JP2008255378A - Method for producing silver particulate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably and efficiently producing fine silver particulates having high dispersibility and suitable as paste components to form into a wiring material and an electrode material of an electronic device. <P>SOLUTION: Regarding the method for producing silver particulates, in a method where ammonia and a reducing agent are added to a silver ion solution so as to reductively precipitate silver particulates, the reducing agent is added within 20 sec after the addition of the ammonia, thus the fine silver particulates are precipitated. By regulating the time from the addition of the ammonia to the addition of the reducing agent, the particle diameter of the silver particulates to be precipitated is controlled. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for producing fine silver particles stably and efficiently in a technique for producing silver particles by reduction of silver ions. More specifically, the present invention relates to a technique for stably and efficiently producing fine, highly dispersible silver particles suitable as a paste component that becomes a wiring material or an electrode material of an electronic device.

  In recent years, there has been a demand for miniaturization and high density of electronic devices in order to improve the functionality of electronic equipment. In order to achieve finer wiring and electrodes, silver used as a paste material for forming them As for the fine particles, finer and highly dispersible fine particles are required.

Conventionally, as a method for producing silver fine particles used in electronic device materials, there is a method of obtaining silver fine particles having an average particle diameter of about several μm by reducing silver salt ammine complexes to precipitate silver fine particles, and washing and drying them. Are known. For example, JP-A-8-134513 discloses a method for producing fine silver particles by reducing the silver ammine complex to precipitate silver fine particles and adjusting the liquid temperature during reduction to 25 to 60 ° C. (Patent Document 1). Japanese Patent Laid-Open No. 2001-107101 discloses that after adding ammonia water to a silver nitrate solution to form a silver ammine complex solution, the reducing agent is mixed within 20 seconds when the reducing agent is added. A method for precipitating fine silver particles having a surface area of 0.25 m ² / g or more is described (Patent Document 2). However, in these production methods, it is difficult to produce fine silver particles having a uniform particle size and 0.2 to 2.5 μm because the particle size distribution of the precipitated silver particles is wide and the particles are likely to aggregate. There was a problem.

Therefore, a method is known in which silver fine particles having a small crystallite diameter are produced by reducing the silver in the pipe by joining the organic reducing agent solution in the middle of the flow path through which the silver ammine complex aqueous solution flows (patent) References 3, 4). However, in this production method, the silver ammine complex is reduced in the pipe, so that the flow path becomes narrow due to silver deposition, and the silver particles deposited on the pipe wall peel off and coarse particles are mixed. There is. In addition, in order to obtain fine silver particles, a silver ammine complex aqueous solution having a very low silver concentration is used, so that the production efficiency is low.
JP-A-8-134513 JP 2001-107101 A JP-A-2005-48236 JP 2005-48237 A

  The present invention provides a method for producing silver fine particles that solves the above-mentioned problems in conventional production methods, and provides a method and apparatus for producing fine silver particles stably and efficiently.

According to this invention, the manufacturing method and apparatus of the silver fine particle which solved the said subject with the following structures are provided.
(1) In the method of reducing and precipitating silver fine particles by adding ammonia and a reducing agent to a silver ion solution, the method is characterized in that fine silver fine particles are precipitated by adding the reducing agent within 20 seconds after the addition of ammonia. A method for producing fine silver particles.
(2) The method for producing silver fine particles according to the above (1), wherein the particle size of the precipitated silver fine particles is controlled by adjusting the time from the addition of ammonia to the addition of the reducing agent.
(3) In the method of (1) or (2) above, the time (elapsed time) from the addition of ammonia to the addition of the reducing agent is (i) the elapsed time is set to 0.3 seconds to 0.5 seconds. (Ii) silver having an average particle diameter of 0.5 μm to 1.5 μm within a period of 0.5 second to 2 seconds, and depositing silver fine particles having an average particle diameter of 0.2 μm to 0.5 μm. A method of precipitating fine particles, (iii) a method of precipitating silver fine particles having an average particle size of 1.5 μm to 2.0 μm within 2 to 5 seconds, or (iv) a time of 5 seconds to A method of depositing silver fine particles having an average particle diameter of 2.0 μm to 2.5 μm within 20 seconds.
(4) A production apparatus for reducing and precipitating silver fine particles by adding ammonia and a reducing agent to a silver ion solution, comprising a silver ion solution tank, an ammonia aqueous solution tank, and a reducing solution tank, and a tube of the silver ion solution tank The crossing position A between the channel and the ammonia aqueous solution tank is provided closer to the silver ion solution tank than the crossing position B between the pipe of the silver ion solution tank and the pipe of the reducing solution tank. Silver fine particle production equipment.
(5) The manufacturing apparatus according to the above (4), wherein both pipes are installed slightly opposite to each other at the crossover position B, and the distance from the crossover position A to the crossover position B can be adjusted.

In the production method of the present invention, by adding a reducing agent within 20 seconds after the addition of ammonia, silver hydroxide (AgOH) or silver oxide (Ag ₂ O) temporarily formed before the silver ammine complex is formed. Serves as a nucleus, and silver crystalline primary particles having a crystallite size of 25 nm to 150 nm are formed, and the primary particles aggregate to form silver fine particles. When the number of nuclei is large and the number of aggregation centers increases, the size of the silver fine particles becomes small. Therefore, the reducing agent should be added within 20 seconds after the addition of ammonia in which many silver hydroxides and silver oxides are present. Thus, fine silver fine particles can be obtained stably and efficiently. Specifically, for example, fine silver particles having an average particle size of 2.5 μm or less can be obtained in a yield of 99% or more. On the other hand, if the time from the addition of ammonia to the addition of the reducing agent is long, almost all of the silver hydroxide or silver oxide produced in the initial stage of mixing has changed into a silver ammine complex, so it can function as a nucleus. Since the nucleation number cannot be controlled, the synthesized silver particle size is not stable.

  Moreover, according to the production method of the present invention, silver fine particles having an average particle diameter of 0.2 μm to 2.5 μm can be produced by adjusting the elapsed time from the addition of ammonia to the addition of the reducing agent.

  In the production apparatus of the present invention, the crossing position A between the pipe of the silver ion solution tank and the pipe of the aqueous ammonia solution tank is more than the crossing position B of the pipe of the silver ion solution tank and the pipe of the reducing solution tank. It is provided on the silver ion solution tank side, and the above production method can be easily carried out. In addition, the manufacturing apparatus of the present invention can change the distance from the crossing position A to the crossing position B by forming the connecting portion of the crossing position A so that it can move, and after the ammonia is added until the reducing agent is added. The elapsed time can be easily adjusted.

Hereinafter, the present invention will be specifically described with examples.
The method of the present invention is a method for reducing and precipitating silver fine particles by adding ammonia and a reducing agent to a silver ion solution. By adding a reducing agent within 20 seconds after adding ammonia, fine silver fine particles are precipitated. Is a method for producing silver fine particles.

As the silver ion solution, a silver nitrate solution or the like can be used. When ammonia is added to the silver nitrate solution, a silver ammine complex is formed, and silver is precipitated by reducing this. As the reducing agent, a hydroquinone solution (OH (C ₆ H ₄ ) OH, hereinafter sometimes abbreviated as H ₂ Q) may be used. The amount of ammonia to be added is preferably such that silver ions that do not form an ammine complex do not remain in the solution, and the amount is such that ammonia is 2 to 3 moles per mole of silver. The amount of the reducing agent added is preferably such that no unreacted silver ammine complex remains in the solution. When hydroquinone is used as the reducing agent, the amount of hydroquinone is 0.3 to 1.0 mole per mole of silver. This is the amount.

In the production method of the present invention, the reducing agent is added within 20 seconds after adding ammonia to the silver ion solution. By adding a reducing agent within a short period of time after the addition of ammonia, silver is temporarily formed from silver hydroxide (AgOH) or silver oxide (Ag ₂ O) that forms temporarily before the silver ammine complex is formed. Crystalline primary particles are formed, and the primary particles are aggregated to form silver fine particles. Within 20 seconds after the addition of ammonia, a large amount of silver hydroxide or silver oxide that does not form an ammine complex remains and becomes a nucleus, which is earlier than when silver cluster nuclei are produced by reduction of silver ions. Since the number of nuclei can be increased and the number of aggregation centers of primary particles can be increased, for example, fine silver particles having an average particle diameter of 2.5 μm or less are obtained. On the other hand, when 20 seconds or more have passed after the addition of ammonia, the silver oxide and silver oxide that are initially formed become a silver ammine complex, and crystalline primary particles having the initial nuclei of silver hydroxide and silver oxide cannot be formed. It is difficult to obtain fine silver fine particles because the number of initial nuclei of silver cluster nuclei generated by the reduction of silver ions is small and the number of aggregation centers of primary particles is also small.

  Since the production method of the present invention is a method of adding a reducing agent within 20 seconds after adding ammonia to a silver ion solution, a silver ammine complex formed by adding ammonia to a silver ion solution in advance, What added the reducing agent previously to the ionic solution is not used.

  The production method of the present invention can control the particle size of silver fine particles deposited by adjusting the elapsed time from the addition of ammonia to the addition of the reducing agent within a range of 20 seconds after the addition of ammonia. Specifically, the particle size of the silver fine particles can be controlled as follows.

(i) Silver fine particles having an average particle diameter of 0.2 μm to 0.5 μm can be precipitated by adjusting the elapsed time to be within 0.3 seconds to 0.5 seconds.
(ii) Silver fine particles having an average particle diameter of 0.5 μm to 1.5 μm can be precipitated by adjusting the elapsed time to be within 0.5 second to 2 seconds.
(iii) Silver fine particles having an average particle diameter of 1.5 μm to 2.0 μm can be precipitated by adjusting the elapsed time within 2 seconds to 5 seconds.
(iv) Silver fine particles having an average particle size of 2.0 μm to 2.5 μm can be precipitated by setting the elapsed time to 5 seconds to 20 seconds or more.

  The production apparatus of the present invention is a production apparatus for reducing and precipitating silver fine particles by adding ammonia and a reducing agent to a silver ion solution. An example of the configuration is shown in FIG. As illustrated, the apparatus of the present invention includes a silver ion solution tank 10, an aqueous ammonia solution tank 11, and a reducing solution tank 12. The crossing position A between the pipe line 13 of the silver ion solution tank 10 and the pipe line 14 of the aqueous ammonia solution tank 11 is more silver than the crossing position B between the pipe line 13 of the silver ion solution tank 11 and the pipe line 15 of the reducing solution tank 12. It is provided on the ion solution tank side.

  In the above apparatus configuration, ammonia water is first added to the silver ion solution at the crossover position A of the pipe 13 and then mixed with the reducing solution at the crossover position B of the pipe 13. The time from the addition of ammonia to the addition of the reducing liquid is determined by the distance L from the crossover position A to the crossover position B, and the distance L is set so that the reducing liquid is added within 20 seconds after the addition of ammonia.

  It should be noted that the connecting point between the pipe line 13 and the pipe line 14 is formed to be movable, or the pipe line from the crossing position A to the crossing position B is formed to be extendable, so that the crossing position A reaches the crossing position B. The distance L can be adjusted, and the elapsed time from the addition of ammonia to the addition of the reducing solution can be adjusted.

  In the above apparatus configuration, it is preferable that the pipe line 13 and the pipe line 15 at the crossing position B are installed so that the pipe end openings are slightly separated from each other. By installing the pipe end openings slightly opposite each other, the ammonia-added silver ion solution flowing through the pipe line 13 and the reducing liquid flowing through the pipe line 15 are mixed outside the pipe line, Since the silver fine particle deposition field is formed in an open space outside the pipe, silver fine particles do not adhere to the inner wall of the pipe, and there is no problem of mixing coarse exfoliated particles. Fine particles can be obtained.

Hereinafter, the present invention will be specifically described by way of examples.
[Examples and Comparative Examples]
Using silver nitrate solution (AgNO ₃ solution) and ammonia water (NH ₃ water) shown in Table 1, using hydroquinone solution (OH (C ₆ H ₄ ) OH solution) as the reducing agent, mixing the ammonia water with the silver nitrate solution While maintaining 8.0 to 8.2, a reducing agent was added within 20 seconds after the addition to reduce and precipitate silver fine particles. The elapsed time until the reducing solution was added was adjusted as shown in Table 2, and the average particle size of the precipitated silver fine particles was measured by a laser scattering method.

  The results of the samples A1 to A7 of the present invention are shown in Table 2. The results of Comparative Samples B1 to B5 are shown in Table 3. FIG. 2 shows the relationship between the elapsed time from the addition of aqueous ammonia to the silver nitrate solution and the addition of the reducing agent and the particle size of the silver particles. The electron micrograph which shows the particle state of the silver particle of sample A1-A5 was shown in FIGS.

  As shown in Table 2 and FIG. 2, (i) When the elapsed time is within 0.3 seconds to 0.5 seconds, silver fine particles having an average particle diameter of 0.2 μm to 0.5 μm are deposited. (ii) When the elapsed time is within 0.5 second to 2 seconds, silver fine particles having an average particle diameter of 0.5 μm to 1.5 μm are deposited. (iii) When the elapsed time is within 2 seconds to 5 seconds, silver fine particles having an average particle diameter of 1.5 μm to 2.0 μm are deposited. (iv) When the elapsed time is within 5 seconds to 20 seconds, silver fine particles having an average particle diameter of 2.0 μm to 2.5 μm are deposited.

Conceptual diagram of apparatus configuration of the present invention Graph of elapsed time after addition of ammonia and average particle diameter of silver fine particles in Examples Electron micrograph showing the particle state of the silver particles of sample A1 Electron micrograph showing the particle state of the silver particles of sample A2. Electron micrograph showing the particle state of the silver particles of sample A3 Electron micrograph showing the particle state of the silver particles of sample A4 Electron micrograph showing the particle state of the silver particles of Sample A7

Explanation of symbols

10-silver ion solution tank, 11-ammonia aqueous solution tank, 12-reduction liquid tank, 13-silver ion solution tank line, 14-ammonia aqueous solution tank line, 15-reduction liquid tank line, A-tube Crossing position of the line 13 and the pipe line 14, B-crossing position of the pipe line 13 and the pipe line 15.

Claims (5)

In a method for reducing and precipitating silver fine particles by adding ammonia and a reducing agent to a silver ion solution, silver fine particles are precipitated by adding a reducing agent within 20 seconds after the addition of ammonia. Manufacturing method.
The method for producing silver fine particles according to claim 1, wherein the particle size of the silver fine particles to be precipitated is controlled by adjusting the time from the addition of ammonia to the addition of the reducing agent.
3. The method according to claim 1 or 2, wherein the time (elapsed time) from the addition of ammonia to the addition of the reducing agent is set as follows: (i) The average particle size is set within the range of 0.3 to 0.5 seconds. (Ii) a method of precipitating silver fine particles having an average particle diameter of 0.5 μm to 1.5 μm by depositing silver fine particles of 0.2 to 0.5 μm, and (iii) ) A method of precipitating silver fine particles with an average particle size of 1.5 μm to 2.0 μm with the elapsed time within 2 to 5 seconds, or (iv) An average particle size of 2 with the elapsed time within 5 to 20 seconds. A method of depositing silver fine particles of 0.0 μm to 2.5 μm.
A manufacturing apparatus for reducing and precipitating silver fine particles by adding ammonia and a reducing agent to a silver ion solution, having a silver ion solution tank, an aqueous ammonia solution tank, and a reducing solution tank, and a silver ion solution tank line and ammonia The silver fine particle characterized in that the crossing position A with the pipe of the aqueous solution tank is provided closer to the silver ion solution tank than the crossing position B of the pipe of the silver ion solution tank and the pipe of the reducing liquid tank. Manufacturing equipment.
5. The manufacturing apparatus according to claim 4, wherein both pipe lines are installed slightly opposite to each other at the crossover position B, and the distance from the crossover position A to the crossover position B can be adjusted.