JPH0550126B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to improving the anodizing process when manufacturing electrode capacitors, and more specifically, by adding a unique compound to the chemical solution for anodizing, it is possible to improve the anodic oxidation process with fewer defects. The present invention relates to an anodic oxidation method for forming an oxide film. [Prior art] Electrolytic capacitors are small, large capacity, inexpensive, and have excellent characteristics such as smoothing rectified output, and are one of the important components of various electrical and electronic devices. It is created by using a film of a valve metal such as aluminum that has been converted into an oxide film by anodization (anodization) as an anode, and using this oxide film as a dielectric with an electrolyte interposed between it and a current collecting cathode. Electrolytic capacitors are used while constantly regenerating the dielectric oxide film while undergoing chemical reactions during use. maintain,
It is important to maintain a good oxide film on the valve metal such as aluminum, which serves as a dielectric, to stabilize performance. Indices of capacitor characteristics include capacitance (Cap), dielectric loss tangent (tanδ), and leakage current (LC). The loss angle tangent, that is, the dielectric loss tangent, which is the difference between the phase of the charging current and the phase of the external electric field, is used as a measure of the power consumption of a capacitor, and a small value indicates that the power consumption is low. Leakage current, which is the current that flows when a certain value is reached after the start of charging, is due to the steady movement of charge carriers in the dielectric, and ions generated by dissociation of impurities in the dielectric move the charge carriers. It is thought to be the main
The magnitude of leakage current reflects the stability of the electrochemical state of the dielectric. Generally, aluminum electrolytic capacitors are made by pre-treating aluminum foil, etching it in an aqueous chloride solution such as common salt, anodizing (forming) it in an electrolyte containing ammonium borate, cutting it, and then using paper and cathode foil. Create an element by winding and impregnating it with electrolyte,
Manufactured by sealing and aging. Among these, the anodizing process is a process of forming an oxide film that will be used as the dielectric of the capacitor, and the aluminum foil that has been etched in the previous process to enlarge its surface area is used as the anode.
This method performs continuous anodic oxidation. Silicon and titanium compounds are commonly used as coupling agents with surfactants and metal polymers. In particular, titanium is a metal that can be used for capacitor electrodes, and capacitors using alloys with aluminum have been studied, and it has been found that, apart from cost, they have better characteristics than aluminum alone. Therefore, we continued to study the possibility of applying silicon and titanium compounds to the manufacturing of electrolytic capacitors, and as a result, we found that adding a specific silicon or titanium compound to the anodizing chemical solution improved the properties of the oxide film that was produced. I finally figured out what to do. [Problems to be Solved by the Invention] The present invention performs anodic oxidation that forms a strong oxide film with few defects by adding a specific compound to the chemical solution for anodic oxidation, thereby achieving low leakage current. The purpose of the present invention is to obtain an electrolytic capacitor with high voltage resistance. [Means for Solving the Problems] According to the present invention, anodic oxidation is performed to form an oxide film of a valve metal to be used as a dielectric of an electrolytic capacitor on an anode body of a valve metal in a chemical solution containing an electrolyte. On this occasion,

[expression] or

Provided is a method for anodizing a valve metal, which comprises adding an inorganic polymer having the structure of [Formula] in its molecular chain and made water-soluble by introducing a hydrophilic group into a chemical conversion solution. be done. Metals that can be used as the anode of electrolytic capacitors are limited to those that produce a dense oxide with good insulation properties when anodized in an electrolyte, such as aluminum or tantalum. Such metals are collectively called valve metals or valve metals. It is preferable to use an electrolytic solution such as ammonium borate, ammonium phosphate, or organic acid + ammonia as the chemical solution (electrolytic solution), and perform the anodic oxidation at a voltage that is about twice as high as the rated voltage of the capacitor. The method of the present invention includes a single-stage method, a multi-stage method,
Any method is useful, such as a method in which a pseudo-boehmite film is formed on the outermost surface by boiling in pure water before anodizing. After completing the prescribed steps, the foil is cut, the paper and the cathode foil are wound together to create an element, which is impregnated with an electrolytic solution, sealed, and aged to create an electrolytic capacitor. When the substituent is R and the inorganic polymer is represented by the following formula (n is an integer):

【formula】 [Effect]

The mechanism by which the addition of the above-mentioned polymer of the present invention to the chemical conversion liquid makes the oxide film used as the dielectric of the electrolytic capacitor a strong film with few defects is not clear. However, even when anodic oxidation is performed with the addition of a normal nonmetallic surfactant, the effect of reducing leakage current and increasing withstand voltage is small. It is a part.

【formula】

It is presumed that [Formula] is deeply involved. Si and Ti compounds are widely used as coupling agents to strengthen the bonds between organic and inorganic substances. It is presumed that due to this action, the inorganic part of the polymer is adsorbed or chemically bonded to the surface of the oxide film, and in some cases, some of it penetrates into the interior, making the oxide film strong with few defects. . in the molecular chain

【formula】 〔Effect of the invention〕

According to the present invention, the properties of the oxide film used as a dielectric are improved by performing anodic oxidation to form a strong oxide film with few defects by adding a compound with a predetermined structure to the chemical solution for anodic oxidation. However, by manufacturing an electrolytic capacitor using this, an electrolytic capacitor having low leakage current and high voltage resistance can be obtained. [Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples. Example 1 A silicon polymer surfactant was added to a chemical solution containing 150 g of boric acid and 1.5 ml of ammonia water.

[Formula] was added in an amount of 1% by weight, and anodic oxidation was carried out by chemical conversion at a liquid temperature of 85°C and a voltage of 400V. This chemically formed foil was cut into pieces of 7 x 100 mm, and the paper and cathode foil were wound together to form an element, which was then impregnated with an electrolytic solution having a composition of 88.3% by weight of ethylene glycol, 2.8% by weight of pure water, and 8.9% by weight of ammonium benzoate. An electrolytic capacitor was created using a conventional method. Rating is 250V, 5.4μF, size is 8φ
×11.5 initial values of capacitance (Cap), dielectric loss tangent (tanδ), leakage current (LC), values after long-term use at high temperature (110℃, 1000 hours), and failure occurrence (per 10 pieces) Table 1 shows the test results for the shot number). Example 2 Titanium polymer surfactant instead of silicon polymer surfactant

An electrolytic capacitor was produced by anodizing in the same manner as in Example 1 except that 1% by weight of [Formula] was added. Test results first
Shown in the table. Comparative Example 1 Example 1 except that 1% by weight of the hydrocarbon surfactant polyethylene glycol monolaurate was added instead of the silicon polymer surfactant.
Anodizing was performed in the same manner as above to create an electrolytic capacitor. The test results are shown in Table 1. Comparative Example 2 An electrolytic capacitor was produced by anodizing in the same manner as in Example 1 except that no surfactant was added. The test results are shown in Table 1.

[Table] As can be seen from Table 1, the electrolytic capacitors produced by anodizing according to the present invention had small leakage currents and no shoots correlated with withstand voltage properties were generated. The increase in dielectric loss tangent, which is a measure of the increase in power consumption after long-term use at high temperatures, was also suppressed to a lower level than with conventional electrolytic capacitors.

Claims (1)

[Scope of Claims] 1. When performing anodic oxidation to form an oxide film of a valve metal as a dielectric of an electrolytic capacitor on an anode body of a valve metal in a chemical solution containing an electrolyte,
An anode of a valve metal, characterized in that an inorganic polymer having the structure of [Formula] or [Formula] in its molecular chain and made water-soluble by introducing a hydrophilic group is added to the chemical solution. Oxidation method.