Ionically conductive thin film and actuator element including the ionically conductive thin film

Abstract

To provide a novel actuator having high transparency and a high expansion / contraction ratio.SOLUTION: An ionically conductive thin film comprises a vinyl polymer, a plasticizer, and an ionic liquid, wherein the content of the ionic liquid in the ionically conductive thin film exceeds 10 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an ion conductive thin film and an actuator element including the ion conductive thin film.

Background Art

[0002] As an actuator element that can operate in air or in a vacuum, the development of a dielectric gel actuator has been underway. For example, a dielectric gel actuator composed of polyvinyl chloride and dibutyl adipate is known (Non-Patent Document 1). However, the above dielectric gel actuator required an applied voltage of several hundred volts or more. Therefore, it has been desired to develop an actuator element that is superior to a transparent and low-voltage-driven (10 - 20 V) dielectric gel actuator.

[0003] Also, a polymer flexible actuator made of a PVC gel using a mixture of 10 parts by weight of polyvinyl chloride, 85 parts by weight of dibutyl adipate, and 5 parts by weight of trihexyl(tetradecyl)phosphonium methanesulfonate and a polymer flexible actuator made of a PVC gel using a mixture of 10 parts by weight of polyvinyl chloride, 88 parts by weight of dibutyl adipate, and 2 parts by weight of trihexyl(tetradecyl)phosphonium methanesulfonate are also known (Patent Document 2). However, the development of an actuator with a higher expansion and contraction rate when a voltage is applied compared to such polymer flexible actuators is still eagerly desired. Under such circumstances, the present inventors have developed a transparent laminate having a transparent ion conductive thin film layer and a transparent conductive thin film layer containing a polymer having an oxidation-reduction function, wherein the ion conductive thin film is composed of an organosilicon-based polymer and an ionic liquid, and have obtained a patent (Patent Document 1). However, even in such a situation, further development of a novel actuator having high transparency and expansion and contraction rate with a composition different from that of the above laminate is desired.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Non-Patent Document

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a novel actuator having high transparency and high elongation rate.

Means for Solving the Problems

[0007] Under such circumstances, as a result of intensive studies by the present inventors, an ion-conductive thin film containing a vinyl polymer, a plasticizer, and an ionic liquid, wherein the content of the ionic liquid in the ion-conductive thin film exceeds 10% by mass, has been found to provide an actuator with high transparency and high elongation rate. Based on such new findings, the present inventors have further conducted extensive trial and error regarding the types and blending amounts of the vinyl polymer, plasticizer, and ionic liquid, and as a result, have completed the present invention. Therefore, the present invention provides the following items: Item 1. An ion-conductive thin film containing a vinyl polymer, a plasticizer, and an ionic liquid, wherein the content of the ionic liquid in the ion-conductive thin film exceeds 10% by mass.

[0008] Item 2. The ion-conductive thin film according to Item 1, wherein the vinyl polymer is polyvinyl chloride (PVC).

[0009] Item 3. The ion-conductive thin film according to Item 1, wherein the plasticizer is dibutyl adipate (DBA).

[0010] Item 4. The ion-conductive thin film according to Item 1, wherein the ionic liquid contains TFSI, FSI or Cl as an anion and contains a cation represented by any one of the following general formulas (I) to (IV):

[0011]

Chemical formula

[0012] [In the above formulas (I) to (IV), R represents a linear or branched alkyl group having 1 to 12 carbon atoms or a linear or branched alkyl group containing an ether bond and having a total number of carbon and oxygen atoms of 3 to 12. In formula (I), R 1 represents a linear or branched alkyl group having 1 to 4 carbon atoms or a hydrogen atom. In formulas (III) and (IV), x is an integer of 1 to 4 respectively. In formulas (III) and (IV), when x is 2 to 4, two R groups may combine with the nitrogen atom or phosphorus atom to which they are attached to form a heterocyclic group of a 3- to 8-membered ring, preferably a 5- or 6-membered ring.]

[0013] Item 5. The ion-conductive thin film according to Item 1, wherein the composition containing the vinyl polymer, plasticizer and ionic liquid constituting the ion-conductive thin film has a light transmittance of 80.0% or more at 550 nm when the thickness is 350 μm.

[0014] Item 6. An actuator element comprising the ion-conductive thin film according to any one of Items 1 to 5.

[0015] Item 7. The actuator element according to Item 6, having a expansion and contraction rate of 0.010% or more when a rectangular wave voltage of ±5.0 V is applied at a voltage frequency of 0.05 Hz.

Advantages of the Invention

[0016] According to the present invention, a novel actuator with high transparency and high elongation can be provided. On the other hand, Patent Document 2 only discloses, as the actuators specifically described in its examples, a polymer flexible actuator made of a PVC gel using a mixture of 10 parts by weight of polyvinyl chloride, 85 parts by weight of dibutyl adipate, and 5 parts by weight of trihexyl(tetradecyl)phosphonium methanesulfonate, and a polymer flexible actuator made of a PVC gel using a mixture of 10 parts by weight of polyvinyl chloride, 88 parts by weight of dibutyl adipate, and 2 parts by weight of trihexyl(tetradecyl)phosphonium methanesulfonate, that is, a polymer flexible actuator having an ionic liquid content of 5% by mass or less. Further, Patent Document 2 describes that it is particularly preferable that the ionic liquid concentration in the solution is about 5% by weight. Therefore, the effect of the present invention that a novel actuator with high transparency and high elongation can be provided by using an ion conductive thin film containing a vinyl polymer, a plasticizer, and an ionic liquid, wherein the content of the ionic liquid in the ion conductive thin film exceeds 10% by mass, is unexpected from the prior art.

Brief Description of Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0018] Ionic conductive thin film In one embodiment, the present invention provides an ion-conductive thin film containing a vinyl polymer, a plasticizer, and an ionic liquid, wherein the content of the ionic liquid in the ion-conductive thin film exceeds 10% by mass.

[0019] Examples of the vinyl polymer used in the present invention include polyvinyl chloride-based polymers, polyethylene-based polymers, polypropylene-based polymers, polyacrylonitrile-based polymers, etc., and preferably polyvinyl chloride-based polymers, etc. In the present invention, the term polyvinyl chloride-based polymer includes polyvinyl chloride (PVC) obtained by polymerizing only vinyl chloride monomer, as well as polymers obtained by copolymerizing acrylic monomers, vinylidene monomers, vinyl acetate monomers, etc. that copolymerize with vinyl chloride. In the present invention, polyvinyl chloride (PVC) is preferred. Similarly, polyethylene-based polymers, polypropylene-based polymers, and polyacrylonitrile-based polymers may also include polymers obtained by copolymerizing acrylic monomers, vinylidene monomers, vinyl acetate monomers, etc. that copolymerize with these raw material monomers in addition to polyethylene, polypropylene, polyacrylonitrile, etc. These vinyl polymers can be used alone or in combination of two or more.

[0020] Examples of the plasticizer include adipic acid esters such as methyl adipate and dibutyl adipate; phosphate esters such as tributyl phosphate, tributoxyethyl phosphate, and triphenyl phosphate; phthalic acid esters such as dibutyl phthalate and di-2-ethylhexyl phthalate; citrate esters such as tributyl acetyl citrate; alkylene oxide adducts of alcohols such as di-2-ethylhexanol, etc. Preferred examples include adipic acid esters. As the adipic acid ester, dibutyl adipate is preferred. These plasticizers can be used alone or in combination of two or more.

[0021] The ionic liquid used in the present invention, also referred to as a room temperature molten salt or simply a molten salt, etc., is a salt that exhibits a molten state in a wide temperature range including room temperature (ambient temperature), for example, a salt that exhibits a molten state at 0 °C, preferably -20 °C, more preferably -40 °C. Further, the ionic liquid used in the present invention preferably has high ionic conductivity.

[0022] In the present invention, various known ionic liquids can be used, but those that are stable and exhibit a liquid state at room temperature (ambient temperature) or a temperature close to room temperature are preferred. Preferred ionic liquids used in the present invention include a cation (preferably an imidazolium ion or a quaternary ammonium ion) represented by any of the following general formulas (I) to (IV), and an anion (X - ).

[0023]

Chemical formula

[0024] In the above formulas (I) to (IV), R represents a linear or branched alkyl group having 1 to 12 carbon atoms or a linear or branched alkyl group containing an ether bond and having a total number of carbon and oxygen atoms of 3 to 12. In formula (I), R 1represents an alkyl group having a straight-chain or branched chain of 1 to 4 carbon atoms or a hydrogen atom. In formula (I), R and R 1 are preferably not the same. In formulas (III) and (IV), x is an integer of 1 to 4 respectively. In formulas (III) and (IV), two R groups may together form an aliphatic saturated cyclic group having a 3- to 8-membered ring, preferably a 5- or 6-membered ring. In a preferred embodiment, examples of the cation include those represented by formula (I) or formula (III).

[0025] Examples of the alkyl group having a straight-chain or branched chain of 1 to 12 carbon atoms include groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl. The number of carbon atoms is preferably 1 to 8, more preferably 1 to 6.

[0026] Examples of the alkyl group having a straight-chain or branched chain of 1 to 4 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl.

[0027] Examples of the alkyl group having a straight-chain or branched chain containing an ether bond and having a total number of carbon and oxygen atoms of 3 to 12 include CH2OCH3, CH2CH2OCH3, CH2OCH2CH3, CH2CH2OCH2CH3, (CH2) p (OCH2CH2) q OR 2 (where p is an integer of 1 to 4, q is an integer of 1 to 4, and R 2 represents CH3 or C2H5).

[0028] Examples of the anion (X - ) include bis(trifluoromethanesulfonyl)imide ion (TFSI) ((CF3SO2)2N - ), bis(fluoromethanesulfonyl)imide ion (FSI) ((FSO2)2N - ), bis(pentafluoroethanesulfonyl)imide ion ((CF3CF2SO2)2N -Tetrafluoroborate ion (BF4 - ), BF3CF3 - , BF3C2F5 - , BF3C3F7 - , BF3C4F9 - , hexafluorophosphate ion (PF6 - ), perchlorate ion (ClO4 - ), tris(trifluoromethanesulfonyl) carbonate ion (CF3SO2)3C - ), trifluoromethanesulfonate ion (CF3SO3 - ), trifluoroacetate ion (CF3COO - ), etc. fluorine-containing anions; halogen ions; cyanide-containing anions such as dicyanamide ion ((CN)2N - ), etc.; organic carboxylic acid ions, etc. can be exemplified, and fluorine-containing anions, halogen ions, etc. are preferred. As the fluorine-containing anion, bis(fluoroalkanesulfonyl)imide ions such as bis(trifluoromethanesulfonyl)imide ion, bis(fluoromethanesulfonyl)imide ion, bis(pentafluoroethanesulfonyl)imide ion, etc. are preferred. As the fluoroalkanesulfonyl group in the bis(fluoroalkanesulfonyl)imide ion, for example, a group corresponding to a structure in which part or all of the hydrogen atoms of an alkyl group having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms, and even more preferably 1 carbon atom [for example, 1 to (2n + 1) (n represents the number of carbon atoms of the alkyl group)] are substituted with fluorine, such as sulfonyl substituted with such a group, can be mentioned.

[0029] Among these, as the ionic liquid, for example, a cation is a cation represented by the formula (I) or the formula (III) (for example, 1-ethyl-3-methylimidazolium ion, or trihexyl, tetradecylphosphonium ion, etc.), and an anion is a fluorine-containing anion or a halogen ion (for example, bis(trifluoromethanesulfonyl)imide ion, bis(fluoromethanesulfonyl)imide ion, chlorine ion, etc.), and such can be specifically exemplified. In the present invention, the ionic liquid is not limited to these, and various ones can be used, and the conductivity is 0.1 Sm-1 The above are preferred. These ionic liquids can be used alone or in combination of two or more. Specifically, for example, two or more cations and / or anions can be used to further lower the melting point.

[0030] In the present invention, the content of the ionic liquid in the ion conductive thin film is characterized by exceeding 10% by mass, preferably 11% by mass or more, more preferably 12% by mass or more, 13% by mass or more, and the like. The upper limit of the content of the ionic liquid in the ion conductive thin film is not limited, but for example, preferably 30% by mass or less, 25% by mass or less, 20% by mass or less, 16% by mass or less, and the like. From the viewpoint of the elongation and contraction rate of the ion conductive thin film, it is preferable that the content of the ionic liquid in the ion conductive thin film is within the above range.

[0031] In the present invention, the content of the vinyl polymer in the ion conductive thin film is not limited, but preferably 15% by mass or more, more preferably 18% by mass or more, more preferably 19% by mass or more, more preferably 20% by mass or more, and the like. The upper limit of the content of the vinyl polymer in the ion conductive thin film is also not limited, but for example, preferably 35% by mass or less, 30% by mass or less, 25% by mass or less, 22% by mass or less, and the like. From the viewpoint of the elongation and contraction rate of the ion conductive thin film, it is preferable that the content of the vinyl polymer in the ion conductive thin film is within the above range.

[0032] In the present invention, the content of the plasticizer in the ion conductive thin film is not limited, but preferably 50% by mass or more, more preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 63% by mass or more, and the like. The upper limit of the content of the plasticizer in the ion conductive thin film is not limited, but for example, preferably 70% by mass or less, 67% by mass or less, 66% by mass or less, 65% by mass or less, and the like. From the viewpoint of the elongation and contraction rate of the ion conductive thin film, it is preferable that the content of the plasticizer in the ion conductive thin film is within the above range.

[0033] In the present invention, the content of the ionic liquid relative to the total amount of the vinyl polymer, plasticizer, and ionic liquid is preferably 11% by mass or more, more preferably 12% by mass or more, and examples thereof include 13% by mass or more. The upper limit of the content of the ionic liquid in the ion-conductive thin film is not limited, and for example, it is preferably 30% by mass or less, 25% by mass or less, 20% by mass or less, 16% by mass or less, and the like. From the viewpoint of the elongation and contraction rate of the ion-conductive thin film, it is preferable that the content of the ionic liquid relative to the total amount of the vinyl polymer, plasticizer, and ionic liquid is within the above range.

[0034] In the present invention, the content of the vinyl polymer relative to the total amount of the vinyl polymer, plasticizer, and ionic liquid is not limited, but preferably 15% by mass or more, more preferably 18% by mass or more, more preferably 19% by mass or more, more preferably 20% by mass or more, and the like. The upper limit of the content of the vinyl polymer in the ion-conductive thin film is not limited, and for example, it is preferably 35% by mass or less, 30% by mass or less, 25% by mass or less, 22% by mass or less, and the like. From the viewpoint of the elongation and contraction rate of the ion-conductive thin film, it is preferable that the content of the vinyl polymer relative to the total amount of the vinyl polymer, plasticizer, and ionic liquid is within the above range.

[0035] In the present invention, the content of the plasticizer relative to the total amount of the vinyl polymer, plasticizer, and ionic liquid is not limited, but preferably 50% by mass or more, more preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 63% by mass or more, and the like. The upper limit of the content of the plasticizer in the ion-conductive thin film is not limited, and for example, it is preferably 70% by mass or less, 67% by mass or less, 66% by mass or less, 65% by mass or less, and the like. From the viewpoint of the elongation and contraction rate of the ion-conductive thin film, it is preferable that the content of the plasticizer relative to the total amount of the vinyl polymer, plasticizer, and ionic liquid is within the above range.

[0036] In addition, an organic silicon-based polymer may be added to the ion-conductive thin film of the present invention as long as the effects of the present invention can be obtained. In such an embodiment, examples of the organic silicon-based polymer include polysiloxane-based compounds, polydiorganosiloxane-based compounds, and polydiorganosiloxane-based copolymers. Further, those obtained by combining these compounds may also be used. The polysiloxane-based compound is a compound having an organic group, and when a raw material having no organic group such as tetramethoxysilane or tetraethoxysilane is used, it can be obtained by using at least one alkoxysilane having one or two organic groups. Specifically, partial hydrolyzates of silane compounds having a hydrolyzable silyl group such as tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropylmethyldimethoxysilane, organosilica sols in which fine particles of silicic anhydride are stably dispersed in an organic solvent, or those obtained by adding the above silane compound having radical polymerizability to the organosilica sol can be used.

[0037] Examples of the polydiorganosiloxane compound include polydimethylsiloxane compounds such as polydimethylsiloxane, alkyl-modified polydimethylsiloxane, carboxyl-modified polydimethylsiloxane, amino-modified polydimethylsiloxane, epoxy-modified polydimethylsiloxane, fluorine-modified polydimethylsiloxane, and (meth)acrylate-modified polydimethylsiloxane; polydiethylsiloxane compounds such as polydiethylsiloxane, alkyl-modified polydiethylsiloxane, carboxyl-modified polydiethylsiloxane, amino-modified polydiethylsiloxane, epoxy-modified polydiethylsiloxane, fluorine-modified polydiethylsiloxane, and (meth)acrylate-modified polydiethylsiloxane; and polydiphenylsiloxane compounds such as polydiphenylsiloxane, alkyl-modified polydiphenylsiloxane, carboxyl-modified polydiphenylsiloxane, amino-modified polydiphenylsiloxane, epoxy-modified polydiphenylsiloxane, fluorine-modified polydiphenylsiloxane, and (meth)acrylate-modified polydiphenylsiloxane.

[0038] The organosiloxane copolymer may be any of a block copolymer, a graft copolymer, and a random copolymer, with block copolymers and graft copolymers being preferred.

[0039] The organosiloxane copolymer can be produced by a living polymerization method, a polymer initiator method, a polymer chain transfer method, or the like.

[0040] Examples of vinyl monomers used in copolymers with organosiloxanes such as polysiloxane compounds and polydiorganosiloxanes include methyl acrylate, phenyl acrylate, n-butyl acrylate, isobutyl acrylate, octyl acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, methyl methacrylate, phenyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-phenylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, methyl vinyl ether, phenyl vinyl ether, n-propyl vinyl ether, styrene, α-methylstyrene, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, maleic anhydride, acrylamide, methacrylamide, N-methylolacrylamide, N,N-dimethylacrylamide, N,N-dimethylaminophenyl methacrylate, N,N-diphenylaminophenyl methacrylate, diacetone acrylamide, 2-hydroxyphenyl acrylate, 2-hydroxyphenyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, allyl alcohol, and the like.

[0041] Organosiloxane copolymers are usually produced by solution polymerization. In such solution polymerization, aromatic hydrocarbon solvents such as toluene and xylene, ketone solvents such as acetone, methyl phenyl ketone, and methyl isobutyl ketone, ester solvents such as phenyl acetate, propyl acetate, isobutyl acetate, and butyl acetate, alcohol solvents such as ethanol, isopropanol, butanol, and isobutanol are used alone or as a mixed solvent. In addition, a polymerization initiator such as benzoyl peroxide or azobisisobutyronitrile is used in combination as necessary. The polymerization reaction is preferably carried out at 50 to 150 °C for 3 to 12 hours.

[0042] In addition, in the synthesis of the organosiloxane copolymer, by using a monomer having an isocyanate group (for example, (meth)acrylate having an isocyanate group) and a monomer having a hydroxyl group (for example, (meth)acrylate having a hydroxyl group), an organosiloxane copolymer curable by active energy rays can be obtained.

[0043] In a typical embodiment, the ion-conductive thin film of the present invention is obtained by preparing a solution containing a vinyl polymer, a plasticizer, an ionic liquid, and a solvent, and optionally further an ionic liquid different from the ionic liquid, and forming a film from the obtained solution by a casting method, and evaporating and drying the solvent. The ion-conductive thin film can be formed by coating, printing, extrusion, casting, injection, or the like. Here, the solvent may be a mixed solvent of a hydrophilic solvent and a hydrophobic solvent. Examples of the solvent include dimethylacetamide, propylene carbonate, methyl pentanone, chloroform, dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, diethyl ether, ethyl acetate, acetone, methyl ethyl ketone, dimethylacetamide, dioxane, dichloromethane, methanol, ethanol, and the like. These solvents can be used alone or in combination of two or more. As the ionic liquid different from the ionic liquid, those commonly used in the technical field to which the present invention belongs can be appropriately used.

[0044] It is preferable to use the ion-conductive thin film of the present invention because an actuator having high transparency and stretchability can be obtained. In a preferred embodiment, in the ion-conductive thin film of the present invention, a composition containing a vinyl polymer, a plasticizer, and an ionic liquid constituting the ion-conductive thin film is formed into a thin film having a width of 0.5 cm, a length of 1.5 cm, and a thickness of 350 μm, and the thin film is sandwiched between electrodes so that the movable length becomes 1.0 cm, and when a rectangular wave voltage of ±5.0 V is applied at a voltage frequency of 0.005 Hz, the expansion and contraction rate is preferably 0.050% or more, more preferably 0.100% or more, and still more preferably 0.150% or more. In a preferred embodiment, the ion-conductive thin film of the present invention is such that a composition containing a vinyl polymer, a plasticizer, and an ionic liquid that constitute the ion-conductive thin film forms a thin film with a width of 0.5 cm, a length of 1.5 cm, and a thickness of 350 μm, the thin film is sandwiched between electrodes so that the movable length is 1.0 cm, and when a rectangular wave voltage of ±5.0 V is applied at a voltage frequency of 0.01 Hz, the expansion and contraction rate is 0.040% or more, more preferably 0.050% or more, and even more preferably 0.070% or more. In a preferred embodiment, the ion-conductive thin film of the present invention is such that a composition containing a vinyl polymer, a plasticizer, and an ionic liquid that constitute the ion-conductive thin film forms a thin film with a width of 0.5 cm, a length of 1.5 cm, and a thickness of 350 μm, the thin film is sandwiched between electrodes so that the movable length is 1.0 cm, and when a rectangular wave voltage of ±5.0 V is applied at a voltage frequency of 0.05 Hz, the expansion and contraction rate is 0.010% or more, more preferably 0.020% or more. In a preferred embodiment, the ion-conductive thin film of the present invention is such that a composition containing a vinyl polymer, a plasticizer, and an ionic liquid that constitute the ion-conductive thin film forms a thin film with a width of 0.5 cm, a length of 1.5 cm, and a thickness of 350 μm, the thin film is sandwiched between electrodes so that the movable length is 1.0 cm, and when a rectangular wave voltage of ±5.0 V is applied at a voltage frequency of 0.10 Hz, the expansion and contraction rate is 0.005% or more, more preferably 0.008% or more, and even more preferably 0.011% or more. In these embodiments, the expansion and contraction rate of the ion-conductive thin film can be measured by the method described in the examples below. Also, in one embodiment, the ion-conductive thin film of the present invention is such that a composition containing a vinyl polymer, a plasticizer, and an ionic liquid that constitute the ion-conductive thin film, when formed into a thin film with a thickness of 350 μm, has a total light transmittance measured in accordance with JIS K 7361-1:1997 of 40.0% or more, 50.0% or more, 55.0% or more, 60.0% or more, 65.0% or more, 70.0% or more, 75.0% or more, 80.0% or more, 85.0% or more, or 90.0% or more. In one embodiment, for the ion-conductive thin film of the present invention, when the composition containing the vinyl polymer, plasticizer, and ionic liquid that constitute the ion-conductive thin film is made into a thin film with a thickness of 350 μm, the transmittance of visible light with a wavelength in the range of 400 - 700 nm is preferably 60.0% or more, 65.0% or more, 70.0% or more, 75.0% or more, or 80.0% or more. In one embodiment, for the ion-conductive thin film of the present invention, when the composition containing the vinyl polymer, plasticizer, and ionic liquid that constitute the ion-conductive thin film is made into a thin film with a thickness of 350 μm, the light transmittance at 550 nm is preferably 60.0% or more, 65.0% or more, 70.0% or more, 75.0% or more, 80.0% or more, 85.0% or more, or 90.0% or more. The light transmittance at 550 nm can be measured by the method described in the examples below.

[0045] Typically, the ion-conductive thin film of the present invention has a flat plate shape. The thickness of the ion-conductive thin film of the present invention is not limited, but is preferably 5 - 500 μm, and more preferably 200 - 400 μm. The ion-conductive thin film of the present invention is not particularly limited, and examples include polygons (triangle, quadrilateral, pentagon, hexagon, etc.), circle, ellipse, combinations thereof, etc. Examples of the quadrilateral include square, rectangle, parallelogram, trapezoid, etc. When the ion-conductive thin film of the present invention is flat plate-shaped, the area of the main plane (the area of one of the front and back surfaces) is not limited, but can be appropriately set, for example, in the range of 0.01 - 1000 cm 2 , 0.1 - 100 cm 2 , 1 - 10 cm 2 and so on.

[0046] Actuator element In another embodiment, the present invention provides an actuator element including the ion-conductive thin film. The composition, shape, function, manufacturing method, etc. of the ion-conductive thin film in this embodiment are the same as those described above. In the present invention, for example, either the ion-conductive thin film itself may be used as the actuator element, or a laminate in which the ion-conductive thin film is sandwiched between a plurality of conductive thin films may be used as the actuator element. In the present invention, it is preferable to use the ion-conductive thin film itself as the actuator element.

[0047] In a preferred embodiment, the actuator element of the present invention preferably has a expansion / contraction rate of 0.050% or more, more preferably 0.100% or more, and even more preferably 0.150% or more when a rectangular wave voltage of ±5.0 V is applied at a voltage frequency of 0.005 Hz. In a preferred embodiment, the actuator element of the present invention preferably has a expansion / contraction rate of 0.040% or more, more preferably 0.050% or more, and even more preferably 0.070% or more when a rectangular wave voltage of ±5.0 V is applied at a voltage frequency of 0.01 Hz. In a preferred embodiment, the actuator element of the present invention preferably has a expansion / contraction rate of 0.010% or more, more preferably 0.020% or more when a rectangular wave voltage of ±5.0 V is applied at a voltage frequency of 0.05 Hz. In a preferred embodiment, the actuator element of the present invention preferably has a expansion / contraction rate of 0.005% or more, more preferably 0.008% or more, and even more preferably 0.011% or more when a rectangular wave voltage of ±5.0 V is applied at a voltage frequency of 0.10 Hz. In these embodiments, the expansion / contraction rate of the ion-conductive thin film can be measured by the method described in the examples below. Also, in one embodiment, the actuator element of the present invention preferably has a total light transmittance of 40.0% or more, 50.0% or more, 55.0% or more, 60.0% or more, 65.0% or more, 70.0% or more, 75.0% or more, 80.0% or more, 85.0% or more, or 90.0% or more as measured in accordance with JIS K7361-1:1997. In one embodiment, the actuator element of the present invention preferably has a visible light transmittance of 60.0% or more, 65.0% or more, 70.0% or more, 75.0% or more, or 80.0% or more at a wavelength in the range of 400 - 700 nm. In one embodiment, the actuator element of the present invention preferably has a light transmittance of 60.0% or more, 65.0% or more, 70.0% or more, 75.0% or more, 80.0% or more, 85.0% or more, or 90.0% or more at 550 nm. The light transmittance at 550 nm can be measured by the method described in the examples below.

[0048] The thickness of the actuator element of the present invention is not limited, but is preferably 5 - 500 μm, and more preferably 200 - 400 μm.

[0049] In a typical embodiment, when a DC voltage of 10 - 20 V is applied between the electrodes (the electrodes are connected to the conductive thin film layer) of the actuator element of the present invention, a displacement of about 10% of the element length (movable length) can be obtained within 100 seconds. In a typical embodiment, when an AC voltage, for example, a rectangular wave voltage of ±5.0 V to ±10.0 V and a voltage frequency of 0.01 Hz, is applied between the electrodes of the actuator element of the present invention, a displacement of about 10% of the element length (movable length) can also be obtained within one cycle (within 100 seconds). Further, this actuator element can operate flexibly in air or in a vacuum. The operating principle of such an actuator element is composed of both functions of a dielectric gel actuator and an ion conductive actuator.

[0050] In a typical embodiment, the actuator element of the present invention operates durably in air and in vacuum, and also operates flexibly at a low voltage. Therefore, it is optimal as an actuator for robots that come into contact with people who require safety (for example, actuators for personal robots such as home robots, pet robots, and amusement robots), robots that operate in special environments such as for space, inside a vacuum chamber, and for rescue, medical and welfare robots such as surgical devices and muscle suits, and further for actuators for micromachines and the like.

[0051] In particular, in order to obtain a high-purity product in material manufacturing under a vacuum environment and an ultra-clean environment, the requirements for actuators for sample transportation, positioning, etc. are increasing in order to obtain a high-purity product. The actuator element of the present invention using an ionic liquid that does not evaporate at all can be effectively used as an actuator for processes under a vacuum environment as an actuator without worry of contamination.

[0052] The transparent actuator of the present invention can be integrated on a flat panel display, enabling the driving of an object on the display. By using such a transparent actuator, for example, it becomes possible to link the movement of the virtual world and real objects to present tactile information to the user, and for the user to interact with the video through real objects. Also, by connecting a non-transparent object (for example, paper) to the transparent actuator and driving the actuator, an impression can be given that the non-transparent object is moving by itself, and applications to advertisements and amusement are expected. Since the actuator of the present invention has a large driving force, it is also advantageous for these applications.

[0053] Specific embodiments of the present invention will be described in more detail below using examples. However, the present invention is not limited to the following examples.

Examples

[0054] <Common description of experimental methods> 1. Chemicals and materials used The following chemicals were used in the fabrication of the actuator element. Polyvinyl chloride (PVC) (MW ca. 233,000; Aldrich) and dibutyl adipate (DBA) (FUJIFILM Wako Pure Chemical Corporation) were used without further purification. The following ionic liquids (ILs) were used: 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI[TFSI], IoLiTec), 1-Ethyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide (EMI[FSI], Kanto Chemical Co., Inc.), Trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide (THTDP[TFSI]; IoLiTec), Trihexyltetradecylphosphonium chloride (THTDP[Cl]; IoLiTec). These ionic liquids were used without further purification.

[0055] Also, tetrahydrofuran (THF, FUJIFILM Wako Pure Chemical Corporation) was used as a solvent without further purification.

[0056] The structures of the ionic liquids (ILs), vinyl polymer (PVC), and plasticizer (DBA) used in this example are shown below.

[0057] [Chemical formula]

[0058] 2. Method for measuring displacement of actuator element Using a laser displacement meter described in Patent Document 1, the element was cut into a strip of 5 mm x 15 mm, and the displacement at the 9-mm position when the obtained element was sandwiched between electrodes and a voltage was applied so that the movable length became 10 mm was measured. The elongation rate (ε) was calculated according to the following formula (1).

[0059] [Number]

[0060] L: Element length (movable length) when no voltage is applied d: Thickness of the element δ: Displacement 3. Light transmittance The light transmittance of the gel was measured for wavelengths from 300 to 700 nm using a UV-visible spectrometer (UV-3600, Shimadzu Co., Ltd.).

[0061] 4. Ionic conductivity The ionic conductivity of the gel was determined by impedance measurement using an impedance analyzer (Solartron 1250).

[0062] 5. Measurement of gel electrolyte film thickness The thicknesses of the fabricated electrode film, gel electrolyte film, and actuator element film composed of a laminate thereof were measured using a micrometer (manufactured by Mitsutoya Corporation).

[0063] Example 1 Fabrication of actuator element To prepare a transparent PVC / DBA / IL gel actuator, 300 mg of PVC, 900 mg of DBA, and 200 mg of IL (any of the aforementioned ionic liquids) were mixed in 6 mL of THF and stirred for 5 hours. Then, 3.5 mL of the resulting solution was cast into a Teflon (registered trademark) mold (2.5 × 2.5 cm 2 ), and then the solvent was evaporated. The thickness of the obtained gel was about 350 μm. The obtained gel was cut into a rectangle with a width of 0.5 cm and a length of 1.5 cm and used as an actuator element.

[0064] Table 1 shows the results of the characteristics of the actuator element fabricated using EMI[TFSI] as the IL. Table 2 shows the displacements observed when rectangular wave voltages of ±5.0 V with different frequencies were applied between the electrodes.

[0065]

Table 1

[0066]

Table 2

[0067] Also, FIGS. 2 to 4 show the current (FIG. 3) and displacement (FIG. 4) observed when a rectangular wave voltage (FIG. 2) of ±10.0 V and a voltage frequency of 0.01 Hz was applied to the actuator element of Example 1. Further, FIGS. 5 to 7 show the current (FIG. 6) and displacement (FIG. 7) observed when a rectangular wave voltage (FIG. 5) of ±5.0 V and a voltage frequency of 0.01 Hz was applied to the actuator element of Example 1.

[0068] The above actuator element has a higher transmittance, ionic conductivity, and displacement than the comparative examples described later. Therefore, it can be seen that the above actuator element is a transparent high-performance actuator element with a high response speed and a large bending (strain rate).

[0069] Example 2 Fabrication of Actuator Element An actuator element was fabricated in the same manner as in Example 1 except that EMI[FSI] was used as the IL, and various evaluations were performed. Table 3 shows the results of the characteristics of the obtained actuator element. Table 4 shows the displacements observed when rectangular wave voltages of ±5.0 V with different frequencies were applied between the electrodes.

[0070]

Table 3

[0071]

Table 4

[0072] The above actuator element has higher transmittance, ionic conductivity, and displacement than those in the comparative examples described later. Therefore, it can be seen that the above actuator element is a transparent high-performance actuator element with a high response speed and a large bending (stretching rate).

[0073] Example 3 Fabrication of Gel Film An actuator element was fabricated and various evaluations were performed in the same manner as in Example 1, except that THTDP[TFSI] was used as the IL. The results of the characteristics of the obtained actuator element are shown in Table 5. Table 6 shows the displacements observed when rectangular wave voltages of ±5.0 V with different frequencies were applied between the electrodes.

[0074] [Table 5]

[0075] [Table 6]

[0076] The above actuator element has higher transmittance, ionic conductivity, and displacement than those in the comparative examples described later. Therefore, it can be seen that the above actuator element is a transparent high-performance actuator element with a high response speed and a large bending (stretching rate).

[0077] Example 4 An actuator element was fabricated and various evaluations were performed in the same manner as in Example 1, except that THTDP[Cl] was used as the IL. The results of the characteristics of the obtained actuator element are shown in Table 7. Table 8 shows the displacements observed when rectangular wave voltages of ±5.0 V with different frequencies were applied between the electrodes.

[0078] [Table 7]

[0079]

Table 8

[0080] The above actuator element has higher transmittance, ionic conductivity, and displacement than those in the comparative examples described later. Therefore, it can be seen that the above actuator element is a transparent high-performance actuator element with a high response speed and a large bending (strain rate).

[0081] Comparative Example 1 Fabrication of Actuator Element An actuator element was fabricated and various evaluations were performed in the same manner as in Example 1 except that IL was not used. The results of the characteristics of the obtained actuator element are shown in Table 9. Table 10 shows the displacements observed when rectangular wave voltages of ±5.0 V with different frequencies were applied between the electrodes.

[0082]

Table 9

[0083]

Table 10

[0084] Light Transmittance The measurement results of the light transmittance of the gel (PVC / DBA / TFSI) prepared in Example 1 and the gel (PVC / DBA) prepared in the comparative example are shown in FIG. 8.

[0085] As is clear from the results of the above examples and comparative examples, the actuator elements of each example have higher transmittance, ionic conductivity, and displacement than those of the comparative examples. Therefore, it can be seen that the actuator elements of each example are transparent high-performance actuator elements with a large bending (strain rate).

Claims

1. An ion-conductive thin film comprising a vinyl polymer, a plasticizer, and an ionic liquid, wherein the content of the ionic liquid in the ion-conductive thin film exceeds 10% by mass.

2. The ion-conductive thin film according to Claim 1, wherein the vinyl polymer is polyvinyl chloride (PVC).

3. The ion-conductive thin film according to Claim 1, wherein the plasticizer is dibutyl adipate (DBA).

4. The ion-conductive thin film according to Claim 1, wherein the ionic liquid contains TFSI, FSI, or Cl as an anion and contains a cation represented by any one of the following general formulas (I) to (IV): 【Chemical 1】 In the above formulas (I) to (IV), R represents a linear or branched alkyl group having 1 to 12 carbon atoms or an alkyl group having a linear or branched structure with a total number of carbon and oxygen atoms of 3 to 12 and containing an ether bond. In formula (I), R １ represents a linear or branched alkyl group having 1 to 4 carbon atoms or a hydrogen atom. In formulas (III) and (IV), x is an integer of 1 to 4 respectively. In formulas (III) and (IV), when x is 2 to 4, two R groups may combine with the nitrogen atom or phosphorus atom to which they are attached to form a heterocyclic group having a 3- to 8-membered ring, preferably a 5- or 6-membered ring.]

5. The ion-conductive thin film according to Claim 1, wherein the composition containing the vinyl polymer, the plasticizer, and the ionic liquid constituting the ion-conductive thin film has a light transmittance of 80.0% or more at 550 nm when the thickness is 350 μm.

6. An actuator element comprising the ion-conductive thin film according to any one of Claims 1 to 5.

7. The actuator element according to Claim 6, wherein the expansion and contraction rate is 0.010% or more when a rectangular wave voltage of ±5.0 V is applied at a voltage frequency of 0.05 Hz.

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