JPH0746674B2 - Method for Preventing Deterioration of Aluminum Foil for Electrolytic Capacitor Electrode - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for aging aluminum foil for electrolytic capacitor electrodes, that is, a method for preventing the etching characteristics of the aluminum foil from aging.

2. Description of the Related Art Aluminum foil used as an aluminum electrode material for electrolytic capacitors is required to have a surface area as large as possible and a large capacitance per unit volume. For this reason, it is generally performed to increase the effective surface area of the aluminum foil by performing an electrochemical or chemical etching process. Further, in order to increase the surface expansion ratio as much as possible, etching holes are formed. Very tight controls are also applied in the manufacturing process of the foil, as well as tight control of the material composition and etching method with respect to making more, deeper and thicker.

The problem to be solved by the invention is that even if a high quality aluminum foil electrode material manufactured under severe manufacturing conditions is etched after being manufactured and stored for a long time, the initial etching characteristics There are cases where the phenomenon of deterioration is seen. Particularly, when it is stored under an abnormally high temperature and high humidity, a phenomenon in which the etching characteristics are considerably deteriorated is observed.

From the recognition of the above phenomenon, the present invention is capable of maintaining a high quality level of the aluminum foil for electrolytic capacitor electrodes after the final annealing for a long period of time, thereby improving storage suitability and performing etching after storage. The purpose is to improve the performance of the electrode material when applied.

Means for Solving the Problems The inventors of the present invention have conducted various studies on the cause of the deterioration phenomenon of the etching characteristics due to the storage as described above. It was found that the change was caused by the influence of.

Thus, the present invention is based on the above knowledge that the surface of the aluminum foil after the final annealing is subjected to a predetermined surface treatment so as to prevent it from reacting with moisture or oxygen. It is a thing.

That is, the present invention, the surface of the aluminum foil after the final annealing is brought into contact with an aqueous solution containing an acid or a compound thereof having a high adsorptivity to aluminum so that the ions of the acid or the compound are adsorbed on the foil surface. A gist of the present invention is a method for preventing deterioration with time of an aluminum foil for an electrolytic capacitor electrode, which is characterized by performing a surface treatment.

The acid contained in the aqueous solution used for the surface treatment is not particularly limited as long as it has high adsorptivity to aluminum, and specifically, vanadic acid, nitric acid, phosphoric acid. , Silicic acid, chromic acid and their compounds can be mentioned as suitable substances. From the viewpoint of action, these acids and their compounds have substantially homogeneity, and thus any one or more of them can be selected and used.

The concentration of the acid and its compound in the aqueous solution varies depending on the type of the acid and the compound, but it is effective at 1 ppm or more. However, it is preferable to set the concentration in the range of 5 to 10,000 ppm from the viewpoint of processing stability and economy.

With respect to the treatment temperature, a stable treatment effect can be obtained when the liquid temperature is in the range of 10 to 70 ° C.

Further, as the contact treatment method of the aqueous solution, a method of immersing the aluminum foil in the aqueous solution, a shower treatment method of sprinkling the aqueous solution, or the like can be suitably adopted. The treatment time is slightly different depending on the treatment method, but a sufficient effect can be obtained with a contact treatment time of 30 seconds or less.

EFFECTS OF THE INVENTION According to the present invention, since the surface treatment is performed in which the aluminum foil surface after the final annealing is brought into contact with an aqueous solution containing a predetermined acid or its compound, the acid of the acid in the aqueous solution or the ion of the compound is adsorbed on the foil surface. , Suppresses the reaction of water and oxygen on the surface of the foil after that. Therefore, the aluminum foil subjected to the surface treatment according to the present invention after finishing the final annealing by the usual manufacturing process does not significantly deteriorate the initial etching characteristics even after being stored for a long period of time, and immediately after the final annealing. It is possible to maintain the high quality performance of, and to improve the storage suitability, and it is possible to obtain the effect of improving the capacitance of the electrode material to be manufactured by using etching after storage.

Example Annealed aluminum foil having a purity of 99.99% and a thickness of 0.1 mm was immersed in various treatment liquids (liquid temperature: 50 ° C.) having the compositions shown in Table 1 below for 15 seconds, and various surface-treated electrodes according to the present invention were applied. The aluminum foil for use was obtained.

All of these were stored in a thermo-hygrostat at a temperature of 50 ° C and a concentration of 90% for 30 days and 60
The changes in the etching characteristics after the lapse of days were examined and compared with the state immediately after the initial annealing and the equivalent to the conventional product which was not surface-treated. The results are shown in Table 1 below.

The etching test was performed for 5 minutes by applying a direct current of 10 A / dm ² in a 5% hydrochloric acid aqueous solution at 75 ° C. Since the electrostatic capacity is determined by the surface area ratio after the etching, the etching characteristics were evaluated by the electrostatic capacity when formed into 200 V in a 5% aqueous boric acid solution after the etching. The numerical value of this evaluation shows the electrostatic capacity of other samples as a relative index with respect to the electrostatic capacity of the aluminum foil which is not subjected to the surface treatment immediately after the final annealing as 100.

As shown in Table 1 above, the aluminum foil for electrodes produced by the production method of the present invention has almost no deterioration in etching characteristics over time due to the storage environment, and can maintain high quality immediately after annealing even after storage. I was able to confirm that there was.

Continuation of front page (56) Reference JP-A-50-159429 (JP, A) JP-A-50-88552 (JP, A) JP-A-60-163426 (JP, A)

Claims (2)

[Claims] 1. The surface of an aluminum foil which has been subjected to final annealing is brought into contact with an aqueous solution containing an acid having high adsorptivity to aluminum or a compound thereof in a concentration range of 5 to 10,000 ppm to obtain the acid or its compound. A method for preventing deterioration with time of an aluminum foil for an electrolytic capacitor electrode, which comprises subjecting a foil surface to surface adsorption. 2. The acid contained in the aqueous solution used for the surface treatment is
The deterioration with time of the aluminum foil for electrolytic capacitor electrodes according to claim 1, comprising one or more selected from the group consisting of vanadic acid, nitric acid, phosphoric acid, silicic acid, chromic acid and compounds thereof. Prevention method.