JPS6043005B2 - Chemical formation method for aluminum electrodes for electrolytic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the chemical conversion method by anodic oxidation of the electrode, which is also important in the manufacturing process of aluminum electrode capacitors.

Aluminum for electrodes of aluminum electrode capacitors is usually coated with an oxide film on its surface by anodic oxidation in an aqueous solution of an organic acid such as boric acid, phosphoric acid, or adipic acid, or a salt thereof.

This process is called chemical formation, and when assembled into a capacitor element, the oxide film formed by chemical formation comes into contact with the driving electrolyte and acts as a dielectric. A particular problem in terms of the performance of aluminum electrolytic capacitors is the deterioration of the oxide film described above, which is caused by the reaction between the oxide film and the driving electrolyte in contact with it.

That is, the driving electrolyte gradually destroys the oxide film formed by chemical formation and deteriorates its voltage resistance.

This deterioration is unlikely to occur when voltage is applied, but the rate of deterioration increases when left unloaded, especially when left unloaded at high temperatures, and as a result of this deterioration, leakage occurs when voltage is applied. The current increases, and there is a risk of destruction, especially if the device is left unused for a long period of time. Recently, etched aluminum foil with high area magnification has been used for aluminum electrolytic capacitors, and low loss is also required.

For this reason, it has become unavoidable to use a driving electrolyte with high activity. Therefore, the above-mentioned problem of deterioration is extremely serious, and there is an urgent need in the industry for a chemical formation method that produces a strong oxide film that is less likely to deteriorate. In view of the above points, the present invention has been developed by incorporating a certain compound when chemically converting aluminum to form an oxide film, so that the above-mentioned deterioration can be extremely reduced and compared to the case of a conventional chemical conversion bath at the same withstand voltage. The purpose of this paper is to provide a method for obtaining a high-quality withstand voltage film with a large capacitance compared to that of a cycloaliphatic unsaturated compound. An electrolytic solution containing at least one type of organic acid or its salt having two carboxyl groups and having one or two double bonds in a six-membered ring or three in a seven-membered ring is used. This method is characterized in that aluminum is chemically converted by anodic oxidation. In the present invention, among alicyclic unsaturated compounds, the organic compound having two carboxyl groups (dicarboxylic acid) and the number of carbon atoms in the cyclic structure is limited to 6 to 7. less than 6 (e.g. cyclopentene, cyclopentadiene dicarboxylic acid)
It is thought that there is a good possibility that it has the same properties as those with 6 or 7 carbon atoms, but unfortunately, it has 6 or 7 carbon atoms.
If the sample is less than 100%, a large amount of halogen, which has a strong oxide film deterioration property, is retained as an impurity during the manufacturing process, and it is difficult to remove the halogen. This is due to circumstances in which the intended effects of the present invention could not be confirmed in the current situation.

Alicyclic unsaturated compounds having a cyclic structure with 6 to 7 carbon atoms include dicarboxylic acid-based organic compounds such as cyclohexene, cyclohexadiene, and cycloheptatriene, that is, anhydrous-cyclohexene-1,2-dicarboxylic acid. 3,5-cyclohexadiene-1,2-dicarboxylic anhydride 1,3,
There are 6-cycloheptatriene-1,2-dilbonic acids, etc., and all of them have been recognized to have effective effects, but in the case of industrialization, cyclohexene dicarboxylic acid Acid-based compounds are best.

There are two ways in which such compounds can be used in electrolytes.

One method is to dissolve the above compound in water, adjust the pH value with an alkali such as ammonia, and use it as an electrolyte for chemical formation. This method involves mixing it with an electrolyte. According to experiments, the amount of dicarboxylic acid compounds in the electrolyte is 0.0
Favorable results are obtained in the range of 1 to 1% by weight; if the concentration is too low, the effect will be small, and if the concentration is too high, crystal precipitation will occur, making it difficult to use.

The reason why the electrolytic solution containing the dicarboxylic acid compound in the present invention is particularly suitable for obtaining a high-quality oxide film compared to other electrolytes is not clear, but it is probably due to its good deterioration resistance and capacitance. Judging from the fact that an increase in It is presumed that this is due to the formation of a dense voltage-resistant film.

Examples of the present invention will be described below, and a comparison with a conventional case will be shown below. Example 1 1 Electrolytic capacitor according to the present invention An electrolytic solution in which cyclohexenedicarboxylic acid anhydride 4y was dissolved in pure water 1e and the pH value was adjusted to 6.8 with aqueous ammonia was raised to 70'C. A commercially available etched aluminum foil was chemically converted by applying a DC voltage of 62V,
Anode foil made by this (anode foil size 14 pieces x 27
0Tf0n) and a commercially available etched aluminum foil for cathodes were rolled up through a commercially available separator paper, impregnated with a commonly used driving electrolyte to assemble the required electrolytic capacitor, and then aged at 85°C for 8 hours. .

2 The electrolytic solution used in the conventional method is an electrolytic solution in which 1.5y of ammonium hydrogen phosphate is dissolved in pure water 1e (this electrolytic solution is said to give the best results in the conventional method).
After assembling an electrolytic capacitor under the same conditions as in Section 1 above, the capacitor was aged at 85° C. and an applied voltage of 58 V for 8 hours.

As is clear from the above results, it is understood that the rate of change in capacitance and the deterioration of leakage current are more stable than in the conventional method, similar to Examples 1 and 2.

Furthermore, the aging time performed by applying a voltage to the completed capacitor was reduced to 114 in Examples 1 and 2.1'3 The capacitance and leakage current of the electrolytic capacitors in Items 1 and 2 above were measured at 20°C, respectively. Then, it was left unloaded for 500 hours in a constant temperature bath at 85°C. Next, after leaving it at 20℃ for 4 hours, a DC voltage of 50V was applied.
The leakage current and capacitance after 1 minute were measured. The results are as follows. As is clear from the above results, the capacitance of the electrolytic capacitor according to the present invention is approximately 7.5% larger than that of the electrolytic capacitor according to the conventional method.
Changes caused by leaving the device unloaded are as follows: -3, 2 when using the conventional method
%, whereas in the case of the present invention it is -1.1%, which means that the change in capacitance is small, and the increase in leakage current is also significantly smaller in the case of the present invention.

Example The chemical formation voltage in Example 1 was changed from 62V to 15V, and the composition of the electrolytic solution was changed by dissolving 2.5y of cycloheptatriene dicarboxylic acid anhydride in pure water 1e, and adjusting the pH value to 6 with ammonia water. The other conditions were the same as in Example 1, and the capacitance and leakage current were measured before and after being left unloaded.

However, the aging voltage is 11.5V, and the measurement voltage is 1
It is 0V. The results are as follows. As is clear from the above results, it is understood that in the case of the present invention, a larger capacitance can be obtained, the rate of change before and after being left unloaded is smaller, and the increase in leakage current is also significantly smaller.

Example ■ For chemical conversion at the same chemical formation voltage as in Example ■, that is, a DC voltage of 15 V, 3.5y of cyclohexadiene cicarboxylic acid was dissolved in pure water 1e as an electrolyte, and the pH value was adjusted to 6.5 with aqueous ammonia. Adjust other conditions to the above example ■
As in the case of , the capacitance and leakage current were measured before and after being left unloaded, and the results are as follows.

Claims (1)

[Claims] 1. Among alicyclic unsaturated compounds, the number of carbon atoms in the cyclic structure is 6 to 7, and the number of double bonds is 1 to 2 in a 6-membered ring, or 3 in a 7-membered ring. and carboxyl group 2
1. A method for chemically forming an aluminum electrode for an electrolytic capacitor, characterized in that aluminum is chemically formed by anodic oxidation using an electrolytic solution containing at least one type of an organic acid or a salt thereof. 2 The content of the compound described in claim 1 is 0
．． 1. A method for chemically forming aluminum electrodes for electrolytic capacitors, characterized in that an electrical liquid having a concentration of 0.01 to 10% by weight is used. 3. A method for chemically forming an aluminum electrode for an electrolytic capacitor, characterized in that the pH value of the electrolytic solution according to claim 1 or 2 is set to 4 to 8.