JP2864477B2 - Aluminum electrode for electrolytic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an aluminum electrode used for an electrolytic capacitor, and particularly to an aluminum electrode used for a cathode.

[Prior art]

BACKGROUND ART Electrolytic capacitors are small, large-capacity, inexpensive, and have excellent characteristics for applications such as smoothing of rectified output, and are one of important components of various electric and electronic devices. Electrolytic capacitors generally use a so-called valve metal as the anode, on which an insulating oxide film such as aluminum can be formed,
Using the insulating oxide film as a dielectric layer, a capacitor element is formed by interposing an electrolytic solution held by a separator between the current collector and a cathode electrode for current collection, and the capacitor element is housed in a closed container. . As mentioned above, the anode material is aluminum,
Tantalum, niobium, titanium and the like are used. The same metal as the anode material is used as the cathode electrode material for current collection. However, the valve metal generally has an oxide film layer formed on the surface by natural oxidation. This tendency is particularly remarkable in aluminum. And because this natural oxide film is an extremely thin insulating layer, a capacitance is also formed on the cathode side, and the electrolytic capacitor becomes a combined capacitance in which the anode side capacitance and the cathode side capacitance are connected in series. , The desired capacitance cannot be obtained. In addition, in order to obtain a desired capacitance, it is necessary to increase the capacitance on the anode side more than necessary. In order to reduce this effect, if the capacitance value on the cathode side is significantly higher than the capacitance value on the anode side, the effect due to the capacitance on the cathode side can be almost neglected. The capacitance per unit area of the anode of the electrolytic capacitor described above is at a considerably high level, and it is difficult to further increase the capacitance, and the reduction of the capacitance value due to the combined capacitance cannot be avoided. Therefore, in order to further increase the capacitance value on the cathode side, there is a method of increasing the surface area by etching the surface of the cathode electrode. However, while the technology for increasing this surface area is now highly sophisticated, it is becoming increasingly difficult to dramatically increase the capacitance of an electrolytic capacitor using only this technology. Rather, in order to solve the problem of the decrease in capacitance due to the combined capacitance with the cathode, the surface of the cathode is covered with a thin film made of a conductive metal that does not form an insulating oxide film. It can be considered that the capacitance value is prevented from lowering due to the above. As such a device, for example, a device in which various kinds of conductive metals are vacuum-deposited is known as disclosed in Japanese Patent Application Laid-Open No. 60-1826. In addition, in order to form a thin film, there are various physical methods such as an ion plating method, a sputtering method, and a plasma CVD method, in addition to the above-described vacuum deposition. However, among conductive metals, so-called noble metals such as gold and platinum hardly react with chemicals, and can maintain good conductivity even when used as an electrolytic capacitor for a long time. However, this kind of noble metal has not been adopted for an electrolytic capacitor which is required to be inexpensive and mass-produced for economic reasons. For other metals, a chemical reaction occurs in the presence of the electrolyte,
Since the surface condition changes over time, corrosion accidents occur,
There is a disadvantage that the characteristics of the electrolytic capacitor are not stable.

[Problems to be solved by the invention]

This invention is conductive on the surface of high purity aluminum,
Further, it is an object of the present invention to form a thin film having high stability in characteristics when used as an electrolytic capacitor, to efficiently obtain a highly reliable electrode for an electrolytic capacitor having a large capacitance per unit area.

[Means for Solving the Problems]

The present invention focuses on the fact that titanium nitride forms a thin film suitable for the purpose of the present invention, and the electrode for an electrolytic capacitor of the present invention has a thickness of 0.1 μm to 2.0 μm on a high-purity aluminum surface by cathodic arc evaporation. It is characterized in that a μm titanium nitride layer is formed. That is, the present invention achieves the object of the present invention by coating the surface of the aluminum electrode with a thin film of titanium nitride. According to the present invention, as the material to be treated, high-purity foil-like or plate-like aluminum used for a cathode of an ordinary electrolytic capacitor can be used. The surface of the aluminum is previously cleaned by a degreasing treatment or the like. The aluminum surface may be subjected to an etching treatment, or may be used even if it is a plain surface.
However, at the time of etching, it may be necessary to select the range of fineness of the unevenness by etching by means of forming a titanium nitride layer. The thickness of the titanium nitride layer to be formed needs to uniformly cover at least the aluminum surface. When the thickness is more than necessary, the coating process takes a long time. Therefore, the thickness is preferably 0.02 to 5 μm, more preferably 0.1 to 5 μm.
To 2 μm.

[Action]

Titanium nitride is a hard compound having a specific resistance as low as 22 to 130 μΩ · cm, and is known for applications such as protection of a chip surface of a cutting tool and coating of a watch case. Further, since titanium nitride has good reactivity with aluminum, a dense thin film having low specific resistance is formed on the surface of aluminum. As a result, the aluminum electrode is stable with titanium nitride, as it is on the very thin natural oxide film with a high capacity formed on the surface, or on the metal surface with high conductivity where almost no natural oxide film is formed on specific minute parts. Therefore, it is considered that a high electrostatic capacitance value is obtained as the whole electrode. Titanium nitride hardly reacts with the electrolytic solution, and stably maintains the surface state of the electrode for a long time. As a means for forming a titanium nitride thin film, various means can be applied, but in general, a thin film is preferable, and a dry process by physical means for easily controlling the thickness and the state is preferable. The arc deposition method is superior in processing speed and thinness of the thin film.

【Example】

Hereinafter, the present invention will be described in more detail with reference to examples. A high-purity aluminum-treated material having a titanium nitride thin film of the present invention formed on its surface was prepared as in the following examples.
Then, as a comparative example, one in which a titanium nitride thin film was formed by an ion plating method, and one in which a non-nitride metal titanium layer was formed to have the same film thickness, instead of using the cathodic arc evaporation method, were further prepared. Comparative examples 1 to 4 were obtained by subjecting a conventionally used high-purity aluminum surface to only an etching treatment. Example High purity aluminum foil (purity 99.95%, thickness 100μ)
m) was cut into 50 mm x 100 mm as a material to be treated, and was deposited by a cathodic arc deposition method in a chamber containing nitrogen gas at a total pressure of 5 x ^10-3 Torr. The deposition conditions were as follows: the material to be treated was heated to 200 ° C., a deposition distance of 200 mm, an arc discharge voltage of 100 V, an arc current of 100 A, a deposition rate of 0.05 μm / min, and a 0.2 μm-thick titanium nitride layer was formed. Processing time was 4 minutes. Comparative Example 1 A titanium nitride thin film was formed on the same high-purity aluminum as in the example by an ion plating method. The formation conditions are such that the total pressure including nitrogen gas in the chamber is 1
In a × 10 ^-2 Torr atmosphere, a voltage of 1200 V was applied between the material to be treated and the titanium electrode as a vapor deposition source to form a 0.2 μm-thick titanium nitride layer on the surface of high-purity aluminum. The processing time at this time was 20 minutes. Comparative Example 2 The same material as in the example was used as the material to be treated, and a titanium metal thin film was formed at room temperature under the same cathodic arc vapor deposition method as in example 1 in a chamber in an argon gas atmosphere of 2 × 10 ⁻³ Torr. Formed. The deposition conditions were as follows: arc discharge voltage 100 V, arc current 100 A, deposition temperature 0.02 μm / min, film thickness 0.2 μm.
m of titanium metal was deposited. The processing time at this time was 10 minutes. Comparative Example 3 A thin film of titanium metal was formed by the same ion plating method as in the example. The same material as in Example 1 was used as the material to be treated. The thin film was formed under a 2 × 10 ⁻² Torr argon gas atmosphere by applying a voltage of 1200 V between the material to be treated and the evaporation source to form a 0.2 μm thick titanium metal film. The processing time at this time was 18 minutes. Comparative Example 4 A high-purity aluminum material made of the same material as that of the example was subjected to an etching treatment by an alternating current electrolysis method to prepare a material. For these materials to be processed in each of the examples and comparative examples,
When the capacitance value per unit area was measured,
The results shown in Table 1 were obtained. As is clear from these results, it can be seen that each of the examples according to the present invention has a higher capacitance per unit area than the comparative example. The time for forming a thin film having a thickness of 0.2 μm varies depending on various conditions, but it has been found that the method according to the embodiment of the present invention is the most efficient. Next, in order to examine the stability of the formed thin film, an electrolytic capacitor was prepared using each of the materials to be treated as a cathode of the electrolytic capacitor, and a life test was performed to examine a change in characteristics. The created electrolytic capacitor is an electrolytic capacitor with the same direction of the lead wire.The element in which the foil electrode is wound together with the separator is impregnated with the electrolytic solution, stored in a metal case, and the opening is sealed with sealing rubber. It is. The materials constituting the electrolytic capacitor were all the same except that the cathode foil used in each of the above Examples and Comparative Examples was used. The same applies to the assembling method. Rated voltage of electrolytic capacitor is 6.3V, rated capacity is 47μ
F, external dimensions are 5mm in diameter and 7mm in length. The composition of the electrolyte used was composed of 78% by weight of ethylene glycol, 10% by weight of ammonium adipate, and 12% by weight of water, and the content of water was larger than that of a commonly used electrolyte. . This is because the occurrence of hydration deterioration of the electrode foil due to water was remarkable. Apply rated voltage to this electrolytic capacitor, and
The rate of change between the capacitance value after the time life test and the initial capacitance value was examined. Table 2 shows the results. As can be seen from the results, the electrolytic capacitor using the aluminum electrode of the present invention has a high capacitance value even at the initial value, and has a hydrated surface even after the high-temperature load life test. It can be seen that the characteristics do not deteriorate, so that the electrical characteristics have little fluctuation and stable characteristics can be maintained for a long period of time.

【The invention's effect】

As described above, according to the present invention, as an electrode for an electrolytic capacitor, it is possible to increase the capacitance per unit area. Electrodes
It becomes possible to obtain efficiently. Further, since the electrode surface is protected by titanium nitride and deterioration of the electrode surface such as hydration deterioration is prevented, stable characteristics can be maintained for a long period of time.

Claims (1)

(57) [Claims] 1. An aluminum electrode for an electrolytic capacitor, wherein a titanium nitride layer having a thickness of 0.1 μm to 2.0 μm is formed on a high-purity aluminum surface by cathodic arc deposition.