyanoethyl acrylate, 0.6 g of 2-ethylhexyl acrylate, 0.15 g of S,S-dibenzyltrithiocarbonate, 9 mg of azobisisobutyronitrile (AIBN), and 1.4 g of N-methyl-2-pyrrolidone (NMP) were mixed in a flask and stirred under a nitrogen atmosphere at 70°C for 20 hours to carry out a polymerization reaction. The reaction solution was poured into 20 ml of methanol to generate a precipitate, which was then cooled to -70°C for 1 hour and then centrifuged (4800 rpm). The resulting precipitate was dissolved in 1 ml of tetrahydrofuran (THF) and poured into 20 ml of methanol to generate a precipitate again. The precipitate was then cooled to -70°C for 1 hour and then centrifuged (4800 rpm). The resulting precipitate was dried in vacuum to obtain the compound represented by the following formula (4):

[0065] [ka]

[0066] 0.88 g of an acrylic polymer having a 2-cyanoethyl group and a 2-ethylhexyl group in the side chain, represented by the formula: was obtained. The designed molecular weight of this acrylic polymer was 2200. This synthesis was carried out multiple times to secure the required amount of the acrylic polymer.

[0067] (Synthesis Example 2) <Synthesis of (meth)acrylic polymer> 3.85 g of glycidyl acrylate, 2.96 g of 2-ethylhexyl acrylate, 2.82 g of methoxytriethylene glycol acrylate, 0.158 g of S,S-dibenzyltrithiocarbonate, 90 mg of azobisisobutyronitrile (AIBN), 0.15 g of lithium bromide monohydrate (LiBr·HO), and 14 g of N-methyl-2-pyrrolidone (NMP) were mixed and polymerized under a carbon dioxide atmosphere at 1 atmosphere pressure at 70°C for 20 hours with stirring. The resulting solution was poured into 150 ml of methanol and cooled to -70°C to form a precipitate, which was then collected by centrifugation (4800 rpm). The resulting precipitate was dissolved in 125 ml of methanol, cooled to -70°C, and again to form a precipitate. The precipitate was then collected by centrifugation (4800 rpm). The resulting precipitate was dried in vacuo to obtain the product of the following formula (5):

[0068] [ka]

[0069] The resulting polymer had an ethylene carbonate structure, a 2-ethylhexyl group, and a methoxytriethylene glycol chain in the side chain, and had a designed molecular weight of about 2066.

[0070] (Synthesis Example 3) <Synthesis of (meth)acrylic polymer> 0.4 g of glycidyl acrylate, 0.6 g of dodecyl acrylate, 0.16 g of S,S-dibenzyltrithiocarbonate, 9 mg of azobisisobutyronitrile (AIBN), 15 mg of lithium bromide monohydrate (LiBr·HO), and 1.4 g of N-methyl-2-pyrrolidone (NMP) were mixed and polymerized under a carbon dioxide atmosphere at 1 atmosphere pressure at 70°C for 20 hours with stirring. The resulting solution was poured into 20 ml of methanol to form a precipitate, which was then collected by centrifugation (5000 rpm). The resulting precipitate was dissolved in 2 ml of tetrahydrofuran (THF) and poured into 20 ml of methanol to form another precipitate, which was then collected by centrifugation (5000 rpm). The resulting precipitate was dried in vacuum to obtain the compound represented by the following formula (6):

[0071] [ka]

[0072] The resulting polymer had an ethylene carbonate structure and a dodecyl group in the side chain, and the designed molecular weight of the polymer was approximately 2100. This synthesis was repeated multiple times to obtain the required amount of the polymer.

[0073] (Comparative Synthesis Example 1) <Synthesis of (meth)acrylic polymer> 0.4 g of glycidyl acrylate, 0.6 g of methoxytriethylene glycol acrylate, 0.159 g of S,S-dibenzyltrithiocarbonate, 9 mg of azobisisobutyronitrile (AIBN), 15 mg of lithium bromide monohydrate (LiBr·HO), and 1.4 g of N-methyl-2-pyrrolidone (NMP) were mixed and polymerized under a carbon dioxide atmosphere at 1 atmosphere pressure at 70°C for 20 hours with stirring. The resulting solution was poured into 20 ml of methanol and cooled to -75°C to form a precipitate, which was then collected by centrifugation (5000 rpm). The resulting precipitate was dissolved in 1 ml of tetrahydrofuran (THF) and poured into 20 ml of methanol. The solution was cooled to -75°C to form another precipitate, which was then collected by centrifugation (5000 rpm). The resulting precipitate was dried in vacuum to obtain the compound represented by the following formula (7):

[0074] [ka]

[0075] 0.42 g of an acrylic polymer having an ethylene carbonate structure and a methoxytriethylene glycol chain in the side chain was obtained. The designed molecular weight of this acrylic polymer was approximately 2100. This synthesis was carried out multiple times to secure the required amount of the acrylic polymer.

[0076] Example 1 <Preparation of (meth)acrylic polymer-containing polybutadiene film> 3.95 g of hydroxypropylated adamantane polyrotaxane (HAPR, ring-shaped molecule: α-cyclodextrin, axial molecule: polyethylene glycol (average molecular weight: 35,000), terminal group: adamantane group) prepared according to the method described in WO 2008 / 108411, 1.94 g of polymethylene polyphenyl polyisocyanate (Polymeric MDI "Millionate MR200" manufactured by Tosoh Corporation), and a hydroxypropyl ...

[0077] [ka]

[0078] 8.74 g of hydroxyl-terminated liquid polybutadiene represented by the formula ("Poly bd R-15HT" manufactured by Idemitsu Kosan Co., Ltd.) was dissolved in 9.53 g of toluene and stirred to prepare a uniform solution.

[0079] To this solution were added 0.24 g of an antioxidant (Rianlon's "Thanox 1726," 4,6-bis(dodecylthiomethyl)-o-cresol), 0.2 g of a surface conditioner (Gelest's silicone additive "DBL-C31," both ends alcohol-modified silicone: caprolactone-dimethylsiloxane-caprolactone block copolymer, toluene solution with a solids concentration of 30% by mass), and 0.41 g of a hydrolysis inhibitor (Nisshinbo Chemical Inc.'s "Carbodilite V-09GB," toluene solution with a concentration of 30% by mass), and the mixture was stirred to prepare a uniform solution.

[0080] To this solution, 1.27 g of the acrylic polymer having 2-cyanoethyl groups and 2-ethylhexyl groups on the side chains obtained in Synthesis Example 1 (10 parts by mass per 100 parts by mass of the total amount (resin component amount) of the hydroxypropylated adamantane polyrotaxane and the hydroxyl group-terminated liquid polybutadiene) was added and stirred to prepare a uniform resin solution.

[0081] After degassing the resin solution, it was coated onto a substrate film using a slit die coater, and the resulting coating was cured by standing in an oven at 130°C under reduced pressure for 5 hours. The resulting cured film was then peeled off from the substrate film. The thickness of the cured film was 0.05 mm.

[0082] Example 2 A cured film was prepared in the same manner as in Example 1, except that the amount of the acrylic polymer having 2-cyanoethyl and 2-ethylhexyl groups in its side chains obtained in Synthesis Example 1 was changed to 2.54 g (20 parts by mass per 100 parts by mass of the total amount (resin component amount) of the hydroxypropylated adamantane polyrotaxane and the hydroxyl group-terminated liquid polybutadiene). The thickness of this cured film was 0.05 mm.

[0083] Example 3 A cured film was prepared in the same manner as in Example 1, except that the amount of the acrylic polymer having 2-cyanoethyl and 2-ethylhexyl groups in its side chains obtained in Synthesis Example 1 was changed to 3.81 g (30 parts by mass per 100 parts by mass of the total amount (resin component amount) of the hydroxypropylated adamantane polyrotaxane and the hydroxyl group-terminated liquid polybutadiene). The thickness of this cured film was 0.05 mm.

[0084] Example 4 A cured film was prepared in the same manner as in Example 1, except that 1.27 g (10 parts by mass per 100 parts by mass of the total amount (resin component amount) of the hydroxypropylated adamantane polyrotaxane and the hydroxyl group-terminated liquid polybutadiene) of an acrylic polymer having an ethylene carbonate structure, a 2-ethylhexyl group, and a methoxytriethylene glycol chain in the side chain obtained in Synthesis Example 2 was added instead of the acrylic polymer having a 2-cyanoethyl group and a 2-ethylhexyl group in the side chain obtained in Synthesis Example 1. The thickness of this cured film was 0.05 mm.

[0085] Example 5 A cured film was prepared in the same manner as in Example 4, except that the amount of the acrylic polymer having an ethylene carbonate structure, a 2-ethylhexyl group, and a methoxytriethylene glycol chain in the side chain obtained in Synthesis Example 2 was changed to 2.54 g (20 parts by mass per 100 parts by mass of the total amount (resin component amount) of the hydroxypropylated adamantane polyrotaxane and the hydroxyl group-terminated liquid polybutadiene). The thickness of this cured film was 0.05 mm.

[0086] Example 6 A cured film was prepared in the same manner as in Example 4, except that the amount of the acrylic polymer having an ethylene carbonate structure, a 2-ethylhexyl group, and a methoxytriethylene glycol chain in the side chain obtained in Synthesis Example 2 was changed to 3.81 g (30 parts by mass per 100 parts by mass of the total amount (resin component amount) of the hydroxypropylated adamantane polyrotaxane and the hydroxyl group-terminated liquid polybutadiene). The thickness of this cured film was 0.05 mm.

[0087] Example 7 A cured film was prepared in the same manner as in Example 1, except that 1.27 g (10 parts by mass per 100 parts by mass of the total amount (resin component amount) of the hydroxypropylated adamantane polyrotaxane and the hydroxyl group-terminated liquid polybutadiene) of the acrylic polymer having an ethylene carbonate structure and a dodecyl group in the side chain obtained in Synthesis Example 3 was added instead of the acrylic polymer having a 2-cyanoethyl group and a 2-ethylhexyl group in the side chain obtained in Synthesis Example 1. The thickness of this cured film was 0.05 mm.

[0088] (Comparative Example 1) A cured film was prepared in the same manner as in Example 1, except that the acrylic polymer having a 2-cyanoethyl group and a 2-ethylhexyl group in the side chain obtained in Synthesis Example 1 was not added. The thickness of this cured film was 0.05 mm.

[0089] (Comparative Example 2) A cured film was prepared in the same manner as in Example 1, except that 3.81 g (30 parts by mass per 100 parts by mass of the total amount (resin component amount) of the hydroxypropylated adamantane polyrotaxane and the hydroxyl group-terminated liquid polybutadiene) of the acrylic polymer having an ethylene carbonate structure and a methoxytriethylene glycol chain in the side chain obtained in Comparative Synthesis Example 1 was used instead of the acrylic polymer having a 2-cyanoethyl group and a 2-ethylhexyl group in the side chain obtained in Synthesis Example 1. The thickness of this cured film was 0.05 mm.

[0090] [Dielectric constant] Gold was evaporated onto both sides of the resulting cured film using an auto-fine coater (JEOL Ltd., "JEC-3000FC") to form electrode films (15 mm diameter). The capacitance was measured using a precision impedance analyzer (Agilent Corp., "4294A") with a dielectric constant measurement probe, and the relative dielectric constant was calculated. The results are shown in Table 1.

[0091] [Table 1]

[0092] As shown in Table 1, when an acrylic polymer having a 2-cyanoethyl group and a 2-ethylhexyl group in the side chain was added to a dielectric elastomer layer consisting of a cured resin component including a polyrotaxane and a diene-based polymer having a hydroxyl group (Examples 1 to 3), it was confirmed that the relative dielectric constant was improved compared to when no acrylic polymer was added (Comparative Example 1).

[0093] Furthermore, it was confirmed that when an acrylic polymer having an ethylene carbonate structure, a 2-ethylhexyl group, and a methoxytriethylene glycol chain in the side chain was added to a dielectric elastomer layer consisting of a cured resin component including polyrotaxane and a diene-based polymer having a hydroxyl group (Examples 4 to 6), the relative dielectric constant was improved compared to when no such polymer was added (Comparative Example 1).

[0094] Furthermore, it was confirmed that when an acrylic polymer having an ethylene carbonate structure and a dodecyl group in the side chain was added to a dielectric elastomer layer consisting of a cured resin component including polyrotaxane and a diene-based polymer having a hydroxyl group (Example 7), the relative dielectric constant was improved compared to when no acrylic polymer was added (Comparative Example 1).

[0095] Furthermore, when the addition amount is the same, it was found that the acrylic polymers having an ethylene carbonate structure, a 2-ethylhexyl group, and a methoxytriethylene glycol chain in the side chain (Examples 4 to 6) have a greater effect of improving the relative dielectric constant than the acrylic polymers having a 2-cyanoethyl group and a 2-ethylhexyl group in the side chain (Examples 1 to 3).

[0096] On the other hand, when an acrylic polymer having an ethylene carbonate structure and a methoxytriethylene glycol chain in the side chain was added to a dielectric elastomer layer consisting of a cured resin component containing polyrotaxane and a diene-based polymer having a hydroxyl group (Comparative Example 2), the relative dielectric constant was improved compared to when no acrylic polymer was added (Comparative Example 1).However, it was found that the effect of improving the relative dielectric constant was inferior compared to when an acrylic polymer having a 2-cyanoethyl group and a 2-ethylhexyl group in the side chain was added (Example 3) and when an acrylic polymer having an ethylene carbonate structure, a 2-ethylhexyl group, and a methoxytriethylene glycol chain in the side chain was added (Example 6) when the same amount was added.

[0097] [Dispersibility of (meth)acrylic polymer] A fluorescent lamp was placed at a height of 150 cm above the obtained cured films, and the image of the fluorescent lamp reflected on the surface of the cured films was observed. Figures 1 to 3 show the images of the fluorescent lamp reflected on the surface of the cured films obtained in Examples 3 and 6 and Comparative Example 2.

[0098] When an acrylic polymer having a 2-cyanoethyl group and a 2-ethylhexyl group in the side chain was added to a dielectric elastomer layer made of a cured resin component containing a polyrotaxane and a diene polymer having a hydroxyl group (Example 3, Figure 1), or when an acrylic polymer having an ethylene carbonate structure, a 2-ethylhexyl group, and a methoxytriethylene glycol chain in the side chain was added (Example 6, Figure 2), the shape of the reflected image of the fluorescent light on the surface of the cured film was clear, confirming that the acrylic polymer was uniformly dispersed in the dielectric elastomer layer. On the other hand, when an acrylic polymer having an ethylene carbonate structure and a methoxytriethylene glycol chain in the side chain was added (Comparative Example 2, Figure 3), the shape of the reflected image of the fluorescent light on the surface of the cured film became unclear due to light scattering, confirming that the acrylic polymer was aggregated and separated in the dielectric elastomer layer. In the cured film obtained in Comparative Example 2, the acrylic polymer did not have a hydrocarbon chain in the side chain that has good affinity with the diene polymer, and therefore the dispersibility of the acrylic polymer was thought to be lower than in the cured films (Examples 3 and 6) in which an acrylic polymer having a hydrocarbon chain in the side chain was added.

[0099] As described above, in the dielectric elastomer layer according to the present invention, the (meth)acrylic polymer having a linear or branched hydrocarbon chain and a cyclic carbonate structure or a cyano group in its side chain, which is a high dielectric component, is uniformly dispersed without aggregation, so that the electric field within the layer is uniform, dielectric breakdown is unlikely to occur, and the dielectric breakdown voltage is high. Actuators and sensors employing such a dielectric elastomer layer with a high dielectric breakdown voltage can be used at high voltages, and can achieve significant improvements in output and sensitivity.

[0100] On the other hand, in dielectric elastomer layers in which the high-dielectric component is not uniformly dispersed and aggregation and phase separation have occurred, such as in dielectric elastomer layers containing acrylic polymers with ethylene carbonate structures and methoxytriethylene glycol chains in their side chains, the electric field is concentrated between the high-dielectric phases, resulting in localized high electric fields, which can cause breakdown to occur from these points even at low voltages, i.e., the breakdown voltage is low. Furthermore, even when such dielectric elastomer layers with low breakdown voltages are applied to actuators and sensors, they can only be used at low voltages, making it difficult to sufficiently improve output and sensitivity. [Industrial Applicability]

[0101] As described above, according to the present invention, it is possible to form a dielectric elastomer layer that suppresses a decrease in breakdown voltage and improves the dielectric constant. Therefore, since the polymer actuator of the present invention includes such a dielectric elastomer layer, it can be operated at high voltage and can be used in a variety of fields, such as industrial and nursing care robots, artificial muscles, sensors, and haptics.

Claims

1. a dielectric elastomer layer and two electrodes disposed on opposite sides of the dielectric elastomer layer; A polymer actuator characterized in that the dielectric elastomer layer is made of a cured product of a composition containing a resin component including polyrotaxane and a diene-based polymer having a hydroxyl group, and a (meth)acrylic polymer having a cyclic carbonate structure or a cyano group and a linear or branched hydrocarbon chain in its side chain.

2. 2. The polymer actuator according to claim 1, wherein the (meth)acrylic polymer further has a polyalkylene glycol chain in a side chain.

3. The (meth)acrylic polymer is represented by the following formula (1): 【Chemistry 1】 (In the above formula, R １ represents a hydrogen atom or a methyl group, R ２ represents an alkylene group, and D represents a cyclic carbonate structure or a cyano group. and a repeating unit represented by the following formula (2): 【Chemistry 2】 (In the above formula, R ３ represents a hydrogen atom or a methyl group, R ４ represents a linear or branched hydrocarbon chain.

3. The polymer actuator according to claim 1, wherein the polymer actuator comprises a repeating unit represented by the formula:

4. A sensor comprising the polymer actuator according to claim 1.

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