JPS6386878A - Production of aluminum foil for electrode of electrolytic capacitor - Google Patents

Abstract

PURPOSE:To inhibit the reaction of the surface of rolled Al foil with moisture and acid and to prevent the deterioration of the etchability with the lapse of time by bringing the Al foil as an electrode material for an electrolytic capacitor into contact with an aq. soln. contg. a specified acid or a compd. thereof to adsorb ions of the acid or compd. and by annealing the foil. CONSTITUTION:High purity Al foil rolled to 0.1mm thickness as an electrode material for an electrolytic capacitor is cleaned with alkali, washed with water and dried. The Al foil is brought into contact with an aq. soln. contg. 5-10,000ppm one or more kinds of acids or compds. selected among vanadic acid, nitric acid, phosphoric acid, silicic acid, chromic acid and compds. of the acids at 10-70 deg.C by dipping or showering and then the Al foil is annealed. Since ions of the acids or compds. are adsorbed on the surface of the Al foil, the reaction of the surface of the foil with moisture and acid is inhibited and the deterioration of the etchability with the lapse of time can be prevented, so the surface area of the foil as an electrode for an electrolytic capacitor is well increased even after storage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a method for manufacturing aluminum foil for electrolytic capacitor electrodes, in particular a method for preventing deterioration of the etching properties of the aluminum foil over time, and also for improving expansion by etching. The present invention relates to a method of manufacturing aluminum foil that can further increase the area ratio.

BACKGROUND OF THE INVENTION Aluminum foil used as an aluminum electrode material for electrolytic capacitors is required to have as large a surface area as possible and a large capacitance per unit volume. For this reason, the effective surface area of the aluminum foil is generally expanded by electrochemical or chemical etching treatment, and etching holes are also added to increase the area expansion ratio as much as possible. There is also very tight control over the stone manufacturing process, as well as tight control over the composition of the material and the etching method to make it thicker, deeper and thicker.

Problems to be Solved by the Invention However, even if a high-quality aluminum foil electrode material is manufactured under strict manufacturing conditions, if it is stored for a long time after manufacturing and then subjected to etching, the initial etching characteristics will deteriorate. A phenomenon of deterioration may be observed. In particular, when stored under abnormally high temperature and high humidity, a phenomenon in which the etching properties deteriorate considerably is observed.

In recognition of the above phenomenon, this invention maintains aluminum foil for electrolytic capacitor electrodes stably against changes in the storage environment, maintains high performance over a long period of time, and furthermore The purpose is to further increase the capacitance.

Means for Solving the Problems The inventors have conducted various studies into the causes of the deterioration of etching properties due to storage as described above, and have found that the surface of aluminum foil is exposed to moisture and oxygen in the storage atmosphere. We found that this is due to the fact that it reacts with and changes due to the influence of the elements.

Based on the above findings, the present invention aims to prevent the surface of aluminum foil from reacting with moisture and oxygen during storage, and in particular, to prevent the surface of aluminum foil from reacting with moisture and oxygen during storage. The purpose is to perform processing.

That is, the present invention is characterized in that the surface of the aluminum foil after foil rolling is subjected to an adsorption treatment in which it is brought into contact with an aqueous solution containing an acid or a compound thereof that is highly adsorbent to aluminum, and then annealing is performed. , the gist of which is a method for manufacturing aluminum foil for electrolytic capacitor electrodes.

The acid contained in the aqueous solution used for the above adsorption treatment may be any acid that exhibits high adsorption to aluminum, and its type is not particularly limited. , silicic acid, chromic acid and their compounds are suitable. Since these acids and their compounds are substantially equivalent in terms of action, 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 acid and compound, but it is effective at 1 ppm or more.

However, from the viewpoint of processing stability and economy, the cost is 5 to 10,000 p.
It is preferable to set it in the range of pm.

A stable treatment effect can be obtained by adjusting the adsorption treatment temperature to a liquid temperature range of 10 to 70°C.

Further, as the adsorption treatment method by contact with an aqueous solution, a method of immersing an aluminum foil in an aqueous solution, a shower treatment method of sprinkling an aqueous solution, etc. are suitably adopted. Although the treatment time varies slightly depending on the treatment method, a sufficient effect can be obtained with a contact treatment time of 30 seconds or less.

Effects of the Invention According to this invention, since an adsorption treatment is performed in which an aqueous solution containing a predetermined acid or its compound is brought into contact with the surface of the aluminum foil after foil rolling, ions of the acid or its compound are adsorbed on the foil surface, and then suppresses reactions with moisture and oxygen on the surface of the foil.

In addition, since annealing is performed after the adsorption treatment, the adsorbed ions are not simply adsorbed, but become a more stable film due to the annealing, which not only maintains better stability against changes in the storage environment, but also improves this stability. The film suppresses the progress of complete dissolution of the foil surface during etching, and as a result, further promotes the effect of increasing the area enlargement ratio by etching.

Therefore, according to the present invention, it is possible to achieve the effects of improving storage suitability, further increasing the area expansion ratio, and further increasing the capacitance.

Example foil After rolling and before annealing, purity 99.99%, thickness 0, 1 m
After the rolled aluminum foil of + is washed with alkaline, washed with water, and dried, it is treated with various treatment solutions having the compositions shown in Table 1 below (liquid temperature;
50°C) for 15 seconds to perform ion adsorption treatment. After that, it was washed with water, dried, and heated for 50 minutes in an inert gas atmosphere.
Final annealing was performed for 1 hour at 0'' CX to obtain various aluminum foils for electrodes according to the present invention.

Both of these were kept in a constant temperature and humidity chamber at a temperature of 50°C and a concentration of 90%, and changes in etching characteristics were examined after 30 days and 60 days. A comparison was made with a conventional product that was not treated. The results are shown in Table 1 below.

The etching test was conducted in a 5% aqueous hydrochloric acid solution at 75° C. by applying a direct current of 10 A/drA2 for 5 minutes. Since the capacitance is determined by the area enlargement ratio after etching, the etching characteristics were evaluated based on the capacitance when converted to 200 V in a 5% boric acid aqueous solution after etching. The numerical value for this evaluation was determined by setting the capacitance of the aluminum foil without surface treatment immediately after final annealing as 100, and calculating the capacitance of other samples as a relative index to that value.

Table 1: Capacitance (Etching Characteristics) As shown in Table 1 above, the aluminum foil manufactured by the method of the present invention has a higher initial capacity after annealing than a conventional product that is not subjected to ion adsorption treatment. Even better than that. It possesses etching properties, and in addition, there is no surface change even when stored under harsh environmental conditions.
It was confirmed that the original etching characteristics were maintained and high capacitance was exhibited.

that's all

Claims (3)

[Claims] (1) An electrolytic capacitor characterized in that the surface of the aluminum foil after foil rolling is subjected to an adsorption treatment in which it is brought into contact with an aqueous solution containing an acid or its compound that is highly adsorbent to aluminum, and then annealed. Method for manufacturing aluminum foil for electrodes. (2) Claims that the acid contained in the aqueous solution used for adsorption treatment is one or more selected from the group consisting of vanadic acid, nitric acid, phosphoric acid, silicic acid, chromic acid, and compounds thereof. 2. The method for producing aluminum foil for electrolytic capacitor electrodes according to item 1. (3) The concentration of the acid or its compound in the aqueous solution is 5
The method for producing an aluminum foil for electrolytic capacitor electrodes according to claim 1 or 2, wherein the content is 10,000 ppm.