JPH0892611A - Silver powder manufacturing method - Google Patents

Abstract

(57) [Summary] [Object] The present invention is for forming electrodes of electronic parts such as chip capacitors, chip inductors, chip resistors, ceramic capacitors, ceramic thermistors, ceramic varistor, piezoelectric elements, dielectric filters and HICs. It is an object of the present invention to provide a method for adjusting an optimum monodisperse silver powder having a narrow particle size distribution in a wider range of the average particle diameter of the silver powder. [Structure] A silver nitrate solution is added to a reducing agent solution containing sulfite and hydroquinone at a reaction temperature of 100 ° C. or lower, and then ammonia is added to a reaction solution containing crystal nuclei.

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.

Conventionally, the above-mentioned silver powder for paste has been obtained by reducing an aqueous solution of silver nitrate, 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, it has been found that there is a problem when the silver paste using the silver powder obtained by such a conventional method is used for the multilayer substrate for HIC.

That is, the HIC has been further highly integrated, and a glass paste that can be fired at a relatively low temperature of several hundreds of degrees Celsius is used as the silver paste for the multilayer substrate used for the HIC. The silver paste obtained by using such glass and conventionally used silver powder has a problem that the silver diffuses into the glass during firing and deteriorates the insulation resistance of the substrate. It is said that this phenomenon can be prevented by using silver powder having a particle size of several μm.

Among the methods studied to solve such problems, there is a method for producing silver powder by using an aromatic compound solution having an OH group as a reducing agent. For example, Japanese Unexamined Patent Publication
No. 11706, No. 2-11707, No. 2-1
There are those disclosed in Japanese Patent Nos. 1708 and 2-11709. In these methods, an OH group-containing aromatic compound solution having a controlled pH value is used as a reducing agent, and the particle size is controlled by changing the pH value and the kind of the aromatic compound.

Further, Japanese Patent Application Laid-Open No. 04-59904 discloses a method for producing silver powder by controlling pH value by using hydroquinone and sulfite in combination. In this method, sulfite is used only to convert the quinone formed during the reduction reaction into a water-soluble hydroquinone sulfonate.

In any case, at most 2
Only silver powder having a particle size of a little less than μm can be obtained, and silver powder having a large particle size of several μm that satisfies the above requirements cannot be manufactured.

[0008]

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.

[0009]

The method of the present invention for solving the above-mentioned problems is a method of reacting a reducing agent solution with a solution containing silver ions to obtain silver powder, wherein a sulfite salt and hydroquinone are mixed as a reducing agent solution. A solution is used, and a silver nitrate solution is used as a solution containing silver ions. A solution containing silver ions is added to the reducing agent solution so that the reaction temperature is 100 ° C. or lower, and ammonia is added after crystal nuclei are generated. It is a thing. Then, by adjusting the ratio of ammonium sulfite and hydroquinone, the average particle size is 0.3 to 6 μm.
It is within the range of m and is a monodisperse silver powder having a narrow particle size distribution.

The number of crystal nuclei can be adjusted by adjusting the ratio of sulfite and hydroquinone in the reducing agent solution, or by adjusting the reaction time from the addition of the silver nitrate solution to the reducing agent solution until the addition of ammonia, or both of these. It can be done by adjustment. The relationship between these relationships and the average particle size of the obtained silver powder is influenced by the device constant, and therefore it is preferable to determine in advance.

[0011]

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, when sulfite coexists, quinone reacts with sulfite ion to convert quinone into a water-soluble compound, which facilitates separation from 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.

The sulfite ion has a function of slowing down the reduction reaction rate of silver ion in addition to the formation of the above water-soluble compound. On the other hand, ammonium ion has a function of increasing the reduction reaction rate. Therefore, it is possible to control the concentration of crystal nuclei in the reaction liquid by extremely slowing the reduction reaction rate by making the amount of sulfite added excessively during the production of silver powder. Then, by adding aqueous ammonia in a state where a proper amount of crystal nuclei are generated in the solution to accelerate the reduction reaction,
It is possible to obtain silver powder having a large particle size. Naturally, conversely, if the reduction rate is increased while the solution contains almost no crystal nuclei, silver powder having a small particle size will be produced.

In the method of the present invention, any sulfite that can be used may be any of water-soluble salts having sulfite groups such as ammonium sulfite, sodium sulfite and potassium sulfite.

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 when the pH is less than 7, 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. And the produced silver powder aggregates. Meanwhile p
Even if H is high, only the reaction rate increases, and there is no problem. Therefore, the pH needs to be 7 or higher.

The reaction temperature is also important in order to make 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 100 ° C. or lower.

The above effects are weakened when the 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.

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.

[0021]

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

(Example 1) Purity 9 manufactured by Kanto Chemical Co., Inc.
After 0.25 mol of 9% hydroquinone and 3 mol of ammonium sulfite having a purity of 90% were dissolved in 3000 ml of water, water was added to adjust the total volume to 4000 ml.

Then, a silver nitrate solution obtained by dissolving 1 mol of silver nitrate in 600 ml of pure water was added at a reaction temperature of 10 ° C. and stirred.

8 minutes after the addition of the silver nitrate solution was completed, the concentration was 29
% Ammonia water was added to the reaction solution in an amount of 0.921 mol in terms of ammonia, and the mixture was stirred for 30 minutes after the addition of ammonia water. Table 1 shows the average particle size of the obtained silver powder. In addition,
In the present invention, all average particle diameters were measured by a laser diffraction type particle size distribution meter. Moreover, as a result of observing the silver powder using an SEM photograph, it was found that the shape was spherical.

In this embodiment, the reduction reaction itself is completed in about 1 minute after the addition of aqueous ammonia.

(Examples 2 to 4) Addition of ammonia water
Example 1 except that the silver nitrate solution was added immediately (Example 2), after 15 minutes (Example 3), and after 30 minutes (Example 4).
Silver powder was obtained in the same manner as. Table 1 shows the average particle size of the obtained silver powder. Moreover, as a result of observing the silver powder using an SEM photograph, it was found that the shape was spherical.

Also in this embodiment, the reduction reaction itself is completed in about 1 minute after the addition of the ammonia water.

[0028] (Example 5) 0.25 mol of 99% pure hydroquinone manufactured by Kanto Kagaku Co., Ltd. and 95% pure potassium sulfite 3
After dissolving the moles in 3000 ml of pure water, water was added to make the total volume 4000 ml. To this, a silver nitrate solution obtained by dissolving 1 mol of silver nitrate in 600 ml of pure water was added and stirred at a temperature of 10 ° C. 10 minutes after the total amount of the silver nitrate solution was added, 0.293 mol of ammonia water having a concentration of 29% was added in terms of ammonia, and stirring was continued for 30 minutes thereafter, and solid-liquid separation was performed to obtain silver powder.

When the average particle size of the obtained silver powder was examined, it was 3.2 μm, and it was found from the observation results using the SEM photograph that it was a spherical silver powder.

(Example 6) Silver powder was obtained in the same manner as in Example 5 except that ammonia water was added 20 minutes after the total addition of the silver nitrate solution.

When the average particle size of the obtained silver powder was examined, it was 5.3 μm, and it was found from the observation results using the SEM photograph that it was spherical silver powder.

[0032]

According to the method of the present invention, the reaction rate is slowed by using sulfite ions, and after reacting for a predetermined time to produce a desired amount of crystal nuclei, the amount of ammonium ions is increased to increase the crystal nuclei. Prioritize growth. As a result, it becomes possible to control in a wide range of 0.3 to 6.0 μm of the average particle diameter of the silver powder, which cannot be achieved by the conventional synthesis method.

Therefore, according to the method of the present invention, it is not necessary to change the manufacturing equipment, reagents, etc. for each required particle size, and it is possible to manufacture an inexpensive and extremely useful silver powder.

Claims (3)

[Claims] 1. A silver nitrate solution is added to a reducing agent solution containing sulfite and hydroquinone at a reaction temperature of 100 ° C. or lower,
Then, ammonia is added to the reaction liquid containing crystal nuclei, wherein the average particle diameter is in the range of 0.3 to 6 μm, and the method for producing silver powder is a monodisperse silver powder having a narrow particle size distribution. 2. The method for producing silver powder according to claim 1, wherein the ratio of sulfite and hydroquinone in the reducing agent solution is adjusted. 3. The method according to claim 1, wherein after adding the silver nitrate solution to the reducing agent solution, the reaction is continued for a desired time to generate crystal nuclei, and then ammonia is added to the reaction solution containing the crystal nuclei. Alternatively, the method for producing silver powder according to 2.