JP2002180293A - Method of forming titanium oxidized coating and titanium electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium electrolytic capacitor of a small size, a large capacity and a small leak current through a method of forming a stable oxidized a having a high dielectric constant on the surface of the titanium. SOLUTION: This method of forming the oxidized coating on a metal titanium substrate comprises applying titanic acid or organic titanium compound on the surface of the metal titanium substrate to form the oxidized coating thereon, firing the oxidized coating in a vacuum, then subjecting the oxidized coating to heat treatment in the presence of oxygen and subjecting the oxidized coating to anodic oxidation in an electrolyte-containing solution, thereby forming the oxidized coating again on the surface of the metal titanium substrate. This titanium electrolytic capacitor uses the metal titanium substrate having the oxidized coating formed again by utilizing the above as an anode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an oxide film and a capacitor, and more particularly, to a method for forming a dense oxide film having large capacitance and excellent insulating properties on a titanium metal substrate, and a method for forming the same. The present invention relates to a titanium electrolytic capacitor using a metal titanium substrate having a dense oxide film as an anode utilizing the above method.

[0002]

2. Description of the Related Art A tantalum electrolytic capacitor and an aluminum electrolytic capacitor are typically put into practical use as small and large-capacity electrolytic capacitors typified by conventional solid electrolytic capacitors.

A tantalum electrolytic capacitor is manufactured by using a porous sintered body of metal tantalum as an electrode and anodizing the electrode to form a dielectric oxide film. The tantalum oxide film thus formed is very stable, and thus has characteristics of good dielectric properties and long life. An aluminum electrolytic capacitor is similarly manufactured by forming aluminum oxide as a dielectric on a metal aluminum foil or sintered body by anodic oxidation. FIG. 4 is a schematic diagram showing an example of a tantalum electrolytic capacitor and an aluminum electrolytic capacitor together for convenience. Here, tantalum oxide (Ta ₂ O ₅ ) is used as an anode and as an insulator layer.
Ta powder porous sintered body having Al or Al powder porous sintered body having aluminum oxide (Al ₂ O ₃ ) as an insulator layer, wherein Ta wire or Al wire is used as anode lead wire in the sintered body. Embedded in each. The cathode is exemplified by a manganese dioxide (MnO ₂ ) solid electrolyte and a carbon + Ag cathode (cathode conductive layer).

In the case of a tantalum electrolytic capacitor, for example,
Tantalum powder having a particle size of 10 to 20 μm is compression-molded by a press and sintered to form a porous sintered body. This is anodized to obtain an oxide film. Since this porous sintered body has an extremely large surface area, a large capacitance can be obtained. Thereafter, a manganese compound such as manganese sulfate is heat-treated on the oxide film to make manganese oxide a cathode, or the porous sintered body is immersed in an aqueous solution of manganese nitrate, and thermally decomposed in an electric furnace. The manganese dioxide layer is grown by repeating the process of converting the manganese dioxide into a manganese dioxide layer to form a sufficient electrolyte layer. Manganese dioxide fills and covers every corner of the pores of the porous sintered body. Alternatively, a capacitor can be formed using a conductive polymer compound as a cathode. An external lead wire (not shown) is soldered by depositing a carbon layer thereon to lower the conductive resistance and further applying a silver paste.
After the formation of manganese dioxide, a double structure in which a conductive polymer is formed may be employed. The use of a liquid electrolyte is also possible. The same applies to aluminum electrolytic capacitors.

However, tantalum electrolytic capacitors have a problem that tantalum is expensive. On the other hand, in the aluminum electrolytic capacitor, aluminum is inexpensive, but as shown in a partially enlarged view of the aluminum electrolytic capacitor in FIG. 4, when the capacitor is formed, oxygen defects occur in the aluminum oxide film, There has been a problem that the life is short due to a large leakage current generated due to the formation of a semiconductor, and that the aluminum has a dielectric constant per unit area smaller than that of tantalum, making it difficult to produce a small-sized, large-capacity capacitor.

In order to solve the above-mentioned conventional problems,
Many attempts have been made to develop titanium electrolytic capacitors using titanium metal as an anode and forming an oxide film such as titanium oxide or composite titanium oxide on the anode. In other words, titanium is less expensive than tantalum, and titanium oxide has a much higher dielectric constant than tantalum oxide or aluminum oxide. It has great potential for development.

FIG. 1 shows a conceptual diagram of a titanium electrolytic capacitor (in FIG. 4, Ta and Al powders are converted to Ti powders,
a, Al oxide to Ti oxide and Ta, Al wire to T
i-line). A titanium oxide film 2 is formed on a titanium substrate anode 1 to form an anode. A titanium wire is attached to the anode. Similar to FIG. 3, MnO ₂ is exemplified as the solid electrolyte 3, a carbon layer 4 is adhered thereon to lower the conductive resistance, and further, a silver paste 5 is applied and external lead wires (not shown) are soldered. Is illustrated. The finished device is sealed in a case 6 to protect it from external moisture and contamination. In order to develop such a titanium electrolytic capacitor, various attempts have been made mainly on improving the dielectric constant of a titanium oxide film as a dielectric film.

For example, in Japanese Patent Application Laid-Open No. 5-121275, the anodization of a titanium metal plate is terminated before the current starts to rise during the anodization at a constant voltage in an electrolyte-containing aqueous solution. Anodizing is performed at a temperature of 60 ° C. or less using an electrolytic solution composed of an organic solvent having a water content of 60% by weight or less to form an oxide film on a titanium plate.
Heat treatment is performed at a temperature of 0 to 350 ° C., and the obtained titanium is used as an anode, and a solid electrode (manganese dioxide or the like) or an electrolyte solution (4% by weight of ammonium phosphate-36% by weight of water-ethylene glycol) is used as a cathode on an oxide film. 60% by weight)
Discloses a method for manufacturing a titanium electrolytic capacitor by forming an electrode (platinum foil) through the substrate. The titanium plate having an oxide film obtained by anodic oxidation in an aqueous solution is again subjected to anodic oxidation using an electrolytic solution comprising an organic solvent having a water content of 60% by weight or less to form an oxide film on titanium. And

Japanese Patent Application Laid-Open No. 9-17684 discloses a porous sintered body composed of a metal containing titanium as a main component and a perovskite-type composite oxide such as strontium titanate formed on the surface of the sintered body. A dielectric film as a main component,
An electrode made of a conductor or a semiconductor formed on the surface of the dielectric film, and a counter electrode (a graphite layer, a silver electrode layer) which is electrically connected to the dielectric or the semiconductor electrode and faces the sintered body; Alternatively, a capacitor is disclosed in which the semiconductor has a two-layer structure of a metal oxide such as manganese or nickel and a conductive polymer compound (polypyrrole). Since an electrode made of a conductor or a semiconductor is formed on the dielectric film, a large capacitance can be realized without increasing the size of the entire capacitor.

Further, Japanese Patent Application Laid-Open No. 2000-77274 discloses that a porous sintered body composed of a metal containing titanium as a main component is formed by using A ion (A is at least one of Ba, Sr and Pb), B ion (B is at least one of Zr or Ti) in an aqueous alkali solution containing
Forming an ABO ₃ coating on the surface of the porous sintered body,
The porous sintered body on which the ABO ₃ coating was formed was converted to C ions (C
Is heat-treated in an alkaline aqueous solution containing at least one of Ba and Sr) and Pb ions to obtain conductive CPb.
A capacitor obtained by forming an O ₃ thin film as a counter electrode, and then forming a graphite layer and a silver electrode layer, and a method of manufacturing the same are disclosed. It states that a capacitor that is small, has a large capacitance, and is easy to manufacture will be manufactured.

[0011]

In the above prior art, the dielectric constant of the dielectric film is improved, and a capacitor having a large capacitance is produced. However, the titanium-based oxide film on the surface of titanium metal produced by the above-described conventional technique has a high dielectric constant, but lacks its denseness and stability, and has a very large leakage current when used as a capacitor. Was still inadequate.

Accordingly, an object of the present invention is to develop a method for forming a stable oxide film having a large dielectric constant on the surface of a titanium metal substrate. The present invention is to provide a titanium electrolytic capacitor having a small lifetime and a long life.

[0013]

Means for Solving the Problems In view of the above-mentioned problems of the prior art, the present inventors have conducted intensive studies on a method of forming an oxide film mainly composed of titanium oxide on the surface of a titanium metal substrate. Thus, a new method for forming a stable oxide film having a high dielectric constant and a small leakage current has been found, and the present invention has been achieved. That is, an oxide film is formed by applying a titanic acid or an organic titanium compound to the surface of a metal titanium substrate, and the oxide film is baked in a vacuum to apparently disappear and the titanium surface is substantially returned to a metallic state. It was found that a very dense oxide film can be obtained by forming an oxide film by a reoxidation method in which the metal titanium surface is reoxidized by heat treatment in the presence and anodizing in an electrolyte-containing solution. It was issued.

Based on the above findings, the method for forming an oxide film according to the present invention is to form an oxide film by applying titanic acid or an organic titanium compound on the surface of a titanium metal substrate, baking in a vacuum, Under heat treatment and anodizing in an electrolyte-containing solution to re-form an oxide film on the surface of the titanium metal substrate. The titanic acid is peroxotitanic acid, the organotitanium compound is alkoxytitanium, and the firing in vacuum and the heat treatment in the presence of oxygen are all 5 times.
It is preferable to carry out at a temperature of 00 to 900 ° C.

Further, by utilizing this method for forming an oxide film, the present invention provides an oxide film by applying a titanic acid or an organic titanium compound to the surface of a titanium metal substrate, firing the film in a vacuum, and then firing in the presence of oxygen. The present invention provides a titanium electrolytic capacitor characterized by using a metal titanium substrate having an oxide film reformed by heat treatment below and anodizing in an electrolyte-containing solution as an anode.

In the present invention, the term "oxide film" includes not only a titanium oxide film but also a composite oxide of titanium oxide such as strontium titanate and barium titanate containing other elements such as strontium and barium.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As already described with reference to FIG. 1, a titanium oxide substrate 2 is formed on a titanium anode substrate 1 to form an anode. A titanium wire is attached to the anode.
An example of the solid electrolyte 3 is MnO ₂ , on which a carbon layer 4 is adhered to lower the conductive resistance.
Is applied, and an external lead wire (not shown) is soldered. The finished device is sealed in a case 6 to protect it from external moisture and contamination.

The titanium metal substrate used in the present invention is a porous sintered body obtained by sintering a titanium metal plate or titanium powder. Usually, when a titanium electrolytic capacitor is produced, the latter metal is used as an anode. A porous sintered body obtained by sintering titanium powder is used. When making this porous sintered body, metal titanium powder may be used as a raw material,
Embrittled titanium hydride powder can also be used.
When titanium hydride powder is used, heat treatment is performed under reduced pressure before, during or after sintering to perform dehydrogenation.

In preparing the porous sintered body of the above-mentioned metal titanium powder, the metal titanium powder to be used usually has a particle size of 1 to 1.
50 μm, average particle size 5 to 100 μm. A known method can be adopted as a method for producing the porous sintered body. For example, first, titanium powder is pressure-formed by a press-forming machine. At this time, a binder such as a styrene resin, an acrylic resin, or camphor is mixed with the titanium powder as needed. The molded product is fired at 600 to 900 ° C. in a vacuum. When the porous sintered body thus produced is used for a capacitor, a titanium wire is attached at the time of pressure molding or after firing. In order to increase the capacitance when a capacitor is made, it is necessary to make the porous sintered body as large as possible in specific surface area.
Specifically, the sintered density of the porous sintered body (the ratio of the density of the porous sintered body to the true specific gravity of metallic titanium) is 30 to 70.
%. As the sintering density increases, the specific surface area decreases. If the sintering density is too low, the specific surface area will increase, but the strength of the porous sintered body will decrease, making it impossible to use it as a capacitor.

Hereinafter, the process of the present invention will be described step by step. Formation of oxide film by titanic acid or organotitanium compound on the surface of titanium metal substrate: The titanium metal substrate has a thickness of 50 nm or more, preferably 50 to 500 nm, on its surface.
More preferably, an oxide film having a thickness of 100 to 200 nm is formed. In the present invention, the oxide film thickness was measured by measuring the oxygen concentration distribution near the surface of the metal titanium plate by Auger electron spectroscopy, and measuring the thickness of the oxide film from the oxygen concentration distribution. The measurement by Auger electron spectroscopy is PHISI
Using a PHI-680 type device manufactured by CAL ELECTRONICS, the acceleration voltage of the electron gun was 5 kV, the material current was about 10 nA, the ion species of the ion gun was Ar ⁺ , the beam voltage was 5 kV, and the sputtering rate was about 43 nm / min. The measurement area of the sample was about 3 μm square. In the present invention, the oxide film includes not only a titanium oxide film but also a composite oxide of titanium oxide such as strontium titanate and barium titanate containing other elements such as strontium and barium.

For the formation of the oxide film, for example, a heat treatment in the presence of oxygen, a surface treatment with titanium tetrachloride, or an electrochemical treatment may be considered. It has been found suitable.

The above metal titanium substrate is coated with titanic acid or an organic titanium compound, and is used after being diluted with an aqueous solvent or an organic solvent dissolving titanic acid such as alcohol.

The titanic acid used in the present invention is ortho titan
Acid, metatitanic acid, peroxotitanic acid and the like.
Among them, the pH of the aqueous solution can be used in the neutral range.
Peroxotitanic acid is preferred. The above peroxocita
Acid is also called peroxytitanic acid or titanium peroxide
Whose structure is H_FourTiO_Five, Ti (OOH)
(OH)_ThreeOr TiO_Three・ 2H _TwoIndicated by O. Perok
Sotitanic acid is usually yellow, tan or reddish brown
It is handled in an aqueous solution (sol solution) and is commercially available
Can be used. As a commercially available product, for example, "PTA-8
5 "and" PTA-170 "(both manufactured by Tanaka Transcription Co., Ltd.)
PTA aqueous solution). Also, those who are known
It is also possible to prepare by the method, for example, tetrachloride
Hydrolysis of titanium aqueous solution with ammonia water
After producing a slurry containing
Hydrogen is added to obtain an aqueous solution of peroxytitanic acid. Also Yes
As a titanium compound, alkoxy titanium is preferred.
Specifically, tetra n-propoxy titanium, tetri
Sopropoxy titanium, tetra n-butoxy titanium, tet
Lysobutoxytitanium and the like. These al
Organotitanium compounds, including koxytitanium, are usually
Alcohol such as alcohol, ether or carbonized
It is used as a solution using a hydrogen solvent or the like as a solvent. Titanic acid
Alternatively, the method of applying the organic titanium compound is a titanic acid aqueous solution.
Metallic titanium substrate in solution or organic titanium compound solution
Immersion method, or titanic acid aqueous solution on titanium metal substrate
Spray liquid or organic titanium compound solution
A method of spraying is exemplified. At this time, metal titanium base
After applying to form an oxide film uniformly on the body surface,
Repeat the operation of drying and applying again several times.
Is desirable. In addition, when coating,
When air bubbles adhere, a uniform oxide film can be finally formed.
There is no metal titanium base in vacuum to prevent this.
Titanic acid solution or organic titanation applied to body surface
It is desirable to degas the compound solution.

Prior to the above coating operation, it is desirable to perform a surface treatment for removing dirt adhering to the surface of the metal titanium substrate and for improving the specific surface area of the substrate surface. Specifically, it is treated with an acid such as hydrogen fluoride or another oxidizing agent.

B. Baking (annealing) treatment: After applying titanic acid or an organic titanium compound as described above, baking is performed in a vacuum, and the temperature at that time is usually 500 to 800 ° C.
It is preferably at 550 to 750 ° C. for 10 minutes to 5 hours, preferably 30 minutes to 3 hours. The degree of vacuum is usually 1 × 10
⁻² Pa to 1 × 10 ⁻⁴ Pa. The thickness of the oxide film after firing is preferably 10 nm or less, more preferably 5 nm.
m to 0 nm. In particular, it is preferable to eliminate the oxide film. By sintering the oxide film formed on the surface of the titanium metal substrate as described above, the oxygen component in the oxide film is diffused and permeated into the titanium metal. Usually, in the state where the oxide film is formed, a gradient of oxygen concentration is seen from the surface of the titanium metal substrate to the inside (the oxygen concentration in the titanium metal decreases from the surface to the inside). It is desirable that the titanium surface has a state in which the oxygen concentration decreases and the oxygen concentration gradient near the surface disappears.

C. Reoxidation treatment: Thereafter, the surface of the metal titanium substrate is oxidized to form an oxide film again. It is preferable to re-form an oxide film having a thickness of 50 nm or more. The thinner the oxide film, the larger the capacitance can be. However, if the oxide film is too thin, it lacks denseness and robustness, and tends to cause leakage current. It has been found that a combination of (a) a heat treatment in the presence of oxygen and (b) an electrochemical treatment is suitable as a method of the reoxidation treatment.

The fired substrate is fired in the presence of oxygen.
The temperature at that time is usually 500-800 ° C., preferably 5 ° C.
10 minutes to 5 hours at 50 to 750 ° C., preferably 30 minutes to
3 hours. The oxygen concentration may be in the air, usually 2
0% to 100%.

Thereafter, the titanium metal substrate coated with titanic acid or an organic titanium compound and calcined is anodized in an electrolyte-containing solution. As the electrolyte used at this time, a known electrolyte is used. , Adipates, borates, phthalates, maleates, benzoates, citrates and other alkali metal salts or ammonium salts, and sulfuric acid. In a non-aqueous solution, ammonium borate, sodium acetate In an ethylene glycol solution of phosphoric acid or a molten salt, NaNO ₃ , KNO _{3 and the} like can be mentioned. In the anodizing method, the metal titanium substrate treated as described above is used as an anode, and anodized by applying a voltage in the above-mentioned electrolyte-containing solution. The voltage applied at this time is 5 to 600 V, preferably 10 to 50 V, particularly preferably 20 to 40 V.
Minutes to 10 hours, preferably 1 to 30 minutes, particularly preferably 1 to 10 minutes. The reaction is usually carried out at room temperature. After anodic oxidation, the surface of the substrate is sufficiently washed with water and then dried to obtain a metal titanium substrate having an oxide film formed thereon.

As described above, an oxide film is formed by applying a titanic acid or an organotitanium compound, fired once in a vacuum, fired in the presence of oxygen, and oxidized again on the surface of the metal titanium base, thereby obtaining the metal titanium base. Oxygen permeates in a deeper direction, and a uniform and stronger oxide film can be formed.

D. Firing-oxidation mechanism: As described above, the surface of the metal titanium substrate having a certain amount of oxide film is once fired in a vacuum or in an inert gas atmosphere, and subjected to a process of diffusing oxygen of the oxide film into the metal titanium. Thereafter, the oxide film formed by the new oxidation treatment is uniform and strong, and when a solid electrolytic capacitor is manufactured using the oxide film, a capacitor having a high dielectric constant and a small leakage current can be obtained. FIG. 2 is a graph schematically showing the state of the oxygen concentration from the titanium surface to the inside of titanium in each state of the Ti plate, after oxidation, after firing, and after re-oxidation. Oxygen concentration was measured by Auger analysis. In the state where the oxide film is formed, a gradient of oxygen concentration is seen from the surface to the inside of the titanium metal substrate (the oxygen concentration in the titanium metal decreases from the surface to the inside), but the oxygen concentration decreases on the surface of the titanium metal after the firing step. However, it can be seen that the oxygen concentration gradient near the surface disappears. A thick oxide film is formed by the reoxidation treatment.
In FIG. 3, (a) shows an oxide film on the surface of the Ti plate in the oxidized state, and (b) shows the surface state of the Ti plate after firing. It can be seen that the oxide film has disappeared. In this case, the oxygen component of the oxide film is diffused and penetrated into titanium. After that, by reoxidation, it is not clarified, but the oxygen that has penetrated inside has some effect, or the surface condition of the substrate is improved by reoxidation, and a uniform, strong, dense oxide film is formed. Form. When a normal 30 V anodized film and a 30 V anodized film formed by the re-oxidation method were compared and observed by a backscattered electron image of the cross section of the oxide film, a different phase (presumed to be carbon) at the interface between the film and the substrate in the normal 30 V anodized film ) And the reoxidation method confirmed that the film grew thicker.

The metal titanium substrate having such a dense oxide film can be used not only for electrolytic capacitors but also for applications such as metal titanium materials having a photocatalytic function on the surface.

E. Electrolytic capacitor: A solid electrolytic capacitor can be prepared using the metal titanium substrate having an oxide film obtained as described above as an anode. At this time, as a cathode, similarly to a tantalum electrolytic capacitor, a manganese compound such as manganese sulfate is heat-treated on an oxide film to make manganese oxide a cathode, or a porous sintered body is immersed in an aqueous solution of manganese nitrate. The step of thermally decomposing the manganese dioxide in an electric furnace to produce manganese dioxide can be repeated to grow a manganese dioxide layer, or a capacitor can be prepared using a conductive polymer compound as a cathode. An external lead wire (not shown) is soldered by depositing a carbon layer thereon to lower the conductive resistance and further applying a silver paste. After the formation of manganese dioxide, a double structure in which a conductive polymer is formed may be employed. The use of a liquid electrolyte is also possible. Any known cathode structure as exemplified above as the prior art, including a solid electrolyte and a liquid electrolyte, can be employed.

[0033]

EXAMPLES The effects of the present invention will be specifically described below with reference to examples and comparative examples. Here, the evaluation of the insulating property of the formed oxide film and the measurement of the electric capacity were carried out by the following methods.

1) Evaluation of insulation (measurement of leakage current) A test sample of a titanium plate was masked with an insulating tape to leave an electrode area of about 1 cm ² . This was used as a positive electrode, and a mesh-shaped Pt plate (50 mm × 50 m) was used as a counter electrode (negative electrode).
m), and using an aqueous solution of 150 g / L ammonium adipate as an electrolyte and applying an applied voltage of 5 V, 10 V, 15 V,
One minute after each of 20 V and 30 V, a current value (leakage current) flowing between the positive electrode and the counter electrode was measured. Since the measured value of the leakage current changes depending on the order of applying the voltage,
It is necessary to always perform measurement from the low voltage side, and when bubbles are generated on the electrode surface, it is necessary to sufficiently stir the liquid until the bubbles disappear after turning off the voltage.

2) Measurement of Electric Capacitance Using a test sample in which the leakage current was measured as a positive electrode and a titanium plate (20 mm × 100 mm) as a counter electrode, an LCR (inductance / capacitance / resistance) meter was used to directly measure the electric potential of the film under the following conditions. The capacity was measured.・ Measurement conditions Electrolyte: 150 g / L aqueous solution of ammonium adipate Frequency: 120 Hz Amplitude: 1 V (Note) In this measurement method, the capacity of the surface of the counter electrode is added in series, but the capacity of the Ti plate is sufficient compared to the test electrode. Large and negligible (1 / total capacity = 1 / sample capacity + 1 /
Since it is expressed by the capacity of the Ti plate, the capacity of the Ti plate can be neglected if it is sufficiently large compared to the sample volume).

Example 1 Vacuum degassing (degassing under reduced pressure) was performed while immersing a metal titanium plate in a 1.7% by weight aqueous solution of peroxotitanic acid to completely remove bubbles on the surface of the metal titanium plate. After removing, pulling speed 35mm / min
And dried in a dryer at 80 ° C. for 10 minutes.
Thereafter, the metal titanium plate was immersed in an aqueous solution of peroxotitanic acid having a concentration of 1.7% by weight for 1 minute, pulled up at a speed of 105 mm / min, and coated with peroxotitanic acid.
For 10 minutes. This process was repeated 20 times to form a titanium oxide film of about 0.46 μm.
Approximately 1 × 1 metal titanium plate with titanium oxide coating
It was baked at 600 ° C. for 2 hours in a vacuum of 0 ⁻³ Pa. Then, it is heat-treated in oxygen at 700 ° C. for 2 hours.
A voltage of 0 V was applied for 5 minutes to form an oxide film. With respect to this oxide film, insulation evaluation and electric capacity were measured. Table 1 shows the obtained results.

Example 2 Vacuum defoaming was performed while immersing the metal titanium plate in a 1.7% by weight aqueous solution of peroxotitanic acid to completely remove bubbles on the surface of the metal titanium plate, and then the pulling speed was 35 mm. / Min, and dried in a dryer at 80 ° C. for 10 minutes. After this, the concentration 1.
A metal titanium plate is immersed in a 7% by weight aqueous solution of peroxotitanic acid for 1 minute, pulled up at a rate of 105 mm / min, and coated with peroxotitanic acid.
Dried for minutes. This step is repeated 10 times to obtain about 0.16
A μm titanium oxide film was obtained.

The metal titanium plate on which the titanium oxide film was formed was fired at 700 ° C. for 2 hours in a vacuum of about 1 × 10 ⁻³ Pa. Then, it was baked at 700 ° C. for 2 hours in oxygen. Thereafter, electrodes were formed, and a voltage of 30 V was applied in a 150 g / L aqueous solution of ammonium adipate for 5 minutes to form an oxide film. With respect to this oxide film, insulation evaluation and electric capacity were measured. Table 1 shows the obtained results.

<Embodiment 3> HF processing (HF:
A metal titanium plate immersed in a solution of H ₂ O ₂ : H ₂ O = 1.5: 1.5: 7 for 1 minute and washed with water) is vacuum immersed in a 1.7% by weight aqueous solution of peroxotitanic acid. After defoaming and completely removing the air bubbles on the surface of the metal titanium plate,
It was pulled up at a pulling rate of 35 mm / min and dried in a dryer at 80 ° C. for 10 minutes. Thereafter, the metal titanium plate is immersed in an aqueous solution of peroxotitanic acid having a concentration of 1.7% by weight for 1 minute, pulled up at a speed of 105 mm / min, coated with peroxotitanic acid, and then dried in a dryer at 80 ° C. for 10 minutes. I let it. This step was repeated 10 times to obtain a titanium oxide film having a thickness of about 0.17 μm.

The metal titanium plate on which the titanium oxide film was formed was fired at 700 ° C. for 2 hours in a vacuum of about 1 × 10 ⁻³ Pa. Thereafter, the resultant was baked in oxygen at 700 ° C. for 2 hours, further turned into an electrode, and a voltage of 30 V was applied in a 150 g / L aqueous ammonium adipate solution for 5 minutes to form an oxide film. With respect to this oxide film, insulation evaluation and electric capacity were measured. Table 1 shows the obtained results.

<Comparative Example 1> A metal titanium plate was formed into an electrode.
30 V in a 50 g / L aqueous ammonium adipate solution,
A voltage was applied for 5 minutes to form an oxide film. With respect to this oxide film, insulation evaluation and electric capacity were measured.
Table 1 shows the obtained results.

Comparative Example 2 An experiment was performed in the same manner as in Comparative Example 1 except that the voltage was changed to 50 V, and an oxide film was formed. With respect to this oxide film, the evaluation of the insulating property and the measurement of the electric capacity were performed, and the obtained results are shown in Table 1.

Comparative Example 3 A metal titanium plate was placed in air at 700
C. for 2 hours to form an oxide film. With respect to this oxide film, the evaluation of the insulating property and the measurement of the electric capacity were performed, and the obtained results are shown in Table 1.

<Comparative Example 4> A metal titanium plate was placed in air at 800
C. for 2 hours to form an oxide film. With respect to this oxide film, the evaluation of the insulating property and the measurement of the electric capacity were performed, and the obtained results are shown in Table 1.

<Comparative Example 5> A metal titanium plate was placed in air at 900
C. for 2 hours to form an oxide film. With respect to this oxide film, the evaluation of the insulating property and the measurement of the electric capacity were performed, and the obtained results are shown in Table 1.

[0046]

[Table 1]

From Table 1, it can be seen that the oxide film formed by the method of the present invention is a strong oxide film having a high insulating property when a voltage is applied, despite its small film pressure and high electric capacity.

[0048]

The present invention provides a method for forming a stable and dense oxide film having a large dielectric constant on the surface of a titanium metal substrate. By using such an oxide film, a small-sized, large-capacity, and low-leakage-current lifetime is provided. Succeeded in developing a long titanium electrolytic capacitor.

[Brief description of the drawings]

FIG. 1 shows a conceptual diagram of a titanium electrolytic capacitor.

FIG. 2 is a graph schematically showing the state of the oxygen concentration from the titanium surface to the inside of titanium in each state of the Ti plate, after oxidation, after firing, and after re-oxidation.

FIG. 3 (a) shows an oxide film on the surface of a Ti plate in an oxidized state, and FIG. 3 (b) is an electron micrograph showing the surface state of the Ti plate after firing. (15KV, 2
0000 times).

FIG. 4 is a schematic diagram showing both a tantalum electrolytic capacitor and an aluminum electrolytic capacitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Titanium base anode 2 Titanium oxide film 3 Solid electrolyte 4 Carbon layer 5 Silver paste 6 Case

Claims (5)

[Claims] 1. An oxide film is formed by applying a titanic acid or an organotitanium compound on the surface of a titanium metal substrate, baking in a vacuum, then heat-treating in the presence of oxygen, and anodizing in a solution containing an electrolyte. Forming an oxide film on the surface of the titanium metal substrate by the method according to claim 1. 2. The method according to claim 1, wherein the titanic acid is peroxotitanic acid. 3. The method according to claim 1, wherein the organic titanium compound is an alkoxy titanium. 4. The method according to claim 1, wherein the firing in vacuum and the heat treatment in the presence of oxygen are both performed at a temperature of 500 to 900 ° C. 5. An oxide film is formed by applying a titanic acid or an organotitanium compound on the surface of a titanium metal substrate, baking in a vacuum, heat-treating in the presence of oxygen, and anodizing in a solution containing an electrolyte. A titanium electrolytic capacitor, characterized in that a titanium metal substrate having an oxide film reformed by the above method is used as an anode.