JP7645094B2 - Method for manufacturing fine linear bodies - Google Patents

Description

The present invention relates to a method for manufacturing fine linear bodies using a metal as a base material.

Due to their tiny size and high aspect ratio, so-called nanowires are expected to exhibit physical and chemical properties (e.g., electrical conductivity, thermal conductivity, luminescence properties, catalytic activity, etc.) that are not found in conventional materials. The applicant previously proposed ultrafine metal filaments described in Patent Document 1 as a conventional technique related to such nanowires.

In Patent Document 1, ultrafine metal filaments are produced by electrolytically reducing metal ions in a nonaqueous electrolyte containing the metal ions. The metal ions are present in the nonaqueous electrolyte in the form of a stable complex. Specifically, a charge-neutralized body formed by electrically neutralizing the complex in the aqueous phase with a counter ion having an opposite charge to the complex is continuously extracted from the aqueous phase into the nonaqueous electrolyte, and the metal ions in the charge-neutralized body extracted into the nonaqueous electrolyte are electrolytically reduced. In the electrolytic reduction, a wire is used as the cathode, and the tip of the wire is opposed to the anode.

JP 2009-299103 A

According to the method described in Patent Document 1, it is possible to manufacture very thin and long ultrafine metal filaments. However, this method uses two phases, an aqueous phase and a non-aqueous electrolyte phase, and therefore the manufacturing process is complicated, and there is room for improvement in terms of industrial productivity.
SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a method for producing fine metal filaments with good productivity.

The present invention provides a method for producing a fine linear body having a metal base material, the method comprising the steps of depositing a metal on a cathode by electrolytic reduction using an electrolyte solution containing a metal element source, the method comprising the steps of:
The present invention provides a method for producing fine linear bodies, in which electrolytic reduction is carried out in a state in which an oily substance is present on the surface of the cathode.

The method of the present invention makes it possible to produce fine metal filaments with high productivity.

FIG. 1 is a scanning electron microscope image of the fine linear bodies obtained in Example 1.

The present invention will be described below based on its preferred embodiments. The present invention relates to a method for producing fine linear bodies. In the following description, the term "fine linear body" may refer to an individual linear body or to a collection of multiple linear bodies, depending on the context. The fine linear body produced according to the production method of the present invention (hereinafter also referred to as "the present production method") is typically a linear body extending in one direction. The state in which the linear body extends in one direction varies depending on the state of the linear body when observed. For example, the linear body extends in a straight line, or extends in one direction while meandering in a curved manner. This linear body is characterized by its long length despite being very thin.

In the present invention, electrolysis is preferably used to manufacture the fine filaments. This is because electrolysis allows the electrolyte to be reused repeatedly, so less liquid is required to manufacture the fine filaments, and at the same time, the amount of waste liquid to be treated can be reduced. Another method for manufacturing metal powder is the atomization method, but it is not possible to manufacture anisotropic shapes such as fine filaments. Another method is the wet reduction method, but this method does not allow the solution to be reused repeatedly, and it is impossible to increase the concentration of the desired metal element above a certain level, so it is not possible to manufacture fine filaments with good productivity.

When producing fine filaments by electrolysis, for example, an anode and a cathode are immersed in a sulfuric acid electrolyte containing a metal element source, a direct current is passed through the electrolyte to perform electrolytic reduction, and fine filaments are precipitated on the surface of the cathode, and the precipitated fine filaments are scraped off and collected by a mechanical or electrical method, and the collected fine filaments are washed with water, dried, and sieved as necessary.

There is no particular restriction on the type of metal element used in the present manufacturing method, so long as the fine linear bodies can be manufactured by the present manufacturing method. Considering the balance between high electrical conductivity and ease of industrial use, copper, zinc, tin, iron, nickel, cobalt, lead, bismuth, silver, gold, or platinum can be mentioned. These metal elements have in common that they can be electrolytically deposited from an aqueous solution, so that they can be manufactured in the same manner according to the present manufacturing method, regardless of which metal element is used. Among these, it is particularly preferable to use copper or zinc as the base material. Note that "using copper or zinc as the base material" means that the proportion of copper or zinc in the fine linear bodies is 70% by mass or more, preferably 90% by mass or more.
The fine linear bodies obtained by the present manufacturing method may be composed of only the desired metal element, excluding inevitable impurities, or may be composed of an alloy of the desired metal element, excluding inevitable impurities, or may be composed of a combination of two or more of the above-mentioned metal elements, excluding inevitable impurities.

When manufacturing fine filaments by the above-mentioned procedure, the inventors have found that it is advantageous to carry out electrolytic reduction with an oily substance attached to the surface of the cathode. By reducing the ions of the metal elements under such conditions, it is possible to control the reduction reaction. The details are as follows.
The amount of oily substance to be attached to the cathode surface is expressed in thickness, and is on average several hundred nm or more, preferably several to several hundred μm. However, the thickness varies locally due to the fluctuation of the electrolyte. Although almost no metal ions coexist in the oily substance, the electrolyte containing metal ions may float in the form of droplets in the oily substance, or a very small amount of the electrolyte may be intermittently drawn to the vicinity of the electrode by the force of the electric field formed by applying electricity. Under such circumstances, a reduction reaction of the metal occurs on the surface of the cathode, and a metal protrusion is formed locally. The thickness of the oily substance directly above this protrusion is thinner than other parts, so the electrical resistance in that part decreases, the current becomes concentrated there, and the protrusion becomes linear and grows. In this way, fine filaments of metal are formed by electrolysis.

Methods for attaching the oily substance to the surface of the cathode described above include, for example, a method of directly applying the oily substance to the surface of the cathode, a method of immersing the cathode in a container containing the oily substance and attaching it to the surface of the cathode by floating the oily substance on the electrolyte and immersing the cathode from above. Another method is to suspend the oily substance in the electrolyte and stir the suspended electrolyte so that the suspended oily substance hits the surface of the cathode and adheres to the surface of the cathode as it is. In addition, if the oily substance has the property of dissolving in a small amount in the electrolyte, even if the suspended oily substance does not directly touch the electrode, the oily substance once dissolved in the electrolyte will be continuously adsorbed onto the electrode surface and will ultimately exhibit the same effect as adhering to the surface.

Examples of the oily substance to be attached to the surface of the cathode include various organic compounds that are poorly soluble or insoluble in water and have a viscosity sufficient to be retained on the surface of the cathode after being attached thereto. Note that "poorly soluble or insoluble in water" means that the compound has a dissolution amount of 100 g or less in 1 L of water at the temperature when the fine linear bodies are produced.
The oily substance may be in a liquid or solid form. The oily substance may be dissolved in a liquid solvent at room temperature (20 to 30° C.) before use.
For the purpose of making it easier to control the physical properties of the precipitated fine linear bodies, additives such as benzoic acid, fumaric acid, citric acid, benzotriazoles, etc. may be further used in the oily substance.

The organic compound may be, provided that it is poorly soluble or insoluble in water, an aliphatic hydrocarbon, an aromatic hydrocarbon, an aliphatic alcohol, an aromatic alcohol, an aliphatic aldehyde, an aromatic aldehyde, an aliphatic ether, an aromatic ether, an aliphatic ketone, an aromatic ketone, an aliphatic carboxylic acid and its salt, an aromatic carboxylic acid and its salt, an amide of an aliphatic carboxylic acid, an amide of an aromatic carboxylic acid, an ester of an aliphatic carboxylic acid, an ester of an aromatic carboxylic acid, a silicone (e.g., dimethyl silicone), an aliphatic amine, an aromatic amine, a nitrogen-containing heterocyclic compound, tributyl phosphate, a thiol, a fluorine-based solvent, an ionic liquid, etc. In this specification, the term "aliphatic alcohol" refers to an alcohol having 5 or more carbon atoms.
As a result of the inventor's investigations, it has been found that fine filaments can be produced more successfully by using, as the oily substance, particularly, a fatty acid or a salt thereof, an ester thereof, or an amide thereof, an aromatic carboxylic acid, an aliphatic hydrocarbon, an aliphatic alcohol, an aliphatic amine, a silicone (e.g., dimethyl silicone), or a mixture thereof.

The fatty acid may be a lower fatty acid or a higher fatty acid. The lower fatty acid may be a saturated or unsaturated aliphatic carboxylic acid having preferably 9 or less carbon atoms. The higher fatty acid may be a saturated or unsaturated aliphatic carboxylic acid having preferably 10 to 25 carbon atoms, more preferably 10 to 22 carbon atoms, and even more preferably 11 to 20 carbon atoms.
Examples of saturated aliphatic carboxylic acids include caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, arachidic acid, henicosylic acid, behenic acid, tricosylic acid, and lignoceric acid.

The unsaturated aliphatic carboxylic acid may have one or more unsaturated carbon bonds in the molecule.
Examples of unsaturated aliphatic carboxylic acids having one unsaturated carbon bond in the molecule include crotonic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid, erucic acid, and nervonic acid.
Examples of unsaturated aliphatic carboxylic acids having two or more unsaturated carbon bonds in the molecule include linoleic acid, eicosadienoic acid, docosadienoic acid, and linolenic acid.

Examples of aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid, trimellitic acid, trimesic acid, mellophanic acid, prenylic acid, pyromellitic acid, mellitic acid, diphenic acid, toluic acid, xylyl acid, hemellitic acid, mesitylene acid, prenylic acid, and γ-isoduryl acid. duric acid, β-isodurric acid, mesic acid, α-isodurric acid, cumic acid, ubitolic acid, α-toluic acid, hydratropic acid, atropic acid, hydrocinnamic acid, cinnamic acid, salicylic acid, anisic acid, cresotinic acid, o-homosalicylic acid, o-cresotinic acid, m-homosalicylic acid, m-cresotinic acid, p-homosalicylic acid, p-cresotinic acid, o-pyrocatechuic acid, β-resorcylic acid, gentisic acid, γ-resorcylic acid, protocatechuic acid, α-resorcylic acid, vanillic acid, isovanillic acid, veratrum, o-veratric acid, orsellinic acid , m-hemipinic acid, gallic acid, syringic acid, asaronic acid, mandelic acid, vanillic acid, mandelic acid, homoanisic acid, homogentisic acid, homoprotocatechuic acid, homovanillic acid, homoisovanillic acid, homoveratric acid, o-homoveratric acid, homophthalic acid, homoisophthalic acid, homoterephthalic acid, phthalonic acid, isophthalonic acid, terephthalonic acid, benzilic acid, atrolactic acid, tropic acid, mellitic acid, phloretic acid, hydrocaffeic acid, hydroferulic acid, hydroisoferulic acid, p-coumaric acid, umbellic acid, caffeic acid, ferulic acid, isoferulic acid, sinapic acid, benzoyl, phthaloyl, isophthaloyl, terephthaloyl, toluic acid oil, xyloyl, cumoyl, α-toluoyl, hydroatropoyl, atropoyl, hydrocinnamoyl, cinnamoyl, salicyloyl, anisoyl, cresotoyl, o-pyrocatechuyl, β-resorcyloyl, gentisoyl, γ-resorcyloyl, protocatechuyl, α-resorcyloyl, vanilloyl, isovanilloyl, o-veratroyl, veratroyl, galloyl, syringoyl, mandeloyl, vanilmandeloyl, homogentisoyl, homovanilloyl, homoveratroyl, benzylloyl, tropoyl, caffeoyl, feruloyl, perbenzoic acid, ibuprofen, ketoprofen, and felbinac.

Among the above fatty acids, it is preferable to use saturated aliphatic carboxylic acids or unsaturated aliphatic carboxylic acids, since this allows for more successful production of fine linear bodies.

The ester of the fatty acid is preferably an ester with a saturated aliphatic alcohol or an unsaturated aliphatic alcohol. The carbon number of this alcohol is preferably 1 to 18. The ester of the fatty acid is more preferably an ester with a saturated aliphatic alcohol having 1 to 18 carbon atoms. An example of such an ester is ethyl acetate.

The amount of oily substance adhered to the surface of the cathode is preferably 0.1 g/m2 or ^more and 500 g/m2 or ^less per unit surface area of the cathode, more preferably 1 g/m2 or ^more and 500 g/ ^m2 or less, even more preferably 3 g/ ^m2 or more and 200 g/m2 or ^less , and even more preferably 5 g/ ^m2 or more and 100 g/ ^m2 or less.

The anode and cathode may be made of any known material without any particular limitations. For example, the anode and cathode may be made of titanium or copper. An insoluble metal electrode (DSE) may also be used for the anode.
In relation to this, the current density during reduction is preferably 5 A/m2 or ^more and 3000 A/ ^m2 or less, more preferably 10 A/ ^m2 or more and 1000 A/ ^m2 or less, and even more preferably 50 A/ ^m2 or more and 500 A/ ^m2 or less.

Usually, in the deposition of metals by electrolysis, a good surface shape can be obtained by passing an amount of electricity corresponding to a reduction rate slower than the supply rate of metal ions from the electrolytic solution (for example, in the case of plating, a state in which a metallic luster is obtained on the surface). Similarly, in the electrolysis of the present invention, it is preferable that the concentration of ions of metal elements in the electrolytic solution is a concentration that can supply metal ions without excess or deficiency to the reaction rate of reduction of the metal ions, and from this viewpoint, the concentration of metal ions is preferably 1 g/L or more and 80 g/L or less, and more preferably 3 g/L or more and 60 g/L or less.
From the same viewpoint, it is preferable to stir or circulate the electrolytic solution in the electrolytic cell during electrolysis.
The electrolyte may be used in an unheated state, such as at room temperature (25° C.), or in a heated state.
From the same viewpoint, it is preferable to adjust the size of the electrolytic cell, the number of electrodes, the shape of the electrodes (plate-like, drum-like), the distance between the electrodes, and the amount of electrolyte circulation so as to constantly maintain a high metal ion concentration in the electrolyte near the electrodes.

The fine linear bodies thus produced are very thin, preferably having a thickness of 30 nm to 10 μm, more preferably 30 nm to 1000 nm, even more preferably 40 nm to 500 nm, and even more preferably 45 nm to 300 nm. Despite being very thin, the fine linear bodies are long, preferably having a length of 0.3 μm to 300 μm, more preferably 0.5 μm to 100 μm, even more preferably 2 μm to 70 μm, and even more preferably 2 μm to 50 μm. By combining such thickness and length, the fine linear bodies are excellent in handleability and can be excellent in filling when used, for example, as a bonding material.
The aspect ratio (length of the fine linear body [m]/thickness of the fine linear body [m]) is preferably 5 or more and 2,500 or less, more preferably 10 or more and 2,500 or less, even more preferably 40 or more and 2,500 or less, and even more preferably 40 or more and 1,500 or less.
The thickness of the fine filaments is measured by observation under an electron microscope, and their length is measured by panoramic stitching of electron microscope photographs.

The fine filaments obtained by this manufacturing method may have a shape in which the thickness is almost uniform over their entire length, or a shape in which the thickness is not uniform but is bead-like. The fine filaments obtained by this manufacturing method have at least one end that is tapered. A "tapered shape" refers to a shape in which, when observing the end region of the fine filaments, the thickness gradually decreases toward the tip.

The shape of the fine linear bodies obtained by this manufacturing method is typically linear bodies extending in one direction, and the fine linear bodies may or may not have a main chain portion extending in one direction and a branched structure branched from the middle of the main chain portion. From the viewpoint of imparting sufficient conductivity to an object with a small amount and from the viewpoint of making it difficult for the conductivity of the object to decrease when the conductive object is stretched or bent, it is preferable that the fine linear bodies have a non-branched structure having only a main chain portion. On the other hand, from the viewpoint of the aggregate of the fine linear bodies exhibiting a bulky structure, it is preferable that the fine linear bodies have one or more branched parts. When the fine linear bodies have a branched part, it is preferable that the thickness at the parts before and after the branching is substantially the same from the viewpoint of making it easier for the aggregate of the linear bodies to exhibit a cotton-like bulky structure.

When the fine linear bodies obtained by the present production method are an aggregate containing a plurality of fine linear bodies, the aggregate may contain particles having a shape other than that of linear bodies, although it is preferable that particles having a shape other than that of linear bodies are not present in the aggregate as much as possible from the viewpoint of preventing a decrease in electrical conductivity even when the aggregate is subjected to deformation such as bending or stretching.
When the ratio of particles having a shape other than linear bodies in the aggregate is defined as the "irregular shape ratio," the irregular shape ratio is preferably 50% or less, more preferably 30% or less, and even more preferably 20% or less. By producing fine linear bodies by this production method, it is possible to easily reduce the irregular shape ratio to 50% or less.
The irregularity rate is determined by observing the sample under a scanning electron microscope (hereinafter referred to as "SEM") and calculating the percentage of [area of irregular shapes/area of fine linear bodies] in a 5000x field of view. "Irregular shapes" refers to shapes other than linear bodies (e.g., spheres, lumps, fern-like leaves, etc.).

The fine linear bodies obtained by this manufacturing method may have a structure having a main body made of a first metal element or an alloy of the first metal element, and a coating layer of a second metal element other than the first metal element arranged on the surface of the main body.
Examples of the first metal element include copper, zinc, tin, iron, nickel, cobalt, lead, bismuth, silver, gold, and platinum, as described above. Examples of the second metal element include silver, cobalt, iron, nickel, zinc, lead, tin, platinum, gold, palladium, etc., and alloys containing one or more of these metals (e.g., nickel alloys, iron alloys, etc.), provided that they are different from the first metal element. In particular, it is preferable that the second metal element has a higher conductivity than the first metal element constituting the main body or an alloy of the metal element, from the viewpoint of further increasing the conductivity imparted to the target object. From this viewpoint, when the first metal element is copper or zinc, it is preferable that the second metal element is silver.

As a method for forming a coating layer on the surface of the main body, for example, after forming the main body using the method described above, a catalyst that enables displacement plating or electroless plating is applied to the fine linear body, and then the desired metal is plated, or it can be formed using a dry method.

The fine linear bodies obtained by this manufacturing method can be combined with other substances to impart electrical conductivity to the substances. For example, the fine linear bodies obtained by this manufacturing method can be combined with other metal elements to form a bonding material, and the bonding material can be sintered to form a sintered body. These bonding materials and sintered bodies are used, for example, as materials for bonding semiconductor chips and substrates.
Moreover, the fine linear bodies obtained by the present production method can be incorporated into a resin to obtain a resin composition containing the fine linear bodies and the resin. The resin composition exhibits electrical conductivity by containing the fine linear bodies.
To impart electrical conductivity to a resin, for example, fine linear bodies may be dispersed in the resin. Alternatively, a layer containing fine linear bodies may be formed on the surface of a substrate containing a resin. In either embodiment, the resin composition can be molded into various shapes. For example, it can be molded into one-dimensional shapes such as fibers, two-dimensional shapes such as films, plates, and strips, and various three-dimensional shapes. In either shape, the resin composition exhibits sufficient electrical conductivity with the addition of a relatively small amount of fine linear bodies. The resin composition differs from conventional conductive resin compositions containing copper powder as a filler in that the electrical conductivity of the resin composition is low before and after stretching or bending the resin composition. From this perspective, when the resin composition is stretchable or bendable, the characteristics of the fine linear bodies of the present invention are effectively exhibited. Conventional conductive resin compositions tend to be easily reduced in electrical conductivity when stretched or bent.

The resin composition containing the fine linear bodies and resin obtained by this manufacturing method is suitable for use in applications that require electrical conductivity and are subject to deformation due to external forces, such as wearable devices such as bioelectrodes and flexible displays.

The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

Example 1
In this example, a fine linear body made of copper was produced.
An electrolyte solution was prepared from copper sulfate and sulfuric acid so that the copper ion concentration was 4 g/L and the free sulfuric acid concentration was 5 g/L, and 800 mL of the solution was placed in an electrolytic cell measuring 10 cm x 8 cm x 12 cm (capacity: approximately 1000 mL) and stirred. The electrolyte temperature was 40°C.
A copper plate of 8 cm x 8 cm was used as the cathode. Oleic acid was evenly applied to the surface of the cathode. The amount of application was 7 g/ ^m2 . A copper plate of 8 cm x 8 cm was used as the anode. Both electrodes were suspended in an electrolytic cell so that the distance between the cathode and anode was 8 cm.
The current density was adjusted to 160 A/ ^m2 and electrolysis was carried out for 30 minutes. In this manner, copper was electrodeposited on the surface of the cathode.
The copper electrodeposited on the surface of the cathode was collected, and the collected copper was washed with ethanol. When the obtained electrodeposit was observed using an SEM, fine linear bodies were confirmed. The irregularity rate was 1%. The linear bodies had a thickness of 50 nm and a length of 2.6 μm, and each end had a tapered shape. The thickness of the fine linear bodies was obtained by reading the thickness of 10 lines from a 20,000x SEM image and taking the arithmetic average. The length was obtained by reading the length of 20 lines from a 10,000x SEM image and taking the arithmetic average.
The productivity of the fine linear bodies was about 1.5 g per hour per L of electrolyte solution. FIG.

Example 2
In this example, fine filaments made of zinc were produced.
An electrolyte solution was prepared from zinc sulfate and sulfuric acid so that the zinc ion concentration was 50 g/L and the free sulfuric acid concentration was 25 g/L, and 800 mL of the solution was placed in an electrolytic cell measuring 10 cm x 8 cm x 12 cm (capacity: approximately 1000 mL) and stirred. The electrolyte temperature was 40°C.
The same 8 cm x 8 cm copper plate as in Example 1 was used as the cathode. Oleic acid was evenly applied to the surface of the cathode. The amount of oleic acid applied was 20 g/ ^m2 . An 8 cm x 8 cm insoluble metal electrode (manufactured by DSE De Nora Permelec) was used as the anode. Both electrodes were suspended in the electrolytic cell so that the distance between the cathode and anode was 8 cm.
The current density was adjusted to 160 A/ ^m2 and electrolysis was carried out for 30 minutes. In this manner, zinc was electrodeposited on the surface of the cathode.
The zinc electrodeposited on the surface of the cathode was collected and washed with acetone. The obtained electrodeposit was observed using a SEM, and fine linear bodies were confirmed. The irregularity rate was 20%. The linear bodies were 5 μm in diameter and 50 μm in length, and each end was tapered.
The productivity of the fine linear bodies was about 1.5 g per hour for 1 L of electrolyte.

Comparative Example 1
This comparative example corresponds to Example 1 of Patent Document 1.
0.72 g of copper(I) oxide, 7.5 ml of 64% sulfuric acid, 8.6 ml of acetonitrile, 1 g of sodium chloride, and pure water were added to a beaker and thoroughly stirred to obtain 90 ml of an aqueous phase containing a charge-neutralized complex [ ^{M m L} _{x ] s} [Y ⁿ ] _t consisting of a copper(I) acetonitrile complex [M m L x ] and a chloride ion [Y ⁿ ]. The liquid temperature of the aqueous phase was 25° C.
Separately from the aqueous phase, 90 ml of MIBK as a non-aqueous electrolyte and 0.05 g of TBAP as a supporting electrolyte were placed in a beaker and thoroughly stirred to obtain an organic phase consisting of a low-conductivity non-aqueous electrolyte.
A platinum electrode as a cathode, a copper electrode as an anode, and a stirrer were set in a beaker. The anode was set through an insulating sleeve. The aqueous phase and the organic phase were put into this beaker in equal volumes, and electrolytic reduction was performed by constant potential electrolysis while gently stirring with a stirrer. The electrolytic reduction was performed at a potential of -1.5 V with respect to a non-aqueous solvent reference electrode (Ag/Ag ⁺ ). A plurality of filaments produced by electrolytic reduction were slowly pulled out of the organic phase and dried to obtain an assembly in which the filaments were aligned in one direction. A part of the filaments was taken out of the resulting assembly and observed by SEM, confirming fine filaments. The filaments had a thickness of 50 nm and a length of 5 cm.
The productivity of the fine linear bodies was about 0.02 g per hour per 1 L of electrolyte.

Claims (5)

A method for producing fine linear bodies having a thickness of 30 nm to 10 μm, a length of 0.3 μm to 300 μm, an aspect ratio defined as length/thickness of 5 to 2500, and having a non-branched structure or one branched portion, the method comprising the steps of:
The method includes a step of depositing a metal on a cathode by electrolytic reduction using an electrolyte solution containing a metal element source,
carrying out electrolytic reduction in the presence of an oily substance on the surface of the cathode;
The method for producing fine filaments , wherein the oily substance contains a higher fatty acid having 10 to 25 carbon atoms or a salt thereof . The method according to claim 1 , wherein the oily substance has a dissolution amount of 100 g or less per 1 L of water . The amount of the oily substance present on the surface of the cathode is 5 g/m per unit surface area of the cathode. ² More than 100g/m ² The method according to claim 1 or 2, wherein: The method according to any one of claims 1 to 3 , wherein the metal element is copper, zinc, tin, iron, nickel, cobalt, lead, bismuth, silver, gold or platinum. The method of causing the oily substance to be present on the surface of the cathode comprises:
A method of directly applying the oily substance to the surface of the cathode;
A method of immersing the cathode in a container containing the oily substance and attaching it to the cathode;
A method in which the oily substance is floated on the electrolytic solution and the cathode is immersed in the solution from above to cause the oily substance to adhere to the surface of the cathode; or
The method according to any one of claims 1 to 4, comprising suspending the oily substance in the electrolyte and stirring the suspended electrolyte to cause the suspended oily substance to adhere to the surface of the cathode.