Electret material and skin-attached electret environment generator using same

Abstract

Provided are: an electret material having high charge retention and stretchability; and a skin-attached electret environmental power generator using the electret material. A perfluoroelastomer containing iodine and / or bromine or a crosslinked elastomer obtained by crosslinking the elastomer is used as the electret material. These materials are stretchable and can form an electret by being charged by soft X-rays. In addition, the electret is formed on one of two comb-shaped electrodes arranged in a manner that the electrodes are parallel to each other, and a skin-attached electret environment power generator is formed.

Description

Technical Field

[0001] The present invention relates to an electret material and a skin-attached electret environmental power generator using the electret material. Background Art

[0002] An electret is a dielectric into which charges are injected and can generate an electric field semi-permanently. An electret power generator is an element that converts vibrations in the environment into electricity by electrostatic induction using the electric field generated by an electret, and effectively converts low-frequency vibrations such as vibrations of the human body accompanying environmental vibrations or human walking into electricity, and can obtain high output. Therefore, it has attracted much attention as a power source that can continuously drive low-power electronic devices such as wearable devices or wireless sensors without a battery. For example, in Patent Document 1 below, a charging device and a charged body manufacturing method are disclosed that can charge a dielectric material to a high and time-stable surface potential through short-term charging treatment.

[0003] However, the power generation output of an electret power generation device is proportional to the square of the surface potential of the electret, and the durability and heat resistance of the device are greatly affected by the charge characteristics of the electret. Therefore, in order to improve the performance of an electret power generation device, it is necessary to develop an electret material that can stably hold more charges for a long time.

[0004] For example, Patent Document 2 discloses an example of using CYTOP (registered trademark), a polymer having a fluorinated aliphatic ring structure as the main chain, in an electret material. In addition, Patent Document 3 discloses an example of using CYTOP (registered trademark) having 2,2’,2”-triaminotriethylamine bonded to the terminal group in an electret material.

[0005] In addition, in conventional electret power generation devices, an induced current is taken out to an external circuit for power generation by opposing an electret to a collector electrode and changing the overlapping area or the distance between the surfaces of the two over time. For example, Patent Document 2 below discloses an example in which CYTOP (registered trademark) is used in an electret material, and an electret formed in a strip shape is moved relative to a collector electrode in the horizontal direction to change the overlapping area.

[0006] On the other hand, a skin-attached electronic device is also called a skin electronic device. Considering development in fields such as information terminals that integrate the human body and electronic devices, home care that obtains biological data from the skin, and soft robotics, it is a necessary condition to have flexibility and stretchability so that there is no sense of incongruity when attached to the skin. For example, Patent Document 4 below discloses a circuit board example that achieves flexibility and stretchability by forming wiring and functional components on one surface of a substrate having a cross-section with an uneven shape having a stress adjustment layer.

[0007] Prior Art Documents

[0008] Patent document

[0009] Patent document 1: Pamphlet No. WO2012 / 053617

[0010] Patent document 2: Japanese Unexamined Patent Application Publication No. 2011-91996

[0011] Patent document 3: Japanese Unexamined Patent Application Publication No. 2020-65055

[0012] Patent document 4: Japanese Unexamined Patent Application Publication No. 2019-75409 Summary of the invention

[0013] The stretchability of the conventional electret material is insufficient, and it is particularly difficult to be used in a skin-attached electret power generation device. In addition, in the structure of the conventional power generator, it is necessary to relatively move the substrate provided with the electret and the substrate provided with the current collecting electrode, and the structure becomes complicated and it is difficult to be used in a skin-attached electret power generation device.

[0014] An object of the present invention is to provide an electret material having high charge retention and stretchability, and a skin-attached electret environmental power generator using the electret material.

[0015] In order to achieve the above object, the present invention includes the following aspects.

[0016] [1] An electret material, characterized in that it is a perfluoroelastomer having a repeating unit based on tetrafluoroethylene and a repeating unit based on 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 is a perfluoroelastomer containing iodine and / or bromine.

[0017] [2] An electret material, characterized in that it is a perfluoroelastomer which is a polymer of one or more perfluoro monomers selected from tetrafluoroethylene and CF2=CF-O-R f and a monomer containing iodine and / or bromine, and is a perfluoroelastomer containing iodine and / or bromine.

[0018] [3] An electret material, characterized in that it is a perfluoroelastomer which is a copolymer of one or more perfluoro monomers selected from tetrafluoroethylene and CF2=CF-O-R f and a monomer containing iodine and / or bromine and one or both of the compounds represented by I-R f2 -I (wherein, R f2 is a perfluoroalkylene group having 1 to 8 carbon atoms which may have an etheric oxygen atom.), and is a perfluoroelastomer containing iodine and / or bromine.

[0019] [4] The electret material according to [1], characterized in that the perfluoroelastomer containing iodine and / or bromine is crosslinked by a crosslinking aid containing a heteroatom in the molecule.

[0020] [5] The electret material according to [4], wherein the crosslinking aid is triallyl isocyanurate.

[0021] [6] A skin-adhesive electret environmental power generator, comprising: a substrate having stretchability and one main surface attachable to the skin; two comb-shaped electrodes formed on the other main surface of the substrate and arranged with the electrodes parallel to each other; and an electret formed on one of the electrodes of the comb-shaped electrodes; the electret uses the electret material described in any one of [1] to [5], and the skin-adhesive electret environmental power generator uses a single substrate that changes the induced charge amount generated by the electrostatic fringe field by changing the horizontal direction interval between the electrode and the electret.

[0022] According to the present invention, an electret material with high charge retention force and stretchability, and a skin-adhesive electret environmental power generator with a simple structure formed by a single substrate using the electret material can be provided. Brief Description of the Drawings

[0023] Figure 1 It is a perspective view of a structural example of the skin-adhesive electret environmental power generator of the present invention.

[0024] Figure 2 It is a cross-sectional view for explaining the operation of the skin-adhesive electret environmental power generator of the present invention.

[0025] Figure 3 It is an explanatory diagram of the charging process of the electret material.

[0026] Figure 4 It is a graph showing the measurement results of the change over time of the surface potential of the electret.

[0027] Figure 5 It is a graph showing the brief structure of the measurement method of the thermally stimulated current (TSD).

[0028] Figure 6 It is a graph of the TSD spectrum showing the measurement results of the TSD.

[0029] Figure 7 It is a graph showing the evaluation results of the stability of the charge captured by the electret with respect to the stretching operation.

[0030] Figure 8 It is a graph showing the output current waveform of the skin-adhesive electret environmental power generator of the example. Detailed Description of the Invention

[0031] The following describes a mode for implementing the present invention (hereinafter referred to as an embodiment) based on the accompanying drawings.

[0032] The electret material of the present invention is characterized in that it is a perfluoroelastomer having repeating units based on tetrafluoroethylene (hereinafter denoted as TFE) and repeating units based on CF2═CF—O—R f (wherein R f is a perfluoroalkyl group having 1 to 20 carbon atoms that may have an etheric oxygen atom).), and is a perfluoroelastomer containing iodine and / or bromine.

[0033] One or more of the above CF2═CF—O—R f can be used. Preferred 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.

[0034] In addition, the preferred range of the number of carbon atoms of R f is 1 to 20, and the more preferred range is 1 to 8.

[0035] The copolymerization ratio in the fluorine-containing copolymer (perfluoroelastomer) is preferably based on the repeating unit of TFE / based on CF2═CF—O—R f repeating unit = 30 to 80 / 70 to 20 (molar ratio). If within this range, the rubber physical properties are excellent.

[0036] As the perfluoroelastomer, a perfluoroelastomer substantially free of hydrogen atoms is preferably used, and a perfluoroelastomer obtained by using a substance containing a small amount of hydrogen atoms in a chain transfer agent or comonomer can also be used. Examples of the chain transfer agent containing hydrogen atoms include chain-like 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 chain transfer agents can be used.

[0037] In addition, examples of the comonomer containing a hydrogen atom 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, CF2=CF-O-CF2CF2(CF3)-O-CF2CF2CH2-Br, etc. One or more kinds of the comonomer containing a hydrogen atom can be used. However, if the content of the hydrogen atom increases, not only the properties of the perfluororubber such as heat resistance and chemical resistance decrease, but also the electrical insulation and the charge retention property of the electret decrease due to the decrease in the volume resistivity.

[0038] Therefore, the content of the hydrogen atom in the perfluoroelastomer used in the present invention is 0.1% by mass or less, preferably 0.07% by mass or less, more preferably 0.05% by mass or less.

[0039] As the perfluoroelastomer, a perfluoroelastomer obtained by copolymerizing a fluorodiene as a comonomer can also be used. The fluorodiene refers to a compound having one or more fluorine atoms, two polymerizable double bonds, and no cyclopolymerizability.

[0040] Examples of the fluorodiene include perfluorodienes composed of carbon atoms and fluorine atoms, perfluorodienes composed of carbon atoms, fluorine atoms and oxygen atoms, fluorodienes having hydrogen atoms, etc. As the fluorodiene, from the aspect of excellent heat resistance and chemical resistance of the crosslinked product, perfluorodienes are preferred, and perfluorodienes composed of carbon atoms, fluorine atoms and oxygen atoms are more preferred, and perfluorodienes having a perfluoro vinyl ether group are most preferred.

[0041] Specific examples of the perfluorodiene having a perfluoro vinyl ether group include CF2=CFO(CF2)3OCF=CF2, CF2=CFO(CF2)4OCF=CF2, CF2=CFO(CF2)5OCF=CF2, CF2=CFO(CF2)6OCF=CF2, CF2=CFO(CF2)4OCF(CF3)CF2OCF=CF2, etc.

[0042] If the perfluoroelastomer has a structural unit based on a fluorodiene, the perfluoroelastomer has a branched structure, and the number average of the polymer terminal groups per molecule exceeds 2. Therefore, in the case of a perfluoroelastomer having an iodine atom or a bromine atom at the polymer chain end, the perfluoroelastomer composition containing the perfluoroelastomer having a structural unit based on a fluorodiene has excellent crosslinking reactivity as compared with the perfluoroelastomer composition containing a linear perfluoroelastomer having no branch.

[0043] In the perfluoroelastomer, the content of the fluorodiene-based constituent unit is preferably 0.01 to 5 mol%, more preferably 0.01 to 3 mol%, and most preferably 0.05 to 1 mol% based on all the constituent units in the perfluoroelastomer.

[0044] In addition, the electret material of the present invention is characterized in that it is a perfluoroelastomer which is a polymer of one or more perfluoro monomers selected from tetrafluoroethylene and CF2=CF-O-R f and a monomer containing iodine and / or bromine, and is a perfluoroelastomer containing iodine and / or bromine, or is a perfluoroelastomer which is a copolymer of one or more perfluoro monomers selected from tetrafluoroethylene and CF2=CF-O-R f and a monomer containing iodine and / or bromine and a compound represented by I-R f2 -I (wherein R f2 is a perfluoroalkylene having 1 to 8 carbon atoms which may have an etheric oxygen atom), and is a perfluoroelastomer containing iodine and / or bromine.

[0045] Examples of the monomer containing iodine and / or bromine 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, CF2=CF-O-CF2CF2(CF3)-O-CF2CF2CH2-Br, and the like.

[0046] In addition, specific examples of the above I-R f2 -I include diiododifluoromethane, 1,2-diiodoperfluoroethane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,7-diiodoperfluoroheptane, 1,8-diiodoperfluorooctane, etc. Among them, 1,4-diiodoperfluorobutane and 1,6-diiodoperfluorohexane are preferred, and 1,4-diiodoperfluorobutane is particularly preferred.

[0047] The content of iodine and / or bromine in the perfluoroelastomer used in the present invention is not particularly limited, and 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. If it is within this range, a crosslinked rubber composition excellent in rubber physical properties such as tensile strength, elongation at break, resilience, and compression set can be obtained.

[0048] The glass transition temperature (hereinafter referred to as Tg.) of the perfluoroelastomer used in the present invention is 15°C or lower, preferably -50 to 10°C, more preferably -50 to 0°C, and most preferably -50 to -3°C.

[0049] In addition, the perfluoroelastomer containing iodine and / or bromine as the electret material of the present invention is preferably crosslinked by a crosslinking aid containing a heteroatom in the molecule.

[0050] When crosslinking the perfluoroelastomer composition containing iodine and / or bromine of the present invention, a crosslinking aid is preferably contained. If a crosslinking aid is contained, the crosslinking efficiency is high. Specific examples of the crosslinking aid include triallyl cyanurate, triallyl isocyanurate (TAIC), trimethylallyl isocyanurate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, triallyl trimellitate, m-phenylenediamine bismaleimide, p-quinone dioxime, p,p'-dibenzoylquinone dioxime, diallyl terephthalate, diallyl phthalate, N,N',N",N"'-tetraallyl terephthalamide, vinyl-containing silicone oligomers such as polymethylvinylsiloxane and polymethylphenylvinylsiloxane.

[0051] Particularly preferred are triallyl cyanurate, triallyl isocyanurate, and trimethylallyl isocyanurate, and more preferably triallyl isocyanurate (TAIC). The content of the crosslinking aid is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the perfluoroelastomer. If it is within this range, crosslinked physical properties with a balance of strength and elongation can be obtained.

[0052] In addition, by using a crosslinking aid containing a heteroatom, a charge trapping structure can be introduced into the perfluoroelastomer, and positive and negative charges can be stably retained.

[0053] The perfluoroelastomer of the present invention is cured by a crosslinking reaction using an organic peroxide in the presence of a crosslinking aid.

[0054] The organic peroxide is not particularly limited. Preferably, half of the amount of the organic peroxide has a decomposition temperature in 1 minute, that is, an organic peroxide with a 1-minute half-life temperature of 150 to 250 °C, more preferably 150 to 200 °C. As specific examples, dialkyl peroxides such as di-tert-butyl peroxide, tert-butyl cumyl 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, etc., 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroxy peroxide, benzoyl peroxide, tert-butylbenzene peroxide, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, tert-butyl maleate peroxide, tert-butyl isopropyl carbonate peroxide, etc. One or more than two kinds of organic peroxides can be used.

[0055] Relative to 100 parts by mass of the perfluoroelastomer of the present invention, the addition amount of the organic peroxide 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. If it is within this range, a composition that provides a crosslinked rubber, that is, a fluororubber molded product, with excellent heat resistance and rubber physical properties can be obtained.

[0056] The perfluoroelastomer containing iodine and / or bromine as the electret material of the present invention is an amorphous fluororubber and has stretchability, excellent chemical resistance, heat resistance, weather resistance, and mechanical strength. In addition, the Young's modulus of the perfluoroelastomer containing iodine and / or bromine is about 1 MPa. Since the Young's modulus of human skin is in the range of 0.5 to 1.95 MPa, it does not hinder the stretching of the skin, so it is comfortable to stick on the skin and is suitable as a material for a skin-attached electret environmental generator. The same is true when the perfluoroelastomer containing iodine and / or bromine is crosslinked.

[0057] Another embodiment of the present invention is a skin-attached electret environmental generator. Figure 1 FIG. shows a perspective view of a configuration example of the skin-attached electret environmental generator of the present invention. In Figure 1In [the figure], the skin-attached electret environmental power generator 100 can attach one main surface (the back surface in the figure) of a stretchable substrate 10 such as silicone rubber to a human skin using an adhesive or the like, and a set of comb-shaped electrodes 12a and 12b arranged such that the electrodes are substantially parallel to each other are formed on the other main surface (the front surface in the figure). The attachment to the skin is preferably performed using an adhesive suitable for applications such as medical use that has little impact on the skin. For example, a polyurethane adhesive for skin manufactured by AGC Inc. can be cited. In addition, an electret 14 is formed on one of the set of (two) comb-shaped electrodes 12a and 12b, i.e., on comb-shaped electrode 12a.

[0058] The electret 14 is formed by charging the above-mentioned perfluoroelastomer containing iodine and / or bromine (including the case of crosslinking) with positive charges by soft X-rays as an electret material. It should be noted that it can also be charged with negative charges.

[0059] Figure 2 (a), (b), and (c) of [the figure] show cross-sectional views for explaining the operation of the skin-attached electret environmental power generator of the present invention. Figure 2 (a) and (c) of [the figure] are Figure 1 cross-sectional views taken along line II-II of [the figure]. In Figure 2 (a) of [the figure], 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 charges possessed by the electret 14 formed on the comb-shaped electrode 12a, and negative charges are induced in the comb-shaped electrode 12b by this fringe field. As Figure 2 (c) of [the figure] shows, when the substrate 10 expands and contracts between the expanded state (the horizontal distance between the comb-shaped electrode 12b and the electret 14 is G0 + ΔG0) and the original state of Figure 2 (a) of [the figure], the horizontal distance between the comb-shaped electrode 12b and the electret 14 changes (varies between G0 and G0 + ΔG0), and the amount of induced charge induced in the comb-shaped electrode 12b changes. As a result, an induced current I is generated and can be taken out as power generation output to an external circuit. In this way, the skin-attached electret environmental power generator of the present invention can change the horizontal distance between the comb-shaped electrode 12b and the electret 14 by the expansion and contraction of a single substrate, thereby changing the amount of induced charge generated by the electrostatic fringe field to generate electricity. Therefore, if the skin-attached electret environmental power generator of the present invention is attached to a human skin, power can be taken out from the expansion and contraction movement of the skin generated by human activities.

[0060] It should be noted that, in Figure 2 (a) and (c) of [the figure], the electret 14 is only formed on the comb-shaped electrode 12a, but as Figure 2As shown in (b) of , the electret 14 is formed on the entire surface including the comb-shaped electrode 12b, and it operates in the same manner when charges are injected only on the comb-shaped electrode 12a or when charges of opposite signs are injected on the comb-shaped electrode 12a and the comb-shaped electrode 12b.

[0061] Embodiment

[0062] Specific embodiments of the present invention will be described below. It should be noted that the following embodiments are examples for easy understanding of the present invention, and the present invention is not limited to these embodiments.

[0063] <Sample Preparation>

[0064] (a) As an example of the electret material, AFLAS (registered trademark) PM-1100 (Example 1) manufactured by AGC Inc., which is the above-mentioned perfluoroelastomer containing iodine and / or bromine, was used. In addition, as another example of the electret material, a crosslinked elastomer (Example 2) obtained by crosslinking AFLAS (registered trademark) PM-1100 with triallyl isocyanurate (TAIC, manufactured by Comb-Block) was used.

[0065] The preparation of the crosslinkable composition of Example 2 is as follows. In a 50 ml eggplant-shaped flask, AFLAS (registered trademark) PM-1100, TAIC, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DBPH, manufactured by Acros) as an initiator were mixed in a fluorine-based solvent (trade name ASAHIKLIN AC2000, manufactured by AGC), and then stirred at 35 °C for 1 hour to dissolve. Further, it was stirred at 90 °C for 30 minutes. Then, the above mixed solution was placed in an inert oven, and the solvent was evaporated and removed under a nitrogen atmosphere to obtain a crosslinkable elastomer composition.

[0066] In addition, as a comparative example of the electret material, polydimethylsiloxane (PDMS) (Example 3) was used.

[0067] The crosslinkable composition of Example 2 was pressed at 170 °C and 10 MPa for 15 minutes using a small press (H300-10D, manufactured by AS ONE) to obtain a cured film of the crosslinked elastomer. In addition, the material of Example 1 was also pressed under the same conditions as Example 2 to obtain a self-supporting film.

[0068] (b) Charges were injected into the films formed of the respective resins using the above electret materials to make them charged, thereby forming electrets. Here, the film thickness of the electret of Example 1 was 18.5 μm, the film thickness of the electret of Example 2 was 75 μm, and the film thickness of the electret of Example 3 was 53 μm. Figure 3 shows an explanatory diagram of the charging process. In Figure 3In this case, a bias voltage of -2.2 kV was applied between the copper plate 16 on which the films 15 of Examples 1 to 3 were placed and the aluminum foils 18 disposed on each film by an external power source. When soft X-rays were irradiated from the soft X-ray source 20 (HAMAMATSU PhotoIonizer L9490) to ionize nitrogen molecules in the air in this state, nitrogen ions were attracted to the film by the above bias voltage. The surface potential of the film gradually canceled out the bias voltage, and charging was completed when the surface potential of the film was consistent with the bias voltage, forming the electrets of Examples 1 to 3. The initial surface potential of the electrets of Examples 1 to 3 formed was approximately 2.2 kV.

[0069] <Performance Evaluation>

[0070] (c) Tensile Test

[0071] For the films of Examples 1 to 3 fabricated in (a) above (before charging), a small bench-top testing machine (EZ-SX, manufactured by Shimadzu Corporation) was used to elongate them at an elongation rate of 1 mm / min, and the Young's modulus of each was measured.

[0072] The size of the film of Example 1 used in the test was 11 mm in length × 0.5 mm in width (thickness 0.5 mm), the size of the film of Example 2 was 25 mm in length × 1 mm in width (thickness 0.075 mm), and the size of the film of Example 3 was 7 mm in length × 3 mm in width (thickness 0.05 mm).

[0073] The film of Example 1 fractured when it was elongated to 190%. The Young's modulus up to a strain of 70% was approximately 1 MPa, and plastic deformation occurred thereafter. The film of Example 2 elongated linearly approximately to 180% and then fractured. No obvious yield point was observed until fracture, and the Young's modulus was approximately 1 MPa. The film of Example 3 fractured when it was elongated to 165%. No obvious yield point was observed until fracture, but the slope increased starting from around an elongation rate of 50%. The Young's modulus was 1 MPa up to a strain of 50% and approximately 3 MPa after a strain of 100%.

[0074] In summary, it was confirmed that the Young's moduli of the films of Examples 1 and 2 were of the same level as that of human skin. Furthermore, in the film of Example 2, no yield occurred until fracture, and it returned to its original length after elongation. Therefore, it was found to have preferable characteristics as a stretchable electret film.

[0075] (d) For the electrets of Examples 1 to 3 fabricated in (b) above, the time-dependent change in the surface potential was measured using a MONROE ELECTRONICS ISOPROBEELECTROSTATIC VOLTMETET Model 279.

[0076] The measurement results are shown in Figure 4 . In Figure 4In this case, the surface potential is shown on the vertical axis, and the elapsed time since the charging ended is shown on the horizontal axis.

[0077] As Figure 4 shown, in the electret of Example 3, the surface potential drops sharply and the surface potential disappears within 1 hour. On the other hand, the initial surface potential of the electret of Example 1 is 2.0 kV, and the surface potential after 1200 hours is 0.25 kV. In addition, the initial surface potential of the electret of Example 2 is 2.2 kV, and the surface potential after 700 hours is 1.0 kV.

[0078] In summary, it can be confirmed that the electrets of Example 1 and Example 2 can maintain the surface potential for a sufficiently long time.

[0079] (e) For the electrets of Example 1 and Example 2 fabricated in (b) above, in order to evaluate the thermal stability of the trapped charges, thermally stimulated discharge (TSD) measurements were performed.

[0080] Figure 5 shows a schematic configuration of the measurement method of TSD (self-made device). In Figure 5 , a copper plate 22 on which each electret as a sample is placed is fixed to an electrode 26 in a metal measurement chamber 24, and the temperature is raised from 40 °C to 200 °C at 1 °C / min using a heater 28, and the change in the induced charge amount (thermally stimulated (TSD) current value) of the probe electrode 30 is measured using a microammeter (Keithley 6430, manufactured by Keithley Instruments, Inc.) 32. It should be noted that the temperature of the above electret is controlled by adjusting the operation of the heater 28 by a temperature controller 36 controlled by a computer 34.

[0081] Figure 6 shows the TSD spectrum of the measurement results. In Figure 6 , the vertical axis shows the normalized TSD current value, and the horizontal axis shows the temperature of the electret. Figure 6 The TSD spectrum shown in shows the amount of charge (detrapped charge) released from the electret in terms of the TSD current, and a peak appears at the temperature at which the most charge is released. Therefore, the higher the peak temperature, the higher the thermal stability of the charge of the electret, and it becomes an index indicating the thermal stability of the charge trapped by the electret.

[0082] In Figure 6 , for the temperature (peak temperature) at which the TSD spectrum shows a peak, it is 46 °C for Example 1 and 79 °C for Example 2. Therefore, it can be seen that the thermal stability of the charge trapped by the electret is improved by crosslinking.

[0083] (f) For the electrets of Example 1 and Example 2 fabricated in (b) above, evaluate the stability of the trapped charge with respect to the stretching operation.

[0084] As samples, the films of Example 1 and Example 2 were sized 20 mm in length, 40 mm in width, and 0.12 mm in thickness. After being charged by soft X-rays for 24 hours, the charged films (electrets) were fixed to an electromagnetic shaker (APS-113, manufactured by APSDNAMICS). The strain of the above electret was measured using a laser displacement meter (LT-9500, manufactured by KEYENCE), and the above electret was stretched with a constant vibration frequency of 2 Hz.

[0085] Figure 7 shows the evaluation results of the stability of the charge trapped by the electret with respect to the stretching operation. In Figure 7 the vertical axis shows the surface potential and the horizontal axis shows the number of stretching times. As Figure 7 shown, the surface potential of the electret of Example 1 before the stretching test was 0.8 kV, and the surface potential of the electret of Example 2 was 1.7 kV.

[0086] The surface potentials of the electrets of Example 1 and Example 2 after stretching 10,000 times with a 20% strain were almost unchanged from the above initial values. On the other hand, when stretched 10,000 times with a 40% strain, the surface potential of the electret of Example 2 was almost unchanged from the above initial value, showing good stability. However, the surface potential of the electret of Example 1 decreased by 30% from the above initial value. Therefore, it can be seen that crosslinking improves the stability of the charge trapped by the electret with respect to the stretching operation.

[0087] As described above, compared with the electret of Example 1, the stability of the trapped charge of the electret of Example 2 with respect to the stretching operation is improved, but the electret of Example 1 is also sufficiently stable. It can be seen that the stability of the trapped charge of the electrets of Example 1 and Example 2 with respect to the stretching operation is high, and they are suitable for a skin-attached type electret environmental power generator.

[0088] <Fabrication and Evaluation of Skin-Attached Type Electret Environmental Power Generator>

[0089] (g) Using the film of Example 2 as the electret material, it was cut into a size of 20 mm in length × 20 mm in width (0.125 mm in thickness). Using a polyimide substrate with a rectangular hole formed as a hard mask, a 200-nm-thick copper thin film was electron beam evaporated on one main surface of this film, thereby forming only a pair of Figure 2(b) The same comb electrodes 12a and 12b. Electron beam evaporation was performed using MUE-ECO-EB manufactured by ULVAC, Inc. The horizontal distance (spacing) G0 between the comb electrodes 12a and 12b was 2 mm. As the substrate 10, a 0.5-mm-thick silicone rubber sheet (manufactured by Tokawa Rubber Co., Ltd.) was used.

[0090] Similar to Figure 2 in (b), by Figure 3 the charging process shown in FIG., soft X-rays were irradiated onto the region corresponding to the comb electrode 12a (the region on the comb electrode 12a) in the film of Example 2 to form an electret with a surface potential of +2.5 kV, thereby forming a skin-attached electret environmental power generator.

[0091] The skin-attached electret environmental power generator formed as described above was attached to an electromagnetic vibrator (manufactured by APS Co., Ltd., APS-113), and a strain of 10% was applied at a frequency of 1 Hz. At this time, the comb electrodes 12a and 12b were directly connected to a programmable current amplifier (manufactured by NF Corporation, CA5350). After converting the short-circuit current into a voltage, it was input to a computer via an AD converter (manufactured by Turtle Co., Ltd., TUSB0224ADM), and the output current waveform was recorded.

[0092] Figure 8 shows the output current waveform of the skin-attached electret environmental power generator of 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 , although only a single pair of comb electrodes 12a and 12b were formed in the skin-attached electret environmental power generator of this embodiment, a peak short-circuit current of about 30 nA was obtained, indicating that the power generator of the present invention can be constructed.

[0093] Industrial Applicability

[0094] The electret of the present invention can be used for electrostatic induction type conversion elements such as power generation devices and microphones, and is particularly suitable for skin-attached electret environmental power generators.

[0095] It should be noted that 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 hereby incorporated by reference as the disclosure of the specification of the present invention.

[0096] Symbol Explanation

[0097] 10 Substrate, 12a, 12b Comb electrodes, 14 Electret, 15 Membrane, 16 Copper plate, 18 Aluminum foil, 20 Soft X-ray source, 22 Copper plate, 24 Metal measurement chamber, 26 Electrode, 28 Heater, 30 Probe electrode, 32 Microammeter, 34 Computer, 36 Temperature regulator, 100 Skin-attached electret environmental power generator.

Claims

1. An electret material, characterized in that, is a perfluoroelastomer having repeating units based on tetrafluoroethylene and repeating units based on CF2═CF—O—R f and is a perfluoroelastomer containing iodine and / or bromine, where R f is a perfluoroalkyl group having 1 to 20 carbon atoms which may have an etheric oxygen atom.

2. An electret material, characterized in that, is a perfluoroelastomer that is a polymer of one or more perfluoro monomers selected from tetrafluoroethylene and CF2═CF—O—R f and a monomer containing iodine and / or bromine, and is a perfluoroelastomer containing iodine and / or bromine.

3. An electret material, characterized in that, is a perfluoroelastomer that is a copolymer of one or more perfluoro monomers selected from tetrafluoroethylene and CF2=CF-O-R f and a monomer containing iodine and / or bromine and one or both of the compounds represented by I-R f2 -I, and is a perfluoroelastomer containing iodine and / or bromine. In the formula, R f2 is a perfluoroalkylene having 1 to 8 carbon atoms that may have an etheric oxygen atom.

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

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

6. A skin-attached electret environmental power generator, comprising: A substrate having stretchability and one main surface attachable to the skin, Two comb-shaped electrodes formed on the other main surface of the substrate and arranged with the electrodes parallel to each other, and An electret formed on one electrode of the comb-shaped electrodes; The electret uses the electret material according to any one of claims 1 to 5, The skin-attached electret environmental power generator uses a single substrate that changes the induced charge amount generated by the electrostatic fringe field by changing the horizontal direction interval between the electrode and the electret.

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