JP2651931B2 - Aluminum alloy foil for cathode of electrolytic capacitor and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an aluminum alloy foil having excellent etching characteristics and suitable for obtaining an electrolytic capacitor cathode foil exhibiting high capacitance, and a method for producing the same.

[Prior art]

As the foil for the cathode of the electrolytic capacitor, an aluminum alloy foil having a purity of about 99.85% Al and an aluminum alloy foil having a purity of about 99.50% Al to which Cu or Cu and Fe are added have been mainly used. The former is superior in durability to the latter, but has the disadvantage that it is difficult to obtain a material having a high capacitance due to poor etching characteristics. The etching is performed to form fine irregularities on the surface of the aluminum alloy foil, increase the surface area of the foil, and increase the capacitance. The etching process
It is performed in an aqueous solution containing chloride ions. Generally, the higher the chloride ion concentration, the greater the surface area expansion rate of the aluminum alloy foil and the higher the capacitance. But,
If the chloride ion concentration exceeds a certain limit, the dissolution of the aluminum alloy foil surface becomes excessive, resulting in the destruction of fine irregularities formed at the beginning of etching, reducing the surface area, and reducing the capacitance. May also be lower. In order to suppress such excessive dissolution, etching is performed by adding an acid such as sulfuric acid or oxalic acid to an etching solution. However, in the currently used aluminum alloy foil having a purity of 99.85% Al, even if the above-described etching treatment is performed, there is a disadvantage that excessive melting is apt to occur, and it is difficult to obtain a high capacitance.

[Problems to be solved by the invention]

In general, the mechanism of electrochemical dissolution of an aluminum alloy foil in an acidic solution (etching solution) is that an alloy element or an impurity element having an electrode potential higher than the electrode potential of Al is present as a precipitate, Al forms a local cell in which the anode acts as the anode and the precipitate acts as the cathode. Therefore, a current flows from the cathode to the anode, and Al as the anode becomes a cation and dissolves in the acidic solution. And this becomes more remarkable as the number of the cathodes, that is, the number of precipitates whose electrode potential is higher than that of Al is increased. The present inventors believe that this melting mechanism occurs during the etching process of the aluminum alloy foil with 99.85% Al purity, and that excessive melting occurs due to this, and by adding a specific element to the aluminum alloy, As a result, the aluminum alloy foil for the electrolytic capacitor cathode having a purity of about 99.85% Al having excellent etching characteristics was successfully obtained by preventing excessive melting as much as possible.

Means and Action for Solving the Problems

That is, the present invention relates to Si 0.010 to 0.050%, Fe 0.020 to 0.075%.
%, Mg 0.002-0.010%, Zn 0.005-0.012%, Cu 0.003% or less as unavoidable impurities and 0.002% or less of other unavoidable elements, the balance being Al, and the intermetallic compound between Mg and Fe or Si The present invention relates to an aluminum alloy foil for a cathode of an electrolytic capacitor, which is formed, and a method for producing the alloy foil. The composition range of the constituent components of the aluminum alloy foil for an electrolytic capacitor cathode according to the present invention is as follows. In addition, in this invention, all% represent weight%. Si is 0.010 to 0.050%. Si is contained in bauxite, which is a raw material of aluminum. For aluminum that does not go through the purification process of three-layer electrolysis or segregation,
This amount of Si is contained. In order to reduce the content of Si to less than 0.010%, a special aluminum refining step must be performed, which is not preferable because aluminum becomes expensive.
If the Si content exceeds 0.050%, the Al purity decreases, which is not preferable for use as an electrolytic capacitor. Fe is 0.020 to 0.075%. Fe is also included in bauxite. Aluminum that has not been subjected to a purification step such as a three-layer electrolysis method contains such an amount of Fe. In order to make Fe less than 0.020%, a special aluminum refining process must be performed, which is not preferable because aluminum becomes expensive. If Fe exceeds 0.075%, the presence of Fe precipitates cannot be avoided, and this precipitate and Al
And a local battery is formed between them, and Al is excessively dissolved in the etching solution, which is not preferable. Mg is 0.002-0.010%. Mg is not generally contained in bauxite and is a characteristic component in the present invention. Mg forms an intermetallic compound with the above-mentioned Fe and Si, and prevents the formation of a local battery between Fe and Al. Mg has a lower standard electrode potential than Al,
When an intermetallic compound is made with Fe having a higher standard electrode potential than Al, the intermetallic compound has a standard electrode potential close to that of Al. Therefore, the difference in the standard electrode potential between Al and Fe, Si, or the like does not become remarkable, and overdissolution of Al in the etching solution can be prevented. If the Mg content is less than 0.002%, the amount is insufficient to produce an intermetallic compound with Fe or Si, which is not preferable. If Mg exceeds 0.010%, the purity of Al decreases, which is not preferable for use in electrolytic capacitors. Zn is 0.005 to 0.012%. Zn is also generally not contained in bauxite and is a characteristic component in the present invention. Zn dissolves well in Al and improves the strength of the obtained aluminum alloy foil. If Zn is less than 0.005%, the strength of the aluminum alloy foil is not sufficiently improved, which is not preferable. When Zn exceeds 0.012%, the standard electrode potential of Al in which Zn forms a solid solution decreases, the difference between the standard electrode potentials of Al and Fe, etc. increases, and Al is easily dissolved in the etching solution. This is not preferable for use in electrolytic capacitors. In the present invention, unavoidable impurities may be mixed in addition to the above components. Cu is the first inevitable impurity
And its allowable limit is 0.003%. Cu may be contained in bauxite, and aluminum that has not been subjected to a purification process such as a three-layer electrolysis method contains about 0.003% or less of C
u may be included. Some types of bauxite do not contain Cu, in which case Cu is not contained in the aluminum alloy foil. Cu is 0.00
If it exceeds 3%, the Al purity is lowered, which is not preferable for use in electrolytic capacitors. Ti is typically given as an inevitable element other than Cu. This may be contained in the bauxite, and the Ti content of about 0.002% or less
May be included. 0.002 unavoidable elements such as Ti
%, The purity of Al decreases, which is not preferable for use in electrolytic capacitors. Among the unavoidable elements, Ti has a standard electrode potential lower than that of Al and hardly forms a solid solution with Al. Accordingly, an increase in the content results in an increase in the amount of deposited Ti, which is not preferable because a local battery is formed between Al and Ti and Al is excessively dissolved in the etching solution. In the present invention, it is necessary that an intermetallic compound is formed between Mg and Fe or Si. Mg has a lower standard electrode potential than Al and forms an intermetallic compound with Fe or the like having a higher standard electrode potential than Al. This intermetallic compound has a standard electrode potential similar to that of Al. Therefore, the difference in the standard electrode potential between Al and Fe or Si does not become remarkable, and Al
Overdissolution can be prevented. Next, a method for producing the aluminum alloy foil for a cathode of an electrolytic capacitor according to the present invention will be described. The production method according to the present invention comprises: Si 0.010 to 0.050%, Fe 0.02%
0-0.075%, Mg0.002-0.010%, Zn0.005-0.012%, Cu0.003% or less as unavoidable impurities and other unavoidable elements
0.002% or less, the remaining Al ingot is homogenized at a temperature of 500 ° C to 550 ° C for 20 hours or more, and then at a temperature of 400 ° C.
Hot rough rolling under the above conditions, hot finish rolling under the conditions of inlet side temperature 400 ° C or higher, outlet side temperature 250 ° C or lower, time 2 minutes or less, and then cold rolling without intermediate annealing It is characterized by doing. In the present invention, first, before infusing an aluminum base metal and flowing it into a mold, Mg, Zn, or the like is added to produce an ingot having a specific component composition. The reason for setting the specific component composition and the like are as described above. The ingot is homogenized at a temperature of 500 to 550 ° C. for a time of 20 hours or more. The homogenization treatment is performed to uniformly disperse each component in the ingot. Temperature 500
If the temperature is lower than ℃, it is difficult to form an intermetallic compound of Mg and Fe or Si, which is not preferable. In short, it is not preferable because each component element may not be uniformly distributed. When the temperature exceeds 550 ° C., it is not preferable because an intermetallic compound of Mg and Fe or Si is hardly formed. Similarly, when the time is less than 20 hours, it is difficult to form an intermetallic compound of Mg and Fe or Si, which is not preferable. Industrially, about 20 to 25 hours are preferable. After the homogenization treatment, the ingot is subjected to hot rough rolling. Hot rough rolling is performed under the condition of 400 ° C. or higher. 400 ℃
If it is less than 1, Fe or Si may be precipitated, which is not preferable. After hot rough rolling, hot finish rolling is performed. The hot finish rolling is performed under the conditions of a temperature of 400 ° C. or more on the incoming side, a temperature of 250 ° C. or less on the outgoing side, and a time of 2 minutes or less. 400 inlet temperature
It is not preferable that the temperature is less than 0 ° C., the temperature on the outlet side exceeds 250 ° C., or the time exceeds 2 minutes and hot finish rolling is performed, because Fe, Si and the like may be precipitated. Immediately after the hot finish rolling, the cold rolling is performed without performing the intermediate annealing. An aluminum alloy foil for a cathode having a desired thickness is obtained by cold rolling. Further, final annealing can be performed after cold rolling to obtain an aluminum alloy foil for a cathode of an electrolytic capacitor. Then, an electrolytic capacitor cathode foil can be obtained by subjecting them to an etching treatment.

【Example】

An ingot (400 mm thick) having the composition shown in Table 1 was prepared. This ingot was homogenized under the conditions (temperature and time) shown in Table 2 and hot rough-rolled at an inlet temperature of 480 ° C. and an outlet temperature of 400 ° C. for 5 minutes (thickness after rough rolling). 25mm), then hot finish rolling at 400 ° C inlet temperature and 230 ° C outlet temperature for 1 minute mm was obtained. This was cold-rolled into an aluminum foil having the thickness shown in Table 2. The final annealing after cold rolling was performed as desired. In order to evaluate the performance of the obtained aluminum foil, the loss on dissolution (mg / cm ² ) and the capacitance (μF / cm ² ) were measured.
These are prepared by immersing an aluminum foil in an aqueous solution in which 4.5% by weight of hydrochloric acid and 0.5% by weight of oxalic acid are dissolved, and applying AC 0.3 A / cm ²
Was measured after flowing the current for 2 minutes and performing electrolytic etching. The capacitance was measured in an aqueous solution of 8.3% by weight of nitric acid at 0 vf. Using a capacitance meter. The performance results of the dissolution weight loss and the capacitance are as shown in Table 2. As is clear from these results, Examples 1 to 9
It can be seen that the aluminum alloy foil obtained in (1) has a large capacitance with respect to the loss on melting, and that fine concave portions are formed on the surface. On the other hand, Comparative Examples 1 to 6 have a small capacitance with respect to the loss on dissolution, and have irregularities formed on the surface, but are not finer than the examples. In Comparative Examples 4 to 6, the content of the constituent elements was as in Examples 1 to 6.
Same as 4, but with different homogenization conditions, Mg and Fe or
It is considered that no intermetallic compound was formed with Si, and as a result, the capacitance was small.

【The invention's effect】

As described above, the aluminum alloy foil for an electrolytic capacitor cathode according to the present invention has excellent etching characteristics, and the electrolytic capacitor cathode foil obtained by etching the aluminum alloy foil has a large capacitance and a large capacitance per unit area. Is obtained. Furthermore, since the aluminum alloy foil for a cathode of an electrolytic capacitor according to the present invention may have a low Al purity, there is an effect that it can be obtained at low cost using aluminum which has not been subjected to a purification step. Further, according to the production method of the present invention, there is an effect that an aluminum alloy foil for an electrolytic capacitor cathode having excellent characteristics as described above can be reliably obtained.

Claims (2)

(57) [Claims] (1) Si 0.010 to 0.050%, Fe 0.020 to 0.075%, Mg
It consists of 0.002 to 0.010%, Zn 0.005 to 0.012%, unavoidable impurities of 0.003% or less of Cu and 0.002% or less of other unavoidable elements, and the balance of Al. An aluminum alloy foil for a cathode of an electrolytic capacitor, characterized in that: (2) Si 0.010 to 0.050%, Fe 0.020 to 0.075%, Mg
0.002 to 0.010%, Zn 0.005 to 0.012%, Cu 0.003% or less as inevitable impurities and 0.002% or less of other inevitable elements, the balance of ingot of Al, temperature 500 ° C to 550 ° C, time 20 hours or more , Then hot rough rolling at a temperature of 400 ° C or higher, and an inlet temperature of 400 ° C or higher and an outlet temperature of 250 ° C
A method for producing an aluminum alloy foil for a cathode of an electrolytic capacitor, comprising: performing hot finish rolling under the conditions of 2 minutes or less, and then performing cold rolling without performing intermediate annealing.