JP7042945B2 - Silver-coated metal powder and its manufacturing method - Google Patents

Description

The present invention relates to a silver-coated metal powder and a method for producing the same, and more particularly to a silver-coated copper powder or a silver-coated copper alloy powder used for a conductive paste or the like and a method for producing the same.

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. ..

However, although silver powder has an extremely low volume resistivity and is a good conductive substance, it is a precious metal powder, so that the cost is high. On the other hand, copper powder has a low volume resistivity and is a good conductive substance, but it is easily oxidized, so that it is inferior in storage stability (reliability) to silver powder.

In order to solve these problems, silver-coated metal powder in which the surface of copper or copper alloy powder is coated with silver is used as the metal powder used for the conductive paste.

However, the conventional silver-coated metal powder has a problem that migration resistance is deteriorated because a layer of silver alone is present on the surface of the powder of copper or a copper alloy.

In order to solve such a problem, a method for producing silver-diffused copper powder by heat-treating a silver-coated copper powder composed of copper particles coated with silver on the surface at a temperature of 150 to 600 ° C. in a non-oxidizing atmosphere. (For example, see Patent Document 1) and a method of heating silver-coated copper powder in a wet reducing atmosphere has been proposed (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2001-11502 (paragraph number 0006) Japanese Unexamined Patent Publication No. 2003-105404 (paragraph number 0017)

However, in the conventional silver-coated metal powders such as the silver-diffused copper powder produced by the method of Patent Document 1 and the silver-coated copper powder of Patent Document 2, the particles are easily sintered with each other, and the particles are used as the conductive powder of the conductive paste. When used, there are problems that the dispersibility of the silver-coated metal powder decreases and the viscosity of the conductive paste increases with time, making it difficult to use as the conductive paste.

Therefore, in view of such conventional problems, the present invention is a silver-coated metal that makes it difficult for particles to sinter with each other and can suppress an increase in the viscosity of the conductive paste over time when used in a conductive paste. It is an object of the present invention to provide a powder and a method for producing the same.

As a result of diligent research to solve the above problems, the present inventors have coated a copper or copper alloy powder with a silver-containing layer, and then coated the copper or copper alloy powder with the silver-containing layer in a reducing atmosphere. By heating at 60 to 160 ° C. for 0.5 to 50 hours to modify the surface, it is difficult for the particles to be sintered and the increase in the viscosity of the conductive paste over time is suppressed when it is used for the conductive paste. We have found that it is possible to produce a silver-coated metal powder that can be used, and have completed the present invention.

That is, in the method for producing a silver-coated metal powder according to the present invention, copper or a copper alloy powder is coated with a silver-containing layer, and then the copper or copper alloy powder coated with the silver-containing layer is 60 to 160 in a reducing atmosphere. It is characterized in that surface modification is performed by heating at ° C. for 0.5 to 50 hours.

In this method for producing a silver-coated metal powder, the coating amount of the silver-containing layer is preferably 7 to 50% by mass with respect to the powder of copper or a copper alloy coated with the silver-containing layer, and the silver-containing layer is silver or It is preferably a layer made of a silver compound. Further, it is preferable that the copper alloy contains 1 to 50% by mass of zinc, and the balance is composed of copper and unavoidable impurities. Further, the reducing atmosphere is preferably a hydrogen atmosphere, and it is preferable to surface-treat a copper or copper alloy powder coated with a silver-containing layer with a surface treatment agent before or after surface modification. Further, it is preferable to produce copper or copper alloy powder by an atomizing method, and the volume-based cumulative 50% particle diameter (D ₅₀ diameter) measured by a laser diffraction type particle size distribution device for copper or copper alloy powder is 0.1. It is preferably ~ 15 μm.

Further, in the silver-coated metal powder according to the present invention, copper or a copper alloy powder is coated with a silver-containing layer, and a laser diffraction type particle size distribution with respect to a particle size _DBET (μm) calculated from a BET specific surface area with the particle shape as a true sphere is obtained. The ratio (D ₅₀ / D _BET ) of the volume-based cumulative 50% particle diameter (D ₅₀ diameter) measured by the apparatus is 3.5 or less, and the copper ion elution amount when immersed in a sulfuric acid aqueous solution of pH 0 for 30 minutes is 450 mg. It is characterized by being less than / L.

In this silver-coated metal powder, the coating amount of the silver-containing layer is preferably 7 to 50% by mass with respect to the powder of copper or copper alloy coated with the silver-containing layer, and the silver-containing layer is made of silver or a silver compound. It is preferably a layer consisting of. Further, it is preferable that the copper alloy contains 1 to 50% by mass of zinc, and the balance is composed of copper and unavoidable impurities. Further, it is preferable that the volume-based cumulative 50% particle diameter (D ₅₀ diameter) measured by a laser diffraction type particle size distribution device for copper or copper alloy powder is 0.1 to 15 μm.

Further, the conductive paste according to the present invention is characterized by containing a resin, a solvent and at least one of a reactive diluent, and containing the above-mentioned silver-coated metal powder as the conductive powder.

According to the present invention, it is possible to provide a silver-coated metal powder and a method for producing the same, which are difficult to sinter the particles together and can suppress an increase in the viscosity of the conductive paste over time when used in a conductive paste. can.

In the embodiment of the method for producing a silver-coated metal powder according to the present invention, a copper or copper alloy powder is coated with a silver-containing layer, and then the copper or copper alloy powder coated with the silver-containing layer is coated in a reducing atmosphere. Surface modification is performed by heating at ~ 160 ° C. for 0.5 to 50 hours.

In this method for producing a silver-coated metal powder, the silver-containing layer is preferably a layer made of silver or a silver compound. The coating amount of the silver-containing layer is preferably 7 to 50% by mass, more preferably 8 to 45% by mass, and 9 to 9 to 50% by mass with respect to the powder of copper or copper alloy coated with the silver-containing layer. Most preferably, it is 40% by mass. If the coating amount of the silver-containing layer is less than 7% by mass, the conductivity of the silver-coated metal powder is adversely affected, which is not preferable. On the other hand, if it exceeds 50% by mass, the cost increases due to an increase in the amount of silver used, which is not preferable.

When the copper alloy powder is coated with a silver-containing layer, the copper alloy contains 1 to 50% by weight (preferably 1 to 10% by weight, more preferably 2 to 5% by weight) of zinc, with the balance being copper and unavoidable. It preferably has a composition consisting of impurities. If the zinc content is less than 1% by mass, the copper in the copper alloy powder is significantly oxidized, which causes a problem in oxidation resistance, which is not preferable. On the other hand, if it exceeds 50% by mass, it adversely affects the conductivity of the silver-coated metal powder, which is not preferable.

The particle size of the copper or copper alloy powder is preferably 0.1 to 15 μm in volume-based cumulative 50% particle size (D ₅₀ size) measured by a laser diffraction type particle size distribution device (by the Heros method). It is more preferably 3 to 10 μm, and most preferably 1 to 5 μm. If the volume-based cumulative 50% particle diameter (D ₅₀ diameter) is less than 0.1 μm, it adversely affects the conductivity of the silver-coated metal powder, which is not preferable. On the other hand, if it exceeds 15 μm, it becomes difficult to form fine wiring, which is not preferable.

Copper or copper alloy powder may be produced by a wet reduction method, an electrolysis method, a gas phase method, etc., but the alloy component is melted at a melting temperature or higher, and high-pressure gas or high-pressure water is applied while dropping from the lower part of the tundish. It is preferably produced by a so-called atomizing method (gas atomizing method, water atomizing method, etc.), which is obtained by colliding and quenching and solidifying to form a fine powder. In particular, when manufactured by the so-called water atomization method in which high-pressure water is sprayed, a copper or copper alloy powder having a small particle size can be obtained. Therefore, when the copper or copper alloy powder is used as a conductive paste, contact between the particles It is possible to improve the conductivity by increasing the number of points.

As a method of coating the powder of copper or a copper alloy with a silver-containing layer, a silver or a silver compound is applied to the surface of the powder of the copper or a copper alloy by a method using a substitution reaction between copper and silver or a reduction method using a reducing agent. A method of precipitating can be used, for example, a method of precipitating silver or a silver compound on the surface of a copper or copper alloy powder while stirring a solution containing the copper or copper alloy powder and a silver or silver compound in a solvent. Alternatively, a solution containing a copper or copper alloy powder and an organic substance in the solvent and a solution containing a silver or silver compound and an organic substance in the solvent are mixed and stirred to form a silver or silver compound on the surface of the copper or copper alloy powder. Can be used, such as a method of precipitating.

As the solvent, water, an organic solvent, or a solvent obtained by mixing them can be used. When using a solvent in which water and an organic solvent are mixed, it is necessary to use an organic solvent that becomes liquid at room temperature (20 to 30 ° C.), but the mixing ratio of water and the organic solvent depends on the organic solvent used. It can be adjusted as appropriate. Further, as the water used as the solvent, distilled water, ion-exchanged water, industrial water and the like can be used as long as there is no risk of impurities being mixed.

Since silver ions need to be present in the solution as a raw material for the silver-containing layer, it is preferable to use silver nitrate having high solubility in water and many organic solvents. Further, in order to carry out the reaction of coating the powder of copper or a copper alloy with the silver-containing layer as uniformly as possible (silver coating reaction), silver nitrate is used as a solvent (water, an organic solvent or a mixed solvent thereof) instead of solid silver nitrate. It is preferable to use a silver nitrate solution dissolved in. The amount of the silver nitrate solution to be used, the concentration of silver nitrate in the silver nitrate solution, and the amount of the organic solvent can be determined according to the amount of the target silver-containing layer.

A chelating agent may be added to the solution to form the silver-containing layer more uniformly. As the chelating agent, it is preferable to use a chelating agent having a high complex stability constant with respect to copper ions and the like so that copper ions and the like that are by-produced by the substitution reaction between silver ions and metallic copper do not reprecipitate. .. In particular, since the copper or copper alloy powder that is the core of the silver-coated metal powder contains copper (as a main component), it is preferable to select the chelating agent while paying attention to the complex stability constant with copper. .. Specifically, as the chelating agent, a chelating agent selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid, diethylenetriamine, triethylenediamine and salts thereof can be used.

A pH buffer may be added to the solution in order to carry out the silver coating reaction stably and safely. As this pH buffering agent, ammonium carbonate, ammonium hydrogencarbonate, aqueous ammonia, sodium hydrogencarbonate and the like can be used.

During the silver coating reaction, copper or copper alloy powder is placed in the solution and stirred before adding the silver salt, and silver is sufficiently dispersed in the solution. It is preferable to add a solution containing salt. The reaction temperature during this silver coating reaction may not be a temperature at which the reaction solution solidifies or evaporates, but is preferably set in the range of 10 to 40 ° C, more preferably 15 to 35 ° C. The reaction time varies depending on the coating amount of silver or the silver compound and the reaction temperature, but can be set in the range of 1 minute to 5 hours.

The surface modification is carried out by subjecting a copper or copper alloy powder coated with a silver-containing layer to 60 to 160 ° C., preferably 80 to 150 ° C., more preferably 80 to 140 ° C. for 0.5 to 50 hours in a reducing atmosphere. It is preferably carried out by heating for 1 to 40 hours. When the heating temperature is lower than 60 ° C., the viscosity of the conductive paste increases with the passage of time when used for the conductive paste, and when the heating temperature is higher than 160 ° C., the particles are sintered and the particles are sintered when used for the conductive paste. The dispersibility of the silver-coated metal powder is reduced. Further, the reducing atmosphere is preferably a hydrogen atmosphere (atmosphere of 100% hydrogen gas).

Before or after this surface modification, the copper or copper alloy powder coated with the silver-containing layer is preferably surface-treated with a surface treatment agent, and the surface treatment agent is preferably fatty acid or benzotriazole. These fatty acids include butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, pelargonic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, palmitreic acid, margaric acid, stearic acid, oleic acid, bacenoic acid. , Linol acid, linolenic acid, arachidic acid, eikosazienoic acid, eikosatrienic acid, eikosatetraenoic acid, arachidonic acid, behenic acid, lignoseric acid, nervonic acid, serotic acid, montanic acid, melicic acid, etc. can be used. Although possible, it is preferred to use palmitic acid, stearic acid or oleic acid.

The amount of the surface treatment agent added is preferably 0.1 to 7% by mass, more preferably 0.3 to 6% by mass, and more preferably 0.3 to 5% by mass with respect to the silver-coated metal powder. Most preferably. The surface treatment may be performed by mixing a copper or copper alloy powder coated with a silver-containing layer and a surface treatment agent, or a surface treatment agent may be added to a slurry of copper or copper alloy powder coated with a silver-containing layer. It may be added. By surface-treating the silver-coated metal powder with a surface treatment agent (preferably 0.1 to 7% by mass of the surface treatment agent), the tap density is increased and the dispersibility is improved, and the volume resistivity of the conductive film is increased. It is possible to reduce the rate and impart oxidation resistance to reduce the rate of change in volume resistivity.

Further, in the embodiment of the silver-coated metal powder according to the present invention, a copper or copper alloy powder is coated with a silver-containing layer, and a laser with respect to a particle size _DBET (μm) calculated from the BET specific surface area with the particle shape as a true sphere is used. The ratio (D ₅₀ / D _BET ) of the volume-based cumulative 50% particle diameter (D ₅₀ diameter) measured by the diffraction type particle size distribution device is 3.5 or less, preferably 3.0 or less, and 30 in a sulfuric acid aqueous solution having a pH of 0. The elution amount of copper ions when immersed for a minute is 450 mg / L or less, preferably 420 mg / L or less. When D ₅₀ / D _BET is 3.5 or less, there is little sintering between particles, the dispersibility of the silver-coated metal powder is good when used in a conductive paste, and the elution amount of copper ions is 450 mg /. When it is L or less, it is possible to suppress an increase in the viscosity of the conductive paste with the passage of time after producing the conductive paste.

In this silver-coated metal powder, the silver-containing layer is preferably a layer made of silver or a silver compound. The coating amount of the silver-containing layer is preferably 7 to 50% by mass, more preferably 8 to 45% by mass, and 9 to 9 to 50% by mass with respect to the powder of copper or copper alloy coated with the silver-containing layer. Most preferably, it is 40% by mass. Further, it is preferable that the copper alloy contains 1 to 50% by mass of zinc, and the balance is composed of copper and unavoidable impurities. Further, the particle size of the copper or copper alloy powder is preferably 0.1 to 15 μm in volume-based cumulative 50% particle size (D ₅₀ diameter) measured by a laser diffraction type particle size distribution device (by the Heros method). , 0.3 to 10 μm is more preferable, and 1 to 5 μm is most preferable.

Hereinafter, examples of the silver-coated metal powder according to the present invention and the method for producing the same will be described in detail.

[Example 1]
While dropping 7.6 kg of copper and 0.4 kg of zinc from the bottom of the tundish, high-pressure water is sprayed to quench and solidify, filter, wash with water, dry, crush, classify, and copper alloy. A powder (copper-zinc alloy powder) was obtained.

When the composition and volume-based cumulative 50% particle diameter (D ₅₀ diameter) of the copper alloy powder thus obtained (before silver coating) were determined, the copper content in the copper alloy powder was 95.1 mass. The content of% and zinc was 4.9% by mass, and the copper alloy powder was a powder of Cu ₉₅ Zn ₅ alloy. The volume-based cumulative 50% particle diameter (D ₅₀ diameter) of the copper alloy powder was 2.0 μm. The content of copper and zinc in the copper alloy powder is determined by laying the copper alloy powder (about 2.5 g) in a vinyl chloride ring (inner diameter 3.2 mm x thickness 4 mm) and then compressing it into a tablet mold. A load of 100 kN was applied by a machine (model number BRE-50 manufactured by Maekawa Test Mfg. Co., Ltd.) to prepare pellets of copper alloy powder, and the pellets were placed in a sample holder (opening diameter 3.0 cm) for fluorescent X-ray analysis. The software attached to the device is based on the results of measurement under the conditions of setting the measurement position in the device (RIX2000 manufactured by Rigaku Co., Ltd.), setting the measurement atmosphere to reduced pressure (8.0 Pa), and setting the X-ray output to 50 kV and 50 mA. The ratio of components excluding light elements less than sodium was calculated by automatic calculation in. The volume-based cumulative 50% particle diameter (D ₅₀ diameter) of the copper alloy powder was measured by a laser diffraction type particle size distribution device (Heros particle size distribution measuring device (HELOS & RODOS) manufactured by SYSTEMC).

Further, a solution (solution 1) in which 61.9 g of EDTA-2Na dihydrate and 61.9 g of ammonium carbonate were dissolved in 720 g of pure water, and 307.1 g of EDTA-2Na dihydrate and 153.5 g of ammonium carbonate were purely prepared. A solution (solution 2) obtained by adding a solution of 51.2 g of silver nitrate in 158 g of pure water to a solution dissolved in 1223 g of water was prepared.

Next, 130 g of the obtained copper alloy powder (copper-zinc alloy powder) was added to Solution 1 under a nitrogen atmosphere, and the temperature was raised to 25 ° C. with stirring. Solution 2 is added to the solution in which this copper alloy powder (copper-zinc alloy powder) is dispersed, and the mixture is stirred for 1 hour, filtered, washed with water, dried, and silver-coated copper alloy powder (silver-coated copper-zinc alloy powder). ) Was obtained.

The silver-coated copper alloy powder was held at 80 ° C. for 10 hours in a hydrogen gas (100%) atmosphere to modify the surface of the silver-coated copper alloy powder.

The composition of the silver-coated copper alloy powder thus obtained, the volume-based cumulative 50% particle diameter ( _D50 diameter), and the BET specific surface area were determined.

The content of copper and zinc in the silver-coated copper alloy powder was determined by preparing pellets of the silver-coated copper alloy powder by the same method as the content of copper and zinc in the copper alloy powder before silver coating. Further, after processing the cross section of the silver-coated copper alloy powder with a focused ion beam (FIB) processing observation device (JEM-9310FIB manufactured by JEOL Ltd.), a field emission scanning electron microscope (FE-SEM) (JEOL Ltd.) When observed with JSM-6700F) manufactured by the company, it was confirmed that the surface of the copper alloy powder was coated with silver. Further, the coating amount of silver (Ag) in the silver-coated copper alloy powder was also determined by the same method as the content of copper and zinc in the silver-coated copper alloy powder. As a result, the silver coating amount of the silver-coated copper alloy powder was 21.8% by mass, the copper content was 74.9% by mass, and the zinc content was 3.3% by mass.

The volume-based cumulative 50% particle diameter ( _D50 diameter) of the silver-coated copper alloy powder was measured by a laser diffraction type particle size distribution device (Heros particle size distribution measuring device (HELOS & RODOS) manufactured by SYMPATEC). As a result, the volume-based cumulative 50% particle diameter (D ₅₀ diameter) was 2.2 μm.

The BET specific surface area of the silver-coated copper alloy powder was determined by the BET method using a BET specific surface area measuring device (4 Sorb US manufactured by Your Sionics Co., Ltd.). As a result, the BET specific surface area of the silver-coated copper alloy powder was 0.78 m ² / g. Further, the true density of this silver-coated copper alloy powder is the density of a single metal of Ag, Cu and Zn (Ag: 10.49 g / cm ³ , Cu: 8.92 g / cm ³ , Zn: 7.14 g / cm ³ ). When calculated as a weighted average value of, it becomes 9.20 g / cm ³ , and the particle diameter D _BET (μm) = 6 / (BET specific surface area (m ² / g) × true) calculated from the BET specific surface area with the particle shape as a true sphere. The density (g / cm ³ ) is 0.84 μm. Further, when D ₅₀ / D _BET is calculated as an index indicating the degree of sintering of the silver-coated copper alloy powder, it is 2.6. It should be noted that D ₅₀ / D. If _BET = 1, the volume-based cumulative 50% particle diameter (D ₅₀ diameter) measured by the laser diffraction type particle size distribution device and the D _BET calculated from the BET specific surface area are equal, that is, the individual particles are completely dispersed. The larger the D ₅₀ / D _BET , the larger the volume-based cumulative 50% particle diameter (D ₅₀ diameter) measured by the laser diffraction type particle size distribution device with respect to the D _BET calculated from the BET specific surface area. It indicates that the particles are large, that is, the particles are being sintered.

Further, 5 g of silver-coated copper alloy powder was placed in a wide-mouthed polypropylene bottle having a capacity of 100 mL together with 45 g of a sulfuric acid aqueous solution having a liquid temperature of 25 ° C. and a pH of 0. The amount of copper ions (copper ion elution amount) in the eluent obtained by solid-liquid separation of the obtained slurry with a 0.2 μm filter was determined by the ICP method and found to be 325 mg / L.

Further, 5 g of a vehicle prepared by dissolving 5 g of the obtained silver-coated copper alloy powder in 4 g of ethyl cellulose (100 cps) and 5 g of hydroxypropylmethyl cellulose phthalate (HP-55S manufactured by Shin-Etsu Chemical Co., Ltd.) in 91 g of terpineol (reagent). After mixing with a kneading and defoaming machine, a conductive paste was prepared by passing three rolls 5 times and uniformly dispersing them. The viscosity η1 immediately after the production of this conductive paste and the viscosity η2 measured after being left at a constant temperature of 25 ° C. for 4 days were measured at 1 rpm using a viscometer (DV-III viscometer manufactured by Brookfield, CP-52 cone). When the viscosity increase rate = (η2-η1) / η1 was determined by measuring at (slip rate 2 sec ^-1 ), the viscosity increase rate of the conductive paste was 25%.

[Example 2]
The composition and volume standard cumulative 50% of the silver-coated copper alloy powder obtained by the same method as in Example 1 except that the heating time for surface modification was set to 40 hours by the same method as in Example 1. The particle size (D ₅₀ diameter) and BET specific surface area were determined, the true density, D _BET , and D ₅₀ / D _BET were calculated, the amount of copper ions in the eluent was determined, and the viscosity increase rate of the conductive paste was determined.

As a result, the silver coating amount of the silver-coated copper alloy powder was 22.0% by mass, the copper content was 74.8% by mass, and the zinc content was 3.2% by mass. The volume-based cumulative 50% particle diameter (D ₅₀ diameter) was 2.3 μm, and the BET specific surface area was 0.75 m ² / g. The true density is 9.21 g / cm ³ , the DB _BET is 0.87 μm, and the D ₅₀ / D _BET is 2.6. The amount of copper ions in the eluate was 237 mg / L, and the viscosity increase rate of the conductive paste was 24%.

[Example 3]
The composition and volume standard cumulative 50% of the silver-coated copper alloy powder obtained by the same method as in Example 1 except that the heating temperature at the time of surface modification was set to 100 ° C. by the same method as in Example 1. The particle size (D ₅₀ diameter) and BET specific surface area were determined, the true density, D _BET , and D ₅₀ / D _BET were calculated, the amount of copper ions in the eluent was determined, and the rate of increase in viscosity of the conductive paste was determined.

As a result, the silver coating amount of the silver-coated copper alloy powder was 21.8% by mass, the copper content was 74.8% by mass, and the zinc content was 3.4% by mass. The volume-based cumulative 50% particle diameter (D ₅₀ diameter) was 2.1 μm, and the BET specific surface area was 0.77 m ² / g. The true density is 9.20 g / cm ³ , the DB _BET is 0.85 μm, and the D ₅₀ / D _BET is 2.4. The amount of copper ions in the eluate was 203 mg / L, and the viscosity increase rate of the conductive paste was 17%.

[Example 4]
The composition of the silver-coated copper alloy powder obtained by the same method as in Example 1 was obtained by the same method as in Example 1 except that the heating temperature at the time of surface modification was 150 ° C. and the heating time was 40 hours. , Volume-based cumulative 50% particle diameter (D ₅₀ diameter), BET specific surface area, true density, D _BET , D ₅₀ / D _BET , copper ion amount in eluent, viscosity of conductive paste The rate of increase was calculated.

As a result, the silver coating amount of the silver-coated copper alloy powder was 22.1% by mass, the copper content was 74.9% by mass, and the zinc content was 3.0% by mass. The volume-based cumulative 50% particle diameter (D ₅₀ diameter) was 3.0 μm, and the BET specific surface area was 0.62 m ² / g. The true density is 9.21 g / cm ³ , the DB _BET is 1.05 μm, and the D ₅₀ / D _BET is 2.9. The amount of copper ions in the eluate was 175 mg / L, and the viscosity increase rate of the conductive paste was 17%.

[Example 5]
A molten metal heated with 8 kg of copper was dropped from the lower part of the tundish and sprayed with high-pressure water to quench and solidify, filtered, washed with water, dried, crushed and classified to obtain copper powder.

When the volume-based cumulative 50% particle diameter (D ₅₀ diameter) of the copper powder thus obtained (before silver coating) was determined by the same method as in Example 1, the volume-based cumulative 50% particles of the copper powder were obtained. The diameter (D ₅₀ diameter) was 2.3 μm.

Further, a solution (solution 1) in which 61.9 g of EDTA-2Na dihydrate and 61.9 g of ammonium carbonate were dissolved in 720 g of pure water, and 136.5 g of EDTA-2Na dihydrate and 68.2 g of ammonium carbonate were purely prepared. A solution (solution 2) obtained by adding a solution of 22.7 g of silver nitrate in 70 g of pure water to a solution dissolved in 544 g of water was prepared.

Next, 130 g of the obtained copper powder was added to the solution 1 under a nitrogen atmosphere, and the temperature was raised to 25 ° C. with stirring. Solution 2 was added to the solution in which the copper powder was dispersed, and the mixture was stirred for 1 hour, filtered, washed with water, and dried to obtain silver-coated copper powder.

The silver-coated copper powder was held at 100 ° C. for 1 hour in a hydrogen gas (100%) atmosphere to modify the surface of the silver-coated copper powder.

Next, 80 g of the obtained silver-coated copper powder and 0.24 g of palmitic acid (0.3% by mass based on the silver-coated copper powder) were placed in a cutter mill and crushed for 20 seconds twice to obtain palmitic acid. A silver-coated copper powder surface-treated with acid was obtained.

For the silver-coated copper powder thus obtained, the composition, volume-based cumulative 50% particle diameter (D ₅₀ diameter), and BET specific surface area were determined by the same method as in Example 1, and the true density, _DBET , and D were obtained. ₅₀ / D _BET was calculated, the amount of copper ions in the eluent was determined, and the viscosity increase rate of the conductive paste was determined.

As a result, the silver coating amount of the silver-coated copper powder was 10.6% by mass, and the copper content was 89.4% by mass. The volume-based cumulative 50% particle diameter (D ₅₀ diameter) was 2.3 μm, and the BET specific surface area was 0.51 m ² / g. The true density is 9.09 g / cm ³ , the DB _BET is 1.29 μm, and the D ₅₀ / D _BET is 1.8. The amount of copper ions in the eluate was 404 mg / L, and the viscosity increase rate of the conductive paste was 29%.

[Example 6]
The composition of the silver-coated copper powder obtained by the same method as in Example 5 except that the heating temperature at the time of surface modification was 120 ° C. and the heating time was 10 hours was prepared by the same method as in Example 1. Volume-based cumulative 50% particle diameter (D ₅₀ diameter), BET specific surface area are calculated, true density, _{DB BET} , D ₅₀ / D _BET are calculated, the amount of copper ions in the eluent is determined, and the viscosity of the conductive paste is increased. I asked for the rate.

As a result, the silver coating amount of the silver-coated copper powder was 10.4% by mass, and the copper content was 89.6% by mass. The volume-based cumulative 50% particle diameter (D ₅₀ diameter) was 2.3 μm, and the BET specific surface area was 0.48 m ² / g. The true density is 9.08 g / cm ³ , the DB _BET is 1.38 μm, and the D ₅₀ / D _BET is 1.7. The amount of copper ions in the eluate was 297 mg / L, and the viscosity increase rate of the conductive paste was 22%.

[Comparative Example 1]
Regarding the silver-coated copper alloy powder obtained by the same method as in Example 1 except that the surface was not modified, the composition and volume-based cumulative 50% particle diameter ( _D50 diameter) were obtained by the same method as in Example 1. ), The BET specific surface area was calculated, the true density, D _BET , and D ₅₀ / D _BET were calculated, the amount of copper ions in the eluent was determined, and the viscosity increase rate of the conductive paste was determined.

As a result, the silver coating amount of the silver-coated copper alloy powder was 22.0% by mass, the copper content was 74.9% by mass, and the zinc content was 3.1% by mass. The volume-based cumulative 50% particle diameter (D ₅₀ diameter) was 2.0 μm, and the BET specific surface area was 0.82 m ² / g. The true density is 9.21 g / cm ³ , the DB _BET is 0.79 μm, and the D ₅₀ / D _BET is 2.5. The amount of copper ions in the eluate was 467 mg / L, and the viscosity increase rate of the conductive paste was 54%.

[Comparative Example 2]
Regarding the silver-coated copper powder obtained by the same method as in Example 5 except that the surface was not modified, the composition and volume-based cumulative 50% particle diameter ( _D50 diameter) were obtained by the same method as in Example 1. , BET specific surface area was determined, true density, _DBBET , and _D50 / _DBET were calculated, the amount of copper ions in the eluent was determined, and the rate of increase in viscosity of the conductive paste was determined.

As a result, the silver coating amount of the silver-coated copper powder was 10.5% by mass, and the copper content was 89.5% by mass. The volume-based cumulative 50% particle diameter (D ₅₀ diameter) was 2.2 μm, and the BET specific surface area was 0.54 m ² / g. The true density is 9.20 g / cm ³ , the DB _BET is 1.23 μm, and the D ₅₀ / D _BET is 1.7. The amount of copper ions in the eluate was 463 mg / L, and the viscosity increase rate of the conductive paste was 69%.

[Comparative Example 3]
The composition of the silver-coated copper alloy powder obtained by the same method as in Example 1 except that the heating temperature at the time of surface modification was set to 200 ° C. and the heating time was set to 40 hours by the same method as in Example 1. , Volume-based cumulative 50% particle diameter (D ₅₀ diameter), BET specific surface area, true density, D _BET , D ₅₀ / D _BET , copper ion amount in eluent, viscosity of conductive paste The rate of increase was calculated.

As a result, the silver coating amount of the silver-coated copper alloy powder was 21.8% by mass, the copper content was 74.9% by mass, and the zinc content was 3.3% by mass. The volume-based cumulative 50% particle diameter (D ₅₀ diameter) was 4.1 μm, and the BET specific surface area was 0.57 m ² / g. The true density is 9.20 g / cm ³ , the DB _BET is 1.14 μm, and the D ₅₀ / D _BET is 3.6. The amount of copper ions in the eluate was 187 mg / L, and the viscosity increase rate of the conductive paste was 19%.

[Comparative Example 4]
The silver-coated copper alloy powder obtained by the same method as in Example 4 except that the surface modification was carried out in the air atmosphere was subjected to the same method as in Example 1 in terms of composition and volume-based cumulative 50% particle diameter (50% by volume). D ₅₀ diameter), BET specific surface area was determined, true density, D _BET , and D ₅₀ / D _BET were calculated, the amount of copper ions in the eluent was determined, and the rate of increase in viscosity of the conductive paste was determined.

As a result, the silver coating amount of the silver-coated copper alloy powder was 22.2% by mass, the copper content was 74.9% by mass, and the zinc content was 2.9% by mass. The volume-based cumulative 50% particle diameter (D ₅₀ diameter) was 2.3 μm, and the BET specific surface area was 0.85 m ² / g. The true density is 9.22 g / cm ³ , the DB _BET is 0.77 μm, and the D ₅₀ / D _BET is 2.9. Further, the amount of copper ions in the eluate was 2210 mg / L, and the viscosity of the conductive paste increased remarkably, and the rate of increase in viscosity could not be determined.

Tables 1 to 3 show the production conditions and characteristics of the silver-coated metal powders of these Examples and Comparative Examples.

As can be seen from Tables 1 to 4, in the silver-coated metal powders (silver-coated copper powder or silver-coated copper alloy powder) of Examples 1 to 6, the _D50 / D _BET is low and the sintering of particles is progressing. There wasn't. Further, in the silver-coated metal powders of Examples 1 to 6, the amount of copper ions in the eluate was low, and the viscosity increase rate of the conductive paste prepared by using the silver-coated metal powders of Examples 1 to 6 was low. On the other hand, in the silver-coated metal powder (silver-coated copper alloy powder) of Comparative Example 3, the D ₅₀ / D _BET was high, and the sintering of the particles proceeded. Further, in the silver-coated metal powders (silver-coated copper powder or silver-coated copper alloy powder) of Comparative Examples 1, 2 and 4, the amount of copper ions in the eluent was high, and the silver-coated metal powders of Comparative Examples 1, 2 and 4 were obtained. The rate of increase in viscosity of the conductive paste prepared using (silver-coated copper powder or silver-coated copper alloy powder) was high.

Claims (8)

After coating the copper alloy powder with a layer made of silver, the surface of the copper alloy powder coated with the layer made of silver is modified by heating at 60 to 160 ° C. for 0.5 to 50 hours in an atmosphere of 100% hydrogen gas. A method for producing a silver-coated metal powder, which comprises performing quality. The method for producing a silver-coated metal powder according to claim 1, wherein the copper alloy contains 1 to 50% by mass of zinc, and the balance is composed of copper and unavoidable impurities. After coating the copper powder with a layer made of silver, the copper powder coated with the layer made of silver is heated at 60 to 140 ° C. for 0.5 to 50 hours in an atmosphere of 100% hydrogen gas to modify the surface. A method for producing a silver-coated metal powder, which comprises performing. The invention according to any one of claims 1 to 3, wherein the coating amount of the silver layer is 7 to 50% by mass with respect to the copper or copper alloy powder coated with the silver layer. How to make silver-coated metal powder. The silver coating according to any one of claims 1 to 4, wherein the copper or copper alloy powder coated with the layer made of silver is surface-treated with a surface treatment agent before or after the surface modification. Method for manufacturing metal powder. The method for producing a silver-coated metal powder according to any one of claims 1 to 5, wherein the copper or copper alloy powder is produced by an atomizing method. Volume-based cumulative 50% particle size (D) measured by the laser diffraction type particle size distribution device for copper or copper alloy powder. ₅₀ The method for producing a silver-coated metal powder according to any one of claims 1 to 6, wherein the diameter) is 0.1 to 15 μm. In a conductive paste containing a resin and a solvent and containing a silver-coated metal powder as a conductive powder, the silver-coated metal powder is coated with a layer in which copper or a copper alloy powder is made of silver, and the particle shape is a true sphere. Particle diameter D calculated from specific surface area _BET Volume-based cumulative 50% particle size (D) measured by a laser diffraction type particle size distribution device for (μm) ₅₀ Ratio of diameter (D) ₅₀ / D _BET ) Is 3.5 or less, and the copper ion elution amount when immersed in a sulfuric acid aqueous solution having a pH of 0 for 30 minutes is 450 mg / L or less, and the conductive paste is a silver-coated metal powder.