JP2012172170A - Method for producing metal particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing metal particles, by which the formation of metal particles having an average diameter of 50 nm or more is restrained.SOLUTION: An acidic reaction solution containing metal ions, a titanium trichloride as a reducing agent, a complexing agent, and a dispersing agent is adjusted to have alkaline, and the resulting reaction solution is stirred to precipitate metal particles. As the complexing agent, at least one of malic acid, a malate, gluconic acid, and a gluconate is used.

Description

  The present invention relates to a method for producing metal particles in which metal particles are precipitated by reducing metal ions with titanium trichloride.

  As a method for producing metal particles, those shown in the following patent documents are known. In the technique of Patent Document 1, nickel particles are formed by reducing nickel hydroxide with hydrazine. In the technique of Patent Document 2, nickel particles are formed by reducing nickel ions with a polyol in a solution containing carboxylic acids.

  Patent Document 1 lists production conditions for metal particles having an average particle size of 300 μm or more. On the other hand, Patent Document 2 lists production conditions for metal particles having an average particle diameter of 50 nm or more.

JP-A-5-51610 JP 2007-9275 A

  By the way, along with the recent demand for miniaturization of electronic components such as capacitors, there has been an increasing demand for further miniaturization of metal particles as the material. As a guide, there is a demand for metal particles having an average particle diameter of 50 nm or less. However, in the manufacturing methods listed above, the growth of metal particles cannot be restricted in the manufacturing process, and the size of the metal particles is 50 nm or more in terms of average particle size.

  This invention is made | formed in view of such a situation, The objective is to provide the manufacturing method of the metal particle which can suppress that an average particle diameter becomes 50 nm or more.

In the following, means for achieving the above object and its effects are described.
(1) The invention described in claim 1 is directed to a metal ion, titanium trichloride as a reducing agent for reducing the metal ion, and a complex for stabilizing the metal ion and the titanium ion of the titanium trichloride in a solution. The reaction solution is adjusted to be alkaline by mixing the reaction solution with a pH adjuster using an acidic aqueous solution containing a oxidant and a dispersant that disperses the metal particles precipitated by the reduction reaction in the solution. A method for producing metal particles in which the reaction solution is stirred to precipitate metal particles, wherein the complexing agent includes at least one of malic acid, malate, gluconic acid, and gluconate. To do.

  By the way, a method of reducing metal ions with trivalent titanium in a solution to deposit metal particles is known. In this method, a complexing agent is used to stabilize metal ions and trivalent titanium in solution.

  However, it has been difficult to form metal particles having an average particle size of 50 nm or less. Therefore, the present inventor has intensively studied, and as a result, has found that when malic acid or gluconic acid or a salt thereof is used as a complexing agent, metal particles having an average particle diameter of 50 nm or less are formed.

  Malic acid or gluconic acid or a salt thereof is considered to further reduce the reaction rate of trivalent titanium ions and metal ions as compared with other complexing agents. By slowing down the metal growth by reducing the speed of the metal ion reduction reaction, the dispersant is adsorbed on the metal particles before the metal particles exceed 50 nm, and the growth is stopped. Thereby, it can suppress that a metal particle becomes 50 nm or more by an average particle diameter.

(2) The invention according to claim 2 is characterized in that the dispersant is a salt of a maleic acid copolymer having a molecular weight of 10,000 to 50,000.
The dispersant prevents the deposited metal particles from aggregating with each other. In particular, it has been found that the use of a dispersant having the above configuration suppresses the metal particles from having an average particle diameter of 50 nm or more. That is, according to the present invention, it is possible to suppress the metal particles from having an average particle size of 50 nm or more by using the dispersant having the above-described configuration.

  (3) The invention according to claim 3 is the method for producing metal particles according to claim 1 or 2, wherein the mass per unit volume of the dispersant is 0.3 with respect to the amount of deposited metal per unit volume. The gist is that it is twice or more.

  When the concentration of the dispersant is lowered, the metal particles tend to be larger. In this respect, in the present invention, since the lower limit of the concentration of the dispersant is defined with respect to the metal deposition amount, it is possible to suppress the metal particles from becoming large.

  (4) The invention according to claim 4 is the method for producing metal particles according to any one of claims 1 to 3, wherein the molar concentration of the complexing agent is 0 with respect to the molar concentration of the titanium ions. The gist is that it is 5 to 5.0 times.

  When the ratio of the molar concentration of the complexing agent to the molar concentration of titanium ions is less than 0.5, titanium hydroxide may be generated. On the other hand, when the ratio of the molar concentration of the complexing agent to the molar concentration of titanium ions exceeds 5.0, the solubility of the pH adjusting agent or the like decreases. For this reason, it is preferable to set the molar concentration of the complexing agent within the above range.

  (5) The invention according to claim 5 is the method for producing metal particles according to any one of claims 1 to 4, wherein the reaction solution contains at least nickel ions as the metal ions. And According to this invention, since nickel ions in the reaction solution are reduced to trivalent titanium ions, metal particles containing nickel can be formed.

  (6) The invention according to claim 6 is the method for producing metal particles according to any one of claims 1 to 4, wherein the reaction solution contains a plurality of types of metal ions, and the molarity of each metal ion. The gist is to adjust the concentration based on the deposition ratio of each metal.

  According to the method of reducing metal ions with trivalent titanium, the deposition ratio of metal ions is constant under certain conditions. For this reason, the metal particle of a target composition can be formed by adjusting the molar concentration of each metal ion in a solution according to the deposition ratio of each metal.

  (7) The invention according to claim 7 is the method for producing metal particles according to claim 6, wherein the metal ions are tungsten, tantalum, rhenium, iron, cobalt, nickel, copper, silver, gold, or platinum. The gist is that there are at least two types selected from the group consisting of each ion.

  Metal ions of tungsten, tantalum, rhenium, iron, cobalt, nickel, copper, silver, gold, and platinum are reduced by trivalent titanium ions. Since two or more kinds of these metals are present in the reaction solution, metal particles containing at least two kinds of metals can be formed.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the metal particle which can suppress that it becomes 50 nm or more by an average particle diameter can be provided.

The table which shows the manufacturing conditions of an Example and a comparative example. The table which shows ratio of the total density | concentration of 1st metal salt, 2nd metal salt, and titanium trichloride, and the density | concentration of a complexing agent about each Example. The table which shows the relationship between a solution nickel ratio and the ratio of nickel in a metal particle about each Example.

  Hereinafter, the manufacturing method of the nickel particle concerning this embodiment is demonstrated. The nickel particles are used, for example, for forming an electrode of a multilayer ceramic capacitor. Hereinafter, nickel particles refer to metal particles that contain 50 atomic% or more of nickel. In order to distinguish between nickel and a metal other than nickel for each metal constituting the metal particles, nickel is a first metal and a metal other than nickel is a second metal. These salts are referred to as a first metal salt and a second metal salt, respectively. The first metal ion is the first metal ion, and the second metal ion is the second metal ion.

The nickel particles are formed by a metal ion reduction method.
First, a reaction solution containing metal ions to be deposited and a reducing agent is formed. Next, by adjusting the pH of the reaction solution to make it alkaline, the oxidation-reduction reaction between the metal ions and the reducing agent is started to deposit metal particles. Hereinafter, each step will be described.

<Formation of reducing agent>
Titanium trichloride is used as the reducing agent. When preparing the reaction solution, a hydrochloric acid solution of titanium trichloride is used. A hydrochloric acid solution of titanium trichloride is formed by reducing a hydrochloric acid solution of titanium tetrachloride by an electrolytic reduction method. Specifically, a 20% hydrochloric acid aqueous solution of titanium tetrachloride is placed in the cathode chamber of the electrolytic cell. An ammonium chloride solution is placed in the anode chamber of the electrolytic cell. The cathode chamber and the anode chamber are partitioned by an ion exchange membrane that transmits chlorine ions. Since titanium trichloride reacts with oxygen in the air and oxidizes, electrolysis is performed in an argon atmosphere. According to this method, tetravalent titanium ions can be reduced to substantially 100% trivalent titanium ions.

<Reaction solution>
The reaction solution for forming metal particles includes metal ions that form metal particles, titanium trichloride as a reducing agent, a complexing agent that stabilizes metal ions and trivalent titanium ions in the solution, and precipitation. And a dispersing agent that suppresses aggregation of metal particles to be aggregated. The reaction solution is obtained by dissolving a metal compound, a complexing agent, and a dispersing agent that are the source of metal ions in a hydrochloric acid solution of titanium trichloride.

  Examples of the metal ion include Pt, Au, Ag, Cu, Co, Ni, Fe, Re, Ta, and W. These are all metal species reduced by trivalent titanium ions. Trivalent titanium ions are highly reducible and reduce most metal ions.

  Titanium trichloride in the reaction solution is adjusted using a hydrochloric acid solution of titanium trichloride. As the hydrochloric acid solution of titanium trichloride, a 20% aqueous hydrochloric acid solution having a titanium trichloride concentration of 0.21 mol / L is used. In addition, although the hydrochloric acid solution of titanium trichloride can be adjusted by the said manufacturing method, the hydrochloric acid solution of titanium trichloride used here is not limited to what is adjusted by the said manufacturing method.

  As the complexing agent, one that forms a complex with any of metal ions and titanium ions and allows each metal ion to exist independently in an acidic solution is used. For example, since titanium ions react with water in a hydrochloric acid solution to form hydroxides, a complexing agent is used for the purpose of suppressing this formation.

  Further, as the complexing agent, one that reduces the oxidation-reduction reaction rate between metal ions and titanium ions, that is, the metal deposition rate, as compared with conventional complexing agents is employed. Specifically, what reduces the oxidation-reduction reaction rate of a metal ion and a titanium ion is employ | adopted rather than the complexing agent used when forming a metal particle with an average particle diameter larger than 50 nm. In addition, an average particle diameter shows the value (D50) of the integrated value 50% in the integrated distribution of a particle size. The integrated distribution is created based on a value obtained by volume conversion from a circle radius measured by image analysis of 500 particles observed with a scanning electron microscope (SEM).

  Examples of complexing agents include malic acid, gluconic acid, or their alkali metal salts or their alkaline earth metal salts. Examples of the alkali metal salt include sodium gluconate and sodium malate.

  The dispersant is one that suppresses the aggregation of metal particles deposited in the reaction solution, and suppresses the growth of metal particles so that the average particle size is 50 nm or less. Used. That is, a material that adsorbs to metal particles by a diameter exceeding 50 nm, suppresses the growth of metal particles, and suppresses bonding between metal particles is used.

  As such a dispersant, a carboxyl anionic surfactant is used. In particular, maleic acid surfactants are preferred. Among the maleic acid-based surfactants, styrene maleic acid copolymer salts or olefin maleic acid copolymer salts having a molecular weight of 10,000 to 50,000 are preferred.

<Formation of metal particles>
When forming metal particles, the pH is adjusted to 8.0 to 10.0 by dissolving a pH adjuster in the reaction solution maintained at the reaction temperature, and stirring is continued for several tens of minutes to several hours at 500 rpm. As a result, metal particles are deposited. As the adjuster, sodium carbonate, 25% ammonia aqueous solution, sodium hydroxide, potassium hydroxide, ammonium carbonate, or the like is used.

  Thereafter, the container containing the reaction solution is allowed to stand to precipitate the metal particles. And a solution and a metal particle are isolate | separated with a centrifuge, and it wash | cleans with a pure water. Impurities are removed by repeating the centrifugation and washing several times. Then, a metal dispersion liquid in which metal particles are dispersed is formed using water as a dispersion medium. Further, the metal dispersion is dried with an 80 ° C. vacuum dryer. Thereby, metal particles are obtained.

  Hereinafter, examples and comparative examples will be described with reference to FIGS. FIG. 1 shows the manufacturing conditions of the examples and comparative examples. FIG. 2 shows the ratio of the total concentration of the first metal salt, the second metal salt, and titanium trichloride to the concentration of the complexing agent.

<Example 1>
In this example, metal particles containing nickel and tungsten were formed.
Nickel chloride hexahydrate (first metal salt) and sodium tungstate dihydrate (second metal salt) were used as metal species of metal ions. The concentration of nickel chloride hexahydrate was 0.042 mol / L, and the concentration of sodium tungstate dihydrate was 0.050. Sodium gluconate was used as a complexing agent. As shown in FIG. 2, the concentration of the complexing agent was 1.44 times the molar concentration of titanium ions (titanium trichloride). Further, the concentration of the complexing agent was 1.0 times the total concentration (molar concentration) of nickel chloride hexahydrate, sodium tungstate dihydrate and titanium trichloride. Specifically, the concentration of the complexing agent was 0.3 mol. As the dispersant, an ammonium salt of a styrene maleic acid copolymer having a molecular weight of 30,000 was used. The concentration of the dispersing agent was 2 g / L. This is 0.36 times the amount of the deposited metal amount of 5.5 g / L. The amount of deposited metal is a value determined by the production of metal particles performed prior to the production of the metal particles of this example. The concentration of titanium trichloride was adjusted to be excessive with respect to the sum of the concentration of the first metal ion and the concentration of the second metal ion. Specifically, the concentration of titanium trichloride was 0.21 mol / L.

  Next, sodium carbonate was dissolved in the reaction solution until the pH reached 8.5. Further, the reaction temperature was maintained at 35 ° C., and stirring was continued for 120 minutes. Thereafter, the precipitate was repeatedly separated from the solvent and the metal particles by a centrifugal separator and washed to obtain metal particles. At this time, some tungsten ions remained in the solution without being precipitated. On the other hand, almost no nickel ions remained. As shown in FIG. 3, the composition of the metal particles was 70 atomic% for nickel and 30 atomic% for tungsten. The average particle size of the metal particles was 20 nm.

<Example 2>
In this example, metal particles containing nickel and tungsten were formed.
The production conditions of the metal particles are different from Example 1 only in the concentration of sodium tungstate dihydrate (second metal salt) and the concentration of the dispersant. Same as above. The concentration of sodium tungstate dihydrate was 0.030. The concentration of the dispersant was 5.5 g / L. This is a value that is 1.0 times the amount of precipitated metal of 5.5 g / L. The concentration of the complexing agent is the same as that of Example 1 with respect to the reaction solution, but the concentration of the complexing agent with respect to the total concentration of nickel chloride hexahydrate, sodium tungstate dihydrate, and titanium trichloride. The ratio increases to 1.07 as the amount of sodium tungstate dihydrate decreases (see FIG. 2).

  The metal particles were deposited in the same manner as in Example 1. The composition of the metal particles was 90 atomic% for nickel and 10 atomic% for tungsten (see FIG. 3). The average particle diameter of the metal particles was 30 nm.

<Comparative Example 1>
This comparative example differs from Example 2 in the following points. That is, in Example 2, sodium gluconate was used as the complexing agent, but in this comparative example, trisodium citrate dihydrate was used as the complexing agent. The concentration of trisodium citrate dihydrate was 0.031 mol / L. In this case, the composition of the metal particles was 90 atomic% for nickel and 10 atomic% for tungsten. The average particle size of the metal particles was 150 nm.

<Evaluation>
Examples 1 and 2 and Comparative Example 1 are compared, and the change in the average particle diameter due to the difference in the production conditions of the metal particles is evaluated.

  In Examples 1 and 2, sodium gluconate was used as a complexing agent. Further, the concentration of the dispersant was set to 0.3 times or more with respect to the amount of deposited metal, and the molecular weight of the dispersant was set to 10,000 to 50,000. Under these conditions, the average particle size could be 50 nm or less.

  On the other hand, in Comparative Example 1, metal particles were precipitated under conditions different from Example 2 only in the complexing agent, but the average particle size exceeded 50 nm. From the above, when sodium gluconate is used as a complexing agent, metal particles having an average particle diameter of 50 nm or less can be formed, but in the case of trisodium citrate dihydrate, metal particles having a particle diameter of 50 nm or less are formed. It turns out that it is difficult to form. That is, sodium gluconate suppresses the metal particles from becoming larger than 50 nm in average particle size.

<Example 3>
In this example, metal particles containing nickel and cobalt were formed.
Nickel chloride hexahydrate (first metal salt) and cobalt chloride hexahydrate (second metal salt) were used as metal species of metal ions. The concentration of nickel chloride hexahydrate in the reaction solution was 0.042 mol / L, and the concentration of cobalt chloride hexahydrate was 0.020 mol / L. Sodium malate was used as a complexing agent. As shown in FIG. 2, the concentration of the complexing agent was 1.44 times the molar concentration of titanium ions (titanium trichloride). Further, the concentration of the complexing agent was 1.11 times the total concentration of nickel chloride hexahydrate, cobalt chloride hexahydrate and titanium trichloride. Specifically, the concentration of the complexing agent was 0.3 mol. As the dispersant, a sodium salt of an olefin maleic acid copolymer having a molecular weight of 20,000 was used. The concentration of the dispersant was 5 g / L. This is a value 1.4 times as large as the amount of deposited metal of 3.5 g / L. The concentration of titanium trichloride was 0.21 mol / L.

  The metal particles were deposited in the same manner as in Example 1. The composition of the metal particles was 67 atomic% for nickel and 33 atomic% for cobalt (see FIG. 3). The average particle diameter of the metal particles was 40 nm.

<Example 4>
In this example, metal particles containing nickel and cobalt were formed.
The production conditions of the metal particles are different from Example 3 only in the concentration of cobalt hexahydrate (second metal salt) and the type of dispersant, and the other conditions are the same as in Example 3. did. The concentration of cobalt hexahydrate was 0.00042 mol / L. As the dispersant, a sodium salt of a styrene maleic acid copolymer having a molecular weight of 25,000 was used. The concentration of the dispersant was 5 g / L. The concentration of the complexing agent is the same as that in Example 3 with respect to the reaction solution, but the concentration of the complexing agent with respect to the total concentration of nickel chloride hexahydrate, cobalt chloride hexahydrate, and titanium trichloride is The ratio increases as the amount of cobalt ions decreases, and is 1.20 (see FIG. 2).

  The metal particles were deposited in the same manner as in Example 1. The composition of the metal particles was 99 atomic% for nickel and 1 atomic% for cobalt (see FIG. 3). The average particle diameter of the metal particles was 20 nm.

<Comparative Example 2>
This comparative example differs from Example 4 in the following points. That is, in Example 4, sodium malate was used as the complexing agent, but in this comparative example, potassium tartrate / sodium tartrate tetrahydrate was used as the complexing agent. The concentration of potassium tartrate / sodium tetrahydrate was 0.030 mol / L. In this case, the composition of the metal particles was 99 atomic% for nickel and 1 atomic% for cobalt. The average particle size of the metal particles was 250 nm.

<Evaluation>
Examples 3 and 4 and Comparative Example 2 are compared, and the change in the average particle diameter due to the difference in the production conditions of the metal particles is evaluated.

  In Examples 3 and 4, sodium malate was used as the complexing agent. Moreover, the density | concentration of the dispersing agent was 0.3 times or more with respect to the metal precipitation amount, and the molecular weight of the dispersing agent was 10,000-50,000. Under these conditions, the average particle size could be 50 nm or less.

  On the other hand, in Comparative Example 2, metal particles were deposited under conditions different from Example 4 only in the complexing agent, but the average particle size exceeded 50 nm. From the above, when sodium malate is used as the complexing agent, metal particles having an average particle size of 50 nm or less can be formed, but in the case of potassium tartrate / sodium tetrahydrate, metal particles having a particle size of 50 nm or less are used. It turns out that it is difficult to form. That is, sodium malate suppresses the metal particles from becoming larger than 50 nm in average particle size.

<Example 5>
In this example, metal particles containing nickel and silver were formed.
Nickel chloride hexahydrate (first metal salt) and silver nitrate (second metal salt) were used as metal species of metal ions. The concentration of nickel chloride hexahydrate was 0.042 mol / L, and the concentration of silver nitrate was 0.010. Malic acid was used as a complexing agent. As shown in FIG. 2, the concentration of the complexing agent was 1.44 times the molar concentration of titanium ions (titanium trichloride). Further, the concentration of the complexing agent was 1.15 times the total concentration of nickel chloride hexahydrate, silver nitrate and titanium trichloride. Specifically, the concentration of the complexing agent was 0.3 mol. As the dispersant, an ammonium salt of a styrene maleic acid copolymer having a molecular weight of 30,000 was used. The concentration of the dispersant was 10 g / L. This is a value of 2.9 times the amount of precipitated metal of 3.4 g / L. The concentration of titanium trichloride was 0.21 mol / L.

  The deposition method of the metal particles is substantially the same as in Example 1, but the pH adjuster is different from Example 1 in that 25% ammonia water is used and the pH is adjusted to 9.0. In this case, the composition of the metal particles was 80 atomic% for nickel and 20 atomic% for silver (see FIG. 3). The average particle diameter of the metal particles was 25 nm.

<Evaluation>
Examples 1 to 5 and Comparative Examples 1 and 2 are compared, and the change in the average particle diameter due to the difference in the production conditions of the metal particles is evaluated.

  Gluconic acid, malic acid, or a salt thereof (hereinafter referred to as “specific complexing agent”) can form metal particles having an average particle size smaller than that of trisodium citrate or potassium sodium tartrate. It is. The specific complexing agent is considered to reduce the reaction rate of the oxidation-reduction reaction between the metal ion and the trivalent titanium ion that is the reducing agent, as compared with other complexing agents.

  The specific complexing agent suppresses the metal particles from becoming larger than 50 nm in average particle diameter regardless of the metal species. This is based on the results of the examples. That is, in each of the above-described examples, the average particle diameter of the metal particles is reduced regardless of the metal species to be precipitated, so that it is considered that there is no influence of the metal species.

<Comparative Example 3>
This comparative example differs from Example 5 in the following points. In this comparative example, the concentration of the dispersant was set to 3/100 of the concentration of the dispersant of Example 5. Specifically, the concentration of the dispersant was set to 0.3 g / L. This is a value that is 0.1 times the amount of precipitated metal of 3.4 g / L. In this case, the composition of the metal particles was the same as in Example 5. The average particle diameter of the metal particles was 80 nm.

<Comparative Example 4>
This comparative example differs from Example 5 in the following points. That is, in Example 5, an ammonium salt of a styrene maleic acid polymer having a molecular weight of 30,000 was used as the dispersant. In this comparative example, the dispersant has a lower molecular weight than that used in Example 5. That is, a sodium salt of a styrene maleic acid polymer having a molecular weight of 8,000 was used. In this case, the composition of the metal particles was the same as in Example 5. The average particle diameter of the metal particles was 90 nm.

<Comparative Example 5>
This comparative example differs from Example 5 in the following points. That is, in Example 5, an ammonium salt of a styrene maleic acid polymer having a molecular weight of 30,000 was used as the dispersant, but in this comparative example, a dispersant having a higher molecular weight than that used in Example 5, That is, a sodium salt of a styrene maleic acid polymer having a molecular weight of 60,000 was used. In this case, the composition of the metal particles was the same as that of Example 5. The average particle diameter of the metal particles was 80 nm.

<Comparative Example 6>
This comparative example differs from Example 5 in the following points. That is, in Example 5, an ammonium salt of a styrene maleic acid polymer having a molecular weight of 30,000 was used as a dispersant, but in this comparative example, polyethyleneimine ethoxylate having a molecular weight of 30,000 was used. In this case, the composition of the metal particles was the same as in Example 5. The average particle diameter of the metal particles was 400 nm.

<Evaluation>
Examples 1-5 and Comparative Examples 3-6 are compared and the change of the average particle diameter by the difference in the manufacturing conditions of a metal particle is evaluated.

  In Examples 1-5, the density | concentration of the dispersing agent was 0.3 times or more with respect to the amount of deposit metal. In this case, the average particle diameter of the metal particles was 50 nm or less. On the other hand, in Comparative Example 3, the concentration of the dispersant was set to 0.1 times the amount of deposited metal. In this case, the average particle diameter of the metal particles was 80 nm. That is, the size of the metal particles to be deposited can be adjusted by the concentration of the dispersant. In order to make the average particle size of the metal particles 50 nm or less, it is preferable to use a maleic acid copolymer and make the concentration of the dispersant 0.3 times or more with respect to the amount of deposited metal.

  In Examples 1 to 5, a maleic acid surfactant having a molecular weight of 10,000 to 50,000 is used. In this case, the average particle diameter of the metal particles was 50 nm or less. On the other hand, in Comparative Example 4, a maleic acid surfactant having a molecular weight of 8,000 is used. In this case, the average particle diameter of the metal particles was 90 nm. In Comparative Example 5, a maleic acid surfactant having a molecular weight of 60,000 is used. In this case, the average particle diameter of the metal particles was 80 nm. That is, the size of the metal particles to be deposited can be adjusted by the molecular weight of the dispersant. In order to make the average particle size of the metal particles 50 nm or less, it is preferable to use a maleic acid copolymer having a molecular weight of 10,000 to 50,000.

  In Examples 1 to 5, a maleic acid surfactant is used as a dispersant. On the other hand, in Comparative Example 6, polyethyleneimine ethoxylate having a molecular weight of 30,000 was used as a dispersant. In this case, the average particle diameter of the metal particles was 400 nm. That is, in order to make the average particle diameter of the metal particles 50 nm or less, it is preferable to use a maleic acid-based surfactant.

  Referring to FIG. 3, the ratio of the first metal salt (nickel chloride salt) to the total concentration of the first metal salt (nickel chloride salt) and the second metal salt, and the ratio of nickel (first metal) in the metal particles The relationship will be described.

  In the same figure, about Examples 1-5, the density | concentration of 1st metal salt (nickel chloride hexahydrate), the density | concentration of 2nd metal salt, these total density | concentrations, and 1st metal with respect to this total density | concentration A salt concentration ratio (hereinafter, “solution nickel ratio”), a nickel ratio (atomic%) in the metal particles, and a second metal ratio (atomic%) in the metal particles are shown. Furthermore, the ratio of the nickel ratio in the metal particles to the solution nickel ratio (hereinafter, “precipitation ratio”) is shown.

  As shown in the figure, according to the method for producing metal particles, the deposition ratio takes a constant value depending on the type of the second metal. For example, when the second metal is a metal that is less likely to be reduced than nickel, such as tungsten, if the concentration of nickel ions and tungsten ions in the solution is the same, the amount of nickel deposited is greater than that of tungsten. That is, the content of nickel in the metal particles is higher than the ratio of nickel ions to the total amount of first metal ions and second metal ions. In this example, the deposition ratio is 1.5. The deposition ratio is constant regardless of the concentration of tungsten in the reaction solution.

  In addition, when the second metal is a metal whose reducibility is equivalent to nickel, such as cobalt, if the concentration of nickel ions and cobalt ions in the solution is the same, the amount of nickel deposited and the amount of cobalt deposited And the same level. That is, the ratio of nickel ions to the total amount of first metal ions and second metal ions is substantially the same as the content of nickel in the metal particles. In this example, the deposition ratio is 1.0. Further, when the second metal is silver, the result is the same as that of cobalt. That is, the precipitation ratio is 1.0.

  Thus, since the precipitation ratio of nickel becomes constant depending on the type of the second metal type, metal particles having a desired composition can be formed by obtaining this precipitation ratio in advance. Moreover, although the precipitation ratio is calculated | required by the combination of nickel and another metal in an Example, this can be expand | deployed also to metals other than nickel and can be calculated | required similarly.

According to this embodiment, the following effects can be obtained.
(1) In the present embodiment, an acidic reaction solution containing metal ions, titanium trichloride as a reducing agent, a complexing agent, and a dispersant is adjusted to be alkaline, and the reaction solution is stirred, Deposit metal particles. As the complexing agent, malic acid, gluconic acid or a salt thereof is used. According to this method, the metal particles can be prevented from having an average particle diameter of 50 nm or more.

  (2) In this embodiment, a maleic acid copolymer salt having a molecular weight of 10,000 to 50,000 is used as the dispersant. Thereby, it can suppress that a metal particle becomes larger than 50 nm by an average particle diameter.

  (3) In the present embodiment, the concentration of the dispersant is set to 0.3 times or more with respect to the amount of deposited metal per unit volume. Thus, since the minimum of the density | concentration of a dispersing agent is prescribed | regulated with respect to the metal precipitation amount, it can suppress that a metal particle becomes large.

  (4) In this embodiment, the molar concentration of the complexing agent is 0.5 to 5.0 times the molar concentration of titanium ions. Thereby, it is possible to suppress the formation of titanium hydroxide and the decrease in solubility such as pH adjustment.

  (5) In this embodiment, a reaction solution containing at least nickel ions is used as the metal ions. Since nickel ions are reduced to trivalent titanium ions, metal particles containing nickel can be formed.

  (6) In this embodiment, the concentration of the second metal salt is adjusted so that the nickel ratio (atomic%) in the metal particles is 50 atomic%. The concentration of the second metal salt can be adjusted by adjusting the molar concentration of each metal ion based on the deposition ratio of each metal.

  (7) In this embodiment, as the metal ions to be deposited, at least two types selected from the group consisting of ions of tungsten, tantalum, rhenium, iron, cobalt, nickel, copper, silver, gold, and platinum are selected. To do. Thereby, the metal particle containing 2 or more types of metals can be formed.

(Other embodiments)
In addition, the embodiment of the present invention is not limited to the embodiment shown in the above-described embodiment, and the embodiment can be modified as shown below, for example. Further, the following modifications are not applied only to the above-described embodiments, and different modifications can be combined with each other.

  -In the above-mentioned embodiment, although the manufacturing method of the metal particle containing two types of metals is shown, the metal particle which makes an average particle diameter 50 nm or less is formed with the above-mentioned manufacturing method also about the metal particle which consists of a single metal. be able to. For example, metal particles having a nickel content of approximately 100% can be formed under the same conditions as in Example 4.

  -In the said embodiment, tungsten, tantalum, rhenium, iron, cobalt, copper, silver, gold | metal | money, platinum is mentioned as a 2nd metal, but if it is reduce | restored by trivalent titanium, a 2nd metal Can be used as

  In the above embodiment, a manufacturing method that enables formation of metal particles having an average particle diameter of 50 nm or less is shown, but the above method may be applied to the case of forming metal particles of 50 nm or more. it can. That is, as shown in the comparative example, by changing the concentration of the dispersant and the molecular weight of the dispersant, the average particle size of the metal particles can be adjusted to form metal particles having a desired size.

  -In the said embodiment, although one type of complexing agent is used when manufacturing a metal particle, it can also be used in combination of 2 or more types among the specific complexing agents mentioned above. In addition, this invention does not restrict | limit mixing other complexing agents besides a specific complexing agent. In view of the size of the target metal particles, other complexing agents may be appropriately combined.

  -In the said embodiment, when depositing a metal particle, the temperature of the reaction solution is 35 degreeC. However, the temperature of the process of depositing metal particles is not limited to this value. Since the temperature range in which the metal precipitates is 5 ° C. to 60 ° C., the temperature of the reaction solution can be set within this range.

  In the above embodiment, the manufacturing method for nickel particles has been described. However, metal particles having an average particle diameter of 50 nm or less can be formed by using the above manufacturing method for metal particles mainly composed of other metals. it can.

  -In the said embodiment, the material of the electrode of a multilayer ceramic capacitor is mentioned as a use of a metal particle. However, the use of the metal particles by the manufacturing method is not limited to this. For example, the metal particles of the present embodiment can be used as a material for the conductive layer of a printed wiring board substrate having a conductive layer formed on the surface. It can also be used for ink. Furthermore, it can also be used as a filler for via holes in printed wiring boards.

Claims (7)

Metal ions, titanium trichloride as a reducing agent for reducing the metal ions, a complexing agent for stabilizing the metal ions and titanium ions of the titanium trichloride in a solution, and metal particles precipitated by a reduction reaction. An acidic aqueous solution containing a dispersant dispersed in the solution is used as a reaction solution, the reaction solution and the pH adjuster are mixed to adjust the reaction solution to be alkaline, and the reaction solution is stirred to deposit metal particles. A method for producing metal particles, comprising:
As the complexing agent, at least one of malic acid, malate, gluconic acid and gluconate is used. In the manufacturing method of the metal particle of Claim 1,
The dispersant is a salt of a maleic acid copolymer having a molecular weight of 10,000 to 50,000. In the manufacturing method of the metal particle of Claim 1 or 2,
The method for producing metal particles, wherein the mass per unit volume of the dispersing agent is 0.3 times or more the metal deposition amount per unit volume. In the manufacturing method of the metal particle as described in any one of Claims 1-3,
The method for producing metal particles, wherein the molar concentration of the complexing agent is 0.5 to 5.0 times the molar concentration of the titanium ions. In the manufacturing method of the metal particle as described in any one of Claims 1-4,
The reaction solution contains at least nickel ions as the metal ions. In the manufacturing method of the metal particle as described in any one of Claims 1-4,
The reaction solution contains a plurality of types of metal ions,
A method for producing metal particles, wherein the molar concentration of each metal ion is adjusted based on the deposition ratio of each metal. In the manufacturing method of the metal particle of Claim 6,
The metal ions are at least two kinds selected from the group consisting of tungsten, tantalum, rhenium, iron, cobalt, nickel, copper, silver, gold, and platinum ions. Method.

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