JP7459466B2 - Dispersions and coatings for thermoelectric conversion - Google Patents

Description

The present invention relates to a dispersion for thermoelectric conversion and a coating film thereof.

In recent years, thermoelectric power generation, which uses temperature differences caused by waste heat to generate electricity using thermoelectric conversion elements, has been attracting attention, and its application to automobiles, industrial machinery, electronic equipment, etc. is progressing. A thermoelectric conversion element converts a temperature difference generated between both ends of the element into electric power using the Seebeck effect. The figure of merit of thermoelectric conversion is expressed as Z=S2σκ−1 using Seebeck coefficient S, electrical conductivity σ, and thermal conductivity κ. Furthermore, a power factor PF (=S ² ·σ) may be used. That is, there is a need for a thermoelectric semiconductor material that has a high Seebeck coefficient S, a high electrical conductivity σ, and a low thermal conductivity κ.

As described in Non-Patent Document 1, the Seebeck coefficient S and the electrical conductivity σ are expressed by the following formula.
S=k _B /e(−log n/n 0 + δ) (Equation 1)
σ is σ=Nneμ (Equation 2)
Here, _kB is the Boltzmann constant, e is the Napier's number, n is the carrier density, n0 is the optimum carrier density, δ is a constant with a magnitude of about 1, N is the number of valleys, and μ is the mobility. When the carrier density n, which is common to both, is increased, the electrical conductivity σ is improved, but the Seebeck coefficient S is reduced, and this trade-off is an issue.

For example, Patent Document 1 discloses that a film is formed from a chloroform dispersion of poly(2-butoxy-5-methoxy-1,4-phenylenevinylene), which is a type of conductive polymer, and the film is doped with iodine. A thermoelectric conversion material and a thermoelectric conversion element obtained by the method are disclosed. However, since the carrier density is improved by adding a dopant to the dispersion after the film is formed, the electrical conductivity is improved, but there is a problem in that the Seebeck coefficient is low.

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

Japanese Patent Application Publication No. 2003-332639

The problem to be solved by the present invention is to provide a thermoelectric conversion dispersion liquid and a coating film thereof for forming a thermoelectric conversion element that can achieve both a high Seebeck coefficient and high electrical conductivity.

The present inventors have conducted extensive research to solve the above problems, and as a result, have arrived at the present invention. That is, the present invention provides a dispersion liquid for thermoelectric conversion comprising a thermoelectric conversion material and a dispersion medium, and when the nonvolatile content concentration in the dispersion liquid is 0.5% by mass, In the measurement, the dispersion for thermoelectric conversion satisfies 0.2≦A≦10, where A (/mm) is the attenuation rate of the dispersion at 20 MHz.

The present invention also relates to the above-mentioned dispersion for thermoelectric conversion, which satisfies 2≦A/B≦20 when the nonvolatile content in the dispersion is 0.5% by mass in measurement with an ultrasonic particle size distribution analyzer and the attenuation rate of the dispersion at 10 MHz is B (/mm).

The present invention also relates to the above-mentioned dispersion for thermoelectric conversion, which further contains a dispersant.

The present invention also relates to the above-mentioned thermoelectric conversion ink, in which the thermoelectric conversion material contains carbon nanotubes.

The present invention also relates to a coating film of the above dispersion for thermoelectric conversion.

The present invention makes it possible to provide a thermoelectric conversion dispersion and a coating film thereof for forming a thermoelectric conversion element that can achieve both a high Seebeck coefficient and high electrical conductivity.

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated concretely.
The dispersion liquid for thermoelectric conversion of the present invention is a dispersion liquid for thermoelectric conversion comprising a thermoelectric conversion material and a dispersion medium, and when the nonvolatile content concentration in the dispersion liquid is 0.5% by mass, ultrasonic wave When the attenuation rate of the dispersion liquid at 20 MHz is A (/mm) in measurement using a particle size distribution meter, the dispersion liquid for thermoelectric conversion satisfies 0.2≦A≦10. By manufacturing a thermoelectric conversion element using a dispersion liquid having such a predetermined attenuation rate, a thermoelectric conversion element that exhibits excellent thermoelectric conversion performance that has both Seebeck coefficient and conductivity and exhibits a high power factor can be produced. We discovered that it can be manufactured.

<Thermoelectric conversion materials>
The thermoelectric conversion material is not particularly limited as long as it exhibits the Seebeck effect and can be used as a thermoelectric material, but examples thereof include inorganic thermoelectric conversion materials, organic low molecular weight materials, organic conductive materials such as conductive polymers and polymer composite materials, and carbon materials. Carbon materials are preferred from the viewpoint of durability and elasticity. From the viewpoint of achieving both the Seebeck coefficient and the electrical conductivity, the carbon material is preferably at least one selected from the group consisting of carbon nanotubes, carbon black, and graphene (including graphene nanoplates), more preferably carbon nanotubes, and particularly preferably single-walled carbon nanotubes.

Inorganic thermoelectric conversion materials are not particularly limited as long as they have thermoelectric conversion ability, but examples include zinc oxide, tin oxide, strontium titanate, barium titanate, (Zn, Al)O, NaCo ₂ O ₄ , Ca ₃ Metal oxides and sulfides such as Co ₄ O ₉ , Bi ₂ Sr ₂ Co ₂ Oy, and silver sulfide; Bi, Sb, Ag, Pb, Ge, Cu, Sn, As, Se, Te, Fe, Mn, Examples include metal element composite materials containing at least two or more elements selected from Co and Si. Suitable examples of metal element composite materials include BiTe-based, BiSb-based, BiSbTe-based, BiSbSe-based, CoSb-based, PbTe-based, TeSe-based, and SiGe-based materials, and magnesium silicide-based materials (Mg ₂ Si-based materials). can be mentioned.

The conductive polymer is not particularly limited, and examples thereof include polyaniline conductive polymer, polypyrrole conductive polymer, polythiophene conductive polymer, polyacetylene conductive polymer, polyphenylene conductive polymer, and polyphenylene vinylene conductive polymer. Examples include conductive polymers, polyaniline conductive polymers, polyacene conductive polymers, polythiophene vinylene conductive polymers, and copolymers thereof. From the viewpoint of stability in air, polyaniline-based conductive polymers, polypyrrole-based conductive polymers, and polythiophene-based conductive polymers are preferred, and from the viewpoint of conductivity, polythiophene-based conductive polymers are more preferred. The conductive polymers can be used alone or in combination of two or more.

Examples of polyaniline-based conductive polymers include polyaniline, poly(2-methylaniline), poly(3-isobutylaniline), poly(2-aniline sulfonic acid), poly(3-aniline sulfonic acid), and the like.

Examples of polypyrrole-based conductive polymers include polypyrrole, poly(N-methylpyrrole), poly(3-methylpyrrole), poly(3-ethylpyrrole), poly(3-n-propylpyrrole), poly(3-butylpyrrole), poly(3-octylpyrrole), poly(3-decylpyrrole), poly(3-dodecylpyrrole), poly(3,4-dimethylpyrrole), poly(3,4-dibutylpyrrole), poly(3-carboxypyrrole), poly(3-methyl-4-carboxypyrrole), poly(3-methyl-4-carboxyethylpyrrole), poly(3-methyl-4-carboxybutylpyrrole), poly(3-hydroxypyrrole), poly(3-methoxypyrrole), poly(3-ethoxypyrrole), poly(3-butoxypyrrole), poly(3-hexyloxypyrrole), and poly(3-methyl-4-hexyloxypyrrole).

Polythiophene-based conductive polymers include polythiophene, poly(3-methylthiophene), poly(3-ethylthiophene, poly(3-propylthiophene), poly(3-butylthiophene), poly(3-hexylthiophene), poly(3-heptylthiophene), poly(3-octylthiophene), poly(3-decylthiophene), poly(3-dodecylthiophene), poly(3-octadecylthiophene), poly(3-bromothiophene), poly(3-chlorothiophene), poly(3-iodothiophene), poly(3-cyanothiophene), poly(3-phenylthiophene), poly(3,4-dimethylthiophene), poly(3,4-dibutylthiophene), and poly(3-hydrothiophene). poly(3-methoxythiophene), poly(3-ethoxythiophene), poly(3-butoxythiophene), poly(3-hexyloxythiophene), poly(3-heptyloxythiophene), poly(3-octyloxythiophene), poly(3-decyloxythiophene), poly(3-dodecyloxythiophene), poly(3-octadecyloxythiophene), poly(3,4-dihydroxythiophene), poly(3,4-dimethoxythiophene), poly(3,4-diethoxythiophene), poly(3,4-dipropoxythiophene), poly(3,4-dibutoxythiophene), poly(3,4-dihexyloxythiophene), poly(3,4-diheptyloxythiophene), oxythiophene), poly(3,4-dioctyloxythiophene), poly(3,4-didecyloxythiophene), poly(3,4-didodecyloxythiophene), poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), poly(3,4-butylenedioxythiophene), poly(3-methyl-4-methoxythiophene), poly(3-methyl-4-ethoxythiophene), poly(3-carboxythiophene), poly(3-methyl-4-carboxythiophene), poly(3-methyl-4-carboxyethylthiophene), poly(3-methyl-4-carboxybutylthiophene), poly(2,3-dihydrothieno[3,4-b]-[1,4] dioxepin-3-yloxy]-1-propanesulfonic acid sodium salt), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-propanesulfonic acid potassium salt), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-methyl-1-propanesulfonic acid sodium salt), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-ethyl-1-propanesulfonic acid sodium salt), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-propyl-1-propanesulfonic acid sodium salt), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-butyl-1-propanesulfonate), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-pentyl-1-propanesulfonate), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-hexyl-1-propanesulfonate), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-isopropyl-1-propanesulfonate), poly(3-[( sodium 2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-isobutyl-1-propanesulfonate), poly(3-[(sodium 2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-isopentyl-1-propanesulfonate), poly(3-[(sodium 2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-fluoro-1-propanesulfonate), poly(3-[(potassium 2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-methyl-1-propanesulfonate), poly(3-[(potassium 2,3-dihydrothieno[3,4-b ]-[1,4]dioxepin-3-yloxy]-1-methyl-1-propanesulfonic acid), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-methyl-1-propanesulfonic acid ammonium), poly(3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-methyl-1-propanesulfonic acid triethylammonium), poly(4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-butanesulfonic acid sodium), poly(4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-methyl-1-propanesulfonic acid butanesulfonate), poly(4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-methyl-1-butanesulfonate sodium), poly(4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-methyl-1-butanesulfonate potassium), poly(4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-fluoro-1-butanesulfonate sodium), or poly(4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxepin-3-yloxy]-1-fluoro-1-butanesulfonate potassium).

In addition to the above-mentioned carbon materials, examples of flaky 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, and LEP manufactured by Nippon Graphite Industries Co., Ltd. , F#1, F#2, F#3, BF-3AK, FBF, BF-15AK, CBR, CPB-6S, CPB-3, 96L, 96L-3, K-3, SC-120, SC-60, HLP, CP-150, SB-1 manufactured by Chuetsu Graphite Co., Ltd., EC1500, EC1000, EC500, EC300, EC100, EC50 manufactured by Ito Graphite Co., Ltd., 10099M, 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 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.

Examples of commercially available carbon black include Tokai Carbon's Toka Black #4300, #4400, #4500, and #5500; Degussa's Printex L; and Colombian's Raven 7000, 5750, 5250, 5000 ULTRA III, 5000 ULTRA, Conductex SC ULTRA, and 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.

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 Corporation, 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. From the viewpoint of electrical conductivity, TUBALL manufactured by OcSiAl Corporation is particularly preferred.

These carbon materials may be modified by introducing substituents as necessary, or may be used in the presence of a compound capable of promoting charge transfer. Further, from the viewpoint of thermoelectric properties, the content of the thermoelectric conversion material in the dispersion is 30 to 100% by mass, preferably 40 to 85% by mass, based on nonvolatile components.

<Dispersion medium>
The dispersion medium used in the present invention is used to dissolve or disperse the thermoelectric conversion material, and makes it possible to improve coating properties by forming it into an ink. The dispersion medium that can be used is not particularly limited as long as the thermoelectric conversion material can be dissolved or dispersed well, and examples thereof include organic solvents and water, and 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, and diethylene glycol methyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; tetrahydrofuran, dioxane, and ethylene glycol dimethyl ether; Ethers such as diethylene glycol dimethyl ether, hydrocarbons such as hexane, heptane, octane, aromatics such as benzene, toluene, xylene, cumene, esters such as ethyl acetate, butyl acetate, terpineol, dihydroterpineol, 2,4- It can be appropriately selected from diethyl-1,5-pentanediol, 1,3-butylene glycol, isobornylcyclohexanol, N-methylpyrrolidone, etc. as required. As the solvent for dispersing the thermoelectric conversion material, N-methylpyrrolidone is particularly preferred from the viewpoint of solubility and dispersibility.

<Other ingredients>
From the viewpoint of improving the characteristics of the thermoelectric conversion element, in addition to the thermoelectric conversion material and the dispersion medium, other components may be contained, such as a dispersant, a semiconductor, an antioxidant, a leveling agent, a resin, etc. From the viewpoint of electrical conductivity, the concentration of the other components in the non-volatile content is preferably 60 mass % or less, more preferably 50 mass % or less.

(Dispersant)
The dispersant is used to uniformly disperse inorganic or organic materials in a medium to prepare a stable dispersion, which enables further improvement in coatability, electrical conductivity, and thermoelectric properties. The type of dispersant is not particularly limited, and any conventionally known dispersant used for dispersing thermoelectric conversion materials can be used. The dispersant may be used alone or in combination of two or more types.

Examples of dispersants include acidic dispersants, basic dispersants, amphoteric dispersants, and nonionic dispersants. Examples of the acidic functional groups of acidic dispersants include carboxylic acid groups, sulfonic acid groups, and phosphoric acid groups. Examples of the polar functional groups of basic dispersants include primary amino groups, secondary amino groups, tertiary amino groups, and quaternary ammonium base groups. Examples of the nonionic functional groups of nonionic dispersants include hydroxyl groups, amide groups, ketone groups, epoxy groups, and ester groups.

Examples of commercially available basic dispersants include SOLSPERSE-9000, 11200, 13240, 13650, 13940, 16000, 17000, 18000, 20000, 22000, 24000, 24000SC, 24000GR, 26000, 28000, 32000, 32500, 32550, 32600, 33000, 34750, 35100, 35200, 37500, 38500, 39000, 53095, 56000, 71000, 76500, and X300 manufactured by Lubrizol Japan Co., Ltd., and DISPERBYK-108, 109, 112, 116, 118, and 120 manufactured by BYK Japan Co., Ltd. 30, 161, 162, 163, 164, 166, 167, 168, 182, 183, 184, 185, 2000, 2008, 2009, 2022, 2050, 2150, 2155, 2163, 2164, 9077, 101, 106, 140, 142, 145, 180, 2001, 2020, 2025 , 2070, 9076, etc., Ajinomoto Fine-Techno Co., Ltd.'s Ajisper PB821, PB822, PB824, PB881, etc., and BASF's EFKA-4015, 4020, 4046, 4047, 4050, 4055, 4080, 4300, 4330, 4400, 4401, 4402, etc.

Examples of commercially available acidic dispersants include SOLSPERSE-3000, 5000, 21000, 36000, 36600, 41000, 41090, 43000, 44000, 46000, 47000, and 55000 manufactured by Lubrizol Japan, DISPERBYK-102, 110, 111, 170, 171, 174, P104, P104S, P105, and 220S manufactured by BYK Japan, and AJISPER PA111 manufactured by Ajinomoto Fine-Techno Co., Ltd.

Examples of commercially available nonionic dispersants include SOLSPERSE-27000 and 54000 manufactured by Nippon Lubrizol.

The dispersant may be either a low molecule or a polymer, but in order not to inhibit the conductive path of the carbon material, it is preferably a low molecule, more preferably has a molecular weight of 100 or more and 1,000 or less, particularly preferably is 200 or more and 600 or less. It is preferable that the molecular weight of the dispersant is 100 or more and 1,000 or less because it can be dispersed by only partially adsorbing on the surface of the carbon material and high conductivity can be efficiently exhibited. In addition, when a dispersant is a polymer, let the value of mass average molecular weight (Mw) be molecular weight. Furthermore, an organic dye derivative or a triazine derivative may be used as a dispersant.

From the viewpoint of dispersibility, the content of the dispersant is preferably 5 to 200% by mass, more preferably 10 to 150% by mass, and 20 to 80% by mass based on the total amount of the thermoelectric conversion material. % is more preferable. When the content is 5 to 200% by mass, the dispersion stability of the thermoelectric conversion material over time improves.

(semiconductor)
The semiconductor is not particularly limited as long as it is a known semiconductor, and is used for improving the Seebeck coefficient. The Seebeck coefficient can be improved by increasing the content of semiconductor, but if the content is increased too much, the insulation properties may increase and the conductivity may decrease. The upper limit is preferably 400% by mass or less, more preferably 200% by mass or less, even more preferably 120% by mass or less, particularly preferably 100% by mass or less, based on the total amount of the thermoelectric conversion material. The semiconductors may be used alone or in combination of two or more. Moreover, the lower limit is preferably 25% by mass or more. Within the above content range, the Seebeck coefficient and dispersion stability over time are improved.

The method for producing the thermoelectric conversion dispersion liquid is not particularly limited as long as a thermoelectric conversion dispersion liquid that satisfies the conditions of the present invention is obtained, and can be appropriately selected. For example, it can be obtained by mixing a thermoelectric conversion material, a dispersion medium, and other components as necessary, and then dispersing the mixture using a disperser or ultrasonic waves. There are no particular restrictions on the dispersion machine; for example, kneaders, attritors, ball mills, sand mills using glass beads or zirconia beads, media dispersion machines such as Scandex, Eiger mills, paint conditioners, paint shakers, colloid mills, etc. can be used. can do.

<Attenuation rate>
The attenuation rate in the present invention represents the value of an ultrasonic attenuation spectrum in an ultrasonic particle size distribution system. Let A (/mm) be the attenuation rate at 20 MHz, B (/mm) be the attenuation rate at 10 MHz, and let this ratio be A/B.

In the ultrasonic attenuation method, when a suspension is irradiated with ultrasonic waves, the particles in the suspension move relative to the solvent, and the attenuation rate of the acoustic energy caused by this movement is calculated as In this method, the particle size distribution is determined from the characteristics of the particles. The ultrasonic attenuation method is the most suitable method for measuring the average particle size and distribution pattern of concentrated solutions. Further, as a particle size distribution measuring device using an ultrasonic attenuation method, there may be mentioned the product name DT-1200 manufactured by Nippon Luft Co., Ltd., and the like.

The above ultrasonic attenuation method is performed by pouring a suspension for measurement from the top of the measurement chamber and basically circulating it, and the circulation speed can be changed as necessary. In addition, for slurries with almost no sediment, the measurement is performed with the circulation stopped. The ultrasonic attenuation method described above irradiates a suspension in a chamber with ultrasonic waves of 3 to 100 MHz from a vibrator installed on one side, and receives the ultrasonic waves with a vibrator installed on the other side. An attenuation rate curve can be obtained by measuring the attenuation rate (attenuation rate) during propagation in the turbid liquid for each of a plurality of set frequencies. This curve is called the ultrasonic attenuation spectrum. This method calculates and evaluates the dispersion state and particle distribution state from the shape and slope of this ultrasonic attenuation spectrum. The specific measurement method of the above-mentioned ultrasonic attenuation method can be measured in the same manner as described in "Shokuzai, 75 [11], 530-537 (2002), Shinichi Takeda, Okayama University".

(Dispersion Attenuation Rate)
The attenuation factor A (/mm) at 20 MHz corresponds to the density of the agglomerates of the thermoelectric conversion material, and the higher the attenuation factor, the lower the density. When the density of the agglomerates decreases, a larger conductive path is formed, and the conductivity of the agglomerates improves. Therefore, the attenuation factor at 20 MHz is preferably 0.2≦A≦10, and more preferably 0.3≦A≦5.

A/B, which is the ratio of the attenuation rate B (/mm) at 10 MHz to the attenuation rate A at 20 MHz, is proportional to the size of the agglomerate, and the smaller the agglomerate size, the larger A/B becomes. The smaller the agglomerates of the thermoelectric conversion material are, the more closely they come into contact with each other when formed into a film, improving electrical conductivity. Therefore, it is preferable that A/B be 2≦A/B≦20.

(Coating film of dispersion liquid for thermoelectric conversion)
The coating film may be a film obtained by applying a thermoelectric conversion dispersion onto a base material. Since the dispersion liquid for thermoelectric conversion has excellent moldability, it is easy to obtain a good film by a coating method. A wet film forming method is mainly used to form a thermoelectric conversion film. Specifically, spin coat method, spray method, roller coat method, gravure coat method, die coat method, comma coat method, roll coat method, curtain coat method, bar coat method, inkjet method, dispenser method, silk screen printing, flexographic method. Examples include methods using various means such as printing. The method can be appropriately selected from the above methods depending on the thickness to be applied, the viscosity of the material, etc.

The thickness of the coating film is not particularly limited, but it is preferable that the coating 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. In one embodiment, from the viewpoint of thermoelectric properties, 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 even more preferably in the range of 1 to 50 μm.

In addition, as a base material to which the thermoelectric conversion material is applied, a plastic film made of materials such as polyethylene, polyethylene terephthalate, polyethylene naphthalate, polyether sulfone, polypropylene, polyimide, polycarbonate, and cellulose triacetate, or glass, etc. Can be used.

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 may be performed.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the following Examples do not limit the scope of the present invention in any way. Note that unless otherwise specified, "parts" represent "parts by mass." Also. "NMP" stands for N-methylpyrrolidone.

(Production of Thermoelectric Conversion Material Dispersion)
[Example 1]
0.2 parts of single-walled carbon nanotubes (TUBALL, manufactured by OcSiAl Corporation) and 39.6 parts of NMP were weighed and mixed. The mixture was then shaken for 120 minutes using a Scandex to obtain a thermoelectric conversion material dispersion 1.

[Examples 2 to 19, Comparative Example 1]
Dispersions 2 to 19 and 21 were obtained in the same manner as in Example 1, except that the materials, compositions and dispersion conditions were changed as shown in Table 1. Note that blanks in Table 1 indicate that no compounding or no operation was performed. Also, "PF" represents a power factor calculated from the volume conductivity and Seebeck coefficient obtained by the measurement method described below.

[Example 20]
0.2 parts of single-walled carbon nanotubes (TUBALL, manufactured by OcSiAl Corporation), 0.1 parts of dispersant A (triazine derivative), and 39.6 parts of NMP were weighed and mixed. Ultrasonic waves were irradiated for 30 minutes using an ultrasonic water bath to obtain a thermoelectric conversion material dispersion liquid 20.

The materials listed in Table 1 are as follows:
<Thermoelectric conversion materials>
- TUBALL (OcSiAl, single-walled carbon nanotubes)
・ZEONAN (Zeon Nanotechnology, single-walled carbon nanotubes)
<Dispersant>
Dispersant A (triazine derivative) represented by the following structural formula:

・Solspers 24000 (manufactured by Lubrizol, dispersant)
<Semiconductor>
・Pyrene (manufactured by Tokyo Kasei Kogyo Co., Ltd.)
・DETX-S (2,4-diethylthioxanthene-9-one, manufactured by Tokyo Kasei Kogyo Co., Ltd.)
・Rose Bengal (manufactured by Tokyo Kasei Kogyo Co., Ltd.)

<Evaluation of thermoelectric conversion material dispersion>
(Measurement and calculation method of attenuation rate)
A portion of each of the dispersions 1 to 21 was sampled, diluted with NMP so that the nonvolatile content concentration was 0.5% by mass, and analyzed using an ultrasonic attenuation method particle size distribution analyzer (manufactured by Nippon Luft Co., Ltd., trade name DT-1200). ) was used to measure the decay rate at 25°C. The attenuation rate was measured for each set frequency below between 3 and 100 MHz. The set frequencies are 3.0MHz, 3.7MHz, 4.5MHz, 5.6MHz, 6.8MHz, 8.4MHz, 10.3MHz, 12.7MHz, 15.6MHz, 19.2MHz, 23.5MHz, 28. They were 9 MHz, 35.5 MHz, 43.7 MHz, 53.6 MHz, 81.0 MHz and 99.5 MHz. The measurement was carried out multiple times using a deaerated dispersion liquid, and when the error from the previous measurement at each measurement point was within 5%, the measurement was terminated and the final measurement value was adopted. Deaeration was carried out after placing the dispersion liquid in a device capable of reducing the pressure, repeating the process between reduced pressure and normal pressure several times, and then allowing it to stand still for several hours. The attenuation rate at 20 MHz calculated from an approximate curve based on a linear function determined by the least squares method based on the attenuation rates at 15.6 MHz, 19.2 MHz, and 23.5 MHz was defined as A (/mm). Further, the attenuation rate at 10 MHz calculated from an approximate curve based on a quadratic function determined by the least squares method based on the attenuation rates at 8.4 MHz, 10.3 MHz, and 12.7 MHz was defined as B (/mm). The ratio A/B of these two attenuation rates was calculated.

(Method for measuring dispersion stability over time)
Each of Dispersions 1 to 21 was visually confirmed, and the dispersibility was evaluated based on the following evaluation criteria.

(Evaluation criteria)
◎: No agglomeration immediately after dispersion, no precipitation even after 48 hours (very good)
○: No agglomeration immediately after dispersion, no precipitation even after 24 hours (good)
△: No agglomeration immediately after dispersion, but precipitation occurs after 24 hours (within practical range)
×: Agglomerates remain even immediately after dispersion, making it impossible to obtain a uniform dispersion (defective)

<Thickness of coating films of Examples 1 to 20 and Comparative Example 1>
Dispersions 1 to 21 were each applied to a polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc., Lumirror (registered trademark) E20 #75, thickness 75 μm) using a 20 mil applicator, and heated at 80°C for 4 minutes and then at 120°C. After drying for 30 minutes, coating films 1 to 21 were obtained, respectively.
For the obtained coating film, the thickness of the coated area (a) and the thickness of the non-coated area (b) were measured using a dial gauge specified in Japanese Industrial Standards (JIS) B7503, and the following values were measured: The film thickness (c) of the coating film was determined from the calculation formula.
(c)=(a)-(b)

<Method for measuring volume conductivity>
For coating films 1 to 21, resistivity meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd., Loresta GP MCP-T610 type resistivity meter, JIS-K7194 compliant, 4 terminal 4 probe legal current application method) (4 terminals at 0.5 cm intervals) The volume conductivity (S/cm) was measured using a terminal probe).

<Method of measuring Seebeck coefficient>
For each of the coating films 1 to 21, the Seebeck coefficient (μV/K) at 80° C. was measured using a ZEM-3LW manufactured by Advance Riko Co., Ltd.

Claims (4)

A dispersion liquid for thermoelectric conversion comprising a thermoelectric conversion material, a dispersion medium, and a dispersant ,
the dispersion medium contains N-methylpyrrolidone,
The dispersant includes a dispersant having a molecular weight of 100 or more and 1,000 or less, or a basic dispersant having a polymer chain,
When the nonvolatile content concentration in the dispersion is 0.5% by mass, when the attenuation rate of the dispersion at 20MHz is A (/mm) in measurement using an ultrasonic particle size distribution meter, 0.2≦A≦ A dispersion liquid for thermoelectric conversion satisfying 10. In measurement using an ultrasonic particle size distribution meter, when the nonvolatile concentration in the dispersion is 0.5% by mass and the attenuation rate of the dispersion at 10MHz is B (/mm), 2≦A/B≦ The dispersion liquid for thermoelectric conversion according to claim 1, which satisfies 20. 3. The dispersion for thermoelectric conversion according to claim 1 , wherein the thermoelectric conversion material comprises carbon nanotubes. A coating film of the dispersion liquid for thermoelectric conversion according to any one of claims 1 to 3 .