JP6309758B2 - Silver-coated copper powder and method for producing the same - Google Patents

Description

  The present invention relates to silver-coated copper powder and a method for producing the same.

  Conventionally, copper powder has been widely used as a raw material for conductive paste. Conductive pastes are widely used because of their ease of handling, from experimental purposes to applications in the electronics industry. In particular, silver coated copper powder whose surface is coated with a silver coating layer is processed into a conductive paste and applied to circuit formation of printed wiring boards using a screen printing method, various electrical contacts, etc. It has been used as a material for ensuring conduction. The reason for this is that silver-coated copper powder is superior in electrical conductivity compared to normal copper powder. Also, silver-coated copper powder is economically advantageous because it is not expensive, unlike silver powder consisting only of silver. Therefore, when a conductor is formed with a conductive paste using silver-coated copper powder having excellent conductive properties, a low-resistance conductor can be manufactured at low cost.

  Silver-coated copper powder has generally been produced by an electroless displacement plating method using a substitution reaction between copper and silver. For example, Patent Document 1 proposes a method of depositing metallic silver on the surface of metallic copper powder while vigorously stirring a solution containing metallic copper powder and silver nitrate. The present applicant has also previously proposed a method for producing silver-coated copper powder by electroless displacement plating (see Patent Document 2). In this method, the copper powder is dispersed in an acidic solution before the silver substitution reaction to reliably remove the oxide on the surface of the copper powder. Further, a pH is adjusted by adding a buffer to the copper powder slurry to which the chelating agent is added, and the silver substitution reaction rate is kept constant by continuously adding the silver ion solution.

  In addition to the above technique, in Patent Document 3, a silver ion solution is continuously added to a copper powder slurry having a pH of 3.5 to 4.5 in which copper powder is dispersed in a reducing agent, and electroless displacement plating is performed. It describes that a silver layer is formed on the surface of copper powder by reduction-type electroless plating. Examples of the reducing agent 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.

  In Patent Document 4, after copper powder is dispersed in water, and then a chelating agent is added, a water-soluble silver salt is added and subjected to a substitution reaction, and the surface layer of the copper powder particles is substituted with silver. A method for producing a silver-coated copper powder in which the obtained silver-coated copper powder is taken out of the solution and washed with a chelating agent is described.

JP-A-10-212501 JP 2004-052044 A JP 2011-2104080 A JP 2013-001917 A

  However, when silver is reduced by the displacement plating method, a large number of pores are formed in the copper coat layer due to the copper eluting instead of the reduced silver, and copper, which is a metal that is easily oxidized through the pores, is exposed to the outside. Will be exposed. As a result, oxidation progresses with the passage of time and the conductivity of the powder decreases.

  Therefore, the subject of this invention is providing the silver coat copper powder which can eliminate the various fault which the prior art mentioned above has, and its manufacturing method.

  The present invention provides a silver-coated copper powder having core particles made of copper and a silver coat layer located on the surface of the core particles and having a sulfur content of 5 ppm to 500 ppm.

The present invention also includes a first step in which silver ions and core particles made of copper are contacted in water to perform displacement plating, and silver is deposited on the surface of the core particles to obtain precursor particles;
A method for producing a silver-coated copper powder, comprising a second step of bringing the precursor particles, silver ions, and a silver ion reducing agent into contact with each other in water to further precipitate silver on the surfaces of the precursor particles. And
In the first step, prior to bringing the silver ions and the core particles into contact, an organic sulfonic acid is added to the water in which the core particles are dispersed, and the core particles are subjected to a surface treatment.
In the second step, prior to bringing the precursor particles, silver ions, and the reducing agent into contact with each other, an organic sulfonic acid is added to the water in which the precursor particles are dispersed, The present invention provides a method for producing a silver-coated copper powder, in which surface treatment is performed, or after silver is precipitated in the second step, organic sulfonic acid is added to water to perform the surface treatment of the precipitated silver.

  According to the present invention, it is possible to easily produce a silver-coated copper powder in which the surface of core particles made of copper is coated with a uniform and dense silver layer. This silver-coated copper powder has high conductivity and is difficult to be oxidized, so that a decrease in conductivity over time is suppressed.

1 is a scanning electron microscope image of a cross section of the silver-coated copper powder obtained in Example 1. FIG. FIG. 2 is a scanning electron microscope image of a cross section of the silver-coated copper powder obtained in Comparative Example 1.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. First, a suitable method for producing the silver-coated copper powder of the present invention will be described. In this production method, core particles made of copper are prepared, and a silver coat layer is formed on the surface of the core particles. This manufacturing method has one of the characteristics in the formation method of a silver coat layer. The formation of the silver coat layer is performed by the following two steps, a first step and a second step.

[First step]
Displacement plating is performed by bringing silver ions and core particles made of copper into contact in water, and silver is deposited on the surfaces of the core particles. Precursor particles are obtained by this precipitation.
[Second step]
The precursor particles obtained in the first step, silver ions, and a silver ion reducing agent are brought into contact in water to further precipitate silver on the surfaces of the precursor particles.

The core particles used in the first step can be produced by various methods. For example, core particles can be obtained by wet reduction of copper compounds such as copper acetate and copper sulfate using various reducing agents such as hydrazine. Alternatively, core particles can be obtained by an atomizing method using a molten copper. The preferred particle size of the core particles thus obtained is 0.01 to ₅₀ μm, expressed as a volume cumulative particle size D ₅₀ at a cumulative volume of 50% by volume by a laser diffraction / scattering particle size distribution measurement method. 1 to 10 μm, especially 0.5 to 10 μm. A method for measuring D ₅₀ will be described later. The shape of the core particles is preferably spherical from the viewpoint of improving the conductivity of the intended silver-coated copper powder, but may be other shapes such as flakes or spindles. Core particles having such a particle size and shape are brought into contact with silver ions in water.

  Silver ions are generated from a silver compound serving as a silver source. As the silver compound, for example, a water-soluble silver compound such as silver nitrate can be used. The concentration of silver ions in water is preferably set to 0.01 to 10 mol / L, particularly 0.04 to 2.0 mol / L from the viewpoint that a desired amount of silver can be precipitated on the surface of the core particles.

  On the other hand, the amount of the core particles in water is preferably 1 to 1000 g / L, particularly 50 to 500 g / L, from the viewpoint that a desirable amount of silver can be deposited on the surface of the core particles.

  In the first step, prior to bringing silver ions and core particles into contact with each other, an organic sulfonic acid is added to a slurry in which the core particles are dispersed in water to perform surface treatment of the core particles. Specifically, an organic sulfonic acid is added to a slurry containing core particles, and the surface of the core particles dispersed in water is treated with the organic sulfonic acid. When a film of copper oxide is generally formed on the surface of the core particle, the film is removed by performing a surface treatment with an organic sulfonic acid. Since the coating made of copper oxide is a portion where the substitution plating reaction with silver ions does not occur, it does not elute in water and remains on the surface of the core particle after the substitution plating reaction. It becomes a cause of generating voids and cracks in the coated copper powder. Therefore, in this production method, prior to the displacement plating reaction, the coating made of copper oxide is removed with organic sulfonic acid, and the displacement plating reaction is performed with the fresh surface of the metallic copper exposed. . As a result, the above-mentioned voids and cracks can be effectively prevented. The organic sulfonic acid also has an effect of improving the adhesion between the silver coating layer and the copper core particles.

  The surface treatment with the organic sulfonic acid may be performed under heating or may be performed under non-heating. When the surface treatment is performed under heating, the heating temperature of the slurry is preferably 25 ° C. or higher and 80 ° C. or lower, more preferably 30 ° C. or higher and 50 ° C. or lower.

  In order to remove the film made of copper oxide, it is also possible to use a substance other than organic sulfonic acid. However, when organic sulfonic acid is used, not only the effect of removing the film made of copper oxide but also the effect of slowing the silver deposition rate during displacement plating can be achieved. The ability to slow the deposition rate of silver during displacement plating is advantageous in that the adhesion between the deposited silver and the core particles is improved, and the silver is uniformly deposited. By these things, the electroconductivity of the target silver coat copper powder improves. Therefore, it is advantageous to use an organic sulfonic acid in this production method.

  As the organic sulfonic acid, a sulfonic acid having an aliphatic hydrocarbon group or a sulfonic acid having an aromatic hydrocarbon group can be used. An organic sulfonic acid can be used individually by 1 type or in combination of 2 or more types. Regardless of whether the organic sulfonic acid has an aliphatic hydrocarbon group or an aromatic hydrocarbon group, the amount of sulfur contained in the target silver-coated copper powder decreases as the carbon number of the organic group decreases. As a result of the study by the present inventor, it has been found (see Examples 1 and 5 to 8 described later).

  As the aliphatic hydrocarbon group, saturated and unsaturated hydrocarbon groups having 1 to 11 carbon atoms, particularly 1 to 3 carbon atoms can be used. Particularly preferred aliphatic hydrocarbon groups are alkyl groups having 1 to 3 carbon atoms. In particular, it is preferable to use methanesulfonic acid or ethanesulfonic acid. On the other hand, as the sulfonic acid having an aromatic hydrocarbon group, for example, benzenesulfonic acid or benzenesulfonic acid in which one or more hydrogen atoms on the benzene ring are substituted with a substituent can be used. Examples of the substituent include an alkyl group having 1 to 3 carbon atoms and a hydroxyl group. Examples of benzenesulfonic acid substituted with a substituent include p-toluenesulfonic acid and phenolsulfonic acid. Of the sulfonic acid having an aliphatic hydrocarbon group and the sulfonic acid having an aromatic hydrocarbon group, from the viewpoint of the performance of removing the film made of copper oxide and the ability to slow the deposition rate of silver during displacement plating It is preferable to use a sulfonic acid having an aliphatic hydrocarbon group.

  The addition amount of the organic sulfonic acid is preferably 10% by mass or more and 150% by mass or less, and more preferably 25% by mass or more and 90% by mass or less with respect to the mass of the core particles. By setting the addition amount of the organic sulfonic acid within this range, the film made of copper oxide can be surely removed, and the silver deposition rate at the time of displacement plating becomes appropriate.

  After the surface treatment of the core particles with the organic sulfonic acid, the core particles and silver ions are then contacted. There are no particular restrictions on the order of addition of the core particles and silver ions. For example, the surface-treated core particles and silver ions can be simultaneously added to water. From the viewpoint of ease of control of silver deposition by displacement plating, it is preferable to prepare a slurry by predispersing the surface-treated core particles in water and add a silver compound as a silver source to the slurry. . In this case, the slurry may be at room temperature or in the temperature range of 0 to 80 ° C. Prior to the addition of the silver compound, a complexing agent such as ethylenediaminetetraacetic acid, triethylenediamine, iminodiacetic acid, citric acid or tartaric acid, or a salt thereof is added to the slurry to control the reduction of silver. It may be.

  The addition of the silver compound is preferably performed in the state of an aqueous solution. This aqueous solution can be added all at once in the slurry, or can be added continuously or discontinuously over a predetermined time. From the viewpoint of easily controlling the reaction of the displacement plating, it is preferable to add the aqueous silver compound solution continuously or discontinuously to the slurry over a predetermined time.

  Silver is deposited on the surface of the core particles by displacement plating to obtain precursor particles. The amount of silver deposited in the precursor particles is 0.1 to 50% by mass, particularly 1 to 10% by mass of the amount of silver in the finally obtained silver-coated copper powder, thereby forming a dense silver-coated layer. It is preferable from the point which can do.

  By the above operation, precursor particles are obtained in the first step. The precursor particles are subjected to the second step. In this production method, after the precursor particles are formed in the first step, the copper ions eluted in water due to the displacement plating performed in the first step before the precursor particles are subjected to the second step. Is advantageously removed from the slurry. The reason for this is as follows. As will be described later, in the second step, silver ions are reduced using a reducing agent. If copper ions are present in the water during this reduction, not only the reduction of silver ions but also the reduction of copper ions will occur unintentionally. Unintentional reduction of copper ions contributes to a decrease in the conductivity of the intended silver-coated copper powder. This is because copper is a substance having lower electrical conductivity than silver. Therefore, in this production method, copper ions are removed from the slurry before the second step, and only the reduction of silver ions occurs in the second step.

  In order to remove copper ions from the slurry containing the precursor particles obtained in the first step, for example, the slurry may be repulp washed to remove copper ions dissolved in water. In this case, it is preferable to measure the electrical conductivity of the slurry over time and repeat the repulp washing until the electrical conductivity decreases to a predetermined value. For example, it is preferable to repeat the repulp washing until the conductivity becomes 300 μS or less.

  In the second step, silver ions and a silver ion reducing agent are added to the slurry containing the precursor particles after the copper ions are removed by the above-described method. In this case, the precursor particles may be solid-liquid separated and then dispersed in water to form a slurry, or the precursor particle slurry after the copper ions are removed may be directly used in the second step. .

  In the second step, it is preferable to add organic sulfonic acid to the slurry in which the precursor particles are dispersed in water prior to bringing the precursor particles, silver ions, and the reducing agent into contact with each other. The purpose of adding the organic sulfonic acid is the same as in the first step. In this case, the organic sulfonic acid added in the second step and the organic sulfonic acid added in the first step may be the same or different. Further, the surface treatment with organic sulfonic acid can be generally performed at room temperature, for example, at 20 ° C. or more and 25 ° C. or less. If necessary, the surface treatment may be performed in a state where the dispersion is heated.

  The addition amount of the organic sulfonic acid is preferably 10% by mass or more and 150% by mass or less, and more preferably 25% by mass or more and 90% by mass or less with respect to the mass of the core particles.

  Once the organic sulfonic acid is added and the precursor particles are surface treated, silver ions and a reducing agent are added to the slurry. The silver ions added in the second step are generated from a water-soluble silver compound as in the first step. The silver compound is preferably added to the slurry in the form of an aqueous solution. The concentration of silver ions in the aqueous silver solution is preferably 0.01 to 10 mol / L, more preferably 0.1 to 2.0 mol / L. The silver aqueous solution having a concentration in this range is 0.1 to 55 parts by mass, particularly 100 to 100 parts by mass of the precursor particles in the slurry containing 1 to 1000 g / L, particularly 50 to 500 g / L of precursor particles. It is preferable to add 1 to 25 parts by mass from the viewpoint that a dense silver coat layer can be formed.

  As a reducing agent to be added in the second step, a reducing agent having a reducing power capable of causing silver displacement plating and reduction plating to proceed simultaneously is used. By using such a reducing agent, a dense silver coat layer can be successfully formed. When a reducing agent having a strong reducing property is used, reduction plating proceeds unilaterally and it is not easy to form a silver coat layer having a desired dense structure. On the other hand, when a reducing agent having a weak reducing property is used, it is difficult to proceed with reduction plating of silver ions, and it is not easy to form a silver coat layer having a dense structure due to this. From the above viewpoint, as the reducing agent, it is preferable to use an organic reducing agent that exhibits acidity when dissolved in water. Specific examples include formic acid, oxalic acid, L-ascorbic acid, erythorbic acid, and formaldehyde. These organic reducing agents may be used individually by 1 type, or may be used in combination of 2 or more type. Among these, it is preferable to use L-ascorbic acid. The term “acidic” as used herein means that an aqueous solution obtained by dissolving 0.1 mol of an organic reducing agent in 1000 g of water exhibits a pH of 1 to 6 at 25 ° C.

  The addition amount of the reducing agent is 0.5 to 5.0 equivalents, particularly 1.0 to 2.0 equivalents, based on the silver ions in the silver solution to be added. This is preferable from the viewpoint of easy progress.

  There is no particular limitation on the order in which the reducing agent and silver ions are added to the slurry containing the precursor particles. From the viewpoint of controlling the reduction of silver ions to form a dense silver coat layer, it is preferable to add silver ions after adding a reducing agent to the slurry. The silver compound to be a silver source can be added all at once in the slurry, or can be added continuously or discontinuously over a predetermined time. From the viewpoint of easily controlling the reduction of silver ions, the silver compound is preferably added to the slurry in a state of an aqueous solution over a predetermined time.

  In the second step, when silver displacement plating and reduction plating are simultaneously performed, the slurry may be kept at room temperature or may be heated in a temperature range of 0 to 80 ° C.

  In the second step, after surface treatment of the precursor particles with organic sulfonic acid, before adding silver ions and a reducing agent to the slurry, ethylenediaminetetraacetic acid, triethylenediamine are added to the slurry in which the precursor particles are dispersed. In addition, a complexing agent such as iminodiacetic acid, citric acid or tartaric acid, or a salt thereof may be added to control the reduction of silver. The kind of complexing agent to be added may be the same as or different from the complexing agent used in the first step.

  In the second step, the intended silver-coated copper powder is obtained by appropriately adjusting the reaction time and the concentration of silver ions. The silver-coated copper powder obtained in this manner is obtained by coating the surface of core particles made of copper with a layer made of silver (hereinafter also referred to as “silver coat layer”). The silver coat layer continuously covers the surface of the core particles made of copper. As a result, the entire surface of the silver-coated copper powder is made of only silver, and the underlying copper is not exposed at all on the surface of the silver-coated copper powder.

  The silver coat layer is very dense with very few pores. By covering the entire surface of the core particle made of copper with the silver coat layer having such a structure, oxidation of copper is suppressed as much as possible. As a result, even after long-term storage, the silver-coated copper powder suppresses the decrease in electrical resistance as much as possible. In contrast, in the silver-coated copper particles described in Patent Documents 1 and 2 in which the silver coat layer is considered to have a large number of pores, the surface of the core particles made of copper is exposed to the outside through the pores. Since it becomes easy to contact | connect, there exists a tendency for copper to be oxidized by the preservation | save for a long period of time, and electrical resistance falls easily resulting from it.

  In the present invention, the silver coat layer may be surface-treated with an organic sulfonic acid after silver is deposited in the second step to form a silver coat layer. In this case, the use amount of the organic sulfonic acid is preferably 10% by mass or more and 150% by mass or less, and more preferably 25% by mass or more and 90% by mass or less with respect to the core particles. Examples of the organic sulfonic acid that can be used are the same as those described above. By subjecting the silver coat layer to a surface treatment with an organic sulfonic acid, it is possible to effectively prevent the formation of voids in the intended silver-coated copper powder.

  In the above method, the surface treatment with the organic sulfonic acid is performed in both the first step and the second step and after the second step. Instead, the surface treatment with the organic sulfonic acid is performed only in the first step. Alternatively, the surface treatment with the organic sulfonic acid may be performed only in the second step, or the surface treatment with the organic sulfonic acid may be performed only after the second step. Further, the surface treatment with the organic sulfonic acid may be performed only in the first step and the second step, only after the first step and the second step, or only after the second step and the second step.

  The silver ratio in the silver-coated copper powder is preferably 0.1 to 35% by mass, and preferably 0.5 to 30% by mass from the viewpoint of evenly covering the surface of the copper core particles and the economical point of view. % Is more preferable, 0.5 to 25% by mass is more preferable, and 1 to 25% by mass is even more preferable. The proportion of silver in the silver-coated copper powder can be measured, for example, by completely dissolving the silver-coated copper powder using an acid and analyzing the solution by ICP emission spectroscopy.

  The silver-coated copper powder contains sulfur due to the organic sulfonic acid used in the production process. The ratio of sulfur contained in the silver-coated copper powder is preferably 5 ppm or more and 500 ppm or less, more preferably 10 ppm or more and 500 ppm or less, and still more preferably 30 ppm or more and 100 ppm or less. The proportion of sulfur in the silver-coated copper powder can be measured by high-frequency heating combustion-infrared absorption method or the like of the silver-coated copper powder in an oxygen stream. “Ppb” and “ppm” are based on mass. Sulfur contained in the silver-coated copper powder is mainly present in the interface between the silver-coated layer and the copper core particles or in the silver-coated layer. The position where sulfur is present can be observed, for example, by elemental mapping of the cross section of the silver-coated copper powder.

  In particular, when the treatment with organic sulfonic acid is performed in the first step, sulfur is present between the copper core particles and the silver coat layer. In contrast, when the treatment with organic sulfonic acid is performed in the second step, sulfur is present in the silver coat layer and / or on the surface of the silver coat layer. Therefore, when the treatment with the organic sulfonic acid is performed only in the first step, sulfur is mainly unevenly distributed between the copper core particles and the silver coat layer (see Example 2 described later). Further, when the treatment with the organic sulfonic acid is performed only in the second step, sulfur is mainly unevenly distributed in the silver coat layer and / or on the surface of the silver coat layer (see Example 3 described later). Further, when the treatment with the organic sulfonic acid is performed only after the second step, sulfur is mainly unevenly distributed on the surface of the silver coat layer (see Example 4 described later). It can be judged from the combined state of sulfur obtained by X-ray photoelectron spectroscopy (XPS) measurement to be described later where sulfur is present in the silver-coated copper powder.

  When sulfur is present between the copper core particles and the silver coat layer, copper, sulfur and silver are combined (hereinafter referred to as "Cu-S-Ag-Ag"). .) When it has this "Cu-S-Ag-Ag" coupling | bonding form, there exists an advantage that the coupling | bonding force of a copper core particle and a silver coat layer increases. In the second step, when the treatment with organic sulfonic acid is carried out and sulfur is present in the silver coat layer, sulfur is taken into the silver coat layer and forms a bond form similar to silver sulfide (hereinafter referred to as this form). The bond form is described as “Cu—Ag—S—Ag—Ag”). When it has this "Cu-Ag-S-Ag-Ag" coupling | bonding form, there exists an advantage that the adhesiveness of a silver coat layer improves. When the treatment with organic sulfonic acid is performed in both the first step and the second step, sulfur becomes the two types of bonding forms (hereinafter referred to as “Cu—S—Ag—S—Ag—Ag”). To describe.) When this “Cu—S—Ag—S—Ag—Ag” bond form is present, a high percentage of sulfur is observed. In addition, when the treatment with the organic sulfonic acid is performed after the second step, the sulfur is combined with silver existing on the surface of the silver coat layer (hereinafter, this combined form is referred to as “Ag—Cu—Ag—Ag— S ”.)

  The binding state of sulfur in the silver-coated copper particles as described above can be known, for example, by X-ray photoelectron spectroscopy (XPS) measurement. The binding energy of the sulfur 2p orbit measured by XPS is usually 164 eV. However, when sulfur is present in the vicinity of copper or silver and the copper or silver has a bond with sulfur, this binding energy is shifted. For example, the binding energy in the case of having a Cu-S-Ag bond shifts to 162.8 eV. The binding energy in the case of having an Ag-S-Ag bond is shifted to 160.8 eV. By measuring the degree of shift of the binding energy in this way, it is possible to specify the sulfur binding state.

  Silver coat copper powder is used suitably in the state of the conductive composition containing this. For example, silver-coated copper powder can be mixed with a vehicle, glass frit and the like to form a conductive paste. Alternatively, silver-coated copper powder can be mixed with an organic solvent or the like to form an ink. A conductive film having a desired pattern can be obtained by applying the conductive paste or ink thus obtained to the surface of the object to be applied.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”.

[Example 1]
(1) First Step 1000 g of core particles made of copper and 5000 mL of pure water heated to 40 ° C. were charged into a 10 L beaker to prepare a copper slurry. The core particles had a volume cumulative particle diameter D ₅₀ in the cumulative volume 50% by volume by laser diffraction scattering particle size distribution measuring method is of 4 [mu] m. 270 g of methanesulfonic acid was added to this copper slurry and stirred for 30 minutes. Then 42.5 g of disodium ethylenediaminetetraacetate and 66.7 g of citric acid were added. Subsequently, 0.9 mol / L silver nitrate aqueous solution was continuously added at a rate of 40 mL / min over 1 minute. In this way, displacement plating was performed. After completion of the displacement plating, repulp washing was performed with pure water until the conductivity of the slurry was 300 μS or less.

(2) Second Step To the slurry obtained in the first step, 5000 mL of 40 ° C. pure water and 270 g of methanesulfonic acid were added. Then 42.5 g of disodium ethylenediaminetetraacetate and 66.7 g of citric acid were added. Subsequently, 9.7 g of ascorbic acid was added continuously, and an aqueous 0.9 mol / L silver nitrate solution was continuously added at a rate of 40 mL / min over 5 minutes. Thereby, reduction plating was performed to obtain a target silver-coated copper powder.

[Example 2]
In the second step of Example 1, no surface treatment with organic sulfonic acid was performed. Except this, it carried out similarly to Example 1, and obtained the silver coat particle.

Example 3
In the first step of Example 1, no surface treatment with organic sulfonic acid was performed. Except this, it carried out similarly to Example 1, and obtained the silver coat particle.

Example 4
In Example 1, surface treatment with organic sulfonic acid was not performed in the first step and the second step, and 270 g of methanesulfonic acid was added after the silver coat layer was formed in the second step. After the addition, the liquid was stirred for 5 minutes and surface-treated with methanesulfonic acid. As a result, the intended silver-coated copper powder was obtained.

Example 5
Instead of the organic sulfonic acid used in the first step and the second step of Example 1, 310 g of ethanesulfonic acid was used in each step. Except this, it carried out similarly to Example 1, and obtained silver coat copper powder.

Example 6
Instead of the organic sulfonic acid used in the first step and the second step of Example 1, 440 g of benzenesulfonic acid was used in each step. Except this, it carried out similarly to Example 1, and obtained silver coat copper powder.

Example 7
Instead of the organic sulfonic acid used in the first step and the second step of Example 1, 490 g of phenolsulfonic acid was used in each step. Except this, it carried out similarly to Example 1, and obtained silver coat copper powder.

Example 8
As the organic sulfonic acid used in the first step and the second step of Example 1, 480 g of p-toluenesulfonic acid was used in each step. Except this, it carried out similarly to Example 1, and obtained silver coat copper powder.

[Comparative Example 1]
This comparative example is an example in which silver-coated copper powder was produced only by displacement plating. In 5000 mL of pure water heated to 40 ° C., 1000 g of the same core particles used in Example 1 were added to form a slurry. While stirring the slurry, 63.8 g of disodium ethylenediaminetetraacetate was added and dissolved. Furthermore, 2400 mL of a 0.44 mol / L silver nitrate aqueous solution was continuously added to this slurry for 30 minutes to perform displacement plating, and silver was deposited on the surface of the copper particles to obtain silver-coated copper powder.

[Evaluation]
About the silver coat copper powder obtained by the Example and the comparative example, the cross section of the particle | grains was cut out using the cross section polisher, and the cross section was observed with the electron microscope. Based on the observation results, the degree of void generation was evaluated according to the following criteria. Moreover, the electron microscope image of the silver coat copper powder of Example 1 and Comparative Example 1 is shown in FIG.1 and FIG.2.
Moreover, about the silver coat copper powder obtained by the Example and the comparative example, Ag amount and S amount (The ratio (mass%) of silver in silver coat copper powder, and the ratio (ppm) of sulfur) are measured by the method mentioned above. did. Further, the BET specific surface area was measured by the following method, and the volume cumulative particle diameter D ₅₀ at a cumulative volume of 50% by volume was measured by a laser diffraction scattering type particle size distribution measurement method. Further, the bonding state of each element on the surface of the silver-coated copper powder by XPS was measured. Further, the dust resistance was measured. The measurement results are shown in Table 1 below.

[Degree of void formation]
(Double-circle): A space | gap is not observed at all.
○: Slight minute voids are observed.
Δ: Several minute voids are observed.
X: Large voids are observed.

[BET specific surface area of silver-coated copper powder]
A silver-coated silver powder (2.0 g) was subjected to a deaeration treatment at 75 ° C. for 10 minutes and then measured by a BET 1-point method using a monosorb (manufactured by Kantachrome).

[D ₅₀ by laser diffraction scattering particle size distribution measuring method of the silver-coated copper powder]
A 0.1 g sample was mixed with a 0.1% aqueous solution of SN Dispersant 5468 (manufactured by San Nopco), and then dispersed for 5 minutes with an ultrasonic homogenizer (US-300T, manufactured by Nippon Seiki Seisakusho). And the particle size distribution was measured using the laser diffraction scattering type particle size distribution measuring device Micro Trac HRA 9320-X100 type (Leeds + Northrup).

[XPS measurement of silver-coated copper powder]
Survey measurement (qualitative analysis) and narrow measurement (semi-quantitative analysis) were performed using an X-ray photoelectron spectrometer (Quantum 2000, manufactured by ULVAC-PHI Co., Ltd.). And the presence or absence of observation of a Cu-S-Ag bond energy band and an Ag-S-Ag bond energy band was investigated. The case where it was observed was set as “◯”, and the case where it was not observed was set as “×”.
The survey measurement conditions are as follows.
・ Measurement range: 0 to 1400eV
・ Pass energy: 58.7 eV
・ Step size: 1.0eV
・ Integrated time: 20 minutes Narrow measurement conditions are as follows <S2P>
Measurement range: 158 to 178 eV
・ Pass energy: 23.5eV
・ Step size: 0.1eV
・ Total number of times: 10 times

[Crushing resistance of silver-coated copper powder]
15 g of silver-coated copper powder was pressed at a pressure of 500 kgf to produce pellets with a diameter of 25 mm. The electrical resistance of the pellet was measured by a four-terminal method using PD-41 made by Dia Instruments.

As is clear from the comparison between FIG. 1 and FIG. 2, the silver-coated copper powder of the first example (product of the present invention) has no voids observed at the interface between the copper core particles and the silver coating layer, In the silver-coated copper powder of Comparative Example 1, it can be seen that large voids are observed at the interface between the copper core particles and the silver coating layer, and voids are also observed inside the core particles (in FIG. 2, arrows). The position indicated by.)
Moreover, as is clear from the results shown in Table 1, it can be seen that the silver-coated copper powder of the example has a low dust resistance as compared with the comparative example.
Furthermore, as is apparent from the results of Examples 1 and 5 to 8, when compared under the same production conditions, the smaller the molecular weight of the organic group bonded to the sulfonic acid group, the greater the amount of sulfur incorporated into the particles. I understand that.

Claims (12)

A core particle made of copper, and a silver coating layer positioned on the surface of the core particle, Ri 100 ppm der less content than 5ppm sulfur, Cu-S-Ag binding energy band and Ag in XPS measurement silver-coated copper powder -S-Ag binding energy band Ru observed.   The silver coat copper powder according to claim 1 in which sulfur exists between said core particles and said silver coat layer.   The silver coat copper powder according to claim 1 in which sulfur exists in said silver coat layer.   The silver coat copper powder according to claim 1 in which sulfur exists between said core particles and said silver coat layer, and in said silver coat layer.   The silver coat copper powder according to claim 1 in which sulfur exists in the surface of said silver coat layer. A first step in which silver ions and copper core particles are contacted in water to perform displacement plating, and silver is deposited on the surface of the core particles to obtain precursor particles;
A method for producing a silver-coated copper powder, comprising a second step of bringing the precursor particles, silver ions, and a silver ion reducing agent into contact with each other in water to further precipitate silver on the surfaces of the precursor particles. And
In the first step, prior to bringing the silver ions and the core particles into contact, an organic sulfonic acid is added to the water in which the core particles are dispersed, and the core particles are subjected to a surface treatment.
In the second step, prior to bringing the precursor particles, silver ions, and the reducing agent into contact with each other, an organic sulfonic acid is added to the water in which the precursor particles are dispersed, A method for producing a silver-coated copper powder, in which surface treatment is performed, or after silver is precipitated in the second step, organic sulfonic acid is added to water to perform surface treatment of the precipitated silver. In the first step, surface treatment of the core particles with organic sulfonic acid is performed,
The manufacturing method according to claim 6, wherein after the precursor particles are generated in the first step, copper ions eluted in water due to displacement plating are removed from the water, and then the second step is performed. In the first step, surface treatment of the core particles with organic sulfonic acid is performed,
The production method according to claim 6 or 7, wherein a surface treatment of the precursor particles with an organic sulfonic acid is performed in the second step.   The production method according to any one of claims 6 to 8, wherein a sulfonic acid having an aliphatic hydrocarbon group is used as the organic sulfonic acid.   The complexing agent is added to the water in which the precursor particles are dispersed in the second step, after adding the organic sulfonic acid and before adding the silver ions and the reducing agent. Manufacturing method.   11. The complexing agent according to claim 6, wherein a complexing agent is added to water in which the core particles are dispersed after adding the organic sulfonic acid and before adding silver ions in the first step. Manufacturing method.   The method according to any one of claims 6 to 11, wherein the reducing agent is an organic reducing agent that exhibits acidity when dissolved in water.