TW202415810A - Method for producing metal nanowires - Google Patents

Abstract

The present invention addresses the problem of providing a metal nanowire production method that makes it possible to obtain a metal nanowire having high joining strength at the time of joining. A metal nanowire production method according to the present invention comprises: an anodization step for forming an anodization film that has pores on a surface of a valve metal substrate; a metal filling step for filling a metal into the pores; an isolation step for isolating the metal used for filling from the anodization film and the valve metal substrate; and a crushing step for crushing the isolated metal to obtain a metal nanowire.

Description

Method for manufacturing metal nanowires

The present invention relates to a method for manufacturing metal nanowires.

In recent years, various studies have been conducted on conductive materials using metal nanowires or metal nanocolumns. As such conductive materials, porous alumina is known to be used as a template for making nanomaterials. For example, Patent Document 1 describes a method for obtaining metal nanowires by sequentially subjecting an aluminum substrate to an anodic oxidation treatment, an aluminum substrate removal treatment, a penetration treatment, a metal filling treatment, and an anodic oxide film removal treatment ([0025], [Figure 1]).

[Patent Document 1] Japanese Patent Application Publication No. 2012-238592

The inventors of the present invention have studied the metal nanowires described in Patent Document 1 and found that when used in a conductive bonding material (for example, a material for bonding a semiconductor chip and a substrate), the bonding strength is sometimes insufficient.

The subject of the present invention is to provide a method for manufacturing metal nanowires capable of obtaining metal nanowires having high bonding strength when bonded.

The inventors of the present invention have made painstaking research to achieve the above-mentioned subject. As a result, they have found that by isolating the metal filled in the porous body from the anodic oxide film and the valve metal substrate and then performing a crushing step, metal nanowires with high bonding strength can be obtained when bonding, and the present invention has been completed. That is, they have found that the above-mentioned subject can be achieved by the following structure.

[1] A method for producing metal nanowires, comprising: an anodic oxidation step, forming an anodic oxide film having multiple pores on the surface of a valve metal substrate; a metal filling step, filling the multiple pores with metal; an isolation step, isolating the filled metal from the anodic oxide film and the valve metal substrate; and a crushing step, crushing the isolated metal to obtain metal nanowires. [2] The method for producing metal nanowires as described in [1], wherein between the isolation step and the crushing step, there is also a drying step of drying the isolated metal. [3] The method for producing metal nanowires as described in [1] or [2], wherein between the isolation step and the crushing step, there is also a step of reducing or removing the surface oxide layer of the isolated metal. [4] The method for producing metal nanowires as described in any one of [1] to [3], which also includes a protective layer forming step of forming a protective layer containing an anti-corrosion agent on the isolated metal. [5] The method for producing metal nanowires as described in any one of [1] to [4], wherein the valve metal substrate comprises aluminum. [6] The method for producing metal nanowires as described in any one of [1] to [5], wherein the metal filling step includes a coating step. [7] A method for producing metal nanowires as described in any one of [1] to [6], wherein the isolation step includes a dissolution step. [8] A method for producing metal nanowires as described in any one of [1] to [7], wherein the crushing step is performed in water or an aqueous solution having an alkali or acid concentration of less than 1 mass %. [Effect of the invention]

The present invention can provide a method for manufacturing metal nanowires that can obtain metal nanowires having high bonding strength when bonded.

The present invention is described in detail below. The description of the constituent elements described below is sometimes based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. In addition, in this specification, the numerical range represented by "～" refers to the range including the numerical values described before and after "～" as the lower limit and upper limit.

[Method for producing metal nanowires] The method for producing metal nanowires of the present invention (hereinafter, also referred to as "the method for producing the present invention") comprises: an anodic oxidation step, forming an anodic oxide film having multiple pores on the surface of a valve metal substrate; a metal filling step, filling the multiple pores with metal; an isolation step, isolating the filled metal from the anodic oxide film and the valve metal substrate; and a crushing step, crushing the isolated metal (hereinafter, also referred to as "isolation metal") to obtain metal nanowires.

In the present invention, as described above, after isolating the filled metal from the anodic oxide film and the valve metal substrate (isolation step), a metal nanowire having high bonding strength when joined can be obtained by performing a crushing step. Therefore, although the details of the reason why metal nanowires having high bonding strength when joined can be obtained are unclear, it is roughly estimated as follows. That is, it is believed that by crushing the isolation metal, the proportion of metal nanowires existing in a condensed state (for example, a bundle state) is reduced, and the proportion of metal nanowires existing in a random state in direction is increased, and the flexibility is improved when used as a bonding material, thereby improving the bonding strength.

Next, after explaining the overview of each step in the manufacturing method of the present invention using FIG. 1A to FIG. 1E , each processing step is described in detail.

As shown in FIG. 1A and FIG. 1B , in the anodic oxidation step, the surface of the valve metal substrate 1 is anodic oxidized to form an anodic oxide film 3 having pores (micropores) 2 on the surface of the valve metal substrate 1. Then, as shown in FIG. 1C , in the metal filling step, the pores 2 are filled with metal 4. Then, as shown in FIG. 1D , in the isolation step, the filled metal 4 is isolated from the anodic oxide film 3 and the valve metal substrate 1. Furthermore, the state shown in FIG. 1D shows the state in which the isolation metal 5 obtained by the isolation step is recovered (a state in which a part of the isolation metal is attached). Then, as shown in FIG. 1E , in the crushing step, the metal nanowire 10 in which the isolation metal 5 is crushed can be obtained.

[Valve metal substrate] The valve metal substrate used in the manufacturing method of the present invention is not particularly limited as long as it is a substrate containing a valve metal. Here, as valve metal, specifically, for example, aluminum, tantalum, niobium, titanium, tungsten, bismuth, zirconium, zinc, tungsten, bismuth, antimony, etc. can be cited. Among them, aluminum is preferred because it has good dimensional stability and is relatively cheap. Therefore, in the manufacturing method of the present invention, it is preferred to use a substrate containing aluminum (hereinafter, simply referred to as "aluminum substrate") as the valve metal substrate.

The aluminum substrate is not particularly limited, and specific examples thereof include a pure aluminum plate; an alloy plate having aluminum as a main component and containing a trace amount of foreign elements; a substrate having high-purity aluminum vapor-deposited on low-purity aluminum (e.g., recycled material); a substrate having high-purity aluminum coated on the surface of a silicon wafer, quartz, glass, etc. by sputtering or the like; a resin substrate obtained by pressing an aluminum layer, etc.

The valve metal purity of the surface of the valve metal substrate on one side of the valve metal substrate subjected to the anodic oxidation treatment in the anodic oxidation step described later is preferably 99.5 mass % or more, more preferably 99.9 mass % or more, and even more preferably 99.99 mass % or more. If the valve metal purity is within the above range, the arrangement regularity of the through-channel becomes sufficient.

In addition, it is preferred that the surface of one side of the valve metal substrate that is subjected to anodic oxidation treatment in the anodic oxidation step described later is previously subjected to heat treatment, degreasing treatment, and mirror finishing treatment. Here, regarding the heat treatment, degreasing treatment, and mirror finishing treatment, the same treatment as that described in paragraphs [0044] to [0054] of Japanese Patent Publication No. 2008-270158 can be performed.

[Anodic oxidation step] The anodic oxidation step is a step of forming a porous anodic oxide film on the surface of the valve metal substrate by performing an anodic oxidation treatment on the surface of the valve metal substrate.

The anodic oxidation treatment in the above-mentioned anodic oxidation step can use a conventionally known method, but in order to isolate the filled metal with less diameter deviation in the isolation step described later, it is preferable to use a self-ordering method or a constant pressure treatment. Here, regarding the self-ordering method or the constant pressure treatment of the anodic oxidation treatment, the same treatment as that described in paragraphs [0056] to [0108] and [Figure 3] of Japanese Patent Publication No. 2008-270158 can be implemented.

Anodic oxidation treatment can be performed by, for example, applying electricity to the valve metal substrate as an anode in a solution having an acid concentration of 1 to 10 mass%. As a solution for anodic oxidation treatment, an acid solution is preferred, and sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfonamide, benzenesulfonic acid, aminosulfonic acid, glycolic acid, tartaric acid, apple acid, citric acid, etc. are more preferred, among which sulfuric acid, phosphoric acid, and oxalic acid are further preferred, and oxalic acid is particularly preferred. These acids can be used alone or in combination of two or more.

The conditions of the polar oxidation treatment vary depending on the electrolyte used and therefore cannot be determined in general. Generally, the electrolyte concentration is 0.1-20 mass%, the liquid temperature is -10-30°C, the current density is 0.01-20A/dm ² , the voltage is 3-300V, and the electrolysis time is 0.5-30 hours. The electrolyte concentration is 0.5-15 mass%, the liquid temperature is -5-25°C, the current density is 0.05-15A/dm ² , the voltage is 5-250V, and the electrolysis time is 1-25 hours. The electrolyte concentration is 1-10 mass%, the liquid temperature is 0-20°C, the current density is 0.1-10A/dm ² , the voltage is 10-200V, and the electrolysis time is 2-20 hours.

The treatment time of the anodic oxidation treatment is preferably 0.5 minute to 16 hours, more preferably 1 minute to 12 hours, and further preferably 2 minutes to 8 hours.

The thickness of the anodic oxide film formed by the above-mentioned anodic oxidation step is not particularly limited, but from the perspective of adjusting the length of the metal nanowire, 0.3 to 300 μm is preferred, 0.5 to 120 μm is more preferred, and 0.5 to 100 μm is further preferred. In addition, regarding the thickness of the anodic oxide film, the anodic oxide film can be cut in the thickness direction using a focused ion beam (FIB), and its cross section can be photographed using a field emission scanning electron microscope (FE-SEM) (magnification of 50,000 times), and the average value of 10 points can be calculated.

The density of the porous structure formed by the above-mentioned anodic oxidation step is not particularly limited, but preferably ² million/ ^mm2 or more, more preferably 10 million/mm2 or more, further preferably 50 million/ ^mm2 or more, and particularly preferably 100 million/ ^mm2 or more. Furthermore, the density of the porous structure can be measured and calculated by the method described in paragraphs [0168] and [0169] of Japanese Patent Publication No. 2008-270158.

The average opening diameter of the pores formed by the above-mentioned anodic oxidation step is not particularly limited, but from the perspective of adjusting the diameter of the metal nanowires, 5 to 500 nm is preferred, 20 to 400 nm is more preferred, 40 to 200 nm is further preferred, and 50 to 100 nm is particularly preferred. In addition, the average opening diameter of the pores can be calculated by taking a surface photograph (magnification of 50,000 times) using FE-SEM and taking it as the average value of 50 points.

[Metal filling step] The metal filling step is a step of filling the porous interior with metal after the anodic oxidation step.

<Metal> The metal is preferably a material having a resistivity of 10 ³ Ω·cm or less, and specific examples thereof include gold (Au), silver (Ag), copper (Cu), aluminum (Al), titanium (Ti), nickel (Ni), and cobalt (Co). Among them, from the viewpoint of electrical conductivity, Cu, Au, Al, Ni, and Co are preferred, Cu, Ni, and Co are more preferred, and Cu is further preferred.

<Filling method> As a method for filling the above metal into the porous interior, for example, the same methods as those described in paragraphs [0123] to [0126] and [Figure 4] of Japanese Patent Publication No. 2008-270158 can be cited.

In the manufacturing method of the present invention, the metal filling step preferably includes a coating step because it is difficult to include a hollow portion in the metal nanowire to be manufactured. Specifically, as a method for filling the above metal into the porous interior, it is preferable to use an electroplating treatment method, for example, electroplating or electroless plating can be used. Here, in the conventionally known electroplating method used for coloring, it is difficult to selectively precipitate (grow) the metal in the hole with a high aspect ratio. This is considered to be because the precipitated metal is consumed in the hole, and even if electrolysis is performed for a certain time or more, the coating will not grow. Therefore, in the manufacturing method of the present invention, when filling the metal by electroplating, it is necessary to set a stop time during pulse electrolysis or constant potential electrolysis. The stop time needs to be more than 10 seconds, preferably 30 to 60 seconds. In addition, in order to promote the stirring of the electrolyte, it is also better to apply ultrasound. In addition, the electrolysis voltage is usually below 20V, preferably below 10V. It is better to measure the deposition potential of the target metal in the electrolyte used in advance and perform constant potential electrolysis within this potential + 1V. Furthermore, when performing constant potential electrolysis, it is better to use cyclic voltammetry in combination, and constant potential devices such as Solartron, BAS, HOKUTO DENKO CORPORATION, IVIUM, etc. can be used.

The plating solution can use a conventionally known electroplating solution. Specifically, when copper is precipitated, a copper sulfate aqueous solution is generally used, and the concentration of copper sulfate is preferably 1 to 300 g/L, and more preferably 100 to 200 g/L. In addition, if hydrochloric acid is added to the electrolyte, precipitation can be promoted. In this case, the hydrochloric acid concentration is preferably 10 to 20 g/L. In addition, when gold is precipitated, it is preferably plated by alternating current electrolysis using a sulfuric acid solution of gold tetrachloride.

Furthermore, in the electroless plating method, it takes a long time to completely fill the metal into the pores formed by the porous structure with a high aspect ratio. Therefore, in the manufacturing method of the present invention, it is preferred to fill the metal by electroplating.

In the manufacturing method of the present invention, as the electroplating treatment method, it is preferable to use a treatment method that combines the AC electroplating method and the DC electroplating method in sequence. Here, in the AC electroplating method, for example, the voltage is modulated into a sine wave at a predetermined frequency and then applied. Furthermore, the waveform when the voltage is modulated is not limited to a sine wave, and can be, for example, a rectangular wave, a triangular wave, a sawtooth wave, or a reverse sawtooth wave. In addition, in the DC electroplating method, the treatment method in the above-mentioned electroplating method can be appropriately used.

In the manufacturing method of the present invention, the time for manufacturing metal nanowires can be shortened. As shown in FIG. 1C , the metal filling step is preferably performed on the entire area from the bottom of the porous body to the opening, and the area from the middle of the porous body to the opening is preferably performed on the metal filling step.

[Isolation step] The isolation step is a step of isolating the filled metal from the anodic oxide film and the valve metal substrate after the metal filling step. Here, the method of isolating the filled metal from the anodic oxide film and the valve metal substrate is not particularly limited. For example, a method of removing the anodic oxide film and the valve metal substrate (for example, dissolving, peeling, etc.) and isolating the filled metal can be preferably cited. Therefore, as a state after the isolation step, for example, it also includes a state in which the filled metal is dispersed in an isolated state in the treatment solution used for the dissolution step (dissolution treatment) described later.

In the manufacturing method of the present invention, the method for removing the above-mentioned anodic oxide film and the above-mentioned valve metal substrate is not particularly limited. For example, it can be removed by grinding. However, considering that the length of the produced metal nanowire becomes uniform, the above-mentioned isolation step includes a dissolution step, that is, it is better to remove at least a portion of the above-mentioned anodic oxide film and the above-mentioned valve metal substrate by dissolution treatment.

In the manufacturing method of the present invention, for the reason of maintaining the shape or size of the manufactured metal nanowire, the above-mentioned isolation step is preferably a one-stage removal step including removing the above-mentioned anodic oxide film and removing the above-mentioned valve metal substrate, and it is more preferable that the above-mentioned anodic oxide film is removed by dissolving treatment. In addition, for the same reason, the above-mentioned isolation step may be a two-stage removal step including removing the above-mentioned valve metal substrate and then removing the above-mentioned anodic oxide film. In this case, it is more preferable that both the two-stage removal steps are removed by dissolving treatment.

<Removal of valve metal substrate> In the removal of the valve metal substrate, it is preferred to use a treatment liquid that does not easily dissolve the anodic oxide film but easily dissolves the valve metal. Such a treatment liquid preferably has a dissolution rate of 1 μm/minute or more for valve metal, more preferably 3 μm/minute or more, and more preferably 5 μm/minute or more. Similarly, the dissolution rate of the anodic oxide film is preferably 0.1 nm/minute or less, more preferably 0.05 nm/minute or less, and more preferably 0.01 nm/minute or less. Specifically, a treatment liquid containing at least one metal compound having a lower ionization tendency than the valve metal and having a pH of 4 or less or 8 or more is preferred, and the pH is more preferably 3 or less or 9 or more, and more preferably 2 or less or 10 or more.

As such a treatment liquid, an acid or alkaline aqueous solution is used as a base and a compound (e.g., platinum chloride) of manganese, zinc, chromium, iron, cadmium, cobalt, nickel, tin, lead, antimony, bismuth, copper, mercury, silver, palladium, platinum, gold, fluorides of these, chlorides of these, etc. is preferably mixed. Among them, an acid aqueous solution base is preferred, and a mixed chloride is preferred. From the viewpoint of treatment tolerance, a treatment liquid in which mercury chloride is mixed in a hydrochloric acid aqueous solution (hydrochloric acid/mercury chloride) and a treatment liquid in which cupric chloride is mixed in a hydrochloric acid aqueous solution (hydrochloric acid/cupric chloride) are particularly preferred. Furthermore, the composition of such a treatment solution is not particularly limited, and for example, a bromine/methanol mixture, a bromine/ethanol mixture, aqua regia, etc. can be used.

Furthermore, the acid or alkaline concentration of such a treatment solution is preferably 0.01 to 10 mol/L, and more preferably 0.05 to 5 mol/L. In addition, the treatment temperature of such a treatment solution is preferably -10°C to 80°C, and more preferably 0°C to 60°C.

Furthermore, the removal of the valve metal substrate is performed by contacting the valve metal substrate after the metal filling step with the treatment solution. The contact method is not particularly limited, and examples thereof include immersion and spraying. Among them, immersion is preferred. The contact time at this time is preferably 10 seconds to 5 hours, and more preferably 1 minute to 3 hours.

<Removal of anodic oxide film> In the removal of the anodic oxide film, a solvent that does not dissolve the metal filled in the pores but selectively dissolves the anodic oxide film can be used, and either an alkaline aqueous solution or an acidic aqueous solution can be used.

Here, when an alkaline aqueous solution is used, it is preferred to use an aqueous solution of at least one alkali selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide, and it is more preferred to use an aqueous solution of potassium hydroxide. In addition, the concentration of the alkaline aqueous solution is preferably 1 to 30% by mass. The temperature of the alkaline aqueous solution is preferably 10 to 60°C, more preferably 20 to 60°C, and further preferably 30 to 60°C. On the other hand, when an acid aqueous solution is used, it is preferred to use an aqueous solution of an inorganic acid such as chromic acid, sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, oxalic acid, or a mixture thereof, and it is more preferred to use an aqueous solution of chromic acid. In addition, the concentration of the acid aqueous solution is preferably 1 to 30% by mass. The temperature of the acid aqueous solution is preferably 15 to 80°C, more preferably 20 to 60°C, and even more preferably 30 to 50°C.

Furthermore, the removal of the above-mentioned anodic oxide film is carried out by contacting it with the above-mentioned alkaline aqueous solution and acid aqueous solution after the above-mentioned metal filling step (preferably after removing the valve metal substrate). The contact method is not particularly limited, and for example, immersion method and spraying method can be cited. Among them, immersion method is preferred. The immersion time in the alkaline aqueous solution and the acid aqueous solution is preferably 1 to 120 minutes, 2 to 90 minutes is more preferred, 3 to 60 minutes is further preferred, and 3 to 30 minutes is particularly preferred. Among them, 3 to 20 minutes is preferred, and 3 to 10 minutes is more preferred.

[Crushing step] The crushing step is a step of crushing the isolation metal after the isolation step. The method of crushing the isolation metal is not particularly limited, and a method of crushing the isolation metal by applying impact to the isolation metal in a liquid is preferably cited. The liquid (solvent) used for crushing is not particularly limited as long as it does not change or dissolve the isolation metal, and examples thereof include water, ethanol, methanol, acetone, methyl ethyl ketone, butanol, ethyl acetate, butyl acetate, tetrahydrofuran, toluene, dimethylformamide, cyclohexane, cyclohexanone, etc. Among them, water is preferred from the viewpoint of safety. Furthermore, from the perspective of producing metal nanowires with higher bonding strength when joined, the above-mentioned crushing step is preferably performed in water or an aqueous solution with an alkali or acid concentration of less than 1 mass%. As crushing treatment, for example, crushing treatment using pore corrosion, crushing treatment by collision of ceramic balls, etc. can be cited, and devices such as ultrasonic cleaning machines, ultrasonic homogenizers, air flow mills, and wet atomization devices can be used. Among them, crushing treatment using pore corrosion or crushing treatment by collision of ceramic balls is preferred, and crushing treatment using pore corrosion is more preferred.

In the present invention, the concentration of the isolation metal in the liquid when the pressure is applied in the liquid is preferably 0.1 to 50% by mass for the sake of uniform processing and improved productivity. In addition, the concentration of the isolation metal in the liquid when the pressure is applied in the liquid is preferably 0.5 to 30% by mass or more, and more preferably 1 to 10% by mass for the sake of obtaining metal nanowires with higher bonding strength during bonding.

[Drying step] In the manufacturing method of the present invention, it is preferable to have a drying step of drying the isolation metal between the isolation step and the crushing step, because the effect of the present invention that metal nanowires with higher bonding strength can be obtained during bonding becomes apparent. Here, the method of drying the isolation metal is not particularly limited. After removing the anodic oxide film and the valve metal substrate, the separated metal can be recovered and dried by performing separation operations such as filtration using a filter or centrifugal separation.

[Protective layer formation step] Considering the reason that metal nanowires with low connection resistance can be obtained, the manufacturing method of the present invention preferably has a step of forming a protective layer containing an anti-corrosion agent on the above-mentioned isolation metal after the above-mentioned isolation step (after the above-mentioned drying step when the above-mentioned drying step is included).

The above-mentioned anticorrosive agent is not particularly limited, and a known anticorrosive agent can be applied. As an anticorrosive agent, for example, a compound containing at least one of a nitrogen atom, an oxygen atom, and a sulfur atom can be cited. From the viewpoint of durability, the anticorrosive agent is preferably a heterocyclic compound containing at least one of a nitrogen atom and an oxygen atom, and a compound containing a 5-membered ring structure containing one or more nitrogen atoms is more preferred. At least one compound selected from the group including a compound containing a triazole structure, a compound containing a benzimidazole structure, and a compound containing a thiadiazole structure is particularly preferred. The 5-membered ring structure containing one or more nitrogen atoms may be a monocyclic structure or a partial structure constituting a condensed ring.

In addition, considering that it is easy to adsorb on the surface of the isolation metal, the anticorrosive agent is preferably a compound containing at least one of an acid containing a polar group and an alkali containing a polar group. As polar groups possessed by the acid containing a polar group and the alkali containing a polar group, for example, carboxylic acid group (carboxyl group), sulfonic acid group (sulfonic group), phosphonic acid group, phosphoric acid group, primary to quaternary ammonium salt groups, carboxylic acid salt groups, sulfonic acid salt groups, phosphonic acid salt groups, phosphate groups, etc. can be cited.

In addition, since the anticorrosive agent forms complex ions by bonding with metal ions, thereby isolating the metal surface and making it easier to protect, it is preferred that the anticorrosive agent be a compound containing a carboxyl group.

Specific examples of the above-mentioned corrosion inhibitors include imidazole, benzimidazole, 1,2,4-triazole, benzotriazole (BTA), tolyltriazole (TTA), butylbenzyltriazole, alkyldithiothiadiazole, alkylthiol, 2-aminopyrimidine, 5,6-dimethylbenzimidazole, 2-amino-5-butyl-1,3,4-thiadiazole, 2,5-dibutyl-1,3,4-thiadiazole (DMTDA), 2-butylpyrimidine, 2-butylbenzoxazole, 2-butylbenzothiazole (MBT), 2-butylbenzimidazole, and the like.

Other specific examples of the above-mentioned preservatives include aliphatic carboxylic acids such as acetic acid, propionic acid, palmitic acid, stearic acid, lauric acid, arachidic acid, terephthalic acid, and oleic acid; carboxylic acids such as glycolic acid, lactic acid, oxalic acid, malic acid, tartaric acid, and citric acid; amino polycarboxylic acids such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), ethylenediaminediacetic acid (EDDA), and ethylene glycol diethyl ether diaminetetraacetic acid (GEDA); uric acid; gallic acid, etc.

The corrosion inhibitor may be used alone or in combination of two or more. In addition, considering that the stability over time is improved, the corrosion inhibitor preferably includes a compound containing a nitrogen atom (nitrogen-containing compound), more preferably a nitrogen-containing compound, and even more preferably a heterocyclic compound containing at least one of a nitrogen atom and a sulfur atom.

The method for forming the protective layer containing such an anti-corrosion agent is not particularly limited, and examples thereof include a method of adding the isolation metal recovered in the above-mentioned drying step to an aqueous solution containing the anti-corrosion agent and stirring the solution; a method of adding the anti-corrosion agent to a washing solvent for washing the isolation metal recovered in the above-mentioned drying step, and the like.

[Reduction or removal step] Considering the reason that metal nanowires with low connection resistance can be obtained, the manufacturing method of the present invention preferably has a step of reducing or removing the surface oxide layer of the isolation metal between the isolation step and the crushing step (before the drying step when the drying step is included). As the reduction or removal step, for example, there can be cited a step of implementing an immersion treatment using an alkaline aqueous solution and an acid aqueous solution as described in the removal treatment of the anodic oxide film.

[Composition] The metal nanowires produced by the production method of the present invention are preferably used as a composition containing metal nanowires, and are more preferably used as a composition in a paste state. In the following description, the composition containing metal nanowires produced by the production method of the present invention is formally referred to as "the composition of the present invention". Therefore, the content (concentration) of the metal nanowires in the composition of the present invention is not particularly limited, but considering that the dispersion stability over time can be well maintained and the uniformity during dilution is also good, it is preferably 30 to 99 mass% relative to the total mass of the composition of the present invention, and 50 to 90 mass% is more preferably.

[Solvent] As any solvent included in the composition of the present invention, an organic solvent is mainly used. When water and a mixed organic solvent are used, water can be used together with the organic solvent at a ratio of 20% by volume or less. As the above-mentioned organic solvent, for example, an alcohol compound having a boiling point of 50°C to 250°C, more preferably 55°C to 200°C, can be preferably used. By using such an alcohol compound in combination, the coating in the coating step when forming a conductive film can be improved and the drying load can be reduced. The above-mentioned alcohol compound is not particularly limited and can be appropriately selected according to the purpose. As specific examples thereof, polyethylene glycol, polypropylene glycol, alkylene glycol, glycerin, etc. can be cited. These can be used alone or in combination of two or more. Specifically, ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 2,3-butylene glycol, etc., which have low viscosity at room temperature, are preferred, but pentanediol, hexanediol, octanediol, polyethylene glycol, etc., which have large carbon numbers, can also be used. Among them, diethylene glycol is the best solvent.

[Surfactant] Considering that the dispersion stability becomes better, it is preferable to use a surfactant in the composition of the present invention. As the above-mentioned surfactant, for example, non-ionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, fluorine-based surfactants, etc. can be cited, and these surfactants can be used alone or in combination of two or more.

The above-mentioned nonionic surfactant is not particularly limited, and conventionally known surfactants can be used. For example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polystyryl phenyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, glycerol fatty acid partial esters, sorbitan fatty acid partial esters, pentaerythritol fatty acid partial esters, propylene glycol mono fatty acid esters, sucrose fatty acid partial esters, polyoxyethylene sorbitan fatty acid partial esters, polyoxyethylene sorbitan fatty acid partial esters, polyethylene glycol fatty acid esters, polyglycerol fatty acid partial esters, polyoxyethylene castor oils, polyoxyethylene glycerol fatty acid partial esters, fatty acid diethanolamides, N,N-bis-2-hydroxyalkylamines, polyoxyethylene alkylamines, triethanolamine fatty acid esters, trialkylamine oxides, polyethylene glycol (for example, polyethylene glycol monostearate, etc.), and copolymers of polyethylene glycol and polypropylene glycol can be cited.

The above-mentioned anionic surfactant is not particularly limited, and conventionally known ones can be used. For example, fatty acid salts, rosin acid salts, hydroxy alkane sulfonates, alkane sulfonates, dialkyl sulfosuccinate salts, linear alkylbenzene sulfonates, branched alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkylphenoxy polyoxyethylene propyl sulfonates, polyoxyethylene alkyl sulfophenyl ether salts, N-methyl-N-oleyl taurine sodium salt, N-alkyl sulfosuccinic acid monoamide disodium salt, petroleum sulfonates, sulfated tallow oil, sulfuric acid of fatty acid alkyl esters can be cited. Esters, alkyl sulfates, polyoxyethylene alkyl ether sulfates, fatty acid monoglyceride sulfates, polyoxyethylene alkyl phenyl ether sulfates, polyoxyethylene styrene phenyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, polyoxyethylene alkyl phenyl ether phosphates, partially saponified styrene/maleic anhydride copolymers, partially saponified olefin/maleic anhydride copolymers, naphthalenesulfonate formalin condensates.

The cationic surfactant is not particularly limited, and any conventionally known surfactant can be used. Examples thereof include alkylamine salts, quaternary ammonium salts, polyoxyethylene alkylamine salts, and polyethylene polyamine derivatives.

The above-mentioned amphoteric surfactant is not particularly limited, and conventionally known surfactants can be used. For example, carboxybetaines, aminocarboxylic acids, sulfobetaines, aminosulfates, and imidazolines can be mentioned.

Furthermore, in the above-mentioned surfactants, "polyoxyethylene" can also be replaced by "polyoxyalkylene" such as polyoxymethylene, polyoxypropylene, polyoxybutylene, etc., and in the present invention, these surfactants can also be used.

In the present invention, as a preferred surfactant, a fluorine-based surfactant having a perfluoroalkyl group in the molecule can be cited. As such a fluorine-based surfactant, for example, anionic types such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and perfluoroalkyl phosphates; amphoteric types such as perfluoroalkyl betaines; cationic types such as perfluoroalkyl trimethylammonium salts; nonionic types such as perfluoroalkyl amine oxides, perfluoroalkyl ethylene oxide adducts, oligomers having perfluoroalkyl groups and hydrophilic groups, oligomers having perfluoroalkyl groups and lipophilic groups, oligomers having perfluoroalkyl groups, hydrophilic groups, and lipophilic groups, and amine esters having perfluoroalkyl groups and lipophilic groups can be cited. Also, the fluorine-based surfactants described in the Japanese Patent Publication No. 62-170950, Japanese Patent Publication No. 62-226143, and Japanese Patent Publication No. 60-168144 are also preferred.

Furthermore, in the present invention, among the surfactants, it is preferred to use an HLB value of 10 or more because the dispersion stability becomes further improved. Here, the HLB value (Hydrophile-Lipophile Balance) is a value indicating the affinity of the surfactant to water and oil (organic compounds insoluble in water). The HLB value is a value between 0 and 20, and the closer to 0, the higher the lipophilicity, and the closer to 20, the higher the hydrophilicity.

In the present invention, the surfactants may be used alone or in combination of two or more. In addition, the content of the surfactants is preferably 0.001 to 10% by mass, and more preferably 0.01 to 5% by mass, relative to the total mass of the metal nanowires.

[Water-soluble dispersant] The composition of the present invention can use water-soluble organic molecules having a hydroxyl group, carboxyl group, sulfonyl group, phosphate group, amine group, SH group, etc. at the end, such as succinic acid, polyvinyl alcohol (PVA), polyvinyl pyrrole (PVP) and other water-soluble dispersants.

[Conductive particles] The composition of the present invention may further contain conductive particles other than metal nanowires. Here, the conductive particles preferably contain metals, and more preferably contain at least one metal selected from the group consisting of gold, silver, copper, aluminum, nickel, zinc, and cobalt. Furthermore, the conductive particles may contain one or more conductive components other than metals.

In the present invention, the shape of the conductive particles is not particularly limited, and may be solid or hollow. In addition, the average major diameter of the conductive particles in the smallest enclosing ellipse is preferably 0.01 μm or more and 50 μm or less. In addition, the average major diameter of the conductive particles in the smallest enclosing ellipse is preferably 1 to 10 times the average minor diameter. Here, the smallest enclosing ellipse refers to the ellipse with the smallest volume that contains the conductive particles, and also includes an ellipse with the same major diameter and minor diameter (i.e., a sphere). In addition, the average major diameter in the minimum enclosing ellipse can be obtained by observing the cross section in the thickness direction of the layer formed by the dispersion using a microscope (e.g., an electron microscope), measuring the major diameters of 100 arbitrary microparticles, and calculating the average. Similarly, the average minor diameter in the minimum enclosing ellipse can be obtained by observing the cross section in the thickness direction of the layer formed by the dispersion using a microscope (e.g., an electron microscope), measuring the minor diameters of 100 arbitrary microparticles, and calculating the average. In addition, the median particle size (D50) described below refers to the median particle size of the diameter when the volume of the conductive particles is approximated to a sphere, and can be obtained by laser diffraction scattering method or dynamic light scattering method.

In the present invention, when the conductive particles are contained, the content of the conductive particles is not particularly limited, but is preferably 5 to 70 parts by mass, more preferably 10 to 45 parts by mass, based on 100 parts by mass of the metal nanowires.

The composition of the present invention can be preferably used as a conductive ink for forming a circuit pattern of a wiring substrate. When used as a conductive ink, the circuit pattern can be printed by inkjet. The content (concentration) of the above-mentioned metal nanowires in the composition of the present invention is preferably 10 to 30 mass % relative to the total mass of the composition of the present invention, and more preferably 15 to 20 mass %.

[Conductive bonding material] The composition of the present invention can be preferably used to form a conductive bonding material. Here, in the present invention, the conductive bonding material is a concept that includes not only a film formed on the entire surface of the desired substrate, but also the above-mentioned circuit pattern, etc. In addition, the substrate for forming the conductive film or the method for forming the conductive film is not particularly limited, for example, the substrate or the method for forming the conductive film described in Japanese Patent Publication No. 2010-84173 can be adopted. The conductive bonding material of the present invention can be preferably used as a semiconductor bonding component, a touch panel, an electrode bonding material for a display, an electromagnetic wave shielding member, a sintered material, an electrode material for a thin-layer ceramic capacitor, and a conductive bonding material used in various other devices, etc. [Examples]

The present invention is further described in detail below based on the embodiments. The materials, usage amounts, ratios, processing contents, processing procedures, etc. shown in the following embodiments can be appropriately changed as long as they do not deviate from the purpose of the present invention. Therefore, the scope of the present invention should not be limited by the embodiments shown below.

[Example 1] ＜Preparation of aluminum substrate＞ A molten metal was prepared using an aluminum alloy containing Si: 0.06 mass%, Fe: 0.30 mass%, Cu: 0.005 mass%, Mn: 0.001 mass%, Mg: 0.001 mass%, Zn: 0.001 mass%, Ti: 0.03 mass% and the remainder being Al and inevitable impurities. After molten metal treatment and filtration, a casting with a thickness of 500 mm and a width of 1200 mm was produced using a DC (Direct Chill) casting method. Then, the surface was shaved to an average thickness of 10 mm using a face shaving machine, and then the surface was maintained at 550°C for about 5 hours. When the temperature was lowered to 400°C, a rolled plate with a thickness of 2.7 mm was produced using a hot rolling machine. Furthermore, after heat treatment at 500°C using a continuous annealing machine, the aluminum substrate was finished to a thickness of 1.0 mm by cold rolling to obtain a JIS (Japanese Industrial Standard) 1050 material. After the aluminum substrate was formed into a wafer shape with a diameter of 200 mm (8 inches), the following treatments were performed.

<Electrolytic polishing> The aluminum substrate was subjected to electrolytic polishing using the electrolytic polishing liquid of the following composition at a voltage of 25 V, a liquid temperature of 65°C, and a liquid flow rate of 3.0 m/min. The cathode was a carbon electrode, and the power source was GP0110-30R (manufactured by TAKASAGO LTD.). The flow rate of the electrolyte was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE Corporation). (Electrolytic polishing liquid composition) · 85 mass% phosphoric acid (a reagent manufactured by Wako Pure Chemical Industries, Ltd.) 660 mL · Pure water 160 mL · Sulfuric acid 150 mL · Ethylene glycol 30 mL

<Anodic oxidation step> Then, the aluminum substrate after electrolytic polishing was subjected to anodic oxidation treatment based on the self-ordering method according to the procedure described in Japanese Patent Publication No. 2007-204802. The aluminum substrate after electrolytic polishing was subjected to pre-anodic oxidation treatment for 5 hours using an electrolyte solution of 0.50 mol/L oxalic acid at a voltage of 40 V, a liquid temperature of 16°C, and a liquid flow rate of 3.0 m/min. Afterwards, the aluminum substrate after pre-anodic oxidation was immersed in a mixed aqueous solution of 0.2 mol/L chromic anhydride and 0.6 mol/L phosphoric acid (liquid temperature: 50°C) for 12 hours for film removal treatment. After that, a 0.50 mol/L oxalic acid electrolyte was used to perform re-anodization for 5 hours at a voltage of 40 V, a liquid temperature of 16°C, and a liquid flow rate of 3.0 m/min to obtain an anodic oxide film with a film thickness of 40 μm. In addition, in the pre-anodization treatment and the re-anodization treatment, the cathode was set to a stainless steel electrode, and the power source used was GP0110-30R (manufactured by TAKASAGO LTD.). In addition, as a cooling device, NeoCool BD36 (manufactured by Yamato Scientific co., ltd.) was used, and as a stirring and heating device, a counter stirrer PS-100 (manufactured by TOKYO RIKAKIKAI CO, LTD.) was used. Furthermore, the flow rate of the electrolyte was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE Corporation.).

<Metal filling step> Next, electroplating was performed using the aluminum substrate as the cathode and platinum as the positive electrode. Specifically, a metal-filled microstructure in which copper is filled inside the porous (micropores) was produced by performing constant current electrolysis using a copper plating solution of the composition shown below. Here, in constant current electrolysis, a plating device manufactured by YAMAMOTO-MS Co., Ltd. and a power source (HZ-3000) manufactured by HOKUTO DENKO CORPORATION were used, and cyclic voltammetry was performed in the plating solution to confirm the deposition potential, and then the treatment was performed under the conditions shown below. (Copper plating solution composition and conditions) • Copper sulfate 100g/L • Sulfuric acid 50g/L • Hydrochloric acid 15g/L • Temperature 25℃ • Current density 10A/ ^dm2

The surface of the anodic oxide film after the pores were filled with metal was observed by FE-SEM, and the sealing rate (number of sealed pores/1000) was calculated by observing whether there were any pores sealed with metal among 1000 pores, and the result was 96%. In addition, the anodic oxide film after the pores were filled with metal was cut in the thickness direction by FIB, and the cross-section was photographed by FE-SEM (magnification of 50,000 times), and the inside of the pores was confirmed. The result showed that in the sealed pores, the filling height from the bottom of the pores was 35μm.

<Isolation step> The filled metal is isolated from the anodic oxide film and the aluminum substrate by immersing in a 60°C potassium hydroxide aqueous solution (concentration: 5 mol/L) for 300 seconds to obtain an isolated metal. Specifically, the anodic oxide film is dissolved by immersing in a 60°C potassium hydroxide aqueous solution (concentration: 5 mol/L) for 300 seconds, and the aluminum substrate is peeled off while the anodic oxide film is dissolved (after 300 seconds) to isolate the filled metal.

<Drying step> Next, the isolation metal was recovered by suction filtration using a membrane (0.4 μm, PTFE, manufactured by Omnipore) and dried.

<Washing/Protective layer forming step/Reduction or removal step> Next, the isolation metal recovered on the membrane was washed for 1 minute using the washing solvent shown below. Furthermore, in Example 1, since an anti-corrosion agent was added to the washing solvent, the protective layer was formed while washing. Also, in Example 1, since citric acid was used as an anti-corrosion agent, the surface oxide layer of the isolation metal was removed while forming the protective layer. Thereafter, the isolation metal on the membrane was recovered. (Washing solvent) Aqueous solution containing 1 mass% citric acid

<Crushing step> Next, 1 mass % of the recovered isolation metal was added to water, and a crushing treatment based on pores was performed using Star BurstMini manufactured by Sugino Machine. After that, the isolation metal subjected to the crushing treatment was recovered by suction filtration using a membrane (0.4μm, PTFE, manufactured by Omnipore), and was dried under reduced pressure for 12 hours to produce metal nanowires.

[Example 2] The steps from "preparation of aluminum substrate" to "cleaning/protective layer formation step/reduction or removal step" in Example 1 were repeated twice, and twice the amount of isolation metal as in Example 1 was recovered. Thereafter, metal nanowires were produced by the same method as in Example 1 except that the concentration of isolation metal during the crushing process was changed to 40% by mass.

[Example 3] Metal nanowires were produced by the same method as Example 1 except that the concentration of the isolation metal during the crushing process was changed to 0.5 mass %.

[Example 4] Metal nanowires were produced by the same method as Example 1 except that the washing solvent in the washing/protective layer forming step/reduction or removal step was changed to water. That is, in Example 4, no protective layer was formed.

[Example 5] Metal nanowires were produced by the same method as Example 1 except that the washing solvent in the washing/protective layer formation step/reduction or removal step was changed to an aqueous solution containing 1 mass % of citric acid and benzotriazole, respectively.

[Example 6] Metal nanowires were produced by the same method as in Example 1 except that the aluminum substrate was dissolved and removed by immersing in a 0.5 mass% Cu-12% HCl aqueous solution at 10°C for 1 hour before immersing in an aqueous solution of potassium hydroxide in the isolation step.

[Example 7] Metal nanowires were produced by the same method as Example 1 except that the liquid used in the crushing step was changed to water and a 1 mass % citric acid aqueous solution was used.

[Example 8] Metal nanowires were produced by the same method as Example 1 except that the type of metal used in the metal filling step was changed to Ni.

[Example 9] Metal nanowires were produced by the same method as Example 1 except that an electroless Au plating treatment was performed after the crushing step.

[Example 10] Metal nanowires were produced by the same method as Example 1 except that the washing solvent in the washing/protective layer formation step/reduction or removal step was changed to an aqueous solution containing 1 mass % of citric acid and 2-hydroxybenzothiazole, respectively.

[Example 11] Metal nanowires were produced by the same method as Example 1 except that the metal filling height in the metal filling step was set to 15 μm.

[Example 12] Before the cleaning/protective layer forming step/reduction or removal step, the surface oxide layer of the metal nanowire was reduced or removed by immersing it in a 10 mass % aqueous solution of sulfuric acid at 35°C for 15 seconds. Metal nanowires were manufactured by the same method as in Example 1.

[Comparative Example 1] Metal nanowires were produced by the same method as Example 1 except that the crushing step was not performed.

[Evaluation] 〔Preparation of composition〕 The recovered metal nanowires were added to polyethylene glycol (molecular weight 200) until the concentration reached 80 wt%, and the composition was prepared by centrifugal stirring using Awatori Rentaro (ARE-400TWIN, manufactured by THINKY CORPORATION). The prepared composition was in a paste state.

[Connecting resistor] Using a metal mask (opening: 1×1mm×0.2mm), the prepared composition was applied to a Cu plate (10mm×10mm×0.5mm) with a scraper, and a Cu plate (5mm×5mm×0.5mm) was placed on the applied composition. After that, a bonding device (WP-100, manufactured by PMT) was used, and the atmosphere in the device was replaced with a reducing gas (N2: 85%, formic acid: 15%), and then hot-pressed at 250°C, 1 minute, and 5MPa for bonding. Next, using Loresta GP manufactured by Dia Instruments Co., Ltd., the distance between the measuring terminals (pins) was set to 3 mm, the measuring terminals were placed on the upper and lower copper plates, and the pressing pressure (spring pressure) of the measuring terminals was set to 200 g to measure the connection resistance, and the evaluation was performed according to the following criteria. The results are shown in Table 1 below. <Evaluation Criteria> A: Resistance of 120% or less relative to copper B: Resistance of more than 120% and less than 150% relative to copper C: Resistance of more than 150% relative to copper

[Joint strength] For the samples for which the connection resistance was measured, the die shear strength was measured using a 4000 universal bonding strength tester manufactured by Nordson and evaluated according to the following criteria. The results are shown in Table 1 below. <Evaluation criteria> A: 15MPa or more B: 10MPa or more and less than 15MPa C: less than 10MPa

【Table 1】 Metal filling steps Removal of valve metal substrate Removal of anodic oxide film Restore/Remove Cleaning/protective layer formation step Crushing steps Reviews Metal Type Filling height Technique Dissolution method Concentration time Concentration Anticorrosive Solvent Needle metal concentration Connecting resistor Bonding strength μm mol/L Second Sulfuric acid treatment Quality% Quality% Embodiment 1 Cu 35 Removal of anodic oxide film when it dissolves KOH 5 300 - 1 Citric Acid - water 1 A A Embodiment 2 Cu 35 Removal of anodic oxide film when it dissolves KOH 5 300 - 1 Citric Acid - water 40 A B Embodiment 3 Cu 35 Removal of anodic oxide film when it dissolves KOH 5 300 - 1 Citric Acid - water 0.5 A A Embodiment 4 Cu 35 Removal of anodic oxide film when it dissolves KOH 5 300 - - - - water 1 C B Embodiment 5 Cu 35 Removal of anodic oxide film when it dissolves KOH 5 300 - 1 Citric Acid Benzotriazole water 1 A A Embodiment 6 Cu 35 Immersion in aqueous hydrochloric acid solution KOH 5 300 - 1 Citric Acid - water 1 A A Embodiment 7 Cu 35 Removal of anodic oxide film when it dissolves KOH 5 300 - 1 Citric Acid - 1wt% Citric acid 1 A B Embodiment 8 Ni 35 Removal of anodic oxide film when it dissolves KOH 5 300 - 1 Citric Acid - water 1 B B Embodiment 9 Cu/Au 35 Removal of anodic oxide film when it dissolves KOH 5 300 - 1 Citric Acid - water 1 A B Embodiment 10 Cu 35 Removal of anodic oxide film when it dissolves KOH 5 300 - 1 Citric Acid 2-Benzothiazole water 1 A A Embodiment 11 Cu 15 Removal of anodic oxide film when it dissolves KOH 5 300 - 1 Citric Acid - water 1 A A Embodiment 12 Cu 35 Removal of anodic oxide film when it dissolves KOH 5 300 have 1 Citric Acid - water 1 A A Comparison Example 1 Cu 35 Removal of anodic oxide film when it dissolves KOH 5 300 - 1 Citric Acid - -

From the results shown in Table 1, it can be seen that when the crushing step is not performed, the bonding strength of the produced metal nanowire (isolated metal) becomes low (Comparative Example 1). In contrast, it can be seen that when the crushing step is not performed, the bonding strength of the produced metal nanowire becomes high (Examples 1 to 12). In particular, from the comparison of Examples 1 to 3, it can be seen that when the concentration of the isolated metal during the crushing process is 0.5 to 30 mass%, a metal nanowire with high bonding strength during bonding can be produced. In addition, from the comparison of Example 1 and Example 7, it can be seen that when the crushing is performed using an aqueous solution with an alkali or acid concentration of less than 1 mass%, a metal nanowire with high bonding strength during bonding can be produced.

1: Valve metal substrate 2: Porous (micropores) 3: Anodic oxide film 4: Metal 5: Isolation metal 10: Metal nanowires

FIG. 1A is a schematic cross-sectional view of a valve metal substrate before an anodic oxidation step in a procedure of an example of a method for manufacturing a metal nanowire of the present invention. FIG. 1B is a schematic cross-sectional view of a structure after an anodic oxidation step in a procedure of an example of a method for manufacturing a metal nanowire of the present invention. FIG. 1C is a schematic cross-sectional view of a structure after a metal filling step in a procedure of an example of a method for manufacturing a metal nanowire of the present invention. FIG. 1D is a schematic cross-sectional view of a structure after an isolation step in a procedure of an example of a method for manufacturing a metal nanowire of the present invention. FIG. 1E is a schematic cross-sectional view of a structure (metal nanowire) after a crushing step in a procedure of an example of a method for manufacturing a metal nanowire of the present invention.

4:Metal

10: Metal nanowires

Claims (8)

A method for manufacturing metal nanowires, comprising: an anodic oxidation step, forming a porous anodic oxide film on the surface of a valve metal substrate; a metal filling step, filling the porous pores with metal; an isolation step, isolating the filled metal from the anodic oxide film and the valve metal substrate; and a crushing step, crushing the isolated metal to obtain metal nanowires. The method for manufacturing metal nanowires as described in claim 1, wherein between the aforementioned isolation step and the aforementioned crushing step, there is also a drying step of drying the aforementioned metal isolated. The method for manufacturing metal nanowires as described in claim 1 or claim 2, wherein between the aforementioned isolation step and the aforementioned crushing step, there is also a step of reducing or removing the surface oxide layer of the isolated aforementioned metal. The method for manufacturing metal nanowires as described in claim 1 or claim 2 further comprises a protective layer forming step of forming a protective layer containing an anti-corrosion agent on the isolated metal. A method for manufacturing metal nanowires as described in claim 1 or claim 2, wherein the valve metal substrate comprises aluminum. A method for manufacturing metal nanowires as described in claim 1 or claim 2, wherein the aforementioned metal filling step includes a coating step. A method for manufacturing metal nanowires as described in claim 1 or claim 2, wherein the aforementioned isolation step includes a dissolution step. A method for producing metal nanowires as described in claim 1 or claim 2, wherein the aforementioned crushing step is performed in water or an aqueous solution having an alkali or acid concentration of less than 1 mass %.

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