JP7500968B2 - Thermoelectric conversion materials and thermoelectric conversion elements - Google Patents

Description

The present invention relates to a thermoelectric conversion material and a thermoelectric conversion element.

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

Thermoelectric conversion materials that can convert between thermal energy and electrical energy are used in thermoelectric conversion elements such as thermoelectric power generation elements and Peltier elements. Thermoelectric conversion elements are elements that convert heat into electricity and are made up of a combination of semiconductors and metals. Representative thermoelectric conversion elements 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.

Thermoelectric conversion elements, such as Peltier elements, are also used as thermoelectric modules, which are made by combining a large number of elements into a plate or cylinder shape. Because they can directly convert thermal energy into electricity, they can be used, for example, as a power source for wristwatches that are powered by 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, etc.

As described in Non-Patent Document 1, a dimensionless thermoelectric figure of merit ZT is used as an index representing the performance of a thermoelectric conversion material. In addition, a power factor PF (= ^S2 ·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)/k)·T Equation (1)
Here, 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 formula (2).
κ = α ρ C Equation (2)
Here, 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 thermoelectric conversion performance (hereinafter also referred to as thermoelectric properties), it is important to increase the Seebeck coefficient or electrical conductivity while decreasing the thermal conductivity.

Typical thermoelectric conversion materials include inorganic materials such as bismuth-tellurium (Bi-Te) for temperatures from room temperature to 500 K, lead-tellurium (Pb-Te) for temperatures from room temperature to 800 K, and silicon-germanium (Si-Ge) for temperatures from room temperature to 1000 K.

However, these inorganic thermoelectric conversion materials often contain rare elements and are therefore expensive, or may contain harmful substances. In addition, inorganic materials are difficult to process, making the manufacturing process complicated. As a result, the manufacturing energy and manufacturing costs of inorganic thermoelectric conversion materials are high, making them difficult to generalize. Furthermore, inorganic thermoelectric conversion materials are rigid, making it difficult to manufacture flexible thermoelectric conversion elements that can be processed into shapes that are not flat. In addition, inorganic thermoelectric conversion materials generally have a high specific gravity, which poses the issue of the weight being easily increased when elements are combined into a module.

In response to this, research is underway into thermoelectric conversion elements that use organic materials instead of conventional inorganic materials. Organic materials are lightweight, have excellent moldability, and are more flexible than inorganic materials, making them highly versatile within the temperature range in which they do not decompose. In addition, they are more advantageous than inorganic materials in terms of manufacturing energy and costs, as they can be easily produced using printing techniques, etc.

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 and a substituent containing an alkyl group are bonded, 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. Furthermore, the invention of Patent Document 2 has a low conductivity of 10 ^-8 to 10 ^-7 S/cm, and is unable to provide a practical value as a thermoelectric conversion element.

International Publication No. 2015/050113 International Publication No. 2015/129877

Takenobu Kajikawa, "Thermoelectric Conversion Technology Handbook (First Edition)", NTS Publishing, p. 19

The problem that the present invention aims to solve is to provide a thermoelectric conversion material that has excellent suitability for coating on substrates and can achieve both thermoelectric conversion performance and electrical conductivity. It is also to provide a thermoelectric conversion element that exhibits excellent thermoelectric performance.

The present inventors have conducted intensive research to solve the above problems, and have arrived at the present invention. That is, the present invention relates to a thermoelectric conversion material comprising a polymer (A) and a conductive material (B), characterized in that the polymer (A) is a copolymer that contains monomer units derived from (meth)acrylonitrile, as well as one or more monomer units selected from the group consisting of active hydrogen group-containing monomers, basic monomers, and (meth)acrylic acid alkyl esters, and contains 40% by mass or more but less than 100% by mass of monomer units derived from (meth)acrylonitrile.

The present invention also relates to the above thermoelectric conversion material, characterized in that the polymer (A) contains active hydrogen group-containing monomer units, and the active hydrogen group-containing monomer units contain monomer units derived from a hydroxyl group-containing monomer and/or a carboxyl group-containing monomer.

The present invention also relates to the above thermoelectric conversion material, characterized in that polymer (A) contains a total of 1 to 25 mass % of monomer units derived from a hydroxyl group-containing monomer and monomer units derived from a carboxyl group-containing monomer.

The present invention also relates to the above thermoelectric conversion material, which further comprises at least one selected from the group consisting of inorganic metal salts, inorganic bases, and organic bases.

The present invention also relates to the above thermoelectric conversion material, characterized in that the content of the polymer (A) is 5 to 100 mass % relative to the total amount of the conductive material (B).

The present invention also relates to a thermoelectric conversion element having a thermoelectric conversion film containing the above-mentioned thermoelectric conversion material and electrodes, the thermoelectric conversion film and the electrodes being electrically connected.

The present invention can provide a thermoelectric conversion material that has excellent suitability for application to substrates and achieves both a high Seebeck coefficient and electrical conductivity. In addition, the material can be used to provide a thermoelectric conversion element that exhibits excellent thermoelectric performance.

1 is a schematic diagram showing a structure of an example of a thermoelectric conversion element according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a method for measuring the electromotive force of a thermoelectric conversion element according to an embodiment of the present invention.

The following describes an embodiment of the present invention. In this specification, unless otherwise specified, the terms "(meth)acrylic", "(meth)acryloyl", "(meth)acrylic acid", "(meth)acrylate", and "(meth)acryloyloxy" refer to "acrylic or methacrylic", "acryloyl or methacryloyl", "acrylic acid or methacrylic acid", "acrylate or methacrylate", and "acryloyloxy or methacryloyloxy", respectively.

<Thermoelectric conversion materials>
The thermoelectric conversion material of the present invention is characterized by containing a polymer (A) and a conductive material (B), and can achieve both a high Seebeck coefficient and electrical conductivity, and can exhibit excellent thermoelectric performance. This is because the Seebeck improvement effect occurs due to the movement of holes or electrons (carriers) generated in the thermally excited polymer (A) to the conductive material (B), and the dispersibility of the conductive material (B) is improved due to the presence of the polymer (A), so that a conductive path in the film is efficiently formed, the mobility of the carriers is improved, and as a result, excellent electrical conductivity is expressed. In addition, when the polymer (A) has a cyclic structure, the affinity between the polymer (A) and the conductive material (B) is further improved, making it possible to exhibit high performance.
Hereinafter, an embodiment of the present invention will be described in detail.

<Polymer (A)>
The polymer (A) is a copolymer containing a monomer unit derived from (meth)acrylonitrile and a unit derived from one or more monomers selected from the group consisting of an active hydrogen group-containing monomer, a basic monomer, and an alkyl (meth)acrylate ester.

Polymer (A) can be synthesized by either random polymerization or block polymerization. Polymer (A) contains 40% by mass or more of units derived from (meth)acrylonitrile. The strong polarization of the non-hydrogen-bonding cyano group and the carbon chain of the polymer main chain increase the adsorptivity to the conductive material (B) and affinity to the dispersion medium, functioning as a dispersant for the conductive material (B), suppressing the aggregation of the conductive material (B), and enabling it to exist stably in the thermoelectric conversion material.

<Active hydrogen group-containing monomer>
The active hydrogen group-containing monomer is not particularly limited as long as it has one or more active hydrogen groups per molecule. Examples of active hydrogen groups include hydroxyl groups, carboxyl groups, primary amino groups, secondary amino groups, and mercapto groups. Here, the term "primary amino group" refers to -NH ₂ (amino group), and the term "secondary amino group" refers to a group in which one hydrogen atom on a primary amino group is substituted with an organic residue such as an alkyl group. However, in this specification, the primary amino group and the secondary amino group in an acid amide are not considered to be active hydrogen groups. In addition, "-C(=O)-O-C(=O)-" (referred to as "acid anhydride group" in this specification), which is a group having a structure in which two carboxyl groups are dehydrated and condensed, is also considered to be an active hydrogen group in this specification, since it forms a carboxyl group by hydrolysis.

Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, polyhydroxy (meth)acrylates such as glycerol mono(meth)acrylate and trimethylolpropane mono(meth)acrylate, and others such as 2-hydroxy-3-phenoxypropyl acrylate and 4-hydroxyvinylbenzene. Other examples include caprolactone adducts (addition mole number 1 to 5) of the above hydroxyl group-containing monomers.

Examples of carboxyl group-containing monomers include unsaturated fatty acids such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxypropyl phthalate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl hexahydrophthalate, ethylene oxide-modified succinic acid (meth)acrylate, and carboxyl group-containing (meth)acrylate such as β-carboxyethyl (meth)acrylate. In addition, examples include acid anhydride group-containing monomers such as maleic anhydride, itaconic anhydride, and citraconic anhydride, which are polymers of the above hydroxyl group-containing monomers, and monofunctional alcohol adducts thereof.

Primary amino group-containing monomers include aminomethyl (meth)acrylate, aminoethyl (meth)acrylate, allylamine hydrochloride, dihydrogen allylamine phosphate, 2-isopropenylaniline, 3-vinylaniline, 4-vinylaniline, etc.

Secondary amino group-containing monomers include N-methylaminoethyl (meth)acrylate, N-ethylaminoethyl (meth)acrylate, and N-t-butylaminoethyl (meth)acrylate.

Examples of mercapto group-containing monomers include 2-(mercaptoacetoxy)ethyl acrylate and allyl mercaptan.

Among the active hydrogen group-containing monomers, hydroxyl group-containing monomers and carboxyl group-containing monomers are preferred from the viewpoints of availability of raw materials, ease of handling, affinity with the dispersion medium described below, and the like. As the hydroxyl group-containing monomer, hydroxyalkyl (meth)acrylate is preferred, hydroxyethyl (meth)acrylate is more preferred, and hydroxyethyl acrylate is even more preferred. As the carboxyl group-containing monomer, unsaturated fatty acid is preferred, (meth)acrylic acid is more preferred, and acrylic acid is even more preferred.

It is preferable that polymer (A) contains an active hydrogen group-containing monomer as a constituent unit. In addition, when polymer (A) contains an active hydrogen group-containing monomer as a constituent unit, it is preferable that the active hydrogen group-containing monomer contains a hydroxyl group-containing monomer and/or a carboxyl group-containing monomer. In this case, the total of the hydroxyl group-containing monomer and the carboxyl group-containing monomer is preferably contained in an amount of 1 to 25 mass% of the total monomer units constituting polymer (A), and more preferably 10 to 25 mass%. When contained in this range, it is expected that the affinity with conductive material (B) and the dispersion medium will be further increased, and the coating suitability will be further improved.

<Basic Monomer>
The basic monomer is a monomer having a basic group, provided that the basic monomer is a monomer other than the above-mentioned active hydrogen group-containing monomer.

For example, N,N-dialkylaminoalkyl (meth)acrylates such as N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate;
N,N-dialkyl(meth)acrylamides such as (meth)acrylamide, N,N-diethyl(meth)acrylamide, and N-isopropyl(meth)acrylamide;
Cyclic (meth)acrylamides such as acryloylmorpholine;
Heterocyclic aromatic amine-containing vinyl monomers such as 1-vinylpyridine, 4-vinylpyridine, 1-vinylimidazole, etc.;
N-substituted maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide;
etc.

Among the basic monomers, from the viewpoints of availability of raw materials, ease of handling, and affinity with the dispersion medium described below, N,N-dialkylaminoalkyl (meth)acrylate is preferred, dimethylaminoethyl (meth)acrylate and dimethylaminopropyl (meth)acrylate are more preferred, and dimethylaminoethyl acrylate is even more preferred.

<(Meth)acrylic acid alkyl ester>
Next, the (meth)acrylic acid alkyl ester will be described. In this specification, the term "(meth)acrylic acid alkyl ester" includes not only alkyl esters of (meth)acrylic acid, but also (meth)acrylic acid alkyl esters in which the alkyl group in the alkyl ester is substituted with an aromatic ring, a fluorine atom, an epoxy group, a silyl ether group, an alkylene glycol monoalkyl ether group, a cyclic polymerizable group, or the like. It also includes (meth)acrylic acid esters in which the alkyl group in the alkyl ester is substituted with an aliphatic cyclic hydrocarbon group such as a cycloalkyl group. However, the (meth)acrylic acid alkyl ester is a monomer other than the above-mentioned active hydrogen group-containing monomer and basic monomer.

For example, linear alkyl group-containing (meth)acrylic acid esters such as methyl (meth)acrylate and ethyl (meth)acrylate;
(meth)acrylic acid esters containing a branched alkyl group, such as 2-ethylhexyl (meth)acrylate and isostearyl (meth)acrylate;
(meth)acrylic acid esters containing an aliphatic cyclic hydrocarbon group, such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate;
(meth)acrylic acid alkyl esters substituted with an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate;
Fluorine atom-substituted (meth)acrylic acid alkyl esters, such as trifluoroethyl (meth)acrylate and tetrafluoropropyl (meth)acrylate;
Epoxy-substituted (meth)acrylic acid alkyl esters, such as glycidyl (meth)acrylate and (3-ethyloxetan-3-yl)methyl (meth)acrylate;
(Meth)acrylic acid alkyl esters substituted with a silyl ether group, such as 3-methacryloxypropylmethyldimethoxysilane;
(meth)acrylic acid alkyl esters substituted with an alkylene glycol monoalkyl ether group, such as 2-methoxyethyl (meth)acrylate and polyethylene glycol monomethyl ether (meth)acrylate;
Cyclopolymerizable monomers such as methyl 2-(allyloxymethyl)acrylate;
etc.

Among the (meth)acrylic acid alkyl esters, from the viewpoints of availability of raw materials, ease of handling, and affinity with the dispersion medium described below, linear or branched alkyl group-containing (meth)acrylic acid esters are preferred. As linear alkyl group-containing (meth)acrylic acid esters, ethyl (meth)acrylate, butyl (meth)acrylate, and lauryl (meth)acrylate are preferred, with ethyl acrylate, butyl acrylate, and lauryl acrylate being more preferred. As branched alkyl group-containing (meth)acrylic acid esters, 2-ethylhexyl (meth)acrylate is preferred, with 2-ethylhexyl acrylate being more preferred.

The polymer (A) may contain other monomers as constituent units other than the above monomers. Examples of the other monomers include:
Styrenes such as styrene and α-methylstyrene;
Vinyl ethers such as ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether;
vinyl fatty acid vinyl compounds such as vinyl acetate and vinyl propionate;
heterocyclic (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, 3-methyloxetanyl (meth)acrylate, etc.; and the like.

When producing the thermoelectric conversion material, a dispersion medium as described below can be used. When water is used as the dispersion medium, the monomer constituting polymer (A) preferably contains a carboxyl group-containing monomer, and when N-methylpyrrolidone (sometimes abbreviated as "NMP") is used as the dispersion medium, it preferably contains a hydroxyl group-containing monomer.

The method for producing the polymer (A) is not particularly limited, and may be any of, for example, solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, precipitation polymerization, etc., with solution polymerization or precipitation polymerization being preferred, and precipitation polymerization being most preferred. The polymer (A) obtained by the precipitation polymerization method can be quickly removed after polymerization from low molecular weight components and residual monomers that dissolve in the solvent used during polymerization, making it possible to narrowly control the molecular weight distribution, and the amount of residual monomers can be reduced as much as possible, making it possible to efficiently obtain a polymer (A) with a molecular weight that functions as a dispersant. As the polymerization reaction system, addition polymerization such as ionic polymerization, free radical polymerization, and living radical polymerization can be used, with free radical polymerization or living radical polymerization being preferred. In addition, as the radical polymerization initiator, a compound selected from peroxides, azo-based initiators, etc., or a mixture thereof can be used, and a molecular weight regulator such as a chain transfer agent may be used as necessary.

The polymer (A) contains 40% by mass or more and less than 100% by mass of units derived from (meth)acrylonitrile. It preferably contains 65% by mass or more and 95% by mass or less, and more preferably 75% by mass or more and 95% by mass or less. By containing units derived from (meth)acrylonitrile in the above range, it is possible to control the adsorptivity to the conductive material (B) and the affinity to the dispersion medium.

The molecular weight of the polymer (A), in terms of polystyrene equivalent weight average molecular weight, is preferably in the range of 3,000 to 500,000, more preferably in the range of 4,000 to 200,000, and even more preferably in the range of 5,000 to 50,000. By setting the weight average molecular weight within the above range, it is possible to obtain good adsorption to the conductive material (B) and good affinity to the dispersion medium.

When polymer (A) has a structure in which some of the monomer units derived from (meth)acrylonitrile are changed into a cyclic structure, the properties of the thermoelectric conversion material are further improved. When treated with alkali, the units derived from acrylonitrile are changed into a cyclic structure such as a hydrogenated naphthyridine ring. Although the detailed mechanism of this cyclization reaction is not clear, the properties of the thermoelectric conversion material are improved by having such a cyclic structure. This is presumably because the cyclic structure increases the adsorption of polymer (A) to conductive material (B), facilitating carrier transfer from polymer (A) to conductive material (B).

<Conductive Material (B)>
The conductive material (B) contributes to improving the electrical conductivity, and therefore, the electrical conductivity can be 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 having conductivity (such as a carbon material, a metal material, or a conductive polymer). For example, examples of the carbon material include graphite, carbon nanotubes, carbon black, and graphene (including graphene nanoplates).
Examples of metal materials include metal powders such as 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 ZnSe, CdS, InP, GaN, SiC, and SiGe. Examples of metal materials include fine particles coated with a material different from the core material, specifically, for example, silver-coated copper powder, which has a core material of copper and is coated with silver. Examples of metal oxide powders include 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 polystyrenesulfonic acid), polyaniline, polyacetylene, polypyrrole, polythiophene, and polyparaphenylene.
The conductive material may be used alone or in combination of two or more kinds.

The shape of the conductive material (B) is not particularly limited, and amorphous, aggregated, scaly, microcrystalline, spherical, flake, wire, etc. can be used as appropriate.

From the viewpoint of achieving both a high Seebeck coefficient and electrical conductivity, it is preferable that the material is at least one selected from the group consisting of carbon nanotubes, carbon black, and graphene (including graphene nanoplates), more preferably carbon nanotubes, and even more preferably single-walled carbon nanotubes.

Examples of carbon materials include flaky graphite, such as 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, and F manufactured by Nippon Graphite Industries Co., Ltd. Examples of the natural graphite 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 Chuetsu Graphite Co., Ltd., EC1500, EC1000, EC500, EC300, EC100, and EC50 manufactured by Ito Graphite Co., Ltd., and 10099M and PB-99 manufactured by Nishimura Graphite Co., Ltd. Examples of the spherical natural graphite include CGC-20, CGC-50, CGB-20, and CGB-50 manufactured by Nippon Graphite Co., Ltd. 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, and BSP-100A manufactured by Chuetsu Graphite Co., Ltd. K, WF-15C, and SEC Carbon's 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.

Commercially available 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 OCSiAl, and ZEONANO manufactured by Zeon Nano Technology Co., Ltd., FloTube 9000, FloTube 7000, and FloTube 2000 manufactured by CNano Corporation, NC7000 manufactured by Nanocyl Corporation, and 100T and 200P manufactured by Knano Corporation.

Examples of commercially available carbon black include Toka Black #4300, #4400, #4500, and #5500 manufactured by Tokai Carbon Co., Ltd., Printex L manufactured by Degussa Co., Ltd., and Raven 7000, 5750, 5250, 5000 ULTRA III, and 500 manufactured by Columbian Co., Ltd.
0ULTRA, Conductex SC ULTRA, Conductex 975 Examples of suitable blacks include furnace blacks such as ULTRA, PUERBLACK 100, 115, and 205, #2350, #2400B, #2600B, #3050B, #3030B, #3230B, #3350B, #3400B, and #5400B manufactured by Mitsubishi Chemical Corporation, MONARCH 1400, 1300, and 900, Vulcan XC-72R, and BlackPearls 2000 manufactured by Cabot Corporation, Ensaco 250G, Ensaco 260G, Ensaco 350G, and Super P-Li manufactured by TIMCAL Corporation, Ketjen blacks such as EC-300J and EC-600JD manufactured by Lion Corporation, and acetylene blacks such as Denka Black, Denka Black HS-100, and FX-35 manufactured by Denki Kagaku Kogyo Co., Ltd. These are not particularly limited.

The polymer (A) also contributes to the dispersion of the conductive material (B) in the thermoelectric conversion material and the improvement of the Seebeck coefficient. By increasing the content of the polymer (A), the dispersibility and the Seebeck coefficient can be improved, but generally, if the content of components other than the conductive material (B) is increased too much, the insulating property may also increase and the conductivity may decrease. The polymer (A) of the present invention has the characteristic that it can improve the dispersibility of the conductive material (B) and is unlikely to inhibit the conductive path in the material, but from the viewpoint of achieving both the Seebeck coefficient and the conductivity, the content of the polymer (A) is preferably 400% by mass or less, more preferably 200% by mass or less, even more preferably 120% by mass or less, and particularly preferably 100% by mass or less, relative to the total amount of the conductive material (B). In order to exert the effect of the polymer (A), the lower limit is preferably 5% by mass or more, more preferably 20% by mass or more.

In order to maintain the thermoelectric properties, it is preferable that the thermoelectric conversion material of the present invention does not contain a compound that generates radicals. The thermoelectric conversion material of the present invention preferably consists of only the polymer (A) and the conductive material (B), and if necessary, at least one selected from inorganic metal salts, inorganic bases, and organic bases, but may contain other components if necessary from the viewpoint of coating and film formation.

<Inorganic metal salts, inorganic bases, organic bases>
The thermoelectric conversion material of the present invention may contain an inorganic base, an inorganic metal salt, or an organic base. This improves the stability of the thermoelectric conversion material over time. For example, chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, borates, etc. of alkali metals or alkaline earth metals may be mentioned. The metal contained in the inorganic base and the inorganic metal salt may be a transition metal.

Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide.
Examples of the hydroxides of alkaline earth metals include calcium hydroxide and magnesium hydroxide.
Examples of the carbonate of an alkali metal include lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, and potassium hydrogen carbonate.
Examples of the carbonate of an alkaline earth metal include calcium carbonate and magnesium carbonate.

Of the above, from the viewpoint of easy supply of cations, chlorides, hydroxides, or carbonates of alkali metals or alkaline earth metals are preferred, hydroxides or carbonates of alkali metals or alkaline earth metals are more preferred, and hydroxides or carbonates of alkali metals are even more preferred. As hydroxides of alkali metals, lithium hydroxide and sodium hydroxide are preferred. As carbonates of alkali metals, lithium carbonate and sodium carbonate are preferred.

Organic bases include primary, secondary, or tertiary alkylamines having 1 to 40 carbon atoms.

Primary alkylamines having 1 to 40 carbon atoms include propylamine, butylamine, isobutylamine, octylamine, 2-ethylhexylamine, laurylamine, stearylamine, oleylamine, 2-aminoethanol, 3-aminopropanol, 3-ethoxypropylamine, 3-lauryloxypropylamine, etc.

Secondary alkylamines having 1 to 40 carbon atoms include dibutylamine, diisobutylamine, N-methylhexylamine, dioctylamine, distearylamine, and 2-methylaminoethanol.

Examples of tertiary alkylamines having 1 to 40 carbon atoms include triethylamine, tributylamine, N,N-dimethylbutylamine, N,N-diisopropylethylamine, dimethyloctylamine, trioctylamine, dimethyldecylamine, dimethyllaurylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dilaurylmonomethylamine, triethanolamine, and 2-(dimethylamino)ethanol.

Of these, primary, secondary or tertiary alkylamines having 1 to 30 carbon atoms are preferred, and primary, secondary or tertiary alkylamines having 1 to 20 carbon atoms are even more preferred.

As organic bases, compounds containing basic nitrogen atoms such as 1,8-diazabicyclo[5.4.0]undecene-7 (DBU), 1,5-diazabicyclo[4.3.0]nonene-5 (DBN), 1,4-diazabicyclo[2.2.2]octane (DABCO), tri-n-butylamine, dimethylbenzylamine, monoethanolamine, imidazole, and 1-methylimidazole may be used.

The amount of inorganic base, inorganic metal salt, and organic base to be blended is preferably 1 to 50% by mass relative to 100% by mass of polymer (A). Also, the amount is preferably 1 to 20% by mass, and more preferably 2 to 15% by mass, relative to 100% by mass of conductive material (B). Blending in appropriate amounts further improves dispersibility.

(Dispersion medium)
The dispersion medium can be used as a medium when mixing the polymer (A) and the conductive material (B), and can improve the applicability when printing or applying as an ink or paste. The dispersion medium that can be used is not particularly limited as long as it can dissolve or disperse the polymer (A) and the conductive material (B), and examples of the dispersion medium that can be used include organic solvents and water. Only one type of dispersion medium may be used, or two or more types may be used in combination.

Examples of organic solvents include alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol methyl ether, diethylene glycol methyl ether, terpineol, dihydroterpineol, 2,4-diethyl-1,5-pentanediol, 1,3-butylene glycol, isobornylcyclohexanol, ethylene glycol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, glycerin, polyethylene glycol, polypropylene glycol, trifluoroethanol, m-cresol, and thiodiglycol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, ethers such as tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether, hydrocarbons such as hexane, heptane, and octane, aromatics such as benzene, toluene, xylene, and cumene, esters such as ethyl acetate and butyl acetate, and N-methylpyrrolidone. These can be appropriately selected as needed.
From the viewpoint of dispersibility and solubility of the polymer (A) and the conductive material (B), N-methylpyrrolidone is particularly preferred.

(Auxiliary Agent)
Usable auxiliary agents are not particularly limited, and examples thereof include lactams, alcohols, aminoalcohols, carboxylic acids, acid anhydrides, ionic liquids, etc. Specific examples are as follows.
Lactams: pyrrolidone, caprolactam, N-methylcaprolactam, N-octylpyrrolidone, and the like.
Alcohols: sucrose, glucose, fructose, lactose, sorbitol, mannitol, xylitol, etc.
Amino alcohols: diethanolamine, triethanolamine, and the like.
Carboxylic acids: 2-furancarboxylic acid, 3-furancarboxylic acid, dichloroacetic acid, trifluoroacetic acid, and the like.
Acid anhydrides: acetic anhydride, propionic anhydride, acrylic anhydride, methacrylic anhydride, benzoic anhydride, succinic anhydride, maleic anhydride, itaconic anhydride, glutaric anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride (also known as cyclohexane-1,2-dicarboxylic anhydride), trimellitic anhydride, hexahydrotrimellitic anhydride, pyromellitic anhydride, himic anhydride, biphenyltetracarboxylic anhydride, 1,2,3,4-butanetetracarboxylic anhydride, naphthalenetetracarboxylic anhydride, and 9,9-fluorenylidenebisphthalic anhydride, etc. Copolymers of maleic anhydride and other vinyl monomers, such as styrene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, and alkyl vinyl ether-maleic anhydride copolymer.

The content of the auxiliary agent is preferably in the range of 0.1 to 30 mass %, more preferably in the range of 1 to 10 mass %, and even more preferably in the range of 1 to 5 mass %, based on the total mass of the thermoelectric conversion material. By making the content of the auxiliary agent 0.1 mass % or more, it is possible to easily obtain the effect of improving the electrical conductivity and thermoelectric properties. Furthermore, by making the content of the auxiliary agent 50 mass % or less, it is possible to suppress the deterioration of the film properties.

(resin)
The thermoelectric conversion material of the present invention may contain a resin to the extent that the electrical conductivity and thermal properties are not affected, for the purpose of adjusting the film-forming property and film strength, etc. However, the resin referred to in this specification is one other than the polymer (A).
The resin is not particularly limited as long as it is compatible with or disperses in each component of the thermoelectric conversion material, and examples thereof include polyurethane resin, polyester resin, polyester urethane resin, alkyd resin, butyral resin, acetal resin, polyamide resin, acrylic resin, styrene-acrylic resin, styrene resin, nitrocellulose, benzyl cellulose, cellulose (tri)acetate, casein, shellac, Gilsonite, gelatin, styrene-maleic anhydride resin, polybutadiene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinylidene fluoride resin, polyvinyl acetate resin, ethylene vinyl acetate resin, vinyl chloride/vinyl acetate copolymer resin, vinyl chloride/vinyl acetate copolymer resin, and vinyl chloride/vinyl acetate copolymer resin. Examples of the resins include ethylene/maleic acid copolymer resins, fluororesins, silicone resins, epoxy resins, phenoxy resins, phenolic resins, maleic acid resins, urea resins, melamine resins, benzoguanamine resins, ketone resins, petroleum resins, rosin, rosin esters, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, carboxymethyl ethyl cellulose, carboxymethyl nitro cellulose, ethylene/vinyl alcohol resins, and chlorinated polyurethane resins. These resins may be used alone or in combination of two or more. Copolymers of these resins may also be used.
Although there are no particular limitations, in one embodiment, polyurethane resin, polyether resin, acrylic resin, and acrylamide resin are preferable.

When a resin is contained, from the viewpoint of electrical conductivity, the content of the resin is preferably 99% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, based on the total amount of the polymer (A) and the conductive material (B).

(Inorganic thermoelectric conversion materials)
The thermoelectric conversion material of the present invention may contain an inorganic thermoelectric conversion material as necessary in order to improve the thermoelectric conversion performance. The inorganic thermoelectric conversion material is not particularly limited, and any material generally known as a thermoelectric conversion material can be used. For example, Bi-(Te,Se)-based, Si-Ge-based, Mg-Si-based, Pb-Te-based, GeTe-AgSbTe-based, (Co,Ir,Ru)-Sb-based, (Ca,Sr,Bi) _{Co2O5 -} based, etc. can be mentioned. More specifically, _Bi2Te3 , _PbTe , _AgSbTe2 , GeTe, _Sb2Te3 , _{NaCo2O4 , CaCoO3} , _SrTiO3 , _ZnO , SiGe, _{Mg2Si ,} FeSi2 _{, Ba8Si46} , _MnSi1.73 , ZnSb, _Zn4Sb3 , _GeFe3CoSb12 , _LaFe3CoSb12 , etc. may be mentioned. In this case, impurities may be added to the inorganic thermoelectric conversion material to control _the polarity (p-type, n _{- type} ) and electrical conductivity. When using an inorganic thermoelectric conversion material, the amount of the inorganic thermoelectric conversion material is adjusted within a range that does not affect the film forming property or film strength.

The method for producing the thermoelectric conversion material of the present invention is not particularly limited, and can be produced, for example, by stirring and mixing the polymer (A) and the conductive material (B), or the polymer (A), the conductive material (B) and at least one selected from the group consisting of inorganic metal salts, inorganic bases, and organic bases, with a dispersion medium and, if necessary, other optional components. The stirring and mixing machine is not particularly limited, and examples thereof include a disperser, a mixer, a kneader, a scandex, a paint conditioner, a sand mill, a mortar and pestle machine, a media-less disperser, a three-roll mill, and a bead mill.

<Thermoelectric conversion element>
The thermoelectric conversion element of the present invention has a thermoelectric conversion film formed using the thermoelectric conversion material and electrodes, and the thermoelectric conversion film and the electrodes are electrically connected. The thermoelectric conversion film of the present invention 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 produced.

The thermoelectric conversion film may be a film obtained by applying a thermoelectric conversion material onto a substrate. Since the thermoelectric conversion material has excellent moldability, it is easy to obtain a good film by application or printing. There are no particular limitations on the method for producing the thermoelectric conversion film as long as the desired thermoelectric conversion film can be obtained, and the method can be appropriately selected depending on the properties of the thermoelectric conversion material, such as viscosity, and the required film thickness, area, shape, and other conditions. Examples of methods include 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.

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, and thermoelectric properties, but as described below, it is preferable that the film is formed to have a certain thickness or more so that a temperature difference can be generated and transmitted in the thickness direction or surface direction of the thermoelectric conversion film. From the viewpoint of thermoelectric properties and flexibility, the film 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.

The substrate is not particularly limited, but examples include nonwoven fabric, paper, plastic films made of materials such as polyethylene, polyethylene terephthalate (PET), polyethylene naphthalate, polyethersulfone, polypropylene, polyimide, polycarbonate, and cellulose triacetate, and glass. These substrates may have an aluminum deposition layer or a barrier layer on the substrate surface to prevent deterioration of the thermoelectric conversion material due to the effects of water and oxygen.

In order to improve the adhesion between the substrate and the thermoelectric conversion film, various treatments can be performed on the substrate surface. Specifically, prior to application of the thermoelectric conversion material, UV ozone treatment, corona treatment, plasma treatment, or easy-adhesion treatment can be performed.

The thermoelectric conversion film of the present invention may be a laminated film of a substrate in which the thermoelectric conversion film is formed on the substrate as described above, or may be a free-standing film without a substrate. When a free-standing film is to be formed, there is no particular restriction, but it can be obtained, for example, by forming a thermoelectric conversion film on a release sheet and then removing the release coat.

Examples of release sheets include plastic films such as polyester film, polyethylene film, polypropylene film, and polyimide film that have been subjected to a release treatment.

The thermoelectric conversion element according to the embodiment of the present invention can be constructed by applying techniques well known in the art, except that it is constructed using the above-mentioned thermoelectric conversion material. A more specific configuration of the thermoelectric conversion element and its manufacturing method will be described below.

In a thermoelectric conversion element, the thermoelectric conversion film and the electrodes are electrically connected. Here, "electrically connected" means that they are joined together or can conduct electricity through other components such as wires.

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

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, or application of a paste in which fine particles of the electrode material are dispersed. From the viewpoint of process simplicity, methods using thermocompression bonding of an electrode material foil or a film having an electrode material film, or application of a paste in which the electrode material is dispersed are preferred.

Typical examples of the structure of a thermoelectric conversion element 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. For example, a thermoelectric conversion element having the structure (1) above can be obtained 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. In this way, a thermoelectric conversion element in which electrodes are formed on both ends of the thermoelectric conversion film can easily increase the distance between the two electrodes. Therefore, it is easy to generate a large temperature difference between the two electrodes and perform efficient thermoelectric conversion.

A thermoelectric conversion element having the structure of (2) above can be obtained, for example, by applying silver paste onto 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 on top of that to form a second electrode. In this way, a thermoelectric conversion element in which the thermoelectric conversion film of the present invention is sandwiched between two electrodes can utilize the temperature difference in the film thickness direction of the thermoelectric conversion film, i.e., in the direction perpendicular to the substrate, and can 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 of (2) above, it is also possible to ensure a temperature difference by increasing the film thickness to increase the distance between the two electrodes.

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 two or more thermoelectric conversion elements connected together. According to the present invention, the thermoelectric conversion element has excellent flexibility, so that it can be well installed even on a heat source that is not flat.

Thermoelectric conversion element may have a heat absorption layer or heat storage layer to efficiently transfer heat from the heat source, and may also have a heat insulation layer or heat dissipation layer to ensure a temperature difference. Furthermore, depending on the application and the amount of power required, the extracted electricity can be boosted using a boost circuit, or the extracted electrical energy can be temporarily stored in a capacitor, a secondary battery, etc. for use.

The present invention will be explained in more detail below using experimental examples, but the present invention is not limited to these examples. In the examples, "parts" means "parts by mass" and "%" means "% by mass." Also, "NMP" refers to N-methylpyrrolidone.

(Method of measuring weight average molecular weight (Mw))
The weight average molecular weight (Mw) was measured by gel permeation chromatography (GPC) equipped with an RI detector. The apparatus used was HLC-8320GPC (manufactured by Tosoh Corporation), and three separation columns were connected in series. The packing materials were Tosoh Corporation's "TSK-GELSUPERAW-4000", "AW-3000" and "AW-2500", respectively. The oven temperature was 40°C, and an N,N-dimethylformamide solution of 30 mM triethylamine and 10 mM LiBr was used as the eluent, and the measurement was performed 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 above eluent, and 20 μL was injected. The molecular weight is a polystyrene equivalent value.

<Production of Polymer (A)>
(Production Example 1)
(Production of Polymer (A-1))
A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer was charged with 100 parts of acetonitrile and substituted with nitrogen gas. The reaction vessel was heated to 70°C, and a mixture consisting of 50 parts of acrylonitrile, 25 parts of acrylic acid, 25 parts of styrene, 2 parts of 3-mercapto-1,2-propanediol, and 0.4 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (NOF Corp.: V-65) was dropped into the reaction vessel over 3 hours to carry out a polymerization reaction. After the dropwise addition, the reaction was carried out at 70°C for 1 hour, and then 0.1 parts of V-65 was added, and the reaction was continued at 70°C for another 1 hour. Thereafter, it was confirmed that the conversion rate exceeded 98% by measuring the nonvolatile content. The product was filtered out by vacuum filtration, washed with 100 parts of acetonitrile, and the solvent was completely removed by vacuum drying to obtain a polymer (A-1). The Mw of the polymer (A-1) was 15,000.

(Production Examples 2 to 18)
(Production of Polymers (A-2) to (A-18))
Polymers (A-2) to (A-18) were produced in the same manner as in Production Example 1, except that the type and amount of monomers were changed as shown in Table 1. The Mw of each polymer is shown in Table 1. In the synthesis of polymers (A-2) to (A-18), the Mw was adjusted by adding a chain transfer agent, adjusting the amount of polymerization initiator, and appropriately changing the reaction conditions, etc. As the chain transfer agent, 3-mercapto-1,2-propanediol was used. In Table 1, the numerical values represent "parts", and blanks mean that no compound was added. The abbreviations in Table 1 are shown below.
AA: Acrylic acid HEA: Hydroxyethyl acrylate DMAEA: Dimethylaminoethyl acrylate BA: Butyl acrylate 2EHA: 2-Ethylhexyl acrylate LA: Lauryl acrylate

(Production Example 19)
(Production of Polymer (A-19))
50 parts of the polymer (A-3) obtained in Production Example 3 was added to 198 parts of water and stirred with a disperser to form a slurry. Then, 2 parts of a 1N aqueous sodium hydroxide solution was added dropwise at 25° C., and the mixture was stirred with a disperser for 2 hours. It was confirmed that a part of the monomer units derived from acrylonitrile was changed to a cyclic structure by a decrease in the absorption peak (2230 cm ⁻¹ ) derived from the cyano group in the IR spectrum and an increase in two absorption peaks at 300 nm and 380 nm derived from the cyclization of the cyano group in the UV spectrum. Then, the mixture was washed with water, filtered, and dried to obtain a polymer (A-19). The weight average molecular weight (Mw) of the polymer (A-19) was 14,000.

(Manufacture Example 20)
(Production of Polymer (A-20))
A polymer (A-20) having a hydrogenated naphthyridine ring was obtained in the same manner as in Production Example 19, except that the polymer (A-3) was replaced with the polymer (A-7). The weight average molecular weight (Mw) was 14,000.

<Production of Dispersion Containing Thermoelectric Conversion Material>
[Example 1]
(Dispersion 1)
0.1 parts of polymer (A), 0.4 parts of GNP (graphene nanoplate "xGNP-M-5" manufactured by XG Sciences), and 79.5 parts of NMP were weighed and mixed. Beads were further added, and the mixture was shaken with Scandex for 4 hours, and then filtered to remove the beads, to obtain a dispersion liquid 1 of a thermoelectric conversion material.

[Examples 2 to 25, Comparative Examples 1 to 4]
(Dispersions 2 to 25, Dispersions 101 to 104)
Thermoelectric conversion material dispersions 2 to 25 and dispersions 101 to 104 were obtained in the same manner as dispersion 1, except that the types and amounts of materials were changed as shown in Table 2.

The materials listed in Table 2 are as follows:
Conductive material (B)
GNP (Graphene nanoplatelets "xGNP-M-5" manufactured by XGSciences)
CB (Ketjen Black "EC-300J" manufactured by Lion Corporation)
Graphite (expanded graphite SMF manufactured by Chuetsu Graphite Co., Ltd.)
MWCNT (Kumho Petrochemical's multi-walled carbon nanotube "Knanos100P")
SWCNT (OCSiAl's single-walled carbon nanotube "TUBALL")
PEDOT/PSS (Heraeus "Clevios PH1000")
PVP: Nippon Catalyst, Polyvinylpyrrolidone K-30, 100% non-volatile content
PVA: Kuraray POVAL PVA403, non-volatile content 100%

<Evaluation of Thermoelectric Conversion Materials>
The obtained dispersions 1 to 25 and dispersions 101 to 104 were applied to a 75 μm thick PET film, which was a sheet-like substrate, using an applicator, and then dried at 120° C. for 30 minutes to obtain a laminate having a thermoelectric conversion film with a thickness of 5 μm. The coating suitability when the dispersion was applied to the substrate was evaluated according to the method shown below. In addition, the conductivity (electrical conductivity) and Seebeck coefficient of the obtained laminate having a thermoelectric conversion film (hereinafter also referred to as a coating film) were evaluated according to the method shown below. The results are shown in Table 2.

(Conductivity (Resistivity))
The obtained laminate was cut into a size of 2.5 cm x 5 cm, and the electrical conductivity was measured by a four-probe method using a Lores et al. GX MCP-T700 (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) in accordance with JIS-K7194. The electrical conductivity is shown in Table 2 as a relative value when the electrical conductivity of Comparative Example 1 was set to 1.0.

(Seebeck coefficient)
The obtained 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. When the absolute value of the Seebeck coefficient of Comparative Example 1 was set to 1.00, the relative values to the absolute value of the Seebeck coefficient in each Example are shown in Table 2.

(Coating suitability)
The coatability of the dispersion was evaluated using a grind gauge (groove depth 50 μm).
◎: No streaks or coarse particles of 10 μm or more (very good)
◯: Although there are streaks or coarse particles caused by coarse particles of 10 μm or more, there are no streaks or coarse particles caused by coarse particles of 20 μm or more (good).
△: Streaks or coarse particles of 20 μm or more are present, but streaks or coarse particles of 30 μm or more are not present (usable)
×: Streaks or coarse particles of 30 μm or more are present (unusable)

As shown in Table 2, the thermoelectric conversion material of the present invention exhibited high electrical conductivity and Seebeck coefficient. Furthermore, all dispersions containing the thermoelectric conversion material of the present invention exhibited good coating suitability (coating film state). This is because the improved dispersibility led to good formation of conductive paths in the thermoelectric conversion material, which promoted carrier transfer efficiency and made it possible to achieve both high electrical conductivity and a high Seebeck coefficient.

<Manufacture of Thermoelectric Conversion Element>
The above dispersions were applied onto a PET film having a thickness of 50 μm, and five thermoelectric conversion layers each having a thickness of 20 μm and a shape of 5 mm × 30 mm were prepared at intervals of 10 mm. Next, four silver circuits (electrodes) having a thickness of 10 μm and a shape of 5 mm × 33 mm were prepared using silver paste so that each thermoelectric conversion layer was connected in series, and thermoelectric conversion elements were manufactured. As the above silver paste, REXALPHA RA-FS 074 manufactured by Toyo Ink Co., Ltd. was used. When the electromotive force of each thermoelectric conversion element was measured, it was confirmed that the thermoelectric conversion elements manufactured using the dispersions manufactured in Examples 1 to 25 had a superior electromotive force to the thermoelectric conversion elements manufactured using the dispersions manufactured in Comparative Examples 101 to 104.

The thermoelectric conversion material according to an embodiment of the present invention has both electrical conductivity and a Seebeck coefficient, and also has excellent thermoelectric properties, so that the above material can be used to provide a high-performance thermoelectric conversion element.

1: Substrate 2: Thermoelectric conversion film 3: Circuit 10: Test sample of thermoelectric conversion element 20: Hot plate

Claims (5)

A thermoelectric conversion material comprising a polymer (A) and a conductive material (B),
The polymer (A) is a copolymer containing monomer units derived from (meth)acrylonitrile and an active hydrogen group-containing monomer, the active hydrogen group-containing monomer units containing monomer units derived from a hydroxyl group-containing monomer and/or a carboxyl group-containing monomer, and containing 40 mass% or more and less than 100 mass% of monomer units derived from (meth)acrylonitrile,
A thermoelectric conversion material, characterized in that the conductive material (B) contains a carbon material and/or a conductive polymer. The thermoelectric conversion material according to claim 1 , characterized in that the polymer (A) contains 1 to 25 mass% in total of monomer units derived from a hydroxyl group-containing monomer and monomer units derived from a carboxyl group-containing monomer. The thermoelectric conversion material according to claim 1 or 2, further comprising at least one selected from the group consisting of inorganic metal salts, inorganic bases, and organic bases. 2. The thermoelectric conversion material according to claim 1 , wherein the content of the polymer (A) is 5 to 100 mass % based on the total amount of the conductive material (B). A thermoelectric conversion element comprising a thermoelectric conversion film comprising the thermoelectric conversion material according to any one of claims 1 to 4 and electrodes, the thermoelectric conversion film and the electrodes being electrically connected to each other.

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