JP5571435B2 - Method for producing silver-plated copper fine powder - Google Patents

Description

The present invention relates to a method of manufacturing a silver-plated copper fine powder, in particular through-holes, via holes, a method for producing useful silver plated copper fine powder with respect to a conductive paste such as for MLCC inner and outer electrodes.

  Silver-plated copper fine powder with a silver layer coated on it is processed into a conductive paste and applied to circuit formation of printed wiring boards using screen printing methods, various electrical contacts, etc., and used as a material for ensuring electrical continuity Has been. This is because silver-plated copper fine powder is more excellent in electrical conductivity than copper fine powder when compared with normal copper fine powder that does not cover the surface with a silver layer. Moreover, although it will become expensive only by silver powder, if silver is plated on copper, it will become cheap as the whole electroconductive powder, and manufacturing cost can be reduced significantly. Therefore, a conductive paste made of copper fine powder plated with silver, which is superior in conductive properties, has a great merit that a low-resistance conductor can be manufactured at low cost.

  Conventionally, in order to take advantage of such advantages of silver-plated copper fine powder, various characterizations have been made on silver-plated copper fine powder.

In WO2008 / 059789 (Patent Document 1), a surface treatment process is introduced before and after the silver plating reaction, and a silver layer is formed on the surface of the copper fine powder by electroless displacement plating and reduction plating. The silver-plated copper fine powder has excellent tap reproducibility and has the same tap density as the raw copper fine powder. Specifically, a silver-plated copper fine powder having an average particle diameter of 1 to 30 μm, a tap density of 2.4 g / cm ³ or more and a specific surface area of 0.9 m ² / g or less is described.

  In Patent Document 1, as a method for producing this silver-plated copper fine powder, the copper fine powder is washed with an organic solution on the surface of the copper fine powder in an alkaline solution and washed with water, and then the oxide on the surface of the copper fine powder is pickled in an acidic solution. After washing with water, a reducing agent is added to the acidic solution in which the copper fine powder is dispersed to adjust the pH to prepare a copper fine powder slurry, and a silver ion solution is continuously added to the copper fine powder slurry. A method for producing silver-plated copper fine powder is described in which a silver layer is formed on the surface of the copper fine powder by electrolytic displacement plating and reduction-type electroless plating.

  On the other hand, in WO2009 / 001710 (Patent Document 2), in an aqueous medium containing an additive of a natural resin, a polysaccharide or a derivative thereof for the purpose of rapidly and efficiently producing a fine copper fine powder. A method for producing fine copper powder by disproportionation reaction in which a cuprous oxide is added to prepare a slurry, and a 5-50% aqueous acid solution is added to the slurry at once within 15 minutes to perform a disproportionation reaction Is described.

WO2008 / 059789 WO2009 / 001710

  The method for producing silver-plated copper fine powder described in Patent Document 1 is certainly effective, but if the silver-plated copper fine powder is further refined, it will be advantageous from the viewpoint of fine pitch. The present inventor initially anticipated that this problem would be solved if the method described in Patent Document 1 was applied after obtaining fine copper fine powder by the method described in Patent Document 2, but silver plating was performed. It has been found that as the particle size of the copper fine powder before application decreases to less than 1 μm, aggregation tends to occur and it is difficult to obtain fine silver-plated copper fine powder.

Accordingly, the present invention is a challenge to provide a method for producing a silver-plated copper fine powder which very thin silver plating layer on the surface of the ultrafine copper fine powder is formed so as to have an average particle size of less than 1μm To do .

  As a result of repeated investigations to solve the above problems, the present inventors have conducted filtration washing and dehydration of the copper fine powder obtained by the disproportionation reaction to form dry copper fine powder. I found it easy to progress. Then, after obtaining the slurry-like copper fine powder by disproportionation reaction, when continuously moving to the silver plating process while maintaining the wet conditions, the dispersion of the copper fine powder is maintained in the plating solution, causing aggregation. We found that ultra-thin silver plating is possible without any problems. Furthermore, when the average particle diameter (D50) of the copper fine powder was less than 0.4 μm, it was found that it was not sufficient, and it was necessary to perform silver plating while irradiating with ultrasonic waves.

In the method for producing silver-plated copper fine powder according to the present invention , a slurry is prepared by adding cuprous oxide into an aqueous medium containing an additive of a natural resin, polysaccharide or derivative thereof, and an acidic aqueous solution is added to the slurry. Step 1 for producing a copper fine powder slurry having a particle diameter (D50) of 0.05 to 0.9 μm with a cumulative weight of 50% by adding within minutes and performing a disproportionation reaction, and the copper Process 2 in which the fine powder slurry is treated with an alkaline solution to remove organic substances on the surface of the copper fine powder; Process 3 in which the copper fine powder is treated with an acidic solution to remove oxide on the surface of the copper fine powder; Step 4 for preparing a copper fine powder slurry having a pH of 3.5 to 4.5 dispersed therein, and by continuously adding a silver ion solution to the copper fine powder slurry, electroless displacement plating and reduced electroless plating To form a silver layer on the copper fine powder surface And step 5 of, is a step 6 of solid-liquid separation of silver-plated copper fine powder slurry obtained in the step 5 in which comprises performing in sequence.

  In one embodiment, the method for producing a silver-plated copper fine powder according to the present invention produces a copper fine powder slurry having a cumulative particle weight (D50) of less than 0.4 μm in Step 1 and having a cumulative weight of less than 0.4 μm. The ultrasonic wave is irradiated during the addition of the silver ion solution.

  In another embodiment of the method for producing a silver-plated copper fine powder according to the present invention, in step 5, ultrasonic irradiation is continued for 10 minutes or more even after the addition of the silver ion solution is completed.

  In another embodiment of the method for producing silver-plated copper fine powder according to the present invention, the oscillation frequency of ultrasonic waves to be irradiated is 16 to 50 kHz.

According to the present invention, it is possible to produce a silver-plated copper fine powder in which an ultrathin silver-plated layer is formed on the surface of an ultrafine copper fine powder having an average particle size of less than 1 μm. Thereby, it is possible to meet the demand for fine pitch, and it is particularly suitable for the use of conductive paste for through holes, via holes, MLCC internal electrodes and external electrodes.

<Step 1: Preparation of spherical copper fine powder>
In the production method according to the present invention, as a raw material for silver-plated copper fine powder, the particle diameter (herein also referred to as “average particle diameter” or “D50”) at which the cumulative weight is 50% is 0.05 to 0.9 μm. The copper fine powder which is can be used, and when aiming at refinement | miniaturization among these, spherical copper fine powder whose D50 is 0.05-0.3 micrometer can be used. This is to increase the packing density as much as possible when used as a conductive paste application.

  The copper fine powder can be spherical. Here, the term “spherical” means that the ratio of the minor axis to the major axis of each copper particle is 150% or less on average, particularly 120% or less on average. Therefore, the ratio of the minor axis to the major axis exceeding 150% on average has a flat shape, which is not called spherical. Specifically, the average of the ratio between the minor axis and the major axis is given as an average value of 20 particles or more by directly measuring the minor axis and major axis of the copper particle image obtained from the SEM photograph. The diameter of the smallest circle that can surround each particle was the major axis, and the diameter of the largest circle that was surrounded by the particles was the minor axis.

  The spherical copper fine powder itself having an average particle size in this range is known and can be produced by the method described in WO2009 / 001710 (Patent Document 2), for example, but will be briefly described below.

  The spherical copper fine powder can be produced by a disproportionation reaction between cuprous oxide and an acid. Specifically, a slurry in which cuprous oxide is dispersed in water is prepared, and an aqueous acid solution is added thereto to obtain a spherical copper fine powder slurry, which is produced by solid-liquid separation.

  By adding a natural resin, a polysaccharide or a derivative thereof to the cuprous oxide slurry, the particle size of the obtained spherical copper fine powder can be reduced. This is because these additives have a function of suppressing particle growth as a protective colloid and a function of reducing the contact frequency between particles. As additives, natural rubbers or gelatins can be used. Specifically, rosin, gelatin, glue, carboxymethyl cellulose (CMC), starch, dextrin, gum arabic, casein and the like are effective.

  In addition, the particle size can be reduced by shortening the addition time of the acid aqueous solution added to the cuprous oxide slurry. For example, it can be added all at once within 20 minutes, further within 15 minutes, further within 3 minutes, and even within 1 minute.

  The slurry of spherical copper fine powder obtained by the wet method (disproportionation reaction) is preferably used in the silver plating step as it is without being dried. This is because the step of once filtering or drying the spherical copper fine powder can be omitted, and the copper fine powder can be connected to the step 2 without being exposed to the air, and the progress of oxidation can be prevented. Moreover, it is because it is easy to ensure the dispersibility of copper fine powder and can suppress aggregation by performing silver plating continuously on wet conditions.

<Step 2: Alkali treatment of copper fine powder>
After Step 1, the copper fine powder is treated with an alkaline solution to remove organic substances on the surface of the copper fine powder. Thereby, the rust preventive film and impurity component on the surface of the copper fine powder can be removed, and the pickling treatment of the next process can be performed more effectively. The alkaline solution is not particularly limited as long as it is an alkaline solution that can reliably remove organic substances adhering to the copper fine powder surface. For example, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium phosphate An aqueous solution may be mentioned. Among these, when stronger basicity is required for hydrolysis or the like, it is preferable to use an aqueous potassium hydroxide solution. For example, an alkaline solution having a concentration of 0.1 to 5.0% by mass can be used in an amount of 50 to 500 ml with respect to 100 g of copper powder.

  A specific method for the alkali treatment is not particularly limited as long as the copper fine powder and the alkaline solution are sufficiently contacted. For example, after the copper fine powder is dispersed in the alkaline solution, a certain time (for example, 10 ~ 20 minutes) The method of stirring is simple and reliable. The liquid temperature may be room temperature. It is preferable from the viewpoint of preventing oxidation of copper fine powder that the copper fine powder slurry produced by the wet method is used as it is in the step 2 without making it dry.

<Step 3: Pickling treatment of copper fine powder>
After step 2, the copper fine powder is treated with an acidic solution to remove oxides on the surface of the copper fine powder. Thereby, a clean copper surface is obtained, and silver plating with a uniform thickness becomes possible. The acidic solution is not particularly limited as long as it is an acidic solution that can reliably remove the copper oxide on the surface of the copper fine powder, and examples thereof include sulfuric acid, hydrochloric acid, phosphoric acid, sulfuric acid-chromic acid, and sulfuric acid-hydrochloric acid. Among these, sulfuric acid is preferable because it is used at the time of producing copper fine powder in the previous step and is available at a relatively low cost. It should be noted that the acid type and concentration to be selected should not excessively dissolve the copper fine copper itself.

  The pH of this acidic solution is desirably in the acidic range of 2.0 to 5.0. If the pH exceeds 5.0, the oxide of the copper fine powder cannot be sufficiently dissolved and removed, and if the pH is lower than 2.0, the copper powder is dissolved and the aggregation of the copper fine powder itself easily proceeds.

  A specific method of pickling treatment is not particularly limited as long as the copper fine powder and the acidic solution are sufficiently contacted. For example, the copper fine powder is dispersed in the acidic solution and then stirred for a certain time. Is simple and reliable. Preferably, after step 2, the alkaline solution is separated from the copper fine powder by decantation treatment, and then washed with water by decantation treatment as appropriate, and then the copper fine powder slurry dispersed in water is used in step 3.

  Decantation treatment is also called a gradient method, which is an operation in which a liquid containing a precipitate is allowed to stand and a solid is settled, and then the container is gently tilted and only the supernatant liquid is poured away. Thereby, it becomes possible to shift to the next step (here, from step 2 to step 3) without bringing the copper fine powder into contact with the atmosphere.

<Step 4: Dispersion of copper fine powder in reducing agent>
After step 3, a copper fine powder slurry having a pH of 3.5 to 4.5 in which the copper fine powder is dispersed in a reducing agent is prepared. As a specific method for dispersing, there is a method of stirring the copper fine powder in the reducing agent for a certain time (for example, 10 to 20 minutes). The liquid temperature may be room temperature.
As the reducing agent that can be used in the present invention, various reducing agents can be used. A preferred reducing agent is a weak reducing agent. This is because a silver film is formed by substitution deposition due to the addition of silver ions, but oxides (CuO, Cu ₂ O, AgO, Ag ₂ O) are generated as by-products of the substitution reaction, and this must be reduced. This is because even the complex ions of copper are not reduced.
A weak reducing agent that can be used in the present invention is a reducing organic compound. Examples of such a reducing agent include carbohydrates, polyvalent carboxylic acids and salts thereof, and aldehydes. Specific examples include glucose (glucose), malonic acid, succinic acid, glycolic acid, lactic acid, malic acid, tartaric acid, oxalic acid, sodium potassium tartrate (Rochelle salt), formalin and the like.
Among the reducing agents, sodium potassium tartrate (Rochelle salt) is preferable. Since it has a mild reducing action, it is often used as a reducing agent when performing electroless plating of silver.
For example, 100-1000 ml of reducing agent aqueous solution with a density | concentration of 0.1-5.0 mass% can be used with respect to 100g of copper powder.

  The reason for adjusting the pH to 3.5 to 4.5 here is the same as the effect of the pickling treatment. A preferred pH is 3.7 to 4.3. The pH can be adjusted appropriately with acid or alkali. The acid is not particularly limited as long as it is an acidic solution that can reliably remove the copper oxide on the surface of the copper fine powder. For example, sulfuric acid, hydrochloric acid, phosphoric acid, sulfuric acid -Chromic acid, sulfuric acid-hydrochloric acid. Among them, sulfuric acid is preferable because it is used in the copper fine powder of the previous step and is available at a relatively low cost. The alkali is not particularly limited as long as it is an alkaline solution that can reliably remove organic substances adhering to the copper fine powder surface. For example, an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, or sodium phosphate Is mentioned. Among them, potassium hydroxide is preferable when stronger basicity is required for hydrolysis or the like.

  In dispersing the copper fine powder in the reducing agent, after step 3, the acidic solution is separated from the copper fine powder by decantation treatment, and then appropriately washed with water by decantation treatment and then dispersed in water. It is preferred to use the slurry in step 4 in order to avoid contact with the atmosphere as well.

<Step 5: Formation of silver layer>
By continuously adding a silver ion solution to the copper fine powder slurry obtained in step 4, a silver layer is formed on the surface of the copper fine powder by electroless displacement plating and reduction type electroless plating. The silver ion solution may be any known solution as a silver plating solution, but a silver nitrate solution is preferable. The silver nitrate concentration can be 20 to 300 g / L, preferably 50 to 100 g / L. The silver nitrate solution is preferably provided as an ammoniacal silver nitrate solution because complex formation is easy and relatively inexpensive. The liquid temperature may be room temperature.

The speed of the silver ion solution added to the copper fine powder slurry is 200 mL / min or less, preferably 100 mL / min or less. The silver nitrate solution in the above concentration range is continuously added at a relatively slow addition rate, practically 20 to 200 mL / min, so that a uniform silver layer can be reliably coated on the copper fine powder surface. Can do. By slowly adding a silver ion solution, silver is easily plated with a uniform thickness. If the addition is fast, there is a concern that the silver coating becomes non-uniform and the variation among particles becomes large. By continuously adding the silver ion solution, it is possible to contribute to uniform silver film formation and reduction in variation among particles. At this time, it is preferable to supply the silver ion solution into the reaction system at a constant rate.
Moreover, the silver ion solution addition time can be set to 10 to 60 minutes according to the silver plating coating amount, and is preferably set so that the addition is completed in 20 to 40 minutes. If the addition of the silver ion solution is fast, there is a concern that the silver coating becomes non-uniform and the variation among particles becomes large. Further, when the addition of the silver ion solution is slow, there is no problem in the reaction, but the time required for the process becomes long, which is disadvantageous economically. As a result, when the silver plating coating amount is large, the silver ion solution addition rate is high, and conversely, when the silver plating coating amount is small, the silver ion solution addition rate is low.

  Here, if the particle size of the copper fine powder before silver plating is 0.4 μm or more, a thin silver plating film can be obtained without irradiating ultrasonic waves at the time of silver plating. Aggregation is likely to occur at the time of plating, and silver plating must be performed while irradiating with ultrasonic waves in order to obtain fine and uniform silver-plated copper fine powder. When the oscillation frequency of the ultrasonic wave is too low, the effect is insufficient. On the other hand, when it is too high, the silver plating film is difficult to grow into copper powder, and therefore, it is preferably 16 to 50 kHz, and more preferably 25 to 45 kHz. It is desirable from the viewpoint of preventing aggregation that the ultrasonic wave is continued for 10 minutes or longer, preferably 20 minutes or longer, for example, 10 to 40 minutes after addition of the silver ion solution during addition of the silver ion solution.

<6. Solid-liquid separation>
Silver-plated spherical copper fine powder is obtained by solid-liquid separation of the silver-plated copper fine powder slurry obtained in step 5 by any known means. Examples of the solid-liquid separation method include a method in which the plating solution and silver-plated spherical copper fine powder are separated by decantation treatment, and then the silver-plated spherical copper fine powder is dispersed in water and washed, followed by filtration and drying. .

<7. Characteristics of silver-plated spherical copper powder>
The silver-plated spherical copper fine powder obtained by the above method can have the following characteristics.

The silver-plated spherical copper fine powder obtained by the production method according to the embodiment of the present invention has a silver thickness of 0.1 nm to 0.2 μm, preferably 0.2 nm to 0.05 μm, for example, 0.01 to 0.05 μm. By providing an extremely thin silver coating on the outermost surface of copper, the oxidation resistance, which is a drawback of copper, is improved, and an inexpensive conductive filler is obtained.

The silver-plated spherical copper fine powder obtained by the production method according to the embodiment of the present invention has a silver weight of 1 to 25% by mass. Thereby, the filler for electrically conductive paste excellent in electroconductivity and oxidation resistance is obtained. Preferably it is 1-20 mass%, More preferably, it is 2-15 mass%. In the present invention, the weight ratio of silver contained in the silver-plated spherical copper fine powder is measured with an ICP emission spectroscopic analyzer.

The silver-plated copper fine powder obtained by the production method according to the embodiment of the present invention has a particle diameter (D50) at which the cumulative weight by laser diffraction scattering type particle size distribution measurement is 50% is less than 1 μm, and is typically 0. .05 μm or more and 0.9 μm or less. By using the slurry-like submicron powder obtained by the wet reaction as a raw material as it is, fine silver-plated copper fine powder that cannot be reached when atomized powder or electrolytic powder is used as a raw material is obtained. D50 of silver plating spherical copper fine powder becomes like this. Preferably it is 0.05-0.5 micrometer, More preferably, it is 0.05-0.3 micrometer. D50 measured here is the average particle size of the secondary particles.

The silver-plated copper fine powder obtained by the production method according to the embodiment of the present invention has a BET specific surface area of 1.0 to 10.0 m ² / g. As a result, it can be inferred that submicron spherical silver-plated copper fine powder having a good dispersion state is obtained. When silver plating is performed in an aggregated state, the BET specific surface area is lower than the above range. The BET specific surface area is preferably 3.0 to 10.0 m ² / g, more preferably 5.0 to 10.0 m ² / g.

The silver-plated copper fine powder obtained by the manufacturing method according to the embodiment of the present invention has a tap density larger than the apparent density, an apparent density of 1.0 to 3.0 g / cm ³ , and a tap density of 2. 0 to 4.0 g / cm ³ . A powder having a higher tap density is advantageous because it can increase the packing density during paste production and firing. Therefore, the tap density is preferably 2.5 to 4.0 g / cm ³ , more preferably 3.0 to 4.0 g / cm ³ .
In the present invention, the apparent density is measured by the method of JISZ2504.
In the present invention, the tap density is measured by the method of JISZ2512.

A conductive paste can be produced by adding a resin and a solvent to the silver-plated copper fine powder obtained by the production method according to the embodiment of the present invention , and kneading it into a paste. Since this conductive paste has a dense interface between copper and silver, it is excellent in conductivity (volume specific resistance value (specific resistance value)).

  Examples of the present invention will be described below together with comparative examples, but these examples are provided for better understanding of the present invention and its advantages, and are not intended to limit the invention.

Example 1 (no ultrasonic irradiation)
8 g of gum arabic was dissolved in 7 liters of pure water, 1000 g of cuprous oxide was added and suspended while stirring, and the cuprous oxide slurry was kept at 7 ° C. The concentration of cuprous oxide in the slurry is about 143 g / L, and the concentration of gum arabic in the slurry is about 1.14 g / L.
Next, 2000 cc of dilute sulfuric acid (concentration 24 mass%: 9 N, molar ratio (acid aqueous solution / slurry): 1.3) maintained at 7 ° C. was added over 16 minutes with stirring, and stirring was continued for 10 minutes after the addition was completed. Continued. The stirring speed was 500 rpm and no ultrasonic irradiation was performed. It was confirmed by FE-SEM observation that the produced copper powder was spherical. A part of the slurry of the produced spherical copper fine powder was collected and the average particle diameter (D50) was measured with a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, model SALD-2100). The average particle size was 0.79 μm. The yield of spherical copper fine powder is estimated to be 440 g.
440 g of this spherical copper fine powder slurry was added to 880 mL of 1% aqueous potassium hydroxide solution and stirred for 20 minutes, followed by primary decantation treatment, and further 880 mL of pure water was added and stirred for several minutes.
Then, the secondary decantation process was performed, 2200 mL of sulfuric acid aqueous solution with a sulfuric acid concentration of 15 g / L was added, and it stirred for 30 minutes.
Furthermore, the tertiary decantation process was performed, 2200 mL of pure water was added, and it stirred for several minutes.
Next, quaternary decantation treatment was performed, and 2200 mL of 1% sodium potassium tartrate solution was added and stirred for several minutes to form a copper slurry.
A dilute sulfuric acid or potassium hydroxide solution was added to the copper slurry to adjust the pH of the copper slurry to 3.5 to 4.5.
Replacement reaction treatment while adding 880 mL of silver nitrate ammonia solution (adjusted to 880 mL of silver nitrate by adding 77.0 g of silver nitrate to water) to the copper slurry adjusted in pH over 30 minutes. Then, a reduction reaction treatment was performed, and stirring was further performed for 30 minutes to obtain a slurry of silver-plated copper fine powder.
Then, the fifth decantation process was performed, 3500 mL of pure water was added, and it stirred for several minutes.
Further, a sixth decantation treatment was performed, 3500 mL of pure water was added, and the mixture was stirred for several minutes. The silver-plated copper fine powder and the solution were separated by suction filtration, and the silver-plated copper fine powder was dried at a temperature of 90 ° C. for 2 hours.
It was 0.85 micrometer when the average particle diameter (D50) of this silver plating spherical copper fine powder was measured with the laser diffraction type particle size distribution measuring apparatus (Corporation | KK Shimadzu make, type SALD-2100). By obtaining spherical copper fine powder by disproportionation reaction, filtering and washing the spherical copper fine powder, and continuously silver plating in the slurry state without suction dehydration, it is almost the same as the spherical copper fine powder which is the original powder efficiently Silver-plated spherical copper fine powder having the same particle size (about 107% with respect to the original powder) can be obtained. Apparent density 2.35 g / cm ^3, a tap density of 3.51g / cm ^3, BET specific surface area was 1.68m ² / g. The mass% of silver was 10.4 mass%.

Example 2 (without ultrasonic irradiation)
8 g of glue was dissolved in 7 liters of pure water, 1000 g of cuprous oxide was added and suspended while stirring, and the cuprous oxide slurry was kept at 7 ° C. The cuprous oxide concentration in the slurry is about 143 g / L, and the glue concentration in the slurry is about 1.14 g / L.
Subsequently, 2000 cc of dilute sulfuric acid (concentration 24 mass%: 9 N, molar ratio (acid aqueous solution / slurry): 1.3) maintained at 7 ° C. was added in 16 minutes. A part of the slurry of the produced spherical copper fine powder was collected and the average particle diameter (D50) was measured with a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, model SALD-2100). The average particle size was 0.53 μm. The yield of spherical copper fine powder is estimated to be 440 g.
Thereafter, silver plating was performed in the same manner as in Example 1.
It was 0.68 micrometer when the average particle diameter (D50) of this silver plating spherical copper fine powder was measured with the laser diffraction type particle size distribution measuring apparatus (Corporation | KK Shimadzu make, type SALD-2100). By obtaining spherical copper fine powder by disproportionation reaction, filtering and washing the spherical copper fine powder, and continuously silver plating in the slurry state without suction dehydration, it is almost the same as the spherical copper fine powder which is the original powder efficiently Silver-plated spherical copper fine powder having the same particle size (about 128% with respect to the original powder) can be obtained. The apparent density was 2.08 g / cm ³ , the tap density was 2.79 g / cm ³ , and the BET specific surface area was 3.96 m ² / g. The mass% of silver was 10.1 mass%.

Example 3 (with ultrasonic irradiation)
8 g of glue was dissolved in 7 liters of pure water, 1000 g of cuprous oxide was added and suspended while stirring, and the cuprous oxide slurry was kept at 7 ° C. The cuprous oxide concentration in the slurry is about 143 g / L, and the glue concentration in the slurry is about 1.14 g / L.
Subsequently, 2000 cc of dilute sulfuric acid (concentration 24 mass%: 9 N, molar ratio (acid aqueous solution / slurry): 1.3) maintained at 7 ° C. was added in 5 seconds. A part of the slurry of the produced spherical copper fine powder was collected and the average particle diameter (D50) was measured with a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, model SALD-2100). The average particle size was 0.10 μm. The yield of spherical copper fine powder is estimated to be 440 g.
Thereafter, silver plating was carried out in the same manner as in Example 1 except that ultrasonic irradiation was performed at a total oscillation time of 40 kHz for a total of 60 minutes including a continuous addition time of 30 minutes for the silver nitrate ammonia solution and a subsequent stirring time of 30 minutes.
It was 0.12 micrometer when the average particle diameter (D50) of this silver plating spherical copper fine powder was measured with the laser diffraction type particle size distribution measuring apparatus (Corporation | KK Shimadzu make, type SALD-2100). By obtaining spherical copper fine powder by disproportionation reaction, filtering and washing the spherical copper fine powder, and continuously silver plating in the slurry state without suction dehydration, it is almost the same as the spherical copper fine powder which is the original powder efficiently Silver-plated spherical copper fine powder having the same particle size (about 120% with respect to the original powder) can be obtained. The apparent density was 2.23 g / cm ³ , the tap density was 3.09 g / cm ³ , and the BET specific surface area was 6.05 m ² / g. The mass% of silver was 10.2 mass%.

Comparative example (no ultrasonic irradiation)
8 g of glue was dissolved in 7 liters of pure water, 1000 g of cuprous oxide was added and suspended while stirring, and the cuprous oxide slurry was kept at 7 ° C. The cuprous oxide concentration in the slurry is about 143 g / L, and the glue concentration in the slurry is about 1.14 g / L.
Subsequently, 2000 cc of dilute sulfuric acid (concentration 24 mass%: 9 N, molar ratio (acid aqueous solution / slurry): 1.3) maintained at 7 ° C. was added in 5 seconds. A part of the slurry of the produced spherical copper fine powder was collected and the average particle diameter (D50) was measured with a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, model SALD-2100). The average particle size was 0.10 μm. The yield of spherical copper fine powder is estimated to be 440 g.
Thereafter, silver plating was performed in the same manner as in Example 1.
It was 0.78 micrometer when the average particle diameter (D50) of this silver plating spherical copper fine powder was measured with the laser diffraction type particle size distribution measuring apparatus (Corporation | KK Shimadzu make, type SALD-2100). By obtaining spherical copper fine powder by disproportionation reaction, filtering and washing the spherical copper fine powder, and continuously silver plating in a slurry state without suction dehydration, the spherical copper fine powder that is the original powder is efficiently Thus, a silver-plated spherical copper fine powder having a considerably large particle size (about 780% with respect to the original powder) can be obtained. The apparent density was 1.65 g / cm ³ , the tap density was 2.44 g / cm ³ , and the BET specific surface area was 11.06 m ² / g. The mass% of silver was 9.0 mass%.

The above results are summarized in Table 1. The thickness of the silver plating was a value obtained by subtracting the average particle diameter of the spherical copper fine powder from the average particle diameter of the silver plated spherical copper fine powder.

  From these results, if the average particle diameter of the raw spherical copper fine powder is about 0.4 μm or more, the surface of the ultrafine copper fine powder having an average particle diameter of less than 1 μm by continuous silver plating under wet conditions It is possible to provide a silver-plated copper fine powder in which a very thin silver-plated layer is formed. However, when the average particle size is less than about 0.4 μm, the degree of agglomeration becomes high, and it is understood that continuous silver plating under wet conditions and ultrasonic irradiation treatment during silver plating are required.

Claims (4)

  A cuprous oxide is added to an aqueous medium containing an additive of a natural resin, a polysaccharide or a derivative thereof to prepare a slurry, and an acidic aqueous solution is added to the slurry within 16 minutes to perform a disproportionation reaction. Then, the process 1 which manufactures the copper fine powder slurry whose particle diameter (D50) from which cumulative weight will be 50% is 0.05-0.9 micrometer, and the said copper fine powder slurry are processed with an alkaline solution, and the copper fine powder surface is processed. Step 2 for removing organic substances, Step 3 for treating the copper fine powder with an acidic solution to remove oxides on the surface of the copper fine powder, and pH 3.5 to 4.5 in which the copper fine powder is dispersed in a reducing agent. Step 4 for preparing a copper fine powder slurry, and Step 5 for forming a silver layer on the surface of the copper fine powder by electroless displacement plating and reduction type electroless plating by continuously adding a silver ion solution to the copper fine powder slurry. , Silver plating obtained in step 5 Method for producing a silver-plated copper fine powder comprising performing the steps 6 to solid-liquid separation fine powder slurry in order. The copper fine powder slurry in which the particle diameter (D50) with a cumulative weight of 50% is less than 0.4 μm is produced in the step 1, and the ultrasonic wave is irradiated during the addition of the silver ion solution in the step 5. The manufacturing method as described. The process according to claim 2 , wherein in step 5, ultrasonic irradiation is continued for 10 minutes or more after the addition of the silver ion solution is completed. The production method according to claim 2 or 3 , wherein an oscillation frequency of the ultrasonic wave to be irradiated is 16 to 50 kHz.