Thermoelectric conversion material composition

Abstract

To provide a composition for a thermoelectric conversion material with high coatability, which achieve both Seebeck coefficient and conductivity and can produce a thermoelectric conversion material showing high power factor.SOLUTION: In a composition for a thermoelectric conversion material including a clay minerals (A), a conductive material (B) and a solvent (C) other than water, desirably further includes a resin (D) having either a hydroxyl group, an amide group or a carboxyl group. The solubility parameter of the solvent (C) other than water is 18 or more and 25 or less, and the mass ratio calculated from the conductive material (B) / (clay mineral (A)+conductive material (B)) is 0.2 or more and 0.99 or less, and the conductive material (A) includes carbon nanotubes.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a composition for thermoelectric conversion materials. [Background technology]

[0002] Thermoelectric materials that can convert between thermal energy and electrical energy are used in thermoelectric conversion elements such as thermoelectric generators 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. Thermoelectric conversion elements utilize the Seebeck effect, which generates an electromotive force when heat is applied to create a temperature difference between both ends of a semiconductor. To obtain a larger potential difference, thermoelectric conversion elements generally use a combination of p-type and n-type semiconductors as materials.

[0003] Thermoelectric conversion elements are also used as thermoelectric modules, which are made by combining a number of elements into a plate or cylinder shape. They can directly convert thermal energy into electricity, and can be used, for example, as a power source for wristwatches that operate with body heat, and for power generation on the ground and in artificial satellites. The performance of a thermoelectric conversion element depends on the performance of the thermoelectric conversion material and the durability of the module.

[0004] As described in Non-Patent Document 1, the dimensionless thermoelectric figure of merit (ZT) is used as an index representing the performance of a thermoelectric conversion material. In addition, the power factor PF (=S 2 ·σ) may also be used. The dimensionless thermoelectric figure of merit "ZT" is expressed by the following formula (1). ZT=(S 2 σ T) / κ 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)). Thermal conductivity κ is expressed by the following equation (2). κ = α ρ C Equation (2) where α is the thermal diffusivity (m 2 / s), ρ is 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 improve the Seebeck coefficient or electrical conductivity while decreasing the thermal conductivity.

[0005] In response to this, research is being conducted into thermoelectric conversion elements that use organic materials instead of conventional inorganic materials. Organic materials have excellent moldability and are more flexible than inorganic materials, so they are highly versatile within the temperature range in which they do not decompose. In addition, they are more advantageous than inorganic materials in terms of production energy and production costs, as they can be easily processed using printing and coating techniques.

[0006] In particular, the ability to print or coat means that thermoelectric conversion materials can be easily integrated in the direction of the thermal gradient, and the use of such materials makes it possible to fabricate efficient thermoelectric conversion elements that can extract high power from a small area.

[0007] For example, in Patent Document 1, a thermoelectric conversion element is created using carbon nanotubes (CNTs), organic low molecular weight compounds, and low molecular weight surfactants. However, due to the low affinity between the conductive material and the solvent, the carbon nanotubes and the solvent separate and spread after printing on the film in the dispersion used to create the thermoelectric conversion layer, making it difficult to integrate the thermoelectric conversion layer in a small area and making it impossible to extract electricity efficiently. In addition, Patent Document 2 describes a thermoelectric conversion material that has good CNT dispersibility, is suitable for coating methods, and exhibits excellent thermoelectromotive force by binding an organic dye skeleton to a polymer dispersant and containing it together with carbon nanotubes (CNTs). However, this invention does not provide sufficient thermoelectric conversion performance, and further improvement is required. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2018 / 159685 [Patent Document 2] International Publication No. 2015 / 050113 [Non-patent literature]

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

[0010] The problem to be solved by the present invention is to provide a composition for thermoelectric conversion materials that has high suitability for coating and that can be used to prepare a thermoelectric conversion material that achieves both a high Seebeck coefficient and electrical conductivity and exhibits a high power factor. [Means for solving the problem]

[0011] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention. That is, the present invention relates to a composition for thermoelectric conversion materials, comprising a clay mineral (A), a conductive material (B), and a solvent other than water (C).

[0012] The present invention also relates to the above composition for thermoelectric conversion materials, further comprising a resin (D) having any one of a hydroxyl group, an amide group, or a carboxyl group.

[0013] The present invention also relates to the composition for thermoelectric conversion materials, wherein the solubility parameter of the solvent (C) other than water is 18 or more and 25 or less.

[0014] The present invention also relates to the above composition for thermoelectric conversion materials, wherein the mass ratio calculated from conductive material (B) / (clay mineral (A)+conductive material (B)) is 0.2 or more and 0.99 or less.

[0015] The present invention also relates to the above composition for thermoelectric conversion materials, wherein the conductive material (A) contains carbon nanotubes. Effect of the Invention

[0016] The present invention provides a composition for a thermoelectric conversion material that has high coating suitability and can produce a thermoelectric conversion material that achieves both a high Seebeck coefficient and electrical conductivity and exhibits a high power factor. In addition, the composition can be used to provide a thermoelectric conversion material and a thermoelectric conversion element that exhibit excellent thermoelectric performance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] <Composition for thermoelectric conversion materials> The thermoelectric conversion material composition of the present invention is characterized by containing a clay mineral (A), a conductive material (B), and a solvent (C). This specific combination makes it possible to create a thermoelectric conversion material that has both a high Seebeck coefficient and electrical conductivity, exhibits a high power factor, and exhibits high coating suitability. Hereinafter, an embodiment of the present invention will be described in detail.

[0018] <Clay Minerals (A)> The clay mineral (A) contributes to improving the suitability for coating. If the thermoelectric conversion material composition has poor affinity between the conductive material and the solvent, separation will progress during the coating process, and the phenomenon of the solvent seeping out from the initially coated area will occur (hereinafter referred to as liquid separation). By adding an appropriate amount of clay mineral (A), separation of the conductive material and the solvent can be suppressed, and liquid separation can be suppressed. In order to extract high voltages by thermoelectric conversion, it is necessary to accumulate a large number of thermoelectric conversion materials parallel to the thermal gradient direction, and to make the intervals between the thermoelectric conversion materials as narrow as possible. By adding clay mineral (A), the occurrence of such liquid separation can be suppressed, thereby preventing the thermoelectric conversion material composition from invading the adjacent thermoelectric conversion materials during coating, and the thermoelectric conversion materials can be coated with a narrow interval between them, making it easy to extract high voltages.

[0019] The clay mineral (A) is usually charged, and may be either positively or negatively charged, but is preferably negatively charged. Examples of the clay mineral (A) include layered silicate minerals such as kaolinite, hectorite, montmorillonite, saponite, and illite, and rod-shaped silicate minerals such as sepiolite, attapulgite, allophane, and imogolite. Of these, bentonite is particularly preferred.

[0020] The bulk density of the clay mineral (A) is preferably 100 to 500 g / L. When the bulk density is 100 g / L or more, coating suitability can be achieved without impairing electrical conductivity. When the bulk density is 500 g / L or less, liquid separation can be sufficiently suppressed and coating suitability can be obtained. In this specification, the bulk density of the clay mineral (A) is a value calculated based on the following method.

[0021] <Calculation of bulk density> Volume 25cm 3 An excess amount of clay mineral (A) was placed in a metal cylindrical container with an inner diameter of 20 mm, and the exfoliated clay mineral protruding from the container was scraped off with a metal plate, and the mass of the clay mineral was measured. The bulk density was calculated by dividing this mass by the volume of the container.

[0022] <Conductive material (B)> The conductive material (B) is not particularly limited as long as it is a carbon material, a metal material, or a conductive polymer having conductivity, and examples of the carbon material include graphite, carbon nanotubes, Ketjen black, graphene nanoplates, graphene, etc., and examples of the metal material 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 ZnSe, CdS, InP, GaN, SiC, SiGe, and alloys and composite powders thereof. In addition, fine particles coated with a core and a material different from the core material, specifically, for example, silver-coated copper powder, in which the core material is copper and the surface is coated with silver, can be mentioned. Other examples include powders of metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide, ruthenium oxide, ITO (tin-doped indium oxide), AZO (aluminum-doped zinc oxide), and GZO (gallium-doped zinc oxide), as well as powders surface-coated with these metal oxides, and examples of conductive polymers include a composite (PEDOT / PSS) of poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid, polyaniline, polyacetylene, polypyrrole, polythiophene, polyparaphenylene, etc. The type of conductive material used may be one type, or two or more types may be used in combination.

[0023] The shape of the conductive material (B) is not particularly limited, and amorphous, aggregated, scaly, microcrystalline, spherical, flake, wire, etc. may be appropriately used.

[0024] From the viewpoint of achieving both a high Seebeck coefficient and high electrical conductivity, at least one selected from the group consisting of carbon nanotubes, Ketjen black, graphene nanoplates, and graphene is preferred, more preferably carbon nanotubes, and particularly preferably single-walled carbon nanotubes.

[0025] Examples of the conductive material (B) include flake 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, and F#1 manufactured by Nippon Graphite Industries Co., Ltd. , 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 Industries Co., Ltd., EC1500, EC1000, EC500, EC300, EC100, EC50 manufactured by Ito Graphite Industries Co., Ltd., 10099M, PB-99 manufactured by Nishimura Graphite Co., Ltd., etc. are listed. Examples of spherical natural graphite include CGC-20, CGC-50, CGB-20, CGB-50 manufactured by Nippon Graphite Industries Co., Ltd. Examples of amorphous graphite include blue P, AP, AOP, P#1 manufactured by Nippon Graphite Industries Co., Ltd., and APR, K-5, AP-2000, AP-6, 300F, 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.; G-4AK, G-6S, G-3G-150, G-30, G-80, G-50, SMF, EMF, SFF, SFF-80B, SS-100, BSP-15AK, BSP-100AK, and WF-15C manufactured by Chuetsu Graphite Co., Ltd.; and SGP-100, SGP-50, SGP-25, SGP-15, SGP-5, SGP-1, SGO-100, SGO-50, SGO-25, SGO-15, SGO-5, SGO-1, SGX-100, SGX-50, SGX-25, SGX-15, SGX-5, and SGX-1 manufactured by SEC Carbon Co., Ltd.Examples of commercially available carbon black include Tokai Carbon's Tokablack #4300, #4400, #4500, and #5500; Degussa's Printex L; and Colombian's Raven7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, Conductex SC ULTRA, and Conductex 975. Examples of furnace blacks include ULTRA, PUERBLACK 100, 115, and 205; #2350, #2400B, #2600B, #3050B, #3030B, #3230B, #3350B, #3400B, and #5400B manufactured by Mitsubishi Chemical Corporation; MONARCH 1400, 1300, 900, Vulcan XC-72R, and Black Pearls 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. Examples of 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 Kusumoto Chemicals Co., Ltd., and ZEONANO manufactured by Zeon Nano Technology Co., Ltd., FloTube9000, FloTube7000, and FloTube2000 manufactured by CNano Co., Ltd., NC7000 manufactured by Nanocyl Co., Ltd., and 100T and 200P manufactured by Knano Co., Ltd. These are not particularly limited, and may be used alone or in combination of two or more kinds.

[0026] The mass ratio calculated from the conductive material (B) / (clay mineral (A)+conductive material (B)) is preferably 0.2 to 0.99. By being in the above range, sufficient thermoelectric conversion performance can be achieved without impairing the electrical conductivity.

[0027] <Solvent (C)> The solvent (C) refers to a substance that is not water and is liquid at 25°C. Coating properties can be improved by adding a solvent, mixing the clay material (A) and the conductive material (B) to form a dispersion. In order to improve the stability of the conductive material and inhibit oxidation, the solvent (C) preferably has a solubility parameter of 18 or more and 25 or less.

[0028] Examples of the solvent (C) include halogen-based solvents such as chloroform, alcohol-based solvents such as 2-propanol, ether-based solvents such as tetrahydrofuran, ester-based solvents such as ethyl acetate, aromatic solvents such as toluene, nitrile-based solvents such as acetonitrile, and amine-based solvents such as N-methyl-2-pyrrolidone and dimethylformamide.

[0029] The mass of the solvent (C) is preferably from 50% to 99.9%, and more preferably from 80% to 99.9%, of the total mass of the thermoelectric conversion material composition.

[0030] <Resin (D)> The thermoelectric conversion material composition of the present invention may further contain a resin (D). The resin (D) refers to a resin having any of a hydroxyl group, an amide group, or a carboxyl group. By having the above functional group, it is possible to cause an interaction with the clay material, which can further suppress liquid separation and improve the coating suitability.

[0031] Examples of the resin (D) include vinyl resins such as polyvinyl alcohol, and acrylic resins such as polyhydroxyethyl(meth)acrylate, poly(meth)acrylamide, and poly(meth)acrylic acid.

[0032] The mass average molecular weight of the resin (D) is preferably 10,000 to 200,000. When the mass average molecular weight is 10,000 or more, the interaction with the viscous material can be enhanced, and when the mass average molecular weight is 200,000 or less, deterioration of the coatability due to thickening can be suppressed.

[0033] <Other ingredients> The thermoelectric conversion material composition of the present invention may contain other components, such as organic semiconductors, as necessary, in order to improve its properties.

[0034] <Organic semiconductor> The organic semiconductor preferably has an energy level of the highest occupied molecular orbital (HOMO) of -7.0 eV to -5.0 eV, and can be selected from known organic semiconductors. By adding an organic semiconductor, carriers (holes or electrons) generated in the organic semiconductor by thermal excitation are transferred to the conductive material (B), and the gradient of carrier density generated in the conductive material (B) is strengthened, thereby enabling efficient thermoelectric conversion.

[0035] Examples of the organic semiconductor include perylene derivatives, diketopyrrolopyrrole derivatives, and thiazolothiazole derivatives.

[0036] <Thermoelectric conversion element> The thermoelectric conversion element can be obtained by removing the solvent from the thermoelectric conversion material composition and providing electrodes. For example, the thermoelectric conversion element can be produced by applying the thermoelectric conversion material composition to a substrate, drying in an oven to remove the solvent, and depositing gold on two ends of the obtained film by gold sputtering. EXAMPLES

[0037] The present invention will be described in more detail below with reference to experimental examples. In the examples, "parts" means "parts by mass" and "%" means "% by mass" unless otherwise specified.

[0038] <Production of Thermoelectric Conversion Material Composition> [Example 1] As the conductive material (B), 0.4 parts of TUBALL (Kusumoto Chemical Industries, Ltd. single-walled carbon nanotube, abbreviated as SWCNT), 0.2 parts of organic semiconductor DPP having the structure of chemical formula 1, 0.1 parts of GARAMITE-1958 (BYK Japan Co., Ltd.) as the clay mineral (A), and 79.2 parts of N-methyl-2-pyrrolidone (solubility parameter: 22.9, abbreviated as NMP) as the solvent (C) were weighed and mixed. Furthermore, 140 parts of zirconia beads (φ1.25 mm) were added, and the mixture was shaken with Scandex for 2 hours, and then filtered to remove the zirconia beads, and a thermoelectric conversion material composition 1 was obtained.

[0039] [ka]

[0040] [Examples 2 to 6, 10 to 14 and Comparative Examples 1 and 2] Thermoelectric conversion material compositions 2 to 6, 10 to 14, 22, and 23 were obtained in the same manner as in Example 1, except that the types of materials constituting the thermoelectric conversion material compositions were changed to the materials shown in Table 1. However, thermoelectric conversion material composition 22 was produced without blending GARAMITE-1958.

[0041] [Example 15] A thermoelectric conversion material composition 7 was obtained in the same manner as in Example 1, except that the amount of GARAMITE-1958 (manufactured by BYK Japan KK) was changed to 0.01 part.

[0042] [Example 16] A thermoelectric conversion material composition 8 was obtained in the same manner as in Example 1, except that the amount of GARAMITE-1958 (manufactured by BYK Japan KK) was changed to 0.4 parts.

[0043] [Example 17] A thermoelectric conversion material composition 9 was obtained in the same manner as in Example 1, except that the amount of GARAMITE-1958 (manufactured by BYK Japan KK) was changed to 1.5 parts. [Example 18] A thermoelectric conversion material composition 18 was obtained in the same manner as in Example 1, except that 0.1 parts of polyvinyl alcohol 500, fully saponified type (FUJIFILM Wako Pure Chemical Industries, Ltd.) was further added to the blend of Example 1. [Example 19] A thermoelectric conversion material composition 19 was obtained in the same manner as in Example 1, except that 0.05 parts of polyvinyl alcohol 500, fully saponified type (FUJIFILM Wako Pure Chemical Industries, Ltd.) was further added to the blend of Example 1. [Example 20] A composition for thermoelectric conversion materials 20 was obtained in the same manner as in Example 1, except that 0.1 parts of POLYACRYLAMIDE AVERAGE MN 40,000 (Merck Ltd.) was further added to the blend of Example 1. [Example 21] A thermoelectric conversion material composition 21 was obtained in the same manner as in Example 1, except that 0.1 parts of polyacrylic acid 25,000 (FUJIFILM Wako Pure Chemical Industries, Ltd.) was further added to the blend of Example 1.

[0044] <Evaluation of liquid release properties> The obtained thermoelectric conversion material compositions 1 to 23 were applied to a sheet-shaped substrate, a polyimide film with a thickness of 50 μm, using a SuperΣC Using M-V2 and a syringe needle with a gauge of 30G, a thin line of 2um width and 5cm length was applied. The rate of liquid separation 10 minutes after application was evaluated based on the following criteria. Percentage of liquid separation = (line width where solvent spreads due to liquid separation) / (line width of coated area)-1 ◎: Liquid separation rate is less than 20% (very good) ○: Liquid separation rate is 20% or more and less than 50% (good) △: Liquid separation rate is 50% or more but less than 100% (practical) ×: The liquid separation rate is 100% or more (not practical).

[0045] <Evaluation of thermoelectric conversion properties and electrical conductivity> The obtained thermoelectric conversion material compositions 1 to 23 were applied to a 50 μm-thick polyimide film, which was a sheet-like substrate, using an applicator, and then dried by heating at 130° C. for 30 minutes to obtain a laminate having a 5 μm-thick thermoelectric conversion film on the polyimide film. The electrical conductivity, Seebeck coefficient, and power factor (PF) of the obtained laminate having a thermoelectric conversion film (hereinafter also referred to as a coating film) were evaluated as follows. The results are shown in Table 1.

[0046] (conductivity) The obtained laminate was cut into a size of 2.5 cm x 5 cm, and the electrical conductivity was measured by a four-terminal method using Loresta GX MCP-T700 (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) in accordance with JIS-K7194.

[0047] (Seebeck coefficient) The obtained laminate was cut into a size of 3 mm x 10 mm, and the Seebeck coefficient (μW / K) at 80°C was measured using a ZEM-3LW manufactured by Advance Riko Co., Ltd.

[0048] (Power Factor (PF)) Using the obtained electrical conductivity and Seebeck coefficient, the PF (=S2·σ) at 80°C was calculated and evaluated according to the following criteria. ◎: PF is 20μW / (mK 2 ) or better (very good) ○: PF is 10μW / (mK 2 ) or more, 20μW / (mK 2 ) (Good) △: PF is 2.5μW / (mK 2 ) or more, 10μW / (mK 2 ) (practical) ×: PF is 2.5μW / (mK 2 ) (not practical)

[0049] Details of the materials in Table 1 are as follows: <Clay Minerals (A)> CLAYTONE-APA: Bentonite manufactured by BYK Japan Co., Ltd. Bulkiness 590g / l GARAMITE-7305: Bentonite manufactured by BYK Japan Co., Ltd. Bulking 130g / l GARAMITE-1958: Bentonite manufactured by BYK Japan Co., Ltd. Bulkiness 130g / l Sben NE: Bentonite made by Hojun Co., Ltd. Bulkiness 250g / l Sben NEZ: Bentonite made by Hojun Co., Ltd. Bulk 250g / l PANGEL B40: Sepiolite made by TOLSA, bulk 200g / l

[0050] <Conductive material (B)> SWCNT: Single-walled carbon nanotube "TUBALL" manufactured by Kusumoto Chemicals MWCNT: Multi-walled carbon nanotube "100P" manufactured by Knano GNP: Graphene nanoplatelets "xGNP-M-5" manufactured by XG Sciences KB: Lion Ketjen Black "EC-300J" Graphite: Nippon Graphite Co., Ltd. graphite "CPB" PEDOT / PSS: Heraeus "Clevios PH1000"

[0051] <Resin (D)> PVA: Fujifilm Wako Pure Chemical Corporation Polyvinyl alcohol 500, fully saponified PAAm: Merck Ltd. POLYACRYLAMIDE AVERAGE MN 40,000 PAA: Fujifilm Wako Pure Chemical Industries, Ltd.: Polyacrylic acid 25,000

[0052] As shown in Table 1, the thermoelectric conversion material composition of the present invention has superior coatability compared to the comparative thermoelectric conversion material compositions, and it was possible to produce a thermoelectric conversion material with excellent thermoelectric properties. [Industrial Applicability]

[0053] The thermoelectric conversion material composition according to an embodiment of the present invention has excellent coatability and can provide a thermoelectric conversion material having excellent thermoelectric properties.

[0054] [Table 1]

Claims

1. The thermoelectric conversion material composition comprises a clay mineral (A), a conductive material (B), and a solvent other than water (C), wherein the mass ratio calculated from the conductive material (B) / (clay mineral (A)+conductive material (B)) is 0.2 or more and 0.99 or less.

2. 2. The thermoelectric conversion material composition according to claim 1, further comprising a resin (D) having any one of a hydroxyl group, an amide group, and a carboxyl group.

3. 3. The thermoelectric conversion material composition according to claim 1, wherein the solvent (C) other than water has a solubility parameter of 18 or more and 25 or less.

4. The thermoelectric conversion material composition according to any one of claims 1 to 3, wherein the conductive material (A) comprises carbon nanotubes.

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