JP2007039765A - Method for producing metal particulate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which solves the problem that, when a metallic compound is reduced in a solvent liquid in the presence of protective colloid to produce metal particulate having the protective colloid on the surfaces of the particles, since the metal particulate produced in the presence of the protective colloid are highly dispersed, filtering is hardly performed, and can easily recover the metal particulate. <P>SOLUTION: A protective colloid removal agent of decomposing or dissolving protective colloid is added to a dispersion liquid obtained by reducing a metallic compound in a solvent liquid in the presence of protective colloid, the protective colloid is removed to flocculate metal particulate, and next, filtering is performed using a pressure filtering machine, a vacuum filtering machine, a suction filtering machine or the like. For example, in the case protein such as gelatine is used as protective colloid, proteinase is used as the protective colloid removal agent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing metal fine particles, and more particularly to a method for producing metal fine particles suitably used for producing a multilayer ceramic capacitor or an electrode formed on a printed wiring board.

  The metal fine particles are excellent in electric conductivity, heat conductivity and the like, and have unique properties such as having a metallic luster, so that they are used in various applications. For example, fine particles such as silver, palladium, nickel, and copper are materials having good electrical conductivity, and ensure electrical continuity of electrode members such as circuits of printed wiring boards and various electrical contact members. Widely used as a material. In particular, since copper and nickel are inexpensive materials, they have recently been used for internal electrodes of multilayer ceramic capacitors.

  As a method for producing such metal fine particles, a method of obtaining copper fine particles by reducing copper oxide with a hydrazine-based reducing agent in an aqueous medium containing a protective colloid such as gum arabic (see Patent Document 1), a noble metal compound A first solution in which water and a lower alcohol are mixed with a second solution in which a reducing agent is mixed with a protective colloid such as polyacrylic acid or polyvinylpyrrolidone is mixed, and a reduction reaction is performed. A method of obtaining noble metal fine particles such as silver, platinum and palladium (Patent Document 2) is known. Further, the present applicant has proposed a method of obtaining copper fine particles by reducing copper oxide in the presence of a protective compound colloid such as a sulfur compound and gelatin (see Patent Document 3).

Japanese Patent Publication No. 61-55562 JP 2004-43892 A JP 2004-315853 A

  In the methods described in Patent Documents 1 to 3, a metal compound is reduced in a liquid medium in the presence of a protective colloid to generate metal fine particles having the protective colloid on the particle surface. The reason for this is that, since the surface energy is large due to the small particle size of the generated metal particles, protective colloid is used as a dispersion stabilizer to protect the particle surface in order to obtain a monodispersed state without agglomerating the metal particles. This is because it is essential to deposit (or adsorb) the colloid. However, due to the presence of protective colloids, the resulting metal fine particles are highly dispersed, so even if flocculants are added, the metal compound used during the reduction reaction, the remainder of the reducing agent, the protective colloid, pH adjuster, etc. There is a problem that it is difficult to solid-liquid-separate metal fine particles from a dispersion containing a large amount of anions and cations derived from these additives, and ultrafiltration unsuitable for mass production must be performed.

  As a result of intensive research to solve these problems, the present inventors have added a protective colloid remover to a dispersion containing protective colloid and metal fine particles to remove the protective colloid, so that the metal fine particles are aggregated. It is easy to filter, it can be filtered by ordinary means, the protective colloid can be removed after the metal particles are generated and the metal fine particles can be aggregated, and then it can be easily re-dispersed to the primary particles. The present invention was completed by finding that the yield was improved and the filtration and washing time could be shortened.

  That is, the present invention is a method for producing metal fine particles, comprising adding a protective colloid remover to a dispersion containing protective colloid and metal fine particles to agglomerate the metal fine particles, followed by fractionation.

  According to the present invention, the dispersion containing the metal fine particles can be advantageously filtered industrially to separate the metal fine particles into solid and liquid. The solid metal fine particles obtained by filtration can be sufficiently washed to remove impurities, and high purity metal fine particle solids and dried metal fine particles can be obtained. Such solid metal fine particles and dried metal fine particles are less likely to form agglomerated particles even if the content of protective colloid is small, and are easy to disperse again in water or organic solvents, so fluidity of metal pastes, paints, inks, etc. When the composition is used for, for example, an internal electrode of a multilayer ceramic capacitor, a circuit of a printed wiring board, other electrodes, etc., a thin film and a high-density electrode can be obtained.

  In the present invention, a protective colloid remover is added to a dispersion containing protective colloid and metal fine particles to aggregate the metal fine particles, and then fractionated. In the present invention, the metal species constituting the metal fine particles are not particularly limited, and can be transition metal elements, typical metal elements, etc., and in particular, Group VIII of the periodic table (iron, cobalt, nickel, ruthenium, rhodium) , Palladium, osmium, iridium, platinum) and group IB (copper, silver, gold) can be used for many applications. Among them, gold, silver, platinum, palladium, copper, and nickel are preferable because of their excellent conductivity, copper, silver, and nickel are more preferable, and inexpensive copper is particularly preferable. One kind of metal may be selected and used, or two or more kinds may be used as an alloy or laminated. In addition, the present invention can be applied to any fine metal particles, but the finer the particles, the more difficult the filtration, so the effect of the present invention is great. For example, the primary average particle diameter is in the range of 2.0 μm or less. Is preferably applied, more preferably in the range of 0.005 to 1.0 μm, still more preferably in the range of 0.01 to 0.75 μm. The primary average particle diameter is expressed as a cumulative 50% diameter measured by electron microscopy.

  The dispersion containing the protective colloid and the metal fine particles can be produced using a known method. For example, a method of reacting a metal compound and a reducing agent in a liquid medium in the presence of a protective colloid can be mentioned. Similarly, when a metal compound and a reducing agent are reacted in the medium in the presence of a protective colloid and a complexing agent, the shape of the particles is uniform, and fine metal particles that do not contain aggregated particles are more easily obtained. This is preferable. The order of adding each raw material is not particularly limited as long as a protective colloid or a protective colloid and a complexing agent are present during the reaction between the metal compound and the reducing agent. For example, (1) a method in which a metal compound and a reducing agent are simultaneously added to a medium containing a protective colloid, (2) a method in which a reducing agent is added to a medium containing a protective colloid and a metal compound, etc. Is mentioned. Further, if the complexing agent is used in combination with the protective colloid, for example, (3) a method of simultaneously adding a metal compound and a reducing agent to a medium containing the protective colloid and the complexing agent, (4) A method of adding a reducing agent to a medium containing a protective colloid, a complexing agent and a metal compound. (5) A complexing agent and a reducing agent are added simultaneously to a medium containing a protective colloid and a metal compound. Examples thereof include (6) a method of adding a mixed solution of a complexing agent and a reducing agent to a medium containing a protective colloid and a metal compound. Among these, the methods (5) and (6) are preferable because the reaction is easily controlled, and the method (6) is particularly preferable. “Simultaneous parallel addition” refers to a method in which a metal compound and a reducing agent or a complexing agent and a reducing agent are added separately at the same time during the reaction period, and both are continuously added during the reaction period. In addition to this, it includes adding one or both intermittently.

  As the “metal compound”, sulfates, nitrates, carbonates, chlorides, oxides, and the like of the metals such as gold, silver, platinum, palladium, copper, and nickel can be used. As the medium solution for dissolving the metal compound, for example, an aqueous solvent or an organic solvent medium such as alcohol, preferably an aqueous medium is used. The reduction reaction temperature is preferably in the range of 10 ° C. to the boiling point of the liquid medium used, because the reaction easily proceeds, and more preferably in the range of 40 to 95 ° C. It is preferable to adjust the pH of the reaction solution in the range of 3 to 12 in advance with an acid or an alkali because precipitation of the metal compound can be prevented and the reaction can be performed uniformly. The reaction time can be set by controlling the addition time of raw materials such as a reducing agent. For example, about 10 minutes to 6 hours is appropriate.

  As the “reducing agent”, known ones can be used. For example, hydrazine reducing agents such as hydrazine, hydrazine hydrochloride, hydrazine sulfate, hydrazine hydrate and the like, sodium borohydride, sodium sulfite, sodium hydrogen sulfite Sodium thiosulfate, sodium nitrite, sodium hyponitrite, phosphorous acid and its salts such as sodium phosphite, hypophosphorous acid and its salts such as sodium hypophosphite, aldehydes, alcohols, amines , Saccharides and the like, and one or more of these may be used. In particular, hydrazine-based reducing agents are preferred because of their strong reducing power. The amount of the reducing agent used can be appropriately set as long as it can generate metal fine particles from the metal compound, and is preferably in the range of 0.2 to 5 mol with respect to 1 mol of the metal contained in the metal compound. .

  The “protective colloid” acts as a dispersion stabilizer for the generated metal fine particles. In the present invention, known colloids can be used, such as gelatin, gum arabic, casein, sodium caseinate, ammonium caseinate, and other natural polymers such as starch, dextrin, agar, sodium alginate, and the like. , Celluloses such as hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose; vinyls such as polyvinyl alcohol and polyvinylpyrrolidone; acrylic acids such as sodium polyacrylate and ammonium polyacrylate; and synthetic polymers such as polyethylene glycol. These may be used alone or in combination of two or more. Since the protective colloid of a polymer has a high effect of dispersion stabilization, it is preferable to use this, and when reacting in an aqueous medium, it is preferable to use a water-soluble one, particularly gelatin, polyvinyl alcohol, polyvinyl pyrrolidone, Polyethylene glycol is preferred. The amount of the protective colloid used can be appropriately set, and it is preferably in the range of 1 to 100 parts by weight with respect to 100 parts by weight of the metal compound because the generated metal fine particles can be easily dispersed and stabilized.

A “complexing agent” is considered to act in the process of elution of metal ions from a metal compound or formation of a metal by reduction of the metal compound, which binds to the donor atom of the ligand it has and the metal ion or metal And a compound capable of forming a metal complex compound, and examples of the donor atom include nitrogen, oxygen, sulfur and the like. In particular,
(1) As complexing agents in which nitrogen is a donor atom, (a) amines (for example, primary amines such as butylamine, ethylamine, propylamine, ethylenediamine, dibutylamine, diethylamine, dipropylamine, and piperidine Secondary amines such as imines such as pyrrolidine, tertiary amines such as tributylamine, triethylamine, and tripropylamine, and those having two or more primary to tertiary amines in one molecule of diethylenetriamine and triethylenetetramine ), (B) nitrogen-containing heterocyclic compounds (eg, imidazole, pyridine, bipyridine, etc.), (c) nitriles (eg, acetonitrile, benzonitrile, etc.) and cyanide compounds, (d) ammonia and ammonium compounds (eg, Ammonium chloride, ammonium sulfate, etc.), (e) oximes, etc. It is below.
(2) Complexing agents in which oxygen is a donor atom include (a) carboxylic acids (for example, oxycarboxylic acids such as citric acid, malic acid, tartaric acid and lactic acid, monocarboxylic acids such as acetic acid and formic acid, oxalic acid, Dicarboxylic acids such as malonic acid, aromatic carboxylic acids such as benzoic acid, etc.), (b) ketones (eg, monoketones such as acetone, diketones such as acetylacetone and benzoylacetone), (c) aldehydes, ( d) Alcohols (monohydric alcohols, glycols, glycerins, etc.), (e) quinones, (f) ethers, (g) phosphoric acid (normal phosphoric acid) and phosphoric acid compounds (eg hexametaphosphoric acid) , Pyrophosphoric acid, phosphorous acid, hypophosphorous acid, etc.), (h) sulfonic acid or sulfonic acid compounds.
(3) As a complexing agent in which sulfur is a donor atom, (a) aliphatic thiols (for example, methyl mercaptan, ethyl mercaptan, propyl mercaptan, isopropyl mercaptan, n-butyl mercaptan, allyl mercaptan, dimethyl mercaptan, etc.), (b) Alicyclic thiols (such as cyclohexylthiol), (c) Aromatic thiols (such as thiophenol), (d) Thioketones, (e) Thioethers, (f) Polythiols, (g) Thiocarbonic acid (H) sulfur-containing heterocyclic compounds (eg, dithiol, thiophene, thiopyran, etc.), (i) thiocyanates and isothiocyanates, (j) inorganic sulfur compounds (eg, sodium sulfide, Potassium sulfide, hydrogen sulfide, etc.).
(4) Complexing agents having two or more types of donor atoms include (a) amino acids (donor atoms are nitrogen and oxygen: neutral amino acids such as glycine and alanine, basic amino acids such as histidine and arginine) , Acidic amino acids such as aspartic acid and glutamic acid), (b) aminopolycarboxylic acids (the donor atom is nitrogen and oxygen: for example, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), ethylenediamine Diacetic acid (EDDA), ethylene glycol diethyl ether diamine tetraacetic acid (GEDA), etc.), (c) alkanolamines (donor atoms are nitrogen and oxygen, such as ethanolamine, diethanolamine, triethanolamine, etc.), (d) nitroso Compounds and nitrosyl compounds (donor atom is nitrogen and Oxygen), (e) mercaptocarboxylic acids (donor is sulfur and oxygen: for example, mercaptopropionic acid, mercaptoacetic acid, thiodipropionic acid, mercaptosuccinic acid, dimercaptosuccinic acid, thioacetic acid, thiodiglycolic acid, etc.), f) Thioglycols (donor is sulfur and oxygen: e.g. mercaptoethanol, thiodiethylene glycol, etc.), (g) thioic acids (donor is sulfur and oxygen), (h) thiocarbonates (donor atoms are sulfur and oxygen: e.g. , Monothiocarbonate, dithiocarbonate, thiocarbonate), (i) aminothiols (donor is sulfur and nitrogen: aminoethyl mercaptan, thiodiethylamine, etc.), (j) thioamides (donor atoms are sulfur and nitrogen: thioformamide, for example) Etc.), (k) thioureas (donor atoms are sulfur and nitrogen), (l) thiazoles (donor atoms are sulfur And nitrogen: for example thiazole, benzothiazole, etc.), (m) sulfur-containing amino acids (the donor sulfur, nitrogen and oxygen: cysteine, methionine, etc.) and the like.
(5) Examples of salts and derivatives of the above compounds include alkali metal salts such as trisodium citrate, sodium / potassium tartrate, sodium hypophosphite, disodium ethylenediaminetetraacetate, carboxylic acids, and phosphoric acids. And esters such as sulfonic acid.
Among such complexing agents, at least one kind can be used. The amount of the complexing agent used can be appropriately set, and it is preferable to set the complexing agent in the range of 0.01 to 200 parts by weight with respect to 1000 parts by weight of the metal compound because the effects of the present invention can be easily obtained.

  If the copper fine particles are obtained by the method described above, it is preferable to use a copper oxide as the copper compound because the reduction reaction is more easily controlled. “Copper oxide” is used to include copper hydrated oxides and copper hydroxides in addition to ordinary copper oxides. Copper oxides include cuprous oxide (or oxidized oxides). Monocopper), copper oxide (or cupric oxide), or the like can be used. There is no particular limitation on the method for producing the oxide, and for example, an electrolytically produced method, a chemical conversion method, a heat oxidation method, a thermal decomposition method, an indirect wet method, or the like can be used. Since it is considered that the particle diameter is related to the particle diameter of the copper fine particles to be generated, the copper oxide particle diameter can be appropriately set to obtain copper fine particles having a target particle diameter. .

  When copper fine particles are obtained using copper oxide, the amount of protective colloid used is preferably in the range of 1 to 100 parts by weight with respect to 100 parts by weight of copper oxide because the produced copper fine particles are easily dispersed and stabilized. The range of 2 to 50 parts by weight is more preferable. If the protective colloid and the complexing agent are used in combination, it is preferable to set the complexing agent in the range of 0.01 to 200 parts by weight with respect to 1000 parts by weight of the copper oxide because the effect of the present invention can be easily obtained. The range of 0.1 to 200 parts by weight is more preferable, and the range of 0.5 to 150 parts by weight is even more preferable. The amount of the reducing agent used can be appropriately set as long as it is an amount capable of producing copper fine particles from the copper oxide, and is in the range of 0.2 to 5 mol with respect to 1 mol of copper contained in the copper oxide. Is preferred. If the reducing agent is less than the above range, the reaction is difficult to proceed, and copper fine particles are not sufficiently formed. Furthermore, the usage-amount of a preferable reducing agent is the range of 0.3-2 mol.

  Next, the protective colloid remover is added to the dispersion containing the protective colloid and the metal fine particles produced as described above to aggregate the metal fine particles, and then fractionated. “Protective colloid remover” is a compound that decomposes or dissolves the protective colloid to suppress the action of the protective colloid. If the protective colloid cannot be completely removed from the dispersion, it can be removed. The effects of the invention can be obtained. The kind of protective colloid remover is appropriately selected according to the protective colloid used. Specifically, for protein-based protective colloids, proteolysis such as serine protease (eg, trypsin, chymotrypsin), thiol protease (eg, papain), acidic protease (eg, pepsin), metalloprotease, etc. As the enzyme, starch-degrading enzymes such as amylase and maltase can be used for starch, and cellulose-degrading enzymes such as cellulase and cellobiase can be used for cellulose. For protective colloids such as vinyl, acrylic acid, and polyethylene glycol, organic solvents such as formamide, glycerin, and glycol, acids, alkalis, and the like can be used. The addition amount of the protective colloid remover may be an amount that can remove the protective colloid to such an extent that the fine metal particles can be aggregated and separated, and varies depending on the type of the protective colloid removal agent. The range of 0.001-1000 weight part is preferable, 0.01-200 weight part is more preferable, 0.01-100 weight part is still more preferable. The temperature of the dispersion at the time of adding the protective colloid remover can be set as appropriate, and may be in a state where the reduction reaction temperature is maintained, or as long as it is in the range of 10 ° C. to the boiling point of the medium used, the protective colloid. Is preferable because it is easy to proceed, and more preferably in the range of 40 to 95 ° C. After the protective colloid removing agent is added, the protective colloid can be decomposed by appropriately maintaining the state, and for example, about 10 minutes to 10 hours is appropriate. After the protective colloid is removed and the metal fine particles are aggregated, they are separated by a usual method. The separation means is not particularly limited, and may be gravity filtration, pressure filtration, vacuum filtration, suction filtration, centrifugal filtration, natural sedimentation, etc., but industrially pressure filtration, vacuum filtration, and suction filtration are preferable. It is preferable to use a filter such as a filter press or a roll press because it has a high dewatering capability and can be processed in large quantities.

  It is preferable to add a flocculant after adding the protective colloid remover because the yield is further improved. As the flocculant, known ones can be used. Specifically, anionic flocculants (for example, polyacrylamide partial hydrolysis products, acrylamide / sodium acrylate copolymers, sodium alginate, etc.), cationic ones Examples include flocculants (for example, polyacrylamide, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, polyamidine, chitosan, etc.), amphoteric flocculants (for example, acrylamide / dimethylaminoethyl acrylate / acrylic acid copolymer). The amount of the flocculant added can be appropriately set according to need, and is preferably in the range of 0.5 to 100 parts by weight, more preferably in the range of 1 to 50 parts by weight with respect to 1000 parts by weight of the metal fine particles.

  Alternatively, even if the protective colloid remover is added instead of using a flocculant, and the pH of the dispersion is adjusted to a range of 6 or less using an acid, the same yield improving effect can be obtained. When the pH is lower than 3, depending on the metal species constituting the metal fine particles, for example, copper or the like corrodes or dissolves. Therefore, the range of 3 to 6 is a preferable pH range, and the range of 4 to 6 is an acid. This is more preferable because the amount of use can be reduced.

  After solid-liquid separation of the metal fine particles, the obtained solid matter of the metal fine particles can be used, for example, by dispersing it in an organic solvent medium such as aqueous or alcohol, preferably in an aqueous medium. Alternatively, the solid metal fine particles can be dried by a usual method. If it is easy to oxidize like a copper fine particle, in order to suppress oxidation, it is preferable to perform drying in the atmosphere of inert gas, such as nitrogen and argon. After drying, you may grind | pulverize as needed.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Examples 1-3
24 g of industrial copper oxide (N-120: manufactured by NC Tech Co., Ltd.) and 9.6 g of gelatin as a protective colloid were added to 300 ml of pure water, mixed, and the pH of the mixture was adjusted to 11 using 15% aqueous ammonia. After the adjustment, the temperature was raised from room temperature to 90 ° C. over 20 minutes. After the temperature rise, with stirring, a solution of a complexing agent (type and amount of complexing agent shown in Table 1) and 28 g of 80% hydrazine monohydrate were mixed in 150 ml of pure water. The solution was added and reacted with copper oxide for 1 hour to produce copper fine particles. After the formation of the copper fine particles, 5 ml of serine protease (Proteenase K: manufactured by Washington Biochemical Co.) was added as a protective colloid remover and held for 1 hour. The amount of serine protease added was 100 parts by weight with respect to 1000 parts by weight of gelatin.

Examples 4-6
In Examples 1 to 3, a proteolytic enzyme was added and held for 1 hour, and a polyamidine polymer flocculant (SC-700: manufactured by Hymo) was further added as a flocculant. The addition amount of the polyamidine polymer flocculant was 30 parts by weight with respect to 1000 parts by weight of the metal fine particles.

Examples 7-9
In Examples 1 to 3, after adding a proteolytic enzyme and keeping it for 1 hour, the pH was adjusted to 5 using sulfuric acid.

Comparative Examples 1-3
In Examples 1 to 3, the same operation as in Examples 1 to 3 was performed except that no proteolytic enzyme was added.

Evaluation 1: Evaluation of Yield and Filtration / Washing Time Examples 1 to 9 and Comparative Examples 1 to 3 were subjected to solid-liquid separation by suction filtration using a Buchner funnel, washed with pure water during filtration, and filtrated. The time required for the specific conductivity to reach 100 μS / cm or less was measured. Further, the weight of the collected copper fine particles was measured, and the yield ((recovered amount of copper fine particles / prepared amount of metal copper calculated from copper oxide) × 100) was calculated. The results are shown in Table 1. It can be seen that the yield and filtration cleaning properties are improved by the use of the protective colloid remover and the combined use of the protective colloid remover and the flocculant or pH adjustment.

Evaluation 2: Measurement of average particle diameter of primary particles and secondary particles In Examples 1 to 9 and Comparative Examples 1 to 3, after solid-liquid separation, drying was performed at a temperature of 60 ° C. for 10 hours in an atmosphere of nitrogen gas. Copper fine particles were obtained. Each is designated as Samples A-L. The average particle diameter (D) of the primary particles of samples A to L is measured by electron microscopy, and the average particle diameter (d) of the secondary particles is measured using a dynamic light scattering particle size distribution analyzer (Microtrack UPA type: D / D was calculated using Nikkiso Co., Ltd. For measurement of secondary particles, an aqueous slurry was used in which the sample was sufficiently dispersed in water using an ultrasonic disperser and the concentration was adjusted so that the signal intensity of the laser was 0.6 to 0.8. The results are shown in Table 2. The closer the d / D is to 1, the better the dispersibility and the lower the degree of aggregation. By the production method of the present invention, copper fine particles containing almost no aggregated particles can be obtained even if the protective colloid is removed. You can see that

Metal fine particles obtained by the present invention, especially copper fine particles, are useful as electrode materials for electronic devices, etc. When used as fluid compositions such as metal pastes, paints, and inks, internal electrodes of multilayer ceramic capacitors, printed wiring It is useful for circuit boards and other electrodes.

Claims (8)

A method for producing fine metal particles, comprising adding a protective colloid remover to a dispersion containing protective colloid and fine metal particles to aggregate the fine metal particles, followed by fractionation. The method for producing fine metal particles according to claim 1, wherein a protein-based protective agent is used as the protective colloid, and a proteolytic enzyme is used as the protective colloid removing agent. The method for producing fine metal particles according to claim 2, wherein a proteolytic enzyme in the range of 0.001 to 1000 parts by weight is used with respect to 1000 parts by weight of the protein-based protective colloid. The method for producing metal fine particles according to claim 1, wherein after the protective colloid removing agent is added, a flocculant is further added to agglomerate the metal fine particles. 2. The method for producing metal fine particles according to claim 1, wherein after adding the protective colloid remover, the pH of the dispersion is further adjusted to 6 or less to aggregate the metal fine particles. 2. The method for producing metal fine particles according to claim 1, wherein a dispersion containing the protective colloid and the metal fine particles is produced by reacting the metal compound and the reducing agent in a medium in the presence of the protective colloid. 7. The method for producing fine metal particles according to claim 6, wherein the reaction between the metal compound and the reducing agent is carried out in the presence of the protective colloid and the complexing agent. The method for producing fine metal particles according to any one of claims 6 and 7, wherein the metal compound is copper oxide, and the obtained fine metal particles are copper fine particles.