KR101522738B1 - Copper Powder For Conductive Paste and Method For Preparation Thereof - Google Patents

Abstract

DISCLOSURE OF THE INVENTION The present invention is a copper fine particle having dispersed fine particles with sharp particle size distribution, no assembly, and a shape close to a true spherical shape, and is capable of thinning the electrode while avoiding adverse effects on electrical characteristics A copper powder for a conductive paste, and a method for stably producing such a copper powder for a conductive paste.

A method for producing a copper powder which comprises adding a reducing agent to an aqueous solution containing bivalent copper ions to reduce and precipitate copper particles, comprising the steps of: preparing an aqueous solution containing copper ions, which is an aqueous solution of copper sulfate, copper nitrate or a mixture thereof, (A nucleating agent) containing a water-soluble polymer such as polyethyleneimine or methyl cellulose as an aggregation inhibitor, Ag particles having an average particle diameter of 10 to 100 nm and Pd At least one of the particles is present.

Conductive paste, copper powder, copper fine particles, divalent copper ion, reducing agent,

Description

Technical Field [0001] The present invention relates to a copper powder for conductive paste,

The present invention relates to a copper powder for conductive paste and a method for producing the same, and more particularly, to an internal electrode of a multilayer ceramic electronic component such as a multilayer ceramic capacitor or a multilayer ceramic inductor, or an external electrode such as a small-sized multilayer ceramic capacitor or a multilayer ceramic inductor And a method for producing the copper powder.

In a general method for producing a multilayer ceramic capacitor, first, a plurality of dielectric ceramic green sheets such as barium titanate ceramic are prepared, conductive pastes for internal electrodes are printed on each sheet in a predetermined pattern, Thereby producing a laminate in which a dielectric ceramic green sheet and a conductive paste layer are alternately laminated. This laminate is cut into a plurality of chips having a predetermined shape, and is then simultaneously fired at a high temperature to produce a laminated ceramic capacitor body. Next, an external electrode is formed by applying and drying an electroconductive paste for an external electrode mainly composed of a conductive powder, a glass powder, and an organic vehicle on an end face of the internal electrode of the element body, which is exposed, and then firing at a high temperature. Thereafter, a plating layer such as nickel or tin is formed on the external electrode by electroplating or the like as necessary.

Conventionally, palladium, silver-palladium, platinum, and the like have been used as metal materials for use in conductive pastes for forming internal electrodes such as multilayer ceramic capacitors. However, they are expensive and expensive. For this reason, the use of non-metals such as nickel or copper has been the mainstream in recent years. At present, nickel fine particles having an average particle diameter of 0.1 to 0.5 탆, which are different mainly depending on the size and the capacity of the multilayer ceramic capacitor, ) Are used. Since copper has a higher conductivity and a lower melting point than nickel, it is possible to improve the characteristics of the multilayer ceramic capacitor and to contribute to energy saving during production such as lowering the temperature at the time of firing. Therefore, Is expected as one of.

On the other hand, in recent years, in order to increase the capacity and miniaturization of multilayer ceramic capacitors and the like, a thinner internal electrode has been required. In addition, multilayer ceramic capacitors and the like having characteristics such that internal inductors are small and high-frequency characteristics can be used up to GHz orders by the expansion of applications such as multilayer ceramic capacitors are demanded.

From this background, it is desired that copper microparticles having mono-dispersed fine particles, sharp particle size distribution, no assembly, and a shape close to a true spherical shape are required as internal electrode metal materials such as multilayer ceramic capacitors .

At present, copper microparticles are mainly used for conductive pastes for external electrodes such as multilayer ceramic capacitors. The size of copper microparticles varies from 0.5 to 10 mu m depending on the size of the multilayer ceramic capacitor and the like, and spherical, flaky, Copper microparticles having various shapes are used. In addition, copper particles having the above-described size and shape are mixed and used in general conductive paste for external electrodes.

As a method for producing such copper microparticles, there is a method of reducing a copper sulfate solution with L-ascorbic acid or L-ascorbic acid salt (see, for example, Patent Document 1), adding a copper sulfate solution to D-erythorbic acid or D- (See, for example, Patent Document 3), a method of reducing the copper sulfate solution with a borohydride compound (see, for example, Patent Document 3), a method of reducing the copper sulfate solution with an aromatic compound containing a hydroxyl A reduction initiator is added to a mixed aqueous solution containing copper ions, a reducing agent and a complexing agent, followed by a reduction reaction, and then a copper ion, a reducing agent, and a pH adjusting agent are added to the resulting mixture to form a copper fine powder. (See, for example, Patent Document 5), an alkali hydroxide is mixed with an aqueous solution of a copper salt having a bivalent copper ion to produce cupric oxide, and a reducing sugar (See, for example, Patent Document 6), reducing the cuprous oxide with cuprous oxide and adding a hydrazine-based reducing agent to the cupric oxide (see, for example, Patent Document 6) , And a method of producing copper microparticles by reacting copper oxide with a reducing agent such as hydrazine (see, for example, Patent Document 7).

[Patent Document 1] Japanese Unexamined Patent Publication (Kokai) No. 63-186803 (page 1)

[Patent Document 2] Japanese Unexamined Patent Publication (Kokai) No. 63-186805 (page 1)

[Patent Document 3] Japanese Unexamined Patent Publication (Kokai) No. 63-186811 (page 1)

[Patent Document 4] JP-A-1-225705 (page 1)

[Patent Document 5] Japanese Unexamined Patent Publication (Kokai) No. 63-274706 (page 2)

[Patent Document 6] Japanese Patent Application Laid-Open No. 2003-342621 (paragraph No. 0012)

[Patent Document 7] Japanese Patent Application Laid-Open No. 2004-256857 (paragraph No. 0006-0013)

However, since the average particle diameter of copper microparticles obtained by the method of Patent Document 1 is 1.0 to 1.8 占 퐉, it is not sufficient for use as copper microparticles for internal electrodes. In addition, since an aqueous solution of copper ions whose pH is adjusted and a solution of a reducing agent whose pH is adjusted are used to reduce copper ions from copper ions to copper particles via copper oxide, the control of the particle diameter is unstable, Occurs, the shape is not fixed, and the particle size distribution is sometimes widened.

Further, since the average particle diameter of the copper microparticles obtained by the method of Patent Document 2 is 0.8 to 2.0 占 퐉, it is not enough to be used as the copper microparticles for internal electrodes. In addition, since an aqueous solution of a pH-adjusted copper ion and an aqueous solution of a pH-adjusted reducing agent are used to reduce copper ions from copper ions to copper particles via copper oxide, control of the particle diameter is unstable and congealing , The shape is not fixed, and the particle size distribution is sometimes widened.

The average particle diameter of the copper fine particles obtained by the method of Patent Document 3 is 0.3 to 0.7 占 퐉 and copper fine particles smaller than the copper fine particles obtained by the methods of Patent Documents 1 and 2 can be obtained. Lt; / RTI > Further, since a borohydride compound is used as a reducing agent, when the pH is adjusted at the time of pH adjustment of the reducing agent, self-decomposition occurs, which may deteriorate workability and stability. On the other hand, when the pH is increased, the borohydride compound is stabilized. In this case, however, since the reduction reaction of the copper ion is carried out via the cuprous oxide, the control of the particle diameter is unstable, the coagulation (bonding of the particles) occurs, And the particle size distribution may be widened.

Further, since the average particle diameter of the copper microparticles obtained by the method of Patent Document 4 is 0.7 to 1.5 占 퐉, it is not enough to be used as the copper microparticles for internal electrodes. Further, hydroquinone is used as a reducing agent, and it is difficult to make the copper particles more fine particles even by adjusting the reaction pH, the reaction temperature, and the like. In addition, since an aqueous solution of a pH-adjusted copper ion and an aqueous solution of a pH-adjusted reducing agent are used to reduce copper ions from copper ions to copper particles via copper oxide, control of the particle diameter is unstable and congealing , The shape is not fixed, and the particle size distribution is sometimes widened.

The average particle diameter of the copper microparticles obtained by the method of Patent Document 5 is 0.16 to 0.61 占 퐉 and it is considered that the copper microparticles can be used as the internal electrode copper powder as judged from the average particle diameter. However, in this method, since the reduction reaction is performed in a high pH range (pH 12 to 13.5), the copper ions are reduced to copper particles through copper hydroxide, copper oxide, and copper oxide to control the particle diameter, Bonding between the particles) is generated, the shape is not fixed, and the particle size distribution is sometimes widened.

In addition, since the average particle diameter of the copper microparticles obtained by the method of Patent Document 6 is 0.5 to 4.0 占 퐉, it is not sufficient for use as the copper microparticles for internal electrodes. The reaction of this method is a reaction in which cupric oxide produced from divalent copper ions is reduced with cuprous oxide and then further reduced to copper particles, and a reduction reaction from cupric oxide to copper particles Is a reaction called dissolution precipitation type. When this method is used for the production of copper particles having a somewhat large particle diameter, stable control can be performed and the particle size distribution can be sharpened. However, it is difficult to obtain fine copper fine particles used as copper fine particles for internal electrodes And no coagulated particles or coagulated particles), it is difficult to obtain separated fine particles.

The average particle diameter of the copper microparticles obtained by the method of Patent Document 7 is presumably used as the internal electrode copper powder when the average particle diameter is judged to be 0.25 to 0.5 탆 in primary particle diameter and 0.3 to 0.6 탆 in secondary particle diameter . Further, the tap density is 3.2 to 3.4 g / cm < 3 >, the fine particles have a high tap density and can be said to have excellent dispersibility. However, since the reaction of the method of Patent Document 7 is a reaction in the presence of a sulfur compound, there is a possibility that a sulfur compound is contained in the inside or the surface of the copper microparticle. In general, sulfur is a substance that adversely affects the reliability of an electronic part, and therefore, it is not preferable to be included in the copper powder for conductive paste.

Accordingly, in view of such conventional problems, it is an object of the present invention to provide a copper microparticle which is monodispersed fine particles, sharp particle size distribution, does not include an assembly, has a shape such as a true spherical shape, And it is an object of the present invention to provide a method for stably producing a copper powder for a conductive paste and a copper powder for an electroconductive paste which can make an electrode thinner while avoiding an adverse effect of the copper powder.

As a result of intensive studies to solve the above problems, the present inventors have found that, in a method of producing copper powder for reducing copper particles by adding a reducing agent to an aqueous solution containing bivalent copper ions, an aqueous solution containing bivalent copper ions and a reducing agent A copper fine particle having mono-dispersed fine particles, sharp particle size distribution, no assembly, and a shape close to a true spherical shape by the presence of a reaction promoter containing at least one of It is possible to stably produce a copper powder for electroconductive paste enabling the electrode to be thinned while avoiding adverse effects on the characteristics, and thus the present invention has been accomplished.

That is, the method for producing a copper powder for electroconductive paste according to the present invention is a method for producing copper powder in which a reducing agent is added to an aqueous solution containing bivalent copper ions to reduce and precipitate copper particles, And a reducing agent, wherein the reaction accelerator comprises an anti-aggregation agent. In this method for producing a copper powder for conductive pastes, it is preferable that the reaction promoter contains particles of a metal precious than copper, more preferably at least one of Ag particles and Pd particles having an average particle diameter of 10 to 100 nm. Further, the anti-aggregation agent is preferably a water-soluble polymer, and more preferably polyethyleneimine or methylcellulose. It is also preferred that the reducing agent is L-ascorbic acid, D-erythorbic acid or a mixture thereof. It is also preferable that the aqueous solution containing divalent copper ions is an aqueous solution of copper sulfate, copper nitrate or a mixture thereof. Further, a compound containing at least one selected from the group consisting of Al, Ba, Ti and Si may be deposited on the surface of the copper particles subjected to reduction precipitation, or the surface of the copper particles subjected to reduction precipitation may be coated with Al, Ba, Ti, Si, and the like.

The copper powder for electroconductive paste according to the present invention preferably has a 50% particle diameter (D ₅₀ ) of 0.1 to 0.5 μm and a maximum particle diameter (D _max ) of 1.5 μm or less as measured by a laser diffraction particle size distribution measuring apparatus , 10 to 10000 ppm of Ag and Pd. In this copper paste for electroconductive paste, the ratio of the 50% particle size (aggregated particle size) of the aggregated particles observed by the laser diffraction particle size distribution measuring device to the average particle size (single particle size) of copper single particles observed by SEM Tea particle diameter / primary particle diameter) is preferably 2.0 or less. In addition, it is preferable that the number ratio of copper particles which are a single substantially spherical shape among the copper particles observed by SEM is 90% or more. The surface of the copper powder for conductive paste may be coated with a compound containing at least one element selected from the group consisting of Al, Ba, Ti and Si, Si, and the like.

Further, the conductive paste according to the present invention is characterized in that it contains copper powder for the conductive paste as the conductive powder.

According to the present invention, there is provided a copper microparticle having mono-dispersed fine particles, sharp particle size distribution, no assembly, and a shape close to a true spherical shape, It is possible to stably produce a copper powder for electroconductive paste enabling thinning.

In the method for producing a copper powder for producing a copper powder for a conductive paste according to the present invention, a reducing agent is added to an aqueous solution containing bivalent copper ions to reduce and precipitate the copper particles, At least one of the aqueous solution and the reducing agent contains a reaction promoter (nucleating agent) containing an anti-aggregation agent.

An embodiment of the method for producing copper powder for conductive paste according to the present invention is a method for directly reducing an aqueous solution containing bivalent copper ions to copper particles without passing through copper hydroxide, copper oxide, copper oxide or a mixture thereof to be. By taking such a reaction step, the reaction promoter that exists to control the particle diameter and the particle size distribution effectively works. Further, since the reduction reaction of the dissolved precipitation type via the intermediates of copper hydroxide, copper oxide or copper oxide does not take place, highly dispersed copper fine particles in which aggregation, coagulation and bonding of the particles are suppressed can be obtained. That is, divalent copper ions are reduced on the surface of the reaction promoter to become copper fine particles.

In a conventional general method for producing copper powder by a wet reaction, copper hydroxide was neutralized by neutralizing bivalent copper ions, and the dehydration reaction was promoted by adjusting the temperature to produce copper oxide. There is also known a method in which copper oxide is first reduced to copper oxide with a weak reducing agent such as saccharide, and the resulting copper oxide is subjected to secondary reduction to a copper particle with a strong reducing agent such as hydrazine. In the second reduction reaction (reduction from copper oxide to copper) of this method, copper ions are precipitated from a solid of copper oxide, and then a part thereof is reduced to form fine nuclei of copper, . In this case, two reactions are performed: a reaction in which copper ions are dissolved from copper oxide and a reaction in which dissolved copper ions are reduced to copper particles. For this reason, it is difficult to strictly separate the step of producing fine nuclei of copper and the step of growing the nuclei. As a result, secondary nuclei are generated, thereby widening the particle size distribution and making it difficult to control the grain size. Further, since the supply amount of copper ions in the initial stage of reduction is small (most of the copper is present in the copper oxide rather than in the reaction solution), it is difficult to generate a large amount of nuclei, and it is difficult to obtain fine particles. Further, when the amount of the reducing agent is increased or the reaction temperature is increased, the amount of the copper ions dissolved can be increased in order to generate a large amount of nuclei. At the same time, the reduction reaction is promoted. As a result, There is a problem that a large number of release particles (particles in which the particles are condensed or joined to each other and distorted) are generated. In addition, since the reaction is abrupt, liquid spray or boiling occurs, which is not preferable from the viewpoints of safety and reproducibility of the reaction.

Therefore, in the embodiment of the method for producing a copper powder for a conductive paste according to the present invention, in the reaction system in which a reaction promoter is present, a copper oxide powder is obtained by dissolving copper hydroxide, copper oxide, copper oxide, , And copper particles are also directly reduced.

The reason why divalent copper ions are used is that, in the case of monovalent copper ions, there is no raw material that can be easily handled in a water-soluble reaction system. For example, in the case of copper (I) cyanide (via copper hydroxide or copper oxide during the reduction reaction to copper in an alkali solution), toxic hydrogen cyanide is generated in the acidic solution. Equipment is required, and restrictions on handling are increased. It is preferable to use copper sulfate (including hydrate), copper nitrate (including hydrate), or a mixture thereof as a raw material to be a source of a divalent copper ion from the viewpoints of cost, ease of acquisition, and safety of handling.

As the reducing agent for reducing bivalent copper ions to copper fine particles, it is preferable to use L-ascorbic acid, D-erythorbic acid or a mixture thereof. It is preferable that the reducing agent reduces divalent copper ions to copper on the acid side. The reason why the acidic side is preferable is that, depending on the pH-potential of copper, when the reduction reaction is carried out on the neutral to alkaline side, copper hydroxide may be generated by neutralization reaction of bivalent copper ions, There is a risk of copper being generated. Further, the pH can not be strictly determined because the reducing potential at each pH of the divalent copper ion is changed by the complexing agent or chelating agent to be used. However, the pH can not be strictly determined, but the divalent copper ion It is preferable to use a reducing agent that reduces copper to copper. In addition, the lower the reaction pH, the less preferable. If the reaction pH is low, the solubility of the bivalent copper ions may be high and the reduction may be inhibited, and the re-dissolution of the produced copper particles may occur, so that the reaction pH is preferably 1 to 4.

Examples of such reducing agents include L-ascorbic acid, D-erythorbic acid, hypophosphoric acid, sodium hypophosphite, boron hydride compounds and hydrazines. However, the present inventors have conducted intensive studies, and as a result, it has been found that hydrazines can reduce bivalent copper ions even on the acidic side, but have a weak reducing power on the acidic side and fail to obtain copper particles with desired grain diameters. In addition, in the case of hypophosphorous acid or hypophosphorous acid, the release particles (particles in which the particles are condensed or bound to each other and distorted) are generated, and copper particles having a desired shape and particle diameter can not be obtained. Further, the borohydride compound is subject to self-decomposition (water reduction) on the acidic side, which makes handling difficult. On the other hand, since L-ascorbic acid and D-erythorbic acid can reduce divalent copper ions to copper on the acid side and are easy to handle and obtain desired copper fine particles, L-ascorbic acid and D- Or a mixture thereof.

As the reaction accelerator, it is preferable to use at least one of Ag particles and Pd particles having an average particle size of 10 to 100 nm observed from TEM. Au, Pt, a platinum group element or the like can be used in addition to Ag or Pd. However, Ag particles or Pd particles are preferable because the reduction rate becomes faster (precious) in order to obtain a fine reaction accelerator (nucleating agent) (average particle diameter of 10 to 100 nm) Metal), and as a result, it is sufficient for a small amount of use, so that it is not costly, and is generally a substance which does not concern human body and environment (such as Hg).

The particle diameter of the obtained copper fine particles is determined depending on how many Ag particles or Pd particles used as a reaction promoter exist for the copper ions to be injected. When the particle size of the reaction promoter is larger than 100 nm, the ratio of Ag or Pd to be used increases, resulting in cost disadvantage. When the target copper microparticles have a particle diameter of 0.1 占 퐉, it is preferable to use at least one of Ag particles and Pd particles smaller than the Ag particles as the reaction accelerator. (Because the amount of bivalent copper ions to be injected and the amount of the reducing agent are limited when more reaction promoter is added), the Ag particles as a reaction promoter having a size of 1/50 to 1/5 of the intended copper particle size and It is preferable to use at least one of Pd particles. Therefore, as the reaction accelerator, it is preferable to use at least one of Ag particles and Pd particles having an average particle size of 10 to 100 nm observed from TEM.

The anti-coagulation agent contained in the reaction promoter is not an agent for preventing the coagulation of copper particles but an anti-coagulation agent for preventing agglomeration of Ag particles or Pd particles generated as a reaction promoter and prevents the copper from being reduced and precipitated on its surface And a water-soluble polymer can be used. The amount of the water-soluble polymer is preferably 1 to 10 times as much as the weight of the Ag particles or the Pd particles, though it varies depending on the particle diameter to be produced.

Examples of the water-soluble polymer include cellulose derivatives, gelatin, soluble starch, dextrin, gum arabic, chitin, chitosan, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, polyethyleneimine, polyacrylamide, acrylic acid Sodium hydroxide (partial) neutralized product of an acid anhydride copolymer, water-soluble polyurethane, and the like can be used. Examples of the cellulose derivative include methylcellulose, ethylcellulose, hydroxyethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, hydroxypropylcellulose, and saponified products thereof, and cationized cellulose. Examples of the acrylic acid (salt) -containing polymer include sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, sodium hydroxide partial neutralization product of polyacrylic acid, and sodium acrylate-acrylic acid ester copolymer. Examples of the water-soluble polyurethane include reaction products of polyethylene glycol and polyisocyanate. Of these water-soluble polymers, polyethyleneimine or methylcellulose is preferably used.

It is preferable that the reaction promoter containing an anti-aggregation agent is present in at least one of an aqueous solution containing a divalent copper ion and a reducing agent. The reaction promoter may be added to at least one of an aqueous solution containing a divalent copper ion and a reducing agent immediately before the reduction of the divalent copper ion. Alternatively, an aqueous solution containing a reaction promoter may be first prepared, An aqueous solution containing copper ions or a solution containing a reducing agent is prepared and a divalent copper ion and another one of the reducing agents are added to the solution in which the reaction promoter and one of the divalent copper ions and the reducing agent are present, . In this reduction reaction, since the number of Ag particles or Pd particles as reaction promoters is a main factor for determining the particle size of the copper particles, there is a degree of freedom in the reaction, and the reproducibility of the reaction is excellent.

The Pd raw material or Ag raw material used in the production of the reaction promoter is preferably water-soluble, easily available, and easy to handle, and examples thereof include Pd nitrate, Ag Ag, and Ag Ag.

If the ion concentration of Ag or Pd in the aqueous solution of the reaction promoter is too high, it becomes difficult to obtain Ag particles or Pd particles of 10 to 100 nm by reduction reaction, and if it is too low (the amount of bivalent copper ions to be injected or the purpose , The amount of the reaction promoter to be added is increased, so that it is preferably 0.00001 to 0.01 mol / L.

The reducing agent used for reducing the Ag ion or the Pd ion solution is preferably as strong as possible as possible, and examples thereof include hydrazines and boron hydride compounds. The amount of the reducing agent added needs to be stoichiometrically larger than the amount capable of reducing Ag ions or Pd ions. If the amount of the reducing agent to be added is too small, a sufficient reducing power can not be obtained. If the amount of Ag or Pd to be added is too large, the reducing power of the reducing agent remaining in the subsequent step The influence of the pH of the solution and the like can not be ignored. Therefore, although it can not be said uniformly depending on the state of the concentration of the Ag ion or the Pd ion and the reducing condition (the conditions of injection of copper, etc.), the amount of the reducing agent to be added is preferably 1 to 40 equivalents relative to Ag ion or Pd ion Do. The reaction temperature may be about 20 캜 to 80 캜.

As the method of adding the reducing agent, it is preferable to add the solution to be added at one time in order to realize a uniform reaction in the solution. The specific addition time may not be uniformly determined depending on the stirring method (diffusion rate of the solution) and the reaction scale of the reaction solution, but is preferably as fast as possible, for example, within 1 minute. It is also preferable to stir the reaction solution at the time of reduction.

In order to prevent agglomeration of Ag particles or Pd particles obtained by reduction, it is preferable to add polyethyleneimine or methylcellulose as an anti-aggregation agent. The anti-aggregation agent may be added before or after the reduction of Ag ion or Pd ion.

The amount of the reducing agent added when divalent copper ions are reduced to copper needs to be stoichiometrically more than the amount capable of reducing copper ions to bivalent copper ions. When the amount of the reducing agent is excessively large, it is disadvantageous in terms of cost. Therefore, it is preferably 1 to 10 moles with respect to the raw material of the divalent copper ion.

As a stirring method in this reduction reaction, a method in which a reaction liquid is homogeneously mixed is preferable, and for example, a method of stirring by a magnetic stirrer, or a method in which a stirring rod equipped with a blade is placed in a reaction solution and rotated by an external motor And a method of stirring. The reaction temperature at the time of reduction may be about 20 to 100 ° C, and it is preferably 40 to 80 ° C from the controllability of the reaction.

The ratio of the Ag particles and the Pd particles as the reaction promoter can be appropriately determined from the particle diameter (10 to 100 nm) of the generated Ag particles or Pd particles, the amount of the copper ions to be injected and the intended particle size (0.1 to 0.5 탆).

In the reduction reaction with copper, it is preferable to add the added solution at one time in order to realize a uniform reaction in the solution. The specific addition time may not be uniformly determined depending on the stirring method (diffusion rate of the solution) and the reaction scale of the reaction solution, but is preferably within 1 minute, for example. In this reduction reaction, a reaction occurs immediately when an aqueous solution containing a bivalent copper ion is mixed with a reducing agent, so that it is not necessary to react for a long time, specifically, it may be within 10 minutes.

The copper powder-containing slurry thus obtained is filtered and washed with water to obtain a massive copper cake. As a method of filtration and rinsing, a method of washing with water in a state in which the powder is fixed by a filter press or the like, or a method in which the slurry is decanted, the supernatant is removed, pure water is added and stirred, A method of repetitively performing an operation of repeating the removal of the copper powder after filtration and a method of repeatedly filtering the copper powder after the filtration after the filtration is repeated may be used. However, it is also possible to use an impurity locally remaining in the copper powder It is preferable to use a method capable of removing as much as possible. Thus, the effect of preventing coagulation during the drying treatment and the degree of activity of the functional groups present on the surface of the copper powder are increased, whereby fatty acids and surface treatment agents It is believed that there is an effect that the adhesion rate to the copper powder is increased. Thereafter, a substance having an anti-corrosive effect such as a fatty acid or benzotriazole (BTA) may be dissolved in a lower alcohol or the like, and then coated with the substance by passing or repulping the washed copper cake, or the copper cake may be rapidly dried , The moisture in the copper cake may be replaced by a lower alcohol. Further, copper microparticles can be obtained by drying (drying or vacuum drying in an atmosphere of nitrogen) in an atmosphere in which the obtained copper cake is not oxidized. Further, it is also possible to carry out treatments such as dry crushing treatment, sieving, wind power classification and the like as necessary.

In addition, a substance that forms a complex or a chelate with the bivalent copper ion and a dispersant that suppresses the aggregation of the copper fine particles may be added to an aqueous solution containing bivalent copper ions (however, by adding them, It is necessary to prevent the pH region from passing through copper or copper oxide). For example, a substance having a carboxyl group such as citric acid or acetic acid, a substance having a carboxyl group with an amino group such as glycine or alanine, a chelating agent such as polyethyleneimine, or a dispersing agent such as gum arabic or gelatin may be added.

When the copper powder thus produced is used for the internal electrode of the multilayer ceramic capacitor, in order to change the thermal shrinkage behavior (sintering behavior) of the copper powder when sintered together with the dielectric green sheet, (For example, barium titanate, titania, alumina, silica, and the like) may be deposited on the surface of the copper powder (or the surface of the copper powder may be coated with the compound). According to this process, when the copper powder is used for the internal electrode of the multilayer ceramic capacitor, the sintering behavior of the dielectric material and the copper powder can be matched with each other. As a result, defects due to the occurrence of delamination can do.

It is preferable that the method of depositing on the surface of the copper powder (or the method of covering the surface of the copper powder) is a method that does not aggregate the produced copper particles. For example, a method in which a metal alkoxide is added to a solution in which the copper powder is dispersed in alcohol (which is a material containing a dielectric material), followed by hydrolysis followed by filtration and drying, a method in which copper powder ) And a metal alkoxide solution, a method of mixing the copper powder with a substance used as a dielectric (having a particle diameter equal to or less than the particle diameter of the copper powder) and dry powder or wet powder. Further, the amount of coating or the amount of coating may be an amount that does not deteriorate the conductivity of the internal electrode and is effective for the shrinkage behavior, and is preferably about 0.1 to 10 mass%, for example, with respect to the copper particles.

The copper powder for electroconductive paste produced according to the embodiment of the method for producing a copper powder for conductive paste according to the present invention described above is a monodispersed fine particle and has sharp particle size distribution and does not include an assembly, And is a copper powder suitable for a conductive paste of an internal electrode of a multilayer ceramic capacitor or as a copper powder for a conductive paste of an external electrode and a conductive paste is produced by a known method using the copper powder for the conductive paste . The conductive paste thus produced can be used as a conductive paste for an internal electrode or an external electrode of a multilayer ceramic capacitor, since the electrode can be made thinner while avoiding adverse effects on electrical properties.

The copper powder for conductive paste prepared according to the embodiment of the method for producing a copper powder for a conductive paste according to the present invention has a 50% particle diameter (D ₅₀ ) measured by a laser diffraction type particle size distribution measuring apparatus of 0.1 to 0.5 Mu m, a maximum particle diameter ( _Dmax ) of detection of 1.5 mu m or less, and 10 to 10,000 ppm of Ag and Pd. When the 50% particle diameter (D ₅₀ ) measured by a laser diffraction particle size distribution measuring apparatus is 0.1 to 0.5 탆, the thickness of the internal electrode required for high capacity and miniaturization of multilayer ceramic capacitors and the like Or less) can be realized. When the maximum particle diameter ( _Dmax ) of the detection is not more than 1.5 占 퐉, there is a fear that the internal electrode and the dielectric ceramic green sheet are laminated, breakage of the dielectric layer due to the presence of the internal electrode in the thin layer, none. Also, it is preferable that at least one of Ag and Pd in the range of 10 to 10000 ppm is included in the reaction accelerator necessary for obtaining the copper microparticles having the above-mentioned particle size. If it is less than 10 ppm, it becomes difficult to obtain the copper microparticles having the above-mentioned particle sizes. If it is more than 10,000 ppm, the cost becomes high and the quality may be adversely affected.

In addition, the existence of aggregated particles adversely affects the formation of the internal electrode as well as the presence of the maximum particle diameter (D _max ) of the above-mentioned detection. Therefore, it is preferable that the copper powder for conductive paste is in a form in which only primary particles (monolithic particles) exist respectively. Specifically, the average particle size (single particle size) of single particles (primary particles) observed by a field emission type scanning electron microscope (SEM) is measured by using the aggregated particles observed by the laser diffraction type particle size distribution measuring apparatus (Secondary particle diameter / primary particle diameter) of the 50% particle diameter (aggregated particle diameter) of the particles (particle diameter) is 2.0 or less.

Also, as in the presence of a maximum diameter (D _max) of the above-mentioned detection, combined or agglomerated particles (coalition size) there is adverse effect on the formation of the internal electrode (reduction in the cause and the electrode film density at the time of formation of coarse particles (powder Degradation of the TAP density of the characteristic)). In the specification, the term "aggregated particles" refers to one large particle (a particle produced after a reduction reaction) in which several single particles are physically aggregated by several tens or so from the action of electrostatic attraction or the like, (Coarse particles) "refers to particles having a shape in which copper particles are grown on the surface of roughly spherical particles by the reduction reaction of copper ions and distorted. The aggregated particles can be broken down to a single particle (primary particle) by a relatively weak force, but the bonded or coagulated particles (soft particles) can be broken (peeled) The surface characteristics of the particles are different from those inherently possessed by the surface due to the exposure of the surface of the peeled portion so that they can not be adversely affected when used in the conductive paste or dispersed well in the crushing operation or paste kneading operation, There is a possibility that cohesion occurs (cohesion or coagulated particles become one coarse particle) to become coarse particles. Therefore, it is preferable that the ratio of the number of single copper spheres in the copper particles observed by the SEM is 90% or more.

<Examples>

Hereinafter, embodiments of the copper powder for conductive paste and the method for producing the copper powder according to the present invention will be described in detail.

[Example 1]

First, 3410 g of pure water was put into a 5 L reaction tank, nitrogen was supplied from the upper part of the reaction tank at a flow rate of 5 L / min, the inside of the reaction tank was maintained in a nitrogen atmosphere, the rotation speed of the stirring rod in the reaction tank was adjusted to 200 rpm , And the temperature of pure water in the reaction tank was adjusted to 25 캜. Then, a solution prepared by dissolving 0.0922 g of palladium (II) nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) in 250 g of pure water was placed in a reaction vessel and stirred for 2 minutes to be uniformly mixed. Subsequently, 100 g of a 0.1% hydrazine hydrate solution (80% hydrazine hydrate manufactured by Otsuka Chemical Co., Ltd., diluted with pure water) as a reducing agent was added once to the solution in the reaction tank to perform a reduction reaction. Next, a solution prepared by dissolving 0.4256 g of polyethyleneimine (PEI) (manufactured by Wako Pure Chemical Industries, Ltd., average molecular weight 10000) in 210 g of pure water as an anti-aggregation agent was added to the solution in the reaction tank and stirred for 10 minutes to prepare a solution of the reaction promoter . The reaction promoter in the obtained solution was clear and light black. The solution was observed with a transmission electron microscope (TEM), and the reaction promoter in the solution was particles having an average particle diameter of 25 nm.

Further, 600 g of pure water was added to a 2 L beaker, and 33.0 g of L-ascorbic acid (Wako Pure Chemical Industries, Ltd.) as a reducing agent was added and dissolved while adjusting the pure water temperature to 60 캜 to obtain a reducing agent solution. To the reducing agent solution, 447 g of the above-mentioned reaction accelerator was metered and added, and the mixture was stirred for 1 minute to be uniformly mixed.

Further, 3000 g of pure water was placed in a reaction vessel of 5 L, nitrogen was supplied from the upper portion of the reaction vessel at a flow rate of 5 L / min, the inside of the reaction vessel was maintained in a nitrogen atmosphere, the rotation speed of the stirring rod in the reaction vessel was adjusted to 290 rpm , 37.5 g of copper sulfate pentahydrate (manufactured by Onahama Seiren KK) was added and dissolved while adjusting the temperature of pure water in the reaction tank to 60 캜 to obtain an aqueous solution containing bivalent copper ions.

Then, a reducing agent solution to which the above-mentioned reaction promoter was added was added at once from the upper part of the reaction tank into which the aqueous solution containing the divalent copper ions was injected, followed by reduction reaction. It was confirmed that copper particles were formed immediately after the addition of the reducing agent solution. The amount of Pd in the reaction promoter added was about 500 ppm with respect to Cu. The solution in the reaction tank was continuously stirred and aged for 5 minutes in this state, stirring was stopped, washed and dried to obtain copper microparticles.

[Example 2]

A reaction accelerator was added to an aqueous solution containing bivalent copper ions without adding it to the reducing agent solution, and then a reducing agent solution was added to the aqueous solution containing the bivalent copper ions to which the reaction accelerator was added. Copper microparticles were obtained.

[Example 3]

Copper microparticles were obtained in the same manner as in Example 1 except that D-erythorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of L-ascorbic acid as a reducing agent.

[Example 4]

Copper fine particles were obtained in the same manner as in Example 1 except that 36.2 g of copper (II) nitrate trihydrate (manufactured by Katayama Chemical Industry Co., Ltd.) was used instead of copper sulfate pentahydrate as a raw material of divalent copper ion.

[Example 5]

Copper microparticles were obtained in the same manner as in Example 1 except that the temperature at the preparation of the aqueous solution containing the reducing agent solution and the divalent copper ion was 80 ° C.

[Example 6]

Copper microparticles were obtained in the same manner as in Example 1 except that the temperature at the time of preparing the aqueous solution containing the reducing agent solution and the divalent copper ion was changed to 40 占 폚.

[Example 7]

Except that polyethyleneimine (manufactured by Wako Pure Chemical Industries, Ltd., average molecular weight: 10000) was added in an amount of 1% by mass based on the amount of copper introduced into the aqueous solution containing bivalent copper ions in the same manner as in Example 1 Copper microparticles were obtained.

[Example 8]

Copper fine particles were obtained in the same manner as in Example 1 except that 0.125 mol of glycine (manufactured by KANTO CHEMICAL Co., Ltd.) was further added to the aqueous solution containing bivalent copper ions.

[Example 9]

Copper microparticles were obtained in the same manner as in Example 1 except that arabic rubber (manufactured by Wako Pure Chemical Industries, Ltd.) was added in an amount of 5% by mass based on the amount of copper introduced into the aqueous solution containing divalent copper ions .

[Example 10]

Copper microparticles were obtained in the same manner as in Example 1 except that palladium nitrate and polyethylenimine as an anti-aggregation agent were simultaneously added when preparing a solution of the reaction promoter. The reaction promoter obtained in this Example was light in color as compared with Example 1, and the solution of this reaction promoter was observed by TEM. As a result, the reaction promoter in the solution was particles having an average particle diameter of 20 nm.

[Example 11]

When preparing the solution of the reaction accelerator, the amount of the palladium nitrate, the reducing agent (hydrazine hydrate solution) and the anti-aggregation agent (polyethyleneimine) is 8 times, and when the reducing agent solution containing the reaction accelerator is prepared, 55.9 g of the reaction accelerator is added to the reducing agent solution (The amount of Pd in the added reaction promoter was adjusted to about 500 ppm with respect to Cu) by the same method as in Example 1. The copper microparticles were obtained in the same manner as in Example 1. The reaction accelerator obtained in this Example was dark gray solution as compared with Example 1. The solution of the reaction accelerator was observed by TEM. As a result, the reaction accelerator in the solution was particles having an average particle size of 28 nm.

[Example 12]

Ascorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was used in the preparation of a reducing agent solution in such a manner that the addition amount of copper sulfate pentahydrate (manufactured by Onahama Seiren K.K.) was 187.3 g when an aqueous solution containing bivalent copper ion was prepared, Copper fine particles were obtained in the same manner as in Example 1 except that the amount of the reaction accelerator added was 165.1 g and the amount of the reaction promoter added to the reducing agent solution was 277.4 g.

[Example 13]

The procedure of Example 1 was repeated except that an aqueous solution containing bivalent copper ions was added to the reducing agent solution to which the reaction accelerator was added instead of adding the reducing agent solution containing the reaction accelerator to the aqueous solution containing bivalent copper ions Copper microparticles were obtained. That is, 3000 g of pure water was placed in a reaction tank of 5 L, nitrogen was supplied from the upper part of the reaction tank at a flow rate of 5 L / min, the inside of the reaction tank was maintained in a nitrogen atmosphere, the rotation speed of the stirring rod in the reaction tank was adjusted to 290 rpm , 33.0 g of L-ascorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was added and dissolved while adjusting the temperature of the pure water in the reaction tank to 60 캜 to obtain a reducing agent solution. Further, 600 g of pure water was added to a 2 L beaker, and 37.5 g of copper sulfate pentahydrate (manufactured by Onahama Seiren Co., Ltd.) was added while adjusting the pure water temperature to 60 ° C to obtain an aqueous solution containing bivalent copper ions.

[Example 14]

First, 1900 g of pure water was placed in the reaction tank, nitrogen was supplied from the upper part of the reaction tank at a flow rate of 5 L / min to maintain the inside of the reaction tank in a nitrogen atmosphere, the rotation speed of the stirring rod in the reaction tank was adjusted to 200 rpm, The temperature of pure water was adjusted to 25 캜. Subsequently, a solution prepared by dissolving 0.34 g of silver nitrate (manufactured by KANTO CHEMICAL Co., Ltd.) in 250 g of pure water was placed in a reaction vessel and stirred for 2 minutes to be uniformly mixed. Subsequently, 625 g of a 0.1% hydrazine hydrate solution (80% hydrazine hydrate manufactured by Otsuka Chemical Co., Ltd., diluted with pure water) as a reducing agent was added once to the solution in the reaction tank, and the reduction reaction was carried out. Subsequently, a solution obtained by dissolving 2.16 g of polyethyleneimine (manufactured by Wako Pure Chemical Industries, Ltd., average molecular weight 10000) in 1080 g of pure water as an anti-aggregation agent was added to the solution in the reaction tank and stirred for 10 minutes to obtain a reaction accelerator solution. Observation of the obtained reaction promoter by TEM revealed that the reaction promoter in the solution was an average particle diameter of 60 nm.

Further, 600 g of pure water was added to a 1 L beaker, and 33.0 g of L-ascorbic acid (Wako Pure Chemical Industries, Ltd.) was added as a reducing agent while adjusting the pure water temperature to 60 ° C to dissolve the solution to obtain a reducing agent solution. To the reducing agent solution, 875 g of the above-mentioned reaction accelerator was added thereto by weighing and the mixture was stirred for 1 minute to be uniformly mixed.

Further, 2500 g of pure water was placed in a reaction vessel of 5 L, nitrogen was supplied from the upper part of the reaction vessel at a flow rate of 5 L / min, the inside of the reaction vessel was maintained in a nitrogen atmosphere, the rotation speed of the stirring rod in the reaction vessel was adjusted to 290 rpm , 37.5 g of copper sulfate pentahydrate (manufactured by Onahama Seiren KK) was added and dissolved while adjusting the temperature of pure water in the reaction tank to 60 캜 to obtain an aqueous solution containing bivalent copper ions.

Subsequently, a reducing agent solution to which the above-mentioned reaction promoter was added was added at once from the upper part of the reaction tank into which the aqueous solution containing the divalent copper ions was injected, and the reduction reaction was carried out. It was confirmed that copper particles were formed immediately after the addition of the reducing agent solution. The amount of Ag in the added reaction promoter was about 5000 ppm with respect to Cu. The solution in the reaction tank was continuously stirred and aged for 5 minutes in this state, stirring was stopped, washed and dried to obtain copper microparticles.

[Example 15]

First, 1900 g of pure water was placed in the reaction tank, nitrogen was supplied from the upper part of the reaction tank at a flow rate of 5 L / min to maintain the inside of the reaction tank in a nitrogen atmosphere, the rotation speed of the stirring bar in the reaction tank was adjusted to 200 rpm, The temperature of pure water was adjusted to 25 캜. Subsequently, a solution prepared by dissolving 0.34 g of silver nitrate (manufactured by KANTO CHEMICAL Co., Ltd.) in 250 g of pure water was placed in a reaction vessel and stirred for 2 minutes to be uniformly mixed. Subsequently, a solution obtained by dissolving 0.475 g of sodium borohydride (manufactured by Wako Pure Chemical Industries, Ltd.) as a reducing agent in 625 g of pure water was added to the solution in the reaction tank at once to perform a reduction reaction. Subsequently, a solution obtained by dissolving 2.16 g of polyethyleneimine (manufactured by Wako Pure Chemical Industries, Ltd., average molecular weight 10000) in 1080 g of pure water as an anti-aggregation agent was added to the solution in the reaction tank and stirred for 10 minutes to obtain a reaction promoter solution. Observation of the obtained reaction promoter by TEM revealed that the reaction promoter in the solution was an average particle diameter of 50 nm.

Further, 600 g of pure water was added to a 1 L beaker, 12.5 g of copper sulfate pentahydrate (manufactured by Onahama Seiren KK) was added while adjusting the temperature of the pure water to 60 ° C, and an aqueous solution containing divalent copper ions .

Further, 1250 g of pure water was placed in a reaction tank of 5 L, nitrogen was supplied from the upper part of the reaction tank at a flow rate of 5 L / min, the inside of the reaction tank was maintained in a nitrogen atmosphere, the rotation speed of the stirring rod in the reaction tank was adjusted to 200 rpm , 99.0 g of L-ascorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) as a reducing agent was added and dissolved while adjusting the temperature of the pure water in the reaction tank to 60 캜 to obtain a reducing agent solution. To the reducing agent solution, 2095 g of the above-mentioned reaction promoter was added thereto by metering, and the mixture was stirred for 1 minute to be uniformly mixed.

Subsequently, an aqueous solution containing the above-mentioned divalent copper ions was added from the upper part of the reaction vessel into which the reducing agent solution to which the reaction promoter was added was injected once to perform a reduction reaction. It was confirmed that copper particles were formed immediately after the addition of the reducing agent solution containing the reaction accelerator. The amount of Ag in the added reaction promoter was about 4000 ppm relative to Cu. The solution in the reaction tank was continuously stirred and aged for 5 minutes in this state, stirring was stopped, washed and dried to obtain copper microparticles.

[Example 16]

First, 2560 g of pure water was placed in a reaction vessel of 5 L, nitrogen was supplied from the upper part of the reaction vessel at a flow rate of 5 L / min, the inside of the reaction vessel was maintained in a nitrogen atmosphere, the rotation speed of the stirring rod in the reaction vessel was adjusted to 200 rpm , And the temperature of pure water in the reaction tank was adjusted to 25 캜. Subsequently, a solution prepared by dissolving 0.216 g of silver nitrate (manufactured by KANTO CHEMICAL Co., Ltd.) in 100 g of pure water was placed in a reaction vessel and stirred for 2 minutes to be uniformly mixed. Subsequently, a solution prepared by dissolving 0.498 g of 80% hydrazine hydrate (manufactured by Otsuka Chemical Co., Ltd.) as a reducing agent in 100 g of pure water was added to the solution in the reaction tank at once to perform a reduction reaction. Subsequently, a solution prepared by dissolving 1.373 g of polyethyleneimine (manufactured by Wako Pure Chemical Industries, Ltd., average molecular weight 10000) in 500 g of pure water as an anti-aggregation agent was added to the solution in the reaction tank and stirred for 10 minutes to obtain a solution of the reaction promoter. Observation of the resulting reaction promoter solution by TEM revealed that the reaction promoter in the solution was particles having an average particle size of 55 nm.

Further, 600 g of pure water was added to a 1 L beaker, and 118.9 g of L-ascorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) as a reducing agent was added and dissolved while adjusting the pure water temperature to 60 캜 to obtain a reducing agent solution .

Further, 600 g of pure water was added to a 1 L beaker, 134.8 g of copper sulfate pentahydrate (manufactured by Onahama Seiren K.K.) was added while adjusting the pure water temperature to 60 ° C, and an aqueous solution containing divalent copper ions was added thereto .

Then, the above-described reducing agent solution was added while adjusting the rotational speed of the stirring rod in the reaction vessel of 5 L into which the solution of the reaction promoter was injected at 290 rpm, while adjusting the temperature of pure water in the reaction vessel to 60 ° C., After mixing to homogeneity by stirring, an aqueous solution containing the above-mentioned divalent copper ions was added in one time to perform a reduction reaction. It was confirmed that copper particles were formed immediately after the addition of the aqueous solution containing this divalent copper ion. The amount of Ag in the added reaction promoter was about 4000 ppm relative to Cu. Thereafter, the solution in the reaction tank was continuously stirred and aged for 5 minutes in this state, stirring was stopped, washed and dried to obtain copper microparticles.

[Example 17]

Copper fine particles were obtained in the same manner as in Example 16 except that the temperature at the time of preparing the reaction accelerator was changed to 40 캜. When the solution of the obtained reaction promoter was observed by TEM, the reaction promoter in the solution was particles having an average particle size of 55 nm.

[Example 18]

Copper fine particles were obtained in the same manner as in Example 16 except that the amount of the polyethyleneimine to be added when preparing the reaction accelerator was 0.137 g and erosorbic acid was used as the reducing agent. When the solution of the obtained reaction promoter was observed by TEM, the reaction promoter in the solution was particles having an average particle diameter of 70 nm.

[Example 19]

Copper microparticles were obtained in the same manner as in Example 16 except that 1.373 g of methyl cellulose (Methylcellulose 4000, manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of polyethyleneimine as an anti-aggregation agent in the preparation of the reaction accelerator. When the solution of the obtained reaction promoter was observed by TEM, the reaction promoter in the solution was particles having an average particle diameter of 45 nm.

[Example 20]

0.666 g of ethyl acetoacetate aluminum diisopropylate (S-75P manufactured by Kawaken Fine Chemicals Co., Ltd.) was added to a solution of 10 g of the copper particles obtained in Example 16 and 100 g of isopropyl alcohol in a 200 mL beaker while thoroughly stirring and mixing, And the mixture was stirred for 1 hour. Then, 5 g of pure water was added for 10 minutes while stirring was continued. After completion of the addition of the pure water, the mixture was further stirred for 1 hour, followed by filtration and drying to obtain a copper powder (or a copper powder coated with the A1 compound) on which the A1 compound was deposited as the metal compound used for the dielectric material.

[Example 21]

0.5 g of titanium ethylacetoacetate (TEAA, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was added to a solution of 10 g of the copper particles obtained in Example 16 and 100 g of isopropyl alcohol in a 200 mL beaker while thoroughly stirring, After stirring for a period of time, 5 g of pure water was added for 10 minutes while stirring was continued. After completion of the addition of pure water, the mixture was further stirred for 1 hour, followed by filtration and drying to obtain a copper powder (or a copper powder coated with a Ti compound) on which a Ti compound was deposited as a metal compound used for a dielectric material.

[Example 22]

0.64 g of titanium (IV) tetraisopropoxide (manufactured by Wako Pure Chemical Industries, Ltd.) was added to a solution in which 10 g of the copper particles obtained in Example 16 and 100 g of isopropyl alcohol were thoroughly stirred and mixed in a 200 mL beaker, A mixed solution of 2.9 g of a barium methoxide solution (a solution of barium metal dissolved in methanol and adjusted to a Ba concentration of 0.00075 mol / g) was added and stirred for 1 hour. Then, while stirring was continued, 5 g of pure water was added for 10 minutes . After completion of the addition of pure water, the mixture was further stirred for 1 hour, filtered and dried to obtain a copper powder (or a copper powder coated with a Ba-Ti compound) on which a Ba-Ti compound was deposited as a metal compound used for a dielectric material .

[Example 23]

0.62 g of tetraethoxysilane (ethyl silicate 28, manufactured by Colcoat Co., Ltd.) was added to a solution of 10 g of the copper particles obtained in Example 16 and 100 g of isopropyl alcohol in a 200 mL beaker while sufficiently stirring, After stirring, 1.3 g of 28% aqueous ammonia (manufactured by Wako Pure Chemical Industries, Ltd.) was added for 45 minutes. After the addition of ammonia water was completed, the mixture was further stirred for 1 hour, filtered and dried to obtain a copper powder (or a copper powder coated with a Si compound) on which a Si compound was deposited as a metal compound used for a dielectric material.

[Comparative Example 1]

A bivalent copper ion reduction reaction was carried out in the same manner as in Example 1 except that no reaction promoter was added. In this Comparative Example, the reaction was stopped because the reduction to copper was not completed within 5 minutes.

[Comparative Example 2]

Divalent copper ion reduction reaction was carried out in the same manner as in Example 1 except that the reaction accelerator was not added and the amount of L-ascorbic acid was changed to 264 g. In this Comparative Example, copper could be reduced by aging for 5 minutes, but it took more time to reduce to copper than in Example 1.

[Comparative Example 3]

Copper particles were obtained by performing a reduction reaction of divalent copper ions in the same manner as in Example 1 except that 0.010 g of palladium (II) nitrate was dissolved in an aqueous solution containing bivalent copper ions instead of the reducing agent solution . Further, in this comparative example, the amount of Pd in the added reaction promoter was about 500 ppm relative to Cu.

[Comparative Example 4]

Copper particles were obtained by carrying out a reduction reaction of divalent copper ions in the same manner as in Example 1 except that 0.075 g of silver nitrate was dissolved in an aqueous solution containing bivalent copper ions as a reaction promoter. Further, in this comparative example, the amount of Ag in the added reaction promoter was about 5000 ppm relative to Cu.

[Comparative Example 5]

The procedure of Example 1 was repeated except that nano-Ag particles prepared by reducing silver nitrate with hydrazine in the presence of heptanoic acid as a protecting agent were used as a reaction accelerator and the reaction accelerator was dispersed in water together with the surfactant. Copper ions were subjected to a reduction reaction to obtain copper particles. Further, in this comparative example, the amount of Ag in the added reaction promoter was 500 ppm relative to Cu. The Ag particles used were observed by TEM and found to have an average particle diameter of 23 nm.

[Comparative Example 6]

Copper particles were obtained by carrying out a reduction reaction of divalent copper ions by the same method as in Example 16 except that polyethyleneimine was not added as an anti-aggregation agent in the production of the reaction accelerator. In this comparative example, it was visually confirmed that Ag particles were agglomerated by continuing stirring after obtaining a reaction promoter (Ag particle) by a reduction reaction.

[Comparative Example 7]

Copper particles were obtained by performing a reduction reaction of divalent copper ions in the same manner as in Example 1 except that sodium hydroxide solution (50%) was added to the reducing agent solution to adjust the pH to 7. [ Further, in this Comparative Example, when the reducing agent solution was added to an aqueous solution (copper sulfate solution) containing bivalent copper ions, the copper sulfate solution was changed to an orange color, so that copper oxide was expected to be generated. In addition, since the reduction to copper was slow, the reaction time (aging time) was made longer than that of Example 1 by 5 minutes to make 10 minutes.

[Comparative Example 8]

The copper oxide produced by adding glucose to the copper hydroxide solution obtained by neutralizing copper sulfate with sodium hydroxide was filtered, washed and dried. 10.73 g of the copper oxide was weighed and redispersed in 3410 g of pure water, Ion was prepared in the same manner as in Example 1 except that 5.85 g of hydrazine hydrate as a reducing agent was added to 600 g of pure water in a 2 L beaker and a uniformly mixed reducing agent solution was used instead of the aqueous solution containing copper ions Reduction reaction was carried out to obtain copper particles. In this comparative example, it took about 7 hours until the completion of the reduction to copper.

[Comparative Example 9]

2 L Beaker was subjected to a reduction reaction of divalent copper ions to obtain 600 g of pure water, except that 23.5 g of hydrazine hydrate as a reducing agent was added and a uniformly mixed reducing agent solution was used to obtain copper particles . In this comparative example, it took about 3 hours until the completion of the reduction to copper.

[Comparative Example 10]

Except that 39.6 g of a 50% hypophosphorous acid solution (manufactured by Wako Pure Chemical Industries, Ltd.) was used in place of L-ascorbic acid, to thereby obtain copper particles.

[Comparative Example 11]

The procedure of Example 1 was repeated except that 36.2 g of copper nitrate trihydrate was used instead of copper sulfate pentahydrate and 38.4 g of sodium hypophosphite monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of L-ascorbic acid The reduction reaction of divalent copper ions was carried out. In this comparative example, since the reduction to the copper did not proceed, the stirring was continued for 20 minutes, but the reduction reaction was still not stopped and the reduction was stopped.

[Comparative Example 12]

Reduction reaction of divalent copper ions was carried out in the same manner as in Comparative Example 11, except that the temperature at the preparation of the aqueous solution containing the reducing agent solution and the divalent copper ion was 80 ° C. In this comparative example, since the reduction to the copper did not proceed for 5 minutes, when the stirring was continued, about 15 minutes after the injection of the reducing agent solution, an abrupt reaction occurred and copper particles could be obtained.

[Comparative Example 13]

Ascorbic acid was prepared in the same manner as in Example 1 except that a solution prepared by dissolving 11.8 g of hydrazine hydrate in 600 g of pure water was adjusted to pH 3 with diluted acetic acid and the reaction accelerator was added to the solution containing a divalent copper ion Copper particles were obtained in the same manner as in Example 1, except that the copper particles were added to the aqueous solution. In this Comparative Example, the reduction time to copper was not as fast as in Example 1, but it was possible to reduce to copper within 5 minutes.

[Comparative Example 14]

A solution prepared by dissolving 3.6 g of sodium borohydride in 600 g of pure water in place of the reducing agent solution of L-ascorbic acid was adjusted to pH 3.5 with dilute hydrochloric acid and the reaction accelerator was added to the solution containing the divalent copper ion Copper particles were obtained in the same manner as in Example 1, except that the copper particles were added to the aqueous solution. In this comparative example, since no change in color or the like was observed immediately after the addition of the reducing agent solution, after 5 minutes, the same amount of the reducing agent solution as the above-mentioned reducing agent solution (pH adjustment One solution) could be added to reduce copper to copper. The aging time was 10 minutes after the addition of the first reducing agent solution.

The particle size distribution, 50% particle size (D ₅₀ ), D _min (minimum particle size of detection) and D _max (maximum particle size of detection) of the copper powder obtained in Examples and Comparative Examples were measured with a laser diffraction particle size distribution analyzer ㆍ LS-230 manufactured by Coulter, Inc.). The results are shown in Tables 1 to 4. As a measurement sample, a liquid obtained by sufficiently dispersing the copper powder and 2-propanol obtained in Examples and Comparative Examples in a beaker using an ultrasonic dispersion tank or the like was used.

The particle shape and average particle size of the copper powder obtained in the examples and comparative examples were evaluated by a field emission scanning electron microscope (SEM) (S-4700 type, manufactured by Hitachi, Ltd.). The average particle diameter (single particle diameter) of the copper single particles observed by SEM was calculated from the average value of the ferule diameters of 50 particles. In addition, the particle size was calculated using a photographing field of 50,000 times, but when the number of particles of 50 could not be measured, the particle size was calculated using the field of view by lowering the magnification. Further, the ratio of the 50% particle diameter (D ₅₀ ) measured by the laser diffraction type particle size distribution measuring device to the average particle size of copper single particles measured by SEM was calculated. Further, the number and the ratio of copper particles (coagulated or bonded coarse particles), which are a single substantially spherical shape, were determined from 50 copper particles observed by SEM. The results are shown in Tables 5 and 6.

Further, the content of Ag or Pd in the copper particles was measured by ICP (IRIS / IRIS-AP, manufactured by Nippon Zerol Co., Ltd.). The results are shown in Tables 5 and 6. Further, in Examples 20 to 22, the amounts of Al, Ti, and Ba deposited on the copper particles (or coated with copper particles) were measured by ICP as well. In Example 20, the amount of Al was 0.47 mass% Ti was 0.52% by mass in Example 21, 1.01% by mass in Ti and 2.86% by mass in Example 22. Further, in Example 23, the amount of Si deposited (or coated with copper particles) on the copper particles was measured in accordance with JIS H1061, and found to be 0.72% by mass.

From the results shown in Tables 5 and 6, it can be seen that, in the method for producing copper powder in which a reducing agent is added to an aqueous solution containing bivalent copper ions to reduce and precipitate copper particles as in the examples, an aqueous solution containing bivalent copper ions and a reducing agent By stably producing copper microparticles having mono-dispersed microparticles, sharp particle size distribution, no assembly, and a shape close to a true spherical shape, by the presence of a reaction promoter containing at least one anti- I can see that I can do it.

The copper powder for conductive paste according to the present invention can be used for an internal electrode of a multilayer ceramic electronic component such as a multilayer ceramic capacitor or a multilayer ceramic inductor or an electroconductive paste for forming an external electrode such as a small multilayer ceramic capacitor or a multilayer ceramic inductor .

Claims (15)

A method for producing a copper powder for reducing and precipitating copper particles by adding a reducing agent solution to an aqueous solution containing bivalent copper ions, A reducing agent solution prepared by dissolving a reducing agent which reduces copper ions of bivalent copper into water is used as the reducing agent solution, Adding a reaction promoter solution containing at least one of an aqueous solution containing the bivalent copper ions and an aqueous solution of the reducing agent and an anti-flocculant for preventing the agglomeration of particles of the reaction promoter to an aqueous solution containing the bivalent copper ions, And adding a reducing agent solution to directly reduce the bivalent copper ions to copper to precipitate the copper particles. The method for producing a copper powder for conductive paste according to claim 1, wherein the reaction promoter comprises particles of a metal that is more valuable than copper. The method for producing a copper powder for conductive paste according to claim 1, wherein the reaction promoter comprises at least one of Ag particles and Pd particles having an average particle size of 10 to 100 nm. The method for producing a copper powder for conductive paste according to any one of claims 1 to 3, wherein the anti-aggregation agent is a water-soluble polymer. The method according to any one of claims 1 to 3, wherein the coagulation inhibitor is polyethyleneimine or methyl cellulose. The method for producing a copper powder for conductive paste according to any one of claims 1 to 3, wherein the reducing agent is L-ascorbic acid, D-erythorbic acid or a mixture thereof. The method for producing a copper powder for conductive paste according to any one of claims 1 to 3, wherein the aqueous solution containing bivalent copper ions is an aqueous solution of copper sulfate, copper nitrate or a mixture thereof. The method according to any one of claims 1 to 3, wherein a compound containing at least one selected from the group consisting of Al, Ba, Ti and Si is deposited on the surface of the copper particles precipitated by reduction , A method for producing a copper powder for conductive paste. 4. The method according to any one of claims 1 to 3, characterized in that the surface of the copper particles precipitated by reduction is coated with a compound containing at least one element selected from the group consisting of Al, Ba, Ti and Si , A method for producing a copper powder for conductive paste. Wherein the 50% particle diameter (D ₅₀ ) measured by the laser diffraction particle size distribution measuring apparatus is in the range of 0.1 to 0.5 μm, the maximum particle diameter (D _max ) of the detection, Of not more than 1.5 mu m and at least one of Ag and Pd of 10 to 10,000 ppm. The method according to claim 10, wherein the ratio of the 50% particle size (aggregated particle size) of the aggregated particles observed by the laser diffraction particle size distribution measuring device to the average particle size (monodispersed particle size) of the copper monodispersed particles observed by SEM Particle diameter / primary particle diameter) of the copper powder is 2.0 or less. 12. The copper powder for electroconductive paste according to claim 10 or 11, wherein the ratio of the number of single spherical copper particles in the copper particles observed by SEM is 90% or more. The conductive paste according to claim 10 or 11, wherein the surface of the copper powder for conductive paste is coated with a compound containing at least one selected from the group consisting of Al, Ba, Ti and Si Copper powder. The conductive paste according to claim 10 or 11, wherein the surface of the copper powder for conductive paste is coated with a compound containing at least one selected from the group consisting of Al, Ba, Ti and Si Copper powder. A conductive paste comprising the copper powder for conductive paste according to claim 10 or 11 as the conductive powder.