JP2011074476A - Method for producing copper nanoparticle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing copper nanoparticles in which particle diameter is the nanosize of ≤10 nm, and also, a particle size distribution width is narrow. <P>SOLUTION: In the method for producing copper nanoparticles, cupic hydroxide (Cu(OH)<SB>2</SB>) in a reduction reaction aqueous solution is brought into reduction reaction with an organic dispersant (D) in the presence of sodium borohydride (NaBH<SB>4</SB>) as a reducing agent while stirring, copper ions formed by the dissolution of the cupic hydroxide and undissolved cupic hydroxide are coexistent in the aqueous solution during the reduction reaction, the copper ions in the aqueous solution are reduced so as to produce copper atoms and copper nanoparticles by the progression of the reduction reaction, in accordance with the same, the undissolved cupic hydroxide is continuously dissolved into the aqueous solution so as to produce copper ions, and the reduction reaction is performed at the saturated solubility of the cupic hydroxide or at a concentration less than that in the aqueous solution. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing nanosized copper fine particles having a narrow particle size distribution by reduction of cupric hydroxide using a reducing agent in a reduction reaction aqueous solution, and copper fine particles obtained by the production method.

  It is known that nano-sized (particle size is 1 μm or less) fine particles such as metals and alloys have various unique characteristics not found in bulk materials. Various engineering applications that take advantage of this property are now highly expected in various fields such as electronics, biotechnology, and energy.

  Among them, nano-sized fine particles made of copper and its alloys are used as materials for forming mounting parts such as conductive circuits, bumps, vias, pads, magnetic elements for high-density magnetic storage media and antennas, gas reforming filters and fuel cell electrodes. It is highly expected as a catalyst material.

  Recently, attention has been paid to a technique of forming a wiring pattern by an ink jet method using an ink containing copper fine particles and baking it to form a wiring. However, when an ink containing copper fine particles is used as an ink for inkjet, it is important to maintain the dispersibility in the ink for a long time. A method has been proposed.

Patent Document 1 discloses a method for producing copper fine particles in which metal oxide fine particles are produced by reducing copper oxide or copper chloride in a polyethylene glycol solution or an aqueous solution thereof. In the examples, it is described that copper hydroxide (Cu (OH) ₂ ) was reduced with hydrazine to obtain fine particles having a particle diameter of 2 to 6 nm.
Patent Document 2 includes (a) copper chloride (CuCl ₂ ), copper nitrate (Cu (NO ₃ ) ₂ ), copper sulfate (CuSO ₄ ), copper acetate ((CH ₃ COO) ₂ Cu), or copper hydroxide. A step of mixing and stirring a copper precursor composed of (Cu (OH) ₂ ) or the like and an amine compound, (b) a step of raising the temperature of the mixed solution to 90 to 170 ° C., and then reacting at that temperature; (C) After the reaction is completed, the mixed solution is added to a non-aqueous solvent to lower the temperature of the solution to 20 to 50 ° C., and (d) an alcoholic solvent is added to the mixed solution to precipitate nanoparticles. And a method for producing a cubic form of copper nanoparticles.
The example describes that acetylacetonato copper was reduced under the above conditions to synthesize cubic particles having a size of about 15 nm.

In Patent Document 3, (a) copper chloride (CuCl ₂ ), copper nitrate (Cu (NO ₃ ) ₂ ), copper sulfate (CuSO ₄ ), copper acetate ((CH ₃ COO) ₂ Cu), acetylacetonato copper Or preparing a mixed solution containing a copper salt such as copper hydroxide (Cu (OH) ₂ ), a dispersing agent, a reducing agent and an organic solvent, and (b) raising the temperature of the mixed solution to 30 to 50 ° C. Producing copper nanoparticles comprising: heating and stirring; (c) irradiating the mixed solution with microwaves; and (d) reducing the temperature of the mixed solution to obtain copper nanoparticles. A method is disclosed. The example describes that copper sulfate was reduced under the above conditions to obtain spherical copper particles having a size of 30 to 50 nm.

Japanese Patent Laid-Open No. 04-176806 JP 2008-57041 A JP 2008-75181 A

In the conventional copper compound reduction method described above, if the resulting copper fine particles have a large particle size or a wide particle size distribution range, clogging is likely to occur in an inkjet nozzle when added to an inkjet dispersion. However, when stored in the ink state, there is a problem that the aggregation of particles occurs and the stability of the ink is lowered. When such a reduced stability ink is patterned on a substrate by an ink jet means and then dried and fired, the conductivity after sintering is lowered, and a desired conductive wiring or the like cannot be obtained.
Therefore, it has been desired to establish a technique for obtaining high-concentration copper fine particles having a particle size of nanometer of 10 nm or less and a narrow particle size distribution in a reduction reaction aqueous solution.
An object of the present invention is to solve the above-described problems and to provide a method for producing copper fine particles having a nano size of 10 nm or less and a narrow particle size distribution width.

As a result of intensive studies on the above-described conventional problems, the present inventors have used cupric hydroxide (Cu (OH) ₂ ) as a raw material having extremely low solubility in an aqueous solution of a reduction reaction, The present inventors have found that the above problems can be solved by coexisting undissolved solid copper oxide in the presence of an organic dispersant and sodium borohydride, which is a reducing agent, to arrive at the present invention.

That is, the gist of the present invention is the invention described in the following (1) to (9).
(1) Reduction reaction The cupric hydroxide (Cu (OH) ₂ ) in the aqueous solution is subjected to a reduction reaction with stirring in the presence of the organic dispersant (D) and the reducing agent sodium borohydride (NaBH ₄ ). The copper fine particle production method, wherein the aqueous solution contains copper ions dissolved and dissolved in the aqueous solution during the reduction reaction, and undissolved cupric hydroxide coexists. As the copper ions in the aqueous solution are reduced and copper atoms and fine copper particles are generated as the process proceeds, the undissolved cupric hydroxide is continuously dissolved in the aqueous solution to form copper ions. A method for producing copper fine particles, wherein the reduction reaction is carried out in the aqueous solution at a concentration equal to or lower than the saturated solubility of cupric hydroxide (hereinafter, sometimes referred to as “first embodiment”).
(2) The method for producing copper fine particles according to (1) above, wherein the amount of cupric hydroxide added to the aqueous reduction reaction solution is 15 to 150 mmol / liter.
(3) The method for producing copper fine particles according to (1) or (2) above, wherein the concentration of copper ion (I) in the aqueous reduction reaction solution is 5 × 10 ⁻² mmol / liter or less. .
(4) The average particle size of 90% by mass or more of cupric hydroxide added to the reduction reaction aqueous solution is in the range of 0.1 to 100 μm. The manufacturing method of the copper fine particle in any one.

(5) Ratio [(sodium borohydride) / (cupric hydroxide)] (molar ratio) of sodium borohydride and cupric hydroxide added to the reduction reaction aqueous solution is 0.5. It is -2.0, The manufacturing method of the copper fine particle in any one of said (1) thru | or (4) characterized by the above-mentioned.
(6) The organic dispersant (D) is one or more selected from polyvinyl pyrrolidone, polyethyleneimine, polyacrylic acid, carboxymethylcellulose, polyacrylamide, polyvinyl alcohol, polyethylene oxide, starch, and gelatin. The method for producing copper fine particles according to any one of (1) to (5) above, wherein
(7) The copper primary particles obtained by the reduction reaction have an average primary particle diameter of 4 to 8 nm and a coefficient of variation of 15% or less, according to any one of (1) to (6), A method for producing copper fine particles.

(8) Copper ions and undissolved water produced by dissolution of cupric hydroxide in the presence of the organic dispersant (D) and sodium borohydride (NaBH ₄ ) as the reducing agent in the reduction reaction aqueous solution. Copper fine particles (hereinafter referred to as “second embodiment”) having an average primary particle diameter of 4 to 8 nm and a coefficient of variation of 15% or less, obtained by a reduction reaction in the presence of cupric oxide. is there).

In the reduction reaction of the present invention described in the above (1) and (3), since cupric hydroxide is used as the raw material for the copper fine particles, in addition to the case of using other copper salts, in addition to the copper atom, Is characterized in that essentially no impurities are derived from the raw material copper compound because it contains only hydrogen and oxygen atoms. Moreover, due to the low solubility of cupric hydroxide in aqueous solution, it is reduced by a reducing agent in an environment where the concentration of copper ions generated by dissolution of cupric hydroxide in the reduction reaction aqueous solution is low. Therefore, copper fine particles having a small average primary particle size and a narrow particle size distribution can be stably obtained by the reduction reaction.
In the reduction reaction of the present invention described in (2) above, undissolved cupric hydroxide can be added to the aqueous solution of the reduction reaction. It becomes possible to obtain.
In the reduction reaction of the present invention described in the above (4), by controlling the particle size of cupric hydroxide used as a raw material for the reduction reaction, the average primary particle size of the obtained copper fine particles and the reduction reaction time are determined. It becomes possible to control.

In the reduction reaction of the present invention described in the above (5), compared with the case where other metal salt, for example, copper acetate is used, cupric hydroxide has a relatively high pH in an aqueous solution. Since the decomposition function of certain sodium borohydride can be suppressed and the reduction function of sodium borohydride can be efficiently exhibited, (sodium borohydride) / (cupric hydroxide)] (molar ratio) is 0.5-2. The reduction reaction of cupric hydroxide can be completed within the range of 0.0.
In the invention described in the above (6), the organic dispersant (D) exhibits a function of dispersing the copper fine particles generated by the reduction reaction in the reduction reaction aqueous solution, so that the average primary particle size is reduced by the reduction reaction and the particle size is reduced. It becomes possible to obtain copper fine particles having a narrow distribution.
According to the method for producing copper fine particles described in (1) to (6), copper fine particles having an average primary particle diameter of 4 to 8 μm and a coefficient of variation of 15% or less described in (7) are obtained. A copper fine particle dispersion obtained by dispersing such copper fine particles in a dispersion solution is excellent in dispersion stability, and can be suitably used for copper ink for substrate wiring.
When the reduction reaction described in the above (8) is adopted, it becomes possible to obtain copper fine particles having an average primary particle diameter of 4 to 8 μm and a coefficient of variation of 15% or less. Therefore, such copper fine particles are dispersed in a dispersion solution. Since the copper fine particle dispersion obtained by this process is excellent in dispersion stability, the copper fine particle dispersion obtained by dispersing the fine particles in the dispersion is used as a functional material such as a wiring material, a coloring material, an optical filter, and a catalyst. A homogeneous performance can be obtained, and furthermore, a conductive material having high conductivity can be obtained even when fired at a copper fine particle dispersion solution firing temperature (300 ° C. or lower).

2 is an enlarged view of a microscopic photograph of copper fine particles obtained in Example 1. FIG. 2 is a histogram showing the particle size distribution of copper fine particles obtained in Example 1. FIG. 4 is a histogram showing the particle size distribution of copper fine particles obtained in Example 2. 6 is a histogram showing the particle size distribution of copper fine particles obtained in Example 3. It is an enlarged view by the microscope picture of the copper fine particle obtained by the comparative example 1, and obtained by reduce | restoring copper acetate with sodium borohydride. 6 is a histogram showing the particle size distribution of copper fine particles obtained in Comparative Example 1.

[1] The “copper fine particle production method” (first aspect) of the present invention and [2] “copper fine particle” (second aspect) of the present invention will be described below.
[1] “Method for producing copper fine particles” according to the first aspect of the present invention
The “method for producing copper fine particles” according to the first aspect of the present invention includes cupric hydroxide (Cu (OH) ₂ ) in a reduction reaction aqueous solution, an organic dispersant (D), and a borohydride as a reducing agent. A method for producing copper fine particles, wherein a reduction reaction is performed with stirring in the presence of sodium (NaBH ₄ ),
During the reduction reaction, cupric hydroxide dissolved in the aqueous solution coexists with undissolved cupric hydroxide, and the copper ion in the aqueous solution is reduced by the progress of the reduction reaction. As the copper atoms and copper fine particles are generated, the undissolved cupric hydroxide dissolves in the aqueous solution and copper ions are continuously generated, and the reduction reaction is hydroxylated in the aqueous solution. It is characterized in that it is carried out at a concentration of cupric saturation solubility or lower.
Hereinafter, the “method for producing copper fine particles” of the present invention will be described.

(1) About cupric hydroxide, sodium borohydride, and organic dispersant (D) used as raw materials (1-1) Cupric hydroxide In the present invention, hydroxide hydroxide used as a raw material for copper fine particles Dicopper is a bluish white powder or blue crystal with low solubility in water, and is about 5.85 × 10 ⁻⁵ mol / liter at room temperature (about 25 ° C.). In the “method for producing copper fine particles” of the present invention, when forming copper fine particles from copper ions with a reducing agent in a reduction reaction aqueous solution, due to the low solubility in aqueous solution of cupric hydroxide, Since the concentration of copper ions dissolved in the reduction reaction aqueous solution is also low, copper fine particles having a small particle size and a narrow particle size distribution can be stably obtained when copper fine particles are formed from a low copper ion concentration.
The cupric hydroxide may be in the form of particles or particles obtained by pulverizing particles.
Since the dissolution rate of cupric hydroxide in an aqueous solution is slow, by using cupric hydroxide with a small particle size by pulverization, the reduction reaction can be promoted and the primary particle size can be made relatively large. It becomes possible. When using fine cupric hydroxide, the average particle diameter of 90% by mass or more is preferably 0.1 to 100 μm. When the average particle diameter exceeds 100 μm, the dissolution rate of cupric hydroxide in the reduction reaction aqueous solution is lowered, the copper ion concentration in the aqueous solution is lowered, and the time required for the reduction reaction may be increased.
Cupric hydroxide can be pulverized by dry ball pulverization or wet pulverization, but in a clean environment using a ceramic pulverizer, ceramic ball pulverization media, etc. to avoid contamination by impurities. It is desirable to implement.

(1-2) Sodium borohydride Sodium borohydride used as a reducing agent in the present invention is widely used as a reducing agent for the reduction of various substances. Since sodium borohydride decomposes in an acidic or neutral aqueous solution to generate hydrogen, when adding sodium borohydride to the reduction reaction aqueous solution, a basic compound is added to the aqueous solution in advance to make it alkaline. Alternatively, a solution obtained by dissolving sodium borohydride in an aqueous solution having a pH of 10.5 to 13 in advance may be added to the aqueous reduction reaction solution. As the basic compound to be added, for example, alkali metal or alkaline earth metal hydroxide or carbonate such as sodium hydroxide, potassium hydroxide or calcium hydroxide, ammonium compound such as ammonia, basic such as amines, etc. A compound can be mentioned.

(1-3) Organic dispersant (D)
The organic dispersant (D) promotes the reduction reaction to copper atoms by coordinating to the copper ions generated by the reduction reaction, and coordinates to the surface of the copper particles formed from the copper atoms. It also has a function of uniformly dispersing in an aqueous solution. In particular, when a large amount of copper hydroxide is added to the reduction reaction aqueous solution, it exhibits a function to disperse the copper fine particles generated in the aqueous solution in order to obtain copper fine particles having a small average primary particle size and a narrow particle size distribution. The addition of dispersing agents is important.
The organic dispersant (D) is preferably an amine polymer such as polyvinylpyrrolidone or polyethyleneimine; a hydrocarbon polymer having a carboxylic acid group such as polyacrylic acid or carboxymethylcellulose; an acrylamide such as polyacrylamide; One or more selected from among alcohol, polyethylene oxide, starch, and gelatin.
Specific examples of the organic dispersant (D) exemplified above include polyvinylpyrrolidone (molecular weight: 1000 to 500,000), polyethyleneimine (molecular weight: 100 to 100,000), carboxymethyl cellulose (carboxyl of hydroxyl group Na salt of alkali cellulose). Degree of substitution to methyl group: 0.4 or more, molecular weight: 1000 to 100,000, polyacrylamide (molecular weight: 100 to 6,000,000), polyvinyl alcohol (molecular weight: 1000 to 100,000), polyethylene glycol ( Molecular weight: 100 to 50,000), polyethylene oxide (molecular weight: 50,000 to 900,000), gelatin (average molecular weight: 61,000 to 67,000), high molecular organic dispersants such as water-soluble starch ( D).

The number average molecular weight of each polymeric organic dispersant (D) is shown in the parentheses, and those having such a molecular weight range are water-soluble and can be used preferably in the present invention. In addition, these 2 or more types can also be mixed and used.
Moreover, although the addition amount of an organic dispersing agent (D) is based also on the density | concentration of the copper fine particle produced | generated from reduction reaction aqueous solution, 1-100 weight part is preferable with respect to 100 weight part of this copper atom, and 5-100 weight. Part is more preferred. When the amount of the organic dispersant (D) added is less than 1, the effect of suppressing aggregation may not be sufficiently obtained. On the other hand, when the amount exceeds 100 parts by weight, the reduction reaction is performed even if there is no problem in dispersion. When the aggregation promoter is added after the completion to remove the organic dispersant (D), inconvenience may occur.

(2) Reduction of cupric hydroxide with sodium borohydride (2-1) Reduction reaction aqueous solution The reduction reaction aqueous solution used in the method for producing copper fine particles of the present invention includes at least the cupric hydroxide. , Sodium borohydride, and organic dispersant (D) are contained, and a basic compound is added as a sodium borohydride stabilizer so that the pH is adjusted to about pH 10.5-13. The cupric hydroxide added to the reduction reaction aqueous solution is preferably in the range of 15 to 150 mmol / liter in the aqueous solution. The productivity of the copper fine particles in the reduction reaction aqueous solution can be improved at 15 mmol / liter or more, whereas if it exceeds 150 mmol / liter, stirring in the reduction reaction aqueous solution may be difficult.
The amount of sodium borohydride added to the reduction reaction aqueous solution is the ratio of sodium borohydride to cupric hydroxide [(sodium borohydride) / (cupric hydroxide)] (molar ratio). Is preferably 0.5 to 2.0, more preferably 0.5 to 1.0.
If the amount of sodium borohydride added to cupric hydroxide is less than 0.5 molar ratio, the reduction reaction may not proceed sufficiently. On the other hand, if the molar ratio exceeds 2.0, unreacted hydrogenation may occur. There is a risk that a large amount of hydrogen is generated from sodium boron and that a large amount of sodium ions are mixed.

The addition amount of the basic compound that is a stabilizer of sodium borohydride to the aqueous solution of the reduction reaction is preferably 50 mmol / liter or more, and the concentration ratio of the basic compound and copper ion ([basic compound] / [ Copper ion]) (molar ratio) is preferably 4.7 or more.
In the reduction reaction aqueous solution, when the basic compound as a stabilizer is in the above range, the formation of copper fine particles is facilitated by the reduction reaction.
In addition, ([BH ^{4 −} ] / [Cu ²⁺ ]) (molar ratio) in the reduction reaction aqueous solution is preferably 0.2 or more, and ([OH ⁻ ] / [Cu ²⁺ ]) / ([BH ⁴⁻ ] / [Cu ²⁺ ]) is preferably 3.2 or more. When [BH ⁴⁻ ], [Cu ²⁺ ], and [OH ⁻ ] are present in such a ratio in the reduction reaction aqueous solution, the formation of copper fine particles is facilitated by the reduction reaction.

(2-2) Reductive reaction While stirring, while preferably ventilating an inert gas, the aqueous reductive reaction solution to which at least cupric hydroxide, the organic dispersant (D), and the reducing agent sodium borohydride are added is preferably used. The reduction reaction proceeds.
The inert gas is preferably at least one selected from the group consisting of nitrogen, argon, and helium. Moreover, it is preferable that the temperature of the reduction reaction aqueous solution at the time of the reduction is 60 ° C or less, more preferably 40 ° C or less, and further preferably 10 to 30 ° C.
The reduction reaction is presumed to proceed by the following route. First, cupric hydroxide is dissolved in the reduction reaction aqueous solution to form copper ions, and then the copper ions are reduced by [BH ⁴⁺ ] generated by dissociation of sodium borohydride to generate copper atoms. Further, when the copper atom becomes supersaturated with the aqueous solution, copper fine particles are generated. An organic dispersant (D) is coordinated to the produced copper fine particles and dispersed in the aqueous reduction reaction solution.
While the reduction reaction proceeds, after [BH ⁴⁺ ] acts as a reducing agent, it is released from the reduction reaction aqueous solution as hydrogen gas. Therefore, the completion of the reduction reaction can be confirmed by stopping the generation of hydrogen gas.
Since the reduction reaction time tends to be shortened as the particle size of cupric hydroxide as a raw material is smaller, in the reduction reaction, cupric hydroxide is dissolved in the reduction reaction aqueous solution and copper ions are dissolved. It is assumed that the process to be formed is at the rate-determining stage.

(3) Recovery of copper fine particles When the reduction reaction is completed, when an amount of sodium borohydride exceeding the amount necessary for reducing cupric hydroxide is added, hydrogen from the reduction reaction aqueous solution is added as described above. Can be confirmed at the end of the occurrence of. In this case, almost all of the copper atoms in the cupric hydroxide added to the reduction reaction aqueous solution are reduced to form copper fine particles.
In the condition where the total amount of copper in the cupric hydroxide added to the reduction reaction aqueous solution is not reduced, after the reduction reaction is completed, if the stirring in the reduction reaction aqueous solution is stopped, When cupric is present, cupric hydroxide precipitates at the bottom of the aqueous solution, so unreacted cupric hydroxide can be easily removed out of the system.
The copper fine particles dispersed in the reduction reaction aqueous solution can be collected by adding a flocculant to aggregate the copper fine particles. The flocculant is not particularly limited as long as it is liquid or gas at normal temperature or operating temperature, and is added to the aqueous solution after the reduction reaction so that the fine particles are aggregated and the organic dispersant (D) is not precipitated. Although not intended, preferred examples include acetone, halogenated hydrocarbons, and the like. As the halogenated hydrocarbon, halogen compounds such as chlorine compounds and bromine compounds having 1 to 4 carbon atoms, and chlorine-based and bromine-based halogenated aromatic compounds are preferable.

Specific examples of the flocculant include chlorine compounds having 1 carbon atom such as methyl chloride, methylene chloride, chloroform) and carbon tetrachloride; ethyl chloride, 1,1-dichloroethane, 1,2-dichloroethane, 1,1-dichloro Chlorine compounds having 2 carbon atoms such as chloroethylene, 1,2-dichloroethylene, trichloroethylene, acetylene tetrachloride, ethylene chlorohydrin; chlorines having 3 carbon atoms such as 1,2-dichloropropane and allyl chloride Compounds such as chloroprene, chlorobenzene, chlorobenzene, chlorobenzene, benzyl chloride, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, α-chloronaphthalene, β-chloronaphthalene, etc. aromatic chlorine compounds; bromoform, bromine compounds such as bromine benzol; and hexane (C 6 _{H 14),} Fine cyclohexane (C 6 _{H 12)} 6 carbons, such as hydrocarbons, at least one selected from among may be exemplified.
The amount of the flocculant (C1) added is 0.01 or more in a ratio of ([flocculant (mol)] / [fine particles (g)]) to the copper fine particles formed by the reduction reaction. Preferably, the upper limit is not particularly limited, but 0.01 to 50 is more preferable and 0.1 to 20 is more preferable from a practical aspect. If the blending ratio is less than 0.01, the effect of addition may not be sufficiently exhibited.

After removing unreacted cupric hydroxide from the reduction reaction aqueous solution by the above method, etc., when chloroform having a specific gravity greater than water is added as an aggregating agent to the aqueous solution in which the copper fine particles are dispersed, stirring is performed. When it is later decanted, it is separated into two phases, an upper phase composed of an aqueous phase and a lower phase composed of an aggregating agent, and the fine particles are present in a state of being aggregated in the lower portion of the aqueous phase that is the upper phase. When the specific gravity of the flocculant is smaller than that of water, after stirring, the upper phase is the flocculant phase and the lower phase is the aqueous phase. In this case, the metal fine particles are also aggregated in the lower part of the aqueous phase. May exist. Therefore, since the added flocculant is separated from the aqueous solution by standing, the flocculant can be efficiently removed from the copper fine particles. The state of aggregation or precipitation after adding a flocculant and stirring includes a state where fine particles are concentrated and floated below the aqueous phase.
The flocculant is added to the aqueous solution in which the copper fine particles are dispersed and stirred, and the fine particles are agglomerated or precipitated, and then the agglomerated or precipitated fine particles are separated from the aqueous solution by an operation such as filtration. When obtaining the fine particles, if the organic dispersant (D) cannot be sufficiently removed from the copper fine particles only by the separation / collection operation such as filtration, the copper fine particles have 1 carbon atom after the fine particles are separated from the aqueous solution. It can be washed with a solvent such as about 7 to alcohol. Thus, copper fine particles can be recovered from the reduction reaction aqueous solution.

(4) Shape of copper fine particles obtained by reduction reaction The shape of copper fine particles obtained by the reduction reaction has an average primary particle diameter of 4 to 8 nm and a variation coefficient of 15% or less.
Here, the “average primary particle diameter” is a simple average value of primary particle diameters of copper fine particles measured from observation with a transmission electron microscope (TEM) (for example, JEOL Ltd., model: JEF-3100F). is there.
“Variation coefficient” is a value obtained by dividing the standard deviation value of primary particles by the average primary particle size.
Coefficient of variation = (standard deviation) / (average primary particle size)
Further, the mode diameter of the copper fine particles obtained by the reduction reaction is 5.0 to 8.0 nm. Here, the mode diameter is a value indicating the maximum value of the particle distribution.
The particle size distribution and the like of the copper fine particles are described in the section “Copper fine particles according to the second aspect” below.

[2] “Copper fine particles” according to the second aspect of the present invention
The “copper fine particles” according to the second aspect of the present invention are prepared by adding cupric hydroxide in the reduction reaction aqueous solution in the presence of the organic dispersant (D) and sodium borohydride (NaBH ₄ ) as the reducing agent. It is obtained by a reduction reaction in which copper ions generated by dissolution and undissolved cupric hydroxide coexist, and has an average primary particle diameter of 4 to 8 nm and a coefficient of variation of 15% or less.
(1) Regarding the reduction reaction of cupric hydroxide in the second embodiment The reduction reaction is carried out in the presence of the organic dispersant (D) and the reducing agent sodium borohydride (NaBH ₄ ) in the reduction reaction aqueous solution. It is a reduction reaction in which copper ions generated by dissolution of cupric hydroxide and undissolved cupric hydroxide coexist, and the organic dispersant (D), sodium borohydride, and cupric hydroxide Is as described in the first embodiment.
As described above, in the “method for producing copper fine particles” according to the first aspect, cupric hydroxide is used as a raw material for the copper fine particles, so that the solubility of cupric hydroxide in an aqueous solution is low. Thus, since the cupric hydroxide dissolved in the reduction reaction aqueous solution is reduced by the reducing agent in an environment where the concentration of copper ions is low, the average primary particle size described below is 4 to 4 by the reduction reaction. Copper fine particles having a narrow particle size distribution with a coefficient of variation of 15% or less at 8 nm can be stably obtained.

(2) Copper fine particles According to the second aspect, the average primary particle diameter of the copper fine particles is 4 to 8 nm and the coefficient of variation is 15% or less.
When reducing in the presence of the reducing agent sodium borohydride (NaBH ₄ ) in the reduction reaction aqueous solution, copper acetate having a high solubility in an aqueous solution, which has been widely known as a raw material for copper fine particles, was used. Compared to the case, the use of cupric hydroxide is characterized in that copper fine particles having a particularly narrow particle size distribution can be obtained stably.
The solubility of cupric hydroxide in an aqueous solution is 5.85 × 10 ⁻⁵ mol / liter, and the solubility of acetic acid in an aqueous solution is 3.96 × 10 ⁻¹ mol / liter. It can be seen that when cupric oxide is used as the raw material, the copper ion concentration in the aqueous reduction reaction solution is extremely low compared to the case where copper acetate is used as the raw material.
When copper acetate is used as the raw material, the coefficient of variation as the particle size distribution of the copper fine particles obtained by the reduction reaction is 30% or more, whereas the coefficient of variation of the copper fine particles obtained when cupric hydroxide is used as the raw material is It is characteristic that it becomes 15% or less.
When copper fine particles having an average primary particle diameter of 10 nm or less and a coefficient of variation as a particle size distribution of 15% or less are dispersed in a dispersion solution, a fine particle dispersion solution having excellent dispersion stability is obtained.

For example, when cupric hydroxide particles having a particle size range of 0.1 to 100 μm are used as a raw material when reducing in the presence of sodium borohydride (NaBH ₄ ) in an aqueous reduction reaction solution, the average primary particle size is 10 nm or less. Of copper fine particles can be obtained. Note that when the particle size range of the cupric hydroxide particles is relatively large, the average primary particle diameter and mode diameter of the copper fine particles obtained by the reduction reaction tend to be small and the reduction reaction time tends to be long. However, if cupric hydroxide particles are used as the raw material, the coefficient of variation of the copper fine particles obtained by the reduction reaction with sodium borohydride is almost 15% or less in most cases. It is an effect.

When forming a conductive material obtained by coating (patterning) a copper fine particle dispersion on a substrate, drying and then sintering in an inert gas atmosphere, the average primary particle diameter of the copper fine particles in the particle dispersion is 4 When the coefficient of variation is 15% or less at ˜8 nm, the conductive material obtained by firing at a low firing temperature is excellent in storage stability in the dispersion solution and can be expected to have high conductivity.
Thus, when cupric hydroxide is used as a raw material, copper fine particles having an average primary particle diameter of 10 nm or less and a coefficient of variation of 15% or less can be stably obtained in the following Examples and Comparative Examples. It has been confirmed.

Next, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples.
In the following examples and comparative examples, the average particle size of primary particles in the fine particle dispersion was determined from observation with a transmission electron microscope (TEM) (manufactured by JEOL Ltd., model: JEF-3100F).
A cupric hydroxide reagent grade 1 product was used. In Example 1, the reagent was used as it was, and in Examples 2 and 3, the reagent was pulverized in a mortar for 15 minutes and 30 minutes, respectively.
As the copper acetate, a reagent first grade product was used.

[Example 1]
(1) Preparation and Reduction Reaction of Reduction Reaction Aqueous Solution A particle size range of 0.1 to 100 μm as a raw material for copper fine particles was prepared by dissolving 10 g of polyvinylpyrrolidone (PVP, number average molecular weight of about 3500) in 197.93 ml of distilled water. 2.9268 g (30 mmol) of cupric hydroxide (Cu (OH) ₂ ) was added. Then, while stirring in a nitrogen gas atmosphere, 2.073 ml of an aqueous solution containing 15 mmol of sodium borohydride and 48 mmol of sodium hydroxide was added dropwise, and then the reduction reaction was carried out with good stirring for 45 minutes. It was.
The end of the reduction reaction was the time when the generation of hydrogen gas from the reaction system was completed.
By the reduction reaction, a fine particle dispersion in which copper fine particles at least partially covered with a polymer dispersant are dispersed in an aqueous solution was obtained.
(2) Evaluation and Results The obtained copper fine particle dispersion was applied on a copper vapor deposited copper mesh, dried, and observed with the above transmission electron microscope (TEM).
The photograph by the transmission electron microscope (TEM) of the copper fine particle obtained in FIG. 1 is shown. FIG. 2 shows a histogram of the obtained copper fine particles.
As a result of observation by the transmission electron microscope (TEM), the obtained copper fine particles had an average primary particle diameter of 4.77 nm, a mode diameter obtained from a histogram of 5.0 nm, and a coefficient of variation of 13.6%. It was.

[Examples 2 and 3]
(1) Preparation of reduction reaction aqueous solution and reduction reaction In Examples 2 and 3, Example 1 except that the particle size ranges of cupric hydroxide used as a raw material were 0.1 to 50 μm and 0.1 to 10 μm, respectively. In the same manner as described above, a reduction reaction was performed.
In addition, in Examples 2 and 3, the time when generation of hydrogen gas was completed was 35 minutes and 30 minutes after the completion of the dropping, respectively.
(2) Evaluation and Results The obtained copper fine particle dispersion was applied on a copper vapor deposited copper mesh, dried, and observed with the above transmission electron microscope (TEM).
The histograms of the copper fine particles obtained in Examples 2 and 3 are shown in FIGS.
As a result of observation by the transmission electron microscope (TEM), the obtained copper fine particles show the average particle diameter, mode diameter, and coefficient of variation of the primary particles in Table 2.

[Comparative Example 1]
(1) Preparation and reduction reaction of reduction reaction aqueous solution It described in Example 1 except having used the copper acetate instead of cupric hydroxide as a raw material, and having shown the preparation amount and reduction temperature to reduction reaction aqueous solution in Table 1. A reduction reaction was carried out in the same manner as above.
The added copper acetate was completely dissolved to form a uniform aqueous solution.
(2) Evaluation and Results The same evaluation as described in Example 1 was performed. The photograph by the transmission electron microscope (TEM) of the copper fine particle obtained in FIG. 5 is shown. FIG. 6 shows a histogram of the obtained copper fine particles.
The production conditions of Examples 1 to 3 and Comparative Example 1 are summarized in Table 1, and the evaluation results are summarized in Table 2.

Claims (8)

Copper fine particles that cause a reduction reaction of cupric hydroxide (Cu (OH) ₂ ) in an aqueous reduction reaction solution while stirring in the presence of an organic dispersant (D) and a reducing agent, sodium borohydride (NaBH ₄ ). A manufacturing method of
During the reduction reaction, cupric hydroxide dissolved in the aqueous solution coexists with undissolved cupric hydroxide, and the copper ion in the aqueous solution is reduced by the progress of the reduction reaction. As the copper atoms and copper fine particles are formed, the undissolved cupric hydroxide is continuously dissolved in the aqueous solution to produce copper ions, and the reduction reaction is hydroxylated in the aqueous solution. A method for producing copper fine particles, which is performed at a saturation solubility or lower than that of cupric copper.   2. The method for producing copper fine particles according to claim 1, wherein the amount of cupric hydroxide added to the reduction reaction aqueous solution is 15 to 150 mmol / liter. 3. The method for producing copper fine particles according to claim 1, wherein the concentration of copper ion (I) in the aqueous reduction reaction solution is 5 × 10 ⁻² mmol / liter or less.   The copper according to any one of claims 1 to 3, wherein an average particle diameter of 90% by mass or more of cupric hydroxide added to the reduction reaction aqueous solution is in a range of 0.1 to 100 µm. A method for producing fine particles.   The ratio [(sodium borohydride) / (cupric hydroxide)] (molar ratio) of sodium borohydride and cupric hydroxide added to the reduction reaction aqueous solution is 0.5-2. The method for producing copper fine particles according to claim 1, wherein the copper fine particles are zero.   The organic dispersant (D) is one or more selected from polyvinylpyrrolidone, polyethyleneimine, polyacrylic acid, carboxymethylcellulose, polyacrylamide, polyvinyl alcohol, polyethylene oxide, starch, and gelatin. The method for producing copper fine particles according to any one of claims 1 to 5, wherein:   The average primary particle diameter of the copper fine particles obtained by the reduction reaction is 4 to 8 nm, and the coefficient of variation is 15% or less. The production of copper fine particles according to any one of claims 1 to 6, Method. Copper ions formed by dissolution of cupric hydroxide in the presence of the organic dispersant (D) and the reducing agent sodium borohydride (NaBH ₄ ) in the reduction reaction aqueous solution and undissolved second hydroxide Copper fine particles characterized by having an average primary particle diameter of 4 to 8 nm and a coefficient of variation of 15% or less, obtained by a reduction reaction in which copper coexists.