Method for producing copper nanowire

Abstract

Provided is a method for producing copper nanowires that is excellent in selectivity of obtained copper nanowires and that can be carried out with a simple configuration. The method for producing copper nanowires includes the following step 1.　Step 1: A step for bringing a mixed liquid containing copper oxide (a), halogen ions (b), a nonionic polymer compound (c), alkyl quaternary ammonium ions (d), a reducing agent (e), and water (f) to 50°C or higher to cause copper nanowires to precipitate.

Description

Method for manufacturing copper nanowires

[0001] This invention relates to a method for producing copper nanowires.

[0002] In recent years, methods for producing inexpensive copper nanowires as conductive materials for imparting conductivity to transparent substrates have been reported. For example, Japanese Patent Publication No. 2020-29580 discloses a method for producing copper nanowires that allows for easy production of copper nanowires with a desired aspect ratio by controlling the diameter and length of the resulting copper nanowires. This method is characterized by adjusting the pH of an aqueous solution containing ascorbic acid, copper chloride, alkali metal halide or alkaline earth metal halide, and polyvinylpyrrolidone to 2.5 to 4.0, and reducing and precipitating copper into a wire shape to obtain copper nanowires.

[0003] Japanese Patent Publication No. 2013-194290 discloses a method for producing copper nanowires, which has the following steps, with the objective of providing a manufacturing method that can be used even under conditions of high concentration of copper content of 1% by mass or more, at atmospheric pressure, at a mild temperature in water, and using a small amount of reaction reagent, without using special equipment: (1) a step of heating an aqueous solution containing a monovalent or divalent copper compound (a), chloride ions (b), and a copolymer (C) having a polyethyleneimine skeleton (c1) and a polyethylene glycol skeleton (c2) at 100°C or below; (2) a step of adding a reducing agent (d) that reduces the divalent copper compound to a monovalent copper compound to the aqueous solution obtained in (1), and heating at 100°C or below; (3) a step of removing solids from the reaction solution obtained in (2).

[0004] The present invention relates to a method for producing copper nanowires, comprising the following step 1: Step 1: A mixture containing copper oxide (a), halogen ions (b), a nonionic polymer compound (c), alkyl quaternary ammonium ions (d), a reducing agent (e), and water (f) is heated to 50°C or higher to precipitate copper nanowires.

[0005] This is a scanning electron microscope image of the precipitate obtained in Example 1. This is a scanning electron microscope image of the precipitate obtained in Example 2. This is a scanning electron microscope image of the precipitate obtained in Comparative Example 1. This is a scanning electron microscope image of the precipitate obtained in Comparative Example 2. This is a scanning electron microscope image of the precipitate obtained in Comparative Example 3. Detailed description of the invention

[0006] However, the selectivity of the copper nanowires obtained by these conventional manufacturing methods is not sufficient. Furthermore, the manufacturing method described in Japanese Patent Application Publication No. 2013-194290 requires a specific copolymer as a capping agent, which presents challenges in terms of ease of production.

[0007] Therefore, the object of the present invention is to provide a method for producing copper nanowires that has excellent selectivity and can be implemented with a simple configuration.

[0008] The present invention relates to a method for producing copper nanowires, comprising the following step 1: Step 1: A mixture containing copper oxide (a), halogen ions (b), a nonionic polymer compound (c), alkyl quaternary ammonium ions (d), a reducing agent (e), and water (f) is heated to 50°C or higher to precipitate copper nanowires.

[0009] According to the present invention, it is possible to provide a method for manufacturing copper nanowires that exhibits excellent selectivity and can be implemented with a simple configuration.

[0010] [Method for Manufacturing Copper Nanowires] The method for manufacturing copper nanowires of the present invention includes the following step 1. Step 1: A mixture containing copper oxide (a), halogen ions (b), a nonionic polymer compound (c), alkyl quaternary ammonium ions (d), a reducing agent (e), and water (f) is heated to 50°C or higher to precipitate copper nanowires.

[0011] <Definition> In this invention, "copper nanowire" means copper in wire form with a diameter of 500 nm or less and an aspect ratio [ratio of length to diameter] of 5 or more. In this specification, "diameter of 500 nm or less" includes copper nanowires in which 80% or more of the total length has a diameter (thickness) of 500 nm or less. In this invention, "selectivity of copper nanowire" means the ratio (percentage) of the number of copper nanowires to the number of precipitates randomly extracted from images taken of the obtained precipitates with a scanning electron microscope, where 100 or more precipitates (for example, 180) are extracted.

[0012] The reason why the copper nanowire manufacturing method of the present invention achieves its effects due to the above configuration is not entirely clear, but it is presumed to be as follows. In the copper nanowire manufacturing method of the present invention, monovalent copper is obtained from copper oxide (a), for example, copper(II) oxide, by the action of a reducing agent (e), and further, zero-valent copper is produced by a disproportionation reaction of the monovalent copper. Here, it is thought that the zero-valent copper becomes copper nanowires via double twinning, and in this process, the presence of halogen ions (b) causes copper that has become other crystalline forms to dissolve and reform seeds, thereby promoting the formation of double twinning. Furthermore, alkyl quaternary ammonium ions (d) disperse and stabilize this double twinning, thus increasing the amount of double twinning produced. Furthermore, when crystals grow from the generated double twinning, the nonionic polymer compound (c) acts as a capping agent on the unstable (100) plane, promoting crystal growth in a specific direction ((111) plane) to form a wire shape. In other words, it is thought that the combined action of the above components ultimately improves the selectivity of copper nanowires.

[0013] <Step 1> Step 1 of the present invention is a step of precipitating copper nanowires by heating a mixture containing copper oxide (a), halogen ions (b), a nonionic polymer compound (c), alkyl quaternary ammonium ions (d), a reducing agent (e), and water (f) to 50°C or higher. In Step 1, a mixture of the above-mentioned components in predetermined amounts is used to allow the reaction to proceed at a temperature of 50°C or higher. The components used in the method for producing copper nanowires of the present invention will be described below.

[0014] [Copper(a) oxide] (also called component (a)) The copper(a) oxide used in this invention is a component that serves as a raw material for the target copper nanowire. This component (a) can be any copper oxide, and in this invention, by using copper oxide as a raw material, the induction period is short and the reduction reaction is completed in a relatively short time, so the desired reaction can be carried out stably. Specifically, component (a) is cuprous oxide (copper(I) oxide, Cu ２ Either copper(II) oxide (CuO) or copper(II) oxide (CuO) may be used, but from the viewpoint of the stability of the raw material compound, copper(II) oxide (CuO) is preferred.

[0015] The content of component (a) in the mixed solution is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more, and preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5.0% by mass or less, and even more preferably 2% by mass or less, and from the viewpoint of improving the selectivity of copper nanowires, preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.05% by mass or more and 10% by mass or less, even more preferably 0.1% by mass or more and 5.0% by mass or less, and even more preferably 0.5% by mass or more and 2% by mass or less.

[0016] [Halogen ion (b)] (also called component (b)) The halogen ion (b) used in the present invention is a component that promotes the formation of double twins. In the method for producing copper nanowires of the present invention, first, seeds (seed crystals) that will serve as nuclei for crystals are generated from copper oxide. At this time, in addition to double twins that can be grown into copper nanowires, seeds such as single crystals are also generated. Generally, seeds other than double twins are mainly formed. In the present invention, however, by introducing halogen ions, the seeds that have been formed are dissolved again, thereby providing an opportunity to re-form double twins from seeds other than double twins.

[0017] Examples of halogen ions include fluoride ions, chloride ions, bromide ions, and iodide ions, among which chloride ions are preferred from the viewpoint of promoting the formation of double twins and improving the selectivity of copper nanowires.

[0018] To introduce halogen ions into the aforementioned mixture, a halogen-containing compound that releases halogen ions upon dissolution in water can be used. Examples of such halogen-containing compounds include alkali metal halides and alkaline earth metal halides. Furthermore, in this invention, to introduce alkyl quaternary ammonium ions as component (d), which will be described later, a compound containing component (b) as a counterion of component (d) is also possible. From the viewpoint of ease of operation and simplicity in copper nanowire manufacturing, a compound containing component (b) as a counterion of component (d) is preferred.

[0019] Examples of halogen-containing compounds include NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, and MgCl. ２ MgBr ２ CaCl ２ Examples include the above. Furthermore, it is preferable to use compounds containing component (b) as a counterion of component (d), such as stearyltrimethylammonium chloride, cetyltrimethylammonium chloride (CTAC, hexadecyltrimethylammonium chloride), lauryltrimethylammonium chloride, and tetramethylammonium chloride (TMAC).

[0020] The content of component (b) in the mixed solution is preferably 0.001 mol / L or more, more preferably 0.005 mol / L or more, even more preferably 0.01 mol / L or more, and even more preferably 0.025 mol / L or more, and preferably 1 mol / L or less, more preferably 0.5 mol / L or less, even more preferably 0.06 mol / L or less, and even more preferably 0.038 mol / L or less, and from the viewpoint of improving the selectivity of copper nanowires, preferably 0.001 mol / L or more and 1 mol / L or less, more preferably 0.005 mol / L or more and 0.5 mol / L or less, even more preferably 0.01 mol / L or more and 0.06 mol / L or less, and even more preferably 0.025 mol / L or more and 0.038 mol / L or less.

[0021] [Nonionic polymer compound (c)] (also called component (c)) The nonionic polymer compound (c) used in the present invention is a component that improves the selectivity of copper nanowires by promoting the anisotropic growth of double twins as a capping agent. Component (c) is a component that, when double twins grow anisotropically, selectively adsorbs onto the (100) plane, thereby promoting the growth of copper crystals in a specific direction ((111) plane) and contributing to the formation of a wire shape, and can also disperse and stabilize the copper nanowires.

[0022] Component (c) includes polysaccharides such as cellulose polymers and starch polymers; synthetic polymers such as vinyl polymers and polyalkylene glycol polymers; and the like. Examples of cellulose polymers include carboxymethylcellulose, methylcellulose, and hydroxyethylcellulose. Examples of starch polymers include dextrin. Examples of vinyl polymers include polyvinylpyrrolidone (PVP) and poly(vinyl alcohol) (PVA). Examples of polyalkylene glycol polymers include polyethylene glycol (PEG) and polypropylene glycol (PPG). In particular, from the viewpoint of improving the selectivity of copper nanowires, component (c) preferably includes polyvinylpyrrolidone (PVP).

[0023] Regarding polyvinylpyrrolidone (PVP), its K value is widely known as a viscous property value that correlates with its molecular weight. This viscous property value (K value) can be calculated by applying the relative viscosity value (25°C) measured by a capillary viscometer to the Fikentscher formula (H. Fikentscher, Cellulosechemie 13 (1932) 58-64 und 71-74). Specifically, it can be determined by the method described for povidone in the Japanese Pharmacopoeia.

[0024] The viscosity property value (K value) of this polyvinylpyrrolidone is preferably 5 or higher, more preferably 10 or higher, and preferably 100 or lower, and more preferably 50 or lower, from the viewpoint of improving the selectivity of copper nanowires.

[0025] The content of component (c) in the mixed solution is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, even more preferably 1% by mass or less, and from the viewpoint of improving the selectivity of copper nanowires, preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.05% by mass or more and 5% by mass or less, even more preferably 0.1% by mass or more and 3% by mass or less, and even more preferably 0.2% by mass or more and 1% by mass or less.

[0026] [Alkyl quaternary ammonium ion (d)] (also called component (d)) The alkyl quaternary ammonium ion (d) used in the present invention is a component that contributes to the stabilization of the double twin. That is, as described above, component (b) promotes the formation of the double twin, and this component (d) contributes to the dispersion stabilization of the double twin, thereby increasing the proportion of double twins formed as seeds, and thereby improving the selectivity of copper nanowires.

[0027] The component (d) is preferably a mono or di-long-chain alkyl quaternary ammonium ion represented by the following chemical formula. The counterion to this component may be a halogen ion, a methyl sulfate ion, an ethyl sulfate ion, etc.

[0028]

[0029] (Here, in the formula, R １１ represents a linear or branched alkyl group having 1 or 8 or more and 22 or less carbon atoms, which may be interrupted by an ester group or an ether group, and R １２ represents a linear or branched alkyl group having 1 or more and 22 or less carbon atoms, which may be interrupted by an ester group or an ether group, R １３ and R １４ each independently represent an alkyl group having 1 or more and 3 or less carbon atoms.) In R １１ , the number of carbon atoms of the linear or branched alkyl group is 1 or 8 or more and 22 or less, preferably 1 or 12 or more and 18 or less. In R １２ , the number of carbon atoms of the linear or branched alkyl group having 1 or more and 22 or less carbon atoms is preferably 1 or more and 3 or less when component (d) is a mono-long-chain alkyl quaternary ammonium, and preferably 8 or more and 22 or less, more preferably 12 or more and 18 or less when component (d) is a di-long-chain alkyl quaternary ammonium.

[0030] Component (d) is preferably an ammonium ion having one linear or branched alkyl group having 8 or more and 22 or less carbon atoms and three alkyl groups having 1 or more and 3 or less carbon atoms, more preferably an ammonium ion having one linear or branched alkyl group having 12 or more and 18 or less carbon atoms and three alkyl groups having 1 or more and 3 or less carbon atoms, and still more preferably an ammonium ion having one linear alkyl group having 12 or more and 18 or less carbon atoms and three methyl groups.

[0031] Specifically, examples of component (d) include one or more selected from the group consisting of behenyltrimethylammonium ion, stearyltrimethylammonium ion, cetyltrimethylammonium ion, lauryltrimethylammonium ion, dialkyl (C12 - C18) dimethylammonium ion, octadecyloxypropyltrimethylammonium ion, and tetramethylammonium ion.

[0032] Component (d) is preferably one or more selected from the group consisting of stearyltrimethylammonium ion, cetyltrimethylammonium ion, lauryltrimethylammonium ion, and tetramethylammonium ion, more preferably one or more selected from the group consisting of cetyltrimethylammonium ion, lauryltrimethylammonium ion, and tetramethylammonium ion, and even more preferably cetyltrimethylammonium ion and tetramethylammonium ion, from the viewpoint of improving the selectivity of copper nanowires.

[0033] To introduce alkylquaternary ammonium ions into the aforementioned mixture, an alkylquaternary ammonium compound that releases alkylquaternary ammonium ions upon dissolution in water can be used. Examples of such alkylquaternary ammonium compounds include the ammonium ion halides, methyl sulfate salts, and ethyl sulfate salts exemplified above.

[0034] From the viewpoint of ease of operation and simplicity in copper nanowire production, the alkyl quaternary ammonium compound is preferably one or more selected from the group consisting of stearyltrimethylammonium chloride, cetyltrimethylammonium chloride (CTAC), lauryltrimethylammonium chloride, and tetramethylammonium chloride (TMAC), even more preferably one or more selected from the group consisting of cetyltrimethylammonium chloride (CTAC), lauryltrimethylammonium chloride, and tetramethylammonium chloride (TMAC), and even more preferably cetyltrimethylammonium chloride (CTAC) and tetramethylammonium chloride (TMAC). In this way, when using an ammonium ion halide, it is preferable that components (b) and (d) can be combined by adding a single compound.

[0035] The content of component (d) in the mixed solution is preferably 0.001 mol / L or more, more preferably 0.005 mol / L or more, even more preferably 0.01 mol / L or more, and even more preferably 0.025 mol / L or more, and preferably 1 mol / L or less, more preferably 0.5 mol / L or less, even more preferably 0.1 mol / L or less, and even more preferably 0.035 mol / L or less, and from the viewpoint of improving the selectivity of copper nanowires, preferably 0.001 mol / L or more and 1 mol / L or less, more preferably 0.005 mol / L or more and 0.5 mol / L or less, even more preferably 0.01 mol / L or more and 0.1 mol / L or less, and even more preferably 0.025 mol / L or more and 0.035 mol / L or less.

[0036] [Reducing agent (e)] (also called component (e)) The reducing agent (e) used in the present invention is a component for reducing the copper oxide of component (a) to precipitate copper. Preferably, component (e) is a mild reducing agent that reduces divalent copper oxide to monovalent copper but does not rapidly reduce it to zero-valent copper.

[0037] Examples of such components (e) include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, brassic acid, dodecanoic acid, thapsic acid, maleic acid, fumaric acid, gluconic acid, traumatic acid, muconic acid, gluticic acid, citraconic acid, mesaconic acid, aspartic acid, glutamic acid, diaminopimelic acid, tartonic acid, arabinalic acid, saccharic acid, mesoxalic acid, oxaloacetate, and acetone dicarbonate. Examples include acids, phthalic acid, isophthalic acid, terephthalic acid, diphenic acid, tartaric acid, sodium potassium tartrate, ascorbic acid, citric acid, reducing sugars such as glucose, fructose, glyceraldehyde, lactose, arabinose, and maltose. From the viewpoint of improving the selectivity of copper nanowires, it is preferable to include reducing sugars such as glucose, fructose, glyceraldehyde, lactose, arabinose, and maltose, ascorbic acid, and more preferably ascorbic acid.

[0038] The content of component (e) is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, still more preferably 1.5% by mass or more, even more preferably 2% by mass or more, from the viewpoint of improving the selectivity of copper nanowires in the mixed solution, and is preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, even more preferably 4% by mass or less, and from the viewpoint of improving the selectivity of copper nanowires, it is preferably 0.5% by mass or more and 15% by mass or less, more preferably 1.0% by mass or more and 10% by mass or less, still more preferably 1.5% by mass or more and 5% by mass or less, even more preferably 2% by mass or more and 4% by mass or less.

[0039] [Water (f)] (also referred to as component (f)) The water (f) used in the liquid crystal composition of the present invention may be any water that can mix the above components (a) to (e) and precipitate copper nanowires, and examples include distilled water, deionized water, tap water, industrial water, etc. Among them, from the viewpoint of improving the selectivity of copper nanowires, distilled water or deionized water is preferred.

[0040] This component (f) can efficiently promote the production of copper nanowires in the mixed solution, particularly by sufficiently allowing the respective ions of component (b) and component (d) to exist due to the dissolution of the compound. Component (f) is the remainder of components (a) to (e) in the mixed solution.

[0041] The above-described components (a) to (f) are mixed to prepare a predetermined mixed solution. At this time, the molar ratio [(a) / (d)] of copper oxide (a) to alkyl quaternary ammonium ion (d) in the mixed solution is preferably 0.1 or more, more preferably 0.5 or more, still more preferably 1 or more, even more preferably 3.5 or more, from the viewpoint of improving the selectivity of copper nanowires, and is preferably 100 or less, more preferably 50 or less, still more preferably 10 or less, even more preferably 5 or less, and from the viewpoint of improving the selectivity of copper nanowires, it is preferably 0.1 or more and 100 or less, more preferably 0.5 or more and 50 or less, still more preferably 1 or more and 10 or less, even more preferably 3.5 or more and 5 or less.

[0042] Also, in the mixed solution, the molar ratio [(b) / (d)] of the halogen ion (b) to the alkyl quaternary ammonium ion (d) is preferably 0.05 or more, more preferably 0.1 or more, still more preferably 0.5 or more, even more preferably 0.8 or more, from the viewpoint of improving the selectivity of copper nanowires, and is preferably 50 or less, more preferably 10 or less, still more preferably 3 or less, even more preferably 1.2 or less, and from the viewpoint of improving the selectivity of copper nanowires, it is preferably 0.05 or more and 50 or less, more preferably 0.1 or more and 10 or less, still more preferably 0.5 or more and 3 or less, even more preferably 0.8 or more and 1.2 or less.

[0043] Also, in the mixed solution, the molar ratio [(b) / (a)] of the halogen ion (b) to the copper oxide (a) is preferably 0.01 or more, more preferably 0.05 or more, still more preferably 0.1 or more, even more preferably 0.2 or more, from the viewpoint of improving the selectivity of copper nanowires, and is preferably 50 or less, more preferably 10 or less, still more preferably 1 or less, even more preferably 0.3 or less, and from the viewpoint of improving the selectivity of copper nanowires, it is preferably 0.01 or more and 50 or less, more preferably 0.05 or more and 10 or less, still more preferably 0.1 or more and 1 or less, even more preferably 0.2 or more and 0.3 or less.

[0044] Also, in the mixed solution, the molar ratio [(e) / (a)] of the reducing agent (e) to the copper oxide (a) is preferably 0.05 or more, more preferably 0.1 or more, still more preferably 0.5 or more, even more preferably 1 or more, from the viewpoint of improving the selectivity of copper nanowires, and is preferably 50 or less, more preferably 10 or less, still more preferably 3 or less, even more preferably 2 or less, and from the viewpoint of improving the selectivity of copper nanowires, it is preferably 0.05 or more and 50 or less, more preferably 0.1 or more and 10 or less, still more preferably 0.5 or more and 3 or less, even more preferably 1 or more and 2 or less.

[0045] Then, the reaction is carried out at a temperature of 50°C or higher to precipitate copper nanowires. The temperature of the mixture when reducing and precipitating the copper nanowires is 50°C or higher, preferably 60°C or higher, more preferably 65°C or higher, even more preferably 68°C or higher, and preferably 100°C or lower, more preferably 95°C or lower, even more preferably 90°C or lower, and even more preferably 85°C or lower.

[0046] The heating to the aforementioned temperature may be carried out by heating a premixture containing some of the components (a) to (f) to 50°C or higher, then adding the remaining components to the premixture and maintaining the temperature at 50°C or higher, or by mixing all of the components (a) to (f) and then heating to 50°C or higher. However, it is preferable to heat a premixture containing some of the components (a) to (f) to 50°C or higher, then add the remaining components and maintain the temperature at 50°C or higher. In this case, the order in which the components (a) to (f) are mixed does not matter, but from the viewpoint of managing and controlling the reaction, it is preferable to add the reducing agent (e) last.

[0047] In other words, it is more preferable to prepare a preliminary mixture by mixing components (a) to (d) and (f), heat this preliminary mixture to preferably 50°C or higher, add component (e) to the preliminary mixture, and allow the reaction to proceed while maintaining a temperature of 50°C or higher.

[0048] By raising the mixture to a temperature of 50°C or higher, copper oxide (a), for example, copper(II) oxide, becomes monovalent copper due to the action of a reducing agent (e), and further, a disproportionation reaction of monovalent copper produces zero-valent copper. At this time, the presence of halide ions (b) and alkyl quaternary ammonium ions (d) in the mixture promotes the formation of double twins, increasing the amount of double twins produced. When crystals grow from the double twins, the nonionic polymer compound (c) acts as a capping agent, promoting anisotropic growth and resulting in a wire shape. It is believed that the selectivity of copper nanowires is improved by the combined action of these components (a) to (e).

[0049] Here, the heating temperature of the mixture may be maintained at a constant temperature within the aforementioned temperature range, or the temperature may be changed during the reaction. From the viewpoint of improving the selectivity of copper nanowires, it is preferable to set a high temperature at the beginning of the reaction and then decrease the temperature thereafter. That is, it is preferable to decrease the temperature of the mixture during the reaction. From the viewpoint of improving the selectivity of copper nanowires, the range of temperature decrease is preferably 3°C or more, more preferably 5°C or more, and even more preferably 8°C or more, with an upper limit of preferably 20°C or less.

[0050] Specifically, when changing the temperature in this way, it is preferable to raise the temperature to 75°C or higher at the beginning of the reaction, and then lower it to below 75°C to allow the reaction to proceed. It is thought that by heating to a high temperature of 75°C or higher at the beginning of the reaction, double twins that will serve as seeds for copper nanowires can be efficiently formed, and then by lowering the temperature to below 75°C, crystal growth can proceed slowly, and the desired wire shape can be successfully formed from the double twins.

[0051] Here, the holding time for the temperature is not particularly limited as long as the target copper nanowires can be formed, but it is preferably 1 hour or more, more preferably 1.2 hours or more, and from the viewpoint of improving productivity, it is preferably 25 hours or less, more preferably 7 hours or less, and even more preferably 4 hours or less.

[0052] Furthermore, when the heating temperature is changed as described above, the holding time for the initial temperature of the reaction (preferably a holding time of 75°C or higher) is preferably 10 minutes or more, more preferably 15 minutes or more, and preferably 1 hour or less, more preferably 45 minutes or less. Subsequently, the holding time for the reaction temperature after the temperature has been lowered (preferably a holding time of less than 75°C) is preferably 30 minutes or more, more preferably 50 minutes or more, even more preferably 1 hour or more, from the viewpoint of sufficiently forming copper nanowires and improving their selectivity, and preferably 24 hours or less, more preferably 6 hours or less, even more preferably 3 hours or less, from the viewpoint of improving productivity.

[0053] After the above heat treatment is performed to allow the reaction to proceed sufficiently and precipitate copper nanowires, the reaction mixture is cooled to room temperature (approximately 23°C) to obtain copper nanowires. The precipitate (copper nanowires) obtained by this reaction can be easily isolated and recovered by known solid-liquid separation methods such as filtration and centrifugation after being diluted with water as needed. Furthermore, from the viewpoint of improving the selectivity of copper nanowires, the pH of the mixture during the reaction is preferably 1.5 or higher, more preferably 2.0 or higher, and similarly, preferably 3.5 or lower, more preferably 3 or lower.

[0054] In this specification, copper nanowires are defined as copper wires with a diameter of 500 nm or less and an aspect ratio [ratio of length to diameter] of 5 or more, as described above. The average length of the obtained copper nanowires is the number average length obtained by randomly extracting 100 or more (e.g., 180) copper nanowires from the precipitate in an image taken with a scanning electron microscope, measuring their lengths, and calculating the number average length. The average length of these copper nanowires is preferably 1 μm or more and 100 μm or less.

[0055] The average diameter (average thickness) of the obtained copper nanowires is the number-average diameter obtained by randomly extracting 100 or more (e.g., 180) copper nanowires from the precipitate in an image taken with a scanning electron microscope, measuring their diameters, and calculating the number-average diameter. This average diameter (average thickness) of the copper nanowires is preferably between 50 nm and 300 nm.

[0056] The present invention includes the following embodiments: [1] A method for producing copper nanowires, comprising the following step 1: Step 1: A step of reacting a mixture containing copper oxide (a), halogen ions (b), a nonionic polymer compound (c), alkyl quaternary ammonium ions (d), a reducing agent (e), and water (f) at 50°C or higher to precipitate copper nanowires.

[0057] [2] The manufacturing method according to [1], wherein the content of component (a) in the mixed solution is preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.05% by mass or more and 10% by mass or less, even more preferably 0.1% by mass or more and 5.0% by mass or less, and even more preferably 0.5% by mass or more and 2% by mass or less.

[0058] [3] The manufacturing method according to [1] or [2], wherein the halogen ion (b) is preferably a fluoride ion, a chloride ion, a bromide ion, and an iodide ion, and more preferably a chloride ion.

[0059] [4] The manufacturing method according to any one of [1] to [3], wherein the content of component (b) is preferably 0.001 mol / L or more and 1 mol / L or less, more preferably 0.005 mol / L or more and 0.5 mol / L or less, even more preferably 0.01 mol / L or more and 0.06 mol / L or less, and even more preferably 0.025 mol / L or more and 0.038 mol / L or less.

[0060] [5] The method for producing the nonionic polymer compound (c) according to any one of [1] to [4], wherein the nonionic polymer compound (c) preferably comprises a vinyl polymer, and more preferably polyvinylpyrrolidone (PVP).

[0061] [6] The manufacturing method according to any one of [1] to [5], wherein the content of component (c) is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.05% by mass or more and 5% by mass or less, even more preferably 0.1% by mass or more and 3% by mass or less, and even more preferably 0.2% by mass or more and 1% by mass or less.

[0062] [7] The manufacturing method according to any one of [1] to [6], wherein component (d) comprises an ammonium ion having one linear or branched alkyl group having 8 to 22 carbon atoms and three alkyl groups having 1 to 3 carbon atoms.

[0063] [8] The manufacturing method according to any one of [1] to [7], wherein component (d) comprises an ammonium ion having one linear or branched alkyl group having 12 to 18 carbon atoms and three alkyl groups having 1 to 3 carbon atoms, preferably one or more selected from the group consisting of stearyltrimethylammonium ion, cetyltrimethylammonium ion and lauryltrimethylammonium ion, more preferably one or more selected from the group consisting of cetyltrimethylammonium ion and lauryltrimethylammonium ion, and even more preferably cetyltrimethylammonium ion.

[0064] [9] A manufacturing method according to any one of [1] to [8], wherein the compound comprising a halogen ion (b) and an alkyl quaternary ammonium ion (d) preferably comprises one or more selected from the group consisting of stearyltrimethylammonium chloride, cetyltrimethylammonium chloride (CTAC), and lauryltrimethylammonium chloride, more preferably one or more selected from the group consisting of cetyltrimethylammonium chloride (CTAC) and lauryltrimethylammonium chloride, and even more preferably cetyltrimethylammonium chloride (CTAC).

[0065]

[10] The manufacturing method according to any one of [1] to [9], wherein the content of component (d) is preferably 0.001 mol / L or more and 1 mol / L or less.

[0066]

[11] The manufacturing method according to any one of [1] to

[10] , wherein the content of component (d) is more preferably 0.005 mol / L or more and 0.5 mol / L or less.

[0067]

[12] The manufacturing method according to any one of [1] to

[11] , wherein the content of component (d) is more preferably 0.01 mol / L or more and 0.1 mol / L or less.

[0068]

[13] The manufacturing method according to any one of [1] to

[12] , wherein the content of component (d) is more preferably 0.025 mol / L or more and 0.035 mol / L or less.

[0069]

[14] The reducing agent (e) comprises one or more selected from the group consisting of reducing sugars such as glucose, fructose, glyceraldehyde, lactose, arabinose, maltose, and ascorbic acid, and more preferably ascorbic acid, according to any one of [1] to

[13] .

[0070]

[15] The manufacturing method according to any one of [1] to

[14] , wherein the content of component (e) is preferably 0.5% by mass or more and 15% by mass or less, more preferably 1.0% by mass or more and 10% by mass or less, even more preferably 1.5% by mass or more and 5% by mass or less, and even more preferably 2% by mass or more and 4% by mass or less.

[0071]

[16] The molar ratio of copper oxide (a) to alkyl quaternary ammonium ion (d) [(a) / (d)] is preferably 0.1 or more and 100 or less, according to any one of [1] to

[15] .

[0072]

[17] The manufacturing method according to any one of [1] to

[16] , wherein the molar ratio of copper oxide (a) to alkyl quaternary ammonium ion (d) [(a) / (d)] is more preferably 0.5 or more and 50 or less.

[0073]

[18] The molar ratio of copper oxide (a) to alkyl quaternary ammonium ion (d) [(a) / (d)] is more preferably 1 or more and 10 or less, according to any one of [1] to

[17] .

[0074]

[19] The manufacturing method according to any one of [1] to

[18] , wherein the molar ratio of copper oxide (a) to alkyl quaternary ammonium ion (d) [(a) / (d)] is more preferably 3.5 or more and 5 or less.

[0075]

[20] The molar ratio of halogen ions (b) to alkyl quaternary ammonium ions (d) [(b) / (d)] is preferably 0.05 or more and 50 or less, according to any one of [1] to

[19] .

[0076]

[21] The manufacturing method according to any one of [1] to

[20] , wherein the molar ratio of halogen ions (b) to alkyl quaternary ammonium ions (d) [(b) / (d)] is more preferably 0.1 or more and 10 or less.

[0077]

[22] The molar ratio of halogen ions (b) to alkyl quaternary ammonium ions (d) [(b) / (d)] is more preferably 0.5 or more and 3 or less, according to any one of [1] to

[21] .

[0078]

[23] The manufacturing method according to any one of [1] to

[22] , wherein the molar ratio of halogen ion (b) to alkyl quaternary ammonium ion (d) [(b) / (d)] is more preferably 0.8 or more and 1.2 or less.

[0079]

[24] The manufacturing method according to any one of [1] to

[23] , wherein the molar ratio of halogen ions (b) to copper oxide (a) [(b) / (a)] is preferably 0.01 or more and 50 or less, more preferably 0.05 or more and 10 or less, even more preferably 0.1 or more and 1 or less, and even more preferably 0.2 or more and 0.3 or less.

[0080]

[25] The manufacturing method according to any one of [1] to

[24] , wherein the molar ratio of the reducing agent (e) to copper oxide (a) [(e) / (a)] is preferably 0.05 or more and 50 or less, more preferably 0.1 or more and 10 or less, even more preferably 0.5 or more and 3 or less, and even more preferably 1 or more and 2 or less.

[0081]

[26] A manufacturing method according to any one of [1] to

[25] , comprising mixing components (a) to (d) and component (f) to prepare a premix, preferably heating the premix to 50°C or higher, and then adding component (e) to the premix and reacting while maintaining a temperature of 50°C or higher.

[0082]

[27] A manufacturing method according to any one of [1] to

[26] , wherein the temperature of the mixed solution is reduced during the reaction.

[0083]

[28] The manufacturing method according to

[27] , wherein the temperature range over which the mixture is lowered during the reaction is preferably 3°C or more, more preferably 5°C or more, and even more preferably 8°C or more, with an upper limit of preferably 20°C or less.

[0084]

[29] The manufacturing method according to any one of [1] to

[28] , wherein the temperature of the mixed solution when reducing and precipitating copper nanowires is 50°C or higher, preferably 60°C or higher, more preferably 65°C or higher, even more preferably 68°C or higher, and preferably 100°C or lower, more preferably 95°C or lower, even more preferably 90°C or lower, and even more preferably 85°C or lower.

[0085]

[30] The method of manufacturing according to any one of [1] to

[29] , wherein the time for holding the temperature is preferably 1 hour or more, more preferably 2 hours or more, and preferably 25 hours or less, more preferably 7 hours or less, and even more preferably 4 hours or less.

[0086]

[31] A manufacturing method according to any one of [1] to

[30] , wherein the temperature of the mixed solution is set to 75°C or higher in the initial stage of the reaction, and then to less than 75°C to allow the reaction to proceed.

[0087]

[32] The method for producing the product according to

[31] , wherein the time for maintaining a temperature of 75°C or higher in the initial stage of the reaction is preferably 10 minutes or more, more preferably 15 minutes or more, and preferably 1 hour or less, more preferably 45 minutes or less.

[0088]

[33] The method for manufacturing according to

[31] or

[32] , wherein the time for holding the reaction temperature after subsequently lowering the temperature to below 75°C is preferably 50 minutes or more, more preferably 1 hour or more, and preferably 24 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.

[0089] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to the scope of the examples. The measurements and evaluations in the examples were performed by the following methods. Furthermore, all raw materials and reagents used were manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0090] [Selectivity and Average Diameter of Copper Nanowires] Images of the obtained precipitates were taken using a scanning electron microscope (SEM; JEOL Ltd., product name: JSM-IT500HR) (magnification: 10,000x, Comparative Example 1: 5,000x). 180 precipitates were randomly extracted from these images, and the ratio (percentage) of the number of copper nanowires (diameter 500 nm or less, aspect ratio 5 or more) to the number of extracted precipitates was calculated to determine the selectivity of copper nanowires. In addition, the diameter of the copper nanowires was measured from the obtained images using the image analysis software imageJ, and the average value of these measurements was calculated to determine the average diameter of the copper nanowires.

[0091] (Example 1) 1.0 g of copper(II) oxide (chemical grade) (CuO; powder, model number: 038-04345), 1.0 g of cetyltrimethylammonium chloride (CTAC; Wako Grade 1, model number: 087-06032), and 0.6 g of polyvinylpyrrolidone (PVP; Wako Grade 2, model number: 161-17032, viscosity characteristic value (K value) 30) were added to a 150 mL four-neck separable flask, and then 79 g of deionized water was added. Then, while stirring at 500 rpm using a magnetic stirrer, the internal temperature was raised to 80°C using a heating device (Personal Organic Synthesis Device PPV-3461, manufactured by Tokyo Rikakikai Co., Ltd.). To this, an aqueous reducing agent solution was added, prepared by dissolving 2.8 g of L(+)-ascorbic acid (reagent grade, model number: 014-04801) in 15.6 g of deionized water, and the reaction was initiated. The pH during the reaction was 2.4. At this time, nitrogen was flowed into the reaction solution at a flow rate of 50 mL / min, and a reflux condenser was attached to prevent loss of the reaction solution due to volatilization. Thirty minutes after the start of the reaction, the reaction solution was cooled to 70°C in one minute. The temperature was then maintained at 70°C, and 1 hour and 30 minutes after the start of the reaction, a 0.5 g sample of the reaction solution was taken and added to 13 g of deionized water, after which centrifugation (3000 rpm, 1 minute) was performed and the precipitate was collected.

[0092] The recovered precipitate was redispersed in 2 g of deionized water to obtain a copper nanowire dispersion as a sample for imaging with a scanning electron microscope (SEM). Figure 1 shows an SEM image of the precipitate in this dispersion (magnification 10,000x). From this image, the selectivity and average diameter of the copper nanowires were calculated and are shown in Table 1.

[0093] (Example 2) 1.0 g of copper(II) oxide (chemical grade) (CuO; powder, model number: 038-04345), 1.0 g of cetyltrimethylammonium chloride (CTAC; Wako Grade 1, model number: 087-06032), and 0.6 g of polyvinylpyrrolidone (PVP; Wako Grade 2, model number: 161-17032, viscosity characteristic value (K value) 30) were added to a 150 mL four-neck separable flask, and then 79 g of deionized water was added. Then, while stirring at 500 rpm using a magnetic stirrer, the internal temperature was raised to 70°C using a heating device (Personal Organic Synthesis Device PPV-3461, manufactured by Tokyo Rikakikai Co., Ltd.). To this, an aqueous reducing agent solution was added, prepared by dissolving 2.8 g of L(+)-ascorbic acid (reagent grade, model number: 014-04801) in 15.6 g of deionized water, and the reaction was initiated. The pH during the reaction was 2.4. At this time, nitrogen was flowed into the reaction solution at a flow rate of 50 mL / min, and a reflux condenser was attached to prevent loss of the reaction solution due to volatilization. The reaction was carried out at 70°C, and 1 hour and 30 minutes after the start of the reaction, 0.5 g of the reaction solution was sampled, added to 13 g of deionized water, and then centrifuged (3000 rpm, 1 minute) to collect the precipitate.

[0094] The recovered precipitate was redispersed in 2 g of deionized water to obtain a copper nanowire dispersion as a sample for imaging with a scanning electron microscope. Figure 2 shows an SEM image (magnification 10,000x) of the precipitate in this dispersion. From this image, the selectivity and average diameter of the copper nanowires were calculated and are shown in Table 1.

[0095] (Example 3) The procedure was carried out in the same manner as in Example 2, except that 1.0 g of copper(II) oxide (chemical grade) (CuO; powder, model number: 038-04345), 1.0 g of cetyltrimethylammonium chloride (CTAC; Wako Grade 1, model number: 087-06032), and 0.6 g of polyvinylpyrrolidone (PVP; Wako Grade 1, model number: 161-17032, viscosity characteristic value (K value) 30) were added to a 150 mL four-neck separable flask, and an additional 0.031 g of sodium chloride (NaCl: Wako Reagent Grade) was added.

[0096] (Example 4) The procedure was carried out in the same manner as in Example 2, except that 0.33 g of tetramethylammonium chloride (TMAC; Tokyo Chemical Industry, model number: T0136) was used instead of 1.0 g of cetyltrimethylammonium chloride (CTAC; Wako Grade 1, model number: 087-06032).

[0097] (Example 5) The procedure was the same as in Example 2, except that the internal temperature was raised to 80°C and the reaction was carried out at 80°C.

[0098] (Comparative Example 1) 1.0 g of copper(II) oxide (chemical grade) (CuO; powder, model number: 038-04345), 0.18 g of sodium chloride (NaCl; reagent grade, model number: 191-01665), and 0.6 g of polyvinylpyrrolidone (PVP; Wako special grade, model number: 161-17032, viscosity characteristic value (K value) 30) were added to a 150 mL four-neck separable flask, and then 79 g of deionized water was added. Then, while stirring at 500 rpm using a magnetic stirrer, the internal temperature was raised to 70°C using a heating device (Personal Organic Synthesis Device PPV-3461, manufactured by Tokyo Rikakikai Co., Ltd.). To this, an aqueous reducing agent solution was added, prepared by dissolving 2.8 g of L(+)-ascorbic acid (reagent grade, model number: 014-04801) in 16.42 g of deionized water, and the reaction was initiated. At this time, nitrogen was flowed into the reaction solution at a flow rate of 50 mL / min, and a reflux condenser was attached to prevent loss of the reaction solution due to volatilization. The reaction was carried out at 70°C, and 1 hour and 30 minutes after the start of the reaction, 0.5 g of the reaction solution was sampled and added to 13 g of deionized water, after which centrifugation (3000 rpm, 1 minute) was performed and the precipitate was collected.

[0099] The recovered precipitate was redispersed in 2 g of deionized water to obtain a copper nanowire dispersion as a sample for imaging with a scanning electron microscope. Figure 3 shows an SEM image (magnification 10,000x) of the precipitate in this dispersion. From this image, the selectivity and average diameter of the copper nanowires were calculated and are shown in Table 1.

[0100] (Comparative Example 2) 1.0 g of copper(II) oxide (chemical grade) (CuO; powder, model number: 038-04345) and 1.0 g of cetyltrimethylammonium chloride (CTAC; Wako Grade 1, model number: 087-06032) were added to a 150 mL four-neck separable flask, and 79 g of deionized water was added thereto. Then, while stirring at 500 rpm using a magnetic stirrer, the internal temperature was raised to 70°C using a heating device (Tokyo Rikakikai Co., Ltd., Personal Organic Synthesis Apparatus PPV-3461). To this, an aqueous reducing agent solution prepared by dissolving 2.8 g of L(+)-ascorbic acid (reagent grade, model number: 014-04801) in 16.2 g of deionized water was added, and the reaction was started. During the reaction, nitrogen was supplied to the reaction solution at a flow rate of 50 mL / min, and a reflux condenser was attached to prevent loss of the reaction solution due to volatilization. The reaction was carried out at 70°C, and 1 hour and 30 minutes after the start of the reaction, 0.5 g of the reaction solution was sampled and added to 13 g of deionized water. The solution was then centrifuged (3000 rpm, 1 minute) and the precipitate was collected.

[0101] The recovered precipitate was redispersed in 2 g of deionized water to obtain a copper nanowire dispersion as a sample for imaging with a scanning electron microscope. Figure 4 shows an SEM image (magnification 10,000x) of the precipitate in this dispersion. From this image, the selectivity and average diameter of the copper nanowires were calculated and are shown in Table 1.

[0102] (Comparative Example 3) 2.14 g of copper(II) chloride dihydrate, 1.0 g of cetyltrimethylammonium chloride (CTAC; Wako Grade 1, Model No.: 087-06032), and 0.6 g of polyvinylpyrrolidone (PVP; Wako Grade 2, Model No.: 161-17032, viscosity characteristic value (K value) 30) were added to a 150 mL four-neck separable flask, and 79 g of deionized water was added. Then, while stirring at 500 rpm using a magnetic stirrer, the internal temperature was raised to 70°C using a heating device (Tokyo Rikakikai Co., Ltd., Personal Organic Synthesis Device PPV-3461). Then, an aqueous reducing agent solution prepared by dissolving 2.8 g of L(+)-ascorbic acid (Reagent Grade, Model No.: 014-04801) in 14.46 g of deionized water was added, and the reaction was started. During the reaction, nitrogen was supplied to the reaction solution at a flow rate of 50 mL / min, and a reflux condenser was attached to prevent loss of the reaction solution due to volatilization. After 2 hours and 30 minutes, no brown suspension resembling that of reduced copper oxide was observed, and a white, lumpy precipitate of about 1-2 cm was found at the bottom of the flask.

[0103] A portion of the lumpy precipitate was collected, added to 2 g of deionized water, and then finely dispersed by ultrasonic dispersion to obtain a dispersion of copper chloride particles as a sample for imaging with a scanning electron microscope. Figure 5 shows an SEM image (magnification 10,000x) of the precipitate in this dispersion. The selectivity of copper nanowires was calculated from this image and is shown in Table 1.

[0104]

[0105] Table 1 shows that the copper nanowire manufacturing method of the present invention (Examples 1-5) can improve the selectivity of copper nanowires. On the other hand, while copper nanowires were obtained in Comparative Example 1, which did not contain CTAC or TMAC, and Comparative Example 2, which did not contain PVP, the selectivity was very low. In Comparative Example 3, which used copper chloride as a raw material, insoluble copper(I) chloride crystals precipitated instead of copper nanowires, and in all cases, copper nanowires could not be obtained with high selectivity.

[0106] According to the present invention, a method for manufacturing copper nanowires that exhibits excellent nanowire selectivity and can be implemented with a simple configuration can be provided.

Claims

1. A method for producing copper nanowires, comprising the following step 1. Process 1: A process to precipitate copper nanowires by heating a mixture containing copper oxide (a), halogen ions (b), a nonionic polymer compound (c), alkyl quaternary ammonium ions (d), a reducing agent (e), and water (f) to 50°C or higher.

2. The manufacturing method according to claim 1, wherein the content of component (b) is preferably 0.001 mol / L or more and 1 mol / L or less.

3. The manufacturing method according to claim 1 or 2, wherein component (c) is a vinyl polymer.

4. The manufacturing method according to any one of claims 1 to 3, wherein the content of component (c) is 0.01% by mass or more and 10% by mass or less.

5. The manufacturing method according to any one of claims 1 to 4, wherein the content of component (d) is 0.001 mol / L or more and 1 mol / L or less.

6. The manufacturing method according to any one of claims 1 to 5, wherein the molar ratio of component (a) to component (d) [(a) / (d)] is 0.1 or more and 100 or less.

7. The manufacturing method according to any one of claims 1 to 6, wherein component (d) comprises an ammonium ion having one linear or branched alkyl group having 8 to 22 carbon atoms and three alkyl groups having 1 to 3 carbon atoms.

8. The manufacturing method according to any one of claims 1 to 7, wherein the molar ratio of component (b) to component (d) [(b) / (d)] is 0.05 or more and 50 or less.

9. The manufacturing method according to any one of claims 1 to 8, wherein the molar ratio of component (b) to component (a) [(b) / (a)] is 0.01 or more and 50 or less.

10. The manufacturing method according to any one of claims 1 to 9, wherein component (c) contains polyvinylpyrrolidone.

11. The manufacturing method according to any one of claims 1 to 10, wherein component (d) comprises one or more selected from the group consisting of stearyltrimethylammonium ion, cetyltrimethylammonium chloride, and lauryltrimethylammonium chloride.

12. The manufacturing method according to any one of claims 1 to 11, wherein component (e) comprises one or more selected from the group consisting of reducing sugars such as glucose, fructose, glyceraldehyde, lactose, arabinose, maltose, and ascorbic acid.

13. The manufacturing method according to any one of claims 1 to 12, wherein component (e) contains ascorbic acid.

14. A manufacturing method according to any one of claims 1 to 13, wherein the temperature of the mixed solution is reduced during the reaction.

15. The manufacturing method according to any one of claims 1 to 14, wherein the temperature of the mixed solution is set to 75°C or higher in the initial stage of the reaction, and then the temperature is set to below 75°C to allow the reaction to proceed.

Images