Thermoelectric conversion material and thermoelectric conversion element

Abstract

To provide a thermoelectric conversion material having excellent thermoelectric conversion performance and excellent stability over time at high temperature and high humidity, and a thermoelectric conversion element using the same.SOLUTION: The thermoelectric conversion material includes 1,5,7-triazabicyclo[4.4.0]deca-5-ene (A), a conductive material (B), and a polymer (C) including a monomer unit derived from (meth)acrylonitrile. The thermoelectric conversion element has a thermoelectric conversion film formed using the thermoelectric conversion material and an electrode. The thermoelectric conversion film and the electrode are electrically connected to each other.SELECTED DRAWING: None

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to a thermoelectric conversion material and a thermoelectric conversion element. [Background technology]

[0002] Thermoelectric conversion technology, which converts heat into electricity, is attracting attention as a clean energy source. Thermoelectric conversion technology can convert various types of heat found in nature, as well as weak heat energy such as exhaust heat from factories, cars, and homes, and body heat, into electricity. There are various thermoelectric effects that can be used in thermoelectric conversion technology, but the most common is a system that utilizes the Seebeck effect. In the Seebeck effect, when two different temperatures are applied to both ends of a material made up of a combination of semiconductors or metals, an electromotive force is generated by the electron gradient that occurs within the material in response to the temperature difference.

[0003] Thermoelectric materials, which can convert thermal energy and electrical energy back and forth, are used in thermoelectric power generation elements or thermoelectric conversion elements such as Peltier elements. Thermoelectric conversion elements are elements that convert heat into electricity and are generally composed of a combination of semiconductors or metals. Typical thermoelectric conversion element configurations are classified into p-type semiconductors alone, n-type semiconductors alone, and combinations of p-type and n-type semiconductors. To obtain a larger potential difference, thermoelectric conversion elements generally use a combination of p-type and n-type semiconductors as materials.

[0004] Thermoelectric conversion elements, such as Peltier elements, are also used as thermoelectric modules, which are made up of a number of elements assembled into a plate or cylinder. Thermoelectric conversion elements can directly convert thermal energy into electricity. For this reason, thermoelectric conversion elements can be used, for example, as a power source for wristwatches that operate on body heat, and for terrestrial and satellite power generation. The performance of a thermoelectric conversion element depends on the performance of the thermoelectric conversion material and the durability of the module.

[0005] As described in Non-Patent Document 1, the dimensionless thermoelectric figure of merit ZT is used as an index representing the performance of a thermoelectric conversion material. In addition, the power factor PF (= S σ) is sometimes used as an index representing the performance of a thermoelectric conversion material. The dimensionless thermoelectric figure of merit ZT is expressed by the following formula (1). ZT=((S2·σ) / к)·T Equation (1) where S is the Seebeck coefficient (V / K), σ is the electrical conductivity (S / m), T is the absolute temperature (K), and κ is the thermal conductivity (W / (m·K)). The thermal conductivity κ is expressed by the following equation (2): к=α·ρ·C Equation (2) where α is the thermal diffusivity (m 2 / s), ρ is the density (kg / m 3 ), and C is the specific heat capacity (J / (kg·K)). That is, in order to improve the performance of a thermoelectric conversion material (hereinafter also referred to as thermoelectric properties), it is important to improve the Seebeck coefficient or electrical conductivity, while decreasing the thermal conductivity.

[0006] In recent years, research has been progressing on thermoelectric conversion elements using organic materials instead of conventional inorganic materials. In addition to being lightweight, organic materials have excellent moldability and are more flexible than inorganic materials. Therefore, organic materials are highly versatile within the temperature range in which they do not decompose. Furthermore, organic materials are more advantageous than inorganic materials in terms of manufacturing energy and manufacturing costs because they can easily be manufactured using printing techniques, etc.

[0007] For example, Patent Document 1 discloses a thermoelectric conversion material containing a polymer dispersant having an organic dye skeleton and carbon nanotubes (CNTs), and a thermoelectric conversion element using the same. Patent Document 2 discloses a thermoelectric conversion material containing a conductive compound in which a polycyclic aromatic ring having carrier transport properties is bonded to a substituent containing an alkyl group, and a thermoelectric conversion element using the same. However, the invention of Patent Document 1 does not provide sufficient performance as a thermoelectric conversion element. -8 ~10-7 The electrical conductivity is low at only S / cm, which is not practical for use as a thermoelectric conversion element. In addition to their performance as thermoelectric conversion elements, conventional thermoelectric conversion elements also have poor stability over time under high temperature and humidity conditions. For these reasons, there is a need for the development of thermoelectric conversion materials that can improve the performance of thermoelectric conversion elements. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2015 / 050113 [Patent Document 2] International Publication No. 2015 / 129877 [Non-patent literature]

[0009] [Non-Patent Document 1] Takenobu Kajikawa, "Thermoelectric Conversion Technology Handbook (First Edition)", NTS Publishing, p. 19 Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, in view of the above circumstances, the present invention provides a thermoelectric conversion material that has excellent thermoelectric conversion performance and excellent stability over time at high temperatures and high humidity, and a thermoelectric conversion element using the thermoelectric conversion material. [Means for solving the problem]

[0011] The present inventors have conducted extensive research to solve the above problems and have completed the present invention. That is, embodiments of the present invention relate to the following. However, the present invention is not limited to the embodiments described below and includes various embodiments. One embodiment of the present invention relates to a thermoelectric conversion material containing 1,5,7-triazabicyclo[4.4.0]dec-5-ene (A), a conductive material (B), and a polymer (C) containing monomer units derived from (meth)acrylonitrile.

[0012] In the above embodiment, the content of the monomer units derived from (meth)acrylonitrile in the polymer (C) is preferably 50 to 100% by mass.

[0013] In the above embodiment, the content of the polymer (C) is preferably 5 to 100% by mass relative to the total mass of the conductive material (B).

[0014] Another embodiment of the present invention relates to a thermoelectric conversion element having a thermoelectric conversion film formed using the thermoelectric conversion material of the above embodiment and electrodes, wherein the thermoelectric conversion film and the electrodes are electrically connected. [Effects of the Invention]

[0015] According to an embodiment of the present invention, it is possible to provide a thermoelectric conversion material that has excellent thermoelectric conversion performance and excellent stability over time at high temperatures and high humidity, and a thermoelectric conversion element using the thermoelectric conversion material. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described. In this specification, unless otherwise specified, the terms "(meth)acrylic", "(meth)acrylo", and "(meth)acrylic acid" mean "acrylic or methacrylic", "acrylo or methacrylo", and "acrylic acid or methacrylic acid", respectively. Furthermore, when "(meth)acrylate" and "(meth)acryloyloxy" are written, they mean "acrylate or methacrylate" and "acryloyloxy or methacryloyloxy", respectively, unless otherwise specified. In addition, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (A) may be abbreviated as compound (A).

[0017] <Thermoelectric conversion materials> One embodiment of the present invention relates to a thermoelectric conversion material containing 1,5,7-triazabicyclo[4.4.0]dec-5-ene (A), a conductive material (B), and a polymer (C) containing a monomer unit derived from (meth)acrylonitrile. The thermoelectric conversion material containing the compound (A), the conductive material (B), and the polymer (C) is presumed to exhibit primarily n-type semiconductor properties. Each component will be specifically described below.

[0018] <Compound (A)> The compound (A) can stably supply electrons to the conductive material (B), thereby contributing to improved thermoelectric conversion performance. The compound (A) is commercially available, but a compound synthesized according to a method well known to those skilled in the art can also be used. The content of the compound (A) is preferably 25% by mass or more, more preferably 50% by mass or more, and even more preferably 75% by mass or more, based on the total mass of the conductive material (B). The content of the compound (A) may be 100% by mass. When the content of the compound (A) is adjusted to be within the above range, excellent conductivity can be easily obtained.

[0019] <Conductive material (B)> The conductive material (B) is a material that contributes to electrical conductivity. Therefore, the electrical conductivity can be easily improved by increasing the content of the conductive material (B). The conductive material (B) is not particularly limited as long as it is a material that has electrical conductivity. For example, a carbon material, a metal material, or a conductive polymer can be used.

[0020] Examples of carbon materials include graphite, carbon nanotubes, carbon black, and graphene (including graphene nanoplates).

[0021] Examples of metal materials include powders of gold, silver, copper, nickel, chromium, palladium, rhodium, ruthenium, indium, silicon, aluminum, tungsten, molybdenum, germanium, gallium, and platinum, as well as alloys and composite powders of these metals. Examples of alloys of the above metals include ZnSe, CdS, InP, GaN, SiC, and SiGe. The metal material may be a fine particle having a core and a coating of a material different from the core material. Specific examples include silver-coated copper powder, which has a copper core and a silver coating on its surface. Examples of the metal material include powders of metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide, ruthenium oxide, ITO (tin-doped indium oxide), AZO (aluminum-doped zinc oxide), and GZO (gallium-doped zinc oxide), as well as powders surface-coated with these metal oxides. Examples of conductive polymers include PEDOT / PSS (a composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid), polyaniline, polyacetylene, polypyrrole, polythiophene, and polyparaphenylene.

[0022] The conductive material may be used alone or in combination of two or more. The shape of the conductive material (B) is not particularly limited and may have various shapes. For example, conductive materials having shapes such as amorphous, aggregated, scale-like, microcrystalline, spherical, flake-like, and wire-like shapes can be used.

[0023] From the viewpoint of achieving both a high Seebeck coefficient and electrical conductivity, the conductive material (B) preferably contains at least a carbon material. Among the carbon materials, it is more preferable that the conductive material (B) contains at least one selected from the group consisting of carbon nanotubes, carbon black, and graphene (including graphene nanoplates). In one embodiment, the conductive material (B) more preferably contains carbon nanotubes, and particularly preferably contains single-walled carbon nanotubes.

[0024] Carbon materials that can be used in embodiments of the present invention are commercially available. Examples of flake graphite include CMX, UP-5, UP-10, UP-20, UP-35N, CSSP, CSPE, CSP, CP, CB-150, CB-100, ACP, ACP-1000, ACB-50, ACB-100, ACB-150, SP-10, SP-20, J-SP, SP-270, HOP, GR-60, LEP, F#1, F#2, and F#3, and Chuetsu, manufactured by Nippon Graphite Industries Co., Ltd. Examples include BF-3AK, FBF, BF-15AK, CBR, CPB-6S, CPB-3, 96L, 96L-3, K-3, SC-120, SC-60, HLP, CP-150, and SB-1 manufactured by Graphite Industries Co., Ltd., EC1500, EC1000, EC500, EC300, EC100, and EC50 manufactured by Ito Graphite Industries Co., Ltd., and 10099M and PB-99 manufactured by Nishimura Graphite Co., Ltd. Examples of spherical natural graphite include CGC-20, CGC-50, CGB-20, and CGB-50 manufactured by Nippon Graphite Industries Co., Ltd.

[0025] Examples of amorphous graphite include Blue P, AP, AOP, and P#1 manufactured by Nippon Graphite Industries Co., Ltd., and APR, K-5, AP-2000, AP-6, 300F, and 150F manufactured by Chuetsu Graphite Co., Ltd. Examples of artificial graphite include PAG-60, PAG-80, PAG-120, PAG-5, HAG-10W, and HAG-150 manufactured by Nippon Graphite Industries Co., Ltd., and G-4AK, G-6S, G-3G-150, G-30, G-80, G-50, SMF, EMF, SFF, SFF-80B, SS-100, BSP-15AK, BSP-100AK manufactured by Chuetsu Graphite Co., Ltd. and WF-15C, as well as SGP-100, SGP-50, SGP-25, SGP-15, SGP-5, SGP-1, SGO-100, SGO-50, SGO-25, SGO-15, SGO-5, SGO-1, SGX-100, SGX-50, SGX-25, SGX-15, SGX-5, and SGX-1 manufactured by SEC Carbon Corporation.

[0026] Examples of conductive carbon fibers and carbon nanotubes include vapor grown carbon fibers such as VGCF manufactured by Showa Denko K.K., single-walled carbon nanotubes such as EC1.5 and EC1.5-P manufactured by Meijo Nano Carbon Co., Ltd., TUBALL manufactured by Kusumoto Chemicals Co., Ltd., and ZEONANO manufactured by Zeon Nano Technology Inc., FloTube9000, FloTube7000, and FloTube2000 manufactured by CNano, NC7000 manufactured by Nanocyl, and 100T and 200P manufactured by CNano.

[0027] Examples of carbon black include Tokablack #4300, #4400, #4500, and #5500 manufactured by Tokai Carbon Co., Ltd., Printex L manufactured by Degussa Corporation, and Raven 7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, Conductex SC ULTRA, and Conductex 975 manufactured by Colombian. Examples of suitable blacks include ULTRA, PUERBLACK 100, 115, and 205; Mitsubishi Chemical Corporation's #2350, #2400B, #2600B, #3050B, #3030B, #3230B, #3350B, #3400B, and #5400B; Cabot Corporation's MONARCH 1400, 1300, 900, Vulcan XC-72R, and BlackPearls 2000; TIMCAL Corporation's Ensaco 250G, Ensaco 260G, Ensaco 350G, and Super P-Li furnace blacks; Lion Corporation's EC-300J and EC-600JD ketjen blacks; and Denka Black, Denka Black HS-100, and FX-35 acetylene blacks.

[0028] The conductive material (B) may contain one or more of the compounds exemplified above as carbon materials, but is not particularly limited to the compounds exemplified above as carbon materials and may contain various carbon materials.

[0029] The content of the conductive material (B) is preferably 15% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 80% by mass or less, and even more preferably 30% by mass or more and 60% by mass or less, based on the total mass of the compound (A), the conductive material (B), and the polymer (C). When the content of the conductive material (B) is adjusted within the above range, excellent conductivity can be easily obtained by forming conductive paths. Furthermore, the conductive material (B) can be sufficiently dispersed, and excellent coating film formability and coating film properties can be easily obtained.

[0030] <Polymer (C)> The polymer (C) is a polymer containing a monomer unit derived from (meth)acrylonitrile. Examples of the polymer containing a monomer unit derived from (meth)acrylonitrile include poly(meth)acrylonitrile and a copolymer containing a monomer unit derived from (meth)acrylonitrile and another monomer unit. When the polymer (C) is a copolymer, it may be in the form of either a random copolymer or a block copolymer.

[0031] Examples of other monomers that can be used to form the copolymer include aromatic hydrocarbons having a double bond, (meth)acrylic acid, and (meth)acrylic acid esters. Examples of aromatic hydrocarbons having a double bond include styrene and styrene macromers. Examples of the (meth)acrylic acid ester include alkyl (meth)acrylate, hydroxyalkyl (meth)acrylate, polyalkylene glycol (meth)acrylate, and alkoxypolyalkylene glycol (meth)acrylate.

[0032] In one embodiment, the other monomer is preferably at least one selected from the group consisting of styrene, styrene macromer, (meth)acrylic acid alkyl ester, (meth)acrylic acid hydroxyalkyl ester, and (meth)acrylic acid alkoxypolyalkylene glycol. In one embodiment, the other monomer is more preferably styrene or (meth)acrylic acid alkoxypolyalkylethylene glycol.

[0033] In one embodiment, polymer (C) is preferably a copolymer composed of monomer units derived from (meth)acrylonitrile and other monomer units. The copolymer is preferably a copolymer of (meth)acrylonitrile and at least one selected from the group consisting of acrylic acid, 2-hydroxyethyl acrylate, methoxypolyethylene glycol monomethacrylate, styrene, and butyl acrylate. The copolymer is more preferably a copolymer of (meth)acrylonitrile and one selected from the group consisting of acrylic acid, 2-hydroxyethyl acrylate, methoxypolyethylene glycol monomethacrylate, styrene, and butyl acrylate. The copolymer is even more preferably a copolymer of (meth)acrylonitrile and methoxypolyethylene glycol monomethacrylate or styrene.

[0034] The strong polarity of the cyano group in the monomer unit derived from (meth)acrylonitrile improves the adsorption of polymer (C) to conductive material (B), which in turn improves the adsorption of compound (A) to conductive material (B). As a result, it is presumed that aggregation of conductive material (B) and adsorption of moisture to conductive material (B) are suppressed, thereby improving the stability of the thermoelectric conversion material.

[0035] From the above viewpoint, the content of the monomer forming the monomer unit derived from (meth)acrylonitrile in the polymer (C) may be 50 to 100 mass% based on the total mass of the monomers used as raw materials to constitute the polymer (C).

[0036] In one embodiment, the content of monomer units derived from (meth)acrylonitrile in polymer (C) is more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more. In one embodiment, the content may be 100% by mass. That is, polymer (C) may be a homopolymer of (meth)acrylonitrile. In another embodiment, the polymer (C) may be a copolymer of (meth)acrylonitrile and another monomer, and the content may be preferably 50 to 95 mass%, more preferably 60 to 90 mass%, and even more preferably 75 to 85 mass%.

[0037] The content of polymer (C) is preferably 5% by mass or more, more preferably 25% by mass or more, even more preferably 50% by mass or more, and particularly preferably 60% by mass or more, based on the total mass of conductive material (B). The content of polymer (C) may be 100% by mass, but is more preferably 80% by mass or less. In one embodiment, the content of polymer (C) may be preferably in the range of 5 to 100% by mass, more preferably 50 to 100% by mass, and even more preferably 50 to 80% by mass.

[0038] The method for producing the polymer (C) is not particularly limited, and methods well known in the art can be applied. For example, any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, or precipitation polymerization can be used. In one embodiment, the method for producing the polymer (C) is preferably solution polymerization or precipitation polymerization, and most preferably precipitation polymerization.

[0039] In precipitation polymerization, low-molecular-weight components and residual monomers dissolve in the solvent used during polymerization, allowing them to be quickly removed after polymerization. Therefore, precipitation polymerization makes it possible to narrowly control the molecular weight distribution of polymer (C) and minimize the amount of residual monomers, efficiently producing polymer (C) with a molecular weight sufficient to function as a dispersant. The polymerization reaction can be carried out using addition polymerization methods such as ionic polymerization, free radical polymerization, and living radical polymerization. In one embodiment, free radical polymerization or living radical polymerization is preferred. It is preferable to use a radical polymerization initiator during the reaction. For example, a compound selected from peroxides and azo-based initiators, or a mixture thereof, can be used. Furthermore, a molecular weight modifier such as a chain transfer agent may be used during the reaction, if necessary.

[0040] The molecular weight of the polymer (C), in terms of polystyrene equivalent weight average molecular weight, is preferably in the range of 3,000 to 500,000, more preferably 4,000 to 200,000, still more preferably 5,000 to 100,000, and particularly preferably 10,000 to 100,000. When the polymer (C) having a weight average molecular weight within the above range is used, the adsorptivity to the conductive material (B) can be easily improved.

[0041] (dispersion medium) In one embodiment, the thermoelectric conversion material of the above embodiment preferably further contains a dispersion medium. The dispersion medium can be used as a medium when mixing the compound (A) and the conductive material (B), or when mixing the compound (A), the conductive material (B), and the polymer (C). By including a dispersion medium, the thermoelectric conversion material is in the form of an ink or paste, and therefore a thermoelectric conversion film can be formed by printing or coating. The dispersion medium is preferably a medium that can dissolve or disperse the compound (A), the conductive material (B), and the polymer (C). Specific examples include organic solvents and water. The dispersion medium may be used alone or in combination of two or more.

[0042] Examples of organic solvents that can be used as dispersion media include alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol methyl ether, terpineol, dihydroterpineol, 2,4-diethyl-1,5-pentanediol, 1,3-butylene glycol, isobornylcyclohexanol, ethylene glycol, 1,3-propanediol, 1,4-butanediol, glycerin, trifluoroethanol, m-cresol, and thiodiglycol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ethers such as tetrahydrofuran, dioxane, and ethylene glycol dimethyl ether; hydrocarbons such as hexane, heptane, and octane; aromatic hydrocarbons such as benzene, toluene, xylene, and cumene; Esters such as ethyl acetate and butyl acetate, and Nitrogen-containing heterocycles such as N-methylpyrrolidone, etc. These exemplified compounds may be used alone or in combination of two or more as needed. In one embodiment, N-methylpyrrolidone is particularly preferred from the viewpoints of dispersibility and solubility.

[0043] (Inorganic thermoelectric conversion materials) In one embodiment, the thermoelectric conversion material of the above embodiment may further contain an inorganic thermoelectric conversion material as needed to enhance thermoelectric conversion performance. The inorganic thermoelectric conversion material is not particularly limited, and materials well known in the art as thermoelectric conversion materials can be used.

[0044] (polymer) In one embodiment, the thermoelectric conversion material of the above embodiment may further contain a polymer other than polymer (C) as necessary. A polymer other than polymer (C) means a polymer that does not contain a monomer unit derived from (meth)acrylonitrile in the molecule. Such a polymer is not particularly limited, and materials well known as polymers in the technical field can be used.

[0045] <Thermoelectric conversion element> Another embodiment of the present invention relates to a thermoelectric conversion element. The thermoelectric conversion element has a thermoelectric conversion film formed using the thermoelectric conversion material of the above embodiment and electrodes, and has a structure in which the thermoelectric conversion film and the electrodes are electrically connected. The thermoelectric conversion film is excellent in heat resistance and flexibility in addition to electrical conductivity and thermoelectric properties. Therefore, a high-quality thermoelectric conversion element can be easily fabricated using the thermoelectric conversion material of the above embodiment.

[0046] The thermoelectric conversion film may be, for example, a film obtained by applying a thermoelectric conversion material to a substrate. Thermoelectric conversion materials have excellent formability. Therefore, a good film can be easily obtained by applying or printing the thermoelectric conversion material. The method for producing the thermoelectric conversion film is not particularly limited as long as the desired thermoelectric conversion film can be obtained, and can be appropriately selected depending on the properties of the thermoelectric conversion material, such as viscosity, and the required film thickness, area, and shape.

[0047] As a method for producing a thermoelectric exchange membrane, various means can be applied, such as spin coating, spray coating, roll coating, gravure coating, flexo coating, die coating, lip coating, knife coating, blade coating, comma coating, roll coating, curtain coating, bar coating, dip coating, dispenser, screen coating, and inkjet printing.

[0048] The thickness of the thermoelectric conversion film is not particularly limited and can be set according to the required electrical properties such as current value, voltage value, and resistance, as well as thermoelectric properties. For example, as will be described later, it is preferable that the thermoelectric conversion film be formed to have a certain thickness or more so that a temperature difference can be generated and transmitted in the thickness direction or in the plane direction of the thermoelectric conversion film. In one embodiment, from the viewpoint of thermoelectric properties and flexibility, the thickness of the thermoelectric conversion film is preferably in the range of 0.1 to 200 μm, more preferably in the range of 1 to 100 μm, and particularly preferably in the range of 1 to 60 μm.

[0049] The substrate is not particularly limited. For example, nonwoven fabric, paper, plastic films made of materials such as polyethylene, polyethylene terephthalate (PET), polyethylene naphthalate, polyethersulfone, polypropylene, polyimide, polycarbonate, and cellulose triacetate, or glass can be used. An aluminum vapor deposition layer or a barrier layer may be provided on the surface of these substrates to prevent deterioration of the thermoelectric conversion material due to the effects of water or oxygen.

[0050] In order to improve the adhesion between the substrate and the thermoelectric conversion film, the surface of the substrate may be subjected to various treatments. Specifically, prior to application of the thermoelectric conversion material, UV ozone treatment, corona treatment, plasma treatment, or adhesion enhancing treatment may be performed.

[0051] The thermoelectric conversion film may be laminated on a substrate or may be a free-standing film without a substrate. When producing a free-standing film, there are no particular limitations on the method. For example, a free-standing film can be obtained by forming the thermoelectric conversion film on a release sheet and then removing the release coating.

[0052] The release sheet may be, for example, a plastic film such as a polyester film, a polyethylene film, a polypropylene film, or a polyimide film, the surface of which has been subjected to a release treatment.

[0053] The thermoelectric conversion element can be constructed using techniques well known in the art, except that it is constructed using the thermoelectric conversion material of the above embodiment. The configuration and manufacturing method of the thermoelectric conversion element will be described in more detail below.

[0054] In a thermoelectric conversion element, the thermoelectric conversion film and the electrodes are electrically connected. Here, "electrically connected" means that they are joined to each other or can conduct electricity via other components such as wires.

[0055] The electrode material is not particularly limited as long as it functions as an electrode. The electrode material can be selected from, for example, metals, alloys, and semiconductors. In one embodiment, metals and alloys are preferred because they have high conductivity and low contact resistance of the thermoelectric conversion film. The electrode preferably contains at least one selected from the group consisting of gold, silver, copper, platinum, nickel, and aluminum. It is more preferred that the electrode contain silver.

[0056] The method for forming the electrodes is not particularly limited, and they can be formed by methods such as vacuum deposition, thermocompression bonding of an electrode material foil or a film having an electrode material film, coating of a paste in which fine particles of the electrode material are dispersed, etc. From the viewpoint of process simplicity, methods using thermocompression bonding of an electrode material foil or a film having an electrode material film, and coating of a paste in which the electrode material is dispersed are preferred.

[0057] Typical examples of the structure of thermoelectric conversion elements can be broadly classified into (1) a structure in which electrodes are formed on both ends of the thermoelectric conversion film of the present invention, and (2) a structure in which the thermoelectric conversion film of the present invention is sandwiched between two electrodes, based on the positional relationship between the thermoelectric conversion film and a pair of electrodes.

[0058] A thermoelectric conversion element having the structure (1) above can be obtained, for example, by forming a thermoelectric conversion film on a substrate and then applying silver paste to both ends of the film to form first and second electrodes. A thermoelectric conversion element having electrodes formed on both ends of the thermoelectric conversion film in this way can easily increase the distance between the two electrodes. Therefore, a large temperature difference can be generated between the two electrodes, making it easy to perform efficient thermoelectric conversion.

[0059] A thermoelectric conversion element having the structure (2) above can be obtained, for example, by applying silver paste to a substrate to form a first electrode, forming the thermoelectric conversion film of the present invention on top of that, and then applying silver paste to form a second electrode on top of that. A thermoelectric conversion element having the thermoelectric conversion film of the present invention sandwiched between two electrodes in this way can utilize the temperature difference in the thickness direction of the thermoelectric conversion film, i.e., in the direction perpendicular to the substrate, and can therefore be used in a form attached to a heat source. This is preferable because it has the advantage of being able to extract heat from a wide range from the heat source. In a thermoelectric conversion element having the structure (2) above, it is also possible to increase the distance between the two electrodes by increasing the film thickness, thereby ensuring a sufficient temperature difference.

[0060] Thermoelectric conversion elements can generate a high voltage when connected in series, and can generate a large current when connected in parallel. The thermoelectric conversion element may be formed by connecting two or more thermoelectric conversion elements. According to an embodiment of the present invention, the thermoelectric conversion element has excellent flexibility, and therefore can be suitably installed even on a heat source having a non-flat shape.

[0061] In one embodiment, the thermoelectric conversion element may further include a heat absorption layer or a heat storage layer to efficiently transfer heat from the heat source, and may further include a heat insulation layer or a heat dissipation layer to ensure a temperature difference. Depending on the application and the amount of power required, the electrical energy extracted from the thermoelectric conversion element may be boosted using a boost circuit before use. Alternatively, the electrical energy extracted from the thermoelectric conversion element may be temporarily stored in a condenser, a capacitor, a secondary battery, or the like. [Example]

[0062] The present invention will be described in more detail below with reference to experimental examples, but the present invention is not limited to these examples. In the following description, "parts" means "parts by mass" and "%" means "% by mass".

[0063] (Method for measuring weight average molecular weight (Mw)) The weight-average molecular weight (Mw) was measured by gel permeation chromatography (GPC) equipped with a refractive index (RI) detector. The instrument used was a Tosoh HLC-8320GPC, with three separation columns connected in series. The packing materials for the three separation columns were Tosoh TSK-GELSUPERAW-4000, AW-3000, and AW-2500, respectively. The measurement was carried out at an oven temperature of 40°C, using an N,N-dimethylformamide solution containing 30 mM triethylamine and 10 mM LiBr as an eluent, and at a flow rate of 0.6 mL / min. The measurement sample was adjusted to a concentration of 1% in the dispersion medium consisting of the eluent, and 20 μL was injected. The molecular weight is a polystyrene equivalent value.

[0064] <1> Preparation of polymer (C) <Production Example 1> (Production of Polymer (C-1)) A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 100 parts of acetonitrile as a solvent, 100 parts of acrylonitrile, and 1 part of 3-mercapto-1,2-propanediol as a chain transfer agent, and the atmosphere inside the reaction vessel was replaced with nitrogen gas. The reaction vessel was heated to 70°C, and a mixture consisting of 10 parts of acetonitrile and 0.4 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (V-65, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was added dropwise to the reaction vessel over 6 hours to carry out the polymerization reaction. After the dropwise addition was completed, the mixture was reacted at 70°C for 1 hour, and then 0.1 parts of V-65 was added. The reaction was continued at 70°C for another 1 hour, and the target product was obtained as a precipitate. Subsequently, measurement of the nonvolatile content confirmed that the conversion rate exceeded 98%. The product (precipitate) was filtered off under reduced pressure, washed with 100 parts of acetonitrile, and the solvent was completely removed by drying under reduced pressure to obtain polymer (C-1).

[0065] <Production Examples 2 to 20> (Production of Polymers (C-2) to (C-20)) Polymers (C-2) to (C-20) were produced in the same manner as in Production Example 1, except that the types and amounts of monomers were changed as shown in Table 1. The Mw of each polymer is shown in Table 1. In the production of polymers (C-2) to (C-20), the Mw was adjusted by adding a chain transfer agent, adjusting the amount of polymerization initiator, and further by appropriately changing the reaction conditions, reaction solvent, etc. 2,2'-azobis(2,4-dimethylvaleronitrile) was used as the polymerization initiator, and 3-mercapto-1,2-propanediol was used as the chain transfer agent.

[0066] In Table 1, unless otherwise specified, the numerical values ​​represent "parts," and blank spaces indicate that the component is not blended. The abbreviations listed in Table 1 are as follows. AA: acrylic acid HEA: 2-hydroxyethyl acrylate PME1000: methoxypolyethylene glycol monomethacrylate (NOF Corporation, Blenmer (registered trademark) PME-1000, number of oxyethylene groups: 23) St: styrene BA: butyl acrylate

[0067] <2-1> Preparation of dispersion containing thermoelectric conversion material [Example 1] (Dispersion 1) 0.4 parts of compound (A), 0.4 parts of SWCNT (single-walled carbon nanotubes "TUBALL" manufactured by OCSiAl Corporation), 0.3 parts of polymer (C-1), and 79.3 parts of NMP (N-methylpyrrolidone) were weighed and mixed. Beads were then added, and the mixture was shaken in a Scandex for 4 hours. The beads were then removed by filtration, and dispersion liquid 1 of the thermoelectric conversion material was obtained.

[0068] [Examples 2 to 35, Comparative Examples 1 and 2] (Dispersion 2~35, 101~102) Thermoelectric conversion material dispersions 2 to 35 and 101 were obtained in the same manner as dispersion 1, except that the types and amounts of materials were changed as shown in Table 2.

[0069] The abbreviations for the materials listed in Table 2 are as follows: Conductive material (B) SWCNT: OCSiAl's single-walled carbon nanotubes "TUBALL" MWCNT: (Kumho Petrochemical's multi-walled carbon nanotubes "Knanos100P") CB: (Lion Ketjenblack "EC-300J")

[0070] <2-2> Evaluation of thermoelectric conversion materials Dispersions 1 to 35 and 101 to 102 obtained in each of the Examples and Comparative Examples were applied to a substrate using an applicator. A 75 μm-thick PET film, which is a sheet-like substrate, was used as the substrate. The resulting coating was then dried at 120°C for 30 minutes to obtain a laminate having a thermoelectric conversion film with a thickness of 5 μm. The laminate having the thermoelectric conversion film (hereinafter also referred to as the coating film) obtained as described above was evaluated for electrical conductivity, Seebeck coefficient, and stability over time at 100°C according to the following methods. The results are shown in Table 2.

[0071] (Electrical conductivity (resistivity)) Immediately after production, the laminate was cut into a piece measuring 2.5 cm × 5 cm, and its conductivity was measured by the four-probe method using a Loresta GX MCP-T700 (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) in accordance with JIS-K7194. The measured values ​​are shown in Table 2 as relative values ​​when the conductivity of Comparative Example 1 was set to 1.

[0072] (Seebeck coefficient) Immediately after production, the laminate was cut into a size of 3 mm × 10 mm, and the Seebeck coefficient (μV / K) at 80°C was measured using a ZEM-3LW manufactured by Advance Riko Co., Ltd. The measured values ​​are shown in Table 2 as relative values ​​when the Seebeck coefficient of Comparative Example 1 was set to 1.

[0073] (Stability over time under high temperature and humidity conditions) The laminate immediately after preparation was left to stand for 20 days in an environment of 85°C and 85% relative humidity, and then the Seebeck coefficient was measured under the same conditions as above. The rate of change in the Seebeck coefficient relative to the Seebeck coefficient of the laminate immediately after preparation (the Seebeck coefficient listed in Table 2) was determined and evaluated based on the following criteria. The smaller the rate of change in the Seebeck coefficient, the better, and a rate of change of more than 70% is poor. That is, the following evaluation criteria of "1" to "7" are good, and the smaller the number, the better the stability over time. Evaluation criteria of "8" are poor. (Evaluation criteria) 1: The rate of change in the Seebeck coefficient is 10% or less. 2: The rate of change of the Seebeck coefficient is greater than 10% and less than or equal to 15%. 3: The rate of change of the Seebeck coefficient is greater than 15% and less than 20%. 4: The rate of change of the Seebeck coefficient is greater than 20% and less than 25%. 5: The rate of change of the Seebeck coefficient is greater than 25% and less than or equal to 30%. 6: The rate of change of the Seebeck coefficient is greater than 30% and less than or equal to 50%. 7: The rate of change of the Seebeck coefficient is greater than 50% and less than or equal to 70%. 8: The rate of change of the Seebeck coefficient is greater than 70%.

[0074] As can be seen from Table 2, the thermoelectric conversion material according to the embodiment of the present invention exhibits high electrical conductivity and a high Seebeck coefficient, and has been confirmed to have excellent stability over time under high-temperature and high-humidity conditions. This is thought to be due to the stable adsorption of compound (A) to conductive material (B). Furthermore, it is thought that the addition of polymer (C) to the thermoelectric conversion material further enhances the adsorption of compound (A) to conductive material (B). These factors are thought to suppress aggregation of conductive material (B) or adsorption of moisture to conductive material (B), making it possible to maintain the stable presence of conductive material (B) in the thermoelectric conversion material.

[0075] <3> Manufacturing of thermoelectric conversion elements Five thermoelectric conversion layers, each 20 μm thick and 5 mm × 30 mm in size, were fabricated at 10 mm intervals by applying the dispersions obtained in each Example and Comparative Example to a 50 μm thick PET film. Next, four silver circuits (electrodes) 10 μm thick and 5 mm × 33 mm in size were fabricated using silver paste so that the thermoelectric conversion layers were connected in series, thereby producing thermoelectric conversion elements. The silver paste used was REXALPHA RA-FS 074 manufactured by Toyo Ink Co., Ltd. The electromotive force of each of the obtained thermoelectric conversion elements was measured, and it was confirmed that the thermoelectric conversion elements manufactured using the dispersions manufactured in Examples 1 to 35 all had a superior Seebeck coefficient to the thermoelectric conversion element manufactured using the dispersion manufactured in Comparative Example 1.

[0076] [Table 1]

[0077] [Table 2]

Claims

1. The composition contains 1,5,7-triazabicyclo[4.4.0]dec-5-ene (A), a conductive material (B), and a polymer (C) containing a monomer unit derived from (meth)acrylonitrile, A thermoelectric conversion material, wherein the content of the 1,5,7-triazabicyclo[4.4.0]dec-5-ene (A) is 25 mass% or more relative to the total mass of the conductive material (B).

2. 2. The thermoelectric conversion material according to claim 1, wherein the content of the monomer units derived from (meth)acrylonitrile in the polymer (C) is 50 to 100 mass%.

3. 3. The thermoelectric conversion material according to claim 1, wherein the content of the polymer (C) is 5 to 100 mass% with respect to the total mass of the conductive material (B).

4. 2. The thermoelectric conversion material according to claim 1, wherein the conductive material (B) is at least one selected from the group consisting of graphite, carbon nanotubes, and carbon black.

5. 2. The thermoelectric conversion material according to claim 1, wherein the polymer (C) is a copolymer of (meth)acrylonitrile and methoxypolyethylene glycol monomethacrylate or styrene.

6. A thermoelectric conversion element comprising a thermoelectric conversion film formed using the thermoelectric conversion material according to any one of claims 1 to 5 and electrodes, wherein the thermoelectric conversion film and the electrodes are electrically connected.

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