JPS6332247B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides improved rated voltage reconstitution methods.
This article relates to a method for manufacturing tantalum solid electrolytic capacitors that exceed 20V.DC. In general, tantalum solid electrolytic capacitors are formed by forming an anodized film on a tantalum sintered body, and sequentially laminating a manganese dioxide layer, a graphite layer, and a conductive layer on the surface of the tantalum solid electrolytic capacitor. When forming a tantalum sintered body with an anodic oxide film formed thereon, the tantalum sintered body is immersed in a manganese nitrate aqueous solution, the sintered body is impregnated with the manganese nitrate aqueous solution, and then taken out and placed in a high-temperature atmosphere such as an electric furnace. Decomposed by heating. In order to repair the anodic oxide film that has deteriorated due to this thermal decomposition, re-forming is performed, and this operation of impregnation, thermal decomposition and re-forming is repeated several to ten times to form a manganese dioxide layer, and the anodized film is The membrane is being repaired.
The electrolytic solution used for the reconstitution is disclosed in, for example, JP-A-57-
As described in Publication No. 21811, phosphoric acid is usually used extensively, but since a part of phosphoric acid remains in the manganese dioxide layer, the resistance value of manganese dioxide is greatly influenced by the thermal decomposition temperature, and the first As shown in the curve A shown in the figure, the minimum value is shown at a temperature around 400°C.
On the other hand, when an aqueous solution such as nitric acid or acetic acid that does not oxidize into the manganese dioxide layer is used as a reconstitution electrolyte, the resistance value of manganese dioxide remains almost constant as shown in curve B shown in Figure 1 depending on the thermal decomposition temperature. , and the resistance value itself is small. However, tantalum solid electrolytic capacitors using nitric acid, acetic acid, or the like as a reconstituted electrolyte have the drawbacks of low capacitance at the same volume and large leakage current. In addition, Japanese Patent Publication No. 45-620 states that the same aqueous solution is used for both primary and secondary anodization;
and sodium nitrate as the molten salt of the first anodization,
A technique has been disclosed that uses potassium nitrate and ammonium nitrate, ammonium borate, and ammonium acetate as aqueous solutions for secondary anodization, but when these reconstitution solutions are used, good characteristics are not achieved at rated voltages of 20 V or less. However, when the voltage exceeds 20V, the capacitance, loss, leakage current, and capacitance change rate are poor. The present invention eliminates the above-mentioned drawbacks by:
Li ₂ SO ₄ , Na ₂ SO ₄ , K ₂ SO ₄ , which has excellent chemical forming properties as a reconversion electrolyte and whose boiling point is higher than the thermal decomposition temperature of manganese nitrate and remains in the manganese dioxide layer as a solid.
_MgSO4 , _CaSO4 , _NaHSO4 , _KHSO4 ,
One or two of (NH ₄ ) ₂ SO ₄ and (NH ₄ )HSO ₄
A method for manufacturing a tantalum solid electrolytic capacitor that increases capacitance, reduces loss and leakage current, and has excellent frequency and temperature characteristics by using a 0.005 to 1% by weight aqueous solution containing a solute or more as a solute. This is what we intend to provide. The details of the present invention will be explained below. That is,
An anodic oxide film is formed on a tantalum sintered body made of tantalum metal powder, immersed in an aqueous solution of manganese nitrate to impregnate the tantalum sintered body, taken out, and thermally decomposed in a high temperature atmosphere to remove the anodized film. Forms a manganese dioxide layer on the surface. Therefore, rechemical formation is performed to repair the anodic oxide film that has deteriorated in the thermal decomposition process, and as mentioned above, this rechemical formation repairs the anodic oxide film that has deteriorated due to the thermal decomposition of manganese nitrate. In addition to the role of chemical conversion, the solute in the reconversion electrolyte also acts as a binder that brings the anodic oxide film and the manganese dioxide layer into close contact.
and has a boiling point higher than the thermal decomposition temperature of the manganese nitrate and remains in the manganese dioxide layer as a solid.
Li ₂ SO ₄ , Na ₂ SO ₄ , K ₂ SO ₄ , MgSO ₄ , CaSO ₄ ,
NaHSO ₄ , KHSO ₄ , (NH ₄ ) ₂ SO ₄ , (NH ₄ )
One or more types of HSO ₄ are used as solutes
Reconstitution is carried out using a 0.005 to 1% by weight aqueous solution. In the reconstitution step, the operations of impregnation in the aqueous manganese nitrate solution, thermal decomposition, and reconstitution are repeated several times to more than ten times. The alkali metal salt, alkaline earth metal salt, or ammonium salt of sulfuric acid used as the reconstitution electrolyte has excellent chemical formation properties and has a boiling point higher than the thermal decomposition temperature of manganese nitrate, remaining as a solid in the manganese dioxide layer and having a low It has low resistance. In this way, the operations of impregnation, thermal decomposition, and reconstitution are repeated to form a manganese dioxide layer and repair the anodic oxide film, and then a graphite layer and a conductive layer are sequentially laminated and formed. For example, a solid electrolytic capacitor is constructed by storing the capacitor in a container or by covering it with a resin coating or the like. As described above, the present invention provides an alkali metal salt or alkaline earth metal salt of sulfuric acid that has excellent chemical forming properties as a re-forming electrolyte, has a boiling point higher than the thermal decomposition temperature of manganese nitrate, and remains in the manganese dioxide layer as a solid. Alternatively, by using ammonium salt, capacitance can be increased and loss and leakage current can be reduced.
Moreover, a tantalum solid electrolytic capacitor with excellent frequency characteristics and temperature characteristics can be obtained. FIG. 2 shows the change in leakage current of a tantalum solid electrolytic capacitor with a rating of 35 V.DC-47 μF when the concentration of the alkali metal salt, alkaline earth metal salt, or ammonium salt of sulfuric acid as the reconstituted electrolyte is changed.
In Figure 2, curve 1 is when an ammonium hydrogen sulfate aqueous solution is used, curve 2 is when a potassium hydrogen sulfate aqueous solution is used, and curve 3 is the primary anode shown in the table on page 2 of Japanese Patent Publication No. 45-620. This is a case where a mixed aqueous solution of oxidized potassium nitrate + sodium nitrate is used, but since the rating is 35V.DC, curve 3 has the largest leakage current value, and curves 1 and 2 have a leakage current value of 0.005 to 1.
Good results were obtained in the range of % by weight. Next, an example of comparison of characteristics between an example of the present invention and a conventional reference example will be shown. A tantalum sintered body is anodized in an aqueous phosphoric acid solution to form an anodic oxide film.
Thereafter, the impregnated tantalum sintered body is immersed in an aqueous manganese nitrate solution with a specific gravity of 1.70, and the impregnated tantalum sintered body is thermally decomposed at a temperature of 300°C to form a manganese dioxide layer. In order to repair the anodic oxide film deteriorated by the thermal decomposition, reconversion is performed using the reconversion electrolyte shown in Table 1.

[Table] This operation of impregnation, thermal decomposition, and reconstitution was repeated six times each. Example 1, Reference Example 2, Reference Example 3, and Reference Example 4 obtained by such a manufacturing method
Figures 3 to 7 show a comparison of the characteristics of tantalum solid electrolytic capacitors (all rated voltage 35V.DC). In other words, FIG. 3 shows the average value and variation of capacitance obtained using tantalum sintered bodies of the same size and shape, and the capacitance of Example 1 is larger than that of Example 1. is the smallest, followed by Reference Example 2, but it can be seen that Reference Example 3 and Reference Example 4 have significant variations compared to these. FIG. 4 shows the change in loss corresponding to temperature, and it can be seen that Example 1 and Reference Example 2 have a small loss and little change, but Example 1 has a small value. Figure 5 shows the change in leakage current corresponding to temperature and its dispersion. Example 1 and Reference Example 2 have small values and small variations, but especially Example 1 has a small absolute value. . FIG. 6 shows the change in impedance corresponding to frequency, and compared to Reference Examples 3 and 4, Example 1,
In Reference Example 2, the value is small and there is little change. FIG. 7 shows the change in capacitance corresponding to frequency, and it can be seen that the change in Example 1 is significantly smaller than that in Reference Example 2, Reference Example 3, and Reference Example 4. Therefore, it can be seen that in all properties, Example 1 is better than Reference Examples 2, 3, and 4, and exhibits stable properties with less variation. According to the inventor's experiments, using the potassium nitrate aqueous solution used in Reference Example 2 as a reconversion liquid exhibits the same characteristic values as ammonium hydrogen sulfate at a rated voltage of 20 V.DC or lower, but the rated voltage of the above example
If it exceeds 20V.DC, such as 35V.DC, it shows properties inferior to ammonium hydrogen sulfate and is not suitable. In addition, although the case where an aqueous ammonium hydrogen sulfate solution was used was described in the example, Li ₂ SO ₄ ,
Na ₂ SO ₄ , K ₂ SO ₄ , MgSO ₄ , CaSO ₄ , NaHSO ₄ ,
A similar effect can be obtained with a 0.005 to 1% by weight aqueous solution containing one or more of KHSO ₄ and (NH ₄ ) ₂ SO ₄ as a solute. As detailed above, according to the present invention, the alkali metal salt of sulfuric acid, which has excellent chemical forming properties as a re-forming electrolytic solution and whose boiling point is higher than the thermal decomposition temperature of manganese nitrate and remains in the manganese dioxide layer as a solid, By using an aqueous solution consisting of earth metal salts or ammonium salts, the capacitance can be increased, loss,
It is possible to provide a method for manufacturing a tantalum solid electrolytic capacitor with reduced leakage current and excellent frequency characteristics and temperature characteristics.

[Brief explanation of the drawing]

Figure 1 is a curve diagram showing the change in the resistance value of manganese dioxide corresponding to the thermal decomposition temperature when the reconversion electrolyte is changed, and Figure 2 is a curve diagram showing the change in leakage current corresponding to the concentration of the reconversion electrolyte. Curve diagrams, Figures 3 to 7
Each figure shows a comparison of the characteristics of tantalum solid electrolytic capacitors according to an embodiment of the present invention and a conventional reference example. Characteristic diagram showing the variation, Figure 4 is a curve diagram showing the change in loss corresponding to temperature, Figure 5 is a curve diagram showing the change in leakage current and variation in response to temperature, Figure 6 is a curve diagram showing the change in leakage current corresponding to temperature, and Figure 6 is the impedance diagram corresponding to frequency. FIG. 7 is a curve diagram showing changes in capacitance corresponding to frequency.

Claims (1)

[Claims] 1 After forming an anodized film on a tantalum sintered body, it is impregnated with a manganese nitrate aqueous solution and thermally decomposed to form a manganese dioxide layer on the surface of the anodic oxide film, and then the anodic oxide film deteriorated in the thermal decomposition step is removed. Lithium sulfate, sodium sulfate,
One of potassium sulfate, magnesium sulfate, calcium sulfate, sodium hydrogen sulfate, potassium hydrogen sulfate, ammonium sulfate, ammonium hydrogen sulfate
0.005 to 1% by weight of a species or two or more species as solutes
A method for manufacturing a tantalum solid electrolytic capacitor characterized by using an aqueous solution.