JP2014005491A - Method for producing metal powder, metal powder, conductive paste and laminated ceramic electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a metal powder that can afford good electrode coverage and can suppress structural defects such as cracks, delamination or the like and is suitable for a conductive material for an internal electrode of a laminated ceramic electronic component.SOLUTION: A method for producing a metal powder comprises: (a) preparing a suspension solution 5 comprising a metal particle 2 having an oxide film 6 formed on at least a part of the surface thereof and a reducing agent solution containing a reducing agent; (b) reducing and removing the oxide film 6; and (c) adding a sulfur-containing substance to the suspension solution 5, bringing the metal particle 2 in contact with the sulfur-containing substance to react them in the presence of the reducing agent, and coating at least a part of the surface of the metal particle 2 with a metal compound 3 composed mainly of a sulfide to produce a metal powder 1. A conductive paste is produced using the metal powder as a conductive material. A laminated ceramic electronic component such as a laminated ceramic capacitor or the like is manufactured using the conductive paste.

Description

  The present invention relates to a metal powder manufacturing method, a metal powder, a conductive paste, and a multilayer ceramic electronic component. More specifically, the present invention relates to a metal powder manufacturing method suitable for a conductive material of an internal electrode for a multilayer ceramic electronic component. The present invention relates to a metal powder manufactured using the method, a conductive paste using the metal powder as a conductive material, and a multilayer ceramic electronic component manufactured using the conductive paste.

  Today, multilayer ceramic electronic components such as multilayer ceramic capacitors are mounted on various electronic devices.

  Conventionally, this type of multilayer ceramic electronic component is usually manufactured by the following method.

  That is, first, a ceramic laminate is formed in such a form that ceramic green sheets formed by processing ceramic raw material powder into a sheet and conductive films formed by applying conductive paste are alternately laminated. Next, the ceramic laminate is subjected to a degreasing treatment (heat treatment) to burn out the binder resin contained in the ceramic green sheet or the conductive paste, and after removing the binder resin, a firing treatment is performed. Thus, a ceramic body in which internal electrodes are embedded is manufactured, and then external electrodes are formed on both ends of the ceramic body to manufacture a multilayer ceramic electronic component.

  As the conductive material, various metal powders having good conductivity such as noble metal materials such as Ag and Pd and base metal materials such as Ni and Cu are used.

  By the way, the multilayer ceramic electronic component is degreased in the manufacturing process as described above to remove the binder resin contained in the ceramic green sheet and the conductive film. However, Ag, Pd, which are the main components of the conductive film, are removed. It is known that metal powders such as Ni and Cu have a catalytic action that promotes a combustion reaction when in contact with a binder resin. Therefore, when a metal powder having such a catalytic action is used as a conductive material, the catalytic action of such a metal powder promotes rapid combustion of the binder resin during the degreasing treatment, and therefore, the gas inside the ceramic laminate is As a result, the internal pressure of the ceramic laminate increases, and structural defects such as cracks and delamination (delamination) may occur.

Therefore, conventionally, a metal sulfide is formed on the surface of the metal powder, thereby suppressing a rapid combustion of the binder resin during the degreasing process.

  For example, Patent Document 1 proposes a nickel powder containing sulfur: 0.01 to 1.0% by mass and carbon: 0.01 to 1.0% by mass and having a surface coated or adhered with a sulfur-containing compound. ing.

  In Patent Document 1, for example, as shown in FIG. 4, after adding a sulfur-containing compound solution 102 such as thiourea to the Ni powder slurry 101, airflow drying treatment 103 is performed at a temperature of 200 to 300 ° C. for a short time, Thereafter, a heat treatment 104 is performed at 100 to 400 ° C. in an oxidizing atmosphere such as an air atmosphere, whereby the surface of the nickel powder is covered or adhered with a sulfur-containing compound (nickel sulfide).

  Patent Document 2 proposes a nickel fine powder having an average particle size of 0.1 to 1.0 μm and a sulfur content of 0.02 to 1.0%.

  In Patent Document 2, as shown in FIG. 5, hydrogen gas 112 is supplied together with a carrier gas such as Ar into a reaction vessel containing nickel chloride gas 111 and hydrogen sulfide gas 113 in which nickel chloride is vaporized. Then, a gas phase hydrogen reduction treatment 114 is performed to obtain a nickel fine powder containing a sulfur component. That is, the nickel chloride gas 111 and the hydrogen gas 112 are reacted in the reaction vessel to produce nickel particles, and at the same time the nickel chloride gas 111 and the hydrogen sulfide gas 113 are reacted to coat the surfaces of the nickel particles with nickel sulfide. Nickel fine powder is obtained.

  Patent Document 3 discloses a method for producing nickel fine particles, in which nickel fine particles are wet-treated with a solution of a sulfur compound so as to contain sulfur in a range of 0.05 to 1.0% by weight with respect to the nickel fine particles. Proposed.

  In Patent Document 3, as shown in FIG. 6, nickel fine particles 122 are added to a sulfur-containing compound solution 121 such as ammonium sulfate containing sulfur, wet-treated 123, and then heated and dried to put the sulfur compounds in the nickel fine particles. It is contained uniformly.

International Publication No. 2005/123307 (claims 1 and 2, paragraph numbers [0037] to [0039], [0045], etc.) Japanese Patent Laid-Open No. 11-80817 (Claim 1, paragraph numbers [0009], [0010], etc.) JP 2007-191771 A (Claim 1, paragraph numbers [0010], [0023], etc.)

  However, in Patent Document 1, after the airflow drying process 103 is performed, the heat treatment 104 is performed at a temperature of 100 to 400 ° C. in an oxidizing atmosphere. There is a risk of coarsening. And, when a conductive paste is produced using such coarsened nickel powder, the dispersibility of the nickel powder is reduced, so that smoothness is good even if the conductive paste is applied on the ceramic green sheet. It is difficult to form a conductive film, and the electrode coverage may be reduced or structural defects such as delamination may be caused.

  In Patent Document 2, nickel chloride is gasified in a high temperature atmosphere, and gas phase hydrogen reduction treatment 114 is performed using the high temperature atmosphere, thereby forming nickel sulfide on the surface of the nickel particles simultaneously with the production of the nickel particles. doing. For this reason, nickel fine particles may condense during the reaction process, and the particle size may become coarse. Therefore, as in Patent Document 1, it becomes difficult to form a conductive film with good smoothness even when a conductive paste is applied on a ceramic green sheet, and the electrode coverage is reduced or structural defects such as delamination are present. May occur.

  Further, in Patent Document 3, nickel fine particles 122 are added to the sulfur-containing compound solution 121 and wet processing 123 is performed. Therefore, even if heat-dried thereafter, sulfur is only adsorbed on the surface of the nickel particles. it is conceivable that.

  That is, at least a part of the surface of metal particles such as nickel particles inevitably comes into contact with the atmosphere, and therefore the surface is usually coated with an oxide film made of a metal oxide. Since this metal oxide hardly reacts with the sulfur compound, even if the nickel fine particles 122 are added to the sulfur-containing compound solution 121, no metal sulfide is formed on the surface of the nickel particles, and the nickel particles And a mixed solution of sulfur-containing compounds. Therefore, it is considered that the sulfur compound is only adsorbed on the nickel particles even if it is subsequently dried by heating.

  Even when the conductive paste is prepared using the nickel fine particles having the sulfur compound adsorbed on the surface in this way, the sulfur compound is detached from the surface of the nickel particles during the preparation of the conductive paste, and the degreasing treatment is performed. The catalytic action of the nickel particles cannot be suppressed.

  That is, in the method for producing metal powder as in Patent Document 3, the catalytic action of the metal particles cannot be effectively suppressed, and the binder resin is likely to be rapidly burned during the degreasing treatment. Gas is generated and the pressure rises, which may cause structural defects such as cracks and delamination.

  The present invention has been made in view of such circumstances, and it is possible to obtain a good electrode coverage and to suppress the occurrence of structural defects such as cracks and delamination, and for internal electrodes of multilayer ceramic electronic components. Manufacturing method of metal powder suitable for conductive material, metal powder manufactured using this manufacturing method, conductive paste using this metal powder as conductive material, and manufacturing using this conductive paste An object of the present invention is to provide a multilayer ceramic electronic component such as a multilayer ceramic capacitor.

  As described above, since metal particles such as Ag, Pd, Ni, and Cu inevitably come into contact with the atmosphere, an oxide film is usually formed on the surface.

  Therefore, the present inventors conducted extensive research, and after removing the oxide film on the surface by treating the metal particles with a reducing agent, the metal particles were added by adding a sulfur component in the presence of the reducing agent. As a result, the inventors have found that a metal compound containing a sulfur component can be formed on the surface of a metal particle by a chemical reaction without performing a heat treatment.

  The present invention has been made on the basis of such knowledge, and the method for producing a metal powder according to the present invention comprises treating a metal particle having an oxide film formed on at least a part of its surface with a reducing agent, In the presence of a reducing agent, the metal particles and the sulfur component are contacted to react the metal particles and the sulfur component, and at least a part of the surface of the metal particles is coated with the metal compound containing the sulfur component. It is characterized by that.

  Accordingly, the surface of the metal particles can be coated with the metal compound by a chemical reaction in the liquid phase without performing a heat treatment in the gas phase. Therefore, the metal particles are not condensed due to the heat treatment, and the conductive paste using the metal powder as a conductive material can form a highly smooth conductive film even when applied to a substrate. And good electrode coverage can be secured.

  In addition, as described above, the surface of the metal particles is coated with the metal compound containing a sulfur component, so that the catalytic action of the metal can be suppressed, thereby performing the degreasing process in the manufacturing process of the multilayer ceramic electronic component. However, it is possible to suppress the rapid burning of the binder resin, and to avoid the occurrence of structural defects such as cracks and delamination as much as possible.

  In the metal powder manufacturing method of the present invention, it is preferable that the metal particles contain at least one of Ni, Ag, Cu, and Pd.

  The metal powder manufacturing method is directed to metal particles having an oxide film formed on the surface. However, the metal powder may be applied to a liquid phase reduction method in which a metal salt solution is treated with a reducing agent to obtain metal particles. The same operations and effects as described above can be obtained.

  That is, in the method for producing metal powder according to the present invention, a metal salt solution containing metal ions is treated with a reducing agent to produce a redox reaction to produce metal particles, and then in the presence of the reducing agent, The metal particles and the sulfur component are brought into contact with each other to react the metal particles with the sulfur component, and at least a part of the surface of the metal particles is coated with the metal compound containing the sulfur component.

  In the method for producing a metal powder of the present invention, it is preferable that the metal ions include at least one of Ni ions, Ag ions, Cu ions, and Pd ions.

  Further, in the method for producing a metal powder of the present invention, the sulfur component is in the form of an inorganic sulfur-containing material containing at least one or more of a sulfide group including sulfur alone, hydrosulfide and polysulfide, It is preferable to add to the metal particles.

  In the metal powder production method of the present invention, the metal compound preferably contains a sulfide as a main component.

  Moreover, it is preferable that the manufacturing method of the metal powder of this invention is 0.01-5 mass% in conversion of the sulfur component in the said metal powder into a density | concentration.

  Furthermore, in the method for producing a metal powder of the present invention, the average powder diameter of the metal powder is preferably 0.01 μm or more.

  In the method for producing metal powder of the present invention, the reaction between the metal particles and the sulfur component is preferably performed in a solution having a pH exceeding 2.

  Furthermore, in the method for producing a metal powder of the present invention, the reaction between the metal particles and the sulfur component is preferably performed at a temperature of 20 to 200 ° C.

  Further, in the method for producing a metal powder of the present invention, the reducing agent is hydrazine, borohydride compound, titanium halide, hypophosphite, phosphite, aldehydes, ascorbic acid, hydrogen gas, alcohols. And at least one selected from polyhydric alcohols.

  In addition, the metal powder according to the present invention is manufactured using any of the manufacturing methods described above.

  The conductive paste according to the present invention is a conductive paste containing at least a conductive material, a binder resin, and a solvent, and the conductive material has the metal powder. It is said.

  The multilayer ceramic electronic component according to the present invention is a multilayer ceramic electronic component in which an internal electrode is embedded in a ceramic body. The internal electrode is formed by sintering the conductive paste. .

  According to the method for producing metal powder of the present invention, after treating metal particles (for example, Ni, Cu, Ag, Pd, etc.) having an oxide film formed on at least a part of the surface with a reducing agent such as hydrazine, In the presence of a reducing agent, the metal particles and a sulfur component (for example, sulfur alone, sulfide, etc.) are brought into contact with each other to react the metal particles with the sulfur component, thereby containing the sulfur component such as sulfide. Since the compound is coated on at least a part of the metal particles, a sulfur compound can be formed on the metal surface by a chemical reaction in the liquid phase without accompanying heat treatment in the gas phase during the production process. Therefore, the metal particles are not condensed due to the heat treatment, and the conductive paste using the metal powder as a conductive material can form a highly smooth conductive film even when applied to a substrate. And good electrode coverage can be secured.

  Moreover, since at least a part of the surface of the metal particles is coated with the metal compound containing the sulfur component as described above, the catalytic action of the metal can be effectively suppressed. Even if the degreasing treatment is performed in the manufacturing process, the binder resin can be prevented from burning rapidly, and the occurrence of structural defects such as cracks and delamination can be avoided as much as possible.

  Further, according to the method for producing a metal powder of the present invention, a metal salt solution containing a metal ion is treated with a reducing agent to produce a redox reaction to produce metal particles, and then in the presence of the reducing agent. The metal particles and the sulfur component are brought into contact with each other, the metal particles and the sulfur component are reacted, and at least a part of the surface of the metal particles is coated with the metal compound containing the sulfur component. Even in the case of obtaining metal particles by a liquid phase reduction method in which a metal salt solution is treated with a reducing agent instead of the metal particles on which a film is formed, the same actions and effects as described above can be obtained.

  Further, according to the conductive paste of the present invention, it is a conductive paste containing at least a conductive material, a binder resin, and a solvent, and since the conductive material has the metal powder, Since the metal particles do not condense and the coarsening of the powder diameter is suppressed, a conductive film with high smoothness can be formed even if the conductive paste is applied to the base material, and a good electrode coating The rate can be secured. Also, because it uses a conductive material with reduced catalytic action, the binder resin will not burn rapidly even if it is degreased during the manufacturing process of multilayer ceramic electronic components, and the binder resin will be burned out. Can do.

  The multilayer ceramic electronic component according to the present invention is a multilayer ceramic electronic component in which an internal electrode is embedded in a ceramic body, and the internal electrode is a good electrode because the conductive paste is sintered. The coverage can be ensured, and a highly reliable multilayer ceramic electronic component in which occurrence of structural defects such as cracks and delamination is suppressed can be obtained.

It is sectional drawing which shows typically one Embodiment of the metal powder manufactured using the manufacturing method of this invention. It is a manufacturing process figure which shows typically the manufacturing process of the manufacturing method of the metal powder which concerns on this invention. 1 is a cross-sectional view schematically illustrating an embodiment of a multilayer ceramic capacitor as a multilayer ceramic electronic component according to the present invention. It is a manufacturing process figure which shows the manufacturing method of the nickel powder described in patent document 1. It is a manufacturing process figure which shows the manufacturing method of the nickel super powder described in patent document 2. FIG. It is a manufacturing process figure which shows the manufacturing method of the nickel fine particle described in patent document 3. FIG.

  Next, an embodiment of the present invention will be described in detail.

  FIG. 1 is a cross-sectional view schematically showing one embodiment of a metal powder produced using the production method of the present invention.

  That is, in the metal powder 1, a metal compound 3 containing a sulfur component is formed on the surface of the metal particles 2.

  Hereinafter, this metal powder manufacturing method will be described in detail with reference to FIG.

  First, as shown in FIG. 2A, the metal particles 2 are put into a reducing agent solution 4 containing a reducing agent, and a suspension solution 5 composed of the metal particles 2 and the reducing agent solution 4 is produced.

  Since the metal particles 2 usually inevitably come into contact with the atmosphere, the surface is oxidized, and an oxide film 6 made of a metal oxide is formed. The oxide film 6 is reduced and removed by the action of the reducing agent by coming into contact with the reducing agent solution 4. As shown in FIG. 2 (b), the suspension solution 5 includes the reducing agent solution 4, the metal particles 1, and the like. A mixed solution of

  Next, a sulfur-containing material containing a sulfur component is added to the suspension solution 5 to bring the metal particles 2 into contact with the sulfur-containing material. Then, the metal particle 2 reacts with the sulfur-containing material on the surface of the metal particle 2, and as shown in FIG. 2C, a metal compound 3 mainly composed of sulfide is formed on the surface of the metal particle 2, Thereby, the metal powder 1 is formed.

  The reason why the metal particles 2 are reacted with the sulfur-containing material in the presence of the reducing agent is as follows.

  As shown in FIGS. 2 (a) and 2 (b), by bringing the metal particles 2 into contact with the reducing agent solution 4, the oxide film (metal oxide) 6 formed on the surface of the metal particles 2 can be easily formed. Although it can be reduced and removed, if the metal particles 2 are exposed in the absence of a reducing agent, the oxide film 6 may be formed again on the surfaces of the metal particles 2. And since the metal oxide which forms the oxide film 6 does not easily react with the sulfur-containing material, it is difficult to form a sulfide on the surface of the metal particle 2.

  Therefore, in the present embodiment, the metal particles 2 and the sulfur-containing material are brought into contact with each other in the presence of a reducing agent so that both react smoothly.

  Unlike the case where the oxide film 6 remains by contacting the metal particles 2 from which the oxide film 6 has been reduced and removed with the sulfur-containing material, the metal particles 1 and the sulfur-containing material react smoothly. And the metal compound 3 which has a sulfide as a main component is easily formed in the surface of the metal particle 2. FIG.

  Moreover, in the manufacturing method described above, the metal compound 3 is formed by causing a chemical reaction in the liquid phase without performing heat treatment in the gas phase as in Patent Document 1 and Patent Document 2, so that the metal particles 2 The metal powder 1 having a desired particle size can be easily obtained without being condensed and coarsened.

  Therefore, a conductive film having high smoothness can be formed by producing a conductive paste using the metal powder 3 as a conductive material and applying the conductive paste to a base material. Coverage can be ensured.

  In addition, since the metal powder 1 whose surface of the metal particle 2 is coated with the metal compound 3 is used as a conductive material, even if a degreasing process is performed in the manufacturing process of the multilayer ceramic electronic component, the metal catalytic action is suppressed. Can do. Therefore, it becomes possible to avoid the rapid combustion of the binder resin, and it is possible to prevent the generation of gas inside the ceramic laminate and prevent the internal pressure from increasing, and cracks, delamination, etc. The occurrence of structural defects can be suppressed.

  The sulfur-containing material containing such a sulfur component is not particularly limited as long as sulfide ions are generated in the suspension solution 5, and hydrogen sulfide gas is dissolved in water. A sulfur-containing aqueous solution may be added to the suspension solution 5, but sulfur alone, sulfides such as sodium sulfide and ammonium sulfide, hydrosulfides such as sodium hydrogen sulfide and ammonium hydrogen sulfide, sodium polysulfide and ammonium polysulfide, etc. It is preferable to use an inorganic sulfur-containing material containing at least one polysulfide. That is, even if an organic sulfur compound is added to the suspension solution 5, sulfide can be formed on the surface of the metal particles 2, and it is possible to suppress the occurrence of structural defects. There exists a possibility that the carbon component contained in a compound may remain on the surface of a metal particle. Therefore, in consideration of such points, it is preferable to add to the metal particles 2 an inorganic sulfur-containing material containing the above-described simple sulfur, sulfide, hydrosulfide, or polysulfide.

  Further, the sulfur concentration in the metal powder 1 is not particularly limited, but in order to further suppress the occurrence of structural defects and ensure a better electrode coverage, the sulfur concentration is 0.01. -5 mass% is preferable, More preferably, it is 0.05-2 mass%. When the sulfur concentration in the metal powder 1 is less than 0.01% by mass, the sulfur content decreases, so that the surface of the metal particles may not be covered with the metal compound. On the other hand, when the sulfur concentration exceeds 5% by mass, the content of the metal particles 2 in the metal powder 1 is relatively decreased, which may cause a decrease in electrode coverage.

  Further, the reducing agent is not particularly limited, but a reducing agent having a strong reducing power is preferable. Hydrazine, sodium borohydride, titanium trichloride, sodium hypophosphite, sodium phosphite, aldehydes, ascorbine At least one selected from acids, hydrogen gas, alcohols such as 1-butanol, and polyhydric alcohols such as ethylene glycol can be preferably used.

  Further, the average powder diameter of the metal powder 1 is not particularly limited, but from the viewpoint of further reducing the structural defects, the average powder diameter is preferably 0.01 μm or more, more preferably 0.1 μm or more. is there. When the average powder diameter is less than 0.01 μm, the specific surface area of the metal particles 2 also increases, and in order to cover the surfaces of all the metal particles 2, it is necessary to increase the sulfur concentration. In addition, when the average powder diameter is 1 μm or more, the occurrence of structural defects can be sufficiently suppressed without increasing the sulfur concentration, and the electrode coverage increases as the average particle diameter of the metal particles becomes finer. Therefore, the average powder diameter of the metal powder 1 is preferably 1 μm or less.

  In addition, since the average powder diameter of the metal powder 1 is approximated by the average particle diameter of the metal particles 2 on which the oxide film 6 is formed, it can be managed by the average particle diameter of the metal particles 1 before the reduction treatment.

  Further, the pH of the suspension solution 5 in which the metal particles 1 react with the sulfur-containing material is not particularly limited, but sodium bicarbonate, sodium hydroxide, sulfuric acid, acetic acid, acetic acid so that the metal powder does not dissolve. It is preferable to adjust the pH of the suspension using a pH adjusting agent such as sodium. Specifically, the pH of the suspension solution 5 is preferably more than 2. By adjusting the pH of the suspension 5 in this way, a metal compound containing a desired sulfide as a main component can be formed on the surface of the metal particles 2, and even if a degreasing treatment is performed, the metal catalytic action Can be suppressed. The sulfide ion can generate hydrogen sulfide in an acidic region having a pH of less than 7. Therefore, in consideration of work safety, the pH of the suspension solution is more preferably 7 or more neutral or alkaline solution.

  Moreover, although it does not specifically limit about reaction temperature, In order to suppress generation | occurrence | production of a structural defect more effectively, 20-200 degreeC is preferable, More preferably, it is 60-200 degreeC. That is, in the suspension solution 5, it is necessary to sequentially proceed with a reduction reaction for reducing and removing the oxide film and a sulfide generation reaction between the metal particles and the sulfur-containing material, but when the reaction temperature is less than 20 ° C., Both of the reactions described above are difficult to proceed, and it may be difficult to coat the surface of the metal particles with metal sulfide. In addition, when the reaction temperature is higher than 200 ° C., the metal sulfide formation reaction proceeds locally, which may make it difficult to uniformly coat the surface of the metal particles with the metal sulfide.

  The type of metal particles 1 applicable in the present invention is not particularly limited as long as the reaction proceeds with a sulfur-containing material to form a sulfide. The metal species used for the conductive material of the internal electrode, such as Ni, Cu, Ag, and Pd, can be preferably used.

  Next, a multilayer ceramic electronic component using the metal powder will be described in detail.

  FIG. 3 is a cross-sectional view schematically showing an embodiment of a multilayer ceramic capacitor as a multilayer ceramic electronic component according to the present invention.

  In the multilayer ceramic capacitor, internal electrodes 8a to 8f are embedded in a ceramic body 7, external electrodes 9a and 9b are formed at both ends of the ceramic body 7, and the surfaces of the external electrodes 9a and 9b are further formed. Are formed with first plating films 10a and 10b and second plating films 11a and 11b.

  That is, the ceramic body 7 is formed by alternately laminating dielectric ceramic layers 12a to 12g and internal electrode layers 8a to 8f using the metal powder 1 of the present invention as a conductive material, and the internal electrode layers 8a, 8c, 8e is electrically connected to the external electrode 9a, and the internal electrode layers 8b, 8d, and 8f are electrically connected to the external electrode 9b. A capacitance is formed between the opposing surfaces of the internal electrode layers 8a, 8c, and 8e and the internal electrode layers 8b, 8d, and 8f.

  Next, a method for manufacturing the multilayer ceramic capacitor will be described in detail.

  First, an internal electrode conductive paste is prepared.

  That is, the above-described metal powder 1 and the organic vehicle are weighed and mixed so as to have a predetermined mixing ratio, and dispersed and kneaded using a three-roll mill, a sand mill, a pot mill or the like, thereby making the metal powder conductive. A conductive paste made of a conductive material is prepared.

  Here, the organic vehicle is prepared such that the binder resin is dissolved in an organic solvent, and the mixing ratio of the binder resin and the organic solvent is, for example, 1 to 3: 7 to 9 by volume ratio. .

  The binder resin is not particularly limited, and for example, ethyl cellulose resin, nitrocellulose resin, acrylic resin, alkyd resin, butyral resin, or a combination thereof can be used. Also, the organic solvent is not particularly limited, and α-terpineol, xylene, toluene, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, etc. alone or in combination thereof Can be used. In addition, it is also preferable to add a dispersing agent, a plasticizer, etc. to this electroconductive paste for internal electrodes as needed.

  Next, a multilayer ceramic capacitor is produced using the conductive paste for internal electrodes.

  That is, ceramic raw materials such as a Ba compound and a Ti compound are prepared. Then, a predetermined amount of these ceramic raw materials are weighed, and these weighed materials are put into a ball mill together with a grinding medium such as PSZ (Partially Stabilized Zirconia) balls and pure water, and sufficiently wet-mixed and pulverized and dried. After that, a calcination treatment is performed at a temperature of 950 to 1150 ° C. for a predetermined time, thereby preparing a calcination powder mainly composed of barium titanate.

  Next, additives such as Re compound containing rare earth element Re, Si compound containing Si, M compound containing alkaline earth metal M, Mn compound containing Mn and V compound containing V are required. Accordingly, a predetermined amount is weighed, and these weighed materials are put into a ball mill together with the calcined powder, pulverization medium and pure water, sufficiently wet-mixed and pulverized, and subjected to a drying treatment, thereby producing a ceramic raw material powder.

  Next, the ceramic raw material powder is put into a ball mill together with an organic binder, an organic solvent, and a grinding medium and wet mixed to produce a ceramic slurry. The ceramic slurry is formed into a sheet using a lip method or a doctor blade method. Then, a ceramic green sheet is produced.

  Next, screen printing is performed on the ceramic green sheet using the above-described internal electrode conductive paste, and a conductive film having a predetermined pattern is formed on the surface of the ceramic green sheet.

  Next, a plurality of ceramic green sheets on which a conductive film is formed are laminated in a predetermined direction, sandwiched between ceramic green sheets on which a conductive film is not formed, pressure-bonded, and cut into predetermined dimensions to produce a ceramic laminate. Thereafter, the binder removal treatment is performed at a temperature of 300 to 500 ° C., and further, the firing treatment is performed for about 2 hours with a predetermined firing profile in an air atmosphere or a reducing atmosphere. Thereby, the conductive film and the ceramic green sheet are co-sintered, and the ceramic body 7 in which the internal electrodes 8a to 8f are embedded is obtained.

  Next, a conductive paste for external electrodes is applied to both end faces of the ceramic body 7, and a baking treatment is performed at a temperature of 600 to 800 ° C. to form the external electrodes 9a and 9b.

  The conductive material contained in the external electrode conductive paste is not particularly limited, but from the viewpoint of cost reduction, a material mainly composed of Ag, Cu, or an alloy thereof is used. Is preferred.

  Finally, electrolytic plating is performed to form first plating films 10a and 10b made of Ni, Cu, Ni—Cu alloy or the like on the surfaces of the external electrodes 9a and 9b, and further, the first plating film 10a, Second plating films 11a and 11b made of solder, tin or the like are formed on the surface of 10b, whereby a multilayer ceramic capacitor is manufactured.

  In the multilayer ceramic capacitor formed in this way, the metal powder is used for the conductive material of the internal electrode, so that the metal particles do not condense and the metal particles are prevented from being coarsened. Therefore, even when a conductive paste is applied to a ceramic green sheet, a highly smooth conductive film can be formed, and a multilayer ceramic electronic component having a good electrode coverage can be obtained. it can. Moreover, since the metal compound 1 which has a sulfide as a main component is effectively formed on the surface of the metal particle 2, the metal powder 1 is suppressed in the catalytic action of the metal, and in the conductive paste during the degreasing process. A highly reliable monolithic ceramic electronic component capable of suppressing the occurrence of structural defects such as cracks and delamination without causing the binder resin to burn suddenly and causing an increase in internal pressure can be obtained. .

  In the above embodiment, the oxide film 6 formed on the surface of the metal particle 2 is reduced and removed, and then the metal particle 2 and the sulfur-containing material are reacted in the presence of the reducing agent. And a reducing agent solution are brought into contact with each other to cause a redox reaction, thereby generating metal particles, and then the metal particles and the sulfur-containing material may be reacted in the presence of the reducing agent.

  In this case, specifically, the metal powder can be produced by the following method.

First, a metal salt is prepared. Here, the metal salt is not particularly limited as long as it is reduced by a reducing agent and can be easily reduced to metal particles. For example, nickel sulfate hexahydrate (NiSO ₄ .6H ₂ O) , silver nitrate (AgNO _3), copper sulfate pentahydrate _{(CuSO 4 · 5H 2 O)} , may be used palladium sulfate (PdSO ₄₎ or the like.

  Then, the metal salt is dissolved in an aqueous solution containing a complexing agent or the like, thereby preparing an aqueous metal salt solution. Here, the complexing agent is not particularly limited, and for example, trisodium citrate, malonic acid, glycine, nitrilotriacetic acid and the like can be used.

  Next, as in the above embodiment, a reducing agent solution containing a reducing agent is prepared.

  And these metal salt aqueous solution and a reducing agent solution are mixed, heating at predetermined temperature, and an oxidation-reduction reaction is produced. Then, metal ions are reduced to metal, thereby producing fine metal particles. Thereafter, in the presence of this reducing agent, the metal particles and the sulfur-containing material are reacted in the same manner as in the above embodiment, thereby producing a metal powder coated with a metal compound mainly composed of sulfide. Can do.

  Thus, even when a metal salt is used as a starting material instead of the metal particles 2 having the oxide film 6 formed on the surface, the metal particles coated with the metal compound can be obtained without condensing the metal particles. Can be obtained.

  By using this metal powder for the conductive material, a conductive film having good smoothness can be obtained as described above, and a multilayer ceramic capacitor having a good electrode coverage can be obtained. Moreover, since the catalytic action of the metal can be suppressed, the multilayer ceramic capacitor in which the occurrence of structural defects such as cracks and delamination is suppressed without causing the binder resin to rapidly burn during the degreasing process.

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the multilayer ceramic capacitor is exemplified, but it is needless to say that the present invention can also be applied to other multilayer ceramic electronic components that are degreased, such as multilayer piezoelectric components.

  Next, examples of the present invention will be specifically described.

[Sample preparation]
(Sample No. 1)
A reducing agent solution containing hydrazine (H ₂ NNH ₂ ) as a reducing agent (hydrazine concentration: 5% by weight, and Pd particles having an average particle diameter of 0.4 μm as metal particles was prepared. The suspension solution was prepared.

  Next, sodium hydroxide was used as a pH adjuster, the pH of the suspension was adjusted so that the pH was 13, and the suspension was further heated to 60 ° C. on a hot water bath.

  Next, sodium sulfide was prepared as a sulfur compound. Then, while stirring the suspension solution using a stirring blade, sodium sulfide is added to the suspension solution, Pd and sodium sulfide are reacted for 30 minutes, then filtered, washed with water, dried, A metal powder of sample number 1 was obtained.

  Next, a conductive paste for internal electrodes was produced using this metal powder as a conductive material.

  First, prepare ethyl cellulose resin as binder resin and α-terpineol as organic solvent. Dissolve ethyl cellulose resin in α-terpineol so that the mixing ratio of ethyl cellulose resin and α-terpineol is 1: 9 by volume. This produced an organic vehicle.

  Next, the metal powder and the organic vehicle are mixed so that the metal powder is 45% by weight, and dispersed and kneaded using a three-roll mill, thereby using the metal powder as a conductive material for internal electrodes. A conductive paste was prepared.

  Next, a multilayer ceramic capacitor was produced using this conductive paste for internal electrodes.

  That is, first, a ceramic raw material powder mainly composed of barium titanate was prepared.

  Next, the ceramic raw material powder was placed in a ball mill together with a polyvinyl butyral organic binder, an organic solvent such as ethanol, and PSZ balls, and wet mixed to prepare a ceramic slurry. Next, the ceramic slurry was formed using a doctor blade method to produce a ceramic green sheet.

  Next, screen printing was performed on the ceramic green sheet using the above-described internal electrode conductive paste, and a conductive film having a predetermined pattern was formed on the surface of the ceramic green sheet.

  Next, a plurality of ceramic green sheets on which a conductive film was formed were laminated in a predetermined direction, sandwiched between ceramic green sheets on which a conductive film was not formed, pressure-bonded, and cut into predetermined dimensions to produce a ceramic laminate. Thereafter, the binder removal treatment was performed at a temperature of 350 ° C., and the firing treatment was further performed in the atmosphere at a firing temperature of 1200 ° C. for about 2 hours. As a result, the conductive film and the ceramic green sheet were co-sintered, and a ceramic body in which internal electrodes were embedded was obtained.

  Next, a conductive paste for external electrodes mainly composed of Ag was applied to both end faces of the ceramic body, and a baking treatment was performed at a temperature of 700 ° C. to form external electrodes. Thereafter, electrolytic plating was performed to sequentially form a Ni film and a Sn film on the surface of the external electrode, thereby preparing a sample of sample number 1 (multilayer ceramic capacitor). The outer dimensions of the obtained sample were length L: 2.0 mm, width W: 1.2 mm, thickness T: 1.2 mm, and the effective number of layers was 100 layers.

(Sample No. 2)
After mixing Pd particles having an average particle size of 0.4 μm and a sodium hydroxide solution, a pH adjusting agent was added to prepare a suspension solution having a pH of 13, and heated to 60 ° C. on a hot water bath. Subsequently, this suspension solution was filtered, washed with water, and dried to prepare a metal powder of Sample No. 2.

  Thereafter, this metal powder was used as a conductive material, a conductive paste was prepared by the same method and procedure as in Sample No. 1, and a multilayer ceramic capacitor of Sample No. 2 was prepared using the conductive paste.

(Sample No. 3)
Pd particles were charged into the reducing agent solution by the same method and procedure as Sample No. 1, and a suspension solution adjusted to have a pH of 13 using a pH adjuster was prepared. Subsequently, this suspension solution was heated on a hot water bath and kept at a temperature of 60 ° C., then filtered, washed with water and dried to obtain a metal powder of Sample No. 3.

  After that, a conductive paste using the metal powder of sample number 3 as a conductive material was prepared by the same method and procedure as in sample number 1, and a multilayer ceramic capacitor of sample number 3 was prepared using the conductive paste. did.

(Sample No. 4)
Pd particles having an average particle size of 0.4 μm were dissolved in a sodium hydroxide solution, and a pH adjusting agent was added to prepare a suspension solution having a pH of 13, which was heated to 60 ° C. on a hot water bath. Subsequently, sodium sulfide was added to this suspension solution, and Pd particles and sodium sulfide were brought into contact with each other. Then, after filtration, washed with water and dried, a metal powder of sample number 4 was produced.

  Thereafter, this metal powder was used as a conductive material, a conductive paste was prepared by the same method and procedure as in Sample No. 1, and a multilayer ceramic capacitor of Sample No. 4 was manufactured using the conductive paste.

(Sample No. 5)
After preparing Pd powder slurry by slurrying Pd particles, Na ₂ S is added to the Pd powder slurry, followed by air drying at a temperature of 250 ° C., followed by heat treatment at 200 ° C. in the atmosphere. A metal powder of Sample No. 5 was produced.
After that, a conductive paste using a metal powder as a conductive material was prepared by the same method and procedure as Sample No. 1, and the conductive paste was used.

Thus, a sample No. 5 was prepared.

(Sample evaluation)
About each sample of sample numbers 1-5, the sulfur density | concentration in metal powder, the presence or absence of the sulfide formation in the Pd particle surface, the electrode coverage of an internal electrode were measured, and the generation | occurrence | production state of the structural defect was evaluated.

  Here, the sulfur concentration in the metal powder was measured using a CS meter.

  The presence or absence of the sulfide formation was confirmed by the following method.

The chemical state of sulfur in the metal powder was analyzed using an X-ray photoelectron spectroscopic analyzer (XPS apparatus) (Quantum 2000 manufactured by Physical Electronics Co., Ltd.). That is, from the S2p spectrum obtained by the XPS apparatus, a first peak indicating the S ²⁻ state and a second peak indicating the SO ₄ ²⁻ state are obtained, and (first peak) / (first peak Samples having a peak + second peak) of 30% or more were judged to be sulfides.

  The electrode coverage of the internal electrodes was measured by the following method for each of five samples.

  That is, each sample after sintering was cut at the center in the stacking direction, the cut surface was observed with an optical microscope, image analysis was performed to calculate the area ratio of the measured area to the theoretical area of the internal electrode, and the average value Was determined as the electrode coverage.

  The state of occurrence of structural defects was evaluated by confirming whether or not cracks and delamination occurred on 400 samples 1 to 5 by the following method.

  That is, first, each sample was visually inspected to confirm whether or not a crack had occurred.

  Next, the sample was placed in a predetermined position of the ultrasonic microscope so that the LT surface of the sample having the length L and the thickness T was the upper surface, and it was confirmed whether or not an abnormality occurred in the ultrasonic microscope. And when it was judged that abnormality had arisen as a result of observing with this ultrasonic microscope, the grinding | polishing process was further performed and the internal abnormal state was confirmed. Then, the number of samples in which at least one of delamination of 10 μm or more and cracks occurred in the L direction was counted, and the ratio with respect to all samples was calculated to obtain the structural defect occurrence rate.

  Further, samples having a structural defect occurrence rate of less than 1% are excellent (（), 1% or more and less than 3% are good (◯), 3% or more and less than 5% are acceptable (Δ), and 5% or more are defective (× ) And the occurrence of structural defects was evaluated.

  Table 1 shows the metal powder preparation conditions and the measurement / evaluation results for the samples Nos. 1 to 4.

  Since sample No. 2 uses Pd particles that have not been subjected to reduction treatment or addition treatment of sulfur-containing material, the number of occurrence of structural defects was increased, resulting in poor evaluation results. This is because sulfides are not formed on the surface of the Pd particles, and therefore the binder resin undergoes a rapid combustion due to the catalytic action of the Pd particles during the degreasing process, resulting in an increase in the internal pressure of the sample, resulting in delamination and cracks. It seems that the number of structural defects such as

  Sample No. 3 has undergone a reduction treatment, but no addition of sulfur-containing material to the Pd particles. Therefore, the number of structural defects generated increased for the same reason as Sample No. 2, and the evaluation result was It became defective.

  Sample No. 4 was subjected to the addition treatment of the sulfur-containing material, but the number of structural defects generated was increased, resulting in poor evaluation results. That is, in Sample No. 4, since the reduction treatment is not performed on the Pd particles, it is considered that Pd oxide is formed on the surface of the Pd particles. Since the Pd oxide and the sulfur compound do not easily react, sulfide is not formed on the surface of the Pd particles, and as a result, the number of occurrence of structural defects increases as in the case of the sample numbers 2 and 3. It seems to have been.

  Sample No. 5 had an electrode coverage as low as 58%, a large number of structural defects, and the evaluation result was poor. This is because although a sulfur compound is formed on the surface of the Pd particles, the heat treatment is performed, so the Pd particles are condensed together, so that the Pd particles having a coarse particle size are mixed in the conductive paste, which is good. It seems that the conductive film having smoothness could not be formed, and the electrode coverage decreased and the number of structural defects generated increased.

  On the other hand, in sample No. 1, after reducing the Pd particles, sodium sulfide (sulfur-containing material) was added in the presence of hydrazine (reducing agent), whereby palladium sulfide (sulfide) was added to the surface of the Pd particles. Therefore, it was found that the electrode coverage was as high as 72% and the structural defect occurrence rate was as low as less than 1%, and a multilayer ceramic capacitor with good reliability was obtained.

  A suspension solution containing hydrazine as a reducing agent and Pd particles as metal particles is prepared by the same method and procedure as in Sample No. 1, and then a pH adjuster so that the pH is 13 as in Sample No. 1. The pH of the suspension was adjusted and the suspension was kept at a temperature of 60 ° C.

  Next, the sulfur containing material shown in Table 2 was prepared. Then, while stirring the suspension solution using a stirring blade, the sulfur-containing material is added to the suspension solution, Pd and the sulfur-containing material are reacted, then filtered, washed with water, dried, The metal powder of sample numbers 11-16 was obtained.

  Then, using this metal powder, the conductive pastes of Sample Nos. 11 to 16 and the multilayer ceramic capacitor were produced by the same method and procedure as Sample No. 1.

  Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the state of occurrence of structural defects was further evaluated.

  Table 2 shows the production conditions and measurement / evaluation results of the samples Nos. 11 to 16.

  As is apparent from Table 2, as the sulfur-containing material, various sulfides such as ammonium sulfide, sulfur alone, water flow products such as sodium hydrosulfide and ammonium hydrogen sulfide, polyflow products such as sodium polysulfide and ammonium polysulfide, Even when using only sulfur, as in the case where sodium sulfide is used for the sulfur-containing material, sulfide is formed on the surface of the Pd particles, the structural defect occurrence rate is less than 1%, and good results are obtained. It turns out that it is obtained.

  A suspension solution containing the reducing agent shown in Table 3 and Pd particles as metal particles is prepared by the same method and procedure as Sample No. 1, and then the pH is adjusted with a pH adjuster so that the pH is 13. Further, the suspension solution was kept at a temperature of 60 to 150 ° C.

  Next, while stirring the suspension solution using a stirring blade, sodium sulfide is added to the suspension solution, Pd and various sulfur-containing materials are reacted, then filtered, washed with water, dried, As a result, metal powders of sample numbers 21 to 29 were obtained.

  Then, using this metal powder, the conductive paste of Sample Nos. 21 to 29 and the multilayer ceramic capacitor were produced by the same method and procedure as Sample No. 1.

  Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the state of occurrence of structural defects was further evaluated.

  Table 3 shows the production conditions and the measurement / evaluation results of the samples Nos. 21 to 29.

  As apparent from Table 3, titanium trichloride, hypophosphite, sodium borohydride, sodium phosphite, formaldehyde, ascorbic acid, hydrogen gas, 1-butanol, and diethylene glycol were used as the reducing agent. Even in this case, as in the case where hydrazine was used as the reducing agent, sulfides were formed on the surface of the Pd particles, and the occurrence rate of structural defects was less than 1%, indicating that good results were obtained.

  As metal particles, Ag particles having an average particle size of 0.3 μm, Cu particles having an average particle size of 0.5 μm, and Ni particles having an average particle size of 0.2 μm were prepared.

  Next, a suspension solution containing hydrazine as a reducing agent and each of the above metal particles is prepared by the same method and procedure as in Sample No. 1, and then the pH adjuster is adjusted so that the pH is 13 as in Sample No. 1. The pH was adjusted with and the suspension was kept at a temperature of 60 ° C.

  Next, while stirring the suspension solution using a stirring blade, sodium sulfide as a sulfur component-containing material is added to the suspension solution, each metal particle and sodium sulfide are reacted, then filtered and washed with water. After drying, metal powders of sample numbers 41 to 43 were obtained.

  As the metal particles, Ag particles, Cu particles, and Ni particles having an average particle diameter of 0.2 μm were prepared.

  And using these metal particles, the metal powder of sample numbers 44-46 which did not perform a reduction process and the addition process of a sulfur containing material by the method and procedure similar to the sample number 2 was produced.

Next, using the metal powder of sample numbers 41 to 46, the conductive paste of sample numbers 41 to 46 and the multilayer ceramic capacitor were prepared by the same method and procedure as in Example 1. However, each sample of the metal powder being Ni powder and Cu powder was fired in a reducing atmosphere composed of H ₂ —N ₂ —H ₂ O gas having an oxygen partial pressure adjusted to 10 ⁻¹⁰ MPa.

  Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the state of occurrence of structural defects was further evaluated.

  Table 4 shows the preparation conditions and measurement / evaluation results of the samples Nos. 41 to 46.

  Since sample numbers 44 to 46 use metal particles (Ag particles, Cu particles, Ni particles) that are not subjected to reduction treatment or addition treatment of sulfur-containing materials, sulfides are formed on the surfaces of the metal particles. However, for the same reason as Sample No. 2 (see Example 1), the number of occurrences of structural defects increased and the evaluation results were poor.

  On the other hand, sample numbers 41 to 43 use metal particles (Ag particles, Cu particles, Ni particles) subjected to reduction treatment and addition treatment of sodium sulfide. Sulfides were formed on the surface, and as a result, the structural defect occurrence rate was less than 1%, and good results were obtained.

  And it was confirmed that the production method of the present invention can be applied to Ag, Cu, and Ni other than Pd as well as Pd.

  Metal powders of Sample Nos. 51 to 59 were prepared by the same method and procedure as Sample No. 1 except that the amount of sodium sulfide added as a sulfur-containing material was varied.

  Then, using these metal powders, the conductive paste of Sample Nos. 51 to 59 and the multilayer ceramic capacitor were produced by the same method and procedure as in Example 1.

  Subsequently, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, the electrode coverage was further measured, and the occurrence state of structural defects was evaluated.

  Table 5 shows the production conditions and the measurement / evaluation results of the samples Nos. 51 to 59.

  In Sample No. 51, sulfide was formed, the electrode coverage was as good as 72%, and the structural defect occurrence rate was less than 5%, but the sulfur concentration in the metal powder was as low as 0.001% by mass. The structural defect generation rate was 3% or more, and the number of structural defects generated was slightly increased. This is because when the sulfur concentration in the metal powder is as low as 0.001% by mass, it becomes difficult to coat the surface of the Pd particles with sulfide, and the exposed Pd particles come into contact with the binder resin, and the catalytic action of the Pd particles. This is considered to cause a rapid combustion of the binder resin.

  On the other hand, since the sample numbers 52 to 59 have the sulfur concentration in the metal powder in the range of 0.01 to 5% by mass, the structural defect generation rate can be suppressed to less than 3%. Further, it was found that the structural defect occurrence rate can be suppressed to less than 1% when the sulfur concentration is in the range of 0.05 to 2% by mass, and a more reliable multilayer ceramic capacitor can be obtained.

  Thus, from the viewpoint of further suppressing the occurrence rate of structural defects, it is confirmed that the sulfur concentration in the metal powder is preferably 0.01 to 5% by mass, more preferably 0.05 to 2% by mass. It was done.

  In addition, when the sulfur concentration is 5% by mass, the electrode coverage is reduced to 67%. Therefore, it is considered that when the sulfur concentration exceeds 5% by mass, the electrode coverage is further decreased. However, when the sulfur concentration increases, the sulfur component increases in the conductive material and the ratio of the metal component decreases. For this reason, it seems that the electrode coverage ratio is reduced.

  Metal powders of Sample Nos. 61 to 67 were prepared by the same method and procedure as Sample No. 1 except that Pd particles having different average particle diameters were used as the metal particles.

  Then, using these metal powders, the conductive pastes of Sample Nos. 61 to 67 and the multilayer ceramic capacitor were produced by the same method and procedure as in Example 1.

  Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the occurrence state of structural defects was evaluated.

  Table 6 shows the production conditions and the measurement / evaluation results of the samples Nos. 61 to 67.

  In sample No. 61, sulfide was formed and the structural defect occurrence rate was less than 5%. However, the average particle size of Pd particles was as small as 0.005 μm, so the structural defect occurrence rate was 3% or more. The number of defects was slightly increased. When the average particle size becomes as small as about 0.005 μm, the specific surface area of the Pd particles increases, and in order to cover the surface of all the Pd particles with sulfide, it is necessary to increase the sulfur concentration. Therefore, in sample No. 61, the sulfur concentration was increased to 1.0 mass%, but it was found that it was still difficult to coat the entire surface of the Pd particles with sulfide.

  On the other hand, in Sample Nos. 62 to 67, the average particle size of Pd particles is in the range of 0.01 to 2 μm. % Could be suppressed. Also, the structural defect occurrence rate can be suppressed to less than 1% when the average particle size is in the range of 0.05 to 2% by mass, and a highly reliable multilayer ceramic capacitor in which the number of structural defects is further reduced can be obtained. I understood.

  Thus, from the viewpoint of further suppressing the occurrence rate of structural defects, it was confirmed that the average particle size of the Pd particles is preferably 0.01 μm or more, more preferably 0.1 μm or more.

  As is clear from the comparison between Sample No. 66 and Sample No. 67, when the average particle size is 1 μm or more, good results are obtained for the occurrence of structural defects without increasing the sulfur concentration. The average particle size of the metal particles is considered to be preferably 1 μm or less.

  The same method as Sample No. 1 except that Ni particles having an average particle diameter of 0.2 μm and 0.4 μm were used as metal particles, and the pH of the suspension solution was varied using a pH adjuster. The metal powder of sample numbers 71-76 was produced by the procedure.

  Then, using these metal powders, conductive pastes of sample numbers 71 to 76 and multilayer ceramic capacitors were produced by the same method and procedure as in Example 1.

  Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the occurrence state of structural defects was evaluated.

  Table 7 shows the production conditions and the measurement / evaluation results for the samples Nos. 71 to 76.

  In sample No. 71, sulfide was formed and the structural defect occurrence rate was less than 5%, but the pH of the suspension solution was as low as 2, so the structural defect occurrence rate was 3% or more, and the occurrence of structural defects occurred. The number increased slightly. This is presumably because in Sample No. 71, the suspension solution was strongly acidic, so that some of the Ni particles were dissolved in the suspension solution, resulting in a metal powder in which the surface of the Ni particles was not coated with sulfide.

  On the other hand, Sample Nos. 72 to 76 were able to suppress the structural defect occurrence rate to less than 3% because the pH of the suspension solution was adjusted to 5 or higher. Further, it was found that the structural defect occurrence rate can be suppressed to less than 1% when the pH of the suspension solution is 7 or more, and a highly reliable multilayer ceramic capacitor in which the number of structural defects generated is further reduced can be obtained. .

  Thus, from the viewpoint of further suppressing the occurrence rate of structural defects, the pH is preferably in a range where the metal particles do not dissolve in the suspension solution, that is, the pH is preferably higher than 2, more preferably higher than 5. It was confirmed that it was good.

  Metal powders of Sample Nos. 81 to 87 were prepared by the same method and procedure as Sample No. 1 except that the reaction temperatures of Pd particles and sodium sulfide were varied.

  Then, using these metal powders, conductive pastes of sample numbers 81 to 87 and a multilayer ceramic capacitor were produced by the same method and procedure as in Example 1.

  Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the state of occurrence of structural defects was further evaluated.

  Table 8 shows the production conditions and measurement / evaluation results of the samples Nos. 81 to 87.

  In Sample No. 81, sulfide was formed and the structural defect occurrence rate was less than 5%, but the reaction temperature was as low as 10 ° C., so the structural defect occurrence rate was 3% or more, and the number of structural defects generated was Slightly more. Since the reaction temperature is as low as 10 ° C., it is considered that the reduction reaction or the sulfide formation reaction in the suspension solution does not proceed easily. Therefore, it is considered that the entire surface of the Pd particles could not be covered with the sulfide.

  On the other hand, in Sample No. 87, sulfide was formed and the structural defect occurrence rate was less than 5%, but the reaction temperature was as high as 300 ° C. Therefore, the structural defect occurrence rate was 3% or more, and the occurrence of structural defects occurred. The number increased slightly. Since the reaction temperature is as high as 300 ° C., it is considered that the sulfide formation reaction locally progressed, so that the surface of the Pd particles could not be uniformly coated with sulfide.

  On the other hand, since the sample numbers 82-86 have adjusted the reaction temperature to 20-200 degreeC and an appropriate temperature range, they could suppress the structural defect generation rate to less than 3%. Further, it was found that in the range of 60 to 200 ° C., the structural defect occurrence rate can be suppressed to less than 1%, and a highly reliable multilayer ceramic capacitor in which the number of structural defects generated is further reduced can be obtained.

  Thus, from the viewpoint of further suppressing the occurrence rate of structural defects, it was confirmed that the reaction temperature is preferably 20 to 200 ° C, more preferably 60 to 200 ° C.

  In the said Examples 1-8, although the effect of this invention at the time of using a metal particle was confirmed, it replaced with a metal particle and the metal salt was used in the following Examples 9-16, and the effect of this invention was confirmed. did.

[Sample preparation]
(Sample No. 91)
First, hydrazine hydrate: 300 g (hydrazine concentration: 60% by weight) is added to a sodium hydroxide aqueous solution in which 240 g of sodium hydroxide is dissolved in 700 ml of water, and further water is added to reduce the total amount of the reducing agent aqueous solution to 1500 mL. Adjusted.

Also, nickel sulfate hexahydrate (NiSO ₄ .6H ₂ O): 517 g and copper sulfate pentahydrate (CuSO ₄ .5H ₂ O): 0.05 g, trisodium citrate as complexing agent: 0 .9 mol was dissolved in water, whereby a total amount of 1500 mL of a metal salt solution containing nickel ions and a complexing agent was prepared.

  The reducing agent solution and the metal salt solution are each heated to 60 ° C. on a hot water bath, and then the metal salt solution is added to the reducing agent solution to react the hydrazine with nickel sulfate / hexahydrate to produce nickel. Ions were reduced to prepare a suspension solution in which Ni particles were generated.

  Thereafter, the pH of the suspension is adjusted to 13 using a pH adjuster, and sodium sulfide is added while warming to 60 ° C. on a hot water bath, thereby removing Ni particles and sodium sulfide. A reaction solution containing metal powder was obtained by reaction. The reaction solution was filtered, washed with water, and dried to obtain a metal powder of sample number 91.

  And after observing the metal powder after this reaction with a scanning electron microscope (SEM) and analyzing the image to determine the average powder diameter, the average powder diameter was 0.2 μm.

  Thereafter, using this metal powder, a conductive paste was produced by the same method and procedure as in Sample No. 1, and a multilayer ceramic capacitor of Sample No. 91 was obtained using the conductive paste.

(Sample No. 92)
The nickel sulfate hexahydrate was reduced with hydrazine in the same method and procedure as sample number 91 to produce Ni particles, and then heated to 60 ° C. in a hot water bath, using a pH adjuster. The pH was adjusted to 13 to obtain a suspension solution. The suspension was then filtered, washed with water, and dried to obtain a metal powder of sample number 92.

  As for Sample No. 91, the average powder diameter of this metal powder was 0.2 μm.

  Thereafter, a conductive paste was prepared by the same method and procedure as in Example 1, and a multilayer ceramic capacitor of sample number 92 was obtained using the conductive paste.

(Sample No. 93)
Nickel sulfate hexahydrate was reduced with hydrazine by the same method and procedure as Sample No. 91 to produce Ni particles.

  Next, a hydrazine solution (hydrazine concentration: 5% by weight) is added to the powder of Ni particles, and then heated to 60 ° C. on a hot water bath, and the pH is adjusted to 13 using a pH adjuster. A cloudy solution was obtained. Then, this suspension solution was filtered and dried to obtain a metal powder of sample number 93.

  And also about this metal powder, when the average powder diameter was calculated | required similarly to the sample number 91, the average powder diameter was 0.2 micrometer.

Thereafter, using this metal powder, a conductive paste was prepared by the same method and procedure as in Example 1, and a multilayer ceramic capacitor of Sample No. 93 was obtained using the conductive paste.
(Sample No. 94)
Nickel sulfate hexahydrate is reduced with hydrazine by the same method and procedure as Sample No. 91 to prepare Ni particles, then heated to 60 ° C. in a hot water bath, and pH adjusted using a pH adjuster. Was adjusted to 13 to obtain a suspension.
Then, sodium sulfide was added while heating this suspension solution at 60 ° C. on a hot water bath, thereby reacting Ni particles with sodium sulfide to obtain a reaction solution containing metal powder. The reaction solution was filtered, washed with water, and dried to obtain a metal powder of sample number 94.
As for Sample No. 91, the average powder diameter of this metal powder was 0.2 μm.
Thereafter, a conductive paste was prepared by the same method and procedure as in Example 1, and a multilayer ceramic capacitor of sample number 94 was obtained using the conductive paste.
Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the occurrence state of structural defects was evaluated.
Table 9 shows the preparation conditions and measurement / evaluation results of the samples Nos. 91 to 94.

Sample No. 92 uses Ni particles that have not been subjected to reduction treatment or sulfur compound addition treatment, so that no sulfide is formed on the surface of the Ni particles, which is the same as Sample No. 2 in Example 1. For this reason, the number of structural defects generated increased, and the evaluation results were poor.
Sample No. 93 has been subjected to a reduction treatment, but has not been subjected to the addition treatment of the sulfur-containing material to the Ni particles. For the same reason as Sample No. 2, the number of occurrences of structural defects increased, and the evaluation results Became bad.
In Sample No. 94, although the addition treatment of sodium sulfide was performed, the reduction treatment was not performed on the Ni particles. Therefore, the number of structural defects generated increased for the same reason as Sample No. 4 in Example 1, and the evaluation was performed. The result was bad.
On the other hand, sample No. 91 was formed by adding sodium sulfide in the presence of a reducing agent after reducing the nickel sulfate hexahydrate, thereby forming a sulfide on the surface of the Ni particles. It was found that the structural defect occurrence rate was good at less than 1%, and therefore a highly reliable multilayer ceramic capacitor having a good electrode coverage and a reduced number of structural defect occurrences was obtained.

Ni particles were reduced and produced by the same method and procedure as in Sample No. 91, the pH was adjusted with a pH adjusting agent so that the pH was 13, and the suspension was kept at a temperature of 60 ° C.
Next, the sulfur containing material shown in Table 10 was prepared. Then, while stirring the suspension solution using a stirring blade, the sulfur component-containing material is added to the suspension solution, the Ni particles and the sulfur-containing material are reacted, then filtered and washed with water, and then dried. As a result, metal powders of sample numbers 101 to 106 were obtained.
Then, using this metal powder, the conductive pastes of sample numbers 101 to 106 and the multilayer ceramic capacitor were produced by the same method and procedure as in Example 1.
Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the state of occurrence of structural defects was further evaluated.
Table 10 shows the production conditions and the measurement / evaluation results of the samples Nos. 101 to 106.

  As is apparent from Table 10, as the sulfur-containing material, various sulfides such as ammonium sulfide, sulfur alone, water sulphides such as sodium hydrosulfide and ammonium hydrosulfide, polysulfides such as sodium polysulfide and ammonium polysulfide, Even when single sulfur was used, it was found that sulfide was formed on the surface of Ni particles and the rate of occurrence of structural defects was less than 1%, as in the case of sodium sulfide, and good results were obtained.

Metal powders of sample numbers 111 to 114 were prepared in the same manner as sample number 91 except that Ni particles were prepared using the reducing agent shown in Table 11. However, the reaction between the Ni particles and sodium sulfide was performed while maintaining the temperature at 60 ° C. for samples 111 to 113 and maintaining the temperature at 150 ° C. for sample number 114.
Then, using this metal powder, the conductive pastes of Sample Nos. 111 to 114 and the multilayer ceramic capacitor were produced by the same method and procedure as in Example 1.
Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the state of occurrence of structural defects was further evaluated.
Table 11 shows the production conditions and measurement results of the samples Nos. 111 to 114.

  As is apparent from Table 11, even when titanium trichloride, hypophosphite, sodium borohydride, or hydrogen gas is used as the reducing agent, the surface of the Ni particles is the same as in the case of hydrazine. It was found that sulfide was formed and the structural defect occurrence rate was less than 1%, and good results were obtained.

Nitrate as the metal salt (AgNO _3), copper sulfate pentahydrate _{(CuSO 4 · 5H 2 O)} , were prepared palladium sulfate (PdSO _4).
Next, the metal particles are reduced and produced in substantially the same manner and procedure as in sample number 91, and then, as in sample number 91, the pH is adjusted with a pH adjusting agent so that the pH is 13, and the suspension solution is further added. The temperature was kept at 60 ° C.
Next, while stirring the suspension solution using a stirring blade, sodium sulfide as a sulfur component-containing material is added to the suspension solution to react the metal particles with sodium sulfide, and then filtered and washed with water. And dried, thereby obtaining metal powders of sample numbers 121 to 123.
Moreover, the metal powder of the sample numbers 124-126 which did not perform the reduction process and the addition process of a sulfur containing material by the method and procedure similar to the sample number 92 using the said metal salt was produced.
Next, using this metal powder, the conductive paste of Sample Nos. 121 to 126 and the multilayer ceramic capacitor were produced by the same method and procedure as in Example 1.
Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the occurrence state of structural defects was evaluated.
Table 12 shows the preparation conditions and measurement / evaluation results of the samples Nos. 121 to 126.

Since sample numbers 124 to 126 use solid metal particles (Ag particles, Cu particles, Ni particles) that are not subjected to reduction treatment or addition treatment of sulfur compounds, sulfides are formed on the surfaces of the metal particles. For the same reason as Sample No. 2 (see Example 1), the number of structural defects generated was large, and the evaluation results were poor.
On the other hand, Sample Nos. 121 to 123 use metal powder that has been subjected to reduction treatment and addition treatment of sodium sulfide, and as in Sample No. 1, sulfide is formed on the surface of the metal particles. The structural defect occurrence rate was also less than 1%, and it was found that good results were obtained.
Thus, it was confirmed that the production method of the present invention can be applied to Ag, Cu, and Ni other than Pd.

Metal powders of Sample Nos. 131 to 138 were prepared by the same method and procedure as Sample No. 91, except that the amount of sodium sulfide added as a sulfur-containing substance was varied.
Then, using these metal powders, conductive pastes of sample numbers 131 to 138 and multilayer ceramic capacitors were produced by the same method and procedure as in Example 1.
Subsequently, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, the electrode coverage was further measured, and the occurrence state of structural defects was evaluated.
Table 13 shows the production conditions and the measurement / evaluation results of the samples Nos. 131 to 138.

In Sample No. 131, sulfide was formed, the electrode coverage was as good as 74%, and the structural defect occurrence rate was less than 5%, but the sulfur concentration in the metal powder was as low as 0.001% by mass. For the same reason as Sample No. 51 in Example 5, the structural defect occurrence rate was 3% or more, and the number of structural defects generated was slightly increased.
On the other hand, since the sample numbers 132 to 138 have a sulfur concentration in the metal powder in the range of 0.01 to 5% by mass, the structural defect occurrence rate can be suppressed to less than 3%. In addition, the structural defect occurrence rate can be suppressed to less than 1% when the sulfur concentration is in the range of 0.05 to 2% by mass, and a highly reliable multilayer ceramic capacitor in which the number of structural defects generated is further reduced can be obtained. I understood.
Thus, the same results as in Example 5 were obtained when the metal salt was used as the starting material.

The addition amount of the complexing agent (trisodium citrate) contained in the suspension solution was varied, thereby producing metal powders of sample numbers 141 to 146 having different average powder diameters.
Then, using these metal powders, the conductive pastes of sample numbers 141 to 146 and the multilayer ceramic capacitor were produced by the same method and procedure as in Example 1.
Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the occurrence state of structural defects was evaluated.
Table 14 shows the production conditions and the measurement / evaluation results of the samples Nos. 141 to 146.

Sample No. 141 was formed with sulfide and had a structural defect occurrence rate of less than 5%. However, the average powder diameter of the metal powder was as small as 0.005 μm, and it was structured for the same reason as Sample No. 61 in Example 6. The defect generation rate was 3% or more, and the number of structural defects generated was slightly increased.
On the other hand, sample numbers 142 to 146 have an average powder diameter of Ni in the range of 0.01 to 1 μm, so that the structural defect occurrence rate can be suppressed to less than 3%. Moreover, the structural defect occurrence rate can be suppressed to less than 1% when the average powder diameter is in the range of 0.1 to 1% by mass, and a highly reliable multilayer ceramic capacitor in which the number of structural defects is further reduced can be obtained. I understood.

Metal powders of Sample Nos. 151 to 157 were prepared by the same method and procedure as Sample No. 91, except that the pH of the suspension was varied using a pH adjuster.
Then, using these metal powders, the conductive pastes of sample numbers 151 to 157 and the multilayer ceramic capacitor were produced by the same method and procedure as in Example 1.
Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the state of occurrence of structural defects was further evaluated.
Table 15 shows the production conditions and the measurement / evaluation results of the samples Nos. 151 to 157.

Sample Nos. 151 and 152 had sulfides formed and the structural defect occurrence rate was less than 5%, but the pH of the suspension was as small as 2 or less, and the structure was the same as for Sample No. 71 in Example 7. The defect generation rate was 3% or more, and the number of structural defects generated was slightly increased.
On the other hand, since the sample numbers 153 to 157 adjusted the pH of the suspension to 5 or more, the structural defect generation rate could be suppressed to less than 3%. Further, it was found that the structural defect occurrence rate can be suppressed to less than 1% when the pH of the suspension solution is 7 or more, and a highly reliable multilayer ceramic capacitor in which the number of structural defects generated is further reduced can be obtained. .
Thus, as in Example 7, from the viewpoint of further suppressing the occurrence rate of structural defects, it was confirmed that the pH is preferably higher than 2, more preferably higher than 5. .

Metal powders of Sample Nos. 161 to 167 were prepared by the same method and procedure as Sample No. 91 except that the reaction temperatures of Ni particles and sodium sulfide were varied.
Then, using these metal powders, the conductive pastes of Sample Nos. 161 to 167 and the multilayer ceramic capacitor were produced by the same method and procedure as in Example 1.
Next, the sulfur concentration was measured by the same method and procedure as in Example 1, the presence or absence of sulfide formation was confirmed, and the state of occurrence of structural defects was further evaluated.
Table 16 shows the production conditions and measurement / evaluation results of the samples Nos. 161 to 167.

In Sample No. 161, sulfide was formed and the structural defect occurrence rate was less than 5%, but the reaction temperature was as low as 10 ° C., and the structural defect occurrence rate was 3 for the same reason as Sample No. 81 in Example 8. % Or more, and the number of structural defects generated was slightly increased.
On the other hand, in Sample No. 167, sulfide was formed and the structural defect occurrence rate was less than 5%, but the reaction temperature was as high as 300 ° C., and the structural defect occurrence rate was the same as in Sample No. 87 in Example 8. Was 3% or more, and the number of structural defects generated was slightly increased.
On the other hand, since the sample numbers 162 to 166 have the reaction temperature adjusted to an appropriate temperature range of 20 to 200 ° C., the structural defect generation rate can be suppressed to less than 3%. Furthermore, it was found that in the range of 60 to 200 ° C., the structural defect occurrence rate can be suppressed to less than 1%, and a highly reliable multilayer ceramic capacitor in which the number of structural defects generated is further reduced can be obtained.
Thus, like Example 8, from the viewpoint of further suppressing the occurrence rate of structural defects, it was confirmed that the reaction temperature was preferably 20 to 200 ° C, more preferably 60 to 200 ° C.

  Even when used as a conductive material for internal electrodes for multilayer ceramic electronic components, metal particles do not condense during metal powder production, and binder resin does not cause rapid combustion during degreasing, ensuring good electrode coverage In addition, the generation of structural defects can be suppressed.

DESCRIPTION OF SYMBOLS 1 Metal powder 2 Metal particle 3 Metal compound 6 Oxide film 7 Ceramic body 8a-8f Internal electrode

Claims (14)

  After the metal particles having an oxide film formed on at least a part of the surface are treated with a reducing agent, the metal particles and the sulfur component are reacted by bringing the metal particles into contact with the sulfur component in the presence of the reducing agent. And at least a part of the surface of the metal particles is coated with a metal compound containing the sulfur component.   The method for producing metal powder according to claim 1, wherein the metal particles contain at least one of Ni, Ag, Cu, and Pd.   A metal salt solution containing metal ions is treated with a reducing agent to produce a redox reaction to produce metal particles, and then in the presence of the reducing agent, the metal particles and a sulfur component are brought into contact with each other to form the metal. A method for producing a metal powder, comprising reacting particles with the sulfur component and coating at least a part of the surface of the metal particle with a metal compound containing the sulfur component.   The said metal ion contains at least 1 sort (s) of Ni ion, Ag ion, Cu ion, and Pd ion, The manufacturing method of the metal powder of Claim 3 characterized by the above-mentioned.   The sulfur component is added to the metal particles in the form of an inorganic sulfur-containing material containing at least one or more of a sulfide group including sulfur alone, hydrosulfide, and polysulfide. The manufacturing method of the metal powder in any one of Claims 1 thru | or 4.   6. The method for producing a metal powder according to claim 1, wherein the metal compound contains a sulfide as a main component.   The method for producing a metal powder according to any one of claims 1 to 6, wherein the sulfur component in the metal powder is 0.01 to 5% by mass in terms of concentration.   The method for producing a metal powder according to claim 1, wherein an average powder diameter of the metal powder is 0.01 μm or more.   The method for producing a metal powder according to any one of claims 1 to 8, wherein the reaction between the metal particles and the sulfur component is performed in a solution having a pH exceeding 2.   The method for producing a metal powder according to any one of claims 1 to 9, wherein the reaction between the metal particles and the sulfur component is performed at a temperature of 20 to 200 ° C.   The reducing agent is at least selected from hydrazine, borohydride compounds, titanium halides, hypophosphites, phosphites, aldehydes, ascorbic acid, hydrogen gas, alcohols, polyhydric alcohols. The method for producing a metal powder according to claim 1, wherein the metal powder is one type.   A metal powder produced by using the production method according to any one of claims 1 to 11. A conductive paste containing at least a conductive material, a binder resin, and a solvent,
A conductive paste, wherein the conductive material is formed of the metal powder according to claim 12. A multilayer ceramic electronic component in which an internal electrode is embedded in a ceramic body,
The multilayer ceramic electronic component, wherein the internal electrode is formed by sintering the conductive paste according to claim 13.

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