JPH0892612A - Production of silver powder - Google Patents

Abstract

PURPOSE: To produce a monodisperse silver powder narrowed in particle size distribution and having a specified average particle diameter by adding a silver nitrate soln. to the mixed soln. of ammonium sulfite, aq. ammonia and hydroquinone to bring about a reaction at a specified temp. CONSTITUTION: The mixed soln. of ammonium sulfite, aq. ammonia and hydroquinone is used as a reducing agent soln., a silver nitrate soln. is used as a soln. contg. silver ion, and the soln. contg. silver ion is added to the reducing agent soln. so that the reaction temp. is controlled to <=50 deg.C. In thus case, 0.2-1mol of hydroquinone per mol of silver, 1-12mols of ammonium sulfite and 0.1-1 mol of aq. ammonia, expressed in terms of ammonia, are preferably used. Consequently, a monodisperse silver powder having 0.3-2μm average particle diameter and narrowed in particle size distribution is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a chip capacitor,
The present invention relates to a method for producing a silver powder for a conductor silver paste used for forming electrodes of electronic parts such as a chip inductor, a chip resistor, a ceramic capacitor, a ceramic thermistor, a ceramic varistor, a piezoelectric element, a dielectric filter and a HIC.

[0002]

Thick film electronic components, such as chip resistors, are
A silver paste prepared by kneading glass, a resin called a vehicle, and silver powder with a three-roll mill is printed with an electrode pattern on an alumina substrate by a screen printing method, and then heat-treated at 850 ° C. for about 10 minutes to form a silver electrode. Create
Then, a resistance ink prepared by kneading ruthenium oxide, glass, and a vehicle with a three-roll mill was printed between the silver electrodes by a screen printing method, and the resistance ink was printed at 850 ° C. for about 10 minutes.
It is created by performing heat treatment again for a minute.

In recent years, there has been a strong demand for cost reduction of electronic parts, and in the above manufacturing method as well, after printing a silver paste, a resistance ink is printed without heat treatment and then heat treatment is performed to form a chip resistor. The method has been changed. The silver paste used in this method is required to have properties such that shrinkage during sintering is smaller than that of conventional silver paste, an equivalent dense fired film can be obtained, and it does not react with the resistance ink during firing. There is. In order to satisfy such characteristics, silver powder having a particle size of submicron or less and 1 μm
A silver paste having a particle diameter of m or more is mixed to form a silver paste.

By the way, conventionally, silver powder is an aqueous solution of silver nitrate,
The solution was obtained by reducing an aqueous solution of silver ammonium complex, silver oxide or the like with a reducing agent such as hydrazine, formaldehyde or sodium borohydride. Then, the particle size of the obtained silver powder was adjusted by controlling the pH value during the reaction, the addition rate of the additive, the reaction temperature, and the like. However, according to the conventional method, the particle size of the silver powder obtained by changing such conditions is at most 0. It is possible to change only about several μm, and it is necessary to change the reducing agent itself in order to obtain a silver powder having a particle diameter farther away.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and in obtaining a silver powder having a monodispersed and narrow particle size distribution, the average particle size of the silver powder is adjusted in a wider range. The challenge is to provide a method of doing so.

[0006]

The method of the present invention for solving the above-mentioned problems is a method for obtaining a silver powder by reacting a reducing agent solution with a solution containing silver ions, wherein ammonium sulfite and aqueous ammonia are used as the reducing agent solution. A mixed solution with hydroquinone is used, a silver nitrate solution is used as a solution containing silver ions, and the solution containing silver ions is added to the reducing agent solution at a reaction temperature of 50 ° C. or lower. And
By adjusting the ratio of ammonium sulfite, ammonia water, and hydroquinone, the average particle size is 0.3 to 2 μm.
Within a range of 1, and is a monodisperse silver powder having a narrow particle size distribution.

When silver powder is produced by the method of the present invention, 1 mol of silver nitrate is added to reduce the amount of ammonium sulfite to 1 to 1.
12 mol, the amount of ammonia water is 0.1 to 0.1 in terms of ammonia.
It is more preferable to select 1 mol and the amount of hydroquinone in the range of 0.2 to 1 mol.

[0008]

The silver ion reacts with hydroquinone according to the formula 1 to produce silver and quinone.

Formula 1 2Ag ⁺ + C ₆ H ₄ (OH) ₂ --- → 2Ag ⁰ + C ₆
H ₄ (═O) _2, that is, 2 mol of silver ion reacts with 1 mol of hydroquinone to generate 2 mol of silver and 1 mol of quinone. The quinone produced by this reaction has a low solubility in water. Therefore, the reaction product is a mixture of silver powder and quinone. Then, in order to remove quinone from this mixture and obtain silver powder as a product, a large amount of washing water and a lot of labor are required.

In the method of the present invention, ammonium sulfite and ammonium ions are allowed to coexist in hydroquinone.
This is for the following reason.

First, the coexistence of sulfite causes the quinone to react with the sulfite ion so that the quinone becomes a water-soluble compound and is easily separated from the silver powder. Further, in this case, the coexisting sulfite ion itself contributes to the reduction of silver ion, and it becomes possible to reduce the required consumption amount of expensive hydroquinone. Further, the sulfite ion has a function of delaying the time for completing the reduction reaction of silver ion in addition to the production of the water-soluble compound described above.

The reason why ammonium ions are allowed to coexist in the method of the present invention is that ammonia water has a function of increasing the reduction reaction rate. That is, the reduction reaction rate can be controlled by adjusting the coexisting amount of sulfite ion and ammonium ion. The fact that the reduction reaction rate can be controlled means that the number of growth nuclei generated within a unit time can be controlled and the grain size of the obtained silver powder can be adjusted. Specifically, if sulfite ion is excessively added, the reaction rate becomes slow and the particle size of the obtained silver particles becomes large. Then, if ammonium ions are added excessively, the reaction rate becomes faster, and the particle size of the obtained silver particles becomes smaller.

The above effects are weakened when silver ions are complex ions such as ammonium ions, and the grain size cannot be adjusted sufficiently. Therefore, the silver nitrate solution is most preferable as the solution containing silver ions.

It is well known that the reaction rate is affected by the pH during the reaction. The same applies to the method of the present invention, and if the pH is less than 8, the reaction rate is remarkably reduced, and the reduction reaction does not end even after several hours from the start of the reaction, resulting in poor productivity. When the pH is 10 or more, the reaction rate remarkably increases, and it becomes difficult to control the reaction rate by adjusting the coexisting amount of ammonium ions. As described above, in the method of the present invention, the pH does not have to be a value at which the reduction reaction takes place, but must be pH 8 to 10. The reason why ammonium sulfite is used as the sulfite in the present invention is that the pH can be maintained in the range of 8 to 10 by doing so. For example, if sodium sulfite or potassium sulfite is used, the pH will rise and it will be difficult to control the particle size using ammonium ions.

The reaction temperature is also important for making the finally obtained particles monodisperse. If the temperature is too high, the purified silver particles will agglomerate. From this point, in the method of the present invention, the reaction temperature is set to 50 ° C. or lower.

In the method of the present invention, it is needless to say that addition of a water-soluble polymer compound such as gelatin or a decomposition product thereof to the reaction solution is effective because it is easy to prevent aggregation of the silver particles produced. That is.

[0017]

EXAMPLES Next, examples of the present invention and comparative examples will be described.

(Examples 1 to 4 and Comparative Example 1) 0.25 mol of 99% pure hydroquinone manufactured by Kanto Kagaku Co., Ltd. was dissolved in 3000 ml of pure water, and 1 mol of ammonium sulfite having 90% purity was dissolved therein. (Example 1) 2 mol (Example 2), 3 mol (Example 3), 4 mol (Example 4) were added, and further, a concentration of 29% ammonia water was added in an amount of 0.283 mol in terms of ammonia. After that, water was added to adjust the volume of each to 4000 ml. Thus, 5 types of reducing agent solutions having different sulfite ion concentrations were prepared.

Next, a silver nitrate solution obtained by dissolving 5 mol of silver nitrate in 3 liters of pure water was prepared, and 600 ml of each was added to each of the above-mentioned 5 kinds of reducing agent solutions.
The mixture was added and stirred at a reaction temperature of 10 ° C. Table 1 shows the time required until the completion of the reduction reaction and the average particle size of the obtained silver powder.

[0020] From Table 1, it is understood that the particle size can be adjusted by increasing the sulfite ion concentration.

(Examples 5-8, Comparative Example 1) 0.25 mol of hydroquinone was dissolved in 3000 ml of pure water, 3 mol of ammonium sulfite was added and dissolved therein, and then 0.142 mol of aqueous ammonia was added ( Comparative example 1), 0.2
12 mol (Example 5), 0.283 mol (Example 6),
After adding 0.425 mol (Example 7) and 0.921 mol (Example 8) so as to adjust the total volume of each to 4000 ml, 5 kinds of reducing agents were added. An aqueous solution was created.

Next, a silver nitrate solution obtained by dissolving 5 mol of silver nitrate in 3 liters of pure water was prepared, and 600 ml of each was added to each of the above-mentioned 5 kinds of reducing agent solutions.
The mixture was added and stirred at a reaction temperature of 10 ° C. Table 2 shows the time required to complete the reduction reaction and the average particle size of the obtained silver powder.

[0023] As can be seen from Table 2, in the case of adding 0.142 mol of aqueous ammonia, it took 4 hours or more to complete the reaction, and the obtained silver powder was aggregated. However, it is understood that when 0.212 mol or more is added, the particle size of silver powder becomes smaller as the amount of ammonium ions increases.

Comparative Example 2 0.25 mol of hydroquinone was dissolved in 3000 ml of pure water, and water was added to 400
A reducing agent solution adjusted to 0 ml was prepared. A solution prepared by dissolving 1 mol of silver nitrate in 600 ml of pure water was added and stirred at 10 ° C. 144
The reaction was allowed to proceed for 0 minutes, but the reduction reaction did not end. Quinone was generated during the reduction reaction, and the produced silver powder was a dendritic one containing coarse particles.

(Comparative Examples 3 to 5) 0.25 mol of hydroquinone was dissolved in 3000 ml of pure water, and ammonium sulphite (Comparative Example 3), potassium sulfite (Comparative Example 4) and sodium sulfite (Comparative Example 5) were dissolved therein. Was dissolved in 3 mol, and water was added to prepare 3 types of reducing agent aqueous solutions adjusted to 4000 ml. To each of these, 1 mol of silver nitrate dissolved in 600 ml of pure water was added and stirred at 10 ° C. The reaction was continued for 240 minutes, but the reduction reaction was not completed. It was observed that for several minutes after the aqueous solution of silver nitrate was added, the solution was colorless and transparent, hardly reacted, and gradually changed to an ocher-colored opaque solution. In addition, no quinone was produced by the reduction reaction. An attempt was made to observe the produced silver powder by SEM, but it could not be observed under the order of tens of thousands of times.

(Comparative Examples 6 to 9) 0.25 mol of hydroquinone was dissolved in 3000 ml of pure water, 3 mol of potassium sulfite was added and dissolved therein, and then 0.073 mol of aqueous ammonia was prepared (Comparative Example 6). , 0.147 mol (Comparative Example 7), 0.220 mol (Comparative Example 8), 0.29
After adding 3 mol (Comparative Example 9), water was added to adjust the total volume of each to 4000 ml to prepare four types of reducing agent aqueous solutions.

Next, a silver nitrate solution obtained by dissolving 5 mol of silver nitrate in 3 liters of pure water was prepared, and 600 ml of each was added to each of the above four kinds of reducing agent solutions.
The mixture was added and stirred at a reaction temperature of 10 ° C. Table 3 shows the time required until the end of the reduction reaction and the average particle size of the obtained silver powder.

[0028] It can be seen from Table 3 that the reaction end time can be adjusted by changing the amount of ammonia water added, but it is difficult to adjust the particle size. It should be noted that, compared with the case where ammonium sulfite was used, the reaction completion time greatly changed with a slight difference in the amount of ammonia water added.

Comparative Examples 10 to 13 Hydroquinone 0.2
5 mol was dissolved in 3000 ml of pure water, 3 mol of sodium sulfite was added to and dissolved therein, and then ammonia water was added to 0.073 mol (Comparative Example 10), respectively.
147 mol (Comparative Example 11), 0.220 mol (Comparative Example 1)
2) and 0.293 mol (Comparative Example 13) were added, and then the total volume of each was adjusted to 4000 cc by adding water.

Then, a silver nitrate solution obtained by dissolving 5 mol of silver nitrate in 3 liters of pure water was prepared, and 600 ml of each of the above four kinds of reducing agent solutions was prepared.
The mixture was added and stirred at a reaction temperature of 10 ° C. Table 4 shows the time required until the completion of the reduction reaction and the average particle size of the obtained silver powder.

[0031] It can be seen from Table 4 that the reaction end time varies depending on the amount of ammonia water added, but the amount of change is too large to be adjusted substantially, and that the particle size is also difficult to adjust.

Comparative Examples 14 to 16 0.25 mol of hydroquinone was dissolved in 2000 ml of water and 0.5 mol of ammonium sulfite (Comparative Example 14) and 3 (Comparative Example 1).
5) was added to each to prepare a dissolved reducing agent aqueous solution and a reducing agent solution (Comparative Example 16) in which 0.5 mol of ammonium sulfite and 0.954 mol of aqueous ammonia were dissolved.

Next, 3 mol of silver nitrate was dissolved in 900 ml of water, and 2 mol of aqueous ammonia was added thereto to obtain a silver ammonium complex solution. This liquid was added to each of the above three types of reducing solutions at 300C and stirred at 10 ° C. Table 5 shows the reaction completion time and the particle size of the obtained silver particles.

[0034] Table 5 shows that it is difficult to adjust the reaction end time and the particle size by these methods.

[0035]

As is apparent from the above description, according to the method of the present invention for controlling the coexisting amount of sulfite ion and ammonium ion in the reducing agent, the grain size of silver powder which cannot be achieved by the conventional method, It is possible to control over a wide range such as 0.3 to 2.0 μm. Therefore, the method of the present invention is a method capable of producing an extremely useful silver powder at a low cost without the need to change the production equipment, reagents, etc. for each required particle size, and there is no prior art, It's a breakthrough.

Claims (3)

[Claims] 1. A reducing agent solution and a solution containing silver ions are reacted to have an average particle size in the range of 0.3 to 2 μm,
In the method of obtaining a silver powder having a narrow particle size distribution width by monodispersion,
As a reducing agent solution, a mixed solution of ammonium sulfite, ammonia water and hydroquinone is used, and as a solution containing silver ions, a silver nitrate solution is used, and a solution containing silver ions is added to the reducing agent solution at a reaction temperature of 50 ° C. or lower. A method for producing silver powder, which comprises adding. 2. The method for producing silver powder according to claim 1, wherein the ratio of ammonium sulfite, aqueous ammonia and hydroquinone in the reducing agent solution is adjusted. 3. Use of 0.2 to 1 mol of hydroquinone, 1 to 12 mol of ammonium sulfite, and 0.1 to 1 mol of ammonia water in terms of ammonia with respect to 1 mol of silver nitrate. The method for producing silver powder according to 1 or 2.