Electret material and skin-attachable electret energy harvester using the same

Abstract

[Problem] The present invention provides an electret material which has high charge retention ability and stretchability; and a skin-patch type electret energy harvesting device which uses this electret material. [Solution] According to the present invention, a perfluoroelastomer containing iodine and / or bromine or a crosslinked elastomer obtained by crosslinking this elastomer is used as an electret material. These materials have stretchability and are capable of forming an electret by being charged by means of a soft X-ray. In addition, a skin-patch type electret energy harvesting device is achieved by forming the electret on one of two comb-shaped electrodes that are arranged to be parallel to each other.

Description

[Technical Field]

[0001] This invention relates to an electret material and a skin-attachable electret energy harvester using the same. [Background technology]

[0002] An electret is a dielectric material into which an electric charge has been implanted, and it can generate an electric field semi-permanently. An electret generator is a device that converts vibrations in the environment into electricity through electrostatic induction using an electric field generated by an electret. It efficiently converts low-frequency vibrations such as environmental vibrations and vibrations of the human body caused by walking into electricity, and can produce high output, so it is attracting attention as a power source that can continuously drive low-power electronic devices such as wearable devices and wireless sensors without batteries. For example, Patent Document 1 below discloses a charging device and a method for manufacturing a charged body that can charge a dielectric material to a high and stable surface potential over time with a short charging process.

[0003] However, the power output of an electret power generation device is proportional to the square of the electret's surface potential, and the device's durability and heat resistance are greatly influenced by the electret's charge characteristics. Therefore, in order to improve the performance of electret power generation devices, it is necessary to develop electret materials that can stably retain more charge over a long period of time.

[0004] For example, Patent Document 2 discloses an example in which CYTOP®, a polymer having a fluorine-containing aliphatic ring structure in its main chain, is used as an electret material. Furthermore, Patent Document 3 discloses an example in which CYTOP®, in which 2,2',2''-triaminotriethylamine is bonded to the terminal group, is used as an electret material.

[0005] Furthermore, in conventional electret power generation devices, the electret and the current collector electrode are placed facing each other, and power is generated by extracting an induced current into an external circuit by changing the overlapping area or the distance between their surfaces over time. For example, Patent Document 2 below discloses an example in which CYTOP (registered trademark) is used as the electret material, and the overlapping area is changed by moving the electret, which is patterned in a strip shape, and the current collector electrode in a horizontal relative motion.

[0006] On the other hand, skin-attached electronic devices, also known as skin electronics, are being considered for applications in fields such as information terminals that integrate the human body and electronic devices, home care through the acquisition of biometric data from the skin, and soft robotics. Therefore, it is essential that they be flexible and stretchable so that they do not cause discomfort when attached to the skin. For example, Patent Document 4 discloses an example of a circuit board that achieves flexibility and stretchability by forming wiring and functional members on one surface of a substrate having a cross-sectional shape with an uneven surface and a stress adjustment layer. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] WO2012 / 053617 pamphlet [Patent Document 2] Japanese Patent Publication No. 2011-91996 [Patent Document 3] Japanese Patent Publication No. 2020-65055 [Patent Document 4] Japanese Patent Publication No. 2019-75409 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The conventional electret materials described above lack sufficient elasticity, making them particularly difficult to use in skin-attached electret power generation devices. Furthermore, conventional power generation structures require relative motion between the substrate on which the electret is placed and the substrate on which the current collector electrodes are placed, resulting in a complex structure that is difficult to use in skin-attached electret power generation devices.

[0009] The object of the present invention is to provide an electret material having high charge retention capacity and elasticity, and a skin-attachable electret environmental power generator using the same. [Means for solving the problem]

[0010] To achieve the above objectives, the present invention includes the following embodiments.

[0011] [1] Repeating units based on tetrafluoroethylene and CF2=CF-OR f (In the formula, R f An electret material characterized by being a perfluoroelastomer having repeating units based on (a perfluoroalkyl group having 1 to 20 carbon atoms which may have an etheric oxygen atom), and being an iodine and / or bromine-containing perfluoroelastomer.

[0012] [2] Tetrafluoroethylene and CF2=CF-OR f An electret material characterized by being an iodine and / or bromine-containing perfluoroelastomer, which is a polymer of one or more perfluoromonomers selected from the group consisting of and , and an iodine and / or bromine-containing monomer.

[0013] [3] Tetrafluoroethylene and CF2=CF-OR f One or more perfluoromonomers selected from the group consisting of and , and iodine and / or bromine-containing monomers and IR f2 -I (where R f2It is a perfluoroalkylene group having 1 to 8 carbon atoms which may have an etheric oxygen atom. A perfluoroelastomer which is a copolymer of one or both of the compounds represented by ) and, characterized in that it is an iodine and / or bromine-containing perfluoroelastomer as an electret material.

[0014] [4] The electret material according to [1], characterized in that the iodine and / or bromine-containing perfluoroelastomer is crosslinked by a crosslinking aid containing a heteroatom in the molecule.

[0015] [5] The electret material according to [4], characterized in that the crosslinking aid is triallyl isocyanurate.

[0016] [6] A skin-attachable type electret environmental power generator using a single substrate, comprising a substrate having elasticity and one main surface attachable to the skin, two comb-shaped electrodes formed on the other main surface of the substrate and arranged such that the electrodes are parallel to each other, and an electret formed on one of the electrodes of the comb-shaped electrodes, wherein the electret uses the electret material according to any one of [1] to [5] and changes the amount of induced charge by the fringe field of static electricity according to the change in the horizontal distance between the electrode and the electret.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide an electret material having a high charge retention ability and elasticity, and a skin-attachable type electret environmental power generator having a simple structure using a single substrate.

Brief Description of the Drawings

[0018] [Figure 1] It is a perspective view of a configuration example of a skin-attachable type electret environmental power generator according to the present invention. [Figure 2] It is a cross-sectional view for explaining the operation of a skin-attachable type electret environmental power generator according to the present invention. [Figure 3]It is an explanatory diagram of the charging process of an electret material. [Figure 4] It is a diagram showing the measurement results of the change over time of the surface potential of an electret. [Figure 5] It is a diagram showing the schematic configuration of the measurement method of thermally stimulated current (TSD). [Figure 6] It is a diagram showing the TSD spectrum of the measurement results of TSD. [Figure 7] It is a diagram showing the evaluation results of the stability of the electret against the expansion and contraction operation of the trapped charges. [Figure 8] It is a diagram showing the output current waveform of the skin-attached type electret environmental power generator according to the embodiment.

Mode for Carrying Out the Invention

[0019] Hereinafter, a mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings.

[0020] The electret material according to the present invention includes a repeating unit based on tetrafluoroethylene (hereinafter referred to as TFE), and CF2=CF-O-R f (wherein, R f is a perfluoroalkyl group having 1 to 20 carbon atoms which may have an etheric oxygen atom.) and a repeating unit based on, and is a perfluoroelastomer, and is characterized in that it is an iodine and / or bromine-containing perfluoroelastomer.

[0021] The CF2=CF-O-R f can be used singly or in combination of two or more. Preferred ones are CF2=CF-O-CF3, CF2=CF-O-CF2CF3, CF2=CF-O-CF2CF2CF3, CF2=CF-O-CF2CF(CF3)OCF2CF2CF3, CF2=CF-O-CF2CF2-O-CF2CF3, etc., and more preferred is CF2=CF-O-CF3.

[0022] Also, R fThe preferred range for the number of carbon atoms is 1 to 20, and the more preferred range is 1 to 8.

[0023] The copolymerization ratio in the fluorine-containing copolymer (perfluoroelastomer) is given by the repeating units / CF2 = CF-OR based on TFE. f A repeating unit of 30-80 / 70-20 (molar ratio) is preferred. Excellent rubber properties are achieved within this range.

[0024] As the perfluoroelastomer, it is preferable to use one that is substantially free of hydrogen atoms, but it is also possible to use a perfluoroelastomer obtained by using one that contains a small amount of hydrogen atoms in the chain transfer agent or comonomer. Examples of chain transfer agents containing hydrogen atoms include linear or cyclic saturated hydrocarbons such as methane, ethane, propane, butane, pentane, hexane, and cyclohexane; alcohols such as methanol, ethanol, and propanol; and mercaptans such as tert-dodecyl mercaptan, n-dodecyl mercaptan, and n-octadecyl mercaptan. One or more types of chain transfer agents can be used.

[0025] Examples of comonomers containing hydrogen atoms include CF2=CF-O-CH2CF3, CF2=CF-O-CH2CF2CF2CF3, CF2=CF-O-CH2(CF2CF2)2H, CF2=CF-O-CF2CF2CH2-I, CF2=CF-O-CF2CF2CH2-Br, CF2=CF-O-CF2CF2(CF3)-O-CF2CF2CH2-I, and CF2=CF-O-CF2CF2(CF3)-O-CF2CF2CH2-Br. One or more types of comonomers containing hydrogen atoms can be used. However, as the hydrogen atom content increases, not only does the performance of the perfluororubber, such as heat resistance and chemical resistance, decrease, but the electrical insulation and electret charge retention performance also decrease due to a decrease in volume resistivity.

[0026] Therefore, the hydrogen atom content in the perfluoroelastomer used in the present invention is 0.1% by mass or less, preferably 0.07% by mass or less, and more preferably 0.05% by mass or less.

[0027] As a perfluoroelastomer, a perfluoroelastomer copolymerized with fluorodiene as a comonomer can also be used. A fluorodiene is a compound that has one or more fluorine atoms, two polymerizable double bonds, and does not exhibit cyclization properties.

[0028] Examples of fluorodienes include perfluorodienes composed of carbon atoms and fluorine atoms, perfluorodienes composed of carbon atoms, fluorine atoms and oxygen atoms, and fluorodienes having hydrogen atoms. Among fluorodienes, perfluorodienes are preferred because the crosslinked product has excellent heat resistance and chemical resistance, perfluorodienes composed of carbon atoms, fluorine atoms and oxygen atoms are more preferred, and perfluorodienes having a perfluorovinyl ether group are most preferred.

[0029] Specific examples of perfluorodienes having a perfluorovinyl ether group include CF2=CFO(CF2)3OCF=CF2, CF2=CFO(CF2)4OCF=CF2, CF2=CFO(CF2)5OCF=CF2, CF2=CFO(CF2)6OCF=CF2, and CF2=CFO(CF2)4OCF(CF3)CF2OCF=CF2.

[0030] When a perfluoroelastomer has a fluorodiene-based structural unit, it acquires a branched structure, with an average of more than two polymer end groups per molecule. Therefore, in the case of perfluoroelastomers having iodine or bromine atoms at the polymer chain ends, a perfluoroelastomer composition containing a perfluoroelastomer with a fluorodiene-based structural unit exhibits superior crosslinking reactivity compared to a perfluoroelastomer composition containing a linear, unbranched perfluoroelastomer.

[0031] In the perfluoroelastomer, the content of fluorodiene-based structural units is preferably 0.01 to 5 mol%, more preferably 0.01 to 3 mol%, and most preferably 0.05 to 1 mol% relative to the total structural units in the perfluoroelastomer.

[0032] Furthermore, the electret material according to the present invention is tetrafluoroethylene and CF2=CF-OR f A perfluoroelastomer which is a polymer of one or more perfluoromonomers selected from the group consisting of and and an iodine and / or bromine-containing monomer, wherein the iodine and / or bromine-containing perfluoroelastomer, or tetrafluoroethylene and CF2=CF-OR f One or more perfluoromonomers selected from the group consisting of and , and iodine and / or bromine-containing monomers and IR f2 -I (where R f2 The compound represented by is a perfluoroalkylene group having 1 to 8 carbon atoms which may have an etheric oxygen atom. The perfluoroelastomer is a copolymer of one or both of the compounds represented by and is characterized by being an iodine and / or bromine-containing perfluoroelastomer.

[0033] Examples of the iodine and / or bromine-containing monomers include CF2=CFBr, CH2=CHCF2CF2Br, CF2=CF-O-CF2CF2-I, CF2=CF-O-CF2CF2-Br, CF2=CF-O-CF2CF2CH2-I, CF2=CF-O-CF2CF2CH2-Br, CF2=CF-O-CF2CF2(CF3)-O-CF2CF2CH2-I, and CF2=CF-O-CF2CF2(CF3)-O-CF2CF2CH2-Br.

[0034] Furthermore, the aforementioned IR f2Specific examples of -I include diiododifluoromethane, 1,2-diiodoperfluoroethane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,7-diiodoperfluoroheptane, and 1,8-diiodoperfluorooctane, among which 1,4-diiodoperfluorobutane and 1,6-diiodoperfluorohexane are preferred, and 1,4-diiodoperfluorobutane is particularly preferred.

[0035] The iodine and / or bromine content in the perfluoroelastomer used in the present invention is not particularly limited, but is preferably 0.1 to 1.5% by mass, more preferably 0.1 to 1.0% by mass, and particularly preferably 0.2 to 1.0% by mass. Within this range, a crosslinked rubber composition with excellent rubber properties such as tensile strength, elongation, rebound elasticity, and compression set can be obtained.

[0036] The glass transition temperature (hereinafter referred to as Tg) of the perfluoroelastomer used in the present invention is 15°C or lower, but is preferably -50 to 10°C, more preferably -50 to 0°C, and most preferably -50 to -3°C.

[0037] Furthermore, the iodine and / or bromine-containing perfluoroelastomer, which is the electret material according to the present invention, is preferably crosslinked with a crosslinking aid that contains heteroatoms in its molecule.

[0038] When crosslinking the iodine and / or bromine-containing perfluoroelastomer composition of the present invention, it is preferable to include a crosslinking aid. The presence of a crosslinking aid results in high crosslinking efficiency. Specific examples of crosslinking aids include triallyl cyanurate, triallyl isocyanurate (TAIC), trimethacryl isocyanurate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, triallyl trimellitate, m-phenylenediamine bismaleimide, p-quinone dioxime, p,p'-dibenzoylquinone dioxime, dipropargyl terephthalate, diallyl phthalate, N,N',N'',N'''-tetraaryl terephthalamide, polymethylvinylsiloxane, polymethylphenylvinylsiloxane, and other vinyl group-containing siloxane oligomers.

[0039] In particular, triallyl cyanurate, triallyl isocyanurate, and trimethacrylate isocyanurate are preferred, and triallyl isocyanurate (TAIC) is more preferred. The content of the crosslinking aid is preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of perfluoroelastomer. Within this range, a crosslinked material with a good balance of strength and elongation can be obtained.

[0040] Furthermore, by using crosslinking aids containing heteroatoms, charge trapping structures can be introduced into the perfluoroelastomer, allowing for the stable retention of positive and negative charges.

[0041] The perfluoroelastomer of the present invention is cured by carrying out a crosslinking reaction using an organic peroxide in the presence of a crosslinking aid.

[0042] The organic peroxide is not particularly limited, but an organic peroxide with a one-minute half-life temperature of 150 to 250°C (the temperature at which half of the organic peroxide decomposes in one minute) is preferred, and 150 to 200°C is more preferred. Specific examples include di-tert-butyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide, α,α-bis(tert-butylperoxy)-p-diisopropylbenzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane-3, 1,3-bis(tert-butylperoxyisopropyl)benzene, and other dialkyl peroxides, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroxyperoxide, benzoyl peroxide, tert-butylperoxybenzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butylperoxymaleic acid, and tert-butylperoxyisopropyl carbonate. One or more organic peroxides can be used.

[0043] The amount of organic peroxide added is preferably 0.05 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and most preferably 0.5 to 3 parts by mass, per 100 parts by mass of the perfluoroelastomer of the present invention. Within this range, a composition is obtained that provides a fluororubber molded article, which is a crosslinked rubber with excellent heat resistance and rubber properties.

[0044] The iodine and / or bromine-containing perfluoroelastomer, which is an electret material according to the present invention, is an amorphous fluorine-containing elastomer that is stretchable and has excellent chemical resistance, heat resistance, weather resistance, and mechanical strength. Furthermore, the iodine and / or bromine-containing perfluoroelastomer has a Young's modulus of approximately 1 MPa, which is within the range of 0.5 to 1.95 MPa for human skin, so it does not hinder the stretching and contracting of the skin, resulting in a comfortable fit against the skin and making it suitable as a material for skin-attached electret energy harvesters. This is also true when the iodine and / or bromine-containing perfluoroelastomer is crosslinked.

[0045] A further embodiment of the present invention is a skin-attachable electret harvester. Figure 1 shows a perspective view of an example configuration of a skin-attachable electret harvester according to the present invention. In Figure 1, the skin-attachable electret harvester 100 has one main surface (back side in the figure) of a stretchable substrate 10 made of silicone rubber or the like that can be attached to human skin with an adhesive, and a pair of comb-shaped electrodes 12a and 12b are formed on the other main surface (front side in the figure) so that the electrodes are substantially parallel to each other. For attachment to the skin, it is preferable to use an adhesive suitable for skin attachment, such as a medical adhesive, which has little effect on the skin. For example, a urethane adhesive for skin manufactured by AGC Inc. can be used. Furthermore, an electret 14 is formed on one of the comb-shaped electrodes 12a of the pair (2) of comb-shaped electrodes 12a and 12b.

[0046] Electret 14 was formed by using the iodine and / or bromine-containing perfluoroelastomer (including when it is crosslinked) as the electret material and charging it positively with soft X-rays. Alternatively, it may be charged negatively.

[0047] Figures 2(a), (b), and (c) show cross-sectional views illustrating the operation of the skin-attached electret energy harvester according to the present invention. Figures 2(a) and (c) are cross-sectional views taken along line II-II of Figure 1. In Figure 2(a), the horizontal distance between the comb-shaped electrode 12b and the electret 14 formed on the comb-shaped electrode 12a is G0. An electric field (fringe field) is generated by the action of the positive charge on the electret 14 formed on the comb-shaped electrode 12a, and a negative charge is induced on the comb-shaped electrode 12b by this fringe field. As shown in Figure 2(c), when the substrate 10 is stretched (the horizontal distance between the comb-shaped electrode 12b and the electret 14 is G0 + ΔG0), and when the substrate 10 expands or contracts between this state and the original state shown in Figure 2(a), the horizontal distance between the comb-shaped electrode 12b and the electret 14 changes (it changes between G0 and G0 + ΔG0), and the amount of induced charge induced in the comb-shaped electrode 12b changes. This generates an induced current I, which can be extracted as a power output to an external circuit. Thus, the skin-attached electret environment generator according to the present invention can generate electricity by changing the amount of induced charge due to the electrostatic fringe field as the horizontal distance between the comb-shaped electrode 12b and the electret 14 changes due to the expansion and contraction of a single substrate. Therefore, when the skin-attached electret environment generator according to the present invention is attached to a person's skin, electricity can be extracted from the expansion and contraction movements of the skin that occur in conjunction with the person's activities.

[0048] In Figures 2(a) and (c), the electret 14 is formed only on the comb-shaped electrode 12a, but as shown in Figure 2(b), the electret 14 is formed over the entire surface, including the comb-shaped electrode 12b, and the device operates similarly when charge is injected only on the comb-shaped electrode 12a, or when charges of opposite signs are injected on both the comb-shaped electrode 12a and the comb-shaped electrode 12b. [Examples]

[0049] The following describes specific embodiments of the present invention. Note that the following embodiments are provided to facilitate understanding of the present invention, and the present invention is not limited to these embodiments.

[0050] <Sample preparation> (a) As an example of an electret material, AFLAS® PM-1100, an iodine and / or bromine-containing perfluoroelastomer manufactured by AGC Inc., was used (Example 1). Another example of an electret material was a crosslinked elastomer obtained by crosslinking AFLAS® PM-1100 with triallyl isocyanurate (manufactured by TAIC, Comb-Block) (Example 2).

[0051] The crosslinkable composition for Example 2 was prepared as follows: In a 50 ml round-bottom flask, AFLAS® PM-1100, TAIC, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DBPH, Acros) as an initiator were mixed in a fluorine-based solvent (product name Asahi Clean AC2000, AGC Inc.), and then stirred at 35°C for 1 hour to dissolve. Further stirring was carried out at 90°C for 30 minutes. Next, the above mixed solution was placed in an inert oven, and the solvent was evaporated and removed under a nitrogen atmosphere to obtain the crosslinkable elastomer composition.

[0052] Furthermore, polydimethylsiloxane (PDMS) was used as a comparative example of an electret material (Example 3).

[0053] The crosslinkable composition of Example 2 was pressed using a small press (H300-10D, manufactured by AS ONE Corporation) at 170°C and 10 MPa for 15 minutes to obtain a cured film of crosslinked elastomer. The material of Example 1 was also pressed under the same conditions as in Example 2 to obtain a self-supporting film.

[0054] (b) Electrets were formed by charging films made using the respective resins of the electret materials described above. Here, the film thickness of the electret in Example 1 was 18.5 μm, the film thickness of the electret in Example 2 was 75 μm, and the film thickness of the electret in Example 3 was 53 μm. Figure 3 shows an explanatory diagram of the charging process. In Figure 3, a bias voltage of -2.2 kV was applied by an external power supply between the copper plate 16 on which the films 15 of Examples 1 to 3 were placed and the aluminum foil 18 placed on each film. In this state, when soft X-rays were irradiated from a soft X-ray source 20 (HAMAMATSU PhotoIonizer L9490) to ionize nitrogen molecules in the air, nitrogen ions were attracted to the film by the bias voltage. The surface potential of the film gradually cancels out the bias voltage, and when the surface potential of the film matches the bias voltage, charging is completed and the electrets of Examples 1 to 3 are formed. The initial surface potential of the electrets formed in Examples 1-3 was approximately 2.2 kV.

[0055] <Performance Evaluation> (c) Tensile test The films (before charging) of Examples 1-3 prepared in (a) above were stretched at an elongation rate of 1 mm / min using a small benchtop test machine (EZ-SX, manufactured by Shimadzu Corporation), and their Young's moduli were measured.

[0056] The membrane used in the test was 11 mm long x 0.5 mm wide (0.5 mm thick), the membrane in Example 2 was 25 mm long x 1 mm wide (0.075 mm thick), and the membrane in Example 3 was 7 mm long x 3 mm wide (0.05 mm thick).

[0057] The film in Example 1 stretched to 190% before breaking. The Young's modulus was approximately 1 MPa up to 70% strain, after which it underwent plastic deformation. The film in Example 2 stretched almost linearly to 180% before breaking. No clear yield point was observed before breaking, and the Young's modulus was approximately 1 MPa. The film in Example 3 stretched to 165% before breaking. No clear yield point was observed before breaking, but the slope increased from around 50% elongation, and the Young's modulus was 1 MPa up to 50% strain, and approximately 3 MPa after 100% strain.

[0058] From the above, it was confirmed that the Young's modulus of the membranes in Example 1 and Example 2 is similar to that of human skin. Furthermore, in the membrane of Example 2, yielding does not occur until rupture, and it returns to its original length after stretching, indicating that it has desirable properties as a stretchable electret membrane.

[0059] (d) For the electrets of Examples 1 to 3 prepared in (b) above, the change in surface potential over time was measured using the MONROE ELECTRONICS ISOPROBE ELECTROSTATIC VOLTMETET Model 279.

[0060] The measurement results are shown in Figure 4. In Figure 4, the vertical axis shows the surface potential, and the horizontal axis shows the elapsed time since the end of charging.

[0061] As shown in Figure 4, the surface potential of the electret in Example 3 decreased rapidly and disappeared within 1 hour. On the other hand, the initial surface potential of the electret in Example 1 was 2.0 kV, and after 1200 hours it was 0.25 kV. Also, the initial surface potential of the electret in Example 2 was 2.2 kV, and after 700 hours it was 1.0 kV.

[0062] From the above, it was confirmed that the electrets in Example 1 and Example 2 can maintain their surface potential for a sufficiently long time.

[0063] (e) Thermally stimulated discharge (TSD) measurements were performed on the electrets of Example 1 and Example 2 prepared in (b) above to evaluate the thermal stability of the trapped charge.

[0064] Figure 5 shows a schematic configuration of the TSD measurement method (a self-made apparatus). In Figure 5, the copper plate 22 on which each electret sample is placed is fixed to the electrode 26 in the metal measurement chamber 24, and the temperature is raised from 40°C to 200°C at a rate of 1°C / min by the heater 28, and the change in the amount of induced charge (thermal stimulation (TSD) current value) of the probe electrode 30 is measured with a microammeter (Keithley 6430, manufactured by Keithley Instruments, Inc.) 32. The temperature of the electret is controlled by adjusting the operation of the heater 28 with a temperature controller 36 controlled by a computer 34.

[0065] Figure 6 shows the TSD spectrum of the measurement results. In Figure 6, the normalized TSD current value is shown on the vertical axis, and the electret temperature is shown on the horizontal axis. The TSD spectrum shown in Figure 6 represents the amount of charge emitted from the electret (detrapping charge) as a TSD current, and a peak appears at the temperature where the charge emission is greatest. Therefore, a higher peak temperature means that the thermal stability of the electret's charge is higher, and it serves as an indicator of the thermal stability of the charge trapped in the electret.

[0066] In Figure 6, the temperature at which the TSD spectrum shows a peak (peak temperature) was 46°C for Example 1 and 79°C for Example 2. Therefore, it was clear that bridging improves the thermal stability of the charge trapped in the electret.

[0067] (f) The stability of the electrets of Example 1 and Example 2, which were prepared in (b) above, against the expansion and contraction of the trapped charge was evaluated.

[0068] As samples, the films from Example 1 and Example 2 were prepared to a size of 20 mm in length, 40 mm in width, and 0.12 mm in thickness. After a 24-hour charging operation using soft X-rays, the charged films (electrets) were fixed to an electromagnetic vibrator (APS-113, manufactured by APS DYNAMICS). While measuring the strain of the electrets using a laser displacement meter (LT-9500, manufactured by Keyence Corporation), the electrets were expanded and contracted at a constant frequency of 2 Hz.

[0069] Figure 7 shows the evaluation results of the stability of the charge trapped in the electret against stretching and contracting operations. In Figure 7, the vertical axis shows the surface potential and the horizontal axis shows the number of stretching and contracting cycles. As shown in Figure 7, the surface potential of the electret in Example 1 before the stretching and contracting test was 0.8 kV, and the surface potential of the electret in Example 2 was 1.7 kV.

[0070] In both Example 1 and Example 2, the surface potential after 10,000 stretches and contractions at a 20% strain remained almost unchanged from the initial value. On the other hand, when stretched 10,000 times at a 40% strain, the surface potential of the electret in Example 2 remained almost unchanged from the initial value, demonstrating good stability. However, the surface potential of the electret in Example 1 decreased by 30% from the initial value. Therefore, it was clear that bridging improves the stability of the charge trapped in the electret against stretching and contraction operations.

[0071] As described above, the electret in Example 2 shows improved stability against the expansion and contraction of the trapped charge compared to the electret in Example 1. However, the electret in Example 1 is also sufficiently stable. Both the electrets in Example 1 and Example 2 exhibit high stability against the expansion and contraction of the trapped charge and are suitable for skin-attached electret energy harvesters.

[0072] <Fabrication and evaluation of skin-attached electret energy harvesting devices> (g) The film from Example 2 was used as the electret material and cut to a size of 20 mm in length x 20 mm in width (thickness 0.125 mm). A polyimide substrate with rectangular holes formed on one main surface of this film was used as a hard mask, and a 200 nm thick copper thin film was deposited by electron beam evaporation to form only one pair of comb-shaped electrodes 12a and 12b similar to those in Figure 2(b). The electron beam evaporation was performed using the MUE-ECO-EB manufactured by ULVAC, Inc. The horizontal distance (spacing) G0 between the comb-shaped electrodes 12a and 12b was set to 2 mm. A 0.5 mm thick silicone rubber sheet (manufactured by Togawa Rubber Co., Ltd.) was used as the substrate 10.

[0073] In the same manner as in Figure 2(b), the region of the film in Example 2 corresponding to the comb-shaped electrode 12a (the region above the comb-shaped electrode 12a) was irradiated with soft X-rays using the charging process shown in Figure 3 to create an electret with a surface potential of +2.5kV, thereby forming a skin-attachable electret energy harvester.

[0074] The skin-attached electret energy harvester formed as described above was attached to an electromagnetic vibrator (APS-113, manufactured by APS Corporation) and subjected to a 10% distortion at a frequency of 1 Hz. At this time, the comb-shaped electrodes 12a and 12b were directly connected to a programmable current amplifier (CA5350, manufactured by NF Circuit Design Co., Ltd.) to convert the short-circuit current into a voltage, which was then input to a computer via an AD converter (TUSB0224ADM, manufactured by Turtle Industries Co., Ltd.) and the output current waveform was recorded.

[0075] Figure 8 shows the output current waveform of the skin-attached electret harvester according to this embodiment. In Figure 8, the vertical axis shows the output current value and the horizontal axis shows the elapsed time. As can be seen from Figure 8, the skin-attached electret harvester according to this embodiment, despite having only a single pair of comb-shaped electrodes 12a and 12b, obtains a peak short-circuit current of approximately 30 nA, demonstrating that the generator according to the present invention can be constructed. [Industrial applicability]

[0076] The electret of the present invention can be used in electrostatic induction type conversion elements such as power generation devices and microphones, and is particularly suitable for skin-attached electret energy harvesters. Furthermore, the entire contents of the specifications, claims, drawings, and abstracts of Japanese Patent Application No. 2022-177440, filed on November 4, 2022, and Japanese Patent Application No. 2023-150068, filed on September 15, 2023, are incorporated herein by reference as disclosure of the specification of the present invention. [Explanation of symbols]

[0077] 10 Substrate, 12a, 12b Comb-shaped electrodes, 14 Electret, 15 Film, 16 Copper plate, 18 Aluminum foil, 20 Soft X-ray source, 22 Copper plate, 24 Metal measuring chamber, 26 Electrode, 28 Heater, 30 Probe electrode, 32 Microammeter, 34 Computer, 36 Temperature controller, 100 Skin-attachable electret energy harvester.

Claims

1. Repeating units based on tetrafluoroethylene and CF ２ =CF-O-R ｆ (In the formula, R ｆ An electret material characterized by having repeating units based on (a perfluoroalkyl group having 1 to 20 carbon atoms which may have an etheric oxygen atom), and being an iodine and / or bromine-containing perfluoroelastomer.

2. Tetrafluoroethylene and CF ２ =CF-O-R ｆ An electret material characterized by being an iodine and / or bromine-containing perfluoroelastomer, which is a polymer of one or more perfluoromonomers selected from the group consisting of and , and an iodine and / or bromine-containing monomer.

3. Tetrafluoroethylene and CF ２ =CF - O - R ｆ one or more perfluoromonomers selected from the group consisting of, an iodine and / or bromine-containing monomer and I - R ｆ２ -I (wherein R ｆ２ is a perfluoroalkylene group having 1 to 8 carbon atoms which may have an etheric oxygen atom.), a perfluoroelastomer which is a copolymer of one or both of the compounds represented by the formula, characterized in that it is an iodine and / or bromine-containing perfluoroelastomer, an electret material.

4. The electret material according to claim 1, characterized in that the iodine and / or bromine-containing perfluoroelastomer is crosslinked with a crosslinking aid containing heteroatoms in its molecule.

5. The electret material according to claim 4, wherein the crosslinking agent is triallyl isocyanurate.

6. A substrate that is stretchable and has one main surface that can be attached to the skin, Two comb-shaped electrodes are formed on the other main surface of the substrate and arranged so that the electrodes are parallel to each other, An electret formed on one electrode of the comb-shaped electrode, Equipped with, The electret is a skin-attachable electret energy harvester using a single substrate, wherein the electret uses the electret material described in any one of claims 1 to 5, and the amount of induced charge due to the electrostatic fringe field is changed by changing the horizontal distance between the electrode and the electret.

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