JP2013100592A - Silvered copper powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide silvered copper powders having further superior conductivity.SOLUTION: There is provided the dendritic silvered copper powder in which the surface of copper powder particle is coated with silver. According to the observation of the copper powder by an SEM (scanning electronic microscope), the copper powder particle has one main shaft. Plural branches diverge slantwise from the main shaft and express a dendritic form grown two- or three-dimensionally. The thickness a of the main shaft is 0.3-5.0 μm, and the length (b) of the longest branch among the branches extending from the main shaft is 0.6-10.0 μm.

Description

  The present invention relates to a silver-coated copper powder that can be suitably used as a material such as a conductive paste.

  The conductive paste is a fluid composition in which conductive powder is dispersed in a vehicle composed of a resin binder and a solvent, and the formation of an electric circuit, the formation of an external electrode of a ceramic capacitor, the formation of an electromagnetic shielding film, Widely used for forming bonding films.

  This type of conductive paste has a resin-cured type in which conductive powder is pressure-bonded by curing the resin to ensure conduction, and an organic component is volatilized by firing to sinter the conductive powder to ensure conduction. It is classified as a firing mold.

  The former resin-curable conductive paste is generally a paste-like composition containing conductive powder made of metal powder and an organic binder made of thermosetting resin such as epoxy resin, and applies heat. As a result, the thermosetting resin is cured and shrunk together with the conductive powder, and the conductive powder is pressed and brought into contact with each other through the resin, thereby ensuring conductivity. This resin-curable conductive paste can be processed in a relatively low temperature range from 100 ° C. to 200 ° C. and has little thermal damage, so it can be used for printed wiring boards, heat-sensitive resin substrates, electromagnetic shielding films, bonding films, etc. Mainly used.

On the other hand, the latter fired conductive paste is a paste-like composition in which conductive powder (metal powder) and glass frit are generally dispersed in an organic vehicle. By firing at 500 to 900 ° C., Conductivity is ensured by volatilization of the organic vehicle and sintering of the conductive powder. At this time, the glass frit has a function of adhering the conductive film to the substrate, and the organic vehicle functions as an organic liquid medium for enabling printing of the metal powder and the glass frit.
Firing-type conductive paste cannot be used for printed wiring boards or resin materials because of its high firing temperature, but it can be reduced in resistance because it is sintered and the metal is integrated. It is used for external electrodes.

  Since silver is excellent in conductivity, it is used as a main constituent material of various conductive materials such as anisotropic conductive films, conductive pastes, and conductive adhesives. For example, a silver paste can be mixed with a binder and a solvent to form a conductive paste, and a circuit pattern can be printed on the substrate using this conductive paste and baked to form a printed wiring board or an electric circuit of an electronic component. it can.

However, since silver is very expensive, conductive powder called coating powder, which is obtained by plating a noble metal film on the surface of core material particles by electroless plating or the like, has been developed and used. For example, Patent Document 1 discloses a silver compound-coated copper powder obtained by coating the surface of silver-coated copper particles as a core material with a silver compound of silver oxide, silver carbonate, and organic acid silver, and SSA (M ³ / g) is 0.1 to 10.0, D50 (μm) is 0.5 to 10.0, and a silver compound is adhered to the particle surface at a rate of 1 wt% to 40 wt%. Silver compound-coated copper powder is disclosed.

  As a method for coating the surface of the copper powder particles with silver, there can be mentioned two types, ie, a reduction plating coating method and a displacement plating coating.

  The reduction plating coating method is a method in which fine particles of silver reduced with a reducing agent are densely coated on the surface of copper powder particles. For example, Patent Document 2 discloses metallic copper in an aqueous solution in which a reducing agent is dissolved. A method for producing a silver-coated copper powder in which powder and silver nitrate are reacted is proposed.

  On the other hand, in the displacement plating coating method, silver ions exchange electrons with metallic copper at the interface of copper powder particles, silver ions are reduced to metallic silver, and instead metallic copper is oxidized into copper ions. That is, a method in which the surface layer of the copper powder particles is a silver layer. A method for producing silver-coated copper powder for coating the surface of copper particles is described.

JP 2008-106368 A JP 2000-248303 A JP 2006-161081 A

  If the conductive powder particles contained in the conductive paste have a dendritic shape, the number of contact points between the particles will increase compared to spherical particles, etc. Can be increased.

  Therefore, the present invention intends to provide a new silver-coated copper powder having further excellent conductivity.

  The present invention is a silver-coated copper powder composed of silver-coated copper powder particles whose surface is coated with silver, and when the silver-coated copper powder particles are observed using a scanning electron microscope (SEM), It has a single main shaft, a plurality of branches are obliquely branched from the main shaft to form a dendritic shape that grows two-dimensionally or three-dimensionally, and the thickness a of the main shaft is 0.3 μm to 5 μm. Proposing a silver-coated copper powder containing silver-coated copper powder particles having a dendrite shape with a length b of 0.6 μm to 10.0 μm, which is 0.0 μm and the longest branch length b is 0.6 μm to 10.0 μm It is.

  The silver-coated copper powder proposed by the present invention is more dendritic than a conventional silver-coated copper powder. Specifically, more branches branch from the main shaft, or the length of the branched branches. This includes silver-coated copper powder particles having a longer shape. If the conductive powder particles have a dendritic shape that grows and develops more, the number of contact points between the particles is further increased, so that even better electrical conductivity can be obtained, and the amount of the conductive powder Even if the amount is reduced, the conductive characteristics can be improved. Therefore, the silver-coated copper powder proposed by the present invention can be used particularly effectively as a material such as a conductive paste.

It is a model figure of the particle shape of the silver covering copper powder particle which comprises the silver covering copper powder of this invention. It is a SEM photograph at the time of observing a part of powder arbitrarily selected from silver covering copper powder obtained in Example 1 at a magnification of 10,000 times using a scanning electron microscope (SEM).

  Hereinafter, although the embodiment of the present invention is described in detail, the scope of the present invention is not limited to the following embodiment.

  The copper powder according to the present embodiment is a silver-coated copper powder (referred to as “main silver-coated copper powder particles”) made of silver-coated copper powder particles obtained by coating the surface of copper powder particles as a core with silver. This is referred to as “silver-coated copper powder”.

(Particle shape)
The present silver-coated copper powder contains the present silver-coated copper powder particles having a dendritic shape.
Here, as shown in the model diagram of FIG. 1, the “dendritic shape” includes a single main axis when observed with an electron microscope (500 to 20,000 times), and a plurality of the main axes from the main axis. This means a particle that has a two-dimensional or three-dimensional growth shape, with branches branching diagonally, with wide leaves gathering together to form a pinecone, and numerous needle-like parts extending radially. Does not include

The present silver-coated copper powder particles contain, among the dendritic copper powder particles, particles exhibiting a dendritic shape having the following predetermined characteristics when observed with an electron microscope (500 to 20,000 times). preferable.
It is important that the thickness a of the main shaft is 0.3 μm to 5.0 μm, especially 0.4 μm or more or 4.5 μm or less, especially 0.5 μm or more or 4.0 μm or less. preferable. When the thickness a of the dendrite is 0.3 μm or less, branches are difficult to grow because the main axis is not solid. On the other hand, when the thickness is larger than 5.0 μm, the particles tend to aggregate and become pine cones. End up.
-The longest branch length b (referred to as "branch length b") among the branches extending from the main axis indicates the degree of dendrite growth, and it is important that the length is 0.6 μm to 10.0 μm. In particular, 0.7 μm or more or 9.0 μm or less, more preferably 0.8 μm or more or 8.0 μm or less. If the branch length b is less than 0.6 μm, it cannot be said that the dendrite has grown sufficiently. On the other hand, when the branch length b exceeds 10.0 μm, the fluidity of the copper powder is lowered and the handling becomes difficult.
The number of branches relative to the major axis L of the main axis (number of branches / major axis L) indicates the number of dendrite branches, and is preferably 0.5 / μm to 4.0 / μm. .6 / μm or more or 3.5 / μm or less, more preferably 0.8 / μm or more or 3.0 / μm or less. If the number of branches / major axis L is 0.5 / μm or more, the number of branches is sufficiently large and sufficient contact can be secured, while if the number of branches / major axis L is 4.0 / μm or less, It can prevent that the fluidity | liquidity of this copper powder becomes inferior because there are too many branches.

  However, when observed with an electron microscope (500 to 20,000 times), if many of them are occupied by the dendritic particles as described above, the dendritic particles as described above may be used even if particles of other shapes are mixed. The effect similar to the copper powder which consists only of can be acquired. Therefore, from this viewpoint, when the present silver-coated copper powder is observed with an electron microscope (500 to 20,000 times), the present silver-coated copper powder particles are preferably 80% or more of the total copper powder particles, preferably As long as it occupies 90% or more, non-dendritic copper powder particles that are not recognized as dendritic may be included.

(BET specific surface area)
The BET specific surface area (SSA) of the present silver-coated copper powder is preferably, for example, 0.30 to 1.50 m ² / g. If it is remarkably smaller than 0.30 m ² / g, the branches are not developed and close to a pinecone to a sphere, so that the dendrite shape defined by the present invention cannot be exhibited. On the other hand, if it is significantly larger than 1.50 m ² / g, the dendrite branch may become too thin, and problems such as branch breakage may occur in the paste processing step, and the target conductivity may not be ensured. There is sex.
Therefore, the specific surface area as measured by single point method BET of the silver-coated copper powder 0.30~1.50m ² / g at and even good properly, inter alia 0.40 m ² / g or more or 1.40 m ² / g Hereinafter, among these, it is more preferable that it is 1.00 m < ² > / g or less especially.

(Amount of silver)
In the present silver-coated copper powder, the silver content is preferably 0.5 to 35.0 mass% with respect to the entire present silver-coated copper powder. If the silver content occupies 0.5% by mass or more of the total silver-coated copper powder, when the particles overlap, the surface silver comes into contact with each other, so that the conductivity can be increased. On the other hand, if it is 35.0 mass% or less, it will be sufficient to obtain electroconductivity, and it is economical, without covering silver more than necessary. In other words, if it is 35.0% by mass or less, although it depends on the production method, it is preferable because it is economically superior to silver particles. From such a viewpoint, the silver content is preferably 0.5 to 35.0 mass% of the total silver-coated copper powder, and more preferably 3.0 mass% or more or 25.0 mass% or less. Of these, 5.0% by mass or more or 20.0% by mass or less is more preferable.

(D50)
The central particle size (D50) of the present silver-coated copper powder, that is, the volume cumulative particle size D50 measured by a laser diffraction / scattering particle size distribution analyzer is preferably 3.0 μm to 30.0 μm. If the particles are large as the conductive particles, the conductive particle network in the paste is reduced, which may reduce the conductive performance. On the other hand, if the particle diameter is too small, it is necessary to increase the silver content in order to eliminate unevenness in the silver coating, which is economically wasteful.
Therefore, the center particle diameter (D50) of the present silver-coated copper powder is preferably 3.0 μm to 30.0 μm, more preferably 4.0 μm or more and 25.0 μm or less, and particularly preferably 20.0 μm or less. Further preferred.

(Production method)
This silver-coated copper powder disperses copper powder as a core material in water, adds a chelating agent, and then adds a water-soluble silver salt to perform a substitution reaction to replace the surface layer of the copper powder particles with silver. Then, the obtained silver-coated copper powder is taken out of the solution, washed with a chelating agent, and dried. However, it is not limited to this manufacturing method.

  Compared to the reduction plating coating method, the displacement plating coating method can not only uniformly coat the surface of the core material (copper powder particles) with silver, but also can suppress the aggregation of particles after coating. Therefore, it is preferable to employ the displacement plating coating method because it has a feature that it can be manufactured at a lower cost.

In the conventional displacement plating coating method, when silver-coated copper powder is taken out from the reaction solution, it is filtered and washed with water or the like, but only by washing with water, some of the copper ions are adsorbed on the silver-coated copper powder. Therefore, copper ions remain on the particle surface, and when dried in this state, the copper ions form copper oxide, and a copper oxide film can be formed on the particle surface.
In contrast, by washing with a chelating agent, copper re-adsorption after the substitution reaction can be prevented, so that copper ions remaining on the particle surface can be suppressed. Conductivity can be improved by suppressing the formation of a copper film.
In the case of washing with a chelating agent, the chelating agent may remain, so that it is preferable to wash with pure water or the like.

  Examples of the chelating agent include ethylenediaminetetraacetic acid salt (hereinafter referred to as “EDTA”), aminocarboxylic acid-based chelating agents such as diethylenetriaminepentaacetic acid and iminodiacetic acid, hydroxyethylethylenediaminetriacetic acid, dihydroxyethylethylenediaminediacetic acid), 1 , 3-propanediaminetetraacetic acid, one or two or more selected from propanediaminetetraacetic acid can be mentioned, and among these, EDTA is preferably used.

When adding a silver salt, it is preferable to adjust the pH of the solution, that is, the pH of the solution at the time of the substitution reaction to 3 to 4.
Silver salts soluble in water, that is, Ag ion sources include silver nitrate, silver perchlorate, silver acetate, silver oxalate, silver chlorate, silver hexafluorophosphate, and boron tetrafluoride. One or more selected from acid silver, silver hexafluoroarsenate, and silver sulfate can be mentioned.

  The addition amount of the silver salt is preferably equal to or greater than the theoretical equivalent, for example, when copper is used as the core material, the silver salt is added in an amount of 2 mol or more, particularly 2.1 mol or more with respect to 1 mol of copper. When the amount is less than 2 mol, the substitution is insufficient and a large amount of copper remains in the silver powder particles. However, it is not economical to add 2.5 mol or more.

The silver content in the silver powder particles can be adjusted by the amount of silver salt added, the reaction time, the reaction rate, the amount of chelating agent added, and the like.
After completion of the substitution reaction, the silver powder particles are preferably thoroughly washed and dried.

  As the copper powder used as the core material, it is preferable to use an electrolytic copper powder exhibiting a dendritic shape with sufficiently developed branches. If silver is coated by the above method, the shape of the copper powder particles used as the core material can be converted into the particle shape of the present silver-coated copper powder almost as it is.

  The electrolytic copper powder having a dendritic shape with sufficiently developed branches as described above can be produced by the following electrolytic method.

  As an electrolysis method, for example, an anode and a cathode are immersed in a sulfuric acid electrolytic solution containing copper ions, and a direct current is passed through the electrolyte to conduct electrolysis. An example is a method of producing electrolytic copper powder by scraping and collecting by an electric method, washing, drying, and passing through a sieving step as necessary.

When copper powder is produced by the electrolytic method, the copper ions in the electrolyte solution are consumed as copper is deposited, so the copper ion concentration in the electrolyte solution near the electrode plate is reduced, and the electrolytic efficiency decreases as it is. End up. Therefore, normally, in order to increase the electrolysis efficiency, the electrolyte solution in the electrolytic cell is circulated so that the copper ion concentration of the electrolyte solution between the electrodes does not become thin.
However, it has been found that in order to develop the dendrite of each copper powder particle, in other words, in order to promote the growth of branches extending from the main axis, it is preferable that the copper ion concentration in the electrolyte solution near the electrode is low. Therefore, in the production of electrolytic copper powder, the size of the electrolytic cell, the number of electrodes, the distance between the electrodes, and the circulation amount of the electrolytic solution are adjusted, and the copper ion concentration of the electrolytic solution in the vicinity of the electrodes is adjusted to be low. It is preferable to adjust so that the copper ion concentration of the electrolyte solution between electrodes is always thinner than the copper ion concentration of the electrolyte solution at the bottom.

Here, when introducing a model case, the size of the electrolytic cell is 2m ³ through 10m ^3, the electrode number is 10 to 40 sheets, when the inter-electrode distance is 5Cm～50cm, copper ion concentration 1 g / By adjusting the circulation amount of the electrolytic solution of L to 50 g / L to 10 to 100 L / min, dendrites can be developed, and electrolytic copper powder having a dendritic shape with sufficiently developed branches can be obtained.

In order to adjust the particle size of the dendritic copper powder particles, conditions may be set as appropriate based on common general technical knowledge within the range of the above conditions. For example, if it is intended to obtain dendritic copper powder particles having a large particle size, the copper concentration is preferably set to a relatively high concentration within the above preferred range, and the current density is relatively low within the above preferred range. The density is preferably set, and the electrolysis time is preferably set to a relatively long time within the above preferable range. If it is intended to obtain dendritic copper powder particles having a small particle size, it is preferable to set the respective conditions based on the opposite concept. As an example, the copper concentration may be 1 g / L to 10 g / L, the current density may be 100 A / m ^{2 to} 1000 A / m ² , and the electrolysis time may be 5 minutes to 3 hours.

  If necessary, the core material may be subjected to a treatment for removing the surface oxide (oxide film) before the substitution reaction. For example, after the core material is put into water and stirred and mixed, a reducing agent such as hydrazine is added and stirred and mixed to react. At this time, it is preferable that the added reducing agent is sufficiently washed and removed from the core material.

(Use)
Since the silver-coated copper powder has excellent conductive properties, the silver-coated copper powder can be used for various conductive materials such as conductive resin compositions such as conductive pastes and conductive adhesives, and conductive paints. It can be suitably used as a main constituent material.

For example, in order to produce a conductive paste, the present silver-coated copper powder can be mixed with a binder and a solvent, and further, if necessary, a curing agent, a coupling agent, a corrosion inhibitor, etc. to produce a conductive paste.
In this case, examples of the binder include liquid epoxy resins, phenol resins, unsaturated polyester resins, and the like, but are not limited thereto.
Examples of the solvent include terpineol, ethyl carbitol, carbitol acetate, butyl cellosolve and the like.
Examples of the curing agent include 2-ethyl 4-methylimidazole.
Examples of the corrosion inhibitor include benzothiazole and benzimidazole.

  The conductive paste can be used to form a circuit pattern on a substrate to form various electric circuits. For example, it is possible to form a printed wiring board, an electric circuit of various electronic components, external electrodes, and the like by applying or printing on a fired substrate or an unfired substrate, heating, pressurizing and baking as necessary. Moreover, it can utilize also for formation of an electromagnetic wave shield film, a bonding film, etc.

(Explanation of words)
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” or “preferably more than Y” with the meaning of “X to Y” unless otherwise specified. The meaning of “small” is also included.
In addition, when expressed as “X or more” (X is an arbitrary number), it means “preferably larger than X” unless otherwise specified, and expressed as “Y or less” (Y is an arbitrary number). In the case, unless otherwise specified, the meaning of “preferably smaller than Y” is included.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

<Observation of particle shape>
With a scanning electron microscope (5,000 times), the shape of 500 particles was observed in each of 100 arbitrary visual fields, and the thickness of the main axis a (“main axis thickness a”) and the branch extending from the main axis The longest branch length b (“branch length b”) and the number of branches with respect to the major axis of the main axis (“number of branches / major axis L”) were measured, and the average values are shown in Table 1.

<Particle size measurement>
Take a small amount of silver-coated copper powder (sample) in a small beaker, add a few drops of 3% Triton X solution (Kanto Chemical), and let it blend into the powder. Then 0.1% SN Dispersant 41 solution (San Nopco) ) 50 mL was added, and then a measurement sample was prepared by dispersing for 2 minutes using an ultrasonic disperser TIPφ20 (manufactured by Nippon Seiki Seisakusho).
The volume accumulation standard D50 of this measurement sample was measured using a laser diffraction / scattering particle size distribution measuring device MT3300 (manufactured by Nikkiso).

<Measurement of BET specific surface area>
The specific surface area was measured by the BET single point method using a monosorb manufactured by Yuasa Ionics, and shown in Table 1 as the BET specific surface area.

<Evaluation of conductivity (specific resistance) of conductive paste>
To the silicone sealant (manufactured by ThreeBond Co., Ltd., model number 5211), silver-coated copper powder (sample) is blended at a ratio of 70% by mass, and toluene having the same mass as the silver-coated copper powder (sample) is added. After thoroughly mixing using Awatori Netaro (model number AR-100), a 1 cm × 10 cm band-like pattern was printed on a glass plate by screen printing. The paste was dried in the atmosphere at 70 ° C. for 60 minutes, and then the electrical resistance was measured with a digital voltmeter (manufactured by Yokogawa Electronics Works).
The film thickness is measured with a micrometer, and the specific resistance (Ω · cm) = width (cm) × film thickness (μm) × electric resistance (Ω) / (length (cm) × 10 ⁴ ) The conductivity (specific resistance) of the conductive paste was calculated and shown in Table 1.

<Example 1>
In an electrolytic cell having a size of 2.5 m × 1.1 m × 1.5 m (about 4 m ³ ), nine copper cathode plates and a copper anode plate (electrodes) each having a size (1.0 m × 1.0 m) are electrodes. Suspended so as to have a distance of 5 cm, and circulated a copper sulfate solution as an electrolytic solution at 30 L / min, immersed an anode and a cathode in this electrolytic solution, and conducted a direct current to conduct electrolysis. Powdered copper was deposited on the cathode surface.
At this time, the electrolytic solution to be circulated was adjusted to a Cu concentration of 5 g / L, a sulfuric acid (H ₂ SO ₄ ) concentration of 100 g / L, and a current density of 80 A / m ² for electrolysis for 1 hour.
During electrolysis, the copper ion concentration of the electrolyte solution between the electrodes was always kept lower than the copper ion concentration of the electrolyte solution at the bottom of the electrolytic cell.

Then, the copper deposited on the cathode surface was mechanically scraped and collected, and then washed to obtain a hydrated copper powder cake equivalent to 1 kg of copper powder. This cake was dispersed in 3 L of water, 1 L of an industrial gelatin (made by Nitta Gelatin Co., Ltd.) 10 g / L aqueous solution was added, stirred for 10 minutes, filtered through a Buchner funnel, washed, and then under reduced pressure (1 × 10 ⁻³ Pa) at 80 ° C. for 6 hours to obtain electrolytic copper powder.

25 kg of the obtained electrolytic copper powder was put into 50 L of pure water kept at 50 ° C. and stirred well. Separately, 4.5 kg of silver nitrate was put into 5 L of pure water to prepare a silver nitrate solution. The silver nitrate solution was added all at once to the solution in which the copper powder was dissolved. In this state, stirring was performed for 2 hours to obtain a silver-coated copper powder slurry.
Next, the silver-coated copper powder slurry is filtered by vacuum filtration. After the filtration is completed, the slurry is washed with a solution obtained by dissolving 600 g of EDTA (ethylenediaminetetraacetic acid) in 6 L of pure water, followed by 3 L of pure water. Residual EDTA was washed with water. Then, it was made to dry at 120 degreeC for 3 hours, and dendritic silver covering copper powder (sample) was obtained. The silver coating amount was 10.8% by mass of the total silver-coated copper powder.

When the obtained dendrite-like silver-coated copper powder (sample) was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and from the main axis It was confirmed that a plurality of branches were obliquely branched and had a dendritic shape that grew three-dimensionally.
Moreover, when the electroconductivity of this silver covering copper powder was measured as shown in Table 1, the favorable value was shown.

<Example 2>
An electrolytic copper powder was obtained in the same manner as in Example 1 except that the electrolysis time was 40 minutes and the circulating fluid amount was 20 L / min. Then, silver was coated in the same manner as in Example 1 to obtain a dendrite-like silver-coated copper powder (sample). The silver coating amount was 10.9% by mass of the total silver-coated copper powder.

When the obtained dendrite-like silver-coated copper powder (sample) was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and from the main axis It was confirmed that a plurality of branches were obliquely branched and had a dendritic shape that grew three-dimensionally.
Moreover, when the electroconductivity of this silver covering copper powder was measured as shown in Table 1, the favorable value was shown.

<Example 3>
An electrolytic copper powder was obtained in the same manner as in Example 1 except that the electrolysis time was 40 minutes, the Cu concentration of the electrolytic solution was 1 g / L, and the amount of circulating liquid was 10 L / min. Then, silver was coated in the same manner as in Example 1 to obtain a dendrite-like silver-coated copper powder (sample). The silver coating amount was 10.8% by mass of the total silver-coated copper powder.

When the obtained dendrite-like silver-coated copper powder (sample) was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and from the main axis It was confirmed that a plurality of branches were obliquely branched and had a dendritic shape that grew three-dimensionally.
Moreover, when the electroconductivity of this silver covering copper powder was measured as shown in Table 1, the favorable value was shown.

<Example 4>
In an electrolytic cell having a size of 5.0 m × 1.1 m × 1.5 m (about 8 m ³ ), 19 copper cathode plates and copper anode plates each having a size (1.0 m × 1.0 m) are electrodes. Suspended so as to have a distance of 10 cm, circulated a copper sulfate solution as an electrolytic solution at 40 L / min, immersed an anode and a cathode in the electrolytic solution, and conducted a direct current to conduct electrolysis. Powdered copper was deposited on the cathode surface.
At this time, the electrolytic solution to be circulated was adjusted to a Cu concentration of 5 g / L, a sulfuric acid (H ₂ SO ₄ ) concentration of 200 g / L, and a current density of 150 A / m ² for electrolysis for 1 hour.
During electrolysis, the copper ion concentration of the electrolyte solution between the electrodes was always kept lower than the copper ion concentration of the electrolyte solution at the bottom of the electrolytic cell.

The copper deposited on the cathode surface was mechanically scraped and collected, and then washed to obtain a hydrous copper powder cake equivalent to 1 kg of copper powder. This cake was dispersed in 6 L of water, 2 L of an industrial gelatin (made by Nitta Gelatin) 10 g / L aqueous solution 2 L was added, stirred for 10 minutes, filtered through a Buchner funnel, washed, and then under reduced pressure (1 × 10 ^-3 Pa) at 80 ° C. for 6 hours to obtain electrolytic copper powder.
Then, silver was coated in the same manner as in Example 1 to obtain a dendrite-like silver-coated copper powder (sample). The silver coating amount was 10.7% by mass of the entire silver-coated copper powder.

When the obtained dendrite-like silver-coated copper powder (sample) was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and from the main axis It was confirmed that a plurality of branches were obliquely branched and had a dendritic shape that grew three-dimensionally.
Moreover, when the electroconductivity of this silver covering copper powder was measured as shown in Table 1, the favorable value was shown.

<Example 5>
An electrolytic copper powder was obtained in the same manner as in Example 4 except that the Cu concentration was 1 g / L, the electrolysis time was 30 minutes, and the circulating fluid amount was 20 L / min.
Then, silver was coated in the same manner as in Example 1 to obtain a dendrite-like silver-coated copper powder (sample). The silver coating amount was 10.8% by mass of the total silver-coated copper powder.

When the obtained dendrite-like silver-coated copper powder (sample) was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and from the main axis It was confirmed that a plurality of branches were obliquely branched and had a dendritic shape that grew three-dimensionally.
Moreover, when the electroconductivity of this silver covering copper powder was measured as shown in Table 1, the favorable value was shown.

<Example 6>
In the same manner as in Example 5, an electrolytic copper powder was obtained.

25 kg of the obtained electrolytic copper powder was put into 50 L of pure water kept at 50 ° C. and stirred well. Separately, 2.25 kg of silver nitrate was introduced into 3 L of pure water to prepare a silver nitrate solution. The silver nitrate solution was added all at once to the solution in which the copper powder was dissolved. In this state, stirring was performed for 2 hours to obtain a silver-coated copper powder slurry.
Next, the silver-coated copper powder slurry is filtered by vacuum filtration. After the filtration is finished, the slurry is washed with a solution of 300 g of EDTA (ethylenediaminetetraacetic acid) in 3 L of pure water, followed by 1.5 L. The residual EDTA was washed with pure water. Then, it was made to dry at 120 degreeC for 3 hours, and dendritic silver covering copper powder (sample) was obtained. The silver coating amount was 5.4% by mass of the total silver-coated copper powder.

When the obtained dendrite-like silver-coated copper powder (sample) was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and from the main axis It was confirmed that a plurality of branches were obliquely branched and had a dendritic shape that grew three-dimensionally.
Moreover, when the electroconductivity of this silver covering copper powder was measured as shown in Table 1, the favorable value was shown.

<Example 7>
In the same manner as in Example 5, an electrolytic copper powder was obtained.

25 kg of the obtained electrolytic copper powder was put into 50 L of pure water kept at 50 ° C. and stirred well. Separately, 9.0 kg of silver nitrate was added to 10 L of pure water to prepare a silver nitrate solution. The silver nitrate solution was added all at once to the solution in which the copper powder was dissolved. In this state, stirring was performed for 2 hours to obtain a silver-coated copper powder slurry.
Next, the silver-coated copper powder slurry is filtered by vacuum filtration. After the filtration is completed, the slurry is washed with a solution of 1200 g of EDTA (ethylenediaminetetraacetic acid) in 12 L of pure water, and subsequently 6.0 L. The residual EDTA was washed with pure water. Then, it was made to dry at 120 degreeC for 3 hours, and dendritic silver covering copper powder (sample) was obtained. The silver coating amount was 20.3% by mass of the total silver-coated copper powder.

When the obtained dendrite-like silver-coated copper powder (sample) was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and from the main axis It was confirmed that a plurality of branches were obliquely branched and had a dendritic shape that grew three-dimensionally.
Moreover, when the electroconductivity of this silver covering copper powder was measured as shown in Table 1, the favorable value was shown.

<Comparative Example 1>
In an electrolytic cell having a size of 2.5 m × 1.1 m × 1.5 m (about 4 m ³ ), nine copper cathode plates and a copper anode plate (electrodes) each having a size (1.0 m × 1.0 m) Suspend so that the distance is 5 cm, circulate a copper sulfate solution as an electrolytic solution at 2 L / min, immerse the anode and the cathode in this electrolytic solution, conduct a direct current through this to perform electrolysis, Powdered copper was deposited on the cathode surface.
At this time, electrolysis was carried out for 5 hours while adjusting the Cu concentration of the electrolyte to be circulated to 100 g / L, the sulfuric acid (H ₂ SO ₄ ) concentration to 100 g / L, and the current density to 80 A / m ² .
During electrolysis, the copper ion concentration in the electrolyte solution between the electrodes was always higher than the copper ion concentration in the electrolyte solution at the bottom of the electrolytic cell.

The copper deposited on the cathode surface was mechanically scraped and collected, and then washed to obtain a hydrous copper powder cake equivalent to 1 kg of copper powder. This cake was dispersed in 3 L of water, 1 L of an industrial gelatin (made by Nitta Gelatin) 10 g / L aqueous solution was added and stirred for 10 minutes, and then filtered through a Buchner funnel. It was dried for 6 hours to obtain electrolytic copper powder.
Then, silver was coated in the same manner as in Example 1 to obtain a silver-coated copper powder (sample). The silver coating amount was 10.7% by mass of the entire silver-coated copper powder.

When the obtained silver-coated copper powder (sample) was observed using a scanning electron microscope (SEM), the particle shape of the obtained electrolytic copper powder was pinecone, and the main shaft thickness, branch length, number of branches / The major axis L could not be measured.
Moreover, as shown in Table 1, when the conductivity of this silver-coated copper powder was measured, it showed an inferior value as compared with the developed dentlite.

<Comparative example 2>
In an electrolytic cell having a size of 5.0 m × 1.1 m × 1.5 m (about 8 m ³ ), 19 copper cathode plates and copper anode plates each having a size (1.0 m × 1.0 m) are electrodes. Suspended so as to have a distance of 10 cm, and circulated a copper sulfate solution as an electrolytic solution at 150 L / min, immersed an anode and a cathode in the electrolytic solution, and conducted a direct current to conduct electrolysis. Powdered copper was deposited on the cathode surface.
At this time, the electrolytic solution to be circulated was adjusted to a Cu concentration of 70 g / L, a sulfuric acid (H ₂ SO ₄ ) concentration of 200 g / L, and a current density of 90 A / m ² for electrolysis for 6 hours.
During electrolysis, the copper ion concentration of the electrolyte solution between the electrodes was equal to the copper ion concentration of the electrolyte solution at the bottom of the electrolytic cell.

The copper deposited on the cathode surface was mechanically scraped and collected, and then washed to obtain a hydrous copper powder cake equivalent to 1 kg of copper powder. This cake was dispersed in 6 L of water, 2 L of an industrial gelatin (made by Nitta Gelatin Co., Ltd.) 10 g / L aqueous solution 2 L was added, stirred for 10 minutes, filtered through a Buchner funnel, washed, and then washed at 120 ° C. in an air atmosphere. It was dried for 5 hours to obtain electrolytic copper powder.
Then, silver was coated in the same manner as in Example 1 to obtain a silver-coated copper powder (sample). The silver coating amount was 10.8% by mass of the total silver-coated copper powder.

When the obtained silver-coated copper powder (sample) was observed using a scanning electron microscope (SEM), the particle shape of the obtained electrolytic copper powder was pinecone, and the main shaft thickness, branch length, number of branches / The major axis L could not be measured.
Moreover, as shown in Table 1, when the conductivity of this silver-coated copper powder was measured, it showed an inferior value as compared with the developed dentlite.

(Discussion)
Considering the above examples and the test results conducted so far, the thickness a of the main shaft is 0.3 μm to 5.0 μm, and the longest branch length among the branches extending from the main shaft is 0. It is found that if the silver-coated copper powder particles exhibiting a dendritic shape of .6 μm to 10.0 μm, the dendrite has grown sufficiently and sufficiently to obtain excellent conductivity, and excellent conductivity can be obtained. It was.

Claims (3)

A silver-coated copper powder composed of silver-coated copper powder particles whose surface is coated with silver,
When observing silver-coated copper powder particles using a scanning electron microscope (SEM), it has a single main axis, and a plurality of branches are obliquely branched from the main axis, two-dimensionally or three-dimensionally. It has a dendritic shape that grows, the thickness a of the main axis is 0.3 μm to 5.0 μm, and the length b of the longest branch among the branches extending from the main axis is 0.6 μm to 10.0 μm. A silver-coated copper powder comprising silver-coated copper powder particles having a dendritic shape.   The silver-coated copper powder particles having a dendritic shape according to claim 1 are characterized in that the number of branches branches (number of branches / major axis L) is 0.5 / μm to 4.0 / μm with respect to the major axis L of the main axis. The silver-coated copper powder according to claim 1. The silver-coated copper powder according to claim 1 or 2, wherein the silver coating amount is 0.5 to 35.0 mass% of the entire silver-coated copper powder.