JPH08134513A - Production of fine silver powder - Google Patents

Abstract

PURPOSE: To produce a monodisperse silver grain and to easily control the grain diameter by reducing a silver salt, etc., with a soln. using hydroquinone as a reducing agent and a sulfite as a reduction assistant and specifying the temp. of the soln. CONSTITUTION: A fine silver powder as the material for a silver paste for the circuit in the electronic industry is produced by reducing a silver salt or a silver-ammonium complex. In this case, hydroquinone is used as a reducing agent and a sulfite as the reduction assistant, and the soln. is controlled to 25-60 deg.C in the reduction reaction. A fine silver powder having 1-5μm grain diameter is obtained since the hydroquinone is used, the generation of quinone hardly soluble in water caused when hydroquinone alone is used is suppressed by the addition of the sulfite, and the fine silver powder is easily separated from the reaction soln. Further, the grain diameter of the fine silver powder to be obtained is controlled by controlling the temp. of the soln. when reduction is conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silver paste for circuits in the electronics industry, and a method for producing fine silver powder which is a raw material of the silver paste.

[0002]

2. Description of the Related Art A conventional method for producing fine silver powder, which is a raw material for producing a silver paste used in the electronics industry, is to add sodium hydroxide to an aqueous solution of silver nitrate to form silver oxide at room temperature, or to add an aqueous solution of silver nitrate to carbonate. A method is known in which sodium carbonate is added to form silver carbonate, and the silver oxide or the silver carbonate is reduced with formalin or hydrazine.
However, since the silver fine powder obtained by these methods is an agglomerate, there is a problem that sodium ions are unavoidable even after careful washing with water. To solve this problem, for example, Japanese Patent Application Laid-Open No. 4-59904 and Japanese Patent Application Laid-Open No. 4-59904.
Japanese Patent No. 333504 discloses a method for producing monodisperse silver fine powder. By the way, fine silver powder used as an electronic material is strongly required to have particle size adjustment and stability in order to control the sintering behavior. Therefore, a technique for controlling the particle size is required.

[0003]

According to the conventional method, if the manufacturing method is determined, the particle size of the obtained silver fine powder is almost determined, and it is difficult to easily change the particle size of the silver fine powder. It is an object of the present invention to solve the above problems, to provide a monodisperse silver particle, and to provide a method for producing a fine silver powder, the particle size of which can be easily adjusted.

[0004]

To achieve the above object, in the present invention, a silver salt or a silver ammonia complex is reduced in a solution using hydroquinone as a reducing agent and sulfite as a reducing auxiliary. In producing silver fine powder, the temperature of the solution during the reduction reaction should be 25 to 6
The particle size of the obtained fine silver powder can be adjusted by the step of adjusting in the range of 0 ° C. Furthermore, in the present invention, the particle size of the silver fine powder can be adjusted by adding colloidal silica.

[0005]

In the present invention, hydroquinone is used as a reducing agent for reducing a silver salt or a silver ammonia complex. By using hydroquinone, fine silver powder having a particle size of 1 to 5 μm can be obtained. At this time, sulfite is added to hydroquinone to assist the reducing action. In other words, the addition of sulfite turns the reducing agent into a water-soluble sulfonic acid compound, which can suppress the formation of sparingly water-soluble quinone that occurs when reducing with only hydroquinone, and easily separates silver fine powder from the reaction solution. it can. In addition, by controlling the temperature of the solution when performing the reducing action, it is possible to control the particle size of the obtained silver fine powder. That is, as the temperature of the solution is increased, the particle size of the fine silver powder becomes smaller. The reason is that the reducing ability of hydroquinone used as a reducing agent is strongly dependent on temperature, and increasing the temperature increases the reducing ability of hydroquinone and increases the number of nuclei produced at the initial stage of the reduction reaction. To be

Furthermore, by adding colloidal silica at the same time as the sulfite, it is possible to obtain a silver fine powder having a particle size smaller than that of the silver fine powder obtained when the reduction is carried out without adding the colloidal silica. It is considered that this is because the silica component of colloidal silica serves as a nucleus during the formation of the silver fine powder, so that the number of generated nuclei in the initial stage of the reaction increases and the particle size of the silver fine powder after the growth decreases. In this way, when the silica component is introduced into the reaction system, a synergistic effect between the temperature of the solution when performing the reducing action and the silica component is obtained.

[0007]

【Example】

Example 1 Dissolving 340 g of silver nitrate in 500 ml of water,
Ammonia water (29%) was added to the silver nitrate aqueous solution 4
00 ml was added, and the silver salt was used as a silver ammonia complex. Next, 500 g of ammonium sulfite-hydrate in 7.0 l of water.
And 70 g of hydroquinone were dissolved to prepare a reducing solution. After adjusting each of the above two solutions to 25 ° C, add the silver ammonia complex solution to the reducing solution while stirring, and
The temperature was maintained at to obtain 212 g of silver fine powder. The obtained silver fine powder was monodisperse and spherical, and the average particle diameter (SEM diameter) was 4.9 μm.

Example 2 By the same method as in Example 1, a silver ammonia complex solution and a reducing solution were prepared. Fine silver powder was obtained in the same manner as in Example 1 except that the temperature of the solution was 33 ° C. The fine silver powder obtained was monodisperse and spherical as in Example 1, and had an average particle diameter (SEM diameter) of 3.9 μm.

Example 3 A silver ammonia complex solution and a reducing solution were prepared in the same manner as in Example 1. Fine silver powder was obtained in the same manner as in Example 1 except that the temperature of the solution was 45 ° C. The fine silver powder obtained was monodisperse and spherical as in Example 1, and had an average particle diameter (SEM diameter) of 2.9 μm.

Example 4 In the same manner as in Example 1, a silver ammonia complex solution and a reducing solution were prepared. Fine silver powder was obtained in the same manner as in Example 1 except that the temperature of the solution was 54 ° C. The fine silver powder obtained was monodisperse and spherical as in Example 1, and had an average particle diameter (SEM diameter) of 2.4 μm.

Example 5 A silver ammonia complex solution and a reducing solution were prepared in the same manner as in Example 1. Fine silver powder was obtained in the same manner as in Example 1 except that the temperature of the solution was 60 ° C. The fine silver powder obtained was monodisperse and spherical as in Example 1, and had an average particle diameter (SEM diameter) of 2.0 μm.

Example 6 A silver ammonia complex solution and a reducing solution were prepared in the same manner as in Example 1. In this example, in order to introduce a silica component into the reaction system, 0.3 g of colloidal silica (Nissan Chemical Co., Ltd., Snowtex) was added to the reducing solution, and two solutions were prepared in the same manner as in Example 1. Were mixed to obtain fine silver powder. The fine silver powder obtained was monodisperse and spherical as in Example 1, and had an average particle size (SEM).
The diameter) was 4.0 μm.

Example 7 In order to introduce a silica component into the reaction system, 0.3 g of colloidal silica (Nissan Chemical Co., Ltd., Snowtex) was added to the reducing solution, and the same procedure as in Example 2 was performed. The two solutions were mixed to obtain fine silver powder. The obtained silver fine powder was monodisperse and spherical as in Example 2, and the average particle diameter (SEM diameter) was 3.9 μm or less.

Example 8 A silver ammonia complex solution and a reducing solution were prepared in the same manner as in Example 1. In order to introduce a silica component into the reaction system, colloidal silka (Nissan Chemical Co., Ltd., Snowtex) was added to the reducing solution.
0 g was added and the two solutions were mixed in the same manner as in Example 1,
A fine silver powder was obtained. The fine silver powder obtained was monodisperse and spherical as in Example 1, and had an average particle diameter (SEM diameter) of 3.0 μm.

[Example 9] A silver ammonia complex solution and a reducing solution were prepared in the same manner as in Example 1. Colloidal silka (Nissan Chemical Co., Ltd., Snowtex) was added to the reducing solution in order to introduce silica into the reaction system.
0 g was added and the two solutions were mixed in the same manner as in Example 1,
A fine silver powder was obtained. The fine silver powder obtained was monodisperse and spherical as in Example 1, and had an average particle diameter (SEM diameter) of 2.5 μm.

[Embodiment 10] In the same manner as in Embodiment 1,
A silver ammonia complex solution and a reducing solution were prepared. next,
0.3 g of colloidal silka (Nissan Chemical Co., Ltd., Snowtex) was added to the reducing solution, the temperature of each liquid was set to 20 ° C, and the temperature was maintained at 20 ° C in the same manner as in Example 1, A fine silver powder was obtained. The fine silver powder obtained was obtained in Example 1.
Similarly to the above, it was monodisperse and spherical, and the average particle diameter (SEM diameter) was 4.2 μm.

[Comparative Example] A silver ammonia complex solution and a reducing solution were prepared in the same manner as in Example 1, and the respective liquid temperatures were set to 20 ° C. In the same manner as in Example 1, the temperature was raised to 20 ° C. Maintained to obtain fine silver powder. The fine silver powder obtained was obtained in Example 1.
It has a monodisperse shape and a spherical shape similar to, but has an average particle size (SE
The M diameter) was 5.0 μm.

The results of Examples 1 to 5 and Comparative Example are shown in FIG. 1 in terms of the relationship between particle size and temperature.

[0019]

Since the present invention is configured as described above, it has the following effects. (1) It is possible to provide a method for producing a fine silver powder which is spherical, monodisperse, and whose particle size can be easily changed. (2) It becomes easy to control the sintering behavior by adjusting the particle size of the fine silver powder used as an electronic material.

[Brief description of drawings]

FIG. 1 is a graph showing a result of an example according to the present invention as a relationship between a particle size and a temperature.

Claims (2)

[Claims] 1. A solution containing hydroquinone as a reducing agent and sulfite as a reducing auxiliary, wherein the silver salt or the silver ammonia complex is reduced to produce fine silver powder, and the temperature of the solution during the reduction reaction is used. Is adjusted in the range of 25 to 60 ° C. to adjust the particle size of the silver fine powder. 2. The production method according to claim 1, wherein colloidal silica is added as an additive.