JP2003342775A - Method of producing silver powder, silver powder and electronic parts - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain inexpensive silver powder which has a desired fine grain size while realizing the reduction of environmental loads. <P>SOLUTION: A titanium sulfate as a feed source of Ti<SP>3+</SP>and a water soluble barium salt are added to an aliphatic sulfonic acid aqueous solution 2, and chemical reaction is caused to produce and recover barium sulfate. Thereafter, electrolysis is performed with an Ag sheet 3 as an anode in the aliphatic sulfonic acid aqueous solution 2, and oxidation-reduction reaction is caused between Ag<SP>+</SP>and Ti<SP>3+</SP>eluted from the Ag sheet 3 to produce Ag powder. After the recovery of the Ag powder, an oxide produced by the oxidation-reduction reaction is reduced to Ti<SP>3+</SP>by electrolytic reaction in the aliphatic sulfonic acid aqueous solution 2, and the aliphatic sulfonic acid aqueous solution 2 is reutilized. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing silver powder,
And silver powder, and electronic parts, more specifically, a method for producing silver powder used as an electrode material for various electronic parts such as a capacitor, an inductance element, a resistance element, a thermistor, a varistor, a piezoelectric element, or a dielectric filter,
And silver powder, and electronic parts manufactured using the silver powder.

[0002]

2. Description of the Related Art Conventionally, in various electronic parts of this type,
Although silver powder is widely used as an electrode material, when such a silver powder is produced by an electrolysis method, only fine silver powder having an average particle size of about 5 to 10 μm can be obtained, and moreover, it has a dendritic shape. Therefore, it has been difficult to produce silver powder having an average particle diameter of 1 μm or less required for fine wiring and the like.

Therefore, a method for producing a fine silver powder by utilizing a chemical reduction method has been developed. For example, an aqueous solution of silver sulfate and one of sodium phosphinate, formaldehyde and hydroquinone are used as a reducing agent. A method of carrying out a reaction using polyvinylpyrrolidone has been proposed (JP-A-6-122905; hereinafter referred to as "first conventional technology").

In the first prior art, silver ions in an aqueous solution of silver nitrate are reduced to silver by an oxidizing reaction of a reducing agent, and fine silver powder having a particle size of 1 μm or less is obtained.

As another method for producing silver powder by the chemical reduction method, a slurry containing an ammine complex solution of a silver salt and an ammine complex of a heavy metal salt is mixed with a solution containing potassium sulfite and gum arabic. A technique for reducing an ammine complex of a silver salt to recover silver particles has been proposed (JP-A-11-189812; hereinafter referred to as "second conventional technique").

In the second prior art, by using an ammine complex of a heavy metal salt which acts as a habit modifier in the reduction reaction, potassium sulfite as a reducing agent, and gum arabic as a protective colloid, A granular silver powder having a particle size of 0.1 to 1 μm, low aggregation and a narrow particle size distribution is obtained.

On the other hand, copper powder is widely used in addition to silver powder as an electrode material. As a method for producing such copper powder, an aqueous sulfuric acid solution containing Ti ³⁺ (Cu reduction electrolytic cell) is used.
In the inside, electrolysis is performed using metallic copper as an anode, thereby Cu ²⁺ eluted from the anode is reduced with Ti ³⁺ to produce and recover copper powder, and further, a Ti ³⁺ oxidation product (TiO ^{2+) is} produced in a Ti reduction electrolytic bath. ) Is reduced to Ti ³⁺ and is circulated in the Cu reduction electrolyzer (Japanese Patent Laid-Open No. Hei 4-
88104 gazette; hereinafter, referred to as "third prior art").

[0008]

However, in the above-mentioned first and second prior arts, a reducing agent is used to deposit silver, but such reducing agent is generally expensive and When formaldehyde is used as an agent, a bad odor is generated, the working environment is deteriorated, and there is a concern that the human body may be adversely affected. In addition, there is a problem in that waste liquid and waste water must be treated separately because they cannot be reused by recycling.

On the other hand, the above-mentioned third prior art relates to copper powder, but such a technology is applied to the production of silver powder,
When electrolysis is performed in a sulfuric acid acid aqueous solution using metallic silver as an anode, sparingly soluble silver sulfate is generated and deposited, and Ag ⁺ is less likely to be eluted from the anode. There is a problem in that it cannot be diverted as it is to the method for producing powder.

The present invention has been made in view of the above circumstances, and is a method for producing a silver powder, which makes it possible to obtain a silver powder having a desired fine particle size at low cost while realizing a reduction in environmental load, and It is an object to provide a silver powder manufactured by the manufacturing method, and an electronic component manufactured by using the silver powder.

[0011]

Means for Solving the Problems As a result of intensive studies for achieving the above object, the present inventors have used an acidic aqueous solution containing an alkyl group and a sulfo group and mixed Ti ³⁺ into the acidic aqueous solution. By performing electrolysis using an Ag plate as an anode, it is possible to promote the elution of Ag ⁺ from the anode without producing a sparingly soluble Ag salt and to easily produce a desired silver powder. Obtained.

The present invention has been made on the basis of such findings, and the method for producing silver powder according to the present invention is
³⁺ performs electrolysis as an anode of silver plate in an acidic aqueous solution containing at least an alkyl group and a sulfo group mixed, and causing a redox reaction between the Ag ⁺ and Ti ³⁺ eluted from the silver plate It is characterized by producing silver powder.

Further, in the method for producing a silver powder of the present invention, after recovering the silver powder, electrolysis is performed in the acidic aqueous solution to reduce the oxide produced by the redox reaction to Ti ^3+. It has a feature.

According to the above-mentioned manufacturing method, after the produced silver powder is recovered, the oxide produced at the time of producing the silver powder is converted into Ti.
Since it is reduced to ³⁺ , the acidic aqueous solution used for producing the silver powder can be reused without discarding it.

In addition, Ti³⁺As a source of
It is preferable to use sulfate for ease of use, but in this case
Avoiding the formation of poorly soluble silver sulfate on the anode
Needed, for that purpose acidic with titanium sulphate
Addition of a water-soluble barium salt to the solution makes the sparingly soluble burrs of sulfuric acid.
To produce SO and recover and remove the barium sulfate to remove SO _Four
^2-It is necessary to eliminate the effect of.

That is, the method for producing silver powder of the present invention is as follows:
Ti ³⁺ is characterized by being supplied from titanium sulfate,
Further, it is characterized in that the titanium sulfate and the water-soluble barium salt are added to an acidic aqueous solution containing at least an alkyl group and a sulfo group to cause a chemical reaction, and the generated barium sulfate is recovered.

From the viewpoint of allowing Ag ⁺ to stably exist in an acidic aqueous solution, the acidic aqueous solution containing at least an alkyl group and a sulfo group is an aliphatic sulfonic acid, particularly methanesulfonic acid or ethanesulfonic acid. It is preferable to include either one.

That is, the method for producing silver powder of the present invention is as follows:
The acidic aqueous solution is an aqueous solution containing an aliphatic sulfonic acid as a main component, and the aliphatic sulfonic acid is characterized by containing either methanesulfonic acid or ethanesulfonic acid.

Further, the silver powder according to the present invention is characterized by being manufactured by the above-mentioned manufacturing method, whereby a fine particle silver powder having an average particle diameter of 1 μm or less suitable for fine wiring or the like can be manufactured at low cost. It is possible to obtain it easily.

Further, the electronic component according to the present invention is characterized in that the electrode portion having a predetermined pattern is formed of the silver powder.

According to the above construction, an electronic component having an electrode portion formed of an electrode material using a silver powder having a fine grain size can be manufactured, and an electronic component having a complicated and fine electrode pattern can be efficiently manufactured. it can.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, 1 is an Ag reduction electrolysis cell, and the Ag reduction electrolysis cell 1 is filled with an aliphatic sulfonic acid aqueous solution 2 containing an alkyl group and a sulfo group,
An Ag plate 3 as an anode and a Pt-coated Ti plate 4 as a cathode are immersed in 2 in the aliphatic sulfonic acid aqueous solution. Further, the Ti plate 4 prevents the Ag ⁺ eluted from the Ag plate 3 from being deposited on the Ti plate 4 by the electrolytic diaphragm 5.

Further, Ti ³⁺ is contained in the Ag reduction electrolysis cell 1.
Is mixed in. That is, in the present embodiment, Ti
Using Ti ₂ (SO ₄ ) ₃ (titanium (III) sulfate), which is relatively easy to obtain as a salt, as a source of Ti ³⁺ ,
i ³⁺ is mixed in the Ag reduction electrolytic cell 1.

By the way, when Ti ₂ (SO ₄ ) ₃ is used as a Ti ³⁺ supply source as described above, SO ₄ ²⁻ produces a sparingly soluble Ag ₂ SO ₄ (silver sulfate) on the anode. Therefore, the elution of Ag ⁺ from the Ag plate 3 that is the anode is hindered, and further, Ag ₂ SO ₄ attached to the anode falls,
Settle and deposit.

Therefore, in the present embodiment, Ti ₂ (SO
_{4) 3} was previously added water-soluble barium salt in the aliphatic sulfonate aqueous solution containing, by reacting Ba ²⁺ and _SO ^{4 2-and} generates a sparingly soluble BaSO ₄ (barium sulfate), the BaSO ₄ By avoiding the production of Ag ₂ SO ₄ , the influence of SO ₄ ²⁻ is eliminated.

The water-soluble barium salt is not particularly limited as long as it is water-soluble, and Ba (OH)
₂ (barium hydroxide) or BaO (barium oxide) can be used.

If the amount of barium salt added is too small, the amount of the aqueous solution of aliphatic sulfonic acid 2 which is the electrolytic solution is changed to SO ₄ ^2−.
Therefore, the water-soluble barium salt is preferably added so as to have a molar concentration of about 1.0 to 1.2 times the concentration of SO ₄ ²⁻ .

Then, when an external power source is applied between the anode (Ag plate 3) and the cathode (Ti plate 4), an electrolysis reaction occurs in the aliphatic sulfonic acid aqueous solution 2, and the chemical reaction formula (1) is shown. As described above, the Ag plate 3 is dissolved and Ag ⁺ is eluted in the aliphatic sulfonic acid aqueous solution 2, and the eluted Ag ⁺ is reduced by Ti ³⁺ in the aliphatic sulfonic acid aqueous solution 2 to deposit silver powder.・ Generate.

Ag ⁺ + Ti ³⁺ + H ₂ O → Ag + TiO ²⁺ + 2H ⁺ (1) Here, the kind of the aliphatic sulfonic acid is not particularly limited, and methanesulfonic acid, ethanesulfone Acid, 1,
2-ethanedisulfonic acid, 1-propanesulfonic acid, 2
-Propanesulfonic acid, 1,1-propanedisulfonic acid, 2,2-propanedisulfonic acid and the like can be used, but from the viewpoint of solubility of Ag ⁺ , water solubility of itself, and easy availability, methane is used. It is preferable to use an acidic aqueous solution containing one or both of sulfonic acid and ethanesulfonic acid.

Further, in this embodiment, the volume fraction of the aliphatic sulfonic acid in the aqueous solution is set within the range of 3 vol% to 30 vol%.

That is, the electrolytic current density can be increased by increasing the volume fraction of the aliphatic sulfonic acid, but in the present embodiment, as described later, the oxidation product of Ti ³⁺ is reduced to reduce the fat. Since the aqueous solution of the aromatic sulfonic acid 2 is reused, the volume fraction of the aliphatic sulfonic acid is 3 from this viewpoint.
When it exceeds 0 vol%, T which is an oxidation product of Ti ³⁺ ion
The reducing action of iO ²⁺ is reduced. On the other hand, when the volume fraction of the aliphatic sulfonic acid is less than 3 vol%, it becomes difficult to stably exist Ti ³⁺ in the aliphatic sulfonic acid aqueous solution 2.

Therefore, in this embodiment, the volume fraction of the aliphatic sulfonic acid is 3 to 30 vol%, preferably 5 to 20 vol.
It was set in the range of%.

Further, in the present embodiment, the mass concentration of Ti ^{3+ in} the aliphatic sulfonic acid aqueous solution is 0.1 to 40 kg / m 2.
^It is set to ³ .

That is, the mass concentration of Ti ³⁺ is 40 kg /
When it exceeds m ³ , the produced Ag powder becomes coarse and it becomes difficult to stably exist in the aliphatic sulfonic acid aqueous solution. On the other hand, when the mass concentration of Ti ³⁺ is less than 0.1 kg / m ³ , the Ag powder becomes finer, but A per unit volume
The production rate of g powder decreases.

Therefore, in the present embodiment, the mass concentration of Ti ^{3+ in} the aliphatic sulfonic acid aqueous solution is 0.1 to 40 kg /
It was set to m ³ , preferably 1 to 20 kg / m ³ .

In addition to the mass concentration of Ti ^{3+ in} the aliphatic sulfonic acid aqueous solution 2, the particle size of the Ag powder can be adjusted by the elution rate of Ag ⁺ , that is, the anode current density. Then, the anode current density is 0.1 to 20 A /
It is set to dm ² .

That is, the anode current density is 0.1 A / dm.
^When it is less than ² , the desired electrolysis reaction is hindered, while when the anode current density exceeds 20 A / dm ² , A
Although the generation rate of g powder increases, Ag powder becomes coarse,
Moreover, oxidation of Ti ³⁺ ions on the anode causes Ag 3
The efficiency of powder generation is reduced.

Therefore, in this embodiment, the anode current density is 0.1 to 20 A / dm ² , preferably 0.5 to 10 A.
It was set to / dm ² .

Then, in this embodiment, after the Ag powder thus produced is recovered, the TiO ²⁺ produced by the chemical reaction formula (1) is electrolytically reduced to Ti ³⁺ again, This makes it possible to reuse the aliphatic sulfonic acid aqueous solution.

That is, when the Ag powder is deposited and produced in the Ag reduction electrolysis tank 1, the Ag powder is separated by a filtration method or a centrifugal separation method and recovered, and then, as shown in FIG. The aqueous acid solution 2 is transferred to the Ti reduction electrolytic bath 6.

In the Ti reduction electrolysis tank 6, an insoluble anode plate 7 such as Pb or Pt and a Ti plate 8 as a cathode are immersed in the aliphatic sulfonic acid aqueous solution 2. Further, the insoluble anode 7 is isolated by the electrolytic diaphragm 9, and thereby Ti ³⁺ produced by reduction is prevented from being oxidized by the insoluble anode 7.

The external power source is the insoluble anode 7 and Ti.
When applied between the plates 8 (cathode), an electrolysis reaction occurs in the aliphatic sulfonic acid aqueous solution 2, and TiO ²⁺ is reduced to Ti ³⁺ as shown in the chemical reaction formula (2).

TiO ²⁺ + 4H ⁺ + 3e ⁻ → Ti ³⁺ + 2H ₂ O (2) It is necessary to wash the Ag powder when collecting the produced Ag powder, but unnecessary components are mixed or accumulated during the electrolytic reaction. Therefore, it is possible to concentrate the drainage liquid required for cleaning and return it to the aqueous solution of the aliphatic sulfonic acid 2, thereby suppressing the generation of waste such as waste liquid.

FIG. 3 is a cross-sectional view showing an embodiment of an electronic component according to the present invention. The electronic component is a ceramic element body 10 made of barium titanate, barium titanate zirconate or the like. The Ag powder is applied and baked to form the electrode portion 11.

As described above, in this embodiment, since the electrode portion 11 is formed of Ag powder having an average particle size of 1 μm or less obtained by the above manufacturing method, an electronic component having an electrode pattern with a complicated shape is formed. Can be easily obtained.

[0047]

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

[Example 1] The present inventor used 10 vol% CH
_ThreeSO_ThreeTi in H (methanesulfonic acid) aqueous solution_Two(SO
_Four)_Three5 kg / m^ThreeAfter dissolution, 10.8 kg / m
^ThreeBa (OH) _TwoIs dissolved in the aqueous solution to form a precipitate.
BaSO_FourTo generate the BaSO_FourWas recovered.

Then, in this CH ₃ SO ₃ H aqueous solution, A
The g-plate was used as an anode, the Pt-coated Ti plate was used as a cathode, and the cathode was isolated by an electrolytic diaphragm for electrolysis. The anode current density is 1 A / dm ² and the quantity of electricity is 1
It was 000C.

As a result, Ag ⁺ is satisfactorily obtained from the anode.
Was eluted and about 0.8 g of Ag powder having a particle size of 0.3 to 0.5 μm was obtained.

Example 2 The present inventor has found that 20 vol% C ₂
H ₅ SO ₃ H TiOSO to (ethanesulfonic acid) solution
₄ (titanium oxysulfate (IV)) was dissolved in 10 kg / m ³ and then BaO was dissolved in 22 kg / m ³ to produce BaSO ₄ as a precipitate, and the BaSO ₄ was recovered.

Then, in this C ₂ H ₅ SO ₃ H aqueous solution, a Ti plate was used as a cathode, a Pt plate was used as an anode, and the Pt plate was isolated by an electrolytic diaphragm, and TiO ²⁺ was ^converted into Ti ³⁺ at a total current of 5A. Electrolytically reduced to.

After that, the Ag plate was used as the anode, the Ti plate coated with Pt was used as the cathode, and the cathode was isolated by the electrolytic diaphragm, and the anode current density was 5 A / d.
Electrolysis was performed at m ² and an electric quantity of 2000C.

As a result, Ag ⁺ was eluted from the anode and about 1.8 g of Ag powder having a particle size of 0.6 to 0.9 μm was obtained.

[Comparative Example 1] The present inventor used 10 vol% CH.
₃ SO ₃ H (methanesulfonic acid) aqueous solution with Ti ₂ (SO
₄ ) ₃ was dissolved in 5 kg / m ³ and an Ag plate was used as an anode in this CH ₃ SO ₃ H aqueous solution, a Ti plate coated with Pt was used as a cathode, and the cathode was isolated by an electrolytic diaphragm. Electrolysis was performed under the same conditions as in Example 1.

However, after 10 seconds from the start of electrolysis, A
It was confirmed that the g-plate did not dissolve, and that insoluble Ag ₂ SO ₄ was formed in the trace amount of Ag powder deposited after the electrolysis.

[Comparative Example 2] The present inventor used 10 vol% HN
Ti ₂ (SO ₄ ) ₃ was dissolved in an O ₃ aqueous solution at 5 kg / m ³ and electrolysis was attempted under the same conditions as in Example 1.
Due to the oxidation action of NO ₃ ⁻ , Ti ³⁺ was oxidized to TiO ²⁺ , so that Ag ⁺ ions eluted from the Ag plate could not be reduced and Ag powder could not be produced.

[Comparative Example 3] The present inventor used 10 vol% H_Two
SO_FourTi in aqueous solution_Two(SO_Four)_Three5 kg / m ^ThreeDissolution
Let this H_TwoSO_FourAqueous solution under the same conditions as in Example 2.
It was electrolyzed.

However, after a few seconds from the start of electrolysis, the Ag plate does not dissolve and only a very small amount of Ag powder is produced. Moreover, as in Comparative Example 1, there is a very small amount of Ag powder. The formation of sparingly soluble Ag ₂ SO ₄ was observed.

[Comparative Example 4] The present inventor used 10 vol% HC
5 kg / m ³ of TiCl ₃ (titanium trichloride) in an aqueous solution.
It was dissolved and electrolyzed with this aqueous HCl solution under the same conditions as in Example 2.

However, immediately after the start of electrolysis, Ag
Elution of ⁺ was unlikely to occur, and the formation of sparingly soluble AgCl was observed in a very small amount of Ag powder.

[0062]

As described above in detail, the method for producing a silver powder according to the present invention uses the acidic aqueous solution (preferably methanesulfonic acid or ethanesulfone) containing at least an alkyl group and a sulfo group mixed with Ti ^3+. In an aliphatic sulfonic acid typified by acid), electrolysis is performed using an Ag plate as an anode
Since redox reaction is caused between Ag ⁺ and Ti ³⁺ eluted from the Ag plate to generate Ag powder,
_{It is} possible to facilitate the elution of Ag ⁺ from the anode without easily forming a hardly soluble Ag salt such as ₂ SO ₄ or AgCl, and to easily produce the desired fine particle Ag powder.

Further, in the present invention, after the Ag powder is recovered, electrolysis is performed in the acidic aqueous solution to reduce the oxide produced by the redox reaction to Ti ³⁺ ,
The aqueous solution containing the oxide produced by oxidation can be reused without waste treatment such as waste treatment.

Further, in the present invention, Ti ³⁺ is supplied from titanium sulfate, and further, the titanium sulfate and the water-soluble barium salt are added to the acidic aqueous solution to cause a chemical reaction to generate sulfuric acid. Since barium is recovered, the influence of SO ₄ ²⁻ in the aqueous solution can be eliminated, and it is possible to avoid the formation of hardly soluble Ag ₂ SO ₄ on the anode.

Further, since the Ag powder according to the present invention is manufactured by the above manufacturing method, it is possible to easily, efficiently and inexpensively obtain fine Ag powder having an average particle size of 1 μm or less, which is suitable for fine wiring and the like. .

As described above, according to the method for producing a silver powder and the silver powder of the present invention, a fine granular silver powder can be stably obtained, and at the same time, the reducing agent can be electrochemically regenerated. It is possible to avoid waste as much as possible and to manufacture at low cost.

Further, in the electronic component according to the present invention, since the electrode portion having the predetermined pattern is formed of the silver powder, the electrode portion is formed of the desired fine particle Ag powder and has a fine and complicated pattern shape. A desired electronic component including an electrode portion can be obtained with high efficiency and at low cost.

[Brief description of drawings]

FIG. 1 is an Ag illustrating a method for producing a silver powder according to the present invention.
It is a figure of an electrolytic reduction tank.

FIG. 2 is a Ti explaining a method for producing a silver powder according to the present invention.
It is a figure of an electrolytic reduction tank.

FIG. 3 is a sectional view showing an embodiment of an electronic component according to the present invention.

[Explanation of symbols]

2 Acidic aqueous solution (aliphatic sulfonic acid aqueous solution) 3 silver plate

Claims (8)

[Claims] 1. A silver plate as an anode is electrolyzed in an acidic aqueous solution containing at least an alkyl group and a sulfo group mixed with trivalent titanium ions, and the silver ions eluted from the silver plate and the trivalent A method for producing a silver powder, which comprises producing a silver powder by causing an oxidation-reduction reaction with titanium ions. 2. The silver powder is recovered, and then electrolyzed in the acidic aqueous solution to reduce the oxide produced by the redox reaction to trivalent titanium ions. Manufacturing method of silver powder. 3. The trivalent titanium ion is supplied from titanium sulfate.
A method for producing the silver powder described above. 4. The barium sulfate formed is recovered by adding the titanium sulfate and the water-soluble barium salt to an acidic aqueous solution containing at least an alkyl group and a sulfo group to cause a chemical reaction. The method for producing the silver powder according to claim 3. 5. The method for producing a silver powder according to claim 1, wherein the acidic aqueous solution is an aqueous solution containing an aliphatic sulfonic acid as a main component. 6. The method for producing silver powder according to claim 5, wherein the aliphatic sulfonic acid contains either methanesulfonic acid or ethanesulfonic acid. 7. A silver powder manufactured by the manufacturing method according to claim 1. 8. The electrode part having a predetermined pattern is defined in claim 7.
An electronic component formed of the silver powder as described above.