Method for manufacturing dielectric film and method for manufacturing actuator using the same

Abstract

To provide a method for manufacturing a dielectric film using a polymer material and a polar group-containing organic compound.SOLUTION: A method for manufacturing a dielectric film includes a step of dissolving a polymeric material and a polar group-containing organic compound in a solvent to prepare a mixed solution of the polymeric material and the polar group-containing organic compound, a step of coating the mixed solution onto a substrate, and a step of curing the polymeric material coated onto the substrate to form a thin film. The mixed solution is prepared such that the internal structure of the cured thin film is phase-separated into a continuous phase made of the polymeric material and a dispersed phase mainly made of the polar group-containing organic compound.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a polymer actuator, and more particularly to a method for manufacturing a dielectric film used in the polymer actuator. [Background technology]

[0002] Polymer actuators, which are flexible, lightweight, and easy to mold, are expected to be used as smart materials. In general, polymer actuators are driven by external stimuli such as light, heat, magnetic field, electric field, temperature, solvent, and pH. Polymer actuators are broadly classified into current-driven and voltage-driven types, with ion-conductive polymers, conductive polymers, and carbon nanotubes being used for current-driven types, and piezoelectric polymers, dielectric gels, and dielectric elastomers being used for voltage-driven types. Actuators using dielectric elastomers that are driven in air are flexible, and materials such as acrylic, silicone, and polyurethane elastomers are being investigated.

[0003] In order to increase the electrostatic attraction against the applied voltage and improve the performance of the actuator, it is necessary to increase the relative dielectric constant of the dielectric film. For this reason, various dielectric films have been proposed in which dielectric particles with a high relative dielectric constant, such as barium titanate, are blended with an elastomer. For example, Patent Document 1 describes that a dielectric film containing an elastomer and dielectric particles and satisfying condition (A) [average number of reference particles is 0.8 particles / μm or more], condition (B) [average number of large particles is 0.2 particles / μm or less], and condition (C) [number of unit regions in which the area ratio of the elastomer is 30% or less is 10 or less] in a cross-sectional photograph in the thickness direction taken by a scanning electron microscope is flexible, has a high relative dielectric constant, and has a high dielectric breakdown strength even when made thin.

[0004] Dielectric particles such as barium titanate generally tend to aggregate, making it difficult to disperse them uniformly in elastomers. The present inventors have reported on a polymer actuator that can deform based on the non-uniformity of the space charge distribution when a direct current voltage is applied by combining a silicone elastomer with a polar group-containing organic compound such as cyanoethylsucrose instead of barium titanate (see Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] S. Tamura, R. Kiyono, T. Hirai, Dielectric elastomer actuator behavior of silicone / cyanoethylsucrose composite films: Morphology and space-charge distribution. Nano Select 2021;1-11https: / / doi.org / 10.1002 / nano.202100023 [Patent documents]

[0006] [Patent Document 1] JP 2015-189776 A Summary of the Invention [Problem to be solved by the invention]

[0007] The dielectric film described in Non-Patent Document 1 certainly generates non-uniform space charge distribution due to the formation of an asymmetric cross-sectional internal structure, but it is not clear how the manufacturing conditions of the dielectric film can be controlled to form such a special internal structure.

[0008] Therefore, an object of the present invention is to provide a method for producing a dielectric film using a polymer material and a polar group-containing organic compound. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors conducted extensive research and found that a dielectric film excellent as an actuator material can be obtained by using a solvent that has affinity with the polymer material used in the production of the dielectric film and adjusting the film formation conditions.

[0010] (1) A method for producing a dielectric film, comprising the steps of: dissolving a polymeric material and a polar group-containing organic compound in a solvent to prepare a mixed solution of the polymeric material and the polar group-containing organic compound; applying the mixed solution onto a substrate; and curing the polymeric material applied onto the substrate to form a thin film, wherein the mixed solution is prepared so that the internal structure of the cured thin film is phase-separated into a continuous phase made of the polymeric material and a dispersed phase mainly made of the polar group-containing organic compound. (2) The method according to (1), wherein the blending ratio of the polymer material to the polar group-containing organic compound is 3:1 to 1:1 by mass. (3) The method according to (1) or (2), wherein the content of the solvent in the total amount of the mixed solution is 20 to 50 mass %. (4) The method according to any one of (1) to (3), wherein the mixed solution has a viscosity of 1 Pa·s or less at 20° C. (5) The method according to any one of (1) to (4), wherein the mixed solution applied to the substrate is held for at least 30 minutes before the polymer material is cured. (6) The manufacturing method according to any one of (1) to (5), wherein the polymeric material comprises one or more elastomers selected from silicone, polyurethane, polyacrylonitrile, nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), nylon, polyethylene terephthalate, polypropylene, polyethylene, polyketone, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate, polymethyl methacrylate, poly-n-butyl acrylate, cellulose, and wool. (7) The method according to any one of (1) to (6), wherein the polar group-containing organic compound is a cyanoethyl group-containing organic compound, a modified silicone oil, a phthalocyanine, or an ionic liquid. (8) The method according to any one of (1) to (7), wherein the polymer material is silicone and the polar group-containing organic compound is cyanoethylsucrose. (9) The process according to any one of (1) to (8), wherein the solvent is tetrahydrofuran or a mixed solvent of tetrahydrofuran and acetone. (10) A method for producing an actuator, comprising the steps of: adding an electrode layer to each of both sides of a dielectric film produced by the method according to any one of (1) to (9). Effect of the Invention

[0011] According to the present invention, a novel method for producing a dielectric film using a polymer material and a polar group-containing organic compound can be provided. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a dielectric film according to one embodiment. [Diagram 2] FIG. 2 shows a schematic diagram (a) illustrating the procedure for producing the PDMS composite membrane produced in the examples, and the produced film (b). [Diagram 3] FIG. 3 is a schematic diagram of the electrode part of the pulsed electrostatic acoustic nondestructive testing device (PEANUT) used to measure the space charge distribution. [Figure 4] FIG. 4 is a schematic diagram of a deformation measurement sample. [Diagram 5] Figure 5 shows the experimental setup for measuring the deformation. [Figure 6] FIG. 6 is a graph showing the relationship between the viscosity of the PDMS / CR-U solution and the THF content. [Figure 7] FIG. 7 is a graph showing the relationship between the elastic modulus of the PDMS / CR-U composite membrane and the THF content. [Figure 8]Figure 8 shows cross-sectional images of the PDMS / CR-U composite membrane. (a) shows PDMS / CR-U (A100 / T0), (b) shows PDMS / CR-U (A50 / T50), (c) shows PDMS / CR-U (A25 / T75), and (d) shows PDMS / CR-U (A0 / T100). [Figure 9] FIG. 9 is a graph showing the dependence of sphere diameter and skin thickness on THF content. [Figure 10] FIG. 10 is a graph showing the time dependence of the deformation amount (a) and the electric field (b). [Figure 11] 11 is a graph showing the relationship between the maximum deformation amount and the THF content. Electric field: 3 kV / mm. [Figure 12] FIG. 12 is a graph showing the relationship between the maximum deformation amount and the electric field intensity. [Figure 13] Figure 13 shows a schematic diagram of the space charge distribution and deformation mechanism. (a) The AIR side is attached to the anode, and (b) the AIR side is attached to the cathode. [Figure 14] FIG. 14 is a graph showing the relationship between the peak value of the hetero charge and the electric field strength. [Figure 15] FIG. 15 is a graph showing the relationship between the maximum deformation amount and the heterocharge peak value intensity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Next, each embodiment of the present invention will be described with reference to the drawings. Note that each embodiment described below does not limit the invention according to the claims, and all of the elements and combinations thereof described in each embodiment are not necessarily essential to the solution of the present invention.

[0014] <Dielectric film> The dielectric film according to the manufacturing method of the present invention contains a polymer material and a polar group-containing organic compound, and its internal structure shows a sea-island structure as shown in FIG. 1. The dielectric film 10 shown in FIG. 1 contains a dispersed phase 14 mainly made of a polar group-containing organic compound in a base polymer 13. The dielectric film 10 has a dense layer 11 made of a base polymer on one surface (the upper surface in FIG. 1). The dense layer 11 is a uniform layer (sometimes called a "skin layer") made substantially of the base polymer. The dielectric film 10 preferably has a thickness of 500 μm or less in order to be easily deformed, and the dense layer 11 preferably has a thickness of about 5 to 50 μm. The dispersed phase is mainly composed of a polar group-containing organic compound, and its shape may be spherical (true spherical or approximately spherical), ellipsoidal (elliptical sphere), polygonal (polygonal pyramid, polygonal prism such as cuboid or rectangular prism, etc.), plate-like (flat, scale-like or thin plate-like, etc.), rod-like or rod-like, fibrous, irregular, etc., but it is preferable to form a spherical dispersed phase.

[0015] On the other hand, an interface 15 exists between the sea-island structure 12 and the dense layer 11. Based on such an asymmetric structure, when an electric field is applied to both sides of the dielectric film 10, it is considered that the leakage of charges in the sea-island structure is suppressed by the dense layer 11 made of the base polymer, and hetero-charges accumulate in the vicinity thereof. From the viewpoint of efficiently causing the accumulation of hetero-charges, it is preferable that the dispersed phase 14 is spherical and has a spherical diameter of about 1 to 100 μm. More preferably, the spherical diameter of the dispersed layer is 10 to 100 μm. In this specification, the term "hetero-charge" refers to a charge of the opposite polarity to that of an electrode that exists in the vicinity of the electrode. Hereinafter, the polymer material constituting the base polymer and the polar group-containing organic compound constituting the dispersed layer will be described in detail.

[0016] [Polymer materials] The base polymer used in this embodiment is not particularly limited in type as long as it is a flexible elastomer. For example, it is preferable to include one or more elastomers selected from silicone, polyurethane, polyvinyl chloride, polyacrylonitrile, nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), nylon, polyethylene terephthalate, polypropylene, polyethylene, polyketone, polyvinyl alcohol, polyvinyl acetate, polymethyl methacrylate, poly-n-butyl acrylate, cellulose, and wool. The elastomer may be appropriately selected according to the performance required for the actuator. For example, from the viewpoint of increasing the deformation with respect to the applied voltage, it is desirable to adopt an elastomer with a large polarity, that is, a large relative dielectric constant. Specifically, an elastomer with a relative dielectric constant of 2.8 or more (measurement frequency 100 Hz) is preferable. Examples of elastomers with a large relative dielectric constant include nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), chlorinated polyethylene, chlorosulfonated polyethylene, and polyurethane. In addition, even if the relative dielectric constant is small, an elastomer with a large electric resistance is desirable in that it is less likely to cause insulation breakdown when a voltage is applied. Examples of elastomers with high electrical resistance include silicone rubber. In addition, elastomers modified by introducing functional groups may be used. Suitable modified elastomers include, for example, carboxyl group-modified nitrile rubber (X-NBR) and carboxyl group-modified hydrogenated nitrile rubber (XH-NBR).

[0017] Thermoplastic elastomers are suitable because they do not use crosslinking agents and are therefore less susceptible to impurities. Thermoplastic elastomers include styrene-based (SBS, SEBS, SEPS), olefin-based (TPO), polyvinyl chloride-based (TPVC), urethane-based (TPU), ester-based (TPEE), amide-based (TPAE), and copolymers and blends of these.

[0018] [Polar group-containing organic compound] The polar group-containing organic compound of the present embodiment includes, but is not limited to, a cyanoethyl group-containing organic compound, modified silicone oil, phthalocyanines, various ionic liquids, etc. For example, it may be selected from various polar materials that are compatible or partially incompatible with the base polymer.

[0019] (Organic compounds containing cyanoethyl groups) As a preferred embodiment, the "cyanoethyl group-containing organic compound" is not particularly limited as long as it is a compound having a cyanoethyl group in the molecule, but it is preferable to use an organic polymer or organic oligomer containing a cyanoethyl group. Since the cyanoethyl group-containing organic compound has a cyanoethyl group with high polarity in the molecule, it forms a large dipole moment when placed in an electric field and exhibits a high dielectric constant.

[0020] The cyanoethyl group-containing organic compound is preferably an organic dielectric material having a dielectric constant of 10 or more. Specific examples of the cyanoethyl group-containing polymer include cyanoethyl saccharose (cyanoethyl sucrose, dielectric constant 24), cyanoethyl pullulan (dielectric constant 18), cyanoethyl cellulose (dielectric constant 16), cyanoethyl hydroxyethyl cellulose (dielectric constant 18), cyanoethyl hydroxypropyl cellulose (dielectric constant 14), cyanoethyl amylose (dielectric constant 17), cyanoethyl starch (dielectric constant 17), cyanoethyl dihydroxypropyl starch (dielectric constant 18), cyanoethyl glycidol pullulan (dielectric constant 20), cyanoethyl polyvinyl alcohol (dielectric constant 20), cyanoethyl polyhydroxymethylene (dielectric constant 10), and cyanoethyl sorbitol (dielectric constant 40). In addition, organic dielectric materials having a dielectric constant of 10 or more other than these may be used as long as they do not go against the object of the present invention.

[0021] The cyanoethyl group-containing organic compound is preferably contained in an amount of 5 to 60 mass %, and more preferably 25 to 45 mass %, based on the total amount of the composition constituting the dielectric film of this embodiment. When the content of the cyanoethyl group-containing organic compound is 5 mass % or more, the effect of improving the displacement of the actuator is high, and when it is 60 mass % or less, the stability of the actuator member is high. These cyanoethyl group-containing organic compounds are sold by Shin-Etsu Chemical Co., Ltd. under the product name Cyanoresin (registered trademark), for example.

[0022] (Other polar materials) The polar group-containing organic compound contained in the dielectric film of this embodiment may be modified silicone oil, phthalocyanines, various ionic liquids, or the like.

[0023] As the modified silicone oil, for example, a silicone oil that is liquid at room temperature (15 to 25° C.) and is obtained by modifying a compound having a polydimethylsiloxane skeleton with a polar group can be used.

[0024] The polar group that modifies polydimethylsiloxane is -CH 2 CH 2 CF 3 Group (fluoroalkyl modified), O(EO) n - group (polyether modified), -OH group (hydroxyl modified), -NH 2 Group (amino modified), -CH 2 Examples include OH groups (carbinol modified), -COOH groups (carboxyl modified), etc. The modified silicone oils having these polar groups may be either side chain modified copolymer types or straight chain modified copolymer types, and the part modified with the polar group may be any of the side chains, one end, or both ends.

[0025] Among these, modified silicone oils are carboxyl-modified silicone oils modified by -COOH groups, -CH 2 CH 2 CF 3 Modified silicone oil modified with fluoroalkyl groups and -NH 2Modified silicone oils that are amino-modified with a group are preferred.

[0026] As the ionic liquid, imidazolium salts, piperidinium salts, pyridinium compounds, pyrrolidinium salts, etc. can be used, but examples of the ionic liquid that can be used in the dielectric film of this embodiment include 1-methyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMI][BF4]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMI][BF4]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMI][BF4]), 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy)-ethylsulfate ([EMI][MEES]), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([BMP][TFSI]), etc. It has also been reported that phthalocyanines, which are metal complexes having Mg, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Mo, Ru, Rh, Pd, Re, Os, Ir or Pt as the central metal, act as charge capture agents in the dielectric polymer layer and become charged inside the actuator (see JP 2005-323482 A).

[0027] [Other ingredients] The dielectric film of the present invention may contain other components in addition to the above-mentioned polymer material and polar group-containing organic compound. Examples of other components include crosslinking agents, reinforcing materials, plasticizers, antioxidants, colorants, etc. For example, by blending insulating inorganic particles or the like as reinforcing materials, the mechanical strength and electrical resistance of the dielectric film can be increased. This increases the dielectric breakdown strength of the dielectric film and improves its durability when it is repeatedly deformed.

[0028] <Method of manufacturing dielectric film> The method for producing a dielectric film of the present invention includes a mixed solution preparation step, a coating step, and a film formation step. Each step will be described below in order.

[0029] [Mixed solution preparation process] This step is a step of dissolving the above-mentioned polymeric material and the polar group-containing organic compound in a solvent to prepare a mixed solution of the polymeric material and the polar group-containing organic compound, and is the most important step in producing a dielectric film having a desired internal structure. In order for the dielectric film to form a desired internal structure, the blending ratio of the polymeric material to the polar group-containing organic compound is preferably 4:1 to 1:1 by mass ratio. By setting the blending ratio of the polar group-containing organic compound to the polymeric material to 1 / 5 or more, a dielectric film having a sufficient relative dielectric constant can be produced, while by setting the blending ratio of the polar group-containing organic compound to 1 / 2 or less, a dielectric film having sufficient durability can be provided.

[0030] The solvent is preferably one that dissolves the polymer material and the polar group-containing organic compound, and examples of the solvent include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as pentane, hexane, cyclohexane, heptane, and cyclopentane; halogenated hydrocarbons such as chloroform, dichloromethane, and carbon tetrachloride; amides such as N,N-dimethylformamide (DMF), dimethylacetamide, and N-methylpyrrolidone; sulfoxides such as dimethylsulfoxide (DMSO); sulfones such as sulfolane; ethers such as dimethyl ether (DME), diethyl ether, diisopropyl ether, diglyme, tetrahydrofuran (THF), 1,4-dioxane, and t-butyl methyl ether; nitriles such as acetonitrile; esters such as methyl acetate, ethyl acetate, and propionocarbonate; and ketones such as acetone and methyl ethyl ketone. These solvents may be used alone or in combination. In order to sufficiently dissolve the polymeric material and the polar group-containing organic compound, it is preferable to use a solvent in an amount of at least 20 mass% based on the total amount of the mixed solution, and more preferably, the content of the solvent in the total amount of the mixed solution is 20 to 50 mass%.

[0031] In one embodiment, the viscosity of the mixed solvent at 20°C is preferably 1 Pa·s or less. If the viscosity of the mixed solvent is greater than 1 Pa·s, the fluidity of the mixed solution decreases in the film-forming process for hardening the polymer material, making it difficult for the dielectric film to form a desired internal structure. In order to form a dispersed phase mainly composed of a polar group-containing organic compound, the viscosity of the mixed solvent at 20°C is more preferably 0.5 Pa·s or less. The lower limit of the viscosity of the mixed solvent at 20°C is not particularly limited, but may be 0.01 Pa·s, preferably 0.1 Pa·s, and more preferably 0.2 Pa·s. The viscosity of the solvent at 20°C can be measured, for example, by using a tuning fork vibro viscometer SV-10A [product name] (manufactured by A&D Co., Ltd.) for the solvent whose temperature has been adjusted in a thermostatic bath at 20°C.

[0032] In the dielectric film, if many particles with a large particle diameter are contained relative to the film thickness, the particles are likely to become the starting point and cause dielectric breakdown. Therefore, in order to improve the dielectric breakdown strength of the dielectric film, it is desirable to make the particle diameter of the particles forming the dispersed phase smaller relative to the film thickness. However, when the particle diameter of the particles forming the dispersed phase becomes smaller, the accumulation of heterocharges becomes smaller. Therefore, in order to increase the accumulation of heterocharges in the dielectric film, it is desirable to make the particle diameter of the particles forming the dispersed phase as large as possible. Therefore, the particle diameter of the particles forming the dispersed phase may be appropriately determined in consideration of the thickness of the dielectric film and the efficient accumulation of heterocharges. Therefore, in addition to the viscosity of the mixed solvent, a solvent having excellent solubility for polymer materials and polar group-containing organic compounds, and a solvent having a vapor pressure that optimizes the drying speed of the solvent may be selected to prepare the mixed solution.

[0033] [Coating process] In the coating step, the resin composition of the present embodiment is coated on the surface of the support. The support is not particularly limited as long as it has heat resistance to the heating temperature in the subsequent film formation step (heating step) and has good releasability in the peeling step. Examples of the support include glass substrates, such as alkali-free glass substrates; silicon wafers; resin substrates such as PET (polyethylene terephthalate), OPP (oriented polypropylene), polyethylene glycol terephthalate, polyethylene glycol naphthalate, polycarbonate, polyimide, polyamideimide, polyetherimide, polyetheretherketone, polyethersulfone, polyphenylenesulfone, and polyphenylenesulfide; and metal substrates such as stainless steel, alumina, copper, and nickel.

[0034] Examples of the coating method generally include coating methods using a doctor blade knife coater, air knife coater, roll coater, rotary coater, flow coater, die coater, bar coater, etc., coating methods using spin coating, spray coating, dip coating, etc., and printing techniques such as screen printing and gravure printing, etc. The temperature in the coating step may be room temperature, or the mixed solvent may be heated to, for example, 40 to 80° C. in order to reduce the viscosity and improve workability.

[0035] [Optional drying process] A drying step may be performed following the coating step, or the drying step may be omitted and the process may proceed directly to the next film formation step (heating step). The drying step can be performed by placing the mixed solvent under a vacuum condition of 100 Pa or less for the purpose of removing the solvent in the mixed solvent. When performing the drying step, a suitable device such as a hot plate, a box-type dryer, or a conveyor-type dryer can be used. The temperature of the drying step is preferably 80 to 200°C, more preferably 100 to 150°C. The time for which the drying step is performed is preferably 1 minute to 10 hours, more preferably 3 minutes to 5 hours.

[0036] [Film formation process] Subsequently, a film forming step (heating step) is performed. The heating step is a step for removing the solvent contained in the coating film and for promoting the curing reaction of the elastomer in the coating film. This heating step can be performed by placing the resin composition under a vacuum condition of 100 Pa or less using an apparatus such as an inert gas oven, a hot plate, a box-type dryer, or a conveyor-type dryer. This step can be performed simultaneously with the drying step, or both steps can be performed sequentially.

[0037] <Actuator> The actuator of the present invention comprises the dielectric film of the present invention and a plurality of electrodes arranged via the dielectric film. The actuator of the present invention may be configured by alternately laminating a plurality of dielectric films and a plurality of electrodes. An intermediate layer having an intermediate electrical resistance between the dielectric film and the electrode may be interposed between them. By employing a laminated structure, a larger force can be generated. The configuration and manufacturing method of the dielectric film of the present invention are as described above.

[0038] In the actuator of the present invention, the material of the electrodes is not particularly limited. It is desirable that the electrodes are expandable and contractible following the deformation of the dielectric film. In this case, the deformation of the dielectric film is less likely to be restricted by the electrodes. Therefore, the actuator of the present invention is more likely to obtain a desired output. For example, the electrodes can be formed from a conductive paste or conductive paint in which a conductive material is mixed with a binder such as oil or elastomer. As the conductive material, carbon materials such as carbon black, ketjen black, carbon nanotubes, and graphene, and metal powders such as silver may be used. The electrodes may also be formed by weaving carbon fibers or metal fibers into a mesh shape.

[0039] The actuator of the present invention operates as an actuator by applying a voltage between the electrodes and generates stress. When the dielectric film deforms and the distance between the electrodes changes, the capacitance changes. This allows the actuator of the present invention to function as a capacitance-type sensor. The actuator of the present invention also functions as a power generation element by utilizing the charge generated when the dielectric film deforms as a current.

[0040] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the following examples, the unit % of the numerical values ​​showing the amount of each component added means % by mass. EXAMPLES

[0041] <Preparation of silicone composite film> [material] The silicone used was SILPOT184 / CAT184 (DuPont Toray Specialty Materials Co., Ltd.). This is an addition reaction type PDMS. The polar group-containing material was a cyanoethyl group (-CH 2 CH 2 We used CR-U (Shin-Etsu Chemical Co., Ltd.) having a cation exchange ratio of 1:1 (CN). CR-U has a very high viscosity and is difficult to handle. Therefore, CR-U was dissolved in tetrahydrofuran (hereinafter referred to as "THF") or acetone (hereinafter referred to as "ACT"), which are good solvents for CR-U, to prepare 50 wt% solutions of CR-U (T) and CR-U (A).

[0042] [Preparation of PDMS / CR-U / solvent casting solution] The base SILPOT184 and the curing agent CAT184 were mixed in a mass ratio of 10:1. CR-U(T) and CR-U(A) were added to this solution so that the CR-U content relative to the base SILPOT184 and CAT184 was 42.9 wt%. The mixture was stirred at 2000 rpm for 6 minutes using a revolution stirrer (ARE-310, THINKY) to prepare a PDMS / CR-U / solvent casting solution. Table 1 shows the composition of the PDMS / CR-U / solvent casting solution.

[0043] [Table 1]

[0044] [Preparation of silicone composite film] As shown in FIG. 2(a), the casting solution was poured onto a PET film 16 placed on a glass plate 17 using a four-sided film applicator (052-6, Allgood Corporation). After keeping the solution at room temperature for 60 minutes, it was heated and cured in an oven at 150° C. for 30 minutes to obtain the PDMS / CR-U(A) shown in Table 1. x / T y ) was prepared. (x and y indicate the contents (wt%) of ACT and THF relative to the total amount of solvent, respectively. Films with thicknesses of 150 to 280 μm were used to measure the deformation amount. As shown in Figure 2(b), the surface in contact with the PET film was defined as the "PET side," and the opposite surface in contact with air was defined as the "AIR side."

[0045] <Casting liquid viscosity measurement> Viscosity was measured at 20°C using a tuning-fork vibrometer (SV-10A, A&D Instrument Ltd.). The tuning-fork vibrometer consists of two thin sensor plates that vibrate a constant sine wave in opposite phase like a tuning fork, driving the sensor with electromagnetic force of the same frequency. The vibration of the sensor plate is controlled to a constant amplitude by the electromagnetic drive. The drive current is detected as the magnitude of the viscosity generated between the sensor plate and the sample liquid. This viscosity can be calculated from the torque required to resonate the vibrator in the fluid and move the vibrator at a constant amplitude.

[0046] <Space charge distribution measurement> The spatial charge distribution was measured using a pulsed electrostatic acoustic nondestructive testing device (PEANUT) manufactured by Five Labs. Figure 3 shows an overview of the electrode part of the PEANUT device. The upper electrode 22 is made of semiconductive rubber, and the lower electrode 24 is made of aluminum. In the PEANUT method, a pulsed electrostatic force acts on the charge, generating an elastic wave with a charge distribution shape. This elastic wave was converted into an electrical signal by a piezoelectric element, and the spatial charge distribution was measured. The bias condition was 3 kV / mm, and the pulse condition was 200 V x 400 Hz.

[0047] <Bending deformation measurement> [Specimen preparation] A schematic diagram of the deformation measurement sample is shown in Figure 4. The prepared silicone elastomer film 31 was cut to a width of 5 mm and a length of 20 mm, and gold foil 32 (Katani Sangyo Co., Ltd.) with a width of 4 mm, a length of 15 mm, and a thickness of 0.1 μm was attached to the front and back to prepare the deformation measurement sample.

[0048] [Deformation measurement] Figure 5 shows the experimental setup for measuring deformation. A DC power supply 44 was used with a square wave output of 850 V maximum output. To avoid the influence of its own weight, the test piece 43 was placed vertically to the floor, clamped with a Kelvin clip (12 mm from the clip to the tip of the test piece in a cantilevered state), and a DC voltage was applied. The deformation amount was observed and measured under an electric field with a digital microscope 41 placed on the sample, and recorded by a computer 42.

[0049] <Electrical characteristics> The dielectric constant and impedance were measured with an impedance analyzer (SI1260, SII1296, Solartron Co., Ltd.), a high voltage interface (HVI-100, TOYO Corporation), and a bipolar amplifier (BOP-1000M, KEPCO, INC.) (electrode diameter 10 mm and specimen thickness 170 μm).

[0050] <Measurement of elastic modulus> The tensile modulus of the silicone composite film was measured using a Tensilon tensile measuring device (RTC-1250A, A&D Co., Ltd.). The silicone composite film was compressed at a speed of 50 mm / min with a 10 N load cell. The tensile modulus was calculated from the initial slope of the tensile stress curve at low tensile stress. The flexural modulus was calculated by measuring the amount of deformation of the cantilever due to the static weight of the test specimen (test specimen for deformation measurement).

[0051] <Structural composition> The structural composition was measured using FT / IR-4600 type A (JASCO Corporation) at an incident angle of 45 degrees.

[0052] <Image capture> Cross-sectional images of the samples were taken with a laser microscope (OLYMPUS LEXT OLS4100).

[0053] <Result> [Viscosity of PDMS / CR-U solution] The dependence of the viscosity of the PDMS / CR-U solution on the THF content is shown in Figure 6. The viscosity of the PDMS / CR-U solution decreased with increasing THF content. It has been reported that ACT shows high and low affinity for CR-U and PDMS, respectively, and THF shows high affinity for CR-U and PDMS. As the viscosity of the PDMS solution increases with increasing ACT content, its affinity for PDMS decreases.

[0054] In Figure 6, the logarithmic viscosity of the PDMS / CR-U / solvent casting solution is plotted against the THF content. The viscosity decreased with increasing THF content. This is believed to be due to the low affinity of ACT for PDMS, as described in Non-Patent Document 1.

[0055] [Elastic modulus of PDMS composite film] To understand the potential applications of PDMS / CR-U composite membranes, basic mechanical properties are necessary. Figure 7 shows the dependence of the elastic modulus of PDMS / CR-U composite membranes on the THF content. The flexural modulus showed a minimum quadratic curve at a THF content of 50%. The flexural modulus of the film with 100% THF was greater than that of the film with 100% ACT. Furthermore, the tensile modulus tended to increase with increasing THF content.

[0056] [Morphology of PDMS composite membrane] Figure 8 shows cross-sectional images of each sample, from (a) PDMS / CR-U (A100 / T0) to (d) PDMS / CR-U (A0 / T100). The composite film showed a phase-separated structure with a spherical phase dispersed in a continuous phase. FT-IR analysis identified the continuous phase as PDMS and the spherical phase as CR-U. The film prepared using ACT (PDMS / CR-U( / T0)) had a symmetrical cross-sectional structure with small CR-U spheres uniformly dispersed. The diameter of the spheres tended to increase with increasing THF / ACT mixed solvent content. With increasing THF content, a thin skin layer was observed on the AIR side of the film. This layer was identified as PDMS containing CR-U. The thickness of this skin layer increased with increasing THF content. Thus, the membrane prepared using THF (PDMS / CR-U(A0 / T100)) had an asymmetric cross section, with a PDMS skin layer on the air side and sizable CR-U spheres dispersed in the film body.

[0057] Generally, it is believed that highly hydrophobic PDMS and CR-U, which has hydrophilic functional groups such as -CN groups, are not miscible. The casting solution of PDMS / CRU(A100 / T0) had an extremely high viscosity, as shown in Figure 6. In a highly viscous solution, CR-U molecules do not move quickly, so it is expected that it is not easy for the CR-U molecules to aggregate together and form large spheres. Since the casting solution was cured under such conditions, PDMS / CR-U(A100 / T0) had a symmetrical cross-sectional structure with small CR-U spheres uniformly dispersed.

[0058] It is expected that the CR-U molecules will move and aggregate more easily when the viscosity of the casting solution increases. In addition, the density of CR-U (1.23) is higher than that of PDMS (1.03). As a result, it was considered that PDMS / CR-U (A0 / T100) has an asymmetric cross-sectional shape with a thin PDMS skin layer on the AIR-side surface of the film and large CR-U spheres dispersed in the PDMS continuous phase (membrane body).

[0059] Figure 9 shows the dependence of the diameter of the spherical shape and the thickness of the skin layer of CR-U obtained by image analysis on the THF content. With the increase in the THF content, the spherical shape and the thickness of the skin layer of CR-U increased as the viscosity of the casting solution decreased (see Figure 6).

[0060] <Deformation behavior> Maximum deformation Figure 10 shows the time dependence of the deformation of PDMS / CR-U when an electric field is applied. An electric field was applied at t = 0 min so that the electrode on the AIR side became the anode, and the field was removed after t = 30 min. Negative values ​​of the deformation indicate that the film was bent toward the PET side. The deformation increased immediately after the voltage was applied, and gradually reached a steady state over time. The deformation decreased instantly after the voltage was turned off, and returned to the steady state after 10 min with some hysteresis. The difference between these two steady states was taken as the maximum deformation.

[0061] [ACT / THF solvent ratio dependence (THF content dependence)] Figure 11 plots the maximum deformation of the composite membrane measured by applying a DC electric field of 3 kV / mm against the THF content. Regardless of the polarity of the electric field, the composite membrane deformed toward the PET side. PDMS / CR-U (A100 / T0) had a symmetric cross-sectional structure, with small CR-U spheres uniformly dispersed without a skin layer, and therefore showed little deformation. With increasing THF content, the maximum deformation gradually increased, and in PDMS / CR-U (A0 / T100), which had an asymmetric cross-sectional shape with large CR-U spheres dispersed and aggregated within the PDMS continuous phase and a thin skin layer of PDMS on the AIR side, large deformation was observed.

[0062] [Field strength dependence] The electric field strength dependence of deformation of PDMS / CR-U(A100 / T0)-PDMS / CR-U(A0 / T100) is shown in Figure 12. (Bonding and bending from the PET side to the AIR side were zero for all films, regardless of electric field strength or polarity). PDMS / CR-U(A100 / T0) showed almost no deformation, regardless of electric field strength or polarity. The maximum deformation amount tended to increase with increasing THF content, and especially large deformation was observed in PDMS / CR-U(A0 / T100). The maximum deformation amount also increased with increasing electric field strength.

[0063] <Space charge distribution> Figure 13 shows the space charge distribution of PDMS / CR-U(A100 / T0)-PDMS / CR-U(A0 / T100) 5 minutes after bias loading. The horizontal axis represents the thickness (position) of the sample. The electrode interface is set to 0, and the vertical axis represents the space charge density. In addition, the maximum value of the opposite side charge accumulated in the film near the electrode interface on the AIR side was taken as the heterocharge peak value.

[0064] In Fig. 13(a), the anode electrode / film interface on the AIR side was defined as zero on the depth axis. Inside PDMS / CR-U(A12.5 / T87.5) and PDMS / CR-U(A0 / T100), accumulation of small and significantly large negative charges (indicated by diagonal lines in the figure) opposite to the polarity of the anode, i.e., heterogeneous charges, was observed near the anode interface. However, no accumulation of heterogeneous (positive) charges was observed inside the film near the cathode interface, confirming the asymmetry of the space charge distribution. On the other hand, no accumulation of heterogeneous charges was observed inside the film in the space charge distribution of PDMS / CR-U(A100 / T0)-(A25 / T75).

[0065] In Fig. 13(b), the cathode electrode / AIR side of the membrane interface is defined as zero on the depth axis. Heterogeneous charge accumulation in PDMS / CR-U(A0 / T100) was confirmed near both electrodes, with the amount of accumulation on the cathode side being greater than that on the anode side. As a result, asymmetry of the spatial charge distribution was confirmed. In PDMS / CR-U(A12.5 / T87.5), heterogeneous charge accumulation was confirmed near the interface between both electrodes. However, both values ​​were small and almost the same amount. On the other hand, in the PDMS / CR-U composite membranes other than PDMS / CR-U(A0 / T100) and PDMS / CR-U(A12.5 / T87.5), heterogeneous charge was not accumulated inside the membrane, and spatial charge distribution was observed.

[0066] In the case of PDMS / CR-U(A0 / T100), it was found that a large heterocharge accumulated near the interface between the air side and the electrode side, regardless of the polarity of the electric field. Furthermore, the location of the heterocharge accumulation was almost the same as the thickness of the skin layer. Thus, the skin layer suppressed the leakage of the charge, and the charge accumulated near the skin layer. It is clear that the deformation behavior of PDMS / CR-U(A0 / T100) is due to the electrostatic repulsion of the charge accumulated in the skin layer. It is thought that the expansion of the skin layer induces the deformation of the membrane toward the non-skin layer side.

[0067] <Relationship between deformation and space charge distribution Deformation and peak value of hetero charge> Figure 14 shows the relationship between the hetero charge peak value on the AIR side and the THF content. The hetero charge peak value increases significantly at THF 82.5 wt% or more. Figure 15 shows the relationship between the maximum deformation amount and the hetero charge peak value. Figure 15 shows the relationship between the maximum deformation amount and the hetero charge peak value, and the maximum deformation amount also increases significantly at THF 82.5 wt% or more. These results show that charge accumulation is the main cause of deformation. [Explanation of symbols]

[0068] 10 Dielectric film 11 Dense layer (skin layer) 12 Sea-island structure 13 Base polymer (continuous phase) 14 Dispersed phase 15 Interface 16 PET film 17 Glass Plate 21 Al electrode 22 Upper electrode (semi-conductive rubber) 23, 31, 43 Silicone elastomer film (dielectric film) 24 Lower electrode (Al) 25 Piezo element (sensor) 32 Gold leaf 41 Digital Microscope 42 Computer 43 DC power supply

Claims

1. A step of dissolving a polymer material and a polar group-containing organic compound in a solvent to prepare a mixed solution of the polymer material and the polar group-containing organic compound; applying the mixed solution onto a substrate; curing the polymeric material applied onto the substrate to form a thin film; Equipped with A method for manufacturing a dielectric film, comprising preparing the mixed solution so that the internal structure of the cured thin film is phase-separated into a continuous phase consisting of the polymer material and a dispersed phase consisting mainly of the polar group-containing organic compound.

2. The method according to claim 1, wherein a blending ratio of the polymer material to the polar group-containing organic compound is 3:1 to 1:1 by mass.

3. The method according to claim 1 or 2, wherein the content of the solvent is 20 to 50 mass% based on the total amount of the mixed solution.

4. The method according to any one of claims 1 to 3, wherein the mixed solution has a viscosity of 1 Pa·s or less at 20°C.

5. The method according to any one of claims 1 to 4, wherein the mixed solution applied onto the substrate is kept for at least 30 minutes before the polymeric material is cured.

6. The method according to any one of claims 1 to 5, wherein the polymeric material comprises one or more elastomers selected from silicone, polyurethane, polyacrylonitrile, nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), nylon, polyethylene terephthalate, polypropylene, polyethylene, polyketone, polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate, polymethyl methacrylate, poly n-butyl acrylate, cellulose, and wool.

7. The method according to any one of claims 1 to 6, wherein the polar group-containing organic compound is a cyanoethyl group-containing organic compound, a modified silicone oil, a phthalocyanine, or an ionic liquid.

8. The method according to any one of claims 1 to 7, wherein the polymeric material is silicone, and the polar group-containing organic compound is cyanoethylsucrose.

9. The process according to any one of claims 1 to 8, wherein the solvent is tetrahydrofuran or a mixed solvent of tetrahydrofuran and acetone.

10. A method for manufacturing an actuator, comprising the steps of: adding an electrode layer to each of both sides of a dielectric film manufactured by the method according to any one of claims 1 to 9.

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