JPH0334525A - Formation of electrolyte layer for solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To form a uniform and powdery electrolyte layer of a definite thickness by a method wherein an electrode body where a dielectric oxide film has been formed on the surface of a porous body is immersed in a manganese nitrate solution and is impregnated with this solution, one part of the manganese nitrate solution is then pyrolyzed to produce a consistent substance, the body is immersed in an electrolyte powder tank and a powdery electrolyte is applied to the surface. CONSTITUTION:An electrode body 4 on which a dielectric oxide film 3 has been formed is immersed in a manganese nitrate solution whose specific gravity is 1.20; it is impregnated with the solution; it is pyrolyzed at 250 deg.C for 5min. This process is repeated two times. In succession, the electrode body 4 is immersed in a manganese nitrate solution whose specific gravity is 1.60; it is pulled up; after that, it is heated for 10min in an atmosphere of 150 deg.C; water and one part of the manganese nitrate solution are subjected to a pyrolytic reaction to produce a semisolid and consistent substance 5. After that, the electrode body 4 which has produced this semisolid and consistent substance 5 is immersed in an electrolyte powder tank which has been filled with a gamma-manganese dioxide powder whose particle diameter is 30 to 80mum; a manganese dioxide powder particle layer 6 is formed on the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for forming an electrolyte layer of a solid electrolytic capacitor.

Prior Art Conventionally, when forming an electrolyte layer of a solid electrolytic capacitor, the following method was used.

That is, the first method is to immerse the electrode body in a low-concentration manganese nitrate solution with low viscosity to impregnate it, repeat the operation several times to thermally decompose it at an appropriate temperature, and then fill the interior with manganese dioxide. Subsequently, a manganese dioxide electrolyte layer was formed on the surface by immersing the material in a highly concentrated manganese nitrate solution with a specific gravity of 1.76 or more, impregnating it, and thermally decomposing it at an appropriate temperature several times.

The second method is to immerse the electrode body in a low-concentration manganese nitrate solution with low specific gravity to impregnate it, and then thermally decompose it at an appropriate temperature, which is repeated several times to fill the interior with manganese dioxide. After that, a manganese dioxide electrolyte layer was formed on the surface by immersing it in a slurry solution made by dispersing manganese dioxide powder in a manganese nitrate solution, and then pyrolyzing it at an appropriate temperature, which was repeated several times. .

Moreover, the third method is disclosed in Japanese Patent Application Laid-Open No. 63-265417.
As shown in the publication, after repeating three times the operation of immersing a unipolar body in a low-concentration manganese nitrate solution with a low specific gravity and performing thermal decomposition at an appropriate temperature, an appropriate concentration is obtained. impregnated by immersion in manganese nitrate solution, and then
Wipe off the manganese nitrate solution on the surface with gauze or cotton cloth, or dry it at 50°C for 6 to 10 minutes to make it semi-dry, and then sprinkle manganese dioxide powder on the surface for thermal decomposition. A manganese dioxide electrolyte layer was formed.

Problems to be Solved by the Invention However, these methods have the following drawbacks. In the first method, in order to form the necessary and sufficient thickness of the manganese dioxide electrolyte layer, the impregnation step with the manganese nitrate solution and the thermal decomposition step have to be repeated many times, which increases the cost. The drawback was that it was difficult to obtain a uniform manganese dioxide electrolyte layer on the surface.

In addition, in order to form the necessary and sufficient thickness of the manganese dioxide electrolyte layer with a small number of thermal decomposition cycles, the specific gravity is 1.76.
A manganese nitrate solution with a high concentration as described above must be used, but this high concentration manganese nitrate solution with a high specific gravity has a high hygroscopicity, and therefore has the drawback that adjustment and management of the concentration is extremely difficult.

In addition, the second method has the feature of reducing the number of ab cycles in the manganese nitrate solution impregnation step and thermal decomposition step, but it is difficult to always uniformly disperse the manganese dioxide powder in the slurry solution. In addition, it is difficult to adjust and control the composition of the slurry solution, and it is difficult to apply a uniform slurry layer to the surface by dipping.

This method had the disadvantage of resulting in a non-uniform manganese dioxide electrolyte layer.

In the third method, the manganese nitrate aqueous solution is preferentially absorbed by the manganese dioxide powder from the place where it was blown, and then the manganese nitrate aqueous solution seeps onto the surface of the manganese dioxide powder due to capillary action. Since the manganese dioxide powder that is sprinkled on top of the surface adheres to the top, the amount of manganese dioxide powder that has been sprayed last is insufficient due to the lack of manganese nitrate aqueous solution, and as a result, the entire surface of the electrode body is It is difficult to form a layer of uniform thickness on the surface, especially when processing many electrode bodies at the same time. It had the drawback of being filtery. Also, in this case,
Due to the weak adhesion, the sprinkled manganese dioxide powder falls apart due to vibrations during the process, resulting in further unevenness. Furthermore, even if the film was dried at 50° C. as a pretreatment, the above-mentioned drawbacks could not be sufficiently eliminated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming an electrolyte layer of a solid electrolytic capacitor that can eliminate the above-mentioned conventional drawbacks.

Means for Solving the Problems In order to solve the above-mentioned conventional problems, a method for forming an electrolyte layer of a solid electrolytic capacitor according to the present invention includes a method for forming an electrolyte layer of a solid electrolytic capacitor, in which a dielectric material is formed on the surface of a porous body having an anode lead wire made of a valve metal. After impregnating the electrode body on which the oxide film has been formed with a manganese nitrate solution and adhering it to the surface, this is heated at 120°C to 180°C to cause a thermal decomposition reaction in a part of the manganese nitrate solution, and half of the manganese nitrate solution is heated. A solid viscous substance is produced, and then the viscous substance is immersed in an electrolyte powder bath to deposit powdered electrolyte on the surface of the viscous substance, followed by thermal decomposition.

Effect: According to the above-described formation method, it is possible to extremely easily form a solid, uniform powdery electrolyte layer of a constant thickness on the surface of the electrode body. In other words, since the surface of the polarized body is made of a viscous substance, even if powdered electrolyte is attached, it will not ooze out to the surface due to capillary action, and will only adhere to the surface of the viscous substance. Therefore, a uniform powdery electrolyte layer with a certain thickness can be formed.

Moreover, there is no need to sprinkle or spray.
Uniform adhesion can be achieved simply by dipping into an electrolyte powder bath. It was a residue. Since it is attached to a viscous substance, strong adhesion can be achieved. By thermally decomposing this, a uniform electrolyte layer with a constant thickness can be easily formed.

Embodiments Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. FIG. 1 shows a model diagram of a state in which manganese dioxide powder serving as an electrolyte is attached to an electrode body of a solid electrolytic capacitor according to an embodiment of the present invention. First, the anode lead wire 1 is made of a tantalum metal which is a valve metal.
After connecting the tantalum porous material of MM to the stainless steel plate 2 at the anode lead wire 1, a voltage of 116 V is applied to this surface by a general anodizing method to form a dielectric oxide film 3.
was formed to constitute the electrode body 4. Then, this electrode body 4 was immersed in a manganese nitrate solution with a specific gravity of 1.20 in a general manner to impregnate it, and after adding sufficient liquid to the surface, the temperature was increased to 260°C.
The process of pyrolysis for 6 minutes was repeated twice. Next, this electrode body 4 was immersed in a manganese nitrate solution with a specific gravity of 1.60 and pulled up, and then heated in an atmosphere of 160°C for 10 minutes to remove the water contained therein and thermally decompose it into a part of the manganese nitrate solution. The reaction was caused to produce a semi-solid viscous substance 6.

In this case, the generated semi-solid viscous substance 6 may have irregularities, so in such a case, the surface can be made smooth by blowing it off with air.

In addition, since the semi-solid viscous substance 5 has strong heat absorbing properties,
When taken out of an atmosphere at 150°C and exposed to the atmosphere, it absorbs moisture in the air within a few seconds to several tens of seconds, becoming less viscous and becoming more adhesive with manganese dioxide powder, resulting in a semi-solid viscous state. After producing the cold substance 6, it may be allowed to stand at room temperature for 10 seconds or more.

The semi-solid viscous substance 6 is heated at an ambient temperature of 1
It cannot be obtained at temperatures below 00°C, and if it exceeds 180°C, it will completely decompose and become solid.
It can be carried out within the range of 0°C, but it can be carried out at 120°C to 180°C.
℃ range is most desirable.

Thereafter, the electrode body 4 on which the semi-solid viscous substance 6 had been generated was immersed in an electrolyte powder tank filled with r-manganese dioxide powder having a particle size of 30 to 80 μ9 so that the electrode body 4 was buried. Excess manganese dioxide powder particles clinging to the surfaces of the anode lead-out wire 1 and the electrode body 4 were shaken off by applying vibration to form a manganese dioxide powder particle layer 6 on the surfaces.

According to the above-mentioned forming method, since the adhesive force is strong,
Even if a slight vibration is applied, the manganese dioxide powder attached to the semi-solid viscous substance 6 will not fall off. Further, it is preferable that the manganese dioxide powder is sufficiently dehydrated and has good fluidity. This is to prevent excess manganese dioxide powder particles from sticking to the manganese dioxide powder adhering to the surfaces of the anode lead wire 1 and the electrode body 4. This is because the material easily adheres to the semi-solid viscous substance 6. Further, it is preferable that the manganese dioxide powder has a uniform particle size of about 40 μm to 6 μm. This is because it is desirable that the particles have a particle size that can ensure the thickness of the manganese dioxide powder particle layer e necessary to ensure the withstand voltage of the capacitor.

In addition, when the particle size of manganese dioxide powder is as small as 10 μm, the voids between the particles are small, so they are easily pushed up by water vapor and nitrogen oxide gas generated during the boiling phenomenon during thermal decomposition9, and adhesion. Since the uniform manganese dioxide powder particle layer 6 is destroyed, the average particle size is 10μ.
Wind or higher is preferable. In this case, as the particle size increases, the particles become heavier and uniform adsorption becomes more difficult.

It was experimentally confirmed that a wind of 100μ or less is desirable.

On the other hand, when trying to firmly adhere heavy, large particles of 100 microns or more, it is essential to adhere to a viscous substance.

In addition to the manganese dioxide powder shown in the example, as the powdered electrolyte to be attached to the semi-solid viscous substance-i5,
Similar effects can be obtained by using particles such as manganese hydroxide powder and lead dioxide.

After forming the manganese dioxide powder particle layer 6, it was pulled and then thermally decomposed for 6 minutes in an electric furnace at 260°C. Thereafter, the manganese dioxide powder particle layer 6 is further immersed in a manganese nitrate solution with a specific gravity of 1.40 and subjected to thermal decomposition at 260° C. for 6 minutes, which is repeated twice to form an electrolyte layer.
completed the formation of.

Next, a carbon layer and a silver paint layer are sequentially laminated on this manganese dioxide powder particle layer 6, and an anode terminal is connected to the anode lead wire 1, a cathode terminal is connected to the silver paint layer, and then a resin exterior is formed. A 35 V 6.8 μF solid electrolytic capacitor was completed by applying the following steps.

Table 1 shows the measurement results of process defect rate and withstand voltage.

Table 1 and Table 2 show the results of short circuit failures in high temperature load tests and failures in moisture resistance tests (r/nr: number of failures n:
number of trials).

As is clear from Tables 1 and 2 above, according to the method of the present invention, the yield b can be improved, and the short circuit failure rate in the high temperature load test and the failure rate in the moisture resistance test can be reduced. This resulted in improvements in quality that could not be obtained with conventional methods, such as smaller variations in withstand voltage.

Effects of the Invention As is clear from the description of the above embodiments, the method for forming an electrolyte layer of a solid oxide capacitor of the present invention has the following excellent effects.

O) Since a uniform powder electrolyte layer of a constant thickness can be extremely easily formed on the surface of the electrode body, trouble μ in the process can be largely eliminated and productivity can be improved.

@) Since an electrolyte layer of the required thickness can be formed with a small number of thermal decomposition cycles, the process can be shortened.

rs) Since it is possible to form an electrolyte layer of the required thickness using a manganese nitrate solution with a lower concentration (lower specific gravity) than before, it becomes very easy to control the concentration of the solution.

(4) Since it is possible to form a uniform powder electrolyte layer with a certain thickness on the surface of the electrode body, it is possible to improve yield, as well as short-circuit failure rate in high-temperature load trial production and moisture resistance tests. It is possible to improve the failure rate of capacitors, and as a result, the quality of capacitors can be significantly improved, such as by reducing variations in withstand voltage.

[Brief explanation of drawings]

FIG. 1 is a model diagram of a solid electrolytic capacitor according to an embodiment of the present invention in which manganese dioxide powder serving as an electrolyte is attached to an electrode body. 1...Anode lead wire, 3...Dielectric oxide film, 4...'electrode body, 5...Semi-solid viscous substance , 6... Manganese dioxide powder particles 4 (electrolyte layer).

Claims (3)

[Claims] (1) An electrode body with a dielectric oxide film formed on the surface of a porous body having an anode lead wire made of a valve metal is impregnated with a manganese nitrate solution and attached to the surface, and then heated at 120°C to A part of the manganese nitrate solution is heated at 180°C to cause a thermal decomposition reaction to produce a semi-solid viscous substance, and then immersed in an electrolyte powder bath to form powder on the surface of the viscous substance. 1. A method for forming an electrolyte layer of a solid electrolytic capacitor, the method comprising depositing an electrolyte of 100% or less on the solid electrolytic capacitor, and then thermally decomposing a manganese nitrate solution. (2) After impregnating an electrode body with a dielectric oxide film formed on the surface of a porous body having an anode lead wire made of a valve metal and adhering it to the surface of the manganese nitrate solution, the electrode body is heated at 120°C to A part of the manganese nitrate solution is heated at 180°C to cause a thermal decomposition reaction to produce a semi-solid viscous substance, and then allowed to absorb moisture at room temperature for 10 seconds or more to reduce its viscosity. A method for forming an electrolyte layer of a solid electrolytic capacitor, comprising: thereafter immersing the substance in an electrolyte powder bath to deposit a powdered electrolyte on the surface of the low-viscosity substance. (3) The method for forming an electrolyte layer of a solid electrolytic capacitor according to claim 1 or 2, wherein the powdered electrolyte is manganese dioxide powder.