JPH0369168B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD This invention relates to a method of etching aluminum foil for electrodes of electrolytic capacitors. BACKGROUND OF THE INVENTION Aluminum foils for electrodes of electrolytic capacitors are 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 aluminum foil is generally enlarged by electrochemical or chemical etching treatment, and etching holes are also formed to increase the area enlargement ratio as much as possible. Various studies have been conducted on making the area larger, deeper, and thicker. Problems to be Solved by the Invention However, in practice, in conventionally known etching techniques, in general, when attempting to increase the number of etching holes, the surface of the aluminum foil progresses at the same time, which not only impairs the mechanical strength of the foil. Since the etching holes are not deep, there is a problem in that it is difficult to obtain the expected effect of increasing the area enlargement ratio. This invention solves these problems, allows aluminum foil to have the necessary mechanical strength, and allows etching to be as large and deep as possible, resulting in an excellent surface area ratio, that is, capacitance. The present invention is intended to provide a possible etching method. Means for Solving the Problems For the above purpose, as a result of various experiments and research, the present invention has been made by adding a predetermined amount of a specific acid or a salt thereof that is adsorbent to aluminum into a solution containing chlorine ions. Using etching solution,
This was accomplished by discovering that the area enlargement ratio could be dramatically increased by performing etching treatment in this solution. Therefore, the method of etching aluminum foil for electrolytic capacitor electrodes according to the present invention uses hydrochloric acid 2 to 15
%, and at least one corrosion inhibitor consisting of vanadate, zirconate, molybdic acid, tungstic acid, polyphosphoric acid, nitrous acid, titanic acid, or a salt thereof, which is adsorbent to aluminum.
The etching process is performed in an aqueous solution containing 0.01 to 20% of the etching process. If the concentration of hydrochloric acid in the etching solution is less than 2%, the desired etching effect cannot be obtained;
If it exceeds 15%, the entire surface of the aluminum foil will be completely dissolved, the strength of the foil will deteriorate, and a good etching effect cannot be obtained. Therefore, the concentration should most preferably be in the range of about 5 to 8% within the above range. Corrosion inhibitors added to etching solutions containing hydrochloric acid are effective in suppressing surface dissolution of aluminum foil and forming many and deep etching holes, and are adsorbent to aluminum. Acids or their salts are used. Specific examples of this corrosion inhibitor include vanadic acid, zirconic acid, molybdic acid, tungstic acid, polyphosphoric acid, nitrous acid, titanic acid, and salts thereof. Alternatively, the above effects can be achieved by adding two or more kinds. The concentration of corrosion inhibitor in the etching solution is
If it is less than 0.1%, it will not have the above-mentioned effect, that is, the effect of suppressing dissolution on the foil surface, and if it exceeds 20%, it will not be possible to form a uniform adsorption layer or film on the foil surface and form many etching nuclei. . Therefore, it is preferable that the concentration is within the above range, particularly within the range of about 0.5 to 7.0%. It goes without saying that the etching effect is affected not only by the composition of the etching solution mentioned above, but also by the solution temperature, current density, amount of electricity, etc., but these etching processing conditions are all different from conventionally known methods. It may be carried out within the following suitable range. Just to be sure, their specific scope is as follows. First, if the liquid temperature is less than 60°C, the etching effect will be small, and if it exceeds 95°C, the entire surface will dissolve. Therefore, the temperature is preferably in the range of 60 to 95°C, particularly preferably in the range of 70 to 90°C. On the other hand, if the current density is less than 5A/ ^dm2 , the etching effect will be poor;
When it exceeds 40 A/dm ² , total melting occurs. Within this range, it should therefore particularly preferably be between 10 and 25 A/dm ² . In addition, the amount of electricity is preferably in the range of 500 to 3000 coulombs/ ^dm2 , especially 1500 to 2000 coulombs/dm2.
A range of m ² is optimal. i.e. 500 coulombs/d
If it is less than 3000 coulombs/dm ² , the etching effect will be small, and if it exceeds 3000 coulombs/dm ² , complete dissolution will proceed. By performing etching in an etching solution having the above-mentioned liquid composition under such processing conditions, an adsorption layer or film of the corrosion inhibitor is formed on the surface of the aluminum foil, thereby suppressing the entire surface dissolution of the aluminum foil. On the other hand, only the portion of the etched hole formed is intensively eroded to form a deep and thick etched hole. Moreover, the density of etched holes, that is, the number per unit area, is also significantly increased compared to the case of conventionally known etching methods. The reason for this is not clear, but the adsorption layer or film of the corrosion inhibitor formed on the aluminum foil surface is not uniform and has many defects or weak adsorption areas. This is thought to be due to the formation of many etching holes as etching nuclei. Effects of the Invention Therefore, according to the implementation of the present invention, melting of the aluminum foil surface can be suppressed. Etching holes can be formed to be large, deep, and wide, resulting in a high area expansion ratio.As a result, electrodes with extremely large capacitance and excellent electrical characteristics can be obtained without compromising mechanical strength. It is possible to obtain aluminum foil. Note that the present invention may be implemented by carrying out this step as a first-stage etching step, and then performing a separate second-stage etching step. That is, after the first-stage etching process according to the present invention, a second-stage etching process is performed in an etching solution containing hydrochloric acid or hydrochloric acid and an oxidizing acid such as oxalic acid or phosphoric acid, thereby further eliminating the etching holes formed in the previous stage. It is also good to make it thick and deep. Examples of the present invention will be shown below along with comparative examples. Example Annealed aluminum foil with a purity of 99.99% and a thickness of 0.1 mm was used as a test sample, and etched using various etching solution compositions and processing conditions shown in Table 1 below.

[Table] After each of the etched foils obtained above was chemically converted to 230V in a boric acid aqueous solution, their capacitance was
and tensile strength were measured. The results were as shown in Table 2 below.

【table】

[Table] As is clear from the results in Table 2, compared to the comparative example in which etching was performed in an etching solution without the addition of a corrosion inhibitor, the example of the present invention has a relatively lower mechanical strength. It was possible to obtain an etched foil having excellent electrical performance and even more excellent electrical performance in terms of capacitance.

Claims (1)

[Scope of Claims] 1. Corrosion inhibitor consisting of 2 to 15% hydrochloric acid and vanadate, zirconate, molybdic acid, tungstic acid, polyphosphoric acid, nitrous acid, titanic acid, or their salts, which are adsorbent to aluminum. 1. A method for etching aluminum foil for electrolytic capacitor electrodes, the method comprising performing electrolytic etching treatment in an aqueous solution containing 0.01 to 20% of at least one of the above agents. 2. The method of etching aluminum foil for electrolytic capacitor electrodes according to claim 1, wherein the electrolytic etching treatment is carried out at a liquid temperature of 60 to 90° C. and a current density of 5 to 40 A/dm ² .