JPS63288008A - Aluminum foil for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To improve pertaining to the electrostatic capacitance of an electrolytic capacitor by a method wherein an aluminum foil for an electrolytic capacitor having on average concentration of lead contained in the surface layer part or 10-100 ppm is used. CONSTITUTION:When the average lead concentration of the layer from the surface to the depth of 0.1 mum is 10-100 ppm, desirably when the average concentration of lead contained in the layer from the surface to the depth of 0.05 mum is 14-150 ppm, the number of tunnel pits is increased, and the decrease in surface area due to incorporation is small. The number of tunnel pits becomes small when the lead present on the surface layer is 10 ppm or less, and when the lead concentration exceeds 100 ppm, the surface area of the etched foil is reduced on the contrary by the generation of consolidation of the tunnel pits. There are a plating, a sputtering, a flame spraying, a vapor deposition, and a cludding methods and the like as the method in which lead is added to the surface layer of the electrolytic capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an aluminum foil for electrolytic capacitors, and particularly to an aluminum foil for anodes of high-voltage electrolytic capacitors that can obtain high capacitance.

[Prior Art] As an aluminum foil for an anode of an electrolytic capacitor, a material that can obtain a large surface area by etching is preferable because it has a high electrostatic capacity of 1q. However, even if a foil is made from ultra-high purity aluminum (for example, 99.999% AI) and subjected to direct current etching in hydrochloric acid, the number of tunnel bits is generally small. This is because trace elements that are the core of tunnel bit generation are It is thought that this is because it is not included.

To this end, trace amounts of other elements are added to high-purity aluminum to obtain a high surface area during etching. The elements added for this purpose are A(J,
B, Ba, B i , Ca, Cd, Cr, Ga, In
, Mn, N i , P, Pb, Sb, Sn, Sr, Th
, T1, Zn, Zr, etc.

Problem to be Solved by the Invention 1 The functions and effects of the above-mentioned trace additive elements are not all the same. It clarifies the relationship and provides an effective aluminum foil.

[Means for Solving the Problems] The structure of the present invention for achieving the above object is to use an aluminum foil for electrolytic capacitors whose surface layer portion has an average lead permeability of 10 to 1100 pp.

The capacitance of an aluminum electrolytic capacitor is expressed as the combined capacitance of the anode and cathode as shown below.

1/C= 1/CA +1/Cc,', C=CA/(1+CA/Cc) However, C...Capacitance of electrolytic capacitor CA...Capacitance of anode CC...Static capacity of cathode Since the capacitance is practically designed to be in the state of C(, >, > CA, the above two equations can be regarded as CA /CC:O, and the above equation becomes C'':, CA.

That is, in order to increase the electrostatic capacitance of an electrolytic capacitor and to reduce the size of this capacitor, it is important to increase the electrostatic capacitance of the anode.

The capacitance of the anode is as follows, and is proportional to the surface area of the anode.

CA = KXε It can be seen that it is important to increase the

The aluminum foil for the anode is electrochemically or chemically etched in an aqueous solution containing chloride ions to increase its surface area by several tens to two hundred times.

The conditions for this etching vary depending on the chemical conversion treatment voltage in the post-process, but direct current etching is used for so-called high-pressure etching where chemical conversion is performed at 200 V or more, and tunnel-shaped etch pits are formed smoothly.

The surface area of the anode after high pressure DC etching is related to the density of the tunnel bit. That is, as the density of the tunnel bits increases, the surface area increases, but when the density exceeds a certain limit, the tunnels coalesce and the surface area of the product decreases. Therefore, the highest capacitance is obtained when there is a moderate density of tunnel bits.

As explained above, many trace elements have been proposed to be the core of this etching process, but lead is effective.
Moreover, it has been found that lead does not need to be present in the entire aluminum foil, but only in the very surface layer.

That is, since lead acts as a nucleus for the generation of tunnel bits, it only needs to be present on the surface layer of the aluminum foil, and it does not necessarily have to be present inside the foil.

As a result of various studies on the amount of lead present in this surface layer,
The average lead concentration in the layer from the surface to 0.1 μm is 10 to 1
00 ppH, preferably the average 10 concentration in the layer from the surface to a depth of 0.05 μm is 14-150 pl) In
At a certain time, the number of tunnel bits is large, and the surface area decrease due to coalescence is small.

When the amount of lead present in the surface layer is less than 10 ppm, the number of tunnel bits is small, and when it exceeds i ooppm, coalescence of tunnel bits occurs and the surface area of the etched foil becomes smaller.

Methods for adding lead to the surface layer include plating, sputtering, thermal spraying, vapor deposition, and cladding. Needless to say, it may be added during the usual melting of aluminum metal.

After lead is added, processing such as rolling or heat treatment may be performed, and it is only necessary that a predetermined amount of lead be present on the surface layer when the foil is finally etched.

[Example] Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 Component composition: 3i, each 10 ppm of Fe, 45 ppm of Cu
i ppm of Pb was added to 99.99% A1 containing m and other impurities, and after melting and casting, a foil with a thickness of o and im was produced by hot rolling and cold rolling.

After heating this foil at 580° C. for 10 hours in a vacuum, an analysis of lead on the surface layer and an etching test were conducted.

In the etching test, the above part with a thickness of 0.1 mm was etched for 150 m.
115I hydrochloric acid and 20ml 1/9. Temperature 9 consisting of sulfuric acid of
90 at a current density of 200 mA/cm' in a mixed acid at 0°C.
After direct current etching for 2 seconds, direct current etching was performed for 600 seconds at a current density of 50 mA/cm' in a mixed acid of 50 ml of hydrochloric acid and 20 ml of sulfuric acid at a temperature of 85°C.

The number of tunnel bits of the etched foil was measured, and a voltage of 37°C was measured in an aqueous ammonium borate solution.
The capacitance after chemical conversion treatment to 5V was measured.

Example 2 Thickness 1 manufactured under the same conditions as Example 1 without adding lead
Both sides of the board of 00II1111 were coated with A I -50ppm.
It was clad with a Pb alloy foil having a thickness of 0.105 mm, and then rolled to a thickness of 0.11 mm, annealed under the same conditions as in Example 1, and tested.

Example 3 △1-1-1 on both sides of a 100mm thick aluminum plate
The same treatment as in Example 2 was carried out, except that the O0pp b alloy was sprayed in an inert gas to a thickness of 0.05 mm.

Comparative Example 1 Example except that lead was not added to the aluminum base metal]
Foils were made under the same conditions and tested under the same conditions.

Comparative Example 2 A foil was made under the same conditions as in Example 2, except that it was clad with a 0.05 mm thick foil of AI-150pl)mPb, and tested under the same conditions.

Regarding the samples of Examples 1 to 3 and Comparative Examples 1 to 2 above,
The results of analysis and etching tests are shown in the table below.

From the results above in the table, the average of 101 degrees for the surface layer 0.1 μm is 10~
1001) It can be seen that a high capacitance can be obtained when pttl.

[Effects of the Invention] As explained above, by using the aluminum foil of the present invention, the capacitance of an electrolytic capacitor can be improved.

Claims (1)

[Scope of Claims] An aluminum foil for an electrolytic capacitor, characterized in that the average lead concentration contained in the surface layer is 10 to 100 ppm.