JP7065676B2 - A silver-coated metal powder and a method for producing the same, a conductive paste containing the silver-coated metal powder, and a method for producing a conductive film using the conductive paste. - Google Patents

Description

The present invention is a method for producing a silver-coated metal powder in which a metal powder such as copper powder is silver-coated under predetermined conditions, and for example, a silver-coated metal powder produced by such a method, a conductive paste containing the silver-coated metal powder. , And a method for producing a conductive film using a conductive paste.

Conventionally, in order to form electrodes and wiring of electronic parts by a printing method or the like, a conductive paste prepared by mixing a solvent, a resin, a dispersant, etc. with a conductive metal powder such as silver powder or copper powder has been used. There is. While silver powder is excellent in conductivity and oxidation resistance, it has problems such as high cost and easy migration. On the other hand, copper powder has excellent conductivity and cost, and is less likely to cause migration, but has a problem of poor oxidation resistance.

Therefore, silver-coated copper powder has been developed in order to enjoy the merits of silver powder and copper powder. As a method for producing this silver-coated copper powder, Patent Document 1 describes that copper powder is dispersed in an acidic solution (pH 2 to 5), a chelating agent is added to the copper powder dispersion to prepare a copper powder slurry, and then buffered. It is disclosed that a silver layer is formed on the surface of copper powder by a substitution reaction by adding an agent to adjust the pH to about 4 and continuously adding a silver ion solution to the copper powder slurry. By doing so, it is said that silver-coated copper powder having little change in conductivity with time can be obtained even if it is left in the atmosphere.

Further, in Patent Document 2, copper or copper can be produced in order to produce a silver-coated metal powder in which particles are difficult to sinter with each other and when used in a conductive paste, the increase in the viscosity of the conductive paste over time can be suppressed. After coating the alloy powder with a silver-containing layer, the copper or copper alloy powder coated with the silver-containing layer is heated at 60 to 160 ° C. for 0.5 to 50 hours in a reducing atmosphere to perform surface modification. Is disclosed. Further, Patent Document 2 describes the copper elution amount of the silver-coated copper (alloy) powder thus produced, the viscosity change rate of the conductive paste, and the particle size of D ₅₀ / D _BET (D _BET is the particle size calculated from the BET specific surface area). ) Is disclosed.

Japanese Unexamined Patent Publication No. 2004-52044 Japanese Unexamined Patent Publication No. 2016-176093

However, when a silver ion solution is added to a copper powder slurry having a pH of about 4 and a silver coating reaction is carried out as in Patent Document 1, copper oxide may be generated and the conductivity of the silver-coated copper powder may be adversely affected. .. This is because copper oxide can be produced at pH 4 in the pH-potential diagram of copper. As a result, agglomeration of the powder may occur in the obtained silver-coated copper powder.

Patent Document 2 provides a silver-coated copper (alloy) powder having a small D ₅₀ / D _BET and suppressed sintering and aggregation of particles. However, in recent years, there have been demands for miniaturization and high performance of electronic components. Therefore, in order to enable fine line drawing and formation of a thin and smooth conductive film, further improvement in aggregation suppression is required. Further, when the aggregation is suppressed, the filling property of the powder is generally improved and the conductivity is improved.

From the above, it is an object of the present invention to further provide a silver-coated copper (alloy) powder having excellent conductivity in which agglomeration of particles is suppressed and a method for producing the same.

As a result of diligent studies to solve the above problems, the present inventors have conducted a silver coating reaction for forming a silver coating layer on the surface of copper (alloy) powder particles in a liquid medium containing silver ions. Oxidation is carried out by carrying out the reaction by allowing a chelating agent to be present in the reaction solution in the reaction and keeping the pH of the reaction solution at 2.6 or less (a region where copper oxide is not generated in the pH-potential diagram of copper). It is possible to uniformly coat the surface of copper (alloy) particles with silver while suppressing the formation of copper, thereby suppressing aggregation of the particles and obtaining silver-coated copper (alloy) powder with excellent conductivity. We found that and came to complete the present invention.

That is, the present invention comprises a silver-coated metal powder having a silver-coated layer for forming a silver-coated layer on the surface of metal powder particles having a copper mass ratio of 80% by mass or more in a mixed solution containing silver ions and a liquid medium. It is a production method for producing a silver-coated metal powder, wherein the mixed solution contains a chelating agent, and the silver-coated step is carried out while keeping the pH of the mixed solution at 2.6 or less.
In this method for producing a silver-coated metal powder, the metal powder is a copper alloy powder composed of copper, zinc and unavoidable impurities, and the mass of copper with respect to the total mass ratio of copper and zinc in the copper alloy powder is 100% by mass. It may be a copper alloy powder having a ratio of 85.00 to 99.50% by mass and a zinc mass ratio of 0.50 to 15.00% by mass. Further, the metal powder may be a copper powder composed of copper and unavoidable impurities. Further, the metal powder is a copper alloy powder composed of copper, nickel and zinc and unavoidable impurities, and the mass ratio of copper to 100% by mass of the total mass ratio of copper, nickel and zinc in the copper alloy powder is 80.00. Even a copper alloy powder having a mass ratio of ~ 99.50% by mass, a mass ratio of nickel of 0.10 to 10.00% by mass, and a mass ratio of zinc of 0.40 to 19.90% by mass. good.

Further, in the embodiment of the silver-coated metal powder of the present invention, the silver ions are present in the mixed solution in an amount of 0.1 to 100 parts by mass with respect to 100 parts by mass of the metal powder in terms of mass as silver. Is preferable. The chelating agent is preferably at least one selected from the group consisting of ethylenediaminetetraacetic acid, hydroxyethylethylenediaminetriacetic acid, hydroxyethyliminodiacetic acid, nitrilotriacetic acid and salts thereof.

Further, as one aspect of the method for producing a silver-coated metal powder, there is an embodiment in which the silver-coated layer is formed while blowing a non-oxidizing gas into the mixed solution in the silver-coating step.
As another embodiment, in the silver coating step, an aqueous solution containing silver ions is added to the aqueous dispersion while blowing a non-oxidizing gas into the aqueous dispersion in which the chelating agent and the metal powder are dispersed in water. There is an embodiment to be carried out by. In this embodiment, when the pH of the aqueous dispersion is high, a pH adjuster is added to the aqueous dispersion to bring the pH of the aqueous dispersion to 2.6 or less, and then the silver ion is added to the aqueous dispersion. It is preferable to add the contained aqueous solution.

Further, in the method for producing a silver-coated metal powder, the cumulative 50% particle diameter (D ₅₀ ) of the metal powder coated with the silver-coated layer on a volume basis measured by a laser diffraction type particle size distribution measuring device is 0.1. It is preferably about 10.0 μm.

For example, in the embodiment of the silver-coated metal powder of the present invention that can be produced by the above method for producing a silver-coated metal powder, metal core particles having a copper mass ratio of 80% by mass or more and silver covering the metal core particles are used. A silver-coated metal powder having a silver-coated layer composed of a silver-coated metal powder, and a laser diffraction type particle size distribution with respect to a true sphere-equivalent particle size ( _DBET ) calculated from a specific surface area of the silver-coated metal powder measured by the BET one-point method. The ratio (D ₅₀ / D _BET ) of the cumulative 50% particle diameter (D ₅₀ ) based on the volume measured by the measuring device is 1.65 or less.
The metal core particles are composed of copper, zinc and unavoidable impurities, and the mass ratio of copper is 85.00 to 99.50% by mass with respect to the total mass ratio of copper and zinc in the core particles of 100% by mass. The mass ratio of zinc may be 0.50 to 15.00 mass%. Further, the metal core particles may be made of copper and unavoidable impurities. Further, the metal core particles are composed of copper, nickel and zinc and unavoidable impurities, and the mass ratio of copper is 80.00 to 99 with respect to the total mass ratio of copper, nickel and zinc in the metal core particles of 100% by mass. It may be .50% by mass, the mass ratio of nickel is 0.10 to 10.00% by mass, and the mass ratio of zinc is 0.40 to 19.90% by mass.

The amount of copper ion elution when 5 g of the silver-coated metal powder of the present invention is immersed in 45 g of a sulfuric acid aqueous solution having a pH of 0 for 30 minutes is preferably 450 mg / L or less. Further, the product of the BET specific surface area (BET) of this silver-coated metal powder measured by the BET one-point method and the cumulative 50% particle diameter (D ₅₀ ) of the volume standard measured by the laser diffraction type particle size distribution measuring device (BET × D). ₅₀ ) is preferably 1.07 (m ² · μm / g) or less. The product (O × D ₅₀ ) of the oxygen content (O) of the silver-coated metal powder and the cumulative 50% particle size (D ₅₀ ) based on the volume measured by the laser diffraction type particle size distribution measuring device is preferably 0. It is 38 (mass% · μm) or less. The cumulative 50% particle size ( _D50 ) on a volume basis measured by a laser diffraction type particle size distribution measuring device for silver-coated metal powder is preferably 0.1 to 10.0 μm. The mass ratio of the silver-coated layer in the silver-coated metal powder is preferably 0.1 to 50% by mass.

An embodiment of the conductive paste of the present invention comprises the above silver-coated metal powder dispersed in a solvent and / or a resin binder. A method for manufacturing a conductive film, in which this conductive paste is applied onto a substrate to form a coating film and the coating film is fired to form a conductive film on the substrate, is also one of the embodiments of the present invention. Is.

According to the present invention, there is provided a silver-coated copper (alloy) powder having excellent conductivity in which aggregation of particles is suppressed and a method for producing the same.

Hereinafter, the present invention will be described in detail. In the present specification, individual "particles" constitute "powder", and "powder" refers to a set of "particles". In the following explanation, as a general rule, the word "particle" is used when focusing on the individual constituents of the powder, and "powder" or "powder of particles" is used when focusing on the whole set of particles. Use the word. It is not intended to strictly distinguish between individual particles and the powder that is an aggregate thereof.

[Manufacturing method of silver-coated metal powder]
In one embodiment of the method for producing a silver-coated metal powder of the present invention, a silver-coated layer is formed on the surface of metal powder particles having a copper mass ratio of 80% by mass or more in a mixed solution containing silver ions and a liquid medium. In the method for producing a silver-coated metal powder having a silver-coated metal powder, the silver-coated step is carried out while the mixed solution contains a chelating agent and the pH of the mixed solution is maintained at 2.6 or less. Hereinafter, each configuration of the present embodiment will be described.

<Metal powder>
The metal powder is not particularly limited as long as it is a metal powder having a mass ratio of copper of 80% by mass or more, and may be a copper powder composed of copper and unavoidable impurities (1000 ppm or less), or may be copper powder. It may be a copper alloy powder containing other metal elements. Examples of the unavoidable impurities include iron, sodium, potassium, calcium, palladium, magnesium, oxygen, carbon, nitrogen, phosphorus, silicon and chlorine. The unavoidable impurities include trace additive elements contained at a level of about 1000 ppm or less in order to achieve a given purpose.

Examples of copper alloy powders include copper and zinc and copper alloy powders consisting of unavoidable impurities (up to 1000 ppm). By coating this with silver, a silver-coated metal powder having excellent oxidation resistance can be obtained. The mass ratios of copper and zinc to the total mass ratio of 100% by mass in this copper alloy powder are 85.00 to 99.50% by mass for copper and 0.50 to 15.% by mass for zinc from the above-mentioned characteristics. It is preferably 00% by mass, more preferably 88.00 to 98.50% by mass of copper and 1.50 to 12.00% by mass of zinc.

Other examples of copper alloy powder include copper alloy powder consisting of copper, nickel and zinc and unavoidable impurities (up to 1000 ppm). By coating this with silver, a silver-coated metal powder having excellent oxidation resistance can be obtained. The mass ratio of copper, nickel and zinc in this copper alloy powder to 100% by mass is 80.00 to 99.50% by mass for copper and 0.10 to 0.10 for nickel from the above-mentioned characteristics. It is preferably 10.00% by mass and 0.40 to 19.90% by mass of zinc, 88.00 to 97.50% by mass of copper, 0.15 to 10.00% by mass of nickel and 2 of zinc. More preferably, it is 0.00 to 11.80% by mass.

The cumulative 50% particle size ( _D50 ) based on the volume measured by the laser diffraction type particle size distribution measuring device of the metal powder is the fine line drawing and thin conductive film when the produced silver-coated metal powder is used for the conductive paste. From the viewpoint of formation, it is preferably 0.1 to 10.0 μm, more preferably 0.8 to 8.0 μm, and even more preferably 1.2 to 6.0 μm.

The metal powder described above is a wet reduction method in which copper particles are precipitated by reducing copper ions in an aqueous solution, or an atomization method in which a molten metal is dropped and a fluid such as gas or water is collided with the molten metal to form a powder. It can be produced by a known method such as. Commercially available products may be used as the metal powder.

<Silver coating process>
In the silver coating step in the method for producing a silver-coated metal powder of the present embodiment, a mixed solution containing silver ions, a chelating agent and a liquid medium is used, and a silver coating reaction is carried out on the metal powder in this mixed solution. .. More specifically, by stirring the mixed solution containing the metal powder, a substitution reaction between copper and silver on the particle surface of the metal powder occurs, and a silver coating layer is formed. Since a chemical such as a chelating agent coexists in the formation of the silver-coated layer, the silver-coated layer may contain these or their reactants as unavoidable impurities.

The liquid medium constituting the mixed solution is preferably water because silver ions can be stably present, and may be a mixed solvent of water and a small amount of a polar solvent such as alcohol. As the alcohol, an alcohol having 1 to 5 carbon atoms is preferable, and an alcohol having 1 to 3 carbon atoms is more preferable from the viewpoint of polarity. The proportion of water in the mixed solvent is preferably 80% by mass or more, more preferably 95% by mass or more, from the viewpoint that silver ions are stably present and the silver coating is improved.

The silver ions in the mixture are usually supplied by dissolving the silver ion source in a liquid medium. Examples of the silver ion source include silver salts (for example, silver nitrate, silver chloride, silver iodide, silver oxalate, silver carbonate), and silver nitrate is preferable from the viewpoint of high water solubility and cost. The amount of silver ions in the mixed solution may be appropriately changed according to the silver coating ratio of the target metal powder, but in terms of mass as silver, it is usually 0.1 to 100 with respect to 100 parts by mass of the metal powder. It is taken as a part by mass, preferably 5 to 70 parts by mass, and more preferably 8 to 50 parts by mass.

In this embodiment, the mixture further contains a chelating agent. The chelating agent has a function of removing the oxide film on the particle surface of the metal powder charged in the mixed solution and has a function of improving the silver coating. In addition, the chelating agent captures the copper ions eluted from the metal powder in the silver coating reaction (substitution plating reaction) by complexing, so that the progress of the silver coating reaction such as the reprecipitation of the copper ions on the copper particles progresses. Suppress disturbing reactions.

Specific examples of the chelating agent include ethylenediaminetetraacetic acid, hydroxyethylethylenediaminetriacetic acid, hydroxyethyliminodiacetic acid, nitrilotriacetic acid and salts thereof. These may be used alone or in combination of two or more. Examples of the salt include alkali metal salts and alkaline earth metal salts, and specific examples thereof include sodium salt, potassium salt, magnesium salt and calcium salt.

For example, it can be obtained by adding an aqueous solution containing silver ions to a dispersion in which a chelating agent and a metal powder are dispersed in a liquid medium (the aqueous solution may be added all at once or continuously). A silver coating reaction is carried out on the metal powder by stirring the mixed solution, and in this reaction, the pH of the mixed solution (reaction solution) is maintained at 2.6 or less. By holding the pH of the mixed solution in the region where copper oxide is not generated in the copper pH-potential diagram and carrying out the silver coating reaction in this way, the formation of copper oxide is suppressed and the surface of the metal powder particles is made uniform. Can be silver coated. Since the pH is acidic, copper elutes from the surface of the metal powder particles, but this is also captured by the chelating agent, and the disturbing reaction of the progress of the silver coating reaction by the copper ions is suppressed. In this silver coating reaction, the potential of the mixed solution is not particularly limited, but is usually 0 to 1.0 V (against the standard electrode potential). Further, in the present specification, the pH of the mixed solution shall be measured at 25 ° C. by fractionating the pH.

Further, since the pH is acidic at 2.6 or less, the silver coating reaction proceeds relatively slowly, so that a uniform silver coating reaction is performed. From the viewpoint of the uniformity of the reaction, the difference in pH of the mixed solution at the start time and the end time of the silver coating reaction is preferably 1.4 or less. The start time of the silver coating reaction is the moment when silver ions and metal powder coexist in the mixed solution, and the end point of the silver coating reaction is the separation of the vicinity of the surface of the mixed solution with a dropper. This is the point at which the reaction for producing a silver halide does not occur when a halide such as potassium iodide is added to the filtrate obtained by filtering the liquid.

Further, in the present embodiment, the silver coating reaction is preferably carried out while blowing a non-oxidizing gas (for example, nitrogen gas or argon gas) into the mixture to form a silver coating layer. Since the mixture is acidic, copper is easily dissolved in the mixture and may cause aggregation. However, by blowing a non-oxidizing gas to reduce oxygen in the mixture as much as possible, copper can be dissolved. It can be prevented and the obtained silver-coated metal powder can be dispersed.

In the present embodiment, for example, a silver coating reaction is carried out as in the case of adding a pH 1.5 aqueous solution containing silver ions to a pH 3.0 dispersion in which a chelating agent and a metal powder are dispersed in a liquid medium. Even if the pH of the mixed solution is not 2.6 or less for a short time such as the moment of starting, the pH of 2.6 or less may be maintained in the subsequent reaction. If the silver-coated metal powder obtained by carrying out such a silver-coated reaction step corresponds to the silver-coated metal powder of the embodiment of the present invention described later, the embodiment is the silver-coated metal of the present invention. It shall correspond to the powder manufacturing method.

If the pH of the mixed solution is higher than 2.6 due to the components in the mixed solution, the silver coating reaction can be suppressed by adding a pH adjuster to the mixed solution to bring the pH to 2.6 or less and then carrying out the silver coating reaction. This is desirable because a silver-coated metal powder having excellent conductivity can be obtained. Examples of pH regulators include malonic acid, succinic acid, glycolic acid, lactic acid, malic acid, tartaric acid, phthalic acid and salts thereof. These may be used alone or in combination of two or more. They also function as buffers to prevent changes in pH (particularly to the alkaline side) during the silver coating reaction. Examples of the salt include alkali metal salts and alkaline earth metal salts, and specific examples thereof include sodium salt, potassium salt, magnesium salt and calcium salt.

Further, as a preferred embodiment of the present embodiment, a silver-coated reaction is carried out by adding an aqueous solution containing silver ions to the aqueous dispersion while blowing a non-oxidizing gas into the aqueous dispersion in which the chelating agent and the metal powder are dispersed in water. The embodiment of the above is mentioned. Water is inexpensive and can allow the silver coating reaction to proceed well. In this embodiment, when the pH of the aqueous dispersion exceeds 2.6, a pH adjuster is added to bring the pH of the aqueous dispersion to 2.6 or less, and then an aqueous solution containing silver ions is added thereto. Is preferable.

The reaction temperature of the silver coating reaction in the silver coating step described above is not particularly limited, and the silver coating reaction is carried out, for example, at room temperature (1 to 30 ° C.) or under heating conditions (more than 30 ° C. and 70 ° C. or lower). can do. From the viewpoint of uniform silver coating, the reaction temperature is preferably 15 to 50 ° C.

<Other processes>
In addition to the silver-coated step described above, a solid-liquid separation step such as filtration may be performed on the slurry containing the silver-coated metal powder obtained in the step. Further, a cleaning step or a drying step may be carried out on the silver-coated metal powder, or a crushing step or a sieving step may be carried out to adjust the particle size of the silver-coated metal powder.

[Silver-coated metal powder]
Next, the silver-coated metal powder of the present invention will be described. One embodiment of the silver-coated metal powder of the present invention is a silver-coated metal powder having metal core particles having a mass ratio of copper of 80% by mass or more and a silver-coated layer made of silver covering the metal core particles. Therefore, the cumulative 50% particle diameter based on the volume measured by the laser diffraction type particle size distribution measuring device with respect to the true sphere-equivalent particle diameter ( _DBET ) calculated from the specific surface area of the silver-coated metal powder measured by the BET 1-point method. A silver-coated metal powder having a ratio (D ₅₀ / D _BET ) of (D ₅₀ ) of 1.65 or less. This silver-coated metal powder can be produced by the method for producing a silver-coated metal powder according to an embodiment of the present invention. Hereinafter, each configuration of this silver-coated metal powder will be described.

(Metal core particles)
The metal core particles in the present embodiment correspond to the metal powder described in the method for producing the silver-coated metal powder of the present embodiment. That is, the metal composition of the metal core particles is not particularly limited as long as the mass ratio of copper is 80% by mass or more, and the metal core particles may be copper core particles composed of copper and unavoidable impurities, or copper and other metal elements. It may be a copper alloy core particle containing. The unavoidable impurities are the same as those described in the metal powder in the method for producing a silver-coated metal powder according to the embodiment of the present invention. A silver-coated layer is formed on the surface of the metal core particles, and in this silver-coated metal powder, diffusion of elements may occur over time. Therefore, the metal core particles may contain a trace amount of silver.

Examples of the copper alloy core particles include copper alloy core particles composed of copper, zinc and unavoidable impurities. The silver-coated metal powder having a silver-coated layer formed on the surface of the metal core particles has excellent oxidation resistance. From the above-mentioned characteristics, the mass ratio of each element in the total mass ratio of copper and zinc in the copper alloy core particles is 85.00 to 99.50 mass% for copper and 0.50 to 0.50 for zinc. It is preferably 15.00% by mass, more preferably 88.00 to 98.50% by mass of copper and 1.50 to 12.00% by mass of zinc.

Other examples of copper alloy core particles include copper alloy core particles composed of copper, nickel and zinc, and unavoidable impurities. The silver-coated metal powder having a silver-coated layer formed on the surface of the metal core particles has excellent oxidation resistance. From the above-mentioned characteristics, the mass ratio of each element in the total mass ratio of copper, nickel and zinc in the copper alloy core particles is 80.00 to 99.50 mass% for copper and 0. It is preferable that zinc is 0.40 to 19.90% by mass at 10 to 10.00% by mass, copper is 88.00 to 97.50% by mass, and zinc is 0.15 to 10.00% by mass. Is more preferably 2.30 to 11.80% by mass.

(Silver coating layer)
In the embodiment of the silver-coated metal powder of the present invention, the silver-coated layer is formed on the surface of the metal core particles described above. This silver-coated layer is substantially composed of silver, but may contain unavoidable impurities derived from the manufacturing process or raw materials. Then, the constituent elements of the metal core particles may diffuse into the silver-coated layer, and the silver-coated layer may contain these elements.

Further, the silver coating layer does not have to be formed on the entire surface of the metal core particles, but may be formed to such an extent as to exhibit good conductivity, which will be described later, and may cover the surface of the metal core particles. Further, as one index of such coating, it is preferable that the mass ratio of the silver-coated layer in the silver-coated metal powder is 0.1 to 50% by mass. From the viewpoint of good conductivity, the mass ratio of the silver coating layer is more preferably 1 to 40% by mass, further preferably 15 to 30% by mass. On the other hand, from the viewpoint of the production cost of the silver-coated metal powder, the mass ratio of the silver-coated layer is preferably 2 to 12% by mass. The mass ratio of the silver-coated layer shall be determined by measuring the amount of silver in the silver-coated metal powder.

(Ratio of D ₅₀ to D _BET (D ₅₀ / D _BET ))
In the embodiment of the silver-coated metal powder of the present invention, the ratio (D ₅₀ / D _BET ) of the cumulative 50% particle diameter (D ₅₀ ) to the particle diameter ( _DBET ) is 1.65 or less. D ₅₀ is the so-called aggregated particle diameter, and D _BET is the primary particle diameter. Therefore, these ratios are indicators of the degree of aggregation of the powder, and in the embodiment of the silver-coated metal powder of the present invention, this is as small as 1.65 or less, and the aggregation of particles is suppressed. From the viewpoint of suppressing aggregation, the ratio of the silver-coated metal powder (D ₅₀ / D _BET ) is preferably 1.58 or less, more preferably 1.45 or less (usually, D ₅₀ / D _BET is usually used. 1.00 or more).
_{The DBET} is calculated by the following formula (1).
D _BET = 6 / (ρ × BET) ・ ・ ・ (1)
In formula (1), ρ is the specific gravity and composition ratio of each constituent metal element (excluding those corresponding to unavoidable impurities) of the silver-coated metal powder (when the total mass ratio of each constituent metal element is 100% by mass). It is a density (g / cm ³ ) calculated from each mass ratio).

(Copper ion elution amount)
Regarding the embodiment of the silver-coated metal powder of the present invention, the copper ion elution amount when 5 g of this powder is immersed in 45 g of a sulfuric acid aqueous solution having a pH of 0 for 30 minutes is preferably 450 mg / L or less. Details of this dissolution test will be described later in Examples. As described above, when a silver-coated metal powder having a small copper ion elution amount is used to produce a conductive paste, the increase in viscosity of the paste over time is small. From this point, the elution amount of copper ions is more preferably 420 mg / L or less, further preferably 390 mg / L or less (usually 20 mg / L or more). The amount of copper ion elution is determined as the weight of copper corresponding to the amount of copper ion by performing inductively coupled plasma emission spectroscopic analysis on the eluate obtained in the elution test.

(Production of BET specific surface area and average particle size (D ₅₀ ) (BET x D ₅₀ ))
The product (BET × D ₅₀ ) of D ₅₀ and the BET specific surface area (BET) of the embodiment of the silver-coated metal powder of the present invention is preferably 1.07 (m ² · μm / g) or less. BET is affected by the surface shape of the silver-coated metal powder, and its value increases as the surface of the particles constituting the powder has many portions having a shape away from the true sphere, such as irregularities. The BET also changes depending on the particle size of the silver-coated metal powder, and the smaller the particle size, the larger the BET. Therefore, by taking the product of BET and D ₅₀ , it is possible to use it as an index of the shape of the particle surface of the silver-coated metal powder, excluding the influence of the particle size. Metal core particles having a mass ratio of copper of 80% or more are easily oxidized, and even if they are coated with silver, the oxide may remain on the surface, and in this case, the BET becomes large. For example, in the embodiment of the silver-coated metal powder of the present invention produced by the embodiment of the method for producing a silver-coated metal powder of the present invention, the silver coating is uniform and the oxide on the surface of the metal core particles is small. The product (BET × D ₅₀ ) is small. The product (BET × D ₅₀ ) is more preferably 0.95 (m ² · μm / g) or less (it is usually 0.40 (m ² · μm / g) or more).

(Production of oxygen content (O) and average particle size (D ₅₀ ) (O × D ₅₀ ))
The product (O × D ₅₀ ) of the oxygen content (O) and D ₅₀ of the embodiment of the silver-coated metal powder of the present invention is preferably 0.38 (mass% · μm) or less. Since the oxygen content increases as the particle size of the powder decreases, the oxygen content of the silver-coated metal powder excluding the variation due to the particle size can be obtained by taking the product of these. For example, in the embodiment of the silver-coated metal powder of the present invention produced in the embodiment of the production of the silver-coated metal powder of the present invention, it is considered that the amount of oxide on the surface of the metal core particles is small, and the product (O). × D ₅₀ ) is small and has excellent conductivity. From the viewpoint of this conductivity, the product (O × D ₅₀ ) is more preferably 0.37 (mass% · μm) or less (it is usually 0.10 (mass% · μm) or more).

(Average particle size (D ₅₀ ))
The cumulative 50% particle size ( _D50 ) on a volume basis measured by the laser diffraction type particle size distribution measuring device of the embodiment of the silver-coated metal powder of the present invention is fine line drawing or thin conductive film when used for a conductive paste. From the viewpoint of forming the above, 0.1 to 10.0 μm is preferable, 0.8 to 8.0 μm is more preferable, and 1.2 to 6.0 μm is even more preferable.

(Oxygen content)
From the viewpoint of conductivity, the oxygen content of the embodiment of the silver-coated metal powder of the present invention is preferably 0.40% by mass or less, and more preferably 0.07 to 0.25% by mass.

(BET specific surface area)
The specific surface area (BET) measured by the BET one-point method according to the embodiment of the silver-coated metal powder of the present invention is preferably 0.08 to 1.50 m ² / g from the viewpoint of exhibiting good conductivity. It is more preferably 0.10 to 1.00 m ² / g, and particularly preferably 0.15 to 0.80 m ² / g.

(Tap density)
The tap density of the embodiment of the silver-coated metal powder of the present invention is preferably 3.0 to 8.5 g / cm ³ from the viewpoint of increasing the packing density of the powder and exhibiting good conductivity, which is more preferable. Is 4.0 to 7.0 g / cm ³ .

(Carbon content)
The carbon content of the silver-coated metal powder of the present invention is preferably 0.05 to 0.40% by mass, more preferably 0.08 to 0.25% by mass.

(shape)
The shape of the embodiment of the silver-coated metal powder of the present invention is not particularly limited, and may be spherical, substantially spherical, granular, flaky, or amorphous.

[Conductive paste]
Next, an embodiment of the conductive paste of the present invention will be described. This conductive paste comprises embodiments of the silver-coated metal powder of the present invention and a solvent and / or resin binder. The conductive paste consists of a sintered conductive paste that decomposes and volatilizes the solvent and resin components in the paste by firing at a high temperature and sinters the metal powders together, and the resin component by heating at a lower temperature than the sintered type. There is a resin curing type in which metal powders are brought into contact with each other by the shrinkage of the resin at the time of curing to achieve conduction. The embodiment of the conductive paste of the present invention can be used as any conductive paste.

In the embodiment of the conductive paste of the present invention, two or more kinds of silver-coated metal powders having different types in terms of particle size, shape and other points, which correspond to the silver-coated metal powder of the present invention, may be used in combination. good. The content of the silver-coated metal powder in the conductive paste is preferably 50 to 98% by mass, more preferably 70 to 97% by mass, from the viewpoint of forming an appropriate conductive conductive film.

In the embodiment of the conductive paste of the present invention, copper powder, silver powder, aluminum powder, nickel powder, zinc powder, tin powder, bismuth powder and the like, depending on the required properties, as long as the effects of the present invention are not impaired. Metal powders other than the silver-coated metal powder of the present invention, such as phosphorus powder, may be added. The content of the metal powder in the conductive paste is preferably 1 to 48% by mass. Further, the metal powder may be used alone or in combination of two or more.

The total content of the silver-coated metal powder and the metal powder in the conductive paste is preferably 50 to 98% by mass, more preferably 70 to 97% by mass from the viewpoint of forming an appropriate conductive conductive film. Is.

Embodiments of the conductive paste of the present invention include a solvent and / or a resin binder. As the solvent, known solvents can be used without particular limitation as long as the effects of the present invention are not impaired, and examples thereof include texanol (2,2,4-trimethyl-1,3-pentanediol 2-methylpropa). Noart), tarpineol, carbitol acetate (diethylene glycol monoethyl ether acetate), ethylene glycol, dibutyl acetate, diethylene glycol monobutyl ether acetate and other polar solvents can be mentioned. These can be used alone or in combination of two or more. As the resin binder, known resin binders can be used without particular limitation as long as the effects of the present invention are not impaired. Examples thereof include ethyl cellulose, ethyl hydroxyethyl cellulose, hydroxypropylmethyl cellulose, hydroxypropylmethyl cellulose phthalate, rosin and phenoxy. Examples thereof include thermoplastic resins such as resins and polyacetal resins. These may be used alone or in combination of two or more.

Further, the content of the solvent in the embodiment of the conductive paste of the present invention is preferably 0.5 to 49% by mass, more preferably 1 to 28% by mass. The content of the resin binder in the embodiment of the conductive paste of the present invention is preferably 0.5 to 40% by mass, more preferably 1 to 25% by mass.

If necessary, additives such as surfactants, dispersants, stabilizers, plasticizers, and metal oxide powders may be added to the conductive paste of the present invention.

When the conductive paste is a resin-curable conductive paste, the paste contains a curable resin. This can also serve as the above resin binder. The curable resin includes a thermosetting resin and a photocurable resin, and the thermosetting resin includes a phenol resin, a urea resin, an epoxy resin, a polyurethane resin, a polyvinyl butyral resin, a polyimide resin, and a (meth) acrylic resin. Examples of the photocurable resin include (meth) acrylic resin, maleic acid resin, polybutadiene resin, epoxy resin, phenol resin and the like. These curable resins can be used alone or in combination of two or more. The content of the curable resin in the conductive paste is preferably 0.5 to 40% by mass, more preferably 1 to 25% by mass.

In the embodiment of the conductive paste of the present invention, when the paste is cured by heating, a thermal polymerization initiator may be added in order to cure or accelerate the curing. Further, in order to promote curing, a curing agent such as polyamine, acid anhydride, a boron trihalogenated compound, or an amine complex salt of a boron trihalogenated compound may be added.

Further, when the embodiment of the conductive paste of the present invention is photopolymerized, a photopolymerization initiator is contained in the conductive paste. As the photopolymerization initiator, a photoradical generator or a photocationic polymerization initiator is usually used. It is also possible to add a photosensitizer to the conductive paste.

The method for preparing the embodiment of the conductive paste of the present invention described above is not particularly limited. It can be prepared by pre-kneading using a universal stirrer, a kneader, or the like, and then main-kneading with three rolls. Further, if necessary, a solvent may be added thereafter to adjust the viscosity of the conductive paste.

The embodiment of the conductive paste of the present invention can form a conductive film having excellent conductivity. Specifically, when the conductive film is formed as follows, the volume resistivity of the conductive film is preferably 1.5 × 10 ^-5 Ω · cm to 5.5 × 10 ^-5 Ω · cm. , More preferably 2.0 × 10 ^-5 Ω · cm to 4.2 × 10 ^-5 Ω · cm. Details of this resistance evaluation method will be described in Examples.
93 g of silver-coated metal powder, 8.2 g of bisphenol F type epoxy resin as a thermosetting resin, 0.41 g of boron trifluoride monoethylamine, 2.5 g of butyl carbitol acetate as a solvent, and 0.1 g of oleic acid. Is mixed with a kneading and defoaming machine, and then passed through three rolls five times to uniformly disperse the mixture to obtain a conductive paste. This conductive paste is printed on an alumina substrate by a screen printing method (on a screen plate having a line width of 500 μm and a line length of 37.5 mm and a thickness of 20 μm), and then fired in the air at 200 ° C. for 40 minutes to cure. A conductive film is formed by allowing the film to form a conductive film. The volume resistivity of this conductive film is obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[ Reference example 1 ]
<Manufacturing of powder of copper core particles>
While 95 parts by mass of copper and 5 parts by mass of zinc are heated to 1200 ° C. in an atmospheric atmosphere and the molten metal melted is dropped from the lower part of the tundish, high-pressure water is sprayed in the atmospheric atmosphere by a water atomizing device to quench and solidify. The obtained slurry was separated into solid and liquid, and the solid was washed with water, dried, crushed and classified to obtain a copper-zinc alloy powder.
When the alloy composition and particle size distribution of the copper-zinc alloy powder thus obtained were obtained, the mass ratio of copper was 95.10% by mass with respect to the total mass ratio of copper and zinc of 100% by mass. The mass ratio of zinc was 4.90% by mass, and the cumulative 50% particle size ( _D50 ) was 1.7 μm.
The alloy composition of the copper-zinc alloy powder was measured as follows. After laying copper-zinc alloy powder (about 2.5 g) in a vinyl chloride ring (inner diameter 3.2 mm x thickness 4 mm), a tablet-type molding compressor (model number BRE-50 manufactured by Maekawa Test Mfg. Co., Ltd.) Pellets are prepared by applying a load of 100 kN, and the pellets are placed in a sample holder (opening diameter 3.0 cm) and set at the measurement position in a fluorescent X-ray analyzer (RIX2000 manufactured by Rigaku Co., Ltd.) to create a measurement atmosphere. Was measured under reduced pressure (8.0 Pa) and the X-ray output was 50 kV and 50 mA, and the ratio of each metal element was automatically calculated by the software attached to the device. From this calculation result, the mass ratios of copper and zinc were obtained when the total mass ratio was 100% by mass.
For the cumulative 50% particle size (D ₅₀ ) of the copper-zinc alloy powder, a laser diffraction type particle size distribution measuring device (Hellos particle size distribution measuring device (HELOS & RODOS (air flow type drying module)) manufactured by SYSTEMTEC) was used. Then, it was measured as a volume-based cumulative 50% particle diameter (D ₅₀ ) at a dispersion pressure of 5 bar.

<Silver coating>
A solution of 16.2 kg of hydroxyethylethylenediamine trisodium acetate (Kirest HC, manufactured by Chubu Kirest Co., Ltd., sold by Kirest Co., Ltd.) as a chelating agent and 36.8 kg of tartrate acid as a pH adjuster / buffer in 369 kg of pure water. 67 kg of the copper-zinc alloy powder obtained above was added to this solution while stirring to prepare an aqueous dispersion of the copper-zinc alloy powder. The liquid temperature of this aqueous dispersion was 25 ° C., and the pH at this temperature was 2.5. In the pH measurement, zero calibration and span calibration with a pH standard solution were performed according to JISZ8802: 2011 “pH measurement method”.
While blowing nitrogen gas into the aqueous dispersion whose temperature and pH were adjusted in this way (the blowing continues until the end of the substitution reaction), 291.2 kg of silver nitrate aqueous solution (silver nitrate (manufactured by Toyo Kagaku Kogyo Co., Ltd.) 26.2 kg) was added. (Dissolved in 265 kg of pure water) was continuously added over 60 minutes, and the obtained mixed solution (reaction solution) was stirred to carry out a substitution reaction. In this reaction, the pH of the reaction solution gradually decreased, and the pH at the end of the substitution reaction was 1.7 (25 ° C.). The termination of the substitution reaction is determined by the fact that the vicinity of the surface of the reaction solution is separated with a dropper, potassium iodide is added to the filtrate obtained by filtering the separated solution, and no AgI precipitate is formed. bottom.
The reaction solution in which the substitution reaction was completed was filtered, the residue (solid matter) was washed with water, dried, and crushed to obtain a silver-coated copper alloy powder.
The production conditions of the above silver-coated copper alloy powder and the cumulative 50% particle diameter ( _D50 ) of the core particle powder are summarized in Table 1 below. Reference Examples 2 to 4, Examples 4 to 6 , and Comparative Examples 1 and 2 described later are also shown.

得られた銀被覆銅合金粉末について、ＢＥＴ比表面積（ＢＥＴ）、タップ密度、酸素含有量（Ｏ）、炭素含有量、粒度分布、銀被覆層の質量割合（銀量）、銅及び亜鉛の質量割合の合計１００質量％に対するそれぞれの質量割合、Ｄ_ＢＥＴ、Ｄ_５０／Ｄ_ＢＥＴ、ＢＥＴ×Ｄ_５０、Ｏ×Ｄ_５０、硫酸による銅の溶出量、導電性ペーストとしたときの粘度変化率を求め、導電性ペーストの抵抗評価を行った。具体的な測定等の方法は以下の通りである。

About the obtained silver-coated copper alloy powder, BET specific surface area (BET), tap density, oxygen content (O), carbon content, particle size distribution, mass ratio of silver-coated layer (silver content), mass of copper and zinc. Obtain the respective mass ratios to 100% by mass of the total ratio, D _BET , D ₅₀ / D _BET , BET × D ₅₀ , O × D ₅₀ , the amount of copper eluted with sulfuric acid, and the rate of change in viscosity when made into a conductive paste. , The resistance of the conductive paste was evaluated. The specific measurement method is as follows.

BET specific surface area (BET): Using a BET specific surface area measuring instrument (4 Sorb US manufactured by Yuasa Ionics Co., Ltd.), nitrogen gas was flowed through the measuring instrument at 105 ° C. for 20 minutes to degas, and then nitrogen was added. The measurement was carried out by the BET 1-point method while flowing a mixed gas of helium (N ₂ : 30% by volume, He: 70% by volume).
From the _BET specific surface area obtained here, the DBET of the silver-coated copper alloy powder was calculated from the following formula (1).
D _BET = 6 / (ρ × BET) ・ ・ ・ (1)
Here, the density ρ of the silver-coated copper alloy powder was determined as follows. First, the amount of silver is measured by the method described below, and this mass ratio is subtracted from 100% by mass (the obtained value is defined as the value A). Then, the mass ratio of each of copper and zinc in the silver-coated copper alloy powder is determined by the method described below. Multiply each of these mass ratios by the value A. The density ρ of the silver-coated copper alloy powder was obtained by multiplying each mass ratio of silver, copper, and zinc in the silver-coated copper alloy powder thus obtained by the respective densities and adding them. Specifically, the formula is as follows.
ρ = 10.49 (g / cm ³ ) x 22.3% + 8.94 (g / cm ³ ) x (100% -22.3%) x 95.1% + 7.14 (g / cm ³ ) x (100% -22.3%) x 4.9%
= 9.22 (g / cm ³ )

Tap density: Similar to the method described in JP-A-2007-263860, silver-coated copper alloy powder is filled in a bottomed cylindrical die having an inner diameter of 6 mm and a height of 11.9 mm up to 80% of the volume of silver. A coated copper alloy powder layer is formed, and a pressure of 0.160 N / m ² is uniformly applied to the upper surface of the silver-coated copper alloy powder layer until the silver-coated copper alloy powder is no longer densely filled with this pressure. After compressing the silver-coated copper alloy powder, the height of the silver-coated copper alloy powder layer is measured, and the measured value of the height of the silver-coated copper alloy powder layer and the weight of the filled silver-coated copper alloy powder are used. , The density of the silver-coated copper alloy powder was obtained, and this was used as the tap density.

Oxygen content (O): Measured with an oxygen / nitrogen analyzer (TC-436 type manufactured by LECO).

Carbon content: Measured with a carbon / sulfur analyzer (EMIA-22V manufactured by HORIBA, Ltd.).

Particle size distribution: Using a laser diffraction type particle size distribution measuring device (SIMPATEC's Heros particle size distribution measuring device (HELOS & RODOS (air flow type drying module))), a cumulative 10% particle size based on volume at a dispersion pressure of 5 bar ( D ₁₀ ), cumulative 25% particle size (D ₂₅ ), cumulative 50% particle size (D ₅₀ ), cumulative 75% particle size (D ₇₅ ), cumulative 90% particle size (D ₉₀ ) and cumulative 99% particle size (D 90). D ₉₉ ) was sought.

Weight ratio (silver amount) of silver-coated layer: The silver-coated copper alloy powder was dissolved in nitric acid, and then the precipitate of silver chloride (AgCl) produced by adding hydrochloric acid was dried and weighed.
The respective mass ratios of copper and zinc in the silver-coated copper alloy powder: the same as in the case of the copper-zinc alloy powder described above.

Elution amount of copper by sulfuric acid: 45 g of a sulfuric acid aqueous solution having a liquid temperature of 25 ° C. and a pH meter reading of 0 and 5 g of silver-coated copper alloy powder are placed in a 100 ml poly wide-mouthed bottle and used in an ultrasonic cleaner with a high frequency output of 200 W. Ultrasound was applied for 30 minutes. The slurry after application of ultrasonic waves was solid-liquid separated by a 0.2 μm filter, and the amount of copper ions in the obtained eluate was determined by inductively coupled plasma (ICP) emission spectroscopy.

Resistance evaluation of conductive paste: 93 g of silver-coated copper alloy powder, 8.2 g of bisphenol F type epoxy resin (Adecaledin EP-491E manufactured by ADEKA Co., Ltd.) as a thermosetting resin, and 0.41 g of boron trifluoride monoethylamine. After mixing 2.5 g of butyl carbitol acetate and 0.1 g of oleic acid as a solvent with a kneading defoaming machine, a conductive paste was obtained by passing three rolls 5 times and uniformly dispersing them. .. The conductive paste is printed on an alumina substrate by a screen printing method (on a screen plate having a line width of 500 μm and a line length of 37.5 mm and a thickness of 20 μm), and then baked in the air at 200 ° C. for 40 minutes to be cured. As a result, a conductive film was formed, and the volume resistivity of the obtained conductive film was calculated. For the volume resistivity of the conductive film, the line resistivity of the obtained conductive film is measured by a digital multimeter (AD7541A manufactured by ADCC), and the film thickness is measured by a surface roughness shape measuring machine (Surfcom 1500DX type manufactured by Tokyo Precision Co., Ltd.). ), And calculated from the formula of volume resistivity (Ω · cm) = line resistivity (Ω) × film thickness (cm) × line width (cm) / line length (cm).

Viscosity change rate of conductive paste: A vehicle was prepared by dissolving 4 g of ethyl cellulose (Etocell 100 cps: manufactured by The Dow Chemical Company) and 5 g of hydroxypropylmethyl cellulose phthalate (HP-55S manufactured by Shin-Etsu Chemical) in 91 g of terpineol. A conductive paste was obtained by mixing 5 g of the silver-coated copper alloy powder with 5 g of the vehicle with a kneading and defoaming machine, and then passing the three rolls 5 times to uniformly disperse the powder. The paste viscosity was measured at 25 ° C. at 1 rpm (slip rate 2 sec ^-1 ) using a viscometer (DV-III viscometer manufactured by Brookfield, CP-52 cone). The viscosity measured immediately after the paste was prepared was η1, the viscosity at 25 ° C. measured after being left at a constant temperature of 25 ° C. for 4 days was defined as η2, and (η2-η1) / η1 × 100 (%) was defined as the viscosity change rate.

The above results are shown in Tables 2 and 3 below. The results of Reference Examples 2 to 4, Examples 4 to 6 , and Comparative Examples 1 and 2, which will be described later, are also shown.

[ Reference example 2 ]
In the silver coating process, the chelating agent used was changed to 1.6 kg of nitrilotriacetic acid (Kirest NT, manufactured by Chubu Kirest Co., Ltd., sold by Kirest Co., Ltd.), and 11.0 kg of tartaric acid and tartaric acid were used as pH adjusters and buffers. A silver-coated copper alloy powder was produced in the same manner as in Reference Example 1 except that 1.9 kg of sodium was used. The pH of the aqueous dispersion is 2.4 (25 ° C.), the pH of the reaction solution gradually decreases as the silver coating (substitution) reaction progresses, and the pH (25 ° C.) at the end of the substitution reaction is 1. It was 4.

Regarding the obtained silver-coated copper alloy powder, in the same manner as in Reference Example 1 , BET specific surface area, tap density, oxygen content, carbon content, particle size distribution, mass ratio of silver-coated layer (silver content), copper and zinc. Each mass _ratio to a _total of _{100 %} by _mass of Was obtained, and the resistance of the conductive paste was evaluated. The results are as shown in Tables 2 and 3 above.

[ Reference example 3 ]
Silver-coated copper in the same manner as in Reference Example 1 except that the amount of the chelating agent used was changed to 32.4 kg and the amount of the pH adjuster / buffer (tartaric acid) used was changed to 73.6 kg in the silver coating step. Alloy powder was produced. The pH of the aqueous dispersion is 2.3 (25 ° C.), the pH of the reaction solution gradually decreases as the silver coating (substitution) reaction progresses, and the pH (25 ° C.) at the end of the substitution reaction is 1. It was 7.

Regarding the obtained silver-coated copper alloy powder, in the same manner as in Reference Example 1 , BET specific surface area, tap density, oxygen content, carbon content, particle size distribution, mass ratio of silver-coated layer (silver content), copper and zinc. Each mass _ratio to a _total of _{100 %} by _mass of Was obtained, and the resistance of the conductive paste was evaluated. The results are as shown in Tables 2 and 3 above.

[Example 4]
A copper alloy having a cumulative 50% particle diameter (D ₅₀ ) of an alloy composition of 95.00% by mass of copper and 5.00% by mass (and unavoidable impurities) of silver-coated metal core particles. It was changed to powder (manufactured by the water atomizing method as in Reference Example 1 except that the classification conditions were changed), and the chelating agent was hydroxyethylethylenediamine triacetic acid (Kirest HA, manufactured by Chubu Kirest Co., Ltd., Kirest) in the silver coating process. (Sold by Co., Ltd.) A silver-coated copper alloy powder was produced in the same manner as in Reference Example 1 except that the weight was changed to 23.7 kg and the pH adjuster / buffer was changed to 9.2 kg of tartrate acid and 4.7 kg of sodium tartrate. .. The pH of the aqueous dispersion is 2.3 (25 ° C.), the pH of the reaction solution gradually decreases as the silver coating (substitution) reaction progresses, and the pH (25 ° C.) at the end of the substitution reaction is 1. It was 5.

Regarding the obtained silver-coated copper alloy powder, in the same manner as in Reference Example 1 , BET specific surface area, tap density, oxygen content, carbon content, particle size distribution, mass ratio of silver-coated layer (silver content), copper and zinc. Each mass _ratio to a _total of _{100 %} by _mass of Was obtained, and the resistance of the conductive paste was evaluated. The results are as shown in Tables 2 and 3 above.

[Example 5]
The powder of the metal core particles coated with silver is a copper powder having a cumulative 50% particle diameter (D ₅₀ ) of 3.6 μm (as a molten copper, by the water atomization method as in Reference Example 1 except that the classification conditions are changed. In the silver coating process, the chelating agent was changed to 23.7 kg of Kirest HA, the pH adjuster / buffer was changed to 9.2 kg of tartrate acid and 4.7 kg of sodium tartrate, and the silver nitrate solution was changed to silver nitrate. A silver-coated copper powder was produced in the same manner as in Reference Example 1 except that 11.7 kg was changed to a solution dissolved in 118 kg of pure water and the addition time was changed to 30 minutes. The pH of the aqueous dispersion is 2.4 (25 ° C.), the pH of the reaction solution gradually decreases as the silver coating (substitution) reaction progresses, and the pH (25 ° C.) at the end of the substitution reaction is 1. It was 7.

Regarding the obtained silver-coated copper powder, in the same manner as in Reference Example 1 , BET specific surface area, tap density, oxygen content, carbon content, particle size distribution, mass ratio of silver-coated layer (silver content), copper and zinc. The respective mass ratios to the total 100% by mass of the mass ratios, D _BET , D ₅₀ / D _BET , BET × D ₅₀ , O × D ₅₀ , the amount of copper eluted with sulfuric acid, and the rate of change in viscosity when made into a conductive paste. The resistance of the conductive paste was evaluated. The results are as shown in Tables 2 and 3 above.

[Example 6]
The silver-coated metal core particle powder is a copper powder having a cumulative 50% particle diameter (D ₅₀ ) of 2.0 μm (as a molten copper solution, and the classification conditions are changed, but the water atomization method is used in the same manner as in Reference Example 1 . In the silver coating process, the chelating agent was changed to Kirest NT 1.6 kg, the pH adjuster / buffer was changed to 11.0 kg of tartrate acid and 1.9 kg of sodium tartrate, and the silver nitrate aqueous solution was changed to silver nitrate 11. A silver-coated copper powder was produced in the same manner as in Reference Example 1 except that 7 kg was changed to a solution dissolved in 118 kg of pure water and the addition time of the silver nitrate aqueous solution was changed to 30 minutes. The pH of the aqueous dispersion is 2.1 (25 ° C.), the pH of the reaction solution gradually decreases as the silver coating (substitution) reaction progresses, and the pH (25 ° C.) at the end of the substitution reaction is 1. It was 5.

Regarding the obtained silver-coated copper powder, in the same manner as in Reference Example 1 , BET specific surface area, tap density, oxygen content, carbon content, particle size distribution, mass ratio of silver-coated layer (silver content), copper and zinc. The respective mass ratios to the total 100% by mass of the mass ratios, D _BET , D ₅₀ / D _BET , BET × D ₅₀ , O × D ₅₀ , the amount of copper eluted with sulfuric acid, and the rate of change in viscosity when made into a conductive paste. The resistance of the conductive paste was evaluated. The results are as shown in Tables 2 and 3 above.

[ Reference example 4 ]
A silver-coated copper alloy powder was produced in the same manner as in Reference Example 3 except that the temperature of the reaction solution in the silver coating step was set to 20 ° C. The pH of the aqueous dispersion is 2.3 (25 ° C.), the pH of the reaction solution gradually decreases as the silver coating (substitution) reaction progresses, and the pH (25 ° C.) at the end of the substitution reaction is 1. It was 7.

Regarding the obtained silver-coated copper alloy powder, in the same manner as in Reference Example 1 , BET specific surface area, tap density, oxygen content, carbon content, particle size distribution, mass ratio of silver-coated layer (silver content), copper and zinc. The respective mass ratios, D _BET , D ₅₀ / D _BET , BET × D ₅₀ , and O × D ₅₀ with respect to the total mass ratio of 100% by mass were determined, and the resistance of the conductive paste was evaluated. The results are as shown in Tables 2 and 3 above.

[Comparative Example 1]
In the silver coating step, the chelating agent used was changed to 31.7 kg of ethylenediaminetetraacetic acid disodium (EDTA.2Na), the pH adjuster / buffer was changed to 16.7 kg of potassium hydrogen phthalate, and the addition time of the silver nitrate aqueous solution was changed. A silver-coated copper alloy powder was produced in the same manner as in Reference Example 1 except that the value was changed to 135 minutes. The pH of the aqueous dispersion is 4.3 (25 ° C.), the pH of the reaction solution gradually decreases as the silver coating (substitution) reaction progresses, and the pH (25 ° C.) at the end of the substitution reaction is 2. It was eight.

Regarding the obtained silver-coated copper alloy powder, in the same manner as in Reference Example 1 , BET specific surface area, tap density, oxygen content, carbon content, particle size distribution, mass ratio of silver-coated layer (silver content), copper and zinc. Each mass ratio to 100% by mass of the total mass ratio of, D _BET , D ₅₀ / D _BET , BET × D ₅₀ , O × D ₅₀ , the amount of copper eluted with sulfuric acid, resistance evaluation when making a conductive paste, The rate of change in viscosity of the conductive paste was determined. The results are as shown in Tables 2 and 3 above.

[Comparative Example 2]
In the silver coating step, a silver-coated copper alloy powder was produced in the same manner as in Reference Example 1 except that a chelating agent was not used and the pH adjuster / buffer was changed to 1.9 kg of tartaric acid. The pH of the aqueous dispersion is 2.6 (25 ° C.), the pH of the reaction solution gradually decreases as the silver coating (substitution) reaction progresses, and the pH (25 ° C.) at the end of the substitution reaction is 1. It was 5.
Regarding the obtained silver-coated copper alloy powder, in the same manner as in Reference Example 1 , BET specific surface area, tap density, oxygen content, carbon content, particle size distribution, mass ratio of silver-coated layer (silver content), copper and zinc. Each mass ratio to 100% by mass of the total mass ratio of, D _BET , D ₅₀ / D _BET , BET × D ₅₀ , O × D ₅₀ , the amount of copper eluted with sulfuric acid, resistance evaluation when making a conductive paste, The rate of change in viscosity of the conductive paste was determined. The results are as shown in Tables 2 and 3 above.

As shown in Table 3, in Comparative Example 1 in which the pH of the mixed solution was not maintained at 2.6 or less during the silver coating reaction, the _D50 / D _BET of the obtained silver-coated metal powder was 1.79. It is considered that the silver-coated metal powders of Reference Examples 1 to 4 and Examples 4 to 6 are larger than D ₅₀ / D _BET and have more aggregation than the silver-coated metal powders of Examples. Further, it was confirmed that not only the oxygen content was higher than that of Reference Examples 1 to 4 and Examples 4 to 6 , but also the Cu elution amount was high, and the viscosity change rate of the conductive paste was large. Further, it was confirmed that the conductive film obtained by curing the conductive paste containing the silver-coated metal powder has a higher volume resistivity than those of Reference Examples 1 to 4 and Examples 4 to 6 and has low conductivity. Was done.

Further, in Comparative Example 2 in which the chelating agent was not added to the mixed solution, the D ₅₀ / D _BET of the silver-coated metal powder was 1.70, Reference Examples 1 to 4, and Examples 4 to 6 as in Comparative Example 1. It is considered to be larger than D ₅₀ / D _BET of the silver-coated metal powder and have a lot of agglomeration. Further, it was confirmed that the oxygen content and the Cu elution amount were high and the conductivity was low as in Comparative Example 1.

Claims (22)

A method for producing a silver-coated metal powder, which comprises a silver-coated step of forming a silver-coated layer on the particle surface of the metal powder having a copper mass ratio of 80% by mass or more in a mixed solution containing silver ions and a liquid medium. ,
The mixed solution contains a chelating agent and contains
The silver coating step was carried out while keeping the pH of the mixed solution at 2.6 or less .
The chelating agent is at least one selected from the group consisting of ethylenediaminetetraacetic acid, hydroxyethylethylenediaminetriacetic acid, hydroxyethyliminodiacetic acid, nitrilotriacetic acid and salts thereof.
A method for producing a silver-coated metal powder. The metal powder is a copper alloy powder composed of copper, zinc and unavoidable impurities, and the mass ratio of copper to 100% by mass of the total mass ratio of copper and zinc in the copper alloy powder is 85.00 to 99.50% by mass. The method for producing a silver-coated metal powder according to claim 1, wherein the mass ratio of zinc is 0.50 to 15.00 mass%. The method for producing a silver-coated metal powder according to claim 1, wherein the metal powder is a copper powder composed of copper and unavoidable impurities. The metal powder is a copper alloy powder composed of copper, nickel and zinc and unavoidable impurities, and the mass ratio of copper to 100% by mass of the total mass ratio of copper, nickel and zinc in the copper alloy powder is 80.00 to 99. The silver-coated metal according to claim 1, wherein the mass ratio of nickel is .50% by mass, the mass ratio of nickel is 0.10 to 10.00 mass%, and the mass ratio of zinc is 0.40 to 19.90 mass%. How to make powder. The silver-coated metal according to any one of claims 1 to 4, wherein the silver ions are present in the mixed solution in an amount of 0.1 to 100 parts by mass with respect to 100 parts by mass of the metal powder in terms of mass as silver. How to make powder. The method for producing a silver-coated metal powder according to any one of claims 1 to 5 , wherein in the silver-coating step, the silver-coated layer is formed while blowing a non-oxidizing gas into the mixed solution. The silver coating step is carried out by adding an aqueous solution containing silver ions to the aqueous dispersion while blowing a non-oxidizing gas into the aqueous dispersion in which the chelating agent and the metal powder are dispersed in water. Item 6. The method for producing a silver-coated metal powder according to any one of Items 1 to 5 . The silver coating according to claim 7 , wherein a pH adjuster is added to the aqueous dispersion to bring the pH of the aqueous dispersion to 2.6 or less, and then an aqueous solution containing the silver ions is added to the aqueous dispersion. Method for producing metal powder. The silver-coated metal according to any one of claims 1 to 8 , wherein the cumulative 50% particle size (D50) on a volume basis measured by the laser diffraction type particle size distribution measuring device of the metal powder is 0.1 to 10.0 μm. How to make powder. A silver-coated metal powder having a metal core particle having a mass ratio of copper of 80% by mass or more and a silver-coated layer made of silver covering the core metal particle.
Cumulative 50% particle diameter (D ₅₀ ) based on the volume measured by a laser diffraction type particle size distribution measuring device with respect to the true sphere equivalent particle diameter ( _DBET ) calculated from the specific surface area of the silver-coated metal powder measured by the BET 1-point method. ) To less than 1.36 (D ₅₀ / D _BET ), silver-coated metal powder. The ratio (D) ₅₀ / D _BET ) Is 1.31 or less, the silver-coated metal powder according to claim 10. The silver-coated metal powder according to claim 10 or 11, wherein the metal core particles are composed of copper and unavoidable impurities. A silver-coated metal powder having a metal core particle having a mass ratio of copper of 80% by mass or more and a silver-coated layer made of silver covering the core metal particle.
The metal core particles are composed of copper, zinc and unavoidable impurities, and the mass ratio of copper is 85.00 to 99.50% by mass with respect to the total mass ratio of copper and zinc in the metal core particles of 100% by mass. , The mass ratio of zinc is 0.50 to 15.00 mass%,
A true sphere-equivalent particle size (D) calculated from the specific surface area of the silver-coated metal powder measured by the BET 1-point method. _BET ), A cumulative 50% particle diameter (D) based on the volume measured by a laser diffraction type particle size distribution measuring device. ₅₀ ) Ratio (D ₅₀ / D _BET ) Is less than 1.51 silver-coated metal powder. A silver-coated metal powder having a metal core particle having a mass ratio of copper of 80% by mass or more and a silver-coated layer made of silver covering the core metal particle.
The metal core particles are composed of copper, nickel and zinc and unavoidable impurities, and the mass ratio of copper is 80.00 to 99.50 with respect to the total mass ratio of copper, nickel and zinc in the metal core particles of 100% by mass. It is mass%, the mass ratio of nickel is 0.10 to 10.00 mass%, and the mass ratio of zinc is 0.40 to 19.90 mass%.
A true sphere-equivalent particle size (D) calculated from the specific surface area of the silver-coated metal powder measured by the BET 1-point method. _BET ), A cumulative 50% particle diameter (D) based on the volume measured by a laser diffraction type particle size distribution measuring device. ₅₀ ) Ratio (D ₅₀ / D _BET ) Is less than 1.51 silver-coated metal powder. The ratio (D) ₅₀ / D _BET ) Is 1.45 or less, the silver-coated metal powder according to claim 13 or 14. The silver-coated metal powder according to any one of claims 10 to 15 , wherein the copper ion elution amount when 5 g of the silver-coated metal powder is immersed in 45 g of a sulfuric acid aqueous solution having a pH of 0 for 30 minutes is 450 mg / L or less. The product of the BET specific surface area (BET) of the silver-coated metal powder measured by the BET one-point method and the cumulative 50% particle diameter (D ₅₀ ) of the volume standard measured by the laser diffraction type particle size distribution measuring device (BET × D ₅₀ ). ) Is 1.07 (m ² · μm / g) or less, according to any one of claims 10 to 16. The silver-coated metal powder according to any one of claims 10 to 16. The product (O × D ₅₀ ) of the oxygen content (O) of the silver-coated metal powder and the cumulative 50% particle size (D ₅₀ ) based on the volume measured by the laser diffraction type particle size distribution measuring device is 0.38. The silver-coated metal powder according to any one of claims 10 to 17 , which is (% by mass · μm) or less. The silver-coated metal powder according to any one of claims 10 to 18 , wherein the cumulative 50% particle size (D ₅₀ ) on a volume basis measured by a laser diffraction type particle size distribution measuring device is 0.1 to 10.0 μm. The silver-coated metal powder according to any one of claims 10 to 19 , wherein the mass ratio of the silver-coated layer in the silver-coated metal powder is 0.1 to 50% by mass. A conductive paste in which the silver-coated metal powder according to any one of claims 10 to 20 is dispersed in a solvent and / or a resin binder. A method for manufacturing a conductive film, wherein the conductive paste according to claim 21 is applied onto a substrate to form a coating film, and the coating film is fired to form a conductive film on the substrate.