JP2018141180A - Nickel-coated copper powder, method for producing the same, and conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide fine, high-crystal nickel-coated copper powder combining sinterability and oxidation resistance and further excellent in weatherability.SOLUTION: Provided is nickel-coated copper powder obtained by coating the surfaces of copper particles with nickel or a nickel alloy, in which the average particle diameter of the primary particles measured by a scan type electron microscope is 0.1 to 3.0 μm, the relative standard deviation value of the particle diameter as a value obtained by dividing the standard deviation of the primary particles with the average particle diameter is 0.3 or lower, and the value obtained by dividing the crystalline diameter of the copper particles with the average particle diameter is 0.07 or higher. The nickel-coated powder is produced by mixing a copper compound solution, a hydroxide solution of an alkali metal and a dispersant solution to produce a copper salt solution, retaining the copper salt solution and the reducer solution to the temperature range of 50 to 90°C, performing mixing while adding the reducer solution to the copper salt solution to produce copper particles, and next coating the obtained copper particles with nickel or a nickel alloy.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a copper powder (nickel-coated copper powder) coated with nickel (Ni) or a nickel alloy on the surface, a method for producing the same, and a conductive paste. More specifically, the present invention is suitably used as a material such as a conductive paste. The present invention relates to a fine and highly crystalline nickel-coated copper powder having both sinterability and oxidation resistance, a method for producing the same, and a conductive paste.

  Conventionally, metal powder has been used as a wiring forming material for electronic parts such as conductive paste for printed wiring, semiconductor internal wiring, connection between a printed wiring board and electronic parts, and the like. In recent years, in the fields of solar cell electrodes, LEDs, and the like, demand for thinning of wiring has increased, and therefore metal powders for conductive paste that can cope with thinning are demanded.

  In order to form wiring layers, electrodes, and the like in electronic devices, conductive pastes using metal fillers such as silver powder and copper powder, such as resin pastes and fired pastes, are frequently used. The resin-type conductive paste is made of a metal filler, a resin, a curing agent, a solvent, etc., printed on a conductor circuit pattern or terminal, and cured by heating at 100 ° C. to 200 ° C. to form a conductive film. Form. In the resin-type conductive paste, since the thermosetting resin is cured and contracted by heat, the metal fillers are pressed and brought into contact with each other, so that the metal fillers overlap each other, and as a result, an electrically connected current path is formed. . Furthermore, since the metal powder generally has a higher sinterability as the particle size becomes finer, the use of a metal filler having a smaller particle size also increases the sintering effect and lowers the resistance. Since this resin-type conductive paste is processed at a curing temperature of 200 ° C. or lower, it is used for a substrate using a heat-sensitive material such as a printed wiring board.

  Firing type conductive paste is made of a metal filler, glass, solvent, etc., printed on a conductor circuit pattern or terminal, and heated and fired at a high temperature of 600 ° C. to 800 ° C. to form a conductive film. Form. In the firing type conductive paste, it is processed at a high temperature, and the metal filler is sintered to ensure conductivity. Firing-type conductive paste is processed at such a high firing temperature, so it cannot be used for printed wiring boards that use resin materials, but the metal filler sinters during high-temperature processing, resulting in low resistance. it can. Therefore, the fired conductive paste can be suitably used for an external electrode of a multilayer ceramic capacitor.

  Moreover, the paste using the metal filler of silver powder or copper powder is applied or printed on various base materials, and is subjected to heat curing or heat baking treatment to form a conductive film to be a wiring layer or an electrode. Conventionally, silver powder has been mainly used. However, since the price of silver bullion is expensive, alternatives to copper powder are being actively investigated.

  When copper powder as a metal powder material used as a metal filler of such conductive paste is used, it is oxidized and the surface is covered with copper oxide, which adversely affects sinterability, corrosion resistance, weather resistance or conductivity. Sometimes. For this reason, in order to prevent oxidation of the copper powder, the surface of the copper particles is coated with a noble metal such as platinum, palladium, silver, gold, etc., coated with a silica-based oxide, or coated with nickel to resist oxidation. Those with improved chemical properties are known.

  However, if a noble metal is coated on the surface of the copper powder, the cost increases because these noble metals are expensive. Among them, the copper powder coated with silver can be kept at a relatively low price, but silver has a problem that migration is likely to occur. Moreover, although the copper powder coated with the oxide can ensure oxidation resistance, it has problems such as poor sinterability. Therefore, for example, nickel powder is coated on the copper powder disclosed in Patent Document 1 as a low-cost and relatively good weather resistance and sinterability while ensuring oxidation resistance and the like. The method is drawing attention.

  As a method for coating the surface of the copper powder with nickel, a method by electroless nickel plating may be mentioned. The coating method by electroless nickel plating is to perform nickel coating on the copper powder surface by reducing nickel ions in the plating solution with a reducing agent. The types of reducing agents are hypophosphites and borohydrides. And hydrazine compounds. Specifically, in the nickel coating treatment using hypophosphite as the reducing agent, phosphorus (P) is included in the coating during the reduction reaction, so that a Ni-P alloy coating is formed. Further, in the nickel coating treatment using a borohydride compound as a reducing agent, boron (B) is included in the coating during the reduction reaction, and thus a Ni-B alloy coating is formed. Further, in the nickel coating process using a hydrazine compound as a reducing agent, a high-purity Ni coating with few impurities is formed.

  The copper powder as a raw material for coating the surface of such nickel is a copper powder having a granular shape, a uniform particle size of 0.1 μm to 3.0 μm, and excellent in oxidation resistance. However, it has been difficult to produce such copper powder by a production method suitable for industrial mass production. Therefore, there is a demand for a method suitable for industrial mass production that can efficiently produce copper powder that has the above-described characteristics and that is useful for a conductive paste suitable for thinning of wiring.

  Candidates for such a production method include an electrolytic method in which an electrolytic solution containing copper ions is electrolyzed to deposit copper powder on the cathode, a copper raw material is melted, and the molten metal is made into droplets to rapidly cool and solidify. There are known an atomizing method for producing copper powder by making it, a wet method for producing a copper powder by adding a reducing agent in a solution, and the like. These manufacturing methods are employed as industrial production methods because of their high productivity and low manufacturing costs.

  Here, the copper powder obtained by the electrolysis method has a feature that it becomes highly pure, but most of the electrolytic copper powder is precipitated in a dendritic shape and has a coarse particle size of 10 μm or more. Prone. In addition, the particle size distribution is wide and the conductive paste is not suitable for applications such as wiring that requires particularly low resistance.

  In addition, the atomizing method is a method in which a jet fluid is blown into a molten metal melted at a high temperature to form a fine powder as shown in Patent Document 2, for example, and impurities are included when the metal is melted. There is a problem that it is easy to be oxidized, is easily oxidized when sprayed, and copper fine particles of 1 μm or less cannot be produced.

  As described above, the copper powder obtained by the atomization method and the electrolytic method has a grain size of 2 μm or more and is inferior in sinterability, so it is difficult to have low resistance. There are drawbacks such as inferiority, and the field of use as a conductive paste is limited. Furthermore, Patent Document 3 discloses metal copper particles having a BET diameter of 3 μm or less, a spherical shape, and a crystallite size of 0.1 μm to 10 μm. According to the method described in Patent Document 3, it is possible to produce a copper powder having a large crystallite diameter, but in observation of a scanning electron micrograph, particles of 0.3 μm to 7 μm are observed, Particles having a particle size exceeding 3 μm are mixed. As described above, since copper particles having a particle size of 0.1 μm to 3.0 μm are required as the copper powder used in the thin wire copper paste, the use of the copper particles described in Patent Document 3 It becomes difficult. Furthermore, this manufacturing method is a method in which ammonia gas is blown into copper melted at 1120 ° C. or higher, and is not a manufacturing method suitable for industrial mass production in that a harmful gas is used at a high temperature.

  On the other hand, the wet method is a method of reducing and precipitating copper ions or the like in a solution with a reducing agent. For example, Patent Document 4 includes a step of mixing a slurry of cuprous oxide powder with a mixed acid of hydroxycarboxylic acid and sulfuric acid and a step of stirring and holding the mixed solution, and mixing the cuprous oxide powder slurry and the mixed acid. Disclosed is a method for producing copper fine powder in which the time is less than 5 minutes, the average particle diameter of the obtained copper fine powder is 10 nm to 50 nm, and the ratio of the crystallite diameter to the average particle diameter is 0.5 or less. ing. However, in this manufacturing method, only copper particles having a particle size of 50 nm or less can be produced, and particles having a particle size of 50 nm or less are not easily pasted because of strong aggregation. Therefore, it becomes difficult to use the copper particles described in this document as the copper powder of the copper paste for fine wires.

  In addition, as shown in Patent Document 5, an alkali agent is added to a solution containing a copper salt and reacted to precipitate copper hydroxide, and then a reducing agent such as glucose is added to reduce to cuprous oxide. Further, a method has been proposed in which a secondary reducing agent such as hydrazine is further added to reduce the metal copper to obtain copper powder. Such a wet method has a feature that a very fine spherical copper fine powder of submicron can be produced. However, as in Patent Document 2, it is polycrystalline and has grain boundaries, resulting in poor oxidation resistance. The field of use is limited as a conductive paste.

  On the other hand, Patent Documents 6 and 7 propose a method for obtaining single crystal copper powder having a constant crystal orientation, but the main particle size is about 2 μm to 5 μm, and the curing temperature is 100 ° C. to 200 ° C. The resin type conductive paste does not satisfy the low resistance. On the other hand, if the curing temperature is 200 ° C. or higher in order to reduce the resistance, the oxidation resistance becomes insufficient.

  In Patent Document 6, in order to produce a copper powder having a regular octagonal pyramidal single crystal, a solution containing tartaric acid and alkali hydroxide in a molar ratio of 1 to 5 times the copper salt and copper is used. It is described that formaldehyde is added as a reducing agent within 1 minute.

  Moreover, since the manufacturing method of patent document 7 requires chelating agents, such as tartrate, in the molar ratio of 1 time-5 times with respect to copper, chemical | medical solution cost becomes high, and the cost of waste liquid processing also becomes high simultaneously. Therefore, there is also a problem that the manufacturing cost becomes high. Furthermore, there is a condition that formaldehyde as a reducing agent is added within 1 minute for reduction, which is not suitable for industrial mass production. On the other hand, the copper powder obtained by the method described in Patent Document 7 is highly crystalline but plate-like, has a high specific surface area and is easily oxidized, and the wiring edge becomes uneven. Not suitable for use.

  In general, when a conductive paste is used for an IC substrate, a printed circuit board, or the like, in order to form a fine pattern, for example, an acid resistance of 1% by mass or less at an oxidation increase of 200 ° C. in the atmosphere by thermogravimetric (TG) analysis. There is a demand for metal fillers that are excellent in chemical properties, fine, and have good dispersibility. In addition, the contact resistance when the resin is cured at a low temperature and contracted is reduced due to the heat resistance of the substrate, and when the filler is baked in the air, for example, the powder resistivity baked in the air is 500 μΩ · cm or less. Low resistance is required. However, in the case of metal powders, particularly copper powders, there is a tendency to oxidize more easily as the particle size becomes finer. Therefore, a method for obtaining copper powders that are fine and excellent in oxidation resistance is desired. It has been.

  Therefore, Patent Document 8 proposes a method for obtaining single crystal copper fine powder by gas phase reaction, and the obtained copper powder is chamfered polyhedron when observed using a scanning electron microscope (SEM). In addition, since the powder particles are single crystals, the surface is smooth, there are no defects, and the oxidation resistance is excellent. However, in the production of copper powder by gas phase reaction, cuprous chloride is reacted with a reducing gas at a high temperature of 700 ° C. or higher to obtain single crystal copper powder, which complicates the mechanism of the apparatus and increases production costs. Furthermore, there is a problem that the yield is poor, for example, the obtained copper powder is remelted and connected.

  Therefore, a fine copper powder excellent in oxidation resistance, nickel-coated copper powder with improved weather resistance is required without sinterability by covering the surface with nickel or a nickel alloy, There is also a need for a method suitable for industrially inexpensive production.

JP 2006-28630 A Japanese Patent No. 4342746 JP 2004-124257 A Japanese Patent No. 4687599 Japanese Patent No. 4406738 Japanese Patent Publication No.7-111592 JP 2014-58713 A Japanese Patent Publication No. 6-76609

  In view of the above-mentioned conventional problems, the present invention can be suitably used as a material such as a conductive paste, and has fine and highly crystalline nickel having both sinterability and oxidation resistance and excellent weather resistance. It aims at providing a coated copper powder, its manufacturing method, and an electrically conductive paste.

  This inventor repeated earnest examination in order to solve the subject mentioned above. As a result, a copper salt solution containing a dispersant was prepared, the temperature of the copper salt solution and the reducing agent aqueous solution was controlled within a specific range, the reducing agent solution was added to the copper salt solution, and the temperature By causing a reduction reaction while maintaining the conditions, it was possible to obtain copper particles (copper powder) having a uniform particle size of 0.1 μm to 3.0 μm and a large crystallite size. It has been found that nickel-coated copper powder with higher weather resistance can be obtained at a relatively low cost by coating the surface of the copper particles with nickel or a nickel alloy, and the present invention has been completed.

  (1) The first invention of the present invention is nickel-coated copper powder in which the surface of copper particles is coated with nickel or a nickel alloy, and the average particle size of primary particles measured by a scanning electron microscope is 0.00. 1 μm or more and 3.0 μm or less, the standard deviation value of the particle size of the primary particles divided by the average particle size is a relative standard deviation value of the particle size of 0.3 or less, and crystals of copper particles It is nickel coat copper powder whose value which remove | divided the child diameter by the said average particle diameter is 0.07 or more.

  (2) 2nd invention of this invention is nickel coat copper powder whose crystallite diameter of the said copper particle is 60 nm or more in 1st invention.

  (3) 3rd invention of this invention is nickel coat copper powder whose shape of the said nickel coat copper powder is a granular form in 1st or 2nd invention.

  (4) According to a fourth invention of the present invention, in any of the first to third inventions, the carbon content of the nickel-coated copper powder is 0.05% by mass or more and 0.5% by mass or less. Nickel-coated copper powder.

  (5) According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the coating amount of nickel or a nickel alloy is 1% by mass to 100% by mass of the entire nickel-coated copper powder. It is a nickel coat copper powder which is 33 mass%.

  (6) According to a sixth aspect of the present invention, in the fifth aspect, the surface of the copper particles is coated with a nickel alloy, and cobalt, zinc, tungsten, molybdenum, palladium, platinum, tin, phosphorus, and boron It is nickel coat copper powder coat | covered with the nickel alloy which contained at least 1 sort (s) chosen from 0.1 to 20 mass% with respect to 100 mass of the said nickel alloy.

  (7) According to a seventh aspect of the present invention, in any one of the first to sixth aspects, when heating is performed at a temperature rising rate of 10 ° C./min from room temperature in the atmosphere by measurement using a thermal analyzer. The nickel-coated copper powder has a 0.5% weight increase temperature exceeding 230 ° C.

  (8) An eighth invention of the present invention is a conductive paste formed by kneading the nickel-coated copper powder according to any one of the first to seventh inventions, a resin, and a solvent.

  (9) A ninth invention of the present invention is a method for producing nickel-coated copper powder in which the surface of copper particles is coated with nickel or a nickel alloy, comprising a solution containing a copper compound and an alkali metal hydroxide. A copper salt solution production step of producing a copper salt solution by mixing a solution containing and a solution containing a dispersant; and a copper particle production step of producing copper particles by mixing the copper salt solution and the reducing agent solution. And a nickel coating step of coating the copper particles with nickel or a nickel alloy, and in the copper particle generation step, the temperature of the copper salt solution and the reducing agent solution is in the range of 50 ° C. or more and 90 ° C. or less, It is a manufacturing method of nickel coat copper powder which mixes by adding this reducing agent solution to this copper salt solution.

  (10) According to a tenth aspect of the present invention, in the ninth aspect, in the copper salt solution preparation step, the amount of the dispersant added is 0.01% by mass or more based on the amount of copper in the copper compound. It is a manufacturing method of nickel coat copper powder made into the range of 10 mass% or less.

  (11) In an eleventh aspect of the present invention, in the ninth or tenth aspect, the dispersant is polyvinyl alcohol, polyethyleneimine, polyvinyl pyrrolidone, a modified silicone oil surfactant, or a polyether surfactant. It is a manufacturing method of nickel coat copper powder which is at least 1 sort chosen from.

  (12) A twelfth aspect of the present invention is the method for producing nickel-coated copper powder according to any one of the ninth to twelfth aspects, wherein the copper compound is copper sulfate pentahydrate.

  (13) The thirteenth aspect of the present invention is the method for producing nickel-coated copper powder according to any one of the ninth to twelfth aspects, wherein the alkali metal hydroxide is sodium hydroxide.

  (14) In a fourteenth aspect of the present invention, in any one of the ninth to thirteenth aspects, in the copper particle generation step, the amount of the reducing agent added is 1 with respect to the amount of copper in the copper compound. It is a manufacturing method of nickel coat copper powder made into an equivalent or more and 7 equivalent or less.

  (15) In a fifteenth aspect of the present invention, in any one of the ninth to fourteenth aspects, the reducing agent is one or more selected from organic compounds having a lactone structure, formalin, glucose, and polysaccharides. This is a method for producing a nickel-coated copper powder.

  (16) The sixteenth invention of the present invention is the method for producing nickel-coated copper powder in the fifteenth invention, wherein the reducing agent comprises one or more selected from ascorbic acid or a derivative thereof.

  (17) According to a seventeenth aspect of the present invention, in any one of the ninth to sixteenth aspects, the nickel-coated copper powder has a crystallite diameter of the nickel-coated copper powder, the nickel-coated copper powder It is a manufacturing method of nickel coat copper powder whose value divided by the average particle diameter of the primary particle measured by observation with a scanning electron microscope is 0.07 or more.

  (18) The eighteenth aspect of the present invention is the method for producing nickel-coated copper powder according to the seventeenth aspect, wherein the crystallite diameter of the copper particles is 60 nm or more.

  (19) According to a nineteenth aspect of the present invention, in the seventeenth or eighteenth aspect, the nickel-coated copper powder has a standard deviation value of a particle diameter of primary particles of the nickel-coated copper powder as the average particle diameter. It is a manufacturing method of nickel coat copper powder whose relative standard deviation value of the particle size which is the value which divided is 0.3 or less.

  (20) In a twentieth aspect of the present invention according to any one of the ninth to nineteenth aspects, in the nickel coating step, a coating amount of nickel or a nickel alloy on the copper particles It is a manufacturing method of nickel coat copper powder made into 1 mass%-33 mass% to mass 100%.

  (21) According to a twenty-first aspect of the present invention, in the twentieth aspect, in the nickel coating step, a surface of the copper particles is coated with a nickel alloy, and cobalt, zinc, tungsten, molybdenum, palladium, platinum, tin, The manufacturing method of the nickel coat copper powder which coat | covers the nickel alloy which contains at least 1 sort (s) chosen from phosphorus and boron in the ratio of 0.1 mass%-20 mass% with respect to 100 mass of the said nickel alloy It is.

  (22) In a twenty-second aspect of the present invention, in any one of the ninth to twenty-first aspects, the nickel-coated copper powder has a carbon content of 0.05% by mass or more and 0.5% by mass or less. Method for producing nickel-coated copper powder.

  (23) A twenty-third invention of the present invention is a method for producing a conductive paste, which is produced by kneading a nickel-coated copper powder, a resin, and a solvent according to any one of the first to seventh inventions. is there.

  According to the present invention, the shape is granular, the particle size is 0.1 μm to 3.0 μm, uniform, excellent in oxidation resistance, nickel or nickel alloy is coated on the surface, and weather resistance is also high. In addition, a nickel-coated copper powder and a method for producing the same can be provided. And the nickel coat | court copper powder can be used suitably as metal fillers, such as an electrically conductive paste used for wiring materials etc. Further, according to the method for producing nickel-coated copper powder according to the present invention, in the production of copper particles, since it is a method by a wet method, not a gas phase reaction that increases the production cost, a relatively inexpensive raw material, simple It can be manufactured by a simple process and is industrially low cost.

It is a SEM observation photograph figure of the copper powder (copper powder before nickel coating) obtained in Example 1. FIG.

  Hereinafter, specific embodiments of the present invention (hereinafter referred to as “present embodiments”) will be described in detail. However, the present invention is not limited to the following embodiments and does not depart from the gist of the present invention. As long as it can be changed as appropriate. In this specification, “X to Y” (X and Y are arbitrary numerical values) means “X or more and Y or less”.

<< 1. Nickel-coated copper powder >>
The nickel (Ni) -coated copper powder according to the present embodiment is obtained by coating the surface of copper particles with nickel or a nickel alloy, and the average particle diameter of primary particles measured by a scanning electron microscope (SEM) Is 0.1 μm or more and 3.0 μm or less, and the relative standard deviation value of the particle size, which is a value obtained by dividing the standard deviation value of the particle size of the primary particles by the average particle size, is 0.3 or less, and the copper particles The value obtained by dividing the crystallite diameter by the average particle diameter of the nickel-coated copper powder is 0.07 or more.

  More specifically, the nickel-coated copper powder has a granular shape, and the average particle size is in the range of 0.1 μm to 3.0 μm, more preferably 0.3 μm to 2.5 μm. It is a range. By using the nickel-coated copper powder having an average particle diameter in such a range, a conductive (nickel-coated copper powder) paste suitable for forming a thinned wiring can be obtained.

  Here, an average particle diameter is an average value calculated | required from the particle diameter of the primary particle which observed the fixed number nickel-coated copper powder with SEM, and was measured by the observation. The primary particles refer to those considered as unit particles from the SEM observation image, and do not mean so-called secondary particles formed by aggregation and bonding of the unit particles.

  When the average particle size of the nickel-coated copper powder is less than 0.1 μm, the particles are likely to aggregate and difficult to form a paste. On the other hand, when the average particle size exceeds 3.0 μm, it becomes difficult to narrow the line width when the wiring is formed by the paste containing the nickel-coated copper powder, and it is difficult to make the wiring thin. .

  The nickel-coated copper powder has a relative standard deviation value of 0.3 or less, which is a value obtained by dividing the standard deviation value of the primary particle diameter by the average particle diameter measured by the SEM described above. is there. When the relative standard deviation value of the particle diameter exceeds 0.3, the nickel-coated copper powder particles do not exist uniformly in the printed film, so that the thickness and thickness of the wiring and electrodes are not uniform. In addition, since the curing or firing is not uniform, the resistance of the conductive film is increased, and the conductive film tends to be brittle and weak.

  The nickel-coated copper powder has a value obtained by dividing the crystallite diameter of the copper particles by the average particle diameter measured by the SEM described above (the crystallite diameter of the copper particles / the average particle diameter of the nickel-coated copper powder) is 0. .07 or more. The crystallite diameter can be calculated from the X-ray diffraction result using the Scherrer method. The higher the index expressed by crystallite diameter / average particle diameter, the smaller the number of crystal grains of the copper particles constituting the nickel-coated copper powder, that is, the higher the crystallinity. As described above, the nickel-coated copper powder having a high crystallinity of crystallite diameter / average particle diameter of 0.07 or more as a core material improves the oxidation resistance by being coated with nickel. In addition, the crystal grain boundaries of the copper particles are reduced, making it difficult to oxidize. Although details are unknown, nickel coating or nickel alloy coating on the surface of copper particles with few crystal grain boundaries tends to have few grain boundaries and high crystallinity, and further improves oxidation resistance. Therefore, it becomes more desirable as a metal material for conductive paste.

  Here, the crystallite diameter of the copper particles constituting the nickel-coated copper powder according to the present embodiment is 60 nm or more, and preferably 130 nm or more. The upper limit value of the crystallite diameter is not particularly limited, but is preferably 900 nm or less.

  Further, the upper limit value of the crystallite diameter / average particle diameter value of the copper particles is not particularly limited, but is preferably 0.3 or less. The crystallite diameter / average particle diameter of the copper particles is more preferably 0.08 or more and 0.3 or less, and particularly preferably 0.1 or more and 0.2 or less.

  The nickel-coated copper powder according to the present embodiment preferably has a carbon content of 0.05% by mass or more and 0.5% by mass or less, and is 0.1% by mass or more and 0.4% by mass or less. It is more preferable. Carbon content shows the adhesion amount of the organic substance derived from the dispersing agent etc. in the nickel coat copper powder surface. As will be described later, in the present embodiment, when producing nickel-coated copper powder based on the copper particles and the copper particles, a dispersant is used as one of the purposes to suppress aggregation of the produced particles. Although it is used, agglomeration can be suppressed by attaching an appropriate amount of a dispersant to the surface of the obtained nickel-coated copper powder. Moreover, the dispersibility when it is set as the electrically conductive paste using the nickel coat copper powder can be improved.

  If the carbon content of the nickel-coated copper powder is less than 0.05% by mass, a sufficient aggregation suppressing effect cannot be obtained, and the desired dispersibility may not be obtained when a conductive paste is obtained. On the other hand, as the carbon content increases, the aggregation suppressing effect and the dispersibility improving effect increase, but the organic matter adhered to the surface of the nickel-coated copper powder is a nickel-coated copper powder when the conductive paste is heat-cured. This is a factor that hinders sintering. From this, when carbon content exceeds 0.5 mass%, sinterability may fall.

  Moreover, the nickel coat copper powder which concerns on this Embodiment is excellent in oxidation resistance, and is suitable as a nickel coat copper powder used for the electrically conductive paste for fine wires. Specifically, the oxidation resistance can be quantitatively evaluated by, for example, “0.5% weight increase temperature” by measurement using a thermal analyzer. In this nickel-coated copper powder, In addition, the 0.5% weight increase temperature exceeds 230 ° C. when heated from room temperature to 10 ° C./min in the atmosphere.

  In the nickel-coated copper powder having these shapes, the surface is a smooth surface, and when observed with a scanning electron microscope (SEM), the nickel-coated copper powder having this highly crystalline structure in the visual field. Accounts for 60% or more of the total number of nickel-coated copper powders. This number occupies a number of 70% or more, and more preferably 80% or more. If 60% or more of the total number of nickel-coated copper powders is such a nickel-coated copper powder, high sinterability and high oxidation resistance can be sufficiently exhibited as will be described later. The upper limit of the number of all nickel-coated copper powders is not limited, but is preferably 95% or less, for example.

  The nickel-coated copper powder according to this embodiment is preferably nickel or nickel at a ratio of 1% by mass to 33% by mass with respect to 100% by mass of the entire nickel-coated copper powder on the copper particles before being coated with nickel or a nickel alloy. The alloy is coated. As the thickness (coating thickness) of nickel or nickel alloy, for example, when the average particle diameter is 1 μm, it is an extremely thin film having a thickness of 0.05 μm or less, preferably 0.03 μm or less. For this reason, the nickel-coated copper powder retains the granular shape of the copper particles before being coated with nickel or a nickel alloy.

  As described above, the coating amount of nickel or nickel alloy in the nickel-coated copper powder is preferably in the range of 1% by mass to 33% by mass with respect to 100% by mass of the entire nickel-coated copper powder. The coating amount of nickel or nickel alloy is preferably as small as possible from the viewpoint of cost. However, if it is too small, a uniform nickel or nickel alloy coating cannot be secured on the surface of the copper particles, and improvement in weather resistance cannot be expected. Therefore, the coating amount of nickel or nickel alloy is preferably 1% by mass or more, more preferably 2% by mass or more, more preferably 5% by mass or more with respect to 100% by mass of the entire nickel-coated copper powder. More preferably it is.

  On the other hand, if the coating amount of nickel or nickel alloy becomes too large, it is not preferable from the viewpoint of cost. From this, the coating amount of nickel or nickel alloy is preferably 33% by mass or less, more preferably 20% by mass or less, and more preferably 15% by mass with respect to 100% by mass of the entire nickel-coated copper powder. More preferably, it is as follows.

  Further, as will be described in detail later, in the nickel-coated copper powder, the nickel coated on the surface of the copper particles may be a nickel alloy. The element added as the nickel alloy is preferably at least one selected from zinc, cobalt, tungsten, molybdenum, palladium, platinum, tin, phosphorus, and boron.

≪2. Manufacturing method of nickel-coated copper powder by wet method >>
Next, the manufacturing method of the nickel coat copper powder which has the characteristic structure mentioned above is demonstrated.

  The nickel-coated copper powder according to the present embodiment includes a step of producing a copper salt solution, a step of mixing the produced copper salt solution and a reducing agent solution to produce copper particles, and nickel or And coating a nickel alloy. And in this manufacturing method, while adjusting and maintaining the copper salt solution and the reducing agent solution in a specific temperature range, the reducing agent solution is added to the copper salt solution to produce copper particles. It is a feature.

  Here, the conventional method for producing copper particles has a problem that copper powder having a granular shape, a small particle size, a uniform particle size, and a large crystallite diameter cannot be produced by a method suitable for industrial production. It was. However, according to the inventor's research, a copper salt solution containing a dispersant is prepared, the temperature of the copper salt solution and the reducing agent aqueous solution is adjusted to a specific range, and the copper salt solution as a raw material is reduced. It was found that copper particles having a granular shape, a small particle diameter, and a large crystallite diameter can be obtained by adding an agent solution and causing a reduction reaction while maintaining the temperature condition.

  More specifically, the temperature of the copper salt solution and the reducing agent solution is adjusted to the range of 50 ° C. or higher and 90 ° C. or lower, and the copper salt solution is added to the copper salt solution while maintaining the temperature. Is generated. According to such a manufacturing method, copper particles having a granular shape, small and uniform particle size, and large crystallite diameter, which are useful for conductive paste suitable for thinning of wiring, It can be manufactured industrially.

<2-1. Method for producing copper particles>
Hereinafter, the manufacturing method of a copper particle is demonstrated more concretely. In the following description, the liquid after the copper salt solution and the reducing agent solution are mixed is also referred to as “reaction liquid”. In addition, copper particle is synonymous with the copper powder before coat | covering nickel or a nickel alloy.

(1) Production of copper salt solution In the method for producing copper particles, first, a copper salt solution which is a raw material solution for producing copper particles is produced. Specifically, a solution containing a copper compound, a solution containing an alkali metal hydroxide, and a solution containing a dispersant are mixed to prepare a copper salt solution.

(Copper compound solution)
With respect to the solution containing the copper compound, the copper compound as a starting material is not particularly limited, and various copper compounds such as copper sulfate, copper chloride, copper carbonate, copper acetate, copper phosphate, etc. are dissolved in an aqueous solution. Any salt can be used, and one kind can be used alone, or a plurality of kinds can be used in combination. Among these, copper sulfate, copper chloride, and copper carbonate are preferable from the viewpoint that the anionic elements are not mixed in the copper powder, the impurities are small, and the wastewater treatment cost is low. Furthermore, copper sulfate and copper carbonate are more preferable in view of the reliability of electronic components in which the conductive paste is used. In addition, although these copper salts are melt | dissolved and it is set as a copper compound solution, it is preferable that the solvent used for melt | dissolution is a pure water in order to prevent mixing of an impurity.

  The copper concentration in the solution is not particularly limited. A solution in which copper is dissolved to such an extent that the solution once becomes uniform and does not become supersaturated may be adjusted by adjusting the pH.

  Further, the concentration of the copper compound is not particularly limited, but the copper concentration is 5 g / L to 2000 g / in that the copper concentration in the obtained copper salt solution is industrially high and can be stably produced. It is preferable to be in the range of L. Furthermore, it is more preferable to make it become the range of 100g / L-250Lg / L. Even if the concentration of copper is low, particle growth occurs and copper particles can be obtained. However, if the copper concentration in the copper salt solution is less than 5 g / L, productivity cannot be increased. In addition, the amount of drainage increases and the cost increases. On the other hand, when the concentration of copper exceeds 2000 g / L, it is close to solubility in water and may not be sufficiently dissolved.

(Alkali metal hydroxide solution)
With respect to a solution containing an alkali metal hydroxide, various hydroxides can be used as the alkali metal hydroxide. Among them, sodium hydroxide and potassium hydroxide are preferably used, It is more preferable to use sodium oxide. These alkali metal hydroxides are readily available and are less expensive than other hydroxides.

  The concentration of the alkali metal hydroxide is such that the copper salt has a pH at which the reduction reaction of the reducing agent proceeds sufficiently in the reaction solution after adding the reducing agent solution described later to the copper salt solution. It is preferable to adjust the concentration in the solution. Specifically, for example, when ascorbic acid is used as the reducing agent, it is preferable that the pH of the reaction solution is 3.0 or more. If the pH of the reaction solution is less than 3.0, the reduction reaction with ascorbic acid that is a reducing agent may not easily proceed.

  When the pH of the reaction solution is increased, copper hydroxide is formed in the reaction solution, and copper particles are generated by the reduction reaction from the copper hydroxide. The reaction in which copper particles are produced from copper hydroxide has a lower rate than the reaction in which copper particles are produced from copper ions, so that crystals grow gradually, resulting in highly crystalline copper particles. It becomes easy. For this reason, it is more preferable that the pH of the reaction solution is 4.0 or more.

(Dispersant solution)
In the method for producing copper particles, in preparing a copper salt solution, an aqueous solution of a dispersant is mixed so that the copper particles generated by the reduction reaction with the reducing agent do not aggregate. In addition, the dispersant has an effect of slowing down the reduction reaction as the concentration in the reaction solution increases. From this, by making a copper salt solution contain a dispersing agent, the reaction rate of a reductive reaction can be reduced and a highly crystalline copper particle can be obtained.

  Here, it is important to obtain copper particles having a small crystal grain boundary and a large crystallite diameter. For this purpose, the crystal grain boundaries are given priority by the growth of each crystal of the copper particles due to the high crystallinity. It is preferable to set the conditions to be less. From such a point, it is preferable to control the rate of the reduction reaction, and it is preferable to control the concentration of the dispersant in the reaction solution to be within an appropriate range.

  Specifically, the concentration of the dispersant is preferably 0.1% by mass or more and 10% by mass or less, and 0.3% by mass or more and 7% by mass with respect to the copper amount of the copper compound in the reaction solution. % Or less, more preferably 0.5% by mass or more and 5% by mass or less. When the concentration of the dispersing agent is less than 0.1% by mass in the reaction solution, the rate of the reduction reaction is increased, and a highly crystalline copper powder may not be obtained. On the other hand, if the concentration of the dispersant exceeds 10% by mass in the reaction solution, the rate of the reduction reaction is too low, the productivity is deteriorated, and in some cases, the reduction reaction may not proceed.

  The dispersant is not particularly limited and may be, for example, at least one selected from polyvinyl alcohol, polyethyleneimine, polyvinylpyrrolidone, modified silicone oil surfactants, polyether surfactants, and the like. preferable. Two or more of these dispersants may be used in combination.

(2) Production of copper particles by addition of reducing agent Next, the produced copper salt solution and the reducing agent solution are mixed to produce copper particles. At this time, in the present embodiment, the temperatures of the copper salt solution and the reducing agent solution are controlled within a specific range, and the reducing agent solution is added to the copper salt solution that is the raw material solution.

(Reducing agent solution)
The reducing agent is not particularly limited, but it is preferable to use a compound having a relatively low reducing power. For example, ascorbic acid, an organic compound having a lactone structure such as an acid derivative of ascorbic acid, formalin, glucose, and polysaccharides One or more types may be used. In particular, ascorbic acid or a derivative thereof has a slow reducing action, and it is more preferable to use an organic compound having such a lactone structure, and copper particles having high crystallinity can be efficiently generated. Therefore, as a reducing agent, it is preferable to contain 1 or more types chosen from ascorbic acid or its derivative (s).

  In this method for producing copper powder, the solution containing the reducing agent described above is added to the copper salt solution. The amount of the reducing agent added is 1 in the reaction solution relative to the copper amount of the copper compound. It is preferable to set the amount corresponding to an equivalent amount or more and 7 equivalents or less. When the amount of the reducing agent added is less than 1 equivalent with respect to the copper amount of the copper compound, an unreduced copper salt may remain, whereas when it exceeds 7 equivalents, the production cost increases.

  Here, in the present embodiment, when producing copper particles, it is important to add a reducing agent solution to a copper salt solution that is a raw material solution. Can be generated automatically.

  Moreover, when adding a reducing agent solution with respect to a copper salt solution, the temperature of the copper salt solution and a reducing agent solution is controlled to a specific range. Specifically, the range is from 50 ° C. to 90 ° C. Moreover, it is preferable to set it as the range of 60 degreeC or more and 80 degrees C or less. By controlling the temperature of the copper salt solution and the reducing agent solution in such a temperature range and maintaining this temperature range to cause a reduction reaction, copper particles having high crystallinity can be generated. When the reaction temperature is less than 50 ° C., the crystallinity of the copper particles is lowered. On the other hand, when the reaction temperature exceeds 90 ° C., the reaction rate increases and the particle size tends to become non-uniform.

  Moreover, the retention time of the reaction solution after adding the reducing agent solution to the copper salt solution is not particularly limited, but is preferably 1 hour or longer. If the retention time of the reaction solution is less than 1 hour, the reduction reaction may not be completed, and an unreduced copper salt may remain. On the other hand, the upper limit of the retention time of the reaction solution is not particularly limited, but it should be, for example, within 5 hours from the viewpoint that the reduction reaction with a reducing agent having a relatively low reducing power such as ascorbic acid is completely completed. Is preferred. The holding time of the reaction solution is more preferably 1 hour or more and 4 hours or less, and particularly preferably 2 hours or more and 3 hours or less.

  If necessary, additives such as a pH adjuster, a complexing agent, and an antifoaming agent can be appropriately added to the reaction solution. What is necessary is just to adjust suitably the addition amount of these additives according to the objective.

(3) Treatment after copper particle generation When copper particle slurry containing copper particles is generated as described above, copper particles are separated by washing the slurry, washed and dried, and dried copper. The copper particle slurry may be taken out as a particle, or the copper particle slurry may be washed after removing the reducing agent by decantation or the like to obtain an aqueous slurry of copper particles.

  The cleaning method is not particularly limited. For example, after adding water to copper particles or a copper particle slurry and stirring using a stirrer or an ultrasonic cleaner, a suction filter or a filter press is used as necessary. It can carry out by the method of filtering by etc. Further, in the cleaning method, it is preferable to repeat the operation consisting of charging into water and stirring and cleaning several times. As cleaning water, it is preferable to use water that does not contain an impurity element harmful to copper particles, particularly pure water.

  In order to prevent aggregation of copper particles, a surface treatment agent may be added to washing water or the like in the washing treatment, and the copper powder may be surface treated during the washing. For example, a surface treatment with a carboxylic acid solution can be added during the cleaning treatment. In addition, when such a surface treatment is performed, it is preferable to wash | clean after that and to remove an excess surface treating agent.

  Next, in the drying process in the case of taking out as copper particles, the drying method is not particularly limited. For example, the cleaned copper particles are placed on a stainless steel vat and a commercially available drying apparatus such as an atmospheric oven or a vacuum dryer is used. And can be performed by heating at a temperature of about 40 ° C. to 80 ° C.

<2-2. Method of coating nickel or nickel alloy>
In the method for producing the nickel-coated copper powder according to the present embodiment, the surface of the copper particles produced by the operation of the above-described process is coated with nickel or a nickel alloy by using, for example, an electroless plating method. Powder can be produced.

  In order to coat nickel or a nickel alloy with a uniform thickness on the surface of the copper powder, it is preferable to perform the washing before the nickel plating treatment, and the copper particles are dispersed in the washing liquid, or the copper particles are washed in a water slurry. And washing can be performed while stirring. This washing treatment is preferably carried out in an acidic solution. After washing, filtration and separation of copper particles and washing with water are repeated as appropriate to obtain a water slurry in which copper particles are dispersed in water. In addition, what is necessary is just to use a well-known method about filtration, isolation | separation, and water washing.

  Specifically, when nickel is coated (coated) on the surface of the copper particles by the electroless plating method, for example, an electroless nickel plating solution is added to the copper particle slurry obtained after the cleaning treatment, or the electroless nickel plating solution The surface of the copper particles can be more uniformly coated with nickel or a nickel alloy by adding the copper particle slurry therein and stirring uniformly.

  The electroless nickel plating solution is not particularly limited. The electroless nickel plating solution is a coating of nickel by reducing nickel ions obtained from the nickel source in the plating solution with a reducing agent. The types of reducing agents are hypophosphite and borohydride. Compounds, and hydrazine compounds.

  Specifically, examples of hypophosphites include hypophosphites such as potassium hypophosphite and sodium hypophosphite, and phosphites such as potassium phosphite and sodium phosphite. It is done.

  Examples of the borohydride compound include dimethylhexaborane, dimethylamineborane (DMAB), diethylamineborane, morpholineborane, pyridineamineborane, piperidineborane, ethylenediamineborane, ethylenediaminebisborane, t-butylamineborane, imidazoleborane, methoxy Examples include ethylamine borane and sodium borohydride.

  As the hydrazine compound, hydrazine and hydrates thereof, hydrazine salts such as hydrazine sulfate and hydrazine hydrochloride, hydrazine derivatives such as pyrazoles, triazoles, and hydrazides can be used. Among these hydrazine derivatives, pyrazoles such as 3,5-dimethylpyrazole and 3-methyl-5-pyrazolone can be used as pyrazoles in addition to pyrazole. As triazoles, 4-amino-1,2,4-triazole, 1,2,3-triazole, and the like can be used. As hydrazides, adipic hydrazide, maleic hydrazide, carbohydrazide, and the like can be used. As hydrazines, hydrazine sulfate, hydrazine hydrochloride, adipic hydrazide, maleic hydrazide, carbohydrazide, and the like can be used.

  Examples of the nickel source include nickel salts such as nickel sulfate, nickel chloride, nickel acetate, and nickel sulfamate.

  Further, the plating solution can contain a complexing agent, a pH buffering agent, and a pH adjusting agent.

  Specifically, a known complexing agent can be used as the complexing agent. For example, amino acids such as glycine, citrates such as sodium citrate and ammonium citrate, lactic acid, oxalic acid, malonic acid, malic acid, tartaric acid, aspartic acid, glutamic acid, gluconic acid, sodium salts or ammonium salts, ammonia, etc. Is mentioned.

  A known complexing agent can be used as the pH buffering agent. For example, ammonium chloride, ammonium sulfate, boric acid, sodium acetate and the like can be mentioned.

  A known complexing agent can be used as the pH adjuster. For example, an acid or alkali compound can be used, and examples thereof include alkali metal hydroxides such as ammonia and sodium hydroxide, nickel carbonate, sulfuric acid, and hydrochloric acid. In addition, when using ammonia, it can supply as ammonia water.

  Moreover, you may use an antifoamer and a dispersing agent as needed.

  Furthermore, in order to improve the permeability of the plating solution, a surfactant can be contained. As the surfactant, any of nonionic, cationic, anionic and amphoteric surfactants can be used, and one kind can be used alone, or two or more kinds can be used in combination.

  Here, in the nickel coating by electroless plating, the deposited nickel film differs depending on the hypophosphorous acid bath salt, the borohydride compound, and the hydrazine compound which are reducing agents in the electroless nickel plating solution. Specifically, when hypophosphorous acid bath salt is used as the reducing agent, phosphorus (P) is included in the coating during the reduction reaction, and thus a Ni-P alloy coating is formed. Further, when a borohydride compound is used as the reducing agent, boron (B) is included in the coating during the reduction reaction, so that a Ni-B alloy coating is formed. Moreover, when a hydrazine compound is used as the reducing agent, a high-purity nickel film with few impurities is formed.

  Furthermore, by making the nickel coating to contain other elements, that is, by forming a nickel alloy coating on the surface of the copper particles, using the nickel-coated copper powder, heat resistance and corrosion resistance In addition, an excellent conductive paste or the like can be realized.

  Specifically, as an element to be included in the nickel film, that is, as an element other than nickel constituting the nickel alloy, elements of Groups 6 to 14 of the periodic table can be mentioned, and among them, zinc, palladium , Cobalt, rhodium, iron, platinum, iridium, tungsten, molybdenum, chromium, tin, and the like. In particular, one or more elements selected from zinc, cobalt, tungsten, molybdenum, palladium, platinum, and tin are preferable. By forming a nickel alloy containing these elements, a nickel alloy film having excellent conductivity is formed. can do.

  The content of the elements constituting the nickel alloy is preferably 0.1% by mass to 20% by mass with respect to 100% by mass of the nickel alloy from the viewpoint of conductivity and dispersibility, and preferably 1% by mass to 15%. More preferably, it is more preferably 2% by mass to 10% by mass. In addition, also about the Ni-P alloy and Ni-B alloy which are each formed with the kind of reducing agent mentioned above, the content of the phosphorus and boron is 0.1 mass%-100 mass of nickel alloy similarly. It is preferably 20% by mass, more preferably 1% by mass to 15% by mass, and further preferably 2% by mass to 10% by mass.

  When the content of an element other than nickel is excessive when a nickel alloy is used, the conductivity is lowered, so that the content is preferably 20% by mass or less. On the other hand, if the content is less than 0.1% by mass, the effect of improving heat resistance and corrosion resistance cannot be sufficiently obtained even if these elements are contained together with nickel to form a nickel alloy. In addition, content of the element in a nickel alloy can be measured by converting content of each element which comprises nickel coat | court copper powder, for example with a high frequency inductively coupled plasma (ICP) emission spectroscopy analysis method. In addition, each element in the nickel alloy coating can be quantitatively analyzed from the cross section of the nickel-coated copper powder or the like by energy dispersive X-ray spectroscopy (EDX) method or Auger electron spectroscopy (AES) method.

  As a method of forming a nickel alloy film, an ion such as cobalt, zinc, tungsten, molybdenum, palladium, platinum, and tin is added to the above-described electroless nickel plating solution, and electroless plating using the plating solution is performed. Can be formed. The ion source such as cobalt, zinc, tungsten, molybdenum, palladium, platinum, and tin is not particularly limited as long as it is a soluble metal salt.

  Specifically, the cobalt ion source is not particularly limited as long as it is soluble in the plating solution as a cobalt compound and can obtain an aqueous solution having a predetermined concentration. Examples thereof include cobalt sulfate, cobalt chloride, and cobalt sulfamate. These cobalt compounds can be used alone or in combination of two or more.

  The zinc ion source is not particularly limited as long as it is soluble in the plating solution as a zinc compound and can obtain an aqueous solution having a predetermined concentration. For example, zinc chloride, zinc sulfamate, zinc sulfate, zinc acetate and the like can be mentioned. These zinc compounds can be used alone or in combination of two or more.

  The tungsten ion source is not particularly limited as long as it is soluble in a plating solution as a tungsten compound and can obtain an aqueous solution having a predetermined concentration. Examples thereof include sodium tungstate, potassium tungstate, and ammonium tungstate. These tungsten compounds can be used alone or in combination of two or more.

  The molybdenum ion source is not particularly limited as long as it is soluble in a plating solution as a molybdenum compound and can obtain an aqueous solution having a predetermined concentration. Examples thereof include molybdenum trioxide, sodium molybdate, diammonium molybdate, calcium molybdate, molybdic acid, phosphomolybdic acid, and molybdate gluconic acid complex. These molybdenum compounds can be used alone or in combination of two or more.

  The palladium ion source is not particularly limited as long as it is soluble in the plating solution as a palladium compound and can obtain an aqueous solution having a predetermined concentration. For example, water-soluble palladium compounds such as palladium sulfate, palladium chloride, palladium acetate, dichlorodiethine rediamine palladium, and tetraammine palladium dichloride can be used. Further, as the palladium compound, a so-called palladium solution in which palladium is made into a solution can also be used. As the palladium solution, for example, a dichlorodiethylenediamine palladium solution or a tetraammine palladium dichloride solution can be used. These palladium compounds can be used alone or in combination of two or more.

  The platinum ion source is not particularly limited as long as it is soluble in a plating solution as a platinum compound and can obtain an aqueous solution having a predetermined concentration. For example, platinum chloride, chloroplatinic acid, chloroplatinic acid salt, platinum hydroxide acid, platinum hydroxide salt, dinitrodiammine platinum complex salt, dinitrosulfitoplatinum complex salt, tetraammine platinum complex salt, hexaammine platinum complex salt can be mentioned. A platinum compound can be used individually by 1 type or in combination of 2 or more types.

  The tin ion source is not particularly limited as long as it is a tin compound that is soluble in the plating solution and can obtain an aqueous solution having a predetermined concentration. For example, stannous chloride, stannous chloride, stannous sulfate, stannous sulfate, tin pyrophosphate and other inorganic acid salts of tin, stannous citrate, stannous citrate, stannous oxalate Of tin carboxylates such as stannic oxalate, tin methanesulfonate, tin 1-ethanesulfonate, tin 2-ethanesulfonate, tin 1-propanesulfonate, tin 3-propanesulfonate Alkane sulfonate, tin methanol sulfonate, tin hydroxyethane-1-sulfonate, tin 1-hydroxypropane-1-sulfonate, tin hydroxyethane-2-sulfonate, tin 1-hydroxypropane-3-sulfonate, etc. Alkanol sulfonates of the above, stannous hydroxides such as stannous hydroxide and stannic hydroxide, and metastannic acid. A tin compound can be used individually by 1 type or in combination of 2 or more types.

  In addition, as a method of forming a nickel alloy film, it is not limited to the method by the electroless plating method mentioned above. For example, an element other than nickel constituting the nickel alloy is contained in the copper particles before being coated with nickel, and after forming a coating made only of nickel (nickel coating), it is previously contained in the copper particles. The nickel alloy film can also be formed by diffusing the element in the nickel film.

  As described above in detail, according to the manufacturing method of the nickel-coated copper powder according to the present embodiment, it is granular, has a small and uniform particle size, and has a high crystalline nickel coat with a large crystallite size of copper particles. Copper powder can be produced. Such nickel-coated copper powder is fine and has a relatively narrow particle size distribution, but is a highly crystalline particle, so it has a smooth appearance, no defects, good crystallinity, and stability (surface stability). It becomes high and has excellent oxidation resistance.

  From this, for example, when used as a material (metal filler) of a conductive paste, it exhibits excellent dispersibility in which it is uniformly dispersed without agglomeration in the resin. Further, by having oxidation resistance, the conductive paste using the electrolytic copper powder as a metal filler can be appropriately subjected to a baking treatment such as high-temperature baking even in an oxidizing atmosphere.

≪3. Conductive paste >>
As described above, the nickel-coated copper powder according to the present embodiment is obtained by coating the surface of copper particles with nickel or a nickel alloy, and the average particle size of primary particles measured by SEM is 0.1 μm. The relative standard deviation of the particle size, which is a value obtained by dividing the standard deviation value of the primary particle size by the average particle size, is 0.3 or less, and the crystallite size of the copper particles is 3.0 μm or less. The value obtained by dividing by the average particle size is 0.07 or more. Such nickel-coated copper powder can be suitably used as a raw material for a conductive paste suitable for thinning wiring while suppressing aggregation.

  The conductive paste can be manufactured by mixing at least the nickel-coated copper powder, the resin (binder resin), and the solvent, and kneading them. Moreover, in order to improve the electroconductivity after hardening, additives, such as antioxidant and a coupling agent, can be mix | blended as needed.

  Although the kind of resin is not specifically limited, An epoxy resin, a phenol resin, an ethyl cellulose resin, etc. can be used.

  Moreover, as a solvent, organic solvents, such as ethylene glycol, diethylene glycol, triethylene glycol, glycerol, and terpineol, can be used. Further, the amount of the organic solvent is not particularly limited, but the addition amount is adjusted in consideration of the average particle diameter of the nickel-coated copper powder so as to have a viscosity suitable for a conductive film forming method such as screen printing or a dispenser. be able to.

  Moreover, the kind of antioxidant is not specifically limited, For example, hydroxycarboxylic acid etc. can be mentioned. More specifically, hydroxycarboxylic acids such as citric acid, malic acid, tartaric acid, and lactic acid are preferable, and citric acid or malic acid having a high adsorptive power to copper is particularly preferable. In addition to the antioxidant, a coupling agent, a viscosity modifier, a dispersant, a flame retardant, an anti-settling agent, and the like can be used as the additive.

  This conductive paste can be manufactured by a method similar to the conventional technique as long as the above-described constituent components can be uniformly dispersed. For example, the above-described constituent components can be uniformly kneaded by a three roll mill or the like.

  The timing of adding the above-mentioned additives is not particularly limited, and the nickel-coated copper powder and the binder resin may be added to the solvent and kneaded at the same time, or the nickel-coated copper powder and the binder resin may be mixed. It may be mixed in a solvent and kneaded, and then added using a self-revolving mixer or the like.

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

<Evaluation method>
About the nickel coat copper powder obtained by the following Example and the comparative example, 0.5% weight increase temperature regarding the observation of the shape, the average particle diameter, the crystallite diameter of the copper particle, and the evaluation of oxidation resistance by the following method The carbon content, sintering resistance, and weather resistance were measured.

(Observation of shape)
Using a scanning electron microscope (SEM, manufactured by JEOL Ltd., JSM-7100F), 20 visual fields were arbitrarily observed at a predetermined magnification, and nickel-coated copper powder contained in the visual field was observed.

(Average particle size)
About the average particle diameter of the obtained nickel coat copper powder, it observed using SEM, and the average value was calculated | required and made into the average particle diameter by measuring the particle diameter of 300 or more primary particles of copper powder. .

(Crystallite diameter)
About the crystallite diameter of the copper particle which comprises the obtained nickel coat copper powder, it measured using the X-ray-diffraction apparatus (the product made by PAN, X'pert PRO), and generally from the obtained X-ray-diffraction pattern, Calculations were made using a known method known as the Scherrer equation.

(0.5% weight increase temperature)
About the 0.5% weight increase temperature of the obtained nickel-coated copper powder, the nickel-coated copper powder obtained by drying was made into a cylindrical pellet having a diameter of about 3 mm and a thickness of 2 mm by a tableting press, and a thermal analyzer (Bruker, TG-DTA2000SR), the air flow rate is 100 mL / min, the weight increase when the temperature is raised at 10 ° C./min is measured, and the temperature when the weight increases by 0.5% Was determined as a 0.5% weight gain temperature.

(Carbon content)
About the carbon content of the obtained nickel coat copper powder, it measured by the high frequency combustion-infrared absorption method using the carbon sulfur analyzer (the LECO company make, CS-600).

(Sintering resistance)
The resistance value of the pellet after TG evaluation related to oxidation resistance was measured by a four-terminal resistance measuring instrument (manufactured by Mitsubishi Chemical Analytical Co., Ltd.), and the resistivity (μΩ · cm) was calculated from the pellet shape.

(Weatherability)
The pellets whose sintering resistance was measured were held at a constant temperature and humidity of 85 ° C. and a relative humidity of 85% (RH) for 500 hours, and then the resistivity of the pellet was calculated by the same method as that for resistance measurement. The rate of increase was calculated. The rate of increase is the percentage difference between the resistivity after 500 hours of exposure to constant temperature and humidity and the resistivity at 0 hours before exposure, and 20% or less is a reliable conductive paste. evaluated.

[Example 1] (Nickel coating: Ni-P alloy)
500 g of copper sulfate pentahydrate (manufactured by Sumitomo Metal Mining Co., Ltd.) is dissolved in 3 L of pure water, to which 600 mL of 25% aqueous sodium hydroxide solution (manufactured by Kanto Chemical Co., Ltd.) and polyvinyl alcohol (stock) A dispersant solution prepared by dissolving 1.28 g of PVA205 (manufactured by Kuraray Co., Ltd.) in 1 L of pure water was added. Further, an antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times by volume, and 10 mL of this antifoaming agent dilution was added. Thereby, a copper salt solution was prepared.

  Next, while maintaining the prepared copper salt solution at 60 ° C. while stirring, a reducing agent solution obtained by dissolving 881 g of ascorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) in 2 L of pure water and heating to 60 ° C. The mixture was added and held at 60 ° C. with stirring for 3 hours.

  After completion of the stirring, the reaction solution was filtered using a suction filter, and the copper particles in the reaction solution were separated into solid and liquid. Subsequently, the recovered copper particles are put into 2 L of pure water, and 2.5 g of stearic acid emulsion (manufactured by Chukyo Yushi Co., Ltd., Cellosol 920) is added thereto and stirred for 15 minutes, followed by filtration with a suction filter. And recovered. Subsequently, the recovered copper particles were put into 2 L of pure water, and an operation including washing by stirring for 15 minutes and filtration by a suction filter was performed. Thereafter, the copper particles were transferred onto a stainless bat and dried at 60 ° C. for 10 hours with a vacuum dryer to obtain copper powder. 1 is an SEM observation image of the copper powder (copper powder before nickel coating) obtained in Example 1. FIG. As shown in FIG. 1, the obtained copper powder had a granular shape.

  Next, using the copper powder produced by the method described above, the surface of the copper powder was coated with nickel by electroless nickel plating to produce a nickel-coated copper powder. In addition, since the electroless nickel plating solution containing a hypophosphite as a reducing agent was used, the obtained film turns into a Ni-P alloy film.

  Specifically, as an electroless nickel plating solution, nickel sulfate 20 g / L, sodium hypophosphite 25 g / L, sodium acetate 10 g / L, sodium citrate 10 g / L are added at each concentration, and sodium hydroxide is further added. 500 mL of a plating solution adjusted to pH 5.0 by adding the above was prepared.

  In this electroless nickel plating solution, a slurry in which 100 g of copper powder prepared by the above-described method is dispersed in 100 mL of water is stirred and stirred at 25 ° C. for 10 minutes, and then the bath temperature is heated to 90 ° C. and stirred for 60 minutes. did. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol.

  The shape of the nickel-coated copper powder thus obtained was observed by the method using the SEM described above. The nickel-coated copper powder had a granular shape. The number of nickel-coated copper powders was 80% or more of the total number.

  In addition, the average particle size obtained by measuring the particle size of 300 or more primary particles from the SEM image and averaging them by the number of particles is 1.80 μm, and the standard deviation value of the particle size of the primary particles is averaged. The relative standard deviation value of the particle size divided by the particle size was 0.19. Moreover, the crystallite diameter of the copper particle which comprises nickel coat copper powder was 153 nm, and the value represented by crystallite diameter / average particle diameter was 0.08.

  Subsequently, when the coating amount of the nickel alloy was measured, it was 10.4% by mass with respect to 100% by mass of the entire nickel-coated copper powder. Further, the content of phosphorus contained in the nickel alloy was 6.1% by mass with respect to 100% by mass of the nickel alloy. Further, the 0.5% weight increase temperature was 240 ° C., which exceeded 230 ° C., and had good oxidation resistance. The resistivity was as low as 205 μΩ · cm. Moreover, regarding the weather resistance, the difference in resistivity was 7%, which was favorable. Moreover, carbon content of the obtained nickel coat copper powder was 0.25 mass%.

[Example 2]
25.0 g of copper sulfate pentahydrate (manufactured by Sumitomo Metal Mining Co., Ltd.) is dissolved in 150 mL of pure water, and 30 mL of 25% sodium hydroxide aqueous solution (manufactured by Kanto Chemical Co., Ltd.) and polyvinyl alcohol as a dispersant are added thereto. A dispersant solution in which 0.06 g (manufactured by Kuraray Co., Ltd., PVA205) was dissolved in 50 mL of pure water was added. Furthermore, an antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times by volume, and 5 mL of this antifoaming agent dilution was added. Thereby, a copper salt solution was prepared.

  Next, the prepared copper salt solution is kept at 80 ° C. while stirring, and 44 g of ascorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) is dissolved in 100 mL of pure water and heated to 80 ° C. The mixture was added and held at 80 ° C. with stirring for 3 hours. And conditions other than having made the temperature of a reaction liquid into 80 degreeC were performed similarly to Example 1. FIG.

  After completion of the stirring, the reaction solution was filtered using a suction filter, and the copper particles in the reaction solution were separated into solid and liquid. Subsequently, the recovered copper particles are put into 200 mL of pure water, and 0.13 g of stearic acid emulsion (manufactured by Chukyo Yushi Co., Ltd., Cellosol 920) is added thereto and stirred for 15 minutes, followed by filtration with a suction filter. And recovered. Subsequently, the recovered copper particles were put into 200 mL of pure water, and an operation consisting of washing with stirring for 15 minutes and filtration with a suction filter was performed. Thereafter, the copper particles were transferred onto a stainless bat and dried at 60 ° C. for 10 hours with a vacuum dryer to obtain copper powder.

  Thereafter, similarly to Example 1, the surface of the copper powder was coated with nickel by electroless nickel plating to produce a nickel-coated copper powder.

  The shape of the nickel-coated copper powder thus obtained was observed by the method using the SEM described above. The nickel-coated copper powder had a granular shape. The number of nickel-coated copper powders was 80% or more of the total number.

  In addition, the average particle size obtained by measuring the particle size of 300 or more primary particles from the SEM image and averaging them by the number of particles is 2.28 μm, and the standard deviation value of the particle size of the primary particles is the average particle size. The relative standard deviation value of the particle diameter divided by the diameter was 0.23. Moreover, the crystallite diameter of the copper particle which comprises nickel coat copper powder was 296 nm, and the value represented by crystallite diameter / average particle diameter was 0.12.

  Subsequently, when the coating amount of the nickel alloy was measured, it was 12.2% by mass with respect to 100% by mass of the entire nickel-coated copper powder. Moreover, content of phosphorus contained in the nickel alloy was 7.8% by mass with respect to 100% by mass of the nickel alloy. The 0.5% weight increase temperature was 258 ° C., which exceeded 230 ° C., and had good oxidation resistance. The resistivity was as low as 190 μΩ · cm. Moreover, regarding the weather resistance, the difference in resistivity was 6%, which was favorable. Moreover, the carbon content of the obtained nickel-coated copper powder was 0.28% by mass.

[Example 3] (Nickel coating: Ni-B alloy)
Using the copper powder obtained in Example 1, a nickel coating was formed on the surface of the copper powder using an electroless nickel plating solution containing a borohydride compound as a reducing agent. In addition, as a nickel film obtained, it becomes a Ni-B alloy film.

  Specifically, as an electroless nickel plating solution, nickel sulfate 30 g / L, sodium succinate 50 g / L, boric acid 30 g / L, ammonium chloride 30 g / L, dimethylamine borane 4 g / L were added at each concentration, Further, 500 mL of a plating solution adjusted to pH 6.0 by adding sodium hydroxide was prepared.

  To this electroless nickel plating solution, a slurry in which 100 g of copper powder was dispersed in 100 mL of water was added and stirred at 25 ° C. for 10 minutes, and then the bath temperature was heated to 60 ° C. and stirred for 60 minutes. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol.

  The shape of the nickel-coated copper powder thus obtained was observed by the method using the SEM described above. The nickel-coated copper powder had a granular shape. The number of nickel-coated copper powders was 80% or more of the total number.

  Subsequently, when the coating amount of the nickel alloy was measured, it was 14.0% by mass with respect to 100% by mass of the entire nickel-coated copper powder. Further, the content of boron contained in the nickel alloy was 4.9% by mass with respect to 100% by mass of the nickel alloy. The 0.5% weight increase temperature was 260 ° C., which exceeded 230 ° C., and had good oxidation resistance. The resistivity was as low as 330 μΩ · cm. Moreover, regarding the weather resistance, the difference in resistivity was 10%, which was favorable. Moreover, carbon content of the obtained nickel coat copper powder was 0.26 mass%.

[Example 4] (Nickel coating: pure Ni)
Using the copper powder obtained in Example 1, an electroless nickel plating solution containing a hydrazine compound as a reducing agent was used to form a nickel coating on the surface of the copper powder. The obtained nickel coating is nickel that has not been alloyed (pure nickel).

  Specifically, nickel acetate was added to a slurry in which 100 g of copper powder was dispersed in 500 mL of water so as to have a concentration of 12.4 g / L, and 6 g of an 80% by mass aqueous solution of hydrazine monohydrate was added to the bath. The solution was added dropwise with gradual stirring over a period of minutes. At this time, the bath temperature was controlled to 60 ° C. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol.

  The shape of the nickel-coated copper powder thus obtained was observed by the method using the SEM described above. The nickel-coated copper powder had a granular shape. The number of nickel-coated copper powders was 80% or more of the total number.

  Subsequently, when the coating amount of the nickel alloy was measured, it was 9.4% by mass with respect to 100% by mass of the entire nickel-coated copper powder. The 0.5% weight increase temperature was 239 ° C., which exceeded 230 ° C., and had good oxidation resistance. The resistivity was as low as 175 μΩ · cm. Moreover, regarding the weather resistance, the difference in resistivity was 5.8%, which was favorable. Moreover, carbon content of the obtained nickel coat copper powder was 0.26 mass%.

[Examples 5 to 11] (Nickel coating: Ni-metal element alloy)
Using the copper powder obtained in Example 1, a nickel alloy film was formed on the surface of the copper powder using various electroless nickel plating solutions.

  As an electroless nickel plating solution for an alloy, nickel acetate was added to a slurry in which 100 g of copper powder was dispersed in 500 mL of water to a concentration of 12.4 g / L, and 3.2 g of hydrazine was added to the bath. The solution was added dropwise with gradual stirring over a period of minutes. The bath temperature was controlled to 60 ° C.

  At this time, each metal compound was added to a bath containing a slurry of copper powder and nickel acetate so that a desired nickel alloy film was formed, and hydrazine was gradually added.

  As a metal compound, in Example 5, 1.5 g of sodium tungstate was added to form a Ni—W alloy film. In Example 6, 2 g of cobalt sulfate was added to form a Ni—Co alloy film. In Example 7, 4 g each of zinc sulfate heptahydrate and sodium citrate were added to form a Ni—Zn alloy film. In Example 8, 2 g of palladium chloride was added to form a Ni—Pd alloy film. In Example 9, 2 g of potassium tetrachloroplatinate and 1 g of glycine were added to form a Ni—Pt alloy film. In Example 10, 1 g each of sodium molybdate and trisodium citrate was added to form a Ni—Mo alloy coating. In Example 11, 1 g of sodium stannate was added to form a Ni—Sn alloy film.

  After completion of each reaction, the powder was filtered, washed with water and dried through ethanol.

  The shape of the nickel-coated copper powder thus obtained was observed by the method using the SEM described above. The nickel-coated copper powder had a granular shape. The number of nickel-coated copper powders was 80% or more of the total number.

  Subsequently, the measurement of the nickel alloy coating amount, the nickel alloy coating amount, the alloy element content, the 0.5% weight increase temperature, the resistivity, the weather resistance, and the carbon content were measured. Table 1 below summarizes each measurement result.

[Example 12] (Nickel coating: Ni-P-W alloy)
Using the copper powder obtained in Example 1, using an electroless nickel plating solution containing hypophosphite as a reducing agent and further containing tungstate, a nickel coating is formed on the surface of the copper powder. It was. In addition, as a nickel film obtained, it becomes a Ni-P-W alloy film.

  Specifically, as an electroless nickel plating solution, a plating solution in which nickel sulfate 20 g / L, sodium hypophosphite 25 g / L, sodium acetate 10 g / L, and sodium citrate 10 g / L are added at each concentration, 500 g of a plating solution prepared by adding 1.5 g of sodium tungstate and adjusting the pH to 5.0 by adding sodium hydroxide was prepared.

  To this electroless nickel plating solution, a slurry in which 100 g of copper powder was dispersed in 100 mL of water was added and stirred at 25 ° C. for 10 minutes, and then the bath temperature was heated to 90 ° C. and stirred for 60 minutes. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol.

  The shape of the nickel-coated copper powder thus obtained was observed by the method using the SEM described above. The nickel-coated copper powder had a granular shape. The number of nickel-coated copper powders was 80% or more of the total number.

  Subsequently, when the coating amount of the nickel alloy was measured, it was 11.1% by mass with respect to 100% by mass of the entire nickel-coated copper powder. The contents of phosphorus and tungsten contained in the nickel alloy were 3.8% by mass and 2.0% by mass, respectively, with respect to 100% by mass of the nickel alloy. The 0.5% weight increase temperature was 260 ° C., which exceeded 230 ° C., and had good oxidation resistance. The resistivity was as low as 351 μΩ · cm. Moreover, regarding the weather resistance, the difference in resistivity was 9.7%, which was favorable. Moreover, carbon content of the obtained nickel coat copper powder was 0.26 mass%.

[Comparative Example 1]
In the production of copper powder, copper powder was produced in the same manner as in Example 2, except that the temperature of the copper salt solution, the reducing agent aqueous solution, and the reaction solution during the holding time was 40 ° C., respectively. And the nickel coating was formed on the obtained copper powder on the conditions similar to Example 2, and the nickel coat copper powder was produced.

  The shape of the obtained nickel-coated copper powder was observed by the method using the SEM described above. The nickel-coated copper powder was in a granular shape. Furthermore, it was expected that the nickel-coated copper powder observed by SEM had a rough surface and was rounded and had low crystallinity, but the number of nickel-coated copper powders was 80% or more of the total number.

  In addition, the average particle size obtained by measuring the particle size of 300 or more primary particles from the SEM image and averaging them by the number of particles is 1.81 μm, and the standard deviation value of the particle size of the primary particles is the average particle size. The relative standard deviation value of the particle diameter divided by the diameter was 0.29. However, the crystallite diameter of the copper particles constituting the nickel-coated copper powder was as small as 97 nm, and as a result, the value represented by crystallite diameter / average particle diameter was 0.05, which was a polycrystalline structure.

  Subsequently, when the coating amount of the nickel alloy was measured, it was 13.0% by mass with respect to 100% by mass of the entire nickel-coated copper powder. The content of phosphorus contained in the nickel alloy was 8.0% by mass with respect to 100% by mass of the nickel alloy. Moreover, carbon content of the obtained nickel coat copper powder was 0.25 mass%.

  In such a nickel-coated copper powder having a polycrystalline structure, the 0.5% weight increase temperature was 220 ° C., and the oxidation resistance of 230 ° C. or less was not satisfactory. Furthermore, the resistivity was as high as 520 μΩ · cm, and the weather resistance was also deteriorated by a difference in resistivity of 25%.

[Comparative Example 2]
A copper powder was produced in the same manner as in Example 1 except that polyvinyl alcohol was not added during the production of the copper powder. And the nickel coating was formed on the obtained copper powder on the conditions similar to Example 1, and the nickel coat copper powder was produced.

  The shape of the obtained nickel-coated copper powder was observed by the method using the SEM described above. The nickel-coated copper powder has a relatively high crystal appearance, and the number of nickel-coated copper powders having this structure was 80% or more of the total number.

  In addition, the average particle size obtained by measuring the particle size of 300 or more primary particles from the SEM image and averaging them by the number of particles is 3.8 μm, and the standard deviation value of the particle size of the primary particles is the average particle size. The relative standard deviation value of the particle diameter divided by the diameter was 0.19. Moreover, the crystallite diameter of the copper particle which comprises nickel coat copper powder was 187 nm, and the value represented by crystallite diameter / average particle diameter was 0.05.

  Subsequently, when the coating amount of the nickel alloy was measured, it was 10.0% by mass with respect to 100% by mass of the entire nickel-coated copper powder. The content of phosphorus contained in the nickel alloy was 7.0% by mass with respect to 100% by mass of the nickel alloy. Moreover, the 0.5% weight increase temperature was 220 degreeC, and the oxidation resistance deteriorated to 230 degrees C or less. Also, the resistivity was as high as 600 μΩ · cm. In addition, regarding the weather resistance, the difference in resistivity was 14%, which was favorable. Moreover, the carbon content of the obtained nickel-coated copper powder was 0.20% by mass.

  The nickel-coated copper powder of the present invention can be suitably used as a metal filler as a raw material for resin-type pastes and low-temperature firing-type pastes in order to form wiring layers and electrodes in electronic devices.

Claims (23)

A nickel-coated copper powder in which nickel or a nickel alloy is coated on the surface of copper particles,
The average particle size of primary particles measured by a scanning electron microscope is 0.1 μm or more and 3.0 μm or less,
The standard deviation value of the particle size of the primary particles divided by the average particle size is a relative standard deviation value of the particle size of 0.3 or less,
A value obtained by dividing the crystallite diameter of copper particles by the average particle diameter is 0.07 or more. The nickel coat copper powder according to claim 1 whose crystallite diameter of said copper particles is 60 nm or more. The nickel-coated copper powder according to claim 1 or 2, wherein the shape of the nickel-coated copper powder is granular. The nickel-coated copper powder according to any one of claims 1 to 3, wherein a carbon content of the nickel-coated copper powder is 0.05% by mass or more and 0.5% by mass or less. The nickel-coated copper powder according to any one of claims 1 to 4, wherein a coating amount of nickel or a nickel alloy is 1% by mass to 33% by mass with respect to 100% by mass of the entire nickel-coated copper powder. The surface of the copper particles is coated with a nickel alloy,
Contains at least one selected from cobalt, zinc, tungsten, molybdenum, palladium, platinum, tin, phosphorus, and boron in a proportion of 0.1% by mass to 20% by mass with respect to 100% by mass of the nickel alloy. The nickel-coated copper powder according to claim 5, wherein the nickel-coated copper powder is coated with a nickel alloy. The 0.5% weight increase temperature when heated at a rate of temperature increase from room temperature to 10 ° C / min in the air by measurement using a thermal analyzer exceeds 230 ° C. The nickel-coated copper powder described. A conductive paste obtained by kneading the nickel-coated copper powder according to any one of claims 1 to 7, a resin, and a solvent. A method for producing nickel-coated copper powder in which the surface of copper particles is coated with nickel or a nickel alloy,
A copper salt solution preparation step of preparing a copper salt solution by mixing a solution containing a copper compound, a solution containing an alkali metal hydroxide, and a solution containing a dispersant;
A copper particle production step of producing copper particles by mixing the copper salt solution and the reducing agent solution;
A nickel coating step of coating the copper particles with nickel or a nickel alloy,
In the copper particle generation step, the temperature of the copper salt solution and the reducing agent solution is set in a range of 50 ° C. or more and 90 ° C. or less, and mixing is performed by adding the reducing agent solution to the copper salt solution. Method for producing nickel-coated copper powder. 10. The nickel-coated copper powder according to claim 9, wherein in the copper salt solution preparation step, the amount of the dispersant added is in the range of 0.01% by mass to 10% by mass with respect to the amount of copper in the copper compound. Manufacturing method. The nickel-coated copper powder according to claim 9 or 10, wherein the dispersant is at least one selected from polyvinyl alcohol, polyethyleneimine, polyvinylpyrrolidone, a modified silicone oil surfactant, and a polyether surfactant. Manufacturing method. The method for producing nickel-coated copper powder according to claim 9, wherein the copper compound is copper sulfate pentahydrate. The method for producing nickel-coated copper powder according to any one of claims 9 to 12, wherein the alkali metal hydroxide is sodium hydroxide. 14. The nickel-coated copper powder according to claim 9, wherein in the copper particle generation step, the amount of the reducing agent added is 1 equivalent to 7 equivalents with respect to the amount of copper in the copper compound. Manufacturing method. The method for producing nickel-coated copper powder according to any one of claims 9 to 14, wherein the reducing agent is at least one selected from organic compounds having a lactone structure, formalin, glucose, and polysaccharides. The method for producing a nickel-coated copper powder according to claim 15, wherein the reducing agent includes one or more selected from ascorbic acid or a derivative thereof. The nickel-coated copper powder has a value obtained by dividing the crystallite diameter of the nickel-coated copper powder by the average particle diameter of primary particles measured by observing the nickel-coated copper powder with a scanning electron microscope. It is 07 or more. The manufacturing method of the nickel coat copper powder of any one of Claims 9 thru | or 16. The method for producing nickel-coated copper powder according to claim 17, wherein the crystallite diameter of the copper particles is 60 nm or more. The nickel-coated copper powder has a relative standard deviation value of a particle diameter, which is a value obtained by dividing a standard deviation value of a particle diameter of primary particles of the nickel-coated copper powder by the average particle diameter, of 0.3 or less. The manufacturing method of the nickel coat copper powder of 17 or 18. In the said nickel coating process, the coating amount of the nickel or nickel alloy with respect to the said copper particle shall be 1 mass%-33 mass% with respect to 100 mass of the said nickel coat copper powder whole, The any one of Claim 9 thru | or 19 The manufacturing method of the nickel coat copper powder of description. In the nickel coating step,
The surface of the copper particles is coated with a nickel alloy,
Contains at least one selected from cobalt, zinc, tungsten, molybdenum, palladium, platinum, tin, phosphorus, and boron in a proportion of 0.1% by mass to 20% by mass with respect to 100% by mass of the nickel alloy. The method for producing a nickel-coated copper powder according to claim 20, wherein the nickel alloy is coated. The method for producing the nickel-coated copper powder according to any one of claims 9 to 21, wherein the nickel-coated copper powder has a carbon content of 0.05 mass% or more and 0.5 mass% or less. The manufacturing method of the electrically conductive paste manufactured by knead | mixing the nickel coat | court copper powder in any one of Claims 1 thru | or 7, resin, and a solvent.