JPH0828312B2 - Aluminum alloy electrode for electrolytic capacitors - Google Patents

Description

The present invention relates to an aluminum alloy electrode used as an anode of an electrolytic capacitor.

[Prior Art] A so-called valve metal capable of electrochemically forming a very thin dielectric oxide film is used as an anode material of an electrolytic capacitor. Among them, at present, aluminum having a purity of 99.9% or 99.99% and tantalum are widely used.

Among them, the relative dielectric constant of the aluminum oxide film Al ₂ O ₃ is about 7 to 10, and for example, compared with 25.2 of Ta ₂ O ₅ and 66.1 of TiO ₂ which are oxide films of other valve metals, Quite small. For this reason, the electrode foil used for the anode of the aluminum electrolytic capacitor is mechanically, electrochemically or chemically etched at a considerably high magnification in order to increase the capacitance by increasing the surface area. But,
At present, this etching ratio does not exceed 100 times.

In addition, it has been attempted to improve the capacitance by devising an anodization method. This is a composite film of pseudo boehmite film by hot water treatment and anodized film by electrolytic reaction,
A composite film of a chemical conversion film formed by boric acid solution and a chemical conversion film formed by phosphoric acid solution, a composite film formed by a special pretreatment and an anodized film formed by electrolytic reaction, and the like. The increase in capacitance due to such a composite film is within 30% of the increase in the film due to the usual electrolytic reaction.

Further, recently, as shown in JP-A-60-66806, a solid solution alloy foil of aluminum and titanium or other valve metal is used in place of high-purity aluminum, and a ratio such as Al ₂ O ₃ + TiO _{2 is formed} by chemical conversion. Attempts have also been made to make alloy oxide films with a high dielectric constant, for example line 1 in the figure.
As shown in, it has been successful in improving the CV product, which indicates the quality of the capacitor.

[Problems to be solved by the invention]

With the above-mentioned high-purity aluminum anode material, it is no longer possible to increase the etching magnification to the current 2-3 times. That is, even if the electrochemical or chemical etching is strongly performed, the etching hole does not grow deeply, and conversely, the aluminum near the entrance of the hole melts and the etching member decreases, so that the thickness of the foil is simply reduced. Etching magnification does not necessarily increase as the thickness decreases. Further, even if a deep etching hole is formed and the apparent etching ratio is increased, the oxide film is clogged during the anodization and the etching ratio cannot be utilized. Even if an electrolytic capacitor is manufactured using such an anode material, the contact interface with the electrolytic solution is reduced, and foil resistance and tanδ
And the impedance and the like are deteriorated, and the characteristics are deteriorated.

When an alloy of aluminum and another valve metal is used, such an alloy has a structure close to that of a perfect solid solution alloy due to the relationship of being manufactured by the ultra-quenching method, and due to the corrosion resistance of the solid solution alloy. , When electrochemical or chemical etching is performed, if the distribution of the starting points of etching is rough and an attempt is made to perform high etching, the initially formed etching portion will melt and decrease, resulting in a worm-eating state. Therefore, the effect of etching is not sufficiently improved,
There are many practical difficulties.

[Means for solving problems]

The present invention solves the above problems and uses an alloy of aluminum and another valve metal to form a dielectric film having a high relative dielectric constant in order to increase the capacitance of an electrolytic capacitor, and It aims to eliminate obstacles on etching. That is, an alloy of aluminum and one or more members of the metal group consisting of titanium, tantalum, zirconium, hafnium and niobium is used as the anode of the electrolytic capacitor, and the precipitate of intermetallic compound is finely divided in aluminum. It is dispersed.

The grain size and distribution density of this precipitate can be adjusted depending on the composition of the alloy and the production conditions. Generally, as the content of other valve metals in aluminum increases,
The number of precipitated particles of the intermetallic compound increases and the precipitated particle size also increases. Further, if the quenching rate during alloy production is extremely increased, only the solid solution alloy is produced without precipitation of the intermetallic compound, and the precipitation amount of the intermetallic compound gradually increases as the solid solution alloy is delayed. When quenching using a cooling roll, increasing the roll speed to increase the quenching rate causes very little precipitation of intermetallic compounds on the roll surface and a large amount of fine particles on the free surface. Slowing down
A large amount of precipitated particles also exist on the roll surface, and the particle size of the precipitated particles becomes large on the free surface.

When the volume ratio of the intermetallic compound appearing in this aluminum alloy is 2.0% or more, the effect begins to appear, and when it exceeds 60%, the dielectric breakdown voltage is lowered. This tendency is the same even if the type of other valve metal added to aluminum changes.

[Work]

As described above, when the intermetallic compound particles of appropriate size are precipitated in the aluminum alloy at an appropriate density, the concentration of other valve metals solid-dissolved in aluminum around the precipitated particles is concentrated. Microscopic changes occur in the microstructure, which causes a difference in electrode potential in minute portions, and corrosion progresses along the periphery of the precipitated grains. As a result, it is possible to perform etching to an ideal pore diameter, density and depth with almost no loss due to melting of the etching portion formed in the initial stage.

Further, in order to increase the withstand voltage of the electrolytic capacitor, it is necessary to select a large hole diameter for the etching hole due to the formation of a thick dielectric film. However, such adjustment of the hole diameter for the etching hole also causes some precipitation. It can be achieved by adjusting the particle size and density of the intermetallic compound.

In this way, the etching magnification can be effectively increased and the capacitance of the capacitor can be significantly increased. The valve metal added in the present invention also contributes considerably to the improvement of the relative permittivity of the oxide film, and thus contributes to the increase of the capacitance of the capacitor together with the improvement of the etching ratio.

〔Example〕

Example 1 A mother alloy was prepared by adding 6 atomic% of zirconium to 94 atomic% of aluminum. In producing the ultra-quenched alloy, a single roll method using a copper roller was adopted, and an argon gas atmosphere was used to prevent oxidation. The mother alloy was once melted, passed through a nozzle heated at high frequency, sprayed onto a rotating copper roller in an argon gas atmosphere, solidified, and rapidly cooled in accordance with the method described in Japanese Patent Application No. 61-27242. did. The injection pressure was kept at 0.4 Kg / cm ² , and the rapid cooling rate was adjusted by the rotation speed of the copper roller.

When the quenching rate was changed depending on the rotation speed of the roller, the thickness of the superquenched alloy produced also changed, but the size of the precipitated intermetallic compound grains decreased as the quenching rate increased.

The produced ultra-quenched alloy was etched with a 6% hydrochloric acid solution at a direct current of 30 Coulomb / cm ² and then with a boric acid solution.
The formation of V and 60V was performed, and the capacitance and film withstand voltage were measured. The film withstand voltage was 0.1 mA / cm ^{2 in} the chemical conversion solution, and the voltage after 1 minute of the voltage rise curve was taken as the film withstand voltage.

 The results are shown in Tables 1 and 2.

From Table 1, it was found that the most suitable roll peripheral velocity for the 20V conversion coating during production was 23.5 m / sec. this is,
The particle size and distribution of the precipitated particles at that speed lead to an effect of increasing the surface area by etching, and when the roll peripheral speed becomes higher than that, clogging of etching holes by the chemical conversion film and the effect of reducing the etching portion appear. It depends.

On the other hand, from Table 2, it was found that the optimum roll peripheral speed for the 60V conversion coating was 20.0 m / sec, which was slower than that for the 20V conversion coating. This is because the 60V chemical conversion film is thicker than the 20V chemical conversion film, and therefore there is an etching hole that causes clogging during the 60V chemical conversion even though the 60V chemical conversion film does not clog during the 20V chemical conversion.

Example 2 Titanium was added to aluminum in an amount of 0.2 atomic% and 0.5, respectively.
Atomic%, 3.0 atomic%, 10 atomic%, 15 atomic% and 20 atomic%
The contained master alloy was prepared, and an ultra-quenched alloy was prepared using the same apparatus as in Example 1. The injection pressure is kept at 0.3 Kg / cm ² , and the roll peripheral speed is 16.3 m / sec so that a foil product can be obtained.
To 20.0 m / sec.

The produced foil was etched and formed in the same manner as in Example 1.
The formation of V and 60V was performed. The results are shown in FIGS. 3 and 4.
Shown in the figure and as lines 2 and 3 in the figure.

From Tables 3 and 4, the amount of titanium added is 0.5 atom%.
When the above is reached, the capacitance starts to increase rapidly, but when observing the prepared ultra-quenched alloy, the precipitation phase of the intermetallic compound Al ₃ Ti begins to appear clearly, and it is from 0.5 atomic%, and its behavior is corresponding. are doing. When the amount of titanium added is further increased, the capacitance also increases, and becomes maximum at 10 to 15%.
This is because when the amount of titanium added is 0.5 atomic% or more, a precipitation phase of intermetallic compounds appears, and etching proceeds smoothly around the precipitation particles, which increases the electrode surface area and increases the capacitance. Because it is connected.

However, when the amount of titanium added reaches 20 atomic%, the withstand voltage of the dielectric film is significantly reduced. This is because the properties of the n-type semiconductor due to titanium oxide are increased, which induces a decrease in film breakdown voltage and an increase in wetting current.

Further, when the amount of titanium added reaches 20 atomic%, the electrostatic capacity tends to decrease. This is because the size and distribution density of the precipitated particles increase too much, the etching growth space is sandwiched, and the etching ratio decreases on the contrary, while the increase in the relative permittivity due to the increase in titanium oxide results in an increase in the etching ratio. This is because it cannot follow the decrease.

Therefore, the CV product that shows the quality of the capacitor is shown in Fig. 1 as line 2
As shown in 3 and 3, excellent values are obtained when the amount of titanium added is 0.5 to 15 atomic%, and the volume ratio of the intermetallic compound at this time is 2.0 to 60%.

Example 3 Aluminum, titanium, tantalum, zirconium,
A sample to which 2 atom% of hafnium and niobium were added was manufactured by the same manufacturing method as in Example 2, and these and 99.99% aluminum foil were prepared in a 6% hydrochloric acid solution to have a diameter of 30 coulomb / cm ^2.
Etching was carried out, and 20 V chemical conversion was performed from a neutral ammonium phosphate solution. Table 5 shows the results.

As seen in Table 5, when comparing an aluminum alloy containing an intermetallic compound of aluminum and another valve metal with high-purity aluminum, in each case, the electric power generation is twice or more than that of aluminum. Capacity is obtained. This is because the oxides of valve metals other than aluminum have a higher relative dielectric constant than aluminum oxides, and the etching progresses smoothly to contribute to the increase of electrostatic capacity, and the loss of etching parts is small. This is due to the fact.

〔The invention's effect〕

As described above, in the present invention, by adjusting the composition and the quenching rate during the production of the electrode alloy, it is possible to perform the optimum etching according to the withstand voltage of the capacitor. By forming a dielectric film having a higher relative dielectric constant than that, it is possible to greatly contribute to the increase in the capacitance of the electrolytic capacitor.

[Brief description of drawings]

The figure is a diagram showing the relationship between the Ti addition amount and the CV product in the conventional method and the present invention. 1: CV product characteristic line according to conventional method 2 and 3: CV product characteristic line according to the present invention

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kazuo Takeno, Kazuo Takeno, Oike Dori, Karasuma Higashiiri, Nakagyo-ku, Kyoto Prefecture 1618 Ida, Nakahara-ku, Kawasaki-shi, Japan Inside the 1st technological research institute of Nippon Steel Corporation (72) Inventor Michio Endo 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Inside the 1st technological research institute of Nippon Steel (72) ) Inventor Tetsuya Sugai 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Nippon Steel Works Ltd.

Claims (2)

[Claims] 1. At least one kind of intermetallic compound of aluminum and one or more members of a metal group consisting of titanium, tantalum, zirconium, hafnium and niobium is finely dispersed in aluminum. Aluminum alloy electrodes for electrolytic capacitors. 2. The aluminum alloy electrode for an electrolytic capacitor according to claim 1, wherein the volume ratio of the intermetallic compound contained in the aluminum alloy is 2.0% to 60%.