WO2018179570A1 - Conductive paste, and conductive material and conductive member each of which uses said conductive paste - Google Patents

Abstract

The present invention provides: a conductive paste which is capable of providing a conductive member that exhibits excellent conductivity when stretched; and a conductive material and a conductive member, each of which uses this conductive paste. A conductive paste which contains an aqueous polyurethane dispersion and conductive particles, and which is characterized in that: the aqueous polyurethane dispersion is obtained by dispersing a polyurethane in water, said polyurethane being obtained by reacting a polyisocyanate, a polyol, a polyol having a hydrophilic group and a chain extender; and the polyol contains a polycarbonate polyol.

Description

Conductive paste, conductive material using the conductive paste, and conductive member

The present invention relates to a conductive paste, a conductive material using the conductive paste, and a conductive member.

In recent years, attention has been focused on soft electronic device technologies such as organic semiconductors and continuous roll-to-roll processes using plastic substrates, and as a result, stretch and flexibility are required for metal wiring. It has become. Stretchable flexible wiring is an important material not only in the field of electronic devices such as wearable computers and flexible devices, but also in the field of medical materials such as artificial muscle and artificial skin that require stretchability.

As such a flexible wiring, (A) a wiring formed by drying an aqueous polyurethane dispersion and a conductive paste of conductive particles, and (B) a conductive member having a flexible substrate are disclosed in Patent Document 1. Is disclosed. However, even the conductive member is not sufficient in terms of conductivity when stretched.

JP 2012-54192 A

The present invention has been made based on the circumstances as described above, and an object thereof is to use a conductive paste capable of providing a conductive member having excellent conductivity when stretched, and the paste. An object is to provide a conductive material and a conductive member.

The present invention provides the following [1] to [6].
[1] A conductive paste containing a polyurethane water dispersion and conductive particles, wherein the polyurethane water dispersion is obtained by reacting a polyisocyanate, a polyol, a polyol having a hydrophilic group, and a chain extender. An electrically conductive paste, wherein the polyol contains a polycarbonate polyol.
[2] The conductive paste according to [1], wherein the content of the polycarbonate polyol is 25 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the polyol.
[3] The conductive paste according to [1] or [2], wherein the polyol contains a polyol having a number average molecular weight of 400 or less.
[4] The conductive paste according to any one of [1] to [3], wherein the polyisocyanate contains an aliphatic and / or alicyclic diisocyanate.
[5] A conductive material comprising the conductive paste according to any one of [1] to [4].
[6] A conductive member comprising the conductive material according to [5] and a substrate.

The present invention can provide a conductive paste that can provide a conductive member having excellent conductivity when stretched, and a conductive material and a conductive member using the paste.

The conductive paste of the present invention contains a polyurethane water dispersion. The polyurethane water dispersion is obtained by dispersing a polyurethane resin obtained by reacting a polyisocyanate, a polyol, a polyol having a hydrophilic group, and a chain extender in water.

The polyisocyanate is not particularly limited, and polyisocyanates generally used in the technical field can be used. Specific examples include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, and araliphatic polyisocyanates.

Aliphatic polyisocyanates include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1 , 5-diisocyanate, 3-methylpentane-1,5-diisocyanate and the like.

Examples of alicyclic polyisocyanates include isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, and the like. Can be mentioned.

Aromatic polyisocyanates include tolylene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), 4,4′-dibenzyl diisocyanate, 1,5 -Naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate and the like.

Examples of the araliphatic polyisocyanate include dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α, α, α, α-tetramethylxylylene diisocyanate and the like. Moreover, modified bodies, such as a dimer, a trimer of these organic polyisocyanate, and a buret-ized isocyanate, can be mentioned. These may be used alone or in combination of two or more.

Among the above polyisocyanates, aliphatic and / or alicyclic polyisocyanates are preferable, and 4,4'-dicyclohexylmethane diisocyanate is particularly preferable in that a conductive material having excellent strength and elongation can be obtained.

In the present invention, the polyol contains a polycarbonate polyol.

The polycarbonate polyol is not particularly limited, and a polycarbonate polyol generally used in the technical field can be used. Specifically, carbonate polyol of 1,6-hexanediol, carbonate polyol of 1,4-butanediol and 1,6-hexanediol, carbonate of 1,5-pentanediol and 1,6-hexanediol, 3- Carbonate polyols of methyl-1,5-pentanediol and 1,6-hexanediol, carbonates of 1,9-nonanediol and 2-methyl-1,8-octanediol, 1,4-cyclohexanedimethanol and 1,6 -Hexanediol carbonate, 1,4-cyclohexanedimethanol carbonate, and these are PCDL T-6001, T-6002, T-5651, T-5651, T-5650J, T manufactured by Asahi Kasei Chemicals Corporation. -4671, T-4672, Kuraray ( Kuraray polyols C-590, C-1050, C-1050R, C-1090, C-2050, C-2050R, C-2070, C-2070R, C-2090, C-2090R, C-3090, C -3090R, C-4090, C-4090R, C-5090, C-5090R, C-1065N, C-2065N, C-1015N, C-2015N and ETERNACOLL UH-50, UH-100 manufactured by Ube Industries, Ltd. , UH-200, UH-300, UM-90 (3/1), UM-90 (1/1), UM-90 (1/3), UC-100, and the like. The number average molecular weight of the polycarbonate polyol is preferably 500 or more and 3,000 or less in that a conductive material excellent in strength and elongation can be obtained.

Specific examples of polyols other than the above polycarbonate polyols in the present invention include known polyethers, polyesters, polyether esters, polyacetals, polyolefins, fluorine-based, vegetable oil-based and the like. More specifically, ethylene glycol, propylene glycol, propanediol, butanediol, pentanediol, 3-methyl-1,5-pentanediol, hexanediol, neopetyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene Glycol, dipropylene glycol, tripropylene glycol, 1,4-cyclohexanedimethanol, bisphenol A, bisphenol F, bisphenol S, hydrogenated bisphenol A, dibromobisphenol A, 1,4-cyclohexanedimethanol, dihydroxyethyl terephthalate, hydroquinone dihydroxy Polyhydric alcohols such as ethyl ether, trimethylolpropane, glycerin, pentaerythritol, and their oxy Sialkylene derivatives or their polyhydric alcohols and oxyalkylene derivatives and polycarboxylic acids, polyhydric carboxylic acid anhydrides, or ester compounds from polyhydric carboxylic acid esters, polycaprolactone polyols, polyester polyols, polythioether polyols Polyols, polyacetal polyols, polytetramethylene glycols, polybutadiene polyols, castor oil polyols, soybean oil polyols, fluorine polyols, silicon polyols and the like, and modified products thereof. Examples of the alkylene oxide include ethylene oxide, propylene oxide, and butylene oxide. These compounds having a group having two or more active hydrogen groups may be used alone or in combination of two or more. Among these, it is preferable to contain polytetramethylene glycol from the viewpoint of obtaining a conductive material excellent in impact resilience.

In the present invention, the content of the polycarbonate polyol is preferably 25 parts by mass or more and 100 parts by mass or less, and more preferably 50 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the polyol. When the content of the polycarbonate polyol is within the above range, it is preferable in that the conductive material has good conductivity and the resistance change during tensile deformation is small.

In the present invention, the polyol preferably contains a polyol having a number average molecular weight of 400 or less because the strength of the conductive material is improved.

The polyol having a number average molecular weight of 400 or less is the following polyol among the above-mentioned polyols. That is, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 3-methylpentanediol, , 6-hexanediol, 1,8-octanediol, 2-methyl-1,3-propanediol, bisphenol A, hydrogenated bisphenol A, cyclohexanedimethanol, glycerin, or trimethylolpropane.

The content of the polyol having a number average molecular weight of 400 or less is preferably 1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the polyurethane resin. In the case of more than 5 parts by mass, the solubility of the urethane prepolymer is remarkably lowered and the synthesis may be difficult.

Examples of the hydrophilic group of the polyol having the hydrophilic group include an anionic hydrophilic group, a cationic hydrophilic group, and a nonionic hydrophilic group. Specifically, the anionic hydrophilic group includes a carboxyl group and a salt thereof, a sulfone. Acid groups and salts thereof include tertiary ammonium salts and quaternary ammonium salts as cationic hydrophilic groups, and groups composed of ethylene oxide repeating units, ethylene oxide repeating units and other alkylenes as nonionic hydrophilic groups. Examples thereof include a group consisting of an oxide repeating unit.

Examples of the polyol having a carboxyl group include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dioxymaleic acid, 2,6-dioxybenzoic acid, 3, In addition to carboxylic acid-containing compounds such as 4-diaminobenzoic acid and derivatives thereof and salts thereof, polyester polyols obtained by using these compounds can be mentioned. Further examples include amino acids such as alanine, aminobutyric acid, aminocaproic acid, glycine, glutamic acid, aspartic acid, and histidine, and carboxylic acids such as succinic acid, adipic acid, maleic anhydride, phthalic acid, and trimellitic anhydride.

Examples of the polyol having a sulfonic acid group and a salt thereof include 2-oxyethanesulfonic acid, phenolsulfonic acid, sulfobenzoic acid, sulfosuccinic acid, 5-sulfoisophthalic acid, sulfanilic acid, and 1,3-phenylenediamine-4. Sulfonic acid-containing compounds such as 1,6-disulfonic acid and 2,4-diaminotoluene-5-sulfonic acid and derivatives thereof, and polyester polyols, polyamide polyols, polyamide polyester polyols obtained by copolymerizing these, and the like. . By neutralizing these carboxyl groups or sulfonic acid groups into salts, the finally obtained polyurethane can be made water-dispersible. Examples of the neutralizing agent in this case include non-volatile bases such as sodium hydroxide and potassium hydroxide, tertiary amines such as trimethylamine, triethylamine, dimethylethanolamine, methyldiethanolamine and triethanolamine, and volatile properties such as ammonia. Examples include bases. Neutralization can be performed before, during or after the urethanization reaction.

Examples of the polyol having the tertiary ammonium salt include alkanolamines such as methylaminoethanol and methyldiethanolamine. By neutralizing these with organic carboxylic acids such as formic acid and acetic acid and inorganic acids such as hydrochloric acid and sulfuric acid to form salts, the polyurethane can be made water-dispersible. Neutralization can be performed before, during or after the urethanization reaction. Of these, those obtained by neutralizing methyldiethanolamine with an organic carboxylic acid are preferred from the viewpoint of ease of emulsification.

The polyol having the quaternary ammonium salt is a compound obtained by quaternizing the alkanolamine such as methylaminoethanol or methyldiethanolamine with a halogenated alkyl such as methyl chloride or methyl bromide or a dialkylsulfuric acid such as dimethylsulfuric acid. . Among these compounds, methyldiethanolamine is quaternized with dimethylsulfate from the viewpoint of ease of emulsification.

The polyol having a nonionic hydrophilic group is not particularly limited, but is preferably a compound containing at least 30% by weight or more of ethylene oxide repeating units and having a number average molecular weight of 300 to 20,000, such as polyoxyethylene glycol or polyoxyethylene glycol. Nonionic group-containing compounds such as oxyethylene-polyoxypropylene copolymer glycol, polyoxyethylene-polyoxybutylene copolymer glycol, polyoxyethylene-polyoxyalkylene copolymer glycol or monoalkyl ethers thereof, or copolymers thereof A polyester polyether polyol obtained by polymerization may be mentioned.

In the present invention, the polyol having the hydrophilic group is preferably a polyol having the carboxyl group, particularly preferably 2,2-dimethylolpropionic acid, from the viewpoint of storage stability of the polyurethane water dispersion.

The chain extender contains a primary or secondary polyamine. The polyamine reacts polyurethane prepolymers, which are reaction products of the polyisocyanate, the polyol, and the polyol having a hydrophilic group, via a chain extender, and the polyurethane prepolymers are chained. By reacting via an extender, the polyurethane prepolymers are polymerized while a urea bond is formed, thereby producing a polyurethane. That is, the polyamine is at least one of a primary amine or a secondary amine that can react with an isocyanate group.

Examples of the polyamine include ethylenediamine, trimethylenediamine, 4,4'-diaminodiphenylmethane, diamines such as piperazine and isophoronediamine, triamines such as diethylenetriamine and dipropylenetriamine, and tetramines such as triethylenetetramine. Moreover, these polyamine components can also be used in combination.

The method for producing the polyurethane water dispersion of the present invention is not particularly limited, but generally, the total of the polyol, the polyol having the hydrophilic group, the hydroxyl group and the amino group contained in the chain extender. Further, an equivalent ratio of the stoichiometric excess of the isocyanate groups of the polyisocyanate to the total amount of hydroxyl groups and amino groups is 1: 0.85 to 1.1 in the absence of a solvent or in an organic solvent having no active hydrogen groups. In order to synthesize an isocyanate-terminated urethane prepolymer by neutralization, an anionic hydrophilic group or a cationic hydrophilic group is neutralized or quaternized as necessary, and then dispersed and emulsified in water. Thereafter, an equivalent chain extender (equivalent ratio of isocyanate group to amino group in the chain extender 1: 0.5 to 0.9) less than the remaining isocyanate group was added to add the isocyanate group in the emulsion micelle. A chain extender is subjected to an interfacial polymerization reaction to form a urea bond. Thereby, a polyurethane water dispersion is obtained by increasing the molecular weight in the emulsion micelle. Then, the polyurethane water dispersion can be obtained by removing the solvent used as needed.

The organic solvent having no active hydrogen group is not particularly limited, and specific examples include dioxane, methyl ethyl ketone, dimethylformamide, tetrahydrofuran, N-methyl-2-pyrrolidone, toluene, propylene glycol monomethyl ether acetate and the like. These hydrophilic organic solvents used in the reaction are preferably finally removed.

In the present invention, the number average molecular weight of the polyurethane in the polyurethane water dispersion is preferably as large as possible, preferably 50,000 or more. Increasing the molecular weight is preferable in terms of improving the strength, elongation, and impact resilience of the conductive material. The conductive paste of the present invention contains conductive particles.

The conductive particles may be any conductive particles conventionally used as a conductivity imparting agent. Examples of conductive particles include furnace black such as ketjen black and vulcan, carbon black such as acetylene black, thermal black, channel black, amorphous carbon powder, natural graphite powder, artificial graphite powder, expanded graphite powder, pitch microbeads, carbon Examples thereof include vapor-grown carbon fibers such as fibers, and carbon-based fine particles such as carbon nanotubes and carbon nanofibers. Also, fine metal powders such as Ag, Cu, Sn, Pb, Ni, Li, Bi, and In alloys thereof, fine metal oxide powders such as ZnO, SnO2, In2O3, CuI, TiO2 / SnO2 / Sb, Al, etc. Metal flakes, metal fibers such as Al, Ni, and stainless steel, metal surface-coated glass beads, and metal-plated carbon. These may be used alone or in combination of two or more.

The shape of the conductive particles is not particularly limited, such as a spherical shape, a needle shape (elliptical spherical shape), a flake shape, and an indefinite shape. The size of the conductive particles is about 0.1 μm or more and 10 μm or less, preferably 0.5 μm or more and 5 μm or less. When the shape of the conductive particles is granular, the average particle diameter is preferably 0.5 μm or more and 5 μm or less. When the shape of the conductive particles is elongated (in the case of carbon fiber or metal flakes), fine long particles (for example, nanotubes and nanorods) having a major axis of 3 μm or less and an aspect ratio in the range of 10 to 200 Is preferred. The flakes preferably have an average particle size of 1 μm to 10 μm and a thickness of 100 nm to 500 nm.

The conductive particles (for example, metal fine powder) may be coated with a dispersant such as a higher fatty acid or a natural polymer compound in order to prevent the particles from sticking to each other.

The amount of the conductive particles is 70 parts by mass or more and 99 parts by mass or less, preferably 75 parts by mass or more and 97 parts by mass or less, more preferably 80 parts by mass with respect to 100 parts by mass in total of the conductive particles and polyurethane (solid content). More than 90 parts by mass. If the amount is less than 75 parts by mass, the conductivity may be reduced, and if it exceeds 99 parts by mass, the stretchability may be impaired.

The conductive paste containing the conductive particles and the aqueous polyurethane dispersion may contain other additives as long as the effects of the present invention are not hindered.

Examples of the other additives include organic conductive materials, liquid conductive materials, dispersants, and colorants.

The content of the additive may be, for example, 50 parts by mass or less, particularly 0.1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass in total of the conductive particles and polyurethane (solid content).

The conductive member of the present invention comprises a conductive material and a substrate obtained by drying the conductive paste.

The substrate is preferably bendable and stretchable in the plane direction (uniaxial or biaxial). Specific examples include paper, cloth (for example, cotton cloth, polyester cloth), resin (for example, polyethylene terephthalate (PET), vinyl chloride (PVC), polyethylene, polyimide, and elastomer (for example, stretchable polyurethane). It is preferably an elastomer, and is preferably a stretchable polyurethane substrate (generally an elastomer).

The conductive member of the present invention can be manufactured by a method comprising a step of obtaining a conductive paste by mixing a polyurethane water dispersion and conductive particles, and a step of applying the conductive paste to a substrate and drying.

A conductive material formed of a conductive paste is formed by applying a conductive paste containing conductive particles and an aqueous polyurethane dispersion to a substrate and drying the conductive paste film.

The conductive paste may be applied with the substrate stretched.

The step of applying the conductive paste on the substrate is not particularly limited as long as the conductive paste of the present invention can be applied to the substrate surface. For example, you may carry out by the printing method, the coating method, etc. Examples of the printing method include screen printing method, offset printing method, ink jet printing method, flexographic printing method, gravure printing method, stamping, dispensing, squeegee printing, silk screen printing, spraying, and brush coating. The thickness of the applied conductive paste is, for example, not less than 0.01 μm and not more than 1000 μm.

The step of heating the coated substrate may be performed in a non-oxidizing atmosphere such as an inert gas (for example, nitrogen gas) atmosphere, in the atmosphere, in a vacuum atmosphere, in an oxygen or mixed gas atmosphere, in an air current, or the like. You may go. The heating temperature may be 20 ° C. or more and 150 ° C., and the heating time may be 0.1 hours or more and 50 hours or less, for example, 0.2 hours or more and 5 hours or less.

The thickness and width of the conductive material obtained by heating are not limited. The thickness of the conductive material may be, for example, 0.01 μm or more and 1000 μm or less, and particularly 0.05 μm or more and 400 μm or less. The width of the conductive material may be 0.01 μm or more and 10 mm or less.

By heating, the polyurethane aqueous dispersion becomes polyurethane containing no water, and a stretchable wiring that functions as a binder for binding the conductive particles is formed.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

<Synthesis of polyurethane water dispersion>
[Synthesis Example 1]
Add 36.82 parts of polycarbonate polyol with a molecular weight of 2000, 36.82 parts of polytetramethylene glycol with a molecular weight of 2000, 1.93 parts of 1,4-butanediol and 36.00 parts of methyl ethyl ketone, and dissolve with sufficient stirring. -23.23 parts of dicyclohexylmethane diisocyanate (H12MDI) was added and reacted at 75 ° C for 1 hour. Thereafter, 1.20 parts of dimethylolpropionic acid (DMPA) and 19.83 parts of methyl ethyl ketone were added and further reacted at 75 ° C., and then diluted by adding 5.10 parts of methyl ethyl ketone, and the NCO content was 1.72%. A prepolymer solution having terminal isocyanate groups was obtained. Next, this prepolymer solution was cooled to 45 ° C., 0.97 parts of triethylamine, 6.00 parts of nonionic surfactant and 136.42 parts of water were added and emulsified using a homomixer, and then 1,2- 1.47 parts of propanediamine (1,2-PDA) was added and the chain extension reaction was carried out at 30 ° C. for 30 minutes. Methyl ethyl ketone was distilled off from the resin solution under reduced pressure, to obtain a polyurethane water dispersion 1 (PUD-1) having a solid content of 47%.

[Synthesis Example 2] to [Synthesis Example 5] Polyurethane water dispersions 2 to 5 (PUD-) were produced in the same manner as in Synthesis Example 1 except that the types and amounts of the raw materials were changed as shown in Table 1 below. 2 to 5) were obtained.

[Example 1]
(Conductive paste)
Flakes of silver microparticles (trade name AgC-A, manufactured by Fukuda Metal Foil Powder Co., Ltd., specific surface area 1.2 m ² / g, 50% average particle diameter 3.5 μm) and polyurethane water synthesized in Synthesis Example 1 Dispersion 1 was weighed into a container and mixed using a planetary stirring and degassing apparatus to obtain conductive paste 1. The mixing ratio was 80% by mass of silver microparticles and 20% by mass of the polyurethane water dispersion.

(Creation of conductive members)
The conductive paste 1 produced above is applied in a rectangular pattern with a width of 3 mm, a length of 20 mm, and a thickness of 15 μm on a substrate made of urethane having an Asker hardness C of 70 of 20 mm × 50 mm × film thickness of 1 mm. Then, a heat treatment was performed in a heating furnace at a temperature of 130 ° C. for 20 minutes, and the mixture was allowed to cool at room temperature (25 ° C.) to produce a conductive material 1. The paste film thickness after the heat treatment was 15 μm.

[Example 2], [Example 3], [Comparative Example 1], [Comparative Example 2]
Except having changed the polyurethane water dispersion 1 as shown in following Table 2, it produced similarly to Example 1, and created the electrically-conductive materials 2-5.

<Evaluation of conductive member>
The following evaluation was performed on the conductive materials 1 to 5. The evaluation results are shown in Table 2.

[Measurement of electrical resistivity]
The electrical resistivity of the formed conductive material was measured by eliminating the influence of the contact resistance of the lead wire and the probe by a constant current method such as a four-terminal method, a four-probe method, and a van der Pau method. .

[Measurement of electrical resistivity in stretched state]
The conductive material 1 produced above was stretched in the length direction, and when the stretch rate reached 10%, the electrical resistivity was measured by holding for 10 minutes. Thereafter, the same operation was repeated every 10% up to an elongation rate of 50%.

表２より、ポリオールにポリカーボネートポリオールを含まないポリウレタン水分散体を使用した場合（比較例１）合には、実施例１ないし４に比べて伸長前の電気抵抗率が高く、さらに伸長時に顕著に導電性が低下した。

From Table 2, when the polyurethane water dispersion which does not contain polycarbonate polyol in the polyol is used (Comparative Example 1), the electrical resistivity before extension is higher than that of Examples 1 to 4, and further, it is remarkable at the time of extension. The conductivity decreased.

The conductive member of the present invention is soft and stretchable, and can be used as a part of various electronic devices such as sensors (particularly medical sensors and robot sensors), displays, artificial muscles and computers.

Claims (6)

A conductive paste containing a polyurethane water dispersion and conductive particles, wherein the polyurethane water dispersion is prepared by reacting a polyurethane obtained by reacting a polyisocyanate, a polyol, a polyol having a hydrophilic group, and a chain extender with water. A conductive paste which is dispersed and the polyol contains a polycarbonate polyol. The conductive paste according to claim 1, wherein the content of the polycarbonate polyol is 25 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the polyol. The conductive paste according to claim 1 or 2, wherein the polyol contains a polyol having a number average molecular weight of 400 or less. The conductive paste according to any one of claims 1 to 3, wherein the polyisocyanate contains an aliphatic and / or alicyclic diisocyanate. 5. A conductive material comprising the conductive paste according to any one of claims 1 to 4. A conductive member comprising the conductive material according to claim 5 and a substrate.