CN102811830A - Silver-plated copper micropowder and preparation method thereof - Google Patents

Abstract

The present invention provides silver-plated copper fine powder having an extremely thin silver-plated layer formed on the surface of ultrafine copper fine powder. The present invention provides silver-plated copper micropowder, which is copper micropowder with silver plating on the surface, wherein the weight of silver is 1-25% by mass, and the cumulative weight measured by laser diffraction scattering particle size distribution reaches the particle size of 50% ( D50) is less than 1 μm, and the thickness of the silver plating film is 0.1 nm to 0.2 μm.

Description

Silver-plated copper micropowder and preparation method thereof

technical field

The present invention relates to silver-plated copper micropowder and preparation method thereof, particularly relate to the useful silver-plated copper micropowder and preparation method thereof of conductive paste such as through hole, guide hole (via hole), MLCC internal electrode and external electrode.

Background technique

Silver-plated copper fine powder coated with a silver layer on the surface can be processed into a conductive paste, which is used as a material for ensuring electrical conductivity in circuit formation of printed wiring boards by screen printing, various electrical contact parts, etc. The reason for this is that the silver-plated copper fine powder has better conductivity than the copper fine powder when compared with the normal copper fine powder whose surface is not coated with a silver layer. In addition, this is because the price is high if only silver powder is used, but if silver is plated on copper, the conductive powder as a whole becomes cheap, and the production cost can be greatly reduced. Therefore, the conductive paste made of silver-plated copper fine powder plated with more excellent conductive properties can obtain a great advantage of being able to prepare low-resistance conductors at low cost.

Currently, in order to utilize such advantages of the silver-plated copper fine powder, various characteristics are given to the silver-plated copper fine powder.

In WO2008/059789 (Patent Document 1), by introducing a surface treatment process before and after the silver plating reaction and forming a silver layer on the surface of copper micropowder by electroless displacement plating and reduction plating, the reproduction of silver plating can be obtained. Silver-plated copper fine powder with excellent properties and a tap density equivalent to that of raw copper fine powder. Specifically, it describes 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.

In Patent Document 1, as a preparation method of the silver-plated copper fine powder, the following preparation method of the silver-plated copper fine powder is described: remove the organic matter on the surface of the copper fine powder in an alkaline solution, wash it with water, and then treat the copper fine powder in an acidic solution. The oxide on the surface of the copper micropowder is pickled and washed with water, and then a reducing agent is added to the acidic solution in which the copper micropowder is dispersed, and the pH is adjusted to prepare a copper micropowder slurry, by continuously adding a silver ion solution to the copper micropowder slurry, A silver layer is formed on the surface of copper micropowder by electroless displacement electroplating and reduction electroless electroplating.

On the other hand, WO2009/001710 (Patent Document 2) describes a method for preparing copper micropowder utilizing disproportionation reaction: in order to prepare fine copper micropowder quickly, efficiently and stably, a compound containing natural resin, polysaccharide or its derivative Add cuprous oxide to the aqueous medium of the additive of the substance to prepare a slurry, and add 5-50% acid aqueous solution to the slurry within 15 minutes to carry out the disproportionation reaction.

prior art literature

patent documents

Patent Document 1: WO2008/059789

Patent Document 2: WO2009/001710.

Contents of the invention

The problem to be solved by the invention

Although the preparation method of the silver-plated copper fine powder described in Patent Document 1 is indeed effective, if the silver-plated copper fine powder is further miniaturized, it is advantageous in terms of fine pitch (fine pitch). The present inventor originally expected that this problem could be solved by applying the method described in Patent Document 1 after obtaining the fine copper powder by the method described in Patent Document 2, but it was found that as the fine copper powder before silver plating was implemented, When the particle size is reduced to less than 1 μm, aggregation tends to occur, making it difficult to obtain fine silver-plated copper fine powder.

Therefore, one of the subjects of the present invention is to provide silver-plated copper fine powder in which an extremely thin silver-plated layer is formed on the surface of ultrafine copper fine powder having an average particle diameter of less than 1 μm. In addition, another subject of the present invention is to provide a method for preparing such silver-plated copper fine powder.

means of solving problems

The inventors of the present invention have found that when the copper fine powder obtained by the disproportionation reaction is filtered, washed or dehydrated to obtain a dry copper fine powder through repeated studies in order to solve the above-mentioned problems, aggregation tends to proceed. Furthermore, it has been found that if the slurry-like copper fine powder is obtained by the disproportionation reaction, if the wet process condition is maintained directly and at the same time continuously transferred to the silver plating process, the dispersion of the copper fine powder can be maintained in the electroplating bath, and extremely thin silver plating can be performed without agglomeration. . In addition, it was also found that if the average particle diameter (D50) of the copper fine powder is less than 0.4 μm, this alone is not sufficient, and silver plating needs to be performed simultaneously with ultrasonic irradiation.

The present invention is completed based on the above knowledge. On the one hand, it is a silver-plated copper fine powder, and the fine powder is a copper fine powder with silver plating on the surface, wherein the cumulative weight measured by laser diffraction scattering particle size distribution reaches a particle size of 50% ( D50) is less than 1 μm, and the thickness of the silver plating film is 0.1 nm to 0.2 μm.

Regarding the silver-plated copper fine powder related to the present invention, in one embodiment, it is a copper fine powder with silver plating on the surface, wherein the weight of silver is 1-25% by mass.

Regarding the silver-plated copper micropowder according to the present invention, in one embodiment, D50 is 0.05-0.5 μm, and the thickness of the silver-plated film is 0.2 nm-0.05 μm.

Regarding the silver-plated copper fine powder of the present invention, in another embodiment, the BET specific surface area is 3.0-10.0 m ² /g.

As far as the silver-plated copper micropowder involved in the present invention is concerned, in yet another embodiment, the tap density is greater than the apparent density, the apparent density is 1.0-3.0 g/cm ³ , and the tap density is 2.0-4.0 g/cm 3 . cm ³ .

With regard to the silver-plated copper micropowder involved in the present invention, in still another embodiment, the cumulative weight of the copper micropowder before silver-plating utilizes laser diffraction scattering particle size distribution measurement to reach 50% particle diameter (D50) is 0.05 ~0.9 μm.

Another aspect of the present invention is a method for preparing silver-plated copper micropowder. The preparation method includes sequentially implementing the following steps: adding cuprous oxide to an aqueous medium containing additives such as natural resins, polysaccharides or derivatives thereof to prepare a slurry material, add an acidic aqueous solution to the slurry within 16 minutes, and carry out a disproportionation reaction, thereby preparing a step 1 of a copper micropowder slurry with a particle size (D50) of 0.05 to 0.9 μm with a cumulative weight of 50%. Step 2 of treating the copper fine powder slurry with an alkaline solution to remove organic matter on the surface of the copper fine powder, and treating the copper fine powder with an acidic solution to remove oxides on the surface of the copper fine powder Step 4 of the copper micropowder slurry with a pH of 3.5 to 4.5 in the agent, by continuously adding silver ion solution to the copper micropowder slurry, utilizing electroless displacement electroplating and reduced electroless electroplating to form a silver layer on the surface of the copper micropowder Step 5 of Step 5, and Step 6 of solid-liquid separation of the silver-plated copper fine powder slurry obtained in Step 5.

As far as the preparation method of the silver-plated copper micropowder involved in the present invention is concerned, in one embodiment, the particle size (D50) of preparing cumulative weight reaching 50% is the copper micropowder slurry of less than 0.4 μm in operation 1, In 5, ultrasonic waves are irradiated during the addition of the silver ion solution.

Regarding the preparation method of the silver-plated copper micropowder involved in the present invention, in another embodiment, the ultrasonic radiation is continued for more than 10 minutes after the addition of the silver ion solution in step 5.

Regarding the preparation method of the silver-plated copper micropowder involved in the present invention, in another embodiment, the oscillating frequency of the radiated ultrasonic waves is 16-50 kHz.

Still another aspect of the present invention is an electrically conductive paste containing the silver-plated copper fine powder according to the present invention.

The effect of the invention

According to the present invention, it is possible to provide silver-plated copper fine powder in which an extremely thin silver-plated layer is formed on the surface of ultrafine copper fine powder having an average particle diameter of less than 1 μm. Therefore, it can meet the requirements of finer pitch, and is especially suitable for the application of conductive pastes such as via holes, guide holes, MLCC internal electrodes and external electrodes.

Detailed ways

<Process 1: Preparation of spherical copper fine powder>

As the raw material of the silver-plated copper micropowder involved in the present invention, the particle diameter (here also referred to as "average particle diameter" or "D50 " that can be used to reach 50% by cumulative weight) is the copper micropowder of 0.05～0.9 μ m, wherein when For the purpose of miniaturization, spherical copper fine powder with D50 of 0.05~0.3μm can be used. This is to increase the filling density as much as possible when used as a conductive paste.

As the copper fine powder, spherical copper fine powder can be used. Here, the spherical shape means that the ratio of the minor axis to the major axis of each copper particle is 150% or less on average, especially 120% or less on average. Therefore, particles having a ratio of a short diameter to a long diameter exceeding 150% on average have a flattened shape and are not called spherical. Specifically, the average of the ratio of the short axis to the long axis is obtained by directly measuring the short axis and the long axis of the copper particle image obtained from the SEM photograph, and taking an average value of 20 or more particles. The diameter of the smallest circle that can surround each particle is defined as the major axis, and the diameter of the largest circle surrounded by the particles is defined as the minor axis.

Spherical copper fine powder having an average particle diameter within this range is known per se, and can be prepared, for example, by the method described in WO2009/001710 (Patent Document 2), and will be briefly described below.

Spherical copper powder can be prepared by the disproportionation reaction of cuprous oxide and acid. Specifically, it was prepared by preparing a slurry in which cuprous oxide was dispersed in water, adding an aqueous acid solution to obtain a spherical copper fine powder slurry, and performing solid-liquid separation.

The particle size of the obtained spherical copper micropowder can be reduced by adding natural resin, polysaccharides or derivatives thereof to the cuprous oxide slurry. The reason for this is that these additives act as a protective colloid to inhibit the growth of particles and also act to reduce the frequency of contact between particles. As additives, natural rubber or gelatin can be used. Specifically, rosin, gelatin, gum, carboxymethylcellulose (CMC), starch, dextrin, acacia, casein, and the like are effective.

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

The slurry of the spherical copper fine powder obtained by the wet method (disproportionation reaction) is preferably used in the silver plating step without being dried. This is because the step of temporarily filtering or drying the spherical copper fine powder can be omitted, and the step 2 can be continued without exposing the copper fine powder to the air, thereby preventing the progress of oxidation. In addition, this is because, by continuously performing silver plating under wet conditions, the dispersibility of the copper fine powder can be easily ensured, and aggregation can be suppressed.

<Process 2: Alkali treatment of fine copper powder>

After Step 1, the fine copper powder is treated with an alkaline solution to remove organic matter on the surface of the fine copper powder. In this way, the antirust film or impurity components on the surface of the copper micropowder can be removed, and the pickling treatment in the next step can be carried out more effectively. The alkaline solution is not particularly limited as long as it is an alkaline solution that can reliably remove organic matter adhering to the surface of the copper fine powder, and examples include aqueous solutions of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, and sodium phosphate . Among them, when stronger alkalinity is required due to hydrolysis or the like, an aqueous potassium hydroxide solution is preferably used. For example, 50 to 500 ml of an alkali solution with a concentration of 0.1 to 5.0% by mass can be used with respect to 100 g of copper powder.

As a specific method of the alkali treatment, there is no particular limitation as long as it is a method that can sufficiently bring the copper fine powder into contact with the alkaline solution. For example, after dispersing the copper fine powder in the alkaline solution, stir for a certain period of time (for example, 10 to 20 minutes). method is simple and reliable. The liquid temperature may be room temperature. In terms of preventing the oxidation of the copper fine powder, it is preferable not to make the slurry of the copper fine powder prepared by the wet method into a dry powder and use it directly in the step 2.

<Process 3: Pickling treatment of copper fine powder>

After step 2, the fine copper powder is treated with an acidic solution to remove oxides on the surface of the fine copper powder. Thereby, a clean copper surface can be obtained, and silver plating can be performed with a uniform thickness. The acidic solution is not particularly limited as long as it 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 them, sulfuric acid is preferred because it is used in the production of copper fine powder in the previous step and can be obtained relatively cheaply. It should be noted that the type or concentration of the selected acid should be careful not to excessively dissolve the copper itself of the copper fine powder.

It is desirable to make the pH of this acidic solution into the acidic range of 2.0-5.0. If the pH exceeds 5.0, the oxides of the copper fine powder cannot be sufficiently dissolved and removed, and if the pH is less than 2.0, the copper powder dissolves, and the aggregation of the copper fine powder itself tends to proceed.

The specific method of pickling treatment is not particularly limited as long as it can sufficiently contact the copper fine powder with the acid solution. For example, the method of stirring the copper fine powder for a certain period of time after dispersing the copper fine powder in the acid solution is simple and reliable. Preferably used in step 3 is a copper fine powder slurry in which the alkali solution is separated from the fine copper powder by decantation after step 2, washed with water by appropriate decantation, and then dispersed in water.

Decantation treatment, also known as tilting method, refers to the operation of slowly tilting the container to allow only the supernatant to flow out after the liquid containing the precipitate is placed to allow the solid matter to settle. Thereby, the fine copper powder can be transferred to the next step (here, transfer from step 2 to step 3) without contacting the atmosphere.

<Process 4: Dispersion of copper fine powder in reducing agent>

After process 3, the copper fine powder slurry of pH3.5-4.5 which disperse|distributed this copper fine powder in a reducing agent is prepared. As a specific method for dispersing, a method of stirring copper fine powder in a reducing agent for a certain period of time (for example, 10 to 20 minutes) is mentioned. The liquid temperature may be room temperature.

As the reducing agent usable in the present invention, various reducing agents can be used. Preferred reducing agents are weak reducing agents. The reason for this is that although the silver film is formed by displacement precipitation by adding silver ions, oxides (CuO, _Cu2O , AgO, _Ag2O ) are produced as by-products of this displacement reaction, and they need to be reduced. Copper complex ions also cannot reduce it.

The weak reducing agent usable in the present invention includes reducing organic compounds, and examples of such substances include carbohydrates, polycarboxylic acids and their salts, and aldehydes. Specific examples thereof 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 preferred. Because of its mild reducing effect, it is often used as a reducing agent in electroless plating of silver.

For example, 100 to 1000 ml of a reducing agent aqueous solution having a concentration of 0.1 to 5.0% by mass can be used with respect to 100 g of copper powder.

Here, the reason for adjusting the pH to 3.5 to 4.5 is the same as the effect of the pickling treatment. The preferred pH is 3.7~4.3. The pH adjustment can be appropriately performed with an acid or an alkali, and 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. Examples include sulfuric acid, hydrochloric acid, phosphoric acid, sulfuric acid-chromic acid, and sulfuric acid. -hydrochloric acid. Among them, sulfuric acid is preferable because it is used in the copper fine powder in the previous process and can be obtained relatively cheaply. The base is not particularly limited as long as it is an alkaline solution of an organic substance that can reliably adhere to the surface of the copper fine powder, and examples thereof include aqueous solutions of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, and sodium phosphate. Among them, potassium hydroxide is preferable when stronger alkalinity is required due to hydrolysis or the like.

When 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, followed by water washing by decantation treatment as appropriate, and then dispersed in water for copper fine powder slurry In step 4, contact with air can also be avoided, which is preferable.

<Step 5: Formation of silver layer>

For the copper micropowder slurry obtained in step 4, a silver layer is formed on the surface of the copper micropowder by means of electroless displacement electroplating and reduction electroless electroplating by continuously adding silver ion solution. As the silver ion solution, any solution known as a silver plating solution may be used, but a silver nitrate solution is preferable. The concentration of silver nitrate can be set to 20~300g/L, preferably 50~100g/L. In addition, since the silver nitrate solution easily forms a complex and is relatively cheap, it is preferably provided as an ammoniacal silver nitrate solution. The liquid temperature may be room temperature.

The rate of the silver ion solution added to the copper fine powder slurry is set to be 200 mL/min or less, preferably 100 mL/min or less. By continuously adding the silver nitrate solution in the above concentration range at a relatively slow adding rate, practically 20-200mL/min, a uniform silver layer can be reliably coated on the surface of the copper micropowder. Easy to plate silver with uniform thickness by slowly adding silver ion solution. If it is added quickly, the silver film will become non-uniform, and there is a possibility that the variation among particles will increase. The continuous addition of silver ion solution can help to form a uniform silver film and reduce the deviation between particles. At this time, it is preferable to supply the silver ion solution to the reaction system at a constant rate.

In addition, the time for adding the silver ion solution can be set to 10 to 60 minutes according to the amount of silver plating coating, and it is preferably set to finish the addition in 20 to 40 minutes. If the addition of the silver ion solution is fast, the silver coating may become non-uniform and the variation among particles may increase. In addition, if the addition of the silver ion solution is slow, there is no problem in reaction, but the time required for the process is prolonged, which is economically disadvantageous. As a result, if the coating amount of silver plating is large, the addition rate of the silver ion solution is accelerated, and conversely, if the coating amount of silver plating is small, the addition rate of the silver ion solution becomes slow.

Here, if the particle size of the copper fine powder before silver plating is 0.4 μm or more, a thin silver-plated film can be obtained without ultrasonic radiation during silver plating, but if it is less than 0.4 μm, aggregation will easily occur during silver plating , in order to obtain fine and uniform silver-coated copper powder, it is necessary to carry out silver plating at the same time as ultrasonic radiation. If the oscillation frequency of the ultrasonic wave is too low, the effect will be insufficient. On the other hand, if it is too high, the silver-plated coating will be difficult to grow on the copper powder. Therefore, it is preferably 16 to 50 kHz, more preferably 25 to 45 kHz. From the viewpoint of preventing aggregation, it is desirable to continue to irradiate ultrasonic waves for 10 minutes or more, preferably 20 minutes or more, for example, 10 to 40 minutes, except during the addition of the silver ion solution, except during the addition of the silver ion solution.

<6. Solid-liquid separation>

Silver-plated spherical copper fine powder can be obtained by solid-liquid separation of the silver-plated copper fine powder slurry obtained in step 5 by any known method. As a method of solid-liquid separation, for example, the electroplating solution and the silver-plated spherical copper fine powder are separated by decantation, and then the silver-plated spherical copper fine powder is dispersed in water, filtered and dried after washing.

<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.

Regarding the silver-plated spherical copper micropowder according to the present invention, in one embodiment, the thickness of silver is 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 film on the surface of copper, an inexpensive conductive filler can be obtained while improving oxidation resistance, which is a disadvantage of copper.

Regarding the silver-plated spherical copper fine powder related to the present invention, in one embodiment, the weight of silver is 1 to 25% by mass. Thereby, the filler for electrically conductive pastes excellent in electroconductivity and oxidation resistance can be 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 by an ICP emission spectrometer.

Regarding the silver-plated copper fine powder related to the present invention, in one embodiment, the particle size (D50) at which the cumulative weight reaches 50% by laser diffraction scattering particle size distribution measurement is less than 1 μm, typically 0.05 μm or more and 0.9 μm or less. By directly using the slurry-like sub-micron powder obtained by wet reaction as a raw material, it is possible to obtain fine silver-plated copper powder that cannot be obtained when atomized powder or electrolytic powder is used as raw material. The D50 of the silver-plated spherical copper powder is preferably 0.05-0.5 μm, more preferably 0.05-0.3 μm. D50 measured here is the average particle diameter of secondary particles.

In one embodiment, the silver-plated copper fine powder according to the present invention has a BET specific surface area of 1.0 to 10.0 m ² /g. From this, it can be inferred that submicron-order spherical silver-plated copper fine powder with a good dispersion state can be obtained. If the silver is plated in an aggregated state, the BET specific surface area will be 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.

As for the silver-plated copper micropowder involved in the present invention, in one embodiment, the tap density is greater than the apparent density, the apparent density is 1.0-3.0 g/cm ³ , and the tap density is 2.0-4.0 g/cm ³ . A powder with a high tap density is advantageous because it can increase the filling density during paste preparation and calcination. 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 according to the method of JISZ2504.

In the present invention, the tap density is measured according to the method of JISZ2512.

The conductive paste can be prepared by adding a resin and a solvent to the silver-plated copper fine powder according to the present invention, kneading and pasting. Since the interface between copper and silver is dense, this conductive paste is excellent in conductivity (volume intrinsic resistance value (specific resistance value)).

Example

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

Embodiment 1 (without ultrasonic radiation)

8 g of gum arabic was dissolved in 7 liters of pure water, and 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 was about 143 g/L, and the gum arabic concentration in the slurry was about 1.14 g/L.

Next, 2000 cc of dilute sulfuric acid (concentration: 24% by mass: 9N, molar ratio (acid solution/slurry): 1.3) maintained at 7° C. was added over 16 minutes while stirring, and stirring was continued for 10 minutes after the addition was completed. The stirring speed was set at 500 rpm, and no ultrasonic irradiation was performed. It was confirmed by FE-SEM observation that the produced copper powder was spherical. Collect a part of the resulting spherical copper fine powder slurry, and when the average particle diameter (D50) is measured by a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, model SALD-2100), the average particle size of the spherical copper fine powder The particle size is 0.79 μm. The yield of spherical copper fine powder is estimated to be 440g.

440 g of the spherical copper fine powder slurry was added to 880 mL of 1% potassium hydroxide aqueous solution and stirred for 20 minutes, followed by decantation once, and 880 mL of pure water was further added and stirred for several minutes.

Then, a second decantation treatment was performed, and 2200 mL of sulfuric acid aqueous solution having a sulfuric acid concentration of 15 g/L was added and stirred for 30 minutes.

Furthermore, decantation treatment was performed three times, and 2200 mL of pure water was added and stirred for several minutes.

Next, decantation was performed four times, and 2200 mL of 1% potassium sodium tartrate solution was added and stirred for several minutes to form a copper slurry.

Dilute sulfuric acid or potassium hydroxide solution is added to the copper slurry to adjust the pH of the copper slurry to 3.5-4.5.

Slowly add 880 mL of silver nitrate ammonium solution (77.0 g of silver nitrate to water, add ammonia water, and adjust to 880 mL) to the pH-adjusted copper slurry over a period of 30 minutes, and at the same time, replace Reaction treatment and reduction reaction treatment, and further stirring for 30 minutes to obtain a slurry of silver-plated copper fine powder.

Then, decantation treatment was performed five times, and 3500 mL of pure water was added and stirred for several minutes.

Furthermore, decantation treatment was performed six times, and 3500 mL of pure water was added and stirred for several minutes. Then, the silver-plated copper fine powder was separated from the solution by suction filtration, and the silver-plated copper fine powder was dried at a temperature of 90° C. for 2 hours.

The average particle diameter (D50) of the silver-plated spherical copper fine powder was measured with a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, model SALD-2100), and it was 0.85 μm. Spherical copper micropowder is obtained by disproportionation reaction, and the spherical copper micropowder is not filtered and washed, suction dehydrated, and directly silver-plated in a slurry state, so that the particle size is basically the same as that of the spherical copper micropowder as the raw material powder (relative to the raw material). The powder is about 107%) silver-plated spherical copper powder. The apparent density is 2.35g/cm ³ , the tap density is 3.51g/cm ³ , and the BET specific surface area is 1.68m ² /g. The % mass of silver is 10.4% mass.

Embodiment 2 (without ultrasonic radiation)

8 g of the gel 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 was about 143 g/L, and the glue concentration in the slurry was about 1.14 g/L.

Next, 2000 cc of dilute sulfuric acid maintained at 7° C. (concentration: 24% by mass: 9N, molar ratio (acid aqueous solution/slurry): 1.3) was added within 16 minutes. A part of the resulting spherical copper fine powder slurry was collected, and the average particle diameter (D50) was measured by a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, model SALD-2100). The result was the average particle size of the spherical copper fine powder. The particle size is 0.53 μm. The yield of spherical copper fine powder is estimated to be 440g.

Hereinafter, silver plating was carried out in the same manner as in Example 1.

The average particle diameter (D50) of the silver-plated spherical copper fine powder was measured with a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, model SALD-2100), and it was 0.68 μm. Spherical copper micropowder is obtained by disproportionation reaction, and the spherical copper micropowder is not filtered and washed, suction dehydrated, and directly silver-plated in a slurry state, so that the particle size is basically the same as that of the spherical copper micropowder as the raw material powder (relative to the raw material). The powder is about 128%) silver-plated spherical copper powder. The apparent density is 2.08g/cm ³ , the tap density is 2.79g/cm ³ , and the BET specific surface area is 3.96m ² /g. The % by mass of silver is 10.1% by mass.

Embodiment 3 (there is ultrasonic radiation)

8 g of the gel 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 was about 143 g/L, and the glue concentration in the slurry was about 1.14 g/L.

Next, 2000 cc of dilute sulfuric acid maintained at 7° C. (concentration: 24% by mass: 9N, molar ratio (acid aqueous solution/slurry): 1.3) was added within 5 seconds. A part of the spherical copper fine powder slurry generated was collected, and the average particle diameter (D50) was measured by a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, model SALD-2100). As a result, the average particle size of the spherical copper fine powder was The diameter is 0.10 μm. The yield of spherical copper fine powder is estimated to be 440g.

Silver plating was carried out in the same manner as in Example 1, except that the 30-minute continuous addition of the ammonium silver nitrate solution and the subsequent 30-minute stirring time were combined into 60 minutes and the oscillation frequency was set to 40 kHz for ultrasonic irradiation.

When the average particle diameter (D50) of the silver-plated spherical copper fine powder was measured with a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, model SALD-2100), it was 0.12 μm. Spherical copper micropowder is obtained by disproportionation reaction, and the spherical copper micropowder is not filtered and washed, suction dehydrated, and directly silver-plated in a slurry state, so that the particle size is basically the same as that of the spherical copper micropowder as the raw material powder (relative to the raw material). The powder is about 120%) silver-plated spherical copper powder. The apparent density is 2.23g/cm ³ , the tap density is 3.09g/cm ³ , and the BET specific surface area is 6.05m ² /g. The % mass of silver is 10.2% mass.

Comparative example (no ultrasonic radiation)

8 g of the gel 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 was about 143 g/L, and the glue concentration in the slurry was about 1.14 g/L.

Next, 2000 cc of dilute sulfuric acid maintained at 7° C. (concentration: 24% by mass: 9N, molar ratio (acid aqueous solution/slurry): 1.3) was added within 5 seconds. A part of the spherical copper fine powder slurry generated was collected, and the average particle diameter (D50) was measured by a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, model SALD-2100). As a result, the average particle size of the spherical copper fine powder was The diameter is 0.10 μm. The yield of spherical copper fine powder is estimated to be 440g.

Hereinafter, silver plating was carried out in the same manner as in Example 1.

The average particle diameter (D50) of the silver-plated spherical copper fine powder was measured with a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, model SALD-2100), and it was 0.78 μm. Spherical copper micropowder is obtained by disproportionation reaction, and the spherical copper micropowder is not filtered and washed, suction dehydrated, and directly silver-plated continuously in a slurry state, so that the particle size can be effectively obtained relative to the spherical copper micropowder as raw material powder (relative to The raw material powder is about 780%) silver-plated spherical copper powder. The apparent density is 1.65g/cm ³ , the tap density is 2.44g/cm ³ , and the BET specific surface area is 11.06m ² /g. The % by mass of silver is 9.0% by mass.

The above results are summarized in Table 1. The thickness of the silver plating was set to 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.

[Table 1]

From these results, it can be known that if the average particle diameter of the raw material spherical copper powder is more than about 0.4 μm, then the continuous silver plating under wet conditions can provide an extremely thin layer formed on the surface of the ultrafine copper powder with an average particle diameter less than 1 μm. The silver-plated copper micropowder of the silver-plated layer. However, if the average particle size is less than about 0.4 μm, the degree of aggregation increases, so continuous silver plating under wet conditions and ultrasonic radiation treatment during silver plating are required.

Claims (11)

1. silver-plated copper micro mist, it has silver-plated copper fine powder for implementing on the surface, and wherein, utilizing the accumulating weight of laser diffraction and scattering formula particle size distribution to reach 50% particle diameter (D50) is less than 1 μ m, and the thickness of silver-plated film is 0.1nm ~ 0.2 μ m.

2. the silver-plated copper micro mist of claim 1, it has silver-plated copper fine powder for implementing on the surface, it is characterized in that, and the weight of silver is 1 ~ 25% quality.

3. claim 1 or 2 silver-plated copper micro mist, wherein D50 is 0.05 ~ 0.5 μ m, the thickness of silver-plated film is 0.2nm ~ 0.05 μ m.

4. each silver-plated copper micro mist in the claim 1 ~ 3, wherein, the BET specific area is 3.0 ~ 10.0m ²/ g.

5. each silver-plated copper micro mist in the claim 1 ~ 4, wherein, tap density is greater than apparent density, and apparent density is 1.0 ~ 3.0g/cm ³, tap density is 2.0 ~ 4.0g/cm ³

6. the silver-plated copper micro mist of claim 1 ~ 5, wherein, implementing copper fine powder before silver-plated, to utilize the accumulating weight of laser diffraction and scattering formula particle size distribution to reach 50% particle diameter (D50) be 0.05 ~ 0.9 μ m.

7. silver-plated copper micropowder preparing process; Said preparation method comprises and implements following operation successively: in the aqueous medium of the additive that contains natural resin, polysaccharide or derivatives thereof, add cuprous oxide and prepare slurry; Added acidic aqueous solution at 16 minutes in introversive this slurry; Carry out disproportionated reaction; It is the operation 1 of the copper fine powder slurry of 0.05 ~ 0.9 μ m that thereby the preparation accumulating weight reaches 50% particle diameter (D50), and said copper fine powder slurry is handled the organic operation 2 of removing the copper fine powder surface with alkaline solution, said copper fine powder is handled the operation 3 of the oxide of removing the copper fine powder surface with acid solution; Preparation makes said copper fine powder be scattered in the operation 4 of the copper fine powder slurry of pH3.5 ~ 4.5 in the reducing agent; Through in said copper fine powder slurry, adding silver ion solution continuously, utilize no electrolysis displacement plating and reduced form electroless plating to carry out the operation 6 of Separation of Solid and Liquid in the operation 5 of copper fine powder surface formation silver layer with to the silver-plated copper micro mist slurry that in operation 5, obtains.

8. the preparation method of claim 7, wherein, the preparation accumulating weight reaches 50% particle diameter (D50) and is the copper fine powder slurry of less than 0.4 μ m in operation 1, in operation 5 in the interpolation process of silver ion solution radiate supersonic wave.

9. the preparation method of claim 8 wherein, still continues the ultrasonic wave radiation more than 10 minutes after the interpolation of silver ion solution finishes in operation 5.

10. claim 8 or 9 preparation method, wherein, hyperacoustic frequency of oscillation of institute's radiation is 16 ~ 50kHz.

11. conduction is stuck with paste, said conduction is stuck with paste the silver-plated copper micro mist that contains in the claim 1 ~ 6 each.