Charging Film and Triboelectric Generator

Abstract

To provide a charging film which contributes to improvement of output of a friction power generator.SOLUTION: A charging film (first film (1)) is a charging film containing a film base resin and ionic liquid. The ionic liquid is contained in an amount of more than 0 ppm and 50 ppm or less based on weight of the film base resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrically charged film and a triboelectric generator. [Background technology]

[0002] In recent years, research and development of friction generators has been progressing. A friction generator is a generator that uses the potential difference between the charges generated by friction between two charged bodies to generate current to an external load. The output of a friction generator is determined by the amount of charge and the potential difference.

[0003] As a method for increasing the potential difference, Patent Document 1 discloses a friction generator in which the relative permittivity of the particles in a dielectric layer having a matrix and particles is made higher than that of the matrix. As a method for increasing the frictional charge, Non-Patent Document 1 proposes incorporating alumina particles into the triboelectric layer. Similarly, Non-Patent Document 2 proposes mixing approximately 10% by weight of an ionic liquid into the polyvinylidene fluoride, which is the charging layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-193495 [Non-patent literature]

[0005] [Non-Patent Document 1] Sequential Infiltration Synthesis of Doped Polymer Films with Tunable Electrical Properties for Efficient Triboelectric Nanogenerator Development, Advanced Materials, 2015, 27(33), pp 4938-4944 [Non-patent document 2] Enhancing the output performance of fluid-based triboelectric nanogenerator by using poly(vinylidene fluoride-co-hexafluoropropylene) / ionic liquid nanoporous membrane, Int J Energy Res. 2021;45:8960-8970 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned conventional technologies leave room for improvement in the mechanical properties of the charging member. That is, when additives are added to a charging film, the charging film becomes harder or softer as the amount of additive increases. Patent Document 1 discloses a charging film containing particles with a high relative dielectric constant, Non-Patent Document 1 discloses alumina particles, and Non-Patent Document 2 discloses a charging film containing a relatively large amount of ionic liquid. It is believed that the mechanical properties of these charging films change from those of the film base resin due to the presence of additives, and this point leaves room for improvement.

[0007] Furthermore, the structure of the charged body has not been thoroughly investigated, leaving room for the development of a friction generator with improved output.

[0008] One aspect of the present invention aims to provide a charged film whose mechanical properties are not significantly different from those of the film base resin, and a frictional generator using the same. Another aspect of the present invention aims to provide a charged film that contributes to improving the output of a frictional generator. [Means for solving the problem]

[0009] The charging film according to one aspect of the present invention comprises: 1. An electrocharged film comprising a film base resin and an ionic liquid, The ionic liquid is contained in an amount of more than 0 ppm and 50 ppm or less based on the weight of the film base resin. [Effects of the Invention]

[0010] According to one aspect of the present invention, there is provided a charged film having mechanical properties not significantly different from those of the film base resin, and a friction generator using the same. According to another aspect of the present invention, there is provided a charged film that contributes to improving the output of a friction generator. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating an outline of the configuration of a friction generator according to one aspect of the present invention. [Figure 2] 1 is a schematic diagram illustrating an estimated mechanism of action of a friction generator according to an embodiment of the present invention. [Figure 3] FIG. 1 is a schematic diagram illustrating an outline of the configuration of a friction generator produced in an example. [Figure 4] 1 shows the waveform of power generation from the friction generator fabricated in Example 1. The ionic liquid concentration is 0 ppm. [Figure 5] 1 shows the waveform of power generation from the friction generator fabricated in Example 1. The ionic liquid concentration is 3 ppm. [Figure 6] 1 shows the waveform of power generation from the friction generator fabricated in Example 1. The ionic liquid concentration is 27 ppm. [Figure 7] 1 shows the waveform of power generation from the friction generator fabricated in Example 1. The ionic liquid concentration is 134 ppm. [Figure 8] 1 is a graph showing the amount of ionic liquid added on the horizontal axis and the maximum positive voltage (black circles) and maximum negative voltage (white circles) in the power generation waveform on the vertical axis for the friction generator produced in Example 1. [Figure 9] 1 is a graph showing the power consumed by a load resistance in the friction generator produced in Example 1. [Figure 10] 1 is a graph showing the relationship between the concentration of an ionic liquid contained in a charged film and the relative permittivity of the charged film. [Figure 11]1 is a graph showing the film thickness of the charged film on the horizontal axis and the maximum positive voltage (black circles) and maximum negative voltage (white circles) in the power generation waveform on the vertical axis for the friction generator produced in Example 2. [Figure 12] 1 is a graph showing the amount of ionic liquid added on the horizontal axis and the maximum positive voltage (black circles) and maximum negative voltage (white circles) in the power generation waveform on the vertical axis for the friction generator produced in Example 3. The type of ionic liquid used is different from that in Example 1. [Figure 13] 1 is a graph showing the power consumed by a load resistance in the friction generator produced in Example 3. The type of ionic liquid used is different from that in Example 1. [Figure 14] 1 is a graph showing the amount of ionic liquid added on the horizontal axis and the maximum positive voltage (black circles) and maximum negative voltage (white circles) in the power generation waveform on the vertical axis for the friction generator produced in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the description. Embodiments in which the technical means disclosed in different embodiments are appropriately combined are also included in the technical scope of the present invention.

[0013] In this specification, "A to B" representing a numerical range means "A or more and B or less."

[0014] [1. Charging film] An electrostatically charged film according to one embodiment of the present invention includes a film base resin and an ionic liquid, wherein the concentration of the ionic liquid in the electrostatically charged film is greater than 0 ppm and not greater than 50 ppm, based on the weight of the film base resin.

[0015] [1.1. Film base resin] The film base resin is a resin that constitutes the matrix of the electrostatically charged film. The material of the film base resin is not particularly limited, and any resin used in this technical field can be used. The film base resin may be composed of only one type of resin, or may be composed of two or more types of resins.

[0016] In one embodiment, the film base resin is one or more selected from the group consisting of polyamides (such as nylon); polyimides; polyolefins (such as polyethylene, polypropylene, and polyisobutylene); polyesters (such as polyethylene terephthalate); polycarbonates (such as polydiphenyl carbonate); polyurethanes; vinyl resins (such as polystyrene, polyacrylonitrile, polyvinyl alcohol, and polyvinyl butyral); acrylic resins (such as polymethyl methacrylate); chlorine-based resins (such as polyvinyl chloride, polyvinylidene chloride, chlorinated polyethers, and polychloroprene); fluorine-based resins (such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymers, polyvinylidene fluoride, and copolymers having vinylidene fluoride units); silicone resins (such as polydimethylsiloxane); and natural rubber.

[0017] In this specification, the above-mentioned film base resin may be a copolymer. For example, "polyamide" may be a resin in which 50% by weight or more (preferably 70% by weight or more, more preferably 90% by weight or more) of the repeating units constituting the main chain are polyamide. Of the repeating units constituting the main chain of "polyamide," 50% by weight or less (preferably 30% by weight or less, more preferably 10% by weight or less) may have a structure other than polyamide. The other resins exemplified may also be copolymers.

[0018] In one embodiment, the film base resin is one or more selected from the group consisting of vinylidene fluoride-trifluoroethylene copolymer and polydimethylsiloxane.

[0019] [1.2. Ionic Liquids] An ionic liquid is a substance that contains anions and cations and is liquid at 100°C (preferably at 20°C). The type of ionic liquid contained in the charged film is not particularly limited. The charged film may contain only one type of ionic liquid, or two or more types of ionic liquid.

[0020] Examples of cations that constitute ionic liquids include imidazolium-based cations, pyrrolidinium-based cations, pyridinium-based cations, piperidinium-based cations, ammonium-based cations, phosphonium-based cations, and sulfonium-based cations. The structures of each cation are shown below.

[0021] [ka]

[0022] In the formula, R 1 ~R 4 are independently a C1 to C30 hydrocarbon group, preferably a C1 to C20 hydrocarbon group, and more preferably a C1 to C10 hydrocarbon group. Examples of the hydrocarbon group include an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, an alkynyl group, a cycloalkynyl group, an aryl group, and an alkylaryl group.

[0023] In one embodiment, the ionic liquid comprises an imidazolium-based cation, hi one embodiment, the ionic liquid comprises one or more selected from 1-hexyl-3-methylimidazolium cation and 1-benzyl-3-methylimidazolium cation.

[0024] Examples of anions that make up ionic liquids include Br - , Cl - , I - , B(C2O4)2 - , B.F. 4- , [B(CN)4] - (also known as TCB), CF3COO - , CF3SO3 -, HSO4 - , CH3SO4 - , CH3SO3 - , CH3CH2OSO3 - , CH3(OCH2CH2)2OSO3 - , C6H4CH3SO3 - , C(CN)3 - , SCN - , (NC)2N - , (FSO2)2N - (also known as FSI), (CF3SO2)2N - (also known as TFSI), (C2F5SO2)2N - , PF6 - , [P(C2F5)3F3] - (also known as FAP), FeCl4 - , AlCl4 - Examples include:

[0025] In one embodiment, the ionic liquid comprises TFSI.

[0026] Specific examples of the ionic liquid include 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. In one embodiment, the ionic liquid is one or more selected from the group consisting of 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

[0027] Alternatively, commercially available ionic liquids may be used, such as ionic liquid-modified oligomer X-40-2450 (Shin-Etsu Chemical Co., Ltd., silicone-based).

[0028] It is preferable to select an ionic liquid that is highly compatible with the film base resin. To this end, it is preferable that the ionic liquid has a structure similar to that of the film base resin. By selecting such an ionic liquid, it is possible to reduce bleeding out from the film base resin.

[0029] The lower limit of the concentration of the ionic liquid contained in the charged film is more than 0 ppm, preferably 0.5 ppm or more, more preferably 1 ppm or more, and even more preferably 2 ppm or more, based on the weight of the film base resin.The upper limit of the concentration of the ionic liquid contained in the charged film is 50 ppm or less, preferably 40 ppm or less, more preferably 30 ppm or less, and even more preferably 20 ppm or less, based on the weight of the film base resin.

[0030] By setting the concentration of the ionic liquid within the above range, the power generation characteristics of a friction generator using a charged film can be improved. For example, the amount of charge on the charged film can be increased. Alternatively, the output power of the friction generator can be improved.

[0031] Furthermore, setting the concentration of the ionic liquid within the above range also contributes to maintaining the mechanical properties of the charged film at the same level as those of the film base resin. In conventional technology, when additives (e.g., ionic liquids, filler particles, etc.) were added to charged films, the amount was typically on the order of several to several tens of weight percent (see, for example, Non-Patent Document 2). However, adding such a large amount of additives tends to significantly alter the inherent physical properties of the film base resin. As a result, the hardness and heat resistance of the charged film tend to decrease. In contrast, the present invention adds a much smaller amount of ionic liquid. This is thought to be why the above-mentioned drawbacks can be overcome. In relation to this, ionic liquids are highly heat-resistant substances and are not easily decomposed even at the melting temperature of the film base resin. In this respect, too, ionic liquids are excellent additives for charged films.

[0032] In other words, after considering various additives to be added to the charged film, their ratios, compositions, etc., the inventors discovered that by controlling the amount of ionic liquid added to a very small amount based on the weight of the film base resin, it is possible to significantly improve the output characteristics of the friction generator without significantly changing the mechanical properties inherent to the film base resin.

[0033] [1.3. Shape and manufacturing method of the charged film] The charged film can be produced using a film base resin and an ionic liquid as materials by a conventionally known method, for example, as follows. Method 1: A film base resin and an ionic liquid are mixed with a solvent or dispersion medium to form a slurry. The resulting slurry is applied to form a film. The solvent or dispersion medium is then removed. Method 2: The film base resin is heated and melted, and mixed with an ionic liquid. The resulting mixture is then cast into a film. Method 3: The porous film is immersed in a low-concentration ionic liquid solution. Method 4: The ionic liquid is heated to evaporate it, and the evaporated ionic liquid is adsorbed onto a porous film.

[0034] The inventors have found that, when the amount of ionic liquid added is constant, the power generation characteristics of the friction generator begin to improve when the thickness of the charged film exceeds a certain point (see Example 2). The film thickness at which the power generation characteristics begin to improve is thought to be thinner when the amount of ionic liquid added is large, and thicker when the amount added is small. The film thickness of the charged film is preferably 30 μm or more, more preferably 35 μm or more, and even more preferably 40 μm or more.

[0035] The upper limit of the film thickness of the charged film can be, for example, 100 μm or less or 200 μm or less. If the upper limit of the film thickness is within the above range, the time required for the charge generated by friction to move will not be too long, preventing the output from taking too long to stabilize. Furthermore, the distance from the friction surface to the electrode will not be too large, so sufficient induced charge can be obtained.

[0036] [2. Friction Generator] One aspect of the present invention is a friction generator equipped with the charging film described in Section [1]. The structure of the friction generator will be outlined below with reference to FIG.

[0037] The friction generator 10 comprises a first film 1 and a second film 2. The first film 1 and the second film 2 are each connected to an electrode 3. The two electrodes 3 are electrically connected via an external load R. The potential difference between the two electrodes 3 causes a current to flow in the external load R, generating electrical energy.

[0038] [2.1. First Film and Second Film] The first film 1 is the charged film described in Section [1]. Therefore, the first film 1 includes a film base resin and an ionic liquid, and the content of the ionic liquid is more than 0 ppm and not more than 50 ppm based on the weight of the film base resin.

[0039] The second film 2 includes a film base resin. The second film 2 may or may not be the charged film described in Section [1]. The second film 2 may be a film that does not include an ionic liquid, or may be a film that includes an ionic liquid. When the second film 2 includes an ionic liquid, the content of the ionic liquid may be more than 0 ppm and not more than 50 ppm, or may be more than 50 ppm, based on the weight of the film base resin. Preferably, the second film 2 is the charged film described in Section [1].

[0040] The film base resin contained in the second film 2 and the ionic liquid that may be contained in the second film 2 are as explained in Section [1], and therefore will not be described again. When the second film 2 contains an ionic liquid, the type of ionic liquid contained in the second film 2 may be the same as or different from the type of ionic liquid contained in the first film 1.

[0041] In the friction generator 10, electric charge accumulates as the first film 1 and the second film 2 repeatedly come into contact with and separate from each other. For this reason, the film base resin of the first film 1 and the film base resin of the second film 2 are different from each other. Therefore, it is preferable that the film base resin of the first film 1 and the film base resin of the second film 2 are a combination of materials that are separated in the triboelectric series. Examples of materials that are likely to be positively or negatively charged in the triboelectric series include the following: · Materials that are easily positively charged: polyamide, rayon, wool, cellulose nanofiber Materials that easily become negatively charged: Polytetrafluoroethylene, polyvinylidene fluoride, polyimide, tetrafluoroethylene-hexafluoropropylene copolymer

[0042] In one embodiment, the second film 2 is the charged film described in Section [1]. In one embodiment, the film base resin of the second film 2 is polyamide. Polyamide is one of the substances that is most likely to be positively charged in the triboelectric series, and is therefore considered suitable for the purpose of improving the power generation characteristics of a friction generator. In one embodiment, the film base resin of the first film 1 is vinylidene fluoride-trifluoroethylene copolymer, and the film base resin of the second film 2 is polyamide. In one embodiment, the film base resin of the first film 1 is polydimethylsiloxane, and the film base resin of the second film 2 is polyamide.

[0043] [2.2. Electrode] The electrode 3 is made of a highly electrically conductive material, such as metals (aluminum, copper, silver, gold, platinum, iron, nickel, chromium, molybdenum, indium, etc.) and metal alloys, semiconductors (doped silicon, etc.), metal oxides (indium tin oxide (ITO), etc.), and conductive polymers (PEDOT-PSS, etc.).

[0044] [2.3. Estimated mechanism of action] The presumed mechanism of action of one embodiment of the present invention will be explained below with reference to Figure 2. However, this explanation is intended to aid in understanding one embodiment of the present invention, and therefore, this explanation does not serve as a basis for restrictively interpreting the scope of the invention described in the claims.

[0045] When no ionic liquid is added to the first film 1 (Figure 2a), the charge generated by frictional charging remains only near the surface of the first film 1. The charge accumulated in the first film 1 generates an induced charge in the electrode 3. The induced charge flows as a current to the external load R, and electrical energy is extracted.

[0046] On the other hand, when a very small amount of ionic liquid 5 is added to the first film 1 (Figure 2b), sites that capture charges are also formed inside the first film 1 (because the first film 1 is made of resin, which is a non-conductive material, such sites are not formed unless ionic liquid 5 is added). As a result, the charges generated by friction are distributed not only near the surface of the first film 1, but also inside it. In other words, the amount of charge on the entire first film 1 increases. Furthermore, because the charges exist inside the first film, the distance between the charges and the electrode becomes shorter, and the amount of induced charge generated increases.

[0047] It is believed that if too much ionic liquid 5 is added to the first film 1, the conductivity of the first film 1 increases, causing the electric charge generated by frictional charging to pass through the inside of the first film 1 and move to the electrodes, resulting in a decrease in the power generation efficiency of the frictional generator 10.

[0048] Furthermore, the phenomenon in which the power generation characteristics of the friction generator begin to improve when the thickness of the first film 1 exceeds a certain point, assuming a constant amount of ionic liquid added, can be explained as follows: That is, when the amount of ionic liquid added is constant, the conductivity of the first film 1 decreases as the film thickness increases, and increases as the film thickness decreases. As mentioned above, if the conductivity becomes too high, the power generation efficiency of the friction generator 10 decreases, so it is preferable that the film thickness of the first film 1 be somewhat thick.

[0049] [3. Uses of charged film other than friction generators] The use of the charged film according to one embodiment of the present invention is not limited to friction generators. For example, charged films are sometimes used in air purifiers installed in air conditioners. The charged film according to one embodiment of the present invention has mechanical properties equivalent to those of the film base resin and also has high charging properties, making it suitable for such applications.

[0050] [4. Summary] The present invention includes the following aspects. <1> 1. An electrocharged film comprising a film base resin and an ionic liquid, An electrostatically charged film, wherein the ionic liquid is contained in an amount of more than 0 ppm and 50 ppm or less based on the weight of the film base resin. <2> The ionic liquid contains one or more imidazolium cations. <1> The electrostatically charged film according to claim 1. <3> The ionic liquid is at least one selected from the group consisting of 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. <2> The electrostatically charged film according to claim 1. <4> The thickness of the charged film is 30 μm or more; <1> ~ <3> 10. The electrostatically charged film according to any one of claims 1 to 9. <5> The film base resin is at least one selected from the group consisting of polyamide, polyimide, polyolefin, polyester, polycarbonate, polyurethane, vinyl resin, acrylic resin, chlorine-based resin, fluorine-based resin, silicone resin, and natural rubber. <1> ~ <4> 10. The electrostatically charged film according to any one of claims 1 to 9. <6> The film base resin is at least one selected from the group consisting of vinylidene fluoride-trifluoroethylene copolymer and polydimethylsiloxane. <5> The electrostatically charged film according to claim 1. <7> 1. A friction generator comprising a first film and a second film, The first film is <1> ~ <6> The charging film according to any one of the preceding claims, the second film includes a film base resin, The first film and the second film have different film base resins, The first film and the second film are disposed opposite to each other. Friction generator. <8> The second film is <1> ~ <6> The charging film according to any one of the preceding claims. <7> The friction generator described in <9> The film base resin of the second film is polyamide. <7> or <8> The friction generator described in

[0051] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by combining the technical means disclosed in different embodiments also fall within the technical scope of the present invention. [Example]

[0052] Hereinafter, one embodiment of the present invention will be described in detail with reference to examples, although the present invention is not limited to these examples.

[0053] [Configuration of friction generator] The structure of the friction generator used in the examples will be described with reference to FIG. 3. The friction generator 10 includes a first film 1, a second film 2, and an electrode 3. The first film 1 was a charged film according to one embodiment of the present invention. The detailed structure of the first film 1 will be described in the section for each example. The second film 2 was a polyamide film (thickness: 15 μm). The electrode 3 was a conductive nonwoven fabric.

[0054] More specifically, an electrode 3 was attached to silicone rubber A (thickness: 1 mm), and a first film 1 or a second film 2 was attached to the electrode 3 to form a friction generator 10. The surface of silicone rubber A had cylindrical projections and recesses with a height of 0.5 mm and a diameter of 1.5 mm. The two electrodes 3 were connected via a 50 MΩ load resistor.

[0055] Example 1 An electrically charged film was fabricated using vinylidene fluoride-trifluoroethylene copolymer (PVDF-TFE) as the film base resin and 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (see below for structure) as the ionic liquid, and used as the first film 1. The concentration of the ionic liquid added to the electrically charged film was changed, and the performance of the friction generator 10 was evaluated.

[0056] [ka]

[0057] [Preparation of charged film] A charged film was produced by the following steps. 1. PVDF-TFE (FC20, Piezotech) was added to dimethylacetamide. The concentration of PVDF-TFE was 100 ppm. 2. The PVDF-TFE was completely dispersed using an ultrasonic cleaner at a temperature of 40°C. 3. The ionic liquid was added to the resulting dispersion and mixed in a mortar to prepare a slurry. The concentration of the ionic liquid was adjusted to 0 ppm, 2 ppm, 3 ppm, 14 ppm, 27 ppm, 64 ppm, or 134 ppm relative to the weight of PVDF-TFE. 4. Aluminum foil was attached to a glass plate, and the slurry was blade coated onto it to form a film with a thickness of 40 μm. 5. The film was stored in a vacuum desiccator together with the aluminum foil for 30 minutes, and then allowed to air dry for at least 24 hours. 6. The dried film was peeled off from the aluminum foil to obtain a charged film. The thickness of the charged film was measured with a micrometer and found to be approximately 40 μm.

[0058] [Performance evaluation of friction generators] The produced charged film was used as the first film 1 to assemble a friction generator 10. A load was repeatedly applied and removed from silicone rubber A at a cycle of 2 Hz. The voltage across the load resistor during this process was observed with an oscilloscope, and the power generation waveform of the friction generator 10 was obtained.

[0059] [result] As a representative example, the power generation waveforms when the ionic liquid concentration was 0 ppm, 3 ppm, 27 ppm, and 134 ppm are shown in Figures 4 to 7. As can be seen from these figures, the output voltage changed significantly depending on the ion concentration.

[0060] Figure 8 shows a graph with the amount of ionic liquid added on the horizontal axis and the maximum positive voltage (black circles) and maximum negative voltage (white circles) in the power generation waveform on the vertical axis. Figure 9 shows the power consumed by the load resistance. As can be seen from these figures, the output voltage and output power began to increase as ionic liquid was added, reached a maximum when the ionic liquid concentration was 3 to 5 ppm, and then decreased as the ionic liquid concentration increased. The output power when the ionic liquid concentration was 3 ppm was approximately four times the output power when the ionic liquid concentration was 0 ppm.

[0061] The results of Example 1 suggest that the power generation characteristics of the friction generator 10 are improved if the ionic liquid concentration is in the range of more than 0 ppm and not more than 50 ppm (preferably 2 ppm or more and not more than 20 ppm).

[0062] [Reference example] It was confirmed that the improvement in the charging characteristics of the charged film produced in Example 1 was not due to a change in the dielectric constant. Specifically, the capacitance between the electrodes was measured using an LCR meter by the electrode contact method, and the dielectric constant was estimated from the results. The concentrations of the ionic liquid were set to 0 ppm, 5 ppm, 10 ppm, 15 ppm, 20 ppm, 30 ppm, 40 ppm, or 50 ppm.

[0063] [result] The results are shown in Figure 10. As can be seen from Figure 10, even when the ionic liquid concentration was changed, the relative dielectric constant remained in the range of approximately 10 to approximately 15, with almost no change. From this, it can be assumed that even if a small amount of ionic liquid is added to the charged film, there is no change in the relative dielectric constant, or that this change is extremely small.

[0064] The catalog value for the relative dielectric constant of PVDF-TFE is 11, but the actual measured value when the ionic liquid concentration was 0 ppm was slightly higher than 11. This is thought to be an error caused by the influence of the air film between the electrodes.

[0065] Example 2 The performance of the friction generator 10 was evaluated by varying the film thickness of the charged film. Specifically, charged films with film thicknesses of 10 μm, 25 μm, or 40 μm were fabricated using the same process as in Example 1. The concentration of the ionic liquid was set to 3 ppm. The fabricated charged film was used as the first film 1, and the power generation waveform of the friction generator 10 was obtained in the same manner as in Example 1.

[0066] [result] Figure 11 shows a graph with the film thickness of the charged film on the horizontal axis and the maximum positive voltage (black circles) and maximum negative voltage (white circles) in the generated waveform on the vertical axis. As can be seen from Figure 11, when the film thickness was 40 μm, the output voltage improved.

[0067] The results of Example 2 suggest that when the amount of ionic liquid added is constant, increasing the film thickness of the charged film to a certain level or greater (e.g., 30 μm or greater) can improve the power generation characteristics of the friction generator 10.

[0068] Example 3 A friction generator 10 was assembled in the same manner as in Example 1, except that the ionic liquid was changed to 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (structure shown below). The concentration of the ionic liquid added to the charged film was varied, and the performance of the friction generator 10 was evaluated. The ionic liquid concentrations were 0 ppm, 6 ppm, 15 ppm, 39 ppm, 78 ppm, 163 ppm, and 530 ppm.

[0069] [ka]

[0070] [result] Figure 12 shows a graph with the amount of ionic liquid added on the horizontal axis and the maximum positive voltage (black circles) and maximum negative voltage (white circles) in the power generation waveform on the vertical axis. Figure 13 shows the power consumed by the load resistance. As can be seen from these figures, the positive voltage changed little with the addition of ionic liquid, but the negative voltage increased with the addition of ionic liquid. The output power reached a maximum when the ionic liquid concentration was approximately 5 ppm, and then decreased as the ionic liquid concentration increased.

[0071] The results of Example 3 suggest that the power generation characteristics of the friction generator 10 are improved even when a different ionic liquid (particularly an ionic liquid containing an imidazolium-based cation) is added.

[0072] Example 4 An electrically charged film was produced using polydimethylsiloxane as the film base resin and a silicone-based ionic liquid added, and used as the first film 1. The concentration of the ionic liquid added to the electrically charged film was changed, and the performance of the friction generator 10 was evaluated.

[0073] [Preparation of charged film] A charged film was produced by the following steps. 1. A curing agent was added to silicone rubber KE-12 (Shin-Etsu Chemical Co., Ltd.). 2. Ionic liquid-modified oligomer X-40-2450 (Shin-Etsu Chemical Co., Ltd., silicone-based) was further added as an ionic liquid, mixed, and degassed under vacuum. The concentration of the ionic liquid was 0 ppm, 4 ppm, 13 ppm, or 42 ppm relative to the weight of the silicone rubber. 3. The resulting solution was applied to the surface of a conductive nonwoven fabric using a coater. The film thickness was 40 μm. 4. Using the obtained laminate, a friction generator was fabricated in the same manner as in Example 1, and its performance was evaluated.

[0074] [result] Figure 14 shows a graph with the amount of ionic liquid added on the horizontal axis and the maximum positive voltage (black circles) and maximum negative voltage (white circles) in the power generation waveform on the vertical axis. As can be seen from Figure 14, when the amount of ionic liquid added was 13 ppm, the output voltage was approximately twice as high as when no ionic liquid was added. This result suggests that the power generation characteristics of friction generator 10 can be improved even when a different film base resin is used.

[0075] [Summary of results of Examples] As described above, by adding an ionic liquid in an amount greater than 0 ppm and less than 50 ppm based on the weight of the film base resin, a charged film was obtained whose mechanical properties were not significantly different from those of the film base resin. Furthermore, a friction generator using this charged film had improved output. In other words, by including specific materials in specific numerical ranges (using very small amounts of ionic liquid), special technical features can be obtained. [Industrial Applicability]

[0076] The present invention can be used for a friction generator or the like. [Explanation of symbols]

[0077] 1: First film 2: Second film 3: Electrode 5: Ionic liquid 10: Friction generator

Claims

1. A charging film for a friction generator, comprising a film base resin and an ionic liquid, The ionic liquid is contained in an amount of more than 0 ppm and not more than 50 ppm based on the weight of the film base resin.

2. The charged film for a friction generator according to claim 1 , wherein the ionic liquid contains one or more imidazolium cations.

3. The charging film for a friction generator according to claim 2, wherein the ionic liquid is at least one selected from the group consisting of 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

4. 4. The charging film for a friction generator according to claim 1, wherein the thickness of the charging film for a friction generator is 30 μm or more.

5. 5. The electrostatically charged film for a friction generator according to claim 1, wherein the film base resin is one or more selected from the group consisting of polyamide, polyimide, polyolefin, polyester, polycarbonate, polyurethane, vinyl resin, acrylic resin, chlorine-based resin, fluorine-based resin, silicone resin, and natural rubber.

6. 6. The charging film for a friction generator according to claim 5, wherein the film base resin is at least one selected from the group consisting of vinylidene fluoride-trifluoroethylene copolymer and polydimethylsiloxane.

7. 1. A friction generator comprising a first film and a second film, The first film is the charging film for a frictional generator according to any one of claims 1 to 6, the second film includes a film base resin, the first film and the second film have different film base resins, The first film and the second film are disposed opposite to each other. Friction generator.

8. The friction generator according to claim 7, wherein the second film is the charging film for a friction generator according to any one of claims 1 to 6.

9. 9. The friction generator according to claim 7, wherein the base resin of the second film is polyamide.

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